[
    {
        "anchor": "Ultracold Bose and Fermi dipolar gases : a quantum Monte Carlo study: The object of study of this thesis are dipolar systems in the quantum\ndegenerate regime. In general, dealing with many-body systems and evaluating\ntheir properties requires to deal with the Schr\\\"odinger equation. In the\npresent study we employ different Monte Carlo methods, that are stochastic\ntechniques that allow to find numerical solutions to it.",
        "positive": "Dimensional crossover for universal scaling far from equilibrium: We perform a dynamical finite-size scaling analysis of a nonequilibrium Bose\ngas which is confined in the transverse plane. Varying the transverse size, we\nestablish a dimensional crossover for universal scaling properties far from\nequilibrium. Our results suggest that some aspects of the dynamical universal\nbehavior of anisotropic systems can be classified in terms of fractional\nspatial dimensions. We discuss our findings in view of recent experimental\nresults with quasi one-dimensional setups of quenched ultracold quantum gases."
    },
    {
        "anchor": "Time-of-flight images of Mott insulators in the Hofstadter-Bose-Hubbard\n  model: We analyze the momentum distribution function and its artificial-gauge-field\ndependence for the Mott insulator phases of the Hofstadter-Bose-Hubbard model.\nBy benchmarking the results of the random-phase approximation (RPA) approach\nagainst those of the strong-coupling expansion (SCE) for the Landau and\nsymmetric gauges, we find pronounced corrections to the former results in two\ndimensions.",
        "positive": "Collective Dissipative Molecule Formation in a Cavity: We propose a mechanism to realize high-yield molecular formation from\nultracold atoms. Atom pairs are continuously excited by a laser, and a\ncollective decay into the molecular ground state is induced by a coupling to a\nlossy cavity mode. Using a combination of analytical and numerical techniques,\nwe demonstrate that the molecular yield can be improved by simply increasing\nthe number of atoms, and can overcome efficiencies of state-of-the-art\nassociation schemes. We discuss realistic experimental setups for diatomic\npolar and nonpolar molecules, opening up collective light matter interactions\nas a tool for quantum state engineering, enhanced molecule formation,\ncollective dynamics, and cavity mediated chemistry."
    },
    {
        "anchor": "Quantum phase transitions in the dimerized extended Bose-Hubbard model: We present an unbiased numerical density-matrix renormalization group study\nof the one-dimensional Bose-Hubbard model supplemented by nearest-neighbor\nCoulomb interaction and bond dimerization. It places the emphasis on the\ndetermination of the ground-state phase diagram and shows that, besides\ndimerized Mott and density-wave insulating phases, an intermediate\nsymmetry-protected topological Haldane insulator emerges at weak Coulomb\ninteractions for filling factor one, which disappears, however, when the\ndimerization becomes too large. Analyzing the critical behavior of the model,\nwe prove that the phase boundaries of the Haldane phase to Mott insulator and\ndensity-wave states belong to the Gaussian and Ising universality classes with\ncentral charges $c=1$ and $c=1/2$, respectively, and merge in a tricritical\npoint. Interestingly we can demonstrate a direct Ising quantum phase transition\nbetween the dimerized Mott and density-wave phases above the tricritical point.\nThe corresponding transition line terminates at a critical end point that\nbelongs to the universality class of the dilute Ising model with $c=7/10$. At\neven stronger Coulomb interactions the transition becomes first order.",
        "positive": "Crossover trimers connecting continuous and discrete scaling regimes: For a system of two identical fermions and one distinguishable particle\ninteracting via a short-range potential with a large s-wave scattering length,\nthe Efimov trimers and Kartavtsev-Malykh trimers exist in different regimes of\nthe mass ratio. The Efimov trimers are known to exhibit a discrete scaling\ninvariance, while the Kartavtsev-Malykh trimers feature a continuous scaling\ninvariance. We point out that a third type of trimers, \"crossover trimers\",\nexist universally regardless of short-range details of the potential. These\ncrossover trimers have neither the discrete nor continuous scaling invariance.\nWe show that the crossover trimers continuously connect the discrete and\ncontinuous scaling regimes as the mass ratio and the scattering length are\nvaried. We identify the regions for the Kartavtsev-Malykh trimers, Efimov\ntrimers, crossover trimers, and non-universal trimers as a function of the mass\nratio and the s-wave scattering length by investigating the scaling property\nand model-independence of the trimers."
    },
    {
        "anchor": "Control of light-atom solitons and atomic transport by optical vortex\n  beams propagating through a Bose-Einstein Condensate: We model propagation of far-red-detuned optical vortex beams through a\nBose-Einstein Condensate using nonlinear Schr\\\"odinger and Gross-Pitaevskii\nequations. We show the formation of coupled light/atomic solitons that rotate\nazimuthally before moving off tangentially, carrying angular momentum. The\nnumber, and velocity, of solitons, depends on the orbital angular momentum of\nthe optical field. Using a Bessel-Gauss beam increases radial confinement so\nthat solitons can rotate with fixed azimuthal velocity. Our model provides a\nhighly controllable method of channelling a BEC and atomic transport.",
        "positive": "Half-solitons in a polariton quantum fluid behave like magnetic\n  monopoles: Monopoles are magnetic charges, point-like sources of magnetic field.\nContrary to electric charges they are absent in Maxwell's equations and have\nnever been observed as fundamental particles. Quantum fluids such as spinor\nBose-Einstein condensates have been predicted to show monopoles in the form of\nexcitations combining phase and spin topologies. Thanks to its unique spin\nstructure and the direct optical control of the fluid wavefunction, an ideal\nsystem to experimentally explore this phenomenon is a condensate of\nexciton-polaritons in a semiconductor microcavity. We use this system to create\nhalf-solitons, non-linear excitations with mixed spin-phase geometry. By\ntracking their trajectory, we demonstrate that half-solitons behave as\nmonopoles, magnetic charges accelerated along an effective magnetic field\npresent in the microcavity. The field-induced spatial separation of\nhalf-solitons of opposite charges opens the way to the generation of magnetic\ncurrents in a quantum fluid."
    },
    {
        "anchor": "Droplet crystal ground states of a dipolar Bose gas: We show that the ground state of a dipolar Bose gas in a cylindrically\nsymmetric harmonic trap has a rich phase diagram, including droplet crystal\nstates in which a set of droplets arrange into a lattice pattern that breaks\nthe rotational symmetry. An analytic model for small droplet crystals is\ndeveloped and used to obtain a zero temperature phase diagram that is\nnumerically validated. We show that in certain regimes a coherent low-density\nhalo surrounds the droplet crystal giving rise to a novel phase with localized\nand extended features.",
        "positive": "Universality in nonlinear passage through the miscible-immiscible phase\n  transition in two component Bose-Einstein condensates: In this study, we investigate the formation of domain defects and the\nuniversal critical real-time dynamics in a two-component Bose-Einstein\ncondensate with nonlinear quenching across the miscible-immiscible phase\ntransition. By analyzing the Bogoliubov excitations, we obtain the power-law\nrelations among the defect density, the phase transition delay and the quench\ntime near the phase transition. Moreover, by simulating the real-time dynamics\nacross the miscible-immiscible phase transition, we clearly show the formation\nof domain defects and the delay of the phase transition. Furthermore, we find\nthat the domain defects are suppressed by large nonlinear coefficients and long\nquench times. To accurately characterize the domain defects, we quantify the\ndefect excitations using the correlation length and the domain number. In\naddition, by combining the power-law relations between the phase transition\ndelay and the quench time, we extract the critical exponents for different\nnonlinear coefficients. Our study not only confirms that the critical exponents\ndo not sensitively depend on the nonlinear quenches but also provides a dynamic\npath toward the suppression of nonadiabatic excitation."
    },
    {
        "anchor": "Fermi polarons and beyond: These lecture notes give a brief introduction to the so-called Fermi-polaron\nproblem, which explores the behaviour of a mobile impurity introduced into an\nideal Fermi gas. While this problem has been considered now for more than a\ndecade in ultracold atomic gases, it continues to generate surprises and\ninsights as new quantum mixtures emerge, both in atomic gases and in the solid\nstate. Here we summarise the basic theory for the Fermi polaron with a focus on\nthe three-dimensional case, although the results can be straightforwardly\ngeneralised to two dimensions. Our aim is to provide a pedagogical treatment of\nthe subject and we thus cover fundamental topics such as scattering theory and\nrenormalisation. We discuss the ground state of the Fermi polaron and how it is\nconnected to the phase diagram of the spin-imbalanced Fermi gas, and we also\ngive a brief overview of the energy spectrum and non-equilibrium dynamics.\nThroughout, we highlight how the static and dynamic behaviour of the Fermi\npolaron is well described using intuitive variational approaches.",
        "positive": "Variational approach for Bose-Einstein condensates in strongly\n  disordered traps: Recently, Nattermann and Pokrovsky [PRL 100, 060402 (2008)] have proposed a\nscaling approach for studying Bose-Einstein condensates in strongly disordered\ntraps. In this paper we implement their scaling argument in the framework of\nthe variational method for solving the time dependent Gross-Pitaevskii\nequation. We consider atomic gases with both short range s-wave interaction and\nlong range anisotropic dipolar interaction. The theory is addressed to the\nregime of strong disorder and weak interactions where the physics is dominated\nby the collective pinning due to the disorder. The phenomenon of condensate\nfragmentation in dipolar gases is also analyzed."
    },
    {
        "anchor": "Pairing sizes in attractively interacting Fermi gases with Spin-orbit\n  Couplings: Extensive research has been lavished on effects of spin-orbit couplings (SOC)\nin attractively interacting Fermi systems in both neutral cold atom systems and\ncondensed matter systems. Recently, it was suggested that a SOC drives a new\nclass of BCS to BEC crossover which is different than the conventional one\nwithout a SOC. Here, we explore what are the most relevant physical quantities\nto describe such a new BCS to BEC crossover and their experimental detections.\n  We extend the concepts of the pairing length and \"Cooper-pair size\" in the\nabsence of SOC to Fermi systems with SOC. We investigate the dependence of\nchemical potential, pairing length, \"Cooper-pair size\" on the SOC strength and\nthe scattering length at $ 3d $ (the bound state energy at $ 2d $) for three\nattractively interacting Fermi gases with 3 dimensional (3d) Rashba, 3d Weyl\nand 2d Rashba SOC respectively. We show that only the pairing length can be\nused to characterize this new BCS to BEC crossover. Furthermore, it is the only\nlength which can be directly measured by radio-frequency dissociation spectra\ntype of experiments. We stress crucial differences among the pairing length,\n\"Cooper-pair size \" and the two-body bound state size. Our results provide the\nfundamental and global picture of the new BCS to BEC crossover and its\nexperimental detections in various cold atom and condensed matter systems.",
        "positive": "Perpetual motion of a mobile impurity in a one-dimensional quantum gas: Consider an impurity particle injected in a degenerate one-dimensional gas of\nnoninteracting fermions (or, equivalently, Tonks-Girardeau bosons) with some\ninitial momentum $p_0$. We examine the infinite-time value of the momentum of\nthe impurity, $p_\\infty$, as a function of $p_0$. A lower bound on\n$|p_\\infty(p_0)|$ is derived under fairly general conditions. The derivation,\nbased on the existence of the lower edge of the spectrum of the host gas, does\nnot resort to any approximations. The existence of such bound implies the\nperpetual motion of an impurity in a one-dimensional gas of noninteracting\nfermions or Tonks-Girardeau bosons at zero temperature. The bound has an\nespecially simple and useful form when the interaction between the impurity and\nhost particles is everywhere repulsive."
    },
    {
        "anchor": "Anderson localization of matter waves in quantum-chaos theory: We study the Anderson localization of atomic gases exposed to\nthree-dimensional optical speckles by analyzing the statistics of the\nenergy-level spacings. This method allows us to consider realistic models of\nthe speckle patterns, taking into account the strongly anisotropic correlations\nwhich are realized in concrete experimental configurations. We first compute\nthe mobility edge $E_c$ of a speckle pattern created using a single laser beam.\nWe find that $E_c$ drifts when we vary the anisotropy of the speckle grains,\ngoing from higher values when the speckles are squeezed along the beam\npropagation axis, to lower values when they are elongated. We also consider the\ncase where two speckle patterns are superimposed forming interference fringes,\nand we find that $E_c$ is increased compared to the case of idealized isotropic\ndisorder. We discuss the important implications of our findings for cold-atoms\nexperiments.",
        "positive": "Two-band superfluidity and intrinsic Josephson effect in alkaline-earth\n  Fermi gases across an orbital Feshbach resonance: We first show that the many-body Hamiltonian governing the physical\nproperties of an alkaline-earth Yb-173 Fermi gas across the recently-realized\norbital Feshbach resonance is exactly analogous to that of two-band s-wave\nsuperconductors with contact interactions: i.e., even though the free-particle\nbands have a tunable energy offset in between and are coupled by a\nJosephson-type attractive inter-band pair scattering, the intra-band\ninteractions have exactly the same strength. We then introduce two intra-band\norder parameters within the BCS mean-field approximation, and investigate the\ncompetition between their in-phase and out-of-phase (i.e., the so-called\n\\pi-phase) solutions in the entire BCS-BEC evolution at zero temperature."
    },
    {
        "anchor": "Cooling and thermometry of atomic Fermi gases: We review the status of cooling techniques aimed at achieving the deepest\nquantum degeneracy for atomic Fermi gases. We first discuss some physical\nmotivations, providing a quantitative assessment of the need for deep quantum\ndegeneracy in relevant physics cases, such as the search for unconventional\nsuperfluid states. Attention is then focused on the most widespread technique\nto reach deep quantum degeneracy for Fermi systems, sympathetic cooling of\nBose-Fermi mixtures, organizing the discussion according to the specific\nspecies involved. Various proposals to circumvent some of the limitations on\nachieving the deepest Fermi degeneracy, and their experimental realizations,\nare then reviewed. Finally, we discuss the extension of these techniques to\noptical lattices and the implementation of precision thermometry crucial to the\nunderstanding of the phase diagram of classical and quantum phase transitions\nin Fermi gases.",
        "positive": "Magnon BEC and Spin Superfluidity: a 3He primer: Bose-Einstein condensation (BEC) is a quantum phenomenon of formation of the\ncollective quantum state, in which the macroscopic number of particles occupies\nthe lowest energy state and thus is governed by a single wave function. Here we\nhighlight the BEC in a magnetic subsystem -- the BEC of magnons, elementary\nmagnetic excitations. Magnon BEC is manifested as the spontaneously emerging\nstate of the precessing spins, in which all spins precess with the same\nfrequency and phase even in the inhomogeneous magnetic field. We consider this\nphenomenon on example of spin precession in superfluid phases of $^3$He. The\nmagnon BEC in these phases has all the properties of spin superfluidity. The\nstates of the phase-coherent precession belong to the class of the coherent\nquantum states, which manifest themselves by superfluidity, superconductivity,\nquantum Hall effect, Josephson effect and many other macroscopic quantum\nphenomena."
    },
    {
        "anchor": "Quantum entanglement of spin-1 bosons with coupled ground states in\n  optical lattices: We examine particle entanglement, characterized by pseudo-spin squeezing, of\nspin-1 bosonic atoms with coupled ground states in a one-dimensional optical\nlattice. Both the superfluid and Mott-insulator phases are investigated\nseparately for ferromagnetic and antiferromagnetic interactions. Mode\nentanglement is also discussed in the Mott insulating phase. The role of a\nsmall but nonzero angle between the polarization vectors of counter-propagating\nlasers forming the optical lattice on quantum correlations is investigated as\nwell.",
        "positive": "Fractional quantum Hall states of few bosonic atoms in geometric gauge\n  fields: We employ the exact diagonalization method to analyze the possibility of\ngenerating strongly correlated states in two-dimensional clouds of ultracold\nbosonic atoms which are subjected to a geometric gauge field created by\ncoupling two internal atomic states to a laser beam. Tuning the gauge field\nstrength, the system undergoes stepwise transitions between different ground\nstates, which we describe by analytical trial wave functions, amongst them the\nPfaffian, the Laughlin, and a Laughlin quasiparticle many-body state. The\nadiabatic following of the center of mass movement by the lowest energy dressed\ninternal state, is lost by the mixing of the second internal state. This\nmixture can be controlled by the intensity of the laser field. The\nnon-adiabaticity is inherent to the considered setup, and is shown to play the\nrole of circular asymmetry. We study its influence on the properties of the\nground state of the system. Its main effect is to reduce the overlap of the\nnumerical solutions with the analytical trial expressions by occupying states\nwith higher angular momentum. Thus, we propose generalized wave functions\narising from the Laughlin and Pfaffian wave function by including components,\nwhere extra Jastrow factors appear, while preserving important features of\nthese states. We analyze quasihole excitations over the Laughlin and\ngeneralized Laughlin states, and show that they possess effective fractional\ncharge and obey anyonic statistics. Finally, we study the energy gap over the\nLaughlin state as the number of particles is increased keeping the chemical\npotential fixed. The gap is found to decrease as the number of particles is\nincreased, indicating that the observability of the Laughlin state is\nrestricted to a small number of particles."
    },
    {
        "anchor": "Non-local state-swapping of polar molecules in bilayers: The observation of significant dipolar effects in gases of ultra-cold polar\nmolecules typically demands a strong external electric field to polarize the\nmolecules. We show that even in the absence of a significant polarization,\ndipolar effects may play a crucial role in the physics of polar molecules in\nbilayers, provided that the molecules in each layer are initially prepared in a\ndifferent rotational state. Then, inter-layer dipolar interactions result in a\nnon-local swap of the rotational state between molecules in different layers,\neven for weak applied electric fields. The inter-layer scattering due to the\ndipole-dipole interaction leads to a non-trivial dependence of the swapping\nrate on density, temperature, inter-layer spacing, and population imbalance.\nFor reactive molecules like KRb, chemical recombination immediately follows a\nnon-local swap and dominates the losses even for temperatures well above\nquantum degeneracy, and could be hence observed under current experimental\nconditions.",
        "positive": "Bloch Oscillations Along a Synthetic Dimension of Atomic Trap States: Synthetic dimensions provide a powerful approach for simulating condensed\nmatter physics in cold atoms and photonics, whereby a set of discrete degrees\nof freedom are coupled together and re-interpreted as lattice sites along an\nartificial spatial dimension. However, atomic experimental realisations have\nbeen limited so far by the number of artificial lattice sites that can be\nfeasibly coupled along the synthetic dimension. Here, we experimentally realise\nfor the first time a very long and controllable synthetic dimension of atomic\nharmonic trap states. To create this, we couple trap states by dynamically\nmodulating the trapping potential of the atomic cloud with patterned light. By\ncontrolling the detuning between the frequency of the driving potential and the\ntrapping frequency, we implement a controllable force in the synthetic\ndimension. This induces Bloch oscillations in which atoms move periodically up\nand down tens of atomic trap states. We experimentally observe the key\ncharacteristics of this behaviour in the real space dynamics of the cloud, and\nverify our observations with numerical simulations and semiclassical theory.\nThis experiment provides an intuitive approach for the manipulation and control\nof highly-excited trap states, and sets the stage for the future exploration of\ntopological physics in higher dimensions."
    },
    {
        "anchor": "Resonance Scattering in Optical Lattices and Molecules: Interband versus\n  Intraband Effects: We study the low-energy two-body scattering in optical lattices with all\nhigher-band effects included in an effective potential, using a renormalization\ngroup approach. As the potential depth reaches a certain value, a resonance of\nlow energy scattering occurs even when the negative s-wave scattering length\n$(a_s)$ is much shorter than the lattice constant. These resonances can be\nmainly driven either by interband or intraband effects or by both, depending on\nthe magnitude of $a_s$. Furthermore the low-energy scattering matrix in optical\nlattices has a much stronger energy-dependence than that in free space. We also\ninvestigate the momentum distribution for molecules when released from optical\nlattices.",
        "positive": "Probing Confinement Through Dynamical Quantum Phase Transitions: From\n  Quantum Spin Models to Lattice Gauge Theories: Confinement is an intriguing phenomenon prevalent in condensed matter and\nhigh-energy physics. Exploring its effect on the far-from-equilibrium\ncriticality of quantum many-body systems is of great interest both from a\nfundamental and technological point of view. Here, we employ large-scale\nuniform matrix product state calculations to show that a qualitative change in\nthe type of dynamical quantum phase transitions (DQPTs) accompanies the\nconfinement-deconfinement transition in three paradigmatic models -- the\npower-law interacting quantum Ising chain, the two-dimensional quantum Ising\nmodel, and the spin-$S$ $\\mathrm{U}(1)$ quantum link model. By tuning a\nconfining parameter in these models, it is found that \\textit{branch}\n(\\textit{manifold}) DQPTs arise as a signature of (de)confinement. Whereas\nmanifold DQPTs are associated with a sign change of the order parameter, their\nbranch counterparts are not, but rather occur even when the order parameter\nexhibits considerably constrained dynamics. Our conclusions can be tested in\nmodern quantum-simulation platforms, such as ion-trap setups and cold-atom\nexperiments of gauge theories."
    },
    {
        "anchor": "Matter-wave soliton interferometer based on a nonlinear splitter: We elaborate a model of the interferometer which, unlike previously studied\nones, uses a local (delta-functional) nonlinear repulsive potential, embedded\ninto a harmonic-oscillator trapping potential, as the splitter for the incident\nsoliton. An estimate demonstrates that this setting may be implemented by means\nof the localized Feshbach resonance controlled by a focused laser beam. The\nsame system may be realized as a nonlinear waveguide in optics. Subsequent\nanalysis produces an exact solution for scattering of a plane wave in the\nlinear medium on the delta-functional nonlinear repulsive potential, and an\napproximate solution for splitting of the incident soliton when the ambient\nmedium is nonlinear. The most essential result, obtained by means of systematic\nsimulations, is that the use of the nonlinear splitter provides the sensitivity\nof the soliton-based interferometer to the target, inserted into one of its\narms, which is much higher than the sensitivity provided by the usual linear\nsplitter.",
        "positive": "A study of coherently coupled two-component Bose-Einstein Condensates: We present a self-consistent study of coherently coupled two-component\nBose-Einstein condensates. Finite spin-flipping coupling changes the first\norder demixing phase transition for Bose-Bose mixtures to a second order phase\ntransition between an unpolarized and a polarized state. We analise the\nexcitation spectrum and the structure factor along the transition for a\nhomogeneous system. We discuss the main differences at the transition between a\ncoherent coupled gas and a two-component mixture. We finally study the ground\nstate when spin-(in)dependent trapping potentials are added to the system,\nfocusing on optical lattices, which give rise to interesting new\nconfigurations."
    },
    {
        "anchor": "Double-degenerate Bose-Fermi mixture of strontium: We report on the attainment of a spin-polarized Fermi sea of 87-Sr in thermal\ncontact with a Bose-Einstein condensate (BEC) of 84-Sr. Interisotope collisions\nthermalize the fermions with the bosons during evaporative cooling. A\ndegeneracy of T/T_F=0.30(5) is reached with 2x10^4 87-Sr atoms together with an\nalmost pure 84-Sr BEC of 10^5 atoms.",
        "positive": "The halon: a quasiparticle featuring critical charge fractionalization: The halon is a special critical state of an impurity in a quantum-critical\nenvironment. The hallmark of the halon physics is that a well-defined integer\ncharge gets fractionalized into two parts: a microscopic core with half-integer\ncharge and a critically large halo carrying a complementary charge of $\\pm\n1/2$. The halon phenomenon emerges when the impurity--environment interaction\nis fine-tuned to the vicinity of a boundary quantum critical point (BQCP), at\nwhich the energies of two quasiparticle states with adjacent integer charges\napproach each other. The universality class of such BQCP is captured by a model\nof pseudo-spin-$1/2$ impurity coupled to the quantum-critical environment, in\nsuch a way that the rotational symmetry in the pseudo-spin $xy$-plane is\nrespected, with a small local \"magnetic\" field along the pseudo-spin $z$-axis\nplaying the role of control parameter driving the system away from the BQCP. On\nthe approach to BQCP, the half-integer projection of the pseudo-spin on its\n$z$-axis gets delocalized into a halo of critically divergent radius, capturing\nthe essence of the phenomenon of charge fractionalization. With large-scale\nMonte Carlo simulations, we confirm the existence of halons---and quantify\ntheir universal features---in O(2) and O(3) quantum critical systems."
    },
    {
        "anchor": "Correlations in few two-component quantum walkers on a tilted lattice: We study the effect of inter-component interactions on the dynamical\nproperties of quantum walkers. We consider the simplest situation of two\nindistinguishable non-interacting walkers on a tilted optical lattice\ninteracting with a walker from a different component. The mediated effect of\nthe third particle is then analyzed in the backdrop of various controlling\nparameters. The interaction-induced two-particle correlations are shown to be\nnon-trivially affected by the particle statistics, choice of initial states,\nand tilting configurations of the lattice. Our analysis thus offers an overall\npicture and serves as a starting point of a study of interacting\nmulti-component quantum walkers.",
        "positive": "N\u00e9el transition of lattice fermions in a harmonic trap: a real-space\n  DMFT study: We study the magnetic ordering transition for a system of harmonically\ntrapped ultracold fermions with repulsive interactions in a cubic optical\nlattice, within a real-space extension of dynamical mean-field theory (DMFT).\nUsing a quantum Monte Carlo impurity solver, we establish that\nantiferromagnetic correlations are signaled, at strong coupling, by an enhanced\ndouble occupancy. This signature is directly accessible experimentally and\nshould be observable well above the critical temperature for long-range order.\nDimensional aspects appear less relevant than naively expected."
    },
    {
        "anchor": "Synthetic Flux Attachment: Topological field theories emerge at low energy in strongly-correlated\ncondensed matter systems and appear in the context of planar gravity. In\nparticular, the study of Chern-Simons terms gives rise to the concept of flux\nattachment when the gauge field is coupled to matter, yielding flux-charge\ncomposites. Here we investigate the generation of flux attachment in a\nBose-Einstein condensate in the presence of non-linear synthetic gauge\npotentials. In doing so, we identify the U(1) Chern-Simons gauge field as a\nsingular density-dependent gauge potential, which in turn can be expressed as a\nBerry connection. We envisage a proof-of-concept scheme where the artificial\ngauge field is perturbatively induced by an effective light-matter detuning\ncreated by interparticle interactions. At a mean field level, we recover the\naction of a \"charged\" superfluid minimally coupled to both a background and a\nChern-Simons gauge field. Remarkably, a localised density perturbation in\ncombination with a non-linear gauge potential gives rise to an effective\ncomposite boson model of fractional quantum Hall effect, displaying anyonic\nvortices.",
        "positive": "Extracting information from non adiabatic dynamics: excited symmetric\n  states of the Bose-Hubbard model: Using Fourier transform on a time series generated by unitary evolution, we\nextract many-body eigenstates of the Bose-Hubbard model corresponding to low\nenergy excitations, which are generated when the insulator-superfluid phase\ntransition is realized in a typical experiment. The analysis is conducted in a\nsymmetric external potential both without and with and disorder. A simple\nclassification of excitations in the absence disorder is provided. The\nevolution is performed assuming the presence of the parity symmetry in the\nsystem rendering many-body quantum states either symmetric or antisymmetric.\nUsing symmetry-breaking technique, those states are decomposed into elementary\none-particle processes."
    },
    {
        "anchor": "Reentrant transition of bosons in a quasiperiodic potential: We investigate the behavior of a two dimensional array of Bose-Einstein\ncondensate tubes described by means of a Bose-Hubbard Hamiltonian. Using a\nWannier function expansion for the wavefunction in each tube, we compute the\nBose-Hubbard parameters related to two different longitudinal potentials,\nperiodic and quasiperiodic. We predict that - upon increasing the external\npotential strength along the direction of the tubes - the condensate can\nexperience a reentrant transition between a Mott insulating phase and the\nsuperfluid one.",
        "positive": "Half-Quantum Vortices in an Antiferromagnetic Spinor Bose-Einstein\n  Condensate: We report on the observation of half-quantum vortices (HQVs) in the\neasy-plane polar phase of an antiferromagnetic spinor Bose-Einstein condensate.\nUsing in situ magnetization-sensitive imaging, we observe that pairs of HQVs\nwith opposite core magnetization are generated when singly charged quantum\nvortices are injected into the condensate. The dynamics of HQV pair formation\nis characterized by measuring the temporal evolutions of the pair separation\ndistance and the core magnetization, which reveals the short-range nature of\nthe repulsive interactions between the HQVs. We find that spin fluctuations\narising from thermal population of axial magnon excitations do not\nsignificantly affect the HQV pair formation dynamics. Our results demonstrate\nthe instability of a singly charged vortex in the antiferromagnetic spinor\ncondensate."
    },
    {
        "anchor": "Bunching, clustering, and the buildup of few-body correlations in a\n  quenched unitary Bose gas: We study the growth of two- and three-body correlations in an ultracold Bose\ngas quenched to unitarity. This is encoded in the dynamics of the two- and\nthree-body contacts analyzed in this work. Via a set of relations connecting\nmany-body correlations dynamics with few-body models, signatures of the Efimov\neffect are mapped out as a function of evolution time at unitarity over a range\nof atomic densities $n$. For the thermal resonantly interacting Bose gas, we\nfind that atom-bunching leads to an enhanced growth of few-body correlations.\nThese atom-bunching effects also highlight the interplay between few-body\ncorrelations that occurs before genuine many-body effects enter on Fermi\ntimescales.",
        "positive": "Momentum distribution and non-local high order correlation functions of\n  1D strongly interacting Bose gas: The Lieb-Liniger model is a prototypical integrable model and has been turned\ninto the benchmark physics in theoretical and numerical investigations of low\ndimensional quantum systems.\n  In this note, we present various methods for calculating local and nonlocal\n$M$-particle correlation functions, momentum distribution and static structure\nfactor. In particular, using the Bethe ansatz wave function of the strong\ncoupling Lieb-Liniger model, we analytically calculate two-point correlation\nfunction, the large moment tail of momentum distribution and static structure\nfactor of the model in terms of the fractional statistical parameter $\\alpha\n=1-2/\\gamma$, where $\\gamma$ is the dimensionless interaction strength. We also\ndiscuss the Tan's adiabatic relation and other universal relations for the\nstrongly repulsive Lieb-Liniger model in term of the fractional statistical\nparameter."
    },
    {
        "anchor": "The inverse-square interaction phase diagram: unitarity in the bosonic\n  ground state: Ground-state properties of bosons interacting via inverse square potential\n(three dimensional Calogero-Sutherland model) are analyzed. A number of\nquantities scale with the density and can be naturally expressed in units of\nthe Fermi energy and Fermi momentum multiplied by a dimensionless constant\n(Bertsch parameter). Two analytical approaches are developed: the Bogoliubov\ntheory for weak and the harmonic approximation (HA) for strong interactions.\nDiffusion Monte Carlo method is used to obtain the ground-state properties in a\nnon-perturbative manner. We report the dependence of the Bertsch parameter on\nthe interaction strength and construct a Pad\\'e approximant which fits the\nnumerical data and reproduces correctly the asymptotic limits of weak and\nstrong interactions. We find good agreement with beyond-mean field theory for\nthe energy and the condensate fraction. The pair distribution function and the\nstatic structure factor are reported for a number of characteristic\ninteractions. We demonstrate that the system experiences a gas-solid phase\ntransition as a function of the dimensionless interaction strength. A\npeculiarity of the system is that by changing the density it is not possible to\ninduce the phase transition. We show that the low-lying excitation spectrum\ncontains plasmons in both phases, in agreement with the Bogoliubov and HA\ntheories. Finally, we argue that this model can be interpreted as a realization\nof the unitary limit of a Bose system with the advantage that the system stays\nin the genuine ground state contrarily to the metastable state realized in\nexperiments with short-range Bose gases.",
        "positive": "Exact periodic and solitonic states in the spinor condensates: We propose a method to analytically solve the one-dimensional coupled\nnonlinear Gross-Pitaevskii equations which govern the motion of the spinor\nBose-Einstein condensates. In a uniform external potential, the Hamiltonian\ncomprises the kinetic energy, the linear and the quadratic Zeeman energies.\nSeveral classes of exact periodic and solitonic solutions, either in real or in\ncomplex forms, are obtained for both the F=1 and F=2 condensates. These\nsolutions are general that contain neither approximations nor constraints on\nthe system parameters."
    },
    {
        "anchor": "Bright solitons in ultracold atoms: We review old and recent experimental and theoretical results on bright\nsolitons in Bose-Einstein condensates made of alkali-metal atoms and under\nexternal optical confinement. First we deduce the three-dimensional\nGross-Pitaevskii equation (3D GPE) from the Dirac-Frenkel action of interacting\nidentical bosons within a time-dependent Hartree approximation. Then we discuss\nthe dimensional reduction of the GPE from 3D to 1D, deriving the 1D GPE and\nalso the 1D nonpolynomial Schr\\\"odinger equation (1D NPSE). Finally, we analyze\nthe bright solition solutions of both 1D GPE and 1D NPSE and compare these\ntheoretical predictions with the available experimental data.",
        "positive": "Emptiness Formation in Polytropic Quantum Liquids: We study large deviations in interacting quantum liquids with the polytropic\nequation of state $P(\\rho)\\sim \\rho^\\gamma$, where $\\rho$ is density and $P$ is\npressure. By solving hydrodynamic equations in imaginary time we evaluate the\ninstanton action and calculate the emptiness formation probability (EFP), the\nprobability that no particle resides in a macroscopic interval of a given size.\nAnalytic solutions are found for a certain infinite sequence of rational\npolytropic indexes $\\gamma$ and the result can be analytically continued to any\nvalue of $\\gamma\\ge 1$. Our findings agree with (and significantly expand on)\npreviously known analytical and numerical results for EFP in quantum liquids.\nWe also discuss interesting universal spacetime features of the instanton\nsolution."
    },
    {
        "anchor": "Dynamics of the relativistic Gross-Pitaevskii equation with harmonic\n  potential: Following the variational approach: The role of the collective excitations as well as the free expansion dynamics\nprovide a key diagnostic tools for trapped Bose-Einstein condensations. Based\non such dynamics we proposed to study the relativistic version of them in the\ncontext of a macroscopic occupation of the ground-state for spin-0 particles.\nTherefore we used the Higgs model where the external trap is introduced by a\nnon-minimal coupling. Along with variational method, we obtained a nonlinear\ncoupling between dipolar and monopolar modes. Furthermore, the free expansion\nis no longer ballistic reaching a relativistic confinement.",
        "positive": "Bose-Einstein condensates in an eightfold symmetric optical lattice: We investigate the properties of Bose-Einstein condensates (BECs) in a\ntwo-dimensional quasi-periodic optical lattice (OL) with eightfold rotational\nsymmetry by numerically solving the Gross-Pitaevskii equation. In a stationary\nexternal harmonic trapping potential, we first analyze the evolution of\nmatter-wave interference pattern from periodic to quasi-periodic as the OL is\nchanged continuously from four-fold periodic and eight-fold quasi-periodic. We\nalso investigate the transport properties during this evolution for different\ninteratomic interaction and lattice depth, and find that the BEC crosses over\nfrom ballistic diffusion to localization. Finally, we focus on the case of\neightfold symmetric lattice and consider a global rotation imposed by the\nexternal trapping potential. The BEC shows vortex pattern with eightfold\nsymmetry for slow rotation, becomes unstable for intermediate rotation, and\nexhibits annular solitons with approximate axial symmetry for fast rotation.\nThese results can be readily demonstrated in experiments using the same\nconfiguration as in Phys. Rev. Lett. 122, 110404 (2019)."
    },
    {
        "anchor": "Beating dark-dark solitons in Bose-Einstein condensates: Motivated by recent experimental results, we study beating dark-dark solitons\nas a prototypical coherent structure that emerges in two-component\nBose-Einstein condensates. We showcase their connection to dark- bright\nsolitons via SO(2) rotation, and infer from it both their intrinsic beating\nfrequency and their frequency of oscillation inside a parabolic trap. We\nidentify them as exact periodic orbits in the Manakov limit of equal inter- and\nintra-species nonlinearity strengths with and without the trap and showcase the\npersistence of such states upon weak deviations from this limit. We also\nconsider large deviations from the Manakov limit illustrating that this\nbreathing state may be broken apart into dark-antidark soliton states. Finally,\nwe consider the dynamics and interactions of two beating dark-dark solitons in\nthe absence and in the presence of the trap, inferring their typically\nrepulsive interaction.",
        "positive": "Poincar\u00e9 crystal on the one-dimensional lattice: In this paper, we develop the quantum theory of particles that has discrete\nPoincar\\'{e} symmetry on the one-dimensional Bravais lattice. We review the\nrecently discovered discrete Lorentz symmetry, which is the unique Lorentz\nsymmetry that coexists with the discrete space translational symmetry on a\nBravais lattice. The discrete Lorentz transformations and spacetime\ntranslations form the discrete Poincar\\'{e} group, which are represented by\nunitary operators in a quantum theory. We find the conditions for the existence\nof representation, which are expressed as the congruence relation between\nquasi-momentum and quasi-energy. We then build the Lorentz-invariant many-body\ntheory of indistinguishable particles by expressing both the unitary operators\nand Floquet Hamiltonians in terms of the field operators. Some typical\nHamiltonians include the long-range hopping which fluctuates as the distance\nbetween sites increases. We calculate the Green's functions of the lattice\ntheory. The spacetime points where the Green's function is nonzero display a\nlattice structure. During the propagation, the particles stay localized on a\nsingle or a few sites to preserve the Lorentz symmetry."
    },
    {
        "anchor": "All-optical production of a superfluid Bose-Fermi mixture of $^6$Li and\n  $^7$Li: We report the first all-optical production of a superfluid Bose-Fermi mixture\nwith two spin states of $^6$Li (fermion) and one spin state of $^7$Li (boson)\nunder the resonant magnetic field of the s-wave Feshbach resonance of the\nfermions. Fermions are cooled efficiently by evaporative cooling and they serve\nas coolant for bosons. As a result, a superfluid mixture can be achieved by\nusing a simple experimental apparatus and procedures, as in the case of the\nall-optical production of a single Bose-Einstein condensate (BEC). We show that\nthe all-optical method enables us to realize variety of ultracold Bose-Fermi\nmixtures.",
        "positive": "Ultracold Atoms in Disordered Potentials: Elastic Scattering Time in the\n  Strong Scattering Regime: We study the elastic scattering time $\\tau_\\mathrm{s}$ of ultracold atoms\npropagating in optical disordered potentials in the strong scattering regime,\ngoing beyond the recent work of J. Richard \\emph{et al.} \\textit{Phys. Rev.\nLett.} \\textbf{122} 100403 (2019). There, we identified the crossover between\nthe weak and the strong scattering regimes by comparing direct measurements and\nnumerical simulations to the first order Born approximation. Here we focus\nspecifically on the strong scattering regime, where the first order Born\napproximation is not valid anymore and the scattering time is strongly\ninfluenced by the nature of the disorder. To interpret our observations, we\nconnect the scattering time $\\tau_\\mathrm{s}$ to the profiles of the spectral\nfunctions that we estimate using higher order Born perturbation theory or\nself-consistent Born approximation. The comparison reveals that self-consistent\nmethods are well suited to describe $\\tau_\\mathrm{s}$ for Gaussian-distributed\ndisorder, but fails for laser speckle disorder. For the latter, we show that\nthe peculiar profiles of the spectral functions, as measured independently in\nV. Volchkov \\emph{et al.} \\textit{Phys. Rev. Lett.} \\textbf{120}, 060404\n(2018), must be taken into account. Altogether our study characterizes the\nvalidity range of usual theoretical methods to predict the elastic scattering\ntime of matter waves, which is essential for future close comparison between\ntheory and experiments, for instance regarding the ongoing studies on Anderson\nlocalization."
    },
    {
        "anchor": "Low-momentum dynamic structure factor of a strongly interacting Fermi\n  gas at finite temperature: A two-fluid hydrodynamic description: We provide a description of the dynamic structure factor of a homogeneous\nunitary Fermi gas at low momentum and low frequency, based on the dissipative\ntwo-fluid hydrodynamic theory. The viscous relaxation time is estimated and is\nused to determine the regime where the hydrodynamic theory is applicable and to\nunderstand the nature of sound waves in the density response near the\nsuperfluid phase transition. By collecting the best knowledge on the shear\nviscosity and thermal conductivity known so far, we calculate the various\ndiffusion coefficients and obtain the damping width of the (first and second)\nsounds. We find that the damping width of the first sound is greatly enhanced\nacross the superfluid transition and very close to the transition the second\nsound might be resolved in the density response for the transferred momentum up\nto the half of Fermi momentum. Our work is motivated by the recent measurement\nof the local dynamic structure factor at low momentum at Swinburne University\nof Technology and the on-going experiment on sound attenuation of a homogeneous\nunitary Fermi gas at Massachusetts Institute of Technology. We discuss how the\nmeasurement of the velocity and damping width of the sound modes in\nlow-momentum dynamic structure factor may lead to an improved determination of\nthe universal superfluid density, shear viscosity and thermal conductivity of a\nunitary Fermi gas.",
        "positive": "Polariton Condensation and Lasing: The similarities and differences between polariton condensation in\nmicrocavities and standard lasing in a semiconductor cavity structure are\nreviewed. The recent experiments on \"photon condensation\" are also reviewed."
    },
    {
        "anchor": "Observation of Quantized Conductance in Neutral Matter: In transport experiments the quantum nature of matter becomes directly\nevident when changes in conductance occur only in discrete steps, with a size\ndetermined solely by Planck's constant h. The observations of quantized steps\nin the electric conductance have provided important insights into the physics\nof mesoscopic systems and allowed for the development of quantum electronic\ndevices. Even though quantized conductance should not rely on the presence of\nelectric charges, it has never been observed for neutral, massive particles. In\nits most fundamental form, the phenomenon requires a quantum degenerate Fermi\ngas, a ballistic and adiabatic transport channel, and a constriction with\ndimensions comparable to the Fermi wavelength. Here we report on the\nobservation of quantized conductance in the transport of neutral atoms. We\nemploy high resolution lithography to shape light potentials that realize\neither a quantum point contact or a quantum wire for atoms. These constrictions\nare imprinted on a quasi two-dimensional ballistic channel connecting two\nadjustable reservoirs of quantum degenerate fermionic lithium atoms. By tuning\neither a gate potential or the transverse confinement of the constrictions, we\nobserve distinct plateaus in the conductance for atoms. The conductance in the\nfirst plateau is found to be equal to 1/h, the universal conductance quantum.\nFor low gate potentials we find good agreement between the experimental data\nand the Landauer formula, with all parameters determined a priori. Our\nexperiment constitutes the cold atom version of a mesoscopic device and can be\nreadily extended to more complex geometries and interacting quantum gases.",
        "positive": "Full-Bloch beams and ultrafast Rabi-rotating vortices: Strongly-coupled quantum fields, such as multi-component atomic condensates,\noptical fields and polaritons, are remarkable systems where the simple dynamics\nof coupled oscillators can meet the intricate phenomenology of quantum fluids.\nWhen the coupling between the components is coherent, not only the particles\nnumber, but also their phase texture that maps the linear and angular momentum,\ncan be exchanged. Here, on a system of exciton-polaritons, we have realized a\nso-called full-Bloch beam: a configuration in which all superpositions of the\nupper and the lower polariton -- all quantum states of the associated Hilbert\nspace -- are simultaneously present at different points of the physical space,\nevolving in time according to Rabi-oscillatory dynamics. As a result, the light\nemitted by the cavity displays a peculiar dynamics of spiraling vortices\nendowed with oscillating linear and angular momentum and exhibiting ultrafast\nmotion of their cores with striking accelerations to arbitrary speeds. This\nremarkable vortex motion is shown to result from distortions of the\ntrajectories by a homeomorphic mapping between the Rabi rotation of the full\nwavefunction on the Bloch sphere and Apollonian circles in the real space where\nthe observation is made. Such full-Bloch beams offer new prospects at a\nfundamental level regarding their topological properties or in the\ninterpretation of quantum mechanics, and the Rabi-rotating vortices they yield\nshould lead to interesting applications such as ultrafast optical tweezers."
    },
    {
        "anchor": "Efimov physics in the complex plane: Efimov effect is characterized by an infinite number of three-body bound\nstates following a universal geometric scaling law at two-body resonances. In\nthis paper, we investigate the influence of two-body loss which can be\ndescribed by a complex scattering length $a_c$ on these states. Interestingly,\nbecause of the complexity of the scattering length $a_c$, the trimer energy is\nno longer constrained on the negative real axis, and it is allowed to have a\nnonvanishing imaginary part and a real part which may exceed the three-body or\nthe atom-dimer scattering threshold. Indeed, by taking the\n$^{133}$Cs-$^{133}$Cs-$^6$Li system as a concrete example, we calculate the\ntrimer energies by solving the generalized Skorniakov-Ter-Martirosian equation\nand find such three-body bound states with energies that have positive real\nparts and obey a generalized geometric scaling law. Remarkably, we also find\nthat in some regions these three-body bound states have longer lifetimes\ncompared with the corresponding two-body bound states. The lifetimes for these\ntrimer states can even tend to infinity. Our work paves the way for the future\nexploration of few-body bound states in the complex plane.",
        "positive": "Can a Bose gas be saturated?: Bose-Einstein condensation is unique among phase transitions between\ndifferent states of matter in the sense that it occurs even in the absence of\ninteractions between particles. In Einstein's textbook picture of an ideal gas,\npurely statistical arguments set an upper bound on the number of particles\noccupying the excited states of the system, and condensation is driven by this\nsaturation of the quantum vapour. Dilute ultracold atomic gases are celebrated\nas a realisation of Bose-Einstein condensation in close to its purely\nstatistical form. Here we scrutinise this point of view using an ultracold gas\nof potassium (39K) atoms, in which the strength of interactions can be tuned\nvia a Feshbach scattering resonance. We first show that under typical\nexperi-mental conditions a partially condensed atomic gas strongly deviates\nfrom the textbook concept of a saturated vapour. We then use measurements at a\nrange of interaction strengths and temperatures to extrapolate to the\nnon-interacting limit, and prove that in this limit the behaviour of a Bose gas\nis consistent with the saturation picture. Finally, we provide evidence for the\nuniversality of our observations through additional measurements with a\ndifferent atomic species, 87Rb. Our results suggest a new way of characterising\ncondensation phenomena in different physical systems."
    },
    {
        "anchor": "Pure Mott phases in confined ultracold atomic systems: We propose a novel scheme for confining atoms to optical lattices by\nengineering a spatially-inhomogeneous hopping matrix element in the\nHubbard-model (HM) description, a situation we term off-diagonal confinement\n(ODC). We show, via an exact numerical solution of the boson HM with ODC, that\nthis scheme possesses distinct advantages over the conventional method of\nconfining atoms using an additional trapping potential, including the presence\nof incompressible Mott phases at commensurate filling and a phase diagram that\nis similar to the uniform HM. The experimental implementation of ODC will thus\nallow a more faithful realization of correlated phases of interest in cold atom\nexperiments.",
        "positive": "DC transport in a dissipative superconducting quantum point contact: We study the current-voltage characteristics of a superconducting junction\nwith particle losses at the contacts. We adopt the Keldysh formalism to compute\nthe steady-state current for varying transmission of the contact. In the low\ntransmission regime, the dissipation leads to an enhancement of the current at\nlow bias, a nonmonotonic dependence of current on dissipation, and the\nemergence of new structures in the current-voltage curves. The effect of\ndissipation by particle loss is found to be qualitatively different from that\nof a finite temperature and a finite inelastic scattering rate in the\nreservoirs."
    },
    {
        "anchor": "On a fragmented condensate in a uniform Bose system: According to the well-known analysis by Nozi\\'{e}res, the fragmentation of\nthe condensate increases the energy of a uniform interacting Bose system.\nTherefore, at $T= 0$ the condensate should be nonfragmented. We perform a more\ndetailed analysis and show that the result by Nozi\\'{e}res is not general. We\nfind that, in a dense Bose system, the formation of a crystal-like structure\nwith a fragmented condensate is possible. The effect is related to a nonzero\nsize of real atoms. Moreover, the wave functions studied by Nozi\\'{e}res are\nnot eigenfunctions of the Hamiltonian and, therefore, do not allow one to judge\nwith confidence about the structure of the condensate in the ground state. We\nhave constructed the wave functions in such a way that they are eigenfunctions\nof the Hamiltonian. The results show that the fragmentation of the condensate\n(quasicondensate) is possible for a finite one-dimensional uniform system at\nlow temperatures and a weak coupling.",
        "positive": "Quantum-State Controlled Penning Ionization Reactions between Ultracold\n  Alkali and Metastable Helium Atoms: In an ultracold, optically trapped mixture of $^{87}$Rb and metastable\ntriplet $^4$He atoms we have studied trap loss for different spin-state\ncombinations, for which interspecies Penning ionization is the main two-body\nloss process. We observe long trapping lifetimes for the purely quartet\nspin-state combination, indicating strong suppression of Penning ionization\nloss by at least two orders of magnitude. For the other spin-mixtures we\nobserve short lifetimes that depend linearly on the doublet character of the\nentrance channel. We compare the extracted loss rate coefficient with recent\npredictions of multichannel quantum-defect theory for reactive collisions\ninvolving a strong exothermic loss channel and find near-universal loss for\ndoublet scattering. Our work demonstrates control of reactive collisions by\ninternal atomic state preparation."
    },
    {
        "anchor": "Attractive polaron formed in doped nonchiral/chiral parabolic system\n  within ladder approximation: We investigate the properties of attractive polaron formed by a single\nimpurity dressed with the particle-hole excitations in a three-dimensional (3D)\ndoped (extrinsic) parabolic system. %at zero-temperature limit. Base on the\nsingle particle-hole variational ansatz, we study the pair propagator,\nself-energy, and the non-self-consistent medium $T$-matrix. The\nnon-self-consistent $T$-matrix discussed in this paper contains only the open\nchannel since we don't consider the shift of center-of-mass due to the\nresonance (e.g., induced by the magnetic field). Besides, since we focus on the\nlow-density regime of the majority particles, the effective Fermi wave vector\nis small. The scattering form factor is discussed in detail for the chiral case\nand compared to the non-chiral one. The effects of the bare coupling strength,\nwhich is momentum-cutoff-dependent, are also discussed. %within the pair\npropagator due to the scattering %with a certain scattering angle. We found\nthat the pair propagator and the related quantities, like the self-energy,\nspectral function, induced effective mass, and residue (spectral weight), all\nexhibit different features in the low-momentum regime and the high one, which\nalso related to the polaronic instabilities as well as the many-body\nfluctuation and nonadiabatic/adiabatic dynamics. The pair-propagator and the\nenergy relaxation time at finite temperature are also explored.",
        "positive": "Chiral odd Chern number lattice supersolidity with tunable unpaired\n  Majorana fermions in a Rydberg-dressed Fermi gas: There is growing interest to search the chiral Majorana fermions that could\narise as the quasi-particle edge state of a two-dimensional topological state\nof matter. Here we propose a new platform, i.e., a two-dimensional chiral odd\nChern number lattice supersolid state, for supporting multiple number-tunable\nchiral Majorana fermions from a single component Rydberg-dressed Fermi gas in\nan optical lattice. The attractiveness of our idea rests on the fact that by\nintroducing the unveiled competition between two distinct length scales, i.e.,\nlattice period and the distance of resonant Rydberg-dressing, can provide a new\nway to manipulate the spatial dependence of both the strength and sign of the\neffective Rydberg-dressed interaction. Such a designed effective interaction\nturns out, can induce an unveiled odd Chern number lattice supersolid state,\nwhich is confirmed by both the mean-field and Monte Carlo calculations.\nFurthermore, we also find that the spontaneously formed density modulation\nresulted from the discrete translational symmetry breaking provides a natural\nway of tuning the system's topology arising from the superfluidity induced by\nthe $U(1)$ symmetry breaking. It thus provide an alternative way for\nmanipulating the chiral Majorana fermions, which would be useful in topological\nquantum computation."
    },
    {
        "anchor": "Spin-1 bosons in an external magnetic field and a three body interaction\n  potential: We perform a thorough study of the effect of an external magnetic field on a\nspin-1 ultracold Bose gas via mean field approach corresponding to the both\nsigns of the spin dependent interaction. In contrast to some of the earlier\nstudies, the magnetic field in our work is included through both the hopping\nfrequencies (via Peierls coupling) and the zeeman interaction, thereby\nfacilitating an explo- ration for competition between the two. The phase\ndiagrams in the antiferromagnetic case shows that the Mott insulating (MI)\nphase with even particle occupancies is stable at low magnetic fields. At\nhigher magnetic fields, due to a competition between the hopping and the zeeman\ninteraction terms, the latter tries to destabilize the MI phase by suppressing\nthe formation of singlet pairs, while the former tends to stabilize the MI\nphase. In the ferromagnetic case, the MI lobes become more stable with\nincreasing flux strengths. Further inclusion of a three body interaction\npotential in order to ascertain its role on the phase diagram, we found that in\nabsence of the magnetic field, the MI lobes become more stable compared to the\nsuperfluid (SF) phase and the location of the transition point for the MI-SF\nphase increases with increasing the three body interaction strength. A strong\ncoupling perturbative calculation has also been done to provide a comparison\nwith our mean field phase diagrams. Lastly, with inclusion of the external\nfield, the insulating phases are found to be further stabilized by the three\nbody interaction potential.",
        "positive": "Phases of one-dimensional SU(N) cold atomic Fermi gases --from molecular\n  Luttinger liquids to topological phases: Alkaline-earth and ytterbium cold atomic gases make it possible to simulate\nSU(N)-symmetric fermionic systems in a very controlled fashion. Such a high\nsymmetry is expected to give rise to a variety of novel phenomena ranging from\nmolecular Luttinger liquids to (symmetry- protected) topological phases. We\nreview some of the phases that can be stabilized in a one dimensional lattice.\nThe physics of this multicomponent Fermi gas turns out to be much richer and\nmore exotic than in the standard SU(2) case. For N > 2, the phase diagram is\nquite rich already in the case of the single-band model, including a molecular\nLuttinger liquid (with dominant superfluid instability in the N-particle\nchannel) for incommensurate fillings, as well as various Mott-insulating phases\noccurring at commensurate fillings. Particular attention will be paid to the\ncases with additional orbital degree of freedom (which is accessible\nexperimentally either by taking into account two atomic states or by putting\natoms in the p-band levels). We introduce two microscopic models which are\nrelevant for these cases and discuss their symmetries and strong coupling\nlimits. More intriguing phase diagrams are then presented including, for\ninstance, symmetry protected topological phases characterized by non-trivial\nedge states."
    },
    {
        "anchor": "Single-particle properties and pseudogap effects in the BCS-BEC\n  crossover regime of an ultracold Fermi gas above Tc: We investigate strong-coupling effects on normal state properties of an\nultracold Fermi gas. Within the framework of $T$-matrix approximation in terms\nof pairing fluctuations, we calculate the single-particle density of states\n(DOS), as well as the spectral weight, over the entire BCS-BEC crossover region\nabove the superfluid phase transition temperature $T_{\\rm c}$. Starting from\nthe weak-coupling BCS regime, we show that the so-called pseudogap develops in\nDOS above $T_{\\rm c}$, which becomes remarkable in the crossover region. The\npseudogap structure continuously changes into a fully gapped one in the\nstrong-coupling BEC regime, where the gap energy is directly related to the\nbinding energy of tightly bound molecules. We determine the pseudogap\ntemperature $T^*$ where the dip structure in DOS vanishes. The value of $T^*$\nis shown to be very different from another characteristic temperature $T^{**}$\nwhere a BCS-type double peak structure disappears in the spectral weight. While\none finds $T^*>T^{**}$ in the BCS regime, $T^{**}$ becomes higher than $T^*$ in\nthe crossover region and BEC regime. Including this, we determine the pseudogap\nregion in the phase diagram of ultracold Fermi gases. Our results would be\nuseful in the search for the pseudogap region in ultracold $^6$Li and $^{40}$K\nFermi gases.",
        "positive": "Dynamics of spin-1 bosons in an optical lattice: spin mixing, quantum\n  phase revival spectroscopy and effective three-body interactions: We study the dynamics of spin-1 atoms in a periodic optical-lattice potential\nand an external magnetic field in a quantum quench scenario where we start from\na superfluid ground state in a shallow lattice potential and suddenly raise the\nlattice depth. The time evolution of the non-equilibrium state, thus created,\nshows collective collapse-and-revival oscillations of matter-wave coherence as\nwell as oscillations in the spin populations. We show that the complex pattern\nof these two types of oscillations reveals details about the superfluid and\nmagnetic properties of the initial many-body ground state. Furthermore, we show\nthat the strengths of the spin-dependent and spin-independent atom-atom\ninteractions can be deduced from the observations. The Hamiltonian that\ndescribes the physics of the final deep lattice not only contains two-body\ninteractions but also effective multi-body interactions, which arise due to\nvirtual excitations to higher bands. We derive these effective spin-dependent\nthree-body interaction parameters for spin-1 atoms and describe how spin-mixing\nis affected. Spinor atoms are unique in the sense that multi-body interactions\nare directly evident in the in-situ number densities in addition to the\nmomentum distributions. We treat both antiferromagnetic (e.g. $^{23}$Na atoms)\nand ferromagnetic (e.g. $^{87}$Rb and $^{41}$K) condensates."
    },
    {
        "anchor": "Mixing of 0$^+$ and 0$^-$ observed in hyperfine and Zeeman structure of\n  ultracold Rb$_2$ molecules: We study the combination of hyperfine and Zeeman structure in the spin-orbit\ncoupled $A^1\\Sigma_u^+-b^3\\Pi_u$ complex of $^{87}\\textrm{Rb}_2$. For this\npurpose, absorption spectroscopy at a magnetic field around\n$B=1000\\:\\textrm{G}$ is carried out. We drive optical dipole transitions from\nthe lowest rotational state of an ultracold Feshbach molecule to various\nvibrational levels with $0^+$ symmetry of the $A-b$ complex. In contrast to\nprevious measurements with rotationally excited alkali-dimers, we do not\nobserve equal spacings of the hyperfine levels. In addition, the spectra vary\nsubstantially for different vibrational quantum numbers, and exhibit large\nsplittings of up to $160\\:\\textrm{MHz}$, unexpected for $0^+$ states. The level\nstructure is explained to be a result of the repulsion between the states $0^+$\nand $0^-$ of $b^3\\Pi_u$, coupled via hyperfine and Zeeman interactions. In\ngeneral, $0^-$ and $0^+$ have a spin-orbit induced energy spacing $\\Delta$,\nthat is different for the individual vibrational states. From each measured\nspectrum we are able to extract $\\Delta$, which otherwise is not easily\naccessible in conventional spectroscopy schemes. We obtain values of $\\Delta$\nin the range of $\\pm 100\\:\\textrm{GHz}$ which can be described by coupled\nchannel calculations if a spin-orbit coupling is introduced that is different\nfor $0^-$ and $0^+$ of $b^3\\Pi_u$.",
        "positive": "Robustness of fragmented condensate many-body states for continuous\n  distribution amplitudes in Fock space: We consider a two-mode model describing scalar bosons with two-body\ninteractions in a single trap, taking into account coherent pair-exchange\nbetween the modes. It is demonstrated that the resulting fragmented many-body\nstates with continuous (nonsingular) Fock-space distribution amplitudes are\nrobust against perturbations due to occupation number and relative phase\nfluctuations, Josephson-type tunneling between the modes, and weakly broken\nparity of orbitals, as well as against perturbations due to interaction with a\nthird mode."
    },
    {
        "anchor": "Phase separation of a Bose-Bose mixture: impact of the trap and particle\n  number imbalance: We explore a few-body mixture of two bosonic species confined in\nquasi-one-dimensional parabolic traps of different length scales. The ground\nstate phase diagrams in the three-dimensional parameter space spanned by the\nharmonic length scale ratio, inter-species coupling strength and particle\nnumber ratio are investigated. As a first case study we use the mean-field\nansatz (MF) to perform a detailed analysis of the separation mechanism. It\nallows us to derive a simple and intuitive rule predicting which of the\nimmiscible phases is energetically more favorable at the miscible-immiscible\nphase boundary. We estimate the critical coupling strength for the\nmiscible-immiscible transition and perform a comparison to correlated many-body\nresults obtained by means of the Multi-Layer Multi-Configuration Time Dependent\nHartree method for bosonic mixtures (ML-X). At a critical ratio of the trap\nfrequencies, determined solely by the particle number ratio, the deviations\nbetween MF and ML-X are very pronounced and can be attributed to a high degree\nof entanglement between the components. As a result, we evidence the breakdown\nof the effective one-body picture. Additionally, when many-body correlations\nplay a substantial role, the one-body density is in general not sufficient for\ndeciding upon the phase at hand which we demonstrate exemplarily.",
        "positive": "Groundstate and Collective Modes of a Spin-Polarized Dipolar\n  Bose-Einstein Condensate in a Harmonic Trap: We report new results for the Thomas-Fermi groundstate and the quadrupolar\nmodes of density oscillations of a spin- polarized dipolar interacting\nBose-Einstein condensate for the case when the external magnetic field is not\norientated parallel to a principal axis of a harmonic anisotropic trap."
    },
    {
        "anchor": "Bosenova and three-body loss in a Rb-85 Bose-Einstein condensate: Collapsing Bose-Einstein condensates are rich and complex quantum systems for\nwhich quantitative explanation by simple models has proved elusive. We present\nnew experimental data on the collapse of high density Rb-85 condensates with\nattractive interactions and find quantitative agreement with the predictions of\nthe Gross-Pitaevskii equation. The collapse data and measurements of the decay\nof atoms from our condensates allow us to put new limits on the value of the\nRb-85 three-body loss coefficient K_3 at small positive and negative scattering\nlengths.",
        "positive": "Signatures of two-step impurity mediated vortex lattice melting in\n  Bose-Einstein Condensates: We simulate a rotating 2D BEC to study the melting of a vortex lattice in\npresence of random impurities. Impurities are introduced either through a\nprotocol in which vortex lattice is produced in an impurity potential or first\ncreating the vortex lattice in the absence of random pinning and then cranking\nup the (co-rotating) impurity potential. We find that for a fixed strength,\npinning of vortices at randomly distributed impurities leads to the new states\nof vortex lattice. It is unearthed that the vortex lattice follow a two-step\nmelting via loss of positional and orientational order. Also, the comparisons\nbetween the states obtained in two protocols show that the vortex lattice\nstates are metastable states when impurities are introduced after the formation\nof an ordered vortex lattice. We also show the existence of metastable states\nwhich depend on the history of how the vortex lattice is created."
    },
    {
        "anchor": "Vortex shedding frequency of a moving obstacle in a Bose-Einstein\n  condensate: We experimentally investigate the periodic vortex shedding dynamics in a\nhighly oblate Bose-Einstein condensate using a moving penetrable Gaussian\nobstacle. The shedding frequency $f_v$ is measured as a function of the\nobstacle velocity $v$ and characterized by a linear relationship of\n$f_v=a(v-v_c)$ with $v_c$ being the critical velocity. The proportionality\nconstant $a$ is linearly decreased with a decrease in the obstacle strength,\nwhereas $v_c$ approaches the speed of sound. When the obstacle size increases,\nboth $a$ and $v_c$ are decreased. The critical vortex shedding is further\ninvestigated for an oscillating obstacle and found to be consistent with the\nmeasured $f_v$. When the obstacle's maximum velocity exceeds $v_c$ but its\noscillation amplitude is not large enough to create a vortex dipole, we observe\nthat vortices are generated in the low-density boundary region of the trapped\ncondensate, which is attributed to the phonon emission from the oscillating\nobstacle. Finally, we discuss a possible asymptotic association of $a$ with the\nStrouhal number in the context of universal shedding dynamics of a superfluid.",
        "positive": "Exciting the long-lived Higgs mode in superfluid Fermi gases with\n  particle removal: Experimental evidence of the Higgs mode in strongly interacting superfluid\nFermi gases had not been observed until recently [Behrle et al., Nat. Phys. 14,\n781 (2018)]. Due to the coupling with other collective modes and quasiparticle\nexcitations, generating stable Higgs-mode oscillations is challenging. We study\nhow to excite long-lived Higgs-mode oscillations in a homogeneous superfluid\nFermi gas in the BCS-BEC crossover. We find that the Higgs mode can be excited\nby time-periodically modulating the scattering length at an appropriate\namplitude and frequency. However, even for a modulation frequency below twice\nthe pairing-gap energy, quasiparticles are still excited through the generation\nof higher harmonics due to nonlinearity in the superfluid. More importantly, we\nfind that persistent Higgs-mode oscillations with almost constant amplitude can\nbe produced by removing particles at an appropriate momentum, and the\noscillation amplitude can be controlled by the number of removed particles.\nFinally, we propose two ways to experimentally realize particle removal."
    },
    {
        "anchor": "Breakdown of the scale invariance in the vicinity of Tonks-Girardeau gas: In this article, we consider the monopole excitations of the harmonically\ntrapped Bose gas in the vicinity of the Tonks-Girardeau limit. Using\nGirardeau's Fermi-Bose duality and subsequently an effective fermion-fermion\nodd-wave interaction, we obtain the dominant correction to the\nscale-invariance-protected value of the excitation frequency, for\nmicroscopically small excitation amplitudes. We produce a series of diffusion\nMonte Carlo results that confirm our analytic prediction for three particles.\nAnd less expectedly, our result stands in excellent agreement with the result\nof a hydrodynamic simulation of the microscopically large but macroscopically\nsmall excitations.",
        "positive": "Realization of a cross-linked chiral ladder with neutral fermions in an\n  optical lattice by orbital-momentum coupling: We report the experimental realization of a cross-linked chiral ladder with\nultracold fermionic atoms in an optical lattice. In the ladder, the legs are\nformed by the orbital states of the optical lattice and the complex inter-leg\nlinks are generated by the orbital-changing Raman transitions that are driven\nby a moving lattice potential superimposed onto the optical lattice. The\neffective magnetic flux per ladder plaquette is tuned by the spatial\nperiodicity of the moving lattice, and the chiral currents are observed from\nthe asymmetric momentum distributions of the orbitals. The effect of the\ncomplex cross links is demonstrated in quench dynamics by measuring the\nmomentum dependence of the inter-orbital coupling strength. We discuss the\ntopological phase transition of the chiral ladder system for the variations of\nthe complex cross links."
    },
    {
        "anchor": "Connecting dynamical quantum phase transitions and topological\n  steady-state transitions by tuning the energy gap: Considerable theoretical and experimental efforts have been devoted to the\nquench dynamics, in particular, the dynamical quantum phase transition (DQPT)\nand the steady-state transition. These developments have motivated us to study\nthe quench dynamics of the topological systems, from which we find the\nconnection between these two transitions, that is, the DQPT, accompanied by a\nnonanalytic behavior as a function of time, always merges into a steady-state\ntransition signaled by the nonanalyticity of observables in the steady limit.\nAs the characteristic time of the DQPT diverges, it exhibits universal scaling\nbehavior, which is related to the scaling behavior at the corresponding\nsteady-state transition.",
        "positive": "Low-temperature thermodynamics of the unitary Fermi gas: superfluid\n  fraction, first sound and second sound: We investigate the low-temperature thermodynamics of the unitary Fermi gas by\nintroducing a model based on the zero-temperature spectra of both bosonic\ncollective modes and fermonic single-particle excitations. We calculate the\nHelmholtz free energy and from it we obtain the entropy, the internal energy\nand the chemical potential as a function of the temperature. By using these\nquantities and the Landau's expression for the superfluid density we determine\nanalytically the superfluid fraction, the critical temperature, the first sound\nvelocity and the second sound velocity. We compare our analytical results with\nother theoretical predictions and experimental data of ultracold atoms and\ndilute neutron matter."
    },
    {
        "anchor": "A modular implementation of an effective interaction approach for\n  harmonically trapped fermions in 1D: We introduce a generic and accessible implementation of an exact\ndiagonalization method for studying few-fermion models. Our aim is to provide a\ntestbed for the newcomers to the field as well as a stepping stone for trying\nout novel optimizations and approximations. This userguide consists of a\ndescription of the algorithm, and several examples in varying orders of\nsophistication. In particular, we exemplify our routine using an\neffective-interaction approach that fixes the low-energy physics. We benchmark\nthis approach against the existing data, and show that it is able to deliver\nstate-of-the-art numerical results at a significantly reduced computational\ncost.",
        "positive": "Two interacting fermions in a 1D harmonic trap: matching the Bethe\n  ansatz and variational approaches: In this work, combining the Bethe ansatz approach with the variational\nprinciple, we calculate the ground state energy of the relative motion of a\nsystem of two fermions with spin up and down interacting via a delta-function\npotential in a 1D harmonic trap. Our results show good agreement with the\nanalytical solution of the problem, and provide a starting point for the\ninvestigation of more complex few-body systems where no exact theoretical\nsolution is available."
    },
    {
        "anchor": "Dissipation Induced Structural Instability and Chiral Dynamics in a\n  Quantum Gas: Dissipative and unitary processes define the evolution of a many-body system.\nTheir interplay gives rise to dynamical phase transitions and can lead to\ninstabilities. We discovered a non-stationary state of chiral nature in a\nsynthetic many-body system with independently controllable unitary and\ndissipative couplings. Our experiment is based on a spinor Bose gas interacting\nwith an optical resonator. Orthogonal quadratures of the resonator field\ncoherently couple the Bose-Einstein condensate to two different atomic spatial\nmodes whereas the dispersive effect of the resonator losses mediates a\ndissipative coupling between these modes. In a regime of dominant dissipative\ncoupling we observe the chiral evolution and map it to a positional\ninstability.",
        "positive": "The Theory of Generalised Hydrodynamics for the One-dimensional Bose Gas: This article reviews the recent developments in the theory of generalised\nhydrodynamics (GHD) with emphasis on the repulsive one-dimensional Bose gas. We\ndiscuss the implications of GHD on the mechanisms of thermalisation in\nintegrable quantum many-body systems as well as its ability to describe\nfar-from-equilibrium behaviour of integrable and near integrable systems in a\nvariety of quantum quench scenarios. We outline the experimental tests of GHD\nin cold-atom gases and its benchmarks with other microscopic theoretical\napproaches. Finally, we offer some perspectives on the future direction of the\ndevelopment of GHD."
    },
    {
        "anchor": "Long-lived states with well-defined spins in spin-$1/2$ homogeneous Bose\n  gases: Many-body eigenfunctions of the total spin operator can be constructed from\nthe spin and spatial wavefunctions with non-trivial permutation symmetries.\nSpin-dependent interactions can lead to relaxation of the spin eigenstates to\nthe thermal equilibrium. A mechanism that stabilizes the many-body entangled\nstates is proposed here. Surprisingly, in spite coupling with the chaotic\nmotion of the spatial degrees of freedom, the spin relaxation can be suppressed\nby destructive quantum interference due to spherical vector and tensor terms of\nthe spin-dependent interactions. Tuning the scattering lengths by the method of\nFeshbach resonances, readily available in cold atomic labs, can enhance the\nrelaxation timescales by several orders of magnitude.",
        "positive": "Superdiffusion of quantized vortices uncovering scaling behavior of\n  quantum turbulence: Generic scaling laws, such as the Kolmogorov's 5/3-law, are milestone\nachievements of turbulence research in classical fluids. For quantum fluids\nsuch as atomic Bose-Einstein condensates, superfluid helium, and superfluid\nneutron stars, turbulence can also exist in the presence of a chaotic tangle of\nevolving quantized vortex lines. However, due to the lack of suitable\nexperimental tools to directly probe the vortex-tangle motion, so far little is\nknown about possible scaling laws that characterize the velocity correlations\nand trajectory statistics of the vortices in quantum-fluid turbulence (QT).\nAcquiring such knowledge could greatly benefit the development of advanced\nstatistical models of QT. Here we report an experiment where a tangle of\nvortices in superfluid $^4$He are decorated with solidified deuterium tracer\nparticles. Under experimental conditions where these tracers follow the motion\nof the vortices, we observed an apparent superdiffusion of the vortices. Our\nanalysis shows that this superdiffusion is not due to L\\'{e}vy flights, i.e.,\nlong-distance hops that are known to be responsible for superdiffusion of\nrandom walkers. Instead, a previously unknown power-law scaling of the\nvortex-velocity temporal correlation is uncovered as the cause. This finding\nmay motivate future research on hidden scaling laws in QT."
    },
    {
        "anchor": "Cooperative excitation and many-body interactions in a cold Rydberg gas: The dipole blockade of Rydberg excitations is a hallmark of the strong\ninteractions between atoms in these high-lying quantum states. One of the\nconsequences of the dipole blockade is the suppression of fluctuations in the\ncounting statistics of Rydberg excitations, of which some evidence has been\nfound in previous experiments. Here we present experimental results on the\ndynamics and the counting statistics of Rydberg excitations of ultra-cold\nRubidium atoms both on and off resonance, which exhibit sub- and\nsuper-Poissonian counting statistics, respectively. We compare our results with\nnumerical simulations using a novel theoretical model based on Dicke states of\nRydberg atoms including dipole-dipole interactions, finding good agreement\nbetween experiment and theory.",
        "positive": "Topological Quantum Matter with Ultracold Gases in Optical Lattices: Since the discovery of topological insulators, many topological phases have\nbeen predicted and realized in a range of different systems, providing both\nfascinating physics and exciting opportunities for devices. And although new\nmaterials are being developed and explored all the time, the prospects for\nprobing exotic topological phases would be greatly enhanced if they could be\nrealized in systems that were easily tuned. The flexibility offered by\nultracold atoms could provide such a platform. Here, we review the tools\navailable for creating topological states using ultracold atoms in optical\nlattices, give an overview of the theoretical and experimental advances and\nprovide an outlook towards realizing strongly correlated topological phases."
    },
    {
        "anchor": "Formation of granular structures in trapped Bose-Einstein condensates\n  under oscillatory excitations: We present experimental observations and numerical simulations of\nnonequilibrium spatial structures in a trapped Bose-Einstein condensate subject\nto oscillatory perturbations. In experiment, first, there appear collective\nexcitations, followed by quantum vortices. Increasing the amount of the\ninjected energy leads to the formation of vortex tangles representing quantum\nturbulence. We study what happens after the regime of quantum turbulence, with\nincreasing further the amount of injected energy. In such a strongly\nnonequilibrium Bose-condensed system of trapped atoms, vortices become\ndestroyed and there develops a new kind of spatial structure exhibiting\nessentially heterogeneous spatial density. The structure reminds fog consisting\nof high-density droplets, or grains, surrounded by the regions of low density.\nThe grains are randomly distributed in space, where they move. They live\nsufficiently long time to be treated as a type of metastable objects. Such\nstructures have been observed in nonequilibrium trapped Bose gases of\n$^{87}$Rb, subject to the action of alternating fields. Here we present\nexperimental results and support them by numerical simulations. The granular,\nor fog structure is essentially different from the state of wave turbulence\nthat develops after increasing further the amount of injected energy.",
        "positive": "Impact of the transverse direction on the many-body tunneling dynamics\n  in a two-dimensional bosonic Josephson junction: Tunneling in a many-body system appears as one of the novel implications of\nquantum physics, in which particles move in space under an otherwise\nclassically-forbidden potential barrier. Here, we theoretically describe the\nquantum dynamics of the tunneling phenomenon of a few intricate bosonic clouds\nin a closed system of a two-dimensional symmetric double-well potential. We\nexamine how the inclusion of the transverse direction, orthogonal to the\njunction of the double-well, can intervene in the tunneling dynamics of bosonic\nclouds. We use a well-known many-body numerical method, called the\nmulticonfigurational time-dependent Hartree for bosons (MCTDHB) method. MCTDHB\nallows one to obtain accurately the time-dependent many-particle wavefunction\nof the bosons which in principle entails all the information of interest about\nthe system under investigation. We analyze the tunneling dynamics by preparing\nthe initial state of the bosonic clouds in the left well of the double-well\neither as the ground, longitudinally or transversely excited, or a vortex\nstate. We unravel the detailed mechanism of the tunneling process by analyzing\nthe evolution in time of the survival probability, depletion and fragmentation,\nand the many-particle position, momentum, and angular-momentum expectation\nvalues and their variances. As a general rule, all objects lose coherence while\ntunneling through the barrier and the states which include transverse\nexcitations do so faster. Implications are briefly discussed."
    },
    {
        "anchor": "Thermodynamic equivalence of two-dimensional imperfect attractive Fermi\n  and repulsive Bose gases: We consider two-dimensional imperfect attractive Fermi and repulsive Bose\ngases consisting of spinless point particles whose total interparticle\ninteraction energy is represented by $a N^2/2 V$ with $a=-a_{F}\\leq 0$ for\nfermions, and $a=a_{B}\\geq 0$ for bosons. We show that in spite of the\nattraction the thermodynamics of $d=2$ imperfect Fermi gas remains well defined\nfor $0 \\leq a_{F}\\leq a_{0}=h^2/2\\pi m$, and is exactly the same as the one of\nthe repulsive imperfect Bose gas with $a_{B}=a_{0}-a_{F}$. In particular, for\n$a_{F}=a_{0}$ one observes the thermodynamic equivalence of the attractive\nimperfect Fermi gas and the ideal Bose gas.",
        "positive": "BCS - BEC crossover and quantum hydrodynamics in p-wave superfluids with\n  a symmetry of the A1 - phase: We solve the Leggett equations for the BCS - BEC crossover in the three\ndimension resonance p-wave superfluid with the symmetry of the A1 - phase. We\ncalculate the sound velocity, the normal density, and the specific heat for the\nBCS-domain (\\mu > 0), BEC-domain (\\mu < 0), and close to important point \\mu =\n0 in 100% polarized case. We find the indications of quantum phase - transition\nclose to the point \\mu(T = 0) = 0. Deep in the BCS and BEC-domains the\ncrossover ideas of Leggett and Nozieres, Schmitt-Rink work pretty well. We\ndiscuss the spectrum of orbital waves, the paradox of intrinsic angular\nmomentum and complicated problem of chiral anomaly in the BCS A1 - phase at T =\n0. We present two different approaches to a chiral anomaly: one based on\nsupersymmetric hydrodynamics, another one on the formal analogy with the Dirac\nequation in quantum electrodynamics. We evaluate the damping of nodal fermions\ndue to different decay processes in superclean case at T = 0 and find that we\nare in a ballistic regime \\omega\\tau >> 1. We propose to use aerogel or\nnonmagnetic impurities to reach hydrodynamic regime \\omega\\tau<< 1 at T = 0. We\ndiscuss the concept of the spectral flow and exact cancellations between\ntime-derivatives of anomalous and quasiparticle currents in the equation for\nthe total linear momentum conservation. We propose to derive and solve the\nkinetic equation for the nodal quasiparticles both in the hydrodynamic and in\nthe ballistic regimes to demonstrate this cancellation explicitly. We briefly\ndiscuss the role of the other residual interactions different from damping and\ninvite experimentalists to measure the spectrum and damping of orbital waves in\nA-phase of 3He at low temperatures."
    },
    {
        "anchor": "Three-dimensional spin-orbit coupled Fermi gases: Fulde-Ferrell pairing,\n  Majorana fermions, Weyl fermions and gapless topological superfluidity: We theoretically investigate a three-dimensional Fermi gas with Rashba\nspin-orbit coupling in the presence of both out-of-plane and in-plane Zeeman\nfields. We show that, driven by a sufficiently large Zeeman field, either\nout-of-plane or in-plane, the superfluid phase of this system exhibits a number\nof interesting features, including inhomogeneous Fulde-Ferrell pairing, gapped\nor gapless topological order and exotic quasi-particle excitations known as\nWeyl fermions that have linear energy dispersions in momentum space (i.e.,\nmassless Dirac fermions). The topological superfluid phase can have either four\nor two topologically protected Weyl nodes. We present the phase diagrams at\nboth zero and finite temperatures and discuss the possibility of their\nobservation in an atomic Fermi gas with synthetic spin-orbit coupling. In this\ncontext, topological superfluid phases with an imperfect Rashba spin-orbit\ncoupling are also studied.",
        "positive": "Faraday waves in Bose--Einstein condensate: From instability to\n  nonlinear dynamics: We numerically study the dynamics of Faraday waves in a pancake-shaped\nBose--Einstein condensate (BEC) subject to periodic modulation of the\ninteraction. After the modulation starts, Faraday waves appear and, thereafter,\nthe BEC enters the \"nonlinear regime\", in which several collective modes are\nexcited. By maintaining the modulation without dissipation, the kinetic energy\nthat contributes to the density gradient causes quasiperiodic motion and\nincreases monotonically. In the nonlinear regime, the dips in the density\nsimilar to dark solitons move around in the BEC, intersecting with each other\nand maintaining their shapes. On the other hand, even by turning off the\nmodulation, Faraday waves and the nonlinear regime appear. The kinetic energy\nconverges to the statistical steady state. The calculation of the modulation\nwith the dissipation illustrates the collapse and revival of Faraday waves.\nWhen the dissipation is small, the appearance and collapse of the Faraday waves\nand the nonlinear regime occur again."
    },
    {
        "anchor": "Drag dynamics in one-dimensional Fermi systems: We study drag dynamics of several fermions in a fermion cloud in\none-dimensional continuous systems, with particular emphasis on the non-trivial\nquantum many-body effects in systems whose parameters change gradually in real\ntime. We adopt the Fermi--Hubbard model and the time-dependent density matrix\nrenormalization group method to calculate the drag force on a trapped fermion\ncluster in a cloud of another fermion species with contact interaction. The\nsimulation result shows that a non-trivial peak in the resistance force is\nobserved in the high cloud density region, which implies a criterion of\neffective ways in diffusive transport in a fermion cloud. We compare the DMRG\nsimulation result with a mean-field result, and it is suggested that some\ninternal degrees of freedom have a crucial role in the excitation process when\nthe cloud density is high. This work emphasizes the difference between the\nfull-quantum calculation and the semiclassical calculation, which is the\nquantum effects, in slow dynamics of many-body systems bound in a fermion\ncloud.",
        "positive": "Quantum superpositions of flow states on a ring: We propose a scheme to generate quantum superpositions of macroscopically\ndistinct flow states of ultracold atoms on a ring using Raman coupling\nemploying a quantized laser field that is a cat-like superposition of optical\nvortices with opposite winding numbers. For atoms initially in their ground\nstate and entangled optical vortices of coherent states, this scheme can\nproduce a superposition of rotating and non-rotating states. We find fidelities\nof the quantum superpositions around 0.9 even before optimization."
    },
    {
        "anchor": "Three-body recombination in a single-component Fermi gas with $p$-wave\n  interaction: We study the three-body recombination of identical fermionic atoms. Using a\nzero-range model for the $p$-wave interaction, we show that the rate constant\nof three-body recombination into weakly bound $p$-wave dimers can be written as\n$\\alpha_{\\rm rec} \\propto v^{5/2}R^{1/2} k_T^4 (1+ C k_T^2 l_{\\rm d}^2)$ for\nlarge and positive scattering volume $v$. Here $R$ is the $p$-wave effective\nrange, $k_T^2$ gives the average thermal kinetic energy of the colliding atoms,\nand $l_{\\rm d}$ is the size of the $p$-wave dimer. The leading term is\ndifferent from the usually stated $v^{8/3}$-scaling law, but is consistent with\nan earlier two-channel calculation. For the subleading term, we compute the\nconstant $C$ by solving the relevant three-body problem perturbatively when the\nparameter $\\gamma\\equiv R/v^{1/3}$ is small. The additional $C k_T^2 l_{\\rm\nd}^2$ term provides important corrections for the temperature and interaction\ndependence of $\\alpha_{\\rm rec}$, especially close to resonance when $k_T\nl_{\\rm d}$ is relatively large.",
        "positive": "Exotic paired states with anisotropic spin-dependent Fermi surfaces: We propose a model for realizing exotic paired states in cold atomic Fermi\ngases. By using a {\\it spin dependent} optical lattice it is possible to\nengineer spatially anisotropic Fermi surfaces for each hyperfine species, that\nare rotated 90 degrees with respect to one another. We consider a balanced\npopulation of the fermions with an attractive interaction. We explore the BCS\nmean field phase diagram as a function of the anisotropy, density, and\ninteraction strength, and find the existence of an unusual paired superfluid\nstate with coexisting pockets of momentum space with gapless unpaired carriers.\nThis state is a relative of the Sarma or breached pair states in polarized\nmixtures, but in our case the Fermi gas is unpolarized. We also propose the\npossible existence of an exotic paired \"Cooper-pair Bose-Metal\" (CPBM) phase,\nwhich has a gap for single fermion excitations but gapless and uncondensed\n\"Cooper pair\" excitations residing on a \"Bose-surface\" in momentum space."
    },
    {
        "anchor": "Normal and superfluid fractions of inhomogeneous nonequilibrium quantum\n  fluids: We present a theoretical analysis of the normal and superfluid fractions of\nquantum fluids described by a nonequilibrium extension of the Gross-Pitaevskii\nequation in the presence of an external potential. Both disordered and regular\npotentials are considered. The normal and superfluid fractions are defined by\nthe response of the nonequilibrium quantum fluid to a vector potential, in\nanalogy with the equilibrium case. We find that the physical meaning of these\ndefinitions breaks down out of equilibrium. The normal and superfluid fractions\nno longer add up to one and for some types of external potentials, they can\neven become negative.",
        "positive": "Strongly interacting impurities in a dilute Bose condensate: An impurity in a Bose gas is commonly referred to as Bose polaron. For a\ndilute Bose gas its properties are expected to be universal, that is dependent\nonly on a few parameters characterizing the boson-impurity interactions. When\nboson-impurity interactions are weak, it has been known for some time that the\nproperties of the polaron depend only on the scattering length of these\ninteractions. In this paper which accompanies and extends Ref. [Phys. Rev.\nLett. 126, 123403 (2021)] (where some of these results have already been\nreported) we examine stronger boson-impurity interactions, keeping their range\nfinite. We demonstrate that for attractive interactions between impurity and\nthe bosons up to and including the unitary point of these interactions, all\nstatic properties of a Bose polaron in a dilute Bose gas can be calculated in\nterms of the scattering length and an additional parameter which characterizes\nthe range of the impurity-boson interactions. We show that our approach to this\nproblem is valid if this parameter does not deviate too much from the\nscattering length of intra-boson interactions, with the precise criterion given\nin the text. We produce explicit expressions for the energy and other\nproperties of polaron for the case when the impurity-boson scattering length is\ntuned to unitarity, and we also provide the first correction away from it."
    },
    {
        "anchor": "Experimental realization of strong effective magnetic fields in an\n  optical lattice: We use Raman-assisted tunneling in an optical superlattice to generate large\ntunable effective magnetic fields for ultracold atoms. When hopping in the\nlattice, the accumulated phase shift by an atom is equivalent to the\nAharonov-Bohm phase of a charged particle exposed to a staggered magnetic field\nof large magnitude, on the order of one flux quantum per plaquette. We study\nthe ground state of this system and observe that the frustration induced by the\nmagnetic field can lead to a degenerate ground state for non-interacting\nparticles. We provide a measurement of the local phase acquired from\nRaman-induced tunneling, demonstrating time-reversal symmetry breaking of the\nunderlying Hamiltonian. Furthermore, the quantum cyclotron orbit of single\natoms in the lattice exposed to the magnetic field is directly revealed.",
        "positive": "Three-dimensional quantum phase diagram of the exact ground states of a\n  mixture of two species of spin-1 Bose gases with interspecies spin exchange: We find nearly all the exact ground states of a mixture of two species of\nspin-1 atoms with both interspecies and intraspecies spin exchanges in absence\nof a magnetic field. The quantum phase diagram in the three-dimensional\nparameter space and its two-dimensional cross sections are described. The\nboundaries where the ground states are either continuous or discontinuous are\ndetermined, with the latter identified as where quantum phase transitions take\nplace. The two species are always disentangled if the interspecies spin\ncoupling is ferromagnetic or zero. Quantum phase transitions occur when the\ninterspecies spin coupling varies between antiferromagtic and zero or\nferromagnetic while the two intraspecies spin couplings both remain\nferromagnetic. On the other hand, by tuning the interspecies spin coupling from\nzero to antiferromagnetic and then back to zero, one can circumvent the quantum\nphase transition due to sign change of the intraspecies spin coupling of a\nsingle species, which is spin-decoupled with the other species with\nferromagnetic intraspecies spin coupling. Overall speaking, interplay among\ninterspecies and two intraspecies spin exchanges significantly enriches quantum\nphases of spinor atomic gases."
    },
    {
        "anchor": "Experimental Characterization of Two-Particle Entanglement through\n  Position and Momentum Correlations: Quantum simulation is a rapidly advancing tool to gain insight into complex\nquantum states and their dynamics. Trapped ion systems have pioneered\ndeterministic state preparation and comprehensive state characterization,\noperating on localized and thus distinguishable particles. With ultracold atom\nexperiments, one can prepare large samples of delocalized particles, but the\nsame level of characterization has not yet been achieved. Here, we present a\nmethod to measure the positions and momenta of individual particles to obtain\ncorrelations and coherences. We demonstrate this with deterministically\nprepared samples of two interacting ultracold fermions in a coupled double\nwell. As a first application, we use our technique to certify and quantify\ndifferent types of entanglement.",
        "positive": "Self-amplifying Hawking radiation and its background: a numerical study: We numerically study an analogue black hole with two horizons with similar\nparameters to a recent experiment. We find that the Hawking radiation exists on\na background which contains a density oscillation, a zero-frequency ripple. The\nHawking radiation evolves from spontaneous to self-amplifying, while the\nbackground ripple grows steadily with no qualitative change. It is seen that\nthe self-amplifying Hawking radiation has a non-zero frequency. The background\nripple appears even before the inner horizon is created, in contrast to\npredictions. This work is in agreement with the recent observation of\nself-amplifying Hawking radiation, and explains some of the features seen. In\ncontrast to recent works, our study differentiates between the Hawking\nradiation observed, and the evolution of the background."
    },
    {
        "anchor": "Quantum phase diagram for two species hardcore bosons in one-dimensional\n  optical lattices with the resonantly driven Rabi frequency: We propose an experimental realization of the time-periodically modulated\nRabi frequency and suggest density-dependent hoppings of two species hardcore\nbosons in a one-dimensional optical lattice. Distinct from the previous work\n[Phys. Rev. Research {\\bf 2}, 013275 (2020)], we study effects in the first\nresonance region. In the effective Hamiltonian, the intra-species hopping\noccurs only if the density discrepancy of the other species on these sites is\nzero, while the inter-species one is allowed once the relevant density\ndiscrepancy becomes nonzero. At integer-$1$ filling, the quantum phase diagram\nof the effective Hamiltonian is determined by the perturbation analysis\ntogether with numerical calculations. We find that in the limit of dominant\n$J_{1}$, the system becomes a double-degenerate dimerized state, with\nspontaneously breaking the translation symmetry. The interplay of $J_{0}$,\n$J_{1}$ and the fixed ${\\bar U}=1$ leads to three BKT transition lines and a\ntricritical BKT point. Exact transition lines are obtained by the level\nspectroscopic technique. Besides, general physical properties, including the\ncharge gap, neutral gap, superfluid density and dimerization strength, are\ninvestigated as well.",
        "positive": "Anisotropic acoustics in dipolar Fermi gases: We consider plane wave modes in ultracold, but not quantum degenerate,\ndipolar Fermi gases in the hydrodynamic limit. Longitudinal waves present\nanisotropies in both the speed of sound and their damping, and experience a\nsmall, undulatory effect in their flow velocity. Two distinct types of shear\nwaves appear, a ``familiar\" one, and another that is accompanied by nontrivial\ndensity and temperature modulations. We propose these shear modes as an\nexperimental means to measure the viscosity coefficients, including their\nanisotropies."
    },
    {
        "anchor": "Manifold approach for a many-body Wannier-Stark system: localization and\n  chaos in energy space: We study the resonant tunneling effect in a many-body Wannier-Stark system,\nrealized by ultracold bosonic atoms in an optical lattice subjected to an\nexternal Stark force. The properties of the many-body system are effectively\ndescribed in terms of upper-band excitation manifolds, which allow for the\nstudy of the transition between regular and quantum chaotic spectral\nstatistics. We show that our system makes it possible to control the spectral\nstatistics locally in energy space by the competition of the force and the\ninterparticle interaction. By a time-dependent sweep of the Stark force the\ndynamics is reduced to a Landau-Zener problem in the single-particle setting.",
        "positive": "Unitary thermodynamics from thermodynamic geometry II: Fit to a local\n  density approximation: Strongly interacting Fermi gasses at low density possess universal\nthermodynamic properties which have recently seen very precise $PVT$\nmeasurements by a group at MIT. This group determined local thermodynamic\nproperties of a system of ultra cold $^6\\mbox{Li}$ atoms tuned to Feshbach\nresonance. In this paper, I analyze the MIT data with a thermodynamic theory of\nunitary thermodynamics based on ideas from critical phenomena. This theory was\nintroduced in the first paper of this sequence, and characterizes the scaled\nthermodynamics by the entropy per particle $z= S/N k_B$, and energy per\nparticle $Y(z)$, in units of the Fermi energy. $Y(z)$ is in two segments,\nseparated by a second-order phase transition at $z=z_c$: a \"normal\" segment for\n$z>z_c$, and a \"superfluid\" segment for $z<z_c$. For small $z$, the theory\nobeys a series $Y(z)=y_0+y_1 z^{\\alpha }+y_2 z^{2 \\alpha}+\\cdots,$ where\n$\\alpha$ is a constant exponent, and $y_i$ ($i\\ge 0$) are constant series\ncoefficients. For large $z$, the theory obeys a perturbation of the ideal gas\n$Y(z)= \\tilde{y}_0\\,\\mbox{exp}[2\\gamma z/3]+\n\\tilde{y}_1\\,\\mbox{exp}[(2\\gamma/3-1)z]+\n\\tilde{y}_2\\,\\mbox{exp}[(2\\gamma/3-2)z]+\\cdots$ where $\\gamma$ is a constant\nexponent, and $\\tilde{y}_i$ ($i\\ge 0$) are constant series coefficients. This\nlimiting form for large $z$ differs from the series used in the first paper,\nand was necessary to fit the MIT data. I fit the MIT data by adjusting four\nfree independent theory parameters: $(\\alpha,\\gamma,\\tilde{y}_0,\\tilde{y}_1)$.\nThis fit process was augmented by trap integration and comparison with earlier\nthermal data taken at Duke University. The overall match to both the data sets\nwas good, and had $\\alpha=1.21(3)$, $\\gamma=1.21(3)$, $z_c=0.69(2)$, scaled\ncritical temperature $T_c/T_F=0.161(3)$, where $T_F$ is the Fermi temperature,\nand Bertsch parameter $\\xi_B=0.368(5)$."
    },
    {
        "anchor": "The equilibrium state of a trapped two-dimensional Bose gas: We study experimentally and numerically the equilibrium density profiles of a\ntrapped two-dimensional $^{87}$Rb Bose gas, and investigate the equation of\nstate of the homogeneous system using the local density approximation. We find\na clear discrepancy between in-situ measurements and Quantum Monte Carlo\nsimulations, which we attribute to a non-linear variation of the optical\ndensity of the atomic cloud with its spatial density. However, good agreement\nbetween experiment and theory is recovered for the density profiles measured\nafter time-of-flight, taking advantage of their self-similarity in a\ntwo-dimensional expansion.",
        "positive": "Polarization Suppression and Nonmonotonic Local Two-Body Correlations in\n  the Two-Component Bose Gas in One Dimension: We study the interplay of quantum statistics, strong interactions and finite\ntemperatures in the two-component (spinor) Bose gas with repulsive\ndelta-function interactions in one dimension. Using the Thermodynamic Bethe\nAnsatz, we obtain the equation of state, population densities and local density\ncorrelation numerically as a function of all physical parameters (interaction,\ntemperature and chemical potentials), quantifying the full crossover between\nlow-temperature ferromagnetic and high-temperature unpolarized regimes. In\ncontrast to the single-component, Lieb-Liniger gas, nonmonotonic behaviour of\nthe local density correlation as a function of temperature is observed."
    },
    {
        "anchor": "Is an Ultra-Cold Strongly Interacting Fermi Gas a Perfect Fluid?: Fermi gases with magnetically tunable interactions provide a clean and\ncontrollable laboratory system for modeling interparticle interactions between\nfermions in nature. The s-wave scattering length, which is dominant a low\ntemperature, is made to diverge by tuning near a collisional (Feshbach)\nresonance. In this regime, two-component Fermi gases are stable and strongly\ninteracting, enabling tests of nonperturbative many-body theories in a variety\nof disciplines, from high temperature superconductors to neutron matter and\nquark-gluon plasmas. We have developed model-independent methods for measuring\nthe entropy and energy of this model system, providing a benchmark for\ncalculations of the thermodynamics. Our experiments on the expansion of\nrotating strongly interacting Fermi gases in the normal fluid regime reveal\nextremely low viscosity hydrodynamics. Combining the thermodynamic and\nhydrodynamic measurements enables an estimate of the ratio of the shear\nviscosity to the entropy density. A strongly interacting Fermi gas in the\nnormal fluid regime is found to be a nearly perfect fluid, where the ratio of\nthe viscosity to the entropy density is close to a universal minimum that has\nbeen conjectured by string theory methods.",
        "positive": "Ultracold atoms in a square lattice with spin-orbit coupling: Charge\n  order, superfluidity, and topological signatures: We present an $\\textit{ab initio}$, numerically exact study of attractive\nfermions in square lattices with Rashba spin-orbit coupling. The ground state\nof this system is a supersolid, with co-existing charge and superfluid order.\nThe superfluid is composed of both singlet and triplet pairs induced by\nspin-orbit coupling. We perform large-scale calculations using auxiliary-field\nquantum Monte Carlo to provide the first full, quantitative description of the\ncharge, spin, and pairing properties of the system. In addition to\ncharacterizing the exotic physics, our results will serve as essential\nhigh-accuracy benchmarks for the intense theoretical and especially\nexperimental efforts in ultracold atoms to realize and understand an expanding\nvariety of quantum Hall and topological superconductor systems."
    },
    {
        "anchor": "Finite temperature effective field theory and two-band superfluidity in\n  Fermi gases: We develop a description of fermionic superfluids in terms of an effective\nfield theory for the pairing order parameter. Our effective field theory\nimproves on the existing Ginzburg - Landau theory for superfluid Fermi gases in\nthat it is not restricted to temperatures close to the critical temperature.\nThis is achieved by taking into account long-range fluctuations to all orders.\nThe results of the present effective field theory compare well with the results\nobtained in the framework of the Bogoliubov - de Gennes method. The advantage\nof an effective field theory over Bogoliubov - de Gennes calculations is that\nmuch less computation time is required. In the second part of the paper, we\nextend the effective field theory to the case of a two-band superfluid. The\npresent theory allows us to reveal the presence of two healing lengths in the\ntwo-band superfluids, to analyze the finite-temperature vortex structure in the\nBEC-BCS crossover, and to obtain the ground state parameters and spectra of\ncollective excitations. For the Leggett mode our treatment provides an\ninterpretation of the observation of this mode in two-band superconductors.",
        "positive": "CONAN -- the cruncher of local exchange coefficients for strongly\n  interacting confined systems in one dimension: We consider a one-dimensional system of particles with strong zero-range\ninteractions. This system can be mapped onto a spin chain of the Heisenberg\ntype with exchange coefficients that depend on the external trap. In this\npaper, we present an algorithm that can be used to compute these exchange\ncoefficients. We introduce an open source code CONAN (Coefficients of\nOne-dimensional N-Atom Networks) which is based on this algorithm. CONAN works\nwith arbitrary external potentials and we have tested its reliability for\nsystem sizes up to around 35 particles. As illustrative examples, we consider a\nharmonic trap and a box trap with a superimposed asymmetric tilted potential.\nFor these examples, the computation time typically scales with the number of\nparticles as $O(N^{3.5 \\pm 0.4})$. Computation times are around 10 seconds for\n$N=10$ particles and less than 10 minutes for $N=20$ particles."
    },
    {
        "anchor": "Intercomponent entanglement entropy and spectrum in binary Bose-Einstein\n  condensates: We study the entanglement entropy and spectrum between components in binary\nBose-Einstein condensates in $d$ spatial dimensions. We employ effective field\ntheory to show that the entanglement spectrum exhibits an anomalous square-root\ndispersion relation in the presence of an intercomponent tunneling (a Rabi\ncoupling) and a gapped dispersion relation in its absence. These spectral\nfeatures are associated with the emergence of long-range interactions in terms\nof the superfluid velocity and the particle density in the entanglement\nHamiltonian. Our results demonstrate that unusual long-range interactions can\nbe emulated in a subsystem of multicomponent BECs that have only short-range\ninteractions. We also find that for a finite Rabi coupling the entanglement\nentropy exhibits a volume-law scaling with subleading logarithmic corrections\noriginating from the Nambu-Goldstone mode and the symmetry restoration for a\nfinite volume.",
        "positive": "Preparation of Low Entropy Correlated Many-body States via Conformal\n  Cooling Quenches: We analyze a method for preparing low-entropy many-body states in isolated\nquantum optical systems of atoms, ions and molecules. Our approach is based\nupon shifting entropy between different regions of a system by spatially\nmodulating the magnitude of the effective Hamiltonian. We conduct two case\nstudies, on a topological spin chain and the spinful fermionic Hubbard model,\nfocusing on the key question: can a \"conformal cooling quench\" remove\nsufficient entropy within experimentally accessible timescales? Finite\ntemperature, time-dependent matrix product state calculations reveal that even\nmoderately sized \"bath\" regions can remove enough energy and entropy density to\nexpose coherent low temperature physics. The protocol is particularly natural\nin systems with long-range interactions such lattice-trapped polar molecules\nand Rydberg dressed atoms where the magnitude of the Hamiltonian scales\ndirectly with the density. To this end, we propose a simple implementation of\nconformal cooling quenches in a dilutely-filled optical lattice, where\nsignatures of quantum magnetism can be observed."
    },
    {
        "anchor": "Non-equilibrium steady states of ideal bosonic and fermionic quantum\n  gases: We investigate non-equilibrium steady states of driven-dissipative ideal\nquantum gases of both bosons and fermions. We focus on systems of sharp\nparticle number that are driven out of equilibrium either by the coupling to\nseveral heat baths of different temperature or by time-periodic driving in\ncombination with the coupling to a heat bath. Within the framework of\n(Floquet-)Born-Markov theory, several analytical and numerical methods are\ndescribed in detail. This includes a mean-field theory in terms of occupation\nnumbers, an augmented mean-field theory taking into account also non-trivial\ntwo-particle correlations, and quantum-jump-type Monte-Carlo simulations. For\nthe case of the ideal Fermi gas, these methods are applied to simple lattice\nmodels and the possibility of achieving exotic states via bath engineering is\npointed out. The largest part of this work is devoted to bosonic quantum gases\nand the phenomenon of Bose selection, a non-equilibrium generalization of Bose\ncondensation, where multiple single-particle states are selected to acquire a\nlarge occupation [Phys. Rev. Lett. 111, 240405 (2013)]. In this context, among\nothers, we provide a theory for transitions where the set of selected states\nchanges, describe an efficient algorithm for finding the set of selected\nstates, investigate beyond-mean-field effects, and identify the dominant\nmechanisms for heat transport in the Bose selected state.",
        "positive": "Bouncing motion and penetration dynamics in multicomponent Bose-Einstein\n  condensates: We investigate dynamic properties of bouncing and penetration in colliding\nbinary and ternary Bose-Einstein condensates comprised of different Zeeman or\nhyperfine states of 87Rb. Through the application of magnetic field gradient\npulses, two- or three-component condensates in an optical trap are spatially\nseparated and then made to collide. The subsequent evolutions are classified\ninto two categories: repeated bouncing motion and mutual penetration after\ndamped bounces. We experimentally observed mutual penetration for immiscible\ncondensates, bouncing between miscible condensates, and domain formation for\nmiscible condensates. From numerical simulations of the Gross-Pitaevskii\nequation, we find that the penetration time can be tuned by slightly changing\nthe atomic interaction strengths."
    },
    {
        "anchor": "Enhanced heat flow in the hydrodynamic-collisionless regime: We study the heat conduction of a cold, thermal cloud in a highly asymmetric\ntrap. The cloud is axially hydrodynamic, but due to the asymmetric trap\nradially collisionless. By locally heating the cloud we excite a thermal dipole\nmode and measure its oscillation frequency and damping rate. We find an\nunexpectedly large heat conduction compared to the homogeneous case. The\nenhanced heat conduction in this regime is partially caused by atoms with a\nhigh angular momentum spiraling in trajectories around the core of the cloud.\nSince atoms in these trajectories are almost collisionless they strongly\ncontribute to the heat transfer. We observe a second, oscillating hydrodynamic\nmode, which we identify as a standing wave sound mode.",
        "positive": "Observing atom bunching by the Fourier slice theorem: By a novel reciprocal space analysis of the measurement, we report a\ncalibrated in situ observation of the bunching effect in a 3D ultracold gas.\nThe calibrated measurement with no free parameters confirms the role of the\nexchange symmetry and the Hanbury Brown-Twiss effect in the bunching. Also, the\nenhanced fluctuations of the bunching effect give a quantitative measure of the\nincreased isothermal compressibility. We use 2D images to probe the 3D gas,\nusing the same principle by which computerized tomography reconstructs a 3D\nimage of a body. The powerful reciprocal space technique presented is\napplicable to systems with one, two, or three dimensions."
    },
    {
        "anchor": "Formation dynamics of black- and white-hole horizons in an analogue\n  gravity model: We investigate the formation dynamics of sonic horizons in a Bose gas\nconfined in a (quasi) one-dimensional trap. This system is one of the most\npromising realizations of the analogue gravity paradigm and has already been\nsuccessfully studied experimentally. Taking advantage of the exact solution of\nthe one-dimensional, hard-core, Bose model (Tonks-Girardeau gas) we show that,\nby switching on a step potential, either a sonic (black-hole-like) horizon or a\nblack/white hole pair may form, according to the initial velocity of the fluid.\nOur simulations never suggest the formation of an isolated white-hole horizon,\nalthough a stable stationary solution of the dynamical equations with those\nproperties is analytically found. Moreover, we show that the semiclassical\ndynamics, based on the Gross-Pitaevskii equation, conforms to the exact\nsolution only in the case of fully subsonic flows while a stationary solution\nexhibiting a supersonic transition is never reached dynamically.",
        "positive": "Some exact solutions of the local induction equation for motion of a\n  vortex in a Bose-Einstein condensate with Gaussian density profile: The dynamics of a vortex filament in a trapped Bose-Einstein condensate is\nconsidered when the equilibrium density of the condensate, in rotating with\nangular velocity ${\\bf\\Omega}$ coordinate system, is Gaussian with a quadratic\nform ${\\bf r}\\cdot\\hat D{\\bf r}$. It is shown that equation of motion of the\nfilament in the local induction approximation admits a class of exact solutions\nin the form of a straight moving vortex, ${\\bf R}(\\beta,t)=\\beta {\\bf M}(t)\n+{\\bf N}(t)$, where $\\beta$ is a longitudinal parameter, and $t$ is the time.\nThe vortex is in touch with an ellipsoid, as it follows from the conservation\nlaws ${\\bf N}\\cdot \\hat D {\\bf N}=C_1$ and ${\\bf M}\\cdot \\hat D {\\bf N}=C_0=0$.\nEquation of motion for the tangent vector ${\\bf M}(t)$ turns out to be closed,\nand it has the integrals ${\\bf M}\\cdot \\hat D {\\bf M}=C_2$, $(|{\\bf M}| -{\\bf\nM}\\cdot\\hat G{\\bf \\Omega})=C$, where the matrix $\\hat G=2(\\hat I \\mbox{Tr\\,}\n\\hat D -\\hat D)^{-1}$. Intersection of the corresponding level surfaces\ndetermines trajectories in the phase space."
    },
    {
        "anchor": "Thomas-Fermi Approximation for a Condensate with Higher-order\n  Interactions: We consider the ground state of a harmonically trapped Bose-Einstein\ncondensate within the Gross-Pitaevskii theory including the effective-range\ncorrections for a two-body zero-range potential. The resulting non-linear\nSchr\\\"odinger equation is solved analytically in the Thomas-Fermi approximation\nneglecting the kinetic energy term. We present results for the chemical\npotential and the condensate profiles, discuss boundary conditions, and compare\nto the usual Thomas-Fermi approach. We discuss several ways to increase the\ninfluence of effective-range corrections in experiment with magnetically\ntunable interactions. The level of tuning required could be inside experimental\nreach in the near future.",
        "positive": "Pseudogap phenomena near the BKT transition of a two-dimensional\n  ultracold Fermi gas in the crossover region: We investigate strong-coupling properties of a two-dimensional ultracold\nFermi gas in the normal phase. In the three-dimensional case, it has been shown\nthat the so-called pseudogap phenomena can be well described by a\n(non-self-consistent) $T$-matrix approximation (TMA). In the two-dimensional\ncase, while this strong coupling theory can explain the pseudogap phenomenon in\nthe strong-coupling regime, it unphysically gives large pseudogap size in the\ncrossover region, as well as in the weak-coupling regime. We show that this\ndifficulty can be overcome when one improve TMA to include higher order pairing\nfluctuations within the framework of a self-consistent $T$-matrix approximation\n(SCTMA). The essence of this improvement is also explained. Since the\nobservation of the BKT transition has recently been reported in a\ntwo-dimensional $^6$Li Fermi gas, our results would be useful for the study of\nstrong-coupling physics associated with this quasi-long-range order."
    },
    {
        "anchor": "Metastable decoherence-free subspaces and electromagnetically induced\n  transparency in interacting many-body systems: We investigate the dynamics of a generic interacting many-body system under\nconditions of electromagnetically induced transparency (EIT). This problem is\nof current relevance due to its connection to non-linear optical media realized\nby Rydberg atoms. In an interacting system the structure of the dynamics and\nthe approach to the stationary state becomes far more complex than in the case\nof conventional EIT. In particular, we discuss the emergence of a metastable\ndecoherence free subspace, whose dimension for a single Rydberg excitation\ngrows linearly in the number of atoms. On approach to stationarity this leads\nto a slow dynamics which renders the typical assumption of fast relaxation\ninvalid. We derive analytically the effective non-equilibrium dynamics in the\ndecoherence free subspace which features coherent and dissipative two-body\ninteractions. We discuss the use of this scenario for the preparation of\ncollective entangled dark states and the realization of general unitary\ndynamics within the spin-wave subspace.",
        "positive": "Quantum phases of bosonic chiral molecules in helicity lattices: We reveal the existence of polarizing quantum phases for the enantiomers of\ncold, interacting chiral molecules in an optical helicity lattice by means of\nan extended Bose-Hubbard model. These recently proposed lattices have sites\nwith alternating helicity which exert a discriminatory force on chiral\nmolecules with different handedness. In our study of the phase diagram we find\nthat a strong dipolar repulsion between molecules results in the separation of\nleft and right enantiomers."
    },
    {
        "anchor": "Nonlinear Spectroscopic Effects in Quantum Gases Induced by Atom-Atom\n  Interactions: We consider nonlinear spectroscopic effects - interaction-enhanced double\nresonance and spectrum instability - that appear in ultracold quantum gases\nowing to collisional frequency shift of atomic transitions and, consequently,\ndue to the dependence of the frequencies on the population of various internal\nstates of the particles. Special emphasis is put to two simplest cases, (a) the\ngas of two-level atoms and (b) double resonance in a gas of three-level bosons,\nin which the probe transition frequency remains constant.",
        "positive": "Coherent molecule formation in anharmonic potentials near\n  confinement-induced resonances: We perform a theoretical and experimental study of a system of two ultracold\natoms with tunable interaction in an elongated trapping potential. We show that\nthe coupling of center-of-mass and relative motion due to an anharmonicity of\nthe trapping potential leads to a coherent coupling of a state of an unbound\natom pair and a molecule with a center of mass excitation. By performing the\nexperiment with exactly two particles we exclude three-body losses and can\ntherefore directly observe coherent molecule formation. We find quantitative\nagreement between our theory of inelastic confinement-induced resonances and\nthe experimental results. This shows that the effects of center-of-mass to\nrelative motion coupling can have a significant impact on the physics of\nquasi-1D quantum systems."
    },
    {
        "anchor": "Decay of a superfluid current of ultra-cold atoms in a toroidal trap: Using a numerical implementation of the truncated Wigner approximation, we\nsimulate the experiment reported by Ramanathan et al. in Phys. Rev. Lett. 106,\n130401 (2011), in which a Bose-Einstein condensate is created in a toroidal\ntrap and set into rotation via a phase imprinting technique. A potential\nbarrier is then placed in the trap to study the decay of the superflow. We find\nthat the current decays via thermally activated phase slips, which can also be\nvisualized as vortices crossing the barrier region in the radial direction.\nAdopting the notion of critical velocity used in the experiment, we determine\nit to be lower than the local speed of sound at the barrier, in contradiction\nto the predictions of the zero-temperature Gross-Pitaevskii equation. We map\nout the superfluid decay rate and critical velocity as a function of\ntemperature and observe a strong dependence. Thermal fluctuations offer a\npartial explanation of the experimentally observed reduction of the critical\nvelocity from the phonon velocity.",
        "positive": "Periodic waves in two-component Bose-Einstein condensates with repulsive\n  interactions between atoms: We consider periodic waves in miscible two-component Bose-Einstein\ncondensates with repulsive nonlinear interactions constants. Exact one-phase\nsolution is found for the case when all these constants are equal to each other\n(i.e., for Manakov limit). New types of nonlinear polarization waves are\nconsidered in detail. The connection of the solutions found with experimentally\nobserved periodic structures in two-component condensates is discussed."
    },
    {
        "anchor": "Polariton superfluids reveal quantum hydrodynamic solitons: A quantum fluid passing an obstacle behaves differently from a classical one.\nWhen the flow is slow enough, the quantum gas enters a superfluid regime and\nneither whirlpools nor waves form around the obstacle. For higher flow\nvelocities, it has been predicted that the perturbation induced by the defect\ngives rise to the turbulent emission of quantised vortices and to the\nnucleation of solitons. Using an interacting Bose gas of exciton-polaritons in\na semiconductor microcavity, we report the transition from superfluidity to the\nhydrodynamic formation of oblique dark solitons and vortex streets in the wake\nof a potential barrier. The direct observation of these topological excitations\nprovides key information on the mechanisms of superflow and shows the potential\nof polariton condensates for quantum turbulence studies.",
        "positive": "Spin-orbit coupled two-electron Fermi gases of ytterbium atoms: We demonstrate all-optical implementation of spin-orbit coupling (SOC) in a\ntwo-electron Fermi gas of $^{173}$Yb atoms by coupling two hyperfine ground\nstates with a narrow optical transition. Due to the SU($N$) symmetry of the\n$^1$S$_0$ ground-state manifold which is insensitive to external magnetic\nfields, an optical AC Stark effect is applied to split the ground spin states,\nwhich exhibits a high stability compared with experiments on alkali and\nlanthanide atoms, and separate out an effective spin-1/2 subspace from other\nhyperfine levels for the realization of SOC. The dephasing spin dynamics when a\nmomentum-dependent spin-orbit gap being suddenly opened and the asymmetric\nmomentum distribution of the spin-orbit coupled Fermi gas are observed as a\nhallmark of SOC. The realization of all-optical SOC for ytterbium fermions\nshould offer a new route to a long-lived spin-orbit coupled Fermi gas and\ngreatly expand our capability in studying novel spin-orbit physics with\nalkaline-earth-like atoms."
    },
    {
        "anchor": "Density-induced geometric frustration of ultra-cold bosons in optical\n  lattices: A density-dependent gauge field may induce density-induced geometric\nfrustration, leading to a non-trivial interplay between density modulation and\nfrustration, which we illustrate for the particular case of ultra-cold bosons\nin zig-zag optical lattices with a density-dependent hopping. We show that the\ndensity-induced frustration leads in a rich landscape of quantum phases,\nincluding Mott and bond-order insulators, two-component superfluids, chiral\nsuperfluids, and partially-paired superfluids. We show as well that the\ndensity-dependent hopping results in an effective repulsive or attractive\ninteractions, and that for the latter case the vacuum may be destabilized\nleading to a strong compressibility. Finally, we discuss how the predicted\nphases may be experimentally observed and characterized in time-of-flight\nmeasurements using their characteristic signatures in the momentum\ndistribution.",
        "positive": "Engineering the Dynamics of Effective Spin-Chain Models for Strongly\n  Interacting Atomic Gases: We consider a one-dimensional gas of cold atoms with strong contact\ninteractions and construct an effective spin-chain Hamiltonian for a\ntwo-component system. The resulting Heisenberg spin model can be engineered by\nmanipulating the shape of the external confining potential of the atomic gas.\nWe find that bosonic atoms offer more flexibility for tuning independently the\nparameters of the spin Hamiltonian through interatomic (intra-species)\ninteraction which is absent for fermions due to the Pauli exclusion principle.\nOur formalism can have important implications for control and manipulation of\nthe dynamics of few- and many-body quantum systems; as an illustrative example\nrelevant to quantum computation and communication, we consider state transfer\nin the simplest non-trivial system of four particles representing\nexchange-coupled qubits."
    },
    {
        "anchor": "Fractional Time Crystals: Time crystals are quantum systems which are able to reveal condensed matter\nbehavior in the time domain. It is known that crystalization in time can be\nobserved in a periodically driven many-body system when interactions between\nparticles force a system to evolve with a period which is an integer multiple\nof a driving period. This phenomenon is dubbed discrete time crystal formation.\nHere, we consider ultra-cold atoms bouncing on an oscillating atom mirror and\nshow that the system can spontaneously form a discrete time crystal where the\nratio of a period of its motion and a driving period is a rational number. This\nkind of discrete time crystals requires higher order resonant driving which is\nanalyzed here with the help of an original approach.",
        "positive": "Nonperturbative thermodynamics of an interacting Bose gas: We discuss the thermodynamics of a non-relativistic gas of bosons with a\nlocal repulsive interaction. In particular, we compute the temperature and\ndensity dependence of pressure, energy and entropy-density, superfluid and\ncondensate-fraction, correlation length, specific heat, isothermal and\nadiabatic compressibility and various sound velocities. The T->0 limit\napproaches the quantum phase transition, while the universal critical behavior\nof a classical second order phase transition in the O(2) universality class\ndetermines the region around the critical temperature. Our non-perturbative\nflow equations based on exact functional renormalization cover all regions in\nthe phase diagram."
    },
    {
        "anchor": "Enhancing sensitivity to rotations with quantum solitonic currents: Quantum mechanics is characterized by quantum coherence and entanglement.\nAfter having discovered how these fundamental concepts govern physical reality,\nscientists have been devoting intense efforts to harness them to shape future\nscience and technology. This is a highly nontrivial task because most often\nquantum coherence and entanglement are difficult to access. Here, we\ndemonstrate the enhancement of the sensitivity of a quantum many-body system\nwith specific coherence and entanglement properties. Our physical system is\nmade of strongly correlated attracting neutral bosons flowing in a ring-shaped\npotential of mesoscopic size. Because of attractive interactions, quantum\nanalogs of bright solitons are formed. As a genuine quantum-many-body feature,\nwe demonstrate that angular momentum fractionalization occurs. As a\nconsequence, the matter-wave current in our system can react to very small\nchanges of rotation or other artificial gauge fields. We work out a protocol to\nentangle such quantum solitonic currents, allowing them to operate rotation\nsensors and gyroscopes to Heisenberg-limited sensitivity.",
        "positive": "2DEG on a cylindrical shell with a screw dislocation: A two dimensional electron gas on a cylindrical surface with a screw\ndislocation is considered. More precisely, we investigate how both the geometry\nand the deformed potential due to a lattice distortion affect the Landau levels\nof such system. The case showing the deformed potential can be thought in the\ncontext of 3D common semiconductors where the electrons are confined on a\ncylindrical shell. We will show that important quantitative differences exist\ndue to this lattice distortion. For instance, the effective cyclotron frequency\nis diminished by the deformed potential, which in turn enhances the Hall\nconductivity."
    },
    {
        "anchor": "Symmetry-protected topological phase transition in one-dimensional Kondo\n  lattice and its realization with ultracold atoms: We propose that ultracold alkaline-earth-like atoms confined in\none-dimensional optical lattice can realize a Kondo lattice model which hosts a\nsymmetry-protected topological (SPT) phase and an associated quantum phase\ntransition in a controllable manner. The symmetry protection of the phase\ntransition is discussed from two different viewpoints: topological properties\nrelated to spatial patterns of Kondo singlets, and symmetry eigenvalues of the\nspin states. We uncover the role of various symmetries in the phase diagram of\nthis system by combining a weak-coupling approach by Abelian bosonization and\nstrong-coupling pictures of ground states. Furthermore, we show that the\nbosonization approach correctly describes a crossover from a fermionic SPT\nphase to a bosonic SPT phase and an associated change of protecting symmetries\nas the charge degrees of freedom are frozen by the Hubbard repulsion.",
        "positive": "Pomeranchuk cooling of the SU($2N$) ultra-cold fermions in optical\n  lattices: We investigate the thermodynamic properties of a half-filled SU(2N)\nFermi-Hubbard model in the two-dimensional square lattice using the\ndeterminantal quantum Monte Carlo simulation, which is free of the fermion\n\"sign problem\". The large number of hyperfine-spin components enhances spin\nfluctuations, which facilitates the Pomeranchuk cooling to temperatures\ncomparable to the superexchange energy scale at the case of SU$(6)$. Various\nquantities including entropy, charge fluctuation, and spin correlations have\nbeen calculated."
    },
    {
        "anchor": "Dissociation of Feshbach molecules via spin-orbit coupling in ultracold\n  Fermi gases: We study the dissociation of Feshbach molecules in ultracold Fermi gases with\nspin-orbit (SO) coupling. Since SO coupling can induce quantum transition\nbetween the Feshbach molecules and the fully polarized Fermi gas, the Feshbach\nmolecules can be dissociated by the SO coupling. We experimentally realized\nthis new type of dissociation in ultracold gases of 40K atoms with SO coupling\ncreated by Raman beams, and observed that the dissociation rate is highly\nnon-monotonic on both the positive and negative Raman-detuning sides. Our\nresults show that the dissociation of Feshbach molecules can be controlled by\nnew degrees of freedoms, i.e., the SO-coupling intensity or the momenta of the\nRaman beams, as well as the detuning of the Raman beams.",
        "positive": "Spontaneous formation and relaxation of spin domains in\n  antiferromagnetic spin-1 quasi-condensates: Quantum systems of many interacting particles at low temperatures generally\norganize themselves into ordered phases of matter, whose nature and symmetries\nare captured by an order parameter. In the simplest cases, this order parameter\nis spatially uniform. For example, a system of localized spins with\nferromagnetic interactions align themselves to a common direction and build up\na macroscopic magnetization on large distances. However, non-uniform situations\nalso exist in nature, for instance in antiferromagnetism where the\nmagnetization alternates in space. The situation becomes even richer when the\nspin-carrying particles are mobile, for instance in the so-called stripe phases\nemerging for itinerant electrons in strongly-correlated materials.\nUnderstanding such inhomogeneously ordered states is of central importance in\nmany-body physics. In this work, we study experimentally the magnetic ordering\nof itinerant spin-1 bosons in inhomegeneous spin domains at nano-Kelvin\ntemperatures. We demonstrate that spin domains form spontaneously after a phase\nseparation transition, \\textit{i.e.} in the absence of external magnetic force,\npurely because of the antiferromagnetic interactions between the atoms.\nFurthermore, we explore how the equilibrium domain configuration emerges from\nan initial state prepared far-from-equilibrium."
    },
    {
        "anchor": "Josephson effect with superfluid fermions in the two-dimensional BCS-BEC\n  crossover: We investigate the macroscopic quantum tunneling of fermionic superfluids in\nthe two-dimensional BCS-BEC crossover by using an effective tunneling energy\nwhich explicitly depends on the condensate fraction and the chemical potential\nof the system. We compare the mean-field effective tunneling energy with the\nbeyond-mean-field one finding that the mean-field tunneling energy is not\nreliable in the BEC regime of the crossover. Then we solve the Josephson\nequations of the population imbalance and the relative phase calculating the\nfrequency of tunneling oscillation both in the linear regime and in the\nnonlinear one. Our results show that the Josephson frequency is larger in the\nintermediate regime of the BCS-BEC crossover due to the peculiar behavior of\nthe effective tunneling energy in the crossover.",
        "positive": "Quantum dynamics of impurities coupled to a Fermi sea: We consider the dynamics of an impurity atom immersed in an ideal Fermi gas\nat zero temperature. We focus on the coherent quantum evolution of the impurity\nfollowing a quench to strong impurity-fermion interactions, where the\ninteractions are assumed to be short range like in cold-atom experiments. To\napproximately model the many-body time evolution, we use a truncated basis\nmethod, where at most two particle-hole excitations of the Fermi sea are\nincluded. When the system is initially non-interacting, we show that our method\nexactly captures the short-time dynamics following the quench, and we find that\nthe overlap between initial and final states displays a universal non-analytic\ndependence on time in this limit. We further demonstrate how our method can be\nused to compute the impurity spectral function, as well as describe many-body\nphenomena involving coupled impurity spin states, such as Rabi oscillations in\na medium or highly engineered quantum quenches."
    },
    {
        "anchor": "Harmonically trapped Fermi gas: Temperature dependence of the Tan\n  contact: Ultracold atomic gases with short-range interactions are characterized by a\nnumber of universal species-independent relations. Many of these relations\ninvolve the two-body Tan contact. Employing the canonical ensemble, we\ndetermine the Tan contact for small harmonically trapped two-component Fermi\ngases at unitarity over a wide range of temperatures, including the zero and\nhigh temperature regimes. A cluster expansion that describes the properties of\nthe N-particle system in terms of those of smaller subsystems is introduced and\nshown to provide an accurate description of the contact in the high temperature\nregime. Finite-range corrections are quantified and the role of the Fermi\nstatistics is elucidated by comparing results for Fermi, Bose and Boltzmann\nstatistics.",
        "positive": "Moving Bose mixtures with dipole-dipole interactions: We study the properties of moving uniform dipolar Bose-Bose mixtures using\nthe full Hartree-Fock-Bogoliubov theory. The analytical and numerical\ncalculations emphasize that the competition between the relative motion of two\nfluids and the interspecies dipole-dipole interactions may affect the behavior\nof the condensed depletion, the anomalous density, the ground-state energy and\nsecond-order pair correlation. It is found that in the lower branch of the\nmixture, these quantities are unimportant and present an unconventional\nbehavior."
    },
    {
        "anchor": "A high-flux source system for matter-wave interferometry exploiting\n  tunable interactions: Atom interferometers allow determining inertial effects to high accuracy.\nQuantum-projection noise as well as systematic effects impose demands on large\natomic flux as well as ultra-low expansion rates. Here we report on a high-flux\nsource of ultra-cold atoms with free expansion rates near the Heisenberg limit\ndirectly upon release from the trap. Our results are achieved in a\ntime-averaged optical dipole trap and enabled through dynamic tuning of the\natomic scattering length across two orders of magnitude interaction strength\nvia magnetic Feshbach resonances. We demonstrate BECs with more than $6\\times\n10^{4}$ particles after evaporative cooling for $170$ ms and their subsequent\nrelease with a minimal expansion energy of $4.5$ nK in one direction. Based on\nour results we estimate the performance of an atom interferometer and compare\nour source system to a high performance chip-trap, as readily available for\nultra-precise measurements in micro-gravity environments.",
        "positive": "Bosonic self-energy functional theory: We derive the self-energy functional theory for bosonic lattice systems with\nbroken $U(1)$ symmetry by parametrizing the bosonic Baym-Kadanoff effective\naction in terms of one- and two-point self-energies. The formalism goes beyond\nother approximate methods such as the pseudoparticle variational cluster\napproximation, the cluster composite boson mapping, and the Bogoliubov+U\ntheory. It simplifies to bosonic dynamical-mean field theory when constraining\nto local fields, whereas when neglecting kinetic contributions of non-condensed\nbosons it reduces to the static mean-field approximation. To benchmark the\ntheory we study the Bose-Hubbard model on the two- and three-dimensional cubic\nlattice, comparing with exact results from path integral quantum Monte Carlo.\nWe also study the frustrated square lattice with next-nearest neighbor hopping,\nwhich is beyond the reach of Monte Carlo simulations. A reference system\ncomprising a single bosonic state, corresponding to three variational\nparameters, is sufficient to quantitatively describe phase-boundaries, and\nthermodynamical observables, while qualitatively capturing the spectral\nfunctions, as well as the enhancement of kinetic fluctuations in the frustrated\ncase. On the basis of these findings we propose self-energy functional theory\nas the omnibus framework for treating bosonic lattice models, in particular, in\ncases where path integral quantum Monte Carlo methods suffer from severe sign\nproblems (e.g. in the presence of non-trivial gauge fields or frustration).\nSelf-energy functional theory enables the construction of diagrammatically\nsound approximations that are quantitatively precise and controlled in the\nnumber of optimization parameters, but nevertheless remain computable by modest\nmeans."
    },
    {
        "anchor": "Interaction and filling induced quantum phases of dual Mott insulators\n  of bosons and fermions: Many-body effects are at the very heart of diverse phenomena found in\ncondensed-matter physics. One striking example is the Mott insulator phase\nwhere conductivity is suppressed as a result of a strong repulsive interaction.\nAdvances in cold atom physics have led to the realization of the Mott\ninsulating phases of atoms in an optical lattice, mimicking the corresponding\ncondensed matter systems. Here, we explore an exotic strongly-correlated system\nof Interacting Dual Mott Insulators of bosons and fermions. We reveal that an\ninter-species interaction between bosons and fermions drastically modifies each\nMott insulator, causing effects that include melting, generation of composite\nparticles, an anti-correlated phase, and complete phase-separation. Comparisons\nbetween the experimental results and numerical simulations indicate intrinsic\nadiabatic heating and cooling for the attractively and repulsively interacting\ndual Mott Insulators, respectively.",
        "positive": "Ground state phase diagram of the 2d Bose-Hubbard model with anisotropic\n  hopping: We compute the ground state phase diagram of the 2d Bose-Hubbard model with\nanisotropic hopping using quantum Monte Carlo simulations, connecting the 1d to\nthe 2d system. We find that the tip of the lobe lies on a curve controlled by\nthe 1d limit over the full anisotropy range while the universality class is\nalways the same as in the isotropic 2d system. This behavior can be derived\nanalytically from the lowest RG equations and has a form typical for the\nunderlying Kosterlitz-Thouless transition in 1d. We also compute the phase\nboundary of the Mott lobe for strong anisotropy and compare it to the 1d\nsystem. Our calculations shed light on recent cold gas experiments monitoring\nthe dynamics of an expanding cloud."
    },
    {
        "anchor": "Transport with ultracold atoms at constant density: We investigate the transport through a few-level quantum system described by\na Markovian master equation with temperature- and particle-density dependent\nchemical potentials. From the corresponding Onsager relations we extract linear\nresponse transport coefficients in analogy to the electronic conductance,\nthermal conductance and thermopower. Considering ideal Fermi and Bose gas\nreservoirs we observe steady-state currents against the thermal bias as a\nresult of the non-linearities introduced by the constraint of a constant\nparticle density in the reservoirs. Most importantly, we find signatures of the\non-set of Bose-Einstein condensation in the transport coefficients.",
        "positive": "Occupation numbers in strongly polarized Fermi gases and the Luttinger\n  theorem: We study a two-component Fermi gas that is so strongly polarized that it\nremains normal fluid at zero temperature. We calculate the occupation numbers\nwithin the particle-particle random-phase approximation, which is similar to\nthe Nozieres-Schmitt-Rink approach. We show that the Luttinger theorem is\nfulfilled in this approach. We also study the change of the chemical potentials\nwhich allows us to extract, in the limit of extreme polarization, the polaron\nenergy."
    },
    {
        "anchor": "Non-equilibrium Berezinskii-Kosterlitz-Thouless Transition in a Driven\n  Open Quantum System: The Berezinskii-Kosterlitz-Thouless mechanism, in which a phase transition is\nmediated by the proliferation of topological defects, governs the critical\nbehaviour of a wide range of equilibrium two-dimensional systems with a\ncontinuous symmetry, ranging from superconducting thin films to two-dimensional\nBose fluids, such as liquid helium and ultracold atoms. We show here that this\nphenomenon is not restricted to thermal equilibrium, rather it survives more\ngenerally in a dissipative highly non-equilibrium system driven into a\nsteady-state. By considering a light-matter superfluid of polaritons, in the\nso-called optical parametric oscillator regime, we demonstrate that it indeed\nundergoes a vortex binding-unbinding phase transition. Yet, the exponent of the\npower-law decay of the first order correlation function in the (algebraically)\nordered phase can exceed the equilibrium upper limit -- a surprising\noccurrence, which has also been observed in a recent experiment. Thus we\ndemonstrate that the ordered phase is somehow more robust against the quantum\nfluctuations of driven systems than thermal ones in equilibrium.",
        "positive": "Creation and characterization of vortex clusters in atomic Bose-Einstein\n  condensates: We show that a moving obstacle, in the form of an elongated paddle, can\ncreate vortices that are dispersed, or induce clusters of like-signed vortices\nin 2D Bose-Einstein condensates. We propose new statistical measures of\nclustering based on Ripley's K-function which are suitable to the small size\nand small number of vortices in atomic condensates, which lack the huge number\nof length scales excited in larger classical and quantum turbulent fluid\nsystems. The evolution and decay of clustering is analyzed using these\nmeasures. Experimentally it should prove possible to create such an obstacle by\na laser beam and a moving optical mask. The theoretical techniques we present\nare accessible to experimentalists and extend the current methods available to\ninduce 2D quantum turbulence in Bose-Einstein condensates."
    },
    {
        "anchor": "The density of a one-dimensional Bose gas far from an impurity: We consider an impurity in a one-dimensional weakly-interacting Bose gas and\nanalytically calculate the density profile of the Bose gas. Within the\nmean-field approximation, by increasing the distance from the impurity, the\nBose gas density saturates exponentially fast to its mean thermodynamic-limit\nvalue at distances beyond the healing length. The effect of quantum\nfluctuations drastically changes this behavior, leading to a power law decay of\nthe density deviation from the mean density. At distances longer than the\nhealing length and shorter than a new length scale proportional to the impurity\ncoupling strength, the power-law exponent is $2$, while at longest distances\nthe corresponding exponent becomes $3$. The latter crossover does not exist in\ntwo special cases. The first one is realized for infinitely strongly coupled\nimpurity; then the density deviation always decays with the exponent $2$. The\nsecond special case occurs when the new length scale is smaller than the\nhealing length, i.e., at weak impurity coupling; then the density deviation\nalways decays with the exponent $3$. The obtained results are exact in the\nimpurity coupling strength and account for the leading order in the interaction\nbetween the particles of the Bose gas.",
        "positive": "Imaginary spin-orbital coupling in parity-time symmetric systems with\n  momentum-dependent gain and loss: Spin-orbital coupling (SOC) and parity-time ($\\mathcal{PT}$) symmetry both\nhave attracted paramount research interest in condensed matter physics, cold\natom physics, optics and acoustics to develop spintronics, quantum computation,\nprecise sensors and novel functionalities. Natural SOC is an intrinsic\nrelativistic effect. However, there is an increasing interest in synthesized\nSOC nowadays. Here, we show that in a $\\mathcal{PT}$-symmetric spin-1/2 system,\nthe momentum-dependent balanced gain and loss can synthesize a new type of SOC,\nwhich we call imaginary SOC. The imaginary SOC can substantially change the\nenergy spectrum of the system. Firstly, we show that it can generate a pure\nreal energy spectrum with a double-valleys structure. Therefore, it has the\nability to generate supersolid stripe states. Especially, the imaginary SOC\nstripe state can have a high contrast of one. Moreover, the imaginary SOC can\nalso generate a spectrum with tunable complex energy band, in which the waves\nare either amplifying or decaying. Thus, the imaginary SOC would also find\napplications in the engineering of $\\mathcal{PT}$-symmetry-based coherent wave\namplifiers/absorbers. Potential experimental realizations of imaginary SOC are\nproposed in cold atomic gases and systems of coupled waveguides constituted of\nnonlocal gain and loss."
    },
    {
        "anchor": "Superfluidity and BEC in a Model of Interacting Bosons in a Random\n  Potential: We present a mathematically rigorous analysis of the superfluid properties of\na Bose-Einstein condensate in the many-body ground state of a one-dimensional\nmodel of interacting bosons in a random potential.",
        "positive": "Constructing the generalized Gibbs ensemble after a quantum quench: Using a numerical renormalization group based on exploiting an underlying\nexactly solvable non- relativistic theory, we study the out-of-equilibrium\ndynamics of a 1D Bose gas (as described by the Lieb-Liniger model) released\nfrom a parabolic trap. Our method allows us to track the post-quench dynamics\nof the gas all the way to infinite time. We also exhibit a general\nconstruction, applicable to all integrable models, of the thermodynamic\nensemble that has been suggested to govern this dynamics, the generalized Gibbs\nensemble. We compare the predictions of equilibration from this ensemble\nagainst the long time dynamics observed using our method."
    },
    {
        "anchor": "Design of a millimetre-scale magnetic surface trap for cold atoms: We study a novel millimetre-scale magnetic trap for ultracold atoms, in which\nthe current carrying conductors can be situated outside the vacuum region, a\nfew mm away from the atoms. This design generates a magnetic field gradient in\nexcess of \\SI{1000}{G/cm} at a distance of \\SI{2}{mm} from the conductors. We\nperform electromagnetic and thermo-mechanical characterisation using Finite\nElement Methods (FEM). The predicted behaviour has been verified by electrical\nand thermal measurements on a prototype, but has not been implemented on an\napparatus with cold atoms. Operating this trap at the highest gradient allows\nfor rapid evaporative cooling comparable to that achieved by atom chips.",
        "positive": "Chiral edge states and fractional charge separation in interacting\n  bosons on a Kagome lattice: We consider the extended hard-core Bose-Hubbard model on a Kagome lattice\nwith boundary conditions on two edges. We find that the sharp edges lift the\ndegeneracy and freeze the system into a striped order at 1/3 and 2/3 filling\nfor zero hopping. At small hopping strengths, holes spontaneously appear and\nseparate into fractional charges which move to the edges of the system. This\nleads to a novel edge liquid phase, which is characterized by fractional\ncharges near the edges and a finite edge compressibility but no superfluid\ndensity. The compressibility is due to excitations on the edge which display a\nchrial symmetry breaking that is reminiscent of the quantum Hall effect and\ntopological insulators. Large scale Monte Carlo simulations confirm the\nanalytical considerations."
    },
    {
        "anchor": "Exciting the Higgs mode in a strongly-interacting Fermi gas by\n  interaction modulation: We study the Higgs mode of a strongly-interacting Fermi gas in the crossover\nregime between a fermionic and bosonic superfluid. By periodically modulating\nthe interaction strength of the gas, we parametrically excite the Higgs mode\nand study its resonance frequency and line width as a function of both\ninteraction strength and temperature. We find that the resonance frequency at\nlow temperature agrees with a local-density approximation of the pairing gap.\nBoth frequency and line width do not exhibit a pronounced variation with\ntemperature, which is theoretically unexpected, however, in qualitative\nagreement with a different recent study.",
        "positive": "Speed of sound in a Bose-Einstein condensate: In the present work we determine the speed of sound in a Bose-Einstein\ncondensate confined by an isotropic harmonic oscillator trap. The deduction of\nthis physical parameter is done resorting to the $N$-body Hamiltonian operator.\nThe single-particle eigenfunctions that have been employed in this formalism\nare those stemming from the corresponding harmonic oscillator potential, and an\nexpression for the dependence of this speed on the temperature is also deduced.\nThese functions are used in the calculation of the scaterring length, etc. The\nsituation for a Bose-Einstein condensate of sodium is evaluated and the\ncorresponding speed of sound is obtained and compared against the known\nexperimental outcomes. The possibility that the solution, to the existing\ndiscrepancy between experiment and theoretical predictions, could be given by\nthe Zaremba-Nikuni-Griffin formalism is also explored."
    },
    {
        "anchor": "Characteristic temperature for the immiscible-miscible transition of\n  binary condensates in optical lattices: We study a two-species Bose-Einstein condensates confined in\nquasi-two-dimensional (quasi-2D) optical lattices at finite temperatures,\nemploying the Hartree-Fock-Bogoliubov theory with the Popov approximation. We\nexamine the role of thermal fluctuations on the ground-state density\ndistributions, and the quasiparticle mode evolution. At zero temperature, the\ngeometry of the ground-state in the immiscible domain is side-by-side. Our\nresults show that the thermal fluctuations enhance the miscibility of the\ncondensates, and at a characteristic temperature the system becomes miscible\nwith rotationally symmetric overlapping density profiles. This\nimmiscible-miscible transition is accompanied by a discontinuity in the\nexcitation spectrum, and the low-lying quasiparticle modes such as slosh mode\nbecomes degenerate at the characteristic temperature.",
        "positive": "High-order symbolic strong-coupling expansion for the Bose-Hubbard model: Combining the process-chain method with a symbolized evaluation we work out\nin detail a high-order symbolic strong-coupling expansion (HSSCE) for\ndetermining the quantum phase boundaries between the Mott insulator and the\nsuperfluid phase of the Bose-Hubbard model for different fillings in hypercubic\nlattices of different dimensions. With a subsequent Pad{\\'e} approximation we\nachieve for the quantum phase boundaries a high accuracy, which is comparable\nto high-precision quantum Monte-Carlo simulations, and show that all the Mott\nlobes can be rescaled to a single one. As a further cross-check, we find that\nthe HSSCE results coincide with a hopping expansion of the quantum phase\nboundaries, which follow from the effective potential Landau theory (EPLT)."
    },
    {
        "anchor": "Synthetic spin-orbit interactions and magnetic fields in ring-cavity QED: The interactions between light and matter are strongly enhanced when atoms\nare placed in high-finesse quantum cavities, offering tantalizing opportunities\nfor generating exotic new quantum phases. In this work we show that both\nspin-orbit interactions and strong synthetic magnetic fields result when a\nneutral atom is confined within a ring cavity, whenever the internal atomic\nstates are coupled to two off-resonant counter-propagating modes. We\ndiagonalize the resulting cavity polariton Hamiltonian and find characteristic\nspin-orbit dispersion relations for a wide range of parameters. An adjustable\nuniform gauge potential is also generated, which can be converted into a\nsynthetic magnetic field for neutral atoms by applying an external magnetic\nfield gradient. Very large synthetic magnetic fields are possible as the\nstrength is proportional to the (average) number of photons in each of the\ncavity modes. The results suggest that strong-coupling cavity quantum\nelectrodynamics can be a useful environment for the formation of topological\nstates in atomic systems.",
        "positive": "Emergence and scaling of spin turbulence in quenched antiferromagnetic\n  spinor Bose-Einstein condensates: We investigate the phase transition dynamics of a quasi-2D antiferromagnetic\nspin-1 Bose-Einstein condensate from the easy-axis polar phase to the\neasy-plane polar phase, which is initiated by suddenly changing the sign of the\nquadratic Zeeman energy $q$. We observe the emergence and decay of spin\nturbulence and the formation of half-quantum vortices (HQVs) in the quenched\ncondensate. The characteristic time and length scales of the turbulence\ngeneration dynamics are proportional to $|q|^{-1/2}$ as inherited from the\ndynamic instability of the initial state. In the evolution of the spin\nturbulence, spin wave excitations develop from large to small length scales,\nsuggesting a direct energy cascade, and the spin population for the axial polar\ndomains exhibit a nonexponential decay. The final equilibrated condensate\ncontains HQVs, and the number is found to increase and saturate with increasing\n$|q|$. Our results demonstrate the time-space scaling properties of the phase\ntransition dynamics near the critical point and the peculiarities of the spin\nturbulence state of the antiferromagnetic spinor condensate."
    },
    {
        "anchor": "Multi-band Bose-Einstein condensate at four-particle scattering\n  resonance: Superfluidity and superconductivity are macroscopic manifestations of quantum\nmechanics, which have fascinated scientists since their discoveries roughly a\ncentury ago. Ever since the initial theories of such quantum fluids were\nformulated, there has been speculation as to the possibility of multi-component\nquantum order. A particularly simple multi-component condensate is built from\nparticles occupying different quantum states, or bands, prior to condensation.\nThe particles in one or both bands may undergo condensation, as seen for\ncertain solids and anticipated for certain cold atom systems. For bulk solids,\nthe different bands always order simultaneously, with conventional pairing\ncharacterized by complex order parameters describing the condensates in each\nband. Another type of condensate, notably occurring at room temperature, has\nbeen identified for magnons, the magnetic analogue of lattice vibrations,\ninjected by microwaves into yttrium iron garnet. Here we show that magnon\nquantization for thin samples results in a new multi-band magnon condensate. We\nestablish a phase diagram, as a function of microwave drive power and frequency\nrelative to the magnon bands, revealing both single and multi-band\ncondensation. The most stable multi-band condensate is found in a narrow regime\nfavoured on account of a resonance in the scattering between two bands. Our\ndiscovery introduces a flexible non-equilibrium platform operating at room\ntemperature for a well-characterised material, exploiting a Feshbach-like\nresonance, for examining multi-band phenomena. It points to qualitatively new\nways to engineer and control condensates and superconducting states in\nmultiband systems and potential devices containing multiple interacting\ncondensates.",
        "positive": "A two-band Bose-Hubbard model for many-body resonant tunneling in the\n  Wannier-Stark system: We study an experimentally realizable paradigm of complex many-body quantum\nsystems, a two-band Wannier-Stark model, for which diffusion in Hilbert space\nas well as many-body Landau-Zener processes can be engineered. A cross-over\nbetween regular to quantum chaotic spectra is found within the many-body\navoided crossings at resonant tunneling conditions. The spectral properties are\nshown to determine the evolution of states across a cascade of Landau-Zener\nevents. We apply the obtained spectral information to study the non-equilibrium\ndynamics of our many-body system in different parameter regimes."
    },
    {
        "anchor": "Vortices in fermion droplets with repulsive dipole-dipole interactions: Vortices are found in a fermion system with repulsive dipole-dipole\ninteractions, trapped by a rotating quasi-two-dimensional harmonic oscillator\npotential. Such systems have much in common with electrons in quantum dots,\nwhere rotation is induced via an external magnetic field. In contrast to the\nCoulomb interactions between electrons, the (externally tunable) anisotropy of\nthe dipole-dipole interaction breaks the rotational symmetry of the\nHamiltonian. This may cause the otherwise rotationally symmetric exact\nwavefunction to reveal its internal structure more directly.",
        "positive": "p-wave superfluidity in mixtures of ultracold Fermi and spinor Bose\n  gases: We reveal that the p-wave superfluid can be realized in a mixture of\nfermionic and F=1 bosonic gases. We derive a general set of the gap equations\nfor gaps in the s- and p-channels. It is found that the spin-spin bose-fermi\ninteractions favor the p-wave pairing and naturally suppress the pairing in the\ns-channel. The gap equations for the polar phase of p-wave superfluid fermions\nare numerically solved. It is shown that a pure p-wave superfluid can be\nobserved in a well-controlled environment of atomic physics."
    },
    {
        "anchor": "Spin-Depairing Transition of Attractive Fermi Gases on a Ring Driven by\n  Synthetic Gauge Fields: Motivated by the recent experimental realization of synthetic gauge fields in\nultracold atoms, we investigate one-dimensional attractive Fermi gases with a\ntime-dependent gauge flux on the spin sector. By combining the methods of the\nBethe ansatz with complex twists and Landau-Dykhne, it is shown that a\nspin-depairing transition occurs, which may represent a nonequilibrium\ntransition from fermionic superfluids to normal states with spin currents\ncaused by a many-body quantum tunneling. For the case of the Hubbard ring at\nhalf filling, our finding forms a dual concept with the dielectric breakdown of\nthe Mott insulator discussed in Phys. Rev. B 81, 033103 (2010). We analyze\ncases of arbitrary filling and continuum model, and show how the filling\naffects the transition probability.",
        "positive": "High Controllable and Robust 2D Spin-Orbit Coupling for Quantum Gases: We report the realization of a robust and highly controllable two-dimensional\n(2D) spin-orbit (SO) coupling with topological non-trivial band structure. By\napplying a retro-reflected 2D optical lattice, phase tunable Raman couplings\nare formed into the anti-symmetric Raman lattice structure, and generate the 2D\nSO coupling with precise inversion and $C_4$ symmetries, leading to\nconsiderably enlarged topological regions. The life time of the 2D SO coupled\nBose-Einstein condensate reaches several seconds, which enables the exploring\nof fine tuning interaction effects. These essential advantages of the present\nnew realization open the door to explore exotic quantum many-body effects and\nnon-equilibrium dynamics with novel topology."
    },
    {
        "anchor": "Role of interactions in time-of-flight expansion of atomic clouds from\n  optical lattices: We calculate the effect of interactions on the expansion of ultracold atoms\nfrom a single site of an optical lattice. We use these results to predict how\ninteractions influence the interference pattern observed in a time of flight\nexperiment. We find that for typical interaction strengths their influence is\nnegligible, yet that they reduce visibility near a scattering resonance.",
        "positive": "A 3-photon process for producing a degenerate gas of metastable\n  alkaline-earth atoms: We present a method for creating a quantum degenerate gas of metastable\nalkaline-earth atoms. This has yet to be achieved due to inelastic collisions\nthat limit evaporative cooling in the metastable states. Quantum degenerate\nsamples prepared in the $^{1}S_{0}$ ground state can be rapidly transferred to\neither the $^{3}P_{2}$ or $^{3}P_{0}$ state via a coherent 3-photon process.\nNumerical integration of the density matrix evolution for the fine structure of\nbosonic alkaline-earth atoms shows that transfer efficiencies of $\\simeq90\\%$\ncan be achieved with experimentally feasible laser parameters in both Sr and\nYb. Importantly, the 3-photon process can be set up such that it imparts no net\nmomentum to the degenerate gas during the excitation, which will allow for\nstudies of metastable samples outside the Lamb-Dicke regime. We discuss several\nexperimental challenges to successfully realizing our scheme, including the\nminimization of differential AC Stark shifts between the four states connected\nby the 3-photon transition."
    },
    {
        "anchor": "Superfluidity and pairing phenomena in ultracold atomic Fermi gases in\n  one-dimensional optical lattices, Part I: Balanced case: The superfluidity and pairing phenomena in ultracold atomic Fermi gases have\nbeen of great interest in recent years, with multiple tunable parameters. Here\nwe study the BCS-BEC crossover behavior of balanced two-component Fermi gases\nin a one-dimensional optical lattice, which is distinct from the simple\nthree-dimensional (3D) continuum and a fully 3D lattice often found in a\ncondensed matter system. We use a pairing fluctuation theory which includes\nself-consistent feedback effects at finite temperatures, and find widespread\npseudogap phenomena beyond the BCS regime. As a consequence of the lattice\nperiodicity, the superfluid transition temperature $T_c$ decreases with pairing\nstrength in the BEC regime, where it approaches asymptotically $T_c = \\pi\nan/2m$, with $a$ being the $s$-wave scattering length, and $n$ ($m$) the\nfermion density (mass). In addition, the quasi-two dimensionality leads to fast\ngrowing (absolute value of the) fermionic chemical potential $\\mu$ and pairing\ngap $\\Delta$, which depends exponentially on the ratio $d/a$. Importantly,\n$T_c$ at unitarity increases with the lattice constant $d$ and hopping integral\n$t$. The effect of the van Hove singularity on $T_c$ is identified. The\nsuperfluid density exhibits $T^{3/2}$ power laws at low $T$, away from the\nextreme BCS limit. These predictions can be tested in future experiments.",
        "positive": "Improved Hilbert space exploration algorithms for finite temperature\n  calculations: Computing correlation functions in strongly-interacting quantum systems is\none of the most important challenges of modern condensed matter theory, due to\ntheir importance in the description of many physical observables.\nSimultaneously, this challenge is one of the most difficult to address, due to\nthe inapplicability of traditional perturbative methods or the few-body\nlimitations of numerical approaches. For special cases, where the model is\nintegrable, methods based on the Bethe Ansatz have succeeded in computing the\nspectrum and given us analytical expressions for the matrix elements of\nphysically important operators. However, leveraging these results to compute\ncorrelation functions generally requires the numerical evaluation of summations\nover eigenstates. To perform these summations efficiently, Hilbert space\nexploration algorithms have been developed which has resulted most notably in\nthe ABACUS library. While this performs quite well for correlations on ground\nstates or low-entropy states, the case of high entropy states (most importantly\nat finite temperatures or after a quantum quench) is more difficult, and leaves\nroom for improvement. In this work, we develop a new Hilbert space exploration\nalgorithm for the Lieb-Liniger model, specially tailored to optimize the\ncomputational order on finite-entropy states for correlations of\ndensity-related operators."
    },
    {
        "anchor": "Reentrant BCS-BEC crossover and a superfluid-insulator transition in\n  optical lattices: We study thermodynamics of a two-species Feshbach-resonant atomic Fermi gas\nin a periodic potential, focusing in a deep optical potential where a tight\nbinding model is applicable. We show that for more than half-filled band the\ngas exhibits a reentrant crossover with decreased detuning (increased\nattractive interaction), from a paired BCS superfluid to a Bose-Einstein\ncondensate (BEC) of molecules of holes, back to the BCS superfluid, and finally\nto a conventional BEC of diatomic molecules. This behavior is associated with\nthe non-monotonic dependence of the chemical potential on detuning and the\nconcomitant Cooper-pair/molecular size, larger in the BCS and smaller in the\nBEC regimes. For a single filled band we find a quantum phase transition from a\nband insulator to a BCS-BEC superfluid, and map out the corresponding phase\ndiagram.",
        "positive": "Dipole Oscillations in Fermionic Mixtures: We study dipole oscillations in a general fermionic mixture: starting from\nthe Boltzmann equation, we classify the different solutions in the parameter\nspace through the number of real eigenvalues of the small oscillations matrix.\nWe discuss how this number can be computed using the Sturm algorithm and its\nrelation with the properties of the Laplace transform of the experimental\nquantities. After considering two components in harmonic potentials having\ndifferent trapping frequencies, we study dipole oscillations in three-component\nmixtures. Explicit computations are done for realistic experimental setups\nusing the classical Boltzmann equation without intra-species interactions. A\nbrief discussion of the application of this classification to general\ncollective oscillations is also presented."
    },
    {
        "anchor": "Generation and Decay of Two-Dimensional Quantum Turbulence in a Trapped\n  Bose-Einstein Condensate: In a recent experiment, Kwon et. al (arXiv:1403.4658 [cond-mat.quant-gas])\ngenerated a disordered state of quantum vortices by translating an oblate\nBose-Einstein condensate past a laser-induced obstacle and studying the\nsubsequent decay of vortex number. Using mean-field simulations of the\nGross-Pitaevskii equation, we shed light on the various stages of the observed\ndynamics. We find that the flow of the superfluid past the obstacle leads\ninitially to the formation of a classical-like wake, which later becomes\ndisordered. Following removal of the obstacle, the vortex number decays due to\nvortices annihilating and reaching the boundary. Our results are in excellent\nagreement with the experimental observations. Furthermore, we probe thermal\neffects through phenomenological dissipation.",
        "positive": "Many-body Quantum Chaos and Entanglement in a Quantum Ratchet: We uncover signatures of quantum chaos in the many-body dynamics of a\nBose-Einstein condensate-based quantum ratchet in a toroidal trap. We propose\nmeasures including entanglement, condensate depletion, and spreading over a\nfixed basis in many-body Hilbert space which quantitatively identify the region\nin which quantum chaotic many-body dynamics occurs, where random matrix theory\nis limited or inaccessible. With these tools we show that many-body quantum\nchaos is neither highly entangled nor delocalized in the Hilbert space,\ncontrary to conventionally expected signatures of quantum chaos."
    },
    {
        "anchor": "Three-body correlations in a two-dimensional SU(3) Fermi gas: We consider a three-component Fermi gas that has SU(3) symmetry and is\nconfined to two dimensions (2D). For realistic cold atomic gas experiments, we\nshow that the phase diagram of the quasi-2D system can be characterized using\ntwo 2D scattering parameters: the scattering length and the effective range.\nUnlike the case in 3D, we argue that three-body bound states (trimers) in the\nquasi-2D system can be stable against three-body losses. Using a low-density\nexpansion coupled with a variational approach, we investigate the fate of such\ntrimers in the many-body system as the attractive interactions are decreased\n(or, conversely, as the density of particles is increased). We find that\nremnants of trimers can persist in the form of strong three-body correlations\nin the weak-coupling (high-density) limit.",
        "positive": "Dynamical realization of magnetic states in a strongly interacting Bose\n  mixture: We describe the dynamical preparation of magnetic states in a strongly\ninteracting two-component Bose gas in a harmonic trap. By mapping this system\nto an effective spin chain model, we obtain the dynamical spin densities and\nthe fidelities for a few-body system. We show that the spatial profiles transit\nbetween ferromagnetic and antiferromagnetic states as the intraspecies\ninteraction parameter is slowly increased."
    },
    {
        "anchor": "Stochastic Dynamics and Bound States of Heavy Impurities in a Fermi Bath: We investigate the dynamics of heavy impurities embedded in an ultra-cold\nFermi gas by using a Generalized Langevin equation. The latter -- derived by\nmeans of influence functional theory -- describes the stochastic classical\ndynamics of the impurities and the quantum nature of the fermionic bath\nmanifests in the emergent interaction between the impurities and in the\nviscosity tensor. By focusing on the two-impurity case, we predict the\nexistence of bound states, in different conditions of coupling and temperature,\nand whose life-time can be analytically estimated. Our predictions should be\ntestable using cold-gases platforms within current technology.",
        "positive": "Quench dynamics of Hopf insulators: Hopf insulators are exotic topological states of matter outside the standard\nten-fold way classification based on discrete symmetries. Its topology is\ncaptured by an integer invariant that describes the linking structures of the\nHamiltonian in the three-dimensional momentum space. In this paper, we\ninvestigate the quantum dynamics of Hopf insulators across a sudden quench and\nshow that the quench dynamics is characterized by a $\\mathbb{Z}_2$ invariant\n$\\nu$ which reveals a rich interplay between quantum quench and static band\ntopology. We construct the $\\mathbb{Z}_2$ topological invariant using the loop\nunitary operator, and prove that $\\nu$ relates the pre- and post-quench Hopf\ninvariants through $\\nu=(\\mathcal{L}-\\mathcal{L}_0)\\bmod 2$. The $\\mathbb{Z}_2$\nnature of the dynamical invariant is in sharp contrast to the $\\mathbb{Z}$\ninvariant for the quench dynamics of Chern insulators in two dimensions. The\nnon-trivial dynamical topology is further attributed to the emergence of\n$\\pi$-defects in the phase band of the loop unitary. These $\\pi$-defects are\ngenerally closed curves in the momentum-time space, for example, as nodal rings\ncarrying Hopf charge."
    },
    {
        "anchor": "Equation of state and self-bound droplet in Rabi-coupled Bose mixtures: Laser induced transitions between internal states of atoms have been playing\na fundamental role to manipulate atomic clouds for many decades. In absence of\ninteractions each atom behaves independently and their coherent quantum\ndynamics is described by the Rabi model. Since the experimental observation of\nBose condensation in dilute gases, static and dynamical properties of\nmulticomponent quantum gases have been extensively investigated. Moreover, at\nvery low temperatures quantum fluctuations crucially affect the equation of\nstate of many-body systems. Here we study the effects of quantum fluctuations\non a Rabi-coupled two-component Bose gas of interacting alkali atoms. The\ndivergent zero-point energy of gapless and gapped elementary excitations of the\nuniform system is properly regularized obtaining a meaningful analytical\nexpression for the beyond-mean-field equation of state. In the case of\nattractive inter-particle interaction we show that the quantum pressure arising\nfrom Gaussian fluctuations can prevent the collapse of the mixture with the\ncreation of a self-bound droplet. We characterize the droplet phase and\ndiscover an energetic instability above a critical Rabi frequency provoking the\nevaporation of the droplet. Finally, we suggest an experiment to observe such\nquantum droplets using Rabi-coupled internal states of $^{39}$K atoms.",
        "positive": "Spin-charge separation in a 1D Fermi gas with tunable interactions: Ultracold atoms confined to periodic potentials have proven to be a powerful\ntool for quantum simulation of complex many-body systems. We confine fermions\nto one-dimension to realize the Tomonaga-Luttinger liquid model describing the\nhighly collective nature of their low-energy excitations. We use Bragg\nspectroscopy to directly excite either the spin or charge wave for various\nstrength of repulsive interaction. We observe that the velocity of the spin and\ncharge excitations shift in opposite directions with increasing interaction, a\nhallmark of spin-charge separation. The excitation spectra are in quantitative\nagreement with the Tomonaga-Luttinger liquid theory, and furthermore, we find\nthat the spin excitations become dispersive at large interaction, signaling the\nonset of the nonlinear Luttinger liquid regime."
    },
    {
        "anchor": "The response to dynamical modulation of the optical lattice for fermions\n  in the Hubbard model: Fermionic atoms in a periodic optical lattice provide a realization of the\nsingle-band Hubbard model. Using Quantum Monte Carlo simulations along with the\nMaximum Entropy Method, we evaluate the effect of a time-dependent perturbative\nmodulation of the optical lattice amplitude on atomic correlations, revealed in\nthe fraction of doubly-occupied sites. Our treatment extends previous\napproaches which neglected the time dependence of the on-site interaction, and\nshows that this term changes the results in a quantitatively significant way.\nThe effect of modulation depends strongly on the filling-- the response of the\ndouble occupation is significantly different in the half-filled Mott insulator\nfrom the doped Fermi liquid region.",
        "positive": "Emergence of a new pair-coherent phase in many-body quenches of\n  repulsive bosons: We investigate the dynamical mode population statistics and associated first-\nand second-order coherence of an interacting bosonic two-mode model when the\npair-exchange coupling is quenched from negative to positive values. It is\nshown that for moderately rapid second-order transitions, a new pair-coherent\nphase emerges on the positive coupling side in an excited state, which is not\nfragmented as the ground-state single-particle density matrix would prescribe\nit to be."
    },
    {
        "anchor": "Rapid generation of all-optical $^{39}$K Bose-Einstein condensates using\n  a low-field Feshbach resonance: Ultracold potassium is an interesting candidate for quantum technology\napplications and fundamental research as it allows controlling intra-atomic\ninteractions via low-field magnetic Feshbach resonances. However, the\nrealization of high-flux sources of Bose-Einstein condensates remains\nchallenging due to the necessity of optical trapping to use magnetic fields as\nfree parameter. We investigate the production of all-optical $^{39}$K\nBose-Einstein condensates with different scattering lengths using a Feshbach\nresonance near $33$ G. By tuning the scattering length in a range between $75\\,\na_0$ and $300\\, a_0$ we demonstrate a trade off between evaporation speed and\nfinal atom number and decrease our evaporation time by a factor of $5$ while\napproximately doubling the evaporation flux. To this end, we are able to\nproduce fully condensed ensembles with $5.8\\times10^4$ atoms within $850$ ms\nevaporation time at a scattering length of $232\\, a_0$ and $1.6\\times10^5$\natoms within $3.9$ s at $158\\, a_0$, respectively. We deploy a numerical model\nto analyse the flux and atom number scaling with respect to scattering length,\nidentify current limitations and simulate the optimal performance of our setup.\nBased on our findings we describe routes towards high-flux sources of\nultra-cold potassium for inertial sensing.",
        "positive": "Weakly interacting Bose-Einstein condensates in temperature-dependent\n  generic traps: The shift in condensation temperature caused by interactions is studied up to\nsecond order in the s-wave scattering length in a Bose-Einstein condensate\ntrapped in a temperature-dependent three-dimensional generic potential. With no\nassumptions other than the mean-field approach and semiclassical approximations\nit is shown that the inclusion of a temperature-dependent trap improves the\nempirical values of the numerical parameters compared to those obtained in\nprevious reports on the temperature shift."
    },
    {
        "anchor": "Chaotic dynamics and fractal structures in experiments with cold atoms: We use tools from nonlinear dynamics to the detailed analysis of cold atom\nexperiments. A powerful example is provided by the recent concept of basin\nentropy which allows to quantify the final state unpredictability that results\nfrom the complexity of the phase space geometry. We show here that this enables\none to reliably infer the presence of fractal structures in phase space from\ndirect measurements. We illustrate the method with numerical simulations in an\nexperimental configuration made of two crossing laser guides that can be used\nas a matter wave splitter.",
        "positive": "Multi-Quantum Dark Solitons in One-Dimensional Bose Gas: Quantum and classical integrable systems share common mathematical\nstructures, and the phenomena appearing in them are interrelated. Solitons,\nwhich universally appear in classical integrable systems, also appear in\nquantum integrable systems. Here, we consider quantum-classical correspondence\nin a one-dimensional Bose gas with repulsive delta-function interaction and\npresent quantum states corresponding to multi-dark solitons. Using an exact\nmethod, we compute the time evolution of the density profile in the\nmulti-quantum dark soliton states. Localized solitary waves that behave like\nclassical dark solitons are observed in the density profile. We observe\ncollisions of quantum dark solitons and show that they exhibit the properties\nof classical solitons: stability against scatterings and position shifts due to\ninteractions."
    },
    {
        "anchor": "Realization of effective super Tonks-Girardeau gases via strongly\n  attractive one-dimensional Fermi gases: A significant feature of the one-dimensional super Tonks-Girardeau gas is its\nmetastable gas-like state with a stronger Fermi-like pressure than for free\nfermions which prevents a collapse of atoms. This naturally suggests a way to\nsearch for such strongly correlated behaviour in systems of interacting\nfermions in one dimension. We thus show that the strongly attractive Fermi gas\nwithout polarization can be effectively described by a super Tonks-Girardeau\ngas composed of bosonic Fermi pairs with attractive pair-pair interaction. A\nnatural description of such super Tonks-Girardeau gases is provided by Haldane\ngeneralized exclusion statistics. In particular, we find that they are\nequivalent to ideal particles obeying more exclusive statistics than\nFermi-Dirac statistics.",
        "positive": "Theory of interacting fermions in shaken square optical lattice: We develop a theory of weakly interacting fermionic atoms in shaken optical\nlattices based on the orbital mixing in the presence of time-periodic\nmodulations. Specifically, we focus on fermionic atoms in circularly shaken\nsquare lattice with near resonance frequencies, i.e., tuned close to the energy\nseparation between $s$-band and the $p$-bands. First, we derive a\ntime-independent four-band effective Hamiltonian in the non-interacting limit.\nDiagonalization of the effective Hamiltonian yields a quasi-energy spectrum\nconsistent with the full numerical Floquet solution that includes all higher\nbands. In particular, we find that the hybridized $s$-band develops multiple\nminima and therefore non-trivial Fermi surfaces at different fillings. We then\nobtain the effective interactions for atoms in the hybridized $s$-band\nanalytically and show that they acquire momentum dependence on the Fermi\nsurface even though the bare interaction is contact-like. We apply the theory\nto find the phase diagram of fermions with weak attractive interactions and\ndemonstrate that the pairing symmetry is $s+d$-wave. Our theory is valid for a\nrange of shaking frequencies near resonance, and it can be generalized to other\nphases of interacting fermions in shaken lattices."
    },
    {
        "anchor": "Creating Entanglement Using Integrals of Motion: A quantum Galilean cannon is a 1D sequence of $N$ hard-core particles with\nspecial mass ratios, and a hard wall; conservation laws due to the reflection\ngroup $A_{N}$ prevent both classical stochastization and quantum diffraction.\nIt is realizable through specie-alternating mutually repulsive bosonic soliton\ntrains. We show that an initial disentangled state can evolve into one where\nthe heavy and light particles are entangled, and propose a sensor, containing\n$N_{\\text{total}}$ atoms, with a $\\sqrt{N_{\\text{total}}}$ times higher\nsensitivity than in a one-atom sensor with $N_{\\text{total}}$ repetitions.",
        "positive": "Phases of lattice hard core bosons in a periodic superlattice: We study by Quantum Monte Carlo simulations the phase diagram of lattice hard\ncore bosons with nearest-neighbour repulsive interactions, in the presence of a\nsuper-lattice of adsorption sites. For a moderate adsorption strength, the\nsystem forms crystal phases registered with the adsorption lattice; a\n\"supersolid\" phase exists, on both the vacancy and interstitial sides, whereas\nat commensuration the superfluid density vanishes. The possible relevance of\nthese results to experiments on $^4$He films adsorbed on graphite is discussed."
    },
    {
        "anchor": "The negative Bogoliubov dispersion in exciton-polariton condensates: Bogoliubov's theory states that self-interaction effects in Bose-Einstein\ncondensates produce a characteristic linear dispersion at low momenta. One of\nthe curious features of Bogoliubov's theory is that the new quasiparticles in\nthe system are linear combinations of creation and destruction operators of the\nbosons. In exciton-polariton condensates, this gives the possibility of\ndirectly observing the negative branch of the Bogoliubov dispersion in the\nphotoluminescence (PL) emission. Here we theoretically examine the PL spectra\nof exciton-polariton condensates taking into account of reservoir effects. At\nsufficiently high excitation densities, the negative dispersion becomes\nvisible. We also discuss the possibility for relaxation oscillations to occur\nunder conditions of strong reservoir coupling. This is found to give a\nsecondary mechanism for making the negative branch visible.",
        "positive": "Directly imaging spin polarons in a kinetically frustrated Hubbard\n  system: The emergence of quasiparticles in quantum many-body systems underlies the\nrich phenomenology in many strongly interacting materials. In the context of\ndoped Mott insulators, magnetic polarons are quasiparticles that usually arise\nfrom an interplay between the kinetic energy of doped charge carriers and\nsuperexchange spin interactions. However, in kinetically frustrated lattices,\nitinerant spin polarons - bound states of a dopant and a spin-flip - have been\ntheoretically predicted even in the absence of superexchange coupling. Despite\ntheir important role in the theory of kinetic magnetism, a microscopic\nobservation of these polarons is lacking. Here we directly image itinerant spin\npolarons in a triangular lattice Hubbard system realised with ultracold atoms,\nrevealing enhanced antiferromagnetic correlations in the local environment of a\nhole dopant. In contrast, around a charge dopant, we find ferromagnetic\ncorrelations, a manifestation of the elusive Nagaoka effect. We study the\nevolution of these correlations with interactions and doping, and use\nhigher-order correlation functions to further elucidate the relative\ncontributions of superexchange and kinetic mechanisms. The robustness of\nitinerant spin polarons at high temperature paves the way for exploring\npotential mechanisms for hole pairing and superconductivity in frustrated\nsystems. Furthermore, our work provides microscopic insights into related\nphenomena in triangular lattice moir\\'{e} materials."
    },
    {
        "anchor": "Resonant dynamics of strongly interacting SU($n$) fermionic atoms in a\n  synthetic flux ladder: We theoretically study the dynamics of $n$-level spin-orbit coupled\nalkaline-earth fermionic atoms with SU($n$) symmetric interactions. We consider\nthree dimensional lattices with tunneling along one dimension, and the internal\nlevels treated as a synthetic dimension, realizing an $n$-leg flux ladder.\nLaser driving is used to couple the internal levels and to induce an effective\nmagnetic flux through the ladder. We focus on the dense and strongly\ninteracting regime, where in the absence of flux the system behaves as a Mott\ninsulator with suppressed motional dynamics. At integer and fractional ratios\nof the laser Rabi frequency to the onsite interactions, the system exhibits\nresonant features in the dynamics. These resonances occur when interactions\nhelp overcome kinetic constraints upon the tunneling of atoms, thus enabling\nmotion. Different resonances allow for the development of complex chiral\ncurrent patterns. The resonances resemble the ones appearing in the\nlongitudinal Hall resistance when the magnetic field is varied. We characterize\nthe dynamics by studying the system's long-time relaxation behavior as a\nfunction of flux, number of internal levels $n$, and interaction strength. We\nobserve a series of non-trivial pre-thermal plateaus caused by the emergence of\nresonant processes at successive orders in perturbation theory. We discuss\nprotocols to observe the predicted phenomena under current experimental\nconditions.",
        "positive": "One-dimensional purely Lee-Huang-Yang fluids dominated by quantum\n  fluctuations in two-component Bose-Einstein condensates: Lee-Huang-Yang (LHY) fluids are an exotic quantum matter dominated purely by\nquantum fluctuations. Recently, the three-dimensional LHY fluids were observed\nin ultracold atoms experiments, while their low-dimensional counterparts have\nnot been well known. Herein, based on the Gross-Pitaevskii equation of\none-dimensional LHY quantum fluids in two-component Bose-Einstein condensates,\nwe reveal analytically and numerically the formation, properties, and dynamics\nof matter-wave structures therein. Considering a harmonic trap, approximate\nanalytical results are obtained based on variational approximation, and\nhigher-order nonlinear localized modes with nonzero nodes are constructed\nnumerically. Stability regions of all the LHY nonlinear localized modes are\nidentified by linear-stability analysis and direct perturbed numerical\nsimulations. Movements and oscillations of single localized mode, and\ncollisions between two modes, under the influence of different initial kicks\nare also studied in dynamical evolutions. The predicted results are available\nto quantum-gas experiments, providing a new insight into LHY physics in\nlow-dimensional settings."
    },
    {
        "anchor": "The Question of Spontaneous Symmetry Breaking in Condensates: The question of whether Bose-Einstein condensation involves spontaneous\nsymmetry breaking is surprisingly controversial. We review the theory of\nspontaneous symmetry breaking in ferromagnets, compare it to the theory of\nsymmetry breaking in condensates, and discuss the different viewpoints on the\ncorrespondence to experiments. These viewpoints include alternative\nperspectives in which we can treat condensates with fixed particle numbers, and\nwhere coherence arises from measurements. This question relates to whether\ncondensates of quasiparticles such as polaritons can be viewed as \"real\"\ncondensates.",
        "positive": "Mobility edge for cold atoms in laser speckle potentials: Using the transfer matrix method, we numerically compute the precise position\nof the mobility edge of atoms exposed to a laser speckle potential, and study\nits dependence vs. the disorder strength and correlation function. Our results\ndeviate significantly from previous theoretical estimates using an approximate\nself-consistent approach of localization. In particular we find that the\nposition of the mobility edge in blue-detuned speckles is much lower than in\nthe red-detuned counterpart, pointing out the crucial role played by the\nasymmetric on-site distribution of speckle patterns."
    },
    {
        "anchor": "Hilbert-space localization in closed quantum systems: Quantum localization within an energy-shell of a closed quantum system stands\nin contrast to the ergodic assumption of Boltzmann, and to the corresponding\neigenstate thermalization hypothesis. The familiar case is the real-space\n\"Anderson localization\" and its many-body Fock-space version. We use the term\n\"Hilbert-space localization\" in order to emphasize the more general phase-space\ncontext. Specifically, we introduce a unifying picture that extends the\nsemiclassical perspective of Heller, which relates the localization measure to\nthe probability of return. We illustrate our approach by considering several\nsystems of experimental interest, referring in particular to the Bosonic\nJosephson tunneling junction. We explore the dependence of the localization\nmeasure on the initial state, and on the strength of the many-body interactions\nusing a novel recursive projection method.",
        "positive": "Controlling particle current in a many-body quantum system by external\n  driving: We propose a method to control the particle current of a one-dimensional\nquantum system by resonating two many-body states through an external driving\nfield. We consider the Bose-Hubbard and spinless Fermi-Hubbard models with the\nPeierls phase which induces net particle currents in the many-body eigenstates.\nA driving field couples the ground state with one of the excited states having\nlarge net currents, enabling us to control the system's current via Rabi\noscillation. Employing the Floquet analysis, we find that the resonate excited\nstates are determined by the symmetry of the driving field, which allows us to\nselectively excite only certain states among the dense spectrum of a many-body\nquantum system."
    },
    {
        "anchor": "Beyond-Luttinger-Liquid thermodynamics of a one-dimensional contact\n  repulsive Bose gas: We present a thorough study of the thermodynamics of a one-dimensional\nrepulsive Bose gas, focusing in particular on corrections beyond the\nLuttinger-liquid description. We compute the chemical potential, the pressure\nand the contact, as a function of temperature and gas parameter with exact\nthermal Bethe-Ansatz. In addition, we provide interpretations of the main\nfeatures in the analytically tractable regimes, based on a variety of\napproaches (Bogoliubov, hard-core, Sommerfeld and virial). The beyond\nLuttinger-liquid thermodynamic effects are found to be non-monotonic as a\nfunction of gas parameter. Such behavior is explained in terms of non-linear\ndispersion and ``negative excluded volume'' effects, for weak and strong\nrepulsion respectively, responsible for the opposite sign corrections in the\nthermal next-to-leading term of the thermodynamic quantities at low\ntemperatures. Our predictions can be applied to other systems including super\nTonks-Girardeau gases, dipolar and Rydberg atoms, helium, quantum liquid\ndroplets in bosonic mixtures and impurities in a quantum bath.",
        "positive": "Synthetic gauge fields stabilize a chiral spin liquid phase: We calculate the phase diagram of the SU($N$) Hubbard model describing\nfermionic alkaline earth atoms in a square optical lattice with on-average one\natom per site, using a slave-rotor mean-field approximation. We find that the\nchiral spin liquid predicted for $N\\ge5$ and large interactions passes through\na fractionalized state with a spinon Fermi surface as interactions are\ndecreased before transitioning to a weakly interacting metal. We also show that\nby adding an artificial uniform magnetic field with flux per plaquette\n$2\\pi/N$, the chiral spin liquid becomes the ground state for all $N\\ge 3$ at\nlarge interactions, persists to weaker interactions, and its spin gap\nincreases, suggesting that the spin liquid physics will persist to higher\ntemperatures. We discuss potential methods to realize the artificial gauge\nfields and detect the predicted phases."
    },
    {
        "anchor": "Energy spectra and fluxes of turbulent rotating Bose-Einstein\n  condensates in two dimensions: We investigate the scaling of the energy cascade in a harmonically trapped,\nturbulent, rotating Bose-Einstein condensate (BEC) in two dimensions. We\nachieve turbulence by injecting a localized perturbation into the condensate\nand gradually increasing its rotation frequency from an initial value to a\nmaximum. The main characteristics of the resulting turbulent state depend on\nthe initial conditions, rotation frequency, and ramp-up time. We analyze the\nenergy and the fluxes of kinetic energy by considering initial profiles without\nvortices and with vortex lattices. In the case without initial vortices, we\nfind the presence of Kolmogorov-like scaling ($k^{-5/3}$) of the incompressible\nkinetic energy in the inertial range. However, with initial vortex lattices,\nthe energy spectrum follows Vinen scaling ($k^{-1}$) at transient iterations.\nFor cases with high rotating frequencies, Kolmogorov-like scaling emerges at\nlonger durations. We observe positive kinetic energy fluxes with both initial\nstates across all final frequencies, indicating a forward cascade of\nincompressible and compressible kinetic energy.",
        "positive": "Theory of unitary Bose gases: We develop an analytical approach for the description of an atomic Bose gas\nat unitarity. By focusing in first instance on the evaluation of the\nsingle-particle density matrix, we derive several universal properties of the\nunitary Bose gas, such as the chemical potential, the contact, the speed of\nsound, the condensate density and the effective interatomic interaction. The\ntheory is also generalized to describe Bose gases with a finite scattering\nlength and then reduces to the Bogoliubov theory in the weak-coupling limit."
    },
    {
        "anchor": "Partial Fermionization---Spectral Universality in 1D Repulsive Bose\n  Gases: Due to the vast growth of the many-body level density with excitation energy,\nits smoothed form is of central relevance for spectral and thermodynamic\nproperties of interacting quantum systems. We compute the cumulative of this\nlevel density for confined one-dimensional continuous systems with repulsive\nshort-range interactions. We show that the crossover from an ideal Bose gas to\nthe strongly correlated, fermionized gas, i.e., partial fermionization,\nexhibits universal behavior: Systems with very few up to many particles share\nthe same underlying spectral features. In our derivation we supplement quantum\ncluster expansions with short-time dynamical information. Our nonperturbative\nanalytical results are in excellent agreement with numerics for systems of\nexperimental relevance in cold atom physics, such as interacting bosons on a\nring (Lieb-Liniger model) or subject to harmonic confinement. Our method\nprovides predictions for excitation spectra that enable access to\nfinite-temperature thermodynamics in large parameter ranges.",
        "positive": "FFLO states and quantum oscillations in mesoscopic superconductors and\n  superfluid ultracold Fermi gases: We have studied the distinctive features of the\nFulde-Ferrel-Larkin-Ovchinnikov (FFLO) instability and phase transitions in\ntwo--dimensional (2D) mesoscopic superconductors placed in magnetic field of\narbitrary orientation and rotating superfluid Fermi gases with imbalanced state\npopulations. Using a generalized version of the phenomenological\nGinzburg-Landau theory we have shown that the FFLO states are strongly modified\nby the effect of the trapping potential confining the condensate. The\nphenomenon of the inhomogeneous state formation is determined by the interplay\nof three length scales: (i) length scale of the FFLO instability; (ii) 2D\nsystem size; (iii) length scale associated with the orbital effect caused\neither by the Fermi condensate rotation or magnetic field component applied\nperpendicular to the superconducting disc. We have studied this interplay and\nresulting quantum oscillation effects in both superconducting and superfluid\nfinite -- size systems with FFLO instability and described the hallmarks of the\nFFLO phenomenon in a restricted geometry. The finite size of the system is\nshown to affect strongly the conditions of the observability of switching\nbetween the states with different vorticities."
    },
    {
        "anchor": "P-Wave Contact Tensor -- Universal Properties of Axisymmetry-Broken\n  P-Wave Fermi Gases: We investigate universal properties of a p-wave Fermi gas with a resonant\ninteraction in which the axisymmetry is broken spontaneously or externally.\nHere, the short-range correlations can be completely characterized by the\nnine-component p-wave contact tensor, which can be measured by applying a\ngeneralized adiabatic sweep theorem. The distinctive features of the p-wave\ncontact tensor emerge in a normal p-wave Fermi gas in an anisotropic trap and\nin a superfluid phase. An experimental scheme to measure the p-wave contact\ntensor and test the adiabatic sweep theorem is also discussed.",
        "positive": "Spin-chain model for strongly interacting one-dimensional Bose-Fermi\n  mixtures: Strongly interacting one-dimensional (1D) Bose-Fermi mixtures form a tunable\nXXZ spin chain. Within the spin-chain model developed here, all properties of\nthese systems can be calculated from states representing the ordering of the\nbosons and fermions within the atom chain and from the ground-state wave\nfunction of spinless noninteracting fermions. We validate the model by means of\nan exact diagonalization of the full few-body Hamiltonian in the strongly\ninteracting regime. Using the model, we explore the phase diagram of the atom\nchain as a function of the boson-boson (BB) and boson-fermion (BF) interaction\nstrengths and calculate the densities, momentum distributions, and trap-level\noccupancies for up to 17 particles. In particular, we find antiferromagnetic\n(AFM) and ferromagnetic (FM) order and a demixing of the bosons and fermions in\ncertain interaction regimes. We find, however, no demixing for equally strong\nBB and BF interactions in agreement with earlier calculations that combined the\nBethe ansatz with a local-density approximation."
    },
    {
        "anchor": "Mott Insulator-Density Ordered Superfluid Transition and \"Shamrock\n  Transition\" in a Frustrated Triangle Lattice: Density order is usually a consequence of the competition between long-range\nand short-range interactions. Here we report a density ordered superfluid\nemergent from a homogeneous Mott insulator due to the competition between\nfrustrations and local interactions. This transition is found in a Bose-Hubbard\nmodel on a frustrated triangle lattice with an extra pairing term. Further, we\nfind a quantum phase transition between two different density ordered\nsuperfluids, which is beyond the Landau-Ginzburg paradigm. Across this\ntransition, a U(1) symmetry is emergent, while the symmetry in each density\nordered superfluid is Z2*Z3. Because there emerges a shamrock-like degenerate\nground state in parameter space, we call the transition \"shamrock transition\".\nEffective low energy theories are established for the two transitions mentioned\nabove and we find their resemblance and differences with clock models.",
        "positive": "Stability of a Bose-Einstein condensate in a driven optical lattice:\n  Crossover between weak and tight transverse confinement: We explore the effect of transverse confinement on the stability of a\nBose-Einstein condensate (BEC) loaded in a shaken one-dimensional or\ntwo-dimensional square lattice. We calculate the decay rate from two-particle\ncollisions. We predict that if the transverse confinement exceeds a critical\nvalue, then, for appropriate shaking frequencies, the condensate is stable\nagainst scattering into transverse directions."
    },
    {
        "anchor": "Quantum Criticality of 1D Attractive Fermi Gas: We obtain an analytical equation of state for one-dimensional strongly\nattractive Fermi gas for all parameter regime in current experiments. From the\nequation of state we derive universal scaling functions that control whole\nthermodynamical properties in quantum critical regimes and illustrate physical\norigin of quantum criticality. It turns out that the critical properties of the\nsystem are described by these of free fermions and those of mixtures of\nfermions with mass $m$ and $2m$. We also show how these critical properties of\nbulk systems can be revealed from the density profile of trapped Fermi gas at\nfinite temperatures and can be used to determine the T=0 phase boundaries\nwithout any arbitrariness.",
        "positive": "Third virial coefficient of the unitary Bose gas: By unitary Bose gas we mean a system composed of spinless bosons with s-wave\ninteraction of infinite scattering length and almost negligible (real or\neffective) range. Experiments are currently trying to realize it with cold\natoms. From the analytic solution of the three-body problem in a harmonic\npotential, and using methods previously developed for fermions, we determine\nthe third cumulant (or cluster integral) b_3 and the third virial coefficient\na_3 of this gas, in the spatially homogeneous case, as a function of its\ntemperature and the three-body parameter R_t characterizing the Efimov effect.\nA key point is that, converting series into integrals (by an inverse residue\nmethod), and using an unexpected small parameter (the three-boson mass angle\nnu=pi/6), one can push the full analytical estimate of b_3 and a_3 up to an\nerror that is in practice negligible. ----- Nous entendons par gaz de Bose\nunitaire un systeme compose de bosons sans spin interagissant dans l'onde s par\nun potentiel de longueur de diffusion infinie et de portee (reelle ou\neffective) presque negligeable, systeme pour l'instant abstrait mais dont la\ntentative de realisation avec des atomes froids est en cours. A partir de la\nsolution analytique connue du probleme a trois corps dans un piege harmonique,\net de methodes precedemment developpees pour des fermions, nous determinons le\ntroisieme cumulant b_3, puis le troisieme coefficient du viriel a_3 de ce gaz,\ndans le cas spatialement homogene, en fonction de sa temperature et du\nparametre a trois corps R_t caracterisant l'effet Efimov. Un point marquant est\nqu'en convertissant des series en des integrales (par une methode des residus\ninverse), puis en utilisant un petit parametre inattendu, l'angle de masse\nnu=pi/6 des trois bosons, on peut pousser l'estimation completement analytique\nde b_3 et de a_3 jusqu'a une erreur en pratique negligeable."
    },
    {
        "anchor": "Directed motion of doublons and holes in periodically driven Mott\n  insulators: Periodically driven systems can lead to a directed motion of particles. We\ninvestigate this ratchet effect for a bosonic Mott insulator where both a\nstaggered hopping and a staggered local potential vary periodically in time. If\ndriving frequencies are smaller than the interaction strength and the density\nof excitations is small, one obtains effectively a one-particle quantum ratchet\ndescribing the motion of doubly occupied sites (doublons) and empty sites\n(holes). Such a simple quantum machine can be used to manipulate the\nexcitations of the Mott insulator. For suitably chosen parameters, for example,\nholes and doublons move in opposite direction. To investigate whether the\nperiodic driving can be used to move particles \"uphill\", i.e., against an\nexternal force, we study the influence of a linear potential $- g x$. For long\ntimes, transport is only possible when the driving frequency $\\omega$ and the\nexternal force $g$ are commensurate, $n_0 g = m_0 \\omega$, with\n$\\frac{n_0}{2},m_0 \\in \\mathbb{Z}$.",
        "positive": "Wigner distribution functions for complex dynamical systems: the\n  emergence of the Wigner-Boltzmann equation: The equation of motion for the reduced Wigner function of a system coupled to\nan external quantum system is presented for the specific case when the external\nquantum system can be modeled as a set of harmonic oscillators. The result is\nderived from the Wigner function formulation of the Feynman-Vernon influence\nfunctional theory. It is shown how the true self-energy for the equation of\nmotion is connected with the influence functional for the path integral.\nExplicit expressions are derived in terms of the bare Wigner propagator.\nFinally, we show under which approximations the resulting equation of motion\nreduces to the Wigner-Boltzmann equation."
    },
    {
        "anchor": "Achieving one-dimensionality with attractive fermions: In this article we discuss the accuracy of effective one-dimensional theories\nused to describe the behavior of ultracold atomic ensembles confined in quantum\nwires by a harmonic trap. We derive within a fully many-body approach the\neffective Hamiltonian describing this class of systems and we calculate the\nbeyond-mean field corrections to the energy of the ground state arising from\nvirtual transitions towards excited state of the confining potential. We find\nthat, due to the Pauli principle, effective finite-range corrections are one of\nmagnitude larger than effective three-body interactions.By comparing to exact\nsolutions of the purely 1D problem, we conclude that a 1D effective theory\nprovides a good description of the ground state of the system for a rather\nlarge range of interaction parameters.",
        "positive": "Magnetic defects in an unbalanced mixture of two Bose-Einstein\n  condensates: When the spectrum of magnetic excitations of a quantum mixture is much softer\nthan the density spectrum, the system becomes effectively incompressible and\ncan host magnetic defects. These are characterized by the presence of a\ntopological defect in one of the two species and by a local modification of the\ndensity in the second one, the total density being practically unaffected. For\nmiscible mixtures interacting with equal intraspecies coupling constants the\nwidth of these magnetic defects is fixed by the difference between the\nintraspecies and interspecies coupling constants and becomes larger and larger\nas one approaches the demixing transition. When the density of the filling\ncomponent decreases, the incompressibility condition breaks down and we predict\nthe existence of a critical filling, below which all the atoms of the minority\ncomponent remain bound in the core of the topological defect. Applications to\nthe sodium case both in uniform and harmonically trapped configurations are\nconsidered and a protocol to produce experimentally these defects is discussed.\nThe case of binary mixtures interacting with unequal intraspecies forces and\nexperiencing buoyancy is also addressed."
    },
    {
        "anchor": "Synthesizing Lattice Structure in Phase Space: We consider a realistic model, i.e., ultracold atoms in a driven optical\nlattice, to realize phase space crystals [Phys. Rev. Lett. 111, 205303 (2013)].\nThe corresponding lattice structure in phase space is more complex and contains\nrich physics. A phase space lattice differs fundamentally from a lattice in\nreal space, because its coordinate system, i.e., phase space, has a\nnoncommutative geometry, which naturally provides an artificial gauge\n(magnetic) field. We study the behavior of the quasienergy band structure as\nfunction of the artificial magnetic field and investigate the thermal\nproperties. Synthesizing lattice structures in phase space is not only a new\nway to create artificial lattice in experiments but also provides a platform to\nstudy the intriguing phenomena of driven systems far away from equilibrium.",
        "positive": "Bose-Einstein condensates in quasi-periodic lattices: bosonic Josephson\n  junction, self-trapping, and multi-mode dynamics: Bose-Einstein condensates loaded in one-dimensional bichromatic optical\nlattices with constituent sublattices having incommensurate periods is\nconsidered. Using the rational approximations for the incommensurate periods,\nwe show that below the mobility edge the localized states are distributed\nnearly homogeneously in the space and explore the versatility of such\npotentials. We show that superposition of symmetric and anti-symmetric\nlocalized can be used to simulate various physical dynamical regimes, known to\noccur in double-well and multi-well traps. As examples, we obtain an\nalternative realization of a bosonic Josephson junction, whose coherent\noscillations display beatings or switching in the weakly nonlinear regime,\ndescribe selftrapping and four-mode dynamics, mimicking coherent oscillations\nand self-trapping in four-well potentials. These phenomena can be observed for\ndifferent pairs of modes, which are localized due to the interference rather\nthan due to a confining trap. The results obtained using few-mode\napproximations are compared with the direct numerical simulations of the\none-dimensional Gross-Pitaevskii equation. The localized states and the related\ndynamics are found to persist for long times even in the repulsive condensates.\nWe also described bifurcations of the families of nonlinear modes, the symmetry\nbreaking and stable minigap solitons."
    },
    {
        "anchor": "Stability of a unitary Bose gas: We study the stability of a thermal $^{39}$K Bose gas across a broad Feshbach\nresonance, focusing on the unitary regime, where the scattering length $a$\nexceeds the thermal wavelength $\\lambda$. We measure the general scaling laws\nrelating the particle-loss and heating rates to the temperature, scattering\nlength, and atom number. Both at unitarity and for positive $a \\ll \\lambda$ we\nfind agreement with three-body theory. However, for $a<0$ and away from\nunitarity, we observe significant four-body decay. At unitarity, the three-body\nloss coefficient, $L_3 \\propto \\lambda^4$, is three times lower than the\nuniversal theoretical upper bound. This reduction is a consequence of\nspecies-specific Efimov physics and makes $^{39}$K particularly promising for\nstudies of many-body physics in a unitary Bose gas.",
        "positive": "Effects of Efimov states on quench dynamics in a three-boson trapped\n  system: We investigate the effects of Efimov states on the post-quench dynamics of a\nsystem of three identical bosons with contact interactions, in a\nspherically-symmetric three-dimensional harmonic trap, which undergoes a quench\nin interaction strength. Using known hyperspherical solutions to the static\nthree-body problem we calculate semi-analytic results for the Ramsey signal and\nparticle separation as functions of time after the system is quenched. We\nconsider the quench from the non-interacting to strongly interacting and vice\nversa for a variety of possible Efimov state energies."
    },
    {
        "anchor": "Persistent Currents in Atomtronic Circuits of SU(N) Fermions: Ultracold atomic systems have emerged as strong contenders amongst the\nvarious quantum systems relevant for developing and implementing quantum\ntechnologies due to their enhanced control and flexibility of the operating\nconditions. In this thesis, we explore persistent currents generated in a\nring-shaped quantum gas of strongly interacting \\textit{N}-component fermions,\nspecifically the so-called SU(\\textit{N}) fermions. Our results, apart from\nbeing a relevant contribution to many-body physics, prove the `primum mobile'\nfor a new concept of matter-wave circuits based on SU(\\textit{N}) fermionic\nplatforms, opening an exciting chapter in the field of atomtronics. Indeed, the\nspecific properties of quantization are expected to provide the core to\nfabricate quantum devices with enhanced sensitivity like interferometers. At\nthe same time, SU(\\textit{N}) fermionic circuits show promise in engineering\ncold atoms quantum simulators with this artificial fermionic matter.",
        "positive": "Unconventional superfluids of fermionic polar molecules in a bilayer\n  system: We study unconventional superfluids of fermionic polar molecules in a\ntwo-dimensional bilayer system with dipoles are head-to-tail across the layers.\nWe analyze the critical temperature of several unconventional pairings as a\nfunction of different system parameters. The peculiar competition between the\n$d$- and the $s$- wave pairings is discussed. We show that the experimental\nobservation of such unconventional superfluids requires ulralow temperatures,\nwhich opens up new possibilities to realize several topological phases."
    },
    {
        "anchor": "Production of a dual-species Bose-Einstein condensate of Rb and Cs atoms: We report the simultaneous production of Bose-Einstein condensates (BECs) of\n$^{87}$Rb and $^{133}$Cs atoms in separate optical traps. The two samples are\nmixed during laser cooling and loading but are separated by $400 \\mu$m for the\nfinal stage of evaporative cooling. This is done to avoid considerable\ninterspecies three-body recombination, which causes heating and evaporative\nloss. We characterize the BEC production process, discuss limitations, and\noutline the use of the dual-species BEC in future experiments to produce\nrovibronic ground state molecules, including a scheme facilitated by the\nsuperfluid-to-Mott-insulator (SF-MI) phase transition.",
        "positive": "Dynamics of Matter-Wave Quantum Emitters in a Structured Vacuum: The characteristics of spontaneous emission can be strongly modified by the\nmode structure of the vacuum. In waveguide quantum-electrodynamics based on\nphotonic crystals, this modification is exploited to engineer atom-photon\ninteractions near a band edge, but the physics of coupling to an entire band\nhas not yet been explored in experiments. Using ultracold atoms in an optical\nlattice, we study the decay dynamics of matter-wave quantum emitters coupled to\na single band of an effective photonic crystal waveguide structure with tunable\ncharacteristics. Depending on the ratio between vacuum coupling and bandwidth,\nwe observe a transition from irreversible decay to fully oscillatory dynamics\nlinked to the interplay of matter-wave bound states near the band edges, whose\nspatial structure we characterize. Our results shed light on the emergence of\ncoherence in an open quantum system in a controllable environment, and are of\nrelevance for the understanding of vacuum-induced decay phenomena in photonic\nsystems."
    },
    {
        "anchor": "Bose-Einstein Condensation in a Plasmonic Lattice: Bose-Einstein condensation is a remarkable manifestation of quantum\nstatistics and macroscopic quantum coherence. Superconductivity and\nsuperfluidity have their origin in Bose-Einstein condensation. Ultracold\nquantum gases have provided condensates close to the original ideas of Bose and\nEinstein, while condensation of polaritons and magnons have introduced novel\nconcepts of non-equilibrium condensation. Here, we demonstrate a Bose-Einstein\ncondensate (BEC) of surface plasmon polaritons in lattice modes of a metal\nnanoparticle array. Interaction of the nanoscale-confined surface plasmons with\na room-temperature bath of dye molecules enables thermalization and\ncondensation in picoseconds. The ultrafast thermalization and condensation\ndynamics are revealed by an experiment that exploits thermalization under\npropagation and the open cavity character of the system. A crossover from BEC\nto usual lasing is realized by tailoring the band structure. This new\ncondensate of surface plasmon lattice excitations has promise for future\ntechnologies due to its ultrafast, room-temperature and on-chip nature.",
        "positive": "Defect-Driven Superfluid Crossover for Two-Dimensional Dipolar Excitons\n  Trapped at Thermodynamic Equilibrium: We study ultra-cold dipolar excitons confined in a 10$\\mu$m trap of a double\nGaAs quantum well. Based on the local density approximation, we unveil for the\nfirst time the equation of state of excitons at pure thermodynamic equilibrium.\nIn this regime we show that, below a critical temperature of about $1$ Kelvin,\na superfluid forms in the inner region of the trap at a local exciton density\n$n \\sim 2-3 \\, 10^{10} \\text{cm}^{-2}$, encircled by a more dilute and normal\ncomponent in the outer rim of the trap. Remarkably, this spatial arrangement\ncorrelates directly with the concentration of defects in the exciton density\nwhich exhibits a sudden decrease at the onset of superfluidity, thus pointing\ntowards an underlying Berezinskii-Kosterlitz-Thouless mechanism."
    },
    {
        "anchor": "Optical visibility and core structure of vortex filaments in a bosonic\n  superfluid: We use optical images of a superfluid consisting of a weakly interacting\nBose-Einstein condensate of sodium atoms to investigate the structure of\nquantized three-dimensional vortex filaments. We find that the measured optical\ncontrast and the width of the vortex core quantitatively agree with the\npredictions of the Gross-Pitaevskii equation.",
        "positive": "Long timescale dynamics of spin textures in a degenerate F=1 $^{87}$ Rb\n  spinor Bose gas: We investigate the long-term dynamics of spin textures prepared by cooling\nunmagnetized spinor gases of F=1 $^{87}$Rb to quantum degeneracy, observing\ndomain coarsening and a strong dependence of the equilibration dynamics on the\nquadratic Zeeman shift $q$. For small values of $|q|$, the textures arrive at a\nconfiguration independent of the initial spin-state composition, characterized\nby large length-scale spin domains, and the establishment of easy-axis\n(negative $q$) or easy-plane (positive $q$) magnetic anisotropy. For larger\n$|q|$, equilibration is delayed as the spin-state composition of the degenerate\nspinor gas remains close to its initial value. These observations support the\nmean-field equilibrium phase diagram predicted for a ferromagnetic spinor\nBose-Einstein condensate, but also illustrate that equilibration is achieved\nunder a narrow range of experimental settings, making the F=1 $^{87}$Rb gas\nmore suitable for studies of nonequilibrium quantum dynamics."
    },
    {
        "anchor": "Free Fermions with a Localized Source: We study an open quantum system of free fermions on an infinite lattice\ncoupled to a localized particle source. In the long time limit, the total\nnumber of fermions in the system increases linearly with growth rate dependent\non the lattice geometry and dimensionality. We express the growth rate in terms\nof lattice Green functions and derive explicit formulae in one dimension and\nfor the square lattice. The interplay between the dynamics and the coupling to\nthe environment leads, in contrast to classical systems, to a non-monotonic\ndependence of the particle growth rate on the input rate. We show that for all\nlattices the particle growth rate is inversely proportional to the input rate\nwhen the latter becomes large. This is a manifestation of the quantum Zeno\neffect.",
        "positive": "Growing quantum states with topological order: We discuss a protocol for growing states with topological order in\ninteracting many-body systems using a sequence of flux quanta and particle\ninsertion. We first consider a simple toy model, the superlattice Bose Hubbard\nmodel, to explain all required ingredients. Our protocol is then applied to\nfractional quantum Hall systems in both, continuum and lattice. We investigate\nin particular how the fidelity, with which a topologically ordered state can be\ngrown, scales with increasing particle number N. For small systems exact\ndiagonalization methods are used. To treat large systems with many particles,\nwe introduce an effective model based on the composite fermion description of\nthe fractional quantum Hall effect. This model also allows to take into account\nthe effects of dispersive bands and edges in the system, which will be\ndiscussed in detail."
    },
    {
        "anchor": "Perturbative analysis of coherent quantum ratchets in cold atom systems: We present a perturbative study of the response of cold atoms in an optical\nlattice to a weak time- and space-asymmetric periodic driving signal. In the\nnoninteracting limit, and for a finite set of resonant frequencies, we show how\na coherent, long lasting ratchet current results from the interference between\nfirst and second order processes. In those cases, a suitable three-level model\ncan account for the entire dynamics, yielding surprisingly good agreement with\nnumerically exact results for weak and moderately strong driving.",
        "positive": "Controlling Dipolar Exchange Interactions in a Dense 3D Array of Large\n  Spin Fermions: Dipolar interactions are ubiquitous in nature and rule the behavior of a\nbroad range of systems spanning from energy transfer in biological systems to\nquantum magnetism. Here, we study magnetization-conserving dipolar induced\nspin-exchange dynamics in dense arrays of fermionic erbium atoms confined in a\ndeep three-dimensional lattice. Harnessing the special atomic properties of\nerbium, we demonstrate control over the spin dynamics by tuning the dipole\norientation and changing the initial spin state within the large 20 spin\nhyperfine manifold. Furthermore, we demonstrate the capability to quickly turn\non and off the dipolar exchange dynamics via optical control. The experimental\nobservations are in excellent quantitative agreement with numerical\ncalculations based on discrete phase-space methods, which capture entanglement\nand beyond-mean field effects. Our experiment sets the stage for future\nexplorations of rich magnetic behaviors in long-range interacting dipoles,\nincluding exotic phases of matter and applications for quantum information\nprocessing."
    },
    {
        "anchor": "Probing the Degree of Coherence through the Full 1D to 3D crossover: We experimentally study a gas of quantum degenerate $^{87}$Rb atoms\nthroughout the full dimensional crossover, from a one-dimensional (1D) system\nexhibiting phase fluctuations consistent with 1D theory to a three-dimensional\n(3D) phase-coherent system, thereby smoothly interpolating between these\ndistinct, well-understood regimes. Using a hybrid trapping architecture\ncombining an atom chip with a printed circuit board, we continuously adjust the\nsystem's dimensionality over a wide range while measuring the phase\nfluctuations through the power spectrum of density ripples in time-of-flight\nexpansion. Our measurements confirm that the chemical potential $\\mu$ controls\nthe departure of the system from 3D and that the fluctuations are dependent on\nboth $\\mu$ and the temperature $T$. Through a rigorous study we quantitatively\nobserve how inside the crossover the dependence on $T$ gradually disappears as\nthe system becomes 3D. Throughout the entire crossover the fluctuations are\nshown to be determined by the relative occupation of 1D axial collective\nexcitations.",
        "positive": "Condensation of Photons coupled to a Dicke Field in an Optical\n  Microcavity: Motivated by recent experiments reporting Bose-Einstein condensation (BEC) of\nlight coupled to incoherent dye molecules in a microcavity, we show that due to\na dimensionality mismatch between the 2D cavity-photons and the 3D arrangement\nof molecules, the relevant molecular degrees of freedom are collective Dicke\nstates rather than individual excitations. For sufficiently high dye\nconcentration the coupling of the Dicke states with light will dominate over\nlocal decoherence. This system also shows Mott criticality despite the absence\nof an underlying lattice in the limit when all dye molecules become excited."
    },
    {
        "anchor": "Spontaneously broken gauge symmetry in a Bose gas with constant particle\n  number: The interplay between spontaneously broken gauge symmetries and Bose-Einstein\ncondensation has long been controversially discussed in science, since the\nequation of motions are invariant under phase transformations. Within the\npresent model it is illustrated that spontaneous symmetry breaking appears as a\nnon-local process in position space, but within disjoint subspaces of the\nunderlying Hilbert space. Numerical simulations show that it is the symmetry of\nthe relative phase distribution between condensate and non-condensate quantum\nfields which is spontaneously broken when passing the critical temperature for\nBose-Einstein condensation. Since the total number of gas particles remains\nconstant over time, the global U(1)-gauge symmetry of the system is preserved.",
        "positive": "Population and mass imbalance in atomic Fermi gases: We develop an accurate theory of resonantly interacting Fermi mixtures with\nboth spin and mass imbalance. We consider Fermi mixtures with arbitrary mass\nimbalances, but focus in particular on the experimentally available\n${}^{6}$Li-${}^{40}$K mixture. We determine the phase diagram of the mixture\nfor different interactions strengths that lie on the BCS side of the Feshbach\nresonance. We also determine the universal phase diagram at unitarity. We find\nfor the mixtures with a sufficiently large mass imbalance, that includes the\n${}^{6}$Li-${}^{40}$K mixture, a Lifshitz point in the universal phase diagram\nthat signals an instability towards a supersolid phase."
    },
    {
        "anchor": "Necessary and sufficient condition for quantum adiabaticity in a driven\n  one-dimensional impurity-fluid system: We study under what conditions the quantum adiabaticity is maintained in a\nclosed many-body system consisting of a one-dimensional fluid and an impurity\nparticle dragged through the latter by an external force. We employ an\neffective theory describing the low-energy sector of the system to derive the\ntime dependence of the adiabaticity figure of merit -- the adiabatic fidelity.\nWe find that in order to maintain adiabaticity in a large system the external\nforce, $F_N$, should vanish with the system size, $N$, as $1/N$ or faster. This\nimproves the necessary adiabatic condition $F_N=O(1/\\log N)$ obtained for this\nsystem earlier [AIP Conf. Proc. 1936, 020024 (2018)]. Experimental implications\nof this result and its relation to the quasi-Bloch oscillations of the impurity\nare discussed.",
        "positive": "Ground state phase diagram of the repulsive SU(3) Hubbard model in\n  Gutzwiller approximation: We perform a variational Gutzwiller calculation to study the ground state of\nthe repulsive SU(3) Hubbard model on the Bethe lattice with infinite\ncoordination number. We construct a ground-state phase diagram focusing on\nphases with a two-sublattice structure and find five relevant phases: (1) a\nparamagnet, (2) a completely polarized ferromagnet, (3) a two-component\nantiferromagnet where the third component is depleted, (4) a two-component\nantiferromagnet with a metallic third component (an \"orbital selective\" Mott\ninsulator), and (5) a density-wave state where two components occupy dominantly\none sublattice and the last component the other one. First-order transitions\nbetween these phases lead to phase separation. A comparison of the SU(3)\nHubbard model to the better-known SU(2) model shows that the effects of doping\nare completely different in the two cases."
    },
    {
        "anchor": "Quantum simulation of extended polaron models using compound atom-ion\n  systems: We consider the prospects for quantum simulation of condensed matter models\nexhibiting strong electron-phonon coupling using a hybrid platform of trapped\nlaser-cooled ions interacting with an ultracold atomic gas. This system\nnaturally posesses a phonon structure, in contrast to the standard optical\nlattice scenarios usually employed with ultracold atoms in which the lattice is\ngenerated by laser light and thus it remains static. We derive the effective\nHamiltonian describing the general system and discuss the arising energy\nscales, relating the results to commonly employed extended Hubbard-Holstein\nmodels. Although for a typical experimentally realistic system the coupling to\nphonons turns out to be small, we provide the means to enhance its role and\nreach interesting regimes with competing orders. Extended Lang-Firsov\ntransformation reveals the emergence of phonon-induced long-range interactions\nbetween the atoms, which can give rise to both localized and extended bipolaron\nstates with low effective mass, indicating the possibility of fermion pairing.",
        "positive": "Photon Bose-Condensate as a Tunable Terahertz Laser Source without\n  Inversion: We develop a theoretical model for a tunable coherent terahertz radiation\nsource based on the long-lived Bose condensate of photons. In the device we\npropose, the original photon pumping is performed incoherently by a blackbody\nradiation emitter. The photons thus produced Bose-condense by the inelastic\nrelaxation on a two-dimensional electron gas in a perpendicular magnetostatic\nfield. The process involves neither population inversion nor light wave\namplification the standard laser sources are built on. The coherence and\ntunability of the light emitted by such a photon condensate are provided and\nsupported by the discrete spectrum of the electron gas in the quantizing\nmagnetic field. The device is a compact-size semiconductor crystal. We propose\nthe design and perform the realistic calculations of the physical properties\nand limiting factors for the terahertz photon Bose-condensate resonator. We\nshow that our terahertz source can deliver the highly coherent light emission\nin the frequency range of 3-30 THz for the magnetic field induction of the\norder of 2 T, with the upper emission frequency limit adjustable by the\nstrength of the magnetic field applied."
    },
    {
        "anchor": "Integer Quantum Hall State in Two-Component Bose Gases in a Synthetic\n  Magnetic Field: We study two-component (or pseudospin-1/2) Bose gases in a strong synthetic\nmagnetic field. Using exact diagonalization, we show that a bosonic analogue of\nan integer quantum Hall state with no intrinsic topological order appears at\nthe total filling factor \\nu=1+1 when the strengths of intracomponent and\nintercomponent interactions are comparable with each other. This provides a\nprime example of a symmetry-protected topological phase in a controlled setting\nof quantum gases. The real-space entanglement spectrum of this state is found\nto be comprised of counter-propagating chiral modes consistent with the edge\ntheory derived from the effective Chern-Simons theory.",
        "positive": "Phase dependent loading of Bloch bands and Quantum simulation of\n  relativistic wave equation predictions with ultracold atoms in variably\n  shaped optical lattice potentials: The dispersion relation of ultracold atoms in variably shaped optical\nlattices can be tuned to resemble that of a relativistic particle, i.e. be\nlinear instead of the usual nonrelativistic quadratic dispersion relation of a\nfree atom. Cold atoms in such a lattice can be used to carry out quantum\nsimulations of relativistic wave equation predictions. We begin this article by\ndescribing a Raman technique that allows to selectively load atoms into a\ndesired Bloch band of the lattice near a band crossing. Subsequently, we review\ntwo recent experiments with quasirelativistic rubidium atoms in a bichromatic\nlattice, demonstrating the analogs of Klein tunneling and Veselago lensing with\nultracold atoms respectively."
    },
    {
        "anchor": "Two mass-imbalanced atoms in a hard-wall trap: Deep learning\n  integrability of many-body systems: The study of integrable systems has led to significant advancements in our\nunderstanding of many-body physics. We design a series of numerical experiments\nto analyze the integrability of a mass-imbalanced two-body system through\nenergy level statistics and deep learning of wavefunctions. The level spacing\ndistributions are fitted by a Brody distribution and the fitting parameter\n$\\omega$ is found to separate the integrable and non-integrable mass ratios by\na critical line $\\omega=0$. The convolutional neural network built from the\nprobability density images could identify the transition points between\nintegrable and non-integrable systems with high accuracy, yet in a much shorter\ncomputation time. A brilliant example of the network's ability is to identify a\nnew integrable mass ratio $1/3$ by learning from the known integrable case of\nequal mass, with a remarkable network confidence of $98.78\\%$. The robustness\nof our neural networks is further enhanced by adversarial learning, where\nsamples are generated by standard and quantum perturbations mixed in the\nprobability density images and the wavefunctions, respectively.",
        "positive": "Staircase Prethermalization and Constrained Dynamics in Lattice Gauge\n  Theories: The dynamics of lattice gauge theories is characterized by an abundance of\nlocal symmetry constraints. Although errors that break gauge symmetry appear\nnaturally in NISQ-era quantum simulators, their influence on the gauge-theory\ndynamics is insufficiently investigated. As we show, a small gauge breaking of\nstrength $\\lambda$ induces a staircase of long-lived prethermal plateaus. The\nnumber of prethermal plateaus increases with the number of matter fields $L$,\nwith the last plateau being reached at a timescale $\\lambda^{-L/2}$, showing an\nintimate relation of the concomitant slowing down of dynamics with the number\nof local gauge constraints. Our results bode well for NISQ quantum devices, as\nthey indicate that the proliferation timescale of gauge-invariance violation is\ncounterintuitively delayed exponentially in system size."
    },
    {
        "anchor": "Spontaneous symmetry breaking in frustrated triangular atom arrays due\n  to cooperative light scattering: We demonstrate the presence of an optical phase transition with\nfrustration-induced spontaneous symmetry breaking in a triangular planar atomic\narray due to cooperative light-mediated interactions. We show how the array\ngeometry of triangle unit cells at low light intensities leads to degenerate\ncollective radiative excitations forming nearly flat bands. We drive degenerate\npairs of collective excitations to be equally populated in both cases of the\natomic polarization in the lattice plane and perpendicular to it. At higher\nintensities, above specific threshold values, this symmetry in the populations\nis spontaneously broken. We also develop an effective few-mode model that\nprovides semianalytic descriptions of the symmetry-breaking threshold and\ninfinite-lattice limit phase transition. Surprisingly, we find how excitations\ndue to dipolar interactions correspond to optical analogs of those found in\nfrustrated magnets and superfluids, with closely related symmetry-breaking\nmechanisms despite the significant physical differences between these systems,\nopening potential for simulating even quantum magnetism. Transmitted light\nthrough the array conveys information about symmetry breaking in the hysteresis\nbehavior of the spectrum. Moreover, in a Mott-insulator state, the atomic\npositions are subject to zero-point quantum fluctuations. Interpreting each\nstochastic realization as a light-induced quantum measurement of the atomic\nposition configuration, we find how strong nonlinearities and even weak\nposition uncertainties lead to considerable measurement-induced symmetry\nbreaking, while ensemble-averaging over many realizations restores the original\nsymmetry and the unbroken state. Larger position uncertainty results in the\nformation of domains of different broken symmetries.",
        "positive": "Two-dimensional non-Hermitian skin effect in an ultracold Fermi gas: The concept of non-Hermiticity has expanded the understanding of band\ntopology leading to the emergence of counter-intuitive phenomena. One example\nis the non-Hermitian skin effect (NHSE), which involves the concentration of\neigenstates at the boundary. However, despite the potential insights that can\nbe gained from high-dimensional non-Hermitian quantum systems in areas like\ncurved space, high-order topological phases, and black holes, the realization\nof this effect in high dimensions remains unexplored. Here, we create a\ntwo-dimensional (2D) non-Hermitian topological band for ultracold fermions in\nspin-orbit-coupled optical lattices with tunable dissipation, and\nexperimentally examine the spectral topology in the complex eigenenergy plane.\nWe experimentally demonstrate pronounced nonzero spectral winding numbers when\nthe dissipation is added to the system, which establishes the existence of 2D\nskin effect. We also demonstrate that a pair of exceptional points (EPs) are\ncreated in the momentum space, connected by an open-ended bulk Fermi arc, in\ncontrast to closed loops found in Hermitian systems. The associated EPs emerge\nand shift with increasing dissipation, leading to the formation of the Fermi\narc. Our work sets the stage for further investigation into simulating\nnon-Hermitian physics in high dimensions and paves the way for understanding\nthe interplay of quantum statistics with NHSE."
    },
    {
        "anchor": "Field-theoretical study of the Bose polaron: We study the properties of the Bose polaron, an impurity strongly interacting\nwith a Bose-Einstein condensate, using a field-theoretic approach and make\npredictions for the spectral function and various quasiparticle properties that\ncan be tested in experiment. We find that most of the spectral weight is\ncontained in a coherent attractive and a metastable repulsive polaron branch.\nWe show that the qualitative behavior of the Bose polaron is well described by\na non-selfconsistent T-matrix approximation by comparing analytical results to\nnumerical data obtained from a fully selfconsistent T-matrix approach. The\nlatter takes into account an infinite number of bosons excited from the\ncondensate.",
        "positive": "Mean-field properties of impurity in Bose gas with three-body forces: We exactly analyze, on the mean-field level, the low-momentum properties of a\nsingle impurity atom loaded in the dilute one-dimensional Bose gas with two-\nand three-body short-range interactions. Particularly the Bose polaron binding\nenergy and the quasiparticle residue are calculated for the considered system\nin the broad region of parameters change. We also explore the generic\nmean-field formula for the polaron effective mass which was shown to depend on\nthe density profile of bath particles with a motionless impurity immersed."
    },
    {
        "anchor": "Collision-induced frequency shifts in bright matter-wave solitons and\n  soliton molecules: A recent experiment has detected collision-induced frequency shifts in bright\nmatter-wave solitons for the first time [Nat. Phys. 10, 918 (2014)]. Using a\nparticle model, we derive the frequency shift for two solitons in a harmonic\ntrap, and compare it to the results of the recent experiment and reported\ntheoretical approximation. We find regimes where the frequency shift is much\nsmaller than previously predicted, and propose experiments to test these\nfindings. We also predict that reducing the experimental trap frequency will\nreveal for the first time soliton molecules or soliton bound states in a cold\natoms system. The dynamics of such bound states are found to be both highly\nphase-dependent, and sensitive to the residual 3D nature of the experiment.",
        "positive": "Contact intensity and extended hydrodynamics in the BCS-BEC crossover: In the first part of this chapter we analyze the contact intensity $C$, which\nhas been introduced by Tan [Ann. Phys. 323, 2952 (2008)] and appears in several\nphysical observables of the strongly correlated two-component Fermi gas. We\ncalculate the contact $C$ in the full BCS-BEC crossover for a uniform\nsuperfluid Fermi gas by using an efficient parametetrization of the\nground-state energy. In the case of harmonic confinement, within the\nThomas-Fermi approximation, we derive analytical formulas of $C$ in the three\nrelevant limits of the crossover. In the second part of this chapter we discuss\nthe extended superfluid hydrodynamics we have recently proposed to describe\nstatic and dynamical collective properties of the Fermi gas in the BCS-BEC\ncrossover. In particular we show the relation with the effective theory for the\nGoldstone field derived by Son and Wingate [Ann. Phys. 321, 197 (2006)] on the\nbasis of conformal invariance. By using our equations of extended hydrodynamics\nwe determine nonlinear sound waves, static response function and structure\nfactor of a generic superfluid at zero temperature."
    },
    {
        "anchor": "Excitation Spectra of Bosons in Optical Lattices from Schwinger-Keldysh\n  Calculation: Within the Schwinger-Keldysh formalism we derive a Ginzburg-Landau theory for\nthe Bose-Hubbard model which describes the real-time dynamics of the complex\norder parameter field. Analyzing the excitations in the vicinity of the quantum\nphase transition it turns out that particle/hole dispersions in the Mott phase\nmap continuously onto corresponding amplitude/phase excitations in the\nsuperfluid phase, which have been detected recently by Bragg spectroscopy\nmeasurements.",
        "positive": "Delocalization to self-trapping transition of a Bose fluid confined in a\n  double well potential. An analysis via one- and two-body correlation\n  properties: We revisit the coherent or delocalized to self-trapping transition in an\ninteracting bosonic quantum fluid confined in a double well potential, in the\ncontext of full quantum calculations. We show that an $N$-particle Bose-Hubbard\nfluid reaches an stationary state through the two-body interactions. These\nstationary states are either delocalized or self-trapped in one of the wells,\nthe former appearing as coherent oscillations in the mean-field approximation.\nBy studying one- and two-body properties in the energy eigenstates and in a set\nof coherent states, we show that the delocalized to self-trapped transition\noccurs as a function of the energy of the fluid, provided the interparticle\ninteraction is above a critical or threshold value. We argue that this is a\ntype of symmetry-breaking continuous phase transition."
    },
    {
        "anchor": "Proof of Bose condensation for weakly interacting lattice bosons: A weakly interacting Bose gas on a simple cubic lattice is considered. We\nprove the existence of the standard or zero-mode Bose condensation at\nsufficiently low temperature. This result is valid for sufficiently small\ninteraction potential and small values of chemical potential. Our method\nexploits infrared bound for the suitable two-point Bogolyubov's inner product.\nWe do not use the reflection positivity or some expansion methods.",
        "positive": "Resonant dynamics of chromium condensates: We numerically study the dynamics of a spinor chromium condensate in low\nmagnetic fields. We show that the condensate evolution has a resonant character\nrevealing rich structure of resonances similar to that already discussed in the\ncase of alkali-atoms condensates. This indicates that dipolar resonances occur\ncommonly in the systems of cold atoms. In fact, they have been already observed\nexperimentally. We further simulate two recent experiments with chromium\ncondensates, in which the threshold in spin relaxation and the spontaneous\ndemagnetization phenomena were observed. We demonstrate that both these effects\noriginate in resonant dynamics of chromium condensate."
    },
    {
        "anchor": "Unruh effect for interacting particles with ultracold atoms: The Unruh effect is a quantum relativistic effect where the accelerated\nobserver perceives the vacuum as a thermal state. Here we propose the\nexperimental realization of the Unruh effect for interacting ultracold fermions\nin optical lattices by a sudden quench resulting in vacuum acceleration with\nvarying interactions strengths in the real temperature background. We observe\nthe inversion of statistics for the low lying excitations in the Wightman\nfunction as a result of competition between the spacetime and BCS Bogoliubov\ntransformations. This paper opens up new perspectives for simulators of quantum\ngravity.",
        "positive": "Quantum dynamics of Bose-Einstein condensates in tilted and driven\n  bichromatic optical lattices: We study the dynamics of Bose-Einstein condensates in tilted and driven\noptical superlattices. For a bichromatic lattice, each Bloch band split up into\ntwo minibands such that the dynamics is governed by the interplay of Bloch\noscillations and transitions between the bands. Thus, bichromatic potentials\nprovide an excellent model system for the study of nonlinear Landau-Zener\ntunneling and allow for a variety of applications in matter wave interferometry\nand quantum metrology. In the present paper we investigate the coherent\ndynamics of an interacting Bose-Einstein condensate as well as its stability.\nDifferent mechanisms of instability are discussed, which lead to a rapid\ndepletion of the condensate."
    },
    {
        "anchor": "Quantum magnetism of ultracold atoms with a dynamical pseudospin degree\n  of freedom: We consider bosons in a Hubbard lattice with an SU($\\cal N$) pseudospin\ndegree of freedom which is made dynamical via a coherent transfer term. It is\nshown that, in the basis which diagonalizes the pseudospin coupling, a generic\nhopping process affects the spin state, similar to a spin-orbit coupling. This\nresults, for the system in the Mott phase, in a ferromagnetic phase with\nvariable quantization axis. In extreme cases, it can even give rise to\nantiferromagnetic order.",
        "positive": "Correlation functions and momentum distribution of one-dimensional\n  hard-core anyons in optical lattices: We address the problem of calculating the correlation functions in a system\nof one-dimensional hard-core anyons that can be experimentally realized in\noptical lattices. Using the summation of form factors we have obtained Fredholm\ndeterminant representations for the time-, space-, and temperature-dependent\nGreen's functions which are particularly suited to numerical investigations. In\nthe static case we have also derived the large distance asymptotic behavior of\nthe correlators and computed the momentum distribution function at zero and\nfinite temperature. We present extensive numerical results highlighting the\ncharacteristic features of one-dimensional systems with fractional statistics."
    },
    {
        "anchor": "Angular spin-orbit coupling in cold atoms: We propose coupling two internal atomic states using a pair of Raman beams\noperated in Laguerre-Gaussian laser modes with unequal phase windings. This\ngenerates a coupling between the atom's pseudo-spin and its orbital angular\nmomentum. We analyze the single-particle properties of the system using\nrealistic parameters and provide detailed studies of the spin texture of the\nground state. Finally, we consider a weakly interacting atomic condensate\nsubject to this angular spin-orbit coupling and show how the inter-atomic\ninteractions modifies the single-particle physics.",
        "positive": "Universality of weakly bound dimers and Efimov trimers close to Li-Cs\n  Feshbach resonances: We study the interspecies scattering properties of ultracold Li-Cs mixtures\nin their two energetically lowest spin channels in the magnetic field range\nbetween 800 G and 1000 G. Close to two broad Feshbach resonances we create\nweakly bound LiCs dimers by radio-frequency association and measure the\ndependence of the binding energy on the external magnetic field strength. Based\non the binding energies and complementary atom loss spectroscopy of three other\nLi-Cs s-wave Feshbach resonances we construct precise molecular singlet and\ntriplet electronic ground state potentials using a coupled-channels\ncalculation. We extract the Li-Cs interspecies scattering length as a function\nof the external field and obtain almost a ten-fold improvement in the precision\nof the values for the pole positions and widths of the s-wave Li-Cs Feshbach\nresonances as compared to our previous work [Pires \\textit{et al.}, Phys. Rev.\nLett. \\textbf{112}, 250404 (2014)]. We discuss implications on the Efimov\nscenario and the universal geometric scaling for LiCsCs trimers."
    },
    {
        "anchor": "Weak Ergodicity Breaking in Non-Hermitian Many-body Systems: The recent discovery of persistent revivals in the Rydberg-atom quantum\nsimulator has revealed a weakly ergodicity-breaking mechanism dubbed quantum\nmany-body scars, which are a set of nonthermal states embedded in otherwise\nthermal spectra. Until now, such a mechanism has been mainly studied in\nHermitian systems. Here, we establish the non-Hermitian quantum many-body scars\nand systematically characterize their nature from dynamic revivals,\nentanglement entropy, physical observables, and energy level statistics.\nNotably, we find the non-Hermitian quantum many-body scars exhibit\nsignificantly enhanced coherent revival dynamics when approaching the\nexceptional point. The signatures of non-Hermitian scars switch from the\nreal-energy axis to the imaginary-energy axis after a real-to-complex spectrum\ntransition driven by increasing non-Hermiticity, where an exceptional point and\na quantum tricritical point emerge simultaneously. We further examine the\nstability of non-Hermitian quantum many-body scars against external fields,\nreveal the non-Hermitian quantum criticality and eventually set up the whole\nphase diagram. The possible connection to the open quantum many-body systems is\nalso explored. Our findings offer insights for realizing long-lived coherent\nstates in non-Hermitian many-body systems.",
        "positive": "Dynamical Critical Phenomena in Driven-Dissipative Systems: We explore the nature of the Bose condensation transition in driven open\nquantum systems, such as exciton-polariton condensates. Using a functional\nrenormalization group approach formulated in the Keldysh framework, we\ncharacterize the dynamical critical behavior that governs decoherence and an\neffective thermalization of the low frequency dynamics. We identify a critical\nexponent special to the driven system, showing that it defines a new dynamical\nuniversality class. Hence critical points in driven systems lie beyond the\nstandard classification of equilibrium dynamical phase transitions. We show how\nthe new critical exponent can be probed in experiments with driven cold atomic\nsystems and exciton-polariton condensates."
    },
    {
        "anchor": "Multiband Effects and the Bose-Hubbard Model in One-Dimensional Lattices: We study phase diagrams of one-dimensional bosons with contact interactions\nin the presence of a lattice. We use the worm algorithm in continuous space and\nfocus on the incommensurate superfluid Mott-insulator transition. Our results\nare compared to those from the one-band Bose-Hubbard model. When Wannier states\nare used to determine the Bose-Hubbard model parameters, the comparison unveils\nan apparent breakdown of the one-band description for strong interactions, even\nfor the Mott-insulating state with an average of one particle per site ($n=1$)\nin deep lattices. We introduce an inverse confined scattering analysis to\nobtain the ratio $U/J$, with which the Bose-Hubbard model provides correct\nresults for strong interactions, deep lattices, and $n=1$.",
        "positive": "Capillary instability in a two-component Bose-Einstein condensate: Capillary instability and the resulting dynamics in an immiscible\ntwo-component Bose-Einstein condensate are investigated using the mean-field\nand Bogoliubov analyses. A long, cylindrical condensate surrounded by the other\ncomponent is dynamically unstable against breakup into droplets due to the\ninterfacial tension arising from the quantum pressure and interactions. A\nheteronuclear system confined in a cigar-shaped trap is proposed for realizing\nthis phenomenon experimentally."
    },
    {
        "anchor": "Dicke Superradiance in Solids: Recent advances in optical studies of condensed matter have led to the\nemergence of phenomena that have conventionally been studied in the realm of\nquantum optics. These studies have not only deepened our understanding of\nlight-matter interactions but also introduced aspects of many-body correlations\ninherent in optical processes in condensed matter systems. This article is\nconcerned with superradiance (SR), a profound quantum optical process predicted\nby Dicke in 1954. The basic concept of SR applies to a general $N$-body system\nwhere constituent oscillating dipoles couple together through interaction with\na common light field and accelerate the radiative decay of the system. In the\nmost fascinating manifestation of SR, known as superfluorescence (SF), an\nincoherently prepared system of $N$ inverted atoms spontaneously develops\nmacroscopic coherence from vacuum fluctuations and produces a delayed pulse of\ncoherent light whose peak intensity $\\propto N^2$. Such SF pulses have been\nobserved in atomic and molecular gases, and their intriguing quantum nature has\nbeen unambiguously demonstrated. Here, we focus on the rapidly developing field\nof research on SR in solids, where not only photon-mediated coupling but also\nstrong Coulomb interactions and ultrafast scattering exist. We describe SR and\nSF in molecular centers in solids, molecular aggregates and crystals, quantum\ndots, and quantum wells. In particular, we will summarize a series of studies\nwe have recently performed on quantum wells in strong magnetic fields. These\nstudies show that cooperative effects in solid-state systems are not merely\nsmall corrections that require exotic conditions to be observed; rather, they\ncan dominate the nonequilibrium dynamics and light emission processes of the\nentire system of interacting electrons.",
        "positive": "Collective excitations of exciton-polariton condensates in a synthetic\n  gauge field: Collective (elementary) excitations of quantum bosonic condensates, including\ncondensates of exciton polaritons in semiconductor microcavities, are a\nsensitive probe of interparticle interactions. In anisotropic microcavities\nwith momentum-dependent TE-TM splitting of the optical modes, the excitations\ndispersions are predicted to be strongly anisotropic, which is a consequence of\nthe synthetic magnetic gauge field of the cavity, as well as the interplay\nbetween different interaction strengths for polaritons in the singlet and\ntriplet spin configurations. Here, by directly measuring the dispersion of the\ncollective excitations in a high-density optically trapped exciton-polariton\ncondensate, we observe excellent agreement with the theoretical predictions for\nspinor polariton excitations. We extract the inter- and intra-spin polariton\ninteraction constants and map out the characteristic spin textures in an\ninteracting spinor condensate of exciton polaritons."
    },
    {
        "anchor": "Born-Oppenheimer description of two atoms in a combined oscillator and\n  lattice trap: We analyze the quantum states of two atoms in a combined harmonic oscillator\nand periodic lattice trap in one spatial dimension. In the case of\ntight-binding and only nearest neighbor tunneling, the equations of motion are\nconveniently represented in the momentum representation. We show that in the\ncase of strong attraction between the particles, the different time scales of\nrelative and center-of-mass motion validate a separation of the problem similar\nto the Born-Oppenheimer approximation applied in the description of electronic\nand nuclear motion in molecules.",
        "positive": "Non-Abelian gauge potential driven localization transition in\n  quasiperiodic optical lattices: Gauge potential is an emergent concept in systems of ultracold atomic gases.\nDerived from quantum waves immersed in an \\emph{Abelian} gauge, the\nquasiperiodic Aubry-Andre-Harper (AAH) model is a simple yet powerful\nHamiltonian to study the Anderson localization of ultracold atoms. In this\nwork, we investigate the localization properties of ultracold atoms trapped in\nquasiperiodic optical lattices subject to a non-Abelian gauge, which can be\ndepicted by a family of non-Abelian AAH models. We identify that the\nnon-Abelian AAH models can bear the self-duality under the Fourier\ntransformation. We thus analyze the localization transition of this self-dual\nnon-Abelian quasiperiodic optical lattices, revealing that the non-Abelian\ngauge involved drives a transition from a pure delocalization phase, then to\ncoexistence phases, and then finally to a pure localization phase. This is in\nstark contrast to the Abelian AAH model that does not support the coexistence\nphases. Our results thus comprise a new insight on the fundamental aspects of\nAnderson localization in quasiperiodic systems, from the perspective of\nnon-Abelian gauge."
    },
    {
        "anchor": "Low-dimensional weakly interacting Bose gases: non-universal equations\n  of state: The zero-temperature equation of state is analyzed in low-dimensional bosonic\nsystems. In the dilute regime the equation of state is universal in terms of\nthe gas parameter, i.e. it is the same for different potentials with the same\nvalue of the s-wave scattering length. Series expansions of the universal\nequation of state are reported for one- and two- dimensional systems. We\npropose to use the concept of energy-dependent s-wave scattering length for\nobtaining estimations of non-universal terms in the energy expansion. We test\nthis approach by making a comparison to exactly solvable one-dimensional\nproblems and find that the generated terms have the correct structure. The\napplicability to two-dimensional systems is analyzed by comparing with results\nof Monte Carlo simulations. The prediction for the non-universal behavior is\nqualitatively correct and the densities, at which the deviations from the\nuniversal equation of state become visible, are estimated properly. Finally,\nthe possibility of observing the non-universal terms in experiments with\ntrapped gases is also discussed.",
        "positive": "Non-local double-path Casimir phase in atom interferometers: We present a quantum open system theory of atom interferometers evolving in\nthe quantized electromagnetic field bounded by an ideal conductor. Our\ntreatment reveals an unprecedented feature of matter-wave propagation, namely\nthe appearance of a non-local double-path phase coherence. Such a non-local\nphase arises from the coarse-graining over the quantized electromagnetic field\nand internal atomic degrees of freedom, yielding a non-Hamiltonian evolution of\nthe atomic waves moving in presence of correlated quantum dipole and field\nfluctuations. We develop a diagrammatic interpretation of this phase, and\nestimate it for realistic experimental parameters."
    },
    {
        "anchor": "Improved Silbey-Harris polaron ansatz for the spin-boson model: In this paper, the well-known Silbey-Harris (SH) polaron ansatz for the\nspin-boson model is improved by adding orthogonal displaced Fock states. The\nobtained results for the ground state in all baths converge very quickly within\nfinite displaced Fock states and corresponding SH results are corrected\nconsiderably. Especially for the sub-Ohmic spin-boson model, the converging\nresults are obtained for 0 < s < 1/2 in the fourth-order correction and very\naccurate critical coupling strengths of the quantum phase transition are\nachieved. Converging magnetization in the biased spin-boson model is also\narrived at. Since the present improved SH ansatz can yield very accurate, even\nalmost exact results, it should have wide applications and extensions in\nvarious spin-boson model and related fields.",
        "positive": "Bloch state tomography using Wilson lines: Topology and geometry are essential to our understanding of modern physics,\nunderlying many foundational concepts from high energy theories, quantum\ninformation, and condensed matter physics. In condensed matter systems, a wide\nrange of phenomena stem from the geometry of the band eigenstates, which is\nencoded in the matrix-valued Wilson line for general multi-band systems. Using\nan ultracold gas of Rb atoms loaded in a honeycomb optical lattice, we realize\nstrong-force dynamics in Bloch bands that are described by Wilson lines and\nobserve an evolution in the band populations that directly reveals the band\ngeometry. Our technique enables a full determination of band eigenstates, Berry\ncurvature, and topological invariants, including single- and multi-band Chern\nand $Z_2$ numbers."
    },
    {
        "anchor": "Multipole Analysis of Radio-Frequency Reactions in Ultra-Cold Atoms: Using the multipole expansion we analyze photo induced reactions in an\nultra-cold atomic gas composed of identical neutral bosons. While the\nFrank-Condon factor dominates the photo induced spin-flip reactions, we have\nfound that for frozen-spin process where the atomic spins are conserved the\nreaction rate is governed by the monopole $r^2$ and the quadrupole terms.\nConsequently, the dependence of the frozen-spin reaction rate on the photon\nwave number $k$ acquires an extra $k^4$ factor in comparison to the spin-flip\nprocess. Comparing the relative strength of the $r^2$ and quadrupole modes in\ndimer photoassociation we predict that the mutual importance of these two modes\nchanges with temperature and scattering length.",
        "positive": "Dissipation-induced anomalous multicritical phenomena: We explore the influence of dissipation on a paradigmatic driven-dissipative\nmodel where a collection of two level atoms interact with both quadratures of a\nquantum cavity mode. The closed system exhibits multiple phase transitions\ninvolving discrete and continuous symmetries breaking and all phases culminate\nin a multicritical point. In the open system, we show that infinitesimal\ndissipation erases the phase with broken continuous symmetry and radically\nalters the model's phase diagram. The multicritical point now becomes brittle\nand splits into two tricritical points where first- and second-order\nsymmetry-breaking transitions meet. A quantum fluctuations analysis shows that,\nsurprisingly, the tricritical points exhibit anomalous finite fluctuations, as\nopposed to standard tricritical points arising in $^3He-\\text{}^4He$ mixtures.\nOur work has direct implications for a variety of fields, including cold atoms\nand ions in optical cavities, circuit-quantum electrodynamics as well as\noptomechanical systems."
    },
    {
        "anchor": "Quantum-tunneling dynamics of a spin-polarized Fermi gas in a\n  double-well potential: We study the exact dynamics of a one-dimensional spin-polarized gas of\nfermions in a double-well potential at zero and finite temperature. Despite the\nsystem is made of non-interacting fermions, its dynamics can be quite complex,\nshowing strongly aperiodic spatio-temporal patterns during the tunneling. The\nextension of these results to the case of mixtures of spin-polarized fermions\nin interaction with self-trapped Bose-Einstein condensates (BECs) at zero\ntemperature is considered as well. In this case we show that the fermionic\ndynamics remains qualitatively similar to the one observed in absence of BEC\nbut with the Rabi frequencies of fermionic excited states explicitly depending\non the number of bosons and on the boson-fermion interaction strength. From\nthis, the possibility to control quantum fermionic dynamics by means of\nFeshbach resonances is suggested.",
        "positive": "Bose-Einstein Condensate in a Honeycomb Optical Lattice: Fingerprint of\n  Superfluidity at the Dirac Point: Mean-field Bloch bands of a Bose-Einstein condensate in a honeycomb optical\nlattice are computed. We find that the topological structure of the Bloch bands\nat the Dirac point is changed completely by the atomic interaction of arbitrary\nsmall strength: the Dirac point is extended into a closed curve and an\nintersecting tube structure arises around the original Dirac point. These tubed\nBloch bands are caused by the superfluidity of the system. Furthermore, they\nimply the inadequacy of the tight-binding model to describe an interacting\nBoson system around the Dirac point and the breakdown of adiabaticity by\ninteraction of arbitrary small strength."
    },
    {
        "anchor": "Efimov Physics in Atom-Dimer Scattering of Lithium-6 Atoms: Lithium-6 atoms in the three lowest hyperfine states display universal\nproperties when the S-wave scattering length between each pair of states is\nlarge. Recent experiments reported four pronounced features arising from Efimov\nphysics in the atom-dimer relaxation rate, namely two resonances and two local\nminima. We use the universal effective field theory to calculate the atom-dimer\nrelaxation rate at zero temperature. Our results describe the four features\nqualitatively and imply there is a hidden local minimum. In the vicinity of the\nresonance at 685 G, we perform a finite temperature calculation which improves\nthe agreement of theory and experiment. We conclude that finite temperature\neffects cannot be neglected in the analysis of the experimental data.",
        "positive": "Singular mean-field states: A brief review of recent results: This article provides a focused review of recent findings which demonstrate,\nin some cases quite counter-intuitively, the existence of bound states with a\nsingularity of the density pattern at the center, while the states are\nphysically meaningful because their total norm converges. One model of this\ntype is based on the 2D Gross-Pitaevskii equation (GPE) which combines the\nattractive potential ~ 1/r^2 and the quartic self-repulsive nonlinearity,\ninduced by the Lee-Huang-Yang effect (quantum fluctuations around the\nmean-field state). The GPE demonstrates suppression of the 2D quantum collapse,\ndriven by the attractive potential, and emergence of a stable ground state\n(GS), whose density features an integrable singularity ~1/r^{4/3} at r --> 0.\nModes with embedded angular momentum exist too, and they have their stability\nregions. A counter-intuitive peculiarity of the model is that the GS exists\neven if the sign of the potential is reversed from attraction to repulsion,\nprovided that its strength is small enough. This peculiarity finds a relevant\nexplanation. The other model outlined in the review includes 1D, 2D, and 3D\nGPEs, with the septimal (seventh-order), quintic, and cubic self-repulsive\nterms, respectively. These equations give rise to stable singular solitons,\nwhich represent the GS for each dimension D, with the density singularity\n~1/r^{2/(4-D). Such states may be considered as a result of screening of a\n\"bare\" delta-functional attractive potential by the respective nonlinearity."
    },
    {
        "anchor": "Far-from-equilibrium spin transport in Heisenberg quantum magnets: We study experimentally the far-from-equilibrium dynamics in ferromagnetic\nHeisenberg quantum magnets realized with ultracold atoms in an optical lattice.\nAfter controlled imprinting of a spin spiral pattern with adjustable wave\nvector, we measure the decay of the initial spin correlations through\nsingle-site resolved detection. On the experimentally accessible timescale of\nseveral exchange times we find a profound dependence of the decay rate on the\nwave vector. In one-dimensional systems we observe diffusion-like spin\ntransport with a dimensionless diffusion coefficient of 0.22(1). We show how\nthis behavior emerges from the microscopic properties of the closed quantum\nsystem. In contrast to the one-dimensional case, our transport measurements for\ntwo-dimensional Heisenberg systems indicate anomalous super-diffusion.",
        "positive": "Reentrance of the Disordered Phase in the Antiferromagnetic Ising Model\n  on a Square Lattice with Longitudinal and Transverse Magnetic Fields: Motivated by recent experiments with Rydberg atoms in an optical tweezer\narray, we accurately map out the ground-state phase diagram of the\nantiferromagnetic Ising model on a square lattice with longitudinal and\ntransverse magnetic fields using the quantum Monte Carlo method. For a small\nbut nonzero transverse field, the transition longitudinal field is found to\nremain nearly constant. By scrutinizing the phase diagram, we uncover a narrow\nregion where the system exhibits reentrant transitions between the disordered\nand antiferromagnetic phases with increasing transverse field. Our phase\ndiagram provides a useful benchmark for quantum simulation of a Rydberg atom\nsystem."
    },
    {
        "anchor": "Many-body chiral edge currents and sliding phases of atomic spinwaves in\n  momentum-space lattice: Collective excitations (spinwaves) of long-lived atomic hyperfine states can\nbe synthesized into a Bose-Hubbard model in momentum space. We explore\nmany-body ground states and dynamics of a two-leg momentum-space lattice formed\nby two coupled hyperfine states. Essential ingredients of this setting are a\nstaggered artificial magnetic field engineered by lasers that couple the\nspinwave states, and a state-dependent long-range interaction, which is induced\nby laser-dressing a hyperfine state to a Rydberg state. The Rydberg dressed\ntwo-body interaction gives rise to a state-dependent blockade in momentum\nspace, and can amplify staggered flux induced anti-chiral edge currents in the\nmany-body ground state in the presence of magnetic flux. When the Rydberg\ndressing is applied to both hyperfine states, exotic sliding insulating and\nsuperfluid/supersolid phases emerge. Due to the Rydberg dressed long-range\ninteraction, spinwaves slide along a leg of the momentum-space lattice without\ncosting energy. Our study paves a route to the quantum simulation of\ntopological phases and exotic dynamics with interacting spinwaves of atomic\nhyperfine states in momentum-space lattice.",
        "positive": "A Monte Carlo wavefunction description of losses in a 1D Bose gas and\n  cooling to the ground state by quantum feedback: The effect of atom losses on a homogeneous one-dimensional Bose gas lying\nwithin the quasi-condensate regime is investigated using a Monte Carlo\nwavefunction approach. The evolution of the system is calculated, conditioned\nby the loss sequence, namely the times of individual losses and the position of\nthe removed atoms. We describe the gas within the linearized Bogoliubov\napproach. For each mode, we find that, for a given quantum trajectory, the\nstate of the system converges towards a coherent state, i.e. the ground state,\ndisplaced in phase space. Provided losses are recorded with a temporal and\nspatially resolved detector, we show that quantum feedback can be implemented\nand cooling to the ground state of one or several modes can be realized."
    },
    {
        "anchor": "Feynman path-integral treatment of the BEC-impurity polaron: The description of an impurity atom in a Bose-Einstein condensate can be cast\nin the form of Frohlich's polaron Hamiltonian, where the Bogoliubov excitations\nplay the role of the phonons. An expression for the corresponding polaronic\ncoupling strength is derived, relating the coupling strength to the scattering\nlengths, the trap size and the number of Bose condensed atoms. This allows to\nidentify several approaches to reach the strong-coupling limit for the quantum\ngas polarons, whereas this limit was hitherto experimentally inaccessible in\nsolids. We apply Feynman's path-integral method to calculate for all coupling\nstrengths the polaronic shift in the free energy and the increase in the\neffective mass. The effect of temperature on these quantities is included in\nthe description. We find similarities to the acoustic polaron results and\nindications of a transition between free polarons and self-trapped polarons.\nThe prospects, based on the current theory, of investigating the polaron\nphysics with ultracold gases are discussed for lithium atoms in a sodium\ncondensate.",
        "positive": "Breakdown of macroscopic quantum self-trapping in coupled mesoscopic one\n  dimensional Bose gases: Two coupled BECs with a large population imbalance exhibit macroscopic\nquantum self-trapping (MQST) if the ratio of interaction energy to tunneling\nenergy is above a critical value. Here we investigate effect of quantum\nfluctuations on MQST. In particular, we analyze the dynamics of a system of two\nelongated Bose gases prepared with a large population imbalance, where due to\nthe quasi one dimensional character of the gas we no longer have true long\nrange order, and the effect of quantum fluctuations is much more important. We\nshow that MQST is possible in this system, but even when it is achieved it is\nnot always dynamically stable. Using this instability one can construct states\nwith sharply peaked momentum distributions around characteristic momenta\ndependent on system parameters. Our other finding is the nonmonotonic\noscillating dependence of the decay rate of the MQST on the length of the\nwires. We also address the interesting question of thermalization in this\nsystem and show that it occurs only in sufficiently long wires."
    },
    {
        "anchor": "A dynamical theory for one-dimensional fermions with strong two-body\n  losses: universal non-Hermitian Zeno physics and spin-charge separation: We study an interacting one-dimensional gas of spin-1/2 fermions with\ntwo-body losses. The dynamical phase diagram that characterises the approach to\nthe stationary state displays a wide quantum-Zeno region, identified by a\npeculiar behaviour of the lowest eigenvalues of the associated non-Hermitian\nHamiltonian. We characterise the universal dynamics of this Zeno regime using\nan approximation scheme based on a effective decoupling of charge and spin\ndegrees of freedom, where the latter effectively evolve in a non-Markovian way\naccording to a non-Hermitian Heisenberg Hamiltonian. We present detailed\nresults for the time evolution from initial states with one particle per site\nwith either incoherent and antiferromagnetic spin order, showing how the two\nnon-equilibrium evolutions build up drastically different charge correlations.",
        "positive": "Interaction-Driven Topological Insulator in Fermionic Cold Atoms on an\n  Optical Lattice: A Design with a Density Functional Formalism: We design an interaction-driven topological insulator for fermionic cold\natoms in an optical lattice, that is, we pose the question of whether we can\nrealize in a continuous space a spontaneous symmetry breaking induced by the\ninter-atom interaction into a topological Chern insulator. Such a state,\nsometimes called a \"topological Mott insulator\", has yet to be realized in\nsolid-state systems, since this requires, in the tight-binding model, large\noffsite interactions on top of a small onsite interaction. Here we overcome the\ndifficulty by introducing a spin-dependent potential, where a spin-selective\noccupation of fermions in $A$ and $B$ sublattices makes the onsite interaction\nPauli-forbidden, while a sizeable inter-site interaction is achieved by a\nshallow optical potential with a large overlap between neighboring Wannier\norbitals. This puts the system away from the tight-binding model, so that we\nadopt the density functional theory for cold-atoms, here extended to\naccommodate non-collinear spin structures emerging in the topological regime,\nto quantitatively demonstrate the phase transition to the topological Mott\ninsulator."
    },
    {
        "anchor": "Luttinger liquid of trimers in Fermi gases with unequal masses: We investigate one dimensional attractive Fermi gases in spin-dependent\noptical lattices. We show that three-body bound states - \"trimers\" - exist as\nsoon as the two tunneling rates are different. We calculate the binding energy\nand the effective mass of a single trimer. We then show numerically that for\nfinite and commensurate densities $n_\\uparrow=n_\\downarrow/2$ an energy gap\nappears, implying that the gas is a one-component Luttinger liquid of trimers\nwith suppressed superfluid ordering. The boundaries of this novel phase are\ngiven. We discuss experimental situations to test our predictions.",
        "positive": "Half-knot in the spinor condensates: We present an exact solution to the stationary coupled nonlinear\nGross-Pitaevskii equations which govern the motion of the spinor Bose-Einstein\ncondensates. The solitonic solution is a twisted half-skyrmion in the\nthree-dimension (3D) space. By making a map from and the Cartesian coordinates\nto the toroidal coordinates, we demonstrate it is a linked half-unknot with a\nfractional Hopf charge."
    },
    {
        "anchor": "Impurity with a resonance in the vicinity of the Fermi energy: We study an impurity with a resonance level whose energy coincides with the\nFermi energy of the surrounding Fermi gas. An impurity causes a rapid variation\nof the scattering phase shift for fermions at the Fermi surface, introducing a\nnew characteristic length scale into the problem. We investigate manifestations\nof this length scale in the self-energy of the impurity and in the density of\nthe bath. Our calculations reveal a model-independent deformation of the\ndensity of the Fermi gas, which is determined by the width of the resonance. To\nprovide a broader picture, we investigate time evolution of the density in\nquench dynamics, and study the behavior of the system at finite temperatures.\nFinally, we briefly discuss implications of our findings for the Fermi-polaron\nproblem.",
        "positive": "Spin-models, dynamics and criticality with atoms in tilted optical\n  superlattices: We show that atoms in tilted optical superlattices provide a platform for\nexploring coupled spin chains of forms that are not present in other systems.\nIn particular, using a period-2 superlattice in 1D, we show that coupled Ising\nspin chains with XZ and ZZ spin coupling terms can be engineered. We use\noptimized tensor network techniques to explore the criticality and\nnon-equilibrium dynamics in these models, finding a tricritical Ising point in\nregimes that are accessible in current experiments. These setups are ideal for\nstudying low-entropy physics, as initial entropy is \"frozen-out\" in realizing\nthe spin models, and provide an example of the complex critical behaviour that\ncan arise from interaction-projected models."
    },
    {
        "anchor": "Interaction effects on $\\mathcal{PT}$-symmetry breaking transition in\n  atomic gases: Non-Hermitian systems having parity-time ($\\mathcal {PT}$) symmetry can\nundergo a transition, spontaneously breaking the symmetry. Ultracold atomic\ngases provide an ideal platform to study interaction effects on the transition.\nWe consider a model system of $N$ bosons of two components confined in a tight\ntrap. Radio frequency and laser fields are coupled to the bosons such that the\nsingle particle Non-Hermitian Hamiltonian $h_{\\mathcal PT}=-i\n\\Gamma\\sigma_z+J\\sigma_x$, which has $\\mathcal {PT}$-symmetry, can be simulated\nin a \\emph{passive} way. We show that when interatomic interactions are tuned\nto maintain the symmetry, the $\\mathcal {PT}$-symmetry breaking transition is\naffected only by the SU(2) variant part of the interactions parameterized by\n$\\delta g$. We find that the transition point $\\Gamma_{\\rm tr}$ decreases as\n$|\\delta g|$ or $N$ increases; in the large $|\\delta g|$ limit, $\\Gamma_{\\rm\ntr}$ scales as $\\sim|\\delta g|^{-(N-1)}$. We also give signatures of the\n$\\mathcal {PT}$-symmetric and the symmetry breaking phases for the interacting\nbosons in experiment.",
        "positive": "Resonance-facilitated three-channel p-wave scattering: Feshbach resonances of arbitrary width are typically described in terms of\ntwo-channel models. Within these models, one usually considers a single dressed\nresonance, with the option to extend the analysis by including resonant\nopen-channel features that can drastically change the observed threshold\neffects. For the strong $^{40}\\mathrm{K}$ p-wave resonance studied in Ref.\n\\cite{ahmed2021}, the interplay between an open-channel shape resonance and the\nFeshbach resonance could explain the unexpected nonlinear variation of the\nbinding energy with magnetic field. However, the presented two-channel\ntreatment relies on the introduction of two independent fitting parameters,\nwhereas the typical Breit-Wigner expression would only account for one. This\nresults in an effective magnetic moment that acquires a nonphysical value,\nwhich is an indication of a major shortcoming of the two-channel model\ntreatment. In this study, we observe how the presence of a closed-channel shape\nresonance explains the physical mechanism behind the observations and\ndemonstrates the need of a three-channel treatment. We introduce our novel\nmodel as \\textit{resonance facilitated}, where all coupling is mediated by the\nFeshbach state, while there is no direct coupling between the additional\nchannel and the open channel. Notably, the resonance-facilitated structure\ngreatly reduces the complexity of the full three-channel model. The typical\nBreit-Wigner form of the two-channel Feshbach formalism is retained and the\nfull effect of the added channel can be captured by a single resonance dressing\nfactor, which describes how the free propagation in the Feshbach state is\ndressed by the added channel."
    },
    {
        "anchor": "Observation of atom-number fluctuations in optical lattices via quantum\n  collapse and revival dynamics: Using the quantum collapse and revival phenomenon of a Bose--Einstein\ncondensate in three-dimensional optical lattices, the atom number statistics on\neach lattice site are experimentally investigated. We observe an interaction\ndriven time evolution of on-site number fluctuations in a constant lattice\npotential with the collapse and revival time ratio as the figure of merit.\nThrough a shortcut loading procedure, we prepare a three-dimensional array of\ncoherent states with Poissonian number fluctuations. The following dynamics\nclearly show the interaction effect on the evolution of the number fluctuations\nfrom Poissonian to sub-Poissonian. Our method can be used to create squeezed\nstates which are important in precision measurement.",
        "positive": "Emergent $\\mathcal{PT}$-symmetry breaking of Anderson-Bogoliubov modes\n  in Fermi superfluids: The spontaneous breaking of parity-time ($\\mathcal{PT}$) symmetry, which\nyields rich critical behavior in non-Hermitian systems, has stimulated much\ninterest. Whereas most previous studies were performed within the\nsingle-particle or mean-field framework, exploring the interplay between\n$\\mathcal{PT}$ symmetry and quantum fluctuations in a many-body setting is a\nburgeoning frontier. Here, by studying the collective excitations of a Fermi\nsuperfluid under an imaginary spin-orbit coupling, we uncover an emergent\n$\\mathcal{PT}$-symmetry breaking in the Anderson-Bogoliubov (AB) modes, whose\nquasiparticle spectra undergo a transition from being completely real to\ncompletely imaginary, even though the superfluid ground state retains an\nunbroken $\\mathcal{PT}$ symmetry. The critical point of the transition is\nmarked by a non-analytic kink in the speed of sound, as the latter completely\nvanishes at the critical point where the system is immune to low-frequency\nperturbations.These critical phenomena derive from the presence of a spectral\npoint gap in the complex quasiparticle dispersion, and are therefore\ntopological in origin."
    },
    {
        "anchor": "Degenerate Raman sideband cooling of 39K: We report on the first realization of sub-Doppler laser cooling of 39K atoms\nusing degenerate 3D Raman sideband cooling. We take advantage of the\nwell-resolved excited hyperfine states on the D1 optical transition to produce\nspin polarized samples with $1.4 \\times 10^8$ atoms at temperatures of 1.8\n$\\mu$K. The phase-space densities are $\\geq 10^{-4}$, which significantly\nimproves the initial conditions for a subsequent evaporative cooling step. The\npresented cooling technique using the D1 line can be adapted to other atomic\nspecies and is applicable to high-resolution imaging schemes in far\noff-resonant optical lattices.",
        "positive": "Three-body losses of repulsively interacting three-component fermionic\n  atoms in optical lattices: We investigate the effects of a repulsive three-body interaction on the Mott\ntransition of the repulsively interacting three-component fermionic atoms in\noptical lattices by means of the self-energy functional approach. We find that\nthe three-body repulsion hardly affects the qualitative features of the Mott\ntransition, because the three-body repulsion does not compete with the two-body\nrepulsions. When the three-body repulsion is extremely strong, the triple\noccupancy vanishes in the Fermi liquid state. This situation is equivalent to\nthat caused by strong three-body losses. Our results imply that three-body\nlosses have little influence on the Mott transitions in the repulsively\ninteracting three-component fermionic atoms in optical lattices."
    },
    {
        "anchor": "Controllable manipulation and detection of local densities and bipartite\n  entanglement in a quantum gas by a dissipative defect: We study the complex dynamics of a one-dimensional Bose gas subjected to a\ndissipative local defect which induces one-body atom losses. In experiments\nthese atom losses occur, for example, when a focused electron or light beam or\na single trapped ion is brought into contact with a quantum gas. We discuss how\nwithin such setups one can measure or manipulate densities locally and specify\nthe excitations that are induced by the defect. In certain situations the\ndefect can be used to generate entanglement in a controlled way despite its\ndissipative nature. The careful examination of the interplay between hole\nexcitations and the collapse of the wave function due to nondetection of loss\nis crucial for the understanding of the dynamics we observe.",
        "positive": "Conventional magnon BEC in YIG film: The conventional magnon Bose-Einstein condensation (BEC of magnons with k =\n0) is a coherent state of excited magnons described by a common wave function.\nIt was observed first in antiferromagnetic superfluid states of 3He. Here we\nreport on the discovery of a very similar magnon BEC in ferrimagnetic film at\nroom temperature. The experiments were performed in Yttrium Iron Garnet (YIG)\nfilms at a magnetic field oriented perpendicular to the film. The high-density\nquasiequilibrium state of excited magnon was formed by methods of pulse and/or\nContinuous Waves (CW) magnetic resonance. We have observed a Long Lived\nInduction Decay Signals (LLIDS), well known as a signature of spin\nsuperfluidity. We demonstrate that the BEC state may maintain permanently by\ncontinuous replenishment of magnons with a small radiofrequency (RF) field. Our\nfinding opens the way for development of potential supermagnonic applications\nat an ambient conditions."
    },
    {
        "anchor": "Polaronic effects of an impurity in a Fermi superfluid away from the BEC\n  limit: In this article we study the interaction between an impurity and the gas of\nBogoliubov excitations of a Fermi superfluid by mapping it on the polaron\nproblem for an impurity in a BEC. The description of the Fermi superfluid\nacross the BEC-BCS crossover regime is based on a recently developed effective\nfield theory presented in [Eur. Phys. J. B 88, 122 (2015)] and provides us with\nthe interaction-dependent dispersion relations for the Bogoliubov excitations.\nThe behavior of the polaronic coupling constant $\\alpha$ and of the effective\nmass of the polaron is examined in a broad window of the BEC-BCS crossover.",
        "positive": "Ultracold atoms in optical lattices induced by photonic crystals: We propose a way of generating optical lattices embedded in photonic\ncrystals. By setting up extended modes in photonic crystals, ultracold atoms\ncan be mounted in different types of field intensity distributions. This novel\nway of constructing optical lattices can be used to produce more elaborate\nperiodic potentials by manufacturing appropriate geometries of photonic\ncrystals. We exemplify this with a square lattice and comment on the\npossibility of using geometries with defects."
    },
    {
        "anchor": "Dynamical formation and interaction-induced stabilization of dark\n  condensates of dipolar excitons: The formation of a dense Bose-Einstein condensate in dark spin states of\ntwo-dimensional dipolar excitons is shown to be driven by a dynamical\ntransition to the long-lived dark states. The condensate is stabilized by\nstrong dipole-dipole interactions up to densities high enough for a dark\nquantum liquid to form. The persistence of dark condensation was observed in\nrecent experiments. A model describing the non-equilibrium dynamics of\nexternally driven coupled dark and bright condensates reproduces the step-like\ndependence of the exciton density on the pump power or on temperature. This\nunique condensate dynamics demonstrates the possibility of observing new\nunexpected collective phenomena in coupled condensed Bose systems, where the\nparticle number is not conserved.",
        "positive": "Condensates of p-wave pairs are exact solutions for rotating\n  two-component Bose gases: We derive exact analytical results for the wave functions and energies of\nharmonically trapped two-component Bose-Einstein condensates with weakly\nrepulsive interactions under rotation. The isospin symmetric wave functions are\nuniversal and do not depend on the matrix elements of the two-body interaction.\nThe comparison with the results from numerical diagonalization shows that the\nground state and low-lying excitations consists of condensates of p-wave pairs\nfor repulsive contact interactions, Coulomb interactions, and the repulsive\ninteractions between aligned dipoles."
    },
    {
        "anchor": "Many-body dynamics of dipolar molecules in an optical lattice: Understanding the many-body dynamics of isolated quantum systems is one of\nthe central challenges in modern physics. To this end, the direct experimental\nrealization of strongly correlated quantum systems allows one to gain insights\ninto the emergence of complex phenomena. Such insights enable the development\nof theoretical tools that broaden our understanding. Here, we theoretically\nmodel and experimentally probe with Ramsey spectroscopy the quantum dynamics of\ndisordered, dipolar-interacting, ultracold molecules in a partially filled\noptical lattice. We report the capability to control the dipolar interaction\nstrength, and we demonstrate that the many-body dynamics extends well beyond a\nnearest-neighbor or mean-field picture, and cannot be quantitatively described\nusing previously available theoretical tools. We develop a novel cluster\nexpansion technique and demonstrate that our theoretical method accurately\ncaptures the measured dependence of the spin dynamics on molecule number and on\nthe dipolar interaction strength. In the spirit of quantum simulation, this\nagreement simultaneously benchmarks the new theoretical method and verifies our\nmicroscopic understanding of the experiment. Our findings pave the way for\nnumerous applications in quantum information science, metrology, and condensed\nmatter physics.",
        "positive": "Short range asymptotic behavior of the wave-functions of interacting\n  spin-half fermionic atoms with spin-orbit coupling: a model study: We consider spin-half fermionic atoms with isotropic Rashba spin-orbit\ncoupling in three directions. The interatomic potential is modeled by a square\nwell potential. We derive the analytic form of the asymptotic wave-functions at\nshort range of two fermions in the subspace of zero net momentum and zero total\nangular momentum. We show that the spin-orbit coupling has perturbative effects\non the short range asymptotic behavior of the wave-functions away from\nresonances. We argue that our conclusion should hold generally."
    },
    {
        "anchor": "Impurity self-energy in the strongly-correlated Bose systems: We proposed the non-perturbative scheme for calculation of the impurity\nspectrum in the Bose system at zero temperature. The method is based on the\npath-integral formulation and describes an impurity as a zero-density ideal\nFermi gas interacting with Bose system for which the action is written in terms\nof density fluctuations. On the example of the $^3$He atom immersed in the\nliquid helium-4 a good consistency with experimental data and results of Monte\nCarlo simulations is shown.",
        "positive": "Spin drag in an ultracold Fermi gas on the verge of a ferromagnetic\n  instability: Recent experiments [Jo et al., Science 325, 1521 (2009)] have presented\nevidence of ferromagnetic correlations in a two-component ultracold Fermi gas\nwith strong repulsive interactions. Motivated by these experiments we consider\nspin drag, i.e., frictional drag due to scattering of particles with opposite\nspin, in such systems. We show that when the ferromagnetic state is approached\nfrom the normal side, the spin drag relaxation rate is strongly enhanced near\nthe critical point. We also determine the temperature dependence of the spin\ndiffusion constant. In a trapped gas the spin drag relaxation rate determines\nthe damping of the spin dipole mode, which therefore provides a precursor\nsignal of the ferromagnetic phase transition that may be used to experimentally\ndetermine the proximity to the ferromagnetic phase."
    },
    {
        "anchor": "Topological orbital superfluid with chiral d-wave order in a rotating\n  optical lattice: Topological superfluid is an exotic state of quantum matter that possesses a\nnodeless superfluid gap in the bulk and Andreev edge modes at the boundary of a\nfinite system. Here, we study a multi-orbital superfluid driven by attractive\ns-wave interaction in a rotating optical lattice. Interestingly, we find that\nthe rotation induces the inter- orbital hybridization and drives the system\ninto topological orbital superfluid in accordance with intrinsically chiral\nd-wave pairing characteristics. Thanks to the conservation of spin, the\ntopological orbital superfluid supports four rather than two chiral Andreev\nedge modes at the boundary of the lattice. Moreover, we find that the intrinsic\nharmonic confining potential forms a circular spatial barrier which accumulates\natoms and supports a mass current under injection of small angular momentum as\nexternal driving force. This feature provides an experimentally detectable\nphenomenon to verify the topological orbital superfluid with chiral d-wave\norder in a rotating optical lattice.",
        "positive": "Density ordering instabilities of quasi-two-dimensional fermionic polar\n  molecules in single-layer and multi-layer configurations: exact treatment of\n  exchange interactions: We study the in-plane and out-of-plane density ordering instabilities of\nquasi-two-dimensional fermionic polar molecules in single-layer and multi-layer\nconfigurations. We locate the soft modes by evaluating linear response\nfunctions within the conserving time-dependent Hartree-Fock (TDHF). The\nshort-range exchange effects are taken into account by solving the\nBethe-Salpeter integral equation numerically. An instability phase diagram is\ncalculated for both single-layer and multi-layer systems and the unstable\nwave-vector is indicated. In all cases, the in-plane density wave instability\nis found to precede the out-of-plane instability. The unstable wave-vector is\nfound to be approximately twice the Fermi wave-vector of one of the subbands at\na time and can change discontinuously as a function of density and dipolar\ninteraction strength. In multi-layer configurations, we find a large\nenhancement of density wave instability driven by dilute quasiparticles in the\nfirst excited subband. Finally, we provide a simple qualitative description of\nthe phase diagrams using a RPA-like approach. Compared to previous works done\nwithin the RPA approximation, we find that inclusion of exchange interactions\nstabilize the normal liquid phase further and increase the critical dipolar\ninteraction strength corresponding to the onset of density-wave instability by\nover a factor of two."
    },
    {
        "anchor": "Topological Time Crystals: By analogy with the formation of space crystals, crystalline structures can\nalso appear in the time domain. While in the case of space crystals we often\nask about periodic arrangements of atoms in space at a moment of a detection,\nin time crystals the role of space and time is exchanged. That is, we fix a\nspace point and ask if the probability density for detection of a system at\nthis point behaves periodically in time. Here, we show that in periodically\ndriven systems it is possible to realize topological insulators, which can be\nobserved in time. The bulk-edge correspondence is related to the edge in time,\nwhere edge states localize. We focus on two examples: Su-Schrieffer-Heeger\n(SSH) model in time and Bose Haldane insulator which emerges in the dynamics of\na periodically driven many-body system.",
        "positive": "Domain wall dynamics in the spinor Bose-Einstein condensates: A dynamical theory is presented for the domain wall in the spinor\nBose-Einstein condensate of \"effective\"one-dimension. The formulation is based\non the time-dependent Landau-Ginzburg (LG) theory written in terms of the\nspinor order parameter. The procedure is carried out in such a way that an\nadiabatic change of the collective coordinates; the kink position as well as\nthe phase function built in the spinor, is adapted to the canonical term (alias\ngeometric phase) in the LG Lagrangian. Two problems are discussed: The first\none is to explore the translational motion of the kink center in the presence\nof the pinning potential, which results in the quantum potential problem. The\nother one concerns the \"steering\" of the domain wall by modulating the\nexternally driven magnetic field assisted with dissipation. The present attempt\nwould shed light on the spinor Bose- Einstein condensates from a novel\nviewpoint."
    },
    {
        "anchor": "Localization and criticality in antiblockaded 2D Rydberg atom arrays: Controllable Rydberg atom arrays have provided new insights into fundamental\nproperties of quantum matter both in and out of equilibrium. In this work, we\nstudy the effect of experimentally relevant positional disorder on Rydberg\natoms trapped in a 2D square lattice under anti-blockade (facilitation)\nconditions. We show that the facilitation conditions lead the connectivity\ngraph of a particular subspace of the full Hilbert space to form a 2D Lieb\nlattice, which features a singular flat band. Remarkably, we find three\ndistinct regimes as the disorder strength is varied: a critical regime, a\ndelocalized but nonergodic regime, and a regime with a disorder-induced flat\nband. The critical regime's existence depends crucially upon the singular flat\nband in our model, and is absent in any 1D array or ladder system. We propose\nto use quench dynamics to probe the three different regimes experimentally.",
        "positive": "Commensurate Supersolid of Three-Dimensional Lattice Bosons: Using an unbiased quantum Monte Carlo method, we obtain convincing evidence\nof the existence of a checkerboard supersolid at a {\\it commensurate} filling\nfactor 1/2 (commensurate supersolid) in the soft-core Bose-Hubbard model with\nnearest-neighbor repulsions on a cubic lattice. In conventional cases,\nsupersolids are realized at incommensurate filling factors by a\ndoped-defect-condensation mechanism, where particles (holes) doped into a\nperfect crystal act as interstitials (vacancies) and delocalize in the crystal\norder. However, in the above model, a supersolid state is stabilized even at\nthe commensurate filling factor 1/2 {\\it without doping}. By performing grand\ncanonical simulations, we obtain a ground-state phase diagram that suggests the\nexistence of a supersolid at a commensurate filling. To obtain direct evidence\nof the commensurate supersolid, we next perform simulations in canonical\nensembles at a particle density $\\rho=1/2$ and exclude the possibility of phase\nseparation. From the obtained snapshots, we discuss the microscopic structure\nand observe that interstitial-vacancy pairs are unbound in the crystal order."
    },
    {
        "anchor": "Dissipation effect in the double-well Bose-Einstein Condensate: Dynamics of the double-well Bose-Einstein condensate subject to energy\ndissipation is studied by solving a reduced one-dimensional time-dependent\nGross-Pitaevskii equation numerically. We first reproduce the phase space\ndiagram of the system without dissipation systematically, and then calculate\nevolutionary trajectories of dissipated systems. It is clearly shown that the\ndissipation can drive the system to evolve gradually from the $\\pi$-mode\nquantum macroscopic self-trapping state, a state with relatively higher energy,\nto the lowest energy stationary state in which particles distribute equally in\nthe two wells. The average phase and phase distribution in each well are\ndiscussed as well. We show that the phase distribution varies slowly in each\nwell but may exhibit abrupt changes near the barrier. This sudden change occurs\nat the minimum position in particle density profile. We also note that the\naverage phase in each well varies much faster with time than the phase\ndifference between two wells.",
        "positive": "Leggett collective excitations in a two-band Fermi superfluid at finite\n  temperatures: The Leggett collective excitations for a two-band Fermi gas with s-wave\npairing and Josephson interband coupling in the BCS-BEC crossover at finite\ntemperatures are investigated within the Gaussian pair fluctuation approach.\nEigenfrequencies and damping factors for Leggett modes are determined in a\nnonperturbative way, using the analytic continuation of the fluctuation\npropagator through a branch cut in the complex frequency plane, as in Phys.\nRev. Lett. 122, 093403 (2019). The treatment is performed beyond the low-energy\nexpansion, which is necessary when the collective excitation energy reaches the\npair-breaking continuum edge. The results are applied in particular to cold\natomic gases at the orbital Feshbach resonance and in a regime far from BEC,\nwhich can be relevant for future experiments."
    },
    {
        "anchor": "High-precision analysis of Feshbach resonances in a Mott insulator: We show that recent high-precision measurements of relative on-site\ninteraction energies $\\Delta U$ in a Mott insulator require a theoretical\ndescription beyond the standard Hubbard-model interpretation, when combined\nwith an accurate coupled-channels calculation. In contrast to more\nsophisticated lattice models, which can be elaborate especially for parameter\noptimization searches, we introduce an easy to use effective description of $U$\nvalid over a wide range of interaction strengths modeling atomic pairs confined\nto single lattice sites. This concise model allows for a straightforward\ncombination with a coupled-channels analysis. With this model we perform such a\ncoupled-channels analysis of high-precision $^7$Li spectroscopic data on the\non-site interaction energy $U$, which spans over four Feshbach resonances and\nprovide an accurate and consistent determination of the associated resonance\npositions. Earlier experiments on three of the Feshbach resonances are\nconsistent with this new analysis. Moreover, we verify our model with a more\nrigorous numerical treatment of the two atom system in an optical lattice.",
        "positive": "Pressure profiles of nonuniform two-dimensional atomic Fermi gases: Spatial profiles of the pressure have been measured in atomic Fermi gases\nwith primarily 2D kinematics. The in-plane motion of the particles is confined\nby a gaussian-shape potential. The two-component deeply-degenerate Fermi gases\nare prepared at different values of the s-wave attraction. The pressure profile\nis found using the force-balance equation, from the measured density profile\nand the trapping potential. The pressure is compared to zero-temperature models\nwithin the local density approximation. In the weakly-interacting regime, the\npressure lies above a Landau Fermi-liquid theory and below the ideal-Fermi-gas\nmodel, whose prediction coincides with that of the Cooper-pair mean-field\ntheory. The values closest to the data are provided by the approach where the\nmean-field of Cooper pairs is supplemented with fluctuations. In the regime of\nstrong interactions, in response to the increasing attraction, the pressure\nshifts below this model reaching lower values calculated within Monte Carlo\nmethods. Comparison to models shows that interaction-induced departure from 2D\nkinematics is either small or absent. In particular, comparison with a lattice\nMonte Carlo suggests that kinematics is 2D in the strongly-interacting regime."
    },
    {
        "anchor": "Soliton dynamics at an interface between uniform medium and nonlinear\n  optical lattice: We study trapping and propagation of a matter-wave soliton through the\ninterface between uniform medium and a nonlinear optical lattice (NOL).\nDifferent regimes for transmission of a broad and a narrow soliton are\ninvestigated. Reflections and transmissions of solitons are predicted as\nfunction of the lattice phase. The existence of a threshold in the amplitude of\nthe nonlinear optical lattice, separating the transmission and reflection\nregimes, is verified. The localized nonlinear surface state, corresponding to\nthe soliton trapped by the interface, is found. Variational approach\npredictions are confirmed by numerical simulations for the original\nGross-Pitaevskii equation with nonlinear periodic potentials.",
        "positive": "Observation of pseudogap behavior in a strongly interacting Fermi gas: Ultracold atomic Fermi gases present an opportunity to study strongly\ninteracting Fermi systems in a controlled and uncomplicated setting. The\nability to tune attractive interactions has led to the discovery of\nsuperfluidity in these systems with an extremely high transition temperature,\nnear T/T_F = 0.2. This superfluidity is the electrically neutral analog of\nsuperconductivity; however, superfluidity in atomic Fermi gases occurs in the\nlimit of strong interactions and defies a conventional BCS description. For\nthese strong interactions, it is predicted that the onset of pairing and\nsuperfluidity can occur at different temperatures. This gives rise to a\npseudogap region where, for a range of temperatures, the system retains some of\nthe characteristics of the superfluid phase, such as a BCS-like dispersion and\na partially gapped density of states, but does not exhibit superfluidity. By\nmaking two independent measurements: the direct observation of pair\ncondensation in momentum space and a measurement of the single-particle\nspectral function using an analog to photoemission spectroscopy, we directly\nprobe the pseudogap phase. Our measurements reveal a BCS-like dispersion with\nback-bending near the Fermi wave vector k_F that persists well above the\ntransition temperature for pair condensation."
    },
    {
        "anchor": "A superfluid-droplet crystal and a free-space supersolid in a\n  dipole-blockaded gas: A novel supersolid phase is predicted for an ensemble of Rydberg atoms in the\ndipole-blockade regime, interacting via a repulsive dipolar potential\n\"softened\" at short distances. Using exact numerical techniques, we study the\nlow temperature phase diagram of this system, and observe an intriguing phase\nconsisting of a crystal of mesoscopic superfluid droplets. At low temperature,\nphase coherence throughout the whole system, and the ensuing bulk\nsuperfluidity, are established through tunnelling of identical particles\nbetween neighbouring droplets.",
        "positive": "Exploring the Single-Particle Mobility Edge in a One-Dimensional\n  Quasiperiodic Optical Lattice: A single-particle mobility edge (SPME) marks a critical energy separating\nextended from localized states in a quantum system. In one-dimensional systems\nwith uncorrelated disorder, a SPME cannot exist, since all single-particle\nstates localize for arbitrarily weak disorder strengths. However, if\ncorrelations are present in the disorder potential, the localization transition\ncan occur at a finite disorder strength and SPMEs become possible. In this\nwork, we find experimental evidence for the existence of such a SPME in a\none-dimensional quasi-periodic optical lattice. Specifically, we find a regime\nwhere extended and localized single-particle states coexist, in good agreement\nwith theoretical simulations, which predict a SPME in this regime."
    },
    {
        "anchor": "Momentum-resolved Raman spectroscopy of non-interacting ultracold Fermi\n  gas: We report the experiment on probing the one-body spectral function in a\ntrapped non-interacting $^{40}$K Fermi gas by means of the momentum-resolved\nRaman spectroscopy The experimental result is in good agreement with the\nexpected quadratic dispersion in the non-interacting regime. Through the\ncomparison with the radio-frequency spectrum, we found that the Raman spectrum\nshows some new characteristics.",
        "positive": "$\\mathbb{Z}_2$ phases and Majorana spectroscopy in paired Bose-Hubbard\n  chains: We investigate the Bose-Hubbard chain in the presence of nearest-neighbor\npairing. The pairing term gives rise to an unusual gapped $\\mathbb{Z}_2$ Ising\nphase that has number fluctuation but no off-diagonal long range order. This\nphase has a strongly correlated many-body doubly degenerate ground state which\nis effectively a gap-protected macroscopic qubit. In the strongly interacting\nlimit, the system can be mapped onto an anisotropic transverse spin chain,\nwhich in turn can be mapped to the better-known fermionic sister of the paired\nBose-Hubbard chain: the Kitaev chain which hosts zero-energy Majorana bound\nstates. While corresponding phases in the fermionic and bosonic systems have\nstarkly different wavefunctions, they share identical energy spectra. We\ndescribe a possible cold-atom realization of the paired Bose-Hubbard model in a\nbiased zig-zag optical lattice with reservoir-induced pairing, opening a\npossible route towards experimental Kitaev chain spectroscopy."
    },
    {
        "anchor": "A Pure Confinement Induced Trimer in One-Dimensional Atomic Waveguides: Shallow trimers composed of three bosonic atoms in one-dimensional harmonic\nwaveguides are studied in the vicinity of a Feshbach resonance. It is shown\nthat for arbitrarily large values of the one-dimensional scattering length, an\nexcited trimer branch exists in coexistence with the dimer and the trimer of\nthe Lieb-Liniger model.",
        "positive": "Momentum-space atom correlations in a Mott insulator: We report on the investigation of the three-dimensional single-atom-resolved\ndistributions of bosonic Mott insulators in momentum-space. Firstly, we measure\nthe two-body and three-body correlations deep in the Mott regime, finding a\nperfectly contrasted bunching whose periodicity reproduces the reciprocal\nlattice. In addition, we show that the two-body correlation length is inversely\nproportional to the in-trap size of the Mott state with a pre-factor in\nagreement with the prediction for an incoherent state occupying a uniformly\nfilled lattice. Our findings indicate that the momentum-space correlations of a\nMott insulator at small tunnelling is that of a many-body ground-state with\nGaussian statistics. Secondly, in the Mott insulating regime with increasing\ntunnelling, we extract the spectral weight of the quasi-particles from the\nmomentum density profiles. On approaching the transition towards a superfluid,\nthe momentum spread of the spectral weight is found to decrease as a result of\nthe increased mobility of the quasi-particles in the lattice. While the shapes\nof the observed spectral weight agree with the ones predicted by perturbative\nmany-body calculations, the fitted mobilities are larger than the theoretical\nones. This discrepancy is similar to that previously reported on the\ntime-of-flight visibility."
    },
    {
        "anchor": "Observation of grand-canonical number statistics in a photon\n  Bose-Einstein condensate: We report measurements of particle number correlations and fluctuations of a\nphoton Bose-Einstein condensate in a dye microcavity using a Hanbury\nBrown-Twiss experiment. The photon gas is coupled to a reservoir of molecular\nexcitations, which serve both as heat bath and particle reservoir to realize\ngrand-canonical conditions. For large reservoirs, we observe strong number\nfluctuations of order of the total particle number extending deep into the\ncondensed phase. Our results demonstrate that Bose-Einstein condensation under\ngrand-canonical ensemble conditions does not imply second-order coherence.",
        "positive": "Coupling ultracold atoms to a superconducting coplanar waveguide\n  resonator: We demonstrate coupling of magnetically trapped ultracold $^87$Rb ground\nstate atoms to a coherently driven superconducting coplanar resonator on an\nintegrated atom chip. We measure the microwave field strength in the cavity\nthrough observation of the AC shift of the hyperfine transition frequency when\nthe cavity is driven off-resonance from the atomic transition. The measured\nshifts are used to reconstruct the field in the resonator, in close agreement\nwith transmission measurements of the cavity, giving proof of the coupling\nbetween atoms and resonator. When driving the cavity in resonance with the\natoms, we observe Rabi oscillations between atomic hyperfine states,\ndemonstrating coherent control of the atomic states through the cavity field.\nThe observation of two-photon Rabi oscillations using an additional external\nradio frequency enables the preparation of magnetically trapped coherent\nsuperposition states near the superconducting cavity, which are required for\nthe implementation of an atomic quantum memory."
    },
    {
        "anchor": "First sound velocity in liquid $^{4}$He: Based on the many-boson system structure factor, which takes into account\nthree- and four-particle direct correlations, there was found the first sound\nvelocity temperature behaviour in liquid $^4$He in the post-RPA approximation.\nThe expression received for the sound velocity matches with the well-known\nresults in both low and high temperature limits. The results of this paper can\nbe used to analyze the contributions of three- and four-particle correlations\ninto thermodynamic and structural features of liquid $^4$He.",
        "positive": "Vortex dynamics in lattice Bose gases in a synthesized magnetic field\n  with a random noise and a dissipation: Study by the stochastic\n  Gross-Pitaevskii equation: In this paper, we investigate vortex dynamics in a two-dimensional\nBose-Hubbard model coupled with a weak artificial magnetic field, a random\nwhite noise and a dissipation. Origin of the noise and dissipation is\nconsidered as thermal fluctuations of atoms that do not participate the\nBose-Einstein condensation (BEC). Solving a stochastic Gross-Pitaevskii\nequation to this system, we show that the interplay of the magnetic field and\nthe white noise generates vortices in the bulk of the BEC and stable steady\nstates of vortices form after a transition period. We calculate the\nincompressible part of the kinetic-energy spectrum of the BEC. In the\ntransition period, a Kolmogorov $k^{-5/3}$ spectrum appears in the infrared\nregime with the wave number $k$, $k<\\zeta^{-1}$, where $\\zeta$ is the healing\nlength, whereas in the ultraviolet region, $k>\\zeta^{-1}$, the spectrum behaves\nas $k^{-3}$. On the other hand in the steady states, another scaling low\nappears. We find a relationship between the above mentioned kinetic-energy\nspectra and the velocity of vortices. By an inverse cascade, the large velocity\nof a few created vortices develops the Kolmogorov $k^{-5/3}$ spectrum."
    },
    {
        "anchor": "Time-optimal variational control of bright matter-wave soliton: Motivated by recent experiments, we present the time-optimal variational\ncontrol of bright matter-wave soliton trapped in a quasi-one-dimensional\nharmonic trap by manipulating the atomic attraction through Feshbach\nresonances. More specially, we first apply a time-dependent variational method\nto derive the motion equation for capturing the soliton's shape, and secondly\ncombine inverse engineering with optimal control theory to design the atomic\ninteraction for implementing time-optimal decompression. Since the time-optimal\nsolution is of bang-bang type, the smooth regularization is further adopted to\nsmooth the on-off controller out, thus avoiding the heating and atom loss,\ninduced from magnetic field ramp across a Feshbach resonance in practice.",
        "positive": "Scattering theory and equation of state of a spherical two-dimensional\n  Bose gas: We analyze the scattering problem of identical bosonic particles confined on\na spherical surface. At low scattering energies and for a radius much larger\nthan the healing length, we express the contact interaction strength in terms\nof the s-wave scattering length. Adopting this relation, we are then able to\nregularize the zero-point energy of the spherical Bose gas and to obtain its\nequation of state, which includes the corrections due to the finite radius of\nthe sphere and coincides with the flat-case result in the infinite-radius\nlimit. We also provide a microscopic derivation of the superfluid density of\nthe system, reproducing a result postulated in a previous work. Our results are\nrelevant for modeling the ongoing microgravity experiments with two-dimensional\nbubble-trapped Bose-Einstein condensates."
    },
    {
        "anchor": "Three-body recombination at finite energy within an optical model: We investigate three-boson recombination of equal mass systems as function of\n(negative) scattering length, mass, finite energy, and finite temperature. An\noptical model with an imaginary potential at short distance reproduces\nexperimental recombination data and allows us to provide a simple\nparametrization of the recombination rate as function of scattering length and\nenergy. Using the two-body van der Waals length as unit we find that the\nimaginary potential range and also the potential depth agree to within thirty\npercent for Lithium and Cesium atoms. As opposed to recent studies suggesting\nuniversality of the threshold for bound state formation, our results suggest\nthat the recombination process itself could have universal features.",
        "positive": "Stability of Excited Dressed States with Spin-Orbit Coupling: We study the decay behaviors of ultracold atoms in metastable states with\nspin-orbit coupling (SOC), and demonstrate that there are two SOC-induced decay\nmechanisms. One arises from the trapping potential and the other is due to\ninteratomic collision. We present general schemes for calculating decay rates\nfrom these two mechanisms, and illustrate how the decay rates can be controlled\nby experimental parameters.We experimentally measure the decay rates over a\nbroad parameter region, and the results agree well with theoretical\ncalculations. This work provides an insight for both quantum simulation\ninvolving metastable dressed states and studies on few-body problems with SO\ncoupling."
    },
    {
        "anchor": "Rashba and Weyl spin-orbit coupling in an optical lattice clock: Recent experimental realization of one-dimensional (1D) spin-orbit coupling\n(SOC) for ultracold alkaline-earth(-like) atoms in optical lattice clocks opens\na new avenue for exploring exotic quantum matter because of the strongly\nsuppressed heating of atoms from lasers comparing with alkaline atoms. Here we\npropose a scheme to realize two-dimensional (2D) Rashba and three-dimensional\n(3D) Weyl types of SOC in a 3D optical lattice clock and explore their\ntopological phases. With 3D Weyl SOC, the system can support topological phases\nwith various numbers as well as types (I or II) of Weyl points. The spin\ntextures of such topological bands for 2D Rashba and 3D Weyl SOC can be\ndetected using suitably designed spectroscopic sequences. Our proposal may pave\nthe way for the experimental realization of robust topological quantum matters\nand their exotic quasiparticle excitations in ultracold atomic gases.",
        "positive": "Quantum Landau damping in dipolar Bose-Einstein condensates: We consider Landau damping of elementary excitations in Bose-Einstein\ncondensates (BECs) with dipolar interactions. We discuss quantum and\nquasi-classical regimes of Landau damping. We use a generalized wave-kinetic\ndescription of BECs which, apart from the long range dipolar interactions, also\ntakes into account the quantum fluctuations and the finite energy corrections\nto short-range interactions. Such a description is therefore more general than\nthe usual mean field approximation. The present wave-kinetic approach is well\nsuited for the study of kinetic effects in BECs, such as those associated with\nLandau damping, atom trapping and turbulent diffusion. The inclusion of quantum\nfluctuations and energy corrections change the dispersion relation and the\ndamping rates, leading to possible experimental signatures of these effects.\n  Quantum Landau damping is described with generality, and particular examples\nof dipole condensates in two and three dimensions are studied. The occurrence\nof roton-maxon configurations, and their relevance to Landau damping is also\nconsidered in detail, as well as the changes introduced by the three different\nprocesses, associated with dipolar interactions, quantum fluctuations and\nfinite energy range collisions. The present approach is mainly based on a\nlinear perturbative procedure, but the nonlinear regime of Landau damping,\nwhich includes atom trapping and atom diffusion, is also briefly discussed."
    },
    {
        "anchor": "Dynamical Control of Order in a Cavity-BEC System: We demonstrate dynamical control of the superradiant transition of cavity-BEC\nsystem via periodic driving of the pump laser. We show that the dominant\ndensity wave order of the superradiant state can be suppressed, and that the\nsubdominant competing order of Bose-Einstein condensation emerges in the steady\nstate. Furthermore, we show that additional, non-equilibrium density wave\norders, which do not exist in equilibrium, can be stabilized dynamically.\nFinally, for strong driving, chaotic dynamics emerges.",
        "positive": "High-momentum distribution with subleading $k^{-3}$ tail in the odd-wave\n  interacting one-dimensional Fermi gases: We study the odd-wave interacting identical fermions in one-dimension with\nfinite effective range. We show that to fully describe the high-momentum\ndistribution $\\rho(k)$ up to $k^{-4}$, one needs four parameters characterizing\nthe properties when two particles {\\it contact} with each other. Two parameters\nare related to the variation of energy with respect to the odd-wave scattering\nlength and the effective range, respectively, determining the $k^{-2}$ tail and\npart of $k^{-4}$ tail in $\\rho(k)$. The other two parameters are related to the\ncenter-of-mass motion of the system, respectively determining the $k^{-3}$ tail\nand the other part of $k^{-4}$ tail. We point out that the unusual $k^{-3}$\ntail, which has not been discovered before in atomic systems, is an intrinsic\ncomponent to complete the general form of $\\rho(k)$ and also realistically\ndetectable under certain experimental conditions. Various other universal\nrelations are also derived in terms of those contact parameters, and finally\nthe results are confirmed through the exact solution of a two-body problem."
    },
    {
        "anchor": "Chiral control of quantum states in non-Hermitian spin-orbit-coupled\n  fermions: Spin-orbit coupling is an essential mechanism underlying quantum phenomena\nsuch as the spin Hall effect and topological insulators. It has been widely\nstudied in well-isolated Hermitian systems, but much less is known about the\nrole dissipation plays in spin-orbit-coupled systems. Here, we implement\ndissipative spin-orbit-coupled bands filled with ultracold fermions, and\nobserve parity-time symmetry breaking as a result of the competition between\nthe spin-orbit coupling and dissipation. Tunable dissipation, introduced by\nstate-selective atom loss, enables us to tune the energy gap and close it at\nthe critical dissipation value, the so-called exceptional point. In the\nvicinity of the critical point, the state evolution exhibits a chiral response,\nwhich enables us to tune the spin-orbit coupling and dissipation dynamically,\nrevealing topologically robust chiral spin transfer when the quantum state\nencircles the exceptional point. This demonstrates that we can explore\nnon-Hermitian topological states with spin-orbit coupling.",
        "positive": "Dynamical nonlinear excitations induced by interaction quench in a\n  two-dimensional box-trapped Bose-Einstein condensate: Manipulating nonlinear excitations, including solitons and vortices, is an\nessential topic in quantum many-body physics. A recent progress in this\ndirection is a new protocol proposed in [Phys. Rev. Res. 2, 043256 (2020)] to\nproduce dark solitons in a one-dimensional atomic Bose-Einstein condensate\n(BEC) by quenching inter-atomic interaction. Motivated by this work, we\ngeneralize the protocol to a two-dimensional BEC and investigate the general\nscenario of its post-quench dynamics. For an isotropic disk trap with a\nhard-wall boundary, we find that successive inward-moving ring dark solitons\n(RDSs) can be induced from the edge, and the number of RDSs can be controlled\nby tuning the ratio of the after- and before-quench interaction strength across\ndifferent critical values. The role the quench played on the profiles of the\ndensity, phase, and sound velocity is also investigated. Due to the snake\ninstability, the RDSs then become vortex-antivortex pairs with peculiar\ndynamics managed by the initial density and the after-quench interaction. By\ntuning the geometry of the box traps, demonstrated as polygonal ones, more\nsubtle dynamics of solitons and vortices are enabled. Our proposed protocol and\nthe discovered rich dynamical effects on nonlinear excitations can be realized\nin future cold-atom experiments."
    },
    {
        "anchor": "Modulated trapping of interacting bosons in one dimension: We investigate the response of harmonically confined bosons with contact\ninteractions (trapped Lieb-Liniger gas) to modulations of the trapping\nstrength. We explain the structure of resonances at a series of driving\nfrequencies, where size oscillations and energy grow exponentially. For strong\ninteractions (Tonks-Girardeau gas), we show the effect of resonant driving on\nthe bosonic momentum distribution. The treatment is `exact' for zero and\ninfinite interactions, where the dynamics is captured by a single-variable\nordinary differential equation. For finite interactions the system is no longer\nexactly solvable. For weak interactions, we show how interactions modify the\nresonant behavior for weak and strong driving, using a variational\napproximation which adds interactions to the single-variable description in a\ncontrolled way.",
        "positive": "Entanglement structure of a quantum simulator: the two-component\n  Bose-Hubbard model: We consider a quantum simulator of the Heisenberg chain with ferromagnetic\ninteractions based on the two-component 1D Bose-Hubbard model at filling equal\nto two in the strong coupling regime. The entanglement properties of the ground\nstate are compared between the original spin model and the quantum simulator as\nthe interspecies interaction approaches the intraspecies one. A numerical study\nof the entanglement properties of the quantum simulator state is supplemented\nwith analytical expressions derived from the simulated Hamiltonian. At the\nisotropic point, the entanglement properties of the simulated system are not\nproperly predicted by the quantum simulator."
    },
    {
        "anchor": "Quantum-Zeno Fermi polaron in the strong dissipation limit: The interplay between measurement and quantum correlations in many-body\nsystems can lead to novel types of collective phenomena which are not\naccessible in isolated systems. In this work, we merge the Zeno-paradigm of\nquantum measurement theory with the concept of polarons in condensed-matter\nphysics. The resulting quantum-Zeno Fermi-polaron is a quasi-particle which\nemerges for lossy impurities interacting with a quantum-degenerate bath of\nfermions. For loss rates of the order of the impurity-fermion binding energy\nthe quasi-particle is short lived. However, we show that in the strongly\ndissipative regime of large loss rates a long-lived polaron branch re-emerges.\nThis quantum-Zeno Fermi-polaron originates from the nontrivial interplay\nbetween the Fermi-surface and the surface of the momentum region forbidden by\nthe quantum Zeno projection. The situation we consider here is realized\nnaturally for polaritonic impurities in charge-tuneable semiconductors and can\nbe also implemented using dressed atomic states in ultracold gases.",
        "positive": "Ground-state phase diagram of a dipolar condensate with quantum\n  fluctuations: We consider the ground state properties of a trapped dipolar condensate under\nthe influence of quantum fluctuations. We show that this system can undergo a\nphase transition from a low density condensate state to a high density droplet\nstate, which is stabilized by quantum fluctuations. The energetically favored\nstate depends on the geometry of the confining potential, the number of atoms\nand the two-body interactions. We develop a simple variational ansatz and\nvalidate it against full numerical solutions. We produce a phase diagram for\nthe system and present results relevant to current experiments with dysprosium\nand erbium condensates."
    },
    {
        "anchor": "Interaction-induced coherence among polar bosons stored in triple-well\n  potentials: We study first-order spatial coherence for interacting polar bosons trapped\nin triple-well potentials. It is argued that besides the well-known coherence\nproduced by couplings related to tunneling between the sites, there exists a\nnonlocal coherence predominantly determined by intersite interactions, which\nprevails between the outer sites of the triple well when their total filling is\nodd. We find that the nonlocal interaction-induced coherence originates from\nthe superposition of degenerate many-body states in symmetric triple wells, and\ndemonstrate its robustness against perturbations due to various tunneling\nmechanisms and thermal fluctuations.",
        "positive": "Lattice supersolid phase of strongly correlated bosons in an optical\n  cavity: We numerically simulate strongly correlated ultracold bosons coupled to a\nhigh-finesse cavity field, pumped by a laser beam in the transverse direction.\nAssuming a weak classical optical lattice added in the cavity direction, we\nmodel this system by a generalized Bose-Hubbard model, which is solved by means\nof bosonic dynamical mean-field theory. The complete phase diagram is\nestablished, which contains two novel self-organized quantum phases, lattice\nsupersolid and checkerboard solid, in addition to conventional phases such as\nsuperfluid and Mott insulator. At finite but low temperature, thermal\nfluctuations are found to enhance the buildup of the self-organized phases. We\ndemonstrate that cavity-mediated long-range interactions can give rise to\nstable lattice supersolid and checkerboard solid phases even in the regime of\nstrong s-wave scattering. In the presence of a harmonic trap, we discuss\ncoexistence of these self-organized phases, as relevant to experiments."
    },
    {
        "anchor": "Raman superradiance and spin lattice of ultracold atoms in optical\n  cavities: We investigate synthesis of a hyperfine spin lattice in an atomic\nBose-Einstein condensate, with two hyperfine spin components, inside a\none-dimensional high-finesse optical cavity, using off-resonant superradiant\nRaman scattering. Spatio-temporal evolution of the relative population of the\nhyperfine spin modes is examined numerically by solving the coupled\ncavity-condensate mean field equations in the dispersive regime. We find,\nanalytically and numerically, that beyond a certain threshold of the transverse\nlaser pump, Raman superradiance and self-organization of the hyperfine spin\ncomponents simultaneously occur and as a result a magnetic lattice is formed.\nThe effects of an extra laser pump parallel to the cavity axis and the\ntime-dependence of the pump strength on the synthesis of a sharper lattice are\nalso addressed.",
        "positive": "Many-body processes in black and grey matter-wave solitons: We perform a comparative beyond mean-field study of black and grey solitonic\nexcitations in a finite ensemble of ultracold bosons confined to a\none-dimensional box. An optimized density-engineering potential is developed\nand employed together with phase-imprinting to cleanly initialize grey\nsolitons. Based on our recently developed Multi-Layer Multi-Configuration\nTime-Dependent Hartree Method for Bosons, we demonstrate an enhancement of the\nquantum fluctuations limited lifetime of the soliton contrast with increasing\nsoliton velocity. A natural orbital analysis reveals a two-stage process\nunderlying the decay of the soliton contrast. The broken parity symmetry of\ngrey solitons results in a local asymmetry of the orbital mainly responsible\nfor the decay, which leads to a characteristic asymmetry of remarkably\nlocalized two-body correlations. The emergence and decay of these correlations\nas well as their displacement from the instantaneous soliton position are\nanalysed in detail. Finally, the role of phase-imprinting for the many-body\ndynamics is illuminated and additional non-local correlations in pairs of\ncounter-propagating grey solitons are unravelled."
    },
    {
        "anchor": "Angular momentum in interacting many-body systems hides in phantom\n  vortices: Vortices are essential to angular momentum in quantum systems such as\nultracold atomic gases. The existence of quantized vorticity in bosonic systems\nstimulated the development of the Gross-Pitaevskii mean-field approximation.\nHowever, the true dynamics of angular momentum in finite, interacting many-body\nsystems like trapped Bose-Einstein condensates is enriched by the emergence of\nquantum correlations whose description demands more elaborate methods. Herein\nwe theoretically investigate the full many-body dynamics of the acquisition of\nangular momentum by a gas of ultracold bosons in two dimensions using a\nstandard rotation procedure. We demonstrate the existence of a novel mode of\nquantized vorticity, which we term the $\\textit{phantom vortex}$ that, contrary\nto the conventional mean-field vortex, can be detected as a topological defect\nof spatial coherence, but $\\textit{not}$ of the density. We describe previously\nunknown many-body mechanisms of vortex nucleation and show that angular\nmomentum is hidden in phantom vortex modes which so far seem to have evaded\nexperimental detection.",
        "positive": "Cluster formation in two-component Fermi gases: Two-component fermions are known to behave like a gas of molecules in the\nlimit of Bose-Einstein condensation of diatomic pairs tightly bound with\nzero-range interactions. We discover that the formation of cluster states\noccurs when the effective range of two-body interaction exceeds roughly $0.46$\ntimes the scattering length, regardless of the details of the short-range\ninteraction. Using explicitly correlated Gaussian basis set expansion approach,\nwe calculate the binding energy of cluster states in trapped few-body systems\nand show the difference of structural properties between cluster states and\ngas-like states. We identify the condition for cluster formation and discuss\npotential observation of cluster states in experiments."
    },
    {
        "anchor": "Realising the Symmetry-Protected Haldane Phase in Fermi-Hubbard Ladders: Topology in quantum many-body systems has profoundly changed our\nunderstanding of quantum phases of matter. The paradigmatic model that has\nplayed an instrumental role in elucidating these effects is the\nantiferromagnetic spin-1 Haldane chain. Its ground state is a disordered state,\nwith symmetry-protected fourfold-degenerate edge states due to fractional spin\nexcitations. In the bulk, it is characterised by vanishing two-point spin\ncorrelations, gapped excitations, and a characteristic non-local order\nparameter. More recently it was understood that the Haldane chain forms a\nspecific example of a more general classification scheme of symmetry protected\ntopological (SPT) phases of matter that is based on ideas connecting to quantum\ninformation and entanglement. Here, we realise such a topological Haldane phase\nwith Fermi-Hubbard ladders in an ultracold-atom quantum simulator. We directly\nreveal both edge and bulk properties of the system through the use of\nsingle-site and particle-resolved measurements as well as non-local correlation\nfunctions. Continuously changing the Hubbard interaction strength of the system\nallows us to investigate the robustness of the phase to charge (density)\nfluctuations far from the regime of the Heisenberg model employing a novel\ncorrelator.",
        "positive": "Non-thermal fixed points of universal sine-Gordon coarsening dynamics: We examine coarsening of field-excitation patterns of the sine-Gordon (SG)\nmodel, in two and three spatial dimensions, identifying it as universal\ndynamics near non-thermal fixed points. The SG model is relevant in many\ndifferent contexts, from solitons in quantum fluids to structure formation in\nthe universe. The coarsening process entails anomalously slow self-similar\ntransport of the spectral distribution of excitations towards low energies,\ninduced by the collisional interactions between the field modes. The focus is\nset on the non-relativistic limit exhibiting particle excitations only,\ngoverned by a Schr\\\"odinger-type equation with Bessel-function non-linearity.\nThe results of our classical statistical simulations suggest that, in contrast\nto wave turbulent cascades, in which the transport is local in momentum space,\nthe coarsening is dominated by rather non-local processes corresponding to a\nspatial containment in position space. The scaling analysis of a kinetic\nequation obtained with path-integral techniques corroborates this numerical\nobservation and suggests that the non-locality is directly related to the\nslowness of the scaling in space and time. Our methods, which we expect to be\napplicable to more general types of models, could open a long-sought path to\nanalytically describing universality classes behind domain coarsening and\nphase-ordering kinetics from first principles, which are usually modelled in a\nnear-equilibrium setting by a phenomenological diffusion-type equation in\ncombination with conservation laws."
    },
    {
        "anchor": "Simulating strongly correlated multiparticle systems in a truncated\n  Hilbert space: Representing a strongly interacting multi-particle wave function in a finite\nproduct basis leads to errors. Simple rescaling of the contact interaction can\npreserve the low-lying energy spectrum and long-wavelength structure of wave\nfunctions in one-dimensional systems and thus correct for the basis set\ntruncation error. The analytic form of the rescaling is found for a\ntwo-particle system where the rescaling is exact. Detailed comparison between\nfinite Hilbert space calculations and exact results for up to 5 particles show\nthat rescaling can significantly improve the accuracy of numerical calculations\nin various external potentials. In addition to ground state energies, the\nlow-lying excitation spectrum, density profile and correlation functions are\nstudied. The results give a promising outlook for numerical simulations of\ntrapped ultracold atoms.",
        "positive": "What can we learn from diffusion about Anderson localization of a\n  degenerate Fermi gas?: Disorder can fundamentally modify the transport properties of a system. A\nstriking example is Anderson localization, suppressing transport due to\ndestructive interference of propagation paths. In inhomogeneous many-body\nsystems, not all particles are localized for finite-strength disorder, and the\nsystem can become partially diffusive. Unravelling the intricate signatures of\nlocalization from such observed diffusion is a long-standing problem. Here, we\nexperimentally study a degenerate, spin-polarized Fermi gas in a disorder\npotential formed by an optical speckle pattern. We record the diffusion in the\ndisordered potential upon release from an external confining potential. We\ncompare different methods to analyze the resulting density distributions,\nincluding a new method to capture particle dynamics by evaluating\nabsorption-image statistics. Using standard observables, such as diffusion\nexponent and coefficient, localized fraction, or localization length, we find\nthat some show signatures for a transition to localization above a critical\ndisorder strength, while others show a smooth crossover to a modified diffusion\nregime. In laterally displaced disorder, we spatially resolve different\ntransport regimes simultaneously which allows us to extract the subdiffusion\nexponent expected for weak localization. Our work emphasizes that the\ntransition toward localization can be investigated by closely analyzing the\nsystem's diffusion, offering ways of revealing localization effects beyond the\nsignature of exponentially decaying density distribution."
    },
    {
        "anchor": "Emergent patterns in a spin-orbit coupled spin-2 Bose-Einstein\n  condensate: The ground-state phases of a spin-orbit (SO) coupled atomic spin-2\nBose-Einstein condensate (BEC) are studied. Interesting density patterns\nspontaneously formed are widespread due to the competition between SO coupling\nand spin-dependent interactions like in a SO coupled spin-1 condensate. Unlike\nthe case of spin-1 condensates, which are characterized by either ferromagnetic\nor polar phase in the absence of SO, spin-2 condensates can take a cyclic\nphase, where we find the patterns formed due to SO are square or triangular in\ntheir spin component densities for axial symmetric SO interaction. Both\npatterns are found to continuously evolve into striped forms with increased\nasymmetry of the SO coupling.",
        "positive": "Quantum heat waves in a one-dimensional condensate: We study the dynamics of phase relaxation between a pair of one-dimensional\ncondensates created by a bi-directional, supersonic `unzipping' of a finite\nsingle condensate. We find that the system fractures into different\n\\emph{extensive} chunks of space-time, within which correlations appear thermal\nbut correspond to different effective temperatures. Coherences between\ndifferent eigen-modes are crucial for understanding the development of such\nthermal correlations; at no point in time can our system be described by a\ngeneralized Gibbs' ensemble despite nearly always appearing locally thermal. We\nrationalize a picture of propagating fronts of hot and cold sound waves,\npopulated at effective, relativistically red- and blue-shifted temperatures to\nintuitively explain our findings. The disparity between these hot and cold\ntemperatures vanishes for the case of instantaneous splitting but diverges in\nthe limit where the splitting velocity approaches the speed of sound; in this\nlimit, a sonic boom occurs wherein the system is excited only along an\ninfinitely narrow, and infinitely hot beam. We expect our findings to apply\ngenerally to the study of superluminal perturbations in systems with emergent\nLorentz symmetry."
    },
    {
        "anchor": "Characterization of Bose-Hubbard Models with Quantum Non-demolition\n  Measurements: We propose a scheme for the detection of quantum phase transitions in the 1D\nBose-Hubbard (BH) and 1D Extended Bose-Hubbard (EBH) models, using the\nnon-demolition measurement technique of quantum polarization spectroscopy. We\nuse collective measurements of the effective total angular momentum of a\nparticular spatial mode to characterise the Mott insulator to superfluid phase\ntransition in the BH model, and the transition to a density wave state in the\nEBH model. We extend the application of collective measurements to the ground\nstates at various deformations of a super-lattice potential.",
        "positive": "Exact Parent Hamiltonian for the Quantum Hall States in a Optical\n  Lattice: We study lattice models of charged particles in uniform magnetic fields. We\nshow how longer range hopping can be engineered to produce a massively\ndegenerate manifold of single-particle ground states with wavefunctions\nidentical to those making up the lowest Landau level of continuum electrons in\na magnetic field. We find that in the presence of local interactions, and at\nthe appropriate filling factors, Laughlin's fractional quantum Hall\nwavefunction is an exact many-body ground state of our lattice model. The\nhopping matrix elements in our model fall off as a Gaussian, and when the flux\nper plaquette is small compared to the fundamental flux quantum one only needs\nto include nearest and next nearest neighbor hoppings. We suggest how to\nrealize this model using atoms in optical lattices, and describe observable\nconsequences of the resulting fractional quantum Hall physics."
    },
    {
        "anchor": "Generalized gradient expansion for inhomogeneous dynamical mean-field\n  theory: Application to ultracold atoms in a harmonic trap: We develop a generalized gradient expansion of the inhomogeneous dynamical\nmean-field theory method for determining properties of ultracold atoms in a\ntrap. This approach goes beyond the well-known local density approximation and\nat higher temperatures, in the normal phase, it shows why the local density\napproximation works so well, since the local density and generalized gradient\napproximations are essentially indistinguishable from each other (and from the\nexact solution within full inhomogeneous dynamical mean-field theory). But\nbecause the generalized gradient expansion only involves nearest-neighbor\ncorrections, it does not work as well at low temperatures, when the systems\nenter into ordered phases. This is primarily due to the problem that ordered\nphases often satisfy some global constraints which determine the spatial\nordering pattern, and the local density and generalized gradient approximations\nare not able to impose those kinds of constraints; they also overestimate the\ntendency to order. The theory is applied to phase separation of different mass\nfermionic mixtures represented by the Falicov-Kimball model and to determining\nthe entropy per particle of a fermionic system represented by the Hubbard\nmodel. The generalized gradient approximation is a useful diagnostic for the\naccuracy of the local density approximation---when both methods agree, they are\nlikely accurate, when they disagree, neither is likely to be correct.",
        "positive": "Analytical approach to relaxation dynamics of condensed Bose gases: The temporal evolution of a perturbation of the equilibrium distribution of a\ncondensed Bose gas is investigated using the kinetic equation which describes\ncollision between condensate and noncondensate atoms. The dynamics is studied\nin the low momentum limit where an analytical treatment is feasible. Explicit\nresults are given for the behavior at large times in different temperature\nregimes."
    },
    {
        "anchor": "Gr\u00fcneisen Parameters: origin, identity and quantum refrigeration: In solid state physics, the Gr\\\"{u}neisen parameter (GP), originally\nintroduced in the study of the effect of changing the volume of a crystal\nlattice on its vibrational frequency, has been widely used to investigate the\ncharacteristic energy scales of systems with respect to the changes of external\npotentials. On the other hand, the GP is little investigated in a strongly\ninteracting quantum gas systems. Here we report on our general results on the\norigin of GP, new identity and caloric effects in quantum gases of ultracold\natoms. We prove that the symmetry of the dilute quantum gas systems leads to a\nsimple identity among three different types of GPs, quantifying caloric effect\ninduced respectively by variations of volume, magnetic field and interaction.\nUsing exact Bethe ansatz solutions, we present a rigorous study of these\ndifferent GPs and the quantum refrigeration in one-dimensional Bose and Femi\ngases. Based on the exact equations of states of these systems, we obtain\nanalytic results for the singular behaviour of the GPs and the caloric effects\nat quantum criticality. We also predict the existence of the lowest temperature\nfor cooling near a quantum phase transition. It turns out that the interaction\nramp-up and -down in quantum gases provides a promising protocol of quantum\nrefrigeration in addition to the usual adiabatic demagnetization cooling in\nsolid state materials.",
        "positive": "For high-precision bosonic Josephson junctions, many-body effects matter: Typical treatments of superconducting or superfluid Josephson junctions rely\non mean-field or two-mode models; we explore many-body dynamics of an isolated,\nultracold, Bose-gas long Josephson junction using time-evolving block\ndecimation simulations. We demonstrate that with increasing repulsive\ninteraction strength, localized dynamics emerge that influence macroscopic\ncondensate behavior and can lead to formation of solitons that directly oppose\nthe symmetry of the junction. Initial state population and phase yield insight\ninto dynamic tunneling regimes of a quasi one-dimensional double well\npotential, from Josephson oscillations to macroscopic self-trapping. Population\nimbalance simulations reveal substantial deviation of many-body dynamics from\nmean-field Gross-Pitaevskii predictions, particularly as the barrier height and\ninteraction strength increase. In addition, the sudden approximation supports\nlocalized particle-hole formation after a diabatic quench, and correlation\nmeasures unveil a new dynamic regime: the Fock flashlight."
    },
    {
        "anchor": "Quantum tri-criticality and phase transitions in spin-orbit coupled\n  Bose-Einstein condensates: We consider a spin-orbit coupled configuration of spin-1/2 interacting bosons\nwith equal Rashba and Dresselhaus couplings. The phase diagram of the system is\ndiscussed with special emphasis to the role of the interaction treated in the\nmean-field approximation. For a critical value of the density and of the Raman\ncoupling we predict the occurrence of a characteristic tri-critical point\nseparating the spin mixed, the phase separated and the single minimum states of\nthe Bose gas. The corresponding quantum phases are investigated analyzing the\nmomentum distribution, the longitudinal and transverse spin-polarization and\nthe emergence of density fringes. The effect of harmonic trapping as well as\nthe role of the breaking of spin symmetry in the interaction Hamiltonian are\nalso discussed.",
        "positive": "Spin-orbit-coupling-induced phase separation in trapped Bose gases: In a trapped spin-1/2 Bose-Einstein condensate with miscible interactions, a\ntwo-dimensional spin-orbit coupling can introduce an unconventional spatial\nseparation between the two components. We reveal the physical mechanism of such\na spin-orbit-coupling-induced phase separation. Detailed features of the phase\nseparation are identified in a trapped Bose-Einstein condensate. We further\nanalyze differences of phase separation in Rashba and anisotropic\nspin-orbit-coupled Bose gases. An adiabatic splitting dynamics is proposed as\nan application of the phase separation."
    },
    {
        "anchor": "Calorimetry of a harmonically trapped Bose gas: We experimentally study the energy-temperature relationship of a harmonically\ntrapped Bose-Einstein condensate by transferring a known quantity of energy to\nthe condensate and measuring the resulting temperature change. We consider two\nmethods of heat transfer, the first using a free expansion under gravity and\nthe second using an optical standing wave to diffract the atoms in the\npotential. We investigate the effect of interactions on the thermodynamics and\ncompare our results to various finite temperature theories.",
        "positive": "Dynamics of Momentum Distribution and Structure Factor in a Weakly\n  Interacting Bose Gas with a Periodical Modulation: The momentum distribution and dynamical structure factor in a weakly\ninteracting Bose gas with a time-dependent periodic modulation in terms of the\nBogoliubov treatment are investigated. The evolution equation related to the\nBogoliubov weights happens to be a solvable Mathieu equation when the coupling\nstrength is periodically modulated. An exact relation between the time\nderivatives of momentum distribution and dynamical structure factor is derived,\nwhich indicates that the single-particle property strongly related to the\ntwo-body property in the evolutions of Bose-Einstein condensates. It is found\nthat the momentum distribution and dynamical structure factor cannot display\nperiodical behavior. For stable dynamics, some particular peaks in the curves\nof momentum distribution and dynamical structure factor appear synchronously,\nwhich is consistent with the derivative relation."
    },
    {
        "anchor": "Suppression of Density Fluctuations in a Quantum Degenerate Fermi Gas: We study density profiles of an ideal Fermi gas and observe Pauli suppression\nof density fluctuations (atom shot noise) for cold clouds deep in the quantum\ndegenerate regime. Strong suppression is observed for probe volumes containing\nmore than 10,000 atoms. Measuring the level of suppression provides sensitive\nthermometry at low temperatures. After this method of sensitive noise\nmeasurements has been validated with an ideal Fermi gas, it can now be applied\nto characterize phase transitions in strongly correlated many-body systems.",
        "positive": "Spin-resolved single-atom imaging of $^6$Li in free space: We present a versatile imaging scheme for fermionic $^6$Li atoms with\nsingle-particle sensitivity. Our method works for freely propagating particles\nand completely eliminates the need for confining potentials during the imaging\nprocess. We illuminate individual atoms in free space with resonant light and\ncollect their fluorescence on an electron-multiplying CCD camera using a\nhigh-numerical-aperture imaging system. We detect approximately \\num{20}\nphotons per atom during an exposure of 20 $\\mu$s and identify individual atoms\nwith a fidelity of $99.4\\pm0.3$ % . By addressing different optical transitions\nduring two exposures in rapid succession, we additionally resolve the hyperfine\nspin state of each particle. The position uncertainty of the imaging scheme is\n4.0 $\\mu$m, given by the diffusive motion of the particles during the imaging\npulse. The absence of confining potentials enables readout procedures, such as\nthe measurement of single-particle momenta in time of flight, which we\ndemonstrate here. Our imaging scheme is technically simple and easily adapted\nto other atomic species."
    },
    {
        "anchor": "Two-dimensional cavity polaritons under the influence of the\n  perpendicular strong magnetic and electric fields. The gyrotropy effects: The properties of the two-dimensional cavity polaritons subjected to the\naction of a strong perpendicular magnetic and electric fields, giving rise to\nthe Landau quantization (LQ) of the 2D electrons and holes accompanied by the\nRashba spin-orbit coupling, by the Zeeman splitting and by the nonparabolicity\nof the heavy-hole dispersion law are investigated. We use the method proposed\nby Rashba [1] and the obtained results are based on the exact solutions for the\neigenfunctions and for the eigenvalues of the Pauli-type Hamilonians with third\norder chirality terms and nonparabolic dispersion law for heavy-holes and with\nthe first order chirality terms for electrons. The selection rules of the\nband-to-band optical quantum transitions as well as of the quantum transitions\nfrom the ground state of the crystal to the magnetoexciton states depend\nessentially on the numbers $n_{e}$ and $n_{h}$ of the LQ levels of the (e-h)\npair forming the magnetoexciton. It is shown that the Rabi frequency\n$\\Omega_{R}$ of the polariton branches and the magnetoexciton oscillator\nstrength $f_{osc}$ increase with the magnetic field strength $B$ as\n$\\Omega_{R}\\sim \\sqrt{B}$, and $f_{osc}\\sim B$. The optical gyrotropy effects\nmay be revealed changing the sign of the photon circular polarization at a\ngiven sign of the wave vector longitudinal projection $k_{z}$ or eqivalently\nchanging the sign of $k_{z}$ at the same selected circular polarization.",
        "positive": "Formation and fragmentation of quantum droplets in a quasi-one\n  dimensional dipolar Bose gas: We theoretically investigate the droplets formation in a tightly trapped\none-dimensional dipolar gas of bosonic atoms. When the strength of the dipolar\ninteraction becomes sufficiently attractive compared to the contact one, we\nshow how a solitonic-like density profile evolves into a liquid-like droplet on\nincreasing the number of particles in the trap. The incipient gas-liquid\ntransition is also signalled by a steep increase of the breathing mode and a\nchange in sign of the chemical potential. Upon a sudden release of the trap,\nvarying the number of trapped atoms and the scattering length, the numerical\nsolution of a time-dependent generalized Gross-Pitaevskii equation shows either\nan evaporation of the cloud, the formation of a single self-bound droplet or a\nfragmentation in multiple droplets.These results can be probed with lanthanides\natoms and help in characterizing the effect of the dipolar interaction in a\nquasi-one-dimensional geometry."
    },
    {
        "anchor": "Spatial separation of degenerate components of magnon Bose-Einstein\n  condensate by using a local acceleration potential: Bose-Einstein condensation (BEC) of magnons is one of few macroscopic quantum\nphenomena observable at room temperature. Due to competition of the exchange\nand the magnetic dipole interactions the minimum-energy magnon state is doubly\ndegenerate and corresponds to two antiparallel non-zero wavevectors.\nCorrespondingly, magnon BEC differs essentially from other condensates, since\nit takes place simultaneously at +/-k_min. The degeneracy of BEC and\ninteraction between its two components have significant impact on the\ncondensate properties. Phase locking of the two condensates causes formation of\na standing wave of the condensate density and quantized vortices. Additionally,\ninteraction between the two components is believed to be important for\nstabilization of the condensate with respect to the real-space collapse. Thus,\nthe possibility to create a non-degenerate, single-component condensate is\ndecisive for understanding of underlying physics of magnon BEC. Here, we\nexperimentally demonstrate an approach, which allows one to accomplish this\nchallenging task. We show that this can be achieved by using a separation of\nthe two components of the degenerate condensate in the real space by applying a\nlocal pulsed magnetic field, which causes their motion in the opposite\ndirections. Thus, after a certain delay, the two clouds corresponding to\ndifferent components become well separated in the real space. We find that the\nmotion of the clouds can be described well based on the peculiarities of the\nmagnon dispersion characteristics. Additionally, we show that, during the\nmotion, the condensate cloud harvests non-condensed magnons, which results in a\npartial compensation of the condensate depletion.",
        "positive": "A quantum gas microscope - detecting single atoms in a Hubbard regime\n  optical lattice: Recent years have seen tremendous progress in creating complex atomic\nmany-body quantum systems. One approach is to use macroscopic, effectively\nthermodynamic ensembles of ultracold atoms to create quantum gases and strongly\ncorrelated states of matter, and to analyze the bulk properties of the\nensemble. The opposite approach is to build up microscopic quantum systems atom\nby atom - with complete control over all degrees of freedom. Until now, the\nmacroscopic and microscopic strategies have been fairly disconnected. Here, we\npresent a \"quantum gas microscope\" that bridges the two approaches, realizing a\nsystem where atoms of a macroscopic ensemble are detected individually and a\ncomplete set of degrees of freedom of each of them is determined through\npreparation and measurement. By implementing a high-resolution optical imaging\nsystem, single atoms are detected with near-unity fidelity on individual sites\nof a Hubbard regime optical lattice. The lattice itself is generated by\nprojecting a holographic mask through the imaging system. It has an arbitrary\ngeometry, chosen to support both strong tunnel coupling between lattice sites\nand strong on-site confinement. On one hand, this new approach can be used to\ndirectly detect strongly correlated states of matter. On the other hand, the\nquantum gas microscope opens the door for the addressing and read-out of\nlarge-scale quantum information systems with ultracold atoms."
    },
    {
        "anchor": "Bose-Einstein Condensation and Supersolids: We consider interacting Bose particles in an external potential. It is shown\nthat a Bose-Einstein condensate is possible at finite temperatures that\ndescribes a supersolid in three dimensions (3D) for a wide range of potentials\nin the absence of an external potential. However, for 2D, a self-organized\nsupersolid exists for finite temperatures provided the interaction between\nbosons is nonlocal and of infinitely long-range. It is interesting that in the\nabsence of the latter type of potential and in the presence of a lattice\npotential, there is no Bose-Einstein condensate and so in such a case, a 2D\nsupersolid is not possible at finite temperatures. We also propose the correct\nBloch form of the condensate wave function valid for finite temperatures, which\nmay be used as the correct trial wave function.",
        "positive": "Dark spherical shell solitons in three-dimensional Bose-Einstein\n  condensates: Existence, stability and dynamics: In this work we study spherical shell dark soliton states in\nthree-dimensional atomic Bose-Einstein condensates. Their symmetry is exploited\nin order to analyze their existence, as well as that of topologically charged\nvariants of the structures, and, importantly, to identify their linear\nstability Bogolyubov-de Gennes spectrum. We compare our effective 1D spherical\nand 2D cylindrical computations with the full 3D numerics. An important\nconclusion is that such spherical shell solitons can be stable sufficiently\nclose to the linear limit of the isotropic condensates considered herein. We\nhave also identified their instabilities leading to the emergence of vortex\nline and vortex ring cages. In addition, we generalize effective particle\npictures of lower dimensional dark solitons and ring dark solitons to the\nspherical shell solitons concerning their equilibrium radius and effective\ndynamics around it. In this case too, we favorably compare the resulting\npredictions such as the shell equilibrium radius, qualitatively and\nquantitatively, with full numerical solutions in 3D."
    },
    {
        "anchor": "Quantum fluids of light: This article reviews recent theoretical and experimental advances in the\nfundamental understanding and active control of quantum fluids of light in\nnonlinear optical systems. In presence of effective photon-photon interactions\ninduced by the optical nonlinearity of the medium, a many-photon system can\nbehave collectively as a quantum fluid with a number of novel features stemming\nfrom its intrinsically non-equilibrium nature. We present a rich variety of\nphoton hydrodynamical effects that have been recently observed, from the\nsuperfluid flow around a defect at low speeds, to the appearance of a\nMach-Cherenkov cone in a supersonic flow, to the hydrodynamic formation of\ntopological excitations such as quantized vortices and dark solitons at the\nsurface of large impenetrable obstacles. While our review is mostly focused on\na class of semiconductor systems that have been extensively studied in recent\nyears (namely planar semiconductor microcavities in the strong light-matter\ncoupling regime having cavity polaritons as elementary excitations), the very\nconcept of quantum fluids of light applies to a broad spectrum of systems,\nranging from bulk nonlinear crystals, to atomic clouds embedded in optical\nfibers and cavities, to photonic crystal cavities, to superconducting quantum\ncircuits based on Josephson junctions. The conclusive part of our article is\ndevoted to a review of the exciting perspectives to achieve strongly correlated\nphoton gases. In particular, we present different mechanisms to obtain\nefficient photon blockade, we discuss the novel quantum phases that are\nexpected to appear in arrays of strongly nonlinear cavities, and we point out\nthe rich phenomenology offered by the implementation of artificial gauge fields\nfor photons.",
        "positive": "Observation of Quantum Phase Transitions with Parity-Symmetry Breaking\n  and Hysteresis: Symmetry-breaking quantum phase transitions play a key role in several\ncondensed matter, cosmology and nuclear physics theoretical models. Its\nobservation in real systems is often hampered by finite temperatures and\nlimited control of the system parameters. In this work we report for the first\ntime the experimental observation of the full quantum phase diagram across a\ntransition where the spatial parity symmetry is broken. Our system is made of\nan ultra-cold gas with tunable attractive interactions trapped in a spatially\nsymmetric double-well potential. At a critical value of the interaction\nstrength, we observe a continuous quantum phase transition where the gas\nspontaneously localizes in one well or the other, thus breaking the underlying\nsymmetry of the system. Furthermore, we show the robustness of the asymmetric\nstate against controlled energy mismatch between the two wells. This is the\nresult of hysteresis associated with an additional discontinuous quantum phase\ntransition that we fully characterize. Our results pave the way to the study of\nquantum critical phenomena at finite temperature, the investigation of\nmacroscopic quantum tunneling of the order parameter in the hysteretic regime\nand the production of strongly quantum entangled states at critical points."
    },
    {
        "anchor": "Single-Particle properties of a strongly-interacting Bose-Fermi mixture\n  with mass and population imbalance: We theoretically investigate strong-coupling properties of a Bose-Fermi\nmixture. In the mass- and population-balanced case, two of the authors have\nshown that a strong hetero-pairing interaction in this mixture brings about\ncoupling phenomena between Fermi atomic excitations and Bose atomic and\ncomposite molecular excitations, that appear as an anomalous multiple peak\nstructure in the single-particle spectral weight (SW). [D. Kharga, {\\it et.\nal.}, J. Phys. Soc. Jpn. {\\bf 86}, 084301 (2017)]. In this paper, extending\nthis previous work, we show that, although these many-body phenomena are\nsensitive to mass and population imbalances between the Bose and Fermi\ncomponents, SW still exhibits the multiple peak structure in a moderately\nmass-imbalanced $^{87}$Rb-$^{40}$K and $^{23}$Na-$^{40}$K mixtures. We also\npoint out that the photoemission spectrum is a useful quantity to observe this\nspectral anomaly. Since a real trapped Bose-Fermi mixture is usually\naccompanied by mass and (local) population imbalance, our results would\ncontribute to the study of a strongly interacting Bose-Fermi mixture, under\nrealistic imbalanced conditions.",
        "positive": "Fluctuation-dissipation relation for a Bose-Einstein condensate of\n  photons: For equilibrium systems, the magnitude of thermal fluctuations is closely\nlinked to the dissipative response to external perturbations. This\nfluctuation-dissipation relation has been described for material particles in a\nwide range of fields. Here we experimentally probe the relation between the\nnumber fluctuations and the response function for a Bose-Einstein condensate of\nphotons coupled to a dye reservoir, demonstrating the fluctuation-dissipation\nrelation for a quantum gas of light. The observed agreement of the scale factor\nwith the environment temperature both directly confirms the thermal nature of\nthe optical condensate and demonstrates the validity of the\nfluctuation-dissipation theorem for a Bose-Einstein condensate."
    },
    {
        "anchor": "Expansion dynamics in two-dimensional Bose-Hubbard lattices:\n  Bose-Einstein condensate and thermal cloud: We study the temporal expansion of an ultracold Bose gas in two-dimensional,\nsquare optical lattices. The gas is described by the Bose-Hubbard model deep in\nthe superfluid regime, with initially all bosons condensed in the central site\nof the lattice. We use the previously developed nonequilibrium propagator\nmethod for capturing the time evolution of an interacting bosonic system, where\nthe many-body Hamiltonian is represented in an appropriate local basis and the\ncorresponding field operators are separated into the classical [Bose-Einstein\ncondensate (BEC)] part and quantum mechanical fluctuations. After a quench,\ni.e. after a sudden switch of the lattice nearest-neighbor hopping, the\nexpanding, bosonic cloud separates spatially into a fast, ballistic forerunner\nand a slowly expanding central part controlled by selftrapping. We show that\nthe forerunner expansion is driven by the coherent dynamics of the BEC and that\nits velocity is consistent with the Lieb-Robinson bound. For smaller lattices\nwe analyze how quasiparticle collisions lead to enhanced condensate depletion\nand oscillation damping.",
        "positive": "Long-lived trimers in a quasi-two-dimensional Fermi system: We consider the problem of three distinguishable fermions confined to a\nquasi-two-dimensional (quasi-2D) geometry, where there is a strong harmonic\npotential in one direction. We go beyond previous theoretical work and\ninvestigate the three-body bound states (trimers) for the case where the\ntwo-body short-range interactions between fermions are unequal. Using the\nscattering parameters from experiments on ultracold $^{6}$Li atoms, we\ncalculate the trimer spectrum throughout the crossover from two to three\ndimensions. We find that the deepest Efimov trimer in the $^{6}$Li system is\nunaffected by realistic quasi-2D confinements, while the first excited trimer\nsmoothly evolves from a 3D-like Efimov trimer to an extended 2D-like trimer as\nthe attractive interactions are decreased. We furthermore compute the excited\ntrimer wave function and quantify the stability of the trimer with respect to\nthree-body recombination by determining the probability that three fermions\napproach each other at short distances. Our results indicate that the lifetime\nof the trimer can be enhanced by at least an order of magnitude in the quasi-2D\ngeometry, thus opening the door to realizing long-lived trimers in\nthree-component Fermi gases."
    },
    {
        "anchor": "Majorana edge states in two atomic wires coupled by pair-hopping: We present evidence for the existence of Majorana edge states in a number\nconserving theory describing a system of spinless fermions on two wires that\nare coupled by a pair hopping. Our analysis is based on the combination of a\nqualitative low energy approach and numerical techniques using the Density\nMatrix Renormalization Group. We also discuss an experimental realization of\npair-hopping interactions in cold atom gases confined in optical lattices, and\nits possible alternative applications to quantum simulation.",
        "positive": "Long distance optical transport of ultracold atoms: A compact setup\n  using a Moir\u00e9 lens: We present a compact and robust setup to optically transport ultracold atoms\nover long distances. Using a focus-tunable Moir\\'e lens that has recently\nappeared on the market, we demonstrate transport of up to a distance of 465 mm.\nA transfer efficiency of 70% is achieved with negligible temperature change at\n11 $\\mu$K. With its high thermal stability and low astigmatism, the Moir\\'e\nlens is superior to fluid-based varifocal lenses. It is much more compact and\nstable than a lens mounted on a linear translation stage, allowing for\nsimplified experimental setups."
    },
    {
        "anchor": "Absence of heating in a uniform Fermi gas created by periodic driving: Ultracold atomic gas provides a useful tool to explore many-body physics. One\nof the recent additions to this experimental toolbox is the Floquet\nengineering, where periodic modulation of the Hamiltonian allows the creation\nof effective potentials that do not exist otherwise. When subject to external\nmodulations, however, generic interacting many-body systems absorb energy, thus\nposing a heating problem that may impair the usefulness of this method. For\ndiscrete systems with bounded local energy, an exponentially suppressed heating\nrate with the driving frequency has been observed previously, leaving the\nsystem in a prethermal state for exceedingly long durations. But for systems in\ncontinuous space, the situation remains unclear. Here we show that Floquet\nengineering can be employed to a strongly interacting degenerate Fermi gas held\nin a flat box-like potential without inducing excessive heating on\nexperimentally relevant timescales. The driving eliminates the effect of a\nspin-dependent potential originating from a simultaneous magnetic levitation of\ntwo different spin states. We calculate the heating rate and obtain a power-law\nsuppression with the drive frequency. To further test the many-body behavior of\nthe driven gas, we measure both the pair-condensation fraction at unitarity and\nthe contact parameter across the BEC-BCS crossover. At low driving frequencies,\nthe condensate fraction is reduced by the time-dependent force, but at higher\nfrequencies, it revives and attains an even higher value than without driving.\nOur results are promising for future exploration of exotic many-body phases of\na bulk strongly-interacting Fermi gas with dynamically engineered Hamiltonians.",
        "positive": "Scaling of Fluctuations in a Trapped Binary Condensate: We demonstrate that measurements of number fluctuations within finite cells\nprovide a direct means to study fluctuation scaling in a trapped two-component\ncondensate. This quantum system supports a second-order phase transition\nbetween miscible (co-spatial) and immiscible (symmetry-broken) states that is\ndriven by a diverging susceptibility to magnetic fluctuations. As the\ntransition is approached from the miscible side the magnetic susceptibility is\nfound to depend strongly on the geometry and orientation of the observation\ncell. However, a scaling exponent consistent with that for the homogenous gas\n($\\gamma = 1$) can be recovered, for all cells considered, as long as the fit\nexcludes the region in the immediate vicinity of the critical point. As the\ntransition is approached from the immiscible side, the magnetic fluctuations\nexhibit a non-trivial scaling exponent $\\gamma \\simeq 1.30$. Experimentally,\nthe observation cells may be formed either by considering individual imaging\npixels or by combining pixels to form larger cells, and fluctuation statistics\ncan be obtained by repeated \\emph{in situ} images. Interestingly, on both sides\nof the transition, we find it best to extract the exponents using an\nobservation cell that covers half of the trapped system. This implies that\nrelatively low-resolution \\emph{in situ} imaging will be adequate for the\ninvestigation of these exponents. We also investigate the gap energy and find\nexponents $\\nu z$ = 0.505 on the miscible side and, unexpectedly, $\\nu z$ =\n0.60(3) for the immiscible phase."
    },
    {
        "anchor": "Noise Correlation Scalings: Revisiting the Quantum Phase Transition in\n  Incommensurate Lattices with Hard-Core Bosons: Finite size scalings of the momentum distribution and noise correlations are\nperformed to study Mott insulator, Bose glass, and superfluid quantum phases in\nhard-core bosons (HCBs) subjected to quasi-periodic disorder. The exponents of\nthe correlation functions at the Superfluid to Bose glass (SF-BG) transition\nare found to be approximately one half of the ones that characterizes the\nsuperfluid phase. The derivatives of the peak intensities of the correlation\nfunctions with respect to quasiperiodic disorder are shown to diverge at the\nSF-BG critical point. This behavior does not occur in the corresponding free\nfermion system, which also exhibits an Anderson-like transition at the same\ncritical point, and thus provides a unique experimental tool to locate the\nphase transition in interacting bosonic systems. We also report on the absence\nof primary sublattice peaks in the momentum distribution of the superfluid\nphase for special fillings.",
        "positive": "Non-Hermitian quantum gases: a platform for imaginary time crystals: One of the most important applications of quantum mechanics is the\nthermodynamic description of quantum gases. Despite the fundamental importance\nof this topic, a comprehensive description of the thermodynamic properties of\nnon-Hermitian quantum gases is still lacking. Here, we investigate the\nproperties of bosonic and fermionic non-Hermitian systems at finite\ntemperatures. We show that non-Hermitian systems exihibit oscillations both in\ntemperature and imaginary time. As such, they can be a possible platform to\nrealize an imaginary time crystal (iTC) phase. The Hatano-Nelson model is\nidentified as a simple lattice model to reveal this effect. In addition, we\nshow that the conditions for the iTC to be manifest are the same as the\nconditions for the presence of disorder points, where the correlation functions\nshow oscillating behavior. This analysis makes clear that our realization of\niTC is effectively a way to filter one specific Matsubara mode. In this\nrealization, the Matsubara frequency, that enters as a mathematical tool to\ncompute correlation functions for finite temperatures, can be measured\nexperimentally."
    },
    {
        "anchor": "The lowest scattering state of one-dimensional Bose gas with attractive\n  interactions: We investigate the lowest scattering state of one-dimensional Bose gas with\nattractive interactions trapped in a hard wall trap. By solving the Bethe\nansatz equation numerically we determine the full energy spectrum and the exact\nwave function for different attractive interaction parameters. The resultant\ndensity distribution, momentum distribution, reduced one body density matrix\nand two body correlation show that the decreased attractive interaction induces\nrich density profiles and specific correlation properties in the weakly\nattractive Bose gas.",
        "positive": "Bose polaron interactions in a cavity-coupled monolayer semiconductor: The interaction between a mobile quantum impurity and a bosonic bath leads to\nthe formation of quasiparticles, termed Bose polarons. The elementary\nproperties of Bose polarons, such as their mutual interactions, can differ\ndrastically from those of the bare impurities. Here, we explore Bose polaron\nphysics in a two-dimensional nonequilibrium setting by injecting $\\sigma^-$\npolarised exciton-polariton impurities into a bath of coherent $\\sigma^+$\npolarised polaritons generated by resonant laser excitation of monolayer\nMoSe$_2$ embedded in an optical cavity. By exploiting a biexciton Feshbach\nresonance between the impurity and the bath polaritons, we tune the interacting\nsystem to the strong-coupling regime and demonstrate the coexistence of two new\nquasiparticle branches. Using time-resolved pump-probe measurements we observe\nhow polaron dressing modifies the interaction between impurity polaritons.\nRemarkably, we find that the interactions between high-energy polaron\nquasiparticles, that are repulsive for small bath occupancy, can become\nattractive in the strong impurity-bath coupling regime. Our experiments provide\nthe first direct measurement of Bose polaron-polaron interaction strength in\nany physical system and pave the way for exploration and control of many-body\ncorrelations in driven-dissipative settings."
    },
    {
        "anchor": "Out-of-equilibrium dynamics of a Bose Einstein condensate in a\n  periodically driven band system: We report on the out-of-equilibrium dynamics of a Bose-Einstein condensate\n(BEC) placed in an optical lattice whose phase is suddenly modulated. The\nfrequency and the amplitude of modulation are chosen to ensure a negative\nrenormalized tunneling rate. Under these conditions, staggered states are\nnucleated by a spontaneous four wave mixing mechanism. The nucleation time is\nexperimentally studied as a function of the renormalized tunnel rate, the\natomic density and the modulation frequency. Our results are quantitatively\nwell accounted for by a Truncated Wigner approach and reveal the nucleation of\ngap solitons after the quench. We discuss the role of quantum versus thermal\nfluctuations in the nucleation process and experimentally address the limit of\nthe effective Hamiltonian approach.",
        "positive": "Adiabatic preparation of many-body states in optical lattices: We analyze a technique for the preparation of low entropy many body states of\natoms in optical lattices based on adiabatic passage. In particular, we show\nthat this method allows preparation of strongly correlated states as stable\nhighest energy states of Hamiltonians that have trivial ground states. As an\nexample, we analyze the generation of antiferromagnetically ordered states by\nadiabatic change of a staggered field acting on the spins of bosonic atoms with\nferromagnetic interactions."
    },
    {
        "anchor": "Topological p_x+ip_y Superfluid Phase of Fermionic Polar Molecules: We discuss the topological p_x+ip_y superfluid phase in a 2D gas of\nsingle-component fermionic polar molecules dressed by a circularly polarized\nmicrowave field. This phase emerges because the molecules may interact with\neach other via a potential V_0(r) that has an attractive dipole-dipole 1/r^3\ntail, which provides p-wave superfluid pairing at fairly high temperatures. We\ncalculate the amplitude of elastic p-wave scattering in the potential V_0(r)\ntaking into account both the anomalous scattering due to the dipole-dipole tail\nand the short-range contribution. This amplitude is then used for the\nanalytical and numerical solution of the renormalized BCS gap equation which\nincludes the second order Gor'kov-Melik-Barkhudarov corrections and the\ncorrection related to the effective mass of the quasiparticles. We find that\nthe critical temperature T_c can be varied within a few orders of magnitude by\nmodifying the short-range part of the potential V_0(r). The decay of the system\nvia collisional relaxation of molecules to dressed states with lower energies\nis rather slow due to the necessity of a large momentum transfer. The presence\nof a constant transverse electric field reduces the inelastic rate, and the\nlifetime of the system can be of the order of seconds even at 2D densities ~\n10^9 cm^{-2}. This leads to T_c of up to a few tens of nanokelvins and makes it\nrealistic to obtain the topological p_x+ip_y phase in experiments with\nultracold polar molecules.",
        "positive": "Self-Bayesian Aberration Removal via Constraints for Ultracold Atom\n  Microscopy: High-resolution imaging of ultracold atoms typically requires custom high\nnumerical aperture (NA) optics, as is the case for quantum gas microscopy.\nThese high NA objectives involve many optical elements each of which\ncontributes to loss and light scattering, making them unsuitable for quantum\nback-action limited \"weak\" measurements. We employ a low cost high NA aspheric\nlens as an objective for a practical and economical-although aberrated-high\nresolution microscope to image ${^{87}\\mathrm{Rb}}$ Bose-Einstein condensates.\nHere, we present a novel methodology for digitally eliminating the resulting\naberrations that is applicable to a wide range of imaging strategies and\nrequires no additional hardware. We recover nearly the full NA of our\nobjective, thereby demonstrating a simple and powerful digital aberration\ncorrection method for achieving optimal microscopy of quantum objects. This\nreconstruction relies on a high quality measure of our imaging system's\neven-order aberrations from density-density correlations measured with\ndiffering degrees of defocus. We demonstrate our aberration compensation\ntechnique using phase contrast imaging, a dispersive imaging technique directly\napplicable to quantum back-action limited measurements. Furthermore, we show\nthat our digital correction technique reduces the contribution of photon shot\nnoise to density-density correlation measurements which would otherwise\ncontaminate the desired quantum projection noise signal in weak measurements."
    },
    {
        "anchor": "More on the universal equation for Efimov states: Efimov states are a sequence of shallow three-body bound states that arise\nwhen the two-body scattering length is much larger than the range of the\ninteraction. The binding energies of these states are described as a function\nof the scattering length and one three-body parameter by a transcendental\nequation involving a universal function of one angular variable. We provide an\naccurate and convenient parametrization of this function. Moreover, we discuss\nthe effective treatment of range corrections in the universal equation and\ncompare with a strictly perturbative scheme.",
        "positive": "Correlation dynamics of dipolar bosons in 1D triple well optical lattice: The concept of spontaneous symmetry breaking and off-diagonal long-range\norder (ODLRO) are associated with Bose-Einstein condensation. However, as in\nthe system of reduced dimension the effect of quantum fluctuation is\ndominating, the concept of ODLRO becomes more interesting, especially for the\nlong-range interaction. In the present manuscript, we study the correlation\ndynamics triggered by lattice depth quench in a system of three dipolar bosons\nin a 1D triple-well optical lattice from the first principle using the\nmulticonfigurational time-dependent Hartree method for bosons (MCTDHB). Our\nmain motivation is to explore how ODLRO develops and decays with time when the\nsystem is brought out-of-equilibrium by a sudden change in the lattice depth.\nWe compare results of dipolar bosons with contact interaction. For forward\nquench $(V_{f} > V_{i})$, the system exhibits the collapse-revival dynamics in\nthe time evolution of normalized first- and second-order Glauber's correlation\nfunction, time evolution of Shannon information entropy both for the contact as\nwell as for the dipolar interaction which is reminiscent of the one observed in\nGreiner's experiment [Nature, {415}, (2002)]. We define the collapse and\nrevival time ratio as the figure of merit ($\\tau$) which can uniquely\ndistinguish the timescale of dynamics for dipolar interaction from that of\ncontact interaction. In the reverse quench process $(V_{i} > V_{f})$, for\ndipolar interaction, the dynamics is complex and the system does not exhibit\nany definite time scale of evolution, whereas the system with contact\ninteraction exhibits collapse-revival dynamics with a definite time-scale. The\nlong-range repulsive tail in the dipolar interaction inhibits the spreading of\ncorrelation across the lattice sites."
    },
    {
        "anchor": "Quantum critical behavior of a three-dimensional superfluid-Mott glass\n  transition: The superfluid to insulator quantum phase transition of a three-dimensional\nparticle-hole symmetric system of disordered bosons is studied. To this end, a\nsite-diluted quantum rotor Hamiltonian is mapped onto a classical\n(3+1)-dimensional XY model with columnar disorder and analyzed by means of\nlarge-scale Monte Carlo simulations. The superfluid-Mott insulator transition\nof the clean, undiluted system is in the 4D XY universality class and shows\nmean-field critical behavior with logarithmic corrections. The clean\ncorrelation length exponent $\\nu = 1/2$ violates the Harris criterion,\nindicating that disorder must be a relevant perturbation. For nonzero dilutions\nbelow the lattice percolation threshold of $p_c = 0.688392$, our simulations\nyield conventional power-law critical behavior with dilution-independent\ncritical exponents $z=1.67(6)$, $\\nu = 0.90(5)$, $\\beta/\\nu = 1.09(3)$, and\n$\\gamma/\\nu = 2.50(3)$. The critical behavior of the transition across the\nlattice percolation threshold is controlled by the classical percolation\nexponents. Our results are discussed in the context of a classification of\ndisordered quantum phase transitions, as well as experiments in superfluids,\nsuperconductors and magnetic systems.",
        "positive": "Dynamic Control of Magnetically Trapped Indirect Excitons by Using\n  External Magnetic Bias: We demonstrate an on demand spatial control of excitonic magnetic lattices\nfor the potential applications of excitonic-based quantum optical devices. A\ntwo dimensional magnetic lattice of indirect excitons can form a transition to\none dimensional lattice configuration under the influence of external magnetic\nbias fields. The transition is identified by measuring the spatial distribution\nof two dimensional photoluminance for several values of the external magnetic\nbias fields. The number of the trapped excitons is found to increase between\nsites along a perpendicular direction exhibiting two to one dimensional lattice\ntransition. This work may apply for various controllable quantum simulations,\nsuch as superfluid-Mott-insulators, in quantum optical devices."
    },
    {
        "anchor": "Super-Tonks-Girardeau quench of dipolar bosons in a one-dimensional\n  optical lattice: A super-Tonks-Giradeau gas is a highly excited yet stable quantum state of\nstrongly attractive bosons confined to one dimension. This state can be\nobtained by quenching the interparticle interactions from the ground state of a\nstrongly repulsive Tonks-Girardeau gas to the strongly attractive regime. While\nthe super-Tonks-Girardeau quench with contact interactions has been thoroughly\nstudied, less is known about the stability of such a procedure when long-range\ninteractions come into play. This is a particularly important question in light\nof recent advances in controlling ultracold atoms with dipole-dipole\ninteractions. In this study, we thus simulate a super-Tonks-Girardeau quench on\ndipolar bosons in a one-dimensional optical lattice and investigate their\ndynamics for many different initial states and fillings. By calculating\nparticle density, correlations, entropy measures, and natural occupations, we\nestablish the regimes of stability as a function of dipolar interaction\nstrength. For an initial unit-filled Mott state, stability is retained at weak\ndipolar interactions. For cluster states and doubly-filled Mott states,\ninstead, dipolar interactions eventually lead to complete evaporation of the\ninitial state and thermalization consistent with predictions from random matrix\ntheory. Remarkably, though, dipolar interactions can be tuned to achieve\nlonger-lived prethermal states before the eventual thermalization. Our study\nhighlights the potential of long-range interactions to explore new mechanisms\nto steer and stabilize excited quantum states of matter.",
        "positive": "Reply to Comment on \"Quantum Entangled Dark Solitons formed by Ultracold\n  Atoms in Optical Lattices\": We reply to Jacek Dziarmaga, Piotr Deuar, and Krzysztof Sacha's comment,\narXiv:1001.1045, supporting the authors' simulations but differentiating\nbetween near-mean-field and strongly quantum regimes. We clarify that we have\nthree lines of evidence on decay of dark solitons and connect our work to\nLieb's Type-II excitations and the true meaning of a quantum dark soliton."
    },
    {
        "anchor": "Faraday waves in binary non-miscible Bose-Einstein condensates: We show by extensive numerical simulations and analytical variational\ncalculations that elongated binary non-miscible Bose-Einstein condensates\nsubject to periodic modulations of the radial confinement exhibit a Faraday\ninstability similar to that seen in one-component condensates. Considering the\nhyperfine states of $^{87}$Rb condensates, we show that there are two\nexperimentally relevant stationary state configurations: the one in which the\ncomponents form a dark-bright symbiotic pair (the ground state of the system),\nand the one in which the components are segregated (first excited state). For\neach of these two configurations, we show numerically that far from resonances\nthe Faraday waves excited in the two components are of similar periods, emerge\nsimultaneously, and do not impact the dynamics of the bulk of the condensate.\nWe derive analytically the period of the Faraday waves using a variational\ntreatment of the coupled Gross-Pitaevskii equations combined with a\nMathieu-type analysis for the selection mechanism of the excited waves.\nFinally, we show that for a modulation frequency close to twice that of the\nradial trapping, the emergent surface waves fade out in favor of a forceful\ncollective mode that turns the two condensate components miscible.",
        "positive": "Few-body perspective on fermionic pairing in one spatial dimension: In this perspective we discuss recent theoretical and experimental concepts\ngiving a route to a better understanding of conventional and unconventional\npairing mechanisms between opposite-spin fermions arising in one-dimensional\nmesoscopic systems. With special attention, we focus on the problem of\nexperimental detectability of correlations between particles. We argue that\nstate-of-the-art experiments with few ultracold fermions may finally break an\nimpasse and give pioneering and unquestionable verification of the existence of\ncorrelated pairs with non-zero center-of-mass momentum."
    },
    {
        "anchor": "Non-equilibrium dynamics of bosonic atoms in optical lattices:\n  Decoherence of many-body states due to spontaneous emission: We analyze in detail the heating of bosonic atoms in an optical lattice due\nto incoherent scattering of light from the lasers forming the lattice. Because\natoms scattered into higher bands do not thermalize on the timescale of typical\nexperiments, this process cannot be described by the total energy increase in\nthe system alone (which is determined by single-particle effects). The heating\ninstead involves an important interplay between the atomic physics of the\nheating process and the many-body physics of the state. We characterize the\neffects on many-body states for various system parameters, where we observe\nimportant differences in the heating for strongly and weakly interacting\nregimes, as well as a strong dependence on the sign of the laser detuning from\nthe excited atomic state. We compute heating rates and changes to\ncharacteristic correlation functions based both on perturbation theory\ncalculations, and a time-dependent calculation of the dissipative many-body\ndynamics. The latter is made possible for 1D systems by combining\ntime-dependent density matrix renormalization group (t-DMRG) methods with\nquantum trajectory techniques.",
        "positive": "Time and temperature-dependent correlation function of an impurity in a\n  one-dimensional Fermi gas as a Fredholm determinant: We investigate a free one-dimensional spinless Fermi gas, and the\nTonks-Girardeau gas interacting with a single impurity particle of equal mass.\nWe obtain a Fredholm determinant representation for the time-dependent\ncorrelation function of the impurity particle. This representation is valid for\nan arbitrary temperature and an arbitrary repulsive or attractive impurity-gas\n$\\delta$-function interaction potential. It includes, as particular cases, the\nrepresentations obtained for zero temperature and arbitrary repulsion in [Nucl.\nPhys. B 892, 83 (2015)], and for arbitrary temperature and infinite repulsion\nin [Nucl. Phys. B 520, 594 (1998)]."
    },
    {
        "anchor": "Two Atoms in a Double Well: An Exact Solution: We propose to experimentally realize an odd parity eigenstate $\\left\\vert\nb\\right\\rangle $ of two atoms in the double well. The occupation probability of\nthis state shows evident dependence on the interaction, distinct from the\nresult of two-mode model adopted in the Heidelberg experiment. The tunneling\ndynamics of two atoms starting from the $NOON$ state with infinite barrier\nheight can be derived from the exactly solved model of $\\delta $-barrier split\ndouble well based on a Bethe ansatz type hypothesis of the wave functions. We\nfind that the single particle tunneling transfer the probabilities between\ndouble occupancy and single occupancy of each well.",
        "positive": "Numerical modeling of exciton-polariton Bose--Einstein condensate in a\n  microcavity: A novel, optimized numerical method of modeling of an exciton-polariton\nsuperfluid in a semiconductor microcavity was proposed. Exciton-polaritons are\nspin-carrying quasiparticles formed from photons strongly coupled to excitons.\nThey possess unique properties, interesting from the point of view of\nfundamental research as well as numerous potential applications. However, their\nnumerical modeling is challenging due to the structure of nonlinear\ndifferential equations describing their evolution. In this paper, we propose to\nsolve the equations with a modified Runge--Kutta method of 4th order, further\noptimized for efficient computations. The algorithms were implemented in form\nof C++ programs fitted for parallel environments and utilizing vector\ninstructions. The programs form the EPCGP suite which have been used for\ntheoretical investigation of exciton-polaritons."
    },
    {
        "anchor": "Ground states of trapped spin-1 condensates in magnetic field: We consider a spin-1 Bose-Einstein condensate trapped in a harmonic potential\nunder the influence of a homogeneous magnetic field. We investigate spatial and\nspin structure of the mean-field ground states under constraints on the number\nof atoms and the total magnetization. We show that the trapping potential can\nmake the antiferromagnetic condensate separate into three, and ferromagnetic\ncondensate into two distinct phases. In the ferromagnetic case, the\nmagnetization is located in the center of the harmonic trap, while in the\nantiferromagnetic case magnetized phases appear in the outer regions. We\ndescribe how the transition from the Thomas-Fermi regime to the single-mode\napproximation regime with decreasing number of atoms results in the\ndisappearance of the domains. We suggest that the ground states can be created\nin experiment by adiabatically changing the magnetic field strength.",
        "positive": "Keldysh Green's function approach to coherence in a non-equilibrium\n  steady state: connecting Bose-Einstein condensation and lasing: Solid state quantum condensates often differ from previous examples of\ncondensates (such as Helium, ultra-cold atomic gases, and superconductors) in\nthat the quasiparticles condensing have relatively short lifetimes, and so as\nfor lasers, external pumping is required to maintain a steady state. On the\nother hand, compared to lasers, the quasiparticles are generally more strongly\ninteracting, and therefore better able to thermalise. This leads to questions\nof how to describe such non-equilibrium condensates, and their relation to\nequilibrium condensates and lasers. This chapter discusses in detail how the\nnon-equilibrium Green's function approach can be applied to the description of\nsuch a non-equilibrium condensate, in particular, a system of microcavity\npolaritons, driven out of equilibrium by coupling to multiple baths. By\nconsidering the steady states, and fluctuations about them, it is possible to\nprovide a description that relates both to equilibrium condensation and to\nlasing, while at the same time, making clear the differences from simple\nlasers."
    },
    {
        "anchor": "Nambu-Goldstone modes in segregated Bose-Einstein condensates: Nambu-Goldstone modes in immiscible two-component Bose-Einstein condensates\nare studied theoretically. In a uniform system, a flat domain wall is\nstabilized and then the translational invariance normal to the wall is\nspontaneously broken in addition to the breaking of two U(1) symmetries in the\npresence of two complex order parameters. We clarify properties of the\nlow-energy excitations and identify that there exist two Nambu-Goldstone modes:\nin-phase phonon with a linear dispersion and ripplon with a fractional\ndispersion. The signature of the characteristic dispersion can be verified in\nsegregated condensates in a harmonic potential.",
        "positive": "Quantum Melting of a Wigner crystal of Rotating Dipolar Fermions in the\n  Lowest Landau Level: We have investigated the behavior and stability of a Wigner crystal of\nrotating dipolar fermions in two dimensions. Using an ansatz wave function for\nthe ground state of rotating two-dimensional dipolar fermions, which occupy\nonly partially the lowest Landau level, we study the correlation energy,\nelastic moduli and collective modes of Wigner crystals in the lowest Landau\nlevel. We then calculate the mean square of the displacement vector of Wigner\ncrystals. The critical filling factor, below which the crystalline state is\nexpected, is evaluated at absolute zero by use of the Lindeman's criterion. We\nfind that the particle (hole) crystal is locally stable for filling factor is\nless than 1/15 (between filling factors 14/15 and 1), where the stable regime\nof the crystal is much narrower than the result from Baranov, Fehrmann and\nLewenstein, [Phys. Rev. Lett. 100, 200402 (2008)]."
    },
    {
        "anchor": "Efimov States of Heavy Impurities in a Bose-Einstein Condensate: We consider the problem of two heavy impurity particles embedded in a gas of\nweakly-interacting light mass bosonic particles in the condensed state. Using\nthe Bogoliubov approach to describe the bosonic gas and the Born-Oppenheimer\napproximation for the three-body dynamics, we calculate the modification to the\nheavy-heavy two-body potential due to the presence of the condensate. For the\ncase of resonant interaction between the light bosons and the impurities, we\npresent (semi)-analytical results for the potential in the limit of a large\ncondensate coherence length. In particular, we find a formula for the\nmodification of the Efimov scaling factor due to the presence of a degenerate\nbosonic gas background.",
        "positive": "Ultracold quantum wires with localized losses: many-body quantum Zeno\n  effect: We study a one-dimensional system of interacting spinless fermions subject to\na localized loss, where the interplay of gapless quantum fluctuations and\nparticle interactions leads to an incarnation of the quantum Zeno effect of\ngenuine many-body nature. This model constitutes a non-equilibrium counterpart\nof the paradigmatic Kane-Fisher potential barrier problem, and it exhibits\nstrong interaction effects due to the gapless nature of the system. As a\ncentral result, we show that the loss probability is strongly renormalized near\nthe Fermi momentum as a realization of the quantum Zeno effect, resulting in a\nsuppression of the emission of particles at the Fermi level. This is reflected\nin the structure of the particle momentum distribution, exhibiting a peak close\nto the Fermi momentum. We substantiate these findings by three complementary\napproaches: a real-space renormalization group of a general microscopic\ncontinuum model, a dynamical Hartree-Fock numerical analysis of a microscopic\nmodel on a lattice, and a renormalization group analysis based on an effective\nLuttinger liquid description incorporating mode-coupling effects."
    },
    {
        "anchor": "Mesoscopic Transport and Interferometry with Wavepackets of Ultracold\n  atoms: Effects of Quantum Coherence and Interactions: We propose a way to simulate mesoscopic transport processes with\ncounter-propagating wavepackets of ultracold atoms in quasi one-dimensional\n(1D) waveguides, and show quantitative agreement with analytical results. The\nmethod allows the study of a broad range of transport processes at the level of\nindividual modes, not possible in electronic systems. Typically suppressed\neffects of quantum coherence become manifest, along with the effects of tunable\ninteractions, which can be used to develop a simpler type of sensitive atom\ninterferometer.",
        "positive": "Localization of correlated fermions in optical lattices with speckle\n  disorder: Strongly correlated fermions in three- and two-dimensional optical lattices\nwith experimentally realistic speckle disorder are investigated. We extend and\napply the statistical dynamical mean-field theory, which treats local\ncorrelations non-perturbatively, to incorporate on-site and hopping-type\nrandomness on equal footing. Localization due to disorder is detected via the\nprobability distribution function of the local density of states. We obtain a\ncomplete paramagnetic ground state phase diagram for experimentally realistic\nparameters and find a strong suppression of the correlation-induced metal\ninsulator transition due to disorder. Our results indicate that the\nAnderson-Mott and the Mott insulator are not continuously connected due to the\nspecific character of speckle disorder. Furthermore, we discuss the effect of\nfinite temperature on the single-particle spectral function."
    },
    {
        "anchor": "Momentum distribution and coherence of a weakly interacting Bose gas\n  after a quench: We consider a weakly interacting uniform atomic Bose gas with a\ntime-dependent nonlinear coupling constant. By developing a suitable Bogoliubov\ntreatment we investigate the time evolution of several observables, including\nthe momentum distribution, the degree of coherence in the system, and their\ndependence on dimensionality and temperature. We rigorously prove that the\nlow-momentum Bogoliubov modes remain frozen during the whole evolution, while\nthe high-momentum ones adiabatically follow the change in time of the\ninteraction strength. At intermediate momenta we point out the occurrence of\noscillations, which are analogous to Sakharov oscillations. We identify two\nwide classes of time-dependent behaviors of the coupling for which an exact\nsolution of the problem can be found, allowing for an analytic computation of\nall the relevant observables. A special emphasis is put on the study of the\ncoherence property of the system in one spatial dimension. We show that the\nsystem exhibits a smooth \"light-cone effect,\" with typically no\nprethermalization.",
        "positive": "Spin liquid phases of Mott insulating ultracold bosons: Mott insulating ultracold gases posses a unique whole-atom exchange\ninteraction which enables large quantum fluctuations between the Zeeman\nsublevels of each atom. By strengthening this interaction---either through the\nuse of large-spin atoms, or by tuning the particle-particle interactions via\noptical Feshbach resonance---one may enhance fluctuations and facilitate the\nappearance of the long sought-after quantum spin liquid phase---all in the\nhighly tunable environment of cold atoms. To illustrate the relationship\nbetween the spin magnitude, interaction strength, and resulting magnetic\nphases, we present and solve a mean field theory for bosons optically confined\nto the one particle-per-site Mott state, using both analytic and numerical\nmethods. We find on a square lattice with bosons of hyperfine spin $f>2$, that\nmaking the repulsive s-wave scattering length through the singlet channel\nsmall---relative to the higher-order scattering channels---accesses a\nshort-range resonating valence bond (s-RVB) spin liquid phase."
    },
    {
        "anchor": "Single vortex-antivortex pair in an exciton polariton condensate: In a homogeneous two-dimensional system at non-zero temperature, although\nthere can be no ordering of infinite range, a superfluid phase is predicted for\na Bose liquid. The stabilization of phase in this superfluid regime is achieved\nby the formation of bound vortex-antivortex pairs. It is believed that several\ndifferent systems share this common behaviour, when the parameter describing\ntheir ordered state has two degrees of freedom, and the theory has been tested\nfor some of them. However, there has been no direct experimental observation of\nthe phase stabilization mechanism by a bound pair. Here we present an\nexperimental technique that can identify a single vortex-antivortex pair in a\ntwo-dimensional exciton polariton condensate. The pair is generated by the\ninhomogeneous pumping spot profile, and is revealed in the time-integrated\nphase maps acquired using Michelson interferometry, which show that the\ncondensate phase is only locally disturbed. Numerical modelling based on open\ndissipative Gross-Pitaevskii equation suggests that the pair evolution is quite\ndifferent in this non-equilibrium system compared to atomic condensates. Our\nresults demonstrate that the exciton polariton condensate is a unique system\nfor studying two-dimensional superfluidity in a previously inaccessible regime.",
        "positive": "Variational cluster approach for strongly correlated lattice bosons in\n  the superfluid phase: We extend the variational cluster approach to deal with strongly correlated\nlattice bosons in the superfluid phase. To this end, we reformulate the\napproach within a pseudoparticle formalism, whereby cluster excitations are\ndescribed by particlelike excitations. The approximation amounts to solving a\nmulticomponent noninteracting bosonic system by means of a multimode Bogoliubov\napproximation. A source-and-drain term is introduced in order to break U(1)\nsymmetry at the cluster level. We provide an expression for the grand\npotential, the single-particle normal and anomalous Green's functions, the\ncondensate density, and other static quantities. As a first nontrivial\napplication of the method we choose the two-dimensional Bose-Hubbard model and\nevaluate results in both the Mott and the superfluid phases. Our results show\nan excellent agreement with quantum Monte Carlo calculations."
    },
    {
        "anchor": "Damping of long wavelength collective modes in spinor Bose-Fermi\n  mixtures: Using an effective field theory we describe the low energy bosonic\nexcitations in a three dimensional ultra-cold mixture of spin-1 bosons and\nspin-1/2 fermions. We establish an interesting fermionic excitation induced\ngeneric damping of the usual undamped long wavelength bosonic collective\nGoldstone modes. Two states with bosons forming either a ferromagnetic or polar\nsuperfluid are studied. The linear dispersion of the bosonic Bogoliubov\nexcitations is preserved with a renormalized sound velocity. For the polar\nsuperfluid we find both gapless modes (density and spin) are damped, whereas in\nthe ferromagnetic superfluid we find the density (spin) mode is (not) damped.\nWe argue quite generally that this holds for any mixture of bosons and fermions\nthat are coupled through at least a density-density interaction. We discuss the\nimplications of our many-body interaction results for experiments on Bose-Fermi\nmixtures.",
        "positive": "How does geometry affect quantum gases?: In this work, we study the thermodynamic functions of quantum gases confined\nto spaces of various shapes, namely, a sphere, a cylinder, and an ellipsoid. We\nstart with the simplest situation, namely, a spinless gas treated within the\ncanonical ensemble framework. As a next step, we consider\n\\textit{noninteracting} gases (fermions and bosons) with the usage of the grand\ncanonical ensemble description. For this case, the calculations are performed\nnumerically. We also observe that our results may possibly be applied to\n\\textit{Bose-Einstein condensate} and to \\textit{helium dimer}. Moreover, the\nbosonic sector, independently of the geometry, acquires entropy and internal\nenergy greater than for the fermionic case. Finally, we also devise a model\nallowing us to perform analytically the calculations in the case of\n\\textit{interacting} quantum gases, and, afterwards, we apply it to a cubical\nbox."
    },
    {
        "anchor": "Universal relations between atomic dipolar relaxation and van der Waals\n  interaction: Dipolar relaxation happens when one or both colliding atoms flip their spins\nexothermically inside a magnetic ($B$) field. This work reports precise\nmeasurements of dipolar relaxation in a Bose-Einstein condensate of ground\nstate $^{87}$Rb atoms together with in-depth theoretical investigations.\nPrevious perturbative treatments fail to explain our observations except at\nvery small $B$-fields. By employing quantum defect theory based on analytic\nsolutions of asymptotic van der Waals interaction $-C_6/R^6$ ($R$ being\ninteratomic spacing), we significantly expand the applicable range of\nperturbative treatment. We find the $B$-dependent dipolar relaxation lineshapes\nare largely universal, determined by the coefficient $C_6$ and the associated\n$s$-wave scattering lengths $a_{\\rm sc}$ of the states before and after spin\nflips. This universality, which applies generally to other atomic species as\nwell, implicates potential controls of dipolar relaxation and related cold\nchemical reactions by tuning $a_{\\rm sc}$.",
        "positive": "Ultracold molecules for quantum simulation: rotational coherences in CaF\n  and RbCs: We explore the uses of ultracold molecules as a platform for future\nexperiments in the field of quantum simulation, focusing on two molecular\nspecies, $^{40}$Ca$^{19}$F and $^{87}$Rb$^{133}$Cs. We report the development\nof coherent quantum state control using microwave fields in both molecular\nspecies; this is a crucial ingredient for many quantum simulation applications.\nWe demonstrate proof-of-principle Ramsey interferometry measurements with\nfringe spacings of $\\sim 1~\\rm kHz$ and investigate the dephasing time of a\nsuperposition of $N=0$ and $N=1$ rotational states when the molecules are\nconfined. For both molecules, we show that a judicious choice of molecular\nhyperfine states minimises the impact of spatially varying transition-frequency\nshifts across the trap. For magnetically trapped $^{40}$Ca$^{19}$F we use a\nmagnetically insensitive transition and observe a coherence time of 0.61(3) ms.\nFor optically trapped $^{87}$Rb$^{133}$Cs we exploit an avoided crossing in the\nAC Stark shift and observe a maximum coherence time of 0.75(6) ms."
    },
    {
        "anchor": "Dispersion properties of transverse waves propagating in the\n  electrically polarized BECs: Further development of the method of quantum hydrodynamics in application for\nBose-Einstein condensates (BECs) is presented. To consider evolution of\npolarization direction along with particles movement we have developed\ncorresponding set of quantum hydrodynamic equations. It includes equations of\nthe polarization evolution and the polarization current evolution along with\nthe continuity equation and the Euler equation (the momentum balance equation).\nDispersion properties of the transverse waves including the electromagnetic\nwaves propagating through the BECs are considered. To this end we consider full\nset of the Maxwell equations for description of electromagnetic field dynamics.\nThis approximation gives us possibility to consider the electromagnetic waves\nalong with the matter waves. We find a splitting of the electromagnetic wave\ndispersion on two branches. As a result we have four solutions, two for the\nelectromagnetic waves and two for the matter waves, the last two are the\nconcentration-polarization waves appearing as a generalization of the\nBogoliubov mode. We also obtain that if the matter wave propagate perpendicular\nto external electric field when dipolar contribution does not disappear (as it\nfollows from our generalization of the Bogoliubov spectrum). In this case exist\na small dipolar frequency shift due to transverse electric field of\nperturbation.",
        "positive": "Antiferromagnetic Spinor Condensates are Quantum Rotors: We establish a theoretical correspondence between spin-one antiferromagnetic\nspinor condensates in an external magnetic field and quantum rotor models in an\nexternal potential. We show that the rotor model provides a conceptually clear\npicture of the possible phases and dynamical regimes of the antiferromagnetic\ncondensate. We also show that this mapping simplifies calculations of the\ncondensate's spectrum and wavefunctions. We use the rotor mapping to describe\nthe different dynamical regimes recently observed in $^{23}$Na condensates. We\nalso suggest a way to experimentally observe quantum mechanical effects\n(collapse and revival) in spinor condensates."
    },
    {
        "anchor": "Noise correlations of one-dimensional Bose mixtures in optical lattices: We study the noise correlations of one-dimensional binary Bose mixtures, as a\nprobe of their quantum phases. In previous work, we found a rich structure of\nmany-body phases in such mixtures, such as paired and counterflow\nsuperfluidity. Here we investigate the signature of these phases in the noise\ncorrelations of the atomic cloud after time-of-flight expansion, using both\nLuttinger liquid theory and the time-evolving block decimation (TEBD) method.\nWe find that paired and counterflow superfluidity exhibit distinctive features\nin the noise spectra. We treat both extended and inhomogeneous systems, and our\nnumerical work shows that the essential physics of the extended systems is\npresent in the trapped-atom systems of current experimental interest. For\npaired and counterflow superfluid phases, we suggest methods for extracting\nLuttinger parameters from noise correlation spectroscopy.",
        "positive": "Triplet character of 2D-fermion dimers arising from $s$-wave attraction\n  via spin-orbit coupling and Zeeman splitting: We theoretically study spin-$1/2$ fermions confined to two spatial dimensions\nand experiencing isotropic short-range attraction in the presence of both\nspin-orbit coupling and Zeeman spin splitting - a prototypical system for\ndeveloping topological superfluidity in the many-body sector. Exact solutions\nfor two-particle bound states are found to have a triplet contribution that\ndominates over the singlet part in an extended region of parameter space where\nthe combined Zeeman- and center-of-mass-motion-induced spin-splitting energy is\nlarge. The triplet character of dimers is purest in the regime of weak $s$-wave\ninteraction strength. Center-of-mass momentum is one of the parameters\ndetermining the existence of bound states, which we map out for both two- and\none-dimensional types of spin-orbit coupling. Distinctive features emerging in\nthe orbital part of the bound-state wave function, including but not limited to\nits $p$-wave character, provide observable signatures of unconventional\npairing."
    },
    {
        "anchor": "Atom-Dimer Scattering in a Three-Component Fermi Gas: Ultracold gases of three distinguishable particles with large scattering\nlengths are expected to show rich few-body physics related to the Efimov\neffect. We have created three different mixtures of ultracold 6Li atoms and\nweakly bound 6Li2 dimers consisting of atoms in three different hyperfine\nstates and studied their inelastic decay via atom-dimer collisions. We have\nfound resonant enhancement of the decay due to the crossing of Efimov-like\ntrimer states with the atom-dimer continuum in one mixture as well as minima of\nthe decay in another mixture, which we interpret as a suppression of exchange\nreactions of the type |12>+|3> -> |23>+|1>. Such a suppression is caused by\ninterference between different decay paths and demonstrates the possiblity to\nuse Efimov physics to control the rate constants for molecular exchange\nreactions in the ultracold regime.",
        "positive": "Thermal disruption of a Luttinger liquid: The Tomonaga-Luttinger liquid (TLL) theory describes the low-energy\nexcitations of strongly correlated one-dimensional (1D) fermions. In the past\nyears, a number of studies have provided a detailed understanding of this\nuniversality class. More recently, theoretical investigations that go beyond\nthe standard low-temperature, linear-response, TLL regime have been developed.\nWhile these provide a basis for understanding the dynamics of the\nspin-incoherent Luttinger liquid, there are few experimental investigations in\nthis regime. Here we report the observation of a thermally-induced,\nspin-incoherent Luttinger liquid in a $^6$Li atomic Fermi gas confined to 1D.\nWe use Bragg spectroscopy to measure the suppression of spin-charge separation\nand the decay of correlations as the temperature is increased. Our results\nprobe the crossover between the coherent and incoherent regimes of the\nLuttinger liquid, and elucidate the roles of the charge and the spin degrees of\nfreedom in this regime."
    },
    {
        "anchor": "Isothermal compressibility determination across Bose-Einstein\n  condensation: We apply the global thermodynamic variables approach to experimentally\ndetermine the isothermal compressibility parameter $\\kappa_T$ of a trapped Bose\ngas across the phase transition. We demonstrate the behavior of $\\kappa_T$\naround the critical pressure, revealing the second order nature of the phase\ntransition. Compressibility is the most important susceptibility to\ncharacterize the system. The use of global variables shows advantages with\nrespect to the usual local density approximation method and can be applied to a\nbroad range of situations.",
        "positive": "Resilience of constituent solitons in multisoliton scattering off\n  barriers: We introduce \"superheated integrability,\" which produces characteristic\nstaircase transmission plots for barrier collisions of breathers of the\nnonlinear Schr\\\"odinger equation. The effect makes tangible the inverse\nscattering transform, which treats the velocities and norms of the constituent\nsolitons as the real and imaginary parts of the eigenvalues of the Lax\noperator. If all the norms are much greater than the velocities, an\nintegrability-breaking potential may nonperturbatively change the velocities\nwhile having no measurable effect on the norms. This could be used to improve\natomic interferometers."
    },
    {
        "anchor": "Cold Atom Qubits: We discuss a laser-trapped cold-atom superfluid qubit system. Each qubit is\nproposed as a macroscopic two-state system based on a set of Bose-Einstein\ncondensate (BEC) currents circulating in a ring, cut with a Josephson barrier.\nWe review the effective low energy description of a single BEC ring. In\nparticular, it is demonstrated that such system has a set of metastable current\nstates which, for certain range of parameters, form an effective two-state\nsystem, or a qubit. We show how this qubit can be initialized and manipulated\nwith currently available laser-trapping techniques. We also discuss mechanisms\nof coupling several such ring qubits as well as measuring individual qubit-ring\nsystems.",
        "positive": "On the thermodynamics of fermions at any temperature based on\n  parametrized partition function: In this work we study the recently developed parametrized partition function\nformulation and show how we can infer the thermodynamic properties of fermions\nbased on numerical simulation of bosons and distinguishable particles at\nvarious temperatures. In particular, we show that in the three dimensional\nspace defined by energy, temperature and the parameter characterizing\nparametrized partition function, we can map the energies of bosons and\ndistinguishable particles to fermionic energies through constant-energy\ncontours. We apply this idea to both noninteracting and interacting Fermi\nsystems and show it is possible to infer the fermionic energies at all\ntemperatures, thus providing a practical and efficient approach to obtain\nthermodynamic properties of Fermi systems with numerical simulation. As an\nexample, we present energies and heat capacities for 10 noninteracting fermions\nand 10 interacting fermions (more fermions are provided in the appendix) and\nshow good agreement with the analytical result for noninteracting case."
    },
    {
        "anchor": "Imaging the decay of quantized vortex rings to decipher quantum\n  dissipation: Like many quantum fluids, superfluid helium-4 (He II) can be considered as a\nmixture of two miscible fluid components: an inviscid superfluid and a viscous\nnormal fluid consisting of thermal quasiparticles [1]. A mutual friction\nbetween the two fluids can emerge due to quasiparticles scattering off\nquantized vortex lines in the superfluid [2]. This quantum dissipation\nmechanism is the key for understanding various fascinating behaviors of the\ntwo-fluid system [3,4]. However, due to the lack of experimental data for\nguidance, modeling the mutual friction between individual vortices and the\nnormal fluid remains an unsettled topic despite decades of research [5-10].\nHere we report an experiment where we visualize the motion of quantized vortex\nrings in He II by decorating them with solidified deuterium tracer particles.\nBy examining how the rings spontaneously shrink and accelerate, we provide\nunequivocal evidences showing that only a recent theory [9] which accounts for\nthe coupled motion of the two fluids with a self-consistent local friction can\nreproduce the observed ring dynamics. Our work eliminates long-standing\nambiguities in our theoretical description of the vortex dynamics in He II,\nwhich will have a far-reaching impact since similar mutual friction concept has\nbeen adopted for a wide variety of quantum two-fluid systems, including atomic\nBose-Einstein condensates (BECs) [11,12], superfluid neutron stars [13-15], and\ngravity-mapped holographic superfluid [16,17].",
        "positive": "Spin-wave growth via Shapiro resonances in a spinor Bose-Einstein\n  condensate: We theoretically study the resonant phenomenon in a spin-1 Bose-Einstein\ncondensate periodically driven by a quadratic Zeeman coupling. This phenomenon\nis closely related to the Shapiro steps in superconducting Josephson junctions,\nand the previous experimental work [Evrard $et al.,$ Phys. Rev. A 100, 023604\n(2019)] for a spin-1 bosonic system observed the resonant dynamics and then\ncalled it Shapiro resonance. In this work, using the spin-1 Gross-Pitaevskii\nequation, we study the Shapiro resonance beyond the single-mode approximation\nused in the previous work, which assumes that all components of the spinor\nwavefunction have the same spatial configuration. Considering resonant dynamics\nstarting from a polar state, we analytically calculate the Floquet-Lyapunov\nexponents featuring an onset of the resonance under a linear analysis and find\nthat spin waves with finite wavenumbers can be excited. This kind of\nnon-uniform excitation cannot be described by the single-mode approximation.\nFurthermore, to study the long-time resonant dynamics beyond the linear\nanalysis, we numerically solve the one-dimensional spin-1 Gross-Pitaevskii\nequation, finding that the nonresonant hydrodynamic variables also grow at\nwavelengths of even multiples of the resonant one due to the nonlinear effect."
    },
    {
        "anchor": "Fulde-Ferrell superfluidity in ultracold Fermi gases with Rashba\n  spin-orbit coupling: We theoretically investigate the inhomogeneous Fulde-Ferrell (FF)\nsuperfluidity in a three dimensional atomic Fermi gas with Rashba spin-orbit\ncoupling near a broad Feshbach resonance. We show that within mean-field theory\nthe FF superfluid state is always more favorable than the standard\nBardeen-Cooper-Schrieffer (BCS) superfluid state when an in-plane Zeeman field\nis applied. We present a qualitative finite-temperature phase diagram near\nresonance and argue that the predicted FF superfluid is observable with\nexperimentally attainable temperatures (i.e., $T\\sim0.2T_{F}$, where $T_{F}$ is\nthe characteristic Fermi degenerate temperature).",
        "positive": "Projected Gross-Pitaevskii equation for ring-shaped Bose-Einstein\n  condensates: We propose an alternative implementation of the Projected Gross-Pitaevskki\nequation adapted for numerical modeling of the atomic Bose-Einstein condensate\ntrapped in a toroidally-shaped potential. We present an accurate and efficient\nscheme to evaluate the required matrix elements and calculate time evolution of\nthe matter wave field. We analyze the stability and accuracy of the developed\nmethod for equilibrium and nonequilibrium solutions in a ring-shaped trap with\nadditional barrier potential corresponding to recent experimental realizations."
    },
    {
        "anchor": "Critical velocity, vortex shedding and drag in a unitary Fermi\n  superfluid: We study the real-time motion of a microscopic object in a cold Fermi gas at\nunitary conditions by using an extended Thomas-Fermi density functional\napproach. We find that spontaneous creation of singly quantized\nvortex-antivortex pairs occurs as a critical velocity is exceeded, which leads\nto a drag between the moving object and the Fermi gas. The resulting force is\nlinear in the velocity for subsonic motion and becomes quadratic for supersonic\nmotion.",
        "positive": "Probing Majorana fermions in spin-orbit coupled atomic Fermi gases: We examine theoretically the visualization of Majorana fermions in a\ntwo-dimensional trapped ultracold atomic Fermi gas with spin-orbit coupling. By\nincreasing an external Zeeman field, the trapped gas transits from\nnon-topological to topological superfluid, via a mixed phase in which both\ntypes of superfluids coexist. We show that the zero-energy Majorana fermion,\nsupported by the topological superfluid and localized at the vortex core, is\nclearly visible through (i) the core density and (ii) the local density of\nstates, which are readily measurable in experiment. We present a realistic\nestimate on experimental parameters for ultracold $^{40}$K atoms."
    },
    {
        "anchor": "Suppression of the quasi-two-dimensional quantum collapse in the\n  attraction field by the Lee-Huang-Yang effect: Quantum collapse in three and two dimensions (3D and 2D) is induced by\nattractive potential ~ -1/r^2. It was demonstrated that the mean-field (MF)\ncubic self-repulsion in the 3D bosonic gas suppresses the collapse and creates\nthe missing ground state (GS). However, the cubic nonlinearity is not strong\nenough to suppress the 2D collapse. We demonstrate that the Lee-Hung-Yang (LHY)\nquartic term, induced by quantum fluctuations around the MF state, is\nsufficient for the stabilization of the 2D gas against the collapse. By means\nof numerical solution of the Gross-Pitaevskii equation including the LHY term,\nas well as with the help of analytical methods, such as expansions of the wave\nfunction at small and large distances from the center and the Thomas-Fermi\napproximation, we construct stable GS, with a singular density, ~ 1/r^{4/3},\nbut convergent integral norm. Counter-intuitively, the stable GS exists even if\nthe external potential is repulsive, with the strength falling below a certain\ncritical value. An explanation to this finding is given. Along with the GS,\nsingular vortex states are produced too, and their stability boundary is found\nanalytically. Unstable vortices spontaneously transform into the stable GS,\nexpelling the vorticity to periphery.",
        "positive": "Heavy-fermion valence-bond liquids in ultracold atoms: Cooperation of\n  Kondo effect and geometric frustration: We analyze a microscopic mechanism behind coexistence of a heavy Fermi liquid\nand geometric frustration in Kondo lattices. We consider a geometrically\nfrustrated periodic Anderson model and demonstrate how orbital fluctuations\nlead to a Kondo-screened phase in the limit of extreme strong frustration when\nonly local {\\it singlet} states participate in the low-energy physics. We also\npropose a setup to realize and study this exotic state with $SU (3)$-symmetric\nalkaline-earth cold atoms."
    },
    {
        "anchor": "Absence of a four-body Efimov effect in the 2 + 2 fermionic problem: In the free three-dimensional space, we consider a pair of identical\n$\\uparrow$ fermions of some species or in some internal state, and a pair of\nidentical $\\downarrow$ fermions of another species or in another state. There\nis a resonant $s$-wave interaction (that is of zero range and infinite\nscattering length) between fermions in different pairs, and no interaction\nwithin the same pair. We study whether this $2+2$ fermionic system can exhibit\n(as the $3+1$ fermionic system) a four-body Efimov effect in the absence of\nthree-body Efimov effect, that is the mass ratio $\\alpha$ between $\\uparrow$\nand $\\downarrow$ fermions and its inverse are both smaller than\n13.6069{\\ldots}. For this purpose, we investigate scale invariant zero-energy\nsolutions of the four-body Schr\\''odinger equation, that is positively\nhomogeneous functions of the coordinates of degree {$s-7/2$}, where $s$ is a\ngeneralized Efimov exponent {that becomes purely imaginary in the presence of a\nfour-body Efimov effect.} Using rotational invariance in momentum space, it is\nfound that the allowed values of $s$ are such that $M(s)$ has a zero\neigenvalue; here the operator $M(s)$, that depends on the total angular\nmomentum $\\ell$, acts on functions of two real variables (the cosine of the\nangle between two wave vectors and the logarithm of the ratio of their moduli),\nand we write it explicitly in terms of an integral matrix kernel. We have\nperformed a spectral analysis of $M(s)$, analytical and for an arbitrary\nimaginary $s$ for the continuous spectrum, numerical and limited to $s = 0$ and\n$\\ell \\le 12$ for the discrete spectrum. We conclude that no eigenvalue of\n$M(0)$ crosses zero over the mass ratio interval $\\alpha \\in [1,\n13.6069\\ldots]$, even if, in the parity sector $(-1)^{\\ell}$, the continuous\nspectrum of $M(s)$ has everywhere a zero lower border. As a consequence, there\nis no possibility of a four-body Efimov effect for the 2+2 fermions. We also\nenunciated a conjecture for the fourth virial coefficient of the unitary\nspin-$1/2$ Fermi gas,inspired from the known analytical form of the third\ncluster coefficient and involving the integral over the imaginary $s$-axis of\n$s$ times the logarithmic derivative of the determinant of $M(s)$ summed over\nall angular momenta.The conjectured value is in contradiction with the\nexperimental results.",
        "positive": "Dynamically generating arbitrary spin-orbit couplings for neutral atoms: Spin-orbit coupling (SOC) can give rise to interesting physics, from spin\nHall to topological insulators, normally in condensed matter systems. Recently,\nthis topical area has extended into atomic quantum gases in searching for\nartificial/synthetic gauge potentials. The prospects of tunable interaction and\nquantum state control promote neutral atoms as nature's quantum emulators for\nSOC. Y.-J. Lin {\\it et al.} recently demonstrated a special form of the SOC\n$k_x\\sigma_y$: which they interpret as an equal superposition of Rashba and\nDresselhaus couplings, in bose condensed atoms [Nature (London) \\textbf{471},\n83 (2011)]. This work reports an idea capable of implementing arbitrary forms\nof SOC by switching between two pairs of Raman laser pulses like that used by\nLin {\\it et al.}. While one pair affects $k_x\\sigma_y$ for some time, a second\npair creates $k_y\\sigma_y$ over other times with Raman pulses from different\ndirections and a subsequent spin rotation into $\\pm k_y\\sigma_x$. With\nsufficient many pulses, the effective actions from different durations are\nsmall and accumulate in the same exponent despite that $k_x\\sigma_y$ and $\\pm\nk_y\\sigma_x$ do not commute. Our scheme involves no added complication, and can\nbe demonstrated within current experiments. It applies equally to bosonic or\nfermionic atoms."
    },
    {
        "anchor": "Thermodynamics of an attractive 2D Fermi gas: Thermodynamic properties of matter are conveniently expressed as functional\nrelations between variables known as equations of state. Here we experimentally\ndetermine the compressibility, density and pressure equations of state for an\nattractive 2D Fermi gas in the normal phase as a function of temperature and\ninteraction strength. In 2D, interacting gases exhibit qualitatively different\nfeatures to those found in 3D. This is evident in the normalized density\nequation of state, which peaks at intermediate densities corresponding to the\ncrossover from classical to quantum behaviour.",
        "positive": "Nonperiodic oscillation of bright solitons in the condensates with a\n  periodically oscillating harmonic potential: Considering a periodically oscillating harmonic potential, we explore the\ndynamics properties of bright solitons in a Bose-Einstein condensate. It is\nfound that under a slower oscillating potential, soliton movement exhibits a\nnonperiodic oscillation while it is hardly affected under a fast oscillating\npotential. Furthermore, the head-on and/or \"chase\" collisions of two solitons\nhave been obtained, which can be controlled by the oscillating frequency of\npotential."
    },
    {
        "anchor": "Lifetime of Single-Particle Excitations in a Dilute Bose-Einstein\n  Condensate at Zero Temperature: We study the lifetime of single-particle excitations in a dilute homogeneous\nBose-Einstein condensate at zero temperature based on a self-consistent\nperturbation expansion of satisfying Goldstone's theorem and conservation laws\nsimultaneously.It is shown that every excitation for each momentum ${\\bf p}$\nshould have a finite lifetime proportional to the inverse $a^{-1}$ of the\n$s$-wave scattering length $a$, instead of $a^{-2}$ for the normal state, due\nto a new class of Feynman diagrams for the self-energy that emerges upon\ncondensation. We calculate the lifetime as a function of $|{\\bf p}|$\napproximately.",
        "positive": "Bose-Einstein condensation with a finite number of particles in a\n  power-law trap: Bose-Einstein condensation (BEC) of an ideal gas is investigated, beyond the\nthermodynamic limit, for a finite number $N$ of particles trapped in a generic\nthree-dimensional power-law potential. We derive an analytical expression for\nthe condensation temperature $T_c$ in terms of a power series in\n$x_0=\\epsilon_0/k_BT_c$, where $\\epsilon_0$ denotes the zero-point energy of\nthe trapping potential. This expression, which applies in cartesian,\ncylindrical and spherical power-law traps, is given analytically at infinite\norder. It is also given numerically for specific potential shapes as an\nexpansion in powers of $x_0$ up to the second order. We show that, for a\nharmonic trap, the well known first order shift of the critical temperature\n$\\Delta T_c/T_c \\propto N^{-1/3}$ is inaccurate when $N \\leqslant 10^{5}$, the\nnext order (proportional to $N^{-1/2}$) being significant. We also show that\nfinite size effects on the condensation temperature cancel out in a cubic\ntrapping potential, e.g. $V(\\mathbi{r}) \\propto r^3$. Finally, we show that in\na generic power-law potential of higher order, e.g. $V(\\mathbi{r}) \\propto\nr^\\alpha$ with $\\alpha > 3$, the shift of the critical temperature becomes\npositive. This effect provides a large increase of $T_c$ for relatively small\natom numbers. For instance, an increase of about +40% is expected with $10^4$\natoms in a $V(\\mathbi{r}) \\propto r^{12}$ trapping potential."
    },
    {
        "anchor": "Interaction-induced transparency for strong-coupling polaritons: The propagation of light in strongly coupled atomic media takes place through\nthe formation of polaritons - hybrid quasi-particles resulting from a\nsuperposition of an atomic and a photonic excitation. Here we consider the\npropagation under the condition of electromagnetically-induced transparency and\nshow that a novel many-body phenomenon can appear due to strong, dissipative\ninteractions between the polaritons. Upon increasing the photon-pump strength,\nwe find a first-order transition between an opaque phase with strongly\nbroadened polaritons and a transparent phase where a long-lived polariton\nbranch with highly tunable occupation emerges. Across this non-equilibrium\nphase transition, the transparency window is reconstructed via nonlinear\ninterference effects induced by the dissipative polariton interactions. Our\npredictions are based on a systematic diagrammatic expansion of the\nnon-equilibrium Dyson equations which is quantitatively valid, even in the\nnon-perturbative regime of large single-atom cooperativities, provided the\npolariton interactions are sufficiently long ranged. Such a regime can be\nreached in photonic crystal waveguides thanks to the tunability of\ninteractions, allowing to observe the interaction-induced-transparency\ntransition even at low polariton densities.",
        "positive": "Self-bound Bose mixtures: Recent experiments confirmed that fluctuations beyond the mean-field\napproximation can lead to self-bound liquid droplets of ultra-dilute binary\nBose mixtures. We proceed beyond the beyond-mean-field approximation, and study\nliquid Bose mixtures using the variational hypernetted-chain Euler Lagrange\nmethod, which accounts for correlations non-perturbatively. Focusing on the\ncase of a mixture of uniform density, as realized inside large saturated\ndroplets, we study the conditions for stability against evaporation of one of\nthe components (both chemical potentials need to be negative) and against\nliquid-gas phase separation (spinodal instability), the latter being\naccompanied by a vanishing speed of sound. Dilute Bose mixtures are stable only\nin a narrow range near an optimal ratio $\\rho_1/\\rho_2$ and near the total\nenergy minimum. Deviations from a universal dependence on the s-wave scattering\nlengths are significant despite the low density."
    },
    {
        "anchor": "Scaling of noise correlations in one-dimensional-lattice-hard-core-boson\n  systems: Noise correlations are studied for systems of hard-core bosons in\none-dimensional lattices. We use an exact numerical approach based on the\nBose-Fermi mapping and properties of Slater determinants. We focus on the\nscaling of the noise correlations with system size in superfluid and insulating\nphases, which are generated in the homogeneous lattice, with period-two\nsuperlattices and with uniformly distributed random diagonal disorder. For the\nsuperfluid phases, the leading contribution is shown to exhibit a\ndensity-independent scaling proportional to the system size, while the first\nsubleading term exhibits a density-dependent power-law exponent.",
        "positive": "Radiofrequency spectroscopy of one-dimensional trapped Bose polarons:\n  crossover from the adiabatic to the diabatic regime: We investigate the crossover of the impurity-induced dynamics, in trapped\none-dimensional Bose polarons subject to radio frequency (rf) pulses of varying\nintensity, from an adiabatic to a diabatic regime. Utilizing adiabatic pulses\nfor either weak repulsive or attractive impurity-medium interactions, a\nmultitude of polaronic excitations or mode-couplings of the impurity-bath\ninteraction with the collective breathing motion of the bosonic medium are\nspectrally resolved. We find that for strongly repulsive impurity-bath\ninteractions, a temporal orthogonality catastrophe manifests in resonances in\nthe excitation spectra where impurity coherence vanishes. When two impurities\nare introduced, impurity-impurity correlations, for either attractive or strong\nrepulsive couplings, induce a spectral shift of the resonances with respect to\nthe single impurity. For a heavy impurity, the polaronic peak is accompanied by\na series of equidistant side-band resonances, related to interference of the\nimpurity spin dynamics and the sound waves of the bath. In all cases, we enter\nthe diabatic transfer regime for an increasing bare Rabi frequency of the rf\nfield with a Lorentzian spectral shape featuring a single polaronic resonance.\nThe findings in this work on the effects of external trap, rf pulse and\nimpurity-impurity interaction should have implications for the new generations\nof cold-atom experiments."
    },
    {
        "anchor": "Spectral weight suppression in response functions of ultracold\n  fermion-boson mixtures: We study the dynamical response of ultracold fermion-boson mixture in the\nBogoliubov regime, where the interactions between fermionic impurities and\nbosonic excitations (phonons) are described by an effective Frohlich model\nunder the Bogoliubov approximation. A characteristic suppression of the\nsingle-particle spectral weight is found in the small momentum region where the\nimpurity band and phonon mode intersect. Using diagrammatic technique we\ncompute the Bragg spectra as well as the momentum dependent force-force\ncorrelation function. We fnd that both of them are heavily affected by the\nspectral weight suppression effect at low impurity densities in both 1D and 2D\nsystems. We show that the the spectral weight suppression feature in Bragg\nspectra, which was previously found in the quantum Monte Carlo simulations and\nwhich cannot be recovered by the random phase approximation, can be accurately\nreproduced with the help of vertex corrections.",
        "positive": "Two dispersion curves for a one-dimensional interacting Bose gas under\n  zero boundary conditions: The influence of boundaries and non-point character of interatomic\ninteraction on the dispersion law has been studied for a uniform Bose gas in a\none-dimensional vessel. The non-point character of interaction was taken into\naccount using the Gross equation, which is more general than the\nGross-Pitaevskii one. In the framework of this approach, the well-known\nBogolyubov dispersion mode \\hbar\\omega(k)=[(\\hbar^{2}k^{2}/2m)\n^{2}+qn\\nu(k)\\hbar^{2}k^{2}/m]^{1/2} (q=1) was obtained, as well as a new one,\nwhich is described by the same formula, but with q= 1/2. The new mode emerges\nowing to the account of boundaries and the non-point character of interaction:\nthis mode is absent when either the Gross equation for a cyclic system or the\nGross-Pitaevskii equation for a cyclic system or a system with boundaries is\nsolved. Capabilities for the new mode to be observed are discussed."
    },
    {
        "anchor": "Radio-frequency dressing of multiple Feshbach resonances: We demonstrate and theoretically analyze the dressing of several proximate\nFeshbach resonances in Rb-87 using radio-frequency (rf) radiation. We present\naccurate measurements and characterizations of the resonances, and the dramatic\nchanges in scattering properties that can arise through the rf dressing. Our\nscattering theory analysis yields quantitative agreement with the experimental\ndata. We also present a simple interpretation of our results in terms of\nrf-coupled bound states interacting with the collision threshold.",
        "positive": "Spatial and temporal coherence of a Bose-condensed gas: The central problem of this chapter is temporal coherence of a\nthree-dimensional spatially homogeneous Bose-condensed gas, initially prepared\nat finite temperature and then evolving as an isolated interacting system. A\nfirst theoretical tool is a number-conserving Bogoliubov approach that allows\nto describe the system as a weakly interacting gas of quasi-particles. This\napproach naturally introduces the phase operator of the condensate: a central\nactor since loss of temporal coherence is governed by the spreading of the\ncondensate phase-change. A second tool is the set of kinetic equations\ndescribing the Beliaev-Landau processes for the quasi-particles. We find that\nin general the variance of the condensate phase-change at long times $t$ is the\nsum of a ballistic term $\\propto t^2$ and a diffusive term $\\propto t$ with\ntemperature and interaction dependent coefficients. In the thermodynamic limit,\nthe diffusion coefficient scales as the inverse of the system volume. The\ncoefficient of $t^2$ scales as the inverse volume squared times the variance of\nthe energy of the system in the initial state and can also be obtained by a\nquantum ergodic theory (the so-called eigenstate thermalisation hypothesis)."
    },
    {
        "anchor": "Ultracold dense samples of dipolar RbCs molecules in the rovibrational\n  and hyperfine ground state: We produce ultracold dense trapped samples of 87Rb133Cs molecules in their\nrovibrational ground state, with full nuclear hyperfine state control, by\nstimulated Raman adiabatic passage (STIRAP) with efficiencies of 90%. We\nobserve the onset of hyperfine-changing collisions when the magnetic field is\nramped so that the molecules are no longer in the hyperfine ground state. A\nstrong quadratic shift of the transition frequencies as a function of applied\nelectric field shows the strongly dipolar character of the RbCs ground-state\nmolecule. Our results open up the prospect of realizing stable bosonic dipolar\nquantum gases with ultracold molecules.",
        "positive": "Disorder driven Thouless charge pump in a quasiperiodic chain: Thouless charge pump enables a quantized transport of charge through an\nadiabatic evolution of the Hamiltonian exhibiting topological phase. While this\ncharge pumping is known to be robust against the presence of weak disorder in\nthe system, it often breaks down with the increase in disorder strength. In\nthis work, however, we show that in a one dimensional Su-Schrieffer-Heeger\nlattice, a unit cell-wise staggered quasiperiodic disorder favors a quantized\ncharge pump. Moreover, we show that such quantized Thouless charge pump is\nachieved by following the standard single cycle pumping protocol which usually\nleads to a breakdown of charge pump in other known models. This unusual\nproperty is found to be due to an emergence of a trivial gapped phase from a\ntopological phase as the quasiperiodic disorder is tuned. This emergent gapped\nto gapped transition also allows us to propose a non-standard pumping scheme\nwhere a modulated disorder favors a quantized Thouless charge pump."
    },
    {
        "anchor": "Coupled oscillator model of a trapped Fermi gas at the BEC-BCS crossover: We address theoretically the puzzling discontinuity of the radial quadrupole\nmode frequency observed in a trapped Fermi gas across the BEC-BCS crossover. We\napply the scaling transformation to a two-channel model of a resonant Fermi\nsuperfluid and argue that the frequency downshift in the crossover region is\ndue to Feshbach coupling of the molecular Bose-Einstein condensate (BEC) to the\nsurrounding Fermi sea. The Bose and Fermi components of the gas act as coupled\nmacroscopic oscillators. The frequency jump corresponds to the point where the\nclosed-channel molecules are entirely converted into the Fermi sea. This\nimplies linear scaling of the \"critical\" detuning between the scattering\nchannels with the Fermi energy, which can be readily verified in an experiment.",
        "positive": "Building Flat-Band Lattice Models from Gram Matrices: We propose a powerful and convenient method to systematically design\nflat-band lattice models, which overcomes the difficulties underlying the\nprevious method. Especially, our method requires no elaborate calculations,\napplies to arbitrary spatial dimensions, and guarantees to result in a\ncompletely flat ground band. We use this method to generate several classes of\nlattice models, including models with both short- and long-range hoppings, both\ntopologically trivial and non-trivial flat bands. Some of these models were\npreviously known. Our method, however, provides crucial new insights. For\nexample, we have reproduced and generalized the Kapit-Mueller model [Kapit and\nMueller, Phys. Rev. Lett. \\textbf{105}, 215303 (2010)] and demonstrated a\nuniversal scaling rule between the flat band degeneracy and the magnetic flux\nthat was not noticed in previous studies. We show that the flat band of this\nmodel results from the (over-)completeness properties of coherent states."
    },
    {
        "anchor": "Dynamics of polar-core spin vortices in a ferromagnetic spin-1\n  Bose-Einstein condensate: A ferromagnetic spin-1 condensate supports polar-core spin vortices (PCVs) in\nthe easy-plane phase. We derive a model for the dynamics of these PCVs using a\nvariational Lagrangian approach. The PCVs behave as massive charged particles\ninteracting under the two dimensional Coulomb interaction, with the mass\narising from interaction effects within the vortex core. We compare this model\nto numerical simulations of the spin-1 Gross-Pitaevskii equations and find\nsemi-quantitative agreement. In addition, the numerical results suggest that\nthe PCV core couples to spin waves, and this affects the PCV dynamics even far\nfrom the core. We identify areas of further research that could extend the\nmodel of PCV dynamics presented here.",
        "positive": "Quantum degenerate mixtures of strontium and rubidium atoms: We report on the realization of quantum degenerate gas mixtures of the\nalkaline-earth element strontium with the alkali element rubidium. A key\ningredient of our scheme is sympathetic cooling of Rb by Sr atoms that are\ncontinuously laser cooled on a narrow linewidth transition. This versatile\ntechnique allows us to produce ultracold gas mixtures with a phase-space\ndensity of up to 0.06 for both elements. By further evaporative cooling we\ncreate double Bose-Einstein condensates of 87Rb with either 88Sr or 84Sr,\nreaching more than 10^5 condensed atoms per element for the 84Sr-87Rb mixture.\nThese quantum gas mixtures constitute an important step towards the production\nof a quantum gas of polar, open-shell RbSr molecules."
    },
    {
        "anchor": "Comment on \"Polar and antiferromagnetic order in f=1 boson systems\": An inequality for the lower bound of the average number of hyperfine\ncomponent $\\mu =0$ particles in the ground state of spin-1 condensates under a\nmagnetic field has been derived in ref.\\cite{tasa13}. It is shown in this\ncomment that, in a broad domain of parameters usually accessed in experiments,\nthe lower bound appears to be negative.\n  Thus the applicability of the inequality is very limited.",
        "positive": "Phase space curvature in spin-orbit coupled ultracold atom systems: We consider a system with spin-orbit coupling and derive equations of motion\nwhich include the effects of Berry curvatures. We apply these equations to\ninvestigate the dynamics of particles with equal Rashba-Dresselhaus spin-orbit\ncoupling in one dimension. In our derivation, the adiabatic transformation is\nperformed first and leads to quantum Heisenberg equations of motion for\nmomentum and position operators. These equations explicitly contain\nposition-space, momentum-space, and phase-space Berry curvature terms.\nSubsequently, we perform the semiclassical approximation, and obtain the\nsemiclassical equations of motion. Taking the low-Berry-curvature limit results\nin equations that can be directly compared to previous results for the motion\nof wavepackets. Finally, we show that in the semiclassical regime, the\neffective mass of the equal Rashba-Dresselhaus spin-orbit coupled system can be\nviewed as a direct effect of the phase-space Berry curvature."
    },
    {
        "anchor": "Observation of St\u00fcckelberg oscillations in accelerated optical\n  lattices: We report the experimental observation of St\\\"{u}ckelberg oscillations of\nmatter waves in optical lattices. Extending previous work on Landau-Zener\ntunneling of Bose-Einstein condensates in optical lattices, we study the\neffects of the accumulated phase between two successive crossings of the\nBrillouin zone edge. Our results agree well with a simple model for multiple\nLandau-Zener tunneling events taking into account the band structure of the\noptical lattice.",
        "positive": "Exact scaling of geometric phase and fidelity susceptibility and their\n  breakdown across the critical points: It was shown via numerical simulations that geometric phase (GP) and fidelity\nsusceptibility (FS) in some quantum models exhibit universal scaling laws\nacross phase transition points. Here we propose a singular function expansion\nmethod to determine their exact form across the critical points as well as\ntheir corresponding constants. For the models such as anisotropic XY model\nwhere the energy gap is closed and reopened at the special points ($k_0 = 0,\n\\pi$), scaling laws can be found as a function of system length $N$ and\nparameter deviation $\\lambda - \\lambda_c$ (where $\\lambda_c$ is the critical\nparameter). Intimate relations for the coefficients in GP and FS have also been\ndetermined. However in the extended models where the gap is not closed and\nreopened at these special points, the scaling as a function of system length\n$N$ breaks down. We also show that the second order derivative of GP also\nexhibits some intriguing scaling laws across the critical points. These exact\nresults can greatly enrich our understanding of GP and FS in the\ncharacterization of quantum phase transitions."
    },
    {
        "anchor": "Enhancement of boson superfluidity in a one-dimensional Bose-Fermi\n  mixture: We examine the effect of boson-fermion interaction in a one-dimensional\nBose-Fermi mixture by using the density matrix renormalization group method. We\nshow that the boson superfluidity is enhanced by fermions for a weak\nboson-fermion coupling at an approximate integer boson filling factor (e.g.,\n$0.935\\le \\rho_b \\le 1.0$), and this enhancement is produced both in a fermion\nmetallic state and in a fermion insulating state. A metal-insulator phase\ntransition of fermions induced by boson-fermion interaction is observed even\nthough there is no fermion-fermion interaction in the parent Hamiltonian.\nFurthermore, we find that the boson superfluid order and density wave order can\ncoexist in a deep fermion Mott region. All these features could be measured in\nfuture experiments and open up the possibility of detecting the new physical\neffect in the Bose-Fermi mixture.",
        "positive": "Scaling behaviour of trapped bosonic particles in two dimensions at\n  finite temperature: In the framework of the trap-size scaling theory, we study the scaling\nproperties of the Bose-Hubbard model in two dimensions in the presence of a\ntrapping potential at finite temperature. In particular, we provide results for\nthe particle density and the density-density correlator at the Mott transitions\nand within the superfluid phase. For the former quantity, numerical outcomes\nare also extensively compared to Local Density Approximation predictions."
    },
    {
        "anchor": "Observation of chiral edge states with neutral fermions in synthetic\n  Hall ribbons: Chiral edge states are a hallmark of quantum Hall physics. In electronic\nsystems, they appear as a macroscopic consequence of the cyclotron orbits\ninduced by a magnetic field, which are naturally truncated at the physical\nboundary of the sample. Here we report on the experimental realization of\nchiral edge states in a ribbon geometry with an ultracold gas of neutral\nfermions subjected to an artificial gauge field. By imaging individual sites\nalong a synthetic dimension, we detect the existence of the edge states,\ninvestigate the onset of chirality as a function of the bulk-edge coupling, and\nobserve the edge-cyclotron orbits induced during a quench dynamics. The\nrealization of fermionic chiral edge states is a fundamental achievement, which\nopens the door towards experiments including edge state interferometry and the\nstudy of non-Abelian anyons in atomic systems.",
        "positive": "Vortex lattice in spin-imbalanced unitary Fermi gas: We investigate the properties of a spin-imbalanced and rotating unitary Fermi\ngas. Using a density functional theory (DFT), we provide insight into states\nthat emerge as a result of a competition between Abrikosov lattice formation,\nspatial phase separation and the emergence of Fulde-Ferrell-Larkin-Ovchinnikov\n(FFLO) state. A confrontation of the experimental data [M. Zwierlein et al.,\nScience 311, 492 (2006)] with theoretical predictions provides a remarkable\nqualitative agreement. In case of gas confined in a harmonic trap, the phase\nseparation into a superfluid core populated by the Abrikosov lattice and a\nspin-polarized corona is the dominant process. Changing confinement to a\nbox-like trap, reverts the spatial location of the component: gas being in the\nnormal state is surrounded by superfluid threaded by quantum vortices. The\nvortex lattice no longer exhibits the triangular symmetry, and emergence of\nexotic geometries may be an indirect signature of the FFLO-like state formation\nin the system."
    },
    {
        "anchor": "Imaging of quantum Hall states in ultracold atomic gases: We examine off-resonant light scattering from ultracold atoms in the quantum\nHall regime. When the light scattering is spin dependent, we show that images\nformed in the far field can be used to distinguish states of the system. The\nspatial dependence of the far-field images is determined by the two-particle\nspin-correlation functions, which the images are related to by a\ntransformation. Quasiholes in the system appear in images of the density formed\nby collecting the scattered light with a microscope, where the quasihole\nstatistics are revealed by the reduction in density at the quasihole position.",
        "positive": "Neutral vortex necklace in a trapped planar superfluid: We study quantum vortex states consisting of a ring of vortices with\nalternating sign, in a homogeneous superfluid confined to a circular domain. We\nfind an exact stationary solution of the point vortex model for the neutral\nvortex necklace. We investigate the stability of the necklace state within both\nthe point-vortex model and the Gross-Pitaevskii equation describing a trapped\natomic Bose-Einstein condensate at low temperature. The point-vortex stationary\nstates are found to also be stationary states of the Gross-Pitaevskii equation\nprovided the finite thickness of the outer fluid boundary is accounted for.\nUnder significant perturbation, the Gross-Pitaevskii evolution and point-vortex\nmodel exhibit instability as expected for metastable states. The perturbed\nvortex necklace exhibits sensitivity to the perturbation, suggesting a route to\nseeding vortex chaos or quantum turbulence."
    },
    {
        "anchor": "Effects of Interactions on the Critical Temperature of a Trapped Bose\n  Gas: We perform high-precision measurements of the condensation temperature of a\nharmonically-trapped atomic Bose gas with widely-tuneable interactions. For\nweak interactions we observe a negative shift of the critical temperature in\nexcellent agreement with mean-field theory. However for sufficiently strong\ninteractions we clearly observe an additional positive shift, characteristic of\nbeyond-mean-field critical correlations. We also discuss non-equilibrium\neffects on the apparent critical temperature for both very weak and very strong\ninteractions.",
        "positive": "Kitaev honeycomb and other exotic spin models with polar molecules: We show that ultracold polar molecules pinned in an optical lattice can be\nused to access a variety of exotic spin models, including the Kitaev honeycomb\nmodel. Treating each molecule as a rigid rotor, we use DC electric and\nmicrowave fields to define superpositions of rotational levels as effective\nspin degrees of freedom, while dipole-dipole interactions give rise to\ninteractions between the spins. In particular, we show that, with sufficient\nmicrowave control, the interaction between two spins can be written as a sum of\nfive independently controllable Hamiltonian terms proportional to the five\nrank-2 spherical harmonics Y_{2,q}(theta,phi), where (theta,phi) are the\nspherical coordinates of the vector connecting the two molecules. To\ndemonstrate the potential of this approach beyond the simplest examples studied\nin [S. R. Manmana et al., arXiv:1210.5518v2], we focus on the realization of\nthe Kitaev honeycomb model, which can support exotic non-Abelian anyonic\nexcitations. We also discuss the possibility of generating spin Hamiltonians\nwith arbitrary spin S, including those exhibiting SU(N=2S+1) symmetry."
    },
    {
        "anchor": "Ehrenfest Dynamics and Frictionless Cooling Methods: Recently introduced methods which result in shortcuts to adiabaticity,\nparticularly in the context of frictionless cooling, are rederived and\ndiscussed in the framework of an approach based on Ehrenfest dynamics. This\nconstruction provides physical insights into the emergence of the Ermakov\nequation, the choice of its boundary conditions, and the use of minimum\nuncertainty states as indicators of the efficiency of the procedure.\nAdditionally, it facilitates the extension of frictionless cooling to more\ngeneral situations of physical relevance, such as optical dipole trapping\nschemes. In this context, we discuss frictionless cooling in the short-time\nlimit, a complementary case to the one considered in the literature, making\nexplicit the limitations intrinsic to the technique when the full\nthree-dimensional case is analyzed.",
        "positive": "Localized collapse and revival of coherence in an ultracold Bose gas: We study the collapse and revival of coherence induced by dipolar spin waves\nin a trapped gas of Rb-87 atoms. In particular we observe spatially localized\ncollapse and revival of Ramsey fringe contrast and show how the pattern of\ncoherence depends on strength of the spin wave excitation. We find that the\nspatial character of the coherence dynamics is incompatible with a simple model\nbased only on position-space overlap of wave functions. This phenomenon\nrequires a full phase-space description of the atomic spin using a quantum\nBoltzmann transport equation, which highlights spin wave-induced coherent spin\ncurrents and the ensuing dynamics they drive."
    },
    {
        "anchor": "Time-dependent self-trapping of Bose-Einstein Condensates in a\n  double-well potential: Based on the mean-field approximation and the phase space analysis, we\ndiscuss the dynamics of Bose-Einstein condensates in a double-well potential.\nBy applying a periodic modulation to the coupling between the condensates, we\nfind the condensates can be trapped in the time-dependent eigenstates of the\neffective Hamiltonian, we refer to this effect as time-dependent self-trapping\nof BECs. A comparison of this self-trapping with the adiabatic evolution is\nmade, finding that the adiabatic evolution beyond the traditional(linear)\nadiabatic condition can be achieved in BECs by manipulating the nonlinearity\nand the ratio of the level bias to the coupling constant. The fixed points for\nthe system are calculated and discussed.",
        "positive": "Dynamics of correlations in shallow optical lattices: We explore how correlations evolve in a gas of lattice bosons when the\nlattice depth is rapidly reduced. We find a simple closed form expression for\nthe static structure factor in the limit of vanishing interactions. The\ncorresponding real-space density correlation function shows multiple spatial\noscillations which linearly disperse as a function of time. By perturbatively\nincluding the effects of the interactions we calculate how the boson\nquasi-momentum evolves following the quench."
    },
    {
        "anchor": "Probing the conformal Calabrese-Cardy scaling with cold atoms: We demonstrate that current experiments using cold bosonic atoms trapped in\none-dimensional optical lattices and designed to measure the second-order Renyi\nentanglement entropy S_2, can be used to verify detailed predictions of\nconformal field theory (CFT) and estimate the central charge c. We discuss the\nadiabatic preparation of the ground state at half-filling where we expect a CFT\nwith c=1. This can be accomplished with a very small hoping parameter J, in\ncontrast to existing studies with density one where a much larger J is needed.\nWe provide two complementary methods to estimate and subtract the classical\nentropy generated by the experimental preparation and imaging processes. We\ncompare numerical calculations for the classical O(2) model with a chemical\npotential on a 1+1 dimensional lattice, and the quantum Bose-Hubbard\nHamiltonian implemented in the experiments. S_2 is very similar for the two\nmodels and follows closely the Calabrese-Cardy scaling, (c/8)\\ln(N_s), for N_s\nsites with open boundary conditions, provided that the large subleading\ncorrections are taken into account.",
        "positive": "Interplay of coherent and dissipative dynamics in condensates of light: Based on the Lindblad master equation approach we obtain a detailed\nmicroscopic model of photons in a dye-filled cavity, which features\ncondensation of light. To this end we generalise a recent non-equilibrium\napproach of Kirton and Keeling such that the dye-mediated contribution to the\nphoton-photon interaction in the light condensate is accessible due to an\ninterplay of coherent and dissipative dynamics. We describe the steady-state\nproperties of the system by analysing the resulting equations of motion of both\nphotonic and matter degrees of freedom. In particular, we discuss the existence\nof two limiting cases for steady states: photon Bose-Einstein condensate and\nlaser-like. In the former case, we determine the corresponding dimensionless\nphoton-photon interaction strength by relying on realistic experimental data\nand find a good agreement with previous theoretical estimates. Furthermore, we\ninvestigate how the dimensionless interaction strength depends on the\nrespective system parameters."
    },
    {
        "anchor": "Response of the Higgs amplitude mode of superfluid Bose gases in a three\n  dimensional optical lattice: We study the Higgs mode of superfluid Bose gases in a three dimensional\noptical lattice, which emerges near the quantum phase transition to the Mott\ninsulator at commensurate fillings. Specifically, we consider responses of the\nHiggs mode to temporal modulations of the onsite interaction and the hopping\nenergy. In order to calculate the response functions including the effects of\nquantum and thermal fluctuations, we map the Bose-Hubbard model onto an\neffective pseudospin-one model and use a perturbative expansion based on the\nimaginary-time Green's function theory. We also include the effects of an\ninhomogeneous trapping potential by means of a local density approximation. We\nfind that the response function for the hopping modulation is equal to that for\nthe interaction modulation within our approximation. At the unit filling rate\nand in the absence of a trapping potential, we show that the Higgs mode can\nexist as a sharp resonance peak in the dynamical susceptibilities at typical\ntemperatures. However, the resonance peak is significantly broadened due to the\ntrapping potential when the modulations are applied globally to the entire\nsystem. We suggest that the Higgs mode can be detected as a sharp resonance\npeak by partial modulations around the trap center.",
        "positive": "Exact quantum dynamics of bosons with finite-range time-dependent\n  interactions of harmonic type: The exactly solvable quantum many-particle model with harmonic one- and\ntwo-particle interaction terms is extended to include time-dependency. We show\nthat when the external trap potential and finite-range interparticle\ninteraction have a time-dependency the exact solutions of the corresponding\ntime-dependent many-boson Schr\\\"odinger equation are still available. We use\nthese exact solutions to benchmark the recently developed multiconfigurational\ntime-dependent Hartree method for bosons (MCTDHB) [Phys. Rev. Lett. {\\bf 99},\n030402 (2007), Phys. Rev. A {\\bf 77}, 033613 (2008)]. In particular, we\nbenchmark the MCTDHB method for: (i) the ground state; (ii) the breathing\nmany-body dynamics activated by a quench scenario where the interparticle\ninteraction strength is suddenly turned on to a finite value; (iii) the\nnon-equilibrium dynamic for driven scenarios where both the trap- and\ninterparticle-interaction potentials are {\\it time-dependent}. Excellent\nconvergence of the ground state and dynamics is demonstrated. The great\nrelevance of the self-consistency and time-adaptivity, which are the intrinsic\nfeatures of the MCTDHB method, is demonstrated by contrasting the MCTDHB\npredictions and those obtained within the standard full configuration\ninteraction method spanning the Fock space of the same size, but utilizing as\none-particle basis set the fixed-shape eigenstates of the one-particle\npotential. Connections of the model's results to ultra-cold Bose-Einstein\ncondensed systems are addressed."
    },
    {
        "anchor": "Interplay between coherent and dissipative dynamics of bosonic doublons\n  in an optical lattice: We observe the dissipative dynamics of a dense, strongly interacting gas of\nbosonic atom pairs in an optical lattice, controlling the strength of the\ntwo-body interactions over a wide parameter regime. We study how three-body\nlosses contribute to the lattice dynamics, addressing a number of open\nquestions related to the effects of strong dissipation in a many-body system,\nincluding the relationship to the continuous quantum Zeno effect. We observe\nrapid break-up of bound pairs for weak interactions, and for stronger\ninteractions we see doublon decay rates that are asymmetric when changing from\nattractive and repulsive interactions, and which strongly depend on the\ninteractions and on-site loss rates. By comparing our experimental data with a\ntheoretical analysis of few-body dynamics, we show that these features\noriginate from a non-trivial combination of dissipative dynamics described by a\nlattice model beyond a standard Bose-Hubbard Hamiltonian, and the modification\nof three-atom dynamics on a single site, which is generated alongside strong\nthree-body loss. Our results open new possibilities for investigating bosonic\natoms with strong three-body loss features, and allow for the better\nunderstanding of the parameter regimes that are required to realize strong\neffective three-body interactions.",
        "positive": "Doublon dynamics of Bose-Fermi mixtures in optical lattices: We study the out-of-equilibrium dynamics of a dilute, lattice-confined\nBose-Fermi mixture initialized in a highly excited state consisting of\nboson-fermion pairs (doublons) occupying single lattice sites. This system\nrepresents a paradigmatic case for studying relaxation dynamics in strongly\ncorrelated systems, and provides a versatile platform for studying\nthermalization and localization phenomena. We provide analytical expressions\nfor the short-time decay of isolated doublons and small doublon clusters due to\nthe competition between tunneling and interparticle interactions. We also\ndiscuss a mechanism for long-time decay that crucially depends on the quantum\nstatistics of the particles constituting the doublon, namely, the conversion of\npairs of neighboring doublons into an unpaired fermion and a site with a\nfermion and two bosons. Building on these insights, we develop a cluster\nexpansion method to describe the dynamics in extended systems and compare it to\nnumerically exact matrix product state simulations in one dimension. Finally,\nwe discuss how our predictions can be observed in experiments with ultracold\nheteronuclear molecules."
    },
    {
        "anchor": "Active Learning Algorithm for Computational Physics: In large-scale computation of physics problems, one often encounters the\nproblem of determining a multi-dimensional function, which can be\ntime-consuming when computing each point in this multi-dimensional space is\nalready time-demanding. In the work, we propose that the active learning\nalgorithm can speed up such calculations. The basic idea is to fit a\nmulti-dimensional function by neural networks, and the key point is to make the\nquery of labeled data economically by using a stratagem called \"query by\ncommittee\". We present the general protocol of this fitting scheme, as well as\nthe procedure of how to further compute physical observables with the fitted\nfunctions. We show that this method can work well with two examples, which are\nquantum three-body problem in atomic physics and the anomalous Hall\nconductivity in condensed matter physics, respectively. In these examples, we\nshow that one reaches an accuracy of few percent error for computing physical\nobservables with less than $10\\%$ of total data points compared with uniform\nsampling. With these two examples, we also visualize that by using the active\nlearning algorithm, the required data are added mostly in the regime where the\nfunction varies most rapidly, which explains the mechanism for the efficiency\nof the algorithm. We expect broad applications of our method on various kind of\ncomputational physics problems.",
        "positive": "Bose condensation of upper-branch exciton-polaritons in a transferrable\n  microcavity: Exciton-polaritons are composite bosonic quasiparticles arising from the\nstrong coupling of excitonic transitions and optical modes. Exciton-polaritons\nhave triggered wide exploration in the past decades not only due to their rich\nquantum phenomena such as superfluidity, superconductivity and quantized\nvortices but also due to their potential applications for unconventional\ncoherent light sources and all-optical control elements. Here, we report the\nobservation of Bose-Einstein condensation of the upper polariton branch in a\ntransferrable WS$_2$ monolayer microcavity. Near the condensation threshold, we\nobserve a nonlinear increase in upper polariton intensity. This sharp increase\nin intensity is accompanied by a decrease of the linewidth and an increase of\nthe upper polariton temporal coherence, all of which are hallmarks of\nBose-Einstein condensation. By simulating the quantum Boltzmann equation, we\nshow that the upper polariton condensation only occurs for a particular range\nof particle density. We can attribute the creation of Bose condensation of the\nupper polariton to the following requirements: 1) the upper polariton is more\nexcitonic than the lower one; 2) there is relatively more pumping in the upper\nbranch; and 3) the conversion time from the upper to the lower polariton branch\nis long compared to the lifetime of the upper polaritons."
    },
    {
        "anchor": "Second Quantized Landau Variables in the Case of Dilute Bose-Einstein\n  Condensates: Landau was the first to advance hydrodynamic concepts such as density and\nvelocity to describe the superfluidity of liquid He$^4$. Due to the recent\nspectacular success of experiments demonstrating Bose Einstein condensation in\ndilute Bose atomic gases, interest has been revitalized in the theoretical\ndescription of Bose Einstein condensates. Many of the properties of these gases\nwere obtained by using the Gross-Pitaevskii equation (GPE) to derive the\nhydrodynamic equations for the gases. However, it is interesting to apply the\nhydrodynamic equations obtained by Yee for bosons. Many of the properties\nobtained for the dilute Bose gases are also consequences of Yee's hydrodynamic\nequations, which derive from a formalism distinct from that of the GPE.",
        "positive": "Mode competition in superradiant scattering of matter waves: Superradiant Rayleigh scattering in a Bose gas released from an optical\nlattice is analyzed with incident light pumping at the Bragg angle for resonant\nlight diffraction. We show competition between superradiance scattering into\nthe Bragg mode and into end-fire modes clearly leads to suppression of the\nlatter at even relatively low lattice depths. A quantum light-matter\ninteraction model is proposed for qualitatively explaining this result."
    },
    {
        "anchor": "Al'tshuler-Aronov-Spivak oscillations of bosonic matter-wave beams in\n  the presence of interaction: We theoretically study the propagation of a guided atom laser across an\nAharonov-Bohm ring which is exposed to a synthetic gauge field. The presence of\ndisorder within the ring gives rise to Al'tshuler-Aronov-Spivak oscillations,\nseen in the disorder average of the transmission as a function of the effective\ngauge flux that is contained within the ring. Those oscillations are induced by\ncoherent backscattering and represent a manifestation of weak localization.\nThrough analytical and numerical calculations that are based on the mean-field\nGross-Pitaevskii approximation for the propagating Bose-Einstein condensate, we\nshow that the presence of a very weak atom-atom interaction within the ring\nleads to an inversion of the Al'tshuler-Aronov-Spivak oscillations, in a very\nsimilar manner as for the coherent backscattering of Bose-Einstein condensates\nwithin two-dimensional disorder potentials. Numerical simulations based on the\nTruncated Wigner method reveal that this signature of weak antilocalization\nbecomes washed out if the interaction strength is increased.",
        "positive": "Isothermal sweep theorems for ultra-cold quantum gases in a canonical\n  ensemble: After deriving the isothermal Hellmann-Feynman theorem (IHFT) that is\nsuitable for mixed states in a canonical ensemble, we use this theorem to\nobtain the isothermal magnetic-field sweep theorems for the free, average and\ntrapping energies, and for the entropy, specific heat, pressure and atomic\ncompressibility of strongly-correlated ultra-cold quantum gases. In particular,\nwe apply the sweep theorems to two-component Fermi gases in the\nweakly-interacting BCS and BEC limits, showing that the temperature dependence\nof the contact parameter can be determined by the variation of either the\nentropy or specific heat with respect to the scattering length. We also use the\nIHFT to obtain the Virial theorem in a canonical ensemble, and discuss its\nimplications for quantum gases."
    },
    {
        "anchor": "Symmetry-breaking instability of leapfrogging vortex rings in a\n  Bose-Einstein condensate: Three coaxial quantized vortex rings in a Bose-Einstein condensate exhibit\naperiodic leapfrogging dynamics. It is found that such circular vortex rings\nare dynamically unstable against deformation breaking axial rotational\nsymmetry. The dynamics of the system are analyzed using the Gross-Pitaevskii\nand vortex-filament models. The dependence of the instability on the initial\narrangement of the vortex rings is investigated. The system is found to be\nsignificantly unstable for a specific configuration of the three vortex rings.",
        "positive": "Coexistence of topological and nontopological Fermi-superfluid phases: The two-dimensional spin-imbalanced Fermi gas subject to s-wave pairing and\nspin-orbit coupling is considered a promising platform for realizing a\ntopological chiral-p-wave superfluid. In the BCS limit of s-wave pairing, i.e.,\nwhen Cooper pairs are only weakly bound, the system enters the topological\nphase via a second-order transition driven by increasing the Zeeman\nspin-splitting energy. Stronger attractive two-particle interactions cause the\nsystem to undergo the BCS-BEC crossover, in the course of which the topological\ntransition becomes first-order. As a result, topological and nontopological\nsuperfluids coexist in spatially separated domains in an extended region of\nphase space spanned by the strength of s-wave interactions and the Zeeman\nenergy. Here we investigate this phase-coexistence region theoretically using a\nzero-temperature mean-field approach. Exact numerical results are presented to\nillustrate basic physical characteristics of the coexisting phases and to\nvalidate an approximate analytical description derived for weak spin-orbit\ncoupling. Besides extending our current understanding of spin-imbalanced\nsuperfluid Fermi systems, the present approach also provides a platform for\nfuture studies of unconventional Majorana excitations that, according to\ntopology, should be present at the internal interface between coexisting\ntopological and nontopological superfluid parts of the system."
    },
    {
        "anchor": "Spontaneous formation of polar superfluid droplets in a p-wave\n  interacting Bose gas: We study the quantum fluctuations in the condensates of a mixture of bosonic\natoms and molecules with interspecies p-wave interaction. Our analysis shows\nthat the quantum phase of coexisting atomic and molecular condensates is\nunstable at the mean-field level. Unlike the mixture of s-wave interaction, the\nLee-Huang-Yang correction of p-wave interaction is unexpectedly found here to\nexhibit an opposite sign with respect to its mean-field term above a critical\nparticle density. This quantum correction to the mean-field energy provides a\nremarkable mechanism to self-stabilize the phase. The order parameter of this\nsuperfluid phase carries opposite finite momenta for the two atomic species\nwhile the molecular component is a polar condensate. Such a correlated order\nspontaneously breaks a rich set of global U(1) gauge, atomic spin, spatial\nrotation and translation, and time-reversal symmetries. For potential\nexperimental observation, the phenomenon of anisotropic polar superfluid\ndroplets is predicted to occur, when the particle number is kept finite.",
        "positive": "Pairing in a system of a few attractive fermions in a harmonic trap: We study a strongly attractive system of a few spin-1/2 fermions confined in\na one-dimensional harmonic trap, interacting via two-body contact potential.\nPerforming exact diagonalization of the Hamiltonian we analyze the ground state\nand the thermal state of the system in terms of one-- and two--particle reduced\ndensity matrices. We show how for strong attraction the correlated pairs emerge\nin the system. We find that the fraction of correlated pairs depends on\ntemperature and we show that this dependence has universal properties analogous\nto the gap function known from the theory of superconductivity. In contrast to\nthe standard approach based on the variational ansatz and/or perturbation\ntheory, our predictions are exact and are valid also in a strong attraction\nlimit. Our findings contribute to the understanding of strongly correlated\nfew-body systems and can be verified in current experiments on ultra-cold\natoms."
    },
    {
        "anchor": "Dynamic Kosterlitz-Thouless transition in 2D Bose mixtures of ultra-cold\n  atoms: We propose a realistic experiment to demonstrate a dynamic\nKosterlitz-Thouless transition in ultra-cold atomic gases in two dimensions.\nWith a numerical implementation of the Truncated Wigner Approximation we\nsimulate the time evolution of several correlation functions, which can be\nmeasured via matter wave interference. We demonstrate that the relaxational\ndynamics is well-described by a real-time renormalization group approach, and\nargue that these experiments can guide the development of a theoretical\nframework for the understanding of critical dynamics.",
        "positive": "Unified theory to characterize Floquet topological phases by quench\n  dynamics: The conventional characterization of periodically driven systems usually\nnecessitates the time-domain information beyond Floquet bands, hence lacking\nuniversal and direct schemes of measuring Floquet topological invariants. Here\nwe propose a unified theory based on quantum quenches to characterize generic\n$d$-dimensional ($d$D) Floquet topological phases, in which the topological\ninvariants are constructed with only minimal information of the static Floquet\nbands. For a $d$D phase which is initially static and trivial, we introduce the\nquench dynamics by suddenly turning on the periodic driving, and show that the\nquench dynamics exhibits emergent topological patterns in ($d-1$)D momentum\nsubspaces where Floquet bands cross, from which the Floquet topological\ninvariants are directly obtained. This prediction provides a simple and unified\ncharacterization, in which one can not only extract the number of conventional\nand anomalous Floquet boundary modes, but also identify the topologically\nprotected singularities in the phase bands. The applications are illustrated\nwith 1D and 2D models which are readily accessible in cold atom experiments.\nOur study opens a new framework for the characterization of Floquet topological\nphases."
    },
    {
        "anchor": "Persistent currents in dipolar Bose-Einstein condensates confined in\n  annular potentials: We consider a dipolar Bose-Einstein condensate confined in an annular\npotential, with all the dipoles being aligned along some arbitrary direction.\nIn addition to the dipole-dipole interaction, we also assume a zero-range\nhard-core potential. We investigate the stability of the system against\ncollapse, as well as the stability of persistent currents as a function of the\norientation of the dipoles and of the strength of the hard-core interaction.",
        "positive": "Role of higher-order interactions on the modulational instability of\n  Bose-Einstein condensate trapped in a periodic optical lattice: In this paper, we investigate the impact of higher-order interactions on the\nmodulational instability (MI) of Bose-Einstein Condensates (BECs) immersed in\nan optical lattice potential. We derive the new variational equations for the\ntime evolution of amplitude, phase of modulational perturbation, and effective\npotential for the system. Through effective potential techniques, we find that\nhigh density attractive and repulsive BECs exhibit new character with direct\nimpact over the MI phenomenon. Results of intensive numerical investigations\nare presented and their convergence with the above semi analytical approach is\nbrought out."
    },
    {
        "anchor": "Bound Bogoliubov quasiparticles in photon superfluids: Bogoliubov's description of Bose gases relies on the linear dynamics of\nnoninteracting quasiparticles on top of a homogeneous condensate. Here, we\ntheoretically explore the weakly-nonlinear regime of a one-dimensional photon\nsuperfluid in which phonon-like elementary excitations interact via their\nbackreaction on the background flow. The generalized dispersion relation\nextracted from spatiotemporal intensity spectra reveals additional branches\nthat correspond to bound Bogoliubov quasiparticles -- phase-locked collective\nexcitations originating from nonresonant harmonic-generation and wave-mixing\nprocesses. These mechanisms are inherent to fluctuation dynamics and highlight\nnon-trivial scattering channels other than resonant interactions that could be\nrelevant in the emergence of dissipative and turbulent phenomena in\nsuperfluids.",
        "positive": "Dynamics of massive point vortices in binary mixture of Bose-Einstein\n  condensates: We study the massive point-vortex model introduced in Ref. [Phys. Rev. A 101,\n013630 (2020)], which describes two-dimensional point vortices of one species\nthat have small cores of a different species. We derive the relevant Lagrangian\nitself, based on the time-dependent variational method with a two-component\nGross-Pitaevskii (GP) trial function. The resulting Lagrangian resembles that\nof charged particles in a static electromagnetic field, where the canonical\nmomentum includes an electromagnetic term. The simplest example is a single\nvortex with a rigid circular boundary, where a massless vortex can only precess\nuniformly. In contrast, the presence of a sufficiently large filled vortex core\nrenders such precession unstable. A small core mass can also lead to small\nradial oscillations, which are, in turn, clear evidence of the associated\ninertial effect. Detailed numerical analysis of coupled two-component GP\nequations with a single vortex and small second-component core confirms the\npresence of such radial oscillations, implying that this more realistic GP\nvortex also acts as if it has a small massive core."
    },
    {
        "anchor": "Chiral Mott insulators in frustrated Bose-Hubbard models on ladders and\n  two-dimensional lattices: a combined perturbative and density matrix\n  renormalization group study: We study the fully gapped chiral Mott insulator (CMI) of frustrated\nBose-Hubbard models on ladders and two-dimensional lattices by perturbative\nstrong-coupling analysis and density matrix renormalization group (DMRG). First\nwe show the existence of a low-lying exciton state on all geometries carrying\nthe correct quantum numbers responsible for the condensation of excitons and\nformation of the CMI in the intermediate interaction regime. Then we perform\nsystematic DMRG simulations on several two-leg ladder systems with $\\pi$-flux\nand carefully characterize the two quantum phase transitions. We discuss the\npossibility to extend the generally very small CMI window by including\nrepulsive nearest-neighbour interactions or changing density and coupling\nratios.",
        "positive": "Two-dimensional spectroscopic diagnosis of quantum coherence in Fermi\n  polarons: We present a full microscopic many-body calculation of a recently-proposed\nnonlinear two-dimensional spectroscopy for Fermi polarons, and show that the\nquantum coherence between the attractive and repulsive polarons, which has\nnever been experimentally examined, can be unambiguously revealed via quantum\nbeats at the two off-diagonal crosspeaks in the two-dimensional spectrum. We\npredict that particle-hole excitations make the two crosspeaks asymmetric and\nlead to an additional side peak near the diagonal repulsive polaron peak. Our\nsimulated spectra can be readily examined in future cold-atom experiments,\nwhere the two-dimensional spectroscopy is to be implemented by using a Ramsey\ninterference sequence of rf pulses in the time domain. Our results also provide\na first-principle understanding of the recent two-dimensional coherent\nspectroscopy of interacting excitons and trions in doped monolayer transition\nmetal dichalcogenides."
    },
    {
        "anchor": "Nonlinear spin diffusion and spin rotation in a trapped Fermi gas: Transverse spin diffusion in a polarized, interacting Fermi gas leads to the\nLeggett-Rice effect, where the spin current precesses around the local\nmagnetization. With a spin-echo sequence both the transverse diffusivity and\nthe spin-rotation parameter $\\gamma$ are obtained; the sign of $\\gamma$ reveals\nthe repulsive or attractive character of the effective interaction. In a\ntrapped Fermi gas the spin diffusion equations become nonlinear, and their\nnumerical solution exhibits an inhomogeneous spin state even at the spin echo\ntime. While the microscopic diffusivity and $\\gamma$ increase at weak coupling,\ntheir apparent values inferred from the trap-averaged magnetization saturate in\nagreement with a recent experiment for a dilute ultracold Fermi gas.",
        "positive": "Stretching p-wave molecules by transverse confinements: We revisit the confinement-induced p-wave resonance in quasi-one-dimensional\n(quasi-1D) atomic gases and study the induced molecules near resonance. We\nderive the reduced 1D interaction parameters and show that they can well\npredict the binding energy of shallow molecules in quasi-1D system.\nImportantly, these shallow molecules are found to be much more spatially\nextended compared to those in three dimensions (3D) without transverse\nconfinement. Our results strongly indicate that a p-wave interacting atomic gas\ncan be much more stable in quasi-1D near the induced p-wave resonance, where\nmost weight of the molecule lies outside the short-range regime and thus the\natom loss could be suppressed."
    },
    {
        "anchor": "Spin-charge separation effects in the low-temperature transport of 1D\n  Fermi gases: We study the transport properties of a one-dimensional spinful Fermi gas,\nafter junction of two semi-infinite sub-systems held at different temperatures.\nThe ensuing dynamics is studied by analysing the space-time profiles of local\nobservables emerging at large distances $x$ and times $t$, as a function of\n$\\zeta = x/t$. At equilibrium, the system displays two distinct species of\nquasi-particles, naturally associated with different physical degrees of\nfreedom. By employing the generalised hy- drodynamic approach, we show that\nwhen the temperatures are finite no notion of separation can be attributed to\nthe quasi-particles. In this case the profiles can not be qualitatively\ndistinguished by those associated to quasi-particles of a single species that\ncan form bound states. On the contrary, signatures of separation emerge in the\nlow-temperature regime, where two distinct characteristic ve- locities appear.\nIn this regime, we analytically show that the profiles display a piece-wise\nconstant form and can be understood in terms of two decoupled Luttinger\nliquids.",
        "positive": "Superfluid fraction in an interacting spatially modulated Bose-Einstein\n  condensate: At zero temperature, a Galilean-invariant Bose fluid is expected to be fully\nsuperfluid. Here we investigate theoretically and experimentally the quenching\nof the superfluid density of a dilute Bose-Einstein condensate due to the\nbreaking of translational (and thus Galilean) invariance by an external 1D\nperiodic potential. Both Leggett's bound fixed by the knowledge of the total\ndensity and the anisotropy of the sound velocity provide a consistent\ndetermination of the superfluid fraction. The use of a large-period lattice\nemphasizes the important role of two-body interactions on superfluidity."
    },
    {
        "anchor": "Solitons as the early stage of quasicondensate formation during\n  evaporative cooling: We calculate the evaporative cooling dynamics of trapped one-dimensional\nBose-Einstein condensates for parameters leading to a range of condensates and\nquasicondensates in the final equilibrium state. We confirm that solitons are\ncreated during the evaporation process, but always eventually dissipate during\nthermalisation. The distance between solitons at the end of the evaporation\nramp matches the coherence length in the final thermal state. Calculations were\nmade using the classical fields method. They bridge the gap between the phase\ndefect picture of the Kibble-Zurek mechanism and the long-wavelength phase\nfluctuations in the thermal state.",
        "positive": "Excitation spectrum and momentum distribution of the ionic Bose-Hubbard\n  model: We investigate the excitation spectrum and momentum distribution of the ionic\nBose-Hubbard model by the standard basis operator method. We derive Green's\nfunctions in the random phase approximation in Mott insulator, superfluid,\ncharge density wave, and supersolid phases. The excitation spectrum has gapped\nmodes and gapless Goldstone modes in the superfluid and supersolid phases. We\nshow that the momentum distribution has a peak at the zone corner in the\nsupersolid phase and the charge density wave phase close to the phase boundary.\nIn addition, we demonstrate that the momentum distribution can be explained by\nthe excitation spectrum and spectral weights of hole excitation modes."
    },
    {
        "anchor": "Bose-Fermi transmutation for one-dimensional harmonic trap: Using Density Matrix renormalization group (DMRG), we study the ground state\nproperties of spin one-half fermions and scalar bosons in the soft-core limit,\nwith weak s-wave inter and intra species interactions. We considered the system\nsubject to one-dimensional (1D) optical lattice and a superimposed potential at\nzero temperature, in the framework of Bose-Fermi-Hubbard model. We found that\nfor certain fillings and interaction parameters, a transmutation occurs between\nthe ground states of bosons and fermions when the densities are exchanged. We\ntoo report that the density distributions of bosons and fermions overlap with\neach other in a bosonic and fermionic Mott plateau, when the interaction\nparameters fulfill the relationship $U_{BB}>U_{BF}<U_{BF}$. We also find that\nthe fermions are repelled out of the central region of the trap for\nsufficiently strong $U_{FF}$ interaction, exhibiting phase separation of Bose\nand Fermi components.",
        "positive": "On the Exponential Decay of Strongly Interacting Cold Atoms from a\n  Double-Well Potential: In this article, we study an exponential decay for the gas of bosons with\nstrong repulsive delta interactions from a double-well potential. We consider\nan exactly solvable model comprising an infinite wall and two Dirac delta\nbarriers. We explore its features both within the exact method and with the\nresonance expansion approach. The study reveals the effect of the splitting\nbarrier on the decay rate in dependence on the number of particles. Among other\nthings, we find that the effect of the splitting barrier on the decay rate is\nmost pronounced in systems with odd particle numbers. During exponential decay,\nthe spatial correlations in an internal region are well captured by the\n\"radiating state\"."
    },
    {
        "anchor": "Controlling the Rotational and Hyperfine State of Ultracold\n  $^{87}$Rb$^{133}$Cs Molecules: We demonstrate coherent control of both the rotational and hyperfine state of\nultracold, chemically stable $^{87}$Rb$^{133}$Cs molecules with external\nmicrowave fields. We create a sample of ~2000 molecules in the lowest hyperfine\nlevel of the rovibronic ground state N = 0. We measure the transition\nfrequencies to 8 different hyperfine levels of the N = 1 state at two magnetic\nfields ~23 G apart. We determine accurate values of rotational and hyperfine\ncoupling constants that agree well with previous calculations. We observe Rabi\noscillations on each transition, allowing complete population transfer to a\nselected hyperfine level of N = 1. Subsequent application of a second microwave\npulse allows transfer of molecules back to a different hyperfine level of N =\n0.",
        "positive": "Rotons in a hybrid Bose-Fermi system: We calculate the spectrum of elementary excitations in a two-dimensional\nexciton superfluid in the vicinity of a two-dimensional electron gas. We show\nthat attraction of excitons due to their scattering with free electrons may\nlead to formation of a roton minimum. The energy of this minimum may go below\nthe ground state energy which manifests breaking of the superfluidity. The\nBerezinsky-Kosterlitz-Thouless phase transition temperature decreases due to\nthe exciton-exciton attraction mediated by electrons."
    },
    {
        "anchor": "Three-dimensional numerical simulation of long-lived quantum vortex\n  knots and links in a trapped Bose-Einstein condensate: Dynamics of simplest vortex knots, unknots, and links of torus type inside an\natomic Bose-Einstein condensate in anisotropic harmonic trap at zero\ntemperature has been numerically simulated using three-dimensional\nGross-Pitaevskii equation. The lifetime for such quasi-stationary rotating\nvortex structures has been found quite long in wide parametric domains of the\nsystem. This result is in qualitative agreement with a previous prediction\nbased on a simplified one-dimensional model approximately describing dynamics\nof vortex filaments [V.P. Ruban, JETP 126, 397 (2018)].",
        "positive": "Harmonically Trapped Four-Boson System: Four identical spinless bosons with purely attractive two-body short-range\ninteractions and repulsive three-body interactions under external spherically\nsymmetric harmonic confinement are considered. The repulsive three-body\npotential prevents the formation of deeply-bound states with molecular\ncharacter. The low-energy spectrum with vanishing orbital angular momentum and\npositive parity for infinitely large two-body $s$-wave scattering length is\nanalyzed in detail. Using the three-body contact, states are classified as\nuniversal, quasi-universal, or strongly non-universal. Connections with the\nzero-range interaction model are discussed. The energy spectrum is mapped out\nas a function of the two-body $s$-wave scattering length $a_s$, $a_s>0$. In the\nweakly- to medium-strongly-interacting regime, one of the states approaches the\nenergy obtained for a hard core interaction model. This state is identified as\nthe energetically lowest-lying \"BEC state\". Structural properties are also\npresented."
    },
    {
        "anchor": "Alternative Route to Strong Interaction: Narrow Feshbach Resonance: We show that a narrow resonance produces strong interaction effects far\nbeyond its width on the side of the resonance where the bound state has not\nbeen formed. This is due to a resonance structure of its phase shift, which\nshifts the phase of a large number of scattering states by $\\pi$ before the\nbound state emerges. As a result, the magnitude of the interaction energy when\napproaching the resonance on the \"upper\" and \"lower\" branch from different side\nof the resonance is highly asymmetric, unlike their counter part in wide\nresonances. Measurements of these effects are experimentally feasible.",
        "positive": "Rayleigh-Taylor instability in a phase-separated three-component\n  Bose-Einstein condensate: We investigate the Rayleigh-Taylor instability at the two interfaces in a\nphase-separated three-component Bose-Einstein condensate in the mean-field\nframework. The subsequent dynamics in the immiscible three-component condensate\nhas been studied in detail for different cases of instigating the instability\nin the system. The rotational symmetry of the system breaks when the atom-atom\ninteraction is tuned in such a way that the interface between the components\nbecomes unstable giving rise to non-linear patterns of mushroom shapes which\ngrow exponentially with time. We also identify these non-linear patterns as the\nsolutions of the angular Mathieu equation, representing the normal modes."
    },
    {
        "anchor": "Dynamical many-body delocalization transition of a Tonks gas in a\n  quasi-periodic driving potential: The quantum kicked rotor is well-known for displaying dynamical (Anderson)\nlocalization. It has recently been shown that a periodically kicked Tonks gas\nwill always localize and converge to a finite energy steady-state. This\nsteady-state has been described as being effectively thermal with an effective\ntemperature that depends on the parameters of the kick. Here we study a\ngeneralization to a quasi-periodic driving with three frequencies which,\nwithout interactions, has a metal-insulator Anderson transition. We show that a\nquasi-periodically kicked Tonks gas goes through a dynamical many-body\ndelocalization transition when the kick strength is increased. The localized\nphase is still described by a low effective temperature, while the delocalized\nphase corresponds to an infinite-temperature phase, with the temperature\nincreasing linearly in time. At the critical point, the momentum distribution\nof the Tonks gas displays different scaling at small and large momenta\n(contrary to the non-interacting case), signaling a breakdown of the\none-parameter scaling theory of localization.",
        "positive": "Nonlinear phase-dynamics in a driven Bosonic Josephson junction: We study the collective dynamics of a driven two mode Bose-Hubbard model in\nthe Josephson interaction regime. The classical phase-space is mixed, with\nchaotic and regular components, that determine the dynamical nature of the\nfringe-visibility. For weak off-resonant drive, where the chaotic component is\nsmall, the many-body dynamics corresponds to that of a Kapitza pendulum, with\nthe relative-phase $\\varphi$ between the condensates playing the role of the\npendulum angle. Using a master equation approach we show that the modulation of\nthe inter-site potential barrier stabilizes the $\\varphi=\\pi$ 'inverted\npendulum' coherent state, and protects the fringe visibility."
    },
    {
        "anchor": "Bose gas: Theory and Experiment: For many years, $^4$He typified Bose-Einstein superfluids, but recent\nadvances in dilute ultra-cold alkali-metal gases have provided new neutral\nsuperfluids that are particularly tractable because the system is dilute. This\nchapter starts with a brief review of the physics of superfluid $^4$He,\nfollowed by the basic ideas of Bose-Einstein condensation (BEC), first for an\nideal Bose gas and then considering the effect of interparticle interactions,\nincluding time-dependent phenomena. Extensions to more exotic condensates\ninclude magnetic dipolar gases, mixtures of two components, and spinor\ncondensates that require a focused infrared laser for trapping of all the\nvarious hyperfine magnetic states in a particular hyperfine $F$ manifold of\n$m_F$ states. With an applied rotation, the trapped BECs nucleate quantized\nvortices. Recent theory and experiment have shown that laser coupling fields\ncan mimic the effect of rotation. The resulting synthetic gauge fields have\nproduced vortices in a nonrotating condensate.",
        "positive": "Supersolid phases of lattice dipoles tilted in three-dimensions: By means of quantum Monte Carlo simulations we study phase diagrams of\ndipolar bosons in a square optical lattice. The dipoles in the system are\nparallel to each other and their orientation can be fixed in any direction of\nthe three-dimensional space. Starting from experimentally tunable parameters\nlike scattering length and dipolar interaction strength, we derive the\nparameters entering the effective Hamiltonian. Depending on the direction of\nthe dipoles, various types of supersolids (e.g. checkerboard, stripe) and\nsolids (checkerboard, stripe, diagonal stripe, and an incompressible phase) can\nbe stabilized. Remarkably, we find a cluster supersolid characterized by the\nformation of horizontal clusters of particles. These clusters order along a\ndirection at an angle with the horizontal. Moreover, we find what we call a\ngrain-boundary superfluid. In this phase, regions with solid order are\nseparated by extended defects -- grain boundaries -- which support\nsuperfluidity. We also investigate the robustness of the stripe supersolid\nagainst thermal fluctuations. Finally, we comment on the experimental\nrealization of the phases found."
    },
    {
        "anchor": "Non-classical critical exponents at Bose-Einstein condensation: We show that ideal Bose-Einstein condensation (BEC) in $d = 3$ dimensions is\na non-classical critical second order phase transition with exponents $\\alpha =\n-1$, $\\beta = 1$, $\\gamma = 1$, $\\delta = 2$, $\\eta = 1$ and $\\nu = 1$, obeying\nall the scaling equalities. These results are found with no approximations or\nassumptions. The previous exponents are a critical universality class on its\nown, different from the so-far accepted notion that BEC belongs to the\nSpherical Model universality class.",
        "positive": "Universality in one-dimensional fermions at finite temperature: Density,\n  pressure, compressibility, and contact: We present finite-temperature, lattice Monte Carlo calculations of the\nparticle number density, compressibility, pressure, and Tan's contact of an\nunpolarized system of short-range, attractively interacting spin-1/2 fermions\nin one spatial dimension, i.e., the Gaudin-Yang model. In addition, we compute\nthe second-order virial coefficients for the pressure and the contact, both of\nwhich are in excellent agreement with the lattice results in the low-fugacity\nregime. Our calculations yield universal predictions for ultracold atomic\nsystems with broad resonances in highly constrained traps. We cover a wide\nrange of couplings and temperatures and find results that support the existence\nof a strong-coupling regime in which the thermodynamics of the system is\nmarkedly different from the noninteracting case. We compare and contrast our\nresults with identical systems in higher dimensions."
    },
    {
        "anchor": "Fluctuation driven topological transition of binary condensates in\n  optical lattices: We show the emergence of a third Goldstone mode in binary condensates at the\nphase-separation in quasi-1D optical lattices. We develop the coupled discrete\nnonlinear Schr\\\"odinger equations (DNLSEs) using Hartree-Fock-Bogoliubov theory\nwith Popov approximation in the Bose-Hubbard model to investigate the mode\nevolution at zero temperature. In particular, as the system is driven from\nmiscible to immiscible phase. We demonstrate that the position swapping of the\nspecies in $^{87}$Rb-$^{85}$Rb system is accompanied by a discontinuity in the\nexcitation spectrum. Our results show that in quasi-1D optical lattices, the\npresence of the fluctuations dramatically change the geometry of the ground\nstate density profile of TBEC.",
        "positive": "Mean field study of 2D quasiparticle condensate formation in presence of\n  strong decay: Bose-condensation in a system of 2D quasiparticles is considered in the scope\nof a microscopic model. Mean-field dynamical equations are derived with the\nhelp of the Schwinger-Keldysh formalism and a simple model is proposed which\nallows to describe key features of condensate formation in systems with various\nquasiparticle decay rates. By analysing stationary solutions of this equation,\nwe obtain the phase diagram of quasiparticle gas, finding a bistability region\nin the parameter space of the system. Finally, as an application of our theory,\nwe study the phase diagram of a 2D exciton-polariton system in CdTe\nmicrocavity."
    },
    {
        "anchor": "Catalyzation of supersolidity in binary dipolar condensates: Breakthrough experiments have newly explored the fascinating physics of\ndipolar quantum droplets and supersolids. The recent realization of dipolar\nmixtures opens further intriguing possibilities. We show that under rather\ngeneral conditions, the presence of a second component catalyzes droplet\nnucleation and supersolidity in an otherwise unmodulated condensate. Droplet\ncatalyzation in miscible mixtures, which may occur even for a surprisingly\nsmall impurity doping, results from a local roton instability triggered by the\ndoping-dependent modification of the effective dipolar strength. The\ncatalyzation mechanism may trigger the formation of a two-fluid supersolid,\ncharacterized by a generally different superfluid fraction of each component,\nwhich opens intriguing possibilities for the future study of spin physics in\ndipolar supersolids.",
        "positive": "Photonic band-gap in a realistic atomic diamond lattice: penetration\n  depth, finite-size and vacancy effects: We study the effects of finite size and of vacancies on the photonic band gap\nrecently predicted for an atomic diamond lattice. Close to a $J_g=0\\to J_e=1$\natomic transition, and for atomic lattices containing up to $N\\approx\n3\\times10^4$ atoms, we show how the density of states can be affected by both\nthe shape of the system and the possible presence of a fraction of unoccupied\nlattice sites. We numerically predict and theoretically explain the presence of\nshape-induced border states and of vacancy-induced localized states appearing\nin the gap. We also investigate the penetration depth of the electromagnetic\nfield which we compare to the case of an infinite system."
    },
    {
        "anchor": "Nonlinear atom interferometer surpasses classical precision limit: Interference is fundamental to wave dynamics and quantum mechanics. The\nquantum wave properties of particles are exploited in metrology using atom\ninterferometers, allowing for high-precision inertia measurements [1, 2].\nFurthermore, the state-of-the-art time standard is based on an interferometric\ntechnique known as Ramsey spectroscopy. However, the precision of an\ninterferometer is limited by classical statistics owing to the finite number of\natoms used to deduce the quantity of interest [3]. Here we show experimentally\nthat the classical precision limit can be surpassed using nonlinear atom\ninterferometry with a Bose-Einstein condensate. Controlled interactions between\nthe atoms lead to non-classical entangled states within the interferometer;\nthis represents an alternative approach to the use of non-classical input\nstates [4-8]. Extending quantum interferometry [9] to the regime of large atom\nnumber, we find that phase sensitivity is enhanced by 15 per cent relative to\nthat in an ideal classical measurement. Our nonlinear atomic beam splitter\nfollows the \"one-axis-twisting\" scheme [10] and implements interaction control\nusing a narrow Feshbach resonance. We perform noise tomography of the quantum\nstate within the interferometer and detect coherent spin squeezing with a\nsqueezing factor of -8.2dB [11-15]. The results provide information on the\nmany-particle quantum state, and imply the entanglement of 170 atoms [16].",
        "positive": "Finite-size scaling behavior of Bose-Einstein condensation in the 1D\n  Bose gas: Through exact numerical solutions we show Bose-Einstein condensation (BEC)\nfor the one-dimensional (1D) bosons with repulsive short-range interactions at\nzero temperature by taking a particular large size limit. Following the\nPenrose-Onsager criterion of BEC, we define condensate fraction by the fraction\nof the largest eigenvalue of the one-particle reduced density matrix. % We show\nthe finite-size scaling behavior such that condensate fraction is given by a\nscaling function of one-variable: interaction parameter multiplied by a power\nof particle number. Condensate fraction is nonzero and constant for any large\nvalue of particle number or system size, if the interaction parameter is\nproportional to the negative power of particle number. %Here the interaction\nparameter is defined by the coupling constant of the delta-function potentials\ndevided by the density. %With the scaling behavior we derive various\nthemodynamic limits where condensate fraction is constant for any large system\nsize; for instance, it is the case even in the system of a finite particle\nnumber."
    },
    {
        "anchor": "Quasi-superfluid and Quasi-Mott phases of strongly interacting bosons in\n  shallow optical lattice: We explore the ground states of strongly interacting bosons in the\nvanishingly small and weak lattices using the multiconfiguration time-dependent\nHartree method for bosons (MCTDHB) which calculate numerically exact many-body\nwave function. Two new many-body phases: fragmented or quasi superfluid (QSF)\nand incomplete fragmented Mott or quasi Mott insulator (QMI) are emerged due to\nthe strong interplay between interaction and lattice depth. Fragmentation is\nutilized as a figure of merit to distinguish these two new phases. We utilize\nthe eigenvalues of the reduced one-body density matrix and define an order\nparameter that characterizes the pathway from a very weak lattice to a deep\nlattice. We provide a detailed investigation through the measures of one- and\ntwo-body correlations and information entropy. We find that the structures in\none- and two-body coherence are good markers to understand the gradual built-up\nof intra-well correlation and decay of inter-well correlation with increase in\nlattice depth.",
        "positive": "Microscopic derivation of the Boltzmann equation for transport\n  coefficients of resonating fermions at high temperature: Motivated by the recently observed failure of the kinetic theory for the bulk\nviscosity, we in turn revisit the shear viscosity and the thermal conductivity\nof two-component fermions with a zero-range interaction both in two and three\ndimensions. In particular, we show that their Kubo formula evaluated exactly in\nthe high-temperature limit to the lowest order in fugacity is reduced to the\nlinearized Boltzmann equation. Previously, such a microscopic derivation of the\nlatter was achieved only incompletely corresponding to the relaxation-time\napproximation. Here, we complete it by resuming all contributions that are\nnaively higher orders in fugacity but become comparable in the zero-frequency\nlimit due to the pinch singularity, leading to a self-consistent equation for a\nvertex function identical to the linearized Boltzmann equation. We then compute\nthe shear viscosity and the thermal conductivity in the high-temperature limit\nfor an arbitrary scattering length and find that the Prandtl number exhibits a\nnonmonotonic behavior slightly below the constant value in the relaxation-time\napproximation."
    },
    {
        "anchor": "Superfluid Condensate Fraction and Pairing Wave Function of the Unitary\n  Fermi Gas: The unitary Fermi gas is a many-body system of two-component fermions with\nzero-range interactions tuned to infinite scattering length. Despite much\nactivity and interest in unitary Fermi gases and its universal properties,\nthere have been great difficulties in performing accurate calculations of the\nsuperfluid condensate fraction and pairing wave function. In this work we\npresent auxiliary-field lattice Monte Carlo simulations using a novel lattice\ninteraction which accelerates the approach to the continuum limit, thereby\nallowing for robust calculations of these difficult observables. As a benchmark\ntest we compute the ground state energy of 33 spin-up and 33 spin-down\nparticles. As a fraction of the free Fermi gas energy $E_{FG}$, we find\n$E_0/E_{FG}= 0.369(2), 0.372(2)$, using two different definitions of the\nfinite-system energy ratio, in agreement with the latest theoretical and\nexperimental results. We then determine the condensate fraction by measuring\noff-diagonal long-range order in the two-body density matrix. We find that the\nfraction of condensed pairs is $\\alpha = 0.43(2)$. We also extract the pairing\nwave function and find the pair correlation length to be $\\zeta_pk_F = 1.8(3)\n\\hbar$, where $k_F$ is the Fermi momentum. Provided that the simulations can be\nperformed without severe sign oscillations, the methods we present here can be\napplied to superfluid neutron matter as well as more exotic P-wave and D-wave\nsuperfluids.",
        "positive": "Stability of attractive bosonic cloud with van der Waals interaction: We investigate the structure and stability of Bose-Einstein condensate of\n$^{7}$Li atoms with realistic van der Waals interaction by using the potential\nharmonic expansion method. Besides the known low-density metastable solution\nwith contact delta function interaction, we find a stable branch at a higher\ndensity which corresponds to the formation of an atomic cluster. Comparison\nwith the results of non-local effective interaction is also presented. We\nanalyze the effect of trap size on the transition between the two branches of\nsolutions. We also compute the loss rate of a Bose condensate due to two- and\nthree-body collisions."
    },
    {
        "anchor": "$Z_2\\times Z_2$ symmetry and $Z_4$ Berry phase of bosonic ladder: Bose gas on a two-leg ladder exhibits an interesting topological phase. We\nshow the presence of a bosonic symmetry-protected-topological (SPT) phase\nprotected by $Z_2\\times Z_2$ symmetry. This symmetry leads to $Z_4$ fractional\nquantization of $Z_4$ Berry phase, that is a topological order parameter to\nidentify the bulk. Using the $Z_4$ Berry phase, we have shown that the\ninteracting bosonic system possesses rich topological phases depending on\nparticle density and strength of interaction. Based on the bulk-edge\ncorrespondence, each edge state of the SPT phases is discussed in relation to\nthe $Z_4$ Berry phases. Especially we have found an intermediate phase that is\nnot adiabatically connected to a simple adiabatic limit, that possesses\nunconventional edge states, which we have numerically demonstrate by employing\nthe density-matrix-renormalization group algorithm.",
        "positive": "Bosonic thermoelectric transport and breakdown of universality: In this paper we compare Bose transport in normal phase atomic gases with its\ncounterpart in Fermi gases, illustrating the non-universality of two\ndimensional bosonic transport associated with different dissipation mechanisms.\nNear the superfluid transition temperature $T_c$, a striking similarity between\nthe fermionic and bosonic transport emerges because super-conducting(fluid)\nfluctuation transport for Fermi gases is dominated by the bosonic, Cooper pair\ncomponent. As in fluctuation theory, one finds that the Seebeck coefficient\nchanges sign at $T_c$ and the Lorenz number approaches zero at $T_c$. Our\nfindings appear semi-quantitatively consistent with recent Bose gas\nexperiments."
    },
    {
        "anchor": "Thermalization of a weakly interacting Bose gas in a disordered trap: Previously we numerically showed that thermalization can occur in an\noscillating Bose-Einstein condensate (BEC) with a disordered harmonic trap when\nhealing length $\\xi$ of the condensate is shorter than the correlation length\n$\\sigma_{D}$ of the disorder [see, for example, the experiment reported in\nPhys. Rev. A \\textbf{82}, 033603 (2010)]. In this work, we investigate the\nweakly interacting or Anderson localization regime $\\xi>\\sigma_{D}$ and show\nthat the oscillating BEC can also exhibit a relaxation process from\nnonequilibrium to equilibrium. In such an isolated quantum system, energy and\nparticle number are conserved and the irreversible evolution towards\nthermodynamic equilibrium is induced by the disorder. The thermodynamic\nequilibrium is evidenced by the maximized entropy $S\\left[n_{k}\\right]$ in\nwhich the waveaction spectrum $n_{k}$ follows the Rayleigh-Jeans distribution.\nBesides, unlike a monotonic irreversible process of thermalization to\nequilibrium, the Fermi-Pasta-Ulam-Tsingou recurrence arises in this system,\nmanifested by the oscillation of the non-equilibrium entropy.",
        "positive": "Effective Hamiltonian with tunable mixed pairing in driven optical\n  lattices: Mixed pairing in ultracold Fermi gases can give rise to interesting many-body\nphases, such as topological nontrivial superfluids that support Majorana zero\nmodes (MZMs) with various spatial configurations. Unfortunately, in ordinary\nlattice systems, the topological phase and the associated MZMs are suppressed\nby the dominant $s$-wave pairing. Here we present a proposal for engineering\neffective Hamiltonians with tunable mixed on- and off-site pairing based on\ndriven optical lattices. The on- and off-site pairing can be changed\nindependently by means of a periodical driving field rather than magnetic\nFeshbach resonances. It paves the way for suppressing the dominant on-site\ninteraction that frustrates the emergence of topological superfluids and for\nsynthesizing MZMs localized in edges or corners."
    },
    {
        "anchor": "Local observation of pair-condensation in a Fermi gas at unitarity: We present measurements of the local (homogeneous) density-density response\nfunction of a Fermi gas at unitarity using spatially resolved Bragg\nspectroscopy. By analyzing the Bragg response across one axis of the cloud we\nextract the response function for a uniform gas which shows a clear signature\nof the Bose-Einstein condensation of pairs of fermions when the local\ntemperature drops below the superfluid transition temperature. The method we\nuse for local measurement generalizes a scheme for obtaining the local pressure\nin a harmonically trapped cloud from the line density and can be adapted to\nprovide any homogeneous parameter satisfying the local density approximation.",
        "positive": "Quantum statistics of bosonic cascades: Bosonic cascades formed by lattices of equidistant energy levels sustaining\nradiative transitions between nearest layers are promising for the generation\nof coherent terahertz radiation. We show how, also for the light emitted by the\ncondensates in the visible range, they introduce new regimes of emission.\nNamely, the quantum statistics of bosonic cascades exhibit super-bunching\nplateaus. This demonstrates further potentialities of bosonic cascade lasers\nfor the engineering of quantum properties of light useful for imaging\napplications."
    },
    {
        "anchor": "Ultracold dipolar bosons trapped in atomtronic circuits: We consider a ring-shaped triple-well potential with few polar bosons with\nin-plane dipole orientation. By diagonalizing the extended Bose-Hubbard\nHamiltonian, we investigate the ground state properties of the system as we\nrotate the dipole angle and vary the on-site and dipole-dipole interaction\nstrengths. We find that the anisotropic character of the dipolar interactions,\nas well as the competition between dipole and on-site interactions lead to\ndifferent ground states and that the entanglement between sites also depends on\nthe number of particles. We further characterize the system by studying the\ncondensed fraction and coherence properties, highlighting the possible effect\nof the dipolar interaction as manipulation tool.",
        "positive": "Induced $p$-wave pairing in Bose-Fermi mixtures: Cooper pairing caused by an induced interaction represents a paradigm in our\ndescription of fermionic superfluidity. Here, we present a strong coupling\ntheory for the critical temperature of $p$-wave pairing between spin polarised\nfermions immersed in a Bose-Einstein condensate. The fermions interact via the\nexchange of phonons in the condensate, and our self-consistent theory takes\ninto account the full frequency/momentum dependence of the resulting induced\ninteraction. We demonstrate that both retardation and self-energy effects are\nimportant for obtaining a reliable value of the critical temperature. Focusing\non experimentally relevant systems, we perform a systematic analysis varying\nthe boson-boson and boson-fermion interaction strength as well as their masses,\nand identify the most suitable system for realising a $p$-wave superfluid. Our\nresults show that such a superfluid indeed is experimentally within reach using\nlight bosons mixed with heavy fermions."
    },
    {
        "anchor": "Instability of insulating states in optical lattices due to collective\n  phonon excitations: The role of collective phonon excitations on the properties of cold atoms in\noptical lattices is investigated. These phonon excitations are collective\nexcitations, whose appearance is caused by intersite atomic interactions\ncorrelating the atoms, and they do not arise without such interactions. These\ncollective excitations should not be confused with lattice vibrations produced\nby an external force. No such a force is assumed. But the considered phonons\nare purely self-organized collective excitations, characterizing atomic\noscillations around lattice sites, due to intersite atomic interactions. It is\nshown that these excitations can essentially influence the possibility of atoms\nto be localized. The states that would be insulating in the absence of phonon\nexcitations can become delocalized when these excitations are taken into\naccount. This concerns long-range as well as local atomic interactions. To\ncharacterize the region of stability, the Lindemann criterion is used.",
        "positive": "Electric dipoles vs. magnetic dipoles - for two molecules in a harmonic\n  trap: We study energy levels of two heteronuclear molecules moving in a spherically\nsymmetric harmonic trap. A role of electric dipole interactions is compared and\ncontrasted with our earlier results (https://arxiv.org/abs/1512.00631) for two\nmagnetic dipolar atoms. We stress importance of a rotational energy with its\nvalue which is very high compared to the energy of dipolar interaction. We show\nthat dipolar forces do not play a significant role in the ground state of the\nsystem under typical experimental conditions. However, there exist excited\nstates that exhibit anticrossings similar to the ones observed for magnetic\ndipoles."
    },
    {
        "anchor": "Signature of Chaos and Delocalization in a Periodically Driven Many Body\n  System : An Out-of-Time-Order Correlation Study: We study out-of-time-order correlation (OTOC) for one-dimensional\nperiodically driven hardcore bosons in the presence of Aubry-Andr\\'e (AA)\npotential and show that both the spectral properties and the saturation values\nof OTOC in the steady state of these driven systems provide a clear distinction\nbetween the localized and delocalized phases of these models. Our results,\nobtained via exact numerical diagonalization of these boson chains, thus\nindicate that OTOC can provide a signature of drive induced delocalization even\nfor systems which do not have a well defined semiclassical (and/or large N)\nlimit. We demonstrate the presence of such signature by analyzing two different\ndrive protocols for hardcore bosons chains leading to distinct physical\nphenomena and discuss experiments which can test our theory.",
        "positive": "Density wave propagation in a two-dimensional random dimer potential:\n  from a single to a bipartite square lattice: We study the propagation of a density perturbation in a weakly interacting\nboson gas confined on a lattice and in the presence of square dimerized\nimpurities. Such a two-dimensional random-dimer model (2D-DRDM), previously\nintroduced in [Capuzzi et al., Phys. Rev. A 92, 053622 (2015)], is the disorder\ntransition from a single square lattice, where impurities are absent, to a\nbipartite square lattice, where the number of impurities is maximum and\ncoincides with half the number of lattice sites. We show that disorder\ncorrelations can play a crucial role in the dynamics for a broad range of\nparameters by allowing density fluctuations to propagate in the 2D-DRDM\nlattice, even in the limit of strong disorder. In such a regime, the\npropagation speed depends on the percentage of impurities, interpolating\nbetween the speed in a single monoperiodic lattice and that in a bipartite one."
    },
    {
        "anchor": "Thermodynamic properties of a dipolar Fermi gas: Based on the semi-classical theory, we investigate the thermodynamic\nproperties of a dipolar Fermi gas. Through a self-consistent procedure, we\nnumerically obtain the phase space distribution function at finite temperature.\nWe show that the deformations in both momentum and real space becomes smaller\nand smaller as one increases the temperature. For homogeneous case, we also\ncalculate pressure, entropy, and heat capacity. In particular, at low\ntemperature limit and in weak interaction regime, we obtain an analytic\nexpression for the entropy, which agrees qualitatively with our numerical\nresult. The stability of a trapped gas at finite temperature is also explored.",
        "positive": "Liquid and crystal phase of dipolar fermions in two dimensions: The liquid and crystal phase of a single-component Fermi gas with dipolar\ninteractions are investigated using quantum Monte Carlo methods in two spatial\ndimensions and at zero temperature. The dipoles are oriented by an external\nfield perpendicular to the plane of motion, resulting in a purely repulsive\n1/r^3 interaction. In the liquid phase we calculate the equation of state as a\nfunction of the interaction strength and other relevant properties\ncharacterizing the Fermi-liquid behavior: effective mass, discontinuity at the\nFermi surface and pair correlation function. In the high density regime we\ncalculate the equation of state of the Wigner crystal phase and the critical\ndensity of the liquid to solid first order phase transition. Close to the\nfreezing density we also search for the existence of a stripe phase, but such a\nphase is never found to be energetically favorable."
    },
    {
        "anchor": "Dynamics of quantized vortices in Bose-Einstein condensates with\n  laser-induced spin-orbit coupling: We study vortex dynamics in trapped two-component Bose-Einstein condensates\nwith a laser- induced spin-orbit coupling using the numerical analysis of the\nGross-Pitaevskii equation. The spin-orbit coupling leads to three distinct\nground state phases, which depend on some experimentally controllable\nparameters. When a vortex is put in one or both of the two-component\ncondensates, the vortex dynamics exhibits very different behaviors in each\nphase, which can be observed in experiments. These dynamical behaviors can be\nunderstood by clarifying the stable vortex structure realized in each phase.",
        "positive": "Collapse and revival oscillations as a probe for the tunneling amplitude\n  in an ultra-cold Bose gas: We present a theoretical study of the quantum corrections to the revival time\ndue to finite tunneling in the collapse and revival of matter wave interference\nafter a quantum quench. We study hard-core bosons in a superlattice potential\nand the Bose-Hubbard model by means of exact numerical approaches and\nmean-field theory. We consider systems without and with a trapping potential\npresent. We show that the quantum corrections to the revival time can be used\nto accurately determine the value of the hopping parameter in experiments with\nultracold bosons in optical lattices."
    },
    {
        "anchor": "Monte Carlo study of fermionic trions in a square lattice with harmonic\n  confinement: We investigate the strong-coupling limit of a three-component Fermi mixture\nin an optical lattice with attractive interactions. In this limit bound states\n(trions) of the three components are formed. We derive an effective Hamiltonian\nfor these composite fermions and show that it is asymptotically equivalent to\nan antiferromagnetic Ising model. By using Monte-Carlo simulations, we\ninvestigate the spatial arrangement of the trions and the formation of a\ntrionic density wave (CDW), both in a homogeneous lattice and in the presence\nof an additional harmonic confinement. Depending on the strength of the\nconfinement and on the temperature, we found several scenarios for the trionic\ndistribution, including coexistence of disordered trions with CDW and band\ninsulator phases. Our results show that, due to a proximity effect, staggered\ndensity modulations are induced in regions of the trap where they would not\notherwise be present according to the local density approximation.",
        "positive": "Universal dynamics of a turbulent superfluid Bose gas: We study the emergence of universal scaling in the time-evolving momentum\ndistribution of a harmonically trapped three-dimensional Bose-Einstein\ncondensate, parametrically driven to a turbulent state. We demonstrate that the\nout-of-equilibrium dynamics post excitation is described by a single function\ndue to nearby non-thermal fixed points. The observed behavior connects the\ndynamics of a quantum turbulent state to several far-from-equilibrium\nphenomena. We present a controllable protocol to explore universality in such\nsystems, obtaining scaling exponents that can serve as reference for future\ntheoretical investigations. Our experimental results thus offer a promising\nroute to investigate the complex dynamics of the quantum turbulent regime under\na novel perspective."
    },
    {
        "anchor": "Ideal Weyl semimetal with 3D spin-orbit coupled ultracold quantum gas: There is an immense effort in search for various types of Weyl semimetals, of\nwhich the most fundamental phase consists of the minimal number of i.e. two\nWeyl points, but is hard to engineer in solids. Here we demonstrate how such\nfundamental Weyl semimetal can be realized in a maneuverable optical Raman\nlattice, with which the three-dimensional (3D) spin-orbit (SO) coupling is\nsynthesised for ultracold atoms. In addition, a new novel Weyl phase with\ncoexisting Weyl nodal points and nodal ring is also predicted here, and is\nshown to be protected by nontrivial linking numbers. We further propose\nfeasible techniques to precisely resolve 3D Weyl band topology through 2D\nequilibrium and dynamical measurements. This work leads to the first\nrealization of the most fundamental Weyl semimetal band and the 3D SO coupling\nfor ultracold quantum gases, which are respectively the significant issues in\nthe condensed matter and ultracold atom physics.",
        "positive": "Spatial entanglement entropy in the ground state of the Lieb-Liniger\n  model: We consider the entanglement between two spatial subregions in the\nLieb-Liniger model of bosons in one spatial dimension interacting via a contact\ninteraction. Using ground state path integral quantum Monte Carlo we\nnumerically compute the R\\'{e}nyi entropy of the reduced density matrix of the\nsubsystem as a measure of entanglement. Our numerical algorithm is based on a\nreplica method previously introduced by the authors, which we extend to\nefficiently study the entanglement of spatial subsystems of itinerant bosons.\nWe confirm a logarithmic scaling of the R\\'{e}nyi entropy with subsystem size\nthat is expected from conformal field theory, and compute the non-universal\nsubleading constant for interaction strengths ranging over two orders of\nmagnitude. In the strongly interacting limit, we find agreement with the known\nfree fermion result."
    },
    {
        "anchor": "Pinpointing Feshbach Resonances and Testing Efimov Universalities in\n  $^{39}$K: Using a combination of bound-state spectroscopy and loss spectroscopy, we\npinpoint eight intrastate Feshbach resonances in $^{39}$K, as well as six\npreviously unexplored interstate ones. We also perform a detailed\ncharacterization of four of the intrastate resonances and two of the interstate\nones. We carry out coupled-channel scattering calculations and find good\nagreement with experiment. The combination of experiment and theory provides a\nfaithful map of the scattering length $a$ and permits precision measurements of\nthe signatures of Efimov physics across four intermediate-strength resonances.\nWe measure the modulation of the $a^4$ scaling of the three-body loss\ncoefficient for both $a<0$ and $a>0$, as well as the many-body loss dynamics at\nunitarity (where $a$ diverges). The absolute positions of the observed Efimov\nfeatures confirm a ubiquitous breakdown of Efimov--van-der-Waals universality\nin $^{39}$K, while their relative positions are in agreement with the universal\nEfimov ratios. The loss dynamics at the three broadest Feshbach resonances are\nuniversal within experimental uncertainties, consistent with observing little\nvariation in the Efimov width parameters.",
        "positive": "Quantum quench and non-equilibrium dynamics in lattice-confined spinor\n  condensates: We present an experimental study on non-equilibrium dynamics of a spinor\ncondensate after it is quenched across a superfluid to Mott insulator (MI)\nphase transition in cubic lattices. Intricate dynamics consisting of\nspin-mixing oscillations at multiple frequencies are observed in time\nevolutions of the spinor condensate localized in deep lattices after the\nquantum quench. Similar spin dynamics also appear after spinor gases in the MI\nphase are suddenly moved away from their ground states via quenching magnetic\nfields. We confirm these observed spectra of spin-mixing dynamics can be\nutilized to reveal atom number distributions of an inhomogeneous system, and to\nstudy transitions from two-body to many-body dynamics. Our data also imply the\nnon-equilibrium dynamics depend weakly on the quench speed but strongly on the\nlattice potential. This enables precise measurements of the spin-dependent\ninteraction, a key parameter determining the spinor physics."
    },
    {
        "anchor": "Observation of the topological soliton state in the Su-Schrieffer-Heeger\n  model: The Su-Schrieffer-Heeger (SSH) model, which captures the most striking\ntransport properties of the conductive organic polymer $trans$-polyacetylene,\nprovides perhaps the most basic model system supporting topological\nexcitations. The alternating bond pattern of polyacetylene chains is captured\nby the bipartite sublattice structure of the SSH model, emblematic of\none-dimensional chiral symmetric topological insulators. This structure\nsupports two distinct nontrivial topological phases, which, when interfaced\nwith one another or with a topologically trivial phase, give rise to\ntopologically-protected, dispersionless boundary states. Using $^{87}$Rb atoms\nin a momentum-space lattice, we realize fully-tunable condensed matter\nHamiltonians, allowing us to probe the dynamics and equilibrium properties of\nthe SSH model. We report on the experimental quantum simulation of this model\nand observation of the localized topological soliton state through quench\ndynamics, phase-sensitive injection, and adiabatic preparation.",
        "positive": "Quantized vortices in dipolar supersolid Bose-Einstein condensed gases: We investigate the properties of quantized vortices in a dipolar\nBose-Einstein condensed gas by means of a generalised Gross-Pitaevskii\nequation. The size of the vortex core hugely increases by increasing the weight\nof the dipolar interaction and approaching the transition to the supersolid\nphase. The critical angular velocity for the existence of an energetically\nstable vortex decreases in the supersolid, due to the reduced value of the\ndensity in the interdroplet region. The angular momentum per particle\nassociated with the vortex line is shown to be smaller than $\\hbar$, reflecting\nthe reduction of the global superfluidity. The real-time vortex nucleation in a\nrotating trap is shown to be triggered, as for a standard condensate, by the\nsoftening of the quadrupole mode. For large angular velocities, when the\ndistance between vortices becomes comparable to the interdroplet distance, the\nvortices are arranged into a honeycomb structure, which coexists with the\ntriangular geometry of the supersolid lattice and persists during the free\nexpansion of the atomic cloud."
    },
    {
        "anchor": "Many-body \\textit{T}-matrix theory of a strongly interacting spin-orbit\n  coupled Fermi gas: Momentum-resolved radio-frequency spectroscopy and\n  fermionic pairing: Interacting Fermi gases with spin-orbit coupling are responsible for many\nintriguing phenomena such as topological superfluids and Majorana fermions.\nHere we characterize theoretically fermionic pairing in a strongly interacting\nspin-orbit coupled Fermi gas, by using momentum-resolved radio-frequency\nspectroscopy. We develop a strong-coupling $T$-matrix theory and present a\nphase diagram near the unitary resonance limit. A smooth transition from atomic\nto molecular responses in the momentum-resolved spectroscopy is predicted, with\na clear signature of anisotropic pairing at and below resonance. Our prediction\nwith many-body pairing can be directly tested in a spin-orbit coupled Fermi gas\nof $^{40}$K or $^{6}$Li atoms near broad Feshbach resonances.",
        "positive": "Vortex and Meissner phases of strongly-interacting bosons on a two-leg\n  ladder: We establish the phase diagram of the strongly-interacting Bose-Hubbard model\ndefined on a two-leg ladder geometry in the presence of a homogeneous flux. Our\nwork is motivated by a recent experiment [Atala et al., Nature Phys. 10, 588\n(2014)], which studied the same system, in the complementary regime of weak\ninteractions. Based on extensive density matrix renormalization group\nsimulations and a bosonization analysis, we fully explore the parameter space\nspanned by filling, inter-leg tunneling, and flux. As a main result, we\ndemonstrate the existence of gapless and gapped Meissner and vortex phases,\nwith the gapped states emerging in Mott-insulating regimes. We calculate\nexperimentally accessible observables such as chiral currents and vortex\npatterns."
    },
    {
        "anchor": "Calculation of the critical temperature of a dilute Bose gas in the\n  Bogoliubov approximation: Following an earlier calculation in 3D, we calculate the 2D critical\ntemperature of a dilute, translation-invariant Bose gas using a variational\nformulation of the Bogoliubov approximation introduced by Critchley and Solomon\nin 1976. This provides the first analytical calculation of the\nKosterlitz-Thouless transition temperature that includes the constant in the\nlogarithm.",
        "positive": "Experimental realization of Josephson junctions for an Atom SQUID: We report the creation of a pair of Josephson junctions on a toroidal dilute\ngas Bose-Einstein condensate (BEC), a configuration that is the cold atom\nanalog of the well-known dc superconducting quantum interference device\n(SQUID). We observe Josephson effects, measure the critical current of the\njunctions, and find dynamic behavior that is in good agreement with the simple\nJosephson equations for a tunnel junction with the ideal sinusoidal\ncurrent-phase relation expected for the parameters of the experiment. The\njunctions and toroidal trap are created with the painted potential, a\ntime-averaged optical dipole potential technique which will allow scaling to\nmore complex BEC circuit geometries than the single atom-SQUID case reported\nhere. Since rotation plays the same role in the atom SQUID as magnetic field\ndoes in the dc SQUID magnetometer, the device has potential as a compact\nrotation sensor."
    },
    {
        "anchor": "Spin-orbit coupled correlated metal phase in Kondo lattices: an\n  implementation with alkaline-earth atoms: We show that an interplay between quantum effects, strong on-site\nferromagnetic exchange interaction and antiferromagnetic correlations in Kondo\nlattices can give rise to an exotic spin-orbit coupled metallic state in\nregimes where classical treatments predict a trivial insulating behavior. This\nphenomenon can be simulated with ultracold alkaline-earth fermionic atoms\nsubject to a laser-induced magnetic field by observing dynamics of spin-charge\nexcitations in quench experiments.",
        "positive": "Readout of the atomtronic quantum interference device: A Bose-Einstein condensate confined in ring shaped lattices interrupted by a\nweak link and pierced by an effective magnetic flux defines the atomic\ncounterpart of the superconducting quantum interference device: the atomtronic\nquantum interference device (AQUID). In this paper, we report on the detection\nof current states in the system through a self-heterodyne protocol. Following\nthe original proposal of the NIST and Paris groups, the ring-condensate\nmany-body wave function interferes with a reference condensate expanding from\nthe center of the ring. We focus on the rf-AQUID which realizes effective qubit\ndynamics. Both the Bose-Hubbard and Gross-Pitaevskii dynamics are studied. For\nthe Bose-Hubbard dynamics, we demonstrate that the self-heterodyne protocol can\nbe applied, but higher-order correlations in the evolution of the interfering\ncondensates are measured to readout of the current states of the system. We\nstudy how states with macroscopic quantum coherence can be told apart analyzing\nthe noise in the time of flight of the ring condensate."
    },
    {
        "anchor": "Trapped Bose-Einstein condensates in the presence of a current\n  nonlinearity: We investigate the effect of a current nonlinearity on the evolution of a\ntrapped atomic Bose-Einstein condensate. We have implemented techniques from\nthe field of nonlinear optics to provide new insights into the irregular\ndynamics associated with chiral superfluids. We have found that the current\nnonlinearity can be treated as a Kerr-like nonlinearity modulated by a\nspatiotemporal function that can lead to a number of processes such as\nbroadening and compression of the wave function. In the long time scale limit,\nthe wave function is drastically deformed and delocalised compared to its\ninitial state. However, localised modes which oscillate with the period of the\ninverse trap frequency can still be observed.",
        "positive": "Bad-Metal Relaxation Dynamics in a Fermi Lattice Gas: We report the discovery of phenomena consistent with bad-metal relaxation\ndynamics in the metallic regime of an optical-lattice Hubbard model. The\ntransport lifetime induced by inter-particle scattering for a mass current of\natoms excited by stimulated Raman transitions is measured, and the\ncorresponding analog of resistivity is inferred. By exploring a range of\ntemperature, we demonstrate incompatibility with weak-scattering theory and a\nkey characteristic of bad metals: anomalous resistivity scaling consistent with\n$T$-linear behavior. We also observe the onset of two behaviors---incoherent\ntransport and the approach to the Mott-Ioffe-Regel limit---associated with bad\nmetals. The interaction and temperature scaling of resistivity are verified to\nbe consistent with dynamic mean-field theory (DMFT) predictions of a bad metal,\nwhich is associated with the reduction of quasiparticle weight by strong\ninteractions."
    },
    {
        "anchor": "Composite fermion basis for two-component Bose gases: Despite its success, the composite fermion (CF) construction possesses some\nmathematical features that have, until recently, not been fully understood. In\nparticular, it is known to produce wave functions that are not necessarily\northogonal, or even linearly independent, after projection to the lowest Landau\nlevel. While this is usually not a problem in practice in the quantum Hall\nregime, we have previously shown that it presents a technical challenge for\nrotating Bose gases with low angular momentum. These are systems where the CF\napproach yields surprisingly good approximations to the exact eigenstates of\nweak short-range interactions, and so solving the problem of linearly dependent\nwave functions is of interest. It can also be useful for studying higher bands\nof fermionic quantum Hall states. Here we present several ways of constructing\na basis for the space of so-called \"simple\" CF states for two-component\nrotating Bose gases in the lowest Landau level, and prove that they all give\nsets of linearly independent wave functions that span the space. Using this\nbasis, we study the structure of the lowest-lying state using so-called\nrestricted wave functions. We also examine the scaling of the overlap between\nthe exact and CF wave functions at the maximal possible angular momentum for\nsimple states.",
        "positive": "Observation of quantum-limited spin transport in strongly interacting\n  two-dimensional Fermi gases: We measure the transport properties of two-dimensional ultracold Fermi gases\nduring transverse demagnetization in a magnetic field gradient. Using a\nphase-coherent spin-echo sequence, we are able to distinguish bare spin\ndiffusion from the Leggett-Rice effect, in which demagnetization is slowed by\nthe precession of spin current around the local magnetization. When the\ntwo-dimensional scattering length is tuned to be comparable to the inverse\nFermi wave vector $k_F^{-1}$, we find that the bare transverse spin diffusivity\nreaches a minimum of $1.7(6)\\hbar/m$, where $m$ is the bare particle mass. The\nrate of demagnetization is also reflected in the growth rate of the s-wave\ncontact, observed using time-resolved spectroscopy. At unitarity, the contact\nrises to $0.28(3) k_F^2$ per particle, measuring the breaking of scaling\nsymmetry. Our observations support the conjecture that in systems with strong\nscattering, the local relaxation rate is bounded from above by $k_B T/\\hbar$."
    },
    {
        "anchor": "Depletion and fluctuations of a trapped dipolar Bose-Einstein condensate\n  in the roton regime: We consider the non-condensate density and density fluctuations of a trapped\ndipolar Bose-Einstein condensate, focusing on the regime where a roton-like\nexcitation spectrum develops. Our results show that a characteristic peak in\nthe non-condensate density occurs at trap center due to the rotons. In this\nregime we also find that the anomalous density becomes positive and peaked,\ngiving rise to enhanced density fluctuations. We calculate the non-condensate\ndensity in momentum space and show that a small momentum halo is associated\nwith the roton excitations.",
        "positive": "Thermodynamics of spin-1/2 fermions on coarse temporal lattices using\n  automated algebra: Recent advances in automated algebra for dilute Fermi gases in the virial\nexpansion, where coarse temporal lattices were found advantageous, motivate the\nstudy of more general computational schemes that could be applied to arbitrary\ndensities, beyond the dilute limit where the virial expansion is physically\nreasonable. We propose here such an approach by developing what we call the\nQuantum Thermodynamics Computational Engine (QTCE). In QTCE, the imaginary-time\ndirection is discretized and the interaction is accounted for via a quantum\ncumulant expansion, where the coefficients are expressed in terms of\nnoninteracting expectation values. The aim of QTCE is to enable the systematic\nresolution of interaction effects at fixed temporal discretization, as in\nlattice Monte Carlo calculations, but here in an algebraic rather than\nnumerical fashion. Using this approach, in combination with numerical\nintegration techniques (both known and alternative ones proposed here), we\nexplore the thermodynamics of spin-1/2 fermions, focusing on the unitary limit\nin 3 spatial dimensions, but also exploring the effects of continuously varying\nthe spatial dimension below 3. We find that, remarkably, extremely coarse\ntemporal lattices, when suitably renormalized using known results from the\nvirial expansion, yield stable partial sums for QTCE's cumulant expansion which\nare qualitatively and quantitatively correct in wide regions, compared with\nknown experimental results."
    },
    {
        "anchor": "Pseudogap and preformed pairs in the imbalanced Fermi gas in two\n  dimensions: The physics of the pseudogap state is intimately linked with the pairing\nmechanism that gives rise to superfluidity in quantum gases and to\nsuperconductivity in high-Tc cuprates, and therefore, both in quantum gases and\nsuperconductors, the pseudogap state and preformed pairs have been under\nintensive experimental scrutiny. Here, we develop a path integral treatment\nthat provides a divergence-free description of the paired state in\ntwo-dimensional Fermi gases. Within this formalism, we derive the pseudogap\ntemperature and the pair fluctuation spectral function, and compare these\nresults with the recent experimental measument of the pairing in the\ntwo-dimensional Fermi gas. The removal of the infrared divergence in the number\nequations is shown both numerically and analytically, through a study of the\nlong-wavelength and low-energy limit of the pair fluctuation density. Besides\nthe pseudogap temperature, also the pair formation temperature and the critical\ntemperature for superfluidity are derived. The latter corresponds to the\nBerezinski-Kosterlitz-Thouless (BKT) temperature. The pseudogap temperature,\nwhich coincides with the pair formation temperature in mean field, is found to\nbe suppressed with respect to the pair formation temperature by fluctuations.\nThis suppression is strongest for large binding energies of the pairs. Finally,\nwe investigate how the pair formation temperature, the pseudogap temperature\nand the BKT temperature behave as a function of both binding energy and\nimbalance between the pairing partners in the Fermi gas. This allows to set up\nphase diagrams for the two-dimensional Fermi gas, in which the superfluid\nphase, the phase-fluctuating quasicondensate, and the normal state can be\nidentified.",
        "positive": "Pairing and radio-frequency spectroscopy in two-dimensional Fermi gases: We theoretically study the normal phase properties of strongly interacting\ntwo-component Fermi gases in two spatial dimensions. In the limit of weak\nattraction, we find that the gas can be described in terms of effective\npolarons. As the attraction between fermions increases, we find a crossover\nfrom a gas of non-interacting polarons to a pseudogap regime. We investigate\nhow this crossover is manifested in the radio-frequency (rf) spectroscopy. Our\nfindings qualitatively explain the differences in the recent rf spectroscopy\nmeasurements of two-dimensional Fermi gases [Sommer et al., Phys. Rev. Lett.\n108, 045302 (2012) and Zhang et al., Phys. Rev. Lett. 108, 235302 (2012)]."
    },
    {
        "anchor": "Exploring Non-Abelian Geometric Phases in Spin-1 Ultracold Atoms: Non-Abelian and non-adiabatic variants of Berry's geometric phase have been\npivotal in the recent advances in fault tolerant quantum computation gates,\nwhile Berry's phase itself is at the heart of the study of topological phases\nof matter. The geometrical and topological properties of the phase space of\nspin$-1$ quantum states is richer than that of spin$-1/2$ quantum states and is\nrelatively unexplored. For instance, the spin vector of a spin-1 system, unlike\nthat of a spin$-1/2$ system, can lie anywhere on or inside the Bloch sphere\nrepresenting the phase space. Recently, a generalization of Berry's phase that\nencapsulates the topology of spin-1 quantum states has been formulated in J.\nMath. Phys., 59(6), 062105. This geometric phase includes loops that go inside\nthe Bloch sphere and is carried by the tensor of spin fluctuations, unlike\nBerry's phase which is carried by the global phase of the quantum state.\nFurthermore, due to a mathematical singularity at the center of the Bloch\nsphere, the class of loops that pass through the center are called singular\nloops and are significant because their geometric phase is non-Abelian. In\ncontrast with Berry's phase for spin$-1/2$ systems, whose properties come from\nthe topology of a sphere, the properties of singular loop geometric phases come\nfrom the topology of the real projective plane $\\mathbb{RP}^2$, which is more\nnon-trivial. Here we use coherent control of ultracold $^{87}$Rb atoms in an\noptical trap to experimentally explore this geometric phase for singular loops\nin a spin-1 quantum system.",
        "positive": "Anomalous frequency shifts in a one-dimensional trapped Bose gas: We consider a system of interacting bosons in one dimension at a two-body\nresonance. This system, which is weakly interacting, is known to give rise to\neffective three-particle interactions, whose dynamics is similar to that of a\ntwo-dimensional Bose gas with two-body interactions, and exhibits an identical\nscale anomaly. We consider the experimentally relevant scenario of a\nharmonically trapped system. We solve the three-body problem exactly and\nevaluate the shifts in the frequency of the lowest compressional mode with\nrespect to the dipole mode, and find that the effect of the anomaly is to\nincrease the mode's frequency. We also consider the weak-coupling regime of the\ntrapped many-boson problem and find, within the local density approximation,\nthat the frequency of the lowest compressional mode is also shifted upwards in\nthis limit. Moreover, the anomalous frequency shifts are enhanced by the higher\nparticle number to values that should be observable experimentally."
    },
    {
        "anchor": "Cavity quantum electrodynamics of ultracold atoms in optical and\n  optomechanical cavities: In this review article, we present the recent theoretical developments and\nsome breakthrough experiments in cavity QED systems (optical and optomechanical\nsystems) and also focus on the experimental realization of the theoretical\nproposals.",
        "positive": "Exact relations for quantum-mechanical few-body and many-body problems\n  with short-range interactions in two and three dimensions: We derive relations between various observables for N particles with\nzero-range or short-range interactions, in continuous space or on a lattice, in\ntwo or three dimensions, in an arbitrary external potential. Some of our\nresults generalise known relations between large-momentum behavior of the\nmomentum distribution, short-distance behavior of the pair correlation function\nand of the one-body density matrix, derivative of the energy with respect to\nthe scattering length or to time, and the norm of the regular part of the\nwavefunction; in the case of finite-range interactions, the interaction energy\nis also related to dE/da. The expression relating the energy to a functional of\nthe momentum distribution is also generalised, and is found to break down for\nEfimov states with zero-range interactions, due to a subleading oscillating\ntail in the momentum distribution. We also obtain new expressions for the\nderivative of the energy of a universal state with respect to the effective\nrange, the derivative of the energy of an efimovian state with respect to the\nthree-body parameter, and the second order derivative of the energy with\nrespect to the inverse (or the logarithm in the two-dimensional case) of the\nscattering length. The latter is negative at fixed entropy. We use exact\nrelations to compute corrections to exactly solvable three-body problems and\nfind agreement with available numerics. For the unitary gas, we compare exact\nrelations to existing fixed-node Monte-Carlo data, and we test, with existing\nQuantum Monte Carlo results on different finite range models, our prediction\nthat the leading deviation of the critical temperature from its zero range\nvalue is linear in the interaction effective range r_e with a model independent\nnumerical coefficient."
    },
    {
        "anchor": "Sign-changing photon-mediated atom interactions in multimode cavity QED: Sign-changing interactions constitute a crucial ingredient in the creation of\nfrustrated many-body systems such as spin glasses. We present here the\ndemonstration of a photon-mediated sign-changing interaction between\nBose-Einstein condensed (BEC) atoms in a confocal cavity. The interaction\nbetween two atoms is of an unusual, nonlocal form proportional to the cosine of\nthe inner product of the atoms' position vectors. This interaction arises from\nthe differing Gouy phase shifts of the cavity's degenerate modes. Moreover,\nthese Gouy phase anomalies induce an extra pattern of Z_2-symmetry-breaking in\nthe atomic density-wave self-ordering that arises from a nonequilibrium\nDicke-type phase transition in the system. This state is detected via the\nholographic imaging of the cavity's superradiant emission. Together with Ref.\n[1], we explore this interaction's influence on superradiant phase transitions\nin multimode cavities. Employing this interaction in cavity QED spin systems\nmay enable the creation of artificial spin glasses and quantum neural networks.",
        "positive": "Collisions of self-bound quantum droplets: We report on the study of binary collisions between quantum droplets formed\nby an attractive mixture of ultracold atoms. We distinguish two main outcomes\nof the collision, i.e. merging and separation, depending on the velocity of the\ncolliding pair. The critical velocity $v_c$ that discriminates between the two\ncases displays a different dependence on the atom number $N$ for small and\nlarge droplets. By comparing our experimental results with numerical\nsimulations, we show that the non-monotonic behavior of $v_c(N)$ is due to the\ncrossover from a compressible to an incompressible regime, where the\ncollisional dynamics is governed by different energy scales, i.e. the droplet\nbinding energy and the surface tension. These results also provide the first\nevidence of the liquid-like nature of quantum droplets in the large $N$ limit,\nwhere their behavior closely resembles that of classical liquid droplets."
    },
    {
        "anchor": "Phase structure of the interacting Su-Schrieffer-Heeger model and the\n  relationship with the Gross-Neveu model on lattice: The $N$-flavor interacting Su-Schrieffer-Heeger (i-SSH) model realizable in\ncold-atoms in an optical lattice is studied. We clarify the relationship\nbetween the i-SSH model and the Chiral-Gross-Neveu-Wilson (CGNW) model.\nFollowing the previous study of the CGNW model in the high-energy physics\ncommunity, the groundstate phases of the i-SSH model are investigated and\ninterpreted from the view of the phases of the CGNW model. The interaction\neffect on the i-SSH model, belonging to the topological BDI class, is grasped\nby following the view of the dynamical breakdown of chiral symmetry in the CGNW\nmodel. Furthermore, we compare the large-$N$ groundstate phase diagram with\nthat of the $N=1$ case obtained by exact diagonalization and then propose a\ntable-top cold-atom quantum simulator to test the model.",
        "positive": "Roton in a few-body dipolar system: We solve numerically exactly the many-body 1D model of bosons interacting via\nshort-range and dipolar forces and moving in the box with periodic boundary\nconditions. We show that the lowest energy states with fixed total momentum can\nbe smoothly transformed from the typical states of collective character to\nstates resembling single particle excitations. In particular, we identify the\ncelebrated roton state. The smooth transition is realized by simultaneous\ntuning short-range interactions and adjusting a trap geometry. With our methods\nwe study the weakly interacting regime as well as the regime beyond the range\nof validity of the Bogoliubov approximation."
    },
    {
        "anchor": "Mixture of scalar bosons and two-color fermions in one dimension:\n  Superfluid-insulator transitions: Superfluid-insulator transitions in a one-dimensional mixture of two-color\nfermions and scalar bosons are studied within the framework of the\nBose-Fermi-Hubbard model. Zero-temperature phase diagrams are constructed for\nrepulsive intraspecies interactions and attractive or repulsive interspecies\ncouplings. In addition to the trivial Mott insulator phases, we report the\nemergence of new non-trivial insulator phases that depend on the sign of the\nboson-fermion interaction. These non-trivial insulator phases satisfy the\nconditions $\\rho_B\\pm\\rho_F=n$ and $\\rho_B\\pm \\tfrac{1}{2}\\rho_F=n$, with the\nplus (minus) sign for repulsive (attractive) interactions and $n$ an integer.\nFar from fermionic half-filling, the boson-fermion interaction drives a\ngapless-gapped transition in the spin sector. Our findings could be observed\nexperimentally in state-of-the-art cold-atom setups.",
        "positive": "Three-Body Interacting Bosons in Free Space: We propose a method of controlling two- and three-body interactions in an\nultracold Bose gas in any dimension. The method requires us to have two coupled\ninternal single-particle states split in energy such that the upper state is\noccupied virtually but amply during collisions. By varying system parameters\none can switch off the two-body interaction while maintaining a strong\nthree-body one. The mechanism can be implemented for dipolar bosons in the\nbilayer configuration with tunnelling or in an atomic system by using\nradio-frequency fields to couple two hyperfine states. One can then aim to\nobserve a purely three-body-interacting gas, dilute self-trapped droplets, the\npaired superfluid phase, Pfaffian state, and other exotic phenomena."
    },
    {
        "anchor": "Orthogonal and antiparallel vortex tubes and energy cascades in quantum\n  turbulence: We investigate the dynamics of energy cascades in quantum turbulence by\ndirectly observing the vorticity distributions in numerical simulations of the\nGross-Pitaevskii equation. By Fourier filtering each scale of the vorticity\ndistribution, we find that antiparallel vortex tubes at a large scale generate\nsmall-scale vortex tubes orthogonal to those at the large scale, which is a\nmanifestation of the energy cascade from large to small scales. We reveal the\ndynamics of quantized vortex lines in these processes.",
        "positive": "Effect of interactions in the interference pattern of Bose Einstein\n  condensates: Understanding the effect of interactions in the phase evolution of expanding\natomic Bose Einstein condensates is fundamental to describe the basic\nphenomenon of matter wave interference. Many theoretical and experimental works\ntackled this problem, always with the implicit assumption that the mutual\ninteraction between two expanding condensates rigidly modifies the phase\nevolution through an effective force. In this paper, we present a combined\nexperimental and theoretical investigation of the interference profile of\nexpanding $^{87}$Rb condensates, with a specific focus on the effect of\ninteractions. We come to the different conclusion that the mutual interaction\nproduces local modifications of the condensate phase only in the region where\nthe wavepackets overlap."
    },
    {
        "anchor": "Stability and dynamics of matter-wave vortices in the presence of\n  collisional inhomogeneities and dissipative perturbations: In this work, the spectral properties of a singly-charged vortex in a In this\nwork, the spectral properties of a singly-charged vortex in a Bose-Einstein\ncondensate confined in a highly anisotropic (disk-shaped) harmonic trap are\ninvestigated. Special emphasis is given on the analysis of the so-called\nanomalous (negative energy) mode of the Bogoliubov spectrum. We use analytical\nand numerical techniques to illustrate the connection of the anomalous mode to\nthe precession dynamics of the vortex in the trap. Effects due to inhomogeneous\ninteratomic interactions and dissipative perturbations motivated by finite\ntemperature considerations are explored. We find that both of these effects may\ngive rise to oscillatory instabilities of the vortex, which are suitably\ndiagnosed through the perturbation-induced evolution of the anomalous mode, and\nbeing monitored by direct numerical simulations.",
        "positive": "Delocalization of ultracold atoms in a disordered potential due to light\n  scattering: We numerically study the expansion dynamics of ultracold atoms in a\none-dimensional disordered potential in the presence of a weak position\nmeasurement of the atoms. We specifically consider this position measurement to\nbe realized by a combination of an external laser and a periodic array of\noptical microcavities along a waveguide. The position information is acquired\nthrough the scattering of a near-resonant laser photon into a specific\neigenmode of one of the cavities. The time evolution of the atomic density in\nthe presence of this light scattering mechanism is described within a Lindblad\nmaster equation approach, which is numerically implemented using the Monte\nCarlo wave function technique. We find that an arbitrarily weak rate of photon\nemission leads to a breakdown of Anderson localization of the atoms."
    },
    {
        "anchor": "Lower bound for the population of hyperfine component $\u03bc=0$ particles\n  in the ground state of spin-1 condensates: An analytical expression for the lower bound of the average number of\nhyperfine component $\\mu =0$ particles in the ground state of spin-1\ncondensates (denoted as $\\overset{\\_\\_}{\\rho _{0}}$) under a magnetic field has\nbeen derived. In the derivation the total magnetization $M$ is kept rigorously\nconserved. Numerical examples are given to show the applicability of the\nanalytical expression. It was found that, in a broad domain of parameters\nspecified in the paper, the lower bound is very close to the actual\n$\\overset{\\_\\_}{\\rho _{0}}$. Thereby, in this domain, $\\overset{\\_\\_}{% \\rho\n_{0}}$ can be directly evaluated simply by using the analytical expression.",
        "positive": "How to observe dipolar effects in spinor Bose-Einstein condensates: We study a spinor condensate of alkali atoms in F = 1 hyperfine state under\nthe presence of an oscillating magnetic field. We find resonances which, due to\nthe dipolar interactions, magnify the transfer of atoms from mF = 1 to mF = 0\nZeeman sublevel. These resonances occur at magnetic fields of the order of\nmilligaus and are broad enough to enable observation of the famous Einstein-de\nHaas effect, which is solely a dipolar effect, in systems of cold alkali gases."
    },
    {
        "anchor": "All-Optical Production of a Lithium Quantum Gas Using Narrow-Line Laser\n  Cooling: We have used the narrow $2S_{1/2} \\rightarrow 3P_{3/2}$ transition in the\nultraviolet (uv) to laser cool and magneto-optically trap (MOT) $^6$Li atoms.\nLaser cooling of lithium is usually performed on the $2S_{1/2} \\rightarrow\n2P_{3/2}$ (D2) transition, and temperatures of $\\sim$300 $\\mu$K are typically\nachieved. The linewidth of the uv transition is seven times narrower than the\nD2 line, resulting in lower laser cooling temperatures. We demonstrate that a\nMOT operating on the uv transition reaches temperatures as low as 59 $\\mu$K.\nFurthermore, we find that the light shift of the uv transition in an optical\ndipole trap at 1070 nm is small and blue-shifted, facilitating efficient\nloading from the uv MOT. Evaporative cooling of a two spin-state mixture of\n$^6$Li in the optical trap produces a quantum degenerate Fermi gas with $3\n\\times 10^{6}$ atoms a total cycle time of only 11 s.",
        "positive": "Superfluid/ferromagnet/superfluid junction and $\u03c0$-phase in a\n  superfluid Fermi gas: We investigate the possibility of superfluid/ferromagnet/superfluid\n(SFS)-junction in a superfluid Fermi gas. To examine this possibility in a\nsimple manner, we consider an attractive Hubbard model at $T=0$ within the\nmean-field theory. When a potential barrier is embedded in a superfluid Fermi\ngas with population imbalance ($N_\\uparrow>N_\\downarrow$, where $N_\\sigma$ is\nthe number of atoms with pseudospin $\\sigma=\\uparrow,\\downarrow$), this barrier\nis shown to be {\\it magnetized} in the sense that excess $\\uparrow$-spin atoms\nare localized around it. The resulting superfluid Fermi gas is spatially\ndivided into two by this {\\it ferromagnet}, so that one obtains a junction\nsimilar to the superconductor/ferromagnet/superconductor-junction discussed in\nsuperconductivity. Indeed, we show that the so-called $\\pi$-phase, which is a\ntypical phenomenon in the SFS-junction, is realized, where the superfluid order\nparameter changes its sign across the junction. Our results would be useful for\nthe study of magnetic effects on fermion superfluidity using an ultracold Fermi\ngas."
    },
    {
        "anchor": "BCS-BEC crossover in atomic Fermi gases in quasi-two-dimensional Lieb\n  lattices: Effects of flat band and finite temperature: We investigate the finite-temperature superfluid behavior of ultracold atomic\nFermi gases in quasi-two-dimensional Lieb lattices with a short-range\nattractive interaction, using a pairing fluctuation theory within the BCS-BEC\ncrossover framework. We find that the presence of a flat band, along with van\nHove singularities, leads to exotic quantum phenomena. As the Fermi level\nenters the flat band, both the gap and the superfluid transition temperature\n$T_c$ as a function of interaction change from a conventional exponential\nbehavior into an unusual power law, and the evolution of superfluid densities\nwith temperature also follows a power law even at weak interactions. The\nquantum geometric effects, manifested by an enhanced effective pair hopping\nintegral, may contribute significantly to both $T_c$ and the superfluidities.\nAs the chemical potential crosses the van Hove singularities in the weak\ninteraction regime, the nature of pairing changes between particle-like and\nhole-like. A pair density wave state emerges at high densities with a\nrelatively strong interaction strength.",
        "positive": "Experimental realization of a long-range antiferromagnet in the Hubbard\n  model with ultracold atoms: Many exotic phenomena in strongly correlated electron systems emerge from the\ninterplay between spin and motional degrees of freedom. For example, doping an\nantiferromagnet gives rise to interesting phases including pseudogap states and\nhigh-temperature superconductors. A promising route towards achieving a\ncomplete understanding of these materials begins with analytic and\ncomputational analysis of simplified models. Quantum simulation has recently\nemerged as a complementary approach towards understanding these models.\nUltracold fermions in optical lattices offer the potential to answer open\nquestions on the low-temperature regime of the doped Hubbard model, which is\nthought to capture essential aspects of the cuprate superconductor phase\ndiagram but is numerically intractable in that parameter regime. A new\nperspective is afforded by quantum gas microscopy of fermions, which allows\nreadout of magnetic correlations at the site-resolved level. Here we report the\nrealization of an antiferromagnet in a repulsively interacting Fermi gas on a\n2D square lattice of approximately 80 sites. Using site-resolved imaging, we\ndetect (finite-size) antiferromagnetic long-range order (LRO) through the\ndevelopment of a peak in the spin structure factor and the divergence of the\ncorrelation length that reaches the size of the system. At our lowest\ntemperature of T/t = 0.25(2) we find strong order across the entire sample. Our\nexperimental platform enables doping away from half filling, where pseudogap\nstates and stripe ordering are expected, but theoretical methods become\nnumerically intractable. In this regime we find that the antiferromagnetic LRO\npersists to hole dopings of about 15%, providing a guideline for computational\nmethods. Our results demonstrate that quantum gas microscopy of ultracold\nfermions in optical lattices can now address open questions on the\nlow-temperature Hubbard model."
    },
    {
        "anchor": "Creating exotic condensates via quantum-phase-revival dynamics in\n  engineered lattice potentials: In the field of ultracold atoms in optical lattices a plethora of phenomena\ngoverned by the hopping energy $J$ and the interaction energy $U$ have been\nstudied in recent years. However, the trapping potential typically present in\nthese systems sets another energy scale and the effects of the corresponding\ntime scale on the quantum dynamics have rarely been considered. Here we study\nthe quantum collapse and revival of a lattice Bose-Einstein condensate (BEC) in\nan arbitrary spatial potential, focusing on the special case of harmonic\nconfinement. Analyzing the time evolution of the single-particle density\nmatrix, we show that the physics arising at the (temporally) recurrent quantum\nphase revivals is essentially captured by an effective single particle theory.\nThis opens the possibility to prepare exotic non-equilibrium condensate states\nwith a large degree of freedom by engineering the underlying spatial lattice\npotential.",
        "positive": "Quasiparticle lifetime in ultracold fermionic mixtures with density and\n  mass imbalance: We show that atomic Fermi mixtures with density and mass imbalance exhibit a\nrich diversity of scaling laws for the quasiparticle decay rate beyond the\nquadratic energy and temperature dependence of conventional Fermi liquids. For\ncertain densities and mass ratios, the decay rate is linear whereas in other\ncases it exhibits a plateau. Remarkably, this plateau extends from the deeply\ndegenerate to the high temperature classical regime of the light species. Many\nof these scaling laws are analogous to what is found in very different systems\nincluding dirty metals, liquid metals, and high temperature plasmas. The Fermi\nmixtures can in this sense span a whole range of seemingly diverse and separate\nphysical systems. Our results are derived in the weakly interacting limit\nmaking them quantitatively reliable. The different regimes can be detected with\nradio-frequency spectroscopy."
    },
    {
        "anchor": "A Hermite-Pad\u00e9 perspective on Gell-Mann--Low renormalization group: an\n  application to the correlation function of Lieb-Liniger gas: While Pad\\'e approximation is a general method for improving convergence of\nseries expansions, Gell-Mann--Low renormalization group normally relies on the\npresence of special symmetries. We show that in the single-variable case, the\nlatter becomes an integral Hermite-Pad\\'e approximation, needing no special\nsymmetries. It is especially useful for interpolating between expansions for\nsmall values of a variable and a scaling law of known exponent for large\nvalues. As an example, we extract the scaling-law prefactor for the one-body\ndensity matrix of the Lieb-Liniger gas. Using a new result for the 4th-order\nterm in the short-distance expansion, we find a remarkable agreement with known\nab initio numerical results.",
        "positive": "Classical-like wakes past elliptical obstacles in atomic Bose-Einstein\n  condensates: We reinvestigate numerically the classic problem of two-dimensional\nsuperfluid flow past an obstacle. Taking the obstacle to be elongated\n(perpendicular to the flow), rather than the usual circular form, is shown to\npromote the nucleation of quantized vortices, enhance their subsequent\ninteractions, and lead to wakes which bear striking similarity to their\nclassical (viscous) counterparts. Then, focussing on the recent experiment of\nKwon et al. (arXiv:1403.4658) in a trapped condensate, we show that an\nelliptical obstacle leads to a cleaner and more efficient means to generate\ntwo-dimensional quantum turbulence."
    },
    {
        "anchor": "Flat band of topological states bound to a mobile impurity: I consider a particle in the topologically non-trivial Su-Schrieffer-Heeger\n(SSH) model interacting strongly with a mobile impurity, whose quantum dynamics\nis described by a topologically trivial Hamiltonian. A particle in the SSH\nmodel admits a topological zero-energy edge mode when a hard boundary is placed\nat a given site of the chain, which may be modelled by a static impurity. By\nsolving the two-body problem analytically I show that, when the impurity is\nmobile, the topological edge states of the Su-Schrieffer-Heeger model remain\nfully robust and a flat band of bound states at zero energy is formed as long\nas the continuum spectrum of the two-body problem remains gapped, without the\nneed for any boundaries in the system. This is guaranteed for a sufficiently\nheavy impurity. As a consequence of the infinite degeneracy of the zero energy\nmodes, it is possible to spatially localise the particle-impurity bound states,\neffectively making the impurity immobile. These effects can be readily observed\nusing two-dimensional photonic lattices.",
        "positive": "Out-of-phase oscillation between superfluid and thermal components for a\n  trapped Bose condensate under oscillatory excitation: The vortex nucleation and the emergence of quantum turbulence induced by\noscillating magnetic fields, introduced by Henn E A L, et al. 2009 (Phys. Rev.\nA 79, 043619) and Henn E A L, et al. 2009 (Phys. Rev. Lett. 103, 045301), left\na few open questions concerning the basic mechanisms causing those interesting\nphenomena. Here, we report the experimental observation of the slosh dynamics\nof a magnetically trapped $^{87}$Rb Bose-Einstein condensate (BEC) under the\ninfluence of a time-varying magnetic field. We observed a clear relative\ndisplacement in between the condensed and the thermal fraction center-of-mass.\nWe have identified this relative counter move as an out-of-phase oscillation\nmode, which is able to produce ripples on the condensed/thermal fractions\ninterface. The out-of-phase mode can be included as a possible mechanism\ninvolved in the vortex nucleation and further evolution when excited by time\ndependent magnetic fields."
    },
    {
        "anchor": "Broad universal Feshbach resonances in the chaotic spectrum of\n  Dysprosium atoms: We report on the observation of weakly-bound dimers of bosonic Dysprosium\nwith a strong universal s-wave halo character, associated with broad magnetic\nFeshbach resonances. These states surprisingly decouple from the chaotic\nbackgound of narrow resonances, persisting across many such narrow resonances.\nIn addition they show the highest reported magnetic moment\n$\\mu\\simeq20\\,\\mu_{\\rm B}$ of any ultracold molecule. We analyze our findings\nusing a coupled-channel theory taking into account the short range van der\nWaals interaction and a correction due to the strong dipole moment of\nDysprosium. We are able to extract the scattering length as a function of\nmagnetic field associated with these resonances and obtain a background\nscattering length $a_{\\rm bg}=91(16)\\,a_0$. These results offer prospects of a\ntunability of the interactions in Dysprosium, which we illustrate by observing\nthe saturation of three-body losses.",
        "positive": "Bose-Einstein condensation in canonical ensemble with fixed total\n  momentum: We consider Bose-Einstein condensation of noninteracting homogeneous\nthree-dimensional gas in canonical ensemble when both particle number $N$ and\ntotal momentum $\\mathbf{P}$ of all particles are fixed. Using the saddle point\nmethod, we derive the large-$N$ analytical approximations for partition\nfunction, free energy, and statistical distributions of occupation numbers of\ndifferent single-particle energy levels. At temperatures below the critical\npoint of phase transition, we predict, in some ranges of $\\mathbf{P}$,\nfragmentation of the condensate, when more than one single-particle level is\nmacroscopically occupied. The occupation number distributions have\napproximately Gaussian shapes for the levels hosting the condensate, and\nexponential shapes for other, noncondensate levels. Our analysis demonstrates\nbreaking of Galilean invariance of moving finite-temperature many-particle\nsystem in the presence of Bose-Einstein condensation and extends the theory of\nmoving and rotating quantum systems to the finite-temperature large-$N$ limit."
    },
    {
        "anchor": "Loading and compression of a single two-dimensional Bose gas in an\n  optical accordion: The experimental realization of 2D Bose gases with a tunable interaction\nstrength is an important challenge for the study of ultracold quantum matter.\nHere we report on the realization of an optical accordion creating a lattice\npotential with a spacing that can be dynamically tuned between 11$\\,\\mu$m and\n2$\\,\\mu$m. We show that we can load ultracold $^{87}$Rb atoms into a single\nnode of this optical lattice in the large spacing configuration and then\ndecrease nearly adiabatically the spacing to reach a strong harmonic\nconfinement with frequencies larger than $\\omega_z/2\\pi=10\\,$kHz. Atoms are\ntrapped in an additional flat-bottom in-plane potential that is shaped with a\nhigh resolution. By combining these tools we create custom-shaped uniform 2D\nBose gases with tunable confinement along the transverse direction and hence\nwith a tunable interaction strength.",
        "positive": "First-order dissipative phase transition in an exciton-polariton\n  condensate: We investigate the phase diagram of a two-dimensional driven-dissipative\nsystem of polaritons coupled to the excitonic reservoir. We find that two\ncritical points exists. The first corresponds to the quasi-condensation and the\nsecond to a first-order phase transition from the non-uniform state with\nspatially modulated density to a uniform state. The latter is related to the\nmodulational instability of a homogeneous state due to the repulsive\ninteractions with the non-condensed reservoir. The first-order character of the\ntransition is evidenced by a discontinuity in the density and the correlation\nlength as well as the phase coexistence and metastability. Moreover, we show\nthat a signature of a Berezinskii-Kosterlitz-Thouless-like transition can be\nobserved in the non-uniform phase."
    },
    {
        "anchor": "Quantum phases of lattice dipolar bosons coupled to a high-finesse\n  cavity: Two types of long range interactions, dipolar interaction and cavity-mediated\ninteraction lead to exotic quantum phases. Both interactions have been realized\nand observed in optical lattice setups. Here, we study quantum phases of\ndipolar bosons trapped in optical lattices and coupled to a high-finesse cavity\nwhere both dipolar interaction and cavity-mediated interaction coexist. We\nperform quantum Monte Carlo simulations, and find that the checkerboard solid\nis enhanced and the checkerboard supersolid phase can exist in a wide range of\ndensities (e.g. $ 0.27\\lesssim n\\lesssim0.73 $). Our unbiased numerical results\nsuggest that both solid and supersolid phases can be achieved experimentally\nwith magnetic atoms coupled to a cavity.",
        "positive": "Zero temperature momentum distribution of an impurity in a polaron state\n  of one-dimensional Fermi and Tonks-Girardeau gases: We investigate the momentum distribution function of a single distinguishable\nimpurity particle which formed a polaron state in a gas of either free fermions\nor Tonks-Girardeau bosons in one spatial dimension. We obtain a Fredholm\ndeterminant representation of the distribution function for the Bethe ansatz\nsolvable model of an impurity-gas $\\delta$-function interaction potential at\nzero temperature, in both repulsive and attractive regimes. We deduce from this\nrepresentation the fourth power decay at a large momentum, and a weakly\ndivergent (quasi-condensate) peak at a finite momentum. We also demonstrate\nthat the momentum distribution function in the limiting case of infinitely\nstrong interaction can be expressed through a correlation function of the\none-dimensional impenetrable anyons."
    },
    {
        "anchor": "Matter wave speckle observed in an out-of-equilibrium quantum fluid: We report the results of a direct comparison of a freely expanding turbulent\nBose-Einstein condensate and the propagation of an optical speckle pattern. We\nfound remarkably similar statistical properties underlying the spatial\npropagation of both phenomena. The calculated second-order correlation together\nwith the typical correlation length of each system is used to compare and\nsubstantiate our observations. We believe that the close analogy existing in\nbetween an expanding turbulent quantum gas and a traveling optical speckle,\nmight burgeon into an exciting new research field investigating disordered\nquantum matter.",
        "positive": "High temperature pairing in a strongly interacting two-dimensional Fermi\n  gas: We observe many-body pairing in a two-dimensional gas of ultracold fermionic\natoms at temperatures far above the critical temperature for superfluidity. For\nthis, we use spatially resolved radio-frequency spectroscopy to measure pairing\nenergies spanning a wide range of temperatures and interaction strengths. In\nthe strongly interacting regime where the scattering length between fermions is\non the same order as the inter-particle spacing, the pairing energy in the\nnormal phase significantly exceeds the intrinsic two-body binding energy of the\nsystem and shows a clear dependence on local density. This implies that pairing\nin this regime is driven by many-body correlations, rather than two-body\nphysics. We find this effect to persist at temperatures close to the Fermi\ntemperature which demonstrates that pairing correlations in strongly\ninteracting two-dimensional fermionic systems are remarkably robust against\nthermal fluctuations."
    },
    {
        "anchor": "Resonant superfluidity in the Rabi-coupled spin-dependent Fermi-Hubbard\n  model: We investigate the ground-state phase diagram of the one-dimensional\nattractive Fermi-Hubbard model with spin-dependent hoppings and an on-site Rabi\ncoupling using the density matrix renormalization group method. In particular,\nwe show that even in the limit of one component being immobile the pair\nsuperfluidity can be resonantly enhanced when the Rabi coupling is on the order\nof the interaction strength just before the system starts to strongly polarize.\nWe derive an effective spin-1/2 XXZ model in order to understand the\nground-state properties in the strong attraction limit.",
        "positive": "The quantum solitons atomtronic interference device: We study a quantum many-body system of attracting bosons confined in a\nring-shaped potential and interrupted by a weak link. With such architecture,\nthe system defines atomtronic quantum interference devices harnessing quantum\nsolitonic currents. We demonstrate that the system is characterized by the\nspecific interplay between the interaction and the strength of the weak link.\nIn particular, we find that, depending on the operating conditions, the current\ncan be a universal function of the relative size between the strength of the\nimpurity and interaction. The low lying many-body states are studied through a\nquench dynamical protocol that is the atomtronic counterpart of Rabi\ninterferometry. With this approach, we demonstrate how our system defines a two\nlevel system of coupled solitonic currents. The current states are addressed\nthrough the analysis of the momentum distribution."
    },
    {
        "anchor": "Temperature-induced miscibility of impurities in trapped Bose gases: We study the thermal properties of impurities embedded in a repulsive Bose\ngas under a harmonic trapping potential. In order to obtain exact structural\nproperties in this inhomogeneous many-body system, we resort to the\npath-integral Monte Carlo method. We find that, at low temperatures, a single\nimpurity is expelled to the edges of the bath cloud if the impurity-boson\ncoupling constant is larger than the boson-boson one. However, when the\ntemperature is increased, but still in the Bose-condensed phase, the impurity\noccupies the core of the trap and, thus, the system becomes miscible. This\nthermal-induced miscibility transition is also observed for a finite\nconcentration of impurities in this inhomogeneous system. We find that the\ntransition temperature for miscibility depends on the impurity-boson\ninteraction and we indicate a novel nondestructive method to measure the\ntemperature of a system based on the studied phenomenon.",
        "positive": "Rydberg optical Feshbach resonances in cold gases: We propose a novel scheme to efficiently tune the scattering length of two\ncolliding ground-state atoms by off-resonantly coupling the scattering-state to\nan excited Rydberg-molecular state using laser light. For the s-wave scattering\nof two colliding ${^{87}}\\mathrm{Rb}$ atoms, we demonstrate that the effective\noptical length and pole strength of this Rydberg optical Feshbach resonance can\nbe tuned over several orders of magnitude, while incoherent processes and\nlosses are minimised. Given the ubiquity of Rydberg molecular states, this\ntechnique should be generally applicable to homo-nuclear atomic pairs as well\nas to atomic mixtures with s-wave (or even p-wave) scattering."
    },
    {
        "anchor": "Blast waves in a paraxial fluid of light: We study experimentally blast wave dynamics on a weakly interacting fluid of\nlight. The fluid density and velocity are measured in 1D and 2D geometries.\nUsing a state equation arising from the analogy between optical propagation in\nthe paraxial approximation and the hydrodynamic Euler's equation, we access the\nfluid hydrostatic and dynamic pressure. In the 2D configuration, we observe a\nnegative differential hydrostatic pressure after the fast expansion of a\nlocalized over-density, which is a typical signature of a blast wave for\ncompressible gases. Our experimental results are compared to the Friedlander\nwaveform hydrodynamical model. Velocity measurements are presented in 1D and 2D\nconfigurations and compared to the local speed of sound, to identify supersonic\nregion of the fluid. Our findings show an unprecedented control over\nhydrodynamic quantities in a paraxial fluid of light.",
        "positive": "Macroscopic random Paschen-Back effect in ultracold atomic gases: We consider spin- and density-related properties of single-particle states in\na one-dimensional system with random spin-orbit coupling. We show that the\npresence of an additional Zeeman field $\\Delta$ induces both nonlinear spin\npolarization and delocalization of states localized at $\\Delta=0$,\ncorresponding to a random macroscopic analogue of the Paschen-Back effect.\nWhile the conventional Paschen-Back effect corresponds to a saturated\n$\\Delta-$dependence of the spin polarization, here the gradual suppression of\nthe spin-orbit coupling effects by the Zeeman field is responsible both for the\nspin saturation and delocalization of the particles."
    },
    {
        "anchor": "Universal few-body physics in a harmonic trap: Few-body systems with resonant short-range interactions display universal\nproperties that do not depend on the details of their structure or their\ninteractions at short distances. In the three-body system, these properties\ninclude the existence of a geometric spectrum of three-body Efimov states and a\ndiscrete scaling symmetry. Similar universal properties appear in 4-body and\npossibly higher-body systems as well. We set up an effective theory for\nfew-body systems in a harmonic trap and study the modification of universal\nphysics for 3- and 4-particle systems in external confinement. In particular,\nwe focus on systems where the Efimov effect can occur and investigate the\ndependence of the 4-body spectrum on the experimental tuning parameters.",
        "positive": "Novel techniques to cool and rotate Bose-Einstein condensates in\n  time-averaged adiabatic potentials: We report two novel techniques for cooling and rotating Bose-Einstein\ncondensates in a dilute rubidium vapour that highlight the control and\nversatility afforded over cold atom systems by time-averaged adiabatic\npotentials (TAAPs). The intrinsic loss channel of the TAAP has been\nsuccessfully employed to evaporatively cool a sample of trapped atoms to\nquantum degeneracy. The speed and efficiency of this process compares well with\nthat of conventional forced rf-evaporation. In an independent experiment, we\nimparted angular momentum to a cloud of atoms forming a Bose-Einstein\ncondensate by introducing a rotating elliptical deformation to the TAAP\ngeometry. Triangular lattices of up to 60 vortices were created. All findings\nreported herein result from straightforward adjustments of the magnetic fields\nthat give rise to the TAAP."
    },
    {
        "anchor": "Anisotropic superfluidity in a dipolar Bose gas: We study the superfluid character of a dipolar Bose-Einstein condensate\n(DBEC) in a quasi-two dimensional (q2D) geometry. In particular, we allow for\nthe dipole polarization to have some non-zero projection into the plane of the\ncondensate so that the effective interaction is anisotropic in this plane,\nyielding an anisotropic dispersion for propagation of quasiparticles. By\nperforming direct numerical simulations of a probe moving through the DBEC, we\nobserve the sudden onset of drag or creation of vortex-antivortex pairs at\ncritical velocities that depend strongly on the direction of the probe's\nmotion. This anisotropy emerges because of the anisotropic manifestation of a\nroton-like mode in the system.",
        "positive": "Competing Chiral Orders in the Topological Haldane-Hubbard Model of\n  Spin-1/2 Fermions and Bosons: Motivated by experiments on ultracold atoms which have realized the Haldane\nmodel for a Chern insulator, we consider its strongly correlated Mott limit\nwith spin-$1/2$ fermions. We find that slave rotor mean field theory yields\ngapped or gapless chiral spin liquid Mott insulators. To study competing\nmagnetic orders, we consider the strong coupling effective spin Hamiltonian\nwhich includes chiral three-spin exchange. We obtain its classical phase\ndiagram, uncovering various chiral magnetic orders including tetrahedral, cone,\nand noncoplanar spiral states which can compete with putative chiral quantum\nspin liquids. We study the effect of thermal fluctuations on these states,\nidentifying crossovers in the spin chirality, and phase transitions associated\nwith lattice symmetry breaking. We also discuss analogous effective spin\nHamiltonians for correlated spin-$1/2$ bosons. Finally, we point out possible\nexperimental implications of our results for cold atom experiments."
    },
    {
        "anchor": "Two-body and three-body substructures served as building blocks in small\n  spin-3 condensates: It was found that stable few-body spin-structures, pairs and triplexes, may\nexist as basic constituents in small spin-3 condensates, and they will play the\nrole as building blocks when the parameters of interaction are appropriate.\nSpecific method is designed to find out these constituents.",
        "positive": "Strongly-Interacting Bosons in a Two-Dimensional Quasicrystal Lattice: Quasicrystals exhibit exotic properties inherited from the self-similarity of\ntheir long-range ordered, yet aperiodic, structure. The recent realization of\noptical quasicrystal lattices paves the way to the study of correlated Bose\nfluids in such structures, but the regime of strong interactions remains\nlargely unexplored, both theoretically and experimentally. Here, we determine\nthe quantum phase diagram of two-dimensional correlated bosons in an eightfold\nquasicrystal potential. Using large-scale quantum Monte Carlo calculations, we\ndemonstrate a superfluid-to-Bose glass transition and determine the critical\nline. Moreover, we show that strong interactions stabilize Mott insulator\nphases, some of which have spontaneously broken eightfold symmetry. Our results\nare directly relevant to current generation experiments and, in particular,\ndrive prospects to the observation of the still elusive Bose glass phase in two\ndimensions and exotic Mott phases."
    },
    {
        "anchor": "Analytical approach to the two-site Bose-Hubbard model: from Fock states\n  to Schr\u00f6dinger cat states and entanglement entropy: We study the interpolation from occupation number Fock states to\nSchr\\\"odinger cat states on systems modeled by two-mode Bose-Hubbard\nHamiltonian, like, for instance, bosons in a double well or superconducting\nCooper pair boxes. In the repulsive interaction regime, by a simplified single\nparticle description, we calculate, analytically, energy, number fluctuations,\nstability under coupling to a heat bath, entanglement entropy and Fisher\ninformation, all in terms of hypergeometric polynomials of the single particle\noverlap parameter. Our approach allows us to find how those quantities scale\nwith the number of bosons. In the attractive interaction regime we calculate\nthe same physical quantities in terms of the imbalance parameter, and find that\nthe symmetry breaking, occurring at interaction Uc, predicted by a\nsemiclassical approximation, is valid only in the limit of infinite number of\nbosons. For a large but finite number, we determine a characteristic strength\nof interaction, Uc*, which can be promoted as the crossover point from coherent\nto incoherent regimes and can be identified as the collapse threshold.\nMoreover, we find that the Fisher information is always in direct ratio to the\nvariance of on-site number of bosons, for both positive and negative\ninteractions. We finally show that the entanglement entropy is maximum close to\nUc* and exceeds its coherent value within the whole range of interaction\nbetween 2Uc and zero.",
        "positive": "Tunable Spin-orbit Coupling and Quantum Phase Transition in a Trapped\n  Bose-Einstein Condensate: Spin-orbit coupling (SOC), the intrinsic interaction between a particle spin\nand its motion, is responsible for various important phenomena, ranging from\natomic fine structure to topological condensed matter physics. The recent\nexperimental breakthrough on the realization of SOC for ultra-cold atoms\nprovides a completely new platform for exploring spin-orbit coupled superfluid\nphysics. However, the SOC strength in the experiment, determined by the applied\nlaser wavelengths, is not tunable. In this Letter, we propose a scheme for\ntuning the SOC strength through a fast and coherent modulation of the laser\nintensities. We show that the many-body interaction between atoms, together\nwith the tunable SOC, can drive a \\textit{quantum phase transition} (QPT) from\nspin-balanced to spin-polarized ground states in a harmonic trapped\nBose-Einstein condensate (BEC). This transition realizes the long-sought QPT in\nthe quantum Dicke model, and may have important applications in quantum optics\nand quantum information. We characterize the QPT using the periods of\ncollective oscillations (center of mass motion and scissors mode) of the BEC,\nwhich show pronounced peaks and damping around the quantum critical point."
    },
    {
        "anchor": "Nonclassical states in strongly correlated bosonic ring ladders: We study the ground state of a bosonic ring ladder under a gauge flux in the\nvortex phase, corresponding to the case where the single-particle dispersion\nrelation has two degenerate minima. By combining exact diagonalization and an\napproximate fermionization approach we show that the ground state of the system\nevolves from a fragmented state of two single-particle states at weak\ninterparticle interactions to a fragmented state of two Fermi seas at large\ninteractions. Fragmentation is inferred from the study of the eigenvalues of\nthe reduced single-particle density matrix as well as from the calculation of\nthe fidelity of the states. We characterize these nonclassical states by the\nmomentum distribution, the chiral currents and the current-current\ncorrelations.",
        "positive": "Non-Perturbative Dynamical Effects in Nearly Scale Invariant Systems:\n  The Action of Breaking Scale Invariance: In this work we develop a general formalism that categorizes the action of\nbroken scale invariance on the non-equilibrium dynamics of non-relativistic\nquantum systems. This approach is equally applicable to both strongly and\nweakly interacting systems. We show that any small deviation from the strongly\ninteracting fixed point, in three spatial dimensions, leads to non-pertubative\neffects in the long time dynamics, dramatically altering the dynamics observed\nat the scale invariant fixed point. As a concrete example, we apply this\napproach to the non-equilibrium dynamics for the interacting two-body problem,\nand for a non-interacting quantum gas in the presence of an impurity, both in\nthree spatial dimensions. Slightly away from the resonantly-interacting scale\ninvariant fixed point, we show that the dynamics are altered by a\nnon-perturbative log-periodic beat. The presence of the beat depends only on\ndeviating from the resonant fixed point, while the frequency depends on the\nmicroscopic parameters of the system."
    },
    {
        "anchor": "Universal Short-Distance Structure of the Single-Particle Spectral\n  Function of Dilute Fermi Gases: We show that the universal $1/k^4$ tail in the momentum distribution of\ndilute Fermi gases implies that the spectral function $A(\\kk,\\omega)$ must have\nweight below the chemical potential for large momentum $k \\gg k_F$, with\nobservable consequences in RF spectroscopy experiments. We find that this\nincoherent spectral weight is centered about $\\omega \\simeq - \\epsilon(\\kk)$ in\na range of energies of order $v_F k$. This \"bending back\" in the dispersion,\nwhile natural for superfluids, is quite surprising for normal gases. This\nuniversal structure is present in the hard-sphere gas as well as the Fermi\nliquid ground state of the highly imbalanced, attractive gas near unitarity. We\nargue that, even in the BCS superfluid, this bending back at large $k$ is\ndominated by interaction effects which do not reflect the pairing gap.",
        "positive": "Slightly imbalanced system of a few attractive fermions in a\n  one-dimensional harmonic trap: The ground-state properties of the two-flavored mixture of a few attractive\nfermions confined in a one-dimensional harmonic trap is studied. It is shown\nthat for slightly imbalanced system the pairing between fermions of opposite\nspins has completely different features that in the balanced case. The fraction\nof correlated pairs is suppressed by the presence of additional particle and\nanother uncorrelated two-body orbital dominates in the ground-state of the\nsystem."
    },
    {
        "anchor": "Geometry and superfluidity of the flat band in a non-Hermitian optical\n  lattice: We propose an ultracold-atom setting where a fermionic superfluidity with\nattractive s-wave interaction is uploaded in a non-Hermitian Lieb optical\nlattice. The existence of a real-energy flat band solution is revealed. We show\nthat the interplay between the skin effect and flat-band localization leads to\nexotic localization properties. We develop a multiband mean-field description\nof this system and use both order parameters and superfluid weight to describe\nthe phase transition. A relation between the superfluid weight and\nnon-Hermitian quantum metric of the quantum states manifold is built. We find\nnon-monotone criticality depending on the non-Hermiticity, and the\nnon-reciprocity prominently enhances the phase coherence of the pairing field,\nsuggesting ubiquitous critical behavior of the non-Hermitian fermionic\nsuperfluidity.",
        "positive": "$\\mathcal{PT}$-Symmetry Enhanced Berezinskii-Kosterlitz-Thouless\n  Superfluidity: Berezinskii-Kosterlitz-Thouless (BKT) transition, the topological phase\ntransition to a quasi-long range order in a two-dimensional (2D) system, is a\nhallmark of low-dimensional topological physics. The recent emergence of\nnon-Hermitian physics, particularly parity-time ($\\mathcal{PT}$) symmetry,\nraises a natural question about the fate of low-dimensional orders (e.g., BKT\ntransition) in the presence of complex energy spectrum. Here we investigate the\nBKT phase transition in a 2D degenerate Fermi gas with an imaginary Zeeman\nfield obeying $\\mathcal{PT}$-symmetry. Despite complex energy spectrum,\n$\\mathcal{PT}$-symmetry guarantees that the superfluid density and many other\nquantities are real. Surprisingly, the imaginary Zeeman field enhances the\nsuperfluid density, yielding higher BKT transition temperature than that in\nHermitian systems. In the weak interaction region, the transition temperature\ncan be much larger than that in the strong interaction limit. Our work\nshowcases a surprising interplay between low-dimensional topological defects\nand non-Hermitian effects, paving the way for studying non-Hermitian\nlow-dimensional phase transitions."
    },
    {
        "anchor": "The Snake Instability of Ring Dark Solitons in Toroidally Trapped\n  Bose-Einstein Condensates: We show that the onset of the snake instability of ring dark solitons\nrequires a broken symmetry. We also elucidate explicitly the connection between\nimaginary Bogoliubov modes and the snake instability, predicting the number of\nvortex-anti-vortex pairs produced. In addition, we propose a simple model to\ngive a physical motivation as to why the snake instability takes place.\nFinally, we show that tight confinement in a toroidal potential actually\nenhances soliton decay due to inhibition of soliton motion.",
        "positive": "Kolmogorov-Hinze scales in turbulent superfluids: When a two-component mixture of immiscible fluids is stirred, the fluids are\nsplit into smaller domains with more vigorous stirring. We numerically\ninvestigate the sizes of such domains in a fully-developed turbulent state of a\ntwo-component superfluid stirred with energy input rate $\\epsilon$. For the\nstrongly immiscible condition, the typical domain size is shown to be\nproportional to $\\epsilon^{-2/5}$, as predicted by the Kolmogorov-Hinze theory\nin classical fluids. For the weakly immiscible condition, quantum effects\nbecome pronounced and the power changes from $-2 / 5$ to $-1 / 4$."
    },
    {
        "anchor": "Gray molasses cooling of $^{39}$K to a high phase-space density: We present new techniques in cooling 39K atoms using laser light close to the\nD1 transition. First, a new compressed-MOT configuration is taking advantage of\ngray molasses type cooling induced by blue-detuned D1 light. It yields an\noptimized density of atoms. Then, we use pure D1 gray molasses to further cool\nthe atoms to an ultra-low temperature of 6\\,$\\mu$K. The resulting phase-space\ndensity is $2 \\times 10^{-4}$ and will ease future experiments with ultracold\npotassium. As an example, we use it to directly load up to $3\\times 10^7$ atoms\nin a far detuned optical trap, a result that opens the way to the all-optical\nproduction of potassium degenerate gases.",
        "positive": "Manifold formation and crossings of ultracold lattice spinor atoms in\n  the intermediate interaction regime: Ultracold spinor atoms in the weak and strong interaction regime have\nreceived extensive investigations, while the behavior in the intermediate\nregime is less understood. We numerically investigate ultracold spinor atomic\nensembles of finite size in the intermediate interaction regime, and reveal the\nevolution of the eigenstates from the strong to the intermediate regime. In the\nstrong interaction regime, it has been well known that the low-lying\neigenenergy spectrum presents the well-gaped multi-manifold structure, and the\nenergy gaps protect the categorization of the eigenstates. In the intermediate\ninteraction regime, it is found that the categorization of the eigenstates is\npreserved, and the eigenenergy spectrum become quasi-continuum, with different\nmanifolds becoming overlapped. The overlapping induces both direct and avoided\ncrossings between close-lying manifolds, which is determined by the combined\nsymmetries of the eigenstates involved in the crossing. A modified t-J model is\nderived to describe the low-lying eigenstates in the intermediate regime, which\ncan capture the formation and crossings of the manifolds. State preparation\nthrough the avoided crossings is also investigated."
    },
    {
        "anchor": "Chaotic dynamics of Bose-Einstein condensate in a density-dependent\n  gauge field: In this work we study the effect of density-dependent gauge field on the\ncollective dynamics of a harmonically trapped Bose-Einstein condensate, beyond\nthe linear response regime. The densitydependent gauge field, as a backaction\nof the condensate, can in turn affect the condensate dynamics, resulting in\nhighly nonlinear equations of motion. We find that the dipole and breathing\noscillations of the condensate along the direction of gauge field are coupled\nby this field. For a quasi-onedimensional condensate, this coupling makes the\ncollective motion quasiperiodic. While for a quasitwo-dimensional condensate,\nthe gauge field can also induce a Hall effect, manifested as an additional\ncoupling between dipole and breathing oscillations in perpendicular direction.\nWhen the densitydependent gauge field is strong, the interplay between these\noscillations can cause the collective dynamics of the condensate to become\nchaotic. Our findings reveal an important effect of dynamical gauge field on\nthe nonlinear dynamics of a Bose-Einstein condensate.",
        "positive": "Bose-glass phase of a one-dimensional disordered Bose fluid: metastable\n  states, quantum tunneling and droplets: We study a one-dimensional disordered Bose fluid using bosonization, the\nreplica method and a nonperturbative functional renormalization-group approach.\nWe find that the Bose-glass phase is described by a fully attractive\nstrong-disorder fixed point characterized by a singular disorder correlator\nwhose functional dependence assumes a cuspy form that is related to the\nexistence of metastable states. At nonzero momentum scale $k$, quantum\ntunneling between the ground state and low-lying metastable states leads to a\nrounding of the cusp singularity into a quantum boundary layer (QBL). The width\nof the QBL depends on an effective Luttinger parameter $K_k\\sim k^\\theta$ that\nvanishes with an exponent $\\theta=z-1$ related to the dynamical critical\nexponent $z$. The QBL encodes the existence of rare \"superfluid\" regions,\ncontrols the low-energy dynamics and yields a (dissipative) conductivity\nvanishing as $\\omega^2$ in the low-frequency limit. These results reveal the\nglassy properties (pinning, \"shocks\" or static avalanches) of the Bose-glass\nphase and can be understood within the \"droplet\" picture put forward for the\ndescription of glassy (classical) systems."
    },
    {
        "anchor": "Fractional angular momentum in cold atom systems: The quantum statistics of bosons or fermions are manifest through even or odd\nrelative angular momentum of a pair. We show theoretically that, under certain\nconditions, a pair of certain test particles immersed in a fractional quantum\nHall state possesses, effectively, a fractional relative angular momentum,\nwhich can be interpreted in terms of fractional braid statistics. We propose\nthat the fractionalization of the angular momentum can be detected directly\nthrough the measurement of the pair correlation function in rotating ultra-cold\natomic systems in the fractional quantum Hall regime. Such a measurement will\nalso provide direct evidence for the effective magnetic field, resulting from\nBerry phases arising from attached vortices, and of excitations with fractional\nparticle number, analogous to fractional charge of electron fractional quantum\nHall effect.",
        "positive": "Spin Rotations in a Bose-Einstein Condensate Driven by Counterflow and\n  Spin-independent Interactions: We observe spin rotations caused by atomic collisions in a non-equilibrium\nBose-condensed gas of $^{87}$Rb. Reflection from a pseudomagnetic barrier\ncreates counterflow in which forward- and backward-propagating matter waves\nhave partly transverse spin directions. Even though inter-atomic interaction\nstrengths are state-independent, the indistinguishability of parallel spins\nleads to spin dynamics. A local magnetodynamic model, which captures the\nsalient features of the observed spin textures, highlights an essential\nconnection between four-wave mixing and collisional spin rotation. The observed\nphenomenon has previously been thought to exist only in nondegenerate gases;\nour observations and model clarify the nature of these effective-magnetic spin\nrotations."
    },
    {
        "anchor": "Collision of one-dimensional fermion clusters: We study cluster-cluster collisions in one-dimensional Fermi systems with\nparticular emphasis on the non-trivial quantum effects of the collision\ndynamics. We adopt the Fermi-Hubbard model and the time-dependent density\nmatrix renormalization group method to simulate collision dynamics between two\nfermion clusters of different spin states with contact interaction. It is\nelucidated that the quantum effects become extremely strong with the\ninteraction strength, leading to the transmittance much more enhanced than\nexpected from semiclassical approximation. We propose a concise model based on\none-to-one collisions, which unveils the origin of the quantum effects and also\nexplains the overall properties of the simulation results clearly. Our concise\nmodel can quite widely describe the one-dimensional collision dynamics with\ncontact interaction. Some potential applications, such as repeated collisions,\nare addressed.",
        "positive": "Universality and scaling in the $N$-body sector of Efimov physics: Universal behaviour has been found inside the window of Efimov physics for\nsystems with $N=4,5,6$ particles. Efimov physics refers to the emergence of a\nnumber of three-body states in systems of identical bosons interacting {\\it\nvia} a short-range interaction becoming infinite at the verge of binding two\nparticles. These Efimov states display a discrete scale invariance symmetry,\nwith the scaling factor independent of the microscopic interaction. Their\nenergies in the limit of zero-range interaction can be parametrized, as a\nfunction of the scattering length, by a universal function. We have found,\nusing a particular form of finite-range scaling, that the same universal\nfunction can be used to parametrize the energies of $N\\le6$ systems inside the\nEfimov-physics window. Moreover, we show that the same finite-scale analysis\nreconciles experimental measurements of three-body binding energies with the\nuniversal theory."
    },
    {
        "anchor": "Repulsive Fermi polarons in a resonant mixture of ultracold ${}^6$Li\n  atoms: We employ radio-frequency spectroscopy to investigate a polarized\nspin-mixture of ultracold ${}^6$Li atoms close to a broad Feshbach scattering\nresonance. Focusing on the regime of strong repulsive interactions, we observe\nwell-defined coherent quasiparticles even for unitarity-limited interactions.\nWe characterize the many-body system by extracting the key properties of\nrepulsive Fermi polarons: the energy $E_+$, the effective mass $m^*$, the\nresidue $Z$ and the decay rate $\\Gamma$. Above a critical interaction, $E_+$ is\nfound to exceed the Fermi energy of the bath while $m^*$ diverges and even\nturns negative, thereby indicating that the repulsive Fermi liquid state\nbecomes energetically and thermodynamically unstable.",
        "positive": "Dislocation-mediated melting of one-dimensional Rydberg crystals: We consider cold Rydberg atoms in a one-dimensional optical lattice in the\nMott regime with a single atom per site at zero temperature. An external laser\ndrive with Rabi frequency \\Omega and laser detuning \\Delta, creates Rydberg\nexcitations whose dynamics is governed by an effective spin-chain model with\n(quasi) long-range interactions. This system possesses intrinsically a large\ndegree of frustration resulting in a ground-state phase diagram in the\n(\\Delta,\\Omega) plane with a rich topology. As a function of \\Delta, the\nRydberg blockade effect gives rise to a series of crystalline phases\ncommensurate with the optical lattice that form a so-called devil's staircase.\nThe Rabi frequency, \\Omega, on the other hand, creates quantum fluctuations\nthat eventually lead to a quantum melting of the crystalline states. Upon\nincreasing \\Omega, we find that generically a commensurate-incommensurate\ntransition to a floating Rydberg crystal occurs first, that supports gapless\nphonon excitations. For even larger \\Omega, dislocations within the floating\nRydberg crystal start to proliferate and a second,\nKosterlitz-Thouless-Nelson-Halperin-Young dislocation-mediated melting\ntransition finally destroys the crystalline arrangement of Rydberg excitations.\nThis latter melting transition is generic for one-dimensional Rydberg crystals\nand persists even in the absence of an optical lattice. The floating phase and\nthe concomitant transitions can, in principle, be detected by Bragg scattering\nof light."
    },
    {
        "anchor": "Shock Waves in a Superfluid with Higher-Order Dispersion: Higher-order dispersion can lead to intriguing dynamics that are becoming a\nfocus of modern hydrodynamics research. Such systems occur naturally, for\nexample in shallow water waves and nonlinear optics, for which several types of\nnovel dispersive shocks structures have been identified. Here we introduce\nultracold atoms as a tunable quantum simulations platform for higher-order\nsystems. Degenerate quantum gases are well controlled model systems for the\nexperimental study of dispersive hydrodynamics in superfluids and have been\nused to investigate phenomena such as vortices, solitons, dispersive shock\nwaves and quantum turbulence. With the advent of Raman-induced spin-orbit\ncoupling, the dispersion of a dilute gas Bose-Einstein condensate can be\nmodified in a flexible way, allowing for detailed investigations of\nhigher-order dispersion dynamics. Here we present a combined experimental and\ntheoretical study of shock structures generated in such a system. The breaking\nof Galilean invariance by the spin-orbit coupling allows two different types of\nshock structures to emerge simultaneously in a single system. Numerical\nsimulations suggest that the behavior of these shock structures is affected by\ninteractions with vortices in a manner reminiscent of emerging viscous\nhydrodynamics due to an underlying quantum turbulence in the system. This\nresult suggests that spin-orbit coupling can be used as a powerful means to tun\nthe effective viscosity in cold-atom experiments serving as quantum simulators\nof turbulent hydrodynamics, with applications from condensed matter and optics\nto quantum simulations of neutron stars.",
        "positive": "Short note on the Rabi model: The spectral density of the Rabi model is calculated exactly within a\ncontinued fraction approach. It is shown that the method yields a convergent\nsolution."
    },
    {
        "anchor": "Effect of anisotropic spin-orbit coupling on condensation and\n  superfluidity of a two dimensional Fermi gases: We investigated the ground state properties of a two dimensional Fermi\nsuperfluid with an anisotropic spin-orbit coupling (SOC) using path-integral\nfield theoretical method. Within the framework of mean-field theory, we\nobtained the condensed fraction including contributions from both singlet and\ntriple pairing fields. We found that for small interaction parameters and large\nanisotropic parameters, the total condensed fraction changes non-monotonically\nwhen increasing the strength of SOC and has a global maximum. But this feature\ndisappears with decreasing the anisotropic parameter and increasing the\ninteraction parameter. However, condensed fraction always decrease with\nincreasing the anisotropic parameters. Because of the anisotropy of the SOC,\nthe superfluid fraction becomes a tensor. We obtained the superfluid fraction\ntensor by deriving the effective action of the phase field of the order\nparameter. Our numerical results show that for small interaction parameters and\nlarge anisotropic parameters, superfluid fraction of the $x$ component\n$\\rho_{x}$ has a minimum as a function of the SOC strength. And this minimum of\n$\\rho_{x}$ disappears when decreasing the anisotropic parameters. In the strong\ninteraction regime, $\\rho_{x}$ always decreases with increasing the strength of\nSOC. While for the $y$ component of the superfluid fraction $\\rho_{y}$, no\nmatter how large the interaction parameters and anisotropic parameters are, it\nalways has a minimum as a function of the SOC strength. As a function of the\nanisotropic parameter, for strong SOC strength, $\\rho_{x}<\\rho_{y}$ with\n$\\rho_{x}$ having a minimum. For small SOC parameters $\\rho_{x}>\\rho_{y}$ with\n$\\rho_{y}$ developing a minimum only in the weak interaction limit.",
        "positive": "Quantum oscillations in the kinetic energy density: Gradient corrections\n  from the Airy gas: We derive a closed form expression for the quantum corrections to the kinetic\nenergy density (KED) in the Thomas-Fermi (TF) limit of a linear potential model\nsystem in three dimensions (the Airy gas). The universality of the expression\nis tested numerically in a number of three dimensional model systems: (i)\njellium surfaces, (ii) hydrogen-like potentials, (iii) systems confined by an\nharmonic potential in one and (iv) all three dimensions, and (v) a system with\na cosine potential (the Mathieu gas). Our results confirm that the usual\ngradient expansion of extended Thomas-Fermi theory (ETF) does not describe the\nquantum oscillations for systems that incorporate surface regions where the\nelectron density drops off to zero. We find that the correction derived from\nthe Airy gas is universally applicable to relevant spatial regions of systems\nof type (i), (ii), and (iv), but somewhat surprisingly not (iii). We discuss\npossible implications of our findings to the development of functionals for the\nkinetic energy density."
    },
    {
        "anchor": "Spin-asymmetric Josephson plasma oscillations: The spin-asymmetric Josephson effect is a proposed quantum-coherent\ntunnelling phenomenon where Cooper-paired fermionic spin-$\\frac{1}{2}$\nparticles, which are subjected to spin-dependent potentials across a Josephson\njunction, undergo frequency-synchronized alternating-current Josephson\noscillations with spin-dependent amplitudes. Here, in line with present-day\ntechniques in ultracold Fermi gas setups, we consider the regime of small\nJosephson oscillations and show that the Josephson plasma oscillation amplitude\nbecomes spin-dependent in the presence of spin-dependent potentials while the\nJosephson plasma frequency is the same for both spin-components. Detecting\nthese spin-dependent Josephson plasma oscillations provides a possible means to\nestablish the yet-unobserved spin-asymmetric Josephson effect with ultracold\nFermi gases using existing experimental tools.",
        "positive": "Square Pattern Formation as Stable Fixed Point in Driven Two-Dimensional\n  Bose-Einstein Condensates: We investigate pattern formation in two-dimensional Bose-Einstein condensates\n(BECs) caused by temporal periodic modulation of the interatomic interaction.\nTemporal modulation of the interaction causes the so-called Faraday instability\nin the condensate, which we show generically leads to a stable square grid\ndensity pattern. We take the amplitudes in each of the two directions spanning\nthe two-dimensional density pattern as order parameters in pattern formation\nand derive a set of simultaneous time evolution equations for those order\nparameters from the Gross--Pitaevskii (GP) equation with a time-periodic\ninteraction. We identify the fixed points of the time evolution and show by\nstability analysis that the inhomogeneous density exhibits a square grid\npattern as a stable fixed point."
    },
    {
        "anchor": "Matter wave soliton bouncer: Dynamics of a matter wave soliton bouncing on the reflecting surface (atomic\nmirror) under the effect of gravity has been studied by analytical and\nnumerical means. The analytical description is based on the variational\napproach. Resonant oscillations of the soliton's center of mass and width,\ninduced by appropriate modulation of the atomic scattering length and the slope\nof the linear potential are analyzed. In numerical experiments we observe the\nFermi type acceleration of the soliton when the vertical position of the\nreflecting surface is periodically varied in time. Analytical predictions are\ncompared with the results of numerical simulations of the Gross-Pitaevskii\nequation and qualitative agreement between them is found.",
        "positive": "Universal properties of dipolar Bose polarons in two dimensions: We study the quasiparticle properties of a dipolar impurity immersed in a\ntwo-dimensional dipolar bath. We use the ab-initio Diffusion Monte Carlo\ntechnique to determine the polaron energy, effective mass and quasiparticle\nresidue. We find that these quantities follow a universal behaviour when\nproperly scaled in terms of the polarization angle and scattering length. This\ntrend is maintained over a wide range of values of the gas parameter, even in\nthe highly correlated regime. Additionally, we show that the anisotropy of the\nimpurity-bath interaction leads to an anisotropic effective mass that is\nunexpectedly larger in the direction of minimum repulsion of the impurity-bath\ninteraction. Finally, we use our Monte Carlo results to check the accuracy of\nperturbative approaches and determine their range of validity in terms of the\ngas parameter."
    },
    {
        "anchor": "Effects of a rotating periodic lattice on coherent quantum states in a\n  ring topology: The case of negative nonlinearity: We study the spectrum and stationary states in a ring-shaped lattice\npotential in the context of ultracold atoms with attractive interatomic\ninteractions. We determine analytical solutions in the absence of a lattice by\nmapping them to those for repulsive interactions, and then we numerically\nfollow the transformation of those solutions as the lattice is introduced and\nstrengthened. Several features emerge that are specific to negative\nnonlinearity, that include: Soliton branches detaching to create new ground\nstates; gaps opening up at the bottom of the primary spectral branch; multiple\nsplitting and rejoining of some branches. We correlate the spectral features\nwith the behavior of the density and phase of the corresponding eigenstates,\nand track them along branches and as various system parameters change. We find\nthat the phase is sensitive to how a specific point in the spectrum is\napproached, particularly relevant at certain persistent gaps in the spectrum.\nThe symmetry and stability properties are generally found to be opposite of\nthat found for repulsive interactions.",
        "positive": "Floquet time crystals in clock models: We construct a class of period-$n$-tupling discrete time crystals based on\n$\\mathbb{Z}_n$ clock variables, for all the integers $n$. We consider two\nclasses of systems where this phenomenology occurs, disordered models with\nshort-range interactions and fully connected models. In the case of short-range\nmodels we provide a complete classification of time-crystal phases for generic\n$n$. For the specific cases of $n=3$ and $n=4$ we study in details the dynamics\nby means of exact diagonalisation. In both cases, through an extensive analysis\nof the Floquet spectrum, we are able to fully map the phase diagram. In the\ncase of infinite-range models, the mapping onto an effective bosonic\nHamiltonian allows us to investigate the scaling to the thermodynamic limit.\nAfter a general discussion of the problem, we focus on $n=3$ and $n=4$,\nrepresentative examples of the generic behaviour. Remarkably, for $n=4$ we find\nclear evidence of a new crystal-to-crystal transition between period\n$n$-tupling and period $n/2$-tupling."
    },
    {
        "anchor": "Universal thermodynamics of an SU($N$) Fermi-Hubbard Model: The SU(2) symmetric Fermi-Hubbard model (FHM) plays an essential role in\nstrongly correlated fermionic many-body systems. In the one particle per site\nand strongly interacting limit ${U/t \\gg 1}$, it is effectively described by\nthe Heisenberg Hamiltonian. In this limit, enlarging the spin and extending the\ntypical SU(2) symmetry to SU($N$) has been predicted to give exotic phases of\nmatter in the ground state, with a complicated dependence on $N$. This raises\nthe question of what -- if any -- are the finite-temperature signatures of\nthese phases, especially in the currently experimentally relevant regime near\nor above the superexchange energy. We explore this question for thermodynamic\nobservables by numerically calculating the thermodynamics of the SU($N$) FHM in\nthe two-dimensional square lattice near densities of one particle per site,\nusing determinant Quantum Monte Carlo and Numerical Linked Cluster Expansion.\nInterestingly, we find that for temperatures above the superexchange energy,\nwhere the correlation length is short, the energy, number of on-site pairs, and\nkinetic energy are universal functions of $N$. Although the physics in the\nregime studied is well beyond what can be captured by low-order\nhigh-temperature series, we show that an analytic description of the scaling is\npossible in terms of only one- and two-site calculations.",
        "positive": "Dynamics of atoms in a time-orbiting-potential trap: consequences of the\n  classical description: The classical model that describes the motion of an atom in a magnetic trap\nis solved in order to investigate the relationship between the failure of the\nusual adiabatic approximation assumption and the physical parameters of the\ntrap. This allows to evaluate the effect that reversing of the bias field\nrotation produces on the vertical position of the atomic orbit, a displacement\nthat is closely related to the adiabatic character of the trap motion. The\npresent investigation has been motivated by a similar experimental test\npreviously carried out in the actual magnetic time orbiting potential trap. We\nfind that the non-adiabatic effects provided by the classical model are\nextremely small. Thus, we conclude that the theoretical explanation of the\nexperimental measures, requires a quantum description of the dynamics in\nmagnetic traps."
    },
    {
        "anchor": "The p-wave polaron: We consider the properties of a single impurity immersed in a Fermi sea close\nto an interspecies p-wave Feshbach resonance. We calculate its dispersion and\nspectral response to a radiofrequency pulse. In the presence of a magnetic\nfield, dipolar interactions split the resonance and lead to the appearance of\ntwo novel features with respect to the s-wave case: a third polaron branch in\nthe excitation spectrum, in addition to the usual attractive and repulsive\nones; and an anisotropic dispersion of the impurity characterized by different\neffective masses perpendicular and parallel to the magnetic field. The\nanisotropy can be tuned as a function of the field strength and the two\neffective masses may have opposite signs, or become smaller than the bare mass.",
        "positive": "Anomalous suppression of the Bose glass at commensurate fillings in the\n  disordered Bose-Hubbard model: We study the weakly disordered Bose-Hubbard model on a cubic lattice through\na one-loop renormalization group analysis of the corresponding effective field\ntheory which is explicitly derived by combining a strong-coupling expansion\nwith a replica average over the disorder. The method is applied not only to\ngeneric uncorrelated on-site disorder but also to simultaneous hopping disorder\ncorrelated with the differences of adjacent disorder potentials. Such\ncorrelations are inherent in fine-grained optical speckle potentials used as a\nsource of disorder in optical lattice experiments. As a result of strong\ncoupling, the strength of the replica mixing disorder vertex, responsible for\nthe emergence of a Bose glass, crucially depends on the chemical potential and\nthe Hubbard repulsion and vanishes to leading order in the disorder at\ncommensurate boson fillings. As a consequence, at such fillings a direct\ntransition between the Mott-insulator and the superfluid in the presence of\ndisorder cannot be excluded on the basis of a one-loop calculation. At\nincommensurate fillings, at a certain length scale, the Mott insulator will\neventually become unstable towards the formation of a Boss glass. Phase\ndiagrams as a function of the microscopic parameters are presented and the\nfinite-size crossover between the Mott-insulating state and the Bose glass is\nanalyzed."
    },
    {
        "anchor": "Momentum distribution of 1D Bose gases at the quasi-condensation\n  crossover: theoretical and experimental investigation: We investigate the momentum distribution of weakly interacting 1D Bose gases\nat thermal equilibrium both experimentally and theoretically. Momentum\ndistribution of single 1D Bose gases is measured using a focusing technique,\nwhose resolution we improve via a guiding scheme. The momentum distribution\ncompares very well with quantum Monte Carlo calculations for the Lieb-Liniger\nmodel at finite temperature, allowing for an accurate thermometry of the gas\nthat agrees with (and improves upon) the thermometry based on in situ density\nfluctuation measurements. The quasi-condensation crossover is investigated via\ntwo different experimental parameter sets, corresponding to the two different\nsides of the crossover. Classical field theory is expected to correctly\ndescribe the quasi-condensation crossover of weakly interacting gases. We\nderive the condition of validity of the classical field theory, and find that,\nin typical experiments, interactions are too strong for this theory to be\naccurate. This is confirmed by a comparison between the classical field\npredictions and the numerically exact quantum Monte Carlo calculations.",
        "positive": "Diffraction of strongly interacting molecular Bose-Einstein condensate\n  from standing wave light pulses: We study the effects of strong inter-particle interaction on diffraction of a\nBose-Einstein condensate of $^6Li_2$ molecules from a periodic potential\ncreated by pulses of a far detuned optical standing wave. For short pulses we\nobserve the standard Kapitza-Dirac diffraction, with the contrast of the\ndiffraction pattern strongly reduced for very large interactions due to\ninteraction dependent loss processes. For longer pulses diffraction shows the\ncharacteristic for matter waves impinging on an array of tubes and coherent\nchanneling transport. We observe a slowing down of the time evolution governing\nthe population of the momentum modes caused by the strong atom interaction. A\nsimple physical explanation of that slowing down is the phase shift caused by\nthe self-interaction of the forming matter wave patterns inside the standing\nlight wave. Simple 1D mean field simulations qualitatively capture the\nphenomenon, however to quantitatively reproduce the experimental results the\nmolecular scattering length has to be multiplied by factor of 4.2. In addition,\ntwo contributions to interaction-dependent degradation of the coherent\ndiffraction patterns were identified: (i) in-trap loss of molecules during the\nlattice pulse, which involves dissociation of Feshbach molecules into free\natoms, as confirmed by radio-frequency spectroscopy and (ii) collisions between\ndifferent momentum modes during separation. This was confirmed by\ninterferometrically recombining the diffracted momenta into the zero-momentum\npeak, which consequently removed the scattering background."
    },
    {
        "anchor": "Relaxation of ferromagnetic domains in a disordered lattice in 2D: We investigate the relaxation process of ferromagnetic domains in 2D\nsubjected to the influence of both, static disorder of variable strength and\nweak interactions. The domains are represented by a two species bosonic mixture\nof $^{87}$Rb ultracold atoms, such that initially each specie lies on left and\nright halves of a square lattice. The dynamics of the double domain is followed\nby describing the two-component superfluid, at mean field level, through the\ntime dependent Gross-Pitaevskii coupled equations, considering values of the\nintra and inter-species interaction, reachable in current experimental setups,\nthat guaranty miscibility of the components. A robust analysis for several\nvalues inter-species interaction leads us to conclude that the presence of\nstructural disorder leads to slowdown the relaxation process of the initial\nferromagnetic order. As shown by our numerical experiments, magnetization is\nmaintained up to 60 percent of its initial value for the largest disorder\namplitude.",
        "positive": "Dirac and topological phonons with spin-orbital entangled orders: We propose to study novel quantum phases and excitations for a 2D spin-orbit\n(SO) coupled bosonic $p$-orbital optical lattice based on the recent\nexperiments. The orbital and spin degrees of freedom with SO coupling compete\nand bring about nontrivial interacting quantum effects. We develop a\nself-consistent method for bosons and predict a spin-orbital entangled order\nfor the ground phase, in sharp contrast to spinless high-orbital systems.\nFurthermore, we investigate the Bogoliubov excitations, showing that the Dirac\nand topological phonons are obtained corresponding to the predicted different\nspin-orbital orders. In particular, the topological phonons exhibit a bulk gap\nwhich can be several times larger than the single-particle gap of $p$-bands,\nreflecting the enhancement of topological effect by interaction. Our results\nhighlight the rich physics predicted in SO coupled high-orbital systems and\nshall attract experimental efforts in the future."
    },
    {
        "anchor": "Exotic pairing in 1D spin-3/2 atomic gases with $SO(4)$ symmetry: Tuning interactions in the spin singlet and quintet channels of two colliding\natoms could change the symmetry of the one-dimensional spin-3/2 fermionic\nsystems of ultracold atoms while preserving the integrability. Here we find a\nnovel $SO(4)$ symmetry integrable point in thespin-3/2 Fermi gas and derive the\nexact solution of the model using the Bethe ansatz. In contrast to the model\nwith $SU(4)$ and $SO(5)$ symmetries, the present model with $SO(4)$ symmetry\npreserves spin singlet and quintet Cooper pairs in two sets of $SU(2)\\otimes\nSU(2)$ spin subspaces. We obtain full phase diagrams, including the\nFulde-Ferrel-Larkin-Ovchinnikov like pair correlations, spin excitations and\nquantum criticality through the generalized Yang-Yang thermodynamic equations.\nIn particular, various correlation functions are calculated by using\nfinite-size corrections in the frame work of conformal field theory. Moreover,\nwithin the local density approximation, we further find that spin singlet and\nquintet pairs form subtle multiple shell structures in density profiles of the\ntrapped gas.",
        "positive": "Three-body interaction near a narrow two-body zero crossing: We calculate the effective three-body force for bosons interacting with each\nother by a two-body potential tuned to a narrow zero crossing in any dimension.\nWe use the standard two-channel model parametrized by the background atom-atom\ninteraction strength, the amplitude of the open-channel to closed-channel\ncoupling, and the atom-dimer interaction strength. The three-body force\noriginates from the atom-dimer interaction, but it can be dramatically enhanced\nfor narrow crossings, i.e., for small atom-dimer conversion amplitudes. This\neffect can be used to stabilize quasi-two-dimensional dipolar atoms and\nmolecules."
    },
    {
        "anchor": "Polarons and Molecules in a Fermi Gas with Orbital Feshbach Resonance: We study the impurity problem in a gas of $^{173}$Yb atoms near the recently\ndiscovered orbital Feshbach resonance. In an orbital Feshbach resonance, atoms\nin the electronic ground state $^1S_0$ interact with those in the long-lived\nexcited $^3P_0$ state with magnetically tunable interactions. We consider an\nimpurity atom with a given hyperfine spin in the $^3P_0$ state interacting with\na single-component Fermi sea of atoms in the ground $^1S_0$ manifold. Close to\nthe orbital Feshbach resonance, the impurity can induce collective\nparticle-hole excitations out of the Fermi sea, which can be regarded as the\npolaron state. While as tuning toward the BEC regime of the resonance, a\nmolecular state becomes the ground state of the system. We show that a polaron\nto molecule transition exists in $^{173}$Yb atoms close to the orbital Feshbach\nresonance. Furthermore, due to the spin-exchange nature of the orbital Feshbach\nresonance, the formation of both the polaron and the molecule involve\nspin-flipping processes with interesting density distributions among the\nrelevant hyperfine spin states. We show that the polaron to molecule transition\ncan be detected using Raman spectroscopy.",
        "positive": "Exact Yrast Spectra of Cold Atoms on a Ring: We propose a methodology to construct excited states with a fixed angular\nmomentum, namely, \"yrast excited states\" of finite-size one-dimensional bosonic\nsystems with periodic boundary conditions. The excitation energies such as the\nfirst yrast excited energy are calculated through the system-size asymptotic\nexpansion and expressed analytically by dressed energy.\n  Interestingly, they are grouped into sets of almost degenerate energy levels.\nThe low-lying excitation spectrum near the yrast state is consistent with the $\nU(1)$ conformal field theories if the total angular momentum is given by an\nintegral multiple of particle number; i.e., if the system is supercurrent."
    },
    {
        "anchor": "Quantized Floquet topology with temporal noise: Time-periodic (Floquet) drive is a powerful method to engineer quantum phases\nof matter, including fundamentally non-equilibrium states that are impossible\nin static Hamiltonian systems. One characteristic example is the anomalous\nFloquet insulator, which exhibits topologically quantized chiral edge states\nsimilar to a Chern insulator, yet is amenable to bulk localization. We study\nthe response of this topological system to time-dependent noise, which breaks\nthe topologically protecting Floquet symmetry. Surprisingly, we find that the\nquantized response, given by partially filling the fermionic system and\nmeasuring charge pumped per cycle, remains quantized up to finite noise\namplitude. We trace this robust topology to an interplay between diffusion and\nPauli blocking of edge state decay, which we expect should be robust against\ninteractions. We determine the boundaries of the topological phase for a system\nwith spatial disorder numerically through level statistics, and corroborate our\nresults in the limit of vanishing disorder through an analytical Floquet\nsuperoperator approach. This approach suggests an interpretation of the state\nof the system as a non-Hermitian Floquet topological phase. We comment on\nquantization of other topological responses in the absence of Floquet symmetry\nand potential experimental realizations.",
        "positive": "Dynamics of a Fermi gas quenched to unitarity: We present an experimental study of a two component Fermi gas following an\ninteraction quench into the superfluid phase. Starting with a weakly attractive\ngas in the normal phase, interactions are ramped to unitarity at a range of\nrates and we measure the subsequent dynamics as the gas approaches equilibrium.\nBoth the formation and condensation of fermion pairs are mapped via\nmeasurements of the pair momentum distribution and can take place on very\ndifferent timescales, depending on the adiabaticity of the quench. The contact\nparameter is seen to respond very quickly to changes in the interaction\nstrength, indicating that short-range correlations, based on the occupation of\nhigh-momentum modes, evolve far more rapidly than the correlations in\nlow-momentum modes necessary for pair condensation."
    },
    {
        "anchor": "Two-dimensional solitons and quantum droplets supported by competing\n  self- and cross-interactions in spin-orbit-coupled condensates: We study two-dimensional (2D) matter-wave solitons in spinor Bose-Einstein\ncondensates (BECs) under the action of the spin-orbit coupling (SOC) and\nopposite signs of the self- and cross-interactions. Stable 2D two-component\nsolitons of the mixed-mode (MM) type are found if the cross-interaction between\nthe components is attractive, while the self-interaction is repulsive in each\ncomponent. Stable solitons of the semi-vortex type are formed in the opposite\ncase, under the action of competing self-attraction and cross-repulsion. The\nsolitons exist with the total norm taking values below a collapse threshold.\nFurther, in the case of the repulsive self-interaction and inter-component\nattraction, stable 2D self-trapped modes, which may be considered as quantum\ndroplets (QDs), are created if the beyond-mean-field Lee-Huang-Yang (LHY) terms\nare added to the self-repulsion in the underlying system of coupled\nGross-Pitaevskii equations. Stable QDs of the MM type, of a large size with an\nanisotropic density profile, exist with arbitrarily large values of the norm,\nas the LHY terms eliminate the collapse. The effect of the SOC term on\ncharacteristics of the QDs is systematically studied. We also address the\nexistence and stability of QDs in the case of SOC with mixed Rashba and\nDresselhaus terms, which makes the density profile of the QD more isotropic.\nThus, QDs in the spin-orbit-coupled binary BEC are for the first time studied\nin the present work.",
        "positive": "Confinement of Bose-Einstein magnon condensates in adjustable complex\n  magnetization landscapes: Coherent wave states such as Bose-Einstein condensates (BECs), which\nspontaneously form in an overpopulated magnon gas even at room temperature,\nhave considerable potential for wave-based computing and information processing\nat microwave frequencies. The ability to control the transport properties of\nmagnon BECs plays an essential role for their practical use. Here, we\ndemonstrate spatio-temporal control of the BEC density distribution through the\nexcitation of magnon supercurrents in an inhomogeneously magnetized yttrium\niron garnet film. The BEC is created by microwave parametric pumping and probed\nby Brillouin light scattering spectroscopy. The desired magnetization profile\nis prepared by heating the film with optical patterns projected onto its\nsurface using a phase-based wavefront modulation technique. Specifically, we\nobserve a pronounced spatially localized magnon accumulation caused by magnon\nsupercurrents flowing toward each other originating in two heated regions. This\naccumulation effect increases the BEC lifetime due to the constant influx of\ncondensed magnons into the confinement region. The shown approach to manipulate\ncoherent waves provides an opportunity to extend the lifetime of freely\nevolving magnon BECs, create dynamic magnon textures, and study the interaction\nof magnon condensates formed in different regions of the sample."
    },
    {
        "anchor": "Exactly solvable tight-binding models on two scale-free networks with\n  identical degree distribution: We study ideal Bose gas upon two scale-free structures with identical degree\ndistribution. Energy spectra belonging to tight-binding Hamiltonian are exactly\nsolved and the related spectral dimensions of $G_1$ and $ G_2$ are obtained as\n$d_{s_1} = 2$ and $d_{s_2} = 2 \\ln 4/ \\ln 3$. We show Bose-Einstein\ncondensation will only take place upon $G_2$ instead of $G_1$. The topology and\nthermodynamical property of the two structures are proven to be totally\ndifferent.",
        "positive": "Quantum Chaos in Ultracold Collisions of Erbium: Atomic and molecular samples reduced to temperatures below 1 microkelvin, yet\nstill in the gas phase, afford unprecedented energy resolution in probing and\nmanipulating how their constituent particles interact with one another. For\nsimple atoms, such as alkalis, scattering resonances are extremely\nwell-characterized. However, ultracold physics is now poised to enter a new\nregime, where far more complex species can be cooled and studied, including\nmagnetic lanthanide atoms and even molecules. For molecules, it has been\nspeculated that a dense forest of resonances in ultracold collision cross\nsections will likely express essentially random fluctuations, much as the\nobserved energy spectra of nuclear scattering do. According to the\nBohigas-Giannoni-Schmit conjecture, these fluctuations would imply chaotic\ndynamics of the underlying classical motion driving the collision. This would\nprovide a paradigm shift in ultracold atomic and molecular physics,\nnecessitating new ways of looking at the fundamental interactions of atoms in\nthis regime, as well as perhaps new chaos-driven states of ultracold matter. In\nthis report we provide the first experimental demonstration that random spectra\nare indeed found at ultralow temperatures. In the experiment, an ultracold gas\nof erbium atoms is shown to exhibit many Fano-Feshbach resonances, for bosons\non the order of 3 per gauss. Analysis of their statistics verifies that their\ndistribution of nearest-neighbor spacings is what one would expect from random\nmatrix theory. The density and statistics of these resonances are explained by\nfully-quantum mechanical scattering calculations that locate their origin in\nthe anisotropy of the atoms' potential energy surface. Our results therefore\nreveal for the first time chaotic behavior in the native interaction between\nultracold atoms."
    },
    {
        "anchor": "Observation of shock waves in a strongly interacting Fermi gas: We study collisions between two strongly interacting atomic Fermi gas clouds.\nWe observe exotic nonlinear hydrodynamic behavior, distinguished by the\nformation of a very sharp and stable density peak as the clouds collide and\nsubsequent evolution into a box-like shape. We model the nonlinear dynamics of\nthese collisions using quasi-1D hydrodynamic equations. Our simulations of the\ntime-dependent density profiles agree very well with the data and provide clear\nevidence of shock wave formation in this universal quantum hydrodynamic system.",
        "positive": "Localization of Bogoliubov quasiparticles in interacting Bose gases with\n  correlated disorder: We study the Anderson localization of Bogoliubov quasiparticles (elementary\nmany-body excitations) in a weakly interacting Bose gas of chemical potential\n$\\mu$ subjected to a disordered potential $V$. We introduce a general mapping\n(valid for weak inhomogeneous potentials in any dimension) of the Bogoliubov-de\nGennes equations onto a single-particle Schr\\\"odinger-like equation with an\neffective potential. For disordered potentials, the Schr\\\"odinger-like equation\naccounts for the scattering and localization properties of the Bogoliubov\nquasiparticles. We derive analytically the localization lengths for correlated\ndisordered potentials in the one-dimensional geometry. Our approach relies on a\nperturbative expansion in $V/\\mu$, which we develop up to third order, and we\ndiscuss the impact of the various perturbation orders. Our predictions are\nshown to be in very good agreement with direct numerical calculations. We\nidentify different localization regimes: For low energy, the effective\ndisordered potential exhibits a strong screening by the quasicondensate density\nbackground, and localization is suppressed. For high-energy excitations, the\neffective disordered potential reduces to the bare disordered potential, and\nthe localization properties of quasiparticles are the same as for free\nparticles. The maximum of localization is found at intermediate energy when the\nquasicondensate healing length is of the order of the disorder correlation\nlength. Possible extensions of our work to higher dimensions are also\ndiscussed."
    },
    {
        "anchor": "Phase separation and hidden vortices induced by spin-orbit coupling in\n  spin-1 Bose-Einstein condensates: We investigate phase separation and hidden vortices in spin-orbit coupled\nferromagnetic BoseEinstein condensates with rotation and Rabi coupling. The\nhidden vortices are invisible in density distribution but are visible in phase\ndistribution, which can carry angular momentum like the ordinary quantized\nvortices. In the absence of the rotation, we observe the phase separation\ninduced by the spin-orbit coupling and determine the entire phase diagram of\nthe existence of phase separation. For the rotation case, in addition to the\nphase separation, we demonstrate particularly that the spin-orbit coupling can\nresult in the hidden vortices and hidden vortex-antivortex pairs. The\ncorresponding entire phase diagrams are determined, depending on the interplay\nof the spin-orbit coupling strength, the rotation frequency, and Rabi\nfrequency, which reveals the critical condition of the occurrence of the hidden\nvortices and vortex-antivortex pairs. The hidden vortices here are proved to be\nlong-lived in the time scale of experiment by the dynamic analysis. These\nfindings not only provide a clear illustration of the phase separation in\nspin-orbit coupled spinor Bose-Einstein condensates, but also open a new\ndirection for investigating the hidden vortices in high-spin quantum system.",
        "positive": "Fermi spin polaron and dissipative Fermi-polaron Rabi dynamics: We consider a spin impurity with multiple energy levels moving in a\nnon-interacting Fermi sea, and theoretically solve this Fermi spin polaron\nproblem at nonzero temperature by using a non-self-consistent many-body\n$T$-matrix theory. We focus on the simplest case with spin half, where the two\nenergy states of the impurity are coupled by a Rabi flip term. At small Rabi\ncoupling, the impurity exhibits damped Rabi oscillations, where the decoherence\nis caused by the interaction with the Fermi sea, as recently reported in Fermi\npolaron experiments with ultracold atoms. We investigate the dependence of Rabi\noscillations on the Rabi coupling strength and examine the additional nonlinear\ndamping due to large Rabi coupling. At finite temperature and at nonzero\nimpurity concentration, the impurity can acquire a pronounced momentum\ndistribution. We show that the momentum/thermal average can sizably reduce the\nvisibility of Rabi oscillations. We compare our theoretical predictions to the\nrecent experimental data and find a good agreement without any adjustable\nparameter."
    },
    {
        "anchor": "Spin-asymmetric Josephson effect: The Josephson effect is a manifestation of the macroscopic phase coherence of\nsuperconductors and superfluids. We propose that with ultracold Fermi gases one\ncan realise a spin-asymmetric Josephson effect in which the two spin components\nof a Cooper pair are driven asymmetrically - corresponding to driving a\nJosephson junction of two superconductors with different voltages V_\\uparrow\nand V_\\downarrow for spin up and down electrons, respectively. We predict that\nthe spin up and down components oscillate at the same frequency but with\ndifferent amplitudes. Our results reveal that the standard description of the\nJosephson effect in terms of bosonic pair tunnelling is insufficient. We\nprovide an intuitive interpretation of the Josephson effect as interference in\nRabi oscillations of pairs and single particles, the latter causing the\nasymmetry.",
        "positive": "Anderson localization of Cooper pairs and Majorana fermions in an\n  ultracold atomic Fermi gas with synthetic spin-orbit coupling: We theoretically investigate two-particle and many-particle Anderson\nlocalizations of a spin-orbit coupled ultracold atomic Fermi gas trapped in a\nquasi-periodic potential and subjected to an out-of-plane Zeeman field. We\nsolve exactly the two-particle problem in a finite length system by exact\ndiagonalization and solve approximately the many-particle problem within the\nmean-field Bogoliubov-de Gennes approach. At a small Zeeman field, the\nlocalization properties of the system are similar to that of a Fermi gas with\nconventional $s$-wave interactions. As the disorder strength increases, the\ntwo-particle binding energy increases and the fermionic superfluidity of many\nparticles disappears above a threshold. At a large Zeeman field, where the\ninteratomic interaction behaves effectively like a $p$-wave interaction, the\nbinding energy decreases with increasing disorder strength and the resulting\ntopological superfluidity shows a much more robust stability against disorder\nthan the conventional $s$-wave superfluidity. We also analyze the localization\nproperties of the emergent Majorana fermions in the topological phase. Our\nresults could be experimentally examined in future cold-atom experiments, where\nthe spin-orbit coupling can be induced artificially by using two Raman lasers,\nand the quasi-periodic potential can be created by using bichromatic optical\nlattices."
    },
    {
        "anchor": "Stable Heteronuclear Few-Atom Bound States in Mixed Dimensions: We study few-body problems in mixed dimensions with $N \\ge 2$ heavy atoms\ntrapped individually in parallel one-dimensional tubes or two-dimensional\ndisks, and a single light atom travels freely in three dimensions. By using the\nBorn-Oppenheimer approximation, we find three- and four-body bound states for a\nbroad region of heavy-light atom scattering length combinations. Specifically,\nthe existence of trimer and tetramer states persist to negative scattering\nlengths regime, where no two-body bound state is present. These few-body bound\nstates are analogous to the Efimov states in three dimensions, but are stable\nagainst three-body recombination due to geometric separation. In addition, we\nfind that the binding energy of the ground trimer and tetramer state reaches\nits maximum value when the scattering lengths are comparable to the separation\nbetween the low-dimensional traps. This resonant behavior is a unique feature\nfor the few-body bound states in mixed dimensions.",
        "positive": "Sound propagation in a Bose-Einstein condensate at finite temperatures: We study the propagation of a density wave in a magnetically trapped\nBose-Einstein condensate at finite temperatures. The thermal cloud is in the\nhydrodynamic regime and the system is therefore described by the two-fluid\nmodel. A phase-contrast imaging technique is used to image the cloud of atoms\nand allows us to observe small density excitations. The propagation of the\ndensity wave in the condensate is used to determine the speed of sound as a\nfunction of the temperature. We find the speed of sound to be in good agreement\nwith calculations based on the Landau two-fluid model."
    },
    {
        "anchor": "Many-body delocalization in the presence of a quantum bath: Closed generic quantum many-body systems may fail to thermalize under certain\nconditions even after long times, a phenomenon called many-body localization\n(MBL). Numerous studies support the stability of the MBL phase in strongly\ndisordered one-dimensional systems. However, the situation is much less clear\nwhen a small part of the system is ergodic, a scenario which also has important\nimplications for the existence of many-body localization in higher dimensions.\nHere we address this question experimentally using a large-scale quantum\nsimulator of ultracold bosons in a two-dimensional optical lattice. We prepare\ntwo-component mixtures of varying relative population and implement a disorder\npotential which is only experienced by one of the components. The second\nnon-disordered ''clean'' component plays the role of a bath of adjustable size\nthat is collisionally coupled to the ''dirty'' component. Our experiments show\nhow the dynamics of the dirty component, which, when on its own, show strong\nevidence of localization, become affected by the coupling to the clean\ncomponent. For a high clean population, the clean component appears to behave\nas an effective bath for the system which leads to its delocalization, while\nfor a smaller clean population, the ability of the bath to destabilize the\nsystem becomes strongly reduced. Our results reveal how a finite-sized quantum\nsystem can bring another one towards thermalization, in a regime of complex\ninterplay between disorder, tunneling and intercomponent interactions. They\nprovide a new benchmark for effective theories aiming to capture the complex\nphysics of MBL in the weakly localized regime.",
        "positive": "Creation of an ultracold gas of ground-state $^{23}\\rm{Na}^{87}\\rm{Rb}$\n  molecules: We report the successful production of an ultracold sample of absolute\nground-state $^{23}$Na$^{87}$Rb molecules. Starting from weakly-bound Feshbach\nmolecules formed via magneto-association, the lowest rovibrational and\nhyperfine level of the electronic ground state is populated following a high\nefficiency and high resolution two-photon Raman process. The high purity\nabsolute ground-state samples have up to 8000 molecules and densities of over\n$10^{11}$ cm$^{-3}$. By measuring the Stark shifts induced by external electric\nfields, we determined the permanent electric dipole moment of the absolute\nground-state $^{23}$Na$^{87}$Rb and demonstrated the capability of inducing an\neffective dipole moment over one Debye. Bimolecular reaction between\nground-state $^{23}$Na$^{87}$Rb molecules is endothermic, but we still observed\na rather fast decay of the molecular sample. Our results pave the way toward\ninvestigation of ultracold molecular collisions in a fully controlled manner,\nand possibly to quantum gases of ultracold bosonic molecules with strong\ndipolar interactions."
    },
    {
        "anchor": "Linear Flavor-Wave Analysis of SU(4)-Symmetric Tetramer Model with\n  Population Imbalance: We study the quantum magnetism of the SU(4) Mott insulator in a square\noptical superlattice, in which atoms with four nuclear-spin components strongly\ninteract with each other, in the presence of an external field that controls\nthe imbalance between the population of two components and that of the other\ntwo. This is a natural extension of the physics of spin-dimer materials under\nstrong magnetic field. We apply an extended linear flavor-wave theory based on\nfour-site plaquettes and unveil the ground-state phase diagram and excitation\nspectra. When the population of the four components is balanced and the\nplaquesttes are weakly coupled, the ground state is approximately given by the\ndirect product of local SU(4)-singlet states. In high-field, the system reaches\na \"saturated state\" where only two components are present. Our main finding is\na nontrivial intermediate phase, which has a checkerboard-like arrangement of\nthe SU(4)-singlet and four-site resonating-valence-bond states.",
        "positive": "Quasi-one-dimensional Hall physics in the Harper-Hofstadter-Mott model: We study the ground-state phase diagram of the strongly interacting\nHarper-Hofstadter-Mott model at quarter flux on a quasi-one-dimensional lattice\nconsisting of a single magnetic flux quantum in $y$-direction. In addition to\nsuperfluid phases with various density patterns, the ground-state phase diagram\nfeatures quasi-one-dimensional analogues of fractional quantum Hall phases at\nfillings $\\nu=1/2$ and $3/2$, where the latter is only found thanks to the\nhopping anisotropy and the quasi-one-dimensional geometry. At integer fillings\n- where in the full two-dimensional system the ground-state is expected to be\ngapless - we observe gapped non-degenerate ground-states: At $\\nu=1$ it shows\nan odd 'fermionic' Hall conductance, while the Hall response at $\\nu=2$\nconsists of the transverse transport of a single particle-hole pair, resulting\nin a net zero Hall conductance. The results are obtained by exact\ndiagonalization and in the reciprocal mean-field approximation."
    },
    {
        "anchor": "Thermoelectricity of cold ions in optical lattices: We study analytically and numerically the thermoelectric properties of cold\nions placed in an optical lattice. Our results show that the transition from\nsliding to pinned phase takes place at a certain critical amplitude of lattice\npotential being similar to the Aubry transition for the Frenkel-Kontorova\nmodel. We show that this critical amplitude is proportional to the cube of ion\ndensity that allows to perform experimental realization of this system at\nmoderate lattice amplitudes. We show that the Aubry phase is characterized by\nthe dimensionless Seebeck coefficient about 50 and the figure of merit being\naround 8. We propose possible experimental investigations of such system with\ncold ions and argue that the experiments with electrons on liquid helium\nsurface can also help to understand its unusual properties. The obtained\nresults represent also a challenge for modern methods of quantum chemistry and\nmaterial science.",
        "positive": "Elementary Excitations in Bose-Einstein Condensates at Large Scattering\n  Lengths: We present a theoretical analysis of excitation modes in Bose-Einstein\ncondensates in ultracold alkali-metal gases for large scattering lengths and\nmomenta where corrections to the mean field approximation become important. We\nassume that the effective interaction in the metastable, single channel,\ngaseous phase has a well defined Fourier transform that scales with the\nscattering length. Based on this we show that for increasing scattering lengths\nor equivalently increasing densities the system becomes less correlated and\nthat at large values of the scattering length Bragg scattering measures\ndirectly the Fourier transform of the effective two-body potential. We\nconstruct model potentials which fit the recently measured line shifts in\n$^{85}$Rb by Papp et al. (Phys. Rev. Lett. {\\bf 101}, 135301 (2008)), and show\nthat they fix the low momentum expansion of the effective range function. We\nfind excellent agreement with the experimental data when the effective range is\n$\\ll 1$ and the coefficient of the $k^4$-term is $-7.5 \\pm 0.5$ in scattering\nlength units. The resolution in Bragg scattering experiments so far does not\nreveal details of the frequency dependence in the dynamic structure function\n$S(k,\\omega)$ and we show that the Feynman spectrum determines the measured\nline shifts. We propose the possibility of a transition to a novel density wave\nstate."
    },
    {
        "anchor": "Supermode-Density-Wave-Polariton Condensation: Phase transitions, where observable properties of a many-body system change\ndiscontinuously, can occur in both open and closed systems. Ultracold atoms\nhave provided an exemplary model system to demonstrate the physics of\nclosed-system phase transitions, confirming many theoretical models and\nresults. Our understanding of dissipative phase transitions in quantum systems\nis less developed, and experiments that probe this physics even less so. By\nplacing cold atoms in optical cavities, and inducing strong coupling between\nlight and excitations of the atoms, one can experimentally study phase\ntransitions of open quantum systems. Here we observe and study a novel form of\nnonequilibrium phase transition, the condensation of\nsupermode-density-wave-polaritons. These polaritons are formed from a hybrid\n\"supermode\" of cavity photons coupled to atomic density waves of a quantum gas.\nBecause the cavity supports multiple photon spatial modes, and because the\nmatter-light coupling can be comparable to the energy splitting of these modes,\nthe composition of the supermode polariton is changed by the matter-light\ncoupling upon condensation. These results, found in the few-mode-degenerate\ncavity regime, demonstrate the potential of fully multimode cavities to exhibit\nphysics beyond mean-field theories. Such systems will provide experimental\naccess to nontrivial phase transitions in driven dissipative quantum systems as\nwell as enabling the studies of novel non-equilibrium spin glasses and\nneuromorphic computation.",
        "positive": "Polaritons are Not Weakly Interacting: Direct Measurement of the\n  Polariton-Polariton Interaction Strength: Exciton-polaritons in a microcavity are composite two-dimensional bosonic\nquasiparticles, arising from the strong coupling between confined light modes\nin a resonant planar optical cavity and excitonic transitions, typically using\nexcitons in semiconductor quantum wells (QWs) placed at the antinodes of the\nsame cavity. Quantum phenomena such as Bose-Einstein condensation (BEC),\nquantized vortices, and macroscopic quantum states have been reported at\ntemperatures from tens of Kelvin up to room temperatures, and polaritonic\ndevices such as spin switches \\cite{Amo2010} and optical transistors have also\nbeen reported. Many of these effects of exciton-polaritons depend crucially on\nthe polariton-polariton interaction strength. Despite the importance of this\nparameter, it has been difficult to make an accurate experimental measurement,\nmostly because of the difficulty of determining the absolute densities of\npolaritons and bare excitons. Here we report the direct measurement of the\npolariton-polariton interaction strength in a very high-Q microcavity\nstructure. By allowing polaritons to propagate over 40 $\\mu$m to the center of\na laser-generated annular trap, we are able to separate the polariton-polariton\ninteractions from polariton-exciton interactions. The interaction strength is\ndeduced from the energy renormalization of the polariton dispersion as the\npolariton density is increased, using the polariton condensation as a benchmark\nfor the density. We find that the interaction strength is about two orders of\nmagnitude larger than previous theoretical estimates, putting polaritons\nsquarely into the strongly-interacting regime. When there is a condensate, we\nsee a sharp transition to a different dependence of the renormalization on the\ndensity, which is evidence of many-body effects."
    },
    {
        "anchor": "Magnetic lattices for ultracold atoms and degenerate quantum gases: We review recent developments in the use of magnetic lattices as a\ncomplementary tool to optical lattices for trapping periodic arrays of\nultracold atoms and degenerate quantum gases. Recent advances include the\nrealisation of Bose-Einstein condensation in multiple sites of a magnetic\nlattice of one-dimensional microtraps, the trapping of ultracold atoms in\nsquare and triangular magnetic lattices, and the fabrication of magnetic\nlattice structures with sub-micron period suitable for quantum tunnelling\nexperiments. Finally, we describe a proposal to utilise long-range interacting\nRydberg atoms in a large spacing magnetic lattice to create interactions\nbetween atoms on neighbouring sites.",
        "positive": "Universal phase diagram and scaling functions of imbalanced Fermi gases: We discuss the phase diagram and the universal scaling functions of\nattractive Fermi gases at finite imbalance. The existence of a quantum\nmulticritical point for the unitary gas at vanishing chemical potential $\\mu$\nand effective magnetic field $h$, first discussed by Nikoli\\'{c} and Sachdev,\ngives rise to three different phase diagrams, depending on whether the inverse\nscattering length $1/a$ is negative, positive or zero. Within a Luttinger-Ward\nformalism, the phase diagram and pressure of the unitary gas is calculated as a\nfunction of the dimensionless scaling variables $T/\\mu$ and $h/\\mu$. The\nresults indicate that beyond the Clogston-Chandrasekhar limit at\n$(h/\\mu)_c\\simeq 1.09$, the unitary gas exhibits an inhomogeneous superfluid\nphase with FFLO order that can reach critical temperatures near unitarity of\n$\\simeq 0.03\\, T_F$."
    },
    {
        "anchor": "Half-Quantum Vortex Molecules in a Binary Dipolar Bose Gas: We study the ground state phases of a rotating two-component, or binary\nBose-Einstein condensate, wherein one component possesses a large magnetic\ndipole moment. A variety of non-trivial phases emerge in this system, including\na half-quantum vortex (HQV) chain phase and a HQV molecule phase, where HQVs of\nopposite charge bind at short distances. We attribute the emergence of these\nphases to the development of a minimum in the adiabatic HQV interaction\npotential, which we calculate explicitly. We thus show that the presence of\ndipolar interactions in this system leads to a rich phase diagram, and the\nformation of HQV molecules.",
        "positive": "Slow Mass Transport and Statistical Evolution of An Atomic Gas Across\n  the Superfluid-Mott Insulator Transition: We study transport dynamics of ultracold cesium atoms in a two-dimensional\noptical lattice across the superfluid-Mott insulator transition based on in\nsitu imaging. Inducing the phase transition with a lattice ramping routine\nexpected to be locally adiabatic, we observe a global mass redistribution which\nrequires a very long time to equilibrate, more than 100 times longer than the\nmicroscopic time scales for on-site interaction and tunneling. When the sample\nenters the Mott insulator regime, mass transport significantly slows down. By\nemploying fast recombination pulses to analyze the occupancy distribution, we\nobserve similarly slow-evolving dynamics, and a lower effective temperature at\nthe center of the sample."
    },
    {
        "anchor": "Integrated coherent matter wave circuits: An integrated coherent matter wave circuit is a single device, analogous to\nan integrated optical circuit, in which coherent de Broglie waves are created\nand then launched into waveguides where they can be switched, divided,\nrecombined, and detected as they propagate. Applications of such circuits\ninclude guided atom interferometers, atomtronic circuits, and precisely\ncontrolled delivery of atoms. Here we report experiments demonstrating\nintegrated circuits for guided coherent matter waves. The circuit elements are\ncreated with the painted potential technique, a form of time-averaged optical\ndipole potential in which a rapidly-moving, tightly-focused laser beam exerts\nforces on atoms through their electric polarizability. The source of coherent\nmatter waves is a Bose-Einstein condensate (BEC). We launch BECs into painted\nwaveguides that guide them around bends and form switches, phase coherent\nbeamsplitters, and closed circuits. These are the basic elements that are\nneeded to engineer arbitrarily complex matter wave circuitry.",
        "positive": "Gr\u00fcneisen parameters for Lieb-Liniger and Yang-Gaudin models: Using the Bethe ansatz solution, we analytically study expansionary, magnetic\nand interacting Gr\\\"uneisen parameters (GPs) for one-dimensional (1D)\nLieb-Liniger and Yang-Gaudin models. These different GPs elegantly quantify the\ndependences of characteristic energy scales of these quantum gases on the\nvolume, the magnetic field and the interaction strength, revealing the caloric\neffects resulted from the variations of these potentials. The obtained GPs\nfurther confirm an identity which is incurred by the symmetry of the thermal\npotential. We also present universal scaling behavior of these GPs in the\nvicinities of the quantum critical points driven by different potentials. The\ndivergence of the GPs not only provides an experimental identification of\nnon-Fermi liquid nature at quantum criticality but also elegantly determine low\ntemperature phases of the quantum gases. Moreover, the pairing and depairing\nfeatures in the 1D attractive Fermi gases can be captured by the magnetic and\ninteracting GPs, facilitating experimental observation of quantum phase\ntransitions. Our results open to further study the interaction- and\nmagnetic-field-driven quantum refrigeration and quantum heat engine in quantum\ngases of ultracold atoms."
    },
    {
        "anchor": "A Gross-Pitaevskii-equation description of the momentum-state lattice:\n  roles of the trap and many-body interactions: We report a theoretical description of the synthetic momentum-state lattices\nwith a 3D Gross-Pitaevskii equation (GPE), where both the external trap\npotential and the mean-field spatial-density-dependent many-body interactions\nare naturally included and exactly treated. The GPE models exhibit better\nperformance than the tight-binding model to depict the experimental\nobservations. Since the trap modifies the dispersion relation for free\nparticles and shapes the spatial density distribution that leads to\ninhomogeneous interactions, decoherences (damping oscillation) appear even for\na short-time evolution. Our parametric calculations for the two-state\noscillation suggest that we should work with a relatively shallow trap in the\nweakly interacting regime, especially when the long-term dynamics are\nconcerned. The impact of the mean-field interaction, i.e., the self-trapping\nbehavior, on the transport dynamics and the topological phase transition in a\nfinite multiple-state lattice chain is also specifically investigated. Such an\naccurate treatment of the inhomogeneous interactions allows for further\ninvestigations on the interplay with disorder, the pair correlation dynamics,\nand the thermalization process in momentum space.",
        "positive": "Quantized vortices and quantum turbulence: We review recent important topics in quantized vortices and quantum\nturbulence in atomic Bose--Einstein condensates (BECs). They have previously\nbeen studied for a long time in superfluid helium. Quantum turbulence is\ncurrently one of the most important topics in low-temperature physics. Atomic\nBECs have two distinct advantages over liquid helium for investigating such\ntopics: quantized vortices can be directly visualized and the interaction\nparameters can be controlled by the Feshbach resonance. A general introduction\nis followed by a description of the dynamics of quantized vortices,\nhydrodynamic instability, and quantum turbulence in atomic BECs."
    },
    {
        "anchor": "\"Gray\" BCS condensate of excitons and internal Josephson effect: It has been recently suggested that the Bose-Einstein condensate formed by\nexcitons in the dilute limit must be dark, i.e., not coupled to photons. Here,\nwe show that, under a density increase, the dark exciton condensate must\nacquire a bright component due to carrier exchange in which dark excitons turn\nbright. This however requires a density larger than a threshold which seems to\nfall in the forbidden region of the phase separation between a dilute exciton\ngas and a dense electron-hole plasma. The BCS-like condensation which is likely\nto take place on the dense side, must then have a dark and a bright component -\nwhich makes it \"gray\". It should be possible to induce an internal Josephson\neffect between these two coherent components, with oscillations of the\nphotoluminescence as a strong proof of the existence for this \"gray\" BCS-like\nexciton condensate.",
        "positive": "Quasi-one- and quasi-two-dimensional Bose-Fermi mixtures from weak\n  coupling to unitarity: We study ultracold superfluid Bose-Fermi mixtures in three dimensions, with\nstronger confinement along one or two directions, using a non-perturbative\nbeyond-mean-field model for bulk chemical potential valid along the\nweak-coupling to unitarity crossover. Although bosons are considered to be in a\nsuperfluid state, we consider two possibilities for the fermions --\nspin-polarized degenerate state and superfluid state. Simplified reduced\nanalytic lower-dimensional models are derived along the weak-coupling to\nunitarity crossover in quasi-one-dimensional (quasi-1D) and\nquasi-two-dimensional (quasi-2D) settings. The only parameters in these models\nare the constants of the beyond-mean-field Bose-Bose and Fermi-Fermi\nLee-Huang-Yang interactions and the respective universal Bertsch parameter at\nunitarity. In addition to the numerical results for a fully-trapped system, we\nalso present results for quasi-2D Bose-Fermi mixtures where one of the\ncomponents is untrapped but localized due to the interaction mediated by the\nother component. We demonstrate the validity of the reduced quasi-1D and\nquasi-2D models via a comparison of the numerical solutions for the ground\nstates obtained from the reduced models and the full three-dimensional (3D)\nmodel."
    },
    {
        "anchor": "Dynamical thermalization of interacting fermionic atoms in a\n  Sinai-oscillator trap: We study numerically the problem of dynamical thermalization of interacting\ncold fermionic atoms placed in an isolated Sinai-oscillator trap. This system\nis characterized by a quantum chaos regime for one-particle dynamics. We show\nthat for a many-body system of cold atoms the interactions, with a strength\nabove a certain quantum chaos border given by the Aberg criterion, lead to the\nFermi-Dirac distribution and relaxation of many-body initial states to the\nthermalized state in absence of any contact with a thermostate. We discuss the\nproperties of this dynamical thermalization and its links with the\nLoschmidt-Boltzmann dispute.",
        "positive": "Dipole-mode and scissors-mode oscillations of a dipolar supersolid: We study dipole-mode and scissors-mode oscillations of a harmonically-trapped\ndipolar supersolid, composed of dipolar droplets arranged on a one-dimensional\n(1D) or a two-dimensional (2D) lattice, to establish the robustness of its\ncrystalline structure under translation and rotation, using a beyond-mean-field\nmodel including a Lee-Huang-Yang interaction. The dipolar atoms are polarized\nalong the $z$ direction with the supersolid crystalline structure lying in the\n$x$-$y$ plane. A stable dipole-mode oscillation was possible in case of both\nquasi-1D and quasi-2D dipolar supersolids, whereas a sustained angular\nscissors-mode oscillation was possible only in the case of a quasi-1D dipolar\nsupersolid between a maximum and a minimum of trap anisotropy in the $x$-$y$\nplane. In both cases there was no visible deformation of the crystalline\nstructure of the dipolar supersolid during the oscillation. The theoretical\nestimate of the scissors-mode-oscillation frequency was in good agreement with\nthe present results and the agreement improved with an increase of the number\nof droplets in the supersolid and also with an increase in the confining trap\nfrequencies. The results of this study can be tested experimentally with\npresent knowhow."
    },
    {
        "anchor": "Phases of attractive spin-imbalanced fermions in square lattices: We determine the relative stability of different ground-state phases of\nspin-imbalanced popula- tions of attractive fermions in square lattices. The\nphases are systematically characterized by the symmetry of the order parameter\nand the real- and momentum-space structures using Hartree- Fock-Bogoliubov\ntheory. We find several type of unidirectional Larkin-Ovchinikov-type phases.\nWe discuss the effect of commensuration between the ordering wave vector and\nthe density imbalance, and describe the mechanism of Fermi surface\nreconstruction and pairing for various orders. A robust supersolid phase is\nshown to exist when the ordering wave vector is diagonally directed.",
        "positive": "Bosonic integer quantum Hall effect in optical flux lattices: In two dimensions strongly interacting bosons in a magnetic field can realize\na bosonic integer quantum Hall state, the simplest two dimensional example of a\nsymmetry protected topological phase. We propose a realistic implementation of\nthis phase using an optical flux lattice. Through exact diagonalization\ncalculations, we show that the system exhibits a clear bulk gap and the\ntopological signature of the bosonic integer quantum Hall state. In particular,\nthe calculation of the many-body Chern number leads to a quantized Hall\nconductance in agreement with the analytical predictions. We also study the\nstability of the phase with respect to some of the experimentally relevant\nparameters."
    },
    {
        "anchor": "Effective approach to impurity dynamics in one-dimensional trapped Bose\n  gases: We investigate a temporal evolution of an impurity atom in a one-dimensional\ntrapped Bose gas following a sudden change of the boson-impurity interaction\nstrength. Our focus is on the effects of inhomogeneity due to the harmonic\nconfinement. These effects can be described by an effective one-body model\nwhere both the mass and the spring constant are renormalized. This is in\ncontrast to the classic renormalization, which addresses only the mass. We\npropose an effective single-particle Hamiltonian and apply the multilayer\nmulticonfiguration time-dependent Hartree method for bosons to explore its\nvalidity. Numerical results suggest that the effective mass is smaller than the\nimpurity mass, which means that it cannot straightforwardly be extracted from\ntranslationally invariant models.",
        "positive": "Advantages of Mass-Imbalanced Ultracold Fermionic Mixtures for\n  Approaching Quantum Magnetism in Optical Lattices: We study magnetic phases of two-component mixtures of ultracold fermions with\nrepulsive interactions in optical lattices in the presence of hopping\nimbalance. Our analysis is based on dynamical mean-field theory (DMFT) and its\nreal-space generalization at finite temperature. We study the temperature\ndependence of the transition into the ordered state as a function of the\ninteraction strength and the imbalance parameter in two and three spatial\ndimensions. We show that below the critical temperature for N\\'{e}el order\nmass-imbalanced mixtures also exhibit a charge-density wave, which provides a\ndirectly observable signature of the ordered state. For the trapped system, we\ncompare our results obtained by real-space DMFT to a local-density\napproximation. We calculate the entropy for a wide range of parameters and\nidentify regions, in which mass-imbalanced mixtures could have clear advantages\nover balanced ones for the purpose of obtaining and detecting quantum\nmagnetism."
    },
    {
        "anchor": "Quantum Shock Waves and Domain Walls in the Real-Time Dynamics of a\n  Superfluid Unitary Fermi Gas: We show that in the collision of two superfluid fermionic atomic clouds one\nobserves the formation of quantum shock waves as discontinuities in the number\ndensity and collective flow velocity. Domain walls, which are topological\nexcitations of the superfluid order parameter, are also generated and exhibit\nabrupt phase changes by $\\pi$ and slower motion than the shock waves. The\ndomain walls are distinct from the gray soliton train or number density ripples\nformed in the wake of the shock waves and observed in the collisions of\nsuperfluid bosonic atomic clouds. Domain walls with opposite phase jumps appear\nto collide elastically.",
        "positive": "Interaction ramps in a trapped Bose condensate: Non-adiabatic interaction ramps are considered for trapped Bose-Einstein\ncondensates. The deviation from adiabaticity is characterized through the\nheating or residual energy produced during the ramp. We find that the\ndependence of the heat on the ramp time is very sensitive to the ramp protocol.\nWe explain features of this dependence through a single-parameter effective\ndescription based on the dynamics of the condensate size."
    },
    {
        "anchor": "Synthetic Gauge Fields for Ultra Cold Atoms: A Primer: We start by reviewing the concept of gauge invariance in quantum mechanics,\nfor Abelian and Non-Ableian cases. Then we idescribe how the various gauge\npotential and field can be associated with the geometrical phase acquired by a\nquantum mechanical wave function while adiabatically evolving in a parameter\nspace. Subsequently we show how this concept is exploited to generate light\ninduced gauge field for neutral ultra cold bosonic atoms. As an example of such\nlight induced Abelian and Non Abelian gauge field for ultra cold atoms we\ndisucss ultra cold atoms in a rotating trap and creation of synthetic spin\norbit coupling for ultra cold atomic systems using Raman lasers.",
        "positive": "A protocol to characterize errors in quantum simulation of many-body\n  physics: Quantum simulation of many-body systems, particularly using ultracold atoms\nand trapped ions, presents a unique form of quantum control -- it is a direct\nimplementation of a multi-qubit gate generated by the Hamiltonian. As a\nconsequence, it also faces a unique challenge in terms of benchmarking, because\nthe well-established gate benchmarking techniques are unsuitable for this form\nof quantum control. Here we show that the symmetries of the target many-body\nHamiltonian can be used to benchmark and characterize experimental errors in\nthe quantum simulation. We consider two forms of errors: (i) unitary errors\narising out of systematic errors in the applied Hamiltonian and (ii) canonical\nnon-Markovian errors arising out of random shot-to-shot fluctuations in the\napplied Hamiltonian. We show that the dynamics of the expectation value of the\ntarget Hamiltonian itself, which is ideally constant in time, can be used to\ncharacterize these errors. In the presence of errors, the expectation value of\nthe target Hamiltonian shows a characteristic thermalization dynamics, when it\nsatisfies the operator thermalization hypothesis (OTH). That is, an oscillation\nin the short time followed by relaxation to a steady-state value in the long\ntime limit. We show that while the steady-state value can be used to\ncharacterize the coherent errors, the amplitude of the oscillations can be used\nto estimate the non-Markovian errors. We develop scalable experimental\nprotocols to characterize these errors."
    },
    {
        "anchor": "Creation of a Dirac monopole-antimonopole pair in a spin-1 Bose-Einstein\n  condensate: We theoretically demonstrate that a pair of Dirac monopoles with opposite\nsynthetic charges can be created within a single spin-1 Bose-Einstein\ncondensate by steering the spin degrees of freedom by external magnetic fields.\nAlthough the net synthetic magnetic charge of this configuration vanishes, both\nthe monopole and the antimonopole are accompanied by vortex filaments carrying\nopposite angular momenta. Such a Dirac dipole can be realized experimentally by\nimprinting a spin texture with a nonlinear magnetic field generated by a pair\nof coils in a modified Helmholtz configuration. We also investigate the case\nwhere the initial state for the dipole-creation procedure is pierced by a\nquantized vortex line with a winding number k. It is shown that if k = -1, the\nresulting monopole and antimonopole lie along the core of a singly quantized\nvortex whose sign is reversed at the locations of the monopoles. For k = -2,\nthe monopole and antimonopole are connected by a vortex line segment carrying\ntwo quanta of angular momentum, and hence the dipole as a whole is an isolated\nconfiguration. In addition, we simulate the long-time evolution of the dipoles\nin the magnetic field used to create them. For k = 0, each of the semi-infinite\ndoubly quantized vortices splits into two singly quantized vortices, as in the\ncase of a single Dirac monopole. For k = -1 and k = -2, the initial vortices\ndeform into a vortex with a kink and a vortex ring, respectively.",
        "positive": "Non-Markovian quantum friction of bright solitons in superfluids: We explore the quantum dynamics of a bright matter-wave soliton in a\nquasi-one-dimensional bosonic superfluid with attractive interactions.\nSpecifically, we focus on the dissipative forces experienced by the soliton due\nto its interaction with Bogoliubov excitations. Using the collective coordinate\napproach and the Keldysh formalism, a Langevin equation of motion for the\nsoliton is derived from the first principle. The equation contains a stochastic\nLangevin force (associated with quantum noise) and a non-local in time\ndissipative force, which appears due to inelastic scattering of Bogoliubov\nquasiparticles off of the moving soliton. It is shown that Ohmic friction\n(i.e., a term proportional to the soliton's velocity) is absent in the\nintegrable setup. However, the Markovian approximation gives rise to the\nAbraham-Lorentz force (i.e., a term proportional to the derivative of the\nsoliton's acceleration), which is known from classical electrodynamics of a\ncharged particle interacting with its own radiation. These Abraham-Lorentz\nequations famously contain a fundamental causality paradox, where the\nsoliton/particle interacts with excitations/radiation originating from future\nevents. We show, however, that the causality paradox is an artifact of the\nMarkovian approximation, and our exact non-Markovian dissipative equations give\nrise to physical trajectories. We argue that the quantum friction discussed\nhere should be observable in current quantum gas experiments."
    },
    {
        "anchor": "Scaling and universality in two dimensions: three-body bound states with\n  short-ranged interactions: The momentum space zero-range model is used to investigate universal\nproperties of three interacting particles confined to two dimensions. The\npertinent equations are first formulated for a system of two identical and one\ndistinct particle and the two different two-body subsystems are characterized\nby two-body energies and masses. The three-body energy in units of one of the\ntwo-body energies is a universal function of the other two-body energy and the\nmass ratio. We derive convenient analytical formulae for calculations of the\nthree-body energy as function of these two independent parameters and exhibit\nthe results as universal curves. In particular, we show that the three-body\nsystem can have any number of stable bound states. When the mass ratio of the\ndistinct to identical particles is greater than 0.22 we find that at most two\nstable bound states exist, while for two heavy and one light mass an increasing\nnumber of bound states is possible. The specific number of stable bound states\ndepends on the ratio of two-body bound state energies and on the mass ratio and\nwe map out an energy-mass phase-diagram of the number of stable bound states.\nRealizable systems of both fermions and bosons are discussed in this framework.",
        "positive": "Ground state energy of the interacting Bose gas in two dimensions: an\n  explicit construction: The isotropic scattering phase shift is calculated for non-relativistic\nbosons interacting at low energies via an arbitrary finite-range potential in d\nspacetime dimensions. Scattering on a (d-1)-dimensional torus is then\nconsidered, and the eigenvalue equation relating the energy levels on the torus\nto the scattering phase shift is derived. With this technology in hand, and\nfocusing on the case of two spatial dimensions, a perturbative expansion is\ndeveloped for the ground-state energy of N identical bosons which interact via\nan arbitrary finite-range potential in a finite area. The leading non-universal\neffects due to range corrections and three-body forces are included. It is then\nshown that the thermodynamic limit of the ground-state energy in a finite area\ncan be taken in closed form to obtain the energy-per-particle in the\nlow-density expansion, by explicitly summing the parts of the finite-area\nenergy that diverge with powers of N. The leading and subleading finite-size\ncorrections to the thermodynamic limit equation-of-state are also computed.\nClosed-form results --some well-known, others perhaps not-- for two-dimensional\nlattice sums are included in an appendix."
    },
    {
        "anchor": "Complex-valued in-medium potential between heavy impurities in ultracold\n  atoms: We formulate the induced potential in a finite temperature cold atomic medium\nbetween two heavy impurities, or polarons, which is shown to be\n\\textit{complex-valued} in general. The imaginary part of the complex-valued\npotential describes a decoherence effect, and thus, the resulting Schr\\\"odinger\nequation for the two polarons acquires a non-Hermitian term. We apply the\ndeveloped formulation to two representative cases of polarons interacting with\nmedium particles through the $s$-wave contact interaction: (i) the normal phase\nof single-component (i.e., spin-polarized) fermions using the fermionic field\ntheory, and (ii) a superfluid phase using the superfluid effective field\ntheory, which is valid either for a Bose-Einstein condensate (BEC) of a\nsingle-component Bose gas or for the BEC-BCS crossover in two-component\nfermions at a low-energy regime. Computing the leading-order term, the\nimaginary part of the potential in both cases is found to show a universal\n$r^{-2}$ behavior at long distance. We propose three experimental ways to\nobserve the effects of the universal imaginary potential in cold atoms.",
        "positive": "Tailored single-atom collisions at ultra-low energies: We employ collisions of individual atomic cesium (Cs) impurities with an\nultracold rubidium (Rb) gas to probe atomic interaction with hyperfine- and\nZeeman-state sensitivity. Controlling the Rb bath's internal state yields\naccess to novel phenomena observed in inter-atomic spin-exchange. These can be\ntailored at ultra-low energies, owing to the excellent experimental control\nover all relevant energy scales. First, detecting spin-exchange dynamics in the\nCs hyperfine state manifold, we resolve a series of previously unreported\nFeshbach resonances at magnetic fields below 300 mG, separated by energies as\nlow as $h\\times 15$ kHz. The series originates from a coupling to molecular\nstates with binding energies below $h\\times 1$ kHz and wave function extensions\nin the micrometer range. Second, at magnetic fields below $\\approx 100\\,$mG, we\nobserve the emergence of a new reaction path for alkali atoms, where in a\nsingle, direct collision between two atoms two quanta of angular momentum can\nbe transferred. This path originates from the hyperfine-analogue of dipolar\nspin-spin relaxation. Our work yields control of subtle ultra-low-energy\nfeatures of atomic collision dynamics, opening new routes for advanced\nstate-to-state chemistry, for controlling spin-exchange in quantum many-body\nsystems for solid state simulations, or for determination of high-precision\nmolecular potentials."
    },
    {
        "anchor": "Nonlinear Luttinger liquid: Exact result for the Green function in terms\n  of the fourth Painlev\u00e9 transcendent: We show that exact time dependent single particle Green function in the\nImambekov-Glazman theory of nonlinear Luttinger liquids can be written, for any\nvalue of the Luttinger parameter, in terms of a particular solution of the\nPainlev\\'e IV equation. Our expression for the Green function has a form\nanalogous to the celebrated Tracy-Widom result connecting the Airy kernel with\nPainlev\\'e II. The asymptotic power law of the exact solution as a function of\na single scaling variable $x/\\sqrt{t}$ agrees with the mobile impurity results.\nThe full shape of the Green function in the thermodynamic limit is recovered\nwith arbitrary precision via a simple numerical integration of a nonlinear ODE.",
        "positive": "Higher-order local and non-local correlations for 1D strongly\n  interacting Bose gas: The correlation function is an important quantity in the physics of ultracold\nquantum gases because it provides information about the quantum many-body wave\nfunction beyond the simple density profile. In this paper we first study the\n$M$-body local correlation functions, $g_M$, of the one-dimensional (1D)\nstrongly repulsive Bose gas within the Lieb-Liniger model using the analytical\nmethod proposed by Gangardt and Shlyapnikov [1,2]. In the strong repulsion\nregime the 1D Bose gas at low temperatures is equivalent to a gas of ideal\nparticles obeying the non-mutual generalized exclusion statistics (GES) with a\nstatistical parameter $\\alpha =1-2/\\gamma$, i.e. the quasimomenta of $N$\nstrongly interacting bosons map to the momenta of $N$ free fermions via\n$k_i\\approx \\alpha k_i^F $ with $i=1,\\ldots, N$. Here $\\gamma$ is the\ndimensionless interaction strength within the Lieb-Liniger model. We rigorously\nprove that such a statistical parameter $\\alpha$ solely determines the\nsub-leading order contribution to the $M$-body local correlation function of\nthe gas at strong but finite interaction strengths. We explicitly calculate the\ncorrelation functions $g_M$ in terms of $\\gamma$ and $\\alpha$ at zero, low, and\nintermediate temperatures. For $M=2$ and $3$ our results reproduce the known\nexpressions for $g_{2}$ and $g_{3}$ with sub-leading terms (see for instance\n[3-5]). We also express the leading order of the short distance\n\\emph{non-local} correlation functions\n$\\langle\\Psi^\\dagger(x_1)\\cdots\\Psi^\\dagger(x_M)\\Psi(y_M)\\cdots\\Psi(y_1)\\rangle$\nof the strongly repulsive Bose gas in terms of the wave function of $M$ bosons\nat zero collision energy and zero total momentum. Here $\\Psi(x)$ is the boson\nannihilation operator. These general formulas of the higher-order local and\nnon-local correlation functions of the 1D Bose gas provide new insights into\nthe many-body physics."
    },
    {
        "anchor": "Condensation and superfluidity of dilute Bose gases with finite-range\n  interaction: We investigate an ultracold and dilute Bose gas by taking into account a\nfinite-range two-body interaction. The coupling constants of the resulting\nLagrangian density are related to measurable scattering parameters by following\nthe effective-field-theory approach. A perturbative scheme is then developed up\nto the Gaussian level, where both quantum and thermal fluctuations are\ncrucially affected by finite-range corrections. In particular, the relation\nbetween spontaneous symmetry breaking and the onset of superfluidity is\nemphasized by recovering the renowned Landau's equation for the superfluid\ndensity in terms of the condensate one.",
        "positive": "S-matrix approach to quantum gases in the unitary limit I: the\n  two-dimensional case: In three spatial dimensions, in the unitary limit of a non-relativistic\nquantum Bose or Fermi gas, the scattering length diverges. This occurs at a\nrenormalization group fixed point, thus these systems present interesting\nexamples of interacting scale-invariant models with dynamical exponent z=2. We\nstudy this problem in two and three spatial dimensions using the S-matrix based\napproach to the thermodynamics we recently developed. It is well suited to the\nunitary limit where the S-matrix equals -1, since it allows an expansion in the\ninverse coupling. We define a meaningful scale-invariant, unitary limit in two\nspatial dimensions, where again the scattering length diverges. In the\ntwo-dimensional case, the integral equation for the pseudo-energy becomes\ntranscendentally algebraic, and we can easily compute the various universal\nscaling functions as a function of \\mu/T, such as the energy per particle. The\nratio of the shear viscosity to the entropy density is above the conjectured\nlower bound of for all cases except attractive bosons. For attractive\n2-component fermions, the ratio is greater than 6.07 times the conjectured\nlower bound, whereas for attractive bosons it is greater than 0.4 times it."
    },
    {
        "anchor": "Observation of the Presuperfluid Regime in a Two-Dimensional Bose Gas: In complementary images of coordinate-space and momentum-space density in a\ntrapped 2D Bose gas, we observe the emergence of pre-superfluid behavior. As\nphase-space density $\\rho$ increases toward degenerate values, we observe a\ngradual divergence of the compressibility $\\kappa$ from the value predicted by\na bare-atom model, $\\kappa_{ba}$. $\\kappa/\\kappa_{ba}$ grows to 1.7 before\n$\\rho$ reaches the value for which we observe the sudden emergence of a spike\nat $p=0$ in momentum space. Momentum-space images are acquired by means of a 2D\nfocusing technique. Our data represent the first observation of non-meanfield\nphysics in the pre-superfluid but degenerate 2D Bose gas.",
        "positive": "Cluster dynamics in two-dimensional lattice gases with inter-site\n  interactions: Sufficiently strong inter-site interactions in extended-Hubbard and XXZ spin\nmodels result in dynamically-bound clusters at neighboring sites. We show that\nthe dynamics of these clusters in two-dimensional lattices is remarkably\ndifferent and richer than that of repulsively-bound on-site clusters in gases\nwithout inter-site interactions. Whereas on-site pairs move in the same lattice\nas individual particles, nearest-neighbor dimers perform an interacting quantum\nwalk in a different lattice geometry, leading to a peculiar dynamics\ncharacterized by more than one time scale. The latter is general for any\nlattice geometry, but it is especially relevant in triangular and diamond\nlattices, where dimers move resonantly in an effective kagome and Lieb lattice,\nrespectively. As a result, dimers experience partial quasi-localization due to\nan effective flat band, and may move slower than longer clusters. This\nsurprising link between anomalously slow quantum walk dynamics in these models\nand flat-band physics may be readily observed in experiments with lanthanide\natoms."
    },
    {
        "anchor": "Polarized Fermi gases in asymmetric optical lattices: The zero-temperature phase diagrams of imbalanced two-species Fermi gases are\ninvestigated in asymmetric optical lattices with arbitrary potential depths,\nbased on the exact spectrum instead of the Fermi-Hubbard model. We study the\neffect of lattice potentials and atomic densities to the fully paired\nBardeen-Cooper-Schrieffer (BCS) state and particularly the\nFulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. It is found that the increasing\nlattice potential favors BCS at low densities because of the enhanced effective\ncoupling; whereas FFLO is favored at intermediate densities when the system\nundergoes a dimensional crossover. Finally using local density approximation we\nstudy the evolution of phase profile in the presence of external harmonic traps\nby merely tuning the lattice potentials.",
        "positive": "Dynamical hadron formation in long-range interacting quantum spin chains: The study of confinement in quantum spin chains has seen a large surge of\ninterest in recent years. It is not only important for understanding a range of\neffective one-dimensional condensed matter realizations, but also shares some\nof the non-perturbative physics with quantum chromodynamics (QCD) which makes\nit a prime target for current quantum simulation efforts. In analogy with QCD,\nthe confinement-induced two-particle boundstates that appear in these models\nare dubbed mesons. Here, we study scattering events due to meson collisions in\na quantum spin chain with long-range interactions such that two mesons have an\nextended interaction. We show how novel hadronic boundstates, e.g. with four\nconstituent particles akin to tetraquarks, may form dynamically in fusion\nevents. In a natural collision their signal is weak as elastic meson scattering\ndominates. However, we propose two controllable protocols which allow for a\nclear observation of dynamical hadron formation. We discuss how this physics\ncan be simulated in trapped ion or Rydberg atom set-ups."
    },
    {
        "anchor": "Rydberg Electrons in a Bose-Einstein Condensate: We investigate a hybrid system composed of ultracold Rydberg atoms immersed\nin an atomic Bose-Einstein condensate (BEC). The coupling between the Rydberg\nelectrons and BEC atoms leads to the excitation of phonons, the exchange of\nwhich induces Yukawa interaction between Rydberg atoms. Due to the small\nelectron mass, the effective charge associated with this\nquasi-particle-mediated interaction can be large, while its range is equal to\nthe healing length of the BEC, which can be tuned by adjusting the scattering\nlength of the BEC atoms. We find that for small healing lengths, the distortion\nof the BEC can \"image\" the wave function density of the Rydberg electron, while\nlarge healing lengths induce an attractive Yukawa potential between the two\nRydberg atoms that can form a new type of ultra-long-range molecule. We discuss\nboth cases for a realistic system.",
        "positive": "Elliptic flow in a strongly-interacting normal Bose gas: We study the anisotropic, elliptic expansion of a thermal atomic Bose gas\nreleased from an anisotropic trapping potential, for a wide range of\ninteraction strengths across a Feshbach resonance. We show that in our system\nthis hydrodynamic phenomenon is for all interaction strengths fully described\nby a microscopic kinetic model with no free parameters. The success of this\ndescription crucially relies on taking into account the reduced thermalising\npower of elastic collisions in a strongly interacting gas, for which we derive\nan analytical theory. We also perform time-resolved measurements that directly\nreveal the dynamics of the energy transfer between the different expansion\naxes."
    },
    {
        "anchor": "Light-cone-like spreading of correlations in a quantum many-body system: How fast can correlations spread in a quantum many-body system? Based on the\nseminal work by Lieb and Robinson, it has recently been shown that several\ninteracting many-body systems exhibit an effective light cone that bounds the\npropagation speed of correlations. The existence of such a \"speed of light\" has\nprofound implications for condensed matter physics and quantum information, but\nhas never been observed experimentally. Here we report on the time-resolved\ndetection of propagating correlations in an interacting quantum many-body\nsystem. By quenching a one-dimensional quantum gas in an optical lattice, we\nreveal how quasiparticle pairs transport correlations with a finite velocity\nacross the system, resulting in an effective light cone for the quantum\ndynamics. Our results open important perspectives for understanding relaxation\nof closed quantum systems far from equilibrium as well as for engineering\nefficient quantum channels necessary for fast quantum computations.",
        "positive": "Majorana edge modes protected by emergent symmetry in a one dimensional\n  fermi gas: We show that a one dimensional ultra-cold Fermi gas with Rashba-like spin\norbit coupling, a Zeeman field and intrinsic attractive interactions exhibits a\nnovel topological superfluid state, which forms in spite of total number\nconservation and the absence of a single particle gap. Majorana zero modes are\nlocalized to the interface between a topological region in the middle of the\ntrap and trivial regions at its wings. Unlike the realization of a topological\nsuperconductor in proximity coupled nano-wires, the Majorana modes do not carry\na quantum number associated with the total fermion parity. Instead, the\ntopological degeneracy is protected by an emergent $Z_2$ symmetry present only\nat low energies. We discuss the experimental implications of the novel zero\nmodes, as manifest for example in the response to modulation of a local\npotential near the position of the Majorana bound states. For the range of\ninteraction strength corresponding to Luttinger parameter $1<K<2$ the zero\nmodes are unseperable from the gapless phonon continuum and therefore show up\nas an algebraic zero bias resonance in the response. For $K>2$, on the other\nhand the zero-mode can be detected as a sharp low frequency response at an\nenergy which generically scales with system size as $1/L^{K/2}$ and is\ntherefore parametrically separated from the phonons."
    },
    {
        "anchor": "Finite size effect on the specific heat of a Bose gas in multifilament\n  cables: The specific heat for an ideal Bose gas confined in semi-infinite\nmultifilament cables is analyzed. We start with a Bose gas inside a\nsemi-infinite tube of impenetrable walls and finite rectangular cross section.\nThe internal filament structure is created by applying to the gas two, mutually\nperpendicular, Kronig-Penney delta-potentials along the tube cross section,\nwhile particles are free to move perpendicular to the cross section. The energy\nspectrum accessible to the particles is obtained and introduced into the grand\npotential to calculate the specific heat of the system as a function of\ntemperature for different values of the periodic structure parameters such as:\nthe cross section area, the wall impenetrability and the number of filaments.\nThe specific heat as a function of temperature shows at least two maxima and\none minimum. The main difference with respect to the infinite case is that the\npeak associated with the BE condensation becomes a smoothed maximum or in other\nwords, there is not a jump in the specific heat derivative, whose temperature\nno longer represents a critical point.",
        "positive": "Strongly interacting two-dimensional Fermi gases: We review the current understanding of the uniform two-dimensional (2D) Fermi\ngas with short-range interactions. We first outline the basics of two-body\nscattering in 2D, including a discussion of how such a 2D system may be\nrealized in practice using an anisotropic confining potential. We then discuss\nthe thermodynamic and dynamical properties of 2D Fermi gases, which cold-atom\nexperiments have only just begun to explore. Of particular interest are the\ndifferent pairing regimes as the interparticle attraction is varied; the\nsuperfluid transition and associated finite-temperature phenomenology; few-body\nproperties and their impact on the many-body system; the Fermi polaron problem;\nand the symmetries underlying the collective modes. Where possible, we include\nthe contributions from 2D experiment. An underlying theme throughout is the\neffect of the quasi-2D geometry, which we view as an added richness to the\nproblem rather than an unwanted complication."
    },
    {
        "anchor": "Lattice modulation spectroscopy of strongly interacting bosons in\n  disordered and quasi-periodic optical lattices: We compute the absorption spectrum of strongly repulsive one-dimensional\nbosons in a disordered or quasi-periodic optical lattice. At commensurate\nfilling, the particle-hole resonances of the Mott insulator are broadened as\nthe disorder strength is increased. In the non-commensurate case, mapping the\nproblem to the Anderson model allows us to study the Bose-glass phase.\nSurprisingly we find that a perturbative treatment in both cases, weak and\nstrong disorder, gives a good description at all frequencies. In particular we\nfind that the infrared absorption rate in the thermodynamic limit is quadratic\nin frequency. This result is unexpected, since for other quantities like the\nconductivity in one dimensional systems, perturbation theory is only applicable\nat high frequencies. We discuss applications to recent experiments on optical\nlattice systems, and in particular the effect of the harmonic trap.",
        "positive": "Mass-imbalanced Fermi mixtures with resonant interactions: In these notes I provide an overview of ongoing theoretical and experimental\nresearch on ultracold atomic mixtures composed by two different fermionic\nspecies. First, I describe a general and simple framework that should allow\nalso a non-expert reader to understand the rich few-body phenomena connected\nwith such systems, and their possible impact at the many-body level. I then\nmove to discuss the specific combination of fermionic lithium ($^6$Li) and\nchromium ($^{53}$Cr) atoms, currently investigated in our lab, highlighting its\npeculiar properties with respect to other Fermi mixtures nowadays available.\nFinally, I summarize recent experimental progress achieved in producing and\ncharacterizing this novel system, providing an outlook for future studies based\non ultracold $^6$Li-$^{53}$Cr Fermi mixtures."
    },
    {
        "anchor": "Phase fluctuations in anisotropic Bose condensates: from cigars to rings: We study the phase-fluctuating condensate regime of ultra-cold atoms trapped\nin a ring-shaped trap geometry, which has been realized in recent experiments.\nWe first consider a simplified box geometry, in which we identify the\nconditions to create a state that is dominated by thermal phase-fluctuations,\nand then explore the experimental ring geometry. In both cases we demonstrate\nthat the requirement for strong phase fluctuations can be expressed in terms of\nthe total number of atoms and the geometric length scales of the trap only. For\nthe ring-shaped trap we discuss the zero temperature limit in which a\ncondensate is realized where the phase is fluctuating due to interactions and\nquantum fluctuations. We also address possible ways of detecting the phase\nfluctuating regime in ring condensates.",
        "positive": "Exact exact solutions of the Gross-Pitaevskii equation for stable vortex\n  modes: We construct exact solutions of the Gross-Pitaevskii equation for solitary\nvortices, and approximate ones for fundamental solitons, in 2D models of\nBose-Einstein condensates with a spatially modulated nonlinearity of either\nsign and a harmonic trapping potential. The number of vortex-soliton (VS) modes\nis determined by the discrete energy spectrum of a related linear\nSchr\\\"{o}dinger equation. The VS families in the system with the attractive and\nrepulsive nonlinearity are mutually complementary. \\emph{% Stable} VSs with\nvorticity $S\\geq 2$ and those corresponding to higher-order radial states are\nreported for the first time, in the case of the attraction and repulsion,\nrespectively."
    },
    {
        "anchor": "Robust finite-temperature disordered Mott insulating phases in\n  inhomogeneous Fermi-Fermi mixtures with density and mass imbalance: Ultracold mixtures of different atomic species have great promise for\nrealizing novel many-body phenomena. In a binary mixture of femions with a\nlarge mass difference and repulsive interspecies interactions, a disordered\nMott insulator phase can occur. This phase displays an incompressible total\ndensity, although the relative density remain compressible. We use\nstrong-coupling and Monte Carlo calculations to show that this phase exists for\na broad parameter region for ultracold gases confined in a harmonic trap on a\nthree-dimensional optical lattice, for experimentally accessible values of the\ntrap parameters.",
        "positive": "Three-body correlation functions and recombination rates for bosons in\n  three and one dimensions: We investigate local three-body correlations for bosonic particles in three\nand one dimensions as a function of the interaction strength. The three-body\ncorrelation function g(3) is determined by measuring the three-body\nrecombination rate in an ultracold gas of Cs atoms. In three dimensions, we\nmeasure the dependence of g(3) on the gas parameter in a BEC, finding good\nagreement with the theoretical prediction accounting for beyond-mean-field\neffects. In one dimension, we observe a reduction of g(3) by several orders of\nmagnitude upon increasing interactions from the weakly interacting BEC to the\nstrongly interacting Tonks-Girardeau regime, in good agreement with predictions\nfrom the Lieb-Liniger model for all strengths of interaction."
    },
    {
        "anchor": "Quench Dynamics in a Trapped Bose-Einstein Condensate with Spin-Orbit\n  Coupling: We consider the phase transition dynamics of a trapped Bose-Einstein\ncondensate subject to Raman-type spin-orbit coupling (SOC). By tuning the\ncoupling strength the condensate is taken through a second order phase\ntransition into an immiscible phase. We observe the domain wall defects\nproduced by a finite speed quench is described by the Kibble-Zurek mechanism\n(KZM), and quantify a power law behavior for the scaling of domain number and\nformation time with the quench speed.",
        "positive": "Stable multi-ring and rotating solitons in two-dimensional spin-orbit\n  coupled Bose-Einstein condensates with a radially-periodic potential: We consider two-dimensional spin-orbit coupled atomic Bose-Einstein\ncondensate in a radially-periodic potential. The system supports different\ntypes of stable self-sustained states including radially-symmetric\nvorticity-carrying modes with different topological charges in two spinor\ncomponents that may have multiring profiles and at the same time remain\nremarkably stable for repulsive interactions. Solitons of the second type show\npersistent rotation with constant angular frequency. They can be stable for\nboth repulsive and attractive interatomic interactions. Due to inequivalence\nbetween clockwise and counterclockwise rotation directions introduced by\nspin-orbit coupling, the properties of such solitons strongly differ for\npositive and negative rotation frequencies. Collision of solitons located in\nthe same or different rings is accompanied by change of the rotation frequency\nthat depends on the phase difference between colliding solitons."
    },
    {
        "anchor": "Self-bound droplets of a dilute magnetic quantum liquid: Self-bound many-body systems are formed through a balance of attractive and\nrepulsive forces and occur in many physical scenarios. Liquid droplets are an\nexample of a self-bound system, formed by a balance of the mutual attractive\nand repulsive forces that derive from different components of the\ninter-particle potential. It has been suggested that self-bound ensembles of\nultracold atoms should exist for atom number densities that are 10^8 times\nlower than in a helium droplet, which is formed from a dense quantum liquid.\nHowever, such ensembles have been elusive up to now because they require forces\nother than the usual zero-range contact interaction, which is either attractive\nor repulsive but never both. On the basis of the recent finding that an\nunstable bosonic dipolar gas can be stabilized by a repulsive many-body term,\nit was predicted that three-dimensional self-bound quantum droplets of magnetic\natoms should exist. Here we report the observation of such droplets in a\ntrap-free levitation field. We find that this dilute magnetic quantum liquid\nrequires a minimum, critical number of atoms, below which the liquid evaporates\ninto an expanding gas as a result of the quantum pressure of the individual\nconstituents. Consequently, around this critical atom number we observe an\ninteraction-driven phase transition between a gas and a self-bound liquid in\nthe quantum degenerate regime with ultracold atoms. These droplets are the\ndilute counterpart of strongly correlated self-bound systems such as atomic\nnuclei and helium droplets.",
        "positive": "Two-body bound state of ultracold Fermi atoms with two-dimensional\n  spin-orbit coupling: In a recent experiment, a two-dimensional spin-orbit coupling (SOC) was\nrealized for fermions in the continuum [Nat. Phys. 12, 540 (2016)], which\nrepresents an important step forward in the study of synthetic gauge field\nusing cold atoms. In the experiment, it was shown that a Raman-induced\ntwo-dimensional SOC exists in the dressed-state basis close to a Dirac point of\nthe single-particle spectrum. By contrast, the short-range inter-atomic\ninteractions of the system are typically expressed in the hyperfine-spin basis.\nThe interplay between synthetic SOC and interactions can potentially lead to\ninteresting few- and many-body phenomena but has so far eluded theoretical\nattention. Here we study in detail properties of two-body bound states of such\na system. We find that, due to the competition between SOC and interaction, the\nstability region of the two-body bound state is in general reduced.\nParticularly, the threshold of the lowest two-body bound state is shifted to a\npositive, SOC-dependent scattering length. Furthermore, the center-of-mass\nmomentum of the lowest two-body bound state becomes nonzero, suggesting the\nemergence of Fulde-Ferrell pairing states in a many-body setting. Our results\nreveal the critical difference between the experimentally realized\ntwo-dimensional SOC and the more symmetric Rashba or Dresselhaus SOCs in an\ninteracting system, and paves the way for future characterizations of\ntopological superfluid states in the experimentally relevant systems."
    },
    {
        "anchor": "Nonequilibrium Landau-Zener Tunneling in Exciton-Polariton Condensates: For a coherent quantum mechanical two-level system driven with a linearly\ntime-dependent detuning, the Landau-Zener model has served over decades as a\ntextbook model of quantum dynamics. A particularly intriguing question is\nwhether that framework can be extended to capture an intrinsical nonequilibrium\nnature for a quantum system with coherent and dissipative dynamics occurring on\nan equal footing. In this work, we are motivated to investigate the\nLandau-Zenner problem of polariton condensates in a periodic potential under\nnonresonant pumping, considering driven-dissipative Gross-Pitaevskii equations\ncoupled to the rate equation of a reservoir. Using a two-mode approach, we find\nfluctuation of the reservoir can be considered as a constant and the relative\nphase plays a very important role. The evolution of the dissipative\nLandau-Zener model we obtain presents its adiabatic process very different from\nthe closed system because the fluctuation of the reservoir has a peak and leads\nto the damping of the condensates. We substitute the fluctuation of the\nreservoir to Hamiltonian and get an effective two-level model. The motion of\nHamiltonian in phase space is also discussed and is directly corresponding to\nthe pumping rate. The instability of the band structure can also be studied by\nthe curvatures in phase space and there may be two loops in the middle of the\nBrillouin zone when the pumping rate is far beyond the threshold.",
        "positive": "Close-coupled model of Feshbach resonances in ultracold $^3$He* and\n  $^4$He* atomic Collisions: Helium atoms in the metastable $2^3{S_{1}}$ state (He$^*$) have unique\nadvantages for ultracold atomic experiments. However, there is no known\naccessible Feshbach resonance in He$^*$, which could be used to manipulate the\nscattering length and hence unlock several new experimental possiblities.\nPrevious experimental and theoretical studies for He$^*$ have produced\ncontradictory results. We aimed to resolve this discrepancy with a theoretical\nsearch for Feshbach resonances, using a new close-coupled model of He$^*$\ncollisions in the presence of an external magnetic field. Several resonances\nwere detected and the existing literature discrepancy was resolved. Although\nnone of the resonances identified are readily experimentally useable, an\ninteresting non-Feshbach scattering length variation with magnetic field was\nobserved in heteronuclear collisions, at field strengths that are\nexperimentally accessible."
    },
    {
        "anchor": "Momentum-space Aharonov-Bohm interferometry in Rashba spin-orbit coupled\n  Bose-Einstein condensates: Since the recent experimental realization of synthetic Rashba spin-orbit\ncoupling paved a new avenue for exploring and engineering topological phases in\nultracold atoms, a precise, solid detection of Berry phase has been desired for\nunequivocal characterization of system topology. Here, we propose a scheme to\nconduct momentum-space Aharonov-Bohm interferometry in a Rashba spin-orbit\ncoupled Bose-Einstein condensate with a sudden change of in-plane Zeeman field,\ncapable of measuring the Berry phase of Rashba energy bands. We find that the\nBerry phase with the presence of a Dirac point is directly revealed by a robust\ndark interference fringe, and that as a function of external Zeeman field is\ncharacterized by the contrast of fringes. We also build a variational model\ndescribing the interference process with semiclassical equations of motion of\nessential dynamical quantities, which lead to agreeable trajectories and\ngeometric phases with the real-time simulation of Gross-Pitaevskii equation.\nOur study would provide timely guidance for the experimental detection of Berry\nphase in ultracold atomic systems and help further investigation on their\ninterference dynamics in momentum space.",
        "positive": "Tunable orbital susceptibility in $\u03b1$-${\\cal T}_3$ tight-binding\n  models: We study the importance of interband effects on the orbital susceptibility of\nthree bands $\\alpha$-${\\cal T}_3$ tight-binding models. The particularity of\nthese models is that the coupling between the three energy bands (which is\nencoded in the wavefunctions properties) can be tuned (by a parameter $\\alpha$)\nwithout any modification of the energy spectrum. Using the gauge-invariant\nperturbative formalism that we have recently developped, we obtain a generic\nformula of the orbital susceptibility of $\\alpha$-${\\cal T}_3$ tight-binding\nmodels. Considering then three characteristic examples that exhibit either\nDirac, semi-Dirac or quadratic band touching, we show that by varying the\nparameter $\\alpha$ and thus the wavefunctions interband couplings, it is\npossible to drive a transition from a diamagnetic to a paramagnetic peak of the\norbital susceptibility at the band touching. In the presence of a gap\nseparating the dispersive bands, we show that the susceptibility inside the gap\nexhibits a similar dia to paramagnetic transition."
    },
    {
        "anchor": "$s$-wave Contacts of Quantum Gases in Quasi-one and Quasi-two Dimensions: In quasi-one- or quasi-two-dimensional traps with strong transverse\nconfinements, quantum gases behave like strictly one- or two-dimensional\nsystems at large length scales. However, at short distance, the two-body\nscattering intrinsically has three-dimensional characteristics such that an\nexact description of any universal thermodynamic relation requires\nthree-dimensional contacts, no matter how strong the confinement is. A\nfundamental question arises as to whether one- or two-dimensional contacts,\nwhich were originally defined for strictly one or two dimensions, are capable\nof describing quantum gases in quasi-one- or quasi-two-dimensional traps. Here,\nwe point out an exact relation between the three- and low-dimensional contacts\nin these highly anisotropic traps. Such relation allows us to directly connect\nphysical quantities at different length scales, and to characterise the\nquasi-one- or quasi-two-dimensional traps using universal thermodynamic\nrelations that were derived for strict one or two dimensions.",
        "positive": "Creation of Quantum-Degenerate Gases of Ytterbium in a Compact\n  2D-/3D-MOT Setup: We report on the first experimental setup based on a 2D-/3D-MOT scheme to\ncreate both Bose-Einstein condensates and degenerate Fermi gases of several\nytterbium isotopes. Our setup does not require a Zeeman slower and offers the\nflexibility to simultaneously produce ultracold samples of other atomic\nspecies. Furthermore, the extraordinary optical access favors future\nexperiments in optical lattices. A 2D-MOT on the strong 1S0-1P1 transition\ncaptures ytterbium directly from a dispenser of atoms and loads a 3D-MOT on the\nnarrow 1S0-3P1 intercombination transition. Subsequently, atoms are transferred\nto a crossed optical dipole trap and cooled evaporatively to quantum\ndegeneracy."
    },
    {
        "anchor": "Squeezed and fragmented states of strongly interacting bosons in a\n  double well. Part II: Quantum Monte Carlo simulations: We present path integral ground state (PIGS) quantum Monte Carlo calculations\nfor the ground state ($T = 0$) properties of repulsively interacting bosons in\na three-dimensional external double well potential over a range of interaction\nstrengths and potential parameters. We focus our calculations on ground state\nnumber statistics and the one-body density matrix in order to understand the\nlevel of squeezing and fragmentation that the system exhibits as a function of\ninteraction strength. We compare our PIGS results to both a two-mode model and\na recently-proposed eight-mode model. For weak interactions, the various models\nagree with the numerically exact PIGS simulations. However, the models fail to\ncorrectly predict the amount of squeezing and fragmentation exhibited by the\nPIGS simulations for strong interactions. One novel and somewhat surprising\nresult from our simulations involves the relationship between squeezing and\ninteraction strength: rather than a monotonic relationship between these\nquantities, we find that for certain barrier heights the squeezing increases as\na function of interaction strength until it reaches a maximum, after which it\ndecreases again. We also see a similar relationship between fragmentation and\ninteraction strength. We discuss the physical mechanisms that account for this\nbehavior and the implications for the design of atom interferometers, which can\nuse squeezed states to reduce measurement uncertainty.",
        "positive": "Quantum quenches to the attractive one-dimensional Bose gas: exact\n  results: We study quantum quenches to the one-dimensional Bose gas with attractive\ninteractions in the case when the initial state is an ideal one-dimensional\nBose condensate. We focus on properties of the stationary state reached at late\ntimes after the quench. This displays a finite density of multi-particle bound\nstates, whose rapidity distribution is determined exactly by means of the\nquench action method. We discuss the relevance of the multi-particle bound\nstates for the physical properties of the system, computing in particular the\nstationary value of the local pair correlation function $g_2$."
    },
    {
        "anchor": "High-dimensional reinforcement learning for optimization and control of\n  ultracold quantum gases: Machine-learning techniques are emerging as a valuable tool in experimental\nphysics, and among them, reinforcement learning offers the potential to control\nhigh-dimensional, multistage processes in the presence of fluctuating\nenvironments. In this experimental work, we apply reinforcement learning to the\npreparation of an ultracold quantum gas to realize a consistent and large\nnumber of atoms at microkelvin temperatures. This reinforcement learning agent\ndetermines an optimal set of thirty control parameters in a dynamically\nchanging environment that is characterized by thirty sensed parameters. By\ncomparing this method to that of training supervised-learning regression\nmodels, as well as to human-driven control schemes, we find that both machine\nlearning approaches accurately predict the number of cooled atoms and both\nresult in occasional superhuman control schemes. However, only the\nreinforcement learning method achieves consistent outcomes, even in the\npresence of a dynamic environment.",
        "positive": "Dynamics of matter-wave solutions of Bose-Einstein condensates in a\n  homogeneous gravitational field: We find a matter-wave solution of Bose-Einstein condensates trapped in a\nharmonic-oscillator potential and subjected to a homogeneous gravitational\nfield, by means of the extended tanhfunction method. This solution has as\nspecial cases the bright and dark solitons. We investigate the dynamics and the\nkinematics of these solutions, and the role of gravity is sketched. It is shown\nthat these solutions can be generated and manipulated by controlling the s-wave\nscattering length, without changing the strengths of the magnetic and\ngravitational fields."
    },
    {
        "anchor": "Squeezing-induced Topological Gap Opening on Bosonic Bogoliubov\n  Excitations: We investigate the role of squeezing interaction in inducing topological\nBogoliubov excitations of a bosonic system. We introduce a squeezing\ntransformation which is capable of reducing the corresponding Bogoliubov-de\nGennes Hamiltonian to an effective non-interacting one with the spectra and\ntopology unchanged. In the weak interaction limit, we apply the perturbation\ntheory to investigate the squeezing-induced topological gap opening on bosonic\nBogoliubov excitations and find that the squeezing interaction plays an\nequivalent role as a spin-orbit or Zeeman-like coupling in the effective\nHamiltonian. We thus apply this formalism to two existed models for providing\ndeeper understandings of their topological structures. We also construct\nminimal models based on the elegant Clifford algebra for realizing bosonic\ntopological Bogoliubov excitations. Our construction is potentially applicable\nfor experiments in bosonic systems.",
        "positive": "Universal Short Range Correlations in Bosonic Helium Clusters: Short-range correlations in bosonic Helium clusters, composed of $^4$He\natoms, are studied utilizing the generalized contact formalism. The emergence\nof universal $n$-body short range correlations is formulated and demonstrated\nnumerically via Monte Carlo simulations. The values of the $n$-particle\ncontacts are evaluated for $n\\le5$. In the thermodynamic limit, the two-body\ncontact is extracted from available experimental measurements of the static\nstructure factor of liquid $^4$He at high momenta, and found in a good\nagreement with the value extracted from our calculations."
    },
    {
        "anchor": "An inequality for spinor Bose-Einstein condensates: An inequality for spin-$F$ Bose-Einstein condensates (BECs) $\nF^2(\\rho^2-|\\Theta|^2)-\\boldsymbol{M}^2\\ge0 $ is reported, where $\\rho$,\n$\\Theta$, and $\\boldsymbol{M}$ represent the density, singlet pair amplitude,\nand magnetization vector, respectively. The distribution of high-symmetry\nspinors in the allowed region by the inequality is elucidated with using the\nMajorana representation. The result is illustrated by the example of spin-2\nBECs.",
        "positive": "Creating topological interfaces and detecting chiral edge modes in a 2D\n  optical lattice: We propose and analyze a general scheme to create chiral topological edge\nmodes within the bulk of two-dimensional engineered quantum systems. Our method\nis based on the implementation of topological interfaces, designed within the\nbulk of the system, where topologically-protected edge modes localize and\nfreely propagate in a unidirectional manner. This scheme is illustrated through\nan optical-lattice realization of the Haldane model for cold atoms, where an\nadditional spatially-varying lattice potential induces distinct topological\nphases in separated regions of space. We present two realistic experimental\nconfigurations, which lead to linear and radial-symmetric topological\ninterfaces, which both allows one to significantly reduce the effects of\nexternal confinement on topological edge properties. Furthermore, the\nversatility of our method opens the possibility of tuning the position, the\nlocalization length and the chirality of the edge modes, through simple\nadjustments of the lattice potentials. In order to demonstrate the unique\ndetectability offered by engineered interfaces, we numerically investigate the\ntime-evolution of wave packets, indicating how topological transport\nunambiguously manifests itself within the lattice. Finally, we analyze the\neffects of disorder on the dynamics of chiral and non-chiral states present in\nthe system. Interestingly, engineered disorder is shown to provide a powerful\ntool for the detection of topological edge modes in cold-atom setups."
    },
    {
        "anchor": "Observation of topological Bloch-state defects and their merging\n  transition: Topological defects in Bloch bands, such as Dirac points in graphene, and\ntheir resulting Berry phases play an important role for the electronic dynamics\nin solid state crystals. Such defects can arise in systems with a two-atomic\nbasis due to the momentum-dependent coupling of the two sublattice states,\nwhich gives rise to a pseudo-spin texture. The topological defects appear as\nvortices in the azimuthal phase of this pseudo-spin texture. Here, we\ndemonstrate a complete measurement of the azimuthal phase in a hexagonal\noptical lattice employing a versatile method based on time-of-flight imaging\nafter off-resonant lattice modulation. Furthermore we map out the merging\ntransition of the two Dirac points induced by beam imbalance. Our work paves\nthe way to accessing geometric properties in optical lattices also with\nspin-orbit coupling and interactions.",
        "positive": "Edge exponent in the dynamic spin structure factor of the Yang-Gaudin\n  model: The dynamic spin structure factor $\\mathcal{S}(k,\\omega)$ of a system of\nspin-1/2 bosons is investigated at arbitrary strength of interparticle\nrepulsion. As a function of $\\omega$ it is shown to exhibit a power-law\nsingularity at the threshold frequency defined by the energy of a magnon at\ngiven $k.$ The power-law exponent is found exactly using a combination of the\nBethe Ansatz solution and an effective field theory approach."
    },
    {
        "anchor": "Pair condensation of polarized fermions in the BCS-BEC crossover: We investigate a two-component Fermi gas with unequal spin populations along\nthe BCS-BEC crossover. By using the extended BCS equations and the concept of\noff-diagonal-long-range-order we derive a formula for the condensate number of\nCooper pairs as a function of energy gap, average chemical potential, imbalance\nchemical potential and temperature. Then we study the zero-temperature\ncondensate fraction of Cooper pairs by varying interaction strength and\npolarization, finding a depletion of the condensate fraction by increasing the\npopulation imbalance. We also consider explicitly the presence of an external\nharmonic confinement and we study, within the local-density approximation, the\nphase separation between superfluid and normal phase regions of the polarized\nfermionic cloud. In particular, we calculate both condensate density profiles\nand total density profiles from the inner superfluid core to the normal region\npassing for the interface, where a finite jump in the density is a clear\nmanifestation of this phase-separated regime. Finally, we compare our\ntheoretical results with the available experimental data on the condensate\nfraction of polarized 6Li atoms [Science 311, 492 (2006)]. These experimental\ndata are in reasonable agreement with our predictions in a suitable range of\npolarizations, but only in the BCS side of the crossover up to unitarity.",
        "positive": "Axis-symmetric Onsager Clustered States of Point Vortices in a Bounded\n  Domain: We study axis-symmetric Onsager clustered states of a neutral point vortex\nsystem confined to a two-dimensional disc. Our analysis is based on the mean\nfield of bounded point vortices in the microcanonical ensemble. The clustered\nvortex states are specified by the inverse temperature $\\beta$ and the rotation\nfrequency $\\omega$, which are the conjugate variables of energy $E$ and angular\nmomentum $L$, respectively. The formation of the axis-symmetric clustered\nvortex states (azimuthal angle independent) involves the separating of vortices\nwith opposite circulation and the clustering of vortices with same circulation\naround origin and edge. The state preserves $\\rm SO(2)$ symmetry while breaks\n$\\mathbb Z_2$ symmetry. We find that, near the uniform state ($E=0$), the\nrotation free state ($\\omega=0$) emerges at particular values of $L^2/E$ and\n$\\beta$. At large energies, we obtain asymptotically exact vortex density\ndistributions, whose validity condition gives rise the lower bound of $\\beta$\nfor the rotation free states. Noticeably, the obtained vortex density\ndistribution near the edge at large energies provides a novel exact vortex\ndensity distribution for the corresponding chiral vortex system."
    },
    {
        "anchor": "Thermodynamics of balanced and slightly spin-imbalanced Fermi gases at\n  unitarity: In this paper we present a Monte Carlo calculation of the critical\ntemperature and other thermodynamic quantities for the unitary Fermi gas with a\npopulation imbalance (unequal number of fermions in the two spin components).\nWe describe an improved worm type algorithm that is less prone to\nautocorrelations than the previously available methods and show how this\nalgorithm can be applied to simulate the unitary Fermi gas in presence of a\nsmall imbalance. Our data indicates that the critical temperature remains\nalmost constant for small imbalances $h=\\Delta\\mu/\\epsilon_F\\lessapprox0.2$. We\nobtain the continuum result $T_c=0.171(5)\\epsilon_F$ in units of Fermi energy\nand derive a lower bound on the deviation of the critical temperature from the\nbalanced limit, $T_c(h)-T_c(0)>-0.5\\epsilon_Fh^2$. Using an additional\nassumption a tighter lower bound can be obtained. We also calculate the energy\nper particle and the chemical potential in the balanced and imbalanced cases.",
        "positive": "Huge quantum particle number fluctuations in a two-component Bose gas in\n  a double-well potential: Two component Bose gas in a double well potential with repulsive interactions\nmay undergo a phase separation transition if the inter-species interactions\noutweigh the intra-species ones. We analyze the transition in the strong\ninteraction limit within the two-mode approximation. Numbers of particles in\neach potential well are equal and constant. However, at the transition point,\nthe ground state of the system reveals huge fluctuations of numbers of\nparticles belonging to the different gas components. That is, probability for\nobservation of any mixture of particles in each potential well becomes uniform."
    },
    {
        "anchor": "Motion of vortices in inhomogeneous Bose-Einstein condensates: We derive a general and exact equation of motion for a quantised vortex in an\ninhomogeneous two-dimensional Bose-Einstein condensate. This equation expresses\nthe velocity of a vortex as a sum of local ambient density and phase gradients\nin the vicinity of the vortex. We perform Gross-Pitaevskii simulations of\nsingle vortex dynamics in both harmonic and hard-walled disk-shaped traps, and\nfind excellent agreement in both cases with our analytical prediction. The\nsimulations reveal that, in a harmonic trap, the main contribution to the\nvortex velocity is an induced ambient phase gradient, a finding that\ncontradicts the commonly quoted result that the local density gradient is the\nonly relevant effect in this scenario. We use our analytical vortex velocity\nformula to derive a point-vortex model that accounts for both density and phase\ncontributions to the vortex velocity, suitable for use in inhomogeneous\ncondensates. Although good agreement is obtained between Gross-Pitaevskii and\npoint-vortex simulations for specific few-vortex configurations, the effects of\nnonuniform condensate density are in general highly nontrivial, and are thus\ndifficult to efficiently and accurately model using a simplified point-vortex\ndescription.",
        "positive": "Linear mapping between magnetic susceptibility and entanglement in\n  conventional and exotic one-dimensional superfluids: We investigate the mapping between magnetic susceptibility and entanglement\nin the metallic, insulating, conventional and exotic polarized superfluid\nphases of one-dimensional fermionic lattice systems as described by the Hubbard\nmodel. Motivated by recent proposals for determining and quantifying\nentanglement via magnetic susceptibility measurements, we numerically study the\nintrinsic relationship between the two quantities at zero temperature. We find\nsignatures of the metal-insulator transition and of the BCS-BEC crossover, but\nthe most relevant result is that for conventional and exotic superfluids the\nmapping between magnetic susceptibility and entanglement is surprisingly\nsimple: inversely proportional. This linear behavior could be exploited to\nquantify entanglement in current cold-atoms and condensed-matter experiments."
    },
    {
        "anchor": "Long distance optical conveyor-belt transport of ultracold $^{133}$Cs\n  and $^{87}$Rb atoms: We report on the transport of ultracold cesium and rubidium atoms over\n$37.2\\,$cm in under $25\\,$ms using an optical conveyor belt formed by two\ncounter-propagating beams with a controllable frequency difference that\ngenerate a movable optical lattice. By carefully selecting the waists and focus\npositions, we are able to use two static Gaussian beams for the transport,\navoiding the need for a Bessel beam or vari-focus lenses. We characterize the\ntransport efficiency for both species, including a comparison of different\ntransport trajectories, gaining insight into the loss mechanisms and finding\nthe minimum jerk trajectory to be optimum. Using the optimized parameters, we\nare able to transport up to $7 \\times 10^6$ cesium or rubidium atoms with an\nefficiency up to $75\\,$%. To demonstrate the viability of our transport scheme\nfor experiments employing quantum gas microscopy, we produce Bose-Einstein\ncondensates of either species after transport and present measurements of the\nsimultaneous transport of both species.",
        "positive": "Ferromagnetic spin correlations in a few-fermion system: We study the spin correlations of a few fermions in a quasi one-dimensional\ntrap. Exact diagonalization calculations demonstrate that repulsive\ninteractions between the two species drives ferromagnetic correlations. The\nejection probability of an atom provides an experimental probe of the spin\ncorrelations. With more than five atoms trapped, the system approaches the\nitinerant Stoner limit. Losses to Feshbach molecules are suppressed by the\ndiscretization of energy levels when fewer than seven atoms are trapped."
    },
    {
        "anchor": "Non-Markovian Dynamics of Open Quantum Systems via Auxiliary Particles\n  with Exact Operator Constraint: We introduce an auxiliary-particle field theory to treat the non-Markovian\ndynamics of driven-dissipative quantum systems of the Jaynes-Cummings type. It\nassigns an individual quantum field to each reservoir state and provides an\nanalytic, faithful representation of the coupled system-bath dynamics. We apply\nthe method to a driven-dissipative photon Bose-Einstein condensate (BEC)\ncoupled to a reservoir of dye molecules with electronic and vibronic\nexcitations. The complete phase diagram of this system exhibits a hidden,\nnon-Hermitian phase transition separating temporally oscillating from\nbiexponentially decaying photon density correlations within the BEC. On one\nhand, this provides a qualitative distinction of the thermal photon BEC from a\nlaser. On the other hand, it shows that one may continuously tune from the BEC\nto the lasing phase by circumventing a critical point. This auxiliary-particle\nmethod is generally applicable to the dynamics of open, non-Markovian quantum\nsystems.",
        "positive": "Quantum Critical Behavior of One-Dimensional Soft Bosons in the\n  Continuum: We consider a zero-temperature one-dimensional system of bosons interacting\nvia the soft-shoulder potential in the continuum, typical of dressed Rydberg\ngases. We employ quantum Monte Carlo simulations, which allow for the exact\ncalculation of imaginary-time correlations, and a stochastic analytic\ncontinuation method, to extract the dynamical structure factor. At finite\ndensities, in the weakly-interacting homogeneous regime, a rotonic spectrum\nmarks the tendency to clustering. With strong interactions, we indeed observe\ncluster liquid phases emerging, characterized by the spectrum of a composite\nharmonic chain. Luttinger theory has to be adapted by changing the reference\nlattice density field. In both the liquid and cluster liquid phases, we find\nconvincing evidence of a secondary mode, which becomes gapless only at the\ntransition. In that region, we also measure the central charge and observe its\nincrease towards c = 3/2, as recently evaluated in a related extended\nBose-Hubbard model, and we note a fast reduction of the Luttinger parameter.\nFor 2-particle clusters, we then interpret such observations in terms of the\ncompresence of a Luttinger liquid and a critical transverse Ising model,\nrelated to the instability of the reference lattice density field towards\ncoalescence of sites, typical of potentials which are flat at short distances.\nEven in the absence of a true lattice, we are able to evaluate the spatial\ncorrelation function of a suitable pseudo-spin operator, which manifests\nferromagnetic order in the cluster liquid phase, exponential decay in the\nliquid phase, and algebraic order at criticality."
    },
    {
        "anchor": "Solitons and solitary vortices in \"pancake\"-shaped Bose-Einstein\n  condensates: We study fundamental and vortical solitons in disk-morphed Bose-Einstein\ncondensates (BECs) subject to strong confinement along the axial direction.\nStarting from the three-dimensional (3D) Gross-Pitaevskii equation (GPE), we\nproceed to an effective 2D nonpolynomial Schroeodinger equation (NPSE) derived\nby means of the integration over the axial coordinate. Results produced by the\nlatter equation are in very good agreement with those obtained from the full 3D\nGPE, including cases when the formal 2D equation with the cubic nonlinearity is\nunreliable. The 2D NPSE is used to predict density profiles and dynamical\nstability of repulsive and attractive BECs with zero and finite topological\ncharge in various planar trapping configurations, including the axisymmetric\nharmonic confinement and 1D periodic potential. In particular, we find a stable\ndynamical regime that was not reported before, viz., periodic splitting and\nrecombination of trapped vortices with topological charge 2 or 3 in the\nself-attractive BEC.",
        "positive": "Spin-orbit-coupling-induced magnetic heterostructure in the bilayer\n  Bose-Hubbard system: We investigate magnetic phase in the bilayer system of ultra-cold bosons in\nan optical lattice, which is involved with Raman-induced spin-orbit (SO)\ncoupling and laser-assisted interlayer tunneling. It is shown that there exit a\nrich of spin textures such as hetero ferromagnet, heterochiral magnet, chiral\nmagnet with interlayer antiferromagnet. In particular, heterochiral magnet\ninduced by SO coupling occurs extremely rarely in real solid-state materials.\nWe present detailed experimental setup of realizing such a model in cold atom\nsystem."
    },
    {
        "anchor": "Dynamic response of spin-2 bosons in one-dimensional optical lattices: We investigate the spin-2 chain model corresponding to the small hopping\nlimit of the spin-2 Bose-Hubbard model using density-matrix\nrenormalization-group and time-evolution techniques. We calculate both static\ncorrelation functions and the dynamic structure factor. The dynamic structure\nfactor in the dimerized phase differs significantly between parameters near the\nSU(5)-symmetric point and those deeper in the phase where the dimerization is\nstrong. In the former case, most of the spectral weight is concentrated in a\nsingle excitation line, while in the latter case, a broad excitation continuum\nshows up. For the trimerized phase, we find gapless excitations at momenta\n$k=\\pm2\\pi/3$ in agreement with previous results, although the visibility of\nthese excitations in the dynamic spin response depends strongly on the specific\nparameters. We also consider parameters for specific atoms which may be\nrelevant for future optical-lattice experiments.",
        "positive": "Probing an Ultracold-Atom Crystal with Matter Waves: Atomic quantum gases in optical lattices serve as a versatile testbed for\nimportant concepts of modern condensed-matter physics. The availability of\nmethods to characterize strongly correlated phases is crucial for the study of\nthese systems. Diffraction techniques to reveal long-range spatial structure,\nwhich may complement \\emph{in situ} detection methods, have been largely\nunexplored. Here we experimentally demonstrate that Bragg diffraction of\nneutral atoms can be used for this purpose. Using a one-dimensional Bose gas as\na source of matter waves, we are able to infer the spatial ordering and on-site\nlocalization of atoms confined to an optical lattice. We also study the\nsuppression of inelastic scattering between incident matter waves and the\nlattice-trapped atoms, occurring for increased lattice depth. Furthermore, we\nuse atomic de Broglie waves to detect forced antiferromagnetic ordering in an\natomic spin mixture, demonstrating the suitability of our method for the\nnon-destructive detection of spin-ordered phases in strongly correlated atomic\ngases."
    },
    {
        "anchor": "SU(3) orbital Kondo effect with ultracold atoms: We propose a simple but novel scheme to realize the Kondo effect with\nultracold atoms. Our system consists of a Fermi sea of spinless fermions\ninteracting with an impurity atom of different species which is confined by an\nisotropic potential. The interspecies attraction can be tuned with an $s$-wave\nFeshbach resonance so that the impurity atom and a spinless fermion form a\nbound dimer that occupies a threefold-degenerate $p$ orbital of the confinement\npotential. Many-body scatterings of this dimer and surrounding spinless\nfermions occur with exchanging their angular momenta and thus exhibit the SU(3)\norbital Kondo effect. The associated Kondo temperature has a universal leading\nexponent given by $T_K\\propto\\exp[-\\pi/(3a_p k_F^3)]$ that depends only on an\neffective $p$-wave scattering volume $a_p$ and a Fermi wave vector $k_F$. We\nalso elucidate a Kondo singlet formation at zero temperature and an anisotropic\ninterdimer interaction mediated by surrounding spinless fermions. The Kondo\neffect thus realized in ultracold atom experiments may be observed as an\nincreasing atom loss by lowering the temperature or with radio-frequency\nspectroscopy. Our scheme and its extension to a dense Kondo lattice will be\nuseful to develop new insights into yet unresolved aspects of Kondo physics.",
        "positive": "Wave packet dynamics and edge transport in anomalous Floquet topological\n  phases: The possibility of attaining chiral edge modes under periodic driving has\nspurred tremendous attention, both theoretically and experimentally, especially\nin light of anomalous Floquet topological phases that feature vanishing Chern\nnumbers unlike any static counterpart. We here consider a periodically\nmodulated honeycomb lattice and experimentally relevant driving protocols,\nwhich allows us to obtain edge modes of various character in a simple model. We\ncalculate the phase diagram over a wide range of parameters and recover an\nanomalous topological phase with quasienergy gaps harbouring edge states with\nopposite chirality. Motivated by the advances in single-site control in optical\nlattices, we investigate wave packet dynamics localized at the edges in\ndistinct Floquet topological regimes that cannot be achieved in equilibrium. We\nanalyse transport properties in edge modes originating from the same bands, but\nwith support at different quasienergies and sublattices as well as possessing\ndifferent chiralities. We find that an anomalous Floquet topological phase can\nin general generate more robust chiral edge motion than a Haldane phase. Our\nresults demonstrate that the rich interplay of wave packet dynamics and\ntopological edge states can serve as a versatile tool in ultracold quantum\ngases in optical lattices."
    },
    {
        "anchor": "Tailoring flat bands and topological phases in a multi-strand Creutz\n  network: We prove that, a suitable correlation between the system parameters can\ntrigger topological phase transition and flat bands in a multi strand Creutz\nladder network, when a staggered second neighbor interaction is included along\nthe x axis. An appropriate change of basis maps such a finite N strand mesh\ninto N or N 1 decoupled Su Schrieffer Heeger chains, depending onNeven or odd.\nA simple intuitive method, using a real space decimation scheme turns out to be\nvery powerful in analytically extracting the flat bands, explaining their\ndegeneracy or a lifting of the same. Our results are analytically exact, and\nmay inspire experiments in photonics and ultracold atomic systems.",
        "positive": "Universal Dynamic Scaling and Contact Dynamics in Quenched Quantum Gases: Recently universal dynamic scaling is observed in several systems, which\nexhibit a spatiotemporal self-similar scaling behavior, analogous to the\nspatial scaling near phase transitions. The latter arises from the emergent\ncontinuous scaling symmetry due to the divergent correlation length. Motivated\nby this, we investigate the relation between the scaling dynamics and\ncontinuous scaling symmetry. We derive a theorem that the scaling invariance of\nthe quenched Hamiltonian and the initial density matrix can lead to the\nuniversal dynamic scaling in quench dynamics. It is demonstrated both in the\ntwo-body problem analytically and in the many-body problem numerically. For the\nlatter one, we calculate the dynamics of quantum gases quenched from\nnoninteracting to finite interaction in the framework of non-equilibrium\nhigh-temperature virial expansion. A dynamic scaling of the momentum\ndistribution appears in certain momentum-time windows at unitarity as well as\nin the weak interacting limit. Remarkably, this universal scaling dynamics\npersists approximately with smaller scaling exponents even if the scaling\nsymmetry is fairly broken. Our findings may offer a new perspective to\ninterpret the related experiments. We also calculate the Contact dynamics in\nthe BEC-BCS crossover. Surprisingly, the half-way time displays a maximum near\nunitarity while some damping oscillations occur on the BEC side due to the\ndimer state, which can be used to detect possible two-body bound states in\nexperiments."
    },
    {
        "anchor": "Nonequilibrium Damping of Collective Motion of Homogeneous Cold Fermi\n  Condensates with Feshbach Resonances: Collisionless damping of a condensate of cold Fermi atoms, whose scattering\nis controlled by a Feshbach resonance, is explored throughout the BCS and BEC\nregimes when small perturbations on its phase and amplitude modes are turned on\nto drive the system slightly out of equilibrium. Using a one-loop effective\naction, we first recreate the known result that for a broad resonance the\namplitude of the condensate decays as $t^{-1/2}$ at late times in the BCS\nregime whereas it decays as $t^{-3/2}$ in the BEC regime. We then examine the\ncase of an idealized narrow resonance, and find that this collective mode\ndecays as $t^{-3/2}$ throughout both the BCS and BEC regimes. Although this\nseems to contradict earlier results that damping is identical for both broad\nand narrow resonances, the breakdown of the narrow resonance limit restores\nthis universal behaviour. More measureably, the phase perturbation may give a\nshift on the saturated value to which the collective amplitude mode decays,\nwhich vanishes only in the deep BCS regime when the phase and amplitude modes\nare decoupled.",
        "positive": "Competing phases, phase separation and co-existence in the extended\n  one-dimensional bosonic Hubbard model: We study the phase diagram of the one-dimensional bosonic Hubbard model with\ncontact ($U$) and near neighbor ($V$) interactions focusing on the gapped\nHaldane insulating (HI) phase which is characterized by an exotic nonlocal\norder parameter. The parameter regime ($U$, $V$ and $\\mu$) where this phase\nexists and how it competes with other phases such as the supersolid (SS) phase,\nis incompletely understood. We use the Stochastic Green Function quantum Monte\nCarlo algorithm as well as the density matrix renormalization group to map out\nthe phase diagram. Our main conclusions are that the HI exists only at\n$\\rho=1$, the SS phase exists for a very wide range of parameters (including\ncommensurate fillings) and displays power law decay in the one body Green\nfunction. In addition, we show that at fixed integer density, the system\nexhibits phase separation in the $(U,V)$ plane."
    },
    {
        "anchor": "Topological Phases of Fermionic Ladders with Periodic Magnetic Fields: In recent experiments bosonic [Atala et al., Nat. Phys. 10, 588 (2014), B. K.\nStuhl et al., Science 349, 1514 (2015)] as well as fermionic ladders [M.\nMancini et al., Science 349, 1510 (2015)] with a uniform flux were studied and\ndifferent interesting many-body states were observed. Motivated by these\nexperiments, we extend the uniform synthetic magnetic field to a periodic case\nand show that a commensurate synthetic magnetic field offers an alternative\nscheme to realize topological phases in many-body systems of ultra-cold Fermi\ngases in ladder-like optical lattices. Using the exact diagonalization, we\nnumerically determine the topological band structure, edge states, non-zero\nChern numbers, Hofstadter-like-butterfly spectrum, and a complete phase diagram\nof non-interacting fermionic ladders.",
        "positive": "Quantum Monte Carlo calculation of the zero-temperature phase diagram of\n  the two-component fermionic hard-core gas in two dimensions: Motivated by potential realizations in cold-atom or cold-molecule systems, we\nhave performed quantum Monte Carlo simulations of two-component gases of\nfermions in two dimensions with hard-core interactions. We have determined the\ngross features of the zero-temperature phase diagram, by investigating the\nrelative stabilities of paramagnetic and ferromagnetic fluids and crystals. We\nhave also examined the effect of including a pairwise, long-range r^(-3)\npotential between the particles. Our most important conclusion is that there is\nno region of stability for a ferromagnetic fluid phase, even if the long-range\ninteraction is present. We also present results for the pair-correlation\nfunction, static structure factor, and momentum density of two-dimensional\nhard-core fluids."
    },
    {
        "anchor": "Polarons and bipolarons in a two-dimensional square lattice: Quasiparticles and their interactions are a key part of our understanding of\nquantum many-body systems. Quantum simulation experiments with cold atoms have\nin recent years advanced our understanding of isolated quasiparticles, but so\nfar they have provided limited information regarding their interactions and\npossible bound states. Here, we show how exploring mobile impurities immersed\nin a Bose-Einstein condensate (BEC) in a two-dimensional lattice can address\nthis problem. First, the spectral properties of individual impurities are\nexamined, and in addition to the attractive and repulsive polarons known from\ncontinuum gases, we identify a new kind of quasiparticle stable for repulsive\nboson-impurity interactions. The spatial properties of polarons are calculated\nshowing that there is an increased density of bosons at the site of the\nimpurity both for repulsive and attractive interactions. We then derive an\neffective Schr\\\"odinger equation describing two polarons interacting via the\nexchange of density oscillations in the BEC, which takes into account strong\nimpurity-boson two-body correlations. Using this, we show that the attractive\nnature of the effective interaction between two polarons combined with the\ntwo-dimensionality of the lattice leads to the formation of bound states --\ni.e. bipolarons. The wave functions of the bipolarons are examined showing that\nthe ground state is symmetric under particle exchange and therefore relevant\nfor bosonic impurities, whereas the first excited state is doubly degenerate\nand odd under particle exchange making it relevant for fermionic impurities.\nOur results show that quantum gas microscopy in optical lattices is a promising\nplatform to explore the spatial properties of polarons as well as to finally\nobserve the elusive bipolarons.",
        "positive": "Concomitant Modulated Superfluidity In Polarized Fermionic Gases: Recent groundbreaking experiments studying the effects of spin polarization\non pairing in unitary Fermi gases encountered mutual qualitative and\nquantitative discrepancies which seem to be a function of the confining\ngeometry. Using novel numerical algorithms we study the solution space for a\n3-dimensional fully self-consistent formulation of realistic systems with up to\n$10^{5}$ atoms. A study of the three types of solutions obtained demonstrates a\ntendency towards metastability as the confining geometry is elongated. One of\nthese solutions, which is consistent with Rice experiments at high trap aspect\nratio, supports a state strikingly similar to the long sought\nFulde-Ferrel-Larkin-Ovchinnikov state. Our study helps to resolve the\nlong-standing controversy concerning the discrepancies between the findings\nfrom two different experimental groups and highlights the versatility of\nactual-size numerical calculations for investigating inhomogeneous fermionic\nsuperfluids."
    },
    {
        "anchor": "Stationary states of Bose-Einstein condensed atoms rotating in an\n  asymmetric ring potential: We consider a Bose-Einstein condensate, which is confined in a very tight\ntoroidal/annular trap, in the presence of a potential, which breaks the axial\nsymmetry of the Hamiltonian. We investigate the stationary states of the\ncondensate, when its density distribution co-rotates with the symmetry-breaking\npotential. As the strength of the potential increases, we have a gradual\ntransition from vortex excitation to solid-body-like motion. Of particular\nimportance are states where the system is static and yet it has a nonzero\ncurrent/circulation, which is a realization of persistent\ncurrents/reflectionless potentials.",
        "positive": "Repulsive polarons in two-dimensional Fermi gases: We consider a single spin-down impurity atom interacting via an attractive,\nshort-range potential with a spin-up Fermi sea in two dimensions (2D).\nSimilarly to 3D, we show how the impurity can form a metastable state (the\n\"repulsive polaron\") with energy greater than that of the non-interacting\nimpurity. Moreover, we find that the repulsive polaron can acquire a finite\nmomentum for sufficiently weak attractive interactions. Even though the energy\nof the repulsive polaron can become sizeable, we argue that saturated\nferromagnetism is unfavorable in 2D because of the polaron's finite lifetime\nand small quasiparticle weight."
    },
    {
        "anchor": "Number-Conserving Approaches for Atomic Bose-Einstein Condensates: An\n  Overview: Assuming the existence of a Bose-Einstein condensate composed of the majority\nof a sample of ultracold, trapped atoms, perturbative treatments to incorporate\nthe non-condensate fraction are common. Here we describe how this may be\ncarried out in an explicitly number-conserving fashion, providing a common\nframework for the work of various authors; we also briefly consider issues of\nimplementation, validity and application of such methods.",
        "positive": "Reshaped Three-Body Interactions and the Observation of an Efimov State\n  in the Continuum: Efimov trimers are exotic three-body quantum states that emerge from the\ndifferent types of three-body continua in the vicinity of two-atom Feshbach\nresonances. In particular, as the strength of the interaction is decreased to a\ncritical point, an Efimov state merges into the atom-dimer threshold and\neventually dissociates into an unbound atom-dimer pair. Here we explore the\nEfimov state in the vicinity of this critical point using coherent few-body\nspectroscopy in $^7$Li atoms using a narrow two-body Feshbach resonance.\nContrary to the expectation, we find that the $^7$Li Efimov trimer does not\nimmediately dissociate when passing the threshold, and survives as a metastable\nstate embedded in the atom-dimer continuum. We identify this behavior with a\nuniversal phenomenon related to the emergence of a repulsive interaction in the\natom-dimer channel which reshapes the three-body interactions in any system\ncharacterized by a narrow Feshbach resonance. Specifically, our results shed\nlight on the nature of $^7$Li Efimov states and provide a path to understand\nvarious puzzling phenomena associated with them."
    },
    {
        "anchor": "Strong Fulde-Ferrell Larkin-Ovchinnikov pairing fluctuations in\n  polarized Fermi systems: We calculate the pair susceptibility of an attractive spin-polarized Fermi\ngas in the normal phase, as a function of the pair momentum. Close to\nunitarity, we find a strong enhancement of Fulde-Ferrell-Larkin-Ovchinnikov\n(FFLO) pairing fluctuations over an extended region of the\ntemperature-polarization phase diagram, which manifests itself as a pronounced\npeak in the pair-momentum distribution at a finite pair momentum. This peak\nshould be amenable to experimental observation at achievable temperatures in a\nbox-like trapping potential, as a fingerprint of FFLO pairing. Our calculations\nrest on a self-consistent t-matrix approach which, for the unitary balanced\nFermi gas, has been validated against experimental data for several\nthermodynamic quantities.",
        "positive": "Pulse propagation in interacting one dimensional Bose liquid: We study wave propagation in interacting Bose liquid, where the short range\npart of the interaction between atoms is of a hard core type, and its long\nrange part scales with a distance as a power law. The cases of Coulomb,\ndipole-dipole and Van der Waals interaction are considered. We employ a\nhydrodynamic approach, based on the exact solution of Lieb-Liniger model, and\nstudy the evolution of a density pulse instantly released from a potential\ntrap. We analyze semi-classical Euler and continuity equations and construct\nthe corresponding Riemann invariants. We supplement our analysis with numerical\ncalculations and discuss experimental applications for ultacold atom\nexperiments."
    },
    {
        "anchor": "Raman scattering of atoms from a quasi-condensate in a perturbative\n  regime: It is demonstrated that measurements of positions of atoms scattered from a\nquasi-condensate in a Raman process provide information on the temperature of\nthe parent cloud. In particular, the widths of the density and second order\ncorrelation functions are sensitive to the phase fluctuations induced by\nnon-zero temperature of the quasi-condensate. It is also shown how these widths\nevolve during expansion of the cloud of scattered atoms. These results are\nuseful for planning future Raman scattering experiments and indicate the degree\nof spatial resolution of atom-position measurements necessary to detect the\ntemperature dependence of the quasi-condensate.",
        "positive": "Quantum Dynamical Phase Transition in a Spin-Orbit Coupled Bose\n  Condensate: Spin-orbit coupled bosons can exhibit rich equilibrium phases at low\ntemperature and in the presence of particle-particle interactions. In the case\nwith a 1D synthetic spin-orbit interaction, it has been observed that the\nground state of a Bose gas can be a normal phase, stripe phase, or magnetized\nphase in different experimentally controllable parameter regimes. The\nmagnetized states are doubly degenerate and consist of a many-particle\ntwo-state system. In this work, we investigate the nonequilibrium quantum\ndynamics by switching on an external perturbation to induce resonant couplings\nbetween the magnetized phases, and predict the novel quantum spin dynamics\nwhich cannot be obtained in the single-particle systems. In particular, due to\nparticle-particle interactions, the transition of the Bose condensate from one\nmagnetized phase to the other is forbidden when the strength of external\nperturbation is less than a critical value, and a full transition can occur\nonly when the perturbation exceeds such critical strength. This phenomenon\nmanifests itself a quantum dynamical phase transition, with the critical point\nbehavior being exactly solvable. From the numerical simulations and exact\nanalytic studies we show that the predicted many-body effects can be well\nobserved with the current experiments."
    },
    {
        "anchor": "Dynamics of dissipative Bose-Einstein condensation: We resolve the real-time dynamics of a purely dissipative $s = 1/2$ quantum\nspin or, equivalently, hard-core boson model on a hypercubic $d$-dimensional\nlattice. The considered quantum dissipative process drives the system to a\ntotally symmetric macroscopic superposition in each of the $S^3$ sectors.\nDifferent characteristic time scales are identified for the dynamics and we\ndetermine their finite-size scaling. We introduce the concept of cumulative\nentanglement distribution to quantify multiparticle entanglement and show that\nthe considered protocol serves as an efficient method to prepare a\nmacroscopically entangled Bose-Einstein condensate.",
        "positive": "Supersolidity of a dipolar Fermi gas in a cubic optical lattice: We study the phase diagram of a dipolar fermi gas at half-filling in a cubic\noptical lattice with dipole moments aligned along the z-axis. The anisotropic\ndipole-dipole interaction leads to the competition between pz-wave superfluid\nand nematic charge-density-wave (CDW) orders at low temperatures. We find that\nthe superfluid phase survives with weak interactions and the CDW phase\ndominates with strong interactions. In between, the supersolid phase appears as\na balance between superfluid and CDW orders. The superfluid density is\nanisotropic in the supersolid and superfluid phases. In the CDW phase, there is\na semimetal to insulator transition with increase of the interaction strength.\nExperimental implications are discussed."
    },
    {
        "anchor": "Landau criterion in a Bose-Condensed Sodium Gas: In light of the experimental evidence for the existence of a superfluid\nregion in a Bose--Condensed Sodium gas a theoretical model is put forward. It\nwill be shown that the predictions of the present work do match with the extant\nexperimental readouts. As a by product we also calculate the speed of sound and\ncompare it against the current experimental results.",
        "positive": "Stability of a Fully Magnetized Ferromagnetic state in Repulsively\n  Interacting Ultracold Fermi Gases: We construct a variational wave function to study whether a fully polarized\nFermi sea is energetically stable against a single spin flip. Our variational\nwave function contains sufficient short-range correlation at least to the same\nlevel as Gutzwiller's projected wave function. For Hubbard lattice model and\ncontinuum model with pure repulsive interaction, we show a fully polarized\nFermi sea is generally unstable even when the repulsive strength becomes\ninfinite. While for a resonance model, ferromagnetic state is possible if the\ns-wave scattering length is positive and sufficiently large, and the system is\nprepared in scattering state orthogonal to molecular bound state. However, we\ncan not rule out the possibility that more exotic correlation can destabilize\nthe ferromagnetic state."
    },
    {
        "anchor": "Preparing Atomic Topological Quantum Matter by Adiabatic Nonunitary\n  Dynamics: Motivated by the outstanding challenge of realizing low-temperature states of\nquantum matter in synthetic materials, we propose and study an experimentally\nfeasible protocol for preparing topological states such as Chern insulators. By\ndefinition, such (non-symmetry protected) topological phases cannot be attained\nwithout going through a phase transition in a closed system, largely preventing\ntheir preparation in coherent dynamics. To overcome this fundamental caveat, we\npropose to couple the target system to a conjugate system, so as to prepare a\nsymmetry protected topological phase in an extended system by intermittently\nbreaking the protecting symmetry. Finally, the decoupled conjugate system is\ndiscarded, thus projecting onto the desired topological state in the target\nsystem. By construction, this protocol may be immediately generalized to the\nclass of invertible topological phases, characterized by the existence of an\ninverse topological order. We illustrate our findings with microscopic\nsimulations on an experimentally realistic Chern insulator model of ultracold\nfermionic atoms in a driven spin-dependent hexagonal optical lattice.",
        "positive": "Shaping topological properties of the band structures in a shaken\n  optical lattice: To realize band structures with non-trivial topological properties in an\noptical lattice is an exciting topic in current studies on ultra cold atoms.\nHere we point out that this lofty goal can be achieved by using a simple scheme\nof shaking an optical lattice, which is directly applicable in current\nexperiments. The photon-assistant band hybridization leads to the production of\nan effective spin-orbit coupling, in which the band index represents the\npseudospin. When this spin-orbit coupling has finite strengths along multiple\ndirections, non-trivial topological structures emerge in the Brillouin zone,\nsuch as topological defects with a winding number 1 or 2 in a shaken square\nlattice. The shaken lattice also allows one to study the transition between two\nband structures with distinct topological properties."
    },
    {
        "anchor": "Spin Mixing in Spinor Fermi Gases: We study a spinor fermionic system under the effect of spin-exchange\ninteraction. We focus on the interplay between the spin-exchange interaction\nand the effective quadratic Zeeman shift. We examine the static and the dynamic\nproperties of both two- and many-body system. We find that the spin-exchange\ninteraction induces coherent Rabi oscillation in the two-body system, but the\noscillation is quickly damped when the system is extended to the many-body\ncase.",
        "positive": "Extraction of the frequency moments of spectral densities from\n  imaginary-time correlation function data: We introduce an exact framework to compute the positive frequency moments\n$M^{(\\alpha)}(\\mathbf{q})=\\braket{\\omega^\\alpha}$ of different dynamic\nproperties from imaginary-time quantum Monte Carlo data. As a practical\nexample, we obtain the first five moments of the dynamic structure factor\n$S(\\mathbf{q},\\omega)$ of the uniform electron gas at the electronic Fermi\ntemperature based on \\emph{ab initio} path integral Monte Carlo simulations. We\nfind excellent agreement with known sum rules for $\\alpha=1,3$, and, to our\nknowledge, present the first results for $\\alpha=2,4,5$. Our idea can be\nstraightforwardly generalized to other dynamic properties such as the\nsingle-particle spectral function $A(\\mathbf{q},\\omega)$, and will be useful\nfor a number of applications, including the study of ultracold atoms, exotic\nwarm dense matter, and condensed matter systems."
    },
    {
        "anchor": "Phonon contribution to the shear viscosity of a superfluid Fermi gas in\n  the unitarity limit: We present a detailed analysis of the contribution of small-angle\nNambu-Goldstone boson (phonon) collisions to the shear viscosity, $\\eta$, in a\nsuperfluid atomic Fermi gas close to the unitarity limit. We show that the\nexperimental values of the shear viscosity coefficient to entropy ratio,\n$\\eta/s$, obtained at the lowest reached temperature can be reproduced assuming\nthat phonons give the leading contribution to $\\eta$. The phonon contribution\nis evaluated considering $1 \\leftrightarrow 2$ processes and taking into\naccount the finite size of the experimental system. In particular, for very low\ntemperatures, $T \\lesssim 0.1 T_F$, we find that phonons are ballistic and the\ncontribution of phonons to the shear viscosity is determined by the processes\nthat take place at the interface between the superfluid and the normal phase.\nThis result is independent of the detailed form of the phonon dispersion law\nand leads to two testable predictions: the shear viscosity should correlate\nwith the size of the optical trap and it should decrease with decreasing\ntemperature. For higher temperatures the detailed form of the phonon dispersion\nlaw becomes relevant and, within our model, we find that the experimental data\nfor $\\eta/s$ can be reproduced assuming that phonons have an anomalous\ndispersion law.",
        "positive": "Efficient two-mode interferometers with spinor Bose-Einstein condensates: We consider general three-mode interferometers using a spin-1 atomic\nBose-Einstein condensate with macroscopic magnetization. We show that these\ninterferometers, combined with the measurement of the number of particles in\neach output port, provide an ultra-high phase sensitivity. We construct\neffective two-mode interferometers which involve two Zeeman modes showing that\nthey also provide an ultra-high phase sensitivity but of a bit reduced factor\nin the corresponding Fisher information. A special case of zero magnetization\nis shown to persist the efficiency of the two-mode interferometry."
    },
    {
        "anchor": "Degenerate Rabi spectroscopy of the Floquet engineered optical lattice\n  clock: Simulating physics with large SU(N) symmetry is one of the unique advantages\nof Alkaline-earth atoms.Introducing periodical driving modes to the system may\nprovide more rich SU(N) physics that static one could not reach. However,\nwhether the driving modes will break the SU(N) symmetry is still lack of\ndiscussions. Here we experimentally study a Floquet engineered degenerate Sr-87\noptical lattice clock (OLC) by periodically shaking the lattice. With the help\nof Rabi spectroscopy, we find that the atoms at different Zeeman sublevels are\ntuned by the same driven function. Meanwhile, our experimental results suggest\nthat uniform distribution among the sublevels will not change despite the\ndriving. Our experimental demonstrations may pave the way to implementation of\nFE on tailoring the SU(N) physics in OLC system.",
        "positive": "Low temperature properties of the infinite-dimensional attractive\n  Hubbard model: We investigate the attractive Hubbard model in infinite spatial dimensions by\ncombining dynamical mean-field theory with a strong-coupling continuous-time\nquantum Monte Carlo method. By calculating the superfluid order parameter and\nthe density of states, we discuss the stability of the superfluid state. In the\nintermediate coupling region above the critical temperature, the density of\nstates exhibits a heavy fermion behavior with a quasi-particle peak in the\ndense system, while a dip structure appears in the dilute system. The formation\nof the superfluid gap is also addressed."
    },
    {
        "anchor": "The three-site Bose-Hubbard model subject to atom losses: the boson-pair\n  dissipation channel and failure of the mean-field approach: We employ the perturbation series expansion for derivation of the reduced\nmaster equations for the three-site Bose-Hubbard model subject to strong atom\nlosses from the central site. The model describes a condensate trapped in a\ntriple-well potential subject to externally controlled removal of atoms. We\nfind that the $\\pi$-phase state of the coherent superposition between the side\nwells decays via two dissipation channels, the single-boson channel (similar to\nthe externally applied dissipation) and the boson-pair channel. The quantum\nderivation is compared to the classical adiabatic elimination within the\nmean-field approximation. We find that the boson-pair dissipation channel is\nnot captured by the mean-field model, whereas the single-boson channel is\ndescribed by it. Moreover, there is a matching condition between the zero-point\nenergy bias of the side wells and the nonlinear interaction parameter which\nseparates the regions where either the single-boson or the boson-pair\ndissipation channel dominate. Our results indicate that the $M$-site\nBose-Hubbard models, for $M>2$, subject to atom losses may require an analysis\nwhich goes beyond the usual mean-field approximation for correct description of\ntheir dissipative features. This is an important result in view of the recent\nexperimental works on the single site addressability of condensates trapped in\noptical lattices.",
        "positive": "Stability and sensitivity of interacting fermionic superfluids to\n  quenched disorder: We probe the response of ultracold, interacting Fermi gases of Lithium (Li)\natoms in the BEC-BCS crossover to strong perturbations in space and time via\nrapidly switched optical disorder potentials with focus on the BEC side. We\nmeasure the time evolution of long-range phase coherence quantified via the\nability of the gas to expand hydrodynamically. While in the presence of static\ndisorder, the effects on a Bardeen-Cooper-Schrieffer (BCS) type superfluid are\npredicted to be much smaller compared to a molecular Bose-Einstein condensate\n(BEC), we find that the quantum properties of a resonantly interacting, unitary\nFermi gas are more strongly suppressed in the presence of quenched disorder\nthan in a molecular BEC. For quenches from a disordered potential, we find that\nthe unitary Fermi gas never recovers quantum hydrodynamics for all parameters\nstudied, while a molecular BEC always recovers quantum hydrodynamics, even when\nthe quench leads to strong particle losses of up to 70 %. Temperature\nmeasurements indicate an additional heating channel specific to gases close to\nresonant interactions, leading to strong local dephasing or pair breaking. Our\nwork illustrates the striking difference between the nonequilibrium phase\ndiagram of the time-dependent disordered BEC-BCS crossover compared to that of\nthe static-disorder case. Moreover, our results suggest an important role of\nlocal dephasing of fermionic pairs by time-dependent local perturbations, which\ncould be a key contribution to the destruction of macroscopic quantum\nproperties for time-dependent perturbations."
    },
    {
        "anchor": "Dark state optical lattice with sub-wavelength spatial structure: We report on the experimental realization of a conservative optical lattice\nfor cold atoms with sub-wavelength spatial structure. The potential is based on\nthe nonlinear optical response of three-level atoms in laser-dressed dark\nstates, which is not constrained by the diffraction limit of the light\ngenerating the potential. The lattice consists of a 1D array of ultra-narrow\nbarriers with widths less than 10~nm, well below the wavelength of the lattice\nlight, physically realizing a Kronig-Penney potential. We study the band\nstructure and dissipation of this lattice, and find good agreement with\ntheoretical predictions. The observed lifetimes of atoms trapped in the lattice\nare as long as 60 ms, nearly $10^5$ times the excited state lifetime, and could\nbe further improved with more laser intensity. The potential is readily\ngeneralizable to higher dimension and different geometries, allowing, for\nexample, nearly perfect box traps, narrow tunnel junctions for atomtronics\napplications, and dynamically generated lattices with sub-wavelength spacings.",
        "positive": "Few-body bound topological and flat-band states in a Creutz Ladder: We investigate the properties of few interacting bosons in a Creutz ladder,\nwhich has become a standard model for topological systems, and which can be\nrealised in experiments with cold atoms in optical lattices. At the\nsingle-particle level, this system may exhibit a completely flat energy\nlandscape with non-trivial topological properties. In this scenario, we\nidentify topological two-body edge states resulting from the bonding of\nsingle-particle edge and flat-band states. We also explore the formation of\ntwo- and three-body bound states in the strongly-interacting limit, and we show\nhow these quasi-particles can be engineered to replicate the flat-band and\ntopological features of the original single-particle model. Furthermore, we\nshow that in this geometry perfect Aharonov-Bohm caging of two-body bound\nstates may occur for arbitrary interaction strengths, and we provide numerical\nevidence that the main features of this effect are preserved in an interacting\nmany-body scenario resulting in many-body Aharonov-Bohm caging."
    },
    {
        "anchor": "Torquing the Condensate: Angular Momentum Transport in Bose-Einstein\n  Condensates by Solitonic \"Corkscrew\": When rotating classical fluid drops merge together, angular momentum can be\nadvected from one to another due to the viscous shear flow at the drop\ninterface. It remains elusive what the corresponding mechanism is in inviscid\nquantum fluids such as Bose-Einstein condensates (BECs). Here we report our\ntheoretical study of an initially static BEC merging with a rotating BEC in\nthree-dimensional space along the rotational axis. We show that a soliton sheet\nresembling a \"corkscrew\" spontaneously emerges at the interface. Rapid angular\nmomentum transfer at a constant rate universally proportional to the initial\nangular momentum density is observed. Strikingly, this transfer does not\nnecessarily involve fluid advection or drifting of the quantized vortices. We\nreveal that the solitonic corkscrew can exert a torque that directly creates\nangular momentum in the static BEC and annihilates angular momentum in the\nrotating BEC. Uncovering this intriguing angular momentum transport mechanism\nmay benefit our understanding of various coherent matter-wave systems, spanning\nfrom atomtronics on chips to dark matter BECs at cosmic scales.",
        "positive": "One-dimensional sawtooth and zigzag lattices for ultracold atoms: We describe tunable optical sawtooth and zigzag lattices for ultracold atoms.\nMaking use of the superlattice generated by commensurate wavelengths of light\nbeams, tunable geometries including zigzag and sawtooth configurations can be\nrealised. We provide an experimentally feasible method to fully control inter-\n($t$) and intra- ($t'$) unit-cell tunnelling in zigzag and sawtooth lattices.\nWe analyse the conversion of the lattice geometry from zigzag to sawtooth, and\nshow that a nearly flat band is attainable in the sawtooth configuration by\nmeans of tuning the lattice parameters. The bandwidth of the first excited band\ncan be reduced up to 2$\\%$ of the ground bandwidth for a wide range of lattice\nsetting. A nearly flat band available in a tunable sawtooth lattice would offer\na versatile platform for the study of interaction-driven quantum many-body\nstates with ultracold atoms."
    },
    {
        "anchor": "Heating rates for an atom in a far-detuned optical lattice: We calculate single atom heating rates in a far detuned optical lattice, in\nconnection with recent experiments. We first derive a master equation,\nincluding a realistic atomic internal structure and a quantum treatment of the\natomic motion in the lattice. The experimental feature that optical lattices\nare obtained by superimposing laser standing waves of different frequencies is\nalso included, which leads to a micromotional correction to the light shift\nthat we evaluate. We then calculate, and compare to experimental results, two\nheating rates, the \"total\" heating rate (corresponding to the increase of the\ntotal mechanical energy of the atom in the lattice), and the ground bande\nheating rate (corresponding to the increase of energy within the ground energy\nband of the lattice).",
        "positive": "Non-Hermitian dynamics and $\\mathcal{PT}$-symmetry breaking in\n  interacting mesoscopic Rydberg platforms: We simulate the dissipative dynamics of a mesoscopic system of long-range\ninteracting particles which can be mapped into non-Hermitian spin models with a\n$\\mathcal{PT}$ symmetry. We find rich $\\mathcal{PT}$-phase diagrams with\n$\\mathcal{PT}$-symmetric and $\\mathcal{PT}$-broken phases. The dynamical\nregimes can be further enriched by modulating tunable parameters of the system.\nWe outline how the $\\mathcal{PT}$ symmetries of such systems may be probed by\nstudying their dynamics. We note that systems of Rydberg atoms and systems of\nRydberg ions with strong dipolar interactions are particularly well suited for\nsuch studies. We show that for realistic parameters, long-range interactions\nallow the emergence of new $\\mathcal{PT}$-symmetric regions, generating new\n$\\mathcal{PT}$-phase transitions. In addition, such $\\mathcal{PT}$-symmetry\nphase transitions are found by changing the Rydberg atoms configurations. We\nmonitor the transitions by accessing the populations of the Rydberg states.\nTheir dynamics display oscillatory or exponential dependence in each phase."
    },
    {
        "anchor": "Density Oscillations Induced by Individual Ultracold Two-Body Collisions: Access to single-particle momenta provides new means of studying the dynamics\nof a few interacting particles. In a joint theoretical and experimental effort,\nwe observe and analyze the effects of a finite number of ultracold two-body\ncollisions on the relative and single-particle densities by quenching two\nultracold atoms with an initial narrow wave packet into a wide trap with an\ninverted aspect ratio. The experimentally observed spatial oscillations of the\nrelative density are reproduced by a parameter-free zero-range theory and\ninterpreted in terms of cross-dimensional flux. We theoretically study the\nlong-time dynamics and find that the system does not approach its thermodynamic\nlimit. The setup can be viewed as an advanced particle collider that allows one\nto watch the collision process itself.",
        "positive": "Self-evaporation dynamics of quantum droplets in a 41K-87Rb mixture: We theoretically investigate the self-evaporation dynamics of quantum\ndroplets in a 41K-87Rb mixture, in free-space. The dynamical formation of the\ndroplet and the effects related to the presence of three-body losses are\nanalyzed by means of numerical simulations. We identify a regime of parameters\nallowing for the observation of the droplet self-evaporation in a feasible\nexperimental setup."
    },
    {
        "anchor": "Realizing the Harper model with Ultracold Atoms in a Ring Lattice: We demonstrate that all of the salient features of the Harper-Hofstadter\nmodel can be implemented with ultracold atoms trapped in a bichromatic\nring-shaped lattice. Using realistic sinusoidal lattice potentials rather than\nassume the idealized tight-binding picture, we determine the optimal conditions\nnecessary to realize the critical point where the spectrum becomes fractal, and\nidentify the nature and cause of the departures from the discrete model\npredictions. We also show that even with a commensurate ring with a few lattice\nsites, the Aubry-Andr\\'e localization transition can be realized. Localized\nstates that behave like edge states with energies that reside in the band gaps\ncan be generated by introducing a surprisingly small local perturbation within\nthe ring. Spectrum oscillation arising from complex coupling can be implemented\nby uniform rotation of the ring, but with certain significant differences that\nare explained",
        "positive": "Observation of many-body long-range tunneling after a quantum quench: Quantum tunneling constitutes one of the most fundamental processes in\nnature. We observe resonantly-enhanced long-range quantum tunneling in\none-dimensional Mott-insulating Hubbard chains that are suddenly quenched into\na tilted configuration. Higher-order many-body tunneling processes occur over\nup to five lattice sites when the tilt per site is tuned to integer fractions\nof the Mott gap. Starting from a one-atom-per-site Mott state the response of\nthe many-body quantum system is observed as resonances in the number of doubly\noccupied sites and in the emerging coherence in momentum space. Second- and\nthird-order tunneling shows up in the transient response after the tilt, from\nwhich we extract the characteristic scaling in accordance with perturbation\ntheory and numerical simulations."
    },
    {
        "anchor": "Generalization of the Kutta-Joukowski theorem for the hydrodynamic\n  forces acting on a quantized vortex: The hydrodynamic forces acting on a quantized vortex in a superfluid have\nlong been a highly controversial issue. A new approach, originally developed in\nthe astrophysical context of compact stars, is presented to determine these\nforces by considering small perturbations of the asymptotically uniform flows\nin the region far from the vortex in the framework of Landau-Khalatnikov\ntwo-fluid model. Focusing on the irrotational part of the flows in the\nHelmholtz decomposition, the classical Kutta-Joukowski theorem from ordinary\nhydrodynamics is thus generalized to superfluid systems. The same method is\napplied to predict the hydrodynamic forces acting on vortices in cold atomic\ncondensates and superfluid mixtures.",
        "positive": "Parametrically driven-dissipative three-level Dicke model: We investigate the three-level Dicke model, which describes a fundamental\nclass of light-matter systems. We determine the phase diagram in the presence\nof dissipation, which we assume to derive from photon loss. Utilizing both\nanalytical and numerical methods we characterize the incommensurate time\ncrystalline, light-induced, and light-enhanced superradiant states in the phase\ndiagram for the parametrically driven system. As a primary application, we\ndemonstrate that a shaken atom-cavity system is naturally approximated via a\nparametrically driven-dissipative three-level Dicke model."
    },
    {
        "anchor": "Normal-Superfluid Phase Separation in Spin-Half Bosons at Finite\n  Temperature: For pseudospin-half bosons with inter-spin attraction and intra-spin\nrepulsion, normal phase and Bose condensed phase can coexist at finite\ntemperature. The homogeneous system is unstable against the spinodal\ndecomposition within a medium density interval, and consequently, a\nnormal-superfluid phase separation takes place. The isothermal\nequation-of-state shows a characteristic plateau in the P-V (pressure-volume)\ndiagram, which is reminiscent of a classical gas-liquid transition, although,\nunlike the latter, the coexistence lines never terminate at a critical point as\ntemperature increases. In a harmonic trap, the phase separation can be revealed\nby the density profile of the atomic cloud, which exhibits a sudden jump across\nthe phase boundary.",
        "positive": "Weak-Measurement-Induced Heating in Bose-Einstein Condensates: Ultracold atoms are an ideal platform for understanding system-reservoir\ndynamics of many-body systems. Here, we study quantum back-action in atomic\nBose-Einstein condensates, weakly interacting with a far-from resonant, i.e.,\ndispersively interacting, probe laser beam. The light scattered by the atoms\ncan be considered as a part of quantum measurement process whereby the change\nin the system state derives from measurement back-action. We experimentally\nquantify the resulting back-action in terms of the deposited energy. We model\nthe interaction of the system and environment with a generalized measurement\nprocess, leading to a Markovian reservoir. Further, we identify two systematic\nsources of heating and loss: a stray optical lattice and probe-induced light\nassisted collisions (an intrinsic atomic process). The observed heating and\nloss rates are larger for blue detuning than for red detuning, where they are\noscillatory functions of detuning with increased loss at molecular resonances\nand reduced loss between molecular resonances."
    },
    {
        "anchor": "Unconventional magnetism via optical pumping of interacting spin systems: We consider strongly interacting systems of effective spins, subject to\ndissipative spin-flip processes associated with optical pumping. We predict the\nexistence of novel magnetic phases in the steady-state of this system, which\nemerge due to the competition between coherent and dissipative processes.\nSpecifically, for strongly anisotropic spin-spin interactions, we find\nferromagnetic, antiferromagnetic, spin-density-wave, and staggered-XY steady\nstates, which are separated by nonequilibrium phase transitions meeting at a\nLifshitz point. These transitions are accompanied by quantum correlations,\nresulting in spin squeezing. Experimental implementations in ultracold atoms\nand trapped ions are discussed.",
        "positive": "Incorporating exact two-body propagators for zero-range interactions\n  into $N$-body Monte Carlo simulations: Ultracold atomic gases are, to a very good approximation, described by\npairwise zero-range interactions. This paper demonstrates that $N$-body systems\nwith two-body zero-range interactions can be treated reliably and efficiently\nby the finite temperature and ground state path integral Monte Carlo\napproaches, using the exact two-body propagator for zero-range interactions in\nthe pair product approximation. Harmonically trapped one- and three-dimensional\nsystems are considered. A new propagator for the harmonically trapped two-body\nsystem with infinitely strong zero-range interaction, which may also have\napplications in real time evolution schemes, is presented."
    },
    {
        "anchor": "Spectral function of Fermi polarons at finite temperature from a\n  self-consistent many-body $T$-matrix approach in real frequency: We theoretically examine the finite-temperature spectral function of Fermi\npolarons in three dimensions, by using a self-consistent many-body $T$-matrix\ntheory in real frequency. In comparison with the previous results from a\nnon-self-consistent many-body $T$-matrix approach, we show that the treatment\nof self-consistency in the impurity Green function leads to notable changes in\nalmost all the dynamical quantities, including the vertex function, impurity\nself-energy and spectral function. Eventually, it gives rise to quantitatively\ndifferent predictions for the measurable radio-frequency spectrum and Raman\nspectrum at finite temperature. Using the recent spectroscopic measurements as\na benchmark, we find that the self-consistent many-body $T$-matrix theory\nsomehow provides a better explanation for the experimental data. The notable\ndifference in the predictions from the non-self-consistent and self-consistent\ntheories suggests that more accurate theoretical descriptions are needed, in\norder to fully account for the current spectroscopic observations on Fermi\npolarons.",
        "positive": "Inhomogeneous Kibble-Zurek mechanism: vortex nucleation during\n  Bose-Einstein condensation: The Kibble-Zurek mechanism is applied to the spontaneous formation of\nvortices in a harmonically trapped thermal gas following a temperature quench\nthrough the critical value for Bose-Einstein condensation. While in the\nhomogeneous scenario vortex nucleation is always expected, we show that it can\nbe completely suppressed in the presence of the confinement potential, whenever\nthe speed of the spatial front undergoing condensation is lower than a\nthreshold velocity. Otherwise, the interplay between the geometry and causality\nleads to different scaling laws for the density of vortices as a function of\nthe quench rate, as we also illustrate for the case of a toroidal trapping\npotential."
    },
    {
        "anchor": "Two-dimensional Mixture of Dipolar Fermions: Equation of State and\n  Magnetic Phases: We study a two-component mixture of fermionic dipoles in two dimensions at\nzero temperature, interacting via a purely repulsive $1/r^3$ potential. This\nmodel can be realized with ultracold atoms or molecules, when their dipole\nmoments are aligned in the confinement direction orthogonal to the plane. We\ncharacterize the unpolarized mixture by means of the Diffusion Monte Carlo\ntechnique. Computing the equation of state, we identify the regime of validity\nfor a mean-field theory based on a low-density expansion and compare our\nresults with the hard-disk model of repulsive fermions. At high density, we\naddress the possibility of itinerant ferromagnetism, namely whether the ground\nstate can be fully polarized in the fluid phase. Within the fixed-node\napproximation, we show that the accuracy of Jastrow-Slater trial wave\nfunctions, even with the typical two-body backflow correction, is not\nsufficient to resolve the relevant energy differences. By making use of the\niterative-backflow improved trial wave functions, we observe no signature of a\nfully-polarized ground state up to the freezing density.",
        "positive": "Rotational states of an asymmetric vortex pair with mass imbalance in\n  binary condensates: We consider massive vortices in binary condensates, where the immiscibility\ncondition entails the trapping of the minority component in the vortex cores of\nthe majority component. We study such vortices by means of a 2D point-like\nmodel, and show how the relevant dynamical equations exhibit vortex-pair\nsolutions characterized by different vortex masses and circular orbits of\ndifferent radii $a$ and $b$. These solutions are validated by the simulations\nof the Gross-Pitaevskii equations for binary condensates. After examining the\nproperties of vortex-pair rotational frequency $\\Omega$ as a function of the\nvortex masses for a given pair geometry, we define the rotational-state diagram\n$\\cal D$, describing all the possible vortex-pair solutions in terms of the\norbit radii at given $\\Omega$. This includes solutions with equal-mass pairs\nbut $a \\ne b$ or with one of the two masses (or both) equal to zero. Also, we\nanalytically find the minimum value of $\\Omega$ for the existence of such\nsolutions, and obtain numerically the critical frequency $\\Omega_c$ below which\n$\\cal D$ changes its structure and the transition to an unstable vortex-pair\nregime takes place. Our work highlights an indirect measurement scheme to infer\nthe vortex masses from orbits radii $a$ and $b$, and a link between the vortex\nmasses and the vortex-pair small-oscillation properties."
    },
    {
        "anchor": "Critical velocity of a finite-temperature Bose gas: We use classical field simulations of the homogeneous Bose gas to study the\nbreakdown of superflow due to vortex nucleation past a cylindrical obstacle at\nfinite temperature. Thermal fluctuations modify the vortex nucleation from the\nobstacle, turning anti-parallel vortex lines (which would be nucleated at zero\ntemperature) into wiggly lines, vortex rings and even vortex tangles. We find\nthat the critical velocity for vortex nucleation decreases with increasing\ntemperature, and scales with the speed of sound of the condensate, becoming\nzero at the critical temperature for condensation.",
        "positive": "Critical Rotation of an Annular Superfluid Bose Gas: We analyze the excitation spectrum of a superfluid Bose-Einstein condensate\nrotating in a ring trap. We identify two important branches of the spectrum\nrelated to outer and inner edge surface modes that lead to the instability of\nthe superfluid. Depending on the initial circulation of the annular condensate,\neither the outer or the inner modes become first unstable. This instability is\ncrucially related to the superfluid nature of the rotating gas. In particular\nwe point out the existence of a maximal circulation above which the superflow\ndecays spontaneously, which cannot be explained by invoking the average speed\nof sound."
    },
    {
        "anchor": "Geometry-induced modification of fluctuation spectrum in\n  quasi-two-dimensional condensates: We report the structural transformation of the low-lying spectral modes,\nespecially the Kohn mode, from radial to circular topology as harmonic\nconfining potential is modified to a toroidal one, and this corresponds to a\ntransition from simply to multiply connected geometry. For this we employ the\nHartree-Fock-Bogoliubov theory to examine the evolution of low energy\nquasiparticles. We, then, use the Hartree-Fock-Bogoliubov theory with the Popov\napproximation to demonstrate the two striking features of quantum and thermal\nfluctuations. At $T=0$, the non-condensate density due to interaction induced\nquantum fluctuations increases with the transformation from pancake to toroidal\ngeometry. The other feature is, there is a marked change in the density profile\nof the non-condensate density at finite temperatures with the modification of\ntrapping potential. In particular, the condensate and non-condensate density\ndistributions have overlapping maxima in the toroidal condensate, which is in\nstark contrast to the case of pancake geometry. The genesis of this difference\nlies in the nature of the thermal fluctuations.",
        "positive": "Non-Markovian polaron dynamics in a trapped Bose-Einstein condensate: We study the dynamics of an impurity embedded in a trapped Bose-Einstein\ncondensate (Bose polaron), by recalling the quantum Brownian motion model. It\nis crucial that the model considers a parabolic trapping potential to resemble\nthe experimental conditions. Thus, we detail here how the formal derivation\nchanges due to the gas trap, in comparison to the homogeneous gas. We first\nfind that the presence of a gas trap leads to a new form of the bath-impurity\ncoupling constant and a larger degree in the super-ohmicity of the spectral\ndensity. This is manifested as a different dependence of the system dynamics on\nthe past history. To quantify this, we introduce several techniques to compare\nthe different amount of memory effects arising in the homogeneous and\ninhomogeneous gas. We find that it is higher in the second case. Moreover, we\ncalculate the position variance of the impurity, represenitng a measurable\nquantity. We show that the impurity experiences super-diffusion and genuine\nposition squeezing. Wdetail how both effects can be enhanced or inhibited by\ntuning the Bose-Einstein condensate trap frequency."
    },
    {
        "anchor": "Effects of a rotating periodic lattice on coherent quantum states in a\n  ring topology: The case of positive nonlinearity: We study the landscape of solutions of the coherent quantum states in a ring\nshaped lattice potential in the context of ultracold atoms with an effective\npositive nonlinearity induced by interatomic interactions. The exact analytical\nsolutions in the absence of lattice are used as a starting point and the\ntransformation of those solutions is mapped as the lattice is introduced and\nstrengthened. This approach allows a simple classification of all the solutions\ninto states with periods commensurate/incommensruate with the lattice period\nand those with/without nodes. Their origins are traced to the primary\ndispersion curve and the swallowtail branches of the lattice-free spectrum. The\ncommensurate states tend to remain delocalized with increasing lattice depth,\nwhereas the incommensurate ones may be localized. The symmetry and stability\nproperties of the solutions are examined and correlated with branch energies.\nThe crucial importance of rotation is highlighted by its utility in\ncontinuously transforming solutions and accessing in a finite ring with a few\nsites the full spectrum of nonlinear Bloch waves on an infinite lattice.",
        "positive": "Properties of bosons in a one-dimensional bichromatic optical lattice in\n  the regime of the Sine-Gordon transition: a Worm Algorithm Monte Carlo study: The properties of interacting bosons in a weak, one-dimensional, and\nbichromatic optical with a rational ratio of the constituting wavelengths\n$\\lambda_1$ and $\\lambda_2$ are numerically examined along a broad range of the\nLieb-Liniger interaction parameter $\\gamma$ passing through the Sine-Gordon\ntransition. It is argued that there should not be much difference in the\nresults between those due to an irrational ratio $\\lambda_1/\\lambda_2$ and due\nto a rational approximation of the latter. For a weak bichromatic optical\nlattice, it is chiefly demonstrated that this transition is robust against the\nintroduction of quasidisorder via a weaker, secondary, and incommensurate\noptical lattice superimposed on the primary one. The properties, such as the\ncorrelation function, Matsubara Green's function, and the single-particle\ndensity matrix, do not respond to changes in the depth of the secondary optical\nlattice $V_1$. For a stronger bichromatic optical lattice, however, a response\nis observed because of changes in $V_1$. It is found accordingly, that holes in\nthe SG regime play an important role in the response of properties to changes\nin $\\gamma$. The continuous-space worm algorithm Monte Carlo method [Boninsegni\n\\ea, Phys. Rev. E $\\mathbf{74}$, 036701 (2006)] is applied for the present\nexamination. It is found that the worm algorithm is able to reproduce the\nSine-Gordon transition that has been observed experimentally [Haller \\ea,\nNature $\\mathbf{466}$, 597 (2010)]."
    },
    {
        "anchor": "Ultracold Bose Mixtures with Spin-Dependent Fermion-Mediated\n  Interactions: We develop a functional integral formulation for binary Bose-Einstein\ncondensates coupled to polarized fermions. We find that spin-dependent\nfermion-mediated interactions have dramatic effects on the properties of the\nbinary condensates. The quasiparticle spectrum features two branches. The upper\nbranch, which is of density nature, gets modified by the induced interactions,\nwhile the lower branch, which is of spin nature, is left intact. The\nground-state phase diagram consists of stable region of miscible phases and\nunstable region toward phase separation. In the stable region, it is further\nclassified by the damping of excitations of the upper branch. We show that it\nis possible to find region of well-defined, long-lived quasiparticle\nexcitations by tuning relevant parameters, such as boson-fermion mass ratio,\nboson-fermion number density ratio, and interspecies interactions between\nbosons as well. We explore the effects of quantum fluctuation due to the\neffective potential on the binary condensates. It turns out that both the\ndensity structure factor and spin density structure factor fulfill the Feynman\nrelation, except that the latter is immune to the fermion-mediated\ninteractions.",
        "positive": "Site-resolved imaging of a fermionic Mott insulator: The complexity of quantum many-body systems originates from the interplay of\nstrong interactions, quantum statistics, and the large number of\nquantum-mechanical degrees of freedom. Probing these systems on a microscopic\nlevel with single-site resolution offers important insights. Here we report\nsite-resolved imaging of two-component fermionic Mott insulators, metals, and\nband insulators using ultracold atoms in a square lattice. For strong repulsive\ninteractions we observe two-dimensional Mott insulators containing over 400\natoms. For intermediate interactions, we observe a coexistence of phases. From\ncomparison to theory we find trap-averaged entropies per particle of\n$1.0\\,k_{\\mathrm{B}}$. In the band-insulator we find local entropies as low as\n$0.5\\,k_{\\mathrm{B}}$. Access to local observables will aid the understanding\nof fermionic many-body systems in regimes inaccessible by modern theoretical\nmethods."
    },
    {
        "anchor": "Triangular Gross-Pitaevskii breathers and Damski-Chandrasekhar shock\n  waves: The recently proposed map [arXiv:2011.01415] between the hydrodynamic\nequations governing the two-dimensional triangular cold-bosonic breathers\n[Phys. Rev. X 9, 021035 (2019)] and the high-density zero-temperature\ntriangular free-fermionic clouds, both trapped harmonically, perfectly explains\nthe former phenomenon but leaves uninterpreted the nature of the initial\n($t=0$) singularity. This singularity is a density discontinuity that leads, in\nthe bosonic case, to an infinite force at the cloud edge. The map itself\nbecomes invalid at times $t<0$. A similar singularity appears at $t = T/4$,\nwhere $T$ is the period of the harmonic trap, with the Fermi-Bose map becoming\ninvalid at $t > T/4$. Here, we first map -- using the scale invariance of the\nproblem -- the trapped motion to an untrapped one. Then we show that in the new\nrepresentation, the solution [arXiv:2011.01415] becomes, along a ray in the\ndirection normal to one of the three edges of the initial cloud, a freely\npropagating one-dimensional shock wave of a class proposed by Damski in\n[Phys.~Rev.~A 69, 043610 (2004)]. There, for a broad class of initial\nconditions, the one-dimensional hydrodynamic equations can be mapped to the\ninviscid Burgers' equation, which is equivalent to a nonlinear transport\nequation. More specifically, under the Damski map, the $t=0$ singularity of the\noriginal problem becomes, verbatim, the initial condition for the wave\ncatastrophe solution found by Chandrasekhar in 1943 [Ballistic Research\nLaboratory Report No. 423 (1943)]. At $t=T/8$, our interpretation ceases to\nexist: at this instance, all three effectively one-dimensional shock waves\nemanating from each of the three sides of the initial triangle collide at the\norigin, and the 2D-1D correspondence between the solution of [arXiv:2011.01415]\nand the Damski-Chandrasekhar shock wave becomes invalid.",
        "positive": "Sound-induced vortex interactions in a zero-temperature two-dimensional\n  superfluid: We present a systematic derivation of the effective action for interacting\nvortices in a non-relativistic two-dimensional superfluid described by the\nGross-Pitaevskii equation by integrating out longitudinal fluctuations of the\norder parameter. There are no logarithmically divergent coefficients in the\nequations of motion. Our analysis is valid in a dilute limit of vortices where\nthe intervortex spacing is large compared to the core size, and where number\nfluctuations of atoms in vortex cores are suppressed. We analyze sound-induced\ncorrections to the dynamics of a vortex-antivortex pair and show that there is\nno instability to annihilation, suggesting that sound-mediated interactions are\nnot strong enough to ruin an inverse energy cascade in two-dimensional\nzero-temperature superfluid turbulence."
    },
    {
        "anchor": "Measuring The Heat Capacity in a Bose-Einstein Condensation using Global\n  Variables: Phase transitions are well understood and generally followed by the behavior\nof the associated thermodynamic quantities, such as in the case of the\n$\\lambda$ point superfluid transition of liquid helium, which is observed in\nits heat capacity. In the case of a trapped Bose-Einstein condensate (BEC), the\nheat capacity cannot be directly measured. In this work, we present a technique\nable to determine the global heat capacity from the density distribution of a\nweakly interacting gas trapped in an inhomogeneous potential. This approach\nrepresents an alternative to models based on local density approximation. By\ndefining a pair of global conjugate variables, we determine the total internal\nenergy and its temperature derivative, the heat capacity. We then apply the\ntechnique to a trapped $^{87}$Rb BEC a $\\lambda$-type transition dependent on\nthe atom number is observed, and the deviations from the non-interacting, ideal\ngas case are discussed. Finally we discuss the chances of using this method to\nstudy the heat capacity at $T \\rightarrow 0$.",
        "positive": "Ferromagnetic Resonance in Spinor Dipolar Bose--Einstein Condensates: We used the Gross--Pitaevskii equations to investigate ferromagnetic\nresonance in spin-1 Bose--Einstein condensates with a magnetic dipole-dipole\ninteraction. By introducing the dipole interaction, we obtained equations\nsimilar to the Kittel equations used to represent ferromagnetic resonance in\ncondensed matter physics. These equations indicated that the ferromagnetic\nresonance originated from dipolar interaction, and that the resonance frequency\ndepended upon the shape of the condensate. Furthermore, spin currents driven by\nspin diffusions are characteristic of this system."
    },
    {
        "anchor": "Two-body momentum correlations in a weakly interacting one-dimensional\n  Bose gas: We analyze the two-body momentum correlation function for a uniform weakly\ninteracting one-dimensional Bose gas. We show that the strong positive\ncorrelation between opposite momenta, expected in a Bose-Einstein condensate\nwith a true long-range order, almost vanishes in a phase-fluctuating\nquasicondensate where the long-range order is destroyed. Using the Luttinger\nliquid approach, we derive an analytic expression for the momentum correlation\nfunction in the quasicondensate regime, showing (i) the reduction and\nbroadening of the opposite-momentum correlations (compared to the singular\nbehavior in a true condensate) and (ii) an emergence of anticorrelations at\nsmall momenta. We also numerically investigate the momentum correlations in the\ncrossover between the quasicondensate and the ideal Bose-gas regimes using a\nclassical field approach and show how the anticorrelations gradually disappear\nin the ideal-gas limit.",
        "positive": "Mode coupling of interaction quenched ultracold few-boson ensembles in\n  periodically driven lattices: The out-of-equilibrium dynamics of interaction quenched finite ultracold\nbosonic ensembles in periodically driven one-dimensional optical lattices is\ninvestigated. It is shown that periodic driving enforces the bosons in the\nouter wells of the finite lattice to exhibit out-of-phase dipole-like modes,\nwhile in the central well the atomic cloud experiences a local breathing mode.\nThe dynamical behavior is investigated with varying driving frequency,\nrevealing a resonant-like behavior of the intra-well dynamics. An interaction\nquench in the periodically driven lattice gives rise to admixtures of different\nexcitations in the outer wells, an enhanced breathing in the center and an\namplification of the tunneling dynamics. We observe then multiple resonances\nbetween the inter- and intra-well dynamics at different quench amplitudes, with\nthe position of the resonances being tunable via the driving frequency. Our\nresults pave the way for future investigations on the use of combined driving\nprotocols in order to excite different inter- and intra-well modes and to\nsubsequently control them."
    },
    {
        "anchor": "Quantum spiral spin-tensor magnetism: The characterization of quantum magnetism in a large spin ($\\geq 1$) system\nnaturally involves both spin-vectors and -tensors. While certain types of\nspin-vector (e.g., ferromagnetic, spiral) and spin-tensor (e.g., nematic in\nfrustrated lattices) orders have been investigated separately, the coexistence\nand correlation between them have not been well explored. Here we propose a\nnovel quantum spiral spin-tensor order on a spin-1 Heisenberg chain subject to\na spiral spin-tensor Zeeman field, which can be experimentally realized using a\nRaman-dressed cold atom optical lattice. We develop a method to fully\ncharacterize quantum phases of such spiral tensor magnetism with the\ncoexistence of spin-vector and spin-tensor orders as well as their correlations\nusing eight geometric parameters. Our method provides a powerful tool for\ncharacterizing spin-1 quantum magnetism and opens an avenue for exploring novel\nmagnetic orders and spin-tensor electronics/atomtronics in large-spin systems.",
        "positive": "Local Correlations in the Super Tonks-Girardeau Gas: We study the local correlations in the super Tonks-Girardeau gas, a highly\nexcited, strongly correlated state obtained in quasi one-dimensional Bose gases\nby tuning the scattering length to large negative values using a\nconfinement-induced resonance. Exploiting a connection with a relativistic\nfield theory, we obtain results for the two-body and three-body local\ncorrelators at zero and finite temperature. At zero temperature our result for\nthe three-body correlator agrees with the extension of the results of Cheianov\net al. [Phys. Rev. A 73, 051604(R) (2006)], obtained for the ground-state of\nthe repulsive Lieb-Liniger gas, to the super Tonks-Girardeau state. At finite\ntemperature we obtain that the three-body correlator has a weak dependence on\nthe temperature up to the degeneracy temperature. We also find that for\ntemperatures larger than the degeneracy temperature the values of the\nthree-body correlator for the super Tonks-Girardeau gas and the corresponding\nrepulsive Lieb-Liniger gas are rather similar even for relatively small\ncouplings."
    },
    {
        "anchor": "Non-degenerate Bound State Solitons in Multi-component Bose-Einstein\n  Condensates: We investigate non-degenerate bound state solitons systematically in\nmulti-component Bose-Einstein condensates, through developing Darboux\ntransformation method to derive exact soliton solutions analytically. In\nparticular, we show that bright solitons with nodes correspond to the excited\nbound eigen-states in the self-induced effective quantum wells, in sharp\ncontrast to the bright soliton and dark soliton reported before (which usually\ncorrespond to ground state and free eigen-state respectively). We further\ndemonstrate that the bound state solitons with nodes are induced by incoherent\ninteractions between solitons in different components. Moreover, we reveal that\nthe interactions between these bound state solitons are usually inelastic,\ncaused by the incoherent interactions between solitons in different components\nand the coherent interactions between solitons in same component. The bound\nstate solitons can be used to discuss many different physical problems, such as\nbeating dynamics, spin-orbital coupling effects, quantum fluctuations, and even\nquantum entanglement states.",
        "positive": "Fragmentation of a trapped bosonic mixture: Fragmentation of bosons and pairs in a trapped imbalanced bosonic mixture is\ninvestigated analytically using an exactly solvable model, the generic\nharmonic-interaction model for mixtures. Closed-form expressions for the\neigenvalues and eigenfunctions of the reduced one-particle and two-particle\ndensity matrices as a function of all parameters, the masses, numbers of\nbosons, and the intraspecies and interspecies interactions, are obtained and\nanalyzed. As an application, we consider a system made of $N_1=100$\nnon-interacting species $1$ bosons embedded in a bath made of $N_2=10^6$\nnon-interacting species $2$ bosons, and show how fragmentation of the system's\nbosons and pairs emerges from the system--bath interaction only. Interestingly,\nthe lighter the bosons comprising the bath are the stronger is the system's\nfragmentation. Further applications are briefly discussed."
    },
    {
        "anchor": "Quantum and Thermal Transitions Out of the Pair-Supersolid Phase of\n  Two-Species Bosons in Lattice: We investigate two-species bosons in a two-dimensional square lattice by\nquantum Monte Carlo method. We show that the inter-species attraction and\nnearest-neighbor intra-species repulsion results in the pair-supersolid phase,\nwhere a diagonal solid order coexists with an off-diagonal pair-superfluid\norder. The quantum and thermal transitions out of the pair-supersolid phase are\ncharacterized. It is found that there is a direct first order transition from\nthe pair-supersolid phase to the double-superfluid phase without an\nintermediate region. Furthermore, the melting of the pair-supersolid occurs in\ntwo steps. Upon heating, first the pair-superfluid is destroyed via a KT\ntransition then the solid order melts via an Ising transition",
        "positive": "Fermionic correlation functions from randomized measurements in\n  programmable atomic quantum devices: We provide a measurement protocol to estimate 2- and 4-point fermionic\ncorrelations in ultra-cold atom experiments. Our approach is based on combining\nrandom atomic beam splitter operations, which can be realized with programmable\noptical landscapes, with high-resolution imaging systems such as quantum gas\nmicroscopes. We illustrate our results in the context of the variational\nquantum eigensolver algorithm for solving quantum chemistry problems."
    },
    {
        "anchor": "Quantum droplets with particle imbalance in one-dimensional optical\n  lattices: We study the formation of particle-imbalanced quantum droplets in a\none-dimensional optical lattice containing a binary bosonic mixture at zero\ntemperature. To understand the effects of the imbalance from both the few- and\nmany-body perspectives, we employ density matrix renormalization group (DMRG)\nsimulations and perform the extrapolation to the thermodynamic limit. In\ncontrast to the particle-balanced case, not all bosons are paired, resulting in\nan interplay between bound states and individual atoms that leads to intriguing\nphenomena. Quantum droplets manage to sustain a small particle imbalance,\nresulting in an effective magnetization. However, as the imbalance is further\nincreased, a critical point is eventually crossed, and the droplets start to\nexpel the excess particles while the magnetization in the bulk remains\nconstant. Remarkably, the unpaired particles on top of the quantum droplet\neffectively form a super Tonks-Girardeau (hard-rod) gas. The expulsion point\ncoincides with the critical density at which the size of the super\nTonks-Girardeau gas matches the size of the droplet.",
        "positive": "Superfluid flow of polaron polaritons above Landau's critical velocity: We develop a theory for the interaction of light with superfluid optical\nmedia, describing the motion of quantum impurities that are created and dragged\nthrough the liquid by propagating photons. It is well known that a mobile\nimpurity suffers dissipation due to phonon emission as soon as it moves faster\nthan the speed of sound in the superfluid - Landau's critical velocity.\nSurprisingly we find that in the present hybrid light-matter setting,\npolaritonic impurities can be protected against environmental decoherence and\nbe allowed to propagate well above the Landau velocity without jeopardizing the\nsuperfluid response of the medium."
    },
    {
        "anchor": "Evolution of Cooper pairs with zero-center-of-mass momentum and their\n  first-order correlation function in a two-dimensional ultracold Fermi gas\n  near the observed Berezinskii-Kosterlitz-Thouless transition: We investigate the center-of-mass momentum distribution $n_{\\boldsymbol Q}$\nof Cooper pairs and their first-order correlation function $g_1(r)$ in a\nstrongly interacting two-dimensional Fermi gas. Recently, the BKT\n(Berezinskii-Kosterlitz-Thouless) transition was reported in a two-dimensional\n$^6$Li Fermi gas, based on (1) the observations of anomalous enhancement of\n$n_{{\\boldsymbol Q}={\\boldsymbol 0}}$ [M. G. Ries, et. al., Phys. Rev. Lett.\n114, 230401 (2015)], as well as (2) a power-law behavior of $g_1(r)$ [P. A.\nMurthy, et. al., Phys. Rev. Lett. 115, 010401 (2015)]. However, including\npairing fluctuations within a $T$-matrix approximation (TMA), we show that\nthese results can still be explained as strong-coupling properties of a\nnormal-state two-dimensional Fermi gas. Our results indicate the importance of\nfurther experimental observations, to definitely confirm the realization of the\nBKT transition in this system. Since the BKT transition has been realized in a\ntwo-dimensional ultracold Bose gas, our results would be useful for the\nachievement of this quasi-long range order in an ultracold Fermi gas.",
        "positive": "Quantum hydrodynamic theory of quantum fluctuations in dipolar\n  Bose-Einstein condensate: Traditional quantum hydrodynamics of Bose-Einstein condensates (BECs) is\nrestricted by the continuity and Euler equations. It corresponds to the\nwell-known Gross-Pitaevskii equation. However, the quantum Bohm potential,\nwhich is a part of the momentum flux, has a nontrivial part with can evolve\nunder the quantum fluctuations. To cover this phenomenon in terms of\nhydrodynamic methods we need to derive equations for the momentum flux, and the\nthird rank tensor. In all equations we consider the main contribution of the\nshort-range interaction (SRI) in the first order by the interaction radius.\nDerived hydrodynamics consists of four hydrodynamic equations. The third moment\nevolution equation contains interaction leading to the quantum fluctuations. It\nincludes new interaction constant. The Gross-Pitaevskii interaction constant is\nthe integral of potential, but the second interaction constant is the integral\nof second derivative of potential. If we have dipolar BECs we deal with a\nlong-range interaction. Its contribution is proportional to the potential of\ndipole-dipole interaction (DDI). The Euler equation contains the derivative of\nthe potential. The third rank tensor evolution equation contains the third\nderivative of the potential. The quantum fluctuations lead to existence of the\nsecond wave solution. Moreover, the quantum fluctuations introduce the\ninstability of BECs. If the DDI is attractive, but being smaller then the\nrepulsive SRI presented by the first interaction constant, there is the\nlong-wavelength instability. For the repulsive DDI these is more complex\npicture. There is the small area with the long-wavelength instability which\ntransits into stability interval, where two waves exist. There is the\nshort-wavelength instability as well. These results are found for the DDI\nstrength comparable with the Gross-Pitaevskii SRI."
    },
    {
        "anchor": "Universal upper bounds on the Bose-Einstein condensate and the Hubbard\n  star: For $N$ hard-core bosons on an arbitrary lattice with $d$ sites and\nindependent of additional interaction terms we prove that the hard-core\nconstraint itself already enforces a universal upper bound on the Bose-Einstein\ncondensate given by $N_{max}=(N/d)(d-N+1)$. This bound can only be attained for\none-particle states $|\\varphi\\rangle$ with equal amplitudes with respect to the\nhard-core basis (sites) and when the corresponding $N$-particle state\n$|\\Psi\\rangle$ is maximally delocalized. This result is generalized to the\nmaximum condensate possible within a given sublattice. We observe that such\nmaximal local condensation is only possible if the mode entanglement between\nthe sublattice and its complement is minimal. We also show that the maximizing\nstate $|\\Psi\\rangle$ is related to the ground state of a bosonic `Hubbard star'\nshowing Bose-Einstein condensation.",
        "positive": "Potential Scattering on a Spherical Surface: The advances in cold atom experiments have allowed construction of confining\ntraps in the form of curved surfaces. This opens up the possibility of studying\nquantum gases in curved manifolds. On closed surfaces, many fundamental\nprocesses are affected by the local and global properties, i.e. the curvature\nand the topology of the surface. In this paper, we study the problem of\npotential scattering on a spherical surface and discuss its difference with\nthat on a 2D plane. For bound states with angular momentum $m$, their energies\n($E_{m}$) on a sphere are related to those on a 2D plane ($-|E_{m,o}|$) as\n$E_{m}= - |E_{m, o}| + E_{R}^{} \\left[ \\frac{m^2-1}{3} + O\\left(\n\\frac{r_o^2}{R^2} \\right) \\right] $, where $E_{R}^{} = \\hbar^2/(2M R^2)$, and\n$R$ is the radius of the sphere. Due to the finite extent of the manifold, the\nphase shifts on a sphere at energies $E\\sim E_{R}^{}$ differ significantly from\nthose on a 2D plane. As energy $E$ approaches zero, the phase shift in the\nplanar case approaches $0$, whereas in the spherical case it reaches a constant\nthat connects the microscopic length scale to the largest length scale $R$."
    },
    {
        "anchor": "Cooperatively-enhanced precision of hybrid light-matter sensors: We consider a hybrid system of matter and light as a sensing device and\nquantify the role of cooperative effects. The latter generically enhance the\nprecision with which modifications of the effective light-matter coupling\nconstant can be measured. In particular, considering a fundamental model of $N$\nqubits coupled to a single electromagnetic mode, we show that the ultimate\nbound for the precision shows double-Heisenberg scaling:\n$\\Delta\\theta\\propto1/(Nn)$, with $N$ and $n$ being the number of qubits and\nphotons, respectively. Moreover, even using classical states and measuring only\none subsystem, a Heisenberg-times-shot-noise scaling, i.e. $1/(N\\sqrt{n})$ or\n$1/(n\\sqrt{N})$, is reached. As an application, we show that a Bose-Einstein\ncondensate trapped in a double-well potential within an optical cavity can\ndetect the gravitational acceleration $g$ with the relative precision of\n$\\Delta g/g\\simeq10^{-9}\\text{Hz}^{-1/2}$. The analytical approach presented in\nthis study takes into account the leakage of photons through the cavity\nmirrors, and allows to determine the sensitivity when $g$ is inferred via\nmeasurements on atoms or photons.",
        "positive": "An instanton-like excitation of a discrete time crystal: Spontaneous symmetry breaking and elementary excitation are two of the\npillars of condensed matter physics that are closely related to each other. The\nsymmetry and its spontaneous breaking not only control the dynamics and\nspectrum of elementary excitations, but also determine their underlying\nstructures. In this paper, we study the excitation properties of a\nnon-equilibrium quantum matter: a discrete time crystal phase that\nspontaneously breaks the temporal translational symmetry. It is shown that such\nan intriguing symmetry breaking allows an instanton-like excitation that\nrepresents a tunneling between two \"degenerate\" time crystal phases.\nFurthermore, we also observe a dynamical transition point at which the\ninstanton \"size\" diverges, a reminiscence of the critical slowing down\nphenomenon in nonequilibrium statistic physics. A phenomenological theory has\nbeen proposed to understand the phase dynamics of the proposed system and the\nexperimental realization and detection have also been discussed."
    },
    {
        "anchor": "Matter-Wave Interference versus Spontaneous Pattern Formation in Spinor\n  Bose-Einstein Condensate: We describe effects of matter-wave interference of spinor states in the\n$^{87}$Rb Bose-Einstein condensate. The components of the F=2 manifold are\npopulated by forced Majorana transitions and then fall freely due to gravity in\nan applied magnetic field. Weak inhomogeneities of the magnetic field, present\nin the experiment, impose relative velocities onto different $m_F$ components,\nwhich show up as interference patterns upon measurement of atomic density\ndistributions with a Stern-Gerlach imaging method. We show that interference\neffects may appear in experiments even if gradients of the magnetic field\ncomponents are eliminated but higher order inhomogeneity is present and the\nduration of the interaction is long enough. In particular, we show that the\nresulting matter-wave interference patterns can mimic spontaneous pattern\nformation in the quantum gas.",
        "positive": "Long-range multi-body interactions and three-body anti-blockade in a\n  trapped Rydberg ion chain: Trapped Rydberg ions represent a flexible platform for quantum simulation and\ninformation processing which combines a high degree of control over electronic\nand vibrational degrees of freedom. The possibility to individually excite ions\nto high-lying Rydberg levels provides a system where strong and long-range\ninteractions between pairs of excited ions can be engineered and tuned via\nexternal laser fields. We show that the coupling between Rydberg pair\ninteractions and collective motional modes gives rise to effective long-range\nmulti-body interactions, consisting of two, three, and four-body terms. Their\nshape, strength, and range can be controlled via the ion trap parameters and\nstrongly depends on both the equilibrium configuration and vibrational modes of\nthe ion crystal. By focusing on an experimentally feasible quasi\none-dimensional setup of $ {}^{88}\\mathrm{Sr}^+ $ Rydberg ions, we demonstrate\nthat multi-body interactions are enhanced by the emergence of a soft mode\nassociated, e.g., with a structural phase transition. This has a striking\nimpact on many-body electronic states and results, for example, in a three-body\nanti-blockade effect. Our study shows that trapped Rydberg ions offer new\nopportunities to study exotic many-body quantum dynamics driven by enhanced\nmulti-body interactions."
    },
    {
        "anchor": "Resonant Floquet Scattering of Ultracold Atoms: In systems of ultracold atoms, pairwise interactions are resonantly enhanced\nby the application of an oscillating magnetic field that is parallel to the\nspin-quantization axis of the atoms. The resonance occurs when the frequency of\nthe applied field is precisely tuned near the transition frequency between the\nscattering atoms and a diatomic molecule. The resulting cross section can be\nmade more than two orders of magnitude larger than the cross section in the\nabsence of the oscillating field. The low momentum resonance properties have a\nuniversal description that is independent of the atomic species. To arrive at\nthese conclusions, we first develop a formal extension of Floquet theory to\ndescribe scattering of atoms with time-periodic, short-range interaction\npotentials. We then calculate the atomic scattering properties by modeling the\natomic interactions with a square well potential with oscillating depth and\nthen explicitly solving the time-dependent Schrodinger equation. We then apply\nthe Floquet formalism to the case of atoms scattering with a contact\ninteraction described by a time-periodic scattering length, obtaining analytic\nresults that agree with those obtained by solving the time-dependent\nSchrodinger equation.",
        "positive": "Detuning control of Rabi vortex oscillations in light matter coupling: We study analytically the dynamics of vortices in strongly coupled\nexciton--photon fields in the presence of energy detuning. We derive equations\nfor the vortex core velocity and mass, where they mainly depend on Rabi\ncoupling and the relative distance between the vortex cores in photon and\nexciton fields, and as the result core positions oscillate in each field. We\nuse Magnus force balanced with a Rabi induced force to show that the core of\nthe vortex behaves as an inertial-like particle. Our analysis reveals that the\ncore is lighter at periphery of the beam and therefore it is faster at that\nregion. While detuning induces oscillations in population imbalance of\ncomponents through relative phase between coupled fields, in the presence of\ntopological charges detuning can control the orbital dynamics of the cores.\nNamely, it brings the vortex core to move on larger or smaller orbits with\ndifferent velocities, and changes angular momentum and energy content of vortex\nfield."
    },
    {
        "anchor": "Out-of-equilibrium states and quasi-many-body localization in polar\n  lattice gases: The absence of energy dissipation leads to an intriguing out-of-equilibrium\ndynamics for ultracold polar gases in optical lattices, characterized by the\nformation of dynamically-bound on-site and inter-site clusters of two or more\nparticles, and by an effective blockade repulsion. These effects combined with\nthe controlled preparation of initial states available in cold gases\nexperiments can be employed to create interesting out-of-equilibrium states.\nThese include quasi-equilibrated effectively repulsive 1D gases for attractive\ndipolar interactions and dynamically-bound crystals. Furthermore,\nnon-equilibrium polar lattice gases can offer a promising scenario for the\nstudy of many-body localization in the absence of quenched disorder. This\nfascinating out-of-equilibrium dynamics for ultra-cold polar gases in optical\nlattices may be accessible in on-going experiments.",
        "positive": "Spin squeezing by tensor twisting and Lipkin-Meshkov-Glick dynamics in a\n  toroidal Bose-Einstein condensate with spatially modulated nonlinearity: We propose a scheme for spin-squeezing in the orbital motion of a\nBose-Einstein condensate (BEC) in a toroidal trap. A circular lattice couples\ntwo counter-rotating modes and squeezing is generated by the nonlinear\ninteraction spatially modulated at half the lattice period. By varying the\namplitude and phase of the modulation, various cases of the twisting tensor can\nbe directly realized, leading to different squeezing regimes. These include\none-axis twisting and the two-axis counter-twisting which are often discussed\nas the most important paradigms for spin squeezing. Our scheme naturally\nrealizes the Lipkin-Meshkov-Glick model with the freedom to vary all its\nparameters simultaneously."
    },
    {
        "anchor": "Non-equilibrium phases of Fermi gas inside a cavity with imbalanced\n  pumping: In this work, we investigate the non-equilibrium dynamics of one-dimensional\nspinless fermions loaded in a cavity with imbalanced pumping lasers. Our study\nis motivated by previous work on a similar setup using bosons, and we explore\nthe unique properties of fermionic systems in this context. By considering the\nimbalance in the pumping, we find that the system exhibits multiple\nsuperradiant steady phases and an unstable phase. Furthermore, by making use of\nthe hysteresis structure of superradiant phases, we propose a unidirectional\ntopological pumping. Unlike the usual topological pumping in which the driving\nprotocol breaks time reversal symmetry, the driving protocol can be time\nreversal invariant in our proposal.",
        "positive": "Stability of the Superfluid State in Three-Component Fermionic Optical\n  Lattice Systems: Three-component fermionic optical lattice systems are investigated in\ndynamical mean-field theory for the Hubbard model. Solving the effective\nimpurity model by means of continuous-time quantum Monte Carlo simulations in\nthe Nambu formalism, we find that the $s$-wave superfluid state proposed\nrecently is indeed stabilized in the repulsively interacting case and appears\nalong the first-order phase boundary between the metallic and paired Mott\nstates in the paramagnetic system. The BCS-BEC crossover in the three-component\nfermionic system is also addressed."
    },
    {
        "anchor": "Macroscopic amplification of electroweak effects in molecular\n  Bose-Einstein condensates: We investigate the possible use of Bose-Einstein condensates of diatomic\nmolecules to measure nuclear spin-dependent parity violation effects, outlining\na detection method based on the internal Josephson effect between molecular\nstates of opposite parity. When applied to molecular condensates, the fine\nexperimental control achieved in atomic bosonic Josephson junctions could\nprovide data on anapole moments and neutral weak couplings.",
        "positive": "Quantum liquids with fractal branching patterns in Rydberg atom arrays: In this study, we propose an exotic quantum liquid state which does not order\nat zero temperature in a Rydberg atom array with antiblockade mechanism. By\nperforming an unbiased large-scale quantum Monte Carlo simulation, we\ninvestigate a minimal model with facilitated excitation in a clean system\nwithout frustration, and find that the wavefunction of its ground state is\ncomposed of configurations with fractal branching structures. This state\nfeatures a quasi-long-range order (correlation functions with algebraic decay)\nas well as a heterogeneous structure of liquid and glass mixture. Thus it is\ndifferent from most well-established quantum phases of matter."
    },
    {
        "anchor": "Emulating Molecular Orbitals and Electronic Dynamics with Ultracold\n  Atoms: In recent years, ultracold atoms in optical lattices have proven their great\nvalue as quantum simulators for studying strongly correlated phases and complex\nphenomena in solid-state systems. Here we reveal their potential as quantum\nsimulators for molecular physics and propose a technique to image the\nthree-dimensional molecular orbitals with high resolution. The outstanding\ntunability of ultracold atoms in terms of potential and interaction offer fully\nadjustable model systems for gaining deep insight into the electronic structure\nof molecules. We study the orbitals of an artificial benzene molecule and\ndiscuss the effect of tunable interactions in its conjugated pi electron system\nwith special regard to localization and spin order. The dynamical time scales\nof ultracold atom simulators are on the order of milliseconds, which allows for\nthe time-resolved monitoring of a broad range of dynamical processes. As an\nexample, we compute the hole dynamics in the conjugated pi system of the\nartificial benzene molecule.",
        "positive": "Magnetism and domain formation in SU(3)-symmetric multi-species Fermi\n  mixtures: We study the phase diagram of an SU(3)-symmetric mixture of three-component\nultracold fermions with attractive interactions in an optical lattice,\nincluding the additional effect on the mixture of an effective three-body\nconstraint induced by three-body losses. We address the properties of the\nsystem in $D \\geq 2$ by using dynamical mean-field theory and variational Monte\nCarlo techniques. The phase diagram of the model shows a strong interplay\nbetween magnetism and superfluidity. In the absence of the three-body\nconstraint (no losses), the system undergoes a phase transition from a color\nsuperfluid phase to a trionic phase, which shows additional particle density\nmodulations at half-filling. Away from the particle-hole symmetric point the\ncolor superfluid phase is always spontaneously magnetized, leading to the\nformation of different color superfluid domains in systems where the total\nnumber of particles of each species is conserved. This can be seen as the SU(3)\nsymmetric realization of a more general tendency to phase-separation in\nthree-component Fermi mixtures. The three-body constraint strongly disfavors\nthe trionic phase, stabilizing a (fully magnetized) color superfluid also at\nstrong coupling. With increasing temperature we observe a transition to a\nnon-magnetized SU(3) Fermi liquid phase."
    },
    {
        "anchor": "Numerically exact approach to few-body problems far from a perturbative\n  regime: Recent developments of experimental techniques in the field of ultra-cold\ngases open a path to study the crossover from 'few' to 'many' on the quantum\nlevel. In this case, accurate description of inter-particle correlations is\nvery important since it is believed that they can be utilized by quantum\nengineers in quantum metrology, quantum thermometry, quantum heat engines, {\\it\netc}. Unfortunately, a theoretical description of these correlations is very\nchallenging since they are far beyond any variational approaches. By contrast,\nthe exact many-body description rapidly hits numerical limitations due to an\nexponential increase of the many-body Hilbert space. In this work, we brush up\na very effective method of constructing a many-body basis which originates in\nthe physical argumentation. We show that, in contrast to the commonly used\napproach of a straightforward cut-off, it enables one to perform exact\ncalculations with very limited numerical resources. As examples, we study\nquantum correlations in systems of spinless bosons and two-component mixtures\nof fermions confined in a one-dimensional harmonic trap being far from the\nperturbative regime.",
        "positive": "Strongly Interacting Fermi Gases: The experimental realization of stable, ultracold Fermi gases near a Feshbach\nresonance allows to study gases with attractive interactions of essentially\narbitrary strength. They extend the classic paradigm of BCS into a regime which\nhas never been accessible before. We review the theoretical concepts which have\nbeen developed in this context, including the Tan relations and the notion of\nfixed points at zero density, which are at the origin of universality. We\ndiscuss in detail the universal thermodynamics of the unitary Fermi gas which\nallows a fit free comparison between theory and experiment for this strongly\ninteracting system. In addition, we adress the consequences of scale invariance\nat infinite scattering length and the subtle violation of scale invariance in\ntwo dimensions. Finally we discuss the Fermionic excitation spectrum accessible\nin momentum resolved RF-spectroscopy and the origin of universal lower bounds\nfor the shear viscosity and the spin diffusion constant."
    },
    {
        "anchor": "Scattering of universal fermionic clusters in the resonating group\n  method: Mixtures of polarised fermions of two different masses can form weakly-bound\nclusters, such as dimers and trimers, that are universally described by the\nscattering length between the heavy and light fermions. We use the resonating\ngroup method to investigate the low-energy scattering processes involving\ndimers or trimers. The method reproduces approximately the known particle-dimer\nand dimer-dimer scattering lengths. We use it to estimate the trimer-trimer\nscattering length, which is presently unknown, and find it to be positive.",
        "positive": "A Path Integral Ground State Monte Carlo Algorithm for Entanglement of\n  Lattice Bosons: A ground state path integral quantum Monte Carlo algorithm is introduced that\nallows for the study of entanglement in lattice bosons at zero temperature. The\nR\\'enyi entanglement entropy between spatial subregions is explored across the\nphase diagram of the one dimensional Bose-Hubbard model for systems consisting\nof up to $L=256$ sites at unit-filling without any restrictions on site\noccupancy, far beyond the reach of exact diagonalization. The favorable scaling\nof the algorithm is demonstrated through a further measurement of the R\\'enyi\nentanglement entropy at the two dimensional superfluid-insulator critical point\nfor large system sizes, confirming the existence of the expected entanglement\nboundary law in the ground state. The R\\'enyi estimator is extended to measure\nthe symmetry resolved entanglement that is operationally accessible as a\nresource for experimentally relevant lattice gases with fixed total particle\nnumber."
    },
    {
        "anchor": "Radio-Frequency Manipulation of Fano-Feshbach Resonances in an Ultracold\n  Fermi Gas of $^{40}$K: Experimental control of magnetic Fano-Feshbach resonances in ultracold\n$^{40}$K Fermi gases, using radio-frequency (RF) fields, is demonstrated.\nSpectroscopic measurements are made of three molecular levels within 50 MHz of\nthe atomic continuum, along with their variation with magnetic field. Modifying\nthe scattering properties by an RF field is shown by measuring the loss profile\nversus magnetic field. This work provides the high accuracy locations of ground\nmolecular states near the s-wave Fano-Feshbach resonance, which can be used to\nstudy the crossover regime from a Bose-Einstein condensate to a\nBardeen-Cooper-Schrieffer superfluid in presence of an RF field.",
        "positive": "Tuneable defect interactions and supersolidity in dipolar quantum gases\n  on a lattice potential: Point defects in self-assembled crystals, such as vacancies and\ninterstitials, attract each other and form stable clusters. This leads to a\nphase separation between perfect crystalline structures and defect\nconglomerates at low temperatures. We propose a method that allows one to tune\nthe effective interactions between point defects from attractive to repulsive\nby means of external periodic fields. In the quantum regime, this allows one to\nengineer strongly-correlated many-body phases. We exemplify the microscopic\nmechanism by considering dipolar quantum gases of ground state polar molecules\nand weakly bound molecules of strongly magnetic atoms trapped in a weak optical\nlattice in a two-dimensional configuration. By tuning the lattice depth, defect\ninteractions turn repulsive, which allows us to deterministically design a\nnovel supersolid phase in the continuum limit."
    },
    {
        "anchor": "Localization of a Bose-Einstein condensate vortex in a bichromatic\n  optical lattice: By numerical simulation of the time-dependent Gross-Pitaevskii equation we\nshow that a weakly interacting or noninteracting Bose-Einstein condensate (BEC)\nvortex can be localized in a three-dimensional bichromatic quasi-periodic\noptical-lattice (OL) potential generated by the superposition of two\nstanding-wave polarized laser beams with incommensurate wavelengths. This is a\ngeneralization of the localization of a BEC in a one-dimensional bichromatic OL\nas studied in a recent experiment [Roati et al., Nature 453, 895 (2008)]. We\ndemonstrate the stability of the localized state by considering its time\nevolution in the form of a stable breathing oscillation in a slightly altered\npotential for a large period of time. {Finally, we consider the localization of\na BEC in a random 1D potential in the form of several identical repulsive\nspikes arbitrarily distributed in space.",
        "positive": "Stable giant vortex annuli in microwave-coupled atomic condensates: Stable self-trapped vortex annuli (VAs) with large values of topological\ncharge S (giant VAs) are not only a subject of fundamental interest, but are\nalso sought for various applications, such as quantum information processing\nand storage. However, in conventional atomic Bose-Einstein condensates (BECs)\nVAs with S>1 are unstable. Here, we demonstrate that robust self-trapped\nfundamental solitons (with S=0) and bright VAs (with the stability checked up\nto S=5), can be created in the free space by means of the local-field effect\n(the feedback of the BEC on the propagation of electromagnetic waves) in a\ncondensate of two-level atoms coupled by a microwave (MW) field, as well as in\na gas of MW-coupled fermions with spin 1/2. The fundamental solitons and VAs\nremain stable in the presence of an arbitrarily strong repulsive contact\ninteraction (in that case, the solitons are constructed analytically by means\nof the Thomas-Fermi approximation). Under the action of the moderate attractive\ncontact interaction which, by itself, would lead to collapse, the fundamental\nsolitons and VAs exist and are stable, respectively; it is interesting that\nhigher-order VAs are more robust than their lower-order couterparts, on the\ncontrary to what is known in other systems that may support stable self-trapped\nvortices. Conditions for the experimental realizations of the VAs are\ndiscussed."
    },
    {
        "anchor": "Quasiclassical molecular dynamics for the dilute Fermi gas at unitarity: We study the dilute Fermi gas at unitarity using molecular dynamics with an\neffective quantum potential constructed to reproduce the quantum two-body\ndensity matrix at unitarity. Results for the equation of state, the pair\ncorrelation function and the shear viscosity are presented. These quantities\nare well understood in the dilute, high temperature, limit. Using molecular\ndynamics we determine higher order corrections in the diluteness parameter\n$n\\lambda^3$, where $n$ is the density and $\\lambda$ is the thermal de Broglie\nwave length. In the case of the contact density, which parameterizes the short\ndistance behavior of the correlation function, we find that the results of\nmolecular dynamics interpolates between the truncated second and third order\nvirial expansion, and are in excellent agreement with existing T-matrix\ncalculations. For the shear viscosity we reproduce the expected scaling\nbehavior at high temperature, $\\eta\\sim 1/\\lambda^3$, and we determine the\nleading density dependent correction to this result.",
        "positive": "Fermi edge singularity in neutral electron-hole system: In neutral dense electron-hole (e-h) systems at low temperatures, theory\npredicts Cooper-pair-like excitons at the Fermi energy and a BCS-like exciton\ncondensation. Optical excitation allows creating e-h systems with the densities\ncontrolled by the excitation power. However, the intense optical excitations\nrequired to achieve high densities cause substantial heating of the e-h system\nthat prevents the realization of dense and cold e-h systems in conventional\nsemiconductors. In this work, we study e-h systems created by optical\nexcitation in separated electron and hole layers. The layer separation\nincreases the e-h recombination time and, in turn, the density for a given\noptical excitation by orders of magnitude and, as a result, enables the\nrealization of the dense and cold e-h system. We found a strong enhancement of\nphotoluminescence intensity at the Fermi energy of the neutral dense ultracold\ne-h system that evidences the emergence of excitonic Fermi edge singularity due\nto the Cooper-pair-like excitons at the Fermi energy."
    },
    {
        "anchor": "Path Integral Molecular Dynamics for Bosons: Trapped Bosons exhibit fundamental physical phenomena and are potentially\nuseful for quantum technologies. We present a method for simulating Bosons\nusing path integral molecular dynamics. A main challenge for simulations is\nincluding all permutations due to exchange symmetry. We show that evaluation of\nthe potential can be done recursively, avoiding explicit enumeration of\npermutations, and scales cubically with system size. The method is applied to\nBosons in a 2D trap and agrees with essentially exact results. An analysis of\nthe role of exchange with decreasing temperature is also presented.",
        "positive": "Squeezed field path integral description of second sound in\n  Bose-Einstein condensates: We propose a generalization of the Feynman path integral using squeezed\ncoherent states. We apply this approach to the dynamics of Bose-Einstein\ncondensates, which gives an effective low energy description that contains both\na coherent field and a squeezing field. We derive the classical trajectory of\nthis action, which constitutes a generalization of the Gross Pitaevskii\nequation, at linear order. We derive the low energy excitations, which provides\na description of second sound in weakly interacting condensates as a squeezing\noscillation of the order parameter. This interpretation is also supported by a\ncomparison to a numerical c-field method."
    },
    {
        "anchor": "Manipulating the Mott lobes: optical lattice bosons coupled to an array\n  of atomic quantum dots: We analyze quantum phase transitions in a system of optical lattice bosons\ncoupled to an array of atomic quantum dots, or pseudospins-1/2. The system\nparallels the Bose-Hubbard model with a single difference of the direct\ntunneling between the lattice sites being replaced by an assisted tunneling via\ncoupling to the atomic quantum dots. We calculate the phase diagram of the\ncombined system, numerically within the Gutzwiller ansatz and analytically\nusing the mean-field decoupling approximation. The result of the assisted\nBose-Hubbard model is that the Mott-superfluid transition still takes place,\nhowever, the Mott lobes strongly depend on the system parameters such as the\ndetuning. One can even reverse the usual hierarchy of the lobes with the first\nlobe becoming the smallest. The phase transition in the bosonic subsystem is\naccompanied by a magnetization rotation in the pseudospin subsystem with the\ntilting angle being an effective order parameter. When direct tunneling is\ntaken into account, the Mott lobes can be made disappear and the bosonic\nsubsystem becomes superfluid throughout.",
        "positive": "Quench-induced breathing mode of one-dimensional Bose gases: We measure the position- and momentum- space breathing dynamics of trapped\none-dimensional Bose gases. The profile in real space reveals sinusoidal width\noscillations whose frequency varies continuously through the quasicondensate to\nideal Bose gas crossover. A comparison with theoretical models taking into\naccount the effect of finite temperature is provided. In momentum space, we\nreport the first observation of a frequency doubling in the quasicondensate\nregime, corresponding to a self-reflection mechanism. The disappearance of this\nmechanism through the quasicondensation crossover is mapped out."
    },
    {
        "anchor": "Anderson tower of states and nematic order of spin-1 bosonic atoms on a\n  2D lattice: We investigate the structure of the spectrum of antiferromagnetically coupled\nspin-1 bosons on a square lattice using degenerate perturbation theory and\nexact diagonalizations of finite clusters. We show that the superfluid phase\ndevelops an Anderson tower of states typical of nematic long-range order with\nbroken SU(2) symmetry.We further show that this order persists into the Mott\ninsulating phase down to zero hopping for one boson per site, and down to a\ncritical hopping for two bosons per site, in agreement with mean-field and\nQuantum Monte Carlo results. The connection with the transition between a\nfragmented condensate and a polar one in a single trap is briefly discussed.",
        "positive": "Interference Pattern Formation between Bounded-Solitons and Radiation in\n  Momentum Space: Possible Detection of Radiation from Bounded-Solitons with\n  Bose-Einstein Condensate of Neutral Atoms: We propose an indirect method to observe radiation from an incomplete soliton\nwith sufficiently large amplitude. We show that the radiation causes a notched\nstructure on the envelope of the wave packet in the momentum space. The origin\nof this structure is a result of interference between the main body of\noscillating solitons and the small radiation in the momentum space. We\nnumerically integrate the nonlinear Schr\\\"odinger equation and perform Fourier\ntransformation to confirm that the predicted structure really appears. We also\nshow the simple model which reproduces the qualitative result. Experimental\ndetection of the notched structure with Bose-Einstein condensation of neutral\natoms is discussed and suitable parameters for this detection experiment are\nshown."
    },
    {
        "anchor": "Quantum hydrodynamics of a single particle: Semiconductor devices are strong competitors in the race for the development\nof quantum com-putational systems. In this work, we interface two semiconductor\nbuilding blocks of different di-mensionality and with complementary properties:\n(1) a quantum dot hosting a single exciton andacting as a nearly ideal\nsingle-photon emitter and (2) a quantum well in a 2D microcavity sustain-ing\npolaritons, which are known for their strong interactions and unique\nhydrodynamics propertiesincluding ultrafast real-time monitoring of their\npropagation and phase-mapping. In the presentexperiment we can thus observe how\nthe injected single particles propagate and evolve inside themicrocavity,\ngiving rise to hydrodynamics features typical of macroscopic systems despite\ntheir in-trinsic genuine quantum nature. In the presence of a structural\ndefect, we observe the celebratedquantum interference of a single particle that\nproduces fringes reminiscent of a wave propagation.While this behaviour could\nbe theoretically expected, our imaging of such an interference pattern,together\nwith a measurement of antibunching, constitutes the first demonstration of\nspatial mappingof the self-interference of a single quantum particle hitting an\nobstacle.",
        "positive": "Compressibility and speeds of sound across the superfluid to supersolid\n  phase transition of an elongated dipolar gas: We investigate the excitation spectrum and compressibility of a dipolar\nBose-Einstein condensate in an infinite tube potential in the parameter regime\nwhere the transition between superfluid and supersolid phases occurs. Our study\nfocuses on the density range in which crystalline order develops continuously\nacross the transition. Above the transition the superfluid shows a single\ngapless excitation band, phononic at small momenta and with a roton at a finite\nmomentum. Below the transition, two gapless excitations branches (three at the\ntransition point) emerge in the supersolid. We examine the two gapless\nexcitation bands and their associated speeds of sound in the supersolid phase.\nOur results show that the speeds of sound and the compressibility are\ndiscontinuous at the transition, indicating a second-order phase transition.\nThese results provide valuable insights into the identification of supersolid\nphenomena in dipolar quantum gases and the relationship to supersolidity in\nspin-orbit coupled gases."
    },
    {
        "anchor": "Compressibility and entropy of cold fermions in one dimensional optical\n  lattices: We calculate several thermodynamic quantities for repulsively interacting\none-dimensional fermions.We solve the Hubbard model at both zero and finite\ntemperatures using the Bethe-ansatz method. For arbitrary values of the\nchemical potential, we calculate the particle number density, the double\noccupancy, various compressibilities, and the entropy as a function of\ntemperature and interaction. We find that these thermodynamic quantities show a\ncharacteristic behavior so that measurements of these quantities can be used as\na detection of temperature, the metal-insulator transition, and metallic and\ninsulating phases in the trap environment. Further, we discuss an experimental\nscheme to extract these thermodynamic quantities from the column density\nprofiles. The entropy and the compressibility of the entire trapped atomic\ncloud also reveal characteristic features indicating whether insulating and/or\nmetallic phases coexist in the trap.",
        "positive": "Bichromatic state-dependent disordered potential for Anderson\n  localization of ultracold atoms: The ability to load ultracold atoms at a well-defined energy in a disordered\npotential is a crucial tool to study quantum transport, and in particular\nAnderson localization. In this paper, we present a new method for achieving\nthat goal by rf transfer of atoms of an atomic Bose-Einstein condensate from a\ndisorder insensitive state to a disorder sensitive state. It is based on a\nbichromatic laser speckle pattern, produced by two lasers whose frequencies are\nchosen so that their light-shifts cancel each other in the first state and\nadd-up in the second state. Moreover, the spontaneous scattering rate in the\ndisorder-sensitive state is low enough to allow for long observation times of\nquantum transport in that state. We theoretically and experimentally study the\ncharacteristics of the resulting potential."
    },
    {
        "anchor": "Finite-temperature hydrodynamics for one-dimensional Bose gases:\n  Breathing mode oscillations as a case study: We develop a finite-temperature hydrodynamic approach for a harmonically\ntrapped one-dimensional quasicondensate and apply it to describe the phenomenon\nof frequency doubling in the breathing-mode oscillations of its momentum\ndistribution. The doubling here refers to the oscillation frequency relative to\nthe oscillations of the real-space density distribution, invoked by a sudden\nconfinement quench. We find that the frequency doubling is governed by the\nquench strength and the initial temperature, rather than by the crossover from\nthe ideal Bose gas to the quasicondensate regime. The hydrodynamic predictions\nare supported by the results of numerical simulations based on a\nfinite-temperature c-field approach, and extend the utility of the hydrodynamic\ntheory for low-dimensional quantum gases to the description of\nfinite-temperature systems and their dynamics in momentum space.",
        "positive": "Tan's contact in a cigar-shaped dilute Bose gas: We compute the Tan's contact of a weakly interacting Bose gas at zero\ntemperature in a cigar-shaped configuration. Using an effective one-dimensional\nGross-Pitaeskii equation and Bogoliubov theory, we derive an analytical formula\nthat interpolates between the three-dimensional and the one-dimensional\nmean-field regimes. In the strictly one-dimensional limit, we compare our\nresults with Lieb-Liniger theory. Our study can be a guide for actual\nexperiments interested in the study of Tan's contact in the dimensional\ncrossover."
    },
    {
        "anchor": "Superflow in a toroidal Bose-Einstein condensate: an atom circuit with a\n  tunable weak link: We have created a long-lived (~ 40 s) persistent current in a toroidal\nBose-Einstein condensate held in an all-optical trap. A repulsive optical\nbarrier creates a tunable weak link in the condensate circuit, which can affect\nthe current around the loop. Superflow stops abruptly at a barrier strength\nsuch that the local flow velocity exceeds a critical velocity. The measured\ncritical velocity is consistent with dissipation due to the creation of\nvortex-antivortex pairs. This system is the first realization of an elementary\nclosed-loop atom circuit.",
        "positive": "Frustration-induced supersolids in the absence of inter-site\n  interactions: We discuss a mechanism for the realization of supersolids in lattices in the\nabsence of intersite interactions that surprisingly works as well at unit\nfilling. This mechanism, that we study for the case of the sawtooth lattice, is\nbased on the existence of frustrated and unfrustrated plaquettes. For\nsufficiently large interactions and frustration the particles gather\npreferentially at unfrustrated plaquettes breaking spontaneously translational\ninvariance, resulting in a supersolid. We show that for the sawtooth lattice\nthe supersolid exists for a large region of parameters for densities above half\nfilling. Our results open a feasible path for realizing supersolids in existing\nultracold atomic gases in optical lattices without the need for long-range\ninteractions."
    },
    {
        "anchor": "Feshbach resonances in ultracold gases: In this chapter, we describe scattering resonance phenomena in general, and\nfocus on the mechanism of Feshbach resonances, for which a multi-channel\ntreatment is required. We derive the dependence of the scattering phase shift\non magnetic field and collision energy. From this, the scattering length and\neffective range coefficient can be extracted, expressions which are\nparticularly useful for ultracold gases.",
        "positive": "Kelvin-Helmholtz instability in an atomic superfluid: We demonstrate an experimentally feasible method for generating the classical\nKelvin-Helmholtz instability in a single component atomic Bose-Einstein\ncondensate. By progressively reducing a potential barrier between two\ncounter-flowing channels we seed a line of quantised vortices, which precede to\nform progressively larger clusters, mimicking the classical roll-up behaviour\nof the Kelvin-Helmholtz instability. This cluster formation leads to an\neffective superfluid shear layer, formed through the collective motion of many\nquantised vortices. From this we demonstrate a straightforward method to\nmeasure the effective viscosity of a turbulent quantum fluid in a system with a\nmoderate number of vortices, within the range of current experimental\ncapabilities."
    },
    {
        "anchor": "Cooling schemes for two-component fermions in layered optical lattices: Recently, a cooling scheme for ultracold atoms in a bilayer optical lattice\nhas been proposed [A. Kantian et al., arXiv:1609.03579]. In their scheme, the\nenergy offset between the two layers is increased dynamically such that the\nentropy of one layer is transferred to the other layer. Using the\nfull-Hilbert-space approach, we compute cooling dynamics subjected to the\nscheme in order to show that their scheme fails to cool down two-component\nfermions. We develop an alternative cooling scheme for two-component fermions,\nin which the spin-exchange interaction of one layer is significantly reduced.\nUsing both full-Hilbert-space and matrix-product-state approaches, we find that\nour scheme can decrease the temperature of the other layer by roughly half.",
        "positive": "Low-dimensional quantum gases in curved geometries: Atomic gases confined in curved geometries are characterized by distinctive\nfeatures that are absent in their flat counterparts, such as periodic\nboundaries, local curvature, and nontrivial topologies. The recent experiments\nwith shell-shaped quantum gases and the study of ring-shaped superfluids point\nout that the manifold of a quantum gas could soon become a controllable\nfeature, thus allowing to address the fundamental study of curved many-body\nquantum systems. Here, we review the main geometries realized in the\nexperiments, analyzing the theoretical and experimental status on their phase\ntransitions and on the superfluid dynamics. In perspective, we delineate the\nstudy of vortices, the few-body physics, and the search for analog models in\nvarious curved geometries as the most promising research areas."
    },
    {
        "anchor": "Macroscopic Two-Dimensional Polariton Condensates: We report a record-size, two-dimensional polariton condensate of a fraction\nof a millimeter radius free from the presence of an exciton reservoir. This\nmacroscopically occupied state is formed by the ballistically expanding\npolariton flow that relaxes and condenses over a large area outside of the\nexcitation spot. The density of this trap-free condensate is < 1\npolariton/{\\mu}m^2, reducing the phase noise induced by the interaction energy.\nMoreover, the backflow effect, recently predicted for the nonparabolic\npolariton dispersion, is observed here for the first time in the fast-expanding\nwave packet.",
        "positive": "Hydrodynamic Relaxation in a Strongly Interacting Fermi Gas: We measure the free decay of a spatially periodic density profile in a normal\nfluid strongly interacting Fermi gas, which is confined in a box potential.\nThis spatial profile is initially created in thermal equilibrium by a\nperturbing potential. After the perturbation is abruptly extinguished, the\ndominant spatial Fourier component exhibits an exponentially decaying\n(thermally diffusive) mode and a decaying oscillatory (first sound) mode,\nenabling independent measurement of the thermal conductivity and the shear\nviscosity directly from the time-dependent evolution."
    },
    {
        "anchor": "Strong Quantum Spin Correlations Observed in Atomic Spin Mixing: We have observed sub-Poissonian spin correlations generated by collisionally\ninduced spin mixing in a spin-1 Bose-Einstein condensate. We measure a quantum\nnoise reduction of -7 dB (-10 dB corrected for detection noise) below the\nstandard quantum limit (SQL) for the corresponding coherent spin states. The\nspin fluctuations are detected as atom number differences in the spin states\nusing fluorescent imaging that achieves a detection noise floor of 8 atoms per\nspin component for a probe time of 100 $\\mu$s.",
        "positive": "Anomalous Effects in a Trapped Bose-Einstein Condensate: We study the anomalous density in an ultra-cold trapped bose gas in a\nvariational framework, for both zero and finite temperature. We show that it is\nfinite in 1D, while it is logarithmically and linearly divergent in 2D and 3D.\nThe renormalization that we adopt is more reliable and compatible with the\nvariational scheme. The main outcome is that the anomalous and non condensate\ndensities are of the"
    },
    {
        "anchor": "Engineering Dark Solitary waves in Ring-Trap Bose-Einstein condensates: We demonstrate the feasibility of generation of quasi-stable\ncounter-propagating solitonic structures in an atomic Bose-Einstein condensate\nconfined in a realistic toroidal geometry, and identify optimal parameter\nregimes for their experimental observation. Using density engineering we\nnumerically identify distinct regimes of motion of the emerging macroscopic\nexcitations, including both solitonic motion along the azimuthal ring\ndirection, such that structures remain visible after multiple collisions even\nin the presence of thermal fluctuations, and snaking instabilities leading to\nthe decay of the excitations into vortical structures. Our analysis, which\nconsiders both mean field effects and fluctuations, is based on the ring trap\ngeometry of Murray et al. Phys. Rev. A 88 053615 2013.",
        "positive": "Collective Excitations and Nonequilibrium Phase Transition in\n  Dissipative Fermionic Superfluids: We predict a new mechanism to induce collective excitations and a\nnonequilibrium phase transition of fermionic superfluids via a sudden switch-on\nof two-body loss, for which we extend the BCS theory to fully incorporate a\nchange in particle number. We find that a sudden switch-on of dissipation\ninduces an amplitude oscillation of the superfluid order parameter accompanied\nby a chirped phase rotation as a consequence of particle loss. We demonstrate\nthat when dissipation is introduced to one of the two superfluids coupled via a\nJosephson junction, it gives rise to a nonequilibrium dynamical phase\ntransition characterized by the vanishing dc Josephson current. The\ndissipation-induced collective modes and nonequilibrium phase transition can be\nrealized with ultracold fermionic atoms subject to inelastic collisions."
    },
    {
        "anchor": "Dynamical arrest of ultracold lattice fermions: We theoretically investigate the thermodynamics of an interacting\ninhomogeneous two-component Fermi gas in an optical lattice. Motivated by a\nrecent experiment by L. Hackerm\\\"uller et al., Science, 327, 1621 (2010), we\nstudy the effect of the interplay between thermodynamics and strong\ncorrelations on the size of the fermionic cloud. We use dynamical mean-field\ntheory to compute the cloud size, which in the experiment shows an anomalous\nexpansion behavior upon increasing attractive interaction. We confirm this\nqualitative effect but, assuming adiabaticity, we find quantitative agreement\nonly for weak interactions. For strong interactions we observe significant\nnon-equilibrium effects which we attribute to a dynamical arrest of the\nparticles due to increasing correlations.",
        "positive": "Simulating bosonic Chern insulators in one-dimensional optical\n  superlattices: We study the topological properties of an extended Bose-Hubbard model with\ncyclically modulated hopping and on-site potential parameters, which can be\nrealized with ultracold bosonic atoms in a one-dimensional optical\nsuperlattice. We show that the interacting bosonic chain at half filling and in\nthe deep Mott insulating regime can simulate bosonic Chern insulators with a\ntopological phase diagram similar to that of the Haldane model of\nnoninteracting fermions. Furthermore, we explore the topological properties of\nthe ground state by calculating the many-body Chern number, the quasiparticle\nenergy spectrum with gapless edge modes, the topological pumping of the\ninteracting bosons, and the topological phase transition from normal (trivial)\nto topological Mott insulators. We also present the global phase diagram of the\nmany-body ground state, which contains a superfluid phase and two Mott\ninsulating phases with trivial (a zero Chern number) and nontrivial topologies\n(a nonzero Chern number), respectively."
    },
    {
        "anchor": "Simulating heavy fermion physics in optical lattice: Periodic Anderson\n  model with harmonic trapping potential: Periodic Anderson model (PAM), where local electron orbitals interplay with\nitinerant electronic carriers, plays an essential role in our understanding on\nheavy fermion materials. Motivated by recent proposal of simulating Kondo\nlattice model (KLM) in terms of alkaline-earth metal atoms, we make a further\nstep toward simulation of PAM, which includes crucial charge/valence\nfluctuation of local f-electron beyond purely low-energy spin fluctuation in\nKLM. To realize PAM, transition induced by suitable laser between electronic\nexcited and ground state of alkaline-earth metal atoms\n($^{1}S_{0}$$\\rightleftharpoons$$^{3}P_{0}$) is introduced, and it leads to\neffective hybridization between local electron and conduction electron in PAM.\nGenerally, the $SU(N)$ version of PAM can be realized by our proposal, which\ngives a unique opportunity to detect large-$N$ physics without complexity in\nrealistic materials. In the present work, high temperature physical feature of\nstandard ($SU(2)$) PAM with harmonic trapping potential is detailed analyzed by\nquantum Monte Carlo and dynamic mean-field theory. Indications for near-future\nexperiments are provided. We expect our theoretical proposal and (hopefully)\nforthcoming experiment will deepen our understanding on heavy fermion systems\nand at the same time triggers further studies on related Mott physics, quantum\ncriticality and non-trivial topology in both inhomogeneous and nonequilibrium\nrealm.",
        "positive": "Detecting fractional Chern insulators through circular dichroism: Great efforts are currently devoted to the engineering of topological Bloch\nbands in ultracold atomic gases. Recent achievements in this direction,\ntogether with the possibility of tuning inter-particle interactions, suggest\nthat strongly-correlated states reminiscent of fractional quantum Hall (FQH)\nliquids could soon be generated in these systems. In this experimental\nframework, where transport measurements are limited, identifying unambiguous\nsignatures of FQH-type states constitutes a challenge on its own. Here, we\ndemonstrate that the fractional nature of the quantized Hall conductance, a\nfundamental characteristic of FQH states, could be detected in ultracold gases\nthrough a circular-dichroic measurement, namely, by monitoring the energy\nabsorbed by the atomic cloud upon a circular drive. We validate this approach\nby comparing the circular-dichroic signal to the many-body Chern number, and\ndiscuss how such measurements could be performed to distinguish FQH-type states\nfrom competing states. Our scheme offers a practical tool for the detection of\ntopologically-ordered states in quantum-engineered systems, with potential\napplications in solid state."
    },
    {
        "anchor": "First-order spatial coherence measurements in a thermalized\n  two-dimensional photonic quantum gas: Phase transitions between different states of matter can profoundly modify\nthe order in physical systems, with the emergence of ferromagnetic or\ntopological order constituting important examples. Correlations allow to\nquantify the degree of order and classify different phases. Here we report\nmeasurements of first-order spatial correlations in a harmonically trapped\ntwo-dimensional photon gas below, at, and above the critical particle number\nfor Bose-Einstein condensation, using interferometric measurements of the\nemission of a dye-filled optical microcavity. For the uncondensed gas, the\ntransverse coherence decays on a length scale determined by the thermal de\nBroglie wavelength of the photons, which shows the expected scaling with\ntemperature. At the onset of Bose-Einstein condensation true long-range order\nemerges, and we observe quantum statistical effects as the thermal wave packets\noverlap. The excellent agreement with equilibrium Bose gas theory prompts\nmicrocavity photons as promising candidates for studies of critical scaling and\nuniversality in optical quantum gases.",
        "positive": "Quantum Quench in a Harmonically Trapped One-Dimensional Bose Gas: We study the non-equilibrium dynamics of a one-dimensional Bose gas trapped\nby a harmonic potential for a quench from zero to infinite interaction. The\ndifferent thermodynamic limits required for the equilibrium pre- and\npost-quench Hamiltonians are the origin of a few unexpected phenomena that have\nno counterparts in the translational invariant setting. We find that the\ndynamics is perfectly periodic with breathing time related to the strength of\nthe trapping potential. For very short times, we observe a sudden expansion\nleading to an extreme dilution of the gas and to the emergence of slowly\ndecaying tails in the density profile. The haste of the expansion induces a\nundertow effect with a pronounced local minimum of the density at the center of\nthe trap. At half period there is a refocusing phenomenon characterized by a\nsharp central peak of the density, juxtaposed to algebraically decaying tails.\nWe finally show that the time-averaged density is correctly captured by a\ngeneralized Gibbs ensemble built with the conserved mode occupations."
    },
    {
        "anchor": "Unconventional superfluidity in quasi-one-dimensional systems: We show that an unconventional superfluid triggered by spin-orbit coupling is\nrealized for repulsively interacting quasi-one-dimensional fermions. A\ncompetition between spin-singlet and -triplet pairings occurs due to the\nbreaking of inversion symmetry. We show that both superfluid correlations decay\nalgebraically with the same exponent except for special coupling constants for\nwhich a dominant superfluid is controlled by the spin-orbit coupling. We also\ndiscuss a possible experiment to observe such phases with cold atoms.",
        "positive": "Ferromagnetism in repulsive Fermi gases: upper branch of Feshbach\n  resonance versus hard spheres: We use quantum Monte Carlo, including backflow corrections, to investigate a\ntwo-component Fermi gas on the upper branch of a Feshbach resonance and\ncontrast it with the hard sphere gas. We find that, in both cases, the Fermi\nliquid becomes unstable to ferromagnetism at a $k_F a$ smaller than the mean\nfield result, where $k_F$ is the Fermi wavevector and $a$ the scattering\nlength. Even though the total energies $E(k_F a)$ are similar in the two cases,\ntheir pair correlations and kinetic energies are completely different,\nreflecting the underlying potentials. We discuss the extent to which our\ncalculations shed light on recent experiments."
    },
    {
        "anchor": "Quantum Hall states for $\u03b1= 1/3$ in optical lattices: We examine the quantum Hall (QH) states of the optical lattices with square\ngeometry using Bose-Hubbard model (BHM) in presence of artificial gauge field.\nIn particular, we focus on the QH states for the flux value of $\\alpha = 1/3$.\nFor this, we use cluster Gutzwiller mean-field (CGMF) theory with cluster sizes\nof $3\\times 2$ and $3\\times 3$. We obtain QH states at fillings $\\nu = 1/2, 1,\n3/2, 2, 5/2$ with the cluster size $3\\times 2$ and $\\nu = 1/3, 2/3, 1, 4/3,\n5/3, 2, 7/3, 8/3$ with $3\\times 3$ cluster. Our results show that the geometry\nof the QH states are sensitive to the cluster sizes. For all the values of\n$\\nu$, the competing superfluid (SF) state is the ground state and QH state is\nthe metastable state.",
        "positive": "Quench dynamics of a strongly interacting resonant Bose gas: We explore the dynamics of a Bose gas following its quench to a strongly\ninteracting regime near a Feshbach resonance. Within a self-consistent\nBogoliubov analysis we find that after the initial condensate-quasiparticle\nRabi oscillations, at long time scales the gas is characterized by a\nnonequilibrium steady-state momentum distribution function, with depletion,\ncondensate density and contact that deviate strongly from their corresponding\nequilibrium values. These are in a qualitative agreement with recent\nexperiments on Rb85 by Makotyn, et al. Our analysis also suggests that for\nsufficiently deep quenches close to the resonance the nonequilibrium state\nundergoes a phase transition to a fully depleted state, characterized by a\nvanishing condensate density."
    },
    {
        "anchor": "Fluctuation-induced potential for an impurity in a semi-infinite\n  one-dimensional Bose gas: We consider an impurity in a semi-infinite one-dimensional system of\nweakly-interacting bosons. We calculate the interaction potential for the\nimpurity due to the end of the system, i.e., the wall. For local repulsive\n(attractive) interaction between the impurity and the Bose gas, the interaction\npotential is attractive (repulsive). At short distances from the wall it decays\nexponentially crossing over into a universal $1/r^2$ behavior at separations\n$r$ above the healing length. Our results can also be interpreted as a\nCasimir-like interaction between two impurities, where one of them is\ninfinitely strongly coupled to the Bose gas. We discuss various scenarios for\nthe induced interaction between the impurities using the scattering approach.\nWe finally address the phenomenon of localization of the impurity near the\nwall. In the paper we mainly study the case of a static impurity, however the\nuniversal $1/r^2$ interaction also holds for a slowly moving impurity.",
        "positive": "Calibrating High Intensity Absorption Imaging of Ultracold Atoms: Absorption imaging of ultracold atoms is the foundation for quantitative\nextraction of information from experiments with ultracold atoms. Due to the\nlimited exposure time available in these systems, the signal-to-noise ratio is\nlargest for high intensity absorption imaging where the intensity of the\nimaging light is on the order of the saturation intensity. In this case, the\nabsolute value of the intensity of the imaging light enters as an additional\nparameter making it more sensitive to systematic errors. Here, we present a\nnovel and robust technique to determine the imaging intensity in units of the\neffective saturation intensity to better than 5%. We do this by measuring the\nmomentum transferred to the atoms by the imaging light while varying its\nintensity. We further utilize the method to quantify the purity of the\npolarization of the imaging light and to determine the correct imaging\ndetuning."
    },
    {
        "anchor": "Propagation in media as a probe for topological properties: The central goal of this thesis is to develop methods to experimentally study\ntopological phases. We do so by applying the powerful toolbox of quantum\nsimulation techniques with cold atoms in optical lattices. To this day, a\ncomplete classification of topological phases remains elusive. In this context,\nexperimental studies are key, both for studying the interplay between topology\nand complex effects and for identifying new forms of topological order. It is\ntherefore crucial to find complementary means to measure topological properties\nin order to reach a fundamental understanding of topological phases. In one\ndimensional chiral systems, we suggest a new way to construct and identify\ntopologically protected bound states, which are the smoking gun of these\nmaterials. In two dimensional Hofstadter strips (i.e: systems which are very\nshort along one dimension), we suggest a new way to measure the topological\ninvariant directly from the atomic dynamics.",
        "positive": "Quantum phases of quadrupolar Fermi gases in coupled one-dimensional\n  systems: Following the recent proposal to create quadrupolar gases [S.G. Bhongale et\nal., Phys. Rev. Lett. 110, 155301 (2013)], we investigate what quantum phases\ncan be created in these systems in one dimension. We consider a geometry of two\ncoupled one-dimensional systems, and derive the quantum phase diagram of\nultra-cold fermionic atoms interacting via quadrupole-quadrupole interaction\nwithin a Tomonaga-Luttinger-liquid framework. We map out the phase diagram as a\nfunction of the distance between the two tubes and the angle between the\ndirection of the tubes and the quadrupolar moments. The latter can be\ncontrolled by an external field. We show that there are two magic angles\n$\\theta^{c}_{B,1}$ and $\\theta^{c}_{B,2}$ between $0$ to $\\pi/2$, where the\nintratube quadrupolar interactions vanish and change signs. Adopting a\npseudo-spin language with regards to the two 1D systems, the system undergoes a\nspin-gap transition and displays a zig-zag density pattern, above\n$\\theta^{c}_{B,2}$ and below $\\theta^{c}_{B,1}$. Between the two magic angles,\nwe show that polarized triplet superfluidity and a planar spin-density wave\norder compete with each other. The latter corresponds to a bond order solid in\nhigher dimensions. We demonstrate that this order can be further stabilized by\napplying a commensurate periodic potential along the tubes."
    },
    {
        "anchor": "Universal correlations and coherence in quasi-two-dimensional trapped\n  Bose gases: We study the quasi-two-dimensional Bose gas in harmonic traps at temperatures\nabove the Kosterlitz-Thouless transition, where the gas is in the normal phase.\nWe show that mean-field theory takes into account the dominant interaction\neffects for experimentally relevant trap geometries. Comparing with Quantum\nMonte Carlo calculations, we quantify the onset of the fluctuation regime,\nwhere correlations beyond mean-field become important. Although the density\nprofile depends on the microscopic parameters of the system, we show that the\ncorrelation density (the difference between the exact and the mean-field\ndensity) is accurately described by a universal expression, obtained from\nclassical-field calculations of the homogeneous strictly two-dimensional gas.\nDeviations from universality, due to the finite value of the interaction or to\nthe trap geometry, are shown to be small for current experiments. We further\nstudy coherence and pair correlations on a microscopic scale. Finite-size\neffects in the off-diagonal density matrix allows us to characterize the\ncross-over from Kosterlitz-Thouless to Bose-Einstein behavior for small\nparticle numbers. Bose-Einstein condensation occurs below a characteristic\nnumber of particles which rapidly diverges with vanishing interactions.",
        "positive": "Critical temperature and superfluid gap of the Unitary Fermi Gas from\n  Functional Renormalization: We investigate the superfluid transition of the Unitary Fermi Gas by means of\nthe Functional Renormalization Group, aiming at quantitative precision. We\nextract $T_{\\rm c}/\\mu=0.38(2)$ and $\\Delta/\\mu=1.04(15)$ for the critical\ntemperature and the superfluid gap at zero temperature, respectively, within a\nsystematic improvement of the truncation for the effective average action. The\nkey new ingredient in comparison to previous approaches consists in the use of\nregulators which cut off both frequencies and momenta. We incorporate\nrenormalization effects on both the bosonic and the fermionic propagator,\ninclude higher order bosonic scattering processes, and investigate the\nregulator and specification parameter dependence for an error estimate. The\nratio $\\Delta/T_{\\rm c}=2.7(3)$ becomes less sensitive to the relative cutoff\nscale of bosons and fermions when improving the truncation. The techniques\ndeveloped in this work are easily carried over to the cases of finite\nscattering length, lower dimensionality, and spin-imbalance."
    },
    {
        "anchor": "Ground-state properties of spin-orbit-coupled dipolar Bose-Einstein\n  condensates with in-plane gradient magnetic field: We investigate the ground-state properties of spin-orbit-coupled\npseudo-spin-1/2 dipolar Bose-Einstein condensates (BECs) in a two-dimensional\nharmonic trap and an in-plane quadrupole field. The effects of spin-orbit\ncoupling (SOC), dipole-dipole interaction (DDI) and the in-plane quadrupole\nfield on the ground-state structures and spin textures of the system are\nsystematically analyzed and discussed. For fixed SOC and DDI strengths, the\nsystem shows a quadrupole stripe phase with a half-quantum vortex, or a\nquadrupole Thomas-Fermi phase with a half-quantum antivortex for small\nquadrupole field strength, depending on the ratio between inter- and\nintraspecies interaction. As the quadrupole field strength enhances, the system\nrealizes a ring mixed phase with a hidden vortex-antivortex cluster rather than\nan ordinary giant vortex in each component. Of particular interest, when the\nstrengths of DDI and quadrupole field are fixed, strong SOC leads to the\nformation of criss-crossed vortex string structure. For given SOC and\nquadrupole field, the system for strong DDI displays a sandwich-like structure,\nor a special delaminated structure with a prolate antivortex in the spin-up\ncomponent. In addition, typical spin textures for the ground states of the\nsystem are analyzed. It is shown that the system sustains exotic topological\nstructures, such as a hyperbolic spin domain wall,\nskyrmion-half-antiskyrmion-antiskyrmion lattice,\nhalf-skyrmion-skyrmion-half-antiskyrmion lattice, and a drum-shaped antimeron.",
        "positive": "Fine structure of the stripe phase in ring-shaped Bose-Einstein\n  condensates with spin-orbital-angular-momentum coupling: We report on a theoretical study of a ring-shaped Bose-Einstein condensate\nwith Raman-induced spin-orbital-angular-momentum coupling. We analyze the\nstructure of the ground-state of the system depending different physical\nparameters and reveal a peculiar fine structure within the stripe phase on the\nphase diagram. We demonstrate the existence of the predicted stripe sub-phases\nwithin a wide range of physical parameters, their traceability through physical\nobservables, and compare the results with several commonly used variational\napproximations. We also show that predicted sub-phases of the stripe phase can\nbe observed within experimentally realizable conditions."
    },
    {
        "anchor": "Site-resolved imaging of single atoms with a Faraday quantum gas\n  microscope: We successfully demonstrate a quantum gas microscopy using the Faraday effect\nwhich has an inherently non-destructive nature. The observed Faraday rotation\nangle reaches 3.0(2) degrees for a single atom. We reveal the non-destructive\nfeature of this Faraday imaging method by comparing the detuning dependence of\nthe Faraday signal strength with that of the photon scattering rate. We\ndetermine the atom distribution with deconvolution analysis. We also\ndemonstrate the absorption and the dark field Faraday imaging, and reveal the\ndifferent shapes of the point spread functions for these methods, which are\nfully explained by theoretical analysis. Our result is an important first step\ntowards an ultimate quantum non-demolition site-resolved imaging and\nfurthermore opens up the possibilities for quantum feedback control of a\nquantum many-body system with a single-site resolution.",
        "positive": "Tying Quantum Knots: Knots are familiar entities that appear at a captivating nexus of art,\ntechnology, mathematics, and science. As topologically stable objects within\nfield theories, they have been speculatively proposed as explanations for\ndiverse persistent phenomena, from atoms and molecules to ball lightning and\ncosmic textures in the universe. Recent experiments have observed knots in a\nvariety of classical contexts, including nematic liquid crystals, DNA, optical\nbeams, and water. However, no experimental observations of knots have yet been\nreported in quantum matter. We demonstrate here the controlled creation and\ndetection of knot solitons in the order parameter of a spinor Bose-Einstein\ncondensate. The experimentally obtained images of the superfluid directly\nreveal the circular shape of the soliton core and its accompanying linked\nrings. Importantly, the observed texture corresponds to a topologically\nnon-trivial element of the third homotopy group and demonstrates the celebrated\nHopf fibration, which unites many seemingly unrelated physical contexts. Our\nobservations of the knot soliton establish an experimental foundation for\nfuture studies of their stability and dynamics within quantum systems."
    },
    {
        "anchor": "Two-dimensional spectroscopy of Rydberg gases: Two-dimensional (2D) spectroscopy uses multiple electromagnetic pulses to\ninfer the properties of a complex system. A paradigmatic class of target\nsystems are molecular aggregates, for which one can obtain information on the\neigenstates, various types of static and dynamic disorder and on relaxation\nprocesses. However, two-dimensional spectra can be difficult to interpret\nwithout precise knowledge of how the signal components relate to microscopic\nHamiltonian parameters and system-bath interactions. Here we show that\ntwo-dimensional spectroscopy can be mapped in the microwave domain to highly\ncontrollable Rydberg quantum simulators. By porting 2D spectroscopy to Rydberg\natoms, we firstly open the possibility of its experimental quantum simulation,\nin a case where parameters and interactions are very well known. Secondly, the\ntechnique may provide additional handles for experimental access to coherences\nbetween system states and the ability to discriminate different types of\ndecoherence mechanisms in Rydberg gases. We investigate the requirements for a\nspecific implementation utilizing multiple phase coherent microwave pulses and\na phase cycling technique to isolate signal components.",
        "positive": "Specialising Neural-network Quantum States for the Bose Hubbard Model: Projected variational wavefunctions such as the Gutzwiller, many-body\ncorrelator and Jastrow ansatzes have provided crucial insight into the nature\nof superfluid-Mott insulator transition in the Bose Hubbard model (BHM) in two\nor more spatial dimensions. However, these ansatzes have no obvious tractable\nand systematic way of being improved. A promising alternative is to use\nNeural-network quantum states (NQS) based on Restricted Boltzmann Machines\n(RBMs). With binary visible and hidden units NQS have proven to be a highly\neffective at describing quantum states of interacting spin-1/2 lattice systems.\nThe application of NQS to bosonic systems has so far been based on one-hot\nencoding from machine learning where the multi-valued site occupation is\ndistributed across several binary-valued visible units of an RBM. Compared to\nspin-1/2 systems one-hot encoding greatly increases the number of variational\nparameters whilst also making their physical interpretation opaque. Here we\nrevisit the construction of NQS for bosonic systems by reformulating a one-hot\nencoded RBM into a correlation operator applied to a reference state, analogous\nto the structure of the projected variational ansatzes. In this form we then\npropose a number of specialisations of the RBM motivated by the physics of the\nBHM and the ability to capture exactly the projected variational ansatzes. We\nanalyse in detail the variational performance of these new RBM variants for a\n10 x 10 BHM, using both a standard Bose condensate state and a pre-optimised\nJastrow + many-body correlator state as the reference state of the calculation.\nSeveral of our new ansatzes give robust results as nearly good as one-hot\nencoding across the regimes of the BHM, but at a substantially reduced cost.\nSuch specialised NQS are thus primed tackle bosonic lattice problems beyond the\naccuracy of classic variational wavefunctions."
    },
    {
        "anchor": "Finite-temperature equation of state of polarized fermions at unitarity: We study in a nonperturbative fashion the thermodynamics of a unitary Fermi\ngas over a wide range of temperatures and spin polarizations. To this end, we\nuse the complex Langevin method, a first principles approach for strongly\ncoupled systems. Specifically, we show results for the density equation of\nstate, the magnetization, and the magnetic susceptibility. At zero\npolarization, our results agree well with state-of-the art results for the\ndensity equation of state and with experimental data. At finite polarization\nand low fugacity, our results are in excellent agreement with the third-order\nvirial expansion. In the fully quantum mechanical regime close to the balanced\nlimit, the critical temperature for superfluidity appears to depend only weakly\non the spin polarization.",
        "positive": "Topological Fulde-Ferrel-Larkin-Ovchinnikov states in Spin-orbit Coupled\n  Fermi Gases: Pairing in an attractively interacting two-component Fermi gas in the absence\nof the inversion symmetry and/or the time-reversal symmetry may give rise to\nexotic superfluid states. Notable examples range from the\nFulde-Ferrell-Larkin-Ovchinnikov (FFLO) state with a finite center-of-mass\nmomentum in a polarized Fermi gas, to the topological superfluid state in a\ntwo-dimensional Fermi gas under Rashba spin-orbit coupling and an out-of-plane\nZeeman field. Here, we show that a topological FFLO state can be stabilized in\na two-dimensional Fermi gas with Rashba spin-orbit coupling and both in-plane\nand out-of-plane Zeeman fields. We characterize the topological FFLO state by a\nnon-trivial Berry phase, and demonstrate the stability region of the state on\nthe zero-temperature phase diagram. Given its unique properties in both the\nquasi-particle dispersion spectra and the momentum distribution, signatures of\nthe topological FFLO state can be detected using existing experimental\ntechniques."
    },
    {
        "anchor": "Landau quantization effects in ultracold atom-ion collisions: We study ultracold atom-ion collisions in the presence of an external\nmagnetic field. At low collision energy the field can drastically modify the\ntranslational motion of the ion, which follows quantized cyclotron orbits. We\npresent a rigorous theoretical approach for the calculation of quantum\nscattering amplitudes in these conditions. Collisions in different magnetic\nfield regimes, identified by the size of the cyclotron radius with respect to\nthe range of the interaction potential, are investigated. Our results are\nimportant in cases where use of a magnetic field to control the atom-ion\ncollision dynamics is envisioned.",
        "positive": "Universality and itinerant ferromagnetism in rotating strongly\n  interacting Fermi gases: We analytically determine the properties of three interacting fermions in a\nharmonic trap subject to an external rotation. Thermodynamic quantities such as\nthe entropy and energy are calculated from the third order quantum virial\nexpansion. By parameterizing the solutions in the rotating frame we find that\nthe energy and entropy are universal for all rotations in the strongly\ninteracting regime. Additionally, we find that rotation suppresses the onset of\nitinerant ferromagnetism in strongly interacting repulsive three-body systems."
    },
    {
        "anchor": "Interaction Spectroscopy of a Two-component Mott Insulator: We prepare and study a two-component Mott insulator of bosonic atoms with two\nparticles per site. The mapping of this system to a magnetic spin model, and\nthe subsequent study of its quantum phases, require a detailed knowledge of the\ninteraction strengths of the two components. In this work, we use radio\nfrequency (RF) transitions and an on-site interaction blockade for precise,\nempirical determination of the interaction strengths of different combinations\nof hyperfine states on a single lattice site. We create a map of the\ninteractions of the lowest two hyperfine states of $^7$Li as a function of\nmagnetic field, including measurements of several Feshbach resonances with\nunprecedented sensitivity, and we identify promising regions for the\nrealization of magnetic spin models.",
        "positive": "Stability and collapse of localized solutions of the controlled\n  three-dimensional Gross-Pitaevskii equation: On the basis of recent investigations, a newly developed analytical procedure\nis used for constructing a wide class of localized solutions of the controlled\nthree-dimensional (3D) Gross-Pitaevskii equation (GPE) that governs the\ndynamics of Bose-Einstein condensates (BECs). The controlled 3D GPE is\ndecomposed into a two-dimensional (2D) linear Schr\\\"{o}dinger equation and a\none-dimensional (1D) nonlinear Schr\\\"{o}dinger equation, constrained by a\nvariational condition for the controlling potential. Then, the above class of\nlocalized solutions are constructed as the product of the solutions of the\ntransverse and longitudinal equations. On the basis of these exact 3D\nanalytical solutions, a stability analysis is carried out, focusing our\nattention on the physical conditions for having collapsing or non-collapsing\nsolutions."
    },
    {
        "anchor": "Longitudinal and transversal resonant tunneling of interacting bosons in\n  a two-dimensional Josephson junction: Mean-field and many-body dynamics: We unravel the out-of-equilibrium quantum dynamics of a few interacting\nbosonic clouds in a two-dimensional asymmetric double-well potential at the\nresonant tunneling scenario. At the single-particle level of resonant\ntunneling, particles tunnel under the barrier from, typically, the ground-state\nin the left well to an excited state in the right well, i.e., states of\ndifferent shapes and properties are coupled when their one-particle energies\ncoincide. In two spatial dimensions, two types of resonant tunneling processes\nare possible, to which we refer to as longitudinal and transversal resonant\ntunneling. Longitudinal resonant tunneling implies that the state in the right\nwell is longitudinally-excited with respect to the state in the left well,\nwhereas transversal resonant tunneling implies that the former is\ntransversely-excited with respect to the latter. We show that interaction\nbetween bosons makes resonant tunneling phenomena in two spatial dimensions\nprofoundly rich, and analyze these phenomena in terms of the loss of coherence\nof the junction and development of fragmentation, and coupling between\ntransverse and longitudinal degrees-of-freedom and excitations. To this end, a\ndetailed analysis of the tunneling dynamics is performed by exploring the time\nevolution of a few physical quantities, namely, the survival probability,\noccupation numbers of the reduced one-particle density matrix, and the\nmany-particle position, momentum, and angular-momentum variances. In general,\nwe display the impact of the transversal and longitudinal degrees-of-freedom in\nthe many-boson tunneling dynamics at the resonant tunneling scenarios.",
        "positive": "A two-state model for vortex nucleation in a rotating Bose-Einstein\n  condensate: It is well-known that a rotating Bose-Einstein condensate forms vortices to\ncarry the angular momentum. For a first vortex to nucleate at the trap center,\nthe rotational frequency must become larger than a certain critical value. The\nvortex nucleation process, however, is sensitive to the trap shape. It was\nshown earlier that for a symmetry-breaking potential that preserves parity, at\ncriticality the leading natural orbitals may become degenerate, giving rise to\na maximally entangled quantum state, found from exact solutions for just a few\nbosons. Developing an effective two-state model, we here show that in the limit\nof large particle numbers, the many-body ground state becomes either a\nso-called twin-like or a Schr\\\"odinger cat-like state. We corroborate this\nfinding by a direct comparison to the exact numerical solution of the problem,\nfeasible for moderate particle numbers within the lowest Landau level\napproximation. We show that the nature of the quantum state at criticality can\nbe controlled by both the quadrupolar deformation and the flatness of the\nconfining potential."
    },
    {
        "anchor": "Multi-Regulator Functional Renormalization Group for Many-Fermion\n  Systems: We propose a method of multi-regulator functional renormalization group\n(MR-FRG) which is a novel formulation of functional renormalization group with\nmultiple infrared regulators. It is applied to a two-component fermionic system\nwith an attractive contact interaction to study crossover phenomena between the\nBardeen-Cooper-Schrieffer (BCS) phase and the Bose-Einstein condensation (BEC)\nphase. To control both the fermionic one-particle excitations and the bosonic\ncollective excitations,IR regulators are introduced, one for the fermionic\ntwo-point function and another for the four-fermion vertex. It is shown that\nthe Nozi\\`eres-Schmitt-Rink (NSR) theory, which is successful to capture\nqualitative features of the BCS-BEC crossover, can be derived from MR-FRG. Some\naspects of MR-FRG to go beyond the NSR theory are also discussed.",
        "positive": "Observing the Drop of Resistance in the Flow of a Superfluid Fermi Gas: In this work, we investigate the conduction properties of strongly\ninteracting fermions flowing through a quasi two-dimensional, multimode\nchannel, which connects two atomic reservoirs. The atomic current in the\nchannel is controlled using a repulsive potential created by an off-resonant\nlaser beam. In analogy with an electronic field-effect transistor, this gate\npotential controls the chemical potential in the channel while keeping the\ntemperature imposed by the reservoirs unchanged. With the gate potential as a\ncontrol parameter, we measure the current through the channel over a large\ndynamic range and determine the density distribution in the channel region.\nThis allows us to observe the onset of superfluid flow of strongly interacting\nfermions. These measurements are compared to the case of a weakly interacting\nFermi gas."
    },
    {
        "anchor": "Effect of short-range interaction for collision of ultracold dipoles: We consider the low-energy scattering of two ultracold polarized dipoles with\nboth a short-range interaction (SRI) and a weak dipole-dipole interaction (DDI)\nwhich is far away from shape-resonances. In previous analytical studies, the\nscattering amplitude in this system was often calculated via the first-order\nBorn approximation (FBA). Our results show that significant derivations from\nthis approximation can arise in some cases. In these cases, the SRI can\nsignificantly modify the inter-dipole scattering amplitudes even if the\nscattering amplitudes for the SRI alone are much smaller than the dipolar\nlength of the DDI. We further obtain approximate analytical expressions for\nthese inter-dipole scattering amplitudes.",
        "positive": "Correlations and Pair Formation in a Repulsively Interacting Fermi Gas: A degenerate Fermi gas is rapidly quenched into the regime of strong\neffective repulsion near a Feshbach resonance. The spin fluctuations are\nmonitored using speckle imaging and, contrary to several theoretical\npredictions, the samples remain in the paramagnetic phase for arbitrarily large\nscattering length. Over a wide range of interaction strengths a rapid decay\ninto bound pairs is observed over times on the order of 10\\hbar/E_F, preventing\nthe study of equilibrium phases of strongly repulsive fermions. Our work\nsuggests that a Fermi gas with strong short-range repulsive interactions does\nnot undergo a ferromagnetic phase transition."
    },
    {
        "anchor": "On the Efimov Effect in Higher Partial Waves: Using the framework of effective field theory, we present a detailed study of\nthe Efimov effect in higher partial waves for systems of two identical\nparticles and a third distinguishable particle. Depending on the total angular\nmomentum $L$, the two identical particles must be bosons or fermions. We derive\nanalytical expressions for the elastic and inelastic atom-dimer scattering\ncross sections as well as the atom-dimer relaxation rate at the dimer breakup\nthreshold. For the experimentally most relevant case of P-waves, we numerically\ncalculate the atom-dimer scattering cross sections and relaxation rates as a\nfunction of the scattering length, three-body parameter, and mass ratio for\nenergies away from the breakup threshold.",
        "positive": "Effective Scaling Approach to Frictionless Quantum Quenches in Trapped\n  Bose Gases: We work out the effective scaling approach to frictionless quantum quenches\nin a one-dimensional Bose gas trapped in a harmonic trap. The effective scaling\napproach produces an auxiliary equation for the scaling parameter interpolating\nbetween the noninteracting and the Thomas-Fermi limits. This allows us to\nimplement a frictionless quench by engineering inversely the smooth trap\nfrequency, as compared to the two-jump trajectory. Our result is beneficial to\ndesign the shortcut-to-adiabaticity expansion of trapped Bose gases for\narbitrary values of interaction, and can be directly extended to the\nthree-dimensional case."
    },
    {
        "anchor": "Dissipative preparation of a Floquet topological insulator in an optical\n  lattice via bath engineering: Floquet engineering is an important tool for realizing topologically\nnontrivial band structures for charge-neutral atoms in optical lattices.\nHowever, the preparation of a topological-band-insulator-type state of\nfermions, with one nontrivial quasi-energy band filled completely and the\nothers empty, is challenging as a result of both driving induced heating as\nwell as imperfect adiabatic state preparation (with the latter induced by the\nunavoidable gap closing when passing the topological transition). An\nalternative procedure that has been proposed is to prepare such states\ndissipatively, i.e. as a steady state that emerges when coupling the system to\nreservoirs. Here we discuss a concrete scheme that couples the system to a\nweakly interacting Bose-condensate given by second atomic species acting as a\nheat bath. Our strategy relies on the engineering of the potential for the bath\nparticles, so that they occupy weakly coupled tubes perpendicular to the\ntwo-dimensional system. Using Floquet-Born-Markov theory, we show that the\nresulting nonequilibrium steady state of the driven-dissipative system\napproximates a topological insulator. We even find indications for the\napproximate stabilization of an anomalous Floquet topological insulator, a\nstate that is impossible to realize in equilibrium.",
        "positive": "Superfluidity from correlations in driven boson systems: We investigate theoretically the superfluidity of a one-dimensional boson\nsystem whose hopping energy is periodically modulated with a zero time average,\nwhich results in the suppression of first-order single-particle hopping\nprocesses. The dynamics of this flat band system is entirely driven by\ncorrelations and described by exotic Hamiltonian and current operators. We\nemploy exact diagonalization and compare our results with those of the\nconventional, undriven Bose-Hubbard system. We focus on the two main\nmanifestations of superfluidity, the Hess-Fairbank effect and the metastability\nof supercurrents, with explicit inclusion of an impurity when relevant. Among\nthe novel superfluid features, we highlight the presence of a cat-like ground\nstate, with branches that have opposite crystal momentum but carry the same\nflux-dependent current, and the essential role of the interference between the\ncollective components of the ground-state wave function. Calculation of the\ndynamic form factor reveals the presence of an acoustic mode that guarantees\nsuperfluidity in the thermodynamic limit."
    },
    {
        "anchor": "Superfluid Field response to Edge dislocation motion: We study the dynamic response of a superfluid field to a moving edge\ndislocation line to which the field is minimally coupled. We use a dissipative\nGross-Pitaevskii equation, and determine the initial conditions by solving the\nequilibrium version of the model. We consider the subsequent time evolution of\nthe field for both glide and climb dislocation motion and analyze the results\nfor a range of values of the constant speed $V_D$ of the moving dislocation. We\nfind that the type of motion of the dislocation line is very important in\ndetermining the time evolution of the superfluid field distribution associated\nwith it. Climb motion of the dislocation line induces increasing asymmetry, as\nfunction of time, in the field profile, with part of the probability being, as\nit were, left behind. On the other hand, glide motion has no effect on the\nsymmetry properties of the superfluid field distribution. Damping of the\nsuperfluid field due to excitations associated with the moving dislocation line\noccurs in both cases.",
        "positive": "Different growth rates for spin and superfluid order in a quenched\n  spinor condensate: In this paper we study the coarsening dynamics of a spinor condensate\nquenched into an easy-axis ferromagnetic phase by a sudden change in the\nquadratic Zeeman energy. We show that applying a spin rotation prior to\nchanging the Zeeman energy accelerates the development of local order and\nreduces heating. We examine the longitudinal spin ordering and the superfluid\nordering of the system and show that the respective order parameter correlation\nfunctions exhibit dynamic scaling in the late time dynamics. Our results also\ndemonstrate that these two types of order grow at different rates, i.e.~with\ndifferent dynamic critical exponents. The spin domain area distribution is\ncalculated and is shown to have power law scaling behavior expected from\npercolation theory."
    },
    {
        "anchor": "Many-body entropies, correlations, and emergence of statistical\n  relaxation in interaction quench dynamics of ultracold bosons: We study the quantum many-body dynamics and the entropy production triggered\nby an interaction quench in a system of $N=10$ interacting identical bosons in\nan external one-dimensional harmonic trap. The multiconfigurational\ntime-dependent Hartree method for bosons (MCTDHB) is used for solving the\ntime-dependent Schr\\\"odinger equation at a high level of accuracy. We consider\nmany-body entropy measures such as the Shannon information entropy, number of\nprincipal components, and occupation entropy that are computed from the\ntime-dependent many-body basis set used in MCTDHB. These measures quantify\nrelevant physical features such as irregular or chaotic dynamics, statistical\nrelaxation and thermalization. We monitor the entropy measures as a function of\ntime and assess how they depend on the interaction strength. For larger\ninteraction strength, the many-body information entropy approaches the value\npredicted for the Gaussian orthogonal ensemble of random matrices and implies\nstatistical relaxation. The basis states of MCTDHB are explicitly\ntime-dependent and optimized by the variational principle in a way that\nminimizes the number of significantly contributing ones. It is therefore a\nnon-trivial fact that statistical relaxation prevails in MCTDHB computations.\nMoreover, we demonstrate a fundamental connection between the production of\nentropy, the build-up of correlations and loss of coherence in the system.\nSince the coherence and correlations are experimentally accessible, their\npresent connection to many-body entropies can be scrutinized to detect\nstatistical relaxation. Our results are the first ones obtained for\nthermalization of finite quantum systems using an optimized time-dependent and\ngenuinely many-body basis set.",
        "positive": "Adiabatic state preparation of stripe phases with strongly magnetic\n  atoms: We propose a protocol for realizing the stripe phase in two spin models on a\ntwo-dimensional square lattice, which can be implemented with strongly magnetic\natoms (Cr, Dy, Er, etc.) in optical lattices by encoding spin states into\nZeeman sublevels of the ground state manifold. The protocol is tested with\ncluster-mean-field time-dependent variational ans\\\"atze, validated by\ncomparison with exact results for small systems, which enable us to simulate\nthe dynamics of systems with up to 64 sites during the state-preparation\nprotocol. This allows, in particular, to estimate the time required for\npreparation of the stripe phase with high fidelity under real experimental\nconditions."
    },
    {
        "anchor": "Phase Equilibrium of Binary Mixtures in Mixed Dimensions: We study the stability of a Bose-Fermi system loaded into an array of coupled\none-dimensional (1D) \"tubes\", where bosons and fermions experience different\ndimensions: Bosons are heavy and strongly localized in the 1D tubes, whereas\nfermions are light and can hop between the tubes. Using the 174Yb-6Li system as\na reference, we obtain the equilibrium phase diagram. We find that, for both\nattractive and repulsive interspecies interaction, the exact treatment of 1D\nbosons via the Bethe ansatz implies that the transitions between pure fermion\nand any phase with a finite density of bosons can only be first order and never\ncontinuous, resulting in phase separation in density space. In contrast, the\norder of the transition between the pure boson and the mixed phase can either\nbe second or first order depending on whether fermions are allowed to hop\nbetween the tubes or they also are strictly confined in 1D. We discuss the\nimplications of our findings for current experiments on 174Yb-6Li mixtures as\nwell as Fermi-Fermi mixtures of light and heavy atoms in a mixed dimensional\noptical lattice system.",
        "positive": "Field-linked resonances of polar molecules: Scattering resonances are an essential tool for controlling interactions of\nultracold atoms and molecules. However, conventional Feshbach scattering\nresonances, which have been extensively studied in various platforms, are not\nexpected to exist in most ultracold polar molecules due to the fast loss that\noccurs when two molecules approach at a close distance. Here, we demonstrate a\nnew type of scattering resonances that is universal for a wide range of polar\nmolecules. The so-called field-linked resonances occur in the scattering of\nmicrowave-dressed molecules due to stable macroscopic tetramer states in the\nintermolecular potential. We identify two resonances between ultracold\nground-state sodium-potassium molecules and use the microwave frequencies and\npolarizations to tune the inelastic collision rate by three orders of\nmagnitude, from the unitary limit to well below the universal regime. The\nfield-linked resonance provides a tuning knob to independently control the\nelastic contact interaction and the dipole-dipole interaction, which we observe\nas a modification in the thermalization rate. Our result provides a general\nstrategy for resonant scattering between ultracold polar molecules, which paves\nthe way for realizing dipolar superfluids and molecular supersolids as well as\nassembling ultracold polyatomic molecules."
    },
    {
        "anchor": "Light-induced atomic desorption in a compact system for ultracold atoms: In recent years, light-induced atomic desorption (LIAD) of alkali atoms from\nthe inner surface of a vacuum chamber has been employed in cold atom\nexperiments for the purpose of modulating the alkali background vapour. This is\nbeneficial because larger trapped atom samples can be loaded from vapour at\nhigher pressure, after which the pressure is reduced to increase the lifetime\nof the sample. We present an analysis, based on the case of rubidium atoms\nadsorbed on pyrex, of various aspects of LIAD that are useful for this\napplication. Firstly, we study the intensity dependence of LIAD by fitting the\nexperimental data with a rate-equation model, from which we extract a correct\nprediction for the increase in trapped atom number. Following this, we quantify\na figure of merit for the utility of LIAD in cold atom experiments and we show\nhow it can be optimised for realistic experimental parameters.",
        "positive": "Rotating Bose-Einstein condensates with a finite number of atoms\n  confined in a ring potential: Spontaneous symmetry breaking, beyond the\n  mean-field approximation: Motivated by recent experiments on Bose-Einstein condensed atoms which rotate\nin annular/toroidal traps we study the effect of the finiteness of the atom\nnumber $N$ on the states of lowest energy for a fixed expectation value of the\nangular momentum, under periodic boundary conditions. To attack this problem,\nwe develop a general strategy, considering a linear superposition of the\neigenstates of the many-body Hamiltonian, with amplitudes that we extract from\nthe mean field approximation. This many-body state breaks the symmetry of the\nHamiltonian, it has the same energy to leading order in $N$ as the mean-field\nstate and the corresponding eigenstate of the Hamiltonian, however it has a\nlower energy to subleading order in $N$ and thus it is energetically favorable."
    },
    {
        "anchor": "Quasi-Particle Theory for the Higgs Amplitude Mode: We present a generalized quasi-particle theory for bosonic lattice systems,\nwhich naturally contains all relevant collective modes, including the Higgs\namplitude in the strongly correlated superfluid. In contrast to Bogoliubov\ntheory, this non-perturbative method does not rely on a small condensate\ndepletion and is valid for any interaction strength in three spatial\ndimensions. It is based on an expansion around the bosonic Gutzwiller ground\nstate in terms of appropriately chosen fluctuation operators and lays the\nfoundation for the description of real-time dynamics in terms of the natural,\nweakly interacting quasi-particles. Furthermore, it provides a systematic\nframework for efficiently calculating observables beyond the Gutzwiller\napproximation and for including external perturbations, as well as higher order\ndecay and interactions in terms of quasi-particle operators. It allows for the\nconstruction of an alternative path integral approach in terms of\nquasi-particle coherent states.",
        "positive": "Superfluid Mutual-friction Coefficients from Vortex Dynamics in the\n  Two-dimensional Galerkin-truncated Gross-Pitaevskii Equation: We present algorithms for the ab-initio determination of the temperature\n($T$) dependence of the mutual-friction coefficients $\\alpha$ and $\\alpha'$ and\nthe normal-fluid density $\\rho_{\\rm n}$ in the two-dimensional (2D)\nGalerkin-truncated Gross-Pitaevskii system. Our algorithms enable us to\ndetermine $\\alpha(T)$, even though fluctuations in 2D are considerably larger\nthan they are in 3D. We also examine the implications of our measurements of\n$\\alpha'(T)$ for the Iordanskii force, whose existence is often questioned."
    },
    {
        "anchor": "Fate of the Mollow triplet in strongly-coupled atomic arrays: Subwavelength arrays of quantum emitters have emerged as an interesting\nplatform displaying prominent collective effects. Here we study such arrays\nunder coherent driving, realizing an open quantum many-body problem in a\nstrongly non-linear regime. We show that the combination of dipolar\ninteractions and regular geometry have a dramatic effect on the spectrum of\nemitted light: the famous Mollow triplet characterizing the emission of a\nsingle atom develops a structured broadening with flat sidebands, with a\nbandwidth determined by the dipolar interactions. This emission spectrum\ncharacterizes atomic arrays and distinguishes them from disordered ensembles as\nwell as non-interacting emitters. Our predictions are based on a novel\ndynamical mean-field theory (DMFT) approach to the problem, paving the way for\nfurther studies of these systems.",
        "positive": "Probing the Excitations of a Lieb-Liniger Gas from Weak to Strong\n  Coupling: We probe the excitation spectrum of an ultracold one-dimensional Bose gas of\nCesium atoms with repulsive contact interaction that we tune from the weakly to\nthe strongly interacting regime via a magnetic Feshbach resonance. The\ndynamical structure factor, experimentally obtained using Bragg spectroscopy,\nis compared to integrability-based calculations valid at arbitrary interactions\nand finite temperatures. Our results unequivocally underly the fact that\nhole-like excitations, which have no counterpart in higher dimensions, actively\nshape the dynamical response of the gas."
    },
    {
        "anchor": "Creation of excitations from a uniform impurity motion in the condensate: We investigate a phenomenon of creation of excitations in the homogenous\nBose-Einstein condensate due to an impurity moving with a constant velocity. A\nsimple model is considered to take into account dynamical effects due to\nmotions of the impurity. Based on this model, we show that there can be a\nfinite amount of excitations created even if velocity of the impurity is below\nLandau's critical velocity. We also show that the total number of excitations\nscales differently for large time across the speed of sound. Thus, our result\ndictates the critical behavior across Landau's one and validates Landau's\ninstitution to the problem. We discuss how Landau's critical velocity emerges\nand its validity within our model.",
        "positive": "Bose-Einstein condensation of photons: We review recent work on the Bose-Einstein condensation of photons in a dye\nmicrocavity environment. Other than for material particles, as e.g. cold atomic\nBose gases, photons usually do not condense at low temperatures. For Planck's\nblackbody radiation, the most ubiquitous Bose gas, photon number and\ntemperature are not independently tunable and at low temperatures the photons\nsimply disappear in the system's walls, instead of massively occupying the\ncavity ground mode. In the here described approach, this obstacle is overcome\nby a fluorescence-induced thermalization mechanism in a dye-filled microcavity.\nExperimentally, both the thermalization of the photon gas and, at high photon\ndensities, Bose-Einstein condensation has been observed. This article describes\nthe thermalization mechanism of the photon gas in detail and summarizes so far\nperformed experimental work."
    },
    {
        "anchor": "Hanbury Brown and Twiss correlations across the Bose-Einstein\n  condensation threshold: Hanbury Brown and Twiss (HBT) correlations, i.e. correlations in far-field\nintensity fluctuations, yield fundamental information on the quantum statistics\nof light sources, as highlighted after the discovery of photon bunching.\nDrawing on the analogy between photons and atoms, similar measurements have\nbeen performed for matter-wave sources, probing density fluctuations of\nexpanding ultracold Bose gases. Here we use two-point density correlations to\nstudy how coherence is gradually established when crossing the Bose-Einstein\ncondensation (BEC) threshold. Our experiments reveal a persistent multimode\ncharacter of the emerging matter-wave as seen in the non-trivial spatial shape\nof the correlation functions for all probed source geometries from nearly\nisotropic to quasi-one-dimensional (quasi-1D), and for all probed temperatures.\nThe qualitative features of our observations are captured by ideal Bose gas\ntheory, the quantitative differences illustrate the role of particle\ninteractions.",
        "positive": "Bose-Hubbard realization of fracton defects: Bose-Hubbard models are simple paradigmatic lattice models used to study\ndynamics and phases of quantum bosonic matter. We combine the extended\nBose-Hubbard model in the hard-core regime with ring-exchange hoppings. By\ninvestigating the symmetries and low-energy properties of the Hamiltonian we\nargue that the model hosts fractonic defect excitations. We back up our claims\nwith exact numerical simulations of defect dynamics exhibiting mobility\nconstraints. Moreover, we confirm the robustness of our results against fracton\nsymmetry breaking perturbations. Finally we argue that this model can be\nexperimentally realized in recently proposed quantum simulator platforms with\nbig time crystals, thus paving a way for the controlled study of many-body\ndynamics with mobility constraints."
    },
    {
        "anchor": "Quantum simulating the electron transport in quantum cascade laser\n  structures: We propose to use ultracold fermionic atoms in one-dimensional optical\nlattices to quantum simulate the electronic transport in quantum cascade laser\n(QCL) structures. The competition between the coherent tunneling among (and\nwithin) the wells and the dissipative decay at the basis of lasing is\ndiscussed. In order to validate the proposed simulation scheme, we\nquantitatively address such competition in a simplified one-dimensional model.\nWe show the existence of optimal relationships between the model parameters,\nmaximizing the particle current, the population inversion (or their product),\nand the stimulated emission rate. This substantiates the concept of emulating\nthe QCL operation mechanisms in cold-atom optical lattice simulators, laying\nthe groundwork for addressing open questions, such as the impact of\nelectron-electron scattering and the origin of transport-induced noise, in the\ndesign of new-generation QCLs.",
        "positive": "Dynamical topological invariants and reduced rate functions for\n  dynamical quantum phase transitions in two dimensions: We show that dynamical quantum phase transitions (DQPTs) in the quench\ndynamics of two-dimensional topological systems can be characterized by a\ndynamical topological invariant defined along an appropriately chosen closed\ncontour in momentum space. Such a dynamical topological invariant reflects the\nvorticity of dynamical vortices responsible for the DQPTs, and thus serves as a\ndynamical topological order parameter in two dimensions. We demonstrate that\nwhen the contour crosses topologically protected fixed points in the quench\ndynamics, an intimate connection can be established between the dynamical\ntopological order parameter in two dimensions and those in one dimension. We\nfurther define a reduced rate function of the Loschmidt echo on the contour,\nwhich features non-analyticities at critical times and is sufficient to\ncharacterize DQPTs in two dimensions. We illustrate our results using the\nHaldane honeycomb model and the quantum anomalous Hall model as concrete\nexamples, both of which have been experimentally realized using cold atoms."
    },
    {
        "anchor": "Finite-temperature properties of interacting bosons on a two-leg flux\n  ladder: Quasi-one-dimensional lattice systems such as flux ladders with artificial\ngauge fields host rich quantum-phase diagrams that have attracted great\ninterest. However, so far, most of the work on these systems has concentrated\non zero-temperature phases while the corresponding finite-temperature regime\nremains largely unexplored. The question if and up to which temperature\ncharacteristic features of the zero-temperature phases persist is relevant in\nexperimental realizations. We investigate a two-leg ladder lattice in a uniform\nmagnetic field and concentrate our study on chiral edge currents and\nmomentum-distribution functions, which are key observables in ultracold\nquantum-gas experiments. These quantities are computed for hard-core bosons as\nwell as noninteracting bosons and spinless fermions at zero and finite\ntemperatures. We employ a matrix-product-state based purification approach for\nthe simulation of strongly interacting bosons at finite temperatures and\nanalyze finite-size effects. Our main results concern the\nvortex-fluid-to-Meissner crossover of strongly interacting bosons. We\ndemonstrate that signatures of the vortex-fluid phase can still be detected at\nelevated temperatures from characteristic finite-momentum maxima in the\nmomentum-distribution functions, while the vortex-fluid phase leaves weaker\nfingerprints in the local rung currents and the chiral edge current. In order\nto determine the range of temperatures over which these signatures can be\nobserved, we introduce a suitable measure for the contrast of these maxima. The\nresults are condensed into a finite-temperature crossover diagram for hard-core\nbosons.",
        "positive": "Vortex molecules in Bose-Einstein condensates: Stable vortex dimers are known to exist in coherently coupled two component\nBose-Einstein condensates (BECs). We construct stable vortex trimers in three\ncomponent BECs and find that the shape can be controlled by changing the\ninternal coherent (Rabi) couplings. Stable vortex N-omers are also constructed\nin coherently coupled N-component BECs. We classify all possible N-omers in\nterms of the mathematical graph theory. Next, we study effects of the Rabi\ncoupling in vortex lattices in two-component BECs. We find how the vortex\nlattices without the Rabi coupling known before are connected to the Abrikosov\nlattice of integer vortices with increasing the Rabi coupling. In this process,\nvortex dimers change their partners in various ways at large couplings. We then\nfind that the Abrikosov lattices are robust in three-component BECs."
    },
    {
        "anchor": "Density wave instabilities of tilted fermionic dipoles in a multilayer\n  geometry: We consider the density wave instability of fermionic dipoles aligned by an\nexternal field, and moving in equidistant layers at zero temperature. Using a\nconserving Hartree-Fock approximation, we show that correlations between\ndipoles in different layers significantly decrease the critical coupling\nstrength for the formation of density waves when the distance between the\nlayers is comparable to the inter-particle distance within each layer. This\neffect, which is strongest when the dipoles are oriented perpendicular to the\nplanes, causes the density waves in neighboring layers to be in-phase for all\norientations of the dipoles. We furthermore demonstrate that the effects of the\ninterlayer interaction can be understood from a classical model. Finally, we\nshow that the interlayer correlations are important for experimentally relevant\ndipolar molecules, including the chemically stable $^{23}$Na$^{40}$K and\n$^{40}$K$^{133}$Cs, where the density wave regime is within experimental reach.",
        "positive": "Realization of a quantum degenerate mixture of highly magnetic and\n  nonmagnetic atoms: We report on the experimental realization of a bosonic quantum degenerate\nmixture of highly-magnetic 168Er and nonmagnetic 174Yb. Quantum degeneracy is\nreached by forced evaporation in an all-optical trap. Formation of the two\nBose-Einstein condensates is confirmed by analysis of the cloud shape and the\nobserved inversions of the aspect ratios. The results open a path for possible\nnew experiments on magnetic and nonmagnetic impurity physics as well as on the\nquantum chaotic behavior of Feshbach resonances and their dependencies on minor\nvariations of the reduced masses."
    },
    {
        "anchor": "Feshbach blockade: single-photon nonlinear optics using resonantly\n  enhanced cavity-polariton scattering from biexciton states: We theoretically demonstrate how the resonant coupling between a pair of\ncavity-polaritons and a biexciton state can lead to a large single-photon Kerr\nnonlinearity in a semiconductor solid-state system. A fully analytical model of\nthe scattering process between a pair of cavity-polaritons is developed, which\nexplicitly includes the biexcitonic intermediate state. A dramatic enhancement\nof the polariton-polariton interactions is predicted in the vicinity of the\nbiexciton Feshbach resonance. Application to the generation of non-classical\nlight from polariton dots is discussed.",
        "positive": "Quantum Many-Body Conformal Dynamics: Symmetries, Geometry, Conformal\n  Tower States, and Entropy Production: In this article we study the quench dynamics of Galilean and scale invariant\nmany-body systems which can be prepared using interacting atomic gases. The\nfar-away from equilibrium dynamics are investigated by employing $m$-body\ndensity matrices, which are most conveniently defined in terms of a special\nbasis - the conformal tower states. We explicitly illustrate that, although\nduring the initial stage of the dynamics all symmetries can be broken and\nabsent in the unitary evolution because of the initialization of the state,\nthere is always an emergent conformal symmetry in the long time limit. The\nemergence of this dynamic conformal symmetry is robust, and always occurs; it\nuniquely defines the characteristics of the asymptotic dynamics at a scale\ninvariant fixed point. As an immediate application of the asymptotic dynamics\nof the microscopic density matrices, we have focused on the effects of this\nemergent conformal symmetry on two observables: the moment of inertia tensor,\n$I_{ij}(t)$, $i,j=x,y,z$, and the entropy density field, $S({\\bf r}, t)$, in\nthe hydrodynamic flow of strongly interacting particles. We show that the long\ntime behaviour of these observables is completely set by conformal symmetry,\nwhile the leading long time corrections depend on interference effects between\ndifferent conformal tower states. The emergent conformal symmetry naturally\nleads to entropy conservation, and {\\em conformal cooling}, an energy\nconserving cooling of a strongly interacting gas during free expansion. When\nthe interaction Hamiltonian breaks the scale symmetry, we further demonstrate\nthat there is a direct cause-effect relation between conformal symmetry\nbreaking in the long time limit, and a non-vanishing entropy production. This\nsuggests that the entropy production rate is a natural {\\em parameter} for\ncategorizing the breaking of conformal symmetry."
    },
    {
        "anchor": "Dimensional crossover in ultracold Fermi gases from Functional\n  Renormalisation: We investigate the dimensional crossover from three to two dimensions in an\nultracold Fermi gas across the whole BCS-BEC crossover. Of particular interest\nis the strongly interacting regime as strong correlations are more pronounced\nin reduced dimensions. Our results are obtained from first principles within\nthe framework of the functional renormalisation group (FRG). Here, the\nconfinement of the transverse direction is imposed by means of periodic\nboundary conditions. We calculate the equation of state, the gap parameter at\nzero temperature and the superfluid transition temperature across a wide range\nof transversal confinement length scales. Particular emphasis is put on the\ndetermination of the finite temperature phase diagram for different confinement\nlength scales. In the end, our results are compared with recent experimental\nobservations and we discuss them in the context of other theoretical works.",
        "positive": "Photon-induced sideband transitions in a many-body Landau-Zener process: We investigate the many-body Landau-Zener (LZ) process in a two-site\nBose-Hubbard model driven by a time-periodic field. We find that the driving\nfield may induce sideband transitions in addition to the main LZ transitions.\nThese photon-induced sideband transitions are a signature of the\nphoton-assisted tunneling in our many-body LZ process. In the strong\ninteraction regime, we develop an analytical theory for understanding the\nsideband transitions, which is confirmed by our numerical simulation.\nFurthermore, we discuss the quantization of the driving field. In the effective\nmodel of the quantized driving field, the sideband transitions can be\nunderstood as the LZ transitions between states of different \"photon\" numbers."
    },
    {
        "anchor": "Efimov Trimers in a Harmonic Potential: We study the Efimov effect in a harmonic oscillator in the hyperspherical\nformulation, and show how a reduced model allows for a description that is a\ngeneralization of the Efimov effect in free space and leads to results that are\neasily interpreted. Efimov physics may be observed by varying the value of the\nscattering length, since in the regime where the trimers have a mixed harmonic\noscillator and Efimov character, the inelastic properties of these states are\nstill manageable. The model also allows for the study of non-universal Efimov\ntrimers by including the effective range scattering parameter. While we find\nthat in a certain regime the effective range parameter can take over the role\nof the three-body parameter, interestingly, we obtain a numerical relationship\nbetween these two parameters different from what was found in other models.",
        "positive": "Many-body excitations and de-excitations in trapped ultracold bosonic\n  clouds: We employ the MultiConfiguraional Time-Dependent Hartree for Bosons (MCTDHB)\nmethod to study excited states of interacting Bose-Einstein condensates\nconfined by harmonic and double-well trap potentials. Two approaches to access\nexcitations, a static and a dynamic one, have been studied and contrasted. In\nstatic simulations the low-lying excitations have been computed by utilizing\nthe LR-MCTDHB method - a linear response theory constructed on-top of a static\nMCTDHB solution. Complimentary, we propose two dynamic protocols that address\nexcitations by propagating the MCTDHB wave-function. In particular, we\ninvestigate dipole-like oscillations induced by shifting the origin of the\nconfining potential and breathing-like excitations by quenching frequency of a\nparabolic part of the trap. To contrast static predictions and dynamic results\nwe have computed time-evolutions and their Fourier transforms of several local\nand non-local observables. Namely, we study evolution of the $\\left< x(t)\n\\right>$, its variance $\\operatorname{Var}(x(t))$, and of a local density\ncomputed at a selected position. We found out that the variance is the most\nsensitive and informative quantity - along with excitations it contains\ninformation about the de-excitations even in a linear regime of the induced\ndynamics. The dynamic protocols are found to access the many-body excitations\npredicted by the static LR-MCTDHB approach."
    },
    {
        "anchor": "Droplet-superfluid compounds in binary bosonic mixtures: While quantum fluctuations in binary mixtures of bosonic atoms with\nshort-range interactions can lead to the formation of a self-bound droplet, for\nequal intra-component interactions but an unequal number of atoms in the two\ncomponents, there is an excess part that cannot bind to the droplet. Imposing\nconfinement, as here through periodic boundary conditions in a one-dimensional\nsetting, the droplet becomes amalgamated with a residual condensate. The\nrotational properties of this compound system reveal simultaneous rigid-body\nand superfluid behavior in the ground state and uncover that the residual\ncondensate can carry angular momentum even in the absence of vorticity. In\ncontradiction to the intuitive idea that the superfluid fraction of the system\nwould be entirely made up of the excess atoms not bound by the droplet, we find\nevidence that this fraction is higher than what one would expect in such a\npicture. Our findings are corroborated by an analysis of the elementary\nexcitations in the system, and shed new light on the coexistence of\nlocalization and superfluidity.",
        "positive": "Dynamical localization of interacting bosons in the few-body limit: The quantum kicked rotor is well-known to display dynamical localization in\nthe non-interacting limit. In the interacting case, while the mean-field\n(Gross-Pitaevskii) approximation displays a destruction of dynamical\nlocalization, its fate remains debated beyond mean-field. Here we study the\nkicked Lieb-Liniger model in the few-body limit. We show that for any\ninteraction strength, two kicked interacting bosons always dynamically\nlocalize, in the sense that the energy of the system saturates at long time.\nHowever, contrary to the non-interacting limit, the momentum distribution\n$\\Pi(k)$ of the bosons is not exponentially localized, but decays as $\\mathcal\nC/k^4$, as expected for interacting quantum particles, with Tan's contact\n$\\mathcal C$ which remains finite at long time. We discuss how our results will\nimpact the experimental study of kicked interacting bosons."
    },
    {
        "anchor": "Tunable high-temperature thermodynamics of weakly-interacting dipolar\n  gases: We consider dilute gases of dipolar bosons or fermions in the\nhigh-temperature limit in a spherically symmetric harmonic trapping potential.\nWe examine the system using a virial expansion up to second order in the\nfugacity. Using the Born approximation and assuming purely dipolar\ninteractions, we find that the second-order virial coefficient for both bosons\nand fermions depends quadratically on the dipole length and is negative at high\ntemperature, indicating that to lowest order in the dipole-dipole interactions\nthe dipolar single-component quantum gases are repulsive. If the $s$-wave\nscattering length for the bosonic system is tunable and its absolute value is\nmade small, then the $s$-wave interactions dominate and the dipolar as behaves\nlike a weakly-interacting Bose gas with isotropic $s$-wave interactions. If the\ngeneralized scattering lengths for the fermionic system are tunable, then the\ndipole length can enter linearly in the virial equation of state, enhancing the\ndipole-dipole effects in the thermodynamic observables.",
        "positive": "Universal Trimers induced by Spin-Orbit Coupling in Ultracold Fermi\n  Gases: In this letter we address the issue how synthetic spin-orbit (SO) coupling\ncan strongly affect three-body physics in ultracold atomic gases. We consider a\nsystem which consists of three fermionic atoms, including two spinless heavy\natoms and one spin-1/2 light atom subjected to an isotropic SO coupling. We\nfind that SO coupling can induce universal three-body bound states with\nnegative s-wave scattering length at a smaller mass ratio, where no trimer\nbound state can exist if in the absence of SO coupling. The energies of these\ntrimers are independent of high-energy cutoff, and therefore they are universal\nones. Moreover, the resulting atom-dimer resonance can be effectively\ncontrolled by SO coupling strength. Our results can be applied to systems like\n${}^6$Li and ${}^{40}$K mixture."
    },
    {
        "anchor": "Supersymmetric isospectral formalism for the calculation of near-zero\n  energy states: application to the very weakly bound ${^4}$He trimer excited\n  state: We propose a novel mathematical approach for the calculation of near-zero\nenergy states by solving potentials which are isospectral with the original\none. For any potential, families of strictly isospectral potentials (with very\ndifferent shape) having desirable and adjustable features are generated by\nsupersymmetric isospectral formalism. The near-zero energy Efimov state in the\noriginal potential is effectively trapped in the deep well of the isospectral\nfamily and facilitates more accurate calculation of the Efimov state.\nApplication to the first excited state in 4He trimer is presented.",
        "positive": "Tan's two-body contact in a planar Bose gas: experiment vs theory: We determine the two-body contact in a planar Bose gas confined by a\ntransverse harmonic potential, using the nonperturbative functional\nrenormalization group. We use the three-dimensional thermodynamic definition of\nthe contact where the latter is related to the derivation of the pressure of\nthe quasi-two-dimensional system with respect to the three-dimensional\nscattering length of the bosons. Without any free parameter, we find a\nremarkable agreement with the experimental data of Zou {\\it et al.} [Nat. Comm.\n{\\bf 12}, 760 (2021)] from low to high temperatures, including the vicinity of\nthe Berezinskii-Kosterlitz-Thouless transition. We also show that the\nshort-distance behavior of the pair distribution function and the high-momentum\nbehavior of the momentum distribution are determined by two contacts: the\nthree-dimensional contact for length scales smaller than the characteristic\nlength $\\ell_z=\\sqrt{\\hbar/m\\omega_z}$ of the harmonic potential and, for\nlength scales larger than $\\ell_z$, an effective two-dimensional contact,\nrelated to the three-dimensional one by a geometric factor depending on\n$\\ell_z$."
    },
    {
        "anchor": "Decay of Bogoliubov quasiparticles in a nonideal one-dimensional Bose\n  gas: We study the relaxation of excitations in a system of one-dimensional weakly\ninteracting bosons. Due to residual weak interactions, Bogoliubov\nquasiparticles in this system have finite lifetimes. As a result of the\nconservation laws in one dimension, at zero temperature the leading mechanism\nof decay of a quasiparticle is disintegration into three others. We focus on\nphonon quasiparticles and find that their decay rate is proportional to the\nseventh power of momentum. In the integrable case of contact interaction\nbetween the bosons, the decay rate vanishes.",
        "positive": "Physics of Cold Atomic Fermi Gases: We consider a cold two-species atomic Fermi gas confined in a trap. We\ncombine the Hermitian coupling between the states (we assume them to be the\nstates with different spins) with the Cooper pairing of atoms with these\ndifferent spins. This opens up a new prospect for investigation of interplay\nbetween various phenomena involving Raman coupling (e.g., atom lasers,\ndark-state polaritons) and effects caused by Cooper pairing of particles (e.g.,\nsuperfluidity). We have obtained a threshold of transition from oscillatory to\namplifying behavior of matter waves."
    },
    {
        "anchor": "Oscillations and decay of superfluid currents in a one-dimensional Bose\n  gas on a ring: We study the time evolution of a supercurrent imprinted on a one-dimensional\nring of interacting bosons in the presence of a defect created by a localized\nbarrier. Depending on interaction strength and temperature, we identify various\ndynamical regimes where the current oscillates, is self-trapped or decays with\ntime. We show that the dynamics are captured by a dual Josephson model and\ninvolve phase slips of thermal or quantum nature.",
        "positive": "Influence of Cooper pairing on the inelastic processes in a gas of Fermi\n  atoms: Correlation properties in ultracold Fermi gas with negative scattering length\nand its impact on the three-body recombination is analyzed. We find that Cooper\npairing enhances the recombination rate in contrast to the decrease of this\nrate accompanying Bose-Einstein condensation in a Bose gas. This trend is\ncharacteristic for all interval of temperatures T<Tc."
    },
    {
        "anchor": "Analytical framework for non-equilibrium phase transition to\n  Bose--Einstein condensate: The theoretical description of non-equilibrium Bose--Einstein condensate\n(BEC) is one of the main challenges in modern statistical physics and kinetics.\nThe non-equilibrium nature of BEC makes it impossible to employ the\nwell-established formalism of statistical mechanics. We develop a framework for\nthe analytical description of a non-equilibrium phase transition to BEC that,\nin contrast to previously developed approaches, takes into account the infinite\nnumber of continuously distributed states. We consider the limit of fast\nthermalization and obtain an analytical expression for the full density matrix\nof a non-equilibrium ideal BEC which also covers the equilibrium case. For the\nparticular cases of 2D and 3D, we investigate the non-equilibrium formation of\nBEC by finding the temperature dependence of the ground state occupation and\nsecond-order coherence function. We show that for a given pumping rate, the\nmacroscopic occupation of the ground state and buildup of coherence may occur\nat different temperatures. Moreover, the buildup of coherence strongly depends\non the pumping scheme. We also investigate the condensate linewidth and show\nthat the Schawlow--Townes law holds for BEC in 3D and does not hold for BEC in\n2D.",
        "positive": "Observation of Weak Collapse in a Bose-Einstein Condensate: We study the collapse of an attractive atomic Bose-Einstein condensate\nprepared in the uniform potential of an optical-box trap. We characterise the\ncritical point for collapse and the collapse dynamics, observing universal\nbehaviour in agreement with theoretical expectations. Most importantly, we\nobserve a clear experimental signature of the counterintuitive weak collapse,\nnamely that making the system more unstable can result in a smaller particle\nloss. We experimentally determine the scaling laws that govern the\nweak-collapse atom loss, providing a benchmark for the general theories of\nnonlinear wave phenomena."
    },
    {
        "anchor": "Inducing Transport in a Dissipation-Free Lattice with Super Bloch\n  Oscillations: Particles in a perfect lattice potential perform Bloch oscillations when\nsubject to a constant force, leading to localization and preventing\nconductivity. For a weakly-interacting Bose-Einstein condensate (BEC) of Cs\natoms, we observe giant center-of-mass oscillations in position space with a\ndisplacement across hundreds of lattice sites when we add a periodic modulation\nto the force near the Bloch frequency. We study the dependence of these \"super\"\nBloch oscillations on lattice depth, modulation amplitude, and modulation\nfrequency and show that they provide a means to induce linear transport in a\ndissipation-free lattice. Surprisingly, we find that, for an interacting\nquantum system, super Bloch oscillations strongly suppress the appearance of\ndynamical instabilities and, for our parameters, increase the phase-coherence\ntime by more than a factor of hundred.",
        "positive": "Collective modes of ultracold fermionic alkaline-earth gases with SU(N)\n  symmetry: We calculate the collective modes of ultracold trapped alkaline-earth\nfermionic atoms, which possess an SU($N$) symmetry of the nuclear spin degree\nof freedom, and a controllable $N$, with $N$ as large as $10$. We calculate the\nbreathing and quadrupole modes of two-dimensional and three-dimensional\nharmonically trapped gases in the normal phase. We particularly concentrate on\ntwo-dimensional gases, where the shift is more accessible experimentally, and\nthe physics has special features. We present results as a function of\ntemperature, interaction strength, density, and $N$. We include calculations\nacross the collisionless to hydrodynamic crossover. We assume the gas is\ninteracting weakly, such that it can be described by a Boltzmann-Vlasov\nequation that includes both mean-field terms and the collision integral. We\nsolve this with an approximate scaling ansatz, taking care in two-dimensions to\npreserve the scaling symmetry of the system. We predict the collective mode\nfrequency shifts and damping, showing that these are measurable in\nexperimentally relevant regimes. We expect these results to furnish powerful\ntools to characterize interactions and the state of alkaline-earth gases, as\nwell as to lay the foundation for future work, for example on strongly\ninteracting gases and SU($N$) spin modes."
    },
    {
        "anchor": "Observation of conformal symmetry breaking and scale invariance in\n  expanding Fermi gases: We precisely test scale invariance and local thermal equilibrium in the\nhydrodynamic expansion of a Fermi gas of atoms as a function of interaction\nstrength. After release from an anisotropic optical trap, we observe that a\nresonantly interacting gas obeys scale-invariant hydrodynamics, where the mean\nsquare cloud size $\\langle{\\mathbf{r}}^2\\rangle=\\langle x^2+y^2+z^2\\rangle$\nexpands ballistically (like a noninteracting gas) and the energy-averaged bulk\nviscosity is consistent with zero, $0.005(0.016)\\,\\hbar\\,n$, with $n$ the\ndensity. In contrast, the aspect ratios of the cloud exhibit anisotropic\n\"elliptic\" flow with an energy-dependent shear viscosity. Tuning away from\nresonance, we observe conformal symmetry breaking, where\n$\\langle{\\mathbf{r}}^2\\rangle$ deviates from ballistic flow.",
        "positive": "Collective atomic-population-inversion and stimulated radiation for\n  two-componentBose-Einstein condensate in an optical cavity: In this paper we investigate the ground-state properties and related quantum\nphase transitions for the two-component Bose-Einstein condensate in a\nsingle-mode optical cavity. Apart from the usual normal and superradiant phases\nmulti-stable macroscopic quantum states are realized by means of the\nspin-coherent-state variational method. We demonstrate analytically the\nstimulated radiation from collective state of atomic population inversion,\nwhich does not exist in the normal Dicke model with single-component atoms. It\nis also revealed that the stimulated radiation can be generated only from one\ncomponent of atoms and the other remains in the ordinary superradiant state.\nHowever the order of superradiant and stimulatedradiation states is\ninterchangeable between two components of atoms by tuning the relative\natom-field couplings and the frequency detuning as well."
    },
    {
        "anchor": "Quantum Analogs of Classical Wakes in Bose-Einstein Condensates: We show that an elliptical obstacle moving through a Bose-Einstein condensate\ngenerates wakes of quantum vortices which resemble those of classical viscous\nflow past a cylinder or sphere. The role of ellipticity is to facilitate the\ninteraction of the vortices nucleated by the obstacle. Initial steady symmetric\nwakes lose their symmetry and form clusters of like-signed vortices, in analogy\nto the classical B\\'enard-von K\\'arm\\'an vortex street. Our findings,\ndemonstrated numerically in both two and three dimensions, confirm the\nintuition that a sufficiently large number of quanta of circulation reproduce\nclassical physics.",
        "positive": "Spin Liquid Condensate of Spinful Bosons: We introduce the concept of a bosonic spin liquid condensate (SLC), where\nspinful bosons in a lattice form a zero-temperature spin disordered charge\ncondensate that preserves the spin rotation symmetry, but breaks the U(1)\nsymmetry due to a spinless order parameter with charge one. It has an energy\ngap to all the spin excitations. We show that such SLC states can be realized\nin a system of spin $S\\ge 2$ bosons. In particular, we analyze the SLC phase\ndiagram in the spin 2 case using a mean-field variational wave function method.\nWe show there is a direct analogy between the SLC and the\nresonating-valence-bond (RVB) state."
    },
    {
        "anchor": "Critical correlations in an ultracold Bose gas revealed by means of a\n  temporal Talbot-Lau interferometer: We study experimentally the critical correlation in an ultra-cold Bose gas\nwith a temporal Talbot-Lau (TL) interferometer. Near the critical temperature,\nwe observe a bi-modal density distribution in an ultra-cold Bose gas after the\napplication of the TL interferometer. The measured fraction of the narrower\npeak in the density distribution displays a clear peak within the critical\nregime. The peak position agrees with the critical temperature calculated with\nthe finite-size and interaction corrections. The critical exponents are\nextracted from the peak and they agree with the critical exponents for the\ncorrelation length.",
        "positive": "Exact three-body local correlations for excited states of the 1D Bose\n  gas: We derive an exact analytic expression for the three-body local correlations\nin the Lieb-Liniger model of 1D Bose gas with contact repulsion. The local\nthree-body correlations control the thermalization and particle loss rates in\nthe presence of terms which break integrability, as is realized in the case of\n1D ultracold bosons. Our result is valid not only at finite temperature but\nalso for a large class of non-thermal excited states in the thermodynamic\nlimit. We present finite temperature calculations in the presence of external\nharmonic confinement within local density approximation, and for a highly\nexcited state that resembles an experimentally realized configuration."
    },
    {
        "anchor": "Bose-Einstein Condensation of Photons in a Four-Site Quantum Ring: Thermalization of radiation by contact to matter is a well-known concept, but\nthe application of thermodynamic methods to complex quantum states of light\nremains a challenge. Here we observe Bose-Einstein condensation of photons into\nthe hybridized ground state of a four-site ring potential with coherent tunnel\ncouplings. In our experiment, the periodically-closed ring lattice superimposed\nby a weak harmonic trap for photons is realized inside a spatially structured\ndye-filled microcavity. Photons thermalize to room temperature, and above a\ncritical photon number macroscopically occupy the symmetric linear combination\nof the site eigenstates with zero phase winding, which constitutes the ground\nstate of the system. The mutual phase coherence of photons at different lattice\nsites is verified by optical interferometry.",
        "positive": "Collective modes in multicomponent condensates with anisotropy: We report the effects of anisotropy in the confining potential on two\ncomponent Bose-Einstein condensates (TBECs) through the properties of the low\nenergy quasiparticle excitations. Starting from generalized Gross Pitaevskii\nequation, we obtain the Bogoliubov de-Gennes (BdG) equation for TBECs using the\nHartree-Fock-Bogoliubov (HFB) theory. Based on this theory, we present the\ninfluence of radial anisotropy on TBECs in the immiscible or the\nphase-separated domain. In particular, the TBECs of $^{85}$Rb~-$^{87}$Rb and\n$^{133}$Cs~-$^{87}$Rb TBECs are chosen as specific examples of the two possible\ninterface geometries, shell-structured and side by side, in the immiscible\ndomain. We also show that the dispersion relation for the TBEC shell-structured\ninterface has two branches, and anisotropy modifies the energy scale and\nstructure of the two branches."
    },
    {
        "anchor": "2D dilute Bose mixture at low temperatures: The thermodynamic and superfluid properties of the dilute two-dimensional\nbinary Bose mixture at low temperatures are discussed. We also considered the\nproblem of the emergence of the long-range order in these systems. All\ncalculations are performed by means of celebrated Popov's path-integral\napproach for the Bose gas with a short-range interparticle potential.",
        "positive": "Self-organized structures of two-component laser fields and their active\n  controls in a cold Rydberg atomic gas: We investigate the formation and control of stationary optical patterns in a\ncold Rydberg atomic gas via double electromagnetically induced transparency. We\nshow that, through the modulational instability of plane-wave state of a laser\nfield with two polarization components, the system undergoes a spontaneous\nsymmetry breaking and hence the emergence of plentiful self-organized spatial\noptical structures, which can be manipulated by the ratio between the cross-\nand self-Kerr nonlinearities, the nonlocality degree of the Kerr\nnonlinearities, and the populations initially prepared in the two atomic ground\nstates. Interestingly, a crossover from mixture to separation in space (optical\nphase separation) of the two polarization components occurs when the ratio\nbetween the cross- and self-Kerr nonlinearities exceeds a critical value. We\nalso show that the system supports nonlocal two-component spatial optical\nsolitons and vortices when the parameters of the system are selected suitably.\nThe rich diversity and active controllability of the self-organized optical\nstructures reported here provide a way for realizing novel optical patterns and\nsolitons and their structural phase transitions based on Rydberg atomic gases."
    },
    {
        "anchor": "Dynamics of spatial coherence and momentum distribution of polaritons in\n  a semiconductor microcavity under conditions of Bose-Einstein condensation: The dynamics of spatial coherence and momentum distribution of polaritons in\nthe regime of Bose-Einstein condensation are investigated in a GaAs microcavity\nwith embedded quantum wells under nonresonant excitation with picosecond laser\npulses. It is shown that the onset of the condensate first order sparial\ncoherence is accompanied by narrowing of the polariton momentum distribution.\nAt the same time, at sufficiently high excitation densities, there is\nsignificant qualitative discrepancy between the dynamic behavior of the width\nof the polariton momentum distribution determined from direct measurements and\nthat calculated from the coherence spatial distribution. This discrepancy is\nobserved at the fast initial stage of the polariton system kinetics and,\napparently, results from the strong spatial nonuniformity of the phase of the\ncondensate wave function, which equilibrates on a much longer time scale.",
        "positive": "Mixed Bubbles in a one-dimensional Bose-Bose mixture: We investigate a Bose-Bose mixture across the miscible-immiscible phase\ntransition governed by quantum fluctuations in one dimension. We find the\nrecently predicted so-called mixed bubbles as ground states close to the\nmean-field miscible-immiscible threshold. These bubbles form a pocket of\nmiscibility, separated by one of the components. The collective excitations\nreflect the symmetry breaking resulting from the bubble formation. The partial\nmiscibility of the system allows for persistent currents in an annular\nconfinement. Intriguingly, the mixed bubble acts like an intrinsic weak link,\nconnecting the rotational behavior of the mixed bubble state to current efforts\nin atomtronic applications."
    },
    {
        "anchor": "Turbulence in quantum fluids: This paper reviews briefly the recent important developments in the physics\nof quantum turbulence (QT) in superfluid helium and atomic Bose-Einstain\ncondensates (BECs). After giving basics of quantum hydrodynamics, we discuss\nenergy spectrum, QT created by vibrating structures, visualization among topics\non superfluid helium. For atomic BECs we review three-dimensional QT,\ntwo-component BECs, and spin turbulence in spinor BECs. The last part is\ndevoted to some perspectives of this issue.",
        "positive": "Efimov effect for two particles on a semi-infinite line: The Efimov effect (in a broad sense) refers to the onset of a geometric\nsequence of many-body bound states as a consequence of the breakdown of\ncontinuous scale invariance to discrete scale invariance. While originally\ndiscovered in three-body problems in three dimensions, the Efimov effect has\nnow been known to appear in a wide spectrum of many-body problems in various\ndimensions. Here we introduce a simple, exactly solvable toy model of two\nidentical bosons in one dimension that exhibits the Efimov effect. We consider\nthe situation where the bosons reside on a semi-infinite line and interact with\neach other through a pairwise $\\delta$-function potential with a particular\nposition-dependent coupling strength that makes the system scale invariant. We\nshow that, for sufficiently attractive interaction, the bosons are bound\ntogether and a new energy scale emerges. This energy scale breaks continuous\nscale invariance to discrete scale invariance and leads to the onset of a\ngeometric sequence of two-body bound states. We also study the two-body\nscattering off the boundary and derive the exact reflection amplitude that\nexhibits a log-periodicity. This article is intended for students and\nnon-specialists interested in discrete scale invariance."
    },
    {
        "anchor": "Energy absorption spectroscopy of unitary Fermi gases in a uniform\n  potential: We propose to use the energy absorption spectroscopy to measure the kinetic\ncoefficients of unitary Fermi gases in a uniform potential. We show that in our\nscheme, the energy absorption spectrum is proportional to the dynamic structure\nfactor of the system. The profile of the spectrum depends on the shear\nviscosity $\\eta$, the thermal conductivity $\\kappa$ and the superfluid bulk\nviscosity $\\xi_3$. We show that extraction of these coefficients from the\nspectrum is achievable in present experiments.",
        "positive": "Transition from Tonks-Girardeau gas to super-Tonks-Girardeau gas as an\n  exact many-body dynamics problem: We investigate transition of a one-dimensional interacting Bose gas from a\nstrongly repulsive regime to a strongly attractive regime, where a stable\nhighly excited state known as the super Tonks-Girardeau gas was experimentally\nrealized very recently. By solving exact dynamics of the integrable\nLieb-Liniger Bose gas, we demonstrate that such an excited gas state can be a\nvery stable dynamic state. Furthermore we calculate the breathing mode of the\nsuper Tonks-Girardeau gas which is found to be in good agreement with\nexperimental observation. Our results show that the highly excited super\nTonks-Girardeau gas phase can be well understood from the fundamental theory of\nthe solvable Bose gas."
    },
    {
        "anchor": "Phases of a 2D Bose Gas in an Optical Lattice: Ultra-cold atoms in optical lattices realize simple, fundamental models in\ncondensed matter physics. Our 87Rb Bose-Einstein condensate is confined in a\nharmonic trapping potential to which we add an optical lattice potential. Here\nwe realize the 2D Bose-Hubbard Hamiltonian and focus on the effects of the\nharmonic trap, not present in bulk condensed matter systems. By measuring\ncondensate fraction we identify the transition from superfluid to Mott\ninsulator as a function of atom density and lattice depth. Our results are in\nexcellent agreement with the quantum Monte Carlo universal state diagram,\nsuitable for trapped systems, introduced by Rigol et al. (Phys. Rev. A 79,\n053605 (2009)).",
        "positive": "Calibrating the momentum width of a trapped Bose-Einstein condensate by\n  one-dimensional optical lattice pulse sequences: We experimentally measured the ultra-narrow momentum width of an optical\ntrapped Bose-Einstein condensate (BEC) in situ based on matter-wave\ninterference, which validates our previous theoretical work [arXiv:\n2205.02416]. By sweeping the interval of double stand-wave pulses, the BEC wave\npacket was splitted into different diffraction orders and then we counted the\noscillation curve of the population of zero-momentum state to calibrate the\nmomentum width. Compared with our simplified theory, we observed an accelerated\nevolution of interference fringes in time-domain. We evaluated this\ninterference process minutely by numerically calculating the Gross-Pitaevskii\nequation and using Wigner function to intuitively demonstrate the influence of\nthe external potential and nonlinear term. We confirmed that the reduction of\ninterference fringe evolution period actually originates from the synergistic\ncooperation of the mean-field interaction of the BEC and spatial density\nmodulation caused by the interference between different momentum states. Our\napproach could be generalized to other ultra-cold atomic gases with different\nmomentum distributions, and in principle a single shot can obtain the result.\nThis quantum thermometry is particularly suitable for momentum width\ncalibration in practical deep cooling experiments, while for atomic samples at\npK level the mean-field interaction can be safely ignored."
    },
    {
        "anchor": "Designing nontrivial one-dimensional Floquet topological phases using a\n  spin-1/2 double-kicked rotor: A quantum kicked rotor model is one of the promising systems to realize\nvarious Floquet topological phases. We consider a double-kicked rotor model for\na one-dimensional quasi-spin-1/2 Bose-Einstein condensate with spin-dependent\nand spin-independent kicks which are implementable for cold atomic experiments.\nWe theoretically show that the model can realize all the Altland-Zirnbauer\nclasses with nontrivial topology in one dimension. In the case of class CII, we\nshow that a pair of winding numbers $(w_0,w_\\pi)\\in 2\\mathbb{Z}\\times\n2\\mathbb{Z}$ featuring the edge states at zero and $\\pi$ quasienergy,\nrespectively, takes various values depending on the strengths of the kicks. We\nalso find that the winding numbers change to $\\mathbb{Z}$ when we break the\ntime-reversal and particle-hole symmetries by changing the phase of a kicking\nlattice. We numerically confirm that the winding numbers can be obtained by\nmeasuring the mean chiral displacement in the long-time limit in the present\ncase with four internal degrees of freedom. We further propose two feasible\nmethods to experimentally realize the spin-dependent and spin-independent kicks\nrequired for various topological phases.",
        "positive": "Chaos assisted many-body tunnelling: We study the interplay of chaos and tunnelling between two weakly-coupled\nBose-Josephson junctions. The classical phase space of the composite system has\na mixed structure including quasi-integrable self-trapping islands for\nparticles and excitations, separated by a chaotic sea. We show that the\nmany-body dynamical tunnelling gap between macroscopic Schr\\\"odinger cat states\nsupported by these islands is chaos-enhanced. The many-body tunnelling rate\nfluctuates over several orders of magnitude with small variations of the system\nparameters or the particle number."
    },
    {
        "anchor": "Thermodynamics of the Bose-Hubbard model in a Bogoliubov+U theory: We derive the Bogoliubov+U formalism to study the thermodynamical properties\nof the Bose-Hubbard model. The framework can be viewed as the zero-frequency\nlimit of bosonic dynamical mean-field theory (B-DMFT), but equally well as an\nextension of the mean-field decoupling approximation in which pair creation and\nannihilation of depleted particles is taken into account. The self-energy on\nthe impurity site is treated variationally, minimizing the grand potential. The\ntheory containing just three parameters that are determined self-consistently\nreproduces the T=0 phase diagrams of the three-dimensional and two-dimensional\nBose-Hubbard model with an accuracy of 1% or better. The superfluid to normal\ntransition at finite temperature is also reproduced well and only slightly less\naccurately than in B-DMFT.",
        "positive": "Impurities in quasi-one-dimensional droplets of binary Bose mixtures: Recently created self-bound quantum droplets of binary Bose mixtures open\nintriguing possibilities for the study of impurity physics. We show that the\nproperties of impurities embedded in quasi-one-dimensional droplets are\ndetermined by the interplay between back-action and quantum fluctuations. Due\nto such back-action, repulsive impurities may form a metastable quasi-bound\nstate inside the droplet. In contrast, attractive impurities remain bound to\nthe droplet, leading to the hybridization of droplet and impurity excitations,\nas well as to peculiar scattering resonances. Interestingly, impurity trapping\nmay result solely from the effect of quantum fluctuations. These results may\nreadily be probed experimentally by doping the currently available droplets of\nbinary mixtures."
    },
    {
        "anchor": "Second-order virial expansion for an atomic gas in a harmonic waveguide: The virial expansion for cold two-component Fermi and Bose atomic gases is\nconsidered in the presence of a waveguide and in the vicinity of a Feshbach\nresonance. The interaction between atoms and the coupling with the Feshbach\nmolecules is modeled using a quantitative separable two-channel model. The\nscattering phase-shift in an atomic waveguide is defined. This permits us to\nextend the Beth-Uhlenbeck formula for the second-order virial coefficient to\nthis inhomogeneous case.",
        "positive": "Crossover from weak to strong quench in a spinor Bose-Einstein\n  condensate: We investigate the early-time dynamics of a quasi-two-dimensional spin-1\nantiferromagnetic Bose-Einstein condensate after a sudden quench from the\neasy-plane to the easy-axis polar phase. The post-quench dynamics shows a\ncrossover behavior as the quench strength $\\tilde{q}$ is increased, where\n$\\tilde{q}$ is defined as the ratio of the initial excitation energy per\nparticle to the characteristic spin interaction energy. For a weak quench of\n$\\tilde{q}<1$, long-wavelength spin excitations are dominantly generated,\nleading to the formation of irregular spin domains. With increasing\n$\\tilde{q}$, the length scale of the initial spin excitations decreases, and we\ndemonstrate that the long-wavelength instability is strongly suppressed for\nhigh $\\tilde{q}>2$. The observed crossover behavior is found to be consistent\nwith the Bogoliubov description of the dynamic instability of the initial\nspinor condensate."
    },
    {
        "anchor": "Two parameters scaling approach to Anderson localization of weekly\n  interacting BEC: We numerically study the Anderson localization of weekly interacting\nBose-Einstein condensate in a one-dimensional disordered potential. We show\nthat two parameters are needed to completely describe such system, and the\ndensity profile of which can be described with the sum of two exponential\nfunctions. This is a new attempt for precise description of systems with\ninterplay of disorder and interaction.",
        "positive": "Exotic photonic molecules via Lennard-Jones-like potentials: Ultracold systems offer an unprecedented level of control of interactions\nbetween atoms. An important challenge is to achieve a similar level of control\nof the interactions between photons. Towards this goal, we propose a\nrealization of a novel Lennard-Jones-like potential between photons coupled to\nthe Rydberg states via electromagnetically induced transparency (EIT). This\npotential is achieved by tuning Rydberg states to a F{\\\"o}rster resonance with\nother Rydberg states. We consider few-body problems in 1D and 2D geometries and\nshow the existence of self-bound clusters (\"molecules\") of photons. We\ndemonstrate that for a few-body problem, the multi-body interactions have a\nsignificant impact on the geometry of the molecular ground state. This leads to\nphenomena without counterparts in conventional systems: For example, three\nphotons in 2D preferentially arrange themselves in a line-configuration rather\nthan in an equilateral-triangle configuration. Our result opens a new avenue\nfor studies of many-body phenomena with strongly interacting photons."
    },
    {
        "anchor": "Insights into the Electron-Electron Interaction from Quantum Monte Carlo\n  Calculations: The effective electron-electron interaction in the electron gas depends on\nboth the density and spin local field factors. Variational Diagrammatic Quantum\nMonte Carlo calculations of the spin local field factor are reported and used\nto quantitatively present the full spin-dependent, electron-electron\ninteraction. Together with the charge local field factor from previous\nDiffusion Quantum Monte Carlo calculations, we obtain the complete form of the\neffective electron-electron interaction in the uniform three-dimensional\nelectron gas. Very simple quadratic formulas are presented for the local field\nfactors that quantitatively produce all of the response functions of the\nelectron gas at metallic densities.\n  Exchange and correlation become increasingly important at low densities. At\nthe compressibility divergence at rs = 5.25, both the direct (screened Coulomb)\nterm and the charge-dependent exchange term in the electron-electron\ninteraction at q=0 are separately divergent. However, due to large\ncancellations, their difference is finite, well behaved, and much smaller than\neither term separately. As a result, the spin contribution to the\nelectron-electron interaction becomes an important factor. The static\nelectron-electron interaction is repulsive as a function of density but is less\nrepulsive for electrons with parallel spins.\n  The effect of allowing a deformable, rather than rigid, positive background\nis shown to be as quantitatively important as exchange and correlation. As a\nsimple concrete example, the electron-electron interaction is calculated using\nthe measured bulk modulus of the alkali metals with a linear phonon dispersion.\nThe net electron-electron interaction in lithium is attractive for wave vectors\n$0-2k_F$, which suggests superconductivity, and is mostly repulsive for the\nother alkali metals.",
        "positive": "Signature of Supersolidity in a Driven Cubic-Quartic Nonlinear\n  Schr\u00f6dinger Equation: We present analytical solution, which is periodic in nature, for a driven\ncubic-quartic nonlinear Schr\\\"odinger equation (DCQNLSE) placed in a\nbi-chromatic optical lattice. The solution indicates the creation of density\nwave. Since, beyond mean-field contribution in quasi one dimensional and\none-dimensional geometry differs on the even exponents of the nonlinearity thus\nwe extend our analysis towards quadratic-cubic-quartic and quadratic-cubic\nnonlinearities as well. Later, we study the dynamics of DCQNLSE. Our study\nindicates the existence of stripe phase along with considerable phase\ncoherence. These findings allow us to comment on the possible emergence of\nsupersolid phase in a condensate."
    },
    {
        "anchor": "Three-body interactions on a triangular lattice: We analyze the hard-core Bose-Hubbard model with both the three-body and\nnearest neighbor repulsions on the triangular lattice. The phase diagram is\nachieved by means of the semi-classical approximation and the quantum Monte\nCarlo simulation. For a system with only the three-body interactions, both the\nsupersolid phase and one third solid disappear while the two thirds solid\nstably exists. As the thermal behavior of the bosons with nearest neighbor\nrepulsion, the solid and the superfluid undergo the 3-state Potts and the\nKosterlitz-Thouless type phase transitions, respectively. In a system with both\nthe frustrated nearest neighbor two-body and three-body interactions, the\nsupersolid and one third solid revive. By tuning the strength of the three-body\ninteractions, the phase diagram is distorted, because the one-third solid and\nthe supersolid are suppressed.",
        "positive": "Effects of spin-orbit coupling on the Berezinskii-Kosterlitz-Thouless\n  transition and the vortex-antivortex structure in two-dimensional Fermi gases: We investigate the Berezinskii-Kosterlitz-Thouless (BKT) transition in a\ntwo-dimensional (2D) Fermi gas with spin-orbit coupling (SOC), as a function of\nthe two-body binding energy and a perpendicular Zeeman field. By including a\ngeneric form of the SOC, as a function of Rashba and Dresselhaus terms, we\nstudy the evolution between the experimentally relevant equal\nRashba-Dresselhaus (ERD) case and the Rashba-only (RO) case. We show that in\nthe ERD case, at fixed non-zero Zeeman field, the BKT transition temperature\n$T_{BKT}$ is increased by the effect of SOC for all values of the binding\nenergy. We also find a significant increase in the value of the Clogston limit\ncompared to the case without SOC. Furthermore, we demonstrate that the\nsuperfluid density tensor becomes anisotropic (except in the RO case), leading\nto an anisotropic phase-fluctuation action that describes elliptic vortices and\nantivortices, which become circular in the RO limit. This deformation\nconstitutes an important experimental signature for superfluidity in a 2D Fermi\ngas with ERD SOC. Finally, we show that the anisotropic sound velocities\nexhibit anomalies at low temperatures, in the vicinity of quantum phase\ntransitions between topologically distinct uniform superfluid phases."
    },
    {
        "anchor": "Transition between vacuum and finite-density states in the\n  infinite-dimensional Bose-Hubbard model with spatially inhomogeneous\n  dissipation: We analyze dynamics of the infinite-dimensional Bose-Hubbard model with\nspatially inhomogeneous dissipation in the hardcore boson limit by solving the\nLindblad master equation with use of the Gutzwiller variational method. We\nconsider dissipation processes that correspond to inelastic light scattering in\nthe case of Bose gases in optical lattices. We assume that the dissipation is\napplied to a half of lattice sites in a spatially alternating manner. We focus\non steady states at which the system arrives after long-time evolution. We find\nthat when the average particle density is varied, the steady state exhibits a\ntransition between a state in which the sites without dissipation are vacuum\nand that containing a finite number of particles at those sites. We associate\nthe transition with the tendency of the sites with dissipation towards a local\nstate at infinite temperature.",
        "positive": "Many-body physics in the radio frequency spectrum of lattice bosons: We calculate the radio-frequency spectrum of a trapped cloud of cold bosonic\natoms in an optical lattice. Using random phase and local density\napproximations we produce both trap averaged and spatially resolved spectra,\nidentifying simple features in the spectra that reveal information about both\nsuperfluidity and correlations. Our approach is exact in the deep Mott limit\nand in the deep superfluid when the hopping rates for the two internal spin\nstates are equal. It contains final state interactions, obeys the Ward\nidentities (and the associated conservation laws), and satisfies the $f$-sum\nrule. Motivated by earlier work by Sun, Lannert, and Vishveshwara [Phys. Rev. A\n\\textbf{79}, 043422 (2009)], we also discuss the features which arise in a\nspin-dependent optical lattice."
    },
    {
        "anchor": "Two-mode Bose gas: Beyond classical squeezing: The dynamical evolution of squeezing correlations in an ultracold\nBose-Einstein distributed across two modes is investigated theoretically in the\nframework of the Bose-Hubbard model. It is shown that the eigenstates of the\nHamiltonian do not exploit the full region allowed by Heisenberg's uncertainty\nrelation for number and phase fluctuations. The development of non-classical\ncorrelations and relative number squeezing is studied in the transition from\nthe Josephson to the Fock regime. Comparing the full quantum evolution with\nclassical statistical simulations allows to identify quantum aspects of the\nsqueezing formation. In the quantum regime, the measurement of squeezing allows\nto distinguish even and odd total particle numbers.",
        "positive": "Inter-species entanglement of Bose-Bose mixtures trapped in optical\n  lattices: In the present work we discuss inter-species entanglement in Bose-Bose\nmixtures trapped in optical lattices. This work is motivated by the observation\nthat, in the presence of a second component, the Mott-insulator lobe shifts\n{\\em{differently}} on the hole- and particle-side with respect to the Mott lobe\nof the single species system (Phys. Rev. A 82, 021601, Laser Phys. 21, 1443).\nWe use perturbation theory, formulated in a Hilbert space decomposed by means\nof lattice symmetries, in order to show that the nonuniform shift of the Mott\nlobe is a consequence of an inter-species entanglement which differs in the\nlowest excited states to remove and add a particle. Our results indicate that\ninter-species entanglement in mixtures can provide a new perspective in\nunderstanding quantum phase transitions. To validate our approach, we compare\nour results from perturbation theory with quantum Monte Carlo simulations."
    },
    {
        "anchor": "Supersolid behaviour of a dipolar Bose-Einstein condensate confined in a\n  tube: Motivated by a recent experiment [L.Chomaz et al., Nature Physics 14, 442\n(2018)], we perform numerical simulations of a dipolar Bose-Einstein Condensate\n(BEC) in a tubular confinement at T=0 within Density Functional Theory, where\nthe beyond-mean-field correction to the ground state energy is included in the\nLocal Density Approximation. We study the excitation spectrum of the system by\nsolving the corresponding Bogoliubov-de Gennes equations. The calculated\nspectrum shows a roton minimum, and the roton gap decreases by reducing the\neffective scattering length. As the roton gap disappears, the system\nspontaneously develops in its ground-state a periodic, linear structure formed\nby denser clusters of atomic dipoles immersed in a dilute superfluid\nbackground. This structure shows the hallmarks of a supersolid system, i.e. (i)\na finite non-classical translational inertia along the tube axis and (ii) the\nappearance, besides the phonon mode, of the Nambu-Goldstone gapless mode\ncorresponding to phase fluctuations, and related to the spontaneous breaking of\nthe gauge symmetry. A further decrease in the scattering length eventually\nleads to the formation of a periodic linear array of self-bound droplets.",
        "positive": "Artificial graphene with tunable interactions: We create an artificial graphene system with tunable interactions and study\nthe crossover from metallic to Mott insulating regimes, both in isolated and\ncoupled two-dimensional honeycomb layers. The artificial graphene consists of a\ntwo-component spin mixture of an ultracold atomic Fermi gas loaded into a\nhexagonal optical lattice. For strong repulsive interactions we observe a\nsuppression of double occupancy and measure a gapped excitation spectrum. We\npresent a quantitative comparison between our measurements and theory, making\nuse of a novel numerical method to obtain Wannier functions for complex lattice\nstructures. Extending our studies to time-resolved measurements, we investigate\nthe equilibration of the double occupancy as a function of lattice loading\ntime."
    },
    {
        "anchor": "Superfluid properties of an ultracold Fermi gas with an orbital Feshbach\n  resonance in the BCS-BEC crossover region: We theoretically investigate superfluid properties of a two-band gas of\n$^{173}$Yb Fermi atoms with an orbital Feshbach resonance (OFR). To describe\nthe BCS-BEC crossover region, we include superfluid fluctuations caused by\ninter-band and intra-band pairing interactions associated with OFR, by\nextending the strong-coupling theory developed by Nozi\\`eres and Schmitt-Rink\nto the two-band case below the superfluid phase transition temperature;\nhowever, effects of an experimentally inaccessible deep bound state are\nremoved, to model a real $^{173}$Yb Fermi gas near OFR. We show that the\ncondensate fraction in the upper closed channel gradually becomes smaller than\nthat in the lower open channel, as one moves from the strong- to the\nweak-coupling regime, because the OFR-pairing mechanism tunes the interaction\nstrengths by adjusting the energy difference between the two bands. However,\neven when the closed-channel band is much higher in energy than the\nopen-channel band in the weak-coupling regime, the magnitude of the superfluid\norder parameter in the closed channel is found to be still comparable to that\nin the open channel. As the reason for this, we point out a pair-tunneling\neffect by the OFR-induced inter-band interaction. Besides these superfluid\nquantities, we also examine collective modes, such as the Goldstone mode,\nSchmid (Higgs) mode, as well as Leggett mode, to clarify how they appear in the\nspectral weights of pair-correlation functions in each band. Since the\nrealization of a multi-band superfluid Fermi gas is a crucial issue in cold\nFermi gas physics, our results would contribute to the basic understanding of\nthis type of Fermi superfluid in the BCS-BEC crossover region.",
        "positive": "Impact of anisotropy on vortex clusters and their dynamics: We investigate the effects of anisotropy on the stability and dynamics of\nvortex cluster states which arise in Bose-Einstein condensates. Sufficiently\nstrong anisotropies are shown to stabilize states with arbitrary numbers of\nvortices that are highly unstable in the isotropic limit. Conversely,\nanisotropy can be used to destabilize states which are stable in the isotropic\nlimit. Near the linear limit, we identify the bifurcations of vortex states\nincluding their emergence from linear eigenstates, while in the strongly\nnonlinear limit, a particle-like description of the dynamics of the vortices in\nthe anisotropic trap is developed. Both are in very good agreement with\nnumerical results. Collective modes of stabilized many vortex cluster states\nare demonstrated."
    },
    {
        "anchor": "Ground-state properties of dilute Bose systems with synthetic dispersion\n  laws: Experimental advances in synthesizing spin-orbit couplings in cold atomic\nBose gases promise to create single-particle dispersion laws featuring energy\nminima that are degenerate on a ring or a sphere in momentum space. We show\nthat for arbitrary space dimensionality the ground-state properties of a dilute\nsystem of spin-orbit coupled Bose particles with such dispersion and\nshort-range repulsive interactions are universal: the chemical potential\nexhibits a quadratic dependence on the particle density as found in a\none-dimensional free Fermi gas.",
        "positive": "Floquet approach to $\\mathbb{Z}_{2}$ lattice gauge theories with\n  ultracold atoms in optical lattices: Quantum simulation has the potential to investigate gauge theories in\nstrongly-interacting regimes, which are up to now inaccessible through\nconventional numerical techniques. Here, we take a first step in this direction\nby implementing a Floquet-based method for studying $\\mathbb{Z}_2$ lattice\ngauge theories using two-component ultracold atoms in a double-well potential.\nFor resonant periodic driving at the on-site interaction strength and an\nappropriate choice of the modulation parameters, the effective Floquet\nHamiltonian exhibits $\\mathbb{Z}_2$ symmetry. We study the dynamics of the\nsystem for different initial states and critically contrast the observed\nevolution with a theoretical analysis of the full time-dependent Hamiltonian of\nthe periodically-driven lattice model. We reveal challenges that arise due to\nsymmetry-breaking terms and outline potential pathways to overcome these\nlimitations. Our results provide important insights for future studies of\nlattice gauge theories based on Floquet techniques."
    },
    {
        "anchor": "The Yrast Line of a Rapidly Rotating Bose Gas: Gross-Pitaevskii Regime: We consider an ultracold rotating Bose gas in a harmonic trap close to the\ncritical angular velocity so that the system can be considered to be confined\nto the lowest Landau level. With this assumption we prove that the\nGross-Pitaevskii energy functional accurately describes the ground state energy\nof the corresponding $N$-body Hamiltonian with contact interaction provided the\ntotal angular momentum $L$ is much less than $N^2$. While the Gross-Pitaevskii\nenergy is always an obvious variational upper bound to the ground state energy,\na more refined analysis is needed to establish it as an exact lower bound. We\nalso discuss the question of Bose-Einstein condensation in the parameter range\nconsidered. Coherent states together with inequalities in spaces of analytic\nfunctions are the main technical tools.",
        "positive": "Microwave-induced Fano-Feshbach resonances: We investigate the possibility to control the s-wave scattering length for\nthe interaction between cold bosonic atoms by using a microwave field. Our\nscheme applies to any atomic species with a ground state that is split by\nhyperfine interaction. We discuss more specifically the case of alkali-metal\natoms and calculate the change in the scattering length for 7Li, 23Na, 41K,\n87Rb, and 133Cs. Our results yield optimistic prospects for experiments with\nthe four latter species."
    },
    {
        "anchor": "Memory of the Initial Conditions in an Incompletely-Chaotic Quantum\n  System: Universal Predictions and an Application to Cold Atoms: Two zero-range-interacting atoms in a circular, transversely harmonic\nwaveguide are used as a test-bench for a quantitative description of the\ncrossover between integrability and chaos in a quantum system with no selection\nrules. For such systems we show that the expectation value after relaxation of\na generic observable is given by a linear interpolation between its initial and\nthermal expectation values. The variable of this interpolation is universal; it\ngoverns this simple law to cover the whole spectrum of the chaotic behavior\nfrom integrable regime through the well- developed quantum chaos. The\npredictions are confirmed for the waveguide system, where the mode occupations\nand the trapping energy were used as the observables of interest; a variety of\nthe initial states and a full range of the interaction strengths have been\ntested.",
        "positive": "Estimation of the condensate fraction from the static structure factor: We present an analytical method to estimate the condensate fraction $n_0/n$\nin strongly correlated systems for which the zero-temperature static structure\nfactor $S({\\bf p})$ is known. The advantage of the proposed method is that it\nallows one to predict the long-range behavior of the one-body density matrix\n(i) in macroscopic and mesoscopic systems, (ii) in three- and two-dimensional\ngeometry, (iii) at zero and low finite temperature, and (iv) in weakly and\nstrongly correlated regimes. Our method is tested against exact values obtained\nwith various quantum Monte Carlo methods in a number of strongly correlated\nsystems showing an excellent agreement. The proposed technique is also useful\nin numerical simulations as it allows one to extrapolate the condensate\nfraction to the thermodynamic limit for particle numbers as small as tens to\nhundreds. Our method is especially valuable for extracting the condensate\nfraction from the experimentally measured static structure factor $S({\\bf p})$,\nthus providing a new simple alternative technique for the estimation of\n$n_0/n$. We analyze available experimental data for $S({\\bf p})$ of superfluid\nhelium and find an excellent agreement with the experimental value of $n_0/n$."
    },
    {
        "anchor": "High-density limit of quasi-two-dimensional dipolar Bose gas: We consider a simple model of the quasi-two-dimensional dipolar Bose gas\nconfined in the one-dimensional square well potential. All dipoles are assumed\nto be oriented along the confining axis. By means of hydrodynamic approach it\nis shown that the general structure of the low-lying excitations can be\nanalyzed exactly. We demonstrate that the problem significantly simplifies in\nthe high-density limit for which the density profile in the confined direction\nas well as the leading-order contribution to the ground-state energy and\nspectrum of elementary excitations are calculated. The low-temperature result\nfor the damping rate of the phonon mode is also presented.",
        "positive": "Simulating an interacting gauge theory with ultracold Bose gases: We show how density dependent gauge potentials can be induced in dilute gases\nof ultracold atoms using light-matter interactions. We study the effect of the\nresulting interacting gauge theory and show how it gives rise to novel\ntopological states in the ultracold gas. We find in particular that the onset\nof persistent currents in a ring geometry is governed by a critical number of\nparticles. The density-dependent gauge potential is also found to support\nchiral solitons in a quasi-one-dimensional ultracold Bose gas."
    },
    {
        "anchor": "Engineering Dynamical Phase Diagrams with Driven Lattices in Spinor\n  Gases: We experimentally demonstrate that well-designed driven lattices are\nversatile tools to simultaneously tune multiple key parameters (namely\nspin-dependent interactions, spinor phase, and Zeeman energy) for manipulating\nphase diagrams of spinor gases with negligible heating and atom losses. This\nopens a new avenue for studying dynamical phase transitions in engineered\nHamiltonians. The driven lattice creates additional separatrices in phase space\nat driving-frequency-determined locations, with progressively narrower\nseparatrices at higher Zeeman energies due to modulation-induced higher\nharmonics. The vastly expanded range of magnetic fields at which significant\nspin dynamics occur and improved sensitivities at higher harmonics represent a\nstep towards quantum sensing with ultracold gases.",
        "positive": "Spin-charge-density wave in a squircle-like Fermi surface for ultracold\n  atoms: We derive and discuss an experimentally realistic model describing ultracold\natoms in an optical lattice including a commensurate, but staggered, Zeeman\nfield. The resulting band structure is quite exotic; fermions in the third band\nhave an unusual rounded picture-frame Fermi surface (essentially two concentric\nsquircles), leading to imperfect nesting. We develop a generalized\nSO(3,1)xSO(3,1) theory describing the spin and charge degrees of freedom\nsimultaneously, and show that the system can develop a coupled\nspin-charge-density wave order. This ordering is absent in studies of the\nHubbard model that treat spin and charge density separately."
    },
    {
        "anchor": "Symmetry-Breaking Topological Insulators in the $\\mathbb{Z}_2$\n  Bose-Hubbard Model: In this work, we study a one-dimensional model of interacting bosons coupled\nto a dynamical $\\mathbb{Z}_2$ field, the $\\mathbb{Z}_2$ Bose-Hubbard model, and\nanalyze the interplay between spontaneous symmetry breaking and topological\nsymmetry protection. In a previous work, we showed how this model exhibits a\nspontaneous breaking of the translational symmetry through a bosonic Peierls\ntransition. Here we find how, at half filling, the resulting phase also\ndisplays topological features that coexist with the presence of long-range\norder and yields a topological bond order wave. Using both analytical and\nnumerical methods, we describe the properties of this phase, showing that it\ncannot be adiabatically connected to a bosonic topological phase with vanishing\nHubbard interactions, and thus constitutes an instance of an\ninteraction-induced symmetry-breaking topological insulator.",
        "positive": "Two-time Correlations Probing the Dynamics of Dissipative Many-Body\n  Quantum Systems: Aging and Fast Relaxation: Two-time correlations are a crucial tool to probe the dynamics of many-body\nsystems. We use these correlation functions to study the dynamics of\ndissipative quantum systems. Extending the adiabatic elimination method, we\nshow that the correlations can display two distinct behaviors, depending on the\nobservable of interest: a fast exponential decay, with a timescale of the order\nof the dissipative coupling, or a much slower dynamics. We apply this formalism\nto bosons in a double well subjected to phase noise. While the single-particle\ncorrelations decay exponentially, the density-density correlations display slow\naging dynamics. We also show that the two-time correlations of dissipatively\nengineered quantum states can evolve in a drastically different manner compared\nto their Hamiltonian counterparts."
    },
    {
        "anchor": "Observing dynamical currents in a non-Hermitian momentum lattice: We report on the experimental realization and detection of dynamical currents\nin a spin-textured lattice in momentum space. Collective tunneling is\nimplemented via cavity-assisted Raman scattering of photons by a spinor\nBose-Einstein condensate into an optical cavity. The photon field inducing the\ntunneling processes is subject to cavity dissipation, resulting in effective\ndirectional dynamics in a non-Hermitian setting. We observe that the individual\ntunneling events are superradiant in nature and locally resolve them in the\nlattice by performing real-time, frequency-resolved measurements of the leaking\ncavity field. The results can be extended to a regime exhibiting a cascade of\ncurrents and simultaneous coherences between multiple lattice sites, where\nnumerical simulations provide further understanding of the dynamics. Our\nobservations showcase dynamical tunneling in momentum-space lattices and\nprovide prospects to realize dynamical gauge fields in driven-dissipative\nsettings.",
        "positive": "Measuring Topological Number of a Chern-Insulator from Quench Dynamics: In this letter we show how the topological number of a static Hamiltonian can\nbe measured from a dynamical quench process. We focus on a two-band Chern\ninsulator in two-dimension, for instance, the Haldane model, whose dynamical\nprocess can be described by a mapping from the $[k_x,k_y,t]$ space to the Bloch\nsphere, characterized by the Hopf invariant. Such a mapping has been\nconstructed experimentally by measurements in cold atom systems. We show that,\ntaking any two constant vectors on the Bloch sphere, their inverse images of\nthis mapping are two trajectories in the $[k_x,k_y,t]$ space, and the linking\nnumber of these two trajectories exactly equals to the Chern number of the\nstatic Hamiltonian. Applying this result to a recent experiment from the\nHamburg group, we show that the linking number of the trajectories of the phase\nvortices determines the phase boundary of the static Hamiltonian."
    },
    {
        "anchor": "Spectroscopic probes of quantum many-body correlations in polariton\n  microcavities: We investigate the many-body states of exciton-polaritons that can be\nobserved by pump-probe spectroscopy. Here, a weak-probe `spin-down' polariton\nis introduced into a coherent state of `spin-up' polaritons created by a strong\npump. We show that the $\\downarrow$ impurities become dressed by excitations of\nthe $\\uparrow$ medium, and form new polaronic quasiparticles that feature\ntwo-point and three-point many-body quantum correlations, which, in the low\ndensity regime, arise from coupling to the vacuum biexciton and triexciton\nstates respectively. In particular, we find that these correlations generate\nadditional branches and avoided crossings in the $\\downarrow$ optical\ntransmission spectrum that have a characteristic dependence on the\n$\\uparrow$-polariton density. Our results thus demonstrate a way to directly\nobserve correlated many-body states in an exciton-polariton system that go\nbeyond classical mean-field theories.",
        "positive": "Kardar-Parisi-Zhang universality in discrete two-dimensional\n  driven-dissipative exciton polariton condensates: The statistics of the fluctuations of quantum many-body systems are highly\nrevealing of their nature. In driven-dissipative systems displaying macroscopic\nquantum coherence, as exciton polariton condensates under incoherent pumping,\nthe phase dynamics can be mapped to the stochastic Kardar-Parisi-Zhang (KPZ)\nequation. However, in two dimensions (2D), it was theoretically argued that the\nKPZ regime may be hindered by the presence of vortices, and a non-equilibrium\nBKT behavior was reported close to condensation threshold. We demonstrate here\nthat, when a discretized 2D polariton system is considered, universal KPZ\nproperties can emerge. We support our analysis by extensive numerical\nsimulations of the discrete stochastic generalized Gross-Pitaevskii equation.\nWe show that the first-order correlation function of the condensate exhibits\nstretched exponential behaviors in space and time with critical exponents\ncharacteristic of the 2D KPZ universality class, and find that the related\nscaling function accurately matches the KPZ theoretical one, stemming from\nfunctional Renormalization Group. We also obtain the distribution of the phase\nfluctuations and find that it is non-Gaussian, as expected for a KPZ stochastic\nprocess."
    },
    {
        "anchor": "Multi-mode Bose-Hubbard model for quantum dipolar gases in confined\n  geometries: We theoretically consider ultracold polar molecules in a wave guide. The\nparticles are bosons, they experience a periodic potential due to an optical\nlattice oriented along the wave guide and are polarised by an electric field\northogonal to the guide axis. The array is mechanically unstable by opening the\ntransverse confinement in the direction orthogonal to the polarizing electric\nfield and can undergo a transition to a double-chain (zigzag) structure. For\nthis geometry we derive a multi-mode generalized Bose-Hubbard model for\ndetermining the quantum phases of the gas at the mechanical instability taking\ninto account the quantum fluctuations in all directions of space. Our model\nlimits the dimension of the numerically relevant Hilbert subspace by means of\nan appropriate decomposition of the field operator, which is obtained from a\nfield theoretical model of the linear-zigzag instability. We determine the\nphase diagrams of small systems using exact diagonalization and find that, even\nfor tight transverse confinement, the aspect ratio between the two transverse\ntrap frequencies controls not only the classical but also the quantum\nproperties of the ground state in a non-trivial way. Convergence tests at the\nlinear-zigzag instability demonstrate that our multi-mode generalized\nBose-Hubbard model can catch the essential features of the quantum phases of\ndipolar gases in confined geometries with a limited computational effort.",
        "positive": "Universality of the energy spectrum for two interacting harmonically\n  trapped ultra-cold atoms in one and two dimensions: Motivated by the recent article of P. Shea {\\it et al.} [Am. J. Phys. {\\bf\n77} (6), 2009] we examine the exactly solvable problem of two harmonically\ntrapped ultra-cold bosonic atoms interacting {\\it via} a short range potential\nin one and two dimensions. A straightforward application in one dimension shows\nthat the energy spectrum is universal, provided that the range of the potential\nis much smaller than the oscillator length, in addition to clearly illustrating\nwhy regularization is not required in the limit of zero range. The two\ndimensional problem is less trivial, requiring a more careful treatment as\ncompared to the one dimensional case. Our two dimensional analysis likewise\nreveals that the low-energy physics is also universal, in addition to providing\na simple method for obtaining the appropriately regularized two dimensional\npseudopotential."
    },
    {
        "anchor": "Dynamical Topological Quantum Phase Transitions for Mixed States: We introduce and study dynamical probes of band structure topology in the\npost-quench time-evolution from mixed initial states of quantum many-body\nsystems. Our construction generalizes the notion of dynamical quantum phase\ntransitions (DQPTs), a real-time counterpart of conventional equilibrium phase\ntransitions in quantum dynamics, to finite temperatures and generalized Gibbs\nensembles. The non-analytical signatures hallmarking these mixed state DQPTs\nare found to be characterized by observable phase singularities manifesting in\nthe dynamical formation of vortex-antivortex pairs in the interferometric phase\nof the density matrix. Studying quenches in Chern insulators, we find that\nchanges in the topological properties of the Hamiltonian can be identified in\nthis scenario, without ever preparing a topologically non-trivial or\nlow-temperature initial state. Our observations are of immediate relevance for\ncurrent experiments aimed at realizing topological phases in ultracold atomic\ngases.",
        "positive": "Dipolar Quantum Mixtures of Erbium and Dysprosium Atoms: We report on the first realization of heteronuclear dipolar quantum mixtures\nof highly magnetic erbium and dysprosium atoms. With a versatile experimental\nsetup, we demonstrate binary Bose-Einstein condensation in five different Er-Dy\nisotope combinations, as well as one Er-Dy Bose-Fermi mixture. Finally, we\npresent first studies of the interspecies interaction between the two species\nfor one mixture."
    },
    {
        "anchor": "Observation of Breathers in an Attractive Bose Gas: In weakly nonlinear dispersive systems, solitons are spatially localized\nsolutions which propagate without changing shape through a delicate balance\nbetween dispersion and self-focusing nonlinear effects. These states have been\nextensively studied in Bose-Einstein condensates, where interatomic\ninteractions give rise to such nonlinearities. Previous experimental work with\nmatter wave solitons has been limited to static intensity profiles. The\ncreation of matter wave breathers--dispersionless soliton-like states with\ncollective oscillation frequencies driven by attractive mean-field\ninteractions--have been of theoretical interest due to the exotic behaviour of\ninteracting matter wave systems. Here, using an attractively interacting\nBose-Einstein condensate, we present the first observation of matter wave\nbreathers. A comparison between experimental data and a cubic-quintic\nGross-Pitaevskii equation suggests that previously unobserved three-body\ninteractions may play an important role in this system. The observation of long\nlived stable breathers in an attractively interacting matter wave system\nindicates that there is a wide range of previously unobserved, but\ntheoretically predicted, effects that are now experimentally accessible.",
        "positive": "Quasi-Nambu-Goldstone Modes in Bose-Einstein Condensates: We show that quasi-Nambu-Goldstone (NG) modes, which play prominent roles in\nhigh energy physics but have been elusive experimentally, can be realized with\natomic Bose-Einstein condensates. The quasi-NG modes emerge when the symmetry\nof a ground state is larger than that of the Hamiltonian. When they appear, the\nconventional vacuum manifold should be enlarged. Consequently topological\ndefects that are stable within the conventional vacuum manifold become unstable\nand decay by emitting the quasi-NG modes. Contrary to conventional wisdom,\nhowever, we show that the topological defects are stabilized by quantum\nfluctuations that make the quasi-NG modes massive, thereby suppressing their\nemission."
    },
    {
        "anchor": "Toward an automated-algebra framework for high orders in the virial\n  expansion of quantum matter: The virial expansion provides a non-perturbative view into the thermodynamics\nof quantum many-body systems in dilute regimes. While powerful, the expansion\nis challenging as calculating its coefficients at each order $n$ requires\nanalyzing (if not solving) the quantum $n$-body problem. In this work, we\npresent a comprehensive review of automated algebra methods, which we developed\nto calculate high-order virial coefficients. The methods are computational but\nnon-stochastic, thus avoiding statistical effects; they are also for the most\npart analytic, not numerical, and amenable to massively parallel computer\narchitectures. We show formalism and results for coefficients characterizing\nthe thermodynamics (pressure, density, energy, static susceptibilities) of\nhomogeneous and harmonically trapped systems, and explain how to generalize\nthem to other observables such as the momentum distribution, Tan's contact, and\nthe structure factor.",
        "positive": "Soliton sheets formed by interference of Bose-Einstein condensates in\n  optical lattices: Soliton sheets which are formed by interference of Bose Einstein condensates\noccupying different single-particle states are observed in optical lattice\npotential. This structure consists of one-dimensional stationary solitons\narranged periodically along the peaks of optical lattice (y direction) with the\nphase difference between the two sides of the soliton sheets is a linear\nfunction of y in each period, so we call it soliton sheet. A y component\nvelocity difference exists between the two sides of the soliton sheet. Similar\nvelocity distributions can be produced by the alignment of an infinite number\nof isotropic vortices along the peaks of the optical lattice. Their difference\nis that the soliton sheet structure is not limited by the number of phase\nsingularities and can be generated even without phase singularities."
    },
    {
        "anchor": "Superlattice switching from parametric instabilities in a\n  driven-dissipative BEC in a cavity: We numerically obtain the full time-evolution of a parametrically-driven\ndissipative Bose-Einstein condensate in an optical cavity and investigate the\nimplications of driving for the phase diagram. Beyond the normal and\nsuperradiant phases, a third nonequilibrium phase emerges as a manybody\nparametric resonance. This dynamical normal phase switches between two\nsymmetry-broken superradiant configurations. The switching implies a breakdown\nof the system's mapping to the Dicke model. Unlike the other phases, the\ndynamical normal phase shows features of nonintegrability and thermalization.",
        "positive": "Lattice induced stripe phase in Bose-Einstein condensate under\n  non-inertial and inertial motion: We consider a parametrically forced Bose-Einstein condensate in the combined\npresence of an optical lattice and harmonic oscillator potential in the mean\nfield approach. A spatial symmetry broken Bose-condensed phase in non-inertial\nand inertial frame yields a stripe phase in the presence of both cubic and\nquintic nonlinearities. We show that existence of such stripe phase solely\ndepends on the interplay between the quintic nonlinearity and lattice\npotential. Furthermore, we observe that a time-dependent harmonic oscillator\nfrequency destroys such stripe ordering. A linear stability analysis of the\nobtained solution is performed and we found that the solution is stable. In\norder to gain a better understanding of the underlying physics, we compute the\nenergy, showing nonlinear compression of the condensate in some parameter\ndomain."
    },
    {
        "anchor": "Energy of N two-dimensional bosons with zero-range interactions: We derive an integral equation describing $N$ two-dimensional bosons with\nzero-range interactions and solve it for the ground state energy $B_N$ by\napplying a stochastic diffusion Monte Carlo scheme for up to 26 particles. We\nconfirm and go beyond the scaling $B_N\\propto 8.567^N$ predicted by Hammer and\nSon [Phys. Rev. Lett. {\\bf 93}, 250408 (2004)] in the large-$N$ limit.",
        "positive": "Anyon braiding on a fractal lattice with a local Hamiltonian: There is a growing interest in searching for topology in fractal dimensions\nwith the aim of finding different properties and advantages compared to the\ninteger dimensional case. It has previously been shown that the Laughlin state\ncan be adapted to fractal lattices. A key element in doing so is to replace the\nuniform background charge by a background charge that resides only on the\nlattice sites. This motivates the study of Hofstadter type models on fractal\nlattices, in which the magnetic field is present only at the lattice sites.\nHere, we study such models for hardcore bosons on finite lattices derived from\nthe Sierpinski carpet and on square lattices with open boundary conditions. We\nfind that the system sizes that we can investigate with exact diagonalization\nare generally too small to judge whether these local models are topological or\nnot. Studying the particle densities on the lattices derived from the\nSierpinski carpet, we find that the densities tend to accumulate in the regions\nthat are locally similar to a square lattice. Such accumulation seems to be\nincompatible with the uniform densities in fractional quantum Hall systems,\nwhich might suggest that the models are not topological. Our computations\nprovide guidance for future searches for topology in finite systems. We also\npropose a scheme to implement both fractal lattices and our proposed local\nHamiltonian with ultracold atoms in optical lattices, which could allow for\nquantum simulators to go beyond the numerical results presented here."
    },
    {
        "anchor": "Tuning an effective spin chain of three strongly interacting\n  one-dimensional fermions with the transversal confinement: Strongly interacting one-dimensional fermions form an effective spin chain in\nthe absence of an external lattice potential. We show that the exchange\ncoefficients of such a chain may be locally tuned by properly tailoring the\ntransversal confinement. In particular, in the vicinity of a\nconfinement-induced resonance (CIR) the exchange coefficients may have\nsimultaneously opposite ferromagnetic and antiferromagnetic characters at\ndifferent locations along the trap axis. Moreover, the local exchanges may be\nengineered to induce avoided crossings between spin states at the CIR, and\nhence a ramp across the resonance may be employed to create different spin\nstates and to induce spin dynamics in the chain. We show that such unusual spin\nchains have already been realized in the experiment of Murmann et al. [Phys.\nRev. Lett. 115, 215301 (2015)].",
        "positive": "Preparation of stable excited states in an optical lattice via sudden\n  quantum quench: We study how stable excited many-body states of the Bose-Hubbard model,\nincluding both the gas-like state for strongly attractive bosons and bound\ncluster state for repulsive bosons, can be produced with cold bosonic atoms in\nan one-dimensional optical lattice. Starting from the initial ground states of\nstrongly interacting bosonic systems, we can achieve stable excited states of\nthe systems with opposite interaction strength by suddenly switching the\ninteraction to the opposite limit. By exactly solving dynamics of the\nBose-Hubbard model, we demonstrate that the produced excited state can be a\nvery stable dynamic state. This allows the experimental study of excited state\nproperties of ultracold atoms system in optical lattices."
    },
    {
        "anchor": "Vortex line in spin-orbit coupled atomic Fermi gases: It has recently been shown that the spin-orbit coupling gives rise to\ntopologically-nontrivial and thermodynamically-stable gapless superfluid phases\nwhen the pseudo-spin populations of an atomic Fermi gas is imbalanced, with the\npossibility of featuring Majorana zero-energy quasiparticles. In this paper, we\nconsider a Rashba-type spin-orbit coupling, and use the Bogoliubov-de Gennes\nformalism to analyze a single vortex line along a finite cylinder with a\nperiodic boundary condition. We show that the signatures for the appearance of\ncore- and edge-bound states can be directly found in the density of\nsingle-particle states and particle-current density. In particular, we find\nthat the pseudo-spin components counterflow near the edge of the cylinder, the\nstrength of which increases with increasing spin-orbit coupling.",
        "positive": "Bragg spectroscopy and pair-breaking-continuum mode in a superfluid\n  Fermi gas: The superfluid, pair condensed spin-1/2 Fermi gases are supposed to exhibit\nat nonzero wave vector a still unobserved collective excitation mode in their\npair-breaking continuum. Using BCS theory at zero temperature and in the long\nwavelength limit, we predict that this mode is quantitatively observable (in\nfrequency, width and spectral weight) in the response of a cold atom gas to a\nlaser Bragg excitation, if one measures the perturbation induced on the order\nparameter modulus rather than on the density."
    },
    {
        "anchor": "A generalized effective spin-chain formalism for strongly interacting\n  spinor gases in optical lattice: A generalized effective spin-chain model is developed for studies of strongly\ninteracting spinor gases in a one-dimensional (1D) optical lattice. The spinor\ngas is mapped to a system of spinless fermions and a spin-chain. A generalized\neffective spin-chain Hamiltonian that acts on the mapped system is developed to\nstudy the static and dynamic properties of the spinor gas. This provides a\ncomputationally efficient alternative tool to study strongly interacting spinor\ngases in 1D lattice systems. This formalism permits the study of spinor gases\nwith arbitrary spin and statistics, providing a generalized approach for 1D\nstrongly interacting gases. By virtue of its simplicity, it provides an easier\ntool to study and gain deeper insights into the system. In combination with the\nmodel defined previously for continuum systems, a unified framework is\ndeveloped. Studying the mapped system using this formalism recreates the\nphysics of spinor gas in 1D lattice. Additionally, the time evolution of a\nquenched system is studied. The generalized effective spin-chain formalism has\npotential applications in the study of a multitude of interesting phenomena\narising in lattice systems such as high-$T_c$ superconductivity and the\nspin-coherent \\& spin-incoherent Luttinger liquid regimes.",
        "positive": "Non-Bloch quench dynamics: We study the quench dynamics of non-Hermitian topological models with\nnon-Hermitian skin effects. Adopting the non-Bloch band theory and projecting\nquench dynamics onto the generalized Brillouin zone, we find that emergent\ntopological structures, in the form of dynamic skyrmions, exist in the\ngeneralized momentum-time domain, and are correlated with the non-Bloch\ntopological invariants of the static Hamiltonians. The skyrmion structures\nanchor on the fixed points of dynamics whose existence are conditional on the\ncoincidence of generalized Brillouin zones of the pre- and post-quench\nHamiltonians. Global signatures of dynamic skyrmions, however, persist well\nbeyond such a condition, thus offering a general dynamic detection scheme for\nnon-Bloch topology in the presence of non-Hermitian skin effects. Applying our\ntheory to an experimentally relevant, non-unitary quantum walk, we explicitly\ndemonstrate how the non-Bloch topological invariants can be revealed through\nthe non-Bloch quench dynamics."
    },
    {
        "anchor": "Bogoliubov phonons in a Bose-Einstein condensate from the one-loop\n  perturbative renormalization group: Wilson's renormalization-group approach to the weakly-interacting\nsingle-component Bose gas is discussed within the symmetry-broken, condensate\nphase. Extending upon the work by Bijlsma and Stoof [Phys. Rev. A 54, 5085\n(1996), see http://doi.org/10.1103/PhysRevA.54.5085 ], wave-function\nrenormalization of the temporal derivative contributions to the effective\naction is included in order to capture sound-like quasiparticle excitations\nwith wave lengths larger than the healing-length scale. By means of a suitable\nrescaling scheme we achieve convergence of the coupling flows, which serve as a\nmeans to determine the condensate depletion in accordance with Bogoliubov\ntheory, as well as the interaction-induced shift of the critical temperature.",
        "positive": "Cooling Fermions in an Optical Lattice by Adiabatic Demagnetization: The Fermi-Hubbard model describes ultracold fermions in an optical lattice\nand exhibits antiferromagnetic long-ranged order below the N\\'{e}el\ntemperature. However, reaching this temperature in the lab has remained an\nelusive goal. In other atomic systems, such as trapped ions, low temperatures\nhave been successfully obtained by adiabatic demagnetization, in which a strong\neffective magnetic field is applied to a spin-polarized system, and the\nmagnetic field is adiabatically reduced to zero. Unfortunately, applying this\napproach to the Fermi-Hubbard model encounters a fundamental obstacle: the\n$SU(2)$ symmetry introduces many level crossings that prevent the system from\nreaching the ground state, even in principle. However, by breaking the $SU(2)$\nsymmetry with a spin-dependent tunneling, we show that adiabatic\ndemagnetization can achieve low temperature states. Using density matrix\nrenormalization group (DMRG) calculations in one dimension, we numerically find\nthat demagnetization protocols successfully reach low temperature states of a\nspin-anisotropic Hubbard model, and we discuss how to optimize this protocol\nfor experimental viability. By subsequently ramping spin-dependent tunnelings\nto spin-independent tunnelings, we expect that our protocol can be employed to\nproduce low-temperature states of the Fermi-Hubbard Model."
    },
    {
        "anchor": "Kapitza stabilization of a repulsive Bose-Einstein condensate in an\n  oscillating optical lattice: We show that the Kapitza stabilization can occur in the context of nonlinear\nquantum fields. Through this phenomenon, an amplitude-modulated lattice can\nstabilize a Bose-Einstein condensate with repulsive interactions and prevent\nthe spreading for long times. We present a classical and quantum analysis in\nthe framework of Gross-Pitaevskii equation, specifying the parameter region\nwhere stabilization occurs. Effects of nonlinearity lead to a significant\nincrease of the stability domain compared with the classical case. Our proposal\ncan be experimentally implemented with current cold atom settings.",
        "positive": "Time dependent impurity in ultracold fermions: orthogonality catastrophe\n  and beyond: Recent experimental realization of strongly imbalanced mixtures of ultracold\natoms opens new possibilities for studying impurity dynamics in a controlled\nsetting. We discuss how the techniques of atomic physics can be used to explore\nnew regimes and manifestations of Anderson's orthogonality catastrophe (OC),\nwhich could not be accessed in solid state systems. We consider a system of\nimpurity atoms localized by a strong optical lattice potential and immersed in\na sea of itinerant Fermi atoms. Ramsey interference experiments with impurity\natoms probe OC in the time domain, while radio-frequency (RF) spectroscopy\nprobes OC in the frequency domain. The OC in such systems is universal for all\ntimes and is determined by the impurity scattering length and Fermi wave vector\nof itinerant fermions. We calculate the universal Ramsey response and RF\nabsorption spectra. In addition to the standard power-law contribution, which\ncorresponds to the excitation of multiple particle-hole pairs near the Fermi\nsurface, we identify a novel contribution to OC that comes from exciting one\nextra particle from the bottom of the itinerant band. This gives rise to a\nnon-analytic feature in the RF absorption spectra, which evolves into a true\npower-law singularity with universal exponent 1/4 at the unitarity.\nFurthermore, we discuss the manifestations of OC in spin-echo experiments, as\nwell as in the energy counting statistic of the Fermi gas following a sudden\nquench of the impurity state. Finally, systems in which the itinerant fermions\nhave two or more hyperfine states provide an even richer playground for\nstudying non-equilibrium impurity physics, allowing one to explore\nnon-equilibrium OC and to simulate quantum transport through nano-structures.\nThis provides a useful connection between cold atomic systems and mesoscopic\nquantum transport."
    },
    {
        "anchor": "Quantum dynamics of hard-core bosons in tilted bichromatic optical\n  lattices: We study the dynamics of strongly repulsive Bose gas in tilted or driven\nbichromatic optical lattices. Using the Bose-Fermi mapping and exact numerical\nmethod, we calculate the reduced single-particle density matrices, and study\nthe dynamics of density profile, momentum distribution and condensate fraction.\nWe show the oscillating and breathing mode of dynamics, and depletion of\ncondensate for short time dynamics. For long time dynamics, we clearly show the\nreconstruction of system at integer multiples of Bloch-Zener time. We also show\nhow to achieve clear Bloch oscillation and Landau-Zener tunnelling for\nmany-particle systems.",
        "positive": "Effect of Disorder in BCS-BEC Crossover: In this article we have investigated the effect of weak random disorder in\nthe BCS-BEC crossover region. The disorder is included in the mean field\nformalism through NSR theory of superconducting fluctuations. A self consistent\nnumerical solution of the coupled equations involving the superfluid gap\nparameter and density as a function of the disorder strength, albeit unaffected\nin the BCS phase, yields a depleted order parameter in the BEC regime and an\ninteresting nonmonotonic behavior of the condensate fraction in the vicinity of\nthe unitary region, and a gradual depletion thereafter, as the pairing\ninteraction is continuously tuned across the BCS-BEC crossover. The unitary\nregime thus demonstrates a robust paradigm of superfluidity even when the\ndisorder is introduced. To support the above feature and shed light on a\nlingering controversial issue, we have computed the behavior of the sound mode\nacross the crossover that distinctly reveals a suppression of the sound\nvelocity. We also find the Landau critical velocity that shows similar\nnonmonotonicity as that of the condensate fraction data, thereby supporting a\nstable superfluid scenario in the unitary limit."
    },
    {
        "anchor": "Strongly Interacting Fermi Gases: Hydrodynamics and Beyond: This thesis considers out-of-equilibrium dynamics of strongly interacting\nnon-relativistic Fermi gases in several two and three dimensional geometries.\nThe tools of second-order hydrodynamics and gauge-gravity duality will be\nutilized to address this system. Many of the themes of this work are motivated\nby the observed similarities in transport properties between strongly\ninteracting Fermi gases and other very different strongly interacting quantum\nfluids such as the quark-gluon plasma, high temperature superconductors, and\nquantum field theories described by gauge-gravity duality. In particular, these\nsystems all nearly saturate the conjectured lower bound on the ratio of shear\nviscosity to entropy density $\\eta/s \\geq \\hbar/(4 \\pi k_B)$ coming from the\nAdS/CFT correspondence. Among other things, this observation, in conjunction\nwith current experiment and data analysis in atomic, condensed matter, and\nnuclear physics lends itself to the following questions: How perfect of a fluid\nis the strongly interacting Fermi gas, and can one find a more stringent\nconstraint on $\\eta/s$ in Fermi gases? Do the similarities in transport\nproperties among strongly interacting quantum systems extend beyond dynamics\ncontrolled by the hydrodynamical shear viscosity? In regards to the first\nquestion, by utilizing second-order hydrodynamics, it will be demonstrated that\nhigher-order collective modes of a harmonically trapped Fermi gas may serve as\na more sensitive probe of the shear viscosity. For the second question, both\nsecond-order hydrodynamics and a gravity dual theory are used to make\npredictions about dynamics occurring on short timescales where hydrodynamics is\nexpected to break down. In particular the appearance of a class of\n\"non-hydrodynamic\" collective modes not contained within a Navier-Stokes\ndescription of the strongly interacting Fermi gas will be discussed.",
        "positive": "Correlations and synchronization in a Bose-Fermi mixture: We study a Bose-Fermi mixture within the framework of the mean-field theory,\nincluding three possible regimes for the fermionic species: fully polarized,\nBCS, and unitarity. Starting from the 3D description and using the variational\napproximation (VA), we derive 1D and 2D systems of equations, under the\ncorresponding confining potentials. This method produces a pair of nonlinear\nSchr\\\"{o}dinger (NLS) equations coupled to algebraic equations for the\ntransverse widths of the confined state. The equations incorporate interactions\nbetween atoms of the same species and between the species, assuming that the\nlatter can be manipulated by means of the Feshbach resonance (FR). As an\napplication, we explore spatial density correlations in the ground state (GS)\nbetween the species, concluding that they strongly depend on the sign and\nstrength of the inter-species interaction. Also studied are the dynamics of the\nmixture in a vicinity of the GS and the corresponding spatiotemporal\ninter-species correlation. The correlations are strongly affected by the\nfermionic component, featuring the greatest variation in the unitary regime.\nResults produced by the VA are verified by comparison with full numerical\nsolutions."
    },
    {
        "anchor": "Numerically exact treatment of many body self-organization in a cavity: We investigate the full quantum evolution of ultracold interacting bosonic\natoms on a chain and coupled to an optical cavity. Extending the time-dependent\nmatrix product state techniques and the many-body adiabatic elimination\ntechnique to capture the global coupling to the cavity mode and the open nature\nof the cavity, we examine the long time behavior of the system beyond the\nmean-field elimination of the cavity field. We investigate the many body steady\nstates and the self-organization transition for a wide range of parameters. We\nshow that in the self-organized phase the steady state consists in a mixture of\nthe mean-field predicted density wave states and excited states with additional\ndefects. In particular, for large dissipation strengths a steady state with a\nfully mixed atomic sector is obtained crucially different from the predicted\nmean-field state.",
        "positive": "Time fractals and discrete scale invariance with trapped ions: We show that a one-dimensional chain of trapped ions can be engineered to\nproduce a quantum mechanical system with discrete scale invariance and\nfractal-like time dependence. By discrete scale invariance we mean a system\nthat replicates itself under a rescaling of distance for some scale factor, and\na time fractal is a signal that is invariant under the rescaling of time. These\nfeatures are reminiscent of the Efimov effect, which has been predicted and\nobserved in bound states of three-body systems. We demonstrate that discrete\nscale invariance in the trapped ion system can be controlled with two\nindependently tunable parameters. We also discuss the extension to n-body\nstates where the discrete scaling symmetry has an exotic heterogeneous\nstructure. The results we present can be realized using currently available\ntechnologies developed for trapped ion quantum systems."
    },
    {
        "anchor": "Strongly interacting Bose-Fermi mixture: mediated interaction, phase\n  diagram and sound propagation: Motivated by recent surprising experimental findings, we develop a\nstrong-coupling theory for Bose-Fermi mixtures capable of treating resonant\ninter-species interactions while satisfying the compressibility sum rule. We\nshow that the mixture can be stable at large interaction strengths close to\nresonance, in agreement with the experiment but at odds with the widely used\nperturbation theory. We also calculate the sound velocity of the Bose gas in\nthe $^{133}$Cs-$^6$Li mixture, again finding good agreement with the\nexperimental observations both at weak and strong interactions. A central\ningredient of our theory is the generalization of a fermion mediated\ninteraction to strong Bose-Fermi scatterings and to finite frequencies. This\nfurther leads to a predicted hybridization of the sound modes of the Bose and\nFermi gases, which can be directly observed using Bragg spectroscopy.",
        "positive": "Density-Dependent Synthetic Gauge Fields Using Periodically Modulated\n  Interactions: We show that density-dependent synthetic gauge fields may be engineered by\ncombining periodically modu- lated interactions and Raman-assisted hopping in\nspin-dependent optical lattices. These fields lead to a density- dependent\nshift of the momentum distribution, may induce superfluid-to-Mott insulator\ntransitions, and strongly modify correlations in the superfluid regime. We show\nthat the interplay between the created gauge field and the broken sublattice\nsymmetry results, as well, in an intriguing behavior at vanishing interactions,\ncharacterized by the appearance of a fractional Mott insulator."
    },
    {
        "anchor": "Single impurities in a Bose-Einstein condensate can make two polaron\n  flavors: Polarons, self-localized composite objects formed by the interaction of a\nsingle impurity particle with a host medium, are a paradigm of strong\ninteraction many-body physics. We show that dilute gas Bose-Einstein\ncondensates (BEC's) are the first medium known to self-localize the same\nimpurity particles both in a Landau-Pekar polaron state akin to that of\nself-localized electrons in a dielectric lattice, and in a bubble state akin to\nthat of electron bubbles in helium. We also show that the BEC-impurity system\nis fully characterized by just two dimensionless coupling constants, and that\nit can be adiabatically steered from the Landau-Pekar regime to the bubble\nregime in a smooth crossover trajectory.",
        "positive": "Detecting Hidden Order in Fractional Chern Insulators: Topological phase transitions go beyond Ginzburg and Landau's paradigm of\nspontaneous symmetry breaking and occur without an associated local order\nparameter. Instead, such transitions can be characterized by the emergence of\nnon-local order parameters, which require measurements on extensively many\nparticles simultaneously - an impossible venture in real materials. On the\nother hand, quantum simulators have demonstrated such measurements, making them\nprime candidates for an experimental confirmation of non-local topological\norder. Here, building upon the recent advances in preparing few-particle\nfractional Chern insulators using ultracold atoms and photons, we propose a\nrealistic scheme for detecting the hidden off-diagonal long-range order\n(HODLRO) characterizing Laughlin states. Furthermore, we demonstrate the\nexistence of this hidden order in fractional Chern insulators, specifically for\nthe $\\nu=\\frac{1}{2}$-Laughlin state in the isotropic Hofstadter-Bose-Hubbard\nmodel. This is achieved by large-scale numerical density matrix renormalization\ngroup (DMRG) simulations based on matrix product states, for which we formulate\nan efficient sampling procedure providing direct access to HODLRO in close\nanalogy to the proposed experimental scheme. We confirm the characteristic\npower-law scaling of HODLRO, with an exponent $\\frac{1}{\\nu} = 2$, and show\nthat its detection requires only a few thousand snapshots. This makes our\nscheme realistically achievable with current technology and paves the way for\nfurther analysis of non-local topological orders, e.g. in topological states\nwith non-Abelian anyonic excitations."
    },
    {
        "anchor": "Mass-imbalanced Three-body Systems in 2D: bound states and the\n  analytical approach to the adiabatic potential: Three-body systems in two dimensions with zero-range interactions are\nconsidered for general masses and interaction strengths. The problem is\nformulated in momentum space and the numerical solution of the Schr\\\"odinger\nequation is used to study universal properties of such systems with respect to\nthe bound-state energies. The number of universal bound states is represented\nin a form of boundaries in a mass-mass diagram. The number of bound states is\nstrongly mass dependent and increases as one particle becomes much lighter than\nthe other ones. This behavior is understood through an accurate analytical\napproximation to the adiabatic potential for one light particle and two heavy\nones.",
        "positive": "Interacting in-plane molecular dipoles in a zig-zag chain: The system with externally polarized dipole molecules at half-filling moving\nalong a one-dimensional zig-zag chain is studied theoretically, including the\nground-state phase diagram. The dipoles are oriented in-plane. Together with\nthe geometry of the chain this gives rise to a bond-alternating nearest\nneighbor interaction due to simultaneous attractive and repulsive interactions.\nBecause of the quantum Zeno effect due to the reactive nature of molecules the\nsystem can be treated as hard-core. By tuning the ratio between the\nnearest-neighbor interaction and hopping, various phases can be accessed by\ncontrolling the polarization angle. In the ultra-strong coupling limit, the\nsystem simplifies to a frustrated extended axial Ising model. For the small\ncoupling limit, qualitative discussion of the ordering behavior using effective\nfield theory arguments is provided. We show that when chain angle is small, the\nsystem mostly exhibits BKT-type phase transitions, whereas large chain angle\nwould drive the system into a gapped (Ising) dimerized phase, where the hopping\nstrength is closely related to the orientation of dimerized pairs."
    },
    {
        "anchor": "Machine-learning the phase diagram of a strongly-interacting Fermi gas: We determine the phase diagram of strongly correlated fermions in the\ncrossover from Bose-Einstein condensates of molecules (BEC) to Cooper pairs of\nfermions (BCS) utilizing an artificial neural network. By applying advanced\nimage recognition techniques to the momentum distribution of the fermions, a\nquantity which has been widely considered as featureless for providing\ninformation about the condensed state, we measure the critical temperature and\nshow that it exhibits a maximum on the bosonic side of the crossover.\nAdditionally, we back-analyze the trained neural network and demonstrate that\nit interprets physically relevant quantities.",
        "positive": "Ultracold atoms at unitarity within quantum Monte Carlo: Variational and diffusion quantum Monte Carlo (VMC and DMC) calculations of\nthe properties of the zero-temperature fermionic gas at unitarity are reported.\nThe ratio of the energy of the interacting to the non-interacting gas for a\nsystem of 128 particles is calculated to be 0.4517(3) in VMC and 0.4339(1) in\nthe more accurate DMC method. The spherically-averaged pair-correlation\nfunctions, momentum densities, and one-body density matrices are very similar\nin VMC and DMC, but the two-body density matrices and condensate fractions show\nsome differences. Our best estimate of the condensate fraction of 0.51 is a\nlittle smaller than values from other quantum Monte Carlo calculations."
    },
    {
        "anchor": "Rapidity and momentum distributions of 1D dipolar quantum gases: We explore the effect of tunable integrability breaking dipole-dipole\ninteractions in the equilibrium states of highly magnetic 1D Bose gases of\ndysprosium at low temperatures. We experimentally observe that in the strongly\ncorrelated Tonks-Girardeau regime, rapidity and momentum distributions are\nnearly unaffected by the dipolar interactions. By contrast, we also observe\nthat significant changes of these distributions occur when decreasing the\nstrength of the contact interactions. We show that the main experimental\nobservations are captured by modeling the system as an array of 1D gases with\nonly contact interactions, dressed by the contribution of the short-range part\nof the dipolar interactions. Improvements to theory-experiment correspondence\nwill require new tools tailored to near-integrable models possessing both short\nand long-range interactions.",
        "positive": "Resonant light enhances phase coherence in a cavity QED simulator of\n  fermionic superfluidity: Cavity QED experiments are natural hosts for non-equilibrium phases of matter\nsupported by photon-mediated interactions. In this work, we consider a cavity\nQED simulation of the BCS model of superfluidity, by studying regimes where the\ncavity photons act as dynamical degrees of freedom instead of mere mediators of\nthe interaction via virtual processes. We find an enhancement of long time\ncoherence following a quench whenever the cavity frequency is tuned into\nresonance with the atoms. We discuss how this is equivalent to enhancement of\nnon-equilibrium superfluidity and highlight similarities to an analogous\nphenomena recently studied in solid state quantum optics. We also discuss the\nconditions for observing this enhanced resonant pairing in experiments by\nincluding the effect of photon losses and inhomogeneous coupling in our\nanalysis."
    },
    {
        "anchor": "Quantum Dynamics of Cold Atomic Gas with $SU(1,1)$ Symmetry: Motivated by recent advances in quantum dynamics, we investigate the dynamics\nof the system with $SU(1,1)$ symmetry. Instead of performing the time-ordered\nintegral for the evolution operator of the time-dependent Hamiltonian, we show\nthat the time evolution operator can be expressed as an $SU(1,1)$ group\nelement. Since the $SU(1,1)$ group describes the \"rotation\" on a hyperbolic\nsurface, the dynamics can be visualized on a Poincar\\'e disk, a stereographic\nprojection of the upper hyperboloid. As an example, we present the trajectory\nof the revival of Bose-Einstein condensation and that of the scale-invariant\nFermi gas on the Poincar\\'e disk. Further considering the quantum gas in the\noscillating lattice, we also study the dynamics of the system with\ntime-dependent single-particle dispersion. Our results are hopefully to be\nchecked in current experiments.",
        "positive": "Correlation Effects in the Quench-Induced Phase Separation Dynamics of a\n  Two-Species Ultracold Quantum Gas: We explore the quench dynamics of a binary Bose-Einstein condensate crossing\nthe miscibility-immiscibility threshold and vice versa, both within and in\nparticular beyond the mean-field approximation. Increasing the interspecies\nrepulsion leads to the filamentation of the density of each species, involving\nshorter wavenumbers and longer spatial scales in the many-body approach. These\nfilaments appear to be strongly correlated and exhibit domain-wall structures.\nFollowing the reverse quench process multiple dark-antidark solitary waves are\nspontaneously generated and subsequently found to decay in the many-body\nscenario. We simulate single-shot images to connect our findings to possible\nexperimental realizations. Finally, the growth rate of the variance of a sample\nof single-shots probes the degree of entanglement inherent in the system."
    },
    {
        "anchor": "Formation of matter-wave soliton trains by modulational instability: Nonlinear systems can exhibit a rich set of dynamics that are inherently\nsensitive to their initial conditions. One such example is modulational\ninstability, which is believed to be one of the most prevalent instabilities in\nnature. By exploiting a shallow zero-crossing of a Feshbach resonance, we\ncharacterize modulational instability and its role in the formation of\nmatter-wave soliton trains from a Bose-Einstein condensate. We examine the\nuniversal scaling laws exhibited by the system, and through real-time imaging,\naddress a long-standing question of whether the solitons in trains are created\nwith effectively repulsive nearest neighbor interactions, or rather, evolve\ninto such a structure.",
        "positive": "Quench Dynamics and Hall Response of Interacting Chern Insulators: We study the coherent non-equilibrium dynamics of interacting two-dimensional\nsystems after a quench from a trivial to a topological Chern insulator phase.\nWhile the many-body wavefunction is constrained to remain topologically trivial\nunder local unitary evolution, we find that the Hall response of the system can\ndynamically approach a thermal value of the post-quench Hamiltonian, even\nthough the efficiency of this thermalization process is shown to strongly\ndepend on the microscopic form of the interactions. Quite remarkably, the\neffective temperature of the steady state Hall response can be arbitrarily\ntuned with the quench parameters. Our findings suggest a new way of inducing\nand observing low temperature topological phenomena in interacting ultracold\natomic gases, where the considered quench scenario can be realized in current\nexperimental set-ups."
    },
    {
        "anchor": "Stability Criterion for Superfluidity based on the Density Spectral\n  Function: We study a stability criterion hypothesis for superfluids in terms of the the\nlocal density spectral function $I_n (r, \\omega)$ applicable both to\nhomogeneous and inhomogeneous systems. We evaluate the local density spectral\nfunction in the presence of a one-dimensional repulsive/attractive external\npotential within the Bogoliubov theory using solutions of the tunneling\nproblem. We also evaluate the local density spectral function using an\northogonal basis, and calculate the autocorrelation function $C_n (r,t)$. When\nsuperfluids flow below a threshold, we find that in the $d$-dimensional system,\n$I_n (r, \\omega) \\propto \\omega^{d}$ in the low-energy regime and $C_n (r, t)\n\\propto 1/t^{d+1}$ in the long-time regime hold. When superfluids flow with the\ncritical current, on the other hand, we find $I_n (r, \\omega) \\propto\n\\omega^{\\beta}$ in the low-energy regime and $C_n (r,t) \\propto 1/t^{\\beta+1}$\nin the long-time regime with $\\beta < d$. These results support the stability\ncriterion hypothesis recently proposed.",
        "positive": "Probing the optical conductivity of trapped charge-neutral quantum gases: We study a harmonically confined atomic gas which is subjected to an\nadditional external potential such as an optical lattice. Using a linear\nresponse formulation, we determine the response of the gas to a small,\ntime-dependent displacement of the harmonic trap and derive a simple exact\nrelation showing that the centre-of-mass position of the atomic cloud is\ndirectly related to the global optical conductivity of the system. We\ndemonstrate the usefulness of this approach by calculating the optical\nconductivity of bosonic atoms in an optical lattice. In the Mott insulating\nphase, there is clear evidence of an optical Mott gap, providing a\nproof-of-principle demonstration that the global optical conductivity gives\nhigh-quality information about the exci- tations of strongly-correlated quantum\ngases."
    },
    {
        "anchor": "Transport of ultracold Bose gases beyond the Gross-Pitaevskii\n  description: We explore atom-laser-like transport processes of ultracold Bose-condensed\natomic vapors in mesoscopic waveguide structures beyond the Gross-Pitaevskii\nmean-field theory. Based on a microscopic description of the transport process\nin the presence of a coherent source which models the outcoupling from a\nreservoir of perfectly Bose-Einstein condensed atoms, we derive a system of\ncoupled quantum evolution equations that describe the dynamics of a dilute\ncondensed Bose gas in the framework of the Hartree-Fock-Bogoliubov\napproximation. We apply this method to study the transport of dilute Bose gases\nthrough an atomic quantum dot and through waveguides with disorder. Our\nnumerical simulations reveal that the onset of an explictly time-dependent flow\ncorresponds to the appearance of strong depletion of the condensate on the\nmicroscopic level and leads to a loss of global phase coherence.",
        "positive": "Curvature Induced Topological Defects of $p$-wave Superfluid on a Sphere: We study the ground state of spinless fermions living on a sphere across\n$p$-wave Feschbach resonances. By construsting a microscopic model of fermions\non a general curved surface, we show that the Guassian curvature induces an\nemergent magnetic field coupled to the $p\\pm ip$ order parameters. In the case\nof a sphere, the magnetic field corresponds to a Dirac monopole field, which\ncauses topological defects in the superfluid ground state. Using the BCS mean\nfield theory, we calculate its many-body ground state self consistently and\ngive the phase diagram. The ground state may exhibit two types of topological\ndefects, two voritces on the south and north pole or a domain wall which\nseparates $p_\\theta+ ip_\\phi$ and $p_\\theta-ip_\\phi$ superfluids."
    },
    {
        "anchor": "Total momentum and thermodynamic phases of quantum systems: The total momentum of $N$ interacting bosons or fermions in a cube equipped\nwith periodic boundary conditions is a conserved quantity. Its eigenvalues\nfollow a probability distribution, determined by the thermal equilibrium state.\nWhile in non-interacting systems the distribution is normal with variance $\\sim\nN$, interaction couples the single-particle momenta, so that the distribution\nof their sum is unpredictable, except for some implications of Galilean\ninvariance. First, we present these implications which are strong in 1D,\nmoderately strong in 2D, and weak in 3D. Then, we speculate about the possible\nform of the distribution in fluids, crystals, and superfluids. The existence of\nphonons suggests that the total momentum can remain finite when $N\\to\\infty$.\nWe argue that in fluids the finite momenta distribute continuously, but their\nintegrated probability is smaller than 1, because the momentum can also tend to\ninfinity with $N$. In the fluid-crystal transition we expect that the total\nmomentum becomes finite with full probability and distributed over a lattice,\nand that in the fluid-superfluid transition a delta peak appears only at zero\ntotal momentum. Based on this picture, we discuss the superfluid flow in both\nthe frictionless and the dissipative cases, and derive a temperature-dependent\ncritical velocity. Finally, we show that Landau's criterion for excitations in\nmoving superfluids is an in some cases correct result of an erroneous\nderivation.",
        "positive": "The in-plane gradient magnetic field induced vortex lattices in\n  spin-orbit coupled Bose-Einstein condensations: We consider the ground-state properties of the two-component spin-orbit\ncoupled ultracold bosons subject to a rotationally symmetric in-plane gradient\nmagnetic field. In the non-interacting case, the ground state supports\ngiant-vortices carrying large angular momenta without rotating the trap. The\nvorticity is highly tunable by varying the amplitudes and orientations of the\nmagnetic field. Interactions drive the system from a giant-vortex state to\nvarious configurations of vortex lattice states along a ring. Vortices exhibit\nellipse-shaped envelops with the major and minor axes determined by the\nspin-orbit coupling and healing lengths, respectively. Phase diagrams of vortex\nlattice configurations are constructed and their stabilities are analyzed."
    },
    {
        "anchor": "Three-body crossover from a Cooper triple to bound trimer state in\n  three-component Fermi gases near a triatomic resonance: We theoretically investigate ground-state properties of a three-component\nFermi gas with pairwise contact interactions between different components near\na triatomic resonance where bound trimers are about to appear. Using\nvariational equations for in-medium two- and three-body cluster states in three\ndimensions, we elucidate the competition of pair and triple formations due to\nthe Fermi surface effects. We present the ground-state phase diagram that\nexhibits transition from a Cooper pair to Cooper triple state and crossover\nfrom a Cooper triple to tightly bound trimer state at negative scattering\nlengths. This three-body crossover is analogous to the\nBardeen-Cooper-Schrieffer to Bose-Einstein condensation crossover observed in a\ntwo-component Fermi gas. We predict that the threshold scattering length\n$a_{-}$ for three-body states can be shifted towards the weak-coupling side due\nto the emergence of Cooper triples.",
        "positive": "Supersolid Stacks in Antidipolar Bose-Einstein Condensates: We theoretically investigate a novel supersolid structure taking the form of\nstacked, disk-shaped superfluid droplets connected via a dilute superfluid, in\nan antidipolar condensate. A phase diagram is determined for varying the\nparticle number and scattering length, identifying the regions of a regular\ndipolar superfluid, supersolid stacks, and isolated stacked disk-shaped\ndroplets in an experimentally realizable trapping potential. The collective\nBogoliubov excitation spectrum across the superfluid-supersolid phase\ntransition is studied, and the transition point is found to be associated with\nthe breaking of the degeneracy of the two lowest-lying modes. The dynamical\ngeneration of the supersolid stacks is also investigated by ramping down the\nscattering length across the phase transition. Moreover, we have studied the\nimpact of vortex-line penetration on the phase transition. We have found that\nthe presence of a vortex line causes the supersolid region to move towards\nweaker contact interactions. Our detailed numerical simulations highlight that\nan antidipolar condensate can create such supersolid stacks within an\nexperimentally reachable parameter regime."
    },
    {
        "anchor": "Self-consistent field theory of polarized BEC: dispersion of collective\n  excitation: We suggest the construction of a set of the quantum hydrodynamics equations\nfor the Bose-Einstein condensate (BEC), where atoms have the electric dipole\nmoment. The contribution of the dipole-dipole interactions (DDI) to the Euler\nequation is obtained. Quantum equations for the evolution of medium\npolarization are derived. Developing mathematical method allows to study effect\nof interactions on the evolution of polarization. The developing method can be\napplied to various physical systems in which dynamics is affected by the DDI.\nDerivation of Gross-Pitaevskii equation for polarized particles from the\nquantum hydrodynamics is described. We showed that the Gross-Pitaevskii\nequation appears at condition when all dipoles have the same direction which\ndoes not change in time. Comparison of the equation of the electric dipole\nevolution with the equation of the magnetization evolution is described.\nDispersion of the collective excitations in the dipolar BEC, either affected or\nnot affected by the uniform external electric field, is considered using our\nmethod. We show that the evolution of polarization in the BEC leads to the\nformation of a novel type of the collective excitations. Detailed description\nof the dispersion of collective excitations is presented. We also consider the\nprocess of wave generation in the polarized BEC by means of a monoenergetic\nbeam of neutral polarized particles. We compute the possibilities of the\ngeneration of Bogoliubov and polarization modes by the dipole beam.",
        "positive": "Crossover from attractive to repulsive induced interactions and bound\n  states of two distinguishable Bose polarons: We study the impact of induced correlations and quasiparticle properties by\nimmersing two distinguishable impurities in a harmonically trapped bosonic\nmedium. It is found that when the impurities couple both either repulsively or\nattractively to their host, the latter mediates a two-body correlated behavior\nbetween them. In the reverse case, namely the impurities interact oppositely\nwith the host, they feature anti-bunching. Monitoring the impurities relative\ndistance and constructing an effective two-body model to be compared with the\nfull many-body calculations, we are able to associate the induced (anti-)\ncorrelated behavior of the impurities with the presence of attractive\n(repulsive) induced interactions. Furthermore, we capture the formation of a\nbipolaron and trimer state in the strongly attractive regime. The trimer refers\nto the correlated behavior of two impurities and a representative atom of the\nbosonic medium and it is characterized by an ellipsoidal shape of the\nthree-body correlation function. Our results open the way for controlling\npolaron induced correlations and creating relevant bound states."
    },
    {
        "anchor": "Breakdown of Tan's relation in lossy one-dimensional Bose gases: In quantum gases with contact repulsion, the distribution of momenta of the\natoms typically decays as $\\sim 1/|p|^4$ at large momentum $p$. Tan's relation\nconnects the amplitude of that $1/|p|^4$ tail to the adiabatic derivative of\nthe energy with respect to the gas' coupling constant or scattering length.\nHere it is shown that the relation breaks down in the one-dimensional Bose gas\nwith contact repulsion, for a peculiar class of stationary states. These states\nexist thanks to the infinite number of conserved quantities in the system, and\nthey are characterized by a rapidity distribution which itself decreases as\n$1/|p|^4$. In the momentum distribution, that rapidity tail adds to the usual\nTan contact term. Remarkably, atom losses, which are ubiquitous in experiments,\ndo produce such peculiar states. The development of the tail of the rapidity\ndistribution originates from the ghost singularity of the wavefunction\nimmediately after each loss event. This phenomenon is discussed for arbitrary\ninteraction strengths, and it is supported by exact calculations in the two\nasymptotic regimes of infinite and weak repulsion.",
        "positive": "Spontaneous Peierls dimerization and emergent bond order in\n  one-dimensional dipolar gases: We investigate the effect of dipolar interactions in one-dimensional systems\nin connection with the possibility of observing exotic many-body effects with\ntrapped atomic and molecular dipolar gases. By combining analytical and\nnumerical methods, we show how the competition between short- and long-range\ninteractions gives rise to frustrating effects which lead to the stabilization\nof spontaneously dimerized phases characterized by a bond-ordering. This\ngenuine quantum order is sharply distinguished from Mott and spin-density wave\nphases, and can be unambiguously probed by measuring non local order parameters\nin-situ imaging techniques."
    },
    {
        "anchor": "Stable matter-wave soliton in the vortex core of a uniform condensate: We demonstrate a stable, mobile, dipolar or nondipolar three-dimensional\nmatter-wave soliton in the vortex core of a uniform nondipolar condensate. All\nintra- and inter-species contact interactions can be repulsive for a strongly\ndipolar soliton. For a weakly dipolar or nondipolar soliton, the intra-species\ncontact interaction in the soliton should be attractive for the formation of a\ncompact soliton. The soliton can propagate with a constant velocity along the\nvortex core without any deformation. Two such solitons undergo a quasi-elastic\ncollision at medium velocities. We illustrate the findings using realistic\ninteractions in a mean-field model of binary $^{87}$Rb-$^{85}$Rb and\n$^{87}$Rb-$^{164}$Dy systems.",
        "positive": "Phase-space stochastic quantum hydrodynamics for interacting Bose gases: Hydrodynamic theories offer successful approaches that are capable of\nsimulating the otherwise difficult-to-compute dynamics of quantum many-body\nsystems. In this work we derive, within the positive-P phase-space formalism, a\nnew stochastic hydrodynamic method for the description of interacting Bose\ngases. It goes beyond existing hydrodynamic approaches, such as superfluid\nhydrodynamics or generalized hydrodynamics, in its capacity to simulate the\nfull quantum dynamics of these systems: it possesses the ability to compute\nnon-equilibrium quantum correlations, even for short-wavelength phenomena.\nUsing this description, we derive a linearized stochastic hydrodynamic scheme\nwhich is able to simulate such non-equilibrium situations for longer times than\nthe full positive-P approach, at the expense of approximating the treatment of\nquantum fluctuations, and show that this linearized scheme can be directly\nconnected with existing Bogoliubov approaches. Furthermore, we go on to\ndemonstrate the usefulness and advantages of this formalism by exploring the\ncorrelations that arise in a quantum shock wave scenario and comparing its\npredictions to other established quantum many-body approaches."
    },
    {
        "anchor": "Multicomponent exciton gas in cuprous oxide: cooling behaviour and the\n  role of Auger decay: In this paper we present a hydrodynamic model to describe the dynamics of\npara- and orthoexcitons in cuprous oxide at ultralow temperatures inside a\nstress induced potential trap. We take into account the finite lifetime of the\nexcitons, the excitation process and exciton-phonon as well as exciton-exciton\ninteraction. Furthermore, we model the two-body loss mechanism assuming an\nAuger-like effect and compare it to an alternative explanation which relies on\nthe formation of biexcitons. We discuss in detail the influence on the\nnumerical results and compare the predictions to experimental data.",
        "positive": "Robust quantum many-body scars in lattice gauge theories: Quantum many-body scarring is a paradigm of weak ergodicity breaking arising\ndue to the presence of special nonthermal many-body eigenstates that possess\nlow entanglement entropy, are equally spaced in energy, and concentrate in\ncertain parts of the Hilbert space. Though scars have been shown to be\nintimately connected to gauge theories, their stability in such experimentally\nrelevant models is still an open question, and it is generally considered that\nthey exist only under fine-tuned conditions. In this work, we show through\nKrylov-based time-evolution methods how quantum many-body scars can be made\nrobust in the presence of experimental errors through utilizing terms linear in\nthe gauge-symmetry generator or a simplified pseudogenerator in $\\mathrm{U}(1)$\nand $\\mathbb{Z}_2$ lattice gauge theories. Our findings are explained by the\nconcept of quantum Zeno dynamics. Our experimentally feasible methods can be\nreadily implemented in existing large-scale ultracold-atom quantum simulators\nand setups of Rydberg atoms with optical tweezers."
    },
    {
        "anchor": "Phase Diagrams of Spinor Bose Gases: Using effective field theories dictated by the symmetry of the system, as\nwell as microscopic considerations, we map out the magnetic\ncoupling-temperature phase diagrams of spin-1 Bose gases in both two- and\nthree-dimensions. We also determine the nature of all phase boundaries, and\ncritical properties in the case of 2nd order phase transitions at both zero and\nfinite temperatures.",
        "positive": "Early Stage of Superradiance from Bose-Einstein Condensates: We investigate the dynamics of matter and optical waves at the early stage of\nsuperradiant Rayleigh scattering from Bose-Einstein Condensates. Our analysis\nis within a spatially dependent quantum model which is capable of providing\nanalytic solutions for the operators of interest. The predictions of the\npresent model are compared to the predictions of a closely related mean field\nmodel, and we provide a procedure that allows one to calculate quantum\nexpectation values by averaging over semiclassical solutions. The coherence\nproperties of the outgoing scattered light are also analyzed, and it is shown\nthat the corresponding correlation functions may provide detailed information\nabout the internal dynamics of the system."
    },
    {
        "anchor": "Low-field Feshbach resonances and three-body losses in a fermionic\n  quantum gas of $^{161}$Dy: We report on high-resolution Feshbach spectroscopy on a degenerate,\nspin-polarized Fermi gas of $^{161}$Dy atoms, measuring three-body\nrecombination losses at low magnetic field. For field strength up to 1\\,G, we\nidentify as much as 44 resonance features and observe plateaus of very low\nlosses. For four selected typical resonances, we study the dependence of the\nthree-body recombination rate coefficient on the magnetic resonance detuning\nand on the temperature. We observe a strong suppression of losses with\ndecreasing temperature already for small detunings from resonance. The\ncharacterization of complex behavior of three-body losses of fermionic\n$^{161}$Dy is important for future applications of this peculiar species in\nresearch on atomic quantum gases.",
        "positive": "Driving quantum many-body scars in the PXP model: Periodic driving has been established as a powerful technique for engineering\nnovel phases of matter and intrinsically out-of-equilibrium phenomena such as\ntime crystals. Recent work by Bluvstein et al. [Science 371, 1355 (2021)] has\ndemonstrated that periodic driving can also lead to a significant enhancement\nof quantum many-body scarring, whereby certain non-integrable systems can\ndisplay persistent quantum revivals from special initial states. Nevertheless,\nthe mechanisms behind driving-induced scar enhancement remain poorly\nunderstood. Here we report a detailed study of the effect of periodic driving\non the PXP model describing Rydberg atoms in the presence of a strong Rydberg\nblockade - the canonical static model of quantum many-body scarring. We show\nthat periodic modulation of the chemical potential gives rise to a rich phase\ndiagram, with at least two distinct types of scarring regimes that we\ndistinguish by examining their Floquet spectra. We formulate a toy model, based\non a sequence of square pulses, that accurately captures the details of the\nscarred dynamics and allows for analytical treatment in the large-amplitude and\nhigh-frequency driving regimes. Finally, we point out that driving with a\nspatially inhomogeneous chemical potential allows to stabilize quantum revivals\nfrom arbitrary initial states in the PXP model, via a mechanism similar to\nprethermalization."
    },
    {
        "anchor": "Four-Body Scale in Universal Few-Boson Systems: The role of an intrinsic four-body scale in universal few-boson systems is\nthe subject of active debate. We study these systems within the framework of\neffective field theory. For systems of up to six bosons we establish that no\nfour-body scale appears at leading order (LO). However, we find that at\nnext-to-leading (NLO) order a four-body force is needed to obtain renormalized\nresults for binding energies. With the associated parameter fixed to the\nbinding energy of the four-boson system, this force is shown to renormalize the\nfive- and six-body systems as well. We present an original ansatz for the\nshort-distance limit of the bosonic $A$-body wave function from which we\nconjecture that new $A$-body scales appear at N$^{A-3}$LO. As a specific\nexample, calculations are presented for clusters of helium atoms. Our results\napply more generally to other few-body systems governed by a large scattering\nlength, such as light nuclei and halo states, the low-energy properties of\nwhich are independent of the detailed internal structure of the constituents.",
        "positive": "Quasi-particle Lifetime in a Mixture of Bose and Fermi Superfluids: In this letter, to reveal the effect of quasi-particle interactions in a\nBose-Fermi superfluid mixture, we consider the lifetime of quasi-particle of\nBose superfluid due to its interaction with quasi-particles in Fermi\nsuperfluid. We find that this damping rate, i.e. inverse of the lifetime, has\nquite different threshold behavior at the BCS and the BEC side of the Fermi\nsuperfluid. The damping rate is a constant nearby the threshold momentum in the\nBCS side, while it increases rapidly in the BEC side. This is because in the\nBCS side the decay processe is restricted by constant density-of-state of\nfermion quasi-particle nearby Fermi surface, while such a restriction does not\nexist in the BEC side where the damping process is dominated by bosonic\nquasi-particles of Fermi superfluid. Our results are related to collective mode\nexperiment in recently realized Bose-Fermi superfluid mixture."
    },
    {
        "anchor": "Dynamical instability in the S=1 Bose-Hubbard model: We study the dynamical instabilities of superfluid flows in the S=1\nBose-Hubbard model. The time evolution of each spin component in a condensate\nis calculated based on the dynamical Gutzwiller approximation for a wide range\nof interactions, from a weakly correlated regime to a strongly correlated\nregime near the Mott-insulator transition. Owing to the spin-dependent\ninteractions, the superfluid flow of the spin-1 condensate decays at a\ndifferent critical momentum from a spinless case when the interaction strength\nis the same. We furthermore calculate the dynamical phase diagram of this model\nand clarify that the obtained phase boundary has very different features\ndepending on whether the average number of particles per site is even or odd.\nFinally, we analyze the density and spin modulations that appear in association\nwith the dynamical instability. We find that spin modulations are highly\nsensitive to the presence of a uniform magnetic field.",
        "positive": "Regular and chaotic behavior of collective atomic motion in\n  two-component Bose-Einstein condensates: We theoretically study binary Bose-Einstein condensates trapped in a\nsingle-well harmonic potential to probe the dynamics of collective atomic\nmotion. The idea is to choose tunable scattering lengths through Feshbach\nresonances such that the ground-state wave function for two types of the\ncondensates are spatially immiscible where one of the condensates, located at\nthe center of the potential trap, can be effectively treated as a potential\nbarrier between bilateral condensates of the second type of atoms. In the case\nof small wave function overlap between bilateral condensates, one can\nparametrize their spatial part of the wave functions in the two-mode\napproximation together with the time-dependent population imbalance $z$ and the\nphase difference $\\phi$ between two wave functions. The condensate in the\nmiddle can be approximated by a Gaussian wave function with the displacement of\nthe condensate center $\\xi$. As driven by the time-dependent displacement of\nthe central condensate, we find the Josephson oscillations of the collective\natomic motion between bilateral condensates as well as their anharmonic\ngeneralization of macroscopic self-trapping effects. In addition, with the\nincrease in the wave function overlap of bilateral condensates by properly\nchoosing tunable atomic scattering lengths, the chaotic oscillations are found\nif the system departs from the state of a fixed point. The Melnikov approach\nwith a homoclinic solution of the derived $z,\\,\\phi$, and $\\xi$ equations can\nsuccessfully justify the existence of chaos. All results are consistent with\nthe numerical solutions of the full time-dependent Gross-Pitaevskii equations."
    },
    {
        "anchor": "Two- and three- dimensional few-body systems in the universal regime: Macro properties of cold atomic gases are driven by few-body correlations,\neven if the gas has thousands of particles. Quantum systems composed of two and\nthree particles with attractive zero\\=/range pairwise interactions are\nconsidered for general masses and interaction strengths in two and three\ndimensions (2D and 3D). The Faddeev decomposition is used to derive the\nequations for the bound state, which is the starting point for the\ninvestigation of universal properties of few\\=/body systems, i.e. those that\nall potentials with the same physics at low energy are able to describe in a\nmodel\\=/independent form. In 2D, the number of bound states in a three\\=/body\nsystem increases without bound as the mass of one particle becomes much lighter\nthan the other two. The analytic form of an effective potential between the\nheavy particles explains the mass\\=/dependence on the number of bound energy\nlevels. An exact analytic expression for the large\\=/momentum asymptotic\nbehaviour of the spectator function in the Faddeev equation is presented. The\nspectator function and its asymptotic form define the two- and three\\=/body\ncontact parameters. The two\\=/body parameter is found to be independent of the\nquantum state in some specific 2D systems. The 2D and 3D momentum distributions\nhave a distinct sub\\=/leading form whereas the 3D term depends on the mass of\nthe particles. A model that interpolates between 2D and 3D is proposed and a\nsharp transition in the energy spectrum of three-body systems is found.",
        "positive": "Second sound in the BEC-BCS crossover: Second sound is an entropy wave which propagates in the superfluid component\nof a quantum liquid. Because it is an entropy wave, it probes the thermodynamic\nproperties of the quantum liquid which are determined, e.g., by the interaction\nstrength between the particles of the quantum liquid and their temperature.\nHere, we study second sound propagation for a large range of interaction\nstrengths within the crossover between a Bose-Einstein condensate (BEC) and the\nBardeen-Cooper-Schrieffer (BCS) superfluid. In particular, we investigate the\nstrongly-interacting regime where currently theoretical predictions only exist\nin terms of an interpolation between the BEC, BCS and unitary regimes. Working\nwith a quantum gas of ultracold fermionic $^6$Li atoms with tunable\ninteractions, we show that the second sound speed varies only slightly in the\ncrossover regime. We gain deeper insights into sound propagation and excitation\nof second sound by varying the excitation procedure which ranges from a sudden\nforce pulse to a gentle heating pulse at the cloud center. These measurements\nare accompanied by classical-field simulations which help with the\ninterpretation of the experimental data. Furthermore, we determine the spatial\nextension of the superfluid phase and estimate the superfluid density. In the\nfuture, this may be used to construct the so far unknown equation of state\nthroughout the crossover."
    },
    {
        "anchor": "Pauli Blocking Effect on Efimov States Near Feshbach Resonance: In this Letter we study the effect of Pauli blocking on the Efimov states in\na quantum Fermi gas and illustrate that the universal Efimov potential is\naltered at large distances. We obtain the universal spectrum flow of Efimov\ntrimers when the Fermi density is varied and further consider the effect of\nscattering of trimers by the Fermi sea. We argue that the universal flow is\nrobust against fluctuating particle-hole pairs that result in an infrared\ncatastrophe in impurity problems.",
        "positive": "Experimental realization of a non-magnetic one-way spin switch: Controlling magnetism through non-magnetic means is highly desirable for\nfuture electronic devices, as such means typically have ultra-low power\nrequirements and can provide coherent control. In recent years, great\nexperimental progress has been made in the field of electrical manipulation of\nmagnetism in numerous material systems. These studies generally do not consider\nthe directionality of the applied non-magnetic potentials and/or magnetism\nswitching. Here, we theoretically conceive and experimentally demonstrate a\nnon-magnetic one-way spin switch device using a spin-orbit coupled\nBose-Einstein condensate subjected to a moving spin-independent dipole\npotential. The physical foundation of this unidirectional device is based on\nthe breakdown of Galilean invariance in the presence of spin-orbit coupling.\nSuch a one-way spin switch opens an avenue for designing novel quantum devices\nwith unique functionalities and may facilitate further experimental\ninvestigations of other one-way spintronic and atomtronic devices."
    },
    {
        "anchor": "Numerical study of a recent black hole lasing experiment: We theoretically analyse a recent experiment reporting the observation of a\nself-amplifying Hawking radiation in a flowing atomic condensate [J.Steinhauer,\nNature Physics, vol.10, pp.864, Nov 2014]. We are able to accurately reproduce\nthe experimental observations using a theoretical model based on the numerical\nsolution of a mean-field Gross-Pitaevskii equation that does not include\nquantum fluctuations of the matter field. In addition to confirming the black\nhole lasing mechanism, our results show that the underlying dynamical\ninstability has a classical hydrodynamic origin and is triggered by a seed of\ndeterministic nature, linked to the non-stationary of the process, rather than\nby thermal or zero-point fluctuations.",
        "positive": "Mean-field yrast spectrum and persistent currents in a two-component\n  Bose gas with interaction asymmetry: We analyze the mean-field yrast spectrum of a two-component Bose gas in the\nring geometry with arbitrary interaction asymmetry. Of particular interest is\nthe possibility that the yrast spectrum develops local minima at which\npersistent superfluid flow can occur. By analyzing the mean-field energy\nfunctional, we show that local minima can be found at plane-wave states and\narise when the system parameters satisfy certain inequalities. We then go on to\nshow that these plane-wave states can be yrast states even when the yrast\nspectrum no longer exhibits a local minimum. Finally, we obtain conditions\nwhich establish when the plane-wave states cease to be yrast states. Specific\nexamples illustrating the roles played by the various interaction asymmetries\nare presented."
    },
    {
        "anchor": "Stability of nonstationary states of spin-2 Bose-Einstein condensates: The dynamical stability of nonstationary states of homogeneous spin-2\nrubidium Bose-Einstein condensates is studied. The states considered are such\nthat the spin vector remains parallel to the magnetic field throughout the time\nevolution, making it possible to study the stability analytically. These states\nare shown to be stable in the absence of an external magnetic field, but they\nbecome unstable when a finite magnetic field is introduced. It is found that\nthe growth rate and wavelength of the instabilities can be controlled by tuning\nthe strength of the magnetic field and the size of the condensate.",
        "positive": "Spin Transport in Polaronic and Superfluid Fermi Gases: We present measurements of spin transport in ultracold gases of fermionic\nlithium-6 in a mixture of two spin states at a Feshbach resonance. In\nparticular, we study the spin dipole mode, where the two spin components are\ndisplaced from each other against a harmonic restoring force. We prepare a\nhighly-imbalanced, or polaronic, spin mixture with a spin dipole excitation and\nobserve strong, unitarity limited damping of the spin dipole mode. In gases\nwith small spin imbalance, below the Pauli limit for superfluidity, we observe\nstrongly damped spin flow despite the presence of a superfluid core."
    },
    {
        "anchor": "Bloch oscillations and quench dynamics of interacting bosons in an\n  optical lattice: We study the dynamics of interacting superfluid bosons in a one dimensional\nvertical optical lattice after a sudden increase of the lattice potential\ndepth. We show that this system can be exploited to investigate the effects of\nstrong interactions on Bloch oscillations. We perform theoretical modelling of\nthis system, identify experimental challenges and explore a new regime of Bloch\noscillations characterized by interaction-induced matter-wave collapse and\nrevivals which modify the Bloch oscillations dynamics. In addition, we study\nthree dephasing mechanisms: effective three-body interactions, finite value of\ntunneling, and a background harmonic potential. We also find that the center of\nmass motion in the presence of finite tunneling goes through collapse and\nrevivals, giving an example of quantum transport where interaction induced\nrevivals are important. We quantify the effects of residual harmonic trapping\non the momentum distribution dynamics and show the occurrence of\ninteraction-modified temporal Talbot effect. Finally, we analyze the prospects\nand challenges of exploiting Bloch oscillations of cold atoms in the strongly\ninteracting regime for precision measurement of the gravitational acceleration\n$g$.",
        "positive": "Feedback-stabilized dynamical steady states in the Bose-Hubbard model: The implementation of a combination of continuous weak measurement and\nclassical feedback provides a powerful tool for controlling the evolution of\nquantum systems. In this work, we investigate the potential of this approach\nfrom three perspectives. First, we consider a double-well system in the\nclassical large-atom-number limit, deriving the exact equations of motion in\nthe presence of feedback. Second, we consider the same system in the limit of\nsmall atom number, revealing the effect that quantum fluctuations have on the\nfeedback scheme. Finally, we explore the behavior of modest sized Hubbard\nchains using exact numerics, demonstrating the near-deterministic preparation\nof number states, a tradeoff between local and non-local feedback for state\npreparation, and evidence of a feedback-driven symmetry-breaking phase\ntransition."
    },
    {
        "anchor": "Time-dependent condensation of bosonic potassium: We calculate the time-dependent formation of Bose--Einstein condensates\n(BECs) in potassium vapours based on a previously derived exactly solvable\nnonlinear boson diffusion equation (NBDE). Thermalization following a sudden\nenergy quench from an initial temperature $T_\\mathrm{i}$ to a final temperature\n$T_\\mathrm{f}$ below the critical value and BEC formation are accounted for\nusing closed-form analytical solutions of the NBDE. The time-dependent\ncondensate fraction is compared with available $^{39}$K data for various\nscattering lengths.",
        "positive": "Bose-Einstein condensation of photons in a plasma: We study the Bose-Einstein condensation of photons in a plasma, where we\ninclude the cases of both transverse photons and plasmons. We consider\nfour-wave mixing processes of photon and plasmon modes in a relativistic\nisotropic plasma to determine the coupling constant to lowest order. We further\nshow that photon condensation is possible in an unbounded plasma because, in\ncontrast with other optical media, plasmas introduce an effective photon mass.\nThis guarantees the existence of a finite chemical potential and a critical\ntemperature, which is calculated for both transverse photons and plasmons. By\nconsidering four-wave mixing processes, we derive the interactions between the\nphotons in the condensate. We also study the elementary excitations (or\nBogoliubov modes) of the condensed photon and plasmon gases, and determine the\nrespective dispersion relations. Finally, we discuss the kinetics of photon\ncondensation via inverse Compton scattering between the photons and the\nelectrons in the plasma."
    },
    {
        "anchor": "Dynamic density structure factor of a unitary Fermi gas at finite\n  temperature: We present a theoretical investigation of the dynamic density structure\nfactor of a strongly interacting Fermi gas near a Feshbach resonance at finite\ntemperature. The study is based on a gauge invariant linear response theory.\nThe theory is consistent with a diagrammatic approach for the equilibrium state\ntaking into account the pair fluctuation effects and respects some important\nrestrictions like the $f$-sum rule. Our numerical results show that the dynamic\ndensity structure factor at large incoming momentum and at half recoil\nfrequency has a qualitatively similar behavior as the order parameter, which\ncan signify the appearance of the condensate. This qualitatively agrees with\nthe recent Bragg spectroscopy experiment results. We also present the results\nat small incoming momentum.",
        "positive": "Dissipative preparation of phase- and number-squeezed states with\n  ultracold atoms: We develop a dissipative quantum state preparation scheme for the creation of\nphase- and number-squeezed states. It utilizes ultracold atoms in a double-well\nconfiguration immersed in a background Bose-Einstein condensate, with the\nlatter consisting of an atom species different from the atoms in the double\nwell and acting as a dissipative quantum reservoir. We derive a master equation\nfor this system starting from microscopic physics, and show that squeezing\ndevelops on a time scale proportional to $1/N$, where $N$ is the number of\nparticles in the double well. This scaling, caused by bosonic enhancement,\nallows us to make the time scale for the creation of squeezed states very\nshort. The lifetime of squeezed states is limited by dephasing arising from the\nintrinsic structure of the setup. However, the dephasing can be avoided by\nstroboscopically switching the driving off and on. We show that this approach\nleads to robust stationary squeezed states. Finally, we provide the necessary\ningredients for a potential experimental implementation by specifying a\nparameter regime for rubidium atoms that leads to squeezed states."
    },
    {
        "anchor": "A finite element toolbox for the Bogoliubov-de Gennes stability analysis\n  of Bose-Einstein condensates: We present a finite element toolbox for the computation of Bogoliubov-de\nGennes modes used to assess the linear stability of stationary solutions of the\nGross-Pitaevskii (GP) equation. Applications concern one (single GP equation)\nor two-component (a system of coupled GP equations) Bose-Einstein condensates\nin one, two and three dimensions of space. An implementation using the free\nsoftware FreeFem++ is distributed with this paper. For the computation of the\nGP stationary (complex or real) solutions we use a Newton algorithm coupled\nwith a continuation method exploring the parameter space (the chemical\npotential or the interaction constant). Bogoliubov-de Gennes equations are then\nsolved using dedicated libraries for the associated eigenvalue problem. Mesh\nadaptivity is proved to considerably reduce the computational time for cases\nimplying complex vortex states. Programs are validated through comparisons with\nknown theoretical results for simple cases and numerical results reported in\nthe literature.",
        "positive": "Critical Velocity and Arrest of a Superfluid in a Point-Like Disordered\n  Potential: Superfluid flow past a potential barrier is a well studied problem in\nultracold Bose gases, however, fewer studies have considered the case of flow\nthrough a disordered potential. Here we consider the case of a superfluid\nflowing through a channel containing multiple point-like barriers, randomly\nplaced to form a disordered potential. We begin by identifying the relationship\nbetween the relative position of two point-like barriers and the critical\nvelocity of such an arrangement. We then show that there is a mapping between\nthe critical velocity of a system with two obstacles, and a system with a large\nnumber of obstacles. By establishing an initial superflow through a point-like\ndisordered potential, moving faster than the critical velocity, we study how\nthe superflow is arrested through the nucleation of vortices and the breakdown\nof superfluidity, a problem with interesting connections to quantum turbulence\nand coarsening. We calculate the vortex decay rate as the width of the barriers\nis increased, and show that vortex pinning becomes a more important effect for\nthese larger barriers."
    },
    {
        "anchor": "Revealing Excited States of Rotational Bose-Einstein Condensates: Rotational Bose-Einstein condensates can exhibit quantized vortices as\ntopological excitations. In this study, the ground and excited states of the\nrotational Bose-Einstein condensates are systematically studied by calculating\nthe stationary points of the Gross-Pitaevskii energy functional. Various\nexcited states and their connections at different rotational frequencies are\nrevealed in solution landscapes constructed with the constrained high-index\nsaddle dynamics method. Four excitation mechanisms are identified: vortex\naddition, rearrangement, merging, and splitting. We demonstrate changes in the\nground state with increasing rotational frequencies and decipher the evolution\nof the stability of ground states.",
        "positive": "Renormalization of two-body interactions due to higher-body interactions\n  of lattice bosons: We calculate thermodynamic properties of soft-core lattice bosons with\non-site $n$-body interactions using up to twelfth and tenth order strong\ncoupling expansion in one and two dimensional cubic lattices at zero\ntemperature. Using linked cluster techniques, we show that it is possible to\nexactly renormalize the two-body interactions for quasiparticle excitations and\nground-state energy by resumming the three and four body terms in the system,\nwhich suggests that all higher-body on-site interactions may be exactly and\nperturbatively resummed into the two-body terms for similar system observables.\nThe renormalization procedure that we develop is applicable to a broad range of\nsystems analyzable by linked cluster expansions, ranging from perturbative\nquantum chromodynamics to spin models, giving either an exact or approximate\nresummation depending on the specific system and properties. Universality at\nvarious three-body interaction strengths for the two dimensional boson Hubbard\nmodel is checked numerically."
    },
    {
        "anchor": "Protocols for dynamically probing topological edge states and\n  dimerization with fermionic atoms in optical potentials: Topological behavior has been observed in quantum systems including ultracold\natoms. However, background harmonic traps for cold-atoms hinder direct\ndetection of topological edge states arising at the boundary because the\ndistortion fuses the edge states into the bulk. We propose experimentally\nfeasible protocols to probe localized edge states and dimerization of ultracold\nfermions. By confining cold-atoms in a ring lattice and changing the boundary\ncondition from periodic to open using an off-resonant laser sheet to cut open\nthe ring, topological edge states can be generated. A lattice in a topological\nconfiguration can trap a single particle released at the edge as the system\nevolves in time. Alternatively, depleting an initially filled lattice away from\nthe boundary reveals the occupied edge states. Signatures of dimerization in\nthe presence of contact interactions can be found in selected correlations as\nthe system boundary suddenly changes from periodic to open and exhibit memory\neffects of the initial state distinguishing different configurations or phases.",
        "positive": "Diffractive scattering of three particles in one dimension: a simple\n  result for weak violations of the Yang--Baxter equation: We study scattering of three equal mass particles in one dimension.\nIntegrable interactions are synonymous with non-diffractive scattering, meaning\nthat the set of incoming momenta for any scattering event coincides with the\nset of outgoing momenta. A system is integrable if the two particle scattering\nmatrix obeys the Yang--Baxter equation. Nonintegrable interactions correspond\nto diffractive scattering, where the set of outgoing momenta may take on all\nvalues consistent with energy and momentum conservation. Such processes play a\nvital role in the kinetics of one dimensional gases, where binary collisions\nare unable to alter the distribution function.\n  When integrability is broken weakly, the result is a small diffractive\nscattering amplitude. Our main result is a simple formula for the diffractive\npart of the scattering amplitude, when the violation of the Yang--Baxter\nequation is small. Although the derivation is given for delta-function\ninteractions, the result depends only on the two-particle scattering matrix,\nand should therefore also apply to finite-range interactions close to\nintegrable."
    },
    {
        "anchor": "Non-adiabatic preparation of spin crystals with ultracold polar\n  molecules: We study the growth dynamics of ordered structures of strongly interacting\npolar molecules in optical lattices. Using dipole blockade of microwave\nexcitations, we map the system onto an interacting spin-1/2 model possessing\nground states with crystalline order, and describe a way to prepare these\nstates by non-adiabatically driving the transitions between molecular\nrotational levels. The proposed technique bypasses the need to cross a phase\ntransition and allows for the creation of ordered domains of considerably\nlarger size compared to approaches relying on adiabatic preparation.",
        "positive": "Probing interaction-induced ferromagnetism in optical superlattices: We propose a controllable method for observing interaction induced\nferromagnetism in ultracold fermionic atoms loaded in optical superlattices. We\nfirst discuss how to probe and control Nagaoka ferromagnetism in an array of\nisolated plaquettes (four lattice sites arranged in a square). Next, we show\nthat introducing a weak interplaquette coupling destroys the ferromagnetic\ncorrelations. To overcome this instability we propose to mediate long-range\nferromagnetic correlations among the plaquettes via double-exchange processes.\nConditions for experimental realization and techniques to detect such states\nare discussed."
    },
    {
        "anchor": "Interferometric measurement of the current-phase relationship of a\n  superfluid weak link: Weak connections between superconductors or superfluids can differ from\nclassical links due to quantum coherence, which allows flow without resistance.\nTransport properties through such weak links can be described with a single\nfunction, the current-phase relationship, which serves as the quantum analog of\nthe current-voltage relationship. Here, we present a technique for\ninteferometrically measuring the current-phase relationship of superfluid weak\nlinks. We interferometrically measure the phase gradient around a ring-shaped\nsuperfluid Bose-Einstein condensate (BEC) containing a rotating weak link,\nallowing us to identify the current flowing around the ring. While our BEC weak\nlink operates in the hydrodynamic regime, this technique can be extended to all\ntypes of weak links (including tunnel junctions) in any phase-coherent quantum\ngas. Moreover, it can also measure the current-phase relationships of\nexcitations. Such measurements may open new avenues of research in quantum\ntransport.",
        "positive": "Dissipative superfluid hydrodynamics for the unitary Fermi gas: In this work we establish constraints on the temperature dependence of the\nshear viscosity $\\eta$ in the superfluid phase of a dilute Fermi gas in the\nunitary limit. Our results are based on analyzing experiments that measure the\naspect ratio of a deformed cloud after release from an optical trap. We discuss\nhow to apply the two-fluid formalism to the unitary gas, and provide a suitable\nparametrization of the equation of state. We show that in expansion experiments\nthe difference between the normal and superfluid velocities remains small, and\ncan be treated as a perturbation. We find that expansion experiments favor a\nshear viscosity that decreases significantly in the superfluid regime. Using an\nexponential parametrization we find $\\eta(T_c/(2T_F))< 0.37\\eta (T_c/T_F)$,\nwhere $T_c$ is the critical temperature, $T_F$ is the local Fermi temperature\nof the gas."
    },
    {
        "anchor": "Dynamical Mean Field Theory for the Bose-Hubbard Model: The dynamical mean field theory (DMFT), which is successful in the study of\nstrongly correlated fermions, was recently extended to boson systems [Phys.\nRev. B {\\textbf 77}, 235106 (2008)]. In this paper, we employ the bosonic DMFT\nto study the Bose-Hubbard model which describes on-site interacting bosons in a\nlattice. Using exact diagonalization as the impurity solver, we get the DMFT\nsolutions for the Green's function, the occupation density, as well as the\ncondensate fraction on a Bethe lattice. Various phases are identified: the Mott\ninsulator, the Bose-Einstein condensed (BEC) phase, and the normal phase. At\nfinite temperatures, we obtain the crossover between the Mott-like regime and\nthe normal phase, as well as the BEC-to-normal phase transition. Phase diagrams\non the $\\mu/U-\\tilde{t}/U$ plane and on the $T/U-\\tilde{t}/U$ plane are\nproduced ($\\tilde{t}$ is the scaled hopping amplitude). We compare our results\nwith the previous ones, and discuss the implication of these results to\nexperiments.",
        "positive": "Interaction quenches in nonzero temperature fermionic condensates: We revisit the study of amplitude oscillations in a pair condensate of\nfermions after an interaction quench, and generalize it to nonzero temperature.\nFor small variations of the order parameter, we show that the energy transfer\nduring the quench determines both the asymptotic pseudo-equilibrated value of\nthe order parameter and the magnitude of the oscillations, after multiplication\nby, respectively, the static response of the order parameter and spectral\nweight of the pair-breaking threshold. Since the energy transferred to the\ncondensed pairs decreases with temperature as the superfluid contact, the\noscillations eventually disappear at the critical temperature. For deeper\nquenches, we generalize the regimes of persistent oscillations and monotonic\ndecay to nonzero temperatures, and explain how they become more abrupt and are\nmore easily entered at high temperatures when the ratio of the initial to final\ngap either diverges, when quenching towards the normal phase, or tends to zero,\nwhen quenching towards the superfluid phase. Our results are directly relevant\nfor existing and future experiments on the non-equilibrium evolution of Fermi\nsuperfluids near the phase transition."
    },
    {
        "anchor": "Beyond mean-field corrections to the quasiparticle spectrum of\n  superfluid Fermi gases: We investigate the fermionic quasiparticle branch of superfluid Fermi gases\nin the BCS-BEC crossover and calculate the quasiparticle lifetime and energy\nshift due to its coupling with the collective mode. The only close-to-resonance\nprocess that low-energy quasiparticles can undergo at zero temperature is the\nemission of a bosonic excitation from the phononic branch. Close to the minimum\nof the branch we find that the quasiparticles remain undamped, allowing us to\ncompute corrections to experimentally relevant quantities such as the energy\ngap, location of the minimum, effective mass, and Landau critical velocity.",
        "positive": "Time scale for adiabaticity breakdown in driven many-body systems and\n  orthogonality catastrophe: The adiabatic theorem is a fundamental result established in the early days\nof quantum mechanics, which states that a system can be kept arbitrarily close\nto the instantaneous ground state of its Hamiltonian if the latter varies in\ntime slowly enough. The theorem has an impressive record of applications\nranging from foundations of quantum field theory to computational recipes in\nmolecular dynamics. In light of this success it is remarkable that a\npracticable quantitative understanding of what \"slowly enough\" means is limited\nto a modest set of systems mostly having a small Hilbert space. Here we show\nhow this gap can be bridged for a broad natural class of physical systems,\nnamely many-body systems where a small move in the parameter space induces an\northogonality catastrophe. In this class, the conditions for adiabaticity are\nderived from the scaling properties of the parameter dependent ground state\nwithout a reference to the excitation spectrum. This finding constitutes a\nmajor simplification of a complex problem, which otherwise requires solving\nnon-autonomous time evolution in a large Hilbert space. We illustrate our\ngeneral results by analyzing conditions for the transport quantization in a\ntopological Thouless pump."
    },
    {
        "anchor": "Trapped unitary two-component Fermi gases with up to ten particles: The properties of two-component Fermi gases with zero-range interactions are\nuniversal. We use an explicitly correlated Gaussian basis set expansion\napproach to investigate small equal-mass two-component Fermi gases under\nspherically symmetric external harmonic confinement. At unitarity, we determine\nthe ground state energy for systems with up to ten particles interacting\nthrough finite-range two-body potentials for both even and odd number of\nparticles. We extrapolate the energies to the zero-range limit using a novel\nscheme that removes the linear and, in some cases, also the quadratic\ndependence of the ground state energies on the two-body range. Our extrapolated\nzero-range energies are compared with results from the literature. We also\ncalculate the two-body Tan contact and structural properties.",
        "positive": "About conditions of spatial collapse in an infinite system of Bose\n  particles: Using the variational principle, we show that the condition of spatial\ncollapse in a Bose gas is not determined by the value of the scattering length\nof the interaction potential between particles contrary to the result following\nfrom the Gross--Pitaevskii equation, where the collapse should take place at a\nnegative scattering length."
    },
    {
        "anchor": "Floquet engineering of individual band gaps in an optical lattice using\n  a two-tone drive: The dynamic engineering of band structures for ultracold atoms in optical\nlattices represents an innovative approach to understand and explore the\nfundamental principles of topological matter. In particular, the folded Floquet\nspectrum determines the associated band topology via band inversion. We\nexperimentally and theoretically study two-frequency phase modulation to\nasymmetrically hybridize the lowest two bands of a one-dimensional lattice.\nUsing quasi-degenerate perturbation theory in the extended Floquet space we\nderive an effective two-band model that quantitatively describes our setting.\nThe energy gaps are experimentally probed via Landau-Zener transitions between\nFloquet-Bloch bands using an accelerated Bose-Einstein condensate. Separate and\nsimultaneous control over the closing and reopening of these band gaps is\ndemonstrated. We find good agreement between experiment and theory,\nestablishing an analytic description for resonant Floquet-Bloch engineering\nthat includes single- and multi-photon couplings, as well as interference\neffects between several commensurate drives.",
        "positive": "Fragmentation, domain formation and atom number fluctuations of a\n  two-species Bose-Einstein condensate in an optical lattice: We theoretically study the loading of a two-species Bose-Einstein condensate\nto an optical lattice in a tightly-confined one-dimensional trap. Due to\nquantum fluctuations the relative inter and intra species phase coherence\nbetween the atoms and the on-site atom number fluctuations are reduced in the\nmiscible regime. For the immiscible case the fluctuations are enhanced and the\natoms form metastable interleaved spatially separated domains where the domain\nlength and its fluctuations are affected by quantum fluctuations."
    },
    {
        "anchor": "Spatio-temporal Fermionization of Strongly Interacting 1D Bosons: Building on the recent experimental achievements obtained with scanning\nelectron microscopy on ultracold atoms, we study one-dimensional Bose gases in\nthe crossover between the weakly (quasi-condensate) and the strongly\ninteracting (Tonks-Girardeau) regime. We measure the temporal two-particle\ncorrelation function and compare it with calculations performed using the Time\nEvolving Block Decimation algorithm. More pronounced antibunching is observed\nwhen entering the more strongly interacting regime. Even though this mimics the\nonset of a fermionic behavior, we highlight that the exact and simple duality\nbetween 1D bosons and fermions does not hold when such dynamical response is\nprobed. The onset of fermionization is also reflected in the density\ndistribution, which we measure \\emph{in situ} to extract the relevant\nparameters and to identify the different regimes. Our results show agreement\nbetween experiment and theory and give new insight into the dynamics of\nstrongly correlated many-body systems.",
        "positive": "Multiorder topological superfluid phase transitions in a two-dimensional\n  optical superlattice: Higher-order topological superfluids have gapped bulk and symmetry-protected\nMajorana zero modes with various localizations. Motivated by recent advances,\nwe present a proposal for synthesizing multi-order topological superfluids that\nsupport various Majorana zero modes in ultracold atomic gases. For this\npurpose, we use the two-dimensional optical superlattice that introduces a\nspatial modulation to the spin-orbit coupling in one direction, providing an\nextra degree of freedom for the emergent higher-order topological state. We\nfind the topologically trivial superfluids, first-order and second-order\ntopological superfluids, as well as different topological phase transitions\namong them with respect to the experimentally tunable parameters. Besides the\nconventional transition characterized by the Chern number associated with the\nbulk gap closing and reopening, we find the system can support the topological\nsuperfluids with Majorana corner modes, but the topological phase transition\nundergoes no gap-closing of bulk bands. Instead, the transition is refined by\nthe quadrupole moment and signaled out by the gap-closing of edge states. The\nproposal is based on the $s$-wave interaction and is valid using existing\nexperimental techniques, which unifies multi-order topological phase\ntransitions in a simple but realistic system."
    },
    {
        "anchor": "Quaternary-singlet State of Spin-1 Bosons in Optical Lattice: We present the quantum ground state properties of $^{23}$Na spinor\ncondensates, which is confined in a periodic or double-well potential and\nsubject to a magnetic dipole-dipole interaction between nearby wells. A novel\nsinglet state arise in the system and can be discussed in explicit form. Caused\nby the competition between the intra-site spin exchange interactions and the\ninter-site dipole-dipole interactions, this quaternary-singlet\\ state is a\nentangled state formed by at lest four particles and vanish the total spin.\nThis is distinct from the direct product of the two conventional singlet pairs.",
        "positive": "Non-Hermitian superfluid--Mott-insulator transition in the\n  one-dimensional zigzag bosonic chains: We investigated the behavior of non-Hermitian bosonic gases with Hubbard\ninteractions in the one-dimensional zigzag optical lattices through the\ncalculation of dynamic response functions. Our findings showed the existence of\na non-Hermitian quantum phase transition that is dependent on the\npseudo-Hermitian symmetry. The system tends to exhibit a superfluid phase, when\nsubjected to weak dissipation. While under strong dissipation, the\npseudo-Hermitian symmetry of the system is partially broken, leading to a\ntransition towards a normal liquid phase. As the dissipation increases beyond\nthe critical threshold, the pseudo-Hermitian symmetry is completely broken,\nresulting in a Mott-insulator phase. We propose an experimental setup using\none-dimensional zigzag optical lattices containing two-electron atoms to\nrealize this system. Our research emphasizes the key role of non-Hermiticity in\nquantum phase transitions and offers a new theoretical framework as well as\nexperimental methods for understanding the behavior of dissipative quantum\nsystems, implicating significant development of new quantum devices and\ntechnologies."
    },
    {
        "anchor": "Ground-state phases of a mixture of spin-1 and spin-2 Bose-Einstein\n  condensates: We investigate the ground-state phases of a mixture of spin-1 and spin-2\nBose-Einstein condensates at zero magnetic field. In addition to the intra-spin\ninteractions, two spin-dependent interaction coefficients are introduced to\ndescribe the inter-spin interaction. We systematically explore the wide\nparameter space, and obtain phase diagrams containing a rich variety of phases.\nFor example, there exists a phase in which the spin-1 and spin-2 vectors are\ntilted relative to each other breaking the axial symmetry.",
        "positive": "Casimir forces and quantum friction from Ginzburg radiation in atomic\n  BECs: We theoretically propose an experimentally viable scheme to use an impurity\natom in an atomic Bose-Einstein condensate, in order to realize\ncondensed-matter analogs of quantum vacuum effects. In a suitable atomic level\nconfiguration, the collisional interaction between the impurity atom and the\ndensity fluctuations in the condensate can be tailored to closely reproduce the\nelectric-dipole coupling of quantum electrodynamics. By virtue of this analogy,\nwe recover and extend the paradigm of electromagnetic vacuum forces to the\ndomain of cold atoms, showing in particular the emergence, at supersonic atomic\nspeeds, of a novel power-law scaling of the Casimir force felt by the atomic\nimpurity, as well as the occurrence of a quantum frictional force, accompanied\nby the Ginzburg emis- sion of Bogoliubov quanta. Observable consequences of\nthese quantum vacuum effects in realistic spectroscopic experiments are\ndiscussed."
    },
    {
        "anchor": "Superfluid density and Berezinskii-Kosterlitz-Thouless transition of a\n  spin-orbit coupled Fulde-Ferrell superfluid: We theoretically investigate the superfluid density and\nBerezinskii-Kosterlitz-Thouless (BKT) transition of a two-dimensional Rashba\nspin-orbit coupled atomic Fermi gas with both in-plane and out-of-plane Zeeman\nfields. It was recently predicted that, by tuning the two Zeeman fields, the\nsystem may exhibit different exotic Fulde-Ferrell (FF) superfluid phases,\nincluding the gapped FF, gapless FF, gapless topological FF and gapped\ntopological FF states. Due to the FF paring, we show that the superfluid\ndensity (tensor) of the system becomes anisotropic. When an in-plane Zeeman\nfield is applied along the \\textit{x}-direction, the tensor component along the\n\\textit{y}-direction $n_{s,yy}$ is generally larger than $n_{s,xx}$ in most\nparameter space. At zero temperature, there is always a discontinuity jump in\n$n_{s,xx}$ as the system evolves from a gapped FF into a gapless FF state. With\nincreasing temperature, such a jump is gradually washed out. The critical BKT\ntemperature has been calculated as functions of the spin-orbit coupling\nstrength, interatomic interaction strength, in-plane and out-of-plane Zeeman\nfields. We predict that the novel FF superfluid phases have a significant\ncritical BKT temperature, typically at the order of $0.1T_{F}$, where $T_{F}$\nis the Fermi degenerate temperature. Therefore, their observation is within the\nreach of current experimental techniques in cold-atom laboratories.",
        "positive": "Quantum liquid-crystal order in resonant atomic gases: I review recent studies that predict quantum liquid-crystalline orders in\nresonant atomic gases. As examples of such putative systems I will discuss an\ns-wave resonant imbalanced Fermi gas and a p-wave resonant Bose gas. In the\nformer, the liquid-crystalline smectic, nematic and rich variety of other\ndescendant states emerge from strongly quantum- and thermally- fluctuating\nFulde-Ferrell and Larkin-Ovchinnikov states, driven by a competition between\nresonant pairing and Fermi-surface mismatch. In the latter, at intermediate\ndetuning the p-wave resonant interaction generically drives Bose-condensation\nat a finite momentum, set by a competition between atomic kinetic energy and\natom-molecule hybridization. Because of the underlying rotationally-invariant\nenvironment of the atomic gas trapped isotropically, the putative striped\nsuperfluid is a realization of a quantum superfluid smectic, that can melt into\na variety of interesting phases, such as a quantum nematic. I will discuss the\ncorresponding rich phase diagrams and transitions, as well the low-energy\nproperties of the phases and fractional topological defects generic to striped\nsuperfluids and their fluctuation-driven descendants."
    },
    {
        "anchor": "Nonlinear Scattering of a Bose-Einstein Condensate on a Rectangular\n  Barrier: We consider the nonlinear scattering and transmission of an atom laser, or\nBose-Einstein condensate (BEC) on a finite rectangular potential barrier. The\nnonlinearity inherent in this problem leads to several new physical features\nbeyond the well-known picture from single-particle quantum mechanics. We find\nnumerical evidence for a denumerably infinite string of bifurcations in the\ntransmission resonances as a function of nonlinearity and chemical potential,\nwhen the potential barrier is wide compared to the wavelength of oscillations\nin the condensate. Near the bifurcations, we observe extended regions of\nnear-perfect resonance, in which the barrier is effectively invisible to the\nBEC. Unlike in the linear case, it is mainly the barrier width, not the height,\nthat controls the transmission behavior. We show that the potential barrier can\nbe used to create and localize a dark soliton or dark soliton train from a\nphonon-like standing wave.",
        "positive": "Variational determination of approximate bright matter-wave soliton\n  solutions in anisotropic traps: We consider the ground state of an attractively-interacting atomic\nBose-Einstein condensate in a prolate, cylindrically symmetric harmonic trap.\nIf a true quasi-one-dimensional limit is realized, then for sufficiently weak\naxial trapping this ground state takes the form of a bright soliton solution of\nthe nonlinear Schroedinger equation. Using analytic variational and highly\naccurate numerical solutions of the Gross-Pitaevskii equation we systematically\nand quantitatively assess how soliton-like this ground state is, over a wide\nrange of trap and interaction strengths. Our analysis reveals that the regime\nin which the ground state is highly soliton-like is significantly restricted,\nand occurs only for experimentally challenging trap anisotropies. This result,\nand our broader identification of regimes in which the ground state is\nwell-approximated by our simple analytic variational solution, are relevant to\na range of potential experiments involving attractively-interacting\nBose-Einstein condensates."
    },
    {
        "anchor": "Dynamics of trapped one-dimensional bosons for intermediate repulsive\n  interactions: The time-evolution of few number of interacting, harmonically confined\none-dimensional bosons is numerically obtained for arbitrary two-body\n$\\delta-$potential interaction strengths. It is demonstrated that the period of\nthe motion in a Newton's cradle configuration undergoes two crossovers as a\nfunction of interactions. Furthermore, through the evaluation of the structure\nfactor, the dependence of Bragg-scattering peaks on the interaction strength\nranging from the weak coupling regime to the impenetrable Tonks-Girardeau case\nis illustrated.",
        "positive": "Statics and dynamics of a self-bound dipolar matter-wave droplet: We study the statics and dynamics of a stable, mobile, self-bound\nthree-dimensional dipolar matter-wave droplet created in the presence of a tiny\nrepulsive three-body interaction. In frontal collision with an impact parameter\nand in angular collision at large velocities {along all directions} two\ndroplets behave like quantum solitons. Such collision is found to be quasi\nelastic and the droplets emerge undeformed after collision without any change\nof velocity. However, in a collision at small velocities the axisymmeric\ndipolar interaction plays a significant role and the collision dynamics is\nsensitive to the direction of motion. For an encounter along the $z$ direction\nat small velocities, two droplets, polarized along the $z$ direction, coalesce\nto form a larger droplet $-$ a droplet molecule. For an encounter along the $x$\ndirection at small velocities, the same droplets stay apart and never meet each\nother due to the dipolar repulsion. The present study is based on an analytic\nvariational approximation and a numerical solution of the mean-field\nGross-Pitaevskii equation using the parameters of $^{52}$Cr atoms."
    },
    {
        "anchor": "Quantum droplet in a mixture of Bose-Fermi superfluids: We study the formation of quantum droplets in the mixture of a\nsingle-component Bose-Einstein condensate (BEC), and a two-species Fermi\nsuperfluid across a wide Feshbach resonance. With repulsive boson-boson and\nattractive boson-fermion interactions, we show that quantum droplets can be\nstabilized by attractive fermion-fermion interactions in the\nBardeen-Cooper-Schieffer (BCS) side of the resonance, and can also exist in\ndeep BEC regime under weak boson-fermion interactions. We map out the phase\ndiagram for stable droplets with respect to the boson-boson and boson-fermion\ninteractions, and discuss the role of different types of quantum fluctuations\nin the relevant regions of the BCS-BEC crossover. Our work reveals the impact\nof fermion pairing on the formation of quantum droplets in Bose-Fermi mixtures,\nand provides a useful guide for future experiments.",
        "positive": "Mesoscopic Effects in Quantum Phases of Ultracold Quantum Gases in\n  Optical Lattices: We present a wide array of quantum measures on numerical solutions of 1D\nBose- and Fermi-Hubbard Hamiltonians for finite-size systems with open boundary\nconditions. Finite size effects are highly relevant to ultracold quantum gases\nin optical lattices, where an external trap creates smaller effective regions\nin the form of the celebrated \"wedding cake\" structure and the local density\napproximation is often not applicable. Specifically, for the Bose-Hubbard\nHamiltonian we calculate number, quantum depletion, local von-Neumann entropy,\ngeneralized entanglement or Q-measure, fidelity, and fidelity susceptibility;\nfor the Fermi-Hubbard Hamiltonian we also calculate the pairing correlations,\nmagnetization, charge-density correlations, and antiferromagnetic structure\nfactor. Our numerical method is imaginary time propagation via time-evolving\nblock decimation. As part of our study we provide a careful comparison of\ncanonical vs. grand canonical ensembles and Gutzwiller vs. entangled\nsimulations. The most striking effect of finite size occurs for bosons: we\nobserve a strong blurring of the tips of the Mott lobes accompanied by higher\ndepletion, and show how the location of the first Mott lobe tip approaches the\nthermodynamic value as a function of system size."
    },
    {
        "anchor": "Fermi polarons in two dimensions: We theoretically analyze inverse radiofrequency (rf) spectroscopy experiments\nin two-component Fermi gases. We consider a small number of impurity atoms\ninteracting strongly with a bath of majority atoms. In two-dimensional\ngeometries we find that the main features of the rf spectrum correspond to an\nattractive polaron and a metastable repulsive polaron. Our results suggest that\nthe attractive polaron has been observed in a recent experiment [Phys. Rev.\nLett. 106, 105301 (2011)].",
        "positive": "Dynamical phase transitions, temporal orthogonality and the dynamics of\n  observables in one dimensional ultra-cold quantum gases: from the continuum\n  to the lattice: We investigate the dynamics of the rate function and of local observables\nafter a quench in models which exhibit phase transitions between a superfluid\nand an insulator in their ground states. Zeros of the return probability,\ncorresponding to singularities of the rate functions, have been suggested to\nindicate the emergence of dynamical criticality and we address the question of\nwhether such zeros can be tied to the dynamics of physically relevant\nobservables and hence order parameters in the systems. For this we first\nnumerically analyze the dynamics of a hard-core boson gas in a one-dimensional\nwaveguide when a quenched lattice potential is commensurate with the particle\ndensity. Such a system can undergo a pinning transition to an insulating state\nand we find non-analytic behavior in the evolution of the rate function which\nis indicative of dynamical phase transitions. In addition, we perform\nsimulations of the time dependence of the momentum distribution and compare the\nperiodicity of this collapse and revival cycle to that of the non-analyticities\nin the rate function: the two are found to be closely related only for deep\nquenches. We then confirm this observation by analytic calculations on a\nclosely related discrete model of hard-core bosons in the presence of a\nstaggered potential and find expressions for the rate function for the\nquenches. By extraction of the zeros of the Loschmidt amplitude we uncover a\nnon-equilibrium timescale for the emergence of non-analyticities and discuss\nits relationship with the dynamics of the experimentally relevant parity\noperator."
    },
    {
        "anchor": "Measurement of spectral functions of ultracold atoms in disordered\n  potentials: We report on the measurement of the spectral functions of noninteracting\nultracold atoms in a three-dimensional disordered potential resulting from an\noptical speckle field. Varying the disorder strength by 2 orders of magnitude,\nwe observe the crossover from the \"quantum\" perturbative regime of low disorder\nto the \"classical\" regime at higher disorder strength, and find an excellent\nagreement with numerical simulations. The method relies on the use of\nstate-dependent disorder and the controlled transfer of atoms to create\nwell-defined energy states. This opens new avenues for experimental\ninvestigations of three-dimensional Anderson localization.",
        "positive": "Motion of an Impurity in a Bose-Einstein Condensate with Weyl Spin-Orbit\n  Coupling: Non-collinear Drag Force and Anisotropic Critical Velocity: We consider the motion of a point-like impurity through a three-dimensional\ntwo-component Bose-Einstein condensate subject to Weyl spin-orbit coupling.\nUsing linear-response theory, we calculate the drag force felt by the impurity\nand the associated anisotropic critical velocity from the spectrum of\nelementary excitations. The drag force is shown to be generally not collinear\nwith the velocity of the impurity. This unusual behavior is a consequence of\ncondensation into a finite-momentum state due to the spin-orbit coupling."
    },
    {
        "anchor": "Brownian motion of solitons in a Bose-Einstein Condensate: For the first time, we observed and controlled the Brownian motion of\nsolitons. We launched solitonic excitations in highly elongated $^{87}\\rm{Rb}$\nBECs and showed that a dilute background of impurity atoms in a different\ninternal state dramatically affects the soliton. With no impurities and in\none-dimension (1-D), these solitons would have an infinite lifetime, a\nconsequence of integrability. In our experiment, the added impurities scatter\noff the much larger soliton, contributing to its Brownian motion and decreasing\nits lifetime. We describe the soliton's diffusive behavior using a quasi-1-D\nscattering theory of impurity atoms interacting with a soliton, giving\ndiffusion coefficients consistent with experiment.",
        "positive": "Excited-State Phase Diagram of a Ferromagnetic Quantum Gas: The ground-state phases of a quantum many-body system are characterized by an\norder parameter, which changes abruptly at quantum phase transitions when an\nexternal control parameter is varied. Interestingly, these concepts may be\nextended to excited states, for which it is possible to define equivalent\nexcited-state quantum phase transitions. However, the experimental mapping of a\nphase diagram of excited quantum states has not yet been demonstrated. Here we\npresent the experimental determination of the excited-state phase diagram of an\natomic ferromagnetic quantum gas, where, crucially, the excitation energy is\none of the control parameters. The obtained phase diagram exemplifies how the\nextensive Hilbert state of quantum many-body systems can be structured by the\nmeasurement of well-defined order parameters."
    },
    {
        "anchor": "Momentum correlations as signature of sonic Hawking radiation in\n  Bose-Einstein condensates: We study the two-body momentum correlation signal in a quasi one dimensional\nBose-Einstein condensate in the presence of a sonic horizon. We identify the\nrelevant correlation lines in momentum space and compute the intensity of the\ncorresponding signal. We consider a set of different experimental procedures\nand identify the specific issues of each measuring process. We show that some\ninter-channel correlations, in particular the Hawking quantum-partner one, are\nparticularly well adapted for witnessing quantum non-separability, being\nresilient to the effects of temperature and/or quantum quenches.",
        "positive": "Elementary Excitations in a BEC with Isotropic Harmonic Trap: Bogoliubov\n  Equations versus Hydrodynamic Formalism: The elementary excitations for a BEC trapped by means of an isotropic\nharmonic oscillator are studied in the present work. The analysis of these\nperturbations is done in the context of the Bogoliubov equations and not\nresorting to the hydrodynamic version. The comparison between these two\napproaches will allow us to deduce a parameter explaining the role that the\nscattering length and the trap play in the way in which the frequency of these\nelementary excitations acquires information about the angular momentum of the\ncorresponding solutions. It will be shown that outside the validity realm of\nthe Thomas_fermi approximation the frequencies of the perturbations cannot\ninherit the information of the angular momentum codified in the functions\nescribing the elementary excitations."
    },
    {
        "anchor": "Connecting Berezinskii-Kosterlitz-Thouless and BEC phase transitions by\n  tuning interactions in a trapped gas: We study the critical point for the emergence of coherence in a harmonically\ntrapped two-dimensional Bose gas with tuneable interactions. Over a wide range\nof interaction strengths we find excellent agreement with the classical-field\npredictions for the critical point of the Berezinskii-Kosterlitz-Thouless (BKT)\nsuperfluid transition. This allows us to quantitatively show, without any free\nparameters, that the interaction-driven BKT transition smoothly converges onto\nthe purely quantum-statistical Bose-Einstein condensation (BEC) transition in\nthe limit of vanishing interactions.",
        "positive": "Topological quantum matter in synthetic dimensions: In the field of quantum simulation of condensed matter phenomena by\nartificially engineering the Hamiltonian of an atomic, molecular or optical\nsystem, the concept of `synthetic dimensions' has recently emerged as a\npowerful way to emulate phenomena such as topological phases of matter, which\nare now of great interest across many areas of physics. The main idea of a\nsynthetic dimension is to couple together suitable degrees of freedom, such as\na set of internal atomic states, in order to mimic the motion of a particle\nalong an extra spatial dimension. This approach provides a way to engineer\nlattice Hamiltonians and enables the realisation of higher-dimensional\ntopological models in platforms with lower dimensionality. We give an overview\nof the recent progress in studying topological matter in synthetic dimensions.\nAfter reviewing proposals and realizations in various setups, we discuss future\nprospects in many-body physics, applications, and topological effects in three\nor more spatial dimensions."
    },
    {
        "anchor": "Crystallized and amorphous vortices in rotating atomic-molecular\n  Bose-Einstein condensates: Vortex is a topological defect with a quantized winding number of the phase\nin superfluids and superconductors. Here, we investigate the crystallized\n(triangular, square, honeycomb) and amorphous vortices in rotating\natomic-molecular Bose-Einstein condensates (BECs) by using the damped projected\nGross-Pitaevskii equation. The amorphous vortices are the result of the\nconsiderable deviation induced by the interaction of atomic-molecular vortices.\nBy changing the atom-molecule interaction from attractive to repulsive, the\nconfiguration of vortices can change from an overlapped atomic-molecular\nvortices to carbon-dioxide-type ones, then to atomic vortices with interstitial\nmolecular vortices, and finally into independent separated ones. The Raman\ndetuning can tune the ratio of the atomic vortex to the molecular vortex. We\nprovide a phase diagram of vortices in rotating atomic-molecular BECs as a\nfunction of Raman detuning and the strength of atom-molecule interaction.",
        "positive": "Dominant Andreev Reflection through Nonlinear Radio-Frequency Transport: We theoretically propose the laser-induced Andreev reflection between\ntwo-component Fermi superfluid and normal states via spatially-uniform Rabi\ncouplings. By analyzing the tunneling current between the superfluid and normal\nstates up to the fourth order in the Rabi couplings, we find that the Andreev\ncurrent exhibits unconventional non-Ohmic transport at zero temperature.\nRemarkably, the Andreev current gives the only contribution in the synthetic\njunction system at zero detunings regardless of the ratio of the chemical\npotential bias to the superfluid gap, which is in sharp contrast to that in the\nconventional superconductor-normal metal junction. Our result may also pave a\nway for understanding the black hole information paradox through the Andreev\nreflection as a quantum-information mirror."
    },
    {
        "anchor": "Excitation and dynamics in the extended bose-hubbard model: The one-dimensional extended bosonic Hubbard model has been shown to exhibit\na variety of phases ranging from Mott insulator and superfluid to exotic\nsupersolids and Haldane insulators depending on the filling and the relative\nvalue of the contact ($U$) and near neighbor ($V$) interaction strengths. In\nthis paper we use the density matrix renormalization group and the time\nevolving block decimation numerical methods to study in detail the dynamics and\nexcitation spectra of this model in its various phases. In particular, we study\nin detail the behavior of the charge and neutral gaps which characterize the\nMott, charge density and Haldane insulating phases. We also show that in\naddition to the gapless modes at $k=0$, the supersolid phase exhibits gapless\nmodes at a finite $k$ which depends on the filling.",
        "positive": "Arbitrary-angle rotation of the polarization of a dipolar Bose-Einstein\n  condensate: We have employed the theory of harmonically trapped dipolar Bose-Einstein\ncondensates to examine the influence of a uniform magnetic field that rotates\nat an arbitrary angle to its own orientation. This is achieved by\nsemi-analytically solving the dipolar superfluid hydrodynamics of this system\nwithin the Thomas-Fermi approximation and by allowing the body frame of the\ncondensate's density profile to be tilted with respect to the symmetry axes of\nthe nonrotating harmonic trap. This additional degree of freedom manifests\nitself in the presence of previously unknown stationary solution branches for\nany given dipole tilt angle. We also find that the tilt angle of the stationary\nstate's body frame with respect to the rotation axis is a nontrivial function\nof the trapping geometry, rotation frequency and dipole tilt angle. For\nrotation frequencies of at least an order of magnitude higher than the in-plane\ntrapping frequency, the stationary state density profile is almost perfectly\nequivalent to the profile expected in a time-averaged dipolar potential that\neffectively vanishes when the dipoles are tilted along the `magic angle', $54.7\n\\deg$. However, by linearizing the fully time-dependent superfluid\nhydrodynamics about these stationary states, we find that they are dynamically\nunstable against the formation of collective modes, which we expect would\nresult in turbulent decay."
    },
    {
        "anchor": "Optimized Bose-Einstein-condensate production in a dipole trap based on\n  a 1070-nm multifrequency laser: Influence of enhanced two-body loss on the\n  evaporation process: We present an optimized strategy for the production of tightly confined\nBose-Einstein condensates (BEC) of 87Rb in a crossed dipole trap with direct\nloading from a magneto-optical trap. The dipole trap is created with light of a\nmultifrequency fiber laser with a center wavelength of 1070nm. Evaporative\ncooling is performed by ramping down the laser power only. A comparison of the\nresulting atom number in an almost pure BEC to the initial atom number and the\nvalue for the gain in phase space density per atom lost confirm that this\nstraightforward strategy is very efficient. We observe that the temporal\ncharacteristics of evaporation sequence are strongly influenced by\npower-dependent two-body losses resulting from enhanced optical pumping to the\nhigher-energy hyperfine state. We characterize these losses and compare them to\nresults obtained with a single-frequency laser at 1030nm.",
        "positive": "Thermalization of a two-dimensional photon gas in a polymeric host\n  matrix: We investigate thermodynamic properties of a two-dimensional photon gas\nconfined by a dye-filled optical microcavity. A thermally equilibrated state of\nthe photon gas is achieved by radiative coupling to a heat bath that is\nrealized with dye molecules embedded in a polymer at room temperature. The\nchemical potential of the gas is freely adjustable. The optical microcavity\nconsisting of two curved mirrors induces both a non-vanishing effective photon\nmass and a harmonic trapping potential for the photons. While previous\nexperiments of our group have used liquid dye solutions, the measurements\ndescribed here are based on dye molecules incorporated into a polymer host\nmatrix. We describe studies of fluorescence properties of dye-doped polymers,\nand discuss the applicability of Kennard-Stepanov theory in this system. We\nobserve a thermalized two-dimensional photon gas in the solid state based\nmicroresonator system. In the future, dye-based solid state systems hold\npromise for the realization of single-mode light sources in thermal equilibrium\nbased on Bose-Einstein condensation of photons, as well as for solar energy\nconcentrators."
    },
    {
        "anchor": "Quantum kinetics of ultracold fermions coupled to an optical resonator: We study the far-from-equilibrium statistical mechanics of periodically\ndriven fermionic atoms in a lossy optical resonator. We show that the interplay\nof the Fermi surface with cavity losses leads to sub-natural cavity linewidth\nnarrowing, squeezed light, and out-of-equilibrium quantum statistics of the\natoms. Adapting the Keldysh approach, we set-up and solve a quantum kinetic\nBoltzmann equation in a systematic $1/N$ expansion with $N$ the number of\natoms. In the strict thermodynamic limit $N,V\\rightarrow \\infty$,\n$N/V=\\text{const.}$ we find the atoms (fermions or bosons) remain immune\nagainst cavity-induced heating or cooling. At next-to-leading order in $1/N$,\nwe find a \"one-way thermalization\" of the atoms determined by cavity decay. We\nargue that, in absence of an equilibrium fluctuation-dissipation relation, the\nlong-time limit $\\Delta t \\rightarrow \\infty$ does not commute with the\nthermodynamic limit $N\\rightarrow \\infty$, such that for the physically\nrelevant case of large but finite $N$, the dynamics ultimately becomes strongly\ncoupled, especially close to the superradiance phase transition.",
        "positive": "Free expansion of Bose-Einstein condensates with a multicharged vortex: In this work, we analyze the free expansion of Bose-Einstein condensates\ncontaining multicharged vortices. The atomic cloud is initially confined in a\nthree-dimensional asymmetric harmonic trap. We apply both approximate\nvariational solutions and numerical simulations of the Gross-Pitaevskii\nequation. The data obtained provide a way to establish the presence as well as\nthe multiplicity of vortices based only on the properties of the expanded cloud\nwhich can be obtained via time-of-flight measurements. In addition, several\nfeatures such as the evolution of the vortex core size and the asymptotic\nvelocity during free expansion were studied considering the atomic cloud as\nbeing released from different harmonic trap configurations."
    },
    {
        "anchor": "Pump-and-probe optical transmission phase shift as a quantitative probe\n  of the Bogoliubov dispersion relation in a nonlinear channel waveguide: We theoretically investigate the dispersion relation of small-amplitude\noptical waves superimposing upon a beam of polarized monochromatic light\npropagating along a single-mode channel waveguide characterized by an\ninstantaneous and spatially local Kerr nonlinearity. These small luminous\nfluctuations propagate along the waveguide as Bogoliubov elementary excitations\non top of a one-dimensional dilute Bose quantum fluid evolve in time. They\nconsequently display a strongly renormalized dispersion law, of Bogoliubov\ntype. Analytical and numerical results are found in both the absence and the\npresence of one- and two-photon losses. Silicon and silicon-nitride waveguides\nare used as examples. We finally propose an experiment to measure this\nBogoliubov dispersion relation, based on a stimulated four-wave mixing and\ninterference spectroscopy techniques.",
        "positive": "Short range inter-vortex interaction and interacting dynamics of\n  half-quantized vortices in two-component Bose-Einstein condensates: We study the interaction and dynamics of two half-quantized vortices in\ntwo-component Bose- Einstein condensates. Using the Pade approximation for the\nvortex core profile, we calculate the intervortex potential, whose asymptotic\nform for a large distance has been derived by Eto et al. [Phys. Rev. A, 83,\n063603 (2011)]. Through numerical simulations of the two-dimensional\nGross-Pitaevskii equations, we reveal different kinds of dynamical trajectories\nof the vortices depending on the combinations of signs of circulations and the\nintercomponent density coupling. Under the adiabatic limit, we derive the\nequations of motion for the vortex coordinates, in which the motion is caused\nby the balance between Magnus force and the intervortex forces. The initial\nvelocity of the vortex motion can be explained quantitatively by this point\nvortex approximation, but under- standing the long-time behavior of the\ndynamics needs more consideration beyond our model."
    },
    {
        "anchor": "Robust Digital Holography For Ultracold Atom Trapping: We have formulated and experimentally demonstrated an improved algorithm for\ndesign of arbitrary two-dimensional holographic traps for ultracold atoms. Our\nmethod builds on the best previously available algorithm, MRAF, and improves on\nit in two ways. First, it allows for creation of holographic atom traps with a\nwell defined background potential. Second, we experimentally show that for\ncreating trapping potentials free of fringing artifacts it is important to go\nbeyond the Fourier approximation in modelling light propagation. To this end,\nwe incorporate full Helmholtz propagation into our calculations.",
        "positive": "Mode-locked Bloch oscillations in a ring cavity: We present a new technique for stabilizing and monitoring Bloch oscillations\nof ultracold atoms in an optical lattice under the action of a constant\nexternal force. In the proposed scheme, the atoms also interact with a\nunidirectionally pumped optical ring cavity whose one arm is collinear with the\noptical lattice. For weak collective coupling, Bloch oscillations dominate over\nthe collective atomic recoil lasing instability and develop a synchronized\nregime in which the atoms periodically exchange momentum with the cavity field."
    },
    {
        "anchor": "Dynamical creation of entangled bosonic states in a double well: We study the creation of a bosonic N00N state from the evolution of a Fock\nstate in a double well. While noninteracting bosons disappear quickly in the\nHilbert space, the evolution under the influence of a Bose-Hubbard Hamiltonian\nis much more restricted. This restriction is caused by the fragmentation of the\nspectrum into a high-energy part with doubly degenerate levels and a\nnondegenerate low-energy part. This degeneracy suppresses transitions to states\nof the high-energy part of the spectrum. At a moderate interaction strength\nthis effect supports strongly the dynamical formation of a N00N state. The N00N\nstate is suppressed in an asymmetric double well, where the double degeneracy\nis absent.",
        "positive": "Coherence and entanglement in the ground-state of a bosonic Josephson\n  junction:from macroscopic Schr\u00f6dinger cats to separable Fock states: We consider a bosonic Josephson junction made of $N$ ultracold and dilute\natoms confined by a quasi one-dimensional double-well potential within the\ntwo-site Bose-Hubbard model framework. The behaviour of the system is\ninvestigated at zero temperature by varying the inter-atomic interaction from\nthe strongly attractive regime to the repulsive one. We show that the\nground-state exhibits a crossover from a macroscopic Schr\\\"odinger-cat state to\na separable Fock state through an atomic coherent regime. By diagonalizing the\nBose-Hubbard Hamiltonian we characterize the emergence of the mascroscopic cat\nstates by calculating the Fisher information $F$, the coherence by means of the\nvisibility $\\alpha$ of the interference fringes in the momentum distribution,\nand the quantum correlations by using the entanglement entropy $S$. Both Fisher\ninformation and visibility are shown to be related to the ground state energy\nby employing the Hellmann-Feynman theorem. This result, together with a\nperturbative calculation of the ground-state energy, makes possible to obtain\nsimple analytical formulas for $F$ and $\\alpha$ over a range of interactions,\nin excellent agreement with the exact diagonalization of the Bose-Hubbard\nHamiltonian. In the attractive regime the entanglement entropy attains values\nvery close to its upper limit for a specific interaction strength lying in the\nregion where coherence is lost and self trapping sets in."
    },
    {
        "anchor": "Functional renormalization group approach to the BCS-BEC crossover: The phase transition to superfluidity and the BCS-BEC crossover for an\nultracold gas of fermionic atoms is discussed within a functional\nrenormalization group approach. Non-perturbative flow equations, based on an\nexact renormalization group equation, describe the scale dependence of the\nflowing or average action. They interpolate continuously from the microphysics\nat atomic or molecular distance scales to the macroscopic physics at much\nlarger length scales, as given by the interparticle distance, the correlation\nlength, or the size of the experimental probe. We discuss the phase diagram as\na function of the scattering length and the temperature and compute the gap,\nthe correlation length and the scattering length for molecules. Close to the\ncritical temperature, we find the expected universal behavior. Our approach\nallows for a description of the few-body physics (scattering and molecular\nbinding) and the many-body physics within the same formalism.",
        "positive": "Relative Phase States in Quantum-Atom Optics: Relative phase is treated as a physical quantity for two mode systems in\nquantum atom optics, adapting the Pegg-Barnett treatment of quantum optical\nphase to define a linear Hermitian relative phase operator via first\nintroducing a complete orthonormal set of relative phase eigenstates. These\nstates are contrasted with other so-called phase states. Other approaches to\ntreating phase and previous attempts to find a Hermitian phase operator are\ndiscussed. The relative phase eigenstate has maximal two mode entanglement, it\nis a fragmented state with its Bloch vector lying inside the Bloch sphere and\nis highly spin squeezed. The relative phase states are applied to describing\ninterferometry experiments with Bose-Einstein condensates (BEC), particularly\nin the context of a proposed Heisenberg limited interferometry experiment. For\na relative phase eigenstate the fractional fluctuation in one spin operator\ncomponent perpendicular to the Bloch vector is essentially only of order 1/N,\nso if such a highly spin squeezed state could be prepared it may be useful for\nHeisenberg limited interferometry. An approach for preparing a BEC in a state\nclose to a relative phase state is suggested, based on adiabatically changing\nparameters in the Josephson Hamiltonian starting from a suitable energy\neigenstate in the Rabi regime."
    },
    {
        "anchor": "Generalized Hydrodynamics in the 1D Bose gas: theory and experiments: We review the recent theoretical and experimental progress regarding the\nGeneralized Hydrodynamics (GHD) behavior of the one-dimensional Bose gas with\ncontact repulsive interactions, also known as the Lieb-Liniger gas. In the\nfirst section, we review the theory of the Lieb-Liniger gas, introducing the\nkey notions of the rapidities and of the rapidity distribution. The latter\ncharacterizes the Lieb-Liniger gas after relaxation and is at the heart of GHD.\nWe also present the asymptotic regimes of the Lieb-Liniger gas with their\ndedicated approximate descriptions. In the second section we enter the core of\nthe subject and review the theoretical results on GHD in 1D Bose gases. The\nthird and fourth sections are dedicated to experimental results obtained in\ncold atoms experiments: the experimental realization of the Lieb-Liniger model\nis presented in section 3, with a selection of key results for systems at\nequilibrium, and section 4 presents the experimental tests of the GHD theory.\nIn section 5 we review the effects of atom losses, which, assuming slow loss\nprocesses, can be described within the GHD framework. We conclude with a few\nopen questions.",
        "positive": "Kibble-Zurek Dynamics in a Trapped Ultracold Bose Gas: The dynamical evolution of an inhomogeneous ultracold atomic gas quenched at\ndifferent controllable rates through the Bose-Einstein condensation phase\ntransition is studied numerically in the premise of a recent experiment in an\nanisotropic harmonic trap. Our findings based on the stochastic (projected)\nGross-Pitaevskii equation are shown to be consistent at early times with the\npredictions of the homogeneous Kibble-Zurek mechanism. This is demonstrated by\ncollapsing the early dynamical evolution of densities, spectral functions and\ncorrelation lengths for different quench rates, based on an appropriate\ncharacterization of the distance to criticality felt by the quenched system.\nThe subsequent long-time evolution, beyond the identified dynamical critical\nregion, is also investigated by looking at the behaviour of the density\nwavefront evolution and the corresponding phase ordering dynamics."
    },
    {
        "anchor": "Some properties of a long lifetime strongly-coupled molecular plasma\n  produced by high Rydberg excitation of nitric oxide in a supersonic free jet: A long life-time (>0.3 ms) strongly-coupled molecular Rydberg plasma is\ngenerated by the excitation of nitric oxide into the high-n Rydberg threshold\nregion in the high-density region of a supersonic jet expansion. After 310 \\mus\nthe plasma has expanded to a size of ca. 3 cm. When subjected to very small DC\nfields from 0.2 to 1.0 V/cm the plasma reveals a much smaller high-density core\nstructure of only 0.6 cm. The molecular Rydberg plasma is observed over a broad\nrange of excitation energies, from threshold down to Rydberg states as low as n\n= 19.",
        "positive": "Adiabatic sweep theorem for three-dimensional dipolar Bose gases: The variational theorem for the scattering length in the presence of the\ndipole-dipole interaction is developed. The theorem is applied to the spinless\ndipolar Bose gas in three dimensions. We calculated analytically the long-range\ntails of the single-particle momentum distribution and static structure factor,\nand the pair distribution function at short distances. The momentum\ndistribution is inversely proportional to $q^4$ with the anisotropic prefactor.\nIn the absence of the dipole-dipole interaction, Tan's adiabatic sweep theorem\nis reproduced as a particular case. For the homogeneous dilute Bose gas, all\nthe relations are calculated analytically."
    },
    {
        "anchor": "XYZ quantum Heisenberg models with p-orbital bosons: We demonstrate how the spin-1/2 XYZ quantum Heisenberg model can be realized\nwith bosonic atoms loaded in the p band of an optical lattice in the Mott\nregime. The combination of Bose statistics and the symmetry of the p-orbital\nwave functions leads to a nonintegrable Heisenberg model with antiferromagnetic\ncouplings. Moreover, the sign and relative strength of the couplings\ncharacterizing the model are shown to be experimentally tunable. We display the\nrich phase diagram in the one-dimensional case and discuss finite size effects\nrelevant for trapped systems. Finally, experimental issues related to\npreparation, manipulation, detection, and imperfections are considered.",
        "positive": "Fermionic condensation in ultracold atoms, nuclear matter and neutron\n  stars: We investigate the Bose-Einstein condensation of fermionic pairs in three\ndifferent superfluid systems: ultracold and dilute atomic gases, bulk neutron\nmatter, and neutron stars. In the case of dilute gases made of fermionic atoms\nthe average distance between atoms is much larger than the effective radius of\nthe inter-atomic potential. Here the condensation of fermionic pairs is\nanalyzed as a function of the s-wave scattering length, which can be tuned in\nexperiments by using the technique of Feshbach resonances from a small and\nnegative value (corresponding to the Bardeen-Cooper-Schrieffer (BCS) regime of\nCooper Fermi pairs) to a small and positive value (corresponding to the regime\nof the Bose-Einstein condensate (BEC) of molecular dimers), crossing the\nunitarity regime where the scattering length diverges. In the case of bulk\nneutron matter the s-wave scattering length of neutron-neutron potential is\nnegative but fixed, and the condensate fraction of neutron-neutron pairs is\nstudied as a function of the total neutron density. Our results clearly show a\nBCS-quasiunitary-BCS crossover by increasing the neutron density. Finally, in\nthe case of neutron stars, where again the neutron-neutron scattering length is\nnegative and fixed, we determine the condensate fraction as a function of the\ndistance from the center of the neutron star, finding that the maximum\ncondensate fraction appears in the crust of the neutron star."
    },
    {
        "anchor": "Slow-Goldstone mode generated by order from quantum disorder and its\n  experimental detection: The order from quantum disorders (OFQD) phenomenon is well-known and\nubiquitous in particle physics and frustrated magnetic systems. Typically, OFQD\ntransfers a spurious Goldstone mode into a pseudo-Goldstone mode with a tiny\ngap. Here, we report an opposite phenomenon: OFQD transfers a spurious\nquadratic mode into a true linear Goldstone mode with a very small velocity\n(named slow-Goldstone mode). This new phenomenon is demonstrated in an\ninteracting bosonic system subjected to an Abelian flux. We develop a new and\nsystematic OFQD analysis to determine the true quantum ground state and the\nwhole excitation spectrum. In the weak-coupling limit, the superfluid ground\nstate has a 4-sublattice 90? coplanar spin structure, which supports 4 linear\nGoldstone modes with 3 different velocities. One of which is generated by the\nOFQD is much softer than the other 3 Goldstone modes, so it can be easily\ndetected in the cold atom or photonic experiments. In the strong-coupling\nlimit, the ferromagnetic Mott ground state with a true quadratic Goldstone\nmode. We speculate that there could be some topological phases intervening\nbetween the two symmetry broken states. These novel phenomena may be observed\nin the current cold-atom or photonic experiments subjected to an Abelian flux\nat the weak coupling limit where the heatings may be well under control.\nPossible connections to Coleman-Weinberg potential in particle physics, 1/N\nexpansion of Sachdev-Ye-Kitaev models, and zero temperature quantum black hole\nentropy are outlined.",
        "positive": "Validity of the scattering length approximation in strongly interacting\n  Fermi systems: We investigate the energy spectrum of systems of two, three and four spin-1/2\nfermions with short range attractive interactions both exactly, and within the\nscattering length approximation. The formation of molecular bound states and\nthe ferromagnetic transition of the excited scattering state are examined\nsystematically as a function of the 2-body scattering length. Identification of\nthe upper branch (scattering states) is discussed and a general approach valid\nfor systems with many particles is given. We show that an adiabatic\nferromagnetic transition occurs, but at a critical transition point kF a much\nhigher than predicted from previous calculations, almost all of which use the\nscattering length approximation. In the 4-particle system the discrepancy is a\nfactor of 2. The exact critical interaction strength calculated in the\n4-particle system is consistent with that reported by experiment. To make\ncomparisons with the adiabatic transition, we study the quench dynamics of the\npairing instability using the eigenstate wavefunctions."
    },
    {
        "anchor": "Coboson many-body formalism for cold atom dimers with attraction between\n  different fermion species only: Unlike the Coulomb potential that acts between all semiconductor carriers,\nthe potential commonly used for BCS superconductors and cold atom gases acts\nbetween different fermion species only, these species differing by their spin\nor hyperfine index. The coboson formalism we here develop evidences that such\ncomposite bosons interact through fermion exchange only, thus rendering the\nstructure of the Shiva diagrams that visualize their many-body effects far\nsimpler. A separable potential is used to obtain analytical results for the\n$N$-coboson normalization factor and the $N$-coboson ground-state energy within\nthe Born approximation, in terms of the Born dimer-dimer scattering length.\nThis formalism opens the route toward approaching complex many-body effects,\nsuch as Bose-Einstein condensation, through a new perspective.",
        "positive": "Two-dimensional Thouless pumping in time-space crystalline structures: Dynamics of particle in a resonantly driven quantum well can be interpreted\nas that of a particle in a crystal-like structure, with the time playing the\nrole of the coordinate. By introducing an adiabatically varied phase in the\ndriving protocol, we demonstrate a realization of the Thouless pumping in such\na time crystalline structure. Next, we extend the analysis beyond a single\nquantum well by considering a driven one-dimensional optical lattice, thereby\nengineering a 2D time-space crystalline structure. Such a setup allows us to\nexplore adiabatic pumping in the spatial and the temporal dimensions\nseparately, as well as to simulate simultaneous time-space pumping."
    },
    {
        "anchor": "Driving phase slips in a superfluid atom circuit with a rotating weak\n  link: We have observed well-defined phase slips between quantized persistent\ncurrent states around a toroidal atomic (23Na) Bose-Einstein condensate. These\nphase slips are induced by a weak link (a localized region of reduced\nsuperfluid density) rotated slowly around the ring. This is analogous to the\nbehavior of a superconducting loop with a weak link in the presence of an\nexternal magnetic field. When the weak link is rotated more rapidly,\nwell-defined phase slips no longer occur, and vortices enter into the bulk of\nthe condensate. A noteworthy feature of this system is the ability to\ndynamically vary the weak link and hence the critical current, a feature which\nis difficult to implement in superconducting or superfluid helium circuits.",
        "positive": "Universal relations and normal phase of an ultracold Fermi gas with\n  coexisting $s$- and $p$-wave interactions: We study the universal relations and normal-phase thermodynamics of a\ntwo-component ultracold Fermi gas with coexisting $s$- and $p$-wave\ninteractions. Due to the orthogonality of two-body wave functions of different\nscattering channels, the universal thermodynamic relations of the system appear\nto be direct summations of contributions from each partial-wave scattering\nchannels. These universal relations are dictated by a set of contacts, which\ncan be associated with either $s$- or $p$-wave interactions. Interestingly, due\nto the interplay of $s$- and $p$-wave interactions on the many-body level, the\ncontacts, and hence all the relevant thermodynamic quantities, behave\ndifferently from those with only $s$- or $p$-wave interactions. These are\nmanifest in our numerical calculations based on second-order virial expansions\nfor $^{40}$K atoms under typical experimental parameters. A particularly\ninteresting finding is that, due to the coexistence of $s$- and $p$-wave\nscatterings, the interaction energy of the repulsive branch features abrupt\nchanges across the $p$-wave resonances. Our results can be readily checked\nexperimentally for $^{40}$K atoms near the $198$G $p$-wave Feshbach resonance,\nwhere multiple partial-wave scatterings naturally coexist."
    },
    {
        "anchor": "Lattice Induced Resonances in One Dimensional Bosonic Systems: We study the resonant effects produced when a Feshbach dimer crosses a\nscattering continuum band of atoms in an optical lattice. We numerically obtain\nthe exact spectrum of two particles in a one-dimensional lattice and develop an\neffective atom-dimer Hamiltonian that accurately captures resonant effects. The\nlattice-induced resonances lead to the formation of bound states simultaneously\nabove and below the scattering continuum and significantly modify the curvature\nof the dimer dispersion relation. The nature of the atom-dimer coupling depends\nstrongly on the parity of the dimer state leading to a novel coupling in the\ncase of negative parity dimers. From the exact solutions we extract the dimer\nWannier function from which we quantitatively determine the effective\nHamiltonian parameters for a many-body description.",
        "positive": "Four fermions in a one-dimensional harmonic trap: Accuracy of a\n  variational-ansatz approach: Detailed analysis of the system of four interacting ultra-cold fermions\nconfined in a one-dimensional harmonic trap is performed. The analysis is done\nin the framework of a simple variational ansatz for the many-body ground state\nand its predictions are confronted with the results of numerically exact\ndiagonalization of the many-body Hamiltonian. Short discussion on the role of\nthe quantum statistics, i.e. Bose-Bose and Bose-Fermi mixtures is also\npresented. It is concluded that the variational ansatz, although seemed to be\noversimplified, gives surprisingly good predictions of many different\nquantities for mixtures of equal as well as different mass systems. The result\nmay have some experimental importance since it gives quite simple and validated\nmethod for describing experimental outputs."
    },
    {
        "anchor": "Variational Approach to Many-Body Problems Incorporating Many-Body\n  Effects at Finite Temperature: We develop a variational approach at finite temperature that incorporates\nmany-body correlation self-consistently. The grand potential is constructed in\nterms of Green's function expressed by the variational parameters. We apply\nthis formalism to weakly interacting Bose-Einstein condensates to incorporate\nthe dynamical 3/2-body processes, which are considered important in the\ndynamical properties. The processes lower the free energy below the mean-field\nHartree--Fock--Bogoliubov's value in the same way as a previous\nzero-temperature formalism. From our numerical results, the pair creation or\nannihilation processes neglected in the Popov--Shohno approximation are\nenhanced, particularly in the long wavelength region, owing to the many-body\neffects. Because the 3/2-body correlations give a finite contribution to the\nself-energy of quasiparticles, they may change the microscopic properties\nqualitatively, even in the weak-coupling region.",
        "positive": "Mean-field phase diagram of ultracold atomic gases in cavity quantum\n  electrodynamics: We investigate the mean-field phase diagram of the Bose-Hubbard model with\ninfinite-range interactions in two dimensions. This model describes ultracold\nbosonic atoms confined by a two-dimensional optical lattice and dispersively\ncoupled to a cavity mode with the same wavelength as the lattice. We determine\nthe ground-state phase diagram for a grand-canonical ensemble by means of\nanalytical and numerical methods. Our results mostly agree with the ones\nreported in Dogra et al. [PRA 94, 023632 (2016)], and have a remarkable\nqualitative agreement with the quantum Monte Carlo phase diagrams of Flottat et\nal. [PRB 95, 144501 (2017)]. The salient differences concern the stability of\nthe supersolid phases, which we discuss in detail. Finally, we discuss\ndifferences and analogies between the ground state properties of strong\nlong-range interacting bosons with the ones predicted for repulsively\ninteracting dipolar bosons in two dimensions."
    },
    {
        "anchor": "Site-resolved Imaging of Fermionic Lithium-6 in an Optical Lattice: We demonstrate site-resolved imaging of individual fermionic lithium-6 atoms\nin a 2D optical lattice. To preserve the density distribution during\nfluorescence imaging, we simultaneously cool the atoms with 3D Raman sideband\ncooling. This laser cooling technique, demonstrated here for the first time for\nlithium-6 atoms, also provides a pathway to rapid low-entropy filling of an\noptical lattice. We are able to determine the occupation of individual lattice\nsites with a fidelity >95%, enabling direct, local measurement of particle\ncorrelations in Fermi lattice systems. This ability will be instrumental for\ncreating and investigating low-temperature phases of the Fermi-Hubbard model,\nincluding antiferromagnets and d-wave superfluidity.",
        "positive": "Relative and center-of-mass motion in the attractive Bose-Hubbard model: We present first-principle numerical calculations for few particle solutions\nof the attractive Bose-Hubbard model with periodic boundary conditions. We show\nthat the low-energy many-body states found by numerical diagonalization can be\nwritten as translational superposition states of compact composite systems of\nparticles. These compact states break the translational symmetry of the problem\nand their center-of-mass and internal excitations offer simple explanations of\nthe energy spectrum of the full model."
    },
    {
        "anchor": "Chaos and two-level dynamics of the Atomtronic Quantum Interference\n  Device: We study the Atomtronics Quantum Interference Device employing a\nsemiclassical perspective. We consider an $M$ site ring that is described by\nthe Bose-Hubbard Hamiltonian. Coherent Rabi oscillations in the flow of the\ncurrent are feasible, with an enhanced frequency due to to chaos-assisted\ntunneling. We highlight the consequences of introducing a weak-link into the\ncircuit. In the latter context we clarify the phase-space considerations that\nare involved in setting up an effective \"systems plus bath\" description in\nterms of Josephson-Caldeira-Leggett Hamiltonian.",
        "positive": "Bose-Einstein Condensation of Erbium: We report on the achievement of Bose-Einstein condensation of erbium atoms\nand on the observation of magnetic Feshbach resonances at low magnetic field.\nBy means of evaporative cooling in an optical dipole trap, we produce pure\ncondensates of $^{168}$Er, containing up to $7 \\times 10^{4}$ atoms. Feshbach\nspectroscopy reveals an extraordinary rich loss spectrum with six loss\nresonances already in a narrow magnetic-field range up to 3 G. Finally, we\ndemonstrate the application of a low-field Feshbach resonance to produce a\ntunable dipolar Bose-Einstein condensate and we observe its characteristic\nd-wave collapse."
    },
    {
        "anchor": "Precision measurements of s-wave scattering lengths in a two-component\n  Bose-Einstein condensate: We use collective oscillations of a two-component Bose-Einstein condensate\n(2CBEC) of \\Rb atoms prepared in the internal states $\\ket{1}\\equiv\\ket{F=1,\nm_F=-1}$ and $\\ket{2}\\equiv\\ket{F=2, m_F=1}$ for the precision measurement of\nthe interspecies scattering length $a_{12}$ with a relative uncertainty of\n$1.6\\times 10^{-4}$. We show that in a cigar-shaped trap the three-dimensional\n(3D) dynamics of a component with a small relative population can be\nconveniently described by a one-dimensional (1D) Schr\\\"{o}dinger equation for\nan effective harmonic oscillator. The frequency of the collective oscillations\nis defined by the axial trap frequency and the ratio $a_{12}/a_{11}$, where\n$a_{11}$ is the intra-species scattering length of a highly populated component\n1, and is largely decoupled from the scattering length $a_{22}$, the total atom\nnumber and loss terms. By fitting numerical simulations of the coupled\nGross-Pitaevskii equations to the recorded temporal evolution of the axial\nwidth we obtain the value $a_{12}=98.006(16)\\,a_0$, where $a_0$ is the Bohr\nradius. Our reported value is in a reasonable agreement with the theoretical\nprediction $a_{12}=98.13(10)\\,a_0$ but deviates significantly from the\npreviously measured value $a_{12}=97.66\\,a_0$ \\cite{Mertes07} which is commonly\nused in the characterisation of spin dynamics in degenerate \\Rb atoms. Using\nRamsey interferometry of the 2CBEC we measure the scattering length\n$a_{22}=95.44(7)\\,a_0$ which also deviates from the previously reported value\n$a_{22}=95.0\\,a_0$ \\cite{Mertes07}. We characterise two-body losses for the\ncomponent 2 and obtain the loss coefficients\n${\\gamma_{12}=1.51(18)\\times10^{-14} \\textrm{cm}^3/\\textrm{s}}$ and\n${\\gamma_{22}=8.1(3)\\times10^{-14} \\textrm{cm}^3/\\textrm{s}}$.",
        "positive": "Kinetic Thomas-Fermi solutions of the Gross-Pitaevskii equation: Approximate solutions of the Gross-Pitaevskii (GP) equation, obtained upon\nneglection of the kinetic energy, are well known as Thomas-Fermi solutions.\nThey are characterized by the compensation of the local potential by the\ncollisional energy. In this article we consider exact solutions of the\nGP-equation with this property and definite values of the kinetic energy, which\nsuggests the term \"kinetic Thomas-Fermi\" (KTF) solutions. We point out that a\nlarge class of light-shift potentials gives rise to KTF-solutions. As\nelementary examples, we consider one-dimensional and two-dimensional optical\nlattice scenarios, obtained by means of the superposition of two, three and\nfour laser beams, and discuss the stability properties of the corresponding\nKTF-solutions. A general method is proposed to excite two-dimensional\nKTF-solutions in experiments by means of time-modulated light-shift potentials."
    },
    {
        "anchor": "Optical signatures of a fully dark exciton condensate: We propose optical means to reveal the presence of a dark exciton condensate\nthat does not yield any photoluminescence at all. We show that (i) the dark\nexciton density can be obtained from the blueshift of the excitonic absorption\nline induced by dark excitons; (ii) the polarization of the dark condensate can\nbe deduced from the blueshift dependence on probe photon polarization and also\nfrom Faraday effect, linearly polarized dark excitons leaving unaffected the\npolarization plane of an unabsorbed photon beam. These effects result from\ncarrier exchanges between dark and bright excitons.",
        "positive": "Ultra-cold Fermi gases with resonant dipole-dipole interaction: The superfluid phases in the resonant dipolar Fermi gases are investigated by\nthe standard mean-field theory. In contrast to the crossover from Bose-Einstein\ncondensation (BEC) to Bardeen-Cooper-Schrieffer (BCS) superfluid in the Fermi\ngases with the isotropic interactions, the resonant dipolar interaction leads\nto two completely different BEC phases of the tight-binding Fermi molecules on\nboth sides of the resonance, which are characterized by two order parameters\nwith the distinct internal symmetries. We point that near the resonance, the\ntwo competitive phases can coexist, and an emergent relative phase between the\ntwo order parameters spontaneously breaks the time-reversal symmetry, which\ncould be observed in the momentum resolved rf-spectroscopy."
    },
    {
        "anchor": "Tunable spin-orbit coupled Bose-Einstein condensates in deep optical\n  lattices: Binary mixtures of Bose-Einstein condensates trapped in deep optical lattices\nand subjected to equal contributions of Rashba and Dresselhaus spin-orbit\ncoupling (SOC), are investigated in the presence of a periodic time modulation\nof the Zeeman field. SOC tunability is explicitly demonstrated by adopting a\nmean-field tight-binding model for the BEC mixture and by performing an\naveraging approach in the strong modulation limit. In this case, the system can\nbe reduced to an unmodulated vector discrete nonlinear Schr\\\"odinger equation\nwith a rescaled SOC tunning parameter $\\alpha$, which depends only on the ratio\nbetween amplitude and frequency of the applied Zeeman field. The dependence of\nthe spectrum of the linear system on $\\alpha$ has been analytically\ncharacterized. In particular, we show that extremal curves (ground and highest\nexcited states) of the linear spectrum are continuous piecewise functions\n(together with their derivatives) of $\\alpha$, which consist of a finite number\nof decreasing band lobes joined by constant lines. This structure also remains\nin presence of not too large nonlinearities. Most important, the interactions\nintroduce a number of localized states in the band-gaps that undergo change of\nproperties as they collide with band lobes. The stability of ground states in\nthe presence of the modulating field has been demonstrated by real time\nevolutions of the original (un-averaged) system. Localization properties of the\nground state induced by the SOC tuning, and a parameter design for possible\nexperimental observation have also been discussed.",
        "positive": "Exotic topological density waves in cold atomic Rydberg fermions: Versatile controllability of interactions in ultracold atomic and molecular\ngases has now reached an unprecedented era where quantum correlations and\nunconventional many-body phases can be studied with no corresponding analogs in\nsolid state systems. Recent experiments in Rydberg atomic gases have achieved\nexquisite control over non-local interactions, allowing novel quantum phases\nunreachable with the usual local interactions in atomic systems. Here, we study\nRydberg dressed atomic fermions in a three dimensional optical lattice\npredicting the existence of hitherto unheard-of exotic mixed topological\ndensity wave phases. We show that varying spatial range of the non-local\ninteraction leads to a rich phase diagram containing various bond density\nwaves, with unexpected spontaneous time-reversal symmetry breaking.\nQuasiparticles in these chiral phases experience emergent gauge fields and form\nthree dimensional quantum Hall and Weyl semimetal states. Remarkably, certain\ndensity waves even exhibit mixed topologies beyond the existing topological\nclassification. Experimental signatures of density waves and their topological\nproperties are predicted in time-of-flight measurements."
    },
    {
        "anchor": "Brownian motion of a matter-wave bright soliton: realizing a quantum\n  pollen grain: Taking an open quantum systems approach, we derive a collective equation of\nmotion for the dynamics of a matter-wave bright soliton moving through a\nthermal cloud of a distinct atomic species. The reservoir interaction involves\nenergy transfer without particle transfer between the soliton and thermal\ncloud, thus damping the soliton motion without altering its stability against\ncollapse. We derive a Langevin equation for the soliton centre of mass velocity\nin the form of an Ornstein-Uhlenbeck process with analytical drift and\ndiffusion coefficients. This collective motion is confirmed by simulations of\nthe full stochastic projected Gross-Pitaevskii equation for the matter-wave\nfield. The system offers a pathway for experimentally observing the elusive\nenergy-damping reservoir interaction, and a clear realization of collective\nBrownian motion for a mesoscopic superfluid droplet.",
        "positive": "Producing superfluid circulation states using phase imprinting: We propose a method to prepare states of given quantized circulation in\nannular Bose-Einstein condensates (BEC) confined in a ring trap using the\nmethod of phase imprinting without relying on a two-photon angular momentum\ntransfer. The desired phase profile is imprinted on the atomic wave function\nusing a short light pulse with a tailored intensity pattern generated with a\nSpatial Light Modulator. We demonstrate the realization of 'helicoidal'\nintensity profiles suitable for this purpose. Due to the diffraction limit, the\ntheoretical steplike intensity profile is not achievable in practice. We\ninvestigate the effect of imprinting an intensity profile smoothed by a finite\noptical resolution onto the annular BEC with a numerical simulation of the\ntime-dependent Gross-Pitaevskii equation. This allows us to optimize the\nintensity pattern for a given target circulation to compensate for the limited\nresolution."
    },
    {
        "anchor": "Dynamical Fractal in Quantum Gases with Discrete Scaling Symmetry: Inspired by the similarity between the fractal Weierstrass function and\nquantum systems with discrete scaling symmetry, we establish general conditions\nunder which the dynamics of a quantum system will exhibit fractal structure in\nthe time domain. As an example, we discuss the dynamics of the Loschmidt\namplitude and the zero-momentum occupation of a single particle moving in a\nscale invariant $1/r^2$ potential. In order to show these conditions can be\nrealized in ultracold atomic gases, we perform numerical simulations with\npractical experimental parameters, which shows that the dynamical fractal can\nbe observed in realistic time scales. The predication can be directly verified\nin current cold atom experiments.",
        "positive": "Diffused vorticity and moment of inertia of a spin-orbit coupled\n  Bose-Einstein condensate: By developing the hydrodynamic theory of spinor superfluids we calculate the\nmoment of inertia of a harmonically trapped Bose-Einstein condensate with\nspin-orbit coupling. We show that the velocity field associated with the\nrotation of the fluid exhibits diffused vorticity, in contrast to the\nirrotational behavior characterizing a superfluid. Both Raman-induced and\nRashba spin-orbit couplings are considered. In the first case the moment of\ninertia takes the rigid value at the transition between the plane wave and the\nsingle minimum phase, while in the latter case the rigid value is achieved in\nthe limit of isotropic Rashba coupling. A procedure to generate the rigid\nrotation of the fluid and to measure the moment of inertia is proposed. The\nquenching of the quantum of circulation $h/m$, caused by Raman induced\nspin-orbit coupling in a toroidal geometry, is also discussed."
    },
    {
        "anchor": "Effective field theory of the Higgs mode in a two-dimensional dilute\n  Bose gas: We investigate the spectral function of the Higgs mode in a two dimensional\nBose gas, by using the effective field theory in the zero temperature limit.\nOur approach explains the experimental feature that the peak of the spectral\nfunction is a soft continuum rather than a sharp peak, broadened and vanishing\nin the superfluid phase, which cannot be explained in terms of the $O(2)$\nmodel. We also find that the scalar susceptibility is the same as the\nlongitudinal susceptibility.",
        "positive": "Decay of Bogoliubov excitations in one-dimensional Bose gases: We study the decay of Bogoliubov quasiparticles in one-dimensional Bose\ngases. Starting from the hydrodynamic Hamiltonian, we develop a microscopic\ntheory that enables one to systematically study both the excitations and their\ndecay. At zero temperature, the leading mechanism of decay of a quasiparticle\nis disintegration into three others. We find that low-energy quasiparticles\n(phonons) decay with the rate that scales with the seventh power of momentum,\nwhereas the rate of decay of the high-energy quasiparticles does not depend on\nmomentum. In addition, our approach allows us to study analytically the\nquasiparticle decay in the whole crossover region between the two limiting\ncases. When applied to integrable models, including the Lieb-Liniger model of\nbosons with contact repulsion, our theory confirms the absence of the decay of\nquasiparticle excitations. We account for two types of integrability-breaking\nperturbations that enable finite decay: three-body interaction between the\nbosons and two-body interaction of finite range."
    },
    {
        "anchor": "Spatial inversion symmetry breaking of vortex current in biased-ladder\n  superfluid: We investigate the quench dynamics of interacting bosons on a two-leg ladder\nin presence of a uniform Abelian gauge field. The model hosts a variety of\nemergent quantum phases, and we focus on the superfluid biased-ladder phase\nbreaking the $Z_{2}$ symmetry of two legs. We observe an asymmetric spreading\nof vortex current and particle density, i.e., the current behaves particle-like\non the right and wave-like on the left, indicating spontaneous breaking of the\nspatial inversion symmetry. By decreasing the repulsion strength, it is found\nthe particle-like current is more robust than the wave-like one. The evolution\nof entanglement entropy manifests logarithmic growth with time suggesting\nmany-body localization matters.",
        "positive": "Winding number dependence of Bose-Einstein condensates in a ring-shaped\n  lattice: We study the winding number dependence of the stationary states of a\nBose-Einstein condensate in a ring-shaped lattice. The system is obtained by\nconfining atoms in a toroidal trap with equally spaced radial barriers. We\ncalculate the energy and angular momentum as functions of the winding number\nand the barrier height for two quite distinct particle numbers. In both cases\nwe observe two clearly differentiated regimes. For low barriers, metastable\nvortex states are obtained up to a maximum winding number which depends on the\nparticle number and barrier height. In this regime, the angular momentum and\nenergy show, respectively, almost linear and quadratic dependences on the\nwinding number. For large barrier heights, on the other hand, stationary states\nare obtained up to a maximum winding number which depends only on the number of\nlattice sites, whereas energy and angular momentum are shown to be sinusoidal\nfunctions of the winding number."
    },
    {
        "anchor": "Correlated quantum dynamics of two quenched fermionic impurities\n  immersed in a Bose-Einstein Condensate: We unravel the nonequilibrium dynamics of two fermionic impurities immersed\nin a one-dimensional bosonic gas following an interspecies interaction quench\nfrom weak to strong repulsions. Monitoring the temporal evolution of the\nsingle-particle density of each species we reveal the existence of four\ndistinct dynamical regimes. For weak interspecies repulsions both species\neither perform a breathing motion or the impurity density splits into two parts\nwhich interact and disperse within the bosonic cloud. Turning to strong\ninteractions we observe the formation of dark-bright states within the\nmean-field approximation. However, the correlated dynamics shows that the\nfermionic density splits into two repelling density peaks which either travel\ntowards the edges of the bosonic cloud where they equilibrate or they approach\nan almost steady state propagating robustly within the bosonic gas which forms\ndensity dips at the same location. For these strong interspecies interactions\nan energy transfer process from the impurities to their environment occurs at\nthe many-body level, while a periodic energy exchange from the bright states\n(impurities) to the bosonic species is identified in the absence of\ncorrelations. Finally, inspecting the one-body coherence function for strong\ninteractions enables us to conclude on the spatial localization of the\nquench-induced fermionic density humps.",
        "positive": "Novel $p$-wave superfluids of fermionic polar molecules: We show that recently suggested subwavelength lattices offer remarkable\nprospects for the observation of novel superfluids of fermionic polar\nmolecules. It becomes realistic to obtain a topological $p$-wave superfluid of\nmicrowave-dressed polar molecules in 2D lattices at temperatures of the order\nof tens of nanokelvins, which is promising for topologically protected quantum\ninformation processing. Another foreseen novel phase is an interlayer $p$-wave\nsuperfluid of polar molecules in a bilayer geometry."
    },
    {
        "anchor": "Many-body spin rotation by adiabatic passage in spin-1/2 XXZ chains of\n  ultracold atoms: Quantum many-body phases offer unique properties and emergent phenomena,\nmaking them an active area of research. A promising approach for their\nexperimental realization in model systems is to adiabatically follow the ground\nstate of a quantum Hamiltonian from a product state of isolated particles to\none that is strongly-correlated. Such protocols are relevant also more broadly\nin coherent quantum annealing and adiabatic quantum computing. Here we explore\none such protocol in a system of ultracold atoms in an optical lattice. A fully\nmagnetized state is connected to a correlated zero-magnetization state (an\nxy-ferromagnet) by a many-body spin rotation, realized by sweeping the detuning\nand power of a microwave field. The efficiency is characterized by applying a\nreverse sweep with a variable relative phase. We restore up to 50% of the\noriginal magnetization independent of the relative phase, evidence for the\nformation of correlations. The protocol is limited by the many-body gap of the\nfinal state, which is inversely proportional to system size, and technical\nnoise. Our experimental and theoretical studies highlight the potential and\nchallenges for adiabatic preparation protocols to prepare many-body eigenstates\nof spin Hamiltonians.",
        "positive": "Selective Population of Edge States in a 2D Topological Band System: We consider a system of interacting spin-one atoms in a hexagonal lattice\nunder the presence of a synthetic gauge field. Quenching the quadratic Zeeman\nfield is shown to lead to a dynamical instability of the edge modes. This, in\nturn, leads to a spin current along the boundary of the system which grows\nexponentially fast in time following the quench. Tuning the magnitude of the\nquench can be used to selectively populate edge modes of different momenta.\nImplications of the intrinsic symmetries of Hamiltonian on the dynamics are\ndiscussed. The results hold for atoms with both antiferromagnetic and\nferromagnetic interactions."
    },
    {
        "anchor": "Onset and Irreversibility of Granulation of Bose-Einstein condensates\n  under Feshbach Resonance Management: Granulation of quantum matter -- the formation of persistent small-scale\npatterns -- is realized in the images of quasi-one-dimensional Bose-Einstein\ncondensates perturbed by a periodically modulated interaction. Our present\nanalysis of a mean-field approximation suggests that granulation is caused by\nthe gradual transformation of phase undulations into density undulations. This\nis achieved by a suitably large modulation frequency, while for low enough\nfrequencies the system exhibits a quasi-adiabatic regime. We show that the\npersistence of granulation is a result of the irregular evolution of the phase\nof the wavefunction representing an irreversible process. Our model predictions\nagree with numerical solutions of the Schr\\\"odinger equation and experimental\nobservations. The numerical computations reveal the emergent many-body\ncorrelations behind these phenomena via the multi-configurational\ntime-dependent Hartree theory for bosons (MCTDHB).",
        "positive": "Topological Defects in Anisotropic Driven Open Systems: We study the dynamics and unbinding transition of vortices in the compact\nanisotropic Kardar-Parisi-Zhang (KPZ) equation. The combination of\nnon-equilibrium conditions and strong spatial anisotropy drastically affects\nthe structure of vortices and amplifies their mutual binding forces, thus\nstabilizing the ordered phase. We find novel universal critical behavior in the\nvortex-unbinding crossover in finite-size systems. These results are relevant\nfor a wide variety of physical systems, ranging from strongly coupled\nlight-matter quantum systems to dissipative time crystals."
    },
    {
        "anchor": "Three-body recombination at vanishing scattering lengths in an ultracold\n  Bose gas: We report on measurements of three-body recombination rates in an ultracold\ngas of $^7$Li atoms in the extremely nonuniversal regime where the two-body\nscattering length vanishes. We show that the rate is well defined and can be\ndescribed by two-body parameters only: the scattering length $a$ and the\neffective range $R_e$. We find the rate to be energy independent, and, by\nconnecting our results with previously reported measurements in the universal\nlimit, we cover the behavior of the three-body recombination in the whole range\nfrom weak to strong two-body interactions. We identify a nontrivial magnetic\nfield value in the nonuniversal regime where the rate should be strongly\nreduced.",
        "positive": "Non-perturbative method to compute thermal correlations in\n  one-dimensional systems: A brief overview: We develop a highly efficient method to numerically simulate thermal\nfluctuations and correlations in non-relativistic continuous bosonic\none-dimensional systems. We start by noticing the equivalence of their\ndescription through the transfer matrix formalism and a Fokker-Planck equation\nfor a distribution evolving in space. The corresponding stochastic differential\n(It\\={o}) equation is very suitable for computer simulations, allowing the\ncalculation of arbitrary correlation functions. As an illustration, we apply\nour method to the case of two tunnel-coupled quasicondensates of bosonic atoms."
    },
    {
        "anchor": "Quantum fluctuations in a strongly interacting Bardeen-Cooper-Schrieffer\n  polariton condensate at thermal equilibrium: Microcavity electron-hole-photon systems in two-dimensions are long\nanticipated to exhibit a crossover from Bose-Einstein condensate (BEC) to\nBardeen-Cooper-Schrieffer (BCS) superfluid, when carrier density is tuned to\nreach the Mott transition density. Yet, theoretical understanding of such a\nBEC-BCS crossover largely relies on the mean-field framework and the nature of\nthe carriers at the crossover remains unclear to some extent. Here, motivated\nby the recent demonstration of a BCS polariton laser {[}Hu \\textit{et al.},\narXiv:1902.00142{]} and based on a simplified short-range description of the\nelectron-hole attraction, we examine the role of quantum fluctuations in an\nexciton-polariton condensate at thermal equilibrium and determine the number of\ndifferent type carriers at the crossover beyond mean-field. Near Mott density\nand with ultra-strong light-matter coupling, we find an unexpectedly large\nphase window for a strongly correlated BCS polariton condensate, where both\nfermionic Bogoliubov quasi-particles and bosonic excitons are significantly\npopulated and strongly couple to photons. We predict its photoluminescence\nspectra and show that the upper polariton energy gets notably renormalized,\ngiving rise to a high-energy side-peak at large carrier density, as observed in\nrecent experiments.",
        "positive": "Long-Range Coherence and Multiple Steady States in a Lossy Qubit Array: We show that a simple experimental setting of a locally pumped and lossy\narray of two-level quantum systems can stabilize states with strong long-range\ncoherence. Indeed, by explicit analytic construction, we show there is an\nextensive set of steady-state density operators, from minimally to maximally\nentangled, despite this being an interacting open many-body problem. Such\nnonequilibrium steady states arise from a hidden symmetry that stabilizes Bell\npairs over arbitrarily long distances, with unique experimental signatures. We\ndemonstrate a protocol by which one can selectively prepare these states using\ndissipation. Our findings are accessible in present-day experiments."
    },
    {
        "anchor": "Exact solutions to the three-dimensional Gross-Pitaevskii equation with\n  modulated radial nonlinearity: We study the Bose-Einstein condensate trapped in a three-dimensional\nspherically symmetrical potential. Exact solutions to the stationary\nGross-Pitaevskii equation are obtained for properly modulated radial\nnonlinearity. The solutions contain vortices with different winding numbers and\nexhibit the shell-soliton feature in the radial distributions.",
        "positive": "Ultrafast dynamics of cold Fermi gas after a local quench: We consider non-equilibrium dynamics of two initially independent reservoirs\n$A$ and $B$ filled with a cold Fermi gas coupled and decoupled by two quantum\nquenches following one another. We find that the von Neumann entropy production\ninduced by the quench is faster than thermal transport between the reservoirs\nand defines the short-time dynamics of the system. We analyze the energy change\nin the system which adds up the heat transferred between $A$ and $B$ and the\nwork done by the quench to uncouple the reservoirs. In the case when $A$ and\n$B$ interact for a short time, we notice an energy increase in both reservoirs\nupon decoupling. This energy gain results from the quench's work and does not\ndepend on the initial temperature imbalance between the reservoirs. We relate\nthe quench's work to the mutual correlations of $A$ and $B$ expressed through\ntheir von Neumann entropies. Utilizing this relation, we show that once $A$ and\n$B$ become coupled, their entropies grow (on a timescale of the Fermi time)\nfaster than the heat flow within the system. This result may provide a track of\nquantum correlations' generation at finite temperatures which one may probe in\nultracold atoms, where we expect the characteristic timescale of correlations'\ngrowth to be $\\sim 0.1 {\\rm ms}$."
    },
    {
        "anchor": "Light scattering for thermometry of fermionic atoms in an optical\n  lattice: We propose a method for measuring the temperature of fermionic atoms in an\noptical lattice potential from the intensity of the scattered light in the\nfar-field diffraction pattern. We consider a single-component gas in a\ntightly-confined two-dimensional lattice, illuminated by far off-resonant light\ndriving a cycling transition. Our calculations show that thermal correlations\nof the fermionic atoms generate fluctuations in the intensity of the\ndiffraction pattern of light scattered from the atomic lattice array and that\nthis signal can be accurately detected above the shot noise using a lens to\ncollect photons scattered in a forward direction (with the diffraction maxima\nblocked). The sensitivity of the thermometer is enhanced by an additional\nharmonic trapping potential.",
        "positive": "Generalized effective-potential Landau theory for the two-dimensional\n  extended Bose-Hubbard model: We analytically study the quantum phase diagrams of ultracold dipolar Bose\ngases in an optical square lattice at zero temperature by using the generalized\neffective-potential Landau theory (GEPLT). For a weak nearest-neighbor\nrepulsion, our analytical results are better than the third-order\nstrong-coupling expansion theory calculation [M. Iskin et al.,\n\\textcolor[rgb]{0.00,0.00,1.00}{ Phys. Rev. A \\textbf{79}, 053634 (2009)}]. In\ncontrast to a previous quantum Monte Carlo (QMC) simulation [T. Ohgoe et al.,\n\\textcolor[rgb]{0.00,0.00,1.00}{Phys. Rev. B \\textbf{86}, 054520 (2012)}], we\nanalytically calculate phase transition boundaries up to the third-order\nhopping, which are in excellent agreement with QMC simulations for second-order\nphase transition."
    },
    {
        "anchor": "Dissipation-induced d-Wave Pairing of Fermionic Atoms in an Optical\n  Lattice: We show how dissipative dynamics can give rise to pairing for two-component\nfermions on a lattice. In particular, we construct a \"parent\" Liouvillian\noperator so that a BCS-type state of a given symmetry, e.g. a d-wave state, is\nreached for arbitrary initial states in the absence of conservative forces. The\nsystem-bath couplings describe single-particle, number conserving and\nquasi-local processes. The pairing mechanism crucially relies on Fermi\nstatistics. We show how such Liouvillians can be realized via reservoir\nengineering with cold atoms representing a driven dissipative dynamics.",
        "positive": "Circumnavigating an ocean of incompressible light: This is a popular science article to appear on the \"Il Nuovo Saggiatore\"\nmagazine of the Italian Physical Society. It aims at introducing a broad\naudience of physicists to the most recent trends in many-body physics of\ndegenerate quantum gases with a special attention to quantum fluids of light\nand the quest towards quantum Hall liquids of light."
    },
    {
        "anchor": "Quantum magnetism without lattices in strongly interacting\n  one-dimensional spinor gases: We show that strongly interacting multicomponent gases in one dimension\nrealize an effective spin chain, offering an alternative simple scenario for\nthe study of one-dimensional quantum magnetism in cold gases in the absence of\nan optical lattice. The spin-chain model allows for an intuitive understanding\nof recent experiments and for a simple calculation of relevant observables. We\nanalyze the adiabatic preparation of antiferromagnetic and ferromagnetic ground\nstates, and show that many-body spin states may be efficiently probed in\ntunneling experiments. The spin-chain model is valid for more than two\ncomponents, opening the possibility of realizing SU(N) quantum magnetism in\nstrongly interacting one-dimensional alkaline-earth-metal or ytterbium Fermi\ngases.",
        "positive": "Master equation approach to conductivity of bosonic and fermionic\n  carriers in one- and two-dimensional lattices: We discuss the master equation approach to diffusive current of bosonic or\nfermionic carriers in one- and two-dimensional lattices. This approach is shown\nto reproduce all known results of the linear response theory, including the\ninteger quantum Hall effect for fermionic carriers. The main advantage of the\napproach is that it allows to calculate the current beyond the linear response\nregime where new effects are found. In particular, we show that the Hall\ncurrent can be inverted by changing orientation of the static force (electric\nfield) relative to the primary axes of the lattice."
    },
    {
        "anchor": "Pseudogap in fermionic density of states in the BCS-BEC crossover of\n  atomic Fermi gases: We study pseudogap behaviors of ultracold Fermi gases in the BCS-BEC\ncrossover region. We calculate the density of states (DOS), as well as the\nsingle-particle spectral weight, above the superfluid transition temperature\n$T_{\\rm c}$ including pairing fluctuations within a $T$-matrix approximation.\nWe find that DOS exhibits a pseudogap structure in the BCS-BEC crossover\nregion, which is most remarkable near the unitarity limit. We determine the\npseudogap temperature $T^*$ at which the pseudogap structure in DOS disappears.\nWe also introduce another temperature $T^{**}$ at which the BCS-like\ndouble-peak structure disappears in the spectral weight. While one finds\n$T^*>T^{**}$ in the BCS regime, $T^{**}$ becomes higher than $T^*$ in the\ncrossover and BEC regime. We also determine the pseudogap region in the phase\ndiagram in terms of temperature and pairing interaction.",
        "positive": "Two-dimensional Bose gases near resonance: universal three-body effects: We report in this Letter the results of our investigation of 2D Bose gases\nbeyond the dilute limit emphasizing the role played by three-body scattering\nevents. We demonstrate that a competition between three-body attractive\ninteractions and two-body repulsive forces results in the chemical potential of\n2D Bose gases to exhibit a maximum at a critical scattering length beyond which\nthese quantum gases possess a negative compressibility. For larger scattering\nlengths, the increasingly prominent role played by three-body attractive\ninteractions leads to an onset instability at a second critical value. The\nthree-body effects studied here are universal, fully characterized by the\neffective 2D scattering length $a_{2D}$ (or the size of the 2D bound states)\nand are, in comparison to the 3D case, independent of three-body ultraviolet\nphysics. We find, within our approach, the ratios of the contribution to the\nchemical potential due to three-body interactions to the one due to two-body to\nbe 0.27 near the maximum of the chemical potential and 0.73 in the vicinity of\nthe onset instability."
    },
    {
        "anchor": "Stability and chaotic behavior of Bose-Einstein condensates in optical\n  lattices with two- and three-body interactions: The stability and chaotic behaviors of Bose-Einstein condensates with two-\nand three-atom interactions in optical lattices are discussed with analytical\nand numerical methods. It is found that the steady-state relative population\nappears tuning-fork bifurcation when the system parameters are changed to\ncertain critical values. In particular, the existence of three-body interaction\nnot only transforms the bifurcation point of the system but also affects\ngreatly on the macroscopic quantum self-trapping behaviors of the system\nassociated with the critically stable steady-state solution. In addition, we\nalso investigated the influence of the initial conditions, three-body\ninteraction and the energy bias on the macroscopic quantum self-trapping.\nFinally, by applying the periodic modulation on the energy bias, we find that\nthe relative population oscillation exhibits a process from order to chaos, via\na series of period-doubling bifurcations.",
        "positive": "Spatially Modulated Interaction Induced Bound States and Scattering\n  Resonances: We study the two-body problem with a spatially modulated interaction\npotential using a two-channel model, in which the inter-channel coupling is\nprovided by an optical standing wave and its strength modulates periodically in\nspace. As the modulation amplitudes increases, there will appear a sequence of\nbound states. Part of them will cause divergence of the effective scattering\nlength, defined through the phase shift in the asymptotic behavior of\nscattering states. We also discuss how the local scattering length, defined\nthrough short-range behavior of scattering states, modulates spatially in\ndifferent regimes. These results provide a theoretical guideline for new\ncontrol technique in cold atom toolbox, in particular, for alkali-earth-(like)\natoms where the inelastic loss is small."
    },
    {
        "anchor": "Floating Phases in One-Dimensional Rydberg Ising Chains: We report on the quantitative ground state phase diagram of a van der Waals\ninteracting chain of Rydberg atoms. These systems are known to host crystalline\nphases locked to the underlying lattice as well as a gapped, disordered phase.\nWe locate and characterize a third type of phase, the so called floating phase,\nwhich can be seen as a one-dimensional 'crystalline' phase which is not locked\nto the lattice. These phases have been theoretically predicted to exist in the\nphase diagram, but were not reported so far. Our results have been obtained\nusing state-of-the-art numerical tensor network techniques and pave the way for\nthe experimental exploration of floating phases with existing Rydberg quantum\nsimulators.",
        "positive": "Spin drag in noncondensed Bose gases: We show how time-dependent magnetic fields lead to spin motive forces and\nspin drag in a spinor Bose gas. We propose to observe these effects in a\ntoroidal trap and analyze this particular proposal in some detail. In the\nlinear-response regime we define a transport coefficient that is analogous to\nthe usual drag resistivity in electron bilayer systems. Due to Bose enhancement\nof atom-atom scattering, this coefficient strongly increases as temperature is\nlowered. We also investigate the effects of heating."
    },
    {
        "anchor": "Deterministic Preparation of a Tunable Few-Fermion System: Systems consisting of few interacting fermions are the building blocks of\nmatter with atoms and nuclei being the most prominent examples. We have created\nan artificial few-body quantum system with complete control over the system's\nquantum state using ultracold fermionic atoms in an optical dipole trap. We\ndeterministically prepare ground state systems consisting of one to ten\nparticles with fidelities of ~ 90%. We can tune the inter-particle interactions\nto arbitrary values using a Feshbach resonance and have observed the\ninteraction-induced energy shift for a pair of repulsively interacting atoms.\nWith this work, quantum simulation of strongly correlated fewbody systems has\nbecome possible. In addition, these microscopic quantum systems can be used as\nbuilding blocks for scalable quantum information processing.",
        "positive": "Analogue cosmological particle creation in an ultracold quantum fluid of\n  light: In inflationary cosmology, the rapid expansion of the early universe resulted\nin the spontaneous production of cosmological particles from vacuum\nfluctuations, observable today in the cosmic microwave background anisotropies.\nThe analogue of cosmological particle creation in a quantum fluid could provide\ninsight, but an observation has not yet been achieved. Here we report the\nspontaneous creation of analogue cosmological particles in the laboratory,\nusing a quenched 3-dimensional quantum fluid of light. We observe acoustic\npeaks in the density power spectrum, in close quantitative agreement with the\nquantum-field theoretical prediction. We find that the long-wavelength\nparticles provide a window to early times, and we apply this principle to the\ncosmic microwave background. This work introduces a new quantum fluid, as cold\nas an atomic Bose-Einstein condensate."
    },
    {
        "anchor": "Spontaneous currents in a bosonic ring: Nonequilibrium dynamics of noninteracting bosons in a one-dimensional\nring-shaped lattice is studied by means of the Kinetic Monte Carlo method. The\nsystem is approximated by the classical XY model (the kinetic term is\nneglected) and then the simulations are performed for the planar classical\nspins. We study the dynamics that follows a finite-time quench to zero\ntemperature. If the quench is slow enough the system can equilibrate and\nfinally reaches the ground state with uniform spin alignment. However, we show\nthat if the quench is faster than the relaxation rate, the system can get\nlocked in a current-carrying metastable state characterized by a nonzero\nwinding number. We analyze how the zero-temperature state depends on the quench\nrate.",
        "positive": "Topological Superfluid Defects with Discrete Point Group Symmetries: Discrete symmetries are spatially ubiquitous but are often hidden in internal\nstates of systems where they can have especially profound consequences. In this\nwork we create and verify exotic magnetic phases of atomic spinor Bose-Einstein\ncondensates that, despite their continuous character and intrinsic spatial\nisotropy, exhibit complex discrete polytope symmetries in their topological\ndefects. Using carefully tailored spinor rotations and microwave transitions,\nwe engineer singular line defects whose quantization conditions, exchange\nstatistics, and dynamics are fundamentally determined by these underlying\nsymmetries. We show how filling the vortex line singularities with atoms in a\nvariety of different phases leads to core structures that possess magnetic\ninterfaces with rich combinations of discrete and continuous symmetries. Such\ndefects, with their non-commutative properties, could provide unconventional\nrealizations of quantum information and interferometry."
    },
    {
        "anchor": "Radio frequency spectra of Feshbach molecules in quasi-two dimensional\n  geometries: The line shape of radio frequency spectra of tightly bound Feshbach molecules\nin strong transverse confinement can be described by a simple analytic formula\nthat includes final state interactions. By direct comparison to experimental\ndata, we clarify the role of effective range corrections to two-body\nbound-state energies in lower dimensions.",
        "positive": "Bound states of Dipolar Bosons in One-dimensional Systems: We consider one-dimensional tubes containing bosonic polar molecules. The\nlong-range dipole-dipole interactions act both within a single tube and between\ndifferent tubes. We consider arbitrary values of the externally aligned dipole\nmoments with respect to the symmetry axis of the tubes. The few-body structures\nin this geometry are determined as function of polarization angles and dipole\nstrength by using both essentially exact stochastic variational methods and the\nharmonic approximation. The main focus is on the three, four, and five-body\nproblems in two or more tubes. Our results indicate that in the weakly-coupled\nlimit the inter-tube interaction is similar to a zero-range term with a\nsuitable rescaled strength. This allows us to address the corresponding\nmany-body physics of the system by constructing a model where bound chains with\none molecule in each tube are the effective degrees of freedom. This model can\nbe mapped onto one-dimensional Hamiltonians for which exact solutions are\nknown."
    },
    {
        "anchor": "Nonlinear dynamics in a synthetic momentum state lattice: The scope of analog simulation in atomic, molecular, and optical systems has\nexpanded greatly over the past decades. Recently, the idea of synthetic\ndimensions -- in which transport occurs in a space spanned by internal or\nmotional states coupled by field-driven transitions -- has played a key role in\nthis expansion. While approaches based on synthetic dimensions have led to\nrapid advances in single-particle Hamiltonian engineering, strong interaction\neffects have been conspicuously absent from most synthetic dimensions\nplatforms. Here, in a lattice of coupled atomic momentum states, we show that\natomic interactions result in large and qualitative changes to dynamics in the\nsynthetic dimension. We explore how the interplay of nonlinear interactions and\ncoherent tunneling enriches the dynamics of a one-band tight-binding model,\ngiving rise to macroscopic self-trapping and phase-driven Josephson dynamics\nwith a nonsinusoidal current-phase relationship, which can be viewed as\nstemming from a nonlinear band structure arising from interactions.",
        "positive": "Self-consistent theory of a homogeneous binary Bose mixture with strong\n  repulsive interspecies interaction: Multicomponent quantum gases are ideal platforms to study fundamental\nphenomena arising from the mutual interaction between different constituents.\nParticularly, due to the repulsive interactions between two species, the system\nmay exhibit a phase separation. We develop a mean-field-based theory for a\ntwo-component Bose mixture, which is equivalent to the Hartree-Fock-Bogoliubov\napproximation, and derive analytical expressions for the phase boundary and\nmiscibility. The majority of existing theories, which are valid only for weakly\ninteracting Bose gases, predict that the phase boundary is determined by the\ncriterion $g_{ab}\\leqslant\\sqrt{g_{aa} g_{bb}}$ (where $g_{ab}$ is a coupling\nconstant between the components $a$ and $b$). We show that in the\nBose-Einstein-condensation phase ($T\\leqslant T_c$) the system may remain in a\nstable and miscible phase also for larger values of $g_{ab}$, depending on the\ngas parameter $\\gamma$ and temperature."
    },
    {
        "anchor": "Frustrated quantum antiferromagnetism with ultracold bosons in a\n  triangular lattice: We propose to realize the anisotropic triangular-lattice Bose-Hubbard model\nwith positive tunneling matrix elements by using ultracold atoms in an optical\nlattice dressed by a fast lattice oscillation. This model exhibits frustrated\nantiferromagnetism at experimentally feasible temperatures; it interpolates\nbetween a classical rotor model for weak interaction, and a quantum spin-1/2\n$XY$-model in the limit of hard-core bosons. This allows to explore\nexperimentally gapped spin liquid phases predicted recently [Schmied et al.,\nNew J. Phys. {\\bf 10}, 045017 (2008)].",
        "positive": "Quantum criticality and universal scaling of strongly attractive\n  spin-imbalanced Fermi gases in a 1D harmonic trap: We investigate thermodynamics and quantum criticality of strongly attractive\nFermi gases confined in a one-dimensional (1D) harmonic trap. Finite\ntemperature density profiles, entropy, compressibility and susceptibility of\nthe trapped gas are studied using analytic results for the thermodynamics\nwithin the local density approximation. We demonstrate that current experiments\nare capable of measuring universal Tomonaga-Luttinger liquid physics and\nquantum criticality of 1D strongly interacting Fermi gases. The results provide\ninsights on recent measurements of key features of the phase diagram of a\nspin-imbalanced atomic Fermi gas [Liao et al., Nature 467, 567 (2010)] and\npoint to further study of quantum critical phenomena in ultracold atomic Fermi\ngases."
    },
    {
        "anchor": "The three-body parameter for Efimov states in lithium-6: We present a state-of-the-art reanalysis of experimental results on Efimov\nresonances in the three-fermion system of $^6$Li. We discuss different\ndefinitions of the 3-body parameter (3BP) for Efimov states, and adopt a\ndefinition that excludes effects due to deviations from universal scaling for\nlow-lying states. We develop a finite-temperature model for the case of three\ndistinguishable fermions and apply it to the excited-state Efimov resonance to\nobtain the most accurate determination to date of the 3BP in an atomic\nthree-body system. Our analysis of ground-state Efimov resonances in the same\nsystem yields values for the three-body parameter that are consistent with the\nexcited-state result. Recent work has suggested that the reduced 3BP for atomic\nsystems is a near-universal quantity, almost independent of the particular atom\ninvolved. However, the value of the 3BP obtained for $^6$Li is significantly\n($\\sim 20$%) different from that previously obtained from the excited-state\nresonance in Cs. The difference between these values poses a challenge for\ntheory.",
        "positive": "Bose polarons in the strongly interacting regime: When an impurity is immersed in a Bose-Einstein condensate, impurity-boson\ninteractions are expected to dress the impurity into a quasiparticle, the Bose\npolaron. We superimpose an ultracold atomic gas of $^{87}$Rb with a much lower\ndensity gas of fermionic $^{40}$K impurities. Through the use of a Feshbach\nresonance and RF spectroscopy, we characterize the energy, spectral width and\nlifetime of the resultant polaron on both the attractive and the repulsive\nbranches in the strongly interacting regime. The width of the polaron in the\nattractive branch is narrow compared to its binding energy, even as the\ntwo-body scattering length formally diverges."
    },
    {
        "anchor": "Photon Bose-Einstein condensation and lasing in semiconductor cavities: Photon Bose-Einstein condensation and photon thermalisation have been largely\nstudied with molecular gain media in optical cavities. Their observation with\nsemiconductors has remained elusive despite a large body of experimental\nresults and a very well established theoretical framework. We use this\ntheoretical framework as a convenient platform to revisit photon Bose-Einstein\ncondensation in the driven-dissipative regime and compare with the lasing\nregime. We discuss the thermalisation figures of merit and the different\nexperimental procedures to asses thermalization. We compare the definitions of\nlasing and condensation thresholds. Finally, we explore the fluctuations of the\nsystem and their relation to the different regimes.",
        "positive": "Collisional-inhomogeneity-induced generation of matter-wave dark\n  solitons: We propose an experimentally relevant protocol for the controlled generation\nof matter-wave dark solitons in atomic Bose-Einstein condensates (BECs). In\nparticular, using direct numerical simulations, we show that by switching-on a\nspatially inhomogeneous (step-like) change of the s-wave scattering length, it\nis possible to generate a controllable number of dark solitons in a\nquasi-one-dimensional BEC. A similar phenomenology is also found in the\ntwo-dimensional setting of \"disk-shaped\" BECs but, as the solitons are subject\nto the snaking instability, they decay into vortex structures. A detailed\ninvestigation of how the parameters involved affect the emergence and evolution\nof solitons and vortices is provided."
    },
    {
        "anchor": "Microscopic Origin and Universality Classes of the Efimov Three-Body\n  Parameter: The low-energy spectrum of three particles interacting via nearly resonant\ntwo-body interactions in the Efimov regime is set by the so-called three-body\nparameter. We show that the three-body parameter is essentially determined by\nthe zero-energy two-body correlation. As a result, we identify two classes of\ntwo-body interactions for which the three-body parameter has a universal value\nin units of their effective range. One class involves the universality of the\nthree-body parameter recently found in ultracold atom systems. The other is\nrelevant to short-range interactions that can be found in nuclear physics and\nsolid-state physics.",
        "positive": "Bose-Einstein condensation of magnons in atomic hydrogen gas: We report on experimental observation of BEC-like behaviour of quantized\nelectron spin waves (magnons) in a dense gas of spin polarized atomic hydrogen.\nThe magnons are trapped and controlled with inhomogeneous magnetic fields, and\ndescribed by a Schr\\\"odinger-like wave equation, in analogy to the BEC\nexperiments with neutral atoms. We have observed the appearance of a sharp\nfeature in the ESR spectrum displaced from the normal spin wave spectrum. We\nbelieve that this observation corresponds to a sudden growth of the ground\nstate population of the magnons and emergence of their spontaneous coherence\nfor hydrogen gas densities exceeding a critical value, dependent on the\ntrapping potential. We interpret the results as a BEC of non-equilibrium\nmagnons which were formed by applying the rf power."
    },
    {
        "anchor": "Dissipation induced macroscopic entanglement in an open optical lattice: We introduce a method for the dissipative preparation of strongly correlated\nquantum states of ultracold atoms in an optical lattice via localized particle\nloss. The interplay of dissipation and interactions enables different types of\ndynamics. This ushers a new line of experimental methods to maintain the\ncoherence of a Bose-Einstein condensate or to deterministically generate\nmacroscopically entangled quantum states.",
        "positive": "Adiabatic Splitting, Transport, and Self-Trapping of a Bose-Einstein\n  Condensate in a Double-Well Potential: We show that the adiabatic dynamics of a Bose-Einstein condensate (BEC) in a\ndouble well potential can be described in terms of a dark variable resulting\nfrom the combination of the population imbalance and the spatial atomic\ncoherence between the two wells. By means of this dark variable, we extend, to\nthe non-linear matter wave case, the recent proposal by Vitanov and Shore\n[Phys. Rev. A 73, 053402 (2006)] on adiabatic passage techniques to coherently\ncontrol the population of two internal levels of an atom/molecule. We\ninvestigate the conditions to adiabatically split or transport a BEC as well as\nto prepare an adiabatic self trapping state by the optimal delayed temporal\nvariation of the tunneling rate via either the energy bias between the two\nwells or the BEC non-linearity. The emergence of non-linear eigenstates and\nunstable stationary solutions of the system as well as their role in the\nbreaking down of the adiabatic dynamics is investigated in detail."
    },
    {
        "anchor": "Robustness and observability of rotating vortex-lattices in an\n  exciton-polariton condensate: Exciton-polariton condensates display a variety of intriguing pattern-forming\nbehaviors, particularly when confined in potential traps. It has previously\nbeen predicted that triangular lattices of vortices of the same sign will form\nspontaneously as the result of surface instabilities in a harmonic trap.\nHowever, natural disorder, deviation of the external potential from circular\nsymmetry, or higher-order terms modifying the dynamical equations may all have\ndetrimental effects and destabilize the circular trajectories of vortices. Here\nwe address these issues, by characterizing the robustness of the vortex lattice\nagainst disorder and deformations of the trapping potential. Since most\nexperiments use time integrated measurements it would be hard to observe\ndirectly the rotating vortex lattices or distinguish them from vortex-free\nstates. We suggest how these difficulties can be overcome and present an\nexperimentally viable interference-imaging scheme that would allow the\ndetection of rotating vortex lattices.",
        "positive": "Hawking radiation in a two-component Bose-Einstein condensate: We consider a simple realization of an event horizon in the flow of a\none-dimensional two-component Bose-Einstein condensate. Such a condensate has\ntwo types of quasiparticles; In the system we study, one corresponds to density\nfluctuations and the other to polarization fluctuations. We treat the case\nwhere a horizon occurs only for one type of quasiparticles (the polarization\nones). We study the one- and two-body signal associated to the analog of\nspontaneous Hawking radiation and demonstrate by explicit computation that it\nconsists only in the emission of polarization waves. We discuss the\nexperimental consequences of the present results in the domain of atomic\nBose-Einstein condensates and also for the physics of exciton-polaritons in\nsemiconductor microcavities."
    },
    {
        "anchor": "Energy-level crossings and number-parity effects in a bosonic tunneling\n  model: An exactly solved bosonic tunneling model is studied along a line of the\ncoupling parameter space, which includes a quantum phase boundary line. The\nentire energy spectrum is computed analytically, and found to exhibit multiple\nenergy level crossings in a region of the coupling parameter space. Several key\nproperties of the model are discussed, which exhibit a clear dependence on\nwhether the particle number is even or odd.",
        "positive": "Equation of state of non-relativistic matter from automated perturbation\n  theory and complex Langevin: We calculate the pressure and density of polarized non-relativistic systems\nof two-component fermions coupled via a contact interaction at finite\ntemperature. For the unpolarized one-dimensional system with an attractive\ninteraction, we perform a third-order lattice perturbation theory calculation\nand assess its convergence by comparing with hybrid Monte Carlo. In that\nregime, we also demonstrate agreement with real Langevin. For the repulsive\nunpolarized one-dimensional system, where there is a so-called complex phase\nproblem, we present lattice perturbation theory as well as complex Langevin\ncalculations. For our studies, we employ a Hubbard-Stratonovich transformation\nto decouple the interaction and automate the application of Wick's theorem for\nperturbative calculations, which generates the diagrammatic expansion at any\norder. We find excellent agreement between the results from our perturbative\ncalculations and stochastic studies in the weakly interacting regime. In\naddition, we show predictions for the strong coupling regime as well as for the\npolarized one-dimensional system. Finally, we show a first estimate for the\nequation of state in three dimensions where we focus on the polarized unitary\nFermi gas."
    },
    {
        "anchor": "Hartree-Fock-Bogolubov method in the theory of Bose-condensed systems: The Hohenberg-Martin dilemma of conserving versus gapless theories for\nsystems with Bose-Einstein condensate is considered. This dilemma states that,\ngenerally, a theory characterizing a system with broken global gauge symmetry,\nwhich is necessary for Bose-Einstein condensation, is either conserving, but\nhas a gap in its spectrum, or is gapless, but does not obey conservation laws.\nIn other words, such a system either displays a gapless spectrum, which is\nnecessary for condensate existence, but is not conserving, which implies that\nit corresponds to an unstable system, or it respects conservation laws,\ndescribing a stable system, but the spectrum acquires a gap, which means that\nthe condensate cannot appear. An approach is described, resolving this dilemma,\nand it is shown to give good quantitative agreement with experimental data.\nCalculations are accomplished in the Hartree-Fock-Bogolubov approximation.",
        "positive": "Dynamic Localization in Optical Lattices: We recapitulate the principle enabling the phenomenon of dynamic\nlocalization, and provide model calculations for ultracold atoms in driven\noptical lattices which indicate that the localization effect remains almost\nunaffected by interband transitions if the parameters are chosen carefully. In\naddition, we suggest to exploit the underlying quasienergy band collapse for\ncoherently controlling the metal-insulator transition that occurs in the Harper\nmodel, as realized with quasiperiodic optical lattices."
    },
    {
        "anchor": "Numerical solution of the Boltzmann equation for the collective modes of\n  trapped Fermi gases: We numerically solve the Boltzmann equation for trapped fermions in the\nnormal phase using the test-particle method. After discussing a couple of tests\nin order to estimate the reliability of the method, we apply it to the\ndescription of collective modes in a spherical harmonic trap. The numerical\nresults are compared with those obtained previously by taking moments of the\nBoltzmann equation. We find that the general shape of the response function is\nvery similar in both methods, but the relaxation time obtained from the\nsimulation is significantly longer than that predicted by the method of\nmoments. It is shown that the result of the method of moments can be corrected\nby including fourth-order moments in addition to the usual second-order ones\nand that this method agrees very well with our numerical simulations.",
        "positive": "Stable p-wave resonant two-dimensional Fermi-Bose dimers: We consider two-dimensional weakly-bound heterospecies molecules formed in a\nFermi-Bose mixture with attractive Fermi-Bose and repulsive Bose-Bose\ninteractions. Bosonic exchanges lead to an intermolecular attraction, which can\nbe controlled and tuned to a p-wave resonance. Such attractive fermionic\nmolecules can be realized in quasi-two-dimensional ultracold isotopic or\nheteronuclear mixtures. We show that they are stable with respect to the\nrecombination to deeply-bound molecular states and with respect to the\nformation of higher-order clusters (trimers, tetramers, etc.)"
    },
    {
        "anchor": "Dynamics of Phase Coherence Onset in Bose Condensates of Photons by\n  Incoherent Phonon Emission: Recent experiments with photons equilibrating inside a dye medium in a cavity\nhave raised the question of whether Bose condensation can occur in a system\nwith only incoherent interaction with phonons in a bath but without\nparticle-particle interaction. Analytical calculations analogous to those done\nfor a system with particle-particle interactions indicate that a system of\nbosons interacting only with incoherent phonons can indeed undergo Bose\ncondensation and furthermore can exhibit spontaneous amplification of quantum\ncoherence. We review the basic theory for these calculations.",
        "positive": "Relaxation dynamics in the merging of $N$ independent condensates: Controlled quantum systems such as ultracold atoms can provide powerful\nplatforms to study non-equilibrium dynamics of closed many-body quantum\nsystems, especially since a complete theoretical description is generally\nchallenging. In this Letter, we present a detailed study of the rich\nout-of-equilibrium dynamics of an adjustable number $N$ of uncorrelated\ncondensates after connecting them in a ring-shaped optical trap. We observe the\nformation of long-lived supercurrents and confirm the scaling of their winding\nnumber with $N$ in agreement with the geodesic rule. Moreover, we provide\ninsight into the microscopic mechanism that underlies the smoothening of the\nphase profile."
    },
    {
        "anchor": "Density-functional theory for the spin-1 bosons in a one-dimensional\n  harmonic trap: We propose the density-functional theory for one-dimensional harmonically\ntrapped spin-1 bosons in the ground state with repulsive density-density\ninteraction and anti-ferromagnetic spin-exchange interaction. The density\ndistributions of spin singlet paired bosons and polarized bosons with different\ntotal polarization for various interaction parameters are obtained by solving\nthe Kohn-Sham equations which are derived based on the local density\napproximation and the Bethe ansatz exact results for homogeneous system.\nNon-monotonicity of the central densities is attributed to the competition\nbetween the density interaction and spin-exchange. The results reveal the phase\nseparation of the paired and polarized bosons, the density profiles of which\nrespectively approach the Tonks-Girardeau gases of Bose-Bose pairs and scalar\nbosons in the case of strong interaction. We give the R-P phase diagram at\nstrong interaction and find the critical polarization, which paves the way to\ndirect observe the exotic singlet pairing in spinor gas experimentally.",
        "positive": "Number fluctuations of cold spatially split bosonic objects: We investigate the number fluctuations of spatially split many-boson systems\nemploying a theorem about the maximally and minimally attainable variances of\nan observable. The number fluctuations of many-boson systems are given for\ndifferent numbers of lattice sites and both mean-field and many-body wave\nfunctions. It is shown which states maximize the particle number fluctuations,\nboth in lattices and double-wells. The fragmentation of the states is\ndiscussed, and it is shown that the number fluctuations of some fragmented\nstates are identical to those of fully condensed states."
    },
    {
        "anchor": "Influence of periodically modulated cavity field on the generation of\n  atomic-squeezed states: We investigate the influence of periodically time-modulated cavity frequency\non the generation of atomic squeezed states for a collection of N two-level\natoms confined in a non-stationary cavity with a moving mirror. We show that\nthe two-photon character of the field generated from the vacuum state of field\nplays a significant role in producing the atomic or spin squeezed states. We\nfurther show that the maximum amount of persistent atomic squeezing is obtained\nfor the initial cavity field prepared in the vacuum state.",
        "positive": "Observation of Roton Mode Population in a Dipolar Quantum Gas: The concept of a roton, a special kind of elementary excitation, forming a\nminimum of energy at finite momentum, has been essential to understand the\nproperties of superfluid $^4$He. In quantum liquids, rotons arise from the\nstrong interparticle interactions, whose microscopic description remains\ndebated. In the realm of highly-controllable quantum gases, a roton mode has\nbeen predicted to emerge due to magnetic dipole-dipole interactions despite of\ntheir weakly-interacting character. This prospect has raised considerable\ninterest; yet roton modes in dipolar quantum gases have remained elusive to\nobservations. Here we report experimental and theoretical studies of the\nmomentum distribution in Bose-Einstein condensates of highly-magnetic erbium\natoms, revealing the existence of the long-sought roton mode. By quenching the\ninteractions, we observe the roton appearance of peaks at well-defined\nmomentum. The roton momentum follows the predicted geometrical scaling with the\ninverse of the confinement length along the magnetisation axis. From the growth\nof the roton population, we probe the roton softening of the excitation\nspectrum in time and extract the corresponding imaginary roton gap. Our results\nprovide a further step in the quest towards supersolidity in dipolar quantum\ngases."
    },
    {
        "anchor": "The Contact in the BCS-BEC crossover for finite range interacting\n  ultracold Fermi gases: Using mean-field theory for the Bardeen-Cooper-Schriefer (BCS) to the\nBose-Einstein condensate (BEC) crossover we investigate the ground state\nthermodynamic properties of an interacting homogeneous Fermi gas. The\ninteratomic interactions modeled through a finite range potential allows us to\nexplore the entire region from weak to strong interacting regimes with no\napproximations. To exhibit the thermodynamic behavior as a function of the\npotential parameters in the whole crossover region, we concentrate in studying\nthe contact variable, the thermodynamic conjugate of the inverse of the s-wave\nscattering length. Our analysis allows us to validate the mean-field approach\nacross the whole crossover. It also leads to predict a quantum transition-like\nin the case when the potential range becomes large. This finding is a direct\nconsequence of the k-dependent energy gap for finite interaction range\npotentials.",
        "positive": "Ground State Properties of Anti-Ferromagnetic Spinor Bose gases in One\n  Dimension: We investigate the ground state properties of anti-ferromagnetic spin-1 Bose\ngases in one dimensional harmonic potential from the weak repulsion regime to\nthe strong repulsion regime. By diagonalizing the Hamiltonian in the Hilbert\nspace composed of the lowest eigenstates of single particle and spin\ncomponents, the ground state wavefunction and therefore the density\ndistributions, magnetization distribution, one body density matrix, and\nmomentum distribution for each components are obtained. It is shown that the\nspinor Bose gases of different magnetization exhibit the same total density\nprofiles in the full interaction regime, which evolve from the single peak\nstructure embodying the properties of Bose gases to the fermionized shell\nstructure of spin-polarized fermions. But each components display different\ndensity profiles, and magnetic domains emerge in the strong interaction limit\nfor $M=0.25$. In the strong interaction limit, one body density matrix and the\nmomentum distributions exhibit the same behaviours as those of spin-polarized\nfermions. The fermionization of momentum distribution takes place, in contrast\nto the $\\delta$-function-like distribution of single component Bose gases in\nthe full interaction region."
    },
    {
        "anchor": "Lattice polarons across the superfluid to Mott insulator transition: We study the physics of a mobile impurity confined in a lattice, moving\nwithin a Bose-Hubbard bath at zero temperature. Within the Quantum Gutzwiller\nformalism, we develop a beyond-Fr\\\"ohlich model of the bath-impurity\ninteraction. Results for the properties of the polaronic quasiparticle formed\nfrom the dressing of the impurity by quantum fluctuations of the bath are\npresented throughout the entire phase diagram, focusing on the quantum phase\ntransition between the superfluid and Mott insulating phases. Here we find that\nthe modification of the impurity properties is highly sensitive to the\ndifferent universality classes of the transition, providing an unambiguous\nprobe of correlations and collective modes in a quantum critical many-body\nenvironment.",
        "positive": "Generation and Dynamics of Quantized Vortices in a Unitary Fermi\n  Superfluid: Superfluidity and superconductivity are remarkable manifestations of quantum\ncoherence at a macroscopic scale. The dynamics of superfluids has dominated the\nstudy of these systems for decades now, but a comprehensive theoretical\nframework is still lacking. We introduce a local extension of the\ntime-dependent density functional theory to describe the dynamics of fermionic\nsuperfluids. Within this approach one can correctly represent vortex\nquantization, generation, and dynamics, the transition from a superfluid to a\nnormal phase and a number of other large amplitude collective modes which are\nbeyond the scope of two-fluid hydrodynamics, Ginzburg-Landau and/or\nGross-Pitaevskii approaches. We illustrate the power of this approach by\nstudying the generation of quantized vortices, vortex rings, vortex\nreconnection, and transition from a superfluid to a normal state in real time\nfor a unitary Fermi gas. We predict the emergence of a new qualitative\nphenomenon in superfluid dynamics of gases, the existence of stable\nsuperfluidity when the systems are stirred with velocities significantly\nexceeding the nominal Landau critical velocity in these systems."
    },
    {
        "anchor": "Driven dipole oscillations and the lowest energy excitations of strongly\n  interacting lattice bosons in a harmonic trap: We show that the analysis of the time evolution of the occupation of site and\nmomentum modes of harmonically trapped lattice hard-core bosons, under driven\ndipole oscillations, allows one to determine the energy of the lowest\none-particle excitations of the system in equilibrium. The analytic solution of\na single particle in the absence of a lattice is used to identify which\nfunction of those time-dependent observables is best fit for the analysis, as\nwell as to relate the dynamic response of the system to its single-particle\nspectrum. In the presence of the lattice and of multiple particles, a much\nricher and informative dynamical response is observed under the drive.",
        "positive": "Localization and shock waves in curved manifolds for the\n  Gross-Pitaevskii equation: We investigate the dynamics of a Bose-Einstein condensate in a progressively\nbended three dimensional cigar shaped potential. The interplay between geometry\nand nonlinearity is considered. At high curvature, topological localization\noccurs and becomes frustrated by the generation of curved dispersive\nshock-waves when the strength of nonlinearity is increased. The analysis is\nsupported by four-dimensional parallel simulations."
    },
    {
        "anchor": "Boson Core Compressibility: Strongly interacting atoms trapped in optical lattices can be used to explore\nphase diagrams of Hubbard models. Spatial inhomogeneity due to trapping\ntypically obscures distinguishing observables. We propose that measures using\nboson double occupancy avoid trapping effects to reveal key correlation\nfunctions. We define a boson core compressibility and core superfluid stiffness\nin terms of double occupancy. We use quantum Monte Carlo on the Bose-Hubbard\nmodel to empirically show that these quantities intrinsically eliminate edge\neffects to reveal correlations near the trap center. The boson core\ncompressibility offers a generally applicable tool that can be used to\nexperimentally map out phase transitions between compressible and\nincompressible states.",
        "positive": "Higher-dimensional Hofstadter butterfly on Penrose lattice: Quasicrystal is now open to search for novel topological phenomena enhanced\nby its peculiar structure characterized by an irrational number and\nhigh-dimensional primitive vectors. Here we extend the concept of a topological\ninsulator with an emerging staggered local magnetic flux (i.e., without\nexternal fields), similar to the Haldane's honeycomb model, to the Penrose\nlattice as a quasicrystal. The Penrose lattice consists of two different tiles,\nwhere the ratio of the numbers of tiles corresponds to an irrational number.\nContrary to periodic lattices, the periodicity of energy spectrum with respect\nto the magnetic flux no longer exists reflecting the irrational number in the\nPenrose lattice. Calculating the Bott index as a topological invariant, we find\ntopological phases appearing in a fractal energy spectrum like the Hofstadter\nbutterfly. More intriguingly, by folding the one-dimensional aperiodic magnetic\nflux into a two-dimensional periodic flux space, the fractal structure of\nenergy spectrum is extended to higher dimension, whose section corresponds to\nthe Hofstadter butterfly."
    },
    {
        "anchor": "Phases of Attractive Fermi Gases in Synthetic Dimensions: A novel way to produce quantum Hall ribbons in a cold atomic system is to use\nM hyperfine states of atoms in a 1D optical lattice to mimic an additional\n\"synthetic dimension\". A notable aspect here is that the SU(M) symmetric\ninteraction between atoms manifests as \"infinite ranged\" along the synthetic\ndimension. We study the many body physics of fermions with attractive\ninteractions in this system. We use a combination of analytical field theoretic\nand numerical density matrix renormalization group (DMRG) methods to reveal the\nrich ground state phase diagram of the system, including novel phases such as\nsquished baryon fluids. Remarkably, changing the parameters entails unusual\ncrossovers and transitions, e. g., we show that increasing the magnetic field\n(that produces the Hall effect) may convert a \"ferrometallic\" state at low\nfields to a \"squished baryon superfluid\" (with algebraic pairing correlations)\nat high fields. We also show that this system provides a unique opportunity to\nstudy quantum phase separation in a multiflavor ultracold fermionic system.",
        "positive": "Matter-wave dark solitons in box-like traps: Motivated by the experimental development of quasi-homogeneous Bose-Einstein\ncondensates confined in box-like traps, we study numerically the dynamics of\ndark solitons in such traps at zero temperature. We consider the cases where\nthe side walls of the box potential rise either as a power-law or a Gaussian.\nWhile the soliton propagates through the homogeneous interior of the box\nwithout dissipation, it typically dissipates energy during a reflection from a\nwall through the emission of sound waves, causing a slight increase in the\nsoliton's speed. We characterise this energy loss as a function of the wall\nparameters. Moreover, over multiple oscillations and reflections in the\nbox-like trap, the energy loss and speed increase of the soliton can be\nsignificant, although the decay eventually becomes stabilized when the soliton\nequilibrates with the ambient sound field."
    },
    {
        "anchor": "Phase diagrams of Fermi gases in a trap with mass and population\n  imbalances at finite temperature: The pairing and superfluid phenomena in a two-component Fermi gas can be\nstrongly affected by the population and mass imbalances. Here we present phase\ndiagrams of atomic Fermi gases as they undergo BCS--Bose-Einstein condensation\n(BEC) crossover with population and mass imbalances, using a pairing\nfluctuation theory. We focus on the finite temperature and trap effects, with\nan emphasis on the mixture of $^{6}$Li and $^{40}$K atoms. We show that there\nexist exotic types of phase separation in the BEC regime as well as\nsandwich-like shell structures at low temperature with superfluid or\npseudogapped normal state in the central shell in the BCS and unitary regimes,\nespecially when the light species is the majority. Such a sandwich-like shell\nstructure appear when the mass imbalance increases beyond certain threshold.\nOur result is relevant to future experiments on the $^6$Li--$^{40}$K mixture\nand possibly other Fermi-Fermi mixtures.",
        "positive": "Cluster Gutzwiller method for bosonic lattice systems: A versatile and numerically inexpensive method is presented allowing the\naccurate calculation of phase diagrams for bosonic lattice models. By treating\nclusters within the Gutzwiller theory, a surprisingly good description of\nquantum fluctuations beyond the mean-field theory is achieved approaching\nquantum Monte-Carlo predictions for large clusters. Applying this powerful\nmethod to the Bose-Hubbard model, we demonstrate that it yields precise results\nfor the superfluid to Mott-insulator transition in square, honeycomb, and cubic\nlattices. Due to the exact treatment within a cluster, the method can be\neffortlessly adapted to more complicated Hamiltonians in the fast progressing\nfield of optical lattice experiments. This includes state- and site-dependent\nsuperlattices, large confined atomic systems and disordered potentials, as well\nas various types of extended Hubbard models. Furthermore, the approach allows\nan excellent treatment of systems with arbitrary filling factors. We discuss\nthe perspectives that allow for the computation of large, spatially-varying\nlattices, low-lying excitations, and time evolution."
    },
    {
        "anchor": "An extended representation of three spin component Bose Einstein\n  Condensate solitons: We consider a three spin component Bose Einstein Condensate as described by\nas many coupled nonlinear Schroedinger equations. For a very special ratio of\nthe coupling constants, exact N soliton solutions to this set of equations are\nknown. Here we find a simple representation including the N = 1 solution based\non the symmetry of the equations. This symmetry is described by a linear\noperator, the nonlinearity of NLS notwithstanding. Our useful representation\nopens the door to the nonintegrable case of general coupling constants. A new\nclass of solutions is found.",
        "positive": "Three attractively interacting fermions in a harmonic trap: Exact\n  solution, ferromagnetism, and high-temperature thermodynamics: Three fermions with strongly repulsive interactions in a spherical harmonic\ntrap, constitute the simplest nontrivial system that can exhibit the onset of\nitinerant ferromagnetism. Here, we present exact solutions for three trapped,\nattractively interacting fermions near a Feshbach resonance. We analyze energy\nlevels on the upper branch of the resonance where the atomic interaction is\neffectively repulsive. When the s-wave scattering length a is sufficiently\npositive, three fully polarized fermions are energetically stable against a\nsingle spin-flip, indicating the possibility of itinerant ferromagnetism, as\ninferred in the recent experiment. We also investigate the high-temperature\nthermodynamics of a strongly repulsive or attractive Fermi gas using a quantum\nvirial expansion. The second and third virial coefficients are calculated. The\nresulting equations of state can be tested in future quantitative experimental\nmeasurements at high temperatures and can provide a useful benchmark for\nquantum Monte Carlo simulations."
    },
    {
        "anchor": "Spontaneous demagnetization of a dipolar spinor Bose gas at ultra-low\n  magnetic field: Quantum degenerate Bose gases with an internal degree of freedom, known as\nspinor condensates, are natural candidates to study the interplay between\nmagnetism and superfluidity. In the spinor condensates made of alkali atoms\nstudied so far, the spinor properties are set by contact interactions, while\nmagnetization is dynamically frozen, due to small magnetic dipole-dipole\ninteractions. Here, we study the spinor properties of S=3 $^{52}$Cr atoms, in\nwhich relatively strong dipole-dipole interactions allow changes in\nmagnetization. We observe a phase transition between a ferromagnetic phase and\nan unpolarized phase when the magnetic field is quenched to an extremely low\nvalue, below which interactions overwhelm the linear Zeeman effect. The BEC\nmagnetization changes due to magnetic dipole-dipole interactions that set the\ndynamics. Our work opens up the experimental study of quantum magnetism with\nfree magnetization using ultra-cold atoms.",
        "positive": "Optical control of atom-ion collisions using a Rydberg state: We present a method to control collisions between ultracold neutral atoms in\nthe electronic ground state and trapped ions. During the collision, the neutral\natom is resonantly excited by a laser to a low-field-seeking Rydberg state,\nwhich is repelled by the ion. As the atom is reflected from the ion, it is\nde-excited back into its electronic ground level. The efficiency of shielding\nis analyzed as a function of laser frequency and power, initial atom-ion\ncollision energy, and collision angle. The suitability of several Rydberg\nlevels of Na and Rb for shielding is discussed. Useful applications of\nshielding include the suppression of unwanted chemical reactions between atoms\nand ions, a prerequisite for controlled atom-ion interactions."
    },
    {
        "anchor": "Optically trapped Feshbach molecules of fermionic 161Dy and 40K: We report on the preparation of a pure ultracold sample of bosonic DyK\nFeshbach molecules, which are composed of the fermionic isotopes 161Dy and 40K.\nEmploying a magnetic sweep across a resonance located near 7.3 G, we produce up\nto 5000 molecules at a temperature of about 50 nK. For purification from the\nremaining atoms, we apply a Stern-Gerlach technique based on magnetic\nlevitation of the molecules in a very weak optical dipole trap. With the\ntrapped molecules we finally reach a high phase-space density of about 0.1. We\nmeasure the magnetic field dependence of the molecular binding energy and the\nmagnetic moment, refining our knowledge of the resonance parameters. We also\ndemonstrate a peculiar anisotropic expansion effect observed when the molecules\nare released from the trap and expand freely in the magnetic levitation field.\nMoreover, we identify an important lifetime limitation that is imposed by the\n1064-nm infrared trap light itself and not by inelastic collisions. The\nlight-induced decay rate is found to be proportional to the trap light\nintensity and the closed-channel fraction of the Feshbach molecule. These\nobservations suggest a one-photon coupling to electronically excited states to\nlimit the lifetime and point to the prospect of loss suppression by optimizing\nthe wavelength of the trapping light. Our results represent important insights\nand experimental steps on the way to achieve quantum-degenerate samples of DyK\nmolecules and novel superfluids based on mass-imbalanced fermion mixtures.",
        "positive": "Molecular Impurities as a Realization of Anyons on the Two-Sphere: Studies on experimental realization of two-dimensional anyons in terms of\nquasiparticles have been restricted, so far, to only anyons on the plane. It is\nknown, however, that the geometry and topology of space can have significant\neffects on quantum statistics for particles moving on it. Here, we have\nundertaken the first step towards realizing the emerging fractional statistics\nfor particles restricted to move on the sphere, instead of on the plane. We\nshow that such a model arises naturally in the context of quantum impurity\nproblems. In particular, we demonstrate a setup in which the lowest-energy\nspectrum of two linear bosonic/fermionic molecules immersed in a quantum\nmany-particle environment can coincide with the anyonic spectrum on the sphere.\nThis paves the way towards experimental realization of anyons on the sphere\nusing molecular impurities. Furthermore, since a change in the alignment of the\nmolecules corresponds to the exchange of the particles on the sphere, such a\nrealization reveals a novel type of exclusion principle for molecular\nimpurities, which could also be of use as a powerful technique to measure the\nstatistics parameter. Finally, our approach opens up a new numerical route to\ninvestigate the spectra of many anyons on the sphere. Accordingly, we present\nthe spectrum of two anyons on the sphere in the presence of a Dirac monopole\nfield."
    },
    {
        "anchor": "Semiclassical quench dynamics of Bose gases in optical lattices: We analyze the time evolution of the Bose-Hubbard model after a sudden\nquantum quench to a weakly interacting regime. Specifically, motivated by a\nrecent experiment at Kyoto University, we numerically simulate redistribution\nof the kinetic and onsite-interaction energies at an early time, which was\nobserved in non-equilibrium dynamics of ultracold Bose gases in a cubic optical\nlattice starting with a singly-occupied Mott-insulator state. In order to\ncompute the short-time dynamics corresponding to the experimental situation, we\napply the truncated-Wigner approximation (TWA) to the Bose-Hubbard model on a\ncubic lattice. We show that our semiclassical approach quantitatively\nreproduces the fast redistribution dynamics. We further analyze spatial\nspreading of density-density correlations at equal time in the Bose-Hubbard\nmodel on a square lattice with a large filling factor. When the system is\ninitially prepared in a coherent state, we find that a propagation velocity of\nthe correlation wave packet in the correlation function strongly depends on the\nfinal interaction strength, and it is bounded by twice the maximum group\nvelocity of the elementary excitations. In contrast, when the system is\ninitially in a Mott-insulator state, the propagation velocity of the wave\npacket is approximately independent of the final interaction strength.",
        "positive": "High temperature Bose-Einstein condensation into an excited state at\n  equilibrium: We describe Bose-Einstein condensation of strongly interacting particles into\na quantum state which is an excited single-particle state, but becomes the\nground state as density increases because it minimizes the interaction energy\ncompared to other states. Mean field calculations for a graphene potential just\nwide enough for two closely interacting layers of molecular hydrogen show\ncondensation at temperatures up to 60 K. In the condensed state, molecules hop\nbetween layers, increasing the first peak in the pair-correlation function just\npast the hard core repulsion diameter."
    },
    {
        "anchor": "Structure of two-component Bose-Einstein condensates with respective\n  vortex-antivortex superposition states: We investigate the phase structure of two-component Bose-Einstein condensates\n(BECs) with repulsive intra- and interspecies interactions in the presence of\nrespective vortex-antivortex superposition states (VAVSS). We show that\ndifferent winding numbers of vortex and antivortex and different intra- and\ninterspecies interaction strengths may lead to different phase configurations,\nsuch as fully separated phases, inlaid separated phases, asymmetric separated\nphase, and partially mixed phases, where the density profile of each component\ndisplays a petal-like (or modulated petal-like) structure. A phase diagram is\ngiven for the case of equal unit winding numbers of the vortex and antivortex\nin respective components, and it is shown that conventional criterion for phase\nseparation of two-component BECs is not applicable for the present system due\nto the VAVSS. In addition, our nonlinear stability analysis indicates that the\ntypical phase structures of two-component BECs with VAVSS allow to be detected\nin experiments. Moreover, for the case of unequal winding numbers of the vortex\nand antivortex in respective components, we find that each component in any of\nthe possible phase structures is in a cluster state of vortices and\nantivortices, where the topological defects appear in the form of singly\nquantized visible vortex, or hidden vortex, or ghost vortex, depending on the\nspecific parameters of the system. Finally, a general rule between the\nvortex-antivortex cluster state and the winding numbers of vortex and\nantivortex is revealed.",
        "positive": "Matter-wave diffraction from a quasicrystalline optical lattice: Quasicrystals are long-range ordered and yet non-periodic. This interplay\nresults in a wealth of intriguing physical phenomena, such as the inheritance\nof topological properties from higher dimensions, and the presence of\nnon-trivial structure on all scales. Here we report on the first experimental\ndemonstration of an eightfold rotationally symmetric optical lattice, realising\na two-dimensional quasicrystalline potential for ultracold atoms. Using\nmatter-wave diffraction we observe the self-similarity of this quasicrystalline\nstructure, in close analogy to the very first discovery of quasicrystals using\nelectron diffraction. The diffraction dynamics on short timescales constitutes\na continuous-time quantum walk on a homogeneous four-dimensional tight-binding\nlattice. These measurements pave the way for quantum simulations in fractal\nstructures and higher dimensions."
    },
    {
        "anchor": "Self-Trapped Polarons and Topological Defects in a Topological Mott\n  Insulator: Many-body interactions in topological quantum systems can give rise to new\nphases of matter, which simultaneously exhibit both rich spatial features and\ntopological properties. In this work, we consider spinless fermions on a\ncheckerboard lattice with nearest and next-to-nearest neighbor interactions. We\ncalculate the phase diagram at half filling, which presents, in particular, an\ninteraction-induced quantum anomalous Hall phase. We study the system at\nincommensurate fillings using an unrestricted Hartree-Fock ansatz and report a\nrich zoo of solutions such as self-trapped polarons and domain walls above an\ninteraction-induced topological insulator. We find that, as a consequence of\nthe interplay between the interaction-induced topology and topological defects,\nthese domain walls separate two phases with opposite topological invariants and\nhost topologically protected chiral edge states. Finally, we discuss\nexperimental prospects to observe these novel phenomena in a quantum simulator\nbased on laser-dressed Rydberg atoms in an optical lattice.",
        "positive": "Hydrodynamic fluctuations and the minimum shear viscosity of the dilute\n  Fermi gas at unitarity: We study hydrodynamic fluctuations in a non-relativistic fluid. We show that\nin three dimensions fluctuations lead to a minimum in the shear viscosity to\nentropy density ratio $\\eta/s$ as a function of the temperature. The minimum\nprovides a bound on $\\eta/s$ which is independent of the conjectured bound in\nstring theory, $\\eta/s \\geq \\hbar/(4\\pi k_B)$, where $s$ is the entropy\ndensity. For the dilute Fermi gas at unitarity we find $\\eta/s\\gsim 0.2\\hbar$.\nThis bound is not universal -- it depends on thermodynamic properties of the\nunitary Fermi gas, and on empirical information about the range of validity of\nhydrodynamics. We also find that the viscous relaxation time of a hydrodynamic\nmode with frequency $\\omega$ diverges as $1/\\sqrt{\\omega}$, and that the shear\nviscosity in two dimensions diverges as $\\log(1/ \\omega)$."
    },
    {
        "anchor": "Spin Hall mode in a trapped thermal Rashba gas: We theoretically investigate a two-dimensional harmonically-trapped gas of\nidentical atoms with Rashba spin-orbit coupling and no interatomic\ninteractions. In analogy with the spin Hall effect in uniform space, the gas\nexhibits a spin Hall mode. In particular, in response to a displacement of the\ncenter-of-mass of the system, spin-dipole moment oscillations occur. We\ndetermine the properties of these oscillations exactly, and find that their\namplitude strongly depends on the spin-orbit coupling strength and the quantum\nstatistics of the particles.",
        "positive": "Emergent ballistic transport of Bose-Fermi mixtures in one dimension: The degenerate Bose-Fermi (BF) mixtures in one dimension present a novel\nrealization of two decoupled Luttinger liquids with bosonic and fermionic\ndegrees of freedom at low temperatures. However, the transport properties of\nsuch decoupled Luttinger liquids of charges have not yet been studied. Here we\napply generalized hydrodynamics to study the transport properties of\none-dimensional (1D) BF mixtures with delta-function interactions. The initial\nstate is set up as the semi-infinite halves of two 1D BF mixtures with\ndifferent temperatures, joined together at the time $t=0$ and the junction\npoint $x=0$. Using the Bethe ansatz solution, we first rigorously prove the\nexistence of conserved charges for both the bosonic and fermionic degrees of\nfreedom, preserving the Euler-type continuity equations. We then analytically\nobtain the distributions of the densities and currents of the local conserved\nquantities which solely depend on the ratio $\\xi=x/t$. The left and right\nmoving quasiparticle excitations of the two halves form multiple segmented\nlight-cone hydrodynamics that display ballistic transport of the conserved\ncharge densities and currents in different degrees of freedom. Our analytical\nresults provide a deep understanding of the quantum transport of\nmulti-component Luttinger liquids in quantum systems with both bosonic and\nfermionic statistics."
    },
    {
        "anchor": "Dynamics of thermalization of two tunnel-coupled one-dimensional\n  quasicondensates: We study the non-equilibrium dynamics of two tunnel-coupled one-dimensional\nquasicondensates following a quench of the coupling strength from zero to a\nfixed finite value. More specifically, starting from two independent\nquasicondensates in thermal equilibrium, with initial temperature and chemical\npotential imbalance, we suddenly switch on the tunnel-coupling and analyze the\npost-quench equilibration in terms of particle number and energy imbalances. We\nfind that, in certain parameter regimes, the net energy can flow from the\ncolder quasicondensate to the hotter one and is governed by the surplus of low\nenergy particles flowing from the cold to the hot system relative to the\nhigh-energy particles flowing in the reverse direction. In all cases, the\napproach to the new thermal equilibrium occurs through transient, damped\noscillations. We also find that for a balanced initial state the coupled\nquasicondensates can relax into a final thermal equilibrium state in which they\ndisplay a thermal phase coherence length that is larger than their initial\nphase coherence length, even though the new equilibrium temperature is higher.\nThe increase in the phase coherence length occurs due to phase locking which\nmanifests itself via an increased degree of correlation between the local\nrelative phases of the quasicondensates at two arbitrary points.",
        "positive": "Anomalous Scattering of Low-lying Excitations in a Spin-1 Bose-Einstein\n  Condensate: We present the simplest theory of perfect tunneling of an excitation in a\nBose-Einstein condensate (BEC) through an impurity potential with an arbitrary\nshape in the low-momentum limit. That is for the transverse spin wave in the\nferromagnetic phase of a spin-1 BEC. This mode obeys a Schr\\\"odinger-type\nequation; yet, effects of the potential on its transmission coefficient $T$ and\non its scattering cross section $sigma$ vanish in that limit. The order\nparameter determines $T$, and the momentum $p$-dependence of $sigma$ exhibits a\nRayleigh scattering type ($sigma propto p^{4}$). These properties are common\nbetween two types of Nambu-Goldstone modes: this spin wave and the Bogoliubov\nmode."
    },
    {
        "anchor": "Spin 1 microcondensate in a magnetic field: semiclassics and exact\n  solution: We study a spin 1 Bose condensate small enough to be treated as a single\nmagnetic `domain': a system that we term a microcondensate. Because all\nparticles occupy a single spatial mode, this quantum many body system has a\nwell defined classical limit consisting of three degrees of freedom,\ncorresponding to the three macroscopically occupied spin states. We study both\nthe classical limit and its quantization, finding an integrable system in both\ncases. Depending on the sign of the ratio of the spin interaction energy and\nthe quadratic Zeeman energy, the classical limit displays either a separartrix\nin phase space, or Hamiltonian monodromy corresponding to non-trivial phase\nspace topology. We discuss the quantum signatures of these classical phenomena\nusing semiclassical quantization as well as an exact solution using the Bethe\nansatz.",
        "positive": "Pair condensation in the BCS-BEC crossover of ultracold atoms loaded\n  onto a 2D square lattice: We investigate the crossover from the Bardeen-Cooper-Schrieffer (BCS) state\nof weakly-bound Cooper pairs to the Bose-Einstein Condensate (BEC) of\nstrongly-bound molecular dimers in a gas of ultracold atoms loaded on a\ntwo-dimensional optical lattice. By using the the mean-field BCS equations of\nthe emerging Hubbard model and the concept of off-diagonal-long-range-order for\nfermions we calculate analytically and numerically the pair binding energy, the\nenergy gap and the condensate fraction of Cooper pairs as a function of\ninteraction strength and filling fractor of atoms in the lattice at zero\ntemperature."
    },
    {
        "anchor": "Floquet dynamics in driven Fermi-Hubbard systems: We study the dynamics and timescales of a periodically driven Fermi-Hubbard\nmodel in a three-dimensional hexagonal lattice. The evolution of the Floquet\nmany-body state is analyzed by comparing it to an equivalent implementation in\nundriven systems. The dynamics of double occupancies for the near- and\noff-resonant driving regime indicate that the effective Hamiltonian picture is\nvalid for several orders of magnitude in modulation time. Furthermore, we show\nthat driving a hexagonal lattice compared to a simple cubic lattice allows to\nmodulate the system up to 1~s, corresponding to hundreds of tunneling times,\nwith only minor atom loss. Here, driving at a frequency close to the\ninteraction energy does not introduce resonant features to the atom loss.",
        "positive": "The low-energy Goldstone mode in a trapped dipolar supersolid: A supersolid is a counter-intuitive state of matter that combines the\nfrictionless flow of a superfluid with the crystal-like periodic density\nmodulation of a solid. Since the first prediction in the 1950s, experimental\nefforts to realize this state have focussed mainly on Helium, where\nsupersolidity remains elusive. Recently, supersolidity has also been studied\nintensively in ultracold quantum gases, and some of its defining properties\nhave been induced in spin-orbit coupled Bose-Einstein condensates (BECs) and\nBECs coupled to two crossed optical cavities. However, the periodicity of the\ncrystals in both systems is fixed to the wavelength of the applied periodic\noptical potentials. Recently, hallmark properties of a supersolid -- the\nperiodic density modulation and simultaneous global phase coherence -- have\nbeen observed in arrays of dipolar quantum droplets, where the crystallization\nhappens in a self-organized manner due to intrinsic interactions. In this\nletter, we prove the genuine supersolid nature of these droplet arrays by\ndirectly observing the low-energy Goldstone mode. The dynamics of this mode is\nreminiscent of the effect of second sound in other superfluid systems and\nfeatures an out-ofphase oscillation of the crystal array and the superfluid\ndensity. This mode exists only due to the phase rigidity of the experimentally\nrealized state, and therefore confirms the genuine superfluidity of the\nsupersolid."
    },
    {
        "anchor": "Universal Dephasing of Many-Body Rabi Oscillations of Atoms in\n  One-Dimensional Traps: We study a quantum quench in a system of two coupled one-dimensional tubes of\ninteracting atoms. After the quench the system is out of equilibrium and\noscillates between the tubes with a frequency determined by microscopic\nparameters. Despite the high energy at which the system is prepared we find an\nemergent long time scale responsible for the dephasing of the oscillations and\na transition at which this time scale diverges. We show that the universal\nproperties of the dephasing and the transition arise from an infrared\northogonality catastrophe. Furthermore, we show how this universal behavior is\nrealized in a realistic model of fermions with attractive interactions.",
        "positive": "Tuning across Universalities with a Driven Open Condensate: Driven-dissipative systems in two dimensions can differ substantially from\ntheir equilibrium counterparts. In particular, a dramatic loss of off-diagonal\nalgebraic order and superfluidity has been predicted to occur due to the\ninterplay between coherent dynamics and external drive and dissipation in the\nthermodynamic limit. We show here that the order adopted by the system can be\nsubstantially altered by a simple, experimentally viable, tuning of the driving\nprocess. More precisely, by considering the long-wavelength phase dynamics of a\npolariton quantum fluid in the optical parametric oscillator regime, we\ndemonstrate that simply changing the strength of the pumping mechanism in an\nappropriate parameter range can substantially alter the level of effective\nspatial anisotropy induced by the driving laser, and move the system into\ndistinct scaling regimes. These include: (i) the classic algebraically ordered\nsuperfluid below the Berezinskii-Kosterlitz-Thouless (BKT) transition, as in\nequilibrium; (ii) the non-equilibrium, long-wave-length fluctuation dominated\nKardar-Parisi-Zhang (KPZ) phase; and the two associated topological defect\ndominated disordered phases caused by proliferation of (iii) entropic BKT\nvortex-antivortex pairs or (iv) repelling vortices in the KPZ phase. Further,\nby analysing the renormalization group flow in a finite system, we examine the\nlength scales associated with these phases, and assess their observability in\ncurrent experimental conditions."
    },
    {
        "anchor": "Momentum-dependent pseudo-spin dimers of coherently coupled bosons in\n  optical lattices: We study the two-body bound and scattering states of two particles in a one\ndimensional optical lattice in the presence of a coherent coupling between two\ninternal atomic levels. Due to the interplay between periodic potential,\ninteractions and coherent coupling, the internal structure of the bound states\ndepends on their center of mass momentum. This phenomenon corresponds to an\neffective momentum-dependent magnetic field for the dimer pseudo-spin, which\ncould be observed in a chirping of the precession frequency during Bloch\noscillations. The essence of this effect can be easily interpreted in terms of\nan effective bound state Hamiltonian. Moreover for indistinguishable bosons,\nthe two-body eigenstates can present simultaneously attractive and repulsive\nbound-state nature or even bound and scattering properties.",
        "positive": "Gap solitons of a super-Tonks-Girardeau gas in a one-dimensional\n  periodic potential: We study the stability of gap solitons of the super-Tonks-Girardeau bosonic\ngas in one-dimensional periodic potential. The linear stability analysis\nindicates that increasing the amplitude of periodic potential or decreasing the\nnonlinear interactions, the unstable gap solitons can become stable. In\nparticular, the theoretical analysis and numerical calculations show that,\ncomparing to the lower-family of gap solitons, the higher-family of gap\nsolitons are easy to form near the bottoms of the linear Bloch band gaps. The\nnumerical results also verify that the composition relations between various\ngap solitons and nonlinear Bloch waves are general and can exist in the\nsuper-Tonks-Girardeau phase."
    },
    {
        "anchor": "Pairing and pair superfluid density in one-dimensional Hubbard models: We use unbiased computational methods to elucidate the onset and properties\nof pair superfluidity in two-species fermionic and bosonic systems with onsite\ninterspecies attraction loaded in one-dimensional optical lattice. We compare\nresults from quantum Monte Carlo (QMC) and density matrix renormalization group\n(DMRG), emphasizing the one-to-one correspondence between the Drude weight\ntensor, calculated with DMRG, and the various winding numbers extracted from\nthe QMC. Our results show that, for any nonvanishing attractive interaction,\npairs form and are the sole contributors to superfluidity, there are no\nindividual contributions due to the separate species. For weak attraction, the\npair size diverges exponentially, i.e. Bardeen-Cooper-Schrieffer (BCS) pairing\nrequiring huge systems to bring out the pair-only nature of the superfluid.\nThis crucial property is largely overlooked in many studies, thereby\nmisinterpreting the origin and nature of the superfluid. We compare and\ncontrast this with the repulsive case and show that the behavior is very\ndifferent, contradicting previous claims about drag superfluidity and the\nsymmetry of properties for attractive and repulsive interactions. Finally, our\nresults show that the situation is similar for soft core bosons: superfluidity\nis due only to pairs, even for the smallest attractive interaction strength\ncompatible with the largest system sizes that we could attain.",
        "positive": "Exploring limits of dipolar quantum simulators with ultracold molecules: We provide a quantitative blueprint for realizing two-dimensional quantum\nsimulators employing ultracold dipolar molecules or magnetic atoms by studying\ntheir accuracy in predicting ground state properties of lattice models with\nlong-range interactions. For experimentally relevant ranges of potential\ndepths, interaction strengths, particle fillings, and geometric configurations,\nwe map out the agreement between the state prepared in the quantum simulator\nand the target lattice state. We do so by separately calculating numerically\nexact many-body wave functions in the continuum and single- or multi-band\nlattice representations, and building their many-body state overlaps. While the\nagreement between quantum simulator and single-band models is good for deep\noptical lattices with weaker interactions and low particle densities, the\nhigher band population rapidly increases for shallow lattices, stronger\ninteractions, and in particular above half filling. This induces drastic\nchanges to the properties of the simulated ground state, potentially leading to\nfalse predictions. Furthermore, we show that the interplay between\ncommensurability and interactions can lead to quasidegeneracies, rendering a\nfaithful ground state preparation even more challenging."
    },
    {
        "anchor": "Effect of loss on the topological features of dimer chain described by\n  the extended Aubry-Andr\u00e9-Harper model: By introducing loss to one sublattice of a dimer chain described by the\nextended Aubry-Andr\\'e or Harper (AAH) model, we study the topological features\nincluding the edge states, spectrum and winding number of the chain. We find\nthat the parameter region for the system to have real band-gap-closing is\nincreased due to the loss, and the average displacement of the single\nexcitation can still witness the topological features of the chain in the\npresence of loss. The robustness of the zero energy eigenstate against four\nkinds of disorders is also examined. A feasible experiment setup based on\ncoupled waveguides to observe the prediction of this paper is proposed.",
        "positive": "Vortex-lattice formation in a spin-orbit coupled rotating spin-1\n  condensate: We study the vortex-lattice formation in a rotating {Rashba} spin-orbit (SO)\ncoupled quasi-two-dimensional (quasi-2D) hyper-fine spin-1 spinor Bose-Einstein\ncondensate (BEC) in the $x-y$ plane using a numerical solution of the\nunderlying mean-field Gross-Pitaevskii equation. % The wave function for this\nsystem %has three components corresponding to the three projections of\nhyper-fine spin $F_z= +1,0,-1$. In this case, the non-rotating {Rashba}\nSO-coupled spinor BEC can have topological excitation in the form of vortices\nof different angular momenta in the three components, e.g. the $(0,+1,+2)$- and\n$(-1,0,+1)$-type states in ferromagnetic and anti-ferromagnetic spinor BEC: the\nnumbers in the parenthesis denote the intrinsic angular momentum of the vortex\nstates of the three components with the negative sign denoting an anti-vortex.\nThe presence of these states with intrinsic vorticity breaks the symmetry\nbetween rotation with vorticity along the $z$ and $-z$ axes and thus generates\na rich variety of vortex-lattice and anti-vortex-lattice states in a rotating\nquasi-2D spin-1 spinor ferromagnetic and anti-ferromagnetic BEC, not possible\nin a scalar BEC. {For weak SO coupling, } we find two types of symmetries of\nthese states $-$ hexagonal and \"square\". The hexagonal (square) symmetry state\nhas vortices arranged in closed concentric orbits with a maximum of $6, 12,\n18...$ ($8,12,16...$) vortices in successive orbits. Of these two symmetries,\nthe square vortex-lattice state is found to have the smaller energy."
    },
    {
        "anchor": "Collective atomic recoil motion in short-pulse multi-matter-optical wave\n  mixing: An analytical perturbation theory of short-pulse, matter-wave superradiant\nscatterings is presented. We show that Bragg resonant enhancement is\nincapacitated and both positive and negative order scatterings contribute\nequally. We further show that propagation gain is small and scattering events\nprimarily occur at the end of the condensate where the generated field has\nmaximum strength, thereby explaining the apparent ``asymmetry\" in the scattered\ncomponents with respect to the condensate center. In addition, the generated\nfield travels near the speed of light in a vacuum, resulting in significant\nspontaneous emission when the one-photon detuning is not sufficiently large.\nFinally, we show that when the excitation rate increases, the generated-field\nfront-edge-steepening and peak forward-shifting effects are due to depletion of\nthe ground state matter wave.",
        "positive": "Critical dynamics and tree-like spatiotemporal patterns in\n  exciton-polaritoncondensates: We study nonresonantly pumped exciton-polariton system in the vicinity of the\ndynamical instability threshold. We find that the system exhibits unique and\nrich dynamics, which leads to spatiotemporal pattern formation. The patterns\nhave a tree-like structure and are reminiscent of structures that appear in a\nvariety of soft matter systems. Within the approximation of slow and fast time\nscales, we show that the polariton model exhibits self-replication point in\nanalogy to reaction-diffusion systems."
    },
    {
        "anchor": "Nested-sphere description of the N-level Chern number and the\n  generalized Bloch hypersphere: The geometric interpretation of (pseudo)spin 1/2 systems on the Bloch sphere\nhas been appreciated across different areas ranging from condensed matter to\nquantum information and high energy physics. Although similar notions for\nlarger Hilbert spaces are established in mathematics, they have been so far\nless explored beyond the two-level case for practical usage in condensed matter\nsettings, or have involved restrictions to sub manifolds within the full\nHilbert space. We here employ a coherence vector description to theoretically\ncharacterize a general N-level system on the higher dimensional generalized\nBloch (hyper)sphere by respecting the structure of the underlying SU(N) algebra\nand construct physically intuitive geometric pictures for topological concepts.\nFocusing on two spatial dimensions, we reveal a geometric interpretation for\nthe Chern number in larger Hilbert spaces in terms of a nested structure\ncomprising N-1 two-spheres. We demonstrate that for the N-level case, there is\nan exterior two-sphere that provides a useful characterization of the system,\nnotably by playing a primary role in determining the Chern number. The external\nsphere can be directly measured in ultracold atoms via well-established band\nmapping techniques, thereby imparting knowledge of the topological nature of\nstate. We also investigate how the time evolution of the coherence vector\ndefined on the generalized Bloch hypersphere can be utilized to extract the\nfull state vector in experiments, allowing us to develop a tomography scheme\ninvolving quenches for three-level systems. Our geometric description opens up\na new avenue for the interpretation of the topological classification and the\ndynamical illustration of multi-level systems, which in turn is anticipated to\nhelp in the design of new experimental probes.",
        "positive": "Investigation of the bosonic spectrum of two-dimensional optical\n  graphene-type lattices. Normal phase: The band spectrum of bosonic atoms in two-dimensional honeycomb optical\nlattices with the graphene-type structure has been studied. The dispersion laws\nin the bands and the one-particle spectral densities are calculated for the\nnormal phase in the random phase approximation. The temperature-dependent\ngapless spectrum with Dirac points located at the Brillouin zone boundary is\nobtained for the lattice with energetically equivalent sites, with the\ncorresponding chemical potential lying outside the allowed energy band.\nDifferent on-site energies in the sublattices are shown to induce the\nappearance of a gap in the spectrum, so that the chemical potential can be\nlocated between the subbands, which gives rise to a substantial reconstruction\nof the band spectrum. The frequency dependences of the one-particle spectral\ndensity for both sublattices are determined as functions of the chemical\npotential level, the spectral gap magnitude, and the temperature."
    },
    {
        "anchor": "Quantum vortex stability in draining fluid flows: Quantum vortices with more than a single circulation quantum are usually\nunstable and decay into clusters of smaller vortices. One way to prevent the\ndecay is to place the vortex at the centre of a convergent (draining) fluid\nflow, which tends to force vortices together. It is found that whilst the\nprimary splitting instability is suppressed in this way (and completely\nquenched for strong enough flows) a secondary instability can emerge in\ncircular trapping geometries. This behaviour is related to an instability of\nrotating black holes when superradiantly amplified waves are confined inside a\nreflective cavity. The end state of the secondary instability is dramatic,\nmanifesting as a shock wave that propagates round the circular wall and\nnucleates many more vortices.",
        "positive": "Effective field theories for two-component repulsive bosons on lattice\n  and their phase diagrams: In this paper, we consider the bosonic t-J model, which describes\ntwo-component hard-core bosons with a nearest-neighbor (NN) pseudo-spin\ninteraction and a NN hopping. To study phase diagram of this model, we derive\neffective field theories for low-energy excitations. In order to represent the\nhard-core nature of bosons, we employ a slave-particle representation. In the\npath-integral quantization, we first integrate our the radial degrees of\nfreedom of each boson field and obtain the low-energy effective field theory of\nphase degrees of freedom of each boson field and an easy-plane pseudo-spin.\nCoherent condensates of the phases describe, e.g., a \"magnetic order\" of the\npseudo-spin, superfluidity of hard-core bosons, etc. This effective field\ntheory is a kind of extended quantum XY model, and its phase diagram can be\ninvestigated precisely by means of the Monte-Carlo simulations. We then apply a\nkind of Hubbard-Stratonovich transformation to the quantum XY model and obtain\nthe second-version of the effective field theory, which is composed of fields\ndescribing the pseudo-spin degrees of freedom and boson fields of the original\ntwo-component hard-core bosons. As application of the effective-field theory\napproach, we consider the bosonic t-J model on the square lattice and also on\nthe triangular lattice, and compare the obtained phase diagrams with the\nresults of the numerical studies. We also study low-energy excitations rather\nin detail in the effective field theory. Finally we consider the bosonic t-J\nmodel on a stacked triangular lattice and obtain its phase diagram. We compare\nthe obtained phase diagram with that of the effective field theory to find\nclose resemblance."
    },
    {
        "anchor": "Comment on \"Normal phase of an imbalanced Fermi gas\": Recently Mora and Chevy [Phys. Rev. Lett. 104, 230402 (2010),\narXiv:1003.0213v2], in studying the energy of an atomic Fermi gas consisting of\na majority species, 1, and a minority species, 2, showed that, due to\ninteratomic interactions, the energy density E of the gas has a contribution of\nthe form E^(2)= f n_2^2 /2, where n_i is the density of species i. They\nattribute this term to a `modification of the single polaron properties due to\nPauli blocking'. In this Comment, we demonstrate that E^(2) may equivalently be\nunderstood in terms of the familiar interaction between minority atoms induced\nby the majority component.",
        "positive": "Three-Body Problem of Bosons nearby a d-wave Resonance: Motivated by recent experimental progresses, we investigate few-body\nproperties of interacting spinless bosons nearby a d-wave resonance. Using the\nSkorniakov-Ter-Martirosion (STM) equations, we calculate the scattering length\nbetween an atom and a d-wave dimer, and we find that the atom-dimer scattering\nlength is positive and is much smaller the result from the mean-field\napproximation. We also reveal unique properties of the three-body recombination\nrate for a degenerate Bose condensate nearby the d-wave resonance. We find that\nthe total recombination rate is nearly a constant at the quasi-bound side, in\ncontrast to the behavior of a thermal gas nearby high-partial wave resonance.\nWe also find that the recombination rate monotonically increases across the\nunitary point toward the bound side, which is due to the largely enhanced\ncoupling between the atom and the d-wave dimer with deeper binding energy. This\nmonotonic behavior is also qualitatively different from that of a degenerate\ngas nearby an s-wave resonance counterpart."
    },
    {
        "anchor": "Artificial Gauge Field for Photons in Coupled Cavity Arrays: We propose and characterize solid-state photonic structures where light\nexperiences an artificial gauge field. A suitable coupling of the propagation\nand polarization degrees of freedom introduces a geometrical phase for photons\ntunneling between adjacent sites of a coupled cavity array. We then discuss the\nfeasibility of observing strong gauge field effects in the optical spectra of\nrealistic systems, including the Hofstadter butterfly spectrum.",
        "positive": "Black-hole radiation in Bose-Einstein condensates: We study the phonon fluxes emitted when the condensate velocity crosses the\nspeed of sound, i.e., in backgrounds which are analogous to that of a black\nhole. We focus on elongated one dimensional condensates and on stationary\nflows. Our theoretical analysis and numerical results are based on the\nBogoliubov-de Gennes equation without further approximation. The spectral\nproperties of the fluxes and of the long distance density-density correlations\nare obtained, both with and without an initial temperature. In realistic\nconditions, we show that the condensate temperature dominates the fluxes and\nthus hides the presence of the spontaneous emission (the Hawking effect). We\nalso explain why the temperature amplifies the long distance correlations which\nare intrinsic to this effect. This confirms that the correlation pattern offers\na neat signature of the Hawking effect. Optimal conditions for observing the\npattern are discussed, as well as correlation patterns associated with\nscattering of classical waves. Flows associated with white holes are also\nconsidered."
    },
    {
        "anchor": "Integrated Atom Detector Based on Field Ionization near Carbon Nanotubes: We demonstrate an atom detector based on field ionization and subsequent ion\ncounting. We make use of field enhancement near tips of carbon nanotubes to\nreach extreme electrostatic field values of up to 9x10^9 V/m, which ionize\nground state rubidium atoms. The detector is based on a carpet of multiwall\ncarbon nanotubes grown on a substrate and used for field ionization, and a\nchannel electron multiplier used for ion counting. We measure the field\nenhancement at the tips of carbon nanotubes by field emission of electrons. We\ndemonstrate the operation of the field ionization detector by counting atoms\nfrom a thermal beam of a rubidium dispenser source. By measuring the ionization\nrate of rubidium as a function of the applied detector voltage we identify the\nfield ionization distance, which is below a few tens of nanometers in front of\nnanotube tips. We deduce from the experimental data that field ionization of\nrubidium near nanotube tips takes place on a time scale faster than 10^(-10)s.\nThis property is particularly interesting for the development of fast atom\ndetectors suitable for measuring correlations in ultracold quantum gases. We\nalso describe an application of the detector as partial pressure gauge.",
        "positive": "Artificial Staggered Magnetic Field for Ultracold Atoms in Optical\n  Lattices: A time-dependent optical lattice with staggered particle current in the\ntight-binding regime was considered that can be described by a time-independent\neffective lattice model with an artificial staggered magnetic field. The low\nenergy description of a single-component fermion in this lattice at\nhalf-filling is provided by two copies of ideal two-dimensional massless Dirac\nfermions. The Dirac cones are generally anisotropic and can be tuned by the\nexternal staggered flux $\\p$. For bosons, the staggered flux modifies the\nsingle-particle spectrum such that in the weak coupling limit, depending on the\nflux $\\p$, distinct superfluid phases are realized. Their properties are\ndiscussed, the nature of the phase transitions between them is establised, and\nBogoliubov theory is used to determine their excitation spectra. Then the\ngeneralized superfluid-Mott-insulator transition is studied in the presence of\nthe staggered flux and the complete phase diagram is established. Finally, the\nmomentum distribution of the distinct superfluid phases is obtained, which\nprovides a clear experimental signature of each phase in ballistic expansion\nexperiments."
    },
    {
        "anchor": "Measurement of the atom number distribution in an optical tweezer using\n  single photon counting: We demonstrate in this paper a method to reconstruct the atom number\ndistribution of a cloud containing a few tens of cold atoms. The atoms are\nfirst loaded from a magneto-optical trap into a microscopic optical dipole trap\nand then released in a resonant light probe where they undergo a Brownian\nmotion and scatter photons. We count the number of photon events detected on an\nimage intensifier. Using the response of our detection system to a single atom\nas a calibration, we extract the atom number distribution when the trap is\nloaded with more than one atom. The atom number distribution is found to be\ncompatible with a Poisson distribution.",
        "positive": "Phase-matching condition for enhanced entanglement of colliding\n  indistinguishable quantum bright solitons in a harmonic trap: We investigate finite number effects in collisions between two states of an\ninitially well defined number of identical bosons with attractive contact\ninteractions, oscillating in the presence of harmonic confinement in one\ndimension. We investigate two $N/2$ atom bound states, which are initially\ndisplaced (symmetrically) from the trap center, and then left to freely evolve.\nFor sufficiently attractive interactions, these bound states are like those\nfound through use of the Bethe Ansatz (quantum solitons). However, unlike the\nfree case, the integrability is lost due to confinement, and collisions can\ncause mixing into different bound state configurations. We study the system\nnumerically for the simplest case of $N=4$, via an exact diagonalization of the\nHamiltonian within a finite basis, investigating left/right number uncertainty\nas our primary measure of entanglement. We find that for certain interaction\nstrengths, a phase matching condition leads to resonant transfer to different\nbound state configurations with highly non-Poissonian relative number\nstatistics."
    },
    {
        "anchor": "Critical Josephson current in BCS-BEC crossover superfluids: We develop a microscopic model to describe the Josephson dynamics between two\nsuperfluid reservoirs of ultracold fermionic atoms which accounts for the\ndependence of the critical current on both the barrier height and the\ninteraction strength along the crossover from BCS to BEC. Building on a\nprevious study [F. Meier & W. Zwerger, Phys. Rev. A, 64 033610 (2001)] of\nweakly-interacting bosons, we derive analytic results for the Josephson\ncritical current at zero temperature for homogeneous and trapped systems at\narbitrary coupling. The critical current exhibits a maximum near the unitarity\nlimit which arises from the competition between the increasing condensate\nfraction and a decrease of the chemical potential along the evolution from the\nBCS to the BEC limit. Our results agree quantitatively with numerical\nsimulations and recent experimental data.",
        "positive": "The quantum hydrodynamic description of quantum gases with different\n  interactions: We describe recent development of quantum hydrodynamics for ultracold Bose\nparticle studying and consider different kinds of interactions. The method of\nderivation of equations describing the evolution of the neutral Bose particle\nsystem at low temperatures is described. Despite the fact that we consider the\nneutral particles we account the short-range interaction between particles. We\nconsider the particles in the Bose-Einstein condensate (BEC) state. This method\nis called the method of quantum hydrodynamics, because natural for of the\nquantum mechanics rewritten in terms of material fields of observable\nquantities in three dimensional space is the set of equations, which look like\nthe hydrodynamics equations. It can be shown that from the quantum\nhydrodynamics equations can be derived macroscopic non-linear Schrodinger\nequation. Most famous non-linear Schrodinger equation is the Gross-Pitaevskii\n(GP) equation, which contains nonlinearity of the third degree. There are\ngeneralizations of the GP equation. New term appears in the GP equation at\naccount of the three-particle interaction. This term contains nonlinearity of\nthe fifth degree. At more detailed account of the two particle interaction we\ncome to the nonlocal non-linear Schrodinger equation. This equation contains\nspatial derivatives of the order parameter in the non-linear terms caused by\nthe interaction. In this terminology the GP equation corresponds to the first\norder by the interaction radius. For the BEC of the neutral particles with\nanisotropic long-range dipole-dipole interaction the generalization of the GP\nequation was also suggested. Detailed analyses of the applicability conditions\nshows that this equation valid for the system of dipoles parallel to each\nother, which do not change their direction, and where the dipole-dipole\ninteraction interferences translational motion of particles."
    },
    {
        "anchor": "Scale invariance and universality in a cold gas of indirect excitons: We address theoretically the puzzling similarity observed in the\nthermodynamic behaviour of independent clouds of cold dipolar excitons in\ncoupled semiconductor quantum wells. We argue that the condensation of\nself-trapped exciton gas starts at the same critical temperature in all traps\ndue to the specific scaling rule. As a consequence of the reduced\ndimensionality of the system, the scaling parameters appear to be insensitive\nto disorder.",
        "positive": "Wavepacket Dynamics in Nonlinear Schr\u00f6dinger Equations: Coherent states play an important role in quantum mechanics because of their\nunique properties under time evolution. Here we explore this concept for\none-dimensional repulsive nonlinear Schr\\\"odinger equations, which describe\nweakly interacting Bose-Einstein condensates or light propagation in a\nnonlinear medium. It is shown that the dynamics of phase-space translations of\nthe ground state of a harmonic potential is quite simple: the centre follows a\nclassical trajectory whereas its shape does not vary in time. The parabolic\npotential is the only one that satisfies this property. We study the time\nevolution of these nonlinear coherent states under perturbations of their\nshape, or of the confining potential. A rich variety of effects emerges. In\nparticular, in the presence of anharmonicities, we observe that the packet\nsplits into two distinct components. A fraction of the condensate is\ntransferred towards uncoherent high-energy modes, while the amplitude of\noscillation of the remaining coherent component is damped towards the bottom of\nthe well."
    },
    {
        "anchor": "Helical spin textures in dipolar Bose-Einstein condensates: We numerically study elongated helical spin textures in ferromagnetic spin-1\nBose-Einstein condensates subject to dipolar interparticle forces. Stationary\nstates of the Gross-Pitaevskii equation are solved and analyzed for various\nvalues of the helical wave vector and dipolar coupling strength. We find two\nhelical spin textures which differ by the nature of their topological defects.\nThe spin structure hosting a pair of Mermin-Ho vortices with opposite mass\nflows and aligned spin currents is stabilized for a nonzero value of the\nhelical wave vector.",
        "positive": "Geometrical pumping with a Bose-Einstein condensate: We realized a quantum geometric \"charge\" pump for a Bose-Einstein condensate\n(BEC) in the lowest Bloch band of a novel bipartite magnetic lattice.\nTopological charge pumps in filled bands yield quantized pumping set by the\nglobal -- topological -- properties of the bands. In contrast, our geometric\ncharge pump for a BEC occupying just a single crystal momentum state exhibits\nnon-quantized charge pumping set by local -- geometrical -- properties of the\nband structure. Like topological charge pumps, for each pump cycle we observed\nan overall displacement (here, not quantized) and a temporal modulation of the\natomic wavepacket's position in each unit cell, i.e., the polarization."
    },
    {
        "anchor": "Suppressed solitonic cascade in spin-imbalanced superfluid Fermi gas: Cold atoms experiments offer invaluable information on superfluid dynamics,\nincluding decay cascades of topological defects. While the cascade properties\nare well established for Bose systems, our understanding of their behavior in\nFermi counterparts is very limited, in particular in spin-imbalanced systems,\nwhere superfluid (paired) and normal (unpaired) particles naturally coexist\ngiving rise to complex spatial structure of the atomic cloud. Here we show,\nbased on a newly developed microscopic approach, that the decay cascades of\ntopological defects are dramatically modified by the spin-polarization. We\ndemonstrate that decay cascades end up at different stages: \"dark soliton\",\n\"vortex ring\" or \"vortex line\", depending on the polarization. We reveal that\nit is caused by sucking of unpaired particles into the soliton's internal\nstructure. As a consequence vortex reconnections are hindered and we anticipate\nthat quantum turbulence phenomenon can be significantly affected, indicating\nnew physics induced by polarization effects.",
        "positive": "Rotational properties of dipolar Bose-Einstein condensates confined in\n  anisotropic harmonic potentials: We study the rotational properties of a dipolar Bose-Einstein condensate\nconfined in a quasi-two- dimensional anisotropic trap, for an arbitrary\norientation of the dipoles with respect to their plane of motion. Within the\nmean-field approximation we find that the lowest-energy state of the system\ndepends strongly on the relative strength between the dipolar and the contact\ninteractions, as well as on the size and the orientation of the dipoles, and\nthe size and the orientation of the deformation of the trapping potential."
    },
    {
        "anchor": "Skyrmionic vortex lattices in coherently coupled three-component\n  Bose-Einstein condensates: We show numerically that a harmonically trapped and coherently Rabi-coupled\nthree-component Bose-Einstein condensate can host unconventional vortex\nlattices in its rotating ground state. The discovered lattices incorporate\nsquare and zig-zag patterns, vortex dimers and chains, and doubly quantized\nvortices, and they can be quantitatively classified in terms of a skyrmionic\ntopological index, which takes into account the multicomponent nature of the\nsystem. The exotic ground-state lattices arise due to the intricate interplay\nof the repulsive density-density interactions and the Rabi couplings as well as\nthe ubiquitous phase frustration between the components. In the frustrated\nstate, domain walls in the relative phases can persist between some components\neven at strong Rabi coupling, while vanishing between others. Consequently, in\nthis limit the three-component condensate effectively approaches a\ntwo-component condensate with only density-density interactions. At\nintermediate Rabi coupling strengths, however, we face unique vortex physics\nthat occurs neither in the two-component counterpart nor in the purely\ndensity-density-coupled three-component system.",
        "positive": "Matter wave interference of dilute Bose gases in the critical regime: Ultra-cold atomic gases provide new chance to study the universal critical\nbehavior of phase transition. We study theoretically the matter wave\ninterference for ultra-cold Bose gases in the critical regime. We demonstrate\nthat the interference in the momentum distribution can be used to extract the\ncorrelation in the Bose gas. A simple relation between the interference\nvisibility and the correlation length is found and used to interpret the\npioneering experiment about the critical behavior of dilute Bose gases [Science\n{\\bf 315}, 1556 (2007)]. Our theory paves the way to experimentally study\nvarious types of ultra-cold atomic gases with the means of matter wave\ninterference."
    },
    {
        "anchor": "Periodic quenches across the Berezinskii-Kosterlitz-Thouless phase\n  transition: The quenched dynamics of an ultracold homogeneous atomic two-dimensional Bose\ngas subjected to periodic quenches across the Berezinskii-Kosterlitz-Thouless\n(BKT) phase transition are discussed. Specifically, we address the effect of\nperiodic cycling of the effective atomic interaction strength between a thermal\ndisordered state above, and a highly ordered state below the critical BKT\ninteraction strength, by means of numerical simulations of the stochastic\nprojected Gross-Pitaevskii equation. Probing the emerging dynamics as a\nfunction of the frequency of sinusoidal driving from low to high frequencies\nreveals diverse dynamical features, including phase-lagged quasi adiabatic\nreversible condensate formation, resonant excitation consistent with an\nintrinsic system relaxation timescale, and gradual establishment of\ndynamically-recurring or time-averaged non-equilibrium states with enhanced\ncoherence which are neither condensed, nor thermal. Our study paves the way for\nexperimental observation of such driven non-equilibrium ultracold superfluid\nstates.",
        "positive": "Non-exponential one-body loss in a Bose-Einstein condensate: We have studied the decay of a Bose-Einstein condensate of metastable helium\natoms in an optical dipole trap. In the regime where two- and three-body losses\ncan be neglected we show that the Bose-Einstein condensate and the thermal\ncloud show fundamentally different decay characteristics. The total number of\natoms decays exponentially with time constant tau; however, the thermal cloud\ndecays exponentially with time constant (4/3)tau and the condensate decays much\nfaster, and non-exponentially. We show that this behaviour, which should be\npresent for all BECs in thermal equilibrium with a considerable thermal\nfraction, is due to a transfer of atoms from the condensate to the thermal\ncloud during its decay."
    },
    {
        "anchor": "Wave function Monte Carlo method for polariton condensates: We present a quantum jump approach to describe coupled quantum and classical\nsystems in the context of Bose-Einstein condensation in the solid state. In our\nformalism, the excitonic gain medium is described by classical rate equations,\nwhile the polariton modes are described fully quantum mechanically. We show the\nequivalence of our method with a master equation approach. As an application,\nwe compute the linewidth of a single mode polariton condensate. Both the line\nbroadening due to the interactions between polaritons and the interactions with\nthe reservoir excitons is taken into account.",
        "positive": "Symmetry breaking and singularity structure in Bose-Einstein condensates: We determine the trajectories of vortex singularities that arise after a\nsingle vortex is broken by a discretely symmetric impulse in the context of\nBose-Einstein condensates in a harmonic trap. The dynamics of these\nsingularities are analyzed to determine the form of the imprinted motion. We\nfind that the symmetry-breaking process introduces two effective forces: a\nrepulsive harmonic force that causes the daughter trajectories to be ejected\nfrom the parent singularity, and a Magnus force that introduces a torque about\nthe axis of symmetry. For the analytical non-interacting case we find that the\nparent singularity is reconstructed from the daughter singularities after one\nperiod of the trapping frequency. The interactions between singularities in the\nweakly interacting system do not allow the parent vortex to be reconstructed.\nAnalytic trajectories were compared to the actual minima of the wavefunction,\nshowing less 0.5% error for impulse strength of (v=0.00005). We show that these\nsolutions are valid within the impulse regime for various impulse strengths\nusing numerical integration of the Gross-Pitaevskii equation. We also show that\nthe actual duration of the symmetry breaking potential does not significantly\nchange the dynamics of the system as long as the strength is below (v=0.0005)."
    },
    {
        "anchor": "Strongly correlated gases of Rydberg-dressed atoms: quantum and\n  classical dynamics: We discuss techniques to generate long-range interactions in a gas of\ngroundstate alkali atoms, by weakly admixing excited Rydberg states with laser\nlight. This provides a tool to engineer strongly correlated phases with reduced\ndecoherence from inelastic collisions and spontaneous emission. As an\nillustration, we discuss the quantum phases of dressed atoms with dipole-dipole\ninteractions confined in a harmonic potential, as relevant to experiments. We\nshow that residual spontaneous emission from the Rydberg state acts as a\nheating mechanism, leading to a quantum-classical crossover.",
        "positive": "Scattering of atomic dark-bright solitons from narrow impurities: In this work, we study the collision of an atomic dark-bright soliton, in a\ntwo-component Bose-Einstein condensate, with a Gaussian barrier or well. First,\nwe present the results of an experiment, illustrating the classical particle\nphenomenology (transmission or reflection) in the case of an equal barrier or\nwell in both components. Then, motivated by the experimental observations, we\nperform systematic simulations considering not only the case of equal heights,\nbut also the considerably more complex setting, where the potential affects\nonly one of the two components. We systematically classify the ensuing cases\nwithin a two-parameter diagram of barrier amplitudes in the two components, and\nprovide intuitive explanations for the resulting observations, as well as of\ntheir variations as the size of the barrier changes."
    },
    {
        "anchor": "Mapping polariton Bose--Einstein condensate onto vibrational degrees of\n  freedom: We demonstrate a macro-coherent regime in molecular exciton-polariton\nsystems, where nonequilibrium polariton Bose--Einstein condensation coexists\nwith macroscopically occupied vibrational states. Strong vibronic coupling in\nmolecules induces an effective optomechanical interaction between cavity\npolaritons and vibrational degrees of freedom of molecules, leading to\nvibrational amplification in a resonant blue-detuned configuration. This\ninteraction maps out properties of the condensate to vibrational states,\noffering a novel approach to achieve vibrational condensation with potential\napplications in cavity-controlled chemistry, nonlinear and quantum optics.",
        "positive": "Currents algebra for an atom-molecule Bose-Einstein condensate model: I present an interconversion currents algebra for an atom-molecule\nBose-Einstein condensate model and use it to get the quantum dynamics of the\ncurrents. For different choices of the Hamiltonian parameters I get different\ncurrents dynamics."
    },
    {
        "anchor": "Probing the Superfluid to Mott Insulator Transition at the Single Atom\n  Level: Quantum gases in optical lattices offer an opportunity to experimentally\nrealize and explore condensed matter models in a clean, tunable system. We\ninvestigate the Bose-Hubbard model on a microscopic level using single\natom-single lattice site imaging; our technique enables space- and\ntime-resolved characterization of the number statistics across the\nsuperfluid-Mott insulator quantum phase transition. Site-resolved probing of\nfluctuations provides us with a sensitive local thermometer, allows us to\nidentify microscopic heterostructures of low entropy Mott domains, and enables\nus to measure local quantum dynamics, revealing surprisingly fast transition\ntimescales. Our results may serve as a benchmark for theoretical studies of\nquantum dynamics, and may guide the engineering of low entropy phases in a\nlattice.",
        "positive": "BCS-BEC crossover in a quasi-two-dimensional Fermi gas: We consider a two-component gas of fermionic atoms confined to a\nquasi-two-dimensional (quasi-2D) geometry by a harmonic trapping potential in\nthe transverse direction. We construct a mean field theory of the BCS-BEC\ncrossover at zero temperature that allows us to extrapolate to an infinite\nnumber of transverse harmonic oscillator levels. In the extreme BEC limit,\nwhere the confinement length exceeds the dimer size, we recover 3D dimers\nconfined to 2D with weak repulsive interactions. However, even when the\ninteractions are weak and the Fermi energy is less than the confinement\nfrequency, we find that the higher transverse levels can substantially modify\nfermion pairing. We argue that recent experiments on pairing in quasi-2D Fermi\ngases [Y. Zhang et al., Phys. Rev. Lett. 108, 235302 (2012)] have already\nobserved the effects of higher transverse levels."
    },
    {
        "anchor": "Non equilibrium quantum dynamics in ultra-cold quantum gases: Advances in controlling and measuring systems of ultra-cold atoms provided\nstrong motivation to theoretical investigations of quantum dynamics in closed\nmany-body systems. Fundamental questions on quantum dynamics and statistical\nmechanics are now within experimental reach: How is thermalization achieved in\na closed quantum system? How does quantum dynamics cross over to effective\nclassical physics? Can such a thermal or classical fate be evaded? In these\nlectures, given at the Les Houches Summer School of Physics \"Strongly\nInteracting Quantum Systems Out of Equilibrium\", I introduce the students to\nthe novel properties that make ultra-cold atomic systems a unique platform for\nstudy of non equilibrium quantum dynamics. I review a selection of recent\nexperimental and theoretical work in which universal features and emergent\nphenomena in quantum dynamics are highlighted.",
        "positive": "Observation of many-body localization of interacting fermions in a\n  quasi-random optical lattice: We experimentally observe many-body localization of interacting fermions in a\none-dimensional quasi-random optical lattice. We identify the many-body\nlocalization transition through the relaxation dynamics of an\ninitially-prepared charge density wave. For sufficiently weak disorder the time\nevolution appears ergodic and thermalizing, erasing all remnants of the initial\norder. In contrast, above a critical disorder strength a significant portion of\nthe initial ordering persists, thereby serving as an effective order parameter\nfor localization. The stationary density wave order and the critical disorder\nvalue show a distinctive dependence on the interaction strength, in agreement\nwith numerical simulations. We connect this dependence to the ubiquitous\nlogarithmic growth of entanglement entropy characterizing the generic many-body\nlocalized phase."
    },
    {
        "anchor": "Ultracold $O_2$+$O_2$ collisions in a magnetic field: on the role of the\n  potential energy surface: The collision dynamics of $^{17}O_2(^3\\Sigma_g^-) +^{17}O_2(^3\\Sigma_g^-)$ in\nthe presence of a magnetic field is studied within the close-coupling formalism\nin the range between 10 nK and 50 mK. A recent global {\\em ab initio} potential\nenergy surface (PES) is employed and its effect on the dynamics is analyzed and\ncompared with previous calculations where an experimentally derived PES was\nused [New J. Phys {\\bf 11}, 055021 (2009)]. In contrast to the results using\nthe older PES, magnetic field dependence of the low-field-seeking state in the\nultracold regime is characterized by quite a large background scattering\nlength, $a_{bg}$, and, in addition, cross sections exhibit broad and pronounced\nFeshbach resonances. The marked resonance structure is somewhat surprising\nconsidering the influence of inelastic scattering, but it can be explained by\nresorting to the analytical van der Waals theory, where the short range\namplitude of the entrance channel wave function is enhanced by the large\n$a_{bg}$. This strong sensitivity to the short range of the {\\em ab initio} PES\npersists up to relatively high energies (10 mK). After this study and despite\nquantitative predictions are very difficult, it can be concluded that the ratio\nbetween elastic and spin relaxation scattering is generally small, except for\nmagnetic fields which are either low or close to an asymmetric Fano-type\nresonance. Some general trends found here, such as a large density of\nquasibound states and a propensity towards large scattering lengths, could be\nalso characteristic of other anisotropic molecule-molecule systems.",
        "positive": "Quantum optical lattices for emergent many-body phases of ultracold\n  atoms: Confining ultracold gases in cavities creates a paradigm of quantum trapping\npotentials. We show that this allows to bridge models with global collective\nand short-range interactions as novel quantum phases possess properties of\nboth. Some phases appear solely due to quantum light-matter correlations. Due\nto global, but spatially structured, interaction, the competition between\nquantum matter and light waves leads to multimode structures even in\nsingle-mode cavities, including delocalized dimers of matter-field coherences\n(bonds), beyond density orders as supersolids and density waves."
    },
    {
        "anchor": "Bose-Bose mixtures in an optical lattice: First-order\n  superfluid-insulator transition and elementary excitations: We study ground-state phase diagrams and excitation spectra of Bose-Bose\nmixtures in an optical lattice by applying the Gutzwiller approximation to the\ntwo-component Bose-Hubbard model. A case of equal hoppings and equal\nintra-component interactions for both components is considered. Due to the\nexistence of inter-component interaction, there appear several quantum phases,\nsuch as the superfluid, paired superfluid, and counterflow superfluid phases.\nWe find that the transition from superfluid (SF) to Mott insulator (MI) with\neven filling factors can be of the first order for a wide range of the chemical\npotential. We calculate the excitation spectra as a useful probe to identify\nthe quantum phases and the SF-to-MI transitions. In the excitation spectra of\nthe SF phase, there are two gapless modes and a few gapful modes, which\nrespectively correspond to phase and amplitude fluctuations of the order\nparameters. At the SF-to-MI transition point, we show that the energy gaps of\ncertain amplitude modes reach zero for the second-order transition while they\nremain finite for the first-order one. Since the excitation spectrum can be\nmeasured by the Bragg scattering, we calculate the dynamical structure factor\nby using the linear response theory. We consider three types of density\nfluctuations, and show that the density fluctuations are coupled to different\nexcitation branches in different quantum phases.",
        "positive": "Interferences between Bogoliubov excitations and their impact on the\n  evidence of superfluidity in a paraxial fluid of light: Paraxial fluids of light represent an alternative platform to atomic\nBose-Einstein condensates and superfluid liquids for the study of the quantum\nbehaviour of collective excitations. A key step in this direction is the\nprecise characterization of the Bogoliubov dispersion relation, as recently\nshown in two experiments. However, the predicted interferences between the\nphonon excitations that would be a clear signature of the collective superfluid\nbehaviour have not been observed to date. Here, by analytically, numerically,\nand experimentally exploring the phonon phase-velocity, we observe the presence\nof interferences between counter-propagating Bogoliubov excitations and\ndemonstrate their critical impact on the measurement of the dispersion\nrelation. These results are evidence of a key signature of light superfluidity\nand provide a novel characterization tool for quantum simulations with photons."
    },
    {
        "anchor": "Dispersion law for a one-dimensional weakly interacting Bose gas with\n  zero boundary conditions: From the time-dependent Gross equation, we find the quasiparticle dispersion\nlaw for a one-dimensional weakly interacting Bose gas with a non-point\ninteratomic potential and zero boundary conditions (BCs). The result coincides\nwith the dispersion law for periodic BCs, i.e. the Bogolyubov law $E_{B}(k) =\n\\sqrt{\\left (\\frac{\\hbar^{2} k^2}{2m}\\right )^{2} + n_{0}\\nu(k)\\frac{\\hbar^2\nk^2}{m}}$. In the case of periodic BCs, the dispersion law can be easily\nderived from Gross' equation. However, for zero BCs, the analysis is not so\nsimple.",
        "positive": "Amorphous quantum magnets in a two-dimensional Rydberg atom array: Amorphous solids, i.e., systems which feature well-defined short-range\nproperties but lack long-range order, constitute an important research topic in\ncondensed matter. While their microscopic structure is known to differ from\ntheir crystalline counterpart, there are still many open questions concerning\nthe emergent collective behavior in amorphous materials. This is particularly\nthe case in the quantum regime, where the numerical simulations are extremely\nchallenging. In this article, we instead propose to explore amorphous quantum\nmagnets with an analog quantum simulator. To this end, we first present an\nalgorithm to generate amorphous quantum magnets, suitable for Rydberg\nsimulators of the Ising model. Subsequently, we use semiclassical approaches to\nget a preliminary insight of the physics of the model. In particular, we\ncalculate mean-field phase diagrams, and use the linear-spin-wave theory to\nstudy localization properties and dynamical structure factors of the\nexcitations. Finally, we outline an experimental proposal based on Rydberg\natoms in programmable tweezer arrays, thus opening the road towards the study\nof amorphous quantum magnets in regimes difficult to simulate classically."
    },
    {
        "anchor": "Atom interferometry with trapped Bose-Einstein condensates: Impact of\n  atom-atom interactions: Interferometry with ultracold atoms promises the possibility of ultraprecise\nand ultrasensitive measurements in many fields of physics, and is the basis of\nour most precise atomic clocks. Key to a high sensitivity is the possibility to\nachieve long measurement times and precise readout. Ultra cold atoms can be\nprecisely manipulated at the quantum level, held for very long times in traps,\nand would therefore be an ideal setting for interferometry. In this paper we\ndiscuss how the non-linearities from atom-atom interactions on one hand allow\nto efficiently produce squeezed states for enhanced readout, but on the other\nhand result in phase diffusion which limits the phase accumulation time. We\nfind that low dimensional geometries are favorable, with two-dimensional (2D)\nsettings giving the smallest contribution of phase diffusion caused by\natom-atom interactions. Even for time sequences generated by optimal control\nthe achievable minimal detectable interaction energy $\\Delta E^{\\rm min}$ is on\nthe order of 0.001 times the chemical potential of the BEC in the trap. From\nthere we have to conclude that for more precise measurements with atom\ninterferometers more sophisticated strategies, or turning off the interaction\ninduced dephasing during the phase accumulation stage, will be necessary.",
        "positive": "Controlling the group velocity of colliding atomic Bose-Einstein\n  condensates with Feshbach resonances: We report on a proposal to change the group velocity of a small Bose Einstein\nCondensate (BEC) upon collision with another BEC in analogy to slowing of light\npassing through dispersive media. We make use of ultracold collisions near a\nmagnetic Feshbach resonance, which gives rise to a sharp variation in\nscattering length with collision energy and thereby changes the group velocity.\nA generalized Gross-Pitaveskii equation is derived for a small BEC moving\nthrough a larger stationary BEC. We denote the two condensates by laser and\nmedium BEC, respectively, to highlight the analogy to a laser pulse travelling\nthrough a medium. We derive an expression for the group velocity in a\nhomogeneous medium as well as for the difference in distance, $\\delta$, covered\nby the laser BEC in the presence and absence of a finite-sized medium BEC with\na Thomas-Fermi density distribution. For a medium and laser of the same\nisotopic species, the shift $\\delta$ has an upper bound of twice the\nThomas-Fermi radius of the medium. For typical narrow Feshbach resonances and a\nmedium with number density $10^{15}$ cm$^{-3}$ up to 85% of the upper bound can\nbe achieved, making the effect experimentally observable. We also derive\nconstraints on the experimental realization of our proposal."
    },
    {
        "anchor": "Finite-temperature phase structures of hard-core bosons in an optical\n  lattice with an effective magnetic field: We study finite-temperature phase structures of hard-core bosons in a\ntwo-dimensional optical lattice subject to an effective magnetic field by\nemploying the gauged CP$^1$ model. Based on the extensive Monte Carlo\nsimulations, we study their phase structures at finite temperatures for several\nvalues of the magnetic flux per plaquette of the lattice and mean particle\ndensity. Despite the presence of the particle number fluctuation, the\nthermodynamic properties are qualitatively similar to those of the frustrated\nXY model with only the phase as a dynamical variable. This suggests that cold\natom simulators of the frustrated XY model are available irrespective of the\nparticle filling at each site.",
        "positive": "Dynamical instability and loss of p-band bosons in optical lattices: We study how the bosonic atoms on the excited p-band of an optical lattice\nare coupled to the lowest s-band and the 2nd excited d-band. We find that in\nsome parameter regimes the atom-atom interactions can cause a dynamical\ninstability of the p-band atoms towards decay to the s- and d-bands.\nFurthermore, even when dynamical instability is not expected s- and d-bands can\nbecome substantially populated."
    },
    {
        "anchor": "Intercomponent correlations in attractive one-dimensional\n  mass-imbalanced few-body mixtures: Ground-state properties of a few attractively interacting ultra-cold atoms of\ndifferent mass confined in a one-dimensional harmonic trap are studied in terms\nof the correlation noise. Depending on the mass ratio between the components'\natoms, the inter-particle correlations change their properties significantly\nfrom a strong pair-like correlation to an almost uncorrelated phase. This\nchange is accompanied by the undergoing change in the structure of the\nmany-body ground state. A crucial role of the quantum statistics is emphasized\nby comparing properties of the Fermi-Fermi mixture with a corresponding\nFermi-Bose system.",
        "positive": "Magnetic solitons in an immiscible two-component Bose-Einstein\n  condensate: We investigate magnetic solitons in an immiscible binary Bose-Einstein\ncondensate (BEC), where the intraspecies interactions are slightly weaker than\nthe interspecies interactions. While their density and phase profiles are\nanalogous to dark-bright solitons, other characteristic properties such as\nvelocities, widths, total density depletions, and in-trap oscillations are\ndifferent. In the low velocity regime, a magnetic soliton reduces to a\ntraveling pair of magnetic domain walls. Collisional behaviors of the solitons\nare also briefly discussed. We further demonstrate that these solitonic states\ncan be realized in a quasi-one-dimensional (quasi-1D) spin-1 ferromagnetic BEC\nwith weak spin interaction, e.g., a Rb87 BEC."
    },
    {
        "anchor": "An exact solution to the Bertsch problem and the non-universality of the\n  Unitary Fermi Gas: We analyze the universality of the Unitary Fermi Gas in its ground state from\na Wilsonian renormalization point of view and compute the effective range\ndependence of the Bertsch parameter $\\xi$ exactly. To this end we construct an\neffective block-diagonal two-body separable interaction with the Fermi momentum\nas a cut-off which reduces the calculation to the mean field level. The\ninteraction is separable in momentum space and is determined by Tabakin's\ninverse scattering formula. For a vanishing effective range we get $\\xi =\n\\frac{176}{9 \\pi }-\\frac{17}{3} = 0.56$. By using phase-equivalent similarity\ntransformations we can show that there is a class of exact solutions with any\nvalue in the range $ 0.56 \\ge \\xi \\ge -1/3$.",
        "positive": "First and second sound of a unitary Fermi gas in highly oblate harmonic\n  traps: We theoretically investigate first and second sound modes of a unitary Fermi\ngas trapped in a highly oblate harmonic trap at finite temperatures. Following\nthe idea by Stringari and co-workers {[}Phys. Rev. Lett. \\textbf{105}, 150402\n(2010){]}, we argue that these modes can be described by the simplified\ntwo-dimensional two-fluid hydrodynamic equations. Two possible schemes - sound\nwave propagation and breathing mode excitation - are considered. We calculate\nthe sound wave velocities and discretized sound mode frequencies, as a function\nof temperature. We find that in both schemes, the coupling between first and\nsecond sound modes is large enough to induce significant density fluctuations,\nsuggesting that second sound can be directly observed by measuring\n\\textit{in-situ} density profiles. The frequency of the second sound breathing\nmode is found to be highly sensitive to the superfluid density."
    },
    {
        "anchor": "BCS-BEC Crossover in Bilayers of Cold Fermionic Polar Molecules: We investigate the quantum and thermal phase diagram of fermionic polar\nmolecules loaded in a bilayer trapping potential with perpendicular dipole\nmoment. We use both a BCS theory approach that is most realiable at\nweak-coupling and a strong-coupling approach that considers the two-body bound\ndimer states with one molecules in each layer as the relevant degree of\nfreedom. The system ground state is a Bose-Einstein condensate (BEC) of dimer\nbound states in the low density limit and a paired superfluid (BCS) state in\nthe high density limit. At zero temperature, the intralayer repulsion is found\nto broaden the regime of BCS-BEC crossover, and can potentially induce system\ncollapse through the softening of roton excitations. The BCS theory and the\nstrongly-coupled dimer picture yield similar predictions for the parameters of\nthe crossover regime. The BKT transition temperature of the dimer superfluid is\nalso calculated. The crossover can be driven by many-body effects and is\nstrongly affected by the intralayer interaction which was ignored in previous\nstudies.",
        "positive": "A Spectroscopic Method to Measure the Superfluid Fraction of an\n  Ultracold Atomic Gas: We perform detailed analytical and numerical studies of a recently proposed\nmethod for a spectroscopic measurement of the superfluid fraction of an\nultracold atomic gas [N. R. Cooper and Z. Hadzibabic, Phys. Rev. Lett. 104,\n030401 (2010)]. Previous theoretical work is extended by explicitly including\nthe effects of non-zero temperature and interactions, and assessing the\nquantitative accuracy of the proposed measurement for a one-component Bose gas.\nWe show that for suitably chosen experimental parameters the method yields an\nexperimentally detectable signal and a sufficiently accurate measurement. This\nis illustrated by explicitly considering two key examples: First, for a weakly\ninteracting three-dimensional Bose gas it reproduces the expected result that\nbelow the critical temperature the superfluid fraction closely follows the\ncondensate fraction. Second, it allows a clear quantitative differentiation of\nthe superfluid and the condensate density in a strongly interacting Bose gas."
    },
    {
        "anchor": "Site-resolved imaging of a bosonic Mott insulator using ytterbium atoms: We demonstrate site-resolved imaging of a strongly correlated quantum system\nwithout relying on laser-cooling techniques during fluorescence imaging. We\nobserved the formation of Mott shells in the insulating regime and realized\nthermometry on the atomic cloud. This work proves the feasibility of the\nnoncooled approach and opens the door to extending the detection technology to\nnew atomic species.",
        "positive": "From Coherent Modes to Turbulence and Granulation of Trapped Gases: The process of exciting the gas of trapped bosons from an equilibrium initial\nstate to strongly nonequilibrium states is described as a procedure of symmetry\nrestoration caused by external perturbations. Initially, the trapped gas is\ncooled down to such low temperatures, when practically all atoms are in\nBose-Einstein condensed state, which implies the broken global gauge symmetry.\nExcitations are realized either by imposing external alternating fields,\nmodulating the trapping potential and shaking the cloud of trapped atoms, or it\ncan be done by varying atomic interactions by means of Feshbach resonance\ntechniques. Gradually increasing the amount of energy pumped into the system,\nwhich is realized either by strengthening the modulation amplitude or by\nincreasing the excitation time, produces a series of nonequilibrium states,\nwith the growing fraction of atoms for which the gauge symmetry is restored. In\nthis way, the initial equilibrium system, with the broken gauge symmetry and\nall atoms condensed, can be excited to the state, where all atoms are in the\nnormal state, with completely restored gauge symmetry. In this process, the\nsystem, starting from the regular superfluid state, passes through the states\nof vortex superfluid, turbulent superfluid, heterophase granular fluid, to the\nstate of normal chaotic fluid in turbulent regime. Both theoretical and\nexperimental studies are presented."
    },
    {
        "anchor": "The Avalanche Mechanism for Atom Loss near an Atom-Dimer Efimov\n  Resonance: An Efimov trimer near the atom-dimer threshold can increase the atom loss\nrate in ultracold trapped atoms through the {\\it avalanche mechanism} proposed\nby Zaccanti et al. A 3-body recombination event creates an energetic atom and\ndimer, whose subsequent elastic collisions produce additional atoms with\nsufficient energy to escape from the trapping potential. We use Monte Carlo\nmethods to calculate the average number of atoms lost and the average heat\ngenerated by recombination events in both a Bose-Einstein condensate and a\nthermal gas. We take into account the energy-dependence of the cross sections\nand the spatial structure of the atom cloud. We confirm that the number of\natoms lost can be much larger than the naive value 3 if there is an Efimov\ntrimer near the atom-dimer threshold. This does not produce a narrow loss\nfeature, but it can significantly affect the determination of Efimov\nparameters.",
        "positive": "Semiclassical dynamics of atomic Bose-Einstein condensates: An atomic Bose-Einstein condensate (BEC) is often described as a macroscopic\nobject which can be approximated by a coherent state. This, on the surface,\nwould appear to indicate that its behavior should be close to being classical.\nIn this paper, we clarify the extent of how \"classical\" a BEC is by exploring\nthe semiclassical equations for BECs under the mean field Gaussian\napproximation. Such equations describe the dynamics of a condensate in the\nclassical limit in terms of the variables < x > and < p > as well as their\nrespective variances. We compare the semiclassical solution with the full\nquantum solution based on the Gross-Pitaevskii Equation (GPE) and find that the\ninteratomic interactions which generate nonlinearity make the system less\n\"classical.\" On the other hand, many qualitative features are captured by the\nsemiclassical equations, and the equations to be solved are far less\ncomputationally intensive than solving the GPE which make them ideal for\nproviding quick diagnostics, and for obtaining new intuitive insight."
    },
    {
        "anchor": "Tan's contact scaling behaviour for trapped Lieb-Liniger bosons: from\n  two to many: We show that the contact parameter of N harmonically-trapped interacting 1D\nbosons at zero temperature can be analytically and accurately obtained by a\nsimple rescaling of the exact two-boson solution, and that N-body effects can\nbe almost factorized. The small deviations observed between our analytical\nresults and DMRG calculations are more pronounced when the interaction energy\nis maximal (i.e. at intermediate interaction strengths) but they remain bounded\nby the large-N local-density approximation obtained from the Lieb-Liniger\nequation of state stemming from the Bethe Ansatz. The rescaled two-body\nsolution is so close to the exact ones, that is possible, within a simple\nexpression interpolating the rescaled two-boson result to the local-density, to\nobtain N-boson contact and ground state energy functions in very good agreement\nwith DMRG calculations. Our results suggest a change of paradigm in the study\nof interacting quantum systems, giving to the contact parameter a more\nfundamental role than energy.",
        "positive": "Stability of persistent currents in spinor Bose-Einstein condensates: Motivated by a recent experiment [S. Beattie, S. Moulder, R. J. Fletcher, and\nZ. Hadzibabic, PRL 110, 025301 (2013)] we study the superflow of atomic spinor\nBose-Einstein condensates optically trapped in a ring-shaped geometry. Within a\ndissipative mean-field approach we simulate a two-component condensate in\nconditions adapted to the experiment. In qualitative agreement with the\nexperimental findings, we observe persistent currents, if the spin-population\nimbalance is above some well-defined `critical' value. The triply charged\nvortices decay in quantized steps. The vortex lines escape from the center of\nthe ring through dynamically created regions in the condensate annulus with\nreduced density of one component filled by atoms of the other component. The\nvortices then leave the ring-shaped high density region of the condensate and\nfinally decay into elementary excitations."
    },
    {
        "anchor": "Spectrum of elementary excitations in Galilean-invariant integrable\n  models: The spectrum of elementary excitations in one-dimensional quantum liquids is\ngenerically linear at low momenta. It is characterized by the sound velocity\nthat can be related to the ground state energy. Here we study the spectrum at\nhigher momenta in Galilean invariant integrable models. Somewhat surprisingly,\nwe show that the spectrum at arbitrary momentum is fully determined by the\nproperties of the ground state. We find general exact relations for the\ncoefficients of several terms in the expansion of the excitation energy at low\nmomenta and arbitrary interaction and express them in terms of the Luttinger\nliquid parameter. We apply the obtained formulas to the Lieb-Liniger model and\nobtain several new results.",
        "positive": "The Wavefunction of the Collapsing Bose-Einstein Condensate: Bose-Einstein condensates with tunable interatomic interactions have been\nstudied intensely in recent experiments. The investigation of the collapse of a\ncondensate following a sudden change in the nature of the interaction from\nrepulsive to attractive has led to the observation of a remnant condensate that\ndid not undergo further collapse. We suggest that this high-density remnant is\nin fact the absolute minimum of the energy, if the attractive atomic\ninteractions are nonlocal, and is therefore inherently stable. We show that a\nvariational trial function consisting of a superposition of two distinct\ngaussians is an accurate representation of the wavefunction of the ground state\nof the conventional local Gross-Pitaevskii field equation for an attractive\ncondensate and gives correctly the points of emergence of instability. We then\nuse such a superposition of two gaussians as a variational trial function in\norder to calculate the minima of the energy when it includes a nonlocal\ninteraction term. We use experimental data in order to study the long range of\nthe nonlocal interaction, showing that they agree very well with a\ndimensionally derived expression for this range."
    },
    {
        "anchor": "Bayesian Optimization of Bose-Einstein Condensates: Machine Learning methods are emerging as faster and efficient alternatives to\nnumerical simulation techniques. The field of Scientific Computing has started\nadopting these data-driven approaches to faithfully model physical phenomena\nusing scattered, noisy observations from coarse-grained grid-based simulations.\nIn this paper, we investigate data-driven modelling of Bose-Einstein\nCondensates (BECs). In particular, we use Gaussian Processes (GPs) to model the\nground state wave function of BECs as a function of scattering parameters from\nthe dimensionless Gross Pitaveskii Equation (GPE). Experimental results\nillustrate the ability of GPs to accurately reproduce ground state wave\nfunctions using a limited number of data points from simulations. Consistent\nperformance across different configurations of BECs, namely Scalar and\nVectorial BECs generated under different potentials, including harmonic, double\nwell and optical lattice potentials pronounces the versatility of our method.\nComparison with existing data-driven models indicates that our model achieves\nsimilar accuracy with only a small fraction 1/50th of data points used by\nexisting methods, in addition to modelling uncertainty from data. When used as\na simulator post-training, our model generates ground state wave functions $36\n\\times $ faster than Trotter Suzuki, a numerical approximation technique that\nuses Imaginary time evolution. Our method is quite general; with minor changes\nit can be applied to similar quantum many-body problems.",
        "positive": "Attractive Fermi polarons at nonzero temperature with finite\n  impurityconcentration: We theoretically investigate how quasi-particle properties of an attractive\nFermi polaron are affected by nonzero temperature and finite impurity\nconcentration. By applying both non-self-consistent and self-consistent\nmany-body $T$-matrix theories, we calculate the polaron energy (including decay\nrate), effective mass, and residue, as functions of temperature and impurity\nconcentration. The temperature and concentration dependences are weak on the\nBCS side with a negative impurity-medium scattering length. Toward the strong\nattraction regime across the unitary limit, we find sizable dependences. In\nparticular, with increasing temperature the effective mass quickly approaches\nthe bare mass and the residue is significantly enhanced. At the temperature\n$T\\sim0.1T_{F}$, where $T_{F}$ is the Fermi temperature of the background Fermi\nsea, the residual polaron-polaron interaction seems to become attractive. This\nleads to a notable down-shift in the polaron energy. We show that, by taking\ninto account the temperature and impurity concentration effects, the measured\npolaron energy in the first Fermi polaron experiment {[}A. Schirotzek\n\\textit{et al.}, Phys. Rev. Lett. \\textbf{102}, 230402 (2009){]} can be better\ntheoretically explained."
    },
    {
        "anchor": "Topological magnon insulator and quantized pumps from\n  strongly-interacting bosons in optical superlattices: We propose a scheme realizing topological insulators and quantized pumps for\nmagnon excitations, based on strongly-interacting two-component ultracold atoms\ntrapped in optical superlattices. Specifically, we show how to engineer the\nSu-Schrieffer-Heeger model for magnons using state-independent superlattices,\nand the Rice-Mele model using state-dependent superlattices. We describe\nrealistic experimental protocols to detect the topological signatures of magnon\nexcitations in these two models. In particular, we show that the\nnon-equilibrium dynamics of a single magnon can be exploited to directly detect\ntopological winding numbers and phase transitions. We also describe how\ntopological (quantized) pumps can be realized with magnons, and study how this\nphenomenon depends on the initial magnon state preparation. Our study opens a\nnew avenue for exploring magnonic topological phases of matter and their\npotential applications in the context of topological magnon transport.",
        "positive": "Phase diagram of the rotating two-component Fermi gas including vortices: We determine the conditions under which superfluidity with and without\nquantized vortices appears in a weakly interacting two-component atomic Fermi\ngas that is trapped in a rotating cylindrical symmetric harmonic potential. We\ncompute the phase diagram as a function of rotation frequency, scattering\nlength, temperature, total number of trapped atoms, and population imbalance."
    },
    {
        "anchor": "Trial wave functions for ring-trapped ions and neutral atoms:\n  Microscopic description of the quantum space-time crystal: A constructive theoretical platform for the description of quantum space-time\ncrystals uncovers for $N$ interacting and ring-confined rotating particles the\nexistence of low-lying states with proper space-time crystal behavior. The\nconstruction of the corresponding many-body trial wave functions proceeds first\nvia symmetry breaking at the mean-field level followed by symmetry restoration\nusing projection techniques. The ensuing correlated many-body wave functions\nare stationary states and preserve the rotational symmetries, and at the same\ntime they reflect the point-group symmetries of the mean-field crystals. This\nbehavior results in the emergence of sequences of select magic angular momenta\n$L_m$. For angular-momenta away from the magic values, the trial functions\nvanish. Symmetry breaking beyond mean field can be induced by superpositions of\nsuch good-$L_m$ many-body stationary states. We show that superposing a pair of\nadjacent magic angular momenta states leads to formation of special\nbroken-symmetry states exhibiting quantum space-time-crystal behavior. In\nparticular, the corresponding particle densities rotate around the ring,\nshowing undamped and nondispersed periodic crystalline evolution in both space\nand time. The experimental synthesis of such quantum space-time-crystal wave\npackets is predicted to be favored in the vicinity of ground-state energy\ncrossings of the Aharonov-Bohm-type spectra accessed via an externally applied\nmagnetic field. These results are illustrated here for Coulomb-repelling\nfermionic ions and for a lump of contact-interaction attracting bosons.",
        "positive": "Inverse Energy Cascade in Forced 2D Quantum Turbulence: We demonstrate an inverse energy cascade in a minimal model of forced 2D\nquantum vortex turbulence. We simulate the Gross-Pitaevskii equation for a\nmoving superfluid subject to forcing by a stationary grid of obstacle\npotentials, and damping by a stationary thermal cloud. The forcing injects\nlarge amounts of vortex energy into the system at the scale of a few healing\nlengths. A regime of forcing and damping is identified where vortex energy is\nefficiently transported to large length scales via an inverse energy cascade\nassociated with the growth of clusters of same-circulation vortices, a\nKolmogorov scaling law in the kinetic energy spectrum over a substantial\ninertial range, and spectral condensation of kinetic energy at the scale of the\nsystem size. Our results provide clear evidence that the inverse energy cascade\nphenomenon, previously observed in a diverse range of classical systems, can\nalso occur in quantum fluids."
    },
    {
        "anchor": "Beyond superfluidity in driven non-equilibrium Bose-Einstein condensates: The phenomenon of superfluidity in open Bose-Einstein condensates (BEC) is\nanalysed numerically and analytically. It is found that a superfluid phase is\nfeasible even above the speed of sound, when forces due to inhomogeneous\nnon-equilibrium processes oppose the contributions of homogeneous processes.\nFurthermore a regime of accelerating impurities can be observed for particular\npumping/decay strategies. All findings are derived within the complex\nGross-Pitaevskii (GP) theory with creation and annihilation terms. Utilising\nthis framework the effective force acting on an impurity as it moves with\nvelocity v through the open condensate can be calculated. The result shows that\nthe force is continuously increasing/decreasing with increasing velocity\nstarting from the state of zero motion at v = 0, a property that can be traced\ndown to the additional homogeneous annihilation/creation term in the extended\nGP model. Our findings stand in stark contrast to the concept of a topological\nphase transition to frictionless flow below a critical velocity as observed for\nequilibrium Bose-Einstein condensates analytically, numerically and for trapped\natoms experimentally.",
        "positive": "Moment of Inertia and Dynamical Rotational Response of a Supersolid\n  Dipolar Gas: We show that the knowledge of the time dependent response of a trapped gas,\nsubject to a sudden rotation of a confining harmonic potential, allows for the\ndetermination of the moment of inertia of dipolar supersolid configurations.\nWhile in the presence of one-dimensional arrays of droplets the frequency of\nthe resulting scissors oscillation provides accurate access to the value of the\nmoment of inertia, two-dimensional like configurations are characterized by a\nmulti-frequency structure in the rotating signal, reflecting the presence of\nsignificant rigid body components in the rotational motion. Using the formalism\nof response function theory and simulations based on the so-called extended\ntime dependent Gross-Pitaevskii equation, we point out the crucial role played\nby the low frequency components in the determination of the moment of inertia\nand of its deviations from the irrotational value. We also propose a protocol\nbased on the stationary rotation of the trap, followed by its sudden stop,\nwhich might provide a promising alternative to the experimental evaluation of\nthe moment of inertia."
    },
    {
        "anchor": "Spontaneous Formation of Star-Shaped Surface Patterns in a Driven\n  Bose-Einstein Condensate: We observe experimentally the spontaneous formation of star-shaped surface\npatterns in driven Bose-Einstein condensates. Two-dimensional star-shaped\npatterns with $l$-fold symmetry, ranging from quadrupole ($l=2$) to heptagon\nmodes ($l=7$), are parametrically excited by modulating the scattering length\nnear the Feshbach resonance. An effective Mathieu equation and Floquet analysis\nare utilized, relating the instability conditions to the dispersion of the\nsurface modes in a trapped superfluid. Identifying the resonant frequencies of\nthe patterns, we precisely measure the dispersion relation of the collective\nexcitations. The oscillation amplitude of the surface excitations increases\nexponentially during the modulation. We find that only the $l=6$ mode is\nunstable due to its emergent coupling with the dipole motion of the cloud. Our\nexperimental results are in excellent agreement with the mean-field framework.\nOur work opens a new pathway for generating higher-lying collective excitations\nwith applications, such as the probing of exotic properties of quantum fluids\nand providing a generation mechanism of quantum turbulence.",
        "positive": "Scattering of two heavy Fermi polarons: resonances and quasibound states: Impurities in a Fermi sea, or Fermi polarons, experience a Casimir\ninteraction induced by quantum fluctuations of the medium. When there is\nshort-range attraction between impurities and fermions, also the induced\ninteraction between two impurities is strongly attractive at short distance and\noscillates in space for larger distances. We theoretically investigate the\nscattering properties and compute the scattering phase shifts and scattering\nlengths between two heavy impurities in an ideal Fermi gas at zero temperature.\nWhile the induced interaction between impurities is weakly attractive for weak\nimpurity-medium interactions, we find that impurities strongly and attractively\ninteracting with the medium exhibit resonances in the induced scattering with a\nsign change of the induced scattering length and even strong repulsion. These\nresonances occur whenever a three-body Efimov bound state appears at the\ncontinuum threshold. At energies above the continuum threshold, we find that\nthe Efimov state in medium can turn into a quasibound state with a finite decay\nwidth."
    },
    {
        "anchor": "Localization of a spin-orbit coupled Bose-Einstein condensate in a\n  bichromatic optical lattice: We study the localization of a noninteracting and weakly interacting\nBose-Einstein condensate with spin-orbit coupling loaded in a quasiperiodic\nbichromatic optical lattice potential using the numerical solution and\nvariational approximation of a binary mean-field Gross-Pitaevskii equation with\ntwo pseudo-spin components. We confirm the existence of the stationary\nlocalized states in the presence of the spin-orbit and Rabi couplings for an\nequal distribution of atoms in the two components. We find that the interaction\nbetween the spin-orbit and Rabi couplings favors the localization or\ndelocalization of the BEC depending on the the phase difference between the\ncomponents. We also studied the oscillation dynamics of the localized states\nfor an initial population imbalance between the two components.",
        "positive": "Prospects for single photon sideband cooling of optically trapped\n  neutral atoms: We propose a novel cooling scheme for realising single photon sideband\ncooling on particles trapped in a state-dependent optical potential. We develop\na master rate equation from an ab-initio model and find that in experimentally\nfeasible conditions it is possible to drastically reduce the average occupation\nnumber of the vibrational levels by applying a frequency sweep on the cooling\nlaser that sequentially cools all the motional states. Notably, this cooling\nscheme works also when a particle experiences a deeper trap in its internal\nground state than in its excited state, a condition for which conventional\nsingle photon sideband cooling does not work. In our analysis, we consider two\ncases: a two-level particle confined in an optical tweezer and Li atoms\nconfined in an optical lattice, and find conditions for efficient cooling in\nboth cases. The results from the model are confirmed by a full quantum Monte\nCarlo simulation of the system Hamiltonian. Our findings provide an alternative\ncooling scheme that can be applied in principle to any particle, e.g. atoms,\nmolecules or ions, confined in a state-dependent optical potential."
    },
    {
        "anchor": "Localization of a Bose-Fermi mixture in a bichromatic optical lattice: We study the localization of a cigar-shaped super-fluid Bose-Fermi mixture in\na quasi-periodic bichromatic optical lattice (OL) for inter-species attraction\nand intra-species repulsion. The mixture is described by the Gross-Pitaevskii\nequation for the bosons, coupled to a hydrodynamic mean-field equation for\nfermions at unitarity. We confirm the existence of the symbiotic localized\nstates in the Bose-Fermi mixture and Anderson localization of the Bose\ncomponent in the interacting Bose-Fermi mixture on a bichromatic OL. The phase\ndiagram in boson and fermion numbers showing the regions of the symbiotic and\nAnderson localization of the Bose component is presented. Finally, the\nstability of symbiotic and Anderson localized states is established under small\nperturbations.",
        "positive": "Dilute quantum liquid in a K-Rb Bose mixture: A quantum liquid in a heterogeneous mixture of $^{41}$K and $^{87}$Rb atoms\nis studied using the diffusion Monte Carlo method and Density Functional\nTheory. The perturbative Lee-Huang-Yang term for a heterogeneous mixture is\nverified and it is proved to be valid only near the gas-liquid transition.\nBased on the equations of state of the bulk mixture, calculated with diffusion\nMonte Carlo, extensions to Lee-Huang-Yang corrected mean-field energy\nfunctionals (MF+LHY) are presented. Using Density Functional Theory, a\nsystematic comparison between different functionals is performed, focusing on\nthe critical atom number, surface tension, surface width, Tolman length, and\ncompressibility. These results are given as a function of the inter-species\ninteraction strength, within the stability domain of the liquid mixture."
    },
    {
        "anchor": "Quantum rotor model for a Bose-Einstein condensate of dipolar molecules: We show that a Bose-Einstein condensate of heteronuclear molecules in the\nregime of small and static electric fields is described by a quantum rotor\nmodel for the macroscopic electric dipole moment of the molecular gas cloud. We\nsolve this model exactly and find the symmetric, i.e., rotationally invariant,\nand dipolar phases expected from the single-molecule problem, but also an axial\nand planar nematic phase due to many-body effects. Investigation of the\nwavefunction of the macroscopic dipole moment also reveals squeezing of the\nprobability distribution for the angular momentum of the molecules.",
        "positive": "Anisotropic light-shift and magic-polarization of the intercombination\n  line of Dysprosium atoms in a far-detuned dipole trap: We characterize the anisotropic differential ac-Stark shift for the Dy $626$\nnm intercombination transition, induced in a far-detuned $1070$ nm optical\ndipole trap, and observe the existence of a \"magic polarization\" for which the\npolarizabilities of the ground and excited states are equal. From our\nmeasurements we extract both the scalar and tensorial components of the dynamic\ndipole polarizability for the excited state, $\\alpha_E^\\text{s} = 188\n(12)\\,\\alpha_\\text{0}$ and $\\alpha_E^\\text{t} = 34 (12)\\,\\alpha_\\text{0}$,\nrespectively, where $\\alpha_\\text{0}$ is the atomic unit for the electric\npolarizability. We also provide a theoretical model allowing us to predict the\nexcited state polarizability and find qualitative agreement with our\nobservations. Furthermore, we utilize our findings to optimize the efficiency\nof Doppler cooling of a trapped gas, by controlling the sign and magnitude of\nthe inhomogeneous broadening of the optical transition. The resulting initial\ngain of the collisional rate allows us, after forced evaporation cooling, to\nproduce a quasi-pure Bose-Einstein condensate of $^{162}$Dy with $3\\times 10^4$\natoms."
    },
    {
        "anchor": "Discrete Time Crystals with Absolute Stability: We show that interacting bosons on a ring which are driven periodically by a\nrotating potential can support discrete time crystals whose absolute stability\ncan be proven. The absolute stability is demonstrated by an exact mapping of\ndiscrete time crystal states to low-lying eigenstates of a time-independent\nmodel that reveals spontaneous breaking of space translation symmetry. The\nmapping ensures that there are no residual time-dependent terms that could lead\nto heating of the system and destruction of discrete time crystals. We also\nanalyze periodically kicked bosons where the mapping is approximate only and\ncannot guarantee the absolute stability of discrete time crystals. Besides\nillustrating potential sources of instability, the kicked bosons model\ndemonstrates a rich field for investigating the interplay between different\ntime and space symmetry breaking, as well as the stability of time crystal\nbehavior in contact with a thermal reservoir.",
        "positive": "Commensurate and incommensurate 1D interacting quantum systems: Single-atom imaging resolution of many-body quantum systems in optical\nlattices is routinely achieved with quantum-gas microscopes. Key to their great\nversatility as quantum simulators is the ability to use engineered light\npotentials at the microscopic level. Here, we employ dynamically varying\nmicroscopic light potentials in a quantum-gas microscope to study commensurate\nand incommensurate 1D systems of interacting bosonic Rb atoms. Such\nincommensurate systems are analogous to doped insulating states that exhibit\natom transport and compressibility. Initially, a commensurate system with unit\nfilling and fixed atom number is prepared between two potential barriers. We\ndeterministically create an incommensurate system by dynamically changing the\nposition of the barriers such that the number of available lattice sites is\nreduced while retaining the atom number. Our systems are characterised by\nmeasuring the distribution of particles and holes as a function of the lattice\nfilling, and interaction strength, and we probe the particle mobility by\napplying a bias potential. Our work provides the foundation for preparation of\nlow-entropy states with controlled filling in optical-lattice experiments."
    },
    {
        "anchor": "Topological quantum critical points in the extended Bose-Hubbard model: The combination of topology and quantum criticality can give rise to an\nexotic mix of counterintuitive effects. Here, we show that unexpected\ntopological properties take place in a paradigmatic strongly-correlated\nHamiltonian: the 1D extended Bose-Hubbard model. In particular, we reveal the\npresence of two distinct topological quantum critical points with localized\nedge states and gapless bulk excitations. Our results show that the topological\ncritical points separate two phases, one topologically protected and the other\ntopologically trivial, both characterized by a long-range ordered string\ncorrelation function. The long-range order persists also at the topological\ncritical points and it reflects the presence of localized edge states protected\nby a finite charge gap. Finally, we introduce a super-resolution quantum gas\nmicroscopy scheme for dipolar dysprosium atoms, which provides a reliable route\ntowards the experimental study of topological quantum critical points.",
        "positive": "Universal Rephasing Dynamics after a Quantum Quench via Sudden Coupling\n  of Two Initially Independent Condensates: We consider a quantum quench in which two initially independent condensates\nare suddenly coupled, and study the subsequent \"rephasing\" dynamics. For weak\ncouplings, the time-evolution of physical observables is predicted to follow\nuniversal scaling laws, connecting the short-time dynamics to the long-time\nnon-perturbative regime. We first present a two-mode model valid in two and\nthree dimensions and then move to one dimension, where the problem is described\nby a gapped Sine-Gordon theory. Combining analytical and numerical methods, we\ncompute universal time-dependent expectation values, allowing a quantitative\ncomparison with future experiments."
    },
    {
        "anchor": "A general theory of flattened dipolar condensates: We develop theory for a flattened dipolar Bose-Einstein condensate (BEC)\nproduced by harmonic confinement along one direction. The role of both\nshort-ranged contact interactions and long-ranged dipole-dipole interactions\n(DDIs) is considered, and the dipoles are allowed to be polarised along an\narbitrary direction. We discuss the symmetry properties of the condensate and\nthe part of the excitation spectrum determining stability, and introduce two\neffective interaction parameters that allow us to provide a general description\nof the condensate properties, rotons, and stability. We diagonalize the full\ntheory to obtain benchmark results for the condensate and quasiparticle\nexcitations, and characterize the exact mean field stability of the system. We\nprovide a unified formulation for a number of approximate schemes to describe\nthe condensate and quasiparticles, including the standard quasi-two-dimensional\n(quasi-2D) approximation, two kinds of variational ansatz, and a Thomas-Fermi\n(TF) approximation. Some of these schemes have been widely used in the\nliterature despite not being substantiated against the exact theory. We provide\nthis validation and establish the regimes where the various theories perform\nwell.",
        "positive": "Spontaneous magnetization and anomalous Hall effect in an emergent Dice\n  lattice: Ultracold atoms in optical lattices serve as a tool to model different\nphysical phenomena appearing originally in condensed matter.\n  To study magnetic phenomena one needs to engineer synthetic fields as atoms\nare neutral.\n  Appropriately shaped optical potentials force atoms to mimic charged\nparticles moving in a given field. We present the realization of artificial\ngauge fields for the observation of anomalous Hall effect. Two species of\nattractively interacting ultracold fermions are considered to be trapped in a\nshaken two dimensional triangular lattice. A combination of interaction induced\ntunneling and shaking can result in an emergent Dice lattice. In such a lattice\nthe staggered synthetic magnetic flux appears and it can be controlled with\nexternal parameters. The obtained synthetic fields are non-Abelian. Depending\non the tuning of the staggered flux we can obtain either anomalous Hall effect\nor its quantized version. Our results are reminiscent of Anomalous Hall\nconductivity in spin-orbit coupled ferromagnets."
    },
    {
        "anchor": "Rossby-Haurwitz wave in a rotating bubble-shaped Bose-Einstein\n  condensate: A Rossby-Haurwitz (RH) wave is an excitation mode of a fluid on a rotating\nspherical surface, which propagates westward in the rotating frame of\nreference. Motivated by the recent realization of the shell-shaped\nBose-Einstein condensate in microgravity, we investigate the RH wave in a\nsuperfluid rotating on a spherical-surface geometry. We employ the point-vortex\nmodel and the three-dimensional Gross-Pitaevskii equation, and numerically\ndemonstrate that RH waves can be observed in the system of a superfluid with\nquantized vortices.",
        "positive": "Expansion dynamics of the Fulde-Ferrell-Larkin-Ovchinnikov state: We consider a two-component Fermi gas in the presence of spin imbalance,\nmodeling the system in terms of a one-dimensional attractive Hubbard\nHamiltonian initially in the presence of a confining trap potential. With the\naid of the time-evolving block decimation method, we investigate the dynamics\nof the initial state when the trap is switched off. We show that the dynamics\nof a gas initially in the Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) state is\ndecomposed into the independent expansion of two fluids, namely the paired and\nthe unpaired particles. In particular, the expansion velocity of the unpaired\ncloud is shown to be directly related to the FFLO momentum. This provides an\nunambiguous signature of the FFLO state in a remarkably simple way."
    },
    {
        "anchor": "Quantum fluctuations in atomic Josephson junctions: the role of\n  dimensionality: We investigate the role of quantum fluctuations in the dynamics of a bosonic\nJosephson junction in $D$ spatial dimensions, by using beyond mean-field\nGaussian corrections. We derive some key dynamical properties in a systematic\nway for $D=3, 2, 1$. In particular, we compute the Josephson frequency in the\nregime of low population imbalance. We also obtain the critical strength of the\nmacroscopic quantum self-trapping. Our results show that quantum corrections\nincrease the Josephson frequency in spatial dimensions $D=2$ and $D=3$, but\nthey decrease it in the $D=1$ case. The critical strength of macroscopic\nquantum self-trapping is instead reduced by quantum fluctuations in $D=2$ and\n$D=3$ cases, while it is enhanced in the $D=1$ configuration. We show that the\ndifference between the cases of D = 2 and D = 3 on one side, and D = 1 on the\nother, can be related to the qualitatively different dependence of the\ninteraction strength on the scattering length in the different dimensions.",
        "positive": "Momentum Dependent Higher Partial Wave Interactions in Bose Einstein\n  condensate: We have investigated the role of momentum dependent s-wave and higher partial\nwave strong interactions to determine the ground state properties and the\ncolumn densities in the Bose-Einstein condensate (BEC) for large scattering\nlength (a) such that ka >>1 even for small values of momentum where the\nmomentum p=(h/2pi)k and k is the wave number. Since the scattering length is\nlarge we have included the first correction (Lee-Huang-Yang correction) both\nfor the k-dependent (s-wave + higher partial wave) interactions and\nk-independent contact interactions (s-wave). We have derived the\ntime-independent equations from the corresponding energy functionals and found\nthat the ground state properties and the column densities differ significantly\nfor these two types of interactions even for moderate values of scattering\nlength (a = 3000 a_0) in BEC of cylindrically trapped 85Rb atoms at 100 nK. The\neffect of higher partial wave (d-wave) increases with increase in a and it is >\n20% for peak density at a= 8700 a_0 which can be experimentally detected.\nDependence of column density on particle number density has been studied.\nColumn densities have been compared with experimental results."
    },
    {
        "anchor": "The Equation of State of the Unitary Fermi Gas: An Update on Lattice\n  Calculations: The thermodynamic properties of the unitary Fermi gas (UFG) have recently\nbeen measured to unprecedented accuracy at the MIT. In particular, these\nmeasurements provide an improved understanding of the regime below T/eF ~ 0.20,\nwhere a transition into a superfluid phase occurs. In light of this\ndevelopment, we present an overview of state-of-the-art auxiliary field quantum\nMonte Carlo (AFQMC) results for the UFG at finite temperature and compare them\nwith the MIT data for the energy, chemical potential, and density. These AFQMC\nresults have been obtained using methods based on the hybrid Monte Carlo (HMC)\nalgorithm, which was first introduced within the context of lattice QCD.",
        "positive": "Molecular state in a spin-orbital-angular-momentum coupled Fermi gas: We study the two-body bound states in a spin-orbital-angular-momentum (SOAM)\ncoupled quantum gas of fermions. Two different configurations are considered:\nan attractive $s$-wave interaction exists between two spin species that are\nSOAM coupled; and an atom with SOAM coupled internal spins interacts\nstate-selectively with another atom. For both cases, we identify the condition\nfor the emergence of molecular states with finite total angular momenta.These\nmolecular states with quantized total angular momenta correspond to the\nSOAM-coupling-induced vortices in the corresponding Fermi superfluid. We\npropose to detect the molecules through Raman spectroscopy with\nLaguerre-Gaussian lasers. As the molecular states can form above the superfluid\ntemperature, they offer an experimentally more accessible route toward the\nstudy of the underlying pairing mechanism under SOAM coupling."
    },
    {
        "anchor": "Reentrant phase behavior in systems with density-induced tunneling: Open many body quantum systems play a paramount role in various branches of\nphysics, such as quantum information, nonlinear optics or condensed matter. The\ndissipative character of open systems has gained a lot of interest especially\nwithin the fields of quantum optics, due to unprecedented stabilization of\nquantum coherence, and quantum information, with its desire to control\nenvironmental degrees of freedom. We look beyond the typical mechanism of\ndissipation associated with an external source and show that strongly\ninteracting many particle systems can create quantum decoherence within\nthemselves. We study a quantum bosonic two-dimensional many body system with\nextended interactions between particles. Analytical calculations show that the\nsystem can be driven out of its coherent state, which is prevalent among\ncommonly used setups. However, we also observe a revival of the superfluid\nphase within the same framework for sufficiently large interaction strength.\nThe breakdown of quantum coherence is inevitable, but can be misinterpreted if\none assumes improper coupling between the constituents of the many particle\nsystem. We show an adequate path to retrieve physically relevant results and\nconsider its limitations. The system displays a natural cutoff that enforces\nthe breakdown of superfluidity.",
        "positive": "Phase diagram of a generalized off-diagonal Aubry-Andr\u00e9 model with\n  p-wave pairing: Off-diagonal Aubry-Andr\\'{e} (AA) model has recently attracted a great deal\nof attention as they provide condensed matter realization of topological\nphases. We numerically study a generalized off-diagonal AA model with p-wave\nsuperfluid pairing in the presence of both commensurate and incommensurate\nhopping modulations. The phase diagram as functions of the modulation strength\nof incommensurate hopping and the strength of the p-wave pairing is obtained by\nusing the multifractal analysis. We show that with the appearance of the p-wave\npairing, the system exhibits mobility-edge phases and critical phases with\nvarious number of topologically protected zero-energy modes. Predicted\ntopological nature of these exotic phases can be realized in a cold atomic\nsystem of incommensurate bichromatic optical lattice with induced p-wave\nsuperfluid pairing by using a Raman laser in proximity to a molecular\nBose-Einstein condensation."
    },
    {
        "anchor": "Parafermionic zero modes in ultracold bosonic systems: Exotic topologically protected zero modes with parafermionic statistics (also\ncalled fractionalized Majorana modes) have been proposed to emerge in devices\nfabricated from a fractional quantum Hall system and a superconductor. The\nfractionalized statistics of these modes takes them an important step beyond\nthe simplest non-Abelian anyons, Majorana fermions. Building on recent advances\ntowards the realization of fractional quantum Hall states of bosonic ultracold\natoms, we propose a realization of parafermions in a system consisting of\nBose-Einstein-condensate trenches within a bosonic fractional quantum Hall\nstate. We show that parafermionic zero modes emerge at the endpoints of the\ntrenches and give rise to a topologically protected degeneracy. We also discuss\nmethods for preparing and detecting these modes.",
        "positive": "Nonequilibrium dynamics of weakly and strongly paired superconductors: We study small oscillations of the order parameter in weakly and strongly\npaired superconductors driven slightly out of equilibrium, in the collisionless\napproximation. While it was known for quite some time that the amplitude of the\noscillations in a weakly paired superconductor decays as 1/t^(1/2), we show\nthat in a superconductor sufficiently strongly paired so that its fermions form\nbound states usually referred to as molecules, these oscillations decay as\n1/t^(3/2). The transition between these two regimes happens when the chemical\npotential of the superconductor vanishes, thus the behavior of the oscillations\ncan be used to distinguish weakly and strongly paired superconductors. These\nresults are obtained in the mean field approximation which may not be reliable\nin the crossover region between the strong and weak pairing, so we also obtain\nidentical results within the two-channel model, which can be tuned to be\nreliable throughout the entire crossover, although it then describes a special\ntype of interactions between the fermions which may be difficult to observe\nexperimentally. Finally, we interpret the result in the strongly paired\nsuperconductor as the probability of the molecular decay as a function of time."
    },
    {
        "anchor": "Change in the adiabatic invariant in a nonlinear Landau-Zener problem: We study a nonlinear generalization of the Landau-Zener resonance-crossing\nproblem relevant to coherent photo- and magneto-association of ultracold atoms.\nDue to the structure of the corresponding classical phase space, the adiabatic\ntheorem breaks down even at very small sweep rates, and the adiabatic\napproximation diverges because of the crossing of a separatrix. First, by\nintroducing a complex term into the Hamiltonian of the system, we eliminate\nthis divergence and construct a valid zero-order approximation. Further, taking\ninto account that the molecular conversion efficiency and the change of the\nclassical adiabatic invariant at the separatrix crossing are related\nquantities, we calculate the change of the action for the situation when the\nsystem starts from the all-atomic state that corresponds to the case of zero\ninitial action. The absolute error of the presented formula for the change in\nthe action is of the order of or less than 10^-4.",
        "positive": "On a scale-invariant Fermi gas in a time-dependent harmonic potential: We investigate a scale-invariant two-component Fermi gas in a time-dependent\nisotropic harmonic potential. The exact time evolution of the density\ndistribution in position space in any spatial dimension is obtained. Two\nexperimentally relevant examples, an abrupt change and a periodic modulation of\nthe trapping frequency are solved. Small deviations from scale invariance and\nisotropy of the confinement are addressed within first order perturbation\ntheory. We discuss the consequences for experiments with ultracold quantum\ngases such as the excitation of a tower of undamped breathing modes and a new\nalternative for measuring the Tan contact."
    },
    {
        "anchor": "Momentum resolved Floquet-engineered pair and single particle filter in\n  the Fermi Hubbard model: We investigate the transport properties of a Fermi-Hubbard chain with an\nimpurity which is formed by a site with a periodically modulated chemical\npotential. We determine the momentum resolved transmission through this\nimpurity in dependence of the modulation frequency and strength for a single\nparticle and a pair of fermions. We find that the pair transmission has a very\ndistinct behaviour from the single particle transmission. Different situations\ncan occur, where only the single particle or the pair with a certain momentum\nare transmitted or filtered out.",
        "positive": "Gauge-Symmetry Violation Quantum Phase Transition in Lattice Gauge\n  Theories: Gauge symmetry plays a key role in our description of subatomic matter. The\nvanishing photon mass, the long-ranged Coulomb law, and asymptotic freedom are\nall due to gauge invariance. Recent years have seen tantalizing progress in the\nmicroscopic reconstruction of gauge theories in engineered quantum simulators.\nYet, many of these are plagued by a fundamental question: When gauge symmetry\nis only approximate in the quantum device, do we actually quantum-simulate a\ngauge theory? Here, we answer this question in the affirmative for a paradigm\ngauge theory akin to quantum electrodynamics. Analytically, we derive a\nrenormalized gauge symmetry that is at least exponentially accurate. Further,\nnumerically computing the phase diagram in the thermodynamic limit, we find\nthat the long-distance behavior of the gauge theory is only compromised upon\nreaching a sharp quantum phase transition. This behavior is enabled by an\nenergy penalty term, which lends a mass to the Higgs boson to which the\ncoherent gauge breaking couples. Our results not only lend validity to ongoing\ngauge-theory quantum simulations, they also probe the fundamental question of\nhow gauge symmetry could emerge in nature."
    },
    {
        "anchor": "Dynamics of a solitonic vortex in an anisotropically trapped superfluid: We analytically study the dynamics of a solitonic vortex (SV) in a superfluid\nconfined in a non-axisymmetric harmonic trap. The study provides a framework\nfor analyzing the role of the trap anisotropy in the oscillation of SVs\nobserved in recent experiments on atomic Bose and Fermi superfluids. The\nemergence of common and statistics-dependent features is traced in a unified\napproach to both types of fluid. Our description, built in the hydrodynamic\nformalism, is based on a Lagragian approach which incorporates the vortex\nlocation as dynamical parameters of a variational ansatz. Previous operative\nHamiltonian pictures are recovered through a canonically traced procedure. Our\nresults improve the understanding of the experimental findings. Some of the\nobserved features are shown to be specific to the tri-axial anisotropy of the\ntrap. In particular, we characterize the nontrivial dependence of the\noscillation frequency on the trapping transversal to the vortical line. The\nstudy reveals also the crucial role played by the nonlinear character of the\ndynamics in the observed oscillation: for the considered experimental\nconditions, the frequency, and, in turn, the effective inertial mass of the\nvortex, are found to significantly depend on the amplitude of the generated\nmotion. It is also uncovered how the coupling with collective modes of the\nfluid induces a non-negligible shift in the oscillation frequency. The\nappearance of fine-structure features in the SV trajectory is predicted.",
        "positive": "Ground-state properties of the one-dimensional attractive Hubbard model\n  with confinement: a comparative study: We revisit the one-dimensional attractive Hubbard model by using the\nBethe-ansatz based density-functional theory and density-matrix renormalization\nmethod. The ground-state properties of this model are discussed in details for\ndifferent fillings and different confining conditions in weak-to-intermediate\ncoupling regime. We investigate the ground-state energy, energy gap, and\npair-binding energy and compare them with those calculated from the canonical\nBardeen-Cooper-Schrieffer approximation. We find that the Bethe-ansatz based\ndensity-functional theory is computationally easy and yields an accurate\ndescription of the ground-state properties for weak-to-intermediate interaction\nstrength, different fillings, and confinements. In order to characterize the\nquantum phase transition in the presence of a harmonic confinement, we\ncalculate the thermodynamic stiffness, the density-functional fidelity, and\nfidelity susceptibility, respectively. It is shown that with the increase of\nthe number of particles or attractive interaction strength, the system can be\ndriven from the Luther-Emery-type phase to the composite phase of\nLuther-Emery-like in the wings and insulating-like in the center."
    },
    {
        "anchor": "Probing the supersolid order via high-energy scattering: analytical\n  relations among response, density modulation, and superfluid fraction: High-energy scattering spectroscopy is a widely-established technique for\nprobing the characteristic properties of complex physical systems. Motivated by\nthe recent observation of long-sought supersolid states in dipolar quantum Bose\ngases, I investigate the general relationships existing between the density\ncontrast, the superfluid fraction, and the response to a high-energy scattering\nprobe of density-modulated states within a classical-field approach. I focus on\nthe two extreme regimes of \"shallow\" and \"deep\" supersolids, which are of\nparticular interest in describing the phase transitions of the supersolid to a\nuniform superfluid and an incoherent crystal state, respectively. Using\nrelevant Ans\\\"atze for the fields of dipolar supersolid states in these\nregimes, I specify and illustrate the scaling laws relating the three\nobservables. This work was first prompted to develop an intuitive understanding\nof a concomitant study based on experiments and mean-field numerical\nsimulations. Beyond this specific application, this works provides a simple and\ngeneral framework to describe density-modulated states, and in particular the\nintriguing case of supersolids. It describes key properties characterizing the\nsupersolid order and highlights new possibilities for probing such properties\nbased on high-energy scattering response.",
        "positive": "Measurement of Identical Particle Entanglement and the Influence of\n  Antisymmetrisation: We explore the relationship between symmetrisation and entanglement through\nmeasurements on few-particle systems in a multi-well potential. In particular,\nconsidering two or three trapped atoms, we measure and distinguish correlations\narising from two different physical origins: antisymmetrisation of the\nfermionic wavefunction and interaction between particles. We quantify this\nthrough the entanglement negativity of states, and the introduction of an\nantisymmetric negativity, which allows us to understand the role that\nsymmetrisation plays in the measured entanglement properties. We apply this\nconcept both to pure theoretical states and to experimentally reconstructed\ndensity matrices of two or three mobile particles in an array of optical\ntweezers."
    },
    {
        "anchor": "Comment on \"Coherent Ratchets in Driven Bose-Einstein Condensates\": C. E. Creffield and F. Sols (Phys. Rev. Lett. 103, 200601 (2009)) recently\nreported finite, directed time-averaged ratchet current, for a noninteracting\nquantum particle in a periodic potential even when time-reversal symmetry\nholds. As we explain in this Comment, this result is incorrect, that is,\ntime-reversal symmetry implies a vanishing current.",
        "positive": "Non-thermal fixed points: universality, topology, & turbulence in Bose\n  gases: In these notes we discuss recent developments in the field of non-equilibrium\nquantum dynamics. Specifically, we consider nearly coherent Bose gases brought\nfar out of equilibrium and study their behaviour in view of connections between\nuniversal properties, (quasi-)topological field configurations and turbulent\ndynamics. We demonstrate that the isolated Bose gas, on its way back to thermal\nequilibrium, can approach metastable non-equilibrium configurations and spend a\nlong time in their vicinity. In such configurations, which have been termed\nnon-thermal fixed points, the system shows universal long-range properties\nmanifest through scaling, i.e., self-similar correlations. The spatial field\npattern, at the same time, is characterized by the appearance of defects and\ndomain formation whose geometry gives rise to the particular scaling laws seen\nin the correlation functions. We obtain an overall picture which connects\nwell-known concepts for describing universal dynamics such as wave-turbulence,\nsuperfluid turbulence, and (quasi-)topological excitations. This allows to\nbring together a wide range of concepts and methods with a large spectrum of\napplications."
    },
    {
        "anchor": "Quantum gas microscopy with spin, atom-number and multi-layer readout: Atom- and site-resolved experiments with ultracold atoms in optical lattices\nprovide a powerful platform for the simulation of strongly correlated\nmaterials. In this letter, we present a toolbox for the preparation, control\nand site-resolved detection of a tunnel-coupled bilayer degenerate quantum gas.\nUsing a collisional blockade, we engineer occupation-dependent inter-plane\ntransport which enables us to circumvent light-assisted pair loss during\nimaging and count n=0 to n=3 atoms per site. We obtain the first number- and\nsite-resolved images of the Mott insulator \"wedding cake\" structure and observe\nthe emergence of antiferromagnetic ordering across a magnetic quantum phase\ntransition. We are further able to employ the bilayer system for spin-resolved\nreadout of a mixture of two hyperfine states. This work opens the door to\ndirect detection of entanglement and Kosterlitz-Thouless-type phase dynamics,\nas well as studies of coupled planar quantum materials.",
        "positive": "Fulde-Ferrell states in unequally charged Fermi gases: Atoms with different internal states can exhibit different responses to an\nartificial magnetic field. An atomic gas mixture of two different components\ncan therefore be interpreted as a mixture of two atomic gases carrying\ndifferent synthetic charges. We consider the superfluid state of such unequally\ncharged Fermi gases coupled to a magnetic field via the orbital effect and\ntrapped in a torus geometry. The orbital coupling to the magnetic field favors\nan inhomogeneous superfluid state with optimum finite center-of-mass momentum\npairing. The resulting population-balanced orbital Fulde-Ferrell (FF) state is\nrobust against the magnetic field and does not undergo pair breaking unlike the\nconventional BCS and Fulde-Ferrell-Larkin-Ovchinnikov type pairing states under\nthe Zeeman effect. We contrast the homogeneous and inhomogeneous cases\nemphasizing the advantages of the unequally charged systems and present their\nmomentum distributions. We conclude that an unequally charged atomic Fermi gas\nsystem orbitally coupled to an artificial magnetic field provides an ideal\ncandidate for experimental realization of the FF state."
    },
    {
        "anchor": "An ultracold analogue to star formation: Spontaneous concentration of\n  energy in trapped quantum gases: Stars form when cold cosmic nebulae spontaneously develop hot spots that\nsteadily intensify until they reach fusion temperatures. Without this process,\nthe universe would be dark and dead. Yet the spontaneous concentration of heat\nis exactly what the Second Law of Thermodynamics is in most cases supposed to\nforbid. The formation of protostars has been much discussed, for its\nconsistency with the Second Law depends on a thermodynamical property that is\ncommon in systems whose strongest force is their own gravity, but otherwise\nvery rare: negative specific heat. Negative specific heat turns the world\nupside down, thermodynamically; it implies that entropy increases when energy\nflows from lower to higher energy subsystems, opposite to the usual direction.\nRecent experiments have reported negative specific heat in melting atomic\nclusters and fragmenting nuclei, but these arguably represent transient\nphenomena outside the proper scope of thermodynamics. Here we show that the\ncounter-intuitive thermodynamics of spontaneous energy concentration can be\nstudied experimentally with trapped quantum gases, by using optical lattice\npotentials to realize weakly coupled arrays of simple dynamical subsystems that\nshare the peculiar property of self-gravitating protostars, of having negative\nmicro-canonical specific heat. Numerical solution of real-time evolution\nequations confirms the spontaneous concentration of energy in such arrays, with\ninitially dispersed energy condensing quickly into dense 'droplets'. We\ntherefore propose laboratory studies of negative specific heat as an elusive\nbut fundamentally important aspect of thermodynamics, which may shed fresh\nlight on the general problem of how thermodynamics emerges from mechanics.",
        "positive": "Faraday waves in collisionally inhomogeneous Bose-Einstein condensates: We study the emergence of Faraday waves in cigar-shaped collisionally\ninhomogeneous Bose-Einstein condensates subject to periodic modulation of the\nradial confinement. Considering a Gaussian-shaped radially inhomogeneous\nscattering length, we show through extensive numerical simulations and detailed\nvariational treatment that the spatial period of the emerging Faraday waves\nincreases as the inhomogeneity of the scattering length gets weaker, and that\nit saturates once the width of the radial inhomogeneity reaches the radial\nwidth of the condensate. In the regime of strongly inhomogeneous scattering\nlengths, the radial profile of the condensate is akin to that of a hollow\ncylinder, while in the weakly inhomogeneous case the condensate is cigar-shaped\nand has a Thomas-Fermi radial density profile. Finally, we show that when the\nfrequency of the modulation is close to the radial frequency of the trap, the\ncondensate exhibits resonant waves which are accompanied by a clear excitation\nof collective modes, while for frequencies close to twice that of the radial\nfrequency of the trap, the observed Faraday waves set in forcefully and quickly\ndestabilize condensates with weakly inhomogeneous two-body interactions."
    },
    {
        "anchor": "d-Wave Superfluidity in Optical Lattices of Ultracold Polar Molecules: Recent work on ultracold polar molecules, governed by a generalization of the\nt-J Hamiltonian, suggests that molecules may be better suited than atoms for\nstudying d-wave superfluidity due to stronger interactions and larger\ntunability of the system. We compute the phase diagram for polar molecules in a\ncheckerboard lattice consisting of weakly coupled square plaquettes. In the\nsimplest experimentally realizable case where there is only tunneling and an\nXX-type spin-spin interaction, we identify the parameter regime where d-wave\nsuperfluidity occurs. We also find that the inclusion of a density-density\ninteraction destroys the superfluid phase and that the inclusion of a\nspin-density or an Ising-type spin-spin interaction can enhance the superfluid\nphase. We also propose schemes for experimentally realizing the perturbative\ncalculations exhibiting enhanced d-wave superfluidity.",
        "positive": "Breakdown of scale invariance in a quasi-two-dimensional Bose gas due to\n  the presence of the third dimension: In this Rapid Communication, we describe how the presence of the third\ndimension may break the scale invariance in a two-dimensional Bose gas in a\npancake-shaped trap. From the two-dimensional perspective, the possibility of a\nweak spilling of the atomic density beyond the ground-state of the confinement\nalters the two-dimensional chemical potential; in turn, this correction no\nlonger supports scale invariance. We compare experimental data with numerical\nand analytic perturbative results and find a good agreement."
    },
    {
        "anchor": "First Principles Prediction of the Landau Parameter for Fermi Liquids\n  near the Unitarity Limit: This paper explores the behavior of systems of cold fermions as they approach\nunitarity above the critical temperature. As we move away from unitarity, by\ndecreasing the scattering length, the dilaton, the Goldstone boson resulting\nfrom the spontaneous breaking of Schrodinger symmetry by the Fermi sea, becomes\ngapped. At energies below this gap, the interaction between quasi-particles\nwill be dominated by local interactions generated by off-shell dilaton\nexchange. The dilaton mass can, in turn, be related via anomaly matching, to\nthe scattering length and contact parameter within the confines of a systematic\nexpansion. We use this relation to predict the s-wave Landau parameter to be\n$f=\\frac{4\\pi a (2\\epsilon(p_F)-p_F^2/m_\\star)^2 m}{3p_F^4 \\tilde{C}(a)}$ where\n$a$ is the scattering length, $m$ the atomic mass, $m_\\star$, the effective\nmass which can be extracted from heat capacity, and $\\tilde {C}(a)$ is the\ndimensionless contact parameter. The range of validity of this prediction\n(given in eq.(21)) is determined by the value of contact parameter and Fermi\nvelocity, which depend upon the scattering length. It is expected to be valid\nin a range above $k_F a \\sim 1$, but the actual window will depend upon the\nvalues of aforementioned parameters. Given this result for $f$, we predict the\ncompressibility, spin susceptibility and the quasi-particle life-time.",
        "positive": "Creation and counting of defects in a temperature quenched Bose-Einstein\n  Condensate: We study the spontaneous formation of defects in the order parameter of a\ntrapped ultracold bosonic gas while crossing the critical temperature for\nBose-Einstein Condensation (BEC) at different rates. The system has the shape\nof an elongated ellipsoid, whose transverse width can be varied to explore\ndimensionality effects. For slow enough temperature quenches we find a\npower-law scaling of the average defect number with the quench rate, as\npredicted by the Kibble-Zurek mechanism. A breakdown of such a scaling is found\nfor fast quenches, leading to a saturation of the average defect number. We\nsuggest an explanation for this saturation in terms of the mutual interactions\namong defects."
    },
    {
        "anchor": "Self-consistent determination of the many-body state of ultracold\n  bosonic atoms in a one-dimensional harmonic trap: We study zero-temperature quantum fluctuations in harmonically trapped\none-dimensional interacting Bose gases, using the self-consistent\nmulticonfigurational time-dependent Hartree method. We define $phase$\n$fluctuations$ from the full single-particle density matrix by the spatial\ndecay exponent of off-diagonal long-range order. In a regime of mesoscopic\nparticle numbers and moderate contact couplings, we derive the spatial\ndependence of the amplitude of phase fluctuations, determined from the {\\em\nself-consistently} derived shape of the field operator orbitals and Fock space\norbital occupation amplitudes. It is shown that the phase fluctuations display\na peak, which in turn corresponds to a dip of the first-order correlations in\nposition space, akin to what has previously been obtained in the\nTonks-Girardeau limit of very large interactions and low densities.",
        "positive": "Intertwined and vestigial order with ultracold atoms in multiple cavity\n  modes: Atoms in transversely pumped optical cavities \"self-organize\" by forming a\ndensity wave and emitting superradiantly into the cavity mode(s). For a\nsingle-mode cavity, the properties of this self-organization transition are\nwell characterized both theoretically and experimentally. Here, we explore the\nself-organization of a Bose-Einstein condensate in the presence of two cavity\nmodes---a system that was recently experimentally realized [Leonard \\emph{et\nal.}, \\emph{Nature} {\\bf 543}, 87 (2017)]. We argue that this system can\nexhibit a \"vestigially ordered\" phase in which neither cavity mode exhibits\nsuperradiance but the cavity modes are mutually phase-locked by the atoms. We\nargue that this vestigially ordered phase should generically be present in\nmultimode cavity geometries."
    },
    {
        "anchor": "Proposal to directly observe the Kondo effect through enhanced\n  photo-induced scattering of cold fermionic and bosonic atoms: We propose an experimental protocol to directly observe the Kondo effect by\nscattering ultracold atoms with spin-dependent interactions. We propose using\nan optical Feshbach resonance to engineer Kondo-type spin-dependent\ninteractions in a system with ultracold $^6$Li and $^{87}$Rb gases. We\ncalculate the momentum transferred from the $^{87}$Rb gas to the $^6$Li gas in\na scattering experiment and show that it has a logarithmically enhanced\ntemperature dependence, characteristic of the Kondo effect and analogous to the\nresistivity of alloys with magnetic impurities. Experimentally detecting this\nenhancement will give a different perspective on the Kondo effect, and allow us\nto explore a rich variety of problems such as the Kondo lattice problem and\nheavy-fermion systems.",
        "positive": "On topological order in higher composites: The recent experiments reported observation of a state with symmetry-breaking\nappearing at the level of four-electron order parameter (electronic quadruplets\ncondensation) in a multicomponent system. This is in contrast to the\nconventional case where order appears at the level of electron pairing fields.\nRelated states were theoretically demonstrated in mixtures of ultracold atoms.\n  Here, we discuss the topological counterparts of this concept, i.e.,\ntopological order appearing only in higher-than-usual composites under somewhat\nrelated circumstances in multicomponent systems."
    },
    {
        "anchor": "Exact quantum dynamics of yrast states in the finite 1D Bose gas: We demonstrate that the quantum dynamics of yrast states in the\none-dimensional (1D) Bose gas gives an illustrative example to equilibration of\nan isolated quantum many-body system. We first formulate the energy spectrum of\nyrast states in terms of the dressed energy by applying the method of\nfinite-size corrections. We then review the exact time evolution of quantum\nstates constructed from yrast states shown by the Bethe ansatz. In time\nevolution the density profile of an initially localized quantum state\nconstructed from yrast states collapses into a flat profile in the case of a\nlarge particle number such as N=1000, while recurrence of the localized state\noccurs in the case of a small particle number such as N=20. We suggest that the\ndynamical relaxation behavior for the large N case is consistent with the\nviewpoint of typicality for generic quantum states: the expectation values of\nlocal operators valuated in most of quantum states are very close to those of\nthe micro-canonical ensemble.",
        "positive": "Phase diagram of spatiotemporal instabilities in a large magneto-optical\n  trap: Large clouds of cold atoms prepared in a magneto-optical trap are known to\npresent spatiotemporal instabilities when the frequency of the trapping lasers\nis brought close to the atomic resonance. This system bears similarities with\ntrapped plasmas where the role of the Coulomb interaction is played by the\nexchange of scattered photons, and astrophysical objects such as stars whose\nsize is dependent on radiative forces. We present in this paper a study of the\nphase-space of such instabilities, and reveal different dynamical regimes.\nThree dimensional simulations of the highly nonlinear atomic dynamics permit a\ndetailed analysis of the experimental observations."
    },
    {
        "anchor": "Renormalized analytic solution for the enstrophy cascade in\n  two-dimensional quantum turbulence: The forward enstrophy cascade in two-dimensional quantum turbulence in a\nsuperfluid film connected to a thermal bath is investigated using a\nFokker-Planck equation based on Kosterlitz-Thouless renormalization. The\nsteady-state cascade is formed by injecting vortex pairs of large initial\nseparation at a constant rate. They diffuse with a constant flux to smaller\nscales, finally annihilating when reaching the core size. The energy spectrum\nvaries as $k^{-3}$, similar to the spectrum known for 2D classical-fluid\nenstrophy cascades. The dynamics of the cascade can also be studied, and for\nthe case of a sharply peaked initial vortex-pair distribution, it takes about\nfour eddy turnover times for the system to evolve to the decaying $k^{-3}$\ncascade, in agreement with recent computer simulations. These insights into the\nnature of the cascade also allow a better understanding of the phase-ordering\nprocess of temperature-quenched 2D superfluids, where the decay of the\nvorticity is found to proceed via the turbulent cascade. This connection with\nturbulence may be a fundamental characteristic of phase-ordering in general.",
        "positive": "A semiclassical field theory that is freed of the ultraviolet\n  catastrophe: A more accurate semiclassical theory for ultracold gases is derived, in which\nthe occupation of high energy modes is dynamically constrained to the\nBose-Einstein distribution. This regularized version of the SGPE model\npreserves the proper nonlinear energy dependence of coupling to the thermal\nreservoir. As a result, inclusion of high energy modes above $k_BT$ does not\ncause a UV divergence. Instead, the reservoir becomes a constraint on the high\nenergy tails which are included explicitly in the system. Millions of modes can\nbe treated because computational cost scales slowly, like in other\nsemiclassical methods. Implementations in 1d and 3d are presented, among them\nan accurate treatment of the famous case of the quadrupole mode (Jin et al,\n1997), which had so far eluded satisfactory simulations with any field theory.\nOur study reveals that observed frequencies and damping of the thermal cloud\ndepended on the experimental signal to noise ratio."
    },
    {
        "anchor": "Resonant Control of Interaction Between Different Electronic States: We observe a magnetic Feshbach resonance in a collision between the ground\nand metastable states of two-electron atoms of ytterbium (Yb). We measure the\non-site interaction of doubly-occupied sites of an atomic Mott insulator state\nin a three-dimensional optical lattice as a collisional frequency shift in a\nhigh-resolution laser spectroscopy. The observed spectra are well fitted by a\nsimple theoretical formula, in which two particles with an s-wave contact\ninteraction are confined in a harmonic trap. This analysis reveals a wide\nvariation of the interaction with a resonance behavior around a magnetic field\nof about 1.1 Gauss for the energetically lowest magnetic sublevel of\n${}^{170}$Yb, as well as around 360 mG for the energetically highest magnetic\nsublevel of ${}^{174}$Yb. The observed Feshbach resonance can only be induced\nby an anisotropic inter-atomic interaction. This novel scheme will open the\ndoor to a variety of study using two-electron atoms with tunable interaction.",
        "positive": "Exploiting quantum coherence of polaritons for ultra sensitive detectors: Besides being superfluids, microcavity exciton-polariton condensates are\ncapable of spontaneous pattern formation due to their forced-dissipative\ndynamics. Their macroscopic and easily detectable response to small\nperturbations can be exploited to create sensitive devices. We show how\ncontrolled pumping in the presence of a peak-dip shaped potential can be used\nto detect small externally applied velocities which lead to the formation of\ntraveling holes in one dimension and vortex pairs in two dimensions. Combining\nan annulus geometry with a weak link, the set up that we describe can be used\nto create a sensitive polariton gyroscope."
    },
    {
        "anchor": "Generation and Detection of Atomic Spin Entanglement in Optical Lattices: Ultracold atoms in optical lattices offer a great promise to generate\nentangled states for scalable quantum information processing owing to the\ninherited long coherence time and controllability over a large number of\nparticles. We report on the generation, manipulation and detection of atomic\nspin entanglement in an optical superlattice. Employing a spin-dependent\nsuperlattice, atomic spins in the left or right sites can be individually\naddressed and coherently manipulated by microwave pulses with near unitary\nfidelities. Spin entanglement of the two atoms in the double wells of the\nsuperlattice is generated via dynamical evolution governed by spin\nsuperexchange. By observing collisional atom loss with in-situ absorption\nimaging we measure spin correlations of atoms inside the double wells and\nobtain the lower boundary of entanglement fidelity as $0.79\\pm0.06$, and the\nviolation of a Bell's inequality with $S=2.21\\pm 0.08$. The above results\nrepresent an essential step towards scalable quantum computation with ultracold\natoms in optical lattices.",
        "positive": "Electrically controlled mutual interactions of flying waveguide\n  dipolaritons: We show that with a system of electrically-gated wide quantum wells embedded\ninside a simple dielectric waveguide structure, it is possible to excite,\ncontrol, and observe waveguided exciton polaritons that carry an electric\ndipole moment. We demonstrate that the energy of the propagating dipolariton\ncan be easily tuned using local electrical gates, that their excitation and\nextraction can be easily done using simple evaporated metal gratings, and that\nthe dipolar interactions between polaritons and between polaritons and excitons\ncan also be controlled by the applied electric fields. This system of gated\nflying dipolaritons thus exhibit the ability to locally control both the single\npolariton properties as well as the interactions between polaritons, which\nshould open up opportunities for constructing complex polaritonic circuits and\nfor studying strongly-interacting, correlated polariton gases."
    },
    {
        "anchor": "Robust light bullets in Rydberg gases with moir\u00e9 lattice: Rydberg electromagnetically-induced transparency has been widely studied as a\nmedium supporting light propagation under the action of nonlocal\nnonlinearities. Recently, optical potentials based on moir\\'e lattices (MLs)\nwere introduced for exploring unconventional physical states. Here, we predict\na possibility of creating fully three-dimensional (3D) light bullets (LBs) in\ncold Rydberg gases under the action of ML potentials. The nonlinearity includes\nlocal self-defocusing and long-range focusing terms, the latter one induced by\nthe Rydberg-Rydberg interaction. We produce zero-vorticity LB families of the\nfundamental, dipole, and quadrupole types, as well as vortex LBs. They all are\ngap solitons populating finite bandgaps of the underlying ML spectrum. Stable\nsubfamilies are identified utilizing the combination of the\nanti-Vakhitov-Kolokolov criterion, computation of eigenvalues for small\nperturbations, and direct simulations.",
        "positive": "Tunneling Hamiltonian analysis of DC Josephson currents in a\n  weakly-interacting Bose-Einstein condensate: Atomtronics experiments with ultracold atomic gases allow us to explore\nquantum transport phenomena of a weakly-interacting Bose-Einstein condensate\n(BEC). Here, we focus on two-terminal transport of such a BEC in the vicinity\nof zero temperature. By using the tunnel Hamiltonian and Bogoliubov theory, we\nobtain a DC Josephson current expression in the BEC and apply it to\nexperimentally relevant situations such as quantum point contact and planar\njunction. Due to the absence of Andreev bound states but the presence of\ncouplings associated with condensation elements, a current-phase relation in\nthe BEC is found to be different from one in an s-wave superconductor. In\naddition, it turns out that the DC Josephson current in the BEC depends on the\nsign of tunneling elements, which allows to realize the so-called $\\pi$\njunction by using techniques of artificial gauge fields."
    },
    {
        "anchor": "Second sound with ultracold atoms: A brief historical account: We briefly review the research on second sound in ultracold atomic physics,\nwith emphasis on strongly interacting unitary Fermi gases with infinitely large\n$s$-wave scattering length. Second sound is a smoking-gun feature of\nsuperfluidity in any quantum superfluids. The observation and characterization\nof second sound in ultracold quantum gases has been a long-standing challenge,\nand in recent years there are rapid developments due to the experimental\nrealization of a uniform box-trap potential. The purpose of this review is to\npresent a brief historical account of the key research activities on second\nsound over the past two decades. We summarize the initial theoretical works\nthat reveal the characteristics of second sound in a unitary Fermi gas, and\nintroduce its first observation in a highly elongated harmonic trap. We then\ndiscuss the most recent measurement on second sound attenuation in a uniform\nsetup, which may open a new era to understand quantum transport near quantum\ncriticality in the strongly interacting regime. The observation of second sound\nin homogeneous weakly interacting Bose condensates in both two and three\ndimensions are also briefly introduced.",
        "positive": "Discrete truncated Wigner approach to dynamical phase transitions in\n  Ising models after a quantum quench: By means of the discrete truncated Wigner approximation we study dynamical\nphase transitions arising in the steady state of transverse-field Ising models\nafter a quantum quench. Starting from a fully polarized ferromagnetic initial\ncondition these transitions separate a phase with nonvanishing magnetization\nalong the ordering direction from a symmetric phase upon increasing the\ntransverse field. We consider two paradigmatic cases, a one-dimensional\nlong-range model with power-law interactions $\\propto 1/r^{\\alpha}$ decaying\nalgebraically as a function of distance $r$ and a two-dimensional system with\nshort-range nearest-neighbour interactions. In the former case we identify\ndynamical phase transitions for $\\alpha \\lesssim 2$ and we extract the critical\nexponents from a data collapse of the steady state magnetization for up to 1200\nlattice sites. We find identical exponents for $\\alpha \\lesssim 0.5$,\nsuggesting that the dynamical transitions in this regime fall into the same\nuniversality class as the nonergodic mean-field limit. The two-dimensional\nIsing model is believed to be thermalizing, which we also confirm using exact\ndiagonalization for small system sizes. Thus, the dynamical transition is\nexpected to correspond to the thermal phase transition, which is consistent\nwith our data upon comparing to equilibrium quantum Monte-Carlo simulations. We\nfurther test the accuracy of the discrete truncated Wigner approximation by\ncomparing against numerically exact methods such as exact diagonalization,\ntensor network as well as artificial neural network states and we find good\nquantitative agreement on the accessible time scales. Finally, our work\nprovides an additional contribution to the understanding of the range and the\nlimitations of qualitative and quantitative applicability of the discrete\ntruncated Wigner approximation."
    },
    {
        "anchor": "Emergence and Stability of Vortex Clusters in Bose-Einstein Condensates:\n  a Bifurcation Approach near the Linear Limit: We study the existence and stability properties of clusters of alternating\ncharge vortices in Bose-Einstein condensates. It is illustrated that such\nstates emerge from cascades of symmetry-breaking bifurcations that can be\nanalytically tracked near the linear limit of the system via weakly nonlinear\nfew-mode expansions. We present the resulting states that emerge near the first\nfew eigenvalues of the linear limit, and illustrate how the nature of the\nbifurcations can be used to understand their stability. Rectilinear, polygonal\nand diagonal vortex clusters are only some of the obtained states while mixed\nstates, consisting of dark solitons and vortex clusters, are identified as\nwell.",
        "positive": "P-wave Superfluidity by Blockade Effects in a Rydberg-Dressed Fermi Gas: We systematically investigate the p-wave superfluidity of a Rydberg-dressed\nFermi gas, where the soft-core effective interaction is of finite radius\n$R_{c}$ due to blockade effects. After solving the BCS gap equation and\ncomparing the free energy, we obtain the quantum phase diagram, which is\ncomposed of three different phases: polar ($p_{z}$), axial ($p_{x}+ip_{y}$),\nand axi-planar ($p_{x}+i\\beta_{p}p_{y}$) phases. The tri-critical point locates\naround $R_{c}k_{F}\\sim1$, where $k_{F}$ is the Fermi wave vector. We further\nderive the Ginzburg-Landau theory to explain the phase diagram, and estimate\nthe transition temperature to be about 0.1$E_{F}$ in the current experimental\nregime of $^{6}$Li. Our work paves the way for future studies on p-wave\nsuperfluids and related quantum phase transitions in ultracold atoms."
    },
    {
        "anchor": "Spin relaxation in a one-dimensional large-spin degenerate Fermi gas: In this work, we study the dynamics of an atomic harmonically trapped\nlarge-spin Fermi gas in one dimension (1D). We investigate the interplay of\ndifferent collision processes. Coherent spin oscillations, driven by\nspin-changing forward scattering are captured by a mean-field description and\nscale linearly with density regardless of the dimension of the system.\nConversely, \"incoherent\" collision processes which e.g. lead to the damping of\nspin oscillations, behave differently. In the usual three-dimensional (3D)\ncase, the rate of incoherent processes increases faster with density than\nmean-field effects, but in 1D it increases slower. This means, that in the 1D\ncase, incoherent collisions become more important at lower densities. We study\nthese effects by deriving and integrating a quantum Boltzmann equation. We\ndemonstrate that the well known fact that in one dimension, interaction-induced\ncorrelations become more dominant at low densities can be observed in\nfar-from-equilibrium spin dynamics.",
        "positive": "Collision dynamics and entanglement generation of two initially\n  independent and indistinguishable boson pairs in one-dimensional harmonic\n  confinement: We investigate finite number effects in collisions between two states of an\ninitially well known number of identical bosons with contact interactions,\noscillating in the presence of harmonic confinement in one dimension. We\ninvestigate two N/2 (interacting) ground states, which are initially displaced\nfrom the trap center, and the effects of varying interaction strength. The\nnumerics focus on the simplest case of N=4. In the non-interacting case, such a\nsystem would display periodic oscillation with a half harmonic oscillator\nperiod (due to the left-right symmetry). With the addition contact interactions\nbetween the bosons, collisions generate entanglement between each of the states\nand distribute energy into other modes of the oscillator. We study the system\nnumerically via an exact diagonalization of the Hamiltonian with a finite\nbasis, investigating left/right number uncertainty as our primary measure of\nentanglement. Additionally we study the time-evolution and equilibration of the\nsingle-body von Neumann entropy for both the attractive and repulsive cases. We\nidentify parameter regimes for which attractive interactions create\nqualitatively different behavior to repulsive interactions, due to the presence\nof bound states (quantum solitons) and explain the processes behind this."
    },
    {
        "anchor": "Many-Body Physics with Individually-Controlled Rydberg Atoms: Over the last decade, systems of individually-controlled neutral atoms,\ninteracting with each other when excited to Rydberg states, have emerged as a\npromising platform for quantum simulation of many-body problems, in particular\nspin systems. Here, we review the techniques underlying quantum gas microscopes\nand arrays of optical tweezers used in these experiments, explain how the\ndifferent types of interactions between Rydberg atoms allow a natural mapping\nonto various quantum spin models, and describe recent results that were\nobtained with this platform to study quantum many-body physics.",
        "positive": "Quantum fluctuation effects on the quench dynamics of thermal\n  quasicondensates: We study the influence of quantum fluctuations on the phase, density, and\npair correlations in a trapped quasicondensate after a quench of the\ninteraction strength. To do so, we derive a description similar to the\nstochastic Gross-Pitaevskii equation (SGPE) but keeping a fully quantum\ndescription of the low-energy fields using the positive-P representation. This\nallows us to treat both the quantum and thermal fluctuations together in an\nintegrated way. A plain SGPE only allows for thermal fluctuations. The approach\nis applicable to such situations as finite temperature quantum quenches, but\nnot equilibrium calculations due to the time limitations inherent in positive-P\ndescriptions of interacting gases. One sees the appearance antibunching, the\ngeneration of counter-propagating atom pairs, and increased phase fluctuations.\nWe show that the behavior can be estimated by adding the T=0 quantum\nfluctuation contribution to the thermal fluctuations described by the plain\nSGPE."
    },
    {
        "anchor": "Self-bound dipolar droplets and supersolids in molecular Bose-Einstein\n  condensates: We numerically study the many-body physics of molecular Bose-Einstein\ncondensates with strong dipole-dipole interactions. We observe the formation of\nself-bound droplets, and explore phase diagrams that feature a variety of\nexotic supersolid states. In all of these cases, the large and tunable\nmolecular dipole moments enable the study of unexplored regimes and phenomena,\nincluding liquid-like density saturation and universal stability scaling laws\nfor droplets, as well as pattern formation and the limits of droplet\nsupersolidity. We discuss a realistic experimental approach to realize both the\nrequired collisional stability of the molecular gases and the independent\ntunability of their contact and dipolar interaction strengths. Our work\nprovides both a blueprint and a benchmark for near-future experiments with bulk\nmolecular Bose-Einstein condensates.",
        "positive": "Quantized conductance through a dissipative atomic point contact: Signatures of quantum transport are expected to quickly vanish as dissipation\nis introduced in a system. This dissipation can take several forms, including\nthat of particle loss, which has the consequence that the total probability\ncurrent is not conserved. Here, we study the effect of such losses at a quantum\npoint contact (QPC) for ultracold atoms. Experimentally, dissipation is\nprovided by a near-resonant optical tweezer whose power and detuning control\nthe loss rates for the different internal atomic states as well as their\neffective Zeeman shifts. We theoretically model this situation by including\nlosses in the Landauer-B\\\"uttiker formalism over a wide range of dissipative\nrates. We find good agreement between our measurements and our model, both\nfeaturing robust conductance plateaus. Finally, we are able to map out the\natomic density by varying the position of the near-resonant tweezer inside the\nQPC, realizing a dissipative scanning gate microscope for cold atoms."
    },
    {
        "anchor": "Controlled generation and manipulation of vortex dipoles in a\n  Bose-Einstein condensate: We propose methods to generate and manipulate vortex dipoles in a\nBose-Einstein condensate using Gaussian beams of red or blue-detuned laser.\nVelocity-controlled vortex dipoles are shown to be created and launched by a\nred-detuned beam and by two blue-detuned beams. Critical velocities for the\nvortex nucleation are investigated. The launched vortex dipoles can be trapped,\ncurved, accelerated, and decelerated using Gaussian beams. Collisions between\nvortex dipoles are demonstrated.",
        "positive": "Computational Theory of a splitting BEC using a Generalized Wannier\n  basis I: Theory and Statics: We investigate the behavior of a Bose-Einstein Condensate (BEC) under the\ninfluence of a central barrier as the particle number trends towards the\nthermodynamic limit. In order to perform these studies, we present a novel\nmethod which is tractable in the large-$N$ limit. This method employs what may\nbe considered to be a generalized Wannier basis, which successfully\nincorporates features of previous theoretical and computational assays to the\nsplitting problem, including mean field effects, and has access to the\ndimensionality, trap parameters, and particle numbers relevant to recent\nexperiments. At any barrier height we are able to discern between a two-mode\nstate and a state which is described sufficiently by mean field theory and,\nfurther, give a criterion and technique for matching the two-mode theory to the\nzero-barrier state. We compare the basis used in this model to the de-localized\nbasis functions underlying alternate models used in recent theoretical work on\nthe double-well splitting problem and show that only the generalized Wannier\nbasis displays the level crossing and emergence of two complex order parameters\nwith overall $U(1) \\oplus U(1)$ symmetry as expected from a large-$N$ analogue\nof the Superfluid to Mott insulator transition. Using this model, we identify a\nuniversal structure, independent of $N$, in this phase transition. We also\npresent an analytic and model-independent description of this universal\nstructure and discuss its consequences for realizing true two-mode physics with\na BEC which trends towards the thermodynamic limit."
    },
    {
        "anchor": "Dynamical Zeeman resonance in spin-orbit-coupled spin-1 Bose gases: We predict a dynamical resonant effect, which is driven by externally applied\nlinear and quadratic Zeeman fields, in a spin-orbit-coupled spin-1\nBose-Einstein condensate. The Bose-Einstein condensate is assumed to be\ninitialized in some superposed state of Zeeman sublevels and subject to a\nsudden shift of the trapping potential. It is shown that the time-averaged\ncenter-of-mass oscillation and the spin polarizations of the Bose-Einstein\ncondensate exhibit remarkable resonant peaks when the Zeeman fields are tuned\nto certain strengths. The underlying physics behind this resonance can be\ntraced back to the out-of-phase interference of the dynamical phases carried by\ndifferent spinorbit states. By analyzing the single particle spectrum, the\nresonant condition is summarized as a simple algebraic relation, connecting the\nstrengths of the linear and quadratic Zeeman fields. This property is\npotentially applicable in quantum information and quantum precision\nmeasurement.",
        "positive": "Spectrum of collective excitations of a quantum fluid of polaritons: We use a recently developed high-resolution coherent probe spectroscopy\nmethod to investigate the dispersion of collective excitations of a polaritonic\nquantum fluid. We measure the dispersion relation with high energy and\nwavenumber resolution, which allows us to determine the speed of sound in the\nfluid and to evidence the contribution of an excitonic reservoir. We report on\nthe generation of collective excitations at negative energies, on the ghost\nbranch of the dispersion curve. Precursors of dynamical instabilities are also\nidentified. Our methods open the way to the precise study of quantum\nhydrodynamics of quantum fluids of light."
    },
    {
        "anchor": "Vortices and turbulence in trapped atomic condensates: After over a decade of experiments generating and studying the physics of\nquantized vortices in atomic gas Bose-Einstein condensates, research is\nbeginning to focus on the roles of vortices in quantum turbulence, as well as\nother measures of quantum turbulence in atomic condensates. Such research\ndirections have the potential to uncover new insights into quantum turbulence,\nvortices and superfluidity, and also explore the similarities and differences\nbetween quantum and classical turbulence in entirely new settings. Here we\npresent a critical assessment of theoretical and experimental studies in this\nemerging field of quantum turbulence in atomic condensates.",
        "positive": "Ground-state properties of unitary bosons: from clusters to matter: The properties of cold Bose gases at unitarity have been extensively\ninvestigated in the last few years both theoretically and experimentally. In\nthis paper we use a family of interactions tuned to two-body unitarity and very\nweak three-body binding to demonstrate the universal properties of both\nclusters and matter. We determine the universal properties of finite clusters\nup to 60 particles and, for the first time, explicitly demonstrate the\nsaturation of energy and density with particle number and compare with bulk\nproperties. At saturation in the bulk we determine the energy, density, two-\nand three-body contacts and the condensate fraction. We find that uniform\nmatter is more bound than three-body clusters by nearly two orders of\nmagnitude, the two-body contact is very large in absolute terms, and yet the\ncondensate fraction is also very large, greater than 90%. Equilibrium\nproperties of these systems may be experimentally accessible through rapid\nquenching of weakly-interacting boson superfluids."
    },
    {
        "anchor": "Majorana Zero Modes in Fermionic Wires coupled by Aharonov-Bohm Cages: We devise a number-conserving scheme for the realization of Majorana Zero\nModes in an interacting fermionic ladder coupled by Aharonov-Bohm cages. The\nlatter provide an efficient mechanism to cancel single-particle hopping by\ndestructive interference. The crucial parity symmetry in each wire is thus\nencoded in the geometry of the setup, in particular, its translation\ninvariance. A generic nearest-neighbor interaction generates the desired\ncorrelated hopping of pairs. We exhibit the presence of an extended topological\nregion in parameter space, first in a simplified effective model via\nbosonization techniques, and subsequently in a larger parameter regime with\nmatrix-product-states numerical simulations. We demonstrate the adiabatic\nconnection to previous models, including exactly-solvable ones, and we briefly\ncomment on possible experimental realizations in synthetic quantum platforms,\nlike cold atomic samples.",
        "positive": "Laughlin-like states in bosonic and fermionic atomic synthetic ladders: The combination of interactions and static gauge fields plays a pivotal role\nin our understanding of strongly-correlated quantum matter. Cold atomic gases\nendowed with a synthetic dimension are emerging as an ideal platform to\nexperimentally address this interplay in quasi-one-dimensional systems. A\nfundamental question is whether these setups can give access to pristine\ntwo-dimensional phenomena, such as the fractional quantum Hall effect, and how.\nWe show that unambiguous signatures of bosonic and fermionic Laughlin-like\nstates can be observed and characterized in synthetic ladders. We theoretically\ndiagnose these Laughlin-like states focusing on the chiral current flowing in\nthe ladder, on the central charge of the low-energy theory, and on the\nproperties of the entanglement entropy. Remarkably, Laughlin-like states are\nseparated from conventional liquids by Lifschitz-type transitions,\ncharacterized by sharp discontinuities in the current profiles, which we\naddress using extensive simulations based on matrix-product states. Our work\nprovides a qualitative and quantitative guideline towards the observability and\nunderstanding of strongly-correlated states of matter in synthetic ladders. In\nparticular, we unveil how state-of-the-art experimental settings constitute an\nideal starting point to progressively tackle two-dimensional strongly\ninteracting systems from a ladder viewpoint, opening a new perspective for the\nobservation of non-Abelian states of matter."
    },
    {
        "anchor": "Fragmented Condensate in a Two-Component Bose Gas with $p$-wave\n  Interactions: In this Letter, we discuss the effects of $p$-wave attractive interaction in\na spin-$1/2$ Bose gas. With a repulsive $s$-wave background interaction, we\nshow that for weak $p$-wave attraction, one obtains a standard Bose-Einstein\ncondensate at zero momentum with spins fully polarized. Upon increasing the\n$p$-wave attraction, a fragmented condensate state with singlet pair formation\nand $p$-wave correlation emerges. We determine the transition point and\ninvestigate the properties of the fragmented condensate using an ansatz wave\nfunction. We construct the relevant Gross-Pitaevskii equations for the\nfragmented condensate and show that the sound velocities are anisotropic and\nmay vanish in specific directions. Based on the many-body wave function, we\nalso discuss the low-energy spin excitations of the system.",
        "positive": "Dipolar physics: A review of experiments with magnetic quantum gases: Since the achievement of quantum degeneracy in gases of chromium atoms in\n2004, the experimental investigation of ultracold gases made of highly magnetic\natoms has blossomed. The field has yielded the observation of many\nunprecedented phenomena, in particular those in which long-range and\nanisotropic dipole-dipole interactions play a crucial role. In this review, we\naim to present the aspects of the magnetic quantum-gas platform that make it\nunique for exploring ultracold and quantum physics as well as to give a\nthorough overview of experimental achievements."
    },
    {
        "anchor": "Evolution of the Hofstadter butterfly in a tunable optical lattice: Recent advances in realizing artificial gauge fields on optical lattices\npromise experimental detection of topologically non-trivial energy spectra.\nSelf-similar fractal energy structures generally known as Hofstadter\nbutterflies depend sensitively on the geometry of the underlying lattice, as\nwell as the applied magnetic field. The recent demonstration of an adjustable\nlattice geometry [L. Tarruell \\textit{et al.}, Nature 483, 302--305 (2012)]\npresents a unique opportunity to study this dependence. In this paper, we\ncalculate the Hofstadter butterflies that can be obtained in such an adjustable\nlattice and find three qualitatively different regimes. We show that the\nexistence of Dirac points at zero magnetic field does not imply the topological\nequivalence of spectra at finite field. As the real-space structure evolves\nfrom the checkerboard lattice to the honeycomb lattice, two square lattice\nHofstadter butterflies merge to form a honeycomb lattice butterfly. This\nmerging is topologically non-trivial, as it is accomplished by sequential\nclosings of gaps. Ensuing Chern number transfer between the bands can be probed\nwith the adjustable lattice experiments. We also calculate the Chern numbers of\nthe gaps for qualitatively different spectra and discuss the evolution of\ntopological properties with underlying lattice geometry.",
        "positive": "Realization of an Excited, Strongly-Correlated Quantum Gas Phase: Ultracold atomic physics offers myriad possibilities to study strongly\ncorrelated many-body systems in lower dimensions. Typically, only ground state\nphases are accessible. Using a tunable quantum gas of bosonic cesium atoms, we\nrealize and control in one dimensional geometry a highly excited quantum phase\nthat is stabilized in the presence of attractive interactions by maintaining\nand strengthening quantum correlations across a confinement-induced resonance.\nWe diagnose the crossover from repulsive to attractive interactions in terms of\nthe stiffness and the energy of the system. Our results open up the\nexperimental study of metastable excited many-body phases with strong\ncorrelations and their dynamical properties."
    },
    {
        "anchor": "Bath mediated decay of density waves in a disordered Bose lattice gas: Motivated by a recent experiment, we study the dynamics of bosons in a\ndisordered optical lattice, interacting with a variably sized bath of disorder\nfree atoms. As the number of particles in the bath is increased, there is a\ntransition between \"localized\" and \"ergodic\" behavior, which are characterized\nby the long-time behavior of an initial density wave. We model the dynamics\nwith a stochastic mean field theory, reproducing the central observations of\nthe experiment. A key conclusion from our study is that particle loss plays an\nimportant role.",
        "positive": "Dimers, Effective Interactions, and Pauli Blocking Effects in a Bilayer\n  of Cold Fermionic Polar Molecules: We consider a bilayer setup with two parallel planes of cold fermionic polar\nmolecules when the dipole moments are oriented perpendicular to the planes. The\nbinding energy of two-body states with one polar molecule in each layer is\ndetermined and compared to various analytic approximation schemes in both\ncoordinate- and momentum-space. The effective interaction of two bound dimers\nis obtained by integrating out the internal dimer bound state wave function and\nits robustness under analytical approximations is studied. Furthermore, we\nconsider the effect of the background of other fermions on the dimer state\nthrough Pauli blocking, and discuss implications for the zero-temperature\nmany-body phase diagram of this experimentally realizable system."
    },
    {
        "anchor": "Crossed optical cavities with large mode diameters: We report on a compact, ultrahigh-vacuum compatible optical assembly to\ncreate large-scale, two-dimensional optical lattices for use in experiments\nwith ultracold atoms. The assembly consists of an octagon-shaped spacer made\nfrom ultra-low-expansion glass, to which we optically contact four fused-silica\ncavity mirrors, making it highly mechanically and thermally stable. The mirror\nsurfaces are nearly plane-parallel which allows us to create two perpendicular\ncavity modes with diameters $\\sim$1 mm. Such large mode diameters are desirable\nto increase the optical lattice homogeneity, but lead to strong angular\nsensitivities of the coplanarity between the two cavity modes. We demonstrate a\nprocedure to precisely position each mirror substrate that achieves a deviation\nfrom coplanarity of $d = 1(5)$ $\\mu$m. Creating large optical lattices at\narbitrary visible and near infrared wavelengths requires significant power\nenhancements to overcome limitations in the available laser power. The cavity\nmirrors have a customized low-loss mirror coating that enhances the power at a\nset of relevant wavelengths from the visible to the near infrared by up to\nthree orders of magnitude.",
        "positive": "Exact Results for Tunneling Problems of Bogoliubov Excitations in the\n  Critical Supercurrent State: We show the exact solution of Bogoliubov equations at zero-energy in the\ncritical supercurrent state for arbitrary shape of potential barrier. With use\nof this solution, we prove the absence of perfect transmission of excitations\nin the low-energy limit by giving the explicit expression of transmission\ncoefficient. The origin of disappearance of perfect transmission is the\nemergence of zero-energy density fluctuation near the potential barrier."
    },
    {
        "anchor": "Quasiparticle tunneling in a periodically driven bosonic Josephson\n  junction: A resonantly driven bosonic Josephson junction supports stable collective\nexcitations, or quasiparticles, which constitute analogs of the Trojan wave\npackets previously explored with Rydberg atoms in strong microwave fields. We\npredict a quantum beating effect between such symmetryrelated many-body Trojan\nstates taking place on time scales which are long in comparison with the\ndriving period. Within a mean-field approximation, this quantum beating can be\nregarded as a manifestation of dynamical tunneling. On the full N-particle\nlevel, the beating phenomenon leads to an experimentally feasible, robust\nstrategy for probing highly entangled mesoscopic states.",
        "positive": "Trapped fermions in a synthetic non-Abelian gauge field: On increasing the coupling strength ($\\lambda$) of a non-Abelian gauge field\nthat induces a generalized Rashba spin-orbit interaction, the topology of the\nFermi surface of a homogeneous gas of noninteracting fermions of density $\\rho\n\\sim \\kf^3$ undergoes a change at a critical value, $\\lambda_T \\approx \\kf$\n[Phys. Rev. B {\\bf 84}, 014512 (2011)]. In this paper we analyze how this\nphenomenon affects the size and shape of a cloud of spin-$\\half$ fermions\ntrapped in a harmonic potential such as those used in cold atom experiments. We\ndevelop an adiabatic formulation, including the concomitant Pancharatnam-Berry\nphase effects, for the one particle states in the presence of a trapping\npotential and the gauge field, obtaining approximate analytical formulae for\nthe energy levels for some high symmetry gauge field configurations of\ninterest. An analysis based on the local density approximation reveals that,\nfor a given number of particles, the cloud shrinks in a {\\em characteristic\nfashion with increasing $\\lambda$}. For an isotropic harmonic trap, the local\ndensity approximation predicts a spherical cloud for all gauge field\nconfigurations, which are anisotropic in general. We show, via a calculation of\nthe cloud shape using exact eigenstates, that for certain gauge field\nconfigurations there is systematic and observable anisotropy in the cloud shape\nthat increases with increasing gauge coupling $\\lambda$. These results should\nbe useful in the design of cold atom experiments with fermions in non-Abelian\ngauge fields. An important spin-off of our adiabatic formulation is that it\nreveals exciting possibilities for the cold-atom realization of interesting\ncondensed matter Hamiltonians (eg. quantum hall spherical geometry) by using a\nnon-Abelian gauge field in conjunction with another potential."
    },
    {
        "anchor": "The theory of quantum levitators: We develop a unified theory for clocks and gravimeters using the\ninterferences of multiple atomic waves put in levitation by traveling light\npulses. Inspired by optical methods, we exhibit a propagation invariant, which\nenables to derive analytically the wave function of the sample scattering on\nthe light pulse sequence. A complete characterization of the device sensitivity\nwith respect to frequency or to acceleration measurements is obtained. These\nresults agree with previous numerical simulations and confirm the conjecture of\nsensitivity improvement through multiple atomic wave interferences. A realistic\nexperimental implementation for such clock architecture is discussed.",
        "positive": "Normal modes for N identical particles: A study of the evolution of\n  collective behavior from few-body to many-body: Normal mode dynamics are ubiquitous underlying the motions of diverse systems\nfrom rotating stars to crystal structures. These behaviors are composed of\nsimple collective motions of particles which move with the same frequency and\nphase, thus encapsulating many-body effects into simple dynamic motions. In\nregimes such as the unitary regime for ultracold Fermi gases, a single\ncollective mode can dominate, leading to simple behavior as seen in\nsuperfluidity. I investigate the evolution of collective motion as a function\nof N for five types of normal modes obtained from an L=0 group theoretic\nsolution of a general Hamiltonian for confined, identical particles. I show\nusing simple analytic forms that the collective behavior of few-body systems,\nwith the well known motions of molecular equivalents such as ammonia and\nmethane, evolves smoothly to the collective motions expected for large N\nensembles. The transition occurs at quite low values of N. I study a\nHamiltonian known to support collective behavior, the Hamiltonian for Fermi\ngases in the unitary regime. I analyze the evolution of both frequencies and\nthe coefficients that mix the radial and angular coordinates which both depend\non interparticle interactions. This analysis reveals two phenomena that could\ncontribute to the viability of collective behavior. First the mixing\ncoefficients go to zero or unity, i.e. no mixing, as N becomes large resulting\nin solutions that do not depend on the details of the interparticle potential\nas expected for this unitary regime, and that manifest the symmetry of an\nunderlying approximate Hamiltonian. Second, the five normal mode frequencies\nwhich are all close for low values of N, separate as N increases, creating\nlarge gaps that can, in principle, offer stability to collective behavior if\nmechanisms to prevent the transfer of energy to other modes exist (such as low\ntemperature) or can be constructed."
    },
    {
        "anchor": "Superradiant and Lasing States in Driven-Dissipative Dicke Models: We present the non-equilibrium phase diagram of a model which can demonstrate\nboth Dicke--Hepp--Lieb superradiance and regular lasing by varying the coherent\nand incoherent driving terms. We find that the regions in the phase diagram\ncorresponding to superradiance and standard lasing are always separated by a\nnormal region. We analyse the behaviour of the system using a combination of\nexact numerics based on permutation symmetry of the density matrix for small to\nintermediate numbers of molecules, and second order cumulant equations for\nlarge numbers of molecules. We find that the nature of the photon distribution\nin the superradiant and lasing states are very similar, but the emission\nspectrum is very different. We also show that in the presence of both coherent\nand incoherent driving, a period-doubling route to a chaotic state occurs.",
        "positive": "Non-adiabatic polariton condensation in annular optical traps: We explore formation and dynamics of nonequilibrium bosonic exciton-polariton\ncondensates in annular optically induced traps. For the vicinity of\ncondensation pumping threshold, we develop the two-mode model, accounting for\ncounter-rotating quantized vortices and corresponding angular harmonics in the\nincoherent excitonic reservoir density. Identifying the range of parameter, in\nwhich adiabatic elimination of the reservoir is valid, we extend the analytic\nmodel beyond the adiabatic approximation. In the circularly symmetric case, we\npredict a neutral equilibrium phase due to spontaneous breaking of the\ncontinuous symmetry, condensate multistability and limit cycle dynamics. We\nalso account for weak trap asymmetry to show that non-adiabaticity of the\ncoupled condensate-reservoir system prevents formation of giant vortices and\noutline experimental conditions for their observation."
    },
    {
        "anchor": "BCS-BEC crossover in spin-orbit coupled two-dimensional Fermi gases: The recent experimental realization of spin-orbit coupling for ultra-cold\natoms has generated much interest in the physics of spin-orbit coupled\ndegenerate Fermi gases. Although recently the BCS-BEC crossover in\nthree-dimensional (3D) spin-orbit coupled Fermi gases has been intensively\nstudied, the corresponding two-dimensional (2D) crossover physics has remained\nunexplored. In this paper, we investigate, both numerically and analytically,\nthe BCS-BEC crossover physics in 2D degenerate Fermi gases in the presence of a\nRashba type of spin-orbit coupling. We derive the mean field gap and atom\nnumber equations suitable for the 2D spin-orbit coupled Fermi gases and solve\nthem numerically and self-consistently, from which the dependence of the ground\nstate properties (chemical potential, superfluid pairing gap, ground state\nenergy per atom) on the system parameters (e.g., binding energy, spin-orbit\ncoupling strength) is obtained. Furthermore, we derive analytic expressions for\nthese ground state quantities, which agree well with our numerical results\nwithin a broad parameter region. Such analytic expressions also agree\nqualitatively with previous numerical results for the 3D spin-orbit coupled\nFermi gases, where analytic results are lacked. We show that with an increasing\nSOC strength, the chemical potential is shifted by a constant determined by the\nSOC strength. The superfluid pairing gap is enhanced significantly in the BCS\nlimit for strong SOC, but only increases slightly in the BEC limit.",
        "positive": "Observation of universal dissipative dynamics in strongly correlated\n  quantum gas: Dissipation is unavoidable in quantum systems. It usually induces\ndecoherences and changes quantum correlations. To access the information of\nstrongly correlated quantum matters, one has to overcome or suppress\ndissipation to extract out the underlying quantum phenomena. However, here we\nfind an opposite effect that dissipation can be utilized as a powerful tool to\nprobe the intrinsic correlations of quantum many-body systems. Applying\nhighly-controllable dissipation in ultracold atomic systems, we observe a\nuniversal dissipative dynamics in strongly correlated one-dimensional quantum\ngases. The total particle number of this system follows a universal\nstretched-exponential decay, and the stretched exponent measures the anomalous\ndimension of the spectral function, a critical exponent characterizing strong\nquantum fluctuations of this system. This method could have broad applications\nin detecting strongly correlated features, including spin-charge separations\nand Fermi arcs in quantum materials."
    },
    {
        "anchor": "Quantum droplet of a two-component Bose gas in an optical lattice near\n  the Mott insulator transition: We theoretically study dynamical formation of a quantum droplet in a\ntwo-component Bose-Hubbard system with an external trap potential.\nSpecifically, the superfluid in the central region surrounded by the Mott\ninsulator with double filling forms a quantum droplet, which is self-bound\nthanks to the discontinuous nature of the quantum phase transition between the\ntwo phases. We show how to induce the characteristic behavior of the droplet\nthrough the control of the trap potential by using the time-dependent\nGutzwiller simulations in a two-dimensional system. The static and dynamical\nproperties of the droplet can be described qualitatively by the effective\nGinzburg-Landau field theory with cubic-quintic nonlinearities, where the\nattractive cubic nonlinearlity emerges although all the bare interparticle\ninteractions are repulsive.",
        "positive": "Dynamics of a Quantum Phase Transition and Relaxation to a Steady State: We review recent theoretical work on two closely related issues: excitation\nof an isolated quantum condensed matter system driven adiabatically across a\ncontinuous quantum phase transition or a gapless phase, and apparent relaxation\nof an excited system after a sudden quench of a parameter in its Hamiltonian.\nAccordingly the review is divided into two parts. The first part revolves\naround a quantum version of the Kibble-Zurek mechanism including also phenomena\nthat go beyond this simple paradigm. What they have in common is that\nexcitation of a gapless many-body system scales with a power of the driving\nrate. The second part attempts a systematic presentation of recent results and\nconjectures on apparent relaxation of a pure state of an isolated quantum\nmany-body system after its excitation by a sudden quench. This research is\nmotivated in part by recent experimental developments in the physics of\nultracold atoms with potential applications in the adiabatic quantum state\npreparation and quantum computation."
    },
    {
        "anchor": "Direct cooling in an optical lattice by amplitude modulation: We report on a generic cooling technique for atoms trapped in optical\nlattices. It consists in modulating the lattice depth with a proper frequency\nsweeping. This filtering technique removes the most energetic atoms, and\nprovides with the onset of thermalization a cooling mechanism reminiscent of\nevaporative cooling. However, the selection is here performed in quasi-momentum\nspace rather than in position space. Interband selection rules are used to\nprotect the population with a zero quasi-momentum, namely the Bose Einstein\ncondensate. Direct condensation of thermal atoms in an optical lattice is also\nachieved with this technique. It offers an interesting complementary cooling\nmechanism for quantum simulations performed with quantum gases trapped in\noptical lattices.",
        "positive": "Helical superfluid in a frustrated honeycomb Bose-Hubbard model: We study a \"helical\" superfluid, a nonzero-momentum condensate in a\nfrustrated bosonic model. At mean-field Bogoliubov level, such a novel state\nexhibits \"smectic\" fluctuation that are qualitatively stronger than that of a\nconventional superfluid. We develop a phase diagram and compute a variety of\nits physical properties, including the spectrum, structure factor, condensate\ndepletion, momentum distribution, all of which are qualitatively distinct from\nthat of a conventional superfluid. Interplay of fluctuations, interaction and\nlattice effects gives rise to the phenomenon of order-by-disorder, leading to a\ncrossover from the smectic superfluid regime to the anisotropic XY superfluid\nphase. We complement the microscopic lattice analysis with a field theoretic\ndescription for such a helical superfluid, which we derive from microscopics\nand justify on general symmetry grounds, reassuringly finding full consistency.\nPossible experimental realizations are discussed."
    },
    {
        "anchor": "Stabilization of Hubbard-Thouless pumps through nonlocal fermionic\n  repulsion: Thouless pumping represents a powerful concept to probe quantized topological\ninvariants in quantum systems. We explore this mechanism in a generalized\nRice-Mele Fermi-Hubbard model characterized by the presence of competing onsite\nand intersite interactions. Contrary to recent experimental and theoretical\nresults, showing a breakdown of quantized pumping induced by the onsite\nrepulsion, we prove that sufficiently large intersite interactions allow for an\ninteraction-induced recovery of Thouless pumps. Our analysis further reveals\nthat the occurrence of stable topological transport at large interactions is\nconnected to the presence of a spontaneous bond-order-wave in the ground-state\nphase diagram of the model. Finally, we discuss a concrete experimental setup\nbased on ultracold magnetic atoms in an optical lattice to realize the newly\nintroduced Thouless pump. Our results provide a new mechanism to stabilize\nThouless pumps in interacting quantum systems.",
        "positive": "Merging and alignment of Dirac points in a shaken honeycomb optical\n  lattice: Inspired by the recent creation of the honeycomb optical lattice and the\nrealization of the Mott insulating state in a square lattice by shaking, we\nstudy here the shaken honeycomb optical lattice. For a periodic shaking of the\nlattice, a Floquet theory may be applied to derive a time-independent\nHamiltonian. In this effective description, the hopping parameters are\nrenormalized by a Bessel function, which depends on the shaking direction,\namplitude and frequency. Consequently, the hopping parameters can vanish and\neven change sign, in an anisotropic manner, thus yielding different band\nstructures. Here, we study the merging and the alignment of Dirac points and\ndimensional crossovers from the two dimensional system to one dimensional\nchains and zero dimensional dimers. We also consider next-nearest-neighbor\nhopping, which breaks the particle-hole symmetry and leads to a metallic phase\nwhen it becomes dominant over the nearest-neighbor hopping. Furthermore, we\ninclude weak repulsive on-site interactions and find the density profiles for\ndifferent values of the hopping parameters and interactions, both in a\nhomogeneous system and in the presence of a trapping potential. Our results may\nbe experimentally observed by using momentum-resolved Raman spectroscopy."
    },
    {
        "anchor": "Matter wave scattering on an amplitude-modulated optical lattice: We experimentally study the scattering of guided matter waves on an\namplitude-modulated optical lattice. We observe different types of\nfrequency-dependent dips in the asymptotic output density distribution. Their\npositions are compared quantitatively with numerical simulations. A\nsemiclassical model that combines \\emph{local} Floquet-Bloch bands analysis and\nLandau-Zener transitions provides a simple picture of the observed phenomena in\nterms of elementary \\emph{Floquet photon} absorption-emission processes and\nenvelope-induced reflections. Finally, we propose and demonstrate the use of\nthis technique with a bichromatic modulation to design a tunable sub-recoil\nvelocity filter. Such a filter can be transposed to all species since it does\nnot rely on a specific internal level configuration of the atoms.",
        "positive": "Nonadiabatic dynamics of the excited states for the Lipkin-Meshkov-Glick\n  model: We theoretically investigate the impact of the excited state quantum phase\ntransition on the adiabatic dynamics for the Lipkin-Meshkov-Glick model. Using\na time dependent protocol, we continuously change a model parameter and then\ndiscuss the scaling properties of the system especially close to the excited\nstate quantum phase transition where we find that these depend on the energy\neigenstate. On top, we show that the mean-field dynamics with the time\ndependent protocol gives the correct scaling and expectation values in the\nthermodynamic limit even for the excited states."
    },
    {
        "anchor": "High-precision numerical solution of the Fermi polaron problem and\n  large-order behavior of its diagrammatic series: We introduce a simple determinant diagrammatic Monte Carlo algorithm to\ncompute the ground-state properties of a particle interacting with a Fermi sea\nthrough a zero-range interaction. The fermionic sign does not cause any\nfundamental problem when going to high diagram orders, and we reach order\n$N=30$. The data reveal that the diagrammatic series diverges exponentially as\n$(-1/R)^{N}$ with a radius of convergence $R<1$. Furthermore, on the polaron\nside of the polaron-dimeron transition, the value of $R$ is determined by a\nspecial class of three-body diagrams, corresponding to repeated scattering of\nthe impurity between two particles of the Fermi sea. A power-counting argument\nexplains why finite $R$ is possible for zero-range interactions in three\ndimensions. Resumming the divergent series through a conformal mapping yields\nthe polaron energy with record accuracy.",
        "positive": "Imbalanced ultracold Fermi gas in the weakly repulsive regime:\n  Renormalization group approach for p-wave superfluidity: We theoretically study a possible new pairing mechanism for a two-dimensional\npopulation imbalanced Fermi gas with short-range repulsive interactions which\ncan be realized on the upper branch of a Feshbach resonance. We use a\nwell-controlled renormalization group approach, which allows an unbiased study\nof the instabilities of imbalanced Fermi liquid without assumption of a broken\nsymmetry and gives a numerical calculation of the transition temperature from\nmicroscopic parameters. Our results show a leading superfluid instability in\nthe p-wave channel for the majority species. The corresponding mechanism is\nthat there are effective attractive interactions for the majority species,\ninduced by the particle-hole susceptibility of the minority species, where the\nmismatch of the Fermi surfaces of the two species plays an important role. We\nalso propose an experimental protocol for detecting the p-wave superfluidity\nand discuss the corresponding experimental signatures."
    },
    {
        "anchor": "Universal behavior of few-boson systems using potential models: The universal behavior of a three-boson system close to the unitary limit is\nencoded in a simple dependence of many observables in terms of few parameters.\nFor example the product of the three-body parameter $\\kappa_*$ and the two-body\nscattering length $a$, $\\kappa_* a$ depends on the angle $\\xi$ defined by\n$E_3/E_2=\\tan^2\\xi$. A similar dependence is observed in the ratio $a_{AD}/a$\nwith $a_{AD}$ the boson-dimer scattering length. We use a two-parameter\npotential to determine this simple behavior and, as an application, to compute\n$a_{AD}$ for the case of three $^4$He atoms.",
        "positive": "Universal Relations for Fermions with Large Scattering Length: The behavior of fermions with two spin states that interact with a large\nscattering length is constrained by universal relations that hold for any state\nof the system. These relations involve a central property of the system called\nthe contact, which measures the number of pairs of fermions with different\nspins that have small separations. The contact controls the thermodynamics of\nthe system as well as the large-momentum and high-frequency tails of\ncorrelation functions. This review summarizes the current theoretical and\nexperimental status of these universal relations."
    },
    {
        "anchor": "Thermoelectric transport and Peltier cooling of cold atomic gases: This brief review presents the emerging field of mesoscopic physics with cold\natoms, with an emphasis on thermal and 'thermoelectric' transport, i.e. coupled\ntransport of particle and entropy. We review in particular the comparison\nbetween theoretically predited and experimentally observed thermoelectric\neffects in such systems. We also show how combining well designed transport\nproperties and evaporative cooling leads to an equivalent of the Peltier effect\nwith cold atoms, which can be used as a new cooling procedure with improved\ncooling power and efficiency compared to the evaporative cooling currently used\nin atomic gases. This could lead to a new generation of experiments probing\nstrong correlation effects of ultracold fermionic atoms at low temperatures.",
        "positive": "Fractional domain walls from on-site softening in dipolar bosons: We study dipolar bosons in a 1D optical lattice and identify a region in\nparameter space---strong coupling but relatively weak on-site\nrepulsion---hosting a series of stable charge-density-wave (CDW) states whose\nlow-energy excitations, built from \"fractional domain walls,\" have remarkable\nsimilarities to those of non-Abelian fractional quantum Hall states. Here, a\nconventional domain wall between translated CDW's may be split by inserting\nstrings of degenerate, but inequivalent, CDW states. Outside these insulating\nregions, we find numerous supersolids as well as a superfluid regime. The\nmentioned phases should be accessible experimentally and, in particular, the\nfractional domain walls can be created in the ground state using single-site\naddressing, i.e., by locally changing the chemical potential."
    },
    {
        "anchor": "Dynamical Phase Transitions and Instabilities in Open Atomic Many-Body\n  Systems: We discuss an open driven-dissipative many-body system, in which the\ncompetition of unitary Hamiltonian and dissipative Liouvillian dynamics leads\nto a nonequilibrium phase transition. It shares features of a quantum phase\ntransition in that it is interaction driven, and of a classical phase\ntransition, in that the ordered phase is continuously connected to a thermal\nstate. Within a generalized Gutzwiller approach which includes the description\nof mixed state density matrices, we characterize the complete phase diagram and\nthe critical behavior at the phase transition approached as a function of time.\nWe find a novel fluctuation induced dynamical instability, which occurs at long\nwavelength as a consequence of a subtle dissipative renormalization effect on\nthe speed of sound.",
        "positive": "Trapped electrons in the quantum degenerate regime: A full strength Coulomb interaction between trapped electrons can be felt\nonly in absence of a neutralizing background. In order to study quantum\ndegenerate electrons without such a background, an external trap is needed to\ncompensate for the strong electronic repulsion. As a basic model for such a\nsystem, we study a trapped electron pair in a harmonic trap with an explicit\ninclusion of its Coulomb interaction. We find the eigenenergy of the ground\nstate, confirming earlier work in the context of harmonium. We extend this to a\ncomplete set of properly scaled energies for any value of the trapping\nstrength, including the excited states. The problem is solved either\nnumerically or by making harmonic approximations to the potential. As function\nof the trapping strength a crossover can be made from the strongly to the\nweakly-coupled regime, and we show that in both regimes perturbative methods\nbased on a pair-wise electron description would be effective for a\nmany-particle trapped electron system, which resembles a Wigner crystal in the\nground state of the strongly coupled limit."
    },
    {
        "anchor": "Many-body parametric resonances in the driven sine-Gordon model: We study a quantum many-body variant of the parametric oscillator, by\ninvestigating the driven sine-Gordon model with a modulated tunnel coupling via\na semi-classical Truncated Wigner Approximation (TWA). We first analyze the\nparametric resonant regime for driving protocols that retain our model gapped,\nand compare the TWA to a Time-Dependent Gaussian Variational Ansatz (TGVA). We\nthen turn to a drive which closes the gap, resulting in an enhanced energy\nabsorption. While the TGVA approach breaks down in this regime, we can apply\nTWA to explore the dynamics of the mode-resolved energy density, and the\nhigher-order correlations between modes in the prethermal heating regime. For\nweak driving amplitude, we find an exponentially fast energy absorption in the\nmain resonant mode, while the heating of all remaining modes is almost\nperfectly suppressed on short time scales. At later times, the highly excited\nmain resonance provides effective resonant driving terms for its higher\nharmonics through the non-linearities in the Hamiltonian, and gives rise to an\nexponentially fast heating in these particular modes. We capture the strong\ncorrelations induced by these resonant processes by evaluating higher order\nconnected correlation functions. Our results can be experimentally probed in\nultracold atomic settings, with parallel one-dimensional quasi-condensates in\nthe presence of a modulated tunnel coupling.",
        "positive": "Competing orders in one-dimensional half-filled multicomponent fermionic\n  cold atoms: The Haldane-charge conjecture: We investigate the nature of the Mott-insulating phases of half-filled\n2N-component fermionic cold atoms loaded into a one-dimensional optical\nlattice. By means of conformal field theory techniques and large-scale DMRG\ncalculations, we show that the phase diagram strongly depends on the parity of\n$N$. First, we single out charged, spin-singlet, degrees of freedom, that carry\na pseudo-spin ${\\cal S}=N/2$ allowing to formulate a Haldane conjecture: for\nattractive interactions, we establish the emergence of Haldane insulating\nphases when $N$ is even, whereas a metallic behavior is found when $N$ is odd.\nWe point out that the $N=1,2$ cases do \\emph{not} have the generic properties\nof each family. The metallic phase for $N$ odd and larger than 1 has a\nquasi-long range singlet pairing ordering with an interesting edge-state\nstructure. Moreover, the properties of the Haldane insulating phases with even\n$N$ further depend on the parity of N/2. In this respect, within the low-energy\napproach, we argue that the Haldane phases with N/2 even are not topologically\nprotected but equivalent to a topologically trivial insulating phase and thus\nconfirm the recent conjecture put forward by Pollmann {\\it et al.} [Pollmann\n{\\it et al.}, arXiv:0909.4059 (2009)]."
    },
    {
        "anchor": "Real-space detection and manipulation of topological edge modes with\n  ultracold atoms: Conventional topological insulators exhibit exotic gapless edge or surface\nstates, as a result of non-trivial bulk topological properties. In\nperiodically-driven systems the bulk-boundary correspondence is fundamentally\nmodified and knowledge about conventional bulk topological invariants is\ninsufficient. While ultracold atoms provide excellent settings for clean\nrealizations of Floquet protocols, the observation of real-space edge modes has\nso far remained elusive. Here we demonstrate an experimental protocol for\nrealizing chiral edge modes in optical lattices, by creating a topological\ninterface using a potential step that is generated with a programmable optical\npotential. We show how to efficiently prepare particles in these edge modes in\nthree distinct Floquet topological regimes that are realized in a\nperiodically-driven honeycomb lattice. Controlling the height and sharpness of\nthe potential step, we study how edge modes emerge at the interface and how the\ngroup velocity of the particles is modified as the sharpness of the potential\nstep is varied.",
        "positive": "Massive superfluid vortices and vortex necklaces on a planar annulus: We study a superfluid in a planar annulus hosting vortices with massive\ncores. An analytical point-vortex model shows that the massive vortices may\nperform radial oscillations on top of the usual uniform precession of their\nmassless counterpart. Beyond a critical vortex mass, this oscillatory motion\nbecomes unstable and the vortices are driven towards one of the edges. The\nanalogy with the motion of a charged particle in a static electromagnetic field\nleads to the development of a plasma orbit theory that provides a description\nof the trajectories which remains accurate even beyond the regime of small\nradial oscillations. These results are confirmed by the numerical solution of\ncoupled two-component Gross-Pitaevskii equations. The analysis is then extended\nto a necklace of vortices symmetrically arranged within the annulus."
    },
    {
        "anchor": "Simulation of magnetoresistance in disordered ultracold atomic Bose\n  gases: Anderson localization was first investigated in the context of electrons in\nsolids. One of the successes was in explaining the puzzle of negative\nmagneto-resistance - as early as the 1940s it had been observed that electron\ndiffusion rates in some materials can increase with the application of a\nmagnetic field. Anderson localization has now been demonstrated in ultra-cold\natomic gases. We present a theoretical study of the two-dimensional ultra-cold\nBose gas in the presence of disorder, to which we apply a synthetic magnetic\nfield. We demonstrate that, in the ballistic transport regime this leads to\npositive magneto-resistance and that, in the diffusive and strong localization\nregimes, can also lead to negative magneto-resistance. We propose experimental\nscenarios to observe these effects.",
        "positive": "Dynamics of a vortex dipole across a magnetic phase boundary in a spinor\n  Bose-Einstein condensate: Dynamics of a vortex dipole in a spin-1 Bose-Einstein condensate in which\nmagnetic phases are spatially distributed is investigated. When a vortex dipole\ntravels from the ferromagnetic phase to the polar phase, or vice versa, it\npenetrates the phase boundary and transforms into one of the various spin\nvortex dipoles, such as a leapfrogging ferromagnetic-core vortex dipole and a\nhalf-quantum vortex dipole. Topological connections of spin wave functions\nacross the phase boundary are discussed."
    },
    {
        "anchor": "Spatial adiabatic passage of ultracold atoms in optical tweezers: Spatial adiabatic passage (SAP) is a process that facilitates the transfer of\na wave packet between two localized modes that are not directly coupled, but\nrather interact through an intermediate third mode. By employing a\ncounter-intuitive adiabatic pulse sequence, this technique achieves minimal\npopulation in the intermediate state and high transfer efficiency. Here, we\nreport the implementation of SAP for transferring massive particles between\nthree micro-optical traps. We begin by preparing ultracold fermionic atoms in\nlow vibrational eigenstates of one trap and then manipulate the distance\nbetween the three traps to execute the SAP protocol. We observe a smooth\ntransfer of atoms between the two outer traps, accompanied by a low population\nin the central trap. We validate our findings and underscore the significance\nof the counter-intuitive sequence by reversing the order of the pulse sequence.\nAdditionally, we investigate the influence of the tunneling rate and the time\ndelay between the motion of the two external tweezers on the fidelity of the\nprocess. Our results open up new possibilities for advanced control and\nmanipulation schemes in optical tweezer array platforms.",
        "positive": "High-temperature nonequilibrium Bose condensation induced by a hot\n  needle: We investigate theoretically a one-dimensional ideal Bose gas that is driven\ninto a steady state far from equilibrium via the coupling to two heat baths: a\nglobal bath of temperature $T$ and a \"hot needle\", a bath of temperature\n$T_h\\gg T$ with localized coupling to the system. Remarkably, this system\nfeatures a crossover to finite-size Bose condensation at temperatures $T$ that\nare orders of magnitude larger than the equilibrium condensation temperature.\nThis counterintuitive effect is explained by a suppression of long-wavelength\nexcitations resulting from the competition between both baths. Moreover, for\nsufficiently large needle temperatures ground-state condensation is superseded\nby condensation into an excited state, which is favored by its weaker coupling\nto the hot needle. Our results suggest a general strategy for the preparation\nof quantum degenerate nonequilibrium steady states with unconventional\nproperties and at large temperatures."
    },
    {
        "anchor": "Induced superfluidity of imbalanced Fermi gases near unitarity: The induced intraspecies interactions among the majority species, mediated by\nthe minority species, is computed for a population-imbalanced two-component\nFermi gas. Although the Feshbach-resonance mediated interspecies interaction is\ndominant for equal populations, leading to singlet s-wave pairing, we find that\nin the strongly imbalanced regime the induced intraspecies interaction leads to\np-wave pairing and superfluidity of the majority species. Thus, we predict that\nthe observed spin-polaron Fermi liquid state in this regime is unstable to\np-wave superfluidity, in accordance with the results of Kohn and Luttinger,\nbelow a temperature that, near unitarity, we find to be within current\nexperimental capabilities. Possible experimental signatures of the p-wave state\nusing radio-frequency spectroscopy as well as density-density correlations\nafter free expansion are presented.",
        "positive": "Rabi oscillations and magnetization of a mobile spin-1/2 impurity in a\n  Fermi sea: We investigate the behavior of a mobile spin-1/2 impurity atom immersed in a\nFermi gas, where the interacting spin-$\\uparrow$ and non-interacting\nspin-$\\downarrow$ states of the impurity are Rabi coupled via an external\nfield. This scenario resembles the classic problem of a two-state system\ninteracting with a dissipative environment, but with an added dimension\nprovided by the impurity momentum degree of freedom. In this case, the impurity\ncan become \"dressed\" by excitations of the Fermi sea to form a Fermi polaron\nquasiparticle. For the steady-state system, where the impurity has thermalized\nwith the medium, we derive exact thermodynamic relations that connect the\nimpurity magnetization with quasiparticle properties such as the number of\nfermions in the dressing cloud. We show how the thermodynamic properties evolve\nwith increasing Rabi coupling and we present exact analytical results in the\nlimits of weak and strong Rabi coupling. For the dynamics of the Rabi-driven\nFermi polaron, we formulate a theoretical approach based on correlation\nfunctions that respects conservation laws and allows the efficient calculation\nof Rabi oscillations for a range of time scales and impurity momenta beyond\nwhat has been achieved previously. Our results are in good agreement with\nrecent experiments on the Rabi oscillations of the attractive polaron, and they\nreveal how the Rabi oscillations are influenced by the interplay between the\npolaron and its dressing cloud."
    },
    {
        "anchor": "Berezinskii-Kosterlitz-Thouless transition in a photonic lattice: Phase transitions give crucial insight into many-body systems, as crossovers\nbetween different regimes of order are determined by the underlying dynamics.\nThese dynamics, in turn, are often constrained by dimensionality and geometry.\nFor example, in one- and two-dimensional systems with continuous symmetry,\nthermal fluctuations prevent the formation of long-range order[1,2].\nTwo-dimensional systems are particularly significant, as vortices can form in\nthe plane but cannot tilt out of it. At high temperatures, random motion of\nthese vortices destroys large-scale coherence. At low temperatures, vortices\nwith opposite spin can pair together, cancelling their circulation and allowing\nquasi-long-range order to appear. This Berezenskii-Kosterlitz-Thouless (BKT)\ntransition[3,4] is essentially classical, arising for example in the\ntraditional XY model for spins, but to date experimental evidence has been\nobtained only in cold quantum systems. Measurements of superfluid sound\nspeed[5] and critical velocity[6] have been consistent with scaling\npredictions, and vortices have been observed directly in cold atom\nexperiments[7,8]. However, the presence of trapping potentials restricts\nmeasurement to vortex density, rather than number, and obscures the process of\nvortex unbinding. Further, atom and fluid experiments suffer from parasitic\nheating and difficulties in phase recording, leading to results that differ\nfrom theory in many quantitative aspects. Here, we use a nonlinear optical\nsystem to directly observe the ideal BKT transition, including vortex pair\ndynamics and the correlation properties of the wavefunction, for both repulsive\nand attractiveinteractions (the photonic equivalent of ferromagnetic and\nantiferromagnetic conditions[9]). The results confirm the thermodynamics of the\nBKT transition and expose outstanding issues in the crossovers to superfluidity\nand Bose-Einstein condensation.",
        "positive": "BEC phase diagram of a $^{87}$Rb trapped gas in terms of macroscopic\n  thermodynamic parameters: We measure the phase diagram of a $^{87}$Rb Bose gas in a harmonic trap in\nterms of macroscopic parameters obtained from the spatial distribution of\natoms. Considering the relevant variables as size of the cloud ${\\cal V}$,\nnumber of atoms $N$ and temperature $T$, a novel parameter $\\Pi = \\Pi(N,{\\cal\nV},T)$ is introduced to characterize the overall pressure of the system. We\nconstruct the phase diagram ($\\Pi$ vs $T$) identifying new features related to\nBose-Einstein condensation (BEC) transition in a trapped gas. A thermodynamic\ndescription of the phase transition based on purely macroscopic parameters,\nprovide us with properties that do not need the local density approximation. An\nunexpected consequence of this analysis is the suggestion that BEC appears as a\ncontinuous third-order phase transition instead of being a second-order one."
    },
    {
        "anchor": "Eigenmodal Analysis of Anderson Localization: Applications to Photonic\n  Lattices and Bose-Einstein Condensates: We present the eigenmodal analysis techniques enhanced towards calculations\nof optical and non-interacting Bose-Einstein condensate (BEC) modes formed by\nrandom potentials and localized by Anderson effect. The results are compared\nwith the published measurements and verified additionally by the convergence\ncriterion. In 2-D BECs captured in circular areas, the randomness shows edge\nlocalization of the high-order Tamm-modes. To avoid strong diffusive effect,\nwhich is typical for BECs trapped by speckle potentials, a 3-D-lattice\npotential with increased step magnitudes is proposed, and the BECs in these\nlattices are simulated and plotted.",
        "positive": "Pauli blocking effects and Cooper triples in three-component Fermi gases: We investigate the effect of Pauli blocking on universal two- and three-body\nstates in the medium. Their corresponding energies are extracted from the poles\nof two- and three-body in-medium scattering amplitudes. Compared to the vacuum,\nthe binding of dimer and trimer states is reduced by the medium effects. In\ntwo-body scattering, the well-known physics of Cooper pairs is recovered. In\nthe three-body sector, we find a new class of positive energy poles which can\nbe interpreted as Cooper triples."
    },
    {
        "anchor": "Goldstino spectrum in an ultracold Bose-Fermi mixture with explicitly\n  broken supersymmetry: We theoretically investigate a supersymmetric collective mode called\nGoldstino in a Bose-Fermi mixture. The explicit supersymmetry breaking, which\nis unavoidable in cold atom experiments, is considered. We derive the\nGell-Mann--Oakes-Renner (GOR) relation for the Goldstino, which gives the\nrelation between the energy gap at the zero momentum and the explicit breaking\nterm. We also numerically evaluate the gap of Goldstino above the Bose-Einstein\ncondensation temperature within the random phase approximation (RPA). While the\ngap obtained from the GOR relation coincides with that in the RPA for the\nmass-balanced system, there is a deviation from the GOR relation in the\nmass-imbalanced system. We point out the deviation becomes large when the\nGoldstino pole is close to the branch point, although it is parametrically a\nhigher order with respect to the mass-imbalanced parameter. To examine the\nexistence of the goldstino pole in realistic cold atomic systems, we show how\nthe mass-imbalance effect appears in $^6$Li-$^7$Li, $^{40}$K-$^{41}$K, and\n$^{173}$Yb-$^{174}$Yb mixtures. Furthermore, we analyze the Goldstino spectral\nweight in a $^{173}$Yb-$^{174}$Yb mixture with realistic interactions and show\na clear peak due to the Goldstino pole. As a possibility to observe the\nGoldstino spectrum in cold atom experiments, we discuss the effects of the\nGoldstino pole on the fermionic single-particle excitation as well as the\nrelationship between the GOR relation and Tan's contact.",
        "positive": "Coherent Quantum Phase Slip in two-component bosonic Atomtronic Circuits: Coherent Quantum Phase Slip consists in the coherent transfer of vortices in\nsuperfluids. We investigate this phenomenon in two miscible coherently coupled\ncomponents of a spinor Bose gas confined in a toroidal trap. After imprinting\ndifferent vortex states on each component, we demonstrate that during the whole\ndynamics the system remains in a linear superposition of two current states in\nspite of the non-linearity and can be mapped onto a linear Josephson problem.\nWe propose this system as a good candidate for the realization of a\nMooij-Harmans qubit and remark its feasibility for implementation in current\nexperiments with $^{87}\\mbox{Rb}$, since we have used values for the physical\nparameters currently available in laboratories."
    },
    {
        "anchor": "An experimental test of the geodesic rule proposition for the non-cyclic\n  geometric phase: The geometric phase due to the evolution of the Hamiltonian is a central\nconcept in quantum physics, and may become advantageous for quantum technology.\nIn non-cyclic evolutions, a proposition relates the geometric phase to the area\nbounded by the phase-space trajectory and the shortest geodesic connecting its\nend points. The experimental verification of this geodesic rule proposition has\nremained elusive for more than three decades. Here, we report an unambiguous\nexperimental confirmation of the geodesic rule for a non-cyclic geometric phase\nby means of a spatial SU(2) matter-wave interferometer, demonstrating, with\nhigh precision, the predicted phase sign change and pi jumps. We show the\nconnection between our results and the Pancharatnam phase. Finally, we point\nout that the geodesic rule can be applied to obtain the red-shift in general\nrelativity, enabling a completely new quantum tool to measure gravity.",
        "positive": "Novel Mechanism of Supersolid of Ultracold Polar Molecules in Optical\n  Lattices: We study the checkerboard supersolid of the hard-core Bose-Hubbard model with\nthe dipole-dipole interaction. This supersolid is different from all other\nsupersolids found in lattice models in the sense that superflow paths through\nwhich interstitials or vacancies can hop freely are absent in the crystal. By\nfocusing on repulsive interactions between interstitials, we reveal that the\nlong-range tail of the dipole-dipole interaction have the role of increasing\nthe energy cost of domain wall formations. This effect produces the supersolid\nby the second-order hopping process of defects. We also perform exact quantum\nMonte Carlo simulations and observe a novel double peak structure in the\nmomentum distribution of bosons, which is a clear evidence for supersolid. This\ncan be measured by the time-of-flight experiment in optical lattice systems."
    },
    {
        "anchor": "Local observation of antibunching in a trapped Fermi gas: Local density fluctuations and density profiles of a Fermi gas are measured\nin-situ and analyzed. In the quantum degenerate regime, the weakly interacting\n$^6$Li gas shows a suppression of the density fluctuations compared to the\nnon-degenerate case, where atomic shot noise is observed. This manifestation of\nantibunching is a direct result of the Pauli principle and constitutes a local\nprobe of quantum degeneracy. We analyze our data using the predictions of the\nfluctuation-dissipation theorem and the local density approximation,\ndemonstrating a fluctuation-based temperature measurement.",
        "positive": "Kinetic Model of Trapped Finite Temperature Binary Condensates: We construct a fully self-consistent non-equilibrium theory for the dynamics\nof two interacting finite-temperature atomic Bose-Einstein condensates. The\ncondensates are described by dissipative Gross-Pitaevskii equations, coupled to\nquantum Boltzmann equations for the thermal atoms. The density-density\ninteractions between atoms in different components facilitate a number of\ntransport processes of relevance to sympathetic cooling: in particular,\nidentification of an inter-component scattering process associated with\ncollisional \"exchange\" of condensed and thermal atoms between the components,\nis found numerically to dominate close to equilibrium, for both realistic\nmiscible and immiscible trapped atomic $^{87}$Rb-$^{41}$K and\n$^{87}$Rb-$^{85}$Rb condensate mixtures."
    },
    {
        "anchor": "Correlated bosons in a one-dimensional optical lattice: Effects of the\n  trapping potential and of quasiperiodic disorder: We investigate the effect of the trapping potential on the quantum phases of\nstrongly correlated ultracold bosons in one-dimensional periodic and\nquasiperiodic optical lattices. By means of a decoupling meanfield approach, we\ncharacterize the ground state of the system and its behavior under variation of\nthe harmonic trapping, as a function of the total number of atoms. For a small\natom number the system shows an incompressible Mott-insulating phase, as the\nsize of the cloud remains unaffected when the trapping potential is varied.\nWhen the quasiperiodic potential is added the system develops a\nmetastable-disordered phase which is neither compressible nor Mott insulating.\nThis state is characteristic of quasidisorder in the presence of a strong\ntrapping potential.",
        "positive": "Spin-$S$ $\\mathrm{U}(1)$ Quantum Link Models with Dynamical Matter on a\n  Quantum Simulator: Quantum link models (QLMs) offer the realistic prospect for the practical\nimplementation of lattice quantum electrodynamics (QED) on modern quantum\nsimulators, and they provide a venue for exploring various nonergodic phenomena\nrelevant to quantum many-body physics. In these models, gauge and electric\nfields are represented by spin-$S$ operators. So far, large-scale realizations\nof QLMs have been restricted to $S=1/2$ representations, whereas the\nlattice-QED limit is approached at $S\\to\\infty$. Here, we present a bosonic\nmapping for the representation of gauge and electric fields with effective\nspin-$S$ operators for arbitrarily large values of $S$. Based on this mapping,\nwe then propose an experimental scheme for the realization of a large-scale\nspin-$1$ $\\mathrm{U}(1)$ QLM using spinless bosons in an optical superlattice.\nUsing perturbation theory and infinite matrix product state calculations, which\nwork directly in the thermodynamic limit, we demonstrate the faithfulness of\nthe mapping and stability of gauge invariance throughout all accessible\nevolution times. We further demonstrate the potential of our proposed quantum\nsimulator to address relevant high-energy physics by probing the\n(de)confinement of an electron--positron pair by tuning the gauge coupling. Our\nwork provides an essential step towards gauge-theory quantum simulators in the\nquantum-field-theory limit."
    },
    {
        "anchor": "Symmetry-restoring quantum phase transition in a two-dimensional spinor\n  condensate: Bose Einstein condensates of spin-1 atoms are known to exist in two different\nphases, both having spontaneously broken spin-rotation symmetry, a\nferromagnetic and a polar condensate. Here we show that in two spatial\ndimensions it is possible to achieve a quantum phase transition from a polar\ncondensate into a singlet phase symmetric under rotations in spin space. This\ncan be done by using particle density as a tuning parameter. Starting from the\npolar phase at high density the system can be tuned into a strong-coupling\nintermediate-density point where the phase transition into a symmetric phase\ntakes place. By further reducing the particle density the symmetric phase can\nbe continuously deformed into a Bose-Einstein condensate of singlet atomic\npairs. We calculate the region of the parameter space where such a molecular\nphase is stable against collapse.",
        "positive": "Simultaneous Readout of Noncommuting Collective Spin Observables beyond\n  the Standard Quantum Limit: We augment the information extractable from a single absorption image of a\nspinor Bose-Einstein condensate by coupling to initially empty auxiliary\nhyperfine states. Performing unitary transformations in both, the original and\nauxiliary hyperfine manifold, enables the simultaneous measurement of multiple\nspin-1 observables. We apply this scheme to an elongated atomic cloud of $\n^{87} $Rb to simultaneously read out three orthogonal spin directions and with\nthat directly access the spatial spin structure. The readout even allows the\nextraction of quantum correlations which we demonstrate by detecting spin\nnematic squeezing without state tomography."
    },
    {
        "anchor": "Dipole oscillations of fermionic superfluids along the BEC-BCS crossover\n  in disordered potentials: We investigate dipole oscillations of ultracold Fermi gases along the BEC-BCS\ncrossover through disordered potentials. We observe a disorder-induced damping\nof oscillations as well as a change of the fundamental Kohn-mode frequency. The\nmeasurement results are compared to numerical density matrix renormalization\ngroup calculations as well as to a three-dimensional simulation of\nnon-interacting fermions. Experimentally, we find a disorder-dependent damping,\nwhich grows approximately with the second power of the disorder strength.\nMoreover, we observe experimentally a change of oscillation frequency which\ndeviates from the expected behavior of a damped harmonic oscillator on a\npercent level. While this behavior is qualitatively expected from the\ntheoretical models used, quantitatively the experimental observations show a\nsignificantly stronger effect than predicted by theory. Furthermore, while the\nfrequency shift seems to scale differently with interaction strength in the BEC\nversus BCS regime, the damping coefficient apparently decreases with the\nstrength of interaction, but not with the sign, which changes for BEC and BCS\ntype Fermi gases. This is surprising, as the dominant damping mechanisms are\nexpected to be different in the two regimes.",
        "positive": "Investigation of the bosonic spectrum of two-dimensional optical\n  graphene-type lattices. Superfluid phase: The energy spectrum of a system of Bose atoms in the superfluid phase in an\noptical lattice of the graphene type has been studied. The dispersion laws for\nthe energy bands and the single particle spectral densities are calculated in\nthe random phase approximation and in the framework of the hard-core boson\nformalism, and their changes at the transition from the normal phase to the\nsuperfluid one are described. As a result of this transformation, the number of\nsubbands doubles. In the case of the subband energetic equivalence, the Dirac\npoints in the spectrum survive, and their number becomes twice as much. When\nthe subbands are energetically nonequivalent, the Dirac points are absent. The\nshape of spectral densities is shown to be sensitive to the changes in the\ntemperature and the chemical potential position."
    },
    {
        "anchor": "Excitation spectrum of a two-component Bose-Einstein condensate in a\n  ring potential: A mixture of two distinguishable Bose-Einstein condensates confined in a ring\npotential has numerous interesting properties under rotational and\nsolitary-wave excitation. The lowest-energy states for a fixed angular momentum\ncoincide with a family of solitary-wave solutions. In the limit of weak\ninteractions, exact diagonalization of the many-body Hamiltonian is possible\nand permits evaluation of the complete excitation spectrum of the system.",
        "positive": "Spin and charge modulations in a single hole doped Hubbard ladder --\n  verification with optical lattice experiments: We show that pronounced modulations in spin and charge densities can be\ninduced by the insertion of a single hole in an otherwise half-filled 2-leg\nHubbard ladder. Accompanied with these modulations is a loosely bound structure\nof the doped charge with a spin-1/2, in contrast to the tightly bound case\nwhere such modulations are absent. These behaviors are caused by the\ninterference of the Berry phases associated a string of flipped spins (or\n\"phase strings\") left behind as a hole travels through a spin bath with a\nshort-range anti-ferromagnetic order. The key role of the phase strings is also\nreflected in how the system respond to increasing spin polarization, increasing\nthe on-site repulsion, addition of a second hole, and increasing asymmetry\nbetween intra- and inter-chain hopping. Remarkably, all these properties\npersist down to ladders as short as $\\sim 10$ sites. They can therefore be\nstudied in cold atom experiments using the recently developed fermion\nmicroscope."
    },
    {
        "anchor": "Signatures of pairing and spin-orbit coupling in correlation functions\n  of Fermi gases: We derive expressions for spin and density correlation functions in the\n(greatly enhanced) pseudogap phase of spin-orbit coupled Fermi superfluids.\nDensity-density correlation functions are found to be relatively insensitive to\nthe presence of these Rashba effects. To arrive at spin-spin correlation\nfunctions we derive new $f$-sum rules, valid even in the absence of a spin\nconservation law. Our spin-spin correlation functions are shown to be fully\nconsistent with these $f$-sum rules. Importantly, they provide a clear\nsignature of the Rashba band-structure and separately help to establish the\npresence of a pseudogap.",
        "positive": "Quantum magnetism with ultracold molecules: This article gives an introduction to the realization of effective quantum\nmagnetism with ultracold molecules in an optical lattice, reviews experimental\nand theoretical progress, and highlights future opportunities opened up by\nongoing experiments. Ultracold molecules offer capabilities that are otherwise\ndifficult or impossible to achieve in other effective spin systems, such as\nlong-ranged spin-spin interactions with controllable degrees of spatial and\nspin anisotropy and favorable energy scales. Realizing quantum magnetism with\nultracold molecules provides access to rich many-body behaviors, including many\nexotic phases of matter and interesting excitations and dynamics.\nFar-from-equilibrium dynamics plays a key role in our exposition, just as it\ndid in recent ultracold molecule experiments realizing effective quantum\nmagnetism. In particular, we show that dynamical probes allow the observation\nof correlated many-body spin physics, even in polar molecule gases that are not\nquantum degenerate. After describing how quantum magnetism arises in ultracold\nmolecules and discussing recent observations of quantum magnetism with polar\nmolecules, we survey prospects for the future, ranging from immediate goals to\nlong-term visions."
    },
    {
        "anchor": "Implementation of a stable, high-power optical lattice for quantum gas\n  microscopy: We describe the design and implementation of a stable high-power 1064 nm\nlaser system to generate optical lattices for experiments with ultracold\nquantum gases. The system is based on a low-noise laser amplified by an array\nof four heavily modified, high-power fiber amplifiers. The beam intensity is\nstabilized and controlled with a nonlinear feedback loop. Using real-time\nmonitoring of the resulting optical lattice, we find the stability of the\nlattice site positions to be well below the lattice spacing over the course of\nhours. The position of the harmonic trap produced by the Gaussian envelope of\nthe lattice beams is stable to about one lattice spacing and the long-term\n(six-month) relative RMS stability of the lattice spacing itself is 0.5%.",
        "positive": "Topological States in a One-Dimensional Fermi Gas with Attractive\n  Interactions: We describe a novel topological superfluid state, which forms in a\none-dimensional Fermi gas with Rashba-like spin-orbit coupling, a Zeeman field\nand intrinsic attractive interactions. In spite of total number conservation\nand the presence of gapless excitations, Majorana-like zero modes appear in\nthis system and can be linked with interfaces between two distinct phases that\nnaturally form at different regions of the harmonic trap. As a result, the low\nlying collective excitations of the system, including the dipole oscillations\nand the long-wavelength phonons, are doubly degenerate. While backscattering\nfrom point impurities can lead to a splitting of the degeneracies that scales\nalgebraically with the system size, the smooth confining potential can only\ncause an exponentially small splitting. We show that the topological state can\nbe uniquely probed by a pumping effect induced by a slow sweep of the Zeeman\nfield from a high initial value down to zero field."
    },
    {
        "anchor": "Initial state dependence of the quench dynamics in integrable quantum\n  systems. II. Thermal states: We study properties of isolated integrable quantum systems after a sudden\nquench starting from thermal states. We show that, even if the system is\ninitially in thermal equilibrium at finite temperature, the diagonal entropy\nafter a quench remains a fraction of the entropy in the generalized ensembles\nintroduced to describe integrable systems after relaxation. The latter is also,\nin general, different from the entropy in thermal equilibrium. Furthermore, we\nexamine the difference between the distribution of conserved quantities in the\nthermal and generalized ensembles after a quench and show that they are also,\nin general, different from each other. This explains why these systems fail to\nthermalize. A finite size scaling analysis is presented for each quantity,\nwhich allows us making predictions for thermodynamically large lattice sizes.",
        "positive": "Spin exchange-enabled quantum simulator for large-scale non-Abelian\n  gauge theories: A central requirement for the faithful implementation of large-scale lattice\ngauge theories (LGTs) on quantum simulators is the protection of the underlying\ngauge symmetry. Recent advancements in the experimental realizations of\nlarge-scale LGTs have been impressive, albeit mostly restricted to Abelian\ngauge groups. Guided by this requirement for gauge protection, we propose an\nexperimentally feasible approach to implement large-scale non-Abelian\n$\\mathrm{SU}(N)$ and $\\mathrm{U}(N)$ LGTs with dynamical matter in $d+1$D,\nenabled by two-body spin-exchange interactions realizing local emergent\ngauge-symmetry stabilizer terms. We present two concrete proposals for $2+1$D\n$\\mathrm{SU}(2)$ and $\\mathrm{U}(2)$ LGTs, including dynamical matter and\ninduced plaquette terms, that can be readily implemented in current\nultracold-molecule and next-generation ultracold-atom platforms. We provide\nnumerical benchmarks showcasing experimentally accessible dynamics, and\ndemonstrate the stability of the underlying non-Abelian gauge invariance. We\ndevelop a method to obtain the effective gauge-invariant model featuring the\nrelevant magnetic plaquette and minimal gauge-matter coupling terms. Our\napproach paves the way towards near-term realizations of large-scale\nnon-Abelian quantum link models in analog quantum simulators."
    },
    {
        "anchor": "Separation induced resonances in quasi-one-dimensional ultracold atomic\n  gases: We study the effective one-dimensional (1D) scattering of two distinguishable\natoms confined individually by {\\em separated} transverse harmonic traps. With\nequal trapping frequency for two s-wave interacting atoms, we find that by\ntuning the trap separations, the system can undergo {\\em double} 1D scattering\nresonance, named as the separation induced resonance(SIR), when the ratio\nbetween the confinement length and s-wave scattering length is within\n$(0.791,1.46]$. Near SIR, the scattering property shows unique dependence on\nthe resonance position. The universality of a many-body system on scattering\nbranch near SIR is demonstrated by studying the interaction effect of a\nlocalized impurity coupled with a Fermi sea of light atoms in a quasi-1D trap.",
        "positive": "Universal Thermometry for Quantum Simulation: Quantum simulation is a highly ambitious program in cold atom research\ncurrently being pursued in laboratories worldwide. The goal is to use cold\natoms in optical lattice to simulate models for unsolved strongly correlated\nsystems, so as to deduce their properties directly from experimental data. An\nimportant step in this effort is to determine the temperature of the system,\nwhich is essential for deducing all thermodynamic functions. This step,\nhowever, remains difficult for lattice systems at the moment. Here, we propose\na method based on a generalized fluctuation-dissipation theorem. It does not\nreply on numerical simulations and is a universal thermometry for all quantum\ngases systems including mixtures and spinor gases. It is also unaffected by\nphoton shot noise."
    },
    {
        "anchor": "Correlations generated from high-temperature states: nonequilibrium\n  dynamics in the Fermi-Hubbard model: We study interaction quenches of the Fermi-Hubbard model initiated from\nvarious high-temperature and high-energy states, motivated by cold atom\nexperiments, which currently operate above the ordering temperature(s). We\nanalytically calculate the dynamics for quenches from these initial states,\nwhich are often strongly-interacting, to the non-interacting limit. Even for\nhigh-temperature uncorrelated initial states, transient connected correlations\ndevelop. These correlations share many features for all considered initial\nstates. We observe light-cone spreading of intertwined spin and density\ncorrelations. The character of these correlations is quite different from their\nlow-temperature equilibrium counterparts: for example, the spin correlations\ncan be ferromagnetic. We also show that an initially localized hole defect\naffects spin correlations near the hole, suppressing their magnitude and\nchanging their sign.",
        "positive": "Non-Hermitian skin effect and chiral damping in open quantum systems: One of the unique features of non-Hermitian Hamiltonians is the non-Hermitian\nskin effect, namely that the eigenstates are exponentially localized at the\nboundary of the system. For open quantum systems, a short-time evolution can\noften be well described by the effective non-Hermitian Hamiltonians, while\nlong-time dynamics calls for the Lindblad master equations, in which the\nLiouvillian superoperators generate time evolution. In this Letter, we find\nthat Liouvillian superoperators can exhibit the non-Hermitian skin effect, and\nuncover its unexpected physical consequences. It is shown that the\nnon-Hermitian skin effect dramatically shapes the long-time dynamics, such that\nthe damping in a class of open quantum systems is algebraic under periodic\nboundary condition but exponential under open boundary condition. Moreover, the\nnon-Hermitian skin effect and non-Bloch bands cause a chiral damping with a\nsharp wavefront. These phenomena are beyond the effective non-Hermitian\nHamiltonians; instead, they belong to the non-Hermitian physics of full-fledged\nopen quantum dynamics."
    },
    {
        "anchor": "Polaritonic Rabi and Josephson Oscillations: The dynamics of coupled condensates is a wide-encompassing problem with\nrelevance to superconductors, BECs in traps, superfluids, etc. Here, we provide\na unified picture of this fundamental problem that includes i) detuning of the\nfree energies, ii) different self-interaction strengths and iii) finite\nlifetime of the modes. At such, this is particularly relevant for the dynamics\nof polaritons, both for their internal dynamics between their light and matter\nconstituents, as well as for the more conventional dynamics of two spatially\nseparated condensates. Polaritons are short-lived, interact only through their\nmaterial fraction and are easily detuned. At such, they bring several\nvariations to their atomic counterpart. We show that the combination of these\nparameters results in important twists to the phenomenology of the Josephson\neffect, such as the behaviour of the relative phase (running or oscillating) or\nthe occurrence of self-trapping. We undertake a comprehensive stability\nanalysis of the fixed points on a normalized Bloch sphere, that allows us to\nprovide a generalized criterion to identify the Rabi and Josephson regimes in\npresence of detuning and decay.",
        "positive": "Dynamics of Hot Bose-Einstein Condensates: stochastic Ehrenfest\n  relations for number and energy damping: Describing partially-condensed Bose gases poses a long-standing theoretical\nchallenge. We present exact stochastic Ehrenfest relations for the stochastic\nprojected Gross-Pitaevskii equation, including both number and energy damping\nmechanisms, and all projector terms that arise from the energy cutoff\nseparating system from reservoir. We test the theory by applying it to the\ncentre of mass fluctuations of a harmonically trapped prolate system, finding\nclose agreement between c-field simulations and analytical results. The\nformalism lays the foundation to analytically explore experimentally accessible\nhot Bose-Einstein condensates."
    },
    {
        "anchor": "Controlled engineering of a vortex-bright soliton dynamics using a\n  constant driving force: A vortex-bright soliton can precess around a fix point. Here, we find\nnumerically that the fixed point and the associated precessional orbits can be\nshifted by applying a constant driving force on the bright component, the\ndisplacement is proportional to the force with a minus sign. This robust\ndynamics is then discussed theoretically by treating the vortex-bright soliton\nas an effective point particle, explaining the observed dynamics and predicting\nnew ones that are subsequently confirmed. By appropriately tuning the force,\nthe vortex-bright soliton can be guided following an arbitrary trajectory,\nincluding that it can be pinned and released at will. This finding opens a\nhighly flexible and controllable approach of engineering the dynamics of\nvortical structures in Bose-Einstein condensates.",
        "positive": "Chiral modes at exceptional points in exciton-polariton quantum fluids: We demonstrate generation of chiral modes -- vortex flows with fixed\nhandedness in exciton-polariton quantum fluids. The chiral modes arise in the\nvicinity of exceptional points (non-Hermitian spectral degeneracies) in an\noptically-induced resonator for exciton polaritons. In particular, a vortex is\ngenerated by driving two dipole modes of the non-Hermitian ring resonator into\ndegeneracy. Transition through the exceptional point in the space of the\nsystem's parameters is enabled by precise manipulation of real and imaginary\nparts of the closed-wall potential forming the resonator. As the system is\ndriven to the vicinity of the exceptional point, we observe the formation of a\nvortex state with a fixed orbital angular momentum (topological charge). Our\nmethod can be extended to generate high-order orbital angular momentum states\nthrough coalescence of multiple non-Hermitian spectral degeneracies, which\ncould find application in integrated optoelectronics."
    },
    {
        "anchor": "Design and characterization of a quantum heat pump in a driven quantum\n  gas: We propose the implementation of a quantum heat pump with ultracold atoms. It\nis based on two periodically driven coherently coupled quantum dots using\nultracold atoms. Each dot possesses two relevant quantum states and is coupled\nto a fermionic reservoir. The working principle is based on energy-selective\ndriving-induced resonant tunneling processes, where a particle that tunnels\nfrom one dot to the other either absorbs or emits the energy quantum\n$\\hbar\\omega$ associated with the driving frequency, depending on its energy.\nWe characterize the device using Floquet theory and compare simple analytical\nestimates to numerical simulations based on the Floquet-Born-Markov formalism.\nIn particular, we show that driving-induced heating is directly linked to the\nmicromotion of the Floquet states of the system.",
        "positive": "Quantum hydrodynamics of the spinor Bose-Einstein condensate at non-zero\n  temperatures: Finite temperature hydrodynamic model is derived for the spin-1 ultracold\nbosons by the many-particle quantum hydrodynamic method. It is presented as the\ntwo fluid model of the BEC and normal fluid. The linear and quadratic Zeeman\neffects are included. Scalar and spin-spin like short-range interactions are\nconsidered in the first order by the interaction radius. It is also represented\nas the set of two nonlinear Pauli equations. The spectrum of the bulk\ncollective excitations is considered for the ferromagnetic phase in the small\ntemperature limit. The spin wave is not affected by the presence of the small\ntemperature in the described minimal coupling model, where the thermal part of\nthe spin-current of the normal fluid is neglected. The two sound waves are\naffected by the spin evolution in the same way as the change of spectrum of the\nsingle sound wave in BEC, where speed of sound is proportional to $g_{1}+g_{2}$\nwith $g_{i}$ are the interaction constants."
    },
    {
        "anchor": "One-dimensional superlattices with s-p resonance: We propose a realization of an extended Bose-Hubbard model, which takes into\naccount next-nearest-neighbor tunneling, by one-dimensional double-well optical\nsuperlattice with a resonance between s and p orbitals in the neighboring\nsites. Custom method of finding maximally-localized Wannier functions enables\nus to compute physical tunneling coefficients, which put some restrictions on\nthe studies of the model, what have recently been done using arbitrary values\nof parameters. Furthermore, it turns out that out of s-p resonance the system\nsplits up into two disconnected lattices. We analyze also Zak-Berry phase and\nsingle-particle spectrum of the system. In order to present the problem in the\nfull context, short review of rudiments of optical lattice physics and\nderivation of the standard Bose-Hubbard model is included.",
        "positive": "Generalized lattice Wilson-Dirac fermions in (1+1) dimensions for atomic\n  quantum simulation and topological phases: The Dirac fermion is an important fundamental particle appearing in\nhigh-energy physics and topological insulator physics. In particular, a Dirac\nfermion in a one-dimensional lattice system exhibits the essential properties\nof topological physics. However, the system has not been quantum simulated in\nexperiments yet. Herein, we propose a one-dimensional generalized lattice\nWilson-Dirac fermion model and study its topological phase structure. We show\nthe experimental setups of an atomic quantum simulator for the model, in which\ntwo parallel optical lattices with the same tilt for trapping cold fermion\natoms and a laser-assisted hopping scheme are used. Interestingly, we find that\nthe model exhibits nontrivial topological phases characterized by gapless edge\nmodes and a finite winding number in the broad regime of the parameter space.\nSome of the phase diagrams closely resemble those of the Haldane model. We also\ndiscuss topological charge pumping and a lattice Gross-Neveu model in the\nsystem of generalized Wilson-Dirac fermions."
    },
    {
        "anchor": "Edge state preparation in one dimensional lattice by quantum Lyapunov\n  control: Quantum Lyapunov control uses a feedback control methodology to determine\ncontrol fields which are applied to control quantum systems in an open-loop\nway. In this work, we adopt two Lyapunov control schemes to prepare an edge\nstate for a fermionic chain consisted of cold atoms loaded in an optical\nlattice. Such a chain can be described by the Harper model. Corresponding to\nthe two schemes, state distance and state error Lyapunov functions are\nconsidered. The results show that both the schemes are effective to prepare the\nedge state within a wide range of parameters. We found that the edge state can\nbe prepared with high fidelity even \\textbf{if} there are moderate fluctuations\nin on-site or hopping potentials. Both control schemes can be extended to\nsimilar chains (3$m+d$, $d$=2) of different lengths. Since regular amplitude\ncontrol field is easier to apply in practice, amplitude-modulated control\nfields are used to replace the unmodulated one to prepare the edge state. Such\ncontrol approaches provide tools to explore edge states for one dimensional\ntopological materials.",
        "positive": "Levy distribution in many-particle quantum systems: Levy distribution, previously used to describe complex behavior of classical\nsystems, is shown to characterize that of quantum many-body systems. Using two\ncomplimentary approaches, the canonical and grand-canonical formalisms, we\ndiscovered that the momentum profile of a Tonks-Girardeau gas, -- a\none-dimensional gas of $N$ impenetrable (hard-core) bosons, harmonically\nconfined on a lattice at finite temperatures, obeys Levy distribution. Finally,\nwe extend our analysis to different confinement setups and demonstrate that the\ntunable Levy distribution properly reproduces momentum profiles in\nexperimentally accessible regions. Our finding allows for calibration of\ncomplex many-body quantum states by using a unique scaling exponent."
    },
    {
        "anchor": "Engineering Frequency-dependent Superfluidity in Bose-Fermi Mixtures: Unconventional superconductivity or superfluidity are among the most exciting\nand fascinating quantum states in condensed matter physics. Usually these\nstates are characterized by non-trivial spatial symmetry of the pairing order\nparameter, such as in $^{3}He$ and high-$T_{c}$ cuprates. Besides spatial\ndependence the order parameter could have unconventional frequency dependence,\nwhich is also allowed by Fermi-Dirac statistics. For instance, odd-frequency\npairing is an exciting paradigm when discussing exotic superfluidity or\nsuperconductivity and is yet to be realized in the experiments. In this paper\nwe propose a symmetry-based method of controlling frequency dependence of the\npairing order parameter via manipulating the inversion symmetry of the system.\nFirst, a toy model is introduced to illustrate that frequency dependence of the\norder parameter can be adjusted by controlling the inversion symmetry of the\nsystem. Second, taking advantage of the recent rapid developments of shaken\noptical lattices in ultracold gases, we propose a Bose-Fermi mixture to realize\nsuch frequency dependent superfluids. The key idea is introducing the\nfrequency-dependent attraction between Fermions mediated by Bogoliubov phonons\nwith asymmetric dispersion. Our proposal should pave an alternative way for\nexploring frequency-dependent superconductors or superfluids with cold atoms.",
        "positive": "Fragility of the fractional quantum spin Hall effect in quantum gases: We consider the effect of contact interaction in a prototypical quantum spin\nHall system of pseudo-spin-1/2 particles. A strong effective magnetic field\nwith opposite directions for the two spin states restricts two-dimensional\nparticle motion to the lowest Landau level. While interaction between same-spin\nparticles leads to incompressible correlated states at fractional filling\nfactors as known from the fractional quantum Hall effect, these states are\ndestabilized by interactions between opposite spin particles. Exact results for\ntwo particles with opposite spin reveal a quasi-continuous spectrum of extended\nstates with a large density of states at low energy. This has implications for\nthe prospects of realizing the fractional quantum spin Hall effect in\nelectronic or ultra-cold atom systems. Numerical diagonalization is used to\nextend the two-particle results to many bosonic particles and trapped systems.\nThe interplay between an external trapping potential and spin-dependent\ninteractions is shown to open up new possibilities for engineering exotic\ncorrelated many-particle states with ultra-cold atoms."
    },
    {
        "anchor": "New trends in quantum integrability: Recent experiments with ultracold\n  atoms: Over the past two decades quantum engineering has made significant advances\nin our ability to create genuine quantum many-body systems using ultracold\natoms. In particular, some prototypical exactly solvable Yang-Baxter systems\nhave been successfully realized allowing us to confront elegant and\nsophisticated exact solutions of these systems with their experimental\ncounterparts. The new experimental developments show a variety of fundamental\none-dimensional (1D) phenomena, ranging from the generalized hydrodynamics to\ndynamical fermionization, Tomonaga-Luttinger liquids, collective excitations,\nfractional exclusion statistics, quantum holonomy, spin-charge separation,\ncompeting orders with high spin symmetry and quantum impurity problems. This\narticle briefly reviews these developments and provides rigorous understanding\nof those observed phenomena based on the exact solutions while highlighting the\nuniqueness of 1D quantum physics. The precision of atomic physics realizations\nof integrable many-body problems continues to inspire significant developments\nin mathematics and physics while at the same time offering the prospect to\ncontribute to future quantum technology.",
        "positive": "Anisotropic dynamics of a spin-orbit coupled Bose-Einstein condensate: By calculating the density response function we identify the excitation\nspectrum of a Bose-Einstein condensate with equal Rashba and Dresselhaus\nspin-orbit coupling. We find that the velocity of sound along the direction of\nspin-orbit coupling is deeply quenched and vanishes when one approaches the\nsecond-order phase transition between the plane wave and the zero momentum\nquantum phases. We also point out the emergence of a roton minimum in the\nexcitation spectrum for small values of the Raman coupling, providing the onset\nof the transition to the stripe phase. Our findings point out the occurrence of\na strong anisotropy in the dynamic behavior of the gas. A hydrodynamic\ndescription accounting for the collective oscillations in both uniform and\nharmonically trapped gases is also derived."
    },
    {
        "anchor": "Three-body problem in heteronuclear mixtures with resonant interspecies\n  interaction: We use the zero-range approximation to study a system of two identical bosons\ninteracting resonantly with a third particle. The method is derived from\neffective field theory. It reduces the three-body problem to an integral\nequation which we then solve numerically. We also develop an alternative\napproach which gives analytic solutions of the integral equation in coordinate\nrepresentation in the limit of vanishing total energy. The atom-dimer\nscattering length, the rates of atom-dimer relaxation and three-body\nrecombination to shallow and to deep molecular states are calculated either\nanalytically or numerically with a well controlled accuracy for various\nenergies as functions of the mass ratio, scattering length, and three-body\nparameter. We discuss in detail the relative positions of the recombination\nloss peaks, which in the universal limit depend only on the mass ratio. Our\nresults have implications for ongoing and future experiments on Bose-Bose and\nBose-Fermi atomic mixtures.",
        "positive": "Bubbles with attached quantum vortices in trapped binary Bose-Einstein\n  condensates: Specific topological excitations of energetically stable \"core-and-mantle\"\nconfigurations of trapped two-component immiscible Bose-Einstein condensates\nare studied numerically within the coupled Gross-Pitaevskii equations.\nNon-stationary long-lived coherent structures, that consist of several quantum\nvortex filaments penetrating the \"mantle\" from outside to inside and vice-versa\nand demonstrate quite nontrivial dynamics, are observed in simulations for the\nfirst time. The ends of filaments can remain attached to the interface between\nthe \"mantle\" and the \"core\" if the latter is large enough while the surface\ntension is not small. The shapes of such \"bubbles\" are strongly affected by the\nvortices and sometimes are far from being spherical."
    },
    {
        "anchor": "Evidence for a Bose-Einstein condensate of excitons: The demonstration of Bose-Einstein condensation in atomic gases at\nmicro-Kelvin temperatures is a striking landmark while its evidence for\nsemiconductor excitons still is a long-awaited milestone. This situation was\nnot foreseen because excitons are light-mass boson-like particles with a\ncondensation expected to occur around a few Kelvins. An explanation can be\nfound in the underlying fermionic nature of excitons which rules their\ncondensation. Precisely, it was recently predicted that, at accessible\nexperimental conditions, the exciton condensate shall be \"gray\" with a dominant\ndark part coherently coupled to a weak bright component through fermion\nexchanges. This counter-intuitive quantum condensation, since excitons are\nmostly known for their optical activity, directly follows from the excitons\ninternal structure which has an optically inactive, i.e., dark, ground state.\nHere, we report compelling evidence for such a \"gray\" condensate. We use an\nall-optical approach in order to produce microscopic traps which confine a\ndense exciton gas that yet exhibits an anomalously weak photo-emission at\nsub-Kelvin temperatures. This first fingerprint for a \"gray\" condensate is then\nconfirmed by the macroscopic spatial coherence and the linear polarization of\nthe weak excitonic photoluminescence emitted from the trap, as theoretically\npredicted.",
        "positive": "Observation of Efimov molecules created from a resonantly interacting\n  Bose gas: We convert a strongly interacting ultracold Bose gas into a mixture of atoms\nand molecules by sweeping the interactions from resonant to weak. By analyzing\nthe decay dynamics of the molecular gas, we show that in addition to Feshbach\ndimers it contains Efimov trimers. Typically around 8\\% of the total atomic\npopulation is bound into trimers, identified by their density-independent\nlifetime of about 100~$\\mu$s. The lifetime of the Feshbach dimers shows a\ndensity dependence due to inelastic atom-dimer collisions, in agreement with\ntheoretical calculations. We also vary the density of the gas across a factor\nof 250 and investigate the corresponding atom loss rate at the interaction\nresonance."
    },
    {
        "anchor": "Far-from-equilibrium quantum many-body dynamics: The theory of real-time quantum many-body dynamics as put forward in Ref.\n[arXiv:0710.4627] is evaluated in detail. The formulation is based on a\ngenerating functional of correlation functions where the Keldysh contour is\nclosed at a given time. Extending the Keldysh contour from this time to a later\ntime leads to a dynamic flow of the generating functional. This flow describes\nthe dynamics of the system and has an explicit causal structure. In the present\nwork it is evaluated within a vertex expansion of the effective action leading\nto time evolution equations for Green functions. These equations are applicable\nfor strongly interacting systems as well as for studying the late-time\nbehaviour of nonequilibrium time evolution. For the specific case of a bosonic\nN-component phi^4 theory with contact interactions an s-channel truncation is\nidentified to yield equations identical to those derived from the 2PI effective\naction in next-to-leading order of a 1/N expansion. The presented approach\nallows to directly obtain non-perturbative dynamic equations beyond the widely\nused 2PI approximations.",
        "positive": "The nonlinear Dirac equation in Bose-Einstein condensates: Vortex\n  solutions and spectra in a weak harmonic trap: We analyze the vortex solution space of the $(2 +1)$-dimensional nonlinear\nDirac equation for bosons in a honeycomb optical lattice at length scales much\nlarger than the lattice spacing. Dirac point relativistic covariance combined\nwith s-wave scattering for bosons leads to a large number of vortex solutions\ncharacterized by different functional forms for the internal spin and overall\nphase of the order parameter. We present a detailed derivation of these\nsolutions which include skyrmions, half-quantum vortices, Mermin-Ho and\nAnderson-Toulouse vortices for vortex winding $\\ell = 1$. For $\\ell \\ge 2$ we\nobtain topological as well as non-topological solutions defined by the\nasymptotic radial dependence. For arbitrary values of $\\ell$ the\nnon-topological solutions are bright ring-vortices which explicitly demonstrate\nthe confining effects of the Dirac operator. We arrive at solutions through an\nasymptotic Bessel series, algebraic closed-forms, and using standard numerical\nshooting methods. By including a harmonic potential to simulate a finite trap\nwe compute the discrete spectra associated with radially quantized modes. We\ndemonstrate the continuous spectral mapping between the vortex and free\nparticle limits for all of our solutions."
    },
    {
        "anchor": "Semiclassical dynamics of a disordered two-dimensional Hubbard model\n  with long-range interactions: Quench dynamics in a two-dimensional system of interacting fermions is\nanalyzed within the semiclassical truncated Wigner approximation (TWA). The\nmodels with short-range and long-range interactions are considered. We show\nthat in the latter case, the TWA is very accurate, becoming asymptotically\nexact in the infinite-range limit, provided that the semiclassical Hamiltonian\nis correctly identified. Within the TWA, different dynamical timescales of\ncharges and spins can be clearly distinguished. Interestingly, for a weak and\nmoderate disorder strength, we observe subdiffusive behavior of charges, while\nspins exhibit diffusive dynamics. At strong disorder, the quantum Fisher\ninformation shows logarithmic growth in time with a slower increase for charges\nthan for spins. It is shown that in contrast to the short-range model, strong\ninhomogeneities such as domain walls in the initial state can significantly\nslow down thermalization dynamics, especially at weak disorder. This behavior\ncan put additional challenges in designing cold-atom experimental protocols\naimed to analyze possible many-body localization in such systems. While within\nthis approach we cannot make any definite statements about the existence of a\nmany-body localized phase, we see a very fast crossover as a function of\ndisorder strength from rapidly thermalizing to a slow glassy like regime both\nfor the short-range and long-range models.",
        "positive": "Coherence time of a Bose-Einstein condensate: Temporal coherence is a fundamental property of macroscopic quantum systems,\nsuch as lasers in optics and Bose-Einstein condensates in atomic gases and it\nis a crucial issue for interferometry applications with light or matter waves.\nWhereas the laser is an \"open\" quantum system, ultracold atomic gases are\nweakly coupled to the environment and may be considered as isolated. The\ncoherence time of a condensate is then intrinsic to the system and its\nderivation is out of the frame of laser theory. Using quantum kinetic theory,\nwe predict that the interaction with non-condensed modes gradually smears out\nthe condensate phase, with a variance growing as A t^2+B t+C at long times t,\nand we give a quantitative prediction for A, B and C. Whereas the coefficient A\nvanishes for vanishing energy fluctuations in the initial state, the\ncoefficients B and C are remarkably insensitive to these fluctuations. The\ncoefficient B describes a diffusive motion of the condensate phase that sets\nthe ultimate limit to the condensate coherence time. We briefly discuss the\npossibility to observe the predicted phase spreading, also including the effect\nof particle losses."
    },
    {
        "anchor": "Realizing one-dimensional topological superfluids with ultracold atomic\n  gases: We propose an experimental implementation of a topological superfluid with\nultracold fermionic atoms. An optical superlattice is used to juxtapose a 1D\ngas of fermionic atoms and a 2D conventional superfluid of condensed Feshbach\nmolecules. The latter acts as a Cooper pair reservoir and effectively induces a\nsuperfluid gap in the 1D system. Combined with a spin-dependent optical lattice\nalong the 1D tube and laser-induced atom tunneling, we obtain a topological\nsuperfluid phase. In the regime of weak couplings to the molecular fl eld and\nfor a uniform gas the atomic system is equivalent to Kitaev's model of a p-wave\nsuperfluid. Using a numerical calculation we show that the topological\nsuperfluidity is robust beyond the perturbative limit and in the presence of a\nharmonic trap. Finally we describe how to investigate some physical properties\nof the Majorana fermions located at the topological superfluid boundaries. In\nparticular we discuss how to prepare and detect a given Majorana edge state.",
        "positive": "Spin-incoherent Luttinger liquid of one-dimensional spin-1\n  Tonks-Girardeau Bose gas: Spin-dependent properties: Spin-incoherent Luttinger liquid (SILL) is a different universal class from\nthe Luttinger liquid.\\ This difference results from the spin incoherence of the\nsystem when the thermal energy of the system is higher than the spin excitation\nenergy.\\ We consider one-dimensional spin-$1$ Bose gas in the SILL regime and\ninvestigate its spin-dependent many-body properties.\\ In Tonks-Girardeau limit,\nwe are able to write down the general wave functions in a harmonic trap.\\ We\nnumerically calculate the spin-dependent (spin-plus, minus, and $0$) momentum\ndistributions in the sector of zero magnetization which allows to demonstrate\nthe most significant spin-incoherent feature compared to the spinless or\nspin-polarized case.\\ In contrast to the spinless Bose gas, the momentum\ndistributions are broadened and in the large momentum limit follow the same\nasymptotic $1/p^4$ dependence but with reduced coefficients.\\ While the density\nmatrices and momentum distributions differ between different spin components\nfor small $N$, at large $N$ they approach each other.\\ We show these by\nanalytic arguments and numerical calculations up to $N$ $=$ $16$."
    },
    {
        "anchor": "BEC-BCS crossover and universal relations in unitary Fermi gases: The contact parameter in unitary Fermi Gases governs the short-distance,\nhigh-momentum, and high-energy properties of the system. We perform accurate\nquantum Monte Carlo calculations with highly optimized trial functions to\nprecisely determine this parameter at T=0, demonstrate its universal\napplication to a variety of observables, and determine the regions of momentum\nand energy over which the leading short-range behavior is dominant. We derive\nTan's expressions for the contact parameter using just the short-range behavior\nof the ground-state many-body wave function, and use this behavior to calculate\nthe two-body distribution function, one-body density matrix, and the momentum\ndistribution of unitary Fermi gases; providing a precise value of the contact\nparameter that can be compared to experiments.",
        "positive": "Nonlinear Thouless Pumping of Solitons Across an Impurity: The nonlinear Thouless pumping is an exciting frontier of topological\nphysics. While recent works have revealed the quantized motion of solitons in\nThouless pumps, the interplay between the topology, nonlinearity and disorder\nremains largely unexplored. Here, we investigate the nonlinear Thouless pumping\nof solitons in the presence of an impurity in the context of a Bose-Einstein\ncondensate. Using both the Gross-Pitaevskii equation and Lagrangian variational\napproach, we analyze the interaction between a moving soliton and an impurity.\nWithout the pump, the soliton can pass through a light impurity, but gets\ntrapped by the impurity with large mass. In marked contrast, we find the\nsoliton in Thouless pumps can always transit through the impurity, and its\nmotion is topologically quantized. Our result explicitly showcases the\nrobustness of topological soliton pumping against microscopic imperfections,\nand opens a new perspective in the information processing with solitons."
    },
    {
        "anchor": "Viscous damping in weltering motion of trapped hydrodynamic dipolar\n  Fermi gases: We consider collective motion and damping of dipolar Fermi gases in the\nhydrodynamic regime. We investigate the trajectories of collective oscillations\n-- here dubbed ``weltering'' motions -- in cross-dimensional rethermalization\nexperiments via Monte Carlo simulations, where we find stark differences from\nthe dilute regime. These observations are interpreted within a semi-empirical\ntheory of viscous hydrodynamics for gases confined to anisotropic harmonic\npotentials. The derived equations of motion provide a simple effective theory\nthat show favorable agreement with full numerical solutions. To do so, the\ntheory must carefully account for the size and shape of the effective volume\nwithin which the gas' behavior is hydrodynamic. Although formulated for dipolar\nmolecules, our theoretical framework retains a flexibility to accommodate\narbitrary elastic cross sections.",
        "positive": "Control of the symmetry breaking in double-well potentials by the\n  resonant nonlinearity management: We introduce a one-dimensional model of Bose-Einstein condensates (BECs),\ncombining the double-well potential, which is a well-known setting for the\nonset of spontaneous-symmetry-breaking (SSB) effects, and time-periodic\nmodulation of the nonlinearity, which may be implemented by means of the\nFeshbach-resonance-management (FRM) technique. Both cases of the nonlinearity\nwhich is repulsive or attractive on the average are considered. In the former\ncase, the main effect produced by the application of the FRM is spontaneous\nself-trapping of the condensate in either of the two potential wells in\nparameter regimes where it would remain untrapped in the absence of the\nmanagement. In the weakly nonlinear regime, the frequency of intrinsic\noscillations in the FRM-induced trapped state is very close to half the FRM\nfrequency, suggesting that the effect is accounted for by a parametric\nresonance. In the case of the attractive nonlinearity, the FRM-induced effect\nis the opposite, i.e., enforced detrapping of a state which is self-trapped in\nits unmanaged form. In the latter case, the frequency of oscillations of the\nuntrapped mode is close to a quarter of the driving frequency, suggesting that\na higher-order parametric resonance may account for this effect."
    },
    {
        "anchor": "Searching for Majorana Fermions in 2D Spin-orbit Coupled Fermi\n  Superfluids at Finite Temperature: Recent experimental breakthrough in realizing spin-orbit (SO) coupling for\ncold atoms has spurred considerable interest in the physics of 2D SO coupled\nFermi superfluids, especially topological Majorana fermions (MFs) which were\npredicted to exist at zero temperature. However, it is well known that\nlong-range superfluid order is destroyed in 2D by the phase fluctuation at\nfinite temperature and the relevant physics is the\nBerezinskii-Kosterlitz-Thouless (BKT) transition. In this Letter, we examine\nfinite temperature effects on SO coupled Fermi gases and show that finite\ntemperature is indeed necessary for the observation of MFs. MFs are\ntopologically protected by a quasiparticle energy gap which is found to be much\nlarger than the temperature. The restrictions to the parameter region for the\nobservation of MFs have been obtained.",
        "positive": "Inelastic collisions of ultracold triplet Rb$_\\textbf{2}$ molecules in\n  the rovibrational ground state: Exploring inelastic and reactive collisions on the quantum level is a main\ngoal of the developing field of ultracold chemistry. We present first\nexperimental studies of inelastic collisions of metastable ultracold triplet\nmolecules in the vibrational ground state. The measurements are performed with\nnonpolar $\\textrm{Rb}_2$ dimers which are prepared in precisely-defined quantum\nstates and trapped in an array of quasi-1D potential tubes. In particular, we\ninvestigate collisions of molecules in the absolute lowest triplet energy level\nwhere any inelastic process requires a change of the electronic state.\nNevertheless, we find similar decay rates as for collisions between\nrotationally or vibrationally excited triplet molecules and they are close to\nthe rates for universal reactions. As anticipated theoretically, the measured\ndecay rate constants vary considerably when confinement and collision energy\nare changed. This might be exploited to control the collisional properties of\nmolecules."
    },
    {
        "anchor": "Dark solitons in Bose-Einstein condensates: a dataset for many-body\n  physics research: We establish a dataset of over $1.6\\times10^4$ experimental images of\nBose--Einstein condensates containing solitonic excitations to enable machine\nlearning (ML) for many-body physics research. About $33~\\%$ of this dataset has\nmanually assigned and carefully curated labels. The remainder is automatically\nlabeled using SolDet -- an implementation of a physics-informed ML data\nanalysis framework -- consisting of a convolutional-neural-network-based\nclassifier and OD as well as a statistically motivated physics-informed\nclassifier and a quality metric. This technical note constitutes the definitive\nreference of the dataset, providing an opportunity for the data science\ncommunity to develop more sophisticated analysis tools, to further understand\nnonlinear many-body physics, and even advance cold atom experiments.",
        "positive": "Scaling Flows and Dissipation in the Dilute Fermi Gas at Unitarity: We describe recent attempts to extract the shear viscosity of the dilute\nFermi gas at unitarity from experiments involving scaling flows. A scaling flow\nis a solution of the hydrodynamic equations that preserves the shape of the\ndensity distribution. The scaling flows that have been explored in the\nlaboratory are the transverse expansion from a deformed trap (\"elliptic flow\"),\nthe expansion from a rotating trap, and collective oscillations. We discuss\nadvantages and disadvantages of the different experiments, and point to\nimprovements of the theoretical analysis that are needed in order to achieve\ndefinitive results. A conservative bound based on the current data is that the\nminimum of the shear viscosity to entropy density ration is that eta/s is less\nor equal to 0.5 hbar/k_B."
    },
    {
        "anchor": "Universal quantum behaviors of interacting fermions in 1D traps: from\n  few particles to the trap thermodynamic limit: We investigate the ground-state properties of trapped fermion systems\ndescribed by the Hubbard model with an external confining potential. We discuss\nthe universal behaviors of systems in different regimes: from few particles,\ni.e. in dilute regime, to the trap thermodynamic limit.\n  The asymptotic trap-size (TS) dependence in the dilute regime (increasing the\ntrap size l keeping the particle number N fixed) is described by a universal TS\nscaling controlled by the dilute fixed point associated with the\nmetal-to-vacuum quantum transition. This scaling behavior is numerically\nchecked by DMRG simulations of the one-dimensional (1D) Hubbard model. In\nparticular, the particle density and its correlations show crossovers among\ndifferent regimes: for strongly repulsive interactions they approach those of a\nspinless Fermi gas, for weak interactions those of a free Fermi gas, and for\nstrongly attractive interactions they match those of a gas of hard-core bosonic\nmolecules.\n  The large-N behavior of systems at fixed N/l corresponds to a 1D trap\nthermodynamic limit. We address issues related to the accuracy of the local\ndensity approximation (LDA). We show that the particle density approaches its\nLDA in the large-l limit. When the trapped system is in the metallic phase,\ncorrections at finite l are O(l^{-1}) and oscillating around the center of the\ntrap. They become significantly larger at the boundary of the fermion cloud,\nwhere they get suppressed as O(l^{-1/3}) only. This anomalous behavior arises\nfrom the nontrivial scaling at the metal-to-vacuum transition occurring at the\nboundaries of the fermion cloud.",
        "positive": "Influence of the energy-band structure on ultracold reactive processes\n  in lattices: We study theoretically ultracold collisions in quasi one-dimensional optical\ntraps for bosonic and fermionic reactive molecules in the presence of a\nperiodic potential along the trap axis. Elastic, reactive, and umklapp\nprocesses due to non-conservation of the center of mass motion are investigated\nfor parameters of relevant experimental interest. The model naturally keeps\ninto account the effect of excited energy bands and is particularly suited for\nbeing adapted to rigorous close-coupled calculations. Our formalism shows that\na correct derivation of the parameters in tight-binding effective models must\ninclude the strong momentum dependence of the coupling constant we predict even\nfor deep lattices."
    },
    {
        "anchor": "Simple method for producing Bose-Einstein condensates of metastable\n  helium using a single beam optical dipole trap: We demonstrate a simple scheme to reach Bose-Einstein condensation (BEC) of\nmetastable triplet helium atoms using a single beam optical dipole trap with\nmoderate power of less than 3 W. Our scheme is based on RF-induced evaporative\ncooling in a quadrupole magnetic trap and transfer to a single beam optical\ndipole trap that is located below the magnetic trap center. We transfer 1x10^6\natoms into the optical dipole trap, with an initial temperature of 14 \\mu K,\nand observe efficient forced evaporative cooling both in a hybrid trap, in\nwhich the quadrupole magnetic trap operates just below the levitation gradient,\nand in the pure optical dipole trap, reaching the onset of BEC with 2x10^5\natoms and a pure BEC of 5x10^4 atoms. Our work shows that a single beam hybrid\ntrap can be applied for a light atom, for which evaporative cooling in the\nquadrupole magnetic trap is strongly limited by Majorana spin-flips, and the\nvery small levitation gradient limits the axial confinement in the hybrid trap.",
        "positive": "Comment on \"Lack of a genuine time crystal in a chiral soliton model\" by\n  Syrwid, Kosior, and Sacha: We present a comment on A. Syrwid, A. Kosior, and K. Sacha, \"Lack of a\ngenuine time crystal in a chiral soliton model,\" arXiv:2005.12313."
    },
    {
        "anchor": "Direct probing of the Mott crossover in the SU($N$) Fermi-Hubbard model: The Fermi-Hubbard model (FHM) is a cornerstone of modern condensed matter\ntheory. Developed for interacting electrons in solids, which typically exhibit\nSU($2$) symmetry, it describes a wide range of phenomena, such as metal to\ninsulator transitions and magnetic order. Its generalized SU($N$)-symmetric\nform, originally applied to multi-orbital materials such as transition-metal\noxides, has recently attracted much interest owing to the availability of\nultracold SU($N$)-symmetric atomic gases. Here we report on a detailed\nexperimental investigation of the SU($N$)-symmetric FHM using local probing of\nan atomic gas of ytterbium in an optical lattice to determine the equation of\nstate through different interaction regimes. We prepare a low-temperature\nSU($N$)-symmetric Mott insulator and characterize the Mott crossover,\nrepresenting important steps towards probing predicted novel SU($N$)-magnetic\nphases.",
        "positive": "Parity breakdown, vortices, and dark soliton states in a Bose gas of\n  resonantly excited polaritons: A new mechanism of parity breakdown in a spinor Bose gas is predicted; it\ncauses a single-mode state of polaritons to be spontaneously divided into\ndifferent polarization domains which annihilate each other at the interface\nareas. In a polariton wire, such interface is a dark soliton that can run in\nspace without dissipation. In a planar cavity, quantized vortices arise in\nwhich phase difference of orthogonally polarized components makes one complete\nturn around the core. Coupled vortex-antivortex pairs and straight filaments\ncan form in analogy to Bose-Einstein condensates and superconductors. However,\nthe rotational symmetry is broken even for individual vortices, which makes\nthem interact on a large scale and form internally ordered structures. These\nstates come into being under resonant excitation if the spin coupling rate\nsignificantly exceeds the decay rate."
    },
    {
        "anchor": "Dynamical formation of a magnetic polaron in a two-dimensional quantum\n  antiferromagnet: We numerically study the real-time dynamics of a single hole created in the\n$t-J$ model on a square lattice. Initially, the hole spreads ballistically with\na velocity proportional to the hopping matrix element. At intermediate to long\ntimes, the dimensionality as well as the spin background determine the hole\ndynamics. A hole created in the ground state of a two dimensional quantum\nantiferromagnet propagates again ballistically at long times but with a\nvelocity proportional to the spin exchange coupling, showing the formation of a\nmagnetic polaron. We provide an intuitive explanation of this dynamics in terms\nof a parton construction, which leads to a good quantitative agreement with the\nnumerical simulations. In the limit of infinite temperature and no spin\nexchange couplings, the dynamics can be approximated by a quantum random walk\non the Bethe lattice. Adding Ising interactions corresponds to an effective\ndisordered potential, which can dramatically slow down the hole propagation,\nconsistent with subdiffusive dynamics.",
        "positive": "Coherent multi-flavour spin dynamics in a fermionic quantum gas: Microscopic spin interaction processes are fundamental for global static and\ndynamical magnetic properties of many-body systems. Quantum gases as pure and\nwell isolated systems offer intriguing possibilities to study basic magnetic\nprocesses including non-equilibrium dynamics. Here, we report on the\nrealization of a well-controlled fermionic spinor gas in an optical lattice\nwith tunable effective spin ranging from 1/2 to 9/2. We observe long-lived\nintrinsic spin oscillations and investigate the transition from two-body to\nmany-body dynamics. The latter results in a spin-interaction driven melting of\na band insulator. Via an external magnetic field we control the system's\ndimensionality and tune the spin oscillations in and out of resonance. Our\nresults open new routes to study quantum magnetism of fermionic particles\nbeyond conventional spin 1/2 systems."
    },
    {
        "anchor": "Two-state Bose-Hubbard model in the hard-core boson limit: Phase transition into the phase with Bose-Einstein (BE) condensate in the\ntwo-band Bose-Hubbard model with the particle hopping in the excited band only\nis investigated. Instability connected with such a transition (which appears at\nexcitation energies $\\delta<\\lvert t_0' \\rvert$, where $\\lvert t_0' \\rvert$ is\nthe particle hopping parameter) is considered. The re-entrant behaviour of\nspinodales is revealed in the hard-core boson limit in the region of positive\nvalues of chemical potential. It is found that the order of the phase\ntransition undergoes a change in this case and becomes the first one; the\nre-entrant transition into the normal phase does not take place in reality.\nFirst order phase transitions also exist at negative values of $\\delta$ (under\nthe condition $\\delta>\\delta_{\\mathrm{crit}}\\approx-0.12\\lvert t_0' \\rvert$).\nAt $\\mu<0$ the phase transition mostly remains to be of the second order. The\nbehaviour of the BE-condensate order parameter is analyzed, the $(\\Theta,\\mu)$\nand $(\\lvert t_0' \\rvert,\\mu)$ phase diagrams are built and localizations of\ntricritical points are established. The conditions are found at which the\nseparation on the normal phase and the phase with the BE condensate takes\nplace.",
        "positive": "Stability and Anomalous Compressibility of Bose Gases Near Resonance:\n  The scale-dependent interactions and thermal effects: The stability of Bose gases near resonance has been a puzzling problem in\nrecent years. In this Letter, we demonstrate that in addition to generating\nthermal pressure, thermal atoms enhance the repulsiveness of the\nscale-dependent interactions between condensed atoms due to renormalization\neffect and further stabilize the Bose gases. Consequently, we find that, as a\nprecursor of instability, the compressibility develops an anomalous structure\nas a function of scattering length and is drastically reduced compared with the\nmean-field value. Furthermore, the density profile of a Bose gas in a harmonic\ntrap is found to develop a flat top near the center. This is due to the\nanomalous behavior of compressibility and can be a potential smoking gun for\nprobing such an effect."
    },
    {
        "anchor": "Spin-Orbit Coupled Spinor Bose-Einstein Condensates: An effective spin-orbit coupling can be generated in cold atom system by\nengineering atom-light interactions. In this letter we study spin-1/2 and\nspin-1 Bose-Einstein condensates with Rashba spin-orbit coupling, and find that\nthe condensate wave function will develop non-trivial structures. From\nnumerical simulation we have identified two different phases. In one phase the\nground state is a single plane wave, and often we find the system splits into\ndomains and an array of vortices plays the role as domain wall. In this phase,\ntime-reversal symmetry is broken. In the other phase the condensate wave\nfunction is a standing wave and it forms spin stripe. The transition between\nthem is driven by interactions between bosons. We also provide an analytical\nunderstanding of these results and determines the transition point between the\ntwo phases.",
        "positive": "Exchange-induced crystallization of soft core bosons: We study the phase diagram of a two-dimensional assembly of bosons\ninteracting via a soft core repulsive pair potential of varying strength, and\ncompare it to that of the equivalent system in which particles are regarded as\ndistinguishable. We show that quantum-mechanical exchanges stabilize a \"cluster\ncrystal\" phase in a wider region of parameter space than predicted by\ncalculations in which exchanges are neglected. This physical effect is\ndiametrically opposite to that which takes place in hard core Bose systems such\nas $^4$He, wherein exchanges strengthen the fluid phase. It is underlain in the\ncluster crystal phase of soft core bosons by the free energy gain associated to\nthe formation of local Bose-Einstein condensates."
    },
    {
        "anchor": "The induced interaction in a Fermi gas with a BEC-BCS crossover: We study the effect of the induced interaction on the superfluid transition\ntemperature of a Fermi gas with a BEC-BCS crossover. The\nGorkov-Melik-Barkhudarov theory about the induced interaction is extended from\nthe BCS side to the entire crossover, and the pairing fluctuation is treated in\nthe approach by Nozi\\`{e}res and Schmitt-Rink. At unitarity, the induced\ninteraction reduces the transition temperature by about twenty percent. In the\nBCS limit, the transition temperature is reduced by a factor about 2.22, as\nfound by Gorkov and Melik-Barkhudarov. Our result shows that the effect of the\ninduced interaction is important both on the BCS side and in the unitary\nregion.",
        "positive": "Interaction of a Bose-Einstein condensate with a surface: perturbative\n  S-matrix approach: We derive an expression for the collective Casimir-Polder interaction of a\ntrapped gas of condensed bosons with a plane surface through the coupling of\nthe condensate atoms with the electromagnetic field. A systematic perturbation\ntheory is developed based on a diagrammatic expansion of the electromagnetic\nself-energy. In the leading order, the result for the interaction-energy is\nproportional to the number of atoms in the condensate mode. At this order,\natom-atom interactions and recoil effects lead to corrections compared to the\nsingle-atom theory, through shifts of the atomic transition energies. We also\ndiscuss the impact of the spatial delocalization of the condensate mode."
    },
    {
        "anchor": "Lattice bosons in a quasi-disordered environment: In this paper, we study non-interacting bosons in a disordered\none-dimensional optical lattice in a harmonic potential. We consider the case\nof deterministic disorder produced by an Aubry-Andr\\'{e} potential. Using exact\ndiagonalization, we investigate both the zero temperature and the finite\ntemperature properties. We investigate the localization properties by using an\nentanglement measure. We find that the extreme sensitivity of the localization\nproperties to the number of lattice sites in finite size closed chains\ndisappear in open chains. This feature continues to be present in the presence\nof a harmonic confining potential. The disorder is found to strongly reduce the\nBose-Einstein condensation temperature and the condensate fraction in open\nchains. The low temperature thermal depletion rate of the condensate fraction\nincreases considerably with increasing disorder strength. We also find that the\ncritical disorder strength required for localization increases with increasing\nstrength of the harmonic potential. Further, we find that the low temperature\ncondensate fraction undergoes a sharp drop to 0.5 in the localization\ntransition region. The temperature dependence of the specific heat is found to\nbe only marginally affected by the disorder.",
        "positive": "An on-chip optical lattice for cold atom experiments: An atom-chip-based integrated optical lattice system for cold and ultracold\natom applications is presented. The retro-reflection optics necessary for\nforming the lattice are bonded directly to the atom chip, enabling a compact\nand robust on-chip optical lattice system. After achieving Bose-Einstein\ncondensation in a magnetic chip trap, we load atoms directly into a vertically\noriented 1D optical lattice and demonstrate Landau-Zener tunneling. The atom\nchip technology presented here can be readily extended to higher dimensional\noptical lattices."
    },
    {
        "anchor": "A model study on superfluidity of a unitary Fermi gas of atoms\n  interacting with a finite-ranged potential: We calculate Bardeen-Cooper-Schrieffer (BCS) state of a unitary Fermi gas of\natoms interacting with the finite-ranged Jost-Kohn potential which has been\nrecently shown to account for the resonant interactions [2019 {\\rm J. Phys. B:\nAt. Mol. Opt. Phys.} {\\bf 52}, 165004]. Using exact scattering solution of the\npotential, we derive two-body ${\\mathbf T}$-matrix element which is employed to\nconstruct the BCS Hamiltonian in momentum space. We present results on the\nenergy- and range-dependence of the pairing gap and superfluid density and the\nrange-dependence of the chemical potential for a wide variation of the\nscattering length including the unitary regime. In the zero range limit our\ncalculated gap at the Fermi energy is found to be nearly equal to that\ncalculated in mean-field theory with contact potential. The mean gap averaged\nover the full width at half maximum of the gap function in the zero range and\nunitary limits is found to be $0.42 E_F$ which is quite close to the recent\nresult of the quantum Monte Carlo simulation [2018 {\\rm Phys. Rev.A} {\\bf 97},\n013601]. The chemical potential in the zero range limit also agrees well with\nthat for the contact potential.",
        "positive": "Spin squeezing and EPR entanglement of two bimodal condensates in\n  state-dependent potentials: We propose and analyze a scheme to entangle the collective spin states of two\nspatially separated bimodal Bose-Einstein condensates. Using a four-mode\napproximation for the atomic field, we show that elastic collisions in a\nstate-dependent potential simultaneously create spin-squeezing in each\ncondensate and entangle the collective spins of the two condensates. We\ninvestigate mostly analytically the non-local quantum correlations that arise\nin this system at short times and show that Einstein-Podolsky-Rosen (EPR)\nentanglement is generated between the condensates. At long times we point out\nmacroscopic entangled states and explain their structure. The scheme can be\nimplemented with condensates in state-dependent microwave potentials on an atom\nchip."
    },
    {
        "anchor": "Interplay of the pseudogap and the BCS gap for heteropairs in\n  $^{40}$K-$^6$Li mixture: The description of heteropairs like $^{40}$K-$^6$Li near and in the\nsuperconducting state requires a fully selfconsistent theory [see Hanai and\nOhashi, Phys. Rev. A 90, 043622 (2014)]. We derive analytic pseudogap Green's\nfunctions for the \"normal\" and superconducting states from the Luttinger-Ward\ntheory with the T-matrix in the static separable approximation. The\nself-consistency in the closing loop of self-energy has two pronounced effects\non the single-particle spectrum. First, the single-particle excitations decay\nbefore the asymptotic quasiparticle propagation is established, therefore the\nnormal state is not a Fermi liquid. Second, the pseudogap has a V shape even\nfor s-wave pairing. The V-shaped pseudogap and the U-shaped BCS gap interfere\nresulting in slope breaks of the gap walls and the in-gap states in the density\nof states. Various consequences of an incomplete self-consistency are\ndemonstrated.",
        "positive": "Domain-area distribution anomaly in segregating multicomponent\n  superfluids: The domain-area distribution in the phase transition dynamics of ${\\rm Z}_2$\nsymmetry breaking is studied theoretically and numerically for segregating\nbinary Bose--Einstein condensates in quasi-two-dimensional systems. Due to the\ndynamic scaling law of the phase ordering kinetics, the domain-area\ndistribution is described by a universal function of the domain area, rescaled\nby the mean distance between domain walls. The scaling theory for general\ncoarsening dynamics in two dimensions hypothesizes that the distribution during\nthe coarsening dynamics has a hierarchy with the two scaling regimes, the\nmicroscopic and macroscopic regimes with distinct power-law exponents. The\npower law in the macroscopic regime, where the domain size is larger than the\nmean distance, is universally represented with the Fisher's exponent of the\npercolation theory in two dimensions. On the other hand, the power-law exponent\nin the microscopic regime is sensitive to the microscopic dynamics of the\nsystem. This conjecture is confirmed by large-scale numerical simulations of\nthe coupled Gross--Pitaevskii equation for binary condensates. In the numerical\nexperiments of the superfluid system, the exponent in the microscopic regime\nanomalously reaches to its theoretical upper limit of the general scaling\ntheory. The anomaly comes from the quantum-fluid effect in the presence of\ncircular vortex sheets, described by the hydrodynamic approximation neglecting\nthe fluid compressibility. It is also found that the distribution of superfluid\ncirculation along vortex sheets obeys a dynamic scaling law with different\npower-law exponents in the two regimes. An analogy to quantum turbulence on the\nhierarchy of vorticity distribution and the applicability to chiral superfluid\n$^3$He in a slab are also discussed."
    },
    {
        "anchor": "Polarons and dressed molecules near narrow Feshbach resonances: The properties of impurities immersed in a large Fermi sea are naturally\ndescribed in terms of dressed quasiparticles: attractive and repulsive\npolarons, and dressed molecules. Motivated by recent experiments on narrow\nFeshbach resonances, we analyze here how the quasiparticle properties are\naffected by a non-zero resonance range. We find two interesting analytic\nresults. For large range, the ground state energy close to resonance is shown\nto become perturbative in the inverse range. In the limit of broad resonance\ninstead, we provide a new Tan's relation linking the impurity ground state\nenergy $E_\\downarrow$ to the number of atoms in its dressing cloud $\\Delta N$.\nAs a corollary, at unitarity one finds $\\Delta N=-E_\\downarrow/\\epsilon_F $,\nwith $\\epsilon_F$ the Fermi energy of the bath.",
        "positive": "Inelastic collision dynamics of a single cold ion immersed in a\n  Bose-Einstein condensate: We investigate inelastic collision dynamics of a single cold ion in a\nBose-Einstein condensate. We observe rapid ion-atom-atom three-body\nrecombination leading to formation of weakly bound molecular ions followed by\nsecondary two-body molecule-atom collisions quenching the rovibrational states\ntowards deeper binding energies. In contrast to previous studies exploiting\nhybrid ion traps, we work in an effectively field-free environment and generate\na free low-energy ionic impurity directly from the atomic ensemble via Rydberg\nexcitation and ionization. This allows us to implement an energy-resolved\nfield-dissociation technique to trace the relaxation dynamics of the\nrecombination products. Our observations are in good agreement with numerical\nsimulations based on Langevin capture dynamics and provide complementary means\nto study stability and reaction dynamics of ionic impurities in ultracold\nquantum gases."
    },
    {
        "anchor": "Stable symmetry-protected 3D embedded solitons in Bose-Einstein\n  condensates: Embedded solitons are rare self-localized nonlinear structures that,\ncounterintuitively, survive inside a continuous background of resonant states.\nWhile this topic has been widely studied in nonlinear optics, it has received\nalmost no attention in the field of Bose-Einstein condensation. In this work,\nwe consider experimentally realizable Bose-Einstein condensates loaded in\none-dimensional optical lattices and demonstrate that they support continuous\nfamilies of stable three-dimensional (3D) embedded solitons. These solitons can\nexist inside the resonant continuous Bloch bands because they are protected by\nsymmetry. The analysis of the Bogoliubov excitation spectrum as well as the\nlong-term evolution after random perturbations proves the robustness of these\nnonlinear structures against any weak perturbation. This may open up a way for\nthe experimental realization of stable 3D matter-wave embedded solitons as well\nas for monitoring the gap-soliton to embedded-soliton transition.",
        "positive": "Stripe-ordered superfluid and supersolid phases in attractive\n  Hofstadter-Hubbard model: We use microscopic Bogoliubov-de Gennes formalism to explore the ground-state\nphase diagram of the single-band attractive Hofstadter-Hubbard model on a\nsquare lattice. We show that the interplay between the Hofstadter butterfly and\nsuperfluidity breaks spatial symmetry, and gives rise to stripe-ordered\nsuperfluid and supersolid phases in large parameter spaces. We also discuss the\neffects of a trapping potential and comment on the viability of observing\nstripe-ordered phases with cold Fermi gases."
    },
    {
        "anchor": "Anomalous minimum in the shear viscosity of a Fermi gas: We measure the static shear viscosity $\\eta$ in a two-component Fermi gas\nnear a broad collisional (Feshbach) resonance, as a function of interaction\nstrength and energy. We find that $\\eta$ has both a quadratic and a linear\ndependence on the interaction strength $1/({k_{FI}a})$, where $a$ is the s-wave\nscattering length and $k_{FI}$ is the Fermi wave vector for an ideal gas at the\ntrap center. For energies above the superfluid transition, the minimum in\n$\\eta$ as a function of interaction strength is significantly shifted toward\nthe BEC side of resonance, to $1/(k_{FI}a)\\simeq 0.25$.",
        "positive": "Driven-dissipative many-body pairing states for cold fermionic atoms in\n  an optical lattice: We discuss the preparation of many-body states of cold fermionic atoms in an\noptical lattice via controlled dissipative processes induced by coupling the\nsystem to a reservoir. Based on a mechanism combining Pauli blocking and phase\nlocking between adjacent sites, we construct complete sets of jump operators\ndescribing coupling to a reservoir that leads to dissipative preparation of\npairing states for fermions with various symmetries in the absence of direct\ninter-particle interactions. We discuss the uniqueness of these states, and\ndemonstrate it with small-scale numerical simulations. In the late time\ndissipative dynamics, we identify a \"dissipative gap\" that persists in the\nthermodynamic limit. This gap implies exponential convergence of all many-body\nobservables to their steady state values. We then investigate how these pairing\nstates can be used as a starting point for the preparation of the ground state\nof Fermi-Hubbard Hamiltonian via an adiabatic state preparation process also\ninvolving the parent Hamiltonian of the pairing state. We also provide a\nproof-of-principle example for implementing these dissipative processes and the\nparent Hamiltonians of the pairing states, based on Yb171 atoms in optical\nlattice potentials."
    },
    {
        "anchor": "Vortex-antivortex pair dynamics in an exciton-polariton condensate: The study of superfluid and Berezinskii-Kosterlitz-Thouless phases in\nexciton-polaritons requires an understanding of vortex dynamics in a\ndissipative unconfined condensate. In this article we study the motion of\ndynamic vortex-antivortex pairs and show that vortex pair stability defined as\nordered motion as opposed to rapid separation or recombination is the result of\nbalance between dissipative velocities in the condensate and interaction with\nthermal polaritons. The addition of a trapping potential is further shown to\nconsiderably enhance the lifetime of a single vortex pair in this system. These\ninvestigations have important consequences for interpretation of recent results\nand future investigations of two-dimensional superfluid phases in polariton\ncondensates.",
        "positive": "Stability limits for modes held in alternating trapping-expulsive\n  potentials: We elaborate a scheme of trapping-expulsion management (TEM), in the form of\nthe quadratic potential periodically switching between confinement and\nexpulsion, as a means of stabilization of two-dimensional dynamical states\nagainst the backdrop of the critical collapse driven by the cubic\nself-attraction with strength g. The TEM scheme may be implemented, as\nspatially or temporally periodic modulations, in optics or BEC, respectively.\nThe consideration is carried out by dint of numerical simulations and\nvariational approximation (VA). In terms of the VA, the dynamics amounts to a\nnonlinear Ermakov equation, which, in turn, is tantamount to a linear Mathieu\nequation. Stability boundaries are found as functions of g and parameters of\nthe periodic modulation of the trapping potential. Below the usual collapse\nthreshold, which is known, in the numerical form, as g < 5.85 (in the standard\nnotation), the stability is limited by the onset of the parametric resonance.\nThis stability limit, including the setup with the self-repulsive sign of the\ncubic term (g < 0), is accurately predicted by the VA. At g > 5.85, the\ncollapse threshold is found with the help of full numerical simulations. The\nrelative increase of the critical value of g above 5.85 is ~ 1.5%, which is a\nmeaningful result, even if its size is small, because the collapse threshold is\na universal constant, which is difficult to change."
    },
    {
        "anchor": "Dirac monopoles with polar-core vortex induced by spin-orbit coupling in\n  spinor Bose-Einstein condensates: We report Dirac monopoles with polar-core vortex induced by spin-orbit\ncoupling in ferromagnetic Bose-Einstein condensates, which are attached to two\nnodal vortex lines along the vertical axis. These monopoles are more stable in\nthe time scale of experiment and can be detected through directly imaging\nvortex lines. When the strength of spin-orbit coupling increases, Dirac\nmonopoles with vortex can be transformed into those with square lattice. In the\npresence of spin-orbit coupling, increasing the strength of interaction can\ninduce a cyclic phase transition from Dirac monopoles with polar-core vortex to\nthose with Mermin-Ho vortex. The spin-orbit coupled Bose-Einstein condensates\nnot only provide a new unique platform for investigating exotic monopoles and\nrelevant phase transitions, but also can preserve stable monopoles after a\nquadrupole field is turned off.",
        "positive": "2000-times repeated imaging of strontium atoms in clock-magic tweezer\n  arrays: We demonstrate single-atom resolved imaging with a survival probability of\n$0.99932(8)$ and a fidelity of $0.99991(1)$, enabling us to perform repeated\nhigh-fidelity imaging of single atoms in tweezers for thousands of times. We\nfurther observe lifetimes under laser cooling of more than seven minutes, an\norder of magnitude longer than in previous tweezer studies. Experiments are\nperformed with strontium atoms in $813.4~\\text{nm}$ tweezer arrays, which is at\na magic wavelength for the clock transition. Tuning to this wavelength is\nenabled by off-magic Sisyphus cooling on the intercombination line, which lets\nus choose the tweezer wavelength almost arbitrarily. We find that a single not\nretro-reflected cooling beam in the radial direction is sufficient for\nmitigating recoil heating during imaging. Moreover, this cooling technique\nyields temperatures below $5~\\mu$K, as measured by release and recapture.\nFinally, we demonstrate clock-state resolved detection with average survival\nprobability of $0.996(1)$ and average state detection fidelity of $0.981(1)$.\nOur work paves the way for atom-by-atom assembly of large defect-free arrays of\nalkaline-earth atoms, in which repeated interrogation of the clock transition\nis an imminent possibility."
    },
    {
        "anchor": "Full Counting Statistics of the momentum occupation numbers of the\n  Tonks-Girardeau gas: We compute the fluctuations of the number of bosons with a given momentum for\nthe Tonks-Girardeau gas at zero temperature. We show that correlations between\nopposite momenta, which is an important fingerprint of long range order in\nweakly interacting Bose systems, are suppressed and that the full distribution\nof the number of bosons with non zero momentum is exponential. The distribution\nof the quasi-condensate is however quasi Gaussian. Experimental relevance of\nour findings for recent cold atoms experiments are discussed.",
        "positive": "Broken-axisymmetry state and magnetic state diagram of spin-1 condensate\n  through the prism of quadrupole degrees of freedom: We theoretically study a weakly interacting gas of spin-1 atoms with\nBose-Einstein condensate in external magnetic field within the Bogoliubov\napproach. To this end, in contrast to previous studies, we employ the general\nHamiltonian, which includes both spin and quadrupole exchange interactions as\nwell as the couplings of the spin and quadrupole moment with the external\nmagnetic field (the linear and quadratic Zeeman terms). The latter is\nresponsible for the emergence of the broken-axisymmetry state. We also\nre-examine ferromagnetic, quadrupolar, and paramagnetic states employing the\nproposed Hamiltonian. For all magnetic states, we find the relevant\nthermodynamic characteristics such as magnetization, quadrupole moment,\nthermodynamic potential, as well as excitation energies for broken-axisymmetry\nstate. We show that the broken-axisymmetry state can be prepared at three\ndifferent regimes of applied magnetic field. We also present the magnetic state\ndiagrams for each regime of realizing the broken-axisymmetry state."
    },
    {
        "anchor": "Quantum nanofriction in trapped ion chains with a topological defect: Trapped ion systems constitute a well controllable scenario for the study and\nemulation of nanofriction, and in particular of Frenkel-Kontorova-like models.\nThis is in particular the case when a topological defect is created in a zigzag\nion Coulomb crystal, which results in an Aubry transition from free sliding to\npinned phase as a function of the trap aspect ratio. We explore the quantum\neffects of the Aubry transition by means of an effective simplified model, in\nwhich the defect is treated like a single quantum particle that experiences an\neffective Peierls-Nabarro potential and a position-dependent mass. We\ndemonstrate the relevance of quantum tunneling in a finite range of aspect\nratios close the critical point, showing that the quantum effects may be\nobserved in the kink dynamics for sufficiently low temperatures. Finally, we\ndiscuss the requirements to reveal quantum effects at the Aubry transition in\nfuture experiments on trapped ions.",
        "positive": "Interaction-induced exotic vortex states in an optical lattice clock\n  with spin-orbit coupling: Motivated by a recent experiment [L. F. Livi, et al., Phys. Rev. Lett. 117,\n220401(2016)], we study the ground-state properties of interacting fermions in\na one-dimensional optical lattice clock with spin-orbit coupling. As the\nelectronic and the hyperfine-spin states in the clock-state manifolds can be\ntreated as effective sites along distinct synthetic dimensions, the system can\nbe considered as multiple two-leg ladders with uniform magnetic flux\npenetrating the plaquettes of each ladder. As the inter-orbital spin-exchange\ninteractions in the clock-state manifolds couple individual ladders together,\nwe show that exotic interaction-induced vortex states emerge in the\ncoupled-ladder system, which compete with existing phases of decoupled ladders\nand lead to a rich phase diagram. Adopting the density matrix renormalization\ngroup approach, we map out the phase diagram, and investigate in detail the\ncurrents and the density-density correlations of the various phases. Our\nresults reveal the impact of interactions on spin-orbit coupled systems, and\nare particularly relevant to the on-going exploration of spin-orbit coupled\noptical lattice clocks."
    },
    {
        "anchor": "Non-abelian anyons from degenerate Landau levels of ultracold atoms in\n  artificial gauge potentials: We show that non-abelian potentials acting on ultracold gases with two\nhyperfine levels can give rise to ground states with non-abelian excitations.\nWe consider a realistic gauge potential for which the Landau levels can be\nexactly determined: the non-abelian part of the vector potential makes the\nLandau levels non-degenerate. In the presence of strong repulsive interactions,\ndeformed Laughlin ground states occur in general. However, at the degeneracy\npoints of the Landau levels, non-abelian quantum Hall states appear: these\nground states, including deformed Moore-Read states (characterized by Ising\nanyons as quasi-holes), are studied for both fermionic and bosonic gases.",
        "positive": "Tuning anomalous Floquet topological bands with ultracold atoms: The Floquet engineering opens the way to create new topological states\nwithout counterparts in static systems. Here, we report the experimental\nrealization and characterization of new anomalous topological states with\nhigh-precision Floquet engineering for ultracold atoms trapped in a shaking\noptical Raman lattice. The Floquet band topology is manipulated by tuning the\ndriving-induced band crossings referred to as band inversion surfaces (BISs),\nwhose configurations fully characterize the topology of the underlying states.\nWe uncover various exotic anomalous topological states by measuring the\nconfigurations of BISs which correspond to the bulk Floquet topology. In\nparticular, we identify an unprecedented anomalous Floquet valley-Hall state\nthat possesses anomalous helicallike edge modes protected by valleys and a\nchiral state with high Chern number."
    },
    {
        "anchor": "Mean-field spin-oscillation dynamics beyond the single-mode\n  approximation for a harmonically trapped spin-1 Bose-Einstein condensate: Compared to single-component Bose-Einstein condensates, spinor Bose-Einstein\ncondensates display much richer dynamics. In addition to density oscillations,\nspinor Bose-Einstein condensates exhibit intriguing spin dynamics that is\nassociated with population transfer between different hyperfine components.\nThis work analyzes the validity of the widely employed single-mode\napproximation when describing the spin dynamics in response to a quench of the\nsystem Hamiltonian. The single-mode approximation assumes that the different\nhyperfine states all share the same time-independent spatial mode. This implies\nthat the resulting spin Hamiltonian only depends on the spin interaction\nstrength and not on the density interaction strength. Taking the spinor sodium\nBose-Einstein condensate in the $f=1$ hyperfine manifold as an example and\nworking within the mean-field theory framework, it is found numerically that\nthe single-mode approximation misses, in some parameter regimes, intricate\ndetails of the spin and spatial dynamics. We develop a physical picture that\nexplains the observed phenomenon. Moreover, using that the population\noscillations described by the single-mode approximation enter into the\neffective potential felt by the mean-field spinor, we derive a\nsemi-quantitative condition for when dynamical mean-field induced corrections\nto the single-mode approximation are relevant. Our mean-field results have\nimplications for a variety of published and planned experimental studies.",
        "positive": "Phonon-assisted coherent transport of excitations in Rydberg-dressed\n  atom arrays: Polarons, which arise from the self-trapping interaction between electrons\nand lattice distortions in a solid, have been known and extensively\ninvestigated for nearly a century. Nevertheless, the study of polarons\ncontinues to be an active and evolving field, with ongoing advancements in both\nfundamental understanding and practical applications. Here, we present a\nmicroscopic model that exhibits a diverse range of dynamic behavior, arising\nfrom the intricate interplay between two excitation-phonon coupling terms. The\nderivation of the model is based on an experimentally feasible Rydberg-dressed\nsystem with dipole-dipole interactions, making it a promising candidate for\nrealization in a Rydberg atoms quantum simulator. Remarkably, our analysis\nreveals a growing asymmetry in Bloch oscillations, leading to a macroscopic\ntransport of non-spreading excitations under a constant force. Moreover, we\ncompare the behavior of excitations, when coupled to either acoustic or optical\nphonons, and demonstrate the robustness of our findings against on-site random\npotential. Overall, this work contributes to the understanding of polaron\ndynamics with their potential applications in coherent quantum transport and\noffers valuable insights for research on Rydberg-based quantum systems."
    },
    {
        "anchor": "Floquet engineering Hz-Level Rabi Spectra in Shallow Optical Lattice\n  Clock: Quantum metrology with ultra-high precision usually requires atoms prepared\nin an ultra-stable environment with well-defined quantum states. Thus, in\noptical lattice clock systems deep lattice potentials are used to trap\nultra-cold atoms. However, decoherence, induced by Raman scattering and higher\norder light shifts, can significantly be reduced if atomic clocks are realized\nin shallow optical lattices. On the other hand, in such lattices, tunneling\namong different sites can cause additional dephasing and strongly broadening of\nthe Rabi spectrum. Here, in our experiment, we periodically drive a shallow\n$^{87}$Sr optical lattice clock. Counter intuitively, shaking the system can\ndeform the wide broad spectral line into a sharp peak with 5.4Hz line-width.\nWith careful comparison between the theory and experiment, we demonstrate that\nthe Rabi frequency and the Bloch bands can be tuned, simultaneously and\nindependently. Our work not only provides a different idea for quantum\nmetrology, such as building shallow optical lattice clock in outer space, but\nalso paves the way for quantum simulation of new phases of matter by\nengineering exotic spin orbit couplings.",
        "positive": "Engineering Bright Solitons to Enhance the Stability of Two-Component\n  Bose-Einstein Condensates: We consider a system of coupled Gross-Pitaevskii (GP) equations describing a\nbinary quasi-one-dimensional Bose-Einstein condensate (BEC) with intrinsic\ntime-dependent attractive interactions, placed in a time-dependent expulsive\nparabolic potential, in a special case when the system is integrable (a\ndeformed Manakov's system). Since the nonlinearity in the integrable system\nwhich represents binary attractive interactions exponentially decays with time,\nsolitons are also subject to decay. Nevertheless, it is shown that the\nrobustness of bright solitons can be enhanced in this system, making their\nrespective lifetime longer, by matching the time dependence of the interaction\nstrength (adjusted with the help of the Feshbach-resonance management) to the\ntime modulation of the strength of the parabolic potential. The analytical\nresults, and their stability, are corroborated by numerical simulations. In\nparticular, we demonstrate that the addition of random noise does not impact\nthe stability of the solitons."
    },
    {
        "anchor": "Multiparticle interactions for ultracold atoms in optical tweezers:\n  Cyclic ring-exchange terms: Dominant multi-particle interactions can give rise to exotic physical phases\nwith anyonic excitations and phase transitions without local order parameters.\nIn spin systems with a global $SU(N)$ symmetry, cyclic ring-exchange couplings\nconstitute the first higher-order interaction in this class. In this letter we\npropose a protocol how $SU(N)$ invariant multi-body interactions can be\nimplemented in optical tweezer arrays. We utilize the flexibility to re-arrange\nthe tweezer configuration on time scales short compared to the typical\nlifetimes, in combination with strong non-local Rydberg interactions. As a\nspecific example we demonstrate how a chiral cyclic ring-exchange Hamiltonian\ncan be implemented in a two-leg ladder geometry. We study its phase diagram\nusing DMRG simulations and identify phases with dominant vector chirality, a\nferromagnet, and an emergent spin-$1$ Haldane phase. We also discuss how the\nproposed protocol can be utilized to implement the strongly frustrated $J-Q$\nmodel, a candidate for hosting a deconfined quantum critical point.",
        "positive": "Transverse instability and disintegration of domain wall of relative\n  phase in coherently coupled two-component Bose-Einstein condensates: We study transverse instability and disintegration dynamics of a domain wall\nof a relative phase in two-component Bose-Einstein condensates with a coherent\nRabi coupling. We obtain analytically the stability phase diagram of the\nstationary solution of the domain wall for the one-dimensional coupled\nGross-Pitaevskii equations in the plane of the Rabi frequency and the\nintercomponent coupling constant. Outside the stable region, the domain wall is\ndynamically unstable for the transverse modulation along the direction\nperpendicular to the phase kink. The nonlinear evolution associated with the\ninstability is demonstrated through numerical simulations for both the domain\nwall without edges and that with edges formed by the quantized vortices."
    },
    {
        "anchor": "Colliding clouds of strongly interacting spin-polarized fermions: Motivated by a recent experiment at MIT, we consider the collision of two\nclouds of spin-polarized atomic Fermi gases close to a Feshbach resonance. We\nexplain why two dilute gas clouds, with underlying attractive interactions\nbetween their constituents, bounce off each other in the strongly interacting\nregime. Our hydrodynamic analysis, in excellent agreement with experiment,\ngives strong evidence for a metastable many-body state with effective repulsive\ninteractions.",
        "positive": "Comment on \"Consistent thermostatistics forbids negative absolute\n  temperatures\": In this comment we argue that negative absolute temperatures are a\nwell-established concept for systems with bounded spectra. They are not only\nconsistent with thermodynamics, but are even unavoidable for a consistent\ndescription of the thermal equilibrium of inverted populations."
    },
    {
        "anchor": "Magnetic phases and phase diagram of spin-1 condensate with quadrupole\n  degrees of freedom: We obtain and justify a many-body Hamiltonian of pairwise interacting spin-1\natoms, which includes eight generators of the SU(3) group associated with spin\nand quadrupole degrees of freedom. It is shown that this Hamiltonian is valid\nfor non-local interaction potential, whereas for local interaction specified by\n$s$-wave scattering length, the Hamiltonian should be bilinear in spin\noperators only (of the Heisenberg type). We apply the obtained Hamiltonian to\nstudy the ground-state properties and single-particle excitations of a weakly\ninteracting gas of spin-1 atoms with Bose-Einstein condensate taking into\naccount the quadrupole degrees of freedom. It is shown that the system under\nconsideration can be in ferromagnetic, quadrupolar, and paramagnetic phases.\nThe corresponding phase diagram is constructed and discussed. The main\ncharacteristics such as the density of the grand thermodynamic potential,\ncondensate density, and single-particle excitation spectra modified by\nquadrupole degrees of freedom are determined in different phases.",
        "positive": "Current reversals in rapidly rotating ultra-cold Fermi gases: We study the equilibrium current density profiles of harmonically trapped\nultra-cold Fermi gases in quantum Hall-like states that appear when the\nquasi-two-dimensional trap is set in fast rotation. The density profile of the\ngas (in the rotating reference frame) consists of incompressible strips of\nconstant quantized density separated by compressible regions in which the\ndensity varies. Remarkably, we find that the atomic currents flow in opposite\ndirections in the compressible and incompressible regions -- a prediction that\nshould be amenable to experimental verification."
    },
    {
        "anchor": "Fast production of large 23Na Bose-Einstein condensates in an optically\n  plugged magnetic quadrupole trap: We demonstrate a fast production of large 23Na Bose-Einstein condensates in\nan optically plugged, magnetic quadrupole trap. A single global minimum of the\ntrapping potential is generated by slightly displacing the plug beam from the\ncenter of the quadrupole field. With a dark magneto-optical trap and a simple\nrf evaporation, our system produces a condensate with N = 10^7 atoms every 17\ns. The Majorana loss rates and the resultant heating rates for various\ntemperatures are measured with and without plugging. The average energy of a\nspin-flipped atom is almost linearly proportional to temperature and determined\nto be about 60% of the average energy of a trapped atom. We present a numerical\nstudy of the evaporation dynamics in a plugged linear trap.",
        "positive": "Nonequilibrium-induced enhancement of dynamical quantum coherence and\n  entanglement of spin arrays: The random magnetic field produced by nuclear spins has long been viewed as\nthe dominating source of decoherence in the quantum-dot based spins. Here we\nobtain in both exact and analytical manner the dynamics of spin qubits coupled\nto nuclear spin environments via the hyperfine interaction, going beyond the\nweak system-bath interaction and Markovian approximation. We predict that the\ndetailed-balance breaking produced by chemical potential gradient in nuclear\nbaths leads to the rapid oscillations of populations, quantum coherence and\nentanglement, which are absent in the conventional case (i.e., Overhauser\nnoise). This is attributed to the nonequilibrium feature of the system as shown\nin the relation between the oscillation period and the chemical potential\nimbalance. Our results reveal the essentiality of nonequilibriumness with\ndetailed-balance breaking for enhancing the dynamical coherence and\nentanglement of spin qubits. Moreover, our exact solution explicitly\ndemonstrates that the non-Markovian bath comprised by nuclear spins can\npreserve the collective quantum state, due to the recovery of coherence.\nFinally, we propose an experiment using ultracold trapped ions to observe these\nnonequilibrium and memory effects."
    },
    {
        "anchor": "Buckling transitions and clock order of two-dimensional Coulomb crystals: Crystals of repulsively interacting ions in planar traps form hexagonal\nlattices, which undergo a buckling instability towards a multi-layer structure\nas the transverse trap frequency is reduced. Numerical and experimental results\nindicate that the new structure is composed of three planes, whose separation\nincreases continuously from zero. We study the effects of thermal and quantum\nfluctuations by mapping this structural instability to the six-state clock\nmodel. A prominent implication of this mapping is that at finite temperature,\nfluctuations split the buckling instability into two thermal transitions,\naccompanied by the appearance of an intermediate critical phase. This phase is\ncharacterized by quasi-long-range order in the spatial tripartite pattern. It\nis manifested by broadened Bragg peaks at new wave vectors, whose line-shape\nprovides a direct measurement of the temperature dependent exponent $\\eta(T)$\ncharacteristic of the power-law correlations in the critical phase. A quantum\nphase transition is found at the largest value of the critical transverse\nfrequency: here the critical intermediate phase shrinks to zero. Moreover,\nwithin the ordered phase, we predict a crossover from classical to quantum\nbehavior, signifying the emergence of an additional characteristic scale for\nclock order. We discuss experimental realizations with trapped ions and\npolarized dipolar gases, and propose that within accessible technology, such\nexperiments can provide a direct probe of the rich phase diagram of the quantum\nclock model, not easily observable in condensed matter analogues. Therefore,\nthis works highlights the potential for ionic and dipolar systems to serve as\nsimulators for complex models in statistical mechanics and condensed matter\nphysics.",
        "positive": "Coreless vortex dipoles and bubbles in phase-separated binary\n  condensates: Vortex dipoles are generated when an obstacle moves through a superfluid. In\ncase of phase-separated binary condensates, with appropriate interaction\nparameters in pan-cake shaped traps, we show that coreless vortex dipoles are\ncreated when a Gaussian obstacle beam traverses across them above a critical\nspeed. As the obstacle passes through the inner component, it carries along a\nbubble of the outer component. Using Thomas-Fermi approximation, we show that\nphase-separated binary condensates can either support vortices with empty or\nfilled cores. For time dependent obstacle potentials, ramped down in the\npresent case, relative energy scales of the system influence the dynamical\nevolution of the binary condensate."
    },
    {
        "anchor": "Emergence of glass-like dynamics for dissipative and strongly\n  interacting bosons: We study the dynamics of a strongly interacting bosonic quantum gas in an\noptical lattice potential under the effect of a dissipative environment. We\nshow that the interplay between the dissipative process and the Hamiltonian\nevolution leads to an unconventional dynamical behavior of local number\nfluctuations. In particular we show, both analytically and numerically, the\nemergence of an anomalous diffusive evolution in configuration space at short\ntimes and, at long times, an unconventional dynamics dominated by rare events.\nSuch rare events, common in disordered and frustrated systems, are due here to\nstrong interactions. This complex two-stage dynamics reveals information on the\nlevel structure of the strongly interacting gas.",
        "positive": "A liquid-gas transition for bosons with attractive interaction in one\n  dimension: We consider a one dimensional system of $N$ bosons interacting via an\nattractive Dirac delta function potential. We place the bosonic quantum\nparticles at thermal equilibrium in a box of length $L$ with periodic boundary\nconditions. At large $N$ and for $L$ much larger than the diameter of a two\nparticle bound state, we predict by numerical and analytical studies of a\nsimple model derived from first principles that the system exhibits a first\norder phase transition in a high temperature, non-degenerate regime. The higher\ntemperature phase is an almost pure atomic gas, with a small fraction of\ndimers, a smaller fraction of trimers, etc. The lower temperature phase is a\nmesoscopic or macroscopic bound state that collects all the particles of the\nsystem with the exception of a small gaseous fraction composed mainly of atoms.\nWe term this phase, which is the quantum equivalent of the classical bright\nsoliton, a liquid.---Nous considerons, en dimension un, une assemblee de $N$\nparticules quantiques bosoniques interagissant par un potentiel de Dirac\nattractif, a l'equilibre thermique dans une boite de quantification de longueur\nL avec des conditions aux limites periodiques. Pour de grandes valeurs de N, et\nlorsque L est bien superieur au diametre de l'etat dimere dans l'espace reel,\nnous predisons, par etude numerique et analytique d'un modele simple mais\ndeduit des premiers principes, que le systeme presente, a haute temperature\nc'est-a-dire dans le regime non degenere, une transition du premier ordre entre\ndeux phases. La phase privilegiee a haute temperature est un gaz presque pur\nd'atomes, avec une faible fraction de dimeres, et des fractions encore plus\nfaibles de trimeres, etc. La phase qui la supplante a moins haute temperature\nest un etat lie mesoscopique ou macroscopique que nous qualifions de liquide,\nequivalent quantique du soliton brillant de la theorie de champ classique, et\nqui renferme toutes les particules du systeme, a l'exception d'une petite\nfraction gazeuse composee essentiellement d'atomes."
    },
    {
        "anchor": "Bose-Einstein Condensation and quasicrystals: We consider interacting Bose particles in an external local potential. It is\nshown that large class of external quasicrystal potentials cannot sustain any\ntype of Bose-Einstein condensates. Accordingly, at spatial dimensions $D\\leq 2$\nin such quasicrystal potentials a supersolid is not possible via Bose-Einstein\ncondensates at finite temperatures. The latter also hold true for the\ntwo-dimensional Fibonacci tiling. However, supersolids do arise at $D\\leq 2$\nvia Bose-Einstein condensates from infinitely long-range, nonlocal\ninterparticle potentials.",
        "positive": "Pairing phenomena and superfluidity of atomic Fermi gases in a\n  two-dimensional optical lattice: Unusual effects of lattice-continuum mixing: We study the superfluid behavior of ultracold atomic Fermi gases with a short\nrange attractive interaction in a two-dimensional optical lattice (2DOL) using\na pairing fluctuation theory, within the context of BCS-BEC crossover. We find\nthat the mixing of lattice and continuum dimensions leads to exotic phenomena.\nFor relatively large lattice constant $d$ and small hopping integral $t$, the\nsuperfluid transition temperature $T_c$ exhibits a remarkable reentrant\nbehavior as a function of the interaction strength, and leads to a pair density\nwave ground state, where $T_c$ vanishes, for a range of intermediate coupling\nstrength. In the unitary and BCS regimes, the nature of the in-plane and\noverall pairing changes from particle-like to hole-like, with an unexpected\nnonmonotonic dependence of the chemical potential on the pairing strength. The\nBEC asymptotic behaviors exhibit distinct power law dependencies on the\ninteraction strength compared to cases of pure 3D lattice, 3D continuum, and\n1DOL. These predictions can be tested in future experiments."
    },
    {
        "anchor": "Dynamical Cluster Quantum Monte Carlo Study of the Single Particle\n  Spectra of Strongly Interacting Fermion Gases: We study the single-particle spectral function of resonantly-interacting\nfermions in the unitary regime, as described by the three-dimensional\nattractive Hubbard model in the dilute limit. Our approach, based on the\nDynamical Cluster Approximation and the Maximum Entropy Method, shows the\nemergence of a gap with decreasing temperature, as reported in recent cold-atom\nphotoemission experiments, for coupling values that span the BEC-BCS crossover.\nBy comparing the behavior of the spectral function to that of the imaginary\ntime dynamical pairing susceptibility, we attribute the development of the gap\nto the formation of local bound atom pairs.",
        "positive": "Three interacting atoms in a one-dimensional trap: A benchmark system\n  for computational approaches: We provide an accurate calculation of the energy spectrum of three atoms\ninteracting through a contact force in a one-dimensional harmonic trap,\nconsidering both spinful fermions and spinless bosons. We use fermionic\nenergies as a benchmark for exact-diagonalization technique (also known as full\nconfiguration interaction), which is found to slowly converge in the case of\nstrong interatomic attraction."
    },
    {
        "anchor": "Tuning the dipole-dipole interaction in a quantum gas with a rotating\n  magnetic field: We demonstrate the tuning of the magnetic dipole-dipole interaction (DDI)\nwithin a dysprosium Bose-Einstein condensate by rapidly rotating the\norientation of the atomic dipoles. The tunability of the dipolar mean-field\nenergy manifests as a modified gas aspect ratio after time-of-flight expansion.\nWe demonstrate that both the magnitude and the sign of the DDI can be tuned\nusing this technique. In particular, we show that a magic rotation angle exists\nat which the mean-field DDI can be eliminated, and at this angle, we observe\nthat the expansion dynamics of the condensate is close to that predicted for a\nnon-dipolar gas. The ability to tune the strength of the DDI opens new avenues\ntoward the creation of exotic soliton and vortex states as well as unusual\nquantum lattice phases and Weyl superfluids.",
        "positive": "Dark solitons dynamics and snake instability in superfluid Fermi gases\n  trapped by an anisotropic harmonic potential: We present an investigation of generation, dynamics and stability of dark\nsolitons in anisotropic Fermi gases for a range of particle numbers and trap\naspect ratios within the framework of the order-parameter equation. We\ncalculate the periods of dark solitons oscillating in a trap, and find a good\nagreement with the results based on the Bogoliubov-de Gennes equations. By\nstudying the stability of initially off-center dark solitons under various\ntight transverse confinements in the unitarity limit, we not only give the\ncriterion of dynamical stability, but also find that the soliton and a hybrid\nof solitons and vortex rings can be characterized by different oscillation\nperiod. The stability criterion is not fulfilled by the parameters of the\nrecent experiment [Nature {\\bf 499}, 426 (2013)]. Therefore, instead of a very\nslow oscillation as observed experimentally, we find that the created dark\nsoliton undergoes a transverse snake instability with collapsing into vortex\nrings, which propagate in soliton-like manner with a nearly two times larger\nperiod."
    },
    {
        "anchor": "Enhanced fermion pairing and superfluidity by an imaginary magnetic\n  field: We show that an imaginary magnetic field(IMF), which can be generated in\nnon-Hermitian systems with spin-dependent dissipations, can greatly enhance the\ns-wave pairing and superfluidity of spin-1/2 fermions, in distinct contrast to\nthe effect of a real magnetic field. The enhancement can be attributed to the\nincreased coupling constant in low-energy space and the reduced spin gap in\nforming singlet pairs. We have demonstrated this effect in a number of\ndifferent fermion systems with and without spin-orbit coupling, using both the\ntwo-body exact solution and many-body mean-field theory. Our results suggest an\nalternative route towards strong fermion superfluid with high superfluid\ntransition temperature.",
        "positive": "Efimov physics and the three-body parameter for shallow van der Waals\n  potentials: Extremely weakly-bound three-boson systems are predicted to exhibit\nintriguing universal properties such as discrete scale invariance. Motivated by\nrecent experimental studies of the ground and excited helium trimers, this work\nanalyzes the three-body parameter and the structural properties of three helium\natoms as the s-wave scattering length is tuned artificially. Connections with\ntheoretical and experimental studies of the Efimov scenario as it pertains to\ncold atom systems are made."
    },
    {
        "anchor": "Critical points of the anyon-Hubbard model: Anyons are particles with fractional statistics that exhibit a nontrivial\nchange in the wavefunction under an exchange of particles. Anyons can be\nconsidered to be a general category of particles that interpolate between\nfermions and bosons. We determined the position of the critical points of the\none-dimensional anyon-Hubbard model, which was mapped to a modified\nBose-Hubbard model where the tunneling depends on the local density and the\ninterchange angle. We studied the latter model by using the density matrix\nrenormalization group method and observed that gapped (Mott insulator) and\ngapless (superfluid) phases characterized the phase diagram, regardless of the\nvalue of the statistical angle. The phase diagram for higher densities was\ncalculated and showed that the Mott lobes increase (decrease) as a function of\nthe statistical angle (global density). The position of the critical point\nseparating the gapped and gapless phases was found using quantum information\ntools, namely the block von Neumann entropy. We also studied the evolution of\nthe critical point with the global density and the statistical angle and showed\nthat the anyon-Hubbard model with a statistical angle $\\theta =\\pi/4$ is in the\nsame universality class as the Bose-Hubbard model with two body interactions.",
        "positive": "Mobile impurity near the superfluid-Mott insulator quantum critical\n  point in two dimensions: We consider bosonic atoms in an optical lattice at integer filling, tuned to\nthe superfluid-Mott insulator critical point, and coupled to a single, mobile\nimpurity atom of a different species. This setup is inspired by current\nexperiments with quantum gas microscopes, which enable tracking of the impurity\nmotion. We describe the evolution of the impurity motion from quantum wave\npacket spread at short times, to Brownian diffusion at long times. This\ndynamics is controlled by the interplay between dangerously irrelevant\nperturbations at the strongly-interacting field theory describing the\nsuperfluid-insulator transition in two spatial dimensions."
    },
    {
        "anchor": "Thermalization and localization of an oscillating Bose-Einstein\n  condensate in a disordered trap: We numerically simulate an oscillating Bose-Einstein condensate in a\ndisordered trap [Phys. Rev. A 82, 033603 (2010)] and the results are in good\nagreement with the experiment. It allows us to verify that total energy and\nparticle number are conserved in this quantum system. The disorder acts as a\nmedium, which results in a relaxation from nonequilibrium to equilibrium, i.e.,\nthermalization. An algebraic localization is realized when the system\napproaches the equilibrium, and if the system falls into the regime when the\nhealing length of the condensate exceeds the correlation length of the\ndisorder, exponential Anderson localization is to be observed.",
        "positive": "Superposition states of ultracold bosons in rotating rings with a\n  realistic potential barrier: In a recent paper [Phys. Rev. A 82, 063623 (2010)] Hallwood et al. argued\nthat it is feasible to create large superposition states with strongly\ninteracting bosons in rotating rings. Here we investigate in detail how the\nsuperposition states in rotating-ring lattices depend on interaction strength\nand barrier height. With respect to the latter we find a trade-off between\nlarge energy gaps and high cat quality. Most importantly, we go beyond the\n\\delta-function approximation for the barrier potential and show that the\nenergy gap decreases exponentially with the number of particles for weak\nbarrier potentials of finite width. These are crucial issues in the design of\nexperiments to realize superposition states."
    },
    {
        "anchor": "Analytical solutions of the coupled Gross-Pitaevskii equations for the\n  three-species Bose-Einstein condensates: The coupled Gross-Pitaevskii equations for the g.s. of the three-species\ncondensates (3-BEC) have been solved analytically under the Thomas-Fermi\napproximation. Six types of spatial configurations in miscible phase are found.\nThe whole parameter-space has been divided into zones each supports a specific\nconfiguration (miscible or immiscible). The borders of the zones are described\nby analytical formulae. Due to the division, the variation of the spatial\nconfiguration against the parameters can be visualized, and the effects of the\nparameters can be thereby understood. There are regions in the parameter-space\nwhere the configuration is highly sensitive to the parameters. These regions\nare tunable and valuable for the determination of the parameters.",
        "positive": "Particle fluctuations in nonuniform and trapped Bose gases: The problem of particle fluctuations in arbitrary nonuniform systems with\nBose-Einstein condensate is considered. This includes the case of trapped Bose\natoms. It is shown that the correct description of particle fluctuations for\nany nonuniform system of interacting atoms always results in thermodynamically\nnormal fluctuations."
    },
    {
        "anchor": "Large photon number extraction from individual atoms trapped in an\n  optical lattice: The atom-by-atom characterization of quantum gases requires the development\nof novel measurement techniques. One particularly promising new technique\ndemonstrated in recent experiments uses strong fluorescent laser scattering\nfrom neutral atoms confined in a short-period optical lattice to measure the\nposition of individual atoms in the sample. A crucial condition for the\nmeasurements is that atomic hopping between lattice sites must be strongly\nsuppressed despite substantial photon recoil heating. This article models\nthree-dimensional polarization gradient cooling of atoms trapped within a\nfar-detuned optical lattice. The atomic dynamics are simulated using a hybrid\nMonte Carlo and master equation analysis in order to predict the frequency of\nprocesses which give rise to degradation or loss of the fluorescent signal\nduring measurements. It is shown, consistent with the experimental results,\nthat there exists a wide parameter range in which the lifetime of\nstrongly-fluorescing isolated lattice-trapped atoms is limited by background\ngas collisions rather than radiative processes. In these cases the total number\nof scattered photons can be as large as 10^8 per atom. The performance of the\ntechnique is related to relevant experimental parameters.",
        "positive": "Interaction Induced Hall Response in a Spin-Orbit Coupled Bose-Einstein\n  Condensate: In this letter we consider the dynamic behaviors of spin-orbit coupled Bose\ncondensates realized in recent experiments. We show that there exists an\ninteraction induced ac Hall response which is absent in a non-interacting\nsystem. This condensate has two distinct equilibrium phases known as the plane\nwave phase and the stripe phase. In the plane wave phase, we show that an ac\nlongitudinal current will induce an ac radial current in the transverse\ndirection, and vice versa, as a cooperation effect of spin-velocity locking and\nspin-dependent interaction. In the stripe phase, we show that the dominant\nlongitudinal response to a transverse radial current is sliding of the density\nstripe, because it is the low-lying excitation mode originated from spontaneous\nspatial translational symmetry breaking in this phase."
    },
    {
        "anchor": "Massive particle interferometry with lattice solitons: robustness\n  against ionization: We revisit the proposal of Castin and Weiss [Phys. Rev. Lett. vol. 102,\n010403 (2009)] for using the scattering of a quantum matter-wave soliton on a\nbarrier in order to create a coherent superposition state of the soliton being\nentirely to the left of the barrier and being entirely to the right of the\nbarrier. In that proposal, is was assumed that the scattering is perfectly\nelastic, i.e. that the center-of-mass kinetic energy of the soliton is lower\nthan the chemical potential of the soliton. Here we relax this assumption.\nAlso, we introduce an interferometric scheme, which uses interference of\nsoltions, that can be used to detect the degree of coherence between the\nreflected and transmitted part of the soliton. Using exact diagonalization, we\nnumerically simulate a complete interferometric cycle for a soliton consisting\nof six atoms. We find that the interferometric fringes persist even when the\ncenter-of-mass kinetic energy of the soliton is above the energy needed for\ncomplete dissociation of the soliton into constituent atoms.",
        "positive": "Leading Order $k_Fa$ Corrections to the Free Energy and Phase Separation\n  in Two-component Fermion Systems: We study phase separation in a dilute two-component Fermi system with\nattractive interactions as a function of the coupling strength and the\npolarization or number density asymmetry between the two components. In weak\nand strong couplings with a finite number density asymmetry, phase separation\nis energetically more favorable. A heterogeneous phase containing a symmetric\nsuperfluid component and an asymmetric normal phase has lower energy than a\nhomogeneous normal phase. We show that for a small number density asymmetry,\ntaking into consideration the leading order corrections at order $k_Fa$ of the\ninteraction parameter, phase separation is stable against the normal phase in\nthe whole BCS range. We investigate the consequences of the consideration of\nthe leading order $k_Fa$ corrections to the thermodynamic potentials of the\nnormal and BCS phase on the Chandrasekhar-Clogston limit. We have also\ninvestigated the stability of a Bose-Fermi mixture in the far-BEC limit. We\nfind that the molecular BEC is locally stable against an external magnetic\nfield $h$, provided $|h|$ is smaller than the pairing gap $\\Delta_{gap}$."
    },
    {
        "anchor": "Bose-Einstein condensate in an optical lattice with Raman-assisted\n  two-dimensional spin-orbit coupling: In a recent experiment by Wu {\\textit et al.} (arXiv:1511.08170), a\nRaman-assisted two-dimensional spin-orbit coupling has been realized for a\nBose-Einstein condensate in an optical lattice potential. In light of this\nexciting progress, we study in detail key properties of the system. As the\nRaman lasers inevitably couple atoms to high-lying bands, the behaviors of the\nsystem in both the single- and many-particle sectors are significantly\naffected. In particular, the high-band effects enhance the plane-wave phase and\nlead to the emergence of \"roton\" gaps at low Zeeman fields. Furthermore, we\nidentify high-band-induced topological phase boundaries in both the\nsingle-particle and the quasi-particle spectra. We then derive an effective\ntwo-band model, which captures the high-band physics in the experimentally\nrelevant regime. Our results not only offer valuable insights into the novel\ntwo-dimensional lattice spin-orbit coupling, but also provide a systematic\nformalism to model high-band effects in lattice systems with Raman-assisted\nspin-orbit couplings.",
        "positive": "Dynamics of Weyl quasiparticles emerged in an optical lattice: We investigate the dynamics of the Weyl quasiparticles emerged in an optical\nlattice where the topological Weyl semimental and trivial band insulator phases\ncan be adjusted with the on-site energy. The evolution of the density\ndistribution is demonstrated to have an anomalous velocity in Weyl semimental\nbut a steady Zitterbewegung effect in the band insulator. Our analysis\ndemonstrates that the topological Chern number and the chirality of the system\ncan be directly determined from the positions of the atomic center-of-mass.\nFurthermore, the amplitude and the period of the relativistic Zitterbewegung\noscillations are shown to be observable with the time-of-flight experiments."
    },
    {
        "anchor": "Quantum spin ice in three-dimensional Rydberg atom arrays: Quantum spin liquids are exotic phases of matter whose low-energy physics is\ndescribed as the deconfined phase of an emergent gauge theory. With recent\ntheory proposals and an experiment showing preliminary signs of $\\mathbb{Z}_2$\ntopological order [G. Semeghini et al., Science 374, 1242 (2021)], Rydberg atom\narrays have emerged as a promising platform to realize a quantum spin liquid.\nIn this work, we propose a way to realize a $U(1)$ quantum spin liquid in three\nspatial dimensions, described by the deconfined phase of $U(1)$ gauge theory in\na pyrochlore lattice Rydberg atom array. We study the ground state phase\ndiagram of the proposed Rydberg system as a function of experimentally relevant\nparameters. Within our calculation, we find that by tuning the Rabi frequency,\none can access both the confinement-deconfinement transition driven by a\nproliferation of \"magnetic\" monopoles and the Higgs transition driven by a\nproliferation of \"electric\" charges of the emergent gauge theory. We suggest\nexperimental probes for distinguishing the deconfined phase from ordered\nphases. This work serves as a proposal to access a confinement-deconfinement\ntransition in three spatial dimensions on a Rydberg-based quantum simulator.",
        "positive": "Trapped imbalanced fermionic superfluids in one dimension: A variational\n  approach: We propose and analyze a variational wave function for a\npopulation-imbalanced one-dimensional Fermi gas that allows for\nFulde-Ferrell-Larkin-Ovchinnikov (FFLO) type pairing correlations among the two\nfermion species, while also accounting for the harmonic confining potential. In\nthe strongly interacting regime, we find large spatial oscillations of the\norder parameter, indicative of an FFLO state. The obtained density profiles\nversus imbalance are consistent with recent experimental results as well as\nwith theoretical calculations based on combining Bethe ansatz with the local\ndensity approximation. Although we find no signature of the FFLO state in the\ndensities of the two fermion species, we show that the oscillations of the\norder parameter appear in density-density correlations, both in-situ and after\nfree expansion. Furthermore, above a critical polarization, the value of which\ndepends on the interaction, we find the unpaired Fermi-gas state to be\nenergetically more favorable."
    },
    {
        "anchor": "A dark state of Chern bands: Designing flat bands with higher Chern\n  number: We introduce a scheme by which flat bands with higher Chern number $\\vert\nC\\vert>1$ can be designed in ultracold gases through a coherent manipulation of\nBloch bands. Inspired by quantum-optics methods, our approach consists in\ncreating a \"dark Bloch band\" by coupling a set of source bands through resonant\nprocesses. Considering a $\\Lambda$ system of three bands, the Chern number of\nthe dark band is found to follow a simple sum rule in terms of the Chern\nnumbers of the source bands: $C_D\\!=\\!C_1+C_2-C_3$. Altogether, our dark-state\nscheme realizes a nearly flat Bloch band with predictable and tunable Chern\nnumber $C_D$. We illustrate our method based on a $\\Lambda$ system, formed of\nthe bands of the Harper-Hofstadter model, which leads to a nearly flat Chern\nband with $C_D\\!=\\!2$. We explore a realistic sequence to load atoms into the\ndark Chern band, as well as a probing scheme based on Hall drift measurements.\nDark Chern bands offer a practical platform where exotic fractional quantum\nHall states could be realized in ultracold gases.",
        "positive": "Dynamics of interacting fermions in spin-dependent potentials: Recent experiments with dilute trapped Fermi gases observed that weak\ninteractions can drastically modify spin transport dynamics and give rise to\nrobust collective effects including global demagnetization, macroscopic spin\nwaves, spin segregation, and spin self-rephasing. In this work we develop a\nframework for studying the dynamics of weakly interacting fermionic gases\nfollowing a spin-dependent change of the trapping potential which illuminates\nthe interplay between spin, motion, Fermi statistics, and interactions. The key\nidea is the projection of the state of the system onto a set of lattice spin\nmodels defined on the single-particle mode space. Collective phenomena,\nincluding the global spreading of quantum correlations in real space, arise as\na consequence of the long-ranged character of the spin model couplings. This\napproach achieves good agreement with prior measurements and suggests a number\nof directions for future experiments."
    },
    {
        "anchor": "Enhanced quantum spin fluctuations in a binary Bose-Einstein condensate: For quantum fluids, the role of quantum fluctuations may be significant in\nseveral regimes such as when the dimensionality is low, the density is high,\nthe interactions are strong, or for low particle numbers. In this paper we\npropose a fundamentally different regime for enhanced quantum fluctuations\nwithout being restricted by any of the above conditions. Instead, our scheme\nrelies on the engineering of an effective attractive interaction in a dilute,\ntwo-component Bose-Einstein condensate (BEC) consisting of thousands of atoms.\nIn such a regime, the quantum spin fluctuations are significantly enhanced\n(atom bunching with respect to the noninteracting limit) since they act to\nreduce the interaction energy - a remarkable property given that spin\nfluctuations are normally suppressed (anti-bunching) at zero temperature. In\ncontrast to the case of true attractive interactions, our approach is not\nvulnerable to BEC collapse. We numerically demonstrate that these quantum\nfluctuations are experimentally accessible by either spin or single-component\nBragg spectroscopy, offering a useful platform on which to test\nbeyond-mean-field theories. We also develop a variational model and use it to\nanalytically predict the shift of the immiscibility critical point, finding\ngood agreement with our numerics.",
        "positive": "PT invariant Weyl semimetals in gauge symmetric systems: Weyl semimetals typically appear in systems in which either time-reversal (T)\nor inversion (P}) symmetry are broken. Here we show that in the presence of\ngauge potentials these topological states of matter can also arise in fermionic\nlattices preserving both T and P. We analyze in detail the case of a cubic\nlattice model with $\\pi$-fluxes, discussing the role of gauge symmetries in the\nformation of Weyl points and the difference between the physical and the\ncanonical T and P symmetries. Motivated by advances in ultracold atom\nexperiments and by the possibility of using synthetic magnetic fields, we\nexamine the robustness of the Weyl semimetal phase in the presence of trapping\npotentials and random perturbations of the magnetic fluxes, which can be\ncompared to a local disorder in realistic scenarios."
    },
    {
        "anchor": "Weakly-interacting Bose-Bose mixtures from the functional\n  renormalisation group: We provide a detailed presentation of the functional renormalisation group\n(FRG) approach for weakly-interacting Bose-Bose mixtures, including a complete\ndiscussion on the RG equations. To test this approach, we examine thermodynamic\nproperties of balanced three-dimensional Bose-Bose gases at zero and finite\ntemperatures and find a good agreement with related works. We also study\nground-state energies of repulsive Bose polarons by examining mixtures in the\nlimit of infinite population imbalance. Finally, we discuss future applications\nof the FRG to novel problems in Bose-Bose mixtures and related systems.",
        "positive": "Searching for Perfect Fluids: Quantum Viscosity in a Universal Fermi Gas: We measure the shear viscosity in a two-component Fermi gas of atoms, tuned\nto a broad s-wave collisional (Feshbach) resonance. At resonance, the atoms\nstrongly interact and exhibit universal behavior, where the equilibrium\nthermodynamic properties and the transport coefficients are universal functions\nof the density $n$ and temperature $T$. We present a new calibration of the\ntemperature as a function of global energy, which is directly measured from the\ncloud profiles. Using the calibration, the trap-averaged shear viscosity in\nunits of $\\hbar\\,n$ is determined as a function of the reduced temperature at\nthe trap center, from nearly the ground state to the unitary two-body regime.\nLow temperature data is obtained from the damping rate of the radial breathing\nmode, while high temperature data is obtained from hydrodynamic expansion\nmeasurements. We also show that the best fit to the high temperature expansion\ndata is obtained for a vanishing bulk viscosity. The measured trap-averaged\nentropy per particle and shear viscosity are used to estimate the ratio of the\nshear viscosity to the entropy density, which is compared that conjectured for\na perfect fluid."
    },
    {
        "anchor": "Induced interactions and quench dynamics of bosonic impurities immersed\n  in a Fermi sea: We unravel the ground state properties and the non-equilibrium quantum\ndynamics of two bosonic impurities immersed in an one-dimensional fermionic\nenvironment by applying a quench of the impurity-medium interaction strength.\nIn the ground state, the impurities and the Fermi sea are phase-separated for\nstrong impurity-medium repulsions while they experience a localization tendency\naround the trap center for large attractions. We demonstrate the presence of\nattractive induced interactions mediated by the host for impurity-medium\ncouplings of either sign and analyze the competition between induced and direct\ninteractions. Following a quench to repulsive interactions triggers a breathing\nmotion in both components, with an interaction dependent frequency and\namplitude for the impurities, and a dynamical phase-separation between the\nimpurities and their surrounding for strong repulsions. For attractive\npost-quench couplings a beating pattern owing its existence to the dominant\nrole of induced interactions takes place with both components showing a\nlocalization trend around the trap center. In both quench scenarios, attractive\ninduced correlations are manifested between non-interacting impurities and are\nfound to dominate the direct ones only for quenches to attractive couplings.",
        "positive": "Quantum correlations and entanglement in far-from-equilibrium spin\n  systems: By applying complementary analytic and numerical methods, we investigate the\ndynamics of spin-$1/2$ XXZ models with variable-range interactions in arbitrary\ndimensions. The dynamics we consider is initiated from uncorrelated states that\nare easily prepared in experiments, and can be equivalently viewed as either\nRamsey spectroscopy or a quantum quench. Our primary focus is the dynamical\nemergence of correlations and entanglement in these far-from-equilibrium\ninteracting quantum systems: we characterize these correlations by the\nentanglement entropy, concurrence, and squeezing, which are inequivalent\nmeasures of entanglement corresponding to different quantum resources. In one\nspatial dimension, we show that the time evolution of correlation functions\nmanifests a non-perturbative dynamic singularity. This singularity is\ncharacterized by a universal power-law exponent that is insensitive to small\nperturbations. Explicit realizations of these models in current experiments\nusing polar molecules, trapped ions, Rydberg atoms, magnetic atoms, and\nalkaline-earth and alkali atoms in optical lattices, along with the relative\nmerits and limitations of these different systems, are discussed."
    },
    {
        "anchor": "Microscopic Study on Superexchange Dynamics of Composite Spin-1 Bosons: We report on an experimental simulation of the spin-1 Heisenberg model with\ncomposite bosons in a one-dimensional chain based on the two-component\nBose-Hubbard model. Exploiting our site-and spin-resolved quantum gas\nmicroscope, we observed faster superexchange dynamics of the spin-1 system\ncompared to its spin-1/2 counterpart, which is attributed to the enhancement\neffect of multi-bosons. We further probed the non-equilibrium spin dynamics\ndriven by the superexchange and single-ion anisotropy terms, unveiling the\nlinear expansion of the spin-spin correlations, which is limited by the\nLieb-Robinson bound. Based on the superexchange process, we prepared and\nverified the entangled qutrits pairs with these composite spin-1 bosons,\npotentially being applied in qutrit-based quantum information processing.",
        "positive": "Nonlinear Atom-Photon Interaction Induced Population Inversion and\n  Inverted Quantum Phase Transition of Bose-Einstein Condensate in an Optical\n  Cavity: In this paper we explore the rich structure of macroscopic many-particle\nquantum states for Bose- Einstein condensate in an optical cavity with the\ntunable nonlinear atom-photon interaction [Nature (London) 464, 1301 (2010)].\nPopulation inversion, bistable normal phases and the coexistence of\nnormal{superradiant phases are revealed by adjusting of the experimentally\nrealizable interaction strength and pump-laser frequency. For the negative\n(effective) cavity-frequency we observe remark- ably an inverted quantum phase\ntransition (QPT) from the superradiant to normal phases with the increase of\natom-field coupling, which is just opposite to the QPT in the normal Dicke\nmodel. The bistable macroscopic states are derived analytically in terms of the\nspin-coherent-state variational method by taking into account of both normal\nand inverted pseudospin states."
    },
    {
        "anchor": "Self-localization of a small number of Bose particles in a superfluid\n  Fermi system: We consider self-localization of a small number of Bose particles immersed in\na large homogeneous superfluid mixture of fermions in three and one dimensional\nspaces. Bosons distort the density of surrounding fermions and create a\npotential well where they can form a bound state analogous to a small polaron\nstate. In the three dimensional volume we observe the self-localization for\nrepulsive interactions between bosons and fermions. In the one dimensional case\nbosons self-localize as well as for attractive interactions forming, together\nwith a pair of fermions at the bottom of the Fermi sea, a vector soliton. We\nanalyze also thermal effects and show that small non-zero temperature affects\nthe pairing function of the Fermi-subsystem and has little influence on the\nself-localization phenomena.",
        "positive": "Coherent Interaction of a Single Fermion with a Small Bosonic Field: We have experimentally studied few-body impurity systems consisting of a\nsingle fermionic atom and a small bosonic field on the sites of an optical\nlattice. Quantum phase revival spectroscopy has allowed us to accurately\nmeasure the absolute strength of Bose-Fermi interactions as a function of the\ninterspecies scattering length. Furthermore, we observe the modification of\nBose-Bose interactions that is induced by the interacting fermion. Because of\nan interference between Bose-Bose and Bose-Fermi phase dynamics, we can infer\nthe mean fermionic filling of the mixture and quantify its increase (decrease)\nwhen the lattice is loaded with attractive (repulsive) interspecies\ninteractions."
    },
    {
        "anchor": "Observation of Algebraic Time Order for Two-Dimensional Dipolar Excitons: Emergence of algebraic quasi-long-range order is a key feature of superfluid\nphase transitions at two dimensions. For this reduced dimensionality\ninteractions prevent Bose-Einstein condensation with true long range order, at\nany finite temperature. Here, we report the occurence of algebraic order in a\nstrongly interacting quantum liquid formed by dipolar excitons confined in a\nbilayer semiconductor heterostructure. We observe a transition from exponential\nto algebraic decay of the excitons temporal coherence, accompanied by a\nuniversal scaling behaviour of the equation of state. Our results provide\nstrong evidence for a Berezinskii-Kosterlitz-Thouless (BKT) transition in a\nmulti-component boson-like system governed by strong dipolar interactions.",
        "positive": "Spin-orbit coupling driven superfluid states in optical lattices at zero\n  and finite temperatures: We investigate the quantum phase transitions of a two-dimensional\nBose-Hubbard model in the presence of a Rashba spin-orbit coupling with and\nwithout thermal fluctuations. The interplay of single-particle hopping,\nstrength of spin-orbit coupling, and interspin interaction leads to superfluid\nphases with distinct properties. With interspin interactions weaker than\nintraspin interactions, the spin-orbit coupling induces two finite-momentum\nsuperfluid phases. One of them is a phase-twisted superfluid that exists at low\nhopping strengths and reduces the domain of insulating phases. At comparatively\nhigher hopping strengths, there is a transition from the phase-twisted to a\nfinite momenta stripe superfluid. With interspin interactions stronger than the\nintraspin interactions, the system exhibits phase-twisted to ferromagnetic\nphase transition. At finite temperatures, the thermal fluctuations destroy the\nphase-twisted superfluidity and lead to a wide region of normal-fluid states.\nThese findings can be observed in recent quantum gas experiments with\nspin-orbit coupling in optical lattices."
    },
    {
        "anchor": "Cyclotron Dynamics of a Kondo Singlet in a Spin-Orbit-Coupled\n  Alkaline-Earth Atomic Gas: We propose a scheme to investigate the interplay between Kondo-exchange\ninteraction and quantum spin Hall effect with ultracold fermionic\nalkaline-earth atoms trapped in two-dimensional optical lattices using\nultracold collision and laser-assisted tunneling. In the strong Kondo-coupling\nregime, though the loop trajectory of the mobile atom disappears, collective\ndynamics of an atom pair in two clock states can exhibit an unexpected\nspin-dependent cyclotron orbit in a plaquette, realizing the quantum spin Hall\neffect of the Kondo singlet. We demonstrate that the collective cyclotron\ndynamics of the spin-zero Kondo singlet is governed by an effective\nHarper-Hofstadter model in addition to second-order diagonal tunneling.",
        "positive": "Simulation method for evaporative cooling of trapped Bose gases at\n  finite temperatures: We develop a simulation method for evaporative cooling of trapped\nBose-Einstein condensate at finite temperatures using Zaremba-Nikuni-Griffin\n(ZNG) formalism. ZNG formalism includes the generalized GP equation and a\nsemiclassical kinetic equation for the thermal cloud, which treats the\nexcitations semiclassically within the Hartree Fock approximation. The\ngeneralized GP equation includes the mean field due to the thermal cloud and\nthe source term associated with collisions between the condensate and the\nthermal cloud. Our method is based on the numerical approach developed by\nJackson and Zaremba, which simulates the kinetic equation using test particles.\nA key point of our method is to mimic the evaporative cooling process by\neliminating the test particles with high energy. We show that our method\nsuccessfully describes condensate growth during evaporative cooling. We also\nnumerically simulate vortex lattice formation during evaporative cooling in the\npresence of the rotating thermal cloud."
    },
    {
        "anchor": "The ground state of the bose-hubbard model is a supersolid: The Bose-Hubbard model is well-defined description of a Bose solid which may\nbe realistic for cold atoms in a periodic optical lattice. We show that\ncontrary to accepted theories it can never have as a ground state a perfect\nMott insulator solid and that it has a low-energy spectrum of vortex-like phase\nfluctuations. Whether the ground state is necessarily commensurate remains an\nopen question.",
        "positive": "Response of fermions in Chern bands to spatially local quenches: We study the dynamical evolution of Chern-band systems after subjecting them\nto local quenches. For open-boundary systems, we show for half-filling that the\nchiral nature of edge states is manifested in the time-dependent chiral\nresponse to local density quenches on the edge. In the presence of power-law\ntraps, we show how to mimic the half-filling situation by choosing the\nappropriate number of fermions depending on the trap size, and explore chiral\nresponses of edges to local quenches in such a configuration. We find that\nperturbations resulting from the quenches propagate at different group\nvelocities depending on the bulk band gap. Our results provide different routes\nto check dynamically the non-trivial nature of Chern bands."
    },
    {
        "anchor": "Gradient corrections to the local density approximation for trapped\n  superfluid Fermi gases: Two species superfluid Fermi gas is investigated on the BCS side up to the\nFeshbach resonance. Using the Greens's function technique gradient corrections\nare calculated to the generalized Thomas-Fermi theory including Cooper pairing.\nTheir relative magnitude is found to be measured by the small parameter\n$(d/R_{TF})^4$, where $d$ is the oscillator length of the trap potential and\n$R_{TF}$ is the radial extension of the density $n$ in the Thomas-Fermi\napproximation. In particular at the Feshbach resonance the universal %constant\n$A_{TF}$ has the %correction in the center $A=A_{TF}+A_2(d/R_{TF})^4+\\...$\ncorrections to the local density approximation are calculated and a universal\nprefactor $\\kappa_W=7/27$ is derived for the von Weizs\\\"acker type correction\n$\\kappa_W(\\hbar^2/2m)(\\nabla^2 n^{1/2}/n^{1/2})$.",
        "positive": "Spin-Nematic Vortex States in Cold Atoms: The (pseudo-)spin degrees of freedom greatly enriches the physics of cold\natoms. This is particularly so for systems with high spins (i.e., spin quantum\nnumber larger than 1/2). For example, one can construct not only the rank-1\nspin vector, but also the rank-2 spin tensor in high spin systems. Here we\npropose a simple scheme to couple the spin tensor and the center-of-mass\norbital angular momentum in a spin-1 cold atom system, and show that this leads\nto a new quantum phase of the matter: the spin-nematic vortex state that\nfeatures vorticity in an SU(2) spin-nematic tensor subspace. Under proper\nconditions, such states are characterized by quantized topological numbers. Our\nwork opens up new avenues of research in topological quantum matter with high\nspins."
    },
    {
        "anchor": "Order parameter and detection for crystallized dipolar bosons in\n  lattices: We explore the ground-state properties of bosons with dipole-dipole\ninteractions in a one-dimensional optical lattice. Remarkably, a\ncrystallization process happens for strong dipolar interactions. Herein, we\nprovide a detailed characterization and a way to measure the resulting crystal\nphase. Using the eigenvalues of the reduced one-body density matrix we define\nan order parameter that yields a phase diagram in agreement with an analysis of\nthe density and two-body density. We demonstrate that the phase diagram can be\ndetected experimentally using the variance of single-shot measurements.",
        "positive": "Exploring the ferromagnetic behaviour of a repulsive Fermi gas via spin\n  dynamics: Ferromagnetism is a manifestation of strong repulsive interactions between\nitinerant fermions in condensed matter. Whether short-ranged repulsion alone is\nsufficient to stabilize ferromagnetic correlations in the absence of other\neffects, like peculiar band dispersions or orbital couplings, is however\nunclear. Here, we investigate ferromagnetism in the minimal framework of an\nultracold Fermi gas with short-range repulsive interactions tuned via a\nFeshbach resonance. While fermion pairing characterises the ground state, our\nexperiments provide signatures suggestive of a metastable Stoner-like\nferromagnetic phase supported by strong repulsion in excited scattering states.\nWe probe the collective spin response of a two-spin mixture engineered in a\nmagnetic domain-wall-like configuration, and reveal a substantial increase of\nspin susceptibility while approaching a critical repulsion strength. Beyond\nthis value, we observe the emergence of a time-window of domain immiscibility,\nindicating the metastability of the initial ferromagnetic state. Our findings\nestablish an important connection between dynamical and equilibrium properties\nof strongly-correlated Fermi gases, pointing to the existence of a\nferromagnetic instability."
    },
    {
        "anchor": "Analytical approach to a bosonic ladder subject to a magnetic field: We examine a bosonic two-leg ladder model subject to a magnetic flux, and\nespecially focus on a regime where the lower energy band has two minima. By\nusing a low-energy field theory approach, we study several issues discussed in\nthe system: the existence of local patterns in density and current,\nchiral-current reversal, and the effect of a nearest-neighbor interaction along\nthe rung direction. In our formalism, the local patterns are interpreted as a\nresult of breaking of discrete symmetry. The chiral-current reversal occurs\nthrough a competition between a current component determined at a commensurate\nvortex density causing an enlargement of the unit cell, and another component,\nwhich is proportional to the magnetic field doping from the corresponding\ncommensurate flux. The nearest-neighbor interaction along the rung direction\navailable with the technique on a synthetic dimension is shown to favor a\npopulation-imbalance solution in an experimentally relevant regime.",
        "positive": "Universal relations and normal-state properties of a Fermi gas with\n  laser-dressed mixed-partial-wave interactions: In a recent experiment [P. Peng, $et$ $al.$, Phys. Rev. A \\textbf{97}, 012702\n(2018)], it has been shown that the $p$-wave Feshbach resonance can be shifted\ntoward the $s$-wave Feshbach resonance by a laser field. Based on this\nexperiment, we study the universal relations and the normal-state properties in\nan ultracold Fermi gas with coexisting $s$- and $p$-wave interactions under\noptical control of a $p$-wave magnetic Feshbach resonance. Within the\noperator-product expansion, we derive the high-momentum tail of various\nobservable quantities in terms of contacts. We find that the high-momentum tail\nbecomes anisotropic. Adopting the quantum virial expansion, we calculate the\nnormal-state contacts with and without a laser field for $^{40}$K atoms using\ntypical experimental parameters. We show that the contacts are dependent on the\nlaser dressing. We also reveal the interplay of laser dressing and different\npartial-wave interactions on various contacts. In particular, we demonstrate\nthat the impact of the laser dressing in the $p$-wave channel can be probed by\nmeasuring the $s$-wave contacts, which is a direct manifestation of few-body\neffects on the many-body level. Our results can be readily checked\nexperimentally."
    },
    {
        "anchor": "Quantum simulation of many-body spin interactions with ultracold polar\n  molecules: We present an architecture for the quantum simulation of many-body spin\ninteractions based on ultracold polar molecules trapped in optical lattices.\nOur approach employs digital quantum simulation, i.e., the dynamics of the\nsimulated system is reproduced by the quantum simulator in a stroboscopic\npattern, and allows to simulate both coherent and dissipative dynamics. We\ndiscuss the realization of Kitaev's toric code Hamiltonian, a paradigmatic\nmodel involving four-body interactions, and we analyze the requirements for an\nexperimental implementation.",
        "positive": "Quantum simulation of $(1+1)$-dimensional U(1) gauge-Higgs model on a\n  lattice by cold Bose gases: We present a theoretical study of quantum simulations of $(1+1)$-dimensional\nU(1) lattice gauge-Higgs models, which contain a compact U(1) gauge field and a\nHiggs matter field, by using ultra-cold bosonic gases on a one-dimensional\noptical lattice. Starting from the extended Bose-Hubbard model with on-site and\nnearest-neighbor interactions, we derive the U(1) lattice gauge-Higgs model as\na low-energy effective theory. The derived gauge-Higgs model exhibits\nnontrivial phase transitions between confinement and Higgs phases, and we\ndiscuss the relation with the phase transition in the extended Bose-Hubbard\nmodel. Finally, we study real-time dynamics of an electric flux by the\nGross-Pitaevskii equations and the truncated Wigner approximation. The dynamics\nis governed by a bosonic analog of the Schwinger mechanism, i.e., shielding of\nan electric flux by a condensation of Higgs fields, which occurs differently in\nthe Higgs and the confinement phase. These results, together with the obtained\nphase diagrams, shall guide experimentalists in designing quantum simulations\nof the gauge-Higgs models by cold gases."
    },
    {
        "anchor": "BCS pairing state of a Dilute Bose Gas with Spin-Orbit Coupling: We study a two-component Bose gas with a symmetric spin-orbit coupling, and\nfind that two atoms can form a bound state with any intra- or inter-species\nscattering length. Consequently, in the dilute limit, the\nBardeen-Cooper-Shrieffer (BCS) pairing state of bosons can be formed with\nweakly-attractive inter-species and repulsive intra-species interactions. The\nquasiparticle excitation energies are anisotropic due to spin-orbit coupling.\nThis BCS paring state is energetically favored over Bose-Einstein condensation\n(BEC) of atoms at low densities. As the density increases, there is a\nfirst-order transition from the BCS to BEC states.",
        "positive": "The cross-over from Townes solitons to droplets in a 2D Bose mixture: When two Bose-Einstein condensates -- labelled 1 and 2 -- overlap spatially,\nthe equilibrium state of the system depends on the miscibility criterion for\nthe two fluids. Here, we theoretically focus on the non-miscible regime in two\nspatial dimensions and explore the properties of the localized wave packet\nformed by the minority component 2 when immersed in an infinite bath formed by\ncomponent 1. We address the zero-temperature regime and describe the two-fluid\nsystem by coupled classical field equations. We show that such a wave packet\nexists only for an atom number $N_2$ above a threshold value corresponding to\nthe Townes soliton state. We identify the regimes where this localized state\ncan be described by an effective single-field equation up to the droplet case,\nwhere component 2 behaves like an incompressible fluid. We study the\nnear-equilibrium dynamics of the coupled fluids, which reveals specific\nparameter ranges for the existence of localized excitation modes."
    },
    {
        "anchor": "Realistic Time-Reversal Invariant Topological Insulators With Neutral\n  Atoms: We lay out an experiment to realize time-reversal invariant topological\ninsulators in alkali atomic gases. We introduce an original method to\nsynthesize a gauge field in the near-field of an atom-chip, which effectively\nmimics the effects of spin-orbit coupling and produces quantum spin-Hall\nstates. We also propose a feasible scheme to engineer sharp boundaries where\nthe hallmark edge states are localized. Our multi-band system has a large\nparameter space exhibiting a variety of quantum phase transitions between\ntopological and normal insulating phases. Due to their remarkable versatility,\ncold-atom systems are ideally suited to realize topological states of matter\nand drive the development of topological quantum computing.",
        "positive": "Low-energy prethermal phase and crossover to thermalization in nonlinear\n  kicked rotors: In the presence of interactions, periodically-driven quantum systems\ngenerically thermalize to an infinite-temperature state. Recently, however, it\nwas shown that in random kicked rotors with local interactions, this long-time\nequilibrium could be strongly delayed by operating in a regime of weakly\nfluctuating random phases, leading to the emergence of a metastable thermal\nensemble. Here we show that when the random kinetic energy is smaller than the\ninteraction energy, this system in fact exhibits a much richer dynamical phase\ndiagram, which includes a low-energy pre-thermal phase characterized by a\nlight-cone spreading of correlations in momentum space. We develop a\nhydrodynamic theory of this phase and find a very good agreement with exact\nnumerical simulations. We finally explore the full dynamical phase diagram of\nthe system and find that the transition toward full thermalization is\ncharacterized by relatively sharp crossovers."
    },
    {
        "anchor": "Accelerating the convergence of exact diagonalization with the\n  transcorrelated method: Quantum gas in one dimension with contact\n  interactions: Exact diagonalization expansions of Bose or Fermi gases with contact\ninteractions converge very slowly due to a non-analytic cusp in the wave\nfunction. Here we develop a transcorrelated approach where the cusp is treated\nexactly and folded into the many-body Hamiltonian with a similarity\ntransformation that removes the leading order singularity. The resulting\ntranscorrelated Hamiltonian is not hermitian but can be treated numerically\nwith a standard projection approach. The smoothness of the wave function\nimproves by at least one order and thus the convergence rate for the ground\nstate energy improves. By numerical investigation of a one-dimensional gas of\nspin-$\\frac{1}{2}$ fermions we find the error in the transcorrelated energy to\nscale as $M^{-3}$ with a single-particle basis of $M$ plane waves compared to\n$M^{-1}$ for the expansion of the original Hamiltonian and $M^{-2}$ using\nconventional lattice renormalization.",
        "positive": "Multiple dark-bright solitons in atomic Bose-Einstein condensates: We present experimental results and a systematic theoretical analysis of\ndark-br ight soliton interactions and multiple-dark-bright soliton complexes in\natomic t wo-component Bose-Einstein condensates. We study analytically the\ninteractions b etween two-dark-bright solitons in a homogeneous condensate and,\nthen, extend ou r considerations to the presence of the trap. An effective\nequation of motion is derived for the dark-bright soliton center and the\nexistence and stability of stationary two-dark-bright soliton states is\nillustrated (with the bright components being either in- or out-of-phase). The\nequation of motion provides the characteristic oscillation frequencies of the\nsolitons, in good agreement with the eigenfrequencies of the anomalous modes of\nthe system."
    },
    {
        "anchor": "Bose Gases Near Unitarity: We study the properties of strongly interacting Bose gases at the density and\ntemperature regime when the three-body recombination rate is substantially\nreduced. In this regime, one can have a Bose gas with all particles in\nscattering states (i.e. the \"upper branch\") with little loss even at unitarity\nover the duration of the experiment. We show that because of bosonic\nenhancement, pair formation is shifted to the atomic side of the original\nresonance (where scattering length $a_s<0$), opposite to the fermionic case. In\na trap, a repulsive Bose gas remains mechanically stable when brought across\nresonance to the atomic side until it reaches a critical scattering length\n$a_{s}^{\\ast}<0$. For $a_s<a_{s}^{\\ast}$, the density consists of a core of\nupper branch bosons surrounded by an outer layer of equilibrium phase. The\nconditions of low three-body recombination requires that the particle number\n$N<\\alpha (T/\\omega)^{5/2}$ in a harmonic trap with frequency $\\omega$, where\n$\\alpha$ is a constant.",
        "positive": "Characterizing twin-particle entanglement in double-well potentials: We consider a pair of twin atoms trapped in double-well potentials. For each\natom, two orthogonal spatial modes are accessible: the states $ |L\\rangle$ and\n$|R\\rangle$ spatially localized in the left and right wells respectively.\nFurthermore the twin atoms are distinguishable thanks to an additional degree\nof freedom. We propose a method for experimentally quantifying the particle\nentanglement between these atoms which allows us to probe a violation of Bell's\ninequality. It is based on measuring the correlations in the atoms' momentum\ndistribution. If the tunneling and the energy difference between the wells are\ntunable, then full state tomography is achievable."
    },
    {
        "anchor": "Extracting non-local inter-polaron interactions from collisional\n  dynamics: This study develops a novel experimental method of deducing the profile of\ninteraction induced between impurities in a trapped gas of ultracold Fermi/Bose\natoms, which are often referred to as Fermi/Bose polarons. In this method, we\nconsider a two-body Fermi/Bose polaron collision experiment in which impurities\nand atoms interact only weakly. Numerical simulations of the quantum dynamics\nreveal the possibility to obtain information regarding the non-local induced\ninteraction between two polarons from a measured profile of the polaron wave\npacket at several snapshots. This is because the potential of the induced\ninteraction is well balanced by the quantum potential whenever the WKB\napproximation for the relevant Schr\\\"{o}dinger equation is applicable.",
        "positive": "Stability of trapped degenerate dipolar Bose and Fermi gases: Trapped degenerate dipolar Bose and Fermi gases of cylindrical symmetry with\nthe polarization vector along the symmetry axis are only stable for the\nstrength of dipolar interaction below a critical value. In the case of bosons,\nthe stability of such a dipolar Bose-Einstein condensate (BEC) is investigated\nfor different strengths of contact and dipolar interactions using variational\napproximation and numerical solution of a mean-field model. In the disk shape,\nwith the polarization vector perpendicular to the plane of the disk, the atoms\nexperience an overall dipolar repulsion and this fact should contribute to the\nstability. However, a complete numerical solution of the dynamics leads to the\ncollapse of a strongly disk-shaped dipolar BEC due to the long-range\nanisotropic dipolar interaction. In the case of fermions, the stability of a\ntrapped single-component degenerate dipolar Fermi gas is studied including the\nHartree-Fock exchange and Brueckner-Goldstone correlation energies in the local\ndensity approximation valid for a large number of atoms. Estimates for the\nmaximum allowed number of polar Bose and Fermi molecules in BEC and degenerate\nFermi gas are given."
    },
    {
        "anchor": "Spin Susceptibility and Strong Coupling Effects in an Ultracold Fermi\n  Gas: We investigate magnetic properties and strong coupling corrections in the BCS\n(Bardeen-Cooper-Schrieffer)-BEC (Bose-Einstein condensation) crossover regime\nof an ultracold Fermi gas. Within the framework of an extended $T$-matrix\ntheory, we calculate the spin susceptibility $\\chi$ above the superfluid phase\ntransition temperature $T_{\\rm c}$. In the crossover region, the formation of\npreformed Cooper pairs is shown to cause a non-monotonic temperature dependence\nof $\\chi$, which is similar to the so-called spin-gap phenomenon observed in\nthe under-doped regime of high-$T_{c}$ cuprates. From this behavior of $\\chi$,\nwe determine the spin-gap temperature as the temperature at which $\\chi$ takes\na maximum value, in the BCS-BEC crossover region. Since the spin susceptibility\nis sensitive to the formation of singlet Cooper pairs, our results would be\nuseful in considering the temperature region where pairing fluctuations are\nimportant in the BCS-BEC crossover regime of an ultracold Fermi gas.",
        "positive": "Interaction quench in a trapped one-dimensional Bose gas: We study the non-equilibrium quench dynamics from free to hard-core\none-dimensional bosons in the presence of a hard-wall confining potential. We\ncharacterise the density profile and the two-point fermionic correlation\nfunction in the stationary state as well as their full time evolution. We find\nthat for long times the system relaxes to a uniform density profile, but the\ncorrelation function keeps memory of the initial state with a stationary\nalgebraic long-distance decay as opposite to the exponential behaviour found\nfor the same quench in the periodic setup. We also compute the stationary\nbosonic two-point correlator which turns out to decay exponentially for large\ndistances. We show that a two-step mechanism governs the time evolution: a\nquick approach to an almost stationary value is followed by a slow algebraic\nrelaxation to the true stationary state."
    },
    {
        "anchor": "Exact spectral function of a Tonks-Girardeau gas in a lattice: The single-particle spectral function of a strongly correlated system is an\nessential ingredient to describe its dynamics and transport properties. We\ndevelop a general method to calculate the exact spectral function of a strongly\ninteracting one-dimensional Bose gas in the Tonks-Girardeau regime, valid for\nany type of confining potential, and apply it to bosons on a lattice to obtain\nthe full spectral function, at all energy and momentum scales. We find that it\ndisplays three main singularity lines. The first two can be identified as the\nanalogs of Lieb-I and Lieb-II modes of a uniform fluid; the third one, instead,\nis specifically due to the presence of the lattice. We show that the spectral\nfunction displays a power-law behaviour close to the Lieb-I and Lieb-II\nsingularities, as predicted by the non-linear Luttinger liquid description, and\nobtain the exact exponents. In particular, the Lieb-II mode shows a divergence\nin the spectral function, differently from what happens in the dynamical\nstructure factor, thus providing a route to probe it in experiments with\nultracold atoms.",
        "positive": "Skyrmion dynamics and disintegration in a spin-1 Bose-Einstein\n  condensate: Dynamics of skyrmionic spin texture in the spin-1 Bose-Einstein condensate is\nexamined by analytical and numerical means. We show the skyrmion (coreless\nvortex) to be inherently unstable in the sense that the state initially\nprepared purely within the antiferromagnetic (ferromagnetic) order parameter\nmanifold inevitably evolves into a mixture of both. The vorticity-dependent\ndrift in the presence of the trapping potential also contributes to the\ndisintegration of the initial spin texture manifold. We argue that the notion\nof a skyrmion as a topologically protected entity becomes ill defined during\nthe dynamical evolution process."
    },
    {
        "anchor": "Dynamics of one-dimensional quantum droplets: The structure and dynamics of one-dimensional binary Bose gases forming\nquantum droplets is studied by solving the corresponding amended\nGross-Pitaevskii equation. Two physically different regimes are identified,\ncorresponding to small droplets of an approximately Gaussian shape and large\n`puddles' with a broad flat-top plateau. Small droplets collide\nquasi-elastically, featuring the soliton-like behavior. On the other hand,\nlarge colliding droplets may merge or suffer fragmentation, depending on their\nrelative velocity. The frequency of a breathing excited state of droplets, as\npredicted by the dynamical variational approximation based on the Gaussian\nansatz, is found to be in good agreement with numerical results. Finally, the\nstability diagram for a single droplet with respect to shape excitations with a\ngiven wave number is drawn, being consistent with preservation of the Weber\nnumber for large droplets.",
        "positive": "Qubit Analog with Polariton Superfluid in an Annular Trap: We report on the experimental realization and characterization of a qubit\nanalog with semiconductor exciton-polaritons. In our system, a condensate of\nexciton-polaritons is confined by a spatially-patterned pump laser in an\nannular trap that supports energy-degenerate circulating currents of the\npolariton superfluid. Using temporal interference measurements, we observe\ncoherent oscillations between a pair of counter-circulating superfluid vortex\nstates of the polaritons coupled by elastic scattering off the laser-imprinted\npotential. The qubit basis states correspond to the symmetric and antisymmetric\nsuperpositions of the two vortex states forming orthogonal double-lobe spatial\nwavefunctions. By engineering the potential, we tune the coupling and coherent\noscillations between the two circulating current states, control the energies\nof the qubit basis states, and initialize the qubit in the desired state. The\ndynamics of the system is accurately reproduced by our theoretical two-state\nmodel, and we discuss potential avenues to achieve complete control over our\npolaritonic qubits and realize controllable interactions between such qubits to\nimplement quantum gates and algorithms analogous to quantum computation with\nstandard qubits."
    },
    {
        "anchor": "Bright solitons in a 2D spin-orbit-coupled dipolar Bose-Einstein\n  condensate: We study a two-dimensional spin-orbit-coupled dipolar Bose-Einstein\ncondensate with repulsive contact interactions by both the variational method\nand the imaginary time evolution of the Gross-Pitaevskii equation. The dipoles\nare completely polarized along one direction in the 2D plane so as to provide\nan effective attractive dipole-dipole interaction. We find two types of\nsolitons as the ground states arising from such attractive interactions: a\nplane wave soliton with a spatially varying phase and a stripe soliton with a\nspatially oscillating density for each component. Both types of solitons\npossess smaller size and higher anisotropy than the soliton without spin-orbit\ncoupling. Finally, we discuss the properties of moving solitons, which are\nnontrivial because of the violation of Galilean invariance.",
        "positive": "Interacting bosons in topological optical flux lattices: An interesting route to the realization of topological Chern bands in\nultracold atomic gases is through the use of optical flux lattices. These\nmodels differ from the tight-binding real-space lattice models of Chern\ninsulators that are conventionally studied in solid-state contexts. Instead,\nthey involve the coherent coupling of internal atomic (spin) states, and can be\nviewed as tight-binding models in reciprocal space. By changing the form of the\ncoupling and the number $N$ of internal spin states, they give rise to Chern\nbands with controllable Chern number and with nearly flat energy dispersion. We\ninvestigate in detail how interactions between bosons occupying these bands can\nlead to the emergence of fractional quantum Hall states, such as the Laughlin\nand Moore-Read states. In order to test the experimental realization of these\nphases, we study their stability with respect to band dispersion and band\nmixing. We also probe novel topological phases that emerge in these systems\nwhen the Chern number is greater than 1."
    },
    {
        "anchor": "Dynamics of elliptical vortices in a trapped quantum fluid: The nonequilibrium dynamics of vortices in 2D quantum fluids can be predicted\nby accounting for the way in which vortex ellipticity is coupled to the\ngradient in background fluid density. In the absence of nonlinear interactions,\na harmonically trapped fluid can be analyzed analytically to show that single\nvortices will move in an elliptic trajectory that has the same orientation and\naspect ratio as the vortex projection itself. This allows the vortex\nellipticity to be estimated through observation of its trajectory. A\ncombination of analysis and numerical simulation is then used to show that\nnonlinear interactions cause the vortex orientation to precess, and that the\nrate of vortex precession is once again mimicked by a precession of the\nelliptical trajectory. Both vortex ellipticity and rate of precession can\ntherefore be inferred by observing its motion in a trap. An ability to\nanticipate and control local vortex structure and vortex trajectory is expected\nto prove useful in designing few-vortex systems in which ellipticity is a\nubiquitous, as-yet-unharnessed feature.",
        "positive": "Macroscopic Quantum Tunneling Escape of Bose-Einstein Condensates: Recent experiments on macroscopic quantum tunneling reveal a non-exponential\ndecay of the number of atoms trapped in a quasibound state behind a potential\nbarrier. Through both experiment and theory, we demonstrate this\nnon-exponential decay results from interactions between atoms. Quantum\ntunneling of tens of thousands of 87 Rb atoms in a Bose-Einstein condensate is\nmodeled by a modified Jeffreys-Wentzel-Kramers-Brillouin model, taking into\naccount the effective time-dependent barrier induced by the mean-field.\nThree-dimensional Gross-Pitaevskii simulations corroborate a mean-field result\nwhen compared with experiments. However, with one-dimensional modeling using\ntime-evolving block decimation, we present an effective renormalized mean-field\ntheory that suggests many-body dynamics for which a bare mean-field theory may\nnot apply."
    },
    {
        "anchor": "Stable non-equilibrium Fulde-Ferrell-Larkin-Ovchinnikov state in a\n  spin-imbalanced driven-dissipative Fermi gas loaded on a three-dimensional\n  cubic optical lattice: We theoretically investigate a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) type\nsuperfluid phase transition in a driven-dissipative two-component Fermi gas.\nThe system is assumed to be in the non-equilibrium steady state, which is tuned\nby adjusting the chemical potential difference between two reservoirs that are\ncoupled with the system. Including pairing fluctuations by extending the\nstrong-coupling theory developed in the thermal-equilibrium state by Nozieres\nand Schmitt-Rink to this non-equilibrium case, we show that a non-equilibrium\nFFLO (NFFLO) phase transition can be realized without spin imbalance, under the\nconditions that (1) the two reservoirs imprint a two-edge structure on the\nmomentum distribution of Fermi atoms, and (2) the system is loaded on a\nthree-dimensional cubic optical lattice. While the two edges work like two\nFermi surfaces with different sizes, the role of the optical lattice is to\nprevent the NFFLO long-range order from destruction by NFFLO pairing\nfluctuations. We also draw the non-equilibrium mean-field phase diagram in\nterms of the chemical potential difference between the two reservoirs, a\nfictitious magnetic field to tune the spin imbalance of the system, and the\nenvironmental temperature of the reservoirs, to clarify the relation between\nthe NFFLO state and the ordinary thermal-equilibrium FFLO state discussed in\nspin-imbalanced Fermi gases.",
        "positive": "Dipolar condensates confined in a toroidal trap: ground state and\n  vortices: We study a Bose-Einstein condensate of 52Cr atoms confined in a toroidal trap\nwith a variable strength of s-wave contact interactions. We analyze the effects\nof the anisotropic nature of the dipolar interaction by considering the\nmagnetization axis to be perpendicular to the trap symmetry axis. In the\nabsence of a central repulsive barrier, when the trap is purely harmonic, the\neffect of reducing the scattering length is a tuning of the geometry of the\nsystem: from a pancake-shaped condensate when it is large, to a cigar-shaped\ncondensate for small scattering lengths. For a condensate in a toroidal trap,\nthe interaction in combination with the central repulsive Gaussian barrier\nproduces an azimuthal dependence of the particle density for a fixed radial\ndistance. We find that along the magnetization direction the density decreases\nas the scattering length is reduced but presents two symmetric density peaks in\nthe perpendicular axis. For even lower values of the scattering length we\nobserve that the system undergoes a dipolar-induced symmetry breaking\nphenomenon. The whole density becomes concentrated in one of the peaks,\nresembling an origin-displaced cigar-shaped condensate. In this context we also\nanalyze stationary vortex states and their associated velocity field, finding\nthat this latter also shows a strong azimuthal dependence for small scattering\nlengths. The expectation value of the angular momentum along the z direction\nprovides a qualitative measure of the difference between the velocity in the\ndifferent density peaks."
    },
    {
        "anchor": "Two-dimensional quasi-ideal Fermi gas with Rashba spin-orbit coupling: We investigate the zero-temperature properties of a quasi-ideal Fermi gas\nwith Rashba spin-orbit coupling. We find that the spin-orbit term strongly\naffects the speeds of zero sound and first sound in the Fermi gas, due to the\npresence of a third-order quantum phase transition. In addition, including a 2D\nharmonic confinement we show that also the shape of the density profile of the\ncloud crucially depends on the strength of the Rashba coupling.",
        "positive": "Integrable two-channel p_x+ip_y-wave superfluid model: We present a new two-channel integrable model describing a system of spinless\nfermions interacting through a p-wave Feshbach resonance. Unlike the BCS-BEC\ncrossover of the s-wave case, the p-wave model has a third order quantum phase\ntransition. The critical point coincides with the deconfinement of a single\nmolecule within a BEC of bound dipolar molecules. The exact many-body\nwavefunction provides a unique perspective of the quantum critical region\nsuggesting that the size of the condensate wavefunction, that diverges\nlogarithmically with the chemical potential, could be used as an experimental\nindicator of the phase transition."
    },
    {
        "anchor": "Condensation versus Long-range Interaction: Competing Quantum Phases in\n  Bosonic Optical Lattice Systems at Near-resonant Rydberg Dressing: Recent experiments have shown that (quasi-)crystalline phases of\nRydberg-dressed quantum many-body systems in optical lattices (OL) are within\nreach. Rydberg systems naturally possess strong long-range interactions due to\nthe large polarizability of Rydberg atoms. Thus a wide range of quantum phases\nhave been predicted, such as a devil's staircase of lattice incommensurate\ndensity wave phases as well as more exotic lattice supersolid order for bosonic\nsystems, as considered in our work. Guided by results in the \"frozen\" gas\nlimit, we study the ground state phase diagram at finite hopping amplitudes and\nin the vicinity of resonant Rydberg driving, while fully including the\nlong-range tail of the van der Waals interaction. Simulations within real-space\nbosonic dynamical mean-field theory (RB-DMFT) yield an extension of the devil's\nstaircase into the supersolid regime where the competition of condensation and\ninteraction leads to a sequence of crystalline phases.",
        "positive": "Enhanced backscattering of a dilute Bose-Einstein condensate: We study experimentally and numerically the quasi-bidimensional transport of\na $^{87}$Rb Bose-Einstein condensate launched with a velocity $v_0$ inside a\ndisordered optical potential created by a speckle pattern. A time-of-flight\nanalysis reveals a pronounced enhanced density peak in the backscattering\ndirection $-v_0$, a feature reminiscent of coherent backscattering. Detailed\nnumerical simulations indicate however that other effects also contribute to\nthis enhancement, including a \"backscattering echo\" due to the\nposition-momentum correlations of the initial wave packet."
    },
    {
        "anchor": "Above-Barrier Reflection of Cold Atoms by Resonant Laser Light within\n  the Gross-Pitaevskii Approximation: Above-barrier reflection of cold alkali atoms by resonant laser light was\nconsidered analytically within the Gross-Pitaevskii approximation. Correction\nfor the reflection coefficient because of a weak nonlinearity of the stationary\nSchroedinger equation has been derived using multiscale analysis as a form of\nperturbation theory. The nonlinearity adds spatial harmonics to linear incident\nand reflecting waves. It was shown that the role of nonlinearity increases when\nthe kinetic energy of an atom is nearly to the height of the potential barrier.\nResults are compared to the known numerical derivations for wave functions of\nthe Gross-Pitaevskii equation with the step potential.",
        "positive": "Postquench prethermalization in a disordered quantum fluid of light: We study the coherence of a disordered and interacting quantum light field\nafter propagation along a nonlinear optical fiber. Disorder is generated by a\ncross-phase modulation with a randomized auxiliary classical light field, while\ninteractions are induced by self-phase modulation. When penetrating the fiber\nfrom free space, the incoming quantum light undergoes a disorder and\ninteraction quench. By calculating the coherence function of the transmitted\nquantum light, we show that the decoherence induced by the quench spreads in a\nlight-cone fashion in the nonequilibrium many-body quantum system, leaving the\nlatter prethermalize with peculiar features originating from disorder."
    },
    {
        "anchor": "Unconventional superfluid in a two-dimensional Fermi gas with\n  anisotropic spin-orbit coupling and Zeeman fields: We study the phase diagram of a two-dimensional ultracold Fermi gas with the\nsynthetic spin-orbit coupling (SOC) that has recently been realized at NIST.\nDue to the coexistence of anisotropic SOC and effective Zeeman fields in the\nNIST scheme, the system shows rich structure of phase separation involving\nexotic gapless superfluid and Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) pairing\nstates with different center-of-mass momentum. In particular, we characterize\nthe stability region of FFLO states and demonstrate their unique features under\nSOC. We then show that the effective transverse Zeeman field in the NIST scheme\ncan qualitatively change the landscape of the thermodynamic potential which\nleads to intriguing effects such as the disappearance of pairing instability,\nthe competition between different FFLO states, and the stabilization of a fully\ngapped FFLO state. These interesting features may be probed for example by\nmeasuring the in-situ density profiles or by the momentum-resolved\nradio-frequency spectroscopy.",
        "positive": "Integer partition manifolds and phonon damping in one dimension: We develop a quantum model based on the correspondence between energy\ndistribution between harmonic oscillators and the partition of an integer\nnumber. A proper choice of the interaction Hamiltonian acting within this\nmanifold of states allows us to examine both the quantum typicality and the\nnon-exponential relaxation in the same system. A quantitative agreement between\nthe field-theoretical calculations and the exact diagonalization of the\nHamiltonian is demonstrated."
    },
    {
        "anchor": "Quantum Oscillations between weakly coupled Bose-Einstein Condensates:\n  Evolution in a Non-degenerate Double Well: We discuss coherent atomic oscillations between two weakly coupled\nBose-Einstein condensates that are energetically different. The weak link is\nnotionally provided by a laser barrier in a (possibly asymmetric) multi-well\ntrap or by Raman coupling between condensates in different hyperfine levels.\nThe resultant boson Josephson junction dynamics is described by a double-well\nnonlinear Gross-Pitaevskii equation. On the basis of a new set of Jacobian\nelliptic function solutions, we describe the period of the oscillations as well\nas associated quantities and predict novel observable consequences of the\ninterplay of the energy difference and initial phase difference between the two\ncondensate populations.",
        "positive": "Probing early phase coarsening in a rapidly quenched Bose gas using\n  off-resonant matter-wave interferometry: We experimentally investigate the evolution of spatial phase correlations in\na rapidly quenched inhomogeneous Bose gas of rubidium using off-resonant\nmatter-wave interferometry. We measure the phase coherence length $\\ell$ of the\nsample and directly probe its increase during the early stage of condensate\ngrowth before vortices are formed. Once the vortices are formed stably in the\nquenched condensate, the measured value of $\\ell$ is shown to be linearly\nproportional to the mean distance between the vortices. These results confirm\nthe presence of phase coarsening prior to vortex formation, which is crucial\nfor a quantitative understanding of the resultant defect density in samples\nundergoing critical phase transitions."
    },
    {
        "anchor": "Interactive optomechanical coupling with nonlinear polaritonic systems: We study a system of interacting matter quasiparticles strongly coupled to\nphotons inside an optomechanical cavity. The resulting normal modes of the\nsystem are represented by hybrid polaritonic quasiparticles, which acquire\neffective nonlinearity. Its strength is influenced by the presence of the\nmechanical mode and depends on the resonance frequency of the cavity. This\nleads to an interactive type of optomechanical coupling, being distinct from\nthe previously studied dispersive and dissipative couplings in optomechanical\nsystems. The emergent interactive coupling is shown to generate effective\noptical nonlinearity terms of high order, being quartic in the polariton\nnumber. We consider particular systems of exciton-polaritons and dipolaritons,\nand show that the induced effective optical nonlinearity due to the interactive\ncoupling can exceed in magnitude the strength of Kerr nonlinear terms, such as\nthose arising from polariton-polariton interactions. As applications, we show\nthat the higher order terms give rise to localized bright flat top solitons,\nwhich may form spontaneously in polariton condensates.",
        "positive": "Goldstino in supersymmetric Bose-Fermi mixtures in the presence of Bose\n  Einstein condensate: We analyze the spectral properties of the Goldstino excitation in a\nBose-Fermi mixture of cold atoms, whose masses and interaction strengths are\ntuned so that the hamiltonian is supersymmetric. We consider systems at zero\ntemperature and assume that, in the weak coupling regime, the fermions form a\nFermi sea, while the bosons form a Bose-Einstein condensate. We study the\nexcitation spectrum within a simple extension of the random phase\napproximation, taking into account the mixing between the supercharge and the\nfermion caused by the condensate. This mixing affects the fermion spectrum\nstrongly. We argue that the corresponding modification of the fermion spectrum,\nand the associated fermion distribution in momentum space, could be accessible\nexperimentally, and potentially allow for a determination of the Goldstino\nproperties."
    },
    {
        "anchor": "Stability analysis of ground states in a one-dimensional trapped spin-1\n  Bose gas: In this work we study the stability properties of the ground states of a\nspin-1 Bose gas in presence of a trapping potential in one spatial dimension.\nTo set the stage we first map out the phase diagram for the trapped system by\nmaking use of a, so-called, continuous-time Nesterov method. We present an\nextension of the method, which has been previously applied to one-component\nsystems, to our multi-component system. We show that it is a powerful and\nrobust tool for finding the ground states of a physical system without the need\nof an accurate initial guess. We subsequently solve numerically the Bogoliubov\nde-Gennes equations in order to analyze the stability of the ground states of\nthe trapped spin-1 system. We find that the trapping potential retains the\noverall structure of the stability diagram, while affecting the spectral\ndetails of each of the possible ground state waveforms. It is also found that\nthe peak density of the trapped system is the characteristic quantity\ndescribing dynamical instabilities in the system. Therefore replacing the\nhomogeneous density with the peak density of the trapped system leads to good\nagreement of the homogeneous Bogoliubov predictions with the numerically\nobserved maximal growth rates of dynamically unstable modes. The stability\nconclusions in the one-dimensional trapped system are independent of the spin\ncoupling strength and the normalized trap strength over several orders of\nmagnitude of their variation.",
        "positive": "Chiral magnetic effect by synthetic gauge fields: We study the dynamical generation of the chiral chemical potential in a Weyl\nmetal constructed from a three-dimensional optical lattice and subject to\nsynthetic gauge fields. By numerically solving the Boltzmann equation with the\nBerry curvature in the presence of parallel synthetic electric and magnetic\nfields, we find that the spectral flow and the ensuing chiral magnetic current\nemerge. We show that the spectral flow and the chiral chemical potential can be\nprobed by time-of-flight imaging."
    },
    {
        "anchor": "Matter waves in atomic-molecular condensates with Feshbach resonance\n  management: The dynamics of matter waves in the atomic to molecular condensate transition\nwith a time-modulated atomic scattering length is investigated. Both the cases\nof rapid and slow modulations are studied. In the case of rapid modulations,\nthe average over oscillations for the system is derived. The corresponding\nconditions for dynamical suppression of the association of atoms into the\nmolecular field, or of second-harmonic generation in nonlinear optical systems,\nare obtained. For the case of slow modulations, we find resonant enhancement in\nthe molecular field. We then illustrate chaos in the atomic-molecular BEC\nsystem. We suggest a sequential application of the two types of modulations,\nslow and rapid, when producing molecules.",
        "positive": "Longitudinal waves in electrically polarized quantum Fermi gas: quantum\n  hydrodynamics approximation: The method of many-particle quantum hydrodynamics has been recently\ndeveloped, particularly this method has been used for an electrically polarized\nBose-Einstein condensate. In this paper, we present the development of this\nmethod for an electrically polarized three dimensional Fermi gas. We derive\ncorresponding dynamical equations: equation polarization and equation of\npolarization current evolution as well as the Euler and continuity equations.\nWe study dispersion dependencies of collective excitations in a polarized Fermi\ngas and consider interference of an equilibrium polarization on dispersion\nproperties."
    },
    {
        "anchor": "Three-body contact for fermions. I. General relations: We consider the resonant Fermi gas, that is, spin 1/2 fermions in three\ndimensions interacting by a short-range potential of large scattering length.\nWe introduce a quantity, the three-body contact, that determines several\nobservables. Within the zero-range model, the number of nearby fermion\ntriplets, the large-momentum tail of the center-of-mass momentum distribution\nof nearby fermion pairs, as well as the large-momentum tail of the two-particle\nmomentum distribution, are expressed in terms of the three-body contact. For a\nsmall finite interaction range, the formation rate of deeply bound dimers by\nthree-body recombination, as well as the three-body contribution to the\nfinite-range correction to the energy, are expressed in terms of the three-body\ncontact and of a three-body parameter. This three-body parameter, which\nvanishes in the zero-range limit, is defined through the asymptotic behavior of\nthe zero-energy scattering state at distances intermediate between the range\nand the two-body scattering length. In general, the three-body contact has\ndifferent contributions labeled by spin and angular momentum indices, and the\nthree-body parameter can depend on those indices. We also include the\ngeneralization to unequal masses for $\\uparrow$ and $\\downarrow$ particles.\nWith respect to the relation between three-body loss rate and number of nearby\ntriplets stated in [Petrov, Salomon and Shlyapnikov, PRL 93, 090404 (2004)],\nthe present work adds a derivation, expresses the proportionality factor in\nterms of the three-body parameter, and includes the general case where there\nare several contributions to the three-body contact and several three-body\nparameters.",
        "positive": "Generalized parametric resonance in a spin-1 Bose-Einstein condensate: We propose a generalized Mathieu equation (GME) which describes well the\ndynamics for two different models in spin-1 Bose-Einstein condensates. The\nstability chart of this GME differs significantly from that of Mathieu's\nequation and the unstable dynamics under this GME is called generalized\nparametric resonance. A typical region of $\\epsilon \\gtrsim 1$ and $\\delta\n\\approx 0.25$ can be used to distinguish these two equations. The GME we\npropose not only explains the experimental results of Hoang et al. [Nat.\nCommun. 7, 11233 (2016)] in nematic space with a small driving strength, but\npredicts the behavior in the regime of large driving strength. In addition, the\nmodel in spin space we propose, whose dynamics also obeys this GME, can be\nwell-tuned such that it is easily implemented in experiments."
    },
    {
        "anchor": "Critical region of the superfluid transition in the BCS-BEC crossover: We determine the size of the critical region of the superfluid transition in\nthe BCS-BEC crossover of a three-dimensional fermion gas, using a\nrenormalization-group approach to a bosonic theory of pairing fluctuations. For\nthe unitary Fermi gas, we find a sizable critical region $[T_G^-,T_G^+]$, of\norder $T_c$, around the transition temperature $T_c$ with a pronounced\nasymmetry: $|T_G^+-T_c|/|T_G^--T_c|\\sim8$. The critical region is strongly\nsuppressed on the BCS side of the crossover but remains important on the BEC\nside.",
        "positive": "Emergence of Topological and Strongly Correlated Ground States in\n  trapped Rashba Spin-Orbit Coupled Bose Gases: We theoretically study an interacting few-body system of Rashba spin-orbit\ncoupled two-component Bose gases confined in a harmonic trapping potential. We\nsolve the interacting Hamiltonian at large Rashba coupling strengths using\nExact Diagonalization scheme, and obtain the ground state phase diagram for a\nrange of interatomic interactions and particle numbers. At small particle\nnumbers, we observe that the bosons condense to an array of topological states\nwith n+1/2 quantum angular momentum vortex configurations, where n = 0, 1, 2,\n3... At large particle numbers, we observe two distinct regimes: at weaker\ninteraction strengths, we obtain ground states with topological and symmetry\nproperties that are consistent with mean-field theory computations; at stronger\ninteraction strengths, we report the emergence of strongly correlated ground\nstates."
    },
    {
        "anchor": "Zero-temperature phase transitions in dilute bosonic superfluids on a\n  lattice: Kinetic energy driven phase transitions in Bose superfluids occur at low\nvalues of the repulsion when the values of the next-to-nearest and\nnext-to-next-to-nearest hopping term attain certain critical values, resulting\nin alterations in the wave vector of the condensate. We map out the space of\npossible phases allowed by particular forms of the single-particle energy\ndispersion in the superfluid state, noting the appearance of a new phase, and\nexamine in more detail the effects of additional repulsive terms on the form of\nthe condensate wavefunction. We also examine the effect of these additional\nhopping terms on the formation of inhomogeneities in the condensate.",
        "positive": "Probing an effective-range-induced super fermionic Tonks-Girardeau gas\n  with ultracold atoms in one-dimensional harmonic traps: We theoretically investigate an ultracold spin-polarized atomic Fermi gas\nwith resonant odd-channel ($p$-wave) interactions trapped in one-dimensional\nharmonic traps. We solve the Yang-Yang thermodynamic equations based on the\nexact Bethe ansatz solution, and predict the finite-temperature density profile\nand breathing mode frequency, by using a local density approximation to take\ninto account the harmonic trapping potential. The system features an exotic\nsuper fermionic Tonks-Girardeau (super-fTG) phase, due to the large effective\nrange of the interatomic interactions. We explore the parameter space for such\na fascinating super-fTG phase at finite temperature and provide smoking-gun\nsignatures of its existence in both breathing mode frequencies and density\nprofiles. Our results suggest that the super-fTG phase can be readily probed at\ntemperature at about $0.1T_{F}$, where $T_{F}$ is the Fermi temperature. These\nresults are to be confronted with future cold-atom experiments with $^{6}$Li\nand $^{40}$K atoms."
    },
    {
        "anchor": "Supersymmetric waves in Bose-Fermi mixtures: Interacting Bose-Fermi mixtures possess a fermionic (super)symmetry when\nbosons and fermions in the mixture have equal masses, and when the interaction\nstrengths are appropriately tuned. This symmetry is spontaneously broken in the\nground state of the mixture, leading to a novel Goldstone mode with fermionic\nstatistics and quadratic dispersion. Here we examine the effect of explicit\nsymmetry-breaking perturbations on the Goldstone mode. When the symmetry is not\nexact and the system is allowed to deviate from the symmetric point, we find\nthat the Goldstone mode acquires an energy gap. We show that the excitations\nmanifest themselves as a non-analyticity of the thermodynamic pressure.",
        "positive": "Effective-range approximations for resonant scattering of cold atoms: Studies of cold atom collisions and few-body interactions often require the\nenergy dependence of the scattering phase shift, which is usually expressed in\nterms of an effective-range expansion. We use accurate coupled-channel\ncalculations on $^{6}$Li, $^{39}$K and $^{133}$Cs to explore the behavior of\nthe effective range in the vicinity of both broad and narrow Feshbach\nresonances. We show that commonly used expressions for the effective range\nbreak down dramatically for narrow resonances and near the zero-crossings of\nbroad resonances. We present an alternative parametrization of the effective\nrange that is accurate through both the pole and the zero-crossing for both\nbroad and narrow resonances. However, the effective range expansion can still\nfail at quite low collision energies, particularly around narrow resonances. We\ndemonstrate that an analytical form of an energy and magnetic field-dependent\nphase shift, based on multichannel quantum defect theory, gives accurate\nresults for the energy-dependent scattering length."
    },
    {
        "anchor": "Multi-second magnetic coherence in a single domain spinor Bose-Einstein\n  condensate: We describe a compact, robust and versatile system for studying magnetic\ndynamics in a spinor Bose-Einstein condensate. Condensates of 87 Rb are\nproduced by all-optical evaporation in a 1560 nm optical dipole trap, using a\nnon-standard loading sequence that employs an auxiliary 1529 nm beam for\npartial compensation of the strong differential light shift induced by the\ndipole trap itself. We use near-resonance Faraday rotation probing to\nnon-destructively track the condensate magnetization, and demonstrate\nfew-Larmor-cycle tracking with no detectable degradation of the spin\npolarization. In the ferromagnetic F = 1 ground state, we observe magnetic T1\nand T2$^*$ coherence times limited only by the several-second residence time of\nthe atoms in the trap.",
        "positive": "Dimer XXZ Spin Ladders: Phase diagram and a Non-Trivial\n  Antiferromagnetic Phase: We study the dimer $XXZ$ spin model on two-leg ladders with isotropic\nHeisenberg interactions on the rung and anisotropic $XXZ$ interactions along\nthe rail in an external field. Combining both analytical and numerical methods,\nwe set up the ground state phase diagram and investigate the quantum phase\ntransitions and the properties of rich phases, including the full polarized,\nsinglet dimer, Luttinger liquid, triplon solid, and a non-trivial\nantiferromagnetic phases with gap. The analytical analyses based on solvable\neffective Hamiltonians are presented for clear view of the phases and\ntransitions. Quantum Monte Carlo and exact diagonalization methods are employed\non finite system to verify the exact nature of the phases and transitions. Of\nall the phases, we pay a special attention to the gapped antiferromagnetic\nphase, which is disclosed to be a non-trivial one that exhibits the\ntime-reversal symmetry. We also discuss how our findings could be detected in\nexperiment in the light of ultracold atoms technology advances."
    },
    {
        "anchor": "Tuning photon-mediated interactions in a multimode cavity: from\n  supersolid to insulating droplets hosting phononic excitations: Ultracold atoms trapped in laser-generated optical lattices serve as a\nversatile platform for quantum simulations. However, as these lattices are\ninfinitely stiff, they do not allow to emulate phonon degrees of freedom. This\nrestriction can be lifted in emerged optical lattices inside multimode\ncavities. Motivated by recent experimental progress in multimode cavity QED, we\npropose a scheme to implement and study supersolid and droplet states with\nphonon-like lattice excitations by coupling a Bose gas to many longitudinal\nmodes of a ring cavity. The interplay between contact collisional and\ntunable-range cavity-mediated interactions leads to a rich phase diagram, which\nincludes elastic supersolid as well as insulating droplet phases exhibiting\nroton-type mode softening for a continuous range of momenta across the\nsuperradiant phase transition. The non-trivial dynamic response of the system\nto local density perturbations further proves the existence of phonon-like\nmodes.",
        "positive": "Temporal Coherence of Spatially Indirect Excitons across Bose-Einstein\n  Condensation: the Role of Free Carriers: We study the time coherence of the photoluminescence radiated by spatially\nindirect excitons confined in a 10 $\\mu$m electrostatic trap. Above a critical\ntemperature of 1 Kelvin, we show that the photoluminescence has a homogeneous\nspectral width of about 500 $\\mu$eV which weakly varies with the exciton\ndensity. By contrast, the spectral width reduces by two-fold below the critical\ntemperature and for experimental parameters at which excitons undergo a gray\nBose-Einstein condensation. In this regime, we find evidence showing that the\nexcitons temporal coherence is limited by their interaction with a\nlow-concentration of residual excess charges, leading to a minimum\nphotoluminescence spectral width of around 300 $\\mu$eV."
    },
    {
        "anchor": "A quantum Boltzmann equation for intrinsic decoherence in a dilute gas: We use a careful treatment of time-dependent wave-mechanical scattering to\ndetermine the conditions under which a dilute, non-degenerate quantum gas can\nobey a Boltzmann equation. If the gas possesses weak long-range coherence, such\nas may occur when a gas is quantum mechanically throttled by tunnelling through\na barrier, collisions within the gas will suppress this long range coherence.\nWe calculate its decay rate and find it to be related to the Boltzmann\nequation's loss term.",
        "positive": "Ground State Energy for Fermions in a 1D Harmonic Trap with Delta\n  Function Interaction: Conjectures are made for the ground state energy of a large spin 1/2 Fermion\nsystem trapped in a 1D harmonic trap with delta function interaction. States\nwith different spin J are separately studied. The Thomas-Fermi method is used\nas an effective test for the conjecture."
    },
    {
        "anchor": "Breakup of quantum liquid filaments into droplets: We have investigated how the Rayleigh-Plateau instability of a filament made\nof a 41K-87Rb self-bound mixture may lead to an array of identical quantum\ndroplets, with typical breaking times which are shorter than the lifetime of\nthe mixture. If the filament is laterally confined -- as it happens in a\ntoroidal trap -- and atoms of one species are in excess with respect to the\noptimal, equilibrium ratio, the droplets are immersed into a superfluid\nbackground made by the excess species which provides global phase coherence to\nthe system, suggesting that the droplets array in the unbalanced system may\ndisplay supersolid character. This possibility has been investigated by\ncomputing the non-classical translational inertia coefficient. The filament may\nbe a reasonable representation of a self-bound mixture subject to toroidal\nconfinement when the bigger circle radius of the torus is much larger than the\nfilament radius.",
        "positive": "Ideal n-body correlations with massive particles: In 1963 Glauber introduced the modern theory of quantum coherence, which\nextended the concept of first-order (one-body) correlations, describing phase\ncoherence of classical waves, to include higher-order (n-body) quantum\ncorrelations characterizing the interference of multiple particles. Whereas the\nquantum coherence of photons is a mature cornerstone of quantum optics, the\nquantum coherence properties of massive particles remain largely unexplored. To\ninvestigate these properties, here we use a uniquely correlated source of atoms\nthat allows us to observe n-body correlations up to the sixth-order at the\nideal theoretical limit (n!). Our measurements constitute a direct\ndemonstration of the validity of one of the most widely used theorems in\nquantum many-body theory--Wisck's theorem--for a thermal ensemble of massive\nparticles. Measurements involving n-body correlations may play an important\nrole in the understanding of thermalization of isolated quantum systems and the\nthermodynamics of exotic many-body systems, such as Efimov trimers."
    },
    {
        "anchor": "Observation of a two-dimensional Fermi gas of atoms: We have prepared a degenerate gas of fermionic atoms which move in two\ndimensions while the motion in the third dimension is \"frozen\" by tight\nconfinement and low temperature. {\\it In situ} imaging provides direct\nmeasurement of the density profile and temperature. The gas is confined in a\ndefect-free optical potential, and the interactions are widely tunable by means\nof a Fano--Feshbach resonance. This system can be a starting point for\nexploration of 2D Fermi physics and critical phenomena in a pure, controllable\nenvironment.",
        "positive": "Impurity induced Modulational instability in Bose-Einstein condensates: By means of linear stability analysis (LSA) and direct numerical simulations\nof the coupled Gross-Pitaevskii(GP)equations, we address the impurity induced\nmodulational instability (MI) and the associated nonlinear dynamics in\nBose-Einstein condensates (BECs). We explore the dual role played by the\nimpurities within the BECs -- the instigation of MI and the dissipation of the\ninitially generated solitary waves. Because of the impurities, the repulsive\nBECs are even modulationally unstable and this tendency towards MI increases\nwith increasing impurity fraction and superfluid-impurity coupling strength.\nHowever, the tendency of a given BEC towards the MI decreases with the\ndecreasing mass of the impurity atoms while the sign of the superfluid-impurity\ninteraction plays no role. The above results are true even for attractive BECs\nexcept for a weak superfluid-impurity coupling, where the MI phenomenon is\nmarginally suppressed by the presence of impurities. The dissipation of the\nsolitons reduces their lifetime and is eminent for a larger impurity fraction\nand strong superfluid-impurity strength respectively."
    },
    {
        "anchor": "Competition between symmetry breaking and onset of collapse in weakly\n  coupled atomic condensates: We analyze the symmetry breaking of matter-wave solitons in a pair of\ncigar-shaped traps coupled by tunneling of atoms. The model is based on a\nsystem of linearly coupled nonpolynomial Schr\\\"odinger equations (NPSEs).\nUnlike the well-known spontaneous-symmetry-breaking (SSB) bifurcation in\ncoupled cubic equations, in the present model the SSB competes with the onset\nof collapse in this system. Stability regions of symmetric and asymmetric\nsolitons, as well as the collapse region, are identified in the parameter space\nof the system.",
        "positive": "Nonrelativistic Banks-Casher relation and random matrix theory for\n  multi-component fermionic superfluids: We apply QCD-inspired techniques to study nonrelativistic N-component\ndegenerate fermions with attractive interactions. By analyzing the\nsingular-value spectrum of the fermion matrix in the Lagrangian, we derive\nseveral exact relations that characterize the spontaneous symmetry breaking\nU(1)xSU(N)$\\to$Sp(N) through bifermion condensates. These are nonrelativistic\nanalogues of the Banks-Casher relation and the Smilga-Stern relation in QCD.\nNon-local order parameters are also introduced and their spectral\nrepresentations are derived, from which a nontrivial constraint on the phase\ndiagram is obtained. The effective theory of soft collective excitations is\nderived and its equivalence to random matrix theory is demonstrated in the\nepsilon-regime. We numerically confirm the above analytical predictions in\nMonte Carlo simulations."
    },
    {
        "anchor": "Perturbative Analysis of Potential Scattering Problems in the\n  Lieb-Liniger Model: The Lieb-Liniger model which has a weak external potential term under the\nperiodic boundary condition is investigated. By exploiting the Bethe states as\nbases, we perform a perturbation analysis up to the first order to obtain the\nshifts of eigenenergies and corresponding eigenstates which have been brought\nabout by the external potential. If we take a sufficiently large system, the\neigenstates can be \"the Schr\\\"odinger's cat states\". Expectation values of the\ndensity operator taken between two Bethe states can be calculated with the aid\nof the Slavnov's formula and we evaluate the influence of the many-body\ninteraction to the system under the external potential. The system is\ninsensitive to the external potential because of the many-body interaction.",
        "positive": "Emergence of pairing glue in repulsive Fermi gases with soft-core\n  interactions: Recent quantum gas experiments are ushering in an era of fine-tailored\ntwo-body interactions. These include for example atoms with long-range\ndipole-dipole interactions and Rydberg-dressed atoms created by optical\ncoupling to highly excited electronic states. These systems differ from the\n``canonical system\" of cold atoms with contact interactions characterized by a\nsingle parameter, the scattering length. Inspired by these experiments with\ncontrollable atomic interactions, here we consider a model many-body system of\nspinless Fermi gas in two dimensions, where the bare two-body interaction takes\nthe form of a soft-core disk potential. We show that the repulsive interaction\ncan drive the system to a series of nontrivial superfluid states with higher\npartial wave paring, for example in the $f$- and $h$-wave channels instead of\nthe $p$-wave channel. The zero temperature phase diagram is obtained by\nnumerical functional renormalization group (FRG), which goes beyond leading\norder perturbation theory and retains the interaction vertices in all channels.\nWe also carry out a perturbative analysis which is justified in the dilute\nlimit and show that the second order Kohn-Luttinger diagrams provide a\nqualitative understanding of the onsets of the various superfluid phases. The\nperturbative arguments however fail to capture the quantitative phase\nboundaries predicted by FRG. Our findings illustrate that the shape of the bare\natomic interaction matters in producing the pairing glue in repulsive Fermi\ngases, and tuning the interaction potential offers a promising route to realize\nexotic many-body phases in cold atomic gases."
    },
    {
        "anchor": "Observing the Rosensweig instability of a quantum ferrofluid: Ferrofluids show unusual hydrodynamic effects due to the magnetic nature of\ntheir constituents. For increasing magnetization a classical ferrofluid\nundergoes a Rosensweig instability and creates self-organized ordered surface\nstructures or droplet crystals. A Bose-Einstein condensate with strong dipolar\ninteractions is a quantum ferrofluid that also shows superfluidity. The field\nof dipolar quantum gases is motivated by the search for new phases that break\ncontinuous symmetries. The simultaneous breaking of continuous symmetries like\nthe phase invariance for the superfluid state and the translational symmetry\nfor a crystal provides the basis of novel states of matter. However,\ninteraction-induced crystallization in a superfluid has not been observed. Here\nwe use in situ imaging to directly observe the spontaneous transition from an\nunstructured superfluid to an ordered arrangement of droplets in an atomic\ndysprosium Bose-Einstein condensate. By utilizing a Feshbach resonance to\ncontrol the interparticle interactions, we induce a finite-wavelength\ninstability and observe discrete droplets in a triangular structure, growing\nwith increasing atom number. We find that these states are surprisingly\nlong-lived and measure a hysteretic behaviour, which is typical for a\ncrystallization process and in close analogy to the Rosensweig instability. Our\nsystem can show both superfluidity and, as shown here, spontaneous\ntranslational symmetry breaking. The presented observations do not probe\nsuperfluidity in the structured states, but if the droplets establish a common\nphase via weak links, this system is a very good candidate for a supersolid\nground state.",
        "positive": "Polariton Condensation in a One-Dimensional Disordered Potential: We study the coherence and density modulation of a non-equilibrium\nexciton-polariton condensate in a one-dimensional valley with disorder. By\nmeans of interferometric measurements we evidence a modulation of the\nfirst-order coherence function and we relate it to a disorder-induced\nmodulation of the condensate density, that increases as the pump power is\nincreased. The non-monotonous spatial coherence function is found to be the\nresult of the strong non-equilibrium character of the one-dimensional system,\nin the presence of disorder."
    },
    {
        "anchor": "Nonequilibrium Hole Dynamics in Antiferromagnets: Damped Strings and\n  Polarons: We develop a nonperturbative theory for hole dynamics in antiferromagnetic\nspin lattices, as described by the $t$-$J$ model. This is achieved by\ngeneralizing the selfconsistent Born approximation to nonequilibrium systems,\nmaking it possible to calculate the full time-dependent many-body wave\nfunction. Our approach reveals three distinct dynamical regimes, ultimately\nleading to the formation of magnetic polarons. Following the initial ballistic\nstage of the hole dynamics, coherent formation of string excitations gives rise\nto characteristic oscillations in the hole density. Their damping eventually\nleaves behind magnetic polarons that undergo ballistic motion with a greatly\nreduced velocity. The developed theory provides a rigorous framework for\nunderstanding nonequilibrium physics of defects in quantum magnets and\nquantitatively explains recent observations from cold-atom quantum simulations\nin the strong coupling regime.",
        "positive": "An acoustic analog to the dynamical Casimir effect in a Bose-Einstein\n  condensate: We have realized an acoustic analog to the Dynamical Casimir effect. The\ndensity of a trapped Bose-Einstein condensate is modulated by changing the trap\nstiffness. We observe the creation of correlated excitations with equal and\nopposite momenta, and show that for a well defined modulation frequency, the\nfrequency of the excitations is half that of the trap modulation frequency."
    },
    {
        "anchor": "Bound impurities in a one-dimensional Bose lattice gas: low-energy\n  properties and quench-induced dynamics: We study two mobile bosonic impurities immersed in a one-dimensional optical\nlattice and interacting with a bosonic bath. We employ the exact\ndiagonalization method for small periodic lattices to study stationary\nproperties and dynamics. We consider the branch of repulsive interactions that\ninduce the formation of bound impurities, akin to the bipolaron problem. A\ncomprehensive study of ground-state and low-energy properties is presented,\nincluding the characterization of the critical strength for the formation of\nbound impurities. We also study the dynamics induced after an\ninteraction-quench to examine the stability of the bound impurities. We reveal\nthat after large interaction quenches from strong to weak interactions the\nsystem can show large oscillations over time with revivals of the dimer states.\nWe find that the oscillations are driven by selected eigenstates with\nphase-separated configurations.",
        "positive": "A Superradiant Topological Peierls Insulator inside an Optical Cavity: We consider a spinless ultracold Fermi gas tightly trapped along the axis of\nan optical resonator and transversely illuminated by a laser closely tuned to a\nresonator mode. At a certain threshold pump intensity the homogeneous gas\ndensity breaks a $\\mathbf{Z}_2$ symmetry towards a spatially periodic order,\nwhich collectively scatters pump photons into the cavity. We show that this\nknown self-ordering transition also occurs for low field seeking fermionic\nparticles when the laser light is blue-detuned to an atomic transition. The\nemergent superradiant optical lattice in this case is homopolar and possesses\ntwo distinct dimerizations. Depending on the spontaneously chosen dimerization\nthe resulting Bloch bands can have a non-trivial topological structure\ncharacterized by a non-vanishing Zak phase. In the case the Fermi momentum is\nclose to half the cavity-mode wavenumber, a Peierls-like instability here\ncreates a topoloical insulator with a gap at the Fermi surface, which hosts a\npair of edge states. The topological features of the system can be\nnon-destructively observed via the cavity output: the Zak phase of the bulk\ncoincides with the relative phase between laser and cavity field, while the\nfingerprint of edge states can be observed as additional broadening in a well\ndefined frequency window of the cavity spectrum."
    },
    {
        "anchor": "Spin squeezing and many-body dipolar dynamics in optical lattice clocks: The recent experimental realization of a three-dimensional (3D) optical\nlattice clock not only reduces the influence of collisional interactions on the\nclock's accuracy but also provides a promising platform for studying dipolar\nmany-body quantum physics. Here, by solving the governing master equation, we\ninvestigate the role of both elastic and dissipative long-range interactions in\nthe clock's dynamics and study its dependence on lattice spacing,\ndimensionality, and dipolar orientation. For small lattice spacing, i.e.,\n$k_0a\\ll 1$, where $a$ is the lattice constant and $k_0$ is the transition\nwavenumber, a sizable spin squeezing appears in the transient state which is\nfavored in a head-to-tail dipolar configuration in 1D systems and a\nside-by-side configuration in 2D systems, respectively. For large lattice\nspacing, i.e., $k_0a\\gg 1$, the single atomic decay rate can be effectively\nsuppressed due to the destructive dissipative emission of neighboring atoms in\nboth 1D and 2D. Our results will not only aid in the design of the future\ngeneration of ultraprecise atomic clocks but also illuminates the rich\nmany-body physics exhibited by radiating dipolar system.",
        "positive": "Self-organized cavity bosons beyond the adiabatic elimination\n  approximation: The long-time behavior of weakly interacting bosons moving in a\ntwo-dimensional optical lattice and coupled to a lossy cavity is investigated\nnumerically in the regime of high particle filling. The truncated Wigner\nrepresentation allows us to take into full account the dynamics of the cavity\nmode, quantum fluctuations, and self-organization of individual runs. We\nobserve metastability at very long times and superfluid quasi-long range order,\nin sharp contrast with the true long range order found in the ground state of\nthe approximate Bose-Hubbard model with extended interactions, obtained by\nadiabatically eliminating the cavity field. As the strength of the light-matter\ncoupling increases, the system first becomes supersolid at the Dicke\nsuperradiant transition and then turns into a charge-density wave via the\nBerezinskii-Kosterlitz-Thouless mechanism. The two phase transitions are\ncharacterized via an accurate finite-size scaling."
    },
    {
        "anchor": "Ground States of a Mixture of Two Species of Spinor Bose Gases with\n  Interspecies Spin Exchange: We consider a mixture of two species of spin-1 atoms with interspecies spin\nexchange, which may cooperate or compete with the intraspecies spin exchanges\nand thus dramatically affect the ground state. It represents a new class of\nbosonic gases differing from single-species spinor gases. We determine the\nexact ground states in several parameter regimes, and study the composite\nstructures by using the generating function method generalized here to be\napplicable to a mixture of two species of spinor gases. The most interesting\nphase is the so-called entangled Bose-Einstein condensation (BEC), which is\nfragmented BEC with quantum entanglement between the two species, and with both\ninterspecies and intraspecies singlet pairs. For comparison, we also apply the\ngenerating function method to a mixture of two species of pseudospin-1/2 atoms,\nfor which the total spin quantum number of each species is fixed as half of the\natom number, in contrast with the case of spin-1, for which it is a variable\ndetermined by energetics. Consequently, singlet pairs in entangled BEC of a\npseudospin-1/2 mixture are all interspecies. Interspecies spin exchange leads\nto novel features beyond those of spinor BEC of a single species of atoms as\nwell as mixtures without interspecies spin exchange.",
        "positive": "Disentangling Pauli blocking of atomic decay from cooperative radiation\n  and atomic motion in a 2D Fermi gas: The observation of Pauli blocking of atomic spontaneous decay via direct\nmeasurements of the atomic population requires the use of long-lived atomic\ngases where quantum statistics, atom recoil and cooperative radiative processes\nare all relevant. We develop a theoretical framework capable of simultaneously\naccounting for all these effects in a regime where prior theoretical approaches\nbased on semi-classical non-interacting or interacting frozen atom\napproximations fail. We apply it to atoms in a single 2D pancake or arrays of\npancakes featuring an effective $\\Lambda$ level structure (one excited and two\ndegenerate ground states). We identify a parameter window in which a factor of\ntwo extension in the atomic lifetime clearly attributable to Pauli blocking\nshould be experimentally observable in deeply degenerate gases with $\\sim\n10^{3} $ atoms. Our predictions are supported by observation of a\nnumber-dependent excited state decay rate on the\n${}^{1}\\rm{S_0}-{}^{3}\\rm{P_1}$ transition in $^{87}$Sr atoms."
    },
    {
        "anchor": "Doppler Spectroscopy of an Ytterbium Bose-Einstein Condensate on the\n  Clock Transition: We describe Doppler spectroscopy of Bose-Einstein condensates of ytterbium\natoms using a narrow optical transition. We address the optical clock\ntransition around 578 nm between the ${^1}S_0$ and ${^3}P_0$ states with a\nlaser system locked on a high-finesse cavity. We show how the absolute\nfrequency of the cavity modes can be determined within a few tens of kHz using\nhigh-resolution spectroscopy on molecular iodine. We show that optical spectra\nreflect the velocity distribution of expanding condensates in free fall or\nafter releasing them inside an optical waveguide. We demonstrate sub-kHz\nspectral linewidths, with long-term drifts of the resonance frequency well\nbelow 1 kHz/hour. These results open the way to high-resolution spectroscopy of\nmany-body systems.",
        "positive": "A Strongly Interacting Polaritonic Quantum Dot: Polaritons are an emerging platform for exploration of synthetic materials\n[1] and quantum information processing [2] that draw properties from two\ndisparate particles: a photon and an atom. Cavity polaritons are particularly\npromising, as they are long-lived and their dispersion and mass are\ncontrollable through cavity geometry [3]. To date, studies of cavity polaritons\nhave operated in the mean-field regime, using short-range interactions between\ntheir matter components [4]. Rydberg excitations have recently been\ndemonstrated as a promising matter-component of polaritons [5], due to their\nstrong interactions over distances large compared to an optical wavelength. In\nthis work we explore, for the first time, the cavity quantum electrodynamics of\nRydberg polaritons, combining the non-linearity of polaritonic quantum wires\nwith the zero-dimensional strong coupling of an optical resonator. We assemble\na quantum dot composed of $\\sim 150$ strongly interacting, Rydberg-dressed\n$^{87}$Rb atoms in a cavity, and observe blockaded polariton transport as well\nas coherent quantum dynamics of a single polaritonic super-atom. This work\nestablishes a new generation of photonic quantum information processors and\nquantum materials, along with a clear path to topological quantum matter [6]."
    },
    {
        "anchor": "Ground-state Properties and Bogoliubov Modes of a Harmonically Trapped\n  One-Dimensional Quantum Droplet: We study the stationary and excitation properties of a one-dimensional\nquantum droplet in the two-component Bose mixture trapped in a harmonic\npotential. By constructing the energy functional for the inhomogeneous mixture,\nwe elaborate the extended the Gross-Pitaevskii equation applicable to both\nsymmetric and asymmetric mixtures into a universal form, and the equations in\ntwo different dimensionless schemes are in a duality relation, i.e. the unique\nparameters left are inverse of each other. The Bogoliubov equations for the\ntrapped droplet are obtained by linearizing the small density fluctuation\naround the ground state and the low-lying excitation modes are calculated\nnumerically.It is found that the confinement trap changes easily the flat-top\nstructure for large droplets and alters the mean square radius and the chemical\npotential intensively. The breathing mode of the confined droplet connects the\nself-bound and ideal gas limits, with the excitation in the weakly interacting\nBose condensate for large particle numbers lying in between. We explicitly show\nhow the continuum spectrum of the excitation is split into discrete modes, and\nfinally taken over by the harmonic trap. Two critical particle numbers are\nidentified by the minimum size of the trapped droplet and the maximum breathing\nmode energy, both of which are found to decrease exponentially with the\ntrapping parameter.",
        "positive": "Complex contact interaction for systems with short-range two-body loss: Contact interaction is a fundamental concept that appears in various areas of\nphysics. It simplifies physical models by replacing the detailed short-range\ninteraction with a zero-range contact potential which reproduces the same\nlow-energy scattering parameter, i.e. the $s$-wave scattering length. In this\nwork, we generalize this concept to a system with short-range two-body loss. We\nshow that the short-range two-body loss can effectively be replaced by a\nzero-range complex contact potential with proper regularization characterized\nby a complex scattering length. We develop appropriate ways to regularize this\npotential in the Lindblad master equation and apply them to the dynamic problem\nof Bose-Einstein condensate with weak interaction and two-body loss."
    },
    {
        "anchor": "Pair-correlation properties and momentum distribution of finite number\n  of interacting trapped bosons in three dimension: We study the ground state pair-correlation properties of a weakly interacting\ntrapped Bose gas in three dimension by using a correlated many-body method. Use\nof the van der Waals interaction potential and an external trapping potential\nshows realistic features. We also test the validity of shape-independent\napproximation in the calculation of correlation properties.",
        "positive": "Excitations and Stripe Phase Formation in a 2D Dipolar Bose Gas with\n  Tilted Polarization: We present calculations of the ground state and excitations of an anisotropic\ndipolar Bose gas in two dimensions, realized by a non-perpendicular\npolarization with respect to the system plane. For sufficiently high density an\nincrease of the polarization angle leads to a density instability of the gas\nphase in the direction where the anisotropic interaction is strongest. Using a\ndynamic many-body theory, we calculate the dynamic structure function in the\ngas phase which shows the anisotropic dispersion of the excitations. We find\nthat the energy of roton excitations in the strongly interacting direction\ndecreases with increasing polarization angle and almost vanishes close to the\ninstability. Exact path integral ground state Monte Carlo simulations show that\nthis instability is indeed a quantum phase transition to a stripe phase,\ncharacterized by long-range order in the strongly interacting direction."
    },
    {
        "anchor": "Engineering and probing non-Abelian chiral spin liquids using\n  periodically driven ultracold atoms: We propose a scheme to implement Kitaev's honeycomb model with cold atoms,\nbased on a periodic (Floquet) drive, in view of realizing and probing\nnon-Abelian chiral spin liquids using quantum simulators. We derive the\neffective Hamiltonian to leading order in the inverse-frequency expansion, and\nshow that the drive opens up a topological gap in the spectrum without mixing\nthe effective Majorana and vortex degrees of freedom. We address the challenge\nof probing the physics of Majorana fermions, while having only access to the\noriginal composite spin degrees of freedom. Specifically, we propose to detect\nthe properties of the chiral spin liquid phase using gap spectroscopy and edge\nquenches in the presence of the Floquet drive. The resulting chiral edge\nsignal, which relates to the thermal Hall effect associated with neutral\nMajorana currents, is found to be robust for realistically-prepared states. By\ncombining strong interactions with Floquet engineering, our work paves the way\nfor future studies of non-Abelian excitations and quantized thermal transport\nusing quantum simulators.",
        "positive": "Dimers, trimers, tetramers, and other multimers in a multiband\n  Bose-Hubbard model: We study the bound states of $N$ identical bosons that are described by a\nmultiband Bose-Hubbard model with generic hoppings and an attractive onsite\ninteraction. Using a variational approach, we first derive exact integral\nequations for the dimers, trimers, tetramers, and other multimers, and then\napply them to a one-dimensional sawtooth model that features two bands. In\nparticular we reveal the presence of not only the offsite dimer states which\nconsist of two monomers on different sites even in the strong-coupling limit\nbut also the offsite trimer states which consist of either a dimer on one site\nand a monomer on another site or three monomers on three different sites. Our\nvariational calculations for the ground states of onsite dimers, onsite trimers\nand offsite trimers benchmark perfectly well with the DMRG simulations. We also\npresent DMRG results for the ground states of onsite tetramers, offsite\ntetramers, onsite pentamers, offsite pentamers, and for those of other\nmultimers."
    },
    {
        "anchor": "Strong optical self-focusing effect in coherent light scattering with\n  condensates: We present a theoretical investigation of optical self-focusing effects in\nlight scattering with condensates. Using long (>200 \\mu s), red-detuned pulses\nwe show numerically that a non-negligible self-focusing effect is present that\ncauses rapid optical beam width reduction as the scattered field propagates\nthrough a medium with an inhomogeneous density distribution. The rapid growth\nof the scattered field intensity and significant local density feedback\npositively to further enhance the wave generation process and condensate\ncompression, leading to highly efficient collective atomic recoil motion.",
        "positive": "Quasi-thermalization of collisionless particles in quadrupole potentials: We analyze several puzzling features of a recent experiment with a\nnoninteracting gas of atoms in a quadrupole trap. After an initial momentum\nkick, the system reaches a stationary, quasi-thermal state even without\ncollisions, due to the dephasing of individual particle trajectories.\nSurprisingly, the momentum distribution remains anisotropic at long times,\ncharacterized by different \"temperatures\" along the different directions. In\nparticular, there is no transfer of the kick energy between the axial and\nradial trap directions. To understand these effects we discuss and solve two\nclosely related models: a spherically symmetric trap $V(r)\\simeq r^\\alpha$ and\na strongly confined gas along one direction (a \"pancake\" trap). We find that in\nthe isotropic trap, the gas unexpectedly also preserves the anisotropy of the\nkick at long times, which we are able to explain using the conservation of\nangular momentum and the virial theorem. Depending on the value of $\\alpha$ we\nfind that the kick can cool or heat the orthogonal directions. The pancake trap\ncase is quantitatively similar to the quadrupole one. We show that for the\nformer, the temperature anisotropy and memory of the kick direction are due to\nthe change in the 2D effective potential resulting from the kick, thereby also\nexplaining the quadrupole experimental results."
    },
    {
        "anchor": "Motion of an impurity in a two-leg ladder: We study the motion of an impurity in a two-leg ladder interacting with two\nfermionic baths along each leg, a simple model bridging cold atom quantum\nsimulators with an idealised description of the basic transport processes in a\nlayered heterostructure. Using the linked-cluster expansion we obtain exact\nanalytical results for the single-particle Green's function and find that the\nlong-time behaviour is dominated by an intrinsic orthogonality catastrophe\nassociated to the motion of the impurity in each one-dimensional chain. We\nexplore both the case of two identical legs as well as the case where the legs\nare characterised by different interaction strengths: in the latter case we\nobserve a subleading correction which can be relevant for intermediate-time\ntransport at an interface between different materials. In all the cases we do\nnot find significant differences between the intra- and inter-leg Green's\nfunctions in the long-time limit.",
        "positive": "Nonequilibrium current-carrying steady states in the anisotropic $XY$\n  spin chain: Out-of-equilibrium behavior is explored in the one-dimensional anisotropic\n$XY$ model. Initially preparing the system in the isotropic $XX$ model with a\nlinearly varying magnetic field to create a domain-wall magnetization profile,\ndynamics is generated by rapidly changing the exchange interaction anisotropy\nand external magnetic field. Relaxation to a nonequilibrium steady state is\nstudied analytically at the critical transverse Ising point, where correlation\nfunctions may be computed in closed form. For arbitrary values of anisotropy\nand external field, an effective generalized Gibbs' ensemble is shown to\naccurately describe observables in the long-time limit. Additionally, we find\nspatial oscillations in the exponentially decaying, transverse spin-spin\ncorrelation functions with wavelength set by the magnetization jump across the\ninitial domain wall. This wavelength depends only weakly on anisotropy and\nmagnetic field in contrast to the current, which is highly dependent on these\nparameters."
    },
    {
        "anchor": "Spin-orbit Coupling Effects on the Superfluidity of Fermi Gas in an\n  Optical Lattice: We investigate the superfluidity of attractive Fermi gas in a square optical\nlattice with spin-orbit coupling (SOC). We show that the system displays a\nvariety of new filling-dependent features. At half filling, a quantum phase\ntransition from a semimetal to a superfluid is found for large SOC. Close to\nhalf filling where the emerging Dirac cones governs the behaviors of the\nsystem, SOC tends to suppress the BCS superfluidity. Conversely, SOC can\nsignificantly enhance both the pairing gap and condensate fraction and lead to\na new BCS-BEC crossover for small fillings. Moreover, we demonstrate that the\nsuperfluid fraction also exhibits many interesting phenomena compared with the\nspin-orbit coupled Fermi gas without lattice.",
        "positive": "Antiferromagnetic topological insulators in cold atomic gases: We propose a spin-dependent optical lattice potential that realizes a\nthree-dimensional antiferromagnetic topological insulator in a gas of cold,\ntwo-state fermions such as alkaline earths, as well as a model that describes\nthe tight-binding limit of this potential. We discuss the physically observable\nresponses of the gas that can verify the presence of this phase. We also point\nout how this model can be used to obtain two-dimensional flat bands with\nnonzero Chern number."
    },
    {
        "anchor": "Collision Dynamics of Bose-Einstein Condensates: We study the collision dynamics of two Bose-Einstein condensates with their\ndynamical wave functions modeled by a set of coupled, time-dependent\nGross-Pitaevskii equations. Beginning with an effective one-dimensional system,\nwe identify regimes characterized by the relationship between inter- and\nintra-atomic interactions and the initial configuration of the system, akin to\nthe equilibrium phase diagram of two interacting Bose condensates. We consider\na dynamical setup in which two wave packets are initially at rest with a small\nseparation about the center of an asymmetric harmonic trap. Upon release, we\nobserve a rapid approach to dynamical equilibrium in the limits of very large\nand very small inter-particle repulsion, characterized by periodic transmission\nor reflection of the condensates as distinguishable units, whereas the\nintermediate, critical regime is characterized by extended transient dynamics,\ndensity fracturing, and dynamical mixing. We therefore have reason to believe\nthat non-trivial behavior may exist during the collisions of Bose-Einstein\ncondensates as a result of their non-linear interactions, and these effects may\nbe observable in a suitable laboratory environment.",
        "positive": "First-order superfluid-Mott-insulator transition for quantum optical\n  switching in cavity QED arrays with two cavity modes: We theoretically investigated the ground states of coupled arrays of cavity\nquantum electrodynamical (cavity QED) systems in presence of two photon modes.\nWithin the Gutzwiller-type variational approach, we found the first-order\nquantum phase transition between Mott insulating and superfluid phases as well\nas the conventional second-order one. The first-order phase transition was\nfound only for specific types of emitter models, and its physical origin is\nclarified based on the analytic arguments which are allowed in the perturbative\nand semiclassical limits. The first-order transition of the correlated photons\nis accompanied with discontinuous change in the emitter states, not only with\nthe appearance of inter-cavity coherence in the superfluid phase. We also\ndiscuss the condition for the first-order transition to occur, which can lead\nto a strategy for future design of quantum optical switching devices with\ncavity QED arrays."
    },
    {
        "anchor": "Cooling of a one-dimensional Bose gas: We experimentally study the dynamics of a degenerate one-dimensional Bose gas\nthat is subject to a continuous outcoupling of atoms. Although standard\nevaporative cooling is rendered ineffective by the absence of thermalizing\ncollisions in this system, we observe substantial cooling. This cooling\nproceeds through homogeneous particle dissipation and many-body dephasing,\nenabling the preparation of otherwise unexpectedly low temperatures. Our\nobservations establish a scaling relation between temperature and particle\nnumber, and provide insights into equilibration in the quantum world.",
        "positive": "Measurement and Significance of Wilson Loops in Synthetic Gauges Fields: We study Wilson loops as a necessary tool for unambiguous identification of\nnon-Abelian synthetic gauge fields, with attention to certain crucial but often\noverlooked features, such as the requirement of at least three distinct loops.\nWe devise a method to determine the complete Wilson loop matrix from the time\nevolved amplitudes of the internal atomic states of laser-coupled ultracold\natoms that does not require lattice confinement. The analysis is done in the\ncontext of a new cyclic model that can realize both Abelian and non-Abelian\nstructures within a single configuration with continuous variation possible\nbetween U(1) and U(2) gauge groups by varying the detuning of the laser fields."
    },
    {
        "anchor": "Chains with loops - synthetic magnetic fluxes and topological order in\n  one-dimensional spin systems: Engineering topological quantum order has become a major field of physics.\nMany advances have been made by synthesizing gauge fields in cold atomic\nsystems. Here, we carry over these developments to other platforms which are\nextremely well suited for quantum engineering, namely trapped ions and\nnano-trapped atoms. Since these systems are typically one-dimensional, the\naction of artificial magnetic fields has so far received little attention.\nHowever, exploiting the long-range nature of interactions, loops with\nnon-vanishing magnetic fluxes become possible even in one-dimensional settings.\nThis gives rise to intriguing phenomena, such as fractal energy spectra, flat\nbands with localized edge states, and topological many-body states. We\nelaborate on a simple scheme for generating the required artificial fluxes by\nperiodically driving an XY spin chain. Concrete estimates demonstrating the\nexperimental feasibility for trapped ions and atoms in waveguides are given.",
        "positive": "Phase separation can be stronger than chaos: We investigate several dynamical regimes characterizing a bosonic binary\nmixture loaded in a ring trimer, with particular reference to the persistence\nof demixing. The degree of phase separation is evaluated by means of the\n\"Entropy of mixing\", an indicator borrowed from Statistical Thermodynamics.\nThree classes of demixed stationary configurations are identified and their\nenergetic and linear stability carefully analyzed. An extended set of\ntrajectories originating in the vicinity of fixed points are explicitly\nsimulated and chaos is shown to arise according to three different mechanisms.\nIn many dynamical regimes, we show that chaos is not able to disrupt the order\nimposed by phase separation, i.e. boson populations, despite evolving in a\nchaotic fashion, do not mix. This circumstance can be explained either with\nenergetic considerations or in terms of dynamical restrictions."
    },
    {
        "anchor": "Radio frequency spectrum of fermions near a narrow Feshbach resonance: We calculate the radio frequency (RF) spectrum of fermionic atoms near a\nnarrow Feshbach resonance, explaining observations made in ultracold samples of\n$^6\\rm{Li}$ [E. L. Hazlett {\\it et al.}, Phys. Rev. Lett. {\\bf 108}, 045304\n(2012)]. We use a two channel resonance model to show that the RF spectrum\ncontains two peaks. In the wide-resonance limit, nearly all spectral weight\nlies in one of these peaks, and typically the second peak is very broad. We\nfind strong temperature dependence, which can be traced to the energy\ndependence of the two-particle scattering. In addition to microscopic\ncalculations, we use sum rule arguments to find generic features of the\nspectrum which are model independent.",
        "positive": "Thermal effects in an imbalanced dipolar fermionic superfluid: We investigate the temperature effects in an imbalanced superfluid atomic\nFermi gas. We consider a bilayer system of two-component dipolar fermionic\natoms with one layer containing atoms of one component and the other layer the\natoms of other component with an imbalance between the populations of the two\ncomponents. This imbalance results in uniform and nonuniform superfluid phases\nsuch as phase-separated BCS, Fulde-Ferrel-Larkin-Ovchinnikov (FFLO), Sarma and\nnormal Fermi liquid phases for different system parameters. Using the\nmean-field BCS theory together with the superfluid mass-density criterion we\nclassify different phases in thermodynamic phase diagram. Our results indicate\nthat for a dipolar Fermi system the Sarma phase is stable for large imbalance\nat finite temperature below the critical temperature, and the FFLO phase is\nstable for intermediate imbalance on the BCS side of a BCS-BCE crossover. The\nphase diagram in the temperature and population imbalance plane indicate three\nLifshitz points: one corresponding to coexistance of BCS, FFLO and normal Fermi\nliquid phase while the other two correspond to the coexistance of the Sarma\nphase, FFLO phase and normal Fermi phase for dipolar interactions."
    },
    {
        "anchor": "Generalized Rashba spin-orbit coupling for cold atoms: We study the possibility to generate a new type of spin-orbit coupling for\nthe center of mass motion of cold atoms, using laser beams that resonantly\ncouple N atomic internal ground states to an extra state. After a general\nanalysis of the scheme, we concentrate on the tetrapod setup (N=4) where the\natomic state can be described by a three-component spinor, evolving under the\naction of a Rashba-type spin-orbit coupling for a spin 1 particle. We\nillustrate a consequence of this coupling by studying the negative refraction\nof atoms at a potential step, and show that the amplitude of the refracted beam\nis significantly increased in comparison to the known case of spin 1/2 Rashba\ncoupling. Finally we explore a possible implementation of this tetrapod setup,\nusing stimulated Raman couplings between Zeeman sublevels of the ground state\nof alkali atoms.",
        "positive": "Dissipation through localised loss in bosonic systems with long-range\n  interactions: In recent years, controlled dissipation has proven to be a useful tool for\nprobing of a quantum system in the ultracold setup. In this paper we consider\ndynamics of bosons induced by a dissipative local defect. We address superfluid\nand supersolid phases close to half-filling that are ground states of an\nextended Bose-Hubbard Hamiltonian. To this end, we solve the master equation\nusing the Gutzwiller approximation and find that in the superfluid phase\nrepulsive nearest neighbour interactions can lead to enhanced dissipation\nprocesses. On the other hand, our mean-field approach indicates that the\neffective loss rates are significantly suppressed deep in the supersolid phase\nwhere repulsive nearest neighbour interactions play a dominant role. Our\nnumerical results are explained by analytical arguments and in particular, in\nthe limit of strong dissipation we recover the quantum Zeno effect."
    },
    {
        "anchor": "Observation of the density dependence of the closed-channel fraction of\n  a $^6$Li superfluid: Atomic Fermi gases provide an ideal platform for studying the pairing and\nsuperfluid physics, using a Feshbach resonance between closed channel molecular\nstates and open channel scattering states. Of particular interest is the\nstrongly interacting regime. We show that the closed-channel fraction $Z_{cc}$\nprovides an effective probe for the important many-body interacting effects,\nespecially through its density dependence, which is absent from two-body\ntheoretical predictions. Here we measure $Z_{cc}$ as a function of interaction\nstrength and the Fermi temperature $T_\\text{F}$ in a trapped $^6$Li superfluid\nthroughout the entire BCS--BEC crossover, in quantitative agreement with theory\nwhen important thermal contributions outside the superfluid core are taken into\naccount. Away from the deep BEC regime, the fraction $Z_{cc}$ is sensitive to\n$T_\\text{F}$. In particular, our data show $Z_{cc} \\propto T_\\text{F}^{\\alpha}$\nwith $\\alpha=1/2$ at unitarity, in quantitative agreement with calculations of\na two-channel pairing fluctuation theory, and $\\alpha$ increases rapidly into\nthe BCS regime, reflecting many-body interaction effects as predicted.",
        "positive": "Functional renormalization for the BCS-BEC crossover: We review the functional renormalization group (RG) approach to the BCS-BEC\ncrossover for an ultracold gas of fermionic atoms. Formulated in terms of a\nscale-dependent effective action, the functional RG interpolates continuously\nbetween the atomic or molecular microphysics and the macroscopic physics on\nlarge length scales. We concentrate on the discussion of the phase diagram as a\nfunction of the scattering length and the temperature which is a paradigm\nexample for the non-perturbative power of the functional RG. A systematic\nderivative expansion provides for both a description of the many-body physics\nand its expected universal features as well as an accurate account of the\nfew-body physics and the associated BEC and BCS limits."
    },
    {
        "anchor": "Degenerate Bose gases with uniform loss: We theoretically investigate a weakly-interacting degenerate Bose gas coupled\nto an empty Markovian bath. We show that in the universal phononic limit the\nsystem evolves towards an asymptotic state where an emergent temperature is set\nby the quantum noise of the outcoupling process. For situations typically\nencountered in experiments, this mechanism leads to significant cooling. Such\ndissipative cooling supplements conventional evaporative cooling and dominates\nin settings where thermalization is highly suppressed, such as in a\none-dimensional quasicondensate.",
        "positive": "Small quench dynamics as a probe for trapped ultracold atoms: Finite systems of bosons and/or fermions described by the Hubbard model can\nbe realized using ultracold atoms confined in optical lattices. The ground\nstates of these systems often exhibit a coexistence of compressible superfluid\nand incompressible Mott insulating regimes. We analyze such systems by studying\nthe out-of-equilibrium dynamics following a weak sudden quench of the trapping\npotential. In particular, we show how the temporal variance of the site\noccupations reveals the location of spatial boundaries between compressible and\nincompressible regions. The feasibility of this approach is demonstrated for\nseveral models using numerical simulations. We first consider integrable\nsystems, hard-core bosons (spinless fermions) confined by a harmonic potential,\nwhere space separated Mott and superfluid phases coexist. Then, we analyze a\nnonintegrable system, a $J-V-V'$ model with coexisting charge density wave and\nsuperfluid phases. We find that the temporal variance of the site occupations\nis a more effective measure than other standard indicators of phase boundaries\nsuch as a local compressibility. Based on these examples, we argue that\nanalyzing temporal fluctuations is a valuable experimental tool for exploring\nphase boundaries in trapped atom systems."
    },
    {
        "anchor": "Excitations at the border of a condensate: We solve the Bogoliubov--de Gennes equations for an inhomogeneous condensate\nin the vicinity of a linear turning point. A stable integration scheme is\ndeveloped using a transformation into an adiabatic basis. We identify boundary\nmodes trapped in a potential whose shape is similar to a Hartree-Fock\nmean-field treatment. These modes are non-resonantly excited when bulk modes\nreflect at the turning point and contribute significantly to the spectrum of\nlocal density fluctuations.",
        "positive": "Crafting the dynamical structure of synchronization by harnessing\n  bosonic multilevel cavity QED: Many-body cavity QED experiments are established platforms to tailor and\ncontrol the collective responses of ensembles of atoms, interacting through one\nor more common photonic modes. The rich diversity of dynamical phases they can\nhost, calls for a unified framework. Here we commence this program by showing\nthat a cavity QED simulator assembled from $N$-levels bosonic atoms, can\nreproduce and extend the possible dynamical responses of collective observables\noccurring after a quench. Specifically, by initializing the atoms in classical\nor quantum states, or by leveraging intra-levels quantum correlations, we craft\non demand the entire synchronization/desynchronization dynamical crossover of\nan exchange model for $SU(N)$ spins. We quantitatively predict the onset of\ndifferent dynamical responses by combining the Liouville-Arnold theorem on\nclassical integrability with an ansatz for reducing the collective evolution to\nan effective few-body dynamics. Among them, we discover a synchronized chaotic\nphase induced by quantum correlations and associated to a first order\nnon-equilibrium transition in the Lyapunov exponent of collective atomic\ndynamics. Our outreach includes extensions to other spin-exchange quantum\nsimulators and a universal conjecture for the dynamical reduction of\nnon-integrable all-to-all interacting systems."
    },
    {
        "anchor": "Universal Scaling Properties of Cold Atom Scattering Dynamics in\n  Confined Low Dimensional Geometries: Intermediate energy scale physics plays a very important role in\nnon-equilibrium dynamics of quasi-low dimensional cold atom systems. In this\narticle we obtain the universal scaling relations for the generalized\nreflection coefficient, i.e., the fraction of atoms scattered out of the\ninitial state, at intermediate energies scales. These intermediate energies are\nlarger than the trap frequency, but necessarily smaller than the effective\nrange of the inter-atomic potential. For harmonically confined one and two\ndimensional geometries, whenever the energy of the system is commensurate with\na transverse energy level, it is shown that the system becomes non-interacting.\nFor energies close to a transverse energy level, the reflection coefficient and\nscattering dynamics take on universal scaling forms, only depending on the\ndifference between the energy of the particles and the transverse energy level.\nIn this article, the universal power law behaviors of these scattering\nobservables are obtained.",
        "positive": "Lieb-Liniger Bosons in a Shallow Quasiperiodic Potential: Bose Glass\n  Phase and Fractal Mott Lobes: The emergence of a compressible insulator phase, known as the Bose glass, is\ncharacteristic of the interplay of interactions and disorder in correlated Bose\nfluids. While widely studied in tight-binding models, its observation remains\nelusive owing to stringent temperature effects. Here we show that this issue\nmay be overcome by using Lieb-Liniger bosons in shallow quasiperiodic\npotentials. A Bose glass, surrounded by superfluid and Mott phases, is found\nabove a critical potential and for finite interactions. At finite temperature,\nwe show that the melting of the Mott lobes is characteristic of a fractal\nstructure and find that the Bose glass is robust against thermal fluctuations\nup to temperatures accessible in quantum gases. Our results raise questions\nabout the universality of the Bose glass transition in such shallow\nquasiperiodic potentials."
    },
    {
        "anchor": "Topological transport of mobile impurities: We study the Hall response of topologically-trivial mobile impurities (Fermi\npolarons) interacting weakly with majority fermions forming a Chern-insulator\nbackground. This setting involves a rich interplay between the genuine\nmany-body character of the polaron problem and the topological nature of the\nsurrounding cloud. When the majority fermions are accelerated by an external\nfield, a transverse impurity current can be induced. To quantify this polaronic\nHall effect, we compute the drag transconductivity, employing controlled\ndiagrammatic perturbation theory in the impurity-fermion interaction. We show\nthat the impurity Hall drag is not simply proportional to the Chern number\ncharacterizing the topological transport of the insulator on its own - it also\ndepends continuously on particle-hole breaking terms, to which the Chern number\nis insensitive. However, when the insulator is tuned across a topological phase\ntransition, a sharp jump of the impurity Hall drag results, for which we derive\nan analytical expression. We describe how the Hall drag and jump can be\nextracted from a circular dichroic measurement of impurity excitation rates,\nparticularly suited for ultracold gas experiments.",
        "positive": "Particle and pair spectra for strongly correlated Fermi gases: A\n  real-frequency solver: The strongly attractive Fermi gas in the BCS-BEC crossover is efficiently\ndescribed in terms of coupled fermions and fermion pairs, or molecules. We\ncompute the spectral functions of both fermions and pairs in the normal state\nnear the superfluid transition using a Keldysh formulation in real frequency.\nThe mutual influence between fermions and pairs is captured by solving the\nself-consistent Luttinger-Ward equations: these include both the damping of\nfermions by scattering off dressed pairs, as well as the decay of pair states\nby dissociation into two dressed fermions. The pair spectra encode contact\ncorrelations between fermions and form the basis for computing dynamical\nresponse functions and transport properties."
    },
    {
        "anchor": "Zeros of Loschmidt echo in the presence of Anderson localization: We study the Loschmidt echo and the dynamical free energy of the Anderson\nmodel after a quench of the disorder strength. If the initial state is extended\nand the eigenstates of the post-quench Hamiltonian are strongly localized, we\nargue that the Loschmidt echo exhibits zeros periodically with the period $2\\pi\n/D$ where $D$ is the width of spectra. At these zeros, the dynamical free\nenergy diverges in a logarithmic way. We present numerical evidence of our\nargument in one- and three-dimensional Anderson models. Our findings connect\nthe dynamical quantum phase transitions to the localization-delocalization\nphase transitions.",
        "positive": "Quantum phase transition modulation in an atomtronic Mott switch: Mott insulators provide stable quantum states and long coherence times to due\nto small number fluctuations, making them good candidates for quantum memory\nand atomic circuits. We propose a proof-of-principle for a 1D Mott switch using\nan ultracold Bose gas and optical lattice. With time-evolving block decimation\nsimulations -- efficient matrix product state methods -- we design a means for\ntransient parameter characterization via a local excitation for ease of\nengineering into more complex atomtronics. We perform the switch operation by\ntuning the intensity of the optical lattice, and thus the interaction strength\nthrough a conductance transition due to the confined modifications of the\n\"wedding cake\" Mott structure. We demonstrate the time-dependence of Fock state\ntransmission and fidelity of the excitation as a means of tuning up the device\nin a double well and as a measure of noise performance. Two-point correlations\nvia the $g^{(2)}$ measure provide additional information regarding superfluid\nfragments on the Mott insulating background due to the confinement of the\npotential."
    },
    {
        "anchor": "Universality in ultradilute liquid Bose-Bose mixtures: We have studied dilute Bose-Bose mixtures of atoms with attractive\ninterspecies and repulsive intraspecies interactions using quantum Monte Carlo\nmethods at $T=0$. Using a number of models for interactions, we determine the\nrange of validity of the universal equation of state of the symmetric liquid\nmixture as a function of two parameters: the $s$-wave scattering length and the\neffective range of the interaction potential. It is shown that the\nLee-Huang-Yang correction is sufficient only for extremely dilute liquids with\nthe additional restriction that the range of the potential is small enough.\nBased on the quantum Monte Carlo equation of state we develop a new density\nfunctional which goes beyond the Lee-Huang-Yang term and use it together with\nlocal density approximation to determine density profiles of realistic\nself-bound drops.",
        "positive": "First principles derivation of NLS equation for BEC with cubic and\n  quintic nonlinearities at non zero temperature. Dispersion of linear waves: In this work we presented a derivation of the quantum hydrodynamic equations\nfor neutral bosons. We considered short range interaction between particles.\nThis interaction consist binary interaction $U(\\textbf{r}_{i},\\textbf{r}_{j})$\nand three particle interaction\n$U(\\textbf{r}_{i},\\textbf{r}_{j},\\textbf{r}_{k})$, the last one does not\ninclude binary interaction between particles. From the quantum hydrodynamic\n(QHD) equations for Bose-Einstein condensate we derive nonlinear\nSchr\\\"{o}dinger equation. This equation includes the nonlinearities of third\nand fifth degree. It is at zero temperature. Explicit form of the constant of\nthree-particle interaction was taken. First of all, developed method we used\nfor studying of dispersion of linear waves. Dispersion characteristics of\nlinear waves were compared for the cases. It were of two-particle interaction\nin approximation third order to interaction radius (TOIR) and three-particle\ninteraction, at zero temperature. We consider influence of temperature on\ndispersion of elementary excitations. For this aim we derive a system of QHD\nequations at non-zero temperature. Obtained system of equation is an analog of\nwell-known two-fluid hydrodynamics. Moreover, it is generalization of two-fluid\nhydrodynamics equations due to three-particle interaction. Evident expressions\nof the velocities of the first and second sound via the concentrations of\nsuperfluid and noncondesate components is calculated."
    },
    {
        "anchor": "Thermodynamics of a Bose Einstein condensate with free magnetization: We study thermodynamic properties of a gas of spin 3 52Cr atoms across Bose\nEinstein condensation. Magnetization is free, due to dipole-dipole interactions\n(DDIs). We show that the critical temperature for condensation is lowered at\nextremely low magnetic fields, when the spin degree of freedom is thermally\nactivated. The depolarized gas condenses in only one spin component, unless the\nmagnetic field is set below a critical value, below which a non ferromagnetic\nphase is favored. Finally we present a spin thermometry efficient even below\nthe degeneracy temperature.",
        "positive": "Engineering Higgs dynamics by spectral singularities: We generalize the dynamical phase diagram of a Bardeen-Cooper-Schrieffer\ncondensate, considering attractive to repulsive, i.e., critical quenches (CQ)\nand a non-constant density of states (DOS). We show that different synchronized\nHiggs dynamical phases can be stabilized, associated with singularities in the\ndensity of states (DOS) and different quench protocols. In particular, the CQ\ncan stabilize an overlooked high-frequency Higgs dynamical phase related to the\nupper edge of the fermionic band. For a compensated Dirac system we find a\nDirac-Higgs mode associated with the cusp singularity at the Fermi level, and\nwe show that synchronized phases become more pervasive across the phase\ndiagram. The relevance of these remarkable phenomena and their realization in\nensembles of fermionic cold atoms confined in optical lattices is also\ndiscussed."
    },
    {
        "anchor": "Variational Bethe Ansatz approach for dipolar one-dimensional bosons: We propose a variational approximation to the ground state energy of a\none-dimensional gas of interacting bosons on the continuum based on the Bethe\nAnsatz ground state wavefunction of the Lieb-Liniger model. We apply our\nvariational approximation to a gas of dipolar bosons in the single mode\napproximation and obtain its ground state energy per unit length. This allows\nfor the calculation of the Tomonaga-Luttinger exponent as a function of density\nand the determination of the structure factor at small momenta. Moreover, in\nthe case of attractive dipolar interaction, an instability is predicted at a\ncritical density, which could be accessed in lanthanide atoms.",
        "positive": "Observation of vortices and vortex stripes in a dipolar Bose-Einstein\n  condensate: Quantized vortices are the prototypical feature of superfluidity. Pervasive\nin all natural systems, vortices are yet to be observed in dipolar quantum\ngases. Here, we exploit the anisotropic nature of the dipole-dipole interaction\nof a dysprosium Bose-Einstein condensate to induce angular symmetry breaking in\nan otherwise cylindrically symmetric pancake-shaped trap. Tilting the magnetic\nfield towards the radial plane deforms the cloud into an ellipsoid through\nmagnetostriction, which is then set into rotation. At stirring frequencies\napproaching the radial trap frequency, we observe the generation of dynamically\nunstable surface excitations, which cause angular momentum to be pumped into\nthe system through vortices. Under continuous rotation, the vortices arrange\ninto a stripe configuration along the field--in close corroboration with\nsimulations--realizing a long sought-after prediction for dipolar vortices."
    },
    {
        "anchor": "Phononic collective excitations in superfluid Fermi gases at nonzero\n  temperatures: We study the phononic collective modes of the pairing field $\\Delta$ and\ntheir corresponding signature in both the order-parameter and density response\nfunctions for a superfluid Fermi gas at all temperatures below $T_c$ in the\ncollisionless regime. The spectra of collective modes are calculated within the\nGaussian Pair Fluctuation approximation. We deal with the coupling of these\nmodes to the fermionic continuum of quasiparticle-quasihole excitations by\nperforming a non-perturbative analytic continuation of the pairing field\npropagator. At low temperature, we recover the known exponential temperature\ndependence of the damping rate and velocity shift of the Anderson-Bogoliubov\nbranch. In the vicinity of $T_c$, we find analytically a weakly-damped\ncollective mode whose velocity vanishes with a critical exponent of $1/2$, and\nwhose quality factor diverges logarithmically with $T_c-T$, thereby clarifying\nan existing debate in the literature (Andrianov et al. Th. Math. Phys. 28, 829,\nOhashi et al. J. Phys. Jap. 66, 2437). A transition between these two phononic\nbranches is visible at intermediary temperatures, particularly in the BCS limit\nwhere the phase-phase response function displays two maxima.",
        "positive": "Universal relations for dipolar quantum gases: We establish that two-dimensional dipolar quantum gases admit a universal\ndescription, i.e., their thermodynamic properties are independent of details of\nthe interaction at short distances. The only relevant parameters are the dipole\nlength as well as the scattering length of the combined short-range plus\ndipolar interaction potential. We derive adiabatic relations that link the\nchange in the thermodynamic potentials with respect to the scattering length\nand the dipole length to a generalized Tan contact parameter and a new dipolar\ncontact, which involves an integral of a short-distance regularized pair\ndistribution function. These two quantities determine the scale anomaly in the\ndifference between pressure and energy density and also the internal energy in\nthe presence of a harmonic confinement. For a weak transverse confinement,\nconfigurations with attractive interactions appear, which lead to a\ndensity-wave instability beyond a critical strength of the dipolar interaction.\nWe show that this instability essentially coincides with the onset of a roton\nminimum in the excitation spectrum and may be understood in terms of a quantum\nanalog of the Hansen-Verlet criterion for freezing of a classical fluid."
    },
    {
        "anchor": "Geometric mass acquisition via quantum metric: an effective band mass\n  theorem for the helicity bands: By taking the virtual inter-band transitions along with the intra-band ones\ninto full account, here we first propose an effective band mass theorem that is\nsuitable for a wide-class of single-particle Hamiltonians exhibiting multiple\nenergy bands. Then, for the special case of two-band systems, we show that the\ninter-band contribution to the effective band mass of a particle at a given\nquantum state is directly controlled by the quantum metric of the corresponding\nstate. As an illustration, we consider a spin-orbit coupled spin-$1/2$ particle\nand calculate its effective band mass at the band minimum of the lower helicity\nband. Independent of the coupling strength, we find that the bare mass $m_0$ of\nthe particle jumps to $2m_0$ for the Rashba and to $3m_0$ for the Weyl\ncoupling. This geometric mass enhancement is a non-perturbative effect,\nuncovering the mystery behind the effective mass of the two-body bound states\nin the non-interacting limit. As a further illustration, we show that a\nmassless Dirac particle acquires a linearly dispersing band mass (equivalent to\nthe effective cyclotron one up to a prefactor) with its momentum through the\nsame mechanism.",
        "positive": "Intertwined Superfluid and Density Wave Order in a $p$-Orbital Bose\n  Condensate: We study a continuum model of the weakly interacting Bose gas in the presence\nof an external field with minima forming a triangular lattice. The second\nlowest band of the single-particle spectrum ($p$-band) has three minima at\nnon-zero momenta. We consider a metastable Bose condensate at these momenta and\nfind that, in the presence of interactions that vary slowly over the lattice\nspacing, the order parameter space is isomorphic to $S^{5}$. We show that the\nenlarged symmetry leads to the loss of topologically stable vortices, as well\nas two extra gapless modes with quadratic dispersion. The former feature\nimplies that this non-Abelian condensate is a \"failed superfluid\" that does not\nundergo a Berezinskii-Kosterlitz-Thouless (BKT) transition. Order-by-disorder\nsplitting appears suppressed, implying that signatures of the $S^5$ manifold\nought to be observable at low temperatures."
    },
    {
        "anchor": "Extended Bose Hubbard model for two leg ladder systems in artificial\n  magnetic fields: We investigate the ground state properties of ultracold atoms with long range\ninteractions trapped in a two leg ladder configuration in the presence of an\nartificial magnetic field. Using a Gross-Pitaevskii approach and a mean field\nGutzwiller variational method, we explore both the weakly interacting and\nstrongly interacting regime, respectively. We calculate the boundaries between\nthe density-wave/supersolid and the Mott-insulator/superfluid phases as a\nfunction of magnetic flux and uncover regions of supersolidity. The mean-field\nresults are confirmed by numerical simulations using a cluster mean field\napproach.",
        "positive": "Dimer-dimer scattering length for fermions with different masses:\n  analytical study for large mass ratio: We study the dimer-dimer scattering length $a_4$ for a two-component Fermi\nmixture in which the different fermions have different masses $m\\us$ and\n$m\\ds$. This is made in the framework of the exact field theoretical method. In\nthe large mass ratio domain the equations are simplified enough to lead to an\nanalytical solution. In particular we link $a_4$ to the fermion-dimer\nscattering length $a_3$ for the same fermions, and obtain the very simple\nrelation $a_4=a_3/2$. The result $a_4 \\simeq a_3/2$ is actually valid whatever\nthe mass ratio with quite good precision. As a result we find an analytical\nexpression providing $a_4$ with a fairly good precision for any masses. To\ndominant orders for large mass ratio it agrees with the literature. We show\nthat, in this large mass ratio domain, the dominant processes are the repeated\ndimer-dimer Born scatterings, considered earlier by Pieri and Strinati. We\nconclude that their approximation, of retaining only these processes, is a\nfairly good one whatever the mass ratio."
    },
    {
        "anchor": "A Renormalization-Group Study of Interacting Bose-Einstein condensates:\n  Absence of the Bogoliubov Mode below Four ($T>0$) and Three ($T=0$)\n  Dimensions: We derive exact renormalization-group equations for the $n$-point vertices\n($n=0,1,2,\\cdots$) of interacting single-component Bose-Einstein condensates\nbased on the vertex expansion of the effective action. They have a notable\nfeature of automatically satisfying Goldstone's theorem (I), which yields the\nHugenholtz-Pines relation $\\Sigma(0)-\\mu=\\Delta(0)$ as the lowest-order\nidentity. Using them, it is found that the anomalous self-energy $\\Delta(0)$\nvanishes below $d_{\\rm c}=4$ ($d_{\\rm c}=3$) dimensions at finite temperatures\n(zero temperature), contrary to the Bogoliubov theory predicting a finite\n\"sound-wave\" velocity $v_{\\rm s}\\propto [\\Delta(0)]^{1/2}>0$. It is also argued\nthat the one-particle density matrix $\\rho({\\bf\nr})\\equiv\\langle\\hat\\psi^\\dagger({\\bf r}_1)\\hat\\psi({\\bf r}_1+{\\bf r})\\rangle$\nfor $d<d_{\\rm c}$ dimensions approaches the off-diagonal-long-range-order value\n$N_{\\bf 0}/V$ asymptotically as $r^{-d+2-\\eta}$ with an exponent $\\eta>0$. The\nanomalous dimension $\\eta$ at finite temperatures is predicted to behave for\n$d=4-\\epsilon$ dimensions ($0<\\epsilon\\ll 1$) as $\\eta\\propto\\epsilon^2$. Thus,\nthe interacting Bose-Einstein condensates are subject to long-range\nfluctuations similar to those at the second-order transition point, and their\nexcitations in the one-particle channel are distinct from the Nambu-Goldstone\nmode with a sound-wave dispersion in the two-particle channel.",
        "positive": "Acoustic Superradiance from a Bose-Einstein Condensate Vortex with a\n  Self-Consistent Background Density Profile: The axisymmetric acoustic perturbations in the velocity potential of a\nBose-Einstein condensate in the presence of a single vortex behave like\nminimally coupled massless scalar fields propagating in a curved (1+1)\ndimensional Lorentzian space-time, governed by the Klein-Gordon wave equation.\nThus far, the amplified scattering of these perturbations from the vortex, as a\nmanifestation of the acoustic superradiance, has been investigated with a\nconstant background density. This paper goes beyond by employing a\nself-consistent condensate density profile that is obtained by solving the\nGross-Pitaevskii equation for an unbound BEC. Consequently, the loci of the\nevent horizon and the ergosphere of the acoustic black hole are modified\naccording to the radially varying speed of sound. The superradiance is\ninvestigated both for transient features in the time-domain and for spectral\nfeatures in the frequency domain. In particular, an effective energy-potential\nfunction defined in the spectral formulation correlates with the existence and\nthe frequency dependence of the acoustic superradiance. The numerical results\nindicate that the constant background density approximation underestimates the\nmaximum superradiance and the frequency at which this maximum occurs."
    },
    {
        "anchor": "A Non-Gaussian Variational Approach to Fermi Polarons in One- and\n  Two-dimensional Lattices: We study the Fermi polaron problem of one mobile spin-up impurity immersed\natop the bath consisting of spin-down fermions in one- and two-dimensional\nsquare lattices. We solve this problem by applying a variational approach with\nnon-Gaussian states after separating the impurity and the background by the\nLee-Low-Pines transformation. The ground state for a fixed total momentum can\nbe obtained via imaginary time evolution for the variational parameters. For\nthe one-dimensional case, the variational results are compared with numerical\nsolutions of the matrix product state method with excellent agreement. In\ntwo-dimensional lattices, we focus on the dilute limit, and find a\npolaron--molecule evolution in consistence with previous results obtained by\nvariational and quantum Monte Carlo methods for models in continuum space.\nComparing to previous works, our method provides the lowest ground state energy\nin the entire parameter region considered, and has an apparent advantage as it\ndoes not need to assume {\\it in priori} any specific form of the variational\nwave function.",
        "positive": "Controlling entanglement in a triple-well system of dipolar atoms: We study the dynamics of entanglement and atomic populations of ultracold\ndipolar bosons in an aligned three-well potential described by an extended\nBose-Hubbard model. We focus on a sufficiently strong interacting regime where\nthe couplings are tuned to obtain an integrable system, in which the time\nevolution exhibits a resonant behavior that can be exactly predicted. Within\nthis framework, we propose a protocol that includes an integrability breaking\nstep by tilting the edge wells for a short time through an external field,\nallowing the production of quantum states with a controllable degree of\nentanglement. We analyze this protocol for different initial states and show\nthe formation of highly entangled states as well as NOON-like states. These\nresults offer valuable insights into how entanglement can be controlled in\nultracold atom systems that may be useful for the proposals of new quantum\ndevices."
    },
    {
        "anchor": "The non-Abelian bosonic quantum ring: We investigate the dynamics of a spinor Bose-Einstein condensate which is\ngoverned by an optically induced non-Abelian gauge potential. Using a ring\nshaped trap to confine the atoms and a hydrodynamic ansatz, nonlinear Josephson\ntype equations are found to describe the system. The degenerate eigenstates\nwhich show rotation are solved exactly. We consider a homogenous filled ring\nand observe population dynamics between the two quasi-spin components but also\nspace dependent Josephson oscillations. Stable mass currents can be observed\nwhich are induced by the constant non-Abelian effective magnetic field in the\nlimit of weak interactions. For strong interactions the appearance of\ntwo-component dark soliton-like objects are observed.",
        "positive": "Spectrum, Landau-Zener theory and driven-dissipative dynamics of a\n  staircase of photons: We study the production of photons in a model of three bosonic atomic modes\nnon-linearly coupled to a cavity mode. In absence of external driving and\ndissipation, the energy levels at different photon numbers assemble into the\nsteps of an energy staircase which can be employed as guidance for preparing\nmulti-photon states. We consider adiabatic photon production, driving the\nsystem through a sequence of Landau-Zener transitions in the presence of\nexternal coherent light pumping. We also analyse the non-equilibrium dynamics\nof the system resulting from the competition of the sudden switch of coherent\nphoton pumping and cavity photon losses, and we find that the system approaches\na plateau with a given number of photons, which becomes metastable upon\nincreasing the rate of photon pumping. We discuss the sensitivity of the time\nscales for the onset of this metastable behaviour to system parameters and\npredict the value of photons attained, solving the driven-dissipative dynamics\nincluding three-body correlations between light and matter degrees of freedom."
    },
    {
        "anchor": "Symplectic ferromagnetism and phase transitions in multi-component\n  fermionic systems: In this paper, we study the itinerant ferromagnetic phase in multi-component\nfermionic systems with symplectic (Sp(4), or isomorphically SO(5)) symmetry.\nTwo different microscopic models have been considered and an effective field\ntheory has been proposed to study the critical behavior of the\nnonmagnetism-magnetism phase transition. It has been shown that such systems\nexhibit intriguing ferromagnetism and critical behavior that different from\nthose in spin-$\\frac 12$ fermionic systems, or in high-spin systems with SU(N)\nsymmetry. An extension of our results to higher spin systems with Sp(2N)\nsymmetry has also been discussed.",
        "positive": "Observation of Dynamical Super Efimovian Expansion in a Unitary Fermi\n  Gas: We report an observation of a dynamical super Efimovian expansion in a\ntwo-component strongly interacting Fermi gas by engineering time dependent\nexternal harmonic trap frequencies. When trap frequency is followed as\n$[1/4t^2+1/t^2\\lambda\\log(t/t_*)]^{1/2}$, where $t_*$ and $\\lambda$ are two\ncontrol parameters, and the change is faster than a critical value, the\nexpansion of such the quantum gas shows a novel dynamics due to its spatial and\ndynamical scaling symmetry. A clear double-log periodicity, which is a hallmark\nof the super Efimov effect, is emergent for the cloud size in the expansion.\nThe universality of such scaling dynamics is verified both in the\nnon-interacting limit and in the unitarity limit. Observing super-Efmovian\nevolution represents a paradigm in probing universal properties and allows in a\nnew way to study many-body nonequilibrium dynamics with experiments."
    },
    {
        "anchor": "Quantum phases and spectrum of collective modes in a spin-1 BEC with\n  spin-orbital-angular-momentum coupling: Motivated by the recent experiments [Chen et al., Phys. Rev. Lett 121, 113204\n(2018), Chen et al., Phys. Rev. Lett. 121, 250401 (2018)], we investigate the\nlow-lying excitation spectrum of the ground-state phases of\nspin-orbital-angular-momentum-coupled (SOAM-coupled) spin-1 condensates.At\nvanishing detuning, a ferromagnetic SOAM-coupled spin-1 BEC can have two\nground-state phases, namely coreless and polar-core vortex states, whereas an\nantiferromagnetic BEC supports only polar-core vortex solution. The angular\nmomentum per particle, longitudinal magnetization, and excitation frequencies\ndisplay discontinuities across the phase boundary between the coreless vortex\nand polar-core vortex phases. The low-lying excitation spectrum evaluated by\nsolving the Bogoliubov-de-Gennes equations is marked by avoided crossings and\nhence the hybridization of the spin and density channels. The spectrum is\nfurther confirmed by the dynamical evolution of the ground state subjected to a\nperturbation suitable to excite a density or a spin mode and a variational\nanalysis for the density-breathing mode.",
        "positive": "Bistable behavior of a two-mode Bose-Einstein condensate in an optical\n  cavity: We consider a two-component Bose-Einstein condensate in a one-dimensional\noptical cavity. Specifically, the condensate atoms are taken to be in two\ndegenerate modes due to their internal hyperfine spin degrees of freedom and\nthey are coupled to the cavity field and an external transverse laser field in\na Raman scheme. A parallel laser is also exciting the cavity mode. When the\npump laser is far detuned from its resonance atomic transition frequency, an\neffective nonlinear optical model of the cavity-condensate system is developed\nunder Discrete Mode Approximation (DMA), while matter-field coupling has been\nconsidered beyond the Rotating Wave Approximation. By analytical and numerical\nsolutions of the nonlinear dynamical equations, we examine the mean cavity\nfield and population difference (magnetization) of the condensate modes. The\nstationary solutions of both the mean cavity field and normalized magnetization\ndemonstrate bistable behavior under certain conditions for the laser pump\nintensity and matter-field coupling strength."
    },
    {
        "anchor": "Transport of dipolar excitons in (Al,Ga)N/GaN quantum wells: We investigate the transport of dipolar indirect excitons along the growth\nplane of polar (Al,Ga)N/GaN quantum well structures by means of spatially- and\ntime-resolved photoluminescence spectroscopy. The transport in these strongly\ndisordered quantum wells is activated by dipole-dipole repulsion. The latter\ninduces an emission blue shift that increases linearly with exciton density,\nwhereas the radiative recombination rate increases exponentially. Under\ncontinuous, localized excitation, we measure a continuous red shift of the\nemission, as excitons propagate away from the excitation spot. This shift\ncorresponds to a steady-state gradient of exciton density, measured over\nseveral tens of micrometers. Time-resolved micro-photoluminescence experiments\nprovide information on the dynamics of recombination and transport of dipolar\nexcitons. We account for the ensemble of experimental results by solving the\nnonlinear drift-diffusion equation. Quantitative analysis suggests that in such\nstructures, exciton propagation on the scale of 10 to 20 microns is mainly\ndriven by diffusion, rather than by drift, due to the strong disorder and the\npresence of nonradiative defects. Secondary exciton creation, most probably by\nthe intense higher-energy luminescence, guided along the sample plane, is shown\nto contribute to the exciton emission pattern on the scale up to 100 microns.\nThe exciton propagation length is strongly temperature dependent, the emission\nbeing quenched beyond a critical distance governed by nonradiative\nrecombination.",
        "positive": "The mixing-demixing phase diagram of ultracold heteronuclear mixtures in\n  a ring trimer: We derive the complete mixing-demixing phase-diagram relevant to a bosonic\nbinary mixture confined in a ring trimer and modeled within the Bose-Hubbard\npicture. The mixing properties of the two quantum fluids, which are shown to be\nstrongly affected by the fragmented character of the confining potential, are\nevaluated by means of a specific indicator imported from Statistical\nThermodynamics and are shown to depend only on two effective parameters\nincorporating the asymmetry between the heteronuclear species. To closely match\nrealistic experimental conditions, our study is extended also beyond the\npointlike approximation of potential wells by describing the systems in terms\nof two coupled Gross-Pitaevskii equations. The resulting mean-field analysis\nconfirms the rich scenario of mixing-demixing transitions of the mixture and\nalso constitutes an effective springboard towards a viable experimental\nrealization. We additionally propose an experimental realization based on a\nrealistic optical-tweezers system and on mixtures of bosonic $^{23}\\mathrm{Na}$\nand $^{39}\\mathrm{K}$, thanks to the large tunability of their intra- and\ninter-species scattering lengths."
    },
    {
        "anchor": "Observation of quantum dynamical oscillations of ultracold atoms in the\n  F and D bands of an optical lattice: We report the observation of quantum dynamical oscillations of ultracold\natomic gases in the F and D bands of a single-well optical lattice. We are able\nto control the Bragg reflections at the Brillouin zone edge up to the third\norder. As a result, we can switch the quantum dynamics from oscillations across\nboth the F and D bands to oscillations only within the F-band. Our capability\nto observe these remarkable oscillations comes from the innovative\nnon-adiabatic technique which allows us to load ultracold atoms efficiently to\nthe G-band of an optical lattice.",
        "positive": "Imaging and addressing of individual fermionic atoms in an optical\n  lattice: We demonstrate fluorescence microscopy of individual fermionic potassium\natoms in a 527-nm-period optical lattice. Using electromagnetically induced\ntransparency (EIT) cooling on the 770.1-nm D$_1$ transition of $^{40}$K, we\nfind that atoms remain at individual sites of a 0.3-mK-deep lattice, with a\n$1/e$ pinning lifetime of $67(9)\\,\\rm{s}$, while scattering $\\sim 10^3$ photons\nper second. The plane to be imaged is isolated using microwave spectroscopy in\na magnetic field gradient, and can be chosen at any depth within the\nthree-dimensional lattice. With a similar protocol, we also demonstrate\npatterned selection within a single lattice plane. High resolution images are\nacquired using a microscope objective with 0.8 numerical aperture, from which\nwe determine the occupation of lattice sites in the imaging plane with 94(2)\\%\nfidelity per atom. Imaging with single-atom sensitivity and addressing with\nsingle-site accuracy are key steps towards the search for unconventional\nsuperfluidity of fermions in optical lattices, the initialization and\ncharacterization of transport and non-equilibrium dynamics, and the observation\nof magnetic domains."
    },
    {
        "anchor": "A cavity-QED simulator of slow and fast scrambling: We study information scrambling, as diagnosed by the out-of-time order\ncorrelations (OTOCs), in a system of large spins collectively interacting via\nspatially inhomogeneous and incommensurate exchange couplings. The model is\nrealisable in a cavity QED system in the dispersive regime. Fast scrambling,\nsignalled by an exponential growth of the OTOCs, is observed when the couplings\ndo not factorise into the product of a pair of local interaction terms, and at\nthe same time the state of the spins points initially coplanar to the equator\nof the Bloch sphere. When one of these conditions is not realised, OTOCs grow\nalgebraically with an exponent sensitive to the orientation of the spins in the\ninitial state. The impact of initial conditions on the scrambling dynamics is\nattributed to the presence of a global conserved quantity, which critically\nslows down the evolution for initial states close to the poles of the Bloch\nsphere.",
        "positive": "Precise characterization of ^6Li Feshbach resonances using trap-sideband\n  resolved RF spectroscopy of weakly bound molecules: We have performed radio-frequency dissociation spectroscopy of weakly bound\n^6Li_2 Feshbach molecules using low-density samples of about 30 molecules in an\noptical dipole trap. Combined with a high magnetic field stability this allows\nus to resolve the discrete trap levels in the RF dissociation spectra. This\nnovel technique allows the binding energy of Feshbach molecules to be\ndetermined with unprecedented precision. We use these measurements as an input\nfor a fit to the ^6Li scattering potential using coupled-channel calculations.\nFrom this new potential, we determine the pole positions of the broad ^6Li\nFeshbach resonances with an accuracy better than 7 \\times 10^{-4} of the\nresonance widths. This eliminates the dominant uncertainty for current\nprecision measurements of the equation of state of strongly interacting Fermi\ngases. For example, our results imply a corrected value for the Bertsch\nparameter \\xi measured by Ku et al. [Science 335, 563 (2012)], which is \\xi =\n0.370(5)(8)."
    },
    {
        "anchor": "Numerical simulation of nonequilibrium states in a trapped Bose-Einstein\n  condensate: In this work we present numerical study of a trapped Bose-Einstein condensate\nperturbed by an alternating potential. The relevant physical situation has been\nrecently realized in experiment, where the trapped condensate of $^{87}$Rb,\nbeing strongly perturbed, exhibits the set of spatial structures. Firstly,\nregular vortices are detected. Further, increasing either the excitation\namplitude or modulation time results in the transition to quantum vortex\nturbulence, followed by a granular state. Numerical simulation of the\nnonequilibrium Bose-condensed system is based on the solution of the\ntime-dependent 3D nonlinear Schr\\\"{o}dinger equation within the static and\ndynamical algorithms. The damped gradient step and time split-step Fourier\ntransform methods are employed. We demonstrate that computer simulations\nqualitatively reproduce the experimental picture, and describe well the main\nexperimental observables.",
        "positive": "Ergoregion instabilities in rotating two-dimensional Bose--Einstein\n  condensates: new perspectives on the stability of quantized vortices: We investigate the stability of vortices in two-dimensional Bose--Einstein\ncondensates. In analogy with rotating spacetimes and with a careful account of\nboundary conditions, we show that the dynamical instability of multiply\nquantized vortices in trapped condensates persists in untrapped, spatially\nhomogeneous geometries and has an ergoregion nature with some modification due\nto the peculiar dispersion of Bogoliubov sound. Our results open new\nperspectives to the physics of vortices in trapped condensates, where multiply\nquantized vortices can be stabilized by interference effects and singly charged\nvortices can become unstable in suitably designed trap potentials. We show how\nsuperradiant scattering can be observed also in the short-time dynamics of\ndynamically unstable systems, providing an alternative point of view on\ndynamical (in)stability phenomena in spatially finite systems."
    },
    {
        "anchor": "Towards a QMC-based density functional including finite-range effects:\n  excitation modes of a $^{39}$K quantum droplet: Some discrepancies between experimental results on quantum droplets made of a\nmixture of $^{39}$K atoms in different hyperfine states and their analysis\nwithin extended Gross-Pitaevskii theory (which incorporates beyond mean-field\ncorrections) have been recently solved by introducing finite-range effects into\nthe theory. Here, we study the influence of these effects on the monopole and\nquadrupole excitation spectrum of extremely dilute quantum droplets using a\ndensity functional built from first-principles quantum Monte Carlo\ncalculations, which can be easily introduced in the existing Gross-Pitaevskii\nnumerical solvers. Our results show differences of up to $20\\%$ with those\nobtained within the extended Gross-Pitaevskii theory, likely providing another\nway to observe finite-range effects in mixed quantum droplets by measuring\ntheir lowest excitation frequencies.",
        "positive": "Collisionless sound of bosonic superfluids in lower dimensions: The superfluidity of low-temperature bosons is well established in the\ncollisional regime. In the collisionless regime, however, the presence of\nsuperfluidity is not yet fully clarified, in particular in lower spatial\ndimensions. Here we compare the Vlasov-Landau equation, which does not take\ninto account the superfluid nature of the bosonic system, with the\nAndreev-Khalatnikov equations, which instead explicitly contain a superfluid\nvelocity. We show that recent experimental data of the sound mode in a\ntwo-dimensional collisionless Bose gas of $^{87}$Rb atoms are in good agreement\nwith both theories but the sound damping is better reproduced by the Andreev\n-Khalatnikov equations below the Berezinskii-Kosterlitz-Thouless critical\ntemperature $T_c$ while above $T_c$ the Vlasov-Landau results are closer to the\nexperimental ones. For one dimensional bosonic fluids, where experimental data\nare not yet available, we find larger differences between the sound velocities\npredicted by the two transport theories and, also in this case, the existence\nof a superfluid velocity reduces the sound damping."
    },
    {
        "anchor": "Thermal destabilization of self-bound ultradilute quantum droplets: We theoretically investigate the temperature effect in a Bose-Bose mixture\nwith attractive inter-species interactions, in the regime where a self-bound\nultradilute quantum droplet forms due to the subtle balance between the\nattractive mean-field force and the repulsive force provided by Lee-Huang-Yang\nquantum fluctuations. We find that in contrast to quantum fluctuations, thermal\nfluctuations destabilize the droplet state and completely destroy it above a\nthreshold temperature. We show that the threshold temperature is determined by\nthe intra-species interaction energy. For a three-dimensional Bose-Bose\nmixture, the threshold temperature is less than one-tenth of the Bose-Einstein\ncondensation temperature under the typical experimental conditions. With\nincreasing temperature, the droplet's equilibrium density gradually decreases\nand can be reduced by several tens of percent upon reaching the threshold\ntemperature. We also consider a one-dimensional quantum droplet and find a\nsimilar destabilization effect due to thermal fluctuations. The threshold\ntemperature in one dimension is roughly set by the binding energy of the\ninter-species dimer. The pronounced thermal instability of a self-bound quantum\ndroplet predicted in our work could be examined in future experiments, by\nmeasuring the temperature dependence of its central density and observing its\nsudden disappearance at the threshold temperature.",
        "positive": "Classical and quantum vortex leapfrogging in two-dimensional channels: The leapfrogging of coaxial vortex rings is a famous effect which has been\nnoticed since the times of Helmholtz. Recent advances in ultra-cold atomic\ngases show that the effect can now be studied in quantum fluids. The strong\nconfinement which characterizes these systems motivates the study of\nleapfrogging of vortices within narrow channels. Using the two-dimensional\npoint vortex model, we show that in the constrained geometry of a\ntwo-dimensional channel the dynamics is richer than in an unbounded domain:\nalongsize the known regimes of standard leapfrogging and the absence of it, we\nidentify new regimes of backward leapfrogging and periodic orbits. Moreover, by\nsolving the Gross-Pitaevskii equation for a Bose-Einstein condensate, we show\nthat all four regimes exist for quantum vortices too. Finally, we discuss the\ndifferences between classical and quantum vortex leapfrogging which appear when\nthe quantum healing length becomes significant compared to the vortex\nseparation or the channel size, and when, due to high velocity, compressibility\neffects in the condensate becomes significant."
    },
    {
        "anchor": "Quench Dynamics of a Fermi Gas with Strong Non-Local Interactions: We induce strong non-local interactions in a 2D Fermi gas in an optical\nlattice using Rydberg dressing. The system is approximately described by a\n$t-V$ model on a square lattice where the fermions experience isotropic\nnearest-neighbor interactions and are free to hop only along one direction. We\nmeasure the interactions using many-body Ramsey interferometry and study the\nlifetime of the gas in the presence of tunneling, finding that tunneling does\nnot reduce the lifetime. To probe the interplay of non-local interactions with\ntunneling, we investigate the short-time relaxation dynamics of charge density\nwaves in the gas. We find that strong nearest-neighbor interactions slow down\nthe relaxation. Our work opens the door for quantum simulations of systems with\nstrong non-local interactions such as extended Fermi-Hubbard models.",
        "positive": "Suppression of two-body collisional loss in an ultracold gas via the\n  Fano effect: The Fano effect (U. Fano, Phys. Rev. \\textbf{15},1866 (1961) shows that an\ninelastic scattering process can be suppressed when the output channel (OC) is\ncoupled to an isolated bound state. In this paper we investigate the\napplication of this effect for the suppression of two-body collisional losses\nof ultracold atoms. The Fano effect is originally derived via a first-order\nperturbation treatment for coupling between the incident channel (IC) and the\nOC. We generalize the Fano effect to systems with arbitrarily strong IC--OC\ncouplings. We analytically prove that, in a system with one IC and one OC, when\nthe inter-atomic interaction potentials are real functions of the inter-atomic\ndistance, the exact s-wave inelastic scattering amplitude can always be\nsuppressed to \\emph{zero} by coupling between the IC or the OC (or both of\nthem) and an extra isolated bound state. We further show that when the\nlow-energy inelastic collision between two ultracold atoms is suppressed by\nthis effect, the real part of the elastic scattering length between the atoms\nis still possible to be much larger than the range of inter-atomic\ninteraction.In addition, when open scattering channels are coupled to two bound\nstates, with the help of the Fano effect, independent control of the elastic\nand inelastic scattering amplitudes of two ultracold atoms can be achieved.\nPossible experimental realizations of our scheme are also discussed."
    },
    {
        "anchor": "Speed of sound of a Bose--Einstein condensate with dipole--dipole\n  interactions: In the present work the case of a chromium Bose-Einstein condensate is\nconsidered. The model includes not only the presence of the so-called contact\ninteraction but also a long range and anisotropic dipole-dipole interaction has\nbeen included. Some thermodynamical properties are analyzed. For instance, the\nsize of the condensate, chemical potential, speed of sound, number of\nparticles, etc., are deduced. It will be shown that this dipole-dipole\ninteraction implies the emergence of anisotropy, for example, in the speed of\nsound. The possible use of this anisotropy as a tool for the analyze of\ndissipative mechanisms, for instance, Landau's criterion for superfluidity,\nwill be also discussed.",
        "positive": "Analytical solutions to the spin-1 Bose-Einstein condensates: We analytically solve the one-dimensional coupled Gross-Pitaevskii equations\nwhich govern the motion of F=1 spinor Bose-Einstein condensates. The nonlinear\ndensity-density interactions are decoupled by making use of the unique\nproperties of the Jacobian elliptical functions. Several types of complex\nstationary solutions are deduced. Furthermore, exact non-stationary solutions\nto the time-dependent Gross-Pitaevskii equations are constructed by making use\nof the spin-rotational symmetry of the Hamiltonian. The spin-polarizations\nexhibit kinked configurations. Our method is applicable to other coupled\nnonlinear systems."
    },
    {
        "anchor": "Persistent current formation in double-ring geometries: Quenching an ultracold bosonic gas in a ring across the Bose-Einstein\ncondensation phase transition is known, and has been experimentally observed,\nto lead to the spontaneous emergence of persistent currents. The present work\nexamines how these phenomena generalize to a system of two experimentally\naccessible explicitly two-dimensional co-planar rings with a common interface,\nor to the related lemniscate geometry, and demonstrates an emerging\nindependence of winding numbers across the rings, which can exhibit flow both\nin the same and in opposite directions. The observed persistence of such\nfindings in the presence of dissipative coupled evolution due to the local\ncharacter of the domain formation across the phase transition and topological\nprotection of the randomly emerging winding numbers should be within current\nexperimental reach.",
        "positive": "Spin current contribution in the spectrum of collective excitations of\n  degenerate partially polarized spin-1/2 fermions at separate dynamics of\n  spin-up and spin-down fermions: The spectrum of collective excitations of degenerate partially polarized\nspin-1/2 fermions is considered. The spin-up fermions and the spin-down\nfermions are considered as different fluids. Corresponding two-fluid\nhydrodynamics consistent with a non-linear Pauli equation is suggested. An\nequation of state for the spin current caused by the distribution of particles\non different energy levels is suggested for the degenerate regime, where the\nspin current is caused by the Pauli blocking. Spectrum of three waves is found\nas a solution of the hydrodynamic equations: two sound waves and one spin wave.\nTheir spectrums are calculated for two regimes: propagation parallel and\nperpendicular to the direction of the equilibrium spin polarization."
    },
    {
        "anchor": "Two-mode Dicke model from non-degenerate polarization modes: We realize a non-degenerate two-mode Dicke model with competing interactions\nin a Bose-Einstein condensate (BEC) coupled to two orthogonal polarization\nmodes of a single optical cavity. The BEC is coupled to the cavity modes via\nthe scalar and vectorial part of the atomic polarizability. We can\nindependently change these couplings and determine their effect on a\nself-organization phase transition. Measuring the phases of the system, we\ncharacterize a crossover from a single-mode to a two-mode Dicke model. This\nwork provides perspectives for the realization of coupled phases of spin and\ndensity.",
        "positive": "Self-similar non-equilibrium dynamics of a many-body system with\n  power-law interactions: The influence of power-law interactions on the dynamics of many-body systems\nfar from equilibrium is much less explored than their effect on static and\nthermodynamic properties. To gain insight into this problem we introduce and\nanalyze here an out-of-equilibrium deposition process in which the deposition\nrate of a given particle depends as a power-law on the distance to previously\ndeposited particles. This model draws its relevance from recent experimental\nprogress in the domain of cold atomic gases which are studied in a setting\nwhere atoms that are excited to high-lying Rydberg states interact through\npower-law potentials that translate into power-law excitation rates. The\nout-of-equilibrium dynamics of this system turns out to be surprisingly rich.\nIt features a self-similar evolution which leads to a characteristic power-law\ntime dependence of observables such as the particle concentration, and results\nin a scale invariance of the structure factor. Our findings show that in\ndissipative Rydberg gases out of equilibrium the characteristic distance among\nexcitations --- often referred to as the blockade radius --- is not a static\nbut rather a dynamic quantity."
    },
    {
        "anchor": "Spinor dynamics in a mixture of spin-1 and spin-2 Bose-Einstein\n  condensates: The spinor dynamics of Bose-Einstein condensates of 87Rb atoms with hyperfine\nspins 1 and 2 were investigated. A technique of simultaneous Ramsey\ninterferometry was developed for individual control of the vectors of two spins\nwith almost the same Zeeman splittings. The mixture of spinor condensates is\ngenerated in the transversely polarized spin-1 and the longitudinally polarized\nspin-2 states. The time evolution of the spin-1 condensate exhibits dephasing\nand rephasing of the Larmor precession due to the interaction with the spin-2\ncondensate. The scattering lengths between spin-1 and -2 atoms were estimated\nby comparison with the numerical simulation using the Gross-Pitaevskii\nequation. The proposed technique is expected to facilitate the further study of\nmultiple spinor condensates.",
        "positive": "Excitation spectrum and supersolidity of a two-leg bosonic ring ladder: We consider a system of weakly interacting bosons confined on a planar double\nlattice ring subjected to two artificial gauge fields. This system is known to\ndisplay three phases, the Meissner phase where the flow of particles is carried\nat the edges of the system without transverse current, a vortex phase\ncharacterized by non-zero transverse current, and a biased-ladder phase,\ncharacterized by an imbalance of the population of the two rings. We use the\nBogoliubov approximation to determine the excitation spectrum in the three\nphases, the dynamic structure factor and the quantum fluctuation corrections to\nthe first-order correlation function. Our analysis reveals supersolid features\nas well as Josephson modes, corresponding to out-of-phase modes of the finite\nring."
    },
    {
        "anchor": "Equation of state of the one- and three-dimensional Bose-Bose gases: We calculate the equation of state of Bose-Bose gases in one and three\ndimensions in the framework of an effective quantum field theory. The\nbeyond-mean-field approximation at zero-temperature and the one-loop\nfinite-temperature results are obtained performing functional integration on a\nlocal effective action. The ultraviolet divergent zero-point quantum\nfluctuations are removed by means of dimensional regularization. We derive the\nnonlinear Schr\\\"odinger equation to describe one- and three-dimensional\nBose-Bose mixtures and solve it analytically in the one-dimensional scenario.\nThis equation supports self-trapped brightlike solitonic-droplets and\nself-trapped darklike solitons. At low temperature, we also find that the\npressure and the number of particles of symmetric quantum droplets have a\nnontrivial dependence on the chemical potential and the difference between the\nintra- and the inter-species coupling constants.",
        "positive": "Theory of non-Hermitian fermionic superfluidity on a honeycomb lattice:\n  Interplay between exceptional manifolds and van Hove Singularity: We study the non-Hermitian fermionic superfluidity subject to dissipation of\nCooper pairs on a honeycomb lattice, for which we analyze the attractive\nHubbard model with a complex-valued interaction. Remarkably, we demonstrate the\nemergence of the dissipation-induced superfluid phase that is anomalously\nenlarged by a cusp on the phase boundary. We find that this unconventional\nphase transition originates from the interplay between exceptional lines and\nvan Hove singularity, which has no counterpart in equilibrium. Moreover, we\ndemonstrate that the infinitesimal dissipation induces the nontrivial\nsuperfluid solution at the critical point. Our results can be tested in\nultracold atoms with photoassociation techniques by postselcting special\nmeasurement outcomes with the use of quantum-gas microscopy and can lead to\nunderstanding the NH many-body physics triggered by exceptional manifolds in\nopen quantum systems."
    },
    {
        "anchor": "Realizing a 1D topological gauge theory in an optically dressed BEC: Topological gauge theories describe the low-energy properties of certain\nstrongly correlated quantum systems through effective weakly interacting\nmodels. A prime example is the Chern-Simons theory of fractional quantum Hall\nstates, where anyonic excitations emerge from the coupling between weakly\ninteracting matter particles and a density-dependent gauge field. Although in\ntraditional solid-state platforms such gauge theories are only convenient\ntheoretical constructions, engineered quantum systems enable their direct\nimplementation and provide a fertile playground to investigate their\nphenomenology without the need for strong interactions. Here, we report the\nquantum simulation of a topological gauge theory by realizing a one-dimensional\nreduction of the Chern-Simons theory (the chiral BF theory) in a Bose-Einstein\ncondensate. Using the local conservation laws of the theory, we eliminate the\ngauge degrees of freedom in favour of chiral matter interactions, which we\nengineer by synthesizing optically dressed atomic states with\nmomentum-dependent scattering properties. This allows us to reveal the key\nproperties of the chiral BF theory: the formation of chiral solitons and the\nemergence of an electric field generated by the system itself. Our results\nexpand the scope of quantum simulation to topological gauge theories and open a\nroute to the implementation of analogous gauge theories in higher dimensions.",
        "positive": "Spatial emergence of Off-Diagonal Long-Range Order throughout the\n  BCS-BEC crossover: In a superfluid system, Off-Diagonal Long-Range Order (ODLRO) is expected to\nbe exhibited in the appropriate reduced density matrices when the relevant\nparticles (either bosons or fermion pairs) are considered to recede\nsufficiently far apart from each other. This concept is usually exploited to\nidentify the value of the condensate density, without explicit concern,\nhowever, on the spatial range over which this asymptotic condition can\neffectively be achieved. Here, based on a diagrammatic approach that includes\nbeyond-mean-field pairing fluctuations in the broken-symmetry phase at the\nlevel of the $t$-matrix also with the inclusion of the Gorkov-Melik-Barkhudarov\n(GMB) correction, we present a systematic study of the two-particle reduced\ndensity matrix for a superfluid fermionic system undergoing the BCS-BEC\ncrossover, when the entities to recede far apart from each other evolve with\ncontinuity from largely overlapping Cooper pairs in the BCS limit to dilute\ncomposite bosons in the BEC limit. By this approach, we not only provide the\ncoupling and temperature dependence of the condensate density at the level of\nour diagrammatic approach which includes the GMB correction, but we also obtain\nthe evolution of the spatial dependence of the two-particle reduced density\nmatrix, from a power-law at low temperature to an exponential dependence at\nhigh temperature in the superfluid phase, when the inter-particle coupling\nspans the BCS-BEC crossover. Our results put limitations on the minimum spatial\nextent of a finite-size system for which superfluid correlations can\neffectively be established."
    },
    {
        "anchor": "A Metal-Insulator transition induced by Random Dipoles: We study the localization properties of a test dipole feeling the disordered\npotential induced by dipolar impurities trapped at random positions in an\noptical lattice. This random potential is marked by correlations which are a\nconvolution of short-range and long-range ones. We show that when short-range\ncorrelations are dominant, extended states can appear in the spectrum.\nIntroducing long-range correlations, the extended states, if any, are wiped out\nand localization is restored over the whole spectrum. Moreover, long-range\ncorrelations can either increase or decrease the localization length at the\ncenter of the band, which indicates a richer behavior than previously\npredicted.",
        "positive": "Quantum metric contribution to the pair mass in spin-orbit coupled Fermi\n  superfluids: As a measure of the quantum distance between Bloch states in the Hilbert\nspace, the quantum metric was introduced to solid-state physics through the\nreal part of the so-called geometric Fubini-Study tensor, the imaginary part of\nwhich corresponds to the Berry curvature measuring the emergent gauge field in\nmomentum space. Here, we first derive the Ginzburg-Landau theory near the\ncritical superfluid transition temperature, and then identify and analyze the\ngeometric effects on the effective mass tensor of the Cooper pairs. By showing\nthat the quantum metric contribution accounts for a sizeable fraction of the\npair mass in a surprisingly large parameter regime throughout the BCS-BEC\ncrossover, we not only reveal the physical origin of its governing role in the\nsuperfluid density tensor but also hint at its plausible roles in many other\nobservables as well."
    },
    {
        "anchor": "Quantum simulation of generic spin exchange models in Floquet-engineered\n  Rydberg atom arrays: Although quantum simulation can give insight into elusive or intractable\nphysical phenomena, many quantum simulators are unavoidably limited in the\nmodels they mimic. Such is also the case for atom arrays interacting via\nRydberg states - a platform potentially capable of simulating any kind of spin\nexchange model, albeit with currently unattainable experimental capabilities.\nHere, we propose a new route towards simulating generic spin exchange\nHamiltonians in atom arrays, using Floquet engineering with both global and\nlocal control. To demonstrate the versatility and applicability of our\napproach, we numerically investigate the generation of several spin exchange\nmodels which have yet to be realized in atom arrays, using only\npreviously-demonstrated experimental capabilities. Our proposed scheme can be\nreadily explored in many existing setups, providing a path to investigate a\nlarge class of exotic quantum spin models.",
        "positive": "Dynamical Kosterlitz-Thouless Theory for Two-Dimensional Ultracold\n  Atomic Gases: In this letter we develop a theory for the first and second sound in a\ntwo-dimensional atomic superfluid across the superfluid transition based on the\ndynamic Koterlitz-Thouless theory. We employ a set of modified two-fluid\nhydrodynamic equations which incorporate the dynamics of the quantised\nvortices, rather than the conventional ones for a three-dimensional superfluid.\nAs far as the sound dispersion equation is concerned, the modification is\nessentially equivalent to replacing the static superfluid density with a\nfrequency dependent one, renormalised by the frequency dependent \"dielectric\nconstant\" of the vortices. This theory has two direct consequences. First,\nbecause the renormalised superfluid density at finite frequencies does not\ndisplay discontinuity across the superfluid transition, in contrast to the\nstatic superfluid density, the sound velocities vary smoothly across the\ntransition. Second, the theory includes dissipation due to free vortices, and\nthus naturally describes the sound-to-diffusion crossover for the second sound\nin the normal phase. With only one fitting parameter, our theory gives a\nperfect agreement with the experimental measurements of sound velocities across\nthe transition, as well as the quality factor in the vicinity of the\ntransition. The predictions from this theory can be further verified by future\nexperiments."
    },
    {
        "anchor": "Matter waves in two-dimensional arbitrary atomic crystals: We present a general scheme to realize a cold-atom quantum simulator of\nbidimensional atomic crystals. Our model is based on the use of two\nindependently trapped atomic species: the first one, subject to a strong\nin-plane confinement, constitutes a two-dimensional matter wave which interacts\nonly with atoms of the second species, deeply trapped around the nodes of a\ntwo-dimensional optical lattice. By introducing a general analytic approach we\nshow that the system Green function can be exactly determined, allowing for the\ninvestigation of the matter-wave transport properties. We propose some\nillustrative applications to both Bravais (square, triangular) and non-Bravais\n(graphene, kagom\\'e) lattices, studying both ideal periodic systems and\nexperimental-size and disordered ones. Some remarkable spectral properties of\nthese atomic artificial lattices are pointed out, such as the emergence of\nsingle and multiple gaps, flat bands, and Dirac cones. All these features can\nbe manipulated via the interspecies interaction, which proves to be widely\ntunable due to the interplay between scattering length and confinements.",
        "positive": "Quantification of the memory effect of steady-state currents from\n  interaction-induced transport in quantum systems: Dynamics of a system in general depends on its initial state and how the\nsystem is driven, but in many-body systems the memory is usually averaged out\nduring evolution. Here, interacting quantum systems without external\nrelaxations are shown to retain long-time memory effects in steady states. To\nidentify memory effects, we first show quasi-steady state currents form in\nfinite, isolated Bose and Fermi Hubbard models driven by interaction imbalance\nand they become steady-state currents in the thermodynamic limit. By comparing\nthe steady state currents from different initial states or ramping rates of the\nimbalance, long-time memory effects can be quantified. While the memory effects\nof initial states are more ubiquitous, the memory effects of switching\nprotocols are mostly visible in interaction-induced transport in lattices. Our\nsimulations suggest the systems enter a regime governed by a generalized Fick's\nlaw and memory effects lead to initial-state dependent diffusion coefficients.\nWe also identify conditions for enhancing memory effects and discuss possible\nexperimental implications."
    },
    {
        "anchor": "From a continuous to a discrete time crystal in a dissipative\n  atom-cavity system: We propose the dynamical stabilization of a nonequilibrium order in a driven\ndissipative system comprised an atomic Bose-Einstein condensate inside a high\nfinesse optical cavity, pumped with an optical standing wave operating in the\nregime of anomalous dispersion. When the amplitude of the pump field is\nmodulated close to twice the characteristic limit-cycle frequency of the\nunmodulated system, a stable subharmonic response is found. The dynamical phase\ndiagram shows that this subharmonic response occurs in a region expanded with\nrespect to that where stable limit-cycle dynamics occurs for the unmodulated\nsystem. In turning on the modulation we tune the atom-cavity system from a\ncontinuous to a discrete time crystal.",
        "positive": "Quantum Hall States in Rapidly Rotating Two-Component Bose Gases: We investigate strongly correlated phases of two-component (or\npseudo-spin-1/2) Bose gases under rapid rotation through exact diagonalization\non a torus geometry. In the case of pseudo-spin-independent contact\ninteractions, we find the formation of gapped spin-singlet states at the\nfilling factors \\nu=k/3+k/3 (k/3 filling for each component) with integer k. We\npresent numerical evidences that the gapped state with k=2 is well described as\na non-Abelian spin-singlet (NASS) state, in which excitations feature\nnon-Abelian statistics. Furthermore, we find the phase transition from the\nproduct of composite fermion states to the NASS state by changing the ratio of\nthe intercomponent to intracomponent interactions."
    },
    {
        "anchor": "From few to many body degrees of freedom: Here, I focus on the use of microscopic, few-body techniques that are\nrelevant in the many-body problem. These methods can be divided into indirect\nand direct. In particular, indirect methods are concerned with the\nsimplification of the many-body problem by substituting the full, microscopic\ninteractions by pseudopotentials which are designed to reproduce collisional\ninformation at specified energies, or binding energies in the few-body sector.\nThese simplified interactions yield more tractable theories of the many-body\nproblem, and are equivalent to effective field theory of interactions. Direct\nmethods, which so far are most useful in one spatial dimension, have the goal\nof attacking the many-body problem at once by using few-body information only.\nHere, I will present non-perturbative direct methods to study one-dimensional\nfermionic and bosonic gases in one dimension.",
        "positive": "Perspectives of optical lattices with state-dependent tunneling in\n  approaching quantum magnetism in the presence of the external harmonic\n  trapping potential: We study theoretically potential advantages of two-component mixtures in\noptical lattices with state-dependent tunneling for approaching\nlong-range-order phases and detecting easy-axis antiferromagnetic correlations.\nWhile we do not find additional advantages of mixtures with large hopping\nimbalance for approaching quantum magnetism in a harmonic trap, it is shown\nthat a nonzero difference in hopping amplitudes remains highly important for a\nproper symmetry breaking in the pseudospin space for the single-site-resolution\nimaging and can be advantageously used for a significant increase of the\nsignal-to-noise ratio and thus detecting long-range easy-axis antiferromagnetic\ncorrelations in the corresponding experiments."
    },
    {
        "anchor": "Optical Kagome lattice for ultra-cold atoms with nearest neighbor\n  interactions: We propose a scheme to implement an optical Kagome lattice for ultra-cold\natoms with controllable s-wave interactions between nearest neighbor sites and\na gauge potential. The atoms occupy three different internal atomic levels with\nelectromagnetically-induced coupling between the levels. We show that by\nappropriately shifting the triangular lattice potentials, experienced by atoms\nin different levels, the Kagome lattice can be realized using only two standing\nwaves, generating a highly frustrated quantum system for the atoms.",
        "positive": "Exact temporal evolution of the two-species Bose-Einstein condensates: We construct exact stationary solutions to the one-dimensional coupled\nGross-Pitaevskii equations for the two-species Bose-Einstein condensates with\nequal intraspecies and interspecies interaction constants. Three types of\ncomplex solutions as well as their soliton limits are derived. By making use of\nthe SU(2) unitary symmetry, we further obtain analytical time-evolving\nsolutions. These solutions exhibit spatiotemporal periodicity."
    },
    {
        "anchor": "Tunable Landau-Zener transitions in a spin-orbit coupled Bose-Einstein\n  condensate: The Landau-Zener (LZ) transition is one of the most fundamental phenomena in\nquantum dynamics. It describes nonadiabatic transitions between quantum states\nnear an avoided crossing that can occur in diverse physical systems. Here we\nreport experimental measurements and tuning of LZ transitions between the\ndressed eigenlevels of a Bose-Einstein condensate (BEC) that is synthetically\nspin-orbit (SO) coupled. We measure the transition probability as the BEC is\naccelerated through the SO avoided crossing and study its dependence on the\ncoupling between the diabatic (bare) states, eigenlevel slope, and eigenstate\nvelocity--the three parameters of the LZ model that are independently\ncontrolled in our experiments. Furthermore, we performed time-resolved\nmeasurements to demonstrate the breaking down of the spin-momentum locking of\nthe spin-orbit-coupled BEC in the nonadiabatic regime, and we determined the\ndiabatic switching time of the LZ transitions. Our observations show\nquantitative agreement with the LZ model and numerical simulations of the\nquantum dynamics in the quasimomentum space. The tunable LZ transition may be\nexploited to enable a spin-dependent atomtronic transistor.",
        "positive": "Field theory of low energy excitations of a mixture of two species of\n  pseudospin-1/2 Bose gases with interspecies spin-exchange: We develop a low energy effective field theory of a mixture of two species of\npseudospin-1/2 atoms with interspecies spin-exchange, in addition to\ndensity-density interaction. This approach is beyond the single orbital-mode\napproximation. In a wide parameter regime, it indicates the existence of the\nfour elementary excitations, especially a gapped mode due to interspecies\nspin-exchange. On the other hand, the spectrum of the effective spin\nHamiltonian yielded by the single mode approximation can be obtained by\nquantizing the homogeneous excitation, which is spin excitation and is the\nlong-wavelength limit of the gapped mode of elementary excitations. These low\nenergy excitations can be experimentally measured by using Bragg spectroscopy."
    },
    {
        "anchor": "Itinerant ferromagnetism of a dipolar Fermi gas with Raman-induced\n  spin-orbit coupling: We elucidate the itinerant ferromagnetism of a dipolar Fermi gas with a\nRaman-induced spin-orbit coupling by investigating the exotic phase diagrams at\nzero and finite temperature. It is revealed that the dipolar interaction along\nwith spin-orbit coupling can corroborate the formation of ferromagnetism and\nthe Raman coupling adversely eliminates the tendency to this ferromagnetism\ntransition, which greatly transcends the general understanding of this subject\nwith contact interaction only. We explore the ground states through the density\nand spin-flip distribution in momentum space, which exhibits novel degeneracy\nat strong Raman coupling indicated by a non-zero entropy at zero temperature.\nWe calculate the transition temperatures well within the reach of an\nexperimental system when altering the dipolar and spin-orbit coupling strength,\nwhich paves a way to the further experimental realization.",
        "positive": "Quantum dark soliton (qubits) in Bose Einstein condensates: We study the possibility of using dark soliton in quasi one dimensional Bose\nEinstein condensates to produce two level system (qubits) by exploiting the\nintrinsic nonlinear and the coherent nature of the matter waves. We calculate\nthe soliton spectrum and the conditions for a qubit to exist. We also compute\nthe coupling between the phonons and the soliton and investigate the emission\nrate of the qubits in that case. Remarkably, the qubit lifetime is estimated to\nbe of the order of a few seconds, being by the dark soliton \"death\" due to\nquantum evaporation."
    },
    {
        "anchor": "Josephson oscillations and self-trapping of superfluid fermions in a\n  double-well potential: We investigate the behaviour of a two-component Fermi superfluid in a\ndouble-well potential. We numerically solve the time dependent Bogoliubov-de\nGennes equations and characterize the regimes of Josephson oscillations and\nself-trapping for different potential barriers and initial conditions. In the\nweak link limit the results agree with a two-mode model where the relative\npopulation and the phase difference between the two wells obey coupled\nnonlinear Josephson equations. A more complex dynamics is predicted for large\namplitude oscillations and large tunneling.",
        "positive": "Magnetic-field dependent trap loss of ultracold metastable helium: We have experimentally studied the magnetic-field dependence of the decay of\na Bose-Einstein condensate of metastable 4He atoms confined in an optical\ndipole trap, for atoms in the m=+1 and m=-1 magnetic substates, and up to 450\nG. Our measurements confirm long-standing calculations of the two-body loss\nrate coefficient that show an increase above 50 G. We demonstrate that for m=-1\natoms, decay is due to three-body recombination only, with a three-body loss\nrate coefficient of 6.5(0.4)(0.6)10^(-27)cm^6s^(-1), which is interesting in\nthe context of universal few-body theory. We have also searched for a\nrecently-predicted d-wave Feshbach resonance, but did not observe it."
    },
    {
        "anchor": "Spinor atom-molecule conversion via laser-induced three-body\n  recombination: We study theoretically several aspects of the dynamics of coherent\natom-molecule conversion in spin-1 Bose-Einstein condensates. Specifically, we\ndiscuss how for a suitable dark-state condition the interplay of spin-exchange\ncollisions and photoassociation leads to the stable creation of an atom-\nmolecule pairs from three initial spin-zero atoms. This process involves two\ntwo-body interactions and can be intuitively viewed as an effective three-body\nrecombination. We investigate the relative roles of photoassociation and of the\ninitial magnetization in the \\resonant\" case where the dark state condition is\nperfectly satisfied. We also consider the \"non-resonant\" regime, where that\ncondition is satisfied either approximately {the so-called adiabatic case {or\nnot at all. In the adiabatic case, we derive an effective non-rigid pendulum\nmodel that allows one to conveniently discuss the onset of an antiferromagnetic\ninstability of an \\atom-molecule pendulum,\" as well as large-amplitude pair\noscillations and atom-molecule entanglement.",
        "positive": "Topological two-body bound states in the interacting Haldane model: We study the topological properties of the two-body bound states in an\ninteracting Haldane model as a function of interparticle interactions. In\nparticular, we identify topological phases where the two-body edge states have\neither the same or the opposite chirality as compared to single-particle edge\nstates. We highlight that in the moderately interacting regime, which is\nrelevant for the experimental realization with ultracold atoms, the topological\ntransition is affected by the internal structure of the bound state, and the\nphase boundaries are consequently deformed."
    },
    {
        "anchor": "Vortex and soliton dynamics in particle-hole symmetric superfluids: We propose to induce topological defects in particle-hole symmetric\nsuperfluids, with the prime example of the BCS state of ultracold atoms and\ndetect their time evolution and decay. We demonstrate that the time evolution\nis qualitatively distinct for particle-hole symmetric superfluids, and point\nout that the dynamics of topological defects is strongly modified in\nparticle-hole symmetric fluids. We obtain results for different charges and\ncompare them with the standard Gross-Pitaevskii prediction for Bose-Einstein\ncondensates. We highlight the observable signatures of the particle-hole\nsymmetry in the dynamics of decaying solitons and subsequent vortices.",
        "positive": "NOON states with ultracold bosonic atoms via resonance- and\n  chaos-assisted tunneling: We theoretically investigate the generation of microscopic atomic NOON\nstates, corresponding to the coherent |N,0> + |0,N> superposition with N ~ 5\nparticles, via collective tunneling of interacting ultracold bosonic atoms\nwithin a symmetric double-well potential in the self-trapping regime. We show\nthat a periodic driving of the double well with suitably tuned amplitude and\nfrequency parameters allows one to substantially boost this tunneling process\nwithout altering its collective character. The time scale to generate the NOON\nsuperposition, which corresponds to half the tunneling time and would be\nprohibitively large in the undriven double well for the considered atomic\npopulations, can thereby be drastically reduced, which renders the realization\nof NOON states through this protocol experimentally feasible. Resonance- and\nchaos-assisted tunneling are identified as key mechanisms in this context. A\nquantitative semiclassical evaluation of their impact onto the collective\ntunneling process allows one to determine the optimal choice for the driving\nparameters in order to generate those NOON states as fast as possible."
    },
    {
        "anchor": "Quantum Information Approach to Rotating Bose-Einstein Condensate: We investigate the 2D weakly interacting Bose-Einstein condensate in a\nrotating trap by the tools of quantum information theory. The critical\nexponents of the ground state fidelity susceptibility and the correlation\nlength of the system are obtained for the quantum phase transition when the\nfrst vortex is formed. We also find the single-particle entanglement can be an\nindicator of the angular momentums for some real ground states. The\nsingle-particle entanglement of fractional quantum Hall states such as Laughlin\nstate and Pfaffian state is also studied.",
        "positive": "Low-momentum interactions for ultracold Fermi gases: We consider a two-component Fermi gas with a contact interaction from the BCS\nregime to the unitary limit. Starting from the idea that many-body effects\nshould not depend on short-distance or high-momentum physics which is encoded\nin the s-wave scattering length, but only on momentum scales of the order of\nthe Fermi momentum, we build effective low-momentum interactions that reproduce\nthe scattering phase shifts of the contact interaction below some momentum\ncutoff. Inspired from recent successes of this method in nuclear structure\ntheory, we use these interactions to describe the equation of state of the\nFermi gas in the framework of Hartree-Fock-Bogliubov theory with perturbative\ncorrections. In the BCS regime, there is a range of cutoffs where we obtain\nfully converged results. Near unitarity, convergence is not yet reached, but we\nobtain promising results for the ground-state energies close to the\nexperimental ones. Limitations and possible extensions of the approach are\ndiscussed."
    },
    {
        "anchor": "Paired Superfluidity and Fractionalized Vortices in Spin-orbit Coupled\n  Bosons: In this letter we study finite temperature properties of spin-1/2 interacting\nbosons with spin-orbit coupling in two dimensions. When the ground state has\nstripe order, we show that thermal fluctuations will first melt the stripe\norder and lead to a superfluid of boson pairs if the spin-orbit coupling is\nisotropic or nearly isotropic. Such a phase supports fractionalized quantum\nvortices. The Kosterlize-Thouless transition from superfluid to normal state is\ndriven by proliferation of half vortices. When the ground state is a plane wave\nstate, the transition to normal state is driven by conventional\nKosterlize-Thouless transition. However, the critical temperature will drop to\nzero for isotropic spin-orbit coupling.",
        "positive": "\"Polar\" and \"antiferromagnetic\" order in f=1 many-boson systems: In a system of interacting f=1 bosons (in the subspace where the total spin\nin the z-direction is vanishing), we prove inequalities for the ground state\nexpectation value of the density of spin-0 bosons. The inequalities imply that\nthe ground state possesses \"polar\" or \"antiferromagnetic\" order when the\nquadratic Zeeman term q is large enough. In the low density limit, the\ninequalities establish the existence of a sharp transition at q=0 when q is\nvaried."
    },
    {
        "anchor": "Dynamics of exciton-polaritons in a Josephson double dimer: We study the dynamics of exciton-polaritons in a double-well configuration.\nThe system consists of two weakly coupled Bose-Josephson junctions, each\ncorresponding to a different circular polarization of the polaritons, forming a\n{\\it Josephson double dimer}. We show that the Josephson oscillation between\nthe wells is strongly coupled to the polarization rotation and that\nconsequently Josephson excitation is periodically exchanged between the two\npolarizations. Linearized analysis agrees well with numerical simulations using\ntypical experimental parameters.",
        "positive": "Nonlinear Excitations, Stability Inversions and Dissipative Dynamics in\n  Quasi-one-dimensional Polariton Condensates: We consider the existence, stability and dynamics of the ground state and\nnonlinear excitations, in the form of dark solitons, for a\nquasi-one-dimensional polariton condensate in the presence of pumping and\nnonlinear damping. We find a series of remarkable features that can be directly\ncontrasted to the case of the typically energy-conserving ultracold alkali-atom\nBose-Einstein condensates. For some sizeable parameter ranges, the nodeless\n(\"ground\") state becomes {\\it unstable} towards the formation of {\\em stable}\nnonlinear single or {\\em multi} dark-soliton excitations. It is also observed\nthat for suitable parametric choices, the instability of single dark solitons\ncan nucleate multi-dark-soliton states. Also, for other parametric regions,\n{\\em stable asymmetric} sawtooth-like solutions exist. Finally, we consider the\ndragging of a defect through the condensate and the interference of two\ninitially separated condensates, both of which are capable of nucleating dark\nmulti-soliton dynamical states."
    },
    {
        "anchor": "Superfluidity of Dirac Fermions in a Tunable Honeycomb Lattice: Cooper\n  Pairing, Collective Modes, and Critical Currents: Motivated by recent experiments on atomic Dirac fermions in a tunable\nhoneycomb optical lattice, we study the attractive Hubbard model of\nsuperfluidity in the anisotropic honeycomb lattice. At weak-coupling, we find\nthat the maximum mean field pairing transition temperature, as a function of\ndensity and interaction strength, occurs for the case with isotropic hopping\namplitudes. In this isotropic case, we go beyond mean field theory and study\ncollective fluctuations, treating both pairing and density fluctuations for\ninteraction strengths ranging from weak to strong coupling. We find evidence\nfor a sharp sound mode, together with a well-defined Leggett mode over a wide\nregion of the phase diagram. We also calculate the superfluid order parameter\nand collective modes in the presence of nonzero superfluid flow. The\nflow-induced softening of these collective modes leads to dynamical\ninstabilities involving stripe-like density modulations as well as a\nLeggett-mode instability associated with the natural sublattice symmetry\nbreaking charge-ordered state on the honeycomb lattice. The latter provides a\nnon-trivial test for the experimental realization of the one-band Hubbard\nmodel. We delineate regimes of the phase diagram where the critical current is\nlimited by depairing or by such collective instabilities, and discuss\nexperimental implications of our results.",
        "positive": "Mott-insulator state of cold atoms in tilted optical lattices: doublon\n  dynamics and multi-level Landau-Zener tunneling: We discuss the dynamical response of strongly interacting Bose atoms in an\nadiabatically tilted optical lattice. The analysis is performed in terms of the\nmulti-level Landau-Zenner tunneling. Different regimes of tunneling are\nidentified and analytical expressions for the doublon number, which is the\nquantity measured in laboratory experiments, are derived."
    },
    {
        "anchor": "Density functional theory versus quantum Monte Carlo simulations of\n  Fermi gases in the optical-lattice arena: We benchmark the ground state energies and the density profiles of atomic\nrepulsive Fermi gases in optical lattices computed via Density Functional\nTheory (DFT) against the results of diffusion Monte Carlo (DMC) simulations.\nThe main focus is on a half-filled one-dimensional optical lattices, for which\nthe DMC simulations performed within the fixed-node approach provide unbiased\nresults. This allows us to demonstrate that the local spin-density\napproximation (LSDA) to the exchange-correlation functional of DFT is very\naccurate in the weak and intermediate interactions regime, and also to\nunderline its limitations close to the strongly-interacting Tonks-Girardeau\nlimit and in very deep optical lattices. We also consider a three dimensional\noptical lattice at quarter filling, showing also in this case the high accuracy\nof the LSDA in the moderate interaction regime. The one-dimensional data\nprovided in this study may represent a useful benchmark to further develop DFT\nmethods beyond the LSDA and they will hopefully motivate experimental studies\nto accurately measure the equation of state of Fermi gases in\nhigher-dimensional geometries.",
        "positive": "Synthetic 3D Spin-Orbit Coupling: We describe a method for creating a three-dimensional analogue to Rashba\nspin-orbit coupling in systems of ultracold atoms. This laser induced coupling\nuses Raman transitions to link four internal atomic states with a tetrahedral\ngeometry, and gives rise to a Dirac point that is robust against environmental\nperturbations. We present an exact result showing that such a spin-orbit\ncoupling in a fermionic system always rise to a molecular bound state."
    },
    {
        "anchor": "Observation of photon droplets and their dynamics: We present experimental evidence of photon droplets in an attractive\n(focusing) nonlocal nonlinear medium. Photon droplets are self-bound,\nfinite-sized states of light that are robust to size and shape perturbations\ndue to a balance of competing attractive and repulsive forces. It has recently\nbeen shown theoretically, via a multipole expansion of the nonlocal\nnonlinearity, that the self-bound state arises due to competition between the\ns-wave and d-wave nonlinear terms, together with diffraction. The theoretical\nphoton droplet framework encompasses both a soliton-like stationary ground\nstate and the non-soliton-like dynamics that ensue when the system is displaced\nfrom equilibrium, i.e. driven into an excited state. We present numerics and\nexperiments supporting the existence of these photon droplet states and\nmeasurements of the dynamical evolution of the photon droplet orbital angular\nmomentum.",
        "positive": "Simulating quantum transport for a quasi-one-dimensional Bose gas in an\n  optical lattice: the choice of fluctuation modes in the truncated Wigner\n  approximation: We study the effect of quantum fluctuations on the dynamics of a\nquasi-one-dimensional Bose gas in an optical lattice at zero-temperature using\nthe truncated Wigner approximation with a variety of basis sets for the initial\nfluctuation modes. The initial spatial distributions of the quantum\nfluctuations are very different when using a limited number of plane-wave (PW),\nsimple-harmonic-oscillator (SHO) and self-consistently determined Bogoliubov\n(SCB) modes. The short-time transport properties of the Bose gas, characterized\nby the phase coherence in the PW basis are distinct from those gained using the\nSHO and SCB basis. The calculations using the SCB modes predict greater phase\ndecoherence and stronger number fluctuations than the other choices.\nFurthermore, we observe that the use of PW modes overestimates the extent to\nwhich atoms are expelled from the core of the cloud, while the use of the other\nmodes only breaks the cloud structure slightly which is in agreement with the\nexperimental observations [1]."
    },
    {
        "anchor": "Superfluidity and spin superfluidity in spinor Bose gases: We show that spinor Bose gases subject to a quadratic Zeeman effect exhibit\ncoexisting superfluidity and spin superfluidity, and study the interplay\nbetween these two distinct types of superfluidity. To illustrate that the basic\nprinciples governing these two types of superfluidity are the same, we describe\nthe magnetization and particle-density dynamics in a single hydrodynamic\nframework. In this description spin and mass supercurrents are driven by their\nrespective chemical potential gradients. As an application, we propose an\nexperimentally accessible stationary state, where the two types of\nsupercurrents counterflow and cancel each other, thus resulting in no mass\ntransport. Furthermore, we propose a straightforward setup to probe spin\nsuperfluidity by measuring the in-plane magnetization angle of the whole cloud\nof atoms. We verify the robustness of these findings by evaluating the\nfour-magnon collision time, and find that the time scale for coherent\n(superfluid) dynamics is separated from that of the slower incoherent dynamics\nby one order of magnitude. Comparing the atom and magnon kinetics reveals that\nwhile the former can be hydrodynamic, the latter is typically collisionless\nunder most experimental conditions. This implies that, while our\nzero-temperature hydrodynamic equations are a valid description of spin\ntransport in Bose gases, a hydrodynamic description that treats both mass and\nspin transport at finite temperatures may not be readily feasible.",
        "positive": "Spontaneous generation of quantum turbulence through the decay of a\n  giant vortex in a two-dimensional superfluid: We show the generation of two-dimensional quantum turbulence through\nsimulations of a giant vortex decay in a trapped Bose-Einstein condensate.\nWhile evaluating the incompressible kinetic energy spectra of the quantum fluid\ndescribed by the Gross-Pitaevskii equation, a bilinear form in a log-log plot\nis verified. A characteristic scaling behavior for small momenta shows\nresemblance to the Kolmogorov $k^{-5/3}$ law, while for large momenta it\nreassures the universal behavior of the core-size $k^{-3}$ power-law. This\nindicates a mechanism of energy transportation consistent with an inverse\ncascade. The feasibility of the described physical system with the currently\navailable experimental techniques to create giant vortices opens up a new route\nto explore quantum turbulence."
    },
    {
        "anchor": "Crossing the superfluid-supersolid transition of an elongated dipolar\n  condensate: We provide a theoretical characterization of the dynamical crossing of the\nsuperfluid-supersolid phase transition for a dipolar condensate confined in an\nelongated trap, as observed in the recent experiment by G. Biagioni et al.\n[Phys. Rev. X 12, 021019 (2022)]. By means of the extended Gross-Pitaevskii\ntheory, which includes the Lee-Huang-Yang quantum fluctuation correction, we\nfirst analyze the ground state configurations of the system as a function of\nthe interparticle scattering length, for both trap configurations employed in\nthe experiment. Then, we discuss the effects of the ramp velocity, by which the\nscattering length is tuned across the transition, on the collective excitations\nof the system in both the superfluid and supersolid phases. We find that, when\nthe transverse confinement is sufficiently strong and the transition has a\nsmooth (continuous) character, the system essentially displays a (quasi) 1D\nbehavior, its excitation dynamics being dominated by the axial breathing modes.\nInstead, for shallower transverse trapping, when the transition becomes\ndiscontinuous, the collective excitations of the supersolid display a coupling\nwith the transverse modes, signalling the onset of a dimensional crossover.",
        "positive": "Suppressing and restoring the Dicke superradiance transition by\n  dephasing and decay: We show that dephasing of individual atoms destroys the superradiance\ntransition of the Dicke model, but that adding individual decay toward the spin\ndown state can restore this transition. To demonstrate this, we present a\nmethod to give an exact solution for the $N$ atom problem with individual\ndephasing which scales polynomially with $N$. By comparing finite size scaling\nof our exact solution to a cumulant expansion, we confirm the destruction and\nrestoration of the superradiance transition holds in the thermodynamic limit."
    },
    {
        "anchor": "Core filling and snaking instability of dark solitons in spin-imbalanced\n  superfluid Fermi gases: We use the time-dependent Bogoliubov de Gennes equations to study dark\nsolitons in three-dimensional spin-imbalanced superfluid Fermi gases. We\nexplore how the shape and dynamics of dark solitons are altered by the presence\nof excess unpaired spins which fill their low-density core. The unpaired\nparticles broaden the solitons and suppress the transverse snake instability.\nWe discuss ways of observing these phenomena in cold atom experiments.",
        "positive": "Comparing models for the ground state energy of a trapped\n  one-dimensional Fermi gas with a single impurity: We discuss the local density approximation approach to calculating the ground\nstate energy of a one-dimensional Fermi gas containing a single impurity, and\ncompare the results with exact numerical values that we have for up to 11\nparticles for general interaction strengths and up to 30 particles in the\nstrongly interacting case. We also calculate the contact coefficient in the\nstrongly interacting regime. The different theoretical predictions are compared\nto recent experimental results with few-atom systems. Firstly, we find that the\nlocal density approximation suffers from great ambiguity in the few-atom\nregime, yet it works surprisingly well for some models. Secondly, we find that\nthe strong interaction theories quickly break down when the number of particles\nincrease or the interaction strength decreases."
    },
    {
        "anchor": "Collective excitation of bosonic quantum Hall state: The recent developments in the theory of rapidly rotating Bose atoms have\nbeen reviewed in this article. Rotation leads to the development of\nquantized-vortices, that cluster into a vortex array, exactly to how superfluid\nhelium behaves. Theoretically, a number of strongly correlated phases are\nprojected to exist in this domain, which might be thought of as bosonic\ncounterparts of fractional quantum Hall effect (FQHE). It is now possible for\nbosons associating with a short-range interaction to exhibit a FQHE, because\nthe system of neutral bosons in a fast rotating atomic trap is analogous to\ncharged bosons placed in a fictitious magnetic field. The neutral collective\nspin-conserving and spin-flip excitation for the rotating ultra-cold dilute\nBose atoms in the FQHE domain are being discussed. We have introduced a\nrealistic interaction between the Bose particles together with long-range\ninteraction and presented a short review article about various fractional\nquantum Hall states and their spin conserving and spin reversed collective\nmodes.",
        "positive": "Heuristic machinery for thermodynamic studies of SU(N) fermions with\n  neural networks: The power of machine learning (ML) provides the possibility of analyzing\nexperimental measurements with an unprecedented sensitivity. However, it still\nremains challenging to probe the subtle effects directly related to physical\nobservables and to understand physics behind from ordinary experimental data\nusing ML. Here, we introduce a heuristic machinery by using machine learning\nanalysis. We use our machinery to guide the thermodynamic studies in the\ndensity profile of ultracold fermions interacting within SU($N$) spin symmetry\nprepared in a quantum simulator. Although such spin symmetry should manifest\nitself in a many-body wavefuction, it is elusive how the momentum distribution\nof fermions, the most ordinary measurement, reveals the effect of spin\nsymmetry. Using a fully trained convolutional neural network (NN) with a\nremarkably high accuracy of $\\sim$94$\\%$ for detection of the spin\nmultiplicity, we investigate how the accuracy depends on various\nless-pronounced effects with filtered experimental images. Guided by our\nmachinery, we directly measure a thermodynamic compressibility from density\nfluctuations within the single image. Our machine learning framework shows a\npotential to validate theoretical descriptions of SU($N$) Fermi liquids, and to\nidentify less-pronounced effects even for highly complex quantum matter with\nminimal prior understanding."
    },
    {
        "anchor": "Collective Excitations of a One-Dimensional Quantum Droplet: We calculate the excitation spectrum of a one-dimensional self-bound quantum\ndroplet in a two-component bosonic mixture described by the Gross-Pitaevskii\nequation (GPE) with cubic and quadratic nonlinearities. The cubic term\noriginates from the mean-field energy of the mixture proportional to the\neffective coupling constant $\\delta g$, whereas the quadratic nonlinearity\ncorresponds to the attractive beyond-mean-field contribution. The droplet\nproperties are governed by a control parameter $\\gamma\\propto \\delta g\nN^{2/3}$, where $N$ is the particle number. For large $\\gamma>0$ the droplet\nfeatures the flat-top shape with the discrete part of its spectrum consisting\nof plane-wave Bogoliubov phonons propagating through the flat-density bulk and\nreflected by edges of the droplet. With decreasing $\\gamma$ these modes cross\ninto the continuum, sequentially crossing the particle-emission threshold at\nspecific critical values. A notable exception is the breathing mode which we\nfind to be always bound. The balance point $\\gamma = 0$ provides implementation\nof a system governed by the GPE with an unusual quadratic nonlinearity. This\ncase is characterized by the ratio of the breathing-mode frequency to the\nparticle-emission threshold equal to 0.8904. As $\\gamma$ tends to $-\\infty$\nthis ratio tends to 1 and the droplet transforms into the soliton solution of\nthe integrable cubic GPE.",
        "positive": "Optically trapped quasi-two-dimensional Bose gases in random\n  environment: quantum fluctuations and superfluid density: We investigate a dilute Bose gas confined in a tight one-dimensional (1D)\noptical lattice plus a superimposed random potential at zero temperature.\nAccordingly, the ground state energy, quantum depletion and superfluid density\nare calculated. The presence of the lattice introduces a crossover to the\nquasi-2D regime, where we analyze asymptotically the 2D behavior of the system,\nparticularly the effects of disorder. We thereby offer an analytical expression\nfor the ground state energy of a purely 2D Bose gas in a random potential. The\nobtained disorder-induced normal fluid density $n_n$ and quantum depletion\n$n_d$ both exhibit a characteristic $1/\\ln\\left(1/n_{2D}a_{2D}^{2}\\right)$\ndependence. Their ratio $n_n/n_d$ increases to $2$ compared to the familiar\n$4/3$ in lattice-free 3D geometry, signifying a more pronounced contrast\nbetween superfluidity and Bose-Einstein condensation in low dimensions.\nConditions for possible experimental realization of our scenario are also\nproposed."
    },
    {
        "anchor": "Lattice model parameters for ultracold nonreactive molecules: chaotic\n  scattering and its limitations: We calculate the parameters of the recently-derived many-channel Hubbard\nmodel that is predicted to describe ultracold nonreactive molecules in an\noptical lattice, going beyond the approximations used in Do\\c{c}aj \\textit{et\nal.}~[Phys. Rev. Lett. \\textbf{116}, 135301 (2016)]. Although those\napproximations are expected to capture the qualitative structure of the model\nparameters, finer details and quantitative values are less certain. To set\nexpectations for experiments, whose results depend on the model parameters, we\ndescribe the approximations' regime of validity and the likelihood that\nexperiments will be in this regime, discuss the impact that the failure of\nthese approximations would have on the predicted model, and develop theories\ngoing beyond these approximations. Not only is it necessary to know the model\nparameters in order to describe experiments, but the connection that we\nelucidate between these parameters and the underlying assumptions that are used\nto derive them will allow molecule experiments to probe new physics. For\nexample, transition state theory, which is used across chemistry and chemical\nphysics, plays a key role in our determination of lattice parameters, thus\nconnecting its physical assumptions to highly accurate experimental\ninvestigation.",
        "positive": "Probing spin correlations in a Bose-Einstein condensate near the single\n  atom level: Using parametric conversion induced by a Shapiro-type resonance, we produce\nand characterize a two-mode squeezed vacuum state in a sodium spin 1\nBose-Einstein condensate. Spin-changing collisions generate correlated pairs of\natoms in the $m=\\pm 1$ Zeeman states out of a condensate with initially all\natoms in $m=0$. A novel fluorescence imaging technique with sensitivity $\\Delta\nN \\sim 1.6$ atom enables us to demonstrate the role of quantum fluctuations in\nthe initial dynamics and to characterize the full distribution of the final\nstate. Assuming that all atoms share the same spatial wave function, we infer a\nsqueezing parameter of 15.3\\,dB."
    },
    {
        "anchor": "A unified theory of strong coupling Bose polarons: From repulsive\n  polarons to non-Gaussian many-body bound states: We address the Bose polaron problem of a mobile impurity interacting strongly\nwith a host Bose-Einstein condensate (BEC) through a Feshbach resonance. On the\nrepulsive side at strong couplings, theoretical approaches predict two distinct\npolaron branches corresponding to attractive and repulsive polarons, but it\nremains unclear how the two are related. This is partly due to the challenges\nresulting from a competition of strongly attractive (destabilizing)\nimpurity-boson interactions with weakly repulsive (stabilizing) boson-boson\ninteractions, whose interplay is difficult to describe with contemporary\ntheoretical methods. Here we develop a powerful variational framework that\ncombines Gaussian correlations among impurity-boson scattering states,\nincluding up to an infinite number of bosonic excitations, with exact\nnon-Gaussian correlations among bosons occupying an impurity-boson bound state.\nThis variational scheme enables a full treatment of strong nonlinearities\narising in the Feshbach molecule on the repulsive side of the resonance. Within\nthis framework, we demonstrate that the interplay of impurity-induced\ninstability and stabilization by repulsive boson-boson interactions results in\na discrete set of metastable many-body bound states at intermediate energies\nbetween the attractive and repulsive polaron branches. These states exhibit\nstrong quantum statistical characteristics in the form of non-Gaussian quantum\ncorrelations, requiring non-perturbative beyond mean-field treatments for their\ncharacterization. Furthermore, these many-body bound states have sizable\nmolecular spectral weights, accessible via molecular spectroscopy techniques.\nThis work provides a unified theory of attractive and repulsive Bose polarons\non the repulsive side of the Feshbach resonance.",
        "positive": "Emergent Orbital Skyrmion Lattice in a Triangular Atom Array: Multi-orbital optical lattices have been attracting rapidly growing research\ninterests in the last several years, providing fascinating opportunities for\norbital-based quantum simulations. Here, we consider bosonic atoms loaded in\nthe degenerate $p$-orbital bands of a two-dimensional triangular optical\nlattice. This system is described by a multi-orbital Bose-Hubbard model. We\nfind the confined atoms in this system develop spontaneous orbital\npolarization, which forms a chiral Skyrmion lattice pattern in a large regime\nof the phase diagram. This is in contrast to its spin analogue which largely\nrequires spin-orbit couplings. The emergence of the Skyrmion lattice is\nconfirmed in both bosonic dynamical mean-field theory (BDMFT) and exact\ndiagonalization (ED) calculations. By analyzing the quantum tunneling induced\norbital-exchange interaction in the strong interaction limit, we find the\nSkyrmion lattice state arises due to the interplay of $p$-orbital symmetry and\nthe geometric frustration of the triangular lattice. We provide experimental\nconsequences of the orbital Skyrmion state, that can be readily tested in cold\natom experiments. Our study implies orbital-based quantum simulations could\nbring exotic scenarios unexpected from their spin analogue."
    },
    {
        "anchor": "Ginzburg-Landau Theory for the Jaynes-Cummings-Hubbard Model: We develop a Ginzburg-Landau theory for the Jaynes-Cummings-Hubbard model\nwhich effectively describes both static and dynamic properties of photons\nevolving in a cubic lattice of cavities, each filled with a two-level atom. To\nthis end we calculate the effective action to first-order in the hopping\nparameter. Within a Landau description of a spatially and temporally constant\norder parameter we calculate the finite-temperature mean-field quantum phase\nboundary between a Mott insulating and a superfluid phase of polaritons.\nFurthermore, within the Ginzburg-Landau description of a spatio-temporal\nvarying order parameter we determine the excitation spectra in both phases and,\nin particular, the sound velocity of light in the superfluid phase.",
        "positive": "Synthetic dissipation and cascade fluxes in a turbulent quantum gas: Scale-invariant fluxes are the defining property of turbulent cascades, but\ntheir direct measurement is a notorious problem. Here we perform such a\nmeasurement for a direct energy cascade in a turbulent quantum gas. Using a\ntime-periodic force, we inject energy at a large lengthscale and generate a\ncascade in a uniformly-trapped Bose gas. The adjustable trap depth provides a\nhigh-momentum cutoff $k_{\\textrm{D}}$, which realises a synthetic dissipation\nscale. This gives us direct access to the particle flux across a momentum shell\nof radius $k_{\\textrm{D}}$, and the tunability of $k_{\\textrm{D}}$ allows for a\nclear demonstration of the zeroth law of turbulence: we observe that for fixed\nforcing the particle flux vanishes as $k_{\\textrm{D}}^{-2}$ in the\ndissipationless limit $k_{\\textrm{D}}\\rightarrow \\infty$, while the energy flux\nis independent of $k_{\\textrm{D}}$. Moreover, our time-resolved measurements\ngive unique access to the pre-steady-state dynamics, when the cascade front\npropagates in momentum space."
    },
    {
        "anchor": "Beyond standard two-mode dynamics in Bosonic Josephson junctions: We examine the dynamics of a Bose-Einstein condensate in a symmetric\ndouble-well potential for a broad range of non-linear couplings. We demonstrate\nthe existence of a region, beyond those of Josephson oscillations and\nself-trapping, which involves the dynamical excitation of the third mode of the\ndouble-well potential. We develop a simple semiclassical model for the coupling\nbetween the second and third modes that describes very satisfactorily the full\ntime-dependent dynamics. Experimental conditions are proposed to probe this\nphenomenon.",
        "positive": "Activity-induced ferromagnetism in one-dimensional quantum many-body\n  systems: We study a non-Hermitian quantum many-body model in one dimension analogous\nto the Vicsek model or active spin models, and investigate its quantum phase\ntransitions. The model consists of two-component hard-core bosons with\nferromagnetic interactions and activity, i.e., spin-dependent asymmetric\nhopping. Numerical results show the emergence of a ferromagnetic order induced\nby the activity, a quantum counterpart of flocking, that even survives in the\nabsence of ferromagnetic interaction. We confirm this phenomenon by proving\nthat activity generally increases the ground state energies of the paramagnetic\nstates, whereas the ground state energy of the ferromagnetic state does not\nchange. By solving the two-particle case, we find that the effective alignment\nis caused by avoiding the bound state formation due to the non-Hermitian skin\neffect in the paramagnetic state. We employ a two-site mean-field theory based\non the two-particle result and qualitatively reproduce the phase diagram. We\nfurther numerically study a variant of our model with the hard-core condition\nrelaxed, and confirm the robustness of ferromagnetic order emerging due to\nactivity."
    },
    {
        "anchor": "Triplet pair correlations in {\\it s-}wave superfluids as a signature of\n  the FFLO state: We show that triplet pairing correlations are generated in purely s-waves\nsuperfluids whenever population imbalance enforces anisotropic Fulde-Ferrell\n(FF) or inhomogeneous Larkin-Ovchinikov (LO) states. The same set of\nquasiparticle states contributes to the triplet component and to the\npolarization, thus spatially correlating them. In the LO case, this set forms a\nnarrow band of Andreev states centered on the nodes of the s-wave order\nparameter. This picture naturally provides a unifying explanation of previous\nfindings that attractive p-wave interaction stabilizes FFLO states. We also\nstudy a similar triplet mixing which occurs when a balanced two-component\nsystem displays FFLO type oscillations due to a spin-dependent optical lattice.\nWe discuss how this triplet component can be measured in systems of ultra-cold\natoms using a rapid ramp across a p-wave Feshbach resonance. This should\nprovide a smoking gun signature of FFLO states.",
        "positive": "Coherent backscattering in the Fock space of ultracold bosonic atoms: We present numerical evidence for the occurrence of coherent backscattering\nin the Fock space of a small disordered Bose-Hubbard system consisting of four\nsites and containing five particles. This many-body interference phenomenon can\nmost conveniently be seen in time evolution processes that start from a Fock\nstate of the Bose-Hubbard system. It manifests itself in an enhanced detection\nprobability of this initial state as compared to other Fock states with\ncomparable total energy. We argue that coherent backscattering in Fock space\ncan be experimentally measured with ultracold bosonic atoms in optical lattices\nusing state-of-the-art single-site detection techniques. A synthetic gauge\nfield can be induced in order to break time-reversal symmetry within the\nlattice and thereby destroy coherent backscattering. While this many-body\ninterference effect is most prominently visible in the presence of eigenstate\nthermalization, we briefly discuss its significance in the opposite regime of\nmany-body localization."
    },
    {
        "anchor": "Superfluid density of an open dissipative condensate: I calculate the superfluid density of a non-equilibrium steady state\ncondensate of particles with finite lifetime. Despite the absence of a simple\nLandau critical velocity, a superfluid response survives, but dissipation\nreduces the superfluid fraction. I also suggest an idea for how the superfluid\ndensity of an example of such a system, i.e. microcavity polaritons, might be\nmeasured.",
        "positive": "Photon Counting as a Probe of Superfluidity in a Two-Band Bose Hubbard\n  System Coupled to a Cavity Field: We show that photon number measurement can be used to detect superfluidity\nfor a two-band Bose-Hubbard model coupled to a cavity field. The atom-photon\ncoupling induces transitions between the two internal atomic levels and results\nin entangled polaritonic states. In the presence of a cavity field, we find\ndifferent photon numbers in the Mott-insulating versus superfluid phases,\nproviding a method of distinguishing the atomic phases by photon counting.\nFurthermore, we examine the dynamics of the photon field after a rapid quench\nto zero atomic hopping by increasing the well depth. We find a robust\ncorrelation between the field's quench dynamics and the initial superfluid\norder parameter, thereby providing a novel and accurate method of determining\nthe order parameter."
    },
    {
        "anchor": "Three-body recombination near a narrow Feshbach resonance in $^6$Li: We experimentally measure, and theoretically analyze the three-atom\nrecombination rate, $L_3$, around a narrow $s$ wave magnetic Feshbach resonance\nof $^6$Li-$^6$Li at 543.3 Gauss. By examining both the magnetic field\ndependence and especially the temperature dependence of $L_3$ over a wide range\nof temperatures from a few $\\mu$K to above 200 $\\mu$K, we show that three-atom\nrecombination through a narrow resonance follows a universal behavior\ndetermined by the long-range van der Waals potential, and can be described by a\nset of rate equations in which three-body recombination proceeds via successive\npairwise interactions. We expect the underlying physical picture to be\napplicable not only to narrow $s$ wave resonances, but also to resonances in\nnonzero partial waves, and not only at ultracold temperatures, but also at much\nhigher temperatures.",
        "positive": "Topological charge pumping in a one-dimensional optical lattice: A topological charge pump [1] transfers charge in a quantized fashion. The\nquantization is stable against the detailed form of the pumping protocols and\nexternal noises and shares the same topological origin as the quantum Hall\neffect. We propose an experiment setup to realize topological charge pumping of\ncold atoms in a one-dimensional optical lattice. The quantization of the pumped\ncharge is confirmed by first-principle simulations of the dynamics of uniform\nand trapped systems. Quantum effects are shown to be crucial for the\ntopological protection of the charge quantization. Finite-temperature and\nnon-adiabatic effect on the experimental observables are discussed. Realization\nof such a topological charge pump servers as a firm step towards exploring\ntopological states and non-equilibrium dynamics using cold atoms."
    },
    {
        "anchor": "Structure and dynamics of binary Bose-Einstein condensates with vortex\n  phase imprinting: The combination of multi-component Bose-Einstein condensates (BECs) and phase\nimprinting techniques provides an ideal platform for exploring nonlinear\ndynamics and investigating the quantum transport properties of superfluids. In\nthis paper, we study abundant density structures and corresponding dynamics of\nphase-separated binary Bose-Einstein condensates with phase-imprinted single\nvortex or vortex dipole. By adjusting the ratio between the interspecies and\nintraspecies interactions, and the locations of the phase singularities, the\ntypical density profiles such as ball-shell structures, crescent-gibbous\nstructures, Matryoshka-like structures, sector-sector structures and\nsandwich-type structures appear, and the phase diagrams are obtained. The\ndynamics of these structures exhibit diverse properties, including the\npenetration of vortex dipoles, emergence of half-vortex dipoles, co-rotation of\nsectors, and oscillation between sectors. The pinning effects induced by a\npotential defect are also discussed, which is useful for controlling and\nmanipulating individual quantum states.",
        "positive": "Nondestructive Probing of Means, Variances, and Correlations of\n  Ultracold-Atomic-System Densities via Qubit Impurities: We show how impurity atoms can measure moments of ultracold atomic gas\ndensities, using the example of bosons in a one-dimensional lattice. This\nbuilds on a body of work regarding the probing of systems by measuring the\ndephasing of an immersed qubit. We show this dephasing is captured by a\nfunction resembling characteristic functions of probability theory, of which\nthe derivatives at short times reveal moments of the system operator to which\nthe qubit couples. For a qubit formed by an impurity atom, in a system of\nultracold atoms, this operator can be the density of the system at the location\nof the impurity, and thus, means, variances, and correlations of the atomic\ndensities are accessible."
    },
    {
        "anchor": "Equilibrium vortex formation in ultrarapidly rotating two-component\n  Bose-Einstein condensates: Equilibrium vortex formation in rotating binary Bose gases with a rotating\nfrequency higher than the harmonic trapping frequency is investigated\ntheoretically. We consider the system being evaporatively cooled to form\ncondensates and a combined numerical scheme is applied to ensure the binary\nsystem being in an authentic equilibrium state. To keep the system stable\nagainst the large centrifugal force of ultrafast rotation, a quartic trapping\npotential is added to the existing harmonic part. Using the Thomas-Fermi\napproximation, a critical rotating frequency \\Omega_c is derived, which\ncharacterizes the structure with or without a central density hole. Vortex\nstructures are studied in detail with rotation frequency both above and below\n?\\Omega_c and with respect to the miscible, symmetrically separated, and\nasymmetrically separated phases in their nonrotating ground-state counterparts.",
        "positive": "Non-thermalized Dynamics of Flat-Band Many-Body Localization: We find that a flat-band fermion system with interactions and without\ndisorders exhibits non-thermalized ergodicity-breaking dynamics, an analog of\nmany-body localization (MBL). In the previous works, we observed flat-band\nmany-body localization (FMBL) in the Creutz ladder model. The origin of FMBL is\na compact localized state governed by local integrals of motion (LIOMs), which\nare to be obtained explicitly. In this work, we clarify the dynamical aspects\nof FMBL. We first study dynamics of two-particles, and find that the states are\nnot substantially modified by weak interactions, but the periodic time\nevolution of entanglement entropy emerges as a result of a specific mechanism\ninherent in the system. On the other hand, as the strength of the interactions\nis increased, the modification of the states takes place with inducing\ninstability of the LIOMs. Furthermore, many-body dynamics of the system at\nfinite fillings is numerically investigated by time-evolving block decimation\n(TEBD) method. For a suitable choice of the filling, non-thermal and low\nentangled dynamics appears. This behavior is a typical example of the\ndisorder-free FMBL."
    },
    {
        "anchor": "Entangled phonons in atomic Bose-Einstein condensates: We theoretically study the entanglement between phonons spontaneously\ngenerated in atomic Bose-Einstein condensates by analog Hawking and dynamical\nCasimir processes. The quantum evolution of the system is numerically modeled\nby a truncated Wigner method based on a full microscopic description of the\ncondensate and state non-separability is assessed by applying a generalized\nPeres-Horodecki criterion. The peculiar distribution of entanglement is\ndescribed in both real and momentum spaces and its robustness against\nincreasing initial temperature is investigated. Viable strategies to\nexperimentally detect the predicted phonon entanglement are briefly discussed.",
        "positive": "Multiconfigurational time-dependent Hartree approaches for\n  indistinguishable particles: In this Colloquium, the wavefunction-based Multiconfigurational\nTime-Dependent Hartree approaches to the dynamics of indistinguishable\nparticles (MCTDH-F for Fermions and MCTDH-B for Bosons) are reviewed. MCTDH-B\nand MCTDH-F or, together, MCTDH-X are methods for describing correlated quantum\nsystems of identical particles by solving the time-dependent Schr\\\"odinger\nequation from first principles. MCTDH-X is used to accurately model the\ndynamics of real-world quantum many-body systems in atomic, molecular, and\noptical physics. The key feature of these approaches is the time-dependence and\noptimization of the single-particle states employed for the construction of a\nmany-body basis set, which yields nonlinear working equations. We briefly\ndescribe the historical developments that have lead to the formulation of the\nMCTDH-X methods and motivate the necessity for wavefunction-based approaches.\nWe sketch the derivation of the unified MCTDH-F and MCTDH-B equations of motion\nfor complete and also specific restricted configuration spaces. The strengths\nand limitations of the MCTDH-X approach are assessed via benchmarks against an\nexactly solvable model and via convergence checks. We highlight some\napplications to instructive and experimentally-realized quantum many-body\nsystems: the dynamics of atoms in Bose-Einstein condensates in magneto-optical\nand optical traps and of electrons in atoms and molecules. We discuss the\ncurrent development and frontiers in the field of MCTDH-X: theories and\nnumerical methods for indistinguishable particles, for mixtures of multiple\nspecies of indistinguishable particles, the inclusion of nuclear motion for the\nnonadiabatic dynamics of atomic and molecular systems, as well as the\nmultilayer and second-quantized-representation approaches, and the\norbital-adaptive time-dependent coupled-cluster theory are discussed."
    },
    {
        "anchor": "Non-linear mixing of Bogoliubov modes in a bosonic Josephson junction: We revisit the dynamics of a Bose-Einstein condensate in a double-well\npotential, from the regime of Josephson plasma oscillations to the\nself-trapping regime, by means of the Bogoliubov quasiparticle projection\nmethod. For very small imbalance between left and right wells only the lowest\nBogoliubov mode is significantly occupied. In this regime the system performs\nplasma oscillations at the corresponding frequency, and the evolution of the\ncondensate is characterized by a periodic transfer of population between the\nground and the first excited state. As the initial imbalance is increased, more\nexcited modes -- though initially not macroscopically occupied -- get coupled\nduring the evolution of the system. Since their population also varies with\ntime, the frequency spectrum of the imbalance turns out to be still peaked\naround a single frequency, which is continuously shifted towards lower values.\nThe nonlinear mixing between Bogoliubov modes eventually drives the system into\nthe the self-trapping regime, when the population of the ground state can be\ntransferred completely to the excited states at some time during the evolution.\nFor simplicity, here we consider a one-dimensional setup, but the results are\nexpected to hold also in higher dimensions.",
        "positive": "Ground-state phase diagram and critical temperature of two-component\n  Bose gases with Rashba spin-orbit coupling: Ground-state phase diagram of two-component Bose gases with Rashba spin-orbit\ncoupling is determined via a variational approach. A phase in which the fully\npolarized condensate occupies zero momentum is identified. This zero-momentum\nphase competes with the spin density wave phase when interspecies interaction\nis stronger than intraspecies interaction, and the former one is always the\nground state for weak spin-orbit coupling. When the energies of these two\nphases are close, there is a phase separation between them. At finite\ntemperature, such a zero-momentum condensation can be induced by a\nferromagnetic phase transition in normal state. The spontaneous spin\npolarization removes the degeneracy of quasiparticles' energy minima, and\nconsequently the modified density of state accommodates a Bose condensation to\nappear below a critical temperature."
    },
    {
        "anchor": "Radial vortex core oscillations in Bose-Einstein condensates: Dilute ultracold quantum gases form an ideal and highly tunable system in\nwhich superuidity can be studied. Recently quantum turbulence in Bose-Einstein\ncondensates was reported [PRL 103, 045310 (2009)], opening up a new\nexperimental system that can be used to study quantum turbulence. A novel\nfeature of this system is that vortex cores now have a finite size. This means\nthat the vortices are no longer one dimensional features in the condensate, but\nthat the radial behaviour and excitations might also play an important role in\nthe study of quantum turbulence in Bose-Einstein condensates. In this paper we\ninvestigate these radial modes using a simplified variational model for the\nvortex core. This study results in the frequencies of the radial modes, which\ncan be compared with the frequencies of the thoroughly studied Kelvin modes.\nFrom this comparison we find that the lowest (l=0) radial mode has a frequency\nin the same order of magnitude as the Kelvin modes. However the radial modes\nstill have a larger energy than the Kelvin modes, meaning that the Kelvin modes\nwill still constitute the preferred channel for energy decay in quantum\nturbulence.",
        "positive": "Path-integral Monte Carlo study on a droplet of a dipolar Bose-Einstein\n  condensate stabilized by quantum fluctuation: Motivated by the recent experiments [H. Kadau et al., Nature (London) 530,\n194 (2016); I. Ferrier-Barbut et al., arXiv:1601.03318] and theoretical\nprediction (F. W\\\"achtler and L. Santos, arXiv:1601.04501), the ground state of\na dysprosium Bose-Einstein condensate with strong dipole-dipole interaction is\nstudied using the path-integral Monte Carlo method. It is shown that quantum\nfluctuation can stabilize the condensate against dipolar collapse."
    },
    {
        "anchor": "Dynamic trapping near a quantum critical point: The study of dynamics in closed quantum systems has recently been revitalized\nby the emergence of experimental systems that are well-isolated from their\nenvironment. In this paper, we consider the closed-system dynamics of an\narchetypal model: spins near a second order quantum critical point, which are\ntraditionally described by the Kibble-Zurek mechanism. Imbuing the driving\nfield with Newtonian dynamics, we find that the full closed system exhibits a\nrobust new phenomenon -- dynamic critical trapping -- in which the system is\nself-trapped near the critical point due to efficient absorption of field\nkinetic energy by heating the quantum spins. We quantify limits in which this\nphenomenon can be observed and generalize these results by developing a\nKibble-Zurek scaling theory that incorporates the dynamic field. Our findings\ncan potentially be interesting in the context of early universe physics, where\nthe role of the driving field is played by the inflaton or a modulus.",
        "positive": "Nonlinear Bosonization and Refermionization in One Dimension with the\n  Keldysh Functional Integral: We develop a self-contained approach to bosonization and refermionization\nusing the Keldysh functional integral. Starting from fermionic particles, we\nbosonize the system and obtain a description in terms of the Tomonaga-Luttinger\nliquid, with, in addition, an infinite series of interaction terms arising from\nthe curvature of the fermionic particle spectrum. We explicitly calculate the\nleading interaction term and check its consistency with a different approach\nbased on the Matsubara framework, within which we calculate the second leading\ninteraction term, as well. Moreover, we bosonize weakly and strongly\ninteracting bosonic particles, and, finally, refermionize interacting phonons\ninto non-interacting fermionic quasiparticles. The work culminates in a map\nbetween bosonic and fermionic particles and effective bosonic and fermionic\nexcitations, representing phonons and fermionic quasiparticles."
    },
    {
        "anchor": "Quantum Phases of Dipolar Bosons in Bilayer Geometry: We investigate the quantum phases of hard-core dipolar bosons confined to a\nsquare lattice in a bilayer geometry. Using exact theoretical techniques, we\ndiscuss the many-body effects resulting from pairing of particles across layers\nat finite density, including a novel pair supersolid phase, superfluid and\nsolid phases. These results are of direct relevance to experiments with polar\nmolecules and atoms with large magnetic dipole moments trapped in optical\nlattices.",
        "positive": "Universal space-time scaling symmetry in the dynamics of bosons across a\n  quantum phase transition: The dynamics of many-body systems spanning condensed matter, cosmology, and\nbeyond is hypothesized to be universal when the systems cross continuous phase\ntransitions. The universal dynamics is expected to satisfy a scaling symmetry\nof space and time with the crossing rate, inspired by the Kibble-Zurek\nmechanism. We test this symmetry based on Bose condensates in a shaken optical\nlattice. Shaking the lattice drives condensates across an effectively\nferromagnetic quantum phase transition. After crossing the critical point, the\ncondensates manifest delayed growth of spin fluctuations and develop\nanti-ferromagnetic spatial correlations resulting from sub-Poisson generation\nof topological defects. The characteristic times and lengths scale as\npower-laws of the crossing rate, yielding the temporal exponent 0.50(2) and the\nspatial exponent 0.26(2), consistent with theory. Furthermore, the fluctuations\nand correlations are invariant in scaled space-time coordinates, in support of\nthe scaling symmetry of quantum critical dynamics."
    },
    {
        "anchor": "Demagnetization dynamics of non-interacting trapped fermions: Motivated by several experimental efforts to understand spin diffusion and\ntransport in ultracold fermionic gases, we study the spin dynamics of initially\nspin-polarized ensembles of harmonically trapped non-interacting spin-1/2\nfermionic atoms, subjected to a magnetic field gradient. We obtain simple\nanalytic expressions for spin observables in the presence of both constant and\nlinear magnetic field gradients, with and without a spin-echo pulse, and at\nzero and finite temperatures. The analysis shows the relevance of spin-motional\ncoupling in the non-interacting regime where the demagnetization decay rate at\nshort times can be faster than the experimentally measured rates in the\nstrongly interacting regime under similar trapping conditions. Our calculations\nalso show that particle motion limits the ability of a spin-echo pulse to\nremove the effect of magnetic field inhomogeneity, and that a spin-echo pulse\ncan instead lead to an increased decay of magnetization at times comparable to\nthe trapping period.",
        "positive": "Cold atoms in rotating optical lattice with nearest neighbour\n  interaction: Extended Bose Hubbard models with nearest neighbour interaction describe\nminimally the effect of long range interaction on ultra cold atoms in deep\noptical lattices. Rotation of such optical lattices subject such neutral cold\natoms to the effect of an artificial magnetic field. The modification of the\nphase boundaries of the density wave and Mott Insulator phases due to this\nrotation are shown to be related to the edge spectrum of spinorial and scalar\nHarper equation. Corresponding profiles of the checkerboard vortex states with\nsublattice modulated superfluid order parameter near density wave phase\nboundary are calculated."
    },
    {
        "anchor": "Maxwell Quasiparticles Emerged in Optical Lattices: We construct a two-dimensional tight-binding model of an optical lattice,\nwhere the low energy excitations should be described by the spin-1 Maxwell\nequations in the Hamiltonian form, and such linear dispersion excitations with\npesudospin-1 are so called as the Maxwell quasiparticles. The system has rich\ntopological features, for examples, the threefold degeneracy points called\nMaxwell points may have nontrivial $\\pm 2\\pi$ Berry phases and the anomalous\nquantum Hall effect with spin-momentum locking may appear in topological\nMaxwell insulators. We propose realistic schemes for realizing the Maxwell\nmetals/insulators and detecting the intrinsic properties of the topological\nMaxwell quasiparticles with ultracold atoms in optical lattices.",
        "positive": "Kondo Effect in Alkali-Earth Atomic Gases with Confinement-induced\n  Resonance: Alkali-earth atoms have a long-lived electronic excited state, which can be\nlocalized in the Fermi sea of ground state atoms by an external potential and\nserve as magnetic impurities, due to the spin-exchange interaction between the\nexcited and the ground state atoms. This can give rise to the Kondo effect.\nHowever, in order to achieve this effect in current atomic gas experiment, it\nrequires the Kondo temperature to be increased to a sizable portion of the\nFermi temperature. In this letter we propose that the spin-exchange interaction\ncan be strongly enhanced by utilizing the confinement-induced resonance (CIR).\nWe analyze this system by the renormalization group approach, and we show that\nnearby a CIR, the Kondo temperature can indeed be increased to the regime\nattainable by current experiments."
    },
    {
        "anchor": "Stripe and junction-vortex phases in linearly coupled Bose-Einstein\n  condensates: Soon after its theoretical prediction, striped-density states in the presence\nof synthetic spin-orbit coupling were realized in Bose-Einstein condensates of\nultracold neutral atoms [J.-R. Li et al., Nature \\textbf{543}, 91 (2017)]. The\nachievement opens avenues to explore the interplay of superfluidity and\ncrystalline order in the search for supersolid features and materials. The\nsystem considered is essentially made of two linearly coupled Bose-Einstein\ncondensates, that is a pseudo-spin-$1/2$ system, subject to a spin-dependent\ngauge field $\\sigma_z \\hbar k_\\ell$. Under these conditions the stripe phase is\nachieved when the linear coupling $\\hbar\\Omega/2$ is small against the gauge\nenergy $m\\Omega/\\hbar k_\\ell^2<1$ . The resulting density stripes have been\ninterpreted as a standing-wave, interference pattern with approximate\nwavenumber $2k_\\ell$. Here, we show that the emergence of the stripe phase is\ninduced by an array of Josephson vortices living in the junction defined by the\nlinear coupling. As happens in superconducting junctions subject to external\nmagnetic fields, a vortex array is the natural response of the superfluid\nsystem to the presence of a gauge field. Also similar to superconductors, the\nJosephson currents and their associated vortices can be present as a metastable\nstate in the absence of gauge field. We provide closed-form solutions to the 1D\nmean field equations that account for such vortex arrays. The underlying\nJosephson currents coincide with the analytical solutions to the sine-Gordon\nequation for the relative phase of superconducting junctions [C. Owen and D.\nScalapino, Phys. Rev. \\textbf{164}, 538 (1967)].",
        "positive": "Phase-Sensitive Detection for Unconventional Bose-Einstein Condensations: We propose a phase-sensitive detection scheme to identify the unconventional\n$p_{x}\\pm ip_{y}$ symmetry of the condensate wavefunctions of bosons, which\nhave already been proposed and realized in high bands in optical lattices.\nUsing the impulsive Raman operation combining with time-of-flight imaging, the\noff-diagonal correlation functions in momentum space give rise to the relative\nphase information between different components of condensate wavefunctions.\nThis scheme is robust against the interaction and interband effects, and\nprovides smoking gun evidence for unconventional Bose-Einstein condensations\nwith nontrivial condensation symmetries."
    },
    {
        "anchor": "Many-Body Localization from Dynamical Gauge Fields: A recent experiment [Nature Physics 10, 1 (2019)] has realized a dynamical\ngauge system with $\\mathbb{Z}_2$ gauge symmetry in a double-well potential. In\nthis work we propose a method to generalize this model from a single double\nwell to a one-dimensional chain. We show that although there is no disordered\npotential in the original model, the phenomenon of many-body localization can\noccur. The key ingredient is that different symmetry sectors with different\nlocal gauge charges play the role of different disorder configurations, which\nbecomes clear after exactly mapping our model to a transverse Ising model in a\nrandom longitudinal field. We show that both the ergodic regime and the\nmany-body localized regime exist in this model from four different metrics,\nwhich include level statistics, volume law versus area law of entanglement\nentropy of eigenstates, quench dynamics of entanglement entropy and physical\nobservables.",
        "positive": "Direct observation of hydrodynamization and local prethermalization: Hydrodynamics accurately describes relativistic heavy-ion collision\nexperiments well before local thermal equilibrium is established. This\nunexpectedly rapid onset of hydrodynamics -- which takes place on the fastest\navailable timescale -- is called hydrodynamization. It occurs when an\ninteracting quantum system is quenched with an energy density that is much\ngreater than its initial energy density. During hydrodynamization, energy gets\nredistributed across very different energy scales. Hydrodynamization precedes\nlocal equilibration among momentum modes, which is local prethermalization to a\ngeneralized Gibbs ensemble in nearly integrable systems or local thermalization\nin non-integrable systems. Many theories of quantum dynamics postulate local\n(pre)thermalization, but the associated timescale has not been quantitatively\nstudied. Here we use an array of 1D Bose gases to directly observe both\nhydrodynamization and local prethermalization. After we apply a Bragg\nscattering pulse, hydrodynamization is evident in the fast redistribution of\nenergy among distant momentum modes, which occurs on timescales associated with\nthe Bragg peak energies. Local prethermalization can be seen in the slower\nredistribution of occupation among nearby momentum modes. We find that the time\nscale for local prethermalization in our system is inversely proportional to\nthe momenta involved. During hydrodynamization and local prethermalization,\nexisting theories cannot quantitatively model our experiment. Exact theoretical\ncalculations in the Tonks-Girardeau limit show qualitatively similar features."
    },
    {
        "anchor": "Variational approach to the two-dimensional Bose polaron: An impurity particle interacting with a Bose-Einstein condensate (BEC) leads\nto the formation of a quasiparticle known as the Bose polaron. We investigate\nthe properties of the two-dimensional Bose polaron, applying a variational\nansatz that contains up to three Bogoliubov excitations of the BEC. Similar to\nits three-dimensional counterpart, we observe the existence of two\nquasiparticle branches, namely the attractive and the repulsive polarons, at\ndifferent coupling strengths. We find that their energies agree well with\nrecent quantum Monte Carlo calculations. In particular, we observe that the\ninclusion of three excitations is crucial to capture the attractive polaron\nenergy towards the regime of strong attraction, where the quasiparticle\nproperties are dominated by few-body correlations. We also calculate the\nattractive polaron effective mass and residue, where we find significant\ndifferences between considering a weakly interacting Bose medium and taking the\nnon-interacting limit, signalling enhanced impurity dressing by excitations in\nthe latter case. By contrast, the spectral weight of the metastable repulsive\npolaron is largely insensitive to the interactions in the BEC and the number of\nBogoliubov excitations. Our model may be experimentally realized in dilute\natomic vapors and atomically thin semiconductors.",
        "positive": "Molecule and polaron in a highly polarized two-dimensional Fermi gas\n  with spin-orbit coupling: We show that spin-orbit coupling (SOC) gives rise to pairing instability in a\nhighly polarized two-dimensional Fermi gas for arbitrary interaction strength.\nThe pairing instability can lead to a Fulde-Ferrell-Larkin-Ovchinnikov-like\nmolecular state, which undergoes a first-order transition into a pairing state\nwith zero center-of-mass momentum as the parameters are tuned. These pairing\nstates are metastable against a polaron state dressed by particle-hole\nfluctuations for small SOC. At large SOC, a polaron-molecule transition exists,\nwhich suggests a phase transition between the topological superfluid state and\nthe normal state for a highly polarized Fermi gas in the thermodynamic limit.\nAs polarization in a Fermi gas with SOC is induced by the effective Zeeman\nfield, we also discuss the influences of the effective Zeeman field on the\nground state of the system. Our findings may be tested directly in future\nexperiments."
    },
    {
        "anchor": "Exact dynamics of two ultra-cold bosons confined in a one-dimensional\n  double-well potential: The dynamics of two ultra-cold bosons confined in a one-dimensional\ndouble-well potential is studied. We compare the exact dynamics governed by a\nfull two-body Hamiltonian with the dynamics obtained in a two-mode model\napproximation. We show that for sufficiently large interactions the two-mode\nmodel breaks down and higher single-particle states have to be taken into\naccount to describe the dynamical properties of the system correctly.",
        "positive": "Stimulated Thermalization of a Parametrically Driven Magnon Gas as a\n  Prerequisite for Bose-Einstein Magnon Condensation: Thermalization of a parametrically driven magnon gas leading to the formation\nof a Bose-Einstein condensate at the bottom of a spin-wave spectrum was studied\nby time- and wavevector-resolved Brillouin light scattering spectroscopy. It\nhas been found that the condensation is preceded by the conversion of initially\npumped magnons into a second group of frequency degenerated magnons, which\nappear due to parametrically stimulated scattering of the initial magnons to a\nshort-wavelength spectral region. In contrast to the first magnon group, which\nwavevectors are orthogonal to the wavevectors of the magnons at the lowest\nenergy states, the secondary magnons can effectively scatter to the bottom of\nthe spectrum and condense there."
    },
    {
        "anchor": "Anisotropy-driven magnetic phase transitions in SU(4)-symmetric Fermi\n  gas in three-dimensional optical lattices: We study SU(4)-symmetric ultracold fermionic mixture in the cubic optical\nlattice with the variable tunneling amplitude along one particular\ncrystallographic axis in the crossover region from the two- to\nthree-dimensional spatial geometry. To theoretically analyze emerging magnetic\nphases and physical observables, we describe the system in the framework of the\nFermi-Hubbard model and apply dynamical mean-field theory. We show that in two\nlimiting cases of anisotropy there are two phases with different\nantiferromagnetic orderings in the zero temperature limit and determine a\nregion of their coexistence. We also study the stability regions of different\nmagnetically-ordered states and density profiles of the gas in the harmonic\noptical trap.",
        "positive": "Feasibility of a Fulde-Ferrell-Larkin-Ovchinnikov superfluid Fermi\n  atomic gas: We theoretically explore a promising route to achieve the\nFulde-Ferrell-Larkin-Ovchinnikov (FFLO) state in a spin-imbalanced ultracold\nFermi gas. In the current stage of cold atom physics, search for this exotic\nFermi superfluid is facing two serious difficulties: One is the desperate\ndestruction of the FFLO long-range order by FFLO pairing fluctuations, which\nprecludes entering the phase through a second-order transition, even in three\ndimension. The other is the fierce competition with the phase separation into\nthe BCS (Bardeen-Cooper-Schrieffer) state and the spin-polarized normal state.\nIncluding strong FFLO pairing fluctuations within the framework of the\nstrong-coupling theory developed by Nozi\\`eres and Schmitt-Rink, we show that\nthe anisotropy of Fermi surface introduced by an optical lattice makes the FFLO\nstate stable against the paring fluctuations. This stabilized FFLO state is\nalso found to be able to overcome the competition with the phase separation\nunder a certain condition. Since the realization of unconventional Fermi\nsuperfluids is one of the most exciting challenges in cold atom physics, our\nresults would contribute to the further development of this field."
    },
    {
        "anchor": "Influence of finite size of molecules on spectrum of fully polarized\n  dipolar BECs: Generalization of Bogoliubov's spectrum: We discuss complete theory of point-like particles in fully polarized BECs\ndescribing difference in behaviour of electrically- and magnetically polarized\nBECs. Next we present generalization of this theory on finite size particles to\ninclude contribution of size of real molecules on dynamical properties of\ndipolar BECs. As an application of obtained equation we calculate spectrum of\nlinear collective excitations getting generalization of the Bogoliubov's\nspectrum. We show absence of roton instability due to positivity of\npolarization contribution in the excitation spectrum. We found that new type of\ninstabilities appears in small wave length limit due to finite size of\nmolecules.",
        "positive": "Mean-field construction for spectrum of one-dimensional Bose polaron: The full momentum dependence of spectrum of a point-like impurity immersed in\na dilute one-dimensional Bose gas is calculated on the mean-field level. In\nparticular we elaborate, to the finite-momentum Bose polaron, the path-integral\napproach whose semi-classical approximation leads to the conventional\nmean-field treatment of the problem while quantum corrections can be easily\naccounted by standard loop expansion techniques. The extracted low-energy\nparameters of impurity spectrum, namely, the binding energy and the effective\nmass of particle, are shown to be in qualitative agreement with the results of\nquantum Monte Carlo simulations."
    },
    {
        "anchor": "Dynamical band flipping in fermionic lattice systems: An ac-field-driven\n  change of the interaction from repulsive to attractive: We show theoretically that the sudden application of an appropriate ac field\nto correlated lattice fermions flips the band structure and effectively\nswitches the interaction from repulsive to attractive. The nonadiabatically\ndriven system is characterized by a negative temperature with a population\ninversion. We numerically demonstrate the converted interaction in an ac-driven\nHubbard model with the nonequilibrium dynamical mean-field theory solved by the\ncontinuous-time quantum Monte Carlo method. Based on this, we propose an\nefficient ramp-up protocol for ac fields that can suppress heating, which leads\nto an effectively attractive Hubbard model with a temperature below the\nsuperconducting transition temperature of the equilibrium system.",
        "positive": "Quenched binary Bose-Einstein condensates: spin domain formation and\n  coarsening: We explore the time evolution of quasi-1D two component Bose-Einstein\ncondensates (BEC's) following a quench from one component BEC's with a ${\\rm\nU}(1)$ order parameter into two component condensates with a ${\\rm\nU}(1)\\shorttimes{\\rm Z}_2$ order parameter. In our case, these two spin\ncomponents have a propensity to phase separate, i.e., they are immiscible.\nRemarkably, these spin degrees of freedom can equivalently be described as a\nsingle component attractive BEC. A spatially uniform mixture of these spins is\ndynamically unstable, rapidly amplifing any quantum or pre-existing classical\nspin fluctuations. This coherent growth process drives the formation of\nnumerous spin polarized domains, which are far from the system's ground state.\nAt much longer times these domains grow in size, coarsening, as the system\napproaches equilibrium. The experimentally observed time evolution is fully\nconsistent with our stochastic-projected Gross-Pitaevskii calculation."
    },
    {
        "anchor": "Quantum diffusion with disorder, noise and interaction: Disorder, noise and interaction play a crucial role in the transport\nproperties of real systems, but they are typically hard to control and study\nboth theoretically and experimentally, especially in the quantum case. Here we\nexplore a paradigmatic problem, the diffusion of a wavepacket, by employing\nultra-cold atoms in a disordered lattice with controlled noise and tunable\ninteraction. The presence of disorder leads to Anderson localization, while\nboth interaction and noise tend to suppress localization and restore transport,\nalthough with completely different mechanisms. When only noise or interaction\nare present we observe a diffusion dynamics that can be explained by existing\nmicroscopic models. When noise and interaction are combined, we observe instead\na complex anomalous diffusion. By combining experimental measurements with\nnumerical simulations, we show that such anomalous behavior can be modeled with\na generalized diffusion equation, in which the noise- and interaction-induced\ndiffusions enter in an additive manner. Our study reveals also a more complex\ninterplay between the two diffusion mechanisms in regimes of strong interaction\nor narrowband noise.",
        "positive": "Light-induced gauge fields for ultracold atoms: Gauge fields are central in our modern understanding of physics at all\nscales. At the highest energy scales known, the microscopic universe is\ngoverned by particles interacting with each other through the exchange of gauge\nbosons. At the largest length scales, our universe is ruled by gravity, whose\ngauge structure suggests the existence of a particle - the graviton - that\nmediates the gravitational force. At the mesoscopic scale, solid-state systems\nare subjected to gauge fields of different nature: materials can be immersed in\nexternal electromagnetic fields, but they can also feature emerging gauge\nfields in their low-energy description. In this review, we focus on another\nkind of gauge field: those engineered in systems of ultracold neutral atoms. In\nthese setups, atoms are suitably coupled to laser fields that generate\neffective gauge potentials in their description. Neutral atoms \"feeling\"\nlaser-induced gauge potentials can potentially mimic the behavior of an\nelectron gas subjected to a magnetic field, but also, the interaction of\nelementary particles with non-Abelian gauge fields. Here, we review different\nrealized and proposed techniques for creating gauge potentials - both Abelian\nand non-Abelian - in atomic systems and discuss their implication in the\ncontext of quantum simulation. While most of these setups concern the\nrealization of background and classical gauge potentials, we conclude with more\nexotic proposals where these synthetic fields might be made dynamical, in view\nof simulating interacting gauge theories with cold atoms."
    },
    {
        "anchor": "Coexistence of Bose condensation and pairing in Boson mixtures: We consider the problem when there are two kinds of Bosons with an attraction\nbetween them. We find the system to consist of two Bose condensates with an\nadditional pairing order between the Bosons. The properties of this state are\ndiscussed.",
        "positive": "Preparation of two-particle total hyperfine spin singlet states via\n  spin-changing dynamics: We present our proposals for generating total hyperfine spin zero state for\ntwo f=1 or two f=2 particles, starting from initial unentangled states. We show\nthat our goal can be achieved by exploiting spin changing dynamics and\nquadratic Zeeman shifts with realistic choices of external magnetic fields and\nevolution time intervals."
    },
    {
        "anchor": "Measurement-induced transitions of the entanglement scaling law in\n  ultracold gases with controllable dissipation: Recent studies of quantum circuit models have theoretically shown that\nfrequent measurements induce a transition in a quantum many-body system, which\nis characterized by the change of the scaling law of the entanglement entropy\nfrom a volume law to an area law. In order to propose a way for experimentally\nobserving this measurement-induced transition, we present numerical analyses\nusing matrix-product states on quench dynamics of a dissipative Bose-Hubbard\nmodel with controllable two-body losses, which has been realized in recent\nexperiments with ultracold atoms. We find that when the strength of dissipation\nincreases, there occurs a measurement-induced transition from volume-law\nscaling to area-law scaling with a logarithmic correction in a region of\nrelatively small dissipation. We also find that the strong dissipation leads to\na revival of the volume-law scaling due to a continuous quantum Zeno effect. We\nshow that dynamics starting with the area-law states exhibits the breaking of\nergodicity, which can be used in experiments for distinguishing them from the\nvolume-law states.",
        "positive": "Exploring the Thermodynamics of a Universal Fermi Gas: From sand piles to electrons in metals, one of the greatest challenges in\nmodern physics is to understand the behavior of an ensemble of strongly\ninteracting particles. A class of quantum many-body systems such as neutron\nmatter and cold Fermi gases share the same universal thermodynamic properties\nwhen interactions reach the maximum effective value allowed by quantum\nmechanics, the so-called unitary limit [1,2]. It is then possible to simulate\nsome astrophysical phenomena inside the highly controlled environment of an\natomic physics laboratory. Previous work on the thermodynamics of a\ntwo-component Fermi gas led to thermodynamic quantities averaged over the trap\n[3-5], making it difficult to compare with many-body theories developed for\nuniform gases. Here we develop a general method that provides for the first\ntime the equation of state of a uniform gas, as well as a detailed comparison\nwith existing theories [6,14]. The precision of our equation of state leads to\nnew physical insights on the unitary gas. For the unpolarized gas, we prove\nthat the low-temperature thermodynamics of the strongly interacting normal\nphase is well described by Fermi liquid theory and we localize the superfluid\ntransition. For a spin-polarized system, our equation of state at zero\ntemperature has a 2% accuracy and it extends the work of [15] on the phase\ndiagram to a new regime of precision. We show in particular that, despite\nstrong correlations, the normal phase behaves as a mixture of two ideal gases:\na Fermi gas of bare majority atoms and a non-interacting gas of dressed\nquasi-particles, the fermionic polarons [10,16-18]."
    },
    {
        "anchor": "Bath-induced band decay of a Hubbard lattice gas: Dissipation is introduced to a strongly interacting ultracold bosonic gas in\nthe Mott-insulator regime of a 3D spin-dependent optical lattice. A weakly\ninteracting superfluid comprised of atoms in a state that does not experience\nthe lattice potential acts as a dissipative bath coupled to the lattice atoms\nvia collisions. Lattice atoms are excited to higher-energy bands via Bragg\ntransitions, and the resulting bath-induced decay is measured using the atomic\nquasimomentum distribution. A competing but slower intrinsic decay mechanism\narising from collisions between lattice atoms is also investigated. The\nmeasured bath-induced decay rate is compared with the predictions of a weakly\ninteracting model with no free parameters. The presence of intrinsic decay,\nwhich cannot be accommodated within this framework, signals that strong\ninteractions may play a central role in the lattice-atom dynamics.",
        "positive": "Majorana Fermions in Equilibrium and Driven Cold Atom Quantum Wires: We introduce a new approach to create and detect Majorana fermions using\noptically trapped 1D fermionic atoms. In our proposed setup, two internal\nstates of the atoms couple via an optical Raman transition---simultaneously\ninducing an effective spin-orbit interaction and magnetic field---while a\nbackground molecular BEC cloud generates s-wave pairing for the atoms. The\nresulting cold atom quantum wire supports Majorana fermions at phase boundaries\nbetween topologically trivial and nontrivial regions, as well as `Floquet\nMajorana fermions' when the system is periodically driven. We analyze\nexperimental parameters, detection schemes, and various imperfections."
    },
    {
        "anchor": "Characteristic features of the strongly-correlated regime: Lessons from\n  a 3-fermion one-dimensional harmonic trap: The transition into a strongly-correlated regime of 3 fermions trapped in a\none-dimensional harmonic potential is investigated. This interesting, but\nlittle-studied system, allows us to identify characteristic features of the\nregime, some of which are also present in strongly-correlated materials\nrelevant to the industry. Furthermore, our findings describe the behavior of\nelectrons in quantum dots, ions in Paul traps, and even fermionic atoms in\none-dimensional optical lattices. Near the ground state, all these platforms\ncan be described as fermions trapped in a harmonic potential. The correlation\nregime can be controlled by varying the natural frequency of the trapping\npotential, and to probe it, we propose to use twisted light. We identify 4\nsignatures of strong correlation in the one-dimensional 3-fermion trap, which\nare likely to be present for any number N of trapped fermions: i) the ground\nstate density is strongly localized with N maximally separated peaks (Wigner\nCrystal) ii) the symmetric and antisymmetric ground state wavefunctions become\ndegenerate (bosonization) iii) the von Neumann entropy grows, iv) the energy\nspectrum is fully characterized by N normal modes or less.",
        "positive": "Cooperative effects in dense cold atomic gases including magnetic dipole\n  interactions: We theoretically investigate cooperative effects in cold atomic gases\nexhibiting both electric and magnetic dipole-dipole interactions, such as\noccurring for example in clouds of dysprosium atoms. We distinguish between the\nquantum degenerate case, where we take a many body physics approach and the\nquantum non-degenerate case, where we use the formalism of open system\ndynamics. For quantum non-degenerate gases, we illustrate the emergence of\ntailorable spin models in the high-excitation limit. In the low-excitation\nlimit, we provide analytical and numerical results detailing the effect of\nmagnetic interactions on the directionality of scattered light and characterize\nsub- and superradiant effects. For quantum degenerate gases, we study the\ninterplay between sub- and superradiance effects and the fermionic or bosonic\nquantum statistics nature of the ensemble."
    },
    {
        "anchor": "Integrability breakdown in longitudinaly trapped, one-dimensional\n  bosonic gases: A system of identical bosons with short-range (contact) interactions is\nstudied. Their motion is confined to one dimension by a tight lateral trapping\npotential and, additionally, subject to a weak harmonic confinement in the\nlongitudinal direction. Finite delay time associated with penetration of\nquantum particles through each other in the course of a pairwise\none-dimensional collision in the presence of the longitudinal potential makes\nthe system non-integrable and, hence, provides a mechanism for relaxation to\nthermal equilibrium. To analyse this effect quantitatively in the limit of a\nnon-degenerate gas, we develop a system of kinetic equations and solve it for\nsmall-amplitude monopole oscillations of the gas. The obtained damping rate is\nlong enough to be neglected in a realistic cold-atom experiment, and therefore\nlongitudinal trapping does not hinder integrable dynamics of atomic gases in\nthe 1D regime.",
        "positive": "Mott Insulator to Superfluid transition in Bose-Bose mixtures in a\n  two-dimensional lattice: We perform a numeric study (Worm algorithm Monte Carlo simulations) of\nultracold two-component bosons in two-dimensional optical lattices. We study\nhow the Mott insulator to superfluid transition is affected by the presence of\na second superfluid bosonic species. We find that, at fixed interspecies\ninteraction, the upper and lower boundaries of the Mott lobe are differently\nmodified. The lower boundary is strongly renormalized even for relatively low\nfilling factor of the second component and moderate (interspecies) interaction.\nThe upper boundary, instead, is affected only for large enough filling of the\nsecond component. Whereas boundaries are renormalized we find evidence of\npolaron-like excitations. Our results are of interest for current experimental\nsetups."
    },
    {
        "anchor": "Progress towards quantum-enhanced interferometry with harmonically\n  trapped quantum matter-wave bright solitons: We model the dynamics of attractively interacting ultracold bosonic atoms in\na quasi-one-dimensional wave-guide with additional harmonic trapping.\nInitially, we prepare the system in its ground state and then shift the zero of\nthe harmonic trap and switch on an additional narrow scattering potential near\nthe center of the trap. After colliding with the barrier twice, we propose to\nmeasure the number of atoms opposite to the initial condition. Quantum-enhanced\ninterferometry with quantum bright solitons allows us to predict detection of\nan offset of the scattering potential with considerably increased precision as\ncompared to single-particle experiments. In a future experimental realization\nthis might lead to measurement of weak forces caused, for example, by small\nhorizontal gradients in the gravitational potential - with a resolution of\nseveral micrometers given essentially by the size of the solitons. Our\nnumerical simulations are based on the rigorously proved effective potential\napproach developed in [Phys. Rev. Lett. 102, 010403 (2009) and Phys. Rev. Lett.\n103, 210402 (2009)]. We choose our parameters such that the prerequisite of the\nproof (that the solitons cannot break apart, for energetic reasons) is always\nfulfilled, thus exploring a parameter regime inaccessible to the mean-field\ndescription via the Gross-Pitaevskii equation due to Schrodinger-cat states\noccurring in the many-particle quantum dynamics.",
        "positive": "Angular topological superfluid and topological vortex in an ultracold\n  Fermi gas: We show that pairing in an ultracold Fermi gas under\nspin-orbital-angular-momentum coupling (SOAMC) can acquire topological\ncharacters encoded in the quantized angular degrees of freedom. The resulting\ntopological superfluid is the angular analog of its counterpart in a\none-dimensional Fermi gas with spin-orbit coupling, but characterized by a Zak\nphase defined in the angular-momentum space. Upon tuning the SOAMC parameters,\na topological phase transition occurs, which is accompanied by the closing of\nthe quasiparticle excitation gap. Remarkably, a topological vortex state can\nalso be stabilized by deforming the Fermi surface, which is topologically\nnon-trivial in both the coordinate and angular-momentum space, offering\ninteresting potentials for applications in quantum information and quantum\ncontrol. We discuss how the topological phase transition and the exotic vortex\nstate can be detected experimentally."
    },
    {
        "anchor": "Analog quantum simulation of the spinor-four Dirac equation with an\n  artificial gauge field: A two-dimensional spatially and temporally modulated Wannier-Stark system of\nultracold atoms in optical lattices is shown to mimic the behavior of a Dirac\nparticle. Suitable additional modulations generate an artificial gauge field\nwhich simulates a magnetic field and imposes the use of the full spinor-four\nDirac equation.",
        "positive": "Quantum Scattering States in a Nonlinear Coherent Medium: We present a comprehensive study of stationary states in a coherent medium\nwith a quadratic or Kerr nonlinearity in the presence of localized potentials\nin one dimension (1D) for both positive and negative signs of the nonlinear\nterm, as well as for barriers and wells. The description is in terms of the\nnonlinear Schr\\\"odinger equation (NLSE) and hence applicable to a variety of\nsystems, including interacting ultracold atoms in the mean field regime and\nlight propagation in optical fibers. We determine the full landscape of\nsolutions, in terms of a potential step and build solutions for rectangular\nbarrier and well potentials. It is shown that all the solutions can be\nexpressed in terms of a Jacobi elliptic function with the inclusion of a\ncomplex-valued phase shift. Our solution method relies on the roots of a cubic\npolynomial associated with a hydrodynamic picture, which provides a simple\nclassification of all the solutions, both bounded and unbounded, while the\nboundary conditions are intuitively visualized as intersections of phase space\ncurves. We compare solutions for open boundary conditions with those for a\nbarrier potential on a ring, and also show that numerically computed solutions\nfor smooth barriers agree qualitatively with analytical solutions for\nrectangular barriers. A stability analysis of solutions based on the Bogoliubov\nequations for fluctuations show that persistent instabilities are localized at\nsharp boundaries, and are predicated by the relation of the mean density change\nacross the boundary to the value of the derivative of the density at the edge.\nWe examine the scattering of a wavepacket by a barrier potential and show that\nat any instant the scattered states are well described by the stationary\nsolutions we obtain, indicating applications of our results and methods to\nnonlinear scattering problems."
    },
    {
        "anchor": "Quantum phases of $sp^2$-orbital bosonic gases in a hexagonal lattice: Orbital degree of freedom plays an important role for understanding quantum\nmany-body phenomena. In this work, we study an experimentally related setup\nwith ultracold bosons loaded into hybridized bands of two-dimensional hexagonal\noptical lattices. We find that the system supports various quantum many-body\nphases at zero temperature, including chiral superfluid and chiral Mott\ninsulator by breaking time-reversal symmetry, and time-reversal-even insulating\nphase, based on dynamical mean-field theory. To explain the time-reversal-even\nphase, a fourth-order orbital-exchange model is derived to explain the\nunderlying mechanics. To relate to experimental situations, we make\nband-structure calculations to obtain the Hubbard parameters, and show that\nthese orbital ordering phases persist also in the presence of\nnext-nearest-neighbor hopping.",
        "positive": "Multi-Orbital Quantum Phase Diffusion: The collapses and revivals of a coherent matter wave field of interacting\nparticles can serve as a sensitive interferometric probe of the interactions\nand the number statistics of the underlying quantum field. Here we show how the\nability to observe long time traces of collapse and revival dynamics of a\nBose-Einstein condensate loaded into a three-dimensional (3D) optical lattice\nallowed us to directly reveal the atom number statistics and the presence of\neffective coherent multi-particle interactions in a lattice. The multi-particle\ninteractions are generated via virtual transitions to higher lattice orbitals\nand can find use for simulations of effective field theories with ultracold\natoms in optical lattices. We measured their absolute strengths up to the case\nof six-particle interactions and compare our findings with theory."
    },
    {
        "anchor": "Feynman path-integral treatment of the Bose polaron beyond the\n  Fr\u00f6hlich model: An impurity immersed in a Bose-Einstein condensate is no longer accurately\ndescribed by the Fr\\\"ohlich Hamiltonian as the coupling between the impurity\nand the boson bath gets stronger. We study the dominant effects of the\ntwo-phonon terms beyond the Fr\\\"ohlich model on the ground-state properties of\nthe polaron using Feynman's variational path-integral approach. The previously\nreported discrepancy in the effective mass between the renormalization group\napproach and this theory is shown to be absent in the beyond-Fr\\\"ohlich model\non the positive side of the Feshbach resonance. Self-trapping, characterized by\na sharp and dramatic increase of the effective mass, is no longer observed for\nthe repulsive polaron once the two-phonon interactions are included. For the\nattractive polaron we find a divergence of the ground-state energy and\neffective mass at weaker couplings than previously observed within the\nFr\\\"ohlich model.",
        "positive": "The role of atomic interactions in cavity-induced continuous time\n  crystals: We consider continuous time-crystalline phases in dissipative many-body\nsystems of atoms in cavities, focusing on the role of short-range interatomic\ninteractions. First, we show that the latter can alter the nature of the time\ncrystal by changing the type of the underlying critical bifurcation. Second, we\ncharacterize the heating mechanism and dynamics resulting from the short-range\ninteractions and demonstrate that they make the time crystal inherently\nmetastable. We argue that this is generic for the broader class of dissipative\ntime crystals in atom-cavity systems whenever the cavity loss rate is\ncomparable to the atomic recoil energy. We observe that such a scenario for\nheating resembles the one proposed for preheating of the early universe, where\nthe oscillating coherent inflation field decays into a cascade of exponentially\ngrowing fluctuations. By extending approaches for dissipative dynamical systems\nto our many-body problem, we obtain analytical predictions for the parameters\ndescribing the phase transition and the heating rate inside the\ntime-crystalline phase. We underpin and extend the analytical predictions of\nthe heating rates with numerical simulations."
    },
    {
        "anchor": "Critical entropies and magnetic-phase-diagram analysis of ultracold\n  three-component fermionic mixtures in optical lattices: We study theoretically many-body equilibrium magnetic phases and\ncorresponding thermodynamic characteristics of ultracold three-component\nfermionic mixtures in optical lattices described by the SU(3)-symmetric\nsingle-band Hubbard model. Our analysis is based on the generalization of the\nexact diagonalization solver for multicomponent mixtures that is used in the\nframework of the dynamical mean-field theory. It allows us to obtain a\nfinite-temperature phase diagram with the corresponding transition lines to\nmagnetically ordered phases at filling one particle per site (1/3 band filling)\nin simple cubic lattice geometry. Based on the developed theoretical approach,\nwe also attain the necessary accuracy to study the entropy dependence in the\nvicinity of magnetically ordered phases that allows us to make important\npredictions for ongoing and future experiments aiming to approach and study\nlong-range-order phases in ultracold atomic mixtures.",
        "positive": "Observation of Anomalous Decay of a Polarized Three-Component Fermi Gas: Systems of fermions with multiple internal states, such as quarks in quantum\nchromodynamics and nucleons in nuclear matter, are at the heart of some of the\nmost complex quantum many-body problems. The stability of such many-body\nmulti-component systems is crucial to understanding, for instance, baryon\nformation and the structure of nuclei, but these fermionic problems are\ntypically very challenging to tackle theoretically. Versatile experimental\nplatforms on which to study analogous problems are thus sought after. Here, we\nreport the creation of a uniform gas of three-component fermions. We\ncharacterize the decay of this system across a range of interaction strengths\nand observe nontrivial competition between two- and three-body loss processes.\nWe observe anomalous decay of the polarized (i.e. spin-population imbalanced)\ngas, in which the loss rates of each component unexpectedly differ. We\nintroduce a generalized three-body rate equation which captures the decay\ndynamics, but the underlying microscopic mechanism is unknown."
    },
    {
        "anchor": "Decay properties of unstable Tonks-Girardeau gases from a split trap: We study the decay properties of Tonks-Girardeau gases escaping from a\ndouble-well potential. Initially, the gases are constrained between two\ninfinite $\\delta$ barriers with an on-center $\\delta$-split potential. The\nstrength of one of the obstacles is suddenly reduced, and the particles start\nto tunnel to the open space. Using the resonance expansion method, we derive\nthe single-term approximate expression for the $N$-particle survival\nprobability and demonstrate its effectiveness in both the exponential and\nnonexponential regimes. We also predict a parity effect and provide physical\ninsights into its nature at different stages of the time evolution. We conclude\nthat only the initial phase of the decay of the many-particle state may comply\nwith an exponential law. The decay properties are dramatically affected by the\npresence of the split barrier. Our results reveal the overall decay mechanism\nof unstable Tonks-Girardeau gases from single and double quantum wells.",
        "positive": "Equal-time approach to real-time dynamics of quantum fields: We employ the equal-time formulation of quantum field theory to derive\neffective kinetic theories, first for a weakly coupled non-relativistic Bose\ngas, and then for a strongly correlated system of self-interacting N-component\nfields. Our results provide the link between state-of-the-art measurements of\nequal-time effective actions using quantum simulator platforms, as employed in\nRefs. [1, 2], and observables underlying effective kinetic or hydrodynamic\ndescriptions. New non-perturbative approximation schemes can be developed and\ncertified this way, where the a priori time-local formulation of the equal-time\neffective action has crucial advantages over the conventional closed-time-path\napproach which is non-local in time."
    },
    {
        "anchor": "Many-body localization due to random interactions: The possibility of observing many body localization of ultracold atoms in a\none dimensional optical lattice is discussed for random interactions. In the\nnon-interacting limit, such a system reduces to single-particle physics in the\nabsence of disorder, i.e. to extended states. In effect the observed\nlocalization is inherently due to interactions and is thus a genuine many-body\neffect. In the system studied, many-body localization manifests itself in a\nlack of thermalization visible in temporal propagation of a specially prepared\ninitial state, in transport properties, in the logarithmic growth of\nentanglement entropy as well as in statistical properties of energy levels.",
        "positive": "Terahertz emission from AC Stark-split asymmetric intersubband\n  transitions: Transitions between the two states of an AC Stark-split doublet are forbidden\nin centro-symmetric systems, and thus almost impossible to observe in\nexperiments performed with atomic clouds. However, electrons trapped in\nnanoscopic heterostructures can behave as artificial atoms, with the advantage\nthat the wavefunction symmetry can be broken by using asymmetric confining\npotentials. Here we develop the many-body theory describing the intra-doublet\nemission of a resonantly pumped intersubband transition in a doped asymmetric\nquantum well, showing that in such a system the intra-doublet emission can be\norders of magnitude higher than in previously studied systems. This emission\nchannel, which lies in the terahertz range, and whose frequency depends upon\nthe pump power, opens the way to the realization of a new class of monolithic\nand tunable terahertz emitters."
    },
    {
        "anchor": "Dynamical emergence of a Kosterlitz-Thouless transition in a disordered\n  Bose gas following a quench: We study the dynamical evolution of a two-dimensional Bose gas after a\ndisorder potential quench. Depending on the initial conditions, the system\nevolves either to a thermal or a superfluid state. Using extensive quasi-exact\nnumerical simulations, we show that the two phases are separated by a\nKosterlitz-Thouless transition. The thermalization time is shown to be longer\nin the superfluid phase, but no critical slowing down is observed at the\ntransition. The long-time phase diagram is well reproduced by a simple\ntheoretical model. The spontaneous emergence of Kosterlitz-Thouless transitions\nfollowing a quench is a generic phenomenon that should arise both in the\ncontext of non-equilibrium quantum gases and nonlinear, classical wave systems.",
        "positive": "Collective excitations of a dilute Bose gas at finite temperature: TDHFB\n  Theory: Using the time-dependent Hartree-Fock-Bogoliubov approach, where the\ncondensate is coupled with the thermal cloud and the anomalous density, we\nstudy the equilibrium and the dynamical properties of three-dimensional\nquantum-degenerate Bose gas at finite temperature. Effects of the anomalous\ncorrelations on the condensed fraction and the critical temperature are\ndiscussed. In uniform Bose gas, useful expressions for the Bogoliubov\nexcitations spectrum, the first and second sound, the condensate depletion and\nthe superfluid fraction are derived. Our results are tested by comparing the\nfindings computed by Quantum Monte Carlo simulations. We present also a\nsystematic investigation of the collective modes of a Bose condensate confined\nin an external trap. Our predictions are in qualitative agreement with previous\nexperimental and theoretical results. We show in particular that our theory is\ncapable of explaining the so-called anomalous behavior of the m=0 mode."
    },
    {
        "anchor": "Instabilities of a Filled Vortex in a Two-Component Bose-Einstein\n  Condensate: A two-component Bose-Einstein condensate of cold atoms with a strong\nintercomponent repulsion leading to the spatial separation of the components\nhas been numerically studied. Configurations with a multiple quantized vortex\nin one component, where the vortex core is filled with the other component, are\nconsidered. The effective radius of the core can exceed the width of the\ntransition layer between components, and then an analogy with a filled\ncylindrical vortex in the classical hydrodynamics of two immiscible ideal\nfluids appears. This analogy allows one to analyze the longitudinal \"sausage\"\ninstability and the transverse instability of the filled vortex in the\ncondensate caused by the \"tangential discontinuity,\" as well as the stable\nregime in the parametric gap between them. The presence of long-lived coherent\nstructures formed in some cases at the nonlinear stages of both instabilities\nis numerically discovered.",
        "positive": "Dynamical Weyl Points and 4D Nodal Rings in Cold Atomic Gases: Controllability of ultracold atomic gases has reached an unprecedented level,\nallowing for experimental realization of the long-sought-after Thouless pump,\nwhich can be interpreted as a dynamical quantum Hall effect. On the other hand,\nWeyl semimetals and Weyl nodal line semimetals with touching points and rings\nin band structures have sparked tremendous interest in various fields in the\npast few years. Here, we show that dynamical Weyl points and dynamical 4D Weyl\nnodal rings, which are protected by the first Chern number on a parameter\nsurface formed by quasi-momentum and time, emerge in a two-dimensional and\nthree-dimensional system, respectively. We find that the topological pump\noccurs in these systems but the amount of pumped particles is not quantized and\ncan be continuously tuned by controlling experimental parameters over a wide\nrange. We also propose an experimental scheme to realize the dynamical Weyl\npoints and 4D Weyl nodal rings and to observe their corresponding topological\npump in cold atomic gases."
    },
    {
        "anchor": "Mott Insulator-like Bose-Einstein Condensation in a Tight-Binding System\n  of Interacting Bosons with a Flat Band: We propose a new class of tight-binding systems of interacting bosons with a\nflat band, which are exactly solvable in the sense that one can explicitly\nwrite down the unique ground state. The ground state is expressed in terms of\nlocal creation operators, and apparently resembles that of a Mott insulator.\nBased on an exact representation in terms of a classical loop-gas model, we\nconjecture that the ground state may exhibit quasi Bose-Einstein condensation\n(BEC) or genuine BEC in dimensions two and three or higher, respectively, still\nkeeping Mott insulator-like character. Our Monte Carlo simulation of the\nloop-gas model strongly supports this conjecture, i.e., the ground state\nundergoes a Kosterlitz-Thouless transition and exhibits quasi BEC in two\ndimensions.",
        "positive": "Feedback Induced Magnetic Phases in Binary Bose-Einstein Condensates: Weak measurement in tandem with real-time feedback control is a new route\ntoward engineering novel non-equilibrium quantum matter. Here we develop a\ntheoretical toolbox for quantum feedback control of multicomponent\nBose-Einstein condensates (BECs) using backaction-limited weak measurements in\nconjunction with spatially resolved feedback. Feedback in the form of a\nsingle-particle potential can introduce effective interactions that enter into\nthe stochastic equation governing system dynamics. The effective interactions\nare tunable and can be made analogous to Feshbach resonances --\nspin-independent and spin-dependent -- but without changing atomic scattering\nparameters. Feedback cooling prevents runaway heating due to measurement\nbackaction and we present an analytical model to explain its effectiveness. We\nshowcase our toolbox by studying a two-component BEC using a stochastic\nmean-field theory, where feedback induces a phase transition between easy-axis\nferromagnet and spin-disordered paramagnet phases. We present the steady-state\nphase diagram as a function of intrinsic and effective spin-dependent\ninteraction strengths. Our result demonstrates that closed-loop quantum control\nof Bose-Einstein condensates is a powerful new tool for quantum engineering in\ncold-atom systems."
    },
    {
        "anchor": "Domain Size Distribution in Segregating Binary Superfluids: Domain size distribution in phase separating binary Bose--Einstein\ncondensates is studied theoretically by numerically solving the\nGross--Pitaevskii equations at zero temperature. We show that the size\ndistribution in the domain patterns arising from the dynamic instability obeys\na power law in a scaling regime according to the dynamic scaling analysis based\non the percolation theory. The scaling behavior is kept during the relaxation\ndevelopment until the characteristic domain size becomes comparable to the\nlinear size of the system, consistent with the dynamic scaling hypothesis of\nthe phase-ordering kinetics. Our numerical experiments indicate the existence\nof a different scaling regime in the size distribution function, which can be\ncaused by the so-called coreless vortices.",
        "positive": "Spin-Flipping Half Vortex in a Macroscopic Polariton Spinor Ring\n  Condensate: We report the observation of vorticity in a macroscopic Bose-Einstein\ncondensate of polaritons in a ring geometry. Because it is a spinor condensate,\nthe elementary excitations are \"half vortices\" in which there is a phase\nrotation of $\\pi$ in connection with a polarization vector rotation of $\\pi$\naround a closed path. This is clearly seen in the experimental observations of\nthe polarization rotation around the ring. In the ring geometry, a new type of\nhalf vortex is allowed in which the handedness of the spin flips from one side\nof the ring to the other, in addition to the rotation of the linear\npolarization component; such a state is not allowed in a simply-connected\ngeometry. Theoretical calculation of the energy of this state shows that when\nmany-body interactions are taken into account, it is lower in energy than a\nsimple half vortex. The direction of circulation of the flow around the ring\nfluctuates randomly between clockwise and counterclockwise from one shot to the\nnext; this corresponds to spontaneous breaking of time-reversal symmetry in the\nsystem. These new, macroscopic polariton ring condensates allow for the\npossibility of direct control of the vorticity of the condensate."
    },
    {
        "anchor": "Bulk viscosity and conformal symmetry breaking in the dilute Fermi gas\n  near unitarity: The dilute Fermi gas at unitarity is scale invariant and its bulk viscosity\nvanishes. We compute the leading contribution to the bulk viscosity when the\nscattering length is not infinite. A measure of scale breaking is provided by\nthe ratio $(P-\\frac{2}{3}{\\cal E})/P$, where $P$ is the pressure and ${\\cal E}$\nis the energy density. In the high temperature limit this ratio scales as\n$\\frac{z\\lambda}{a}$, where $z$ is the fugacity, $\\lambda$ is the thermal wave\nlength, and $a$ is the scattering length. We show that the bulk viscosity\n$\\zeta$ scales as the second power of this parameter, $\\zeta \\sim\n(\\frac{z\\lambda}{a})^2 \\lambda^{-3}$.",
        "positive": "Faraday Waves in Bose-Einstein Condensates -- The Excitation by the\n  Modulation of the Interaction and the Potential: We numerically study the dynamics of Faraday waves for Bose-Einstein\ncondensates(BECs) trapped by anisotropic potentials using the three-dimensional\nGross-Pitaevskii equation. In previous studies, Faraday waves were excited by\nperiodic modulation of the interaction or potential; in contrast, this study\nsystematically addresses the excitations of the two methods. When the\ninteraction is modulated with a modulation frequency resonant with Faraday\nwaves, the breathing mode along the tight confinement direction is excited, and\nthe Faraday waves appear in the direction of weak confinement. A modulation\nfrequency that is not resonant with Faraday waves does not excite Faraday\nwaves. Thus, the dynamics depend on modulation frequencies. The behavior of the\ntotal energy and its decomposition characterize the dynamics. The excitation of\nFaraday waves depends on the anisotropy of the potentials as well; Faraday\nwaves are excited only for elongated BECs. We compare the differences of the\ndynamics in modulation methods. There are no qualitative differences between\nthe modulation of the interaction and potential. When the interaction and\npotential are simultaneously modulated, Faraday waves are excited but they do\nnot necessarily work additively. To understand this phenomenon as a dynamical\nsystem, we choose a few dynamical variables and follow their trajectory in a\nphase space. The trajectory characteristics of Faraday waves and the breathing\nmode show that the methods of modulation are not very relevant; determining the\ntarget mode to excite is important."
    },
    {
        "anchor": "Density fluctuations and compressibility matrix for population or mass\n  imbalanced Fermi-Fermi mixtures: We describe the relation between the isothermal atomic compressibility and\ndensity fluctuations in mixtures of two-component fermions with population or\nmass imbalance. We derive a generalized version of the fluctuation-dissipation\ntheorem which is valid for both balanced and imbalanced Fermi-Fermi mixtures.\nFurthermore, we show that the compressibility, its critical exponents, and\nphase boundaries can be extracted via an analysis of the density fluctuations\nas a function of population imbalance, interaction parameter or temperature.\nLastly, we demonstrate that in the presence of trapping potentials, the local\ncompressibility and local density-density correlations can be extracted via a\ngeneralized fluctuation-dissipation theorem valid within the local density\napproximation.",
        "positive": "In-situ magnetometry for experiments with atomic quantum gases: Precise control of magnetic fields is a frequent challenge encountered in\nexperiments with atomic quantum gases. Here we present a simple method for\nperforming in-situ monitoring of magnetic fields that can readily be\nimplemented in any quantum-gas apparatus in which a dedicated\nfield-stabilization approach is not possible. The method, which works by\nsampling several Rabi resonances between magnetically field sensitive internal\nstates that are not otherwise used in a given experiment, can be integrated\nwith standard measurement sequences at arbitrary fields. For a condensate of\n$^{87}$Rb atoms, we demonstrate the reconstruction of Gauss-level bias fields\nwith an accuracy of tens of microgauss and with millisecond time resolution. We\ntest the performance of the method using measurements of slow resonant Rabi\noscillations on a magnetic-field sensitive transition, and give an example for\nits use in experiments with state-selective optical potentials."
    },
    {
        "anchor": "Exact density profiles and symmetry classification for strongly\n  interacting multi-component Fermi gases in tight waveguides: We consider a mixture of one-dimensional strongly interacting Fermi gases up\nto six components, subjected to a longitudinal harmonic confinement. In the\nlimit of infinitely strong repulsions we provide an exact solution which\ngeneralizes the one for the two-component mixture. We show that an imbalanced\nmixture under harmonic confinement displays partial spatial separation among\nthe components, with a structure which depends on the relative population of\nthe various components. Furthermore, we provide a symmetry characterization of\nthe ground and excited states of the mixture introducing and evaluating a\nsuitable operator, namely the conjugacy class sum. We show that, even under\nexternal confinement, the gas has a definite symmetry which corresponds to the\nmost symmetric one compatible with the imbalance among the components. This\ngeneralizes the predictions of the Lieb-Mattis theorem for a fermionic mixture\nwith more than two components.",
        "positive": "Ultracold Quantum Gases in Optical Lattice with Topological Defects: Its\n  Physics and Experimental Proposal: In this paper we give a proposal to realize optical lattices with manipulated\ndislocations and study the physics of ultracold quantum gas on a\ntwo-dimensional (2D) optical square lattice with dislocations. In particular,\nthe dislocations may induce fractional topological flux on 2D Peierls optical\nlattice. These results pave new approach to study the quantum many-body systems\non an optical lattice with controllable topological lattice-defects, including\nthe dislocations, topological fluxes."
    },
    {
        "anchor": "Zero-temperature phase diagram of hard sphere bosons in asymmetric three\n  dimensional optical lattices: We studied the superfluid-to-Mott insulator transition for bosonic hard\nspheres loaded in asymmetric three-dimensional optical lattices by means of\ndiffusion Monte Carlo calculations. The onset of the transition was monitored\nthrough the change in the chemical potential around the density corresponding\nto one particle per potential well. With this method, we were able to reproduce\nthe results given in the literature for three-dimensional symmetric lattices\nand for systems whose asymmetry makes them equivalent to a set of quasi-one\ndimensional tubes. The location of the same transition for asymmetric systems\nakin to a stack of quasi-two dimensional lattices will be also given. Our\nresults were checked against those given by a Bose-Hubbard model for similar\narrangements.",
        "positive": "The origin of the period-$2T/7$ quasi-breathing in disk-shaped\n  Gross-Pitaevskii breathers: We address the origins of the quasi-periodic breathing observed in [Phys.\nRev.\\ X vol. 9, 021035 (2019)] in disk-shaped harmonically trapped\ntwo-dimensional Bose condensates, where the quasi-period\n$T_{\\text{quasi-breathing}}\\sim$~$2T/7$ and $T$ is the period of the harmonic\ntrap. We show that, due to an unexplained coincidence, the first instance of\nthe collapse of the hydrodynamic description, at $t^{*} =\n\\arctan(\\sqrt{2})/(2\\pi) T \\approx T/7$, emerges as a `skillful impostor' of\nthe quasi-breathing half-period $T_{\\text{quasi-breathing}}/2$. At the time\n$t^{*}$, the velocity field almost vanishes, supporting the requisite\ntime-reversal invariance. We find that this phenomenon persists for\nscale-invariant gases in all spatial dimensions, being exact in one dimension\nand, likely, approximate in all others. In $d$ dimensions, the quasi-breathing\nhalf-period assumes the form $T_{\\text{quasi-breathing}}/2 \\equiv t^{*} =\n\\arctan(\\sqrt{d})/(2\\pi) T$. Remaining unresolved is the origin of the\nperiod-$2T$ breathing, reported in the same experiment."
    },
    {
        "anchor": "Energy relaxation in the Gross-Pitaevskii equation: We introduce a dissipation term in the Gross-Pitaevskii equation that\ndescribes the stimulated relaxation of condensed bosons due to scattering with\na different type of particles. This situation applies to Bose-Einstein\ncondensates of quasi-particles in the solid state, such as magnons and\nexcitons. Our model is compatible with the phenomenology of superfluidity:\nsupercurrents are stable up to a critical speed and decay when they are faster.",
        "positive": "A strongly interacting Sarma superfluid near orbital Feshbach resonances: We investigate the nature of superfluid pairing in a strongly interacting\nFermi gas near orbital Feshbach resonances with spin-population imbalance in\nthree dimensions, which can be well described by a two-band or two-channel\nmodel. We show that a Sarma superfluid with gapless single-particle excitations\nis favored in the closed channel at large imbalance. It is thermodynamically\nstable against the formation of an inhomogeneous Fulde\\textendash\nFerrell\\textendash Larkin\\textendash Ovchinnikov superfluid and features a\nwell-defined Goldstone-Anderson-Bogoliubov phonon mode and a massive Leggett\nmode as collective excitations at low momentum. At large momentum, the Leggett\nmode disappears and the phonon mode becomes damped at zero temperature, due to\nthe coupling to the particle-hole excitations. We discuss possible experimental\nobservation of a strongly interacting Sarma superfluid with ultracold\nalkaline-earth-metal Fermi gases."
    },
    {
        "anchor": "Exciton-polariton condensates in zero-, one-, and two-dimensional\n  lattices: Microcavity exciton-polaritons are quantum quasi-particles arising from the\nstrong light-matter coupling. They have exhibited rich quantum dynamics rooted\nfrom bosonic nature and inherent non-equilibrium condition. Dynamical\ncondensation in microcavity exciton-polaritons has been observed at much\nelevated temperatures in comparison to ultrocold atom condensates. Recently, we\nhave investigated the behavior of exciton-polariton condensates in artificial\ntrap and lattice geometries in zero-dimension, one-dimension (1D) and\ntwo-dimension (2D). Coherent $\\pi$-state with p-wave order in a 1D condensate\narray and d-orbital state in a 2D square lattice are observed. We anticipate\nthat the preparation of high-orbital condensates can be further extended to\nprobe dynamical quantum phase transition in a controlled manner as quantum\nemulation applications.",
        "positive": "Proximity effect and spatial Kibble-Zurek mechanism in atomic Fermi\n  gases with inhomogeneous pairing interactions: Introducing spatially tunable interactions to atomic Fermi gases makes it\nfeasible to study two phenomena, the proximity effect and spatial Kibble-Zurek\nmechanism (KZM), in a unified platform. While the proximity effect of a\nsuperconductor adjacent to a normal metal corresponds to a step-function quench\nof the pairing interaction in real space, the spatial KZM is based on a linear\ndrop of the interaction that can be modeled as a spatial quench. After\nformulating the Fermi gases with spatially varying pairing interactions by the\nBogoliubov-de Gennes equation, we obtain the profiles of the pair wavefunction\nand its correlation function to study their penetration into the noninteracting\nregion. For the step-function quench, both correlation lengths from the pair\nwavefunction and its correlation function follow the BCS coherence length and\nexhibit the same scaling behavior. In contrast, the scaling behavior of the two\ncorrelation lengths are different in the spatial quench, which then allows more\nrefined analyses of the correlation lengths from different physical quantities.\nMoreover, adding a weakly interacting bosonic background does not change the\nscaling behavior. We also discuss relevant experimental techniques that may\nrealize and verify the inhomogeneous phenomena."
    },
    {
        "anchor": "Probing the local rapidity distribution of a 1D Bose gas: One-dimensional Bose gases with contact repulsive interactions are\ncharacterized by the presence of infinite-lifetime quasiparticles whose momenta\nare called the `rapidities'. Here we develop a probe of the local rapidity\ndistribution, based on the fact that rapidities are the asymptotic momenta of\nthe particles after a very long one-dimensional expansion. This is done by\nperforming an expansion of a selected slice of the gas. As a proof of concept,\nwe apply this to a cloud at equilibrium in a trap. While for realistic\nexpansion times the asymptotic regime is barely reached, we show that the\nexpansion dynamics follows the hydrodynamic scaling such that one can use the\ntheory of Generalized Hydrodynamics to analyze the expansion. Our data are in\ngood agreement with the theory.",
        "positive": "Phonon mediated conversion of exciton-polaritons Rabi oscillation into\n  THz radiation: Semiconductor microcavities in the strong-coupling regime exhibit an energy\nscale in the THz frequency range, which is fixed by the Rabi splitting between\nthe upper and lower exciton-polariton states. While this range can be tuned by\nseveral orders of magnitude using different excitonic medium, the transition\nbetween both polaritonic states is dipole forbidden. In this work we show that\nin Cadmium Telluride microcavities, the Rabi-oscillation driven THz radiation\nis actually active without the need for any change in the microcavity design.\nThis feature results from the unique resonance condition which is achieved\nbetween the Rabi splitting and the phonon-polariton states, and leads to a\ngiant enhancement of the second order nonlinearity."
    },
    {
        "anchor": "Ground-state properties of dilute one-dimensional Bose gas with\n  three-body repulsion: We determined perturbatively the low-energy universal thermodynamics of\ndilute one-dimensional bosons with the three-body repulsive forces. The final\nresults are presented for the limit of vanishing potential range in terms of\nthree-particle scattering length. An analogue of Tan`s energy theorem for\nconsidered system is derived in generic case without assuming weakness of the\ninterparticle interaction. We also obtained an exact identity relating the\nthree-body contact to the energy density.",
        "positive": "Superfluid vortex dynamics on a torus and other toroidal surfaces of\n  revolution: The superfluid flow velocity is proportional to the gradient of the phase of\nthe superfluid order parameter, leading to the quantization of circulation\naround a vortex core. In this work, we study the dynamics of a superfluid film\non the surface of a torus. Such a compact surface allows only configurations of\nvortices with zero net vorticity. We derive analytic expressions for the flow\nfield, the total energy, and the time-dependent dynamics of the vortex cores.\nThe local curvature of the torus and the presence of non-contractable loops on\nthis multiply connected surface alter both the superfluid flow and the vortex\ndynamics. Finally we consider more general surfaces of revolution, called\ntoroids."
    },
    {
        "anchor": "Impact of Many-Body Correlations on the Dynamics of an Ion-Controlled\n  Bosonic Josephson Junction: We investigate an atomic ensemble of interacting bosons trapped in a\nsymmetric double well potential in contact with a single tightly trapped ion\nwhich has been recently proposed [R. Gerritsma et al., Phys. Rev. Lett. 109,\n080402 (2012)] as a source of entanglement between a Bose-Einstein condensate\nand an ion. Compared to the previous study, the present work aims at performing\na detailed and accurate many-body analysis of such combined atomic quantum\nsystem by means of the ab-initio multi-configuration time-dependent Hartree\nmethod for bosons, which allows to take into account all correlations in the\nsystem. The analysis elucidates the importance of quantum correlations in the\nbosonic ensemble and reveals that entanglement generation between an ion and a\ncondensate is indeed possible, as previously predicted. Moreover, we provide an\nintuitive picture of the impact of the correlations on the out-of-equilibrium\ndynamics by employing a natural orbital analysis which we show to be indeed\nexperimentally verifiable.",
        "positive": "One-dimensional ultracold atomic gases: Impact of the effective range on\n  integrability: Three identical bosons or fermions are considered in the limit of zero-range\ninteractions and finite effective range. By using a two channel model, we show\nthat these systems are not integrable and that the wave function verifies\nspecific continuity conditions at the contact of three particles. This last\nfeature permits us to solve a contradiction brought by the contact model which\ncan lead to an opposite result concerning the integrability issue. For\nfermions, the vicinity of integrability is characterized by large deviations\nwith respect to the predictions of the Bethe ansatz."
    },
    {
        "anchor": "Blocked populations in ring-shaped optical lattices: We study a special dynamical regime of a Bose-Einstein condensate in a\nring-shaped lattice where the populations in each site remain constant during\nthe time evolution. The states in this regime are characterized by equal\noccupation numbers in alternate wells and non-trivial phases, while the phase\ndifferences between neighboring sites evolve in time yielding persistent\ncurrents that oscillate around the lattice. We show that the velocity\ncirculation around the ring lattice alternates between two values determined by\nthe number of wells and with a specific time period that is only driven by the\nonsite interaction energy parameter. In contrast to the self-trapping regime\npresent in optical lattices, the occupation number at each site does not show\nany oscillation and the particle imbalance does not possess a lower bound for\nthe phenomenon to occur. These findings are predicted with a multimode model\nand confirmed by full three-dimensional Gross-Pitaevskii simulations using an\neffective onsite interaction energy parameter.",
        "positive": "The Prediction of a Gapless Topological \"Haldane Liquid\" Phase in a\n  One-Dimensional Cold Polar Molecular Lattice: We show that ultracold two-component fermionic dipolar gases in an optical\nlattice with strong two-body on-site loss can be used to realize a tunable\neffective spin-one model. Fermion number conservation provides an unusual\nconstraint that $\\sum_i (S^z_i)^2$ is conserved, leading to a novel topological\nliquid phase in one dimension which can be thought of as the gapless analog of\nthe Haldane gapped phase of a spin-one Heisenberg chain. The properties of this\nphase are calculated numerically via the infinite time-evolving block\ndecimation method and analytically via a mapping to a one-mode Luttinger liquid\nwith hidden spin information."
    },
    {
        "anchor": "Novel quantum phases of two-component bosons with pair hopping in\n  synthetic dimension: We study two-component (or pseudospin-1/2) bosons with pair hopping\ninteractions in synthetic dimension, for which a feasible experimental scheme\non a square optical lattice is also presented. Previous studies have shown that\ntwo-component bosons with on-site interspecies interaction can only generate\nnontrivial interspecies paired superfluid (super-counter-fluidity or\npair-superfluid) state. In contrast, apart from interspecies paired superfluid,\nwe reveal two new phases by considering this additional pair hopping\ninteraction. These novel phases are intraspecies paired superfluid (molecular\nsuperfluid) and an exotic non-integer Mott insulator which shows a non-integer\natom number at each site for each species, but an integer for total atom\nnumber.",
        "positive": "Evolution of entanglement entropy in strongly correlated bosons in an\n  optical lattice: We investigate the time evolution of the second-order R\\'enyi entropy (RE)\nfor bosons in a one-dimensional optical lattice following a sudden quench of\nthe hopping amplitude $J$. Specifically, we examine systems that are quenched\ninto the strongly correlated Mott-insulating (MI) regime with $J/U\\ll 1$ ($U$\ndenotes the strength of the on-site repulsive interaction) from the MI limit\nwith $J=0$. In this regime, the low-energy excited states can be effectively\ndescribed by fermionic quasiparticles known as doublons and holons. They are\nexcited in entangled pairs through the quench dynamics. By developing an\neffective theory, we derive a direct relation between the RE and correlation\nfunctions associated with doublons and holons. This relation allows us to\nanalytically calculate the RE and obtain a physical picture for the RE, both in\nthe ground state and during time evolution through the quench dynamics, in\nterms of doublon holon pairs. In particular, we show that the RE is\nproportional to the population of doublon-holon pairs that span the boundary of\nthe subsystem. Our quasiparticle picture introduces some remarkable features\nthat are absent in previous studies on the dynamics of entanglement entropy in\nfree-fermion models. It provides with valuable insights into the dynamics of\nentanglement entropy in strongly-correlated systems."
    },
    {
        "anchor": "Hartree-Fock-Bogoliubov Theory of Dipolar Fermi Gases: We construct a fully self-consistent Hartree-Fock-Bogoliubov theory that\ndescribes a spinless Fermi gas with long-range interaction. We apply this\ntheory to a system of uniform dipolar fermionic polar molecules, which has\nattracted much attention recently, due to rapid experimental progress in\nachieving such systems. By calculating the anisotropic superfluid order\nparameter, and the critical temperature $T_{c}$, we show that, \"hign $T_c$\"\nsuperfluid can be achieved with a quite modest value of interaction strength\nfor polar molecules. In addition, we also show that the presence of the Fock\nexchange interaction enhances superfluid pairing.",
        "positive": "Dependence of interface conductivity on relevant physical parameters in\n  polarized Fermi mixtures: We consider a mass-asymmetric polarized Fermi system in the presence of\nHartree-Fock (HF) potentials. We concentrate on the BCS regime with various\ninteraction strengths and numerically obtain the allowed values of the chemical\nand HF potentials, as well as the mass ratio. The functional dependence of the\nheat conductivity of the N-SF interface on relevant physical parameters, namely\nthe temperature, the mass ratio, and the interaction strength, is obtained. In\nparticular, we show that the interface conductivity starts to drop with\ndecreasing temperature at the temperature, $T_{\\text{m}}$, where the mean\nkinetic energy of the particles is just sufficient to overcome the SF gap. We\nobtain $T_{\\text{m}}$ as a function of the mass ratio and the interaction\nstrength. The variation of the heat conductivity, at fixed temperature, with\nthe HF potentials and the imbalance chemical potential is also obtained.\nFinally, because the range of relevant temperatures increases for larger values\nof the mass ratio, we consider the $^6\\text{Li}$-$^{40}\\text{K}$ mixture\nseparately by taking the temperature dependence of the pair potential into\naccount."
    },
    {
        "anchor": "Spin-orbit coupled ultracold gases in optical lattices: High-band\n  physics and insufficiency of tight-binding models: We study the interplay effect of spin-orbit coupling(SOC) and optical lattice\nto the single-particle physics and superfluid-insulator transition in ultracold\nFermi gases. We consider the type of SOC that has been realized in cold atoms\nexperiments via two-photon Raman processes. Our analyses are based on the\nknowledge of full single-particle spectrum in lattices, without relying on any\ntightbinding approximation.We evaluate existing tight-binding models and point\nout their limitations in predicting the correct single-particle physics due to\nthe missed high-band contributions. Moreover, we show that the Raman field\n(creating SOC) can induce band-gap closing in a two-dimensional optical\nlattice, leading to the intriguing phenomenon of superfluidity-reentrance for\ninteracting fermions at integer filling. We present the superfluid-insulator\nphase diagram in a wide parameter regime of chemical potentials and Raman\nfields. All these results are far beyond any tight-binding model can predict,\nand can be directly probed in current cold atoms experiments.",
        "positive": "Laughlin's topological charge pump in an atomic Hall cylinder: The quantum Hall effect occuring in two-dimensional electron gases was first\nexplained by Laughlin, who envisioned a thought experiment that laid the\ngroundwork for our understanding of topological quantum matter. His proposal is\nbased on a quantum Hall cylinder periodically driven by an axial magnetic\nfield, resulting in the quantized motion of electrons. We realize this\nmilestone experiment with an ultracold gas of dysprosium atoms, the cyclic\ndimension being encoded in the electronic spin and the axial field controlled\nby the phases of laser-induced spin-orbit couplings. Our experiment provides a\nstraightforward manifestation of the non-trivial topology of quantum Hall\ninsulators, and could be generalized to strongly-correlated topological\nsystems."
    },
    {
        "anchor": "Detecting quadrupole interactions in ultracold Fermi gases: We propose to detect quadrupole interactions of neutral ultra-cold atoms via\ntheir induced mean-field shift. We consider a Mott insulator state of\nspin-polarized atoms in a two-dimensional optical square lattice. The\nquadrupole moments of the atoms are aligned by an external magnetic field. As\nthe alignment angle is varied, the mean-field shift shows a characteristic\nangular dependence, which constitutes the defining signature of the quadrupole\ninteraction. For the $^{3}P_{2}$ states of Yb and Sr atoms, we find a frequency\nshift of the order of tens of Hertz, which can be realistically detected in\nexperiment with current technology. We compare our results to the mean-field\nshift of a spin-polarized quasi-2D Fermi gas in continuum.",
        "positive": "Many-body Decay of the Gapped Lowest Excitation of a Bose-Einstein\n  Condensate: We study the decay mechanism of the gapped lowest-lying excitation of a\nquasi-pure box-trapped atomic Bose-Einstein condensate. Owing to the absence of\nlower-energy modes, or direct coupling to an external bath, this excitation is\nprotected against one-body (linear) decay and the damping mechanism is\nexclusively nonlinear. We develop a universal theoretical model that explains\nthis fundamental nonlinear damping as a process whereby two quanta of the\ngapped lowest excitation mode couple to a higher-energy mode, which\nsubsequently decays into a continuum. We find quantitative agreement between\nour experiments and the predictions of this model. Finally, by strongly driving\nthe system below its (lowest) resonant frequency we observe third-harmonic\ngeneration, a hallmark of nonlinear behavior."
    },
    {
        "anchor": "Orbital optical lattices with bosons: This article provides a synopsis of our recent experimental work exploring\nBose-Einstein condensation in metastable higher Bloch bands of optical\nlattices. Bipartite lattice geometries have allowed us to implement appropriate\nband structures, which meet three basic requirements: the existence of\nmetastable excited states sufficiently protected from collisional band\nrelaxation, a mechanism to excite the atoms initially prepared in the lowest\nband with moderate entropy increase, and the possibility of cross-dimensional\ntunneling dynamics, necessary to establish coherence along all lattice axes. A\nvariety of bands can be selectively populated and a subsequent thermalisation\nprocess leads to the formation of a condensate in the lowest energy state of\nthe chosen band. As examples the 2nd, 4th and 7th bands in a bipartite square\nlattice are discussed. In the 2nd and 7th band, the band geometry can be tuned\nsuch that two inequivalent energetically degenerate energy minima arise at the\n$X_{\\pm}$-points at the edge of the 1st Brillouin zone. In this case even a\nsmall interaction energy is sufficient to lock the phase between the two\ncondensation points such that a complex-valued chiral superfluid order\nparameter can emerge, which breaks time reversal symmetry. In the 4th band a\ncondensate can be formed in the $\\Gamma$-point in the center of the 1st\nBrillouin zone, which can be used to explore topologically protected band\ntouching points. The new techniques to access orbital degrees of freedom in\nhigher bands greatly extend the class of many-body scenarios that can be\nexplored with bosons in optical lattices.",
        "positive": "Breakdown of the Meissner effect at the zero exceptional point in\n  non-Hermitian two-band BCS model: The spontaneous symmetry breaking of a continuous symmetry in complex field\ntheory at the exceptional point of the parameter space is known to exhibit\ninteresting phenomena, such as the breakdown of a Higgs mechanism. In this\nwork, we derive the complex Ginzburg-Landau model from a non-Hermitian two-band\nBCS model via path integral and investigate its spontaneous symmetry breaking.\nWe find that analog to the Higgs mechanism, the Meissner effect of the complex\nGinzburg-Landau model also breaks down at the exceptional point while the gap\nparameters stay finite."
    },
    {
        "anchor": "Spin Waves and Dielectric Softening of Polar Molecule Condensates: We consider an oblate Bose-Einstein condensate of heteronuclear polar\nmolecules in a weak applied electric field. This system supports a rich\nquasiparticle spectrum that plays a critical role in determining its bulk\ndielectric properties. In particular, in sufficiently weak fields the system\nundergoes a polarization wave rotonization, leading to the development of\ntextured electronic structure and a dielectric instability that is\ncharacteristic of the onset of a negative static dielectric function.",
        "positive": "Metastable hard-axis polar state of a spinor Bose-Einstein condensate\n  under a magnetic field gradient: We investigate the stability of a hard-axis polar state in a spin-1\nantiferromagnetic Bose-Einstein condensate under a magnetic field gradient,\nwhere the easy-plane spin anisotropy is controlled by a negative quadratic\nZeeman energy $q<0$. In a uniform magnetic field, the axial polar state is\ndynamically unstable and relaxes into the planar polar ground state. However,\nunder a field gradient $B'$, the excited spin state becomes metastable down to\na certain threshold $q_{th}$ and as $q$ decreases below $q_{th}$, its intrinsic\ndynamical instability is rapidly recalled. The incipient spin excitations in\nthe relaxation dynamics appear with stripe structures, indicating the\nrotational symmetry breaking by the field gradient. We measure the dependences\nof $q_{th}$ on $B'$ and the sample size, and we find that $q_{th}$ is highly\nsensitive to the field gradient in the vicinity of $B'=0$, exhibiting power-law\nbehavior of $|q_{th}|\\propto B'^{\\alpha}$ with $\\alpha \\sim 0.5$. Our results\ndemonstrate the significance of the field gradient effect in the quantum\ncritical dynamics of spinor condensates."
    },
    {
        "anchor": "Generalized hydrodynamics in strongly interacting 1D Bose gases: The dynamics of strongly interacting many-body quantum systems are\nnotoriously complex and difficult to simulate. A new theory, generalized\nhydrodynamics (GHD), promises to efficiently accomplish such simulations for\nnearly-integrable systems. It predicts the evolution of the distribution of\nrapidities, which are the momenta of the quasiparticles in integrable systems.\nGHD was recently tested experimentally for weakly interacting atoms, but its\napplicability to strongly interacting systems has not been experimentally\nestablished. Here we test GHD with bundles of one-dimensional (1D) Bose gases\nby performing large trap quenches in both the strong and intermediate coupling\nregimes. We measure the evolving distribution of rapidities, and find that\ntheory and experiment agree well over dozens of trap oscillations, for average\ndimensionless coupling strengths that range from 0.3 to 9.3. By also measuring\nmomentum distributions, we gain experimental access to the interaction energy\nand thus to how the quasiparticles themselves evolve. The accuracy of GHD\ndemonstrated here confirms its wide applicability to the simulation of\nnearly-integrable quantum dynamical systems. Future experimental studies are\nneeded to explore GHD in spin chains, as well as the crossover between GHD and\nregular hydrodynamics in the presence of stronger integrability breaking\nperturbations.",
        "positive": "Quantum phase transition of Bose-Einstein condensates on a ring\n  nonlinear lattice: We study the phase transitions in a one dimensional Bose-Einstein condensate\non a ring whose atomic scattering length is modulated periodically along the\nring. By using a modified Bogoliubov method to treat such a nonlinear lattice\nin the mean field approximation, we find that the phase transitions are of\ndifferent orders when the modulation period is 2 and greater than 2. We further\nperform a full quantum mechanical treatment based on the time-evolving block\ndecimation algorithm which confirms the mean field results and reveals\ninteresting quantum behavior of the system. Our studies yield important\nknowledge of competing mechanisms behind the phase transitions and the quantum\nnature of this system."
    },
    {
        "anchor": "Thermalization dynamics of a gauge theory on a quantum simulator: Gauge theories form the foundation of modern physics, with applications\nranging from elementary particle physics and early-universe cosmology to\ncondensed matter systems. We perform quantum simulations of the unitary\ndynamics of a U(1) symmetric gauge field theory and demonstrate emergent\nirreversible behavior. The highly constrained gauge theory dynamics is encoded\nin a one-dimensional Bose--Hubbard simulator, which couples fermionic matter\nfields through dynamical gauge fields. We investigate global quantum quenches\nand the equilibration to a steady state well approximated by a thermal\nensemble. Our work may enable the investigation of elusive phenomena, such as\nSchwinger pair production and string-breaking, and paves the way for simulating\nmore complex higher-dimensional gauge theories on quantum synthetic matter\ndevices.",
        "positive": "Atomic soliton transmission and induced collapse in scattering from a\n  narrow barrier: We report systematic numerical simulations of the collision of a bright\nmatter-wave soliton made of Bose-condensed alkali-metal atoms through a narrow\npotential barrier by using the three-dimensional Gross-Pitaevskii equation. In\nthis way, we determine how the transmission coefficient depends on the soliton\nimpact velocity and the barrier height. Quite remarkably, we also obtain the\nregions of parameters where there is the collapse of the bright soliton induced\nby the collision. We compare these three-dimensional results with the ones\nobtained by three different one-dimensional nonlinear Schr\\\"odinger equations.\nWe find that a specifically modified nonpolynomial Schr\\\"odinger equation is\nable to accurately assess the transmission coefficient even in a region in\nwhich the usual nonpolynomial Schr\\\"odinger equation does collapse. In\nparticular, this simplified but very effective one-dimensional model takes into\naccount the transverse width dynamics of the soliton with an ordinary\ndifferential equation coupled to the partial differential equation of the axial\nwave function of the Bose-Einstein condensate."
    },
    {
        "anchor": "Mean-field dynamics of a Bose-Hubbard chain coupled to a non-Markovian\n  environment: We study the dynamics of an interacting Bose-Hubbard chain coupled to a\nnon-Markovian environment. Our basic tool is the reduced generating functional\nexpressed as a path integral over spin-coherent states. We calculate the\nleading contribution to the corresponding effective action, and by minimizing\nit, we derive mean-field equations that can be numerically solved. With this\ntool at hand, we examine the influence of the system's initial conditions and\ninterparticle interactions on the dissipative dynamics. Moreover, we\ninvestigate the presence of memory effects due to the non-Markovian\nenvironment.",
        "positive": "Hydrodynamics of vortices in Bose-Einstein condensates: A defect-gauge\n  field approach: This work rectifies the hydrodynamic equations commonly used to describe the\nsuperfluid velocity field in such a way that vortex dynamics are also taken\ninto account. In the field of quantum turbulence, it is of fundamental\nimportance to know the correct form of the equations which play similar roles\nto the Navier-Stokes equation in classical turbulence. Here, such equations are\nobtained by carefully taking into account the frequently overlooked multivalued\nnature of the $U(1)$ phase field. Such an approach provides exact analytical\nexplanations to some numerically observed features involving the dynamics of\nquantum vortices in Bose-Einstein condensates, such as the universal $t^{1/2}$\nbehavior of reconnecting vortex lines. It also expands these results beyond the\nGross-Pitaevskii theory so that some features can be generalized to other\nsystems such as superfluid $^{4}$He, dipolar condensates, and mixtures of\ndifferent superfluid systems."
    },
    {
        "anchor": "Mean-field yrast spectrum of a two-component Bose gas in ring geometry:\n  persistent currents at higher angular momentum: We use analytic soliton solutions of a two-component Bose gas in ring\ngeometry to analyze the mean-field yrast spectrum of the system. We find that\nthe spectrum exhibits a surprisingly rich structure as a result of the\ninterplay of interparticle interactions and population imbalance. We discuss\nthe implication of these results in regard to the possibility of persistent\ncurrents at higher angular momenta.",
        "positive": "Equation of state for the one-dimensional attractive \u03b4-potential\n  Bose gas in the weak-coupling regime: Approximated formulae for real quasi-momentum and the associated energy\nspectrum are presented for one-dimensional Bose gas with weak attractive\ncontact interactions. On the basis of the energy spectrum, we obtain the\nequation of state in the high temperature region, which is found to be the van\nder Waals equation without volume correction."
    },
    {
        "anchor": "Quantum magnetism of spinor bosons in optical lattices with synthetic\n  non-Abelian gauge fields: We study quantum magnetism of interacting spinor bosons at integer fillings\nhopping in a square lattice in the presence of non-Abelian gauge fields. In the\nstrong coupling limit, it leads to the Rotated ferromagnetic Heisenberg model\n(RFHM) which is a new class of quantum spin model. We introduce Wilson loops to\ncharacterize frustrations and gauge equivalent classes. For a special\nequivalent class, we identify a new spin-orbital entangled commensurate ground\nstate. It supports not only commensurate magnons, but also a new gapped\nelementary excitation: in-commensurate magnons with two gap minima continuously\ntuned by the SOC strength. At low temperatures, these magnons lead to dramatic\neffects in many physical quantities such as density of states, specific heat,\nmagnetization, uniform susceptibility, staggered susceptibility and various\nspin correlation functions. The commensurate magnons lead to a pinned central\npeak in the angle resolved light or atom Bragg spectroscopy. However, the\nin-commensurate magnons split it into two located at their two gap minima. At\nhigh temperatures, the transverse spin structure factors depend on the SOC\nstrength explicitly. The whole set of Wilson loops can be mapped out by\nmeasuring the specific heat at the corresponding orders in the high temperature\nexpansion. We argue that one gauge may be realized in current experiments and\nother gauges may also be realized in near future experiments. The results\nachieved along the exact solvable line sets up the stage to investigate\ndramatic effects when tuning away from it by various means. We sketch the\ncrucial roles to be played by these magnons at other equivalent classes, with\nspin anisotropic interactions and in the presence of finite magnetic fields.\nVarious experimental detections of these new phenomena are discussed. Rotated\nAnti-ferromagnetic Heisenberg model are also briefly mentioned.",
        "positive": "Rotonlike instability and pattern formation in spinor Bose-Einstein\n  condensates: We show that metastable phases of an antiferromagnetic spin-1 condensate in a\nsimple model with pure contact interactions can exhibit a rotonlike minimum in\nthe excitation spectrum. The introduction of magnetic field gives rise to the\ninstability of roton modes, which can lead to spontaneous emergence of regular\nperiodic, polygonal, polyhedral or crystalline patterns, as shown in numerical\nsimulations within the truncated Wigner approximation. An explanation of the\noccurrence of rotonlike instability is given based on the energy and spin\nconservation laws."
    },
    {
        "anchor": "Quantum optics and frontiers of physics: The third quantum revolution: The year 2015 was the International Year of Light. It marked, however, also\nthe 20th anniversary of the first observation of Bose-Einstein condensation in\natomic vapors by Eric Cornell, Carl Wieman and Wolfgang Ketterle. This\ndiscovery can be considered as one of the greatest achievements of quantum\noptics that has triggered an avalanche of further seminal discoveries and\nachievements. For this reason we devote this essay for focus issue on \"Quantum\nOptics in the International Year of Light\" to the recent revolutionary\ndevelopments in quantum optics at the frontiers of all physics: atomic physics,\nmolecular physics, condensed matter physics, high energy physics and quantum\ninformation science. We follow here the lines of the introduction to our book\n\"Ultracold atoms in optical lattices: Simulating quantum many-body systems\"\n[1]. The book, however, was published in 2012, and many things has happened\nsince then -- the present essay is therefore upgraded to include the latest\ndevelopments.",
        "positive": "Superfluidity of a dipolar Fermi gas in 2D optical lattices bilayer: We propose a model for addressing the superfluidity of two different Fermi\nspecies confined in a bilayer geometry of square optical lattices. The fermions\nare assumed to be molecules with interlayer s-wave interactions, whose dipole\nmoments are oriented perpendicularly to the layers. Using functional integral\ntechniques we investigate the BCS-like state induced in the bilayer at finite\ntemperatures. In particular, we determine the critical temperature as a\nfunction of the coupling strength between molecules in different layers and of\nthe interlayer spacing. By means of Ginzburg-Landau theory we calculate the\nsuperfluid density. We also study the dimerized BEC phase through the\nBerezinskii-Kosterlitz-Thouless transition, where the effective mass leads to\nidentify the crossover from BCS to BEC regimes. The possibility of tuning the\neffective mass as a direct consequence of the lattice confinement, allows us to\nsuggest a range of values of the interlayer spacing, which would enable\nobserving this superfluidity within current experimental conditions."
    },
    {
        "anchor": "Engineering non-binary Rydberg interactions via phonons in an optical\n  lattice: Coupling electronic and vibrational degrees of freedom of Rydberg atoms held\nin optical tweezer arrays offers a flexible mechanism for creating and\ncontrolling atom-atom interactions. We find that the state-dependent coupling\nbetween Rydberg atoms and local oscillator modes gives rise to two- and\nthree-body interactions which are controllable through the strength of the\nlocal confinement. This approach even permits the cancellation of two-body\nterms such that three-body interactions become dominant. We analyze the\nstructure of these interactions on two-dimensional bipartite lattice geometries\nand explore the impact of three-body interactions on system ground state on a\nsquare lattice. Focusing specifically on a system of $ ^{87} $Rb atoms, we show\nthat the effects of the multi-body interactions can be maximized via a tailored\ndressed potential within a trapping frequency range of the order of a few\nhundred kHz and for temperatures corresponding to a $ >90\\% $ occupation of the\natomic vibrational ground state. These parameters, as well as the multi-body\ninduced time scales, are compatible with state-of-the-art arrays of optical\ntweezers. Our work shows a highly versatile handle for engineering multi-body\ninteractions of quantum many-body systems in most recent manifestations on\nRydberg lattice quantum simulators.",
        "positive": "Quasiparticle Dispersions and Lifetimes in the Normal State of the\n  BCS-BEC Crossover: We compute the spectral density in the normal phase of an interacting\nhomogenous Fermi gas using a T-matrix approximation. We fit the quasiparticle\npeaks of the spectral density to BCS-like dispersion relations, and extract\nestimates of a \"pseudo-gap\" energy scale and an effective Fermi-wavevector as a\nfunction of interaction strength. We find that the effective Fermi-wavevector\nof the quasiparticles vanishes when the inverse scattering length exceeds some\npositive threshold. We also find that near unitarity the quasiparticle\nlifetimes, estimated from the widths of the peaks in the spectral density,\napproach values on the order of the inverse Fermi-energy. These results are\nconsistent with the \"breakdown of Fermi liquid theory\" observed in recent\nexperiments."
    },
    {
        "anchor": "Tuning the mobility of a driven Bose-Einstein condensate via diabatic\n  Floquet bands: We study the response of ultracold atoms to a weak force in the presence of a\ntemporally strongly modulated optical lattice potential. It is experimentally\ndemonstrated that the strong ac-driving allows for a tailoring of the mobility\nof a dilute atomic Bose-Einstein condensate with the atoms moving ballistically\neither along or against the direction of the applied force. Our results are in\nagreement with a theoretical analysis of the Floquet spectrum of a model\nsystem, thus revealing the existence of diabatic Floquet bands in the atom's\nband spectra and highlighting their role in the non-equilibrium transport of\nthe atoms.",
        "positive": "Nonadiabatic multichannel dynamics of a spin-orbit coupled condensate: We investigate the nonadiabatic dynamics of a driven spin-orbit-coupled\nBose-Einstein condensate in both weak and strong driven force. It is shown that\nthe standard Landau-Zener (LZ) tunneling fails in the regime of weak driven\nforce and/or strong spin-orbital coupling, where the full nonadiabatic dynamics\nrequires a new mechanism through multichannel effects. Beyond the semiclassical\napproach, our numerical and analytical results show an oscillating power-law\ndecay in the quantum limit, different from the exponential decay in the\nsemiclassical limit of the LZ effect. Furthermore, the condensate density\nprofile is found to be dynamically fragmented by the multichannel effects and\nenhanced by interaction effects. Our work therefore provides a complete picture\nto understand the nonadiabatic dynamics of a spin-orbit coupled condensate,\nincluding various range of driven force and interaction effects through\nmultichannel interference. The experimental indication of these nonadiabatic\ndynamics is also discussed."
    },
    {
        "anchor": "Impurities in a one-dimensional Bose gas: the flow equation approach: A few years ago, flow equations were introduced as a technique for\ncalculating the ground-state energies of cold Bose gases with and without\nimpurities. In this paper, we extend this approach to compute observables other\nthan the energy. As an example, we calculate the densities, and phase\nfluctuations of one-dimensional Bose gases with one and two impurities. For a\nsingle mobile impurity, we use flow equations to validate the mean-field\nresults obtained upon the Lee-Low-Pines transformation. We show that the\nmean-field approximation is accurate for all values of the boson-impurity\ninteraction strength as long as the phase coherence length is much larger than\nthe healing length of the condensate. For two static impurities, we calculate\nimpurity-impurity interactions induced by the Bose gas. We find that leading\norder perturbation theory fails when boson-impurity interactions are stronger\nthan boson-boson interactions. The mean-field approximation reproduces the flow\nequation results for all values of the boson-impurity interaction strength as\nlong as boson-boson interactions are weak.",
        "positive": "Nanomechanically-induced nonequilibrium quantum phase transition to a\n  self-organized density wave of a Bose-Einstein condensate: We report on a nonequilibrium quantum phase transition (NQPT) in a hybrid\nquantum many-body system consisting of a vibrational mode of a damped\nnanomembrane interacting optomechanically with a cavity, whose output light\ncouples to two internal states of an ultracold Bose gas held in an external\nquasi-one-dimensional box potential. For small effective membrane-atom\ncouplings, the system is in a homogeneous Bose-Einstein condensate (BEC) steady\nstate, with no membrane displacement. Depending on the transition frequency\nbetween the two internal atomic states, either one or both internal states are\noccupied. By increasing the atom-membrane couplings, the system transitions to\na symmetry-broken self-organized BEC phase, which is characterized by a\nconsiderably displaced membrane steady-state and density wave-like BEC\nprofiles. This NQPT can be both discontinuous and continuous for a certain\ninterval of transition frequencies, and is purely discontinuous outside of it."
    },
    {
        "anchor": "Approach for making visible and stable stripes in a spin-orbit-coupled\n  Bose-Einstein superfluid: The striped phase exhibited by a spin-$1/2$ Bose-Einstein condensate with\nspin-orbit coupling is characterized by the spontaneous breaking of two\ncontinuous symmetries: gauge and translational symmetry. This is a peculiar\nfeature of supersolids and is the consequence of interaction effects. We\npropose an approach to produce striped configurations with high-contrast\nfringes, making their experimental detection in atomic gases a realistic\nperspective. Our approach, whose efficiency is directly confirmed by\nthree-dimensional Gross-Pitaevskii simulations, is based on the space\nseparation of the two spin components into a two-dimensional bilayer\nconfiguration, causing the reduction of the effective interspecies interaction\nand the increase of the stability of the striped phase. We also explore the\neffect of a $\\pi/2$ Bragg pulse, causing the increase of the fringe wavelength,\nand of a $\\pi/2$ rf pulse, revealing the coherent nature of the order parameter\nin the spin channel.",
        "positive": "Short Bragg pulse spectroscopy for a paraxial fluids of light: We implement Bragg spectroscopy in a paraxial fluid of light. Analogues of\nshort Bragg pulses are imprinted on a photon fluid by wavefront shaping using a\nspatial light modulator. We measure the dispersion relation and evidence a\nparabolic single-particle regime as well as a linear phonon regime even for\nvery weakly interacting photons and low sound velocity. Finally, we report a\nmeasurement of the static structure factor, $S(k)$, and we demonstrate the\npresence of pair-correlated excitations, revealing indirectly the quantum\ndepletion in a paraxial fluid of light."
    },
    {
        "anchor": "Pairing and the spin susceptibility of the polarized unitary Fermi gas\n  in the normal phase: We theoretically study the pairing behavior of the unitary Fermi gas in the\nnormal phase. Our analysis is based on the static spin susceptibility, which\ncharacterizes the response to an external magnetic field. We obtain this\nquantity by means of the complex Langevin approach and compare our calculations\nto available literature data in the spin-balanced case. Furthermore, we present\nresults for polarized systems, where we complement and expand our analysis at\nhigh temperature with high-order virial expansion results. The implications of\nour findings for the phase diagram of the spin-polarized unitary Fermi gas are\ndiscussed, in the context of the state of the art.",
        "positive": "Resonant trapping in the transport of a matter-wave soliton through a\n  quantum well: We theoretically investigate the scattering of bright solitons in a\nBose-Einstein condensate on narrow attractive potential wells. Reflection,\ntransmission and trapping of an incident soliton are predicted to occur with\nremarkably abrupt transitions upon varying the potential depth. Numerical\nsimulations of the nonlinear Schroedinger equation are complemented by a\nvariational collective coordinate approach. The mechanism for nonlinear\ntrapping is found to rely both on resonant interaction between the soliton and\nbound states in the potential well as well as radiation of small amplitude\nwaves. These results suggest that solitons can be used to probe bound states\nthat are not accessible through scattering with single atoms."
    },
    {
        "anchor": "Collective oscillations in ultracold atomic gases: Using both fluid and kinetic descriptions, where repulsive forces between\nnear by atoms are included, we discuss the basic oscillations and waves of a\ncloud of ultra-cold atoms confined in a magneto-optical trap. The existence of\na hybrid mode, with properties similar to both plasma and acoustic waves is\ndescribed in detail. Tonks-Dattner resonances for confined hybrid modes in a\nspherical cloud are discussed and the prediction of a nonlinear coupling\nbetween the dipole resonanc and the hybrid modes is considered. Landau damping\nprocesses and quasi-linear diffusion in velocity space are also discussed.",
        "positive": "Orbital order of spinless fermions near an optical Feshbach resonance: We study the quantum phases of a three-color Hubbard model that arises in the\ndynamics of the p-band orbitals of spinless fermions in an optical lattice.\nStrong, color-dependent interactions are induced by an optical Feshbach\nresonance. Starting from the microscopic scattering properties of ultracold\natoms, we derive the orbital exchange constants at 1/3 filling on the cubic\noptical lattice. Using this, we compute the phase diagram in a Gutzwiller\nansatz. We find novel phases with 'axial orbital order' in which pz and px +\nipy (or px - ipy) orbitals alternate."
    },
    {
        "anchor": "Competition of spin and charge excitations in the Hubbard model: Motivated by recent experiments with ultracold fermionic atoms in optical\nlattices, we study finite temperature magnetic correlations, as singlet and\ntriplet correlations, and the double occupancy in the one-dimensional Hubbard\nmodel. We point out that for intermediate interaction strengths the double\noccupancy has an intriguing doubly non-monotonic temperature dependence due to\nthe competition between spin and charge modes, related to the Pomeranchuk\neffect. Furthermore, we determine properties of magnetic correlations in the\ntemperature regimes relevant for current cold atom experiments and discuss\neffects of the trap on spatially integrated observables. We estimate the\nentropy and the temperature reached in the experiment by Greif et al., Science\n340, 1307 (2013).",
        "positive": "Large effective three-body interaction in a double-well optical lattice: We study ultracold atoms in an optical lattice with two local minima per unit\ncell and show that the low energy states of a multi-band Bose-Hubbard (BH)\nHamiltonian with only pair-wise interactions is equivalent to an effective\nsingle-band Hamiltonian with strong three-body interactions. We focus on a\ndouble-well optical lattice with a symmetric double well along the $x$ axis and\nsingle well structure along the perpendicular directions. Tunneling and\ntwo-body interaction energies are obtained from an exact band-structure\ncalculation and numerically-constructed Wannier functions in order to construct\na BH Hamiltonian spanning the lowest two bands. Our effective Hamiltonian is\nconstructed from the ground state of the $N$-atom Hamiltonian for each unit\ncell obtained within the subspace spanned by the Wannier functions of two\nlowest bands. The model includes hopping between ground states of neighboring\nunit cells. We show that such an effective Hamiltonian has strong three-body\ninteractions that can be easily tuned by changing the lattice parameters.\nFinally, relying on numerical mean-field simulations, we show that the\neffective Hamiltonian is an excellent approximation of the two-band BH\nHamiltonian over a wide range of lattice parameters, both in the superfluid and\nMott insulator regions."
    },
    {
        "anchor": "Experimental methods of ultracold atomic physics: Experiments on solid-state materials and atomic quantum gases are\nincreasingly investigating similar concepts in many-body quantum physics. Yet,\nthe flavor of experiments on the gaseous atomic materials is different from\nthat of conventional materials research. Here, we summarize some aspects of\natomic physics and some of the common technical elements of cold-atom\nexperiments which underlie the investigations described in the remaining\nchapters of this volume.",
        "positive": "Exploring 4D Quantum Hall Physics with a 2D Topological Charge Pump: The discovery of topological states of matter has profoundly augmented our\nunderstanding of phase transitions in physical systems. Instead of local order\nparameters, topological phases are described by global topological invariants\nand are therefore robust against perturbations. A prominent example thereof is\nthe two-dimensional integer quantum Hall effect. It is characterized by the\nfirst Chern number which manifests in the quantized Hall response induced by an\nexternal electric field. Generalizing the quantum Hall effect to\nfour-dimensional systems leads to the appearance of a novel non-linear Hall\nresponse that is quantized as well, but described by a 4D topological invariant\n- the second Chern number. Here, we report on the first observation of a bulk\nresponse with intrinsic 4D topology and the measurement of the associated\nsecond Chern number. By implementing a 2D topological charge pump with\nultracold bosonic atoms in an angled optical superlattice, we realize a\ndynamical version of the 4D integer quantum Hall effect. Using a small atom\ncloud as a local probe, we fully characterize the non-linear response of the\nsystem by in-situ imaging and site-resolved band mapping. Our findings pave the\nway to experimentally probe higher-dimensional quantum Hall systems, where new\ntopological phases with exotic excitations are predicted."
    },
    {
        "anchor": "Coherence time of a Bose-Einstein condensate in an isolated harmonically\n  trapped gas: We study the condensate phase dynamics in a low-temperature equilibrium gas\nof weakly interacting bosons, harmonically trapped and isolated from the\nenvironment. We find that at long times, much longer than the collision time\nbetween Bogoliubov quasiparticles, the variance of the phase accumulated by the\ncondensate grows with a ballistic term quadratic in time and a diffusive term\naffine in time. We give the corresponding analytical expressions in the limit\nof a large system, in the collisionless regime and in the ergodic approximation\nfor the quasiparticle motion. When properly rescaled, they are described by\nuniversal functions of the temperature divided by the Thomas-Fermi chemical\npotential. The same conclusion holds for the mode damping rates. Such\nuniversality class differs from the previously studied one of the homogeneous\ngas.",
        "positive": "Bound states in a quasi-two-dimensional Fermi gas: We consider the problem of N identical fermions of mass M and one\ndistinguishable particle of mass m interacting via short-range interactions in\na confined quasi-two-dimensional (quasi-2D) geometry. For N=2 and mass ratios\nM/m<13.6, we find non-Efimov trimers that smoothly evolve from 2D to 3D. In the\nlimit of strong 2D confinement, we show that the energy of the N+1 system can\nbe approximated by an effective two-channel model. We use this approximation to\nsolve the 3+1 problem and we find that a bound tetramer can exist for mass\nratios M/m as low as 5 for strong confinement, thus providing the first example\nof a universal, non-Efimov tetramer involving three identical fermions."
    },
    {
        "anchor": "Heat kernel approach for confined quantum gas: In this paper, based on the heat kernel technique, we calculate equations of\nstate and thermodynamic quantities for ideal quantum gases in confined space\nwith external potential. Concretely, we provide expressions for equations of\nstate and thermodynamic quantities by means of heat kernel coefficients for\nideal quantum gases. Especially, using an analytic continuation treatment, we\ndiscuss the application of the heat kernel technique to Fermi gases in which\nthe expansion diverges when the fugacity $z>1$. In order to calculate the\nmodification of heat kernel coefficients caused by external potentials, we\nsuggest an approach for calculating the expansion of the global heat kernel of\nthe operator $-\\Delta+U\\left( x\\right) $ based on an approximate method of the\ncalculation of spectrum in quantum mechanics. At last, we discuss the\nproperties of quantum gases under the condition of weak and complete\ndegeneration, respectively.",
        "positive": "Coherent Manipulation of Orbital Feshbach Molecules of Two-Electron\n  Atoms: Ultracold molecules have experienced increasing attention in recent years.\nCompared to ultracold atoms, they possess several unique properties that make\nthem perfect candidates for the implementation of new quantum-technological\napplications in several fields, from quantum simulation to quantum sensing and\nmetrology. In particular, ultracold molecules of two-electron atoms (such as\nstrontium or ytterbium) also inherit the peculiar properties of these atomic\nspecies, above all the possibility to access metastable electronic states via\ndirect excitation on optical clock transitions with ultimate sensitivity and\naccuracy. In this paper we report on the production and coherent manipulation\nof molecular bound states of two fermionic $^{173}$Yb atoms in different\nelectronic (orbital) states $^1$S$_0$ and $^3$P$_0$ in proximity of a\nscattering resonance involving atoms in different spin and electronic states,\ncalled orbital Feshbach resonance. We demonstrate that orbital molecules can be\ncoherently photoassociated starting from a gas of ground-state atoms in a\nthree-dimensional optical lattices by observing several photoassociation and\nphotodissociation cycles. We also show the possibility to coherently control\nthe molecular internal state by using Raman-assisted transfer to swap the\nnuclear spin of one of the atoms forming the molecule, thus demonstrating a\npowerful manipulation and detection tool of these molecular bound states.\nFinally, by exploiting this peculiar detection technique we provide first\ninformation on the lifetime of the molecular states in a many-body setting,\npaving the way towards future investigations of strongly interacting Fermi\ngases in a still unexplored regime."
    },
    {
        "anchor": "Liquid crystal phases of two-dimensional dipolar gases and\n  Berezinskii-Kosterlitz-Thouless melting: Liquid crystals are phases of matter intermediate between crystals and\nliquids. Whereas classical liquid crystals have been known for a long time and\nare used in electro-optical displays, much less is known about their quantum\ncounterparts. There is growing evidence that quantum liquid crystals play a\ncentral role in many electron systems including high temperature\nsuperconductors, but a quantitative understanding is lacking due to disorder\nand other complications. Here, we analyse the quantum phase diagram of a\ntwo-dimensional dipolar gas, which exhibits stripe, nematic and supersolid\nphases. We calculate the stiffness constants determining the stability of the\nnematic and stripe phases, and the melting of the stripes set by the\nproliferation of topological defects is analysed microscopically. Our results\nfor the critical temperatures of these phases demonstrate that a controlled\nstudy of the interplay between quantum liquid and superfluid phases is within\nexperimental reach for the first time, using dipolar gases.",
        "positive": "Finite-Size Effects with Boundary Conditions on Bose-Einstein\n  Condensation: We investigate the statistical distribution for ideal Bose gases with\nconstant particle density in the 3D box of volume $V=L^{3}$. By changing linear\nsize $L$ and imposing different boundary conditions on the system, we present a\nnumerical analysis on the characteristic temperature and condensate fraction,\nand find that the smaller linear size is efficient to increase the\ncharacteristic temperature and condensate fraction. Moreover, there is a\nsingularity under the antiperiodic boundary condition."
    },
    {
        "anchor": "New theoretical approaches to Bose polarons: The Fr\\\"ohlich polaron model describes a ubiquitous class of problems\nconcerned with understanding properties of a single mobile particle interacting\nwith a bosonic reservoir. Originally introduced in the context of electrons\ninteracting with phonons in crystals, this model found applications in such\ndiverse areas as strongly correlated electron systems, quantum information, and\nhigh energy physics. In the last few years this model has been applied to\ndescribe impurity atoms immersed in Bose-Einstein condensates of ultracold\natoms. The tunability of microscopic parameters in ensembles of ultracold atoms\nand the rich experimental toolbox of atomic physics should allow to test many\ntheoretical predictions and give us new insights into equilibrium and dynamical\nproperties of polarons. In these lecture notes we provide an overview of common\ntheoretical approaches that have been used to study BEC polarons, including\nRayleigh-Schr\\\"odinger and Green's function perturbation theories,\nself-consistent Born approximation, mean-field approach, Feynman's variational\npath integral approach, Monte Carlo simulations, renormalization group\ncalculations, and Gaussian variational ansatz. We focus on the renormalization\ngroup approach and provide details of analysis that have not been presented in\nearlier publications. We show that this method helps to resolve striking\ndiscrepancy in polaron energies obtained using mean-field approximation and\nMonte Carlo simulations. We also discuss applications of this method to the\ncalculation of the effective mass of BEC polarons. As one experimentally\nrelevant example of a non-equililbrium problem we consider Bloch oscillations\nof Bose polarons and demonstrate that one should find considerable deviations\nfrom the commonly accepted phenomenological Esaki-Tsu model. We review which\nparameter regimes of Bose polarons can be achieved in various atomic mixtures.",
        "positive": "Making ghost vortices visible in two-component Bose-Einstein condensates: Ghost vortices constitute an elusive class of topological excitations in\nquantum fluids since the relevant phase singularities fall within regions where\nthe superfluid density is almost zero. Here we present a platform that allows\nfor the controlled generation and observation of such vortices. Upon rotating\nan imbalanced mixture of two-component Bose-Einstein condensates (BECs), one\ncan obtain necklaces of real vortices in the majority component whose cores get\nfilled by particles from the minority one. The wavefunction describing the\nstate of the latter is shown to harbour a number of ghost vortices which are\ncrucial to support the overall dynamics of the mixture. Their arrangement\ntypically mirrors that of their real counterpart, hence resulting in a ``dual\"\nghost-vortex necklace, whose properties are thoroughly investigated in the\npresent paper. We also present a viable experimental protocol for the direct\nobservation of ghost vortices in a ${}^{23}\\mathrm{Na}$ $+$ ${}^{39}\\mathrm{K}$\nultracold mixture. Quenching the inter-component scattering length, some atoms\nare expelled from the vortex cores and, while diffusing, swirl around\nunpopulated phase singularities, thus turning them directly observable."
    },
    {
        "anchor": "Superfluidity of Total Angular Momentum: Spontaneous symmetry breaking of a U(1) symmetry leads to superfluidity of a\ncorresponding conserved charge. We generalize the superfluidity to systems with\nU(1) symmetries acting on both matter fields and two-dimensional spatial\ncoordinates. Such systems can be effectively realized in easy-plane\nferromagnetic systems with spin-orbit coupling where the conserved charge is a\ntotal angular momentum. We clarify that under a steady injection of spin\nangular momentum, the superfluid of the total angular momentum shows spacetime\noscillations of the spin density and geometry-dependent spin hydrodynamics.\nThough a stability analysis shows that the superfluid under the spin injection\nis nonideal, the proposed spin transport persists with weak dissipation of the\nspin angular momentum. Our study broadens the comprehension of superfluidity\nand sheds new light on the interplay between symmetries and phases of matter.",
        "positive": "Effective action for Bose-Einstein condensates: We clarify basic properties of an effective action (i.e., self-consistent\nperturbation expansion) for interacting Bose-Einstein condensates, where field\n$\\psi$ itself acquires a finite thermodynamic average $\\langle \\psi\\rangle$\nbesides two-point Green's function $\\hat G$ to form an off-diagonal long-range\norder. It is shown that the action can be expressed concisely order by order in\nterms of the interaction vertex and a special combination of\n$\\langle\\psi\\rangle$ and $\\hat G$ so as to satisfy both Noether's theorem and\nGoldstone's theorem (I) corresponding to the first proof. The self-energy is\npredicted to have a one-particle-reducible structure due to $\\langle\n\\psi\\rangle\\neq 0$ to transform the Bogoliubov mode into a bubbling mode with a\nsubstantial decay rate."
    },
    {
        "anchor": "Cavity-induced switching between localized and extended states in a\n  non-interacting Bose-Einstein condensate: We study an ultracold atom-cavity coupling system, which had been implemented\nin experiment to display weak light nonlinearity [S. Gupta \\textit{et al}.,\nPhys. Rev. Lett. \\textbf{99}, 213601 (2007)]. The model is described by a\nnon-interacting Bose-Einstein condensate contained in a Fabry-P\\'{e}rot optical\nresonator, in which two incommensurate standing-wave modes are excited and thus\nform a quasiperiodic optical lattice potential for the atoms. Special emphasis\nare paid to the variation of atomic wavefunction induced by the cavity light\nfield. We show that bistability between the atomic localized and extended\nstates can be generated under appropriate conditions.",
        "positive": "Exploring the Stability and Dynamics of Dipolar Matter-Wave Dark\n  Solitons: We study the stability, form and interaction of single and multiple dark\nsolitons in quasi-one-dimensional dipolar Bose-Einstein condensates. The\nsolitons are found numerically as stationary solutions in the moving frame of a\nnon-local Gross Pitaevskii equation, and characterized as a function of the key\nexperimental parameters, namely the ratio of the dipolar atomic interactions to\nthe van der Waals interactions, the polarization angle and the condensate\nwidth. The solutions and their integrals of motion are strongly affected by the\nphonon and roton instabilities of the system. Dipolar matter-wave dark solitons\npropagate without dispersion, and collide elastically away from these\ninstabilities, with the dipolar interactions contributing an additional\nrepulsion or attraction to the soliton-soliton interaction. However, close to\nthe instabilities, the collisions are weakly dissipative."
    },
    {
        "anchor": "Optomechanical effect on the Dicke quantum phase transition and\n  quasi-particle damping in a Bose-Einstein Condensate: A new tool to measure\n  weak force: We make a semi-classical steady state analysis of the influence of mirror\nmotion on the quantum phase transition for an optomechanical Dicke model in the\nthermodynamic limit. An additional external mechanical pump is shown to modify\nthe critical value of atom-photon coupling needed to observe the quantum phase\ntransition. We further show how to choose the mechanical pump frequency and\ncavity-laser detuning to produce extremely cold condensates. The present system\ncan be used as a quantum device to measure weak forces.",
        "positive": "Floquet-surface bound states in the continuum in a resonantly driven 1D\n  tilted defect-free lattice: We study the Floquet-surface bound states embedded in the continuum (BICs)\nand bound states out the continuum (BOCs)in a resonantly driven 1D tilted\ndefect-free lattice. In contrast to fragile single-particle BICs assisted by\nspecially tailored potentials, we find that Floquet-surface BICs, stable\nagainst structural perturbations, can exist in a wide range of parameter space.\nBy using a multiple-time-scale asymptotic analysis in the high-frequency limit,\nthe appearance of Floquet-surface bound states can be analytically explained by\neffective Tamm-type defects at boundaries induced by the resonance between the\nperiodic driving and tilt. The phase boundary of existing Floquet-surface\nstates is also analytically given. Based on the repulsion effect of surface\nstates, we propose to detect transition points and measure the number of\nFloquet-surface bound states by quantum walk. Our work opens a new door to\nexperimental realization of BICs in quantum system."
    },
    {
        "anchor": "Collective oscillations of a trapped quantum gas in low dimensions: We present a comprehensive study of the discretized modes of an atomic gas in\ndifferent conditions of confinement. Starting from the equations of\nhydrodynamics we derive a closed equation for the velocity field, depending on\nthe adiabatic and isothermal compressibilities and applicable to different\ndimensions and quantum statistics. At zero temperature the equation reproduces\nthe irrotational behavior of superfluid hydrodynamics. It is also applicable\nabove the critical temperature in the collisional regime, where the appearence\nof rotational components in the velocity field is caused by the external\npotential. In the presence of harmonic trapping, a general class of analytic\nsolutions is obtained for systems exhibiting a polytropic equation of state,\ncharacterized by a power law isoentropic dependence of the pressure on the\ndensity. Explicit results for the compressional modes are derived for both Bose\nand Fermi gases in the pancake, cigar as well as in the deep 2D and 1D regimes.\nOur results agree with the analytical predictions available in the literature\nin some limiting cases. They are particularly relevant in 1D configurations,\nwhere the study of the collective frequencies could provide a unique test of\nthe achievement of the collisional regime at finite temperature.",
        "positive": "Existence, stability and nonlinear dynamics of vortices and vortex\n  clusters in anisotropic Bose-Einstein condensates: We study vortex excitations in one-component Bose-Einstein condensates, with\na special emphasis on the role of anisotropic confinement for the existence,\nstability and dynamical properties of vortices and particularly few-vortex\nclusters. Symmetry breaking features are pervasive within this system even in\nits isotropic installment, where cascades of symmetry breaking bifurcations\ngive rise to the multi-vortex clusters, but also within the anisotropic realm\nwhich naturally breaks the rotational symmetry of the multi-vortex states. Our\nfirst main tool for analyzing the system consists of a weakly nonlinear\n(bifurcation) approach which starts from the linear states of the problem and\nexamines their continuation and bifurcation into novel symmetry-broken\nconfigurations in the nonlinear case. This is first done in the isotropic limit\nand the modifications introduced by the anisotropy are subsequently presented.\nThe second main tool concerns the highly nonlinear regime where the vortices\ncan be considered as individual topologically charged \"particles\" which precess\nwithin the parabolic trap and interact with each other, similarly to fluid\nvortices. The conclusions stemming from both the bifurcation and the\ninteracting particle picture are corroborated by numerical computations which\nare also used to bridge the gap between these two opposite-end regimes."
    },
    {
        "anchor": "Unconventional color superfluidity in ultra-cold fermions: Quintuplet\n  pairing, quintuple point and pentacriticality: We describe the emergence of color superfluidity in ultra-cold fermions\ninduced by color-orbit and color-flip fields that transform a conventional\nsinglet-pairing s-wave system into an unconventional non-s-wave superfluid with\nquintuplet pairing. We show that the tuning of interactions, color-orbit and\ncolor-flip fields transforms a momentum-independent scalar order parameter into\nan explicitly momentum-dependent tensor order parameter. We classify all\nunconventional superfluid phases in terms of the {\\it loci} of zeros of their\nquasi-particle excitation spectrum in momentum space and we identify several\nLifshitz-type topological transitions. Furthermore, when boundaries between\nphases are crossed, non-analyticities in the compressibility arise. We find a\nquintuple point, which is also pentacritical, where four gapless superfluid\nphases converge into a fully gapped superfluid phase.",
        "positive": "Quantum Flutter: Signatures and Robustness: We investigate the motion of an impurity particle injected with finite\nvelocity into an interacting one-dimensional quantum gas. Using large-scale\nnumerical simulations based on matrix product states, we observe and\nquantitatively analyze long-lived oscillations of the impurity momentum around\na non-zero saturation value, called quantum flutter. We show that the quantum\nflutter frequency is equal to the energy difference between two branches of\ncollective excitations of the model. We propose an explanation of the finite\nsaturation momentum of the impurity based on the properties of the edge of the\nexcitation spectrum. Our results indicate that quantum flutter exists away from\nintegrability, and provide parameter regions in which it could be observed in\nexperiments with ultracold atoms using currently available technology."
    },
    {
        "anchor": "Quantum behavior of a heavy impurity strongly coupled to a Bose gas: We investigate the problem of an infinitely heavy impurity interacting with a\ndilute Bose gas at zero temperature. When the impurity-boson interactions are\nshort ranged, we show that boson-boson interactions induce a quantum blockade\neffect, where a single boson can effectively block or screen the impurity\npotential. Since this behavior depends on the quantum granular nature of the\nBose gas, it cannot be captured within a standard classical-field description.\nUsing a combination of exact quantum Monte Carlo methods and a truncated basis\napproach, we show how the quantum correlations between bosons lead to universal\nfew-body bound states and a logarithmically slow dependence of the polaron\nground-state energy on the boson-boson scattering length. Moreover, we expose\nthe link between the polaron energy and the spatial structure of the quantum\ncorrelations, spanning the infrared to ultraviolet physics.",
        "positive": "Creating p-wave superfluids and topological excitations in optical\n  lattices: We propose to realize a p-wave superfluid using bosons mixed with a single\nspecies of fermions in a deep optical lattice. We analyze with a\nself-consistent method its excitation spectrum in presence of a vortex, and we\npoint out the range of interaction strengths in which the zero-energy mode with\ntopological character exists on a finite optical lattice. Lattice effects are\nstrongest close to fermionic half-filling: here the linearity of the low-lying\nspectrum is lost, and a new class of extended zero-energy modes with\ncheckerboard structure and d-wave symmetry appears."
    },
    {
        "anchor": "Competing insulating phases of dipolar bosons in a dimerized optical\n  lattice: We study the ground state properties of dipolar bosons in a one dimensional\ndimerized optical lattice. In the limit of strong onsite repulsion i.e.\nhardcore bosons, and strong dipole-dipole interaction, a stable density wave\n(DW) phase is obtained at half filling as a function of lattice dimerization.\nInterestingly, at quarter filling we obtain the signatures of an insulating\nphase which has both the character the bond-order (BO) and the DW insulators\nwhich we call a bond-order density wave (BODW) phase. Moreover, we show that\nfor a fixed hopping dimerization there occurs a BO-DW phase crossover as a\nfunction of the dipole-dipole interaction and the BODW phase is more robust\nwhen the hopping dimerization is stronger. We further examine the stability of\nthe BODW phase in the limit of finite onsite interactions.",
        "positive": "Raman spectroscopy of Fermi polarons: By using a non-self-consistent many-body $T$-matrix theory, we calculate the\nfinite-temperature Raman spectroscopy of a mobile impurity immersed in a Fermi\nbath in three dimensions. The dependences of the Raman spectrum on the\ntransferred momentum, temperature, and impurity-bath interaction are discussed\nin detail. We confirm that the peak in the Raman spectrum shows a weaker\ndependence on the impurity concentration than that in the radio-frequency\nspectroscopy, due to the nonzero transferred momentum, as anticipated. We\ncompare our theoretical prediction with the recent measurement by Gal Ness\n\\textsl{et al.} in Physical Review X \\textbf{10}, 041019 (2020) without any\nadjustable parameters. At weak coupling, we find a good quantitative agreement.\nHowever, close to the Feshbach resonance the agreement becomes worse. At strong\ncoupling, we find that an unrealistic Fermi bath temperature might be needed,\nin order to account for the experimental data."
    },
    {
        "anchor": "Shear viscosity and spin sum rules in strongly interacting Fermi gases: Fermi gases with short-range interactions are ubiquitous in ultracold atomic\nsystems. In the absence of spin-flipping processes the number of atoms in each\nspin species is conserved separately, and we discuss the associated Ward\nidentities. For contact interactions the spin conductivity spectral function\nsigma_s(omega) has universal power-law tails at high frequency. We derive the\nspin f-sum rule and show that it is not affected by these tails in d<4\ndimensions. Likewise the shear viscosity spectral function eta(omega) has\nuniversal tails; in contrast they modify the viscosity sum rule in a\ncharacteristic way.",
        "positive": "Fermionization via cavity-assisted infinite-range interactions: We study a one-dimensional array of bosons with infinite-range interactions\nmediated by a laser-driven dissipative optical cavity. The cavity-mediated\ninfinite-range interactions open up a new pathway to fermionization, hitherto\nonly known for dipolar bosons due to their long-range interactions. In\nparameter ranges attainable in state-of-the-art experiments, we systematically\ncompare observables for bosons and fermions with infinite-range interactions.\nAt large enough laser pump power, many observables, including density\ndistributions in real and momentum space, correlation functions, eigenvalues of\nthe one-body density matrix, and superradiance order parameter, become\nidentical for bosons and fermions. We map out the emergence of this\ncavity-induced fermionization as a function of pump power and contact\ninteractions. We discover that cavity-mediated interactions can compensate a\nreduction by several orders of magnitude in the strength of the contact\ninteractions needed to trigger fermionization."
    },
    {
        "anchor": "Anomalous quantum glass of bosons in a random potential in two\n  dimensions: We present a quantum Monte Carlo study of the \"quantum glass\" phase of the 2D\nBose-Hubbard model with random potentials at filling $\\rho=1$. In the narrow\nregion between the Mott and superfluid phases the compressibility has the form\n$\\kappa \\sim {\\rm exp}(-b/T^\\alpha)+c$ with $\\alpha <1$ and $c$ vanishing or\nvery small. Thus, at $T=0$ the system is either incompressible (a Mott glass)\nor nearly incompressible (a Mott-glass-like anomalous Bose glass). At stronger\ndisorder, where a glass reappears from the superfluid, we find a conventional\nhighly compressible Bose glass. On a path connecting these states, away from\nthe superfluid at larger Hubbard repulsion, a change of the disorder strength\nby only $10\\%$ changes the low-temperature compressibility by more than four\norders of magnitude, lending support to two types of glass states separated by\na phase transition or a sharp cross-over.",
        "positive": "Fundamental limitations of the eigenvalue continuation approach: In this work, we show that the eigenvalue continuation approach introduced\nrecently in [Phys. Rev. Lett. {\\bf 121}, 032501 (2018)], despite its many\nadvantages, has some fundamental limitations which cannot be overcome when\nstrongly correlated many-body systems are considered. Taking as a working\nexample a very simple system of several fermionic particles confined in a\nharmonic trap we show that the eigenvector continuation is not able to go\nbeyond the accuracy of the sampling states. We support this observation within\na very simple three-level model capturing directly this obstacle. Since\nmentioned inaccuracy cannot be determined self-consistently within the\neigenvalue continuation approach, support from other complementary methods is\nneeded."
    },
    {
        "anchor": "Metropolis-Hastings thermal state sampling for numerical simulations of\n  Bose-Einstein condensates: We demonstrate the application of the Metropolis-Hastings algorithm to\nsampling of classical thermal states of one-dimensional Bose-Einstein\nquasicondensates in the classical fields approximation, both in untrapped and\nharmonically trapped case. The presented algorithm can be easily generalized to\nhigher dimensions and arbitrary trap geometry. For truncated Wigner simulations\nthe quantum noise can be added with conventional methods (half a quantum of\nenergy in every mode). The advantage of the presented method over the usual\nanalytical and stochastic ones lies in its ability to sample not only from\ncanonical and grand canonical distributions, but also from the generalized\nGibbs ensemble, which can help to shed new light on thermodynamics of\nintegrable systems.",
        "positive": "On the hydrodynamic canonical formalism of the Gross-Pitaevskii field: We derive a canonical formalism for the hydrodynamic representation of the\nGross-Pitaevskii field (nonlinear Schr\\\"odinger field), where the density and\nthe phase of the condensate form a canonical pair of conjugate field variables.\nTo do so, we treat the meanfield as a singular Lagrangian system and apply both\nthe Dirac-Bergmann and Faddeev-Jackiw methods. The Faddeev-Jackiw method is\nfound to be a more direct approach to the problem."
    },
    {
        "anchor": "Phonon dressing of a facilitated one-dimensional Rydberg lattice gas: We study the dynamics of a one-dimensional Rydberg lattice gas under\nfacilitation (anti-blockade) conditions which implements a so-called\nkinetically constrained spin system. Here an atom can only be excited to a\nRydberg state when one of its neighbors is already excited. Once two or more\natoms are simultaneously excited mechanical forces emerge, which couple the\ninternal electronic dynamics of this many-body system to external vibrational\ndegrees of freedom in the lattice. This electron-phonon coupling results in a\nso-called phonon dressing of many-body states which in turn impacts on the\nfacilitation dynamics. In our theoretical study we focus on a scenario in which\nall energy scales are sufficiently separated such that a perturbative treatment\nof the coupling between electronic and vibrational states is possible. This\nallows to analytically derive an effective Hamiltonian for the evolution of\nconsecutive clusters of Rydberg excitations in the presence of phonon dressing.\nWe analyze the spectrum of this Hamiltonian and show -- by employing Fano\nresonance theory -- that the interaction between Rydberg excitations and\nlattice vibrations leads to the emergence of slowly decaying bound states that\ninhibit fast relaxation of certain initial states.",
        "positive": "Generation and spectroscopic signatures of a fractional quantum Hall\n  liquid of photons in an incoherently pumped optical cavity: We theoretically investigate a driven-dissipative model of strongly\ninteracting photons in a nonlinear optical cavity in the presence of a\nsynthetic magnetic field. We show the possibility of using a\nfrequency-dependent incoherent pump to create a strongly-correlated $\\nu = 1/2$\nbosonic Laughlin state of light: thanks to the incompressibility of the\nLaughlin state, fluctuations in the total particle number and excitation of\nedge modes can be tamed by imposing a suitable external potential profile for\nphotons. We further propose angular momentum-selective spectroscopy of the\nemitted light as a tool to obtain unambiguous signatures of the microscopic\nphysics of the quantum Hall liquid of light."
    },
    {
        "anchor": "Statistical Floquet prethermalization of the Bose-Hubbard model: The manipulation of many-body systems often involves time-dependent forces\nthat cause unwanted heating. One strategy to suppress heating is to use\ntime-periodic (Floquet) forces at large driving frequencies. For quantum spin\nsystems with bounded spectra, it was shown rigorously that the heating rate is\nexponentially small in the driving frequency. Recently, the exponential\nsuppression of heating has also been observed in an experiment with ultracold\natoms, realizing a periodically driven Bose-Hubbard model. This model has an\nunbounded spectrum and, hence, is beyond the reach of previous theoretical\napproaches. Here, we study this model with two semiclassical approaches valid,\nrespectively, at large and weak interaction strengths. In both limits, we\ncompute the heating rates by studying the statistical probability to encounter\na many-body resonance, and obtain a quantitative agreement with the exact\ndiagonalization of the quantum model. Our approach demonstrates the relevance\nof statistical arguments to Floquet perthermalization of interacting many-body\nquantum systems.",
        "positive": "Shell-shaped quantum droplet in a three-component ultracold Bose gas: We present a scheme to generate shell-shaped droplet in a three-component\n(1,2,3) ultracold Bose gas. Here binary mixtures (1,2) and (2,3) form quantum\ndroplets due to inter-species attractions, and the two droplets are mutually\nimmiscible due to strong 1-3 repulsion. Importantly, the shared component-2\nserves as a glue to link the two droplets together as a globally self-bound\nobject. In this system, the outer droplet naturally develops a shell structure,\nand its radius and width can be conveniently tuned through the size of core\ndroplet. Moreover, to reach an equilibrium with the shell, the core droplet\ndisplays very different spin densities as compared to the vacuum case. These\nresults have been demonstrated in a realistic $^{23}$Na-$^{39}$K-$^{41}$K\nmixture. Our scheme liberates the shell-shaped Bose gas from stringent\nconditions with microgravity or fine-tuned traps, and can be readily\nimplemented in cold atoms laboratories on Earth. This paves the way for future\nexploration of quantum droplets in curved space with non-trivial real-space\ntopologies."
    },
    {
        "anchor": "Non-Hermitian Squeezed Polarons: Recent experimental breakthroughs in non-Hermitian ultracold atomic lattices\nhave dangled tantalizing prospects in realizing exotic, hitherto unreported,\nmany-body non-Hermitian quantum phenomena. In this work, we discover and\npropose an experimental platform for a radically different non-Hermitian\nphenomenon dubbed polaron squeezing. It is marked by a dipole-like accumulation\nof fermions arising from an interacting impurity in a background of\nnon-Hermitian reciprocity-breaking hoppings. We computed their spatial density\nand found that, unlike Hermitian polarons which are symmetrically localized\naround impurities, non-Hermitian squeezed polarons localize asymmetrically in\nthe direction opposite to conventional non-Hermitian pumping and\nnon-perturbatively modify the entire spectrum, despite having a manifestly\nlocal profile. We investigated their time evolution and found that, saliently,\nthey appear almost universally in the long-time steady state, unlike Hermitian\npolarons which only exist in the ground state. In our numerics, we also found\nthat, unlike well-known topological or skin localized states, squeezed polarons\nexist in the bulk, independently of boundary conditions. Our findings could\ninspire the realization of many-body states in ultracold atomic setups, where a\nsqueezed polaron can be readily detected and characterized by imaging the\nspatial fermionic density.",
        "positive": "Probing Atomic Majorana Fermions in Optical Lattices: We introduce a one-dimensional system of fermionic atoms in an optical\nlattice whose phase diagram includes topological states of different symmetry\nclasses. These states can be identified by their zero-energy edge modes which\nare Majorana fermions. We propose several universal methods of detecting the\nMajorana edge states, based on their genuine features: zero-energy, localized\ncharacter of the wave functions, and induced non-local fermionic correlations."
    },
    {
        "anchor": "Majorana Zero Modes in Synthetic Dimensions: Recent experimental advances in the field of cold atoms led to the\ndevelopment of novel techniques for producing synthetic dimensions and\nsynthetic magnetic fields, thus greatly expanding the utility of cold atomic\nsystems for exploring exotic states of matter. In this paper we investigate the\npossibility of using experimentally tunable interactions in such systems to\nmimic the physics of Majorana chains, currently a subject of intense research.\nCrucially to our proposal, the interactions, which are local in space, appear\nnon-local in the synthetic dimension. We use this fact to induce coupling\nbetween counter-propagating edge modes in the quantum Hall regime. For the case\nof attractive interactions in a system composed of two tunneling-coupled\nchains, we find a gapless quasi-topological phase with a doubly-degenerate\nground state. While the total number of particles in the system is kept fixed,\nthis phase is characterized by strong fluctuations of the pair number in each\nchain. Each ground state is characterized by the parity of the total particle\nnumber in each chain, similar to Majorana wires. However, in our system this\ndegeneracy persists for periodic boundary conditions. For open boundary\nconditions there is a small splitting of this degeneracy due to the\nsingle-particle hopping at the edges. We show how subjecting the system to\nadditional synthetic flux or asymmetric potentials on the two chains can be\nused to control this nonlocal qubit. We propose experimental probes for testing\nthe nonlocal nature of such a qubit and measuring its state.",
        "positive": "Local temperature control of magnon frequency and direction of\n  supercurrents in a magnon Bose-Einstein condensate: The creation of temperature variations in magnetization, and hence in the\nfrequencies of the magnon spectrum in laser-heated regions of magnetic films,\nis an important method for studying Bose-Einstein condensation of magnons,\nmagnon supercurrents, Bogoliubov waves, and similar phenomena. In our study, we\ndemonstrate analytically, numerically, and experimentally that, in addition to\nthe magnetization variations, it is necessary to consider the connected\nvariations of the demagnetizing field. In case of a heat induced local minimum\nof the saturation magnetization, the combination of these two effects results\nin a local increase in the minimum frequency value of the magnon dispersion at\nwhich the Bose-Einstein condensate emerges. As a result, a magnon supercurrent\ndirected away from the hot region is formed."
    },
    {
        "anchor": "Monopole excitations of a harmonically trapped one-dimensional Bose gas\n  from the ideal gas to the Tonks-Girardeau regime: Using a time-dependent modified nonlinear Schr\\\"odinger equation (m-NLSE) --\nwhere the conventional chemical potential proportional to the density is\nreplaced by the one inferred from Lieb-Liniger's exact solution -- we study\nfrequencies of the collective monopole excitations of a one-dimensional (1D)\nBose gas. We find that our method accurately reproduces the results of a recent\nexperimental study [E. Haller et al., Science Vol. 325, 1224 (2009)] in the\nfull spectrum of interaction regimes from the ideal gas, through the mean-field\nregime, through the mean-field Thomas-Fermi regime, all the way to the\nTonks-Giradeau gas. While the former two are accessible by the standard\ntime-dependent NLSE and inaccessible by the time-dependent local density\napproximation (LDA), the situation reverses in the latter case. However, the\nm-NLSE treats all these regimes within a single numerical method.",
        "positive": "Landauer-B\u00fcttiker equation for bosonic carriers: We study the current of Bose particles between two reservoirs connected by a\none-dimensional channel. We analyze the problem from first principles by\nconsidering a microscopic model of conductivity in the noninteracting limit.\nEquations for the transient and the stationary current are derived\nanalytically. The asymptotic current has a form similar to the\nLandauer-B\\\"uttiker equation for electronic current in mesoscopic devices."
    },
    {
        "anchor": "Finite-range effects in dilute Fermi gases at unitarity: We develop a theoretical method going beyond the contact-interaction\napproximation frequently used in mean-field theories of many-fermion systems,\nbased on the low-energy T-matrix of the pair potential to rigorously define the\neffective radius of the interaction. One of the main consequences of our\napproach is the possibility to investigate finite-density effects, which are\noutside the range of validity of approximations based on delta-like potentials.\nWe apply our method to the calculation of density dependent properties of an\nultracold gas of 6Li atoms at unitarity, whose two-body interaction potential\nis calculated using ab initio quantum chemistry methods. We find that density\neffects will be significant in ultracold gases with densities one order of\nmagnitude higher than those attained in current experiments.",
        "positive": "Superfluidity and solid orders in two-component Bose gas with dipolar\n  interactions in an optical lattice: In this paper, we study an extended bosonic t-J model in an optical lattice,\nwhich describes two-component hard-core bosons with a nearest-neighbor (NN)\npseudo-spin interaction, and also inter- and intra-species dipole-dipole\ninteractions (DDI). In particular, we focus on the case in which two component\nhard-core bosons have anti-parallel polarized dipoles with each other. The\nglobal phase diagram is studied by means of the Gutzwiller variational method\nand also the quantum Monte-Carlo simulations (QMC). The both calculations show\nthat a stripe solid order, besides a checkerboard one, appears as a result of\nthe DDI. By the QMC, we find that two kinds of supersolid (SS) form,\ncheckerboard SS and stripe SS, and we also verify the existence of some exotic\nphase between the stripe solid and checkerboard SS. Finally by the QMC, we\nstudy the t-J-like model, which was experimentally realized recently by A. de\nPaz et al. [Phys. Rev. Lett. {\\bf 111}, 185305 (2013)]."
    },
    {
        "anchor": "The van der Waals interaction as the starting point for an effective\n  field theory: We consider the system of three ${}^4$He atoms to assess whether a pure van\nder Waals potential can be used as a starting point for an effective field\ntheory to describe three-body processes in ultracold atomic systems. Using a\nlong-range van der Waals interaction in combination with short-distance\ntwo-body counterterms, we analyze the dependence of two- and three-body\nobservables on the short-distance regulator that is required due to the\nsingular nature of the van der Waals interaction. We benchmark our approach\nwith results obtained with the realistic ${}^4$He-${}^4$He LM2M2 interaction\nand find good agreement. We furthermore show that in this effective field\ntheory approach no three-body force is required at leading order and that\nuniversal van der Waals physics leads to a universal correlation between\nthree-body observables in the absence of an Efimov three-body parameter.",
        "positive": "Dissipation-induced instabilities of a spinor Bose-Einstein condensate\n  inside an optical cavity: We investigate the dynamics of a spinor Bose-Einstein condensate inside an\noptical cavity, driven transversely by a laser with a controllable polarization\nangle. We focus on a two-component Dicke model with complex light-matter\ncouplings, in the presence of photon losses. We calculate the steady-state\nphase diagram and find dynamical instabilities in the form of limit cycles,\nheralded by the presence of exceptional points and level attraction. We show\nthat the instabilities are induced by dissipative processes which generate\nnon-reciprocal couplings between the two collective spins. Our predictions can\nbe readily tested in state-of-the-art experiments and open up the study of\nnon-reciprocal many-body dynamics out of equilibrium."
    },
    {
        "anchor": "Core structure of static ferrodark solitons in a spin-1 Bose-Einstein\n  condensate: We develop an analytical description of static ferrodark solitons, the\n$\\mathbb{Z}_2$ topological defects in the magnetic order, in the easy-plane\nphase of ferromagnetic spin-1 Bose-Einstein condensates. We find that the\ntype-I ferrodark soliton has a single width while the type-II ferrodark soliton\nexhibits two characteristic length scales. The proposed ansatzes show excellent\nagreement with numerical results. Spin-singlet amplitudes, nematic tensor\ndensities and nematic currents of ferrodark solitons are also discussed. The\n$\\mathbb{Z}_2$ topological defects in the mass superfluid order, dark-dark-dark\nvector solitons, are obtained exactly in the parameter regime where exact\nferrodark solitons exist. The dark-dark-dark vector soliton has higher\nexcitation energy than ferrodark solitons.",
        "positive": "Intra-scales energy transfer during the evolution of turbulence in a\n  trapped Bose-Einstein condensate: In turbulence phenomena, including the quantum turbulence in superfluids, an\nenergy flux flows from large to small length scales, composing a cascade of\nenergy. A universal characteristic of turbulent flows is the existence of a\nrange of scales where the energy flux is scale-invariant: this interval of\nscales is often referred to as inertial region. This property is fundamental\nas, for instance, in turbulence of classical fluids it characterizes the\nbehavior of statistical features such as spectra and structure functions. Here\nwe show that also in decaying quantum turbulence generated in trapped\nBose-Einstein condensates (BECs), intervals of momentum space where the energy\nflux is constant can be identified. Indeed, we present a procedure to measure\nthe energy flux using both the energy spectrum and the continuity equation. A\nrange of scales where the flux is constant is then determined employing two\ndistinct protocols and in the same range, the momentum distribution measured is\nconsistent with previous work. The successful identification of a region with\nconstant flux in turbulent BECs is a manifestation of the universal character\nof turbulence in these quantum systems. These measurements pave the way for\nstudies of energy conservation and dissipation in trapped atomic superfluids,\nand also analogies with the related processes that take place in ordinary\nfluids."
    },
    {
        "anchor": "Critical Dynamics of Spontaneous Symmetry Breaking in a Homogeneous Bose\n  gas: We explore the dynamics of spontaneous symmetry breaking in a homogeneous\nsystem by thermally quenching an atomic gas with short-range interactions\nthrough the Bose-Einstein phase transition. Using homodyne matter-wave\ninterferometry to measure first-order correlation functions, we verify the\ncentral quantitative prediction of the Kibble-Zurek theory, namely the\nhomogeneous-system power-law scaling of the coherence length with the quench\nrate. Moreover, we directly confirm its underlying hypothesis, the freezing of\nthe correlation length near the transition due to critical slowing down. Our\nmeasurements agree with beyond mean-field theory, and support the previously\nunverified expectation that the dynamical critical exponent for this\nuniversality class, which includes the $\\lambda$-transition of liquid $^4$He,\nis $z=3/2$.",
        "positive": "Bessel Vortices in Spin-Orbit-Coupled Binary Bose-Einstein Condensates\n  with Zeeman Splitting: We present an analysis of stationary solutions for two-dimensional (2D)\nBose-Einstein condensates (BECs) with the Rashba spin-orbit (SO) coupling and\nZeeman splitting. By introducing the generalized momentum operator, the linear\nversion of the system can be solved exactly. The solutions are semi-vortices of\nthe Bessel-vortex (BV) and modified Bessel-vortex (MBV) types, in the presence\nof the weak and strong Zeeman splitting, respectively. The ground states (GSs)\nof the full nonlinear system are constructed with the help of a specially\ndesigned neural network (NN). The GS of the mixed-mode type appears as\ncross-attraction interaction increases. The spin texture of the GS is produced\nin detail. It exhibits the Neel skyrmion structure for the semi-vortex GS of\nthe BV type, and the respective skyrmion number is found in an analytical form.\nOn the other hand, GSs of the MBV and mixed-mode types do not form skyrmions."
    },
    {
        "anchor": "Energy redistribution and spatio-temporal evolution of correlations\n  after a sudden quench of the Bose-Hubbard model: An optical-lattice quantum simulator is an ideal experimental platform to\ninvestigate non-equilibrium dynamics of a quantum many-body system, which is in\ngeneral hard to simulate with classical computers. Here, we use our quantum\nsimulator of the Bose-Hubbard model to study dynamics far from equilibrium\nafter a quantum quench. We successfully confirm the energy conservation law in\nthe one- and three-dimensional systems and extract the propagation velocity of\nthe single-particle correlation in the one- and two-dimensional systems. We\ncorroborate the validity of our quantum simulator through quantitative\ncomparisons between the experiments and the exact numerical calculations in one\ndimension. In the computationally hard cases of two or three dimensions, by\nusing the quantum-simulation results as references, we examine the performance\nof a numerical method, namely the truncated Wigner approximation, revealing its\nusefulness and limitation. This work constitutes an exemplary case for the\nusage of analog quantum simulators.",
        "positive": "Topological Wigner Crystal of Half-Solitons in a Spinor BEC: We consider a one-dimensional gas of half-solitons in a spinor Bose-Einstein\ncondensate. We calculate the topological interaction potential between the\nhalf-solitons. Using a kinetic equation of the Vlasov-Boltzmann type, we model\nthe coupled dynamics of the interacting solitons. We show that the dynamics of\nthe system in the gaseous phase is marginally stable and spontaneously evolves\ntowards a Wigner crystal."
    },
    {
        "anchor": "Feshbach resonances of harmonically trapped atoms: Employing a short-range two-channel description we derive an analytic model\nof atoms in isotropic and anisotropic harmonic traps at a Feshbach resonance.\nOn this basis we obtain a new parameterization of the energy-dependent\nscattering length which differs from the one previously employed. We validate\nthe model by comparison to full numerical calculations for Li-Rb and explain\nquantitatively the experimental observation of a resonance shift and\ntrap-induced molecules in exited bands. Finally, we analyze the bound state\nadmixture and Landau-Zener transition probabilities.",
        "positive": "Fermionic Superfluid from a Bilayer Band Insulator in an Optical Lattice: We propose a model to realize a fermionic superfluid state in an optical\nlattice circumventing the cooling problem. Our proposal exploits the idea of\ntuning the interaction in a characteristically low entropy state, a\nband-insulator in an optical bilayer system, to obtain a superfluid. By\nperforming a detailed analysis of the model including fluctuations and\naugmented by a variational quantum Monte Carlo calculations of the ground\nstate, we show that the superfluid state obtained has high transition\ntemperature of the order of the hopping energy. Our system is designed to\nsuppress other competing orders such as a charge density wave. We suggest a\nlaboratory realization of this model via an orthogonally shaken optical lattice\nbilayer."
    },
    {
        "anchor": "Many-body dynamics of p-wave Feshbach molecule production: a mean-field\n  approach: We study the mean-field dynamics of p-wave Feshbach molecule production in an\nultra cold gas of Fermi atoms in the same internal state. We derive a separable\npotential to describe the low-energy scattering properties of such atoms, and\nuse this potential to solve the mean-field dynamics during a magnetic field\nsweep. Initially, on the negative scattering length side of a Feshbach\nresonance the gas is described by the BCS theory. We adapt the method by\nSzyma\\'{n}ska et al. [Phys. Rev. Lett. 94, 170402 (2005)] to p-wave interacting\nFermi gases and model the conversion dynamics of the gas into a Bose-Einstein\ncondensate of molecules on the other side of the resonance under the influence\nof a linearly varying magnetic field. We have analyzed the dependence of the\nmolecule production efficiency on the density of the gas, temperature, initial\nvalue of the magnetic field, and magnetic field ramp speed. Our results show\nthat in this approximation molecule production by a linear magnetic field sweep\nis highly dependent on the initial state.",
        "positive": "Bose Polaron in a quantum fluid of light: We study the Bose polaron problem in a nonequilibrium setting, by considering\nan impurity embedded in a quantum fluid of light realized by exciton-polaritons\nin a microcavity, subject to a coherent drive and dissipation on account of\npump and cavity losses. We obtain the polaron effective mass, the drag force\nacting on the impurity, and determine polaron trajectories at a semiclassical\nlevel. We find different dynamical regimes, originating from the unique\nfeatures of the excitation spectrum of driven-dissipative polariton fluids, in\nparticular a non-trivial regime of acceleration against the flow. Our work\npromotes the study of impurity dynamics as an alternative testbed for probing\nsuperfluidity in quantum fluids of light."
    },
    {
        "anchor": "Ultracold Dipolar Gases in Optical Lattices: This tutorial is a theoretical work, in which we study the physics of\nultra-cold dipolar bosonic gases in optical lattices. Such gases consist of\nbosonic atoms or molecules that interact via dipolar forces, and that are\ncooled below the quantum degeneracy temperature, typically in the nK range.\nWhen such a degenerate quantum gas is loaded into an optical lattice produced\nby standing waves of laser light, new kinds of physical phenomena occur. These\nsystems realize then extended Hubbard-type models, and can be brought to a\nstrongly correlated regime. The physical properties of such gases, dominated by\nthe long-range, anisotropic dipole-dipole interactions, are discussed using the\nmean-field approximations, and exact Quantum Monte Carlo techniques (the Worm\nalgorithm).",
        "positive": "Spectroscopy of momentum state lattices: We explore a technique for probing energy spectra in synthetic lattices that\nis analogous to scanning tunneling microscopy. Using one-dimensional synthetic\nlattices of coupled atomic momentum states, we explore this spectroscopic\ntechnique and observe qualitative agreement between the measured and simulated\nenergy spectra for small two- and three-site lattices as well as a uniform\nmany-site lattice. Finally, through simulations, we show that this technique\nshould allow for the exploration of the topological bands and the fractal\nenergy spectrum of the Hofstadter model as realized in synthetic lattices."
    },
    {
        "anchor": "Universal dynamics of a soliton after an interaction quench: We propose a new type of experimentally feasible quantum quench protocol in\nwhich a quantum system is prepared in a coherent, localized excited state of a\nHamiltonian. During the evolution of this solitonic excitation, the microscopic\ninteraction is suddenly changed. We study the dynamics of solitons after this\ninteraction quench for a wide class of systems using a hydrodynamic approach.\nWe find that the post-quench dynamics is universal at short times, i.e. it does\nnot depend on the microscopic details of the physical system. Numerical support\nfor these results is presented using generalized non-linear Schroedinger\nequation, relevant for the implementation of the proposed protocol with\nultracold bosons, as well as for the integrable Calogero model in harmonic\npotential. Finally, it is shown that the effects of integrability breaking by a\nparabolic potential and by a power-law non-linearity do not change the\nuniversality of the short-time dynamics.",
        "positive": "Feedback cooled Bose-Einstein condensation: near and far from\n  equilibrium: Continuously measured interacting quantum systems almost invariably heat,\ncausing loss of quantum coherence. Here, we study Bose-Einstein condensates\n(BECs) subject to repeated weak measurement of the atomic density and describe\nseveral protocols for generating a feedback signal designed to remove\nexcitations created by measurement backaction. We use a stochastic\nGross-Pitaevskii equation to model the system dynamics and find that a feedback\nprotocol utilizing momentum dependant gain and filtering can effectively cool\nboth 1D and 2D systems. The performance of these protocols is quantified in\nterms of the steady state energy, entropy, and condensed fraction. These are\nthe first feedback cooling protocols demonstrated in 2D, and in 1D our optimal\nprotocol reduces the equilibrium energy by more than a factor of 100 as\ncompared with a previous cooling protocol developed using the same methodology.\nWe also use this protocol to quench-cool 1D BECs from non-condensed highly\nexcited states and find that they rapidly condense into a far from equilibrium\nstate with energy orders of magnitude higher than the equilibrium ground state\nenergy for that condensate fraction. We explain this in terms of the\nnear-integrability of our 1D system, whereby efficiently cooled low momentum\nmodes are effectively decoupled from the energetic `reservoir' of the higher\nmomentum modes. We observe that the quench-cooled condensed states can have\nnon-zero integer winding numbers described by quantized supercurrents."
    },
    {
        "anchor": "Nonlocal interactions in collapsing condensates in a box: The collapse of attractive Bose-Einstein condensates in a box with tunable\ninteratomic interactions was studied experimentally recently. Not only were\nremarkably stable remnant condensates observed, but furthermore they often seem\nto involve two stable plateaus. We suggest that these plateaus correspond in\nfact to two minima of the energy, the attractive atomic interactions being\nnonlocal. We show in detail that all the experimental data for these remnant\ncondensates can be accounted for by minimising a variational energy involving a\nnonlocal interatomic potential that is attractive everywhere and that has a\nrange of the order of the magnetic length.",
        "positive": "Crossovers in Unitary Fermi Systems: Universality and crossover is described for attractive and repulsive\ninteractions where, respectively, the BCS-BEC crossover takes place and a\nferromagnetic phase transition is claimed. Crossovers are also described for\noptical lattices and multicomponent systems. The crossovers, universal\nparameters and phase transitions are described within the Leggett and NSR\nmodels and calculated in detail within the Jastrow-Slater approximation. The\nphysics of ultracold Fermi atoms is applied to neutron, nuclear and quark\nmatter, nuclei and electrons in solids whenever possible. Specifically, the\ndifferences between optical lattices and cuprates is discussed w.r.t.\nantiferromagnetic, d-wave superfluid phases and phase separation."
    },
    {
        "anchor": "Collective properties of quantum matter: from Hawking radiation\n  analogues to quantum Hall effect in graphene: The work is divided in three parts. We devote the first part to the study of\nanalog Hawking radiation in Bose-Einstein condensates. We study numerically the\nbirth of a sonic black hole in an outcoupled Bose-Einstein condensate after\nrelaxing the confinement provided by an optical lattice. We also study possible\nsignatures of spontaneous Hawking radiation. We propose that the violation of\nCS inequalities is a smoking gun of the presence of the Hawking effect. We\ncompare this criterion with the presence of entaglement, finding that both are\nequivalent under usual assumptions. Finally, we study a different gravitational\nanalogue: the so-called black-hole laser. The most interesting result is the\nappearance of a regime of continuous and periodic emission of solitons,\nproviding the most strong analogue with optical lasers. In the second part, we\nanalyze the effect of the introduction of a short Bragg pulse in a thermal\ncloud. We show that the induced periodic density pattern decays to the\nequilibrium profile. However, instead of the usual collisional relaxation, the\nmechanism responsible for the decay is the thermal disorder of the particles,\nwith a characteristic time that only depends on the temperature. We find a very\ngood agreement with actual experimental data. In the last part, we switch to a\nvery different system: the $\\nu=0$ quantum Hall state of bilayer graphene.\nAfter re-deriving the corresponding mean-field phase diagram, we compute the\ncollective modes within the zero Landau level. Among the most remarkable\nresults, we have found that at the boundary between the FLP and the F phases a\ngapless mode appears resulting from an accidental symmetry that can be regarded\nas a remanent of a broken $SO(5)$ symmetry. On the other hand, the CAF and PLP\nphases can present dynamical instabilities. We straightforwardly extend the\nprevious results to monolayer graphene.",
        "positive": "Indication of critical scaling in time during the relaxation of an open\n  quantum system: Phase transitions correspond to the singular behavior of physical systems in\nresponse to continuous control parameters like temperature or external fields.\nNear continuous phase transitions, associated with the divergence of a\ncorrelation length, universal power-law scaling behavior with critical\nexponents independent of microscopic system details is found. Recently,\ndynamical quantum phase transitions and universal scaling have been predicted\nand also observed in the non-equilibrium dynamics of isolated quantum systems\nafter a quench, with time playing the role of the control parameter. However,\nsignatures of such critical phenomena in time in open systems, whose dynamics\nis driven by the dissipative contact to an environment, were so far elusive.\nHere, we present results indicating that critical scaling with respect to time\ncan also occur during the relaxation dynamics of an open quantum system\ndescribed by mixed states. We experimentally measure the relaxation dynamics of\nthe large atomic spin of individual Caesium atoms induced by the dissipative\ncoupling via spin-exchange processes to an ultracold Bose gas of Rubidium\natoms. For initial states far from equilibrium, the entropy of the spin state\nis found to peak in time, transiently approaching its maximum possible value,\nbefore eventually relaxing to its lower equilibrium value. Moreover, a\nfinite-size scaling analysis based on numerical simulations shows that it\ncorresponds to a critical point with respect to time of the dissipative system\nin the limit of large system sizes. It is signalled by the divergence of a\ncharacteristic length at a critical time, characterized by critical exponents\nthat are found to be independent of system details."
    },
    {
        "anchor": "Internal energy of many-boson system with three- and four-particle\n  direct correlations taken into account: In this paper we calculate kinetic, potential and full energy with three- and\nfour-particle direct correlations taken into account at wide temperature region\non the base of the density matrix of the interacting Bose-particles [I. O.\nVakarchuk, O. I. Hryhorchak, Journ. Phys. Stud. {\\bf 3}, 3005 (2009)]. In the\nlow temperature limit the obtained expression for the full energy is equal to\nthe wellknown expression for ground state energy in the approximation of \"two\nsums over the wave vector.\" The results of this work can be applied for the\nnumeric calculation of the heat capacity of liquid $^4$He in order to check the\ntheoretical and experimental results quantatively, especially in the\n$\\lambda$-transition region.",
        "positive": "Dynamical spin-flip susceptibility for a strongly interacting ultracold\n  Fermi gas: The Stoner model predicts that a two-component Fermi gas at increasing\nrepulsive interactions undergoes a ferromagnetic transition. Using the\nrandom-phase approximation we study the dynamical properties of the interacting\nFermi gas. For an atomic Fermi gas under harmonic confinement we show that the\ntransverse (spin-flip) dynamical susceptibility displays a clear signature of\nthe ferromagnetic phase in a magnon peak emerging from the Stoner particle-hole\ncontinuum. The dynamical spin susceptibilities could be experimentally explored\nvia spin-dependent Bragg spectroscopy."
    },
    {
        "anchor": "Quantum noise in a transversely pumped cavity Bose--Hubbard model: We investigate the quantum measurement noise effects on the dynamics of an\natomic Bose lattice gas inside an optical resonator. We describe the dynamics\nby means of a hybrid model consisting of a Bose--Hubbard Hamiltonian for the\natoms and a Heisenberg--Langevin equation for the lossy cavity field mode. We\nassume that the atoms are prepared initially in the ground state of the lattice\nHamiltonian and then start to interact with the cavity mode. We show that the\ncavity field fluctuations originating from the dissipative outcoupling of\nphotons from the resonator lead to vastly different effects in the different\npossible ground state phases, i.e., the superfluid, the supersolid, the Mott-\nand the charge-density-wave phases. In the former two phases with the presence\nof a superfluid wavefunction, the quantum measurement noise appears as a\ndriving term leading to excess noise depletion of the ground state. The time\nscale for the system to leave the ground scale is determined analytically. For\nthe latter two incompressible phases, the quantum noise results in the\nfluctuation of the chemical potential. We derive an analytical expression for\nthe corresponding broadening of the quasiparticle resonances.",
        "positive": "Collective fermion excitation in a warm massless Dirac system: Basing on a self-consistent method, we predict theoretically that there\noccurs not only a normal (quasi) fermion mode, but also a collective fermion\nmode, plasmino, in a warm 2D massless Dirac system, especially in a warm\nintrinsic graphene system. Results of Landau damping show that both fermion and\nplasmino are well defined modes. We find that there are sharp differences\nbetween the discussed system and the QCD/QED system. Firstly, the thermal mass\nis proportional to $\\alpha_g^{3/4}T$ but not $\\alpha_g T$. Secondly, at\n$0<q<q_c$, the fermion channel and plasmino channel are nearly degenerate and\nfurthermore, the energy difference between fermion and plasmino becomes more\nand more larger with increasing $q$ at the region $q>q_c$. Thirdly, the fermion\nbehaves as a \"relativity particles\" with none zero mass and the plasmino\nexhibits an anormal dispersion at moderate momentum."
    },
    {
        "anchor": "Significance of dressed molecules in a quasi-two-dimensional polarized\n  Fermi gas: We investigate the properties of a spin-orbit coupled quasi-two-dimensional\nFermi gas with tunable s-wave interaction between the two spin species. By\nanalyzing the two-body bound state, we find that the population of the excited\nstates in the tightly-confined axial direction can be significant when the\ntwo-body binding energy becomes comparable or exceeds the axial confinement.\nSince the Rashba spin-orbit coupling that we study here tends to enhance the\ntwo-body binding energy, this effect can become prominent at unitarity or even\non the BCS side of the Feshbach resonance. To study the impact of these excited\nmodes along the third dimension, we adopt an effective two-dimensional\nHamiltonian in the form of a two-channel model, where the dressed molecules in\nthe closed channel consist of the conventional Feshbach molecules as well as\nthe excited states occupation in the axial direction. With properly\nrenormalized interactions between atoms and dressed molecules, we find that\nboth the density distribution and the phase structure in the trap can be\nsignificantly modified near a wide Feshbach resonance. In particular, the\nstability region of the topological superfluid phase is increased. Our findings\nare helpful for the experimental search for the topological superfluid phase in\nultra-cold Fermi gases, and have interesting implications for\nquasi-low-dimensional polarized Fermi gases in general.",
        "positive": "Mapping the phase diagram of spinor condensates via adiabatic quantum\n  phase transitions: We experimentally study two quantum phase transitions in a sodium spinor\ncondensate immersed in a microwave dressing field. We also demonstrate that\nmany previously unexplored regions in the phase diagram of spinor condensates\ncan be investigated by adiabatically tuning the microwave field across one of\nthe two quantum phase transitions. This method overcomes two major experimental\nchallenges associated with some widely used methods, and is applicable to other\natomic species. Agreements between our data and the mean-field theory for\nspinor Bose gases are also discussed."
    },
    {
        "anchor": "Dynamical mean-field theory for light fermion--heavy boson mixtures on\n  optical lattices: We theoretically analyze Fermi-Bose mixtures consisting of light fermions and\nheavy bosons that are loaded into optical lattices (ignoring the trapping\npotential). To describe such mixtures, we consider the Fermi-Bose version of\nthe Falicov-Kimball model on a periodic lattice. This model can be exactly\nmapped onto the spinless Fermi-Fermi Falicov-Kimball model at zero temperature\nfor all parameter space as long as the mixture is thermodynamically stable. We\nemploy dynamical mean-field theory to investigate the evolution of the\nFermi-Bose Falicov-Kimball model at higher temperatures. We calculate spectral\nmoment sum rules for the retarded Green's function and self-energy, and use\nthem to benchmark the accuracy of our numerical calculations, as well as to\nreduce the computational cost by exactly including the tails of infinite\nsummations or products. We show how the occupancy of the bosons,\nsingle-particle many-body density of states for the fermions, momentum\ndistribution, and the average kinetic energy evolve with temperature. We end by\nbriefly discussing how to experimentally realize the Fermi-Bose Falicov-Kimball\nmodel in ultracold atomic systems.",
        "positive": "Frustration and glassiness in spin models with cavity-mediated\n  interactions: We show that the effective spin-spin interaction between three-level atoms\nconfined in a multimode optical cavity is long-ranged and sign-changing, like\nthe RKKY interaction; therefore, ensembles of such atoms subject to frozen-in\npositional randomness can realize spin systems having disordered and frustrated\ninteractions. We argue that, whenever the atoms couple to sufficiently many\ncavity modes, the cavity-mediated interactions give rise to a spin glass. In\naddition, we show that the quantum dynamics of cavity-confined spin systems is\nthat of a Bose-Hubbard model with strongly disordered hopping but no on-site\ndisorder; this model exhibits a random-singlet glass phase, absent in\nconventional optical-lattice realizations. We briefly discuss experimental\nsignatures of the realizable phases."
    },
    {
        "anchor": "Highly polarized one-dimensional Fermi gases near a narrow $p-$wave\n  resonance: Based on the recently developed interaction renormalization for the\none-dimensional $p$-wave interaction, we study the problem of a single impurity\nimmersed in a highly polarized Fermi sea. They interact through a narrow\n$p$-wave Feshbach resonance, so the effective range $r_{0}$ naturally appears\nin the system. We use the variational approach limited to single-particle-hole\nexcitations on top of the unperturbed Fermi sea. The polaron exhibits two\nbranches of solutions, namely, the attractive and repulsive branches, with\nvarying scattering length across the resonance. We calculate the energy\nspectrum, residue and effective mass for each of the branches. We compare the\npolaronic energy with the energy of the dressed molecule, and find that the\nmolecular state is energetically favored when increasing the interaction\nstrength. The critical interaction strength for the polaron-to-molecule\ntransition will shift to the BCS side of the $p$-wave resonance as the\neffective range increases.",
        "positive": "Two-terminal transport measurements with cold atoms: In the last years, the ability of cold atoms experiments to explore\ncondensed- matter related questions has dramatically progressed. Transport\nexperiments, in particular, have expanded to the point that conductances and\nother transport coefficients can now be measured in a way directly analogous to\nsolid state physics, extending cold atoms based quantum simulations into the\ndomain of quantum electronic devices. In this topical review, we describe the\ntransport experiments performed with cold gases in the two terminals\nconfiguration, with an emphasis on the specific features of cold atomic gases\ncompared to solid state physics. We present the experimental techniques and the\nmain experimental findings, focusing on but not restricted to the recent\nexperiments performed in our group. We eventually discuss the perspectives\nopened by this approach, the main technical and conceptual challenges for\nfuture developments, and the potential applications as a quantum simulator for\ntransport phenomena and mesoscopic physics problems."
    },
    {
        "anchor": "Three-body recombination in heteronuclear mixtures at finite temperature: Within the universal zero-range theory, we compute the three-body\nrecombination rate to deep molecular states for two identical bosons resonantly\ninteracting with each other and with a third atom of another species, in the\nabsence of weakly bound dimers. The results allow for a quantitative\nunderstanding of loss resonances at finite temperature and, combined with\nexperimental data, can be used for testing the Efimov universality and\nextracting the corresponding three-body parameters in a given system.\nCuriously, we find that the loss rate can be dramatically enhanced by the\nresonant heavy-heavy interaction, even for large mass ratios where this\ninteraction is practically irrelevant for the Efimov scaling factor. This\neffect is important for analysing the recent loss measurements in the Cs-Li\nmixture.",
        "positive": "Evolution of static and dynamical density correlations in a\n  one-dimensional soft-core gas from the Tonks-Girardeau limit to a clustering\n  fluid: Repulsive soft-core atomic systems may undergo clustering if their density is\nhigh enough that core overlap is unavoidable. In one-dimensional quantum\nsystems, it has been shown that this instability triggers a transition from a\nLuttinger liquid to various cluster Luttinger liquids. Here, we focus on the\nLuttinger liquid regime and theoretically study the evolution of key\nobservables related to density fluctuations, that manifest a striking\ndependence on density. We tune the interaction so that the low-density regime\ncorresponds to a Tonks-Girardeau gas, and show that as the density is increased\nthe system departs more and more from Tonks-Girardeau behavior, displaying a\nmuch larger compressibility as well as rotonic excitations that finally drive\nthe clustering transition. We compare various theoretical approaches, which are\naccurate in different regimes. Using quantum Monte Carlo methods and analytic\ncontinuation as a benchmark, we investigate the regime of validity of the\nmean-field Bogoliubov and the real-time multiconfiguration time-dependent\nHartree-Fock approaches. Part of the behavior that we describe should be\nobservable in ultracold Rydberg-dressed gases, provided that system losses are\nprevented."
    },
    {
        "anchor": "Bipolaron in one-dimensional $SU(3)$ fermions with three-body\n  interaction: The properties of the one-dimensional $SU(3)$ population-imbalanced fermions\nare discussed. The system is assumed to be in the two-body resonance where all\ntwo-body scattering lengths diverge, and the only interaction between fermions\nthat is taken into account is the short-range three-body one. In particular, we\nconsider the situation when only one `flavor' of fermions is macroscopically\noccupied, and there are exactly two atoms of two others. This system supports\nthe trimer and the medium-induced dimer states studied here in detail and shows\nevidence of color superfluidity.",
        "positive": "Fate of the false vacuum: towards realization with ultra-cold atoms: Quantum decay of a relativistic scalar field from a false vacuum is a\nfundamental idea in quantum field theory. It is relevant to models of the early\nUniverse, where the nucleation of bubbles gives rise to an inflationary\nuniverse and the creation of matter. Here we propose a laboratory test using an\nexperimental model of an ultra-cold spinor Bose gas. A false vacuum for the\nrelative phase of two spin components, serving as the unstable scalar field, is\ngenerated by means of a modulated radio-frequency coupling of the spin\ncomponents. Numerical simulations demonstrate the spontaneous formation of true\nvacuum bubbles with realistic parameters and time-scales."
    },
    {
        "anchor": "Quantum Generalized Hydrodynamics of the Tonks-Girardeau gas: density\n  fluctuations and entanglement entropy: We apply the theory of Quantum Generalized Hydrodynamics (QGHD) introduced in\n[Phys. Rev. Lett. 124, 140603 (2020)] to derive asymptotically exact results\nfor the density fluctuations and the entanglement entropy of a one-dimensional\ntrapped Bose gas in the Tonks-Girardeau (TG) or hard-core limit, after a trap\nquench from a double well to a single well. On the analytical side, the\nquadratic nature of the theory of QGHD is complemented with the emerging\nconformal invariance at the TG point to fix the universal part of those\nquantities. Moreover, the well-known mapping of hard-core bosons to free\nfermions, allows to use a generalized form of the Fisher-Hartwig conjecture to\nfix the non-trivial spacetime dependence of the ultraviolet cutoff in the\nentanglement entropy. The free nature of the TG gas also allows for more\naccurate results on the numerical side, where a higher number of particles as\ncompared to the interacting case can be simulated. The agreement between\nanalytical and numerical predictions is extremely good. For the density\nfluctuations, however, one has to average out large Friedel oscillations\npresent in the numerics to recover such agreement.",
        "positive": "Rapid coherent control of population transfer in lattice systems: We derive the driving potential that accelerates adiabatic population\ntransfer from an initial state to a target state in a lattice system without\nunwanted excitation of other states by extending to discrete systems the\nfast-forward theory of adiabatic transfer. As an example we apply the theory to\na model that describes a Bose-Einstein condensate in a quasi one-dimensional\noptical lattice, and show that modulation of the tilting of the lattice\npotential can transfer the population of the Bose-Einstein condensate from site\nto site with high fidelity and without unwanted excitations."
    },
    {
        "anchor": "Theory of cold atoms: Bose-Einstein statistics: This Tutorial is the continuation of the previous tutorial part, published in\nLaser Phys. 23, 062001 (2013), where the basic mathematical techniques required\nfor an accurate description of cold atoms for both types of quantum statistics\nare expounded. In the present part, the specifics of the correct theoretical\ndescription of atoms obeying Bose-Einstein statistics are explained, including\ntrapped Bose atoms. In the theory of systems exhibiting the phenomenon of\nBose-Einstein condensation, there exists a number of delicate mathematical\npoints, whose misunderstanding often results in principally wrong conclusions.\nThis is why the consideration in the present Tutorial is sufficiently detailed\nin order that the reader could clearly understand the underlying mathematics\nand would avoid confusions.",
        "positive": "Finite temperature superfluid transition of strongly-correlated lattice\n  bosons in various geometries: We study finite-temperature properties of the strongly interacting bosons in\nthree-dimensional lattices by employing the combined Bogoliubov method and the\nquantum rotor approach. Based on the mapping of the Bose-Hubbard Hamiltonian of\nstrongly interacting bosons onto U(1) phase action, we study their\nthermodynamic phase diagrams for several lattice geometries including; simple\ncubic, body- as well as face-centered lattices. The quantitative values for the\nphase boundaries obtained here may be used as a reference for emulation of the\nBose-Hubbard model on a variety of optical lattice structures in order to\ndemonstrate experimental-theoretical consistency for the numerical values\nregarding the location of the critical points."
    },
    {
        "anchor": "Quantum ratchet transport with minimal dispersion rate: We analyze the performance of quantum ratchets by considering the dynamics of\nan initially localized wave packet loaded into a flashing periodic potential.\nThe directed center-of-mass motion can be initiated by the uniform modulation\nof the potential height, provided that the modulation protocol breaks all\nrelevant time- and spatial reflection symmetries. A poor performance of quantum\nratchet transport is characterized by a slow net motion and a fast diffusive\nspreading of the wave packet, while the desirable optimal performance is the\ncontrary. By invoking a quantum analog of the classical P\\'eclet number, namely\nthe quotient of the group velocity and the dispersion of the propagating wave\npacket, we calibrate the transport properties of flashing quantum ratchets and\ndiscuss the mechanisms that yield low-dispersive directed transport.",
        "positive": "Population dynamics in Floquet realisation of Harper-Hofstadter\n  Hamiltonian: We study the recent Floquet-realisation of the Harper-Hofstadter model in a\ngas of cold bosonic atoms. We study in detail the scattering processes in this\nsystem in the weakly interacting regime due to the interplay of particle\ninteractions and the explicit time dependence of the Floquet states that lead\nto band transitions and heating. We focus on the experimentally used parameters\nand explicitly model the transverse confining direction. Based on transition\nrates computed within the Floquet-Fermi golden rule we obtain band population\ndynamics which are in agreement with the dynamics observed in experiment.\nFinally, we discuss whether and how photon-assisted collisions that may be the\nsource heating and band population dynamics might be suppressed in the\nexperimental setup by appropriate design of the transverse confining potential.\nThe suppression of such processes will become increasingly important as the\nexperiments progress into simulating strongly interacting systems in the\npresence of artificial gauge fields."
    },
    {
        "anchor": "Non-equilibrium pre-thermal states in a two-dimensional photon fluid: Thermalization is the dynamical process by which a many-body system evolves\ntoward a thermal equilibrium state that maximizes its entropy. In certain\ncases, however, the establishment of thermal equilibrium is significantly\nslowed down and a phenomenon of pre-thermalization can emerge. It describes the\ninitial relaxation toward a quasi-steady state after a perturbation. While\nhaving similar properties to their thermal counterparts, pre-thermal states\nexhibit a partial memory of initial conditions. Here, we observe the dynamical\nformation of a pre-thermal state in a non-equilibrium, two-dimensional (2D)\nfluid of light after an interaction quench. Direct measurements of the fluid's\nfirst-order correlation function reveal the spontaneous emergence of long-range\nalgebraic correlations spreading within a light-cone, providing a clear\nsignature of a quasi steady-state strongly similar to a 2D thermal superfluid.\nDetailed experimental characterization of the algebraic order is presented and\na partial memory of the initial conditions is demonstrated, in agreement with\nrecent theoretical predictions. Furthermore, by a controlled increase of the\nfluid fluctuations, we unveil a cross-over from algebraic to short-range\n(exponential) correlations, analogous to the celebrated Kosterlitz-Thouless\ntransition observed at thermal equilibrium. These results suggest the existence\nof non-equilibrium precursors for thermodynamic phase transitions.",
        "positive": "Optimizing optical potentials with physics-inspired learning algorithms: We present our new experimental and theoretical framework which combines a\nbroadband superluminescent diode (SLED/SLD) with fast learning algorithms to\nprovide speed and accuracy improvements for the optimization of 1D optical\ndipole potentials, here generated with a Digital Micromirror Device (DMD). To\ncharacterize the setup and potential speckle patterns arising from coherence,\nwe compare the superluminescent diode to a single-mode laser by investigating\ninterference properties. We employ Machine Learning (ML) tools to train a\nphysics-inspired model acting as a digital twin of the optical system\npredicting the behavior of the optical apparatus including all its\nimperfections. Implementing an iterative algorithm based on Iterative Learning\nControl (ILC) we optimize optical potentials an order of magnitude faster than\nheuristic optimization methods. We compare iterative model-based offline\noptimization and experimental feedback-based online optimization. Our methods\nprovide a new route to fast optimization of optical potentials which is\nrelevant for the dynamical manipulation of ultracold gases."
    },
    {
        "anchor": "Simulating a Mott insulator using attractive interaction: We study the particle-hole symmetry in the Hubbard model using ultracold\nfermionic atoms in an optical lattice. We demonstrate the mapping between\ncharge and spin degrees of freedom and, in particular, show the occurrence of a\nstate with \"incompressible\" magnetisation for attractive interactions. Our\nresults present a novel approach to quantum simulation by giving access to\nstrongly-correlated phases of matter through an experimental mapping to easier\ndetectable observables.",
        "positive": "Hetero pairing and component-dependent pseudogap phenomena in an\n  ultracold Fermi gas with mass imbalance: We investigate the superfluid phase transition and single-particle\nexcitations in the BCS (Bareen-Cooper-Schrieffer)-BEC (Bose-Einstein\ncondensation) crossover regime of an ultracold Fermi gas with mass imbalance.\nIn our recent paper [R. Hanai, et. al., Phys. Rev. A 88, 053621 (2013)], we\nshowed that an extended $T$-matrix approximation (ETMA) can overcome the\nserious problem known in the ordinary (non-self-consistent) $T$-matrix\napproximation that it unphysically gives double-valued superfluid phase\ntransition temperature $T_{\\rm c}$ in the presence of mass imbalance. However,\nat the same time, the ETMA was also found to give the vanishing $T_{\\rm c}$ in\nthe weak-coupling and highly mass-imbalanced case. In this paper, we inspect\nthe correctness of this ETMA result, using the self-consistent $T$-matrix\napproximation (SCTMA). We show that the vanishing $T_{\\rm c}$ is an artifact of\nthe ETMA, coming from an internal inconsistency of this theory. The superfluid\nphase transition actually always occurs, irrespective of the ratio of mass\nimbalance. We also apply the SCTMA to the pseudogap problem in a\nmass-imbalanced Fermi gas. We show that pairing fluctuations induce different\npseudogap phenomena between the the light component and heavy component. We\nalso point out that a $^6$Li-$^{40}$K mixture is a useful system for the\nrealization of a hetero pairing state, as well as for the study of\ncomponent-dependent pseudogap phenomena."
    },
    {
        "anchor": "Entanglement entropy and macroscopic quantum states with dipolar bosons\n  in a triple-well potential: We study interacting dipolar atomic bosons in a triple-well potential within\na ring geometry. This system is shown to be equivalent to a three-site\nBose-Hubbard model. We analyze the ground state of dipolar bosons by varying\nthe effective on-site interaction. This analysis is performed both numerically\nand analytically by using suitable coherent-state representations of the ground\nstate. The latter exhibits a variety of forms ranging from the su(3) coherent\nstate in the delocalization regime to a macroscopic cat-like state with fully\nlocalized populations, passing for a coexistence regime where the ground state\ndisplays a mixed character. We characterize the quantum correlations of the\nground state from the bi-partition perspective. We calculate both numerically\nand analytically (within the previous coherent-state representation) the\nsingle-site entanglement entropy which, among various interesting properties,\nexhibits a maximum value in correspondence to the transition from the cat-like\nto the coexistence regime. In the latter case, we show that the ground-state\nmixed form corresponds, semiclassically, to an energy exhibiting two\nalmost-degenerate minima.",
        "positive": "Condensates in double-well potential with synthetic gauge potentials and\n  vortex seeding: We demonstrate an enhancement in the vortex generation when artificial gauge\npotential is introduced to condensates confined in a double well potential.\nThis is due to the lower energy required to create a vortex in the low\ncondensate density region within the barrier. Furthermore, we study the\ntransport of vortices between the two wells, and show that the traverse time\nfor vortices is longer for the lower height of the well. We also show that the\ncritical value of synthetic magnetic field to inject vortices into the bulk of\nthe condensate is lower in the double-well potential compared to the harmonic\nconfining potential."
    },
    {
        "anchor": "Observation of Zitterbewegung in a spin-orbit coupled Bose-Einstein\n  condensate: Spin-orbit coupled ultra-cold atoms provide an intriguing new avenue for the\nstudy of rich spin dynamics in superfluids. In this Letter, we observe\nZitterbewegung, the simultaneous velocity (thus position) and spin\noscillations, of neutral atoms between two spin-orbit coupled bands in a\nBose-Einstein condensate (BEC) through sudden quantum quenches of the\nHamiltonian. The observed Zitterbewegung oscillations are perfect on a short\ntime scale but gradually damp out on a long time scale, followed by sudden and\nstrong heating of the BEC. As an application, we also demonstrate how\nZitterbewegung oscillations can be exploited to populate the upper spin-orbit\nband, and observe a subsequent dipole motion. Our experimental results are\ncorroborated by a theoretical and numerical analysis and showcase the great\nflexibility that ultra-cold atoms provide for investigating rich spin dynamics\nin superfluids.",
        "positive": "Stabilizing confined quasiparticle dynamics in one-dimensional polar\n  lattice gases: The disorder-free localization that occurred in the study of relaxation\ndynamics in far-from-equilibrium quantum systems has been widely explored. Here\nwe investigate the interplay between the dipole-dipole interaction (DDI) and\ndisorder in the hard-core polar bosons in a one-dimensional lattice. We find\nthat the localized dynamics will eventually thermalize in the clean gas, but\ncan be stabilized with the existence of a small disorder proportional to the\ninverse of DDI strength. From the effective dimer Hamiltonian, we show that the\neffective second-order hopping of quasiparticles between nearest-neighbor sites\nis suppressed by the disorder with strength similar to the effective hopping\namplitude. The significant gap between the largest two eigenvalues of the\nentanglement spectrum indicates the dynamical confinement. We also find that\nthe disorder related sample-to-sample fluctuation is suppressed by the DDI.\nFinally, we extend our research from the uncorrelated random disorder to the\ncorrelated quasiperiodic disorder and from the two-dimer model to the\nhalf-filling system, obtaining similar results."
    },
    {
        "anchor": "Drag in Bose-Fermi Mixtures: We use kinetic theory to model the dynamics of a small Bose condensed cloud\nof heavy particles moving through a larger degenerate Fermi gas of light\nparticles. Varying the Bose-Fermi interaction, we find a crossover between bulk\nand surface dominated regimes -- where scattering occurs throughout the Bose\ncloud, or solely on the surface. We calculate the damping and frequency shift\nof the dipole mode in a harmonic trap as a function of the magnetic field\ncontrolling an inter-species Feshbach resonance. We find excellent agreement\nbetween our stochastic model and the experimental studies of Cs-Li mixtures.",
        "positive": "Resonant control of polar molecules in an optical lattice: We study the resonant control of two nonreactive polar molecules in an\noptical lattice site, focussing on the example of RbCs. Collisional control can\nbe achieved by tuning bound states of the intermolecular dipolar potential, by\nvarying the applied electric field or trap frequency. We consider a wide range\nof electric fields and trapping geometries, showing that a three-dimensional\noptical lattice allows for significantly wider avoided crossings than free\nspace or quasi-two dimensional geometries. Furthermore, we find that dipolar\nconfinement induced resonances can be created with reasonable trapping\nfrequencies and electric fields, and have widths that will enable useful\ncontrol in forthcoming experiments."
    },
    {
        "anchor": "Density instabilities in a two-dimensional dipolar Fermi gas: We study the density instabilities of a two-dimensional gas of dipolar\nfermions with aligned dipole moments. We show that the Random Phase\nApproximation (RPA) for the density-density response function is never accurate\nfor the dipolar gas. We incorporate correlations beyond RPA via an improved\nversion of the Singwi-Tosi-Land-Sjolander scheme. In addition to density-wave\ninstabilities, our formalism captures the collapse instability that is expected\nfrom Hartree-Fock calculations but is absent from RPA. Crucially, we find that\nwhen the dipoles are perpendicular to the layer, the system spontaneously\nbreaks rotational symmetry and forms a stripe phase, in defiance of\nconventional wisdom.",
        "positive": "Higher-nodal collective modes in a resonantly interacting Fermi gas: We report on experimental investigations of longitudinal collective\noscillations in a highly elongated, harmonically trapped two-component Fermi\ngas with resonantly tuned s-wave interactions ('unitary Fermi gas'). We focus\non higher-nodal axial modes, which in contrast to the elementary modes have\nreceived little attention so far. We show how these modes can be efficiently\nexcited using a resonant local excitation scheme and sensitively analyzed by a\nFourier transformation of the detected time evolution of the axial density\nprofile. We study the temperature dependence of the mode frequencies across the\nsuperfluid phase transition. The behavior is qualitatively different from the\nelementary modes, where the mode frequencies are independent of the temperature\nas long as the gas stays in the hydrodynamic regime. Our results are compared\nto theoretical predictions based on Landau's two-fluid theory and available\nexperimental knowledge of the equation of state. The comparison shows excellent\nagreement and thus both represents a sensitive test for the validity of the\ntheoretical approach and provides an independent test of the equation of state.\nThe present results obtained on modes of first-sound character represent\nbenchmarks for the observation of second-sound propagation and corresponding\noscillation modes."
    },
    {
        "anchor": "Rapid-prototyping of microscopic thermal landscapes in Brillouin light\n  scattering spectroscopy: Since temperature and its spatial and temporal variations affect a wide range\nof physical properties of material systems, they can be used to create\nreconfigurable spatial structures of various types in physical and biological\nobjects. This paper presents an experimental optical setup for creating tunable\ntwo-dimensional temperature patterns on a micrometer scale. As an example of\nits practical application, we have produced temperature-induced magnetization\nlandscapes in ferrimagnetic yttrium iron garnet films and investigated them\nusing micro-focused Brillouin light scattering spectroscopy. It is shown that,\ndue to the temperature dependence of the magnon spectrum, temperature changes\ncan be visualized even for microscale thermal patterns.",
        "positive": "Scattering of solitons in binary Bose-Einstein condensates with\n  spin-orbit and Rabi couplings: In this paper we study the scattering of solitons in a binary Bose-Einstein\nCondensate (BEC) including SO- and Rabi-couplings. To this end, we derive a\nreduced ODE model in view to provide a variational description of the\ncollisional dynamics. Also, we assume negative intra- and inter-component\ninteraction strengths, such that one obtains localized solutions even in\nabsence of external potentials. By performing extensive numerical simulations\nof this model we observe that, for specific conditions, the final propagation\nvelocity of the scattered solitons could be highly sensitive to small changes\nin the initial conditions, being a possible signature of chaos. Additionally,\nthere are infinitely many intervals of regularity emerging from the obtained\nchaotic-like regions and forming a fractal-like structure of\nreflection/transmission windows. Finally, we investigate how the value of the\nspin-orbit coupling strength changes the critical velocities, which are\nminimum/maximum values for the occurrence of solitons bound-states, as well as\nthe fractal-like structure."
    },
    {
        "anchor": "Condensation transition of ultracold Bose gases with Rashba spin-orbit\n  coupling: We study the Bose-Einstein condensate phase transition of three-dimensional\nultracold bosons with isotropic Rashba spin-orbit coupling. Investigating the\nstructure of Ginzburg-Landau free energy as a function of the condensate\ndensity, we show, within the Bogoliubov approximation, that the condensate\nphase transition is first order with a jump in the condensate density. We\ncalculate the transition temperature and the jump in the condensate density at\nthe transition for large spin-orbit coupling, where the transition temperature\ndepends linearly on the density of particles. Finally, we discuss the\nfeasibility of producing the phase transition experimentally.",
        "positive": "Ground-state thermodynamic quantities of homogeneous spin-$1/2$ fermions\n  from the BCS region to the unitarity limit: We experimentally determined various thermodynamic quantities of interacting\ntwo-component fermions at the zero-temperature limit from the\nBardeen-Cooper-Schrieffer (BCS) region to the unitarity limit. The obtained\nresults are very accurate in the sense that the systematic error is within 4%\naround the unitarity limit. Using this advantage, we can compare our data with\nvarious many-body theories. We found that an extended ${\\it T}$-matrix\napproximation, which is a strong-coupling theory involving fluctuations in the\nCooper channel, well reproduces our experimental results. We also found that\nthe superfluid order parameter ${\\it \\Delta}$ calculated by solving the\nordinary BCS gap equation with the chemical potential of interacting fermions\nis close to the binding energy of the paired fermions directly observed in a\nspectroscopic experiment and that obtained using a quantum Monte Carlo method.\nSince understanding the strong-coupling properties of a superfluid Fermi gas in\nthe BCS-BEC (Bose-Einstein condensation) crossover region is a crucial issue in\ncondensed matter physics and nuclear physics, the results of the present study\nare expected to be useful in the further development of these fields."
    },
    {
        "anchor": "Quenching dynamics of the bright solitons and other localized states in\n  spin-orbit coupled Bose-Einstein condensates: We study the dynamics of binary Bose-Einstein condensates made of ultracold\nand dilute alkali-metal atoms in a quasi-one-dimensional setting. Numerically\nsolving the two coupled Gross-Pitaevskii equations which accurately describe\nthe system dynamics, we demonstrate that the spin transport can be controlled\nby suitably quenching spin-orbit (SO) and Rabi coupling strengths. Moreover, we\npredict a variety of dynamical features induced by quenching: broken\noscillations, breathers-like oscillating patterns, spin-mixing-demixing,\nmiscible-immiscible transition, emerging dark-bright states, dark solitons, and\nspin-trapping dynamics. We also outline the experimental relevance of the\npresent study in manipulating the spin states in $^{39}$K condensates.",
        "positive": "Dynamic polaron response from variational imaginary time evolution: An variational expression for the zero temperature polaron impedance is\nobtained by minimizing the free energy in a generalized quadratic Feynman\nmodel. The impedance function of the quadratic model serves as the variational\nparameter. It is shown that a very small change in the energy can be\naccompanied by a large change in the optical conductivity. This is related to\nthe insensitivity of the Jensen-Feynman free energy to the UV properties of the\nmodel. Analytic and numeric results are derived for the Fr\\\"ohlich polaron in\nweak and strong coupling. Standard results are recovered at weak coupling but,\nmore importantly, strong coupling inconsistencies are removed."
    },
    {
        "anchor": "Scale invariance and viscosity of a two-dimensional Fermi gas: We investigate the collective excitations of a harmonically trapped\ntwo-dimensional Fermi gas from the collisionless (zero sound) to the\nhydrodynamic (first sound) regime. The breathing mode, which is sensitive to\nthe equation of state, is observed at a frequency two times the dipole mode\nfrequency for a large range of interaction strengths and temperatures, and the\namplitude of the breathing mode is undamped. This provides evidence for a\ndynamical SO(2,1) scaling symmetry of the two-dimensional Fermi gas. Moreover,\nwe investigate the quadrupole mode to measure the shear viscosity of the\ntwo-dimensional gas and study its temperature dependence.",
        "positive": "Interaction-Tuned Dynamical Transitions in a Rashba Spin-Orbit Coupled\n  Fermi Gas: We consider the time evolution of the magnetization in a Rashba\nspin-orbit-coupled Fermi gas, starting from a fully-polarized initial state. We\nmodel the dynamics using a Boltzmann equation, which we solve in the\nHartree-Fock approximation. The resulting non-linear system of equations gives\nrise to three distinct dynamical regimes with qualitatively different\nasymptotic behaviors of the magnetization at long times. The distinct regimes\nand the transitions between them are controlled by the interaction strength:\nfor weakly interacting fermions, the magnetization decays to zero. For\nintermediate interactions, it displays undamped oscillations about zero and for\nstrong interactions, a partially magnetized state is dynamically stabilized.\nThe dynamics we find is a spin analog of interaction induced self-trapping in\ndouble-well Bose Einstein condensates. The predicted phenomena can be realized\nin trapped Fermi gases with synthetic spin-orbit interactions."
    },
    {
        "anchor": "Finite temperature phase diagram of spin-1/2 bosons in two-dimensional\n  optical lattice: We study a two-species bosonic Hubbard model on a two-dimensional square\nlattice by means of quantum Monte Carlo simulations and focus on finite\ntemperature effects. We show in two different cases, ferro- and\nantiferromagnetic spin-spin interactions, that the phase diagram is composed of\nsolid Mott phases, liquid phases and superfluid phases. In the\nantiferromagnetic case, the superfluid (SF) is polarized while the Mott\ninsulator (MI) and normal Bose liquid (NBL) phases are not. On the other hand,\nin the ferromagnetic case, none of the phases is polarized. The\nsuperfluid-liquid transition is of the Berezinsky-Kosterlitz-Thouless type\nwhereas the solid-liquid passage is a crossover.",
        "positive": "Deformation of a quantum many-particle system by a rotating impurity: During the last 70 years, the quantum theory of angular momentum has been\nsuccessfully applied to describing the properties of nuclei, atoms, and\nmolecules, their interactions with each other as well as with external fields.\nDue to the properties of quantum rotations, the angular momentum algebra can be\nof tremendous complexity even for a few interacting particles, such as valence\nelectrons of an atom, not to mention larger many-particle systems. In this\nwork, we study an example of the latter: a rotating quantum impurity coupled to\na many-body bosonic bath. In the regime of strong impurity-bath couplings the\nproblem involves addition of an infinite number of angular momenta which\nrenders it intractable using currently available techniques. Here, we introduce\na novel canonical transformation which allows to eliminate the complex angular\nmomentum algebra from such a class of many-body problems. In addition, the\ntransformation exposes the problem's constants of motion, and renders it\nsolvable exactly in the limit of a slowly-rotating impurity. We exemplify the\ntechnique by showing that there exists a critical rotational speed at which the\nimpurity suddenly acquires one quantum of angular momentum from the\nmany-particle bath. Such an instability is accompanied by the deformation of\nthe phonon density in the frame rotating along with the impurity."
    },
    {
        "anchor": "Breaking strong symmetries in dissipative quantum systems: Bosonic atoms\n  coupled to a cavity: In dissipative quantum systems, strong symmetries can lead to the existence\nof conservation laws and multiple steady states. In this work we investigate a\nstrong symmetry for bosonic atoms coupled to an optical cavity, an\nexperimentally relevant system, generalizing the adiabatic elimination\ntechniques and using numerically exact matrix product state methods. We show\nthat for ideal bosons coupled to the cavity multiple steady states exist and in\neach symmetry sector a dissipative phase transition occurs at a different\ncritical point. This implies that phases of very different nature can coexist.\nWe find that the introduction of a slight breaking of the strong symmetry by a\nsmall interaction term leads to a direct transition from multiple steady states\nto a unique steady state. We point out the phenomenon of dissipative freezing,\nthe breaking of the conservation law at the level of individual realizations in\nthe presence of the strong symmetry. For a small breaking of the strong\nsymmetry we see that the behavior of the individual trajectories still shows\nsome signs of this dissipative freezing before it fades out for a larger\nsymmetry breaking terms.",
        "positive": "Strongly correlated bosons and fermions in optical lattices: These lectures are an introduction to the physics of strongly correlated\nfermions and bosons. They are specially targeted for the experimental\nrealizations that have been provided by cold atomic gases in optical lattices."
    },
    {
        "anchor": "Dynamically generated flat-band phases in optical kagome lattices: Motivated by recent advances in the realization of complex two-dimensional\noptical lattices, we investigate theoretically the quantum transport of\nultracold fermions in an optical kagome lattice. In particular, we focus on its\nextensively degenerate localized states (flat band). By loading fermions in a\npartial region of the lattice and depleting the mobile atoms at the far\nboundary of the initially unoccupied region, we find a dynamically generated\nflat-band insulator, which is also a population-inverted state. We further show\nthat inclusion of weak repulsion leads to a dynamical stripe phase for\ntwo-component fermions in a similar setup. Finally, by preparing a topological\ninsulating state in a partially occupied kagome lattice, we find that the\ntopological chiral current decays but exhibits an interesting oscillating\ndynamics during the nonequilibrium transport. Given the broad variety of\nlattice geometries supporting localized or topological states, our work\nsuggests new possibilities to use geometrical effects and their dynamics in\natomtronic devices.",
        "positive": "Quantum dynamics of atomic bright solitons under splitting and\n  re-collision, and implications for interferometry: We numerically study the classical and quantum dynamics of an atomic bright\nsoliton in a highly-elongated one-dimensional harmonic trap with a Gaussian\nbarrier. In the regime of the recent experiment by Dyke {\\it et al.}, the\nsystem realizes a coherent nonlinear soliton beam-splitter and interferometer\nwhose accuracy we analyze. In the case of tighter radial trap confinement and\nenhanced quantum fluctuations, a split soliton can represent a spin-squeezed,\nor alternatively, a fragmented condensate with reduced phase-coherence that can\nbe measured by interfering the split soliton by the barrier. We also find large\nquantum mechanical uncertainties in the soliton's position and momentum due to\nnonlinear interaction with the barrier."
    },
    {
        "anchor": "Two-body mobility edge in the Anderson-Hubbard model in three\n  dimensions: Molecular versus scattering states: Most of our quantitative understanding of disorder-induced metal-insulator\ntransitions comes from numerical studies of simple noninteracting tight-binding\nmodels, like the Anderson model in three dimensions. An important outstanding\nproblem is the fate of the Anderson transition in the presence of additional\nHubbard interactions of strength $U$ between particles. Based on large-scale\nnumerics, we compute the position of the mobility edge for a system of two\nidentical bosons or two fermions with opposite spin components. The resulting\nphase diagram in the interaction-energy-disorder space possesses a remarkably\nrich and counterintuitive structure, with multiple metallic and insulating\nphases. We show that this phenomenon originates from the molecular or\nscattering-like nature of the pair states available at given energy $E$ and\ndisorder strength $W$. The disorder-averaged density of states of the effective\nmodel for the pair is also investigated. Finally, we discuss the implications\nof our results for ongoing research on many-body localization.",
        "positive": "Information scrambling of the dilute Bose gas at low temperature: We calculate the quantum Lyapunov exponent $\\lambda_L$ and butterfly velocity\n$v_B$ in the dilute Bose gas at temperature $T$ deep in the Bose-Einstein\ncondensation phase. The generalized Boltzmann equation approach is used for\ncalculating out-of-time ordered correlators, from which $\\lambda_L$ and $v_B$\nare extracted. At very low temperature where elementary excitations are\nphonon-like, we find $\\lambda_L\\propto T^5$ and $v_B\\sim c$, the sound\nvelocity. At relatively high temperature, we have $\\lambda_L\\propto T$ and\n$v_B\\sim c(T/T_*)^{0.23}$. We find $\\lambda_L$ is always comparable to the\ndamping rate of a quasiparticle, whose energy depends suitably on $T$. The\nchaos diffusion constant $D_L=v_B^2/\\lambda_L$, on the other hand, differs from\nthe energy diffusion constant $D_E$. We find $D_E\\ll D_L$ at very low\ntemperature and $D_E\\gg D_L$ otherwise."
    },
    {
        "anchor": "Symmetry breaking in interacting ring-shaped superflows of Bose-Einstein\n  condensates: We demonstrate that the evolution of superflows in interacting persistent\ncurrents of ultracold gases is strongly affected by symmetry breaking of the\nquantum vortex dynamics. We study counter-propagating superflows in a system of\ntwo parallel rings in regimes of weak (a Josephson junction with tunneling\nthrough the barrier) and strong (rings merging across a reduced barrier)\ninteractions. For the weakly interacting toroidal Bose-Einstein condensates,\nformation of rotational fluxons (Josephson vortices) is associated with\nspontaneous breaking of the rotational symmetry of the tunneling superflows.\nThe influence of a controllable symmetry breaking on the final state of the\nmerging counter-propagating superflows is investigated in the framework of a\nweakly dissipative mean-field model. It is demonstrated that the population\nimbalance between the merging flows and the breaking of the underlying\nrotational symmetry can drive the double-ring system to final states with\ndifferent angular momenta.",
        "positive": "Experimentally accessible witnesses of many-body localisation: The phenomenon of many-body localised (MBL) systems has attracted significant\ninterest in recent years, for its intriguing implications from a perspective of\nboth condensed-matter and statistical physics: they are insulators even at\nnon-zero temperature and fail to thermalise, violating expectations from\nquantum statistical mechanics. What is more, recent seminal experimental\ndevelopments with ultra-cold atoms in optical lattices constituting analog\nquantum simulators have pushed many-body localised systems into the realm of\nphysical systems that can be measured with high accuracy. In this work, we\nintroduce experimentally accessible witnesses that directly probe distinct\nfeatures of MBL, distinguishing it from its Anderson counterpart. We insist on\nbuilding our toolbox from techniques available in the laboratory, including\non-site addressing, super-lattices, and time-of-flight measurements,\nidentifying witnesses based on fluctuations, density-density correlators,\ndensities, and entanglement. We build upon the theory of out of equilibrium\nquantum systems, in conjunction with tensor network and exact simulations,\nshowing the effectiveness of the tools for realistic models."
    },
    {
        "anchor": "Prethermalization and entanglement dynamics in interacting topological\n  pumps: We investigate the formation of quasisteady states in one-dimensional pumps\nof interacting fermions at non-integer filling fraction, in the regime where\nthe driving frequency and interaction strength are small compared to the\ninstantaneous single-particle band gap throughout the driving cycle. The system\nrapidly absorbs energy from the driving field, and approaches a quasisteady\nstate that locally resembles a maximal entropy state subject to the constraint\nof fixed particle number in each of the system's single-particle Floquet bands.\nWe explore the nature of this quasisteady state through one-body observables\nincluding the pumped current and natural orbital occupations, as well as the\n(many-body) entanglement spectrum and entropy. Potential disorder significantly\nreduces the amplitude of fluctuations of the quasisteady state current around\nits universal value, while the lifetime of the quasisteady state remains nearly\nunaffected for disorder strengths up to the scale of the single-particle band\ngap. Interestingly, the natural orbital occupations and entanglement entropy\ndisplay patterns signifying the periodic entangling and disentangling of the\nsystem's degrees of freedom over each driving cycle. Moreover, prominent\nfeatures in the system's time-dependent entanglement spectrum reveal the\nemergence of new long timescales associated with the equilibration of\nmany-particle correlations.",
        "positive": "Density-wave phases of dipolar fermions in a bilayer: We investigate the phase diagram of dipolar fermions with aligned dipole\nmoments in a two-dimensional (2D) bilayer. Using a version of the\nSingwi-Tosi-Land-Sjolander scheme recently adapted to dipolar fermions in a\nsingle layer [M. M. Parish and F. M. Marchetti, Phys. Rev. Lett. 108, 145304\n(2012)], we determine the density-wave instabilities of the bilayer system\nwithin linear response theory. We find that the bilayer geometry can stabilize\nthe collapse of the 2D dipolar Fermi gas with intralayer attraction to form a\nnew density wave phase that has an orientation perpendicular to the density\nwave expected for strong intralayer repulsion. We thus obtain a quantum phase\ntransition between stripe phases that is driven by the interplay between strong\ncorrelations and the architecture of the low dimensional system."
    },
    {
        "anchor": "Quantum Non-equilibrium Many-Body Spin-Photon Systems: In this Ph.D. thesis dissertation concerns the quantum dynamics of\nstrongly-correlated quantum systems in out-of-equilibrium states. The research\nis neither restricted to static properties or long-term relaxation evolutions\nnor does it neglect effects on any relevant subsystem as is frequently done\nwith the environment in master equations approaches. The focus of this work is\nto explore different quantum systems during several regimes of operations, then\ndiscover results that might be of interest to quantum control, and hence to\nquantum computation and quantum information processing. Our main results can be\nsummarized as follows in three parts: Signature of Critical Dynamics, Driven\nDicke Model as a Test-bed of Ultra-Strong Coupling, and Beyond the Kibble-Zurek\nMechanism.",
        "positive": "Spectral Gaps of Spin-orbit Coupled Particles in Deformed Traps: We consider a spin-orbit coupled system of particles in an external trap that\nis represented by a deformed harmonic oscillator potential. The spin-orbit\ninteraction is a Rashba interaction that does not commute with the trapping\npotential and requires a full numerical treatment in order to obtain the\nspectrum. The effect of a Zeeman term is also considered. Our results\ndemonstrate that variable spectral gaps occur as a function of strength of the\nRashba interaction and deformation of the harmonic trapping potential. The\nsingle-particle density of states and the critical strength for superfluidity\nvary tremendously with the interaction parameter. The strong variations with\nRashba coupling and deformation implies that the few- and many-body physics of\nspin-orbit coupled systems can be manipulated by variation of these parameters."
    },
    {
        "anchor": "Microscopic theory of heat capacity of liquid helium-4 for temperatures\n  above the critical point: In this paper, with the corresponding formula for internal energy obtained in\nRef. [J. Phys. Stud. {\\bf 11}, 259 (2007)], combined with a simple calculation\nof the effective mass of interacting Bose particles, the behavior of the heat\ncapacity of liquid $^4$He is analyzed numerically for the entire temperature\nrange. The results agree quite well with experimental data.",
        "positive": "Entanglement spectrum and quantum phase diagram of the long-range XXZ\n  chain: Entanglement is a central feature of many-body quantum systems and plays a\nunique role in quantum phase transitions.\n  In many cases, the entanglement spectrum, which represents the spectrum of\nthe density matrix of a bipartite system, contains valuable information beyond\nthe sole entanglement entropy.\n  Here we investigate the entanglement spectrum of the long-range XXZ model. We\nshow that within the critical phase it exhibits a remarkable self-similarity.\n  The breakdown of self-similarity and the transition away from a Luttinger\nliquid is consistent with renormalization group theory.\n  Combining the two, we are able to determine the quantum phase diagram of the\nmodel and locate the corresponding phase transitions. Our results are confirmed\nby numerically-exact calculations using tensor-network techniques.\n  Moreover, we show that the self-similar rescaling extends to the geometrical\nentanglement as well as the Luttinger parameter in the critical phase.\n  Our results pave the way to further studies of entanglement properties in\nlong-range quantum models."
    },
    {
        "anchor": "Effects of magnetic dipole-dipole interactions in atomic Bose-Einstein\n  condensates with tunable s-wave interactions: The s-wave interaction is usually the dominant form of interactions in atomic\nBose-Einstein condensates (BECs). Recently, Feshbach resonances have been\nemployed to reduce the strength of the s-wave interaction in many atomic\nspeicies. This opens the possibilities to study magnetic dipole-dipole\ninteractions (MDDI) in BECs, where the novel physics resulting from long-range\nand anisotropic dipolar interactions can be explored. Using a variational\nmethod, we study the effect of MDDI on the statics and dynamics of atomic BECs\nwith tunable s-wave interactions. We benchmark our calculation against\npreviously observed MDDI effects in $^{52}$Cr with excellent agreement, and\npredict new effects that should be promising to observe experimentally. A\nparameter of magnetic Feshbach resonances, $\\epsilon_{dd,\\text{max}}$, is used\nto quantitatively indicate the feasibility of experimentally observing MDDI\neffects in different atomic species. We find that strong MDDI effects should be\nobservable in both in-trap and time-of-flight behaviors for the alkali BECs of\n$^{7}$Li, $^{39}$K, and $^{133}$Cs. Our results provide a helpful guide for\nexperimentalists to realize and study atomic dipolar quantum gases.",
        "positive": "Controlling dynamical entanglement in a Josephson tunneling junction: We analyze the evolution of an entangled many-body state in a Josephson\ntunneling junction. A N00N state, which is a superposition of two complementary\nFock states, appears in the evolution with sufficient probability only for a\nmoderate many-body interaction on an intermediate time scale. This time scale\nis inversely proportional to the tunneling rate. Interaction between particles\nsupports entanglement: The probability for creating an entangled state decays\nexponentially with the number of non-interacting particles, whereas it decays\nonly like the inverse square root of the number of interacting particles."
    },
    {
        "anchor": "$N$-boson spectrum from a Discrete Scale Invariance: We present the analysis of the $N$-boson spectrum computed using a soft\ntwo-body potential the strength of which has been varied in order to cover an\nextended range of positive and negative values of the two-body scattering\nlength $a$ close to the unitary limit. The spectrum shows a tree structure of\ntwo states, one shallow and one deep, attached to the ground-state of the\nsystem with one less particle. It is governed by an unique universal function,\n$\\Delta(\\xi)$, already known in the case of three bosons. In the three-particle\nsystem the angle $\\xi$, determined by the ratio of the two- and three-body\nbinding energies $E_3/E_2=\\tan^2\\xi$, characterizes the Discrete Scale\nInvariance of the system. Extending the definition of the angle to the $N$-body\nsystem as $E_N/E_2=\\tan^2\\xi$, we study the $N$-boson spectrum in terms of this\nvariable. The analysis of the results, obtained for up to $N=16$ bosons, allows\nus to extract a general formula for the energy levels of the system close to\nthe unitary limit. Interestingly, a linear dependence of the universal function\nas a function of $N$ is observed at fixed values of $a$. We show that the\nfinite-range nature of the calculations results in the range corrections that\ngenerate a shift of the linear relation between the scattering length $a$ and a\nparticular form of the universal function. We also comment on the limits of\napplicability of the universal relations.",
        "positive": "Driving quantized vortices with quantum vacuum fluctuations: We propose to use a rotating corrugated material plate in order to stir,\nthrough the Casimir-Polder interaction, quantized vortices in an harmonically\ntrapped Bose-Einstein condensate. The emergence of such vortices within the\ncondensate cannot be explained with a computation of the Casimir-Polder\npotential based on the pairwise summation approach or on the proximity force\napproximation. It thus appears as a genuine signature of non-trivial geometry\neffects on the electromagnetic vacuum fluctuations, which fully exploits the\nsuperfluid nature of the sample. In order to discuss quantitatively the\ngeneration of Casimir-driven vortices, we derive an exact non-perturbative\ntheory of the Casimir-Polder potential felt by the atoms in front of the\ngrating. Our numerical results for a Rb condensate close to a Si grating show\nthat the resulting quantum vacuum torque is strong enough to provide a\ncontactless transfer of angular momentum to the condensate and generate\nquantized vortices under realistic experimental conditions at separation\ndistances around $3$ microns."
    },
    {
        "anchor": "Robust Finite-Temperature Many-Body Scarring on a Quantum Computer: Mechanisms for suppressing thermalization in disorder-free many-body systems,\nsuch as Hilbert space fragmentation and quantum many-body scars, have recently\nattracted much interest in foundations of quantum statistical physics and\npotential quantum information processing applications. However, their\nsensitivity to realistic effects such as finite temperature remains largely\nunexplored. Here, we have utilized IBM's Kolkata quantum processor to\ndemonstrate an unexpected robustness of quantum many-body scars at finite\ntemperatures when the system is prepared in a thermal Gibbs ensemble. We\nidentify such robustness in the PXP model, which describes quantum many-body\nscars in experimental systems of Rydberg atom arrays and ultracold atoms in\ntilted Bose--Hubbard optical lattices. By contrast, other theoretical models\nwhich host exact quantum many-body scars are found to lack such robustness, and\ntheir scarring properties quickly decay with temperature. Our study sheds light\non the important differences between scarred models in terms of their algebraic\nstructures, which impacts their resilience to finite temperature.",
        "positive": "Quantum Phase Transitions of the Bose-Hubbard Model inside a Cavity: The superfluid to Mott insulator transition and the superradiant transition\nare textbook examples for quantum phase transition and coherent quantum optics,\nrespectively. Recent experiments in ETH and Hamburg succeeded in loading\ndegenerate bosonic atomic gases in optical lattices inside a cavity, which\nenables the first experimental study of the interplay between these two\ntransitions. In this letter we present the theoretical phase diagram for the\nETH experimental setup, and determine the phase boundaries and the orders of\nthe phase transitions between the normal superfluid phase, the superfluid with\nsuperradiant light, the normal Mott insulator and the Mott insulator with\nsuperradiant light. We find that in contrast to the second-order superradiant\ntransition in a weakly interacting Bose condensate, strong correlations in the\nsuperfluid nearby a Mott transition can render the superradiant transition to a\nfirst order one. Our results will stimulate further experimental studies of\ninteractions between cavity light and strongly interacting quantum matters."
    },
    {
        "anchor": "Self-trapped atomic matter wave in a ring cavity: We studied a system of atomic Bose-Einstein condensate coupled to a ring\ncavity within the mean-field theory. Due to the interaction between atoms and\nlight field, the atoms can be self-trapped. This is verified with both\nvariational and numerical methods. We examined the stability of these\nself-trapped states. For a weakly pumped cavity, they spread during the\nevolution; while at strong pumping, they can maintain the shape for a long\ntime. We also studied the moving dynamics of these self-trapped waves, and\nfound out that it can be strongly affected by the cavity decay rate. For a\nsmall cavity decay rate, the self-trapped waves undergo a damped oscillation.\nIncreasing the cavity decay rate will lead to a deceleration of the\nself-trapped waves. We also compared the main results with the semiclassical\ntheory in which atoms are treated as classical particles.",
        "positive": "Universal Noise in Continuous Transport Measurements of Interacting\n  Fermions: We propose and analyze continuous measurements of atom number and atomic\ncurrents using dispersive probing in an optical cavity. For an atom-number\nmeasurement in a closed system, we relate both the detection noise and the\nheating rate due to measurement back-action to Tan's contact, and identify an\nemergent universal quantum non-demolition (QND) regime in the good-cavity\nlimit. We then show that such a continuous QND measurement of atom number\nserves as a quantum-limited current transducer in a two-terminal setup. We\nderive a universal bound on the precision of current measurement, which results\nfrom a tradeoff between detection noise and back-action of the atomic current\nmeasurement. Our results apply regardless of the strength of interaction or the\nstate of matter and set fundamental bounds on future precision measurements of\ntransport properties in cold-atom quantum simulators."
    },
    {
        "anchor": "Quantum phases of interacting three-component fermions under the\n  influence of spin-orbit coupling and Zeeman fields: We describe the quantum phases of interacting three component fermions in the\npresence of spin-orbit coupling, as well as linear and quadratic Zeeman fields.\nWe classify the emerging superfluid phases in terms of the loci of zeros of\ntheir quasi-particle excitation spectrum in momentum space, and we identify\nseveral Lifshitz-type topological transitions. In the particular case of\nvanishing quadratic Zeeman field, a quintuple point exists where four gapless\nsuperfluid phases with surface and line nodes converge into a fully gapped\nsuperfluid phase. Lastly, we also show that the simultaneous presence of\nspin-orbit and Zeeman fields transforms a momentum-independent scalar order\nparameter into an explicitly momentum-dependent tensor in the generalized\nhelicity basis.",
        "positive": "Effective field theory of a vortex lattice in a bosonic superfluid: Using boson-vortex duality, we formulate a low-energy effective theory of a\ntwo-dimensional vortex lattice in a bosonic Galilean-invariant compressible\nsuperfluid. The excitation spectrum contains a gapped Kohn mode and an\nelliptically polarized Tkachenko mode that has quadratic dispersion relation at\nlow momenta. External rotation breaks parity and time-reversal symmetries and\ngives rise to Hall responses. We extract the particle number current and stress\ntensor linear responses and investigate the relations between them that follow\nfrom Galilean symmetry. We argue that elementary particles and vortices do not\ncouple to the spin connection which suggests that the Hall viscosity at zero\nfrequency and momentum vanishes in a vortex lattice."
    },
    {
        "anchor": "Interaction induced fractionalization and topological superconductivity\n  in the polar molecules anisotropic $t-J$ model: We show that the interplay between antiferromagnetic interaction and hole\nmotion gives rise to a topological superconducting phase. This is captured by\nthe one dimensional anisotropic $t-J$ model which can be experimentally\nachieved with ultracold polar molecules trapped onto an optical lattice. As a\nfunction of the anisotropy strength we find that different quantum phases\nappear, ranging from a gapless Luttinger liquid to spin gapped conducting and\nsuperconducting regimes. In presence of appropriate $z$-anisotropy, we also\nprove that a phase characterized by non-trivial topological order takes place.\nThe latter is described uniquely by a finite non local string parameter and\npresents robust edge spin fractionalization. These results allow to explore\nquantum phases of matter where topological superconductivity is induced by the\ninteraction.",
        "positive": "Diagnosing Potts criticality and two-stage melting in one-dimensional\n  hard-boson models: We investigate a model of hard-core bosons with infinitely repulsive nearest-\nand next-nearest-neighbor interactions in one dimension, introduced by Fendley,\nSengupta and Sachdev in Phys. Rev. B 69, 075106 (2004). Using a combination of\nexact diagonalization, tensor network, and quantum Monte Carlo simulations, we\nshow how an intermediate incommensurate phase separates a crystalline and a\ndisordered phase. We base our analysis on a variety of diagnostics, including\nentanglement measures, fidelity susceptibility, correlation functions, and\nspectral properties. According to theoretical expectations, the\ndisordered-to-incommensurate-phase transition point is compatible with\nBerezinskii-Kosterlitz-Thouless universal behaviour. The second transition is\ninstead non-relativistic, with dynamical critical exponent $z > 1$. For the\nsake of comparison, we illustrate how some of the techniques applied here work\nat the Potts critical point present in the phase diagram of the model for\nfinite next-nearest-neighbor repulsion. This latter application also allows to\nquantitatively estimate which system sizes are needed to match the conformal\nfield theory spectra with experiments performing level spectroscopy."
    },
    {
        "anchor": "Trap anharmonicity and sloshing mode of a Fermi gas: For a gas trapped in a harmonic potential, the sloshing (or Kohn) mode is\nundamped and its frequency coincides with the trap frequency, independently of\nthe statistics, interaction and temperature of the gas. However, experimental\ntrap potentials have usually Gaussian shape and anharmonicity effects appear as\nthe temperature and, in the case of Fermions, the filling of the trap are\nincreased. We study the sloshing mode of a degenerate Fermi gas in an\nanharmonic trap within the Boltzmann equation, including in-medium effects in\nboth the transport and collision terms. The calculated frequency shifts and\ndamping rates of the sloshing mode due to the trap anharmonicity are in\nsatisfactory agreement with the available experimental data. We also discuss\nhigher-order dipole, octupole, and bending modes and show that the damping of\nthe sloshing mode is caused by its coupling to these modes.",
        "positive": "Spin susceptibility and effects of a harmonic trap in the BCS-BEC\n  crossover regime of an ultracold Fermi gas: We theoretically investigate magnetic properties of a trapped ultracold Fermi\ngas. Including pairing fluctuations within the framework of an extended\n$T$-matrix approximation (ETMA), as well as effects of a harmonic trap in the\nlocal density approximation (LDA), we calculate the local spin susceptibility\n$\\chi_{\\rm t}(r,T)$ in the BCS (Bardeen-Cooper-Schrieffer)-BEC (Bose-Einstein\ncondensation) crossover region. We show that pairing fluctuations cause\nnon-monotonic temperature dependence of $\\chi_{\\rm t}(r,T)$. Although this\nbehavior looks similar to the spin-gap phenomenon associated with pairing\nfluctuations in a {\\it uniform} Fermi gas, the trapped case is found to also be\ninfluenced by the temperature-dependent density profile, in addition to pairing\nfluctuations. We demonstrate how to remove this extrinsic effect from\n$\\chi_{\\rm t}(r,T)$, to study the interesting spin-gap phenomenon purely\noriginating from pairing fluctuations. Since experiments in cold atom physics\nare always done in a trap, our results would be useful for the assessment of\npreformed pair scenario, from the viewpoint of spin-gap phenomenon."
    },
    {
        "anchor": "Spontaneous ferromagnetism in the spinor Bose gas with Rashba spin-orbit\n  coupling: We show that in the two-component Bose gas with Rashba spin-orbit coupling an\narbitrarily small attractive interaction between bosons with opposite spin\ninduces spontaneous ferromagnetism below a finite critical temperature $T_c$.\nIn the ferromagnetic phase the single-particle spectrum exhibits a unique\nminimum in momentum space in the direction of the magnetization. For\nsufficiently small temperatures below $T_c$ the bosons eventually condense into\nthe unique state at the bottom of the spectrum, forming a ferromagnetic\nBose-Einstein condensate.",
        "positive": "Fast phase-modulated optical lattice for wave packet engineering: We investigate experimentally a Bose Einstein condensate placed in a 1D\noptical lattice whose phase is modulated at a frequency large compared to all\ncharacteristic frequencies. As a result, the depth of the periodic potential is\nrenormalized by a Bessel function which only depends on the amplitude of\nmodulation, a prediction that we have checked quantitatively using a careful\ncalibration scheme. This renormalization provides an interesting tool to\nengineer in time optical lattices. For instance, we have used it to perform\nsimultaneously a sudden $\\pi$-phase shift (without phase residual errors)\ncombined with a change of lattice depth, and to study the subsequent\nout-of-equilibrium dynamics."
    },
    {
        "anchor": "Fractional Chern insulators of few bosons in a box: Hall plateaus from\n  center-of-mass drifts and density profiles: Realizing strongly-correlated topological phases of ultracold gases is a\ncentral goal for ongoing experiments. And while fractional quantum Hall states\ncould soon be implemented in small atomic ensembles, detecting their signatures\nin few-particle settings remains a fundamental challenge. In this work, we\nnumerically analyze the center-of-mass Hall drift of a small ensemble of\nhardcore bosons, initially prepared in the ground state of the\nHarper-Hofstadter-Hubbard model in a box potential. By monitoring the Hall\ndrift upon release, for a wide range of magnetic flux values, we identify an\nemergent Hall plateau compatible with a fractional Chern insulator state: the\nextracted Hall conductivity approaches a fractional value determined by the\nmany-body Chern number, while the width of the plateau agrees with the spectral\nand topological properties of the prepared ground state. Besides, a direct\napplication of Streda's formula indicates that such Hall plateaus can also be\ndirectly obtained from static density-profile measurements. Our calculations\nsuggest that fractional Chern insulators can be detected in cold-atom\nexperiments, using available detection methods.",
        "positive": "Phase diagrams and Thomas-Fermi estimates for spin-orbit coupled\n  Bose-Einstein Condensates under rotation: We provide complete phase diagrams describing the ground state of a trapped\nspinor BEC under the combined effects of rotation and a Rashba spin-orbit\ncoupling. The interplay between the different parameters (magnitude of\nrotation, strength of the spin-orbit coupling and interaction) leads to a rich\nground state physics that we classify. We explain some features analytically in\nthe Thomas-Fermi approximation, writing the problem in terms of the total\ndensity, total phase and spin. In particular, we analyze the giant skyrmion,\nand find that it is of degree 1 in the strong segregation case. In some regions\nof the phase diagrams, we relate the patterns to a ferromagnetic energy."
    },
    {
        "anchor": "BCS-BEC Crossover and the Unitary Fermi Gas: The crossover from weak coupling Bardeen-Cooper-Schrieffer (BCS) pairing to a\nBose-Einstein condensate (BEC) of tightly bound pairs, as a function of the\nattractive interaction in Fermi systems, has long been of interest to\ntheoretical physicists. The past decade has seen a series of remarkable\nexperimental developments in ultracold Fermi gases that has realized the\nBCS-BEC crossover in the laboratory, bringing with it fresh new insights into\nthe very strongly interacting unitary regime in the middle of this crossover.\nIn this review, we start with a pedagogical introduction to the crossover and\nthen focus on recent progress in the strongly interacting regime. While our\nfocus is on new theoretical developments, we also describe three key\nexperiments that probe the thermodynamics, transport and spectroscopy of the\nunitary Fermi gas. We discuss connections between the unitary regime and other\nareas of physics -- quark-gluon plasmas, gauge-gravity duality and high\ntemperature superconductivity -- and conclude with open questions about\nstrongly interacting Fermi gases.",
        "positive": "Soliton dynamics of a high-density Bose-Einstein condensate subject to a\n  time varying anharmonic trap: In this paper we study the soliton dynamics of a high-density Bose-Einstein\ncondensate (BEC) subject to a time-oscillating trap. The behavior of the BEC is\ndescribed with a modified Gross-Pitaevskii equation (mGPE) which takes into\naccount three-body losses, atomic feeding and quantum fluctuations (up to a\nnovel high-density term). A variational approximation (VA) is used to study the\nbehavior of a Gaussian pulse in a static double-well potential. Direct\nnumerical solutions of the mGPE corroborate that the center of the pulse\nexhibits an oscillatory behavior (as the VA predicts), and show a novel\nphenomenon of fragmentation and regeneration (FR). It is shown that this FR\nprocess is destroyed if we consider a potential with a time-dependent quadratic\nterm, but the FR survives if the time dependence is introduced in a cubic term.\nComparison between the VA and the numerical solution revealed an excellent\nagreement when the oscillations of the pulse remain in one of the potential\nwells. The effects of the quantum fluctuating terms on the FR process are\nstudied. Finally, variational results using a supergaussian trial function are\nobtained."
    },
    {
        "anchor": "Realization of a periodically driven open three-level Dicke model: A periodically driven open three-level Dicke model is realized by resonantly\nshaking the pump field in an atom-cavity system. As an unambiguous signature,\nwe demonstrate the emergence of a dynamical phase, in which the atoms\nperiodically localize between the antinodes of the pump lattice, associated\nwith an oscillating net momentum along the pump axis. We observe this dynamical\nphase through the periodic switching of the relative phase between the pump and\ncavity fields at a small fraction of the driving frequency, suggesting that it\nexhibits a time crystalline character.",
        "positive": "Gapless topological Fulde-Ferrell superfluidity in spin-orbit coupled\n  Fermi gases: Topological superfluids usually refer to a superfluid state which is gapped\nin the bulk but metallic at the boundary. Here we report that a gapless,\ntopologically non-trivial superfluid with inhomogeneous Fulde-Ferrell pairing\norder parameter can emerge in a two-dimensional spin-orbit coupled Fermi gas,\nin the presence of both in-plane and out-of-plane Zeeman fields. The\nFulde-Ferrell pairing - induced by the spin-orbit coupling and in-plane Zeeman\nfield - is responsible for this gapless feature. This exotic superfluid has a\nsignificant Berezinskii-Kosterlitz-Thouless (BKT) transition temperature and\nhas robust Majorana edge modes against disorder owing to its topological\nnature."
    },
    {
        "anchor": "Orbital excitation blockade and algorithmic cooling in quantum gases: Interaction blockade occurs when strong interactions in a confined few-body\nsystem prevent a particle from occupying an otherwise accessible quantum state.\nBlockade phenomena reveal the underlying granular nature of quantum systems and\nallow the detection and manipulation of the constituent particles, whether they\nare electrons, spins, atoms, or photons. The diverse applications range from\nsingle-electron transistors based on electronic Coulomb blockade to quantum\nlogic gates in Rydberg atoms. We have observed a new kind of interaction\nblockade in transferring ultracold atoms between orbitals in an optical\nlattice. In this system, atoms on the same lattice site undergo coherent\ncollisions described by a contact interaction whose strength depends strongly\non the orbital wavefunctions of the atoms. We induce coherent orbital\nexcitations by modulating the lattice depth and observe a staircase-type\nexcitation behavior as we cross the interaction-split resonances by tuning the\nmodulation frequency. As an application of orbital excitation blockade (OEB),\nwe demonstrate a novel algorithmic route for cooling quantum gases. Our\nrealization of algorithmic cooling utilizes a sequence of reversible OEB-based\nquantum operations that isolate the entropy in one part of the system, followed\nby an irreversible step that removes the entropy from the gas. This work opens\nthe door to cooling quantum gases down to ultralow entropies, with implications\nfor developing a microscopic understanding of strongly correlated electron\nsystems that can be simulated in optical lattices. In addition, the close\nanalogy between OEB and dipole blockade in Rydberg atoms provides a roadmap for\nthe implementation of two-qubit gates in a quantum computing architecture with\nnatural scalability.",
        "positive": "Many-Body Formation and Dissociation of a Dipolar Chain Crystal: We propose an experimental scheme to effectively assemble chains of dipolar\ngases with an uniform length in a multi-layer system. The obtained dipolar\nchains can form a chain crystal with the system temperature easily controlled\nby the initial lattice potential and the external field strength during\nprocess. When the density of chains increases, we further observe a second\norder quantum phase transition for the chain crystal to be dissociated toward\nlayers of 2D crystal, where the quantum fluctuation dominates the classical\nenergy and the compressibility diverges at the phase boundary. Experimental\nimplication of such dipolar chain crystal and its quantum phase transition is\nalso discussed."
    },
    {
        "anchor": "Spin transport in a one-dimensional quantum wire: We analyze the spin transport through a finite-size one-dimensional\ninteracting wire connected to noninteracting leads. By combining\nrenormalization-group arguments with other analytic considerations such as the\nmemory function technique and instanton tunneling, we find the temperature\ndependence of the spin conductance in different parameter regimes in terms of\ninteractions and the wire length. The temperature dependence is found to be\nnonmonotonic. In particular, the system approaches perfect spin conductance at\nzero temperature for both attractive and repulsive interactions, in contrast\nwith the static spin conductivity. We discuss the connection of our results to\nrecent experiments with ultracold atoms and compare the theoretical prediction\nto experimental data in the parameter regime where temperature is the largest\nenergy scale.",
        "positive": "Finite temperature ferromagnetic transition in coherently coupled Bose\n  gases: A paramagnetic-ferromagnetic quantum phase transition is known to occur at\nzero temperature in a two-dimensional coherently-coupled Bose mixture of dilute\nultracold atomic gases provided the interspecies interaction strength is large\nenough. Here we study the fate of such a transition at finite temperature by\nperforming numerical simulations with the stochastic (projected)\nGross-Pitaevskii formalism, which includes both thermal and beyond mean-field\neffects. By extracting the average magnetization, the magnetic fluctuations and\ncharacteristic relaxation frequency (or, critical slowing down), we identify a\nfinite temperature critical line for the transition. We find that the critical\npoint shifts linearly with temperature and, in addition, the three quantities\nused to probe the transition exhibit a temperature power-law scaling. The\nscaling of the critical slowing down is found to be consistent with thermal\ncritical exponents and is very well approximated by the square of the spin\nexcitation gap at the zero-temperature."
    },
    {
        "anchor": "Ground state properties of a multi-component bosonic mixture: a\n  Gutzwiller mean-field study: Using the single-site Gutzwiller method, we theoretically study the ground\nstate and the interspecies entanglement properties of interexchange symmetric\nmulti-component (two- and three-) bosonic mixtures in an optical lattice, and\nthe results are generalized to an $n$-component ($n=2,3,4,\\cdots$) system. We\ncompute the mean-field phase diagram, the interspecies entanglement entropy,\nand the ground state spectral decomposition. Three phases namely the\n$n$-component Superfluid state (nSF), the $n$-component Mott insulator state\n(nMI), and the Super-counter-fluid state (SCF) are observed. Interestingly, we\nfind that there are $n-1$ SCF lobes to separate every two neighboring nMI lobes\nin the phase diagram. More importantly, we derive the exact general expression\nof the interspecies entanglement entropy for the SCF phase. In addition, we\nalso investigate the demixing effect of an n-component mixture and demonstrate\nthat the mixing-demixing critical point is independent of n.",
        "positive": "Thermodynamic behavior of a one-dimensional Bose gas at low temperature: We show that the chemical potential of a one-dimensional (1D) interacting\nBose gas exhibits a non-monotonic temperature dependence which is peculiar of\nsuperfluids. The effect is a direct consequence of the phononic nature of the\nexcitation spectrum at large wavelengths exhibited by 1D Bose gases. For low\ntemperatures $T$, we demonstrate that the coefficient in $T^2$ expansion of the\nchemical potential is entirely defined by the zero-temperature density\ndependence of the sound velocity. We calculate that coefficient along the\ncrossover between the Bogoliubov weakly-interacting gas and the Tonks-Girardeau\ngas of impenetrable bosons. Analytic expansions are provided in the asymptotic\nregimes. The theoretical predictions along the crossover are confirmed by\ncomparison with the exactly solvable Yang-Yang model in which the\nfinite-temperature equation of state is obtained numerically by solving\nBethe-{\\it ansatz} equations. A 1D ring geometry is equivalent to imposing\nperiodic boundary conditions and arising finite-size effects are studied in\ndetails. At $T=0$ we calculated various thermodynamic functions, including the\ninelastic structure factor, as a function of the number of atoms, pointing out\nthe occurrence of important deviations from the thermodynamic limit."
    },
    {
        "anchor": "Fate of topological states and mobility edges in one-dimensional slowly\n  varying incommensurate potentials: We investigate the interplay between disorder and superconducting pairing for\na one-dimensional $p$-wave superconductor subject to slowly varying\nincommensurate potentials with mobility edges. With amplitude increments of the\nincommensurate potentials, the system can undergo a transition from a\ntopological phase to a topologically trivial localized phase. Interestingly, we\nfind that there are four mobility edges in the spectrum when the strength of\nthe incommensurate potential is below a critical threshold, and a novel\ntopologically nontrivial localized phase emerges in a certain region. We reveal\nthis energy-dependent metal-insulator transition by applying several numerical\ndiagnostic techniques, including the inverse participation ratio, the density\nof states and the Lyapunov exponent. Nowadays, precise control of the\nbackground potential and the $p$-wave superfluid can be realized in the\nultracold atomic systems, we believe that these novel mobility edges can be\nobserved experimentally.",
        "positive": "Phase separation of quantized vortices in two-component miscible\n  Bose-Einstein condensates in a two-dimensional box potential: The dynamics of quantized vortices in two-dimensional two-component miscible\nBose-Einstein condensates (BECs) trapped by a box potential has been\nnumerically studied using the Gross{ Pitaevskii model. We have discovered a\nnovel phenomenon where the vortices of the two components spatially separate\nfrom each other, which we call the phase separation of the distribution of\nvortices. This phase separation occurs when the inter-component coupling is\nstrong. Onsager vortices, on the other hand, are formed in both components when\nthe inter-component coupling is weak. We distinguish between Onsager vortices\nand phase-separated vortices by two types of effective distances between\nvortices. The dependence of the transition between the Onsager vortices and\nphase-separated vortices on the inter-component interaction is also studied."
    },
    {
        "anchor": "Quantum Cherenkov transition of finite momentum Bose polarons: We investigate the behavior of a finite-momentum impurity immersed in a\nweakly interacting three-dimensional Bose-Einstein condensate (BEC) of\nultra-cold atoms, giving a detailed account of the dynamical quantum Cherenkov\ntransition discussed in Ref. [arXiv:2101.00030]. Using a time-dependent\nvariational approach, we identify a transition in the far-from-equilibrium\ndynamics of the system after the attractive short-range impurity-boson\ninteraction is quenched on. The transition occurs as the impurity's velocity\ncrosses an interaction-dependent critical value, and manifests in the long-time\nbehavior of the Loschmidt echo and average impurity velocity. This behavior is\nalso reflected in the finite momentum ground state of the system, where the\ngroup velocity of the interaction-dressed impurity loses it's dependence on the\ntotal momentum of the system as the critical point is crossed. The transition\nwe discuss should be experimentally observable via a variety of common\nprotocols in ultracold atomic systems such as time-of-flight imaging, RF\nspectroscopy, Ramsey interferometry, and absorption imaging.",
        "positive": "Static structure factor of a strongly correlated Fermi gas at large\n  momenta: We theoretically investigate the static structure factor of an interacting\nFermi gas near the BEC-BCS crossover at large momenta. Due to short-range\ntwo-body interactions, we predict that the structure factor of unlike spin\ncorrelations $S_{\\uparrow\\downarrow}(q)$ falls off as $1/q$ in a universal\nscaling region with large momentum $\\hbar q$ and large scattering length. The\nscaling coefficient is determined by the celebrated Tan's contact parameter,\nwhich links the short-range behavior of many-body systems to their universal\nthermodynamic properties. By implementing this new Tan relation together with\nthe random-phase approximation and the virial expansion theory in various\nlimiting cases, we show how to calculate $S_{\\uparrow\\downarrow}(q)$ at zero\nand finite temperatures for arbitrary interaction strengths, at momentum\ntransfer higher than the Fermi momentum. Our results provide a way to\nexperimentally confirm a new Tan relation and to accurately measure the value\nof contact parameter."
    },
    {
        "anchor": "Visible stripe phases in spin-orbital-angular-momentum coupled\n  Bose-Einstein condensates: Recently, stripe phases in spin-orbit coupled Bose-Einstein condensates\n(BECs) have attracted much attention since they are identified as supersolid\nphases. In this paper, we exploit experimentally reachable parameters and show\ntheoretically that annular stripe phases with large stripe spacing and high\nstripe contrast can be achieved in spin-orbital-angular-momentum coupled\n(SOAMC) BECs. In addition to using Gross-Pitaevskii numerical simulations, we\ndevelop a variational ansatz that captures the essential interaction effects to\nfirst order, which are not present in the ansatz employed in previous\nliterature. Our work should open the possibility toward directly observing\nstripe phases in SOAMC BECs in experiments.",
        "positive": "Single-particle Analysis of Non-interacting Ultracold Bosons in\n  Amplitude Modulated Parabolic Optical Lattice: Ultracold atoms in the combined potential of a parabolic trap and an optical\nlattice is considered a promising tool for coherent manipulation of matter wave\npackets. The recent Aarhus experiment[P. L. Pedersen et al., Phys. Rev. A. 88,\n023620 (2013)] produced wave packets by applying the optical lattice's\namplitude modulation to a Bose-Einstein condensate (BEC) of $^{87}$Rb. The\npresent paper renders a theoretical account with single-particle analysis of\nthis experimental production of the wave packets and their subsequent\ntime-evolution. We focus on the one-dimensional non-interacting bosonic system\nas a fundamental starting point for accurate quantum analysis and for further\ninvestigation of similar experiments. We show that a simple Rabi-oscillation\nmodel gives a good description of the wave packet production in terms of the\ninter-band transition while the first-order perturbation theory proves\ninadequate, that is the recent experiment already reached the realm of\nhigh-order couplings. As a natural extension, we demonstrate enhancement of the\nwave packet production by the two-step Rabi-oscillation method using either\nsingle frequency or dual frequencies. We assess the high-order Bragg reflection\nand Landau-Zener transition at a band gap with the aid of rigorous quantum\ntime-propagation as well as the semi-classical theory exploited earlier by the\nHamburg experiment [J. Heinze et al., PRL 107, 135303(2011)]. Complicated\nreflections and splittings of the wave packet during free evolution may be\nlargely attributed to the intertwining of these two effects."
    },
    {
        "anchor": "Transport of Spin and Mass at Normal-Superfluid Interfaces in the\n  Unitary Fermi Gas: Transport in strongly interacting Fermi gases provides a window into the\nnon-equilibrium behavior of strongly correlated fermions. In particular, the\ninterface between a strongly polarized normal gas and a weakly polarized\nsuperfluid at finite temperature presents a model for understanding transport\nat normal-superfluid and normal-superconductor interfaces. An excess of\npolarization in the normal phase or a deficit of polarization in the superfluid\nbrings the system out of equilibrium, leading to transport currents across the\ninterface. We implement a phenomenological mean-field model of the unitary\nFermi gas, and investigate the transport of spin and mass under non-equilibrium\nconditions. We consider independently prepared normal and superfluid regions\nbrought into contact, and calculate the instantaneous spin and mass currents\nacross the normal-superfluid (NS) interface. For an unpolarized superfluid, we\nfind that spin current is suppressed below a threshold value in the driving\nchemical potential differences, while the threshold nearly vanishes for a\ncritically polarized superfluid. The mass current can exhibit a threshold in\ncases where Andreev reflection vanishes, while in general Andreev reflection\nprevents the occurrence of a threshold in the mass current. Our results provide\nguidance to future experiments aiming to characterize spin and mass transport\nacross NS interfaces.",
        "positive": "Extracting Dynamical Green's Function of Ultracold Quantum Gases via\n  Electromagnetically Induced Transparency: The essential quantum many-body physics of an ultracold quantum gas relies on\nthe single-particle Green's functions.\\ We demonstrate that it can be extracted\nby the spectrum of electromagnetically induced transparency (EIT).\\ The\nsingle-particle Green's function can be reconstructed by the measurements of\nfrequency moments in EIT spectroscopy.\\ This optical measurement provides an\nefficient and nondestructive method to reveal the many-body properties, and we\npropose an experimental setup to realize it.\\ Finite temperature and finite\nsize effects are discussed, and we demonstrate the reconstruction steps of\nGreen's function for the examples of three-dimensional Mott-insulator phase and\none-dimensional Luttinger liquid."
    },
    {
        "anchor": "Relaxation dynamics of a Fermi gas in an optical superlattice: This paper comprises an experimental and theoretical investigation of the\ntime evolution of a Fermi gas following fast and slow quenches of a\none-dimensional optical double-well superlattice potential. We investigate both\nthe local tunneling in the connected double wells and the global dynamics\ntowards a steady state. The local observables in the steady-state resemble\nthose of an equilibrium state, whereas the global properties indicate a strong\nnon-equilibrium situation.",
        "positive": "Short-range correlations in dilute atomic Fermi gases with spin-orbit\n  coupling: We study the short-range correlation strength of three dimensional spin half\ndilute atomic Fermi gases with spin-orbit coupling. The interatomic interaction\nis modeled by the contact pseudopotential. In the high temperature limit, we\nderive the expression for the second order virial expansion of the\nthermodynamic potential via the ladder diagrams. We further evaluate the second\norder virial expansion in the limit that the spin-orbit coupling constants are\nsmall, and find that the correlation strength between the fermions increases as\nthe forth power of the spin-orbit coupling constants. At zero temperature, we\nconsider the cases in which there are symmetric spin-orbit couplings in two or\nthree directions. In such cases, there is always a two-body bound state of zero\nnet momentum. In the limit that the average interparticle distance is much\nlarger than the dimension of the two-body bound state, the system primarily\nconsists of condensed bosonic molecules that fermions pair to form; we find\nthat the correlation strength also becomes bigger compared to that in the\nabsence of spin-orbit coupling. Our results indicate that generic spin-orbit\ncoupling enhances the short-range correlations of the Fermi gases. Measurement\nof such enhancement by photoassociation experiment is also discussed."
    },
    {
        "anchor": "Quantum scars and regular eigenstates in a chaotic spinor condensate: Quantum many-body scars (QMBS) consist of a few low-entropy eigenstates in an\notherwise chaotic many-body spectrum, and can weakly break ergodicity resulting\nin robust oscillatory dynamics. The notion of QMBS follows the original\nsingle-particle scars introduced within the context of quantum billiards, where\nscarring manifests in the form of a quantum eigenstate concentrating around an\nunderlying classical unstable periodic orbit (UPO). A direct connection between\nthese notions remains an outstanding problem. Here, we study a many-body spinor\ncondensate that, owing to its collective interactions, is amenable to the\ndiagnostics of scars. We characterize the system's rich dynamics, spectrum, and\nphase space, consisting of both regular and chaotic states. The former are low\nin entropy, violate the Eigenstate Thermalization Hypothesis (ETH), and can be\ntraced back to integrable effective Hamiltonians, whereas most of the latter\nare scarred by the underlying semiclassical UPOs, while satisfying ETH. We\noutline an experimental proposal to probe our theory in trapped spin-1\nBose-Einstein condensates.",
        "positive": "Realization of a Bosonic Antiferromagnet: Quantum antiferromagnets are of broad interest in condensed matter physics as\nthey provide a platform for studying exotic many-body states including spin\nliquids and high-temperature superconductors. Here, we report on the creation\nof a one-dimensional Heisenberg antiferromagnet with ultracold bosons. In a\ntwo-component Bose-Hubbard system, we switch the sign of the spin-exchange\ninteraction and realize the isotropic antiferromagnetic Heisenberg model in an\nextended 70-site chain. Starting from a low-entropy N\\'eel-ordered state, we\nuse optimized adiabatic passage to approach the bosonic antiferromagnet. We\ndemonstrate the establishment of antiferromagnetism by probing the evolution of\nthe staggered magnetization and spin correlations of the system. Compared with\ncondensed matter systems, ultracold gases in optical lattices can be\nmicroscopically engineered and measured, offering significant advantages for\nexploring bosonic magnetism and spin dynamics."
    },
    {
        "anchor": "State-dependent interactions in ultracold $^{174}$Yb probed by optical\n  clock spectroscopy: We report on the measurement of the scattering properties of ultracold\n$^{174}$Yb bosons in a three-dimensional (3D) optical lattice. Site occupancy\nin an atomic Mott insulator is resolved with high-precision spectroscopy on an\nultranarrow optical clock transition. Scattering lengths and loss rate\ncoefficients for $^{174}$Yb atoms in different collisional channels involving\nthe ground state $^1$S$_0$ and the metastable $^3$P$_0$ are derived. These\nstudies set important constraints for future experimental studies of\ntwo-electron atoms for quantum-technological applications.",
        "positive": "Geometry induced pair condensation: We study a one-dimensional model of interacting bosons on a lattice with two\nflat bands. Regular condensation is suppressed due to the absence of a well\ndefined minimum in the single particle spectrum. We find that interactions\nstabilize a number of non-trivial phases like a pair (quasi-) condensate, a\nsupersolid at incommensurable fillings and valence bond crystals at\ncommensurability. We support our analytical calculations with numerical\nsimulations using the density matrix renormalization group technique.\nImplications for cold-atoms and extensions to higher dimensions are discussed."
    },
    {
        "anchor": "Dynamical Equilibration of Topological Properties: We study the dynamical process of equilibration of topological properties in\nquantum many-body systems undergoing a parameter quench between two\ntopologically inequivalent Hamiltonians. This scenario is motivated by recent\nexperiments on ultracold atomic gases, where a trivial initial state is\nprepared before the Hamiltonian is ramped into a topological insulator phase.\nWhile the many-body wave function must stay topologically trivial in the\ncoherent post-quench dynamics, here we show how the topological properties of\nthe single particle density matrix dynamically change and equilibrate in the\npresence of interactions. In this process, the single particle density matrix\ngoes through a characteristic level crossing as a function of time, which plays\nan analogous role to the gap closing of a Hamiltonian in an equilibrium\ntopological quantum phase transition. As an exact case study exemplifying this\nmechanism, we numerically solve the quench dynamics of an interacting\none-dimensional topological insulator.",
        "positive": "Analytical limits for cold atom Bose gases with tunable interactions: We discuss the equilibrium properties of dilute Bose gases using a\nnon-perturbative formalism based on auxiliary fields related to the normal and\nanomalous densities. We show analytically that for a dilute Bose gas of\nweakly-interacting particles at zero temperature, the leading-order auxiliary\nfield (LOAF) approximation leads to well-known analytical results. Close to the\ncritical point the LOAF predictions are the same as those obtained using an\neffective field theory in the large-N approximation. We also report analytical\napproximations for the LOAF results in the unitarity limit, which compare\nfavorably with our numerical results. LOAF predicts that the equation of state\nfor the Bose gas in the unitarity limit is E / (p V) = 1, unlike the case of\nthe Fermi gas when E / (p V) = 3/2."
    },
    {
        "anchor": "Spin-orbit coupling in quantum gases: Spin-orbit coupling links a particle's velocity to its quantum mechanical\nspin, and is essential in numerous condensed matter phenomena, including\ntopological insulators and Majorana fermions. In solid-state materials,\nspin-orbit coupling originates from the movement of electrons in a crystal's\nintrinsic electric field, which is uniquely prescribed. In contrast, for\nultracold atomic systems, the engineered \"material parameters\" are tuneable: a\nvariety of synthetic spin-orbit couplings can be engineered on demand using\nlaser fields. Here we outline the current experimental and theoretical status\nof spin-orbit coupling in ultracold atomic systems, discussing unique features\nthat enable physics impossible in any other known setting.",
        "positive": "Spontaneous interlayer superfluidity in bilayer systems of cold polar\n  molecules: Quantum degenerate cold-atom gases provide a remarkable opportunity to study\nstrongly interacting systems. Recent experimental progress in producing\nultracold polar molecules with a net electric dipole moment opens up new\npossibilities to realize novel quantum phases governed by the long-range and\nanisotropic dipole-dipole interactions. In this work we predict the existence\nof experimentally observable novel broken-symmetry states with spontaneous\ninterlayer coherence in cold polar molecules. These exotic states appear due to\nstrong repulsive interlayer interactions and exhibit properties of superfluids,\nferromagnets and excitonic condensates."
    },
    {
        "anchor": "The family of quantum droplets keeps expanding: This is an item in the \"View and Perspective\" category, which presents a\nbrief overview of particular aspects of the topic of \"quantum droplets\". It is\nlinked to a new theoretical paper, \"Quantum droplets in two-dimensional optical\nlattices\", which will be published in Frontiers of Physics (Ref. [21] in the\ncurrent preprint).",
        "positive": "Interacting Fermionic Atoms in Optical Lattices Diffuse Symmetrically\n  Upwards and Downwards in a Gravitational Potential: We consider a cloud of fermionic atoms in an optical lattice described by a\nHubbard model with an additional linear potential. While homogeneous\ninteracting systems mainly show damped Bloch oscillations and heating, a finite\ncloud behaves differently: It expands symmetrically such that gains of\npotential energy at the top are compensated by losses at the bottom.\nInteractions stabilize the necessary heat currents by inducing gradients of the\ninverse temperature 1/T, with T<0 at the bottom of the cloud. An analytic\nsolution of hydrodynamic equations shows that the width of the cloud increases\nwith t^(1/3) for long times consistent with results from our Boltzmann\nsimulations."
    },
    {
        "anchor": "Thermometry and Refrigeration in a Two-Component Mott Insulator of\n  Ultracold Atoms: Interesting spin Hamiltonians can be realized with ultracold atoms in a\ntwo-component Mott insulator (2CMI). It was recently demonstrated that the\napplication of a magnetic field gradient to the 2CMI enables new techniques of\nthermometry and adiabatic cooling. Here we present a theoretical description\nwhich provides quantitative analysis of these two new techniques. We show that\nadiabatic reduction of the field gradient is capable of cooling below the Curie\nor N\\'eel temperature of certain spin ordered phases.",
        "positive": "Coleman-Weinberg mechanism in spinor Bose-Einstein condensates: It is argued that a continuous quantum phase transition between different\nordered phases in spinor Bose-Einstein condensates predicted by the mean-field\ntheory is vulnerable to quantum fluctuations. By analyzing Lee-Huang-Yang\ncorrections in the condensate, we demonstrate that the so-called\nColeman-Weinberg mechanism takes place in such a transition, that is, the\ntransition becomes of the first order by quantum fluctuations. A jump to be\nexpected in this first-order transition is induced by a correction from density\nfluctuations despite a transition between different magnetic properties with\nkeeping condensation. We exemplify this with an experimentally relevant case\nand show that a measurement of a condensate depletion can be utilized to\nconfirm the first-order transition."
    },
    {
        "anchor": "Normal State Properties of a resonantly interacting p-wave Fermi Gas: Motivated by the recent experimental progresses in the study of p-wave\nresonant Fermi gas, we investigate the normal state properties of such a gas\nclose to a p-wave scattering resonance. We calculate the universal equation of\nstate and the two p-wave contacts which characterise the universal properties\nof the system, in good agreement with experiments. Our calculation takes\nexplicit account of the effective range correction and obtains the superfluid\ntransition temperature $T_c$ within Nozi\\`eres-Schmitt-Rink (NSR) scheme, and\nshows that it lies within experimental reach. We derive analytic expression for\n$T_c$ in the weak coupling limit and show explicitly the non-perturbative\nnature of the effective range corrections.",
        "positive": "Scaling behavior of density fluctuations in an expanding quasi-2D\n  degenerate Bose gas: We measure the power spectrum of density fluctuations emerged in a freely\nexpanding quasi-two-dimensional (2D) degenerate Bose gas and investigate the\nscaling behavior of the spectrum for the expansion time. The power spectrum\nshows an oscillatory shape for long expansion times, where the spectral peak\npositions are observed to be shifted to lower spatial frequencies than the\ntheoretical prediction for a non-interacting expansion case. We find the\nspectral peak positions in good agreement with the recent numerical simulation\npresented by Mazets [Phys. Rev. A 86, 055603 (2012)], where the atom-atom\ninteractions are taken into account. We present a mean-field description of the\ninteraction effect in the expansion dynamics and quantitatively account for the\nobserved spectral peak shifts. The spectral shift is intrinsic to the free\nexpansion of a quasi-2D Bose gas due to finite axial confinement. Finally, we\ninvestigate the defocussing effect in the power spectrum measurement."
    },
    {
        "anchor": "Topological Phase Diagram of Optimally Shaken Honeycomb Lattices: A Dual\n  Perspective from Stroboscopic and Non-Stroboscopic Floquet Hamiltonians: We present a direct comparison between the stroboscopic and non-stroboscopic\neffective approaches for ultracold atoms in shaken honeycomb lattices, focusing\nspecifically on the optimal driving introduced by A. Verdeny and F. Mintert\n[Phys. Rev. A 92, 063615 (2015)]. In the fast-driving regime, we compare the\neffective non-stroboscopic Hamiltonian derived through a perturbative expansion\nwith a non-perturbative calculation of the stroboscopic Floquet Hamiltonian,\nobtained through a simple non-perturbative numerical approach. We show that\nwhile some of the tunneling parameters are inherently model-dependent, the\ntopological properties of the system remains robust, as expected. Using the\nsame numerical approach we compute the topological phase diagram, arguing that\nit is most effectively represented in terms of the physical parameters\ncharacterizing the driving and the bare Hamiltonian -- parameters directly\naccessible in experiments -- rather than the emergent tunneling parameters,\nthat depend on the model representation.",
        "positive": "Mixing, demixing, and structure formation in a binary dipolar\n  Bose-Einstein condensate: We study static properties of disk-shaped binary dipolar Bose-Einstein\ncondensates of $^{168}$Er-$^{164}$Dy and $^{52}$Cr-$^{164}$Dy mixtures under\nthe action of inter- and intra-species contact and dipolar interactions and\ndemonstrate the effect of dipolar interaction using the mean-field approach.\nThroughout this study we use realistic values of inter- and intra-species\ndipolar interactions and the intra-species scattering lengths and consider the\ninter-species scattering length as a parameter. The stability of the binary\nmixture is illustrated through phase plots involving number of atoms of the\nspecies. The binary system always becomes unstable as the number of atoms\nincreases beyond a certain limit. As the inter-species scattering length\nincreases corresponding to more repulsion, an overlapping mixed state of the\ntwo species changes to a separated demixed configuration. During transition\nfrom a mixed to a demixed configuration as the inter-species scattering length\nis increased for parameters just below the stability line, the binary\ncondensate shows special structures in density in the form of\nred-blood-cell-like biconcave and Saturn-ring-like shapes, which are direct\nmanifestations of dipolar interaction."
    },
    {
        "anchor": "Effective p-wave interaction and topological superfluids in s-wave\n  quantum gases: P-wave interaction in cold atoms may give rise to exotic topological\nsuperfluids. However, the realization of p-wave interaction in cold atom system\nis experimentally challenging. Here we propose a simple scheme to synthesize\neffective $p$-wave interaction in conventional $s$-wave interacting quantum\ngases. The key idea is to load atoms into spin-dependent optical lattice\npotential. Using two concrete examples involving spin-1/2 fermions, we show how\nthe original system can be mapped into a model describing spinless fermions\nwith nearest neighbor p-wave interaction, whose ground state can be a\ntopological superfluid that supports Majorana fermions under proper conditions.\nOur proposal has the advantage that it does not require spin-orbit coupling or\nloading atoms onto higher orbitals, which is the key in earlier proposals to\nsynthesize effective $p$-wave interaction in $s$-wave quantum gases, and may\nprovide a completely new route for realizing $p$-wave topological superfluids.",
        "positive": "Effect of a bias field on disordered waveguides: Universal scaling of\n  conductance and application to ultracold atoms: We study the transmission of a disordered waveguide subjected to a finite\nbias field. The statisticaldistribution of transmission is analytically shown\nto take a universal form. It depends on a singleparameter, the system length\nexpressed in a rescaled metrics, which encapsulates all the microscopicfeatures\nof the medium and the bias field. Excellent agreement with numerics is found\nfor variousmodels of disorder and bias field. For white-noise disorder and a\nlinear bias field, we demonstratethe algebraic nature of the decay of the\ntransmission with distance, irrespective of the value ofthe bias field. It\ncontrasts with the expansion of a wave packet, which features a\ndelocalizationtransition for large bias field. The difference is attributed to\nthe different boundary conditionsfor the transmission and expansion schemes.\nThe observability of these effects in conductancemeasurements for electrons or\nultracold atoms is discussed, taking into account key features, suchas\nfinite-range disorder correlations, nonlinear bias fields, and finite\ntemperatures."
    },
    {
        "anchor": "Topics in the Mathematical Physics of Cold Bose Gases: In these notes of six lectures on selected topics in the theory of cold,\ndilute Bose gases, presented at the 5th Warsaw School of Statistical Physics in\nJune 2013, the following topics are discussed: 1) The concept of BEC, 2) the\nground state energy of a dilute Bose gas with short range interactions, 3)\nGross-Pitaevskii theory and BEC in trapped gases, 4) Bose gases in rotating\ntraps and quantized vortices, and 5) strongly correlated phases in the lowest\nLandau level generated by rapid rotation.",
        "positive": "Boson-vortex duality in compressible spin-orbit coupled BECs: Using a (1+2)-dimensional boson-vortex duality between non-linear\nelectrodynamics and a two-component compressible Bose-Einstein condensate (BEC)\nwith spin-orbit (SO) coupling, we obtain generalised versions of the\nhydrodynamic continuity and Euler equations where the phase defect and\nnon-defect degrees of freedom enter separately. We obtain the generalised\nMagnus force on vortices under SO coupling, and associate the linear\nconfinement of vortices due to SO coupling with instanton fluctuations of the\ndual theory."
    },
    {
        "anchor": "Generation of robust entangled states in a non-hermitian periodically\n  driven two-band Bose-Hubbard system: A many-body Wannier-Stark system coupled to an effective reservoir is studied\nwithin a non-Hermitian approach in the presence of a periodic driving. We show\nhow the interplay of dissipation and driving dynamically induces a subspace of\nstates which are very robust against dissipation. We numerically probe the\nstructure of these asymptotic states and their robustness to imperfections in\nthe initial-state preparation and to the size of the system. Moreover, the\nasymptotic states are found to be strongly entangled making them interesting\nfor further applications.",
        "positive": "Superfluid-Insulator Transitions in Attractive Bose-Hubbard Model with\n  Three-Body Constraint: By means of the method of the effective potential, the phase transitions from\nthe Mott insulating state to either the atomic or the dimer superfluid state in\nthe three-body constrained attractive Bose lattice gas are analyzed. Due to the\nappearance of the Feshbach resonance coupling between the two kinds of order\nparameters in the derived effective potential function, it is found that the\ncontinuous Mott insulator-to-superfluid transitions can be preempted by\nfirst-order ones. Since the employed approach can provide accurate predictions\nof phase boundaries in the strong coupling limit, where the dimer superfluid\nphase can emerge, our work hence sheds light on the search of this novel phase\nin real ultracold Bose gases in optical lattices."
    },
    {
        "anchor": "Reduced quantum anomaly in a quasi-2D Fermi superfluid: The significance\n  of the confinement-induced effective range of interactions: A two-dimensional (2D) harmonically trapped interacting Fermi gas is\nanticipated to exhibit a quantum anomaly and possesses a breathing mode at\nfrequencies different from a classical scale invariant value\n$\\omega_{B}=2\\omega_{\\perp}$, where $\\omega_{\\perp}$ is the trapping frequency.\nThe predicted maximum quantum anomaly ($\\sim10\\%$) has not been confirmed in\nexperiments. Here, we theoretically investigate the zero-temperature density\nequation of state and the breathing mode frequency of an interacting Fermi\nsuperfluid at the dimensional crossover from three to two dimensions. We find\nthat the simple model of a 2D Fermi gas with a single $s$-wave scattering\nlength is not adequate to describe the experiments in the 2D limit, as commonly\nbelieved. A more complete description of quasi-2D leads to a much weaker\nquantum anomaly, consistent with the experimental observations. We clarify that\nthe reduced quantum anomaly is due to the significant confinement-induced\neffective range of interactions, which is overlooked in previous theoretical\nand experimental studies.",
        "positive": "Beyond mean-field behavior of large Bose-Einstein condensates in\n  double-well potentials: For the dynamics of Bose-Einstein condensates (BECs), differences between\nmean-field (Gross-Pitaevskii) physics and $N$-particle quantum physics often\ndisappear if the BEC becomes larger and larger. In particular, the timescale\nfor which both dynamics agree should thus become larger if the particle number\nincreases. For BECs in a double-well potential, we find both examples for which\nthis is the case and examples for which differences remain even for huge BECs\non experimentally realistic short timescales. By using a combination of\nnumerical and analytical methods, we show that the differences remain visible\non the level of expectation values even beyond the largest possible numbers\nrealized experimentally for BECs with ultracold atoms."
    },
    {
        "anchor": "Bogoliubov-Cherenkov Radiation in an Atom Laser: We develop a simple yet powerful technique to study Bogoliubov-Cherenkov\nradiation by producing a pulsed atom laser from a strongly confined\nBose-Einstein condensate. Such radiation results when the atom laser pulse\nfalls past a Bose-Einstein condensate at high-hypersonic speeds, modifying the\nspatial profile to display a characteristic twin jet structure and a\ncomplicated interference pattern. The experimental observations are in\nexcellent agreement with mean-field numerical simulations and an analytic\ntheory. Due to the highly hypersonic regime reached in our experiment, this\nsystem offers a highly controllable platform for future studies of\ncondensed-matter analogs of quantum electrodynamics at ultrarelativistic\nspeeds.",
        "positive": "Ab initio simulations of the thermodynamic properties and phase\n  transition of Fermi systems based on fictitious identical particles and\n  physics-informed neural networks: Fictitious identical particle thermodynamics has emerged as a powerful tool\nto overcome the fermion sign problem, enabling highly accurate simulations of\none thousand fermions in warm dense matter (T. Dornheim et al., J. Phys. Chem.\nLett. 15, 1305 (2024)). However, inferring the thermodynamic properties of\nFermi systems from a large number of exact numerical simulations of the bosonic\nsector still poses subtle challenges, especially in the regime of high quantum\ndegeneracy and in the presence of phase transitions. In this work, we\ndemonstrate that physics-informed neural networks (PINNs), trained on data from\nextensive and sign-problem-free numerical simulations of the bosonic sector,\noffer a valuable means to infer the thermodynamic properties of Fermi systems.\nPINNs can play a particularly crucial role in capturing phase transitions. To\nillustrate the methodology of fictitious identical particles combined with\nPINNs for simulating the thermodynamics of Fermi systems, we explore its\napplication in realistic scenarios, including ultracold Fermi gases in periodic\npotentials, and phase transitions of pair condensation formed in the unitary\nlimit in a three-dimensional harmonic trap. For the spatially continuous\nFermi-Hubbard model, we efficiently and reliably simulated hundreds of fermions\nhere. For the Fermi gas in the unitary limit, based on the fictitious identical\nparticle combined with PINNs, our approach confirms the universal result of the\ncritical temperature with the increasing of the number of fermions, and is\nconsistent with the experimental observations."
    },
    {
        "anchor": "Characterization of density oscillations in confined and degenerate\n  Fermi gases: Friedel oscillations appear in density of Fermi gases due to Pauli exclusion\nprinciple and translational symmetry breaking nearby a defect or impurity. In\nconfined Fermi gases, this symmetry breaking occurs also near to boundaries.\nHere, density oscillations of a degenerate and confined Fermi gas are\nconsidered and characterized. True nature of density oscillations are\nrepresented by analytical formulas for degenerate conditions. Analytical\ncharacterization is first done for completely degenerate case, then temperature\neffects are also incorporated with a finer approximation. Envelope functions\ndefining the upper and lower bounds of these oscillations are determined. It is\nshown that the errors of obtained expressions are negligible as long as the\nsystem is degenerate. Numbers, amplitudes, averages and spatial coordinates of\noscillations are also given by analytical expressions. The results may be\nhelpful to efficiently predict and easily calculate the oscillations in density\nand density-dependent properties of confined electrons at nanoscale.",
        "positive": "Anderson transition of Bogoliubov quasiparticles in the quasiperiodic\n  kicked rotor: We study the dynamics of Bogoliubov excitations of a Bose-Einstein condensate\nin the quasiperiodic kicked rotor. In the weakly interacting regime, the\ncondensate is stable and both the condensate and the excitations undergo a\nphase transition from a quasilocalized to a diffusive regime. The corresponding\ncritical exponents are identical for the condensate and the excitations, and\ncompare very well with the value $\\nu\\approx1.6$ for non-interacting particles."
    },
    {
        "anchor": "Collisional Dynamics of Half-Quantum Vortices in a Spinor Bose-Einstein\n  Condensate: We present an experimental study on the interaction and dynamics of\nhalf-quantum vortices (HQVs) in an antiferromagnetic spinor Bose-Einstein\ncondensate. By exploiting the orbit motion of a vortex dipole in a trapped\ncondensate, we perform a collision experiment of two HQV pairs, and observe\nthat the scattering motions of the HQVs is consistent with the short-range\nvortex interaction that arises from nonsingular magnetized vortex cores. We\nalso investigate the relaxation dynamics of turbulent condensates containing\nmany HQVs, and demonstrate that spin wave excitations are generated by the\ncollisional motions of the HQVs. The short-range vortex interaction and the\nHQV-magnon coupling represent two characteristics of the HQV dynamics in the\nspinor superfluid.",
        "positive": "Plane and Stripe Wave Phases of a Spin-Orbit Coupled Bose-Einstein\n  Condensate in an Optical Lattice with a Zeeman Field: A weakly interacting, spin-orbit coupled, ultracold, dilute Bose gas on a\ntwo-dimensional square lattice with an external Zeeman field is studied. We\nexplore the plane and stripe wave phases of the system involving nonzero\ncondensate momenta, which occur when the Zeeman field is below a critical\nvalue. Their excitation spectra are found using Bogoliubov theory and by two\ndifferent routes. The validity of each method to obtain the excitation spectrum\nis discussed, and it is found that projection on the lowest single-particle\nband is an excellent approximation in the plane wave phase, while it is a poor\napproximation in the stripe wave phase. While the plane wave phase has a phonon\nminimum at its single condensate momentum, revealing a nonzero sound velocity\nof the excitations, the stripe wave phase has quadratic minima at its two\ncondensate momenta showing zero sound velocity of the excitations. We discuss\nhow the presence of more than one condensate momentum is essential for these\ndifferences between the two phases. Additionally, it is emphasized that the\nzero sound velocity in the stripe wave phase is a lattice effect, since\ncontinuum studies of the same phase have shown nonzero sound velocity."
    },
    {
        "anchor": "Superfluidity and Phase Correlations of Driven Dissipative Condensates: We review recent results on the coherence and superfluidity of driven\ndissipative condensates, i.e., systems of weakly-interacting non-conserved\nBosons, such as polariton condensates. The presence of driving and dissipation\nhas dramatically different effects depending on dimensionality and anisotropy.\nIn three dimensions, equilibrium behaviour is recovered at large scales for\nstatic correlations, while the dynamical behaviour is altered by the\nmicroscopic driving. In two dimensions, for an isotropic system, drive and\ndissipation destroy the algebraic order that would otherwise exist, however a\nsufficiently anisotropic system can still show algebraic phase correlations. We\ndiscuss the consequences of this behaviour for recent experiments measuring\nphase coherence, and outline potential measurements that might directly probe\nsuperfluidity.",
        "positive": "Tunable gauge potential for neutral and spinless particles in driven\n  lattices: We present a universal method to create a tunable, artificial vector gauge\npotential for neutral particles trapped in an optical lattice. The necessary\nPeierls phase of the hopping parameters between neighboring lattice sites is\ngenerated by applying a suitable periodic inertial force such that the method\ndoes not rely on any internal structure of the particles. We experimentally\ndemonstrate the realization of such artificial potentials, which generate\nground state superfluids at arbitrary non-zero quasi-momentum. We furthermore\ninvestigate possible implementations of this scheme to create tuneable magnetic\nfluxes, going towards model systems for strong-field physics."
    },
    {
        "anchor": "Quantum droplet states of a binary magnetic gas: Quantum droplets can emerge in bosonic binary magnetic gases (BMGs) from the\ninterplay of short- and long-ranged interactions, and quantum fluctuations. We\ndevelop an extended meanfield theory for this system and use it to predict\nequilibrium and dynamical properties of BMG droplets. We present a phase\ndiagram and characterize miscible and immiscible droplet states. We also show\nthat a single component self-bound droplet can be used to bind another magnetic\ncomponent which is not in the droplet regime. Our results should be realizable\nin experiments with mixtures of highly-magnetic lanthanide atoms.",
        "positive": "Two-dimensional network of atomtronic qubits: Through a combination of laser beams, we engineer a two-dimensional optical\nlattice of Mexican hat potentials able to host atoms in its ring-shaped wells.\nWhen tunneling can be ignored (at high laser intensities), we show that a\nwell-defined qubit can be associated with the states of the atoms trapped in\neach of the rings. Each of these two-level systems can be manipulated by a\nsuitable configuration of Raman laser beams imprinting a synthetic flux onto\neach Mexican hat cell of the lattice. Overall, we believe that the system has\nthe potential to form a scalable architecture for atomtronic flux qubits."
    },
    {
        "anchor": "Cavity-induced spin-orbit coupling in an interacting bosonic wire: We consider theoretically ultra-cold interacting bosonic atoms confined to a\nwire geometry and coupled to the field of an optical cavity. A spin-orbit\ncoupling is induced via Raman transitions employing a cavity mode and a\ntransverse running wave pump beam, the transition imprints a spatial dependent\nphase onto the atomic wavefunction. Adiabatic elimination of the cavity field\nleads to an effective Hamiltonian for the atomic degrees of freedom, with a\nself-consistency condition. We map the spin-orbit coupled bosonic wire to a\nbosonic ladder in a magnetic field, by discretizing the spatial dimension.\nUsing the numerical density matrix renormalization group method, we show that\nin the continuum limit the dynamical stabilization of a Meissner superfluid is\npossible, for parameters achievable by nowadays experiments.",
        "positive": "Spin-orbit-coupled Bose-Einstein-condensed atoms confined in annular\n  potentials: A spin-orbit-coupled Bose-Einstein-condensed cloud of atoms confined in an\nannular trapping potential shows a variety of phases that we investigate in the\npresent study. Starting with the non-interacting problem, the homogeneous phase\nthat is present in an untrapped system is replaced by a sinusoidal density\nvariation in the limit of a very narrow annulus. In the case of an untrapped\nsystem there is another phase with a striped-like density distribution, and its\ncounterpart is also found in the limit of a very narrow annulus. As the width\nof the annulus increases, this picture persists qualitatively. Depending on the\nrelative strength between the inter- and the intra-components, interactions\neither favor the striped phase, or suppress it, in which case either a\nhomogeneous, or a sinusoidal-like phase appears. Interactions also give rise to\nnovel solutions with a nonzero circulation."
    },
    {
        "anchor": "Interplay of Kelvin-Helmholtz and superradiant instabilities of an array\n  of quantized vortices in a two-dimensional Bose--Einstein condensate: We investigate the various physical mechanisms that underlie the dynamical\ninstability of a quantized vortex array at the interface between two\ncounter-propagating superflows in a two-dimensional Bose--Einstein condensate.\nInstabilities of markedly different nature are found to dominate in different\nflow velocity regimes. For moderate velocities where the two flows are\nsubsonic, the vortex lattice displays a quantized version of the hydrodynamic\nKelvin--Helmholtz instability (KHI), with the vortices rolling up and\nco-rotating. For supersonic flow velocities, the oscillation involved in the\nKHI can resonantly couple to acoustic excitations propagating away in the bulk\nfluid on both sides. This makes the KHI rate to be effectively suppressed and\nother mechanisms to dominate: For finite and relatively small systems along the\ntransverse direction, the instability involves a repeated superradiant\nscattering of sound waves off the vortex lattice; for transversally unbound\nsystems, a radiative instability dominates, leading to the simultaneous growth\nof a localized wave along the vortex lattice and of acoustic excitations\npropagating away in the bulk. Finally, for slow velocities, where the KHI rate\nis intrinsically slow, another instability associated to the rigid lateral\ndisplacement of the vortex lattice due to the vicinity of the system's boundary\nis found to dominate.",
        "positive": "Glassy dynamics and Landau-Zener phenomena in trapped quasi-one\n  dimensional coupled Bose-Einstein condensates: The purpose of this article is to address the dynamics of an interacting\nBose-Einstein condensate confined in coupled one-dimensional Landau-Zener\narrays under the influence of disorder and harmonic confinement. In particular,\nwe concentrate in studying the interplay of disorder and interparticle\ninteraction on the transfer of atoms depending on the speed of Landau-Zener\nsweeps. A dynamical phase diagram summarizing the final situation across ground\nstate and inverse sweeps is given in terms of the effect of disorder,\ninteraction and the speed of the sweeps."
    },
    {
        "anchor": "Atom-Dimer Scattering and Stability of Bose and Fermi Mixtures: Motivated by a recent experiment by ENS group on the mixture of Bose and\nFermi superfluids (arxiv:1404.2548), we investigate the effective scattering\nbetween a bosonic atom and a molecule(dimer) of fermion atoms. It is found that\nthe mean-field prediction of the atom-dimer scattering length ($a_{ad}$), as\nsimply given by the boson-fermion scattering length ($a_{bf}$), generically\nfails. Instead, $a_{ad}$ crucially depends on the ratio between $a_{bf}$ and\n$a_{ff}$ (the fermion-fermion scattering length), and in addition\nlog-periodically depends on the three-body parameter. We identify the universal\nparameters in characterizing $a_{ad}$ for a wide range of $a_{ff}$ in the\nmolecular side of the fermion-fermion Feshbach resonance, and further\ndemonstrate that the atom-dimer many-body system can become unstable against\neither phase separation or collapse as tuning $a_{ff}$. Our results have some\nimplications to the ENS experiment.",
        "positive": "Soliton lattices in the Gross-Pitaevskii equation with nonlocal and\n  repulsive coupling: Spatially-periodic patterns are studied in nonlocally coupled\nGross-Pitaevskii equation. We show first that spatially periodic patterns\nappear in a model with the dipole-dipole interaction. Next, we study a model\nwith a finite-range coupling, and show that a repulsively coupled system is\nclosely related with an attractively coupled system and its soliton solution\nbecomes a building block of the spatially-periodic structure. That is, the\nspatially-periodic structure can be interpreted as a soliton lattice. An\napproximate form of the soliton is given by a variational method. Furthermore,\nthe effects of the rotating harmonic potential and spin-orbit coupling are\nnumerically studied."
    },
    {
        "anchor": "Spin fluctuations, susceptibility and the dipole oscillation of a nearly\n  ferromagnetic Fermi gas: We discuss the spin fluctuations and the role played by the magnetic\nsusceptibility in an atomic Fermi gas interacting with positive scattering\nlength. Both thermal and quantum fluctuations are considered. Using a sum rule\napproach and recent {\\it ab initio} Monte Carlo results for the magnetic\nsusceptibility of uniform matter we provide explicit predictions for the\nfrequency of the spin dipole oscillation of a gas trapped by a harmonic\npotential and discuss the deviations from the behaviour of an ideal gas when\nthe system approaches the ferromagnetic transition. The role of the Landau's\nparameters in the characterization of the magnetic properties is also\ndiscussed.",
        "positive": "Quantitative study of two- and three-dimensional strong localization of\n  matter waves by atomic scatterers: We study the strong localization of atomic matter waves in a disordered\npotential created by atoms pinned at the nodes of a lattice, for both\nthree-dimensional (3D) and two-dimensional (2D) systems. The localization\nlength of the matter wave, the density of localized states, and the occurrence\nof energy mobility edges (for the 3D system), are numerically investigated as a\nfunction of the effective scattering length between the atomic matter wave and\nthe pinned atoms. Both positive and negative matter wave energies are explored.\nInteresting features of the density of states are discovered at negative\nenergies, where maxima in the density of bound states for the system can be\ninterpreted in terms of bound states of a matter wave atom with a few pinned\natomic scatterers. In 3D we found evidence of up to three mobility edges, one\nat positive energies, and two at negative energies, the latter corresponding to\ntransitions between extended and localized bound states. In 2D, no mobility\nedge is found, and a rapid exponential-like increase of the localization length\nis observed at high energy."
    },
    {
        "anchor": "Antiferromagnetic behavior in self-bound one-dimensional composite\n  bosons: The structure of self-bound one-dimensional droplets containing a mixture of\nYtterbium fermionic isotopes ($^{173}$Yb, $^{171}$Yb) is calculated by means of\na diffusion Monte Carlo technique. We considered only balanced setups in which\nall the atoms of one isotope are spin-polarized, while the atoms of the other\ncan have up to three different spin values, that difference being a necessary\nrequirement to achieve stable systems. Our results indicate that these droplets\nconsist of consecutive \"molecules\" made up of one $^{173}$Yb and one $^{171}$Yb\natom. In other words, we have up to three different kinds of composite bosons,\ncorresponding to the number of spin components in the non-polarized isotope.\nThe fermionic nature of those Yb atoms makes pairs with identical spin\ncomposition avoid each other, creating a Pauli-like-hole filed by another\nmolecule in which at least one of the Yb atoms has a different spin from that\nof their closest neighbors. This effective repulsion is akin to an\nantiferromagnetic short-range interaction between different kinds of composite\nbosons.",
        "positive": "Collective excitations of two-dimensional Bose-Einstein Condensate in\n  liquid phase with spin-orbit coupling: We have studied the collective excitation of Bose-Einstein condensate of\nshort range weak interacting atoms with spin-orbit coupling (SOC) in two\ndimension in liquid phase. In our study, we have included Rashba, Dresselhaus\nSOC as well as Raman SOC. The study of Bogoliubov excitation shows that in\nsmall interaction case only phonon modes are present and for higher\ninteractions roton modes start to appear. Energy spectra contain two roton\nmodes in the system relatively strong interacting atomic system."
    },
    {
        "anchor": "Experimental Determination of the Finite-Temperature Phase Diagram of a\n  Spin-Orbit Coupled Bose Gas: Spin-orbit (SO) coupling has led to numerously exciting phenomena in electron\nsystems, for instance, the recently discovered topological insulator. The\nsynthesized SO coupling with ultracold neutral atoms opens a new avenue of\nquantum simulation, and gives us an opportunity to study SO coupling in bosonic\nsystems. Indeed, SO coupling leads to many new phenomena of boson superfluidity\nand various condensate phases that spontaneously break different symmetries. A\nricher structure of symmetry breaking always results in a nontrivial\nfinite-temperature phase diagram. While the thermodynamics of the SO coupled\nBose gas at finite temperature is still unknown either in theory or experiment.\nIn this work, we experimentally generate the SO coupling in ultracold Rb-87 gas\nto explore in a large temperature range and get most key features. We discover\na novel phase transition between the stripe ordered phase and the magnetized\nphase, which is reminiscent of temperature-driven transition from the B phase\nto the A phase in super- fluid Helium-3 and from spin-density-wave to spin\nnematic transition in iron pnictide. We also observe that the magnetic phase\ntransition and the Bose condensate transition occur simultaneously as\ntemperature decreases. Our work determines the entire finite-temperature phase\ndiagram of SO coupled Bose gas and further demonstrate the power of quantum\nsimulation.",
        "positive": "The manipulation of ultracold atoms of high orbitals in optical lattices: Ultracold atoms in optical lattices are a powerful tool for quantum\nsimulation, precise measurement, and quantum computation. A fundamental problem\nin applying this quantum system is how to manipulate the higher bands or\norbitals in Bloch states effectively. Here we mainly review our methods for\nmanipulating high orbital ultracold atoms in optical lattices with different\nconfigurations. Based on these methods, we construct the atom-orbital qubit\nunder nonadiabatic holonomic quantum control and Ramsey interferometry with\ntrapped motional quantum states. Then we review the observation of the novel\nquantum states and the study of the dynamical evolution of the high orbital\natoms in optical lattices. The effective manipulation of the high orbitals\nprovides strong support for applying ultracold atoms in the optical lattice in\nmany fields."
    },
    {
        "anchor": "Weak localization with nonlinear bosonic matter waves: We investigate the coherent propagation of dilute atomic Bose-Einstein\ncondensates through irregularly shaped billiard geometries that are attached to\nuniform incoming and outgoing waveguides. Using the mean-field description\nbased on the nonlinear Gross-Pitaevskii equation, we develop a diagrammatic\ntheory for the self-consistent stationary scattering state of the interacting\ncondensate, which is combined with the semiclassical representation of the\nsingle-particle Green function in terms of chaotic classical trajectories\nwithin the billiard. This analytical approach predicts a universal dephasing of\nweak localization in the presence of a small interaction strength between the\natoms, which is found to be in good agreement with the numerically computed\nreflection and transmission probabilities of the propagating condensate. The\nnumerical simulation of this quasi-stationary scattering process indicates that\nthis interaction-induced dephasing mechanism may give rise to a signature of\nweak antilocalization, which we attribute to the influence of non-universal\nshort-path contributions.",
        "positive": "Fermions meet two bosons -- the heteronuclear Efimov effect revisited: In this article, we revisit the heteronuclear Efimov effect in a Bose-Fermi\nmixture with large mass difference in the Born-Oppenheimer picture. As a\nspecific example, we consider the combination of bosonic $^{133}\\mathrm{Cs}$\nand fermionic $^6\\mathrm{Li}$. In a system consisting of two heavy bosons and\none light fermion, the fermion-mediated potential between the two heavy bosons\ngives rise to an infinite series of three-body bound states. The intraspecies\nscattering length determines the three-body parameter and the scaling factor\nbetween consecutive Efimov states. In a second scenario, we replace the single\nfermion by an entire Fermi Sea at zero temperature. The emerging interaction\npotential for the two bosons exhibits long-range oscillations leading to a\nweakening of the binding and a breakup of the infinite series of Efimov states.\nIn this scenario, the binding energies follow a modified Efimov scaling law\nincorporating the Fermi momentum. The scaling factor between deeply bound\nstates is governed by the intraspecies interaction, analogous to the Efimov\nstates in vacuum."
    },
    {
        "anchor": "Cooperation of different exchange mechanisms in confined magnetic\n  systems: The diluted Kondo lattice model is investigated at strong antiferromagnetic\nlocal exchange couplings J, where almost local Kondo clouds drastically\nrestrict the motion of conduction electrons, giving rise to the possibility of\nquantum localization of conduction electrons for certain geometries of impurity\nspins. This localization may lead to the formation of local magnetic moments in\nthe conduction-electron system, and the inverse indirect magnetic exchange\n(IIME), provided by virtual excitations of the Kondo singlets, couples those\nlocal moments to the remaining electrons. Exemplarily, we study the\none-dimensional two-impurity Kondo model with impurity spins near the chain\nends, which supports the formation of conduction-electron magnetic moments at\nthe edges of the chain for sufficiently strong J. Employing degenerate\nperturbation theory as well as analyzing spin gaps numerically by means of the\ndensity-matrix renormalization group, it is shown that the low-energy physics\nof the model can be well captured within an effective antiferromagnetic\nRKKY-like two-spin model (\"RKKY from IIME\") or within an effective central-spin\nmodel, depending on edge-spin distance and system size.",
        "positive": "Emergent Fermi sea in a system of interacting bosons: An understanding of the possible ways in which interactions can produce\nfundamentally new emergent many-body states is a central problem of condensed\nmatter physics. We ask if a Fermi sea can arise in a system of bosons subject\nto contact interaction. Based on exact diagonalization studies and variational\nwave functions, we predict that such a state is likely to occur when a system\nof two-component bosons in two dimensions, interacting via a species\nindependent contact interaction, is exposed to a synthetic magnetic field of\nstrength that corresponds to a filling factor of unity. The fermions forming\nthe SU(2) singlet Fermi sea are bound states of bosons and quantized vortices,\nformed as a result of the repulsive interaction between bosons in the lowest\nLandau level."
    },
    {
        "anchor": "Ultrawide dark solitons and droplet-soliton coexistence in a dipolar\n  Bose gas with strong contact interactions: We look into dark solitons in a quasi-1D dipolar Bose gas and in a quantum\ndroplet. We derive the analytical solitonic solution of a Gross-Pitaevskii-like\nequation accounting for beyond mean-field effects. The results show there is a\ncertain critical value of the dipolar interactions, for which the width of a\nmotionless soliton diverges. Moreover, there is a peculiar solution of the\nmotionless soliton with a non-zero density minimum. We also present the energy\nspectrum of these solitons with an additional excitation subbranch appearing.\nFinally, we perform a series of numerical experiments revealing the coexistence\nof a dark soliton inside a quantum droplet.",
        "positive": "Classical and quantum regimes of two-dimensional turbulence in trapped\n  Bose-Einstein condensates: We investigate two-dimensional turbulence in finite-temperature trapped\nBose-Einstein condensates within damped Gross-Pitaevskii theory. Turbulence is\nproduced via circular motion of a Gaussian potential barrier stirring the\ncondensate. We systematically explore a range of stirring parameters and\nidentify three regimes, characterized by the injection of distinct quantum\nvortex structures into the condensate: (A) periodic vortex dipole injection,\n(B) irregular injection of a mixture of vortex dipoles and co-rotating vortex\nclusters, and (C) continuous injection of oblique solitons that decay into\nvortex dipoles. Spectral analysis of the kinetic energy associated with\nvortices reveals that regime (B) can intermittently exhibit a Kolmogorov\n$k^{-5/3}$ power law over almost a decade of length or wavenumber ($k$) scales.\nThe kinetic energy spectrum of regime (C) exhibits a clear $k^{-3/2}$ power law\nassociated with an inertial range for weak-wave turbulence, and a $k^{-7/2}$\npower law for high wavenumbers. We thus identify distinct regimes of forcing\nfor generating either two-dimensional quantum turbulence or classical weak-wave\nturbulence that may be realizable experimentally."
    },
    {
        "anchor": "Fermionic trimers in spin-dependent optical lattices: We investigate the formation of three-body bound states (trimers) in\ntwo-component Fermi gases confined in one dimensional optical lattice with\nspin-dependent tunneling rates. The binding energy and the effective mass of\nthe trimer are obtained from the solution of the Mattis integral equation\ngeneralized to the case of unequal Bloch masses. We show that this equation\nadmits multiple solutions corresponding to excited bound states, which are only\nstable for large mass asymmetry.",
        "positive": "PT-symmetric non-Hermitian quantum many-body system using ultracold\n  atoms in an optical lattice with controlled dissipation: We report our realization of a parity-time (PT) symmetric non-Hermitian\nmany-body system using cold atoms with dissipation. After developing a\ntheoretical framework on PT-symmetric many-body systems using ultracold atoms\nin an optical lattice with controlled dissipation, we describe our experimental\nsetup utilizing one-body atom loss as dissipation with special emphasis on\ncalibration of important system parameters. We discuss loss dynamics observed\nexperimentally."
    },
    {
        "anchor": "Permanent magnetic microtraps for ultracold atoms: We propose and numerically study two permanent magnetic micro-structures for\ncreating Ioffe-Pritchard microtraps. A bias magnetic field is used to vary the\ndepth, trap frequencies and the minimum of each microtrap. After the\nBose-Einstein condensation achievement, the bias magnetic field can be slowly\nremoved to increase the trap barrier heights for more efficiently holding the\nBose-Einstein condensates. Even without the external magnetic field, it is\npossible to hold ultracold atoms in the microtraps. These microtraps may also\nbe useful for single atom experiments for quantum information processing due to\ntheir very high confinement.",
        "positive": "Mass-imbalanced Fermi gases with spin-orbit coupling: We use the mean-field theory to analyze the ground-state phase diagrams of\nspin-orbit coupled mass-imbalanced Fermi gases throughout the BCS-BEC\nevolution, including both the population-balanced and -imbalanced systems. Our\ncalculations show that the competition between the mass and population\nimbalance and the Rashba-type spin-orbit coupling (SOC) gives rise to very rich\nphase diagrams, involving normal, superfluid and phase separated regions. In\naddition, we find quantum phase transitions between the topologically trivial\ngapped superfluid and the nontrivial gapless superfluid phases, opening the way\nfor the experimental observation of exotic phenomena with cold atom systems."
    },
    {
        "anchor": "Few-body correlations in two-dimensional Bose and Fermi ultracold\n  mixtures: Few-body correlations emerging in two-dimensional harmonically trapped\nmixtures, are comprehensively investigated. The presence of the trap leads to\nthe formation of atom-dimer and trap states, in addition to trimers. The Tan's\ncontacts of these eigenstates are studied for varying interspecies scattering\nlengths and mass ratio, while corresponding analytical insights are provided\nwithin the adiabatic hyperspherical formalism. The two- and three-body\ncorrelations of trimer states are substantially enhanced compared to the other\neigenstates. The two-body contact of the atom-dimer and trap states features an\nupper bound regardless of the statistics, treated semi-classically and having\nan analytical prediction in the limit of large scattering lengths. Such an\nupper bound is absent in the three-body contact. Interestingly, by tuning the\ninterspecies scattering length the contacts oscillate as the atom-dimer and\ntrap states change character through the existent avoided-crossings in the\nenergy spectra. For thermal gases, a gradual suppression of the involved two-\nand three-body correlations is evinced manifesting the impact of thermal\neffects. Moreover, spatial configurations of the distinct eigenstates ranging\nfrom localized structures to angular anisotropic patterns are captured. Our\nresults provide valuable insights into the inherent correlation mechanisms of\nfew-body mixtures which can be implemented in recent ultracold atom experiments\nand will be especially useful for probing the crossover from few- to many-atom\nsystems.",
        "positive": "Spatial dynamics, thermalization, and gain clamping in a photon\n  condensate: We study theoretically the effects of pump-spot size and location on photon\ncondensates. By exploring the inhomogeneous molecular excitation fraction, we\nmake clear the relation between spatial equilibration, gain clamping and\nthermalization in a photon condensate. This provides a simple understanding of\nseveral recent experimental results. We find that as thermalization breaks\ndown, gain clamping is imperfect, leading to \"transverse spatial hole burning\"\nand multimode condensation. This opens the possibility of engineering the gain\nprofile to control the condensate structure."
    },
    {
        "anchor": "Analytic normal mode frequencies for N identical particles: The\n  microscopic dynamics underlying the emergence and stability of excitation\n  gaps from BCS to unitarity: The frequencies of the analytic normal modes for N identical particles are\nstudied as a function of system parameters from the weakly interacting BCS\nregime to the strongly interacting unitary regime. The normal modes were\nobtained previously from a first-order L=0 group theoretic solution of a\nthree-dimensional Hamiltonian with a general two-body interaction for confined,\nidentical particles. In a precursor to this study, the collective behavior of\nthese normal modes was investigated as a function of N from few-body systems to\nmany-body systems analyzing the contribution of individual particles to the\ncollective macroscopic motions. A specific case, the Hamiltonian for Fermi\ngases in the unitary regime was studied in more detail. This regime is known to\nsupport collective behavior in the form of superfluidity and has previously\nbeen successfully described using normal modes. Two phenomena that could\nsustain the emergence and stability of superfluid behavior were revealed,\nincluding the behavior of the normal mode frequencies as N increases. In this\npaper, I focus on a more detailed analysis of these analytic frequencies,\nextending my investigation to include Hamiltonians with a range of\ninterparticle interaction strengths from the BCS regime to the unitary regime\nand analyzing the microscopic dynamics that lead to large gaps at unitarity.\nThe results of the current study suggest that in regimes where higher-order\neffects are small, normal modes an be used to describe the physics of\nsuperfluidity from the weakly interacting BCS regime with the emergence of\nsmall excitation gaps to unitarity with its large gaps, and can offer insight\ninto a possible microscopic understanding of the behavior at unitarity. This\napproach could thus offer an alternative to the two-body pairing models\ncommonly used to describe superfluidity along this transition.",
        "positive": "Lifshitz Point in the Phase Diagram of Resonantly Interacting\n  $^6Li$-$^{40}K$ Mixtures: We consider a strongly interacting ${}^{6}$Li-${}^{40}$K mixture, which is\nimbalanced both in the masses and the densities of the two fermionic species.\nAt present, it is the experimentalist's favorite for reaching the superfluid\nregime. We construct an effective thermodynamic potential that leads to\nexcellent agreement with Monte Carlo results for the normal state. We use it to\ndetermine the universal phase diagram of the mixture in the unitarity limit,\nwhere we find, in contrast to the mass-balanced case, the presence of a\nLifshitz point. This point is characterized by the effective mass of the Cooper\npairs becoming negative, which signals an instability towards a supersolid\nphase."
    },
    {
        "anchor": "Vortex Excitations of Dirac Bose-Einstein Condensates: We explore vortices in non-equilibrium Dirac Bose-Einstein condensates (Dirac\nBEC) described by a stationary Dirac Gross-Pitaevskii equations (GPE). We find\nthat the multi-component structure of Dirac equation enables the difference in\nphase winding of two condensates with respective phase winding number differing\nby one, $\\ell_a - \\ell_b = \\pm 1$. We observe three classes of vortex states\ndistinguished by their far-field behavior: A ring soliton on either of the two\ncomponents in combination with a vortex on the other component, and, in the\ncase of strong inter-component interactions, a vortex profile on both\ncomponents. The latter are multiple core vortices due to the phase winding\ndifference between the components. We also address the role of a Haldane gap on\nthese vortices, which has a similar effect than inter-component by making the\noccupation on either sublattice more costly. We employ a numerical shooting\nmethod to reliably identify vortex solutions and use it to scan large parts of\nthe phase space. We then use a classification algorithm on the integrated\nwavefunctions to establish a phase diagram of the different topological\nsectors.",
        "positive": "Bose-enhanced relaxation of driven atom-molecule condensates: Motivated by recent experiments we study the interconversion between\nultracold atomic and molecular condensates, quantifying the resulting\noscillations and their slow decay. We find that near equilibrium the dominant\ndamping source is the decay of condensed molecules into non-condensed pairs,\nwith a pair kinetic energy that is resonant with the frequency of the\noscillating atom-molecule interconversions. The decay, however, is\nnon-exponential, as strong population of the resonant pairs leads to Bose\nenhancement. Introducing an oscillating magnetic field, which periodically\nmodulates the molecular binding energy, enhances the oscillations at short\ntimes. However, the resulting enhancement of the pair-production process\nresults in an accelerated decay which rapidly cuts off the initial oscillation\ngrowth."
    },
    {
        "anchor": "Two strong nonlinearity regimes in cold molecule formation: Two distinct strongly non-linear scenarios of molecule formation in an atomic\nBose-Einstein condensate (either by photoassociation or Feshbach resonance)\ncorresponding to large and small field detuning are revealed. By examining\narbitrary external field configurations, we show that the association process\nin the first case is almost non-oscillatory in time while in the second case\nthe evolution of the system displays strongly pronounced Rabi-type\noscillations. We construct highly accurate approximate solutions for both limit\ncases. We show that at strong coupling limit the non-crossing models are able\nto provide conversion of no more than one third of the initial atomic\npopulation. Finally, we show that for constant-amplitude models involving a\nfinite final detuning the strong interaction limit is not optimal for molecule\nformation.",
        "positive": "Pair formation of hard core bosons in flat band systems: Hard core bosons in a large class of one or two dimensional flat band systems\nhave an upper critical density, below which the ground states can be described\ncompletely. At the critical density, the ground states are Wigner crystals. If\none adds a particle to the system at the critical density, the ground state and\nthe low lying multi particle states of the system can be described as a Wigner\ncrystal with an additional pair of particles. The energy band for the pair is\nseparated from the rest of the multi-particle spectrum. The proofs use a\nGerschgorin type of argument for block diagonally dominant matrices. In certain\none-dimensional or tree-like structures one can show that the pair is\nlocalised, for example in the chequerboard chain. For this one-dimensional\nsystem with periodic boundary condition the energy band for the pair is flat,\nthe pair is localised."
    },
    {
        "anchor": "Topological bands in the continuum using Rydberg states: The quest to realize topological band structures in artificial matter is\nstrongly focused on lattice systems, and only quantum Hall physics is known to\nappear naturally also in the continuum. In this letter, we present a proposal\nbased on a two-dimensional cloud of atoms dressed to Rydberg states, where\nexcitations propagate by dipolar exchange interaction, while the Rydberg\nblockade phenomenon naturally gives rise to a characteristic length scale,\nsuppressing the hopping on short distances. Then, the system becomes\nindependent of the atoms' spatial arrangement and can be described by a\ncontinuum model. We demonstrate the appearance of a topological band structure\nin the continuum characterized by a Chern number $C=2$ and show that edge\nstates appear at interfaces tunable by the atomic density.",
        "positive": "Fermions in 3D Optical Lattices: Cooling Protocol to Obtain\n  Antiferromagnetism: A major challenge in realizing antiferromagnetic (AF) and superfluid phases\nin optical lattices is the ability to cool fermions. We determine the equation\nof state for the 3D repulsive Fermi-Hubbard model as a function of the chemical\npotential, temperature and repulsion using unbiased determinantal quantum Monte\nCarlo methods, and we then use the local density approximation to model a\nharmonic trap. We show that increasing repulsion leads to cooling, but only in\na trap, due to the redistribution of entropy from the center to the metallic\nwings. Thus, even when the average entropy per particle is larger than that\nrequired for antiferromagnetism in the homogeneous system, the trap enables the\nformation of an AF Mott phase."
    },
    {
        "anchor": "A Strongly Dipolar Bose-Einstein Condensate of Dysprosium: We report the Bose-Einstein condensation (BEC) of the most magnetic atom,\ndysprosium. The Dy BEC is the first for an open f-shell lanthanide (rare-earth)\nelement and is produced via forced evaporation in a crossed optical dipole trap\nloaded by an unusual, blue-detuned and spin-polarized narrow-line\nmagneto-optical trap. Nearly pure condensates of 1.5x10^4 164Dy atoms form\nbelow T = 30 nK. We observe that stable BEC formation depends on the relative\nangle of a small polarizing magnetic field to the axis of the oblate trap, a\nproperty of trapped condensates only expected in the strongly dipolar regime.\nThis regime was heretofore only attainable in Cr BECs via a Feshbach resonance\naccessed at high magnetic field.",
        "positive": "Bound state dynamics in the long-range spin-$\\frac{1}{2}$ XXZ model: Experimental platforms based on trapped ions, cold molecules, and Rydberg\natoms have made possible the investigation of highly-nonlocal spin-${1/2}$\nHamiltonians with long-range couplings. Here, we study the effects of such\nnon-local couplings in the long-range spin-${1/2}$ XXZ Heisenberg Hamiltonian.\nWe calculate explicitly the two-spin energy spectrum, which describes all\npossible energetic configurations of two spins pointing in a specific direction\nembedded in a background of spins with opposite orientation. For fast decay of\nthe spin-spin couplings, we find that the two-spin energy spectrum is\ncharacterized by well-defined discrete values, corresponding to bound states,\nseparated by a set of continuum states describing the scattering region. In the\ndeep long-range regime instead, the bound states disappear as they get\nincorporated by the scattering region. The presence of two-spin bound states\nresults to be crucial to determine both two- and many-spin dynamics. On one\nhand, radically different two-spin spreadings can be observed by tuning the\ndecay of the spin couplings. On the other hand, two-spin bound states enable\nthe dynamical stabilization of effective antiferromagnetic states in the\npresence of ferromagnetic couplings. Finally, we propose a novel scheme based\non a trapped-ion quantum simulator to experimentally realize the long-range XXZ\nmodel and to study its out-of-equilibrium properties."
    },
    {
        "anchor": "Dynamical thermalization in Bose-Hubbard systems: We numerically study a Bose-Hubbard ring of finite size with disorder\ncontaining a finite number of bosons that are subject to an on-site two-body\ninteraction. Our results show that moderate interactions induce dynamical\nthermalization in this isolated system. In this regime the individual many-body\neigenstates are well described by the standard thermal Bose-Einstein\ndistribution for well-defined values of the temperature and the chemical\npotential which depend on the eigenstate under consideration. We show that the\ndynamical thermalization conjecture works well both at positive and negative\ntemperatures. The relations to quantum chaos, quantum ergodicity and to the\nAberg criterion are also discussed.",
        "positive": "Thermal field theory of bosonic gases with finite-range effective\n  interaction: We study a dilute and ultracold Bose gas of interacting atoms by using an\neffective field theory which takes account finite-range effects of the\ninter-atomic potential. Within the formalism of functional integration from the\ngrand canonical partition function we derive beyond-mean-field analytical\nresults which depend on both scattering length and effective range of the\ninteraction. In particular, we calculate the equation of state of the bosonic\nsystem as a function of these interaction parameters both at zero and finite\ntemperature including one-loop Gaussian fluctuation. In the case of zero-range\neffective interaction we explicitly show that, due to quantum fluctuations, the\nbosonic system is thermodynamically stable only for very small values of the\ngas parameter. We find that a positive effective range above a critical\nthreshold is necessary to remove the thermodynamical instability of the uniform\nconfiguration. Remarkably, also for relatively large values of the gas\nparameter, our finite-range results are in quite good agreement with recent\nzero-temperature Monte Carlo calculations obtained with hard-sphere bosons."
    },
    {
        "anchor": "Ultracold atoms in multiple-radiofrequency dressed adiabatic potentials: We present the first experimental demonstration of a multiple-radiofrequency\ndressed potential for the configurable magnetic confinement of ultracold atoms.\nWe load cold $^{87}$Rb atoms into a double well potential with an adjustable\nbarrier height, formed by three radiofrequencies applied to atoms in a static\nquadrupole magnetic field. Our multiple-radiofrequency approach gives precise\ncontrol over the double well characteristics, including the depth of individual\nwells and the height of the barrier, and enables reliable transfer of atoms\nbetween the available trapping geometries. We have characterised the\nmultiple-radiofrequency dressed system using radiofrequency spectroscopy,\nfinding good agreement with the eigenvalues numerically calculated using\nFloquet theory. This method creates trapping potentials that can be\nreconfigured by changing the amplitudes, polarizations and frequencies of the\napplied dressing fields, and easily extended with additional dressing\nfrequencies.",
        "positive": "Correspondence between a shaken honeycomb lattice and the Haldane model: We investigate the correspondence between the tight-binding Floquet\nHamiltonian of a periodically modulated honeycomb lattice and the Haldane\nmodel. We show that - though the two systems share the same topological phase\ndiagram, as reported in a breakthrough experiment with ultracold atoms in a\nstretched honeycomb lattice [Jotzu et al., Nature 515, 237 (2014)] - the\ncorresponding Hamiltonians are not equivalent, the one of the shaken lattice\npresenting a much richer structure."
    },
    {
        "anchor": "Quantum dynamics of impenetrable SU(N) fermions in one-dimensional\n  lattices: We study quantum quench dynamics in the Fermi-Hubbard model, and its SU($N$)\ngeneralizations, in one-dimensional lattices in the limit of infinite onsite\nrepulsion between all flavors. We consider families of initial states with\ngeneralized Neel order, namely, initial state in which there is a periodic\n$N$-spin pattern with consecutive fermions carrying distinct spin flavors. We\nintroduce an exact approach to describe the quantum evolution of those systems,\nand study two unique transient phenomena that occur during expansion dynamics\nin finite lattices. The first one is the dynamical emergence of Gaussian\none-body correlations during the melting of sharp (generalized) Neel domain\nwalls. Those correlations resemble the ones in the ground state of the SU($N$)\nmodel constrained to the same spin configurations. This is explained using an\nemergent eigenstate solution to the quantum dynamics. The second phenomenon is\nthe transformation of the quasimomentum distribution of the expanding strongly\ninteracting SU($N$) gas into the rapidity distribution after long times.\nFinally, we study equilibration in SU($N$) gasses and show that observables\nafter equilibration are described by a generalized Gibbs ensemble. Our approach\ncan be used to benchmark analytical and numerical calculations of dynamics of\nstrongly correlated SU($N$) fermions at large $U$.",
        "positive": "In situ imaging of vortices in Bose-Einstein condensates: Laboratory observations of vortex dynamics in Bose-Einstein condensates\n(BECs) are essential for determination of many aspects of superfluid dynamics\nin these systems. We present a novel application of dark-field imaging that\nenables \\texttt{\\it in situ} detection of two-dimensional vortex distributions\nin single-component BECs, a step towards real-time measurements of complex\ntwo-dimensional vortex dynamics within a single BEC. By rotating a $^{87}$Rb\nBEC in a magnetic trap, we generate a triangular lattice of vortex cores in the\nBEC, with core diameters on the order of 400 nm and cores separated by\napproximately 9 $\\mu$m. We have experimentally confirmed that the positions of\nthe vortex cores can be determined without the need for ballistic expansion of\nthe BEC."
    },
    {
        "anchor": "Drag-induced dynamical formation of dark solitons in Bose mixture on a\n  ring: Andreev-Bashkin drag plays a very important role in multiple areas like\nsuperfluid mixtures, superconductors and dense nuclear matter. Here, we point\nout that the drag phenomenon can be also important in physics of solitons,\nubiquitous objects arising in a wide array of fields ranging from tsunami waves\nand fiber-optic communication to biological systems. So far, fruitful studies\nwere conducted in ultracold atomic systems where nontrivial soliton dynamics\noccurred due to inter-component density-density interaction. In this work we\nshow that current-current coupling between components (Andreev-Bashkin drag)\ncan lead to a substantially different kind of effects, unsupported by\ndensity-density interactions, such as a drag-induced dark soliton generation.\nThis also points out that soliton dynamics can be used as a tool to\nexperimentally study the dissipationless drag effect.",
        "positive": "Analytical expression for a post-quench time evolution of the one-body\n  density matrix of one-dimensional hard-core bosons: We apply the logic of the quench action to give an exact analytical\nexpression for the time evolution of the one-body density matrix after an\ninteraction quench in the Lieb-Liniger model from the ground state of the free\ntheory (BEC state) to the infinitely repulsive regime. In this limit there\nexists a mapping between the bosonic wavefuntions and the free fermionic ones\nbut this does not help the computation of the one-body density matrix which is\nsensitive to particle statistics. The final expression, given in terms of the\ndifference of the square root of two Fredholm determinants, can be numerically\nevaluated and is valid in the thermodynamic limit and for all times after the\nquench."
    },
    {
        "anchor": "Phase diagram of the hardcore Bose-Hubbard model on a checkerboard\n  superlattice: We obtain the complete phase diagram of the hardcore Bose-Hubbard model in\nthe presence of a period-two superlattice in two and three dimensions. First we\nacquire the phase boundaries between the superfluid phase and the `trivial'\ninsulating phases of the model (the completely-empty and completely-filled\nlattices) analytically. Next, the boundary between the superfluid phase and the\nhalf-filled Mott-insulating phase is obtained numerically, using the stochastic\nseries expansion (SSE) algorithm followed by finite-size scaling. We also\ncompare our numerical results against the predictions of several approximation\nschemes, including two mean-field approaches and a fourth-order strong-coupling\nexpansion (SCE), where we show that the latter method in particular is\nsuccessful in producing an accurate picture of the phase diagram. Finally, we\nexamine the extent to which several approximation schemes, such as the random\nphase approximation and the strong-coupling expansion, give an accurate\ndescription of the momentum distribution of the bosons inside the insulating\nphases.",
        "positive": "Exact solitons and manifold mixing dynamics in the spin-orbit-coupled\n  spinor condensates: We derive exact static as well as moving solitonic solutions to the\none-dimensional spin-orbit-coupled F=1 Bose-Einstein condensates. The static\npolar soliton is shown to be the ground state by the imaginary-time evolution\nmethod. It shows a helical modulation of the order parameter due to the\nspin-orbit coupling. In particular, the moving soliton exhibits a periodic\noscillation among the particle numbers of the hyperfine states. We further\nexplore the temporal evolution of the static polar soliton and find that the\nspin-polarization exhibits dynamical oscillations. This disappearance and\nre-emergence of the ferromagnetic state indicates the mixing of the\nferromagnetic and the antiferromagnetic manifolds."
    },
    {
        "anchor": "Hamiltonian Learning in Quantum Field Theories: We discuss Hamiltonian learning in quantum field theories as a protocol for\nsystematically extracting the operator content and coupling constants of\neffective field theory Hamiltonians from experimental data. Learning the\nHamiltonian for varying spatial measurement resolutions gives access to field\ntheories at different energy scales, and allows to learn a flow of Hamiltonians\nreminiscent of the renormalization group. Our method, which we demonstrate in\nboth theoretical studies and available data from a quantum gas experiment,\npromises new ways of addressing the emergence of quantum field theories in\nquantum simulation experiments.",
        "positive": "Properties of a nematic spin vortex in an antiferromagnetic spin-1\n  Bose-Einstein condensate: A spin-1 condensate with antiferromagnetic interactions supports nematic spin\nvortices in the easy-plane polar phase. These vortices have a $2\\pi$ winding of\nthe nematic director, with a core structure that depends on the quadratic\nZeeman energy. We characterize the properties of the nematic spin vortex in a\nuniform quasi-two-dimensional system. We also obtain the vortex excitation\nspectrum and use it to quantify its stability against dissociating into two\nhalf-quantum vortices, finding a parameter regime where the nematic spin vortex\nis dynamically stable. These results are supported by full dynamical\nsimulations."
    },
    {
        "anchor": "Analytic calculation of high order corrections to quantum phase\n  transitions of ultracold Bose gases in bipartite superlattices: We clarify some technical issues in the present generalized\neffective-potential Landau theory (GEPLT) that makes the GEPLT more consistent\nand complete. Utilizing this clarified GEPLT, we analytically study the quantum\nphase transitions of ultracold Bose gases in bipartite superlattices at zero\ntermparture. The corresponding quantum phase boundaries are analytically\ncalculated up to the third-order hopping, which are in excellent agreement with\nthe quantum Monte Carlo (QMC) simulations.",
        "positive": "Probing quasi-particle states in strongly interacting atomic gases by\n  momentum-resolved Raman photoemission spectroscopy: We investigate a momentum-resolved Raman spectroscopy technique which is able\nto probe the one-body spectral function and the quasi-particle states of a gas\nof strongly interacting ultracold atoms. This technique is inspired by\nAngle-Resolved Photo-Emission Spectroscopy, a powerful experimental probe of\nelectronic states in solid-state systems. Quantitative examples of\nexperimentally accessible spectra are given for the most significant regimes\nalong the BEC-BCS crossover. When the theory is specialized to RF spectroscopy,\nagreement is found with recent experimental data. The main advantages of this\nRaman spectroscopy over existing techniques are pointed out."
    },
    {
        "anchor": "Observation of quantum droplets in a strongly dipolar Bose gas: Quantum fluctuations are the origin of genuine quantum many-body effects, and\ncan be neglected in classical mean-field phenomena. Here we report on the\nobservation of stable quantum droplets containing $\\sim$ 800 atoms which are\nexpected to collapse at the mean-field level due to the essentially attractive\ninteraction. By systematic measurements on individual droplets we demonstrate\nquantitatively that quantum fluctuations stabilize them against the mean-field\ncollapse. We observe in addition interference of several droplets indicating\nthat this stable many-body state is phase coherent.",
        "positive": "Quantum Noise Correlation Experiments with Ultracold Atoms: Noise correlation analysis is a detection tool for spatial structures and\nspatial correlations in the in-trap density distribution of ultracold atoms. In\nthis book chapter, we discuss the implementation, properties and limitations of\nthe method applied to ensembles of ultracold atoms in optical lattices, and\ndescribe some instances where it has been applied."
    },
    {
        "anchor": "Kinetics of mobile impurities and correlation functions in\n  one-dimensional superfluids at finite temperature: We scrutinize the hydrodynamic approach for calculating dynamical\ncorrelations in one-dimensional superfluids near integrability and calculate\nthe characteristic time scale {\\tau} beyond which this approach is valid. For\ntime scales shorter than {\\tau} hydrodynamics fails and we develop an approach\nbased on kinetics of fermionic quasiparticles described as mobile impurities.\nNew universal results for the dynamical structure factor relevant to\nexperiments in ultracold atomic gases are obtained.",
        "positive": "Probing Phase Fluctuations in a 2D Degenerate Bose Gas by Free Expansion: We measure the power spectrum of the density distribution of a freely\nexpanding 2D degenerate Bose gas, where irregular density modulations gradually\ndevelop due to the initial phase fluctuations in the sample. The spectrum has\nan oscillatory shape, where the peak positions are found to be independent of\ntemperature and show scaling behavior in the course of expansion. The relative\nintensity of phase fluctuations is estimated from the normalized spectral peak\nstrength and observed to decrease at lower temperatures, confirming the thermal\nnature of the phase fluctuations. We investigate the relaxation dynamics of\nnonequilibrium states using the power spectrum. Free vortices are observed with\nring-shaped density ripples in a perturbed sample after a long relaxation time."
    },
    {
        "anchor": "Singular and regular vortices on top of a background pulled to the\n  center: A recent analysis has revealed singular but physically relevant 2D localized\nvortex states with density ~ 1/r^{4/3} at r --> 0 and a convergent total norm,\nwhich are maintained by the interplay of the potential of the attraction to the\ncenter, ~ -1/r^2, and a self-repulsive quartic nonlinearity, produced by the\nLee-Huang-Yang correction to the mean-field dynamics of Bose-Einstein\ncondensates. In optics, a similar setting, with the density singularity ~ 1/r,\nis realized with the help of quintic self-defocusing. Here we present\nphysically relevant antidark singular-vortex states in these systems, existing\non top of a flat background. Numerical solutions for them are very accurately\napproximated by the Thomas-Fermi wave function. Their stability exactly obeys\nan analytical criterion derived for small perturbations. It is demonstrated\nthat the singular vortices can be excited by the input in the form of ordinary\nnonsingular vortices, hence the singular modes can be created in the\nexperiment. We also consider regular (dark) vortices maintained by the flat\nbackground, under the action of the repulsive central potential ~ +1/r^2. The\ndark modes with vorticities l = 0 and l = 1 are completely stable. In the case\nwhen the central potential is attractive, but the effective one, which includes\nthe centrifugal term, is repulsive, and a weak trapping potential ~ r^2 is\nadded, dark vortices with l = 1 feature an intricate pattern of alternating\nstability and instability regions. Under the action of the instability, states\nwith l = 1 travel along tangled trajectories, which stay in a finite area\ndefined by the trap. The analysis is also reported for dark vortices with l =\n2, which feature a complex structure of alternating intervals of stability and\ninstability against splitting. Lastly, simple but novel flat vortices are found\nat the border between the anidark and dark ones.",
        "positive": "A space-based quantum gas laboratory at picokelvin energy scales: Ultracold quantum gases are ideal sources for high-precision space-borne\nsensing as proposed for Earth observation, relativistic geodesy and tests of\nfundamental physical laws as well as for studying new phenomena in many-body\nphysics extended free fall. By performing experiments with the Cold Atom Lab\naboard the International Space Station, we have achieved exquisite control over\nthe quantum state of single Bose-Einstein condensates paving the way for future\nhigh-precision measurements. In particular, we have applied fast transport\nprotocols to shuttle the atomic cloud over a millimeter distance with\nsub-micrometer accuracy and subsequently drastically reduced the total\nexpansion energy to below 100 pK with matterwave lensing techniques."
    },
    {
        "anchor": "Photon-Induced Spin-Orbit Coupling in Ultracold Atoms inside Optical\n  Cavity: We consider an atom inside a ring cavity, where a plane-wave cavity field\ntogether with an external coherent laser beam induces a two-photon Raman\ntransition between two hyperfine ground states of the atom. This\ncavity-assisted Raman transition induces effective coupling between atom's\ninternal degrees of freedom and its center-of-mass motion. In~the meantime,\natomic dynamics exerts a back-action to cavity photons. We investigate the\nproperties of this system by adopting a mean-field and a full quantum approach,\nand show that the interplay between the atomic dynamics and the cavity field\ngives rise to intriguing nonlinear phenomena.",
        "positive": "Sub-unity superfluid fraction of a supersolid from self-induced\n  Josephson effect: Recently, a new category of superfluids and superconductors has been\ndiscovered in various systems. These could be linked to the idea of a\nsupersolid phase, featuring a macroscopic wavefunction with spatial modulation\nresulting from simultaneous, spontaneous breaking of gauge and translational\nsymmetries. However, this relation has only been recognized in some cases and\nthere is the need for universal properties quantifying the differences between\nsupersolids and ordinary superfluids/superconductors or crystals. A key\nproperty is the superfluid fraction, which measures the reduction in superfluid\nstiffness due to spatial modulation, leading to the non-standard superfluid\ndynamics of supersolids. Here we employ the Josephson effect, common in\nsuperfluids and superconductors, to measure the superfluid fraction in a\nsupersolid. Even without a physical barrier, the Josephson effect arises\nspontaneously in a supersolid due to spatial modulation. Individual lattice\ncells act as self-induced Josephson junctions, allowing the direct\ndetermination of the local superfluid fraction. We studied a cold-atom dipolar\nsupersolid, revealing a significant sub-unity superfluid fraction. Our results\nopen new research directions, enabling the exploration of novel phenomena like\npartially quantized vortices and supercurrents, potentially unifying the\nunderstanding of supersolid-like systems, and introducing a new type of\nJosephson junction."
    },
    {
        "anchor": "Synthetic magnetism for photon fluids: We develop a theory of artificial gauge fields in photon fluids for the cases\nof both second-order and third-order optical nonlinearities. This applies to\nweak excitations in the presence of pump fields carrying orbital angular\nmomentum, and is thus a type of Bogoliubov theory. The resulting artificial\ngauge fields experienced by the weak excitations are an interesting\ngeneralization of previous cases and reflect the PT-symmetry properties of the\nunderlying non-Hermitian Hamiltonian. We illustrate the observable consequences\nof the resulting synthetic magnetic fields for examples involving both\nsecond-order and third-order nonlinearities.",
        "positive": "Scalable, ab initio protocol for quantum simulating SU($N$)$\\times$U(1)\n  Lattice Gauge Theories: We propose a protocol for the scalable quantum simulation of\nSU($N$)$\\times$U(1) lattice gauge theories with alkaline-earth like atoms in\noptical lattices in both one- and two-dimensional systems. The protocol\nexploits the combination of naturally occurring SU($N$) pseudo-spin symmetry\nand strong inter-orbital interactions that is unique to such atomic species. A\ndetailed ab initio study of the microscopic dynamics shows how gauge invariance\nemerges in an accessible parameter regime, and allows us to identify the main\nchallenges in the simulation of such theories. We provide quantitative results\nabout the requirements in terms of experimental stability in relation to\nobserving gauge invariant dynamics, a key element for a deeper analysis on the\nfunctioning of such class of theories in both quantum simulators and computers."
    },
    {
        "anchor": "Majorana-Like Modes of Light in a One-Dimensional Array of Nonlinear\n  Cavities: The search for Majorana fermions in p-wave paired fermionic systems has\nrecently moved to the forefront of condensed-matter research. Here we propose\nan alternative route and show theoretically that Majorana-like modes can be\nrealized and probed in a driven-dissipative system of strongly correlated\nphotons consisting of a chain of tunnel-coupled cavities, where p-wave pairing\neffectively arises from the interplay between strong on-site interactions and\ntwo-photon parametric driving. The nonlocal nature of these exotic modes could\nbe demonstrated through cross-correlation measurements carried out at the ends\nof the chain---revealing a strong photon bunching signature---and their\nnon-Abelian properties could be simulated through tunnel-braid operations.",
        "positive": "Center motions of nonoverlapping condensates coupled by long-range\n  dipolar interaction in bilayer and multilayer stacks: We investigate the effect of anisotropic and long-range dipole-dipole\ninteraction (DDI) on the center motions of nonoverlapping Bose-Einstein\ncondensates (BEC) in bilayer and multilayer stacks. In the bilayer, it is shown\nanalytically that while DDI plays no role in the in-phase modes of center\nmotions of condensates, out-of-phase mode frequency ($\\omega_o$) depends\ncrucially on the strength of DDI ($a_d$). At the small-$a_d$ limit,\n$\\omega_o^2(a_d)-\\omega_o^2(0)\\propto a_d$. In the multilayer stack, transverse\nmodes associated with center motions of coupled condensates are found to be\noptical phonon like. At the long-wavelength limit, phonon velocity is\nproportional to $\\sqrt a_d$."
    },
    {
        "anchor": "Superfluid Vortices in Four Spatial Dimensions: Quantum vortices in superfluids have been an important research area for many\ndecades. Naturally, research on this topic has focused on two and\nthree-dimensional superfluids, in which vortex cores form points and lines,\nrespectively. Very recently, however, there has been growing interest in the\nquantum simulation of systems with four spatial dimensions; this raises the\nquestion of how vortices would behave in a higher-dimensional superfluid. In\nthis paper, we begin to establish the phenomenology of vortices in 4D\nsuperfluids under rotation, where the vortex core can form a plane. In 4D, the\nmost generic type of rotation is a \"double rotation\" with two angles (or\nfrequencies). We show, by solving the Gross-Pitaesvkii equation, that the\nsimplest case of equal-frequency double rotation can stabilise a pair of vortex\nplanes intersecting at a point. This opens up a wide number of future research\ntopics, including unequal-frequency double rotations; the stability and\nreconnection dynamics of intersecting vortex surfaces; and the possibility of\nclosed vortex surfaces.",
        "positive": "Universal scaling in a trapped Fermi super-fluid in the BCS-unitarity\n  crossover: Using numerical simulation based on a density-functional equation for a\ntrapped Fermi super-fluid valid along the BCS-unitarity crossover, we establish\nrobust scaling over many orders of magnitude in the observables of the system\nas a function of fermion number. This scaling allows to predict the static\nproperties of the system, such as energy, chemical potential, etc., for a large\nnumber of fermions, over the crossover, from the knowledge of those for a small\nnumber ($\\sim 4-10$) of fermions."
    },
    {
        "anchor": "The transition from Bose-Einstein condensate to supersolid states in\n  Rydberg-dressed gases beyond Bogoliubov approximation: In this paper, we study Bose-Einstein condensation of Rydberg-dressed atoms\nconsidering finite range interactions. We use Hartree-Fock-Bogoliubov\napproximation based on Mean-Field approach. Moreover, within this approximation\nmodified by the finite-range character of the two-body interaction we shall\nobtain analytical expressions for thermodynamic quantities of Rydberg-dressed\nBose gas. The imaginary part of the quasiparticle spectrum of a BEC signals the\ninstability of the roton mode with respect to the formation of supersolid\nstate. Our theory predicts a second-order quantum phase transition from BEC to\nsupersolid phase for Rydberg-dressed bosons in three dimensions.",
        "positive": "Dielectric response of electron-hole systems. Nondegenerate case and\n  quantum corrections: Analytical results for the dielectric function in RPA are derived for three-,\ntwo-, and one-dimensional semiconductors in the weakly-degenerate limit. Based\non this limit, quantum corrections are derived. Further attention is devoted to\nsystems with linear carrier dispersion and the resulting Dirac-cone physics."
    },
    {
        "anchor": "Double universality of a quantum phase transition in spinor condensates:\n  the Kibble-\u017burek mechanism and a conservation law: We consider a phase transition from antiferromagnetic to phase separated\nground state in a spin-1 Bose-Einstein condensate of ultracold atoms. We\ndemonstrate the occurrence of two scaling laws, for the number of spin\nfluctuations just after the phase transition, and for the number of spin\ndomains in the final, stable configuration. Only the first scaling can be\nexplained by the standard Kibble-\\.Zurek mechanism. We explain the occurrence\nof two scaling laws by a model including post-selection of spin domains due to\nthe conservation of condensate magnetization.",
        "positive": "Quantum-optical magnets with competing short- and long-range\n  interactions: Rydberg-dressed spin lattice in an optical cavity: The fields of quantum simulation with cold atoms [1] and quantum optics [2]\nare currently being merged. In a set of recent pathbreaking experiments with\natoms in optical cavities [3,4] lattice quantum many-body systems with both, a\nshort-range interaction and a strong interaction potential of infinite range\n-mediated by a quantized optical light field- were realized. A theoretical\nmodelling of these systems faces considerable complexity at the interface of:\n(i) spontaneous symmetry-breaking and emergent phases of interacting many-body\nsystems with a large number of atoms $N\\rightarrow\\infty$, (ii) quantum optics\nand the dynamics of fluctuating light fields, and (iii) non-equilibrium physics\nof driven, open quantum systems. Here we propose what is possibly the simplest,\nquantum-optical magnet with competing short- and long-range interactions, in\nwhich all three elements can be analyzed comprehensively: a Rydberg-dressed\nspin lattice [5] coherently coupled to a single photon mode. Solving a set of\ncoupled even-odd sublattice Master equations for atomic spin and photon\nmean-field amplitudes, we find three key results. (R1): Superradiance and a\ncoherent photon field can coexist with spontaneously broken magnetic\ntranslation symmetry. The latter is induced by the short-range nearest-neighbor\ninteraction from weakly admixed Rydberg levels. (R2): This broken even-odd\nsublattice symmetry leaves its imprint in the light via a novel peak in the\ncavity spectrum beyond the conventional polariton modes. (R3): The combined\neffect of atomic spontaneous emission, drive, and interactions can lead to\nphases with anomalous photon number oscillations. Extensions of our work\ninclude nano-photonic crystals coupled to interacting atoms and multi-mode\nphoton dynamics in Rydberg systems."
    },
    {
        "anchor": "Supersolid and pair correlations of the extended Jaynes-Cummings-Hubbard\n  model on triangular lattices: We study the extended Jaynes-Cummings-Hubbard model on triangular cavity\nlattices and zigzag ladders. By using density-matrix renormalization group\nmethods, we observe various types of solids with different density patterns and\nfind evidence for light supersolids, which exist in extended regions of the\nphase diagram of the zigzag ladder. Furthermore, we observe strong pair\ncorrelations in the supersolid phase due to the interplay between the atoms in\nthe cavities and atom-photon interaction. By means of cluster mean-field\nsimulations and a scaling of the cluster size extending our analysis to\ntwo-dimensional triangular lattices, we present evidence for the emergence of a\nlight supersolid in this case also.",
        "positive": "Tan's contact and the phase distribution of repulsive Fermi gases:\n  Insights from QCD noise analyses: Path-integral analyses originally pioneered in the study of the complex-phase\nproblem afflicting lattice calculations of finite-density quantum\nchromodynamics are generalized to non-relativistic Fermi gases with repulsive\ninteractions. Using arguments similar to those previously applied to\nrelativistic theories, we show that the analogous problem in nonrelativistic\nsystems manifests itself naturally in Tan's contact as a nontrivial\ncancellation between terms with varied dependence on extensive thermodynamic\nquantities. We analyze that case under the assumption of gaussian phase\ndistribution, which is supported by our Monte Carlo calculations and\nperturbative considerations. We further generalize these results to observables\nother than the contact, as well as to polarized systems and systems with fixed\nparticle number. Our results are quite general in that they apply to repulsive\nmulti-component fermions, are independent of dimensionality or trapping\npotential, and hold in the ground state as well as at finite temperature."
    },
    {
        "anchor": "Nonadiabatic Diffraction of Matter Waves: Diffraction phenomena usually can be formulated in terms of a potential that\ninduces the redistribution of a wave's momentum. Using an atomic Bose-Einstein\ncondensate coupled to the orbitals of a state-selective optical lattice, we\ninvestigate a hitherto unexplored nonadiabatic regime of diffraction in which\nno diffracting potential can be defined, and in which the adiabatic dressed\nstates are strongly mixed. We show how, in the adiabatic limit, the observed\ncoupling between internal and external dynamics gives way to standard\nKapitza-Dirac diffraction of atomic matter waves. We demonstrate the utility of\nour scheme for atom interferometry and discuss prospects for studies of\ndissipative superfluid phenomena.",
        "positive": "Many-body localization in XY spin chains with long-range interactions:\n  An exact diagonalization study: We investigate the transition from the many-body localized phase to the\nergodic thermalized phase at an infinite temperature in an $XY$ spin chain with\n$L$ spins, which experiences power-law decaying interactions in the form of\n$V_{ij}\\propto1/\\left|i-j\\right|^{\\alpha}$ ($i,j=1,\\cdots,L$) and a random\ntransverse field. By performing large-scale exact diagonalization for the chain\nsize up to $L=18$, we systematically analyze the energy gap statistics,\nhalf-chain entanglement entropy, and uncertainty of the entanglement entropy of\nthe system at different interaction exponents $\\alpha$. The finite-size\ncritical scaling allows us to determine the critical disorder strength $W_{c}$\nand critical exponent $\\nu$ at the many-body localization phase transition, as\na function of the interaction exponent $\\alpha$ in the limit\n$L\\rightarrow\\infty$. We find that both $W_{c}$ and $\\nu$ diverge when $\\alpha$\ndecreases to a critical power $\\alpha_{c}\\simeq1.16\\pm0.17$, indicating the\nabsence of many-body localization for $\\alpha<\\alpha_{c}$. Our result is useful\nto resolve the contradiction on the critical power found in two previous\nstudies, $\\alpha_{c}=3/2$ from scaling argument in Phys. Rev. B \\textbf{92},\n104428 (2015) and $\\alpha_{c}\\approx1$ from quantum dynamics simulation in\nPhys. Rev. A \\textbf{99}, 033610 (2019)."
    },
    {
        "anchor": "Collective emission of matter-wave jets from driven Bose-Einstein\n  condensates: Scattering is an elementary probe for matter and its interactions in all\nareas of physics. Ultracold atomic gases provide a powerful platform in which\ncontrol over pair-wise interactions empowers us to investigate scattering in\nquantum many-body systems. Past experiments on colliding Bose-Einstein\ncondensates have revealed many important features, including matter-wave\ninterference, halos of scattered atoms, four-wave mixing, and correlations\nbetween counter-propagating pairs. However, a regime with strong stimulation of\nspontaneous collisions analogous to superradiance has proven elusive. Here we\naccess that regime, finding that runaway stimulated collisions in condensates\nwith modulated interaction strength cause the emission of matter-wave jets\nwhich resemble fireworks. Jets appear only above a threshold modulation\namplitude and their correlations are invariant even as the ejected atom number\ngrows exponentially. Hence, we show that the structures and occupations of the\njets stem from the quantum fluctuations of the condensate. Our findings\ndemonstrate the conditions for runaway stimulated collisions and reveal the\nquantum nature of the matter-wave emission.",
        "positive": "Systematic corrections to the Thomas-Fermi approximation without a\n  gradient expansion: We improve on the Thomas-Fermi approximation for the single-particle density\nof fermions by introducing inhomogeneity corrections. Rather than invoking a\ngradient expansion, we relate the density to the unitary evolution operator for\nthe given effective potential energy and approximate this operator by a\nSuzuki-Trotter factorization. This yields a hierarchy of approximations, one\nfor each approximate factorization. For the purpose of a first benchmarking, we\nexamine the approximate densities for a few cases with known exact densities\nand observe a very satisfactory, and encouraging, performance. As a bonus, we\nalso obtain a simple fourth-order leapfrog algorithm for the symplectic\nintegration of classical equations of motion."
    },
    {
        "anchor": "Diagrammatic Monte Carlo algorithm for the resonant Fermi gas: We provide a description of a diagrammatic Monte Carlo algorithm for the\nresonant Fermi gas in the normal phase. Details are given on diagrammatic\nframework, Monte Carlo moves, and incorporation of ultraviolet asymptotics.\nApart from the self-consistent bold scheme, we also describe a\nnon-self-consistent scheme, for which the ultraviolet treatment is more\ninvolved.",
        "positive": "Thermalization and Sub-Poissonian Density Fluctuations in a Degenerate\n  Molecular Fermi Gas: We observe thermalization in the production of a degenerate Fermi gas of\npolar ${}^{40}\\text{K}{}^{87}\\text{Rb}$ molecules. By measuring the atom--dimer\nelastic scattering cross section near the Feshbach resonance, we show that\nFeshbach molecules rapidly reach thermal equilibrium with both parent atomic\nspecies. Equilibrium is essentially maintained through coherent transfer to the\nground state. Sub-Poissonian density fluctuations in Feshbach and ground-state\nmolecules are measured, giving an independent characterization of degeneracy\nand directly probing the molecular Fermi--Dirac distribution."
    },
    {
        "anchor": "Prethermalization and Thermalization of a Quenched Interacting Luttinger\n  Liquid: We study the relaxation dynamics of interacting, one-dimensional fermions\nwith band curvature after a weak quench in the interaction parameter. After the\nquench, the system is described by a non-equilibrium initial state, which\nrelaxes towards thermal equilibrium, featuring prethermal behavior on\nintermediate time and length scales. The model corresponds to the class of\ninteracting Luttinger Liquids, which extends the quadratic Luttinger theory by\na weak integrability breaking phonon scattering term. In order to solve for the\nnon-equilibrium time evolution, we use kinetic equations for the phonon\ndensities, exploiting the resonant but subleading character of the phonon\ninteraction term. The interplay between phonon scattering and the quadratic\nLuttinger theory leads to the emergence of three distinct spatio-temporal\nregimes for the fermionic real-space correlation function. It features the\ncrossover from a prequench to a prethermal state, finally evolving towards a\nthermal state on increasing length and time scales. The characteristic\nalgebraically decaying real-space correlations in the prethermalized regime\nbecome modulated by an amplitude, which, as an effect of the interactions, is\ndecaying in time according to a stretched-exponential, while in the thermal\nregime exponentially decaying real-space correlations emerge. The asymptotic\nthermalization dynamics is governed by energy transport over large distances\nfrom the thermalized to the non-thermalized regions, which is carried out by\nmacroscopic, dynamical slow modes. This is revealed in an algebraic decay of\nthe system's effective temperature. The numerical value of the associated\nexponent agrees with the dynamical critical exponent of the Kardar-Parisi-Zhang\nuniversality class, which shares with the present interacting Luttinger Liquid\nthe conservation of total energy and momentum.",
        "positive": "Random-field-induced order in bosonic t-J model: In the present paper, we shall study effect of a random quenched external\nfield for spin order and also multiple Bose-Einstein condensation (BEC). This\nsystem is realized by the cold atomic gases in an optical lattice. In\nparticular, we are interested in the strong-repulsion region of two-component\ngases for which the bosonic t-J model is a good effective model. In the bosonic\nt-J model, a long-range order of the pseudo-spin and also BEC of atoms appear\nquite naturally as in the fermion t-J model for the high-temperature\nsuperconducting materials. Random Raman scattering between two internal states\nof a single atom plays a role of the random external field, and we study its\neffects on the pseudo-spin order and the BEC by means of quantum Monte-Carlo\nsimulations. The random external field breaks a continuous U(1) symmetry\nexisting in the original bosonic t-J model and it induces new orders named\nrandom-field-induced order (RFIO). We show a phase diagram of the bosonic t-J\nmodel with the random external magnetic field and study the robustness of the\nRFIO states. We also study topological excitations like vortices and domain\nwall in the RFIO state. Finally we point out the possibility of a quantum bit\nby the RFIO."
    },
    {
        "anchor": "Pairing in a two-dimensional Fermi gas with population imbalance: Pairing in a population imbalanced Fermi system in a two-dimensional optical\nlattice is studied using Determinant Quantum Monte Carlo (DQMC) simulations and\nmean-field calculations. The approximation-free numerical results show a wide\nrange of stability of the Fulde-Ferrell-Larkin-Ovshinnikov (FFLO) phase.\nContrary to claims of fragility with increased dimensionality we find that this\nphase is stable across wide range of values for the polarization, temperature\nand interaction strength. Both homogeneous and harmonically trapped systems\ndisplay pairing with finite center of mass momentum, with clear signatures\neither in momentum space or real space, which could be observed in cold atomic\ngases loaded in an optical lattice. We also use the harmonic level basis in the\nconfined system and find that pairs can form between particles occupying\ndifferent levels which can be seen as the analog of the finite center of mass\nmomentum pairing in the translationally invariant case. Finally, we perform\nmean field calculations for the uniform and confined systems and show the\nresults to be in good agreement with QMC. This leads to a simple picture of the\ndifferent pairing mechanisms, depending on the filling and confining potential.",
        "positive": "Superfluidity and Density Order in a Bilayer Extended Hubbard Model: We use cluster dynamical mean field theory to study the phase diagram of the\nsquare lattice bilayer Hubbard model with an interlayer interaction. The layers\nare populated by two-component fermions, and the densities in both layers and\nthe strength of the interactions are varied. We find that an attractive\ninterlayer interaction can induce a checkerboard density ordered phase and\nsuperfluid phases, with either interlayer or intralayer pairing. Remarkably,\nthe latter phase does not require an intralayer interaction to be present: it\ncan be attributed to an induced attractive interaction caused by density\nfluctuations in the other layer."
    },
    {
        "anchor": "Mapping out the quasi-condensate transition through the 1D-3D\n  dimensional crossover: By measuring the density fluctuations in a highly elongated weakly\ninteracting Bose gas, we observe and quantify the transition from the ideal gas\nto a quasi-condensate regime throughout the dimensional crossover from a purely\n1D to an almost 3D gas. We show that that the entire transition region and the\ndimensional crossover are described surprisingly well by the modified Yang-Yang\nmodel. Furthermore, we find that at low temperatures the linear density at the\nquasi-condensate transition scales according to an interaction-driven scenario\nof a longitudinally uniform 1D Bose gas, whereas at high temperatures it scales\naccording to the degeneracy-driven critical scenario of transverse condensation\nof a 3D ideal gas.",
        "positive": "Resummation of diagrammatic series with zero convergence radius for\n  strongly correlated fermions: We demonstrate that summing up series of Feynman diagrams can yield unbiased\naccurate results for strongly-correlated fermions even when the convergence\nradius vanishes. We consider the unitary Fermi gas, a model of non-relativistic\nfermions in three-dimensional continuous space. Diagrams are built from\npartially-dressed or fully-dressed propagators of single particles and pairs.\nThe series is resummed by a conformal-Borel transformation that incorporates\nthe large-order behavior and the analytic structure in the Borel plane, which\nare found by the instanton approach. We report highly accurate numerical\nresults for the equation of state in the normal unpolarized regime, and\nreconcile experimental data with the theoretically conjectured fourth virial\ncoefficient."
    },
    {
        "anchor": "Observation of Fermi surface deformation in a dipolar quantum gas: The deformation of a Fermi surface is a fundamental phenomenon leading to a\nplethora of exotic quantum phases. Understanding these phases, which play\ncrucial roles in a wealth of systems, is a major challenge in atomic and\ncondensed-matter physics. Here, we report on the observation of a Fermi surface\ndeformation in a degenerate dipolar Fermi gas of erbium atoms. The deformation\nis caused by the interplay between strong magnetic dipole-dipole interaction\nand the Pauli exclusion principle. We demonstrate the many-body nature of the\neffect and its tunability with the Fermi energy. Our observation provides basis\nfor future studies on anisotropic many-body phenomena in normal and superfluid\nphases.",
        "positive": "Bose-Hubbard ladder subject to effective magnetic field: quench dynamics\n  in a harmonic trap: Motivated by a recent experiment with optical lattices that has realized a\nladder geometry with an effective magnetic field (Atala et al., Nature Physics\n\\textbf{10}, 588 (2014)), we study the dynamics of bosons on a tight-binding\ntwo-leg ladder with complex hopping amplitudes. This system displays a quantum\nphase transition even without interactions. We study the non-equilibrium\ndynamics without and with interactions, in the presence of a harmonic trapping\npotential. In particular we consider dynamics induced by quenches of the\ntrapping potential and of the magnitude of the rung hopping. We present a\nstriking \"slowing down\" effect in the collective mode dynamics near the phase\ntransition. This manifestation of a slowing down phenomenon near a quantum\nphase transition can be visualized unusually directly: the collective mode\ndynamics can be followed experimentally in real time and real space by imaging\nthe atomic cloud."
    },
    {
        "anchor": "Predicting Bubble Fragmentation in Superfluids: In classical fluids, the Weber number is a dimensionless parameter that\ncharacterises the flow of a multi-phase fluid. The superfluid analogy of a\nclassical multi-phase fluid can be realised in a system of two or more\nimmiscible Bose-Einstein condensates. These superfluid mixtures have been shown\nto display a wider variety of exotic dynamics than their single component\ncounterparts. Here we systematically study the dynamics of a binary immiscible\nBose-Einstein Condensate in two dimensions, where a small bubble of the second\ncomponent is used to \"stir\" the first component. We begin by rigorously mapping\nout the critical velocity for vortex shedding as a function of the size of the\nbubble, in analogy to the critical velocity of a laser spoon. Observing that\nthe dynamics of the system depend on the initial size and velocity of the\nbubble, we then show that a dimensionless parameter with the same form as the\nWeber number accurately predicts the resulting bubble fragmentation.",
        "positive": "Chaos-assisted Turbulence in Spinor Bose-Einstein Condensates: We present a turbulence-sustaining mechanism in a spinor Bose-Einstein\ncondensate, which is based on the chaotic nature of internal spin dynamics.\nMagnetic driving induces a complete chaotic evolution of the local spin state,\nthereby continuously randomizing the spin texture of the condensate to maintain\nthe turbulent state. We experimentally demonstrate the onset of turbulence in\nthe driven condensate as the driving frequency changes and show that it is\nconsistent with the regular-to-chaotic transition of the local spin dynamics.\nThis chaos-assisted turbulence establishes the spin-driven spinor condensate as\nan intriguing platform for exploring quantum chaos and related superfluid\nturbulence phenomena."
    },
    {
        "anchor": "Decoherence effects in Bose-Einstein condensate interferometry. I\n  General Theory: The present paper outlines a basic theoretical treatment of decoherence and\ndephasing effects in interferometry based on single component BEC in double\npotential wells, where two condensate modes may be involved. Results for both\ntwo mode condensates and the simpler single mode condensate case are presented.\nA hybrid phase space distribution functional method is used where the\ncondensate modes are described via a truncated Wigner representation, and the\nbasically unoccupied non-condensate modes are described via a positive P\nrepresentation. The Hamiltonian for the system is described in terms of quantum\nfield operators for the condensate and non-condensate modes. The functional\nFokker-Planck equation for the double phase space distribution functional is\nderived. Equivalent Ito stochastic equations for the condensate and\nnon-condensate fields that replace the field operators are obtained, and\nstochastic averages of products of these fields give the quantum correlation\nfunctions used to interpret interferometry experiments. The stochastic field\nequations are the sum of a deterministic term obtained from the drift vector in\nthe functional Fokker-Planck equation, and a noise field whose stochastic\nproperties are determined from the diffusion matrix in the functional\nFokker-Planck equation. The noise field stochastic properties are similar to\nthose for Gaussian-Markov processes in that the stochastic averages of odd\nnumbers of noise fields are zero and those for even numbers of noise field\nterms are sums of products of stochastic averages associated with pairs of\nnoise fields. However each pair is represented by an element of the diffusion\nmatrix rather than products of the noise fields themselves. The treatment\nstarts from a generalised mean field theory for two condensate mode. The\ngeneralized mean field theory solutions are needed for calculations using the\nIto stochastic field equations.",
        "positive": "Capturing the re-entrant behaviour of one-dimensional Bose-Hubbard model: The Bose Hubbard model (BHM) is an archetypal quantum lattice system\nexhibiting a quantum phase transition between its superfluid (SF) and\nMott-insulator (MI) phase. Unlike in higher dimensions the phase diagram of the\nBHM in one dimension possesses regions in which increasing the hopping\namplitude can result in a transition from MI to SF and then back to a MI. This\ntype of re-entrance is well known in classical systems like liquid crystals yet\nits origin in quantum systems is still not well understood. Moreover, this\nunusual re-entrant character of the BHM is not easily captured in approximate\nanalytical or numerical calculations. Here we study in detail the predictions\nof three different and widely used approximations; a multi-site mean-field\ndecoupling, a finite-sized cluster calculation, and a real-space\nrenormalization group (RG) approach. It is found that mean-field calculations\ndo not reproduce re-entrance while finite-sized clusters display a precursor to\nre-entrance. Here we show for the first time that RG does capture the\nre-entrant feature and constitutes one of the simplest approximation able to do\nso. The differing abilities of these approaches reveals the importance of\ndescribing short-ranged correlations relevant to the kinetic energy of a MI in\na particle-number symmetric way."
    },
    {
        "anchor": "Heating and many-body resonances in a periodically driven two-band\n  system: We study the dynamics and stability in a strongly interacting resonantly\ndriven two-band model. Using exact numerical simulations, we find a stable\nregime at large driving frequencies where the time evolution is governed by a\nlocal Floquet Hamiltonian that is approximately conserved out to very long\ntimes. For slow driving, on the other hand, the system becomes unstable and\nheats up to infinite temperature. While thermalization is relatively fast in\nthese two regimes (but to different \"temperatures\"), in the crossover between\nthem we find slow nonthermalizing time evolution: temporal fluctuations become\nstrong and temporal correlations long lived. Microscopically, we trace back the\norigin of this nonthermalizing time evolution to the properties of rare Floquet\nmany-body resonances, whose proliferation at lower driving frequency removes\nthe approximate energy conservation, and thus produces thermalization to\ninfinite temperature.",
        "positive": "One-dimensional spin-1/2 fermionic gases with two-body losses: weak\n  dissipation and spin conservation: We present a theoretical analysis of the dynamics of a one-dimensional\nspin-1/2 fermionic gas subject to weak two-body losses. Our approach highlights\nthe crucial role played by spin conservation in the determination of the full\ntime evolution. We focus in particular on the dynamics of a gas that is\ninitially prepared in a Dicke state with fully-symmetric spin wavefunction, in\na band insulator, or in a Mott insulator. In the latter case, we investigate\nthe emergence of a steady symmetry-resolved purification of the gas. Our\nresults could help the modelisation and understanding of recent experiments\nwith alkaline-earth(-like) gases like ytterbium or fermionic molecules."
    },
    {
        "anchor": "Observation of superfluidity in a strongly correlated two-dimensional\n  Fermi gas: Understanding how strongly correlated two-dimensional (2D) systems can give\nrise to unconventional superconductivity with high critical temperatures is one\nof the major unsolved problems in condensed matter physics. Ultracold 2D Fermi\ngases have emerged as clean and controllable model systems to study the\ninterplay of strong correlations and reduced dimensionality, but direct\nevidence of superfluidity in these systems has been missing. Here, we\ndemonstrate superfluidity in an ultracold 2D Fermi gas by moving a periodic\npotential through the system and observing no dissipation below a critical\nvelocity v$_{\\rm c}$. We measure v$_{\\rm c}$ as a function of interaction\nstrength and find a maximum in the crossover regime between bosonic and\nfermionic superfluidity. Our measurement establishes ultracold Fermi gases as a\npowerful tool for studying the influence of reduced dimensionality on strongly\ncorrelated superfluids.",
        "positive": "Polarons in a Dipolar Condensate: We consider a polaronic model in which impurity fermions interact with\nbackground bosons in a dipolar condensate. The polaron in this model emerges as\nan impurity dressed with a cloud of phonons of the dipolar condensate, which,\ndue to the competition between the attractive and repulsive part of the\ndipole-dipole interaction, obey an anisotropic dispersion spectrum. We study\nhow this anisotropy affects the Cerenkov-like emission of Bogoliubov phonon\nmodes, which can be directly verified by experiments in which a dipolar BEC\nmoves against an obstacle. We also study the spectral function of impurity\nfermions, which is directly accessible to the momentum resolved rf spectroscopy\nin cold atoms."
    },
    {
        "anchor": "Suppression of Unitary Three-body Loss in a Degenerate Bose-Fermi\n  Mixture: We study three-body loss in an ultracold mixture of a thermal Bose gas and a\ndegenerate Fermi gas. We find that at unitarity, where the interspecies\nscattering length diverges, the usual inverse-square temperature scaling of the\nthree-body loss found in non-degenerate systems is strongly modified and\nreduced with the increasing degeneracy of the Fermi gas. While the reduction of\nloss is qualitatively explained within the few-body scattering framework, a\nremaining suppression provides evidence for the long-range RKKY interactions\nmediated by fermions between bosons. Our model based on RKKY interactions\nquantitatively reproduces the data without free parameters, and predicts one\norder of magnitude reduction of the three-body loss coefficient in the deeply\nFermi-degenerate regime.",
        "positive": "Majorana Modes in Driven-Dissipative Atomic Superfluids With Zero Chern\n  Number: We investigate dissipation-induced p-wave paired states of fermions in two\ndimensions and show the existence of spatially separated Majorana zero modes in\na phase with vanishing Chern number. We construct an explicit and natural model\nof a dissipative vortex that traps a single of these modes, and establish its\ntopological origin by mapping the problem to a chiral one-dimensional wire\nwhere we observe a non-equilibrium topological phase transition characterized\nby an abrupt change of a topological invariant (winding number). We show that\nthe existence of a single Majorana zero mode in the vortex core is intimately\ntied to the dissipative nature of our model. Engineered dissipation opens up\npossibilities for experimentally realizing such states with no Hamiltonian\ncounterpart."
    },
    {
        "anchor": "Finite Temperature Phases of Two Dimensional Spin-Orbit Coupled Bosons: We determine the finite temperature phase diagram of two dimensional bosons\nwith two hyperfine (pseudo-spin) states coupled via Rashba-Dresselhaus\nspin-orbit interaction using classical field Monte Carlo calculations. For\nanisotropic spin-orbit coupling, we find a transition to a\nBerenzinskii-Kosterlitz-Thouless superfluid phase with quasi-long range order.\nWe show that the spin-order of the quasi-condensate is driven by the anisotropy\nof interparticle interaction, favoring either a homogeneous plane wave state or\nstripe phase with broken translational symmetry. Both phases show\ncharacteristic behavior in the algebraically decaying spin density correlation\nfunction. For fully isotropic interparticle interaction, our calculations\nindicate a fractionalized quasi-condensate where the mean-field degeneracy of\nplane wave and stripe phase remains robust against critical fluctuations. In\nthe case of fully isotropic spin-orbit coupling, the circular degeneracy of the\nsingle particle ground state destroys the algebraic ordered phase in the\nthermodynamic limit, but a cross-over remains for finite size systems.",
        "positive": "High Order Momentum Modes by Resonant Superradiant Scattering: The spatial and time evolutions of superradiant scattering are studied\ntheoretically for a weak pump beam with different frequency components\ntraveling along the long axis of an elongated Bose-Einstein condensate.\nResulting from the analysis for mode competition between the different resonant\nchannels and the local depletion of the spatial distribution in the\nsuperradiant Rayleigh scattering, a new method of getting a large number of\nhigh-order forward modes by resonant frequency components of the pump beam is\nprovided, which is beneficial to a lager momentum transfer in atom manipulation\nfor the atom interferometry and atomic optics."
    },
    {
        "anchor": "Universal Properties of Anisotropic Dipolar Bosons in Two Dimensions: The energy of ultra-dilute quantum many-body systems is known to exhibit a\nuniversal dependence on the gas parameter $x=n a_0^d$, with $n$ the density,\n$d$ the dimensionality of the space ($d=1,2,3$) and $a_0$ the $s$-wave\nscattering length. The universal regime typically extends up to $x\\approx\n0.001$, while at larger values specific details of the interaction start to be\nrelevant and different model potentials lead to different results. Dipolar\nsystems are peculiar in this regard since the anisotropy of the interaction\nmakes $a_0$ depend on the polarization angle $\\alpha$, so different\ncombinations of $n$ and $\\alpha$ can lead to the same value of the gas\nparameter $x$. In this work we analyze the scaling properties of dipolar bosons\nin two dimensions as a function of the density and polarization dependent\nscattering length up to very large values of the gas parameter $x$. Using\nQuantum Monte Carlo (QMC) methods we study the energy and the main structural\nand coherence properties of the ground state of a gas of dipolar bosons by\nvarying the density and scattering length for fixed gas parameter. We find that\nthe dipolar interaction shows relevant scaling laws up to unusually large\nvalues of $x$ that hold almost to the boundaries in the phase diagram where a\ntransition to a stripe phase takes place.",
        "positive": "Spin squeezing and Quantum Fisher Information in the Jaynes-Cummings\n  Dicke Model: We investigate spin squeezing (SS) and the quantum Fisher information (QFI)\nfor the Jaynes-Cummings Dicke (JC-Dicke) model in a two component atomic\nBose-Einstein condensate (BEC) inside an optical cavity. Analytical expressions\nfor spin squeezing and the reciprocal of the quantum Fisher information per\nparticle (RMQFI) are derived using the frozen spin approximation. It is shown\nthat in the superradiant phase near the critical point, maximum squeezing and\nmaximum quantum entanglement occurs. The present study is relevant to quantum\ninformation processing and precision spectroscopy."
    },
    {
        "anchor": "Observation of a dissipative time crystal: The formation of a phase of matter can be associated with the spontaneous\nbreaking of a symmetry. For crystallization, this broken symmetry is the\nspatial translation symmetry, as the atoms spontaneously localize in a periodic\nfashion. In analogy to spatial crystals, the spontaneous breaking of temporal\ntranslation symmetry results in the formation of time crystals. While recent\nand on-going experiments on driven isolated systems aim to minimize dissipative\nprocesses, as it is an undesired source of decay, well-designed dissipation has\nbeen put forth as a constitutive ingredient in the formation of dissipative\ntime crystals (DTCs). Here, we present the first experimental realisation of a\nDTC, implemented in an atom-cavity system. Its defining feature is a period\ndoubled switching between distinct chequerboard density wave patterns, induced\nby controlled cavity-dissipation and cavity-mediated interactions. We\ndemonstrate the robustness of this phase against system parameter changes and\ntemporal perturbations of the driving. Our work provides a framework for\nrealising phases of matter with spatiotemporal order in presence of\ndissipation. We note that this is the natural environment of matter, and\ntherefore shapes its physical phenomena profoundly, making its study\nimperative.",
        "positive": "Identifying diffusive length scales in one-dimensional Bose gases: In the hydrodynamics of integrable models, diffusion is a subleading\ncorrection to ballistic propagation. Here we quantify the diffusive\ncontribution for one-dimensional Bose gases and find it most influential in the\ncrossover between the main thermodynamic regimes of the gas. Analysing the\nexperimentally measured dynamics of a single density mode, we find diffusion to\nbe relevant only for high wavelength excitations. Instead, the observed\nrelaxation is solely caused by a ballistically driven dephasing process, whose\ntime scale is related to the phonon lifetime of the system and is thus useful\nto evaluate the applicability of the phonon bases typically used in quantum\nfield simulators."
    },
    {
        "anchor": "Generalized Hartree-Fock-Bogoliubov Description of the Frohlich Polaron: We adapt the generalized Hartree-Fock-Bogoliubov (HFB) method to an\ninteracting many-phonon system free of impurities. The many-phonon system is\nobtained from applying the Lee-Low-Pine (LLP) transformation to the Frohlich\nmodel which describes a mobile impurity coupled to noninteracting phonons. We\nspecialize our general HFB description of the Frohlich polaron to Bose polarons\nin quasi-1D cold atom mixtures. The LLP transformed many-phonon system\ndistinguishes itself with an artificial phonon-phonon interaction which is very\ndifferent from the usual two-body interaction. We use the quasi-one-dimensional\nmodel, which is free of an ultraviolet divergence that exists in higher\ndimensions, to better understand how this unique interaction affects polaron\nstates and how the density and pair correlations inherent to the HFB method\nconspire to create a polaron ground state with an energy in good agreement with\nand far closer to the prediction from Feynman's variational path integral\napproach than mean-field theory where HFB correlations are absent.",
        "positive": "Antiferromagnetic bosonic $t$-$J$ models and their quantum simulation in\n  tweezer arrays: The combination of optical tweezer arrays with strong interactions -- via\ndipole-exchange of molecules and van-der-Waals interactions of Rydberg atoms --\nhas opened the door for the exploration of a wide variety of quantum spin\nmodels. A next significant step will be the combination of such settings with\nmobile dopants: This will enable to simulate the physics believed to underlie\nmany strongly correlated quantum materials. Here we propose an experimental\nscheme to realize bosonic t-J models via encoding the local Hilbert space in a\nset of three internal atomic or molecular states. By engineering\nantiferromagnetic (AFM) couplings between spins, competition between charge\nmotion and magnetic order similar to that in high-$T_c$ cuprates can be\nrealized. Since the ground states of the 2D bosonic AFM t-J model we propose to\nrealize have not been studied extensively before, we start by analyzing the\ncase of two dopants -- the simplest instance in which their bosonic statistics\nplays a role, and contrast our results to the fermionic case. We perform\nlarge-scale density matrix renormalization group (DMRG) calculations on\nsix-legged cylinders, and find a strong tendency for bosonic holes to form\nstripes. This demonstrates that bosonic, AFM t-J models may contain similar\nphysics as the collective phases in strongly correlated electrons."
    },
    {
        "anchor": "Bogoliubov-de Gennes study of trapped spin-imbalanced unitary Fermi\n  gases: It is quite common that several different phases exist simultaneously in a\nsystem of trapped quantum gases of ultra-cold atoms. One such example is the\nstrongly-interacting Fermi gas with two imbalanced spin species, which has\nreceived a great amount of attention due to the possible presence of exotic\nsuperfluid phases. By employing novel numerical techniques and algorithms, we\nself-consistently solve the Bogoliubov de-Gennes equations, which describe\nFermi superfluids in the mean-field framework. From this study, we investigate\nthe novel phases of spin-imbalanced Fermi gases and examine the validity of the\nlocal density approximation (LDA), which is often invoked in the extraction of\nbulk properties from experimental measurements within trapped systems. We show\nhow the validity of the LDA is affected by the trapping geometry, number of\natoms and spin imbalance.",
        "positive": "Geometric Stability Spectra of Dipolar Bose Gases in Tunable Optical\n  Lattices: We examine the stability of quasi-two-dimensional dipolar Bose-Einstein\ncondensates in the presence of weak optical lattices of various geometries. We\nfind that when the condensate possesses a roton-maxon quasiparticle dispersion,\nthe conditions for stability exhibit a strong dependence both on the lattice\ngeometry and the polarization tilt. This results in rich structures in the\nsystem's stability diagram akin to spectroscopic signatures. We show how these\nstructures originate from the mode matching of rotons to the perturbing\nlattice. In the case of a one-dimensional lattice, some of the features emerge\nonly when the polarization axis is tilted into the plane of the condensate. Our\nresults suggest that the stability diagram may be used as a novel means to\nspectroscopically measure rotons in dipolar condensates."
    },
    {
        "anchor": "Interference-induced suppression of particle emission from a\n  Bose-Einstein condensate in lattice with time-periodic modulations: Collective emission of particles from a parametrically driven condensate has\nattracted significant experimental and theoretical attention due to the\nappealing visual effects and potential metrological applications. In this\npaper, we investigate the particle emission from a Bose-Einstein condensate\nconfined in a one-dimensional lattice with periodically modulated interparticle\ninteractions. We give the regimes for discrete modes, and find that the\nemission is distinctly suppressed. The configuration induces a broad band, but\ndue to the interference of the matter waves few particles can be ejected. We\nfurther qualitatively model the emission process, and demonstrate the\nshort-time behaviors. This engineering provides a way for manipulating the\npropagation of particles and the corresponding dynamics of condensates in\nlattices, and may find use in other nonequilibrium problems with time-periodic\ndriving.",
        "positive": "Spin orders in the supersolid phases in binary Rydberg-dressed\n  Bose-Einstein condensates: We show that the five possible ordered states in a quantum spin-1/2 system\nwith long-range exchange interactions: Neel, ladder, Peierls, coincidence, and\ndomain states, can be realized in a binary Rydberg-dressed BEC system in the\nsupersolid phase. In such a system, blockade phenomenon is shown to also occur\nfor pairs of different excited-state atoms, which results in similar intra- and\ninter-species long-range interactions between ground-state atoms. It suggests\nthat a pseudo spin-1/2 system can be possibly formed in the ground state of\nultracold rudibium."
    },
    {
        "anchor": "Many-body exceptional points in colliding condensates: Exceptional points describe the coalescence of the eigenmodes of a\nnon-Hermitian matrix. When an exceptional point occurs in the unitary evolution\nof a many-body system, it generically leads to a dynamical instability with a\nfinite wavevector [N. Bernier \\etal, Phys. Rev. Lett. 113, 065303 (2014)].\nHere, we study exceptional points in the context of the counterflow instability\nof colliding Bose-Einstein condensates. We show that the instability of this\nsystem is due to an exceptional point in the Bogoliubov spectrum. We further\nclarify the connection of this effect to the Landau criterion of superfluidity\nand to the scattering of classical particles. We propose an experimental set-up\nto directly probe this exceptional point, and demonstrate its feasibility with\nthe aid of numerical calculations. Our work fosters the observation of\nexceptional points in nonequilibrium many-body quantum systems.",
        "positive": "Exploring the thermodynamics of a two-dimensional Bose gas: Using \\emph{in situ} measurements on a quasi two-dimensional, harmonically\ntrapped $^{87}$Rb gas, we infer various equations of state for the equivalent\nhomogeneous fluid. From the dependence of the total atom number and the central\ndensity of our clouds with the chemical potential and temperature, we obtain\nthe equations of state for the pressure and the phase-space density. Then using\nthe approximate scale invariance of this two-dimensional system, we determine\nthe entropy per particle. We measure values as low as $0.06\\,\\kB$ in the\nstrongly degenerate regime, which shows that a 2D Bose gas can constitute an\nefficient coolant for other quantum fluids. We also explain how to disentangle\nthe various contributions (kinetic, potential, interaction) to the energy of\nthe trapped gas using a time-of-flight method, from which we infer the\nreduction of density fluctuations in a non fully coherent cloud."
    },
    {
        "anchor": "Computation of the asymptotic states of modulated open quantum systems\n  with a numerically exact realization of the quantum trajectory method: Quantum systems out of equilibrium are presently a subject of active\nresearch, both in theoretical and experimental domains. In this work we\nconsider time-periodically modulated quantum systems which are in contact with\na stationary environment. Within the framework of a quantum master equation,\nthe asymptotic states of such systems are described by time-periodic density\noperators. Resolution of these operators constitutes a non-trivial\ncomputational task. To go beyond the current size limits, we use the quantum\ntrajectory method which unravels master equation for the density operator into\na set of stochastic processes for wave functions. The asymptotic density matrix\nis calculated by performing a statistical sampling over the ensemble of quantum\ntrajectories, preceded by a long transient propagation. We follow the ideology\nof event-driven programming and construct a new algorithmic realization of the\nmethod. The algorithm is computationally efficient, allowing for long 'leaps'\nforward in time, and is numerically exact in the sense that, being given the\nlist of uniformly distributed (on the unit interval) random numbers, $\\{\\eta_1,\n\\eta_2,...,\\eta_n\\}$, one could propagate a quantum trajectory (with $\\eta_i$'s\nas norm thresholds) in a numerically exact way. %Since the quantum trajectory\nmethod falls into the class of standard sampling problems, performance of the\nalgorithm %can be substantially improved by implementing it on a computer\ncluster. By using a scalable $N$-particle quantum model, we demonstrate that\nthe algorithm allows us to resolve the asymptotic density operator of the model\nsystem with $N = 2000$ states on a regular-size computer cluster, thus reaching\nthe scale on which numerical studies of modulated Hamiltonian systems are\ncurrently performed.",
        "positive": "Topological two-body bands in a multiband Hubbard model: In a multiband Hubbard model the self-consistency relations for the two-body\nbound-state bands are in the form of a nonlinear eigenvalue problem. Assuming\nthat the resultant eigenvectors form an orthonormal set, e.g., in the\nstrong-binding regime, here we reformulate their Berry curvatures and the\nassociated Chern numbers. As an illustration we solve the two-body problem in a\nHaldane-Hubbard model with attractive onsite interactions, and analyze its\ntopological phase diagrams from weak to strong couplings, i.e., by keeping\ntrack of the gap closings in between the low-lying two-body bands. The\nresultant Chern numbers are consistent with the lobe structure of the phase\ndiagrams in the strong-coupling regime."
    },
    {
        "anchor": "Existence, Stability and Dynamics of Monopole and Alice Ring Solutions\n  in Anti-Ferromagnetic Spinor Condensates: In this work we study the existence, stability, and dynamics of select\ntopological point and line defects in anti-ferromagnetic, polar phase, $F=1$\n$^{23}$Na spinor condensates. Specifically, we leverage fixed-point and\nnumerical continuation techniques in three spatial dimensions to identify\nsolution families of monopole and Alice rings as the chemical potential (number\nof atoms) and trapping strengths are varied within intervals of realizable\nexperimental parameters. We are able to follow the monopole from the linear\nlimit of small atom number all the way to the Thomas-Fermi regime of large atom\nnumber. Additionally, and importantly, our studies reveal the existence of {\\em\ntwo} Alice ring solution branches, corresponding to, relatively, smaller and\nlarger ring radii, that bifurcate from each other in a saddle-center\nbifurcation as the chemical potential is varied. We find that the monopole\nsolution is always dynamically unstable in the regimes considered. In contrast,\nwe find that the larger Alice ring is indeed stable close to the bifurcation\npoint until it destabilizes from an oscillatory instability bubble for a larger\nvalue of the chemical potential. We also report on the possibility of\ndramatically reducing, yet not completely eliminating, the instability rates\nfor the smaller Alice ring by varying the trapping strengths. The dynamical\nevolution of the different unstable waveforms is also probed via direct\nnumerical simulations.",
        "positive": "Relaxation Oscillations and Ultrafast Emission Pulses in a Disordered\n  Expanding Polariton Condensate: Semiconductor microcavities are often influenced by structural imperfections,\nwhich can disturb the flow and dynamics of exciton-polariton condensates.\nAdditionally, in exciton-polariton condensates there is a variety of dynamical\nscenarios and instabilities, owing to the properties of the incoherent\nexcitonic reservoir. We investigate the dynamics of an exciton-polariton\ncondensate which emerges in semiconductor microcavity subject to disorder,\nwhich determines its spatial and temporal behaviour. Our experimental data\nrevealed complex burst-like time evolution under non-resonant optical pulsed\nexcitation. The temporal patterns of the condensate emission result from the\nintrinsic disorder and are driven by properties of the excitonic reservoir,\nwhich decay in time much slower with respect to the polariton condensate\nlifetime. This feature entails a relaxation oscillation in polariton condensate\nformation, resulting in ultrafast emission pulses of coherent polariton field.\nThe experimental data can be well reproduced by numerical simulations, where\nthe condensate is coupled to the excitonic reservoir described by a set of rate\nequations. Theory suggests the existence of slow reservoir temporarily emptied\nby stimulated scattering to the condensate, generating ultrashort pulses of the\ncondensate emission."
    },
    {
        "anchor": "Studying the low-entropy Mott transition of bosons in a\n  three-dimensional optical lattice by measuring the full momentum-space\n  density: We report on a combined experimental and theoretical study of the low-entropy\nMott transition for interacting bosons trapped in a three-dimensional (3D)\ncubic lattice -- namely, the interaction-induced superfluid-to-normal phase\ntransition in the vicinity of the zero-temperature Mott transition. Our\nanalysis relies on the measurement of the 3D momentum distribution, which\nallows us to extract the momentum-space density $\\rho({\\bf k}={\\bf 0})$ at the\ncenter of the Brillouin zone. Upon varying the ratio between the interaction\n$U$ and the tunnelling energy $J$ across the superfluid transition, we observe\nthat $\\rho({\\bf k}={\\bf 0})$ exhibits a sharp transition at a value of $U/J$\nconsistent with the bulk prediction from quantum Monte Carlo. In addition, the\nvariation of $\\rho({\\bf k}={\\bf 0})$ with $U/J$ exhibits a critical behavior\nconsistent with the expected 3D XY universality class. Our results show that\nthe tomographic reconstruction of the momentum distribution of ultracold bosons\ncan reveal traits of the critical behavior of the superfluid transition even in\nan inhomogeneous trapped system.",
        "positive": "Optimized loading of an optical dipole trap for the production of\n  Chromium BECs: We report on a strategy to maximize the number of chromium atoms transferred\nfrom a magneto-optical trap into an optical trap through accumulation in\nmetastable states via strong optical pumping. We analyse how the number of\natoms in a chromium Bose Einstein condensate can be raised by a proper handling\nof the metastable state populations. Four laser diodes have been implemented to\naddress the four levels that are populated during the MOT phase. The individual\nimportance of each state is specified. To stabilize two of our laser diode, we\nhave developed a simple ultrastable passive reference cavity whose long term\nstability is better than 1 MHz."
    },
    {
        "anchor": "Localization phenomena in interacting Rydberg lattice gases with\n  position disorder: Disordered systems provide paradigmatic instances of ergodicity breaking and\nlocalization phenomena. Here we explore the dynamics of excitations in a system\nof Rydberg atoms held in optical tweezers. The finite temperature produces an\nintrinsic uncertainty in the atomic positions, which translates into quenched\ncorrelated disorder in the interatomic interaction strengths. In a simple\napproach, the dynamics in the many-body Hilbert space can be understood in\nterms of a one-dimensional Anderson-like model with disorder on every other\nsite, featuring both localized and delocalized states. We conduct an experiment\non an eight-atom chain and observe a clear suppression of excitation transfer.\nOur experiment accesses a regime which is described by a two-dimensional\nAnderson model on a \"trimmed\" square lattice. Our results thus provide a\nconcrete example in which the absence of excitation propagation in a many-body\nsystem is directly related to Anderson-like localization in the Hilbert space,\nwhich is believed to be the mechanism underlying many-body localization.",
        "positive": "Superfluid-Normal Quantum Phase Transitions in an Imbalanced Fermi Gas: We investigate the superfluid-to-normal zero temperature quantum phase\ntransitions of asymmetric two-component Fermi gases as a function of the\nchemical potential imbalance $h$. The calculations are performed for\nhomogeneous and trapped imbalanced systems. We concentrate at unitarity,\ncharacterized by a divergent interaction parameter $k_F a$, where most of the\ncurrent experiments are realized. For homogeneous systems, we determine the\ncritical chemical potential imbalance $h_c$ at which possible phase transitions\noccur. In the case of trapped gases, we show how $h_c$ can be consistently\ndetermined from experimental observations."
    },
    {
        "anchor": "Vortex structures of rotating spin-orbit coupled Bose-Einstein\n  condensates: We consider the quasi-2D two-component Bose-Einstein condensates with Rashba\nspin-orbit (SO) coupling in a rotating trap. An external Zeeman term favoring\nspin polarization along the radial direction is also considered, which has the\nsame form as the non-canonical part of the mechanical angular momentum. The\nrotating condensate exhibits rich structures as varying the strengths of\ntrapping potential and interaction. With a strong trapping potential, the\ncondensate exhibits a half-quantum vortex-lattice configuration. Such a\nconfiguration is driven to the normal one by introducing the external radial\nZeeman field. In the case of a weak trap potential, the condensate exhibits a\nmulti-domain pattern of plane-wave states under the external radial Zeeman\nfield.",
        "positive": "Condensation phenomena in plasmonics: We study arrays of plasmonic nanoparticles combined with quantum emitters,\nquantum plasmonic lattices, as a platform for room temperature studies of\nquantum many-body physics. We outline a theory to describe surface plasmon\npolariton distributions when they are coupled to externally pumped molecules.\nThe possibility of tailoring the dispersion in plasmonic lattices allows\nrealization of a variety of distributions, including the Bose-Einstein\ndistribution as in photon condensation. We show that the presence of losses can\nrelax some of the standard dimensionality restrictions for condensation."
    },
    {
        "anchor": "Ionic polaron in a Bose-Einstein condensate: The presence of strong interactions in a many-body quantum system can lead to\na variety of exotic effects. Here we show that even in a comparatively simple\nsetup consisting of a charged impurity in a weakly interacting bosonic medium\nthe competition of length scales gives rise to a highly correlated mesoscopic\nstate. Using quantum Monte Carlo simulations, we unravel its vastly different\npolaronic properties compared to neutral quantum impurities. Moreover, we\nidentify a transition between the regime amenable to conventional perturbative\ntreatment in the limit of weak atom-ion interactions and a many-body bound\nstate with vanishing quasi-particle residue composed of hundreds of atoms. In\norder to analyze the structure of the corresponding states we examine the\natom-ion and atom-atom correlation functions which both show nontrivial\nproperties. Our findings are directly relevant to experiments using hybrid\natom-ion setups that have recently attained the ultracold regime.",
        "positive": "Interference effects in the two-dimensional scattering of microcavity\n  polaritons by an obstacle: phase dislocations and resonances: We consider interference effects within the linear description of the\nscattering of two-dimensional microcavity polaritons by an obstacle. The\npolariton wave may exhibit phase dislocations created by the interference of\nthe incident and the scattered fields. We describe these structures within the\ngeneral framework of singular optics. We also discuss another type of\ninterference effects appearing due to the formation of (quasi)resonances in the\npotential of a repulsive obstacle with sharp boundaries. We discuss the\nrelevance of our approach for the description of recent experimental results\nand propose a criterion for evaluating the importance of nonlinear effects."
    },
    {
        "anchor": "Extracting Lyapunov exponents from the echo dynamics of Bose-Einstein\n  condensates on a lattice: We propose theoretically an experimentally realizable method to demonstrate\nthe Lyapunov instability and to extract the value of the largest Lyapunov\nexponent for a chaotic many-particle interacting system. The proposal focuses\nspecifically on a lattice of coupled Bose-Einstein condensates in the classical\nregime describable by the discrete Gross-Pitaevskii equation. We suggest to use\nimperfect time-reversal of system's dynamics known as Loschmidt echo, which can\nbe realized experimentally by reversing the sign of the Hamiltonian of the\nsystem. The routine involves tracking and then subtracting the noise of\nvirtually any observable quantity before and after the time-reversal. We\nsupport the theoretical analysis by direct numerical simulations demonstrating\nthat the largest Lyapunov exponent can indeed be extracted from the Loschmidt\necho routine. We also discuss possible values of experimental parameters\nrequired for implementing this proposal.",
        "positive": "Beyond Lee-Huang-Yang description of self-bound Bose mixtures: We investigate the properties of self-bound ultradilute Bose-Bose mixtures,\nbeyond the Lee-Huang-Yang description. Our approach is based on the\ndetermination of the beyond mean-field corrections to the phonon modes of the\nmixture in a self-consistent way and calculation of the associated equation of\nstate. The newly obtained ground state energies show excellent agreement with\nrecent quantum Monte Carlo calculations, providing a simple and accurate\ndescription of the self-bound mixtures with contact type interaction. We\nfurther show numerical results for the equilibrium properties of the finite\nsize droplet, by adjusting the Gross-Pitaevskii equation. Our analysis is\nextended to the one-dimensional mixtures where an excellent agreement with\nquantum Monte Carlo predictions is found for the equilibrium densities.\nFinally, we discuss the effects of temperature on the stability of the liquid\nphase."
    },
    {
        "anchor": "Instability and Momentum Bifurcation of molecular BEC in Exotic\n  Dispersion with Shaken Lattice: We place a molecular Bose-Einstein condensate in a 1D shaken lattice with a\nFloquet-engineered dispersion, and observe the dynamics in both position and\nmomentum space. At the initial condition of zero momentum, our engineered\ndispersion is inverted, and therefore unstable. We observe that the condensate\nis destabilized by the lattice shaking as expected, but rather than decaying\nincoherently or producing jets, as in other unstable condensates, under our\nconditions the condensate bifurcates into two portions in momentum space, with\neach portion subsequently following semi-classical trajectories that suffer\nminimal spreading in momentum space as they evolve. We can model the evolution\nwith a Gross-Pitaevskii equation, which suggests the initial bifurcation is\nfacilitate by a nearly linear \"inverted V\"-shaped dispersion at the zone\ncenter, while the lack of spreading in momentum space is facilitated by\ninteractions, as in a soliton. We propose that this relatively clean\nbifurcation in momentum space has applications for counter-diabatic preparation\nof exotic ground states in many-body quantum simulation schemes.",
        "positive": "Metastability, excitations, fluctuations, and multiple-swallowtail\n  structures of a superfluid in a Bose-Einstein condensate in the presence of a\n  uniformly moving defect: We solve the Gross-Pitaevskii (GP) and Bogoliubov equations to investigate\nthe metastability of superfluidity in a Bose-Einstein condensate in the\npresence of a uniformly moving defect potential in a two-dimensional torus. We\ncalculate the total energy and momentum as functions of the driving velocity of\nthe moving defect and find metastable states with negative effective-mass near\nthe critical velocity. We also find that the first excited energy (energy gap)\nin the finite-sized torus closes at the critical velocity, that it obeys\none-fourth power-law scaling, and that the dynamical fluctuation of the density\n(amplitude of the order parameter) is strongly enhanced near the critical\nvelocity. We confirm the validity of our results near the critical velocity by\ncalculating the quantum depletion. We find an unconventional swallowtail\nstructure (multiple-swallowtail structure) through calculations of the unstable\nstationary solutions of the GP equation."
    },
    {
        "anchor": "Dimensional crossover for the beyond-mean-field correction in Bose gases: We present a detailed beyond-mean-field analysis of a weakly interacting Bose\ngas in the crossover from three to low dimensions. We find an analytical\nsolution for the energy and provide a clear qualitative picture of the\ncrossover in the case of a box potential with periodic boundary conditions. We\nshow that the leading contribution of the confinement-induced resonance is of\nbeyond-mean-field order and calculate the leading corrections in the three- and\nlow-dimensional limits. We also characterize the crossover for harmonic\npotentials in a model system with particularly chosen short- and long-range\ninteractions and show the limitations of the local-density approximation. Our\nanalysis is applicable to Bose-Bose mixtures and gives a starting point for\ndeveloping the beyond-mean-field theory in inhomogeneous systems with\nlong-range interactions such as dipolar particles or Rydberg-dressed atoms.",
        "positive": "Anomalous buoyancy of quantum bubbles in immiscible Bose mixtures: Buoyancy is a well-known effect in immiscible binary Bose-Einstein\ncondensates. Depending on the differential confinement experienced by the two\ncomponents, a bubble of one component sitting at the center of the other\neventually floats to the surface, around which it spreads either totally or\npartially. We discuss how quantum fluctuations may significantly change the\nvolume and position of immiscible bubbles. We consider the particular case of\ntwo miscible components, forming a pseudo-scalar bubble condensate with\nenhanced quantum fluctuations (quantum bubble), immersed in a bath provided by\na third component, with which they are immiscible. We show that in such a\npeculiar effective binary mixture, quantum fluctuations change the equilibrium\nof pressures that define the bubble volume and modify as well the criterion for\nbuoyancy. Once buoyancy sets in, in contrast to the mean-field case, quantum\nfluctuations may place the bubble at an intermediate position between the\ncenter and the surface. At the surface, the quantum bubble may transition into\na floating self-bound droplet."
    },
    {
        "anchor": "Tunneling-assisted Spin-orbit Coupling in Bilayer Bose-Einstein\n  Condensates: Motivated by a goal of realizing spin-orbit coupling (SOC) beyond\none-dimension (1D), we propose and analyze a method to generate an effective 2D\nSOC in bilayer BECs with laser-assisted inter-layer tunneling. We show that an\ninterplay between the inter-layer tunneling, SOC and intra-layer atomic\ninteraction can give rise to diverse ground state configurations. In\nparticular, the system undergoes a transition to a new type of stripe phase\nwhich spontaneously breaks the time-reversal symmetry. Different from the\nordinary Rashba-type SOC, a fractionalized skyrmion lattice emerges\nspontaneously in the bilayer system without external traps. Furthermore, we\npredict the occurrence of a tetracritical point in the phase diagram of the\nbilayer BECs, where four different phases merge together. The origin of the\nemerging different phases is elucidated.",
        "positive": "Tunable breakdown of the polaron picture for mobile impurities in a\n  topological semimetal: Mobile impurities in cold atomic gases constitute a new platform for\ninvestigating polaron physics. Here we show that when impurity atoms interact\nwith a two-dimensional Fermi gas with quadratic band touching the polaron\npicture may either hold or break down depending on the particle-hole asymmetry\nof the band structure. If the hole band has a smaller effective mass than the\nparticle band, the quasiparticle is stable and its diffusion coefficient varies\nwith temperature as $D(T) \\propto \\ln^2 T$. If the hole band has larger mass,\nthe quasiparticle weight vanishes at low energies due to an emergent\northogonality catastrophe. In this case we map the problem onto a set of\none-dimensional channels and use conformal field theory techniques to obtain\n$D(T)\\propto T^{\\nu}$ with an interaction-dependent exponent $\\nu$. The\ndifferent regimes can be detected in the nonequilibrium expansion dynamics of\nan initially confined impurity."
    },
    {
        "anchor": "Nonlinear Klein-Gordon equation and the Bose-Einstein condensation: The interest in the Klein-Gordon equation with different potentials has\nincreased in recent years due to its possible applications in Cosmology, Hadron\nPhysics and High-Energy Physics. In this work we investigate the solutions of\nthe Klein-Gordon equation for bosons under the influence of an external\npotential by using the Feshbach-Villars method. We present detailed results for\ntwo cases: the Coulombic potential and the harmonic potential. For the latter\ncase, we studied the effects of self-interacting particles by adopting a\nmean-field approach. We show that our results converge smoothly to the solution\nof the Schr\\\"odinger equation for the same systems as the relativistic effects\ndiminish.",
        "positive": "SO(3) \"Nuclear Physics\" with ultracold Gases: An ab initio calculation of nuclear physics from Quantum Chromodynamics\n(QCD), the fundamental SU(3) gauge theory of the strong interaction, remains an\noutstanding challenge. Here, we discuss the emergence of key elements of\nnuclear physics using an SO(3) lattice gauge theory as a toy model for QCD. We\nshow that this model is accessible to state-of-the-art quantum simulation\nexperiments with ultracold atoms in an optical lattice. First, we demonstrate\nthat our model shares characteristic many-body features with QCD, such as the\nspontaneous breakdown of chiral symmetry, its restoration at finite baryon\ndensity, as well as the existence of few-body bound states. Then we show that\nin the one-dimensional case, the dynamics in the gauge invariant sector can be\nencoded as a spin S=3/2 Heisenberg model, i.e., as quantum magnetism, which has\na natural realization with bosonic mixtures in optical lattices, and thus sheds\nlight on the connection between non-Abelian gauge theories and quantum\nmagnetism."
    },
    {
        "anchor": "Topological phases of dipolar particles in elongated Wannier orbitals: We show that topological phases with fractional excitations can occur in\ntwo-dimensional ultracold dipolar gases on a particular class of optical\nlattices. Due to the dipolar interaction and lattice confinement, a quantum\ndimer model emerges naturally as the effective theory describing the low-energy\nbehaviors of these systems under well-controlled approximations. The desired\nhierarchy of interaction energy scales is achieved by controlling the\nanisotropy of the orbital dimers and the dipole moments of the particles.\nExperimental realization and detection of various phases are discussed, as well\nas the possible relevance for quantum computation.",
        "positive": "Yang-Yang method for the thermodynamics of one-dimensional\n  multi-component interacting fermions: Using Yang and Yang's particle-hole description, we present a thorough\nderivation of the thermodynamic Bethe ansatz equations for a general\n$SU(\\kappa)$ fermionic system in one-dimension for both the repulsive and\nattractive regimes under the presence of an external magnetic field. These\nequations are derived from Sutherland's Bethe ansatz equations by using the\nspin-string hypothesis. The Bethe ansatz root patterns for the attractive case\nare discussed in detail. The relationship between the various phases of the\nmagnetic phase diagrams and the external magnetic fields is given for the\nattractive case. We also give a quantitative description of the ground state\nenergies for both strongly repulsive and strongly attractive regimes."
    },
    {
        "anchor": "Dynamical formation of polarons in a Bose-Einstein condensate: A\n  variational approach: We investigate the non-equilibrium dynamics of an impurity coupled to a\nBose-Einstein condensate, systematically compared with recent experimental\nresults [M. G. Skou et al., Nat. Phys. (2021)]. The dynamics of the impurity is\ntracked down by using a time-dependent variational coherent ansatz. For weak\ncoupling between the impurity and the bath, analytical expressions for the\ntime-dependent overlap (or contrast) are derived, matching quite well with\nprevious findings obtained within a master equation approach. For strong\ncoupling instead, the variational ansatz provides a good quantitative\ndescription of the polaron dynamics, in particular, in signaling the transition\nfrom the few to the many-body correlated regime where polarons are expected to\nform.",
        "positive": "Dynamics of harmonically confined systems: some rigorous results: In this paper we consider the dynamics of harmonically-confined atomic gases.\nWe present various general results which are independent of particle\nstatistics, interatomic interactions and dimensionality. Of particular interest\nis the response of the system to external perturbations having either a static\nor dynamic nature. We prove an extended Harmonic Potential Theorem which is\nuseful in determining the damping of the centre of mass motion for some\ninitially prepared nonequilibrium state. We also study the response of the gas\nto a dynamic perturbation in which the external potential oscillates at an\narbitrary frequency. We show in this case that either the energy absorption\nrate or the centre of mass dynamics can serve as a probe of the optical\nconductivity of the system."
    },
    {
        "anchor": "Quench dynamics across the MI-SF quantum phase transition with cluster\n  mean field theory: In this work, we study the quench dynamics of quantum phases of ultracold\nneutral bosons trapped in optical lattices. We investigate the validity of the\nKibble-Zurek (KZ) scaling laws with the single-site Gutzwiller mean-field\n(SGMF) and cluster Gutzwiller mean-field (CGMF) theory. With CGMF, we note the\nevolution of the dynamical wavefunction in the ``impulse\" regime of the\nKibble-Zurek mechanism. We obtain the power law scalings for the crossover time\nand defect density with the quench rate predicted by KZ scaling laws. The\ncritical exponents obtained from dynamics are close to their equilibrium\nvalues. Furthermore, it is observed that the obtained dynamical critical\nexponent $z$ improves towards the equilibrium value with increasing cluster\nsizes in CGMF.",
        "positive": "Impurity effects on BCS-BEC crossover in ultracold atomic Fermi gases: We present a systematic investigation of the effects of \"nonmagnetic\"\nimpurities on the $s$-wave BCS-BEC crossover in atomic Fermi gases within a\npairing fluctuation theory. Both pairing and impurity scattering $T$-matrices\nare treated self-consistently at the same time. While the system is less\nsensitive to impurity scattering in the Born limit, for strong impurity\nscatterers, both the frequency and the gap function are highly renormalized,\nleading to significant suppression of the superfluid $T_c$, the order parameter\nand the superfluid density. We also find the formation of impurity bands and\nsmearing of coherence peak in the fermion density of states, leading to a\nspectrum weight transfer and finite lifetime of Bogoliubov quasiparticles. In\nthe BCS regime, the superfluidity may be readily destroyed by the impurity of\nhigh density. In comparison, the superfluidity in unitary and BEC regimes is\nrelatively more robust."
    },
    {
        "anchor": "Polarons in Extremely Polarized Fermi Gases: The Strongly Interacting\n  6Li-40K Mixture: We study the extremely polarized two-component Fermi gas with a mass\nimbalance in the strongly interacting regime. Specifically we focus on the\nexperimentally available mixture of ${}^6$Li and ${}^{40}$K atoms. In this\nregime spin polarons, i.e., dressed minority atoms, form. We consider the\nspectral function for the minority atoms, from which the lifetime and the\neffective mass of the spin polaron can be determined. Moreover, we predict the\nradio-frequency (RF) spectrum and the momentum distribution for the spin\npolarons for experiments with ${}^6$Li and ${}^{40}$K atoms. Subsequently we\nstudy the relaxation of the motion of the spin polaron due to spin drag.",
        "positive": "Quantum simulation: From basic principles to applications: Envisioned by Richard Feynman in the early 1980s, quantum simulation has\nreceived dramatic impetus thanks to the development of a variety of plateforms\nable to emulate a wide class of quantum Hamiltonians. During the past decade,\nmost of the quantum simulators have implemented rather well-known models, hence\npermitting a direct comparison with theoretical calculations and a precise\nbenchmarking of their reliability. The field has now reached a maturity such\nthat one can address difficult problems, which cannot be solved efficiently\nusing classical algorithms. These advances provide unprecedented opportunities\nto explore previously unreachable fields, test theoretical predictions, and\ninspire novel approaches. This contribution is an introduction to quantum\nsimulation. It is published as a forward to the special issue on Quantum\nSimulation of the Comptes-Rendus de Physique of the French Academy of Sciences."
    },
    {
        "anchor": "Collective quantum stochastic resonance in Rydberg atoms: We study the collective response of a group of dissipative Rydberg atoms to a\nperiodic modulation of the Rydberg excitation laser. Focusing on the emergent\ncollective-jump dynamics, where the system stochastically switches between\nstates with distinct Rydberg excitations, we show that the counting statistics\nof the state switching is qualitatively changed by the periodic drive. The\nimpact is most prominent when the driving frequency is comparable to the\nemergent collective-jump rate, as the jumps tend to synchronize with the\nexternal drive, and their counting statistics exhibits a series of suppressed\nsubharmonics of the driving frequency. These phenomena are manifestations of a\nnovel type of stochastic resonance, where a cooperative collective state\nswitching is facilitated by quantum fluctuations in a many-body open system.\nSuch a collective quantum stochastic resonance further leads to an enhanced\nsignal-to-noise ratio in the power spectrum of the Rydberg excitations, for\nwhich the synchronized collective jumps are viewed as the output signal. We\nconfirm the many-body quantum nature of the resonance by devising a cluster\nmodel, under which the role of many-body correlations is analyzed by changing\nthe size of the atom clusters.",
        "positive": "Excitation Transport through a Domain Wall in a Bose-Einstein Condensate: We investigate the tunneling properties of collective excitations through a\ndomain wall in the ferromagnetic phase of a spin-1 spinor Bose--Einstein\ncondensate. Within the mean-field theory at T=0, we show that the transverse\nspin wave undergoes perfect reflection in the low-energy limit. This reflection\nproperty differs considerably from that of a domain wall in a Heisenberg\nferromagnet where spin-wave excitations exhibit perfect transmission at\narbitrary energy. When the Bogoliubov mode is scattered from this domain wall\nsoliton, the transmission and reflection coefficients exhibit pronounced\nnon-monotonicity. In particular, we find perfect reflection of the Bogoliubov\nmode at energies where bound states appear. This is in stark contrast to the\nperfect transmission of the Bogoliubov mode with arbitrary energy through a\ndark soliton in a scalar Bose--Einstein condensate."
    },
    {
        "anchor": "Insulator phases of a mixture of spinor fermions and hard-core bosons: We study numerically a one-dimensional mixture of spin-$\\tfrac{1}{2}$\nfermions and scalar bosons in the hard-core limit. Considering repulsive\nfermion-fermion and boson-fermion interactions, we find superfluid and\ninsulator states whose phase diagram is calculated. We determine that given a\nfermionic density $\\rho_F$, the insulator states are located at the bosonic\ndensities $\\rho_B=1-\\rho_F$ and $\\rho_B=1-\\tfrac{1}{2}\\rho_F$, and emerge even\nin the absence of fermion-fermion coupling. In addition, the boson-fermion\nrepulsion drives quantum phase transitions inside the insulator lobes with\n$\\rho_B=1/2$. Our predictions could be observed in current cold-atom\nexperimental platforms.",
        "positive": "Pairing of few Fermi atoms in one dimension: We study a few Fermi atoms interacting through attractive contact forces in a\none-dimensional trap by means of numerical exact diagonalization. From the\ncombined analysis of energies and wave functions of correlated ground and\nexcited states we find evidence of BCS-like pairing even for very few atoms.\nFor moderate interaction strength, we reproduce the even-odd oscillation of the\nseparation energy observed in [G. Zuern, A. N. Wenz, S. Murmann, A.\nBergschneider, T. Lompe, and S. Jochim, Phys. Rev. Lett. 111, 175302 (2013)].\nFor strong interatomic attraction the arrangement of dimers in the trap differs\nfrom the homogeneous case as a consequence of Pauli blockade in real space."
    },
    {
        "anchor": "Double-layer Bose-Einstein condensates: A quantum phase transition in\n  the transverse direction, and reduction to two dimensions: We revisit the problem of the reduction of the three-dimensional (3D)\ndynamics of Bose-Einstein condensates, under the action of strong confinement\nin one direction ($z$), to a 2D mean-field equation. We address this problem\nfor the confining potential with a singular term, viz.,\n$V_{z}(z)=2z^{2}+\\zeta^{2}/z^{2}$, with constant $\\zeta$. A quantum phase\ntransition is induced by the latter term, between the ground state (GS) of the\nharmonic oscillator and the 3D condensate split in two parallel non-interacting\nlayers, which is a manifestation of the \"superselection\" effect. A realization\nof the respective physical setting is proposed, making use of resonant coupling\nto an optical field, with the resonance detuning modulated along $z$. The\nreduction of the full 3D Gross-Pitaevskii equation (GPE) to the 2D\nnonpolynomial Schr\\\"odinger equation (NPSE) is based on the factorized ansatz,\nwith the $z$-dependent multiplier represented by an exact GS solution of the\nSchr\\\"odinger equation with potential $V(z)$. For both repulsive and attractive\nsigns of the nonlinearity, the NPSE produces GS and vortex states, that are\nvirtually indistinguishable from the respective numerical solutions provided by\nfull 3D GPE. In the case of the self-attraction, the threshold for the onset of\nthe collapse, predicted by the 2D NPSE, is also virtually identical to its\ncounterpart obtained from the 3D equation. In the same case, stability and\ninstability of vortices with topological charge $S=1$, $2$, and $3$ are\nconsidered in detail. Thus, the procedure of the spatial-dimension reduction,\n3D $\\rightarrow$ 2D, produces very accurate results, and it may be used in\nother settings.",
        "positive": "Magnetic Impurities in Two-Dimensional Superfluid Fermi Gas with\n  Spin-Orbit Coupling: We consider magnetic impurities in a two dimensional superfluid Fermi gas in\nthe presence of spin-orbit coupling. By using the methods of t-matrix and\nGreen's function, we find spin-orbit coupling has some dramatic impacts on the\neffects of magnetic impurities. For the single impurity problem, the number of\nbound states localized around the magnetic impurity is doubled. For the finite\nconcentration $n$ of impurities, the energy gap is reduced and the density of\nstates in the gapless region is greatly modified."
    },
    {
        "anchor": "Ferromagnetism of the Repulsive Atomic Fermi Gas: three-body\n  recombination and domain formation: The simplest model for itinerant ferromagnetism, the Stoner model, has so far\neluded experimental observation in repulsive ultracold fermions due to rapid\nthree-body recombination at large scattering lengths. Here we show that a\nferromagnetic phase can be stabilised by imposing a moderate optical lattice.\nThe reduced kinetic energy drop upon formation of a polarized phase in an\noptical lattice extends the ferromagnetic phase to smaller scattering lengths\nwhere three-body recombination is small enough to permit experimental detection\nof the phase. We also show, using time dependent density functional theory,\nthat in such a setup ferromagnetic domains emerge rapidly from a paramagnetic\ninitial state.",
        "positive": "Tunable zero and first sounds in ultracold Fermi gases with Rabi\n  coupling: We consider a weakly-interacting fermionic gas of alkali-metal atoms\ncharacterized by two hyper- fine states which are Rabi coupled. By using a\nHartree approximation for the repulsive interaction we determine the\nzero-temperature equation of state of this Fermi gas in D spatial dimensions (D\n= 1, 2, 3). Then, adopting the Landau-Vlasov equation and hydrodynamic\nequations, we investi- gate the speed of first sound and zero sound. We show\nthat the two sounds, which occur respectively in collisional and collisionless\nregimes, crucially depend on the interplay between interaction strength and\nRabi coupling. Finally, we discuss for some experimentally relevant cases the\neffect of a trapping harmonic potential on the density profiles of the\nfermionic system."
    },
    {
        "anchor": "Quantum phase transitions in Bose-Einstein condensates from a Bethe\n  ansatz perspective: We investigate two solvable models for Bose-Einstein condensates and extract\nphysical information by studying the structure of the solutions of their Bethe\nansatz equations. A careful observation of these solutions for the ground state\nof both models, as we vary some parameters of the Hamiltonian, suggests a\nconnection between the behavior of the roots of the Bethe ansatz equations and\nthe physical behavior of the models. Then, by the use of standard techniques\nfor approaching quantum phase transition - gap, entanglement and fidelity - we\nfind that the change in the scenery in the roots of the Bethe ansatz equations\nis directly related to a quantum phase transition, thus providing an\nalternative method for its detection.",
        "positive": "Antiferromagnetic correlations in two-dimensional fermionic\n  Mott-insulating and metallic phases: Near zero temperature, quantum magnetism can non-trivially arise from\nshort-range interactions, but the occurrence of magnetic order depends\ncrucially on the interplay of interactions, lattice geometry, dimensionality\nand doping. Even though the consequences of this interplay are not yet fully\nunderstood, quantum magnetism is believed to be connected to a range of complex\nphenomena in the solid state, for example, in the context of high-$T_c$\nsuperconductivity and spin liquids in frustrated lattices. Ultracold atomic\nFermi gases in optical lattices constitute an experimental system with\nunrivalled tunability and detection capabilities to explore quantum magnetism\nby analog quantum simulation. In this work, we study the emergence of\nantiferromagnetic correlations between ultracold fermionic atoms in two\ndimensions with decreasing temperature. We determine the magnetic\nsusceptibility of the Hubbard model from simultaneous measurements of the\nin-situ density of both spin components. At half-filling and strong\ninteractions our data approach the Heisenberg model of localized spins with\nantiferromagnetic correlations. Moreover, we observe the disappearance of\nmagnetic correlations when the system is doped away from half-filling. Our\nobservation of the dependence of quantum magnetism on doping paves the way for\nfuture studies on the emergence of pseudogap and pairing phenomena away from\nhalf-filling."
    },
    {
        "anchor": "Thermalization Dynamics of Two Correlated Bosonic Quantum Wires After a\n  Split: Coherently splitting a one-dimensional Bose gas provides an attractive,\nexperimentally estab- lished platform to investigate many-body quantum\ndynamics. At short enough times, the dynamics is dominated by the dephasing of\nsingle quasi-particles, and well described by the relaxation to- wards a\ngeneralized Gibbs ensemble corresponding to the free Luttinger theory. At later\ntimes on the other hand, the approach to a thermal Gibbs ensemble is expected\nfor a generic, interacting quantum system. Here, we go one step beyond the\nquadratic Luttinger theory and include the lead- ing phonon-phonon\ninteractions. By applying kinetic theory and non-equilibrium Dyson-Schwinger\nequations, we analyze the full relaxation dynamics beyond dephasing and\ndetermine the asymptotic thermalization process in the two-wire system for a\nsymmetric splitting protocol. The major ob- servables are the different phonon\noccupation functions and the experimentally accessible coherence factor, as\nwell as the phase correlations between the two wires. We demonstrate that,\ndepending on the splitting protocol, the presence of phonon collisions can have\nsignificant influence on the asymptotic evolution of these observables, which\nmakes the corresponding thermalization dynamics experimentally accessible.",
        "positive": "Observation of vortex nucleation in a rotating two-dimensional lattice\n  of Bose-Einstein condensates: We report the observation of vortex nucleation in a rotating optical lattice.\nA 87Rb Bose-Einstein condensate was loaded into a static two-dimensional\nlattice and the rotation frequency of the lattice was then increased from zero.\nWe studied how vortex nucleation depended on optical lattice depth and rotation\nfrequency. For deep lattices above the chemical potential of the condensate we\nobserved a linear dependence of the number of vortices created with the\nrotation frequency,even below the thermodynamic critical frequency required for\nvortex nucleation. At these lattice depths the system formed an array of\nJosephson-coupled condensates. The effective magnetic field produced by\nrotation introduced characteristic relative phases between neighbouring\ncondensates, such that vortices were observed upon ramping down the lattice\ndepth and recombining the condensates."
    },
    {
        "anchor": "Validating Simple Dynamical Simulations of the Unitary Fermi Gas: We present a comparison between simulated dynamics of the unitary fermion gas\nusing the superfluid local density approximation (SLDA) and a simplified\nbosonic model, the extended Thomas Fermi (ETF) with a unitary equation of\nstate. Small amplitude fluctuations have similar dynamics in both theories for\nfrequencies far below the pair breaking threshold and wave vectors much smaller\nthan the Fermi momentum, and the low frequency linear responses match well for\nsurprisingly large wave vectors, even up to the Fermi momentum. For non-linear\ndynamics such as vortex generation, the ETF provides a semi-quantitative\ndescription of SLDA dynamics as long as the fluctuations do not have\nsignificant power near the pair breaking threshold, otherwise the dynamics of\nthe ETF cannot be trusted. Nonlinearities in the ETF tends to generate\nhigh-frequency fluctuations, and with no normal component to remove this energy\nfrom the superfluid, features like vortex lattices cannot relax and crystallize\nas they do in the SLDA. We present a heuristic diagnostic for validating the\nreliability of ETF dynamics by considering the approximate conservation of\nsquare of the gap: $\\int|\\Delta|^2$.",
        "positive": "Collisions of ultracold molecules in bright and dark optical dipole\n  traps: Understanding collisions between ultracold molecules is crucial for making\nstable molecular quantum gases and harnessing their rich internal degrees of\nfreedom for quantum engineering. Transient complexes can strongly influence\ncollisional physics, but in the ultracold regime, key aspects of their behavior\nhave remained unknown. To explain experimentally observed loss of ground-state\nmolecules from optical dipole traps, it was recently proposed that molecular\ncomplexes can be lost due to photo-excitation. By trapping molecules in a\nrepulsive box potential using laser light near a narrow molecular transition,\nwe are able to test this hypothesis with light intensities three orders of\nmagnitude lower than what is typical in red-detuned dipole traps. This allows\nus to investigate light-induced collisional loss in a gas of nonreactive\nfermionic $^{23}$Na$^{40}$K molecules. Even for the lowest intensities\navailable in our experiment, our results are consistent with universal loss,\nmeaning unit loss probability inside the short-range interaction potential. Our\nfindings disagree by at least two orders of magnitude with latest theoretical\npredictions, showing that crucial aspects of molecular collisions are not yet\nunderstood, and provide a benchmark for the development of new theories."
    },
    {
        "anchor": "Superfluidity of strongly correlated bosons in two- and\n  three-dimensional traps: We analyze the superfluid phase transition of harmonically confined bosons\nwith long-range interaction in both two and three dimensions in a broad\nparameter range from weak to strong coupling. We observe that the onset of\nsuperfluidity occurs in $3D$ at significantly lower temperatures compared to\n$2D$. This is demonstrated to be a quantum degeneracy effect. In addition, the\nspatial distribution of superfluidity across the shells of the clusters is\ninvestigated. It is found that superfluidity is substantially reduced in the\nouter layers due to increased correlation effects.",
        "positive": "Bose-Einstein condensate fluctuations versus an interparticle\n  interaction: We calculate the Bose-Einstein condensate (BEC) occupation statistics vs. the\ninterparticle interaction in a dilute gas with a nonuniform condensate in a box\ntrap within the Bogoliubov approach. The results are compared against the\npreviously found BEC-occupation statistics in (i) an ideal gas and (ii) a\nweakly interacting gas with a uniform condensate. In particular, we reveal and\nexplicitly describe an appearance of a nontrivial transition from the ideal gas\nto the Thomas-Fermi regime. The results include finding the main regimes of the\nBEC statistics - the anomalous non-Gaussian thermally-dominated fluctuations\nand the Gaussian quantum-dominated fluctuations - as well as a crossover\nbetween them and their manifestations in a mesoscopic system. Remarkably, we\nshow that the effect of the boundary conditions, imposed at the box trap, on\nthe BEC fluctuations does not vanish in the thermodynamic limit of a\nmacroscopic system even in the presence of the interparticle interactions.\nFinally, we discuss a challenging problem of an experimental verification of\nthe theory of the BEC fluctuations addressing a much deeper level of the\nmany-body statistical physics than usually studied quantities related to the\nmean condensate occupation."
    },
    {
        "anchor": "The $\\mathbb{Z}_2$ toric-code and the double-semion topological order of\n  hardcore Bose-Hubbard-type models in the strong-interaction limit: We present a generic framework for the emergence of the $\\mathbb{Z}_2$\ntoric-code and the double-semion topological order in a wide class of hardcore\nBose-Hubbard-type models governed by density-density interaction and in the\nstrong-interaction regime. We fix fractional filling factor and study under\nwhich conditions the density-density interaction gives rise to topological\ndegeneracy. We further specify which dynamics determines the toric-code and the\ndouble-semion topological order. Our results indicate that the specifics of the\ndensity-density interaction determine the long-range entanglement of the model\nwhich possesses \"restricted patterns\" of the long-range entanglement realized\nin corresponding string-net models with the same topological order.",
        "positive": "Oscillating Solitons and AC Josephson Effect in Ferromagnetic Bose-Bose\n  Mixtures: Close to the demixing transition, the degree of freedom associated to\nrelative density fluctuations of a two-component Bose-Einstein condensate is\ndescribed by a non-dissipative Landau-Lifshitz equation. In the quasi\none-dimensional weakly immiscible case, this mapping surprisingly predicts that\na dark-bright soliton should oscillate when subject to a constant force\nfavoring separation of the two components. We propose a realistic experimental\nimplementation of this phenomenon which we interpret as a spin-Josephson effect\nin the presence of a movable barrier."
    },
    {
        "anchor": "Superfluidity of a laser-stirred Bose-Einstein condensate: We study superfluidity of a cigar-shaped Bose-Einstein condensate (BEC) by\nstirring it with a Gaussian potential oscillating back and forth along the\naxial dimension of the condensate, motivated by experiments of C. Raman et al.\nPhys. Rev. Lett. 83, 2502 (1999). Using classical-field simulations and\nperturbation theory we examine the induced heating rate, based on the total\nenergy of the system, as a function of the stirring velocity $v$. We identify\nthe onset of dissipation by a sharply increasing heating rate above a velocity\n$v_c$, which we define as the critical velocity. We show that $v_c$ is\ninfluenced by the oscillating motion, the strength of the stirrer, the\ntemperature and the inhomogeneous density of the cloud. This results in a\nvanishing $v_c$ for the parameters similar to the experiments, which is\ninconsistent with the measurement of nonzero $v_c$. However, if the heating\nrate is based on the thermal fraction after a 100 ms equilibration time, our\nsimulation recovers the experimental observations. We demonstrate that this\ndiscrepancy is due to the slow relaxation of the stirred cloud and dipole mode\nexcitation of the cloud.",
        "positive": "Robust Bilayer Charge-Pumping for Spin- and Density-Resolved Quantum Gas\n  Microscopy: Quantum gas microscopy has emerged as a powerful new way to probe quantum\nmany-body systems at the microscopic level. However, layered or efficient\nspin-resolved readout methods have remained scarce as they impose strong\ndemands on the specific atomic species and constrain the simulated lattice\ngeometry and size. Here we present a novel high-fidelity bilayer readout, which\ncan be used for full spin- and density-resolved quantum gas microscopy of\ntwo-dimensional systems with arbitrary geometry. Our technique makes use of an\ninitial Stern-Gerlach splitting into adjacent layers of a highly-stable\nvertical superlattice and subsequent charge pumping to separate the layers by\n$21\\,\\mu$m. This separation enables independent high-resolution images of each\nlayer. We benchmark our method by spin- and density-resolving two-dimensional\nFermi-Hubbard systems. Our technique furthermore enables the access to advanced\nentropy engineering schemes, spectroscopic methods or the realization of\ntunable bilayer systems."
    },
    {
        "anchor": "Beats and Expansion of Two-Component Bose-Einstein Condensates in the\n  Thomas-Fermi Limit: A unique feature of multi-component BECs is the possibility of beating\nfrequencies in collective oscillations. We analytically determine this beating\nfrequency for the two-component BEC in one-dimension. We also show that the\nThomas-Fermi approximation, where the quantum pressure is neglected, describes\nwell the expansion of the two-component condensate released from an harmonic\ntrap.",
        "positive": "Improved optical standing-wave beam splitters for dilute Bose-Einstein\n  condensates: Bose-Einstein condensate (BEC)-based atom interferometry exploits low\ntemperatures and long coherence lengths to facilitate high-precision\nmeasurements. Progress in atom interferometry promises improvements in\nnavigational devices like gyroscopes and accelerometers, as well as\napplications in fundamental physics such as accurate determination of physical\nconstants. Previous work demonstrates that beam splitters and mirrors for\ncoherent manipulation of dilute BEC momentum in atom interferometers can be\nimplemented with sequences of non-resonant standing-wave light pulses. While\nprevious work focuses on the optimization of the optical pulses' amplitude and\nduration to produce high-order momentum states with high fidelity, we explore\nhow varying the shape of the optical pulses affects optimal beam-splitter\nperformance, as well as the effect of pulse shape on the sensitivity of\noptimized parameters in achieving high fidelity in high-momentum states. In\nsimulations of two-pulse beam splitters utilizing optimized square, triangle,\nand sinc-squared pulse shapes applied to dilute BECs, we, in some cases, reduce\nparameter sensitivity by an order of magnitude while maintaining fidelity."
    },
    {
        "anchor": "Interacting bosons in generalized zig-zag and railroad-trestle models: We theoretically study the ground-state phase diagram of strongly interacting\nbosons on a generalized zig-zag ladder model, the rail-road trestle (RRT)\nmodel. By means of analytical arguments in the limits of decoupled chains and\nthe case of vanishing fillings as well as extensive DMRG calculations we\nexamine the rich interplay between frustration and interaction for various\nparameter regimes. We distinguish three different cases, the fully frustrated\nRRT model where the dispersion relation becomes doubly degenerate and an\nextensive chiral superfluid regime is found, the anti-symmetric RRT with\nalternating $\\pi$ and $0$ fluxes through the ladder plaquettes and the sawtooth\nlimit, which is closely related to the latter case. We study detailed phase\ndiagrams which include besides different single component superfluids, the\nchiral superfluid phases, the two component superfluids and different gaped\nphases, with dimer and a charge-density wave order.",
        "positive": "Topologically protected vortex knots and links: We propose a class of tangled vortex structures, tied from non-Abelian\ntopological vortices, which are immune against decaying through local\nreconnections and strand crossings that are allowed by the system. We refer to\nsuch structures as being topologically protected. We then turn our attention to\ntopological vortices classified by the quaternion group $Q_8$ ($Q_8$-colored\nlinks), which are realizable in systems consisting either of the biaxial\nnematic or the cyclic phase of a spin-2 Bose--Einstein condensate, or of\nbiaxial nematic liquid crystal, and prove the existence of topologically\nprotected $Q_8$-colored links. Remarkably, the strongest invariant we\nconstruct, the $Q$-invariant of $Q_8$-colored links, can be used to classify\n$Q_8$-colored links up to allowed local surgeries on the vortex cores."
    },
    {
        "anchor": "Spin dynamics of large-spin (spinor) fermions in a harmonic trap: Understanding the collective dynamics in a many-body system has been a\ncentral task in condensed matter physics. To achieve this task, we develop a\nHartree-Fock theory to study the collective oscillations of spinor Fermi\nsystem, motivated by recent experiment on spin-9/2 fermions. We observe an\noscillation period shoulder for small rotation angles. Different from previous\nstudies, where the shoulder is found connected to the resonance from periodic\nto running phase, here the system is always in a running phase in the two-body\nphase space. This shoulder survives even in the many-body oscillations, which\ncould be tested in the experiments. We also show how these collective\noscillations evolve from two- to many-body. Our theory provides an alternative\nway to understand the collective dynamics in large-spin Fermi systems.",
        "positive": "Molecular impurities interacting with a many-particle environment: from\n  helium droplets to ultracold gases: In several settings of physics and chemistry one has to deal with molecules\ninteracting with some kind of an external environment, be it a gas, a solution,\nor a crystal surface. Understanding molecular processes in the presence of such\na many-particle bath is inherently challenging, and usually requires\nlarge-scale numerical computations. Here, we present an alternative approach to\nthe problem - that based on the notion of the angulon quasiparticle. We show\nthat molecules rotating inside superfluid helium nanodroplets and Bose-Einstein\nCondensates form angulons, and therefore can be described by straightforward\nsolutions of a simple microscopic Hamiltonian. Casting the problem in the\nlanguage of angulons allows not only to tremendously simplify it, but also to\ngain insights into the origins of the observed phenomena and to make\npredictions for future experimental studies."
    },
    {
        "anchor": "One-dimensional two-component fermions with contact even-wave repulsion\n  and SU(2) breaking near-resonant odd-wave attraction: We consider a one-dimensional (1D) two-component atomic Fermi gas with\ncontact interaction in the even-wave channel (Yang-Gaudin model) and study the\neffect of an SU(2) symmetry breaking near-resonant odd-wave interaction within\none of the components. Starting from the microscopic Hamiltonian, we derive an\neffective field theory for the spin degrees of freedom using the bosonization\ntechnique. It is shown that at a critical value of the odd-wave interaction\nthere is a first-order phase transition from a phase with zero total spin and\nzero magnetization to the spin-segregated phase where the magnetization locally\ndiffers from zero.",
        "positive": "Probing the quantum ground state of a spin-1 Bose-Einstein condensate\n  with cavity transmission spectra: We propose to probe the quantum ground state of a spin-1 Bose-Einstein\ncondensate with the transmission spectra of an optical cavity. By choosing a\ncircularly polarized cavity mode with an appropriate frequency, we can realize\ncoupling between the cavity mode and the magnetization of the condensate. The\ncavity transmission spectra then contain information of the magnetization\nstatistics of the condensate and thus can be used to distinguish the\nferromagnetic and antiferromagnetic quantum ground states. This technique may\nalso be useful for continuous observation of the spin dynamics of a spinor\nBose-Einstein condensate."
    },
    {
        "anchor": "Phase ordering percolation and an infinite domain wall in segregating\n  binary Bose-Einstein condensates: Percolation theory is applied to the phase-transition dynamics of domain\npattern formation in segregating binary Bose--Einstein condensates in\nquasi-two-dimensional systems. Our finite-size-scaling analysis shows that the\npercolation threshold of the initial domain pattern emerging from the dynamic\ninstability is close to 0.5 for strongly repulsive condensates. The percolation\nprobability is universally described with a scaling function when the\nprobability is rescaled by the characteristic domain size in the dynamic\nscaling regime of the phase-ordering kinetics, independent of the\nintercomponent interaction. It is revealed that an infinite domain wall\nsandwiched between percolating domains in the two condensates has an noninteger\nfractal dimension and keeps the scaling behavior during the dynamic scaling\nregime. This result seems to be in contrast to the argument that the dynamic\nscale invariance is violated in the presence of an infinite topological defect\nin numerical cosmology.",
        "positive": "Universal Relation for the Inelastic Two-Body Loss Rate: Strongly-interacting systems consisting of particles that interact through a\nlarge scattering length satisfy universal relations that relate many of their\ncentral properties to the contact, which measures the number of pairs with\nsmall separations. We use the operator product expansion of quantum field\ntheory to derive the universal relation for the inelastic 2-body loss rate. A\nsimple universal relation between the loss rate and the contact is obtained by\ntruncating the expansion after the lowest dimension operator. We verify the\nuniversal relation explicitly by direct calculations in the low-density limit\nat nonzero temperature. This universal relation can be tested experimentally\nusing ultracold quantum gases of atoms in hyperfine states that have an\ninelastic spin-relaxation channel."
    },
    {
        "anchor": "Anomalous Bloch oscillations in one dimensional parity-breaking periodic\n  potentials: We investigate the dynamics of a wave packet in a parity-breaking\none-dimensional periodic potential slowly varied in time and perturbed by a\nlinear potential. Parity is broken by considering an asymmetric double well per\nunit cell. By comparing the prediction of the semiclassical dynamics with the\nfull Schr\\\"odinger solution, we show that Bloch oscillations are strongly\naffected by anomalous velocity corrections related to Berry's phase. We\ncharacterize how these effects depend on the degree of parity breaking of the\npotential and on the modulation parameters. We also discuss how to measure the\neffects of the anomalous velocity in current experiments with non-interacting\nBose-Einstein condensates in bichromatic optical lattices, under the effect of\ngravity.",
        "positive": "Numerical representation of quantum states in the positive-P and Wigner\n  representations: Numerical stochastic integration is a powerful tool for the investigation of\nquantum dynamics in interacting many body systems. As with all numerical\nintegration of differential equations, the initial conditions of the system\nbeing investigated must be specified. With application to quantum optics in\nmind, we show how various commonly considered quantum states can be numerically\nsimulated by the use of widely available Gaussian and uniform random number\ngenerators. We note that the same methods can also be applied to computational\nstudies of Bose-Einstein condensates, and give some examples of how this can be\ndone."
    },
    {
        "anchor": "Composite fermion state of spin-orbit coupled bosons: We consider spinor Bose gas with the isotropic Rashba spin-orbit coupling in\n2D. We argue that at low density its groundstate is a composite fermion state\nwith a Chern-Simons gauge field and filling factor one. The chemical potential\nof such a state scales with the density as \\mu \\propto n^{3/2}. This is a lower\nenergy per particle than \\mu \\propto n for the earlier suggested groundstate\ncandidates: a condensate with broken time-reversal symmetry and a spin density\nwave state.",
        "positive": "Faraday waves on a bubble Bose-Einstein condensed binary mixture: By studying the dynamic stability of Bose-Einstein condensed binary mixtures\ntrapped on the surface of an ideal two-dimensional spherical bubble, we show\nhow the Rabi coupling between the species can modulate the interactions leading\nto parametric resonances. In this spherical geometry, the discrete unstable\nangular modes drive both phase separations and spatial patterns, with Faraday\nwaves emerging and coexisting with an immiscible phase. Noticeable is the fact\nthat, in the context of discrete kinetic energy spectrum, the only parameters\nto drive the emergence of Faraday waves are the $s-wave$ contact interactions\nand the Rabi coupling. Once analytical solutions for population dynamics are\nobtained, the stability of homogeneous miscible species is investigated through\nBogoliubov-de Gennes and Floquet methods, with predictions being analysed by\nfull numerical solutions applied to the corresponding time-dependent coupled\nformalism."
    },
    {
        "anchor": "Quantum phases of hardcore bosons with repulsive dipolar density-density\n  interactions on two-dimensional lattices: We analyse the ground-state quantum phase diagram of hardcore Bosons\ninteracting with repulsive dipolar potentials. The bosons dynamics is described\nby the extended-Bose-Hubbard Hamiltonian on a two-dimensional lattice. The\nground state results from the interplay between the lattice geometry and the\nlong-range interactions, which we account for by means of a classical spin\nmean-field approach limited by the size of the considered unit cells. This\nextended classical spin mean-field theory accounts for the long-range\ndensity-density interaction without truncation. We consider three different\nlattice geometries: square, honeycomb, and triangular. In the limit of zero\nhopping the ground state is always a devil's staircase of solid (gapped)\nphases. Such crystalline phases with broken translational symmetry are robust\nwith respect to finite hopping amplitudes. At intermediate hopping amplitudes,\nthese gapped phases melt, giving rise to various lattice supersolid phases,\nwhich can have exotic features with multiple sublattice densities. At\nsufficiently large hoppings the ground state is a superfluid. The stability of\nphases predicted by our approach is gauged by comparison to the known quantum\nphase diagrams of the Bose-Hubbard model with nearest-neighbour interactions as\nwell as quantum Monte Carlo simulations for the dipolar case on the square\nlattice. Our results are of immediate relevance for experimental realisations\nof self-organised crystalline ordering patterns in analogue quantum simulators,\ne.g., with ultracold dipolar atoms in an optical lattice.",
        "positive": "Continuous atom laser with Bose-Einstein condensates involving\n  three-body interactions: We demonstrate, through numerical simulations, the emission of a coherent\ncontinuous matter wave of constant amplitude from a Bose-Einstein Condensate in\na shallow optical dipole trap. The process is achieved by spatial control of\nthe variations of the scattering length along the trapping axis, including\nelastic three body interactions due to dipole interactions. In our approach,\nthe outcoupling mechanism are atomic interactions and thus, the trap remains\nunaltered. We calculate analytically the parameters for the experimental\nimplementation of this CW atom laser."
    },
    {
        "anchor": "Manipulation of nonequilibrium spin dynamics of an ultracold gas in a\n  moving optical lattice: The isolation and control of disparate degrees of freedom underpin quantum\nsimulators. We advance the programmability of cold atom quantum simulators with\na first realization of the dynamic interplay of spatial and spin degrees of\nfreedom. We experimentally demonstrate that violent spatial evolutions tune\nlong-lived coherent spin dynamics and develop a model of quantum spin-mixing\nincorporating the spatial evolution via time-dependent spin-spin interactions.\nOur results open new paths towards the simulation of quantum spin models with\ntunable interactions via tailored spatial dynamics.",
        "positive": "Bound states of a localized magnetic impurity in a superfluid of paired\n  ultracold fermions: We consider a localized impurity atom that interacts with a cloud of fermions\nin the paired state. We develop an effective scattering length description of\nthe interaction between an impurity and a fermionic atom using their vacuum\nscattering length. Treating the pairing of fermions at the mean-field level, we\nshow that the impurity atom acts like a magnetic impurity in the condensed\nmatter context, and leads to the formation of a pair of Shiba bound states\ninside the superconducting gap. In addition, the impurity atom can lead to the\nformation of deeply bound states below the Fermi sea."
    },
    {
        "anchor": "Inelastic Collisions of Solitary Waves in Anisotropic Bose-Einstein\n  Condensates: Sling-Shot Events and Expanding Collision Bubbles: We study experimentally and theoretically the dynamics of apparent dark\nsoliton stripes in an elongated Bose-Einstein condensate. We show that for the\ntrapping strengths corresponding to our experimental setup, the transverse\nconfinement along one of the tight directions is not strong enough to arrest\nthe formation of solitonic vortices or vortex rings. These solitonic vortices\nand vortex rings, when integrated along the transverse direction, appear as\ndark soliton stripes along the longitudinal direction thereby hiding their true\ncharacter. The latter significantly modifies the interaction dynamics during\ncollision events and can lead to apparent examples of inelasticity and what may\nappear experimentally even as a merger of two dark soliton stripes. We explain\nthis feature by means of the interaction of two solitonic vortices leading to a\nsling shot event with one of the solitonic vortices being ejected at a\nrelatively large speed. Furthermore we observe expanding collision bubbles\nwhich consist of repeated inelastic collisions of a dark soliton stripe pair\nwith an {\\it increasing} time interval between collisions.",
        "positive": "Non-equilibrium effective field theory for absorbing state phase\n  transitions in driven open quantum spin systems: Phase transitions to absorbing states are among the simplest examples of\ncritical phenomena out of equilibrium. The characteristic feature of these\nmodels is the presence of a fluctuationless configuration which the dynamics\ncannot leave, which has proved a rather stringent requirement in experiments.\nRecently, a proposal to seek such transitions in highly tuneable systems of\ncold atomic gases offers to probe this physics and, at the same time, to\ninvestigate the robustness of these transitions to quantum coherent effects.\nHere we specifically focus on the interplay between classical and quantum\nfluctuations in a simple driven open quantum model which, in the classical\nlimit, reproduces a contact process, which is known to undergo a continuous\ntransition in the \"directed percolation\" universality class. We derive an\neffective long-wavelength field theory for the present class of open spin\nsystems and show that, due to quantum fluctuations, the nature of the\ntransition changes from second to first order, passing through a bicritical\npoint which appears to belong instead to the \"tricritical directed percolation\"\nclass."
    },
    {
        "anchor": "Optical excitations of Skyrmions, knotted solitons, and defects in atoms: Analogies between non-trivial topologies of matter and light have inspired\nnumerous studies, including defect formation in structured light and\ntopological photonic band-structures. Three-dimensional topological objects of\nlocalized particle-like nature attract broad interest across discipline\nboundaries from elementary particle physics and cosmology to condensed matter\nphysics. Here we show how simple structured light beams can be transformed into\noptical excitations of atoms with considerably more complex topologies\nrepresenting three-dimensional particle-like Skyrmions. This construction can\nalso be described in terms of linked Hopf maps, analogous to knotted solitons\nof the Skyrme-Faddeev model. We identify the transverse polarization density\ncurrent as the effective magnetic gauge potential for the Chern-Simons helicity\nterm. While we prepare simpler two-dimensional baby-Skyrmions and singular\ndefects using the traditional Stokes vectors on the Poincar\\'e sphere for\nlight, particle-like topologies can only be achieved in the full optical\nhypersphere description that no longer discards the variation of the total\nelectromagnetic phase of vibration.",
        "positive": "Effective potential renormalization and polaronic mass shift in a\n  trapped dynamical impurity-luttinger liquid system: Recent experiments with cold atoms on the impurity motion in one-dimensional\nliquids of interacting bosons have revealed an interesting interplay between\nthe polaronic impurity mass shift and the renormalization of the optical\npotential. We show that the influence of the external trap on the Bose gas\nleads to a steeper effective potential for the impurity. We propose a framework\nin which this potential renormalization and the mass shift can be\nquantitatively understood by combining a semi-classical theory of density wave\nexcitations in the Luttinger liquid with the non equilibrium formalism of a\nquantum Brownian particle. The obtained theoretical results reproduce well\nrecent experimental data."
    },
    {
        "anchor": "Two-body relaxation in a Fermi gas at a p-wave Feshbach resonance: We systematically studied the two-body loss in a two-component Fermi gas of\n$^6$Li atoms near a p-wave Feshbach resonance. The two-body loss rate constants\nwere measured for various temperatures and magnetic fields using atoms trapped\nin three-dimensional and quasi-two-dimensional traps. Our results were nicely\nreproduced by a theoretical model that incorporates the two-body loss as an\nimaginary part to the inverse of the scattering volume in the scattering\namplitude expression. The observed loss suppression in quasi-two-dimensional\ntraps may provide a promising strategy to realize a p-wave superfluid in a\nsystem of ultracold atoms.",
        "positive": "Nonadiabatic creation of macroscopic superpositions with strongly\n  correlated 1D bosons on a ring trap: We consider a strongly interacting quasi-one dimensional Bose gas on a tight\nring trap subjected to a localized barrier potential. We explore the\npossibility to form a macroscopic superposition of a rotating and a nonrotating\nstate under nonequilibrium conditions, achieved by a sudden quench of the\nbarrier velocity. Using an exact solution for the dynamical evolution in the\nimpenetrable-boson (Tonks-Girardeau) limit, we find an expression for the\nmany-body wavefunction corresponding to a superposition state. The\nsuperposition is formed when the barrier velocity is tuned close to multiples\nof integer or half-integer number of Coriolis flux quanta. As a consequence of\nthe strong interactions, we find that (i) the state of the system can be mapped\nonto a macroscopic superposition of two Fermi spheres, rather than two\nmacroscopically occupied single-particle states as in a weakly interacting gas,\nand (ii) the barrier velocity should be larger than the sound velocity to\nbetter discriminate the two components of the superposition."
    },
    {
        "anchor": "Dynamics of a cold trapped ion in a Bose-Einstein condensate: We investigate the interaction of a laser-cooled trapped ion (Ba$^+$ or\nRb$^+$) with an optically confined $^{87}$Rb Bose-Einstein condensate (BEC).\nThe system features interesting dynamics of the ion and the atom cloud as\ndetermined by their collisions and their motion in their respective traps.\nElastic as well as inelastic processes are observed and their respective cross\nsections are determined. We demonstrate that a single ion can be used to probe\nthe density profile of an ultracold atom cloud.",
        "positive": "Vortex reconnections in anisotropic trapped three-dimensional\n  Bose-Einstein condensates: Quantum vortex reconnections can be considered as a fundamental unit of\ninteraction in complex turbulent quantum gases. Understanding the dynamics of\nsingle vortex reconnections as elementary events is an essential precursor to\nthe explanation of the emergent properties of turbulent quantum gases. It is\nthought that a lone pair of quantum vortex lines will inevitably interact given\na sufficiently long time. This paper investigates aspects of reconnections of\nquantum vortex pairs imprinted in a Bose-Einstein condensate held in an\nanisotropic three dimensional trap using an exact many-body treatment. In\nparticular the impact of the interaction strength and the trap anisotropy in\nthe reconnection time is studied. It is found that interaction strength has no\neffect on reconnection time over short time scales and that the trap anisotropy\ncan cause the edge of the condensate to interfere with the reconnection\nprocess. It is also found that the initially coherent system fragments very\nslowly, even for relatively large interaction strength, and therefore the\nsystem likes to stay condensed during the reconnections."
    },
    {
        "anchor": "Higher-order and fractional discrete time crystals in Floquet-driven\n  Rydberg atoms: Higher-order and fractional discrete time crystals (DTCs) are exotic phases\nof matter where the discrete time translation symmetry is broken into\nhigher-order and non-integer category. Generation of these unique DTCs has been\nwidely studied theoretically in different systems. However, no current\nexperimental methods can probe these higher-order and fractional DTCs in any\nquantum many-body systems. We demonstrate an experimental approach to observe\nhigher-order and fractional DTCs in Floquet-driven Rydberg atomic gases. We\nhave discovered multiple $n$-DTCs with integer values of $n$ = 2, 3, and 4, and\nothers ranging up to 14, along with fractional $n$-DTCs with $n$ values beyond\nthe integers. The system response can transition between adjacent integer DTCs,\nduring which the fractional DTCs are investigated. Study of higher-order and\nfractional DTCs expands fundamental knowledge of non-equilibrium dynamics and\nis promising for discovery of more complex temporal symmetries beyond the\nsingle discrete time translation symmetry.",
        "positive": "Superfluid transition temperature and fluctuation theory of spin-orbit\n  and Rabi-coupled fermions with tunable interactions: We obtain the superfluid transition temperature of equal Rashba-Dresselhaus\nspin-orbit and Rabi-coupled Fermi superfluids, from the\nBardeen-Cooper-Schrieffer (BCS) to Bose-Einstein condensate (BEC) regimes in\nthree dimensions for tunable $s$-wave interactions. In the presence of Rabi\ncoupling, we find that spin-orbit coupling enhances (reduces) the critical\ntemperature in the BEC (BCS) limit. For fixed interactions, we show that\nspin-orbit coupling can convert a first-order (discontinuous) phase transition\ninto a second-order (continuous) phase transition, as a function of Rabi\ncoupling. We derive the Ginzburg-Landau free energy to sixth power in the\nsuperfluid order parameter to describe both continuous and discontinuous phase\ntransitions as a function of spin-orbit and Rabi couplings. Lastly, we develop\na time-dependent Ginzburg-Landau fluctuation theory for an arbitrary mixture of\nRashba and Dresselhaus spin-orbit couplings at any interaction strength."
    },
    {
        "anchor": "Bright Matter-Wave Bound Soliton Molecules in Spin-1 Bose-Einstein\n  Condensates with Non-autonomous Nonlinearities: This work deals with matter-wave bright soliton molecules in spin-1\nBose-Einstein condensates described by three-component Gross-Pitaevskii\nequations with non-autonomous nonlinearities that can be tuned by Feshbach\nresonance management. Notably, it portrays the possibility of generating bright\nbound soliton molecules with the help of an exact analytic solution under a\ncontrolled velocity resonance mechanism. Results show that these soliton\nmolecules experience the effects of time-varying nonlinearities and modulate\nthemselves during propagation by keeping their stable properties.\nSignificantly, the chosen periodic and kink-like nonlinearities expose the\nsnaking, bending, compression, and amplification of multi-structured soliton\nmolecules along with appreciable changes in their amplitude, velocity, width,\nand oscillations of the molecule profiles. The present results will add\nsignificant knowledge to a complete understanding beyond the known interaction\ndynamics of matter-wave bright solitons in spinor condensates.",
        "positive": "Multidimensional solitons: Well-established results and novel findings: A brief review is given of some well-known and some very recent results\nobtained in studies of two- and three-dimensional (2D and 3D) solitons. Both\nzero-vorticity (fundamental) solitons and ones carrying vorticity S = 1 are\nconsidered. Physical realizations of multidimensional solitons in atomic\nBose-Einstein condensates (BECs) and nonlinear optics are briefly discussed\ntoo. Unlike 1D solitons, which are typically stable, 2D and 3D ones are\nvulnerable to instabilities induced by the occurrence of the critical and\nsupercritical collapse, respectively, in the same 2D and 3D models that give\nrise to the solitons. Vortex solitons are subject to a still stronger splitting\ninstability. For this reason, a central problem is search for physical settings\nin which 2D and 3D solitons may be stabilized. The brief review addresses one\nwell-established topic, viz., the stabilization of the 3D and 2D states, with S\n= 0 and 1, trapped in harmonic-oscillator (HO) potentials, and another topic\nwhich was developed very recently: the stabilization of 2D and 3D free-space\nsolitons, which juxtapose components with S = 0 and (+/-)1 (semi-vortices and\nmixed modes), in a binary system with the spin-orbit coupling (SOC) between its\ncomponents. The former model is based on the single cubic nonlinear\nSchroedinger/Gross-Pitaevskii equation (NLSE/GPE), while the latter one is\nrepresented by a system of two coupled GPEs. In both cases, generic situations\nare drastically different in the 2D and 3D geometries. In the 2D settings, the\nstabilization mechanism creates a stable ground state (GS, which was absent\nwithout the stabilization), whose norm falls below the threshold value at which\nthe critical collapse sets in. In the 3D geometry, the supercritical collapse\ndoes not allow to create a GS, but metastable solitons can be constructed."
    },
    {
        "anchor": "U(1) $\\times$ U(1) / Z$_2$ Kosterlitz-Thouless transition of the\n  Larkin-Ovchinnikov phase in an anisotropic two-dimensional system: We study Kosterlitz-Thouless (KT) transitions of the Larkin-Ovchinnikov (LO)\nphase for a two-dimensional system composed of coupled one-dimensional tubes of\nfermions. The LO phase here is characterized by a stripe structure (periodic in\nonly one direction) in the order parameter. The low energy excitations involve\nthe oscillation of the stripe and the fluctuation of the phase, which can be\ndescribed by an effective theory composed of two anisotropic XY models. We\ncompute from a microscopic model the coefficients of the XY models from which\nthe KT transition temperatures are determined. We found the $T^{KT} \\propto\nt_{\\perp}$ for small intertube tunneling $t_{\\perp}$. As $t_{\\perp}$ increases\nthe system undergoes a first-order transition to the normal phase at zero\ntemperature. Our method can be used to determine the Goldstone excitations of\nany stripe order involving charge or spin degrees of freedom.",
        "positive": "Electrical control of excitons in GaN/(Al,Ga)N quantum wells: A giant built-in electric field in the growth direction makes excitons in\nwide GaN/(Al, Ga)N quantum wells spatially indirect even in the absence of any\nexternal bias. Significant densities of indirect excitons can accumulate in\nelectrostatic traps imprinted in the quantum well plane by a thin metal layer\ndeposited on top of the heterostructure. By jointly measuring\nspatially-resolved photoluminescence and photo-induced current, we demonstrate\nthat exciton density in the trap can be controlled via an external electric\nbias, which is capable of altering the trap depth. Application of a negative\nbias deepens the trapping potential, but does not lead to any additional\naccumulation of excitons in the trap. This is due to exciton dissociation\ninstigated by the lateral electric field at the electrode edges. The resulting\ncarrier losses are detected as an increased photo-current and reduced\nphotoluminescence intensity. By contrast, application of a positive bias washes\nout the electrode-induced trapping potential. Thus, excitons get released from\nthe trap and recover free propagation in the plane that we reveal by\nspatially-resolved photoluminescence."
    },
    {
        "anchor": "Sticking Transition in a Minimal Model for the Collisions of Active\n  Particles in Quantum Fluids: Particles of low velocity, travelling without dissipation in a superfluid,\ncan interact and emit sound when they collide. We propose a minimal model in\nwhich the equations of motion of the particles, including a short-range\nrepulsive force, are self-consistently coupled with the Gross-Pitaevskii\nequation. We use this model to demonstrate the existence of an effective\nsuperfluid-mediated attractive interaction between the particles; and we study\nnumerically the collisional dynamics of particles as a function of their\nincident kinetic energy and the length-scale of the repulsive force. We find a\ntransition from almost elastic to completely inelastic (sticking) collisions as\nthe parameters are tuned. We find that aggregation and clustering result from\nthis sticking transition in multi-particle systems.",
        "positive": "Finite-size effects in the two-dimensional BCS-BEC crossover: We study the finite-size effects on the BCS-BEC crossover in two dimensions,\noccurring in confined fermionic superfluids. We analyze several thermodynamic\nproperties, such as the chemical potential, the energy gap and the superfluid\ndensity, taking into account unavoidable quantum fluctuations, and, by means of\nrenormalization group procedure, we detect the putative\nBerezinskii-Kosterlitz-Thouless phase transition at finite-size."
    },
    {
        "anchor": "Dual-species Bose-Einstein condensate of 41K and 87Rb in a hybrid trap: We report on the production of a 41K-87Rb dual-species Bose-Einstein\ncondensate in a hybrid trap, consisting of a magnetic quadrupole and an optical\ndipole potential. After loading both atomic species in the trap, we cool down\n87Rb first by magnetic and then by optical evaporation, while 41K is\nsympathetically cooled by elastic collisions with 87Rb. We eventually produce\ntwo-component condensates with more than 10^5 atoms and tunable species\npopulation imbalance. We observe the immiscibility of the quantum mixture by\nmeasuring the density profile of each species after releasing them from the\ntrap.",
        "positive": "Non-Hermitian BCS-BEC evolution with a complex scattering length: Having both elastic and inelastic two-body processes that are characterized\nby a complex $s$-wave scattering length between $\\uparrow$ and $\\downarrow$\nfermions in mind, here we apply the non-Hermitian extension of the mean-field\ntheory to the BCS-BEC evolution at zero temperature. We construct the phase\ndiagram of the system, where we find a reentrant superfluid (SF) transition\nthat is intervened by a normal and/or a metastable phase as a function of\nincreasing inelasticity. This transition occurs in a large parameter regime\naway from the unitarity, i.e., both on the BCS and BEC sides of the resonance,\nand it is mostly governed by the exceptional points. In addition, except for\nthe strongly-inelastic regime, we also show that the SF phase can be\nwell-described by the condensation of weakly-interacting bosonic pairs in the\ntwo-body bound state with a complex binding energy."
    },
    {
        "anchor": "On the survival of the quantum depletion of a condensate after release\n  from a magnetic trap: We present observations of the high momentum tail in expanding Bose-Einstein\ncondensates of metastable Helium atoms released from a harmonic trap. The\nfar-field density profile exhibits features that support identification of the\ntails of the momentum distribution as originating in the in-situ quantum\ndepletion prior to release. Thus, we corroborate recent observations of\nslowly-decaying tails in the far-field beyond the thermal component. This\nobservation is in conflict with the hydrodynamic theory, which predicts that\nthe in-situ depletion does not survive when atoms are released from a trap.\nIndeed, the depleted tails even appear stronger in the far-field than expected\nbefore release, and we discuss the challenges of interpreting this in terms of\nthe Tan contact in the trapped gas. In complement to these observations, full\nquantum simulations of the experiment show that, under the right conditions,\nthe depletion can persist into the far field after expansion. Moreover, the\nsimulations provide mechanisms for survival and for the the large-momentum\ntails to appear stronger after expansion due to an acceleration of the depleted\natoms by the mean-field potential. However, while in qualitative agreement, the\nfinal depletion observed in the experiment is much larger than in the\nsimulation.",
        "positive": "Gauge Invariant Linear Response Theories for Ultracold Fermi Gases with\n  Pseudogap: Recent experimental progresses allow for exploring some important physical\nquantities of ultracold Fermi gases, such as the compressibility, spin\nsusceptibility, viscosity, optical conductivity and spin diffusivity.\nTheoretically, these quantities can be evaluated from suitable linear response\ntheories. For BCS superfluid, it has been found that the gauge invariant linear\nresponse theories can be fully consistent with some stringent consistency\nconstraints. When the theory is generalized to stronger-than-BCS regime, one\nmay meet serious difficulties to satisfy the gauge invariance conditions. In\nthis paper, we try to construct density and spin linear response theories which\nare formally gauge invariant for a Fermi gas undergoing BCS-Bose-Einstein\nCondensation (BEC) crossover, especially below the superfluid transition\ntemperature $T_c$. We adapt a particular $t$-matrix approach which is close to\nthe $G_0G$ formalism to incorporate non-condensed pairing in the normal state.\nWe explicitly show that the fundamental constraints imposed by the Ward\nidentities, $Q$-limit Ward identity are indeed satisfied."
    },
    {
        "anchor": "Dynamics of an itinerant spin-3 atomic dipolar gas in an optical lattice: Arrays of ultra-cold dipolar gases loaded in optical lattices are emerging as\npowerful quantum simulators of the many-body physics associated with the rich\ninterplay between long-range dipolar interactions, contact interactions,\nmotion, and quantum statistics. In this work we report on our investigation of\nthe quantum many-body dynamics of a large ensemble of bosonic magnetic chromium\natoms with spin S = 3 in a three-dimensional lattice as a function of lattice\ndepth. Using extensive theory and experimental comparisons we study the\ndynamics of the population of the different Zeeman levels and the total\nmagnetization of the gas across the superfluid to the Mott insulator\ntransition. We are able to identify two distinct regimes: At low lattice\ndepths, where atoms are in the superfluid regime, we observe that the spin\ndynamics is strongly determined by the competition between particle motion,\nonsite interactions and external magnetic field gradients. Contact spin\ndependent interactions help to stabilize the collective spin length, which sets\nthe total magnetization of the gas. On the contrary, at high lattice depths,\ntransport is largely frozen out. In this regime, while the spin populations are\nmainly driven by long range dipolar interactions, magnetic field gradients also\nplay a major role in the total spin demagnetization. We find that dynamics at\nlow lattice depth is qualitatively reproduced by mean-field calculations based\non the Gutzwiller ansatz; on the contrary, only a beyond mean-field theory can\naccount for the dynamics at large lattice depths. While the cross-over between\nthese two regimes does not correspond to sharp features in the observed\ndynamical evolution of the spin components, our simulations indicate that it\nwould be better revealed by measurements of the collective spin length.",
        "positive": "Effect of quartic-quintic beyond-mean-field interactions on a self-bound\n  dipolar droplet: We study the effect of beyond-mean-field quantum-fluctuation (QF)\nLee-Huang-Yang (LHY) and three-body interactions, with quartic and quintic\nnonlinearities, respectively, on the formation of a stable self-repulsive\n(positive scattering length $a$) and a self-attractive (negative $a$)\nself-bound dipolar Bose-Einstein condensate (BEC) droplet in free space under\nthe action of two-body contact and dipolar interactions. Previous studies of\ndipolar droplets considered either the LHY interaction or the three-body\ninteraction, as either of these interactions could stabilize a dipolar BEC\ndroplet against collapse. We find that the effect of three-body recombination\non the formation of a dipolar droplet could be quite large and for a complete\ndescription of the problem both the QF LHY and three-body interactions should\nbe considered simultaneously, where appropriate. In the self-repulsive case for\nsmall $a$ and in the self-attractive case, no appropriate LHY interaction is\nknown and only three-body interaction should be used, otherwise both\nbeyond-mean-field interactions should be used. We consider a numerical solution\nof a highly-nonlinear beyond-mean-field model as well as a variational\napproximation to it in this investigation and present results for size, shape\nand energy of a dipolar droplet of polarized $^{164}$Dy atoms. The shape is\nfilament-like, along the polarization direction, and could be long, for a large\nnumber of atoms $N$, short for small $N$, thin for negative $a$ and small\npositive $a$, and fat for large positive $a$."
    },
    {
        "anchor": "Accurate numerical verification of the instanton method for macroscopic\n  quantum tunneling: dynamics of phase slips: Instanton methods, in which imaginary-time evolution gives the tunneling\nrate, have been widely used for studying quantum tunneling in various contexts.\nNevertheless, how accurate instanton methods are for the problems of\nmacroscopic quantum tunneling (MQT) still remains unclear because of lack of\ntheir direct comparison with exact time evolution of the many-body Schroedinger\nequation. Here, we verify instanton methods applied to coherent MQT.\nSpecifically applying the quasi-exact numerical method of time-evolving block\ndecimation to the system of bosons in a ring lattice, we directly simulate the\nreal-time quantum dynamics of supercurrents, where a coherent oscillation\nbetween two macroscopically distinct current states occurs due to MQT. The\ntunneling rate extracted from the coherent oscillation is compared with that\ngiven by the instanton method. We show that the error is within 10% when the\neffective Planck's constant is sufficiently small. We also discuss phase slip\ndynamics associated with the coherent oscillations.",
        "positive": "Quantum engineering of a synthetic thermal bath for bosonic atoms in a\n  one-dimensional optical lattice via Markovian feedback control: We propose and investigate a scheme for engineering a synthetic thermal bath\nfor a bosonic quantum gas in a one-dimensional optical lattice based on\nMarkovian feedback control. The performance of our scheme is quantified by the\nfidelity between the steady state of the system and the effective thermal\nstate. For double-well and triple-well systems with non-interacting particles,\nthe steady state is found to be an exact thermal state, which is attributed to\nthe fact that the transfer rates between all pairs of coupled eigenstates\nsatisfy detailed balance condition. The scenario changes when there are more\nlattice sites, where the detailed balance condition does not hold any more, but\nremains an accurate approximation. Remarkably, our scheme performs very well at\nlow and high temperature regimes, with the fidelity close to one. The\nperformance at the intermediate temperature regime (where a crossover into a\nBose condensed regime occurs) is slightly worse, and the fidelity shows a\ngentle decrease with increasing system size. We also discuss the interacting\ncases. In contrast to the non-interacting cases, the scheme is found to perform\nbetter at a higher temperature. Another difference is that the minimal\ntemperature that can be engineered is nonzero and increases with the\ninteraction strength."
    },
    {
        "anchor": "Atom-dimer scattering and long-lived trimers in fermionic mixtures: We consider a heteronuclear fermionic mixture on the molecular side of an\ninterspecies Feshbach resonance and discuss atom-dimer scattering properties in\nuniform space and in the presence of an external confining potential,\nrestricting the system to a quasi-2D geometry. We find that there is a peculiar\natom-dimer p-wave resonance which can be tuned by changing the frequency of the\nconfinement. Our results have implications for the ongoing experiments on\nLithium-Potassium mixtures, where this mechanism allows for switching the\np-wave interaction between a K atom and Li-K dimer from attractive to\nrepulsive, and forming a weakly bound trimer with unit angular momentum. We\nshow that such trimers are long-lived and the atom-dimer resonance does not\nenhance inelastic relaxation in the mixture, making it an outstanding candidate\nfor studies of p-wave resonance effects in a many-body system.",
        "positive": "Topological superfluid in a trapped two-dimensional polarized Fermi gas\n  with spin-orbit coupling: We study the stability region of the topological superfluid phase in a\ntrapped two-dimensional polarized Fermi gas with spin-orbit coupling and across\na BCS-BEC crossover. Due to the competition between polarization, pairing\ninteraction and spin-orbit coupling, the Fermi gas typically phase separates in\nthe trap. Employing a mean field approach that guarantees the ground state\nsolution, we systematically study the structure of the phase separation and\ninvestigate in detail the optimal parameter region for the preparation of the\ntopologically non-trivial superfluid phase. We then calculate the momentum\nspace density distribution of the topological superfluid state and demonstrate\nthat the existence of the phase leaves a unique signature in the trap\nintegrated momentum space density distribution which can survive the\ntime-of-flight imaging process."
    },
    {
        "anchor": "Two trapped particles interacting by a finite-ranged two-body potential\n  in two spatial dimensions: We examine the problem of two particles confined in an isotropic harmonic\ntrap, which interact via a finite-ranged Gaussian-shaped potential in two\nspatial dimensions. We derive an approximative transcendental equation for the\nenergy and study the resulting spectrum as a function of the interparticle\ninteraction strength. Both the attractive and repulsive systems are analyzed.\nWe study the impact of the potential's range on the ground-state energy.\nComplementary, we also explicitly verify by a variational treatment that in the\nzero-range limit the positive delta potential in two dimensions only reproduces\nthe non-interacting results, if the Hilbert space in not truncated. Finally, we\nestablish and discuss the connection between our finite-range treatment and\nregularized zero-range results from the literature.",
        "positive": "Suppression of the critical temperature for superfluidity near the Mott\n  transition: validating a quantum simulator: Ultracold atomic gases in optical lattices have proven to be a controllable,\ntunable and clean implementation of strongly interacting quantum many-body\nsystems. An essential prospect for such quantum simulators is their ability to\nmap out the phase diagram of fundamental many-body model Hamiltonians. However,\nthe results need to be validated first for representative benchmark problems\nvia state-of-the-art numerical methods of quantum many-body theory. Here we\npresent the first ab-initio comparison between experiments and quantum Monte\nCarlo simulations for strongly interacting Bose gases on a lattice for large\nsystems (up to N = 3e5 particles). The comparison has enabled us to perform\nthermometry for the interacting quantum gas and to experimentally determine the\nfinite temperature phase diagram for bosonic superfluids in an optical lattice.\nOur results reveal a downshift of the critical temperature as the transition to\nthe Mott insulator is approached."
    },
    {
        "anchor": "Feshbach modulation spectroscopy: In the vicinity of a Feshbach resonance, a system of ultracold atoms on an\noptical lattice undergoes rich physical transformations which involve molecule\nformation and hopping of molecules on the lattice and thus goes beyond a\nsingle-band Hubbard model description. We propose to probe the behavior of this\nsystem with a harmonic modulation of the magnetic field, and thus of the\nscattering length, across the Feshbach resonance, as an alternative to\nlattice-depth modulation spectroscopy. In the regime in which the single-band\nHubbard model is still valid, we provide simulation data for this type of\nspectroscopy. The method may uncover a route towards the efficient creation of\nultracold molecules and provides an alternate means for lattice modulation\nspectroscopy.",
        "positive": "Spin pumping and measurement of spin currents in optical superlattices: We report on the experimental implementation of a spin pump with ultracold\nbosonic atoms in an optical superlattice. In the limit of isolated double wells\nit represents a 1D dynamical version of the quantum spin Hall effect. Starting\nfrom an antiferromagnetically ordered spin chain, we periodically vary the\nunderlying spin-dependent Hamiltonian and observe a spin current without charge\ntransport. We demonstrate a novel detection method to measure spin currents in\noptical lattices via superexchange oscillations emerging after a projection\nonto static double wells. Furthermore, we directly verify spin transport\nthrough in-situ measurements of the spins' center of mass displacement."
    },
    {
        "anchor": "(2+1)$-dimensional sonic black hole from spin-orbit coupled\n  Bose-Einstein condensate and its analogue Hawking radiation: We study the properties of a $2+1$ dimensional Sonic black hole (SBH) that\ncan be realised, in a quasi-two-dimensional two-component spin-orbit coupled\nBose-Einstein condensate (BEC). The corresponding equation for phase\nfluctuations in the total density mode that describes phonon field in the\nhydrodynamic approximation is described by a scalar field equation in $2+1$\ndimension whose space-time metric is significantly different from that of the\nSBH realised from a single component BEC that was studied experimentally, and,\ntheoretically meticulously in literature. Given the breakdown of the\nirrotationality constraint of the velocity field in such spin-orbit coupled\nBEC, we study in detail how the time evolution of such condensate impacts the\nvarious properties of the resulting SBH. By time evolving the condensate in a\nsuitably created laser-induced potential, we show that such a sonic black hole\nis formed, in an annular region bounded by inner and outer event horizon as\nwell as elliptical ergo-surfaces. We observe amplifying density modulation due\nto the formation of such sonic horizons and show how they change the nature of\nanalogue Hawking radiation emitted from such sonic black hole by evaluating the\ndensity-density correlation at different times, using the truncated Wigner\napproximation (TWA) for different values of spin-orbit coupling parameters. We\nfinally investigate the thermal nature of such analogue Hawking radiation.",
        "positive": "A scanning gate microscope for cold atomic gases: We present a scanning probe microscopy technique for spatially resolving\ntransport in cold atomic gases, in close analogy with scanning gate microscopy\nin semiconductor physics. The conductance of a quantum point contact connected\nto two atomic reservoirs is measured in the presence of a tightly focused laser\nbeam acting as a local perturbation that can be precisely positioned in space.\nBy scanning its position and recording the subsequent variations of\nconductance, we retrieve a high-resolution map of transport through a quantum\npoint contact. We demonstrate a spatial resolution comparable to the extent of\nthe transverse wave function of the atoms inside the channel, and a position\nsensitivity below 10nm. Our measurements agree well with an analytical model\nand ab-initio numerical simulations, allowing us to identify a regime in\ntransport where tunneling dominates over thermal effects. Our technique opens\nnew perspectives for the high-resolution observation and manipulation of cold\natomic gases."
    },
    {
        "anchor": "Charge Pumping of Interacting Fermion Atoms in the Synthetic Dimension: Recently it has been proposed and experimentally demonstrated that a\nspin-orbit coupled multi-component gas in 1d lattice can be viewed as spinless\ngas in a synthetic 2d lattice with a magnetic flux. In this letter we consider\ninteraction effect of such a Fermi gas, and propose signatures in charge\npumping experiment, which can be easily realized in this setting. Using 1/3\nfilling of the lowest 2d band as an example, in strongly interacting regime, we\nshow that the charge pumping value gradually approaches a universal fractional\nvalue for large spin component and low filling of 1d lattice, indicating a\nfractional quantum Hall type behavior; while the charge pumping value is zero\nif the 1d lattice filling is commensurate, indicating a Mott insulator\nbehavior. The charge-density-wave order is also discussed.",
        "positive": "Matter-wave dark solitons: stochastic vs. analytical results: The dynamics of dark matter-wave solitons in elongated atomic condensates are\ndiscussed at finite temperatures. Simulations with the stochastic\nGross-Pitaevskii equation reveal a noticeable, experimentally observable spread\nin individual soliton trajectories, attributed to inherent fluctuations in both\nphase and density of the underlying medium. Averaging over a number of such\ntrajectories (as done in experiments) washes out such background fluctuations,\nrevealing a well-defined temperature-dependent temporal growth in the\noscillation amplitude. The average soliton dynamics is well captured by the\nsimpler dissipative Gross-Pitaevskii equation, both numerically and via an\nanalytically-derived equation for the soliton center based on perturbation\ntheory for dark solitons."
    },
    {
        "anchor": "Effect of interactions on the diffusive expansion of a Bose-Einstein\n  condensate in a 3D random potential: We theoretically study the influence of weak interactions on the diffusive\nexpansion of a Bose-Einstein condensate in a three-dimensional random\npotential. For this purpose we develop a perturbative approach and calculate\nanalytically the first-order nonlinear correction to the ensemble-averaged\natomic density as a function of position and time. We find that interactions\nrenormalize the typical diffusion coefficient of the condensate. The magnitude\nof the nonlinear correction is controlled by a single dimensionless parameter\nthat includes both interaction and disorder strengths.",
        "positive": "Nonrelativistic Conformal Invariance in Mesoscopic Two-Dimensional Fermi\n  Gases: Two-dimensional Fermi gases with universal short-range interactions are known\nto exhibit a quantum anomaly, where a classical scale and conformal invariance\nis broken by quantum effects at strong coupling. We argue that in a quasi\ntwo-dimensional geometry, a conformal window remains at weak interactions.\nUsing degenerate perturbation theory, we verify the conformal symmetry by\ncomputing the energy spectrum of mesoscopic particle ensembles in a harmonic\ntrap, which separates into conformal towers formed by so-called primary states\nand their center-of-mass and breathing-mode excitations, the latter having\nexcitation energies at precisely twice the harmonic oscillator energy. In\naddition, using Metropolis importance sampling, we compute the hyperradial\ndistribution function of the many-body wave functions, which are predicted by\nthe conformal symmetry in closed analytical form. The weakly interacting Fermi\ngas constitutes a system where the nonrelativistic conformal symmetry can be\nrevealed using elementary methods, and our results are testable in current\nexperiments on mesoscopic Fermi gases."
    },
    {
        "anchor": "Revealing the topological nature of the bond order wave in a strongly\n  correlated quantum system: We investigate the topological properties of the bond order wave phase\narising in the extended Fermi-Hubbard model. In particular, we uncover a\ntopological sector, which remained elusive in previous finite-size numerical\nstudies due to boundary effects. We first show that, for an infinite system,\nthe bond order wave regime is characterized by two degenerate bulk states\ncorresponding to the trivial and topological sectors. The latter turns out to\nbe indeed characterized by an even degeneracy of the entanglement spectrum and\nlonge-range order of a string correlation function. For finite size systems, we\nshow that the topological sector can be stabilized by imposing a suitable\nborder potential. This therefore provides a concrete protocol for the\nobservation of topologically protected degenerate edge modes in finite-size\nsystems. Furthermore, we show that the bulk of the system is characterized by\nexotic solitonic solutions interpolating between the trivial and topological\nsectors. Finally, we propose an implementation and detection scheme of this\nstrongly-correlated topological phase in a quantum simulator based on dipolar\nFermi gases in optical lattices.",
        "positive": "Elastic Multi-Body Interactions on a Lattice: We show that by coupling two hyperfine states of an atom in an optical\nlattice one can independently control two-, three-, and four-body on-site\ninteractions in a non-perturbative manner. In particular, under typical\nconditions of current experiments one can have a purely three- or four-body\ninteracting gas of $^{39}$K atoms characterized by on-site interaction shifts\nof several 100Hz."
    },
    {
        "anchor": "Elastic and inelastic transmission in guided atom lasers: a truncated\n  Wigner approach: We study the transport properties of an ultracold gas of Bose-Einstein\ncondensate that is coupled from a magnetic trap into a one-dimensional\nwaveguide. Our theoretical approach to tackle this problem is based on the\ntruncated Wigner method for which we assume the system to consist of two\nsemi-infinite non-interacting leads and a finite interacting scattering region\nwith two constrictions modelling an atomic quantum dot. The transmission is\ncomputed in the steady-state regime and we find a good agreement between\ntruncated Wigner and Matrix-Product State calculations. We also identify clear\nsignatures of inelastic resonant scattering by analyzing the distribution of\nenergy in the transmitted atomic matter wave beam.",
        "positive": "Hierarchical relaxation dynamics in a tilted two-band Bose-Hubbard model: We numerically examine slow and hierarchical relaxation dynamics of\ninteracting bosons described by a tilted two-band Bose-Hubbard model. The\nsystem is found to exhibit signatures of quantum chaos within the spectrum and\nthe validity of the eigenstate thermalization hypothesis for relevant physical\nobservables is demonstrated for certain parameter regimes. Using the truncated\nWigner representation in the semiclassical limit of the system, dynamics of\nrelevant observables reveal hierarchical relaxation and the appearance of\nprethermalized states is studied from the perspective of statistics of the\nunderlying mean-field trajectories. The observed prethermalization scenario can\nbe attributed to different stages of glassy dynamics in the mode-time\nconfiguration space due to dynamical phase transition between ergodic and\nnonergodic trajectories."
    },
    {
        "anchor": "Two-body problem in a multiband lattice and the role of quantum geometry: We consider the two-body problem in a periodic potential, and study the\nbound-state dispersion of a spin-$\\uparrow$ fermion that is interacting with a\nspin-$\\downarrow$ fermion through a short-range attractive interaction. Based\non a variational approach, we obtain the exact solution of the dispersion in\nthe form of a set of self-consistency equations, and apply it to tight-binding\nHamiltonians with onsite interactions. We pay special attention to the\nbipartite lattices with a two-point basis that exhibit time-reversal symmetry,\nand show that the lowest-energy bound states disperse quadratically with\nmomentum, whose effective-mass tensor is partially controlled by the quantum\nmetric tensor of the underlying Bloch states. In particular, we apply our\ntheory to the Mielke checkerboard lattice, and study the special role played by\nthe interband processes in producing a finite effective mass for the bound\nstates in a non-isolated flat band.",
        "positive": "Double-degenerate Fermi mixtures of $^6$Li and $^{53}$Cr atoms: We report on the realization of a novel degenerate mixture of ultracold\nfermionic lithium and chromium atoms. Based on an all-optical approach, with an\noverall duty-cycle of about 13 seconds, we produce large and degenerate samples\nof more than 2$\\times 10^5$ $^6$Li atoms and $10^5$ $^{53}$Cr atoms, with both\nspecies exhibiting normalized temperatures of about $T/T_{F}$=0.25.\nAdditionally, through the exploitation of a crossed bichromatic optical dipole\ntrap, we can controllably vary the density and degree of degeneracy of the two\ncomponents almost independently, and widely tune the lithium-to-chromium\ndensity ratio. Our $^{6}$Li-$^{53}$Cr Fermi mixture opens the way to the\ninvestigation of a variety of exotic few- and many-body regimes of quantum\nmatter, and it appears as an optimally-suited system to realize ultracold\nparamagnetic polar molecules, characterized by both electric and magnetic\ndipole moments. Ultimately, our strategy also provides an efficient pathway to\nproduce dipolar Fermi gases, or spin-mixtures, of ultracold $^{53}$Cr atoms."
    },
    {
        "anchor": "Microscopic Approach to Shear Viscosities in Superfluid Gases: From BCS\n  to BEC: We compute the shear viscosity, $\\eta$, at general temperatures $T$, in a\nBCS-BEC crossover scheme which is demonstrably consistent with conservation\nlaws. The study of $\\eta$ is important because it constrains microscopic\ntheories by revealing the excitation spectra. The onset of a normal state\npairing gap and the contribution from pair degrees of freedom imply that $\\eta$\nat low $T$ becomes small, rather than exhibiting the upturn predicted by most\nothers. Using the local density approximation, we find quite reasonable\nagreement with just-published experiments.",
        "positive": "Counterflow Quantum Turbulence and the Instability in Two-component\n  Bose-Einstein Condensates: We theoretically study the nonlinear dynamics of the instability of\ncounter-superflow in two miscible Bose-Einstein condensates. The condensates\nbecome unstable when the relative velocity exceeds a critical value, which is\ncalled counter-superflow instability. We reveal that the counter-superflow\ninstability can lead to quantum turbulence by numerically solving the coupled\nGross-Pitaevskii equations. The modes amplified by the instability grow into\nsolitons and decay into quantized vortices.Eventually, the vortices become\ntangled and quantum turbulence of two superfluids. We show that this process\nmay occur in experiments by investigating the dynamics in a 2D trapped system."
    },
    {
        "anchor": "Oscillations of a quasi-one-dimensional dipolar supersolid: The properties of a supersolid state (SS) in quasi-one-dimensional dipolar\nBose-Einstein condensate is studied, considering two possible mechanisms of\nrealization - due to repulsive three-body atomic interactions and quantum\nfluctuations in the framework of the Lee-Huang-Yang (LHY) theory. The proposed\ntheoretical model, based on minimization of the energy functional, allows\nevaluating the amplitude of the SS for an arbitrary set of parameters in the\ngoverning Gross-Pitaevskii equation (GPE). To explore the dynamics of the SS\nfirst, we numerically construct its ground state in different settings,\nincluding periodic boundary conditions, box-like trap and parabolic potential,\nthen impose a perturbation. In oscillations of the perturbed supersolid we\nobserve the key manifestation of SS, namely the free flow of the superfluid\nfraction through the crystalline component of the system. Two distinct\noscillation frequencies of the supersolid associated with the superfluid\nfraction and crystalline components of the wave function are identified from\nnumerical simulations of the GPE.",
        "positive": "Probing dynamical criticality near quantum phase transitions: We reveal a prethermal temporal regime upon suddenly quenching to the\nvicinity of a quantum phase transition in the time evolution of 1D spin chains.\nThe prethermal regime is analytically found to be self-similar, and its\nduration is governed by the ground-state energy gap. Based on analytical\ninsights and numerical evidence, we show that this critically prethermal regime\nuniversally exists independently of the location of the probe site, the\npresence of weak interactions, or the initial state. Moreover, the resulting\nprethermal dynamics leads to an out-of-equilibrium scaling function of the\norder parameter in the vicinity of the transition."
    },
    {
        "anchor": "Quasi-one-dimensional spin-orbit- and Rabi-coupled bright dipolar\n  Bose-Einstein-condensate solitons: We study the formation of stable bright solitons in quasi-one-dimensional\n(quasi-1D) spin-orbit- (SO-) and Rabi-coupled two pseudospinor dipolar\nBose-Einstein condensates (BECs) of 164 Dy atoms in the presence of repulsive\ncontact interactions. As a result of the combined attraction-repulsion effect\nof both interactions and the addition of SO and Rabi couplings, two kinds of\nground states in the form of self-trapped bright solitons can be formed, a\nplane-wave soliton (PWS) and a stripe soliton (SS). These quasi-1D solitons\ncannot exist in a condensate with purely repulsive contact interactions and SO\nand Rabi couplings (no dipole). Neglecting the repulsive contact interactions,\nour findings also show the possibility of creating PWSs and SSs. When the\nstrengths of the two interactions are close to each other, the SS develops an\noscillatory instability indicating a possibility of a breather solution,\neventually leading to its destruction. We also obtain a phase diagram showing\nregions where the solution is a PWS or SS.",
        "positive": "Strongly Interacting Bose Gases near a $d$-wave Shape Resonance: Many unconventional quantum matters, such as fractional quantum Hall effect\nand $d$-wave high-Tc superconductor, are discovered in strongly interacting\nsystems. Understanding quantum many-body systems with strong interaction and\nthe unconventional phases therein is one of the most challenging problems in\nphysics nowadays. Cold atom systems possess a natural way to create strong\ninteraction by bringing the system to the vicinity of a scattering resonance.\nAlthough this has been a focused topic in cold atom physics for more than a\ndecade, these studies have so far mostly been limited for $s$-wave resonance.\nHere we report the experimental observation of a broad $d$-wave shape resonance\nin degenerate ${}^{41}$K gas. We further measure the molecular binding energy\nthat splits into three branches as a hallmark of $d$-wave molecules, and find\nthat the lifetime of this many-body system is reasonably long at strongly\ninteracting regime. From analyzing the breathing mode excited by ramping\nthrough this resonance, it suggests that a quite stable low-temperature atom\nand molecule mixture is produced. Putting all the evidence together, our system\noffers great promise to reach a $d$-wave molecular superfluid."
    },
    {
        "anchor": "Relaxation dynamics of conserved quantities in a weakly non-integrable\n  one-dimensional Bose gas: In this work we report preliminary results on the relaxational dynamics of\none dimensional Bose gases, as described by the Lieb-Liniger model, upon\nrelease from a parabolic trap. We explore the effects of integrability and\nintegrability breaking upon these dynamics by placing the gas post-release in\nan integrability breaking one-body cosine potential of variable amplitude. By\nstudying the post-quench evolution of the conserved charges that would exist in\nthe purely integrable limit, we begin to quantify the effects of the weak\nbreaking of integrability on the long time thermalization of the gas.",
        "positive": "Universal One-dimensional Atomic Gases Near Odd-wave Resonance: We show the renormalization of contact interaction for odd-wave scattering in\none-dimension(1D). Based on the renormalized interaction, we exactly solve the\ntwo-body problem in a harmonic trap, and further explore the universal\nproperties of spin-polarized fermions near odd-wave resonance using the\noperator product expansion method. It is found that the high-momentum\ndistribution behaves as $C/k^2$, with $C$ the odd-wave contact. Various\nuniversal relations are derived. Our work suggests a new universal system\nemergent in 1D with large odd-wave scattering length."
    },
    {
        "anchor": "Quasimomentum distribution and expansion of an anyonic gas: We point out that the momentum distribution is not a proper observable for a\nsystem of anyons in two-dimensions. In view of anyons as Wilczek's composite\ncharged flux-tubes, this is a consequence of the fact that the orthogonal\ncomponents of the kinetic momentum operator do not commute at the position of a\nflux tube, and thus cannot be diagonalized in the same basis. As a substitute\nfor the momentum distribution of an anyonic (spatially localized) state, we\npropose to use the asymptotic single-particle density after expansion of anyons\nin free space from the state. This definition is identical with the standard\none when the statistical parameter approaches that for bosons or fermions.\nExact examples of expansion dynamics, which underpin our proposal, and\nobservables that can be used to measure anyonic statistics, are shown.",
        "positive": "Emergent $\\mathbb{Z}_2$ gauge theories and topological excitations in\n  Rydberg atom arrays: Strongly interacting arrays of Rydberg atoms provide versatile platforms for\nexploring exotic many-body phases and dynamics of correlated quantum systems.\nMotivated by recent experimental advances, we show that the combination of\nRydberg interactions and appropriate lattice geometries naturally leads to\nemergent $\\mathbb{Z}_2$ gauge theories endowed with matter fields. Based on\nthis mapping, we describe how Rydberg platforms could realize two distinct\nclasses of topological $\\mathbb{Z}_2$ quantum spin liquids, which differ in\ntheir patterns of translational symmetry fractionalization. We also discuss the\nnatures of the fractionalized excitations of these $\\mathbb{Z}_2$ spin liquid\nstates using both fermionic and bosonic parton theories, and illustrate their\nrich interplay with proximate solid phases."
    },
    {
        "anchor": "Stability of quasicrystalline ultracold fermions to dipolar interactions: Quasiperiodic potentials can be used to interpolate between localization and\ndelocalization in one dimension. However, little is known about the stability\nof quasicrystalline phases to long-range interactions. In this work, we study\nrepulsive ultracold dipolar fermions in a quasiperiodic optical lattice to\ncharacterize the behavior of interacting quasicrystals. We simulate the full\ntime evolution of the typical experimental protocols used to probe\nquasicrystalline order and localization properties. We extract experimentally\nmeasurable dynamical observables and correlation functions to characterize the\nthree phases observed in the noninteracting setting: localized, intermediate,\nand extended. We then study the stability of such phases to repulsive dipolar\ninteractions. We find that dipolar interactions can completely alter the shape\nof the phase diagram by stabilizing the intermediate phase, mostly at the\nexpense of the extended phase. Moreover, in the strongly interacting regime, a\nresonance-like behavior characterized by density oscillations appears.\nRemarkably, strong dipolar repulsions can also localize particles even in the\nabsence of quasiperiodicity if the primary lattice is sufficiently deep. Our\nwork shows that dipolar interactions in a quasiperiodic potential can give rise\nto a complex, tuneable coexistence of localized and extended quantum states.",
        "positive": "Tests of universal three-body physics in an ultracold Bose-Fermi mixture: Recent measurements of Efimov resonances in a number of ultracold atom\nspecies have revealed an unexpected universality, in which three-body\nscattering properties are determined by the van der Waals length of the\ntwo-body interaction potential. To investigate whether this universality\nextends to heteronuclear mixtures, we measure loss rate coefficients in an\nultracold trapped gas of $^{40}$K and $^{87}$Rb atoms. We find an Efimov-like\nresonance in the rate of inelastic collisions between $^{40}$K$^{87}$Rb\nFeshbach molecules and $^{87}$Rb atoms. However, we do not observe any\nEfimov-related resonances in the rates of inelastic collisions between three\natoms. These observations are compared to previous measurements by the LENS\ngroup of Efimov resonances in a $^{41}$K and $^{87}$Rb mixture as well as to\nrecent predictions."
    },
    {
        "anchor": "Quantum dynamics and macroscopic quantum tunneling of two weakly coupled\n  condensates: We study the quantum dynamics of a Bose Josephson junction(BJJ) made up of\ntwo coupled Bose-Einstein condensates. Apart from the usual ac Josephson\noscillations, two different dynamical states of BJJ can be observed by tuning\nthe inter-particle interaction strength, which are known as '$\\pi$-oscillation'\nwith relative phase $\\pi$ between the condensates and 'macroscopic\nself-trapped' (MST) state with finite number imbalance. By choosing appropiate\nintial state we study above dynamical branches quantum mechanically and compare\nwith classical dynamics. The stability region of the '$\\pi$-oscillation' is\nseparated from that of 'MST' state at a critical coupling strength. Also a\nsignificant change in the energy spectrum takes place above the critical\ncoupling strength, and pairs of (quasi)-degenerate excited states appear. The\noriginal model of BJJ can be mapped on to a simple Hamiltonian describing\nquantum particle in an 'effective potential' with an effective Planck constant.\nDifferent dynamical states and degenerate excited states in the energy spectrum\ncan be understood in this 'effective potential' approach. Also possible novel\nquantum phenomena like 'macroscopic quantum tunneling'(MQT) become evident from\nthe simple picture of 'effective potential'. We study decay of metastable\n'$\\pi$-oscillation' by MQT through potential barrier. The doubly degenerate\nexcited states in the energy spectrum are associated with the classically\ndegenerate MST states with equal and opposite number imbalance. We calculate\nthe energy splitting between these quasi-degenerate excited states due to MQT\nof the condensate between classically degenerate MST states.",
        "positive": "Interaction effects on atomic laboratory trapped Bose-Einstein\n  condensates: We discuss the effect of inter-atoms interactions on the condensation\ntemperature $T_c$ of an atomic laboratory trapped Bose-Einstein condensate. We\nshow that, in the mean-field Hartree-Fock and semiclassical approximations,\ninteractions produce a shift $\\Delta T_{c}/T_{c}^{0} \\approx b_1\n(a/\\lambda_{T_c}) + b_2 (a/\\lambda_{T_c})^2 + \\psi[a/\\lambda_{T_c}]$ with $a$\nthe s-wave scattering length, $\\lambda_T$ the thermal wavelength and\n$\\psi[a/\\lambda_{T_c}]$ a non-analytic function such that $\\psi[0] = \\psi'[0] =\n\\psi\"[0] = 0$ and $|\\psi\"'[0]| = \\infty$. Therefore, with no more assumptions\nthan Hartree-Fock and semiclassical approximations, interaction effecs are\nperturbative to second order in $a/\\lambda_{T_c}$ and the expected\nnon-perturbativity of physical quantities at critical temperature appears only\nto third order. We compare this finding with different results by other\nauthors, which are based on more than the Hartree-Fock and semiclassical\napproximations. Moreover, we obtain an analytical estimation for $b_2 \\simeq\n18.8$ which improves a previous numerical result. We also discuss how the\ndiscrepancy between $b_2$ and the empirical value of $b_2 = 46 \\pm 5$ may be\nexplained with no need to resort to beyond-mean field effects."
    },
    {
        "anchor": "Roton-induced Bose polaron in the presence of synthetic spin-orbit\n  coupling: We theoretically investigate the quasiparticle (polaron) properties of an\nimpurity immersing in a Bose-Einstein condensate with equal Rashba and\nDresselhaus spin-orbit coupling at zero temperature. In the presence of\nspin-orbit coupling, all bosons can condense into a single plane-wave state\nwith finite momentum, and the corresponding excitation spectrum shows an\nintriguing roton minimum. We find that the polaron properties are strongly\nmodified by this roton minimum, where the ground state of attractive polaron\nacquires a nonzero momentum and anisotropic effective mass. Across the\nresonance of the interaction between impurity and atoms, the polaron evolves\ninto a tight-binding dimer. We show that the evolution is not smooth when the\nroton structure of the condensate becomes apparent, and a first-order phase\ntransition from a phonon-induced polaron to a roton-induced polaron is observed\nat a critical interaction strength.",
        "positive": "Multichannel effects in the Efimov regime from broad to narrow Feshbach\n  resonances: We study Efimov physics of three identical bosons with pairwise multichannel\ninteractions for Feshbach resonances of adjustable width. We find that the\ntwo-body multichannel nature of the interaction can affect the universal\nthree-body spectrum, especially for resonances of intermediate width. The\nshifts in this universal spectrum are caused by trimer states in the closed\ninteraction channels that couple to the universal Efimov states. However, in\nthe narrow resonance limit we find that the Efimov spectrum is set by the\nresonance width parameter $r^*$ only independent of the interaction potential\nconsidered. In the broad resonance limit all excited Efimov trimer energies\napproach the ones from the corresponding single-channel system for the\nscenarios investigated."
    },
    {
        "anchor": "Excitations and phase ordering of the spin-stripe phase of a binary\n  dipolar condensate: We consider the ground states, excitations and dynamics of a\nquasi-two-dimensional binary dipolar Bose-Einstein condensate. Our focus is on\nthe transition to a spin-stripe ground state in which the translational\ninvariance is spontaneously broken by a striped immiscible pattern of the\nalternating components. We develop a ground state phase diagram showing the\nparameter regime where the spin-stripe state occurs. Using Bogoliubov theory we\ncalculate the excitation spectrum and structure factors. We identify a balanced\nregime where the system has a $\\mathbb{Z}_2$ symmetry, and in the spin-stripe\nstate this yields a nonsymmorphic symmetry. We consider the evolution of the\nsystem following a quench from the uniform to spin-stripe state, revealing\nnovel ordering dynamics involving defects of the stripe order. Using an order\nparameter to characterize the orientational order of the stripes, we show that\nthe phase ordering exhibits dynamic scaling.",
        "positive": "Surface Effects in the Unitary Fermi Gas: We study the extended Thomas-Fermi (ETF) density functional of the superfluid\nunitary Fermi gas. This functional includes a gradient term which is essential\nto describe accurately the surface effects of the system, in particular with a\nsmall number of atoms, where the Thomas-Fermi (local density) approximation\nfails. We find that our ETF functional gives density profiles which are in good\nagreement with recent Monte Carlo results and also with a more sophisticated\nsuperfluid density functional based on Bogoliubov-de Gennes equations. In\naddition, by using extended hydrodynamics equations of superfluids, we\ncalculate the frequencies of collective surface oscillations of the unitary\nFermi gas, showing that quadrupole and octupole modes strongly depend on the\nnumber of trapped atoms."
    },
    {
        "anchor": "Dynamical quantum correlations of Ising models on an arbitrary lattice\n  and their resilience to decoherence: Ising models, and the physical systems described by them, play a central role\nin generating entangled states for use in quantum metrology and quantum\ninformation. In particular, ultracold atomic gases, trapped ion systems, and\nRydberg atoms realize long-ranged Ising models, which even in the absence of a\ntransverse field can give rise to highly non-classical dynamics and long-range\nquantum correlations. In the first part of this paper, we present a detailed\ntheoretical framework for studying the dynamics of such systems driven (at time\nt=0) into arbitrary unentangled non-equilibrium states, thus greatly extending\nand unifying the work of Ref. [1]. Specifically, we derive exact expressions\nfor closed-time-path ordered correlation functions, and use these to study\nexperimentally relevant observables, e.g. Bloch vector and spin-squeezing\ndynamics. In the second part, these correlation functions are then used to\nderive closed-form expressions for the dynamics of arbitrary spin-spin\ncorrelation functions in the presence of both T_1 (spontaneous spin\nrelaxation/excitation) and T_2 (dephasing) type decoherence processes. Even\nthough the decoherence is local, our solution reveals that the competition\nbetween Ising dynamics and T_1 decoherence gives rise to an emergent non-local\ndephasing effect, thereby drastically amplifying the degradation of quantum\ncorrelations. In addition to identifying the mechanism of this deleterious\neffect, our solution points toward a scheme to eliminate it via\nmeasurement-based coherent feedback.",
        "positive": "Non-standard Hubbard models in optical lattices: a review: Originally, the Hubbard model has been derived for describing the behaviour\nof strongly-correlated electrons in solids. However, since over a decade now,\nvariations of it are also routinely being implemented with ultracold atoms in\noptical lattices. We review some of the rich literature on this subject, with a\nfocus on more recent non-standard forms of the Hubbard model. After an\nintroduction to standard (fermionic and bosonic) Hubbard models, we discuss\nbriefly common models for mixtures, as well as the so called extended\nBose-Hubbard models, that include interactions between neighboring sites,\nnext-neighboring sites, and so on. The main part of the review discusses the\nimportance of additional terms appearing when refining the tight-binding\napproximation on the original physical Hamiltonian. Even when restricting the\nmodels to the lowest Bloch band is justified, the standard approach neglects\nthe density-induced tunneling (which has the same origin as the usual on-site\ninteraction). The importance of these contributions is discussed for both\ncontact and dipolar interactions. For sufficiently strong interactions, also\nthe effects related to higher Bloch bands become important even for deep\noptical lattices. Different approaches that aim at incorporating these effects,\nmainly via dressing the basis Wannier functions with interactions, leading to\neffective, density-dependent Hubbard-type models, are reviewed. We discuss also\nexamples of Hubbard-like models that explicitly involve higher $p$-orbitals, as\nwell as models that couple dynamically spin and orbital degrees of freedom.\nFinally, we review mean-field nonlinear-Schr\\\"odinger models of the Salerno\ntype that share with the non-standard Hubbard models the nonlinear coupling\nbetween the adjacent sites. In that part, discrete solitons are the main\nsubject of the consideration. We conclude by listing some future open problems."
    },
    {
        "anchor": "Tunable three-body interactions in driven two-component Bose-Einstein\n  condensates: We propose and demonstrate the appearance of an effective attractive\nthree-body interaction in coherently-driven two-component Bose Einstein\ncondensates. It originates from the spinor degree of freedom that is affected\nby a two-body mean-field shift of the driven transition frequency. Importantly,\nits strength can be controlled with the Rabi-coupling strength and it does not\ncome with additional losses. In the experiment, the three-body interactions are\nadjusted to play a predominant role in the equation of state of a cigar-shaped\ntrapped condensate. This is confirmed though two striking observations: a\ndownshift of the radial breathing mode frequency and the radial collapses for\npositive values of the dressed-state scattering length.",
        "positive": "Collective excitations of self-bound droplets of a dipolar quantum fluid: We calculate the collective excitations of a dipolar Bose-Einstein condensate\nin the regime where it self-binds into droplets stabilized by quantum\nfluctuations. We show that the filament-shaped droplets act as a\nquasi-one-dimensional waveguide along which low angular momentum phonons\npropagate. The evaporation (unbinding) threshold occurring as the atom number\n$N$ is reduced to the critical value $N_c$ is associated with a monopole-like\nexcitation going soft as $\\epsilon_0\\sim(N-N_c)^{1/4}$. Considering the system\nin the presence of a trapping potential, we quantify the crossover from a\ntrap-bound condensate to a self-bound droplet."
    },
    {
        "anchor": "Itinerant ferromagnetism in a two-dimensional atomic gas: Motivated by the first experimental evidence of ferromagnetic behavior in a\nthree-dimensional ultracold atomic gas, we explore the possibility of itinerant\nferromagnetism in a trapped two-dimensional atomic gas. Firstly, we develop a\nformalism that demonstrates how quantum fluctuations drive the ferromagnetic\nreconstruction first order, and consider the consequences of an imposed\npopulation imbalance. Secondly, we adapt this formalism to elucidate the key\nexperimental signatures of ferromagnetism in a realistic trapped geometry.",
        "positive": "Universal Hydrodynamic Transport Times in the Normal Phase of a Unitary\n  Fermi Gas: We determine the hydrodynamic relaxation times $\\tau_\\eta$ for the shear\nviscosity and $\\tau_\\kappa$ for the thermal conductivity in the normal phase of\na unitary Fermi gas confined in a box potential. Using a kinetic theory\nrelaxation model, we extract $\\tau_\\eta$ and $\\tau_\\kappa$ from the\ntime-dependent free-decay of a spatially periodic density perturbation,\nyielding the universal density-shift coefficients for the shear viscosity and\nthermal conductivity."
    },
    {
        "anchor": "Ultracold collisions in the Yb-Li mixture system: We report our experimental results on the collisional physics between\nnon-S-state atoms (ytterbium (Yb), effectively a two-electron system, in the\nmetastable ${}^3\\mathrm{P}_2$ state) and S-state atoms (lithium (Li), an alkali\nmetal, in the ground state). At low magnetic fields, by measuring inelastic\ninterspecies collisional losses in the double quantum degenerate mixture we\nreveal the strong dependence of the inelastic losses on the internal spin\nstates of both species and suppressed losses in stretched state configurations.\nIncreasing the magnetic field up to 800 G we further investigate the magnetic\nfield dependence of the collisional interactions. There, smoothly increasing\ninelastic losses are observed towards higher fields. The combined knowledge of\nboth the magnetic field and the spin state dependence of the collisional losses\nof this prototypical mixture system of non-S-state and S-state atoms provides a\nsignificant step forward towards controllable impurity physics realized in the\nYb-Li ultracold system.",
        "positive": "Correspondence between dark solitons and the type II excitations of\n  Lieb-Liniger model: A one-dimensional model of bosons with repulsive short-range interactions,\nsolved analytically by Lieb and Liniger many years ago, predicts existence of\ntwo branches of elementary excitations. One of them represents Bogoliubov\nphonons, the other, as suggested by some authors, might be related to dark\nsolitons. On the other hand, it has been already demonstrated within a\nframework of the classical field approximation that quasi-one-dimensional\ninteracting Bose gas at equilibrium exhibits excitations which are phonons and\ndark solitons. By showing that statistical distributions of dark solitons\nobtained within the classical field approximation match the distributions of\nquasiparticles of the second kind derived from fully quantum description we\ndemonstrate that type II excitations in the Lieb-Liniger model are, indeed,\nquantum solitons."
    },
    {
        "anchor": "Quantum simulators based on the global collective light-matter\n  interaction: We show that coupling ultracold atoms in optical lattices to quantized modes\nof an optical cavity leads to quantum phases of matter, which at the same time\nposses properties of systems with both short- and long-range interactions. This\nopens perspectives for novel quantum simulators of finite-range interacting\nsystems, even though the light-induced interaction is global (i.e. infinitely\nlong range). This is achieved by spatial structuring of the global light-matter\ncoupling at a microscopic scale. Such simulators can directly benefit from the\ncollective enhancement of the global light-matter interaction and constitute an\nalternative to standard approaches using Rydberg atoms or polar molecules. The\nsystem in the steady state of light induces effective many-body interactions\nthat change the landscape of the phase diagram of the typical Bose-Hubbard\nmodel. Therefore, the system can support non-trivial superfluid states, bosonic\ndimer, trimers, etc. states and supersolid phases depending on the choice of\nthe wavelength and pattern of the light with respect to the classical optical\nlattice potential. We find that by carefully choosing the system parameters one\ncan investigate diverse strongly correlated physics with the same setup, i.e.,\nmodifying the geometry of light beams. In particular, we present the interplay\nbetween the density and bond (or matter-wave coherence) interactions. We show\nhow to tune the effective interaction length in such a hybrid system with both\nshort-range and global interactions.",
        "positive": "Nonlinear dynamics of a spin-orbit-coupled Bose-Einstein condensate: Single-particle dynamics of a spin-orbit-coupled Bose-Einstein condensate has\nrecently been investigated in experiments that explore the physics of\nLandau-Zener tunneling and of the Zitterbewegung. In this paper, we study the\ninfluence of a nonlinearity due to interactions on these dynamics and show that\nthe dispersion relation develops interesting loop strucures. The atoms can move\nalong the nonlinear dispersion curve in the presence of a weak acceleration\nforce and we show that the loops lead to straightforward nonlinear Landau-Zener\ntunneling. However, we find that for the Zitterbewegung, induced by a sudden\nquench in the spin-orbit coupling parameters, the nonlinear dispersion is\nirrelevant."
    },
    {
        "anchor": "Spin-orbital dynamics in a system of polar molecules: Spin-orbit coupling (SOC) in solids normally originates from the electron\nmotion in the electric field of the crystal. It is key to understanding a\nvariety of spin-transport and topological phenomena, such as Majorana fermions\nand recently discovered topological insulators. Implementing and controlling\nspin-orbit coupling is thus highly desirable and could open untapped\nopportunities for the exploration of unique quantum physics. Here, we show that\ndipole-dipole interactions can produce an effective SOC in two-dimensional\nultracold polar molecule gases. This SOC generates chiral excitations with a\nnon-trivial Berry phase $2\\pi$. These excitations, which we call\n\\emph{chirons}, resemble low-energy quasiparticles in bilayer graphene and\nemerge regardless of the quantum statistics and for arbitrary ratios of kinetic\nto interaction energies. Chirons manifest themselves in the dynamics of the\nspin density profile, spin currents, and spin coherences, even for molecules\npinned in a deep optical lattice and should be observable in current\nexperiments.",
        "positive": "Self-consistent time-dependent harmonic approximation for the\n  sine-Gordon model out of equilibrium: We derive a self-consistent time-dependent harmonic approximation for the\nquantum sine-Gordon model out of equilibrium and apply the method to the\ndynamics of tunnel-coupled one-dimensional Bose gases. We determine the time\nevolution of experimentally relevant observables and in particular derive\nresults for the probability distribution of subsystem phase fluctuations. We\ninvestigate the regime of validity of the approximation by applying it to the\nsimpler case of a nonlinear harmonic oscillator, for which numerically exact\nresults are available. We complement our self-consistent harmonic approximation\nby exact results at the free fermion point of the sine-Gordon model."
    },
    {
        "anchor": "Density waves and jet emission asymmetry in Bose Fireworks: A Bose condensate subject to a periodic modulation of the two-body\ninteractions was recently observed to emit matter-wave jets resembling\n\"fireworks\" [Nature 551, 356(2017)]. In this paper, combining experiment with\nnumerical simulation, we demonstrate that these \"Bose fireworks\" represent a\nlate stage in a complex time evolution of the driven condensate. We identify a\n\"density wave\" stage which precedes jet emission and results from interference\nof matterwaves. The density waves self-organize and self-amplify without the\nbreaking of long range translational symmetry. Importantly, this density wave\nstructure deterministically establishes the template for the subsequent\npatterns of the emitted jets. Our simulations, in good agreement with\nexperiment, also address the apparent asymmetry in the jet pattern and show it\nis fully consistent with momentum conservation.",
        "positive": "Quantized Vortices and Four-Component Superfluidity of Semiconductor\n  Excitons: We study spatially indirect excitons of GaAs quantum wells, confined in a 10\nmicrons electrostatic trap. Below a critical temperature of about 1 Kelvin, we\ndetect macroscopic spatial coherence and quantised vortices in the weak\nphotoluminescence emitted from the trap. These quantum signatures are\nrestricted to a narrow range of density, in a dilute regime. They manifest the\nformation of a four-component superfluid, made by a low population of optically\nbright excitons coherently coupled to a dominant fraction of optically dark\nexcitons."
    },
    {
        "anchor": "Spin-Dipole Oscillation and Polarizability of a Binary Bose-Einstein\n  Condensate near the Miscible-Immiscible Phase Transition: We report on the measurement of the spin-dipole (SD) polarizability and of\nthe frequency of the SD oscillation of a two-component Bose-Einstein condensate\nof sodium atoms occupying the $|3^2S_{1/2}, F=1, m_F=\\pm1\\rangle$ hyperfine\nstates. This binary spin-mixture presents the important properties of being, at\nthe same time, fully miscible and rid of the limit set by buoyancy. It is also\ncharacterized by a huge enhancement of the SD polarizability and by the\nconsequent softening of the frequency of the SD oscillation, due to the\nvicinity to the transition to the immiscible phase. The experimental data are\nsuccessfully compared with the predictions of theory.",
        "positive": "Correlation functions of the Lieb-Liniger gas and the LeClair-Mussardo\n  formula: In this letter we derive formulas for multi point correlation functions, in\nthe thermodynamic limit, for the Lieb Liniger gas taken with respect to\narbitrary eigenstates. These results apply for the ground state, thermal states\nand GGE states. We obtain these correlation functions as a series of multiple\nintegrals of progressively higher dimensions. These integrals converge rapidly\nfor short distance correlation functions and low densities of particles. The\nseries derived matches exactly the LeClair Mussardo formula for correlation\nfunctions of relativistic integrable models."
    },
    {
        "anchor": "Analysis of non-Markovian coupling of a lattice-trapped atom to free\n  space: Behavior analogous to that of spontaneous emission in photonic band gap\nmaterials has been predicted for an atom-optical system consisting of an atom\nconfined in a well of a state-dependent optical lattice that is coupled to free\nspace through an internal-state transition [de Vega et al., Phys. Rev. Lett.\n101, 260404 (2008)]. Using the Weisskopf-Wigner approach and considering a\none-dimensional geometry, we analyze the properties of this system in detail,\nincluding the evolution of the lattice-trapped population, the momentum\ndistribution of emitted matter waves, and the detailed structure of an\nevanescent matter-wave state below the continuum boundary. We compare and\ncontrast our findings for the transition from Markovian to non-Markovian\nbehaviors to those previously obtained for three dimensions.",
        "positive": "Observation of Bose-Einstein Condensation of Dipolar Molecules: Ensembles of particles governed by quantum mechanical laws exhibit\nfascinating emergent behavior. Atomic quantum gases, liquid helium, and\nelectrons in quantum materials all show distinct properties due to their\ncomposition and interactions. Quantum degenerate samples of bosonic dipolar\nmolecules promise the realization of novel phases of matter with tunable\ndipolar interactions and new avenues for quantum simulation and quantum\ncomputation. However, rapid losses, even when reduced through collisional\nshielding techniques, have so far prevented cooling to a Bose-Einstein\ncondensate (BEC). In this work, we report on the realization of a BEC of\ndipolar molecules. By strongly suppressing two- and three-body losses via\nenhanced collisional shielding, we evaporatively cool sodium-cesium (NaCs)\nmolecules to quantum degeneracy. The BEC reveals itself via a bimodal\ndistribution and a phase-space-density exceeding one. BECs with a condensate\nfraction of 60(10) % and a temperature of 6(2) nK are created and found to be\nstable with a lifetime close to 2 seconds. This work opens the door to the\nexploration of dipolar quantum matter in regimes that have been inaccessible so\nfar, promising the creation of exotic dipolar droplets, self-organized crystal\nphases, and dipolar spin liquids in optical lattices."
    },
    {
        "anchor": "Observation and control of quantized scattering halos: We investigate the production of s-wave scattering halos from collisions\nbetween the momentum components of a Bose-Einstein condensate released from an\noptical lattice. The lattice periodicity translates in a momentum comb\nresponsible for the quantization of the halos' radii. We report on the\nengineering of those halos through the precise control of the atom dynamics in\nthe lattice: we are able to specifically enhance collision processes with given\ncenter-of-mass and relative momenta. In particular, we observe quantized\ncollision halos between opposite momenta components of increasing magnitude, up\nto 6 times the characteristic momentum scale of the lattice.",
        "positive": "Spin-orbital-angular-momentum coupled Bose-Einstein condensates: We demonstrate coupling between the atomic spin and orbital-angular-momentum\n(OAM) of the atom's center-of-mass motion in a Bose-Einstein condensate (BEC).\nThe coupling is induced by Raman-dressing lasers with a Laguerre-Gaussian beam,\nand creates coreless vortices in a $F=1$ $^{87}$Rb spinor BEC. We observe\ncorrelations between spin and OAM in the dressed state and characterize the\nspin texture; the result is in good agreement with the theory. In the presence\nof the Raman field our dressed state is stable for 0.1~s or longer, and it\ndecays due to collision-induced relaxation. As we turn off the Raman beams, the\nvortex cores in the bare spin $|m_F=1\\rangle$ and $|-1\\rangle$ split. These\nspin-OAM coupled systems with the Raman-dressing approach have great potential\nfor exploring new topological textures and quantum states."
    },
    {
        "anchor": "Sub-Poissonian number differences in four-wave mixing of matter waves: We demonstrate sub-Poissonian number differences in four-wave mixing of\nBose-Einstein condensates of metastable helium. The collision between two\nBose-Einstein condensates produces a scattering halo populated by pairs of\natoms of opposing velocities, which we divide into several symmetric zones. We\nshow that the atom number difference for opposing zones has sub-Poissonian\nnoise fluctuations whereas that of nonopposing zones is well described by shot\nnoise. The atom pairs produced in a dual number state are well adapted to sub\nshot-noise interferometry and studies of Einstein-Podolsky-Rosen-type\nnonlocality tests.",
        "positive": "Non-Abelian Majorana fermions in topological $s$-wave Fermi superfluids: By solving the Bogoliubov--De Gennes equations analytically, we derive the\nfermionic zero-modes satisfying the Majorana property that exist in vortices of\na two-dimensional $s$-wave Fermi superfluid with spin-orbit coupling and Zeeman\nspin-splitting. The Majorana zero-mode becomes normalisable and exponentially\nlocalised to the vicinity of the vortex core when the superfluid is\ntopologically non-trivial. We calculate the energy splitting due to Majorana\nhybridisation and identify that the $s$-wave Majorana vortices obey non-Abelian\nstatistics."
    },
    {
        "anchor": "Topological spinor vortex matter on spherical surface induced by\n  non-Abelian spin-orbital-angular-momentum coupling: We provide an explicit way to implement non-Abelian\nspin-orbital-angular-momentum (SOAM) coupling in spinor Bose-Einstein\ncondensates using magnetic gradient coupling. For a spherical surface trap\naddressable using high-order Hermite-Gaussian beams, we show that this system\nsupports various degenerate ground states carrying different total angular\nmomenta $\\mathbf{J}$, and the degeneracy can be tuned by changing the strength\nof SOAM coupling. For weakly interacting spinor condensates with $f=1$, the\nsystem supports various meta-ferromagnetic phases and meta-polar states\ndescribed by quantized total mean angular momentum $|\\langle \\mathbf{J}\n\\rangle|$. Polar states with $Z_2$ symmetry and Thomson lattices formed by\ndefects of spin vortices are also discussed. The system can be used to prepare\nvarious stable spin vortex states with nontrivial topology, and serve as a\nplatform to investigate strong-correlated physics of neutral atoms with tunable\nground-state degeneracy.",
        "positive": "Quantitative acoustic models for superfluid circuits: We experimentally realize a highly tunable superfluid oscillator circuit in a\nquantum gas of ultracold atoms and develop and verify a simple lumped-element\ndescription of this circuit. At low oscillator currents, we demonstrate that\nthe circuit is accurately described as a Helmholtz resonator, a fundamental\nelement of acoustic circuits. At larger currents, the breakdown of the\nHelmholtz regime is heralded by a turbulent shedding of vortices and density\nwaves. Although a simple phase-slip model offers qualitative insights into the\ncircuit's resistive behavior, our results indicate deviations from the\nphase-slip model. A full understanding of the dissipation in superfluid\ncircuits will thus require the development of empirical models of the turbulent\ndynamics in this system, as have been developed for classical acoustic systems."
    },
    {
        "anchor": "Floquet topological quantum phase transitions in the transverse\n  Wen-plaquette model: Our aim in this work is to study the nonequilibrium behavior of the\ntopological quantum phase transition in the transverse Wen-plaquette model. We\nshow that under the effect of a nonadiabatic driving the system exhibits a new\ntopological phase and a rich phase diagram. We define generalized topological\norder parameters by considering cycle-averaged expectation values of string\noperators in a Floquet state",
        "positive": "Stability of $p$-orbital Bose-Einstein condensates in optical\n  checkerboard and square lattices: We investigate $p$-orbital Bose-Einstein condensates in both the square and\ncheckerboard lattice by numerically solving the Gross-Pitaevskii equation. The\nperiodic potential for the latter lattice is taken exactly from the recent\nexperiment [Nature Phys. 7, 147 (2011)]. It is confirmed that the staggered\norbital-current state is the lowest-energy state in the $p$ band. Our numerical\ncalculation further reveals that for both lattices the staggered $p$-orbital\nstate suffers Landau instability but the situation is remarkably different for\ndynamical instability. A dynamically stable parameter region is found for the\ncheckerboard lattice, but not for the square."
    },
    {
        "anchor": "Soliton trains after interaction quenches in Bose mixtures: We investigate the quench dynamics of a two-component Bose mixture and study\nthe onset of modulational instability, which leads the system far from\nequilibrium. Analogous to the single-component counterpart, this phenomenon\nresults in the creation of trains of bright solitons. We provide an analytical\nestimate of the number of solitons at long times after the quench for each of\nthe two components based on the most unstable mode of the Bogoliubov spectrum,\nwhich agrees well with our simulations for quenches to the weak attractive\nregime when the two components possess equal intraspecies interactions and loss\nrates. We also explain the significantly different soliton dynamics in a\nrealistic experimental homonuclear potassium mixture in terms of different\nintraspecies interaction and loss rates. We investigate the quench dynamics of\nthe particle number of each component estimating the characteristic time for\nthe appearance of modulational instability for a variety of interaction\nstrengths and loss rates. Finally, we evaluate the influence of the\nbeyond-mean-field contribution, which is crucial for the ground-state\nproperties of the mixture, in the quench dynamics for both the evolution of the\nparticle number and the radial width of the mixture. In particular, even for\nquenches to strongly attractive effective interactions, we do not observe the\ndynamical formation of solitonic droplets.",
        "positive": "Frustration induced Itinerant Ferromagnetism of Fermions in Optical\n  Lattice: When the Fermi Hubbard model was first introduced sixty years ago, one of the\noriginal motivations was to understand correlation effects in itinerant\nferromagnetism. In the past two decades, ultracold Fermi gas in an optical\nlattice has been used to study the Fermi Hubbard model. However, the metallic\nferromagnetic correlation was observed only in a recent experiment using\nfrustrated lattices, and its underlying mechanism is not clear yet. In this\nletter, we point out that, under the particle--hole transformation, the\nsingle-particle ground state can exhibit double degeneracy in such a frustrated\nlattice. Therefore, the low-energy state exhibits valley degeneracy,\nreminiscent of multi-orbit physics in ferromagnetic transition metals. The\nlocal repulsive interaction leads to the valley Hund's rule, responsible for\nthe observed ferromagnetism. We generalize this mechanism to distorted\nhoneycomb lattices and square lattices with flux. This mechanism was first\ndiscussed by M\\\"uller-Hartmann in a simpler one-dimension model. However, this\nmechanism has not been widely discussed and has not been related to\nexperimental observations before. Hence, our study not only explains the\nexperimental findings but also enriches our understanding of itinerant\nferromagnetism."
    },
    {
        "anchor": "Critical behavior at dynamical phase transition in the generalized\n  Bose-Anderson model: Critical properties of the dynamical phase transition in the quenched\ngeneralized Bose-Anderson impurity model are studied in the mean-field limit of\nan infinite number of channels. The transition separates the evolution toward\nground state and toward the branch of stable excited states. We perform\nnumerically exact simulations of a close vicinity of the critical quench\namplitude. The relaxation constant describing the asymptotic evolution toward\nground state, as well as asymptotic frequency of persistent phase rotation and\nnumber of cloud particles at stable excited state are power functions of the\ndetuning from the critical quench amplitude. The critical evolution (separatrix\nbetween the two regimes) shows a non-Lyapunov power-law instability arising\nafter a certain critical time. The observed critical behavior is attributed to\nthe irreversibility of the dynamics of particles leaving the cloud and to\nmemory effects related to the low-energy behavior of the lattice density of\nstates.",
        "positive": "Gradient corrections to the kinetic energy density functional of a\n  two-dimensional Fermi gas at finite temperature: We examine the leading order semiclassical gradient corrections to the\nnon-interacting kinetic energy density functional of a two dimensional Fermi\ngas by applying the extended Thomas-Fermi theory at finite temperature. We find\na non-zero von Weizs\\\"acker-like gradient correction, which in the\nhigh-temperature limit, goes over to the familiar functional form\n$(\\hbar^2/24m) (\\nabla\\rho)^2/\\rho$. Our work provides a theoretical\njustification for the inclusion of gradient corrections in applications of\ndensity-functional theory to inhomogeneous two-dimensional Fermi systems at any\n{\\em finite} temperature."
    },
    {
        "anchor": "Properties of Nambu-Goldstone Bosons in a Single-Component Bose-Einstein\n  Condensate: We theoretically study the properties of Nambu-Goldstone bosons in an\ninteracting single-component Bose-Einstein condensate (BEC). We first point out\nthat the proofs of Goldstone's theorem by Goldstone, et al. [Phys. Rev. {\\bf\n127} (1962) 965] may be relevant to distinct massless modes of the BEC: whereas\nthe first proof deals with the poles of the single-particle Green's function\n$\\hat{G}$, the second one concerns those of the two-particle Green's function.\nThus, there may be multiple Nambu-Goldstone bosons even in the single-component\nBEC with broken U(1) symmetry. The second mode turns out to have an infinite\nlifetime in the long-wavelength limit in agreement with the conventional\nviewpoint. In contrast, the first mode from $\\hat{G}$, i.e., the Bogoliubov\nmode in the weak-coupling regime, is shown to be a \"bubbling\" mode fluctuating\ntemporally out of and back into the condensate. The substantial lifetime\noriginates from an \"improper\" structure of the self-energy inherent in the BEC,\nwhich has been overlooked so far and will be elucidated here, and removes\nvarious infrared divergences pointed out previously.",
        "positive": "Off-axis Vortex in a Rotating Dipolar Bose-Einstein Condensation: We consider a singly quantized off-axis straight vortex in a rotating dipolar\nultracold gas in the Thomas-Fermi (TF) regime. We derive analytic results for\nsmall displacements and perform numerical calculations for large displacement\nwithin the TF regime. We show that the dipolar interaction energy increases\n(decreases) as the vortex moves from the trap center to the edge in an oblate\n(a prolate) trap. We find that for an oblate (a prolate) trap, the effect of\nthe dipole-dipole interaction is to lower (raise) both the precession velocity\nof an off-center straight vortex line and the angular velocity representing the\nonset of metastability."
    },
    {
        "anchor": "The Landau critical velocity for a particle in a Fermi superfluid: We determine {\\`a} la Landau the critical velocity $v\\_c^{L}$ of a moving\nimpurity in a Fermi superfluid, that is by restricting to the minimal\nexcitation processes of the superfluid. $v\\_c^{L}$ is then the minimal velocity\nat which these processes are energetically allowed. The Fermi superfluid\nactually exhibits two excitation branches~: one is the fermionic pair-breaking\nexcitation, as predicted by BCS theory; the other one is bosonic and sets pairs\ninto motion, as predicted by Anderson's RPA. $v\\_c^{L}$ is the smallest of the\ntwo corresponding critical velocities $v\\_{c,f}^{L}$ and $v\\_{c,b}^{L}$. In the\nparameter space (superfluid interaction strength, fermion-to-impurity mass\nratio), we identify two transition lines, corresponding to a discontinuity of\nthe first-order and second-order derivatives of $v\\_c^{L}$. These two lines\nmeet in a triple point and split the plane in three domains. We briefly extend\nthis analysis to the very recently realized case at ENS, where the moving\nobject in the Fermi superfluid is a weakly interacting Bose superfluid of\nimpurities, rather than a single impurity. For a Bose chemical potential much\nsmaller than the Fermi energy, the topology of the transition lines is\nunaffected; a key result is that the domain $v\\_c^{L}=c$, where $c$ is the\nsound velocity in the Fermi superfluid, is turned into a domain\n$v\\_c^{L}=c+c\\_B$, where $c\\_B$ is the sound velocity in the Bose superfluid,\nwith slightly shifted boundaries.",
        "positive": "Path Integral Monte Carlo Study of a Doubly-Dipolar Bose Gas: By combining first-principles path integral Monte Carlo methods and\nmean-field techniques, we explore the properties of cylindrically trapped\ndoubly-dipolar Bose gases. We first verify the emergence of a pancake quantum\ndroplet at low temperatures, validating previously mean-field calculations. In\na regime of small doubly-dipolar interactions, first-principles calculations\nagree with the generalized Gross-Pitaevskii equation. Such an accordance\ndisappears in a large interaction limit. Here the path integral Monte Carlo\nestimates the strong doubly-dipolar regime with accuracy. On the contrary, the\nGross-Pitaevskii equation does not seize quantum fluctuations in full. We also\nprovide a complete description of the system's quantum behavior in a wide range\nof parameters. When the system forms a droplet, the superfluid fraction\nexhibits an anisotropic behavior if compared to the usual Bose gas regime.\nInterestingly, we observe that the transition temperature from thermal gas to\ndroplet results higher than that of the thermal gas to a Bose-Einstein\ncondensate, indicating the robustness of the droplet against thermal\nfluctuations. Further, we investigate the anisotropic behavior of the\nsuperfluid fraction during the structural transition from a pancake to a\ncigar-shaped droplet by varying the ratio between electric and magnetic dipole\ninteraction strengths. Our findings furnish evidence that the stability of\ndoubly-dipolar Bose-Einstein condensates can be detected in experiments by\nmeans of dysprosium atoms."
    },
    {
        "anchor": "Pairing of the P\u00f6schl-Teller gas: We report calculations of equation of state of a model system, representative\nfor a cold Fermi gas, of particles interacting via the P\\\"oschl-Teller\ninteraction. In successively more sophisticated calculations, we determine the\nimportance of correlations and non-localities. We show that the gas displays,\nat relatively low density, an instability indicated by a divergence of the\nin-medium scattering length which occurs well before the divergence of the\nvacuum scattering length and the spinodal density. We also calculate the\npairing gap and show that non-local correlations can change the pairing gap by\nalmost an order of magnitude.",
        "positive": "Anderson Localization of cold atomic gases with effective spin-orbit\n  interaction in a quasiperiodic optical lattice: We theoretically investigate the localization properties of a spin-orbit\ncoupled spin-1/2 particle moving in a one-dimensional quasiperiodic potential,\nwhich can be experimentally implemented using cold atoms trapped in a\nquasiperiodic optical lattice potential and external laser fields. We present\nthe phase diagram in the parameter space of the disorder strength and those\nrelated to the spin-orbit coupling. The phase diagram is verified via\nmultifractal analysis of the atomic wavefunctions and the numerical simulation\nof diffusion dynamics. We found that spin-orbit coupling can lead to the\nspectra mixing (coexistence of extended and localized states) and the\nappearance of mobility edges."
    },
    {
        "anchor": "Spin-Orbit Driven Transitions Between Mott Insulators and Finite\n  Momentum Superfluids of Bosons in Optical Lattices: Synthetic spin-orbit coupling in ultracold atomic gases can be taken to\nextremes rarely found in solids. We study a two dimensional Hubbard model of\nbosons in an optical lattice in the presence of spin-orbit coupling strong\nenough to drive direct transitions from Mott insulators to superfluids. Here we\nfind phase-modulated superfluids with finite momentum that are generated\nentirely by spin-orbit coupling. We investigate the rich phase patterns of the\nsuperfluids, which may be directly probed using time-of-flight imaging of the\nspin-dependent momentum distribution.",
        "positive": "Dynamical Quantum Phase Transitions in Interacting Atomic\n  Interferometers: Particle-wave duality has allowed physicists to establish atomic\ninterferometers as celebrated complements to their optical counterparts in a\nbroad range of quantum devices. However, interactions naturally lead to\ndecoherence and have been considered as a longstanding obstacle in implementing\natomic interferometers in precision measurements. Here, we show that\ninteractions lead to dynamical quantum phase transitions between\nSchr\\\"{o}dinger's cats in an atomic interferometer. These transition points\nresult from zeros of Loschmidt echo, which approach the real axis of the\ncomplex time plane in the large particle number limit, and signify pair\ncondensates, another type of exotic quantum states featured with prevailing\ntwo-body correlations. Our work suggests interacting atomic interferometers as\na new tool for exploring dynamical quantum phase transitions and creating\nhighly entangled states to beat the standard quantum limit."
    },
    {
        "anchor": "Synthetic Landau levels and spinor vortex matter on Haldane spherical\n  surface with magnetic monopole: We present a flexible scheme to realize exact flat Landau levels on curved\nspherical geometry in a system of spinful cold atoms. This is achieved by\nFloquet engineering of a magnetic quadrupole field. We show that a synthetic\nmonopole field in real space can be created. We prove that the system can be\nexactly mapped to the electron-monopole system on sphere, thus realizing\nHaldane's spherical geometry for fractional quantum Hall physics. The scheme\nworks for either bosons or fermions. We investigate the ground state vortex\npattern for an $s$-wave interacting atomic condensate by mapping this system to\nthe classical Thompson's problem. We further study the distortion and stability\nof the vortex pattern when dipolar interaction is present. Our scheme is\ncompatible with current experimental setup, and may serve as a promising route\nof investigating quantum Hall physics and exotic spinor vortex matter on curved\nspace.",
        "positive": "Dipole-dipole frequency shifts in multilevel atoms: Dipole-dipole interactions lead to frequency shifts that are expected to\nlimit the performance of next-generation atomic clocks. In this work, we\ncompute dipolar frequency shifts accounting for the intrinsic atomic multilevel\nstructure in standard Ramsey spectroscopy. When interrogating the transitions\nfeaturing the smallest Clebsch-Gordan coefficients, we find that a simplified\ntwo-level treatment becomes inappropriate, even in the presence of large Zeeman\nshifts. For these cases, we show a net suppression of dipolar frequency shifts\nand the emergence of dominant non-classical effects for experimentally relevant\nparameters. Our findings are pertinent to current generations of optical\nlattice and optical tweezer clocks, opening a way to further increase their\ncurrent accuracy, and thus their potential to probe fundamental and many-body\nphysics."
    },
    {
        "anchor": "Low-energy excitations of a one-dimensional Bose gas with weak contact\n  repulsion: We study elementary excitations of a system of one-dimensional bosons with\nweak contact repulsion. We show that the Gross-Pitaevskii regime, in which the\nexcitations are the well-known Bogoliubov quasiparticles and dark solitons,\ndoes not extend to the low energy limit. Instead, the spectra of both\nexcitations have finite curvatures at zero momentum, in agreement with the\nphenomenological picture of fermionic quasiparticles. We describe analytically\nthe crossover between the Gross-Pitaevskii and the low-energy regimes, and\ndiscuss implications of our results for the behavior of the dynamic structure\nfactor.",
        "positive": "Ground state energy of the polarized diluted gas of interacting spin\n  $1/2$ fermions: The effective field theory approach simplifies the perturbative computation\nof the ground state energy of the diluted gas of fermions allowing in the case\nof the unpolarized system to easily re-derive the classic results up to the\n$(k_{\\rm F}a_0)^2$ order (where $k_{\\rm F}$ is the system's Fermi momentum and\n$a_0$ the $s$-wave scattering length) and (with more labour) to extend it up to\nthe order $(k_{\\rm F}a_0)^4$. The corresponding expansion of the ground state\nenergy of the polarized gas of spin $1/2$ fermions is known analytically (to\nour best knowledge) only up to the $k_{\\rm F}a_0$ (where $k_{\\rm F}$ stands for\n$k_{{\\rm F}\\uparrow}$ or $k_{{\\rm F}\\downarrow}$) order.\n  Here we show that the same effective field theory method allows to easily\ncompute also the order $(k_{\\rm F}a_0)^2$ correction to this result."
    },
    {
        "anchor": "Strong correlation effects in a two-dimensional Bose gas with quartic\n  dispersion: Motivated by the fundamental question of the fate of interacting bosons in\nflat bands, we consider a two-dimensional Bose gas at zero temperature with an\nunderlying quartic single-particle dispersion in one spatial direction. This\ntype of band structure can be realized using the NIST scheme of spin-orbit\ncoupling [Y.-J. Lin, K. Jim\\'{e}nez-Garcia, and I. B. Spielman, Nature\n$\\textbf{471}$, 83 (2011)], in the regime where the lower band dispersion has\nthe form $\\varepsilon_{\\textbf{k}} \\sim k_{x}^{4}/4+k_{y}^{2}+\\ldots$, or using\nthe shaken lattice scheme of Parker $\\textit{et al.}$ [C. V. Parker, L.-C. Ha\nand C. Chin, Nature Physics $\\textbf{9}$, 769 (2013)]. We numerically compare\nthe ground state energies of the mean-field Bose-Einstein condensate (BEC) and\nvarious trial wave-functions, where bosons avoid each other at short distances.\nWe discover that, at low densities, several types of strongly correlated states\nhave an energy per particle ($\\epsilon$), which scales with density ($n$) as\n$\\epsilon \\sim n^{4/3}$, in contrast to $\\epsilon \\sim n$ for the weakly\ninteracting Bose gas. These competing states include a Wigner crystal,\nquasi-condensates described in terms properly symmetrized fermionic states, and\nvariational wave-functions of Jastrow type. We find that one of the latter has\nthe lowest energy among the states we consider. This Jastrow-type state has a\nstrongly reduced, but finite condensate fraction, and true off-diagonal long\nrange order, which suggests that the ground state of interacting bosons with\nquartic dispersion is a strongly-correlated condensate reminiscent of\nsuperfluid Helium-4. Our results show that even for weakly-interacting bosons\nin higher dimensions, one can explore the crossover from a weakly-coupled BEC\nto a strongly-correlated condensate by simply tuning the single particle\ndispersion or density.",
        "positive": "Nonlinear looped band structure of Bose-Einstein condensates in an\n  optical lattice: We study experimentally the stability of excited, interacting states of\nbosons in a double-well optical lattice in regimes where the nonlinear\ninteractions are expected to induce \"swallowtail\" looped band structure. By\ncarefully preparing different initial coherent states and observing their\nsubsequent decay, we observe distinct decay rates that provide direct evidence\nfor multivalued, looped band structure. The double well lattice both stabilizes\nthe looped band structure and allows for dynamic preparation of different\ninitial states, including states within the loop structure. We confirm our\nstate preparation procedure with dynamic Gross-Pitaevskii calculations. The\nexcited loop states are found to be more stable than dynamically unstable\nground states, but decay faster than expected based on a mean-field stability\ncalculation, indicating the importance of correlations beyond a mean field\ndescription."
    },
    {
        "anchor": "Layers of Cold Dipolar Molecules in the Harmonic Approximation: We consider the N-body problem in a layered geometry containing cold polar\nmolecules with dipole moments that are polarized perpendicular to the layers. A\nharmonic approximation is used to simplify the hamiltonian and bound state\nproperties of the two-body inter-layer dipolar potential are used to adjust\nthis effective interaction. To model the intra-layer repulsion of the polar\nmolecules, we introduce a repulsive inter-molecule potential that can be\nparametrically varied. Single chains containing one molecule in each layer, as\nwell as multi-chain structures in many layers are discussed and their energies\nand radii determined. We extract the normal modes of the various systems as\nmeasures of their volatility and eventually of instability, and compare our\nfindings to the excitations in crystals. We find modes that can be classified\nas either chains vibrating in phase or as layers vibrating against each other.\nThe former correspond to acoustic and the latter to optical phonons.\nInstabilities can occur for large intra-layer repulsion and produce diverging\namplitudes of molecules in the outer layers. Lastly, we consider experimentally\nrelevant regimes to observe the structures.",
        "positive": "Mott insulators in plaquettes: We study small systems of Mott insulating ultracold atoms under the influence\nof gauge potentials and spin-orbit couplings. We use second order perturbation\ntheory in tunneling, derive an effective theory for the Mott insulators with\none atom per site, and solve it exactly. We find dramatic changes in the level\nstructure and in the amount of degeneracies expected. We also demonstrate the\ndynamical behavior as the barriers between plaquettes are gradually removed and\nfind potentially high overlap with the resonating valence bond (RVB) state of\nthe larger system."
    },
    {
        "anchor": "Polaron Problems in Ultracold Atoms: Role of a Fermi Sea across\n  Different Spatial Dimensions and Quantum Fluctuations of a Bose Medium: The notion of a polaron, originally introduced in the context of electrons in\nionic lattices, helps us to understand how a quantum impurity behaves when\nbeing immersed in and interacting with a many-body background. We discuss the\nimpact of the impurities on the medium particles by considering feedback\neffects from polarons that can be realized in ultracold quantum gas\nexperiments. In particular, we exemplify the modifications of the medium in the\npresence of either Fermi or Bose polarons. Regarding Fermi polarons we present\na corresponding many-body diagrammatic approach operating at finite\ntemperatures and discuss how mediated two- and three-body interactions are\nimplemented within this framework. Utilizing this approach, we analyze the\nbehavior of the spectral function of Fermi polarons at finite temperature by\nvarying impurity-medium interactions as well as spatial dimensions from three\nto one. Interestingly, we reveal that the spectral function of the medium atoms\ncould be a useful quantity for analyzing the transition/crossover from\nattractive polarons to molecules in three-dimensions. As for the Bose polaron,\nwe showcase the depletion of the background Bose-Einstein condensate in the\nvicinity of the impurity atom. Such spatial modulations would be important for\nfuture investigations regarding the quantification of interpolaron correlations\nin Bose polaron problems.",
        "positive": "Field-induced topological pair-density wave states in a multilayer\n  optical lattice: We study the superfluid phases of a Fermi gas in a multilayer optical lattice\nsystem in the presence of out-of-plane Zeeman field, as well as spin-orbit (SO)\ncoupling. We show that the Zeeman field combined with the SO coupling leads to\nexotic topological pair-density wave (PDW) phases in which different layers\npossess different superfluid order parameters, even though each layer\nexperiences the same Zeeman field and the SO coupling. We elucidate the\nmechanism of the emerging PDW phases, and characterize their topological\nproperties by calculating the associated Chern numbers."
    },
    {
        "anchor": "Phase transition of ultracold atoms immersed in a BEC vortex lattice: We investigate the quantum phases of ultracold atoms trapped in a vortex\nlattice using a mixture of two bosonic species (A and B), in the presence of an\nartificial gauge field. Heavy atoms of species B are confined in the array of\nvortices generated in species A, and they are described through a Bose-Hubbard\nmodel. In contrast to the optical-lattice setups, the vortex lattice has an\nintrinsic dynamics, given by its Tkachenko modes. Including these quantum\nfluctuations in the effective model for B atoms yields an extended Bose-Hubbard\nmodel, with an additional \"phonon\"-mediated long-range attraction. The\nground-state phase diagram of this model is computed through a variational\nansatz and the quantum Monte Carlo technique. When compared with the ordinary\nBose-Hubbard case, the long-range interatomic attraction causes a shift and\nresizing of the Mott-insulator regions. Finally, we discuss the experimental\nfeasibility of the proposed scheme, which relies on the proper choice of the\natomic species and on a large control of physical parameters, like the\nscattering lengths and the vorticity.",
        "positive": "Weyl spin-orbit-coupling-induced interactions in uniform and trapped\n  atomic quantum fluids: We establish through analytical and numerical studies of thermodynamic\nquantities for noninteracting atomic gases that the isotropic three-dimensional\nspin-orbit coupling, the Weyl coupling, induces interaction which counters\n\"effective\" attraction (repulsion) of the exchange symmetry present in\nzero-coupling Bose (Fermi) gas. The exact analytical expressions for the grand\npotential and hence for several thermodynamic quantities have been obtained for\nthis purpose in both uniform and trapped cases. It is enunciated that many\ninteresting features of spin-orbit coupled systems revealed theoretically can\nbe understood in terms of coupling-induced modifications in statistical\ninterparticle potential. The temperature-dependence of the chemical potential,\nspecific heat and isothermal compressibility for a uniform Bose gas is found to\nhave signature of the incipient Bose-Einstein condensation in very weak\ncoupling regime although the system does not really go in the Bose-condensed\nphase. The transition temperature in harmonically trapped case decreases with\nincrease of coupling strength consistent with the weakening of the statistical\nattractive interaction. Anomalous behavior of some thermodynamic quantities,\npartly akin to that in dimensions less than two, appears for uniform fermions\nas soon as the Fermi level goes down the Dirac point on increasing the coupling\nstrength. It is suggested that the fluctuation-dissipation theorem can be\nutilized to verify anomalous behaviors from studies of long-wavelength\nfluctuations in bunching and antibunching effects."
    },
    {
        "anchor": "Evidence of attraction between charge-carriers in a doped Mott insulator: Recent progress in optically trapped ultracold atomic gases is now making it\npossible to access microscopic observables in doped Mott insulators, which are\nthe parent states of high-temperature superconductors. This makes it possible\nto address longstanding questions about the temperature scales at which\nattraction between charge carriers are present, and their mechanism.\nControllable theoretical results for this problem are not available at low\ntemperature due to the sign problem. In this work, we employ worm-algorithm\nMonte Carlo to obtain completely unbiased results for two charge carriers in a\nMott insulator. Our method gives access to lower temperatures than what is\ncurrently possible in experiments, and provides evidence for attraction between\ndopants at a temperature scale that is now feasible in ultracold atomic\nsystems. We also report on spin-correlations in the presence of charge\ncarriers, which are directly comparable to experiments.",
        "positive": "2s exciton-polariton revealed in an external magnetic field: We demonstrate the existence of the excited state of an exciton-polariton in\na semiconductor microcavity. The strong coupling of the quantum well heavy-hole\nexciton in an excited 2s state to the cavity photon is observed in non-zero\nmagnetic field due to surprisingly fast increase of Rabi energy of the 2s\nexciton-polariton in magnetic field. This effect is explained by a strong\nmodification of the wave-function of the relative electron-hole motion for the\n2s exciton state."
    },
    {
        "anchor": "Three-body interacting dipolar bosons and the fate of lattice\n  supersolidity: We investigate a system of dipolar bosons in an optical lattice with local\ntwo and three-body interactions. Using the mean-field theory approach, we\nobtain the ground state phase diagram of the extended Bose-Hubbard (EBH) model\nwith both repulsive and attractive three-body interac- tions. We show that the\nadditional three-body on-site interaction has strong effects on the phase\ndiagram especially on the supersolid phase. Positive values of the three-body\ninteraction lead to the enhancement of the gapped phases at densities larger\nthan unity by reducing the supersolid region. However, a small attractive\nthree-body interaction enhances the supersolid phase.",
        "positive": "Homodyne detection of matter-wave fields (shortened): A scheme is discussed that allows one for performing homodyne detection of\nthe matter-wave field of ultracold bosonic atoms. It is based on a pump-probe\nlasers setup, that both illuminates a Bose-Einstein condensate, acting as\nreference system, and a second ultracold gas, composed by the same atoms but in\na quantum phase to determine. Photon scattering outcouples atoms from both\nsystems, which then propagate freely. Under appropriate conditions, when the\nsame photon can either be scattered by the Bose-Einstein condensate or by the\nother quantum gas, both flux of outcoupled atoms and scattered photons exhibit\noscillations, whose amplitude is proportional to the condensate fraction of the\nquantum gas. The setup can be extended to measure the first-order correlation\nfunction of a quantum gas. The dynamics here discussed make use of the\nentanglement between atoms and photons which is established by the scattering\nprocess in order to access detailed information on the quantum state of matter."
    },
    {
        "anchor": "Fulde-Ferrell-Larkin-Ovchinnikov state to topological superfluidity\n  transition in bilayer spin-orbit coupled degenerate Fermi gas: Recently a scheme has been proposed for generating the 2D Rashba-type\nspin-orbit coupling (SOC) for ultracold atomic bosons in a bilayer geometry\n[S.-W. Su et al, Phys. Rev. A \\textbf{93}, 053630 (2016)]. Here we investigate\nthe superfluidity properties of a degenerate Fermi gas affected by the SOC in\nsuch a bilayer system. We demonstrate that a Fulde-Ferrell-Larkin-Ovchinnikov\n(FFLO) state appears in the regime of small to moderate atom-light coupling. In\ncontrast to the ordinary SOC, the FFLO state emerges in the bilayer system\nwithout adding any external fields or spin polarization. As the atom-light\ncoupling increases, the system can transit from the FFLO state to a topological\nsuperfluid state. These findings are also confirmed by the BdG simulations with\na weak harmonic trap added.",
        "positive": "Ultracold Bosons with cavity-mediated long-range interactions: A local\n  mean field analysis of the phase diagram: Ultracold bosonic atoms in optical lattices self-organize into a variety of\nstructural and quantum phases when placed into a single-mode cavity and pumped\nby a laser. Cavity optomechanical effects induce an atom density modulation at\nthe cavity-mode wave length that competes with the optical lattice arrangement.\nSimultaneously short-range interactions via particle hopping promote superfluid\norder, such that a variety of structural and quantum coherent phases can occur.\nWe analyze the emerging phase diagram in two dimensions by means of an extended\nBose-Hubbard model using a local mean field approach combined with a superfluid\ncluster analysis. For commensurate ratios of the cavity and external lattice\nwave lengths the Mott insulator-superfluid transition is modified by the\nappearance of charge density wave and supersolid phases, at which the atomic\ndensity supports the buildup of a cavity field. For incommensurate ratios, the\noptomechanical forces induce the formation of Bose-glass and superglass phases,\nnamely non-superfluid and superfluid phases, respectively, displaying\nquasi-periodic density modulations, which in addition can exhibit structural\nand superfluid stripe formation. The onset of such structures is constrained by\nthe onsite interaction and is favourable at fractional densities. Experimental\nobservables are identified and discussed."
    },
    {
        "anchor": "Controlling and observing nonseparability of phonons created in\n  time-dependent 1D atomic Bose condensates: We study the spectrum and entanglement of phonons produced by temporal\nchanges in homogeneous one-dimensional atomic condensates. To characterize the\nexperimentally accessible changes, we first consider the dynamics of the\ncondensate when varying the radial trapping frequency, separately studying two\nregimes: an adiabatic one and an oscillatory one. Working in momentum space, we\nthen show that in situ measurements of the density-density correlation function\ncan be used to assess the nonseparability of the phonon state after such\nchanges. We also study time-of-flight (TOF) measurements, paying particular\nattention to the role played by the adiabaticity of opening the trap on the\nnonseparability of the final state of atoms. In both cases, we emphasize that\ncommuting measurements can suffice to assess nonseparability. Some recent\nobservations are analyzed, and we make proposals for future experiments.",
        "positive": "D-wave bosonic pair in an optical lattice: We present a bosonic model, in which two bosons may form a bound pair with\nd-wave symmetry via the four-site ring exchange interaction. A d-wave pairing\nsuperfluid as well as a d-wave density wave (DDW) state, are proposed to be\nachievable in this system. This exotic bosonic system can be realized in the\nBEC zone of a two-dimensional attractive p-band spinless fermionic system. By\nthe mean field approach, we find that at low densities, the d-wave pairs may\ncondensate, leading to a d-wave bosonic paired superfluid. At some particular\nfilling factors, a novel phase, d-wave density wave state, emerges. We study\nthis DDW state and its corresponding quantum phase transition in a two-leg\nladder by the time-evolving block decimation (TEBD) method."
    },
    {
        "anchor": "Equilibrium and off-equilibrium trap-size scaling in 1D ultracold\n  bosonic gases: We study some aspects of equilibrium and off equilibrium quantum dynamics of\ndilute bosonic gases in the presence of a trapping potential. We consider\nsystems with a fixed number of particles N and study their scaling behavior\nwith increasing the trap size. We focus on one-dimensional (1D) bosonic\nsystems, such as gases described by the Lieb-Liniger model and its\nTonks-Girardeau limit of impenetrable bosons, and gases constrained in optical\nlattices as described by the Bose-Hubbard model. We study their quantum\n(zero-temperature) behavior at equilibrium and off equilibrium during the\nunitary time evolution arising from changes of the trapping potential, which\nmay be instantaneous or described by a power-law time dependence, starting from\nthe equilibrium ground state for a initial trap size. Renormalization-group\nscaling arguments, analytical and numerical calculations show that the\ntrap-size dependence of the equilibrium and off-equilibrium dynamics can be\ncast in the form of a trap-size scaling in the low-density regime,\ncharacterized by universal power laws of the trap size, in dilute gases with\nrepulsive contact interactions and lattice systems described by the\nBose-Hubbard model. The scaling functions corresponding to several physically\ninteresting observables are computed. Our results are of experimental relevance\nfor systems of cold atomic gases trapped by tunable confining potentials.",
        "positive": "Quantum phases of hard-core bosons on 2D lattices with anisotropic\n  dipole-dipole interaction: By using an unbiased quantum Monte Carlo method, we investigate the hard-core\nBose-Hubbard model on a square lattice with anisotropic dipole-dipole\ninteraction. To study the effect of the anisotropy, dipole moments are assumed\nto be polarized in the $y$ direction on the two-dimensional (2D) $xy$ plane. To\nperform efficient simulations of long-range interacting systems, we use the\nworm algorithm with an O(N) Monte Carlo method. We obtain the ground-state\nphase diagram that includes a superfluid phase and a striped solid phase at\nhalf-filling as two main phases. In addition to these two main phases, we find\na small region where there are multi plateaus in the particle density for small\nhopping amplitudes. In this region, the number of plateaus increases as the\nsystem size increases. This indicates the appearance of numerous competing\nground states due to frustrated interactions. In our simulations, we find no\nevidence of a supersolid phase."
    },
    {
        "anchor": "Mixed bubbles in Bose-Bose mixtures: Repulsive Bose-Bose mixtures are known to either mix or phase-separate into\npure components. Here we predict a mixed-bubble regime in which bubbles of the\nmixed phase coexist with a pure phase of one of the components. This is a\nbeyond-mean-field effect which occurs for unequal masses or unequal\nintraspecies coupling constants and is due to a competition between the\nmean-field term, quadratic in densities, and a nonquadratic beyond-mean-field\ncorrection. We find parameters of the mixed-bubble regime in all dimensions and\ndiscuss implications for current experiments.",
        "positive": "Phase transitions in dipolar gases in optical lattices: We investigate the phase diagrams of two-dimensional lattice dipole systems\nwith variable geometry. For bipartite square and triangular lattices with\ntunable vertical sublattice separation, we find rich phase diagrams featuring a\nsequence of easy-plane magnetically ordered phases separated by incommensurate\nspin-wave states."
    },
    {
        "anchor": "Fractional quantum Hall physics with ultracold Rydberg gases in\n  artificial gauge fields: We study ultracold Rydberg-dressed Bose gases subject to artificial gauge\nfields in the fractional quantum Hall (FQH) regime. The characteristics of the\nRydberg interaction gives rise to interesting many-body ground states different\nfrom standard FQH physics in the lowest Landau level (LLL). The non-local but\nrapidly decreasing interaction potential favors crystalline ground states for\nvery dilute systems. While a simple Wigner crystal becomes energetically\nfavorable compared to the Laughlin liquid for filling fractions $\\nu<1/12$, a\ncorrelated crystal of composite particles emerges already for $\\nu \\leq 1/6$\nwith a large energy gap to the simple Wigner crystal. The presence of a new\nlength scale, the Rydberg blockade radius $a_B$, gives rise to a bubble crystal\nphase for $\\nu\\lesssim 1/4$ when the average particle distance becomes less\nthan $a_B$, which describes the region of saturated, almost constant\ninteraction potential. For larger fillings indications for strongly correlated\ncluster liquids are found.",
        "positive": "Competing exotic quantum phases of spin-$1/2$ ultra-cold lattice bosons\n  with extended spin interactions: Advances in pure optical trapping techniques now allow the creation of\ndegenerate Bose gases with internal degrees of freedom. Systems such as\n${}^{87}$Rb, $^{39}$K or ${}^{23}$Na in the $F=1$ hyperfine state offer an\nideal platform for studying the interplay of superfluidity and quantum\nmagnetism. Motivated by the experimental developments, we study ground state\nphases of a two-component Bose gas loaded on an optical lattice. The system is\ndescribed effectively by the Bose-Hubbard Hamiltonian with onsite and near\nneighbor spin-spin interactions. An important feature of our investigation is\nthe inclusion of interconversion (spin flip) terms between the two species,\nwhich has been observed in optical lattice experiments. Using mean-field theory\nand quantum Monte Carlo simulations, we map out the phase diagram of the\nsystem. A rich variety of phases is identified, including antiferromagnetic\n(AF) Mott insulators, ferromagnetic and AF superfluids."
    },
    {
        "anchor": "Generating soliton trains through Floquet engineering: We study a gas of interacting ultracold bosons held in a parabolic trap in\nthe presence of an optical lattice potential. Treating the system as a\ndiscretised Gross-Pitaevskii model, we show how Floquet engineering, by rapidly\n``shaking'' the lattice, allows the ground-state of the system to be converted\ninto a train of bright solitons by inverting the sign of the hopping energy. We\nstudy how the number of solitons produced depends on the system's nonlinearity\nand the curvature of the trap, show how the technique can be applied both in\nthe high and low driving-frequency regimes, and demonstrate the phenomenon's\nstability against noise. We conclude that the Floquet approach is a useful and\nstable method of preparing solitons in cold atom systems.",
        "positive": "Probing open- and closed-channel p-wave resonances: We study the near-threshold molecular and collisional physics of a strong\n$^{40}$K p-wave Feshbach resonance through a combination of measurements,\nnumerical calculations, and modeling. Dimer spectroscopy employs both\nradio-frequency spin-flip association in the MHz band and resonant association\nin the kHz band. Systematic uncertainty in the measured binding energy is\nreduced by a model that includes both the Franck-Condon overlap amplitude and\ninhomogeneous broadening. Coupled-channels calculations based on mass-scaled\n$^{39}$K potentials compare well to the observed binding energies and also\nreveal a low-energy p-wave shape resonance in the open channel. Contrary to\nconventional expectation, we observe a nonlinear variation of the binding\nenergy with magnetic field, and explain how this arises from the interplay of\nthe closed-channel ramping state with the near-threshold shape resonance in the\nopen channel. We develop an analytic two-channel model that includes both\nresonances as well as the dipole-dipole interactions which, we show, become\nimportant at low energy. Using this parameterization of the energy dependence\nof the scattering phase, we can classify the studied $^{40}$K resonance as\nbroad. Throughout the paper, we compare to the well understood s-wave case, and\ndiscuss the significant role played by van der Waals physics. The resulting\nunderstanding of the dimer physics of p-wave resonances provides a solid\nfoundation for future exploration of few- and many-body orbital physics."
    },
    {
        "anchor": "Thermodynamic engine with a quantum degenerate working fluid: Can quantum mechanical thermodynamic engines outperform their classical\ncounterparts? To address one aspect of this question, we experimentally realize\nand characterize an isentropic thermodynamic engine that uses a Bose-condensed\nworking fluid. In this engine, an interacting quantum degenerate gas of bosonic\nlithium is subjected to trap compression and relaxation strokes interleaved\nwith strokes strengthening and weakening interparticle interactions. We observe\na significant enhancement in efficiency and power when using a Bose-condensed\nworking fluid, compared to the case of a non-degenerate thermal gas. We\ndemonstrate reversibility, and measure power and efficiency as a function of\nengine parameters including compression ratio and cycle time. Results agree\nquantitatively with interacting finite temperature field-theoretic simulations\nthat closely replicate the length and energy scales of the working fluid.",
        "positive": "Nonequilibrium many-body steady states via Keldysh formalism: Many-body systems with both coherent dynamics and dissipation constitute a\nrich class of models which are nevertheless much less explored than their\ndissipationless counterparts. The advent of numerous experimental platforms\nthat simulate such dynamics poses an immediate challenge to systematically\nunderstand and classify these models. In particular, nontrivial many-body\nstates emerge as steady states under non-equilibrium dynamics. While these\nstates and their phase transitions have been studied extensively with mean\nfield theory, the validity of the mean field approximation has not been\nsystematically investigated. In this paper, we employ a field-theoretic\napproach based on the Keldysh formalism to study nonequilibrium phases and\nphase transitions in a variety of models. In all cases, a complete description\nvia the Keldysh formalism indicates a partial or complete failure of the mean\nfield analysis. Furthermore, we find that an effective temperature emerges as a\nresult of dissipation, and the universal behavior including the dynamics near\nthe steady state is generically described by a thermodynamic universality\nclass."
    },
    {
        "anchor": "Squeezing and robustness of frictionless cooling strategies: Quantum control strategies that provide shortcuts to adiabaticity are\nincreasingly considered in various contexts including atomic cooling. Recent\nstudies have emphasized practical issues in order to reduce the gap between the\nidealized models and actual ongoing implementations. We rephrase here the\ncooling features in terms of a peculiar squeezing effect, and use it to\nparametrize the robustness of frictionless cooling techniques with respect to\nnoise-induced deviations from the ideal time-dependent trajectory for the\ntrapping frequency. We finally discuss qualitative issues for the experimental\nimplementation of this scheme using bichromatic optical traps and lattices,\nwhich seem especially suitable for cooling Fermi-Bose mixtures and for\ninvestigating equilibration of negative temperature states, respectively.",
        "positive": "Adiabatic spin cooling using high-spin Fermi gases: Spatial entropy redistribution plays a key role in adiabatic cooling of\nultra-cold lattice gases. We show that high-spin fermions with a spatially\nvariable quadratic Zeeman coupling may allow for the creation of an inner\nspin-1/2 core surrounded by high-spin wings. The latter are always more\nentropic than the core at high temperatures and, remarkably, at all\ntemperatures in the presence of frustration. Combining thermodynamic Bethe\nAnsatz with local density approximation, we study the spatial entropy\ndistribution for the particular case of one-dimensional spin-3/2 lattice\nfermions in the Mott phase. Interestingly, this spatially dependent entropy\nopens a possible path for an adiabatic cooling technique that, in contrast to\nprevious proposals, would specifically target the spin degree of freedom. We\ndiscuss a possible realization of this adiabatic cooling, which may allow for a\nhighly efficient entropy decrease in the spin-1/2 core and help access\nantiferromagnetic order in experiments on ultracold spinor fermions."
    },
    {
        "anchor": "Ferromagnetism in tilted fermionic Mott insulators: We investigate the magnetism in tilted fermionic Mott insulators. With a\nsmall tilt, the fermions are still localized and form a Mott-insulating state,\nwhere the localized spins interact via antiferromagnetic exchange coupling.\nWhile the localized state is naively expected to be broken with a large tilt,\nin fact, the fermions are still localized under a large tilt due to the\nWannier-Stark localization and it can be regarded as a localized spin system.\nWe find that the sign of the exchange coupling is changed and the ferromagnetic\ninteraction is realized under the large tilt. To show this, we employ the\nperturbation theory and the real-time numerical simulation with the fermionic\nHubbard chain. Our simulation exhibits that it is possible to effectively\ncontrol the speed and time direction of the dynamics by changing the size of\ntilt, which may be useful for experimentally measuring the out-of-time ordered\ncorrelators. Finally, we address the experimental platforms, such as ultracold\natoms in an optical lattice, to observe these phenomena.",
        "positive": "Kosterlitz-Thouless transition and vortex-antivortex lattice melting in\n  two-dimensional Fermi gases with $p$- or $d$-wave pairing: We present a theoretical study of the finite-temperature Kosterlitz-Thouless\n(KT) and vortex-antivortex lattice (VAL) melting transitions in two-dimensional\nFermi gases with $p$- or $d$-wave pairing. For both pairings, when the\ninteraction is tuned from weak to strong attractions, we observe a quantum\nphase transition from the Bardeen-Cooper-Schrieffer (BCS) superfluidity to the\nBose-Einstein condensation (BEC) of difermions. The KT and VAL transition\ntemperatures increase during this BCS-BEC transition and approach constant\nvalues in the deep BEC region. The BCS-BEC transition is characterized by the\nnon-analyticities of the chemical potential, the superfluid order parameter,\nand the sound velocities as functions of the interaction strength at both zero\nand finite temperatures; however, the temperature effect tends to weaken the\nnon-analyticities comparing to the zero temperature case. The effect of\nmismatched Fermi surfaces on the $d$-wave pairing is also studied."
    },
    {
        "anchor": "Rydberg atoms in one-dimensional optical lattices: We experimentally realize Rydberg excitations in Bose-Einstein condensates of\nrubidium atoms loaded into quasi one-dimensional traps and in optical lattices.\nOur results for condensates expanded to different sizes in the one-dimensional\ntrap agree well with the intuitive picture of a chain of Rydberg excitations.\nWe also find that the Rydberg excitations in the optical lattice do not destroy\nthe phase coherence of the condensate, and our results in that system agree\nwith the picture of localized collective Rydberg excitations including\nnearest-neighbour blockade.",
        "positive": "Superradiance induced topological vortex phase in a Bose-Einstein\n  condensate: We investigate theoretically a topological vortex phase transition induced by\na superradiant phase transition in an atomic Bose-Einstein condensate driven by\na Laguerre-Gaussian optical mode. We show that superradiant radiation can\neither carry zero angular momentum, or be in a rotating Laguerre-Gaussian mode\nwith angular momentum. The conditions leading to these two regimes are\ndetermined in terms of the width for the pump laser and the condensate size for\nthe limiting cases where the recoil energy is both much smaller and larger than\nthe atomic interaction energy."
    },
    {
        "anchor": "Path integral molecular dynamics for anyons, bosons and fermions: In this article we develop a general method to numerically calculate physical\nproperties for a system of anyons with path integral molecular dynamics. We\nprovide a unified method to calculate the thermodynamics of identical bosons,\nfermions and anyons. Our method is tested and applied to systems of anyons,\nbosons and fermions in a two-dimensional harmonic trap. We also consider a\nmethod to calculate the energy for fermions as an application of the path\nintegral molecular dynamics to simulate the anyon model.",
        "positive": "Isospin Correlations in two-partite Hexagonal Optical Lattices: Two-component mixtures in optical lattices reveal a rich variety of different\nphases. We employ an exact diagonalization method to obtain the relevant\ncorrelation functions in hexagonal optical lattices to characterize those\nphases. We relate the occupation difference of the two species to the magnetic\npolarization. `Iso'-magnetic correlations disclose the nature of the system,\nwhich can be of easy-axis type, bearing phase segregation, or of easy-plane\ntype, corresponding to super-counter-fluidity. In the latter case, the\ncorrelations reveal easy-plane segregation, involving a highly-entangled state.\nWe identify striking correlated supersolid phases appearing within the\nsuperfluid limit."
    },
    {
        "anchor": "Observation of a smooth polaron-molecule transition in a degenerate\n  Fermi gas: Understanding the behavior of an impurity strongly interacting with a Fermi\nsea is a long-standing challenge in many-body physics. When the interactions\nare short-ranged, two vastly different ground states exist: a polaron\nquasiparticle and a molecule dressed by the majority atoms. In the\nsingle-impurity limit, it is predicted that at a critical interaction strength,\na first-order transition occurs between these two states. Experiments, however,\nare always conducted in the finite temperature and impurity density regime. The\nfate of the polaron-to-molecule transition under these conditions, where the\nstatistics of quantum impurities and thermal effects become relevant, is still\nunknown. Here, we address this question experimentally and theoretically. Our\nexperiments are performed with a spin-imbalanced ultracold Fermi gas with\ntunable interactions. Utilizing a novel Raman spectroscopy combined with a\nhigh-sensitivity fluorescence detection technique, we isolate the quasiparticle\ncontribution and extract the polaron energy, spectral weight, and the contact\nparameter. As the interaction strength is increased, we observe a continuous\nvariation of all observables, in particular a smooth reduction of the\nquasiparticle weight as it goes to zero beyond the transition point. Our\nobservation is in good agreement with a theoretical model where polaron and\nmolecule quasiparticle states are thermally occupied according to their quantum\nstatistics. At the experimental conditions, polaron states are hence populated\neven at interactions where the molecule is the ground state and vice versa. The\nemerging physical picture is thus that of a smooth transition between polarons\nand molecules and a coexistence of both in the region around the expected\ntransition.",
        "positive": "Devil's staircases in synthetic dimensions and gauge fields: We study interacting bosonic or fermionic atoms in a high synthetic magnetic\nfield in two dimensions spanned by continuous real space and a synthetic\ndimension. Here, the synthetic dimension is provided by hyperfine spin states,\nand the synthetic field is created by laser-induced transitions between them.\nWhile the interaction is short-range in real space, it is long-range in the\nsynthetic dimension in sharp contrast with fractional quantum Hall systems.\nIntroducing an analog of the lowest-Landau-level approximation valid for large\ntransition amplitudes, we derive an effective one-dimensional lattice model, in\nwhich density-density interactions turn out to play a dominant role. We show\nthat in the limit of a large number of internal states, the system exhibits a\ncascade of crystal ground states, which is known as devil's staircase, in a way\nanalogous to the thin-torus limit of quantum Hall systems."
    },
    {
        "anchor": "Galilean invariance in confined quantum systems: Implications on\n  spectral gaps, superfluid flow, and periodic order: Galilean invariance leaves its imprint on the energy spectrum and eigenstates\nof $N$ quantum particles, bosons or fermions, confined in a bounded domain. It\nendows the spectrum with a recurrent structure which in capillaries or\nelongated traps of length $L$ and cross-section area $s_\\perp$ leads to\nspectral gaps $n^2h^2s_\\perp\\rho/(2mL)$ at wavenumbers $2n\\pi s_\\perp\\rho$,\nwhere $\\rho$ is the number density and $m$ is the particle mass. In zero\ntemperature superfluids, in toroidal geometries, it causes the quantization of\nthe flow velocity with the quantum $h/(mL)$ or that of the circulation along\nthe toroid with the known quantum $h/m$. Adding a \"friction\" potential which\nbreaks Galilean invariance, the Hamiltonian can have a superfluid ground state\nat low flow velocities but not above a critical velocity which may be different\nfrom the velocity of sound. In the limit of infinite $N$ and $L$, if\n$N/L=s_\\perp\\rho$ is kept fixed, translation invariance is broken, the center\nof mass has a periodic distribution, while superfluidity persists at low flow\nvelocities. This conclusion holds for the Lieb-Liniger model.",
        "positive": "One-Body Density Matrix and Momentum Distribution of Strongly\n  Interacting One-Dimensional Spinor Quantum Gases: The one-body density matrix (OBDM) of a strongly interacting spinor quantum\ngas in one dimension can be written as a summation of products of spatial and\nspin parts. We find that there is a remarkable connection between the spatial\npart and the OBDM of a spinless hard-core anyon gas. This connection allows us\nto efficiently calculate the OBDM of the spinor system with particle numbers\nmuch larger than what was previously possible. Given the OBDM, we can easily\ncalculate the momentum distribution of the spinor system, which again is\nrelated to the momentum distribution of the hard-core ayone gas."
    },
    {
        "anchor": "Signatures of a universal jump in the superfluid density in\n  two-dimensional Bose gas with finite number of particles: We study, within the classical fields approximation, a two-dimensional weakly\ninteracting uniform Bose gas of a finite number of atoms. By using a grand\ncanonical ensemble formalism we show that such systems exhibit, in addition to\nthe Berezinskii-Kosterlitz-Thouless (BKT) and thermal phases, the intermediate\nregion. This region is characterized by a decay of current-current correlations\nat low momenta and by an algebraic decay of the first-order correlations with\nan exponent being larger than the critical value predicted by the BKT theory.\nThe density of the superfluid fraction at the temperature which separates the\nBKT phase from the intermediate region approaches the one found by Nelson and\nKosterlitz for two-dimensional superfluids while the number of atoms is\nincreased.",
        "positive": "Quasi-molecular bosonic complexes -- a pathway to atomic analog of SQUID\n  with controlled sensitivity: Recent experimental advances in realizing degenerate quantum dipolar gases in\noptical lattices and the flexibility of experimental setups in attaining\nvarious geometries offer the opportunity to explore exotic quantum many-body\nphases stabilized by anisotropic, long-range dipolar interaction. Moreover, the\nunprecedented control over the various physical properties of these systems,\nranging from the quantum statistics of the particles, to the inter-particle\ninteractions, allow one to engineer novel devices. In this paper, we consider\ndipolar bosons trapped in a stack of one-dimensional optical lattice layers,\npreviously studied in [1]. Building on our prior results, we provide a\ndescription of the quantum phases stabilized in this system which include\ncomposite superfluids, solids, and supercounterfluids, most of which are found\nto be threshold- less with respect to the dipolar interaction strength. We also\ndemonstrate the effect of enhanced sensitivity to rotations of a SQUID-type\ndevice made of two composite superfluids trapped in a ring-shaped optical\nlattice layer with weak links."
    },
    {
        "anchor": "Probing Ferromagnetic Order in Few-Fermion Correlated Spin-Flip Dynamics: We unravel the dynamical stability of a fully polarized one-dimensional\nultracold few-fermion spin-1/2 gas subjected to inhomogeneous driving of the\nitinerant spins. Despite the unstable character of the total spin-polarization\nthe existence of an interaction regime is demonstrated where the\nspin-correlations lead to almost maximally aligned spins throughout the\ndynamics. The resulting ferromagnetic order emerges from the build up of\nsuperpositions of states of maximal total spin. They comprise a decaying\nspin-polarization and a dynamical evolution towards an almost completely\nunpolarized NOON-like state. Via single-shot simulations we demonstrate that\nour theoretical predictions can be detected in state-of-the-art ultracold\nexperiments.",
        "positive": "Exotic quantum liquids in Bose-Hubbard models with spatially-modulated\n  symmetries: We investigate the effect that spatially modulated continuous conserved\nquantities can have on quantum ground states. We do so by introducing a family\nof one-dimensional local quantum rotor and bosonic models which conserve finite\nFourier momenta of the particle number, but not the particle number itself.\nThese correspond to generalizations of the standard Bose-Hubbard model (BHM),\nand relate to the physics of Bose surfaces. First, we show that while having an\ninfinite-dimensional local Hilbert space, such systems feature a non-trivial\nHilbert space fragmentation for momenta incommensurate with the lattice. This\nis linked to the nature of the conserved quantities having a dense spectrum and\nprovides the first such example. We then characterize the zero-temperature\nphase diagram for both commensurate and incommensurate momenta. In both cases,\nanalytical and numerical calculations predict a phase transition between a\ngapped (Mott insulating) and quasi-long range order phase; the latter is\ncharacterized by a two-species Luttinger liquid in the infrared, but dressed by\noscillatory contributions when computing microscopic expectation values.\nFollowing a rigorous Villain formulation of the corresponding rotor model, we\nderive a dual description, from where we estimate the robustness of this phase\nusing renormalization group arguments, where the driving perturbation has\nultra-local correlations in space but power law correlations in time. We\nsupport this conclusion using an equivalent representation of the system as a\ntwo-dimensional vortex gas with modulated Coulomb interactions within a fixed\nsymmetry sector. We conjecture that a Berezinskii-Kosterlitz-Thouless-type\ntransition is driven by the unbinding of vortices along the temporal direction."
    },
    {
        "anchor": "Rotational properties of non-dipolar and dipolar Bose-Einstein\n  condensates confined in annular potentials: We investigate the rotational response of both non-dipolar and dipolar\nBose-Einstein condensates confined in an annular potential. For the non-dipolar\ncase we identify certain critical rotational frequencies associated with the\nformation of vortices. For the dipolar case, assuming that the dipoles are\naligned along some arbitrary and tunable direction, we study the same problem\nas a function of the orientation angle of the dipole moment of the atoms.",
        "positive": "Probing multiple-frequency atom-photon interactions with ultracold atoms: We dress atoms with multiple-radiofrequency fields and investigate the\nspectrum of transitions driven by an additional probe field. A complete\ntheoretical description of this rich spectrum is presented, in which we find\nallowed transitions and determine their amplitudes using the resolvent\nformalism. Experimentally, we observe transitions up to sixth order in the\nprobe field using radiofrequency spectroscopy of Bose-Einstein condensates\ntrapped in single- and multiple-radiofrequency-dressed potentials. We find\nexcellent agreement between theory and experiment, including the prediction and\nverification of previously unobserved transitions, even in the\nsingle-radiofrequency case."
    },
    {
        "anchor": "Coherent merging of counter-propagating exciton-polariton superfluids: We report the formation of a macroscopic coherent state emerging from\ncolliding polariton fluids. Four lasers with random relative phases, arranged\nin a square, pump resonantly a planar microcavity, creating four coherent\npolariton fluids propagating toward each other. When the density (interactions)\nincreases, the four fluids synchronise and the topological excitations (vortex\nor soliton) disappear to form a single superfluid.",
        "positive": "Nonergodic dynamics of the one-dimensional Bose-Hubbard model with a\n  trapping potential: We investigate nonergodic behavior of the one-dimensional Bose-Hubbard model,\nwhich emerges in the unitary quantum dynamics starting with initial-state\n$|\\psi(0)\\rangle=|\\cdots 2020\\cdots \\rangle$ in the presence of a trapping\npotential. We compute the level spacing statistic, the time evolution of the\nnumber imbalance between the odd and the even sites, and the entanglement\nentropy in order to show that the system exhibits nonergodicity in a strongly\ninteracting regime. The trapping potential enhances nonergodicity even when the\ntrapping potential is weak compared to the the hopping energy. We derive the\neffective spin-1/2 {\\it XXZ} Hamiltonian for the strongly interacting regimes\nby using a perturbation method. On the basis of the effective Hamiltonian, we\nshow that the trapping potential is effectively strengthened by the on-site\ninteraction, leading to the enhancement of the nonergodic behavior. We also\ncalculate the real-time dynamics under the effective Hamiltonian and find that\nthe entanglement entropy grows logarithmically in time."
    },
    {
        "anchor": "Vortex Dynamics in a Spin-Orbit Coupled Bose-Einstein Condensate: Vortices in a one-component dilute atomic ultracold Bose-Einstein condensate\n(BEC) usually arise as a response to externally driven rotation. Apart from a\nfew special situations, these vortices are singly quantized with unit\ncirculation. Recently, the NIST group has constructed a two-component BEC with\na spin-orbit coupled Hamiltonian involving Pauli matrices, and I here study the\ndynamics of a two-component vortex in such a spin-orbit coupled condensate.\nThese spin-orbit coupled BECs use an applied magnetic field to split the\nhyperfine levels. Hence they rely on a focused laser beam to trap the atoms. In\naddition, two Raman laser beams create an effective (or synthetic) gauge\npotential. The resulting spin-orbit Hamiltonian is discussed in some detail.\nThe various laser beams are fixed in the laboratory, so that it is not feasible\nto nucleate a vortex by an applied rotation that would need to rotate all the\nlaser beams and the magnetic field. In a one-component BEC, a vortex can also\nbe created by a thermal quench, starting from the normal state and suddenly\ncooling deep into the condensed state. I propose that a similar method would\nwork for a vortex in a spin-orbit coupled BEC. Such a vortex has two\ncomponents, and each has its own circulation quantum number. If both components\nhave the same circulation, I find that the composite vortex should execute\nuniform precession, like that observed in a single-component BEC. In contrast,\nif one component has unit circulation and the other has zero circulation, then\nsome fraction of the dynamical vortex trajectories should eventually leave the\ncondensate, providing clear experimental evidence for this unusual vortex\nstructure. In the context of exciton-polariton condensates, such a vortex is\nknown as a \"half-quantum vortex\".",
        "positive": "Topological phases in small quantum Hall samples: Topological order has proven a useful concept to describe quantum phase\ntransitions which are not captured by the Ginzburg-Landau type of\nsymmetry-breaking order. However, lacking a local order parameter, topological\norder is hard to detect. One way to detect is via direct observation of anyonic\nproperties of excitations which are usually discussed in the thermodynamic\nlimit, but so far has not been realized in macroscopic quantum Hall samples.\nHere we consider a system of few interacting bosons subjected to the lowest\nLandau level by a gauge potential, and theoretically investigate vortex\nexcitations in order to identify topological properties of different ground\nstates. Our investigation demonstrates that even in surprisingly small systems\nanyonic properties are able to characterize the topological order. In addition,\nfocusing on a system in the Laughlin state, we study the robustness of its\nanyonic behavior in the presence of tunable finite-range interactions acting as\na perturbation. A clear signal of a transition to a different state is\nreflected by the system's anyonic properties."
    },
    {
        "anchor": "Floquet edge states in a harmonically driven integer quantum Hall system: Recent theoretical work on time-periodically kicked Hofstadter model found\nrobust counter-propagating edge modes. It remains unclear how ubiquitously such\nanomalous modes can appear, and what dictates their robustness against\ndisorder. Here we shed further light on the nature of these modes by analyzing\na simple type of periodic driving where the hopping along one spatial direction\nis modulated sinusoidally with time while the hopping along the other spatial\ndirection is kept constant. We obtain the phase diagram for the quasienergy\nspectrum at flux 1/3 as the driving frequency $\\omega$ and the hopping\nanisotropy are varied. A series of topologically distinct phases with\ncounter-propagating edge modes appear due to the harmonic driving, similar to\nthe case of a periodically kicked system studied earlier. We analyze the time\ndependence of the pair of Floquet edge states localized at the same edge, and\ncompare their Fourier components in the frequency domain. In the limit of small\nmodulation, one of the Floquet edge mode within the pair can be viewed as the\nedge mode originally living in the other energy gap shifted in quasienergy by\n$\\hbar \\omega$, i.e., by absorption or emission of a \"photon\" of frequency\n$\\omega$. Our result suggests that counter-propagating Floquet edge modes are\ngeneric features of periodically driven integer quantum Hall systems, and not\ntied to any particular driving protocol. It also suggests that the Floquet edge\nmodes would remain robust to any static perturbations that do not destroy the\nchiral edge modes of static quantum Hall states.",
        "positive": "Reentrance of Bose-Einstein condensation in spinor atomic gases in\n  magnetic field: We calculate the Bose-Einstein condensation (BEC) temperature of spin-1\natomic bosons in external magnetic field, taking into account the influence of\nthe quadratic Zeeman effect. In case that the quadratic Zeeman coefficient is\npositive, the BEC temperature exhibits a nontrivial dependance on the magnetic\nfield and a magnetic-field-induced reentrant phenomenon of BEC is observed.\nThis phenomenon could be well understood by the competition between the linear\nand quadratic Zeeman effects. Reentrance of BEC in a trapped spinor Bose gas is\nalso discussed."
    },
    {
        "anchor": "Detecting the Amplitude Mode of Strongly Interacting Lattice Bosons by\n  Bragg Scattering: We report the first detection of the Higgs-type amplitude mode using Bragg\nspectroscopy in a strongly interacting condensate of ultracold atoms in an\noptical lattice. By the comparison of our experimental data with a spatially\nresolved, time-dependent dynamic Gutzwiller calculation, we obtain good\nquantitative agreement. This allows for a clear identification of the amplitude\nmode, showing that it can be detected with full momentum resolution by going\nbeyond the linear response regime. A systematic shift of the sound and\namplitude modes' resonance frequencies due to the finite Bragg beam intensity\nis observed.",
        "positive": "Stability and Dynamics of Cross Solitons in Harmonically Confined\n  Bose-Einstein Condensates: We examine the stability and dynamics of a family of crossed dark solitons in\na harmonically confined Bose-Einstein condensate in two dimensions. Working in\na regime where the fundamental snake instability is suppressed, we show the\nexistence of an instability which leads to an interesting collapse and revival\nof the initial state for the fundamental case of two crossed solitons. The\ninstability originates from the singular point where the solitons cross, and we\ncharacterise it by examining the Bogoliubov spectrum. Finally, we extend the\ntreatment to systems of higher symmetry."
    },
    {
        "anchor": "Dynamics of a tunable superfluid junction: We study the population dynamics of a Bose-Einstein condensate in a\ndouble-well potential throughout the crossover from Josephson dynamics to\nhydrodynamics. At barriers higher than the chemical potential, we observe slow\noscillations well described by a Josephson model. In the limit of low barriers,\nthe fundamental frequency agrees with a simple hydrodynamic model, but we also\nobserve a second, higher frequency. A full numerical simulation of the\nGross-Pitaevskii equation giving the frequencies and amplitudes of the observed\nmodes between these two limits is compared to the data and is used to\nunderstand the origin of the higher mode. Implications for trapped matter-wave\ninterferometers are discussed.",
        "positive": "Emergence of a Bose polaron in a small ring threaded by the\n  Aharonov-Bohm flux: The model of a ring threaded by the Aharonov-Bohm flux underlies our\nunderstanding of a coupling between gauge potentials and matter. The typical\nformulation of the model is based upon a single particle picture, and should be\nextended when interactions with other particles become relevant. Here, we\nillustrate such an extension for a particle in an Aharonov-Bohm ring subject to\ninteractions with a weakly interacting Bose gas. We show that the ground state\nof the system can be described using the Bose polaron concept -- a particle\ndressed by interactions with a bosonic environment. We connect the energy\nspectrum to the effective mass of the polaron, and demonstrate how to change\ncurrents in the system by tuning boson-particle interactions. Our results\nsuggest the Aharonov-Bohm ring as a platform for studying coherence and few- to\nmany-body crossover of quasi-particles that arise from an impurity immersed in\na medium."
    },
    {
        "anchor": "Feshbach spectroscopy of an ultracold $^{41}$K-$^6$Li mixture and\n  $^{41}$K atoms: We have observed 69 $^{41}$K-$^6$Li interspecies Feshbach resonances\nincluding 13 elastic p-wave resonances and 6 broad d-wave resonances of\n$^{41}$K atoms in different spin-state combinations at fields up to 600~G.\nMulti-channel quantum defect theory calculation is performed to assign these\nresonances and the results show perfect agreement with experimental values\nafter improving input parameters. The observed broad p- and d- wave resonances\ndisplay a full resolved multiplet structure. They may serve as important\nsimulators to nonzero partial wave dominated physics.",
        "positive": "Superfluidity and relaxation dynamics of a laser-stirred 2D Bose gas: We investigate the superfluid behavior of a two-dimensional (2D) Bose gas of\n$^{87}$Rb atoms using classical field dynamics. In the experiment by R.\nDesbuquois \\textit{et al.}, Nat. Phys. \\textbf{8}, 645 (2012), a 2D\nquasicondensate in a trap is stirred by a blue-detuned laser beam along a\ncircular path around the trap center. Here, we study this experiment from a\ntheoretical perspective. The heating induced by stirring increases rapidly\nabove a velocity $v_c$, which we define as the critical velocity. We identify\nthe superfluid, the crossover, and the thermal regime by a finite, a sharply\ndecreasing, and a vanishing critical velocity, respectively. We demonstrate\nthat the onset of heating occurs due to the creation of vortex-antivortex\npairs. A direct comparison of our numerical results to the experimental ones\nshows good agreement, if a systematic shift of the critical phase-space density\nis included. We relate this shift to the absence of thermal equilibrium between\nthe condensate and the thermal wings, which were used in the experiment to\nextract the temperature. We expand on this observation by studying the full\nrelaxation dynamics between the condensate and the thermal cloud."
    },
    {
        "anchor": "Dipole mode of a strongly correlated one-dimensional Bose gas in a split\n  trap: parity effect and barrier renormalization: We consider an interacting, one-dimensional Bose gas confined in a split\ntrap, obtained by an harmonic potential with a localized barrier at its center.\nWe address its quantum-transport properties through the study of dipolar\noscillations, which are induced by a sudden quench of the position of the\ncenter of the trap. We find that the dipole-mode frequency strongly depends on\nthe interaction strength between the particles, yielding information on the\nclassical screening of the barrier and on its renormalization due to quantum\nfluctuations. Furthermore, we predict a parity effect which becomes most\nprominent in the strongly correlated regime.",
        "positive": "The phonon dispersion relation of a Bose-Einstein condensate: We measure the oscillations of a standing wave of phonons in a Bose-Einstein\ncondensate, thus obtaining the dispersion relation. We present the technique of\nshort Bragg pulses, which stimulates the standing wave. The subsequent\noscillations are observed in situ. It is seen that the phonons undergo a 3D to\n1D transition, when their wavelength becomes longer than the transverse radius\nof the condensate. The 1D regime contains an inflection point in the dispersion\nrelation, which should decrease the superfluid critical velocity according to\nthe Landau criterion. The inflection point also represents a minimum in the\ngroup velocity, although the minimum is not deep enough to result in a roton.\nThe 3D-1D transition also results in an increase in the lifetime of the\nstanding-wave oscillations, and a breakdown of the local density approximation.\nIn addition, the static structure factor is measured in the long-wavelength\nregime. The measurements are enabled by the high sensitivity of the new\ntechnique."
    },
    {
        "anchor": "Destiny of optical lattices with strong intersite interactions: Optical lattices are considered loaded by atoms or molecules that can exhibit\nstrong interactions between different lattice sites. The strength of these\ninteractions can be sufficient for generating collective phonon excitations\nabove the ground-state energy level. Varying the interaction strength makes it\npossible to create several equilibrium three-dimensional phases, including\nconducting optical lattices, insulating optical lattices, delocalized quantum\ncrystals, and localized quantum crystals. Also, there can exist finite one- and\ntwo-dimensional lattices of chains and planes.",
        "positive": "Detection of Spin Coherence in Cold Atoms via Faraday Rotation\n  Fluctuations: We report non-invasive detection of spin coherence in a collection of\nRaman-driven cold atoms using dispersive Faraday rotation fluctuation\nmeasurements, which opens up new possibilities of probing spin correlations in\nquantum gases and other similar systems. We demonstrate five orders of\nmagnitude enhancement of the measured signal strength than the traditional spin\nnoise spectroscopy with thermal atoms in equilibrium. Our observations are in\ngood agreement with the comprehensive theoretical modeling of the driven atoms\nat various temperatures. The extracted spin relaxation rate of cold rubidium\natoms with atom number density $\\sim$10$^9/$cm$^3$ is of the order of\n2$\\pi\\times$0.5 kHz at 150 $\\mu$K, two orders of magnitude less than $\\sim$\n2$\\pi\\times$50 kHz of a thermal atomic vapor with atom number density\n$\\sim$10$^{12}/$cm$^3$ at 373 K."
    },
    {
        "anchor": "Magnetic phase transition in coherently coupled Bose gases in optical\n  lattices: We describe the ground state of a gas of bosonic atoms with two coherently\ncoupled internal levels in a deep optical lattice in a one dimensional\ngeometry. In the single-band approximation this system is described by a\nBose-Hubbard Hamiltonian. The system has a superfluid and a Mott insulating\nphase which can be either paramagnetic or ferromagnetic. We characterize the\nquantum phase transitions at unit filling by means of a density matrix\nrenormalization group technique and compare it with a mean-field approach. The\npresence of the ferromagnetic Ising-like transition modifies the Mott lobes. In\nthe Mott insulating region the system maps to the ferromagnetic spin-1/2 XXZ\nmodel in a transverse field and the numerical results compare very well with\nthe analytical results obtained from the spin model. In the superfluid regime\nquantum fluctuations strongly modify the phase transition with respect to the\nwell established mean-field three dimensional classical bifurcation.",
        "positive": "Coherent emission of atomic soliton pairs by Feshbach-resonance tuning: We present two simple designs of matter-wave beam splitters in a trapped\nBose-Einstein Condensate (BEC). In our scheme, identical pairs of atomic\nsolitons are produced by an adequate control --- in time and/or space --- of\nthe scattering length. Our analysis is performed by numerical integration of\nthe Gross-Pitaevskii equation and supported by several analytic estimates. Our\nresults show that these devices can be implemented in the frame of current BEC\nexperiments. The system has potential applications for the construction of a\nsoliton interferometer."
    },
    {
        "anchor": "Integrated Mach-Zehnder interferometer for Bose-Einstein condensates: Particle-wave duality enables the construction of interferometers for matter\nwaves, which complement optical interferometers in precision measurement\ndevices. This requires the development of atom-optics analogs to beam\nsplitters, phase shifters, and recombiners. Integrating these elements into a\nsingle device has been a long-standing goal. Here we demonstrate a full\nMach-Zehnder sequence with trapped Bose-Einstein condensates (BECs) confined on\nan atom chip. Particle interactions in our BEC matter waves lead to a\nnon-linearity, absent in photon optics. We exploit it to generate a\nnon-classical state having reduced number fluctuations inside the\ninterferometer. Making use of spatially separated wave packets, a controlled\nphase shift is applied and read out by a non-adiabatic matter-wave recombiner.\nWe demonstrate coherence times a factor of three beyond what is expected for\ncoherent states, highlighting the potential of entanglement as a resource for\nmetrology. Our results pave the way for integrated quantum-enhanced matter-wave\nsensors.",
        "positive": "Effect of Feshbach Resonance on the Entropy Production in the ultra cold\n  Bosonic Atoms: The entropy of the coexisting gas of ultra cold fermionic atoms and Bosonic\nmolecular condensate confined in a magnetic trap has been calculated from\nequation of motion approaches. We have found that the entropy production\ndepends not only to the Feshbach resonance and but also under certain limits to\nRabi type oscillation and Bose Josephson junction type oscillation."
    },
    {
        "anchor": "Drag force in bimodal cubic-quintic nonlinear Schr\u00f6dinger equation: We consider a system of two cubic-quintic non-linear Schr\\\"odinger equations\nin two dimensions, coupled by repulsive cubic terms. We analyse situations in\nwhich a probe lump of one of the modes is surrounded by a fluid of the other\none and analyse their interaction. We find a realization of D'Alembert's\nparadox for small velocities and non-trivial drag forces for larger ones. We\npresent numerical analysis including the search of static and traveling\nform-preserving solutions along with simulations of the dynamical evolution in\nsome representative examples.",
        "positive": "Breaking of SU(4) symmetry and interplay between strongly correlated\n  phases in the Hubbard model: We study the thermodynamic properties of four-component fermionic mixtures\ndescribed by the Hubbard model using the dynamical mean-field-theory approach.\nSpecial attention is given to the system with SU(4)-symmetric interactions at\nhalf filling, where we analyze equilibrium many-body phases and their\ncoexistence regions at nonzero temperature for the case of simple cubic lattice\ngeometry. We also determine the evolution of observables in low-temperature\nphases while lowering the symmetry of the Hamiltonian towards the two-band\nHubbard model. This is achieved by varying interflavor interactions or by\nintroducing the spin-flip term (Hund's coupling). By calculating the entropy\nfor different symmetries of the model, we determine the optimal regimes for\napproaching the studied phases in experiments with ultracold alkali and\nalkaline-earth-like atoms in optical lattices."
    },
    {
        "anchor": "Curved and expanding spacetime geometries in Bose-Einstein condensates: Phonons have the characteristic linear dispersion relation of massless\nrelativistic particles. They arise as low energy excitations of Bose-Einstein\ncondensates and, in nonhomogeneous situations, are governed by a space- and\ntime-dependent acoustic metric. We discuss how this metric can be\nexperimentally designed to realize curved spacetime geometries, in particular,\nexpanding Friedmann-Lema\\^itre-Robertson-Walker cosmologies, with negative,\nvanishing, or positive spatial curvature. A nonvanishing Hubble rate can be\nobtained through a time-dependent scattering length of the background\ncondensate. For relativistic quantum fields this leads to the phenomenon of\nparticle production, which we describe in detail. We explain how particle\nproduction and other interesting features of quantum field theory in curved\nspacetime can be tested in terms of experimentally accessible correlation\nfunctions.",
        "positive": "Dimensional reduction in Bose-Einstein condensed clouds of atoms\n  confined in tight potentials of any geometry and any interaction strength: Motivated by numerous experiments on Bose-Einstein condensed atoms which have\nbeen performed in tight trapping potentials of various geometries (elongated\nand/or toroidal/annular), we develop a general method which allows us to reduce\nthe corresponding three-dimensional Gross-Pitaevskii equation for the order\nparameter into an effectively one-dimensional equation, taking into account the\ninteractions (i.e., treating the width of the transverse profile variationally)\nand the curvature of the trapping potential. As an application of our model we\nconsider atoms which rotate in a toroidal trapping potential. We evaluate the\nstate of lowest energy for a fixed value of the angular momentum within various\napproximations of the effectively one-dimensional model and compare our results\nwith the full solution of the three-dimensional problem, thus getting evidence\nfor the accuracy of our model."
    },
    {
        "anchor": "Theory of SU(N) Fermi liquid: We generalized the Fermi liquid theory to N component systems with SU(N)\nsymmetry. We emphasize the important role of fluctuations when N is large.\nThese fluctuations dramatically modifies the properties for repulsive Fermi\ngases, in particular the spin susceptibility.",
        "positive": "Dynamics of the creation of a rotating Bose-Einstein condensate by\n  two-photon Raman transition using Laguerre-Gaussian pulse: We examine the dynamics associated with the creation of a vortex in a\nBose-Einstein condensate (BEC), from another nonrotating BEC using two-photon\nRaman transition with Gaussian (G) and Laguerre-Gaussian (LG) laser pulses. In\nparticular, we consider BEC of Rb atoms at their hyperfine ground states\nconfined in a quasi two dimensional harmonic trap. Optical dipole potentials\ncreated by G and LG laser pulses modify the harmonic trap in such a way that\ndensity profiles of the condensates during the Raman transition process depend\non the sign of the generated vortex. We investigate the role played by the\nRaman coupling parameter manifested through dimensionless peak Rabi frequency\nand intercomponent interaction on the dynamics of the population transfer\nprocess and on the final population of the rotating condensate. During the\nRaman transition process, the two BECs tend to have larger overlap with each\nother for stronger intercomponent interaction strength."
    },
    {
        "anchor": "Ground-state phase diagram of two-component interacting bosons on a\n  two-leg ladder: Using the cluster Gutzwiller mean-field method, we numerically study the\nground-state phase diagram of the non-hard-core two-component interacting\nbosons trapped in a two-leg ladder with and without an artificial magnetic\nfield. There are three quantum phases namely Mott insulator (MI),\nsupercounterfluid (SCF), and superfluid (SF) are found in the phase diagram.\nInterestingly, several loophole SCF phases are observed at a sufficiently small\nintra- to inter-leg hopping ratio when the magnetic flux is absent. While if\nthe ratio is not so small, the loophole SCF phase would disappear, but it can\nstill be induced by applying a sufficiently large magnetic flux. Additionally,\nwe also find that the presence of the magnetic flux leads to an enlargement of\nthe MI lobe and the conventional SCF lobe. Moreover, the SF-MI phase boundary\nis quantitatively consistent with the strong-couping expansion at a weak\nhopping amplitude.",
        "positive": "The nonlinear Dirac equation in Bose-Einstein condensates: II.\n  Relativistic soliton stability analysis: The nonlinear Dirac equation for Bose-Einstein condensates in honeycomb\noptical lattices gives rise to relativistic multi-component bright and dark\nsoliton solutions. Using the relativistic linear stability equations, the\nrelativistic generalization of the Boguliubov-de Gennes equations, we compute\nsoliton lifetimes against quantum fluctuations and classify the different\nexcitation types. For a Bose-Einstein condensate of $^{87}\\mathrm{Rb}$ atoms,\nwe find that our soliton solutions are stable on time scales relevant to\nexperiments. Excitations in the bulk region far from the core of a soliton and\nbound states in the core are classified as either spin waves or as a\nNambu-Goldstone mode. Thus, solitons are topologically distinct\npseudospin-$1/2$ domain walls between polarized regions of $S_z = \\pm 1/2$.\nNumerical analysis in the presence of a harmonic trap potential reveals a\ndiscrete spectrum reflecting the number of bright soliton peaks or dark soliton\nnotches in the condensate background. For each quantized mode the chemical\npotential versus nonlinearity exhibits two distinct power law regimes\ncorresponding to the free-particle (weakly nonlinear) and soliton (strongly\nnonlinear) limits."
    },
    {
        "anchor": "Twist of generalized skyrmions and spin vortices in a polariton\n  superfluid: We study the spin vortices and skyrmions coherently imprinted into an\nexciton-polariton condensate on a planar semiconductor microcavity. We\ndemonstrate that the presence of a polarization anisotropy can induce a complex\ndynamics of these structured topologies, leading to the twist of their\ncircuitation on the Poincar\\'e sphere of polarizations. The theoretical\ndescription of the results carries the concept of generalized quantum vortices\nin two-component superfluids, which are conformal with polarization loops\naround an arbitrary axis in the pseudospin space.",
        "positive": "Extracting density-density correlations from in situ images of atomic\n  quantum gases: We present a complete recipe to extract the density-density correlations and\nthe static structure factor of a two-dimensional (2D) atomic quantum gas from\nin situ imaging. Using images of non-interacting thermal gases, we characterize\nand remove the systematic contributions of imaging aberrations to the measured\ndensity-density correlations of atomic samples. We determine the static\nstructure factor and report results on weakly interacting 2D Bose gases, as\nwell as strongly interacting gases in a 2D optical lattice. In the strongly\ninteracting regime, we observe a strong suppression of the static structure\nfactor at long wavelengths."
    },
    {
        "anchor": "Quantum vortex instability and black hole superradiance: Vortices and black holes set the scene for many interesting dynamical\nprocesses in physics. Here, we study the dynamical instability of quantised\nvortices and rotational superradiance around rotating black holes, illustrating\nin the process that the same physics is at play in these two seemingly\ndisparate phenomena. We also compare the instability of the vortex to the black\nhole bomb instability, which occurs for massive scalar fields in the Kerr\nspacetime. Taking inspiration from the analogy between black hole bomb modes\nand the hydrogen spectrum, the vortex instability is compared with nuclear\nresonances involved in $\\alpha$-decay.",
        "positive": "Floquet topological phases in a spin-1/2 double kicked rotor: The double kicked rotor model is a physically realizable extension of the\nparadigmatic kicked rotor model in the study of quantum chaos. Even before the\nconcept of Floquet topological phases became widely known, the discovery of the\nHofstadter butterfly spectrum in the double kicked rotor model [J. Wang and J.\nGong, Phys. Rev. A 77, 031405 (2008)] already suggested the importance of\nperiodic driving to the generation of unconventional topological matter. In\nthis work, we explore Floquet topological phases of a double kicked rotor with\nan extra spin-1/2 degree of freedom. The latter has been experimentally\nengineered in a quantum kicked rotor recently by loading Rb87 condensates into\na periodically pulsed optical lattice. Under the on-resonance condition, the\nspin-1/2 double kicked rotor admits fruitful topological phases due to the\ninterplay between its external and internal degrees of freedom. Each of these\ntopological phases is characterized by a pair of winding numbers, whose\ncombination predicts the number of topologically protected 0 and\n\\pi-quasienergy edge states in the system. Topological phases with arbitrarily\nlarge winding numbers can be easily found by tuning the kicking strength. We\ndiscuss an experimental proposal to realize this model in kicked Rb87\ncondensates, and suggest to detect its topological invariants by measuring the\nmean chiral displacement in momentum space."
    },
    {
        "anchor": "Quantum Hall states of bosons in rotating anharmonic traps: We study a model of bosons in the lowest Landau level in a rotating trap\nwhere the confinement potential is a sum of a quadratic and a quartic term. The\nquartic term improves the stability of the system against centrifugal\ndeconfinement and allows to consider rotation frequencies beyond the frequency\nof the quadratic part. The interactions between particles are modeled by a\nDirac delta potential. We derive rigorously conditions for ground states of the\nsystem to be strongly correlated in the sense that they are confined to the\nkernel of the interaction operator, and thus contain the correlations of the\nBose-Laughlin state. Rigorous angular momentum estimates and trial state\narguments indicate a transition from a pure Laughlin state to a state\ncontaining in addition a giant vortex at the center of the trap (Laughlin\nquasi-hole). There are also indications of a second transition where the\ndensity changes from a flat profile in a disc or an annulus to a radial\nGaussian confined to a thin annulus.",
        "positive": "Sub-Doppler cooling of sodium atoms in gray molasses: We report on the realization of sub-Doppler laser cooling of sodium atoms in\ngray molasses using the D1 optical transition ($3s\\, ^2S_{1/2} \\rightarrow 3p\\,\n^2P_{1/2}$) at 589.8 nm. The technique is applied to samples containing\n$3\\times10^9$ atoms, previously cooled to 350 $\\mu$K in a magneto-optical trap,\nand it leads to temperatures as low as 9 $\\mu$K and phase-space densities in\nthe range of $10^{-4}$. The capture efficiency of the gray molasses is larger\nthan 2/3, and we observe no density-dependent heating for densities up to\n$10^{11}$ cm$^{-3}$."
    },
    {
        "anchor": "Connecting strongly correlated superfluids by a quantum point contact: Point contacts provide simple connections between macroscopic particle\nreservoirs. In electric circuits, strong links between metals, semiconductors\nor superconductors have applications for fundamental condensed-matter physics\nas well as quantum information processing. However for complex, strongly\ncorrelated materials, links have been largely restricted to weak tunnel\njunctions. Here we study resonantly interacting Fermi gases connected by a\ntunable, ballistic quantum point contact, finding a non-linear current-bias\nrelation. At low temperature, our observations agree quantitatively with a\ntheoretical model in which the current originates from multiple Andreev\nreflections. In a wide contact geometry, the competition between superfluidity\nand thermally activated transport leads to a conductance minimum. Our system\noffers a controllable platform for the study of mesoscopic devices based on\nstrongly interacting matter.",
        "positive": "Single-branch theory of ultracold Fermi gases with artificial Rashba\n  spin-orbit coupling: We consider interacting ultracold fermions subject to Rashba spin-orbit\ncoupling. We construct a single-branch interacting theory for the Fermi gas\nwhen the system is dilute enough so that the positive helicity branch is not\noccupied at all in the non-interacting ground state. We show that the theory is\nrenormalizable in perturbation theory and therefore yields a model of polarized\nfermions that avoids a multi-channel treatment of the problem. Our results open\nthe path towards a much more straightforward approach to the many-body physics\nof cold atoms subject to artificial vector potentials."
    },
    {
        "anchor": "Topological superfluid transition in bubble-trapped condensates: Ultracold quantum gases are highly controllable and, thus, capable of\nsimulating difficult quantum many-body problems ranging from condensed matter\nphysics to astrophysics. Although experimental realizations have so far been\nrestricted to flat geometries, recently also curved quantum systems, with the\nprospect of exploring tunable geometries, are produced in microgravity\nfacilities as ground-based experiments are technically limited. Here we analyze\nbubble-trapped condensates, in which the atoms are confined on the surface of a\nthin spherically-symmetric shell by means of external magnetic fields. A\nthermally-induced proliferation of vorticity yields a vanishing of\nsuperfluidity. We describe the occurrence of this topological transition by\nconceptually extending the theory of Berezinskii, Kosterlitz and Thouless for\ninfinite uniform systems to such finite-size systems. Unexpectedly, we find\nuniversal scaling relations for the mean critical temperature and the finite\nwidth of the superfluid transition. Furthermore, we elucidate how they could be\nexperimentally observed in finite-temperature hydrodynamic excitations.",
        "positive": "Continuum of classical-field ensembles from canonical to grand canonical\n  and the onset of their equivalence: The canonical and grand-canonical ensembles are two usual marginal cases for\nultracold Bose gases, but real collections of experimental runs commonly have\nintermediate properties. Here we study the continuum of intermediate cases, and\nlook into the appearance of ensemble equivalence as interaction rises for\nmesoscopic 1d systems. We demonstrate how at sufficient interaction strength\nthe distributions of condensate and excited atoms become practically identical\nregardless of the ensemble used. Importantly, we find that features that are\nfragile in the ideal gas and appear only in a strict canonical ensemble can\nbecome robust in all ensembles when interactions become strong. As evidence,\nthe steep cliff in the distribution of the number of excited atoms is\npreserved. To make this study, a straightforward approach for generating\ncanonical and intermediate classical field ensembles using a modified\nstochastic Gross-Pitaevskii equation (SGPE) is developed."
    },
    {
        "anchor": "Interface Dynamics of Strongly interacting Binary Superfluids: Understanding the interface dynamics in non-equilibrium quantum systems\nremains a challenge. We study the interface dynamics of strongly coupled\nimmiscible binary superfluids by using holographic duality. The full nonlinear\nevolution of the binary superfluids with a relative velocity shows rich\nnonlinear patterns toward quantum turbulence, which is reminiscent of the\nquantum Kelvin-Helmholtz instability. The wave number of the fast growing modes\n$k_0$ extracted from the interface pattern yields a non-monotonic dependence of\nthe relative velocity, independent of the temperature and interaction. The\nvalue of $k_0$ first increases with the velocity difference and then decreases,\nwhich stands in sharp contrast to the results of mean-field theory described by\nthe Gross-Pitaevskii equation and is confirmed by using the linear analyses on\ntop of the stationary configuration. We uncover that the critical velocity\nassociated with the maximum correspond to the case when the mean separation of\nvortices generated by interface instabilities becomes comparable to the vortex\nsize, which could be a universal physical mechanism at strongly interacting\nsuperfluids and is directly testable in laboratory experiments.",
        "positive": "A quantum degenerate Bose-Fermi mixture of $^{41}$K and $^6$Li: We report a new apparatus for the study of two-species quantum degenerate\nmixture of $^{41}$K and $^6$Li atoms. We develop and combine several advanced\ncooling techniques to achieve both large atom number and high phase space\ndensity of the two-species atom clouds. Furthermore, we build a high-efficiency\ntwo-species magnetic transport system to transfer atom clouds from the 3D\nmagneto-optical-trap chamber to a full glass science chamber of extreme high\nvacuum environment and good optical access. We perform a forced radio-frequency\nevaporative cooling for $^{41}$K atoms while the $^6$Li atoms are\nsympathetically cooled in an optically-plugged magnetic trap. Finally, we\nachieve the simultaneous quantum degeneracy for the $^{41}$K and $^6$Li atoms.\nThe Bose-Einstein condensate of $^{41}$K has 1.4$\\times$10$^5$ atoms with a\ncondensate fraction of about 62%, while the degenerate Fermi gas of $^6$Li has\na total atom number of 5.4$\\times$10$^5$ at 0.25 Fermi temperature."
    },
    {
        "anchor": "Fulde-Ferrell states and Berezinskii-Kosterlitz-Thouless phase\n  transition in two-dimensional imbalanced Fermi gases: We study the superfluid properties of two-dimensional\nspin-population-imbalanced Fermi gases to explore the interplay between the\nBerezinskii-Kosterlitz-Thouless (BKT) phase transition and the possible\ninstability towards the Fulde-Ferrell (FF) state. By the mean-field\napproximation together with quantum fluctuations, we obtain phase diagrams as\nfunctions of temperature, chemical potential imbalance and binding energy. We\nfind that the fluctuations change the mean-field phase diagram significantly.\nWe also address possible effects of the phase separation and/or the anisotropic\nFF phase to the BKT mechanism. The superfluid density tensor of the FF state is\nobtained, and its transverse component is found always vanishing. This causes\ndivergent fluctuations and possibly precludes the existence of the FF state at\nany non-zero temperature.",
        "positive": "BEC-BCS Crossover with Feshbach Resonance for a Three-Hyperfine-Species\n  Model: We consider the behavior of an ultracold Fermi gas across a narrow Feshbach\nresonance, where the occupation of the closed channel may not be negligible.\nWhile the corrections to the single-channel formulae associated with the\nnonzero chemical potential and with particle conservation have been considered\nin the existing literature, there is a further effect, namely the\n\"inter-channel Pauli exclusion principle\" associated with the fact that a\nsingle hyperfine species may be common to the two channels. We focus on this\neffect and show that, as intuitively expected, the resulting corrections are of\norder $E_F/\\eta$, where $E_F$ is the Fermi energy of the gas in the absence of\ninteractions and $\\eta$ is the Zeeman energy difference between the two\nchannels. We also consider the related corrections to the fermionic excitation\nspectrum, and briefly discuss the collective modes of the system."
    },
    {
        "anchor": "Collective excitations of a harmonically trapped, two-dimensional,\n  spin-polarized dipolar Fermi gas in the hydrodynamic regime: The collective excitations of a zero-temperature, spin-polarized,\nharmonically trapped, two-dimensional dipolar Fermi gas are examined within the\nThomas-Fermi von Weizs\\\"acker hydrodynamic theory. We focus on repulsive\ninteractions, and investigate the dependence of the excitation frequencies on\nthe strength of the dipolar interaction and particle number. We find that the\nmode spectrum can be classified according to bulk modes, whose frequencies are\nshifted upward as the interaction strength is increased, and an infinite ladder\nof surface modes, whose frequencies are {\\em independent} of the interactions\nin the large particle limit. We argue quite generally that it is the {\\em\nlocal} character of the two-dimensional energy density which is responsible for\nthe insensitivity of surface excitations to the dipolar interaction strength,\nand not the precise form of the equation of state. This property will not be\nfound for the collective excitations of harmonically trapped, dipolar Fermi\ngases in one and three dimensions, where the energy density is manifestly\nnonlocal.",
        "positive": "Measuring spin correlations in optical lattices using superlattice\n  potentials: We suggest two experimental methods for probing both short- and long-range\nspin correlations of atoms in optical lattices using superlattice potentials.\nThe first method involves an adiabatic doubling of the periodicity of the\nunderlying lattice to probe neighboring singlet (triplet) correlations for\nfermions (bosons) by the occupation of the new vibrational ground state. The\nsecond method utilizes a time-dependent superlattice potential to generate\nspin-dependent transport by any number of prescribed lattice sites, and probes\ncorrelations by the resulting number of doubly occupied sites. For\nexperimentally relevant parameters, we demonstrate how both methods yield large\nsignatures of antiferromagnetic (AF) correlations of strongly repulsive\nfermionic atoms in a single shot of the experiment. Lastly, we show how this\nmethod may also be applied to probe d-wave pairing, a possible ground state\ncandidate for the doped repulsive Hubbard model."
    },
    {
        "anchor": "Annihilation and recurrence of vortex-antivortex pairs in two-component\n  Bose-Einstein condensates: The annihilation of vortex-antivortex pairs is a key event in two-dimensional\nBose-Einstein condensates (BECs). It is known that dissipation or a catalyst\nvortex is required for the annihilation of the pairs in one-component BECs. We\nnumerically confirmed in two-component BECs that the pairs can be annihilated\neven without any dissipation or catalyst vortices when the intercomponent\ninteraction is strong. In addition, the pair is recreated alternately in two\ncomponents under certain conditions, which we call the recurrence.",
        "positive": "Coherent cross-talk and parametric driving of matter-wave vortices: We show that the interaction between vortices and sound waves in atomic\nBose-Einstein condensates can be elucidated in a double-well trap: with one\nvortex in each well, the sound emitted by each precessing vortex can be driven\ninto the opposing vortex (if of the same polarity). This cross-talk leads to a\nperiodic exchange of energy between the vortices which is long-range and highly\nefficient. The increase in vortex energy (obtained by numerical simulations of\nthe Gross-Pitaevskii equation) is significant and experimentally observable as\na migration of the vortex to higher density over just a few precession periods.\nSimilar effects can be controllably engineered by introducing a precessing\nlocalised obstacle into one well as an artificial generator of sound, thereby\ndemonstrating the parametric driving of energy into a vortex."
    },
    {
        "anchor": "Spin-susceptibility of spin-orbit coupled Fermi superfluids: Under the self-consistent mean-field approach for the BCS-BEC crossover\nproblem, we derive a closed-form analytical expression for the general spin\nresponse of noncentrosymmetric Fermi superfluids with arbitrary spin-orbit\ncoupling and Zeeman fields. In addition to the paramagnetic, i.e., the Pauli\nintra-helicity and Van Vleck type inter-helicity, contributions to the\nspin-susceptibility tensor that have normal-state counterparts, we identify a\ndiamagnetic inter-helicity contribution that is unique to the superfluid state.\nOur extensive numerical calculations for the Weyl, Rashba and equal\nRashba-Dresselhaus spin-orbit couplings illustrate that it is this diamagnetic\ncontribution that grows gradually with pairing and cancels precisely the Van\nVleck contribution away from the BCS regime in general.",
        "positive": "Crossover between few and many fermions in a harmonic trap: The properties of a balanced two-component Fermi gas in a one-dimensional\nharmonic trap are studied by means of the coupled cluster method. For few\nfermions we recover the results of exact diagonalization, yet with this method\nwe are able to study much larger systems. We compute the energy, the chemical\npotential, the pairing gap, and the density profile of the trapped clouds,\nsmoothly mapping the crossover between the few-body and many-body limits. The\nenergy is found to converge surprisingly rapidly to the many-body result for\nevery value of the interaction strength. Many more particles are instead needed\nto give rise to the non-analytic behavior of the pairing gap, and to smoothen\nthe pronounced even-odd oscillations of the chemical potential induced by the\nshell structure of the trap."
    },
    {
        "anchor": "Collective modes of a one-dimensional trapped atomic Bose gas at finite\n  temperatures: We theoretically investigate collective modes of a one-dimensional (1D)\ninteracting Bose gas in harmonic traps at finite temperatures, by using a\nvariational approach and local density approximation. We find that the\ntemperature dependence of collective mode frequencies is notably different in\nthe weakly and strongly interacting regimes. Therefore, the experimental\nmeasurement of collective modes could provide a sensitive probe for different\nquantum phases of a 1D trapped Bose gas, realized by tuning the interatomic\ninteraction strength and temperature. Our prediction on the temperature\ndependence of the breathing mode frequency is in good qualitative agreement\nwith an earlier experimental measurement for a weakly interacting 1D Bose gas\nof rubidium-87 atoms in harmonic traps [Moritz et al., Phys. Rev. Lett. 91,\n250402 (2003)].",
        "positive": "Asymmetric Particle Transport and Light-Cone Dynamics Induced by Anyonic\n  Statistics: We study the non-equilibrium dynamics of Abelian anyons in a one-dimensional\nsystem. We find that the interplay of anyonic statistics and interactions gives\nrise to spatially asymmetric particle transport together with a novel dynamical\nsymmetry that depends on the anyonic statistical angle and the sign of\ninteractions. Moreover, we show that anyonic statistics induces asymmetric\nspreading of quantum information, characterized by asymmetric light cones of\nout-of-time-ordered correlators. Such asymmetric dynamics is in sharp contrast\nwith the dynamics of conventional fermions or bosons, where both the transport\nand information dynamics are spatially symmetric. We further discuss\nexperiments with cold atoms where the predicted phenomena can be observed using\nstate-of-the-art technologies. Our results pave the way toward experimentally\nprobing anyonic statistics through non-equilibrium dynamics."
    },
    {
        "anchor": "Dynamics of Vortices and Solitons in a Bose-Einstein Condensate by an\n  Oscillating Potential: We study numerically the dynamics of quantized vortices and solitons induced\nby an oscillating potential inside a trapped Bose-Einstein condensate. The\ndynamics of the topological defects is much different from the case for a\nlinear uniform object; the metamorphosis between vortices and solitons is\ncharacteristic of the dynamics. We discuss how vortices are nucleated by an\noscillating potential.",
        "positive": "Condensation of Excitons in Cu2O at Ultracold Temperatures: Experiment\n  and Theory: We present experiments on the luminescence of excitons confined in a\npotential trap at milli-Kelvin bath temperatures under cw-excitation. They\nreveal several distinct features like a kink in the dependence of the total\nintegrated luminescence intensity on excitation laser power and a bimodal\ndistribution of the spatially resolved luminescence. Furthermore, we discuss\nthe present state of the theoretical description of Bose-Einstein condensation\nof excitons with respect to signatures of a condensate in the luminescence. The\ncomparison of the experimental data with theoretical results with respect to\nthe spatially resolved as well as the integrated luminescence intensity shows\nthe necessity of taking into account a Bose-Einstein condensed excitonic phase\nin order to understand the behaviour of the trapped excitons."
    },
    {
        "anchor": "Density-functional theory for the crystalline phases of a\n  two-dimensional dipolar Fermi gas: Density-functional theory is utilized to investigate the zero-temperature\ntransition from a Fermi liquid to an inhomogeneous stripe, or Wigner crystal\nphase, predicted to occur in a one-component, spin-polarized, two-dimensional\ndipolar Fermi gas. Correlations are treated semi-exactly within the\nlocal-density approximation using an empirical fit to Quantum Monte Carlo data.\nWe find that the inclusion of the nonlocal contribution to the Hartree-Fock\nenergy is crucial for the onset of an instability to an inhomogeneous density\ndistribution. Our density-functional theory supports a transition to both a\none-dimensional stripe phase, and a triangular Wigner crystal. However, we find\nthat there is an instability first to the stripe phase, followed by a\ntransition to the Wigner crystal at higher coupling.",
        "positive": "Verifying the observer dependence of quasiparticle counts in the\n  analogue gravity of dilute ultracold quantum gases: The quasiparticle content of a quantum field depends on the observer, in\nparticular on its motional state, on the way the observer's detector couples to\nthe quantum field, and on the frequency standard in which the detector carried\nby the observer measures the quanta to be detected. I review a procedure of\nmaking this fundamental property of quantum field theory experimentally\nmanifest using quantum-optical means in Bose-Einstein condensates."
    },
    {
        "anchor": "Expansion of one-dimensional lattice hard-core bosons at finite\n  temperature: We develop an exact approach to study the quench dynamics of hard-core bosons\ninitially in thermal equilibrium in one-dimensional lattices. This approach is\nused to study the sudden expansion of thermal states after confining potentials\nare switched off. We find that a dynamical fermionization of the momentum\ndistribution occurs at all temperatures. This phenomenon is studied for low\ninitial site occupations, for which the expansion of the cloud is self-similar.\nIn this regime, the occupation of the natural orbitals allows one to\ndistinguish hard-core bosons from noninteracting fermions. We also study the\nfree expansion of initial Mott insulating domains at finite temperature, and\nshow that the emergence of off-diagonal one-body correlations is suppressed\ngradually with increasing temperature. Surprisingly, the melting of the Mott\ndomain is accompanied by an effective cooling of the system. We explain this\nphenomenon analytically using an equilibrium description based on an emergent\nlocal Hamiltonian.",
        "positive": "Topological Bose-Mott Insulators in a One-Dimensional Optical\n  Superlattice: We study topological properties of the Bose-Hubbard model with repulsive\ninteractions in a one-dimensional optical superlattice. We find that the Mott\ninsulator states of the single-component (two-component) Bose-Hubbard model\nunder fractional fillings are topological insulators characterized by a nonzero\ncharge (or spin) Chern number with nontrivial edge states. For ultracold atomic\nexperiments, we show that the topological Chern number can be detected through\nmeasuring the density profiles of the bosonic atoms in a harmonic trap."
    },
    {
        "anchor": "Spontaneous Spin Textures in Dipolar Spinor Condensates: A Dirac String\n  Gas Approach: We study the spontaneous spin textures induced by magnetic dipole-dipole\ninteraction in ferromagnetic spinor condensates under various trap geometries.\nAt the mean-field level, we show the system is dual to a Dirac string gas with\na negative string tension in which the ground state spin texture can be easily\ndetermined. We find that three-dimensional condensates prefer a meron-like\nvortex texture, quasi one-dimensional condensates prefer the axially polarized\nflare texture, while condensates in quasi two dimensions exhibit either a meron\ntexture or an in-plane polarized texture.",
        "positive": "Damping of Confined Excitations Modes of 1D Condensates in an Optical\n  Lattice: We study the damping of the collective excitations of Bose-Einstein\ncondensates in a harmonic trap potential loaded in an optical lattice. In the\npresence of a confining potential the system is non-homogeneous and the\ncollective excitations are characterized by a set of discrete confined\nphonon-like excitations. We derive a general convenient analytical description\nfor the damping rate, which takes into account, the trapping potential and the\noptical lattice, for the Landau and Beliaev processes at any temperature, $T$.\nAt high temperature or weak spatial confinement, we show that both mechanisms\ndisplay linear dependence on $T$. In the quantum limit, we found that the\nLandau damping is exponentially suppressed at low temperatures and the total\ndamping is independent of $T$. Our theoretical predictions for the damping rate\nunder thermal regime is in completely correspondence with the experimental\nvalues reported for 1D condensate of sodium atoms. We show that the laser\nintensity can tune the collision process, allowing a \\textit{resonant effect}\nfor the condensate lifetime. Also, we study the influence of the attractive or\nrepulsive non-linear terms on the decay rate of the collective excitations. A\ngeneral expression of the renormalized Goldstone frequency has been obtained as\na function of the 1D non-linear self-interaction parameter, laser intensity and\ntemperature."
    },
    {
        "anchor": "Topological phases in ultracold polar-molecule quantum magnets: We show how to use polar molecules in an optical lattice to engineer quantum\nspin models with arbitrary spin S >= 1/2 and with interactions featuring a\ndirection-dependent spin anisotropy. This is achieved by encoding the effective\nspin degrees of freedom in microwave-dressed rotational states of the molecules\nand by coupling the spins through dipolar interactions. We demonstrate how one\nof the experimentally most accessible anisotropies stabilizes symmetry\nprotected topological phases in spin ladders. Using the numerically exact\ndensity matrix renormalization group method, we find that these interacting\nphases -- previously studied only in the nearest-neighbor case -- survive in\nthe presence of long-range dipolar interactions. We also show how to use our\napproach to realize the bilinear-biquadratic spin-1 and the Kitaev honeycomb\nmodels. Experimental detection schemes and imperfections are discussed.",
        "positive": "Strong coupling Bose polarons in a two-dimensional gas: We study the properties of Bose polarons in two dimensions using quantum\nMonte Carlo techniques. Results for the binding energy, the effective mass, and\nthe quasiparticle residue are reported for a typical strength of interactions\nin the gas and for a wide range of impurity-gas coupling strengths. A lower and\nan upper branch of the quasiparticle exist. The lower branch corresponds to an\nattractive polaron and spans from the regime of weak coupling where the\nimpurity acts as a small density perturbation of the surrounding medium to deep\nbound states which involve many particles from the bath and extend as far as\nthe healing length. The upper branch corresponds to an excited state where due\nto repulsion a low-density bubble forms around the impurity but might be\nunstable against decay into many-body bound states. Interaction effects\nstrongly affect the quasiparticle properties of the polaron. In particular, in\nthe strongly correlated regime, the impurity features a vanishing quasiparticle\nresidue, signaling the transition from an almost free quasiparticle to a bound\nstate involving many atoms from the bath."
    },
    {
        "anchor": "Fate of the \"vacuum point'' and of grey solitons in dispersive quantum\n  shock waves in a one-dimensional Bose gas: We continue the study of dispersive quantum shock waves in a one-dimensional\nBose gas beyond the mean-field approximation. In a recent work by Simmons et\nal. [Phys. Rev. Let. 125, 180401 (2020)], the oscillatory shock wave train\ndeveloping in this system from an initial localized density bump on a uniform\nbackground was interpreted as a result of quantum mechanical self-interference,\nwherein the interference contrast would diminish with the loss of matter-wave\nphase coherence. Such loss of coherence, relative to the mean-field\nGross-Pitaevskii description, occurs due to either quantum or thermal\nfluctuations, as well as in the strongly interacting regime. In this work, we\nextend the analysis of dispersive quantum shock waves in this context to other\ndynamical scenarios. More specifically, the scenarios studied include evolution\nof a sufficiently high density bump, known to lead to the so-called ``vacuum\npoint'' in the mean-field description, and evolution of an initial density dip,\nknown to shed a train of grey solitons in the same mean-field approximation. We\nstudy the fate of these nonlinear wave structures in the presence of quantum\nand thermal fluctuations, as well as at intermediate and strong interactions,\nand show that both the vacuum point and grey solitons cease to manifest\nthemselves beyond the mean-field approach. On the other hand, we find that a\nvacuum point can occur in an ideal (noninteracting) Bose gas evolving from a\nground state of a localized dimple potential. Due to the ubiquity of dispersive\nshock waves in nature, our results should provide useful insights and\nperspectives for a variety of other physical systems known to display nonlinear\nwave phenomena.",
        "positive": "Atom-dimer p-wave resonance for fermionic mixtures with different masses: We show that, near a Feshbach resonance, a strong p-wave resonance is present\nat low energy in atom-dimer scattering for $^6$Li-$^{40}$K fermionic mixtures.\nThis resonance is due to a virtual bound state, in the atom-dimer system, which\nis present at this low energy. When the mass ratio between the two fermionic\nelements is increased, this virtual bound state goes to a known real bound\nstate which appears when the mass ratio reaches 8.17. This resonance should\naffect a number of physical properties. These include the equation of state of\nunbalanced mixtures at very low temperature but also the equation of state of\nbalanced mixtures at moderate or high temperature. The frequency and the\ndamping of collective modes should also provide a convenient way to evidence\nthis resonance. Finally it should be possible to modify the effective mass of\none the fermionic species by making use of an optical lattice. This would allow\nto study the strong dependence of the resonance as a function of the mass ratio\nof the two fermionic elements."
    },
    {
        "anchor": "Phonon-Josephson resonances in atomtronic circuits: We study the resonant excitation of sound modes from Josephson oscillations\nin Bose-Einstein condensates. From the simulations for various setups using the\nGross-Pitaevskii mean-field equations and Josephson equations we observe\nadditional tunneling currents induced by resonant phonons. The proposed\nexperiment may be used for spectroscopy of phonons as well as other low-energy\ncollective excitations in Bose-Einstein condensates. We also argue that the\nobserved effect may mask the observation of Shapiro resonances if not carefully\ncontrolled.",
        "positive": "The condensation of ideal Bose gas in a gravitational field in the\n  framework of Dunkl-statistic: In the framework of the theory of Dunkl-deformed bosons, Bose-Einstein\ncondensation of two and three-dimensional Dunkl-boson gases confined in the\none-dimensional gravitational field is investigated. Using the semi-classical\napproximation method, we calculate the expressions of the Dunkl-critical\ntemperature $T_{c}^{D}$, the ground state population $\\frac{N_{0}^{D}}{N}$ and\nthe Dunkl-mean energy and Dunkl-specific heat functions. Further numerical\ncalculation shows that the condensation temperature ratio\n$\\frac{T_{c}^{D}}{T_{c}^{B}}$ increases with the increasing Wigner parameter."
    },
    {
        "anchor": "Generalized Wick's theorem at finite temperature for a quadratic\n  Hamiltonian: In Gaudin (1960), Michel Gaudin showed the Wick's theorem at finite\ntemperature using a diagonal Hamiltonian. We extend the Gaudin's prove for a\nstatistical density operator which depend on a quadratic Hamiltonian. To\nillustrate the utility of the theorem, we evaluate the ratio\n$\\sqrt{[<\\hat{N}^2>-<\\hat{N}>^2]/<\\hat{N}>}$ of a homogeneous weakly\ninteracting Bose gas at temperature below the Bose-Einstein condensation\ntemperature. At this condition, the quadratic Hamiltonian approximation is\nvalued and, in this evaluation, we show the sub-Poissonian behaviour of the\nfundamental state distribution at zero temperature.",
        "positive": "Thermodynamics of a Bose gas near the superfluid--Mott-insulator\n  transition: We study the thermodynamics near the generic (density-driven)\nsuperfluid--Mott-insulator transition in the three-dimensional Bose-Hubbard\nmodel using the nonperturbative renormalization-group approach. At low energy\nthe physics is controlled by the Gaussian fixed point and becomes universal.\nThermodynamic quantities can then be expressed in terms of the universal\nscaling functions of the dilute Bose gas universality class while the\nmicroscopic physics enters only {\\it via} two nonuniversal parameters, namely\nthe effective mass $m^*$ and the \"scattering length\" $a^*$ of the elementary\nexcitations at the quantum critical point between the superfluid and\nMott-insulating phase. A notable exception is the condensate density in the\nsuperfluid phase which is proportional to the quasi-particle weight $\\Zqp$ of\nthe elementary excitations. The universal regime is defined by $m^*a^*{}^2 T\\ll\n1$ and $m^*a^*{}^2|\\delta\\mu|\\ll 1$, or equivalently $|\\bar n-\\bar\nn_c|a^*{}^3\\ll 1$, where $\\delta\\mu=\\mu-\\mu_c$ is the chemical potential shift\nfrom the quantum critical point $(\\mu=\\mu_c,T=0)$ and $\\bar n-\\bar n_c$ the\ndoping with respect to the commensurate density $\\bar n_c$ of the T=0 Mott\ninsulator. We compute $\\Zqp$, $m^*$ and $a^*$ and find that they vary strongly\nwith both the ratio $t/U$ between hopping amplitude and on-site repulsion and\nthe value of the (commensurate) density $\\bar n_c$. Finally, we discuss the\nexperimental observation of universality and the measurement of $\\Zqp$, $m^*$\nand $a^*$ in a cold atomic gas in an optical lattice."
    },
    {
        "anchor": "Quantum turbulence in trapped atomic Bose-Einstein condensates: Turbulence, the complicated fluid behavior of nonlinear and statistical\nnature, arises in many physical systems across various disciplines, from tiny\nlaboratory scales to geophysical and astrophysical ones. The notion of\nturbulence in the quantum world was conceived long ago by Onsager and Feynman,\nbut the occurrence of turbulence in ultracold gases has been studied in the\nlaboratory only very recently. Albeit new as a field, it already offers new\npaths and perspectives on the problem of turbulence. Herein we review the\ngeneral properties of quantum gases at ultralow temperatures paying particular\nattention to vortices, their dynamics and turbulent behavior. We review the\nrecent advances both from theory and experiment. We highlight, moreover, the\ndifficulties of identifying and characterizing turbulence in gaseous\nBose-Einstein condensates compared to ordinary turbulence and turbulence in\nsuperfluid liquid helium and spotlight future possible directions.",
        "positive": "Engineering Dissipative Quasicrystals: We discuss the systematic engineering of quasicrystals in open quantum\nsystems where quasiperiodicity is introduced through purely dissipative\nprocesses. While the resulting short-time dynamics is governed by non-Hermitian\nvariants of the Aubry-Andre-Harper model, we demonstrate how phases and phase\ntransitions pertaining to the non-Hermitian quasicrystals fundamentally change\nthe long-time, steady-state-approaching dynamics under the Lindblad master\nequation. Our schemes are based on an exact mapping between the eigenspectrum\nof the Liouvillian superoperator with that of the non-Hermitian Hamiltonian,\nunder the condition of quadratic fermionic systems subject to linear\ndissipation. Our work suggests a systematic route toward engineering exotic\nquantum dynamics in open systems, based on insights of non-Hermitian physics."
    },
    {
        "anchor": "Intersubband Polaritons in the Electrical Dipole Gauge: We provide a theoretical description for the coupling between the\nintersubband excitations of a bi-dimensional electron gas with the\nelectromagnetic field. This description, based on the electrical dipole gauge,\napplies to an arbitrary quantum heterostructure embedded in a general\nmultilayered waveguide or a microcavity. We show that the dipole gauge\nHamiltonian automatically takes into account the Coulomb interactions in this\nsystem. Furthermore, it can be conveniently expressed in terms of the many-body\ncollective plasmon modes, which interact both with each other and with the\nlight field. The dipole gauge therefore provides a suitable framework for the\nstudy of solid state Quantum Electrodynamics (QED) phenomena, such as the\nultra-strong light-matter interaction regime, occurring at very high electronic\ndensities.",
        "positive": "Composite bosons in the 2D BCS-BEC crossover from Gaussian fluctuations: We study Gaussian fluctuations of the zero-temperature attractive Fermi gas\nin the 2D BCS-BEC crossover showing that they are crucial to get a reliable\nequation of state in the BEC regime of composite bosons, bound states of\nfermionic pairs. A low-momentum expansion up to the fourth order of the\nquadratic action of the fluctuating pairing field gives an ultraviolent\ndivergent contribution of the Gaussian fluctuations to the grand potential.\nPerforming dimensional regularization we evaluate the effective coupling\nconstant in the beyond-mean-field grand potential. Remarkably, in the BEC\nregime our grand potential gives exactly the Popov's equation of state of 2D\ninteracting bosons, and allows us to identify the scattering length $a_B$ of\nthe interaction between composite bosons as $a_B=a_F/(2^{1/2}e^{1/4})= 0.551...\na_F$, with $a_F$ is the scattering length of fermions. Remarkably, the value\nfrom our analytical relationship between the two scattering lengths is in full\nagreement with that obtained by recent Monte Carlo calculations."
    },
    {
        "anchor": "Highly Polarized Fermi Gases across a Narrow Feshbach Resonance: We address the phase of a highly polarized Fermi gas across a narrow Feshbach\nresonance starting from the problem of a single down spin fermion immersed in a\nFermi sea of up spins. Both polaron and pairing states are considered using the\nvariational wave function approach, and we find that the polaron to pairing\ntransition will take place at the BCS side of the resonance, strongly in\ncontrast to a wide resonance where the transition is located at the BEC side.\nFor pairing phase, we find out the critical strength of repulsive interaction\nbetween pairs above which the mixture of pairs and fermions will not phase\nseparate. Therefore, nearby a narrow resonance, it is quite likely that\nmagnetism can coexist with s-wave BCS superfluidity at large Zeeman field,\nwhich is a remarkable property absent in conventional BCS superconductors (or\nfermion pair superfluids).",
        "positive": "Dynamical evolution of an effective two-level system with PT symmetry: We investigate the dynamics of parity- and time-reversal (PT ) symmetric\ntwo-energy-level atoms in the presence of two optical and a radio-frequency\n(rf) fields. The strength and relative phase of fields can drive the system\nfrom unbroken to broken PT symmetric regions. Compared with the Hermitian\nmodel, Rabi-type oscillation is still observed, and the oscillation\ncharacteristics are also adjusted by the strength and relative phase in the\nregion of unbroken PT symmetry. At exception point (EP), the oscillation breaks\ndown. To better understand the underlying properties we study the effective\nBloch dynamics and find the emergence of the z components of the fixed points\nis the feature of the PT symmetry breaking and the projections in x-y plane can\nbe controlled with high flexibility compared with the standard two-level system\nwith PT symmetry. It helps to study the dynamic behavior of the complex PT\nsymmetric model."
    },
    {
        "anchor": "Superfluid properties of one-component Fermi gas with an anisotropic\n  p-wave interaction: We investigate superfluid properties and strong-coupling effects in a\none-component Fermi gas with an anisotropic p-wave interaction. Within the\nframework of the Gaussian fluctuation theory, we determine the superfluid\ntransition temperature $T_{\\rm c}$, as well as the temperature $T_0$ at which\nthe phase transition from the $p_x$-wave pairing state to the $p_x+ip_y$-wave\nstate occurs below $T_{\\rm c}$. We also show that while the anisotropy of the\np-wave interaction enhances $T_{\\rm c}$ in the strong-coupling regime, it\nsuppresses $T_0$.",
        "positive": "Coherence and Instability in a Driven Bose-Einstein Condensate: A Fully\n  Dynamical Number-Conserving Approach: We consider a Bose-Einstein condensate driven by periodic delta-kicks. In\ncontrast to first-order descriptions, which predict rapid, unbounded growth of\nthe noncondensate in resonant parameter regimes, the consistent treatment of\ncondensate depletion in our fully-time-dependent, second-order description acts\nto damp this growth, leading to oscillations in the (non)condensate population\nand the coherence of the system."
    },
    {
        "anchor": "Creating spin-one fermions in the presence of artificial spin-orbit\n  fields: Emergent spinor physics and spectroscopic properties: We propose the creation and investigation of a system of spin-one fermions in\nthe presence of artificial spin-orbit coupling, via the interaction of three\nhyperfine states of fermionic atoms to Raman laser fields. We explore the\nemergence of spinor physics in the Hamiltonian described by the interaction\nbetween light and atoms, and analyze spectroscopic properties such as\ndispersion relation, Fermi surfaces, spectral functions, spin-dependent\nmomentum distributions and density of states. Connections to spin-one bosons\nand SU(3) systems is made, as well relations to the Lifshitz transition and\nPomeranchuk instability are presented.",
        "positive": "Expansion of Bose-Hubbard Mott insulators in optical lattices: We study the expansion of bosonic Mott insulators in the presence of an\noptical lattice after switching off a confining potential. We use the\nGutzwiller mean-field approximation and consider two different setups. In the\nfirst one, the expansion is restricted to one direction. We show that this\nleads to the emergence of two condensates with well defined momenta, and argue\nthat such a construct can be used to create atom lasers in optical lattices. In\nthe second setup, we study Mott insulators that are allowed to expand in all\ndirections in the lattice. In this case, a simple condensate is seen to develop\nwithin the mean-field approximation. However, its constituent bosons are found\nto populate many nonzero momentum modes. An analytic understanding of both\nphenomena in terms of the exact dispersion relation in the hard-core limit is\npresented."
    },
    {
        "anchor": "The Fine Structure of the Phonon in One Dimension from Quantum\n  Hydrodynamics: We show that the resonant interactions between phonons in one dimension may\nbe treated consistently within Quantum Hydrodynamics by the introduction of\nphonon dispersion. In this way the physics of a nonlinear Luttinger liquid may\nbe described in terms of hydrodynamic (i.e. bosonized) variables without\nrecourse to refermionization or the introduction of fictitious impurities.\n  We focus on the calculation of the dynamic structure factor for a model with\nquadratic dispersion, which has the Benjamin--Ono equation of fluid dynamics as\nits equation of motion. We find singular behavior in the vicinity of upper and\nlower energetic thresholds corresponding to phonon and soliton branches of the\nclassical theory, which may be benchmarked against known results for the\nCalogero--Sutherland model.",
        "positive": "Topological Gauge Fields and the Composite Particle Duality: We introduce topological gauge fields as nontrivial field configurations\nenforced by topological currents. These fields crucially determine the form of\nstatistical gauge fields that couple to matter and transmute their statistics.\nWe discuss the physical mechanism underlying the composite particle picture and\nargue that it is a duality of gauge forms that naturally relates to the notion\nof bosonisation in arbitrary dimensions. This is based on obtaining a\ngeneralised version of flux attachment, which yields a density-dependent gauge\npotential. We recover well-known results, resolve old controversies, and\nsuggest a microscopic mechanism for the emergence of such a gauge field. We\nalso outline potential directions for experimental realisations in ultracold\natom platforms."
    },
    {
        "anchor": "The non-Hermitian geometrical property of 1D Lieb lattice under\n  Majorana's stellar representation: The topological properties of non-Hermitian Hamiltonian is a hot topic, and\nthe theoretical studies along this research line are usually based on the\ntwo-level non-Hermitian Hamiltonian (or, equivalently, a spin-$1/2$\nnon-Hermitian Hamiltonian). We are motivated to study the geometrical phases of\na three-level Lieb lattice model (or, equivalently, a spin-$1$ non-Hermitian\nHamiltonian) with the complex hopping and flat band in the context of a\npolariton condensate, with the emphasis on the higher spin degree of freedom on\ntopological properties of non-Hermitian Hamiltonian. The topological invariants\nare calculated by both winding numbers in the Brillouin zone and the\ngeometrical phase of Majorana stars in the Bloch sphere. Besides, we provide an\nintuitive way to study the topological phase transformation in high dimensions,\nand the flat band offers a platform to define the high spin topological phase\ntransition on the Bloch sphere. According to the trajectories of the Majorana\nstars, we calculate the geometrical phases of the Majorana stars, and we find\nthey have a jump when the parameters change from the trivial phase to the\ntopological phase. Besides, the correlation phase of Majorana stars will rise\nalong with the increase of the imaginary parts of the hopping energy.",
        "positive": "Persistent currents in a two-component Bose-Einstein condensate confined\n  in a ring potential: We present variational and numerical solutions for the problem of stability\nof persistent currents in a two-component Bose-Einstein condensate of\ndistinguishable atoms which rotate in a ring potential. We consider the general\nclass of solutions of constant density in the two components separately, thus\nproviding an alternative approach of the solution of the same problem given\nrecently by Zhigang Wu and Eugene Zaremba [Phys. Rev. A {\\bf 88}, 063640\n(2013)]. Our approach provides a physically transparent solution of this\ndelicate problem. Finally, we give a unified and simple picture of the\nlowest-energy state of the system for large values of the coupling."
    },
    {
        "anchor": "Unconventional Universality Class of One-Dimensional Isolated Coarsening\n  Dynamics in a Spinor Bose Gas: By studying the coarsening dynamics of a one-dimensional spin-1 Bose-Hubbard\nmodel in a superfluid regime, we analytically find an unconventional universal\ndynamical scaling for the growth of the spin correlation length, which is\ncharacterized by the exponential integral unlike the conventional power-law or\nsimple logarithmic behavior, and numerically confirmed with the truncated\nWigner approximation.",
        "positive": "Thermal effects in light scattering from ultracold bosons in an optical\n  lattice: We study the scattering of a weak and far-detuned light from a system of\nultracold bosons in 1D and 3D optical lattices. We show the connection between\nangular distributions of the scattered light and statistical properties of a\nBose gas in a periodic potential. The angular patterns are determined by the\nFourier transform of the second-order correlation function, and thus they can\nbe used to retrieve information on particle number fluctuations and\ncorrelations. We consider superfluid and Mott insulator phases of the Bose gas\nin a lattice, and we analyze in detail how the scattering depends on the system\ndimensionality, temperature and atom-atom interactions."
    },
    {
        "anchor": "Spinor polariton condensates under nonresonant pumping: Steady states\n  and elementary excitations: We theoretically investigate a spinor polariton condensate under nonresonant\npumping, based on driven-dissipative Gross-Pitaevskii equations coupled to the\nrate equation of a spin-unpolarized reservoir. We find the homogeneous\npolariton condensate can transit from the spin-unpolarized phase, where it is\nlinearly polarized, to the spin-polarized phase, where it is elliptically\npolarized, depending on the cross-spin versus same-spin interactions and the\nlinear polarization splitting. In both phases, we study elementary excitations\nusing Bogoliubov approach, in a regime where the decay rate of total exciton\ndensity in reservoir crosses over from the slow to the fast limit. Depending on\nreservoir parameters, the global-phase mode can be either diffusive or gapped.\nBy contrast, the relative-phase mode always possesses a gapped energy, undamped\nin the spin-unpolarized phase but weakly damped in the spin-polarized phase. In\nthe spin-unpolarized phase, both modes are linearly polarized despite pumping\nand decay. However, in the spin-polarized phase, the mode polarization can be\nsignificantly affected by the reservoir and depends strongly on the circular\npolarization degree of the condensate. Interestingly, we demonstrate that the\n`ghost' branch of the Bogoliubov spectrum of the relative-phase mode can be\nvisualized in the photoluminescence emission, distinguishable from that of the\nglobal-phase mode and thus allowing for experimental observation, when the\nspinor polariton condensate is elliptically polarized.",
        "positive": "Solution of the Riemann problem for polarization waves in a\n  two-component Bose-Einstein condensate: We provide a classification of the possible flow of two-component\nBose-Einstein condensates evolving from initially discontinuous profiles. We\nconsider the situation where the dynamics can be reduced to the consideration\nof a single polarization mode (also denoted as \"magnetic excitation\") obeying a\nsystem of equations equivalent to the Landau-Lifshitz equation for an\neasy-plane ferro-magnet. We present the full set of one-phase periodic\nsolutions. The corresponding Whitham modulation equations are obtained together\nwith formulas connecting their solutions with the Riemann invariants of the\nmodulation equations. The problem is not genuinely nonlinear, and this results\nin a non-single-valued mapping of the solutions of the Whitham equations with\nphysical wave patterns as well as to the appearance of new elements --- contact\ndispersive shock waves --- that are absent in more standard, genuinely\nnonlinear situations. Our analytic results are confirmed by numerical\nsimulations."
    },
    {
        "anchor": "Superfluid transition temperature of spin-orbit and Rabi coupled\n  fermions with tunable interactions: We obtain the superfluid transition temperature of equal Rashba-Dresselhaus\nspin-orbit and Rabi coupled Fermi superfluids, from the\nBardeen-Cooper-Schrieffer (BCS) to Bose-Einstein condensate (BEC) regimes in\nthree dimensions. Spin-orbit coupling enhances the critical temperature in the\nBEC limit, and can convert a first order phase transition in the presence of\nRabi coupling into second order, as a function of the Rabi coupling for fixed\ninteractions. We derive the Ginzburg-Landau equation to sixth power in the\nsuperfluid order parameter to describe both first and second order transitions\nas a function of spin-orbit and Rabi couplings.",
        "positive": "Key role of the moire potential for the quasi-condensation of interlayer\n  excitons in van der Waals heterostructures: Interlayer excitons confined in bilayer heterostructures of transition metal\ndichalcogenides (TMDs) offer a promising route to implement two-dimensional\ndipolar superfluids. Here, we study the experimental conditions necessary for\nthe realisation of such collective state. Particularly, we show that the moire\npotential inherent to TMD bilayers yields an exponential increase of the\nexcitons effective mass. To allow for exciton superfluidity at sizeable\ntemperatures it is then necessary to intercalate a high-$\\kappa$ dielectric\nbetween the monolayers confining electrons and holes. Thus the moire lattice\ndepth is sufficiently weak for a superfluid phase to theoretically emerge below\na critical temperature of around 10 K. Importantly, for realistic experimental\nparameters interlayer excitons quasi-condense in a state with finite momentum,\nso that the superfluid is optically inactive and flows spontaneously."
    },
    {
        "anchor": "Quantum walk and Anderson localization of rotational excitations in\n  disordered ensembles of polar molecules: We consider the dynamics of rotational excitations placed on a single\nmolecule in spatially disordered 1D, 2D and 3D ensembles of ultracold molecules\ntrapped in optical lattices. The disorder arises from incomplete populations of\noptical lattices with molecules. This leads to a model corresponding to a\nquantum particle with long-range tunnelling amplitudes moving on a lattice with\nthe same on-site energy but with forbidden access to random sites (vacancies).\nWe examine the time and length scales of Anderson localization for this type of\ndisorder with realistic experimental parameters in the Hamiltonian. We show\nthat for an experimentally realized system of KRb molecules on an optical\nlattice this type of disorder leads to disorder-induced localization in 1D and\n2D systems on a time scale $t \\sim 1$ sec. For 3D lattices with $55$ sites in\neach dimension and vacancy concentration $ 90~\\%$, the rotational excitations\ndiffuse to the edges of the lattice and show no signature of Anderson\nlocalization. We examine the role of the long-range tunnelling amplitudes\nallowing for transfer of rotational excitations between distant lattice sites.\nOur results show that the long-range tunnelling has little impact on the\ndynamics in the diffusive regime but affects significantly the localization\ndynamics in lattices with large concentrations of vacancies, enhancing the\nwidth of the localized distributions in 2D lattices by more than a factor of 2.\nOur results raise a general question whether quantum particles with long-range\ntunnelling can undergo quantum localization in 3D lattices with substitutional\ndisorder.",
        "positive": "Competing magnetic orders in a bilayer Hubbard model with ultracold\n  atoms: Fermionic atoms in optical lattices have served as a compelling model system\nto study and emulate the physics of strongly-correlated matter. Driven by the\nadvances of high-resolution microscopy, the recent focus of research has been\non two-dimensional systems in which several quantum phases, such as\nanti-ferromagnetic Mott insulators for repulsive interactions and\ncharge-density waves for attractive interactions have been observed. However,\nthe aspired emulations of real materials, such as bilayer graphene, have to\ntake into account that their lattice structure composes of coupled layers and\ntherefore is not strictly two-dimensional. In this work, we realize a bilayer\nFermi-Hubbard model using ultracold atoms in an optical lattice and demonstrate\nthat the interlayer coupling controls a crossover between a planar\nanti-ferromagnetically ordered Mott insulator and a band insulator of\nspin-singlets along the bonds between the layers. Our work will enable the\nexploration of further fascinating properties of coupled-layer Hubbard models,\nsuch as theoretically predicted superconducting pairing mechanisms."
    },
    {
        "anchor": "Reservoir interactions of a vortex in a trapped 3D Bose-Einstein\n  condensate: We simulate the dissipative evolution of a vortex in a trapped\nfinite-temperature dilute-gas Bose-Einstein condensate using first-principles\nopen-systems theory. Simulations of the complete stochastic projected\nGross-Pitaevskii equation for a partially condensed Bose gas containing a\nsingle quantum vortex show that the transfer of condensate energy to the\nincoherent thermal component without population transfer provides an important\nchannel for vortex decay. For the lower temperatures considered, this effect is\nsignificantly larger that the population transfer process underpinning the\nstandard theory of vortex decay, and is the dominant determinant of the vortex\nlifetime. A comparison with the Zaremba-Nikuni-Griffin kinetic (two-fluid)\ntheory further elucidates the role of the particle transfer interaction, and\nsuggests the need for experimental testing of reservoir interaction theory. The\ndominance of this particular energetic decay mechanism for this open quantum\nsystem should be testable with current experimental setups, and its observation\nwould have broad implications for the dynamics of atomic matter waves and\nexperimental studies of dissipative phenomena.",
        "positive": "Analysis and resolution of the ground-state degeneracy of the\n  two-component Bose-Hubbard model: We study the degeneracy of the ground-state energy $E$ of the two-component\nBose-Hubbard model and of the perturbative correction $E_1$. We show that the\ndegeneracy properties of $E$ and $E_1$ are closely related to the connectivity\nproperties of the lattice. We determine general conditions under which $E$ is\nnondegenerate. This analysis is then extended to investigate the degeneracy of\n$E_1$. In this case, in addition to the lattice structure, the degeneracy also\ndepends on the number of particles present in the system. After identifying the\ncases in which $E_1$ is degenerate and observing that the standard (degenerate)\nperturbation theory is not applicable, we develop a method to determine the\nzeroth-order correction to the ground state by exploiting the symmetry\nproperties of the lattice. This method is used to implement the perturbative\napproach to the two-component Bose-Hubbard model in the case of degenerate\n$E_1$ and is expected to be a valid tool to perturbatively study the asymmetric\ncharacter of the Mott-insulator to superfluid transition between the particle\nand hole side."
    },
    {
        "anchor": "Rotating quantum droplets confined in a harmonic potential: We investigate the rotational properties of a two-component, two-dimensional\nself-bound quantum droplet, which is confined in a harmonic potential and\ncompare them with the well-known problem of a single-component atomic gas with\ncontact interactions. For a fixed value of the trap frequency, choosing some\nrepresentative values of the atom number, we determine the lowest-energy state,\nas the angular momentum increases. For a sufficiently small number of atoms,\nthe angular momentum is carried via center-of-mass excitation. For larger\nvalues, when the angular momentum is sufficiently small, we observe vortex\nexcitation instead. Depending on the actual atom number, one or more vortices\nenter the droplet. Beyond some critical value of the angular momentum, however,\nthe droplet does not accommodate more vortices and the additional angular\nmomentum is carried via center-of-mass excitation in a \"mixed\" state. Finally,\nthe excitation spectrum is also briefly discussed.",
        "positive": "Conduction electrons localized by charged magneto-acceptors A$^{2-}$ in\n  GaAs/GaAlAs quantum wells: A variational theory is presented of A$^{1-}$ and A$^{2-}$ centers, i.e. of a\nnegative acceptor ion localizing one and two conduction electrons,\nrespectively, in a GaAs/GaAlAs quantum well in the presence of a magnetic field\nparallel to the growth direction. A combined effect of the well and magnetic\nfield confines conduction electrons to the proximity of the ion, resulting in\ndiscrete repulsive energies above the corresponding Landau levels. The theory\nis motivated by our experimental magneto-transport results which indicate that,\nin a heterostructure doped in the GaAs well with Be acceptors, one observes a\nboil-off effect in which the conduction electrons in the crossed-field\nconfiguration are pushed by the Hall electric field from the delocalized Landau\nstates to the localized acceptor states and cease to conduct. A detailed\nanalysis of the transport data shows that, at high magnetic fields, there are\nalmost no conducting electrons left in the sample. It is concluded that one\nnegative acceptor ion localizes up to four conduction electrons."
    },
    {
        "anchor": "Matter-wave solitons and finite-amplitude Bloch waves in optical\n  lattices with a spatially modulated nonlinearity: We investigate solitons and nonlinear Bloch waves in Bose-Einstein\ncondensates trapped in optical lattices. By introducing specially designed\nlocalized profiles of the spatial modulation of the attractive nonlinearity, we\nconstruct an infinite number of exact soliton solutions in terms of the Mathieu\nand elliptic functions, with the chemical potential belonging to the\nsemi-infinite bandgap of the optical-lattice-induced spectrum. Starting from\nthe exact solutions, we employ the relaxation method to construct generic\nfamilies of soliton solutions in a numerical form. The stability of the\nsolitons is investigated through the computation of the eigenvalues for small\nperturbations, and also by direct simulations. Finally, we demonstrate a\nvirtually exact (in the numerical sense) composition relation between nonlinear\nBloch waves and solitons.",
        "positive": "A general T-matrix approach applied to two-body and three-body problems\n  in cold atomic gases: We propose a systematic T-matrix approach to solve few-body problems with\ns-wave contact interactions in ultracold atomic gases. The problem is generally\nreduced to a matrix equation expanded by a set of orthogonal molecular states,\ndescribing external center-of-mass motions of pairs of interacting particles;\nwhile each matrix element is guaranteed to be finite by a proper\nrenormalization for internal relative motions. This approach is able to\nincorporate various scattering problems and the calculations of related\nphysical quantities in a single framework, and also provides a physically\ntransparent way to understand the mechanism of resonance scattering. For\napplications, we study two-body effective scattering in 2D-3D mixed dimensions,\nwhere the resonance position and width are determined with high precision from\nonly a few number of matrix elements. We also study three fermions in a\n(rotating) harmonic trap, where exotic scattering properties in terms of mass\nratios and angular momenta are uniquely identified in the framework of\nT-matrix."
    },
    {
        "anchor": "Universal Dimer in a Collisionally Opaque Medium: Experimental\n  Observables and Efimov Resonances: A universal dimer is subject to secondary collisions with atoms when formed\nin a cloud of ultracold atoms via three-body recombination. We show that in a\ncollisionally opaque medium, the value of the scattering length that results in\nthe maximum number of secondary collisions may not correspond to the Efimov\nresonance at the atom-dimer threshold and thus can not be automatically\nassociated with it. This result explains a number of controversies in recent\nexperimental results on universal three-body states and supports the emerging\nevidence for the significant finite range corrections to the first excited\nEfimov energy level.",
        "positive": "On the higher virial coefficients of a unitary Fermi gas: Third and higher order quantum virial coefficients require the solution of\nthe corresponding quantum many-body problem. Nevertheless, in an earlier paper\n(Phys. Rev. Lett. 108, 260402 (2012)) we proposed that the higher-order cluster\nintegrals of a dilute unitary fermionic gas may be approximated in terms of the\ntwo-body cluster, together with an appropriate suppression factor. Although not\nexact, this ansatz gave a fair agreement up to fugacity z=6 with the\nexperimentally obtained equation of state. The objective of the present note is\nto give some physical arguments in favor of this ansatz."
    },
    {
        "anchor": "Stability of Symmetry Breaking States in Finite-size Dicke Model with\n  Photon Leakage: We investigate the finite-size Dicke model with photon leakage. It is shown\nthat the symmetry breaking states, which are characterized by non-vanishing\n$\\langle \\hat{a} \\rangle \\neq 0$ and correspond to the ground states in the\nsuperradiant phase in the thermodynamic limit, are stable, while the\neigenstates of the isolated finite-size Dicke Hamiltonian conserve parity\nsymmetry. We introduce and analyze an effective master equation that describes\nthe dynamics of a pair of the symmetry breaking states that are the degenerate\nlowest energy eigenstates in the superradiant region with photon leakage. It\nbecomes clear that photon leakage is essential to stabilize the symmetry\nbreaking states and to realize the superradiant phase without the thermodynamic\nlimit. Our theoretical analysis provides an alternative interpretation using\nthe finite-size model to explain results from cold atomic experiments showing\nsuperradiance with the symmetry breaking in an optical cavity.",
        "positive": "Theory of excitations of dipolar Bose-Einstein condensate at finite\n  temperature: We present a systematic study of dilute three-dimensional dipolar Bose gas\nemploying a finite temperature perturbation theory (beyond the mean field). We\nanalyze in particular the behavior of the anomalous density, we find that this\nquantity has a finite value in the limit of weak interactions at both zero and\nfinite temperatures. We show that the presence of the dipole-dipole interaction\n(DDI) enhances fluctuations, the second order correlation function and\nthermodynamic quantities such as the chemical potential, the ground state\nenergy, the compressibility and the superfluid fraction. We identify the\nvalidity criterion of the small parameter of the theory for Bose-condensed\ndipolar gases."
    },
    {
        "anchor": "Characterizing Floquet topological phases by quench dynamics: A\n  multiple-subsystem approach: We investigate the dynamical characterization theory for periodically driven\nsystems in which Floquet topology can be fully detected by emergent topological\npatterns of quench dynamics in momentum subspaces called band-inversion\nsurfaces. We improve the results of a recent work [Zhang et al., Phys. Rev.\nLett. 125, 183001 (2020)] and propose a more flexible scheme to characterize a\ngeneric class of $d$-dimensional Floquet topological phases classified by\n$\\mathbb{Z}$-valued invariants by applying a quench along an arbitrary\nspin-polarization axis. Our basic idea is that by disassembling the Floquet\nsystem into multiple static subsystems that are periodic in quasienergy, a full\ncharacterization of Floquet topological phases reduces to identifying a series\nof bulk topological invariants for time-independent Hamiltonians, which greatly\nenhances the convenience and flexibility of the measurement. We illustrate the\nscheme by numerically analyzing two experimentally realizable models in two and\nthree dimensions, respectively, and adopting two different but equivalent\nviewpoints to examine the dynamical characterization. Finally, considering the\nimperfection of experiment, we demonstrate that the present scheme can also be\napplied to a general situation where the initial state is not completely\npolarized. This study provides an immediately implementable approach for\ndynamically classifying Floquet topological phases in ultracold atoms or other\nquantum simulators.",
        "positive": "Dynamical instability of a spin spiral in an interacting Fermi gas as a\n  probe of the Stoner transition: We propose an experiment to probe ferromagnetic phenomena in an ultracold\nFermi gas, while alleviating the sensitivity to three-body loss and competing\nmany-body instabilities. The system is initialized in a small pitch spin\nspiral, which becomes unstable in the presence of repulsive interactions. To\nlinear order the exponentially growing collective modes exhibit critical\nslowing down close to the Stoner transition point. Also, to this order, the\ndynamics are identical on the paramagnetic and ferromagnetic sides of the\ntransition. However, we show that scattering off the exponentially growing\nmodes qualitatively alters the collective mode structure. The critical slowing\ndown is eliminated and in its place a new unstable branch develops at large\nwave vectors. Furthermore, long-wavelength instabilities are quenched on the\nparamagnetic side of the transition. We study the experimental observation of\nthe instabilities, specifically addressing the trapping geometry and how\nphase-contrast imaging will reveal the emerging domain structure. These probes\nof the dynamical phenomena could allow experiments to detect the transition\npoint and distinguish between the paramagnetic and ferromagnetic regimes."
    },
    {
        "anchor": "Particle current, noise, and counting statistics of quantum transport in\n  the presence of a single-particle loss: How dissipation affects transport is an important theme in quantum science.\nHere we theoretically investigate an impact of a single-particle loss in\nmesoscopic transport, which has been an issue in experiments of ultracold\natomic gases. By explicitly analyzing quantum point contact and quantum dot\nsystems, we obtain a cumulant generating function on the particle current whose\nformal expression turns out to be common to two systems. In terms of this\ngenerating function, behaviors of average current, particle loss rate, and\nnoises in presences of losses introduced in conduction channels are exemplified\nfor free fermions. It is shown that the current noise contains the component\nproportional to the particle loss rate, which may be measurable in experiments.",
        "positive": "Hydrodynamics of compressible superfluids in confined geometries: We present a study of the hydrodynamics of compressible superfluids in\nconfined geometries. We use a perturbative procedure in terms of the\ndimensionless expansion parameter $(v/v_s)^2$ where $v$ is the typical speed of\nthe flow and $v_s$ the speed of sound. A zero value of this parameter\ncorresponds to the incompressible limit. We apply the procedure to two specific\nproblems: the case of a trapped superfluid with a gaussian profile of the local\ndensity, and that of a superfluid confined in a rotating obstructed cylinder.\nWe find that the corrections due to finite compressibility which are, as\nexpected, negligible for liquid He, are important but amenable to the\nperturbative treatment for typical ultracold atomic systems."
    },
    {
        "anchor": "Dark-bright soliton interactions beyond the integrable limit: In this work we present a systematic theoretical analysis regarding\ndark-bright solitons and their interactions, motivated by recent advances in\natomic two-component repulsively interacting Bose-Einstein condensates. In\nparticular, we study analytically via a two-soliton ansatz adopted within a\nvariational formulation the interaction between two dark-bright solitons in a\nhomogeneous environment beyond the integrable regime, by considering general\ninter/intra-atomic interaction coefficients. We retrieve the possibility of a\nfixed point in the case where the bright solitons are out of phase. As the\ninter-component interaction is increased, we also identify an exponential\ninstability of the two-soliton state, associated with a subcritical pitchfork\nbifurcation. The latter gives rise to an asymmetric partition of the bright\nsoliton mass and dynamically leads to spontaneous splitting of the bound pair.\nIn the case of the in-phase bright solitons, we explain via parsing the\nanalytical approximations and monitoring the direct dynamics why no such pair\nis identified, despite its prediction by the variational analysis.",
        "positive": "The normal phase of an imbalanced Fermi gas: Recent experiments on imbalanced Fermi gases have raised interest in the\nphysics of an impurity immersed in a Fermi sea, the so-called Fermi polaron. In\nthis letter, a simple theory is devised to describe dilute Fermi-polaron\nensembles corresponding to the normal phase of an imbalanced Fermi gas. An\nexact formula is obtained for the dominant interaction between polarons,\nexpressed solely in terms of a single polaron parameter. The physics of this\ninteraction is identified as a signature of the Pauli exclusion principle."
    },
    {
        "anchor": "Hard-Wall and Non-Uniform Lattice Monte Carlo Approaches to\n  One-Dimensional Fermi Gases in a Harmonic Trap: We present in detail two variants of the lattice Monte Carlo method aimed at\ntackling systems in external trapping potentials: a uniform-lattice approach\nwith hard-wall boundary conditions, and a non-uniform Gauss-Hermite lattice\napproach. Using those two methods, we compute the ground-state energy and\nspatial density profile for systems of N=4 - 8 harmonically trapped fermions in\none dimension. From the favorable comparison of both energies and density\nprofiles (particularly in regions of low density), we conclude that the\ntrapping potential is properly resolved by the hard-wall basis. Our work paves\nthe way to higher dimensions and finite temperature analyses, as calculations\nwith the hard-wall basis can be accelerated via fast Fourier transforms, the\ncost of unaccelerated methods is otherwise prohibitive due to the unfavorable\nscaling with system size.",
        "positive": "Multi-body correlations in SU(3) Fermi gases: We investigate strong-coupling effects in a three-component atomic Fermi gas.\nIt is a promising candidate for simulating quantum chromodynamics (QCD), and\nfurthermore, the emergence of various phenomena such as color superfluidity and\nEfimov effect are anticipated in this system. In this paper, we study the\neffects of two-body and three-body correlations by means of the many-body\n$T$-matrix approximation (TMA) as well as the Skorniakov-Ter-Martirosian (STM)\nequation with medium corrections. We investigate the effects of finite\ntemperature and chemical potential on the trimer binding energy at the\nsuperfluid critical point of the unitarity limit."
    },
    {
        "anchor": "Spin and mass superfluidity in ferromagnetic spin-1 Bose-Einstein\n  condensate: The paper investigates the coexistence and interplay of spin and mass\nsuperfluidity in a ferromagnetic spin-1 Bose-Einstein condensate. Superfluidity\nis possible only in the presence of uniaxial anisotropy (linear and quadratic\nZeeman effect). This follows from the topology of the order-parameter space\n(vacuum manifold). According to the Landau criterion, the critical phase\ngradients, both for mass and spin supercurrents, vanish at the phase transition\nfrom the easy-plane to the easy-axis anisotropy. However, mass superfluidity is\nstill possible at the phase transition. This is because the Landau criterion\nsignals instability only with respect to nonsingular vortices with special\nratio between circulations of mass and spin currents. Phase slips produced by\nthese vortices are not sufficient for complete decay of supercurrents. Full\ndecay of supercurrents requires phase slips with vortices of another\ntopological class and larger energy. These phase slips are suppressed by\nenergetic barriers up to the upper critical velocity (gradient) exceeding the\nLandau critical velocity. The upper critical velocity does not vanish nor has\nany anomaly in the critical point at the phase transition from the easy-plane\nto the easy-axis anisotropy.",
        "positive": "Finite temperature expansion dynamics of Bose-Einstein condensates: We explore the effects of finite temperature on the dynamics of Bose-Einstein\ncondensates (BECs) after it is released from the confining potential. In\naddition, we examine the variation in the expansion dynamics of the BECs as the\nconfining potential is transformed from a multiply to a simply connected\ngeometry. To include the effects of finite temperatures we use the frozen\nthermal cloud approximation, and observe unique features of the condensate\ndensity distribution when released from the confining potential. We find that\nat $T\\neq 0$, during the initial stages of expansion, the multiply connected\ncondensate has more pronounced interference rings compared to the case of zero\ntemperature. Such difference in the dynamical evolution is also evident for\nsimply connected condensates."
    },
    {
        "anchor": "Direct observation of incommensurate magnetism in Hubbard chains: The interplay between magnetism and doping is at the origin of exotic\nstrongly correlated electronic phases and can lead to novel forms of magnetic\nordering. One example is the emergence of incommensurate spin-density waves\nwith a wave vector that does not match the reciprocal lattice. In one dimension\nthis effect is a hallmark of Luttinger liquid theory, which also describes the\nlow energy physics of the Hubbard model. Here we use a quantum simulator based\non ultracold fermions in an optical lattice to directly observe such\nincommensurate spin correlations in doped and spin-imbalanced Hubbard chains\nusing fully spin and density resolved quantum gas microscopy. Doping is found\nto induce a linear change of the spin-density wave vector in excellent\nagreement with Luttinger theory predictions. For non-zero polarization we\nobserve a decrease of the wave vector with magnetization as expected from the\nHeisenberg model in a magnetic field. We trace the microscopic origin of these\nincommensurate correlations to holes, doublons and excess spins which act as\ndelocalized domain walls for the antiferromagnetic order. Finally, when\ninducing interchain coupling we observe fundamentally different spin\ncorrelations around doublons indicating the formation of a magnetic polaron.",
        "positive": "Driven-dissipative control of cold atoms in tilted optical lattices: We present a sequence of driven-dissipative protocols for controlling cold\natoms in tilted optical lattices. These experimentally accessible examples are\ntemplates that demonstrate how dissipation can be used to manipulate quantum\nmany-body systems. We consider bosonic atoms trapped in a tilted optical\nlattice, immersed in a superfluid bath, and excited by coherent Raman lasers.\nWith these ingredients, we are able to controllably transport atoms in the\nlattice and produce self-healing quantum states: a Mott insulator and the\ntopologically ordered spin-1 AKLT state."
    },
    {
        "anchor": "Local correlations reveal the superfluid to normal boundary in a trapped\n  two-dimensional quantum gas: This paper reports the model free determination of the two-fluid dynamics in\na trapped two-dimensional Bose gas, relying on a local principal component\nanalysis of the dynamics after a sudden excitation.",
        "positive": "Bi-directional universal dynamics in a spinor Bose gas close to a\n  non-thermal fixed point: We numerically study the universal scaling dynamics of an isolated\none-dimensional ferromagnetic spin-1 Bose gas. Preparing the system in a\nfar-from-equilibrium initial state, simultaneous coarsening and refining is\nfound to enable and characterize the approach to a non-thermal fixed point. A\nmacroscopic length scale which scales in time according to $L_{\\Lambda}(t)\\sim\nt^{\\, \\beta}$, with $\\beta\\simeq 1/4$, quantifies the coarsening of the size of\nspin textures. At the same time kink-like defects populating these textures\nundergo a refining process measured by a shrinking microscopic length scale\n$L_{\\lambda}\\sim t^{\\, \\beta'}$, with $\\beta'\\simeq-0.17$. The combination of\nthese scaling evolutions enables particle and energy conservation in the\nisolated system and constitutes a bi-directional transport in momentum space.\nThe value of the coarsening exponent $\\beta$ suggests the dynamics to belong to\nthe universality class of diffusive coarsening of the one-dimensional XY-model.\nHowever, the universal momentum distribution function exhibiting non-linear\ntransport marks the distinction between diffusive coarsening and the approach\nof a non-thermal fixed point in the isolated system considered here. This\nunderlines the importance of the universal scaling function in classifying\nnon-thermal fixed points. Present-day experiments with quantum gases are\nexpected to have access to the predicted bi-directional scaling."
    },
    {
        "anchor": "Universal Spin Transport in a Strongly Interacting Fermi Gas: Transport of fermions is central in many fields of physics. Electron\ntransport runs modern technology, defining states of matter such as\nsuperconductors and insulators, and electron spin, rather than charge, is being\nexplored as a new carrier of information [1]. Neutrino transport energizes\nsupernova explosions following the collapse of a dying star [2], and\nhydrodynamic transport of the quark-gluon plasma governed the expansion of the\nearly Universe [3]. However, our understanding of non-equilibrium dynamics in\nsuch strongly interacting fermionic matter is still limited. Ultracold gases of\nfermionic atoms realize a pristine model for such systems and can be studied in\nreal time with the precision of atomic physics [4, 5]. It has been established\nthat even above the superfluid transition such gases flow as an almost perfect\nfluid with very low viscosity [3, 6] when interactions are tuned to a\nscattering resonance. However, here we show that spin currents, as opposed to\nmass currents, are maximally damped, and that interactions can be strong enough\nto reverse spin currents, with opposite spin components reflecting off each\nother. We determine the spin drag coeffcient, the spin diffusivity, and the\nspin susceptibility, as a function of temperature on resonance and show that\nthey obey universal laws at high temperatures. At low temperatures, the spin\ndiffusivity approaches a minimum value set by the ratio of the reduced Planck's\nconstant to the atomic mass. For repulsive interactions, our measurements\nappear to exclude a metastable ferromagnetic state [7-9].",
        "positive": "Bright solitons in spin-orbit-coupled Bose-Einstein condensates: We study bright solitons in a Bose-Einstein condensate with a spin-orbit\ncoupling that has been realized experimentally. Both stationary bright solitons\nand moving bright solitons are found. The stationary bright solitons are the\nground states and possess well-defined spin-parity, a symmetry involving both\nspatial and spin degrees of freedom; these solitons are real valued but not\npositive definite, and the number of their nodes depends on the strength of\nspin-orbit coupling. For the moving bright solitons, their shapes are found to\nchange with velocity due to the lack of Galilean invariance in the system."
    },
    {
        "anchor": "Quantum wakes in lattice fermions: The wake following a vessel in water is a signature interference effect of\nmoving bodies, and, as described by Lord Kelvin, is contained within a constant\nuniversal angle. However, wakes may accompany different kinds of moving\ndisturbances in other situations and even in lattice systems. Here, we\ninvestigate the effect of moving disturbances on a Fermi lattice gas of\nultracold atoms and analyze the novel types of wake patterns that may occur. We\nshow how at half-filling, the wake angles are dominated by the ratio of the\nhopping energy to the velocity of the disturbance and on the angle of motion\nrelative to the lattice direction. Moreover, we study the difference between\nwakes left behind a moving particle detector versus that of a moving potential\nor a moving particle extractor. We show that these scenarios exhibit\ndramatically different behavior at half-filling, with the \"measurement wake\"\nfollowing an idealized detector vanishing, though the motion of the detector\ndoes still leaves a trace through a \"fluctuation wake.\" Finally, we discuss the\nexperimental requirements to observe our predictions in ultracold fermionic\natoms in optical lattices.",
        "positive": "Supersolid phases of bosonic particles in a bubble trap: Confinement can have a considerable effect on the behavior of particle\nsystems, and is therefore an effective way to discover new phenomena. A notable\nexample is a system of identical bosons at low temperature under an external\nfield mimicking an isotropic bubble trap, which constrains the particles to a\nportion of space close to a spherical surface. Using Path Integral Monte Carlo\nsimulations, we examine the spatial structure and superfluid fraction in two\nemblematic cases. First, we look at soft-core bosons, finding the existence of\nsupersolid cluster arrangements with polyhedral symmetry; we show how different\nnumbers of clusters are stabilized depending on the trap radius and the\nparticle mass, and we characterize the temperature behavior of the cluster\nphases. A detailed comparison with the behavior of classical soft-core\nparticles is provided too. Then, we examine the case, of more immediate\nexperimental interest, of a dipolar condensate on the sphere, demonstrating how\na quasi-one-dimensional supersolid of clusters is formed on a great circle for\nrealistic values of density and interaction parameters. Crucially, this\nsupersolid phase is only slightly disturbed by gravity. We argue that the\npredicted phases can be revealed in magnetic traps with spherical-shell\ngeometry, possibly even in a lab on Earth. Our results pave the way for future\nsimulation studies of correlated quantum systems in curved geometries."
    },
    {
        "anchor": "Stochastic phase slips in toroidal Bose-Einstein condensates: Motivated by recent experiments we study the influence of thermal noise on\nthe phase slips in toroidal Bose-Einstein condensates with a rotating weak\nlink. We derive a generalized Arrhenius-like expression for the rate of\nstochastic phase slips. We develop a method to estimate the energy barrier\nseparating different superflow states. The parameters at which the energy\nbarrier disappears agree with the critical parameters for deterministic phase\nslips obtained from dynamics simulations, which confirms the validity of our\nenergetic analysis. We reveal that adding thermal noise lowers the phase-slip\nthreshold. However, the quantitative impact of the stochastic phase slips turns\nout to be too small to explain the significant discrepancy between theoretical\nand the experimental results.",
        "positive": "Mixing of Bose and Fermi Superfluids: Trapped ultra-cold atom experiments provide a unique opportunity to\nunderstand Bose-Fermi superfluid mixtures occurring in contrasting areas of\nphysics. At present there are several atom-trap experiments that could\npotentially explore this superfluid-mixture regime, thus warranting a detailed\nunderstanding of the occurrence and stability of various possible thermodynamic\nphases in the mixture. In the present work, we therefore construct the finite\ntemperature phase diagram of an interacting atomic mixture of Bose and Fermi\nsuperfluids. Our study reveals a unique region of phase space, where the BCS\ninstability of the Fermi surface coincides with dynamical instability of the\nhomogeneous mixture towards phase separation through a first-order transition.\nWe illustrate how this intriguing interplay manifests in a trapped\nconfiguration, thereby providing important constraints for observing\nsuperfluidity in experiments."
    },
    {
        "anchor": "Atom-light crystallization of BECs in multimode cavities: Nonequilibrium\n  classical and quantum phase transitions, emergent lattices, supersolidity,\n  and frustration: The self-organization of a Bose-Einstein condensate in a transversely pumped\noptical cavity is a process akin to crystallization: when pumped by a laser of\nsufficient intensity, the coupled matter and light fields evolve,\nspontaneously, into a spatially modulated pattern, or crystal, whose lattice\nstructure is dictated by the geometry of the cavity. In cavities having\nmultiple degenerate modes, the quasi-continuum of possible lattice\narrangements, and the continuous symmetry breaking associated with the adoption\nof a particular lattice arrangement, give rise to phenomena such as phonons,\ndefects, and frustration, which have hitherto been unexplored in ultracold\natomic settings involving neutral atoms. The present work develops a\nnonequilibrium field-theoretic approach to explore the self-organization of a\nBEC in a pumped, lossy optical cavity. We find that the transition is well\ndescribed, in the regime of primary interest, by an effective equilibrium\ntheory. At nonzero temperatures, the self-organization occurs via a\nfluctuation-driven first-order phase transition of the Brazovskii class; this\ntransition persists to zero temperature, and crosses over into a quantum phase\ntransition of a new universality class. We make further use of our\nfield-theoretic description to investigate the role of nonequilibrium\nfluctuations on the self-organization transition, as well as to explore the\nnucleation of ordered-phase droplets, the nature and energetics of topological\ndefects, supersolidity in the ordered phase, and the possibility of frustration\ncontrolled by the cavity geometry. In addition, we discuss the range of\nexperimental parameters for which we expect the phenomena described here to be\nobservable, along with possible schemes for detecting ordering and fluctuations\nvia either atomic correlations or the correlations of the light emitted from\nthe cavity.",
        "positive": "Probing the homogeneous spectral function of a strongly interacting\n  superfluid atomic Fermi gas in a trap using phase separation and momentum\n  resolved rf spectroscopy: It is of central importance to probe the \\emph{local} spectral function\n$A(\\mathbf{k},\\omega)$ of a strongly interacting Fermi gas in a trap. Momentum\nresolved rf spectroscopy has been demonstrated to be able to probe the trap\naveraged $A(\\mathbf{k},\\omega)$. However, the usefulness of this technique was\nlimited by the trap inhomogeneity. Independent of a specific theory, here we\npropose that by studying the momentum resolved rf spectra of the minority\nfermions of a phase separated, population imbalanced Fermi gas at low\ntemperature, one can effectively extract $A(\\mathbf{k},\\omega)$ of a\nhomogeneous superfluid Fermi gas (at the trap center). In support, we present\ncalculated spectral functions and spectral intensity maps for various cases\nfrom BCS through BEC regimes using different theories."
    },
    {
        "anchor": "Dissipative dynamics of a heavy impurity in a Bose gas in the strong\n  coupling regime: We study the motion of a heavy impurity in a one-dimensional Bose gas. The\nimpurity experiences the friction force due to scattering off thermally excited\nquasiparticles. We present detailed analysis of an arbitrarily strong\nimpurity-boson coupling in a wide range of temperatures within a microscopic\ntheory. Focusing mostly on weakly interacting bosons, we derive an analytical\nresult for the friction force and uncover new regimes of the impurity dynamics.\nParticularly interesting is the low-temperature $T^2$ dependence of the\nfriction force obtained for a strongly coupled impurity, which should be\ncontrasted with the expected $T^4$ scaling. This new regime applies to systems\nof bosons with an arbitrary repulsion strength. We finally study the evolution\nof the impurity with a given initial momentum. We evaluate analytically its\nnon-stationary momentum distribution function. The impurity relaxation towards\nthe equilibrium is a realization of the Ornstein-Uhlenbeck process in momentum\nspace.",
        "positive": "Collective excitation of a trapped Bose-Einstein condensate with\n  spin-orbit coupling: We investigate the collective excitations of a Raman-induced spin-orbit\ncoupled Bose-Einstein condensate confined in a quasi one-dimension harmonic\ntrap using the Bogoliubov method. By tuning the Raman coupling strength, three\nphases of the system can be identified. By calculating the transition strength,\nwe are able to classify various excitation modes that are experimentally\nrelevant. We show that the three quantum phases possess distinct features in\ntheir collective excitation properties. In particular, the spin dipole and the\nspin breathing modes can be used to clearly map out the phase boundaries. We\nconfirm these predictions by direct numerical simulations of the quench\ndynamics that excites the relevant collective modes."
    },
    {
        "anchor": "Collective modes of a two-dimensional spin-1/2 Fermi gas in a harmonic\n  trap: We derive analytical expressions for the frequency and damping of the lowest\ncollective modes of a two-dimensional Fermi gas using kinetic theory. For\nstrong coupling, we furthermore show that pairing correlations overcompensate\nthe effects of Pauli blocking on the collision rate for a large range of\ntemperatures, resulting in a rate which is larger than that of a classical gas.\nOur results agree well with experimental data, and they recover the observed\ncross-over from collisionless to hydrodynamic behaviour with increasing\ncoupling for the quadruple mode. Finally, we show that a trap anisotropy within\nthe experimental bounds results in a damping of the breathing mode which is\ncomparable to what is observed, even for a scale invariant system.",
        "positive": "Quasiparticle properties of a mobile impurity in a Bose-Einstein\n  condensate: We develop a systematic perturbation theory for the quasiparticle properties\nof a single impurity immersed in a Bose-Einstein condensate. Analytical results\nare derived for the impurity energy, the effective mass, and residue to third\norder in the impurity-boson scattering length. The energy is shown to depend\nlogarithmically on the scattering length to third order, whereas the residue\nand effective mass are given by analytical power series. When the boson-boson\nscattering length equals the boson-impurity scattering length, the energy has\nthe same structure as that of a weakly interacting Bose gas, including terms of\nthe Lee-Huang-Yang and fourth order logarithmic form. Our results, which cannot\nbe obtained within the canonical Fr{\\\"o}hlich model of an impurity interacting\nwith phonons, provide valuable benchmarks for many-body theories and for\nexperiments."
    },
    {
        "anchor": "Scattering off a junction: Scattering off a potential is a fundamental problem in quantum physics. It\nhas been studied extensively with amplitudes derived for various potentials. In\nthis article, we explore a setting with no potentials, where scattering occurs\noff a junction where many wires meet. We study this problem using a\ntight-binding discretization of a star graph geometry -- one incoming wire and\n$M$ outgoing wires intersecting at a point. When an incoming wave scatters, one\npart is reflected along the same wire while the rest is transmitted along the\nothers. Remarkably, the reflectance increases monotonically with $M$, i.e., the\ngreater the number of outgoing channels, the more the particle bounces back. In\nthe $M \\rightarrow \\infty$ limit, the wave is entirely reflected back along the\nincoming wire. We rationalize this observation by establishing a quantitative\nmapping between a junction and an on-site potential. To each junction, we\nassign an equivalent potential that produces the same reflectance. As the\nnumber of wires ($M$) increases, the equivalent potential also increases. A\nrecent article by one of us has drawn an equivalence between junctions and\npotentials from the point of view of bound state formation. Our results here\nshow that the same equivalence also holds for scattering amplitudes. We verify\nour analytic results by simulating wavepacket motion through a junction. We\nextend the wavepacket approach to two dimensions where analytic solutions\ncannot be found. An incoming wave travels on a sheet and scatters off a point\nwhere many sheets intersect. Unlike in 1D, the equivalent potential is\nmomentum-dependent. Nevertheless, for any given momentum, the equivalent\npotential grows monotonically with the number of intersecting sheets. Our\nfindings can be tested in ultracold atom setups and semiconductor structures.",
        "positive": "Mutual friction and diffusion of two-dimensional quantum vortices: We present a microscopic open quantum systems theory of thermally-damped\nvortex motion in oblate atomic superfluids that includes previously neglected\nenergy-damping interactions between superfluid and thermal atoms. This\nmechanism couples strongly to vortex core motion and causes dissipation of\nvortex energy due to mutual friction, as well as Brownian motion of vortices\ndue to thermal fluctuations. We derive an analytic expression for the\ndimensionless mutual friction coefficient that gives excellent quantitative\nagreement with experimentally measured values, without any fitted parameters.\nOur work closes an existing two orders of magnitude gap between dissipation\ntheory and experiments, previously bridged by fitted parameters, and provides a\nmicroscopic origin for the mutual friction and diffusion of quantized vortices\nin two-dimensional atomic superfluids."
    },
    {
        "anchor": "Enhancing quantum coherence with short-range correlated disorder: We introduce a two-dimensional short-range correlated disorder that is the\nnatural generalization of the well-known one-dimensional dual random dimer\nmodel [Phys. Rev. Lett 65, 88 (1990)]. We demonstrate that, as in one\ndimension, this model induces a localization-delocalization transition in the\nsingle-particle spectrum. Moreover we show that the effect of such a disorder\non a weakly-interacting boson gas is to enhance the condensate spatial\nhomogeneity and delocalisation, and to increase the condensate fraction around\nan effective resonance of the two-dimensional dual dimers. This study proves\nthat short-range correlations of a disordered potential can enhance the quantum\ncoherence of a weakly-interacting many-body system.",
        "positive": "Attractive Bose-Einstein condensates in anharmonic traps: Accurate\n  numerical treatment and the intriguing physics of the variance: The dynamics of attractive bosons trapped in one dimensional anharmonic\npotentials is investigated. Particular emphasis is put on the variance of the\nposition and momentum many-particle operators. Coupling of the center-of-mass\nand relative-motion degrees-of-freedom necessitates an accurate numerical\ntreatment. The multiconfigurational time-dependent Hartree for bosons (MCTDHB)\nmethod is used, and high convergence of the energy, depletion and occupation\nnumbers, and position and momentum variances is proven numerically. We\ndemonstrate for the ground state and out-of-equilibrium dynamics, for condensed\nand fragmented condensates, for small systems and {\\it en route} to the\ninfinite-particle limit, that intriguing differences between the density and\nvariance of an attractive Bose-Einstein condensate emerge. Implications are\nbriefly discussed."
    },
    {
        "anchor": "String order in dipole-blockaded quantum liquids: We study the quantum melting of quasi-one-dimensional lattice models in which\nthe dominant energy scale is given by a repulsive dipolar interaction. By\nconstructing an effective low-energy theory, we show that the melting of\ncrystalline phases can occur into two distinct liquid phases, having the same\nalgebraic decay of density-density correlations, but showing a different\nnon-local correlation function expressing string order. We present possible\nexperimental realizations using ultracold atoms and molecules, introducing an\nimplementation based on resonantly driven Rydberg atoms that offers additional\nbenefits compared to a weak admixture of the Rydberg state.",
        "positive": "Weakly interacting Bose gas in the one-dimensional limit: We prepare a chemically and thermally one-dimensional (1d) quantum degenerate\nBose gas in a single microtrap. We introduce a new interferometric method to\ndistinguish the quasicondensate fraction of the gas from the thermal cloud at\nfinite temperature. We reach temperatures down to $kT\\approx\n0.5\\hbar\\omega_\\perp$ (transverse oscillator eigenfrequency $\\omega_\\perp$)\nwhen collisional thermalization slows down as expected in 1d. At the lowest\ntemperatures the transverse momentum distribution exhibits a residual\ndependence on the line density $n_{1d}$, characteristic for 1d systems. For\nvery low densities the approach to the transverse single particle ground state\nis linear in $n_{1d}$."
    },
    {
        "anchor": "Shannon entropies and Fisher information of K-shell electrons of neutral\n  atoms: We represent the two K-shell electrons of neutral atoms by Hylleraas-type\nwave function which fulfils the exact behavior at the electron-electron and\nelectron-nucleus coalescence points and, derive a simple method to construct\nexpressions for single-particle position- and momentum-space charge densities,\n$\\rho(\\vec{r})$ and $\\gamma(\\vec{p})$ respectively. We make use of the results\nfor $\\rho(\\vec{r})$ and $\\gamma(\\vec{p})$ to critically examine the effect of\ncorrelation on bare (uncorrelated) values of Shannon information entropies\n($S$) and of Fisher information ($F$) for the K-shell electrons of atoms from\nhelium to neon. Due to inter-electronic repulsion the values of the\nuncorrelated Shannon position-space entropies are augmented while those of the\nmomentum-space entropies are reduced. The corresponding Fisher information are\nfound to exhibit opposite behavior in respect of this. Attempts are made to\nprovide some plausible explanation for the observed response of $S$ and $F$ to\nelectronic correlation.",
        "positive": "Trapping effect of periodic structures on the thermodynamic properties\n  of Fermi and Bose gases: We report the thermodynamic properties of Bose and Fermi ideal gases immersed\nin periodic structures such as penetrable multilayers or multitubes simulated\nby one (planes) or two perpendicular (tubes) external Dirac comb potentials,\nwhile the particles are allowed to move freely in the remaining directions.\nAlthough the bosonic chemical potential is a constant for $T < T_c$, a non\ndecreasing with temperature anomalous behavior of the fermionic chemical\npotential is confirmed and monitored as the tube bundle goes from 2D to 1D when\nthe wall impenetrability overcomes a critical value. In the specific heat\ncurves dimensional crossovers are very noticeable at high temperatures for both\ngases, where the system behavior goes from 3D to 2D and latter to 1D as the\nwall impenetrability is increased."
    },
    {
        "anchor": "Spatiotemporal scaling of two-dimensional nonequilibrium\n  exciton-polariton systems with weak interactions: We perform a numerical study on the two-dimensional nonequilibrium\nexciton-polariton systems driven by incoherent pumping based on the stochastic\ngeneralized Gross-Pitaevskii equation. We calculate the density fluctuation,\ncoherence function, and scaling function. It is found that the correlations at\nshort range agree with the Bogoliubov linear theory. While at large distance,\nboth static and dynamic correlations are characterized by the nonlinear scaling\nbehaviors of Kardar-Parisi-Zhang (KPZ) universality class, especially when the\ninteraction is weak. In this regime, scaling analyses are crucial to capture\nthe universal KPZ scaling features. In addition, the interaction between\nvortices is modified in the strong KPZ regime and leads to complex\nnonequilibrium vortex patterns.",
        "positive": "Strong-coupling dynamics of Bose-Einstein condensate in a double-well\n  trap: Dynamics of the repulsive Bose-Einstein condensate (BEC) in a double-well\ntrap is explored within the 3D time-dependent Gross-Pitaevskii equation. The\nmodel avoids numerous common approximations (two-mode treatment, time-space\nfactorization, fixed values of the chemical potential and barrier\npenetrability, etc) and thus provides a realistic description of BEC dynamics,\nincluding both weak-coupling (sub-barrier) and strong-coupling (above-barrier)\nregimes and their crossover. The strong coupling regime is achieved by\nincreasing the number $N$ of BEC atoms and thus the chemical potential. The\nevolution with $N$ of Josephson oscillations (JO) and Macroscopic Quantum\nSelf-Trapping (MQST) is examined and the crucial impact of the BEC interaction\nis demonstrated. At weak coupling, the calculations well reproduce the JO/MQST\nexperimental data. At strong coupling, with a significant overlap of the left\nand right BECs, we observe a remarkable persistence of the Josephson-like\ndynamics: the JO and MQST converge to a high-frequency JO-like mode where both\npopulation imbalance and phase difference oscillate around the zero averages.\nThe results open new avenues for BEC interferometry."
    },
    {
        "anchor": "Higher-Harmonic Collective Modes in a Trapped Gas from Second-Order\n  Hydrodynamics: Utilizing a second-order hydrodynamics formalism, the dispersion relations\nfor the frequencies and damping rates of collective oscillations as well as\nspatial structure of these modes up to the decapole oscillation in both two-\nand three- dimensional gas geometries are calculated. In addition to\nhigher-order modes, the formalism also gives rise to purely damped\n\"non-hydrodynamic\" modes. We calculate the amplitude of the various modes for\nboth symmetric and asymmetric trap quenches, finding excellent agreement with\nan exact quantum mechanical calculation. We find that higher-order hydrodynamic\nmodes are more sensitive to the value of shear viscosity, which may be of\ninterest for the precision extraction of transport coefficients in Fermi gas\nsystems.",
        "positive": "Accurate determination of the scattering length of erbium atoms: An accurate knowledge of the scattering length is fundamental in ultracold\nquantum gas experiments and essential for the characterisation of the system as\nwell as for a meaningful comparison to theoretical models. Here, we perform a\ncareful characterisation of the s-wave scattering length $a_s$ for the four\nhighest-abundance isotopes of erbium, in the magnetic field range from 0G to\n5G. We report on cross-dimensional thermalization measurements and apply the\nEnskog equations of change to numerically simulate the thermalization process\nand to analytically extract an expression for the so-called number of\ncollisions per re-thermalization (NCPR) to obtain $a_s$ from our experimental\ndata. We benchmark the applied cross-dimensional thermalization technique with\nthe experimentally more demanding lattice modulation spectroscopy and find good\nagreement for our parameter regime. Our experiments are compatible with a\ndependence of the NCPR with $a_s$, as theoretically expected in the case of\nstrongly dipolar gases. Surprisingly, we experimentally observe a dependency of\nthe NCPR on the density, which might arise due to deviations from an ideal\nharmonic trapping configuration. Finally, we apply a model for the dependency\nof the background scattering length with the isotope mass, allowing to estimate\nthe number of bound states of erbium."
    },
    {
        "anchor": "Exotic roton excitations in quadrupolar Bose-Einstein condensates: We investigate the occurrence of rotons in a quadrupolar Bose-Einstein\ncondensate confined to two dimensions. Depending on the particle density, the\nratio of the contact and quadrupole-quadrupole interactions, and the alignment\nof the quadrupole moments with respect to the confinement plane, the dispersion\nrelation features two or four point-like roton minima, or one ring-shaped\nminimum. We map out the entire parameter space of the roton behavior and\nidentify the instability regions. We propose to observe the exotic rotons by\nmonitoring the characteristic density wave dynamics resulting from a short\nlocal perturbation, and discuss the possibilities to detect the predicted\neffects in state-of-the-art experiments with ultracold homonuclear molecules.",
        "positive": "Dipolar Bose-Einstein condensate in a ring or in a shell: We study properties of a trapped dipolar Bose-Einstein condensate (BEC) in a\ncircular ring or a spherical shell using the mean-field Gross-Pitaevskii\nequation. In the case of the ring-shaped trap we consider different\norientations of the ring with respect to the polarization direction of the\ndipoles. In the presence of long-range anisotropic dipolar and short-range\ncontact interactions, the anisotropic density distribution of the dipolar BEC\nin both traps is discussed in detail. The stability condition of the dipolar\nBEC in both traps is illustrated in phase plot of dipolar and contact\ninteractions. We also study and discuss the properties of a vortex dipolar BEC\nin these traps."
    },
    {
        "anchor": "Vortex Ring Dynamics in Trapped Bose-Einstein Condensates: We use the time-dependent Gross-Pitaevskii equation to study the motion of a\nvortex ring produced by phase imprinting on an elongated cloud of cold atoms.\nOur approach models the experiments of Yefsah et. al. [Nature \\textbf{499},\n426] on $^6$Li in the BEC regime where the fermions are tightly bound into\nbosonic dimers. We find ring oscillation periods which are much larger than the\nperiod of the axial harmonic trap. Our results lend further strength to Bulgac\net. al.'s arguments [arXiv: 1306.4266] that the \"heavy solitons\" seen in those\nexperiments are actually vortex rings. We numerically calculate the periods of\noscillation for the vortex rings as a function of interaction strength, trap\naspect ratio, and minimum vortex ring radius. In the presence of axial\nanisotropies the rings undergo complicated internal dynamics where they break\ninto sets of vortex lines, then later combine into rings. These structures\noscillate with a similar frequency to simple axially symmetric rings.",
        "positive": "Parallel multicomponent interferometer with a spinor Bose-Einstein\n  condensate: Atom interferometry with high visibility is of high demand for precision\nmeasurements. Here, a parallel multicomponent interferometer is achieved by\npreparing a spin-$2$ Bose-Einstein condensate of $^{87}$Rb atoms confined in a\nhybrid magneto-optical trap. After the preparation of a spinor Bose-Einstein\ncondensate with spin degrees of freedom entangled, we observe four spatial\ninterference patterns in each run of measurements corresponding to four\nhyperfine states we mainly populate in the experiment. The atomic populations\nin different Zeeman sublevels are made controllably using magnetic-field-pulse\ninduced Majorana transitions. The spatial separation of atom cloud in different\nhyperfine states is reached by Stern-Gerlach momentum splitting. The high\nvisibility of the interference fringes is reached by designing a proper overlap\nof the interfering wave packets. Due to uncontrollable phase accumulation in\nMajorana transitions, the phase of each individual spin is found to be\nsubjected to unreproducible shift in multiple experimental runs. However, the\nrelative phase across different spins is stable, paving a way towards\nnoise-resilient multicomponent parallel interferometers."
    },
    {
        "anchor": "Non-equilibrium quantum dynamics and formation of the Bose polaron: Advancing our understanding of non-equilibrium phenomena in quantum many-body\nsystems remains among the greatest challenges in physics. Here, we report on\nthe experimental observation of a paradigmatic many-body problem, namely the\nnon-equilibrium dynamics of a quantum impurity immersed in a bosonic\nenvironment. We use an interferometric technique to prepare coherent\nsuperposition states of atoms in a Bose-Einstein condensate with a small\nimpurity-state component, and monitor the evolution of such quantum\nsuperpositions into polaronic quasiparticles. These results offer a systematic\npicture of polaron formation from weak to strong impurity interactions. They\nreveal three distinct regimes of evolution with dynamical transitions that\nprovide a link between few-body processes and many-body dynamics. Our\nmeasurements reveal universal dynamical behavior in interacting many-body\nsystems and demonstrate new pathways to study non-equilibrium quantum\nphenomena.",
        "positive": "Dipole-dipole interaction and polarization mode in BEC: We propose the construction of a set of quantum hydrodynamics equations for\nthe Bose-Einstein condensate (BEC) where atoms have electric dipole moment\n(EDM). The contribution of the dipole-dipole interactions (DDI) to the Euler\nequation is estimated. Quantum equations for the evolution of medium\npolarization are constructed for the first time. The mathematical method we\ndeveloped allows studying the effects of interactions on the evolution of\npolarization. The developed method may be applied to various physical systems\nin which dynamics is affected by DDI. A problem of elementary excitations in\nBEC, either affected or not affected by the uniform external electric field, is\naddressed using our method. We show that the evolution of polarization in BEC\nleads to the formation of a novel type of elementary excitations. Also, we\nconsider the process of wave generation in polarized BEC by means of\nmonoenergetic beam of neutral polarized particles. We compute the possibilities\nof the generation of Bogoliubov's modes and polarization modes by the dipole\nbeam."
    },
    {
        "anchor": "Vortex dynamics in superfluids governed by an interacting gauge theory: We study the dynamics of a vortex in a quasi two-dimensional Bose gas\nconsisting of light matter coupled atoms forming two-component pseudo spins.\nThe gas is subject to a density dependent gauge potential, hence governed by an\ninteracting gauge theory, which stems from a collisionally induced detuning\nbetween the incident laser frequency and the atomic energy levels. This\nprovides a back-action between the synthetic gauge potential and the matter\nfield. A Lagrangian approach is used to derive an expression for the force\nacting on a vortex in such a gas. We discuss the similarities between this\nforce and the one predicted by Iordanskii, Lifshitz and Pitaevskii when\nscattering between a superfluid vortex and the thermal component is taken into\naccount.",
        "positive": "Quantum Impurity in a One-dimensional Trapped Bose Gas: We present a new theoretical framework for describing an impurity in a\ntrapped Bose system in one spatial dimension. The theory handles any external\nconfinement, arbitrary mass ratios, and a weak interaction may be included\nbetween the Bose particles. To demonstrate our technique, we calculate the\nground state energy and properties of a sample system with eight bosons and\nfind an excellent agreement with numerically exact results. Our theory can thus\nprovide definite predictions for experiments in cold atomic gases."
    },
    {
        "anchor": "Localization-delocalization Transition in an electromagnetically induced\n  photonic lattice: We investigate the localization-delocalization transition (LDT) in an\nelectromagnetically induced photonic lattice. A four-level tripod-type scheme\nin atomic ensembles is proposed to generate an effective photonic moir\\'{e}\nlattice through the electromagnetically induced transparency (EIT) mechanism.\nBy taking advantage of the tunable atomic coherence, we show that both periodic\n(commensurable) and aperiodic (incommensurable) structure can be created in\nsuch a photonic moir\\'{e} lattice via adjusting the twist angle between two\nsuperimposed periodic patterns with square primitive. Furthermore, we also find\nthat by tuning the amplitudes of these two superimposed periodic patterns, the\nlocalization-delocalization transition occurs for the light propagating in the\naperiodic moir\\'{e} lattice. Such localization is shown to link the fact that\nthe flat bands of moir\\'{e} lattice support quasi-nondiffracting localized\nmodes and thus induce the localization of the initially localized beam. It\nwould provide a promising approach to control the light propagation via the\nelectromagnetically induced photonic lattice.",
        "positive": "Spin susceptibility and fluctuation corrections in the BCS-BEC crossover\n  regime of an ultracold Fermi gas: We investigate magnetic properties and effects of pairing fluctuations in the\nBCS (Bardeen-Cooper-Schrieffer)-BEC (Bose-Einstein condensation) crossover\nregime of an ultracold Fermi gas. Recently, Liu and Hu, and Parish, pointed out\nthat the strong-coupling theory developed by Nozi\\`eres and Schmitt-Rink (NSR),\nwhich has been extensively used to successfully clarify various physical\nproperties of cold Fermi gases, unphysically gives negative spin susceptibility\nin the BCS-BEC crossover region. The same problem is found to also exist in the\nordinary non-self-consistent T-matrix approximation. In this paper, we clarify\nthat this serious problem comes from incomplete treatment in term of pseudogap\nphenomena originating from strong pairing fluctuations, as well as effects of\nspin fluctuations on the spin susceptibility. Including these two key issues,\nwe construct an extended T-matrix theory which can overcome this problem. The\nresulting positive spin susceptibility agrees well with the recent experiment\non a 6Li Fermi gas done by Sanner and co-workers. We also apply our theory to a\npolarized Fermi gas to examine the superfluid phase transition temperature Tc,\nas a function of the polarization rate. Since the spin susceptibility is an\nimportant physical quantity, especially in singlet Fermi superfluids, our\nresults would be useful in considering how singlet pairs appear above and below\nTc in the BCS-BEC crossover regime of cold Fermi gases."
    },
    {
        "anchor": "Impurity transport through a strongly interacting bosonic quantum gas: Using near-exact numerical simulations we study the propagation of an\nimpurity through a one-dimensional Bose lattice gas for varying bosonic\ninteraction strengths and filling factors at zero temperature. The impurity is\ncoupled to the Bose gas and confined to a separate tilted lattice. The precise\nnature of the transport of the impurity is specific to the excitation spectrum\nof the Bose gas which allows one to measure properties of the Bose gas\nnon-destructively, in principle, by observing the impurity; here we focus on\nthe spatial and momentum distributions of the impurity as well as its reduced\ndensity matrix. For instance we show it is possible to determine whether the\nBose gas is commensurately filled as well as the bandwidth and gap in its\nexcitation spectrum. Moreover, we show that the impurity acts as a witness to\nthe cross-over of its environment from the weakly to the strongly interacting\nregime, i.e., from a superfluid to a Mott insulator or Tonks-Girardeau lattice\ngas and the effects on the impurity in both of these strongly-interacting\nregimes are clearly distinguishable. Finally, we find that the spatial\ncoherence of the impurity is related to its propagation through the Bose gas,\ngiving an experimentally controllable example of noise-enhanced quantum\ntransport.",
        "positive": "Attractive Hofstadter-Hubbard model with imbalanced chemical and vector\n  potentials: We study the interplay between the Hofstadter butterfly, strong interactions\nand Zeeman field within the mean-field Bogoliubov-de Gennes theory in real\nspace, and explore the ground states of the attractive single-band\nHofstadter-Hubbard Hamiltonian on a square lattice, including the exotic\npossibility of imbalanced vector potentials. We find that the cooperation\nbetween the vector potential and superfluid order breaks the spatial symmetry\nof the system, and flourish stripe-ordered Fulde-Ferrell-Larkin-Ovchinnikov\n(FFLO)-like superfluid and supersolid phases that can be distinguished and\ncharacterized according to their coexisting pair-density (PDW), charge-density\n(CDW) and spin-density (SDW) wave orders. We also discuss confined systems and\ncomment on the likelihood of observing such stripe-ordered phases by loading\nneutral atomic Fermi gases on laser-induced optical lattices under\nlaser-generated artificial gauge fields."
    },
    {
        "anchor": "Temporal non-equilibrium dynamics of a Bose Josephson junction in\n  presence of incoherent excitations: The time-dependent non-equilibrium dynamics of a Bose-Einstein condensate\n(BEC) typically generates incoherent excitations out of the condensate due to\nthe finite frequencies present in the time evolution. We present a detailed\nderivation of a general non-equilibrium Green's function technique which\ndescribes the coupled time evolution of an interacting BEC and its\nsingle-particle excitations in a trap, based on an expansion in terms of the\nexact eigenstates of the trap potential. We analyze the dynamics of a Bose\nsystem in a small double-well potential with initially all particles in the\ncondensate. When the trap frequency is larger than the Josephson frequency,\n$\\Delta > \\omega_J$, the dynamics changes at a characteristic time $\\tau_c$\nabruptly from slow Josephson oscillations of the BEC to fast Rabi oscillations\ndriven by quasiparticle excitations in the trap. For times $t<\\tau_c$ the\nJosephson oscillations are undamped, in agreement with experiments. We analyze\nthe physical origin of the finite scale $\\tau_c$ as well as its dependence on\nthe trap parameter $\\Delta$.",
        "positive": "Spin Drag of a Fermi Gas in a Harmonic Trap: Using a Boltzmann equation approach, we analyze how the spin drag of a\ntrapped interacting fermionic mixture is influenced by the non-homogeneity of\nthe system in a classical regime where the temperature is much larger than the\nFermi temperature. We show that for very elongated geometries, the spin damping\nrate can be related to the spin conductance of an infinitely long cylinder. We\ncharacterize analytically the spin conductance both in the hydrodynamic and\ncollisionless limits and discuss the influence of the velocity profile. Our\nresults are in good agreement with recent experiments and provide a\nquantitative benchmark for further studies of spin drag in ultracold gases."
    },
    {
        "anchor": "Emergent Gauge Theory in Rydberg Atom Arrays: Rydberg atom arrays have emerged as a novel platform exhibiting rich quantum\nmany-body physics and offering promise for universal quantum computation. The\nRydberg blockade effect plays an essential role in establishing many-body\ncorrelations in this system. In this review, we will highlight that the lattice\ngauge theory is an efficient description of the Rydberg blockade effect and\noverview recent exciting developments in this system from equilibrium phases to\nquantum dynamics. These developments include realizing exotic ground states\nsuch as spin liquids, discovering quantum many-body scar states violating\nquantum thermalization, and observing confinement-deconfinement transition\nthrough quantum dynamics. We emphasize that the gauge theory description offers\na universal theoretical framework to capture all these phenomena. This\nperspective of Rydberg atom arrays will inspire further the future development\nof quantum simulation and quantum computation in this platform.",
        "positive": "Controlling Nonequilibrium Bose-Einstein Condensation with Engineered\n  Environments: Out of thermal equilibrium, bosonic quantum systems can Bose-condense away\nfrom the ground state, featuring a macroscopic occupation of an excited state\nor even of multiple states in the so-called Bose-selection scenario. In\nprevious work, a theory was developed that predicts, in which states a\ndriven-dissipative ideal Bose gas condenses. Here, we address the inverse\nproblem: Given a target state with desired condensate fractions in certain\nsingle-particle states, how can this configuration be achieved by tuning\navailable control parameters? Which type of experimental setup allows for\nflexible condensation control? We solve these problems, on the one hand, by\ndeveloping a theory to solve the inverse problem based on linear programming\nmethods. On the other, we propose a Bose `condenser', experimentally\nimplementable in a superconducting circuit, where targeted Bose condensation\ninto eigenstates of a chain of resonators is driven through the coupling to\nartificial quantum baths, realized via auxiliary two-level systems. We further\ndiscuss the engineering of transition points between different Bose\ncondensation configurations, which may find application for amplification,\nheat-flow control, and the design of highly-structured quantum baths."
    },
    {
        "anchor": "Trapped Fermi gases with Rashba spin-orbit coupling in two dimensions: We use the Bogoliubov-de Gennes formalism to analyze harmonically trapped\nFermi gases with Rashba-type spin-orbit coupling in two dimensions. We consider\nboth population-balanced and -imbalanced Fermi gases throughout the BCS-BEC\nevolution, and study the effects of spin-orbit coupling on the spontaneously\ninduced countercirculating mass currents and the associated intrinsic angular\nmomentum. In particular, we find that even a small spin-orbit coupling\ndestabilizes Fulde-Ferrel-Larkin-Ovchinnikov (FFLO)-type spatially modulated\nsuperfluid phases as well as the phase-separated states against the polarized\nsuperfluid phase. We also show that the continuum of quasiparticle and\nquasihole excitation spectrum can be connected by zero, one or two discrete\nbranches of interface modes, depending on the number of interfaces between a\ntopologically trivial phase (e.g. locally unpolarized/low-polarized superfluid\nor spin-polarized normal) and a topologically nontrivial one (e.g. locally\nhigh-polarized superfluid) that may be present in a trapped system.",
        "positive": "Quantum quench phase diagrams of an s-wave BCS-BEC condensate: We study the dynamic response of an s-wave BCS-BEC (atomic-molecular)\ncondensate to detuning quenches within the two channel model beyond the weak\ncoupling BCS limit. At long times after the quench, the condensate ends up in\none of three main asymptotic states (nonequilibrium phases), which are\nqualitatively similar to those in other fermionic condensates defined by a\nglobal complex order parameter. In phase I the amplitude of the order parameter\nvanishes as a power law, in phase II it goes to a nonzero constant, and in\nphase III it oscillates persistently. We construct exact quench phase diagrams\nthat predict the asymptotic state (including the many-body wavefunction)\ndepending on the initial and final detunings and on the Feshbach resonance\nwidth. Outside of the weak coupling regime, both the mechanism and the time\ndependence of the relaxation of the amplitude of the order parameter in phases\nI and II are modified. Also, quenches from arbitrarily weak initial to\nsufficiently strong final coupling do not produce persistent oscillations in\ncontrast to the behavior in the BCS regime. The most remarkable feature of\ncoherent condensate dynamics in various fermion superfluids is an effective\nreduction in the number of dynamic degrees of freedom as the evolution time\ngoes to infinity. As a result, the long time dynamics can be fully described in\nterms of just a few new collective dynamical variables governed by the same\nHamiltonian only with \"renormalized\" parameters. Combining this feature with\nthe integrability of the underlying (e.g. the two channel) model, we develop\nand consistently present a general method that explicitly obtains the exact\nasymptotic state of the system."
    },
    {
        "anchor": "Quantitative Analysis of Shock Wave Dynamics in a Fluid of Light: We report on the formation of a dispersive shock wave in a nonlinear optical\nmedium. We monitor the evolution of the shock by tuning the incoming beam\npower. The experimental observations for the position and intensity of the\nsolitonic edge of the shock, as well as the location of the nonlinear\noscillations are well described by recent developments of Whitham modulation\ntheory. Our work constitutes a detailed and accurate benchmark for this\napproach. It opens exciting possibilities to engineer specific configurations\nof optical shock wave for studying wave-mean flow interaction.",
        "positive": "Phase diagram for the trapped p-wave fermionic superfluid with\n  population imbalance: We consider the problem of spin-triplet p-wave superfluid pairing with total\nspin projection $m_s=0$ in atomic Fermi gas across the Feshbach resonance. We\nallow for imbalanced populations and take into account the effects due to\npresence of a parabolic trapping potential. Within the mean-field approximation\nfor the one- and two-channel pairing models we show that depending on the\ndistance from the center of a trap at least two superfluid states will have the\nlowest energy. Superfluid shells which emerge in a trap may have two out of\nthree angular components of the p-wave superfluid order parameter equal to\nzero."
    },
    {
        "anchor": "A full view on the dynamics of an impurity coupled to two\n  one-dimensional fermionic baths: We consider a model for the motion of an impurity interacting with two\nparallel, one-dimensional (bosonized) fermionic baths. The impurity is able to\nmove along any of the baths, and to jump from one to the other. We provide a\nperturbative expression for the state evolution of the system when the impurity\nis injected in one of the baths, with a given wave packet. The nontrivial\nchoice of the unperturbed dynamics makes the approximation formally\ninfinite-order in the impurity-bath coupling, allowing us to reproduce the\northogonality catastrophe. We employ the result for the state evolution to\nobserve the dynamics of the impurity and its effect on the baths, in particular\nin the case when the wave packet is Gaussian. We observe and characterize the\npropagation of the impurity along the baths and the hopping between them. We\nalso analyze the dynamics of the bath density and momentum density (i.e. the\nparticle current), and show that fits an intuitive semi-classical\ninterpretation. We also quantify the correlation that is established between\nthe baths by calculating the inter-bath, equal-time spatial correlation\nfunctions of both bath density and momentum, finding a complex pattern. We show\nthat this pattern contains information on both the impurity motion and on the\nbaths themselves, and that these can be unveiled by taking appropriate \"slices\"\nof the time evolution.",
        "positive": "Exact theory of the finite-temperature spectral function of Fermi\n  polarons with multiple particle-hole excitations: Diagrammatic theory versus\n  Chevy ansatz: By using both diagrammatic theory and Chevy ansatz approach, we derive an\nexact set of equations, which determines the spectral function of Fermi\npolarons with multiple particle-hole excitations at nonzero temperature. In the\ndiagrammatic theory, we find out the complete series of Feynman diagrams for\nthe multi-particle vertex functions, when the unregularized contact interaction\nstrength becomes infinitesimal, a typical situation occurring in two- or three-\ndimensional free space. The latter Chevy ansatz approach is more widely\napplicable, allowing a nonzero interaction strength. We clarify the equivalence\nof the two approaches for an infinitesimal interaction strength and show that\nthe variational coefficients in the Chevy ansatz are precisely the on-shell\nmulti-particle vertex functions divided by an excitation energy. Truncated to a\nparticular order of particle-hole excitations, our exact set of equations can\nbe used to numerically calculate the finite-temperature polaron spectral\nfunction, once the numerical singularities in the equations are appropriately\ntreated. As a concrete example, we calculate the finite-temperature spectral\nfunction of Fermi polarons in one-dimensional lattices, taking into account all\nthe two-particle-hole excitations. We show that the inclusion of\ntwo-particle-hole excitations quantitatively improve the predictions on the\npolaron spectral function. Our results provide a useful way to solve the\nchallenge problem of accurately predicting the finite-temperature spectral\nfunction of Fermi polarons in three-dimensional free space. In addition, our\nclarification of the complete set of Feynman diagrams for the multi-particle\npolaron vertex functions may inspire the development of more accurate\ndiagrammatic theories of population-imbalanced strongly interacting Fermi\ngases, beyond the conventional many-body $T$-matrix approximation."
    },
    {
        "anchor": "On Solving Cubic-Quartic Nonlinear Schr\u00f6dinger Equation in a Cnoidal\n  Trap: The recent observations of quantum droplet in ultra-cold atomic gases have\nopened up new avenues of fundamental research. The competition between\nmean-field and beyond mean-field interactions, in ultra-cold dilute alkali\ngases, are believed to be instrumental in stabilizing the droplets. These new\nunderstanding has motivated us to investigate the analytical solutions of a\ntrapped cubic-quartic nonlinear Schr\\\"odinger equation (CQNLSE). The quartic\ncontribution in the NLSE is derived from the beyond mean-field formalism of\nBose-Einstein condensate (BEC). To the best of our knowledge, a comprehensive\nanalytical description of CQNLSE is non-existent. Here, we study the existence\nof the analytical solutions which are of the cnoidal type for CQNLSE. The\nexternal trapping plays a significant role in the stabilization of the system.\nIn the limiting case, the cnoidal wave solutions lead to the localized solution\nof bright solution and delocalized kink-antikink pair. The nonexistence of the\nsinusoidal mode in the current scheme is also revealed in our analysis.",
        "positive": "Quench dynamics of an ultracold two-dimensional Bose gas: We study the dynamics of a two-dimensional Bose gas after an instantaneous\nquench of an initially ultracold thermal atomic gas across the\nBerezinskii-Kosterlitz-Thouless phase transition, confirming via stochastic\nsimulations that the system undergoes phase ordering kinetics and fulfills\ndynamical scaling hypothesis at late-time dynamics. Specifically, we find in\nthat regime the vortex number decaying in time as $\\langle N_v \\propto\nt^{-1}\\rangle$, consistent with a dynamical critical exponent $z \\approx 2$ for\nboth temperature and interaction quenches. Focusing on finite-size box-like\ngeometries, we demonstrate that such an observation is within current\nexperimental reach."
    },
    {
        "anchor": "Scanning electron microscopy of cold gases: Ultracold quantum gases offer unique possibilities to study interacting\nmany-body quantum systems. Probing and manipulating such systems with ever\nincreasing degree of control requires novel experimental techniques. Scanning\nelectron microscopy is a high resolution technique which can be used for in\nsitu imaging, single site addressing in optical lattices and precision density\nengineering. Here, we review recent advances and achievements obtained with\nthis technique and discuss future perspectives.",
        "positive": "Identifying topological edge states in 2D optical lattices using light\n  scattering: We recently proposed in a Letter [Physical Review Letters 108 255303] a novel\nscheme to detect topological edge states in an optical lattice, based on a\ngeneralization of Bragg spectroscopy. The scope of the present article is to\nprovide a more detailed and pedagogical description of the system - the\nHofstadter optical lattice - and probing method. We first show the existence of\ntopological edge states, in an ultra-cold gas trapped in a 2D optical lattice\nand subjected to a synthetic magnetic field. The remarkable robustness of the\nedge states is verified for a variety of external confining potentials. Then,\nwe describe a specific laser probe, made from two lasers in Laguerre-Gaussian\nmodes, which captures unambiguous signatures of these edge states. In\nparticular, the resulting Bragg spectra provide the dispersion relation of the\nedge states, establishing their chiral nature. In order to make the Bragg\nsignal experimentally detectable, we introduce a \"shelving method\", which\nsimultaneously transfers angular momentum and changes the internal atomic\nstate. This scheme allows to directly visualize the selected edge states on a\ndark background, offering an instructive view on topological insulating phases,\nnot accessible in solid-state experiments."
    },
    {
        "anchor": "Magnetism in the three-dimensional layered Lieb lattice: Enhanced\n  transition temperature via flat-band and Van Hove singularities: We describe the enhanced magnetic transition temperatures $T_c$ of\ntwo-component fermions in three-dimensional layered Lieb lattices, which are\ncreated in cold atom experiments. We determine the phase diagram at\nhalf-filling using the dynamical mean-field theory. The dominant mechanism of\nenhanced $T_c$ gradually changes from the (delta-functional) flat-band to the\n(logarithmic) Van Hove singularity as the interlayer hopping increases. We\nelucidate that the interaction induces an effective flat-band singularity from\na dispersive flat (or narrow) band. We offer a general analytical framework for\ninvestigating the singularity effects, where a singularity is treated as one\nparameter in the density of states. This framework provides a unified\ndescription of the singularity-induced phase transitions, such as magnetism and\nsuperconductivity, where the weight of the singularity characterizes physical\nquantities. This treatment of the flat-band provides the transition temperature\nand magnetization as a universal form (i.e., including the Lambert function).\nWe also elucidate a specific feature of the magnetic crossover in magnetization\nat finite temperatures.",
        "positive": "The roton-assisted chiral p-wave superfluid in a quasi-two-dimensional\n  dipolar Bose-Fermi quantum gas mixture: The chiral p-wave (p_x \\pm ip_y) superfluid has attracted significant\nattention in recent years, mainly because its vortex core supports a Majorana\nfermion which, due to its non-Abelian statistics, can be explored for\nimplementing topological quantum computation. Mixing dipolar bosons with\nfermions in quasi-two-dimensional (2D) space offers the opportunity to use the\nroton minimum as a tool for engineering the phonon-induced attractive\ninteraction between fermions. We study, within the Hartree-Fock-Bogoliubov\napproach, the p-wave superfluid pairings in a quasi-2D dipolar Bose-Fermi\nmixture. We show that enhancing the induced interaction by lowering the roton\nminimum can affect the stability property of the mixture as well as the\neffective mass of the fermions in an important way. We also show that one can\ntune the system to operate in stable regions where chiral p-wave superfluid\npairings can be resonantly enhanced by lowering the energy cost of the phonons\nnear the roton minimum."
    },
    {
        "anchor": "Evidence of a liquid phase in interacting Bosons at intermediate\n  densities: In this paper, we present evidence for a liquid-like phase in systems of many\ninteracting Bosons at intermediate densities. The interacting Bose gas has been\nstudied extensively in the low and high density regimes, in which interactions\ndo not play a physically significant role, and the system behaves similarly to\nthe ideal quantum gas. Instead, we will turn our attention to the intermediate\ndensity regime, and report evidence that the system enters a strongly\ncorrelated phase where its behavior is markedly different from that of the\nideal quantum gas. To do so, we use the Simplified approach to the Bose gas,\nwhich was introduced by Lieb in 1963 and recently found to provide very\naccurate predictions for many-Boson systems at all densities. Using this tool,\nwe will compute predictions for the radial distribution function, structure\nfactor, condensate fraction and momentum distribution, and show that they are\nconsistent with liquid-type behavior.",
        "positive": "Breathing mode of a quantum droplet in a quasi-one-dimensional dipolar\n  Bose gas: We investigate the breathing mode and the stability of a quantum droplet in a\ntightly trapped one-dimensional dipolar gas of bosonic atoms. When the droplet\nwith a flat-top density profile is formed, the breathing mode frequency scales\nas the inverse of the number of atoms in the cloud. This is straightforwardly\nderived within a phenomenological hydrodynamical approach and confirmed using\nboth a variational method based on a generalized Gross-Pitaevskii action\nfunctional and the sum-rule approach. We extend our analysis also to the\npresence of axial confinement showing the effect of the trap on the density\nprofile and therefore on the breathing mode frequency scaling. Our analysis\nconfirms the stability of the quantum droplet against the particles emission\nwhen the flat-top density profile is observed. Our results can be used as a\nguide to the experimental investigations of collective modes to detect the\nformation of quantum droplets in quasi-one-dimensional dipolar gases."
    },
    {
        "anchor": "Vibrational state inversion of a Bose-Einstein condensate: optimal\n  control and state tomography: We present theoretical and experimental results on high-fidelity transfer of\na trapped Bose-Einstein condensate into its first vibrationally excited\neigenstate. The excitation is driven by mechanical motion of the trap, along a\ntrajectory obtained from optimal control theory. Excellent agreement between\ntheory and experiment is found over a large range of parameters. We develop an\napproximate model to map the dynamics of the many-body condensate wave function\nto a driven two-level system.",
        "positive": "Quench Dynamics of the Gaudin-Yang Model: We study the quench dynamics of one dimensional bosons or fermion quantum\ngases with either attractive or repulsive contact interactions. Such systems\nare well described by the Gaudin-Yang model which turns out to be quantum\nintegrable. We use a contour integral approach, the Yudson approach, to expand\ninitial states in terms of Bethe Ansatz eigenstates of the Hamiltonian. Making\nuse of the contour, we obtain a complete set of eigenstates, including both\nfree states and bound states. These states constitute a larger Hilbert space\nthan described by the standard String hypothesis. We calculate the density and\nnoise correlations of several quenched systems such as a static or kinetic\nimpurity evolving in an array of particles."
    },
    {
        "anchor": "Identification of vortices in quantum fluids: finite element algorithms\n  and programs: We present finite-element numerical algorithms for the identification of\nvortices in quantum fluids described by a macroscopic complex wave function.\nTheir implementation using the free software FreeFem++ is distributed with this\npaper as a post-processing toolbox that can be used to analyse numerical or\nexperimental data. Applications for Bose-Einstein condensates (BEC) and\nsuperfluid helium flows are presented. Programs are tested and validated using\neither numerical data obtained by solving the Gross-Pitaevskii equation or\nexperimental images of rotating BEC. Vortex positions are computed as\ntopological defects (zeros) of the wave function when numerical data are used.\nFor experimental images, we compute vortex positions as local minima of the\natomic density, extracted after a simple image processing. Once vortex centers\nare identified, we use a fit with a Gaussian to precisely estimate vortex\nradius. For vortex lattices, the lattice parameter (inter-vortex distance) is\nalso computed. The post-processing toolbox offers a complete description of\nvortex configurations in superfluids. Tests for two-dimensional (giant vortex\nin rotating BEC, Abrikosov vortex lattice in experimental BEC) and\nthree-dimensional (vortex rings, Kelvin waves and quantum turbulence fields in\nsuperfluid helium) configurations show the robustness of the software. The\ncommunication with programs providing the numerical or experimental wave\nfunction field is simple and intuitive. The post-processing toolbox can be also\napplied for the identification of vortices in superconductors.",
        "positive": "Quantum criticality in interacting bosonic Kitaev-Hubbard models: Motivated by recent work on the non-Hermitian skin effect in the bosonic\nKitaev-Majorana model, we study the quantum criticality of interacting bosonic\nKitaev-Hubbard models on a chain and a two-leg ladder. In the hard-core limit,\nwe show exactly that the non-Hermitian skin effect disappears via a\ntransformation from hard-core bosonic models to spin-1/2 models. We also show\nthat hard-core bosons can engineer the Kitaev interaction, the\nDzyaloshinskii-Moriya interaction and the compass interaction in the presence\nof the complex hopping and pairing terms. Importantly, quantum criticalities of\nthe chain with a three-body constraint and unconstrained soft-core bosons are\ninvestigated by the density matrix renormalization group method. This work\nreveals the effect of many-body interactions on the non-Hermitian skin effect\nand highlights the power of bosons with pairing terms as a probe for the\nengineering of interesting models and quantum phase transitions."
    },
    {
        "anchor": "Excited-state quantum phase transitions and periodic dynamics: We investigate signatures of the excited-state quantum phase transition in\nthe periodic dynamics of the Lipkin-Meshkov-Glick model and the Tavis-Cummings\nmodel. In the thermodynamic limit, expectation values of observables in\neigenstates of the system can be calculated using classical trajectories.\nMotivated by this, we suggest a method based on the time evolution of the\nfinite-size system, to find singularities in observables, which arise due to\nthe excited-state quantum phase transition.",
        "positive": "Generalized harmonic-fluid approach for the off-diagonal correlations of\n  a one-dimensional interacting Bose gas: We develop a generalized harmonic-fluid approach, based on a regularization\nof the effective low-energy Luttinger-liquid Hamiltonian, for a one-dimensional\nBose gas with repulsive contact interactions. The method enables us to compute\nthe complete series corresponding to the large-distance, off-diagonal behavior\nof the one-body density matrix for any value of the Luttinger parameter K. We\ncompare our results with the exact ones known in the Tonks-Girardeau limit of\ninfinitely large interactions (corresponding to K=1) and, different from the\nusual harmonic-fluid approach, we recover the full structure of the series. The\nstructure is conserved for arbitrary values of the interaction strength, with\npower laws fixed by the universal parameter K and a sequence of subleading\ncorrections."
    },
    {
        "anchor": "Fermionic properties of two interacting bosons in a two-dimensional\n  harmonic trap: The system of two interacting bosons in a two-dimensional harmonic trap is\ncompared with the system consisting of two noninteracting fermions in the same\npotential. In particular, we discuss how the properties of the ground state of\nthe system, e.g., the different contributions to the total energy, change as we\nvary both the strength and range of the atom-atom interaction. In particular,\nwe focus on the short-range and strong interacting limit of the two-boson\nsystem and compare it to the noninteracting two-fermion system by properly\nsymmetrizing the corresponding degenerate ground state wave functions. In that\nlimit, we show that the density profile of the two-boson system has a tendency\nsimilar to the system of two noninteracting fermions. Similarly, the\ncorrelations induced when the interaction strength is increased result in a\nsimilar pair correlation function for both systems.",
        "positive": "Superfluid flow past an obstacle in annular Bose--Einstein condensates: We investigate the flow of a one-dimensional nonlinear Schrodinger model with\nperiodic boundary conditions past an obstacle, motivated by recent experiments\nwith Bose--Einstein condensates in ring traps. Above certain rotation\nvelocities, localized solutions with a nontrivial phase profile appear. In\nstriking difference from the infinite domain, in this case there are many\ncritical velocities. At each critical velocity, the steady flow solutions\ndisappear in a saddle-center bifurcation. These interconnected branches of the\nbifurcation diagram lead to additions of circulation quanta to the phase of the\nassociated solution. This, in turn, relates to the manifestation of persistent\ncurrent in numerous recent experimental and theoretical works, the connections\nto which we touch upon. The complex dynamics of the identified waveforms and\nthe instability of unstable solution branches are demonstrated."
    },
    {
        "anchor": "Momentum distribution in the unitary Bose gas from first principles: We consider a realistic bosonic N-particle model with unitary interactions\nrelevant for Efimov physics. Using quantum Monte Carlo methods, we find that\nthe critical temperature for Bose-Einstein condensation is decreased with\nrespect to the ideal Bose gas. We also determine the full momentum distribution\nof the gas, including its universal asymptotic behavior, and compare this\ncrucial observable to recent experimental data. Similar to the experiments with\ndifferent atomic species, differentiated solely by a three-body length scale,\nour model only depends on a single parameter. We establish a weak influence of\nthis parameter on physical observables. In current experiments, the\nthermodynamic instability of our model from the atomic gas towards an Efimov\nliquid could be masked by the dynamical instability due to three-body losses.",
        "positive": "(Inverse) Magnetic Catalysis in Bose-Einstein Condensation of Neutral\n  Bound Pairs: The Bose-Einstein condensation of bound pairs made of oppositely charged\nfermions in a magnetic field is investigated. We find that the condensation\ntemperature shows the magnetic catalysis effect in weak coupling and the\ninverse magnetic catalysis effect in strong coupling. The different responses\nto the magnetic field can be attributed to the competition between the\ndimensional reduction by Landau orbitals in pairing dynamics and the anisotropy\nof the kinetic spectrum of fluctuations (bound pairs in the normal phase)"
    },
    {
        "anchor": "Atom lasers: production, properties and prospects for precision inertial\n  measurement: We review experimental progress on atom lasers out-coupled from Bose-Einstein\ncondensates, and consider the properties of such beams in the context of\nprecision inertial sensing. The atom laser is the matter-wave analog of the\noptical laser. Both devices rely on Bose-enhanced scattering to produce a\nmacroscopically populated trapped mode that is output-coupled to produce an\nintense beam. In both cases, the beams often display highly desirable\nproperties such as low divergence, high spectral flux and a simple spatial mode\nthat make them useful in practical applications, as well as the potential to\nperform measurements at or below the quantum projection noise limit. Both\ndevices display similar second-order correlations that differ from thermal\nsources. Because of these properties, atom lasers are a promising source for\napplication to precision inertial measurements.",
        "positive": "Atomic loss and gain as a resource for non-equilibrium phase transitions\n  in optical lattices: Recent breakthroughs in the experimental manipulation of strongly interacting\natomic Rydberg gases in lattice potentials have opened a new avenue for the\nstudy of many-body phenomena. Considerable efforts are currently being\nundertaken to achieve clean experimental settings that show a minimal amount of\nnoise and disorder and are close to zero temperature. A complementary direction\ninvestigates the interplay between coherent and dissipative processes. Recent\nexperiments have revealed a first glimpse into the emergence of a rich\nnon-equilibrium behavior stemming from the competition of laser excitation,\nstrong interactions and radiative decay of Rydberg atoms. The aim of the\npresent theoretical work is to show that local incoherent loss and gain of\natoms can in fact be the source of interesting out-of-equilibrium dynamics.\nThis perspective opens new paths for the exploration of non-equilibrium\ncritical phenomena and, more generally, phase transitions, some of which so far\nhave been rather difficult to study. To demonstrate the richness of the\nencountered dynamical behavior we consider here three examples. The first two\nfeature local atom loss and gain together with an incoherent excitation of\nRydberg states. In this setting either a continuous or a discontinuous phase\ntransition emerges with the former being reminiscent of genuine non-equilibrium\ntransitions of stochastic processes with multiple absorbing states. The third\nexample considers the regime of coherent laser excitation. Here the many-body\ndynamics is dominated by an equilibrium transition of the \"model A\"\nuniversality class."
    },
    {
        "anchor": "Competing Supersolid and Haldane Insulator phases in the extended\n  one-dimensional bosonic Hubbard model: The Haldane Insulator is a gapped phase characterized by an exotic non-local\norder parameter. The parameter regimes at which it might exist, and how it\ncompetes with alternate types of order, such as supersolid order, are still\nincompletely understood. Using the Stochastic Green Function (SGF) quantum\nMonte Carlo (QMC) and the Density Matrix Renormalization Group (DMRG), we study\nnumerically the ground state phase diagram of the one-dimensional bosonic\nHubbard model (BHM) with contact and near neighbor repulsive interactions. We\nshow that, depending on the ratio of the near neighbor to contact interactions,\nthis model exhibits charge density waves (CDW), superfluid (SF), supersolid\n(SS) and the recently identified Haldane insulating (HI) phases. We show that\nthe HI exists only at the tip of the unit filling CDW lobe and that there is a\nstable SS phase over a very wide range of parameters.",
        "positive": "Coherent Oscillations in Small Fermi Polaron Systems: We study the ground state and excitations of a one-dimensional trapped\npolarized Fermi gas interacting with a single impurity. First, we study the\ntunnelling dynamics of the impurity through a potential barrier, such as one\neffectively created by a double-well trap. To this end, we perform an exact\ndiagonalization of the full few-body Hamiltonian and analyze the results in a\nLocal Density Approximation. Off-diagonal and one-particle correlation matrices\nare studied and are shown to be useful for discerning between different\nsymmetries of the states. Second, we consider a radio-frequency (RF)\nspectroscopy of our system and the resulting spectral function. These\ncalculations can motivate future experiments, which can provide a further\ninsight into the physics of a Fermi polaron."
    },
    {
        "anchor": "Entanglement and correlations in an exactly-solvable model of a\n  Bose-Einstein condensate in a cavity: An exactly solvable model of a trapped interacting Bose-Einstein condensate\n(BEC) coupled in the dipole approximation to a quantized light mode in a cavity\nis presented. The model can be seen as a generalization of the\nharmonic-interaction model for a trapped BEC coupled to a bosonic bath. After\nobtaining the ground-state energy and wavefunction in closed form, we focus on\ncomputing the correlations in the system. The reduced one-particle density\nmatrices of the bosons and the cavity are constructed and diagonalized\nanalytically, and the von Neumann entanglement entropy of the BEC and the\ncavity is also expressed explicitly as a function of the number and mass of the\nbosons, frequencies of the trap and cavity, and the cavity-boson coupling\nstrength. The results allow one to study the impact of the cavity on the bosons\nand vice versa on an equal footing. As an application we investigate a specific\ncase of basic interest for itself, namely, non-interacting bosons in a cavity.\nWe find that both the bosons and the cavity develop correlations in a\ncomplementary manner while increasing the coupling between them. Whereas the\ncavity wavepacket broadens in Fock space, the BEC density saturates in real\nspace. On the other hand, while the cavity depletion saturates, and hence does\nthe BEC-cavity entanglement entropy, the BEC becomes strongly correlated and\neventually increasingly fragmented. The latter phenomenon implies single-trap\nfragmentation of otherwise ideal bosons, where their induced long-range\ninteraction is mediated by the cavity. Finally, as a complimentary\ninvestigation, the mean-field equations for the BEC-cavity system are solved\nanalytically as well, and the breakdown of mean-field theory for the cavity and\nthe bosons with increasing coupling is discussed. Further applications are\nenvisaged.",
        "positive": "Topological quantum matter with cold atoms: This is an introductory review of the physics of topological quantum matter\nwith cold atoms. Topological quantum phases, originally discovered and\ninvestigated in condensed matter physics, have recently been explored in a\nrange of different systems, which produced both fascinating physics findings\nand exciting opportunities for applications. Among the physical systems that\nhave been considered to realize and probe these intriguing phases, ultracold\natoms become promising platforms due to their high flexibility and\ncontrollability. Quantum simulation of topological phases with cold atomic\ngases is a rapidly evolving field, and recent theoretical and experimental\ndevelopments reveal that some toy models originally proposed in condensed\nmatter physics have been realized with this artificial quantum system. The\npurpose of this article is to introduce these developments. The article begins\nwith a tutorial review of topological invariants and the methods to control\nparameters in the Hamiltonians of neutral atoms. Next, topological quantum\nphases in optical lattices are introduced in some detail, especially several\ncelebrated models, such as the Su-Schrieffer-Heeger model, the\nHofstadter-Harper model, the Haldane model and the Kane-Mele model. The\ntheoretical proposals and experimental implementations of these models are\ndiscussed. Notably, many of these models cannot be directly realized in\nconventional solid-state experiments. The newly developed methods for probing\nthe intrinsic properties of the topological phases in cold atom systems are\nalso reviewed. Finally, some topological phases with cold atoms in the\ncontinuum and in the presence of interactions are discussed, and an outlook on\nfuture work is given."
    },
    {
        "anchor": "Relaxation and Pre-thermalization in an Isolated Quantum System: Understanding relaxation processes is an important unsolved problem in many\nareas of physics. A key challenge in studying such non-equilibrium dynamics is\nthe scarcity of experimental tools for characterizing their complex transient\nstates. We employ measurements of full quantum mechanical probability\ndistributions of matter-wave interference to study the relaxation dynamics of a\ncoherently split one-dimensional Bose gas and obtain unprecedented information\nabout the dynamical states of the system. Following an initial rapid evolution,\nthe full distributions reveal the approach towards a thermal-like steady state\ncharacterized by an effective temperature that is independent from the initial\nequilibrium temperature of the system before the splitting process. We\nconjecture that this state can be described through a generalized Gibbs\nensemble and associate it with pre-thermalization.",
        "positive": "Spontaneous generation of dark-bright and dark-antidark solitons upon\n  quenching a particle-imbalanced bosonic mixture: We unveil the dynamical formation of multiple localized structures in the\nform of dark-bright and dark-antidark solitary waves that emerge upon quenching\na one-dimensional particle-imbalanced Bose-Bose mixture. Interspecies\ninteraction quenches drive the system out-of-equilibrium while the so-called\nmiscible/immiscible threshold is crossed in a two directional manner.\nDark-bright entities are spontaneously generated for quenches towards the phase\nseparated regime and dark-antidark states are formed in the reverse process.\nThe distinct mechanisms of creation of the aforementioned states are discussed\nin detail and their controlled generation is showcased. In both processes, it\nis found that the number of solitary waves generated is larger for larger\nparticle imbalances, a result that is enhanced for stronger postquench\ninterspecies interactions. Additionally the confining geometry highly affects\nthe production of both types of states with a decaying solitary wave formation\noccurring for tighter traps. Furthermore, in both of the aforementioned\ntransitions, the breathing frequencies measured for the species differ\nsignificantly for highly imbalanced mixtures. Finally, the robustness of the\ndynamical formation of dark-bright and dark-antidark solitons is also\ndemonstrated in quasi one-dimensional setups."
    },
    {
        "anchor": "Role of fourth-order phase-space moments in collective modes of trapped\n  Fermi gases: We study the transition from hydrodynamic to collisionless behavior in\ncollective modes of ultracold trapped Fermi gases. To that end, we solve the\nBoltzmann equation for the trapped Fermi gas via the moments method. We showed\npreviously that it is necessary to go beyond second-order moments if one wants\nto reproduce the results of a numerical solution of the Boltzmann equation.\nHere, we will give the detailed description of the method including\nfourth-order moments. We apply this method to the case of realistic parameters,\nand compare the results for the radial quadrupole and scissors modes at\nunitarity to experimental data obtained by the Innsbruck group. It turns out\nthat the inclusion of fourth-order moments clearly improves the agreement with\nthe experimental data. In particular, the fourth-order moments reduce the\neffect of collisions and therefore partially compensate the effect of the\nenhanced in-medium cross section at low temperatures.",
        "positive": "The Pauli principle in collective motion: Reimagining and reinterpreting\n  Cooper pairs, the Fermi sea, Pauli blocking and superfluidity: Typically visualized from an independent particle viewpoint, the Pauli\nprinciple's role in collective motion is analyzed leading to a reimagination of\nthe microscopic dynamics underlying superfluidity/superconductivity and a\nreinterpretation of several interrelated phenomena: Cooper pairs, the Fermi\nsea, and Pauli blocking. The current approach, symmetry-invariant perturbation\ntheory is a first principles method with no adjustable parameters. An adiabatic\nevolution is employed to transfer the well-known Pauli restrictions for\nidentical, independent particles with two spin values to restrictions on the\ncollective modes of an ensemble of ``spin up'' ``spin down'' particles. The\ncollective modes, analytic N-body normal modes, are obtained from a group\ntheoretic exact solution of the first-order equations. Cooper pairing is\nreinterpreted not as the pairing of two fermions with total zero momentum, but\nas the convergence of the momentum of the entire ensemble to two values, +k and\n-k, as the particles in the normal mode move back and forth with a single\nfrequency and phase. The Fermi sea and Pauli blocking, commonly described using\nindependent fermions that occupy lower states to create a ``sea'' in energy\nspace and block occupation is redescribed as a collective energy phenomena of\nthe entire ensemble. Superfluidity, which has always been viewed as a\ncollective phenomena as Cooper pairs are assumed to condense into a macroscopic\noccupation of a single lowest state, is now reimagined without two-body pairing\nin real space, but as a macroscopic occupation of a low-energy phonon normal\nmode resulting in the convergence of the momentum to two equal and opposite\nvalues. The expected properties of superfluidity including the rigidity of the\nwave function, interactions between fermions in different pairs, convergence of\nthe momentum and the gap in the excitation spectrum are discussed."
    },
    {
        "anchor": "Relativistic linear stability equations for the nonlinear Dirac equation\n  in Bose-Einstein condensates: We present relativistic linear stability equations (RLSE) for\nquasi-relativistic cold atoms in a honeycomb optical lattice. These equations\nare derived from first principles and provide a method for computing\nstabilities of arbitrary localized solutions of the nonlinear Dirac equation\n(NLDE), a relativistic generalization of the nonlinear Schr\\\"odinger equation.\nWe present a variety of such localized solutions: skyrmions, solitons,\nvortices, and half-quantum vortices, and study their stabilities via the RLSE.\nWhen applied to a uniform background, our calculations reveal an experimentally\nobservable effect in the form of Cherenkov radiation. Remarkably, the Berry\nphase from the bipartite structure of the honeycomb lattice induces a\nboson-fermion transmutation in the quasi-particle operator statistics.",
        "positive": "Experimental Realization of a Relativistic Harmonic Oscillator: We report the experimental study of a harmonic oscillator in the relativistic\nregime. The oscillator is composed of Bose-condensed lithium atoms in the third\nband of an optical lattice, which have an energy-momentum relation nearly\nidentical to that of a massive relativistic particle, with an effective mass\nreduced below the bare value and a greatly reduced effective speed of light.\nImaging the shape of oscillator trajectories at velocities up to 98% of the\neffective speed of light reveals a crossover from sinusoidal to nearly\nphoton-like propagation. The existence of a maximum velocity causes the\nmeasured period of oscillations to increase with energy; our measurements\nreveal beyond-leading-order contributions to this relativistic anharmonicity.\nWe observe an intrinsic relativistic dephasing of oscillator ensembles, and a\nmonopole oscillation with exactly the opposite phase of that predicted for\nnon-relativistic harmonic motion. All observed dynamics are in quantitative\nagreement with longstanding but hitherto-untested relativistic predictions."
    },
    {
        "anchor": "Hydrodynamics of cold atomic gases in the limit of weak nonlinearity,\n  dispersion and dissipation: Dynamics of interacting cold atomic gases have recently become a focus of\nboth experimental and theoretical studies. Often cold atom systems show\nhydrodynamic behavior and support the propagation of nonlinear dispersive\nwaves. Although this propagation depends on many details of the system, a great\ninsight can be obtained in the rather universal limit of weak nonlinearity,\ndispersion and dissipation (WNDD). In this limit, using a reductive\nperturbation method we map some of the hydrodynamic models relevant to cold\natoms to well known chiral one-dimensional equations such as KdV, Burgers,\nKdV-Burgers, and Benjamin-Ono equations. These equations have been thoroughly\nstudied in literature. The mapping gives us a simple way to make estimates for\noriginal hydrodynamic equations and to study the interplay between\nnonlinearity, dissipation and dispersion which are the hallmarks of nonlinear\nhydrodynamics.",
        "positive": "Emergent Kardar-Parisi-Zhang phase in quadratically driven condensates: In bosonic gases at thermal equilibrium, an external quadratic drive can\ninduce a Bose-Einstein condensation described by the Ising transition, as a\nconsequence of the explicitly broken U(1) phase rotation symmetry down to\n$\\mathbb{Z}_2$. However, in physical realizations such as exciton-polaritons\nand nonlinear photonic lattices, thermal equilibrium is lost and the state is\nrather determined by a balance between losses and external drive. A fundamental\nquestion is then how nonequilibrium fluctuations affect this transition. Here,\nwe show that in a two-dimensional driven-dissipative Bose system the Ising\nphase is suppressed and replaced by a nonequilibrium phase featuring\nKardar-Parisi-Zhang (KPZ) physics. Its emergence is rooted in a U(1)-symmetry\nrestoration mechanism enabled by the strong fluctuations in reduced\ndimensionality. Moreover, we show that the presence of the quadratic drive term\nenhances the visibility of the KPZ scaling, compared to two-dimensional\nU(1)-symmetric gases, where it has remained so far elusive."
    },
    {
        "anchor": "Self-consistent approach for Bose-condensed atoms in optical lattices: Bose atoms in optical lattices are considered at low temperatures and weak\ninteractions, when Bose-Einstein condensate is formed. A self-consistent\napproach, based on the use of a representative statistical ensemble, is\nemployed, ensuring a gapless spectrum of collective excitations and the\nvalidity of conservation laws. In order to show that the approach is applicable\nto both weak and tight binding, the problem is treated in the Bloch as well as\nin the Wannier representations. Both these ways result in similar expressions\nthat are compared for the self-consistent Hartree-Fock-Bogolubov approximation.\nA convenient general formula for the superfluid fraction of atoms in an optical\nlattice is derived.",
        "positive": "Observation of Chiral-Mode Domains in a Frustrated XY Model on Optical\n  Triangular Lattices: We investigated the relaxation and excitation in a frustrated XY model\nrealized by a Bose gas in Floquet-engineered optical triangular lattices.\nPeriodically driving the position of the entire lattice structure enables the\nsign inversion of tunneling amplitudes, which, in the case of a triangular\nlattice, results in geometrical frustration of the local phase of wave packets.\nWe revealed that the two spiral phases with chiral modes show significant\ndifferences in relaxation time from the initial ferromagnetic phase. While\nspontaneous symmetry breaking is clearly observed at a slow ramp of the Floquet\ndrive, simultaneous occupation of two ground states often occurs at a fast\nramp, which can be attributed to the domain formation of the chiral modes. The\ninterference of the spatially separated chiral modes was observed, using a\nquantum gas microscope. This work leads to exploring the domain formation\nmechanism in a system with U(1)$\\times \\mathbb{Z}_2$ symmetry."
    },
    {
        "anchor": "Bound states in two-dimensional Fermi systems with quadratic band\n  touching: The formation of bound states between mobile impurity particles and fermionic\natoms has been demonstrated in spin-polarized Fermi gases with attractive\ninterspecies interaction. We investigate bound states of mobile impurities\nimmersed in a two-dimensional system with a symmetry-protected quadratic band\ntouching. In addition to the standard s-wave interaction, we consider an\nanisotropic dipolar exchange interaction that locally breaks point group\nsymmetries. Using a weak-coupling renormalization group approach and a ladder\napproximation for the impurity-fermion propagator, we establish that the number\nof bound states can be controlled by varying the anisotropy of the exchange\ninteraction. Our results show that the degeneracy and momentum dependence of\nthe binding energies reflect some distinctive properties of the quadratic band\ntouching.",
        "positive": "Correlations of quasi-2D dipolar ultracold gas at finite temperatures: We study a quasi two dimensional dipolar gas at finite, but ultralow\ntemperatures using the classical field approximation. The method, already used\nfor a contact interacting gas, is extended here to samples with a weakly\ninteracting long-range inter-atomic potential. We present statistical\nproperties of the system for the current experiment with Chromium [Phys. Rev. A\n84 053601 (2011)] and compare them with statistics for atoms with larger\nmagnetic dipole moments. Significant enhancement of the third order correlation\nfunction, relevant for the particle losses, is found."
    },
    {
        "anchor": "Radiation spectrum of systems with condensed light: Experimental observation of Bose-Einstein condensation (BEC) of photons\ninside a microcavity induced an extensive study of the phenomenon. Beyond the\npurely theoretical interest, this phenomenon is believed to be used to create a\nnovel source of light. The shape of radiation spectrum is therefore the main\ncharacteristic of the system with light BEC as an optical device. However,\nuntil now, there were no detailed calculations of this property. In the present\npaper we derive analytically the shape of radiation spectrum and show that our\nresults are in excellent agreement with existing experimental measurements.",
        "positive": "Energy eigenfunctions of the 1D Gross-Pitaevskii equation: We developed a new and powerful algorithm by which numerical solutions for\nexcited states in a gravito optical surface trap have been obtained. They\nrepresent solutions in the regime of strong nonlinearities of the\nGross--Pitaevskii equation. In this context we also shortly review several\napproaches which allow, in principle, for calculating excited state solutions.\nIt turns out that without modifications these are not applicable to strongly\nnonlinear Gross-Pitaevskii equations. The importance of studying excited states\nof Bose-Einstein condensates is also underlined by a recent experiment of\nB\\\"ucker et al in which vibrational state inversion of a Bose-Einstein\ncondensate has been achieved by transferring the entire population of the\ncondensate to the first excited state. Here, we focus on demonstrating the\napplicability of our algorithm for three different potentials by means of\nnumerical results for the energy eigenstates and eigenvalues of the 1D\nGrosss-Pitaevskii-equation. We compare the numerically found solutions and find\nout that they completely agree with the case of known analytical solutions."
    },
    {
        "anchor": "Use of two-body correlated basis functions with van der Waals\n  interaction to study the shape-independent approximation for a large number\n  of trapped interacting bosons: We study the ground state and the low-lying excitations of a trapped Bose gas\nin an isotropic harmonic potential for very small ($\\sim 3$) to very large\n($\\sim 10^7$) particle numbers. We use the correlated two-body basis functions\nand the shape-dependent van der Waals interaction in our many-body\ncalculations. We present an exhaustive study of the effect of inter-atomic\ncorrelations and the accuracy of the mean-field equations considering a wide\nrange of particle numbers. We calculate the ground state energy and the\none-body density for different values of the van der Waals parameter $C_{6}$.\nWe compare our results with those of the modified Gross-Pitaevskii results, the\ncorrelated Hartree hypernetted-chain equations (which also utilize the two-body\ncorrelated basis functions), as well as of the Diffusion Monte Carlo for hard\nsphere interactions. We observe the effect of the attractive tail of the van\nder Waals potential in the calculations of the one-body density over the truly\nrepulsive zero-range potential as used in the Gross-Pitaevskii equation and\ndiscuss the finite-size effects. We also present the low-lying collective\nexcitations which are well described by a hydrodynamic model in the large\nparticle limit.",
        "positive": "Ultracold and dense samples of ground-state molecules in lattice\n  potentials: We produce an ultracold and dense sample of rovibronic ground state Cs_2\nmolecules close to the regime of quantum degeneracy, in a single hyperfine\nlevel, in the presence of an optical lattice. The molecules are individually\ntrapped, in the motional ground state of an optical lattice well, with a\nlifetime of 8 s. For preparation, we start with a zero-temperature atomic\nMott-insulator state with optimized double-site occupancy and efficiently\nassociate weakly-bound dimer molecules on a Feshbach resonance. Despite\nextremely weak Franck-Condon wavefunction overlap, the molecules are\nsubsequently transferred with >50% efficiency to the rovibronic ground state by\na stimulated four-photon process. Our results present a crucial step towards\nthe generation of Bose-Einstein condensates of ground-state molecules and, when\nsuitably generalized to polar heteronuclear molecules such as RbCs, the\nrealization of dipolar many-body quantum-gas phases in periodic potentials."
    },
    {
        "anchor": "Matching universal behavior with potential models: Two-, three-, and four-boson systems are studied close to the unitary limit\nusing potential models constructed to reproduce the minimal information given\nby the two-body scattering length $a$ and the two-body binding energy or\nvirtual state energy $E_2$. The particular path used to reach the unitary limit\nis given by varying the potential strength. In this way the energy spectrum in\nthe three- and four-boson systems is computed. The lowest energy states show\nfinite-range effects absorbed in the construction of level functions that can\nbe used to study real systems. Higher energy levels are free from finite-range\neffects, therefore the corresponding level functions tend to the zero-range\nuniversal function. Using this property a zero-range equation for the\nfour-boson system is proposed and the four-boson universal function is\ncomputed.",
        "positive": "On Many Body System Interactions: We discuss possible relationships between geometric and topological\ninteractions on one side and physical interactions on the other side."
    },
    {
        "anchor": "Quantum quenches and off-equilibrium dynamical transition in the\n  infinite-dimensional Bose-Hubbard model: We study the off-equilibrium dynamics of the infinite dimensional Bose\nHubbard Model after a quantum quench. The dynamics can be analyzed exactly by\nmapping it to an effective Newtonian evolution. For integer filling, we find a\ndynamical transition separating regimes of small and large quantum quenches\nstarting from the superfluid state. This transition is very similar to the one\nfound for the fermionic Hubbard model by mean field approximations.",
        "positive": "Critical velocity in resonantly driven polariton superfluids: We study the necessary condition under which a resonantly driven exciton\npolariton superfluid flowing against an obstacle can generate turbulence. The\nvalue of the critical velocity is well estimated by the transition from\nelliptic to hyperbolic of an operator following ideas developed by Frisch,\nPomeau, Rica for a superfluid flow around an obstacle, though the nature of\nequations governing the polariton superfluid is quite different. We find\nanalytical estimates depending on the pump amplitude and on the pump energy\ndetuning, quite consistent with our numerical computations."
    },
    {
        "anchor": "Theory of inelastic confinement-induced resonances due to the coupling\n  of center-of-mass and relative motion: A detailed study of the anharmonicity-induced resonances caused by the\ncoupling of center-of-mass and relative motion is presented for a system of two\nultracold atoms in single-well potentials. As has been confirmed\nexperimentally, these inelastic confinement-induced resonances are of interest,\nsince they can lead to coherent molecule formation, losses, and heating in\nultracold atomic gases. A perturbative model is introduced to describe the\nresonance positions and the coupling strengths. The validity of the model and\nthe behavior of the resonances for different confinement geometries are\nanalyzed in comparison with exact numerical ab initio calculations. While such\nresonances have so far only been detected for large positive values of the\n$s$-wave scattering length, it is found that they are present also for negative\n$s$-wave scattering lengths, i. e. for attractive interactions. The possibility\nto coherently tune the resonances by a variation of the external confinement\ngeometry might pave the way for coherent molecule association where magnetic\nFeshbach resonances are inaccessible.",
        "positive": "Prethermalization in coupled one-dimensional quantum gases: We consider the problem of the development of steady states in\none-dimensional Bose gas tubes that are weakly coupled to one another through a\ndensity-density interaction. We analyze this development through a Boltzmann\ncollision integral approach. We argue that when the leading order of the\ncollision integral, where single particle-hole excitations are created in\nindividual gases, is dominant, the state of the gas evolves first to a\nnon-thermal fixed point, i.e. a prethermalization plateau. This order is\ndominant when a pair of tubes are inequivalent with, say, different\ntemperatures or different effective interaction parameters, $\\gamma$. We\ncharacterize this non-thermal prethermalization plateau, constructing both the\nquasi-conserved quantities that control the existence of this plateau as well\nas the associated generalized Gibbs ensemble."
    },
    {
        "anchor": "Breakdown of the mean field for dark solitons of dipolar bosons in a\n  one-dimensional harmonic trap: We directly compare the mean-field and the many-body approach in a\none-dimensional Bose system in a harmonic trap. Both contact and dipolar\ninteractions are considered. We propose a multi-atom version of the phase\nimprinting method to generate dark solitons in the system. We begin with a\ngeneral analysis of system dynamics and observe the emergence of a dark soliton\nand a shock wave. Center of mass and soliton motion become decoupled because\nthe shock wave oscillates with the trap frequency and soliton does not. A\ndetailed investigation of frequencies reveals significant differences between\nresults obtained in the mean-field and the many-body pictures.",
        "positive": "Controlling disorder with periodically modulated interactions: We investigate a celebrated problem of one dimensional tight binding model in\nthe presence of disorder leading to Anderson localization from a novel\nperspective. A binary disorder is assumed to be created by immobile heavy\nparticles for the motion of the lighter, mobile species in the limit of no\ninteraction between mobile particles. Fast periodic modulations of interspecies\ninteractions allow us to produce an effective model with small diagonal and\nlarge off-diagonal disorder unexplored in cold atoms experiments. We present an\nexpression for an approximate Anderson localization length and verify the\nexistence of the well known extended resonant mode and analyze the influence of\nnonzero next-nearest neighbor hopping terms. We point out that periodic\nmodulation of interaction allow disorder to work as a tunable band-pass filter\nfor momenta."
    },
    {
        "anchor": "Critical temperature of trapped interacting bosons from large-N based\n  theories: Ultracold atoms provide clues to an important many-body problem regarding the\ndependence of Bose-Einstein condensation (BEC) transition temperature $T_c$ on\ninteractions. However, cold atoms are trapped in harmonic potentials and\ntheoretical evaluations of the $T_c$ shift of trapped interacting Bose gases\nare challenging. While previous predictions of the leading-order shift have\nbeen confirmed, more recent experiments exhibit higher-order corrections beyond\navailable mean-field theories. By implementing two large-N based theories with\nthe local density approximation (LDA), we extract next-order corrections of the\n$T_c$ shift. The leading-order large-N theory produces results quantitatively\ndifferent from the latest experimental data. The leading-order auxiliary field\n(LOAF) theory containing both normal and anomalous density fields captures the\n$T_c$ shift accurately in the weak interaction regime. However, the LOAF theory\nshows incompatible behavior with the LDA and forcing the LDA leads to density\ndiscontinuities in the trap profiles. We present a phenomenological model based\non the LOAF theory, which repairs the incompatibility and provides a prediction\nof the $T_c$ shift in stronger interaction regime.",
        "positive": "Dynamical BCS theory of a two-dimensional attractive Fermi gas:\n  effective interactions from Quantum Monte Carlo calculations: The primary work presented in this paper focuses on the calculation of\ndensity-density dynamical correlations in an attractive two dimensional Fermi\ngas in several physically interesting regimes, including the strongly\ncorrelated BEC-BCS crossover regime. We use state-of-the-art dynamical BCS\ntheory and we address the possibility to renormalize the interaction strength,\nusing unbiased Quantum Monte Carlo results as an asset to validate the\npredictions. We propose that a suitable interplay between dynamical BCS theory,\nwhich is computationally very cheap and yields results directly in real time\ndomain, and Quantum Monte Carlo methods, which are exact but way more demanding\nand limited to imaginary time domain, can be a very promising idea to study\ndynamics in many body systems. We illustrate the idea and provide quantitative\nresults for a few values of the interaction strength in the cold gas."
    },
    {
        "anchor": "Generating scalable entanglement of ultracold bosons in superlattices\n  through resonant shaking: Based on a one-dimensional double-well superlattice with a unit filling of\nultracold atoms per site, we propose a scheme to generate scalable entangled\nstates in the superlattice through resonant lattice shakings. Our scheme\nutilizes periodic lattice modulations to entangle two atoms in each unit cell\nwith respect to their orbital degree of freedom, and the complete atomic system\nin the superlattice becomes a cluster of bipartite entangled atom pairs. To\ndemonstrate this we perform $ab \\ initio$ quantum dynamical simulations using\nthe Multi-Layer Multi-Configuration Time-Dependent Hartree Method for Bosons,\nwhich accounts for all correlations among the atoms. The proposed clusters of\nbipartite entanglements manifest as an essential resource for various quantum\napplications, such as measurement based quantum computation. The lattice\nshaking scheme to generate this cluster possesses advantages such as a high\nscalability, fast processing speed, rich controllability on the target\nentangled states, and accessibility with current experimental techniques.",
        "positive": "Non-equilibrium scale invariance and shortcuts to adiabaticity in a\n  one-dimensional Bose gas: We present experimental evidence for scale invariant behaviour of the\nexcitation spectrum in phase-fluctuating quasi-1d Bose gases after a rapid\nchange of the external trapping potential. Probing density correlations in free\nexpansion, we find that the temperature of an initial thermal state scales with\nthe spatial extension of the cloud as predicted by a model based on adiabatic\nrescaling of initial eigenmodes with conserved quasiparticle occupation\nnumbers. Based on this result, we demonstrate that shortcuts to adiabaticity\nfor the rapid expansion or compression of the gas do not induce additional\nheating."
    },
    {
        "anchor": "Dynamical excitations of one-dimensional Fulde-Ferrell pairing Fermi\n  superfluid: We theoretically investigate a one-dimensional Fulde-Ferrell Fermi superfluid\nat a finite effective Zeeman field $h$, and study entire dynamical excitations\nrelated to density perturbation. By calculating the density dynamic structure\nfactor, we find anisotropic dynamical excitations in both collective modes and\nsingle-particle excitations. Along the direction of centre-of-mass momentum\n$p$, there are two obvious gapless collective modes with different speed. The\nlower collective modes is from the usual gauge symmetry breaking and has a\nlarger speed than the one in the negative direction of $p$. The higher one is\ndue to the direction spontaneous symmetry breaking of centre-of-mass momentum\n$p$, and separates two kinds of single-particle excitations in the positive $p$\ndirection. However, this higher mode disappears in the opposite direction of\n$p$, where two single-particle excitations overlap with each other. These\nsignals of dynamical excitations can do help to distinguish Fulde-Ferrell\nsuperfluid from the conventional Bardeen-Cooper-Schrieffer superfluid in the\nfuture experiment.",
        "positive": "Universality in Four-Boson Systems: We report recent advances on the study of universal weakly bound four-boson\nstates from the solutions of the Faddeev-Yakubovsky equations with zero-range\ntwo-body interactions. In particular, we present the correlation between the\nenergies of successive tetramers between two neighbor Efimov trimers and\ncompare it to recent finite range potential model calculations. We provide\nfurther results on the large momentum structure of the tetramer wave function,\nwhere the four-body scale, introduced in the regularization procedure of the\nbound state equations in momentum space, is clearly manifested. The results we\nare presenting confirm a previous conjecture on a four-body scaling behavior,\nwhich is independent of the three-body one. We show that the correlation\nbetween the positions of two successive resonant four-boson recombination peaks\nare consistent with recent data, as well as with recent calculations close to\nthe unitary limit. Systematic deviations suggest the relevance of range\ncorrections."
    },
    {
        "anchor": "Cavity-induced superconducting and $4k_F$ charge-density-wave states: We propose two experimental setups for fermionic atoms in a high-finesse\noptical resonator in which either a superconducting state with s-wave symmetry\nof the pairs or a 4k F charge density wave can self-organize. In order to\nstabilize the s-wave pairing, a two component attractively in- teracting\nfermionic gas is confined to a one dimensional chain structure by an optical\nlattice. The tunneling of the atoms along the chains is suppressed initially by\nan energy offset between neighbor- ing sites. A Raman transition using the\ncavity mode and a transversal pump laser then reintroduces a cavity-assisted\ntunneling. The feedback mechanism between the cavity field and the atoms leads\nto a spontaneous occupation of the cavity field and of a state of the fermionic\natoms which is dominated by s-wave pairing correlations. Extending the setup to\na quasi-one-dimensional ladder structure where the tunneling of atoms along the\nrungs of the ladder is cavity-assisted, the repul- sively interacting fermionic\natoms self-organize into a 4k F charge density wave. We use adiabatic\nelimination of the cavity field combined with state-of-the-art density matrix\nrenormalization group methods in finite systems in order to identify the steady\nstate phases of the system.",
        "positive": "Effective statistical fringe removal algorithm for high-sensitivity\n  imaging of ultracold atoms: High-sensitivity imaging of ultracold atoms is often challenging when\ninterference patterns are imprinted on the imaging light. Such image noises\nresult in low signal-to-noise ratio and limit the capability to extract subtle\nphysical quantities. Here we demonstrate an advanced fringe removal algorithm\nfor absorption imaging of ultracold atoms, which efficiently suppresses\nunwanted fringe patterns using a small number of sample images without taking\nadditional reference images. The protocol is based on an image decomposition\nand projection method with an extended image basis. We apply this scheme to raw\nabsorption images of degenerate Fermi gases for the measurement of atomic\ndensity fluctuations and temperatures. The quantitative analysis shows that\nimage noises can be efficiently removed with only tens of reference images,\nwhich manifests the efficiency of our protocol. Our algorithm would be of\nparticular interest for the quantum emulation experiments in which several\nphysical parameters need to be scanned within a limited time duration."
    },
    {
        "anchor": "Rotational properties of superfluid Fermi-Bose mixtures in a tight\n  toroidal trap: We consider a mixture of a Bose-Einstein condensate, with a paired Fermi\nsuperfluid, confined in a ring potential. We start with the ground state of the\ntwo clouds, identifying the boundary between the regimes of their phase\nseparation and phase coexistence. We then turn to the rotational response of\nthe system. In the phase-separated regime, we have center of mass excitation.\nWhen the two species coexist, the spectrum has a rich structure, consisting of\ncontinuous and discontinuous phase transitions. Furthermore, for a reasonably\nlarge population imbalance it develops a clear quasi-periodic behaviour, in\naddition to the one due to the periodic boundary conditions. It is then\nfavourable for the one component to reside in a plane-wave state, with a\nhomogeneous density distribution, and the problem resembles that of a\nsingle-component system.",
        "positive": "Nonlinear dynamics of Rydberg-dressed Bose-Einstein condensates in a\n  triple-well potential: We study nonlinear dynamics of Rydberg-dressed Bose-Einstein condensates\n(BECs) trapped in a triple-well potential in the semiclassical limit. The\nRydberg-dressed BECs experience a long-range soft-core interaction, giving rise\nto strong nearest and next-nearest neighbor interactions in the triple-well\nsystem. Using mean-field Gross-Pitaevskii (GP) equations, we show that lower\nbranches of the eigenspectra exhibit loops and level-crossings when the\nsoft-core interaction is strong. The direct level-crossings eliminate the\npossibility of adiabatic Landau-Zener transitions when tilting of the\ntriple-well potential. We demonstrate that the long-range interaction allows\nfor self-trapping in one, two, or three wells, in a far more controllable manor\nthan BECs with short-range or dipolar interactions. Exact quantum simulations\nof the three-well Bose-Hubbard model indicate that self-trapping and\nnonadiabatic transition can be observed with less than a dozen bosons. Our\nstudy is relevant to current research into collective excitation and nonlinear\ndynamics of Rydberg-dressed atoms."
    },
    {
        "anchor": "Black-hole lasing in Bose-Einstein condensates: analysis of the role of\n  the dynamical instabilities in a nonstationary setup: We present a theoretical study on the origin of some findings of recent\nexperiments on sonic analogs of gravitational black holes. We focus on the\nrealization of a black-hole lasing configuration, where the conclusive\nidentification of stimulated Hawking radiation requires dealing with the\nimplications of the nonstationary character of the setup. To isolate the basic\nmechanisms responsible for the observed behavior, we use a toy model where\nnonstationarity can be described in terms of departures from adiabaticity. Our\napproach allows studying which aspects of the characterization of black-hole\nlasing in static models are still present in a dynamical scenario. In\nparticular, variations in the role of the dynamical instabilities can be\ntraced. Arguments to conjecture the twofold origin of the detected\namplification of sound are given: the differential effect of the instabilities\non the mean field and on the quantum fluctuations gives some clues to separate\na deterministic component from self-amplified Hawking radiation. The role of\nclassical noise, present in the experimental setup, is also tackled: we discuss\nthe emergence of differences with the effect of quantum fluctuations when\nvarious unstable modes are relevant to the dynamics.",
        "positive": "Realization of SU(2)*SU(6) Fermi System: We report the realization of a novel degenerate Fermi mixture with an\nSU(2)*SU(6) symmetry in a cold atomic gas. We successfully cool the mixture of\nthe two fermionic isotopes of ytterbium 171Yb with the nuclear spin I=1/2 and\n173Yb with I=5/2 below the Fermi temperature T_ F as 0.46T_F for 171Yb and\n0.54T_F for 173Yb. The same scattering lengths for different spin components\nmake this mixture featured with the novel SU(2)*SU(6) symmetry. The nuclear\nspin components are separately imaged by exploiting an optical Stern-Gerlach\neffect. In addition, the mixture is loaded into a 3D optical lattice to\nimplement the SU(2)*SU(6) Hubbard model. This mixture will open the door to the\nstudy of novel quantum phases such as a spinor Bardeen-Cooper-Schrieffer-like\nfermionic superfluid."
    },
    {
        "anchor": "Few strongly interacting ultracold fermions in one-dimensional traps of\n  different shapes: The ground-state properties of a few spin-1/2 fermions with different masses\nand interacting via short-range contact forces are studied within an exact\ndiagonalization approach. It is shown that, depending on the shape of the\nexternal confinement, different scenarios of the spatial separation between\ncomponents manifested by specific shapes of the density profiles can be\nobtained in the strong interaction limit. We find that the ground-state of the\nsystem undergoes a specific transition between orderings when the confinement\nis changed adiabatically from a uniform box to a harmonic oscillator shape. We\nstudy the properties of this transition in the framework of the finite-size\nscaling method adopted to few-body systems.",
        "positive": "Electrostatic modulation of excitonic fluid in GaN/AlGaN quantum wells\n  by deposition of few-layered graphene and nickel/gold films: Excitons hosted by GaN/(Al,Ga)N quantum wells (QWs) are spatially indirect\ndue to the giant built-in electric field that separates electrons and holes\nalong the growth direction. This electric field, and thus exciton energy, can\nbe reduced by depositing metallic layers on the sample surface. Using\nspatially-resolved micro-photoluminescence spectroscopy we compare the effects\nof two different materials, Nickel/Gold (NiAu) and few-layered graphene (FLG),\non the potential landscape experienced by the excitons. We are able to (i)\ndetermine the potential barriers imposed on QW excitons by deposition of FLG\nand NiAu to be $14$ and $82$~meV, respectively, and (ii) to evidence their\nimpact on the exciton transport at appropriate densities. Optical losses and\ninhomogeneous broadening induced by deposition of NiAu and FLG layers are\nsimilar, and their joined implementation constitute a promising tool for\nelectrostatic modulation of IX densities even in the absence of any applied\nelectric bias."
    },
    {
        "anchor": "Collisions of Ultracold Trapped Cesium Feshbach Molecules: We study collisions in an optically trapped, pure sample of ultracold Cs$_2$\nmolecules in various internal states. The molecular gas is created by Feshbach\nassociation from a near-degenerate atomic gas, with adjustable temperatures in\nthe nanokelvin range. We identify several narrow loss resonances, which point\nto the coupling to more complex molecular states and may be interpreted as\nFeshbach resonances in dimer-dimer interactions. Moreover, in some molecular\nstates we observe a surprising temperature dependence in collisional loss. This\nshows that the situation cannot be understood in terms of the usual simple\nthreshold behavior for inelastic two-body collisions. We interpret this\nobservation as further evidence for a more complex molecular structure beyond\nthe well-understood dimer physics.",
        "positive": "Particle-Localized Ground State of Atom-Molecule Bose-Einstein\n  Condensates in a Double-Well Potential: We study the effect of atom-molecule internal tunneling on the ground state\nof atom-molecule Bose-Einstein condensates in a double-well potential. In the\nabsence of internal tunneling between atomic and molecular states, the ground\nstate is symmetric, which has equal-particle populations in two wells. From the\nlinear stability analysis, we show that the symmetric stationary state becomes\ndynamically unstable at a certain value of the atom-molecule internal tunneling\nstrength. Above the critical value of the internal tunneling strength, the\nground state bifurcates to the particle-localized ground states. The origin of\nthis transition can be attributed to the effective attractive inter-atomic\ninteraction induced by the atom-molecule internal tunneling. This effective\ninteraction is similar to that familiar in the context of BCS-BEC crossover in\na Fermi gas with Feshbach resonance. Furthermore, we point out the possibility\nof reentrant transition in the case of the large detuning between the atomic\nand molecular states."
    },
    {
        "anchor": "Universal Superfluid Transition and Transport Properties of\n  Two-Dimensional Dirty Bosons: We study the phase diagram of two-dimensional, interacting bosons in the\npresence of a correlated disorder in continuous space, using large-scale finite\ntemperature quantum Monte Carlo simulations. We show that the superfluid\ntransition is strongly protected against disorder. It remains of the\nBerezinskii-Kosterlitz-Thouless type up to disorder strengths comparable to the\nchemical potential. Moreover, we study the transport properties in the strong\ndisorder regime where a zero-temperature Bose-glass phase is expected. We show\nthat the conductance exhibits a thermally activated behavior vanishing only at\nzero temperature. Our results point towards the existence of Bose bad-metal\nphase as a precursor of the Bose-glass phase.",
        "positive": "The BHL-BCL crossover: from nonlinear to linear quantum amplification: The black-hole laser (BHL) effect is the self-amplification of Hawking\nradiation between a pair of horizons which act as a resonant cavity. In a\nflowing atomic condensate, the BHL effect arises in a finite supersonic region,\nwhere Bogoliubov-Cherenkov-Landau (BCL) radiation is resonantly excited by any\nstatic perturbation. Thus, experimental attempts to produce a BHL unavoidably\ndeal with the presence of a strong BCL background, making the observation of\nthe BHL effect still a major challenge in the analogue gravity field. Here, we\nperform a theoretical study of the BHL-BCL crossover using an idealized model\nwhere both phenomena can be unambiguously isolated. By drawing an analogy with\nan unstable pendulum, we distinguish three main regimes according to the\ninterplay between quantum fluctuations and classical stimulation: quantum BHL,\nclassical BHL, and BCL. Based on quite general scaling arguments, the nonlinear\namplification of quantum fluctuations up to saturation is identified as the\nmost robust trait of a quantum BHL. A classical BHL behaves instead as a linear\nquantum amplifier, where the output is proportional to the input. The BCL\nregime also acts as a linear quantum amplifier, but its gain is exponentially\nsmaller as compared to a classical BHL. Complementary signatures of black-hole\nlasing are a decrease in the amplification for increasing BCL amplitude or a\nnonmonotonic dependence of the growth rate with respect to the background\nparameters. We also identify interesting analogue phenomena such as\nHawking-stimulated white-hole radiation or quantum BCL-stimulated Hawking\nradiation. The results of this work not only are of interest for analogue\ngravity, where they help to distinguish each phenomenon and to design\nexperimental schemes for a clear observation of the BHL effect, but they also\nopen the prospect of finding applications of analogue concepts in quantum\ntechnologies."
    },
    {
        "anchor": "Berezinskii-Kosterlitz-Thouless phase transition with Rabi-coupled\n  bosons: We theoretically investigate the superfluid-normal-state\nBerezinskii-Kosterlitz-Thouless transition in a binary mixture of bosonic atoms\nwith Rabi coupling under balanced densities. We find the nonmonotonic behavior\nof the transition temperature with respect to the intercomponent coupling and\namplification of the transition temperature for finite values of Rabi coupling,\nbut for small intracomponent couplings. We develop the Nelson-Kosterlitz\nrenormalization-group equations in the two-component Bose mixture and obtain\nthe Nelson-Kosterlitz criterion modified by a fractional parameter, which is\nresponsible for half-integer vortices, and by Rabi coupling. Adopting the\nrenormalization-group approach, we clarify the dependence of the\nBerezinskii-Kosterlitz-Thouless transition temperature on the Rabi coupling and\nthe intercomponent coupling. Analysis of the first and second sound velocities\nalso reveals the suppression of quasicrossing of the two sound modes with a\nfinite Rabi coupling in the low-temperature regime. Our results for a\ntwo-dimensional binary Bose superfluid contribute to the understanding of a\nbroad range of multicomponent quantum systems such as two-dimensional multiband\nsuperconductors.",
        "positive": "Breakdown of the Wiedemann-Franz law in a unitary Fermi gas: We report on coupled heat and particle transport measurements through a\nquantum point contact (QPC) connecting two reservoirs of resonantly\ninteracting, finite temperature Fermi gases. After heating one of them, we\nobserve a particle current flowing from cold to hot. We monitor the temperature\nevolution of the reservoirs and find that the system evolves after an initial\nresponse into a non-equilibrium steady state with finite temperature and\nchemical potential differences across the QPC. In this state any relaxation in\nthe form of heat and particle currents vanishes. From our measurements we\nextract the transport coefficients of the QPC and deduce a Lorenz number\nviolating the Wiedemann-Franz law by one order of magnitude, a characteristic\npersisting even for a wide contact. In contrast, the Seebeck coefficient takes\na value close to that expected for a non-interacting Fermi gas and shows a\nsmooth decrease as the atom density close to the QPC is increased beyond the\nsuperfluid transition. Our work represents a fermionic analog of the fountain\neffect observed with superfluid helium and poses new challenges for microscopic\nmodeling of the finite temperature dynamics of the unitary Fermi gas."
    },
    {
        "anchor": "Spinor Bose-Einstein Condensates of Positronium: Bose-Einstein condensates (BECs) of positronium (Ps) have been of\nexperimental and theoretical interest due to their potential application as the\ngain medium of a $\\gamma$-ray laser. Ps BECs are intrinsically spinor due to\nthe presence of ortho-positronium (o-Ps) and para-positronium (p-Ps), whose\nannihilation lifetimes differ by three orders of magnitude. In this paper, we\nstudy the spinor dynamics and annihilation processes in the p-Ps/o-Ps system\nusing both solutions of the time-dependent Gross-Pitaevskii equations and a\nsemiclassical rate-equation approach. The spinor interactions have an $O(4)$\nsymmetry which is broken to $SO(3)$ by an internal energy difference between\no-Ps and p-Ps. For an initially unpolarized condensate, there is a threshold\ndensity of $\\approx 10^{19}$ cm$^{-3}$ at which spin mixing between o-Ps and\np-Ps occurs. Beyond this threshold, there are unstable spatial modes\naccompanied by spin mixing. To ensure a high production yield above the\ncritical density, a careful choice of external field must be made to avoid the\nspin mixing instability.",
        "positive": "Spin-orbit coupling in the presence of strong atomic correlations: We explore the influence of contact interactions on a synthetically\nspin-orbit coupled system of two ultracold trapped atoms. Even though the\nsystem we consider is bosonic, we show that a regime exists in which the\ncompetition between the contact and spin-orbit interactions results in the\nemergence of a ground state that contains a significant contribution from the\nanti-symmetric spin state. This ground state is unique to few-particle systems\nand does not exist in the mean-field regime. The transition to this state is\nsignalled by an inversion in the average momentum from being dominated by\ncentre-of-mass momentum to relative momentum and also affects the global\nentanglement shared between the real- and pseudo-spin spaces. Indeed,\ncompetition between the interactions can also result in avoided crossings in\nthe groundstate which further enhances these correlations. However, we find\nthat correlations shared between the pseudo-spin states are strongly depressed\ndue to the spin-orbit coupling and therefore the system does not contain\nspin-spin entanglement."
    },
    {
        "anchor": "Coupling vortex dynamics with collective excitations in Bose-Einstein\n  Condensates: Here we analyze the collective excitations as well as the expansion of a\ntrapped Bose-Einstein condensate with a vortex line at its center. To this end,\nwe propose a variational method where the variational parameters have to be\ncarefully chosen in order to produce reliable results. Our variational\ncalculations agree with numerical simulations of the Gross-Pitaevskii equation.\nThe system considered here turns out to exhibit four collective modes of which\nonly three can be observed at a time depending of the trap anisotropy. We also\ndemonstrate that these collective modes can be excited using well established\nexperimental methods such as modulation of the s-wave scattering length.",
        "positive": "Phases, transitions, and patterns in the one-dimensional Extended\n  Bose-Hubbard model: We carry out an extensive study of the phase diagram of the extended Bose\nHubbard model, with a mean filling of one boson per site, in one dimension by\nusing the density matrix renormalization group and show that it can have\nSuperfluid (SF), Mott-insulator (MI), density-wave (DW) and Haldane-insulator\n(HI) phases depending on the precise value of filling and how edge states are\nhandled. We show that the critical exponents and central charge for the HI-DW,\nMI-HI and SF-MI transitions are consistent with those for models in the\ntwo-dimensional Ising, Gaussian, and Berezinskii-Kosterlitz-Thouless (BKT)\nuniversality classes, respectively; and we suggest that the SF-HI transition\nmay be more exotic than a simple BKT transition."
    },
    {
        "anchor": "Atomic Quantum Simulation of Dynamical Gauge Fields coupled to Fermionic\n  Matter: From String Breaking to Evolution after a Quench: Using a Fermi-Bose mixture of ultra-cold atoms in an optical lattice, we\nconstruct a quantum simulator for a U(1) gauge theory coupled to fermionic\nmatter. The construction is based on quantum links which realize continuous\ngauge symmetry with discrete quantum variables. At low energies, quantum link\nmodels with staggered fermions emerge from a Hubbard-type model which can be\nquantum simulated. This allows us to investigate string breaking as well as the\nreal-time evolution after a quench in gauge theories, which are inaccessible to\nclassical simulation methods.",
        "positive": "Enhanced thermalization of exciton-polaritons in optically generated\n  potentials: Equilibrium Bose-Einstein condensation of exciton-polaritons, demonstrated\nwith a long-lifetime microcavity [Phys. Rev. Lett. 118, 016602 (2017)], has\nproven that driven-dissipative systems can undergo thermodynamic phase\ntransitions in the limit where the quasiparticle lifetime exceeds the\nthermalization time. Here, we identify the role of dimensionality and polariton\ninteractions in determining the degree of thermalization in optically generated\ntraps. To distinguish the effect of trapping from interactions and lifetimes,\nwe measured the polariton distribution under four nonresonant Gaussian pumps in\na square geometry and compared it with polariton distributions measured with\neach pump individually. We found that significant redistribution of polaritons\narises by trapping and modification of the density of states. Surprisingly\nefficient polariton-polariton scattering below the condensation threshold is\nevidenced by the depletion of the inflection-point polaritons. Our work\nprovides a deeper understanding of polariton distributions and their\ninteractions under various geometries of optically generated potentials."
    },
    {
        "anchor": "Bose-Hubbard model with random impurities: Multiband and nonlinear\n  hopping effects: We investigate the phase diagrams of theoretical models describing bosonic\natoms in a lattice in the presence of randomly localized impurities. By\nincluding multiband and nonlinear hopping effects we enrich the standard model\ncontaining only the chemical-potential disorder with the site-dependent hopping\nterm. We compare the extension of the MI and the BG phase in both models using\na combination of the local mean-field method and a Hartree-Fock-like procedure,\nas well as, the Gutzwiller-ansatz approach. We show analytical argument for the\npresence of triple points in the phase diagram of the model with\nchemical-potential disorder. These triple points however, cease to exists after\nthe addition of the hopping disorder.",
        "positive": "Phases of a bilayer Fermi gas: We investigate a two-species Fermi gas in which one species is confined in\ntwo parallel layers and interacts with the other species in the\nthree-dimensional space by a tunable short-range interaction. Based on the\ncontrolled weak coupling analysis and the exact three-body calculation, we show\nthat the system has a rich phase diagram in the plane of the effective\nscattering length and the layer separation. Resulting phases include an\ninterlayer s-wave pairing, an intralayer p-wave pairing, a dimer Bose-Einstein\ncondensation, and a Fermi gas of stable Efimov-like trimers. Our system\nprovides a widely applicable scheme to induce long-range interlayer\ncorrelations in ultracold atoms."
    },
    {
        "anchor": "Multimode Organic Polariton Lasing: We present a beyond-mean-field approach to predict the nature of organic\npolariton lasing, accounting for all relevant photon modes in a planar\nmicrocavity. Starting from a microscopic picture, we show how lasing can switch\nbetween polaritonic states resonant with the maximal gain, and those at the\nbottom of the polariton dispersion. We show how the population of non-lasing\nmodes can be found, and by using two-time correlations, we show how the\nphotoluminescence spectrum (of both lasing and non-lasing modes) evolves with\npumping and coupling strength, confirming recent experimental work on the\norigin of blueshift for polariton lasing.",
        "positive": "Stability of the superfluid state in a disordered 1D ultracold fermionic\n  gas: We study a 1D Fermi gas with attractive short range-interactions in a\ndisordered potential by the density matrix renormalization group (DMRG)\ntechnique. This setting can be implemented experimentally by using cold atom\ntechniques. We identify a region of parameters for which disorder enhances the\nsuperfluid state. As disorder is further increased, global superfluidity\neventually breaks down. However this transition occurs before the transition to\nthe insulator state takes place. This suggests the existence of an intermediate\nmetallic `pseudogap' phase characterized by strong pairing but no quasi\nlong-range order."
    },
    {
        "anchor": "Higher first Chern numbers in one dimensional Bose-Fermi mixtures: We propose to use a one-dimensional system consisting of identical fermions\nin a periodically driven lattice immersed in a Bose gas, to realise topological\nsuperfluid phases with Chern numbers larger than 1. The bosons mediate an\nattractive induced interaction between the fermions, and we derive a simple\nformula to analyse the topological properties of the resulting pairing. When\nthe coherence length of the bosons is large compared to the lattice spacing and\nthere is a significant next-nearest neighbour hopping for the fermions, the\nsystem can realise a superfluid with Chern number +/- 2. We show that this\nphase is stable in a large region of the phase diagram as a function of the\nfilling fraction of the fermions and the coherence length of the bosons. Cold\natomic gases offer the possibility to realise the proposed system using\nwell-known experimental techniques.",
        "positive": "Coherent control of phase diffusion in a Bosonic Josephson junction by\n  scattering length modulation: By means of a temporal-periodic modulation of the s-wave scattering length, a\nprocedure to control the evolution of an initial atomic coherent state\nassociated with a Bosonic Josephson junction is presented. The scheme developed\nhas a remarkable advantage of avoiding the quantum collapse of the state due to\nphase and number diffusion. This kind of control could prove useful for atom\ninterferometry using BECs, where the interactions limit the evolution time\nstage within the interferometer, and where the modulation can be induced via\nmagnetic Feshbach resonances as recently experimentally demonstrated."
    },
    {
        "anchor": "Merging Dipolar Supersolids in a Double-Well Potential: We theoretically investigate the merging behaviour of two identical\nsupersolids through dipolar Bose-Einstein condensates confined within a\ndouble-well potential. By adiabatically tuning the barrier height and the\nspacing between the two wells for specific trap aspect ratios, the two\nsupersolids move toward each other and lead to the emergence of a variety of\nground state phases, including a supersolid state, a macrodroplet state, a ring\nstate, and a labyrinth state. We construct a phase diagram that characterizes\nvarious states seen during the merging transition. Further, we calculate the\nforce required to pull the two portions of the gas apart, finding that the\nmerged supersolids act like a deformable plastic material. Our work paves the\nway for future studies of layer structure in dipolar supersolids and the\ninteraction between them in experiments.",
        "positive": "Direct and inverse cascades in turbulent Bose-Einstein condensate: When a Bose-Einstein condensate (BEC) is driven out of equilibrium, density\nwaves interact non-linearly and trigger turbulent cascades. In a turbulent BEC,\nenergy is transferred towards small scales by a direct cascade, whereas the\nnumber of particles displays an inverse cascade toward large scales. In this\nwork, we study analytically and numerically the direct and inverse cascades in\nwave-turbulent BECs. We analytically derive the Kolmogorov-Zakharov spectra,\nincluding the log-correction to the direct cascade scaling and the universal\npre-factor constants for both cascades. We test and corroborate our predictions\nusing high-resolution numerical simulations of the forced-dissipated\nGross-Pitaevskii model in a periodic box and the corresponding wave-kinetic\nequation. Theoretical predictions and data are in excellent agreement, without\nadjustable parameters. Moreover, in order to connect with experiments, we test\nand validate our theoretical predictions using the Gross-Pitaevskii model with\na confining cubic trap. Our results explain previous experimental observations\nand suggest new settings for future studies."
    },
    {
        "anchor": "Efimov physics beyond universality: We provide an exact solution of the Efimov spectrum in ultracold gases within\nthe standard two-channel model for Feshbach resonances. It is shown that the\nfinite range in the Feshbach coupling makes the introduction of an adjustable\nthree-body parameter obsolete. The solution explains the empirical relation\nbetween the scattering length a_- where the first Efimov state appears at the\natom threshold and the van der Waals length l_vdw for open channel dominated\nresonances. There is a continuous crossover to the closed channel dominated\nlimit, where the scale in the energy level diagram as a function of the inverse\nscattering length 1/a is set by the intrinsic length r* associated with the\nFeshbach coupling. Our results provide a number of predictions for\nnon-universal ratios between energies and scattering lengths that can be tested\nin future experiments.",
        "positive": "Hidden long-range order in a spin-orbit coupled two-dimensional Bose gas: A spin-orbit coupled two-dimensional (2D) Bose gas is shown to simultaneously\npossess quasi and true long-range order in the total and relative phase\nsectors, respectively. The total phase undergoes a Berenzinskii-\nKosterlitz-Thouless transition to a low temperature phase with quasi long-range\norder, as expected for a two- dimensional quantum gas. Additionally, the\nrelative phase undergoes an Ising-type transition building up true long-range\norder, which is induced by the anisotropic spin-orbit coupling. Based on the\nBogoliubov approach, expressions for the total- and relative-phase fluctuations\nare derived analytically for the low temperature regime. Numerical simulations\nof the stochastic projected Gross-Pitaevskii equation (SPGPE) give a good\nagreement with the analytical predictions."
    },
    {
        "anchor": "An all-coupling theory for the Fr\u00f6hlich polaron: The Fr\\\"ohlich model describes the interaction of a mobile impurity with a\nsurrounding bath of phonons which leads to the formation of a quasiparticle,\nthe polaron. In this article an efficient renormalization group approach is\npresented which provides a description of Fr\\\"ohlich polarons in all regimes\nranging from weak- to strong coupling. We apply the method to the Bose polaron\nproblem of an ultracold impurity atom interacting with a background gas that is\nBose-condensed. The extended renormalization group approach introduced here is\ncapable to predict ground state properties for arbitrarily small impurity\nmasses. This allows us to obtain the full phase diagram of the corresponding\nBogoliubov-Fr\\\"ohlich Hamiltonian, characterized by two dimensionless coupling\nconstants. Our method is benchmarked by comparison of the ground state energy\nto recent diagrammatic quantum Monte Carlo calculations.",
        "positive": "Emergence of crystalline steady state in a driven superfluid: The spontaneous emergence of structures from initially homogenous systems\nbelongs to the most striking topics in natural science. Systems driven into\ndeeply nonlinear regimes are theoretically difficult to describe and can\nproduce states that do not exist in equilibrium. We observe the emergence of a\nstable square lattice density modulation from an initially homogenous,\ntwo-dimensional, radially symmetric Bose-Einstein condensate when periodically\ndriving the two-particle interaction. We show theoretically that this state can\nbe understood as an attractive fixed point of coupled nonlinear amplitude\nequations, which result from phonon-phonon interactions. As a self-stabilized\nstate characterized by spontaneously broken translational symmetry, our results\nestablish a novel quantum material related to supersolids."
    },
    {
        "anchor": "Geometry and non-adiabatic response in quantum and classical systems: In these lecture notes, partly based on a course taught at the Karpacz Winter\nSchool in March 2014, we explore the close connections between non-adiabatic\nresponse of a system with respect to macroscopic parameters and the geometry of\nquantum and classical states. We center our discussion around adiabatic gauge\npotentials, which are the generators of unitary basis transformations in\nquantum systems and generators of special canonical transformations in\nclassical systems. In quantum systems, eigenstate expectation values of these\npotentials are the Berry connections and the covariance matrix of these gauge\npotentials is the geometric tensor, whose antisymmetric part defines the Berry\ncurvature and whose symmetric part is the Fubini-Study metric tensor. In\nclassical systems one simply replaces the eigenstate expectation value by an\naverage over the micro-canonical shell. For complicated interacting systems, we\nshow that a variational principle may be used to derive approximate gauge\npotentials. We then express the non-adiabatic response of the physical\nobservables of the system through these gauge potentials, specifically\ndemonstrating the close connection of the geometric tensor to the notions of\nLorentz force and renormalized mass. We highlight applications of this\nformalism to deriving counter-diabatic (dissipationless) driving protocols in\nvarious systems, as well as to finding equations of motion for slow macroscopic\nparameters coupled to fast microscopic degrees of freedom that go beyond\nmacroscopic Hamiltonian dynamics. Finally, we illustrate these ideas with a\nnumber of simple examples and highlight a few more complicated ones drawn from\nrecent literature.",
        "positive": "Impurity-induced pairing in two-dimensional Fermi gases: We study induced pairing between two identical fermions mediated by an\nattractively interacting quantum impurity in two-dimensional systems. Based on\na Stochastic Variational Method (SVM), we investigate the influence of\nconfinement and finite interaction range effects on the mass ratio beyond which\nthe ground state of the quantum three-body problem undergoes a transition from\na composite bosonic trimer to an unbound dimer-fermion state. We find that\nconfinement as well as a finite interaction range can greatly enhance trimer\nstability, bringing it within reach of experimental implementations such as\nfound in ultracold atom systems. In the context of solid-state physics, our\nsolution of the confined three-body problem shows that exciton-mediated\ninteractions can become so dominant that they can even overcome detrimental\nCoulomb repulsion between electrons in atomically-thin semiconductors. Our work\nthus paves the way towards a universal understanding of boson-induced pairing\nacross various fermionic systems at finite density, and opens perspectives\ntowards realizing novel forms of electron pairing beyond the conventional\nparadigm of Cooper pair formation."
    },
    {
        "anchor": "Topological Bogoliubov excitations in inversion-symmetric systems of\n  interacting bosons: On top of the mean-field analysis of a Bose-Einstein condensate, one\ntypically applies the Bogoliubov theory to analyze quantum fluctuations of the\nexcited modes. Therefore, one has to diagonalize the Bogoliubov Hamiltonian in\na symplectic manner. In our article we investigate the topology of these\nBogoliubov excitations in inversion-invariant systems of interacting bosons. We\nanalyze how the condensate influences the topology of the Bogoliubov\nexcitations. Analogously to the fermionic case, here we establish a symplectic\nextension of the polarization characterizing the topology of the Bogoliubov\nexcitations and link it to the eigenvalues of the inversion operator at the\ninversion-invariant momenta. We also demonstrate an instructive but\nexperimentally feasible example that this quantity is also related to edge\nstates in the excitation spectrum.",
        "positive": "Thomas-Fermi von Weizs\u00e4cker theory for a harmonically trapped,\n  two-dimensional, spin-polarized dipolar Fermi gas: We systematically develop a density functional description for the\nequilibrium properties of a two-dimensional, harmonically trapped,\nspin-polarized dipolar Fermi gas based on the Thomas-Fermi von Weizs\\\"acker\napproximation. We pay particular attention to the construction of the\ntwo-dimensional kinetic energy functional, where corrections beyond the local\ndensity approximation must be motivated with care. We also present an intuitive\nderivation of the interaction energy functional associated with the dipolar\ninteractions, and provide physical insight into why it can be represented as a\nlocal functional. Finally, a simple, and highly efficient self-consistent\nnumerical procedure is developed to determine the equilibrium density of the\nsystem for a range of dipole interaction strengths."
    },
    {
        "anchor": "Quenching to unitarity: Quantum dynamics in a 3D Bose gas: We study the dynamics of a dilute Bose gas at zero temperature following a\nsudden quench of the scattering length from a noninteracting Bose condensate to\nunitarity (infinite scattering length). We apply three complementary approaches\nto understand the momentum distribution and loss rates. First, using a\ntime-dependent variational ansatz for the many-body state, we calculate the\ndynamics of the momentum distribution. Second, we demonstrate that, at short\ntimes and large momenta compared to those set by the density, the physics can\nbe well understood within a simple, analytic two-body model. We derive a\nquantitative prediction for the evolution of Tan's contact, which increases\nlinearly at short times. We also study the three-body losses at finite\ndensities. Consistent with experiments, we observe lifetimes which are long\ncompared to the dynamics of large momentum modes.",
        "positive": "Spin-orbit coupling induced quantum droplet in ultracold Bose-Fermi\n  mixtures: Quantum droplets have intrigued much attention recently in view of their\nsuccessful observations in the ultracold homonuclear atoms. In this work, we\ndemonstrate a new mechanism for the formation of quantum droplet in\nheteronuclear atomic systems, i.e., by applying the synthetic spin-orbit\ncoupling(SOC). Take the Bose-Fermi mixture for example, we show that by\nimposing a Rashba SOC between the spin states of fermions, the greatly\nsuppressed Fermi pressure can enable the formation of Bose-Fermi droplets even\nfor very weak boson-fermion attractions, which are insufficient to bound a\ndroplet if without SOC. In such SOC-induced quantum droplets, the boson/fermion\ndensity ratio universally depends on the SOC strength, and they occur in the\nmean-field collapsing regime but with a negative fluctuation energy, distinct\nfrom the interaction-induced droplets found in literature. The accessibility of\nthese Bose-Fermi droplets in ultracold Cs-Li and Rb-K mixtures is also\ndiscussed. Our results shed light on the droplet formation in a vast class of\nheteronuclear atomic systems through the manipulation of single-particle\nphysics."
    },
    {
        "anchor": "Theory of superfluidity and drag force in the one-dimensional Bose gas: The one-dimensional Bose gas is an unusual superfluid. In contrast to higher\nspatial dimensions, the existence of non-classical rotational inertia is not\ndirectly linked to the dissipationless motion of infinitesimal impurities.\nRecently, experimental tests with ultracold atoms have begun and quantitative\npredictions for the drag force experienced by moving obstacles have become\navailable. This topical review discusses the drag force obtained from linear\nresponse theory in relation to Landau's criterion of superfluidity. Based upon\nimproved analytical and numerical understanding of the dynamical structure\nfactor, results for different obstacle potentials are obtained, including\nsingle impurities, optical lattices and random potentials generated from\nspeckle patterns. The dynamical breakdown of superfluidity in random potentials\nis discussed in relation to Anderson localization and the predicted\nsuperfluid-insulator transition in these systems.",
        "positive": "Non-adiabatic breaking of topological pumping: We study Thouless pumping out of the adiabatic limit. Our findings show that\ndespite its topological nature, this phenomenon is not {generically} robust to\nnon-adiabatic effects. Indeed we find that the Floquet diagonal ensemble value\nof the pumped charge shows a deviation from the topologically quantized limit\nwhich is quadratic in the driving frequency {for a sudden switch-on of the\ndriving}. This is reflected also in the charge pumped in a single period, which\nshows a non-analytic behaviour on top of an overall quadratic decrease.\nExponentially small corrections are recovered only with a careful tailoring of\nthe driving protocol. We also discuss thermal effects and the experimental\nfeasibility of observing such a deviation."
    },
    {
        "anchor": "Dipolar dark solitons: We numerically generate, and then study the basic properties of dark\nsoliton-like excitations in a dipolar gas confined in a quasi one dimensional\ntrap. These excitations, although very similar to dark solitons in a gas with\ncontact interaction, interact with each other and can form bound states. During\ncollisions these dipolar solitons emit phonons, loosing energy, but\naccelerating. Even after thousands of subsequent collisions they survive as\ngray solitons and finally reach dynamical equilibrium with background\nquasiparticles. Finally, in the frame of classical field approximation, we\nverified, that these solitons appear spontaneously in thermal samples,\nanalogously to the type II excitations in a gas of atoms with contact\ninteraction.",
        "positive": "Reentrant supersolidity: A \"supersolid\" -- a crystal that exhibits an off-diagonal long-range order\nand a superflow -- has been a subject of much research since its first proposal\n[Andreev and Lifshitz 1969], but has not been realized as a ground state of\nshort-range interacting bosons in a continuum. In this note I point out a\nsimple and generic mechanism for a thermally-driven reentrant supersolidity,\nand discuss challenges of experimental realization of this idea. In the limit\nof bosons in a periodic potential, this mechanism reduces to a {\\em reentrant}\nlow-temperature normal-superfluid transition, that should be accessible to\nsimulations and in current experiments on bosonic atoms in an optical periodic\npotential."
    },
    {
        "anchor": "Supersolid-like solitons in spin-orbit coupled spin-2 condensate: We study supersolid-like crystalline structures emerging in the stationary\nstates of a quasi-two-dimensional spin-orbit (SO)-coupled spin-2 condensate in\nthe ferromagnetic, cyclic, and antiferro-magnetic phases by solving a\nmean-field model.Interplay of different strengths of SO coupling and\ninteratomic interactions gives rise to a variety of non-trivial density\npatterns in the emergent solutions. For small SO-coupling strengths $\\gamma$\n($\\gamma \\approx 0.5$), the ground state is an axisymmetric multi-ring soliton\nfor polar, cyclic and weakly-ferromagnetic interactions, whereas for\nstronger-ferromagnetic interactions a circularly-asymmetric soliton emerges as\nthe ground state.Depending on the values of interaction parameters, with an\nincrease in SO-coupling strength, a stripe phase may also emerge as the ground\nstate for polar and cyclic interactions. For intermediate values of SO-coupling\nstrength ($\\gamma \\approx 1$), in addition to these solitons, one could have a\nquasi-degenerate triangular-lattice soliton in all magnetic phases. On further\nincreasing the SO-coupling strength ($\\gamma \\gtrapprox 4$), a square-lattice\nand a superstripe soliton emerge as quasi-degenerate states. The emergence of\nall these solitons can be inferred from a study of solutions of the\nsingle-particle Hamiltonian.",
        "positive": "Observation of dynamical topology in 1D: Nontrivial topology in lattices is characterized by invariants--such as the\nZak phase for one dimensional (1D) lattices--derived from wave functions\ncovering the Brillouin zone. We realized the 1D bipartite Rice-Mele (RM)\nlattice using ultracold $^{87}$Rb and focus on lattice configurations\npossessing various combinations of chiral, time-reversal and particle-hole\nsymmetries. We quenched between configurations and used a form of quantum state\ntomography, enabled by diabatically tuning lattice parameters, to directly\nfollow the time evolution of the Zak phase as well as a chiral winding number.\nThe Zak phase evolves continuously; however, when chiral symmetry transiently\nappears in the out-of-equilibrium system, the chiral winding number is well\ndefined and can take on different integer values. When quenching between two\nconfigurations obeying all three symmetries the Zak phase is time independent;\nwe confirm the contrasting prediction of [M. McGinley and N. R.Cooper, PRL 121\n090401 (2018)] that chiral symmetry is periodically restored, at which times\nthe winding number changes by $\\pm 2$, yielding values that are not present in\nthe native RM Hamiltonian."
    },
    {
        "anchor": "Quenching through Dirac and semi-Dirac points in optical Lattices:\n  Kibble-Zurek scaling for anisotropic Quantum-Critical systems: We propose that Kibble-Zurek scaling can be studied in optical lattices by\ncreating geometries that support, Dirac, Semi-Dirac and Quadratic Band\nCrossings. On a Honeycomb lattice with fermions, as a staggered on-site\npotential is varied through zero, the system crosses the gapless Dirac points,\nand we show that the density of defects created scales as $1/\\tau$, where\n$\\tau$ is the inverse rate of change of the potential, in agreement with the\nKibble-Zurek relation. We generalize the result for a passage through a\nsemi-Dirac point in $d$ dimensions, in which spectrum is linear in $m$ parallel\ndirections and quadratic in rest of the perpendicular $(d-m)$ directions. We\nfind that the defect density is given by $ 1\n/{\\tau^{m\\nu_{||}z_{||}+(d-m)\\nu_{\\perp}z_{\\perp}}}$ where $\\nu_{||}, z_{||}$\nand $\\nu_{\\perp},z_{\\perp}$ are the dynamical exponents and the correlation\nlength exponents along the parallel and perpendicular directions, respectively.\nThe scaling relations are also generalized to the case of non-linear quenching.",
        "positive": "Atom-Number Enhancement by Shielding Atoms from Losses in Strontium\n  Magneto-Optical Traps: We present a scheme to enhance the atom number in magneto-optical traps of\nstrontium atoms operating on the 461 nm transition. This scheme consists of\nresonantly driving the $^1$S$_0\\to^3$P$_1$ intercombination line at 689 nm,\nwhich continuously populates a short-lived reservoir state and, as expected\nfrom a theoretical model, partially shields the atomic cloud from losses\narising in the 461 nm cooling cycle. We show a factor of two enhancement in the\natom number for the bosonic isotopes $^{88}$Sr and $^{84}$Sr, and the fermionic\nisotope $^{87}$Sr, in good agreement with our model. Our scheme can be applied\nin the majority of strontium experiments without increasing the experimental\ncomplexity of the apparatus, since the employed 689 nm transition is commonly\nused for further cooling. Our method should thus be beneficial to a broad range\nof quantum science and technology applications exploiting cold strontium atoms,\nand could be extended to other atomic species."
    },
    {
        "anchor": "Sound, superfluidity and layer compressibility in a ring dipolar\n  supersolid: We propose a protocol to excite the Goldstone modes of a supersolid dipolar\nBose-Einstein condensed gas confined in a ring geometry. By abruptly removing\nan applied periodic modulation proportional to cos($\\varphi$), where $\\varphi$\nis the azimuthal angle, we explore the resulting oscillations of the gas, by\nsolving the extended Gross-Pitaevskii equation. The value of the two\nlongitudinal sound velocities exhibited in the supersolid phase are analyzed\nusing the hydrodynamic theory of supersolids at zero temperature. This approach\nallows for the determination of the layer compressibility modulus as well as of\nthe superfluid fraction $f_S$, in agreement with the Leggett estimate of the\nnon-classical moment of inertia.",
        "positive": "Exploring Quantum Phases of Dipolar Gases through Quasicrystalline\n  Confinement: The effects of frustration on extended supersolid states is a largely\nunexplored subject in the realm of cold-atom systems. In this work, we explore\nthe impact of quasicrystalline lattices on the supersolid phases of dipolar\nbosons. Our findings reveal that weak quasicrystalline lattices can induce a\nvariety of modulated phases, merging the inherent solid pattern with a\nquasiperiodic decoration induced by the external potential. As the lattice\nbecomes stronger, we observe a super quasicrystal phase and a Bose glass phase.\nOur results, supported by a detailed discussion on experimental feasibility\nusing dysprosium atoms and quasicrystalline optical lattice potentials, open a\nnew avenue in the exploration of long-range interacting quantum systems in\naperiodic environments. We provide a solid foundation for future experimental\ninvestigations, potentially confirming our theoretical predictions and\ncontributing profoundly to the field of quantum gases in complex external\npotentials."
    },
    {
        "anchor": "Anomalous Hall Effects of Light and Chiral Edge Modes on the Kagome\n  Lattice: We theoretically investigate a photonic Kagome lattice which can be realized\nin microwave cavity arrays using current technology. The Kagome lattice\nexhibits an exotic band structure with three bands one of which can be made\ncompletely flat. The presence of artificial gauge fields allows to emulate\ntopological phases and induce chiral edge modes which can coexist inside the\nenergy gap with the flat band that is topologically trivial. By tuning the\nartificial fluxes or in the presence of disorder, the flat band can also\nacquire a bandwidth in energy allowing the coexistence between chiral edge\nmodes and bulk extended states; in this case the chiral modes become fragile\ntowards scattering into the bulk. The photonic system then exhibits equivalents\nof both a quantum Hall effect without Landau levels, and an anomalous Hall\neffect characterized by a non-quantized Chern number. We discuss experimental\nobservables such as local density of states and edge currents. We show how\nsynthetic uniform magnetic fields can be engineered, which allows an\nexperimental probe of Landau levels in the photonic Kagome lattice. We then\ndraw on semiclassical Boltzmann equations for transport to devise a method to\nmeasure Berry's phases around loops in the Brillouin zone. The method is based\nsolely on wavepacket interference and can be used to determine band Chern\nnumbers or the photonic equivalent of the anomalous Hall response. We\ndemonstrate the robustness of these measurements towards on-site and\ngauge-field disorder. We also show the stability of the anomalous quantum Hall\nphase for nonlinear cavities and for (artificial) atom-photon interactions.",
        "positive": "The anisotropic Harper-Hofstadter-Mott model: competition between\n  condensation and magnetic fields: We derive the reciprocal cluster mean-field method to study the\nstrongly-interacting bosonic Harper-Hofstadter-Mott model. The system exhibits\na rich phase diagram featuring band insulating, striped superfluid, and\nsupersolid phases. Furthermore, for finite hopping anisotropy we observe\ngapless uncondensed liquid phases at integer fillings, which are analyzed by\nexact diagonalization. The liquid phases at fillings 1 and 3 exhibit the same\nband fillings as the fermionic integer quantum Hall effect, while the phase at\nfilling 2 is CT-symmetric with zero charge response. We discuss how these\nphases become gapped on a quasi-one-dimensional cylinder, leading to a\nquantized Hall response, which we characterize by introducing a suitable\nmeasure for non-trivial many-body topological properties. Incompressible\nmetastable states at fractional filling are also observed, indicating competing\nfractional quantum Hall phases. The combination of reciprocal cluster\nmean-field and exact diagonalization yields a promising method to analyze the\nproperties of bosonic lattice systems with non-trivial unit cells in the\nthermodynamic limit."
    },
    {
        "anchor": "Strongly correlated Fermi superfluid near an orbital Feshbach resonance:\n  Stability, equation of state and Leggett mode: We theoretically study the superfluid phase of a strongly correlated\n$^{173}$Yb Fermi gas near its orbital Feshbach resonance, by developing a\nquantitative pair-fluctuation theory within a two-band model. We examine the\ndensity excitation spectrum of the system and determine a stability phase\ndiagram. We find that the $^{173}$Yb Fermi gas is intrinsically metastable and\nhas a peculiar equation of state, due to the small but positive singlet\nscattering length. The massive Leggett mode, arising from the fluctuation of\nthe relative phase of two order parameters, is severely damped. We discuss the\nparameter space where an undamped Leggett mode may exist.",
        "positive": "Superadiabatic generation of cat states in bosonic Josephson junctions\n  under particle losses: We investigate a superadiabatic scheme to produce a cat state in a bosonic\nJosephson junction in absence and presence of particle losses. The generation\nscheme is based on shortcuts to adiabaticity and strongly relies on the parity\nconservation. The parity conservation also ensures that the produced state is a\nsuperposition of cat states with various sizes, i.e., a \"cats state\". Parity is\nalso the quantity to be measured in order to utilize the produced state in\ninterferometry. The generation scheme still works even if a number of particle\nlosses during generation are substantial."
    },
    {
        "anchor": "Spin-orbit coupled depairing of a dipolar biexciton superfluid: We consider quantum phase transitions in a system of bright dipolar excitons\nwhich can form bound pairs (dipolar biexcitons). We assume a narrow resonance\nin the interaction of excitons with opposite spins. At sufficiently large\ndensity a resonant exciton superfluid transforms into a superfluid of\nbiexcitons. The transition may be either of the first or the second kind. The\naverage relative momenta of excitons in the pairs being beyond the light cone,\nthe transition should be accompanied by reduction of the photoluminescence\nintensity. Effective magnetic fields due to the long-range exchange splitting\nof non-radiative exciton states induce broadening of the biexciton resonance.\nThe fields shift the position of the gap in the elementary excitation spectrum\nto a circle of degenerate minima in the k-space. Closing the new gap defines a\nsecond order phase transition into a mixture of counter-propagating plane-wave\nexcitonic condensates polarized linearly in the direction perpendicular to\ntheir wavevectors. In the resonance energy vs density phase diagram the novel\nphase intervenes between the dark biexciton and radiative exciton superfluids.\nWe conclude that formation of a BCS-like biexciton condensate induces\ncorrelated alignment of the effective magnetic fields and excitonic spins. We\noutline important differences of the emergent mechanism from the phenomenon of\nspin-orbit (SO) coupled Bose-Einstein condensation. We expect existence of\nanalogous mechanisms in SO-coupled fermionic superfluids and superconductors.",
        "positive": "Anisotropic collisions of dipolar Bose-Einstein condensates in the\n  universal regime: We report the measurement of collisions between two Bose-Einstein condensates\nwith strong dipolar interactions. The collision velocity is significantly\nlarger than the internal velocity distribution widths of the individual\ncondensates, and thus, with the condensates being sufficiently dilute, a halo\ncorresponding to the two-body differential scattering cross section is\nobserved. The results demonstrate a novel regime of quantum scattering,\nrelevant to dipolar interactions, in which a large number of angular momentum\nstates become coupled during the collision. We perform Monte-Carlo simulations\nto provide a detailed comparison between theoretical two-body cross sections\nand the experimental observations."
    },
    {
        "anchor": "Production of a highly degenerate Fermi gas of metastable helium-3 atoms: We report on the achievement of quantum degeneracy in both components of a\nBose-Fermi mixture of metastable helium atoms, $^4$He* and $^3$He*. Degeneracy\nis achieved via Doppler cooling and forced evaporation for $^4$He*, and\nsympathetically cooling $^3$He* with $^4$He*. We discuss our simplified\nimplementation, along with the high versatility of our system. This technique\nis able to produce a degenerate Fermi gas with a minimum reduced temperature of\n$T/T_F=0.14(1)$, consisting of $2.5 \\times 10^4$ $^3$He* atoms. Due to the high\ninternal energy of both isotopes single atom detection is possible, opening the\npossibility of a large number of experiments into Bose-Fermi mixtures.",
        "positive": "A kinetic equation for spin polarized Fermi systems: This paper a kinetic Boltzmann equation having a general type of collision\nkernel and modelling spin-dependent Fermi gases at low temperatures modelled by\na kinetic equation of Boltzmann type. The distribution functions have values in\nthe space of positive hermitean 2x2 complex matrices. Global existence of\nbounded weak solutions is proved in L1 to the initial value problem in a\nperiodic box."
    },
    {
        "anchor": "R\u00e9nyi generalization of the operational entanglement entropy: Operationally accessible entanglement in bipartite systems of\nindistinguishable particles could be reduced due to restrictions on the allowed\nlocal operations as a result of particle number conservation. In order to\nquantify this effect, Wiseman and Vaccaro [Phys. Rev. Lett. 91, 097902 (2003)]\nintroduced an operational measure of the von Neumann entanglement entropy.\nMotivated by advances in measuring R\\'enyi entropies in quantum many-body\nsystems subject to conservation laws, we derive a generalization of the\noperational entanglement that is both computationally and experimentally\naccessible. Using the Widom theorem, we investigate its scaling with the size\nof a spatial subregion for free fermions and find a logarithmically violated\narea law scaling, similar to the spatial entanglement entropy, with at most, a\ndouble-log leading-order correction. A modification of the correlation matrix\nmethod confirms our findings in systems of up to $10^5$ particles.",
        "positive": "An Effective Series Expansion to the Equation of State of Unitary Fermi\n  Gases: Using universal properties and a basic statistical mechanical approach, we\npropose a general equation of state for unitary Fermi gases. The universal\nequation of state is written as a series solution to a self consistent integral\nequation where the general solution is a linear combination of Fermi functions.\nFirst, by truncating our series solution to four terms with already known exact\ntheoretical inputs at limiting cases, namely the first \\emph{three} virial\ncoefficients and using the Bertsch parameter as a free parameter, we find a\ngood agreement with experimental measurements in the entire temperature region\nin the normal state. This analytical equation of state agrees with experimental\ndata up to the fugacity $z = 18$, which is a vast improvement over the other\nanalytical equations of state available where the agreements is \\emph{only} up\nto $z \\approx 7$. Second, by truncating our series solution to four terms again\nusing first \\emph{four} virial coefficients, we find the Bertsch parameter $\\xi\n=0.35$, which is in good agreement with the direct experimental measurement of\n$\\xi =0.37$. This second form of equation of state shows a good agreement with\nself-consistent T-matrix calculations in the normal phase."
    },
    {
        "anchor": "Stability and stabilization of unstable condensates: It is possible to condense a macroscopic number of bosons into a single mode.\nAdding interactions the question arises whether the condensate is stable. For\nrepulsive interaction the answer is positive with regard to the ground-state,\nbut what about a condensation in an excited mode? We discuss some results that\nhave been obtained for a 2-mode bosonic Josephson junction, and for a 3-mode\nminimal-model of a superfluid circuit. Additionally we mention the possibility\nto stabilize an unstable condensate by introducing periodic or noisy driving\ninto the system: this is due to the Kapitza and the Zeno effects.",
        "positive": "Quasiparticle scattering rate in a strongly polarised Fermi mixture: We analyse the scattering rate of an impurity atom in a Fermi sea as a\nfunction of momentum and temperature in the BCS-BEC crossover. The cross\nsection is calculated using a microscopic multichannel theory for the Feshbach\nresonance scattering, including finite range and medium effects. We show that\npair correlations significantly increase the cross section for strong\ninteractions close to the unitarity regime. These pair correlations give rise\nto a molecule pole of the cross section at negative energy on the BEC side of\nthe resonance, which smoothly evolves into a resonance at positive scattering\nenergy with a non-zero imaginary part on the BCS side. The resonance is the\nanalogue of superfluid pairing for the corresponding population balanced\nsystem. Using Fermi liquid theory, we then show that the low temperature\nscattering rate of the impurity atom is significantly increased due to these\npair correlations for low momenta. We demonstrate that finite range and mass\nimbalance effects are significant for the experimentally relevant\n$^6$Li-$^{40}$K mixture, and we finally discuss how the scattering rate can be\nmeasured using radio-frequency spectroscopy and Bose-Fermi mixtures."
    },
    {
        "anchor": "The Emergency of Pico-Kelvin Physics: The frontier of low-temperature physics has advanced to the mid pico-Kelvin\n(pK) regime but progress has come to a halt because of the problem of gravity.\nUltra cold atoms must be confined in some type of potential energy well: if the\ndepth of the well is less than the energy an atom gains by falling through it,\nthe atom escapes. This article reviews ultra cold atom research, emphasizing\nthe advances that carried the low temperature frontier to 450 pico-Kelvin. We\nreview micro gravity methods for overcoming the gravitation limit to achieve\nfurther low temperature using free fall techniques such as a drop tower,\nsounding rocket, parabolic flight plane and the Space Station. We describe two\ntechniques that give promise of further advance--an atom chip and an\nall-optical trap--and present recent experimental results. Basic research in\nnew regimes of observation has generally led to scientific discoveries and new\ntechnologies that benefit society. We expect this to be the case as the low\ntemperature frontier advances and we propose some new opportunities for\nresearch.",
        "positive": "Effective action approach to the p-band Mott insulator and superfluid\n  transition: Motivated by the recent experiment on p-orbital band bosons in optical\nlattices, we study theoretically the quantum phases of Mott insulator and\nsuperfluidity in two-dimensions. The system features a novel superfluid phase\nwith transversely staggered orbital current at weak interaction, and a Mott\ninsulator phase with antiferro-orbital order at strong coupling and\ncommensurate filling. We go beyond mean field theory and derive from a\nmicroscopic model an effective action that is capable of describing both the\np-band Mott insulating and superfluid phases in strong coupling. We further\ncalculate the excitation spectra near the quantum critical point and find two\ngapless modes away from the tip of the Mott lobe but four gapless modes at the\ntip. Our effective theory reveals how the phase coherence peak builds up in the\nMott regime when approaching the critical point. We also discuss the finite\ntemperature phase transition of p-band superfluidity."
    },
    {
        "anchor": "Perfect screening of the inter-polaronic interaction: We consider heavy particles immersed in a Fermi sea of light fermions, and\nstudy the interaction between the heavy particles induced by the surrounding\nlight fermions. With the Born-Oppenheimer method, we analytically show that the\ninduced interaction between N heavy particles vanishes for any N in the limit\nof high light-fermion density. The induced interaction vanishes even in the\nunitarity regime. This suggests that the formation of N-body bound states\nassociated with the Efimov effect is suppressed in the presence of the dense\nFermi sea. We ascribe the vanishing induced interaction to the screening effect\nin the neutral Fermi system.",
        "positive": "Long-lived non-thermal states in pumped one-dimensional systems of\n  hard-core bosons: We study a unitary time evolution of a symmetry-broken state in a form of a\ncharge density wave in a finite system of interacting hard-core bosons, which\ncan be mapped onto the XXZ Heisenberg chain. Moreover, we introduce a\nspatially-homogenous and time-dependent vector potential that mimics a short\nlaser pulse. We establish the range of amplitudes of the vector potential for\nwhich the onset of charge density wave order can be controlled. We propose a\nprotocol that reveals non-thermal long-lived states, which are characterized by\na non-zero charge density wave order translated by one lattice site with\nrespect to its initial formation. The life times of these states are large in\ncomparison to all typical times given by the parameters of the system. They\nincrease with the number of lattice sites, but are significantly suppressed by\nthe integrablility breaking perturbations. In view of these findings, we\nspeculate that the long-lived non-thermal states exist in the thermodynamic\nlimit."
    },
    {
        "anchor": "Oscillatory pairing of fermions in spin-split traps: As a means of realizing oscillatory pairing between fermions, we study\nsuperfluid pairing between two fermion \"spin\" species that are confined to\nadjustable spin-dependent trapping potentials. Focusing on the one-dimensional\nlimit, we find that with increasing separation between the spin-dependent traps\nthe fermions exhibit distinct phases, including a fully paired phase, a\nspin-imbalanced phase with oscillatory pairing, and an unpaired fully\nspin-polarized phase. We obtain the phase diagram of fermions in such a\nspin-split trap and discuss signatures of these phases in cold-atom\nexperiments.",
        "positive": "Ultralong-range order in the Fermi-Hubbard model with long-range\n  interactions: We use the dual boson approach to reveal the phase diagram of the\nFermi-Hubbard model with long-range dipole-dipole interactions. By using a\nlarge-scale finite-temperature calculation on a $64 \\times 64$ square lattice\nwe demonstrate the existence of a novel phase, possessing an `ultralong-range'\norder. The fingerprint of this phase -- the density correlation function --\nfeatures a non-trivial behavior on a scale of tens of the lattice sites. We\nstudy the properties and the stability of the ultralong-range ordered phase,\nand show that it is accessible in modern experiments with ultracold polar\nmolecules and magnetic atoms."
    },
    {
        "anchor": "Loading of atoms into an optical trap with high initial phase-space\n  density: We report a method for loading cold atoms into an optical trap with high\ninitial phase-space density (PSD). When the trap beam is overlapped with atoms\nin optical molasses of optimized parameters including large cooling beam\ndetuning compared with conventional detuning used for a magneto-optical trap\n(MOT), more than $3 \\times 10^6$ rubidium atoms with an initial temperature\nless than 20 $\\mu$K are loaded into a single beam trap. The obtained maximum\ninitial PSD is estimated to be $1.1 \\times 10^{-3}$, which is one or two orders\nof magnitude greater than that achieved with the conventional loading into an\noptical trap from atoms in a MOT. The proposed method is promising for creating\na quantum gas with a large number of atoms in a short evaporation time.",
        "positive": "Nonlinear modes in binary bosonic condensates with the\n  pseudo-spin-orbital coupling: We consider a binary Bose-Einstein condensate (BEC) with nonlinear repulsive\ninteractions and linear spin-orbit (SO) and Zeeman-splitting couplings. In the\npresence of the trapping harmonic-oscillator (HO) potential, we report the\nexistence of even, odd, and asymmetric spatial modes. They feature alternating\ndomains with opposite directions of the pseudo-spin, i.e., anti-ferromagnetic\nstructures, which is explained by the interplay of the linear couplings, HO\nconfinement, and repulsive self-interaction. The number of the domains is\ndetermined by the strength of the SO coupling. The modes are constructed\nanalytically in the weakly nonlinear system. The dynamical stability of the\nmodes is investigated by means of the Bogoliubov-de Gennes equations and direct\nsimulations. A notable result is that the multi-domain-wall (DW) structures are\nstable, alternating between odd and even shapes, while the simplest single-DW\nstructure is unstable. Thus, the system features a transition to the complex\nground states under the action of the SO coupling. The addition of the Zeeman\nsplitting transforms the odd modes into asymmetric ones via spontaneous\nsymmetry breaking. The results suggest possibilities for switching the binary\nsystem between states with opposite (pseudo) magnetization by external fields,\nand realization of similar stable states and dynamical effects in solid-state\nand nonlinear-optical settings emulated by the SO-coupled BECs."
    },
    {
        "anchor": "Phase diagrams of Bose-Hubbard model and antiferromagnetic spin-1/2\n  models on a honeycomb lattice: Motivated by the recent experimental realization of the Haldane model by\nultracold fermions in an optical lattice, we investigate phase diagrams of the\nhard-core Bose-Hubbard model on a honeycomb lattice. This model is closely\nrelated with a spin-1/2 antiferromagnetic (AF) quantum spin model.\nNearest-neighbor (NN) hopping amplitude is positive and it prefers an AF\nconfigurations of phases of Bose-Einstein condensates. On the other hand, an\namplitude of the next-NN hopping depends on an angle variable as in the Haldane\nmodel. Phase diagrams are obtained by means of an extended path-integral\nMonte-Carlo simulations. Besides the AF state, a 120$^o$-order state, there\nappear other phases including a Bose metal in which no long-range orders exist.",
        "positive": "In situ observation of chemistry in Rydberg molecules within a coherent\n  solvent: We often infer the state of systems in nature indirectly, for example in high\nenergy physics by recording the tracks particles leave behind in an ambient\nmedium. We adapt this principle to energies 9 orders of magnitude smaller, to\nclassify the final state of exotic molecules after internal conversion of their\nelectronic state, through their interaction with an ambient quantum fluid, a\nBose-Einstein condensate. The BEC is the ground-state of a million bosonic\natoms near zero temperature, and a single embedded ultra-long range Rydberg\nmolecule can coherently excite waves in this fluid, which carry tell-tale\nsignatures of its dynamics. Bond lengths exceeding a micrometer allow us to\nobserve the molecular fingerprint on the BEC in situ, via optical microscopy.\nInterpreting images in comparison with simulations shows that the molecular\nelectronic state rapidly converts from the initially excited S- and D-orbitals\nto a much more complex molecular state (called \"trilobite\"), marked by a\nmaximally localized electron. This internal conversion liberates energy, such\nthat one expects final state particles to move rapidly through the medium,\nwhich is however ruled out by comparing experiment and simulations. The\nmolecule thus must strongly decelerate in the medium, for which we propose a\nplausible mechanism. Our experiment demonstrates a coherent medium that\nfacilitates and records an electronic state change of embedded exotic molecules\nin ultra-cold chemistry, with sufficient sensitivity to constrain velocities of\nfinal state particles."
    },
    {
        "anchor": "Tunnel-coupled optical microtraps for ultracold atoms: Arrays of individual atoms trapped in optical microtraps with\nmicrometer-scale sizes have emerged as a fundamental, versatile, and powerful\nplatform for quantum sciences and technologies. This platform enables the\nbottom-up engineering of quantum systems, offering the capability of\nlow-entropy preparation of quantum states with flexible geometry, as well as\nmanipulation and detection at the single-site level. The utilization of\nultracold itinerant atoms with tunnel coupling in optical microtraps provides\nnew opportunities for quantum simulation, enabling the exploration of exotic\nquantum states, phases, and dynamics, which would otherwise be challenging to\nachieve in conventional optical lattices due to high entropy and limited\ngeometric flexibility. Here the development of tunnel-coupled optical\nmicrotraps for the manipulation of ultracold atomic quantum systems and its\nrecent advances are briefly reviewed.",
        "positive": "Phase-separated vortex-lattice in a rotating binary Bose-Einstein\n  condensate: We study circularly-symmetric phase separation of vortex lattices in a\nrapidly rotating harmonically-trapped quasi--two-dimensional binary\nBose-Einstein condensate (BEC) by introducing a weak quartic trap in one of the\ncomponents. The increase of the rotational frequency in such a system is also\nfound to generate a phase separation of the vortex lattices of an overlapping\nnon-rotating BEC. The phase-separated vortex lattices have different structures\nfor a binary BEC with inter-species repulsion and inter-species attraction. In\nthe former case of a fully repulsive binary BEC the phase separation of the\nvortex-lattices is accompanied by a complete phase separation of component\ndensities. In the latter case of inter-species attraction there is a partial\nphase separation of component densities, although there could be a complete\nphase separation of the generated vortex lattices in the two components. In the\ncase of inter-species attraction, we need to have different intra-species\nrepulsion in the two components for an efficient phase separation. We compare\nand contrast our results with the phase separation obtained in a\nharmonically-trapped binary BEC without any quartic trap."
    },
    {
        "anchor": "Spin dynamics of cold fermions with synthetic spin-orbit coupling: We consider spin relaxation dynamics in cold Fermi gases with a pure-gauge\nspin-orbit coupling corresponding to recent experiments. We show that such\nexperiments can give a direct access to the collisional spin drag rate, and\nestablish conditions for the observation of spin drag effects. In the recent\nexperiments the dynamics is found to be mainly ballistic leading to new regimes\nof reversible spin relaxation-like processes.",
        "positive": "Topological defect dynamics of vortex lattices in Bose--Einstein\n  condensates: Vortex lattices in rapidly rotating Bose--Einstein condensates are systems of\ntopological excitations that arrange themselves into periodic patterns. Here we\nshow how phase-imprinting techniques can be used to create a controllable\nnumber of defects in these lattices and examine the resulting dynamics. Even\nthough we describe our system using the mean-field Gross--Pitaevskii theory,\nthe full range of many particle effects among the vortices can be studied. In\nparticular we find the existence of localized vacancies that are quasi-stable\nover long periods of time, and characterize the effects on the background\nlattice through use of the orientational correlation function, and Delaunay\ntriangulation."
    },
    {
        "anchor": "Superfluid weight and Berezinskii-Kosterlitz-Thouless temperature of\n  spin-imbalanced and spin-orbit-coupled Fulde-Ferrell phases in lattice\n  systems: We study the superfluid weight $D^s$ and Berezinskii-Kosterlitz-Thouless\n(BKT) transition temperatures $T_{BKT}$ in case of exotic Fulde-Ferrell (FF)\nsuperfluid states in lattice systems. We consider spin-imbalanced systems with\nand without spin-orbit coupling (SOC) accompanied with in-plane Zeeman field.\nBy applying mean-field theory, we derive general equations for $D^s$ and\n$T_{BKT}$ in the presence of SOC and the Zeeman fields for 2D Fermi-Hubbard\nlattice models, and apply our results to a 2D square lattice. We show that\nconventional spin-imbalanced FF states without SOC can be observed at finite\ntemperatures and that FF phases are further stabilized against thermal\nfluctuations by introducing SOC. We also propose how topologically non-trivial\nSOC-induced FF phases could be identified experimentally by studying the total\ndensity profiles. Furthermore, the relative behavior of transverse and\nlongitudinal superfluid weight components and the role of the geometric\nsuperfluid contribution are discussed.",
        "positive": "Beliaev theory of spinor Bose-Einstein condensates: By generalizing the Green's function approach proposed by Beliaev [1, 2], we\ninvestigate the effect of quantum depletion on the energy spectra of elementary\nexcitations in an F = 1 spinor Bose-Einstein condensate, in particular, of 87Rb\natoms in an external magnetic field. We find that quantum depletion increases\nthe effective mass of magnons in the spin-wave excitations with quadratic\ndispersion relations. The enhancement factor turns out to be the same for both\nferromagnetic and polar phases, and also independent of the magnitude of the\nexternal magnetic field. The lifetime of these magnons in a 87Rb spinor BEC is\nshown to be much longer than that of phonons. We propose an experimental setup\nto measure the effective mass of these magnons in a spinor Bose gas by\nexploiting the effect of a nonlinear dispersion relation on the spatial\nexpansion of a wave packet of transverse magnetization. This type of\nmeasurement has practical applications, for example, in precision magnetometry."
    },
    {
        "anchor": "Boundary central charge from bulk odd viscosity - chiral superfluids: We derive a low energy effective field theory for chiral superfluids, which\naccounts for both spontaneous symmetry breaking and fermionic ground-state\ntopology. Using the theory, we show that the odd (or Hall) viscosity tensor, at\nsmall wave-vector, contains a dependence on the chiral central charge $c$ of\nthe boundary degrees of freedom, as well as additional non-universal\ncontributions. We identify related bulk observables which allow for a bulk\nmeasurement of $c$. In Galilean invariant superfluids, only the particle\ncurrent and density responses to strain and electromagnetic fields are\nrequired. To complement our results, the effective theory is benchmarked\nagainst a perturbative computation within a canonical microscopic model.",
        "positive": "Sudden quench of harmonically trapped mass-imbalanced fermions: Dynamical properties of two-component mass-imbalanced few-fermion systems\nconfined in a one-dimensional harmonic trap following a sudden quench of\ninteractions are studied. It is assumed that initially the system is prepared\nin the non-interacting ground state and then, after a sudden quench of\ninteractions, the unitary evolution is governed by interacting many-body\nHamiltonian. By careful analysis of the evolution of the Loschmidt echo,\ndensity distributions of the components, and entanglement entropy between them,\nthe role of mass imbalance and particle number imbalance on the system's\nevolution stability are investigated. All the quantities studied manifest a\ndramatic dependence on the number of heavy and lighter fermions in each\ncomponent at a given quench strength. The results may have implications for\nupcoming experiments on fermionic mixtures with a well-defined and small number\nof particles."
    },
    {
        "anchor": "Temperature-dependent excitation spectra of ultra-cold bosons in optical\n  lattices: Trapping ultra-cold atoms in optical lattices provides a unique environment\nfor investigating quantum phase transitions between strongly correlated\nsuperfluid and Mott insulator phases. One of the major complications in the\nanalysis of experiments is establishing of criteria for identifying the\nsuperfluid phase. Sharp features occurring while entering ordered state have\nbeen recognized as a signature of superfluidity. In the present work it is\nshown that sharp peaks are not necessarily a reliable diagnostic of phase\ncoherence in these systems. Using the combined Bogoliubov method and the\nquantum rotor approach for phase variables, we calculate the momentum and\nenergy-resolved single-particle spectral function $A(\\mathbf{k}\\omega)$ at\narbitrary temperature $T$ and its shape in the presence of the superfluid\nphase. We find that in the two-dimensional system even at $T>0$, where\ncondensate fraction vanishes, the remnants of the sharp coherence peak in\n$A(\\mathbf{k}\\omega)$ are present. In contrast, such a feature is not observed\nfor the bosons loaded in the three-dimensional lattice.",
        "positive": "Symmetry breaking in the collisions of double channel BEC solitons: We investigate an attractive Bose-Einstein condensate in two coupled one\ndimensional channels. In this system a stable double channel soliton can be\nformed. It is symmetric for small interaction parameters and asymmetric for\nlarge ones. We study this symmetry breaking phenomenon in detail. Next, we\ninvestigate the dynamics of symmetric double channel soliton collisions. For\nsufficiently strong interactions we observe spontaneous symmetry breaking\nduring the collision. Approximate considerations based on two different\nmethods, Bogoliubov and variational, are used to describe this effect. The\nresults are compatible."
    },
    {
        "anchor": "Undamped Rabi oscillations due to polaron-emitter hybrid states in\n  non-linear photonic wave guide coupled to emitters: The collective dynamics of two non-interacting two-level emitters, which are\ncoupled to a structured wave guide that supports two-photon bound states, is\ninvestigated. Tuning the energy of the two emitters such that they are in\nresonance with the two-photon bound state energy band, we identify parameter\nregimes where the system displays fractional populations and essentially\nundamped Rabi oscillations. The Rabi oscillations, which have no analog in the\nsingle-emitter dynamics, are attributed to the existence of a collective\npolaron-like photonic state that is induced by the emitter-photon coupling. The\nfull dynamics is reproduced by a two-state model, in which the photonic polaron\ninteracts with the state $|e,e,\\text{vac} \\rangle$ (two emitters in their\nexcited state and empty wave guide) through a Rabi coupling frequency that\ndepends on the emitter separation. Our work demonstrates that emitter-photon\ncoupling can lead to an all-to-all momentum space interaction between\ntwo-photon bound states and tunable non-Markovian dynamics, opening up a new\ndirection for emitter arrays coupled to a waveguide.",
        "positive": "Emergent Phases in an Extended Bose-Hubbard Model with Three-body\n  On-site Interaction: We study the Extended Bose-Hubbard Model with a three-body onsite\ninteraction. Using an exact diagonalization method and a variational Matrix\nProduct States algorithm, \\emph{Alps mps-optim}, we compute and analyse the\nenergy charge gap and finite system correlation functions to obtain the phase\nboundaries and determine the phases and phase transitions of the model. For\n\\mbox{$\\frac{V}{U} = 0.6$} and \\mbox{$\\frac{W}{U} = 0$}, we observed the\nemergence of the Haldane insulator (HI) phase at the tip of the \\mbox{$\\rho =\n1$} charge density wave (CDW) lobe and for \\mbox{$\\frac{V}{U} = 0.6$} and\n\\mbox{$\\frac{W}{U} = 1$}, we observed the emergence of the supersolid (SS)\nphase at the tip of the \\mbox{$\\rho = 1/2$} charge density wave (CDW) lobe. We\nalso noticed that the effect of the inclusion of both the three-body onsite and\nnearest neighbor interactions on the phase diagram of the model for filling\nfactor \\mbox{$\\rho = 2$} is to stabilize the Mott insulator (MI) phase such\nthat the system remains in the MI phase for all values of $\\frac{V}{U}$."
    },
    {
        "anchor": "Many-body effects in a Bose-Fermi mixture: We investigate many-body effects on a mixture of interacting bosons and\nfermions loaded in an optical lattice using a generalized dynamical mean field\ntheory combined with the numerical renormalization group. We show that strong\ncorrelation effects emerge in the presence of bosonic superfluidity, leading to\na renormalized peak structure near the Fermi level in the density of states for\nfermions. Remarkably, this kind of strong renormalization appears not only in\nthe metallic phase but also in the insulating phases of fermions such as in the\nempty/filled band limit. A systematic analysis of the relation between the\nquasiparticle weight and the strength of superfluidity reveals that the\nrenormalization effect is indeed caused by the boson degrees of freedom. It is\nfound that such renormalization is also relevant to a supersolid phase\nconsisting of a density wave ordering of fermions accompanied by bosonic\nsuperfluidity. This sheds light on the origin of the peak structure in the\nsupersolid phase.",
        "positive": "Polaritons for testing the universality of an impurity in a\n  Bose-Einstein condensate: Universality is a fundamental concept in physics that allows for the\ndescription of properties of systems that are independent of microscopic\ndetails. In this work, we show that polaritons in a Bose-Einstein condensate\n(BEC) are a suitable platform to probe in a non-demolition way the universal\nhigh-energy spectrum of an impurity strongly coupled to a BEC. Based on a field\ntheory that includes the two-body correlations at the exact level we\ndemonstrate that under appropriate conditions, the damping rate of slow-light\npropagation reveals the high-energy universal tail in the polaron spectrum."
    },
    {
        "anchor": "Discrete Time Quasi-Crystals: Between space crystals and amorphous materials there exists a third class of\naperiodic structures which lack translational symmetry but reveal long-range\norder. They are dubbed quasi-crystals and their formation, similarly as the\nformation of space crystals, is related to spontaneous breaking of\ntranslational symmetry of underlying Hamiltonians. Here, we investigate\nspontaneous emergence of quasi-crystals in periodically driven systems. We\nconsider a quantum many-body system which is driven by a harmonically\noscillating force and show that interactions between particles result in\nspontaneous self-reorganization of the motion of a quantum many-body system and\nin the formation of a quasi-crystal structure in time.",
        "positive": "Collective dynamical Fermi suppression of optically-induced inelastic\n  scattering: We observe strong dynamical suppression of optically-induced loss in a weakly\ninteracting Fermi gas as the $s$-wave scattering length is increased. The\nsingle, cigar-shaped cloud behaves as a large spin lattice in energy space with\na tunable Heisenberg Hamiltonian. The loss suppression occurs as the lattice\ntransitions into a magnetized state, where the fermionic nature of the atoms\ninhibits interactions. The data are quantitatively explained by incorporating\nspin-dependent loss into a quasi-classical collective spin vector model, the\nsuccess of which enables the application of optical control of effective\nlong-range interactions to this system."
    },
    {
        "anchor": "Recombination in the universal four-fermion system: In the systems of spin $\\frac12$ fermions with resonant $S$-wave interactions\nsupporting only weakly bound dimers the antisymmetry forbids recombination of\nthree (or more) fermions at zero energy. However, the fermion-fermion-dimer\nrecombination is only partially suppressed. It is studied in the framework of\nmomentum-space integral equations for the four-particle transition operators.\nIn the vicinity of the unitary limit the fermion-fermion-dimer recombination\nrate, rescaled to build dimensionless quantity, is found to be linear in the\neffective range parameter, enabling a simple and accurate parametrization as\nwell as evaluation of finite-range effects for any potential model. This\nfeature makes the present results very useful in benchmarking different methods\nfor three-cluster breakup and recombination calculations in four-particle\nsystems. The interplay of the three-fermion and fermion-fermion-dimer\nrecombination processes and their consequences for ultracold mixtures of\nfermions and dimers is discussed.",
        "positive": "Confinement-induced p-wave resonances from s-wave interactions: We show that a purely s-wave interaction in three dimensions (3D) can induce\nhigher partial-wave resonances in mixed dimensions. We develop two-body\nscattering theories in all three cases of 0D-3D, 1D-3D, and 2D-3D mixtures and\ndetermine the positions of higher partial-wave resonances in terms of the 3D\ns-wave scattering length assuming a harmonic confinement potential. We also\ncompute the low-energy scattering parameters in the p-wave channel (scattering\nvolume and effective momentum) that are necessary for the low-energy effective\ntheory of the p-wave resonance. We point out that some of the resonances\nobserved in the Florence group experiment [Phys. Rev. Lett. 104, 153202 (2010)]\ncan be interpreted as the p-wave resonances in the 2D-3D mixed dimensions. Our\nstudy paves the way for a variety of physics, such as Anderson localization of\nmatter waves under p-wave resonant scatterers."
    },
    {
        "anchor": "Dissipative hydrodynamic equation of a ferromagnetic Bose-Einstein\n  condensate: Analogy to magnetization dynamics in conducting ferromagnets: The hydrodynamic equation of a spinor Bose-Einstein condensate (BEC) gives a\nsimple description of spin dynamics in the condensate. We introduce the\nhydrodynamic equation of a ferromagnetic BEC with dissipation originating from\nthe energy dissipation of the condensate. The dissipative hydrodynamic equation\nhas the same form as an extended Landau-Lifshitz-Gilbert (LLG) equation, which\ndescribes the magnetization dynamics of ferromagnets interacting with\nspin-polarized currents. Employing the dissipative hydrodynamic equation, we\ndemonstrate the magnetic domain pattern dynamics of a ferromagnetic BEC in the\npresence and absence of a current of particles, and discuss the effects of the\ncurrent on domain pattern formation. We also discuss the characteristic lengths\nof domain patterns that have domain walls with and without finite\nmagnetization.",
        "positive": "Critical behavior of an impurity at the boson superfluid-Mott insulator\n  transition: We present a universal theory for the critical behavior of an impurity at the\ntwo-dimensional superfluid-Mott insulator transition. Our analysis is motivated\nby a numerical study of the Bose-Hubbard model with an impurity site by Huang\net al. (Phys. Rev. B 94, 220502 (2016)), who found an impurity phase transition\nas a function of the trapping potential. The bulk theory is described by the\n$O(2)$ symmetric Wilson-Fisher conformal field theory, and we model the\nimpurity by a localized spin-1/2 degree of freedom. We also consider a\ngeneralized model by considering an $O(N)$ symmetric bulk theory coupled to a\nspin-$S$ degree of freedom. We study this field theory using the $\\epsilon = 3\n- d$ expansion, where the impurity-bulk interaction flows to an infrared stable\nfixed point at the critical trapping potential. We determine the scaling\ndimensions of the impurity degree of freedom and the associated critical\nexponents near the critical point. We also determine the universal contribution\nof the impurity to the finite temperature compressibility of the system at\ncriticality. Our results are compared with recent numerical simulations."
    },
    {
        "anchor": "Soliton-induced Majorana fermions in a one-dimensional atomic\n  topological superfluid: We theoretically investigate the behavior of dark solitons in a\none-dimensional spin-orbit coupled atomic Fermi gas in harmonic traps, by\nsolving self-consistently the Bogoliubov-de Gennes equations. The dark soliton\n- to be created by phase-imprinting in future experiments - is characterized by\na real order parameter, which changes sign at a point node and hosts localized\nAndreev bound states near the node. By considering both cases of a single\nsoliton and of multiple solitons, we find that the energy of these bound states\ndecreases to zero, when the system is tuned to enter the topological superfluid\nphase by increasing an external Zeeman field. As a result, two Majorana\nfermions emerge in the vicinity of each soliton, in addition to the well-known\nMajorana fermions at the trap edges associated with the nontrivial topology of\nthe superfluid. We propose that the soliton-induced Majorana fermions can be\ndirectly observed by using spatially-resolved radio-frequency spectroscopy or\nindirectly probed by measuring the density profile at the point node. For the\nlatter, the deep minimum in the density profile will disappear due to the\noccupation of the soliton-induced zero-energy Majorana fermion modes. Our\nprediction could be tested in a resonantly-interacting spin-orbit coupled\n$^{40}$K Fermi gas confined in a two-dimensional optical lattice.",
        "positive": "Observation of superradiance in a phase fluctuating dipolar\n  Bose-Einstein condensate: Despite the extensive study of matter-wave superradiance in a Bose-Einstein\ncondensate (BEC) using its unique coherence property, the controllability of\nsuperradiant process has remained limited in the previous studies exploiting a\nphase-coherent condensate with isotropic contact interactions. Here, we combine\ntunable s-wave scattering with dipolar interactions in a BEC of $^{168}$Er\natoms wherein the asymmetry and threshold of superradiance are independently\ncontrolled. By changing the s-wave scattering length near the Feshbach\nresonance, we tune the superradiance threshold with increasing phase\nfluctuations. In contrast to collective light scattering from a condensate only\nwith contact interactions, we observe an asymmetric superradiant peak in a\ndipolar BEC by changing the direction of external magnetic field. This results\nfrom the anisotropic excitation spectrum induced by the dipole-dipole\ninteraction. Our observation is expected to bring forth unprecedented\napplication of matter-wave optics leading to controlled emission of matter\nwave."
    },
    {
        "anchor": "Breathing mode in two-dimensional binary self-bound Bose gas droplets: In this work, we present the study of the stationary structures and the\nbreathing mode behavior of a two-dimensional self-bound binary Bose droplet. We\nemploy an analytical approach using a variational ansatz with a super-Gaussian\ntrial order parameter and compare it with the numerical solutions of the\nextended Gross-Pitaevskii equation. We find that the super-Gaussian is superior\nto the often used Gaussian ansatz in describing the stationary and dynamical\nproperties of the system. We find that for sufficiently large non-rotating\ndroplets the breathing mode is energetically favourable compared to the\nself-evaporating process. For small self-bound systems our results differ based\non the ansatz. Inducing angular momentum by imprinting multiply quantized\nvortices at the droplet center, this preference for the breathing mode persists\nindependent of the norm.",
        "positive": "Scattering in Mixed Dimensions with Ultracold Gases: We experimentally investigate the mix-dimensional scattering occurring when\nthe collisional partners live in different dimensions. We employ a binary\nmixture of ultracold atoms and exploit a species-selective 1D optical lattice\nto confine only one atomic species in 2D. By applying an external magnetic\nfield in proximity of a Feshbach resonance, we adjust the free-space scattering\nlength to observe a series of resonances in mixed dimensions. By monitoring\n3-body inelastic losses, we measure the magnetic field values corresponding to\nthe mix-dimensional scattering resonances and find a good agreement with the\ntheoretical predictions based on simple energy considerations."
    },
    {
        "anchor": "Rydberg dressing: Understanding of collective many-body effects and\n  implications for experiments: The strong interaction between Rydberg atoms can be used to control the\nstrength and character of the interatomic interaction in ultracold gases by\nweakly dressing the atoms with a Rydberg state. Elaborate theoretical proposals\nfor the realization of various complex phases and applications in quantum\nsimulation exist. Also a simple model has been already developed that describes\nthe basic idea of Rydberg dressing in a two-atom basis. However, an\nexperimental realization has been elusive so far. We present a model describing\nthe ground state of a Bose-Einstein condensate dressed with a Rydberg level\nbased on the Rydberg blockade. This approach provides an intuitive\nunderstanding of the transition from pure twobody interaction to a regime of\ncollective interactions. Furthermore it enables us to calculate the deformation\nof a three-dimensional sample under realistic experimental conditions in\nmean-field approximation. We compare full three-dimensional numerical\ncalculations of the ground state to an analytic expression obtained within\nThomas-Fermi approximation. Finally we discuss limitations and problems arising\nin an experimental realization of Rydberg dressing based on our experimental\nresults. Our work enables the reader to straight forwardly estimate the\nexperimental feasibility of Rydberg dressing in realistic three-dimensional\natomic samples.",
        "positive": "Phase-separated Ferromagnetism in Spin-imbalanced Fermi Atoms Loaded on\n  an Optical Ladder: a DMRG study: We consider repulsively-interacting cold fermionic atoms loaded on an optical\nladder lattice in a trapping potential. The density-matrix\nrenormalization-group method is used to numerically calculate the ground state\nfor systematically varied values of interaction U and spin imbalance p in the\nHubbard model on the ladder. The system exhibits rich structures, where a fully\nspin polarized phase, spatially separated from other domains in the trapping\npotential, appears for large enough U and p. The phase-separated ferromagnetism\ncan be captured as a real-space image of the energy gap between the\nferromagnetic and other states arising from a combined effect of Nagaoka's\nferromagnetism extended to the ladder and the density dependence of the energy\nseparation between competing states. We also predict how to maximize the\nferromagnetic region."
    },
    {
        "anchor": "Quantum Field Theory for the Three-Body Constrained Lattice Bose Gas --\n  Part I: Formal Developments: We develop a quantum field theoretical framework to analytically study the\nthree-body constrained Bose-Hubbard model beyond mean field and non-interacting\nspin wave approximations. It is based on an exact mapping of the constrained\nmodel to a theory with two coupled bosonic degrees of freedom with polynomial\ninteractions, which have a natural interpretation as single particles and\ntwo-particle states. The procedure can be seen as a proper quantization of the\nGutzwiller mean field theory. The theory is conveniently evaluated in the\nframework of the quantum effective action, for which the usual symmetry\nprinciples are now supplemented with a ``constraint principle'' operative on\nshort distances. We test the theory via investigation of scattering properties\nof few particles in the limit of vanishing density, and we address the\ncomplementary problem in the limit of maximum filling, where the low lying\nexcitations are holes and di-holes on top of the constraint induced insulator.\nThis is the first of a sequence of two papers. The application of the formalism\nto the many-body problem, which can be realized with atoms in optical lattices\nwith strong three-body loss, is performed in a related work [14].",
        "positive": "Squeezing oscillations in a multimode bosonic Josephson junction: Quantum simulators built from ultracold atoms promise to study quantum\nphenomena in interacting many-body systems. However, it remains a challenge to\nexperimentally prepare strongly correlated continuous systems such that the\nproperties are dominated by quantum fluctuations. Here, we show how to enhance\nthe quantum correlations in a one-dimensional multimode bosonic Josephson\njunction, which is a quantum simulator of the sine-Gordon field theory. Our\napproach is based on the ability to track the non-equilibrium dynamics of\nquantum properties. After creating a bosonic Josephson junction at the stable\nfixed point of the classical phase space, we observe squeezing oscillations in\nthe two conjugate variables. We show that the squeezing oscillation frequency\ncan be tuned by more than one order of magnitude, and we are able to achieve a\nspin squeezing close to 10 dB by utilising these oscillatory dynamics. The\nimpact of improved spin squeezing is directly revealed by detecting enhanced\nspatial phase correlations between decoupled condensates. Our work provides new\nways for engineering correlations and entanglement in the external degree of\nfreedom of interacting many-body systems."
    },
    {
        "anchor": "Loading ultracold atoms onto nonlinear Bloch states and soliton states\n  in bichromatic lattices: We simulate and analyze an experimental method of loading interacting\nultracold atoms onto nontrivial quantum states such as nonlinear Bloch wave and\nsoliton solutions in a 1-dimensional bichromatic lattice. Of standard bands,\ninverted bands, and bands with Dirac-like points permitted by a bichromatic\nlattice, we consider the case of an inverted band and examine the loading\nprocess in terms of nonlinear Bloch waves formed by an aggregate of ultracold\natoms described by the mean-field model. Specifically, we solved the\nGross-Pitaevskii equation numerically and found an appropriate standing\nwave-pulse sequence for the inverted band, which sequence proved to be a\nsuitable protocol for producing soliton solutions. In addition, we examined the\neffect of an external potential and dynamical instabilities for the\npost-loading process. We also provide an appropriate data set for future\nexperimental realization of our findings.",
        "positive": "Measurement of Chern numbers through center-of-mass responses: Probing the center-of-mass of an ultracold atomic cloud can be used to\nmeasure Chern numbers, the topological invariants underlying the quantum Hall\neffects. In this work, we show how such center-of-mass observables can have a\nmuch richer dependence on topological invariants than previously discussed. In\nfact, the response of the center of mass depends not only on the current\ndensity, typically measured in a solid-state system, but also on the particle\ndensity, which itself can be sensitive to the topology of the band structure.\nWe apply a semiclassical approach, supported by numerical simulations, to\nhighlight the key differences between center-of-mass responses and more\nstandard conductivity measurements. We illustrate this by analyzing both the\ntwo- and the four-dimensional quantum Hall effects. These results have\nimportant implications for experiments in engineered topological systems, such\nas ultracold gases and photonics."
    },
    {
        "anchor": "Mixture of two unequally charged superfluids in a magnetic field: The artificial magnetic fields engineered for ultra cold gases depend on the\ninternal structure of the neutral atoms. Therefore the components of a mixture\ncomposed of two atomic gases can exhibit a different response to an artificial\nmagnetic field. Such a mixture can be interpreted as a mixture of two atomic\ngases, carrying different synthetic charges. In this article, we consider such\nmixtures of two superfluids with unequal synthetic charges in a ring trap\nsubject to a uniform artificial magnetic field. The charge imbalance in such a\nmixture changes the distribution of excited particles over angular momentum\nstates compared to that of an equally charged mixture. This microscopic\ndifference exhibits macroscopic consequences; such as the occurrence of an\nangular momentum transfer between two unequally charged components. Due to the\ninter-fluid atomic interactions in a ring, the angular momentum transfer can\ncreate a counter flowing persistent current in the weakly charged superfluid.\nEven in the limiting case of a charged and an uncharged superfluid mixture, a\npersistent current can be induced in the uncharged superfluid, despite the fact\nthat it is not directly coupled to the magnetic field. The stability analysis\nshows that the induction depends on the interplay between inter-fluid\ninteraction and the applied magnetic field. We obtain instability boundaries of\nthe system and construct phase diagrams as a function of the inter-fluid\ninteraction and the magnetic field. We investigate these properties employing\nthe Bogoliubov approximation.",
        "positive": "Persistent current by a static non-Hermitian ratchet: We propose a scheme to generate a persistent current in driven-dissipative\nsystems which can be described by the generalized Gross-Pitaevskii (GP)\nequation. Our proposal consists of fabricating a rachet-potential shape of the\nloss-rate profile, which simultaneously breaks the time-reversal and\nparity-inversion symmetry. Unlike existing schemes to generate a current using\na rachet potential in Hermitian systems, no dynamic drive is needed. The basic\nphysics of our scheme is discussed by a simple discrete driven-dissipative GP\nmodel, and the results are also verified by a realistic continuous model.\nFurthermore, we demonstrate the experimental feasibility of our scheme to\ngenerate the persistent current in exciton-polariton condensates in a\nsemiconductor microcavity."
    },
    {
        "anchor": "Taming the snake instabilities in a polariton superfluid: The dark solitons observed in a large variety of nonlinear media are unstable\nagainst the modulational (snake) instabilities and can break in vortex streets.\nThis behavior has been investigated in nonlinear optical crystals and ultracold\natomic gases. However, a deep characterization of this phenomenon is still\nmissing. In a resonantly pumped 2D polariton superfluid, we use an all-optical\nimprinting technique together with the bistability of the polariton system to\ncreate dark solitons in confined channels. Due to the snake instabilities, the\nsolitons are unstable and break in arrays of vortex streets whose dynamical\nevolution is frozen by the pump-induced confining potential, allowing their\ndirect observation in our system. A deep quantitative study shows that the\nvortex street period is proportional to the quantum fluid healing length, in\nagreement with the theoretical predictions. Finally, the full control achieved\non the soliton patterns is exploited to give a proof of principle of an\nefficient, ultra-fast, analog, all-optical maze solving machine in this\nphotonic platform.",
        "positive": "Point bosons in a one-dimensional box: the ground state, excitations and\n  thermodynamics: We determine the ground-state energy and the effective dispersion law for a\none-dimensional system of point bosons under zero boundary conditions. The\nground-state energy is close to the value for a periodic system. But the\ndispersion law is essentially different from that for a periodic system, if the\ncoupling is weak (weak interaction or high concentration) or intermediate. We\npropose also a new method for construction of the thermodynamics for a gas of\npoint bosons. It turns out that the difference in the dispersion laws of\nsystems with periodic and zero boundary conditions does not lead to a\ndifference in the thermodynamic quantities. In addition, under zero boundary\nconditions, the microscopic sound velocity does not coincide with the\nmacroscopic one. This means that either the method of determination of $k$ in\nthe dispersion law $E(k)$ is unsuitable or the low-energy excitations are not\nphonons."
    },
    {
        "anchor": "Theory of Non-Hermitian Fermionic Superfluidity with a Complex-Valued\n  Interaction: Motivated by recent experimental advances in ultracold atoms, we analyze a\nnon-Hermitian (NH) BCS Hamiltonian with a complex-valued interaction arising\nfrom inelastic scattering between fermions. We develop a mean-field theory to\nobtain a NH gap equation for order parameters, which are different from the\nstandard BCS ones due to the inequivalence of left and right eigenstates in the\nNH physics. We find unconventional phase transitions unique to NH systems:\nsuperfluidity shows reentrant behavior with increasing dissipation, as a\nconsequence of non-diagonalizable exceptional points, lines, and surfaces in\nthe quasiparticle Hamiltonian for weak attractive interactions. For strong\nattractive interactions, the superfluid gap never collapses but is enhanced by\ndissipation due to an interplay between the BCS-BEC crossover and the quantum\nZeno effect. Our results lay the groundwork for studies of fermionic\nsuperfluidity subject to inelastic collisions.",
        "positive": "Theory of the spectral function of Fermi polarons at finite temperature: We develop a general theory of Fermi polarons at nonzero temperature,\nincluding particle-hole excitations of the Fermi sea shake-up to arbitrarily\nhigh orders. The exact set of equations of the spectral function is derived by\nusing both Chevy ansatz and diagrammatic approach, and their equivalence is\nclarified to hold in free space only, with an unregularized infinitesimal\ninteraction strength. The correction to the polaron spectral function arising\nfrom two-particle-hole excitations is explicitly examined, for an exemplary\ncase of Fermi polarons in one-dimensional optical lattices. We find\nquantitative improvements at low temperatures with the inclusion of\ntwo-particle-hole excitations, in both polaron energies and decay rates. Our\nexact theory of Fermi polarons with arbitrary orders of particle-hole\nexcitations might be used to better understand the intriguing polaron dynamical\nresponses in two or three dimensions, whether in free space or within lattices."
    },
    {
        "anchor": "Third order corrections to the ground state energy of the gas of spin\n  $s$ fermions with arbitrary densities of different spin projections: Recently we have computed the third order corrections to the ground state\nenergy of the arbitrarily polarized diluted gas of spin 1/2 fermions\ninteracting through a spin-independent repulsive two-body potential. Here we\nextend this result to the gas of spin $s$ fermions - a system the Hamiltonian\nof which has an accidental $SU(2s+1)$ symmetry - with arbitrary densities of\nfermions having different spin projections. The corrections are computed\nsemi-analytically using the effective field theory approach and are\nparametrized by the $s$- and $p$- wave scattering lengths $a_0$ and $a_1$ and\nthe $s$-wave effective radius $r_0$, measurable in the low energy\nfermion-fermion elastic scattering. The result is used to study the impact the\nhigher order corrections can have on the characteristics of the phase\ntransition (at zero temperature) to the ordered phase (on the emergence of the\nitinerant ferromagnetism).",
        "positive": "The Hofstadter Butterfly in a Dynamic Cavity-Induced Synthetic Magnetic\n  Field: Energy bands of electrons in a square lattice potential threaded by a uniform\nmagnetic field exhibit a fractal structure known as the Hofstadter butterfly.\nHere we study a Fermi gas in a 2D optical lattice within a linear cavity with a\ntilt along the cavity axis. The hopping along the cavity axis is only induced\nby resonant Raman scattering of transverse pump light into a standing wave\ncavity mode. Choosing a suitable pump geometry allows to realize the\nHofstadter-Harper model with a cavity-induced dynamical synthetic magnetic\nfield, which appears at the onset of the superradiant phase transition. The\ndynamical nature of this cavity-induced synthetic magnetic field arises from\nthe delicate interplay between collective superradiant scattering and the\nunderlying fractal band structure. Using a sixth-order expansion of the free\nenergy as function of the order parameter and by numerical simulations we show\nthat at low magnetic fluxes the superradiant ordering phase transition is first\norder, while it becomes second order for higher flux. The dynamic nature of the\nmagnetic field induces a non-trivial deformation of the Hofstadter butterfly in\nthe superradiant phase. At strong pump far above the self-ordering threshold we\nrecover the Hofstadter butterfly one would obtain in a static magnetic field."
    },
    {
        "anchor": "Probing the Bose-Glass--Superfluid Transition using Quantum Quenches of\n  Disorder: We probe the transition between superfluid and Bose glass phases using\nquantum quenches of disorder in an ultracold atomic lattice gas that realizes\nthe disordered Bose-Hubbard model. Measurements of excitations generated by the\nquench exhibit threshold behavior in the disorder strength indicative of a\nphase transition. Ab-initio quantum Monte Carlo simulations confirm that the\nappearance of excitations coincides with the equilibrium superfluid--Bose-glass\nphase boundary at different lattice potential depths. By varying the quench\ntime, we demonstrate the disappearance of an adiabatic timescale compared with\nmicroscopic parameters in the BG regime.",
        "positive": "Dynamics and interaction of vortex lines in an elongated Bose-Einstein\n  condensate: We study the real-time dynamics of vortex lines in a large elongated\nBose-Einstein condensate (BEC) of sodium atoms using a stroboscopic technique.\nVortices are spontaneously produced via the Kibble-Zurek mechanism in a quench\nacross the BEC transition and then they slowly precess keeping their\norientation perpendicular to the long axis of the trap as expected for\nsolitonic vortices in a highly anisotropic condensate. Good agreement with\ntheoretical predictions is found for the precession period as a function of the\norbit amplitude and the number of condensed atoms. In configurations with two\nor more vortex lines, we see signatures of vortex-vortex interaction in the\nshape and visibility of the orbits. In addition, when more than two vortices\nare present, their decay is faster than the thermal decay observed for one or\ntwo vortices. The possible role of vortex reconnection processes is discussed."
    },
    {
        "anchor": "Non-Gaussian correlations imprinted by local dephasing in fermionic\n  wires: We study the behavior of an extended fermionic wire coupled to a local\nstochastic field. Since the quantum jump operator is Hermitian and quadratic in\nfermionic operators, it renders the model soluble, allowing investigation of\nthe properties of the non-equilibrium steady-state and the role of\ndissipation-induced fluctuations. We derive a closed set of equations of motion\nsolely for the two-point correlator; on the other hand, we find, surprisingly,\nthat the many-body state exhibits non-Gaussian correlations. Density-density\ncorrelation function demonstrates a crossover from a regime of weak dissipation\ncharacterized by moderate heating and stimulated fluctuations to a quantum Zeno\nregime ruled by strong dissipation, which tames quantum fluctuations. Instances\nof soluble dissipative impurities represent an experimentally viable platform\nto understand the interplay between dissipation and Hamiltonian dynamics in\nmany-body quantum systems.",
        "positive": "Domain percolation in a quenched ferromagnetic spinor condensate: We show that the easy-axis (EA) magnetic domains formed in a quenched\nferromagnetic spinor condensate are described by percolation theory. We\nintroduce a generalized spin rotation to vary the proportion of positive and\nnegative EA domains, allowing us to explore domain percolation. Using\nsimulations we investigate the finite-size scaling behaviour to extract the\ncorrelation length critical exponent and the transition point. We analyse the\nsensitivity of our results to the early-time dynamics of the system, the\nquadratic Zeeman energy, and the threshold condition used to define the\npositive (percolating) domains."
    },
    {
        "anchor": "Robustness of Fractional Quantum Hall States with Dipolar Atoms in\n  Artificial Gauge Fields: The robustness of fractional quantum Hall states is measured as the energy\ngap separating the Laughlin ground-state from excitations. Using thermodynamic\napproximations for the correlation functions of the Laughlin state and the\nquasihole state, we evaluate the gap in a two-dimensional system of dipolar\natoms exposed to an artificial gauge field. For Abelian fields, our results\nagree well with the results of exact diagonalization for small systems, but\nindicate that the large value of the gap predicted in [Phys. Rev. Lett. 94,\n070404 (2005)] was overestimated. However, we are able to show that the small\ngap found in the Abelian scenario is dramatically increased if we turn to\nnon-Abelian fields squeezing the Landau levels.",
        "positive": "Symmetry analysis of crystalline spin textures in dipolar spinor\n  condensates: We study periodic crystalline spin textures in spinor condensates with\ndipolar interactions via a systematic symmetry analysis of the low-energy\neffective theory. By considering symmetry operations which combine real and\nspin space operations, we classify symmetry groups consistent with non-trivial\nexperimental and theoretical constraints. Minimizing the energy within each\nsymmetry class allows us to explore possible ground states."
    },
    {
        "anchor": "Unconventional superfluidity induced by spin-orbital coupling in a\n  polarized two-dimensional Fermi gas: We show the spin-orbital coupling induced by an artificial light-induced\ngauge field can fully restore superfluidity suppressed by population imbalance\nin a two-dimensional (2D) Fermi gas, leading to unconventional superfluid\nstates either with topological Majorana fermion excitations or showing a novel\nmixture of triplet pairing with spin-up (down) components respectively in the\n$p_{x}\\pm ip_{y}$ pairing channels. We self-consistently calculate the zero\ntemperature phase diagram at the BCS\\ side of Feshbach resonance and show that\nthe phase transitions between different superfluid states can be revealed\nthrough measurement of the in-situ density profile of the 2D atomic cloud in a\nweak global trap.",
        "positive": "Effects of Rashba spin-orbit coupling, Zeeman splitting and gyrotropy in\n  two-dimensional cavity polaritons under the influence of the Landau\n  quantization: GaAs-type quantum wells (QWs) with p-type valence band embedded into the\nresonators. The Landau quantization of the electrons and heavy-holes (hh) was\ninvestigated taking into account the Rashba spin-orbit coupling with\nthird-order chirality terms for hh and with nonparabolicity terms in their\ndispersion low including the Zeeman splitting (ZS) effects. The exact solutions\nfor the eigenfunctions and eigenenergies were obtained using the Rashba method\n[1]. We derive in the second quantization representation the Hamiltonians\ndescribing the Coulomb electron-electron and the electron-radiation\ninteractions and determine the magnetoexciton energy branches and the\nmagnetoexciton-photon interaction. The fifth order dispersion equation\ndescribing the energy spectrum of the cavity magnetoexciton-polariton is\ninvestigated. It takes into account the interaction of the cavity photons with\ntwo dipole-active and with two quadrupole-active 2D magnetoexciton energy\nbranches. The cavity photons have the circular polarizations oriented along\ntheir wave vectors, which has the quantized longitudinal component. The\nselection rules of the exciton-photon interaction is expressed through the\nscalar products of the two-types circular polarizations and it is related with\nthe numbers of the LQ levels of electrons and heavy-holes. It is shown that the\nRabi frequency of the polariton branches and the magnetoexciton oscillator\nstrength increase in dependence on the magnetic field strength. The optical\ngyrotropy effects may be revealed if changing the sign of the photon circular\npolarization at a given sign of the wave vector longitudinal projection or\nequivalently changing the sign of the longitudinal projection at the same\nselected light circular polarization."
    },
    {
        "anchor": "Tuning the Topological $\u03b8$-Angle in Cold-Atom Quantum Simulators of\n  Gauge Theories: The topological $\\theta$-angle in gauge theories engenders a series of\nfundamental phenomena, including violations of charge-parity (CP) symmetry,\ndynamical topological transitions, and confinement--deconfinement transitions.\nAt the same time, it poses major challenges for theoretical studies, as it\nimplies a sign problem in numerical simulations. Analog quantum simulators open\nthe promising prospect of treating quantum many-body systems with such\ntopological terms, but, contrary to their digital counterparts, they have not\nyet demonstrated the capacity to control the $\\theta$-angle. Here, we\ndemonstrate how a tunable topological $\\theta$-term can be added to a prototype\ntheory with $\\mathrm{U}(1)$ gauge symmetry, a discretized version of quantum\nelectrodynamics in one spatial dimension. As we show, the model can be realized\nexperimentally in a single-species Bose--Hubbard model in an optical\nsuperlattice with three different spatial periods, thus requiring only standard\nexperimental resources. Through numerical calculations obtained from the\ntime-dependent density matrix renormalization group method and exact\ndiagonalization, we benchmark the model system, and illustrate how salient\neffects due to the $\\theta$-term can be observed. These include charge\nconfinement, the weakening of quantum many-body scarring, as well as the\ndisappearance of Coleman's phase transition due to explicit breaking of CP\nsymmetry. This work opens the door towards studying the rich physics of\ntopological gauge-theory terms in large-scale cold-atom quantum simulators.",
        "positive": "Three-body bound states of two bosonic impurities immersed in a Fermi\n  sea in 2D: We consider two identical impurities immersed in a Fermi sea for a broad\nrange of masses and for both interacting and non-interacting impurities. The\ninteraction between the particles is described through attractive zero-range\npotentials and the problem is solved in momentum space. The two impurities can\nattach to a fermion from the sea and form three-body bound states. The energy\nof these states increase as function of the Fermi momentum $k_F$, leading to\nthree-body bound states below the Fermi energy. The fate of the states depends\nhighly on two- and three-body thresholds and we find evidence of medium-induced\nBorromean-like states in 2D. The corrections due to particle-hole fluctuations\nin the Fermi sea are considered in the three-body calculations and we show that\nin spite of the fact that they strongly affect both the two- and three-body\nsystems, the correction to the point at which the three-body states cease to\nexist is small."
    },
    {
        "anchor": "Harmonically trapped Bose-Bose mixtures: a quantum Monte Carlo study: We study a harmonically confined Bose-Bose mixture using quantum Monte Carlo\nmethods. Our results for the density profiles are systematically compared with\nmean-field predictions derived through the Gross-Pitaevskii equation in the\nsame conditions. The phase space as a function of the interaction strengths and\nthe relation between masses is quite rich. The miscibility criterion for the\nhomogeneous system applies rather well to the system, with some discrepancies\nclose to the critical line for separation. We observe significant differences\nbetween the mean-field results and the Monte Carlo ones, that magnify when the\nasymmetry between masses increases. In the analyzed interaction regime, we\nobserve universality of our results which extend beyond the applicability\nregime for the Gross-Pitaevskii equation.",
        "positive": "BCS theory of time-reversal-symmetric Hofstadter-Hubbard model: The competition between the length scales associated with the periodicity of\na lattice potential and the cyclotron radius of a uniform magnetic field is\nknown to have dramatic effects on the single-particle properties of a quantum\nparticle, e.g., the fractal spectrum is known as the Hofstadter butterfly.\nHaving this intricate competition in mind, we consider a two-component Fermi\ngas on a square optical lattice with opposite synthetic magnetic fields for the\ncomponents, and study its effects on the many-body BCS-pairing phenomenon. By a\ncareful addressing of the distinct superfluid transitions from the semi-metal,\nquantum spin-Hall insulator or normal phases, we explore the low-temperature\nphase diagrams of the model, displaying lobe structures that are reminiscent of\nthe well-known Mott-insulator transitions of the Bose-Hubbard model."
    },
    {
        "anchor": "The role of real-space micromotion for bosonic and fermionic Floquet\n  fractional Chern insulators: Fractional Chern insulators are the proposed phases of matter mimicking the\nphysics of fractional quantum Hall states on a lattice without an overall\nmagnetic field. The notion of Floquet fractional Chern insulators refers to the\npotential possibilities to generate the underlying topological bandstructure by\nmeans of Floquet engineering. In these schemes, a highly controllable and\nstrongly interacting system is periodically driven by an external force at a\nfrequency such that double tunneling events during one forcing period become\nimportant and contribute to shaping the required effective energy bands. We\nshow that in the described circumstances it is necessary to take into account\nalso third order processes combining two tunneling events with interactions.\nReferring to the obtained contributions as micromotion-induced interactions, we\nfind that those interactions tend to have a negative impact on the stability of\nof fractional Chern insulating phases and discuss implications for future\nexperiments.",
        "positive": "Efimov states near a Feshbach resonance and the limits of van der Waals\n  universality at finite background scattering length: We calculate the spectrum of three-body Efimov bound states near a Feshbach\nresonance within a model which accounts both for the finite range of\ninteractions and the presence of background scattering. The latter may be due\nto direct interactions in an open channel or a second overlapping Feshbach\nresonance. It is found that background scattering gives rise to substantial\nchanges in the trimer spectrum as a function of the detuning away from a\nFeshbach resonance, in particular in the regime where the background channel\nsupports Efimov states on its own. Compared to the situation with negligible\nbackground scattering, the regime where van der Waals universality applies is\nshifted to larger values of the resonance strength if the background scattering\nlength is positive. For negative background scattering lengths, in turn, van\nder Waals universality extends to even small values of the resonance strength\nparameter, consistent with experimental results on Efimov states in $^{39}$K.\nWithin a simple model, we show that short-range three-body forces do not affect\nvan der Waals universality significantly. Repulsive three-body forces may,\nhowever, explain the observed variation between around $-8$ and $-10$ of the\nratio between the scattering length where the first Efimov trimer appears and\nthe van der Waals length."
    },
    {
        "anchor": "Nonequilibrium dynamical mean-field theory for bosonic lattice models: We develop the nonequilibrium extension of bosonic dynamical mean field\ntheory (BDMFT) and a Nambu real-time strong-coupling perturbative impurity\nsolver. In contrast to Gutzwiller mean-field theory and strong coupling\nperturbative approaches, nonequilibrium BDMFT captures not only dynamical\ntransitions, but also damping and thermalization effects at finite temperature.\nWe apply the formalism to quenches in the Bose-Hubbard model, starting both\nfrom the normal and Bose-condensed phases. Depending on the parameter regime,\none observes qualitatively different dynamical properties, such as rapid\nthermalization, trapping in metastable superfluid or normal states, as well as\nlong-lived or strongly damped amplitude oscillations. We summarize our results\nin non-equilibrium \"phase diagrams\" which map out the different dynamical\nregimes.",
        "positive": "Towards Quantum Turbulence in Cold Atomic Fermionic Superfluids: Fermionic superfluids provide a new realization of quantum turbulence,\naccessible to both experiment and theory, yet relevant to phenomena from both\ncold atoms to nuclear astrophysics. In particular, the strongly interacting\nFermi gas realized in cold-atom experiments is closely related to dilute\nneutron matter in neutron star crusts. Unlike the liquid superfluids 4He\n(bosons) and 3He (fermions) where quantum turbulence has been studied in the\nlaboratory, superfluid Fermi gases stand apart for a number of reasons. They\nadmit a reliable theoretical description based on a DFT called the TDSLDA that\ndescribes both static and dynamic phenomena. Cold atom experiments demonstrate\nexquisite control over particle number, spin polarization, density,\ntemperature, and interaction strength. Topological defects such as domain walls\nand quantized vortices, which lie at the heart of quantum turbulence, can be\ncreated and manipulated with time-dependent external potentials, and agree with\nthe time-dependent theoretical techniques. While similar experimental and\ntheoretical control exists for weakly interacting Bose gases, the unitary Fermi\ngas is strongly interacting. The resulting vortex line density is extremely\nhigh, and quantum turbulence may thus be realized in small systems where\nclassical turbulence is suppressed. Fermi gases also permit the study of exotic\nsuperfluid phenomena such as a 3D LOFF supersolid, and a finite temperature\npseudo-gap in the regime of classical turbulence. The dynamics associated with\nthese phenomena has only started to be explored. Finally, superfluid mixtures\nhave recently been realized, providing experimental access to phenomena like\nAndreev-Bashkin entrainment. Superfluid Fermi gases thus provide a rich forum\nfor addressing phenomena related to quantum turbulence with applications\nranging from terrestrial superfluidity to astrophysical dynamics in neutron\nstars."
    },
    {
        "anchor": "Pressure, compressibility, and contact of the two-dimensional attractive\n  Fermi gas: Using ab initio lattice methods, we calculate the finite temperature\nthermodynamics of homogeneous two-dimensional spin-1/2 fermions with attractive\nshort-range interactions. We present results for the density, pressure,\ncompressibility, and quantum anomaly (i.e. Tan's contact) for a wide range of\ntemperatures and coupling strengths, focusing on the unpolarized case. Within\nour statistical and systematic uncertainties, our prediction for the density\nequation of state differs quantitatively from the prediction by Luttinger-Ward\ntheory in the strongly coupled region of parameter space, but otherwise agrees\nwell with it. We also compare our calculations with the second- and third-order\nvirial expansion, with which they are in excellent agreement in the\nlow-fugacity regime.",
        "positive": "Few-Body Bound Complexes in One-dimensional Dipolar Gases and\n  Non-Destructive Optical Detection: We consider dipolar interactions between heteronuclear molecules in\nlow-dimensional geometries. The setup consists of two one-dimensional tubes. We\nstudy the stability of possible few-body complexes in the regime of repulsive\nintratube interaction, where the binding arises from intertube attraction. The\nstable dimers, trimers, and tetramers are found and we discuss their properties\nfor both bosonic and fermionic molecules. To observe these complexes we propose\nan optical non-destructive detection scheme that enables in-situ observation of\nthe creation and dissociation of the few-body complexes. A detailed description\nof the expected signal of such measurements is given using the numerically\ncalculated wave functions of the bound states. We also discuss implications on\nthe many-body physics of dipolar systems in tubular geometries, as well as\nexperimental issues related to the external harmonic confinement along the tube\nand the prospect of applying an in-tube optical lattice to increase the\neffective dipole strength."
    },
    {
        "anchor": "Accurate one-dimensional effective description of realistic matter-wave\n  gap solitons: We consider stationary matter-wave gap solitons realized in Bose--Einstein\ncondensates loaded in one-dimensional (1D) optical lattices and investigate\nwhether the effective 1D equation proposed in [Phys. Rev. A \\textbf{77}, 013617\n(2008)] can be a reliable alternative to the three-dimensional treatment of\nthis kind of system in terms of the Gross--Pitaevskii equation (GPE). Our\nresults demonstrate that, unlike the standard 1D GPE (which is not applicable\nin most realistic situations), the above effective model is able to correctly\npredict the distinctive trajectories characterizing the different gap soliton\nfamilies as well as the corresponding axial wavefunctions along the entire band\ngaps. It can also predict the stability properties of the different gap soliton\nfamilies as follows from both a linear stability analysis and a representative\nset of numerical computations. In particular, by numerically solving the\ncorresponding Bogoliubov--de Gennes equations we show that the effective 1D\nmodel gives the correct spectrum of complex eigenfrequencies responsible for\nthe dynamical stability of the system, thus providing us with a useful tool for\nthe physical description of stationary matter-wave gap solitons in 1D optical\nlattices.",
        "positive": "Relation between the noise correlations and the spin structure factor\n  for Mott-insulating states in SU$(N)$ Hubbard models: It is well established that the noise correlations measured by time-of-flight\nimaging in cold-atom experiments, which correspond to the density-density\ncorrelations in the momentum space of trapped atomic gases, can probe the spin\nstructure factor deep in the Mott-insulating regime of SU(2) Hubbard models. We\nexplicitly derive the mathematical relation between the noise correlations and\nthe spin structure factor in the strong-interaction limit of SU$(N)$ Hubbard\nmodels at any integer filling $\\rho$. By calculating the ground states of\none-dimensional SU$(N)$ Fermi-Hubbard models for $2\\leq N\\leq 6$ with use of\nthe density-matrix renormalization-group method, we confirm the relation\nnumerically in the regime of strong interactions $U \\gg t$, where $U$ and $t$\ndenote the onsite interaction and the hopping energy. We show that the\ndeviation between the actual noise correlations and those obtained from the\nspin structure factor scales as approximately $(t/U)^2$ for $\\rho=1$ at\nintermediate and large lattice sizes on the basis of numeric and semi-analytic\narguments."
    },
    {
        "anchor": "Measuring the Chern number of Hofstadter bands with ultracold bosonic\n  atoms: Sixty years ago, Karplus and Luttinger pointed out that quantum particles\nmoving on a lattice could acquire an anomalous transverse velocity in response\nto a force, providing an explanation for the unusual Hall effect in\nferromagnetic metals. A striking manifestation of this transverse transport was\nthen revealed in the quantum Hall effect, where the plateaus depicted by the\nHall conductivity were attributed to a topological invariant characterizing\nBloch bands: the Chern number. Until now, topological transport associated with\nnon-zero Chern numbers has only been revealed in electronic systems. Here we\nuse studies of an atomic cloud's transverse deflection in response to an\noptical gradient to measure the Chern number of artificially generated\nHofstadter bands. These topological bands are very flat and thus constitute\ngood candidates for the realization of fractional Chern insulators. Combining\nthese deflection measurements with the determination of the band populations,\nwe obtain an experimental value for the Chern number of the lowest band\n$\\nu_{\\mathrm{exp}} =0.99(5)$. This result, which constitutes the first\nChern-number measurement in a non-electronic system, is facilitated by an\nall-optical artificial gauge field scheme, generating uniform flux in optical\nsuperlattices.",
        "positive": "Improved walker population control for full configuration interaction\n  quantum Monte Carlo: Full configuration interaction quantum Monte Carlo (FCIQMC) is a stochastic\napproach for finding the ground state of a quantum many-body Hamiltonian. It is\nbased on the dynamical evolution of a walker population in Hilbert space, which\nsamples the ground state configuration vector over many iterations. Here we\npresent a modification of the original protocol for walker population control\nof Booth et al. JCP 131, 054106 (2009) in order to achieve equilibration at a\npre-defined average walker number and to avoid walker number overshoots. The\ndynamics of the walker population is described by a noisy damped harmonic\noscillator and controlled by two parameters responsible for damping and\nforcing, respectively, for which reasonable values are suggested. We further\nintroduce a population growth witness that can be used to detect annihilation\nplateaus related to overcoming the FCIQMC sign problem. Features of the new\npopulation control procedure such as precise walker number control and fast\nequilibration are demonstrated. The standard error of the shift estimator for\nthe ground state energy as well as the population control bias are found to be\nunaffected by the population control procedure or its parameters. The improved\ncontrol of the walker number, and thereby memory consumption, is a desirable\nfeature required for automating FCIQMC calculations and requires minimal\nmodifications to existing code."
    },
    {
        "anchor": "Imaging a single atom in a time-of-flight experiment: We perform fluorescence imaging of a single 87Rb atom after its release from\nan optical dipole trap. The time-of-flight expansion of the atomic spatial\ndensity distribution is observed by accumulating many single atom images. The\nposition of the atom is revealed with a spatial resolution close to 1\nmicrometer by a single photon event, induced by a short resonant probe. The\nexpansion yields a measure of the temperature of a single atom, which is in\nvery good agreement with the value obtained by an independent measurement based\non a release-and-recapture method. The analysis presented in this paper\nprovides a way of calibrating an imaging system useful for experimental studies\ninvolving a few atoms confined in a dipole trap.",
        "positive": "Weak coupling regime of the Landau-Zener transition for association of\n  an atomic Bose-Einstein condensate: In the framework of a basic semiclassical time-dependent nonlinear two-state\nproblem, we study the weak coupling limit of the nonlinear Landau-Zener\ntransition at coherent photo- and magneto-association of an atomic\nBose-Einstein condensate. Using an exact third-order nonlinear differential\nequation for the molecular state probability, we develop a variational approach\nwhich enables us to construct an accurate analytic approximation describing\ntime dynamics of the coupled atom-molecular system for the case of weak\ncoupling. The approximation is written in terms of the solution to an auxiliary\nlinear Landau-Zener problem with some effective Landau-Zener parameter. The\ndependence of this effective parameter on the input Landau-Zener parameter is\nfound to be unexpected: as the generic Landau-Zener parameter increases, the\neffective Landau-Zener parameter first monotonically increases (starting from\nzero), reaches its maximal value and then monotonically decreases again\nreaching zero at some point. The constructed approximation quantitatively well\ndescribes many characteristics of the time dynamics of the system, in\nparticular, it provides a highly accurate formula for the final transition\nprobability to the molecular state. The present result for the final transition\nprobability improves the accuracy of the previous approximation by Ishkhanyan\net al. [Phys. Rev. A 69, 043612 (2004); J. Phys. A 38, 3505 (2005)] by order of\nmagnitude."
    },
    {
        "anchor": "Truncated many-body dynamics of interacting bosons: A variational\n  principle with error monitoring: We develop a method to describe the temporal evolution of an interacting\nsystem of bosons, for which the field operator expansion is truncated after a\nfinite number $M$ of modes, in a rigorously controlled manner. Using\nMcLachlan's principle of least error, we find a self-consistent set of\nequations for the many-body state. As a particular benefit, and in distinction\nto previously proposed approaches, the presently introduced method facilitates\nthe dynamical increase of the number of orbitals during the temporal evolution,\ndue to the fact that we can rigorously monitor the error made by increasing the\ntruncation dimension $M$. The additional orbitals, determined by the condition\nof least error of the truncated evolution relative to the exact one, are\nobtained from an initial trial state by steepest $constrained$ descent.",
        "positive": "Hugenholtz-Pines theorem for multicomponent Bose-Einstein condensates: The Hugenholtz-Pines (HP) theorem is derived for Bose-Einstein condensates\n(BECs) with internal degrees of freedom. The low-energy Ward-Takahashi identity\nis provided in the system with the linear and quadratic symmetry breaking\nterms. This identity serves to organize the HP theorem for multicomponent BECs,\nsuch as the binary BEC as well as the spin-$f$ spinor BEC in the presence of a\nmagnetic field with broken U$(1)$$\\times$SO$(3)$ symmetry. The experimental\nmethod based on the Stern-Gerlach experiment is proposed for studying the\nWard-Takahashi identity."
    },
    {
        "anchor": "Diagrammatic approach to orbital quantum impurities interacting with a\n  many-particle environment: Recently it was shown that an impurity exchanging orbital angular momentum\nwith a surrounding bath can be described in terms of the angulon quasiparticle\n[Phys. Rev. Lett. 118, 095301 (2017)]. The angulon consists of a quantum rotor\ndressed by a many-particle field of boson excitations, and can be formed out\nof, for example, a molecule or a nonspherical atom in superfluid helium, or out\nof an electron coupled to lattice phonons or a Bose condensate. Here we develop\nan approach to the angulon based on the path-integral formalism, which sets the\nground for a systematic, perturbative treatment of the angulon problem. The\nresulting perturbation series can be interpreted in terms of Feynman diagrams,\nfrom which, in turn, one can derive a set of diagrammatic rules. These rules\nextend the machinery of the graphical theory of angular momentum - well known\nfrom theoretical atomic spectroscopy - to the case where an environment with an\ninfinite number of degrees of freedom is present. In particular, we show that\neach diagram can be interpreted as a 'skeleton', which enforces angular\nmomentum conservation, dressed by an additional many-body contribution. This\nconnection between the angulon theory and the graphical theory of angular\nmomentum is particularly important as it allows to systematically and\nsubstantially simplify the analytical representation of each diagram. In order\nto exemplify the technique, we calculate the 1- and 2-loop contributions to the\nangulon self-energy, the spectral function, and the quasiparticle weight. The\ndiagrammatic theory we develop paves the way to investigate next-to-leading\norder quantities in a more compact way compared to the variational approaches.",
        "positive": "Low-Dimensional Self-Bound Quantum Rabi-Coupled Bosonic Droplets: We analytically calculate the leading quantum corrections of the ground-state\nenergy of two- and one-dimensional weakly interacting Rabi-coupled Bose-Bose\nmixtures in the frame of the Bogoliubov approximation. We show that to\nrepulsive intraspecies and attractive interspecies interactions, the effect of\nquantum fluctuations favors the formation of self-bound droplets. These\nliquidlike states are crucially affected by the Rabi coupling, leading thus to\nthe appearance of a quantum instability. We derive meaningful formulas to\ndescribe the droplet phase in the one-dimensional case."
    },
    {
        "anchor": "Cooper pairing and tripling in one-dimensional spinless fermions with\n  attractive two- and three-body forces: We theoretically investigate in-medium three-body correlations in\none-dimensional spinless fermions with antisymmetrized two- and three-body\nattractive interactions. By investigating the variational problem of three-body\nstates above the Fermi sea, we illuminate the fate of the in-medium three-body\ncluster states both in the special case with pure attractive three-body\ninteraction as well as in the case with the coexistence of two- and three-body\ninteractions. Our results testify that the fermion-dimer repulsion is canceled\nby including the three-body interactions, and stable three-body clusters can be\nformed. We further feature a phase diagram consisting of the $p$-wave Cooper\npairing and Cooper tripling phases in a plane of $p$-wave two- and three-body\ncoupling strengths.",
        "positive": "Finding the elusive sliding phase in superfluid-normal phase transition\n  smeared by c-axis disorder: We consider a system composed of a stack of weakly Josephson coupled\nsuperfluid layers with c-axis disorder in the form of random superfluid\nstiffnesses and vortex fugacities in each layer as well as random inter-layer\ncoupling strengths. In the absence of disorder this system has a 3D XY type\nsuperfluid-normal phase transition as a function of temperature. We develop a\nfunctional renormalization group to treat the effects of disorder, and\ndemonstrate that the disorder results in the smearing of the superfluid normal\nphase transition via the formation of a Griffiths phase. Remarkably, in the\nGriffiths phase, the emergent power-law distribution of the inter-layer\ncouplings gives rise to sliding Griffiths superfluid, with an anisotropic\ncritical current, and with a finite stiffness in a-b direction along the\nlayers, and a vanishing stiffness perpendicular to it."
    },
    {
        "anchor": "Probing Sound Speed of an Optically-Trapped Bose Gas with Periodically\n  Modulated Interactions by Bragg Spectroscopy: A Bose-Einstein condensate (BEC) with periodically modulated interactions\n(PMI) has emerged as a novel kind of periodic superfluid, which has been\nrecently experimentally created using optical Feshbach resonance. In this\npaper, we are motivated to investigate the superfluidity of a BEC with PMI\ntrapped in an optical lattice (OL). In particular, we explore the effects of\nPMI on the sound speed and the dynamical structure factor of the model system.\nOur numerical results, combined with the analytical results in both the\nweak-potential limit and the tight-binding limit, have shown that the PMI can\nstrongly modify the sound speed of a BEC. Moreover, we have shown that the\neffects of PMI on sound speed can be experimentally probed via the dynamic\nstructure factor, where the excitation strength toward the first Bogoliubov\nband exhibits marked difference from the non- PMI one. Our predictions of the\neffects of PMI on the sound speed can be tested using the Bragg spectroscopy.",
        "positive": "Correlation evolution in dilute Bose-Einstein condensates after quantum\n  quenches: The universal forms of quantum density and phase correlations after an\ninteraction quench are found for dilute 1d, 2d, and 3d condensates. A\nBogoliubov approach in a local density aproximation is used. We obtain compact\nexpressions for the most visible effects. Our results show how loss of phase\ncoherence and antibunching are built up after the quench by quantum\nfluctuations. We demonstrate further that the density correlations can be\nobserved even with imaging resolution much worse than healing length. This\nindicates that the direct measurement of counterpropagating atom pairs in situ\nin a continuum system is realistic. The conditions in contemporary 1d\nexperiments are especially favorable for the correlation wave observations."
    },
    {
        "anchor": "Zero-point excitation of a circularly moving detector in an atomic\n  condensate and phonon laser dynamical instabilities: We study a circularly moving impurity in an atomic condensate for the\nrealisation of superradiance phenomena in tabletop experiments. The impurity is\ncoupled to the density fluctuations of the condensate and, in a quantum field\ntheory language, it serves as an analog of a detector for the quantum phonon\nfield. For sufficiently large rotation speeds, the zero-point fluctuations of\nthe phonon field induce a sizeable excitation rate of the detector even when\nthe condensate is initially at rest in its ground state. For spatially confined\ncondensates and harmonic detectors, such a superradiant emission of sound waves\nprovides a dynamical instability mechanism leading to a new concept of phonon\nlasing. Following an analogy with the theory of rotating black holes, our\nresults suggest a promising avenue to quantum simulate basic interaction\nprocesses involving fast moving detectors in curved space-times.",
        "positive": "Many-Body Effects and Quantum Fluctuations for Discrete Time Crystals in\n  Bose-Einstein Condensates: We present a fully comprehensive multi-mode quantum treatment based on the\ntruncated Wigner approximation (TWA) to study many-body effects and quantum\nfluctuations on the formation of a discrete time crystal (DTC) in a\nBose-Einstein condensate (BEC) bouncing resonantly on an atom mirror, driven at\nperiod T. Our theoretical approach avoids the restrictions both of mean-field\ntheory, where all bosons are assumed to remain in a single mode, and of\ntime-dependent Bogoliubov theory, which assumes boson depletion from the\ncondensate mode is small. For realistic initial conditions corresponding to a\nharmonic trap condensate mode function, our TWA calculations performed for\nperiod-doubling agree broadly with recent mean-field calculations for times out\nto at least 2000 T, except at interaction strengths very close to the threshold\nvalue for DTC formation where the position probability density differs\nsignificantly from that determined from mean-field theory. For typical\nattractive interaction strengths above the threshold value for DTC formation\nand for the chosen trap and driving parameters, the TWA calculations indicate a\nquantum depletion due to quantum many-body fluctuations of less than about two\natoms out of 600 atoms at times corresponding to 2000 T, in agreement with\ntime-dependent Bogoliubov theory calculations. On the other hand, for\ninteraction strengths very close to the threshold value for DTC formation, the\nTWA calculations predict a large quantum depletion - as high as about 260 atoms\nout of 600. We also show that the mean energy of the DTC does not increase\nsignificantly for times out to at least 2000 mirror oscillations, so TWA theory\npredicts that thermalisation is absent. Finally, we find that the dynamical\nbehaviour is similar for attractive or repulsive boson-boson interactions, and\nthat a stable DTC based on repulsive interactions can be created."
    },
    {
        "anchor": "Dark-soliton-like excitations in the Yang-Gaudin gas of attractively\n  interacting fermions: Yrast states are the lowest energy states at given non-zero momentum and\nprovide a natural extension of the concept of dark solitons to\nstrongly-interacting one-dimensional quantum gases. Here we study the yrast\nstates of the balanced spin-$\\frac{1}{2}$ Fermi gas with attractive\ndelta-function interactions in one dimension with the exactly solvable\nYang-Gaudin model. The corresponding Bethe-ansatz equations are solved for\nfinite particle number and in the thermodynamic limit. Properties corresponding\nto the soliton-like nature of the yrast excitations are calculated including\nthe missing particle number, phase step, and inertial and physical masses. The\ninertial to physical mass ratio, which is related to the frequency of\noscillations in a trapped gas, is found to be unity in the limits of strong and\nweak attraction and falls to $\\approx 0.78$ in the crossover regime. This\nresult is contrasted by one-dimensional mean field theory, which predicts a\ndivergent mass ratio in the weakly attractive limit. By means of an exact\nmapping our results also predict the existence and properties of\ndark-soliton-like excitations in the super Tonks-Girardeau gas. The prospects\nfor experimental observations are briefly discussed.",
        "positive": "Two-dimensional scattering and bound states of polar molecules in\n  bilayers: Low-energy two-dimensional scattering is particularly sensitive to the\nexistence and properties of weakly-bound states. We show that interaction\npotentials $V(r)$ with vanishing zero-momentum Born approximation $\\int d^2r\nV(r)=0$ lead to an anomalously weak bound state which crucially modifies the\ntwo-dimensional scattering properties. This anomalous case is especially\nrelevant in the context of polar molecules in bilayer arrangements."
    },
    {
        "anchor": "Canted Antiferromagnetic Order of Imbalanced Fermi-Fermi mixtures in\n  Optical Lattices by Dynamical Mean-Field Theory: We investigate antiferromagnetic order of repulsively interacting fermionic\natoms in an optical lattice by means of Dynamical Mean-Field Theory (DMFT).\nSpecial attention is paid to the case of an imbalanced mixture. We take into\naccount the presence of an underlying harmonic trap, both in a local density\napproximation and by performing full Real-Space DMFT calculations. We consider\nthe case that the particle density in the trap center is at half filling,\nleading to an antiferromagnetic region in the center, surrounded by a Fermi\nliquid region at the edge. In the case of an imbalanced mixture, the\nantiferromagnetism is directed perpendicular to the ferromagnetic polarization\nand canted. We pay special attention to the boundary structure between the\nantiferromagnetic and the Fermi liquid phase. For the moderately strong\ninteractions considered here, no Stoner instability toward a ferromagnetic\nphase is found. Phase separation is only observed for strong imbalance and\nsufficiently large repulsion.",
        "positive": "BEC immersed in a Fermi sea: Theory of static and dynamic behavior\n  across phase separation: We theoretically study the static and dynamic behavior of a BEC immersed in a\nlarge Fermi sea of ultracold atoms under conditions of tunable interspecies\ninteraction. The degenerate Bose-Fermi mixture is kept in an elongated trap,\ntypical for a single-beam optical dipole trap. We focus on the case of\nrepulsive Bose-Fermi interaction and develop mean-field models to simulate the\nsystem over a wide range of repulsion strength. We further get analytical\nsolutions in the regimes of phase separation and weak interaction. We obtain\nstatic density profiles and the frequency of the radial breathing mode, which\nis an elementary dynamic phenomenon of the mixture. Our results unveil the\nstructure of the Bose-Fermi interface and describe the origin of the frequency\nshift of the breathing mode when the components become phase-separated at\nstrong repulsion. We show that the mediated interaction between bosons induced\nby the Fermi sea can be understood as an adiabatic second-order mean-field\neffect, which is valid also beyond the weak-interaction regime for relevant\nexperimental conditions. These results are consistent with our recent\nobservations in a mixture of $^{41}$K and $^6$Li."
    },
    {
        "anchor": "Weakly interacting Bose gases with generalized uncertainty principle:\n  Effects of quantum gravity: We investigate quantum gravity corrections due to the generalized uncertainty\nprinciple on three-dimensional weakly interacting Bose gases at both zero and\nfinite temperatures using the time-dependent Hatree-Fock-Bogoliubov theory. We\nderive useful formulas for the depletion, the anomalous density and some\nthermodynamic quantities such as the chemical potential, the ground-state\nenergy, the free energy, and the superfluid density. It is found that the\npresence of a minimal length leads to modify the fluctuations of the condensate\nand its thermodynamic properties in the weak and strong quantum gravitational\nregimes. Unexpectedly, the interplay of quantum gravity effects and quantum\nfluctuations stemming from interactions may lift both the condensate and the\nsuperfluid fractions. We show that quantum gravity minimizes the interaction\nforce between bosons leading to the formation of ultradilute Bose condensates.\nOur results which can be readily probed in current experiments may offer a new\nattractive possibility to understand gravity in the framework of quantum\nmechanics.",
        "positive": "Diffraction catastrophes threaded by quantized vortex skeletons caused\n  by atom-optical aberrations induced in trapped Bose-Einstein condensates: We propose a nonlinear atom-optics experiment to create diffraction\ncatastrophes threaded by quantized vortex skeletons in Bose-Einstein condensed\nmatter waves. We show how atom-optical aberrations induced in trapped\nBose-Einstein condensates evolve into specific caustic structures due to\nimperfect focusing. Vortex skeletons, whose cross-sections are staggered vortex\nlattices, are observed to nucleate inside the universal diffraction\ncatastrophes. Our observations shed further light on the structure and dynamics\nof Bose-novae and suggest applications of matter wave diffraction catastrophes,\nincluding detection of the order parameter pairing symmetry in cold gas\nexperiments."
    },
    {
        "anchor": "Tan's Contact for Trapped Lieb-Liniger Bosons at Finite Temperature: The universal Tan relations connect a variety of microscopic features of\nmany-body quantum systems with two-body contact interactions to a single\nquantity, called the contact. The latter has become pivotal in the description\nof quantum gases.We provide a complete characterization of the Tan contact of\nthe harmonically trapped Lieb-Liniger gas for arbitrary interactions and\ntemperature.Combining thermal Bethe ansatz, local-density approximation, and\nexact quantum Monte Carlo calculations,we show that the contact is a universal\nfunction of only two scaling parameters, and determine the scaling function.We\nfind that the temperature dependence of the contact, or equivalently the\ninteraction dependence of the entropy, displays a maximum. The presence of this\nmaximum provides an unequivocal signature of the crossover to the fermionized\nregime and it is accessible in current experiments.",
        "positive": "Topological phase transitions driven by non-Abelian gauge potentials in\n  optical square lattices: We analyze a tight-binding model of ultracold fermions loaded in an optical\nsquare lattice and subjected to a synthetic non-Abelian gauge potential\nfeaturing both a magnetic field and a translationally invariant SU(2) term. We\nconsider in particular the effect of broken time-reversal symmetry and its role\nin driving non-trivial topological phase transitions. By varying the spin-orbit\ncoupling parameters, we find both a semimetal/insulator phase transition and a\ntopological phase transition between insulating phases with different numbers\nof edge states. The spin is not a conserved quantity of the system and the\ntopological phase transitions can be detected by analyzing its polarization in\ntime of flight images, providing a clear diagnostic for the characterization of\nthe topological phases through the partial entanglement between spin and\nlattice degrees of freedom."
    },
    {
        "anchor": "Realizing and Probing Baryonic Excitations in Rydberg Atom Arrays: We propose a realization of mesonic and baryonic quasiparticle excitations in\nRydberg atom arrays with programmable interactions. Recent experiments have\nshown that such systems possess a $\\mathbb{Z}_3$-ordered crystalline phase\nwhose low-energy quasiparticles are defects in the crystalline order. By\nengineering a $\\mathbb{Z}_3$-translational-symmetry breaking field on top of\nthe Rydberg-blockaded Hamiltonian, we show that different types of defects\nexperience confinement, and as a consequence form mesonic or baryonic\nquasiparticle excitations. We illustrate the formation of these quasiparticles\nby studying a quantum chiral clock model related to the Rydberg Hamiltonian. We\nthen propose an experimental protocol involving out-of-equilibrium dynamics to\ndirectly probe the spectrum of the confined excitations. We show that the\nconfined quasiparticle spectrum can limit quantum information spreading in this\nsystem. This proposal is readily applicable to current Rydberg experiments, and\nthe method can be easily generalized to more complex confined excitations (e.g.\n`tetraquarks', `pentaquarks') in phases with $\\mathbb{Z}_q$ order for $q>3$.",
        "positive": "Majorana Doublets, Flat Bands, and Dirac Nodes in s-Wave Superfluids: Topological superfluids protected by mirror and time-reversal symmetries are\nexotic states of matter possessing Majorana Kramers pairs (MKPs), yet their\nrealizations have long been hindered by the requirement of unconventional\npairing. We propose to realize such a topological superfluid by utilizing\n$s$-wave pairing and emergent mirror and time-reversal symmetries in two\ncoupled 1D ultracold atomic Fermi gases with spin-orbit coupling. By stacking\nsuch systems into 2D, we discover topological and Dirac-nodal superfluids\nhosting distinct MKP flat bands. We show that the emergent symmetries make the\nMKPs and their flat bands stable against pairing fluctuations that otherwise\nannihilate paired Majoranas. Exploiting new experimental developments, our\nscheme provides a unique platform for exploring MKPs and their applications in\nquantum computation."
    },
    {
        "anchor": "Correlated dynamics of fermionic impurities induced by the counterflow\n  of an ensemble of fermions: We investigate the nonequilibrium quantum dynamics of a single and two heavy\nfermionic impurities being harmonically trapped and repulsively interacting\nwith a finite ensemble of majority fermions. A quench of the potential of the\nmajority species from a double-well to a harmonic trap is applied, enforcing\nits counterflow which in turn perturbs the impurities. For weak repulsions it\nis shown that the mixture undergoes a periodic mixing and demixing dynamics,\nwhile stronger interactions lead to a more pronounced dynamical spatial\nseparation. In the presence of correlations the impurity exhibits an expansion\ndynamics which is absent in the Hartree-Fock case resulting in an enhanced\ndegree of miscibility. We generalize our results to different impurity masses\nand demonstrate that the expansion amplitude of the impurity reduces for a\nlarger mass. Furthermore, we showcase that the majority species is strongly\ncorrelated and a phase separation occurs on the two-body level. Most\nimportantly, signatures of attractive impurity-impurity induced interactions\nmediated by the majority species are identified in the time-evolution of the\ntwo-body correlations of the impurities, a result that is supported by\ninspecting their spatial size.",
        "positive": "Microscopic evolution of doped Mott insulators from polaronic metal to\n  Fermi liquid: The competition between antiferromagnetism and hole motion in two-dimensional\nMott insulators lies at the heart of a doping-dependent transition from an\nanomalous metal to a conventional Fermi liquid. Condensed matter experiments\nsuggest charge carriers change their nature within this crossover, but a\ncomplete understanding remains elusive. We observe such a crossover in\nFermi-Hubbard systems on a cold-atom quantum simulator and reveal the\ntransformation of multi-point correlations between spins and holes upon\nincreasing doping at temperatures around the superexchange energy. Conventional\nobservables, such as spin susceptibility, are furthermore computed from the\nmicroscopic snapshots of the system. Starting from a magnetic polaron regime,\nwe find the system evolves into a Fermi liquid featuring incommensurate\nmagnetic fluctuations and fundamentally altered correlations. The crossover is\ncompleted for hole dopings around $30\\%$. Our work benchmarks theoretical\napproaches and discusses possible connections to lower temperature phenomena."
    },
    {
        "anchor": "Subharmonic fidelity revival in a driven PXP model: The PXP model hosts a special set of nonergodic states, referred to as\nquantum many-body scars. One of the consequences of quantum scarring is the\nperiodic revival of the wave function fidelity. It has been reported that\nquantum fidelity revival occurs in the PXP model for certain product states,\nand periodic driving of chemical potential can enhance the magnitude of quantum\nrevival, and can even change the frequencies of revival showing the subharmonic\nresponse. Although the effect of the periodic driving in the PXP model has been\nstudied in the limit of certain perturbative regimes, the general mechanism of\nsuch enhanced revival and frequency change has been barely studied. In this\nwork, we investigate how periodic driving in the PXP model can systematically\ncontrol the fidelity revival. Particularly, focusing on the product state so\ncalled a Neel state, we analyze the condition of driving to enhance the\nmagnitude of revival or change the frequencies of revival. To clarify the\nreason of such control, we consider the similarities between the PXP model and\nthe free spin-1/2 model in graph theoretical analysis, and show that the\nquantum fidelity feature in the PXP model is well explained by the free\nspin-1/2 model. In addition, under certain limit of the driving parameters,\nanalytic approach to explain the main features of the fidelity revival is also\nperformed. Our results give an insight of the scarring nature of the\nperiodically driven PXP model and pave the way to understand their\n(sub-)harmonic responses and controls.",
        "positive": "Bose-glass phases of ultracold atoms due to cavity backaction: We determine the quantum ground-state properties of ultracold bosonic atoms\ninteracting with the mode of a high-finesse resonator. The atoms are confined\nby an external optical lattice, whose period is incommensurate with the cavity\nmode wave length, and are driven by a transverse laser, which is resonant with\nthe cavity mode. While for pointlike atoms photon scattering into the cavity is\nsuppressed, for sufficiently strong lasers quantum fluctuations can support the\nbuild-up of an intracavity field, which in turn amplifies quantum fluctuations.\nThe dynamics is described by a Bose-Hubbard model where the coefficients due to\nthe cavity field depend on the atomic density at all lattice sites. Quantum\nMonte Carlo simulations and mean-field calculations show that for large\nparameter regions cavity backaction forces the atoms into clusters with a\ncheckerboard density distribution. Here, the ground state lacks superfluidity\nand possesses finite compressibility, typical of a Bose-glass. This system\nconstitutes a novel setting where quantum fluctuations give rise to effects\nusually associated with disorder."
    },
    {
        "anchor": "Synthetic spin-orbit coupling in ultracold $\u039b$-type atoms: We consider the simulation of non-abelian gauge potentials in ultracold atom\nsystems with atom-field interaction in the $\\Lambda$ configuration where two\ninternal states of an atom are coupled to a third common one with a detuning.\nWe find the simulated non-abelian gauge potentials can have the same structures\nas those simulated in the tripod configuration if we parameterize Rabi\nfrequencies properly, which means we can design spin-orbit coupling simulation\nschemes based on those proposed in the tripod configuration. We show the\nsimulated spin-orbit coupling in the $\\Lambda$ configuration can only be of a\nform similar to $p_{x}\\sigma_{y}$ even when the Rabi frequencies are not much\nsmaller than the detuning.",
        "positive": "Path integral molecular dynamics for thermodynamics and Green's function\n  of ultracold spinor bosons: Most recently, the path integral molecular dynamics has been successfully\nused to consider the thermodynamics of single-component identical bosons and\nfermions. In this work, the path integral molecular dynamics is developed to\nsimulate the thermodynamics, Green's function and momentum distribution of\ntwo-component bosons in three dimensions. As an example of our general method,\nwe consider the thermodynamics of up to sixteen bosons in a three-dimensional\nharmonic trap. For noninteracting spinor bosons, our simulation shows a bump in\nthe heat capacity. As the repulsive interaction strength increases, however, we\nfind the gradual disappearance of the bump in the heat capacity. We believe\nthis simulation result can be tested by ultracold spinor bosons with optical\nlattices and magnetic-field Feshbach resonance to tune the inter-particle\ninteraction. We also calculate Green's function and momentum distribution of\nspinor bosons. Our work facilitates the exact numerical simulation of spinor\nbosons, whose property is one of the major problems in ultracold Bose gases."
    },
    {
        "anchor": "Bose Hubbard Models with Synthetic Spin-Orbit Coupling: Mott Insulators,\n  Spin Textures and Superfluidity: Motivated by the experimental realization of synthetic spin-orbit coupling\nfor ultracold atoms, we investigate the phase diagram of the Bose Hubbard model\nin a non-abelian gauge field in two dimensions. Using a strong coupling\nexpansion in the combined presence of spin-orbit coupling and tunable\ninteractions, we find a variety of interesting magnetic Hamiltonians in the\nMott insulator (MI), which support magnetic textures such as spin spirals and\nvortex and Skyrmion crystals. An inhomogeneous mean field treatment shows that\nthe superfluid (SF) phases inherit these exotic magnetic orders from the MI and\ndisplay, in addition, unusual modulated current patterns. We present a slave\nboson theory which gives insight into such intertwined spin-charge orders in\nthe SF, and discuss signatures of these orders in Bragg scattering, in situ\nmicroscopy, and dynamic quench experiments.",
        "positive": "Quality factor of a matter-wave beam: Imperfections in dilute atomic beams propagating in the paraxial regime and\nin potentials of cylindrical symmetry have been characterized experimentally\nthrough the measurement of a parameter analogous to a beam quality factor [Riou\net al., Phys. Rev. Lett. 96, 070404 (2006)]. We propose a generalization of\nthis parameter, which is suitable to describe dilute matter waves propagating\nbeyond the paraxial regime and in fully general linear atom-optical systems.\nThe presented quality factor shows that the atomic beam symmetry can be traded\nfor a better transverse collimation."
    },
    {
        "anchor": "Mobile impurity in a one-dimensional gas at finite temperatures: We consider the McGuire model of a one-dimensional gas of free fermions\ninteracting with a single impurity. We compute the static one-body function and\nmomentum distribution of the impurity at finite temperatures. The results\ninvolve averages over Fredholm determinants that we further analyse using the\neffective form factors approach. With this approach, we derive the\nlarge-distance behaviour of the one-body function, which takes the form of an\naveraged exponential decay. This method allows us to study an experimentally\nimportant regime of small momenta of the impurity's momentum distribution. We\nalso consider the one-body function at short distances and compute finite\ntemperature Tan's contact.",
        "positive": "Berezinskii-Kosterlitz-Thouless transition of two-dimensional Bose gases\n  in a synthetic magnetic field: We study the Berezinskii-Kosterlitz-Thouless transition of two-dimensional\nBose gases in a synthetic magnetic field using the standard Metropolis Monte\nCarlo method. The system is described by the frustrated XY model and the\ncritical temperature is calculated though the absence of central peak of the\nwave function in momentum space, which can be directly measured by the\ntime-of-flight absorbing imaging in cold atoms experiments. The results of our\nwork show agreement with former studies on superconducting Josephson arrays."
    },
    {
        "anchor": "Characterizing the Cascade of Energy in Fermionic Quantum Turbulence:\n  Pushing the Limits of High-Performance Computing: Ultracold atoms provide a form of analog quantum computer capable of\nsimulating the quantum turbulence that underlies mysterious phenomena like\npulsar glitches in rapidly spinning neutron stars. Unlike other system (e.g.\nliquid helium) ultracold atoms have a viable theoretical framework for\ndynamics, but simulations push the edge of current classical computers. We\npresent the largest simulations of fermionic quantum turbulence to date and\nexplain the computing technology needed, especially improvements in the\nEigenvalue soLvers for Petaflop Applications (elpa) library that enable us to\ndiagonalize matrices of record size (millions by millions). We quantify how\ndissipation and thermalization proceeds in fermionic quantum turbulence, and\nprovide evidence that the temperature-dependence of quantum vortices alters the\ncorrelation between the turbulent cascades of flow energy and total vortex\nlength. All simulation data and source codes are made available to facilitate\nrapid scientific progress in the field of quantum turbulence.",
        "positive": "Strong Quantum Turbulence in Bose Einstein Condensates: By combining experiments and numerical simulations which model the dynamics\nof shaken atomic Bose-Einstein condensates, we reveal the surprising nature of\nquantum turbulence in these systems. Unlike the tangles of vortex lines\ndescribed in the superfluid helium literature, we find that our turbulent\natomic condensate contains a mixture of strong fragmented density fluctuations\nand small random vortex loops which are not homogeneously distributed. This\nunusual form of turbulence, with its own properties and scaling behaviour,\nwhich we call strong quantum turbulence, is significantly different from the\nturbulence which is observed in either classical or other quantum systems, thus\nposing a new challenge in turbulence research."
    },
    {
        "anchor": "Large atom number dual-species magneto-optical trap for fermionic 6Li\n  and 40K atoms: We present the design, implementation and characterization of a dual-species\nmagneto-optical trap (MOT) for fermionic 6Li and 40K atoms with large atom\nnumbers. The MOT simultaneously contains 5.2x10^9 6Li-atoms and 8.0x10^9\n40K-atoms, which are continuously loaded by a Zeeman slower for 6Li and a\n2D-MOT for 40K. The atom sources induce capture rates of 1.2x10^9 6Li-atoms/s\nand 1.4x10^9 40K-atoms/s. Trap losses due to light-induced interspecies\ncollisions of ~65% were observed and could be minimized to ~10% by using low\nmagnetic field gradients and low light powers in the repumping light of both\natomic species. The described system represents the starting point for the\nproduction of a large-atom number quantum degenerate Fermi-Fermi mixture.",
        "positive": "Dynamical Properties of Quasi-One-Dimensional Boson-Fermion Mixtures of\n  Atoms in a Toroidal Potential: We theoretically investigate quantum-mechanical dynamics of\nquasi-one-dimensional boson-fermion mixtures of atomic gases trapped in a\ntoroidal potential, where effective inter-atomic interactions are tunable and\naffect the dynamics. We especially focus on effects of quantum statistics and\nmany-body correlations beyond the Hartree-Fock (HF) mean-field approximation on\nthe dynamics. In order to predict the dynamics, we utilize the numerical exact\ndiagonalization method and also reproduce the calculation in the HF\napproximation for comparison. The toroidal gases originally have a rotational\nsymmetry in the toroidal direction. We firstly prepare a deformed ground state\nas an initial state by adding a weak potential deformed in the toroidal\ndirection, and then remove the potential to start the dynamics. In the\ndynamics, number densities of the deformed gases exhibit oscillations as\ndemonstrated in the present paper. As a result, we find out that the bosons and\nfermions show quite different behaviors owing to quantum statistics. In\nparticular, the bosons exhibit a low-frequency oscillation in the strong\nboson-boson attraction regime owing to the many-body correlations, and it can\nnot be reproduced in the HF approximation. The oscillation of the fermions is\nstrongly influenced by that of the bosons through the boson-fermion interaction\nas a forced oscillator. In addition, we also discuss a relationship between the\nlow-frequency oscillation and restoration of the broken symmetry."
    },
    {
        "anchor": "Superfluid phases and excitations in a cold gas of d-wave interacting\n  bosonic atoms and molecules: Motivated by recent advance in orbitally tuned Feshbach resonance\nexperiments, we analyze the ground-state phase diagram and related low-energy\nexcitation spectra of a d-wave interacting Bose gas. A two-channel model with\nd-wave symmetric interactions and background s-wave interactions is adopted to\ncharacterize the gas. The ground state is found to show three interesting\nphases: atomic, molecular, and atomic-molecular superfluidity. Remarkably\ndifferently from what was previously known in the p-wave case, the atomic\nsuperfluid is found to be momentum-independent in the present d-wave case.\nBogoliubov spectra above each superfluid phase are obtained both analytically\nand numerically.",
        "positive": "Carbon-dioxide-like Skyrmion controlled by spin-orbit coupling in\n  atomic-molecular Bose-Einstein condensates: Atomic-molecular Bose-Einstein condensates (BECs) offer brand new\nopportunities to revolutionize quantum gases and probe the variation of\nfundamental constants with unprecedented sensitivity. The recent realization of\nspin-orbit coupling (SOC) in BECs provides a new platform for exploring\ncompletely new phenomena unrealizable elsewhere. However, there is no study of\nSOC atomic-molecular BECs so far. Here, we find a novel way of creating a\nRashba-Dresselhaus SOC in atomic-molecular BECs by combining the spin dependent\nphotoassociation and Raman coupling, which can control the formation and\ndistribution of a new type of topological excitation -- carbon-dioxide-like\nSkyrmion. This Skyrmion is formed by two half-Skyrmions of molecular BECs\ncoupling with one Skyrmion of atomic BECs, where the two half-Skyrmions locates\nat both sides of one Skyrmion, which can be detected by measuring the vortices\nstructures using the time-of-flight absorption imaging technique in real\nexperiments."
    },
    {
        "anchor": "The Fermi liquid theory with fractional exclusion statistics: The Fermi liquid theory may provide a good description of the thermodynamic\nproperties of an interacting particle system when the interaction between the\nparticles contributes to the total energy of the system with a quantity which\nmay depend on the total particle number, but does not depend on the\ntemperature. In such a situation, the ideal part of the Hamiltonian, i.e. the\nenergy of the system without the interaction energy, also provides a good\ndescription of the system's thermodynamics.\n  If the total interaction energy of the system, being a complicated function\nof the particle populations, is temperature dependent, then the Landau's\nquasiparticle gas cannot describe accurately the thermodynamics of the system.\n  A general solution to this problem is presented in this paper, in which the\nquasiparticle energies are redefined in such a way that the total energy of the\nsystem is identical to the sum of the energies of the quasiparticles. This\nimplies also that the thermodynamic properties of the system and those of the\nquasiparticle gas are identical.\n  By choosing a perspective in which the quasiparticle energies are fixed while\nthe density of states along the quasiparticle axis vary, we transform our\nquasiparticle system into an ideal gas which obey fractional exclusion\nstatistics.",
        "positive": "Metastable Patterns in one- and two-component dipolar Bose-Einstein\n  Condensates: In this paper we study metastable states in single- and two-component dipolar\nBose-Einstein condensates. We show that this system supports a rich spectrum of\nsymmetries that are remarkably stable despite not being ground states. In a\nparameter region where striped phases are ground states, we find such\nmetastable states that are energetically favourable compared to triangular and\nhoneycomb lattices. Among these metastable states we report a peculiar\nring-lattice state, which is led by the competition between triangular and\nhoneycomb symmetries and rarely seen in other systems. In the case of dipolar\nmixtures we show that via tuning the miscibility these states can be stabilized\nin a broader domain by utilising inter-species interactions."
    },
    {
        "anchor": "Universal non-analytic behavior of the non-equilibrium Hall conductance\n  in Floquet topological insulators: We study the Hall conductance in a Floquet topological insulator in the long\ntime limit after sudden switches of the driving amplitude. Based on a high\nfrequency expansion of the effective Hamiltonian and the micromotion operator\nwe demonstrate that the Hall conductance as function of the driving amplitude\nfollows universal non-analytic laws close to phase transitions that are related\nto conic gap closing points, namely a logarithmic divergence for gapped initial\nstates and jumps of a definite height for gapless initial states. This\nconstitutes a generalization of the results known for the static systems to the\ndriven case.",
        "positive": "Flux lattices reformulated: We theoretically explore the optical flux lattices produced for ultra-cold\natoms subject to laser fields where both the atom-light coupling and the\neffective detuning are spatially periodic. We analyze the geometric vector\npotential and the magnetic flux it generates, as well as the accompanying\ngeometric scalar potential. We show how to understand the gauge-dependent\nAharonov-Bohm singularities in the vector potential, and calculate the\ncontinuous magnetic flux through the elementary cell in terms of these\nsingularities. The analysis is illustrated with a square optical flux lattice.\nWe conclude with an explicit laser configuration yielding such a lattice using\na set of five properly chosen beams with two counterpropagating pairs (one\nalong the x axes and the other y axes), together with a single beam along the z\naxis. We show that this lattice is not phase-stable, and identify the one\nphase-difference that affects the magnetic flux. Thus armed with realistic\nlaser setup, we directly compute the Chern number of the lowest Bloch band to\nidentify the region where the non- zero magnetic flux produces a topologically\nnon-trivial band structure."
    },
    {
        "anchor": "An Exactly Solvable Model for the Integrability-Chaos Transition in\n  Rough Quantum Billiards: A central question of dynamics, largely open in the quantum case, is to what\nextent it erases a system's memory of its initial properties. Here we present a\nsimple statistically solvable quantum model describing this memory loss across\nan integrability-chaos transition under a perturbation obeying no selection\nrules. From the perspective of quantum localization-delocalization on the\nlattice of quantum numbers, we are dealing with a situation where every lattice\nsite is coupled to every other site with the same strength, on average. The\nmodel also rigorously justifies a similar set of relationships recently\nproposed in the context of two short-range-interacting ultracold atoms in a\nharmonic waveguide. Application of our model to an ensemble of uncorrelated\nimpurities on a rectangular lattice gives good agreement with ab initio\nnumerics.",
        "positive": "Time-Averaged Adiabatic Potentials: Versatile traps and waveguides for\n  ultracold quantum gases: We demonstrate a novel class of trapping potentials, time-averaged adiabatic\npotentials (TAAP) which allows the generation of a large variety of traps and\nwaveguides for ultracold atoms. Multiple traps can be coupled through\ncontrollable tunneling barriers or merged altogether. We present analytical\nexpressions for pancake-, cigar-, and ring- shaped traps. The ring-geometry is\nof particular interest for guided matter-wave interferometry as it provides a\nperfectly smooth waveguide of controllable diameter, and thus a tunable\nsensitivity of the interferometer."
    },
    {
        "anchor": "Observation of coherent quench dynamics in a metallic many-body state of\n  fermionic atoms: Quantum simulation with ultracold atoms has become a powerful technique to\ngain insight into interacting many-body systems. In particular, the possibility\nto study nonequilibrium dynamics offers a unique pathway to understand\ncorrelations and excitations in strongly interacting quantum matter. So far,\ncoherent nonequilibrium dynamics has exclusively been observed in ultracold\nmany-body systems of bosonic atoms. Here we report on the observation of\ncoherent quench dynamics of fermionic atoms. A metallic state of ultracold\nspin-polarised fermions is prepared along with a Bose-Einstein condensate in a\nshallow three-dimensional optical lattice. After a quench that suppresses\ntunnelling between lattice sites for both the fermions and the bosons, we\nobserve long-lived coherent oscillations in the fermionic momentum\ndistribution, with a period that is determined solely by the Fermi-Bose\ninteraction energy. Our results show that coherent quench dynamics can serve as\na sensitive probe for correlations in delocalised fermionic quantum states and\nfor quantum metrology.",
        "positive": "Efimov physics and universal trimer in spin-orbit coupled ultracold\n  atomic mixtures: We study the two-body and three-body bound states in ultracold atomic\nmixtures with one of the atoms subjected to an isotropic spin-orbit (SO)\ncoupling. We consider a system of two identical fermions interacting with one\nSO coupled atom. It is found that there can exist two types of three-body bound\nstates, Efimov trimers and universal trimers. The Efimov trimers are\nenergetically less favored by the SO coupling, which will finally merge into\nthe atom-dimer threshold as increasing the SO coupling strength. Nevertheless,\nthese trimers exhibit a new kind of discrete scaling law incorporating the SO\ncoupling effect. On the other hand, the universal trimers are more favored by\nthe SO coupling. They can be induced at negative s-wave scattering lengths and\nwith smaller mass ratios than those without SO coupling. These results are\nobtained by both the Born-Oppenheimer approximation and exact solutions from\nthree-body equations."
    },
    {
        "anchor": "Thermodynamics of the 3D Hubbard model on approach to the Neel\n  transition: We study the thermodynamic properties of the 3D Hubbard model for\ntemperatures down to the Neel temperature using cluster dynamical mean-field\ntheory. In particular we calculate the energy, entropy, density, double\noccupancy and nearest-neighbor spin correlations as a function of chemical\npotential, temperature and repulsion strength. To make contact with cold-gas\nexperiments, we also compute properties of the system subject to an external\ntrap in the local density approximation. We find that an entropy per particle\n$S/N \\approx 0.65(6)$ at $U/t=8$ is sufficient to achieve a Neel state in the\ncenter of the trap, substantially higher than the entropy required in a\nhomogeneous system. Precursors to antiferromagnetism can clearly be observed in\nnearest-neighbor spin correlators.",
        "positive": "Many-body effects in the excitations and dynamics of trapped\n  Bose-Einstein condensates: This review explores the dynamics and the low-energy excitation spectra of\nBose-Einstein condensates (BECs) of interacting bosons in external potential\ntraps putting particular emphasis on the emerging many-body effects beyond\nmean-field descriptions. To do so, methods have to be used that, in principle,\ncan provide numerically exact results for both the dynamics and the excitation\nspectra in a systematic manner. Numerically exact results for the dynamics are\npresented employing the well-established multicongurational time-dependent\nHartree for bosons (MCTDHB) method. The respective excitation spectra are\ncalculated utilizing the more recently introduced linear-response theory atop\nit (LR-MCTDHB). The latter theory gives rise to an, in general, non-hermitian\neigenvalue problem. The theory and its newly developed implementation are\ndescribed in detail and benchmarked towards the exactly-solvable\nharmonic-interaction model. Several applications to BECs in one- and\ntwo-dimensional potential traps are discussed. With respect to dynamics, it is\nshown that both the out-of-equilibrium tunneling dynamics and the dynamics of\ntrapped vortices are of many-body nature. Furthermore, many-body effects in the\nexcitation spectra are presented for BECs in different trap geometries. It is\ndemonstrated that even for essentially-condensed systems, the spectrum of the\nlowest-in-energy excitations computed at the many-body level can differ\nsubstantially from the standard mean-field description. In general, it is shown\nthat bosons carrying angular momentum are more sensitive to many-body effects\nthan bosons without. These effects are present in both the dynamics and the\nexcitation spectrum."
    },
    {
        "anchor": "Spin Excitation Spectra of Spin-Orbit Coupled Bosons in Optical Lattice: Spin-wave excitation plays important roles in the investigation of the\nmagnetic phases. In this paper, we study the spin-wave excitation spectra of\ntwo-component Bose gases with spin-orbit coupling on a deep square optical\nlattice using spin-wave theory. We find that, while the excitation spectrum of\nthe vortex crystal phase is gapless with a linear dispersion in the vicinity of\nthe minimum point, the spectra of the commensurate spiral spin phase and the\nskyrmion crystal phase are gapped. Significantly, the spin fluctuations\nstrongly destabilize the classical ground state of the skyrmion phase. It\nsuggests the emergence of a new state in the phase diagram. Such features of\nthe spin excitation spectra provide further insights into the exploration of\nthe exotic spin phases.",
        "positive": "Phantom energy in the nonlinear response of a quantum many-body scar\n  state: Quantum many-body scars are notable as nonthermal states that exist at high\nenergies. Here, we use attractively interacting dysprosium gases to create scar\nstates that are stable enough be driven into a strongly nonlinear regime while\nretaining their character. We uncover an emergent nonlinear many-body\nphenomenon, the effective transmutation of attractive interactions into\nrepulsive interactions. We measure how the kinetic and total energies evolve\nafter quenching the confining potential. Although the bare interactions are\nattractive, the low-energy degrees of freedom evolve as if they repel each\nother: Thus, their kinetic energy paradoxically decreases as the gas is\ncompressed. The missing ``phantom'' energy is quantified by benchmarking our\nexperimental results against generalized hydrodynamics calculations. We present\nevidence that the missing kinetic energy is stored in very high-momentum modes."
    },
    {
        "anchor": "Generating Symmetry-Protected Long-Range Entanglement in Many-Body\n  Systems: Entanglement between spatially distant qubits is perhaps the most\ncounterintuitive and vital resource for distributed quantum computing. However,\ndespite a few special cases, there is no known general procedure to maximally\nentangle two distant parts of an interacting many-body system. Here we present\na symmetry-based approach, whereby one applies several timed pulses to drive a\nsystem to a particular symmetry sector with maximal bipartite long-range\nentanglement. As a concrete example, we demonstrate how a simple sequence of\non-site pulses on a qubit array can efficiently produce any given number of\nstable nonlocal Bell pairs, realizable in several present-day atomic and\nphotonic experimental platforms. More generally, our approach paves a route for\nnovel state preparation by harnessing symmetry. For instance, we show how it\nenables the creation of long-sought-after superconducting $\\eta$ pairs in a\nrepulsive Hubbard model.",
        "positive": "Spectral statistics of molecular resonances in erbium isotopes: How\n  chaotic are they?: We perform a comprehensive analysis of the spectral statistics of the\nmolecular resonances in $^{166}$Er and $^{168}$Er observed in recent ultracold\ncollision experiments [Frisch et al., Nature {\\bf 507}, 475 (2014)] with the\naim of determining the chaoticity of this system. We calculate different\nindependent statistical properties to check their degree of agreement with\nrandom matrix theory (RMT), and analyze if they are consistent with the\npossibility of having missing resonances. The analysis of the short-range\nfluctuations as a function of the magnetic field points to a steady increase of\nchaoticity until $B \\sim 30$ G. The repulsion parameter decreases for higher\nmagnetic fields, an effect that can be interpreted as due to missing\nresonances. The analysis of long-range fluctuations allows us to be more\nquantitative and estimate a $20-25\\%$ fraction of missing levels. Finally, a\nstudy of the distribution of resonance widths provides additional evidence\nsupporting missing resonances of small width compared with the experimental\nmagnetic field resolution. We conclude that further measurements with increased\nresolution will be necessary to give a final answer to the problem of missing\nresonances and the agreement with RMT."
    },
    {
        "anchor": "Dynamics of quantum vortices in a quasi-two-dimensional Bose-Einstein\n  condensate with two \"holes\": The dynamics of interacting quantum vortices in a quasi-two-dimensional\nspatially inhomogeneous Bose-Einstein condensate, whose equilibrium density\nvanishes at two points of the plane with a possible presence of an immobile\nvortex with a few circulation quanta at each point, has been considered in a\nhydrodynamic approximation. A special class of density profiles has been\nchosen, so that it proves possible to calculate analytically the velocity field\nproduced by point vortices. The equations of motion have been given in a\nnoncanonical Hamiltonian form. The theory has been generalized to the case\nwhere the condensate forms a curved quasi-two-dimensional shell in the\nthree-dimensional space.",
        "positive": "The spatial coherence of weakly interacting one-dimensional\n  non-equilibrium Bosonic quantum fluids: We present a theoretical analysis of spatial correlations in a\none-dimensional driven-dissipative non-equilibrium condensate. Starting from a\nstochastic generalized Gross-Pitaevskii equation, we derive a noisy\nKuramoto-Sivashinsky equation for the phase dynamics. For sufficiently strong\ninteractions, the coherence decays exponentially in close analogy to the\nequilibrium Bose gas. When interactions are small on a scale set by the\nnonequilibrium condition, we find through numerical simulations a crossover\nbetween a Gaussian and exponential decay with peculiar scaling of the coherence\nlength on the fluid density and noise strength."
    },
    {
        "anchor": "Exactly solvable model of two trapped quantum particles interacting via\n  finite-range soft-core interactions: The exactly solvable model of two indistinguishable quantum particles (bosons\nor fermions) confined in a one-dimensional harmonic trap and interacting via\nfinite-range soft-core interaction is presented and many properties of the\nsystem are examined. Particularly, it is shown that independently on the\npotential range, in the strong interaction limit bosonic and fermionic\nsolutions become degenerate. For sufficiently large ranges a specific\ncrystallization appears in the system. The results are compared to predictions\nof the celebrated Busch {\\it et al.} model and those obtained in the\nTonks-Girardeau limit. The assumed inter-particle potential is very similar to\nthe potential between ultra-cold dressed Rydberg atoms. Therefore, the model\ncan be examined experimentally.",
        "positive": "A single atom detector integrated on an atom chip: fabrication,\n  characterization and application: We describe a robust and reliable fluorescence detector for single atoms that\nis fully integrated into an atom chip. The detector allows spectrally and\nspatially selective detection of atoms, reaching a single atom detection\nefficiency of 66%. It consists of a tapered lensed single-mode fiber for\nprecise delivery of excitation light and a multi-mode fiber to collect the\nfluorescence. The fibers are mounted in lithographically defined holding\nstructures on the atom chip. Neutral 87Rb atoms propagating freely in a\nmagnetic guide are detected and the noise of their fluorescence emission is\nanalyzed. The variance of the photon distribution allows to determine the\nnumber of detected photons / atom and from there the atom detection efficiency.\nThe second order intensity correlation function of the fluorescence shows\nnear-perfect photon anti-bunching and signs of damped Rabi-oscillations. With\nsimple improvements one can boost the detection efficiency to > 95%."
    },
    {
        "anchor": "Suppression of Faraday waves in a Bose-Einstein condensate in the\n  presence of an optical lattice: We study the formation of Faraday waves in an elongated Bose-Einstein\ncondensate in presence of a one-dimensional optical lattice, where phonons are\nparametrically excited by modulating the radial confinement of the condensate.\nFor very shallow optical lattices, phonons with a well-defined wave vector\npropagate along the condensate, as in the absence of the lattice, and we\nobserve the formation of a Faraday pattern. By increasing the potential depth,\nthe local sound velocity decreases and when it equals the condensate local\nphase velocity, the condensate becomes dynamically unstable and the parametric\nexcitation of Faraday waves is suppressed.",
        "positive": "Production and characterization of a fragmented spinor Bose-Einstein\n  condensate: Understanding the ground state of many-body fluids is a central question of\nstatistical physics. Usually for weakly interacting Bose gases, most particles\noccupy the same state, corresponding to a Bose--Einstein condensate. However,\nanother scenario may occur with the emergence of several, macroscopically\npopulated single-particle states. The observation of such fragmented states\nremained elusive so far, due to their fragility to external perturbations. Here\nwe produce a 3-fragment condensate for a spin 1 gas of $\\sim 100$ atoms, with\nanti-ferromagnetic interactions and vanishing collective spin. Using a\nspin-resolved detection approaching single-atom resolution, we show that the\nreconstructed many-body state is quasi-pure, while one-body observables\ncorrespond to a mixed state. Our results highlight the interplay between\nsymmetry and interaction to develop entanglement in a quantum system."
    },
    {
        "anchor": "Collective excitation of a Bose-Einstein condensate by modulation of the\n  atomic scattering length: We excite the lowest-lying quadrupole mode of a Bose-Einstein condensate by\nmodulating the atomic scattering length via a Feshbach resonance. Excitation\noccurs at various modulation frequencies, and resonances located at the natural\nquadrupole frequency of the condensate and at the first harmonic are observed.\nWe also investigate the amplitude of the excited mode as a function of\nmodulation depth. Numerical simulations based on a variational calculation\nagree with our experimental results and provide insight into the observed\nbehavior.",
        "positive": "Vortical and fundamental solitons in dipolar Bose-Einstein condensates\n  trapped in isotropic and anisotropic nonlinear potentials: We predict the existence of stable fundamental and vortical bright solitons\nin dipolar Bose-Einstein condensates (BECs) with repulsive dipole-dipole\ninteractions (DDI). The condensate is trapped in the 2D plane with the help of\nthe repulsive contact interactions whose local strength grows $\\sim r^{4}$ from\nthe center to periphery, while dipoles are oriented perpendicular to the\nself-trapping plane. The confinement in the perpendicular direction is provided\nby the usual harmonic-oscillator potential. The objective is to extend the\nrecently induced concept of the self-trapping of bright solitons and solitary\nvortices in the pseudopotential, which is induced by the repulsive local\nnonlinearity with the strength growing from the center to periphery, to the\ncase when the trapping mechanism competes with the long-range repulsive DDI.\nAnother objective is to extend the analysis for elliptic vortices and solitons\nin an anisotropic nonlinear pseudopotential. Using the variational\napproximation (VA) and numerical simulations, we construct families of\nself-trapped modes with vorticities $\\ell =0$ (fundamental solitons), $\\ell\n=1$, and $\\ell =2$. The fundamental solitons and vortices with $\\ell =1$ exist\nup to respective critical values of the eccentricity of the anisotropic\npseudopotential, being stable in the entire existence regions. The vortices\nwith $\\ell =2$ are stable solely in the isotropic model."
    },
    {
        "anchor": "Dilute Bose gas in classical environment at low temperatures: The properties of a dilute Bose gas with the non-Gaussian quenched disorder\nare analysed. Being more specific we have considered a system of bosons\nimmersed in the classical bath consisting of the non-interacting particles with\ninfinite mass. Making use of perturbation theory up to second order we have\nstudied the impact of environment on the ground-state thermodynamic and\nsuperfluid characteristics of the Bose component.",
        "positive": "Enhanced coupling between ballistic exciton-polariton condensates\n  through tailored pumping: We propose a method to enhance the spatial coupling between ballistic\nexciton-polariton condensates in a semiconductor microcavity based on available\nspatial light modulator technologies. Our method, verified by numerically\nsolving a generalized Gross-Pitaevskii model, exploits the strong\nnonequilibrium nature of exciton-polariton condensation driven by localized\nnonresonant optical excitation. Tailoring the excitation beam profile from a\nGaussian into a polygonal shape results in refracted and focused radial streams\nof outflowing polaritons from the excited condensate which can be directed\ntowards nearest neighbors. Our method can be used to lower the threshold power\nneeded to achieve polariton condensation and increase spatial coherence in\nextended systems, paving the way towards creating extremely large-scale quantum\nfluids of light."
    },
    {
        "anchor": "BCS pairing in fully repulsive fermion mixtures: We consider a mixture of two neutral cold Fermi gases with repulsive\ninteractions. We show that in some region of the parameter space of the system\nthe effective attraction between fermions of the same type can appear due to\nthe exchange of collective excitations. This leads to the formation of BCS\npairing in the case where bare inter-atomic interactions are repulsive.",
        "positive": "Condensate fraction of a resonant Fermi gas with spin-orbit coupling in\n  three and two dimensions: We study the effects of laser-induced Rashba-like spin-orbit coupling along\nthe BCS-BEC crossover of a Feshbach resonance for a two-spin-component Fermi\ngas. We calculate the condensate fraction in three and two dimensions and find\nthat this quantity characterizes the crossover better than other quantities,\nlike the chemical potential or the pairing gap. By considering both the singlet\nand the triplet pairings, we calculate the condensate fraction and show that a\nlarge enough spin-orbit interaction enhances the singlet condensate fraction in\nthe BCS side while suppressing it on the BEC side."
    },
    {
        "anchor": "Ultradilute quantum liquid drops: Using quantum Monte Carlo methods we have studied dilute Bose-Bose mixtures\nwith attractive interspecies interaction in the limit of zero temperature. The\ncalculations are exact within some statistical noise and thus go beyond\nprevious perturbative estimations. By tuning the intensity of the attraction,\nwe observe the evolution of an $N$-particle system from a gas to a self-bound\nliquid drop. This observation agrees with recent experimental findings and\nallows for the study of an ultradilute liquid never observed before in Nature.",
        "positive": "Numerical calculation of spectral functions of the Bose-Hubbard model\n  using B-DMFT: We calculate the momentum dependent spectral function of the Bose-Hubbard\nmodel on a simple cubic lattice in three dimensions within the bosonic\ndynamical mean-field theory (B-DMFT). The continuous-time quantum Monte Carlo\nmethod is used to solve the self-consistent B-DMFT equations together with the\nmaximum entropy method for the analytic continuation to real frequencies.\nResults for weak, intermediate, and strong interactions are presented. In the\nlimit of weak and strong interactions very good agreement with results obtained\nby perturbation theory is found. By contrast, at intermediate interactions the\nresults differ significantly, indicating that in this regime perturbative\nmethods fail do describe the dynamics of interacting bosons."
    },
    {
        "anchor": "New states of matter with fine-tuned interactions: quantum droplets and\n  dipolar supersolids: Quantum fluctuations can stabilize Bose-Einstein condensates (BEC) against\nthe mean-field collapse. Stabilization of the condensate has been observed in\nquantum degenerate Bose-Bose mixtures and dipolar BECs. The fine-tuning of the\ninteratomic interactions can lead to the emergence of two new states of matter:\nliquid-like selfbound quantum droplets and supersolid crystals formed from\nthese droplets. We review the properties of these exotic states of matter and\nsummarize the experimental progress made using dipolar quantum gases and\nBose-Bose mixtures. We conclude with an outline of important open questions\nthat could be addressed in the future.",
        "positive": "Periodically and Quasi-periodically Driven Dynamics of Bose-Einstein\n  Condensates: We study the quantum dynamics of Bose-Einstein condensates when the\nscattering length is modulated periodically or quasi-periodically in time\nwithin the Bogoliubov framework. For the periodically driven case, we consider\ntwo protocols where the modulation is a square-wave or a sine-wave. In both\nprotocols for each fixed momentum, there are heating and non-heating phases,\nand a phase boundary between them. The two phases are distinguished by whether\nthe number of excited particles grows exponentially or not. For the\nquasi-periodically driven case, we again consider two protocols: the\nsquare-wave quasi-periodicity, where the excitations are generated for almost\nall parameters as an analog of the Fibonacci-type quasi-crystal; and the\nsine-wave quasi-periodicity, where there is a finite measure parameter regime\nfor the non-heating phase. We also plot the analogs of the Hofstadter butterfly\nfor both protocols."
    },
    {
        "anchor": "Numerical Studies of Quantum Turbulence: We review numerical studies of quantum turbulence. Quantum turbulence is\ncurrently one of the most important problems in low temperature physics and is\nactively studied for superfluid helium and atomic Bose--Einstein condensates. A\nkey aspect of quantum turbulence is the dynamics of condensates and quantized\nvortices. The dynamics of quantized vortices in superfluid helium are described\nby the vortex filament model, while the dynamics of condensates are described\nby the Gross--Pitaevskii model. Both of these models are nonlinear, and the\nquantum turbulent states of interest are far from equilibrium. Hence, numerical\nstudies have been indispensable for studying quantum turbulence. In fact,\nnumerical studies have contributed in revealing the various problems of quantum\nturbulence. This article reviews the recent developments in numerical studies\nof quantum turbulence. We start with the motivation and the basics of quantum\nturbulence and invite readers to the frontier of this research. Though there\nare many important topics in the quantum turbulence of superfluid helium, this\narticle focuses on inhomogeneous quantum turbulence in a channel, which has\nbeen motivated by recent visualization experiments. Atomic Bose--Einstein\ncondensates are a modern issue in quantum turbulence, and this article reviews\na variety of topics in the quantum turbulence of condensates e.g.\ntwo-dimensional quantum turbulence, weak wave turbulence, turbulence in a\nspinor condensate, $etc.$, some of which has not been addressed in superfluid\nhelium and paves the novel way for quantum turbulence researches. Finally we\ndiscuss open problems.",
        "positive": "Achieving the Quantum Ground State of a Mechanical Oscillator using a\n  Bose-Einstein Condensate with Back-Action and Cold Damping feedback schemes: We present a detailed study to show the possibility of approaching the\nquantum ground-state of a hybrid optomechanical quantum device formed by a\nBose-Einstein condensate (BEC) confined inside a high-finesse optical cavity\nwith an oscillatory end mirror. Cooling is achieved using two experimentally\nrealizable schemes: back-action cooling and cold damping quantum feedback\ncooling. In both the schemes, we found that increasing the two body atom-atom\ninteraction brings the mechanical oscillator to its quantum ground state. It\nhas been observed that back-action cooling is more effective in the good cavity\nlimit while the cold damping cooling scheme is more relevant in the bad cavity\nlimit. It is also shown that in the cold damping scheme, the device is more\nefficient in the presence of BEC than in the absence of BEC."
    },
    {
        "anchor": "Generalized Stefan-Boltzmann law: We reconsider the thermodynamic derivation by L. Boltzmann of the Stefan law\nand we generalize it for various different physical systems {\\it whose chemical\npotential vanishes}. Being only based on classical arguments, therefore\nindependent of the quantum statistics, this derivation applies as well to the\nsaturated Bose gas in various geometries as to \"compensated\" Fermi gas near a\nneutrality point, such as a gas of Weyl Fermions. It unifies in the same\nframework the thermodynamics of many different bosonic or fermionic\nnon-interacting gases which were until now described in completely different\ncontexts.",
        "positive": "Signatures of spatial inversion asymmetry of an optical lattice observed\n  in matter-wave diffraction: The structure of a two-dimensional honeycomb optical lattice potential with\nsmall inversion asymmetry is characterized using coherent diffraction of\n$^{87}$Rb atoms. We demonstrate that even a small potential asymmetry, with\npeak-to-peak amplitude of $\\leq 2.3\\%$ of the overall lattice potential, can\nlead to pronounced inversion asymmetry in the momentum-space diffraction\npattern. The observed asymmetry is explained quantitatively by considering both\nKapitza-Dirac scattering in the Raman-Nath regime, and also either perturbative\nor full-numerical treatment of the band structure of a periodic potential with\na weak inversion-symmetry-breaking term. Our results have relevance for both\nthe experimental development of coherent atom optics and the proper\ninterpretation of time-of-flight assays of atomic materials in optical\nlattices."
    },
    {
        "anchor": "Kinetic theory of non-thermal fixed points in a Bose gas: We outline a kinetic theory of non-thermal fixed points for the example of a\ndilute Bose gas, partially reviewing results obtained earlier, thereby\nextending, complementing, generalizing and straightening them out. We study\nuniversal dynamics after a cooling quench, focusing on situations where the\ntime evolution represents a pure rescaling of spatial correlations, with time\ndefining the scale parameter. The non-equilibrium initial condition set by the\nquench induces a redistribution of particles in momentum space. Depending on\nconservation laws, this can take the form of a wave-turbulent flux or of a more\ngeneral self-similar evolution, signaling the critically slowed approach to a\nnon-thermal fixed point. We identify such fixed points using a non-perturbative\nkinetic theory of collective scattering between highly occupied long-wavelength\nmodes. In contrast, a wave-turbulent flux, possible in the perturbative\nBoltzmann regime, builds up in a critically accelerated self-similar manner. A\nkey result is the simple analytical universal scaling form of the\nnon-perturbative many-body scattering matrix, for which we lay out the concrete\nconditions under which it applies. We derive the scaling exponents for the time\nevolution as well as for the power-law tail of the momentum distribution\nfunction, for a general dynamical critical exponent $z$ and an anomalous\nscaling dimension $\\eta$. The approach of the non-thermal fixed point is, in\nparticular, found to involve a rescaling of momenta in time $t$ by $t^{\\beta}$,\nwith $\\beta=1/z$, within our kinetic approach independent of $\\eta$. We confirm\nour analytical predictions by numerically evaluating the kinetic scattering\nintegral as well as the non-perturbative many-body coupling function. As a side\nresult we obtain a possible finite-size interpretation of wave-turbulent\nscaling recently measured by Navon et al.",
        "positive": "A proof to Biswas-Mitra-Bhattacharyya conjecture for ideal quantum gas\n  trapped under generic power law potential $U=\\sum_{i=1} ^d c_i |\\frac\n  {x_i}{a_i}|^{n_i}$ in $d$ dimension: The well known relation for ideal classical gas $\\Delta \\epsilon^2=kT^2 C_V$\nwhich does not remain valid for quantum system is revisited. A new connection\nis established between energy fluctuation and specific heat for quantum gases,\nvalid in the classical limit and the degenerate quantum regime as well. Most\nimportantly the proposed Biswas-Mitra-Bhattacharyya (BMB) conjecture (Biswas\n$et.$ $al.$, J. Stat. Mech. P03013, 2015.) relating hump in energy fluctuation\nand discontinuity of specific heat is proved and precised in this manuscript."
    },
    {
        "anchor": "Thermally Fluctuating Inhomogeneous Superfluid State of Strongly\n  Interacting Fermions in an Optical Lattice: The presence of attractive interaction between fermions can lead to pairing\nand superfluidity in an optical lattice. The temperature needed to observe\nsuperfluidity is about a tenth of the tunneling energy in the optical lattice,\nand currently beyond experimental reach. However, at strong coupling the\nprecursors to global superfluidity should be visible at achievable\ntemperatures, in terms of fluctuating domains with strong pairing correlations.\nWe explore this regime of the attractive two dimensional fermion Hubbard model,\nin the presence of a confining potential, using a new Monte Carlo technique. We\ncapture the low temperature inhomogeneous superfluid state with its unusual\nspectral signatures but mainly focus on the experimentally accessible\nintermediate temperature state. In this regime, and for the trap center density\nwe consider, there is a large pairing amplitude at the center, spatially\ncorrelated into domains extending over several lattice spacings. We map out the\nthermal evolution of the local density, the double occupancy, the pairing\ncorrelations, and the momentum distribution function across this phase\nfluctuation window.",
        "positive": "Macroscopic quantum superpositon states of two-component Bose-Einstein\n  condensates: We examine a two-component Bose-Einstein condensate in a double-well\npotential. We propose a model for the creation of many-particle macroscopic\nquantum superposition states. The effect of dissipation on the formation of\nthese states is also investigated with the Monte-Carlo wavefunction technique."
    },
    {
        "anchor": "Josephson junction dynamics in a two-dimensional ultracold Bose gas: We investigate the Berezinskii-Kosterlitz-Thouless (BKT) scaling of the\ncritical current of Josephson junction dynamics across a barrier potential in a\ntwo-dimensional (2D) Bose gas, motivated by recent experiments by Luick\n\\textit{et al.} arXiv:1908.09776. Using classical-field dynamics, we determine\nthe dynamical regimes of this system, as a function of temperature and barrier\nheight. As a central observable we determine the current-phase relation, as a\ndefining property of these regimes. In addition to the ideal junction regime,\nwe find a multimode regime, a second-harmonic regime, and an overdamped regime.\nFor the ideal junction regime, we derive an analytical estimate for the\ncritical current, which predicts the BKT scaling. We demonstrate this scaling\nbehavior numerically for varying system sizes. The estimates of the critical\ncurrent show excellent agreement with the numerical simulations and the\nexperiments. Furthermore, we show the damping of the supercurrent due to phonon\nexcitations in the bulk, and the nucleation of vortex-antivortex pairs in the\njunction.",
        "positive": "Collective Excitations, Nambu-Goldstone Modes and Instability of\n  Inhomogeneous Polariton Condensates: We study non-equilibrium microcavity-polariton condensates (MPCs) in a\nharmonic potential trap theoretically. We calculate and analyze the steady\nstate, collective-excitation modes and instability of MPCs. Within excitation\nmodes, there exist Nambu-Goldstone modes that can reveal the pattern of the\nspontaneous symmetry breaking of MPCs. Bifurcation of the stable and unstable\nmodes is identified in terms of the pumping power and spot size. The unstable\nmechanism associated with the inward supercurrent flow is characterized by the\nexistence of a supersonic region within the condensate."
    },
    {
        "anchor": "Fulde-Ferrell pairing instability of a Rashba spin-orbit coupled Fermi\n  gas: We theoretically analyze the pairing instability of a three-dimensional\nultracold atomic Fermi gas towards a Fulde-Ferrell superfluid, in the presence\nof Rashba spin-orbit coupling and in-plane Zeeman field. We use the standard\nThouless criterion for the onset of superfluidity, with which the effect of\npair fluctuations is partially taken into account by approximately using a\nmean-field chemical potential at zero temperature. This gives rise to an\nimproved prediction of the superfluid transition temperature beyond mean-field,\nparticularly in the strong-coupling unitary limit. We also investigate the\npairing instability with increasing Rashba spin-orbit coupling, along the\ncrossover from a Bardeen-Cooper-Schrieffer superfluid to a Bose-Einstein\ncondensate of Rashbons (i.e., the tightly bound state of two fermions formed by\nstrong Rashba spin-orbit coupling",
        "positive": "Probing quantum properties of black holes with a Floquet-driven optical\n  lattice simulator: In the curved spacetime of a black hole, quantum physics gives rise to\ndistinctive effects such as Hawking radiation. Here, we present a scheme for an\nanalogue quantum simulation of (1 + 1)- dimensional black holes using ultracold\natoms in a locally Floquet-driven 1D optical lattice. We show how the effective\ndynamics of the driven system can generate a position-dependent tunnelling\nprofile that encodes the curved geometry of the black hole. Moreover, we\nprovide a simple and robust scheme to determine the Hawking temperature of the\nsimulated black hole based solely on on-site atom population measurements.\nFinally, we show how this scheme can be directly applied to simulate (2 + 1)D\nblack holes by utilising 2D optical lattices. By incorporating the effect of\natom-atom interactions, our simulator can probe the scrambling of quantum\ninformation which is a fundamental property of black holes."
    },
    {
        "anchor": "Thermodynamic Phase Diagram of Two-Dimensional Bosons in a Quasicrystal\n  Potential: Quantum simulation of quasicrystals in synthetic bosonic matter now paves the\nway to the exploration of these intriguing systems in wide parameter ranges.\nYet thermal fluctuations in such systems compete with quantum coherence, and\nsignificantly affect the zero-temperature quantum phases. Here we determine the\nthermodynamic phase diagram of interacting bosons in a two-dimensional,\nhomogeneous quasicrystal potential. Our results are found using quantum Monte\nCarlo simulations. Finite-size scaling is carefully considered and the quantum\nphases are systematically distinguished from thermal phases. In particular, we\ndemonstrate stabilization of a genuine Bose glass phase against the normal\nfluid in sizable parameter ranges. Our results for strong interactions are\ninterpreted using a fermionization picture and experimental relevance is\ndiscussed.",
        "positive": "Tunable spin-orbit coupling synthesized with a modulating gradient\n  magnetic field: We report the observation of tunable spin-orbit coupling (SOC) for ultracold\n$^{87}$Rb atoms in hyperfine spin-1 states. Different from most earlier\nexperiments where atomic SOC of pseudo-spin-1/2 are synthesized with Raman\ncoupling lasers, the scheme we demonstrate employs a gradient magnetic field\n(GMF) with ground state atoms and is immune to atomic spontaneous emission. The\neffect of the SOC is confirmed through the studies of: 1) the collective dipole\noscillation of an atomic condensate in a harmonic trap after the synthesized\nSOC is abruptly turned on; and 2) the minimum energy state at a finite\nadiabatically adjusted momentum when the SOC strength is slowly ramped up. The\ncoherence properties of the spinor condensates remain very good after\ninteracting with modulating GMFs, which prompts the enthusiastic claim that our\nwork provides a new repertoire for synthesized gauge fields aimed at quantum\nsimulation studies with cold atoms."
    },
    {
        "anchor": "Fragmented Many-body States of Spin-2 Bose Gas: We investigate the fragmented many-body ground states of a spin-2 Bose gas in\nzero magnetic field.\\ We point out that the exact ground state is not simply an\naverage over rotationally-invariant mean-field states, in contrast to the\nspin-1 case with even number of particles N.\\ We construct the exact ground\nstates and compare them with the angular-averaged polar and cyclic states.\\ The\nangular-averaged polar states fail to retrieve the exact eigenstate at $N$\n$\\ge$ $6$ while angular-averaged cyclic states sustain only for N with a\nmultiple of $3$.\\ We calculate the density matrices and two-particle density\nmatrices to show how deviant the angular-averaged state is from the exact one.",
        "positive": "Random walk of a massive quasiparticle in the phonon gas of an ultralow\n  temperature superfluid: We consider a 3D homogeneous superfluid at low temperature $T$ with 2 types\nof excitations, gapless phonons with a linear dispersion relation at low\nwavenumber, and gapped quasiparticles with a quadratic dispersion relation\naround extrema. We calculate the scattering amplitude of a phonon on a\nquasiparticle to leading order in $T$ for all subsonic quasiparticle\nvelocities, with a $S$-matrix formalism between exact asymptotic states dressed\nby virtual phonons. We then characterize the erratic motion of the\nquasiparticle in the superfluid due to its unceasing collisions with thermal\nphonons through mean force $F(k)$, longitudinal and transverse $k$-dependent\nmomentum diffusion coefficients, and spatial diffusion coefficient. At the\nminimum location $k_0$ of the dispersion relation, where the velocity vanishes,\n$F(k)$ varies linearly with velocity with an isotropic friction coefficient; if\n$k_0=0$, the momentum diffusion is also isotropic and $F(k_0)=0$; if $k_0>0$,\nit is not, and $F(k_0)$ is nonzero but subleading with respect to friction by\none order in $T$. The velocity time correlation function, whose integral is the\nspatial diffusion coefficient, decays with the mean velocity damping rate if\n$k_0=0$; if $k_0>0$, it has a second exponential component, with an amplitude\nand a damping rate lower by a factor $\\propto T$ (it is the velocity direction\nthermalization rate). We also characterize force and momentum diffusion close\nto the stability domain sonic edge. Our general expressions are expected to be\nexact to leading order in $T$. We illustrate them in the BCS approximation, for\na fermionic quasiparticle (an unpaired fermion) in a superfluid of spin 1/2\nfermions, realisable with cold atoms in flat bottom traps. We also refute the\nstatement of Lerch, Bartosch and Kopietz (2008), that there would be no\nfermionic quasiparticle in such a superfluid."
    },
    {
        "anchor": "Phase separation in a polarized Fermi gas with spin-orbit coupling: We study the phase separation of a spin polarized Fermi gas with spin-orbit\ncoupling near a wide Feshbach resonance. As a result of the competition between\nspin-orbit coupling and population imbalance, the phase diagram for a uniform\ngas develops a rich structure of phase separation involving gapless superfluid\nstates which are topologically non-trivial. We find that these novel gapless\nphases can be stabilized by intermediate spin-orbit coupling strengths. We then\ndemonstrate the phase separation induced by an external trapping potential and\ndiscuss the optimal parameter region for the experimental observation of the\ngapless superfluid phases.",
        "positive": "Stationary transport above the critical velocity in a one-dimensional\n  superflow past an obstacle: We consider in this work the different possible stationary flows of a one\ndimensional quantum fluid in the mean-field regime. We focus on the supersonic\nregime where a transition from a time dependent flow to a stationary\ndiffractive flow occurs at a given critical velocity. We give nonperturbative\nresults for this critical velocity in the presence of a localised obstacle of\narbitrary size and strength. In addition, we discuss the existence of\nsuperfluid-like solution in the supersonic regime due to resonant transport and\nprovide a complete map of the different regimes of stationary transport of a\nquantum fluid."
    },
    {
        "anchor": "Emergence of turbulence in an oscillating Bose-Einstein condensate: We report on the experimental observation of vortices tangle in an atomic BEC\nof Rb-87 atoms when an external oscillatory perturbation is introduced in the\ntrap. The vortices tangle configuration is a signature of the presence of a\nturbulent regime in the cloud. We also show that this turbulent cloud has\nsuppression of the aspect ratio inversion typically observed in quantum\ndegenerate bosonic gases during free expansion. Instead, the cloud expands\nkeeping the ratio between their axis constant. Turbulence in atomic superfluids\nmay constitute an alternative system to investigate decay mechanisms as well as\nto test fundamental theoretical aspects in this field.",
        "positive": "Phase separation in a mixture of trapped charged Bose-Einstein\n  condensates: We study the phase separation configurations and their rotational properties\nfor a mixture of two interacting charged Bose-Einstein condensates subject to a\nmagnetic field trapped in disc and Corbino geometries. We calculate the ground\nstate energies of azimuthal and radial phase separation configurations using\nthe Gross-Pitaevskii and the Thomas-Fermi approximations. We show that the\nresults for experimentally relevant system parameters from both approaches are\nin good agreement. The immiscible mixture in both geometries with equal\nintracomponent interactions favors the azimuthal phase separation for all\nintercomponent interactions. Only an imbalance in the intracomponent\ninteractions can result in a transition to the radial phase separation, for\nwhich the transition becomes sensitive to the shape of the trap. We present\nphase diagrams as a function of the inter and intracomponent interactions.\nWhile the radial phase separation is widely favoured in disc geometry, the\nazimuthal phase separation is favoured for narrower Corbino geometries. We\nexplore the rotational properties of the spatially separated condensates under\nthe magnetic field, studying their angular momenta and velocity fields. The\nquantization of circulation breaks down for the azimuthal phase separation. In\nthis case, the bulk region of the condensate continues to display superfluid\nflow behavior whereas the velocity field shows a rigid body behavior along the\nphase boundaries."
    },
    {
        "anchor": "Dipolar Bilayer with Antiparallel Polarization -- a Self-Bound Liquid: Dipolar bilayers with antiparallel polarization, i.e. opposite polarization\nin the two layers, exhibit liquid-like rather than gas-like behavior. In\nparticular, even without external pressure a self-bound liquid puddle of\nconstant density will form. We investigate the symmetric case of two identical\nlayers, corresponding to a two-component Bose system with equal partial\ndensities. The zero-temperature equation of state $E(\\rho)/N$, where $\\rho$ is\nthe total density, has a minimum, with an equilibrium density that decreases\nwith increasing distance between the layers. The attraction necessary for a\nself-bound liquid comes from the inter-layer dipole-dipole interaction that\nleads to a mediated intra-layer attraction. We investigate the regime of\nnegative pressure towards the spinodal instability, where the bilayer is\nunstable against infinitesimal fluctuations of the total density, conformed by\ncalculations of the speed of sound of total density fluctuations.",
        "positive": "Canonical partition functions: ideal quantum gases, interacting\n  classical gases, and interacting quantum gases: In statistical mechanics, for a system with fixed number of particles, e.g.,\na finite-size system, strictly speaking, the thermodynamic quantity needs to be\ncalculated in the canonical ensemble. Nevertheless, the calculation of the\ncanonical partition function is difficult.\\textbf{ }In this paper, based on the\nmathematical theory of the symmetric function, we suggest a method for the\ncalculation of the canonical partition function of\\ ideal quantum gases,\nincluding ideal Bose, Fermi, and Gentile gases. Moreover, we express the\ncanonical partition functions of interacting classical and quantum gases given\nby the classical and quantum cluster expansion methods in terms of the Bell\npolynomial in mathematics. The virial coefficients of ideal Bose, Fermi, and\nGentile gases is calculated from the exact canonical partition function. The\nvirial coefficients of interacting classical and quantum gases is calculated\nfrom the canonical partition function by using the expansion of the Bell\npolynomial, rather than calculated from the grand canonical potential."
    },
    {
        "anchor": "O(1) benchmarking of precise rotation in a spin-squeezed Bose-Einstein\n  condensate: Benchmarking a high-precision quantum operation is a big challenge for many\nquantum systems in the presence of various noises as well as control errors.\nHere we propose an $O(1)$ benchmarking of a dynamically corrected rotation by\ntaking the quantum advantage of a squeezed spin state in a spin-1 Bose-Einstein\ncondensate. Our analytical and numerical results show that tiny rotation\ninfidelity, defined by $1-F$ with $F$ the rotation fidelity, can be calibrated\nin the order of $1/N^2$ by only several measurements of the rotation error for\n$N$ atoms in an optimally squeezed spin state. Such an $O(1)$ benchmarking is\npossible not only in a spin-1 BEC but also in other many-spin or many-qubit\nsystems if a squeezed or entangled state is available.",
        "positive": "Finite-Temperature Density-Functional Theory of Bose-Einstein\n  Condensates: The thermodynamic approach to density functional theory (DFT) is used to\nderive a versatile theoretical framework for the treatment of\nfinite-temperature (and in the limit, zero temperature) Bose-Einstein\ncondensates (BECs). The simplest application of this framework, using the\noverall density of bosons alone, would yield the DFT of Nunes (1999). It is\nargued that a significant improvement in accuracy may be obtained by using\nadditional density fields: the condensate amplitude and the anomalous density.\nThus, two advanced schemes are suggested, one corresponding to a generalized\ntwo-fluid model of condensate systems, and another scheme which explicitly\naccounts for anomalous density contributions and anomalous effective\npotentials. The latter reduces to the Hartree-Fock-Bogoliubov approach in the\nlimit of weak interactions. For stronger interactions, a local density\napproximation is suggested, but its implementation requires accurate data for\nthe thermodynamic properties of uniform interacting BEC systems, including\nfictitious perturbed states of such systems. Provided that such data becomes\navailable, e.g., from quantum Monte Carlo computation, DFT can be used to\nobtain high-accuracy theoretical results for the equilibrium states of BECs of\nvarious geometries and external potentials."
    },
    {
        "anchor": "Gain-induced trapping of microcavity exciton polariton condensates: We have performed real and momentum space spectroscopy of exciton polariton\ncondensates in a GaAs-based microcavity under non-resonant excitation with an\nintensity stabilized laser. An effective trapping mechanism is revealed, which\nis due to the stimulated scattering gain inside the finite excitation spot\ncombined with the short lifetime. We observe several quantized modes while the\nlowest state shows Heisenberg-limited real and momentum space distributions.\nThe experimental findings are qualitatively reproduced by an open dissipative\nGross-Pitaevskii equation model.",
        "positive": "Ultrafast coherent control of spinor Bose-Einstein condensates using\n  stimulated Raman adiabatic passage: We propose the use of stimulated Raman adiabatic passage (STIRAP) to offer a\nfast high fidelity method of performing SU(2) rotations on spinor Bose Einstein\ncondensates (BEC). Past demonstrations of BEC optical control suffer from\ndifficulties arising from collective enhancement of spontaneous emission and\ninefficient two-photon transitions originating from selection rules. We present\nhere a novel scheme which allows for arbitrary coherent rotations of\ntwo-component BECs while overcoming these issues. Numerical tests of the method\nshow that for BECs of \\ce{^{87}Rb} with up to $ 10^4 $ atoms and gate times of\n$ \\SI{1}{\\micro\\second} $, decoherence due to spontaneous emission can be\nsuppressed to negligible values."
    },
    {
        "anchor": "Unidirectional spin transport of a spin-orbit-coupled atomic matter wave\n  using a moving Dirac $\u03b4$-potential well: We study the transport of a spin-orbit-coupled atomic matter wave using a\nmoving Dirac $\\delta$-potential well. In a spin-orbit-coupled system, bound\nstates can be formed in both ground and excited energy levels with a Dirac\n$\\delta$ potential. Because Galilean invariance is broken in a\nspin-orbit-coupled system, moving of the potential will induce a\nvelocity-dependent effective detuning. This induced detuning breaks the spin\nsymmetry and makes the ground-state transporting channel be spin-$\\uparrow$\n($\\downarrow$) favored while makes the excited-state transporting channel be\nspin-$\\downarrow$ ($\\uparrow$) favored for a positive-direction\n(negative-direction) transporting. When the $\\delta$-potential well moves at a\nsmall velocity, both the ground-state and the excited-state channels contribute\nto the transportation, and thus both the spin components can be efficiently\ntransported. However, when the moving velocity of the $\\delta$-potential well\nexceeds a critical value, the induced detuning is large enough to eliminate the\nexcited bound state, and makes the ground bound state the only transporting\nchannel, in which only the spin-$\\uparrow$ ($\\downarrow$) component can be\nefficiently transported in a positive (negative) direction. This work\ndemonstrates a prototype of unidirectional spin transport.",
        "positive": "Strong interaction regime of the nonlinear Landau-Zener problem for\n  photo- and magneto-association of cold atoms: We discuss the strong interaction regime of the nonlinear Landau-Zener\nproblem coming up at coherent photo- and magneto-association of ultracold\natoms. We apply a variational approach to an exact third-order nonlinear\ndifferential equation for the molecular state probability and construct an\naccurate approximation describing the whole time dynamics of the coupled\natom-molecular system. The resultant solution improves the accuracy of the\nprevious approximation by A. Ishkhanyan et al. [J. Phys. A 39, 14887 (2006)].\nThe obtained results reveal a remarkable observation that in the strong\ncoupling limit the resonance crossing is mostly governed by the nonlinearity\nwhile the coherent atom-molecular oscillations coming up soon after the\nresonance has been crossed are principally of linear nature. This observation\nis supposed to be general for all the nonlinear quantum systems having the same\ngeneric quadratic nonlinearity, due to the basic attributes of the resonance\ncrossing processes in such systems. The constructed approximation turns out to\nhave a larger applicability range (than it was initially expected) covering the\nwhole moderate coupling regime for which the proposed solution accurately\ndescribes all the main characteristics of the system's evolution except the\namplitude of the coherent atom-molecule oscillation, which is rather\noverestimated."
    },
    {
        "anchor": "The Dynamical Stripes in Spin-Orbit Coupled Bose-Einstein Condensates\n  with Josephson Junctions: The Josephson dynamics of the Bose-Einstein condensation with Raman-induced\nspin-orbit coupling is investigated. A quasi-1D trap is divided into two\nreservoirs by an optical barrier. Before the tunneling between the reservoirs\nis turned on, the system stays in its equilibrium ground state. For different\nspin-orbit coupling parameters and interaction strengthes, the ground state\ndisplays a rich phase diagram. In this work we focus on the plane wave phase\nand the stripe phase. Our calculation shows that, when the tunneling is turned\non, the plane wave phase evolves into a dynamical stripe phase, that is, the\ndensity of the particle changes from uniform to periodically modulated.\nBasically, this stripe is described by a sine function and the wave length, the\namplitude and the initial phase of the function are all varying with time. If\nthe system stays in stripe phase initially, the stripes become ``sliding\" when\nthe tunneling is turned on, which reflects the running of one of the phases of\nthe wave function.",
        "positive": "The one-dimensional Bose gas with strong two-body losses: the effect of\n  the harmonic confinement: We study the dynamics of a one-dimensional Bose gas in presence of strong\ntwo-body losses. In this dissipative quantum Zeno regime, the gas fermionises\nand its dynamics can be described with a simple set of rate equations.\nEmploying the local density approximation and a Boltzmann-like dynamical\nequation, the description is easily extended to take into account an external\npotential. We show that in the absence of confinement the population is\ndepleted in an anomalous way and that the gas behaves as a low-temperature\nclassical gas. The harmonic confinement accelerates the depopulation of the gas\nand introduces a novel decay regime, which we thoroughly characterise."
    },
    {
        "anchor": "Composite pairing and superfluidity in a one-dimensional resonant\n  Bose-Fermi mixture: We study the ground-state properties of one-dimensional mixtures of bosonic\nand fermionic atoms resonantly coupled to fermionic Feshbach molecules. When\nthe particle densities of fermionic atoms and Feshbach molecules differ, the\nsystem undergoes various depletion transitions between binary and ternary\nmixtures, as a function of the detuning parameter. However, when the particle\ndensities of fermionic atoms and Feshbach molecules are identical, the\nmolecular conversion and disassociation processes induce a gap in a sector of\nlow-energy excitations, and the remaining system can be described by a\ntwo-component Tomonaga-Luttinger liquid. Using a bosonization scheme, we derive\nthe effective low-energy Hamiltonian for the system, which has a similar form\nas that of the two-chain problem of coupled Tomonaga-Luttinger liquids. With\nthe help of improved perturbative renormalization group analysis of the latter\nproblem, we determine the ground-state phase diagram and find that it contains\na phase dominated by composite superfluid or pairing correlations between the\nopen and closed resonant channels.",
        "positive": "Anyonic molecules in atomic fractional quantum Hall liquids: a\n  quantitative probe of fractional charge and anyonic statistics: We study the quantum dynamics of massive impurities embedded in a strongly\ninteracting two-dimensional atomic gas driven into the fractional quantum Hall\n(FQH) regime under the effect of a synthetic magnetic field. For suitable\nvalues of the atom-impurity interaction strength, each impurity can capture one\nor more quasi-hole excitations of the FQH liquid, forming a bound molecular\nstate with novel physical properties. An effective Hamiltonian for such anyonic\nmolecules is derived within the Born-Oppenheimer approximation, which provides\nrenormalized values for their effective mass, charge and statistics by\ncombining the finite mass of the impurity with the fractional charge and\nstatistics of the quasi-holes. The renormalized mass and charge of a single\nmolecule can be extracted from the cyclotron orbit that it describes as a free\nparticle in a magnetic field. The anyonic statistics introduces a statistical\nphase between the direct and exchange scattering channels of a pair of\nindistinguishable colliding molecules, and can be measured from the angular\nposition of the interference fringes in the differential scattering cross\nsection. Implementations of such schemes beyond cold atomic gases are\nhighlighted, in particular in photonic systems."
    },
    {
        "anchor": "Phase separation and pattern formation in a binary Bose-Einstein\n  condensate: The miscibility-immiscibility phase transition in binary Bose-Einstein\ncondensates (BECs) can be controlled by a coupling between the two components.\nHere we propose a new scheme that uses coupling-induced pattern formation to\ntest the Kibble-Zurek mechanism (KZM) of topological-defect formation in a\nquantum phase transition. For a binary BEC in a ring trap we find that the\nnumber of domains forming the pattern scales with the coupling quench rate with\nan exponent as predicted by the KZM. For a binary BEC in an elongated harmonic\ntrap we find a different scaling law due to the transition being spatially\ninhomogeneous. We perform a \"simulation\" of the harmonically trapped system in\na ring trap to verify the scaling exponent.",
        "positive": "The eigenstate distribution fluctuation from thermal to localized\n  transitions: We study the thermalization of a quenched disordered Bose-Hubbard model. By\nconsidering the eigenstate distribution fluctuation, we show that the thermal\nto many-body localized transition is always connected to a minimum of this\ndistribution fluctuation. We also observe a Mott-localized regime, where the\nsystem fails to thermalize due to the strong on-site repulsion. At last, we\nshow how to detect this eigenstate distribution fluctuation in cold atom\nsystems, which is equivalent to measure the Loschmidt echo of the system. Our\nwork suggests a way to measure the thermal to localized transitions in\nexperiments, especially for a large system."
    },
    {
        "anchor": "Observation of Thermally Activated Vortex Pairs in a Quasi-2D Bose Gas: We measure the in-plane distribution of thermally activated vortices in a\ntrapped quasi-2D Bose gas, where we enhance the visibility of density-depleted\nvortex cores by radially compressing the sample before releasing the trap. The\npairing of vortices is revealed by the two-vortex spatial correlation function\nobtained from the vortex distribution. The vortex density decreases gradually\nas temperature is lowered, and below a certain temperature, a vortex-free\nregion emerges in the center of the sample. This shows the crossover from a\nBerezinskii-Kosterlitz-Thouless phase containing vortex-pair excitations to a\nvortex-free Bose-Einstein condensate in a finite-size 2D system.",
        "positive": "Non-Hermitian Absorption Spectroscopy: While non-Hermitian Hamiltonians have been experimentally realized in cold\natom systems, it remains an outstanding open question of how to experimentally\nmeasure their complex energy spectra in momentum space for a realistic system\nwith boundaries. The existence of non-Hermitian skin effects may make the\nquestion even more difficult to address given the fact that energy spectra for\na system with open boundaries are dramatically different from those in momentum\nspace; the fact may even lead to the notion that momentum-space band structures\nare not experimentally accessible for a system with open boundaries. Here, we\ngeneralize the widely used radio-frequency spectroscopy to measure both real\nand imaginary parts of complex energy spectra of a non-Hermitian quantum system\nfor either bosonic or fermionic atoms. By weakly coupling the energy levels of\na non-Hermitian system to auxiliary energy levels, we theoretically derive a\nformula showing that the decay of atoms on the auxiliary energy levels reflects\nthe real and imaginary parts of energy spectra in momentum space. We further\nprove that measurement outcomes are independent of boundary conditions in the\nthermodynamic limit, providing strong evidence that the energy spectrum in\nmomentum space is experimentally measurable. We finally apply our non-Hermitian\nabsorption spectroscopy protocol to the Hatano-Nelson model and non-Hermitian\nWeyl semimetals to demonstrate its feasibility."
    },
    {
        "anchor": "Hybrid matter-wave-microwave solitons produced by the local-field effect: It was recently found that the electric local-field effect (LFE) can lead to\nstrong coupling of atomic Bose-Einstein condensates (BECs) to off-resonant\noptical fields. We demonstrate that the magnetic LFE gives rise to a previously\nunexplored mechanism for coupling a (pseudo) spinor BEC or fermion gas to\nmicrowaves (MWs). We present a theory for the magnetic LFE, and find that it\ngives rise to a short-range attractive interaction between two components of\nthe (pseudo) spinor, and a long-range interaction between them. The latter\ninteraction, resulting from deformation of the magnetic field, is locally\nrepulsive but globally attractive, in sharp contrast with its counterpart for\nthe optical LFE, produced by phase modulation of the electric field. Our\nanalytical results, confirmed by the numerical computations, show that the\nlong-range interaction gives rise to modulational instability of the spatially\nuniform state, and creates stable ground states in the form of hybrid\nmatter-wave-microwave solitons (which seem like one-dimensional magnetic\nmonopoles), with a size much smaller than the MW wavelength, even in the\npresence of arbitrarily strong contact inter-component repulsion. The setting\nis somewhat similar to exciton-polaritonic condensates in semiconductor\nmicrocavities. The release of matter waves from the soliton may be used for the\nrealization of an atom laser. The analysis also applies to molecular BECs with\nrotational states coupled by the electric MW field.",
        "positive": "Entropy of a Turbulent Bose-Einstein Condensate: Quantum turbulence deals with the phenomenon of turbulence in quantum fluids,\nsuch as superfluid helium and trapped Bose-Einstein condensates (BECs).\nAlthough much progress has been made in understanding quantum turbulence,\nseveral fundamental questions remain to be answered. In this work, we\ninvestigated the entropy of a trapped BEC in several regimes, including\nequilibrium, small excitations, the onset of turbulence, and a turbulent state.\nWe considered the time evolution when the system is perturbed and let to evolve\nafter the external excitation is turned off. We derived an expression for the\nentropy consistent with the accessible experimental data, that is, using the\nassumption that the momentum distribution is well-known. We related the\nexcitation amplitude to different stages of the perturbed system, and we found\ndistinct features of the entropy in each of them. In particular, we observed a\nsudden increase in the entropy following the establishment of a particle\ncascade. We argue that entropy and related quantities can be used to\ninvestigate and characterize quantum turbulence."
    },
    {
        "anchor": "Signature of existence of a BEC-type state in a dilute gas above the BEC\n  transition temperature: We study quantum coherence properties of a dilute gas at temperatures above,\nbut not much above the transition temperature of Bose-Einstein condensation\n(BEC). In such a gas, a small proportion of the atoms may possess coherence\nlengths longer than the mean neighboring-atomic distance, implying the\nexistence of quantum coherence more than that expected for thermal atoms.\nConjecturing that a part of this proportion of the atoms may lie in a BEC-type\nstate, some unexplained experimental results [Phys. Rev. A, 71, 043615 (2005)]\ncan be explained.",
        "positive": "Bose-Einstein Condensate in a Linear Trap With a Dimple Potential: We study Bose-Einstein condensation in a linear trap with a dimple potential\nwhere we model dimple potentials by Dirac \\del function. Attractive and\nrepulsive dimple potentials are taken into account. This model allows simple,\nexplicit numerical and analytical investigations of noninteracting gases. Thus,\nthe \\Sch is used instead of the Gross-Pitaevski equation. We calculate the\natomic density, the chemical potential, the critical temperature and the\ncondensate fraction. The role of the relative depth of the dimple potential\nwith respect to the linear trap in large condensate formation at enhanced\ntemperatures is clearly revealed. Moreover, we also present a semi-classical\nmethod for calculating various quantities such as entropy analytically.\nMoreover, we compare the results of this paper with the results of a previous\npaper in which the harmonic trap with a dimple potential in 1D was\ninvestigated."
    },
    {
        "anchor": "Vortex Lattices in Strongly Confined Quantum Droplets: Bose mixture quantum droplets display a fascinating stability that relies on\nquantum fluctuations to prevent collapse driven by mean-field effects. Most\ndroplet research focuses on untrapped or weakly trapped scenarios, where the\ndroplets exhibit a liquid-like flat density profile. When weakly trapped\ndroplets rotate, they usually respond through center-of-mass motion or\nsplitting instability. Here, we study rapidly rotating droplets in the strong\nexternal confinement limit where the external potential prevents splitting and\nthe center-of-mass excitation. We find that quantum droplets form a triangular\nvortex lattice as in single-component repulsive Bose-Einstein condensates\n(BEC), but the overall density follows the analytical Thomas-Fermi profile\nobtained from a cubic equation. We observe three significant differences\nbetween rapidly rotating droplets and repulsive BECs. First, the vortex core\nsize changes markedly at finite density, visible in numerically obtained\ndensity profiles. We analytically estimate the vortex core sizes from the\ndroplets' coherence length and find good agreement with the numerical results.\nSecond, the change in the density profile gives a slight but observable\ndistortion to the lattice, which agrees with the distortion expected due to\nnonuniform superfluid density. Lastly, unlike a repulsive BEC, which expands\nsubstantially as the rotation frequency approaches the trapping frequency,\nrapidly rotating droplets show only a fractional change in their size. We argue\nthat this last point can be used to create clouds with lower filling factors,\nwhich may facilitate reaching the elusive strongly correlated regime.",
        "positive": "Quantum tricriticality at the superfluid-insulator transition of binary\n  Bose mixtures: Quantum criticality near a tricritical point (TCP) is studied in the\ntwo-component Bose-Hubbard model on square lattices. The existence of quantum\nTCP on a boundary of superfluid-insulator transition is confirmed by quantum\nMonte Carlo simulations. Moreover, we analytically derive the quantum\ntricritical behaviors on the basis of an effective field theory. We find two\nsignificant features of the quantum tricriticality, that are the chemical\npotential dependence of the superfluid transition temperature and a strong\ndensity fluctuation. We suggest that these features are directly observable in\nexisting experimental setups of Bose-Bose mixtures in optical lattices."
    },
    {
        "anchor": "Permutation symmetry in spinor quantum gases: selection rules,\n  conservation laws, and correlations: Many-body systems of identical arbitrary-spin particles, with separable spin\nand spatial degrees of freedom, are considered. Their eigenstates can be\nclassified by Young diagrams, corresponding to non-trivial permutation\nsymmetries (beyond the conventional paradigm of symmetric--antisymmetric\nstates).\n  The present work obtains (a) selection rules for additional non-separable\n(dependent on spins and coordinates) $k$-body interactions: the Young diagrams,\nassociated with the initial and the final states of a transition, can differ by\nrelocation of no more than $k$ boxes between their rows; and (b) correlation\nrules: eigenstate-averaged local correlations of $k$ particles vanish if $k$\nexceeds the number of columns (for bosons) or rows (for fermions) in the\nassociated Young diagram. It also elucidates the physical meaning of the\nquantities conserved due to permutation symmetry --- in 1929, Dirac identified\nthose with characters of the symmetric group --- relating them to\nexperimentally observable correlations of several particles.\n  The results provide a way to control the formation of entangled states\nbelonging to multidimensional non-Abelian representations of the symmetric\ngroup. These states can find applications in quantum computation and metrology.",
        "positive": "Supersolidity of cnoidal waves in an ultracold Bose gas: A one-dimensional Bose-Einstein condensate may experience nonlinear periodic\nmodulations known as \"cnoidal waves\". We argue that such structures represent\npromising candidates for the study of supersolidity-related phenomena in a\nnon-equilibrium state. A mean-field treatment makes it possible to rederive\nLeggett's formula for the superfluid fraction of the system and to estimate it\nanalytically. We determine the excitation spectrum, for which we obtain\nanalytical results in the two opposite limiting cases of (i) a linearly\nmodulated background and (ii) a train of dark solitons. The presence of two\nGoldstone (gapless) modes -- associated with the spontaneous breaking of\n$\\mathrm{U}(1)$ symmetry and of continuous translational invariance -- at large\nwavelength is verified. We also calculate the static structure factor and the\ncompressibility of cnoidal waves, which show a divergent behavior at the edges\nof each Brillouin zone."
    },
    {
        "anchor": "Reliability of lattice gauge theories: Currently, there are intense experimental efforts to realize lattice gauge\ntheories in quantum simulators. Except for specific models, however, practical\nquantum simulators can never be fine-tuned to perfect local gauge invariance.\nThere is thus a strong need for a rigorous understanding of gauge-invariance\nviolation and how to reliably protect against it. As we show through analytic\nand numerical evidence, in the presence of a gauge invariance-breaking term the\ngauge violation accumulates only perturbatively at short times before\nproliferating only at very long times. This proliferation can be suppressed up\nto infinite times by energetically penalizing processes that drive the dynamics\naway from the initial gauge-invariant sector. Our results provide a theoretical\nbasis that highlights a surprising robustness of gauge-theory quantum\nsimulators.",
        "positive": "Squeezed ensembles and anomalous dynamic roughening in interacting\n  integrable chains: It is widely accepted that local subsystems in isolated integrable quantum\nsystems equilibrate to generalized Gibbs ensembles. Here, we demonstrate the\nfailure of canonical generalized thermalization for a particular class of\ninitial states in certain types of interacting integrable models. Particularly,\nwe show that in the easy-axis regime of the quantum XXZ chain, pure\nnon-equilibrium initial states with no magnetic fluctuations instead locally\nrelax to squeezed generalized Gibbs ensembles, referring to exotic equilibrium\nstates governed by non-local equilibrium Hamiltonians with sub-extensive charge\nfluctuations that violate the self-affine scaling. The behaviour at the\nisotropic point is exceptional and depends on the initial state. We find that\nrelaxation from the N\\'{e}el state is governed by extensive fluctuations and a\nsuper-diffusive dynamical exponent compatible with the Kardar-Parisi-Zhang\nuniversality. On the other hand, there are other non-fluctuating initial states\nthat display diffusive scaling. Our predictions can be directly tested in\nstate-of-the-art cold atomic experimental settings."
    },
    {
        "anchor": "Shear Viscosity in the Strong Interaction Regime of a p-wave Superfluid\n  Fermi Gas: The $p$-wave superfluid state is a promising spin-triplet and non $s$-wave\npairing state in an ultracold Fermi gas. In this work we study the\nlow-temperature shear viscosity of a one-component $p$-wave superfluid Fermi\ngas, by means of Kubo formalism. Our study is done in the strong-coupling limit\nwhere Fermi superfluid reduces into a system of composite bosons. Taking into\naccount ${{p}_{x}}$-wave Cooper channel in the self-energy, the viscous\nrelaxation rates are determined. The relaxation rates related to these\ninteractions are calculated as a function of temperature. Their temperature\ndependence is different from the $s$-wave superfluid Fermi gas, and this is due\nto the anisotropic pairing interaction in the $p$-wave superfluid. Our results\ncontribute to understand how this anisotropy affects transport properties of\nthis unconventional superfluid Fermi gas in low temperature limit.",
        "positive": "Bosonic superfluid on lowest Landau level: We develop a low-energy effective field theory of a two-dimensional bosonic\nsuperfluid on the lowest Landau level at zero temperature and identify a Berry\nterm that governs the dynamics of coarse-grained superfluid degrees of freedom.\nFor an infinite vortex crystal we compute how the Berry term affects the\nlow-energy spectrum of soft collective Tkachenko oscillations and\nnon-dissipative Hall responses of the particle number current and stress\ntensor. This term gives rise to a quadratic in momentum term in the Hall\nconductivity, but does not generate a non-dissipative Hall viscosity."
    },
    {
        "anchor": "Pattern formation in a driven Bose-Einstein Condensate: Pattern formation is ubiquitous in nature from morphogenesis and cloud\nformation to galaxy filamentation. More often than not, patterns arise in a\nmedium driven far from equilibrium due to the interplay of dynamical\ninstability and nonlinear wave mixing. We report, based on momentum and real\nspace pattern recognition, formation of density patterns with two- (D$_2$),\nfour- (D$_4$) and six-fold (D$_6$) symmetries in Bose-Einstein condensates\n(BECs) with atomic interactions driven at two frequencies. The symmetry of the\npattern is controlled by the ratio of the frequencies. The D$_6$ density waves,\nin particular, arise from a resonant wave mixing process that coherently\ncorrelates and enhances the excitations that respect the symmetry.",
        "positive": "Quantum Simulation of Antiferromagnetic Spin Chains in an Optical\n  Lattice: Understanding exotic forms of magnetism in quantum mechanical systems is a\ncentral goal of modern condensed matter physics, with implications from high\ntemperature superconductors to spintronic devices. Simulating magnetic\nmaterials in the vicinity of a quantum phase transition is computationally\nintractable on classical computers due to the extreme complexity arising from\nquantum entanglement between the constituent magnetic spins. Here we employ a\ndegenerate Bose gas confined in an optical lattice to simulate a chain of\ninteracting quantum Ising spins as they undergo a phase transition. Strong spin\ninteractions are achieved through a site-occupation to pseudo-spin mapping. As\nwe vary an applied field, quantum fluctuations drive a phase transition from a\nparamagnetic phase into an antiferromagnetic phase. In the paramagnetic phase\nthe interaction between the spins is overwhelmed by the applied field which\naligns the spins. In the antiferromagnetic phase the interaction dominates and\nproduces staggered magnetic ordering. Magnetic domain formation is observed\nthrough both in-situ site-resolved imaging and noise correlation measurements.\nBy demonstrating a route to quantum magnetism in an optical lattice, this work\nshould facilitate further investigations of magnetic models using ultracold\natoms, improving our understanding of real magnetic materials."
    },
    {
        "anchor": "Verification of an analytic fit for the vortex core profile in\n  superfluid Fermi gases: A characteristic property of superfluidity and -conductivity is the presence\nof quantized vortices in rotating systems. To study the BEC-BCS crossover the\ntwo most common methods are the Bogoliubov-De Gennes theory and the usage of an\neffective field theory. In order to simplify the calculations for one vortex,\nit is often assumed that the hyperbolic tangent yields a good approximation for\nthe vortex structure. The combination of a variational vortex structure,\ntogether with cylindrical symmetry yields analytic (or numerically simple)\nexpressions. The focus of this article is to investigate to what extent this\nanalytic fit truly reflects the vortex structure throughout the BEC-BCS\ncrossover at finite temperatures. The vortex structure will be determined using\nthe effective field theory presented in [Eur. Phys. Journal B 88, 122 (2015)]\nand compared to the variational analytic solution. By doing this it is possible\nto see where these two structures agree, and where they differ. This comparison\nresults in a range of applicability where the hyperbolic tangent will be a good\nfit for the vortex structure.",
        "positive": "Current reversals and metastable states in the infinite Bose-Hubbard\n  chain with local particle loss: We present an algorithm which combines the quantum trajectory approach to\nopen quantum systems with a density-matrix renormalization group scheme for\ninfinite one-dimensional lattice systems. We apply this method to investigate\nthe long-time dynamics in the Bose-Hubbard model with local particle loss\nstarting from a Mott-insulating initial state with one boson per site. While\nthe short-time dynamics can be described even quantitatively by an equation of\nmotion (EOM) approach at the mean-field level, many-body interactions lead to\nunexpected effects at intermediate and long times: local particle currents far\naway from the dissipative site start to reverse direction ultimately leading to\na metastable state with a total particle current pointing away from the lossy\nsite. An alternative EOM approach based on an effective fermion model shows\nthat the reversal of currents can be understood qualitatively by the creation\nof holon-doublon pairs at the edge of the region of reduced particle density.\nThe doublons are then able to escape while the holes move towards the\ndissipative site, a process reminiscent---in a loose sense---of Hawking\nradiation."
    },
    {
        "anchor": "Energy level splitting for weakly interacting bosons in a harmonic trap: We consider identical quantum bosons with weak contact interactions in a\ntwo-dimensional isotropic harmonic trap. When the interactions are turned off,\nthe energy levels are equidistant and highly degenerate. At linear order in the\ncoupling parameter, these degenerate levels split, and we study the patterns of\nthis splitting. It turns out that the problem is mathematically identical to\ndiagonalizing the quantum resonant system of the two-dimensional\nGross-Pitaevskii equation, whose classical counterpart has been previously\nstudied in the mathematical literature on turbulence. Our purpose is to explore\nthe implications of the symmetries and energy bounds of this resonant system,\npreviously studied for the classical case, for the quantum level splitting.\nSimplifications in computing the splitting spectrum numerically result from\nexploiting the symmetries. The highest energy state emanating from each\nunperturbed level is explicitly described by our analytics. We furthermore\ndiscuss the energy level spacing distributions in the spirit of quantum chaos\ntheory. After separating the eigenvalues into blocks with respect to the known\nconservation laws, we observe the Wigner-Dyson statistics within specific large\nblocks, which leaves little room for further integrable structures in the\nproblem beyond the symmetries that are already explicitly known.",
        "positive": "Density-wave-type supersolid of two-dimensional tilted dipolar bosons: We predict a stable density-waves-type supersolid phase of a dilute gas of\ntilted dipolar bosons in a two-dimensional (2D) geometry. This many-body phase\nis manifested by the formation of the stripe pattern and elasticity coexisting\ntogether with the Bose-Einstein condensation and superfluidity at zero\ntemperature. With the increasing the tilting angle the type of the\ngas-supersolid transition changes from the first order to the second one\ndespite the 2D character of the system, whereas the anisotropy and many-body\nstabilizing interactions play crucial role. Our approach is based on the\nnumerical analysis of the phase diagram using the simulated annealing method\nfor a free-energy functional. The predicted supersolid effect can be realized\nin a variety of experimental setups ranging from excitons in heterostructures\nto cold atoms and polar molecules in optical potentials."
    },
    {
        "anchor": "Localization in random fractal lattices: We investigate the issue of eigenfunction localization in random fractal\nlattices embedded in two dimensional Euclidean space. In the system of our\ninterest, there is no diagonal disorder -- the disorder arises from random\nconnectivity of non-uniformly distributed lattice sites only. By adding or\nremoving links between lattice sites, we change the spectral dimension of a\nlattice but keep the fractional Hausdorff dimension fixed. From the analysis of\nenergy level statistics obtained via direct diagonalization of finite systems,\nwe observe that eigenfunction localization strongly depends on the spectral\ndimension. Conversely, we show that localization properties of the system do\nnot change significantly while we alter the Hausdorff dimension. In addition,\nfor low spectral dimensions, we observe superlocalization resonances and a\nformation of an energy gap around the center of the spectrum.",
        "positive": "Fidelity and criticality of quantum Ising chain with long-range\n  interactions: We study the criticality of long-range quantum ferromagnetic Ising chain with\nalgebraically decaying interactions $1/r^{\\alpha}$ via the fidelity\nsusceptibility based on the exact diagonalization and the density matrix\nrenormalization group techniques. We find that critical exponents change\nmonotonously from the mean-field universality class to the short-range Ising\nuniversality class for intermediate $\\alpha$, which are consistent with recent\nresults obtained from renormalization group. In addition, we determine the\ncritical values for $1.8 \\le \\alpha \\le 3$ from the finite-size scaling of the\nfidelity susceptibility. Our work provides very nice numerical data from the\nfidelity susceptibility for the quantum long-range ferromagnetic Ising chain."
    },
    {
        "anchor": "Confinement Induced Frustration in a One-Dimensional $\\mathbb{Z}_2$\n  Lattice Gauge Theory: Coupling dynamical charges to gauge fields can result in highly non-local\ninteractions with a linear confining potential. As a consequence, individual\nparticles bind into mesons which, in one dimension, become the new constituents\nof emergent Luttinger liquids. Furthermore, at commensurate fillings, different\nMott-insulating states can be stabilized by including nearest-neighbour (NN)\ninteractions among charges. However, rich phase diagrams expected in such\nmodels have not been fully explored and still lack comprehensive theoretical\nexplanation. Here, by combining numerical and analytical tools, we study a\nsimple one-dimensional $\\mathbb{Z}_2$ lattice gauge theory at half-filling,\nwhere U$(1)$ matter is coupled to gauge fields and interacts through NN\nrepulsion. We uncover a rich phase diagram where the local NN interaction\nstabilizes a Mott state of individual charges (or partons) on the one hand, and\na Luttinger liquid of confined mesons on the other. Furthermore, at the\ninterface between these two phases, we uncover a highly frustrated regime\narising due to the competition between the local NN repulsion and the non-local\nconfining interactions, realizing a pre-formed parton plasma. Our work is\nmotivated by the recent progress in ultracold atom experiments, where such\nsimple model could be readily implemented. For this reason we calculate the\nstatic structure factor which we propose as a simple probe to explore the phase\ndiagram in an experimental setup.",
        "positive": "Superfluid state of repulsively interacting three-component fermionic\n  atoms in optical lattices: We investigate the superfluid state of repulsively interacting\nthree-component (color) fermionic atoms in optical lattices. When the\nanisotropy of the three repulsive interactions is strong, atoms of two of the\nthree colors form Cooper pairs and atoms of the third color remain a Fermi\nliquid. An effective attractive interaction is induced by density fluctuations\nof the third-color atoms. This superfluid state is stable against changes in\nfilling close to half filling. We determine the phase diagrams in terms of\ntemperature, filling, and the anisotropy of the repulsive interactions."
    },
    {
        "anchor": "Dissipative topological superconductors in number-conserving systems: We discuss the dissipative preparation of p-wave superconductors in\nnumber-conserving one-dimensional fermionic systems. We focus on two setups:\nthe first one entails a single wire coupled to a bath, whereas in the second\none the environment is connected to a two-leg ladder. Both settings lead to\nstationary states which feature the bulk properties of a p-wave superconductor,\nidentified in this number-conserving setting through the long-distance behavior\nof the proper p-wave correlations. The two schemes differ in the fact that the\nsteady state of the single wire is not characterized by topological order,\nwhereas the two-leg ladder hosts Majorana zero modes, which are decoupled from\ndamping and exponentially localized at the edges. Our analytical results are\ncomplemented by an extensive numerical study of the steady-state properties, of\nthe asymptotic decay rate and of the robustness of the protocols.",
        "positive": "First-order phase transitions in spinor Bose gases and frustrated\n  magnets: We show that phase transitions in spin-one Bose gases and stacked triangular\nHeisenberg antiferromagnets -- an example of frustrated magnets with competing\ninteractions -- are described by the same Landau-Ginzburg-Wilson Hamiltonian\nwith O(3)$\\times$O(2) symmetry. In agreement with previous\nnonperturbative-renormalization-group studies of the three-dimensional\nO(3)$\\times$O(2) model, we find that the transition from the normal phase to\nthe superfluid ferromagnetic phase in a spin-one Bose gas is weakly first order\nand shows pseudoscaling behavior. The (nonuniversal) pseudoscaling exponent\n$\\nu$ is fully determined by the scattering lengths $a_0$ and $a_2$. We provide\nestimates of $\\nu$ in $^{87}$Rb, $^{41}$K and $^7$Li atom gases which can be\ntested experimentally. We argue that pseudoscaling comes from either a\ncrossover phenomena due to proximity of the O(6) Wilson-Fisher fixed point\n($^{87}$Rb and $^{41}$K) or the existence of two unphysical fixed points (with\ncomplex coordinates) which slow down the RG flow ($^7$Li). These unphysical\nfixed points are a remnant of the chiral and antichiral fixed points that exist\nin the O($N$)$\\times$O(2) model when $N$ is larger than $N_c\\simeq 5.3$ (the\ntransition being then second order and controlled by the chiral fixed point).\nFinally, we discuss a O(2)$\\times$O(2) lattice model and show that our results,\neven though we find the transition to be first order, are compatible with Monte\nCarlo simulations yielding an apparent second-order transition."
    },
    {
        "anchor": "Hidden order and symmetry protected topological states in quantum link\n  ladders: We show that whereas spin-1/2 one-dimensional U(1) quantum-link models (QLMs)\nare topologically trivial, when implemented in ladder-like lattices these\nmodels may present an intriguing ground-state phase diagram, which includes a\nsymmetry protected topological (SPT) phase that may be readily revealed by\nanalyzing long-range string spin correlations along the ladder legs. We propose\na simple scheme for the realization of spin-1/2 U(1) QLMs based on\nsingle-component fermions loaded in an optical lattice with s- and p-bands,\nshowing that the SPT phase may be experimentally realized by adiabatic\npreparation.",
        "positive": "Universal behavior of repulsive two-dimensional fermions in the vicinity\n  of the quantum freezing point: We show by a meta-analysis of the available Quantum Monte-Carlo (QMC) results\nthat two-dimensional fermions with repulsive interactions exhibit universal\nbehavior in the strongly-correlated regime, and that their freezing transition\ncan be described using a quantum generalization of the classical Hansen-Verlet\nfreezing criterion. We calculate the liquid-state energy and the freezing point\nof the 2D dipolar Fermi gas (2DDFG) using a variational method by taking ground\nstate wave functions of 2D electron gas (2DEG) as trial states. A comparison\nwith the recent fixed-node diffusion Monte-Carlo analysis of the 2DDFG shows\nthat our simple variational technique captures more than 95% of the correlation\nenergy, and predicts the freezing transition within the uncertainty bounds of\nQMC. Finally, we utilize the ground state wave functions of 2DDFG as trial\nstates and provide a variational account of the effects of finite 2D\nconfinement width. Our results indicate significant beyond mean-field effects.\nWe calculate the frequency of collective monopole oscillations of the quasi-2D\ndipolar gas as an experimental demonstration of correlation effects."
    },
    {
        "anchor": "Far-from-equilibrium dynamics of an ultracold Fermi gas: Nonequilibrium dynamics of an N-fold spin-degenerate ultracold Fermi gas is\ndescribed in terms of beyond-mean-field Kadanoff-Baym equations for correlation\nfunctions. Using a nonperturbative expansion in powers of 1/N, the equations\nare derived from the two-particle irreducible effective action in\nSchwinger-Keldysh formulation. The definition of the nonperturbative\napproximation on the level of the effective action ensures vital conservation\nlaws as, e.g., for the total energy and particle number. As an example, the\nlong-time evolution of a homogeneous, twofold spin-degenerate Fermi gas is\nstudied in one spatial dimension after an initial preparation far from thermal\nequilibrium. Analysis of the fluctuation-dissipation relation shows that, at\nlow energies, the gas does not thermalise.",
        "positive": "Density of condensate of a dilute Bose gas in improved Hartree-Fock\n  approximation: In a manner of Cornwal-Jackiw-Tomboulis effective action approach, the\ndensity of condensate of a dilute Bose gas confined between two planar walls is\ninvestigated within the framework of improved Hartree-Fock. Thereby, the\nquantum fluctuations are taken into account with presence of high-order terms\nin the momentum integrals. Our results show that the quantum fluctuations\nsignificantly belittle the density of condensate compared with square of the\nexpectation value of the field operator. The comparison with relating results\nof Gross-Pitaevskii theory is made."
    },
    {
        "anchor": "Enhancing quantum order with fermions by increasing species degeneracy: One of the challenges for fermionic cold atom experiments in optical lattices\nis to cool the systems to low enough temperature that they can form quantum\ndegenerate ordered phases. In particular, there has been significant work in\ntrying to find the antiferromagnetic phase transition of the Hubbard model in\nthree dimensions, without success. Here, we attack this problem from a\ndifferent angle by enhancing the ordering temperature via an increase in the\ndegeneracy of the atomic species trapped in the optical lattice. In addition to\ndeveloping the general theory, we also discuss some potential systems where one\nmight be able to achieve these results experimentally.",
        "positive": "Coupled pair approach for strongly-interacting trapped fermionic atoms: We present a coupled pair approach for studying few-body physics in\nharmonically trapped ultracold gases. The method is applied to a two-component\nFermi system of $N$ particles. A stochastically variational gaussian expansion\nmethod is applied, focusing on optimization of the two-body correlations\npresent in the strongly interacting, or unitary, limit. The groundstate energy\nof the four-, six- and eight-body problem with equal spin populations is\ncalculated with high accuracy and minimal computational effort. We also\ncalculate the structural properties of these systems and discuss their\nimplication for the many-body ultracold gas and other few-body calculations."
    },
    {
        "anchor": "Phase Transitions in a Bose-Hubbard Model with Cavity-Mediated\n  Global-Range Interactions: We study a system with competing short- and global-range interactions in the\nframework of the Bose-Hubbard model. Using a mean-field approximation we obtain\nthe phase diagram of the system and observe four different phases: a\nsuperfluid, a supersolid, a Mott insulator and a charge density wave, where the\ntransitions between the various phases can be either of first or second order.\nWe qualitatively support these results using Monte-Carlo simulations. An\nanalysis of the low-energy excitations shows that the second-order phase\ntransition from the charge density wave to the supersolid is associated with\nthe softening of particle- and hole-like excitations which give rise to a\ngapless mode and an amplitude Higgs mode in the supersolid phase. This\namplitude Higgs mode is further transformed into a roton mode which softens at\nthe supersolid to superfluid phase transition.",
        "positive": "Crystallization of Bosonic Quantum Hall States: The dominance of interactions over kinetic energy lies at the heart of\nstrongly correlated quantum matter, from fractional quantum Hall liquids, to\natoms in optical lattices and twisted bilayer graphene. Crystalline phases\noften compete with correlated quantum liquids, and transitions between them\noccur when the energy cost of forming a density wave approaches zero. A prime\nexample occurs for electrons in high magnetic fields, where the instability of\nquantum Hall liquids towards a Wigner crystal is heralded by a roton-like\nsoftening of density modulations at the magnetic length. Remarkably,\ninteracting bosons in a gauge field are also expected to form analogous liquid\nand crystalline states. However, combining interactions with strong synthetic\nmagnetic fields has been a challenge for experiments on bosonic quantum gases.\nHere, we study the purely interaction-driven dynamics of a Landau gauge\nBose-Einstein condensate in and near the lowest Landau level (LLL). We observe\na spontaneous crystallization driven by condensation of magneto-rotons,\nexcitations visible as density modulations at the magnetic length. Increasing\nthe cloud density smoothly connects this behaviour to a quantum version of the\nKelvin-Helmholtz hydrodynamic instability, driven by the sheared internal flow\nprofile of the rapidly rotating condensate. At long times the condensate\nself-organizes into a persistent array of droplets, separated by vortex\nstreets, which are stabilized by a balance of interactions and effective\nmagnetic forces."
    },
    {
        "anchor": "Formation of spontaneous density-wave patterns in DC driven lattices: Driving a many-body system out of equilibrium induces phenomena such as the\nemergence and decay of transient states, which can manifest itself as pattern\nand domain formation. The understanding of these phenomena expands the scope of\nestablished thermodynamics into the out-of-equilibrium domain. Here, we\nexperimentally and theoretically study the out-of-equilibrium dynamics of a\nbosonic lattice model subjected to a strong DC field, realized as ultracold\natoms in a strongly tilted triangular optical lattice. We observe the emergence\nof pronounced density wave patterns -- which spontaneously break the underlying\nlattice symmetry -- using a novel single-shot imaging technique with\ntwo-dimensional single-site resolution in three-dimensional systems, which also\nresolves the domain structure. Our study suggests that the short-time dynamics\narises from resonant pair tunneling processes within an effective description\nof the tilted Hubbard model. More broadly, we establish the far\nout-of-equilibrium regime of lattice models subjected to a strong DC field, as\nan exemplary and paradigmatic scenario for transient pattern formation.",
        "positive": "Prescaling in a far-from-equilibrium Bose gas: Non-equilibrium conditions give rise to classes of universally evolving\nconfigurations of quantum-many body systems at non-thermal fixed points. While\nthe fixed point and thus full scaling in space and time is generically reached\nat very long evolution times, we propose that systems can show prescaling much\nearlier in time, in particular, on experimentally accessible time scales.\nDuring the prescaling evolution, some well-measurable properties of spatial\ncorrelations already scale with the universal exponents of the fixed point\nwhile others still show scaling violations. Prescaling is characterized by the\nevolution obeying conservation laws associated with the remaining symmetry\nwhich also defines the universality class of the asymptotically reached\nnon-thermal fixed point. Here we consider $N=3$ species of spatially uniform\nthree-dimensional Bose gases, with identical inter- and intra-species\ninteractions. During prescaling, the full $U(N)$ symmetry of the model is\nbroken to $U(N-1)$ while the conserved transport, reflecting explicit and\nemerging symmetries, leads to the buildup of rescaling quasicondensate\ndistributions."
    },
    {
        "anchor": "An analysis of variational wave function for the pairing problem in\n  strongly correlated system: We report a theoretical analysis of variational wave functions for the BCS\npairing problem. Starting with a Jastrow-Feenberg (or, in a more recent\nlanguage \"fixed-node\") wave function for the superfluid state, we develop the\nfull optimized Fermi-Hypernetted Chain (FHNC-EL) equations which sum a local\napproximation of the parquet-diagrams. Close examination of the procedure\nreveals that it is essential to go beyond the usual Jastrow-Feenberg\napproximation to guarantee the correct stability range.",
        "positive": "Extended self-energy functional approach for strongly-correlated lattice\n  bosons in the superfluid phase: Among the various numerical techniques to study the physics of strongly\ncorrelated quantum many-body systems, the self-energy functional approach (SFA)\nhas become increasingly important. In its previous form, however, SFA is not\napplicable to Bose-Einstein condensation or superfluidity. In this paper we\nshow how to overcome this shortcoming. To this end we identify an appropriate\nquantity, which we term $D$, that represents the correlation correction of the\ncondensate order parameter, as it does the self-energy for the Green's\nfunction. An appropriate functional is derived, which is stationary at the\nexact physical realizations of $D$ and of the self-energy. Its derivation is\nbased on a functional-integral representation of the grand potential followed\nby an appropriate sequence of Legendre transformations. The approach is not\nperturbative and therefore applicable to a wide range of models with local\ninteractions. We show that the variational cluster approach based on the\nextended self-energy functional is equivalent to the \"pseudoparticle\" approach\nintroduced in Phys. Rev. B, 83, 134507 (2011). We present results for the\nsuperfluid density in the two-dimensional Bose-Hubbard model, which show a\nremarkable agreement with those of Quantum-Monte-Carlo calculations."
    },
    {
        "anchor": "Energetics of three interacting mass-imbalanced bodies in a\n  three-dimensional spherical harmonic trap: We consider a system of three particles, either three identical bosons or two\nidentical fermions plus an impurity, within a three-dimensional isotropic trap\ninteracting via a contact interaction. Using two approaches, one using an\ninfinite sum of basis states for the wavefunction and the other a closed form\nwavefunction, we calculate the allowable energy eigenstates of the system as a\nfunction of the interaction strength, including the strongly and weakly\ninteracting limits. For the fermionic case this is done while maintaining\ngenerality regarding particle masses. We find that the two methods of\ncalculating the spectrum are in excellent agreement in the strongly interacting\nlimit. However the infinite sum approach is unable to uniquely specify the\nenergy of Efimov states, but in the strongly interacting limit there is, to a\nhigh degree of accuracy, a correspondence between the three-body parameter\nrequired by the boundary condition of the closed form approach and the\nsummation truncation order required by the summation approach. This\nspecification of the energies and wavefunctions forms the basis with which\nthermodynamic variables such as the virial coefficients or Tan contacts, or\ndynamic phenomena like quench dynamics can be calculated.",
        "positive": "Non-equilibrium dynamics of the anyonic Tonks-Girardeau gas at finite\n  temperature: We derive an exact description of the non-equilibrium dynamics at finite\ntemperature for the anyonic Tonks-Girardeau gas extending the results of Atas\net al. [Phys. Rev. A 95, 043622 (2017)] to the case of arbitrary statistics.\nThe one-particle reduced density matrix is expressed as the Fredholm minor of\nan integral operator with the kernel being the one-particle Green's function of\nfree fermions at finite temperature and the statistics parameter determining\nthe constant in front of the integral operator. We show that the numerical\nevaluation of this representation using Nystr\\\"{o}m's method significantly\noutperforms the other approaches present in the literature when there are no\nanalytical expressions for the overlaps of the wave-functions. We illustrate\nthe distinctive features and novel phenomena present in the dynamics of anyonic\nsystems in two experimentally relevant scenarios: the quantum Newton's cradle\nsetting and the breathing oscillations initiated by a sudden change of the trap\nfrequency."
    },
    {
        "anchor": "Non-equilibrium Quantum Spin Dynamics from 2PI Functional Integral\n  Techniques in the Schwinger Boson Representation: We present a non-equilibrium quantum field theory approach to the\ninitial-state dynamics of spin models based on two-particle irreducible (2PI)\nfunctional integral techniques. It employs a mapping of spins to Schwinger\nbosons for arbitrary spin interactions and spin lengths. At next-to-leading\norder (NLO) in an expansion in the number of field components, a wide range of\nnon-perturbative dynamical phenomena are shown to be captured, including\nrelaxation of magnetizations in a 3D long-range interacting system with\nquenched disorder, different relaxation behaviour on both sides of a quantum\nphase transition and the crossover from relaxation to arrest of dynamics in a\ndisordered spin chain previously shown to exhibit many-body-localization. Where\napplicable, we employ alternative state-of-the-art techniques and find rather\ngood agreement with our 2PI NLO results. As our method can handle large system\nsizes and converges relatively quickly to its thermodynamic limit, it opens the\npossibility to study those phenomena in higher dimensions in regimes in which\nno other efficient methods exist. Furthermore, the approach to classical\ndynamics can be investigated as the spin length is increased.",
        "positive": "Comprehensive Characterization of a State-of-the-Art Apparatus for Cold\n  Electromagnetic Dysprosium Dipoles: We developed a new advanced ultra-cold Dysprosium (Dy) apparatus, which\nincorporates a quantum gas microscope (QGM) with a resolution of a quarter\nmicrometer. The QGM and the cooling and trapping regions are within the same\nvacuum glass vessel assuring simple atom transport between them. We demonstrate\nthe essential experimental steps of laser and evaporative cooling, lattice\nloading, transporting and precise positioning of a cloud of the bosonic isotope\n164 Dy at the QGM focal plane. Preliminary basic characterization of the QGM\nand future plans in enabling its full capacity are outlined. We also present a\nfeasible platform for simulating complex spin models of quantum magnetism, such\nas XYZ model, by exploiting a set of closely spaced opposite parity levels in\nDy with a large magnetic and electric dipole moment. We isolate a degenerate\nisospin-1/2 system, which possesses both magnetic and electric dipole-dipole\ncoupling, containing Ising, exchange and spin-orbit terms. The last gives rise\nto a spin model with asymmetric tunable rates, dependable on the lattice\ngeometry."
    },
    {
        "anchor": "Confinement in 1+1D $\\mathbb{Z}_2$ Lattice Gauge Theories at Finite\n  Temperature: Confinement is a paradigmatic phenomenon of gauge theories, and its\nunderstanding lies at the forefront of high-energy physics. Here, we study\nconfinement in a simple one-dimensional \\Zt lattice gauge theory at finite\ntemperature and filling, which is within the reach of current cold-atom and\nsuperconducting-qubit platforms. By employing matrix product states (MPS)\ncalculations, we investigate the decay of the finite-temperature Green's\nfunction and uncover a smooth crossover between the confined and deconfined\nregimes. This is furthermore confirmed by considering the Friedel oscillations\nand string length distributions obtained from snapshots sampled from MPS, both\nof which are experimentally readily available. Finally, we verify that confined\nmesons remain well-defined at finite temperature by probing their quench\ndynamics with exact diagonalization. Our results shed new light on confinement\nat finite temperature from an experimentally relevant standpoint.",
        "positive": "Pseudogaps in strongly interacting Fermi gases: A central challenge in modern condensed matter physics is developing the\ntools for understanding nontrivial yet unordered states of matter. One\nimportant idea to emerge in this context is that of a \"pseudogap\": the fact\nthat under appropriate circumstances the normal state displays a suppression of\nthe single particle spectral density near the Fermi level, reminiscent of the\ngaps seen in ordered states of matter. While these concepts arose in a solid\nstate context, it is now being explored in cold gases. This article reviews the\ncurrent experimental and theoretical understanding of the normal state of\nstrongly interacting Fermi gases, with particular focus on the phenomonology\nwhich is traditionally associated with the pseudogap."
    },
    {
        "anchor": "Optically induced conical intersections in traps for ultracold atoms and\n  molecules: We show that conical intersections can be created in laboratory coordinates\nby dressing a parabolic trap for ultracold atoms or molecules with a\ncombination of optical and static magnetic fields. The resulting ring trap can\nsupport single-particle states with half-integer rotational quantization and\nmany-particle states with persistent flow. Two well-separated atomic or\nmolecular states are brought into near-resonance by an optical field and tuned\nacross each other with an inhomogeneous magnetic field. Conical intersections\noccur at the nodes in the optical field.",
        "positive": "Entanglement entropies in free fermion gases for arbitrary dimension: We study the entanglement entropy of connected bipartitions in free fermion\ngases of N particles in arbitrary dimension d. We show that the von Neumann and\nRenyi entanglement entropies grow asymptotically as N^(1-1/d) ln N, with a\nprefactor that is analytically computed using the Widom conjecture both for\nperiodic and open boundary conditions. The logarithmic correction to the\npower-law behavior is related to the area-law violation in lattice free\nfermions. These asymptotic large-N behaviors are checked against exact\nnumerical calculations for N-particle systems."
    },
    {
        "anchor": "Probing mechanical quantum coherence with an ultracold-atom probe: We propose a scheme to probe quantum coherence in the state of a\nnano-cantilever based on its magnetic coupling (mediated by a magnetic tip)\nwith a spinor Bose Einstein condensate (BEC). By mapping the BEC into a rotor,\nits coupling with the cantilever results in a gyroscopic motion whose\nproperties depend on the state of the cantilever: the dynamics of one of the\ncomponents of the rotor angular momentum turns out to be strictly related to\nthe presence of quantum coherence in the state of the cantilever. We also\nsuggest a detection scheme relying on Faraday rotation, which produces only a\nvery small back-action on the BEC and it is thus suitable for a continuous\ndetection of the cantilever's dynamics.",
        "positive": "Mott insulator of strongly interacting two-dimensional excitons: In condensed-matter physics, electronic Mott insulators have triggered\nconsiderable research due to their intricate relation with high-temperature\nsuperconductors. However, unlike atomic systems for which Mott phases were\nrecently shown for both bosonic and fermionic species, in the solid-state the\nfingerprint of a Mott insulator implemented with bosons is yet to be found.\nHere we unveil such signature by exploring the Bose-Hubbard hamiltonian using\nsemiconductor excitons confined in two-dimensional lattices. We emphasise the\nregime where on-site interactions are comparable to the energy separation\nbetween lattice confined states. We then observe that Mott phases are\naccessible, with at most two excitons uniformly filling lattice sites. The\ntechnology introduced here allows us to program on-demand the geometry of the\nlattice confining excitons. This versatility, combined with the long-range\nnature of dipolar interactions between excitons, provide a new route to explore\nmany-body phases spontaneously breaking the lattice symmetry."
    },
    {
        "anchor": "Numerical solution of the Boltzmann equation for trapped Fermi gases\n  with in-medium effects: Using the test-particle method, we solve numerically the Boltzmann equation\nfor an ultra-cold gas of trapped fermions with realistic particle number and\ntrap geometry in the normal phase. We include a mean-field potential and\nin-medium modifications of the cross-section obtained within a T matrix\nformalism. After some tests showing the reliability of our procedure, we apply\nthe method to realistic cases of practical interest, namely the anisotropic\nexpansion of the cloud and the radial quadrupole mode oscillation. Our results\nare in good agreement with experimental data. Although the in-medium effects\nsignificantly increase the collision rate, we find that they have only a\nmoderate effect on the anisotropic expansion and on frequency and damping rate\nof the quadrupole mode.",
        "positive": "Exotic superfluid of trapped Fermi gases with spin-orbit coupling in\n  dimensional crossover: We have studied the exotic superfluid phases of degenerated Fermi gases with\nspin-orbit coupling in a mixed dimensional system, where the motion of atoms\nare free in the x-direction and the tunneling between nearest tubes in the\ny-direction is permitted. Using the mean-field method, we obtain the phase\ndiagrams of the system during the dimensional crossover between quasi one\ndimension to quasi two dimension. We find the existence of the topological\nstate and Majorana edge mode in the weak tunneling case, and a rich phase\ndiagram including two kinds of nodal superfluid phase and gapped superfluid\nphase in the opposite case. Our results show that topological pairing is\nfavoured in quasi one dimension while nodal pairing state is favoured in quasi\ntwo dimension."
    },
    {
        "anchor": "Equatorial Waves in Rotating Bubble-Trapped Superfluids: As the Earth rotates, the Coriolis force causes several oceanic and\natmospheric waves to be trapped along the equator, including Kelvin, Yanai,\nRossby, and Poincar\\'e modes. It has been demonstrated that the mathematical\norigin of these waves is related to the nontrivial topology of the underlying\nhydrodynamic equations. Inspired by recent observations of Bose-Einstein\ncondensation (BEC) in bubble-shaped traps in microgravity ultracold quantum gas\nexperiments, we show that equatorial modes are supported by a rapidly rotating\ncondensate in a spherical geometry. Based on a zero-temperature coarse-grained\nhydrodynamic framework, we reformulate the coupled oscillations of the\nsuperfluid and the Abrikosov vortex lattice resulting from rotation by a\nSchr\\\"odinger-like eigenvalue problem. The obtained non-Hermitian Hamiltonian\nis topologically nontrivial. Furthermore, we solve the hydrodynamic equations\nfor a spherical geometry and find that the rotating superfluid hosts Kelvin,\nYanai, and Poincar\\'e equatorial modes, but not the Rossby mode. Our\npredictions can be tested with state-of-the-art bubble-shaped trapped BEC\nexperiments.",
        "positive": "An atomic colour superfluid via three-body loss: Large three-body losses in a three-component Fermi gas confined in an optical\nlattice can prevent the occupation of a lattice site by three atoms. This\neffective constraint not only gives rise to a suppression of actual three-body\nloss, but stabilises BCS pairing phases by suppressing the formation of trions.\nWe study the effects of the constraint using bosonisation and density matrix\nrenormalisation group techniques (DMRG). We discuss the case of lithium\nexperiments, and study the dissipative dynamics including loss using\ntime-dependent DMRG with quantum trajectories methods."
    },
    {
        "anchor": "Observability of the Efimov spectrum in an electron-atom-atom system: The bound states of a system consisting of two heavy identical atoms and one\nlight electron interacting through the finite-range pairwise potentials are\nexplored, focusing on their dependence on the electron-atom scattering length.\nIn the case of an exact resonance in the electron-atom interaction, the binding\nenergy of an electron yields an effective $1/r^{2}$ potential for the relative\nmotion of the atoms; One major finding is a universal potential that depends on\nthe polarization length which goes beyond the Efimov region. An analytic\nexpression for that potential is extracted from numerical calculations. The\nspectrum of the e+Rb+Rb system produced by the electron-atom polarization\ninteraction exhibits three main sections, a non-universal transition region, a\nquasi-Efimov region, and a densely packed Efimov region.",
        "positive": "Zitterbewegung effect in spin-orbit coupled spin-1 ultracold atoms: The Zitterbewegung effect in spin-orbit coupled spin-1 cold atoms is\ninvestigated in the presence of the Zeeman field and a harmonic trap. It is\nshown that the Zeeman field and the harmonic trap have significant effect on\nthe Zitterbewegung oscillatory behaviors. The external Zeeman field could\nsuppress or enhance the Zitterbewegung amplitude and change the frequencies of\noscillation. A much slowly damping Zitterbewegung oscillation can be achieved\nby adjusting both the linear and quadratic Zeeman field. Multi-frequency\nZitterbewegung oscillation can be induced by the applied Zeeman field. In the\npresence of the harmonic trap, the subpackets corresponding to different\neigenenergies would always keep coherent, resulting in the persistent\nZitterbewegung oscillations. The Zitterbewegung oscillation would display very\ncomplicated and irregular oscillation characteristics due to the coexistence of\ndifferent frequencies of the Zitterbewegung oscillation. Numerical results show\nthat, the Zitterbewegung effect is robust even in the presence of interaction\nbetween atoms."
    },
    {
        "anchor": "Weyl points in three-dimensional optical lattices: synthetic magnetic\n  monopoles in momentum space: We show that Hamiltonians with Weyl points can be realized for ultracold\natoms using laser-assisted tunneling in three-dimensional optical lattices.\nWeyl points are synthetic magnetic monopoles that exhibit a robust,\nthree-dimensional linear dispersion. They are associated with many interesting\ntopological states of matter, such as Weyl semimetals and chiral Weyl fermions.\nHowever, Weyl points have yet to be experimentally observed in any system. We\nshow that this elusive goal is well-within experimental reach with an extension\nof the techniques recently used to obtain the Harper Hamiltonian.",
        "positive": "Site-Resolved Imaging of Bosonic Mott Insulator of $^7$Li atoms: We demonstrate a single-site and single-atom-resolved fluorescence imaging of\na bosonic Mott insulator of $^7$Li atoms in an optical lattice. The\nfluorescence images are obtained by implementing Raman sideband cooling on a\ndeep two-dimensional square lattice, where we collect scattered photons with a\nhigh numerical aperture objective lens. The square lattice is created by a\nfolded retro-reflected beam configuration that can reach 2.5~mK lattice depth\nfrom a single laser source. The lattice beam is elliptically focused to have a\nlarge area with deep potential. On average 4,000 photons are collected per atom\nduring 1~s of the Raman sideband cooling, and the imaging fidelity is over\n95$\\%$ in the central 80$\\times$80 lattice sites. As a first step to study\ncorrelated quantum phases, we present the site-resolved imaging of a Mott\ninsulator. Tuning the magnetic field near the Feshbach resonance, the\nscattering length can be increased to 680$a_B$, and we are able to produce a\nlarge-sized unity filling Mott insulator with 2,000 atoms at low temperature.\nOur work provides a stepping stone to further in-depth investigations of\nintriguing quantum many-body phases in optical lattices."
    },
    {
        "anchor": "Cavity-assisted preparation and detection of a unitary Fermi gas: We report on the fast production and weakly destructive detection of a Fermi\ngas with tunable interactions in a high finesse cavity. The cavity is used both\nwith far off-resonant light to create a deep optical dipole trap, and with\nnear-resonant light to reach the strong light-matter coupling regime. The\ncavity-based dipole trap allows for an efficient capture of laser-cooled atoms,\nand the use of a lattice-cancellation scheme makes it possible to perform\nefficient intra-cavity evaporative cooling. After transfer in a crossed optical\ndipole trap, we produce deeply degenerate unitary Fermi gases with up to $7\n\\cdot 10^5$ atoms inside the cavity, with an overall $2.85$ s long sequence.\nThe cavity is then probed with near-resonant light to perform five\nhundred-times repeated, dispersive measurements of the population of individual\nclouds, allowing for weakly destructive observations of slow atom-number\nvariations over a single sample. This platform will make possible the real-time\nobservation of transport and dynamics as well as the study of\ndriven-dissipative, strongly correlated quantum matter.",
        "positive": "Coupled $\\ell$-wave confinement-induced resonances in cylindrically\n  symmetric waveguides: A semi-analytical approach to atomic waveguide scattering for harmonic\nconfinement is developed taking into account all partial waves. As a\nconsequence $\\ell$-wave confinement-induced resonances are formed being coupled\nto each other due to the confinement. The corresponding resonance condition is\nobtained analytically using the $K$-matrix formalism. Atomic scattering is\ndescribed by transition diagrams which depict all relevant processes the atoms\nundergo during the collision. Our analytical results are compared to\ncorresponding numerical data and show very good agreement."
    },
    {
        "anchor": "Synthetic dimension-induced pseudo Jahn-Teller effect in one-dimensional\n  confined fermions: We demonstrate the failure of the adiabatic Born-Oppenheimer approximation to\ndescribe the ground state of a quantum impurity within an ultracold Fermi gas\ndespite substantial mass differences between the bath and impurity species.\nIncreasing repulsion leads to the appearance of non-adiabatic couplings between\nthe fast bath and slow impurity degrees of freedom which reduce the parity\nsymmetry of the latter according to the pseudo Jahn-Teller effect. The presence\nof this mechanism is associated to a conical intersection involving the\nimpurity position and the inverse of the interaction strength which acts as a\nsynthetic dimension. We elucidate the presence of these effects via a detailed\nground state analysis involving the comparison of ab initio fully-correlated\nsimulations with effective models. Our study suggests ultracold atomic\nensembles as potent emulators of complex molecular phenomena.",
        "positive": "Green's function approach to the Bose-Hubbard model with disorder: We analyse the distinction between the three different ground states\npresented by a system of spinless bosons with short-range interactions\nsubmitted to a random potential using the disordered Bose-Hubbard model. The\ncriteria for identifying the superfluid, the Mott-insulator, and the Bose-glass\nphases at finite temperatures are discussed for small values of the kinetic\nenergy associated with the tunnelling of particles between potential wells.\nField theoretical considerations are applied in order to construct a\ndiagrammatic hopping expansion to the finite-temperature Green's function. By\nperforming a summation of subsets of diagrams we are able to find the condition\nto the long-range correlations which leads to the phase boundary between\nsuperfluid and insulating phases. The perturbative expression to the local\ncorrelations allows us to calculate an approximation to the single-particle\ndensity of states of low-energy excitations in the presence of small hopping,\nwhich characterizes unambiguously the distinction between the Mott-insulator\nand the Bose-glass phases. We obtain the phase diagram for bounded on-site\ndisorder. It is demonstrated that our analysis is capable of going beyond the\nmean-field theory results for the classification of these different ground\nstates."
    },
    {
        "anchor": "A simple method for generating Bose-Einstein condensates in a weak\n  hybrid trap: We report on a simple novel trapping scheme for the generation of\nBose-Einstein condensates of $^{87}$Rb atoms. This scheme employs a\nnear-infrared single beam optical dipole trap combined with a weak magnetic\nquadrupole field as used for magneto-optical trapping to enhance the\nconfinement in axial direction. Efficient forced evaporative cooling to the\nphase transition is achieved in this weak hybrid trap via reduction of the\nlaser intensity of the optical dipole trap at constant magnetic field gradient.",
        "positive": "Density Fluctuations across the Superfluid-Supersolid Phase Transition\n  in a Dipolar Quantum Gas: Phase transitions share the universal feature of enhanced fluctuations near\nthe transition point. Here we show that density fluctuations reveal how a\nBose-Einstein condensate of dipolar atoms spontaneously breaks its translation\nsymmetry and enters the supersolid state of matter -- a phase that combines\nsuperfluidity with crystalline order. We report on the first direct in situ\nmeasurement of density fluctuations across the superfluid-supersolid phase\ntransition. This allows us to introduce a general and straightforward way to\nextract the static structure factor, estimate the spectrum of elementary\nexcitations and image the dominant fluctuation patterns. We observe a strong\nresponse in the static structure factor and infer a distinct roton minimum in\nthe dispersion relation. Furthermore, we show that the characteristic\nfluctuations correspond to elementary excitations such as the roton modes,\nwhich have been theoretically predicted to be dominant at the quantum critical\npoint, and that the supersolid state supports both superfluid as well as\ncrystal phonons."
    },
    {
        "anchor": "A chromium dipolar Fermi sea: We report on the production of a degenerate Fermi gas of 53Cr atoms,\npolarized in the state F=9/2, m_F=-9/2, by sympathetic cooling with bosonic\nS=3, m_S=-3 52Cr atoms. We load in an optical dipole trap 3.10^4 53Cr atoms\nwith 10^6 52Cr atoms. Despite this initial small number of fermionic atoms, we\nreach a final temperature of T=0.6 T_f (Fermi temperature), with up to 10^3\n53Cr atoms. This surprisingly efficient evaporation stems from an inter-isotope\nscattering length |a_{BF}| = (85+/- 10) a_{Bohr} which is small enough to\nreduce evaporative losses of the fermionic isotope, but large enough to insure\nthermalization.",
        "positive": "Momentum Resolved Optical Lattice Modulation Spectroscopy for Bose\n  Hubbard Model: We propose a new method of optical lattice modulation spectroscopy for\nstudying the spectral function of ultracold bosons in an optical lattice. We\nshow that different features of the single particle spectral function in\ndifferent quantum phases can be obtained by measuring the change in momentum\ndistribution after the modulation. In the Mott phase, this gives information\nabout the momentun dependent gap to particle-hole excitations as well as their\nspectral weight. In the superfluid phase, one can obtain the spectrum of the\ngapless Bogoliubov quasiparticles as well as the gapped amplitude fluctuations.\nThe distinct evolution of the response with modulation frequency in the two\nphases can be used to identify these phases and the quantum phase transition\nseparating them."
    },
    {
        "anchor": "Resonantly enhanced coherence by laser-assisted tunneling: We study quantum coherence of strongly interacting cold bosons in a\ndouble-well potential driven by a laser field. The system is initially in a\nFock state and, for either with or without a static tilting field, evolves into\nthe coherent states. The coherence is resonantly enhanced by the\nphoton-assisted tunneling. For the tilted wells, it reveals a two-branch\npattern which corresponds to the multiple photon absorption or emission,\nrespectively.",
        "positive": "Hysteresis in a Superfluid Atom Circuit: The energy band structure of a rotating BEC with a link in a\nquasi-one-dimensional torus and the role of dissipation is studied. Through\nthis study we are able to give a microscopic interpretation of hysteresis\nrecently observed in the experiment and we confirm that the hysteresis is the\nresult of the presence of metastable state. We consider of both the adiabatic\nchange and the instantaneous change of the rotation, and exhibit the\ndifferences between them. It is found that the sharp and size of the hysteresis\nloop change drastically with the strength of the link."
    },
    {
        "anchor": "Rabi oscillations and Ramsey-type pulses in ultracold bosons: Role of\n  interactions: Double-well systems loaded with one, two, or many quantum particles give rise\nto intriguing dynamics, ranging from Josephson oscillation to self-trapping.\nThis work presents theoretical and experimental results for two distinct\ndouble-well systems, both created using dilute rubidium Bose-Einstein\ncondensates with particular emphasis placed on the role of interaction in the\nsystems. The first is realized by creating an effective two-level system\nthrough Raman coupling of hyperfine states. The second is an effective\ntwo-level system in momentum space generated through the coupling by an optical\nlattice. Even though the non-interacting systems can, for a wide parameter\nrange, be described by the same model Hamiltonian, the dynamics for these two\nrealizations differ in the presence of interactions. The difference is\nattributed to scattering diagrams that contribute in the lattice coupled system\nbut vanish in the Raman coupled system. The internal dynamics of the\nBose-Einstein condensates for both coupling scenarios is probed through a\nRamsey-type interference pulse sequence, which constitutes a key building block\nof atom interferometers. These results have important implications in a variety\nof contexts including lattice calibration experiments and momentum space\nlattices used for quantum analog simulations.",
        "positive": "Excitation spectra of many-body systems by linear response: General\n  theory and applications to trapped condensates: We derive a general linear-response many-body theory capable of computing\nexcitation spectra of trapped interacting bosonic systems, e.g., depleted and\nfragmented Bose-Einstein condensates (BECs). To obtain the linear-response\nequations we linearize the multiconfigurational time-dependent Hartree for\nbosons (MCTDHB) method, which provides a self-consistent description of\nmany-boson systems in terms of orbitals and a state vector (configurations),\nand is in principle numerically-exact. The derived linear-response many-body\ntheory, which we term LR-MCTDHB, is applicable to systems with interaction\npotentials of general form. From the numerical implementation of the LR-MCTDHB\nequations and solution of the underlying eigenvalue problem, we obtain\nexcitations beyond available theories of excitation spectra, such as the\nBogoliubov-de Gennes (BdG) equations. The derived theory is first applied to\nstudy BECs in a one-dimensional harmonic potential. The LR-MCTDHB method\ncontains the BdG excitations and, also, predicts a plethora of additional\nmany-body excitations which are out of the realm of standard linear response.\nIn particular, our theory describes the exact energy of the higher harmonic of\nthe first (dipole) excitation not contained in the BdG theory. We next study a\nBEC in a very shallow one-dimensional double-well potential. We find with\nLR-MCTDHB low-lying excitations which are not accounted for by BdG, even though\nthe BEC has only little fragmentation and, hence, the BdG theory is expected to\nbe valid. The convergence of the LR-MCTDHB theory is assessed by systematically\ncomparing the excitation spectra computed at several different levels of\ntheory."
    },
    {
        "anchor": "Self-Pinning Transition of a Tonks-Girardeau Gas in a Bose-Einstein\n  Condensate: We show that a Tonks-Girardeau (TG) gas that is immersed in a Bose-Einstein\ncondensate can undergo a transition to a crystal-like Mott state with regular\nspacing between the atoms without any externally imposed lattice potential. We\ncharacterize this phase transition as a function of the interspecies\ninteraction and temperature of the TG gas, and show how it can be measured via\naccessible observables in cold atom experiments. We also develop an effective\nmodel that accurately describes the system in the pinned insulator state and\nwhich allows us to derive the critical temperature of the transition.",
        "positive": "Realization of a high power optical trapping setup free from thermal\n  lensing effects: Transmission of high power laser beams through partially absorbing materials\nmodifies the light propagation via a thermally-induced effect known as thermal\nlensing. This may cause changes in the beam waist position and degrade the beam\nquality. Here we characterize the effect of thermal lensing associated with the\ndifferent elements typically employed in an optical trapping setup for cold\natoms experiments. We find that the only relevant thermal lens is represented\nby the $TeO_2$ crystal of the acousto-optic modulator exploited to adjust the\nlaser power on the atomic sample. We then devise a simple and totally passive\nscheme that enables to realize an inexpensive optical trapping apparatus\nessentially free from thermal lensing effects."
    },
    {
        "anchor": "Bose-Einstein condensation at finite momentum and magnon condensation in\n  thin film ferromagnets: We use the Gross-Pitaevskii equation to determine the spatial structure of\nthe condensate density of interacting bosons whose energy dispersion epsilon_k\nhas two degenerate minima at finite wave-vectors q. We show that in general the\nFourier transform of the condensate density has finite amplitudes for all\ninteger multiples of q. If the interaction is such that many Fourier components\ncontribute, the Bose condensate is localized at the sites of a one-dimensional\nlattice with spacing 2pi/q; in this case Bose-Einstein condensation resembles\nthe transition from a liquid to a crystalline solid. We use our results to\ninvestigate the spatial structure of the Bose condensate formed by magnons in\nthin films of ferromagnets with dipole-dipole interactions.",
        "positive": "Ground state of a resonantly interacting Bose gas: We show that a two-channel mean-field theory for a Bose gas near a Feshbach\nresonance allows for an analytic computation of the chemical potential, and\ntherefore the universal constant \\beta, at unitarity. To improve on this\nmean-field theory, which physically neglects condensate depletion, we study a\nvariational Jastrow ansatz for the ground-state wave function and use the\nhypernetted-chain approximation to minimize the energy for all positive values\nof the scattering length. We also show that other important physical quantities\nsuch as Tan's contact and the condensate fraction can be directly obtained from\nthis approach."
    },
    {
        "anchor": "One-dimensional s-p superlattice: The physics of one dimensional optical superlattices with resonant $s$-$p$\norbitals is reexamined in the language of appropriate Wannier functions. It is\nshown that details of the tight binding model realized in different optical\npotentials crucially depend on the proper determination of Wannier functions.\nWe discuss the properties of a superlattice model which quasi resonantly\ncouples $s$ and $p$ orbitals and show its relation with different tight binding\nmodels used in other works.",
        "positive": "Chern numbers for the two-body Hofstadter-Hubbard butterfly: We analyze the two-body spectrum within the Hofstadter-Hubbard model on a\nsquare lattice through an exact variational ansatz and study the topological\nproperties of its low-lying two-body bound-state branches. In particular we\ndiscuss how the Hofstadter-Hubbard butterfly of the two-body branches evolves\nas a function of onsite interactions and how to efficiently calculate their\nChern numbers using the Fukui-Hatsugai-Suzuki approach. Our numerical results\nare fully consistent with the simple picture that appears in the\nstrong-coupling limit, where the attraction between fermions forms a composite\nboson characterized by an effective hopping parameter and an effective\nmagnetic-flux ratio."
    },
    {
        "anchor": "Characterisation of three-body loss in ${}^{166}$Er and optimised\n  production of large Bose-Einstein condensates: Ultracold gases of highly magnetic lanthanide atoms have enabled the\nrealisation of dipolar quantum droplets and supersolids. However, future\nstudies could be limited by the achievable atom numbers and hindered by high\nthree-body loss rates. Here we study density-dependent atom loss in an\nultracold gas of ${}^{166}$Er for magnetic fields below $4\\ \\textrm{G}$,\nidentifying six previously unknown features which display both a strong\ntemperature dependence and also sensitivity to the polarisation and intensity\nof the light used to optically trap the atoms. This detailed knowledge of the\nloss landscape allows us to optimise the production of dipolar BECs with more\nthan $2 \\times 10^5$ atoms and points towards optimal strategies for the study\nof large-atom-number dipolar gases in the droplet and supersolid regimes.",
        "positive": "Spin-orbit-angular-momentum coupling in a spin-1 Bose-Einstein\n  condensate: We propose a simple model with spin and orbit angular momentum coupling in a\nspin-1 Bose- Einstein condensate, where three internal atomic states are Raman\ncoupled by a pair of co- propagating Laguerre-Gaussian beams. The resulting\nRaman transition imposes a transfer of orbital angular momentum between photons\nand the condensate in a spin-dependent way. Focusing on a regime where the\nsingle-particle ground state is nearly three-fold degenerate, we show that the\nweak interatomic interaction in the condensate produces a rich phase diagram,\nand that a many-body Rabi oscillation between two quantum phases can be induced\nby a sudden quench of the quadratic Zeeman shift. We carried out our\ncalculations using both a variational method and a full numerical method, and\nfound excellent agreement."
    },
    {
        "anchor": "Hydrodynamics of a superfluid smectic: We determine the hydrodynamic modes of the superfluid analog of a smectic-A\nphase in liquid crystals, i.e., a state in which both gauge invariance and\ntranslational invariance along a single direction are spontaneously broken.\nSuch a superfluid smectic provides an idealized description of the\nincommensurate supersolid state realized in Bose-Einstein condensates with\nstrong dipolar interactions as well as of the stripe phase in Bose gases with\nspin-orbit coupling. We show that the presence of a finite normal fluid density\nin the ground state of these systems gives rise to a well-defined second-sound\ntype mode even at zero temperature. It replaces the diffusive permeation mode\nof a normal smectic phase and is directly connected with the classic\ndescription of supersolids by Andreev and Lifshitz in terms of a propagating\ndefect mode. An analytic expression is derived for the two sound velocities\nthat appear in the longitudinal excitation spectrum. It only depends on the\nlow-energy parameters associated with the two independent broken symmetries,\nwhich are the effective layer compression modulus and the superfluid fraction.",
        "positive": "Short-range quantum magnetism of ultracold fermions in an optical\n  lattice: The exchange coupling between quantum mechanical spins lies at the origin of\nquantum magnetism. We report on the observation of nearest-neighbor magnetic\nspin correlations emerging in the many-body state of a thermalized Fermi gas in\nan optical lattice. The key to obtaining short-range magnetic order is a local\nredistribution of entropy within the lattice structure. This is achieved in a\ntunable-geometry optical lattice, which also enables the detection of the\nmagnetic correlations. We load a low-temperature two-component Fermi gas with\nrepulsive interactions into either a dimerized or an anisotropic simple cubic\nlattice. For both systems the correlations manifest as an excess number of\nsinglets as compared to triplets consisting of two atoms with opposite spins.\nFor the anisotropic lattice, we determine the transverse spin correlator from\nthe singlet-triplet imbalance and observe antiferromagnetic correlations along\none spatial axis. Our work paves the way for addressing open problems in\nquantum magnetism using ultracold fermions in optical lattices as quantum\nsimulators."
    },
    {
        "anchor": "Three in Many: Efimov physics in the presence of a Fermi sea: Motivated by recent experiments on $^{6}$Li-$^{133}$Cs atomic mixtures with\nhigh mass imbalance, we study the Efimov correlation in atomic system of two\nheavy bosons ($^{133}$Cs) immersed in a bath of light fermions ($^{6}$Li).\nUsing the Born-Oppenheimer approximation, we identify two different regimes,\ndepending on the Fermi momentum of light fermions ($k_F$) and the boson-fermion\nscattering length $a_s(<0)$, where the presence of underlying Fermi sea plays\ndistinct roles in the Efimov-type binding of bosons. Namely, in the regime\n$k_F|a_s|\\lesssim 1$ ($k_F|a_s|\\gtrsim1$), the Fermi sea induces an attractive\n(repulsive) effective interaction between bosons and thus favors (disfavors)\nthe formation of bound state, which can be seen as the Efimov trimer dressed by\nthe fermion cloud. Interestingly, this implies a non-monotonic behavior of\nthese bound states as increasing the fermion density (or $k_F$). Moreover, we\nestablish a generalized universal scaling law for the emergence/variation of\nsuch dressed Efimov bound states when incorporating a new scale ($k_F$) brought\nby the Fermi sea. These results can be directly tested in Li-Cs cold atoms\nexperiment by measuring the modified bound state spectrum and the shifted\nEfimov resonance, which manifest an emergent non-trivial Efimov correlation in\na fermionic many-body environment.",
        "positive": "Resurgent revivals in bosonic quantum gases: a striking signature of\n  many-body quantum interferences: Matter wave revivals depend on a delicate interplay of constructive many-body\nquantum interferences in the developing dynamics of an ultracold bosonic system\nin an optical lattice. It is shown that the interplay between weak intersite\ntunneling and strong onsite interactions can lead to the quantum dynamics of a\ndensity wave displaying several features not found in the mean-field limit:\noccupancy oscillations, resurgent revivals, and a (anti-) synchronization of\nrevival peaks and occupancy oscillation peaks. This implies cooperative\ninterference effects that alternate between constructive and destructive\nfeatures leading to the peak revival behaviors. These many-body quantum\ninterference phenomena create striking features in various observables, which\nare accessible in experimental measurements."
    },
    {
        "anchor": "Rotation and Angular Momentum Transfer in Bose-Einstein Condensates\n  Induced by Spiral Dark Solitons: It is a common view that rotational motion in a superfluid can exist only in\nthe presence of quantized vortices. However, in our numerical studies on the\nmerging of two concentric Bose-Einstein condensates with axial symmetry in\ntwo-dimensional space, we observe the emergence of a spiral dark soliton when\none condensate has a non-zero initial angular momentum. This spiral dark\nsoliton enables the transfer of angular momentum between the condensates and\nallows the merged condensate to rotate even in the absence of quantized\nvortices. We examine the flow field around the soliton and reveal that its\nsharp endpoint can induce flow like a vortex point but with a fraction of a\nquantized circulation. This interesting nontopological \"phase defect\" may\ngenerate broad interests since rotational motion is essential in many quantum\ntransport processes.",
        "positive": "Crow instability in trapped Bose-Einstein condensates: We show theoretically that elongated vortex-antivortex dipoles can be created\ncontrollably in trapped Bose-Einstein condensates, using known experimental\ntechniques. Vortex dipoles of sufficient length are unstable and cascade into\nslow vortex rings which ultimately decay via sound emission. This instability\nof antiparallel vortex line elements, which self-generates Kelvin waves on\nvortex loops and in trapped atomic gases, may play a role in bridging the\nKelvin-wave and Kolmogorov-Richardson cascades of quantum turbulence."
    },
    {
        "anchor": "Suppression of the superfluid Kelvin-Helmholtz instability due to\n  massive vortex cores, friction and confinement: We characterize the dynamical instability responsible for the breakdown of\nregular rows and necklaces of quantized vortices that appear at the interface\nbetween two superfluids in relative motion. Making use of a generalized\npoint-vortex model, we identify several mechanisms leading to the suppression\nof this instability. They include a non-zero mass of the vortex cores,\ndissipative processes resulting from the interaction between the vortices and\nthe excitations of the superfluid, and the proximity of the vortex array to the\nsample boundaries. We show that massive vortex cores not only have a mitigating\neffect on the dynamical instability, but also change the associated scaling law\nand affect the direction along which it develops. The predictions of our\nmassive and dissipative point-vortex model are eventually compared against\nrecent experimental measurements of the maximum instability growth rate\nrelevant to vortex necklaces in a cold-atom platform.",
        "positive": "Nonlinear corrections in the quantization of a weakly nonideal Bose gas\n  at zero temperature. II. The general case: In the present paper, discussion of the canonical quantization of a weakly\nnonideal Bose gas at zero temperature within the framework of the Bogolyubov\napproach is continued. Contrary to the previous paper on this subject, here the\ntwo-body interaction potential is considered in the general form. It is shown\nthat in such a case consideration of the first nonlinear correction also leads\nto the automatic particle number conservation without any additional\nassumptions or modification of the resulting effective Hamiltonian."
    },
    {
        "anchor": "Spinor Bose gas in an elongated trap: We examine a spinor Bose gas confined by an elongated trap. Since a\nspin-independent energy is much higher than a spin-dependent energy in alkali\nspecies, the system exhibits different properties by changing a radial\nconfinement. We show that if a spin-dependent coupling is positive, a\nspin-liquid condensate, which breaks the charge U(1) symmetry but preserves the\nspin rotational symmetry, can be realized in an intermediate confinement\nregime. Properties of the spin-liquid condensate are visible if a temperature\nis lower than a spin gap to characterize the spin-disorder property. If a\ntemperature is higher than the gap but lower than a spin-dependent coupling, on\nthe other hand, a regime in which a spin sector is described by a semiclassical\nwave emerges. A characterization in each regime by means of correlation\nfunctions and topological solitons is also discussed.",
        "positive": "Emergence of triplet orbital pairing and non-Abelian states in ultracold\n  multi-orbital optical lattices with quadratic band touching: It is found that all the {\\em singlet orbital pairing} instabilities are {\\em\nabsent} in a class of spin-polarized multi-orbital systems with quadratic band\ntouching, which opens the way for {\\em triplet orbital pairing} order. The\nground states are found to be {\\em non-Abelian} states with p-wave orbital\npairing in checkerboard (away from 1/2 filling) and kagome (above 1/3 filling)\nlattices with {\\em isotropic} attractive interaction which can be realized in\nultracold multi-orbital optical lattices. The special property of such systems\nis generalized to more classes of multi-orbital systems, where the fully-gapped\n{\\em non-Abelian} states are possibly the ground states. Those findings are\nhelpful in achieving topological quantum computation."
    },
    {
        "anchor": "Soliton splitting in quenched classical integrable systems: We take a soliton solution of a classical non-linear integrable equation and\nquench (suddenly change) its non-linearity parameter. For that we multiply the\namplitude or the width of a soliton by a numerical factor $\\eta$ and take the\nobtained profile as a new initial condition. We find the values of $\\eta$ at\nwhich the post-quench solution consists of only a finite number of solitons.\nThe parameters of these solitons are found explicitly. Our approach is based on\nsolving the direct scattering problem analytically. We demonstrate how it works\nfor Kortewig-de-Vries, sine-Gordon and non-linear Schr\\\"odinger integrable\nequations.",
        "positive": "Degenerate Raman sideband cooling of 40K atoms: We report on the implementation of degenerate Raman sideband cooling of\n$^{40}$K atoms. The scheme incorporates a 3D optical lattice, which confines\nthe atoms and drives the Raman transitions. The optical cooling cycle is closed\nby two optical pumping beams. The wavelength of the laser beams forming the\nlattice is close to the D$_2$ atomic transition, while the optical pumping is\noperated near the D$_1$ transition. With this cooling method, we achieve\ntemperature of $\\sim$$1\\mu$K of a cloud with $\\sim$$10^7$ atoms. This\ncorresponds to a phase space density of $\\ge$$10^{-3}$. Moreover, the fermionic\nensemble is spin polarized to conditions which are favorable for subsequent\nevaporative cooling. We study the dependence of the cooling scheme on several\nparameters, including the applied magnetic field, the detuning, duration, and\nintensity profile of the optical pumping beams. Adding this optical cooling\nstage to current Fermi gas experiments can improve the final conditions and\nincrease the data rate."
    },
    {
        "anchor": "Extended Bose-Hubbard models with Rydberg macrodimer dressing: Extended Hubbard models have proven to bear novel quantum states, but their\nexperimental realization remains challenging. In this work we propose to use\nbosonic quantum gases dressed with molecular bound states in Rydberg\ninteraction potentials for the observation of these quantum states. We study\nthe molecular Rabi coupling with respect to principal quantum number and\ntrapping frequency of the ground state atoms for various molecular potentials\nof Rubidium and Potassium, and the hereby resulting dressed interaction\nstrength. Additionally, we propose a two-color excitation scheme which\nsignificantly increases the dressed interaction and cancels AC Stark shifts\nlimiting the atomic motion in the itinerant regime. We study the various\nequilibrium phases of the corresponding extended Bose-Hubbard model by means of\nthe Cluster Gutzwiller approach and perform time evolution simulations via the\nLindblad master equation. We find a supersolid phase by slowly ramping the\nmolecular Rabi coupling of an initially prepared superfluid and discuss the\nrole of dissipation.",
        "positive": "Floquet-heating-induced Bose condensation in a scar-like mode of an open\n  driven optical-lattice system: Periodically driven quantum systems suffer from heating via resonant\nexcitation. While such Floquet heating guides a generic isolated system towards\nthe infinite-temperature state, a driven open system, coupled to a thermal\nbath, will approach a non-equilibrium steady state. We show that the interplay\nof bath-induced dissipation and controlled Floquet heating can give rise to\nnon-equilibrium Bose condensation in a mode protected from Floquet heating. In\nparticular, we consider a one-dimensional (1D) Bose gas in an optical lattice\nof finite extent, which is coupled weakly to a three-dimensional thermal bath\ngiven by a second atomic species. The bath temperature $T$ lies well above the\ncrossover temperature, below which the majority of the system's particles form\na (finite-size) Bose condensate in the ground state. However, when a strong\nlocal potential modulation is switched on, which resonantly excites the system,\na non-equilibrium Bose condensate is formed in a state that decouples from the\ndrive. Our predictions, which are based on a microscopic model that is solved\nusing kinetic equations of motion derived from Floquet-Born-Markov theory, can\nbe probed under realistic experimental conditions."
    },
    {
        "anchor": "Quantum Criticality from in-situ Density Imaging: We perform large-scale Quantum Monte Carlo (QMC) simulations for strongly\ninteracting bosons in a 2D optical lattice trap, and confirm an excellent\nagreement with the benchmarking in-situ density measurements by the Chicago\ngroup [1]. We further present a general finite temperature phase diagram both\nfor the uniform and the trapped systems, and demonstrate how the universal\nscaling properties near the superfluid(SF)-to-Mott insulator(MI) transition can\nbe observed by analysing the in-situ density profile. The characteristic\ntemperature to find such quantum criticality is estimated to be of the order of\nthe single-particle bandwidth, which should be achievable in the present or\nnear future experiments. Finally, we examine the validity regime of the local\nfluctuation-dissipation theorem (FDT), which can be a used as a thermometry in\nthe strongly interacting regime.",
        "positive": "Ferromagnetic--nematic order and strongly correlated phases of fermions\n  in optical flux lattices: We study a model of a 2D ultracold atomic gas subject to an \"optical flux\nlattice\": a laser configuration where Raman-dressed atoms experience a strong\nartificial magnetic field. This leads to a bandstructure of narrow energy bands\nwith non-zero Chern numbers. We consider the case of two-level (spin-$1/2$)\nfermionic atoms in this lattice, interacting via a repulsive $s$-wave contact\ninteraction. Atoms restricted to the lowest band are described by an effective\nmodel of spinless fermions with interactions that couple states in a\nmomentum-dependent manner across the Brillouin zone; a consequence of the Raman\ndressing of the two spin states. We present the results of detailed exact\ndiagonalization studies of the many-body states for a range of filling factors,\n$\\nu$. First, we present evidence for the existence of a phase with coupled\nferromagnetic--nematic ordering, which was previously suggested by a mean-field\nanalysis. Second, we present evidence indicating the presence of a\nLaughlin-like fractional quantum Hall state occurring at filling factor $\\nu =\n1/3$. Finally, we observe a charge density wave state at $\\nu=1/2$, which we\nare able to cleanly distinguish from the Laughlin-like state by its\ntranslational symmetry breaking and relatively small participation ratio."
    },
    {
        "anchor": "Pair Superfluidity of Three-Body Constrained Bosons in Two Dimensions: We examine the equilibrium properties of lattice bosons with attractive\non-site interactions in the presence of a three-body hard-core constraint that\nstabilizes the system against collapse and gives rise to a dimer superfluid\nphase formed by virtual hopping processes of boson pairs. Employing quantum\nMonte Carlo simulations, the ground state phase diagram of this system on the\nsquare lattice is analyzed. In particular, we study the quantum phase\ntransition between the atomic and dimer superfluid regime and analyze the\nnature of the superfluid-insulator transitions. Evidence is provided for the\nexistence of a tricritical point along the saturation transition line, where\nthe transition changes from being first-order to a continuous transition of the\ndilute bose gas of holes. The Berzinskii-Kosterlitz-Thouless transition from\nthe dimer superfluid to the normal fluid is found to be consistent with an\nanomalous stiffness jump, as expected from the unbinding of half-vortices.",
        "positive": "Enhancing Quantum Otto Engine Performance in Generalized External\n  Potential on Bose-Einstein Condensation Regime: We examine a quantum Otto engine using both Bose-Einstein Condensation (BEC)\nand normal Bose gas as working medium trapped in generalized external\npotential. We treated the engine quasi-statically and endoreversibly. Since the\nexpansion and compression in both quasi-static and endoreversible take place\nisentropic, the expression of efficiency is similar. However, the power output\nin the quasi-static cycle is zero due to infinite and long stroke time. In\ncontrast, with an endoreversible cycle, thermalization with two reservoirs\ntakes place at a finite time. We use Fourier's law in conduction to formulate\nthe relation between temperature of medium and reservoir, making work depend on\nheating and cooling stroke time. Moreover, we maximized the power with respect\nto compression ratio $\\kappa$ to obtain efficiency at maximum power (EMP). We\nfound that EMP is significantly higher when using BEC as a working medium,\nmeanwhile EMP with normal Bose gas is just Curzon-Ahlborn efficiency. We also\ninvestigate the effect of thermal contact time $\\tau$ with hot ($\\tau_{h}$) and\ncold ($\\tau_{l}$) reservoir on EMP. We found that when $\\tau_{h}=\\tau_{l}$\nstroke time occur, there are no significant differences. Nevertheless,\nadjusting various cooling and heating stroke time provide a significant result\non EMP, which is much higher at $\\tau_{h}<\\tau_{l}$ stroke time whilst lower at\n$\\tau_{h}>\\tau_{l}$ stroke time. We conclude this partial thermalization\nenhances the EMP of the engine due to residual coherence."
    },
    {
        "anchor": "Bose-Einstein condensation in the three-sphere and the infinite slab:\n  analytical results: We study the finite size effects on Bose-Einstein condensation (BEC) of an\nideal non-relativistic Bose gas in the three-sphere (spatial section of the\nEinstein universe) and in a partially finite box which is infinite in two of\nthe spatial directions (infinite slab). Using the framework of grand-canonical\nstatistics, we consider the number of particles, the condensate fraction and\nthe specific heat. After obtaining asymptotic expansions for large system size,\nwhich are valid throughout the BEC regime, we describe analytically how the\nthermodynamic limit behaviour is approached. In particular, in the critical\nregion of the BEC transition, we express the chemical potential and the\nspecific heat as simple explicit functions of the temperature, highlighting the\neffects of finite size. These effects are seen to be different for the two\ndifferent geometries. We also consider the Bose gas in a one-dimensional box, a\nsystem which does not possess BEC in the sense of a phase transition even in\nthe infinite volume limit.",
        "positive": "Thermal suppression of demixing dynamics in a binary condensate: We investigate the demixing dynamics in a binary two-dimensional (2D) Bose\nsuperfluid using classical-field dynamics. By quenching the interspecies\ninteraction parameter, we identify a strong and weak separation regime\ndepending on the system temperature and the quench parameter. In the strong\nseparation regime our results are in agreement with the inertial hydrodynamic\ndomain growth law of binary fluids and a Porod scaling law for the structure\nfactor at zero temperature is found. In the weak separation regime thermal\nfluctuations modify both the domain growth law and the Porod tail of the\nstructure factor. Near the superfluid transition temperature the scaling\ndynamics approaches the diffusive growth law of a 2D conserved field. We then\nanalyze the demixing dynamics in a box cloud. For low quench we find\ndistinctive domain dynamics dictated by the boundary condition. Otherwise, the\ndynamics are qualitatively similar to those of systems with periodic boundary\nconditions."
    },
    {
        "anchor": "Quantum Hall Physics with Cold Atoms in Cylindrical Optical Lattices: We propose and study various realizations of a Hofstadter-Hubbard model on a\ncylinder geometry with fermionic cold atoms in optical lattices. The\ncylindrical optical lattice is created by copropagating Laguerre-Gauss beams,\ni.e.~light beams carrying orbital angular momentum. By strong focusing of the\nlight beams we create a real space optical lattice in the form of rings, which\nare offset in energy. A second set of Laguerre-Gauss beams then induces a\nRaman-hopping between these rings, imprinting phases corresponding to a\nsynthetic magnetic field (artificial gauge field). In addition, by rotating the\nlattice potential, we achieve a slowly varying flux through the hole of the\ncylinder, which allows us to probe the Hall response of the system as a\nrealization of Laughlin's thought experiment. We study how in the presence of\ninteractions fractional quantum Hall physics could be observed in this setup.",
        "positive": "New exact eigenstates in the Lesanovsky model, proximity to\n  integrability and the PXP model, and approximate scar states: We study a model of Rydberg atoms in a nearest-neighbor Rydberg blockaded\nregime, introduced by Lesanovsky in Phys. Rev. Lett. 108, 105301 (2012). This\nmany-body model (which has one parameter $z$) has an exactly known gapped\nliquid ground state, and two exactly known low-lying excitations. We discover\ntwo new exact low-lying eigenstates. We also discuss behavior of the model at\nsmall parameter $z$ and its proximity to an integrable model. Lastly, we\ndiscuss connections between the Lesanovsky model at intermediate $z$ and\nso-called PXP model. The PXP model describes a recent experiment that observed\nunusual revivals from a charge density wave initial state, which are attributed\nto a set of many-body \"scar states\" which do not obey the eigenstate\nthermalization hypothesis. We discuss the possibility of scar states in the\nLesanovsky model and present two approximations for them."
    },
    {
        "anchor": "Floquet prethermalization and regimes of heating in a periodically\n  driven, interacting quantum system: We study the regimes of heating in the periodically driven $O(N)$-model,\nwhich represents a generic model for interacting quantum many-body systems. By\ncomputing the absorbed energy with a non-equilibrium Keldysh Green's function\napproach, we establish three dynamical regimes: at short times a\nsingle-particle dominated regime, at intermediate times a stable Floquet\nprethermal regime in which the system ceases to absorb, and at parametrically\nlate times a thermalizing regime. Our simulations suggest that in the\nthermalizing regime the absorbed energy grows algebraically in time with an the\nexponent that approaches the universal value of $1/2$, and is thus\nsignificantly slower than linear Joule heating. Our results demonstrate the\nparametric stability of prethermal states in a generic many-body system driven\nat frequencies that are comparable to its microscopic scales. This paves the\nway for realizing exotic quantum phases, such as time crystals or interacting\ntopological phases, in the prethermal regime of interacting Floquet systems.",
        "positive": "Decondensation in non-equilibrium photonic condensates: when less is\n  more: We investigate the steady state of a system of photons in a pumped dye-filled\nmicrocavity. By varying pump and thermalization the system can be tuned between\nBose-Einstein condensation, multimode condensation, and lasing. We present a\nrich non-equilibrium phase diagram which exhibits transitions between these\nphases, including decondensation of individual modes under conditions that\nwould typically favor condensation."
    },
    {
        "anchor": "The dynamics of a single trapped ion in a high density media: a\n  stochastic approach: Based on the Langevin equation, a stochastic formulation is implemented to\ndescribe the dynamics of a trapped ion in a bath of ultracold atoms, including\nan excess of micromotion. The ion dynamics is described following a hybrid\nanalytical-numerical approach in which the ion is treated as a classical\nimpurity in a thermal bath. As a result, the ion energy's time evolution and\ndistribution are derived from studying the sympathetic cooling process.\nFurthermore, the ion dynamics under different stochastic noise terms is also\nconsidered to gain information on the bath properties' role in the system's\nenergy transfer processes. Finally, the results obtained from this formulation\nare contrasted with those obtained with a more traditional Monte Carlo\napproach.",
        "positive": "Field-theoretical aspects of one-dimensional Bose and Fermi gases with\n  contact interactions: We investigate local quantum field theories for one-dimensional (1D) Bose and\nFermi gases with contact interactions, which are closely connected with each\nother by Girardeau's Bose-Fermi mapping. While the Lagrangian for bosons\nincludes only a two-body interaction, a marginally relevant three-body\ninteraction term is found to be necessary for fermions. Because of this\nthree-body coupling, the three-body contact characterizing a local triad\ncorrelation appears in the energy relation for fermions, which is one of the\nsum rules for a momentum distribution. In addition, we apply in both systems\nthe operator product expansion to derive large-energy and momentum asymptotics\nof a dynamic structure factor and a single-particle spectral density. These\nbehaviors are universal in the sense that they hold for any 1D scattering\nlength at any temperature. The asymptotics for the Tonks-Girardeau gas, which\nis a Bose gas with a hardcore repulsion, as well as the Bose-Fermi\ncorrespondence in the presence of three-body attractions are also discussed."
    },
    {
        "anchor": "Ion induced density bubble in a strongly correlated one dimensional gas: We consider a harmonically trapped Tonks-Girardeau gas of impenetrable bosons\nin the presence of a single embedded ion, which is assumed to be tightly\nconfined in a RF trap. In an ultracold ion-atom collision the ion's charge\ninduces an electric dipole moment in the atoms which leads to an attractive\n$r^{-4}$ potential asymptotically. We treat the ion as a static deformation of\nthe harmonic trap potential and model its short range interaction with the gas\nin the framework of quantum defect theory. The molecular bound states of the\nionic potential are not populated due to the lack of any possible relaxation\nprocess in the Tonks-Girardeau regime. Armed with this knowledge we calculate\nthe density profile of the gas in the presence of a central ionic impurity and\nshow that a density \\textit{bubble} of the order of a micron occurs around the\nion for typical experimental parameters. From these exact results we show that\nan ionic impurity in a Tonks gas can be described using a pseudopotential,\nallowing for significantly easier treatment.",
        "positive": "Competing Superconducting States for Ultracold Atoms in Optical Lattices\n  with Artificial Staggered Magnetic Field: We study superconductivity in an ultracold Bose-Fermi mixture loaded into a\nsquare optical lattice subjected to a staggered flux. While the bosons form a\nsuperfluid at very low temperature and weak interaction, the interacting\nfermions experience an additional long-ranged attractive interaction mediated\nby phonons in the bosonic superfluid. This leads us to consider a generalized\nHubbard model with on-site and nearest-neighbor attractive interactions, which\ngive rise to two competing superconducting channels. We use the\nBardeen-Cooper-Schrieffer theory to determine the regimes where distinct\nsuperconducting ground states are stabilized, and find that the non-local\npairing channel favors a superconducting ground state which breaks both the\ngauge and the lattice symmetries, thus realizing unconventional\nsuperconductivity. Furthermore, the particular structure of the single-particle\nspectrum leads to unexpected consequences, for example, a dome-shaped\nsuperconducting region in the temperature versus filing fraction phase diagram,\nwith a normal phase that comprises much richer physics than a Fermi-liquid.\nNotably, the relevant temperature regime and coupling strength is readily\naccessible in state of the art experiments with ultracold trapped atoms."
    },
    {
        "anchor": "Residual entropy and critical behavior of two interacting boson species\n  in a double well: Motivated by the importance of entanglement and correlation indicators in the\nanalysis of quantum systems, we study the equilibrium and the bipartite\nresidual entropy in a two-species Bose Hubbard dimer when the spatial phase\nseparation of the two species takes place. We consider both the zero and\nnon-zero-temperature regime. We present different kinds of residual entropies\n(each one associated to a different way of partitioning the system), and we\nshow that they strictly depend on the specific quantum phase characterizing the\ntwo species (supermixed, mixed or demixed) even at finite temperature. To\nprovide a deeper physical insight into the zero-temperature scenario, we apply\nthe fully-analytical variational approach based on su(2) coherent states and\nprovide a considerably good approximation of the entanglement entropy. Finally,\nwe show that the effectiveness of bipartite residual entropy as a critical\nindicator at non-zero temperature is unchanged when considering a restricted\ncombination of energy eigenstates.",
        "positive": "Half-integer Mott-insulator phases in the imbalanced honeycomb lattice: Using mean-field theory, we investigate the ground state properties of\nultracold bosons loaded in a honeycomb lattice with on-site repulsive\ninteractions and imbalanced nearest-neighbor hopping amplitudes. Taking into\naccount correlations between strongly coupled neighboring sites through an\nimproved Gutzwiller ansatz, we predict the existence of half-integer\nMott-insulator phases, i.e. states with half-integer filling and vanishing\ncompressibility. These insulating phases result from the interplay between\nquantum correlations and the topology of the honeycomb lattice, and could be\neasily addressed experimentally as they have clear signatures in momentum\nspace."
    },
    {
        "anchor": "Spectroscopic Signatures for the Dark Bose-Einstein Condensation of\n  Spatially Indirect Excitons: We study semiconductor excitons confined in an electrostatic trap of a GaAs\nbilayer heterostructure. We evidence that optically bright excitonic states are\nstrongly depleted while cooling to sub-Kelvin temperatures. In return, the\nother accessible and optically dark states become macroscopically occupied so\nthat the overall exciton population in the trap is conserved. These combined\nbehaviours constitute the spectroscopic signature for the mostly dark\nBose-Einstein condensation of excitons, which in our experiments is restricted\nto a dilute regime within a narrow range of densities, below a critical\ntemperature of about 1K.",
        "positive": "Exact solutions for the dispersion relation of Bogoliubov modes\n  localized near a topological defect - a hard wall - in Bose-Einstein\n  condensate: We consider a Bose-Einstein condensate of bosons with repulsion, described by\nthe Gross-Pitaevskii equation and restricted by an impenetrable \"hard wall\"\n(either rigid or flexible) which is intended to suppress the \"snake\ninstability\" inherent for dark solitons. We solve analytically the Bogoliubov -\nde Gennes equations to find the spectra of gapless Bogoliubov excitations\nlocalized near the \"domain wall\" and therefore split from the bulk excitation\nspectrum of the Bose-Einstein condensate. The \"domain wall\" may model either\nthe surface of liquid helium or of a strongly trapped Bose-Einstein condensate.\nThe dispersion relations for the surface excitations are found for all\nwavenumbers $k$ along the surface up to the \"free-particle\" behavior $k\n\\rightarrow \\infty$, the latter was shown to be bound to the \"hard wall\" with\nsome \"universal\" energy $\\Delta$."
    },
    {
        "anchor": "Few-to-many vortex states of density-angular-momentum coupled\n  Bose-Einstein condensates: Motivated by recent experiments, we theoretically study a gas of atomic\nbosons confined in an elliptical harmonic trap; forming a quasi-two-dimensional\natomic Bose-Einstein condensate subject to a density-dependent gauge potential\nwhich realises an effective density-angular-momentum coupling. We present exact\nThomas-Fermi solutions which allows us to identify the stable regimes of the\nfull parameter space of the model. Accompanying numerical simulations reveal\nthe effect of the interplay of the rigid body and density-angular-momentum\ncoupling for the elliptically confined condensate. By varying the strength of\nthe gauge potential and trap anisotropy we explore how the superfluid state\nemerges in different experimentally accessible geometries, while for large\nrotation strengths dense vortex lattices and concentric vortex ring\narrangements are obtained.",
        "positive": "Reinforcement learning for autonomous preparation of Floquet-engineered\n  states: Inverting the quantum Kapitza oscillator: I demonstrate the potential of reinforcement learning (RL) to prepare quantum\nstates of strongly periodically driven non-linear single-particle models. The\nability of Q-Learning to control systems far away from equilibrium is exhibited\nby steering the quantum Kapitza oscillator to the Floquet-engineered stable\ninverted position in the presence of a strong periodic drive within several\nshaking cycles. The study reveals the potential of the intra-period\n(micromotion) dynamics, often neglected in Floquet engineering, to take\nadvantage over pure stroboscopic control at moderate drive frequencies. Without\nany knowledge about the underlying physical system, the algorithm is capable of\nlearning solely from tried protocols and directly from simulated noisy quantum\nmeasurement data, and is stable to noise in the initial state, and sources of\nrandom failure events in the control sequence. Model-free RL can provide new\ninsights into automating experimental setups for out-of-equilibrium systems\nundergoing complex dynamics, with potential applications in quantum\ninformation, quantum optics, ultracold atoms, trapped ions, and condensed\nmatter."
    },
    {
        "anchor": "Interplay of interlayer pairing and many-body screening in a bilayer of\n  dipolar fermions: In a bilayer system of fermionic dipoles, a full control over the strength of\nthe attractive interactions between two layers leads to the BCS-BEC crossover.\nHere, using the BCS mean field theory, we study such a crossover in symmetric\nbilayers of ultracold dipolar fermions with their dipole moments being\nperpendicular to layers. In particular, we investigate how the pairing between\ntwo layers and the many-body screening of interlayer interaction affect each\nother. We compare results for pairings obtained with three different\napproximations for the interlayer interactions namely, bare dipole-dipole\ninteraction, the random-phase approximation for screening obtained in the\nnormal phase, and the self-consistent superfluid phase screening within the\nrandom-phase approximation. We find that at weak couplings the screening\nfurther suppresses the pairing while at strong couplings, the screening would\nbe suppressed due to the pairing gap in the quasi-particle spectrum. Therefore\na self-consistent treatment of both screening and pairing on equal footings is\nnecessary for obtaining a correct picture of the phase diagram and order\nparameter at both small and large layer spacings and densities. We also notice\nthat the highly speculated density-wave instability in bilayers with the\nparallel polarization of dipoles in two layers is simply an artifact of the\nincorrect screening scheme.",
        "positive": "Comment on \"Density and Spin response of a strongly-interacting Fermi\n  gas in the attractive and quasi-repulsive regime\": This is a comment on Phys. Rev. Lett. 108, 080401 (2012) by Palestini et al.\nWe pointed out that the diagrammatic method in that article violates gauge\ninvariance. As a consequence, there will a Meissner effect in the normal phase\nand the contribution from collective modes are not mentioned in the\nsymmetry-broken phase."
    },
    {
        "anchor": "Vortex-bright solitons in a spin-orbit coupled spin-$1$ condensate: We study the vortex-bright solitons in a quasi-two-dimensional\nspin-orbit-coupled (SO-coupled) hyperfine spin-1 three-component Bose-Einstein\ncondensate (BEC) using variational method and numerical solution of a\nmean-field model. The ground state of these vortex-bright solitons is radially\nsymmetric for weak ferromagnetic and polar interactions. For a sufficiently\nstrong ferromagnetic interaction, we observe the emergence of an asymmetric\nvortex-bright soliton as the ground state. We also numerically investigate\nstable moving solitons and binary collision between them. The present\nmean-field model is not Galilean invariant, and we use a Galilean-transformed\nmodel for generating the moving solitons. At low velocities, the head-on\ncollision between two {\\em in-phase} solitons results either in collapse or\nfusion of the soliton pair. On the other hand, in head-on collision, the two\n{\\em out-of-phase} solitons strongly repel each other and trace back their\ntrajectories before the actual collision. At low velocities, in a collision\nwith an impact parameter, the {\\em out-of-phase} solitons get deflected from\ntheir original trajectory like two rigid classical disks. These {\\em\nout-of-phase solitons} behave like classical disks, and their collision\ndynamics is governed by classical laws of motion. However, at large velocities\ntwo SO-coupled spinor solitons, irrespective of phase difference, can pass\nthrough each other in a head-on collision like two quantum solitons.",
        "positive": "A supercircle description of universal three-body states in two\n  dimensions: We consider bound states of asymmetric three-body systems confined to two\ndimensions. In the universal regime, two energy ratios and two mass ratios\nprovide complete knowledge of the three-body energy measured in units of one\ntwo-body energy. The lowest number of stable bound states is produced when one\nmass is larger than two similar masses. We focus on selected asymmetric systems\nof interest in cold atom physics. The scaled three-body energy and the two\nscaled two-body energies are related through an equation for a supercircle\nwhose radius increases almost linearly with three-body energy. The exponents\nexhibit an increasing behavior with three-body energy. The mass dependence is\nhighly non-trivial. We give a simple relation that predicts the universal\nthree-body energy."
    },
    {
        "anchor": "Low temperature thermodynamic properties of a polarized Fermi gas in a\n  quartic trap: We study low temperature thermodynamic properties of a polarized Fermi gas\ntrapped in a quartic anharmonic potential. We use a semi classical\napproximation and a low temperature series expansion method to derive\nanalytical expressions for various thermodynamic quantities. These quantities\ninclude the total energy, particle number, and heat capacity for both positive\nand negative anharmonic confinements.",
        "positive": "Relaxation of a high-energy quasiparticle in a one-dimensional Bose gas: We evaluate the relaxation rate of high-energy quasiparticles in a weakly\ninteracting one-dimensional Bose gas. Unlike in higher dimensions, the rate is\na nonmonotonic function of temperature, with a maximum at the crossover to the\nstate of suppressed density fluctuations. At the maximum, the relaxation rate\nmay significantly exceed its zero-temperature value. We also find the\ndependence of the differential inelastic scattering rate on the transferred\nenergy. This rate yields information about temperature dependence of local pair\ncorrelations."
    },
    {
        "anchor": "Cooper pairing above the critical temperature in a unitary Fermi gas: We present an ab initio determination of spin responses of the unitary Fermi\ngas, based on finite temperature quantum Monte Carlo calculations and the Kubo\nlinear-response formalism. We determine the temperature dependence of the spin\nsusceptibility and the spin conductivity. We show that both quantities exhibit\nsuppression above the critical temperature of the superfluid to normal phase\ntransition due to presence of the Cooper pairs. The spin diffusion transport\ncoefficient does not display the existence of a minimum in the vicinity of the\ncritical temperature and it drops to very low values D_s approx 0.8hbar/m in\nthe superfluid phase. All these spin observables show a smooth and monotonic\nbehavior with temperature when crossing the critical temperature T_c, until the\nFermi liquid regime is attained at the temperature T*, where the pseudogap\nregime disappears.",
        "positive": "Dynamic instabilities and turbulence of merged rotating Bose-Einstein\n  condensates: We present the simulation results of merging harmonically confined rotating\nBose-Einstein condensates in two dimensions. Merging of the condensate is\ntriggered by positioning the rotation axis at the trap minima and moving both\ncondensates towards each other while slowly ramping their rotation frequency.\nWe analyze the dynamics of the merged condensate by letting them evolve under a\nsingle harmonic trap. We systematically investigate the formation of solitonic\nand vortex structures in the final, unified condensate, considering both\nnon-rotating and rotating initial states. In both cases, merging leads to the\nformation of solitons that decay into vortex pairs through snake instability\nand subsequently, these pairs annihilate. Soliton formation and decay-induced\nphase excitations generate sound waves, more pronounced when the merging time\nis short. We witness no sound wave generation at sufficiently longer merging\ntimes that finally leads to the condensate reaching its ground state. With\nrotation, we notice off-axis merging (where the rotation axes are not aligned),\nleading to the distortion and weakening of soliton formation. The\nincompressible kinetic energy spectrum exhibits a Kolmogorov-like cascade\n[$E(k) \\sim k^{-5/3}$] in the initial stage for merging condensates rotating\nabove a critical frequency and a Vinen-like cascade [$E(k) \\sim k^{-1}$] at a\nlater time for all cases. Our findings hold potential significance for atomic\ninterferometry, continuous atomic lasers, and cosmic events related to the\nremnants of binary neutron-star mergers."
    },
    {
        "anchor": "Curved vortex surfaces in four-dimensional superfluids: I.\n  Unequal-frequency double rotations: The study of superfluid quantum vortices has long been an important area of\nresearch, with previous work naturally focusing on two-dimensional and\nthree-dimensional systems, where rotation stabilises point vortices and line\nvortices respectively. Interestingly, this physics generalises for a\nhypothetical four-dimensional (4D) superfluid to include vortex planes, which\ncan have a much richer phenomenology. In this paper, we study the possibility\nof skewed and curved vortex planes, which have no direct analogue in lower\ndimensions. By analytically and numerically studying the 4D Gross-Pitaevskii\nequation, we show that such vortex surfaces can be stabilised and favoured by\ndouble rotation with unequal rotation frequencies. Our work raises open\nquestions for further research into the physics of these vortex surfaces and\nsuggests interesting future extensions to tilted vortex surfaces under\nequal-frequency double rotation and to more realistic 4D models.",
        "positive": "Floquet Gauge Pumps as Sensors for Spectral Degeneracies Protected by\n  Symmetry or Topology: We introduce the concept of a Floquet gauge pump whereby a dynamically\nengineered Floquet Hamiltonian is employed to reveal the inherent degeneracy of\nthe ground state in interacting systems. We demonstrate this concept in a\none-dimensional XY model with periodically driven couplings and transverse\nfield. In the high-frequency limit, we obtain the Floquet Hamiltonian\nconsisting of the static XY and dynamically generated Dzyaloshinsky-Moriya\ninteraction (DMI) terms. The dynamically generated magnetization current\ndepends on the phases of complex coupling terms, with the XY interaction as the\nreal and DMI as the imaginary part. As these phases are cycled, the current\nreveals the ground-state degeneracies that distinguish the ordered and\ndisordered phases. We discuss experimental requirements needed to realize the\nFloquet gauge pump in a synthetic quantum spin system of interacting trapped\nions."
    },
    {
        "anchor": "Self-bound droplets of light with orbital angular momentum: Systems with competing attractive and repulsive interactions have a tendency\nto condense into droplets. This is the case for water in a sink, liquid helium\nand dipolar atomic gases. Here, we consider a photon fluid which is formed in\nthe transverse plane of a monochromatic laser beam propagating in an attractive\n(focusing) nonlocal nonlinear medium. In this setting we demonstrate the\nformation of the optical analogue of matter wave droplets, and study their\nproperties. The system we consider admits droplets that carry orbital angular\nmomentum. We find bound states possessing liquid-like properties, such as bulk\npressure and compressibility. Interestingly, these droplets of light, as\nopposed to optical vortices, form due to the competition between long-range\ns-wave (monopole) and d-wave (quadrupole) interactions as well as diffraction.",
        "positive": "Direct observation of non-local fermion pairing in an attractive\n  Fermi-Hubbard gas: Pairing of fermions lies at the heart of superconductivity, the hierarchy of\nnuclear binding energies and superfluidity of neutron stars. The Hubbard model\nof attractively interacting fermions provides a paradigmatic setting for\nfermion pairing, featuring a crossover between Bose-Einstein condensation (BEC)\nof tightly bound pairs and Bardeen-Cooper-Schrieffer (BCS) superfluidity of\nlong-range Cooper pairs, and a \"pseudo-gap\" region where pairs form already\nabove the superfluid critical temperature. We here directly observe the\nnon-local nature of fermion pairing in a Hubbard lattice gas, employing spin-\nand density-resolved imaging of $\\sim$1000 fermionic ${}^{40}$K atoms under a\nbilayer microscope. Complete fermion pairing is revealed by the vanishing of\nglobal spin fluctuations with increasing attraction. In the strongly correlated\nregime, the fermion pair size is found to be on the order of the average\ninterparticle spacing. We resolve polaronic correlations around individual\nspins, resulting from the interplay of non-local pair fluctuations and\ncharge-density-wave order. Our techniques open the door toward in-situ\nobservation of fermionic superfluids in a Hubbard lattice gas."
    },
    {
        "anchor": "A self-bound matter-wave boson-fermion quantum ball: We demonstrate the possibility of creating a self-bound stable\nthree-dimensional matter-wave spherical boson-fermion quantum ball in the\npresence of an attractive boson-fermion interaction and a small repulsive\nthree-boson interaction. The three-boson interaction could be attractive or\nrepulsive whereas the fermions are taken to be in a fully-paired super-fluid\nstate in the Bardeen- Cooper-Schreifer ( quasi-noninteracting weak-coupling)\nlimit. We also include the Lee-Huang-Yang (LHY) correction to a repulsive\nbosonic interaction term. The repulsive three-boson interaction and the LHY\ncorrection can stop a global collapse while acting jointly or separately. The\npresent study is based on a mean-field model, where the bosons are subject to a\nGross-Pitaevskii (GP) Lagrangian functional and the fully-paired fermions are\ndescribed by a Galilean-invariant density functional Lagrangian. The\nboson-fermion interaction is taken to be the mean-field Hartree interaction,\nquite similar to the interaction term in the GP equation. The study is\nillustrated by a variational and a numerical solution of the mean-field model\nfor the boson-fermion $^7$Li- $^6$Li system.",
        "positive": "Vinen turbulence via the decay of multicharged vortices in trapped\n  atomic Bose-Einstein condensates: We investigate a procedure to generate turbulence in a trapped Bose-Einstein\ncondensate which takes advantage of the decay of multicharged vortices. We show\nthat the resulting singly-charged vortices twist around each other, intertwined\nin the shape of helical Kelvin waves, which collide and undergo vortex\nreconnections, creating a disordered vortex state. By examining the velocity\nstatistics, the energy spectrum, the correlation functions and the temporal\ndecay, and comparing these properties with the properties of ordinary\nturbulence and observations in superfluid helium, we conclude that this\ndisordered vortex state can be identified with the `Vinen' regime of turbulence\nwhich has been discovered in the context of superfluid helium."
    },
    {
        "anchor": "A coordinate Bethe ansatz approach to the calculation of equilibrium and\n  nonequilibrium correlations of the one-dimensional Bose gas: We use the coordinate Bethe ansatz to exactly calculate matrix elements\nbetween eigenstates of the Lieb-Liniger model of one-dimensional bosons\ninteracting via a two-body delta-potential. We investigate the static\ncorrelation functions of the zero-temperature ground state and their dependence\non interaction strength, and analyze the effects of system size in the\ncrossover from few-body to mesoscopic regimes for up to seven particles. We\nalso obtain time-dependent nonequilibrium correlation functions for five\nparticles following quenches of the interaction strength from two distinct\ninitial states. One quench is from the non-interacting ground state and the\nother from a correlated ground state near the strongly interacting\nTonks-Girardeau regime. The final interaction strength and conserved energy are\nchosen to be the same for both quenches. The integrability of the model highly\nconstrains its dynamics, and we demonstrate that the time-averaged correlation\nfunctions following quenches from these two distinct initial conditions are\nboth nonthermal and moreover distinct from one another.",
        "positive": "Exact solutions and stability of rotating dipolar Bose-Einstein\n  condensates in the Thomas-Fermi limit: We present a theoretical analysis of dilute gas Bose-Einstein condensates\nwith dipolar atomic interactions under rotation in elliptical traps. Working in\nthe Thomas-Fermi limit, we employ the classical hydrodynamic equations to first\nderive the rotating condensate solutions and then consider their response to\nperturbations. We thereby map out the regimes of stability and instability for\nrotating dipolar Bose-Einstein condensates and in the latter case, discuss the\npossibility of vortex lattice formation. We employ our results to propose\nseveral novel routes to induce vortex lattice formation in a dipolar\ncondensate."
    },
    {
        "anchor": "Superoperators vs. Trajectories for Matrix Product State Simulations of\n  Open Quantum System: A Case Study: Quantum trajectories and superoperator algorithms implemented within the\nmatrix product state (MPS) framework are powerful tools to simulate the\nreal-time dynamics of open dissipative quantum systems. As for the unitary\ncase, the reachable time-scales as well as system sizes are limited by the\n(possible) build-up of entanglement entropy. The aforementioned methods\nconstitute complementary approaches how Lindblad master equations can be\nintegrated relying either on a quasi-exact representation of the full density\nmatrix or a stochastic unraveling of the density matrix in terms of pure\nstates. In this work, we systematically benchmark both methods by studying the\ndynamics of a Bose-Hubbard chain in the presence of local as well as global\ndephasing. The build-up as well as system-size scaling of entanglement entropy\nstrongly depends on the method and the parameter regime and we discuss the\napplicability of the methods for these cases as well as study the distribution\nof observables and time discretization errors that can become a limiting factor\nfor global dissipation.",
        "positive": "Number-conserving approaches to $n$-component Bose-Einstein condensates: We develop the number-conserving approach that has previously been used in a\nsingle component Bose-Einstein condensed dilute atomic gas, to describe\nconsistent coupled condensate and noncondensate number dynamics, to an\n$n$-component condensate. The resulting system of equations comprises, for each\ncomponent, of a generalised Gross-Pitaevskii equation coupled to modified\nBogoliubov-de Gennes equations. Lower-order approximations yield general\nformulations for multi-component Gross-Pitaevskii equations, and systems of\nmulti-component Gross-Pitaevskii equations coupled to multi-component modified\nnumber-conserving Bogoliubov-de Gennes equations. The analysis is left general,\nsuch that, in the $n$-component condensate, there may or may not be mutually\ncoherent components. An expansion in powers of the ratio of noncondensate to\ncondensate particle numbers for each coherent set is used to derive the\nself-consistent, second-order, dynamical equations of motion. The advantage of\nthe analysis developed in this article is in its applications to dynamical\ninstabilities that appear when two (or more) components are in conflict and\nwhere a significant noncondensed fraction of atoms is expected to appear."
    },
    {
        "anchor": "A higher-order topological twist on cold-atom SO(5) Dirac fields: Ultracold Fermi gases of spin-3/2 atoms provide a clean platform to realise\nSO(5) models of 4-Fermi interactions in the laboratory. By confining the atoms\nin a two-dimensional Raman lattice, we show how this system can be used as a\nflexible quantum simulator of Dirac quantum field theories (QFTs) that combine\nGross-Neveu and Thirring interactions with a higher-order topological twist. We\nshow that the lattice model corresponds to a regularization of this QFT with an\nanisotropic twisted Wilson mass. This allows us to access higher-order\ntopological states protected by a hidden SO(5) symmetry, a remnant of the\noriginal rotational symmetry of the 4-Fermi interactions that is not explicitly\nbroken by the lattice discretization. Using large-$N$ methods, we show that the\n4-Fermi interactions lead to a rich phase diagram with various competing\nfermion condensates. Our work opens a route for the implementation of\ncorrelated higher-order topological states with tunable interactions that has\ninteresting connections to non-trivial relativistic QFTs of Dirac fermions in\n$D = 2 + 1$ dimensions.",
        "positive": "Universal driven critical dynamics across a quantum phase transition in\n  ferromagnetic spinor atomic Bose-Einstein condensates: We study the equilibrium and dynamical properties of a ferromagnetic spinor\natomic Bose-Einstein condensate. In the vicinity of the critical point for a\ncontinuous quantum phase transition, universal behaviors are observed both in\nthe equilibrium state and in the dynamics when the quadratic Zeeman shift is\nswept linearly. Three distinct dynamical regions are identified for different\nsweeping time scales ($\\tau$), when compared to the time scale $\\tau_{\\rm\nKZ}\\sim N^{(1+\\nu z)/\\nu d}$ decided by external driving in a system with\nfinite size $N$ ($\\nu,z$ are critical exponents and $d$ the dimensionality).\nThey are manifested by the excitation probability $\\mathcal{P}$ and the excess\nheat density $\\mathcal{Q}$. The adiabatic region of\n$\\,\\mathcal{P}\\sim\\mathcal{Q}\\sim\\tau^{-2}\\,$ follows from the adiabatic\nperturbation theory when $\\tau >\\tau_{\\rm KZ}$, while the non-adiabatic\nuniversal region of $\\,\\mathcal{P}\\sim\\mathcal{Q}\\sim\\tau^{-1}\\,$ in the\nthermodynamic limit is described by the Kibble-Zurek mechanism when $\\tau_{\\rm\nKZ}>\\tau >$ the time scale given by initial gap. The Kibble-Zurek scaling\nhypothesis is augmented with finite-size scaling in the latter region and\nseveral experimentally falsifiable features for the finite system we consider\nare predicted. The region of the fastest sweeping is found to be non-universal\nand far-from-equilibrium with $\\mathcal{P}$ and $\\mathcal{Q}$ essentially being\nconstants independent of $\\tau$."
    },
    {
        "anchor": "Radio Frequency Association of Efimov Trimers: The quantum-mechanical three-body problem is one of the fundamental\nchallenges of few-body physics. When the two-body interactions become resonant,\nan infinite series of universal three-body bound states is predicted to occur,\nwhose properties are determined by the strength of the two-body interactions.\nWe report on the association and direct observation of a trimer state\nconsisting of three distinguishable fermions using radio-frequency (RF)\nspectroscopy. The measurements of its binding energy are consistent with\ntheoretical predictions which include non-universal corrections.",
        "positive": "Dissipative Dicke Model with Collective Atomic Decay: Bistability,\n  Noise-Driven Activation and Non-Thermal First Order Superradiance Transition: The Dicke model describes the coherent interaction of a laser-driven ensemble\nof two level atoms with a quantized light field. It is realized within cavity\nQED experiments, which in addition to the coherent Dicke dynamics feature\ndissipation due to e.g. atomic spontaneous emission and cavity photon loss.\nSpontaneous emission supports the uncorrelated decay of individual atomic\nexcitations as well as the enhanced, collective decay of an excitation that is\nshared by $N$ atoms and whose strength is determined by the cavity geometry. We\nderive a many-body master equation for the dissipative Dicke model including\nboth spontaneous emission channels and analyze its dynamics on the basis of\nHeisenberg-Langevin and stochastic Bloch equations. We find that the collective\nloss channel leads to a region of bistability between the empty and the\nsuperradiant state. Transitions between these states are driven by non-thermal,\nmarkovian noise. The interplay between dissipative and coherent elements leads\nto a genuine non-equilibrium dynamics in the bistable regime, which is\nexpressed via a non-conservative force and a multiplicative noise kernel\nappearing in the stochastic Bloch equations. We present a semiclassical\napproach, based on stochastic nonlinear optical Bloch equations, which for the\ninfinite-range Dicke Model become exact in the large-$N$-limit. The absence of\nan effective free energy functional, however, necessitates to include\nfluctuation corrections with $\\mathcal{O}(1/N)$ for finite $N<\\infty$ to locate\nthe non-thermal first-order phase transition between the superradiant and the\nempty cavity."
    },
    {
        "anchor": "Spin diffusion in trapped clouds of strongly interacting cold atoms: We show that puzzling recent experimental results on spin diffusion in a\nstrongly interacting atomic gas may be understood in terms of the predicted\nspin diffusion coefficient for a generic strongly interacting system. Three\nimportant features play a central role: a) Fick's law for diffusion must be\nmodified to allow for the trapping potential, b) the diffusion coefficient is\ninhomogeneous, due to the density variations in the cloud and c) the diffusion\napproximation fails in the outer parts of the cloud, where the mean free path\nis long.",
        "positive": "Quantum phases of spinful Fermi gases in optical cavities: We explore the quantum phases emerging from the interplay between spin and\nmotional degrees of freedom of a one-dimensional quantum fluid of spinful\nfermionic atoms, effectively interacting via a photon-mediating mechanism with\ntunable sign and strength g, as it can be realized in present-day experiments\nwith optical cavities. We find the emergence, in the very same system, of spin-\nand atomic-density wave ordering, accompanied by the occurrence of\nsuperfluidity for g > 0, while cavity photons are seen to drive strong\ncorrelations at all g values, with fermionic character for g > 0, and bosonic\ncharacter for g < 0. Due to the long-range nature of interactions, to infer\nthese results we combine mean-field and exact diagonalization methods supported\nby bosonization analysis."
    },
    {
        "anchor": "Floquet-engineered nonlinearities and controllable pair-hopping\n  processes: From optical Kerr cavities to correlated quantum matter: This work explores the possibility of creating and controlling unconventional\nnonlinearities by periodic driving, in a broad class of systems described by\nthe nonlinear Schr\\\"odinger equation (NLSE). By means of a parent quantum\nmany-body description, we demonstrate that such driven systems are well\ncaptured by an effective NLSE with emergent nonlinearities, which can be finely\ncontrolled by tuning the driving sequence. We first consider a general class of\ntwo-mode nonlinear systems - relevant to optical Kerr cavities, waveguides and\nBose-Einstein condensates - where we find an emergent four-wave mixing\nnonlinearity, which originates from pair-hopping processes in the parent\nquantum picture. Tuning this drive-induced nonlinearity is shown to modify the\nphase-space topology, which can be detected through relative population and\nphase measurements. We then couple individual (two-mode) dimers in view of\ndesigning extended lattice models with unconventional nonlinearities and\ncontrollable pair-hopping processes. Following this general dimerization\nconstruction, we obtain an effective lattice model with drive-induced\ninteractions, whose ground-state exhibits orbital order, chiral currents and\nemergent magnetic fluxes through the spontaneous breaking of time-reversal\nsymmetry. We analyze these intriguing properties both in the weakly-interacting\n(mean-field) regime, captured by the effective NLSE, and in the\nstrongly-correlated quantum regime. Our general approach opens a route for the\nengineering of unconventional optical nonlinearities in photonic devices and\ncontrollable drive-induced interactions in ultracold quantum matter.",
        "positive": "Efimov Enhanced Kondo Effect in Alkaline and Alkaline-Earth Atomic Gas\n  Mixture: Recent experiment has observed Feshbach resonances between alkaline and\nalkaline-earth atoms. These Feshbach resonances are insensitive to the nuclear\nspin of alkaline-earth atoms. Ultilizing this feature, we propose to take this\nsystem as a candidate to perform quantum simulation of the Kondo effect. An\nalkaline atom can form a molecule with an alkaline-earth atom with different\nnuclear spins, which plays the role of spin-exchange scattering responsible for\nthe Kondo effect. Furthermore, we point out that the existence of three-body\nbound state and atom-molecule resonance due to the Efimov effect can enhance\nthis spin-exchange scattering, and therefore enhance the Kondo effect. We\ndiscuss this mechanism first with a three-body problem in free space, and then\ndemonstrate that the same mechanism still holds when the alkaline atom is\nlocalized by an external trap and becomes an impurity embedded in the\nalkaline-earth atomic gases."
    },
    {
        "anchor": "Dynamical scaling of correlations generated by short- and long-range\n  dissipation: We study the spatio-temporal spreading of correlations in an ensemble of\nspins due to dissipation characterized by short- and long-range spatial\nprofiles. We consider systems initially in an uncorrelated state, and find that\ncorrelations widen and contract in a novel pattern intimately related to both\nthe dissipative nature of the dynamical channel and its spatial profile.\nAdditionally, we make a methodological contribution by generalizing\nnon-equilibrium spin-wave theory to the case of dissipative systems and derive\nequations of motion for any translationally invariant spin chain whose dynamics\ncan be described by a combination of Hamiltonian interactions and dissipative\nLindblad channels. Our work aims at extending the study of correlation dynamics\nto purely dissipative quantum simulators and compare them with the established\nparadigm of correlations spreading in hamiltonian systems.",
        "positive": "Ground-states of spin-1 bosons in asymmetric double-wells: In this work we investigate the different states of a system of spin-1 bosons\nin two potential wells connected by tunneling, with spin-dependent interaction.\nThe model utilizes the well-known Bose-Hubbard Hamiltonian, adding a local\ninteraction term that depends on the modulus of the total spin in a well,\nfavoring a high- or low-spin state for different signs of the coupling\nconstant. We employ the concept of fidelity to detect critical values of\nparameters for which the ground state undergoes significant changes. The nature\nof the states is investigated through evaluation of average occupation numbers\nin the wells and of spin correlations. A more detailed analysis is done for a\ntwo-particle system, but a discussion of the three-particle case and some\nresults for larger numbers are also presented."
    },
    {
        "anchor": "Three-Component Fermionic Atoms with Repulsive Interaction in Optical\n  Lattices: We investigate three-component (colors) repulsive fermionic atoms in optical\nlattices using the dynamical mean field theory. Depending on the anisotropy of\nthe repulsive interactions, either a color density-wave state or a color\nselective staggered state appears at half filling. In the former state, pairs\nof atoms with two of the three colors and atoms with the third color occupy\ndifferent sites alternately. In the latter state, atoms with two of the three\ncolors occupy different sites alternately and atoms with the third color are\nitinerant throughout the system. When the interactions are isotropic, both\nstates are degenerate. We discuss the results using an effective model.",
        "positive": "Exotic Topological States with Raman-Induced Spin-Orbit Coupling: We propose a simple experimental scheme to realize simultaneously the\none-dimensional spin-orbit coupling and the staggered spin-flip in ultracold\npseudospin-$1/2$ atomic Fermi gases trapped in square optical lattices. In the\nabsence of interspecies interactions, the system supports gapped Chern\ninsulators and gapless topological semimetal states. By turning on the $s$-wave\ninteractions, a rich variety of gapped and gapless inhomogeneous topological\nsuperfluids can emerge. In particular, a gapped topological Fulde-Ferrell\nsuperfluid, in which the chiral edge states at opposite boundaries possess the\nsame chirality, is predicted."
    },
    {
        "anchor": "Energy spectra of vortex distributions in two-dimensional quantum\n  turbulence: We theoretically explore key concepts of two-dimensional turbulence in a\nhomogeneous compressible superfluid described by a dissipative two-dimensional\nGross-Pitaeveskii equation. Such a fluid supports quantized vortices that have\na size characterized by the healing length $\\xi$. We show that for the\ndivergence-free portion of the superfluid velocity field, the kinetic energy\nspectrum over wavenumber $k$ may be decomposed into an ultraviolet regime\n($k\\gg \\xi^{-1}$) having a universal $k^{-3}$ scaling arising from the vortex\ncore structure, and an infrared regime ($k\\ll\\xi^{-1}$) with a spectrum that\narises purely from the configuration of the vortices. The Novikov power-law\ndistribution of intervortex distances with exponent -1/3 for vortices of the\nsame sign of circulation leads to an infrared kinetic energy spectrum with a\nKolmogorov $k^{-5/3}$ power law, consistent with the existence of an inertial\nrange. The presence of these $k^{-3}$ and $k^{-5/3}$ power laws, together with\nthe constraint of continuity at the smallest configurational scale\n$k\\approx\\xi^{-1}$, allows us to derive a new analytical expression for the\nKolmogorov constant that we test against a numerical simulation of a forced\nhomogeneous compressible two-dimensional superfluid. The numerical simulation\ncorroborates our analysis of the spectral features of the kinetic energy\ndistribution, once we introduce the concept of a {\\em clustered fraction}\nconsisting of the fraction of vortices that have the same sign of circulation\nas their nearest neighboring vortices. Our analysis presents a new approach to\nunderstanding two-dimensional quantum turbulence and interpreting similarities\nand differences with classical two-dimensional turbulence, and suggests new\nmethods to characterize vortex turbulence in two-dimensional quantum fluids via\nvortex position and circulation measurements.",
        "positive": "Spontaneous symmetry breaking induced by interaction in linearly coupled\n  binary Bose Einstein condensates: We analyze the spontaneous symmetry breaking (SSB) induced by one specific\ncomponent of a linearly coupled binary Bose-Einstein condensate (BEC). The\nmodel is based on linearly coupled Schr\\\"odinger equations with cubic\nnonlinearity and with a double-well (DW) potential acting on only one of the\natomic components. By numerical simulations, symmetric and asymmetric\nground-states were obtained, and an induced asymmetry in the partner field was\nobserved. In this sense, we properly demonstrated that the linear coupling\nmixing the two-field component (Rabi coupling) promotes the (in)balance between\natomic species, as well as the appearance of the Josephson and SSB phases."
    },
    {
        "anchor": "Magnetic dipolar interaction between hyperfine clock states in a planar\n  alkali Bose gas: In atomic systems, clock states feature a zero projection of the total\nangular momentum and thus a low sensitivity to magnetic fields. This makes them\nwidely used for metrological applications like atomic fountains or gravimeters.\nHere, we show that a mixture of two such non-magnetic states still display\nmagnetic dipole-dipole interactions. Using high resolution spectroscopy of a\nplanar gas of $^{87}$Rb atoms with a controlled in-plane shape, we explore the\neffective isotropic and extensive character of these interactions and\ndemonstrate their tunability. Our measurements set strong constraints on the\nrelative values of the s-wave scattering lengths $a_{ij}$ involving the two\nclock states.",
        "positive": "Ultra-Fast Converging Path-Integral Approach for Rotating Ideal\n  Bose-Einstein Condensates: A recently developed efficient recursive approach for analytically\ncalculating the short-time evolution of the one-particle propagator to\nextremely high orders is applied here for numerically studying the\nthermodynamical and dynamical properties of a rotating ideal Bose gas of\n$^{87}$Rb atoms in an anharmonic trap. At first, the one-particle energy\nspectrum of the system is obtained by diagonalizing the discretized short-time\npropagator. Using this, many-boson properties such as the condensation\ntemperature, the ground-state occupancy, density profiles, and time-of-flight\nabsorption pictures are calculated for varying rotation frequencies. The\nobtained results improve previous semiclassical calculations, in particular for\nsmaller particle numbers. Furthermore, we find that typical time scales for a\nfree expansion are increased by an order of magnitude for the delicate regime\nof both critical and overcritical rotation."
    },
    {
        "anchor": "Photon-atomic solitons in a Bose-Einstein condensate trapped in a soft\n  optical lattice: We investigate the ground state (GS) of a collisionless Bose-Einstein\ncondensate (BEC) trapped in a soft one-dimensional optical lattice (OL), which\nis formed by two counterpropagating optical beams perturbed by the BEC density\nprofile through the local-field effect (LFE). We show that LFE gives rise to an\nenvelope-deformation potential, a nonlocal potential resulting from the phase\ndeformation, and an effective self-interaction of the condensate. As a result,\nstable photon-atomic lattice solitons, including an optical component, in the\nform of the deformation of the soft OL, in a combination with a localized\nmatter-wave component, are generated in the blue-detuned setting, without any\ndirect interaction between atoms. These self-trapped modes, which realize the\nsystem's GS, are essentially different from the gap solitons supported by the\ninterplay of the OL potential and collisional interactions between atoms. A\ntransition to tightly bound modes from loosely bound ones occurs with the\nincrease of the number of atoms in the BEC.",
        "positive": "Thermodynamic performance of a periodically driven harmonic oscillator\n  correlated with the baths: We consider a harmonic oscillator under periodic driving and coupled to two\nharmonic-oscillator heat baths at different temperatures. We use the\nthermofield transformation with chain mapping for this setup, which allows us\nto study the unitary evolution of the system and the baths up to a time when\nthe periodic steady state emerges in the system. We characterize this periodic\nsteady state, and we show that, by tuning the system and the bath parameters,\none can turn this system from an engine to an accelerator or even to a heater.\nThe possibility to study the unitary evolution of the system and baths also\nallows us to evaluate the steady correlations that build between the system and\nthe baths, and correlations that grow between the baths."
    },
    {
        "anchor": "Local measures of dynamical quantum phase transitions: In recent years, dynamical quantum phase transitions (DQPTs) have emerged as\na useful theoretical concept to characterize nonequilibrium states of quantum\nmatter. DQPTs are marked by singular behavior in an \\textit{effective free\nenergy} $\\lambda(t)$, which, however, is a global measure, making its\nexperimental or theoretical detection challenging in general. We introduce two\nlocal measures for the detection of DQPTs with the advantage of requiring fewer\nresources than the full effective free energy. The first, called the\n\\textit{real-local} effective free energy $\\lambda_M(t)$, is defined in real\nspace and is therefore suitable for systems where locally resolved measurements\nare directly accessible such as in quantum-simulator experiments involving\nRydberg atoms or trapped ions. We test $\\lambda_M(t)$ in Ising chains with\nnearest-neighbor and power-law interactions, and find that this measure allows\nextraction of the universal critical behavior of DQPTs. The second measure we\nintroduce is the \\textit{momentum-local} effective free energy $\\lambda_k(t)$,\nwhich is targeted at systems where momentum-resolved quantities are more\nnaturally accessible, such as through time-of-flight measurements in ultracold\natoms. We benchmark $\\lambda_k(t)$ for the Kitaev chain, a paradigmatic system\nfor topological quantum matter, in the presence of weak interactions. Our\nintroduced local measures for effective free energies can further facilitate\nthe detection of DQPTs in modern quantum-simulator experiments.",
        "positive": "Dynamics of a Bose-Einstein Condensate of Excited Magnons: The emergence of a non-equilibrium Bose-Einstein-like condensation of magnons\nin rf-pumped magnetic thin films has recently been experimentally observed. We\npresent here a complete theoretical description of the non-equilibrium\nprocesses involved. It it demonstrated that the phenomenon is another example\nof the presence of a Bose-Einstein-like condensation in non-equilibrium\nmany-boson systems embedded in a thermal bath, better referred-to as\nFr\\\"{o}hlich-Bose-Einstein condensation. The complex behavior emerges after a\nthreshold of the exciting intensity is attained. It is inhibited at higher\nintensities when the magnon-magnon interaction drives the magnons to internal\nthermalization. The observed behavior of the relaxation to equilibrium after\nthe end of the pumping pulse is also accounted for and the different processes\nfully described."
    },
    {
        "anchor": "Generalized wave-packet model for studying coherence of matter-wave\n  interferometers: We present a generalized model for the evolution of atomic wave-packets in\nmatter-wave interferometers. This method provides an efficient tool for\nanalyzing the performance of atomic interferometers using atom clouds prepared\nin a trap as a Bose-Einstein condensate (BEC) or as a thermal ensemble.\nPredictions of the model for dynamic properties such as wave-packet size and\nphase are in excellent agreement with explicit numerical solutions of the\nnon-linear Gross-Pitaevskii equations and enable fast calculations of\ninterferometric performance in regimes where full numerical solutions become\nimpractical. As a starting point, the static Thomas-Fermi (TF) approximation\nfor a BEC in a harmonic trap is generalized to the whole range of atom-atom\ninteraction strengths: from non-interacting atoms (low densities) to the\nstandard TF limit (high atomic densities, as long as the condensate\napproximation still holds). In particular, this generalization allows a good\nestimation of atomic cloud properties along the transition from a\nthree-dimensional to a quasi-one-dimensional BEC in an elongated trap. We then\ndevelop a theoretical model of wave-packet evolution in time-dependent\nconditions. The model is applicable for a wide range of dynamical problems\ninvolving evolution in time-dependent potentials and in a changing mean-field\natomic repulsion due to splitting and separation of wave-packets. We use the\nmodel for studying two effects that influence interferometric coherence:\nimperfect spatial recombination in a two-state interferometer (the so-called\n\"Humpty-Dumpty effect\") and phase diffusion due to number uncertainty in the\ntwo interferometer arms, which was previously studied thoroughly only for\ninterferometric schemes where the BECs in the two arms stay trapped (for\nexample, in a double-well potential).",
        "positive": "Faraday patterns generated by Rabi oscillation in a binary Bose-Einstein\n  condensate: The interaction between atoms in a two-component Bose-Einstein condensate\n(BEC) is effectively modulated by the Rabi oscillation. This periodic\nmodulation of the effective interaction is shown to generate Faraday patterns\nthrough parametric resonance. We show that there are multiple resonances\narising from the density and spin waves in a two-component BEC, and investigate\nthe interplay between the Faraday-pattern formation and the phase separation."
    },
    {
        "anchor": "Ground state of a homogeneous Bose gas of hard spheres: The ground state of a homogeneous Bose gas of hard spheres is treated in\nself-consistent mean-field theory. It is shown that this approach provides an\naccurate description of the ground state of a Bose-Einstein condensed gas for\narbitrarily strong interactions. The results are in good agreement with Monte\nCarlo numerical calculations. Since all other mean-field approximations are\nvalid only for very small gas parameters, the present self-consistent theory is\na unique mean-field approach allowing for an accurate description of Bose\nsystems at arbitrary values of the gas parameter.",
        "positive": "Paired phases and Bose-Einstein condensation of spin-one bosons with\n  attractive interaction: We analyze paired phases of cold bosonic atoms with the hyper spin S=1 and\nwith an attractive interaction. We derive mean-field self-consistent equations\nfor the matrix order parameter describing such paired bosons on an optical\nlattice. The possible solutions are classified according to their symmetries.\nIn particular, we find that the self-consistent equations for the SO(3)\nsymmetric phase are of the same form as those for the scalar bosons with the\nattractive interaction. This singlet phase may exhibit either the BCS type\npairing instability (BCS phase) or the BEC quasiparticle condensation together\nwith the BCS type pairing (BEC phase) for an arbitrary attraction U_0 in the\nsinglet channel of the two body interaction. We show that both condensate\nphases become stable if a repulsion U_2 in the quintet channel is above a\ncritical value, which depends on U_0 and other thermodynamic parameters."
    },
    {
        "anchor": "Temporal coherence, anomalous moments, and pairing correlations in the\n  classical-field description of a degenerate Bose gas: The coherence properties of degenerate Bose gases have usually been expressed\nin terms of spatial correlation functions, neglecting the rich information\nencoded in their temporal behavior. In this paper we show, using a Hamiltonian\nclassical-field formalism, that temporal correlations can be used to\ncharacterize familiar properties of a finite-temperature degenerate Bose gas.\nThe temporal coherence of a Bose-Einstein condensate is limited only by the\nslow diffusion of its phase, and thus the presence of a condensate is indicated\nby a sharp feature in the temporal power spectrum of the field. We show that\nthe condensate mode can be obtained by averaging the field for a short time in\nan appropriate phase-rotating frame, and that for a wide range of temperatures,\nthe condensate obtained in this approach agrees well with that defined by the\nPenrose-Onsager criterion based on one-body (spatial) correlations. For time\nperiods long compared to the phase diffusion time, the field will average to\nzero, as we would expect from the overall U(1) symmetry of the Hamiltonian. We\nidentify the emergence of the first moment on short time scales with the\nconcept of U(1) symmetry breaking that is central to traditional mean-field\ntheories of Bose condensation. We demonstrate that the short-time averaging\nprocedure constitutes a general analog of the 'anomalous' averaging operation\nof symmetry-broken theories by calculating the anomalous thermal density of the\nfield, which we find to have form and temperature dependence consistent with\nthe results of mean-field theories.",
        "positive": "Experimental Observation of a Generalized Gibbs Ensemble: The connection between the non-equilibrium dynamics of isolated quantum\nmany-body systems and statistical mechanics is a fundamental open question. It\nis generally believed that the unitary quantum evolution of a sufficiently\ncomplex system leads to an apparent maximum-entropy state that can be described\nby thermodynamical ensembles. However, conventional ensembles fail to describe\nthe large class of systems that exhibit non-trivial conserved quantities.\nInstead, generalized ensembles have been predicted to maximize entropy in these\nsystems. In our experiments we explicitly show that a degenerate\none-dimensional Bose gas relaxes to a state that can be described by such a\ngeneralized ensemble. This is verified through a detailed study of correlation\nfunctions up to 10th order. The applicability of the generalized ensemble\ndescription for isolated quantum many-body systems points to a natural\nemergence of classical statistical properties from the microscopic unitary\nquantum evolution."
    },
    {
        "anchor": "Ferromagnetism of cold fermions loaded into a decorated square lattice: We investigate two-component ultracold fermions loaded into a decorated\nsquare lattice, which are described by the Hubbard model with repulsive\ninteractions and nearest neighbor hoppings. By combining the real-space\ndynamical mean-field theory with the numerical renormalization group method, we\ndiscuss how a ferromagnetically ordered ground state in the weak coupling\nregime, which originates from the existence of a dispersionless band, is\nadiabatically connected to a Heisenberg ferrimagnetic state in the strong\ncoupling limit. The effects of level splitting and hopping imbalance are also\naddressed.",
        "positive": "Dicke-type phase transition in a spin-orbit coupled Bose-Einstein\n  condensate: Spin-orbit coupled Bose-Einstein condensates (BECs) provide a powerful tool\nto investigate interesting gauge-field related phenomena. We study the ground\nstate properties of such a system and show that it can be mapped to the\nwell-known Dicke model in quantum optics, which describes the interactions\nbetween an ensemble of atoms and an optical field. A central prediction of the\nDicke model is a quantum phase transition between a superradiant phase and a\nnormal phase. Here we detect this transition in a spin-orbit coupled BEC by\nmeasuring various physical quantities across the phase transition. These\nquantities include the spin polarization, the relative occupation of the nearly\ndegenerate single particle states, the quantity analogous to the photon field\noccupation, and the period of a collective oscillation (quadrupole mode). The\napplicability of the Dicke model to spin-orbit coupled BECs may lead to\ninteresting applications in quantum optics and quantum information science."
    },
    {
        "anchor": "Two-body bound and edge states in the extended SSH Bose-Hubbard model: We study the bosonic two-body problem in a Su-Schrieffer-Heeger dimerized\nchain with on-site and nearest-neighbor interactions. We find two classes of\nbound states. The first, similar to the one induced by on-site interactions,\nhas its center of mass on the strong link, whereas the second, existing only\nthanks to nearest-neighbors interactions, is centered on the weak link. We\nidentify energy crossings between these states and analyse them using exact\ndiagonalization and perturbation theory. In the presence of open boundary\nconditions, novel strongly-localized edge-bound states appear in the spectrum\nas a consequence of the interplay between lattice geometry, on-site and\nnearest-neighbor interactions. Contrary to the case of purely on-site\ninteractions, such EBS persist even in the strongly interacting regime.",
        "positive": "Cooling and Near-equilibrium Dynamics of Atomic Gases Across the\n  Superfluid-Mott Insulator Transition: We study near-equilibrium thermodynamics of bosonic atoms in a\ntwo-dimensional optical lattice by ramping up the lattice depth to convert a\nsuperfluid into an inhomogeneous mixture of superfluid and Mott insulator.\nDetailed study of in situ density profiles shows that, first, locally adiabatic\nramps do not guarantee global thermal equilibrium. Indeed, full thermalization\nfor typical parameters only occurs for experiment times which exceed one\nsecond. Secondly, ramping non-adiabatically to the Mott insulator regime can\nresult in strong localized cooling at short times and global cooling once\nequilibrated. For an initial temperature estimated as 20 nK, we observe local\ntemperatures as low as 1.5 nK, and a final global temperature of 9 nK. Possible\ncooling mechanisms include adiabatic decompression, modification of the density\nof states near the quantum critical regime, and the Joule-Thomson effect.\n**NOTE: Following submission of arXiv:0910.1382v1, a systematic correction was\ndiscovered in the density measurement, stemming from three-body losses during\nthe imaging process. New measurements were performed, and the result is in\nsupport of the claim on the slow global dynamics. Due to the substantially\naltered methods and analysis, a new text has been posted as arXiv:1003.0855."
    },
    {
        "anchor": "Monolithic bowtie cavity traps for ultra-cold gases: We report on trapping and cooling Li-6 atoms in a monolithic ring bowtie\ncavity. To make the cavity insensitive to magnetic fields used to tune atomic\ninteractions, we constructed it entirely from fused silica and Zerodur. The\ncomponents were assembled using hydroxide bonding, which we show can be\ncompatible with ultra-high vacuum. Backscattering in high-finesse ring cavities\nreadily causes trap intensity fluctuations and heating, but with\nphase-controlled bi-directional pumping the trap lifetime can be made long\nenough for quantum gas experiments in both the crossed-beam trap\n(unidirectional pump) and 2D lattice trap (bidirectional pump) configurations.",
        "positive": "Manipulating Goldstone modes via the superradiant light in a bosonic\n  lattice gas inside a cavity: We study the low-energy excitations of a bosonic lattice gas with\ncavity-mediated interactions. By performing two successive Hubbard-Stratonovich\ntransformations, we derive an effective field theory to study the\nstrongly-coupling regime. Taking into account the quantum fluctuation, we\nreport the unusual effect of the superradiant cavity light induced density\nimbalance, which has been shown to have a negligible effect on the single\nparticle excitation in the previous studies. Instead, we show that such\nnegligible fluctuation of density imbalance dramatically changes the behavior\nof the low-energy excitation and results in a free switching between two types\nof Goldstone modes in its single particle excitation, i.e., type I and type II\nwith odd and even power energy-momentum dispersion, respectively. Our proposal\nwould open a new horizon for manipulating Goldstone modes from bridging the\ncavity light and strongly interacting quantum matters."
    },
    {
        "anchor": "Dissipative dynamics and cooling rates of trapped impurity atoms\n  immersed in a reservoir gas: We study the dissipative dynamics of neutral atoms in anisotropic harmonic\npotentials, immersed in a reservoir species that is not trapped by the harmonic\npotential. Considering initial motional excitation of the atoms along one\ndirection, we explore the resulting spontaneous emission of reservoir\nexcitations, across a range of trap parameters from strong to weak radial\nconfinement. In different limits these processes are useful as a basis for\nanalogies to laser cooling, or as a means to introduce controlled dissipation\nto many-body dynamics. For realistic experimental parameters, we analyse the\ndistribution of the atoms during the decay and determine the effects of heating\narising from a finite temperature reservoir.",
        "positive": "Polaronic mass renormalization of impurities in BEC: correlated Gaussian\n  wavefunction approach: We propose a class of variational Gaussian wavefunctions to describe\nFr\\\"ohlich polarons at finite momenta. Our wavefunctions give polaron energies\nthat are in excellent agreement with the existing Monte Carlo results for a\nbroad range of interactions. We calculate the effective mass of polarons and\nfind smooth crossover between weak and intermediate impurity-bosons coupling.\nEffective masses that we obtain are considerably larger than those predicted by\nthe mean-field method. A novel prediction based on our variational\nwavefunctions is a special pattern of correlations between host atoms that can\nbe measured in time-of-flight experiments. We discuss atomic mixtures in\nsystems of ultracold atoms in which our results can be tested with current\nexperimental technology."
    },
    {
        "anchor": "Inhomogeneities and impurities in a dense one-dimensional Rydberg\n  lattice gas: We consider a dense one-dimensional laser-driven Rydberg lattice gas with\nperfect nearest-neighbor blockade. The ground state of this system can be found\nanalytically in certain parameter regimes even when the applied fields are\ninhomogeneous in space. We will use this unique feature to investigate the\neffect of an impurity - introduced by the local variation of the laser\nparameters - on the correlations of the many-body ground state. Moreover, we\nexplore the role of a staggered laser field which alternates from site to site\nthereby breaking the sublattice symmetry. We demonstrate that this technique,\nwhich can be applied experimentally, reveals insights into the role of\nlong-range interactions on the critical properties of a Rydberg gas. Our work\nhighlight novel possibilities for the exploration of many-body physics in\nRydberg lattice gases based on locally tuneable laser fields.",
        "positive": "Coherent tunneling via adiabatic passage in a three-well Bose-Hubbard\n  system: We apply the Bose-Hubbard Hamiltonian to a three-well system and show\nanalytically that coherent transport via adiabatic passage (CTAP) of $N$\nnon-interacting particles across the chain is possible. We investigate the\neffect of detuning the middle well to recover CTAP when on-site interparticle\ninteractions would otherwise disrupt the transport. The case of small\ninteractions is restated using first-order perturbation theory to develop\ncriteria for adibaticity that define the regime where CTAP is possible. Within\nthis regime we investigate restricting the Hilbert space to the minimum\nnecessary basis needed to demonstrate CTAP, which dramatically increases the\nnumber of particles that can be efficiently considered. Finally, we compare the\nresults of the Bose-Hubbard model to a mean-field three-mode Gross-Pitaevskii\nanalysis for the equivalent system."
    },
    {
        "anchor": "Optical Lattice with Torus Topology: We propose an experimental scheme to construct an optical lattice where the\natoms are confined to the surface of a torus. This construction can be realized\nwith spatially shaped laser beams which could be realized with recently\ndeveloped high resolution imaging techniques. We numerically study the\nfeasibility of this proposal by calculating the tunneling strengths for atoms\nin the torus lattice. To illustrate the non-trivial role of topology in atomic\ndynamics on the torus, we study the quantized superfluid currents and\nfractional quantum Hall (FQH) states on such a structure. For FQH states, we\nnumerically investigate the robustness of the topological degeneracy and\npropose an experimental way to detect such a degeneracy. Our scheme for torus\nconstruction can be generalized to Riemann surfaces with higher genus for\nexploration of richer topological physics.",
        "positive": "Bose-Einstein condensation in self-consistent mean-field theory: There is a wide-spread belief in the literature on Bose-Einstein condensation\nof interacting atoms that all variants of mean-field theory incorrectly\ndescribe the condensation phase transition, exhibiting, instead of the\nnecessary second-order transition, a first-order transition, even for weakly\ninteracting Bose gas. In the present paper, it is shown that a self-consistent\nmean-field approach is the sole mean-field theory that provides the correct\nsecond-order condensation transition for Bose systems with atomic interactions\nof arbitrary strength, whether weak or strong."
    },
    {
        "anchor": "Thermalization near integrability in a dipolar quantum Newton's cradle: Isolated quantum many-body systems with integrable dynamics generically do\nnot thermalize when taken far from equilibrium. As one perturbs such systems\naway from the integrable point, thermalization sets in, but the nature of the\ncrossover from integrable to thermalizing behavior is an unresolved and\nactively discussed question. We explore this question by studying the dynamics\nof the momentum distribution function in a dipolar quantum Newton's cradle\nconsisting of highly magnetic dysprosium atoms. This is accomplished by\ncreating the first one-dimensional Bose gas with strong magnetic dipole-dipole\ninteractions. These interactions provide tunability of both the strength of the\nintegrability-breaking perturbation and the nature of the near-integrable\ndynamics. We provide the first experimental evidence that thermalization close\nto a strongly interacting integrable point occurs in two steps:\nprethermalization followed by near-exponential thermalization. Exact numerical\ncalculations on a two-rung lattice model yield a similar two-timescale process,\nsuggesting that this is generic in strongly interacting near-integrable models.\nMoreover, the measured thermalization rate is consistent with a parameter-free\ntheoretical estimate, based on identifying the types of collisions that\ndominate thermalization. By providing tunability between regimes of integrable\nand nonintegrable dynamics, our work sheds light both on the mechanisms by\nwhich isolated quantum many-body systems thermalize, and on the temporal\nstructure of the onset of thermalization.",
        "positive": "Scale Invariant Dynamics and Universal Quantum Beats in Bose Gases: We study the signature of scale invariance in the far-from-equilibrium\nquantum dynamics of two dimensional Bose gases. We show that the density\nprofile displays a scale invariant logarithmic singularity near the center. In\naddition, the density oscillates due to quantum beats with universal\nstructures. Namely, the frequencies of the beats can be connected with one\nanother by a universal discrete scale transformation induced by the scale\ninvariance. The experimental applicability of these results is then discussed."
    },
    {
        "anchor": "Resonant enhancement of three-body loss between strongly interacting\n  photons: Rydberg polaritons provide an example of a rare type of system where\nthree-body interactions can be as strong or even stronger than two-body\ninteractions. The three-body interactions can be either dispersive or\ndissipative, with both types possibly giving rise to exotic,\nstrongly-interacting, and topological phases of matter. Despite past\ntheoretical and experimental studies of the regime with dispersive interaction,\nthe dissipative regime is still mostly unexplored. Using a renormalization\ngroup technique to solve the three-body Schr\\\"odinger equation, we show how the\nshape and strength of dissipative three-body forces can be universally enhanced\nfor Rydberg polaritons. We demonstrate how these interactions relate to the\ntransmission through a single-mode cavity, which can be used as a probe of the\nthree-body physics in current experiments.",
        "positive": "Universal characterizing topological insulator and topological\n  semi-metal with Wannier functions: The nontrivial evolution of Wannier functions (WF) for the occupied bands is\na good starting point to understand topological insulator. By modifying the\ndefinition of WFs from the eigenstates of the projected position operator to\nthose of the projected modular position operator, we are able to extend the\nusage of WFs to Weyl metal where the WFs in the old definition fails because of\nthe lack of band gap at the Fermi energy. This extension helps us to\nuniversally understand topological insulator and topological semi-metal in a\nsame framework. Another advantage of using the modular position operators in\nthe definition is that the higher dimensional WFs for the occupied bands can be\neasily obtained. We show one of their applications by schematically explaining\nwhy the winding numbers $\\nu_{3D}=\\nu_{2D}$ for the 3D topological insulators\nof DIII class presented in Phys. Rev. Lett. 114, 016801(2015)."
    },
    {
        "anchor": "The entanglement spectrum and R\u00e9nyi entropies of non-relativistic\n  conformal fermions: We characterize non-perturbatively the R\\'enyi entropies of degree n=2,3,4,\nand 5 of three-dimensional, strongly coupled many-fermion systems in the\nscale-invariant regime of short interaction range and large scattering length,\ni.e. in the unitary limit. We carry out our calculations using lattice methods\ndevised recently by us. Our results show the effect of strong pairing\ncorrelations on the entanglement entropy, which modify the sub-leading behavior\nfor large subsystem sizes (as characterized by the dimensionless parameter x=kF\nL_A, where kF is the Fermi momentum and L_A the linear subsystem size), but\nleave the leading order unchanged relative to the non-interacting case.\nMoreover, we find that the onset of the sub-leading asymptotic regime is at\nsurprisingly small x=2-4. We provide further insight into the entanglement\nproperties of this system by analyzing the spectrum of the entanglement\nHamiltonian of the two-body problem from weak to strong coupling. The low-lying\nentanglement spectrum displays clear features as the strength of the coupling\nis varied, such as eigenvalue crossing, a sharp change in the Schmidt gap, and\nscale invariance at unitarity. Beyond the low-lying component, the spectrum\nappears as a quasi-continuum distribution, for which we present a statistical\ncharacterization; we find, in particular, that the mean shifts to infinity as\nthe coupling is turned off, which indicates that that part of the spectrum\nrepresents non-perturbative contributions to the entanglement Hamiltonian. In\ncontrast, the low-lying entanglement spectrum evolves to finite values in the\nnoninteracting limit. The scale invariance of the unitary regime guarantees\nthat our results are universal features intrinsic to 3D quantum mechanics and\nrepresent a well-defined prediction for ultracold atom experiments, which were\nrecently shown to have direct access to the entanglement entropy.",
        "positive": "Full counting statistics of interacting lattice gases after an\n  expansion: The role of the condensate depletion in the many-body coherence: We study the full counting statistics (FCS) of quantum gases in samples of\nthousands of interacting bosons, detected atom-by-atom after a long free-fall\nexpansion. In this far-field configuration, the FCS reveals the many-body\ncoherence from which we characterize iconic states of interacting lattice\nbosons, by deducing the normalized correlations $g^{(n)}(0)$ up to the order\n$n=6$. In Mott insulators, we find a thermal FCS characterized by\nperfectly-contrasted correlations $g^{(n)}(0)= n!$. In interacting Bose\nsuperfluids, we observe small deviations to the Poisson FCS and to the ideal\nvalues $g^{(n)}(0)=1$ expected for a pure condensate. To describe these\ndeviations, we introduce a heuristic model that includes an incoherent\ncontribution attributed to the depletion of the condensate. The predictions of\nthe model agree quantitatively with our measurements over a large range of\ninteraction strengths, that includes the regime where the condensate is\nstrongly depleted by interactions. These results suggest that the condensate\ncomponent exhibits a full coherence $g^{(n)}(0) =1$ at any order $n$ up to\n$n=6$ and at arbitrary interaction strengths. The approach demonstrated here is\nreadily extendable to characterize a large variety of interacting quantum\nstates and phase transitions."
    },
    {
        "anchor": "Stability of superfluids in tilted optical lattices with periodic\n  driving: Tilted lattice potentials with periodic driving play a crucial role in the\nstudy of artificial gauge fields and topological phases with ultracold quantum\ngases. However, driving-induced heating and the growth of phonon modes restrict\ntheir use for probing interacting many-body states. Here, we experimentally\ninvestigate phonon modes and interaction-driven instabilities of superfluids in\nthe lowest band of a shaken optical lattice. We identify stable and unstable\nparameter regions and provide a general resonance condition. In contrast to the\nhigh-frequency approximation of a Floquet description, we use the superfluids'\nmicromotion to analyze the growth of phonon modes from slow to fast driving\nfrequencies. Our observations enable the prediction of stable parameter regimes\nfor quantum-simulation experiments aimed at studying driven systems with strong\ninteractions over extended time scales.",
        "positive": "Dynamics of Ultracold Bosons in Artificial Gauge Fields: Angular\n  Momentum, Fragmentation, and the Variance of Entropy: We consider the dynamics of two-dimensional interacting ultracold bosons\ntriggered by suddenly switching on an artificial gauge field. The system is\ninitialized in the ground state of a harmonic trapping potential. As a function\nof the strength of the applied artificial gauge, we analyze the emergent\ndynamics by monitoring the angular momentum, the fragmentation as well the\nentropy and variance of the entropy of absorption or single-shot images. We\nsolve the underlying time-dependent many-boson Schr\\\"odinger equation using the\nmulticonfigurational time-dependent Hartree method for indistinguishable\nparticles (MCTDH-X). We find that the artificial gauge field implants angular\nmomentum in the system. Fragmentation -- multiple macroscopic eigenvalues of\nthe reduced one-body density matrix -- emerges in sync with the dynamics of\nangular momentum: the bosons in the many-body state develop non-trivial\ncorrelations. Fragmentation and angular momentum are experimentally difficult\nto assess; here, we demonstrate that they can be probed by statistically\nanalyzing the variance of the image entropy of single-shot images that are the\nstandard projective measurement of the state of ultracold atomic systems."
    },
    {
        "anchor": "Loosely Bound Few-Body States in a Spin-1 Gas with Near-Degenerate\n  Continua: A distinguishing feature of ultracold collisions of bosonic lithium atoms is\nthe presence of two near-degenerate two-body continua. The influence of such a\nnear-degeneracy on the few-body physics in the vicinity of a narrow Feshbach\nresonance is investigated within the framework of a minimal model with two\natomic continua and one closed molecular channel. The model allows analysis of\nthe spin composition of loosely bound dimers and trimers. In the two-body\nsector the well-established coupled-channels calculations phenomenology of\nlithium is qualitatively reproduced, and its particularities are emphasized and\nclarified. In the three-body sector we find that the Efimov trimer energy\nlevels follow a different functional form as compared to a single continuum\nscenario while the thresholds remain untouched. This three-channel model with\ntwo atomic continua complements our earlier developed three-channel model with\ntwo molecular channels [Y. Yudkin and L. Khaykovich, Phys. Rev. A 103, 063303\n(2021)] and suggests that the experimentally observed exotic behavior of the\nfirst excited Efimov energy level [Y. Yudkin, R. Elbaz and L. Khaykovich,\narXiv:2004.02723] is most probably caused by the short-range details of the\ninteraction potential.",
        "positive": "Superfluid Breakdown and Multiple Roton Gaps in Spin-Orbit Coupled\n  Bose-Einstein Condensates on an Optical Lattice: We investigate the superfluid phases of a Rashba spin-orbit coupled\nBose-Einstein condensate residing on a two dimensional square optical lattice\nin the presence of an effective Zeeman field $\\Omega$. At a critical value\n$\\Omega=\\Omega_c$, the single-particle spectrum $ E_k $ changes from having a\nset of four degenerate minima to a single minimum at $k=0$, corresponding to\ncondensation at finite or zero momentum, respectively. We describe this quantum\nphase transition and the symmetry breaking of the condensate phases. We use the\nBogoliubov theory to treat the superfluid phases and determine the phase\ndiagram, the excitation spectrum and the sound velocity of the phonon\nexcitations. A novel dynamically unstable superfluid regime occurring when\n$\\Omega$ is close to $\\Omega_c$ is analytically identified and the behavior of\nthe condensate quantum depletion is discussed. Moreover, we show that there are\ntwo types of roton excitations occurring in the $\\Omega<\\Omega_c$ regime and\nobtain explicit values for the corresponding energy gaps."
    },
    {
        "anchor": "Spin segregation via dynamically induced long-range interaction in a\n  system of ultracold fermions: We investigate theoretically the time evolution of a one-dimensional system\nof spin-1/2 fermions in a harmonic trap after, initially, a spiral spin\nconfiguration far-from equilibrium is created. We predict a spin segregation\nbuilding up in time already for weak interaction under realistic experimental\nconditions. The effect relies on the interplay between exchange interaction and\nthe harmonic trap, and it is found for a wide range of parameters. It can be\nunderstood as a consequence of an effective, dynamically induced long-range\ninteraction that is derived by integrating out the rapid oscillatory dynamics\nin the trap.",
        "positive": "Two- and three-body problem with Floquet-driven zero-range interactions: We study the two-body scattering problem in the zero-range approximation with\na sinusoidally driven scattering length and calculate the relation between the\nmean value and amplitude of the drive for which the effective scattering\namplitude is resonantly enhanced. In this manner we arrive at a family of\ncurves along which the effective scattering length diverges but the nature of\nthe corresponding Floquet-induced resonance changes from narrow to wide.\nRemarkably, on these curves the driving does not induce heating. In order to\nstudy the effect of these resonances on the three-body problem we consider one\nlight and two heavy particles with driven heavy-light interaction in the\nBorn-Oppenheimer approximation and find that the Floquet driving can be used to\ntune the three-body and inelasticity parameters."
    },
    {
        "anchor": "Ultrastable super-Tonks-Girardeau gases under weak dipolar interactions: The highly excited super-Tonks-Girardeau (sTG) gas was recently observed to\nbe extremely stable in the presence of a weak dipolar repulsion. Here we reveal\nthe underlying reason for this mysterious phenomenon. By exactly solving the\ntrapped small clusters with both contact and dipolar interactions, we show that\nthe reason lies in the distinct spectral responses between sTG gas and its\ndecaying channel (bound state) when turn on a weak dipolar interaction.\nSpecifically, a tiny dipolar force can produce a visible energy shift for the\nlocalized bound state, but can hardly affect the extended sTG branch. As a\nresult, the avoided level crossing between two branches is greatly modified in\nboth location and width in the parameter axis of coupling strength, leading to\na more (less) stable sTG gas for a repulsive (attractive) dipolar force. These\nresults, consistent with experimental observations, are found to robustly apply\nto both bosonic and fermionic systems.",
        "positive": "Many-body spin Hall effect with space-inversion symmetry: In contrast to the ordinary spin Hall effect (SHE), which is a single-body\nphenomenon caused by the spin-orbit interaction (SOI), we propose amany-body\nSHE induced by the dipole-dipole interaction (DDI) between particles and\ndemonstrate it in a system of ultracold magnetic atoms. While the SOI usually\nrequires the breaking of space-inversion symmetry, the DDI preserves it. The\nmany-body SHE can, in principle, be observed in a wide range of systems with\nlarge dipole moments and offers a powerful tool to generate spin currents, an\nessential ingredient in spintronics and atomtronics."
    },
    {
        "anchor": "FORTRESS II: FORTRAN programs for solving coupled Gross-Pitaevskii\n  equations for spin-orbit coupled spin-2 Bose-Einstein condensate: We provide here a set of three OpenMP parallelized FORTRAN 90/95 programs to\ncompute the ground states and the dynamics of trapped spin-2 Bose-Einstein\ncondensates (BECs) with anisotropic spin-orbit (SO) coupling by solving a set\nof five coupled Gross-Pitaevskii equations using a time-splitting Fourier\nspectral method. Depending on the nature of the problem, without any loss of\ngenerality, we have employed the Cartesian grid spanning either three-, two-,\nor one-dimensional space for numerical discretization. To illustrate the\nveracity of the package, wherever feasible, we have compared the numerical\nground state solutions of the full mean-field model with those from the\nsimplified scalar models. The two set of results show excellent agreement, in\nparticular, through the equilibrium density profiles, energies and chemical\npotentials of the ground-states. We have also presented test results for OpenMP\nperformance parameters like speedup and the efficiency of the three codes.",
        "positive": "Coupled density-spin Bose-Einstein condensates dynamics and collapse in\n  systems with quintic nonlinearity: We investigate the effects of spin-orbit coupling and Zeeman splitting on the\ncoupled density-spin dynamics and collapse of the Bose-Einstein condensate\ndriven by the quintic self-attraction in the same- and cross-spin channels. The\ncharacteristic feature of the collapse is the decrease in the width as given by\nthe participation ratio of the density rather than by the expectation values of\nthe coordinate. Qualitative arguments and numerical simulations reveal the\nexistence of a critical spin-orbit coupling strength which either prohibits or\nleads to the collapse, and its dependence on other parameters, such as the\ncondensates norm, spin-dependent nonlinear coupling, and the Zeeman splitting.\nThe entire nonlinear dynamics critically depend on the initial spin sate."
    },
    {
        "anchor": "Experimental observation of the avoided crossing of two $S$-matrix\n  resonance poles in an ultracold atom collider: In quantum mechanics, collisions between two particles are captured by a\nscattering matrix which describes the transfer from an initial entrance state\nto an outgoing final state. Analyticity of the elements of this $S$-matrix\nenables their continuation onto the complex energy plane and opens up a\npowerful and widely used framework in scattering theory, where bound states and\nscattering resonances for a physical system are ascribed to $S$-matrix poles.\nIn the Gedankenexperiment of gradually changing the potential parameters of the\nsystem, the complex energy poles will begin to move, and in their ensuing flow,\ntwo poles approaching will interact. An actual observation of this intriguing\ninteraction between scattering poles in a collision experiment has, however,\nbeen elusive. Here, we expose the interplay between two scattering poles\nrelating to a shape resonance and a magnetically tunable Feshbach resonance by\nstudying ultracold atoms with a laser-based collider. We exploit the tunability\nof the Feshbach resonance to observe a compelling avoided crossing of the poles\nin their energies which is the hallmark of a strongly coupled system.",
        "positive": "Nanoplasmonic planar traps - a tool for engineering p-wave interactions: Engineering strong p-wave interactions between fermions is one of the\nchallenges in modern quantum physics. Such interactions are responsible for a\nplethora of fascinating quantum phenomena such as topological quantum liquids\nand exotic superconductors. In this letter we propose to combine recent\ndevelopments of nanoplasmonics with the progress in realizing laser-induced\ngauge fields. Nanoplasmonics allows for strong confinement leading to a\ngeometric resonance in the atom-atom scattering. In combination with the\nlaser-coupling of the atomic states, this is shown to result in the desired\ninteraction. We illustrate how this scheme can be used for the stabilization of\nstrongly correlated fractional quantum Hall states in ultracold fermionic\ngases."
    },
    {
        "anchor": "Spontaneous inhomogeneous phases in ultracold dipolar Fermi gases: We study the collapse of ultracold fermionic gases into inhomogeneous states\ndue to strong dipolar interaction in both 2D and 3D. Depending on the\ndimensionality, we find that two different types of inhomogeneous states are\nstabilized once the dipole moment reaches a critical value $d>d_c$: the {\\it\nstripe phase} and {\\it phase separation} between high and low densities. In 2D,\nwe prove that the stripe phase is always favored for $d\\gtrsim d_c$, regardless\nof the microscopic details of the system. In 3D, the one-loop perturbative\ncalculation suggests that the same type of instability leads to phase\nseparation. Experimental detection and finite-temperature effects are\ndiscussed.",
        "positive": "Controlled spin domain creation by phase separation: We demonstrate a method of controlled creation of spin domains in spin-1\nantiferromagnetic Bose-Einstein condensates. The method exploits the phenomenon\nof phase separation of spin components in an external potential. By using an\nappropriate time dependent potential, a composition of spin domains can be\ncreated, as we demonstrate in the particular cases of a double well and a\nperiodic potential. In contrast to other methods, which rely on spatially\ninhomogeneous magnetic fields, here the domain structure is completely\ndetermined by the optical fields, which makes the method versatile and\nreconfigurable. It allows for creation of domains of various sizes, with the\nspatial resolution limited by the spin healing length only."
    },
    {
        "anchor": "Contact and sum-rules in a near-uniform Fermi gas at unitarity: We present an experimental study of the high-energy excitation spectra of\nunitary Fermi gases. Using focussed beam Bragg spectroscopy, we locally probe\natoms in the central region of a harmonically trapped cloud where the density\nis nearly uniform, enabling measurements of the dynamic structure factor for a\nrange of temperatures both below and above the superfluid transition. Applying\nsum-rules to the measured Bragg spectra, we resolve the characteristic\nbehaviour of the universal contact parameter, ${\\cal C}$, across the superfluid\ntransition. We also employ a recent theoretical result for the kinetic\n(second-moment) sum-rule to obtain the internal energy of gases at unitarity.",
        "positive": "Flow equation of functional renormalization group for three-body\n  scattering problems: Functional renormalization group (FRG) is applied to the three-body\nscattering problem in the two-component fermionic system with an attractive\ncontact interaction. We establish a new and correct flow equation on the basis\nof FRG and show that our flow equation is consistent with integral equations\nobtained from the Dyson-Schwinger equation. In particular, the relation of our\nflow equation and the Skornyakov and Ter-Martirosyan equation for the\natom-dimer scattering is made clear."
    },
    {
        "anchor": "Exploring quantum quasicrystal patterns: a variational study: We study the emergence of quasicrystal configurations produced purely by\nquantum fluctuations in the ground-state phase diagram of interacting bosonic\nsystems. By using a variational mean-field approach, we determine the relevant\nfeatures of the pair interaction potential that stabilize such quasicrystalline\nstates in two dimensions. Unlike their classical counterpart, in which the\ninterplay between only two wave vectors determines the resulting symmetries of\nthe solutions, the quantum picture relates in a more complex way to the\ninstabilities of the excitation spectrum. Moreover, the quantum quasicrystal\npatterns are found to emerge as the ground state with no need of moderate\nthermal fluctuations. The study extends to the exploration of the excitation\nproperties and the possible existence of super-quasicrystals, i.e.\nsupersolid-like quasicrystalline states in which the long-range non-periodic\ndensity profile coexist with a non-zero superfluid fraction. Our calculations\nshow that, in an intermediate region between the homogeneous superfluid and the\nnormal quasicrystal phases, these exotic states indeed exist at zero\ntemperature. Comparison with full numerical simulations provides a solid\nverification of the variational approach adopted in this work.",
        "positive": "Enhancing the Efimov correlation in Bose polarons with large mass\n  imbalance: We study the effect of Efimov physics (in the few-body sector) to the\nspectral response of Bose polaron, a many-body system consisting of an impurity\nimmersed in a bath of bosonic atoms. We find that the Efimov correlation can be\ngreatly enhanced by increasing the mass ratio between the bosons and the\nimpurity, which results in visible signatures in the rf spectrum of the\npolaron. Using a diagrammatic approach up to the third-order virial expansion,\nwe show how the mass imbalance and the enhanced three-body effect modify the\nline shape and the width of the polaron spectrum. Moreover, we study the effect\nof a finite boson-boson interaction to the spectrum. Taking the realistic\nsystem of Li impurities immersed in Cs bosons with a positive Cs-Cs scattering\nlength, we find a visible Efimov branch, which is associated with the second\nlowest Efimov trimer, in the polaron spectrum. In particular, by adjusting the\nboson density the Efimov branch can greatly hybridize with the attractive\npolaron branch leading to the spectrum broadening near their avoided level\ncrossing. Our results can be directly probed in the cold atoms experiments of\nLi-Cs and Li-Rb Bose polarons."
    },
    {
        "anchor": "Domain walls and bubble-droplets in immiscible binary Bose gases: The existence and stability of domain walls (DWs) and bubble-droplet (BD)\nstates in binary mixtures of quasi-one-dimensional ultracold Bose gases with\ninter- and intra-species repulsive interactions is considered. Previously, DWs\nwere studied by means of coupled systems of Gross-Pitaevskii equations (GPEs)\nwith cubic terms, which model immiscible binary Bose-Einstein condensates\n(BECs). We address immiscible BECs with two- and three-body repulsive\ninteractions, as well as binary Tonks--Girardeau (TG) gases, using systems of\nGPEs with cubic and quintic nonlinearities for the binary BEC, and coupled\nnonlinear Schr\\\"{o}dinger equations with quintic terms for the TG gases. Exact\nDW\\ solutions are found for the symmetric BEC mixture, with equal intra-species\nscattering lengths. Stable asymmetric DWs in the BEC mixtures with dissimilar\ninteractions in the two components, as well as of symmetric and asymmetric DWs\nin the binary TG gas, are found by means of numerical and approximate\nanalytical methods. In the BEC system, DWs can be easily put in motion by phase\nimprinting. Combining a DW and anti-DW on a ring, we construct BD states for\nboth the BEC and TG models. These consist of a dark soliton in one component\n(the \"bubble\"), and a bright soliton (the \"droplet\") in the other. In the BEC\nsystem, these composite states are mobile too.",
        "positive": "BEC polaron in harmonic trap potential at weak coupling regime:\n  Lee-Low-Pines type approach: We have calculated the zero-temperature binding energy of a single impurity\natom immersed in a Bose-Einstein condensate of ultracold atoms that are trapped\nin an axially symmetric harmonic potential, where the impurity interacts with\nbosonic atoms in the condensate via a low-energy s-wave scattering. In this\ncase, bosons are excited around the impurity to form a quasiparticle, namely, a\nBEC polaron. We have developed a variational method, {\\it a la} Lee-Low-Pines\n(LLP) theory for electron-phonon systems, for description of the polaron with a\nconserved angular momentum around the symmetric axis. It is found in numerical\nresults that the binding energy between the impurity and the excited bosons\nbreak the degeneracy with respect to the total angular momentum of the polaron.\nThe angular momentum is partially shared by the excited bosons, which is due to\na mechanism similar to the drag effect on the polaron momentum by a phonon\ncloud in the LLP theory."
    },
    {
        "anchor": "Universal Bose Gases Near Resonance: A Rigorous Solution: We obtain a rigorous solution of universal Bose gases near resonance and\noffer an answer to one of the long-standing challenges of quantum gases at\nlarge scattering lengths, where the standard dilute theory breaks down. The\nsolution was obtained by using an $\\epsilon$ expansion near four spatial\ndimension. In dimension $d = 4 - \\epsilon$, the chemical potential of Bose\ngases near resonances is shown to approach the universal value\n$\\epsilon^{(2/(4-\\epsilon))} \\epsilon_F \\sqrt{2/3} (1 + 0.474 \\epsilon - i\n1.217 \\epsilon + ...)$, where $\\epsilon_F$ is the Fermi energy defined for a\nFermi gas of density $n$, and the condensation fraction is equal to $2/3 (1 +\n0.0877 \\epsilon + ...)$. We also discuss the implications on ultra-cold gases\nin physical dimensions.",
        "positive": "Interaction-induced chiral p_x \\pm i p_y superfluid order of bosons in\n  an optical lattice: The study of superconductivity with unconventional order is complicated in\ncondensed matter systems by their extensive complexity. Optical lattices with\ntheir exceptional precision and control allow one to emulate superfluidity\navoiding many of the complications of condensed matter. A promising approach to\nrealize unconventional superfluid order is to employ orbital degrees of freedom\nin higher Bloch bands. In recent work, indications were found that bosons\ncondensed in the second band of an optical chequerboard lattice might exhibit\np_x \\pm i p_y order. Here we present experiments, which provide strong evidence\nfor the emergence of p_x \\pm i p_y order driven by the interaction in the local\np-orbitals. We compare our observations with a multi-band Hubbard model and\nfind excellent quantitative agreement."
    },
    {
        "anchor": "Classical linear chain behavior from dipolar droplets to supersolids: We investigate the classicality of linear dipolar droplet arrays through a\nnormal mode analysis of the dynamical properties in comparison to the\nsupersolid regime. The vibrational patterns of isolated-droplet crystals that\ntime-evolve after a small initial kick closely follow the properties of a\nlinear droplet chain. For larger kick velocities, however, droplets may\ncoalesce and separate again, showing distinct deviations from classicality. In\nthe supersolid regime the normal modes are eliminated by a counter-flow of mass\nbetween the droplets, signaled by a reduction of the center-of-mass motion.",
        "positive": "Interaction-Induced Dimensional Crossover through Full 3D to 1D: The exploration of dimensional crossover carries profound fundamental\nsignificance, serving as a crucial bridge in comprehending the remarkable\ndisparities observed in transitional phenomena across the two distinct\ndimensions of a physical system. The prevalent strategy for manipulating the\ndimensionality involves meticulously controlling the external trapping\ngeometry, thereby restricting the degrees of freedom of the kinetic energy from\nthree-dimensional (3D) to lower-dimensional spaces, while maintaining the 3D\nnature of the interaction energy degrees of freedom. The aim of this work is to\nintroduce an innovative scenario to achieve dimensional crossover,\ncharacterized by lower-D nature of both the kinetic and the interaction energy\ndegrees of freedom. To accomplish this objective, we delve deeply into the\nrealm of a 2D optically trapped Bose gas, focusing specifically on its\nfinite-range interaction. Our emphasis lies in exploring the lattice-induced\ndimensional crossover from full 3D to 1D in both kinetic and interaction terms.\nUtilizing the functional path integral method, we derive the equation of states\nof the model system, encompassing crucial quantities such as the ground state\nenergy and quantum depletion. These equations enable us to analyze the combined\neffects of finite range interaction and an optical lattice on quantum\nfluctuations of the BEC system. Notably, our analytical findings reconcile the\nLee-Huang-Yang (LHY) correction to the ground state energy in 3D and\nLieb-Liniger (LL) ones in 1D limit, thereby providing fresh insights into the\nintriguing disparities between LHY and LL corrections."
    },
    {
        "anchor": "Non interacting electron gas model of quantum Hall effect: On the basis of our previous studies on energy levels and wave functions of\nsingle electrons in a strong magnetic field, the energy levels and wave\nfunctions of non-interacting electron gas system, electron gas Hall surface\ndensity and Hall resistance of electron gas system are calculated. Then, a\ncomparison is made between non-interaction electron gas model and Laughlin's\ninteraction two dimensional electron gas system. It is found that the former\ncan more quickly and unified the explain the integer and the fractional quantum\nHall effects without the help of concepts proposed by Laughlin, such as\nfractionally charged quasi-particles and quasi-holes which obey fractional\nstatistics. After explicit calculation, it is also discovered that quantum Hall\neffect has the same physical nature as superconducting state.",
        "positive": "Quantum crystals in a trapped Rydberg-dressed Bose-Einstein condensate: Spontaneously crystalline ground states, called quantum crystals, of a\ntrapped Rydberg-dressed Bose-Einstein condensate are numerically investigated.\nAs a result described by a mean-field order parameter, such states\nsimultaneously possess crystalline and superfluid properties. A hexagonal\ndroplet lattice is observed in a quasi-two-dimensional system when dressing\ninteraction is sufficiently strong. Onset of these states is characterized by a\ndrastic drop of the non-classical rotational inertia proposed by Leggett [Phys.\nRev. Lett. 25, 1543 (1970)]. In addition, an AB stacking bilayer lattice can\nalso be attained. Due to an anisotropic interaction possibly induced by an\nexternal electric field, transition from a hexagonal to a nearly square droplet\nlattice is also observed."
    },
    {
        "anchor": "Curving the space by non-Hermiticity: Quantum systems are often classified into Hermitian and non-Hermitian ones.\nExtraordinary non-Hermitian phenomena, ranging from the non-Hermitian skin\neffect to the supersensitivity to boundary conditions, have been widely\nexplored. Whereas these intriguing phenomena have been considered peculiar to\nnon-Hermitian systems, we show that they can be naturally explained by a\nduality between non-Hermitian models in flat spaces and their counterparts,\nwhich could be Hermitian, in curved spaces. For instance, prototypical\none-dimensional (1D) chains with uniform chiral tunnelings are equivalent to\ntheir duals in two-dimensional (2D) hyperbolic spaces with or without magnetic\nfields, and non-uniform tunnelings could further tailor local curvatures. Such\na duality unfolds deep geometric roots of non-Hermitian phenomena, delivers an\nunprecedented routine connecting Hermitian and non-Hermitian physics, and gives\nrise to a theoretical perspective reformulating our understandings of\ncurvatures and distance. In practice, it provides experimentalists with a\npowerful two-fold application, using non-Hermiticity as a new protocol to\nengineer curvatures or implementing synthetic curved spaces to explore\nnon-Hermitian quantum physics.",
        "positive": "Zero-temperature equation of state of a two-dimensional bosonic quantum\n  fluid with finite-range interaction: We derive the two-dimensional equation of state for a bosonic system of\nultracold atoms interacting with a finite-range effective interaction. Within a\nfunctional integration approach, we employ an hydrodynamic parametrization of\nthe bosonic field to calculate the superfluid equations of motion and the\nzero-temperature pressure. The ultraviolet divergences, naturally arising from\nthe finite-range interaction, are regularized with an improved dimensional\nregularization technique."
    },
    {
        "anchor": "Ideal-Gas Approach to Hydrodynamics: Transport is one of the most important physical processes in all energy and\nlength scales. Ideal gases and hydrodynamics are, respectively, two opposite\nlimits of transport. Here, we present an unexpected mathematical connection\nbetween these two limits; that is, there exist situations that the solution to\na class of interacting hydrodynamic equations with certain initial conditions\ncan be exactly constructed from the dynamics of noninteracting ideal gases. We\nanalytically provide three such examples. The first two examples focus on\nscale-invariant systems, which generalize fermionization to the hydrodynamics\nof strongly interacting systems, and determine specific initial conditions for\nperfect density oscillations in a harmonic trap. The third example recovers the\ndark soliton solution in a one-dimensional Bose condensate. The results can\nexplain a recent puzzling experimental observation in ultracold atomic gases by\nthe Paris group and make further predictions for future experiments. We\nenvision that extensive examples of such an ideal-gas approach to hydrodynamics\ncan be found by systematical numerical search, which can find broad\napplications in different problems in various subfields of physics.",
        "positive": "Mobile Spin Impurity in an Optical Lattice: We investigate the Fermi polaron problem in a spin-1/2 Fermi gas in an\noptical lattice for the limit of both strong repulsive contact interactions and\none dimension. In this limit, a polaronic-like behaviour is not expected, and\nthe physics is that of a magnon or impurity. While the charge degrees of\nfreedom of the system are frozen, the resulting tight-binding Hamiltonian for\nthe impurity's spin exhibits an intriguing structure that strongly depends on\nthe filling factor of the lattice potential. This filling dependency also\ntransfers to the nature of the interactions for the case of two magnons and the\nimportant spin balanced case. At low filling, and up until near unit filling,\nthe single impurity Hamiltonian faithfully reproduces a single-band,\nquasi-homogeneous tight-binding problem. As the filling is increased and the\nsecond band of the single particle spectrum of the periodic potential is\nprogressively filled, the impurity Hamiltonian, at low energies, describes a\nsingle particle trapped in a multi-well potential. Interestingly, once the\nfirst two bands are fully filled, the impurity Hamiltonian is a near-perfect\nrealisation of the Su-Schrieffer-Heeger model. Our studies, which go well\nbeyond the single-band approximation, that is, the Hubbard model, pave the way\nfor the realisation of interacting one-dimensional models of condensed matter\nphysics."
    },
    {
        "anchor": "Dissipation-facilitated molecules in a Fermi gas with non-Hermitian\n  spin-orbit coupling: We study the impact of non-Hermiticity on the molecule formation in a\ntwo-component spin-orbit-coupled Fermi gas near a wide Feshbach resonance.\nUnder an experimentally feasible configuration where the two-photon Raman\nprocess is dissipative, the Raman-induced synthetic spin-orbit coupling\nacquires a complex strength. Remarkably, dissipation of the system facilitates\nthe formation and binding of molecules, which, despite their dissipative nature\nand finite lifetime, exist over a wider parameter regime than in the\ncorresponding Hermitian system. These dissipation-facilitated molecules can be\nprobed by the inverse radio-frequency (rf) spectroscopy, provided the Raman\nlasers are blue detuned to the excited state. The effects of dissipation\nmanifest in the rf spectra as shifted peaks with broadened widths, which serve\nas a clear experimental signature. Our results, readily observable in current\ncold-atom experiments, shed light on the fascinating interplay of\nnon-Hermiticity and interaction in few- and many-body open quantum systems.",
        "positive": "Superfluid signatures in a dissipative quantum point contact: We measure superfluid transport of strongly interacting fermionic lithium\natoms through a quantum point contact with local, spin-dependent particle loss.\nWe observe that the characteristic non-Ohmic superfluid transport enabled by\nhigh-order multiple Andreev reflections transitions into an excess Ohmic\ncurrent as the dissipation strength exceeds the superfluid gap. We develop a\nmodel with mean-field reservoirs connected via tunneling to a dissipative site.\nOur calculations in the Keldysh formalism reproduce the observed nonequilibrium\nparticle current, yet do not fully explain the observed loss rate or spin\ncurrent."
    },
    {
        "anchor": "Pseudogap regime of a two-dimensional uniform Fermi gas: We investigate pseudogap phenomena in a two-dimensional Fermi gas. Including\npairing fluctuations within a self-consistent $T$-matrix approximation, we\ndetermine the pseudogap temperature $T^*$ below which a dip appears in the\ndensity of states $\\rho(\\omega)$ around the Fermi level. Evaluating $T^*$, we\nidentify the pseudogap region in the phase diagram of this system. We find\nthat, while the observed BKT (Berezinskii-Kosterlitz-Thouless) transition\ntemperature $T^{\\rm exp}_{\\rm BKT}$ in a $^6$Li Fermi gas is in the pseudogap\nregime, the detailed pseudogap structure in $\\rho(\\omega)$ at $T^{\\rm exp}_{\\rm\nBKT}$ still differs from a fully-gapped one, indicating the importance of\namplitude fluctuations in the Cooper channel there. Since the observed $T^{\\rm\nexp}_{\\rm BKT}$ in the weak-coupling regime cannot be explained by the recent\nBKT theory which only includes phase fluctuations, our results may provide a\nhint about how to improve this BKT theory. Although $\\rho(\\omega)$ has not been\nmeasured in this system, we show that the assessment of our results is still\npossible by using the observable Tan's contact.",
        "positive": "Multi-Stability in Cavity QED with Spin-Orbit Coupled Bose-Einstein\n  Condensate: We investigate the occurrence of steady-state multi-stability in a cavity\nsystem containing spin-orbit coupled Bose-Einstein condensate and driven by a\nstrong pump laser. The applied magnetic field splits the Bose-Einstein\ncondensate into pseudo-spin states, which then became momentum sensitive with\ntwo counter propagating Raman lasers directly interacting with ultra-cold\natoms. After governing the steady-state dynamics for all associated subsystems,\nwe show the emergence of multi-stable behavior of cavity photon number, which\nis unlike with previous investigation on cavity-atom systems. However, this\nmulti-stability can be tuned with associated system parameters. Further, we\nillustrate the occurrence of mixed-stability behavior for atomic population of\nthe pseudo spin-$\\uparrow$ amd spin-$\\downarrow$ states, which are appearing in\nso-called bi-unstable form. The collective behavior of these atomic number\nstates interestingly possesses a transitional interface among the population of\nboth spin states, which can be enhance and controlled by spin-orbit coupling\nand Zeeman field effects. Furthermore, we illustrate the emergence of secondary\ninterface mediated by increasing the mechanical dissipation rate of the\npseudo-spin states. These interfaces could be cause by the non-trivial behavior\nof synthetic spin state mediated by cavity. Our findings are not only crucial\nfor the subject of optical switching, but also could provide foundation for\nfuture studies on mechanical aspect of synthetic atomic states with cavity\nquantum electrodynamics."
    },
    {
        "anchor": "Number and spin densities in the ground state of a trapped mixture of\n  two pseudospin-1/2 Bose gases with interspecies spin-exchange interaction: We consider the ground state of a mixture of two pseudospin-$\\1/2$ Bose gases\nwith interspecies spin exchange in a trapping potential. In the mean field\napproach, the ground state can be described in terms of four wave functions\ngoverned by a set of coupled Gross-Pitaevskii-like (GP-like) equations, which\ndiffer from the usual GP equations in the existence of an interference term due\nto spin-exchange coupling between the two species. Using these GP-like\nequations, we calculate such ground state properties as chemical potentials,\ndensity profiles and spin density profiles, which are directly observable in\nexperiments. We compare the cases with and without spin exchange. It is\ndemonstrated that the spin exchange between the two species lowers the chemical\npotentials, tends to equalize the wave functions of the two pseudospin\ncomponents of each species, and thus homogenizes the spin density. The novel\nfeatures of the density and spin density profiles can serve as experimental\nprobes of this novel Bose system.",
        "positive": "Black hole lasers in Bose-Einstein condensates: We consider elongated condensates that cross twice the speed of sound. In the\nabsence of periodic boundary conditions, the phonon spectrum possesses a\ndiscrete and finite set of complex frequency modes that induce a laser effect.\nThis effect constitutes a dynamical instability and is due to the fact that the\nsupersonic region acts as a resonant cavity. We numerically compute the complex\nfrequencies and density-density correlation function. We obtain patterns with\nvery specific signatures. In terms of the gravitational analogy, the flows we\nconsider correspond to a pair of black hole and white hole horizons, and the\nlaser effect can be conceived as a self-amplified Hawking radiation. This is\nverified by comparing the outgoing flux at early time with the standard black\nhole radiation."
    },
    {
        "anchor": "Quench induced chaotic dynamics of Anderson localized interacting\n  Bose-Einstein condensates in one dimension: We study the effect of atomic interaction on the localization and the\nassociated dynamics of Bose-Einstein condensates in a one-dimensional\nquasiperiodic optical lattice and random Gaussian disordered potentials. When\nthe interactions are absent, the condensates exhibit localization, which\nweakens as we increase the interaction strength beyond a threshold value for\nboth potential types. We inspect the localized and delocalized states by\nperturbing the system via quenching the interaction strength instantaneously to\nzero and studying the dynamics of the condensate, which we further corroborate\nusing the out-of-time-order correlator. The temporal behaviour of the time\ncorrelator displays regular dynamics for the localized state, while it shows\ntemporal chaos for the delocalized state. We confirm this dynamical behaviour\nby analyzing the power spectral density of the time correlator. We further\nidentify that the condensate admits a quasiperiodic route to chaotic dynamics\nfor both potentials. Finally, we present the variation of the maximal Lyapunov\nexponents for different nonlinearity and disorder strengths that have a\npositive value in the regime where the time correlator function shows chaotic\nbehaviour. Through this, we establish the strong connection between the\nspatially delocalized state of the condensate and its temporal chaos.",
        "positive": "Chiral Bogoliubons in Nonlinear Bosonic Systems: We present a versatile scheme for creating topological Bogoliubov excitations\nin weakly interacting bosonic systems. Our proposal relies on a background\nstationary field that consists of a Kagome vortex lattice, which breaks\ntime-reversal symmetry and induces a periodic potential for Bogoliubov\nexcitations. In analogy to the Haldane model, no external magnetic field or net\nflux is required. We construct a generic model based on the two-dimensional\n(2D) nonlinear Schr\\\"odinger equation and demonstrate the emergence of\ntopological gaps crossed by chiral Bogoliubov edge modes. Our scheme can be\nrealized in a wide variety of physical systems ranging from nonlinear optical\nsystems to exciton-polariton condensates."
    },
    {
        "anchor": "A high-flux 2D MOT source for cold lithium atoms: We demonstrate a novel 2D MOT beam source for cold 6Li atoms. The source is\nside-loaded from an oven operated at temperatures in the range 600<T<700 K. The\nperformance is analyzed by loading the atoms into a 3D MOT located 220 mm\ndownstream from the source. The maximum recapture rate of ~10^9 /s is obtained\nfor T=700 K and results in a total of up to 10^10 trapped atoms. The recaptured\nfraction is estimated to be 30(10)% and limited by beam divergence. The\nmost-probable velocity in the beam (alpha_z) is varied from 18 to 70 m/s by\nincreasing the intensity of a push beam. The source is quite monochromatic with\na full-width at half maximum velocity spread of 11 m/s at alpha_z=36 m/s,\ndemonstrating that side-loading completely eliminates beam contamination by hot\nvapor from the oven. We identify depletion of the low-velocity tail of the oven\nflux as the limiting loss mechanism. Our approach is suitable for other atomic\nspecies.",
        "positive": "Producing flow in \"racetrack\" atom circuits by stirring at zero and\n  non-zero temperature: We present a study of how macroscopic flow can be produced in Bose-Einstein\ncondensate confined in a \"racetrack\" potential by stirring with a wide\nrectangular barrier. This potential consists of two half-circle channels\nseparated by straight channels of length $L$ and is a ring potential if $L=0$.\nWe present the results of a large set of simulations where racetrack\ncondensates stirred with a barrier under varying conditions of barrier height,\nstir speed, racetrack geometry, and temperature. We found that stirring was\nreadily able to produce circulation in ring and non-ring geometries but that\nthe exact amount of flow produced was complicated. We therefore also studied\nthe mechanism by which flow was produced in the stirring process. We found that\ncirculation was induced by the swap of a vortex/anti-vortex pair that was\ninitially created by backflow of the condensate in the region of depressed\ndensity by the barrier. When the barrier strength reached a critical value a\nnumber of these vortex-swap events occurred in rapid succession so that flow\nspeed of the circulation produced was enough to exceed the stir speed of the\nbarrier. Flow that was initially localized in the vortices involved in the\nvortex swap was converted into macroscopic flow around the racetrack by pairs\nof disturbances each generated during the vortex swap. Each pair consisted of a\nvortex/anti-vortex pair moving in the anti-stir direction and a compression\nwave moving in the stir direction. This picture of the mechanism for making\nflow will enable the design of stirring schedules that create a desired amount\nof flow."
    },
    {
        "anchor": "Ground State Properties of Spin-Orbit Coupled Bose Gases for Arbitrary\n  Interactions: We develop a field integral formalism to study spin-orbit-coupled (SOC) Bose\ngases with arbitrary interspecies interaction. We identify various features\narising from the interplay of SOC and interspecies interaction, including a\nroton minimum in the excitation spectrum and dual effects of SOC on\nground-state energies depending on interspecies interactions.\nCounterintuitively, we find that at low interspecies interaction the SOC\nstabilizes the system by suppressing the quantum depletion. We show that the\nstatic structure factor is immune to the SOC in the phase space where\ntime-reversal symmetry is preserved. Furthermore, we present an alternate way\nof studying phase fluctuations of the system.",
        "positive": "Dissipative Effects on the Superfluid to Insulator Transition in\n  Mixed-dimensional Optical Lattices: We study the superfluid to Mott insulator transition of a mixture of heavy\nbosons and light fermions loaded in an optical lattice. We focus on the effect\nof the light fermions on the dynamics of the heavy bosons. It is shown that,\nwhen the lattice potential is sufficiently deep to confine the bosons to one\ndimension but allowing the fermions to freely move in three dimensions (i.e. a\nmixed-dimensionality lattice), the fermions act as an ohmic bath for bosons\nleading to screening and dissipation effects on the bosons. Using a\nperturbative renormalization-group analysis, it is shown that the\nfermion-induced dissipative effects have no appreciable impact on the\ntransition from the superfluid to the Mott-insulator state at integer filling.\nOn the other hand, dissipative effects are found to be very important in the\nhalf-filled case near the critical point. In this case, in the presence of a\nfinite incommensurability that destabilizes the Mott phase, the bosons can\nstill be localized by virtue of dissipative effects."
    },
    {
        "anchor": "Stability and internal structure of vortices in spin-1 Bose-Einstein\n  condensates with conserved magnetization: We demonstrate how conservation of longitudinal magnetization can have\npronounced effects on both stability and structure of vortices in the atomic\nspin-1 Bose-Einstein condensate by providing a systematic characterization of\nnonsingular and singular vortex states. Constructing spinor wave functions for\nvortex states that continuously connect ferromagnetic and polar phases we\nsystematically derive analytic models for nonrotating cores of different\nsingular vortices and for composite defect states with distinct small- and\nlarge-distance topology. We explain how the conservation law provides a\nstabilizing mechanism when the coreless vortex imprinted on the condensate\nrelaxes in the polar regime of interatomic interactions. The resulting\nstructure forms a composite defect: the inner ferromagnetic coreless vortex\ndeforms toward an outer singly quantized polar vortex. We also numerically show\nhow other even more complex hierarchies of vortex core topologies may be\nstabilized. Moreover, we analyze the structure of the coreless vortex also in a\nferromagnetic condensate, and show how reducing magnetization leads to a\ndisplacement of the vortex from the trap center and eventually to the\ndeformation and splitting of its core where a singular vortex becomes a\nlower-energy state. For the case of singular vortices, we find that the\nstability and the core structure are notably less influenced by the\nconservation of magnetization.",
        "positive": "Non-Hermitian skin effect in a spin-orbit-coupled Bose-Einstein\n  condensate: We study a Bose-Einstein condensate of ultracold atoms subject to a\nnon-Hermitian spin-orbit coupling, where the system acquires non-Hermitian skin\neffect under the interplay of spin-orbit coupling and laser-induced atom loss.\nThe presence of the non-Hermitian skin effect is confirmed through its key\nsignatures in term of the spectral winding under the periodic boundary\ncondition, the accumulation of eigen wavefunctions at boundaries under an open\nboundary condition, as well as bulk dynamics signaled by a directional flow. We\nshow that the bulk dynamics in particular serves as a convenient signal for\nexperimental detection. The impact of interaction and trapping potentials are\nalso discussed based on non-Hermitian Gross-Pitaevskii equations. Our work\ndemonstrates that the non-Hermitian skin effect and its rich implications in\ntopology, dynamics and beyond are well within reach of current cold-atom\nexperiments."
    },
    {
        "anchor": "Bose-Einstein condensation and non-extensive statistics: We study the Bose-Einstein condensation in non-extensive statistics for a\nfree gas of bosons, and extend the results to the non-relativistic case as\nwell. We present results for the dependence of the critical temperature and the\ncondensate fraction on the entropic index, q, and show that the condensate can\nexist only for a limited range of q in both relativistic and non-relativistic\nsystems. We provide numerical results for other thermodynamics quantities like\nthe internal energy, specific heat and number fluctuations. We discuss the\nimplications for high energy physics and hadron physics. The results for the\nnon-relativistic case can be of interest in cold-atom systems.",
        "positive": "Exploring the limits of ultracold atoms in space: Existing space-based cold atom experiments have demonstrated the utility of\nmicrogravity for improvements in observation times and for minimizing the\nexpansion energy and rate of a freely evolving coherent matter wave. In this\npaper we explore the potential for space-based experiments to extend the limits\nof ultracold atoms utilizing not just microgravity, but also other aspects of\nthe space environment such as exceptionally good vacuums and extremely cold\ntemperatures. The tantalizing possibility that such experiments may one day be\nable to probe physics of quantum objects with masses approaching the Plank mass\nis discussed."
    },
    {
        "anchor": "Spin-gap spectroscopy in a bosonic flux ladder: Ultracold bosonic atoms trapped in a two-leg ladder pierced by a magnetic\nfield provide a minimal and quasi-one-dimensional instance to study the\ninterplay between orbital magnetism and interactions. Using time-dependent\nmatrix-product-states simulations, we investigate the properties of the\nso-called \"Meissner\" and \"vortex\" phases which appear in such system, focusing\non experimentally accessible observables. We discuss how to experimentally\nmonitor the phase transition, and show that the response to a modulation of the\ndensity imbalance between the two legs of the ladder is qualitatively different\nin the two phases. We argue that this technique can be used as a tool for\nmany-body spectroscopy, allowing to quantitatively measure the spin gap in the\nMeissner phase. We finally discuss its experimental implementation",
        "positive": "Emulating Solid-State Physics with a Hybrid System of Ultracold Ions and\n  Atoms: We propose and theoretically investigate a hybrid system composed of a\ncrystal of trapped ions coupled to a cloud of ultracold fermions. The ions form\na periodic lattice and induce a band structure in the atoms. This system\ncombines the advantages of scalability and tunability of ultracold atomic\nsystems with the high fidelity operations and detection offered by trapped ion\nsystems. It also features close analogies to natural solid-state systems, as\nthe atomic degrees of freedom couple to phonons of the ion lattice, thereby\nemulating a solid-state system. Starting from the microscopic many-body\nHamiltonian, we derive the low energy Hamiltonian including the atomic band\nstructure and give an expression for the atom-phonon coupling. We discuss\npossible experimental implementations such as a Peierls-like transition into a\nperiod-doubled dimerized state."
    },
    {
        "anchor": "Bose-Einstein Condensate in a light-induced vector potential using the\n  1064 $nm$ optical dipole trap lasers: We present a simple experiment of creating an effective vector gauge\npotential for Bose-Einstein condensed $^{87}$Rb in the F=2 hyperfine ground\nstate using two crossed 1064 $nm$ optical dipole trap lasers as the Raman\nbeams. Due to the far-detuning from the single-photon resonance with the\nelectronically excited state, the spontaneous emission is strongly reduced, at\nthe same time, the moderate strength of the Raman coupling still can be\nachieved. The atoms at the far detuning of the Raman coupling are loaded\nadiabatically into the dressed states by ramping the homogeneous bias magnetic\nfield to resonance and the different energy dressed states are studied. This\nexperiment is easily extended to produce synthetic magnetic or electric field\nfrom a spatial or time dependence of the effective vector potential.",
        "positive": "Roughness with a finite correlation length in the Microtrap: We analyze the effects of roughness in the magnitude of the magnetic field\nproduced by a current carrying microwire, which is caused by geometric\nfluctuation of the edge of wire. The relation between the fluctuation of the\ntrapping potential and the height that atom trap lies above the wire is\nconsistent with the experimental data very well, when the colored noise with a\nfinite correlation length is considered. On this basis, we generate the random\npotential and get the density distribution of the BEC atoms by solving the\nGross-Pitaevskii equation, which coincides well with the experimental image,\nespecially in the number of fragmentations. The results help us further\nunderstand the nature of the fluctuation and predict the possible application\nin the precise measurement."
    },
    {
        "anchor": "The one-dimensional Bose-Fermi-Hubbard model in the ultrafast-fermion\n  limit: Charge density wave phase and MI - CDW phase separation: In a recent work [1] we presented results for the Bose-Fermi-Hubbard model\n(BFHM) in the limit of ultrafast fermions. The present work gives an overview\nover the used methods and an deeper insight into the implications arising from\nthe treated limit. Starting from the discussion of the phase diagram obtained\nby numerical means, we develop an analytic theory and derive an effective\nbosonic Hamiltonian. Arising issues in the Hamiltonian are overcome by\ninclusion of a back-action, renormalizing the solution of our system. Based on\na detailed analysis of the effective Hamiltonian, the phase diagram in the\nthermodynamic limit is constructed by analytic means and comparison to\nnumerical results obtained by density matrix renormalization group (DMRG)\ntechniques for the full BFHM shows a very reasonable agreement. The most\nprominent feature of the phase diagram, the existence of a phase separation\nbetween Mott insulator (MI) and charge density wave (CDW) is discussed in depth\nwith inclusion of important effects due to the boundary condition.",
        "positive": "Pairing and molecule formation along the BEC-BCS crossover for finite\n  range potentials: We analyze the BCS-BEC crossover transition of a balanced two component\nmixture of fermions interacting via a finite range potential, within a mean\nfield approach. For the analysis we consider three finite range potentials\ncases describing the interaction between different Fermi species: a square\nwell, an exponential and a Yukawa potential. The T = 0 thermodynamics analysis\nalong the BCS-BEC crossover allow us to recognize the proper variables, for\nfinite range interactions, that capture the transition from a thermodynamic\nnon-universal behavior at unitarity, to its universal restoration. On the other\nside, the determination of the pair functions along the crossover suggests that\nthe smooth transition occurs always between the scattering resonance and the\nchange of sign of the chemical potential. This identification follows directly\nfrom the pair wave functions behavior, which in the BCS and BEC sides become\nexponentially localized and oscillatory slowly decaying respectively."
    },
    {
        "anchor": "Polar molecule reactive collisions in quasi-1D systems: We study polar molecule scattering in quasi-one-dimensional geometries.\nElastic and reactive collision rates are computed as a function of collision\nenergy and electric dipole moment for different confinement strengths. The\nnumerical results are interpreted in terms of first order scattering and of\nadiabatic models. Universal dipolar scattering is also discussed. Our results\nare relevant to experiments where control of the collision dynamics through one\ndimensional confinement and an applied electric field is envisioned.",
        "positive": "Quantum anomalous Hall states in the $p$-orbital honeycomb optical\n  lattices: We study the quantum anomalous Hall states in the $p$-orbital bands of the\nhoneycomb optical lattices loaded with the single component fermions. Such an\neffect has not been realized in both condensed matter and cold atom systems\nyet. By applying the available experimental technique developed by Gemelke\n\\textit{et al.} to rotate each lattice site around its own center, the band\nstructures become topologically non-trivial. At a certain rotation angular\nvelocity $\\Omega$, a flat band structure appears with localized eigenstates\ncarrying chiral current moments. With imposing the soft confining potential,\nthe density profile exhibits a wedding-cake shaped distribution with insulating\nplateaus at commensurate fillings. Moreover, the inhomogeneous confining\npotential induces dissipationless circulation currents whose magnitudes and\nchiralities vary with the distance from the trap center. In the insulating\nregions the Hall conductances are quantized, and in the metallic regions the\ndirections and magnitudes of chiral currents cannot be described by the usual\nlocal-density-approximation. The quantum anomalous Hall effects are robust at\ntemperature scales small compared to band gaps, which increases the feasibility\nof experimental realizations."
    },
    {
        "anchor": "Relaxation dynamics of local observables in integrable systems: We show, using the quench action approach [Caux&Essler Phys. Rev. Lett. 110\n(2013)], that the whole post-quench time evolution of an integrable system in\nthe thermodynamic limit can be computed with a minimal set of data which are\nencoded in what we denote the generalized single-particle overlap coefficient\n$s_0^{\\Psi_0}(\\lambda)$. This function can be extracted from the\nthermodynamically leading part of the overlaps between the eigenstates of the\nmodel and the initial state. For a generic global quench the shape of\n$s_0^{\\Psi_0}(\\lambda)$ in the low momentum limit directly gives the exponent\nfor the power law decay to the effective steady state. As an example we compute\nthe time evolution of the static density-density correlation in the interacting\nLieb-Liniger gas after a quench from a Bose-Einstein condensate. This shows an\napproach to equilibrium with power law $t^{-3}$ which turns out to be\nindependent of the post-quench interaction and of the considered observable.",
        "positive": "Quantum walk of two anyons across a statistical boundary: We model a quantum walk of identical particles that can change their exchange\nstatistics by hopping across a domain wall in a 1D lattice. Such a \"statistical\nboundary\" is transparent to single particles and affects the dynamics only by\nswapping multiple particles arriving together. We find that the two-particle\ninterference is dramatically altered by reflections of these bunched waves at\nthe interface, producing strong measurable asymmetries. Depending on the phases\non the two sides, a bunched wavepacket can get completely reflected or split\ninto a superposition of a reflected wave and an antibunched wave. This leads to\nstriking dynamics with two domain walls, where bunched waves can get trapped in\nbetween or fragment into multiple correlated single-particle wavepackets. These\nfindings can be realized with density-dependent hopping in present-day atomic\nsetups and open up a new paradigm of intrinsically many-body phenomena at\nstatistical boundaries."
    },
    {
        "anchor": "Tradeoffs for number-squeezing in collisions of Bose-Einstein\n  condensates: We investigate the factors that influence the usefulness of supersonic\ncollisions of Bose-Einstein condensates as a potential source of entangled\natomic pairs by analyzing the reduction of the number difference fluctuations\nbetween regions of opposite momenta. We show that non-monochromaticity of the\nmother clouds is typically the leading limitation on number squeezing, and that\nthe squeezing becomes less robust to this effect as the density of pairs grows.\nWe develop a simple model that explains the relationship between density\ncorrelations and the number squeezing, allows one to estimate the squeezing\nfrom properties of the correlation peaks, and shows how the multi-mode nature\nof the scattering must be taken into account to understand the behavior of the\npairing. We analyze the impact of the Bose enhancement on the number squeezing,\nby introducing a simplified low-gain model. We conclude that as far as\nsqueezing is concerned the preferable configuration occurs when atoms are\nscattered not uniformly but rather into two well separated regions.",
        "positive": "High-frequency approximation for periodically driven quantum systems\n  from a Floquet-space perspective: We derive a systematic high-frequency expansion for the effective Hamiltonian\nand the micromotion operator of periodically driven quantum systems. Our\napproach is based on the block diagonalization of the quasienergy operator in\nthe extended Floquet Hilbert space by means of degenerate perturbation theory.\nThe final results are equivalent to those obtained within a different approach\n[Phys.\\ Rev.\\ A {\\bf 68}, 013820 (2003), Phys.\\ Rev.\\ X {\\bf 4}, 031027 (2014)]\nand can also be related to the Floquet-Magnus expansion [J.\\ Phys.\\ A {\\bf 34},\n3379 (2000)]. We discuss that the dependence on the driving phase, which\nplagues the latter, can lead to artifactual symmetry breaking. The\nhigh-frequency approach is illustrated using the example of a periodically\ndriven Hubbard model. Moreover, we discuss the nature of the approximation and\nits limitations for systems of many interacting particles."
    },
    {
        "anchor": "Goldstone-mode Instability leading to Fragmentation in a Spinor\n  Bose-Einstein Condensate: We apply the number-conserving Bogoliubov theory to spinor Bose-Einstein\ncondensates and show that the Goldstone magnon leads instability leading to\nfragmentation. Unlike the dynamical instability, where modes with complex\neigenfrequencies grow exponentially, here the zero-energy mode exhibits\nalgebraic growth. We also point out that a small fraction of thermally excited\natoms enhances the fragmentation dynamics.",
        "positive": "Exact two-body solutions and Quantum defect theory of two dimensional\n  dipolar quantum gas: In this paper, we provide the two-body exact solutions of two dimensional\n(2D) Schr\\\"{o}dinger equation with isotropic $\\pm 1/r^3$ interactions. Analytic\nquantum defect theory are constructed base on these solutions and are applied\nto investigate the scattering properties as well as two-body bound states of\nultracold polar molecules confined in a quasi-2D geometry. Interestingly, we\nfind that for the attractive case, the scattering resonance happens\nsimultaneously in all partial waves which has not been observed in other\nsystems. The effect of this feature on the scattering phase shift across such\nresonances is also illustrated."
    },
    {
        "anchor": "Interaction quantum quenches in the one-dimensional Fermi-Hubbard model\n  with spin imbalance: Using the time-dependent density matrix renormalization group method and\nexact diagonalization, we study the non-equilibrium dynamics of the\none-dimensional Fermi-Hubbard model following a quantum quench or a ramp of the\nonsite interaction strength. For quenches from the non-interacting to the\nattractive regime, we investigate the dynamical emergence of\nFulde-Ferrell-Larkin-Ovchinnikov (FFLO) correlations, which at finite spin\npolarizations are the dominant two-body correlations in the ground state, and\ntheir signatures in the pair quasi-momentum distribution function. We observe\nthat the post-quench double occupancy exhibits a maximum as the interaction\nstrength becomes of the order of the bandwidth. Finally, we study quenches and\nramps from attractive to repulsive interactions, which imprint FFLO\ncorrelations onto repulsively bound pairs. We show that a quite short ramp time\nis sufficient to wipe out the characteristic FFLO features in the post-quench\npair momentum distribution functions.",
        "positive": "Hamiltonian formulation of the effective kinetic theory for superfluid\n  Fermi liquids: We present in a local form the time dependent effective description of a\nsuperfluid Fermi liquid which includes Landau damping effects at $T\\neq 0$.\nThis is achieved by the introduction of an additional variable, the\nquasiparticle distribution function, which obeys a simple kinetic equation. The\ntransport equation is coupled with first order equations for the Goldstone mode\nand the particle density. We prove that a main feature of this formulation is\nits Hamiltonian structure relative to a certain Poisson bracket. We construct\nthe Hamiltonian to quadratic order."
    },
    {
        "anchor": "Lifetime of Feshbach dimers in a Fermi-Fermi mixture of $^6$Li and\n  $^{40}$K: We present a joint experimental and theoretical investigation of the lifetime\nof weakly bound dimers formed near narrow interspecies Feshbach resonances in\nmass-imbalanced Fermi-Fermi systems, considering the specific example of a\nmixture of $^6$Li and $^{40}$K atoms. Our work addresses the central question\nof the increase in the stability of the dimers resulting from Pauli suppression\nof collisional losses, which is a well-known effect in mass-balanced fermionic\nsystems near broad resonances. We present measurements of the spontaneous\ndissociation of dimers in dilute samples, and of the collisional losses in\ndense samples arising from both dimer-dimer processes and from atom-dimer\nprocesses. We find that all loss processes are suppressed close to the Feshbach\nresonance. Our general theoretical approach for fermionic mixtures near narrow\nFeshbach resonances provides predictions for the suppression of collisional\ndecay as a function of the detuning from resonance, and we find excellent\nagreement with the experimental benchmarks provided by our $^6$Li-$^{40}$K\nsystem. We finally present model calculations for other Feshbach-resonant\nFermi-Fermi systems, which are of interest for experiments in the near future.",
        "positive": "Classical Phase Space Crystals in an Open Environment: It was recently discovered that a crystalline many-body state can exist in\nthe phase space of a closed dynamical system. A phase space crystal can be an\nanomalous Chern insulator that supports chiral topological transport without\nbreaking physical time-reversal symmetry [L. Guo et al., Phys. Rev. B 105,\n094301 (2022)]. In this work, we further study the effects of an open\ndissipative environment with thermal noise and identify the existence condition\nof classical phase space crystals in realistic scenarios. By defining a crystal\norder parameter, we plot the phase diagram in the parameter space of\ndissipation rate, interaction, and temperature. Our present work paves the way\nto realize phase space crystals and explore anomalous chiral transport in\nexperiments."
    },
    {
        "anchor": "Metrologically useful states of spin-1 Bose condensates with macroscopic\n  magnetization: We study theoretically the usefulness of spin-1 Bose condensates with\nmacroscopic magnetization in a homogeneous magnetic field for quantum\nmetrology. We demonstrate Heisenberg scaling of the quantum Fisher information\nfor states in thermal equilibrium. The scaling applies to both\nantiferromagnetic and ferromagnetic interactions. The effect preserves as long\nas fluctuations of magnetization are sufficiently small. Scaling of the quantum\nFisher information with the total particle number is derived within the\nmean-field approach in the zero temperature limit and exactly in the high\nmagnetic field limit for any temperature. The precision gain is intuitively\nexplained owing to subtle features of the quasi-distribution function in phase\nspace.",
        "positive": "Beliaev damping in quasi-2D dipolar condensates: We study the effects of quasiparticle interactions in a quasi-two dimensional\n(quasi-2D), zero-temperature Bose-Einstein condensate of dipolar atoms, which\ncan exhibit a roton-maxon feature in its quasiparticle spectrum. Our focus is\nthe Beliaev damping process, in which a quasiparticle collides with the\ncondensate and resonantly decays into a pair of quasiparticles. Remarkably, the\nrate for this process exhibits a highly non-trivial dependence on the\nquasiparticle momentum and the dipolar interaction strength. For weak\ninteractions, the low energy phonons experience no damping, and the higher\nenergy quasiparticles undergo anomalously weak damping. In contrast, the\nBeliaev damping rates become anomalously large for stronger dipolar\ninteractions, as rotons become energetically accessible as final states.\nFurther, we find a qualitative anisotropy in the damping rates when the dipoles\nare tilted off the axis of symmetry. Our study reveals the unconventional\nnature of Beliaev damping in dipolar condensates, and has important\nimplications for ongoing studies of equilibrium and non-equilibrium dynamics in\nthese systems."
    },
    {
        "anchor": "Quasiadiabatic dynamics of ultracold bosonic atoms in a one-dimensional\n  optical superlattice: We study the quasiadiabatic dynamics of a one-dimensional system of ultracold\nbosonic atoms loaded in an optical superlattice. Focusing on a slow linear\nvariation in time of the superlattice potential, the system is driven from a\nconventional Mott insulator phase to a superlattice-induced Mott insulator,\ncrossing in between a gapless critical superfluid region. Due to the presence\nof a gapless region, a number of defects depending on the velocity of the\nquench appear. Our findings suggest a power-law dependence similar to the\nKibble-Zurek mechanism for intermediate values of the quench rate. For the\ntemporal ranges of the quench dynamics that we considered, the scaling of\ndefects depends nontrivially on the width of the superfluid region.",
        "positive": "Measuring Zak phase in room-temperature atoms: Cold atoms provide a flexible platform for synthesizing and characterizing\ntopolog-ical matter, where geometric phases play a central role. However, cold\natoms are intrinsically prone to thermal noise, which can overwhelm the\ntopological response and hamper promised applications. On the other hand,\ngeometric phases also de-termine the energy spectra of particles subjected to a\nstatic force, based on the po-larization relation between Wannier-Stark ladders\nand geometric Zak phases. By exploiting this relation, we develop a method to\nextract geometric phases from en-ergy spectra of room-temperature superradiance\nlattices, which are momentum-space lattices of timed Dicke states. In such\nmomentum-space lattices the thermal motion of atoms, instead of being a source\nof noise, provides effective forces which lead to spectroscopic signatures of\nthe Zak phases. We measure Zak phases direct-ly from the anti-crossings between\nWannier-Stark ladders in the Doppler-broadened absorption spectra of\nsuperradiance lattices. Our approach paves the way of measuring topological\ninvariants and developing their applications in room-temperature atoms."
    },
    {
        "anchor": "Disorder effects during the evolution from BCS to BEC superfluidity: We describe the effects of disorder on the critical temperature of s-wave\nsuperfluids from the BCS to the BEC regime, with direct application to\nultracold Fermi atoms. In the BCS regime the pair breaking and phase coherence\ntemperature scales are essentially the same allowing strong correlations\nbetween the amplitude and phase of the order parameter. As non-pair breaking\ndisorder is introduced the largely overlapping Cooper pairs conspire to\nmaintain phase coherence such that the critical temperature remains essentially\nunchanged. However, in the BEC regime the pair breaking and phase coherence\ntemperature scales are very different such that non-pair breaking disorder can\naffect dramatically phase coherence, and thus the critical temperature, without\nthe requirement of breaking tightly-bound fermion pairs simultaneously.\nFinally, we find that the superfluid is more robust against weak disorder in\nthe intermediate region between the two regimes.",
        "positive": "Strongly interacting few-fermion systems in a trap: Few- and many-fermion systems on the verge of stability, and consisting of\nstrongly interacting particles, appear in many areas of physics. The\ntheoretical modeling of such systems is a very difficult problem. In this work\nwe present a theoretical framework that is based on the rigged Hilbert space\nformulation. The few-body problem is solved by exact diagonalization using a\nbasis in which bound, resonant, and non-resonant scattering states are included\non an equal footing. Current experiments with ultracold atoms offer a\nfascinating opportunity to study universal properties of few-body systems with\na high degree of control over parameters such as the external trap geometry,\nthe number of particles, and even the interaction strength. In particular,\nparticles can be allowed to tunnel out of the trap by applying a magnetic-field\ngradient that effectively lowers the potential barrier. The result is a tunable\nopen quantum system that allows detailed studies of the tunneling mechanism. In\nthis Contribution we introduce our method and present results for the decay\nrate of two distinguishable fermions in a one-dimensional trap as a function of\nthe interaction strength. We also study the numerical convergence. Many of\nthese results have been previously published (R. Lundmark, C. Forss\\'en, and J.\nRotureau, arXiv: 1412.7175). However, in this Contribution we present several\ntechnical and numerical details of our approach for the first time."
    },
    {
        "anchor": "Tunneling theory of two interacting atoms in a trap: A theory for the tunneling of one atom out of a trap containing two\ninteracting cold atoms is developed. The quasiparticle wave function, dressed\nby the interaction with the companion atom in the trap, replaces the\nnon-interacting orbital at resonance in the tunneling matrix element. The\ncomputed tunneling time for two 6Li atoms agrees with recent experimental\nresults [G. Zuern, F. Serwane, T. Lompe, A. N. Wenz, M. G. Ries, J. E. Bohn,\nand S. Jochim, arXiv:1111.2727], unveiling the `fermionization' of the wave\nfunction and a novel two-body effect.",
        "positive": "Dipolar Collisions of Ultracold Ground-state Bosonic Molecules: The dipolar collision between ultracold polar molecules is an important topic\nboth by its own right from the fundamental point of view and for the successful\nexploration of many-body physics with strong and long-range dipolar\ninteractions. Here, we report the investigation of collisions between ultracold\nground-state sodium-rubidium molecules in electric fields with induced electric\ndipole moments as large as 0.7$\\;$D. We observe a step-wise enhancement of\nlosses due to the coupling between different partial waves induced by the\nincreasingly stronger anisotropic dipolar interactions. Varying the temperature\nof our sample, we find good agreement with theoretical loss rates assuming\ncomplex formation as the main loss process. Our results shed new light on the\nunderstanding of complex molecular collisions in the presence of strong dipolar\ninteractions and also demonstrate the versatility of modifying molecular\ninteractions with electric fields."
    },
    {
        "anchor": "Pairing and Vortex Lattices for Interacting Fermions in Optical Lattices\n  with a Large Magnetic Field: We study the structure of pairing order parameter for spin-1/2 fermions with\nattractive interactions in a square lattice under a uniform magnetic field.\nBecause the magnetic translation symmetry gives a unique degeneracy in the\nsingle-particle spectrum, the wave function has both zero and finite momentum\ncomponents co-existing, and their relative phases are determined by a\nself-consistent mean-field theory. We present a microscopic calculation that\ncan determine the vortex lattice structure in the superfluid phase for\ndifferent flux densities. Phase transition from a Hofstadter insulator to a\nsuperfluid phase is also discussed.",
        "positive": "Characterizing the phase diagram of finite-size dipolar Bose-Hubbard\n  systems: We use state-of-the-art density matrix renormalization group calculations in\nthe canonical ensemble to determine the phase diagram of the dipolar\nBose-Hubbard model on a finite cylinder. We consider several observables that\nare accessible in typical optical lattice setups and assess how well these\nquantities perform as order parameters. We find that, especially for small\nsystems, the occupation imbalance is less susceptible to boundary effects than\nthe structure factor in uncovering the presence of a periodic density\nmodulation. By analysing the non-local correlations, we find that the\nappearance of supersolid order is very sensitive to boundary effects, which may\nrender it difficult to observe in quantum gas lattice experiments with a few\ntens of particles. Finally, we show how density measurements readily obtainable\non a quantum gas microscope allow distinguishing between superfluid and solid\nphases using unsupervised machine-learning techniques."
    },
    {
        "anchor": "Turbulence scaling laws across the superfluid to supersolid transition: We investigate quantum turbulence in a two-dimensional trapped supersolid and\ndemonstrate that both the wave and vortex turbulence involve triple rather than\ndual cascades, as in a superfluid. Because of the presence of a second gapless\nmode associated with translation symmetry breaking, a new $k^{-13/3}$ scaling\nlaw is predicted to occur in the wave turbulence. Simultaneous fast\nvortex-antivortex creation and annihilation in the interior of the oscillating\nsupersolid results in a $k^{-1}$ scaling law in the vortex turbulence.\nNumerical simulations based on the Gross-Pitaevskii equation confirmed the\npredictions.",
        "positive": "Coherence of an Interacting Bose Gas: from a Single to a Double Well: The low energy properties of a trapped bose gas split by a potential barrier\nare determined over the whole range of barrier heights. We derive a\nself-consistent two-mode model which reduces, for large $N$, to a Bogoliubov\nmodel for low barriers and to a Josephson model for any (asymmetric) double\nwell potential, with explicitly calculated tunneling and pair interaction\nparameters. We compare the numerical results to analytical results that\nprecisely specify the role of number squeezing and finite temperatures in the\nloss of coherence."
    },
    {
        "anchor": "Non-equilibrium topological phase transitions in two-dimensional optical\n  lattices: Recently, concepts of topological phases of matter are extended to\nnon-equilibrium systems, especially periodically driven systems. In this paper,\nwe construct an example which shows non-equilibrium topological phase\ntransitions using ultracold fermions in optical lattices. We show that the Rabi\noscillation has the possibility to induce non-equilibrium topological phases\nwhich are classified into time-reversal-invariant topological insulators for a\ntwo-orbital model of alkaline-earth-metal atoms. Furthermore we study the\nnon-equilibrium topological phases using time-dependent Schrieffer-Wolff-type\nperturbation theory, and we obtain an analytical expression to describe the\ntopological phase transitions from a high-frequency limit of external driving\nfields.",
        "positive": "Dynamical preparation of Floquet Chern insulators: Realizing topological insulators is of great current interest because of\ntheir remarkable properties and possible future applications. There are recent\nproposals, based on Floquet analyses, that one can generate topologically\nnontrivial insulators by periodically driving topologically trivial ones. Here\nwe address what happens if one follows the dynamics in such systems.\nSpecifically, we present an exact study of the time evolution of a\ngraphene-like system subjected to a circularly polarized electric field. We\nprove that, for infinite (translationally invariant) systems, the Chern number\nis conserved under unitary evolution. For systems with boundaries, on the other\nhand, we show that a properly defined topological invariant, the Bott index,\ncan change. Hence, it should be possible to experimentally prepare topological\nstates starting from non-topological ones. We show that the chirality of the\nedge current in such systems can be controlled by adjusting the filling."
    },
    {
        "anchor": "The Zel'dovich effect in harmonically trapped, ultra-cold quantum gases: We investigate the Zel'dovich effect in the context of ultra-cold,\nharmonically trapped quantum gases. We suggest that currently available\nexperimental techniques in cold-atoms research offer an exciting opportunity\nfor a direct observation of the Zel'dovich effect without the difficulties\nimposed by conventional condensed matter and nuclear physics studies. We also\ndemonstrate an interesting scaling symmetry in the level rearragements which\nhas heretofore gone unnoticed.",
        "positive": "Absence of quasiclassical coherence in mean-field dynamics of bosons in\n  a kinetically frustrated regime: We study numerically the dynamics of bosons on a triangular lattice after\nquenching both the on-site interactions and the external trapping potential to\nnegative values. In a similar situation on the square lattice, the dynamics can\nbe understood in terms of an effectively reversed Hamiltonian. On the\ntriangular lattice, however, the kinetic part of the reversed Hamiltonian is\nfrustrated and whether coherence can develop is an open question. The strength\nof the frustration can be changed by tuning the ratio of the hopping rates\nalong different directions. We calculate time-of-flight images at different\ntimes after the quench for different values of the hopping anisotropy. We\nobserve peaks at the maxima of the original non-interacting dispersion relation\nboth in the isotropic case and also in the rhombic limit of high hopping\nanisotropy. For an intermediate value, however, no coherence develops up to the\nlongest simulation times. These results imply that experiments along similar\nlines could study unconventional superfluidity of bosons and aspects of the\nconjectured spin-liquid behavior in the hard-core limit."
    },
    {
        "anchor": "Averaged collision and reaction rates in a two-species gas of ultracold\n  fermions: Reactive or elastic two-body collisions in an ultracold gas are affected by\nquantum statistics. In this paper, we study ensemble-averaged collision rates\nfor a two-species fermionic gas. The two species may have different masses,\ndensities and temperatures. We investigate how averaged collision rates are\naffected by the presence of Fermi spheres in the initial states; Pauli blocking\nof final states is not considered. It is shown that, independently on the\ndetails of the collision, Fermi-averaged collision rates deviate from\nBoltzmann-averaged ones, particularly for a gas with strong imbalance of masses\nor densities.",
        "positive": "Atypical BCS-BEC crossover induced by quantum-size effects: Quantum-size oscillations of the basic physical characteristics of a confined\nfermionic condensate are a well-known phenomenon. Its conventional\nunderstanding is based on the single-particle physics, whereby the oscillations\nfollow the size-dependent changes in the single-particle density of states.\nHere we present a study of a cigar-shaped ultracold superfluid Fermi gas, which\ndemonstrates an important many-body aspect of the quantum-size effects,\noverlooked previously. The many-body physics is revealed in the atypical\ncrossover from the Bardeen-Cooper-Schrieffer (BCS) superfluid to the\nBose-Einstein condensate (BEC) induced by the size quantization of the particle\nmotion. Quantized perpendicular spectrum results in the formation of\nsingle-particle subbands (shells) so that the aggregate fermionic condensate\nbecomes a coherent mixture of subband condensates. Each time when the lower\nedge of a subband crosses the chemical potential, the BCS-BEC crossover is\napproached in this subband, and the aggregate condensate contains both the BCS\nand BEC-like components."
    },
    {
        "anchor": "Pair tunneling, phase separation and dimensional crossover in imbalanced\n  fermionic superfluids in a coupled array of tubes: We study imbalanced fermionic superfluids in an array of one-dimensional\ntubes at the incipient dimensional crossover regime, wherein particles can\ntunnel between neighboring tubes. In addition to single-particle tunneling\n(ST), we consider pair tunneling (PT) that incorporates the interaction effect\nduring the tunneling process. We find that with an increase of PT strength, a\nsystem of low global polarization evolves from a structure with a central\nFulde-Ferrell-Larkin-Ovchinnikov (FFLO) state to one with a central BCS-like\nfully-paired state. For the case of high global polarization, the central\nregion exhibits pairing zeros embedded in a fully paired order. In both cases,\nPT enhances the pairing gap, suppresses the FFLO order, and leads to spatial\nseparation of fully paired and fully polarized regions, the same as in higher\ndimensions. Thus, we show that PT beyond second-order ST processes is of\nrelevance to the development of signatures characteristic of the incipience of\nthe dimensional crossover.",
        "positive": "Generating an effective magnetic lattice for cold atoms: We present a general scheme for synthesizing a spatially periodic magnetic\nfield, or a magnetic lattice (ML), for ultracold atoms using pulsed gradient\nmagnetic fields. Both the period and the depth of the artificial ML can be\ntuned, immune to atomic spontaneous emission often encountered in optical\nlattices. The effective Hamiltonian for our 2-dimensional ML has not been\ndiscussed previously in condensed matter physics. Its band structures show\ninteresting features which can support topologically nontrivial phases. The\ntechnical requirements for implementing our protocol are readily available in\ntoday's cold atom experiments. Realization of our proposal will significantly\nexpand the repertoire for quantum simulation with ultracold atoms."
    },
    {
        "anchor": "Ground state of Tonks-Girardeau gas under density-dependent gauge\n  potential in a one dimensional harmonic potential: In the present paper we investigate the ground state of Tonks-Girardeau gas\nunder density-dependent gauge potential. With Bose-Fermi mapping method we\nobtain the exact ground state wavefunction for the system confined in a\nharmonic potential. Based on the ground state wavefunction, the reduced one\nbody density matrix (ROBDM), natural orbitals and their occupations, and the\nmomentum distributions are obtained. Compared with the case without gauge\npotential, the present wavefunction and ROBDM have additional phase factors\ninduced by gauge potential. The momentum distribution is the convolution of\nthat without gauge potential to the Fourier transformation of definite integral\nof gauge potential. It is shown that because of the density-dependent gauge\npotential the peak of momentum distributions deviate from zero momentum and the\nBose gas take finite total momentum. In particular the momentum distribution is\nno longer symmetric although the total momentum can become zero by adding a\nconstant to the gauge potential.",
        "positive": "Glassy properties of the Bose-glass phase of a one-dimensional\n  disordered Bose fluid: We study a one-dimensional disordered Bose fluid using bosonization, the\nreplica method and a nonperturbative functional renormalization-group approach.\nThe Bose-glass phase is described by a fully attractive strong-disorder fixed\npoint characterized by a singular disorder correlator whose functional\ndependence assumes a cuspy form that is related to the existence of metastable\nstates. At nonzero momentum scale, quantum tunneling between these metastable\nstates leads to a rounding of the nonanalyticity in a quantum boundary layer\nthat encodes the existence of rare superfluid regions responsible for the\n$\\omega^2$ behavior of the (dissipative) conductivity in the low-frequency\nlimit. These results can be understood within the \"droplet\" picture put forward\nfor the description of glassy (classical) systems."
    },
    {
        "anchor": "Relaxation in dipolar spin ladders: from pair production to false-vacuum\n  decay: Ultracold dipolar particles pinned in optical lattices or tweezers provide an\nexcellent platform for studying out-of-equilibrium quantum magnetism with\ndipole-mediated couplings. Starting with an initial state with spins of\nopposite orientation in each of the legs of a ladder lattice, we show that spin\nrelaxation displays an unexpected dependence on inter-leg distance and dipole\norientation. This intricate dependence, stemming from the interplay between\nintra- and inter-leg interactions, results in three distinct dynamical regimes:\n(i) ergodic, characterized by the fast relaxation towards equilibrium of\ncorrelated pairs of excitations generated at exponentially fast rates from the\ninitial state; (ii) metastable, in which the state is quasi-localized in the\ninitial state and only decays at exceedingly long timescales, resembling false\nvacuum decay; and, surprisingly, (iii) partially-relaxed, with coexisting fast\npartial relaxation and very long-lived partial quasi-localization. Realizing\nthese intriguing dynamics is within reach of current state-of-the-art\nexperiments in dipolar gases.",
        "positive": "Emerging dissipative phases in a superradiant quantum gas with tunable\n  decay: Exposing a many-body system to external drives and losses can transform the\nnature of its phases and opens perspectives for engineering new properties of\nmatter. How such characteristics are related to the underlying microscopic\nprocesses of the driven and dissipative system is a fundamental question. Here\nwe address this point in a quantum gas that is strongly coupled to a lossy\noptical cavity mode using two independent Raman drives, which act on the spin\nand motional degrees of freedom of the atoms. This setting allows us to control\nthe competition between coherent dynamics and dissipation by adjusting the\nimbalance between the drives. For strong enough coupling, the transition to a\nsuperradiant phase occurs, as is the case for a closed system. Yet, by\nimbalancing the drives we can enter a dissipation-stabilized normal phase and a\nregion of multistability. Measuring the properties of excitations on top of the\nout-of-equilibrium phases reveals the microscopic elementary processes in the\nopen system. Our findings provide prospects for studying squeezing in\nnon-Hermitian systems, quantum jumps in superradiance, and dynamical spin-orbit\ncoupling in a dissipative setting."
    },
    {
        "anchor": "Optimization as a route towards observing the Einstein-de Haas effect in\n  a rubidium condensate: The main obstacle in experimental realization of the Einstein-de Haas effect\nin a Bose-Einstein condensate is necessity of a very precise control of the\nextremely small (of the order of tens of $\\mu$G) external magnetic field. In\nthis paper we numerically study the response of a rubidium condensate to an\noptimized time-dependent magnetic field. We find a significant transfer of\natoms from the initial maximally polarized state to the next Zeeman component\nat magnetic fields of the order of tens of milligauss. We propose an experiment\nin which such an optimization scheme could enable the observation of the\nEinstein-de Haas effect in a rubidium atom condensate.",
        "positive": "Vortex structures of rotating Bose-Einstein condensates in anisotropic\n  harmonic potential: We found an analytical solution for the vortex structure in a rapidly\nrotating trapped Bose-Einstein condensate in the lowest Landau level\napproximation. This solution is exact in the limit of a large number of\nvortices and is obtained for the case of anisotropic harmonic potential. For\nthe case of symmetric harmonic trap when the rotation frequency is equal to the\ntrapping frequency, the solution coincides with the Abrikosov triangle vortex\nlattice in type-II superconductors.\n  In a general case the coarse grained density is found to be close to the\nThomas-Fermi profile, except the vicinity of edges of a condensate cloud."
    },
    {
        "anchor": "Quantum gas microscopy of a geometrically frustrated Hubbard system: Geometrically frustrated many-particle quantum systems are notoriously hard\nto study numerically but are of profound interest because of their unusual\nproperties and emergent phenomena. In these systems energetic constraints\ncannot be minimized simultaneously, leading to large ground-state degeneracy\nand a variety of exotic quantum phases. Here, we present a platform that\nenables unprecedentedly detailed experimental exploration of geometrically\nfrustrated electronic systems on lattices with triangular geometry. We\ndemonstrate the first realization of triangular atomic Hubbard systems,\ndirectly image Mott insulators in the triangular geometry with single-atom and\nsingle-site resolution, and measure antiferromagnetic spin-spin correlations\nfor all nearest neighbors allowing for thermometry. This platform provides a\npowerful new approach for studying exotic quantum magnetism and direct\ndetection of quantum spin liquid signatures in Hubbard systems.",
        "positive": "Stationary and moving bright solitons in Bose-Einstein condensates with\n  spin-orbit coupling in a Zeeman field: With the discovery of various matter wave solitons in spin-orbit-coupled\nBose-Einstein condensates (BECs), exploring their properties has become\nincreasingly significant. We mainly study stationary and moving bright solitons\nin spin-orbit-coupled spin-1 BECs with or without a Zeeman field. The bright\nsolitons correspond to the plane wave (PW) and standing wave (SW) phases. With\nthe assistance of single-particle energy spectrum, we obtain the existence\ndomains of PW and SW solitons by analytical and numerical methods. The results\nindicate that the interaction between atoms is also a key factor determining\nthe existence of solitons. In addition, we systematically discuss the stability\ndomains of PW and SW solitons, and investigate the impact of different\nparameters on the stability domains. We find that PW solitons are unstable when\nthe linear Zeeman effect reaches a certain threshold, and the threshold is\ndetermined by other parameters. The linear Zeeman effect also leads to the\nalternating distribution of stable and unstable areas of SW solitons, and makes\nSW solitons stably exist in the area with stronger ferromagnetism. Finally, we\nanalyze the collision dynamics of different types of stable solitons."
    },
    {
        "anchor": "Fermion Pairing across a Dipolar Interaction Induced Resonance: It is known from the solution of the two-body problem that an anisotropic\ndipolar interaction can give rise to s-wave scattering resonances, which are\nnamed as dipolar interaction induced resonaces (DIIR). In this letter, we study\nzero-temperature many-body physics of a two-component Fermi gas across a DIIR.\nIn the low-density regime, it is very striking that the resulting pairing order\nparameter is a nearly isotropic singlet pairing and the physics can be well\ndescribed by an s-wave resonant interaction potential with finite range\ncorrections, despite of the anisotropic nature of dipolar interaction. The\npairing energy is as strong as a unitary Fermi gas nearby a magnetic Feshbach\nresonance. In the high density regime, the anisotropic effect plays an\nimportant role. We find phase transitions from singlet pairing to a state with\nmixed singlet and triplet pairing, and then from mixed pairing to pure triplet\npairing. The state with mixed pairing spontaneously breaks the time-reversal\nsymmetry.",
        "positive": "Phase and micromotion of Bose-Einstein condensates in a time-averaged\n  ring trap: Rapidly scanning magnetic and optical dipole traps have been widely utilised\nto form time-averaged potentials for ultracold quantum gas experiments. Here we\ntheoretically and experimentally characterise the dynamic properties of\nBose-Einstein condensates in ring-shaped potentials that are formed by scanning\nan optical dipole beam in a circular trajectory. We find that unidirectional\nscanning leads to a non-trivial phase profile of the condensate that can be\napproximated analytically using the concept of phase imprinting. While the\nphase profile is not accessible through in-trap imaging, time-of-flight\nexpansion manifests clear density signatures of an in-trap phase step in the\ncondensate, coincident with the instantaneous position of the scanning beam.\nThe phase step remains significant even when scanning the beam at frequencies\ntwo orders of magnitude larger than the characteristic frequency of the trap.\nWe map out the phase and density properties of the condensate in the scanning\ntrap, both experimentally and using numerical simulations, and find excellent\nagreement. Furthermore, we demonstrate that bidirectional scanning eliminated\nthe phase gradient, rendering the system more suitable for coherent matter wave\ninterferometry."
    },
    {
        "anchor": "Complete phase diagram and topological properties of interacting bosons\n  in one-dimensional superlattices: The interacting bosons in one-dimensional inversion-symmetric superlattices\nare investigated from the topological aspect. The complete phase diagram is\nobtained by an atomic-limit analysis and quantum Monte Carlo simulations and\ncomprises three kinds of phases: superfluid, persisted charge-density-wave and\nMott insulators, and emergent insulators in the presence of nearest-neighbor\nhoppings. We find that all emergent insulators are topological, which are\ncharacterized by the Berry phase $\\pi$ and a pair of degenerate in-gap boundary\nstates. The mechanism of the topological bosonic insulators is qualitatively\ndiscussed and the ones with higher fillings can be understood as a\n$\\frac{1}{3}$-filling topological phase on a background of trivial\ncharge-density-wave or Mott insulators.",
        "positive": "Topological Quantum Phase Transition in Synthetic Non-Abelian Gauge\n  Potential: The method of synthetic gauge potentials opens up a new avenue for our\nunderstanding and discovering novel quantum states of matter. We investigate\nthe topological quantum phase transition of Fermi gases trapped in a honeycomb\nlattice in the presence of a synthetic non- Abelian gauge potential. We develop\na systematic fermionic effective field theory to describe a topological quantum\nphase transition tuned by the non-Abelian gauge potential and ex- plore its\nvarious important experimental consequences. Numerical calculations on lattice\nscales are performed to compare with the results achieved by the fermionic\neffective field theory. Several possible experimental detection methods of\ntopological quantum phase tran- sition are proposed. In contrast to condensed\nmatter experiments where only gauge invariant quantities can be measured, both\ngauge invariant and non-gauge invariant quantities can be measured by\nexperimentally generating various non-Abelian gauges corresponding to the same\nset of Wilson loops."
    },
    {
        "anchor": "Synthetic partial waves in ultracold atomic collisions: Interactions between particles can be strongly altered by their environment.\nWe demonstrate a technique for modifying interactions between ultracold atoms\nby dressing the bare atomic states with light, creating an effective\ninteraction of vastly increased range that scatters states of finite relative\nangular momentum at collision energies where only s-wave scattering would\nnormally be expected. We collided two optically dressed neutral atomic\nBose-Einstein condensates with equal, and opposite, momenta and observed that\nthe usual s-wave distribution of scattered atoms was altered by the appearance\nof d- and g-wave contributions. This technique is expected to enable quantum\nsimulation of exotic systems, including those predicted to support Majorana\nfermions.",
        "positive": "Ground State Properties of the One-Dimensional Unconstrained\n  Pseudo-Anyon Hubbard Model: We study the (pseudo-) anyon Hubbard model on a one-dimensional lattice\nwithout the presence of a three-body hardcore constraint. In particular, for\nthe pseudo-fermion limit of a large statistical angle $\\theta\\approx\\pi$, we\nobserve a wealth of exotic properties including {a first order transition}\nbetween different superfluid phases and a {two-component} partially paired\nphase for large fillings without need of an additional three-body hardcore\nconstraint.In this limit, we analyze the effect of an induced hardcore\nconstraint, which leads to the stabilization of superfluid {ground states} for\nvanishing or even small attractive on-site interactions. For finite statistical\nangles, we study the unconventional broken-symmetry superfluid peaked at a\nfinite momentum, resulting in an interesting beat phenomenon of single particle\ncorrelation functions.We show how some features of various ground state phases,\nincluding an analog of the partially paired phase in the pseudo-fermion limit,\nmay be reproduced in a naive mean field frame."
    },
    {
        "anchor": "Many-body localization for randomly interacting bosons: We study many-body localization in a one dimensional optical lattice filled\nwith bosons. The interaction between bosons is assumed to be random, which can\nbe realized for atoms close to a microchip exposed to a spatially fluctuating\nmagnetic field. Close to a Feshbach resonance, such controlled fluctuations can\nbe transfered to the interaction strength. We show that the system reveals an\ninverted mobility edge, with mobile particles at the lower edge of the\nspectrum. A statistical analysis of level spacings allows us to characterize\nthe transition between localized and excited states. The existence of the\nmobility edge is confirmed in large systems, by time dependent numerical\nsimulations using tDMRG. A simple analytical model predicts the long time\nbehavior of the system.",
        "positive": "Quantum dynamics of ultracold Bose polarons: We analyze the dynamics of Bose polarons in the vicinity of a Feshbach\nresonance between the impurity and host atoms. We compute the radio-frequency\nabsorption spectra for the case when the initial state of the impurity is\nnon-interacting and the final state is strongly interacting. We compare results\nof different theoretical approaches including a single excitation expansion, a\nself-consistent T-matrix method, and a time-dependent coherent state approach.\nOur analysis reveals sharp spectral features arising from metastable states\nwith several Bogoliubov excitations bound to the impurity atom. This surprising\nresult of the interplay of many-body and few-body Efimov type bound state\nphysics can only be obtained by going beyond the commonly used Fr\\\"ohlich model\nand including quasiparticle scattering processes. Close to the resonance we\nfind that strong fluctuations lead to a broad, incoherent absorption spectrum\nwhere no quasi-particle peak can be assigned."
    },
    {
        "anchor": "Optical lattices with large scattering length: Using few-body physics to\n  simulate an electron-phonon system: We propose to go beyond the usual Hubbard model description of atoms in\noptical lattices and show how few-body physics can be used to simulate\nmany-body phenomena, e.g., an electron-phonon system. We take one atomic\nspecies to be trapped in a deep optical lattice at full filling and another to\nbe untrapped spin-polarized fermions (which do not see the optical lattice) but\nhas an s-wave contact interaction with the first species. For large positive\nscattering length on the order of lattice spacing, the usual two-body bound\n(dimer) states overlap forming giant orbitals extending over the entire\nlattice, which can be viewed as an \"electronic\" band for the untrapped species\nwhile the trapped atoms become the \"ions\" with their own on-site dynamics,\nthereby simulating an electron-phonon system with renormalization of the phonon\nfrequencies and Peierls transitions. This setup requires large scattering\nlengths but minimises losses, does not need higher bands and adds new degrees\nof freedom which cannot easily be described in terms of lattice variables, thus\nopening up intriguing possibilities to explore interesting physics at the\ninterface between few-body and many-body systems.",
        "positive": "Current response, structure factor and hydrodynamic quantities of a two-\n  and three-dimensional Fermi gas from the operator-product expansion: We apply the operator-product expansion to determine the asymptotic form of\nthe current response of a Fermi gas in two and three dimensions. The\nleading-order term away from the one-particle peak is proportional to a\nquantity known as the contact, the coefficient of which is determined exactly.\nWe also calculate the dynamic structure factor and the high-frequency tails of\nthe spectral viscosities as a function of the scattering length. Our results\nare used to derive certain sum rules for the viscosities."
    },
    {
        "anchor": "Predicting Energies of Small Clusters from the Inhomogeneous Unitary\n  Fermi Gas: We investigate the inhomogeneous unitary Fermi gas and use the\nlong-wavelength properties to predict the energies of small clusters of unitary\nfermions trapped in harmonic potentials. The large pairing gap and scale\ninvariance place severe restrictions on the form of the density functional. We\ndetermine the relevant universal constants needed to constrain the functional\nfrom calculations of the bulk in oscillating external potentials. Comparing\nwith exact Quantum Monte Carlo calculations, we find that the same functional\ncorrectly predicts the lack of shell closures for small clusters of fermions\ntrapped in harmonic wells as well as their absolute energies. A rapid\nconvergence to the bulk limit in three dimensions, where the surface to volume\nratio is quite large, is demonstrated. The resulting functional can be tested\nexperimentally, and is a key ingredient in predicting possible polarized\nsuperfluid phases and the properties of the unitary Fermi gas in optical\nlattices.",
        "positive": "Anomalous Dimers in Quantum Mixtures near Broad Resonances: Pauli\n  Blocking, Fermi Surface Dynamics and Implications: We study the energetics and dispersion of anomalous dimers that are induced\nby the Pauli blocking effect in a quantum Fermi gas of majority atoms near\ninterspecies resonances. Unlike in vacuum, we find that both the sign and\nmagnitude of the dimer masses are tunable via Feshbach resonances. We also\ninvestigate the effects of particle-hole fluctuations on the dispersion of\ndimers and demonstrate that the particle-hole fluctuations near a Fermi surface\n(with Fermi momentum $\\hbar k_F$) generally reduce the effective two-body\ninteractions and the binding energy of dimers. Furthermore, in the limit of\nlight minority atoms the particle-hole fluctuations disfavor the formation of\ndimers with a total momentum $\\hbar k_F$, because near $\\hbar k_F$ the modes\nwhere the dominating particle-hole fluctuations appear are the softest. Our\ncalculation suggests that near broad interspecies resonances when the\nminority-majority mass ratio $m_B/m_F$ is smaller than a critical value\n(estimated to be 0.136), dimers in a finite-momentum channel are energetically\nfavored over dimers in the zero-momentum channel. We apply our theory to\nquantum gases of $^{6}$Li$^{40}$K, $^{6}$Li$^{87}$Rb, $^{40}$K$^{87}$Rb and\n$^{6}$Li$^{23}$Na near broad interspecies resonances, and discuss the\nlimitations of our calculations and implications."
    },
    {
        "anchor": "Finite temperature dynamical properties of SU($N$) fermionic Hubbard\n  models in the spin-incoherent regime: We study strongly correlated Hubbard systems extended to symmetric\n$N$-component fermions. We focus on the intermediate-temperature regime between\nmagnetic superexchange and interaction energy, which is relevant to current\nultracold fermionic atom experiments. The $N$-component fermions are\nrepresented by slave particles, and, by using a diagrammatic technique based on\nthe atomic limit, spectral functions are analytically obtained as a function of\ntemperature, filling factor and the component number $N$. We also apply this\nanalytical technique to the calculation of lattice modulation experiments. We\ncompute the production rate of double occupancy induced by modulation of an\noptical lattice potential. Furthermore, we extend the analysis to take into\naccount the trapping potential by use of the local density approximation. We\nfind an excellent agreement with recent experiments on $^{173}$Yb atoms.",
        "positive": "Breakdown of sound in superfluid helium: Like elementary particles carry energy and momentum in the Universe,\nquasiparticles are the elementary carriers of energy and momentum quanta in\ncondensed matter. And, like elementary particles, under certain conditions\nquasiparticles can be unstable and decay, emitting pairs of less energetic\nones. Pitaevskii proposed that such processes exist in superfluid helium, a\nquantum fluid where the very concept of quasiparticles was borne, and which\nprovided the first spectacular triumph of that concept. Pitaevskii's decays\nhave important consequences, including possible breakdown of a quasiparticle.\nHere, we present neutron scattering experiments, which provide evidence that\nsuch decays explain the collapsing lifetime (strong damping) of higher-energy\nphonon-roton sound-wave quasiparticles in superfluid helium. This damping\ndevelops when helium is pressurized towards crystallization or warmed towards\napproaching the superfluid transition. Our results resolve a number of puzzles\nposed by previous experiments and reveal the ubiquity of quasiparticle decays\nand their importance for understanding quantum matter."
    },
    {
        "anchor": "Tunable Wigner States with Dipolar Atoms and Molecules: We study the few-body physics of trapped atoms or molecules with electric or\nmagnetic dipole moments aligned by an external field. Using exact numerical\ndiagonalization appropriate for the strongly correlated regime, as well as a\nclassical analysis, we show how Wigner localization emerges with increasing\ncoupling strength. The Wigner states exhibit non-trivial geometries due to the\nanisotropy of the interaction. This leads to transitions between different\nWigner states as the tilt angle of the dipoles with the confining plane is\nchanged. Intriguingly, while the individual Wigner states are well described by\na classical analysis, the transitions between different Wigner states are\nstrongly affected by quantum statistics. This can be understood by considering\nthe interplay between quantum-mechanical and spatial symmetry properties.\nFinally, we demonstrate that our results are relevant to experimentally\nrealistic systems.",
        "positive": "Ultra high temperature superfluidity in ultracold atomic Fermi gases\n  with mixed dimensionality: Achieving a higher superfluid transition $T_c$ has been a goal for the fields\nof superconductivity and atomic Fermi gases. Here we propose that, by using\nmixed dimensionality, one may achieve ultra high temperature superfluids in two\ncomponent atomic Fermi gases, where one component feels a regular\nthree-dimensional (3D) continuum space, while the other is subject to a 1D\noptic lattice potential. Via tuning the lattice spacing and trap depth, one can\neffectively raise the Fermi level dramatically upon pairing so that\nsuperfluidity may occur at an ultra high temperature (in units of Fermi energy)\neven beyond the quantum degeneracy regime, well surpassing that in an ordinary\n3D Fermi gas and all other known superfluids and superconductors."
    },
    {
        "anchor": "Dissipationless flow in a Bose-Fermi mixture: Interacting mixtures of bosons and fermions are ubiquitous in nature. They\nform the backbone of the standard model of physics, provide a framework for\nunderstanding quantum materials such as unconventional superconductors and\ntwo-dimensional electronic systems, and are of technological importance in\n$^3$He/$^4$He dilution refrigerators. Bose-Fermi mixtures are predicted to\nexhibit an intricate phase diagram featuring coexisting liquids, supersolids,\ncomposite fermions, coupled superfluids, and quantum phase transitions in\nbetween. However, their coupled thermodynamics and collective behavior\nchallenge our understanding, in particular for strong boson-fermion\ninteractions. Clean realizations of fully controllable systems are scarce.\nUltracold atomic gases offer an ideal platform to experimentally investigate\nBose-Fermi mixtures, as the species concentration and interaction strengths can\nbe freely tuned. Here, we study the collective oscillations of a spin-polarized\nFermi gas immersed in a Bose-Einstein condensate (BEC) as a function of the\nboson-fermion interaction strength and temperature. Remarkably, for strong\ninterspecies interactions the fermionic collective excitations evolve to\nperfectly mimic the bosonic superfluid collective modes, and fermion flow\nbecomes dissipationless. With increasing number of thermal excitations in the\nBose gas, the fermions' dynamics exhibit a crossover from the collisionless to\nthe hydrodynamic regime, reminiscent of the emergence of hydrodynamics in\ntwo-dimensional electron fluids. Our findings open the door towards\nunderstanding non-equilibrium dynamics of strongly interacting Bose-Fermi\nmixtures.",
        "positive": "Rapid-cycle Thouless pumping in a one-dimensional optical lattice: An adiabatic cycle around a degeneracy point in the parameter space of a\none-dimensional band insulator is known to result in an integer valued\nnoiseless particle transport in the thermodynamic limit. Recently, it was shown\nthat in the case of an infinite bipartite lattice the adiabatic Thouless\nprotocol can be continuously deformed into a fine tuned finite-frequency cycle\npreserving the properties of noiseless quantized transport. In this paper, we\nnumerically investigate the implementation of such an ideal rapid-cycle\nThouless pumping protocol in a one-dimensional optical lattice. It is shown\nthat the rapidity will cause first order corrections due to\nnext-to-nearest-neighbour hopping and second order corrections due to the\naddition of a harmonic potential. Lastly, the quantization of the change in\ncenter of mass of the particle distribution is investigated, and shown to have\ncorrections in the first order of the potential curvature."
    },
    {
        "anchor": "Analytical solution of the disordered Tavis-Cummings model and its Fano\n  resonances: $\\mathcal{N}$ emitters collectively coupled to a quantised cavity mode are\ndescribed by the Tavis-Cummings model. We present complete analytical solution\nof the model in the presence of inhomogeneous couplings and energetic disorder.\nWe derive the exact expressions for the bright and the dark sectors that\ndecouple the disordered model and find that, in the thermodynamic limit, the\nenergetic disorder transforms the bright sector to Fano's model that can be\neasily solved. We thoroughly explore the effects of energetic disorder assuming\na Gaussian distribution of emitter transition energies. We compare the Fano\nresonances in optical absorption and inelastic electron scattering both in the\nweak and the strong coupling regimes. We study the evolution of the optical\nabsorption with an increase in the disorder strength and find that it changes\nthe lower and upper polaritons to their broadened resonances that finally\ntransform to a single resonance at the bare cavity photon energy, thus taking\nthe system from the strong to the weak coupling regime. Interestingly, we learn\nthat the Rabi splitting can exist even in the weak coupling regime while the\npolaritonic peaks in the strong coupling regime can represent almost excitonic\nstates at intermediate disorder strengths. We also calculate the photon Green's\nfunction to see the effect of cavity leakage and non-radiative emitter losses\nand find that the polariton linewidth exhibits a minimum as a function of\ndetuning when the cavity leakage is comparable to the Fano broadening.",
        "positive": "Cold atoms meet lattice gauge theory: The central idea of this review is to consider quantum field theory models\nrelevant for particle physics and replace the fermionic matter in these models\nby a bosonic one. This is mostly motivated by the fact that bosons are more\n``accessible'' and easier to manipulate for experimentalists, but this\n``substitution'' also leads to new physics and novel phenomena. It allows us to\ngain new information about among other things confinement and the dynamics of\nthe deconfinement transition. We will thus consider bosons in dynamical\nlattices corresponding to the bosonic Schwinger or Z$_2$ Bose-Hubbard models.\nAnother central idea of this review concerns atomic simulators of paradigmatic\nmodels of particle physics theory such as the Creutz-Hubbard ladder, or\nGross-Neveu-Wilson and Wilson-Hubbard models. Finally, we will briefly describe\nour efforts to design experimentally friendly simulators of these and other\nmodels relevant for particle physics."
    },
    {
        "anchor": "Atom-optics simulator of lattice transport phenomena: We experimentally investigate a scheme for studying lattice transport\nphenomena, based on the controlled momentum-space dynamics of ultracold atomic\nmatter waves. In the effective tight-binding models that can be simulated, we\ndemonstrate that this technique allows for a local and time-dependent control\nover all system parameters, and additionally allows for single-site resolved\ndetection of atomic populations. We demonstrate full control over site-to-site\noff-diagonal tunneling elements (amplitude and phase) and diagonal\nsite-energies, through the observation of continuous-time quantum walks, Bloch\noscillations, and negative tunneling. These capabilities open up new prospects\nin the experimental study of disordered and topological systems.",
        "positive": "Spin-orbit coupled weakly interacting Bose-Einstein condensates in\n  harmonic traps: We investigate theoretically the phase diagram of a spin-orbit coupled Bose\ngas in two-dimensional harmonic traps. We show that discrete Landau levels\ndevelop at strong spin-orbit coupling. For a weakly interacting gas, quantum\nstates with skyrmion lattice patterns emerge spontaneously and preserve either\nparity symmetry or combined parity-time-reversal symmetry. These phases can be\nreadily observed by experimentally engineering spin-orbit coupling and\ninteratomic interactions for a cloud of $^{87}$Rb atoms in a highly oblate\ntrap."
    },
    {
        "anchor": "Physics of higher orbital bands in optical lattices: a review: Orbital degree of freedom plays a fundamental role in understanding the\nunconventional properties in solid state materials. Experimental progress in\nquantum atomic gases has demonstrated that high orbitals in optical lattices\ncan be used to construct quantum emulators of exotic models beyond natural\ncrystals, where novel many-body states such as complex Bose-Einstein\ncondensation and topological semimetals emerge. A brief introduction of orbital\ndegree of freedom in optical lattices is given and a summary of exotic orbital\nmodels and resulting many-body phases is provided. Experimental consequences of\nthe novel phases are also discussed.",
        "positive": "Rice-Mele model with topological solitons in an optical lattice: Attractive ultra-cold fermions trapped in a one-dimensional periodically\nshaken opticla lattices are considered. For an appropriate resonant shaking the\nsystem realizes paradigmatic dimes physics described by Rice-Mele model. The\nimportant feature of our system is the possible presence of controlled defects.\nThey result in the creation of topologically protected loclaized modes carrying\nfractional particle number. Their possible experimental signatures are\ndiscussed."
    },
    {
        "anchor": "Nonzero temperature dynamics of a repulsive two-component Fermi gas: We study spin-dipole oscillations of a binary fermionic mixture at nonzero\ntemperatures. We apply the atomic-orbital method combined with the Monte Carlo\ntechnique based sampling to probe finite temperatures. Our results agree\nquantitatively with recent experiment, G. Valtolina et al., Nat. Phys. 13, 704\n(2017), showing the appearance of the ferromagnetic phase at stronger repulsion\nbetween components when the temperature is increased.",
        "positive": "A three-dimensional steerable optical tweezer system for ultracold atoms: We present a three-dimensional steerable optical tweezer system based on two\npairs of acousto-optic deflectors. Radio frequencies used to steer the optical\ntweezers are generated by direct digital synthesis and multiple cross beam\ndipole traps can be produced through rapid frequency toggling and time\naveraging. We demonstrate production of arrays of ultracold atomic clouds in\nboth horizontal and vertical planes and use this as an indicator for the\nthree-dimensional nature of this optical tweezer system."
    },
    {
        "anchor": "A new quantum gas apparatus for ultracold mixtures of K and Cs and KCs\n  ground-state molecules: We present a new quantum gas apparatus for ultracold mixtures of K and Cs\natoms and ultracold samples of KCs ground-state molecules. We demonstrate the\napparatus' capabilities by producing Bose-Einstein condensates (BEC) of 39K and\n133Cs in a manner that will eventually allow sequential condensation within one\nexperimental cycle, precise sample overlap, and magnetic association of atoms\ninto KCs molecules. The condensates are created independently without relying\non sympathetic cooling. Our approach is universal and applicable to other\nspecies combinations when the two species show dramatically different behavior\nin terms of loss mechanisms and post laser cooling temperatures, i.e. species\ncombinations that make parallel generation of quantum degenerate samples\nchallenging. We give an outlook over the next experiments involving e.g. sample\nmixing, molecule formation, and transport into a science chamber for\nhigh-resolution spatial imaging of novel quantum-many body phases based on\nK-Cs.",
        "positive": "Strong Boundary and Trap Potential Effects on Emergent Physics in\n  Ultra-Cold Fermionic Gases: The field of quantum simulations in ultra-cold atomic gases has been\nremarkably successful. In principle it allows for an exact treatment of a\nvariety of highly relevant lattice models and their emergent phases of matter.\nBut so far there is a lack in the theoretical literature concerning the\nsystematic study of the effects of the trap potential as well as the finite\nsize of the systems, as numerical studies of such non periodic, correlated\nfermionic lattices models are numerically demanding beyond one dimension. We\nuse the recently introduced real-space truncated unity functional\nrenormalization group to study these boundary and trap effects with a focus on\ntheir impact on the superconducting phase of the $2$D Hubbard model. We find\nthat in the experiments not only lower temperatures need to be reached compared\nto current capabilities, but also system size and trap potential shape play a\ncrucial role to simulate emergent phases of matter."
    },
    {
        "anchor": "Spin Waves in Quantum Gases --- The Quality Factor of the Identical Spin\n  Rotation Effect: Our recent experimental work on electron spin waves in atomic hydrogen gas\nhas prompted a revisit of the theory of the Identical Spin Rotation Effect\n(ISRE). A key characteristic determining the properties of the spin waves is\nthe quality factor of ISRE. Unfortunately, calculating this quality factor\ntakes some toil. In this paper we summarize some results of the ISRE theory in\ndilute gases. We also derive asymptotic formulae for the quality factor and\nexamine their accuracy for hydrogen and $^3$He.",
        "positive": "Condensed Matter Physics in Time Crystals: Time crystals are physical systems whose time translation symmetry is\nspontaneously broken. Although the spontaneous breaking of continuous\ntime-translation symmetry in static systems is proved impossible for the\nequilibrium state, the discrete time-translation symmetry in periodically\ndriven (Floquet) systems is allowed to be spontaneously broken, resulting in\nthe so-called Floquet or discrete time crystals. While most works so far\nsearching for time crystals focus on the symmetry breaking process and the\npossible stabilising mechanisms, the many-body physics from the interplay of\nsymmetry-broken states, which we call the condensed matter physics in time\ncrystals, is not fully explored yet. This review aims to summarise the very\npreliminary results in this new research field with an analogous structure of\ncondensed matter theory in solids. The whole theory is built on a hidden\nsymmetry in time crystals, i.e., the phase space lattice symmetry, which allows\nus to develop the band theory, topology and strongly correlated models in phase\nspace lattice. In the end, we outline the possible topics and directions for\nthe future research."
    },
    {
        "anchor": "Effective spin-chain model for strongly interacting one-dimensional\n  atomic gases with an arbitrary spin: We present a general form of the effective spin-chain model for strongly\ninteracting atomic gases with an arbitrary spin in the one-dimensional(1D)\ntraps. In particular, for high-spin systems the atoms can collide in multiple\nscattering channels, and we find that the resulted form of spin-chain model\ngenerically follows the same structure as that of the interaction potentials.\nThis is a unified form working for any spin, statistics (Bose or Fermi) and\nconfinement potentials. We adopt the spin-chain model to reveal both the\nferromagnetic(FM) and anti-ferromagnetic(AFM) magnetic orders for strongly\ninteracting spin-1 bosons in 1D traps. We further show that by adding the\nspin-orbit coupling, the FM/AFM orders can be gradually destroyed and\neventually the ground state exhibits universal spin structure and contacts that\nare independent of the strength of spin-orbit coupling.",
        "positive": "Self-localization of polariton condensates in periodic potentials: We predict the existence of novel spatially localized states of\nexciton-polariton Bose-Einstein condensates in semiconductor microcavities with\nfabricated periodic in-plane potentials. Our theory shows that, under the\ncondition of continuous off-resonant pumping and losses associated with\npolariton decay, localization is observed for a wide range of optical pump\nparameters due to effective potentials self-induced by the polariton flows in\nthe spatially periodic system. We reveal that the self-localization of\nexciton-polaritons in the lattice may occur both in the gaps and bands of the\nsingle-particle linear spectrum, and is dominated by the effects of gain and\ndissipation rather than the applied potential, in sharp contrast to the\nconservative condensates of ultracold alkali atoms."
    },
    {
        "anchor": "Analytical approach to the Bose polaron \\\\ via $q$-deformed Lie algebra: We present a novel approach to the Bose polaron based on the notion of\nquantum groups, also known as $q$-deformed Lie algebras. In this approach, a\nmobile impurity can be depicted as a deformation of the Lie algebra of the\nbosonic creation and annihilation operators of the bath, in which the impurity\nis immersed. Accordingly, the Bose polaron can be described as a bath of\nnoninteracting $q$-deformed bosons, which allows us to provide an analytical\nformulation of the Bose polaron at arbitrary couplings. Particularly, we derive\nits ground state energy in the phonon branch of the Bogoliubov dispersion and\ndemonstrate that the previously observed transition from a repulsive to an\nattractive polaron occurs at the vicinity where the quantum group symmetry is\nbroken. Furthermore, our approach has the potential to open up new avenues in\npolaron physics by connecting it with seemingly unrelated research topics where\nquantum groups play an essential role, such as anyons.",
        "positive": "Energetically stable singular vortex cores in an atomic spin-1\n  Bose-Einstein condensate: We analyze the structure and stability of singular singly quantized vortices\nin a rotating spin-1 Bose-Einstein condensate. We show that the singular vortex\ncan be energetically stable in both the ferromagnetic and polar phases despite\nthe existence of a lower-energy nonsingular coreless vortex in the\nferromagnetic phase. The spin-1 system exhibits an energetic hierarchy of\nlength scales resulting from different interaction strengths and we find that\nthe vortex cores deform to a larger size determined by the characteristic\nlength scale of the spin-dependent interaction. We show that in the\nferromagnetic phase the resulting stable core structure, despite apparent\ncomplexity, can be identified as a single polar core with axially symmetric\ndensity profile which is nonvanishing everywhere. In the polar phase, the\nenergetically favored core deformation leads to a splitting of a singly\nquantized vortex into a pair of half-quantum vortices that preserves the\ntopology of the vortex outside the extended core region, but breaks the axial\nsymmetry of the core. The resulting half-quantum vortices exhibit nonvanishing\nferromagnetic cores."
    },
    {
        "anchor": "Spectral and Entanglement Properties of the Bosonic Haldane Insulator: We discuss the existence of a nontrivial topological phase in one-dimensional\ninteracting systems described by the extended Bose-Hubbard model with a mean\nfilling of one boson per site. Performing large-scale density-matrix\nrenormalization group calculations we show that the presence of\nnearest-neighbor repulsion enriches the ground-state phase diagram of the\nparadigmatic Bose-Hubbard model by stabilizing a novel gapped insulating state,\nthe so-called Haldane insulator, which, embedded into superfluid, Mott\ninsulator, and density wave phases, is protected by the lattice inversion\nsymmetry. The quantum phase transitions between the different insulating phases\nwere determined from the central charge via the von Neumann entropy. The\nHaldane phase reveals a characteristic fourfold degeneracy of the entanglement\nspectrum. We finally demonstrate that the intensity maximum of the dynamical\ncharge structure factor, accessible by Bragg spectroscopy, features the gapped\ndispersion known from the spin-1 Heisenberg chain.",
        "positive": "Stochastic differential equation approach to understanding the\n  population control bias in full configuration interaction quantum Monte Carlo: We investigate a systematic statistical bias found in full configuration\nquantum Monte Carlo (FCIQMC) that originates from controlling a walker\npopulation with a fluctuating shift parameter. This bias can become the\ndominant error when the sign problem is absent, e.g. in bosonic systems. FCIQMC\nis a powerful statistical method for obtaining information about the ground\nstate of a sparse and abstract matrix. We show that, when the sign problem is\nabsent, the shift estimator has the nice property of providing an upper bound\nfor the exact ground state energy and all projected energy estimators, while a\nvariational estimator is still an upper bound to the exact energy with\nsubstantially reduced bias. A scalar model of the general FCIQMC population\ndynamics leads to an exactly solvable It\\^o stochastic differential equation.\nIt provides further insights into the nature of the bias and gives accurate\nanalytical predictions for delayed cross-covariance and auto-covariance\nfunctions of the shift energy estimator and the walker number. The model\nprovides a toe-hold on finding a cure for the population control bias. We\nprovide evidence for non-universal power-law scaling of the population control\nbias with walker number in the Bose-Hubbard model for various estimators of the\nground state energy based on the shift or on projected energies. For the\nspecific case of the non-interacting Bose-Hubbard Hamiltonian we obtain a full\nanalytical prediction for the bias of the shift energy estimator."
    },
    {
        "anchor": "Probing two-body exceptional points in open dissipative systems: We study two-body non-Hermitian physics in the context of an open dissipative\nsystem depicted by the Lindblad master equation. Adopting a minimal lattice\nmodel of a handful of interacting fermions with single-particle dissipation, we\nshow that the non-Hermitian effective Hamiltonian of the master equation gives\nrise to two-body scattering states with state- and interaction-dependent\nparity-time transition. The resulting two-body exceptional points can be\nextracted from the trace-preserving density-matrix dynamics of the same\ndissipative system with three atoms. Our results not only demonstrate the\ninterplay of PT symmetry and interaction on the exact few-body level, but also\nserve as a minimal illustration on how key features of non-Hermitian few-body\nphysics can be probed in an open dissipative many-body system.",
        "positive": "On the Equivalence between Spin and Charge Dynamics of the Fermi Hubbard\n  Model: Utilizing the Fermi gas microscope, recently the MIT group has measured the\nspin transport of the Fermi Hubbard model starting from a spin-density-wave\nstate, and the Princeton group has measured the charge transport of the Fermi\nHubbard model starting from a charge-density-wave state. Motivated by these two\nexperiments, we prove a theorem that shows under certain conditions, the spin\nand charge transports can be equivalent to each other. The proof makes use of\nthe particle-hole transformation of the Fermi Hubbard model and a recently\ndiscovered symmetry protected dynamical symmetry. Our results can be directly\nverified in future cold atom experiment with the Fermi gas microscope."
    },
    {
        "anchor": "Pair excitations and parameters of state of imbalanced Fermi gases at\n  finite temperatures: The spectra of low-lying pair excitations for an imbalanced two-component\nsuperfluid Fermi gas are analytically derived within the path-integral\nformalism taking into account Gaussian fluctuations about the saddle point. The\nspectra are obtained for nonzero temperatures, both with and without imbalance,\nand for arbitrary interaction strength. On the basis of the pair excitation\nspectrum, we have calculated the thermodynamic parameters of state of cold\nfermions and the first and second sound velocities. The parameters of pair\nexcitations show a remarkable agreement with the Monte Carlo data and with\nexperiment.",
        "positive": "Geometric phase of Wannier-Stark ladders in alkaline-earth(-like) atoms: We discuss the geometric phase of Wanner-Stark ladders generated by\nperiodically driven clock states in alkaline-earth(-like) atoms. Using\n$^{171}$Yb atoms as a concrete example, we show that clock states driven by two\ndetuned clock lasers can be mapped to two-band Wannier-Stark ladders, where\ndynamics of the system along the ladder is mapped to Bloch oscillations in a\none-dimensional topological lattice. When the adiabatic condition is satisfied,\nthe geometric phase accumulated in one period of the oscillation is quantized,\nand reveals the change of band topology as the laser parameters are tuned. We\nshow how the geometric phase can be experimentally detected through\ninterference between different nuclear spin states. Our study sheds light on\nthe engineering of exotic band structures in Floquet dynamics."
    },
    {
        "anchor": "Sudden-quench dynamics of Bardeen-Cooper-Schrieffer states in deep\n  optical lattices: We determine the exact dynamics of an initial Bardeen-Cooper-Schrieffer (BCS)\nstate of ultra-cold atoms in a deep hexagonal optical lattice. The dynamical\nevolution is triggered by a quench of the lattice potential, such that the\ninteraction strength $U_f$ is much larger than the hopping amplitude $J_f$. The\nquench initiates collective oscillations with frequency $|U_f|/(2\\pi)$ in the\nmomentum occupation numbers and imprints an oscillating phase with the same\nfrequency on the BCS order parameter $\\Delta$. The oscillation frequency of\n$\\Delta$ is not reproduced by treating the time evolution in mean-field theory.\nIn our theory, the momentum noise (i.e. density-density) correlation functions\noscillate at frequency $|U_f|/2\\pi$ as well as at its second harmonic. For a\nvery deep lattice, with zero tunneling energy, the oscillations of momentum\noccupation numbers are undamped. Non-zero tunneling after the quench leads to\ndephasing of the different momentum modes and a subsequent damping of the\noscillations. The damping occurs even for a finite-temperature initial BCS\nstate, but not for a non-interacting Fermi gas. Furthermore, damping is\nstronger for larger order parameter and may therefore be used as a signature of\nthe BCS state. Finally, our theory shows that the noise correlation functions\nin a honeycomb lattice will develop strong anti-correlations near the Dirac\npoint.",
        "positive": "Static and dynamic properties of heavily doped quantum vortices: Quantum vortices in superfluids may capture matter and deposit it inside\ntheir core. By doping vortices with foreign particles one can effectively\nvisualize them and study experimentally. To acquire a better understanding of\nthe interaction of quantum vortices with matter and clarify the details of\nrecent experiments properties of doped vortices are investigated here\ntheoretically in the regimes where the doping mass becomes close to the total\nmass of superfluid particles forming a vortex. Such formations are dynamically\nstable and, possessing both vorticity and enhanced inertia, demonstrate\nproperties which are different from the pure vortex case. The goal of this\npaper is to define and investigate the universal aspects of a heavily doped\nvortex behavior which can be realized in different types of quantum mixtures.\nThe proposed 3D model is based on a system of coupled semiclassical matter wave\nequations which are solved numerically in a wide range of physical parameters.\nThe size, geometry, solubility and binding energy of dopants in different\nregimes are discussed. A coupled motion of a vortex-dopant complex and\ndecoupling conditions are studied. The reconnection of vortices, taken as an\nexample of a fundamental process responsible for the evolution of a quantum\nturbulent state, is modeled to illustrate the difference between the light and\nheavy doping cases."
    },
    {
        "anchor": "Anderson localization of ultracold atoms: Where is the mobility edge?: Recent experiments on non-interacting ultra-cold atoms in correlated disorder\nhave yielded conflicting results regarding the so-called mobility edge, i.e.\nthe energy threshold separating Anderson localized from diffusive states. At\nthe same time, there are theoretical indications that the experimental data\noverestimate the position of this critical energy, sometimes by a large amount.\nThe non-trivial effect of anisotropy in the spatial correlations of\nexperimental speckle potentials have been put forward as a possible cause for\nsuch discrepancy. Using extensive numerical simulations we show that the effect\nof anisotropy alone is not sufficient to explain the experimental data. In\nparticular, we find that, for not-too-strong anisotropy, realistic disorder\nconfigurations are essentially identical to the isotropic case, modulo a simple\nrescaling of the energies.",
        "positive": "Dynamical features of Shannon information entropy of bosonic cloud in a\n  tight trap: We calculate Shannon information entropy of trapped interacting bosons in\nboth the position and momentum spaces, $S_r$ and $S_k$ respectively. The total\nentropy maintains the fuctional form $S=a + b \\ln N$ for repulsive bosons. At\nthe noninteracting limit the lower bound of entropic uncertainty relation is\nalso satisfied whereas the diverging behavior of $S_r$ and $S_k$ at the\ncritical point of collapse for attractive condensate accurately calculates the\nstability factor. Next we study the dynamics of Shannon information entropy\nwith varying interparticle potential. We numerically solve the time-dependent\nGross-Pitaevskii equation and study the influence of increasing nonlinearity in\nthe dynamics of entropy uncertainty relation (EUR). We observe that for small\nnonlinearity the dynamics is regular. With increase in nonlinearity although\nShannon entropy shows large variation in amplitude of the oscillation, the EUR\nis maintained throughout time for all cases and it confirms its generality. We\nalso study the dynamics in a very tight trap when the condensate becomes highly\ncorrelated and strongly inhomogeneous. Time evolution of total entropy exhibits\naperiodic and fluctuating nature in very tight trap. We also calculate\nLandsberg's order parameter for various interaction strengths which supports\nearlier observation that entropy and order are decoupled."
    },
    {
        "anchor": "Wall-vortex composite solitons in two-component Bose-Einstein\n  condensates: We study composite solitons, consisting of domain walls and vortex lines\nattaching to the walls in two-component Bose-Einstein condensates. When the\ntotal density of two components is homogeneous, the system can be mapped to the\nO(3) nonlinear sigma model for the pseudospin representing the two-component\norder parameter and the analytical solutions of the composite solitons can be\nobtained. Based on the analytical solutions, we discuss the detailed structure\nof the composite solitons in two-component condensates by employing the\ngeneralized nonlinear sigma model, where all degrees of freedom of the original\nGross-Pitaevskii theory are active. The density inhomogeneity results in\nreduction of the domain wall tension from that in the sigma model limit. We\nfind that the domain wall pulled by a vortex is logarithmically bent as a\nmembrane pulled by a pin, and it bends more flexibly than not only the domain\nwall in the sigma model but also the expectation from the reduced tension.\nFinally, we study the composite soliton structure for actual experimental\nsituations with trapped immiscible condensates under rotation through numerical\nsimulations of the coupled Gross-Pitaevskii equations.",
        "positive": "Spin textures in condensates with large dipole moments: We have solved numerically the ground states of a Bose-Einstein condensate in\nthe presence of dipolar interparticle forces using a semiclassical approach.\nOur motivation is to model, in particular, the spontaneous spin textures\nemerging in quantum gases with large dipole moments, such as 52Cr or Dy\ncondensates, or ultracold gases consisting of polar molecules. For a\npancake-shaped harmonic (optical) potential, we present the ground state phase\ndiagram spanned by the strength of the nonlinear coupling and dipolar\ninteractions. In an elongated harmonic potential, we observe a novel helical\nspin texture. The textures calculated according to the semiclassical model in\nthe absence of external polarizing fields are predominantly analogous to\npreviously reported results for a ferromagnetic F = 1 spinor Bose-Einstein\ncondensate, suggesting that the spin textures arising from the dipolar forces\nare largely independent of the value of the quantum number F or the origin of\nthe dipolar interactions."
    },
    {
        "anchor": "Stability of supercurrents in a superfluid phase of spin-1 bosons in an\n  optical lattice: We study collective modes and superfluidity of spin-1 bosons with\nantiferromagnetic interactions in an optical lattice based on the\ntime-dependent Ginzburg-Landau (TDGL) equation derived from the spin-1\nBose-Hubbard model. Specifically, we examine the stability of supercurrents in\nthe polar phase in the vicinity of the Mott insulating phase with even filling\nfactors. Solving the linearized TDGL equation, we obtain gapless spin-nematic\nmodes and gapful spin-wave modes in the polar phase that arise due to the\nbreaking of $S^2$ symmetry in spin space. Supercurrents exhibit dynamical\ninstabilities induced by growing collective modes. In contrast to the\nsecond-order phase transition, the critical momentum of mass currents is finite\nat the phase boundary of the first-order superfluid-Mott insulator (SF-MI)\nphase transition. Furthermore, the critical momentum remains finite throughout\nthe metastable SF phase and approaches zero towards the phase boundary, at\nwhich the metastable SF state disappears. We also study the stability of spin\ncurrents motivated by recent experiments for spinor gases. The critical\nmomentum of spin currents is found to be zero, where a spin-nematic mode causes\nthe dynamical instability. We investigate the origin of the zero critical\nmomentum of spin currents and find it attributed to the fact that the polar\nstate becomes energetically unstable even in the presence of an infinitesimal\nspin current. We discuss implications of the zero critical momentum of spin\ncurrents for the stability of the polar state.",
        "positive": "Tricritical physics in two-dimensional $p$-wave superfluids: We study effects of quantum fluctuations on two-dimensional $p+ip$\nsuperfluids near resonance. In the standard paradigm, phase transitions between\nsuperfluids and zero density vacuum are continuous. When strong quantum\nfluctuations near resonance are taken into account, the line of continuous\nphase transitions terminates at two multicritical points near resonance,\nbetween which the transitions are expected to be first-order ones. The size of\nthe window where first-order phase transitions occur is shown to be substantial\nwhen the coupling is strong. Near first-order transitions, superfluids\nself-contract due to phase separations between superfluids and vacuum."
    },
    {
        "anchor": "Orbital-FFLO state in a chain of high spin ultracold atoms: Recent experiments with Yb-173 and Sr-87 isotopes provide new possibilities\nto study high spin two-orbital systems. Within these experiments part of the\natoms are excited to a higher energy metastable electronic state mimicking an\nadditional internal (orbital) degree of freedom. The interaction between the\natoms depends on the orbital states, therefore four different scattering\nchannels can be identified in the system characterized by four independent\ncouplings. When the system is confined into a one-dimensional chain the\nscattering lengths can be tuned by changing the transverse confinement, and\ndriven through four resonances. Using the new available experimental data of\nthe scattering lengths we analyze the phase diagram of the one-dimensional\nsystem as the couplings are tuned via transverse confinement, and the\npopulations of the two orbital states are changed. We found that three orders\ncompete showing power law decay: a state with dominant density wave\nfluctuations, another one with spin density fluctuations, and a third one\ncharacterized by exotic Fulde-Ferrell-Larkin-Ovchinnikov-like pairs consisting\none atom in the electronic ground state and one in the excited state. We also\nshow that sufficiently close to the resonances the compressibility of the\nsystem starts to diverge indicating that the emerging order is unstable and\ncollapses to a phase separated state with a first order phase transition.",
        "positive": "Realization of the Hofstadter Hamiltonian with ultracold atoms in\n  optical lattices: We demonstrate the experimental implementation of an optical lattice that\nallows for the generation of large homogeneous and tunable artificial magnetic\nfields with ultracold atoms. Using laser-assisted tunneling in a tilted optical\npotential we engineer spatially dependent complex tunneling amplitudes. Thereby\natoms hopping in the lattice accumulate a phase shift equivalent to the\nAharonov-Bohm phase of charged particles in a magnetic field. We determine the\nlocal distribution of fluxes through the observation of cyclotron orbits of the\natoms on lattice plaquettes, showing that the system is described by the\nHofstadter model. Furthermore, we show that for two atomic spin states with\nopposite magnetic moments, our system naturally realizes the time-reversal\nsymmetric Hamiltonian underlying the quantum spin Hall effect, i.e., two\ndifferent spin components experience opposite directions of the magnetic field."
    },
    {
        "anchor": "Periodic dynamics of population-imbalanced fermionic condensates in\n  optical lattices: We investigate the dynamics of a population-imbalanced two-species fermionic\nsystem trapped in an optical lattice. The paired fermions here can form bosonic\nmolecules via Feshbach coupling in the presence of an external magnetic field.\nIt is shown that the natural fluctuations of the condensate fraction are\nperiodic beyond a threshold Feshbach detuning; and below this threshold value,\nthe condensate fraction shows no oscillation at all. The oscillation frequency\nvs. detuning curve is linear in nature. The slope and intercept of this line\nare shown to carry important information about the amount of imbalance present\nin the system, and the momentum space structure of the exotic phases.",
        "positive": "Superfluid Vortex Dynamics on Planar Sectors and Cones: We study the dynamics of vortices formed in a superfluid film adsorbed on the\ncurved two-dimensional surface of a cone. To this aim, we observe that a cone\ncan be unrolled to a sector on a plane with periodic boundary conditions on the\nstraight sides. The sector can then be mapped conformally to the whole plane,\nleading to the relevant stream function. In this way, we show that a superfluid\nvortex on the cone precesses uniformly at fixed distance from the apex. The\nstream function also yields directly the interaction energy of two vortices on\nthe cone. We then study the vortex dynamics on unbounded and bounded cones. In\nsuitable limits, we recover the known results for dynamics on cylinders and\nplanar annuli."
    },
    {
        "anchor": "Experimental realization of a high precision tunable hexagonal optical\n  lattice: Hexagonal optical lattices offer a tunable platform to study exotic orbital\nphysics in solid state materials. Here, we present a versatile high-precision\nscheme to implement a hexagonal optical lattice potential, which is engineered\nby overlapping two independent triangular optical sublattices generated by\nlaser beams with slightly different wavelengths around 1064 nm. This enables us\nto precisely control the detailed structure of the hexagonal lattice by\nadjusting the relative position and the relative lattice depth of the two\ntriangular optical sublattices. Taking advantage of the sensitive dependence of\nthe second Bloch band on small lattice deformations, we propose a strategy to\noptimize the optical lattice geometry with an extremely high precision. This\nmethod can also be extended to other lattice configurations involving more than\ntwo sublattices. Our work provides the experimental requirements in the search\nfor novel orbital physics of ultracold atoms, for example, in the flat $p$-band\nof the hexagonal optical lattice.",
        "positive": "Ultracold Feshbach molecules in an orbital optical lattice: Quantum gas systems provide a unique experimental platform to study a\nfundamental paradigm of quantum many-body physics: the crossover between\nBose-Einstein condensed (BEC) molecular pairs and Bardeen Cooper Schrieffer\n(BCS) superfluidity. Some studies have considered quantum gas samples confined\nin optical lattices, however, focusing on the case, when only the lowest Bloch\nband is populated, such that orbital degrees of freedom are excluded. In this\nwork, for the first time, ultracold Feshbach molecules of fermionic $^{40}K$\natoms are selectively prepared in the second Bloch band of an optical square\nlattice, covering a wide range of interaction strengths including the regime of\nunitarity. Binding energies and band relaxation dynamics are measured by means\nof a method resembling mass spectrometry. The longest lifetimes arise for\nstrongly interacting Feshbach molecules at the onset of unitarity with values\naround 300 ms for the lowest band and 100 ms for the second band. In the case\nof strong confinement in a deep lattice potential, we observe bound dimers also\nfor negative values of the s-wave scattering length, extending previous\nfindings for molecules in the lowest band. Our work prepares the stage for\norbital BEC-BCS crossover physics."
    },
    {
        "anchor": "The effect of boson-boson interaction on the Bipolaron formation: Impurities immersed into a surrounding ultra-cold Bose gas experience\ninteractions mediated by the surrounding many-body environment. If one focuses\non two impurities that are sufficiently close to each other, they can form a\nbipolaron pair. Here, we discuss how the standard methods based on linearizing\nthe condensate field lead to results only valid in the weak coupling regime and\nfor sufficiently large impurity separations. We show how those shortcomings can\nbe remedied within the Born-Oppenheimer approximation by accounting for\nboson-boson interactions already on the mean-field level.",
        "positive": "Backscattering suppression in supersonic 1D polariton condensates: We investigate the effects of disorder on the propagation of one-dimensional\npolariton condensates in semiconductor microcavities. We observe a strong\nsuppression of the backscattering produced by the imperfections of the\nstructure when increasing the condensate density. This suppression occurs in\nthe supersonic regime and is simultaneous to the onset of parametric\ninstabilities which enable the \"hopping\" of the condensate through the\ndisorder. Our results evidence a new mechanism for the frictionless flow of\npolaritons at high speeds."
    },
    {
        "anchor": "Atomtronic Many-Body Transport using Husimi Driving: Quantum systems with exact analytic solutions are rare - challenging the\nrealisation of excitation-free transport methods for many-body systems.\nHusimi's 1953 treatment of linearly driven harmonic oscillators constitutes an\nimportant exception, describing a wavepacket which is spatially translated but\notherwise unperturbed by the driving. In this work, we experimentally\ndemonstrate the application of Husimi's solution to an interacting many-body\nsystem, namely optically- and magnetically-trapped Bose-Einstein condensates\nsubject to resonant and off-resonant linear magnetic driving potentials. The\nobserved centre-of-mass motion is consistent with theory and shows minimal\nexcitation of the displaced condensate - a highly desirable property of any\ncondensate manipulation technique. We demonstrate transport 72 times faster\nthan adiabatic rates, and a novel Husimi driving-based trap frequency\nmeasurement. We finally propose future applications based on our experimental\nresults: an atom interferometry scheme, and methods for extended transport and\nprecision control of one-body, few-body, and many-body systems via Husimi\ndriving.",
        "positive": "Anomalous thermodynamics of lattice Bose gases in optical cavities: We investigate thermodynamic properties of lattice Bose gases in optical\ncavities in the Mott-insulator limit. We find the system assumes anomalous\nthermodynamic behavior that can be traced back to the breaking of fundamental\nadditivity by its infinite-long range interaction. Specifically, the system\nshows striking ensemble inequivalence between the canonical ensemble and the\ngrand canonical one, sharply manifesting in the distinct anomalous structure of\nthe thermodynamic phase diagram in the canonical ensemble. In particular, in\nthe temperature regime around half of the on-site energy, the system manifests\nnegative compressibility and anomalous reentrant phase transitions where the\nordered charge density wave phase revives from the disordered homogenous phase\nupon increasing the temperature. Direct experimental observation of the\nanomalous behavior can be realized in the current experiments with\nwell-controlled total particle number fluctuations."
    },
    {
        "anchor": "Effect of beyond mean-field interaction on the structure and dynamics of\n  the one-dimensional quantum droplet: We present simulation results of the ground state structure and dynamics of\nquantum droplets in one-dimensional spin-orbit coupled binary Bose-Einstein\ncondensates. We have considered two cases for this analysis, such as (i) the\nmean-field term has a vanishingly small contribution utilizing the equal and\nopposite inter- and intraspecies interaction and (ii) unequal inter- and\nintraspecies interaction. For both cases, it shows remarkably different natures\nof the quantum droplet. In the former case, it exhibits bright sech-like\ndroplet nature, while in the latter case, we find the flattened sech-like shape\nof the droplet. Further, we analyze the effect of velocity perturbation on the\ndynamics in both cases. For the first case, we find a systematic change from\nthe solitonic droplet nature to the breathing droplet which finally has a\nmoving droplet feature upon increasing the velocity. However, the second case\nshows similar dynamics except having more dynamically stable features than the\nfirst. Finally, we present various dynamics that ensued in the quantum droplet\ndue to the quenching of the interaction parameters, coupling parameters or\nallowing the droplet to undergo collisions.",
        "positive": "Observation of Non-Hermitian Skin Effect and Topology in Ultracold Atoms: The non-Hermitian skin effect (NHSE), the accumulation of eigen wavefunctions\nat boundaries of open systems, underlies a variety of exotic properties that\ndefy conventional wisdom. While NHSE and its intriguing impact on band topology\nand dynamics have been observed in classical or photonic systems, their\ndemonstration in a quantum many-body setting remains elusive. Here we report\nthe experimental realization of a dissipative Aharonov-Bohm chain -- a\nnon-Hermitian topological model with NHSE -- in the momentum space of a\ntwo-component Bose-Einstein condensate. We identify unique signatures of NHSE\nin the condensate dynamics, and perform Bragg spectroscopy to resolve\ntopological edge states against a background of localized bulk states. Our work\nsets the stage for further investigation on the interplay of many-body\nstatistics and interactions with NHSE, and is a significant step forward in the\nquantum control and simulation of non-Hermitian physics."
    },
    {
        "anchor": "Topological States with Broken Translational and Time-Reversal\n  Symmetries in a Honeycomb-Triangular Lattice: We study fermions in a lattice, with on-site and nearest neighbor attractive\ninteractions between two spin species. We consider two geometries: both spins\nin a triangular lattice, and a mixed geometry with up-spins in honeycomb and\ndown-spins in triangular lattices. We focus on the interplay between\nspin-population imbalance, on-site and valence bond pairing, and order\nparameter symmetry. The mixed geometry leads to a rich phase diagram of\ntopologically non-trivial phases. In both geometries, we predict order\nparameters with simultaneous time-reversal and translational symmetry breaking.",
        "positive": "Nonthermal fixed points and solitons in a one-dimensional Bose gas: Single-particle momentum spectra for a dynamically evolving one-dimensional\nBose gas are analysed in the semi-classical wave limit. Representing one of the\nsimplest correlation functions these give information about possible universal\nscaling behaviour. Motivated by the previously discovered connection between\n(quasi-)topological field configurations, strong wave turbulence, and\nnonthermal fixed points of quantum field dynamics, soliton formation is studied\nwith respect to the appearance of transient power-law spectra. A random-soliton\nmodel is developed to describe the spectra analytically, and the analogies and\ndifference between the appearing power laws and those found in a field theory\napproach to strong wave turbulence are discussed. The results open a view on\nsolitary wave dynamics from the point of view of critical phenomena far from\nthermal equilibrium and on a possibility to study this dynamics in experiment\nwithout the necessity of detecting solitons in situ."
    },
    {
        "anchor": "Vacancy Induced Splitting of Dirac Nodal Point in Graphene: We investigate the vacancy effects on quasiparticle band structure of\ngraphene near the Dirac point. It is found that each Dirac nodal point splits\ninto two new nodal points due to the coherent scattering among vacancies. The\nsplitting energy between the two nodal points is proportional to the square\nroot of vacancy concentration. In addition, an extra dispersionless impurity\nband of zero energy due to particle-hole symmetry is found. Our theory offers\nan excellent explanation to the recent experiments.",
        "positive": "Renormalization of interactions of ultracold atoms in simulated Rashba\n  gauge fields: Interactions of ultracold atoms with Rashba spin-orbit coupling, currently\nbeing studied with simulated (artificial) gauge fields, have nontrivial\nultraviolet and infrared behavior. Examining the ultraviolet structure of the\nBethe-Salpeter equation, we show that the linear ultraviolet divergence in the\nbare interaction can be renormalized as usual in terms of low-energy scattering\nlengths, and that for both bosons and fermions ultraviolet logarithmic\ndivergences are absent. Calculating the leading order effective interaction\nwith full dependence on the spin-orbit coupling strength and the center-of-mass\nmomentum of the colliding pair, we elucidate the relation between mean-field\ninteractions and physical three-dimensional scattering lengths. As a\nconsequence of infrared logarithmic divergences in the two-particle propagator,\nthe effective interaction vanishes as the center-of-mass momentum approaches\nzero."
    },
    {
        "anchor": "Dynamical creation of a supersolid in asymmetric mixtures of bosons: We propose a scheme to dynamically create a supersolid state in an optical\nlattice, using an attractive mixture of mass-imbalanced bosons. Starting from a\n\"molecular\" quantum crystal, supersolidity is induced dynamically as an\nout-of-equilibrium state. When neighboring molecular wavefunctions overlap,\nboth bosonic species simultaneously exhibit quasi-condensation and long-range\nsolid order, which is stabilized by their mass imbalance. Supersolidity appears\nin a perfect one-dimensional crystal, without the requirement of doping. Our\nmodel can be realized in present experiments with bosonic mixtures that feature\nsimple on-site interactions, clearing the path to the observation of\nsupersolidity.",
        "positive": "Metal-Mott Insulator Transition and Spin Exchange of Two-Component Fermi\n  Gas with Spin-Orbit Coupling in Two-Dimension Square Optical Lattices: Effects of spin-orbit coupling (SOC) on metal-Mott insulator transition\n(MMIT) and spin exchange physics (SEP) of two-component Fermi gases in\ntwo-dimension half-filling square optical lattices are investigated. In the\nframe of Kotliar and Ruckenstein slave boson and the second order perturbation\ntheory, the phase boundary of paramagnetic MMIT and spin exchange Hamiltonian\nare calculated. In addition by adopting two mean-field ansatzs including\nantiferromagnetic, ferromagnetic and spiral phases, we find that SOC can drive\na quantum phase transition from antiferromagnet to spiral phase."
    },
    {
        "anchor": "Ring solitons and soliton sacks in imbalanced fermionic systems: We show that in superfluids with fermionic imbalance and uniform ground\nstate, there are stable solitons. These solutions are formed of radial density\nmodulations resulting in nodal rings. We demonstrate that these solitons\nexhibit nontrivial soliton-soliton and soliton-vortex interactions and can form\ncomplicated bound states in the form of \"soliton sacks\". In a phase-modulating\n(Fulde-Ferrell) background, we find different solitonic states, in the form of\nstable vortex-antivortex pairs.",
        "positive": "Nonequilibrium quantum thermodynamics of determinantal many-body\n  systems: Application to the Tonks-Girardeau and ideal Fermi gases: We develop a general approach for calculating the characteristic function of\nthe work distribution of quantum many-body systems in a time-varying potential,\nwhose many-body wave function can be cast in the Slater determinant form. Our\nresults are applicable to a wide range of systems including an ideal gas of\nspinless fermions in one dimension (1D), the Tonks-Girardeau (TG) gas of\nhard-core bosons, as well as a 1D gas of hard-core anyons. In order to\nillustrate the utility of our approach, we focus on the TG gas confined to an\narbitrary time-dependent trapping potential. In particular, we use the\ndeterminant representation of the many-body wave function to characterize the\nnonequilibrium thermodynamics of the TG gas and obtain exact and\ncomputationally tractable expressions---in terms of Fredholm determinants---for\nthe mean work, the work probability distribution function, the nonadiabaticity\nparameter, and the Loschmidt amplitude. When applied to a harmonically trapped\nTG gas, our results for the mean work and the nonadiabaticity parameter reduce\nto those derived previously using an alternative approach. We next propose to\nuse periodic modulation of the trap frequency in order to drive the system to\nhighly non-equilibrium states by taking advantage of the phenomenon of\nparametric resonance. Under such driving protocol, the nonadiabaticity\nparameter may reach large values, which indicates a large amount of\nirreversible work being done on the system as compared to sudden quench\nprotocols considered previously. This scenario is realizable in ultracold atom\nexperiments, aiding fundamental understanding of all thermodynamic properties\nof the system."
    },
    {
        "anchor": "Spin-orbit-coupled Bose-Einstein condensates of rotating polar molecules: An experimental proposal for realizing spin-orbit (SO) coupling of\npseudospin-1 in the ground manifold $^1\\Sigma(\\upsilon=0)$ of (bosonic)\nbialkali polar molecules is presented. The three spin components are composed\nof the ground rotational state and two substates from the first excited\nrotational level. Using hyperfine resolved Raman processes through two select\nexcited states resonantly coupled by a microwave, an effective coupling between\nthe spin tensor and linear momentum is realized. The properties of\nBose-Einstein condensates for such SO-coupled molecules exhibiting dipolar\ninteractions are further explored. In addition to the SO-coupling-induced\nstripe structures, the singly and doubly quantized vortex phases are found to\nappear, implicating exciting opportunities for exploring novel quantum physics\nusing SO-coupled rotating polar molecules with dipolar interactions.",
        "positive": "Quench Dynamics of the Anisotropic Heisenberg Model: We develop an analytic approach for the study of the quench dynamics of the\nanisotropic Heisenberg model (XXZ model) on the infinite line. We present the\nexact time-dependent wavefunctions after a quench in an integral form for any\ninitial state and for any anisotropy $\\Delta$ by means of a generalized Yudson\ncontour representation. We calculate the evolution of several observables from\ntwo particular initial states: starting with a local N\\`eel state we calculate\nthe time evolution of the antiferromagnetic order parameter--staggered\nmagnetization; starting with a state with consecutive flipped spins we\ncalculate the propagation of magnons and bound state excitations, and the\ninduced spin currents. We also show how the \"string\" solution of Bethe Ansatz\nequations emerge naturally from the contour approach. We confront our results\nwith experiments and numerical methods where possible."
    },
    {
        "anchor": "Off-resonant many-body quantum carpets in strongly tilted optical\n  lattices: An unit filling Bose-Hubbard Hamilonian embedded in strong Stark field is\nstudied in the off-resonant regime inhibiting single and many-particle first\norder tunneling resonances. We investigate the occurrence of coherent dipole\nwave-like propagation along of an optical lattice by means of an effective\nHamiltonian accounting for second order tunneling processes. It is shown that\ndipole wavefunction evolution in the short-time limit is ballistic and that\nfinite size effects induce dynamical self-interference patterns known as\nquantum carperts. We also present the effects of the border right after the\nfirst reflection showing that the wavefunction diffuses normally with the\nvariance changing linearly in time. This work extends the rich physical\nphenomenology of the tilted one dimensional lattice systems in a scenario of\nmany interacting quantum particles, the so-called many-body Wannier-Stark\nsystem.",
        "positive": "Mass-ratio condition for non-binding of three two-component particles\n  with contact interactions: Binding of two heavy fermions interacting with a light particle via the\ncontact interaction is possible only for sufficiently large heavy-light mass\nratio. In this work, the two-variable inequality is derived to determine a\nspecific value $ \\mu^* $ providing that there are no three-body bound states\nfor the mass ratio smaller than $ \\mu^* $. The value $ \\mu^* = 5.26 $ is\nobtained by analyzing this inequality for a total angular momentum and parity $\nL^P = 1^- $. For other $ L^P $ sectors, the specific mass-ratio values\nproviding an absence of the three-body bound states are found in a similar way.\nFor generality, the method is extended to determine corresponding mass-ratio\nvalues for the system consisting of two identical bosons and a distinct\nparticle for different $ L^P $ ($ L > 0 $) sectors."
    },
    {
        "anchor": "Driven-dissipative Ising model: Dynamical crossover at weak dissipation: Driven quantum systems coupled to an environment typically exhibit\neffectively thermal behavior with relaxational dynamics near criticality.\nHowever, a different qualitative behavior might be expected in the weakly\ndissipative limit due to the competition between coherent dynamics and weak\ndissipation. In this work, we investigate a driven-dissipative infinite-range\nIsing model in the presence of individual atomic dissipation, a model that\nemerges from the paradigmatic open Dicke model in the large-detuning limit. We\nshow that the system undergoes a dynamical crossover from relaxational\ndynamics, with a characteristic dynamical exponent $\\zeta=1/2$, to underdamped\ncritical dynamics governed by the exponent $\\zeta=1/4$ in the weakly\ndissipative regime; a behavior that is markedly distinct from that of\nequilibrium. Finally, utilizing an exact diagrammatic representation, we\ndemonstrate that the dynamical crossover to underdamped criticality is not an\nartifact of the mean-field nature of the model and persists even in the\npresence of short-range perturbations.",
        "positive": "Simple atom interferometer in a double-well potential: We present a detailed study of an atom interferometer which can be realized\nin a double-well potential. We assume that the interferometric phase is\nimprinted in the presence of coherent tunneling between the wells. We calculate\nthe ultimate bounds for the estimation sensitivity and show how they relate to\nthe precision of the Mach-Zehnder interferometer. The interferometer presented\nhere allows for sub shot-noise sensitivity when fed with the spin-squeezed\nstates with reduced either the relative population imbalance or the relative\nphase. We also calculate the precision of the estimation from the population\nimbalance and show that it overcomes the shot-noise level when the entangled\nsqueezed-states are used at the input."
    },
    {
        "anchor": "Probing the scale invariance of the inflationary power spectrum in\n  expanding quasi-two-dimensional dipolar condensates: We consider an analogue de Sitter cosmos in an expanding\nquasi-two-dimensional Bose-Einstein condensate with dominant dipole-dipole\ninteractions between the atoms or molecules in the ultracold gas. It is\ndemonstrated that a hallmark signature of inflationary cosmology, the scale\ninvariance of the power spectrum of inflaton field correlations, experiences\nstrong modifications when, at the initial stage of expansion, the excitation\nspectrum displays a roton minimum. Dipolar quantum gases thus furnish a viable\nlaboratory tool to experimentally investigate, with well-defined and\ncontrollable initial conditions, whether primordial oscillation spectra\ndeviating from Lorentz invariance at trans-Planckian momenta violate standard\npredictions of inflationary cosmology.",
        "positive": "Floquet symmetry-protected topological phases in cold atomic systems: We propose and analyze two distinct routes toward realizing interacting\nsymmetry-protected topological (SPT) phases via periodic driving. First, we\ndemonstrate that a driven transverse-field Ising model can be used to engineer\ncomplex interactions which enable the emulation of an equilibrium SPT phase.\nThis phase remains stable only within a parametric time scale controlled by the\ndriving frequency, beyond which its topological features break down. To\novercome this issue, we consider an alternate route based upon realizing an\nintrinsically Floquet SPT phase that does not have any equilibrium analog. In\nboth cases, we show that disorder, leading to many-body localization, prevents\nrunaway heating and enables the observation of coherent quantum dynamics at\nhigh energy densities. Furthermore, we clarify the distinction between the\nequilibrium and Floquet SPT phases by identifying a unique micromotion-based\nentanglement spectrum signature of the latter. Finally, we propose a unifying\nimplementation in a one-dimensional chain of Rydberg-dressed atoms and show\nthat protected edge modes are observable on realistic experimental time scales."
    },
    {
        "anchor": "Level statistics of the one-dimensional ionic Hubbard model: In this work we analyze the spectral level statistics of the one-dimensional\nionic Hubbard model, the Hubbard model with an alternating on-site potential.\nIn particular, we focus on the statistics of the gap ratios between consecutive\nenergy levels. This quantity is often used in order to signal whether a\nmany-body system is integrable or chaotic. A chaotic system has typically the\nstatistics of a Gaussian ensemble of random matrices while the spectral\nproperties of the integrable system follow a Poisson statistics. We find that\nwhereas the Hubbard model without alternating potential is known to be\nintegrable and its spectral properties follow a Poissonian statistics, the\npresence of an alternating potential causes a drastic change in the spectral\nproperties which resemble the one of a Gaussian ensemble of random matrices.\nHowever, to uncover this behavior one has to separately consider the blocks of\nall symmetries of the ionic Hubbard model.",
        "positive": "Neural-network quantum states for a two-leg Bose-Hubbard ladder under\n  magnetic flux: Quantum gas systems are ideal analog quantum simulation platforms for\ntackling some of the most challenging problems in strongly correlated quantum\nmatter. However, they also expose the urgent need for new theoretical\nframeworks. Simple models in one dimension, well studied with conventional\nmethods, have received considerable recent attention as test cases for new\napproaches. Ladder models provide the logical next step, where established\nnumerical methods are still reliable, but complications of higher dimensional\neffects like gauge fields can be introduced. In this paper, we investigate the\napplication of the recently developed neural-network quantum states in the\ntwo-leg Bose-Hubbard ladder under strong synthetic magnetic fields. Based on\nthe restricted Boltzmann machine and feedforward neural network, we show that\nvariational neural networks can reliably predict the superfluid-Mott insulator\nphase diagram in the strong coupling limit comparable with the accuracy of the\ndensity-matrix renormalization group. In the weak coupling limit, neural\nnetworks also diagnose other many-body phenomena such as the vortex, chiral,\nand biased-ladder phases. Our work demonstrates that the two-leg Bose-Hubbard\nmodel with magnetic flux is an ideal test ground for future developments of\nneural-network quantum states."
    },
    {
        "anchor": "Spin modulation instabilities and phase separation dynamics in trapped\n  two-component Bose condensates: In the study of trapped two-component Bose gases, a widely used dynamical\nprotocol is to start from the ground state of a one-component condensate and\nthen switch half the atoms into another hyperfine state. The slightly different\nintra-component and inter-component interactions can then lead to highly\nnontrivial dynamics. We study and classify the possible subsequent dynamics,\nover a wide variety of parameters spanned by the trap strength and by the\ninter- to intra-component interaction ratio. A stability analysis suited to the\ntrapped situation provides us with a framework to explain the various types of\ndynamics in different regimes.",
        "positive": "Symmetry-induced many-body quantum interference in chaotic bosonic\n  systems: an augmented Truncated Wigner method: Although highly successful, the Truncated Wigner Approximation (TWA) does not\naccount for genuine many-body quantum interference between different solutions\nof the mean-field equations of a bosonic many-body (MB) system. This renders\nthe TWA essentially classical, where a large number of particles formally takes\nthe role of the inverse of Planck's constant $\\hbar$. The failure to describe\ngenuine interference phenomena, such as localization and scarring in Fock\nspace, can be seen as a virtue of this quasiclassical method, which thereby\nallows one to identify genuine quantum effects when being compared with \"exact\"\nquantum calculations that do not involve any a priori approximation. A rather\nprominent cause for such quantum effects that are not accounted for by the TWA\nis the constructive interference between the contributions of symmetry-related\ntrajectories, which would occur in the presence of discrete symmetries provided\nthe phase-space distribution of the initial state and the observable to be\nevaluated feature a strong localization about the corresponding symmetry\nsubspaces. Here we show how one can conceive an augmented version of the TWA\nwhich can account for this particular effect. This augmented TWA effectively\namounts to complementing conventional TWA calculations by separate Truncated\nWigner simulations that are restricted to symmetric subspaces and involve\nweight factors that account for the dynamical stability of sampling\ntrajectories with respect to perpendicular deviations from those subspaces. We\nillustrate the validity of this method at pre- as well as post-Ehrenfest time\nscales in prototypical Bose-Hubbard systems displaying chaotic classical\ndynamics, where it also reveals the existence of additional MB interference\neffects."
    },
    {
        "anchor": "Scissors mode of dipolar quantum droplets of dysprosium atoms: We report on the observation of the scissors mode of a single dipolar quantum\ndroplet. The existence of this mode is due to the breaking of the rotational\nsymmetry by the dipole-dipole interaction, which is fixed along an external\nhomogeneous magnetic field. By modulating the orientation of this magnetic\nfield, we introduce a new spectroscopic technique for studying dipolar quantum\ndroplets. This provides a precise probe for interactions in the system allowing\nto extract a background scattering length for \\textsuperscript{164}Dy of\n$69(4)\\,a_0$. Our results establish an analogy between quantum droplets and\natomic nuclei, where the existence of the scissors mode is also only due to\ninternal interactions. They further open the possibility to explore physics\nbeyond the available theoretical models for strongly-dipolar quantum gases.",
        "positive": "Creating State-Dependent Lattices for Ultracold Fermions by Magnetic\n  Gradient Modulation: We demonstrate a versatile method to create state-dependent optical lattices\nby applying a magnetic field gradient modulated in time. This allows for tuning\nthe relative amplitude and sign of the tunnelling for different internal\nstates. We observe substantially different momentum distributions depending on\nthe spin-state of fermionic 40K atoms. Using dipole-oscillations we probe the\nspin-dependent band structure and find good agreement with theory. In-situ\nexpansion-dynamics demonstrate that one state can be completely localized\nwhilst others remain itinerant. A systematic study shows negligible heating and\nlifetimes of several seconds in the Hubbard regime."
    },
    {
        "anchor": "Mechanism of collisionless sound damping in dilute Bose gas with\n  condensate: We develop a microscopic theory of sound damping due to Landau mechanism in\ndilute gas with Bose condensate. It is based on the coupled evolution equations\nof the parameters describing the system. These equations have been derived in\nearlier works within a microscopic approach which employs the\nPeletminskii-Yatsenko reduced description method for quantum many-particle\nsystems and Bogoliubov model for a weakly nonideal Bose gas with a separated\ncondensate. The dispersion equations for sound oscillations were obtained by\nlinearization of the mentioned evolution equations in the collisionless\napproximation. They were analyzed both analytically and numerically. The\nexpressions for sound speed and decrement rate were obtained in high and low\ntemperature limiting cases. We have shown that at low temperature the\ndependence of the obtained quantities on temperature significantly differs from\nthose obtained by other authors in the semi-phenomenological approaches.\nPossible effects connected with non-analytic temperature dependence of\ndispersion characteristics of the system were also indicated.",
        "positive": "Forming doublons by a quantum quench: Repulsive interactions between particles on a lattice may lead to bound\nstates, so called doublons. Such states may be created by dynamically tuning\nthe interaction strength, e.g. using a Feshbach resonance, from attraction to\nrepulsion. We study the doublon production efficiency as a function of the\ntuning rate at which the on-site interaction is varied. An expectation based on\nthe Landau- Zener law suggests that exponentially few doublons are created in\nthe adiabatic limit. Contrary to such an expectation, we found that the number\nof produced doublons scales as a power law of the tuning rate with the exponent\ndependent on the dimensionality of the lattice. The physical reason for this\nanomaly is the effective decoupling of doublons from the two-particle continuum\nfor center of mass momenta close to the corners of the Brillouin zone. The\nstudy of doublon production may be a sensitive tool to extract detailed\ninformation about the band structure."
    },
    {
        "anchor": "Quantum Zeno suppression of three-body losses in Bose-Einstein\n  condensates: We study the possibility of suppressing three-body losses in atomic\nBose-Einstein condensates via the quantum Zeno effect, which means the delay of\nquantum evolution by frequent measurements. It turns out that this requires\nvery fast measurements with the rate being determined by the spatial structure\nof the three-body form factor, i.e., the point interaction approximation\n$\\delta^3(\\mathbf{r}-\\mathbf{r'})$ is not adequate. Since the molecular binding\nenergy $E_b$ provides a natural limit for the measurement rate, this\nsuppression mechanism can only work if the form factor possesses certain\nspecial properties.",
        "positive": "Mechanism of stimulated Hawking radiation in a laboratory Bose-Einstein\n  condensate: We model a sonic black hole analog in a quasi one-dimensional Bose-Einstein\ncondensate, using a Gross-Pitaevskii equation matching the configuration of a\nrecent experiment by Steinhauer [Nat. Phys. 10, 864 (2014)]. The model agrees\nwell with important features of the experimental observations, demonstrating\ntheir hydrodynamic nature. We find that a zero-frequency bow wave is generated\nat the inner (white hole) horizon, which grows in proportion to the square of\nthe background condensate density. The relative motion of the black and white\nhole horizons produces a Doppler shift of the bow wave at the black hole, where\nit stimulates the emission of monochromatic Hawking radiation. The mechanism is\nconfirmed using temporal and spatial windowed Fourier spectra of the\ncondensate. Mean field behavior similar to that in the experiment can thus be\nfully explained without the presence of self-amplifying Hawking radiation."
    },
    {
        "anchor": "Quantum Boltzmann equation for a mobile impurity in a degenerate\n  Tonks-Girardeau gas: We investigate the large-time asymptotical behavior of a mobile impurity\nimmersed in a degenerate Tonks-Girardeau gas. We derive a correct weak-coupling\nkinetic equation valid for arbitrary ratio of masses of gas and impurity\nparticles. When gas particles are either lighter or heavier than the impurity\nwe find that our theory is equivalent to the Boltzmann theory with the\ncollision integral calculated via the Fermi Golden Rule. On the contrary, in\nthe equal-mass case, Fermi Golden Rule treatment gives false results due to not\naccounting for multiple coherent scattering events. The latter are treated by\nthe ressummation of ladder diagrams, which leads to a new kinetic equation. The\nasymptotic momentum of the impurity produced from this equation coincides with\nthe result obtained by means of the Bethe ansatz.",
        "positive": "Thermalization and Bose-Einstein condensation of quantum light in bulk\n  nonlinear media: We study the thermalization and the Bose-Einstein condensation of a paraxial,\nspectrally narrow beam of quantum light propagating in a lossless bulk Kerr\nmedium. The spatiotemporal evolution of the quantum optical field is ruled by a\nHeisenberg equation analogous to the quantum nonlinear Schr\\\"odinger equation\nof dilute atomic Bose gases. Correspondingly, in the weak-nonlinearity regime,\nthe phase-space density evolves according to the Boltzmann equation.\nExpressions for the thermalization time and for the temperature and the\nchemical potential of the eventual Bose-Einstein distribution are found. After\ndiscussing experimental issues, we introduce an optical setup allowing the\nevaporative cooling of a guided beam of light towards Bose-Einstein\ncondensation. This might serve as a novel source of coherent light."
    },
    {
        "anchor": "Bose-Einstein condensation in two-dimensional traps: In two-dimensional traps, since the theoretical study of Bose-Einstein\ncondensation (BEC) will encounter the problem of divergence, the actual\ncontribution of the divergent terms is often estimated in some indirect ways\nwith the accuracy to the leading order. In this paper, by using an analytical\ncontinuation method to solve the divergence problem, we obtain the analytical\nexpressions of critical temperature and condensate fraction for Bose gases in a\ntwo-dimensional anisotropic box and harmonic trap, respectively. They are\nconsistent with or better than previous studies. Then, we further consider the\nnonvanishing chemical potential, and obtain the expressions of chemical\npotential and more precise condensate fraction. These results agree with the\nnumerical calculation well, especially for the case of harmonic traps. The\ncomparison between the grand canonical and canonical ensembles shows that our\ncalculation in the grand canonical ensemble is reliable.",
        "positive": "Eigenspectrum, Chern Numbers and Phase Diagrams of Ultracold Color-orbit\n  Coupled SU(3) Fermions in Optical Lattices: We study ultracold color fermions with three internal states Red, Green and\nBlue with ${\\rm SU(3)}$ symmetry in optical lattices, when color-orbit coupling\nand color-flip fields are present. This system corresponds to a generalization\nof two-internal state fermions with ${\\rm SU(2)}$ symmetry in the presence of\nspin-orbit coupling and spin-flipping Zeeman fields. We investigate the\neigenspectrum and Chern numbers to describe different topological phases that\nemerge in the phase diagrams of color-orbit coupled fermions in optical\nlattices. We obtain the phases as a function of artificial magnetic,\ncolor-orbit and color-flip fields that can be independently controlled. For\nfixed artificial magnetic flux ratio, we identify topological quantum phases\nand phase transitions in the phase diagrams of chemical potential versus\ncolor-flip fields or color-orbit coupling, where the chirality and number of\nmidgap edge states changes. The topologically non-trivial phases are classified\nin three groups: the first group has total non-zero chirality and exhibit only\nthe quantum charge Hall effect; the second group has total non-zero chirality\nand exhibit both quantum charge and quantum color Hall effects; and the third\ngroup has total zero chirality, but exhibit the quantum color Hall effect.\nThese phases are generalizations of the quantum Hall and quantum spin Hall\nphases for charged spin-$1/2$ fermions. Lastly, we also describe the color\ndensity of states and a staircase structure in the total and color filling\nfactors versus chemical potential for fixed color-orbit, color-flip and\nmagnetic flux ratio. We show the existence of incompressible states at rational\nfilling factors precisely given by a gap-labelling theorem that relates the\nfilling factors to the magnetic flux ratio and topological quantum numbers."
    },
    {
        "anchor": "Energy of strongly attractive Bose-Fermi mixtures: We discuss how approximate theories for Bose-Fermi mixtures recover in the\nmolecular limit the expected expression for Fermi-Fermi mixtures of molecules\nand unpaired fermions. In particular, we compare the energy of the system\nresulting from a T-matrix diagrammatic approach with that obtained with\nVariational and Fixed-Node Diffusion Quantum Monte Carlo methods.",
        "positive": "Hydrodynamic tails and a fluctuation bound on the bulk viscosity: We study the small frequency behavior of the bulk viscosity spectral function\nusing stochastic fluid dynamics. We obtain a number of model independent\nresults, including the long-time tail of the bulk stress correlation function,\nand the leading non-analyticity of the spectral function at small frequency. We\nalso establish a lower bound on the bulk viscosity which is weakly dependent on\nassumptions regarding the range of applicability of fluid dynamics. The bound\non the bulk viscosity $\\zeta$ scales as $\\zeta_{\\it min} \\sim\n(P-\\frac{2}{3}{\\cal E})^2 \\sum_i D_i^{-2}$, where $D_i$ are the diffusion\nconstants for energy and momentum, and $P-\\frac{2}{3}{\\cal E}$, where $P$ is\nthe pressure and ${\\cal E}$ is the energy density, is a measure of scale\nbreaking. Applied to the cold Fermi gas near unitarity, $|\\lambda/a_s|\\geq 1$\nwhere $\\lambda$ is the thermal de Broglie wave length and $a_s$ is the $s$-wave\nscattering length, this bound implies that the ratio of bulk viscosity to\nentropy density satisfies $\\zeta/s \\geq 0.1\\hbar/k_B$. Here, $\\hbar$ is\nPlanck's constant and $k_B$ is Boltzmann's constant."
    },
    {
        "anchor": "Strongly Interacting Isotopic Bose-Fermi Mixture Immersed in a Fermi Sea: We have created a triply quantum degenerate mixture of bosonic $^{41}$K and\ntwo fermionic species $^{40}$K and $^6$Li. The boson is shown to be an\nefficient coolant for the two fermions, spurring hopes for the observation of\nfermionic superfluids with imbalanced masses. We observe multiple heteronuclear\nFeshbach resonances, in particular a wide s-wave resonance for the combination\n$^{41}$K-$^{40}$K, opening up studies of strongly interacting {\\it isotopic}\nBose-Fermi mixtures. For large imbalance, we enter the polaronic regime of\ndressed impurities immersed in a bosonic or fermionic bath.",
        "positive": "Fundamental Limits of Feedback Cooling Ultracold Atomic Gases: We investigate the fundamental viability of cooling ultracold atomic gases\nwith quantum feedback control. Our study shows that the trade-off between the\nresolution and destructiveness of optical imaging techniques imposes\nconstraints on the efficacy of feedback cooling, and that rapid\nrethermalization is necessary for cooling thermal gases. We construct a simple\nmodel to determine the limits to feedback cooling set by the visibility of\ndensity fluctuations, measurement-induced heating, and three-body atomic\nrecombination. We demonstrate that feedback control can rapidly cool\nhigh-temperature thermal clouds in quasi-2D geometries to degenerate\ntemperatures with minimal atom loss compared to traditional evaporation. Our\nanalysis confirms the feasibility of feedback cooling ultracold atomic gases,\nproviding a pathway to new regimes of cooling not achievable with current\napproaches."
    },
    {
        "anchor": "3D quaternionic condensations, Hopf invariants, and skyrmion lattices\n  with synthetic spin-orbit coupling: We study the topological configurations of the two-component condensates of\nbosons with the $3$D $\\vec{\\sigma}\\cdot \\vec{p}$ Weyl-type spin-orbit coupling\nsubject to a harmonic trapping potential. The topology of the condensate\nwavefunctions manifests in the quaternionic representation. In comparison to\nthe $U(1)$ complex phase, the quaternionic phase manifold is $S^3$ and the spin\norientations form the $S^2$ Bloch sphere through the 1st Hopf mapping. The\nspatial distributions of the quaternionic phases exhibit the 3D skyrmion\nconfigurations, and the spin distributions possess non-trivial Hopf invariants.\nSpin textures evolve from the concentric distributions at the weak spin-orbit\ncoupling regime to the rotation symmetry breaking patterns at the intermediate\nspin-orbit coupling regime. In the strong spin-orbit coupling regime, the\nsingle-particle spectra exhibit the Landau-level type quantization. In this\nregime, the three-dimensional skyrmion lattice structures are formed when\ninteractions are below the energy scale of Landau level mixings. Sufficiently\nstrong interactions can change condensates into spin-polarized plane-wave\nstates, or, superpositions of two plane-waves exhibiting helical spin spirals.",
        "positive": "Superfluidity and Chaos in low dimensional circuits: The hallmark of superfluidity is the appearance of \"vortex states\" carrying a\nquantized metastable circulating current. Considering a unidirectional flow of\nparticles in a ring, at first it appears that any amount of scattering will\nrandomize the velocity, as in the Drude model, and eventually the ergodic\nsteady state will be characterized by a vanishingly small fluctuating current.\nHowever, Landau and followers have shown that this is not always the case. If\nelementary excitations (e.g. phonons) have higher velocity than that of the\nflow, simple kinematic considerations imply metastability of the vortex state:\nthe energy of the motion cannot dissipate into phonons. On the other hand if\nthis Landau criterion is violated the circulating current can decay. Below we\nshow that the standard Landau and Bogoliubov superfluidity criteria fail in\nlow-dimensional circuits. Proper determination of the superfluidity\nregime-diagram must account for the crucial role of chaos, an ingredient\nmissing from the conventional stability analysis. Accordingly, we find novel\ntypes of superfluidity, associated with irregular or chaotic or breathing\nvortex states."
    },
    {
        "anchor": "Fragile fate of driven-dissipative XY phase in two dimensions: Driven-dissipative systems define a broad class of non-equilibrium systems\nwhere an external drive (e.g. laser) competes with a dissipative environment.\nThe steady state of dynamics is generically distinct from a thermal state\ncharacteristic of equilibrium. As a representative example, a\ndriven-dissipative system with a continuous symmetry is generically disordered\nin two dimensions in contrast with the well-known algebraic order in\nequilibrium XY phases. In this paper, we study a 2D driven-dissipative model of\nweakly interacting bosons with a continuous $U(1)$ symmetry. Our aim is\ntwo-fold: First, we show that an effectively equilibrium XY phase emerges\ndespite the driven nature of the model, and that it is protected by a natural\n${\\mathbb Z}_2$ symmetry of the dynamics. Second, we argue that this phase is\nunstable against symmetry-breaking perturbations as well as static disorder,\nwhose mechanism in most cases has no analog in equilibrium. In the language of\nrenormalization group theory, we find that, outside equilibrium, there are more\nrelevant directions away from the XY phase.",
        "positive": "Berry's Phase for Ultracold Atoms in an Accelerated Optical Lattice: Berry's phase is investigated for ultracold atoms in a frequency modulated\noptical lattice. It is shown that Berry's phase appears due to Bloch\noscillation and the periodic motion of the optical lattice. Particularly,\nBerry's phase for ultracold atoms under the gravitational force in an\noscillating tight-binding optical lattice is calculated analytically. It is\nfound that the Berry's phase depends linearly on the amplitude of the\noscillation of the optical lattice."
    },
    {
        "anchor": "Rotation of quantum impurities in the presence of a many-body\n  environment: We develop a microscopic theory describing a quantum impurity whose\nrotational degree of freedom is coupled to a many-particle bath. We approach\nthe problem by introducing the concept of an 'angulon' - a quantum rotor\ndressed by a quantum field - and reveal its quasiparticle properties using a\ncombination of variational and diagrammatic techniques. Our theory predicts\nrenormalisation of the impurity rotational structure, such as observed in\nexperiments with molecules in superfluid helium droplets, in terms of a\nrotational Lamb shift induced by the many-particle environment. Furthermore, we\ndiscover a rich many-body-induced fine structure, emerging in rotational\nspectra due to a redistribution of angular momentum within the quantum\nmany-body system.",
        "positive": "Fractional and Integer Vortex Dynamics in Strongly Coupled Two-component\n  Bose-Einstein Condensates from AdS/CFT Correspondence: In order to study the rotating strongly coupled Bose-Einstein\ncondensations(BEC), a holographic model defined in an AdS black hole that duals\nto a coupled two-component condensations in global $U(1)$ symmetry broken phase\nwith intercomponent coupling $\\eta$ and internal coherent coupling $\\epsilon$\nis proposed. By solving the dynamics of the model, we study the process of\nformation and also the crossover from fractional to integer vortex phases. With\nchanging only $\\eta$ from zero to a finite value, fractional vortex lattices\nundergo a transition from hexagon to square lattice and finally to vortex\nsheets. By continuing to turn on $\\epsilon$, we find that two fractional\nvortices in different components constitute dimers, and when $\\eta$ transcend a\ncritical value, multi-dimer like hexamer or tetramer made up of two and three\ndimers appear. As $\\epsilon$ keeps increasing, some dimers rotate to adjust\nthemselves and then constitute the lattice of integer vortices. Under an\ninitial conditions similar to an spinor BEC vortices dynamics experiment, the\nappearance of disordered turbulence is found in the process of fractional\nvortex generation, which matches the experimental observation. While in the\nformation process of integer vortices, the appearance of grooves is predicted."
    },
    {
        "anchor": "Radio-frequency driving of an attractive Fermi gas in a one-dimensional\n  optical lattice: We investigate the response to radio-frequency driving of an ultracold gas of\nattractively interacting fermions in a one-dimensional optical lattice. We\nstudy the system dynamics by monitoring the driving-induced population transfer\nto a third state, and the evolution of the momentum density and pair\ndistributions. Depending on the frequency of the radio-frequency field, two\ndifferent dynamical regimes emerge when considering the evolution of the third\nlevel population. One regime exhibits (off)resonant many-body oscillations\nreminiscent of Rabi oscillations in a discrete two-level system, while the\nother displays a strong linear rise. Within this second regime, we connect, via\nlinear response theory, the extracted transfer rate to the system\nsingle-particle spectral function, and infer the nature of the excitations from\nBethe ansatz calculations. In addition, we show that this radio-frequency\ntechnique can be employed to gain insights into this many-body system coupling\nmechanism away from equilibrium. This is done by monitoring the momentum\ndensity redistributions and the evolution of the pair correlations during the\ndrive. Capturing such non-equilibrium physics goes beyond a linear response\ntreatment, and is achieved here by conducting time-dependent matrix product\nstate simulations.",
        "positive": "Nonequilibrium dynamics of vortex arrest in a finite-temperature\n  Bose-Einstein condensate: We perform finite-temperature dynamical simulations of the arrest of a\nrotating Bose-Einstein condensate by a fixed trap anisotropy, using a\nHamiltonian classical-field method. We consider a quasi-two-dimensional\ncondensate containing a single vortex in equilibrium with a rotating thermal\ncloud. Introducing an elliptical deformation of the trapping potential leads to\nthe loss of angular momentum from the system. We identify the condensate and\nthe complementary thermal component of the nonequilibrium field, and compare\nthe evolution of their angular momenta and angular velocities. By varying the\ntrap anisotropy we alter the relative efficiencies of the vortex-cloud and\ncloud-trap coupling. For strong trap anisotropies the angular momentum of the\nthermal cloud may be entirely depleted before the vortex begins to decay. For\nweak trap anisotropies, the thermal cloud exhibits a long-lived steady state in\nwhich it rotates at an intermediate angular velocity."
    },
    {
        "anchor": "Quantum Rydberg Central Spin Model: We consider dynamics of a Rydberg impurity in a cloud of ultracold bosonic\natoms in which the Rydberg electron can undergo spin-changing collisions with\nsurrounding atoms. This system realizes a new type of the quantum impurity\nproblem that compounds essential features of the Kondo model, the Bose polaron,\nand the central spin model. To capture the interplay of the Rydberg-electron\nspin dynamics and the orbital motion of atoms, we employ a new variational\nmethod that combines an impurity-decoupling transformation with a Gaussian\nansatz for the bath particles. We find several unexpected features of this\nmodel that are not present in traditional impurity problems, including\ninteraction-induced renormalization of the absorption spectrum that eludes\nsimple explanations from molecular bound states, and long-lasting oscillations\nof the Rydberg-electron spin. We discuss generalizations of our analysis to\nother systems in atomic physics and quantum chemistry, where an electron\nexcitation of high orbital quantum number interacts with a spinful quantum\nbath.",
        "positive": "Effects of the non-parabolic kinetic energy on non-equilibrium polariton\n  condensates: In the study of non-equilibrium polariton condensates it is usually assumed\nthat the dispersion relation of polaritons is parabolic in nature. We show that\nconsidering the true non-parabolic kinetic energy of polaritons leads to\nsignificant changes in the behaviour of the condensate due to the curvature of\nthe dispersion relation and the possibility of transfer of energy to high\nwavenumber components in the condensate spatial profile. We present explicit\nsolutions for plane waves and linear excitations, and identify the differences\nin the theoretical predictions between the parabolic and non-parabolic\nmean-field models, showing the possibility of symmetry breaking in the latter.\nWe then consider the evolution of wavepackets and show that self-localisation\neffects may be observed due to the curvature of the dispersion relation.\nFinally, we revisit the dynamics of dark soliton trains and show that\nadditional localized density excitations may emerge in the dynamics due to the\nexcitation of high frequency components, mimicking the appearance of\nnear-bright solitary waves over short timescales."
    },
    {
        "anchor": "Equilibration and Generalized GGE in the Lieb Liniger gas: We study the nonequilibrium properties of the one dimensional Lieb Liniger\nmodel in the finite repulsion regime. Introducing a new version of the Yudson\nrepresentation applicable to finite size systems and appropriately taking the\ninfinite volume limit we are able to study equilibration of the Lieb Liniger\ngas in the thermodynamic limit. We provide a formalism to compute various\ncorrelation functions for highly non equilibrium initial states. We are able to\nfind explicit analytic expressions for the long time limit of the expectation\nof the density, density density and related correlation functions. We show that\nthe gas equilibriates to a diagonal ensemble which we show is equivalent to a\ngeneralized version of the GGE for sufficiently simple correlation functions,\nwhich in particular include density correlations.",
        "positive": "Perron-Frobenius theorem on the superfluid transition of an ultracold\n  Fermi gas: The Perron-Frobenius theorem is applied to identify the superfluid transition\nof a two-component Fermi gas with a zero-range s-wave interaction. According to\nthe quantum cluster expansion method of Lee and Yang, the grand partition\nfunction is expressed by the Lee-Yang contracted 0-graphs. A singularity of an\ninfinite series of ladder-type Lee-Yang contracted 0-graphs is analyzed. We\npoint out that the singularity is governed by the Perron-Frobenius eigenvalue\nof a certain primitive matrix which is defined in terms of the two-body cluster\nfunctions and the Fermi distribution functions. As a consequence, it is found\nthat there exists a unique fugacity at the phase transition point, which\nimplies that there is no fragmentation of Bose-Einstein condensates of dimers\nand Cooper pairs at the ladder-approximation level of Lee-Yang contracted\n0-graphs. An application to a Bose-Einstein condensate of strongly bounded\ndimers is also made."
    },
    {
        "anchor": "Squeezed Ground States in a Spin-1 Bose-Einstein Condensate: We generate spin squeezed ground states in an atomic spin-1 Bose-Einstein\ncondensate tuned nearthe quantum critical point between the polar and\nferromagnetic quantum phases of the interactingspin ensemble. In contrast to\ntypical non-equilibrium methods for preparing atomic squeezed statesby\nquenching through a quantum phase transition, squeezed ground states are\ntime-stationary andremain squeezed for the lifetime of the condensate. A\nsqueezed ground state with a metrologicalimprovement up to 6-8 dB and a\nconstant squeezing angle maintained over 2 s is demonstrated.",
        "positive": "Three Identical Fermions with Resonant p-wave Interactions in Two\n  Dimensions: A new kind of \"super-Efimov\" states of binding energies scaling as\n$\\ln|E_n|\\sim-e^{3n\\pi/4}$ were predicted by a field theory calculation for\nthree fermions with resonant $p$-wave interactions in two dimensions [Phys.\nRev. Lett. \\textbf{110}, 235301 (2013)]. However, the universality of these\n\"super-Efimov\" states has not been proved independently. In this Letter, we\nstudy the three fermion system through the hyperspherical formalism. Within the\nadiabatic approximation, we find that at $p$-wave resonances, the low energy\nphysics of states of angular momentum $\\ell=\\pm1$ crucially depends on the\nvalue of an emergent dimensionless parameter $Y$ determined by the detail of\nthe inter-particle potential. Only if $Y$ is exactly zero, the predicted\n\"super-Efimov\" states exist. If $Y>0$, the scaling of the bound states changes\nto $\\ln|E_n|\\sim-(n\\pi)^2/2Y$, while there are no shallow bound states if\n$Y<0$."
    },
    {
        "anchor": "Criticality and Phase Diagram of Quantum Long-Range $\\text{O(N)}$ models: Several recent experiments in atomic, molecular and optical systems motivated\na huge interest in the study of quantum long-range %spin systems. Our goal in\nthis paper is to present a general description of their critical behavior and\nphases, devising a treatment valid in $d$ dimensions, with an exponent\n$d+\\sigma$ for the power-law decay of the couplings in the presence of an\n$O(N)$ symmetry. By introducing a convenient ansatz for the effective action,\nwe determine the phase diagram for the $N$-component quantum rotor model with\nlong-range interactions, with $N=1$ corresponding to the Ising model. The phase\ndiagram in the $\\sigma-d$ plane shows a non trivial dependence on $\\sigma$. As\na consequence of the fact that the model is quantum, the correlation functions\nare anisotropic in the spatial and time coordinates for $\\sigma$ smaller than a\ncritical value and in this region the isotropy is not restored even at\ncriticality. Results for the correlation length exponent $\\nu$, the dynamical\ncritical exponent $z$ and a comparison with numerical findings for them are\npresented.",
        "positive": "Deep inelastic scattering on ultracold gases: We discuss Bragg scattering on both Bose and Fermi gases with strong\nshort-range interactions in the deep inelastic regime of large wave vector\ntransfer $q$, where the dynamic structure factor is dominated by a resonance\nnear the free-particle energy $\\hbar\\omega=\\varepsilon_{\\bf q}=\\hbar^2q^2/2m$.\nUsing a systematic short-distance expansion, the structure factor at high\nmomentum is shown to exhibit a nontrivial dependence on frequency characterized\nby two separate scaling regimes. First, for frequencies that differ from the\nsingle-particle energy by terms of order ${\\cal O}(q)$ (i.e., small deviations\ncompared to the single-particle energy), the dynamic structure factor is\ndescribed by the impulse approximation of Hohenberg and Platzman. Second,\ndeviations of order ${\\cal O}(q^2)$ (i.e., of the same order or larger than the\nsingle-particle energy) are described by the operator product expansion, with a\nuniversal crossover connecting both regimes. The scaling is consistent with a\nnumber of sum rules in the large momentum limit. Furthermore, we derive an\nexact expression for the shift and width of the single-particle peak at large\nmomentum due to interactions, thus extending a result by Beliaev [JETP 7, 299\n(1958)] for the low-density Bose gas to arbitrary values of the scattering\nlength $a$. The shift exhibits a maximum around $qa \\simeq 1$, which is\nconnected with a maximum in the static structure factor due to strong\nshort-range correlations. For Bose gases with moderate interaction strengths,\nthe theoretically predicted shift is consistent with the value observed by Papp\net al. [Phys. Rev. Lett. 101, 135301 (2008)]. Finally, we develop a\ndiagrammatic theory for the dynamic structure factor which accounts for the\ncorrelations beyond Bogoliubov theory and which covers the full range of\nmomenta and frequencies, showing the correct asymptotic scaling at large\nmomentum."
    },
    {
        "anchor": "Polaronic atom-trimer continuity in three-component Fermi gases: Recently it has been proposed that three-component Fermi gases may exhibit a\nnew type of crossover physics in which an unpaired Fermi sea of atoms smoothly\nevolves into that of trimers in addition to the ordinary BCS-BEC crossover of\ncondensed pairs. Here we study its corresponding polaron problem in which a\nsingle impurity atom of one component interacts with condensed pairs of the\nother two components with equal populations. By developing a variational\napproach in the vicinity of a narrow Feshbach resonance, we show that the\nimpurity atom smoothly changes its character from atom to trimer with\nincreasing the attraction and eventually there is a sharp transition to dimer.\nThe emergent polaronic atom-trimer continuity can be probed in ultracold atoms\nexperiments by measuring the impurity spectral function. Our novel crossover\nwave function properly incorporating the polaronic atom-trimer continuity will\nprovide a useful basis to further investigate the phase diagram of\nthree-component Fermi gases in more general situations.",
        "positive": "Delocalization effects, entanglement entropy and spectral collapse of\n  boson mixtures in a double well: We investigate the ground-state properties of a two-species condensate of\ninteracting bosons in a double-well potential. Each atomic species is described\nby a two-space-mode Bose-Hubbard model. The coupling of the two species is\ncontrolled by the interspecies interaction $W$. To analyze the ground state\nwhen $W$ is varied in both the repulsive ($W>0$) and the attractive ($W<0$)\nregime, we apply two different approaches. First we solve the problem\nnumerically i) to obtain an exact description of the ground-state structure and\nii ) to characterize its correlation properties by studying (the appropriate\nextensions to the present case of) the quantum Fisher information, the\ncoherence visibility and the entanglement entropy as functions of $W$. Then we\napproach analytically the description of the low-energy scenario by means of\nthe Bogoliubov scheme. In this framework the ground-state transition from\ndelocalized to localized species (with space separation for $W>0$, and mixing\nfor $W<0$) is well reproduced. These predictions are qualitatively corroborated\nby our numerical results. We show that such a transition features a spectral\ncollapse reflecting the dramatic change of the dynamical algebra of the\nfour-mode model Hamiltonian."
    },
    {
        "anchor": "Toward precision Fermi liquid theory in two dimensions: The ultra-cold and weakly-coupled Fermi gas in two spatial dimensions is\nstudied in an effective field theory framework. It has long been observed that\nuniversal corrections to the energy density to two orders in the interaction\nstrength do not agree with Monte Carlo simulations in the weak-coupling regime.\nHere, universal corrections to three orders in the interaction strength are\nobtained for the first time, and are shown to provide agreement between theory\nand simulation. Special consideration is given to the scale ambiguity\nassociated with the non-trivial renormalization of the singular contact\ninteractions. The isotropic superfluid gap is obtained to next-to-leading\norder, and nonuniversal contributions to the energy density due to effective\nrange effects, p-wave interactions and three-body forces are computed. Results\nare compared with precise Monte Carlo simulations of the energy density and the\ncontact in the weakly-coupled attractive and repulsive Fermi liquid regimes. In\naddition, the known all-orders sum of ladder and ring diagrams is compared with\nMonte Carlo simulations at weak coupling and beyond.",
        "positive": "A generalized Theory of Diffusion based on Kinetic Theory: We propose to use spin hydrodynamics, a two-fluid model of spin propagation,\nas a generalization of the diffusion equation. We show that in the dense limit\nspin hydrodynamics reduces to Fick's law and the diffusion equation. In the\nopposite limit spin hydrodynamics is equivalent to a collisionless Boltzmann\ntreatment of spin propagation. Spin hydrodynamics avoids unphysical effects\nthat arise when the diffusion equation is used to describe to a strongly\ninteracting gas with a dilute corona. We apply spin hydrodynamics to the\nproblem of spin diffusion in a trapped atomic gas. We find that the observed\nspin relaxation rate in the high temperature limit [Sommer et al., Nature 472,\n201 (2011)] is consistent with the diffusion constant predicted by kinetic\ntheory."
    },
    {
        "anchor": "On the momentum of solitons and vortex rings in a superfluid: This paper is devoted to the calculation of the momentum of localized\nexcitations, such as solitons and vortex rings, moving in a superfluid. The\ndirect calculation of the momentum by integration of the mass flux density\nresults in a badly-converging integral. I suggest a method for the\nrenormalization of the integral with the explicit separation of a term related\nto the vortex line. This term can be calculated explicitly and gives the main\ncontribution for the rings whose size is large compared to the healing length.\nI compare my method with the Jones and Roberts prescription for the\nrenormalization. I investigate the case of a uniform superfluid, and that of a\nsuperfluid in a cylindrical trap. I discuss the calculation of the jump in the\nphase of the order parameter and obtain a simple estimate for this jump for a\nlarge ring in the trap.",
        "positive": "Dynamic formation of quasicondensate and spontaneous vortices in a\n  strongly interacting Fermi gas: We report an experimental study of quench dynamics across the superfluid\ntransition temperature $T_c$ in a strongly interacting Fermi gas by ramping\ndown the trapping potential. The nonzero quasi-condensate number $N_0$ at\ntemperature significantly above $T_c$ in the unitary and the BEC regimes\nreveals the pseudogap physics. Below $T_c$, a rapid growth of $N_0$ is\naccompanied by spontaneous generation of tens of vortices. We observe a power\nlaw scaling of the vortex density versus the quasi-condensate formation time,\nconsistent with the Kibble-Zurek theory. Our work provides an example of\nstudying emerged many-body physics by quench dynamics and paves the way for\nstudying the quantum turbulence in a strongly interacting Fermi gas."
    },
    {
        "anchor": "Nonlinear resonant tunneling of Bose-Einstein condensates in tilted\n  optical lattices: We study the tunneling decay of a Bose-Einstein condensate out of tilted\noptical lattices within the mean-field approximation. We introduce a novel\nmethod to calculate also excited resonance eigenstates of the Gross-Pitaevskii\nequation, based on a grid relaxation procedure with complex absorbing\npotentials. This algorithm works efficiently in a wide range of parameters\nwhere established methods fail. It allows us to study the effects of the\nnonlinearity in detail in the regime of resonant tunneling, where the decay\nrate is enhanced by resonant coupling to excited unstable states.",
        "positive": "Pairing fluctuations and anisotropic pseudogap phenomenon in an\n  ultracold superfluid Fermi gas with plural $p$-wave superfluid phases: We investigate superfluid properties of a one-component Fermi gas with a\nuniaxially anisotropic $p$-wave pairing interaction, $U_x>U_y=U_z$ (where $U_i$\n($i=x,y,z)$ is a $p_i$-wave pairing interaction). This type of interaction is\nconsidered to be realized in a $^{40}$K Fermi gas. Including pairing\nfluctuations within a strong-coupling $T$-matrix theory, we determine the\n$p_x$-wave superfluid phase transition temperature $T^{p_x}_{\\rm c}$, as well\nas the other phase transition temperature $T_{\\rm c}^{p_x+ip_y}$ ($<T_{\\rm\nc}^{p_x}$), below which the superfluid order parameter has the $p_x+ip_y$-wave\nsymmetry. In the normal state near $T^{p_x}_{\\rm c}$, $p_x$-wave pairing\nfluctuations are shown to induce an anisotropic pseudogap phenomenon, where a\ndip structure in the angle-resolved density of states around $\\omega=0$ is the\nmost remarkable in the $p_x$ direction. In the $p_x$-wave superfluid phase\n($T_{\\rm c}^{p_x+ip_y}<T\\le T_{\\rm c}^{p_x}$), while the pseudogap in the $p_x$\ndirection continuously changes to the superfluid gap, the pseudogap in the\nperpendicular direction to the $p_x$ axis is found to continue developing,\nbecause of enhanced $p_y$-wave and $p_z$-wave pairing fluctuations around the\nnode of the $p_x$-wave superfluid order parameter. Since pairing fluctuations\nare always suppressed in the isotropic $s$-wave superfluid state, this\nphenomenon is peculiar to an unconventional Fermi superfluid with a nodal\nsuperfluid order parameter. Since the $p$-wave Fermi superfluid is the most\npromising non $s$-wave pairing state in an ultracold Fermi gas, our results\nwould contribute to understanding how the anisotropic pairing fluctuations, as\nwell as the existence of plural superfluid phases, affect many-body properties\nof this unconventional Fermi superfluid."
    },
    {
        "anchor": "Low-energy scatterings and pseudopotential of polarized quadrupoles: We investigate the low-energy scattering properties of two identical\nparticles interacting via the polarized quadrupolar interaction. It is shown\nthat a series of $s$- and $p$-wave resonances appear for identical bosons and\nfermions, respectively, as the strength of the quadrupolar interaction\nincreases. Interestingly, scattering resonances also appear on the generalized\nscattering length corresponding to the coupling between the $s$ and $d$ waves.\nThis observation inspires us to propose a new pseudopotential for the\nquadupolar interaction. We also explore the bound-state properties of two\nparticles in both free space and harmonic traps.",
        "positive": "Single-exposure absorption imaging of ultracold atoms using deep\n  learning: Absorption imaging is the most common probing technique in experiments with\nultracold atoms. The standard procedure involves the division of two frames\nacquired at successive exposures, one with the atomic absorption signal and one\nwithout. A well-known problem is the presence of residual structured noise in\nthe final image, due to small differences between the imaging light in the two\nexposures. Here we solve this problem by performing absorption imaging with\nonly a single exposure, where instead of a second exposure the reference frame\nis generated by an unsupervised image-completion autoencoder neural network.\nThe network is trained on images without absorption signal such that it can\ninfer the noise overlaying the atomic signal based only on the information in\nthe region encircling the signal. We demonstrate our approach on data captured\nwith a quantum degenerate Fermi gas. The average residual noise in the\nresulting images is below that of the standard double-shot technique. Our\nmethod simplifies the experimental sequence, reduces the hardware requirements,\nand can improve the accuracy of extracted physical observables. The trained\nnetwork and its generating scripts are available as an open-source repository\n(http://absDL.github.io/)."
    },
    {
        "anchor": "Breakdown of the Fermi polaron description near Fermi degeneracy at\n  unitarity: We theoretically investigate attractive Fermi polarons in three dimensions at\nfinite temperature and impurity concentration through the many-body T-matrix\ntheory and high-temperature virial expansion. By using the analytically\ncontinued impurity Green's function, we calculate the direct rf spectroscopy of\nattractive polarons in the unitary regime. Taking the peak value of the rf\nspectroscopy as the polaron energy and the full width half maximum as the\npolaron lifetime, we determine the temperature range of validity for the\nquasi-particle description of Fermi polarons in the unitary limit.",
        "positive": "Negative mass hydrodynamics in a Spin-Orbit--Coupled Bose-Einstein\n  Condensate: A negative effective mass can be realized in quantum systems by engineering\nthe dispersion relation. A powerful method is provided by spin-orbit coupling,\nwhich is currently at the center of intense research efforts. Here we measure\nan expanding spin-orbit coupled Bose-Einstein condensate whose dispersion\nfeatures a region of negative effective mass. We observe a range of dynamical\nphenomena, including the breaking of parity and of Galilean covariance,\ndynamical instabilities, and self-trapping. The experimental findings are\nreproduced by a single-band Gross-Pitaevskii simulation, demonstrating that the\nemerging features - shockwaves, soliton trains, self-trapping, etc. - originate\nfrom a modified dispersion. Our work also sheds new light on related phenomena\nin optical lattices, where the underlying periodic structure often complicates\ntheir interpretation."
    },
    {
        "anchor": "Cooling a Bose gas by three-body losses: We report the first demonstration of cooling by three-body losses in a Bose\ngas. We use a harmonically confined one-dimensional (1D) Bose gas in the\nquasi-condensate regime and, as the atom number decreases under the effect of\nthree-body losses, the temperature $T$ drops up to a factor four. The ratio\n$k_B T/(m c^2)$ stays close to 0.64, where $m$ is the atomic mass and $c$ the\nsound speed in the trap center. The dimensionless 1D interaction parameter\n$\\gamma$, evaluated at the trap center, spans more than two order of magnitudes\nover the different sets of data. We present a theoretical analysis for a\nhomogeneous 1D gas in the quasi-condensate regime, which predicts that the\nratio $k_B T/(mc^2)$ converges towards 0.6 under the effect of three-body\nlosses. More sophisticated theoretical predictions that take into account the\nlongitudinal harmonic confinement and transverse effects are in agreement\nwithin 30% with experimental data.",
        "positive": "Thermal Conductivity of an Ultracold Paramagnetic Bose Gas: We analytically derive the transport tensor of thermal conductivity in an\nultracold, but not yet quantum degenerate, gas of Bosonic lanthanide atoms\nusing the Chapman-Enskog procedure. The tensor coefficients inherit an\nanisotropy from the anisotropic collision cross section for these dipolar\nspecies, manifest in their dependence on the dipole moment, dipole orientation,\nand $s$-wave scattering length. These functional dependencies open up a pathway\nfor control of macroscopic gas phenomena via tuning of the microscopic atomic\ninteractions. As an illustrative example, we analyze the time evolution of a\ntemperature hot-spot which shows preferential heat diffusion orthogonal to the\ndipole orientation, a direct consequence of anisotropic thermal conduction."
    },
    {
        "anchor": "Magnetism in strongly interacting one-dimensional quantum mixtures: We consider two species of bosons in one dimension near the Tonks-Girardeau\nlimit of infinite interactions. For the case of equal masses and equal\nintraspecies interactions, the system can be mapped to a S=1/2 XXZ Heisenberg\nspin chain, thus allowing one to access different magnetic phases. Using a\npowerful ansatz developed for the two-component Fermi system, we elucidate the\nevolution from few to many particles for the experimentally relevant case of an\nexternal harmonic confinement. In the few-body limit, we already find clear\nevidence of both ferromagnetic and antiferromagnetic spin correlations as the\nratio of intraspecies and interspecies interactions is varied. Furthermore, we\nobserve the rapid emergence of symmetry-broken magnetic ground states as the\nparticle number is increased. We therefore demonstrate that systems containing\nonly a few bosons are an ideal setting in which to realize the highly\nsought-after itinerant ferromagnetic phase.",
        "positive": "Momentum correlations of a few ultra-cold bosons escaping from an open\n  well: The dynamical properties of a one-dimensional system of two and three bosons\nescaping from an open potential well are studied in terms of the momentum\ndistributions of particles. In the case of a two-boson system, it is shown that\nthe single- and two-particle momentum distributions undergo a specific\ntransition as the interaction strength is tuned through the point where\ntunneling switches from the pair tunneling to the sequential one.\nCharacteristic features in the momentum spectra can be used to quantitatively\ndetermine the participation of specific decay processes. A corresponding\nanalysis is also performed for the three-boson system, showing a scheme for\ngeneralizations to higher particle numbers. For completeness, the\ntime-dependent Tan's contact of the system is also examined and its dynamics is\nfound to undergo a similar transition. The results provide insight into the\ndynamics of decaying few-body systems and offer potential interest for\nexperimental research."
    },
    {
        "anchor": "Vortices and dynamics in trapped Bose-Einstein condensates: I review the basic physics of ultracold dilute trapped atomic gases, with\nemphasis on Bose-Einstein condensation and quantized vortices. The hydrodynamic\nform of the Gross-Pitaevskii equation (a nonlinear Schr{\\\"o}dinger equation)\nilluminates the role of the density and the quantum-mechanical phase. One\nunique feature of these experimental systems is the opportunity to study the\ndynamics of vortices in real time, in contrast to typical experiments on\nsuperfluid $^4$He. I discuss three specific examples (precession of single\nvortices, motion of vortex dipoles, and Tkachenko oscillations of a vortex\narray). Other unusual features include the study of quantum turbulence and the\nbehavior for rapid rotation, when the vortices form dense regular arrays.\nUltimately, the system is predicted to make a quantum phase transition to\nvarious highly correlated many-body states (analogous to bosonic quantum Hall\nstates) that are not superfluid and do not have condensate wave functions. At\npresent, this transition remains elusive. Conceivably, laser-induced synthetic\nvector potentials can serve to reach this intriguing phase transition.",
        "positive": "Analytical thermodynamics of a strongly attractive three-component Fermi\n  gas in one dimension: Ultracold three-component atomic Fermi gases in one dimension are expected to\nexhibit rich physics due to the presence of trions and different pairing\nstates. Quantum phase transitions from the trion state into a paired phase and\na normal Fermi liquid occur at zero temperature. We derive the analytical\nthermodynamics of strongly attractive three-component one-dimensional fermions\nwith SU(3) symmetry via the thermodynamic Bethe ansatz method in unequal Zeeman\nsplitting fields $H_1$ and $H_2$. We find explicitly that for low temperature\nthe system acts like either a two-component or a three-component\nTomonaga-Luttinger liquid dependent on the system parameters. The phase\ndiagrams for the chemical potential and specific heat are presented for\nillustrative values of the Zeeman splitting. We also demonstrate that crossover\nbetween different Tomonaga-Luttinger liquid phases evolve singular behaviour in\nspecific heat and entropy as the temperature tends to zero. Beyond\nTomonaga-Luttinger liquid physics, we obtain the equation of state which\nprovides a precise description of universal thermodynamics and quantum\ncriticality in three-component strongly attractive Fermi gases."
    },
    {
        "anchor": "Topological insulator and particle pumping in a one-dimensional shaken\n  optical lattice: We propose a simple method to simulate and detect topological insulators with\ncold atoms trapped in a one-dimensional bichromatic optical lattice subjected\nto a time-periodic modulation. The tight-binding form of this shaken system is\nequivalent to the periodically driven Aubry-Andre model. We demonstrate that\nthis model can be mapped into a two-dimensional Chern insulator model, whose\nenergy spectrum hosts a topological phase within an experimentally accessible\nparameter regime. By tuning the laser phase adiabatically, such one-dimensional\nsystem constitutes a natural platform to realize topological particle pumping.\nWe show that the Chern number characterizing the topological features of this\nsystem can be measured by detecting the density shift after one cycle of\npumping.",
        "positive": "Second sound in 2D Bose gas: from the weakly interacting to the strongly\n  interacting regime: Using Landau's theory of two-fluid hydrodynamics, we investigate first and\nsecond sound propagating in a two-dimensional Bose gas. We study the\ntemperature and interaction dependence of both sound modes and show that their\nbehaviour exhibits a deep qualitative change as the gas evolves from the weakly\ninteracting to the strongly interacting regime. Special emphasis is given to\nthe jump of both sounds at the Berezinskii-Kosterlitz-Thouless transition,\ncaused by the discontinuity of the superfluid density. We find that the\nexcitation of second sound through a density perturbation becomes weaker and\nweaker as the interaction strength increases as a consequence of the decrease\nof the thermal expansion coefficient. Our results can be relevant for future\nexperiments on the propagation of sound in the BEC side of the BCS-BEC\ncrossover of a 2D superfluid Fermi gas."
    },
    {
        "anchor": "Non-thermal fixed points: Universal dynamics far from equilibrium: In this article we give an overview of the concept of universal dynamics near\nnon-thermal fixed points in isolated quantum many-body systems. We outline a\nnon-perturbative kinetic theory derived within a Schwinger-Keldysh closed-time\npath-integral approach, as well as a low-energy effective field theory which\nenable us to predict the universal scaling exponents characterizing the time\nevolution at the fixed point. We discuss the role of wave-turbulent transport\nin the context of such fixed points and discuss universal scaling evolution of\nsystems bearing ensembles of (quasi) topological defects. This is rounded off\nby the recently introduced concept of prescaling as a generic feature of the\nevolution towards a non-thermal fixed point.",
        "positive": "Probabilistic Hysteresis in Integrable and Chaotic Isolated Hamiltonian\n  Systems: We propose currently feasible experiments using small, isolated systems of\nultracold atoms to investigate the effects of dynamical chaos in the\nmicroscopic onset of irreversibility. A control parameter is tuned past a\ncritical value, then back to its initial value; hysteresis appears as a finite\nprobability that the atoms fail to return to their initial state even when the\nparameter sweep is arbitrarily slow. We show that an episode of chaotic\ndynamics during part of the sweep time produces distinctive features in the\ndistribution of final states that will be clearly observable in experiments."
    },
    {
        "anchor": "2D Gapless Topological Superfluids Generated by Pairing Phases: We systematically investigate the ground state phase diagram and the finite\ntemperature phase transitions for a Rydberg-dressed Fermi gas loaded in a\nbilayer optical lattice. When an effective finite-ranged attraction is induced,\nour self-consistent mean-field calculation shows that the gapped topological (\n$p$-wave) superfluids in each layer are coupled together by the $s$-wave\npairing in an intermediate inter-layer distance with a spontaneously modulated\nphases between these two order parameters. The obtained ground state is a\ngapless topological superfluid with quantized topological charges\ncharacterizing the gapless points, leading to a zero energy flat band at the\nedges. Finally, we calculate the finite temperature phase diagrams of this\ntwo-dimensional gapless superfluid and observe two distinct critical\ntemperatures, demonstrating the fruitful many-body effects on a paired\ntopological superfluids.",
        "positive": "Real-Time Dynamics of an Impurity in an Ideal Bose Gas in a Trap: We investigate the behavior of a harmonically trapped system consisting of an\nimpurity in a dilute ideal Bose gas after the boson-impurity interaction is\nsuddenly switched on. As theoretical framework, we use a field theory approach\nin the space-time domain within the T-matrix approximation. We establish the\nform of the corresponding T-matrix and address the dynamical properties of the\nsystem. As a numerical application, we consider a simple system of a weakly\ninteracting impurity in one dimension where the interaction leads to\noscillations of the impurity density. Moreover, we show that the amplitude of\nthe oscillations can be driven by periodically switching the interaction on and\noff."
    },
    {
        "anchor": "From few to many bosons inside the unitary window: a transition between\n  universal to non-universal behavior: Universal behaviour in few-bosons systems close to the unitary limit, where\ntwo bosons become unbound, has been intensively investigated in recent years\nboth experimentally and theoretically. In this particular region, called the\nunitary window, details of the inter-particle interactions are not important\nand observables, such as binding energies, can be characterized by a few\nparameters. With an increasing number of particles the short-range repulsion,\npresent in all atomic, molecular or nuclear interactions, gradually induces\ndeviations from the universal behaviour. In the present letter we discuss for\nthe first time a simple way of incorporating non-universal behaviour through\none specific parameter which controls the smooth transition of the system from\nuniversal to non-universal regime. Using a system of $N$ helium atoms as an\nexample we calculate their ground state energies as trajectories within the\nunitary window and also show that the control parameters can be used to\ndetermine the energy per particle in homogeneous systems when $N \\rightarrow\n\\infty$.",
        "positive": "Concept of contact spectrum and its applications in atomic quantum Hall\n  states: A unique feature of ultracold atoms is the separation of length scales,\n$r_0\\ll k_F^{-1}$, where $k_F$ and $r_0$ are the Fermi momentum characterizing\nthe average particle distance and the range of interaction between atoms\nrespectively. For $s$-wave scattering, Shina Tan discovered that such\ndiluteness leads to universal relations, all of which are governed by contact,\namong a wide range of thermodynamic quantities. Here, we show that the concept\nof contact can be generalized to an arbitrary partial-wave scattering. Contact\nof all partial-wave scatterings form a contact spectrum, which establishes\nuniversal thermodynamic relations with notable differences from those in the\npresence of $s$-wave scattering alone. Moreover, such a contact spectrum has an\ninteresting connection with a special bipartite entanglement spectrum of atomic\nquantum Hall states, and enables an intrinsic probe of these highly correlated\nstates using two-body short-ranged correlations."
    },
    {
        "anchor": "Stability of rubidium molecules in the lowest triplet state: Experiments involving ultracold molecules require sufficiently long\nlifetimes, which can be very short for excited rovibrational states in the\nmolecular potentials. For alkali atoms such as rubidium, a lowest rovibrational\nmolecular state can both be found in the electronic singlet and triplet\nconfigurations. The molecular singlet ground state is absolutely stable.\nHowever, the lowest triplet state can decay to a deeper bound singlet molecule\ndue to a radiative decay mechanism that involves the interatomic spin-orbit\ninteraction. We investigate this mechanism, and find the lifetime of rubidium\nmolecules in the lowest triplet rovibrational state to be about 21 minutes.",
        "positive": "Normal form expansions and thermal decay rates of Bose-Einstein\n  condensates with short- and long-range interaction: The thermally induced coherent collapse of Bose-Einstein condensates at\nfinite temperature is the dominant decay mechanism near the critical scattering\nlength in condensates with at least partially attractive interaction. The\ncollapse dynamics out of the ground state is mediated by a transition state\nwhose properties determine the corresponding decay rate or lifetime of the\ncondensate. In this paper, we perform normal form expansions of the ground and\nthe transition state of condensates with short-range scattering interaction as\nwell as with anisotropic and long-range dipolar interaction in a variational\nframework. This method allows one to determine the local properties of these\nstates, i.e. their mean-field energy, their normal modes, the coupling between\ndifferent modes, and the structure of the reaction channel to any desired\norder. We discuss the physical interpretation of the transition state as a\ncertain density distribution of the atomic cloud and the behavior of the single\nnormal form contributions in dependence on the s-wave scattering length.\nMoreover, we investigate the convergence of the local normal form when using\nextended Gaussian variational approaches, and present the condensate's decay\nrate."
    },
    {
        "anchor": "Microscopy of the interacting Harper-Hofstadter model in the few-body\n  limit: The interplay of magnetic fields and interacting particles can lead to exotic\nphases of matter exhibiting topological order and high degrees of spatial\nentanglement. While these phases were discovered in a solid-state setting,\nrecent techniques have enabled the realization of gauge fields in systems of\nultracold neutral atoms, offering a new experimental paradigm for studying\nthese novel states of matter. This complementary platform holds promise for\nexploring exotic physics in fractional quantum Hall systems due to the\nmicroscopic manipulation and precision possible in cold atom systems. However,\nthese experiments thus far have mostly explored the regime of weak\ninteractions. Here, we show how strong interactions can modify the propagation\nof particles in a $2\\times N$, real-space ladder governed by the\nHarper-Hofstadter model. We observe inter-particle interactions affect the\npopulating of chiral bands, giving rise to chiral dynamics whose multi-particle\ncorrelations indicate both bound and free-particle character. The novel form of\ninteraction-induced chirality observed in these experiments demonstrates the\nessential ingredients for future investigations of highly entangled topological\nphases of many-body systems.",
        "positive": "Rotating Fulde-Ferrell-Larkin-Ovchinnikov state in cold Fermi gases: We study an effect of rotation on the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)\nstate of two component Fermi superfluid gases in a toroidal trap. We\ninvestigate a stability of the FFLO states in the quasi-one-dimensional regime\non the basis of the Bogoliubov-de Gennes equation. We find that two novel FFLO\nphases, i.e., the half quantum vortex state and the intermediate state of\nFulde-Ferrell (FF) state and Larkin-Ovchinnikov (LO) state, are stabilized by\nthe rotation. The phase diagram for the FF state, LO state, intermediate state,\nand half quantum vortex state is shown in both T-P plane and T-h plane. We\ndemonstrate characteristic features of these states, such as the order\nparameter, flux quantization, and local polarization. Several related works are\ndiscussed, and the advantages of cold Fermi gases are indicated."
    },
    {
        "anchor": "A Universal Trimer in a Three-Component Fermi Gas: We show that the recently measured magnetic field dependence of three-body\nloss in a three-component mixture of ultracold $^6$Li atoms [1,2] can be\nexplained by the presence of a universal trimer state. Previous work suggested\na universal trimer state as a probable explanation, yet failed to get good\nagreement between theory and experiment over the whole range of magnetic\nfields. For our description we adapt the theory of Braaten and Hammer [3] for\nthree identical bosons to the case of three distinguishable fermions by\ncombining the three scattering lengths $a_{12},$ $a_{23}$ and $a_{13}$ between\nthe three components to an effective interaction parameter $a_m$. We show that\ntaking into account a magnetic field variation of the lifetime of the trimer\nstate is essential to obtain a complete understanding of the observed decay\nrates.",
        "positive": "High Frequency Sound in a Unitary Fermi Gas: We present an experimental and theoretical study of the phonon mode in a\nunitary Fermi gas. Using two-photon Bragg spectroscopy, we measure excitation\nspectra at a momentum of approximately half the Fermi momentum, both above and\nbelow the superfluid critical temperature $T_\\mathrm{c}$. Below $T_\\mathrm{c}$,\nthe dominant excitation is the Bogoliubov-Anderson (BA) phonon mode, driven by\ngradients in the phase of the superfluid order parameter. The temperature\ndependence of the BA phonon is consistent with a theoretical model based on the\nquasiparticle random phase approximation in which the dominant damping\nmechanism is via collisions with thermally excited quasiparticles. As the\ntemperature is increased above $T_\\mathrm{c}$, the phonon evolves into a\nstrongly damped collisional mode, accompanied by an abrupt increase in spectral\nwidth. Our study reveals strong similarities between sound propagation in the\nunitary Fermi gas and liquid helium."
    },
    {
        "anchor": "Uncover band topology via quantized drift in two-dimensional Bloch\n  oscillations: We propose to measure band topology via quantized drift of Bloch oscillations\nin a two-dimensional Harper-Hofstadter lattice subjected to tilted fields in\nboth directions. When the difference between the two tilted fields is large,\nBloch oscillations uniformly sample all momenta, and hence the displacement in\neach direction tends to be quantized at multiples of the overall period,\nregardless of any momentum of initial state. The quantized displacement is\nrelated to a reduced Chern number defined as a line integral of Berry curvature\nin each direction, providing an almost perfect measurement of Chern number. Our\nscheme can apply to detect Chern number and topological phase transitions not\nonly for the energy-separable band, but also for energy-inseparable bands which\ncannot be achieved by conventional Thouless pumping or integer quantum Hall\neffect.",
        "positive": "Monitoring and manipulating Higgs and Goldstone modes in a supersolid\n  quantum gas: Access to collective excitations lies at the heart of our understanding of\nquantum many-body systems. We study the Higgs and Goldstone modes in a\nsupersolid quantum gas that is created by coupling a Bose-Einstein condensate\nsymmetrically to two optical cavities. The cavity fields form a U(1)-symmetric\norder parameter that can be modulated and monitored along both quadratures in\nreal time. This enables us to measure the excitation energies across the\nsuperfluid-supersolid phase transition, establish their amplitude and phase\nnature, as well as characterize their dynamics from an impulse response.\nFurthermore, we can give a tunable mass to the Goldstone mode at the crossover\nbetween continuous and discrete symmetry by changing the coupling of the\nquantum gas with either cavity."
    },
    {
        "anchor": "Non-Equilibrium Universality in the Heating Dynamics of Interacting\n  Luttinger Liquids: We establish a new non-equilibrium scaling regime in the short time evolution\nof one-dimensional interacting open quantum systems subject to a generic\nheating mechanism. This dynamical regime is characterized by uncompensated\nphonon production and a super-diffusive, universal scaling of quasiparticle\nlifetimes with momentum $\\sim q^{-5/3}$, distinct from finite and zero\ntemperature cases. It is separated from a high momentum regime by a time\ndependent scale fading out as $q_0(t) \\sim t^{-4/5}$. In the latter region we\nobserve thermalization to an effective time-dependent equilibrium with linearly\nincreasing temperature. By mapping out the dynamical phase diagram and\ncomputing the dynamical structure factor within an open system Keldysh\nfunctional integral approach, we show how these predictions can be explored in\ncold atom experiments by means of Bragg spectroscopy.",
        "positive": "Pauli paramagnetism of an ideal Fermi gas: We show how to use trapped ultracold atoms to measure the magnetic\nsusceptibility of a two-component Fermi gas. The method is illustrated for a\nnon-interacting gas of $^6$Li, using the tunability of interactions around a\nwide Feshbach resonances. The susceptibility versus effective magnetic field is\ndirectly obtained from the inhomogeneous density profile of the trapped atomic\ncloud. The wings of the cloud realize the high field limit where the\npolarization approaches 100%, which is not accessible for an electron gas."
    },
    {
        "anchor": "Acoustic oscillations in cigar-shaped logarithmic Bose-Einstein\n  condensate in the Thomas-Fermi approximation: We consider the dynamical properties of density fluctuations in the\ncigar-shaped Bose-Einstein condensate described by the logarithmic wave\nequation with a constant nonlinear coupling by using the Thomas-Fermi and\nlinear approximations. It is shown that the propagation of small density\nfluctuations along the long axis of a condensed lump in a strongly anisotropic\ntrap is essentially one-dimensional, while the trapping potential can be\ndisregarded in the linear regime. Depending on the sign of nonlinear coupling,\nthe fluctuations either take the form of translationally symmetric pulses and\nstanding waves, or become oscillations with varying amplitudes. We also study\nthe condensate in an axial harmonic trap, by using elasticity theory's notions.\nLinear particle density and energy also behave differently depending on the\nnonlinear coupling's value. If it is negative, the density monotonously grows\nalong with lump's radius, while energy is a monotonous function of density. For\nthe positive coupling, the density is bound from above, whereas energy grows\nmonotonously as a function of density until it reaches its global maximum.",
        "positive": "Two-dimensional Bose fluids: An atomic physics perspective: The properties of phase transitions and the types of order present in the\nlow-temperature states of matter are fundamentally dependent on the\ndimensionality of physical systems. Generally, highly ordered states are more\nrobust in higher dimensions, while thermal and quantum fluctuations, which\nfavour disordered states, play a more important role in lower dimensions. The\ncase of a two-dimensional (2d) Bose fluid is particularly fascinating because\nof its \"marginal\" behaviour. In an infinite uniform 2d fluid thermal\nfluctuations at any non-zero temperature are strong enough to destroy the fully\nordered state associated with Bose--Einstein condensation, but are not strong\nenough to suppress superfluidity in an interacting system at low, but non-zero\ntemperatures. Further, the presence of residual \"quasi-long-range\" order at low\ntemperatures leads to an interesting interplay between superfluidity and\ncondensation in all experimentally relevant finite-size systems. In these notes\nwe give an introduction to the physics of 2d Bose fluids from an atomic physics\nperspective. Our goal is to summarize the recent progress in theoretical\nunderstanding and experimental investigation of ultra-cold atomic gases\nconfined to 2d geometry, and we also hope to provide a useful introduction to\nthese systems for researchers working on related topics in other fields of\nphysics."
    },
    {
        "anchor": "Second sound and the density response function in uniform superfluid\n  atomic gases: Recently there has been renewed interest in second sound in superfluid Bose\nand Fermi gases. By using two-fluid hydrodynamic theory, we review the density\nresponse $\\chi_{nn}(\\bq,\\omega)$ of these systems as a tool to identify second\nsound in experiments based on density probes. Our work generalizes the\nwell-known studies of the dynamic structure factor $S(\\bq,\\omega)$ in\nsuperfluid $^4$He in the critical region. We show that, in the unitary limit of\nuniform superfluid Fermi gases, the relative weight of second vs. first sound\nin the compressibility sum rule is given by the Landau--Placzek ratio\n$\\lp\\equiv (\\bar{c}_p-\\bar{c}_v)/\\bar{c}_v$ for all temperatures below $T_c$.\nIn contrast to superfluid $^4$He, $\\lp$ is much larger in strongly interacting\nFermi gases, being already of order unity for $T \\sim 0.8 T_c$, thereby\nproviding promising opportunities to excite second sound with density probes.\nThe relative weights of first and second sound are quite different in\n$S(\\bq,\\omega)$ (measured in pulse propagation studies) as compared to\n$\\mathrm{Im}\\chi_{nn}(\\bq,\\omega)$ (measured in two-photon Bragg scattering).\nWe show that first and second sound in $S(\\bq,\\omega)$ in a strongly\ninteracting Bose-condensed gas are similar to those in a Fermi gas at\nunitarity. However, in a weakly interacting Bose gas, first and second sound\nare mainly uncoupled oscillations of the thermal cloud and condensate,\nrespectively, and second sound has most of the spectral weight in\n$S(\\bq,\\omega)$. We also discuss the behaviour of the superfluid and normal\nfluid velocity fields involved in first and second sound.",
        "positive": "Dynamical symmetry and breathers in a two-dimensional Bose gas: A fluid is said to be \\emph{scale-invariant} when its interaction and kinetic\nenergies have the same scaling in a dilation operation. In association with the\nmore general conformal invariance, scale invariance provides a dynamical\nsymmetry which has profound consequences both on the equilibrium properties of\nthe fluid and its time evolution. Here we investigate experimentally the\nfar-from-equilibrium dynamics of a cold two-dimensional rubidium Bose gas. We\noperate in the regime where the gas is accurately described by a classical\nfield obeying the Gross--Pitaevskii equation, and thus possesses a dynamical\nsymmetry described by the Lorentz group SO(2,1). With the further\nsimplification provided by superfluid hydrodynamics, we show how to relate the\nevolutions observed for different initial sizes, atom numbers, trap frequencies\nand interaction parameters by a scaling transform. Finally we show that some\nspecific initial shapes - uniformly-filled triangles or disks - may lead to a\nperiodic evolution, corresponding to a novel type of breather for the\ntwo-dimensional Gross--Pitaevskii equation."
    },
    {
        "anchor": "Landau-Khalatnikov phonon damping in strongly interacting Fermi gases: We derive the phonon damping rate due to the four-phonon Landau-Khalatnikov\nprocess in low temperature strongly interacting Fermi gases using quantum\nhydrodynamics, correcting and extending the original calculation of Landau and\nKhalatnikov [ZhETF, 19 (1949) 637]. Our predictions can be tested in\nstate-of-the-art experiments with cold atomic gases in the collisionless\nregime.",
        "positive": "Spatial and Temporal Coherence in Strongly Coupled Plasmonic\n  Bose-Einstein Condensates: We report first-order spatial and temporal correlations in strongly coupled\nplasmonic Bose-Einstein condensates. The condensate is large, more than twenty\ntimes the spatial coherence length of the polaritons in the uncondensed system\nand hundred times the healing length, making plasmonic lattices an attractive\nplatform for studying long-range spatial correlations in two dimensions (2D).\nWe find that both spatial and temporal coherence display non-exponential decay;\nthe results suggest power-law or stretched exponential behaviour with different\nexponents for spatial and temporal correlation decays."
    },
    {
        "anchor": "The Boson-Hubbard Model on a Kagome Lattice with Sextic Ring-Exchange\n  Terms: High order ring-exchange interactions are crucial for the study of quantum\nfluctuations on highly frustrated systems. We present the first exact quantum\nMonte Carlo study of a model of hard-core bosons with sixth order ring-exchange\ninteractions on a two-dimensional kagome lattice. By using the Stochastic Green\nFunction algorithm, we show that the system becomes unstable in the limit of\nlarge ring-exchange interactions. It undergoes a phase separation at all\nfillings, except at 1/3 and 2/3 fillings for which the superfluid density\nvanishes and an unusual mixed valence bond and charge density ordered solid is\nformed.",
        "positive": "Fragmentation of a spin-1 mixture in a magnetic field: We study the ground state quantum fragmentation in a mixture of a polar\ncondensate and a ferromagnetic condensate when subject to an external magnetic\nfield. We pay more attentions to the polar condensate and find that it will be\nless fragile in the mixture when perturbed by the magnetic field. Both atom\nnumbers and the number fluctuations in the spin-0 component will keep in a high\nmagnitude of order of $N$ when the magnetization of the system is increased.\nThe role of the ferromagnetic condensate is to provide a uniform and stable\nbackground which can delay the rapid shrink of the 0-component population and\nmake it possible to capture the \\textquotedblleft super-fragmentation\n\\textquotedblright. Our method has potential applications in measuring the\ninter-species spin-coupling interaction through adjusting the magnetic field."
    },
    {
        "anchor": "Spin dipole oscillation and relaxation of coherently coupled\n  Bose-Einstein condensates: We study the static and the dynamic response of coherently coupled two\ncomponent Bose-Einstein condensates due to a spin-dipole perturbation. The\nstatic dipole susceptibility is determined and it is shown to be a key quantity\nto identify the second order ferromagnetic transition occurring at large\ninter-species interaction. The dynamics, which is obtained by quenching the\nspin-dipole perturbation, is very much affected by the system being\nparamagnetic or ferromagnetic and by the correlation between the motional and\nthe internal degrees of freedom. In the paramagnetic phase the gas exhibits\nwell defined out-of-phase dipole oscillations, whose frequency can be related\nto the susceptibility of the system using a sum rule approach. In particular in\nthe interaction SU (2) symmetric case, i.e., all the two-body interactions are\nthe same, the external dipole oscillation coincides with the internal Rabi\nflipping frequency. In the ferromagnetic case, where linear response theory in\nnot applicable, the system show highly non linear dynamics. In particular we\nobserve phenomena related to ground state selection: the gas, initially trapped\nin a domain wall configuration, reaches a final state corresponding to the\nmagnetic ground state plus small density ripples. Interestingly the time during\nwhich the gas is unable to escape from its initial configuration is found to be\nproportional to the square root of the wall surface tension.",
        "positive": "Phases of spin- and mass-imbalanced ultracold Fermi gases in harmonic\n  traps: We analyze the phase structure of mass- and spin-imbalanced unitary Fermi\ngases in harmonic traps. To this end, we employ Density Functional Theory in\nthe local density approximation. Depending on the values of the control\nparameters measuring mass and spin imbalance, we observe that three regions\nexist in the trap, namely: a superfluid region at the center, surrounded by a\nmixed region of resonantly interacting spin-up and spin-down fermions, and\nfinally a fully polarized phase surrounding the previous two regions. We also\nfind regimes in the phase diagram where the existence of a superfluid region at\nthe center of the trap is not energetically favored. We point out the\nlimitations of our approach at the present stage, and call for more detailed\n(ab initio) studies of the equation of state of uniform, mass-imbalanced\nunitary Fermi gases."
    },
    {
        "anchor": "Fulde-Ferrell-Larkin-Ovchinnikov state of two-dimensional imbalanced\n  Fermi gases: The ground-state phase diagram of attractively-interacting Fermi gases in two\ndimensions with a population imbalance is investigated. We find the regime of\nstability for the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase, in which\npairing occurs at finite wave vector, and determine the magnitude of the\npairing amplitude $\\Delta$ and FFLO wavevector $q$ in the ordered phase,\nfinding that $\\Delta$ can be of the order of the two-body binding energy. Our\nresults rely on a careful analysis of the zero temperature gap equation for the\nFFLO state, which possesses nonanalyticities as a function of $\\Delta$ and $q$,\ninvalidating a Ginzburg-Landau expansion in small $\\Delta$.",
        "positive": "Half-vicinity model and a phase diagram for quantum oscillations in\n  confined and degenerate Fermi gases: We propose an analytical model for the accurate calculation of size and\ndensity dependent quantum oscillations in thermodynamic and transport\nproperties of confined and degenerate non-interacting Fermi gases. We provide a\nuniversal, material independent, recipe that explicitly separates oscillatory\nquantum regime from stationary classical regime. Our model quite accurately\nestimates quantum oscillations depending on confinement and degeneracy. We\nconstruct a phase diagram representing stationary and oscillatory regimes on\ndegeneracy-confinement space. Analytical expressions of phase transition\ninterfaces are derived for different dimensions. The critical point on the\nphase diagram, which separates entirely stationary and entirely oscillatory\nregions, is determined and their aspect ratio dependencies are examined.\nQuantum oscillations as well as their periods are analytically expressed for\none-dimensional case. Accuracy of our model is verified through quantum\noscillations in electronic specific heat capacity. We also compare the\npredictions of our half-vicinity model, based on bounded sums, with those of\ninfinite sums, for the oscillatory violation of entropy-heat capacity\nequivalence in degenerate limit to show the accuracy of our model. Furthermore,\nsimilarities between functional behaviors of total occupancy variance and\nconventional density of states functions at Fermi level are discussed."
    },
    {
        "anchor": "Out-of-equilibrium steady states of a locally driven lossy qubit array: We find a rich variety of counterintuitive features in the steady states of a\nqubit array coupled to a dissipative source and sink at two arbitrary sites,\nusing a master equation approach. We show there are setups where increasing the\npump and loss rates establishes long-range coherence. At sufficiently strong\ndissipation, the source or sink effectively generates correlation between its\nneighboring sites, leading to a striking density-wave order for a class of\n\"resonant\" geometries. This effect can be used more widely to engineer\nnonequilibrium phases. We show the steady states are generically distinct for\nhard-core bosons and free fermions, and differ significantly from the ones\nfound before in special cases. They are explained by generally applicable\nansatzes for the long-time dynamics at weak and strong dissipation. Our\nfindings are relevant for existing photonic setups.",
        "positive": "High-resolution imaging of ultracold fermions in microscopically\n  tailored optical potentials: We report on the local probing and preparation of an ultracold Fermi gas on\nthe length scale of one micrometer, i.e. of the order of the Fermi wavelength.\nThe essential tool of our experimental setup is a pair of identical,\nhigh-resolution microscope objectives. One of the microscope objectives allows\nlocal imaging of the trapped Fermi gas of 6Li atoms with a maximum resolution\nof 660 nm, while the other enables the generation of arbitrary optical dipole\npotentials on the same length scale. Employing a 2D acousto-optical deflector,\nwe demonstrate the formation of several trapping geometries including a tightly\nfocussed single optical dipole trap, a 4x4-site two-dimensional optical lattice\nand a 8-site ring lattice configuration. Furthermore, we show the ability to\nload and detect a small number of atoms in these trapping potentials. A site\nseparation of down to one micrometer in combination with the low mass of 6Li\nresults in tunneling rates which are sufficiently large for the implementation\nof Hubbard-models with the designed geometries."
    },
    {
        "anchor": "Ultracold Bose gases in disorder potentials with spatiotemporal dynamics: We study experimentally the dissipative dynamics of ultracold bosonic gases\nin a dynamic disorder potential with tunable correlation time. First, we\nmeasure the heating rate of thermal clouds exposed to the dynamic potential and\npresent a model of the heating process, revealing the microscopic origin of\ndissipation from a thermal, trapped cloud of bosons. Second, for Bose-Einstein\ncondensates, we measure the particle loss rate induced by the dynamic\nenvironment. Depending on the correlation time, the losses are either dominated\nby heating of residual thermal particles or the creation of excitations in the\nsuperfluid, a notion we substantiate with a rate model. Our results illuminate\nthe interplay between superfluidity and time-dependent disorder and on more\ngeneral grounds establish ultracold atoms as a platform for studying\nspatiotemporal noise and time-dependent disorder.",
        "positive": "Quantum Atomic Matter Near Two-Dimensional Materials in Microgravity: Novel two-dimensional (2D) atomically flat materials, such as graphene and\ntransition-metal dichalcogenides, exhibit unconventional Dirac electronic\nspectra. We propose to effectively engineer their interactions with cold atoms\nin microgravity, leading to a synergy between complex electronic and atomic\ncollective quantum phases and phenomena. Dirac materials are susceptible to\nmanipulation and quantum engineering via changes in their electronic properties\nby application of strain, doping with carriers, adjustment of their dielectric\nenvironment, etc. Consequently the interaction of atoms with such materials,\nnamely the van der Waals / Casimir-Polder interaction, can be effectively\nmanipulated, leading to the potential observation of physical effects such as\nQuantum Reflection off atomically thin materials and confined Bose-Einstein\nCondensate (BEC) frequency shifts."
    },
    {
        "anchor": "Ultracold nonreactive molecules in an optical lattice: connecting\n  chemistry to many-body physics: We derive effective lattice models for ultracold bosonic or fermionic\nnonreactive molecules (NRMs) in an optical lattice, analogous to the Hubbard\nmodel that describes ultracold atoms in a lattice. In stark contrast to the\nHubbard model, which is commonly assumed to accurately describe NRMs, we find\nthat the single on-site interaction parameter $U$ is replaced by a\nmulti-channel interaction, whose properties we elucidate. The complex,\nmulti-channel collisional physics is unrelated to dipolar interactions, and so\noccurs even in the absence of an electric field or for homonuclear molecules.\nWe find a crossover between coherent few-channel models and fully incoherent\nsingle-channel models as the lattice depth is increased. We show that the\neffective model parameters can be determined in lattice modulation experiments,\nwhich consequently measure molecular collision dynamics with a vastly sharper\nenergy resolution than experiments in an ultracold gas.",
        "positive": "Magnetic phase transition in a mixture of two interacting Bose gases at\n  finite temperature: The miscibility condition for a binary mixture of two interacting\nBose-Einstein condensates is shown to be deeply affected by interaction driven\nthermal fluctuations. These give rise to a first order phase transition to a\ndemixed phase with full spatial separation of the two condensates, even if the\nmixture is miscible at zero temperature. Explicit predictions for the\nisothermal compressibility, the spin susceptibility, and the phase transition\ntemperature $T_M$ are obtained in the framework of Popov theory, which properly\nincludes beyond mean-field quantum and thermal fluctuations in both the spin\nand density channels. For a mixture of two sodium condensates occupying the\nhyperfine states $\\lvert F=1, m_F=1 \\rangle$ and $\\lvert F=1, m_F=-1 \\rangle$\nrespectively, $T_M$ is predicted to occur at about $0.7$ times the usual BEC\ncritical temperature."
    },
    {
        "anchor": "Dissipative Magnetic Polariton Soliton: Dissipative solitons are non-decaying out-of-equilibrium entities that result\nfrom double balances between gain and loss, as well as nonlinearity and\ndispersion. Here we describe a scenario where double balances rely on the\npresence of multiple collective excitation channels in open-dissipative quantum\nsystems. It differs from conventional single-channel scenario for well-known\ndissipative solitons such as dissipative Kerr solitons, in that the soliton\nitself arises in a decoupled excitation channel and hence coherent nonlinear\nexcitation dynamics, but its background state corresponds to other channels and\nis determined by the balance of pumping and dissipation. We demonstrate with a\nspinor polariton Bose-Einstein condensate (BEC) under spatially uniform\nnonresonant pumping, and show the existence of a dissipative magnetic soliton\nas an exact solution to two-component driven-dissipative Gross-Pitaevskii\nequation. This magnetic polariton soliton manifests as a localized spin\npolarization with the background state being linearly polarized, and does not\ndecay when propagating in the dissipative medium. Our present work offers a new\nperspective as well as new benchmarks for understanding and realizing\ndissipative solitons.",
        "positive": "Variational Approach to Quantum Spin Liquid in a Rydberg Atom Simulator: Recently the Rydberg blockade effect has been utilized to realize quantum\nspin liquid on the kagome lattice. Evidence of quantum spin liquid has been\nobtained experimentally by directly measuring non-local string order. In this\nletter, we report a BCS-type variational wave function study of the spin liquid\nstate in this model. This wave function is motivated by mapping the Rydberg\nblockade model to a lattice gauge theory, where the local gauge conservations\nreplace the role of constraints from the Rydberg blockade. We determine the\nvariational parameter from the experimental measurement of the Rydberg atom\npopulation. Then we compare the predictions of this deterministic wave function\nwith the experimental measurements of non-local string order. Combining the\nmeasurements on both open and closed strings, we extract the fluctuations only\nassociated with the closed-loop as an indicator of the topological order. The\nprediction from our wave function agrees reasonably well with the experimental\ndata without any fitting parameter. Our variational wave function provides a\nsimple and intuitive picture of the quantum spin liquid in this system that can\nbe generalized to various generalizations of the current model."
    },
    {
        "anchor": "Supersolid Polar Molecules beyond Pairwise Interactions: We explore the phase diagram of ultracold bosonic polar molecules confined to\na planar optical lattice of triangular geometry. External static electric and\nmicrowave fields can be employed to tune the effective interactions between the\npolar molecules into a regime of extended two- and three-body repulsions of\ncomparable strength, leading to a rich quantum phase diagram. In addition to\nvarious solid phases, an extended supersolid phase is found to persist deep\ninto the three-body dominated regime. While three-body interactions break\nparticle-hole symmetry explicitly, a characteristic supersolid-supersolid\nquantum phase transition is observed, which indicates the restoration of\nparticle-hole symmetry at half-filling. We revisit the spatial structure of the\nsupersolid at this filling, regarding the existence of a further supersolid\nphase with three inequivalent sublattices, and provide evidence that this state\nis excluded also at finite temperatures.",
        "positive": "Superfluidity in Bose-Hubbard circuits: A semiclassical theory is provided for the metastability regime-diagram of\natomtronic superfluid circuits. Such circuits typically exhibit\nhigh-dimensional chaos; and non-linear resonances that couple the Bogoliubov\nexcitations manifest themselves. Contrary to the expectation these resonances\ndo not originate from the familiar Beliaev and Landau damping terms. Rather,\nthey are described by a variant of the Cherry Hamiltonian of celestial\nmechanics. Consequently we study the induced decay process, and its dependence\non the number of sites and of condensed particles."
    },
    {
        "anchor": "Exact Quantum Many-Body Scar States in the Rydberg-Blockaded Atom Chain: A recent experiment in the Rydberg atom chain observed unusual oscillatory\nquench dynamics with a charge density wave initial state, and theoretical works\nidentified a set of many-body \"scar states\" showing nonthermal behavior in the\nHamiltonian as potentially responsible for the atypical dynamics. In the same\nnonintegrable Hamiltonian, we discover several eigenstates at \\emph{infinite\ntemperature} that can be represented exactly as matrix product states with\nfinite bond dimension, for both periodic boundary conditions (two exact $E = 0$\nstates) and open boundary conditions (two $E = 0$ states and one each $E = \\pm\n\\sqrt{2}$). This discovery explicitly demonstrates violation of strong\neigenstate thermalization hypothesis in this model and uncovers exact quantum\nmany-body scar states. These states show signatures of translational symmetry\nbreaking with period-2 bond-centered pattern, despite being in one dimension at\ninfinite temperature. We show that the nearby many-body scar states can be well\napproximated as \"quasiparticle excitations\" on top of our exact $E = 0$ scar\nstates, and propose a quasiparticle explanation of the strong oscillations\nobserved in experiments.",
        "positive": "Atomtronic multi-terminal Aharonov-Bohm interferometer: We study a multi-functional device for cold atoms consisting of a\nthree-terminal ring circuit pierced by a synthetic magnetic flux, where the\nring can be continuous or discretized. The flux controls the atomic current\nthrough the ring via the Aharonov-Bohm effect. Our device shows a flux-induced\ntransition of reflections from an Andreev-like negative density to positive\ndensity. Further, the flux can direct the atomic current into specific output\nports, realizing a flexible non-reciprocal switch to connect multiple atomic\nsystems or sense rotations. By changing the flux linearly in time, we convert\nconstant matter wave currents into an AC modulated current. This effect can be\nused to realize an atomic frequency generator and study fundamental problems\nrelated to the Aharonov-Bohm effect. We experimentally demonstrate\nBose-Einstein condensation into the light-shaped optical potential of the\nthree-terminal ring. Our work opens up the possibility of novel atomtronic\ndevices for practical applications in quantum technologies."
    },
    {
        "anchor": "An optical lattice with sound: Quantised sound waves -- phonons -- govern the elastic response of\ncrystalline materials, and also play an integral part in determining their\nthermodynamic properties and electrical response (e.g., by binding electrons\ninto superconducting Cooper pairs). The physics of lattice phonons and\nelasticity is absent in simulators of quantum solids constructed of neutral\natoms in periodic light potentials: unlike real solids, traditional optical\nlattices are silent because they are infinitely stiff. Optical-lattice\nrealisations of crystals therefore lack some of the central dynamical degrees\nof freedom that determine the low-temperature properties of real materials.\nHere, we create an optical lattice with phonon modes using a Bose-Einstein\ncondensate (BEC) coupled to a confocal optical resonator. Playing the role of\nan active quantum gas microscope, the multimode cavity QED system both images\nthe phonons and induces the crystallisation that supports phonons via\nshort-range, photon-mediated atom-atom interactions. Dynamical susceptibility\nmeasurements reveal the phonon dispersion relation, showing that these\ncollective excitations exhibit a sound speed dependent on the BEC-photon\ncoupling strength. Our results pave the way for exploring the rich physics of\nelasticity in quantum solids, ranging from quantum melting transitions to\nexotic ``fractonic'' topological defects in the quantum regime.",
        "positive": "Constraints on short-range gravity with self-gravitating Bose-Einstein\n  condensates: In this work, we study low-lying collective excitations of a Bose-Einstein\ncondensate with Newtonian and Yukawa-like two-particle interaction and derive\nboundaries for both Yukawa parameters. Using a variational approach, we\nexplicitly show for spherical condensate that the corresponding frequencies\ndepend on the gravitational interaction strength. The acquired results are\npresented in contour plots and compared to experimentally verified data from\nother tests. Furthermore, we discuss experimental requirements to test our\ntheoretical model as well as possibilities to improve the boundaries. In\naddition, we consider axisymmetric condensates, where it turns out that\ndisk-shaped BECs lead to better constraints. We also show that in theory we can\ndetermine the values for both Yukawa parameters independently by a measurement\nof at least two collective frequencies."
    },
    {
        "anchor": "Spin structure of harmonically trapped one-dimensional atoms with\n  spin-orbit coupling: We introduce a theoretical approach to determine the spin structure of\nharmonically trapped atoms with two-body zero-range interactions subject to an\nequal mixture of Rashba and Dresselhaus spin-orbit coupling created through\nRaman coupling of atomic hyperfine states. The spin structure of bosonic and\nfermionic two-particle systems with finite and infinite two-body interaction\nstrength $g$ is calculated. Taking advantage of the fact that the $N$-boson and\n$N$-fermion systems with infinitely large coupling strength $g$ are\nanalytically solvable for vanishing spin-orbit coupling strength $k_{so}$ and\nvanishing Raman coupling strength $\\Omega$, we develop an effective spin model\nthat is accurate to second-order in $\\Omega$ for any $k_{so}$ and infinite $g$.\nThe three- and four-particle systems are considered explicitly. It is shown\nthat the effective spin Hamiltonian, which contains a Heisenberg exchange term\nand an anisotropic Dzyaloshinskii-Moriya exchange term, describes the\ntransitions that these systems undergo with the change of $k_{so}$ as a\ncompetition between independent spin dynamics and nearest-neighbor spin\ninteractions.",
        "positive": "Composite Fermions and their Pair States in a Strongly-Coupled Fermi\n  Liquid: Our goal is to understand the phenomena arising in optical lattice fermions\nat low temperature in an external magnetic field. Varying the field, the\nattraction between any two fermions can be made arbitrarily strong, where\ncomposite bosons form via so-called Feshbach resonances. By setting up\nstrong-coupling equations for fermions, we find that in spatial dimension $d>2$\nthey couple to bosons which dress up fermions and lead to new massive composite\nfermions. At low enough temperature, we obtain the critical temperature at\nwhich composite bosons undergo the Bose-Einstein condensate (BEC), leading to\nBEC-dressing massive fermions. These form tightly bound pair states which are\nnew bosonic quasi-particles producing a BEC-type condensate. A quantum critical\npoint is found and the formation of condensates of complex quasi-particles is\nspeculated over."
    },
    {
        "anchor": "Mobile impurity in a Bose-Einstein condensate and the orthogonality\n  catastrophe: We analyze the properties of an impurity in a dilute Bose-Einstein condensate\n(BEC). First the quasiparticle residue of a static impurity in an ideal BEC is\nshown to vanish with increasing particle number as a stretched exponential,\nleading to a bosonic orthogonality catastrophe. Then we introduce a variational\nansatz, which recovers this exact result and describes the macroscopic dressing\nof the impurity including its back-action onto the BEC as well as boson-boson\nrepulsion beyond the Bogoliubov approximation. This ansatz predicts that the\northogonality catastrophe also occurs for mobile impurities, whenever the BEC\nbecomes ideal. Finally, we show that our ansatz agrees well with experimental\nresults.",
        "positive": "Intrinsic Anomalous Hall Effect in a Bosonic Chiral Superfluid: The anomalous Hall effect has had a profound influence on the understanding\nof many electronic topological materials but is much less studied in their\nbosonic counterparts. We predict that an intrinsic anomalous Hall effect exists\nin a recently realized bosonic chiral superfluid, a $p$-band Bose-Einstein\ncondensate in a 2D hexagonal boron nitride optical lattice [X. Wang et al.,\nhttps://www.nature.com/articles/s41586-021-03702-0 Nature (London) 596, 227\n(2021)]. We evaluate the frequency-dependent Hall conductivity within a\nmulti-orbital Bose-Hubbard model that accurately captures the real experimental\nsystem. We find that in the high frequency limit, the Hall conductivity is\ndetermined by finite loop current correlations on the $s$-orbital residing\nsublattice, the latter a defining feature of the system's chirality. In the\nopposite limit, the dc Hall conductivity can trace its origin back to the\nnon-interacting band Berry curvature at the condensation momentum, although the\ncontribution from atomic interactions can be significant. We discuss available\nexperimental probes to observe this intrinsic anomalous Hall effect at both\nzero and finite frequencies."
    },
    {
        "anchor": "Spin-Injection Spectroscopy of a Spin-Orbit Coupled Fermi Gas: The coupling of the spin of electrons to their motional state lies at the\nheart of recently discovered topological phases of matter. Here we create and\ndetect spin-orbit coupling in an atomic Fermi gas, a highly controllable form\nof quantum degenerate matter. We reveal the spin-orbit gap via spin-injection\nspectroscopy, which characterizes the energy-momentum dispersion and spin\ncomposition of the quantum states. For energies within the spin-orbit gap, the\nsystem acts as a spin diode. To fully inhibit transport, we open an additional\nspin gap, thereby creating a spin-orbit coupled lattice whose spinful band\nstructure we probe. In the presence of s-wave interactions, such systems should\ndisplay induced p-wave pairing, topological superfluidity, and Majorana edge\nstates.",
        "positive": "Doublon-hole correlations and fluctuation thermometry in a Fermi-Hubbard\n  gas: We report on the single atom and single site-resolved detection of the total\ndensity in a cold atom realization of the 2D Fermi-Hubbard model. Fluorescence\nimaging of doublons is achieved by splitting each lattice site into a double\nwell, thereby separating atom pairs. Full density readout yields a direct\nmeasurement of the equation of state, including direct thermometry via the\nfluctuation-dissipation theorem. Site-resolved density correlations reveal the\nPauli hole at low filling, and strong doublon-hole correlations near half\nfilling. These are shown to account for the difference between local and\nnon-local density fluctuations in the Mott insulator. Our technique enables the\nstudy of atom-resolved charge transport in the Fermi-Hubbard model, the\nsite-resolved observation of molecules, and the creation of bilayer\nFermi-Hubbard systems."
    },
    {
        "anchor": "Quantum fluctuations in one-dimensional supersolids: In one-dimension, quantum fluctuations prevent the appearance of long-range\norder in a supersolid, and only quasi long-range order can survive. We derive\nthis quantum critical behavior and study its influence on the superfluid\nresponse and properties of the solid. The analysis is based on an effective\nlow-energy description accounting for the two coupled Goldstone modes. We find\nthat the quantum phase transition from the superfluid to the supersolid is\nshifted by quantum fluctuations from its mean-field prediction. However, for\ncurrent experimental parameters with dipolar atomic gases, this shift is not\nobservable and the transition appears to be mean-field like.",
        "positive": "Cavity-Mediated Strong Matter Wave Bistability in a Spin-1 Condensate: We study matter wave bistability in a spin-1 Bose-Einstein condensate\ndispersively coupled to a unidirectional ring cavity. A unique feature is that\nthe population exchange among different modes of matter fields are accomplished\nvia the spin-exchange collisions. We show that the interplay between the atomic\nspin mixing and the cavity light field can lead to a strong matter wave\nnonlinearity, making matter wave bistability in a cavity at the single-photon\nlevel achievable."
    },
    {
        "anchor": "Tan's two-body contact across the superfluid transition of a planar Bose\n  gas: Tan's contact is a quantity that unifies many different properties of a\nlow-temperature gas with short-range interactions, from its momentum\ndistribution to its spatial two-body correlation function. Here, we use a\nRamsey interferometric method to realize experimentally the thermodynamic\ndefinition of the two-body contact, i.e. the change of the internal energy in a\nsmall modification of the scattering length. Our measurements are performed on\na uniform two-dimensional Bose gas of $^{87}$Rb atoms across the\nBerezinskii-Kosterlitz-Thouless superfluid transition. They connect well to the\ntheoretical predictions in the limiting cases of a strongly degenerate fluid\nand of a normal gas. They also provide the variation of this key quantity in\nthe critical region, where further theoretical efforts are needed to account\nfor our findings.",
        "positive": "Flat-band ferromagnetism in the multilayer Lieb optical lattice: We theoretically study magnetic properties of two-component cold fermions in\nhalf-filled multilayer Lieb optical lattices, i.e., two, three, and several\nlayers, using the dynamical mean-field theory. We clarify that the magnetic\nproperties of this system become quite different depending on whether the\nnumber of layers is odd or even. In odd-number-th layers in an odd-number-layer\nsystem, finite magnetization emerges even with an infinitesimal interaction.\nThis is a striking feature of the flatband ferromagnetic state in multilayer\nsystems as a consequence of the Lieb theorem. In contrast, in even-number\nlayers, magnetization develops from zero on a finite interaction. These\ndifferent magnetic behaviours are triggered by the flat bands in the local\ndensity of states and become identical in the limit of the infinite-layer\n(i.e., three-dimensional) system. We also address how interlayer hopping\naffects the magnetization process. Further, we point out that layer\nmagnetization, which is a population imbalance between up and down atoms on a\nlayer, can be employed to detect the emergence of the flat-band ferromagnetic\nstate without addressing sublattice magnetization."
    },
    {
        "anchor": "Domain-wall melting as a probe of many-body localization: Motivated by a recent optical-lattice experiment by Choi et al.[Science 352,\n1547 (2016)], we discuss how domain-wall melting can be used to investigate\nmany-body localization. First, by considering noninteracting fermion models, we\ndemonstrate that experimentally accessible measures are sensitive to\nlocalization and can thus be used to detect the delocalization-localization\ntransition, including divergences of characteristic length scales. Second,\nusing extensive time-dependent density matrix renormalization group\nsimulations, we study fermions with repulsive interactions on a chain and a\ntwo-leg ladder. The extracted critical disorder strengths agree well with the\nones found in existing literature.",
        "positive": "Sum rules for spin-$1/2$ quantum gases in states with well-defined\n  spins: II. Spin-dependent two-body interactions: Sums of matrix elements of spin-dependent two-body momentum-independent\ninteractions and sums of their products are calculated analytically in the\nbasis of many-body states with given total spin --- the states built from spin\nand spatial wavefunctions belonging to multidimensional irreducible\nrepresentations of the symmetric group, unless the total spin has the maximal\nallowed value. As in the first part of the series [V. A. Yurovsky, Phys. Rev. A\n91, 053601 (2015)], the sum dependence on the many-body states is given by\nuniversal factors, which are independent of the Hamiltonians of non-interacting\nparticles. The sum rules are applied to perturbative analysis of energy spectra\nand to calculation of two-body spin-dependent local correlations."
    },
    {
        "anchor": "Open source Matrix Product States: Opening ways to simulate entangled\n  many-body quantum systems in one dimension: Numerical simulations are a powerful tool to study quantum systems beyond\nexactly solvable systems lacking an analytic expression. For one-dimensional\nentangled quantum systems, tensor network methods, amongst them Matrix Product\nStates (MPSs), have attracted interest from different fields of quantum physics\nranging from solid state systems to quantum simulators and quantum computing.\nOur open source MPS code provides the community with a toolset to analyze the\nstatics and dynamics of one-dimensional quantum systems. Here, we present our\nopen source library, Open Source Matrix Product States (OSMPS), of MPS methods\nimplemented in Python and Fortran2003. The library includes tools for ground\nstate calculation and excited states via the variational ansatz. We also\nsupport ground states for infinite systems with translational invariance.\nDynamics are simulated with different algorithms, including three algorithms\nwith support for long-range interactions. Convenient features include built-in\nsupport for fermionic systems and number conservation with rotational\n$\\mathcal{U}(1)$ and discrete $\\mathbb{Z}_2$ symmetries for finite systems, as\nwell as data parallelism with MPI. We explain the principles and techniques\nused in this library along with examples of how to efficiently use the general\ninterfaces to analyze the Ising and Bose-Hubbard models. This description\nincludes the preparation of simulations as well as dispatching and\npost-processing of them.",
        "positive": "Spontaneous Parity--Time Symmetry Breaking and Stability of Solitons in\n  Bose-Einstein Condensates: We report explicitly a novel family of exact PT-symmetric solitons and\nfurther study their spontaneous PT symmetry breaking, stabilities and\ncollisions in Bose-Einstein condensates trapped in a PT-symmetric harmonic trap\nand a Hermite-Gaussian gain/loss potential. We observe the significant effects\nof mean-field interaction by modifying the threshold point of spontaneous PT\nsymmetry breaking in Bose-Einstein condensates. Our scenario provides a\npromising approach to study PT-related universal behaviors in non-Hermitian\nquantum system based on the manipulation of gain/loss potential in\nBose-Einstein condensates."
    },
    {
        "anchor": "A toolbox for elementary fermions with a dipolar Fermi gas in a 3D\n  optical lattice: There has been growing interest in investigating properties of elementary\nparticles predicted by the standard model. Examples of such studies include\nexploring their low-energy analogs in condensed matter system, where they arise\nas collective states or quasiparticles. Here we show that a toolbox for\nsystematically engineering the emergent elementary fermions, i.e., Dirac, Weyl\nand Majorana fermions, can be built in a single atomic system composed of a\nspinless magnetic dipolar Fermi gas in a 3D optical lattice. The designed\ndirection-dependent dipole-dipole interaction leads to both the basic building\nblock, i.e, in-plane p+ip superfluid pairing instability and the manipulating\ntool, i.e, out-of-plane Peierls instability. It is shown that the Peierls\ninstability provides a natural way of tuning the topological nature of p+ip\nsuperfluids and thus transform the fermion's nature between distinct emergent\nparticles. Our scheme should open up a new thrust towards searching for\nelementary particles through manipulating the topology.",
        "positive": "Tunneling of persistent currents in coupled ring-shaped Bose-Einstein\n  condensates: Considerable progress in experimental studies of atomic gases in a toroidal\ngeometry has opened up novel prospects for the investigation of fundamental\nproperties of superfluid states and creation of new configurations for\natomtronic circuits. In particular, atomic Bose-Einstein condensates loaded in\na dual-ring trap suggest a possibility to consider the tunneling dynamics\nbetween coupled condensates with different angular momenta. Accordingly, we\naddress the tunneling in a pair of coaxial ring-shaped condensates separated by\na horizontal potential barrier. A weak-coupling truncated (finite-mode)\nGalerkin model and direct numerical simulations of the underlying\nthree-dimensional Gross-Pitaevskii equation are used for the analysis of\ntunneling superflows driven by an initial imbalance in atomic populations of\nthe rings. The superflows through the Bose-Josephson junction are strongly\naffected by persistent currents which are present in the rings. Josephson\noscillations of the population imbalance and angular momenta in the coupled\nrings are obtained for co-rotating states and non-rotating ones. On the other\nhand, the azimuthal structure of the tunneling flow implies formation of\nJosephson vortices (fluxons) with zero net current through the junction for\nhybrid states, built of counter-rotating persistent currents in the coupled\nrings."
    },
    {
        "anchor": "Stability of trapless Bose-Einstein condensates with two- and three-body\n  interactions: We study the stabilization of a trapless Bose-Einstein condensate by\nanalysing the mean-field Gross-Pitaevskii equation with attractive two- and\nthree-body interactions through both analytical and numerical methods. Using\nthe variational method we show that there is an enhancement of the condensate\nstability due to the inclusion of a three-body interaction in addition to the\ntwo-body interaction. We also study the stability of the condensates in the\npresence of the time-varying three-body interaction. Finally we confirm the\nstabilization of a trapless condensate from numerical simulation.",
        "positive": "Vortex lattice in the crossover of a Bose gas from weak coupling to\n  unitarity: The formation of a regular lattice of quantized vortices in a fluid under\nrotation is a smoking-gun signature of its superfluid nature. Here we study the\nvortex lattice in a dilute superfluid gas of bosonic atoms at zero temperature\nalong the crossover from the weak-coupling regime, where the inter-atomic\nscattering length is very small compared to the average distance between atoms,\nto the unitarity regime, where the inter-atomic scattering length diverges.\nThis study is based on high-performance numerical simulations of the\ntime-dependent nonlinear Schrodinger equation for the superfluid order\nparameter in three spatial dimensions, using a realistic analytic expression\nfor the bulk equation of state of the system along the crossover from\nweak-coupling to unitarity. This equation of state has the correct\nweak-coupling and unitarity limits and faithfully reproduces the results of an\naccurate multi-orbital microscopic calculation. Our numerical predictions of\nthe number of vortices and root-mean-square sizes are important benchmarks for\nfuture experiments."
    },
    {
        "anchor": "Equivalence of dissipative and dissipationless dynamics of interacting\n  quantum systems with its application to the unitary Fermi gas: We analytically study quantum dissipative dynamics described by the\nCaldirola-Kanai model with inter-particle interactions. We have found that the\ndissipative quantum dynamics of the Caldirola-Kanai model can be exactly mapped\nto a dissipationless quantum dynamics under a negative external harmonic\npotential, even when the particles are strongly interacting. In particular, we\nshow that the mapping is valid for the unitary Fermi gas, which is relevant for\ncold atoms and nuclear matters.",
        "positive": "Implicit ladder summation in the Hartree-Fock-Bogoliubov approach: The fully variational Hartree Fock Bogoliubov approach for bosons is studied\nin the limit of zero range forces in two- and three-dimensions. The equation of\nstate obtained in two-dimensions is expressed in a parametric form. It is shown\nthat the $\\Lambda$ potential permits to perform an implicit summation of the\nladder diagrams without leaving the variational scheme, restoring thus the\nconsistency of this approximation."
    },
    {
        "anchor": "Orbital elementary excitations as probes of entanglement and quantum\n  phase transitions of collective spins in an entangled Bose-Einstein\n  condensate: A mixture of two species of pseudospin-1/2 Bose gases exhibits interesting\ninterplay between spin and orbital degrees of freedom. Expectation values of\nvarious quantities of the collective spins of the two species play crucial\nroles in the Gross-Pitaevskii-like equations governing the four orbital wave\nfunctions in which Bose-Einstein condensation occurs. Consequently, the\nelementary excitations of these orbital wave functions reflect properties of\nthe collective spins. When the coupling between the two collective spins is\nisotropic, the energy gap of the gapped orbital excitation peaks, while there\nis a quantum phase transition in the ground state of the effective Hamiltonian\nof the two collective spins, which have previously been found to be maximally\nentangled.",
        "positive": "Josephson physics of spin-orbit coupled elongated Bose-Einstein\n  condensates: We consider an ultracold bosonic binary mixture confined in a one-dimensional\ndouble-well trap. The two bosonic components are assumed to be two hyperfine\ninternal states of the same atom. We suppose that these two components are\nspin-orbit coupled between each other. We employ the two-mode approximation\nstarting from two coupled Gross-Pitaevskii equations and derive a system of\nordinary differential equations governing the temporal evolution of the\ninter-well population imbalance of each component and that between the two\nbosonic species. We study the Josephson oscillations of these spin-orbit\ncoupled Bose-Einstein condensates by analyzing the interplay between the\ninteratomic interactions and the spin-orbit coupling and the self-trapped\ndynamics of the inter-species imbalance. We show that the dynamics of this\nlatter variable is crucially determined by the relationship between the\nspin-orbit coupling, the tunneling energy, and the interactions."
    },
    {
        "anchor": "SU(3) Spin-Orbit Coupling in Systems of Ultracold Atoms: Motivated by the recent experimental success in realizing synthetic\nspin-orbit coupling in ultracold atomic systems, we consider N-component atoms\ncoupled to a non-Abelian SU(N) gauge field. More specifically, we focus on the\ncase, referred to here as \"SU(3) spin-orbit-coupling,\" where the internal\nstates of three-component atoms are coupled to their momenta via a matrix\nstructure that involves the Gell-Mann matrices (in contrast to the Pauli\nmatrices in conventional SU(2) spin-orbit-coupled systems). It is shown that\nthe SU(3) spin-orbit-coupling gives rise to qualitatively different phenomena\nand in particular we find that even a homogeneous SU(3) field on a simple\nsquare lattice enables a topologically non-trivial state to exist, while such\nSU(2) systems always have trivial topology. In deriving this result, we first\nestablish an exact equivalence between the Hofstadter model with a 1/N Abelian\nflux per plaquette and a homogeneous SU(N) non-Abelian model. The former is\nknown to have a topological spectrum for N>2, which is thus inherited by the\nlatter. It is explicitly verified by an exact calculation for N=3, where we\ndevelop and use a new algebraic method to calculate topological indices in the\nSU(3) case. Finally, we consider a strip geometry and establish the existence\nof three gapless edge states -- the hallmark feature of such an SU(3)\ntopological insulator.",
        "positive": "Observation of parity-time symmetry breaking transitions in a\n  dissipative Floquet system of ultracold atoms: Open physical systems with balanced loss and gain, described by non-Hermitian\nparity-time ($\\mathcal{PT}$) reflection symmetric Hamiltonians, exhibit a\ntransition which could engenders modes that exponentially decay or grow with\ntime and thus spontaneously breaks the $\\mathcal{PT}$-symmetry. Such\n$\\mathcal{PT}$-symmetry breaking transitions have attracted many interests\nbecause of their extraordinary behaviors and functionalities absent in closed\nsystems. Here we report on the observation of $\\mathcal{PT}$-symmetry breaking\ntransitions by engineering time-periodic dissipation and coupling, which are\nrealized through state-dependent atom loss in an optical dipole trap of\nultracold $^6$Li atoms. Comparing with a single transition appearing for static\ndissipation, the time-periodic counterpart undergoes $\\mathcal{PT}$-symmetry\nbreaking and restoring transitions at vanishingly small dissipation strength in\nboth single and multiphoton transition domains, revealing rich phase structures\nassociated to a Floquet open system. The results enable ultracold atoms to be a\nversatile tool for studying $\\mathcal{PT}$-symmetric quantum systems."
    },
    {
        "anchor": "Coupled superfluidity of binary Bose mixtures in two dimensions: We consider a two-component Bose gas in two dimensions at low temperature\nwith short-range repulsive interaction. In the coexistence phase where both\ncomponents are superfluid, inter-species interactions induce a nondissipative\ndrag between the two superfluid flows (Andreev-Bashkin effect). We show that\nthis behavior leads to a modification of the usual\nBerezinskii-Kosterlitz-Thouless (BKT) transition in two dimensions. We extend\nthe renormalization of the superfluid densities at finite temperature using the\nrenormalization group approach and find that the vortices of one component have\na large influence on the superfluid properties of the other, mediated by the\nnondissipative drag. The extended BKT flow equations indicate that the\noccurrence of the vortex unbinding transition in one of the components can\ninduce the breakdown of superfluidity also in the other, leading to a locking\nphenomenon for the critical temperatures of the two gases.",
        "positive": "Dynamics of interacting dark soliton stripes: In the present work we examine the statics and dynamics of multiple parallel\ndark soliton stripes in a two-dimensional Bose-Einstein condensate. Our\nprincipal goal is to study the effect of the interaction between the stripes on\nthe transverse instability of the individual stripes. We use a recently\ndeveloped adiabatic invariant formulation to derive a quasi-analytical\nprediction for the stripe equilibrium position and for the Bogoliubov-de Gennes\nspectrum of excitations of stationary stripes. The cases of two-, three- and\nfour-stripe states are studied in detail. We subsequently test our predictions\nagainst numerical simulations of the full two-dimensional Gross-Pitaevskii\nequation. We find that the number of unstable eigenmodes increases as the\nnumber of stripes increases due to (unstable) relative motions between the\nstripes. Their corresponding growth rates do not significantly change, although\nfor large chemical potentials, the larger the stripe number, the larger the\nmaximal instability growth rate. The instability induced dynamics of multiple\nstripe states and their decay into vortices are also investigated."
    },
    {
        "anchor": "Tunneling of a few strongly repulsive hard-sphere bosons in an optical\n  lattice with tight external harmonic confinement: A quantum Monte Carlo\n  investigation in continuous space: The effect of strongly repulsive interactions on the tunneling amplitude of\nhard-sphere (HS) bosons confined in a simple cubic (sc) optical lattice plus\ntight external harmonic confinement in continuous space is investigated. The\nquantum variational Monte Carlo (VMC) and the variational path integral Monte\nCarlo (VPI) techniques are used at zero temperature. The effects of the lattice\nspacing $\\pi/k$ on the tunneling amplitude is also considered. The occupancies\nof the lattice sites as a function of the repulsion between the bosons are\nfurther revealed. Our chief result is, that for a small number of bosons (N=8)\nthe overlap of the wave functions in neighboring wells does not change with an\nincrease of the repulsive interactions and changes only minimally for a larger\nnumber of particles (N=40). The tunneling amplitude rises with a reduction in\nthe lattice spacing. In addition, the occupancy of the center of the trap\ndecreases in favor of a rise in the occupancy of the lattice sites at the edges\nof the trap with increasing HS repulsion. Further, it was found that the energy\nper particle at certain optical depths is insensitive to the number of\nparticles and variations in the HS diameter of the bosons. In order to support\nour results, we compare the VMC results with corresponding VPI results.",
        "positive": "Quantum Dynamics of Atom-molecule BECs in a Double-Well Potential: We investigate the dynamics of two-component Bose-Josephson junction composed\nof atom-molecule BECs. Within the semiclassical approximation, the multi-degree\nof freedom of this system permits chaotic dynamics, which does not occur in\nsingle-component Bose-Josephson junctions. By investigating the level\nstatistics of the energy spectra using the exact diagonalization method, we\nevaluate whether the dynamics of the system is periodic or non-periodic within\nthe semiclassical approximation. Additionally, we compare the semiclassical and\nfull-quantum dynamics."
    },
    {
        "anchor": "Cavity Quantum Optomechanics of Ultracold Atoms in an Optical Lattice:\n  Normal-Mode Splitting: We consider the dynamics of a movable mirror (cantilever) of a cavity coupled\nthrough radiation pressure to the light scattered from ultracold atoms in an\noptical lattice. Scattering from different atomic quantum states creates\ndifferent quantum states of the scattered light, which can be distinguished by\nmeasurements of the displacement spectrum of the cantilever. We show that for\nlarge pump intensities the steady state displacement of the cantilever shows\nbistable behaviour. Due to atomic back-action, the displacement spectrum of the\ncantilever is modified and depends on the position of the condensate in the\nBrillouin zone. We further analyze the occurrence of splitting of the normal\nmode into three modes due to mixing of the mechanical motion with the\nfluctuations of the cavity field and the fluctuations of the condensate with\nfinite atomic two-body interaction. The present system offers a novel scheme to\ncoherently control ultracold atoms as well as cantilever dynamics.",
        "positive": "Dynamical quantum depletion in polariton condensates: We present a theoretical study of the quantum depletion of microcavity\npolaritons that are excited with a resonant laser pulse. The dynamics of the\nquantum fluctuations are interpreted in the context of quantum quenches in\ngeneral and in terms of the dynamical Casimir effect in particular. We compute\nthe time evolution of the first and second order correlation functions of the\npolariton condensate. Our theoretical modelling is based on the truncated\nWigner approximation for interacting Bose gases. For homogeneous systems,\nanalytical results are obtained in the linearised Bogoliubov approximation.\nInhomogeneous systems are studied numerically by Monte Carlo simulations."
    },
    {
        "anchor": "Diffusion in a system of a few distinguishable fermions in a\n  one-dimensional double-well potential: Dynamical properties of a few ultra-cold fermions confined in a double-well\npotential is studied. We show that the dynamics, which is governed by\nsingle-particle tunnelings for vanishing interactions, is completely different\nfor strong interactions. Depending on the details of the configuration, for\nsufficiently strong interactions (repulsions or attractions) the particle flow\nthrough the barrier can be accelerated or slowed down. This effect cannot be\nexplained with the single-particle picture. It is clarified with direct\ninspection to the spectrum of the few-body Hamiltonian.",
        "positive": "The effect of atom losses on the distribution of rapidities in the\n  one-dimensional Bose gas: We theoretically investigate the effects of atom losses in the\none-dimensional (1D) Bose gas with repulsive contact interactions, a famous\nquantum integrable system also known as the Lieb-Liniger gas. The generic case\nof K-body losses (K = 1,2,3,...) is considered. We assume that the loss rate is\nmuch smaller than the rate of intrinsic relaxation of the system, so that at\nany time the state of the system is captured by its rapidity distribution (or,\nequivalently, by a Generalized Gibbs Ensemble). We give the equation governing\nthe time evolution of the rapidity distribution and we propose a general\nnumerical procedure to solve it. In the asymptotic regimes of vanishing\nrepulsion -- where the gas behaves like an ideal Bose gas -- and hard-core\nrepulsion -- where the gas is mapped to a non-interacting Fermi gas -- we\nderive analytic formulas. In the latter case, our analytic result shows that\nlosses affect the rapidity distribution in a non-trivial way, the time\nderivative of the rapidity distribution being both non-linear and non-local in\nrapidity space."
    },
    {
        "anchor": "Atomic Interactions in Precision Interferometry Using Bose-Einstein\n  Condensates: We present theoretical tools for predicting and reducing the effects of\natomic interactions in Bose-Einstein condensate (BEC) interferometry\nexperiments. To address mean-field shifts during free propagation, we derive a\nrobust scaling solution that reduces the three-dimensional Gross-Pitaevskii\nequation to a set of three simple differential equations valid for any\ninteraction strength. To model the other common components of a BEC\ninterferometer---condensate splitting, manipulation, and recombination---we\ngeneralize the slowly-varying envelope reduction, providing both analytic\nhandles and dramatically improved simulations. Applying these tools to a BEC\ninterferometer to measure the fine structure constant (Gupta, et al., 2002), we\nfind agreement with the results of the original experiment and demonstrate that\natomic interactions do not preclude measurement to better than part-per-billion\naccuracy, even for atomic species with relatively large scattering lengths.\nThese tools help make BEC interferometry a viable choice for a broad class of\nprecision measurements.",
        "positive": "Creating, moving and merging Dirac points with a Fermi gas in a tunable\n  honeycomb lattice: Dirac points lie at the heart of many fascinating phenomena in condensed\nmatter physics, from massless electrons in graphene to the emergence of\nconducting edge states in topological insulators [1, 2]. At a Dirac point, two\nenergy bands intersect linearly and the particles behave as relativistic Dirac\nfermions. In solids, the rigid structure of the material sets the mass and\nvelocity of the particles, as well as their interactions. A different, highly\nflexible approach is to create model systems using fermionic atoms trapped in\nthe periodic potential of interfering laser beams, a method which so far has\nonly been applied to explore simple lattice structures [3, 4]. Here we report\non the creation of Dirac points with adjustable properties in a tunable\nhoneycomb optical lattice. Using momentum-resolved interband transitions, we\nobserve a minimum band gap inside the Brillouin zone at the position of the\nDirac points. We exploit the unique tunability of our lattice potential to\nadjust the effective mass of the Dirac fermions by breaking inversion symmetry.\nMoreover, changing the lattice anisotropy allows us to move the position of the\nDirac points inside the Brillouin zone. When increasing the anisotropy beyond a\ncritical limit, the two Dirac points merge and annihilate each other - a\nsituation which has recently attracted considerable theoretical interest [5-9],\nbut seems extremely challenging to observe in solids [10]. We map out this\ntopological transition in lattice parameter space and find excellent agreement\nwith ab initio calculations. Our results not only pave the way to model\nmaterials where the topology of the band structure plays a crucial role, but\nalso provide an avenue to explore many-body phases resulting from the interplay\nof complex lattice geometries with interactions [11, 12]."
    },
    {
        "anchor": "Superfluid theory of a gas of polarized dipolar Fermi molecules: We present a superfluid theory of a polarized dipolar Fermi gas. For two\ndipolar molecules each of which consists of two atoms with positive charge and\nnegative charge, we derive an effective dipole-dipole pairing interaction.\nUsing this pairing interaction, we show that the resulting BCS gap equation is\nnot suffered from the well-known ultraviolet divergence, so that one can\nquantitatively predict superfluid properties of a dipolar Fermi gas. Using this\ncutoff-free superfluid theory, we examine the symmetry of the superfluid order\nparameter at T=0. We also discuss the deformation of the Fermi surface,\noriginating from the anisotropy of the dipole-dipole interaction.",
        "positive": "Coherent light scattering from a two-dimensional Mott insulator: We experimentally demonstrate coherent light scattering from an atomic Mott\ninsulator in a two-dimensional lattice. The far-field diffraction pattern of\nsmall clouds of a few hundred atoms was imaged while simultaneously laser\ncooling the atoms with the probe beams. We describe the position of the\ndiffraction peaks and the scaling of the peak parameters by a simple analytic\nmodel. In contrast to Bragg scattering, scattering from a single plane yields\ndiffraction peaks for any incidence angle. We demonstrate the feasibility of\ndetecting spin correlations via light scattering by artificially creating a\none-dimensional antiferromagnetic order as a density wave and observing the\nappearance of additional diffraction peaks."
    },
    {
        "anchor": "Local manipulation of quantum magnetism in 1D ultracold Fermi gases\n  across narrow resonances: Effective range is a quantity to characterize the energy dependence in\ntwo-body scattering strength, and is widely used in cold atomic systems\nespecially across narrow resonances. Here we show that the effective range can\nsignificantly modify the magnetic property of one-dimensional (1D) spin-$1/2$\nfermions in the strongly repulsive regime. In particular, the effective range\nbreaks the large spin degeneracy in the hard-core limit, and induces a\nHeisenberg exchange term in the spin chain that is much more sensitive to the\nlocal density than that induced by the bare coupling. With an external harmonic\ntrap, this leads to a very rich magnetic pattern where the anti-ferromagnetic\n(AFM) and ferromagnetic (FM) correlations can coexist and distribute in highly\ntunable regions across the trap. Finally, we propose to detect the\nrange-induced magnetic order in the tunneling experiment. Our results can be\ndirectly tested in 1D Fermi gases across narrow resonance, and suggest a\nconvenient route towards the local manipulation of quantum magnetism in cold\natoms.",
        "positive": "Gauge-Away Effect in Cold Gases on Optical Lattices: It is shown that a simple modification of the geometry in which Raman lasers\nare applied to a cold gas in an optical lattice results in transforming the\nemerging effective electromagnetic field into a pure gauge. This contrived\ngauge-away effect can be observed experimentally by measuring the\nMott-Insulator to Superfluid critical point. The underlying mechanism for this\nphenomenon is the ability to engineer the transfer of the transverse component\nof the gauge potential into its longitudinal one."
    },
    {
        "anchor": "Sound emission and annihilations in a programmable quantum vortex\n  collider: In quantum fluids, the quantisation of circulation forbids the diffusion of a\nvortex swirling flow seen in classical viscous fluids. Yet, a quantum vortex\naccelerating in a superfluid may lose its energy into acoustic radiation, in a\nsimilar way an electric charge decelerates upon emitting photons. The\ndissipation of vortex energy underlies central problems in quantum\nhydrodynamics, such as the decay of quantum turbulence, highly relevant to\nsystems as varied as neutron stars, superfluid helium and atomic condensates. A\ndeep understanding of the elementary mechanisms behind irreversible vortex\ndynamics has been a goal for decades, but it is complicated by the shortage of\nconclusive experimental signatures. Here, we address this challenge by\nrealising a programmable quantum vortex collider in a planar, homogeneous\natomic Fermi superfluid with tunable inter-particle interactions. We create\non-demand vortex configurations and monitor their evolution, taking advantage\nof the accessible time and length scales of our ultracold Fermi gas.\nEngineering collisions within and between vortex-antivortex pairs allows us to\ndecouple relaxation of the vortex energy due to sound emission and interactions\nwith normal fluid, i.e. mutual friction. We directly visualise how the\nannihilation of vortex dipoles radiates a sound pulse in the superfluid.\nFurther, our few-vortex experiments extending across different superfluid\nregimes suggest that fermionic quasiparticles localised inside the vortex core\ncontribute significantly to dissipation, opening the route to exploring new\npathways for quantum turbulence decay, vortex by vortex.",
        "positive": "Supersolid formation in a dipolar condensate by roton instability: We characterize the role of the roton instability in the formation of a\nsupersolid state of an elongated dipolar condensate, following a quench of the\ncontact interactions across the superfluid-supersolid transition, as observed\nin recent experiments. We perform dynamical simulations by means of the\nextended Gross-Pitaevskii equation including quantum corrections, for different\nfinal values of the $s-$wave scattering length. The corresponding excitation\nspectrum is computed using an effective one-dimensional description, revealing\nthat the calculated growth rates of the unstable roton mode accurately\nreproduce the observed behavior. Our results provide valuable insights\nregarding the formation time of the supersolid and its scaling behavior with\nrespect to the $s$-wave scattering length."
    },
    {
        "anchor": "Disorder-free localization with Stark gauge protection: Disorder-free localization in translation-invariant gauge theories presents a\ncounterintuitive yet powerful framework of ergodicity breaking in quantum\nmany-body physics. The fragility of this phenomenon in the presence of\ngauge-breaking errors has recently been addressed, but no scheme has been able\nto reliably stabilize disorder-free localization through all accessible\nevolution times while preserving the disorder-free property. Here, we introduce\nthe concept of \\textit{Stark gauge protection}, which entails a linear sum in\ngauge-symmetry local (pseudo)generators weighted by a Stark potential. Using\nexact diagonalization and Krylov-based methods, we show how this scheme can\nstabilize or even enhance disorder-free localization against gauge-breaking\nerrors in $\\mathrm{U}(1)$ and $\\mathbb{Z}_2$ gauge theories up to all\naccessible evolution times, without inducing \\textit{bona fide} Stark many-body\nlocalization. We show through a Magnus expansion that the dynamics under Stark\ngauge protection is described by an effective Hamiltonian where gauge-breaking\nterms are suppressed locally by the protection strength and additionally by the\nmatter site index, which we argue is the main reason behind stabilizing the\nlocalization up to all accessible times. Our scheme is readily feasible in\nmodern ultracold-atom experiments and Rydberg-atom setups with optical\ntweezers.",
        "positive": "Generating mesoscopic Bell states via collisions of distinguishable\n  quantum bright solitons: We investigate numerically the collisions of two distinguishable quantum\nmatter-wave bright solitons in a one-dimensional harmonic trap. We show that\nsuch collisions can be used to generate mesoscopic Bell states which can\nreliably be distinguished from statistical mixtures. Calculation of the\nrelevant s-wave scattering lengths predicts that such states could potentially\nbe realized in quantum-degenerate mixtures of 85Rb and 133Cs. In addition to\nfully quantum simulations for two distinguishable two-particle solitons, we use\na mean-field description supplemented by a stochastic treatment of quantum\nfluctuations in the soliton's center of mass: We demonstrate the validity of\nthis approach by comparison to a mathematically rigorous effective potential\ntreatment of the quantum many-particle problem."
    },
    {
        "anchor": "Solitons in Multi-Component Nonlinear Schrodinger Models: A Survey of\n  Recent Developments: In this review we try to capture some of the recent excitement induced by\nexperimental developments, but also by a large volume of theoretical and\ncomputational studies addressing multi-component nonlinear Schrodinger models\nand the localized structures that they support. We focus on some prototypical\nstructures, namely the dark-bright and dark-dark solitons. Although our focus\nwill be on one-dimensional, two-component Hamiltonian models, we also discuss\nvariants, including three (or more)-component models, higher-dimensional\nstates, as well as dissipative settings. We also offer an outlook on\ninteresting possibilities for future work on this theme.",
        "positive": "Many-body physics of low-density dipolar bosons in box potentials: Crystallization is a generic phenomenon in classical and quantum mechanics\narising in a variety of physical systems. In this work we focus on a specific\nplatform, ultracold dipolar bosons, which can be realized in experiments with\ndilute gases. We review the relevant ingredients leading to crystallization,\nnamely the interplay of contact and dipole-dipole interactions and system\ndensity, as well as the numerical algorithm employed. We characterize the\nmany-body phases investigating correlations and superfluidity."
    },
    {
        "anchor": "Observation of a superradiant Mott insulator in the Dicke-Hubbard model: It is well known that the bosonic Hubbard model possesses a Mott insulator\nphase. Likewise, it is known that the Dicke model exhibits a self-organized\nsuperradiant phase. By implementing an optical lattice inside of a high finesse\noptical cavity both models are merged such that an extended Hubbard model with\ncavity-mediated infinite range interactions arises. In addition to a normal\nsuperfluid phase, two superradiant phases are found, one of them coherent and\nhence superfluid and one incoherent Mott insulating.",
        "positive": "Phase Coherent Oscillations of Excitonic Photocapacitance and\n  Bose-Einstein Condensation in Quantum Coupled 0D-2D Heterostructure: We report quantum coherent oscillations of photocapacitance of a\ndouble-barrier resonant tunneling heterostructure with bias at 10 K. Periodic\npresence and absence of sharp excitonic transitions in photocapacitance spectra\nwith increasing bias demonstrate strong coupling between InAs quantum dots (0D)\nand triangular GaAs quantum well (2D). Coherent resonant tunneling in this\n0D-2D heterostructure establishes the momentum space narrowing of excitonic\nBose-Einstein Condensation. Drastic increase of indirect exciton densities\nbelow 70 K reveal that excitonic wave functions anchored with each InAs quantum\ndots can laterally overlap across wide region around 200 micron to create a\nmacroscopic quantum state of excitonic Bose-Einstein condensate. This itself\npoints out the difficulties encountered in the usual 2D-2D bilayers and coupled\nquantum well samples used earlier to study excitonic BEC. Finally, we predict\nhow coupled quantum-dots and quantum-well heterostructures can display\nexcitonic Bose-Einstein condensation at even higher temperatures."
    },
    {
        "anchor": "Critical dynamics at the Anderson localization mobility edge: We study the critical dynamics of matter waves at the 3D Anderson mobility\nedge in cold-atom disorder quench experiments. General scaling arguments are\nsupported by precision numerics for the spectral function, diffusion\ncoefficient, and localization length in isotropic blue-detuned speckle\npotentials. We discuss signatures of critical slowdown in the time-dependent\ncentral column density of a spreading wave packet, and evaluate the prospects\nof observing anomalous diffusion right at criticality.",
        "positive": "Ground state properties of a two dimensional Fermi superfluid with an\n  anisotropic spin-orbit coupling: We performed a theoretical investigation on the ground state properties of a\ntwo dimensional ultra-cold Fermi superfluid with an anisotropic spin-orbit\ncoupling (SOC). In the absence of Zeeman field, the system evolves from weak\ncoupling BCS regime to strongly interacting BEC regime (BCS-BEC crossover) with\nincreasing either the two-particle interaction strength or SOC parameters. We\nfocused on the behaviors of pairing parameter and density of states (DOS) when\nincreasing the anisotropic parameter of the SOC. Surprisingly, we discovered\nthat the gap parameter decreases with increasing the anisotropic parameters,\nbut the DOS at the Fermi surface shows non-monotonic behavior as a function of\nthe anisotropic parameter. In the presence of the Zeeman field, we discussed a\nparticular type of topological phase transition by obtaining the analytical\nresult of the topological invariant and directly related this quantum phase\ntransition with a sudden change of the ground state wave-function. Effects of\nhigher partial wave pairing terms on this topological phase transition were\nbriefly discussed."
    },
    {
        "anchor": "Controlled pairing symmetry of the superfluid state in systems of\n  three-component repulsive fermionic atoms in optical lattices: We investigate the pairing symmetry of the superfluid state in repulsively\ninteracting three-component (colors) fermionic atoms in optical lattices. When\ntwo of the three color-dependent repulsions are much larger than the other,\npairing symmetry is an extended s wave, although the superfluid state appears\nadjacent to the paired Mott insulator in the phase diagram. As the difference\nbetween the three repulsions is decreased in square optical lattices, the\nextended s-wave pairing changes into a nodal s-wave pairing and then into a\nd-wave pairing. This change in pairing symmetry is attributed to the\ncompetition among the density fluctuations of unpaired atoms, the quantum\nfluctuations of the color-density wave, and those of the color-selective\nantiferromagnet. This phenomenon can be studied using existing experimental\ntechniques.We investigate the pairing symmetry of the superfluid state in\nrepulsively interacting three-component (color) fermionic atoms in optical\nlattices. When two of the three color-dependent repulsions are much stronger\nthan the other, pairing symmetry is an extended $s$ wave although the\nsuperfluid state appears adjacent to the paired Mott insulator in the phase\ndiagram. On the other hand, when two of the three color-dependent repulsions\nare weaker than the other, pairing symmetry is a d_{x^2-y^2}-wave. This change\nin pairing symmetry is attributed to the change in the dominant quantum\nfluctuations from the density fluctuations of unpaired atoms and the\ncolor-density wave fluctuations to the color-selective antiferromagnet\nfluctuations. This phenomenon can be studied using existing experimental\ntechniques.",
        "positive": "One-body dynamical correlation function of Lieb-Liniger model at finite\n  temperature: The dynamical correlated properties of one-dimensional (1D) Bose gases\nprovide profound understanding of novel physics emergent from collective\nexcitations, for instance, the breakdown of off-diagonal long-range order, and\nthe establishment of Tomonaga-Luttinger liquid (TLL) theory. However, due to\nthe non-perturbative nature of 1D many-body systems, the exact evaluation of\ncorrelation functions is notoriously difficult. Here by means of form factor\napproach based on algebraic Bethe ansatz and numerics, we present a thorough\nstudy on the one-body dynamical correlation function (1BDCF) of the\nLieb-Liniger model at finite temperature. The influence of thermal fluctuation\nand dynamical interaction on the behavior of 1BDCF has been demonstrated and\nanalyzed from various perspectives, including the spectral distribution, the\nline-shape of 1BDCF, and the static correlations etc. The static correlation\nproperties, i.e. the momentum distribution and one body density matrix are\nshown in good agreement with the TLL prediction."
    },
    {
        "anchor": "Exploring ultracold collisions in $^6$Li-$^{53}$Cr Fermi mixtures:\n  Feshbach resonances and scattering properties of a novel alkali-transition\n  metal system: We investigate ultracold collisions in a novel mixture of $^6$Li and\n$^{53}$Cr fermionic atoms, discovering more than 50 interspecies Feshbach\nresonances via loss spectroscopy. Building a full coupled-channel model, we\nunambiguously characterize the $^{6}$Li-$^{53}$Cr scattering properties and\nyield predictions for other isotopic pairs. In particular, we identify various\nFeshbach resonances that enable the controlled tuning of elastic $s$- and\n$p$-wave $^{6}$Li-$^{53}$Cr interactions. Our studies thus make\nlithium-chromium mixtures emerge as optimally-suited platforms for the\nexperimental search of elusive few- and many-body regimes of highly-correlated\nfermionic matter, and for the realization of a new class of ultracold polar\nmolecules possessing both electric and magnetic dipole moments.",
        "positive": "Emergence of Chiral Magnetism in Spinor Bose-Einstein Condensate with\n  Rashba Coupling: Hydrodynamic theory of the spinor BEC condensate with Rashba spin-orbit\ncoupling is presented. A close mathematical analogy of the Rashba-BEC model to\nthe recently developed theory of chiral magnetism is found. Hydrodynamic\nequations for mass density, superfluid velocity, and the local magnetization\nare derived. The mass current is shown to contain an extra term proportional to\nthe magnetization direction, as a result of the Rashba coupling. Elementary\nexcitations around the two known ground states of the Rashba-BEC Hamiltonian,\nthe plane-wave and the stripe states, are worked out in the hydrodynamic\nframework, highlighting the cross-coupling of spin and superflow velocity\nexcitations due to the Rashba term."
    },
    {
        "anchor": "Exposing the quantum geometry of spin-orbit coupled Fermi superfluids: The coupling between a quantum particle's intrinsic angular momentum and its\ncenter-of-mass motion gives rise to the so-called helicity states that are\ncharacterized by the projection of the spin onto the direction of momentum. In\nthis paper, by unfolding the superfluid-density tensor into its intra-helicity\nand inter-helicity components, we reveal that the latter contribution is\ndirectly linked with the total quantum metric of the helicity bands. We\nconsider both Rashba and Weyl spin-orbit couplings across the BCS-BEC\ncrossover, and show that the geometrical inter-helicity contribution is\nresponsible for up to a quarter of the total superfluid density. We believe\nthis is one of those elusive effects that may be measured within the\nhighly-tunable realm of cold Fermi gases.",
        "positive": "Effect on Cavity Optomechanics of the Interaction Between a Cavity Field\n  and a 1D Interacting Bosonic Gas: Revised entirely and a new figure added."
    },
    {
        "anchor": "BCS-BEC crossover of Spin Polarized Fermi Gases with Rashba Spin-Orbit\n  Coupling: We study the BCS-Bose Einstein Condensation (BEC) crossover of a three\ndimensional spin polarized Fermi gas with Rashba spin-orbital-coupling (SOC).\nAt finite temperature, the effects of non-condensed pairs due to the thermal\nexcitation are considered based on the $G_0G$ pair fluctuation theory. These\nfluctuations generate a pseudogap even persistent above $T_c$. Within this\nframework, the Sarma state or the spin polarized superfluid state and polarized\npseudogap state are explored in detail. The resulting $T_c$ curves show that\nthe enhancement of pairing due to the SOC roughly cancels out the suppression\nof pairing due to the population imbalance. Thus we observed that in a large\nportion of the parameter space, the polarized superfluid state are stabilized\nby the SOC.",
        "positive": "An oscillating Casimir potential between two impurities in a spin-orbit\n  coupled Bose-Einstein condensate: We study the Casimir potential between two impurities immersed in a\nspin-orbit coupled BoseEinstein condensate (BEC) with plane-wave order. We find\nthat, by exchanging the virtual phonons/excitations, a remarkable anisotropic\noscillating potential with both positive and negative parts can be induced\nbetween the impurities, with the period of the oscillation depending on the\nspin-orbit coupling strength. As a consequence, this would inevitably lead to a\nnon-central Casimir force, which can be tuned by varying the strength of\nspin-orbit coupling . These results are elucidated for BECs with\none-dimensional Raman-induced and two-dimensional Rashba-type SOC."
    },
    {
        "anchor": "Experimental realization of strong effective magnetic fields in optical\n  superlattice potentials: We present the experimental generation of large effective magnetic fields for\nultracold atoms using photon-assisted tunneling in an optical superlattice. The\nunderlying method does not rely on the internal structure of the atoms and\ntherefore constitutes a general approach to realize widely tunable artificial\ngauge fields without the drawbacks of near-resonant optical potentials. When\nhopping in the lattice, the accumulated phase shift by an atom is equivalent to\nthe Aharonov-Bohm phase of a charged particle exposed to a staggered magnetic\nfield of large magnitude, on the order of one flux quantum per plaquette. We\nstudy the ground state of this system and observe that the frustration induced\nby the magnetic field can lead to a degenerate ground state for non-interacting\nparticles. We provide a local measurement of the phase acquired by single\nparticles due to photon-assisted tunneling. Furthermore, the quantum cyclotron\norbit of single atoms in the lattice exposed to the effective magnetic field is\ndirectly revealed.",
        "positive": "Microscopic pairing theory of a binary Bose mixture with interspecies\n  attractions: bosonic BEC-BCS crossover and ultradilute low-dimensional\n  quantum droplets: Ultradilute quantum droplets are intriguing new state of matter, in which the\nattractive mean-field force can be balanced by the repulsive force from quantum\nfluctuations to avoid collapse. Here, we present a microscopic theory of\nultradilute quantum droplets in three-, one- and two-dimensional two-component\nBose-Bose mixtures, by generalizing the conventional Bogoliubov theory to\ninclude the bosonic pairing arising from the interspecies attraction. Our\npairing theory is fully equivalent to a variational approach and hence gives an\nupper bound for the energy of quantum droplets. In three dimensions, we predict\nthe existence of a strongly interacting Bose droplet at the crossover from\nBose-Einstein condensates (BEC) to Bardeen--Cooper--Schrieffer (BCS)\nsuperfluids and map out the bosonic BEC-BCS crossover phase diagram. In one\ndimension, we find that the energy of the one-dimensional Bose droplet\ncalculated by the pairing theory is in an excellent agreement with the latest\ndiffusion Monte Carlo simulation {[}Phys. Rev. Lett. \\textbf{122}, 105302\n(2019){]}, for nearly all the interaction strengths at which quantum droplets\nexist. In two dimensions, we show that Bose droplets disappear and may turn\ninto a soliton-like many-body bound state, when the interspecies attraction\nexceeds a critical value. Below the threshold, the pairing theory predicts more\nor less the same results as the Bogoliubov theory derived by Petrov and\nAstrakharchik {[}Phys. Rev. Lett. \\textbf{117}, 100401 (2016){]}. The predicted\nenergies from both theories are higher than the diffusion Monte Carlo results,\ndue to the weak interspecies attraction and the increasingly important role\nplayed by the beyond-Bogoliubov-approximation effect in two dimensions."
    },
    {
        "anchor": "Comment on \"Topological Pumping in a Floquet-Bloch Band\": This manuscript is a comment about a published article in PRL 129, 053201\n(2022) by J. Minguzzi et al.",
        "positive": "Two impurities in a Bose-Einstein condensate: from Yukawa to Efimov\n  attracted polarons: The well-known Yukawa and Efimov potentials are two different mediated\ninteraction potentials. The first one arises in quantum field theory from the\nexchange of virtual particles. The second one is mediated by a real particle\nresonantly interacting with two other particles. This Letter shows how two\nimpurities immersed in a Bose-Einstein condensate can exhibit both phenomena.\nFor a weak impurity-boson attractive interactionattraction with the condensate,\nthe two impurities form two polarons that interact through a weak Yukawa\nattraction mediated by virtual excitations. For a resonant attraction with the\ncondensate, the exchanged excitation becomes a real boson and the mediated\ninteraction changes to a strong Efimov attraction that can bind the two\npolarons. The resulting bipolarons turn into in-medium Efimov trimers made of\nthe two impurities and one boson. Evidence of this physics could be seen in\nultracold mixtures of atoms."
    },
    {
        "anchor": "Realization of a stroboscopic optical lattice for cold atoms with\n  subwavelength spacing: Optical lattices are typically created via the ac-Stark shift, which are\nlimited by diffraction to periodicities $\\ge\\lambda/2$, where $\\lambda$ is the\nwavelength of light used to create them. Lattices with smaller periodicities\nmay be useful for many-body physics with cold atoms and can be generated by\nstroboscopic application of a phase-shifted lattice with subwavelength\nfeatures. Here we demonstrate a $\\lambda/4$-spaced lattice by stroboscopically\napplying optical Kronig-Penney(KP)-like potentials which are generated using\nspatially dependent dark states. We directly probe the periodicity of the\n$\\lambda/4$-spaced lattice by measuring the average probability density of the\natoms loaded into the ground band of the lattice. We measure lifetimes of atoms\nin this lattice and discuss the mechanisms that limit the applicability of this\nstroboscopic approach.",
        "positive": "Second root of dilute Bose-Fermi mixtures: We discuss an equilibrium mean-field properties of mixtures consisting of\nbosons and spin-polarized fermionic atoms with a point-like interaction in an\narbitrary dimension $2<d<4$. Particularly, we discuss except the standard\nweak-coupling limit of the system with slightly depleted Bose condensate and\nalmost ideal Fermi gas, the (meta)stable phase with dimers composed exactly of\none boson and one fermion. The peculiarities of the fermion-dimer and the\nboson-dimer three-body effective interactions and their impact on the\nthermodynamic stability of the dilute Bose-Fermi mixtures are elucidated."
    },
    {
        "anchor": "Color superfluidity of neutral ultra-cold fermions in the presence of\n  color-flip and color-orbit fields: We describe how color superfluidity is modified in the presence of color-flip\nand color-orbit fields in the context of ultra-cold atoms, and discuss\nconnections between this problem and that of color superconductivity in quantum\nchromodynamics. We consider s-wave contact interactions between different\ncolors, and we identify superfluid phases, with five being nodal and one being\nfully gapped. When our system is described in a mixed color basis, the\nsuperfluid order parameter tensor is characterized by six independent\ncomponents with explicit momentum dependence induced by color-orbit coupling.\nThe nodal superfluid phases are topological in nature, and the low temperature\nphase diagram of color-flip field versus interaction parameter exhibits a\npentacritical point, where all five nodal color superfluid phases converge.\nThese results are in sharp contrast to the case of zero color-flip and\ncolor-orbit fields, where the system has perfect U(3) symmetry and possess a\nsuperfluid phase that is characterized by fully gapped quasiparticle\nexcitations with a single complex order parameter with no momentum dependence\nand by inert unpaired fermions representing a non-superfluid component.\nFurthermore, we analyse the order parameter tensor in a total pseudo-spin\nbasis, investigate its momentum dependence in the singlet, triplet and quintet\nsectors, and compare the results with the simpler case of spin-1/2 fermions in\nthe presence of spin-flip and spin-orbit fields. Finally, we analyse in detail\nspectroscopic properties of color superfluids in the presence of color-flip and\ncolor-orbit fields, such as the quasiparticle excitation spectrum, momentum\ndistribution, and density of states to help characterize all the encountered\ntopological quantum phases, which can be realized in fermionic isotopes of\nLithium, Potassium and Ytterbium atoms with three internal states trapped.",
        "positive": "Position- and momentum-space two-body correlations in a weakly\n  interacting trapped condensate: We investigate the position- and momentum-space two--body correlations in a\nweakly interacting, harmonically trapped atomic Bose-Einstein condensed gas at\nlow temperatures. The two-body correlations are computed within the Bogoliubov\napproximation and the peculiarities of the trapped gas are highlighted in\ncontrast to the spatially homogeneous case. In the position space, we recover\nthe anti-bunching induced by the repulsive inter-atomic interaction in the\ncondensed fraction localized around the trap center and the bunching in the\nouter thermal cloud. In the momentum space, bunching signatures appear for\neither equal or opposite values of the momentum and display peculiar features\nas a function of the momentum and the temperature. In analogy to the optical\nHanbury Brown and Twiss effect, the amplitude of the bunching signal at\nclose-by momenta is fixed by the chaotic nature of the matter field state and\nits linewidth is shown to be set by the (inverse of the) finite spatial size of\nthe associated in-trap momentum components. In contrast, the linewidth of the\nbunching signal at opposite-momenta is only determined by the condensate size."
    },
    {
        "anchor": "Reply to Comments on \"Universal and Non-Universal Correction Terms of\n  Bose Gases in Dilute Region: A Quantum Monte Carlo Study\": We reply to the comments on our previous paper J. Phys. Soc. Jpn. 91, 024001\n(2022)",
        "positive": "Z2 characterization for three-dimensional multiband Hubbard models: We introduce three numerical methods for characterizing the topological\nphases of three-dimensional multiband Hubbard models based on twisted boundary\nconditions, Wilson loops, as well as the local topological marker. We focus on\nthe half-filled, three-dimensional time-reversal-invariant Hofstadter model\nwith finite spin-orbit coupling. Besides the weak and strong topological\ninsulator phases we find a nodal line semimetal in the parameter regime between\nthe two three-dimensional topological insulator phases. Using dynamical\nmean-field theory combined with the topological Hamiltonian approach we find\nstabilization of these three-dimensional topological states due to the Hubbard\ninteraction. We study surface states which exhibit an asymmetry between left\nand right surface originating from the broken parity symmetry of the system.\nOur results set the stage for further research on inhomogeneous\nthree-dimensional topological systems, proximity effects, topological Mott\ninsulators, non-trivially linked nodal line semimetals and circuit-based\nquantum simulators."
    },
    {
        "anchor": "Topological transitions of interacting bosons in one-dimensional\n  bi-chromatic optical lattices: Ultra-cold atoms in 1D bi-chromatic lattices constitute a surprisingly simple\nsystem for the study of topological insulators. We show that topological phase\ntransitions constitute a general feature of bosons in 1D bi-chromatic lattices,\nand that these transitions may occur both as a function of the superlattice\nstrength and due to inter-site interactions. We discuss in addition the\ntopological character of incommensurate density wave phases in quasi-periodic\nlattices.",
        "positive": "Information entropy for a two-dimensional rotating Bose-Einstein\n  condensate: We study the information entropy, order, disorder, and complexity for the\ntwo-dimensional (2D) rotating and nonrotating Bose-Einstein condensates. The\nchoice of our system is a complete theoretical laboratory where the complexity\nis controlled by the two-body contact interaction strength and the rotation\nfrequency ($\\Omega$) of the harmonic trap. The 2D nonrotating condensate shows\nthe complexity of the category I where the disorder-order transition is\ntriggered by the interaction strength. In the rotating condensates, $\\Omega$ is\nchosen as the disorder parameter when the interaction strength is fixed. With\nrespect to $\\Omega$, the complexity shifts between the maximum and minimum\nconfirm the existence of category II complexity in the rotating condensate.\nAlso, We consider the interaction strength as the disorder parameter when\n$\\Omega$ is unchanged and complexity as a function of interaction strength\nexhibits category III complexity. The present work also includes the\ncalculation of upper bound and lower bound of entropy for 2D quantum systems."
    },
    {
        "anchor": "Emptiness Formation Probability in 1D Bose Liquids: We study emptiness formation probability (EFP) in interacting 1D Bose\nliquids. That is the probability that a snapshot of its ground state reveals\nexactly zero number of particles within the interval $|x|<R$. For a weakly\ninteracting liquid there is parametrically wide regime $n^{-1} < R <\\xi$ (here\n$n$ is the average density and $\\xi$ is the healing length), where EFP exhibits\na non-trivial crossover from the Poisson to the Gaussian behavior. We employ\nthe instanton technique [A. Abanov, 2004] to study quantitative details of\nthese regime and compare it with previously reported limited cases.",
        "positive": "Identifying Quantum Phase Transitions using Artificial Neural Networks\n  on Experimental Data: Machine learning techniques such as artificial neural networks are currently\nrevolutionizing many technological areas and have also proven successful in\nquantum physics applications. Here we employ an artificial neural network and\ndeep learning techniques to identify quantum phase transitions from single-shot\nexperimental momentum-space density images of ultracold quantum gases and\nobtain results, which were not feasible with conventional methods. We map out\nthe complete two-dimensional topological phase diagram of the Haldane model and\nprovide an accurate characterization of the superfluid-to-Mott-insulator\ntransition in an inhomogeneous Bose-Hubbard system. Our work points the way to\nunravel complex phase diagrams of general experimental systems, where the\nHamiltonian and the order parameters might not be known."
    },
    {
        "anchor": "Quantum crystallography of Rydberg-dressed Bose gases on a square\n  lattice: We numerically investigate the quantum crystallographic phases of a\nRydberg-dressed Bose gas loaded on a square lattice by using the mean-field\nGross--Pitaevskii model. For a relatively weak lattice confinement, the phases\nof ground state undergo amorphism, polycrystal, and polymorphism following the\nincrease of the blockade radius, and if the confinement is stronger, a single\ncrystal with a specific filling factor will be formed. In order to\ndistinctively characterize these phases, the structure function is also\nstudied. In such an anisotropic system, we report that the first diagonal\nelement of the superfluid-fraction tensor should be a measurable quantity, and\nan anisotropy parameter can be defined. In addition, for such crystallographic\nphases, the interaction potential can manifest where the grain boundaries\nappear.",
        "positive": "Bose-condensed atomic systems with nonlocal interaction potentials: The general approach for describing systems with Bose-Einstein condensate,\nwhere atoms interact through nonlocal pair potentials, is presented. A special\nattention is paid to nonintegrable potentials, such as the dipolar interaction\npotential. The potentials that are not absolutely integrable can have not well\ndefined Fourier transforms. Using formally such not defined Fourier transforms\nleads to unphysical conclusions. For making the Fourier transform well defined,\nthe interaction potential has to be regularized. This is illustrated by the\nexample of dipolar interactions."
    },
    {
        "anchor": "Emergence of unstable avoided crossing in the collective excitations of\n  spin-1 spin-orbit coupled Bose-Einstein condensates: We present the analytical and numerical results on the collective excitation\nspectrum of quasi-one-dimensional spin-orbit (SO) coupled spin-1 Bose-Einstein\ncondensates. The collective excitation spectrum, using Bogoliubov-de-Gennes\ntheory, reveals the existence of a diverse range of phases in the SO and Rabi\n($k_L-\\Omega$) coupling plane. Based on eigenvalue of the excitation spectrum,\nwe categorize the $k_L-\\Omega$ plane into three distinct regions. In region I,\na stable mode with phonon-like excitations is observed. In region IIa, single\nand multi-band instabilities are noted with a gapped mode, while multi-band\ninstability accompanied by a gapless mode between low-lying and first excited\nstates is realized in region IIb, which also provides evidence of unstable\navoided crossing between low-lying and first excited modes The gap between\nlow-lying and first-excited states increases upon increasing the Rabi coupling\nwhile decreases upon increase of SO coupling. Using eigenvector analysis, we\nconfirm the presence of the spin-dipole mode in the spin-like modes in Region\nII. We corroborate the nature of the collective excitation through real-time\ndynamical evolution of the ground state perturbed with the quench of the trap\nusing the mean-field Gross-Pitaevskii model. This analysis suggests the\npresence of dynamical instability leading to the disappearance of the $0$-th\ncomponent of the condensate. In Region III, mainly encompassing $\\Omega \\sim 0$\nand finite $k_L$, we observe phonon-like excitations in both the first excited\nand the low-lying state. The eigenvectors in this region reveal alternative in-\nand out-of-phase behaviours of the spin components. Numerical analysis reveals\nthe presence of a super stripe phase for small Rabi coupling in this region,\nwherein the eigenvector indicates the presence of more complicated\nspin-like-density mixed modes.",
        "positive": "Ground-state phase diagram and excitation spectrum of a Bose-Einstein\n  condensate with spin-orbital-angular-momentum coupling: We investigate the ground-state phase diagram and excitation spectrum of an\ninteracting spinor Bose-Einstein condensate with spin-orbital-angular-momentum\n(SOAM) coupling realized in recent experiments by introducing atomic Raman\ntransition with a pair of copropagating Laguerre-Gaussian laser beams that\ncarry different orbital angular momenta (OAM) [Chen et al., Phys. Rev. Lett.\n121, 113204 (2018) and Zhang et al., Phys. Rev. Lett. 122, 110402 (2019)].\nBecause of the ground-state degeneracy of the single-particle Hamiltonian at\nvanishing detuning, several angular-stripe phases, which are superposition of\nstates with different angular quantum numbers, appear in the phase diagram.\nHowever, these phases normally exist at small detuning, which makes them hard\nto be probed in experiments. We show that for a large OAM difference of the\nlaser beams, an asymmetric kind of angular-stripe phase can exist even at large\ndetuning. The excitation spectra in different phases exhibit distinct features:\nIn the angular-stripe phase there exist two gapless bands corresponding to the\nbroken U(1) and rotational symmetries, while in the half-skyrmion phase the\ngapless band exhibits a roton-like structure. Our predictions of the\nangular-stripe phases and the low-energy excitations can be examined in\nrecently realized BECs with SOAM coupling."
    },
    {
        "anchor": "Observing Chiral Superfluid Order by Matter-Wave Interference: The breaking of time reversal symmetry via the spontaneous formation of\nchiral order is ubiquitous in nature. Here, we present an unambiguous\ndemonstration of this phenomenon for atoms Bose-Einstein condensed in the\nsecond Bloch band of an optical lattice. As a key tool we use a matter wave\ninterference technique, which lets us directly observe the phase properties of\nthe superfluid order parameter and allows us to reconstruct the spatial\ngeometry of certain low energy excitations, associated with the formation of\ndomains of different chirality. Our work marks a new era of optical lattices\nwhere orbital degrees of freedom play an essential role for the formation of\nexotic quantum matter, similarly as in electronic systems.",
        "positive": "Interaction-Enhanced Group Velocity of Bosons in the Flat Band of an\n  Optical Kagome Lattice: Geometric frustration of particle motion in a kagome lattice causes the\nsingle-particle band structure to have a flat s-orbital band. We probe this\nband structure by exciting a Bose-Einstein condensate into excited Bloch states\nof an optical kagome lattice, and then measuring the group velocity through the\natomic momentum distribution. We find that interactions renormalize the band\nstructure of the kagome lattice, greatly increasing the dispersion of the third\nband that, according to non-interacting band theory, should be nearly\nnon-dispersing. Measurements at various lattice depths and gas densities agree\nquantitatively with predictions of the lattice Gross-Pitaevskii equation,\nindicating that the observed distortion of band structure is caused by the\ndisortion of the overall lattice potential away from the kagome geometry by\ninteractions."
    },
    {
        "anchor": "Constructing classical field for a Bose-Einstein condensate in arbitrary\n  trapping potential; quadrupole oscillations at nonzero temperatures: We optimize the classical field approximation of the version described in J.\nPhys. B 40, R1 (2007) for the oscillations of a Bose gas trapped in a harmonic\npotential at nonzero temperatures, as experimentally investigated by Jin et al.\n[Phys. Rev. Lett. 78, 764 (1997)]. Similarly to experiment, the system response\nto external perturbations strongly depends on the initial temperature and on\nthe symmetry of perturbation. While for lower temperatures the thermal cloud\nfollows the condensed part, for higher temperatures the thermal atoms oscillate\nrather with their natural frequency, whereas the condensate exhibits a\nfrequency shift toward the thermal cloud frequency (m=0 mode), or in the\nopposite direction (m=2 mode). In the latter case, for temperatures approaching\ncritical, we find that the condensate begins to oscillate with the frequency of\nthe thermal atoms, as in the m=0 mode. A broad range of frequencies of the\nperturbing potential is considered.",
        "positive": "Excitation of knotted vortex lines in matter waves: We study the creation of knotted ultracold matter waves in Bose-Einstein\ncondensates via coherent two-photon Raman transitions with a $\\Lambda$ level\nconfiguration. The Raman transition allows an indirect transfer of atoms from\nthe internal state $\\left| a \\right\\rangle$ to the target state $\\left| b\n\\right\\rangle$ via an excited state $\\left| e \\right\\rangle$, that would be\notherwise dipole-forbidden. This setup enables us to imprint three-dimensional\nknotted vortex lines embedded in the the probe field to the density in the\ntarget state. We elaborate on experimental feasibility as well as on subsequent\ndynamics of the matter wave."
    },
    {
        "anchor": "Exact numerical methods for a many-body Wannier Stark system: We present exact methods for the numerical integration of the Wannier-Stark\nsystem in a many-body scenario including two Bloch bands. Our ab initio\napproaches allow for the treatment of a few-body problem with bosonic\nstatistics and strong interparticle interaction. The numerical implementation\nis based on the Lanczos algorithm for the diagonalization of large, but sparse\nsymmetric Floquet matrices. We analyze the scheme efficiency in terms of the\ncomputational time, which is shown to scale polynomially with the size of the\nsystem. The numerically computed eigensystem is applied to the analysis of the\nFloquet Hamiltonian describing our problem. We show that this allows, for\ninstance, for the efficient detection and characterization of avoided crossings\nand their statistical analysis. We finally compare the efficiency of our\nLanczos diagonalization for computing the temporal evolution of our many-body\nsystem with an explicit fourth order Runge-Kutta integration. Both\nimplementations heavily exploit efficient matrix-vector multiplication schemes.\nOur results should permit an extrapolation of the applicability of exact\nmethods to increasing sizes of generic many-body quantum problems with bosonic\nstatistics.",
        "positive": "Transport, atom blockade and output coupling in a Tonks-Girardeau gas: Recent experiments have demonstrated how quantum-mechanical impurities can be\ncreated within strongly correlated quantum gases and used to probe the\ncoherence properties of these systems [S. Palzer, C. Zipkes, C. Sias, and M.\nK\\\"ohl, Phys. Rev. Lett. 103, 150601 (2009).]. Here we present a\nphenomenological model to simulate such an output coupler for a Tonks-Girardeau\ngas that shows qualitative agreement with the experimental results for atom\ntransport and output coupling. Our model allows us to explore nonequilibrium\ntransport phenomena in ultracold quantum gases and leads us to predict a regime\nof atom blockade, where the impurity component becomes localized in the parent\ncloud despite the presence of gravity. We show that this provides a stable\nmixed-species quantum gas in the strongly correlated limit."
    },
    {
        "anchor": "Projection Optimization Method for Open-Dissipative Quantum Fluids and\n  its Application to a Single Vortex in a Photon Bose-Einstein Condensate: Open dissipative systems of quantum fluids have been well studied\nnumerically. In view of a complementary analytical description we extend here\nthe variational optimization method for Bose-Einstein condensates of closed\nsystems to open-dissipative condensates. The resulting projection optimization\nmethod is applied to a complex Gross-Pitaevski equation, which models\nphenomenologically a photon Bose-Einstein condensate. Together with known\nmethods from hydrodynamics we obtain an approximate vortex solution, which\ndepends on the respective open system parameters and has the same properties as\nobtained numerically in the literature.",
        "positive": "Mass-imbalanced Three-Body Systems in Two Dimensions: We consider three-body systems in two dimensions with zero-range interactions\nfor general masses and interaction strengths. The momentum-space Schr\\\"odinger\nequation is solved numerically and in the Born-Oppenheimer (BO) approximation.\nThe BO expression is derived using separable potentials and yields a concise\nadiabatic potential between the two heavy particles. The BO potential is\nCoulomb-like and exponentially decreasing at small and large distances,\nrespectively. While we find similar qualitative features to previous studies,\nwe find important quantitative differences. Our results demonstrate that\nmass-imbalanced systems that are accessible in the field of ultracold atomic\ngases can have a rich three-body bound state spectrum in two dimensional\ngeometries. Small light-heavy mass ratios increase the number of bound states.\nFor 87Rb-87Rb-6Li and 133Cs-133Cs-6Li we find respectively 3 and 4 bound\nstates."
    },
    {
        "anchor": "Stabilizing Gauge Theories in Quantum Simulators: A Brief Review: Quantum simulation is at the heart of the ongoing \"second\" quantum\nrevolution, with various synthetic quantum matter platforms realizing evermore\nexotic condensed matter and particle physics phenomena at high levels of\nprecision and control. The implementation of gauge theories on modern quantum\nsimulators is especially appealing due to three main reasons: (i) it offers a\nnew probe of high-energy physics on low-energy tabletop devices, (ii) it allows\nexploring condensed matter phenomena that are prominent in gauge theories even\nwithout a direct connection to high-energy physics, and (iii) it serves as a\nbanner of experimental benchmarking given the plethora of local constraints\narising from the gauge symmetry that need to be programmed and controlled. In\norder to faithfully model gauge-theory phenomena on a quantum simulator,\nstabilizing the underlying gauge symmetry is essential. In this brief review,\nwe outline recently developed experimentally feasible methods introduced by us\nthat have shown, in numerical and experimental benchmarks, reliable\nstabilization of quantum-simulator implementations of gauge theories. We\nexplain the mechanism behind these \\textit{linear gauge protection} schemes,\nand illustrate their power in protecting salient features such as gauge\ninvariance, disorder-free localization, quantum many-body scars, and other\nphenomena of topical interest. We then discuss their application in experiments\nbased on Rydberg atoms, superconducting qubits, and in particular ultracold\nneutral atoms in optical superlattices. We hope this review will illustrate\nsome facets of the exciting progress in stabilization of gauge symmetry and in\ngauge-theory quantum simulation in general.",
        "positive": "Energy and structural properties of $N$-boson clusters attached to\n  three-body Efimov states: Two-body zero-range interactions and the role of\n  the three-body regulator: The low-energy spectrum of $N$-boson clusters with pairwise zero-range\ninteractions is believed to be governed by a three-body parameter. We study the\nground state of $N$-boson clusters with infinite two-body $s$-wave scattering\nlength by performing {\\em{ab initio}} Monte Carlo simulations. To prevent\nThomas collapse, different finite-range three-body regulators are used. The\nenergy and structural properties for the three-body Hamiltonian with two-body\nzero-range interactions and three-body regulator are in much better agreement\nwith the \"ideal zero-range Efimov theory\" results than those for Hamiltonian\nwith two-body finite-range interactions. For larger clusters we find that the\nground state energy and structural properties of the Hamiltonian with two-body\nzero-range interactions and finite-range three-body regulators are not\nuniversally determined by the three-body parameter, i.e., dependences on the\nspecific form of the three-body regulator are observed. For comparison, we\nconsider Hamiltonian with two-body van der Waals interactions and no three-body\nregulator. For the interactions considered, the ground state energy of the\n$N$-body clusters is---if scaled by the three-body ground state energy---fairly\nuniversal, i.e., the dependence on the short-range details of the two-body van\nder Waals potentials is small. Our results are compared with the literature."
    },
    {
        "anchor": "Strongly interacting one-dimensional quantum gas mixtures with weak\n  p-wave interactions: We study one-dimensional strongly interacting quantum gas mixtures, including\nboth the Bose-Fermi and spin-1/2 Fermi-Fermi mixtures, with weak p-wave\ninteractions between intra-component fermions, and demonstrate that the weak\np-wave interaction can not be omitted in the strongly interacting regime where\nthe strength of p-wave interactions is comparable with the inverse of the\nstrength of strongly repulsive s-wave interactions. While the total density\ndistribution is not sensitive to the weak p-wave interaction, we find that the\np-wave interaction plays an important role in determining the species-dependent\n(or spin-dependent) density distributions and produces significant physical\neffects on the low-energy spin dynamics. We also derive effective spin-exchange\nmodels for strongly interacting quantum gas mixtures with weak p-wave\ninteractions, which indicate that a quantum phase transition from\nanti-ferromagnetic state to ferromagnetic state can be induced by tuning the\nrelative strengths of intra-component and inter-component interactions.",
        "positive": "Decaying quantum turbulence in a two-dimensional Bose-Einstein\n  condensate at finite temperature: We numerically model decaying quantum turbulence in two-dimensional\ndisk-shaped Bose-Einstein condensates, and investigate the effects of finite\ntemperature on the turbulent dynamics. We prepare initial states with a range\nof condensate temperatures, and imprint equal numbers of vortices and\nantivortices at randomly chosen positions throughout the fluid. The initial\nstates are then subjected to unitary time-evolution within the c-field\nmethodology. For the lowest condensate temperatures, the results of the zero\ntemperature Gross-Pitaevskii theory are reproduced, whereby vortex evaporative\nheating leads to the formation of Onsager vortex clusters characterised by a\nnegative absolute vortex temperature. At higher condensate temperatures the\ndissipative effects due to vortex-phonon interactions tend to drive the vortex\ngas towards positive vortex temperatures dominated by the presence of vortex\ndipoles. We associate these two behaviours with the system evolving toward an\nanomalous non-thermal fixed point, or a Gaussian thermal fixed point,\nrespectively."
    },
    {
        "anchor": "Quantum droplets of quasi-one-dimensional dipolar Bose-Einstein\n  condensates: Ultracold dipolar droplets have been realized in a series of ground-breaking\nexperiments, where the stability of the droplet state is attributed to\nbeyond-mean-field effects in the form of the celebrated Lee-Huang-Yang (LHY)\ncorrection. We scrutinize the dipolar droplet states in a one-dimensional\ncontext using a combination of analytical and numerical approaches, and\nidentify experimentally viable parameters for accessing our findings for future\nexperiments. In particular we identify regimes of stability in the restricted\ngeometry, finding multiple roton instabilities as well as regions supporting\nquasi-one-dimensional droplet states. By applying an interaction quench to the\ndroplet, a modulational instability is induced and multiple droplets are\nproduced, along with bright solitons and atomic radiation. We also assess the\ndroplets robustness to collisions, revealing population transfer and droplet\nfission.",
        "positive": "Fermionic Superfluidity: From Cold Atoms to Neutron Stars: From flow without dissipation of energy to the formation of vortices when\nplaced within a rotating container, the superfluid state of matter has proven\nto be a very interesting physical phenomenon. Here we present the key\nmechanisms behind superfluidity in fermionic systems and apply our\nunderstanding to an exotic system found deep within the universe -- the\nsuperfluid found deep within a neutron star. A defining trait of a superfluid\nis the pairing gap, which the cooling curves of neutron stars depend on. The\nextreme conditions surrounding a neutron star prevent us from directly probing\nthe superfluid's properties, however, we can experimentally realize conditions\nresembling the interior through the use of cold atoms prepared in a laboratory\nand simulated on a computer. Experimentalists are becoming increasingly adept\nat realizing cold atomic systems in the lab that mimic the behavior of neutron\nstars and superconductors. In their turn, computational physicists are\nleveraging the power of supercomputers to simulate interacting atomic systems\nwith unprecedented accuracy. This paper is intended to provide a pedagogical\nintroduction to the underlying concepts and the possibility of using cold atoms\nas a tool that can help us make significant strides towards understanding\nexotic physical systems."
    },
    {
        "anchor": "Interplay between temperature and trap effects in one-dimensional\n  lattice systems of bosonic particles: We investigate the interplay of temperature and trap effects in cold particle\nsystems at their quantum critical regime, such as cold bosonic atoms in optical\nlattices at the transitions between Mott-insulator and superfluid phases. The\ntheoretical framework is provided by the one-dimensional Bose-Hubbard model in\nthe presence of an external trapping potential, and the trap-size scaling\ntheory describing the large trap-size behavior at a quantum critical point. We\npresent numerical results for the low-temperature behavior of the particle\ndensity and the density-density correlation function at the Mott transitions,\nand within the gapless superfluid phase.",
        "positive": "Equation of State and Thermometry of the 2D SU($N$) Fermi-Hubbard Model: We characterize the equation of state (EoS) of the SU($N>2$) Fermi-Hubbard\nModel (FHM) in a two-dimensional single-layer square optical lattice. We probe\nthe density and the site occupation probabilities as functions of interaction\nstrength and temperature for $N = 3, 4$ and 6. Our measurements are used as a\nbenchmark for state-of-the-art numerical methods including determinantal\nquantum Monte Carlo (DQMC) and numerical linked cluster expansion (NLCE). By\nprobing the density fluctuations, we compare temperatures determined in a\nmodel-independent way by fitting measurements to numerically calculated EoS\nresults, making this a particularly interesting new step in the exploration and\ncharacterization of the SU($N$) FHM."
    },
    {
        "anchor": "Phase Diagram of a Spin-Orbit Coupled Fermi Gases in a Bilayer Optical\n  Lattice: We investigate the stability of helical superfluid phase in a spin-orbit\ncoupled Fermi gas loaded in a bilayer optical lattice. The phase diagram of the\nsystem is constructed in the mean field framework. We investigate the\ntopological properties of the superfluid phases by a nontrivial application of\nthe Fermi surface topological invariant to our time-reversal invariant system\nwith degeneracies on the Fermi surface. We find that there is a first-order\nphase boundary in the phase diagram of half filling case and the superfluid\nphases are all topological trivial. The superfluid phase is topological\nnontrivial when the filling fraction deviates from the half filling. In the\ntopological nontrivial superfluid phase, a full pairing gap exists in the bulk\nand gapless helical Majorana edge states exist at the boundary.",
        "positive": "Thermodynamics of Trapped Imbalanced Fermi Gases at Unitarity: We present a theory for the low-temperature properties of a resonantly\ninteracting Fermi mixture in a trap, that goes beyond the local-density\napproximation. The theory corresponds essentially to a Landau-Ginzburg-like\napproach that includes self-energy effects to account for the strong\ninteractions at unitarity. We show diagrammatically how these self-energy\neffects arise from fluctuations in the superfluid order parameter. Gradient\nterms of the order parameter are included to account for inhomogeneities. This\napproach incorporates the state-of-the-art knowledge of the homogeneous mixture\nwith a population imbalance exactly and gives good agreement with the\nexperimental density profiles of Shin et al. [Nature 451, 689 (2008)]. This\nallows us to calculate the universal surface tension of the interface between\nthe equal-density superfluid and the partially polarized normal state of the\nmixture. We also discuss the possibility of a metastable state to explain the\ndeformation of the superfluid core that is seen in the experiment of Partridge\net al. [Science 311, 503 (2006)]."
    },
    {
        "anchor": "Pairing properties of an odd-frequency superfluid Fermi gas: We theoretically investigate strong-coupling properties of an odd-frequency\nFermi superfluid. This pairing state has the unique property that Cooper pairs\nare formed between fermions, not at the same time, but at different times. To\nsee whether or not such unequal-time pairs still exhibit bosonic behavior, we\nexamine the space-time structure of the odd-frequency Cooper-pair wavefunction\nat $T=0$, by employing the combined path-integral formalism with the\nBCS-Eagles-Leggett-type superfluid theory. In the strong-coupling regime, the\nodd-frequency pair wavefunction still has different space-time structure from\nthat in the ordinary even-frequency $s$-wave superfluid state, their\n$\\textit{magnitudes}$ are found to become close to each other, except for the\nequal-time pairing component. In this regime, we also evaluate the superfluid\nphase transition temperature $T_{\\rm c}$ within the framework of the\nstrong-coupling theory developed by Nozi\\`eres and Schmitt-Rink. The calculated\n$T_{\\rm c}$ in the strong-coupling regime of the odd-frequency system is found\nto be well described by the Bose-Einstein condensation of tightly bound Bose\nmolecules. Our results indicates that, in spite of vanishing equal-time\npairing, odd-frequency Cooper pairs still behave like bosons in the\nstrong-coupling regime, as in the even-frequency $s$-wave superfluid case.",
        "positive": "Guiding and Trapping Electron Spin Waves in Atomic Hydrogen Gas: We present a high magnetic field study of electron spin waves in atomic\nhydrogen gas compressed to high densities of 10^18 cm^-3 at temperatures\nranging from 0.26 to 0.6 K. We observed a variety of spin wave modes caused by\nthe identical spin rotation effect with strong dependence on the spatial\nprofile of the polarizing magnetic field. We demonstrate confinement of these\nmodes in regions of strong magnetic field and manipulate their spatial\ndistribution by changing the position of the field maximum."
    },
    {
        "anchor": "Quench Dynamics of Finite Bosonic Ensembles in Optical Lattices with\n  Spatially Modulated Interactions: The nonequilibrium quantum dynamics of few boson ensembles which experience a\nspatially modulated interaction strength and are confined in finite optical\nlattices is investigated. We utilize a cosinusoidal spatially modulated\neffective interaction strength which is characterized by its wavevector,\ninhomogeneity amplitude, interaction offset and a phase. Performing quenches\neither on the wavevector or the phase of the interaction profile an enhanced\nimbalance of the interatomic repulsion between distinct spatial regions of the\nlattice is induced. Following both quench protocols triggers various tunneling\nchannels and a rich excitation dynamics consisting of a breathing and a cradle\nmode. All modes are shown to be amplified for increasing inhomogeneity\namplitude of the interaction strength. Especially the phase quench induces a\ndirectional transport enabling us to discern energetically, otherwise,\ndegenerate tunneling pathways. Moreover, a periodic population transfer between\ndistinct momenta for quenches of increasing wavevector is observed, while a\ndirected occupation of higher momenta can be achieved following a phase quench.\nFinally, during the evolution regions of partial coherence are revealed between\nthe predominantly occupied wells.",
        "positive": "Metal-Insulator-Superconductor transition of spin-3/2 atoms on optical\n  lattices: We use a slave-rotor approach within a mean-field theory to study the\ncompetition of metallic, Mott-insulating, and superconducting phases of\nspin-3/2 fermions subjected to a periodic optical lattice potential. In\naddition to the metallic, the Mott-insulating, and the superconducting phases\nthat are associated with the gauge symmetry breaking of the spinon field, we\nidentify a novel emerging superconducting phase that breaks both roton and\nspinon field gauge symmetries. This novel superconducting phase emerges as a\nresult of the competition between spin-0 singlet and spin-2 quintet interaction\nchannels naturally available for spin-3/2 systems. The two superconducting\nphases can be distinguished from each other by quasiparticle weight. We further\ndiscuss the properties of these phases for both two-dimensional square and\nthree-dimensional cubic lattices at zero and finite temperatures."
    },
    {
        "anchor": "Effective Three-Body Interactions in Jaynes-Cummings-Hubbard Systems: A generalisation of the Jaynes-Cummings-Hubbard model for coupled-cavity\narrays is introduced, where the embedded two-level system in each cavity is\nreplaced by a $\\Xi$-type three-level system. We demonstrate that the resulting\neffective polariton-polariton interactions at each site are both two-body and\nthree-body. By tuning the ratio of the two transition dipole matrix elements,\nwe show that the strength and sign of the two-body interaction can be\ncontrolled whilst maintaining a three-body repulsion. We then proceed to\ndemonstrate how different two-body and three-body interactions alter the mean\nfield superfluid-Mott insulator phase diagram, with the possible emergence of a\npair superfluid phase in the two-body attractive regime.",
        "positive": "Heating up quadruply quantized vortices: Splitting patterns and\n  dynamical transitions: Using holographic duality, we investigate the impact of finite temperature on\nthe instability and splitting patterns of quadruply quantized vortices,\nproviding the first-ever analysis in this context. Through linear stability\nanalysis, we reveal the occurrence of two consecutive dynamical transitions. At\na specific low temperature, the dominant unstable mode transitions from the\n$2$-fold rotational symmetry mode to the $3$-fold one, followed by a transition\nfrom the $3$-fold one to the $4$-fold one at a higher temperature. As the\ntemperature is increased, we also observe the $5$ and $6$-fold rotational\nsymmetry unstable modes get excited successively. Employing the full non-linear\nnumerical simulations, we further demonstrate that these two novel dynamical\ntransitions, along with the temperature-induced instabilities for the $5$ and\n$6$-fold rotational symmetry modes, can be identified by examining the\nresulting distinct splitting patterns, which offers a promising route for the\nexperimental verification in the cold atom gases."
    },
    {
        "anchor": "Stable core symmetries and confined textures for a vortex line in a\n  spinor Bose-Einstein condensate: We show how a singly quantized vortex can exhibit energetically stable defect\ncores with different symmetries in an atomic spin-1 polar Bose-Einstein\ncondensate, and how a stable topologically nontrivial Skyrmion texture of lower\ndimensionality can be confined inside the core. The core isotropy and the\nstability of the confined texture are sensitive to Zeeman level shifts. The\nobserved structures have analogies, respectively, in pressure-dependent\nsymmetries of superfluid liquid He-3 vortices and in the models of\nsuperconducting cosmic strings.",
        "positive": "A dipolar self-induced bosonic Josephson junction: We propose a new scheme for observing Josephson oscillations and macroscopic\nquantum self-trapping phenomena in a toroidally confined Bose-Einstein\ncondensate: a dipolar self-induced Josephson junction. Polarizing the atoms\nperpendicularly to the trap symmetry axis, an effective ring-shaped,\ndouble-well potential is achieved which is induced by the dipolar interaction.\nBy numerically solving the three-dimensional time-dependent Gross-Pitaevskii\nequation we show that coherent tunneling phenomena such as Josephson\noscillations and quantum self-trapping can take place. The dynamics in the\nself-induced junction can be qualitatively described by a two-mode model taking\ninto account both s-wave and dipolar interactions."
    },
    {
        "anchor": "Statics and dynamics of atomic dark-bright solitons in the presence of\n  delta-like impurities: Adopting a mean-field description for a two-component atomic Bose-Einstein\ncondensate, we study the stat- ics and dynamics of dark-bright solitons in the\npresence of localized impurities. We use adiabatic perturbation theory to\nderive an equation of motion for the dark-bright soliton center. We show that,\ncounter-intuitively, an attractive (repulsive) delta-like impurity, acting\nsolely on the bright soliton component, induces an effective localized barrier\n(well) in the effective potential felt by the soliton; this way, dark-bright\nsolitons are reflected from (transmitted through) attractive (repulsive)\nimpurities. Our analytical results for the small-amplitude oscil- lations of\nsolitons are found to be in good agreement with results obtained via a\nBogoliubov-de Gennes analysis and direct numerical simulations.",
        "positive": "Thermal decoherence of a nonequilibrium polariton fluid: Exciton-polaritons constitute a unique realization of a quantum fluid\ninteracting with its environment. Using Selenide based microcavities, we\nexploit this feature to warm up a polariton condensate in a controlled way and\nmonitor its spatial coherence. We determine directly the amount of heat picked\nup by the condensate by measuring the phonon-polariton scattering rate and\ncomparing it with the loss rate. We find that upon increasing the heating rate,\nthe spatial coherence length decreases markedly, while localized phase\nstructures vanish, in good agreement with a stochastic mean field theory. From\nthe thermodynamical point-of-view, this regime is unique as it involves a\nnonequilibrium quantum fluid with no well-defined temperature, but which is\nnevertheless able to pick up heat with dramatic effects on the order parameter."
    },
    {
        "anchor": "Specific heat and effects of pairing fluctuations in the BCS-BEC\n  crossover regime of an ultracold Fermi gas: We investigate the specific heat at constant volume $C_V$ in the BCS\n(Bardeen-Cooper-Schrieffer)-BEC (Bose-Einstein condensation) crossover regime\nof an ultracold Fermi gas above the superfluid phase transition temperature\n$T_{\\rm c}$. Within the framework of the strong-coupling theory developed by\nNozi\\`eres and Schmitt-Rink, we show that this thermodynamic quantity is\nsensitive to the stability of preformed Cooper pairs. That is, while\n$C_V(T\\gesim T_{\\rm c})$ in the unitary regime is remarkably enhanced by {\\it\nmetastable} preformed Cooper pairs or pairing fluctuations, it is well\ndescribed by that of an ideal Bose gas of long-lived {\\it stable} molecules in\nthe strong-coupling BEC regime. Using these results, we identify the region\nwhere the system may be viewed as an almost ideal Bose gas of stable pairs, as\nwell as the pseudogap regime where the system is dominated by metastable\npreformed Cooper pairs, in the phase diagram of an ultracold Fermi gas with\nrespect to the strength of a pairing interaction and the temperature. We also\nshow that the calculated specific heat agrees with the recent experiment on a\n$^6$Li unitary Fermi gas. Since the formation of preformed Cooper pairs is a\ncrucial key in the BCS-BEC crossover phenomenon, our results would be helpful\nin considering how fluctuating preformed Cooper pairs appear in a Fermi gas, to\neventually become stable, as one passes through the BCS-BEC crossover region.",
        "positive": "The spin Hall effect in a quantum gas: Electronic properties like current flow are generally independent of the\nelectron's spin angular momentum, an internal degree of freedom present in\nquantum particles. The spin Hall effects (SHEs), first proposed 40 years ago,\nare an unusual class of phenomena where flowing particles experience\northogonally directed spin-dependent Lorentz-like forces, analogous to the\nconventional Lorentz force for the Hall effect, but opposite in sign for two\nspin states. Such spin Hall effects have been observed for electrons flowing in\nspin-orbit coupled materials such as GaAs or InGaAs and for laser light\ntraversing dielectric junctions. Here we observe the spin Hall effect in a\nquantum-degenerate Bose gas, and use the resulting spin-dependent Lorentz\nforces to realize a cold-atom spin transistor. By engineering a spatially\ninhomogeneous spin-orbit coupling field for our quantum gas, we explicitly\nintroduce and measure the requisite spin-dependent Lorentz forces, in excellent\nagreement with our calculations. This atomtronic circuit element behaves as a\nnew type of velocity-insensitive adiabatic spin-selector, with potential\napplication in devices such as magnetic or inertial sensors. In addition, such\ntechniques --- for both creating and measuring the SHE --- are clear\nprerequisites for engineering topological insulators and detecting their\nassociated quantized spin Hall effects in quantum gases. As implemented, our\nsystem realized a laser-actuated analog to the Datta-Das spin transistor."
    },
    {
        "anchor": "Exotic Vortex States with Discrete Rotational Symmetry in Atomic Fermi\n  Gases with Spin-Orbital-Angular-Momentum Coupling: We investigate the superfluidity of a two-component Fermi gas with\nspin-orbital-angular-momentum coupling (SOAMC). Due to the intricate interplay\nof SOAMC, two-photon detuning and atom-atom interaction, a family of vortex\nground states emerge in a broad parameter regime of the phase diagram, in\ncontrast to the usual case where an external rotation or magnetic field is\ngenerally required. More strikingly, an unprecedented vortex state, which\nbreaks the continuous rotational symmetry to a discrete one spontaneously, is\npredicted to occur. The underlying physics are elucidated and verified by\nnumerical simulations. The unique density distributions of the predicted vortex\nstates enable a direct observation in experiment.",
        "positive": "Analysis of shape change of droplet in dipolar Bose-Hubbard model: The long-range and anisotropic nature of the dipolar interaction provides the\nso-called supersolid phases in Bose-Einstein condensates (BECs) in an optical\nlattice. However, in a certain area of dipole interaction parameters, BECs can\nform into a droplet. In this paper, in order to qualitatively understand the\ndroplet formations, we propose a toy model that allows us to estimate the size\nand shape of droplets in dipolar Bose-Hubbard system in the optical lattice. We\ncompare results of the toy model with numerical solutions of the mean-field\ncalculation."
    },
    {
        "anchor": "Exploring beyond-mean-field logarithmic divergences in Fermi-polaron\n  energy: We perform a diagrammatic analysis of the energy of a mobile impurity\nimmersed in a strongly interacting two component Fermi gas to second order in\nthe impurity-bath interaction. These corrections demonstrate divergent behavior\nin the limit of large impurity momentum. We show the fundamental processes\nresponsible for these logarithmically divergent terms.\n  We study the problem in the general case without any assumptions regarding\nthe fermion-fermion interactions in the bath. We show that the divergent term\ncan be summed up to all orders in the Fermi-Fermi interaction and that the\nresulting expression is equivalent to the one obtained in the few body\ncalculation.\n  Finally, we provide a perturbative calculation to the second order in the\nFermi-Fermi interaction in the annex, and we show the diagrams responsible for\nthese terms.",
        "positive": "Distinguishability, degeneracy and correlations in three harmonically\n  trapped bosons in one-dimension: We study a system of two bosons of one species and a third boson of a second\nspecies in a one-dimensional parabolic trap at zero temperature. We assume\ncontact repulsive inter- and intra-species interactions. By means of an exact\ndiagonalization method we calculate the ground and excited states for the whole\nrange of interactions. We use discrete group theory to classify the eigenstates\naccording to the symmetry of the interaction potential. We also propose and\nvalidate analytical ansatzs gaining physical insight over the numerically\nobtained wavefunctions. We show that, for both approaches, it is crucial to\ntake into account that the distinguishability of the third atom implies the\nabsence of any restriction over the wavefunction when interchanging this boson\nwith any of the other two. We find that there are degeneracies in the spectra\nin some limiting regimes, that is, when the inter-species and/or the\nintra-species interactions tend to infinity. This is in contrast with the\nthree-identical boson system, where no degeneracy occurs in these limits. We\nshow that, when tuning both types of interactions through a protocol that keeps\nthem equal while they are increased towards infinity, the systems's ground\nstate resembles that of three indistinguishable bosons. Contrarily, the\nsystems's ground state is different from that of three-identical bosons when\nboth types of interactions are increased towards infinity through protocols\nthat do not restrict them to be equal. We study the coherence and correlations\nof the system as the interactions are tuned through different protocols, which\npermit to built up different correlations in the system and lead to different\nspatial distributions of the three atoms."
    },
    {
        "anchor": "Vortices in self-bound dipolar droplets: Quantized vortices have been observed in a variety of superfluid systems,\nfrom $^4$He to condensates of alkali-metal bosons and ultracold Fermi gases\nalong the BEC-BCS crossover. In this article we study the stability of singly\nquantized vortex lines in dilute dipolar self-bound droplets. We first discuss\nthe energetic stability region of dipolar vortex excitations within a\nvariational ansatz in the generalized nonlocal Gross-Pitaevskii functional that\nincludes quantum fluctuation corrections. We find a wide region where\nstationary solutions corresponding to axially-symmetric vortex states exist.\nHowever, these singly-charged vortex states are shown to be unstable, either by\nsplitting the droplet in two fragments or by vortex-line instabilities\ndeveloped from Kelvin-wave excitations. These observations are the results of\nlarge-scale fully three-dimensional simulations in real time. We conclude with\nsome experimental considerations for the observation of such states and suggest\npossible extensions of this work.",
        "positive": "Ultracold atoms out of equilibrium: The relaxation of isolated quantum many-body systems is a major unsolved\nproblem connecting statistical and quantum physics. Studying such relaxation\nprocesses remains a challenge despite considerable efforts. Experimentally, it\nrequires the creation and manipulation of well-controlled and truly isolated\nquantum systems. In this context, ultracold neutral atoms provide unique\nopportunities to understand non-equilibrium phenomena because of the large set\nof available methods to isolate, manipulate and probe these systems. Here, we\ngive an overview of the rapid experimental progress that has been made in the\nfield over the last years and highlight some of the questions which may be\nexplored in the future."
    },
    {
        "anchor": "Thermometry of ultracold fermions by (super)lattice modulation\n  spectroscopy: We theoretically consider non-interacting fermions confined to optical\nlattices and apply a lattice amplitude modulation that we choose to be either\nhomogeneous or of superlattice geometry. We study the atom excitation rate to\nhigher Bloch bands which can be measured by adiabatic band mapping. We find\nthat the atom excitation rate shows a clear signature of the temperature\ndependent Fermi distribution in the lowest band of the equilibrium lattice as\nexcitations are quasimomentum-resolved. Based on typical experimental\nparameters and incorporating a trapping potential, we find that thermometry of\none- and two-dimensional systems is within the reach of nowadays experiments.\nOur scheme is valid down to temperatures of a few percent of the hopping\namplitude comparable to the N\\'eel temperature in interacting systems.",
        "positive": "Universal Properties of Fermi Gases in One-dimension: In this Rapid Communication, we investigate the universal properties of a\nspin-polarized two-component Fermi gas in one dimension (1D) using Bethe\nansatz. We discuss the quantum phases and phase transitions by obtaining exact\nresults for the equation of state, the contact, the magnetic susceptibility and\nthe contact susceptibility, giving a precise understanding of the 1D analogue\nof the Bose-Einstein condensation and Bardeen-Cooper-Schrieffer crossover in\nthree dimension (3D) and the associated universal magnetic properties. In\nparticular, we obtain the exact form of the magnetic susceptibility $\\chi \\sim\n{1}/{\\sqrt{T}}\\exp(-\\Delta/T)$ at low temperatures, where $\\Delta$ is the\nenergy gap and $T$ is the temperature. Moreover, we establish exact upper and\nlower bounds for the relation between polarization $P$ and the contact $C$ for\nboth repulsive and attractive Fermi gases. Our findings emphasize the role of\nthe pair fluctuations in strongly interacting 1D fermion systems that can shed\nlight on higher dimensions."
    },
    {
        "anchor": "Roton-type mode softening in a quantum gas with cavity-mediated\n  long-range interactions: Long-range interactions in quantum gases are predicted to give rise to an\nexcitation spectrum of roton character, similar to that observed in superfluid\nhelium. We investigate the excitation spectrum of a Bose-Einstein condensate\nwith cavity-mediated long-range interactions, which couple all particles to\neach other. Increasing the strength of the interaction leads to a softening of\nan excitation mode at a finite momentum, preceding a superfluid to supersolid\nphase transition. We study the mode softening spectroscopically across the\nphase transition using a variant of Bragg spectroscopy. The measured spectrum\nis in very good agreement with ab initio calculations and, at the phase\ntransition, a diverging susceptibility is observed. The work paves the way\ntowards quantum simulation of long-range interacting many-body systems.",
        "positive": "Shortcut to Adiabaticity for an Anisotropic Gas Containing Quantum\n  Defects: We present a Shortcut To Adiabaticity (STA) protocol applicable to 3D unitary\nFermi gases and 2D weakly-interacting Bose gases containing defects such as\nvortices or solitons. Our protocol relies on a new class of exact scaling\nsolutions in the presence of anisotropic time-dependent harmonic traps. It\nconnects stationary states in initial and final traps having the same frequency\nratios. The resulting scaling laws exhibit a universal form and also apply to\nthe classical Boltzmann gas. The duration of the STA can be made very short so\nas to realize a quantum quench from one stationary state to another. When\napplied to an anisotropically trapped superfluid gas, the STA conserves the\nshape of the quantum defects hosted by the cloud, thereby acting like a perfect\nmicroscope, which sharply constrasts with their strong distortion occurring\nduring the free expansion of the cloud."
    },
    {
        "anchor": "Propagation of light in cold emitter ensembles with quantum position\n  correlations due to static long-range dipolar interactions: We analyze the scattering of light from dipolar emitters whose disordered\npositions exhibit correlations induced by static, long-range dipole-dipole\ninteractions. The quantum-mechanical position correlations are calculated for\nzero temperature bosonic atoms or molecules using variational and diffusion\nquantum Monte Carlo methods. For stationary atoms in dense ensembles in the\nlimit of low light intensity, the simulations yield solutions for the optical\nresponses to all orders of position correlation functions that involve\nelectronic ground and excited states. We calculate how coherent and incoherent\nscattering, collective linewidths, line shifts, and eigenmodes, and\ndisorder-induced excitation localization are influenced by the static\ninteractions and the density. We find that dominantly repulsive static\ninteractions in strongly confined oblate and prolate traps introduce\nshort-range ordering among the dipoles which curtails large fluctuations in the\nlight-mediated resonant dipole-dipole interactions. This typically results in\nan increase in coherent reflection and optical depth, accompanied by reduced\nincoherent scattering. The presence of static dipolar interactions permits the\nhighly selective excitation of subradiant eigenmodes in dense clouds. This\neffect becomes even more pronounced in a prolate trap, where the resonances\nnarrow below the natural linewidth. When the static dipolar interactions affect\nthe optical transition frequencies, the ensemble exhibits inhomogeneous\nbroadening due to the nonuniformly experienced static dipolar interactions that\nsuppress cooperative effects, but we argue that, e.g., for Dy atoms such\ninhomogeneous broadening is negligible.",
        "positive": "Site-resolved imaging of ytterbium atoms in a two-dimensional optical\n  lattice: We report a high-resolution microscope system for imaging ultracold ytterbium\natoms trapped in a two-dimensional optical lattice. By using the ultraviolet\nstrong transition combined with a solid immersion lens and high-resolution\noptics, our system resolved individual sites in an optical lattice with a\n544-nm spacing. Without any cooling mechanism during the imaging process, the\ndeep potential required to contain the atoms was realized using a combination\nof a shallow ground-state and a deep excited-state potentials. The lifetime and\nlimitations of this setup were studied in detail."
    },
    {
        "anchor": "Control of $^{164}$Dy Bose-Einstein condensate phases and dynamics with\n  dipolar anisotropy: We investigate the quench dynamics of quasi-one and two dimensional dipolar\nBose-Einstein condensates (dBEC) of $^{164}$Dy atoms under the influence of a\nfast rotating magnetic field. The magnetic field thus controls both the\nmagnitude and sign of the dipolar potential. We account for quantum\nfluctuations, critical to formation of exotic quantum droplet and supersolid\nphases in the extended Gross-Pitaevskii formalism, which includes the so-called\nLee-Huang-Yang (LHY) correction. An analytical variational ansatz allows us to\nobtain the phase diagrams of the superfluid and droplet phases. The crossover\nfrom the superfluid to the supersolid phase and to single and droplet arrays is\nprobed with particle number and dipolar interaction. The dipolar strength is\ntuned by rotating the magnetic field with subsequent effects on phase\nboundaries. Following interaction quenches across the aforementioned phases, we\nmonitor the dynamical formation of supersolid clusters or droplet lattices. We\ninclude losses due to three-body recombination over the crossover regime, where\nthe three-body recombination rate coefficient scales with the fourth power of\nthe scattering length ($a_s$) or the dipole length ($a_{dd}$). For fixed values\nof the dimensionless parameter, $\\epsilon_{dd} = a_{dd}/a_s$, tuning the\ndipolar anisotropy leads to an enhancement of the droplet lifetimes.",
        "positive": "Magnetically mediated hole pairing in fermionic ladders of ultracold\n  atoms: Pairing of mobile charge carriers in doped antiferromagnets plays a key role\nin the emergence of unconventional superconductivity. In these strongly\ncorrelated materials, the pairing mechanism is often assumed to be mediated by\nmagnetic correlations, in contrast to phonon-mediated interactions in\nconventional superconductors. A precise understanding of the underlying\nmechanism in real materials is, however, still lacking, and has been driving\nexperimental and theoretical research for the past 40 years. Early theoretical\nstudies established the emergence of binding among dopants in ladder systems,\nwhere idealised theoretical toy models played an instrumental role in the\nelucidation of pairing, despite repulsive interactions. Here, we realise this\nlong-standing theoretical prediction and report on the observation of hole\npairing due to magnetic correlations in a quantum gas microscope setting. By\nengineering doped antiferromagnetic ladders with mixed-dimensional couplings we\nsuppress Pauli blocking of holes at short length scales. This results in a\ndrastic increase in binding energy and decrease in pair size, enabling us to\nobserve pairs of holes predominantly occupying the same rung of the ladder. We\nfind a hole-hole binding energy on the order of the superexchange energy, and,\nupon increased doping, we observe spatial structures in the pair distribution,\nindicating repulsion between bound hole pairs. By engineering a configuration\nin which binding is strongly enhanced, we delineate a novel strategy to\nincrease the critical temperature for superconductivity."
    },
    {
        "anchor": "Transverse Josephson vortices and localized states in stacked\n  Bose-Einstein condensates: The stacks of Bose-Einstein condensates coupled by long Josephson junctions\npresent a rich phenomenology feasible to experimental realization and specially\nsuitable for technological applications as the nonlinear-optics and\nsuperconducting analogues have already proved. Among this, we show that\ntransverse Bloch waves excited in arrays of one-dimensional coupled condensates\ncan carry tunneling superflows whose dynamical stability depends on the\nquasimomentum. Across the stacks with periodic boundary conditions, forming\nclosed ring-shaped systems, such Bloch states yield transverse Josephson\nvortices with a generic non-integer circulation in units of $h/m$.\nAdditionally, the superpositions of degenerate linear Bloch waves can suppress\nthe supercurrents and give rise to families of nonlinear standing-wave states\nwith strong (transverse) spatial localization. Stable states of this type can\nalso be found in finite size systems.",
        "positive": "Quasihole dynamics as a detection tool for quantum Hall phases: Existing techniques for synthesizing gauge fields are able to bring a\ntwo-dimensional cloud of harmonically trapped bosonic atoms into a regime where\nthe occupied single-particle states are restricted to the lowest Landau level\n(LLL). Repulsive short-range interactions drive various transitions from fully\ncondensed into strongly correlated states. In these different phases we study\nthe response of the system to quasihole excitations induced by a laser beam. We\nfind that in the Laughlin state the quasihole performs a coherent constant\nrotation around the center, ensuring conservation of angular momentum. This is\ndistinct to any other regime with higher density, where the quasihole is found\nto decay. At a characteristic time, the decay process is reversed, and revivals\nof the quasihole can be observed in the density. Measuring the period and\nposition of the revival can be used as a spectroscopic tool to identify the\nstrongly correlated phases in systems with a finite number of atoms."
    },
    {
        "anchor": "Universal Early Coarsening of Quenched Bose Gases: We investigate the early coarsening dynamics of an atomic Bose gas quenched\ninto a superfluid phase. Using a two-step quench protocol, we effectively\ncontrol the cooling rates, $r_1$ and $r_2$, during and after passing through\nthe critical region, respectively, and measure the number of quantum vortices\nspontaneously created in the system. The latter cooling rate $r_2$ regulates\nthe temperature during the condensate growth, consequently controlling the\nearly coarsening dynamics in the defect formation. We find that the defect\nnumber shows a scaling behavior with $r_2$ regardless of the initial cooling\nrate $r_1$, indicating universal coarsening dynamics in the early stage of\ncondensate growth. Our results demonstrate that early coarsening not only\nreduces the defect density but also affects its scaling with the quench rate,\nwhich is beyond the Kibble-Zurek mechanism.",
        "positive": "Interaction-driven breakdown of dynamical localization in a kicked\n  quantum gas: Quantum interference can terminate energy growth in a continually kicked\nsystem, via a single-particle ergodicity-breaking mechanism known as dynamical\nlocalization. The effect of many-body interactions on dynamically localized\nstates, while important to a fundamental understanding of quantum decoherence,\nhas remained unexplored despite a quarter-century of experimental studies. We\nreport the experimental realization of a tunably-interacting kicked quantum\nrotor ensemble using a Bose-Einstein condensate in a pulsed optical lattice. We\nobserve signatures of a prethermal localized plateau, followed for interacting\nsamples by interaction-induced anomalous diffusion with an exponent near one\nhalf. Echo-type time reversal experiments establish the role of interactions in\ndestroying reversibility. These results quantitatively elucidate the dynamical\ntransition to many-body quantum chaos, advance our understanding of quantum\nanomalous diffusion, and delimit some possibilities for protecting quantum\ninformation in interacting driven systems."
    },
    {
        "anchor": "The ground state of polaron in an ultracold dipolar Fermi gas: An impurity atom immersed in an ultracold atomic Fermi gas can form a\nquasiparticle, so-called Fermi polaron, due to impurity-fermion interaction. We\nconsider a three-dimensional homogeneous dipolar Fermi gas as a medium, where\nthe interatomic dipole-dipole interaction (DDI) makes the Fermi surface\ndeformed into a spheroidal shape, and, using a Chevy-type variational method,\ninvestigate the ground-state properties of the Fermi polaron: the effective\nmass, the momentum distribution of a particle-hole (p-h) excitation, the drag\nparameter, and the medium density modification around the impurity. These\nquantities are shown to exhibit spatial anisotropies in such a way as to\nreflect the momentum anisotropy of the background dipolar Fermi gas. We have\nalso given numerical results for the polaron properties at the unitarity limit\nof the impurity-fermion interaction in the case in which the impurity and\nfermion masses are equal. It has been found that the transverse effective mass\nand the transverse momentum drag parameter of the polaron both tend to decrease\nby $ \\sim 10\\%$ when the DDI strength is raised from $0$ up to around its\ncritical value, while the longitudinal ones exhibit a very weak dependence on\nthe DDI.",
        "positive": "Fock space exploration by angle resolved transmission through quantum\n  diffraction grating of cold atoms in an optical lattice: Light transmission or diffraction from different quantum phases of cold atoms\nin an optical lattice has recently come up as a useful tool to probe such ultra\ncold atomic systems. The periodic nature of the optical lattice potential\nclosely resembles the structure of a diffraction grating in real space, but\nloaded with a strongly correlated quantum many body state which interacts with\nthe incident electromagnetic wave, a feature that controls the nature of the\nlight transmission or dispersion through such quantum medium. In this paper we\nshow that as one varies the relative angle between the cavity mode and the\noptical lattice, the peak of the transmission spectrum through such cavity also\nchanges reflecting the statistical distribution of the atoms in the illuminated\nsites. Consequently the angle resolved transmission spectrum of such quantum\ndiffraction grating can provide a plethora of information about the Fock space\nstructure of the many body quantum state of ultra cold atoms in such an optical\ncavity that can be explored in current state of the art experiments."
    },
    {
        "anchor": "Effective multi-body SU($N$)-symmetric interactions of ultracold\n  fermionic atoms on a 3-D lattice: Rapid advancements in the experimental capabilities with ultracold\nalkaline-earth-like atoms (AEAs) bring to a surprisingly near term the prospect\nof performing quantum simulations of spin models and lattice field theories\nexhibiting SU($N$) symmetry. Motivated in particular by recent experiments\npreparing high density samples of strongly interacting ${}^{87}$Sr atoms in a\nthree-dimensional optical lattice, we develop a low-energy effective theory of\nfermionic AEAs which exhibits emergent multi-body SU($N$)-symmetric\ninteractions, where $N$ is the number of atomic nuclear spin levels. Our theory\nis limited to the experimental regime of (i) a deep lattice, with (ii) at most\none atom occupying each nuclear spin state on any lattice site. The latter\nrestriction is a consequence of initial ground-state preparation. We fully\ncharacterize the low-lying excitations in our effective theory, and compare\npredictions of many-body interaction energies with direct measurements of\nmany-body excitation spectra in an optical lattice clock. Our work makes the\nfirst step in enabling a controlled, bottom-up experimental investigation of\nmulti-body SU($N$) physics.",
        "positive": "Thermally stable p-wave repulsive Fermi polaron without a two-body bound\n  state: We theoretically investigate the polaron physics of an impurity immersed in a\ntwo-dimensional Fermi sea, interacting via a p-wave interaction at finite\ntemperature. In the unitary limit with a divergent scattering area, we find a\nwell-defined repulsive Fermi polaron at short interaction range, which shows a\nremarkable thermal stability with increasing temperature. The appearance of\nsuch a stable repulsive Fermi polaron in the resonantly interacting limit can\nbe attributed to the existence of a quasi-bound dressed molecule state hidden\nin the two-particle continuum, although there is no bound state in the\ntwo-particle limit. We show that the repulsive Fermi polaron disappears when\nthe interaction range increases or when the scattering area is tuned to the\nweakly-interacting regime. The large interaction range and small scattering\narea instead stabilize attractive Fermi polarons."
    },
    {
        "anchor": "Single shot imaging of trapped Fermi gas: Recently developed techniques allow for simultaneous measurements of the\npositions of all ultra cold atoms in a trap with high resolution. Each such\nsingle shot experiment detects one element of the quantum ensemble formed by\nthe cloud of atoms. Repeated single shot measurements can be used to determine\nall correlations between particle positions as opposed to standard measurements\nthat determine particle density or two-particle correlations only. In this\npaper we discuss the possible outcomes of such single shot measurements in case\nof cloud of ultra-cold non-interacting Fermi atoms. We show that the Pauli\nexclusion principle alone leads to correlations between particle positions that\noriginate from unexpected spatial structures formed by the atoms.",
        "positive": "Rotation-symmetry-enforced coupling of spin and angular momentum for\n  p-orbital bosons: Intrinsic spin angular-momentum coupling of an electron has a relativistic\nquantum origin with the coupling arising from charged-orbits, which does not\ncarry over to charge-neutral atoms. Here we propose a mechanism of spontaneous\ngeneration of spin angular-momentum coupling with spinor atomic bosons loaded\ninto $p$-orbital bands of a two-dimensional optical-lattice. This spin\nangular-momentum coupling originates from many-body correlations and\nspontaneous symmetry breaking in a superfluid, with the key ingredients\nattributed to spin-channel quantum fluctuations and an approximate rotation\nsymmetry. The resultant spin angular-momentum intertwined superfluid has Dirac\nexcitations. In presence of a chemical potential difference for adjacent sites,\nit provides a bosonic analogue of a symmetry-protected-topological insulator.\nThrough a dynamical mean-field calculation, this novel superfluid is found to\nbe a generic low-temperature phase, and it gives way to Mott localization only\nat strong interactions and even-integer fillings. We show the temperature to\nreach this order is accessible with present experiments."
    },
    {
        "anchor": "Fractional quantum Hall states of bosons on cones: Motivated by a recent experiment which synthesizes Landau levels for photons\non cones [Schine {\\em et al.}, Nature 534, 671 (2016)], and more generally the\ninterest in understanding gravitational responses of quantum Hall states, we\nstudy fractional quantum Hall states of bosons on cones. A variety of trial\nwave functions for conical systems are constructed and compared with exact\ndiagonalization results. The tip of a cone is a localized geometrical defect\nwith singular curvature which can modify the density profiles of quantum Hall\nstates. The density profiles on cones can be used to extract some universal\ninformation about quantum Hall states. The values of certain quantities are\ncomputed numerically using the density profiles of some quantum Hall states and\nthey agree with analytical predictions.",
        "positive": "Auxiliary Field quantum Monte Carlo for Strongly Paired Fermions: We demonstrate that the inclusion of a BCS importance function dramatically\nincreases the efficiency of the auxiliary field method for strong pairing. We\ncalculate the ground-state energy of an unpolarized fermi gas at unitarity with\nup to 66 particles and lattices of up to $27^3$ sites. The method has no\nfermion sign problem, and an accurate result is obtained for the universal\nparameter $\\xi$. Several different forms of the kinetic energy adjusted to the\nunitary limit but with different effective ranges extrapolate to the same\ncontinuum limit within error bars. The finite effective range results for\ndifferent interactions are consistent with a linear term proportional to the\nFermi momentum times the effective range. The new method described herein will\nhave many applications in superfluid cold atom systems and in both electronic\nand nuclear structures when pairing is important."
    },
    {
        "anchor": "A mobile ion in a Fermi sea: The remarkable single particle control of individual ions combined with the\nversatility of ultracold atomic gases makes hybrid ion-atom system an exciting\nnew platform for quantum simulation of few- and many-body quantum physics.\nHere, we study theoretically the properties of a mobile ion immersed in a\nquantum degenerate gas of fermionic atoms. Using an effective low-energy\natom-ion interaction together with a well established approach that includes\nexactly two-body correlations, we calculate the full spectral response of the\nion and demonstrate the existence of several quasiparticle branches, which are\ncharged analogues of the Fermi polaron observed in neutral atomic gases. Due to\nthe long-range nature of the atom-ion interaction, these ionic Fermi polarons\nhave several properties distinct from their neutral counterparts such as the\nsimultaneous presence of several stable states and smooth transitions from\nrepulsive to attractive polarons with increasing interaction strength.\nSurprisingly, the residue of the ionic polaron is shown to increase with the\nFermi density for fixed interaction strength, which is in marked contrast to\nthe neutral polaron. The properties of the ionic polaron approach that of the\nneutral polaron only in the low density limit where the average interparticle\nspacing is larger than the characteristic length of the atom-ion interaction.\nWe finally analyse the effects of the Fermi gas on the molecular ions, which\nare bound atom-dimer states.",
        "positive": "Parametric Instability Rates in Periodically-Driven Band Systems: This work analyses the dynamical properties of periodically-driven band\nmodels. Focusing on the case of Bose-Einstein condensates, and using a\nmeanfield approach to treat inter-particle collisions, we identify the origin\nof dynamical instabilities arising due to the interplay between the external\ndrive and interactions. We present a widely-applicable generic numerical method\nto extract instability rates, and link parametric instabilities to uncontrolled\nenergy absorption at short times. Based on the existence of parametric\nresonances, we then develop an analytical approach within Bogoliubov theory,\nwhich quantitatively captures the instability rates of the system, and provides\nan intuitive picture of the relevant physical processes, including an\nunderstanding of how transverse modes affect the formation of parametric\ninstabilities. Importantly, our calculations demonstrate an agreement between\nthe instability rates determined from numerical simulations, and those\npredicted by theory. To determine the validity regime of the meanfield\nanalysis, we compare the latter to the weakly-coupled conserving approximation.\nThe tools developed and the results obtained in this work are directly relevant\nto present-day ultracold-atom experiments based on shaken optical lattices, and\nare expected to provide an insightful guidance in the quest for Floquet\nengineering."
    },
    {
        "anchor": "Universal aspects of a strongly interacting impurity in a dilute Bose\n  condensate: We study the properties of an impurity immersed in a weakly interacting Bose\ngas, i.e., of a Bose polaron. In the perturbatively-tractable of limit weak\nimpurity-boson interactions many of its properties are known to depend only on\nthe scattering length. Here we demonstrate that for strong (unitary)\nimpurity-boson interactions all static quasiproperties of a Bose polaron in a\ndilute Bose gas, such as its energy, its residue, its Tan's contact and the\nnumber of bosons trapped nearby the impurity, depend on the impurity-boson\npotential via a single parameter.",
        "positive": "ac Stark shift and multiphoton-like resonances in low-frequency driven\n  optical lattices: We suggest that Bose-Einstein condensates in optical lattices subjected to ac\nforcing with a smooth envelope may provide detailed experimental access to\nmultiphoton-like transitions between ac-Stark-shifted Bloch bands. Such\ntransitions correspond to resonances described theoretically by avoided\nquasienergy crossings. We show that the width of such anticrossings can be\ninferred from measurements involving asymmetric pulses. We also introduce a\npulse tracking strategy for locating the particular driving amplitudes for\nwhich resonances occur. Our numerical calculations refer to a currently\nexisting experimental set-up [Haller et al., PRL 104, 200403 (2010)]."
    },
    {
        "anchor": "Fractional photon-assisted tunnelling of ultra-cold atoms in\n  periodically shaken double-well lattices: Fractional photon-assisted tunnelling is investigated both numerically and\nanalytically in a double-well lattice. While integer photon-assisted tunnelling\nis a single-particle effect, fractional photon-assisted tunnelling is an\ninteraction-induced many-body effect. Double-well lattices with few particles\nin each double well are ideal to study this effect far from the mean-field\neffects. It is predicted that the 1/4-resonance is observable in such systems.\nFractional photon-assisted tunnelling provides a physically relevant model for\nwhich N-th order time-dependent perturbation theory can be large although all\nprevious orders are small.",
        "positive": "Time bound of atomic adiabatic evolution in the accelerated optical\n  lattice: The accelerated optical lattice has emerged as a valuable technique for the\ninvestigation of quantum transport physics and has found widespread application\nin quantum sensing, including atomic gravimeters and atomic gyroscopes. In our\nstudy, we focus on the adiabatic evolution of ultra-cold atoms within an\naccelerated optical lattice. Specifically, we derive a time bound that delimits\nthe duration of atomic adiabatic evolution in the oscillating system under\nconsideration. To experimentally substantiate the theoretical predictions,\nprecise measurements to instantaneous band populations were conducted within a\none-dimensional accelerated optical lattice, encompassing systematic variations\nin both lattice's depths and accelerations. The obtained experimental results\ndemonstrate a quantitatively consistent correspondence with the anticipated\ntheoretical expressions. Afterwards, the atomic velocity distributions are also\nmeasured to compare with the time bound. This research offers a quantitative\nframework for the selection of parameters that ensure atom trapped throughout\nthe acceleration process. Moreover, it contributes an experimental criterion by\nwhich to assess the adequacy of adiabatic conditions in an oscillating system,\nthereby augmenting the current understanding of these systems from a\ntheoretical perspective."
    },
    {
        "anchor": "Emergent and broken symmetries of atomic self-organization arising from\n  Gouy phase shifts in multimode cavity QED: Optical cavities can induce photon-mediated interactions among\nintracavity-trapped atoms. Multimode cavities provide the ability to tune the\nform of these interactions, e.g., by inducing a nonlocal, sign-changing term to\nthe interaction. By accounting for the Gouy phase shifts of the modes in a\nnearly degenerate, confocal, Fabry-Perot cavity, we provide a theoretical\ndescription of this interaction, along with additional experimental\nconfirmation to complement that presented in the companion paper, Ref. [1].\nFurthermore, we show that this interaction should be written in terms of a\ncomplex order parameter, allowing for a U(1)-symmetry to emerge. This symmetry\ncorresponds to the phase of the atomic density wave arising from\nself-organization when the cavity is transversely pumped above a critical\nthreshold power. We theoretically and experimentally show how this phase\ndepends on the position of the Bose-Einstein condensate (BEC) within the cavity\nand discuss mechanisms that break the U(1)-symmetry and lock this phase. We\nthen consider alternative Fabry-Perot multimode cavity geometries (i.e., beyond\nthe confocal) and schemes with more than one pump laser and show that these\nprovide additional capabilities for tuning the cavity-meditated interaction\namong atoms, including the ability to restore the U(1)-symmetry despite the\npresence of symmetry-breaking effects. These photon-mediated interactions may\nbe exploited for realizing quantum liquid crystalline states and spin glasses\nusing multimode optical cavities.",
        "positive": "Acoustic white holes in flowing atomic Bose-Einstein condensates: We study acoustic white holes in a steadily flowing atomic Bose-Einstein\ncondensate. A white hole configuration is obtained when the flow velocity goes\nfrom a super-sonic value in the upstream region to a sub-sonic one in the\ndownstream region. The scattering of phonon wavepackets on a white hole horizon\nis numerically studied in terms of the Gross-Pitaevskii equation of mean-field\ntheory: dynamical stability of the acoustic white hole is found, as well as a\nsignature of a nonlinear back-action of the incident phonon wavepacket onto the\nhorizon. The correlation pattern of density fluctuations is numerically studied\nby means of the truncated-Wigner method which includes quantum fluctuations.\nSignatures of the white hole radiation of correlated phonon pairs by the\nhorizon are characterized; analogies and differences with Hawking radiation\nfrom acoustic black holes are discussed. In particular, a short wavelength\nfeature is identified in the density correlation function, whose amplitude\nsteadily grows in time since the formation of the horizon. The numerical\nobservations are quantitatively interpreted by means of an analytical\nBogoliubov theory of quantum fluctuations for a white hole configuration within\nthe step-like horizon approximation."
    },
    {
        "anchor": "Quantum Monte Carlo study of the visibility of one-dimensional\n  Bose-Fermi mixtures: The study of ultracold optically trapped atoms has opened new vistas in the\nphysics of correlated quantum systems. Much attention has now turned to\nmixtures of bosonic and fermionic atoms. A central puzzle is the disagreement\nbetween the experimental observation of a reduced bosonic visibility ${\\cal\nV}_b$, and quantum Monte Carlo (QMC) calculations which show ${\\cal V}_b$\nincreasing. In this paper, we present QMC simulations which evaluate the\ndensity profiles and ${\\cal V}_b$ of mixtures of bosons and fermions in\none-dimensional optical lattices. We resolve the discrepancy between theory and\nexperiment by identifying parameter regimes where ${\\cal V}_b$ is reduced, and\nwhere it is increased. We present a simple qualitative picture of the different\nresponse to the fermion admixture in terms of the superfluid and\nMott-insulating domains before and after the fermions are included. Finally, we\nshow that ${\\cal V}_b$ exhibits kinks which are tied to the domain evolution\npresent in the pure case, and also additional structure arising from the\nformation of boson-fermion molecules, a prediction for future experiments.",
        "positive": "Quench Dynamics of Anyon Tonks-Girardeau Gases: We investigate the dynamical evolution of strongly interacting anyons\nconfined in a weak harmonic trap using the exact anyon-fermion mapping method.\nThe density profiles, momentum distribution, and the reduced one-body density\nmatrix are obtained for different statistical parameters. The density profiles\nof anyons display the same behaviors irrespective of statistical parameter\nduring the evolution. As the harmonic trap is turned off suddenly, the momentum\ndistributions exhibit the symmetric fermion-like behaviour in the long time\nevolution. As the trap frequency is quenched, the momentum distribution exhibit\nan asymmetry breath mode during the evolution. The reduced one-body density\nmatrix show the dynamical symmetry broken and reproduced behaviour."
    },
    {
        "anchor": "Determining the interspecies interaction strength of a two-species\n  Bose-Einstein condensate from the density profile of one species: We study harmonically trapped two-species Bose-Einstein condensates within\nthe Gross-Pitaevskii formalism. By invoking the Thomas-Fermi approximation, we\nderive an analytical solution for the miscible ground state in a particular\nregion of the system's parameter space. This solution furnishes a simple\nformula for determining the relative strength of the interspecies interaction\nfrom a measurement of the density distribution of only one of the two species.\nAccompanying numerical simulations confirm its accuracy for sufficiently large\nnumbers of condensed particles. The introduced formula provides a\ncondensate-based scheme that complements the typical experimental methods of\nevaluating interspecies scattering lengths from collisional measurements on\nthermal samples.",
        "positive": "Anisotropic polarizability of erbium atoms: We report on the determination of the dynamical polarizability of ultracold\nerbium atoms in the ground and in one excited state at three different\nwavelengths, which are particularly relevant for optical trapping. Our study\ncombines experimental measurements of the light shift and theoretical\ncalculations. In particular, our experimental approach allows us to isolate the\ndifferent contributions to the polarizability, namely the isotropic scalar and\nanisotropic tensor part. For the latter contribution, we observe a clear\ndependence of the atomic polarizability on the angle between the\nlaser-field-polarization axis and the quantization axis, set by the external\nmagnetic field. Such an angle-dependence is particularly pronounced in the\nexcited-state polarizability. We compare our experimental findings with the\ntheoretical values, based on semi-empirical electronic-structure calculations\nand we observe a very good overall agreement. Our results pave the way to\nexploit the anisotropy of the tensor polarizability for spin-selective\npreparation and manipulation."
    },
    {
        "anchor": "Scissors Modes of a Bose-Einstein Condensate in a Synthetic Magnetic\n  Field: We study the scissors modes of a harmonically trapped Bose-Einstein\ncondensate under the influence of a synthetic magnetic field, which induces\nrigid rotational components in the velocity field. Our investigation reveals\nthat the scissors mode, excited in the plane perpendicular to the synthetic\nmagnetic field, becomes coupled to the quadrupole modes of the condensate,\ngiving rise to typical beating effects. Moreover, the two scissors modes\nexcited in the vertical planes are also coupled together by the synthetic\nmagnetic field, resulting in intriguing gyroscope dynamics. Our analytical\nresults, derived from a spinor hydrodynamic theory, are further validated\nthrough numerical simulations of the three-dimensional Gross-Pitaevskii\nequation. These predictions for the condensates subject to a synthetic magnetic\nfield are experimentally accessible with current cold-atom setups and hold\npromise for potential applications in quantum sensing.",
        "positive": "Truncation effects in the charge representation of the O(2) model: The O(2) model in Euclidean space-time is the zero-gauge-coupling limit of\nthe compact scalar quantum electrodynamics. We obtain a dual representation of\nit called the charge representation. We study the quantum phase transition in\nthe charge representation with a truncation to ``spin $S$,\" where the quantum\nnumbers have an absolute value less than or equal to $S$. The charge\nrepresentation preserves the gapless-to-gapped phase transition even for the\nsmallest spin truncation $S = 1$. The phase transition for $S = 1$ is an\ninfinite-order Gaussian transition with the same critical exponents $\\delta$\nand $\\eta$ as the Berezinskii-Kosterlitz-Thouless (BKT) transition, while there\nare true BKT transitions for $S \\ge 2$. The essential singularity in the\ncorrelation length for $S = 1$ is different from that for $S \\ge 2$. The\nexponential convergence of the phase-transition point is studied in both\nLagrangian and Hamiltonian formulations. We discuss the effects of replacing\nthe truncated $\\hat{U}^{\\pm} = \\exp(\\pm i \\hat{\\theta})$ operators by the spin\nladder operators $\\hat{S}^{\\pm}$ in the Hamiltonian. The marginal operators\nvanish at the Gaussian transition point for $S = 1$, which allows us to extract\nthe $\\eta$ exponent with high accuracy."
    },
    {
        "anchor": "Probing Half-odd Topological Number with Cold Atoms in a Non-Abelian\n  Optical Lattice: We propose an experimental scheme to probe the contribution of a single Dirac\ncone to the Hall conductivity as half-odd topological number sequence. In our\nscheme, the quantum anomalous Hall effect as in graphene is simulated with cold\natoms trapped in an optical lattice and subjected to a laser-induced\nnon-Abelian gauge field. By tuning the laser intensity to change the gauge\nflux, the energies of the four Dirac points in the first Brillouin zone are\nshifted with each other and the contribution of the single Dirac cone to the\ntotal atomic Hall conductivity is manifested. We also show such manifestation\ncan be experimentally probed with atomic density profile measurements.",
        "positive": "Energy bands in a three dimension simple cubic lattice of contact\n  potential: In this work, we investigate energy bands in a three dimensional simple cubic\nlattice of contact potential. The energy bands in the first Brillouin Zone are\nobtained with Ewald's summation method. In comparison with single point\npotential, the presence of lattice potential changes the existence condition of\nnegative energy states near zero energy. It is found that the system always has\nnegative energy states for an arbitrarily weak periodic potential. In addition,\nwe prove that if an irreducible unitary representation is not a trivial\nrepresentation of group of wave vector, the corresponding wave functions at\nlattice sites would be zero. With this theorem, the degeneracy of energy bands\nis explained with group theory. Furthermore, we find that there exists some\nenergy bands which are not affected by the lattice potential. We call their\ncorresponding eigenstates as dark states. The physical mechanism of the dark\nstates is explained by explicitly constructing the standing wave-type Bloch\nwave functions."
    },
    {
        "anchor": "Mean-field phase diagram of the 1-D Bose gas in a disorder potential: We study the quantum phase transition of the 1D weakly interacting Bose gas\nin the presence of disorder. We characterize the phase transition as a function\nof disorder and interaction strengths, by inspecting the long-range behavior of\nthe one-body density matrix as well as the drop in the superfluid fraction. We\nfocus on the properties of the low-energy Bogoliubov excitations that drive the\nphase transition, and find that the transition to the insulator state is marked\nby a diverging density of states and a localization length that diverges as a\npower-law with power 1. We draw the phase diagram and we observe that the\nboundary between the superfluid and the Bose glass phase is characterized by\ntwo different algebraic relations. These can be explained analytically by\nconsidering the limiting cases of zero and infinite disorder correlation\nlength.",
        "positive": "Probing quantum criticality and symmetry breaking at the microscopic\n  level: We report on an experimental study of the Lipkin-Meshkov-Glick model of\nquantum spins interacting at infinite range in a transverse magnetic field,\nwhich exhibits a ferromagnetic phase transition in the thermodynamic limit. We\nuse Dysprosium atoms of electronic spin $J=8$, subjected to a quadratic Zeeman\nlight shift, to simulate $2J=16$ interacting spins $1/2$. We probe the system\nmicroscopically using single magnetic sublevel resolution, giving access to the\nspin projection parity, which is the collective observable characterizing the\nunderlying $\\mathbb{Z}_2$ symmetry. We measure the thermodynamic properties and\ndynamical response of the system, and study the quantum critical behavior\naround the transition point. In the ferromagnetic phase, we achieve coherent\ntunneling between symmetry-broken states, and test the link between symmetry\nbreaking and the appearance of a finite order parameter."
    },
    {
        "anchor": "Topological bound states of a quantum walk with cold atoms: We suggest a method for engineering a quantum walk, with cold atoms as\nwalkers, which presents topologically non-trivial properties. We derive the\nphase diagram, and show that we are able to produce a boundary between\ntopologically distinct phases using the finite beam width of the applied\nlasers. A topologically protected bound state can then be observed, which is\npinned to the interface and is robust to perturbations. We show that it is\npossible to identify this bound state by averaging over spin sensitive measures\nof the atom's position, based on the spin distribution that these states\ndisplay. Interestingly, there exists a parameter regime in which our system\nmaps on to the Creutz ladder.",
        "positive": "Engineering Bright Matter-Wave Solitons of Dipolar Condensates: We present a comprehensive analysis of the form and interaction of dipolar\nbright solitons across the full parameter space afforded by dipolar\nBose-Einstein condensates, revealing the rich behaviour introduced by the\nnon-local nonlinearity. Working within an effective one-dimensional\ndescription, we map out the existence of the soliton solutions and show three\ncollisional regimes: free collisions, bound state formation and soliton fusion.\nFinally, we examine the solitons in their full three-dimensional form through a\nvariational approach; along with regimes of instability to collapse and runaway\nexpansion, we identify regimes of stability which are accessible to current\nexperiments."
    },
    {
        "anchor": "Quantum-torque-induced breaking of magnetic interfaces in ultracold\n  gases: A rich variety of physical effects in spin dynamics arises at the interface\nbetween different magnetic materials. Engineered systems with interlaced\nmagnetic structures have been used to implement spin transistors, memories and\nother spintronic devices. However, experiments in solid state systems can be\ndifficult to interpret because of disorder and losses. Here, we realize\nanalogues of magnetic junctions using a coherently-coupled mixture of ultracold\nbosonic gases. The spatial inhomogeneity of the atomic gas makes the system\nchange its behavior from regions with oscillating magnetization -- resembling a\nmagnetic material in the presence of an external transverse field -- to regions\nwith a defined magnetization, as in magnetic materials with a ferromagnetic\nanisotropy stronger than external fields. Starting from a far-from-equilibrium\nfully polarized state, magnetic interfaces rapidly form. At the interfaces, we\nobserve the formation of short-wavelength magnetic waves. They are generated by\na quantum torque contribution to the spin current and produce strong spatial\nanticorrelations in the magnetization. Our results establish ultracold gases as\na platform for the study of far-from-equilibrium spin dynamics in regimes that\nare not easily accessible in solid-state systems.",
        "positive": "Engineering and Revealing Dirac Strings in Spinor Condensates: Artificial monopoles have been engineered in various systems, yet there has\nbeen no systematic study on the singular vector potentials associated with the\nmonopole field. We show that the Dirac string, the line singularity of the\nvector potential, can be engineered, manipulated, and made manifest in a spinor\natomic condensate. We elucidate the connection among spin, orbital degrees of\nfreedom, and the artificial gauge, and reveal that there exists a mapping\nbetween the vortex filament and the Dirac string. We also devise a proposal\nwhere preparing initial spin states with relevant symmetries can result in\ndifferent vortex patterns, revealing an underlying correspondence between the\ninternal spin states and the spherical vortex structures. Such a mapping also\nleads to a new way of constructing monopole harmonics. Our observation provides\nsignificant insights in quantum matter possessing internal symmetries in curved\nspaces."
    },
    {
        "anchor": "Clock-line photoassociation of strongly bound dimers in a\n  magic-wavelength lattice: We report on the direct optical production and spectroscopy of\n$^1\\mathrm{S}_0\\mbox{-}^3\\mathrm{P}_0$ molecules with large binding energy\nusing the clock transition of $^{171}\\mathrm{Yb}$, and on the observation of\nthe associated orbital Feshbach resonance near $1300\\,\\mathrm{G}$. We measure\nthe magnetic field dependence of the closed-channel dimer and of the\nopen-channel pair state energy via clock-line spectroscopy in a deep optical\nlattice. In addition, we show that the free-to-bound transition into the dimer\ncan be made first-order insensitive to the trap depth by choice of the lattice\nwavelength. Finally, we determine the fundamental intra- and interorbital\nscattering lengths and probe the stability of the corresponding pair states,\nfinding long lifetimes in both interorbital interaction channels. These results\nare promising both for molecular clocks and for the preparation of\nstrongly-interacting multiorbital Fermi gases.",
        "positive": "Collision of two spin polarized fermionic clouds: We study the collision of two spin polarized Fermi clouds in a harmonic trap\nusing a simulation of the Boltzmann equation. As observed in recent experiments\nwe find three distinct regimes of behavior. For weak interactions the clouds\npass through each other. If interactions are increased they approach each other\nexponentially and for strong interactions they bounce off each other several\ntimes. We thereby demonstrate that all these phenomena can be reproduced using\na semiclassical collisional approach and that these changes in behavior are\nassociated with an increasing collision rate. We then show that the oscillation\nof the clouds in the bounce regime is an example of an unusual case in quantum\ngases: a nonlinear coupling between collective modes, namely the spin dipole\nmode and the axial breathing mode which is enforced by collisions. We also\ndetermine the frequency of the bounce as a function of the final temperature of\nthe equilibrated system."
    },
    {
        "anchor": "Strong-coupling study of spin-1 bosons in square and triangular optical\n  lattice: We examine the superfluid-Mott insulator (SF-MI) transition of\nantiferromagnetically interacting spin-1 bosons trapped in a square or\ntriangular optical lattice. We perform a strong-coupling expansion up to the\nthird order in the transfer integral $t$ between the nearest-neighbor lattices.\nAs expected from previous studies, an MI phase with an even number of bosons is\nconsiderably more stable against the SF phase than it is with an odd number of\nbosons. Results for the triangular lattice are similar to those for the square\nlattice, which suggests that the lattice geometry does not strongly affect the\nstability of the MI phase against the SF phase.",
        "positive": "Observation of coherent back-scattering and its dynamics in a transverse\n  2D photonic disorder : from weak to strong localization: We report the first observation of coherent back-scattering (CBS) of light in\na transverse photonic disorder. The CBS peak is recorded in the far-field, at a\nfixed propagation time set by our crystal length, and displays a contrast\napproaching the ideal value of 1, which proves good coherence of transport in\nour system. We study its dynamics for increasing disorder strength, and find a\nnon-monotonous evolution. For weak disorder, the CBS signal increases, and the\nasymmetry of the momentum distribution becomes inverted compared to the initial\ncondition. For stronger disorder, we observe a resymmetrization of the momentum\ndistribution, confirmed by numerical simulations, and compatible with the onset\nof strong (Anderson) localization."
    },
    {
        "anchor": "Stability of a trapped dipolar quantum gas: We calculate the stability diagram for a trapped normal Fermi or Bose gas\nwith dipole-dipole interactions. Our study characterizes the roles of trap\ngeometry and temperature on the stability using Hartree-Fock theory. We find\nthat exchange appreciably reduces stability, and that, for bosons, the double\ninstability feature in oblate trapping geometries predicted previously is still\npredicted by the Hartree-Fock theory. Our results are relevant to current\nexperiments with polar molecules and will be useful in developing strategies to\nobtain a polar molecule Bose-Einstein condensate or degenerate Fermi gas.",
        "positive": "Grassmann Phase Space Theory for the BEC/BCS Crossover in Cold Fermionic\n  Atomic Gases: Grassmann Phase Space Theory (GSPT) is applied to the BEC/BCS crossover in\ncold fermionic atomic gases and used to determine the evolution (over either\ntime or temperature) of the Quantum Correlation Functions (QCF) that specify:\n(a) the positions of the spin up and spin down fermionic atoms in a single\nCooper pair and (b) the positions of the two spin up and two spin down\nfermionic atoms in two Cooper pairs The first of these QCF is relevant to\ndescribing the change in size of a Cooper pair, as the fermion-fermion coupling\nconstant is changed via Feshbach resonance methods through the crossover from a\nsmall Cooper pair on the BEC side to a large Cooper pair on the BCS side. The\nsecond of these QCF is important for describing the correlations between the\npositions of the fermionic atoms in two Cooper pairs, which is expected to be\nsmall at the BEC or BCS sides of the crossover, but is expected to be\nsignificant in the strong interaction unitary regime, where the size of a\nCooper pair is comparable to the separation between Cooper pairs. In GPST the\nQCF are ultimately given via the stochastic average of products of Grassmann\nstochastic momentum fields, and GPST shows that the stochastic average of the\nproducts of Grassmann stochastic momentum fields at a later time (or lower\ntemperature) is related linearly to the stochastic average of the products of\nGrassmann stochastic momentum fields at an earlier time (or higher\ntemperature), and that the matrix elements involved in the linear relations are\nall c-numbers. Expressions for these matrix elements corresponding to a small\ntime or temperature increment have been obtained analytically, providing the\nformulae needed for numerical studies of the evolution that are planned for a\nfuture publication. Various initial conditions are considered, including those\nfor a non-interacting fermionic gas at zero temperature and a high temperature\ngas."
    },
    {
        "anchor": "Inhomogeneous phases in one-dimensional mass- and spin-imbalanced Fermi\n  gases: We compute the phase diagram of strongly interacting fermions in one\ndimension at finite temperature, with mass and spin imbalance. By including the\npossibility of the existence of a spatially inhomogeneous ground state, we find\nregions where spatially varying superfluid phases are favored over homogeneous\nphases. We obtain estimates for critical values of the temperature, mass and\nspin imbalance, above which these phases disappear. Finally, we show that an\nintriguing relation exists between the general structure of the phase diagram\nand the binding energies of the underlying two-body bound-state problem.",
        "positive": "Impact of the range of the interaction on the quantum dynamics of a\n  bosonic Josephson junction: The out-of-equilibrium quantum dynamics of a bosonic Josephson junction (BJJ)\nwith long-range interaction is studied in real space by solving the\ntime-dependent many-body Schr\\\"odinger equation numerically accurately using\nthe multiconfigurational time-dependent Hartree method for bosons. Having the\nmany-boson wave-function at hand we can examine the impact of the range of the\ninteraction on the properties of the BJJ dynamics, viz. density oscillations\nand their collapse, self trapping, depletion and fragmentation, as well as the\nposition variance, both at the mean-field and many-body level. Explicitly, the\nfrequency of the density oscillations and the time required for their collapse,\nthe value of fragmentation at the plateau, the maximal and the minimal values\nof the position variance in each cycle of oscillation and the overall pace of\nits growth are key to our study. We find competitive effect between the\ninteraction and the confining trap. The presence of the tail part of the\ninteraction basically enhances the effective repulsion as the range of the\ninteraction is increased starting from a short, finite range. But as the range\nbecomes comparable with the trap size, the system approaches a situation where\nall the atoms feel a constant potential and the impact of the tail on the\ndynamics diminishes. There is an optimal range of the interaction in which\nphysical quantities of the junction are attaining their extreme values."
    },
    {
        "anchor": "Accurate projective two-band description of topological superfluidity in\n  spin-orbit-coupled Fermi gases: The interplay of spin-orbit coupling and Zeeman splitting in ultracold Fermi\ngases gives rise to a topological superfluid phase in two spatial dimensions\nthat can host exotic Majorana excitations. Theoretical models have so far been\nbased on a four-band Bogoliubov-de Gennes formalism for the combined spin-1/2\nand particle-hole degrees of freedom. Here we present a simpler, yet accurate,\ntwo-band description based on a well-controlled projection technique that\nprovides a new platform for exploring analogies with chiral p-wave\nsuperfluidity and detailed future studies of spatially non-uniform situations.",
        "positive": "Self-interfering matter-wave patterns generated by a moving laser\n  obstacle in a two-dimensional Bose-Einstein condensate inside a power trap\n  cut off by box potential boundaries: We report the observation of highly energetic self-interfering matter-wave\n(SIMW) patterns generated by a moving obstacle in a two-dimensional\nBose-Einstein condensate (BEC) inside a power trap cut off by hard-wall box\npotential boundaries. The obstacle initially excites circular dispersive waves\nradiating away from the center of the trap which are reflected from hard-wall\nbox boundaries at the edges of the trap. The resulting interference between\noutgoing waves from the center of the trap and reflected waves from the box\nboundaries institutes, to the best of our knowledge, unprecedented standing\nwave patterns. For this purpose we simulated the time dependent Gross-\nPitaevskii equation using the split-step Crank-Nicolson method. The obstacle is\nmodelled by a moving impenetrable Gaussian potential barrier. Various trapping\ngeometries are considered."
    },
    {
        "anchor": "Efficient multipole representation for matter-wave optics: Technical optics with matter waves requires a universal description of\nthree-dimensional traps, lenses, and complex matter-wave fields. In analogy to\nthe two-dimensional Zernike expansion in beam optics, we present a\nthree-dimensional multipole expansion for Bose-condensed matter waves and\noptical devices. We characterize real magnetic chip traps, optical dipole\ntraps, and the complex matter-wave field in terms of spherical harmonics and\nradial Stringari polynomials. We illustrate this procedure for typical harmonic\nmodel potentials as well as real magnetic and optical dipole traps. Eventually,\nwe use the multipole expansion to characterize the aberrations of a\nballistically interacting expanding Bose-Einstein condensate in\n(3+1)-dimensions. In particular, we find deviations from the quadratic phase\nansatz in the popular scaling approximation. This universal multipole\ndescription of aberrations can be used to optimize matter-wave optics setups,\nfor example in matter-wave interferometers.",
        "positive": "A local exchange theory for trapped dipolar gases: We develop a practical Hartree-Fock theory for trapped Bose and Fermi gases\nthat interact with dipole-dipole interactions. This theory is applicable at\nzero and finite temperature. Our approach is based on the introduction of local\nmomentum distortion fields that characterize the exchange effects in terms of a\nlocal effective potential. We validate our theory against existing theories,\nfinding excellent agreement with full Hartree-Fock calculations."
    },
    {
        "anchor": "High Resolution Molecular Spectroscopy for Producing Ultracold Absolute\n  Ground-State $^{23}$Na$^{87}$Rb Molecules: We report a detailed molecular spectroscopy study on the lowest excited\nelectronic states of $^{23}\\rm{Na}^{87}\\rm{Rb}$ for producing ultracold\n$^{23}\\rm{Na}^{87}\\rm{Rb}$ molecules in the electronic, rovibrational and\nhyperfine ground state. Starting from weakly-bound Feshbach molecules, a series\nof vibrational levels of the $A^{1}\\Sigma^{+}-b^{3}\\Pi$ coupled excited states\nwere investigated. After resolving, modeling and interpreting the hyperfine\nstructure of several lines, we successfully identified a long-lived level\nresulting from the accidental hyperfine coupling between the $0^+$ and $0^-$\ncomponents of the $b^3\\Pi$ state, satisfying all the requirements for the\npopulation transfer toward the lowest rovibrational level of the X$^1\\Sigma^+$\nstate. Using two-photon spectroscopy, its binding energy was measured to be\n4977.308(3) cm$^{-1}$, the most precise value to date. We calibrated all the\ntransition strengths carefully and also demonstrated Raman transfer of Feshbach\nmolecules to the absolute ground state.",
        "positive": "Quantum spin dynamics of individual neutral impurities coupled to a\n  Bose-Einstein condensate: We report on spin dynamics of individual, localized neutral impurities\nimmersed in a Bose-Einstein condensate. Single Cesium atoms are transported\ninto a cloud of Rubidium atoms, thermalize with the bath, and the ensuing\nspin-exchange between localized impurities with quasi-spin $F_i=3$ and bath\natoms with $F_b=1$ is resolved. Comparing our data to numerical simulations of\nspin dynamics we find that, for gas densities in the BEC regime, the dynamics\nis dominated by the condensed fraction of the cloud. We spatially resolve the\ndensity overlap of impurities and gas by the spin-population of impurities.\nFinally we trace the coherence of impurities prepared in a coherent\nsuperposition of internal states when coupled to a gas of different densities.\nFor our choice of states we show that, despite high bath densities and thus\nfast thermalization rates, the impurity coherence is not affected by the bath,\nrealizing a regime of sympathetic cooling while maintaining internal state\ncoherence. Our work paves the way toward non-destructive probing of quantum\nmany-body systems via localized impurities."
    },
    {
        "anchor": "Quasi-one-dimensional harmonically trapped quantum droplets: We theoretically consider effectively one-dimensional quantum droplets in a\nsymmetric Bose-Bose mixture confined in a parabolic trap. We systematically\ninvestigate ground and excited families of localized trapped modes which\nbifurcate from eigenstates of the quantum harmonic oscillator as the number of\nparticles departs from zero. Families of nonlinear modes have nonmonotonous\nbehavior of chemical potential on the number of particles and feature\nbistability regions. Excited states are unstable close to the linear limit, but\nbecome stable when the number of particles is large enough. In the limit of\nlarge density, we derive a modified Thomas-Fermi distribution. Smoothly\ndecreasing the trapping strength down to zero, one can dynamically transform\nthe ground state solution to the solitonlike quantum droplet, while excited\ntrapped states break in several moving quantum droplets.",
        "positive": "Supersolid phase of a spin-orbit-coupled Bose-Einstein condensate: a\n  perturbation approach: The phase diagram of a Bose-Einstein condensate with Raman-induced spin-orbit\ncoupling includes a stripe phase with supersolid features. In this work we\ndevelop a perturbation approach to study the ground state and the Bogoliubov\nmodes of this phase, holding for small values of the Raman coupling. We obtain\nanalytical predictions for the most relevant observables (including the\nperiodicity of stripes, sound velocities, compressibility, and magnetic\nsusceptibility) which are in excellent agreement with the exact (non\nperturbative) numerical results, obtained for significantly large values of the\ncoupling. We further unveil the nature of the two gapless Bogoliubov modes in\nthe long-wavelength limit. We find that the spin branch of the spectrum,\ncorresponding in this limit to the dynamics of the relative phase between the\ntwo spin components, describes a translation of the fringes of the equilibrium\ndensity profile, thereby providing the crystal Goldstone mode typical of a\nsupersolid configuration. Finally, using sum-rule arguments, we show that the\nsuperfluid density can be experimentally accessed by measuring the ratio of the\nsound velocities parallel and perpendicular to the direction of the spin-orbit\ncoupling."
    },
    {
        "anchor": "Analogue Black Holes in Reactive Molecules: We show that reactive molecules with a unit probability of reaction naturally\nprovide a simulator of some intriguing black hole physics. The unit reaction at\nthe short distance acts as an event horizon and delivers a one-way traffic for\nmatter waves passing through the potential barrier when two molecules interact\nby high partial-wave scatterings or dipole-dipole interactions. In particular,\nthe scattering rate as a function of the incident energy exhibits a\nthermal-like distribution near the maximum of the interaction energy in the\nsame manner as a scalar field scatters with the potential barrier outside the\nevent horizon of a black hole. Such a thermal-like scattering can be extracted\nfrom the temperature-dependent two-body loss rate measured in experiments on\nKRb and other molecules.",
        "positive": "Stability and decay of Bloch oscillations in presence of time-dependent\n  nonlinearity: We consider Bloch oscillations of Bose-Einstein condensates in presence of a\ntime-modulated s-wave scattering length. Generically, interaction leads to\ndephasing and decay of the wave packet. Based on a cyclic-time argument, we\nfind---additionally to the linear Bloch oscillation and a rigid soliton\nsolution---an infinite family of modulations that lead to a periodic time\nevolution of the wave packet. In order to quantitatively describe the dynamics\nof Bloch oscillations in presence of time-modulated interactions, we employ two\ncomplementary methods: collective-coordinates and the linear stability analysis\nof an extended wave packet. We provide instructive examples and address the\nquestion of robustness against external perturbations."
    },
    {
        "anchor": "Quantum Quench and Prethermalization Dynamics in A Two-Dimensional Fermi\n  Gas with Long-range Interactions: We study the effect of suddenly turning on a long-range interaction in a\nspinless Fermi gas in two dimensions. The short to intermediate time dynamics\nis obtained using the method of bosonization of the Fermi surface. This allow\nto calculate the full space-time dependence of the non-equilibrium fermion\ndensity matrix as well as the evolution of the quasiparticle residue after the\nquench. It is thus found that the asymptotic state predicted by bosonization is\nconsistent with the prethermalized state. From the bosonized representation, we\nexplicitly construct the Generalized Gibbs Ensamble that describes the\nprethermalized state. A protocol to perform an interaction quantum quench in a\ndipolar gas of Erbium atoms is also described.",
        "positive": "A Decade of Time Crystals: Quo Vadis?: Ten years ago, the new era of time crystals began. Time crystals are systems\nthat behave in the time dimension like ordinary space crystals do in space\ndimensions. We present a brief history of a decade of research on time\ncrystals, describe current research directions, indicate challenges, and\ndiscuss some future perspectives for condensed matter physics in the time\ndomain."
    },
    {
        "anchor": "Singlet Pathway to the Ground State of Ultracold Polar Molecules: Starting from weakly bound Feshbach molecules, we demonstrate a two-photon\npathway to the dipolar ground state of bi-alkali molecules that involves only\nsinglet-to-singlet optical transitions. This pathway eliminates the search for\na suitable intermediate state with sufficient singlet-triplet mixing and the\nexploration of its hyperfine structure, as is typical for pathways starting\nfrom triplet dominated Feshbach molecules. By selecting a Feshbach state with a\nstretched singlet hyperfine component and controlling the polarization of the\nexcitation laser, we assure coupling to only a single hyperfine component of\nthe $\\textrm{A}^{1}\\Sigma^{+}$ excited potential, even if the hyperfine\nstructure is not resolved. Similarly, we address a stretched hyperfine\ncomponent of the $\\textrm{X}^{1}\\Sigma^{+}$ rovibrational ground state, and\ntherefore an ideal three level system is established. We demonstrate this\npathway with ${}^{6}\\textrm{Li}{}^{40}\\textrm{K}$ molecules. By exploring\ndeeply bound states of the $\\textrm{A}^{1}\\Sigma^{+}$ potential, we are able to\nobtain large and balanced Rabi frequencies for both transitions. This method\ncan be applied to other molecular species.",
        "positive": "Observation of the Mott Insulator to Superfluid Crossover of a\n  Driven-Dissipative Bose-Hubbard System: Dissipation is ubiquitous in nature and plays a crucial role in quantum\nsystems such as causing decoherence of quantum states. Recently, much attention\nhas been paid to an intriguing possibility of dissipation as an efficient tool\nfor preparation and manipulation of quantum states. Here we report the\nrealization of successful demonstration of a novel role of dissipation in a\nquantum phase transition using cold atoms. We realize an engineered dissipative\nBose-Hubbard system by introducing a controllable strength of two-body\ninelastic collision via photo-association for ultracold bosons in a\nthree-dimensional optical lattice. In the dynamics subjected to a slow\nramp-down of the optical lattice, we find that strong on-site dissipation\nfavors the Mott insulating state: the melting of the Mott insulator is delayed\nand the growth of the phase coherence is suppressed. The controllability of the\ndissipation is highlighted by quenching the dissipation, providing a novel\nmethod for investigating a quantum many-body state and its non-equilibrium\ndynamics."
    },
    {
        "anchor": "Vortex gyroscope imaging of planar superfluids: We propose a robust imaging technique that makes it possible to distinguish\nvortices from antivortices in quasi-two-dimensional Bose--Einstein condensates\nfrom a single image of the density of the atoms. Tilting the planar condensate\nprior to standard absorption imaging excites a generalized gyroscopic mode of\nthe condensate revealing the sign and location of each vortex. This technique\nis anticipated to enable experimental measurement of the incompressible kinetic\nenergy spectrum of the condensate and the observation of a negative temperature\nphase transition of the vortex gas, driven by two-dimensional superfluid\nturbulence.",
        "positive": "Dynamics and universality in noise driven dissipative systems: We investigate the dynamical properties of low dimensional systems, driven by\nexternal noise sources. Specifically we consider a resistively shunted\nJosephson junction and a one dimensional quantum liquid in a commensurate\nlattice potential, subject to $1/f$ noise. In absence of nonlinear coupling, we\nhave shown previously that these systems establish a non-equilibrium critical\nsteady state [Nature Phys. 6, 806 (2010)]. Here we use this state as the basis\nfor a controlled renormalization group analysis using the Keldysh path integral\nformulation to treat the non linearities: the Josephson coupling and the\ncommensurate lattice.\n  The analysis to first order in the coupling constant indicates transitions\nbetween superconducting and localized regimes that are smoothly connected to\nthe respective equilibrium transitions. However at second order, the back\naction of the mode coupling on the critical state leads to renormalization of\ndissipation and emergence of an effective temperature. In the Josephson\njunction the temperature is parametrically small allowing to observe a\nuniversal crossover between the superconducting and insulating regimes. The IV\ncharacteristics of the junction displays algebraic behavior controlled by the\nunderlying critical state over a wide range. In the noisy one dimensional\nliquid the generated dissipation and effective temperature are not small as in\nthe junction. We find a crossover between a quasi-localized regime dominated by\ndissipation and another dominated by temperature. However since in the thermal\nregime the thermalization rate is parametrically small, signatures of the\nnon-equilibrium critical state can be seen in transient dynamics."
    },
    {
        "anchor": "Finite-Momentum Dimer Bound State in Spin-Orbit Coupled Fermi Gas: We investigate the two-body properties of a spin-1/2 Fermi gas subject to a\nspin-orbit coupling induced by laser fields. When an attractive s-wave\ninteraction between unlike spins is present, the system may form a dimer bound\nstate. Surprisingly, in the presence of a Zeeman field along the direction of\nthe spin-orbit coupling, the bound state obtains finite center-of-mass\nmechanical momentum, whereas under the same condition but in the absence of the\ntwo-body interaction, the system has zero total momentum. This unusual result\ncan be regarded as a consequence of the broken Galilean invariance by the\nspin-orbit coupling. Such a finite-momentum bound state will have profound\neffects on the many-body properties of the system.",
        "positive": "Computing ground states of Bose-Einstein Condensates with higher order\n  interaction via a regularized density function formulation: We propose and analyze a new numerical method for computing the ground state\nof the modified Gross-Pitaevskii equation for modeling the Bose-Einstein\ncondensate with a higher order interaction by adapting the density function\nformulation and the accelerated projected gradient method. By reformulating the\nenergy functional $E(\\phi)$ with $\\phi$, the wave function, in terms of the\ndensity $\\rho=|\\phi|^2$, the original non-convex minimization problem for\ndefining the ground state is then reformulated to a convex minimization\nproblem. In order to overcome the semi-smoothness of the function $\\sqrt{\\rho}$\nin the kinetic energy part, a regularization is introduced with a small\nparameter $0<\\varepsilon\\ll1$. Convergence of the regularization is established\nwhen $\\varepsilon\\to0$. The regularized convex optimization problem is\ndiscretized by the second order finite difference method. The convergence rates\nin terms of the density and energy of the discretization are established. The\naccelerated projected gradient method is adapted for solving the discretized\noptimization problem. Numerical results are reported to demonstrate the\nefficiency and accuracy of the proposed numerical method. Our results show that\nthe proposed method is much more efficient than the existing methods in the\nliterature, especially in the strong interaction regime."
    },
    {
        "anchor": "Sarma phase in relativistic and non-relativistic systems: We investigate the stability of the Sarma phase in two-component fermion\nsystems in three spatial dimensions. For this purpose we compare\nstrongly-correlated systems with either relativistic or non-relativistic\ndispersion relation: relativistic quarks and mesons at finite isospin density\nand spin-imbalanced ultracold Fermi gases. Using a Functional Renormalization\nGroup approach, we resolve fluctuation effects onto the corresponding phase\ndiagrams beyond the mean-field approximation. We find that fluctuations induce\na second order phase transition at zero temperature, and thus a Sarma phase, in\nthe relativistic setup for large isospin chemical potential. This motivates the\ninvestigation of the cold atoms setup with comparable mean-field phase\nstructure, where the Sarma phase could then be realized in experiment. However,\nfor the non-relativistic system we find the stability region of the Sarma phase\nto be smaller than the one predicted from mean-field theory. It is limited to\nthe BEC side of the phase diagram, and the unitary Fermi gas does not support a\nSarma phase at zero temperature. Finally, we propose an ultracold quantum gas\nwith four fermion species that has a good chance to realize a zero-temperature\nSarma phase.",
        "positive": "Bose gas with generalized dispersion relation plus an energy gap: Bose-Einstein condensation in a Bose gas is studied analytically, in any\npositive dimensionality ($d>0$) for identical bosons with any energy-momentum\npositive-exponent ($s>0$) plus an energy gap $\\Delta$ between the ground state\nenergy $\\varepsilon_0$ and the first excited state, i.e.,\n$\\varepsilon=\\varepsilon_0$ for $k=0$ and $\\varepsilon=\\varepsilon_0 +\\Delta+\nc_sk^s$, for $k>0$, where $\\hbar \\mathbf{k}$ is the particle momentum and $c_s$\na constant with dimensions of energy multiplied by a length to the power $s >\n0$. Explicit formula with arbitrary $d/s$ and $\\Delta$ are obtained and\ndiscussed for the critical temperature and the condensed fraction, as well as\nfor the equation of state from where we deduce a generalized $\\Delta$\nindependent thermal de Broglie wavelength. Also the internal energy is\ncalculated from where we obtain the isochoric specific heat and its jump at\n$T_c$. When $\\Delta > 0$, a Bose-Einstein critical temperature $T_c \\neq 0$\nexists for any $d > 0$ at which the internal energy shows a peak and the\nspecific heat shows a jump. Both the critical temperature and the specific heat\njump increase as functions of the gap but they decrease as of $d/s$. At\nsufficiently high temperatures $\\Delta$- independent classical results are\nrecovered. However, for temperatures below the critical one the gap effects are\npredominant. For $\\Delta = 0$ we recover previous reported results."
    },
    {
        "anchor": "Relaxation of superfluid turbulence in highly oblate Bose-Einstein\n  condensates: We investigate thermal relaxation of superfluid turbulence in a highly oblate\nBose-Einstein condensate. We generate turbulent flow in the condensate by\nsweeping the center region of the condensate with a repulsive optical\npotential. The turbulent condensate shows a spatially disordered distribution\nof quantized vortices and the vortex number of the condensate exhibits\nnonexponential decay behavior which we attribute to the vortex pair\nannihilation. The vortex-antivortex collisions in the condensate are identified\nwith crescent-shaped, coalesced vortex cores. We observe that the\nnonexponential decay of the vortex number is quantitatively well described by a\nrate equation consisting of one-body and two-body decay terms. In our\nmeasurement, we find that the local two-body decay rate is closely proportional\nto $T^2/\\mu$, where $T$ is the temperature and $\\mu$ is the chemical potential.",
        "positive": "Collective excitations of dipolar gases based on local tunneling in\n  superlattices: The collective dynamics of a dipolar fermionic quantum gas confined in a\none-dimensional double-well superlattice is explored. The fermionic gas resides\nin a paramagnetic-like ground state in the weak interaction regime, upon which\na new type of collective dynamics is found when applying a local perturbation.\nThis dynamics is composed of the local tunneling of fermions in separate\nsupercells, and is a pure quantum effect, with no classical counterpart. Due to\nthe presence of the dipolar interactions the local tunneling transports through\nthe entire superlattice, giving rise to a collective dynamics. A well-defined\nmomentum-energy dispersion relation is identified in the ab-initio simulations\ndemonstrating the phonon-like behavior. The phonon-like characteristic is also\nconfirmed by an analytical description of the dynamics within a semiclassical\npicture."
    },
    {
        "anchor": "Polarization of a quasi two-dimensional repulsive Fermi gas with Rashba\n  spin-orbit coupling: a variational study: Motivated by the remarkable experimental control of synthetic gauge fields in\nultracold atomic systems, we investigate the effect of an artificial Rashba\nspin-orbit coupling on the spin polarization of a two-dimensional repulsive\nFermi gas. By using a variational many-body wavefunction, based on a suitable\nspinorial structure, we find that the polarization properties of the system are\nindeed controlled by the interplay between spin-orbit coupling and repulsive\ninteraction. In particular, two main effects are found: 1) The Rashba coupling\ndetermines a gradual increase of the degree of polarization beyond the critical\nrepulsive interaction strength, at variance with conventional 2D Stoner\ninstability. 2) The critical interaction strength, above which finite\npolarization is developed, shows a dependence on the Rashba coupling, i.e. it\nis enhanced in case the Rashba coupling exceeds a critical value. A simple\nanalytic expression for the critical interaction strength is further derived in\nthe context of our variational formulation, which allows for a straightforward\nand insightful analysis of the present problem.",
        "positive": "Three two-component fermions with contact interactions: correct\n  formulation and energy spectrum: Properties of two identical particles of mass $m$ and a distinct particle of\nmass $m_1$ in the universal low-energy limit of zero-range two-body interaction\nare studied in different sectors of total angular momentum $L$ and parity $P$.\nFor the unambiguous formulation of the problem in the interval $\\mu_r(L^P) <\nm/m_1 \\le \\mu_c(L^P)$ ($\\mu_r(1^-) \\approx 8.619$ and $\\mu_c(1^-) \\approx\n13.607$, $\\mu_r(2^+) \\approx 32.948$ and $\\mu_c(2^+) \\approx 38.630$,~etc.) in\neach $L^P$ sector an additional parameter $b$ determining the wave function\nnear the triple-collision point is introduced; thus, a one-parameter family of\nself-adjoint Hamiltonians is defined. Within the framework of this formulation,\ndependence of the bound-state energies on $m/m_1$ and $b$ in the sector of\nangular momentum and parity $L^P$ is calculated for $L \\le 5$ and analysed with\nthe aid of a simple model. A number of the bound states for each $L^P$ sector\nis analysed and presented in the form of `phase diagrams' in the plane of two\nparameters $m/m_1$ and $b$."
    },
    {
        "anchor": "Characterizing fractional topological phases of lattice bosons near the\n  first Mott lobe: The Bose-Hubbard model subjected to an effective magnetic field hosts a\nplethora of phases with different topological orders when tuning the chemical\npotential. Using the density matrix renormalization group method, we identify\nseveral gapped phases near the first Mott lobe at strong interactions. They are\nconnected by a particle-hole symmetry to a variety of quantum Hall states\nstabilized at low fillings. We characterize phases of both particle and hole\ntype and identify signatures compatible with Laughlin, Moore-Read, and Bosonic\nInteger Quantum Hall states by calculating the quantized Hall conductance and\nby extracting the topological entanglement entropy. Furthermore, we analyze the\nentanglement spectrum of a Laughlin state of bosonic particles and holes for a\nrange of interaction strengths, as well as the entanglement spectrum of a\nMoore-Read state. These results further corroborate the existence of\ntopological states at high fillings, close to the first Mott lobe, as hole\nanalogues of the respective low-filling states.",
        "positive": "Coherent Backscattering in Fock Space: a Signature of Quantum Many-Body\n  Interference in Interacting Bosonic Systems: We predict a generic manifestation of quantum interference in many-body\nbosonic systems resulting in a coherent enhancement of the average return\nprobability in Fock space. This enhancement is both robust with respect to\nvariations of external parameters and genuinely quantum insofar as it cannot be\ndescribed within mean-field approaches. As a direct manifestation of the\nsuperposition principle in Fock space, it arises when many-body equilibration\ndue to interactions sets in. Using a semiclassical approach based on\ninterfering paths in Fock space, we calculate the magnitude of the\nbackscattering peak and its dependence on gauge fields that break time-reversal\ninvariance. We confirm our predictions by comparing them to exact quantum\nevolution probabilities in Bose-Hubbard models, and discuss the relevance of\nour findings in the context of many-body thermalization."
    },
    {
        "anchor": "Fermi surface of a trapped dipolar Fermi gas: Under the framework of the semiclassical theory, we investigate the\nequilibrium-state properties of a spin polarized dipolar Fermi gas through full\nnumerical calculation. We show that the Fermi surfaces in both real and\nmomentum spaces are stretched along the attractive direction of dipolar\ninteraction. We further verify that the deformed Fermi surfaces can be well\napproximated by ellipsoids. In addition, the deformation parameters slightly\ndepend on the local real- and momentum-space densities. We also study the\ninteraction strength dependence of the energy and real- and momentum-space\ndensities. By comparing them with variational results, we find that the\nellipsoidal ansatz usually generates accurate results for weak dipolar\ninteraction, while under strong dipolar interaction limit, notable discrepancy\ncan be observed. Finally, we map out the stability boundary of the system.",
        "positive": "Quantum phase transition of a two-dimensional quadrupolar system: Ensembles with long-range interactions between particles are promising for\nrevealing strong quantum collective effects and many-body phenomena. Here we\nstudy the ground-state phase diagram of a two-dimensional Bose system with\nquadrupolar interactions using a diffusion Monte Carlo technique. We predict a\nquantum phase transition from a gas to a solid phase. The Lindemann ratio and\nthe condensate fraction at the transition point are $\\gamma=0.269(4)$ and\n$n_0/n=0.031(4)$, correspondingly. We observe the strong rotonization of the\ncollective excitation branch in the vicinity of the phase transition point. Our\nresults can be probed using state-of-the-art experimental systems of various\nnature, such as quasi-two-dimensional systems of quadrupolar excitons in\ntransition metal dichalcogenide (TMD) trilayers, quadrupolar molecules, and\nexcitons or Rydberg atoms with quadrupole moments induced by strong magnetic\nfields."
    },
    {
        "anchor": "Dynamical formation of the unitary Bose gas: We study the structure of a Bose-condensed gas after quenching interactions\nto unitarity. Using the method of cumulants, we decompose the evolving gas in\nterms of clusters. Within the quantum depletion we observe the emergence of\ntwo-body clusters bound purely by many-body effects, scaling continuously with\nthe atomic density. As the unitary Bose gas forms, three-body Efimov clusters\nare first localized and then sequentially absorbed into the embedded\natom-molecule scattering continuum of the surrounding depletion. These results\nmotivate future experimental probes of a quenched Bose-condensate during\nevolution at unitarity.",
        "positive": "Aharonov-Bohm effect for confined matter in lattice gauge theories: Gauge theories arise in physical systems displaying space-time local\nsymmetries. They provide a powerful description of important realms of physics\nranging from fundamental interactions, to statistical mechanics, condensed\nmatter and more recently quantum computation. As such, a remarkably deep\nunderstanding has been achieved in the field. With the advent of quantum\ntechnology, lower energy analogs, capable to capture important features of the\noriginal quantum field theories through quantum simulation, have been\nintensively studied. Here, we propose a specific scheme implementing an\nanalogic quantum simulation of lattice gauge theories constrained to mesoscopic\nspatial scales. To this end, we study the dynamics of mesons residing in a\nring-shaped lattice of mesoscopic size pierced by an effective magnetic field.\nIn particular, we find a new type of Aharonov-Bohm effect that goes beyond the\nparticle-like effect and reflecting the the features of the confining gauge\npotential. The coherence properties of the meson are quantified by the\npersistent current and by specific features of the correlation functions. When\nthe magnetic field is quenched, Aharonov-Bohm oscillations and correlations\nstart a specific matter-wave current dynamics."
    },
    {
        "anchor": "Fulde-Ferrell superfluids in spinless ultracold Fermi gases: The Fulde-Ferrell (FF) superfluid phase, in which fermions form\nfinite-momentum Cooper pairings, is well studied in spin-singlet superfluids in\npast decades. Different from previous works that engineer the FF state in\nspinful cold atoms, we show that the FF state can emerge in spinless Fermi\ngases confined in optical lattice associated with nearest-neighbor\ninteractions. The mechanism of the spinless FF state relies on the split Fermi\nsurfaces by tuning the chemistry potential, which naturally gives rise to\nfinite-momentum Cooper pairings. The phase transition is accompanied by changed\nChern numbers, in which, different from the conventional picture, the band gap\ndoes not close. By beyond-mean-field calculations, we find the finite-momentum\npairing is more robust, yielding the system promising for maintaining the FF\nstate at finite temperature. Finally we present the possible realization and\ndetection scheme of the spinless FF state.",
        "positive": "Coherence and linewidth of a continuously pumped atom laser at finite\n  temperature: A continuous wave atom laser formed by the outcoupling of atoms from a\ntrapped Bose-Einstein condensate (BEC) potentially has a range of metrological\napplications. However, in order for the device to be truly continuous, a\nmechanism to replenish the atoms in the BEC is required. Here we calculate the\ntemporal coherence properties of a continuously pumped atom laser beam\noutcoupled from a trapped Bose-Einstein condensate which is replenished from a\nreservoir at finite temperature. We find that the thermal fluctuations of the\ncondensate can significantly decrease the temporal coherence of the output beam\ndue to atomic interactions between the trapped BEC and the beam, and this can\nimpact the metrological usefulness of the device. We demonstrate that a Raman\noutcoupling scheme imparting a sufficient momentum kick to the atom laser beam\ncan lead to a significantly reduced linewidth."
    },
    {
        "anchor": "Efficient algorithm to compute the second Chern number in four\n  dimensional systems: Topological insulators are exotic material that possess conducting surface\nstates protected by the topology of the system. They can be classified in terms\nof their properties under discrete symmetries and are characterized by\ntopological invariants. The latter has been measured experimentally for several\nmodels in one, two and three dimensions in both condensed matter and quantum\nsimulation platforms. The recent progress in quantum simulation opens the road\nto the simulation of higher dimensional Hamiltonians and in particular of the\n4D quantum Hall effect. These systems are characterized by the second Chern\nnumber, a topological invariant that appears in the quantization of the\ntransverse conductivity for the non-linear response to both external magnetic\nand electric fields. This quantity cannot always be computed analytically and\nthere is therefore a need of an algorithm to compute it numerically. In this\nwork, we propose an efficient algorithm to compute the second Chern number in\n4D systems. We construct the algorithm with the help of lattice gauge theory\nand discuss the convergence to the continuous gauge theory. We benchmark the\nalgorithm on several relevant models, including the 4D Dirac Hamiltonian and\nthe 4D quantum Hall effect and verify numerically its rapid convergence.",
        "positive": "Pure Goldstone mode in the quench dynamics of a confined ultracold Fermi\n  gas in the BCS-BEC crossover regime: We present a numerical study of the dynamic response of a confined superfluid\nFermi gas to a rapid change of the scattering length (i.e., an interaction\nquench). Based on a fully microscopic time-dependent density-matrix approach\nwithin the full Bogoliubov-de Gennes formalism that includes a 3D harmonic\nconfinement we simulate and identify the emergence of a Goldstone mode of the\nBCS gap in a cigar-shaped $^6$Li gas. By analyzing this Goldstone mode over a\nwide range of parameters, we show that its excitation spectrum is gapless and\nthat its main frequency is not fixed by the trapping potential but that it is\ndetermined by the details of the quench. Thus, we report the emergence of a\npure Goldstone mode of the BCS gap that --in contrast to situations in many\nprevious studies-- maintains its gapless excitation spectrum predicted by the\nGoldstone theorem. Furthermore, we observe that the size-dependent superfluid\nresonances resulting from the atypical BCS-BEC crossover have a direct impact\non this Goldstone mode. Finally, we find that the interaction quench-induced\nGoldstone mode leads to a low-frequency in-phase oscillation of the\nsingle-particle occupations with complete inversion of the lowest-lying\nsingle-particle states which could provide a convenient experimental access to\nthe pure gapless Goldstone mode."
    },
    {
        "anchor": "Ferromagnetic response of a \"high-temperature\" quantum antiferromagnet: We study the finite temperature antiferromagnetic phase of the ionic Hubbard\nmodel in the strongly interacting limit using quantum Monte Carlo based\ndynamical mean field theory. We find that the ionic potential plays a dual role\nin determining the antiferromagnetic order. A small ionic potential (compared\nto Hubbard repulsion) increases the super-exchange coupling in the projected\nsector of the model, leading to an increase in the Neel temperature of the\nsystem. A large ionic potential leads to resonance between projected\nantiferromagnetically ordered configurations and density ordered configurations\nwith double occupancies, thereby killing antiferromagnetism in the system. This\nnovel way of degrading antiferromagnetism leads to spin polarization of the low\nenergy single particle density of states. The dynamic response of the system\nthus mimics ferromagnetic behaviour, although the system is still an\nantiferromagnet in terms of the static spin order.",
        "positive": "Crescent states in charge-imbalanced polariton condensates: We study two-dimensional charge-imbalanced electron-hole systems embedded in\nan optical microcavity. We find that strong coupling to photons favors states\nwith pairing at zero or small center of mass momentum, leading to a condensed\nstate with spontaneously broken time-reversal and rotational symmetry, and\nunpaired carriers that occupy an anisotropic crescent-shaped sliver of momentum\nspace. The crescent state is favoured at moderate charge imbalance, while a\nFulde--Ferrel--Larkin--Ovchinnikov-like state --- with pairing at large center\nof mass momentum --- occurs instead at strong imbalance. The crescent state\nstability results from long-range Coulomb interactions in combination with\nextremely long-range photon-mediated interactions."
    },
    {
        "anchor": "Many-polaron description of impurities in a Bose-Einstein condensate in\n  the weak coupling regime: The weak coupling many-polaron formalism is applied to the case of the\npolaronic system consisting of impurities in a Bose-Einstein condensate. This\nallows to investigate the groundstate properties and the response of the system\nto Bragg spectroscopy. This theory is then applied to the system of\nspin-polarized fermionic lithium-6 impurities in a sodium condensate. The Bragg\nspectrum reveals a peak which corresponds to the emission of Bogoliubov\nexcitations. Both ground state properties and the response spectrum show that\nthe polaronic effect vanishes at large densities. We also look at two\npossibilities to define the polaronic effective mass and observe that this\nresults in a different quantitative behavior if multiple impurities are\ninvolved.",
        "positive": "Properties of dipolar bosonic quantum gases at finite temperatures: The properties of ultracold quantum gases of bosons with dipole-dipole\ninteraction is investigated at finite temperature in the frame of the\nrepresentative ensembles theory. Self-consistent coupled equations of motion\nare derived for the condensate and the non-condensate components. Corrections\ndue to the dipolar interaction to the condensate depletion, the anomalous\ndensity and thermodynamic quantities such as the ground state energy, the\nequation of state, the compressibility and the presure are calculated in the\nhomogeneous case at both zero and finite temperatures. Effects of interaction\nand temperature on the structure factor are also discussed. Within the realm of\nthe local density approximation, we generalize our results to the case of a\ntrapped dipolar gas."
    },
    {
        "anchor": "Nonrelativistic fermions with holographic interactions and the unitary\n  Fermi gas: We present an alternative way of computing nonrelativistic single-particle\nspectra from holography. To this end, we introduce a mass gap in a holographic\nDirac semimetal and subsequently study the nonrelativistic limit of the\nresulting spectral functions. We use this method to compute the momentum\ndistributions and the equation of state of our nonrelativistic fermions, of\nwhich the latter can be used to extract all thermodynamic properties of the\nsystem. We find that our results are universal and reproduce many\nexperimentally and theoretically known features of an ultracold Fermi gas at\nunitarity.",
        "positive": "Bound states in the one-dimensional two-particle Hubbard model with an\n  impurity: We investigate bound states in the one-dimensional two-particle Bose-Hubbard\nmodel with an attractive ($V> 0$) impurity potential. This is a\none-dimensional, discrete analogy of the hydrogen negative ion H$^-$ problem.\nThere are several different types of bound states in this system, each of which\nappears in a specific region. For given $V$, there exists a (positive) critical\nvalue $U_{c1}$ of $U$, below which the ground state is a bound state.\nInterestingly, close to the critical value ($U\\lesssim U_{c1}$), the ground\nstate can be described by the Chandrasekhar-type variational wave function,\nwhich was initially proposed for H$^-$. For $U>U_{c1}$, the ground state is no\nlonger a bound state. However, there exists a second (larger) critical value\n$U_{c2}$ of $U$, above which a molecule-type bound state is established and\nstabilized by the repulsion. We have also tried to solve for the eigenstates of\nthe model using the Bethe ansatz. The model possesses a global $\\Zz_2$-symmetry\n(parity) which allows classification of all eigenstates into even and odd ones.\nIt is found that all states with odd-parity have the Bethe form, but none of\nthe states in the even-parity sector. This allows us to identify analytically\ntwo odd-parity bound states, which appear in the parameter regions $-2V<U<-V$\nand $-V<U<0$, respectively. Remarkably, the latter one can be \\textit{embedded}\nin the continuum spectrum with appropriate parameters. Moreover, in part of\nthese regions, there exists an even-parity bound state accompanying the\ncorresponding odd-parity bound state with almost the same energy."
    },
    {
        "anchor": "Topological transitions of gapless paired states in mixed-geometry\n  lattices: We propose a mixed-geometry system of fermionic species selectively confined\nin lattices of different geometry. We investigate how such asymmetry can lead\nto exotic multiband fermion pairing in an example system of honeycomb and\ntriangular lattices. A rich phase diagram of interband pairing with gapped and\ngapless excitations is found at zero temperature. We find that the two-band\ncontribution of the honeycomb lattices to the paired state helps to stabilize\nthe gapless phase with one or two Fermi surfaces. We also show that the Fermi\nsurface topology further divides the gapless phase into subclasses between\nwhich the system undergoes density-driven Lifshitz transitions.",
        "positive": "Ground state of a tightly bound composite dimer immersed in a Fermi Sea: In this paper we present a theoretical investigation for the ground state of\nan impurity immersed in a Fermi sea. The molecular regime is considered where a\ntwo-body bound state between the impurity and one of the fermions is formed.\nBoth interaction and exchange of the bound fermion take place between the dimer\nand the Fermi sea. We develop a formalism based on a two channel model allowing\nus to expand systematically the ground state energy of this immersed dimer with\nthe scattering length $a$. Working up to order $a^3$, associated to the\ncreation of two particle-hole pairs, reveals the first signature of the\ncomposite nature of the bosonic dimer. Finally, a complementary variational\nstudy provides an accurate estimate of the dimer energy even at large\nscattering length."
    },
    {
        "anchor": "Quantum Zeno control of coherent dissociation: We study the effect of dephasing on the coherent dissociation dynamics of an\natom-molecule Bose-Einstein condensate. We show that when phase-noise intensity\nis strong with respect to the inverse correlation time of the stimulated\nprocess, dissociation is suppressed via a Bose enhanced Quantum Zeno effect.\nThis is complementary to the quantum zeno control of phase-diffusion in a\nbimodal condensate by symmetric noise (Phys. Rev. Lett. {\\bf 100}, 220403\n(2008)) in that the controlled process here is phase-{\\it formation} and the\nrequired decoherence mechanism for its suppression is purely phase noise.",
        "positive": "Dynamics of a degenerate Cs-Yb mixture with attractive interspecies\n  interactions: We probe the collective dynamics of a quantum degenerate Bose-Bose mixture of\nCs and $^{174}$Yb with attractive interspecies interactions. Specifically, we\nexcite vertical center of mass oscillations of the Cs condensate, and observe\nsignificant damping for the Cs dipole mode, due to the rapid transfer of energy\nto the larger Yb component, and the ensuing acoustic dissipation. Numerical\nsimulations based on coupled Gross-Pitaevskii equations provide excellent\nagreement, and additionally reveal the possibility of late-time revivals\n(beating) which are found to be highly sensitive to the Cs and Yb atom number\ncombinations. By further tuning the interaction strength of Cs using a broad\nFeshbach resonance, we explore the stability of the degenerate mixture, and\nobserve collapse of the Cs condensate mediated by the attractive Cs-Yb\ninteraction when $a_{\\mathrm{Cs}}<50 \\, a_0$, well above the single-species\ncollapse threshold, in good agreement with simulations."
    },
    {
        "anchor": "Finite-range effects in the unitary Fermi polaron: Quantum Monte Carlo techniques are employed to study the properties of\npolarons in an ultracold Fermi gas, at $T= 0,$ and in the unitary regime using\nboth a zero-range model and a square-well potential. For a fixed density, the\npotential range is varied and results are extrapolated and compared against a\nzero-range model. A discussion regarding the choice of an interacting potential\nwith a finite range is presented. We compute the polaron effective mass, the\npolaron binding energy, and the effective coupling between them. The latter is\nobtained using the Landau-Pomeranchuk's weakly interacting quasiparticle model.\nThe contact parameter is estimated by fitting the pair distribution function of\natoms in different spin states.",
        "positive": "Spatial interference from well-separated condensates: We use magnetic levitation and a variable-separation dual optical plug to\nobtain clear spatial interference between two condensates axially separated by\nup to 0.25 mm -- the largest separation observed with this kind of\ninterferometer. Clear planar fringes are observed using standard (i.e.\nnon-tomographic) resonant absorption imaging. The effect of a weak inverted\nparabola potential on fringe separation is observed and agrees well with\ntheory."
    },
    {
        "anchor": "Suppression of quantum-mechanical collapse in bosonic gases with\n  intrinsic repulsion: A brief review: It is well known that attractive potential which is inversely proportional to\nthe squared distance from the origin gives rise to the critical quantum\ncollapse in the framework of the three-dimensional (3D) linear Schroedinger\nequation. This article summarizes theoretical analysis, chiefly published in\nseveral original papers, which demonstrates suppression of the collapse caused\nby this potential, and the creation of the otherwise missing ground state in a\n3D gas of bosonic dipoles pulled by the same potential to the central charge,\nwith repulsive contact interactions between them, represented by the cubic term\nin the respective Gross-Pitaevskii equation (GPE). In two dimensions (2D),\nquintic self-repulsion is necessary for the suppression of the collapse;\nalternatively, this may be provided by the effective quartic repulsion,\nproduced by the Lee-Huang-Yang correction to the GPE. 3D states carrying\nangular momentum are constructed in the model with the symmetry reduced from\nspherical to cylindrical by an external polarizing field. Interplay of the\ncollapse suppression and miscibility-immiscibility transition is considered in\na binary condensate. The consideration of the 3D setting in the form of the\nmany-body quantum system, with the help of the Monte Carlo method, demonstrates\nthat, although the quantum collapse cannot be fully suppressed, the\nself-trapped states, predicted by the GPE, exist in the many-body setting as\nmetastable modes protected against the collapse by a tall potential barrier.",
        "positive": "Quantum spin liquids of Rydberg excitations in a honeycomb lattice\n  induced by density-dependent Peierls phases: We show that the nonlinear transport of bosonic excitations in a\ntwo-dimensional honeycomb lattice of spin-orbit coupled Rydberg atoms gives\nrise to disordered quantum phases which are candidates for quantum spin\nliquids. As recently demonstrated in [Lienhard et al. Phys. Rev. X, 10, 021031\n(2020)] the spin-orbit coupling breaks time-reversal and chiral symmetries and\nleads to a tunable density-dependent complex hopping of the hard-core bosons or\nequivalently to complex XY spin interactions. Using exact diagonalization (ED)\nwe numerically investigate the phase diagram resulting from the competition\nbetween density-dependent and direct transport terms. In mean-field\napproximation there is a phase transition from a quasi-condensate to a\n120{\\deg} phase when the amplitude of the complex hopping exceeds that of the\ndirect one. In the full model a new phase with a finite spin gap emerges close\nto the mean-field critical point as a result of quantum fluctuations induced by\nthe density-dependence of the complex hopping. We show that this phase is a\ngenuine disordered one, has a non-vanishing spin chirality and is characterized\nby a non-trivial many-body Chern number. ED simulations of small lattices with\nup to 28 lattice sites point to a non-degenerate ground state and thus to a\nbosonic integer-quantum Hall (BIQH) phase, protected by U(1) symmetry. The\nChern number of C = 1, which is robust to disorder, is however different from\nthe even Chern numbers found in BIQH phases. For very strong, nonlinear\nhoppings of opposite sign we find another disordered regime with vanishing spin\ngap. This phase also has a large spin chirality and could be a gapless\nspin-liquid but lies outside the parameter regime accessible in the Rydberg\nsystem."
    },
    {
        "anchor": "Dynamics of parametric matter wave amplification: We develop a model for parametric amplification, based on a density matrix\napproach, which naturally accounts for the peculiarities arising for matter\nwaves: significant depletion and explicit time-dependence of the source state\npopulation, long interaction times, and spatial dynamics of the amplified\nmodes. We apply our model to explain the details in an experimental study on\ntwin-atom beam emission from a one-dimensional degenerate Bose gas.",
        "positive": "Diffusion Monte Carlo study of strongly interacting two-dimensional\n  Fermi gases: Ultracold atomic Fermi gases have been a popular topic of research, with\nattention being paid recently to two-dimensional (2D) gases. In this work, we\nperform T=0 ab initio diffusion Monte Carlo calculations for a strongly\ninteracting two-component Fermi gas confined to two dimensions. We first go\nover finite-size systems and the connection to the thermodynamic limit. After\nthat, we illustrate pertinent 2D scattering physics and properties of the wave\nfunction. We then show energy results for the strong-coupling crossover, in\nbetween the Bose-Einstein Condensation (BEC) and Bardeen-Cooper-Schrieffer\n(BCS) regimes. Our energy results for the BEC-BCS crossover are parametrized to\nproduce an equation of state, which is used to determine Tan's contact. We\ncarry out a detailed comparison with other microscopic results. Finally, we\ncalculate the pairing gap for a range of interaction strengths in the strong\ncoupling regime, following from variationally optimized many-body wave\nfunctions."
    },
    {
        "anchor": "Dynamics of spinor Bose-Einstein condensate subject to dissipation: We investigate the internal dynamics of the spinor Bose-Einstein Condensates\nsubject to dissipation by solving the Lindblad master equation. It is shown\nthat for the condensates without dissipation its dynamics always evolve along\nspecific orbital in the phase space of ($n_0$, $\\theta$) and display three\nkinds of dynamical properties including Josephson-like oscillation,\nself-trapping-like oscillation and 'running phase'. In contrast, the\ncondensates subject to dissipation will not evolve along the specific dynamical\norbital. If component-1 and component-(-1) dissipate in different rates, the\nmagnetization $m$ will not conserve and the system transits between different\ndynamical regions. The dynamical properties can be exhibited in the phase space\nof ($n_0$, $\\theta$, $m$).",
        "positive": "Stable Fulde-Ferrell-Larkin-Ovchinnikov pairing states in 2D and 3D\n  optical lattices: We present the study of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) pairing\nstates in the $p$-orbital bands in both two and three-dimensional optical\nlattices. Due to the quasi one-dimensional band structure which arises from the\nunidirectional hopping of the orthogonal $p$-orbitals, the pairing phase space\nis not affected by spin imbalance. Furthermore, interactions build up high\ndimensional phase coherence which stabilizes the FFLO states in 2D and 3D\noptical lattices in a large parameter regime in phase diagram. These FFLO\nphases are stable with imposing the inhomogeneous trapping potential. Their\nentropies are comparable to those of the normal states at finite temperatures."
    },
    {
        "anchor": "Two band atomic superfluidity in the presence of orbital Feshbach\n  resonance: We study superfluid properties of alkali-earth-like Fermi atomic systems in\nthe presence of orbital Feshbach resonance. Using a two-band description of the\nground state and excited state and a mean-field approximation of the intra-band\natomic pairing, we investigate the phase transitions and crossover between\nsuperfluid/normal phases. Defining an effective scattering length by combining\nboth inter-band and intra-band interactions, we derive closed form gap and\nnumber density equations for both ground state and excited state atomic bands.\nWe find that our zero-temperature analytical results and finite-temperature\nnumerical results indicate that the system can show smooth crossover between\nBardeen, Cooper, and Schreifer (BCS) and Bose-Einstein Condensate (BEC)\nsuperfluidity for atoms in each band. In addition, we find that inter-band and\nintra-band interactions can induce quantum phase transitions between BCS/BEC\nsuperfluid states of atoms in one band to that of the other. We anticipate that\nour closed form analytical results can be used as a bench mark for future\nexperimental and theoretical investigations and will have an impact on the\ncurrent understanding of two-band superconductors such as MgB$_2$.",
        "positive": "Thermodynamic model of the macroscopically ordered exciton state: We explain the experimentally observed instability of cold exciton gases and\nformation of a macroscopically ordered exciton state (MOES) in terms of a\nthermodynamic model accounting for the phase fluctuations of the condensate. We\nshow that the temperature dependence of the exciton energy exhibits fundamental\nscaling behavior with the signature of the second order phase transition."
    },
    {
        "anchor": "Dynamics of finite Fermi-Hubbard and Bose-Hubbard systems: This paper analyzes dynamical properties of small Fermi-Hubbard and\nBose-Hubbard systems, focusing on the structure of the underlying Hilbert\nspace. We evaluate time-dependent quantities such as the return probability to\nthe initial state and the spin imbalance of spin-1/2 fermions. The results are\ncompared with recent experimental observations in ultracold gases. For the\nsymmetric two-site Fermi-Hubbard model we find that the spin imbalance and the\nreturn probability are controlled by two and three frequencies, respectively.\nThe spin imbalance and the return probability are identical for the asymmetric\nFalicov-Kimball limit and controlled by only one frequency. In general, the\ntransition probabilities between the initial state and energy eigenstates\ndepend strongly on the particle-particle interaction. This is discussed for\n\"self trapping\" of spinless bosons in a double-well potential. We observe that\nthe available Hilbert space is reduced significantly by strong interaction.",
        "positive": "Optomechanical Generation of a photonic Bose-Einstein Condensate: We propose to thermalize a low-dimensional photon gas and obtain photon\nBose-Einstein condensation by optomechanical interactions in a microscopic\noptical cavity, with a single longitudinal mode and many transverse modes. The\ngeometry of the short cavity is such that it provides a low-frequency cutoff at\na photon energy far above the thermal energy, so that thermal emission of\nphotons is suppressed and the photon number is conserved. While previous\nexperiments on photon Bose-Einstein condensation have used dye molecules for\nphoton gas thermalization, we here investigate thermalization owing to\ninteractions with thermally fluctuating nanomechanical oscillators forming the\ncavity mirrors. In the quantum degenerate regime, the nanomechanical cavity\nconverts broadband optical radiation into tuneable coherent radiation."
    },
    {
        "anchor": "Fast control of topological vortex formation in BEC by counter-diabatic\n  driving: Topological vortex formation has been known as the simplest method for vortex\nformation in BEC of alkali atoms. This scheme requires inversion of the bias\nmagnetic field along the axis of the condensate, which leads to atom loss when\nthe bias field crosses zero. In this Letter, we propose a scheme with which the\natom loss is greatly suppressed by adding counter-diabatic magnetic field. A\nnaive counter-diabatic field violates the Maxwell equations and we need to\nintroduce an approximation to make it physically feasible. The resulting field\nrequires an extra currents, which is experimentally challenging. Finally we\nsolve this problem by applying a gauge transformation so that the\ncounter-diabatic field is generated by controlling the original trap field with\nthe additional control of the bias field.",
        "positive": "Scattering and effective interactions of ultracold atoms with spin-orbit\n  coupling: We derive an analytical expression for the scattering amplitude of two\nultracold atoms of arbitrary spin and with general spin-orbit (SO) coupling, on\nthe basis of our recent work (Phys. Rev. A \\textbf{86}, 053608 (2012)). As an\napplication, we demonstrate that SO coupling can induce scattering resonance in\nthe case with finite scattering length. The same approach can be applied to\ncalculate the two-body bound state of SO-coupled ultracold atoms. For the\nultracold spin-1/2 fermi gases in three- or two- dimensional systems with SO\ncoupling, we also obtain the renormalization relation of effective contact\ninteraction with momentum cutoff, as well as the applicability of Huang-Yang\npseudo-potential."
    },
    {
        "anchor": "Studies of Single Component Fermi Gas near a $P$-wave Resonance with\n  Lowest Order Constrained Variational Method: We study single component Fermi gas near a $p$-wave resonance with the lowest\norder constrained variational (LOCV) method. We obtain the energy per particle\nfor the ground state of single component Fermi gas near a $p$-wave resonance\nwith LOCV method. We also calculate compressibility of the single component\nFermi gas near a $p$-wave resonance and it shows that near the $p$-wave\nresonance, the system would lose its stability and collapse. The two $p$-wave\ncontacts are also obtained and their variation tendencies with interaction\nstrength are consistent with recent experimental results.",
        "positive": "Thermodynamics and magnetic properties of the anisotropic 3D Hubbard\n  model: We study the 3D Hubbard model with anisotropic nearest neighbor tunneling\namplitudes using the dynamical cluster approximation and compare the results\nwith a quantum simulation experiment using ultracold fermions in an optical\nlattice, focussing on magnetic correlations. We find that the short-range spin\ncorrelations are significantly enhanced in the direction with stronger\ntunneling amplitudes. Our results agree with the experimental observations and\nshow that the experimental temperature is lower than the strong tunneling\namplitude. We characterize the system by examining the spin correlations beyond\nneighboring sites and determine the distribution of density, entropy and spin\ncorrelation in the trapped system. We furthermore investigate the dependence of\nthe critical entropy at the N\\'eel transition on anisotropy."
    },
    {
        "anchor": "The decay and collisions of dark solitons in superfluid Fermi gases: We study soliton collisions and the decay of solitons into sound in\nsuperfluid Fermi gases across the Bose-Einstein condensate to\nBardeen-Cooper-Schrieffer (BEC-BCS) crossover by performing numerical\nsimulations of the time-dependent Bogoliubov-de Gennes equations. This decay\nprocess occurs when the solitons are accelerated to the bulk pair-breaking\nspeed by an external potential. A similar decay process may occur when solitons\nare accelerated by an inelastic collision with another soliton. We find that\nsoliton collisions become increasingly inelastic as we move from the BEC to BCS\nregimes, and the excess energy is converted into sound. We interpret this\neffect as being due to evolution of Andreev bound states localized within the\nsoliton.",
        "positive": "Quench dynamics and statistics of measurements for a line of quantum\n  spins in two dimensions: Motivated by recent experiments, we investigate the dynamics of a line of\nspin-down spins embedded in the ferromagnetic spin-up ground state of a\ntwo-dimensional xxz model close to the Ising limit. In a situation where the\ncouplings in x and y direction are different, the quench dynamics of this\nsystem is governed by the interplay of one-dimensional excitations (kinks and\nholes) moving along the line and single-spin excitations evaporating into the\ntwo-dimensional background. A semiclassical approximation can be used to\ncalculate the dynamics of this complex quantum system. Recently, it became\npossible to perform projective quantum measurements on such spin systems,\nallowing to determine, e.g., the z-component of each individual spin. We\npredict the statistical properties of such measurements which contain much more\ninformation than correlation functions."
    },
    {
        "anchor": "Zero-Temperature Equation of State and Phase Diagram of Repulsive\n  Fermionic Mixtures: We compute the zero-temperature equation of state of a mixture of two\nfermionic atomic species with repulsive interspecies interactions using\nsecond-order perturbation theory. We vary the interaction strength, the\npopulation and the mass imbalance, and we analyze the competition between\ndifferent states: homogeneous, partially separated and fully separated. The\ncanonical phase diagrams are determined for various mass ratios, including the\nexperimentally relevant case of the 6Li-40K mixture. We find substantial\ndifferences with respect to the equal-mass case: phase separation occurs at\nweaker interaction strength, and the partially-separated state can be stable\neven in the limit of a large majority of heavy atoms. We highlight the effects\ndue to correlations by making comparison with previous mean-field results.",
        "positive": "Polychromatic polariton laser selector switch: Integration of optical elements into scalable chips has been at the center of\na large effort in recent years. Concurrently, the separation between the\ndiverse functions, namely switches, detectors or emitters increases\nsignificantly the final number of components on chip. Such technical\nlimitations may be overcome by introducing agile devices able, for example, to\nsimultaneously detect, process and emit a coherent signal. Such a pathway has\nbeen explored with different approaches that bear advantages and drawbacks.\nPolaritons have often been proposed as promising candidates for multifunctional\ndevices. Here we present an optical switch based on polariton lasing. An\nincident monochromatic signal is channeled into several polariton laser beams\nat different wavelengths by a novel relaxation mechanism which combines\nbistability, phonon interactions, long polariton lifetime and bosonic\nstimulation. We demonstrate spin logic operations conserving the original\npolarization state that is fully imprinted onto the coherently emitted signals."
    },
    {
        "anchor": "Universal many-body response of heavy impurities coupled to a Fermi sea: In this work we discuss the dynamical response of heavy quantum impurities\nimmersed in a Fermi gas at zero and at finite temperature. Studying both the\nfrequency and the time domain allows one to identify interaction regimes that\nare characterized by distinct many-body dynamics. From this theoretical study a\npicture emerges in which impurity dynamics is universal on essentially all time\nscales, and where the high-frequency few-body response is related to the\nlong-time dynamics of the Anderson orthogonality catastrophe by Tan relations.\nOur theoretical description relies on different and complementary approaches:\nfunctional determinants give an exact numerical solution for time- and\nfrequency-resolved responses, bosonization provides analytical expressions at\nlow temperatures, and the theory of Toeplitz determinants allows one to\nanalytically predict response up to high temperatures. Using these approaches\nwe predict the thermal decoherence rate and prove that within the considered\nmodel the fastest rate of long-time decoherence is given by $\\gamma=\\pi\nk_BT/4$. We show that Feshbach resonances in cold atomic systems give access to\nnew interaction regimes where quantum effects prevail even in the thermal\nregime of many-body dynamics. The key signature of this phenomenon is a\ncrossover between exponential decay rates of the real-time Ramsey signal. It is\nshown that the physics of the orthogonality catastrophe is experimentally\nobservable up to temperatures $T/T_F\\lesssim 0.2$ where it leaves its\nfingerprint in a power-law temperature dependence of thermal spectral weight\nand we review how this phenomenon is related to the physics of heavy ions in\nliquid $^3$He and the formation of Fermi polarons. The presented results are in\nexcellent agreement with recent experiments on LiK mixtures, and we predict\nseveral phenomena that can be tested using currently available experimental\ntechnology.",
        "positive": "Effect of the particle-hole channel on BCS--Bose-Einstein condensation\n  crossover in atomic Fermi gases: BCS--Bose-Einstein condensation (BEC) crossover is effected by increasing\npairing strength between fermions from weak to strong in the particle-particle\nchannel. Here we study the effect of the particle-hole channel on the zero $T$\ngap $\\Delta(0)$, superfluid transition temperature $T_{\\text{c}}$ and the\npseudogap at $T_{\\text{c}}$, as well as the mean-field ratio\n$2\\Delta(0)/T_{\\text{c}}^{\\text{MF}}$, from BCS through BEC regimes, in the\nframework of a pairing fluctuation theory which includes self-consistently the\ncontributions of finite-momentum pairs. These pairs necessarily lead to a\npseudogap in single particle excitation spectrum above and below\n$T_{\\text{c}}$. We sum over the infinite particle-hole ladder diagrams so that\nthe particle-particle and particle-hole $T$-matrices are entangled with each\nother. We find that the particle-hole susceptibility has a complex dynamical\nstructure, with strong momentum and frequency dependencies, and is sensitive to\ntemperature, gap size and interaction strength. We conclude that neglecting the\nself-energy feedback causes a serious over-estimate of the particle-hole\nsusceptibility. In the BCS limit, the particle-hole channel effect may be\napproximated by the same reduction in the overall pairing strength so that the\nratio $2\\Delta(0)/T_{\\text{c}}$ is unaffected, in agreement with Gor'kov\n\\textit{et al.} to the leading order. However, the effect becomes more complex\nand pronounced in the crossover regime, where the particle-hole susceptibility\nis reduced by both a smaller Fermi surface and a big (pseudo)gap. Deep in the\nBEC regime, the particle-hole channel contributions drop to zero. We propose\nthat precision measurements of the magnetic field for Feshbach resonance at low\ntemperatures as a function of density can be used to quantify the particle-hole\nsusceptibility and test different theories."
    },
    {
        "anchor": "Wavepacket dynamics on Chern band lattices in a trap: The experimental realization of lattices with Chern bands in ultracold-atom\nand photonic systems has motivated the study of time-dependent phenomena, such\nas spatial propagation, in lattices with nontrivial topology. We study the\ndynamics of gaussian wavepackets on the Haldane honeycomb Chern-band lattice\nmodel, in the presence of a harmonic trap. We focus on the transverse response\nto a force, which is due partly to the Berry curvature and partly to the\ntransverse component of the energy band curvature. We evaluate the accuracy of\na semiclassical description, which treats the wavepacket as a point particle in\nboth real and momentum space, in reproducing the motion of a realistic\nwavepacket with finite extent. We find that, in order to accurately capture the\nwavepacket dynamics, the extent of the wavepacket in momentum space needs to be\ntaken into account. The dynamics is sensitive to the interplay of band\ndispersion and Berry curvature over the finite region of momentum (reciprocal)\nspace where the wavepacket has support. Moreover, if the wavepacket is prepared\nwith a finite initial momentum, the semiclassical analysis reproduces its\nmotion as long as it has a large overlap with the eigenstates of a single band.\nThe semiclassical description generally improves with increasing real-space\nsize of the wavepacket, as long as the external conditions (e.g., external\nforce) remain uniform throughout the spatial extent of the wavepacket.",
        "positive": "Renormalization theory for the Fulde-Ferrell-Larkin-Ovchinnikov states\n  at $T>0$: Within the renormalization group framework we study the stability of\nsuperfluid density wave states, known as Fulde-Ferrell-Larkin-Ovchinnikov\n(FFLO) phases, with respect to thermal order-parameter fluctuations in two and\nthree-dimensional ($d\\in \\{2,3\\}$) systems. We analyze the\nrenormalization-group flow of the relevant ordering wave-vector $\\vec{Q_0}$.\nThe calculation indicates an instability of the FFLO-type states towards either\na uniform superfluid or the normal state in $d\\in\\{2,3\\}$ and $T>0$. In $d=2$\nthis is signaled by $\\vec{Q_0}$ being renormalized towards zero, corresponding\nto the flow being attracted either to the usual Kosterlitz-Thouless fixed-point\nor to the normal phase. We supplement a solution of the RG flow equations by a\nsimple scaling argument, supporting the generality of the result. The tendency\nto reduce the magnitude of $\\vec{Q_0}$ by thermal fluctuations persists in\n$d=3$, where the very presence of long-range order is immune to thermal\nfluctuations, but the effect of attracting $\\vec{Q_0}$ towards zero by the flow\nremains observed at $T>0$."
    },
    {
        "anchor": "Comparing numerical and analytical approaches to strongly interacting\n  two-component mixtures in one dimensional traps: We investigate one-dimensional harmonically trapped two-component systems for\nrepulsive interaction strengths ranging from the non-interacting to the\nstrongly interacting regime for Fermi-Fermi mixtures. A new and powerful\nmapping between the interaction strength parameters from a continuous\nHamiltonian and a discrete lattice Hamiltonian is derived. As an example, we\nshow that this mapping does not depend neither on the state of the system nor\non the number of particles. Energies, density profiles and correlation\nfunctions are obtained both numerically (DMRG and Exact diagonalization) and\nanalytically. Since DMRG results do not converge as the interaction strength is\nincreased, analytical solutions are used as a benchmark to identify the point\nwhere these calculations become unstable. We use the proposed mapping to set a\nquantitative limit on the interaction parameter of a discrete lattice\nHamiltonian above which DMRG gives unrealistic results.",
        "positive": "Phase Diagrams for Spin-1 Bosons in an Optical Lattice: In this paper, the phase diagrams of a polar spin-1 Bose gas in a\nthree-dimensional optical lattice with linear and quadratic Zeeman effects both\nat zero and finite temperatures are obtained within mean-field theory. The\nphase diagrams can be regrouped to two different parameter regimes depending on\nthe magnitude of the quadratic Zeeman effect $Q$. For large $Q$, only a\nfirst-order phase transition from the nematic (NM) phase to the fully magnetic\n(FM) phase is found, while in the case of small $Q$, a first-order phase\ntransition from the nematic phase to the partially magnetic (PM) phase, plus a\nsecond-order phase transition from the PM phase to the FM phase is obtained. If\na net magnetization in the system exists, the first-order phase transition\ncauses a coexistence of two phases and phase separation: for large $Q$, NM and\nFM phases and for small $Q$, NM and PM phases. The phase diagrams in terms of\nnet magnetization are also obtained."
    },
    {
        "anchor": "Quantized vortices in superfluid helium and atomic Bose-Einstein\n  condensates: This article reviews recent developments in the physics of quantized vortices\nin superfluid helium and atomic Bose-Einstein condensates. Quantized vortices\nappear in low-temperature quantum condensed systems as the direct product of\nBose-Einstein condensation. Quantized vortices were first discovered in\nsuperfluid 4He in the 1950s, and have since been studied with a primary focus\non the quantum hydrodynamics of this system. Since the discovery of superfluid\n3He in 1972, quantized vortices characteristic of the anisotropic superfluid\nhave been studied theoretically and observed experimentally using rotating\ncryostats. The realization of atomic Bose-Einstein condensation in 1995 has\nopened new possibilities, because it became possible to control and directly\nvisualize condensates and quantized vortices. Historically, many ideas\ndeveloped in superfluid 4He and 3He have been imported to the field of cold\natoms and utilized effectively. Here, we review and summarize our current\nunderstanding of quantized vortices, bridging superfluid helium and atomic\nBose-Einstein condensates. This review article begins with a basic\nintroduction, which is followed by discussion of modern topics such as quantum\nturbulence and vortices in unusual cold atom condensates.",
        "positive": "The Fermi Gases and Superfluids: Short Review of Experiment and Theory\n  for Condensed Matter Physicists: The study of ultracold atomic Fermi gases is a rapidly exploding subject\nwhich is defining new directions in condensed matter and atomic physics. Quite\ngenerally what makes these gases so important is their remarkable tunability\nand controllability. Using a Feshbach resonance one can tune the attractive\ntwo-body interactions from weak to strong and thereby make a smooth crossover\nfrom a BCS superfluid of Cooper pairs to a Bose-Einstein condensed superfluid.\nFurthermore, one can tune the population of the two spin states, allowing\nobservation of exotic spin-polarized superfluids, such as the Fulde Ferrell\nLarkin Ovchinnikov (FFLO) phase. A wide array of powerful characterization\ntools, which often have direct condensed matter analogues, are available to the\nexperimenter. In this Chapter, we present a general review of the status of\nthese Fermi gases with the aim of communicating the excitement and great\npotential of the field."
    },
    {
        "anchor": "Numerical Study of Evaporative Cooling in the Space Station: In this paper, we numerically studied the effects of mechanical vibration and\nmagnetic fields on evaporative cooling process carried in space station by\ndirect simulation Monte Carlo method. Simulated with the vibration data of\ninternational space station, we found that the cooling process would suffer\ngreat atomic losses until the accelerations reduced tenfold at least. In\naddition, if we enlarge the s-wave scattering length five times by Feshbach\nresonance, the PSD increased to 50 compared to 3 of no magnetic fields\nsituation after 5 seconds evaporative cooling. We also simulated the two stages\ncrossed beam evaporative cooling process (TSCBC) under both physical impacts\nand obtain $4\\times10^5$ $^{85}$Rb atoms with a temperature of 8 pK. These\nresults are of significance to the cold atom experiments carried out on space\nstation in the future.",
        "positive": "Spectroscopic measurement of the excitation spectrum on effectively\n  curved spacetimes in a polaritonic fluid of light: Quantum fields in regions of extreme spacetime curvature give rise to a\nwealth of effects, like Hawking radiation at the horizon of black holes. While\nquantum field theory can only be studied theoretically in black holes, it can\nbe tested in controlled laboratory experiments. Typically, a fluid accelerating\nfrom sub- to supersonic speed will create an effectively curved spacetime for\nthe acoustic field, with an apparent horizon where the speed of the fluid\nequals the speed of sound. Here we create effective curved spacetimes with a\nquantum fluid of light, with smooth and steep acoustic horizons and various\nsupersonic fluid speeds. We use a recently developed spectroscopy method to\nmeasure the spectrum of acoustic excitations on these spacetimes, thus\nobserving negative energy modes in the supersonic regions. This demonstrates\nthe potential of quantum fluids of light for the study of field theories on\ncurved spacetimes."
    },
    {
        "anchor": "Correlated metallic two-particle bound states in Wannier--Stark\n  flatbands: Tight-binding single-particle models on simple Bravais lattices in space\ndimension $d \\geq 2$, when exposed to commensurate DC fields, result in the\ncomplete absence of transport due to the formation of Wannier--Stark flatbands\n[Phys. Rev. Res. $\\textbf{3}$, 013174 (2021)]. The single-particle states\nlocalize in a factorial manner, i.e., faster than exponential. Here, we\nintroduce interaction among two such particles that partially lifts the\nlocalization and results in metallic two-particle bound states that propagate\nin the directions perpendicular to the DC field. We demonstrate this effect\nusing a square lattice with Hubbard interaction. We apply perturbation theory\nin the regime of interaction strength $(U)$ $\\ll$ hopping strength $(t)$ $\\ll$\nfield strength $(\\mathcal{F})$, and obtain estimates for the group velocity of\nthe bound states in the direction perpendicular to the field. The two-particle\ngroup velocity scales as $U {(t/\\mathcal{F})}^\\nu$. We calculate the dependence\nof the exponent $\\nu$ on the DC field direction and on the dominant\ntwo-particle configurations related to the choices of unperturbed flatbands.\nNumerical simulations confirm our predictions from the perturbative analysis.",
        "positive": "Itinerant Ferromagnetism in a Fermi Gas of Ultracold Atoms: Can a gas of spin-up and spin-down fermions become ferromagnetic due to\nrepulsive interactions? This question which has not yet found a definitive\ntheoretical answer was addressed in an experiment with an ultracold\ntwo-component Fermi gas. The observation of non-monotonic behavior of lifetime,\nkinetic energy, and size for increasing repulsive interactions provides strong\nevidence for a phase transition to a ferromagnetic state. It implies that\nitinerant ferromagnetism of delocalized fermions is possible without lattice\nand band structure and validates the most basic model for ferromagnetism\nintroduced by Stoner."
    },
    {
        "anchor": "Stability of solitons in time-modulated two-dimensional lattices: We develop stability analysis for matter-wave solitons in a two-dimensional\n(2D) Bose-Einstein condensate loaded in an optical lattice (OL), to which\nperiodic time modulation is applied, in different forms. The stability is\nstudied by dint of the variational approximation and systematic simulations.\nFor solitons in the semi-infinite gap, well-defined stability patterns are\nproduced under the action of the attractive nonlinearity, clearly exhibiting\nthe presence of resonance frequencies. The analysis is reported for several\ntime-modulation formats, including the case of in-phase modulations of both\nquasi-1D sublattices, which build the 2D square-shaped OL, and setups with\nasynchronous modulation of the sublattices. In particular, when the modulations\nof two sublattices are phase-shifted by {\\delta}={\\pi}/2, the stability map is\nnot improved, as the originally well-structured stability pattern becomes fuzzy\nand the stability at high modulation frequencies is considerably reduced. Mixed\nresults are obtained for anti-phase modulations of the sublattices\n({\\delta}={\\pi}), where extended stability regions are found for low modulation\nfrequencies, but for high frequencies the stability is weakened. The analysis\nis also performed in the case of the repulsive nonlinearity, for solitons in\nthe first finite bandgap. It is concluded that, even though stability regions\nmay be found, distinct stability boundaries for the gap solitons cannot be\nidentified clearly. Finally, the stability is also explored for vortex solitons\nof both the \"square-shaped\" and \"rhombic\" types (i.e., off- and\non-site-centered ones).",
        "positive": "Topologically induced avoided band crossing in an optical chequerboard\n  lattice: We report on the condensation of bosons in the 4th band of an optical\nchequerboard lattice providing a topologically induced avoided band crossing\ninvolving the 2nd, 3rd, and 4th Bloch bands. When the condensate is slowly\ntuned through the avoided crossing, accelerated band relaxation arises and the\nzero momentum approximately $C4$-invariant condensate wave function acquires\nfinite momentum order and reduced $C2$ symmetry. For faster tuning Landau-Zener\noscillations between different superfluid orders arise, which are used to\ncharacterize the avoided crossing."
    },
    {
        "anchor": "Dynamics of an impurity in a one-dimensional lattice: We study the non-equilibrium dynamics of an impurity in an harmonic trap that\nis kicked with a well-defined quasi-momentum, and interacts with a bath of free\nfermions or interacting bosons in a 1D lattice configuration. Using numerical\nand analytical techniques we investigate the full dynamics beyond linear\nresponse, which allows us to quantitatively characterise states of the impurity\nin the bath for different parameter regimes. These vary from a tightly bound\nmolecular state in a strongly interacting limit to a polaron (dressed impurity)\nand a free particle for weak interactions, with composite behaviour in the\nintermediate regime. These dynamics and different parameter regimes should be\nreadily realizable in systems of cold atoms in optical lattices.",
        "positive": "Dynamics of two quantized vortices belonging to different components of\n  binary Bose-Einstein condensates in a circular box potential: This study aims to research on dynamics of two quantized vortices in miscible\ntwo-component Bose--Einstein condensates, trapped by a circular box potential\nby using the Gross--Pitaevskii equation. We consider a situation in which two\nvortices belong to different components and they are initially close. Their\ndynamics are significantly different from those of a vortex pair in a\nsingle-component condensate. When two vortices are initially co-located, they\nare split by dynamical instability or remain co-located depending on their\nintercomponent interaction. If the two split vortices have the same sign of\ncirculation, they rotate around each other. Then, the angular velocity can be\ngiven as a function of the distance between two vortices, which is understood\nthrough the equations of motion and their interaction. If the circulations of\ntwo close vortices have different signs, however, they move in the same\ndirection initially, then overlap during the dynamics. This subsequent overlap\ncan be categorized into two types based on the initial distance between them.\nThe mechanism of this overlapping can be understood from the interaction\nbetween the vortex and its image vortex, which makes the two vortices close to\neach other even if the intrinsic interaction between them is repulsive."
    },
    {
        "anchor": "Ab initio lattice results for Fermi polarons in two dimensions: We investigate the attractive Fermi polaron problem in two dimensions using\nnon-perturbative Monte Carlo simulations. We introduce a new Monte Carlo\nalgorithm called the impurity lattice Monte Carlo method. This algorithm\nsamples the path integral in a computationally efficient manner and has only\nsmall sign oscillations for systems with a single impurity. As a benchmark of\nthe method, we calculate the universal polaron energy in three dimensions in\nthe scale-invariant unitarity limit and find agreement with published results.\nWe then present the first fully non-perturbative calculations of the polaron\nenergy in two dimensions and density correlations between the impurity and\nmajority particles in the limit of zero range interactions. We find evidence\nfor a smooth crossover transition from fermionic quasiparticle to molecular\nstate as a function of interaction strength.",
        "positive": "Conserving symmetries in Bose-Einstein condensate dynamics requires\n  many-body theory: We explain from first principles why satisfying conservation laws in Bose\nEinstein condensate dynamics requires many-body theory. For the\nGross-Pitaevskii mean-field we show analytically and numerically that\nconservation laws are violated. We provide examples for angular momentum and\nlinear momentum conservation. Arbitrarily large violations occur despite\nnegligible depletion and interaction energy. For the case of angular momentum\nwe show through extensive many-body simulations how the conservation law can be\ngradually restored on the many-body level. Implications are discussed."
    },
    {
        "anchor": "Universal $p$-wave tetramers in low-dimensional fermionic systems with\n  three-body interaction: Inspired by the narrow Feshbach resonance in systems with the two-body\ninteraction, we propose the two-channel model of three-component fermions with\nthe three-body interaction that takes into account the finite-range effects in\nlow dimensions. Within this model, the $p$-wave Efimov-like effect in the\nfour-body sector is predicted in fractional dimensions above 1D. The impact of\nthe finite-range interaction on the formation of the four-body bound states in\n$d=1$ is also discussed in detail.",
        "positive": "Effective theory of two-dimensional chiral superfluids: gauge duality\n  and Newton-Cartan formulation: We present a theory of Galilean-invariant conventional and chiral $p_x \\pm\nip_y$ fermionic superfluids at zero temperature in two spatial dimensions in\nterms of a dual gauge theory. Our formulation is general coordinate invariant.\nThe parity-violating effects are encoded in the Wen-Zee term that gives rise to\nthe Hall viscosity and edge current. We show that the relativistic superfluid\nwith the Euler current reduces to the chiral superfluid in the limit\n$c\\to\\infty$. Using Newton-Cartan geometry we construct the covariant\nformulation of the effective theory and calculate the energy current."
    },
    {
        "anchor": "Three dimensional ring vortex solitons and their stability in\n  Bose-Einstein condensates under magnetic confinement: The three-dimensional study of the ring vortex solitons is conducted for both\nattractive and repulsive BECs subject to harmonic potential confinement. A\nfamily of stationary ring vortex solitons, which is defined by the radial\nexcitation number and the winding number of the intrinsic vorticity, are\nobtained numerically for a given atomic interaction strength. We find that\nstabilities of the ground and radially excited states of the ring vortex\nsoliton are dependent on the winding number differently. The ground state of\nthe ring vortex soliton with the large winding number is unstable dynamically\nagainst random perturbation. The radially excited state of the ring vortex\nsoliton with large winding number corresponds to the increased collapse\nthreshold, and therefore can be made stable for sufficiently small atomic\ninteraction strengths. The ground and radially excited states also demonstrate\ndifferent dynamical evolutions under large atomic interaction strengths. The\nformer exhibits simultaneously symmetrical splitting in the transverse plane,\nwhile the latter displays periodically expand-merge cycles in the longitudinal\ndirection.",
        "positive": "Anomalous Lifetimes of Ultracold Complexes Decaying into a Single\n  Channel: What's Taking So Long in There?: We investigate the lifetimes of complexes formed in ultracold molecule\ncollisions. Employing both transition-state-theory and an optical model\napproach we examine processes that can extend the lifetime of complexes beyond\nthat predicted by Rice-Ramsperger-Kassel-Marcus theory. We focus on complexes\nthat possess only one open channel, and find that the extreme distribution of\nwidths for this case favors low decay rates. Thus decay from a complex into a\nsingle energetically available channel can be anomalously slow, and moreover\nnonexponential in time. We apply the theory to two systems of current\nexperimental interest, RbCs and NaRb, finding qualitatively that the empirical\ntime scales can be accounted for in the theory."
    },
    {
        "anchor": "Isobar of an ideal Bose gas within the grand canonical ensemble: We investigate the isobar of an ideal Bose gas confined in a cubic box within\nthe grand canonical ensemble, for a large yet finite number of particles, N.\nAfter solving the equation of the spinodal curve, we derive precise formulae\nfor the supercooling and the superheating temperatures which reveal an N^{-1/3}\nor N^{-1/4} power correction to the known Bose-Einstein condensation\ntemperature in the thermodynamic limit. Numerical computations confirm the\naccuracy of our analytical approximation, and further show that the isobar\nzigzags on the temperature-volume plane if N is greater than or equal to 14393.\nIn particular, for the Avogadro's number of particles, the volume expands\ndiscretely about 10^5 times. Our results quantitatively agree with a previous\nstudy on the canonical ensemble within 0.1% error.",
        "positive": "Dynamics of Stripe Patterns in Supersolid Spin-Orbit-Coupled Bose Gases: Despite ground-breaking observations of supersolidity in spin-orbit-coupled\nBose-Einstein condensates, until now the dynamics of the emerging spatially\nperiodic density modulations has been vastly unexplored. Here, we demonstrate\nthe nonrigidity of the density stripes in such a supersolid condensate and\nexplore their dynamic behavior subject to spin perturbations. We show both\nanalytically in infinite systems and numerically in the presence of a harmonic\ntrap how spin waves affect the supersolid's density profile in the form of\ncrystal waves, inducing oscillations of the periodicity as well as the\norientation of the fringes. Both these features are well within reach of\npresent-day experiments. Our results show that this system is a paradigmatic\nsupersolid, featuring superfluidity in conjunction with a fully dynamic\ncrystalline structure."
    },
    {
        "anchor": "Relaxation of Bosons in One Dimension and the Onset of Dimensional\n  Crossover: We study ultra-cold bosons out of equilibrium in a one-dimensional (1D)\nsetting and probe the breaking of integrability and the resulting relaxation at\nthe onset of the crossover from one to three dimensions. In a quantum Newton's\ncradle type experiment, we excite the atoms to oscillate and collide in an\narray of 1D tubes and observe the evolution for up to 4.8 seconds (400\noscillations) with minimal heating and loss. By investigating the dynamics of\nthe longitudinal momentum distribution function and the transverse excitation,\nwe observe and quantify a two-stage relaxation process. In the initial stage\nsingle-body dephasing reduces the 1D densities, thus rapidly drives the 1D gas\nout of the quantum degenerate regime. The momentum distribution function\nasymptotically approaches the distribution of quasimomenta (rapidities), which\nare conserved in an integrable system. In the subsequent long time evolution,\nthe 1D gas slowly relaxes towards thermal equilibrium through the collisions\nwith transversely excited atoms. Moreover, we tune the dynamics in the\ndimensional crossover by initializing the evolution with different imprinted\nlongitudinal momenta (energies). The dynamical evolution towards the relaxed\nstate is quantitatively described by a semiclassical molecular dynamics\nsimulation.",
        "positive": "Fractonic Quantum Quench in Dipole-constrained Bosons: We investigate the quench dynamics in the dipolar Bose-Hubbard model (DBHM)\nin one dimension. The boson hopping is constrained by dipole conservation and\nshow fractonic dynamics. The ground states at large Hubbard interaction $U$ are\nMott insulators at integer filling and a period-2 charge density wave (CDW) at\nhalf-integer filling. We focus on Mott-to-Mott and CDW-to-CDW quenches and find\nthat dipole correlation spreading shows the light-cone behavior with the\nLieb-Robinson (LR) velocity proportional to the dipole kinetic energy $J$ and\nthe square of the density in the case of Mott quench at integer filling.\nEffective model for post-quench dynamics is constructed under the dilute-dipole\napproximation and fits the numerical results well. For CDW quench we observe a\nmuch reduced LR velocity of order $J^2/U$ and additional periodic features in\nthe time direction. The emergence of CDW ground state and the reduced LR\nvelocity at half-integer filling can both be understood by careful application\nof the second-order perturbation theory. The oscillatory behavior arises from\nquantum scars in the quadrupole sector of the spectrum and is captured by a\nPXP-like model that we derive by projecting the DBHM to the quadrupolar sector\nof the Hilbert space."
    },
    {
        "anchor": "Searching for Supersolidity in Ultracold Atomic Bose Condensates with\n  Rashba Spin-Orbit Coupling: We developed functional integral formulation for the stripe phase of a spinor\nBose-Einstein condensates with Rashba spin-orbit coupling. The excitation\nspectrum is found to exhibit double gapless band structures, identified to be\ntwo Goldstone modes resulting from spontaneously broken internal gauge symmetry\nand translational invariance symmetry. The sound velocities display anisotropic\nbehaviors with the lower branch vanishes in the direction perpendicular to the\nstripe in the x-y plane. At the transition point between the plane wave phase\nand the stripe phase, physical quantities such as fluctuation correction to the\nground state energy and quantum depletion of the condensates exhibit\ndiscontinuity, characteristic of the first order phase transition. Despite\nstrong quantum fluctuations induced by Rashba spin-orbit coupling, we show that\nthe supersolid phase is stable against quantum depletion. Finally we extend our\nformulation to finite temperatures to account for interactions between\nexcitations.",
        "positive": "Ehrenfest breakdown of the mean-field dynamics of Bose gases: The mean-field dynamics of a Bose gas is shown to break down at time $\\tau_h\n= (c_1/\\gamma) \\ln N$ where $\\gamma$ is the Lyapunov exponent of the mean-field\ntheory, $N$ is the number of bosons, and $c_1$ is a system-dependent constant.\nThe breakdown time $\\tau_h$ is essentially the Ehrenfest time that\ncharacterizes the breakdown of the correspondence between classical and quantum\ndynamics. This breakdown can be well described by the quantum fidelity defined\nfor reduced density matrices. Our results are obtained with the formalism in\nparticle-number phase space and are illustrated with a triple-well model. The\nlogarithmic quantum-classical correspondence time may be verified\nexperimentally with Bose-Einstein condensates."
    },
    {
        "anchor": "Interplay between Rashba spin-orbit coupling and adiabatic rotation in a\n  two-dimensional Fermi gas: We explore the trap profiles of a two-dimensional atomic Fermi gas in the\npresence of a Rashba spin-orbit coupling and under an adiabatic rotation. We\nfirst consider a non-interacting gas and show that the competition between the\neffects of Rashba coupling on the local density of single-particle states and\nthe Coriolis effects caused by rotation gives rise to a characteristic\nring-shaped density profile that survives at experimentally-accessible\ntemperatures. Furthermore, Rashba splitting of the Landau levels takes the\ndensity profiles on a ziggurat shape in the rapid-rotation limit. We then\nconsider an interacting gas under the BCS mean-field approximation for local\npairing, and study the pair-breaking mechanism that is induced by the Coriolis\neffects on superfluidity, where we calculate the critical rotation frequencies\nboth for the onset of pair breaking and for the complete destruction of\nsuperfluidity in the system. In particular, by comparing the results of\nfully-quantum-mechanical Bogoliubov-de Gennes approach with those of\nsemi-classical local-density approximation, we construct extensive phase\ndiagrams for a wide-range of parameter regimes in the trap where the\naforementioned competition may, e.g., favor an outer normal edge that is\ncompletely phase separated from the central superfluid core by vacuum.",
        "positive": "Singlet and triplet BCS pairs in a gas of two-species fermionic polar\n  molecules: We investigate the BCS pairing in a mixture of fermionic polar molecules with\ntwo different hyperfine states. We derive a set of coupled gap equations and\nfind that this system supports both spin-singlet and -triplet BCS pairs. We\nalso calculate the critical temperatures and the angular dependence of order\nparameters. In addition, by tuning short-range interaction between\ninter-species molecules, the transition between singlet and triplet paired\nstates may be realized."
    },
    {
        "anchor": "Quantum domain walls induce incommensurate supersolid phase on the\n  anisotropic triangular lattice: We investigate the extended hard-core Bose-Hubbard model on the triangular\nlattice as a function of spatial anisotropy with respect to both tunneling and\nnearest-neighbor interaction strength. At half-filling the system can be tuned\nfrom decoupled one-dimensional chains to a two-dimensional solid phase with\nalternating density order by adjusting the anisotropic coupling. At\nintermediate anisotropy, however, frustration effects dominate and an\nincommensurate supersolid phase emerges, which is characterized by\nincommensurate density order as well as an anisotropic superfluid density. We\ndemonstrate that this intermediate phase results from the proliferation of\ntopological defects in the form of quantum bosonic domain walls. Accordingly,\nthe structure factor has peaks at wave vectors, which are linearly related to\nthe number of domain walls in a finite system in agreement with extensive\nquantum Monte Carlo simulations. We discuss possible connections with the\nsupersolid behavior in the high-temperature superconducting striped phase.",
        "positive": "Anomalous Resistivity at Weak Coupling: Recent cold atom experiments have observed bad and strange metal behaviors in\nstrongly-interacting Fermi-Hubbard systems. Motivated by these results, we\ncalculate the thermoelectric transport properties of a 2D Fermi-Hubbard system\nin the weak coupling limit using quantum kinetic theory. We find that many\nfeatures attributed to strong correlations are also found at weak coupling. In\nparticular, for temperatures $T\\gtrsim t$ the electrical resistivity is nearly\nlinear in temperature despite the fact that the quasiparticle scattering rate\nis non-linear and changes by nearly an order of magnitude. We argue that this\nasymptotic behavior is a general feature of systems with a finite spectral\nwidth, which implies that there is no MIR bound on the resistivity in\nsingle-band models. Due to nesting, the $T$-linear resistivity persists down to\n$T=0$ at half filling. Our work sheds light on the transport regime in\nultracold atom experiments, which can differ substantially from that of\ncondensed matter systems. Disentangling these band-structure effects from the\nphysics of strong correlations is a major challenge for future experiments."
    },
    {
        "anchor": "Who is the Lord of the Rings: Majorana, Dirac or Lifshitz? The\n  Spin-Orbit-Zeeman Saga in Ultra-cold Fermions: We discuss the emergence of rings of zero-energy excitations in momentum\nspace for superfluid phases of ultra-cold fermions when spin-orbit, Zeeman\nfields and interactions are varied. We show that phases containing rings of\nnodes possess non-trivial topological invariants, and that phase transitions\nbetween distinct topological phases belong to the Lifshitz class. Upon crossing\nphase boundaries, existing massless Dirac fermions in the gapless phase\nanihilate to produce bulk zero-mode Majorana fermions at phase boundaries and\nthen become massive Dirac fermions in the gapped phase. We characterize these\ntunable topological phase transitions via several spectroscopic properties,\nincluding excitation spectrum, spectral function and momentum distribution.\nSince the emergence or disappearance of rings leads to topological transitions\nin momentum space, we conclude that Lifshitz is the lord of the rings.",
        "positive": "Signatures of the superfluid to Mott insulator transition in equilibrium\n  and in dynamical ramps: We investigate the equilibrium and dynamical properties of the Bose-Hubbard\nmodel and the related particle-hole symmetric spin-1 model in the vicinity of\nthe superfluid to Mott insulator quantum phase transition. We employ the\nfollowing methods: exact-diagonalization, mean field (Gutzwiller), cluster\nmean-field, and mean-field plus Gaussian fluctuations. In the first part of the\npaper we benchmark the four methods by analyzing the equilibrium problem and\ngive numerical estimates for observables such as the density of double\noccupancies and their correlation function. In the second part, we study\nparametric ramps from the superfluid to the Mott insulator and map out the\ncrossover from the regime of fast ramps, which is dominated by local physics,\nto the regime of slow ramps with a characteristic universal power law scaling,\nwhich is dominated by long wavelength excitations. We calculate values of\nseveral relevant physical observables, characteristic time scales, and an\noptimal protocol needed for observing universal scaling."
    },
    {
        "anchor": "Supersensitive quantum sensor based on criticality in an\n  antiferromagnetic spinor condensate: We consider an antiferromagnetic Bose-Einstein condensate in a traverse\nmagnetic field with a fixed macroscopic magnetization. The system exhibits two\ndifferent critical behaviors corresponding to transitions from polar to\nbroken-axisymmetry and from antiferromagnetic to broken-axisymmetry phases\ndepending on the value of magnetization. We exploit both types of system\ncriticality as a resource in the precise estimation of control parameter value.\nWe quantify the achievable precision by the quantum Fisher information. We\ndemonstrate supersensitivity and show that the precision scales with the number\nof atoms up to $N^4$ around critically. In addition, we study the precision\nbased on the error-propagation formula providing the simple-to-measure signal\nwhich coincides its scaling with the quantum Fisher information. Finally, we\ntake into account the effect of non-zero temperature and show that the sub-shot\nnoise sensitivity in the estimation of the control parameter is achievable in\nthe low-temperature limit.",
        "positive": "Controlled creation of a singular spinor vortex by circumventing the\n  Dirac belt trick: Persistent topological defects and textures are particularly dramatic\nconsequences of superfluidity. Among the most fascinating examples are the\nsingular vortices arising from the rotational symmetry group SO(3), with\nsurprising topological properties illustrated by Dirac's famous belt trick.\nDespite considerable interest, controlled preparation and detailed study of\nvortex lines with complex internal structure in fully three-dimensional spinor\nsystems remains an outstanding experimental challenge. Here, we propose and\nimplement a reproducible and controllable method for creating and detecting a\nsingular SO(3) line vortex from the decay of a non-singular spin texture in a\nferromagnetic spin-1 Bose--Einstein condensate. Our experiment explicitly\ndemonstrates the SO(3) character and the unique spinor properties of the\ndefect. Although the vortex is singular, its core fills with atoms in the\ntopologically distinct polar magnetic phase. The resulting stable, coherent\ntopological interface has analogues in systems ranging from condensed matter to\ncosmology and string theory."
    },
    {
        "anchor": "Shape dependence and anisotropic finite-size scaling of the phase\n  coherence of three-dimensional Bose-Einstein condensed gases: We investigate the equilibrium phase-coherence properties of Bose-condensed\nparticle systems, focusing on their shape dependence and finite-size scaling\n(FSS). We consider three-dimensional (3D) homogeneous systems confined to\nanisotropic L x L x L_a boxes, below the BEC transition temperature $T_c$. We\nshow that the phase correlations develop peculiar anisotropic FSS for any\n$T<T_c$, in the large-$L$ limit keeping the ratio \\lambda = L_a/L^2 fixed. This\nphenomenon is effectively described by the 3D spin-wave (SW) theory. Its\nuniversality is confirmed by quantum Monte Carlo simulations of the 3D\nBose-Hubbard model in the BEC phase. The phase-coherence properties of very\nelongated BEC systems, \\lambda>>1, are characterized by a coherence length\n\\xi_a \\sim A_t \\rho_s/T where A_t is the transverse area and \\rho_s is the\nsuperfluid density.",
        "positive": "Superfluid weight and polarization amplitude in the one-dimensional\n  bosonic Hubbard model: We calculate the superfluid weight and the polarization amplitude for the\none-dimensional bosonic Hubbard model focusing on the strong-coupling regime.\nOther than analytic calculations we apply two methods: variational Monte Carlo\nbased on the Baeriswyl wave function and exact diagonalization. The former\ngives zero superfluid response at integer filling, while the latter gives a\nsuperfluid response at finite hopping. From the polarization amplitude we\nderive the variance and the associated size scaling exponent. Again, the\nvariational study does not produce a finite superfluid weight at integer\nfilling (size scaling exponent is near one), but the Fourier transform of the\npolarization amplitude behaves in a similar way to the result of exact\ndiagonalization, with a peak at small hopping, and suddenly decreasing at the\ninsulator-superfluid transition. On the other hand, exact diagonalization\nstudies result in a finite spread of the total position which increases with\nthe size of the system. In the superfluid phase the size scaling exponent is\ntwo as expected. Importantly, our work addresses the ambiguities that arise in\nthe calculation of the superfluid weight in variational calculations, and we\ncomment on the prediction of Anderson about the superfluid response of the\nmodel at integer filling."
    },
    {
        "anchor": "Observation of scaling in the dynamics of a strongly quenched quantum\n  gas: We report on the experimental observation of scaling in the time evolution\nfollowing a sudden quench into the vicinity of a quantum critical point. The\nexperimental system, a two-component Bose gas with coherent exchange between\nthe constituents, allows for the necessary high level of control of parameters\nas well as the access to time-resolved spatial correlation functions. The\ntheoretical analysis reveals that when quenching the system close to the\ncritical point, the energy introduced by the quench leads to a short-time\nevolution exhibiting crossover reminiscent of the finite-temperature critical\nproperties in the system's universality class. Observing the time evolution\nafter a quench represents a paradigm shift in accessing and probing\nexperimentally universal properties close to a quantum critical point and\nallows in a new way benchmarking of quantum many-body theory with experiments.",
        "positive": "Frustrated extended Bose-Hubbard model and deconfined quantum critical\n  points with optical lattices at the anti-magic wavelength: The study of geometrically frustrated many-body quantum systems is of central\nimportance to uncover novel quantum mechanical effects. We design a scheme\nwhere ultracold bosons trapped in a one-dimensional state-dependent optical\nlattice are modeled by a frustrated Bose-Hubbard Hamiltonian. A derivation of\nthe Hamiltonian parameters based on Cesium atoms, further show large tunability\nof contact and nearest-neighbour interactions. For pure contact repulsion, we\ndiscover the presence of two phases peculiar to frustrated quantum magnets: the\nbond-order-wave insulator with broken inversion symmetry and a chiral\nsuperfluid. When the nearest-neighbour repulsion becomes sizeable, a further\ndensity-wave insulator with broken translational symmetry can appear. We show\nthat the phase transition between the two spontaneously-symmetry-broken phases\nis continuous, thus representing a one-dimensional deconfined quantum critical\npoint not captured by the Landau-Ginzburg-Wilson symmetry-breaking paradigm.\nOur results provide a solid ground to unveil the novel quantum physics induced\nby the interplay of non-local interactions, geometrical frustration, and\nquantum fluctuations."
    },
    {
        "anchor": "Mathematical models and numerical methods for spinor Bose-Einstein\n  condensates: In this paper, we systematically review mathematical models, theories and\nnumerical methods for ground states and dynamics of spinor Bose-Einstein\ncondensates (BECs) based on the coupled Gross-Pitaevskii equations (GPEs). We\nstart with a pseudo spin-1/2 BEC system with/without an internal atomic\nJosephson junction and spin-orbit coupling including (i) existence and\nuniqueness as well as non-existence of ground states under different parameter\nregimes, (ii) ground state structures under different limiting parameter\nregimes, (iii) dynamical properties, and (iv) efficient and accurate numerical\nmethods for computing ground states and dynamics. Then we extend these results\nto spin-1 BEC and spin-2 BEC. Finally, extensions to dipolar spinor systems\nand/or general spin-F (F>=3) BEC are discussed.",
        "positive": "Universality of the Three-Body Parameter for Efimov States in Ultracold\n  Cesium: We report on the observation of triatomic Efimov resonances in an ultracold\ngas of cesium atoms. Exploiting the wide tunability of interactions resulting\nfrom three broad Feshbach resonances in the same spin channel, we measure\nmagnetic-field dependent three-body recombination loss. The positions of the\nloss resonances yield corresponding values for the three-body parameter, which\nin universal few-body physics is required to describe three-body phenomena and\nin particular to fix the spectrum of Efimov states. Our observations show a\nrobust universal behavior with a three-body parameter that stays essentially\nconstant."
    },
    {
        "anchor": "Matter-wave bistability in coupled atom-molecule quantum gases: We study the matter-wave bistability in coupled atom-molecule quantum gases,\nin which heteronuclear molecules are created via an interspecies Feshbach\nresonance involving either two-species Bose or two-species Fermi atoms at zero\ntemperature. We show that the resonant two-channel Bose model is equivalent to\nthe nondegenerate parametric down-conversion in quantum optics, while the\ncorresponding Fermi model can be mapped to a quantum optics model that\ndescribes a single-mode laser field interacting with an ensemble of\ninhomogeneously broadened two-level atoms. Using these analogy and the fact\nthat both models are subject to the Kerr nonlinearity due to the two-body\ns-wave collisions, we show that under proper conditions, the population in the\nmolecular state in both models can be made to change with the Feshbach detuning\nin a bistable fashion.",
        "positive": "Quantum Bose-Bose droplets at a dimensional crossover: We study a liquid quantum droplets in a mixture of two-component\nBose-Einstein condensates under a variable confinement introduced along one or\ntwo spatial dimensions. Despite the atom-atom scattering has a\nthree-dimensional character, discreetness of the available modes in the reduced\ndimension(s) strongly influences the zero-point energy -- the Lee-Huang-Yang\nterm. In a weakly interaction limit, it is the leading correction to the\nmean-field energy at the crossover from three to two dimensions, or from three\nto one dimension. We analyze the properties of the droplets at the dimensional\ncrossovers, and provide the demanding conditions for accessing quasi-low\ndimensions. We predict new kinds of droplets which are formed only due to the\nquantum fluctuations when the mean-field interaction vanishes. Our results pave\nthe way for exploring new states of quantum matter, and are important for\nexperiments with liquid quantum droplets in reduced dimensions."
    },
    {
        "anchor": "Spin-selective insulators in Bose-Fermi mixtures: We investigate an imbalanced mixture composed of two-color fermions and\nscalar bosons in the hard-core limit, considering repulsive and attractive\ninterspecies and intraspecies interactions. The interplay between\ncommensurability, repulsive interactions and imbalance generates three\ninsulating phases: a mixed Mott state and two spin-selective insulators\ncharacterized by the commensurability relations\n$\\rho_B+\\rho^{\\uparrow,(\\downarrow)}_F=1$. For an attractive coupling between\nfermions and bosons, we found the relations\n$\\rho_B-\\rho^{\\uparrow,(\\downarrow)}_F=0$ for the spin-selective insulators.\nState-of-the-art cold-atoms setups constitute ideal platforms to implement\nthese unveiled insulating states and verify their commensurability relations.",
        "positive": "Dark soliton in a disorder potential: We consider dark soliton in a Bose-Einstein condensate in the presence of a\nweak disorder potential. Deformation of the soliton shape is analyzed within\nthe Bogoliubov approach and by employing expansion in eigenstates of the\nP\\\"oschl-Teller Hamiltonian. Comparison of the results with the numerical\nsimulations indicates that the linear response analysis reveals good agreement\neven if the strength of the disorder is of the order of the chemical potential\nof the system. In the second part of the paper we concentrate on quantum nature\nof the dark soliton and demonstrate that the soliton may reveal Anderson\nlocalization in the presence of a disorder. The Anderson localized soliton may\ndecay due to quasi-particle excitations induced by the disorder. However, we\nshow that the corresponding lifetime is much longer than condensate lifetime in\na typical experiment."
    },
    {
        "anchor": "Hartree-Fock-Bogoliubov theory of trapped one-dimensional imbalanced\n  Fermi systems: Ground state Hartree-Fock-Bogoliubov (HFB) theory is applied to imbalanced\nspin-1/2 one-dimensional Fermi systems that are spatially confined by either a\nharmonic or a hard-wall trapping potential. It has been hoped that such\nsystems, which can be realized using ultracold atomic gases, would exhibit the\nlong-sought-after Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superfluid phase. The\nHFB formalism generalizes the standard Bogoliubov quasi-particle\ntransformation, by allowing for Cooper pairing to exist between all possible\nsingle-particle states, and accounts for the effects of the inhomogeneous\ntrapping potential as well as the mean-field Hartree potential. This provides\nan unbiased framework to describe inhomgenous densities and pairing\ncorrelations in the FFLO state of a confined 1D gas. In a harmonic trap,\nnumerical minimization of the HFB ground state energy yields a spatially\noscillating order parameter reminiscent of the FFLO state. However, we find\nthat this state has almost no imprint in the local fermion densities\n(consistent with experiments that found no evidence of the FFLO phase). In\ncontrast, for a hard-wall geometry, we find a strong signature of the spatial\noscillations of the FFLO pairing amplitude reflected in the local in situ\ndensities. In the hard wall case, the excess spins are strongly localized near\nregions where there is a node in the pairing amplitude, creating an\nunmistakeable crystalline modulation of the density.",
        "positive": "Majorana fermions in quasi-1D and higher dimensional ultracold fermionic\n  optical lattices: We show that Majorana fermions (MFs) exist in two- and three-dimensional\n(2D,3D) fermionic optical lattices with strictly 1D spin-orbit coupling (SOC)\nwhich has already been realized in ex- periments. For a quasi-1D topological\nBCS superfluid, there are multiple MFs at each end which are topologically\nprotected by a chiral symmetry. In the generalization to higher dimensions, the\nmultiple MFs form a zero energy flat band. An additional experimentally tunable\nin-plane Zeeman field drives the system to a topological Fulde-Ferrell (FF)\nsuperfluid phase. We find that even though the multiple MFs are robust against\nthe in-plane Zeeman field if the order parameters at the different chains are\nenforced to be identical, they are destroyed in the self-consistently obtained\nFF phase where the order parameters are inhomogeneous on the boundaries. Our\nresults are useful to guide the experimentalists on searching for MFs in the\ncontext of ultracold fermionic atoms."
    },
    {
        "anchor": "Collapse instability of solitons in the nonpolynomial Schr\u00f6dinger\n  equation with dipole-dipole interactions: A model of the Bose-Einstein condensate (BEC) of dipolar atoms, confined in a\ncombination of a cigar-shaped trap and optical lattice acting in the axial\ndirection, is studied in the framework of the one-dimensional (1D)\nnonpolynomial Schr\\\"{o}dinger equation (NPSE) with additional terms describing\nlong-range dipole-dipole (DD) interactions. The NPSE makes it possible to\ndescribe the collapse of localized modes, which was experimentally observed in\nthe self-attractive BEC confined in tight traps, in the framework of the 1D\ndescription. We study the influence of the DD interactions on the dynamics of\nbright solitons, especially as concerns their collapse-induced instability.\nBoth attractive and repulsive contact and DD interactions are considered. The\nresults are summarized in the form of stability/collapse diagrams in a\nrespective parametric space. In particular, it is shown that the attractive DD\ninteractions may prevent the collapse instability in the condensate with\nattractive contact interactions.",
        "positive": "Segregated quantum phases of dipolar bosonic mixtures in two-dimensional\n  optical lattices: We identify the quantum phases in a binary mixture of dipolar bosons in\ntwo-dimensional optical lattices. Our study is motivated by the recent\nexperimental realization of binary dipolar condensate mixtures of Er-Dy [Phys.\nRev. Lett. 121, 213601 (2018)]. We model the system by using the extended\ntwo-species Bose-Hubbard model and calculate the ground-state phase diagrams by\nusing mean-field theory. For selected cases we also obtain analytical phase\nboundaries by using the site-decoupled mean-field theory. For comparison we\nalso examine the phase diagram of two-species Bose-Hubbard model. Our results\nshow that the quantum phases with the long-range intraspecies interaction phase\nseparate with no phase ordering. The introduction of the long-range\ninterspecies interaction modifies the quantum phases of the system. It leads to\nthe emergence of phase-separated quantum phases with phase ordering. The\ntransition from the phase-separated quantum phases without phase ordering to\nphase ordered ones breaks the inversion symmetry."
    },
    {
        "anchor": "Thermalization of isolated Bose-Einstein condensates by dynamical heat\n  bath generation: If and how an isolated quantum system thermalizes despite its unitary time\nevolution is a long-standing, open problem of many-body physics. The eigenstate\nthermalization hypothesis (ETH) postulates that thermalization happens at the\nlevel of individual eigenstates of a system's Hamiltonian. However, the ETH\nrequires stringent conditions to be validated, and it does not address how the\nthermal state is reached dynamically from an inital non-equilibrium state. We\nconsider a Bose-Einstein condensate (BEC) trapped in a double-well potential\nwith an initial population imbalance. We find that the system thermalizes\nalthough the initial conditions violate the ETH requirements. We identify three\ndynamical regimes. After an initial regime of undamped Josephson oscillations,\nthe subsystem of incoherent excitations or quasiparticles (QP) becomes strongly\ncoupled to the BEC subsystem by means of a dynamically generated, parametric\nresonance. When the energy stored in the QP system reaches its maximum, the\nnumber of QPs becomes effectively constant, and the system enters a\nquasi-hydrodynamic regime where the two subsystems are weakly coupled. In this\nfinal regime the BEC acts as a grand-canonical heat reservoir for the QP system\n(and vice versa), resulting in thermalization. We term this mechanism dynamical\nbath generation (DBG).",
        "positive": "Few distinguishable particles with an impurity in a one-dimensional\n  harmonic trap: We study the static properties of a mobile impurity interacting with a bath\nwith a few distinguishable particles trapped in a one-dimensional harmonic\ntrap. We focus on the limiting case where the bath is non-interacting. We\nprovide numerical results for the energy spectra and density profiles by means\nof the exact diagonalization of the Hamiltonian and find that these systems\nshow non-trivial solutions, even in the limit of infinite repulsion. A detailed\nphysical interpretation is provided for the lowest energy states. In\nparticular, we find a seemingly universal transition from the impurity being\nlocalized in the center of the trap to being expelled outside the majority\ncloud. A mean-field approach is developed which captures the transition."
    },
    {
        "anchor": "Ultracold fermions in a one-dimensional bipartite optical lattice:\n  metal-insulator transitions driven by shaking: We describe the behavior of a system of fermionic atoms loaded in a bipartite\none-dimensional optical lattice that is under the action of an external\ntime-periodic driving force. By using Floquet theory, an effective model with\nrenormalized hopping coefficients is derived. The insulating behavior\ncharacterizing the system at half-filling in the absence of driving is\ndynamically suppressed and for particular values of the driving parameter the\nsystem becomes either a standard metal or an unconventional metal with four\nFermi points. We use the bosonization technique to investigate the effect of\non-site Hubbard interactions on the four Fermi-point metal-insulator phase\ntransition. Attractive interactions are expected to enlarge the regime of\nparameters where the unconventional metallic phase arises, whereas repulsive\ninteractions reduce it. This metallic phase is known to be a Luther-Emery\nliquid (spin gapped metal) for both, repulsive and attractive interactions,\ncontrarily to the usual Hubbard model which exhibits a Mott insulator phase for\nrepulsive interactions. Ultracold fermions in driven one-dimensional bipartite\noptical lattices provide an interesting platform for the realization of this\nlong studied four Fermi-point unconventional metal.",
        "positive": "Far-from-equilibrium universal critical behavior of quantum geometry: In this study, we show that the quantum critical point in the ground state of\nquantum many-body systems, can also govern the universal dynamical behavior\nwhen the systems are driven far from equilibrium, which can be captured by the\nevolution of the quantum geometry of the systems. By investigating quantum\nquench dynamics in a variety of quadratic fermionic models, we find that the\nquantum volume of these systems typically grows linearly over time, with a\ngrowth velocity demonstrating universal behavior: its first derivative over the\ncontrol parameter exhibits a discontinuity at the quantum critical point, with\nan universal jump value that is independent of specific models, but is\ncrucially determined by the system dimension. This result reveals universal\ndynamical properties of non-equilibrium quantum many-body systems."
    },
    {
        "anchor": "Vortex lattice solutions to the Gross-Pitaevskii equation with\n  spin-orbit coupling in optical lattices: Effective spin-orbit coupling can be created in cold atom systems using\natom-light interaction. We study the BECs in an optical lattice using the\nGross-Pitaevskii equation with spin-orbit coupling. Bloch states for the linear\nequation are numerically obtained, and compared with stationary solutions to\nthe Gross-Pitaevskii equation with nonlinear terms. Various vortex lattice\nstates are found when the spin-orbit coupling is strong.",
        "positive": "Stability and dynamics across magnetic phases of vortex-bright type\n  excitations in spinor Bose-Einstein condensates: The static properties, i.e., existence and stability, as well as the\nquench-induced dynamics of vortex-bright type excitations in two-dimensional\nharmonically confined spin-1 Bose-Einstein condensates are investigated.\nLinearly stable vortex-bright-vortex and bright-vortex-bright solutions arise\nin both antiferromagnetic and ferromagnetic spinor gases upon quadratic Zeeman\nenergy shift variations. Their deformations across the relevant transitions are\nexposed and discussed in detail evincing also that emergent instabilities can\nlead to pattern formation. Spatial elongations, precessional motion and\nspiraling of the nonlinear excitations when exposed to finite temperatures and\nupon crossing the distinct phase boundaries, via quenching of the quadratic\nZeeman coefficient, are unveiled. Spin-mixing processes triggered by the quench\nlead, among others, to changes in the waveform of the ensuing configurations.\nOur findings reveal an interplay between pattern formation and spin-mixing\nprocesses being accessible in contemporary cold atom experiments."
    },
    {
        "anchor": "Quantum dynamics of a single, mobile spin impurity: Quantum magnetism describes the properties of many materials such as\ntransition metal oxides and cuprate superconductors. One of its elementary\nprocesses is the propagation of spin excitations. Here we study the quantum\ndynamics of a deterministically created spin-impurity atom, as it propagates in\na one-dimensional lattice system. We probe the full spatial probability\ndistribution of the impurity at different times using single-site-resolved\nimaging of bosonic atoms in an optical lattice. In the Mott-insulating regime,\na post-selection of the data allows to reduce the effect of temperature, giving\naccess to a space- and time-resolved measurement of the quantum-coherent\npropagation of a magnetic excitation in the Heisenberg model. Extending the\nstudy to the bath's superfluid regime, we determine quantitatively how the bath\nstrongly affects the motion of the impurity. The experimental data shows a\nremarkable agreement with theoretical predictions allowing us to determine the\neffect of temperature on the coherence and velocity of impurity motion. Our\nresults pave the way for a new approach to study quantum magnetism, mobile\nimpurities in quantum fluids, and polarons in lattice systems.",
        "positive": "Quantum Hydrodynamics in One Dimension beyond the Luttinger Liquid: Recent years have seen the development of a rich phenomenology beyond the\nLuttinger Liquid model of one dimensional quantum fluids, arising from\ninteractions between the elementary phonon excitations. It has been known for\nsome time, however, that the straightforward inclusion of these interactions\npresents technical difficulties that have necessitated approaches based on\nrefermionization or effective impurity models.\n  In this work we show that the nonlinear extensions of the Luttinger model are\ntractable in the phonon basis. We present a calculation of the singularities\npresent in the zero temperature dynamical structure factor in the semiclassical\nlimit where the phonon dispersion is strong.\n  A unitary transformation decouples interactions between left-- and\nright--moving phonons, leaving a nonlinear chiral Hamiltonian. At low momenta,\nthis Hamiltonian has a spectrum bounded above and below by thresholds\nidentified with phonon and soliton excitations in the semiclassical limit. The\nchiral dynamical structure factor therefore has support only in this region,\nwith power law singularities at the thresholds originating in the Anderson\northogonality catastrophe, which we calculate analytically. The dynamical\nstructure factor for the original nonchiral Hamiltonian is a convolution of\nthis chiral correlator with a power law arising from the left--right\ndecoupling."
    },
    {
        "anchor": "A complex Langevin approach to ultracold fermions: The theoretical treatment of Fermi systems consisting of particles with\nunequal masses is challenging. Even in one spatial dimension analytic solutions\nare limited to special configurations and numerical progress with Monte Carlo\nsimulations is hindered by the sign-problem. To circumvent this issue, we\nexploit the Complex Langevin approach and study one-dimensional mass-imbalanced\ntwo-component Fermi gases with attractive and repulsive interactions. We find\nperfect agreement with results obtained by other methods in a range of\nparameter space. Promisingly, our approach is not limited to the specific model\npresented here and can easily be extended to finite spin polarization and, most\nnotably, can also be applied in higher dimensions.",
        "positive": "Universal dynamics on the way to thermalisation: It is demonstrated how a many-body system far from thermal equilibrium can\nexhibit universal dynamics in passing a non-thermal fixed point. As an example,\nthe process of Bose-Einstein (BE) condensation of a dilute cold gas is\nconsidered. If the particle flux into the low-energy modes, induced, e.g., by a\ncooling quench, is sufficiently strong, the Bose gas develops a characteristic\npower-law single-particle spectrum $n(k)\\sim k^{-5}$, and critical slowing down\nin time occurs. The fixed point is shown to be marked by the creation and\ndilution of tangled vortex lines. Alternatively, for a weak cooling quench and\nparticle flux, the condensation process runs quasi adiabatically, passing by\nthe fixed point in far distance, and signatures of critical scaling remain\nabsent."
    },
    {
        "anchor": "Supersolid-like solitons in two-dimensional nonmagnetic spin-orbit\n  coupled spin-1 and spin-2 condensates: We demonstrate spontaneous generation of spatially-periodic supersolid-like\nsuper-lattice and stripe solitons in Rashba spin-orbit (SO) coupled spin-1 and\nspin-2 quasi-two-dimensional nonmagnetic Bose-Einstein condensates (BECs). The\nsolitons in a weakly SO-coupled spin-1 BEC are circularly-symmetric of $(-1, 0,\n+1)$ and $(0, +1, +2)$ types and have inherent vorticity; the numbers in the\nparentheses are the winding numbers in hyper-spin components $+1, 0, -1$,\nrespectively. The circularly-symmetric solitons in an SO-coupled spin-2 BEC are\nof types $(-2, -1, 0, +1, +2)$ and $(-1, 0, +1, +2, +3)$ with the former being\nthe ground state, where the winding numbers correspond to spin components $+2,\n+1, 0, -1, -2$, respectively. For stronger SO-coupling strengths, these\nsolitons acquire a multiring structure while preserving the winding numbers.\nQuasi-degenerate stripe and super-lattice solitons, besides a\ncircularly-asymmetric soliton, also emerge as excited stationary states for\nstronger SO-coupling strengths in spin-1 and spin-2 BECs. pla-cl.tex",
        "positive": "Spin-Seebeck effect in a strongly interacting Fermi gas: We study the spin-Seebeck effect in a strongly interacting, two-component\nFermi gas and propose an experiment to measure this effect by relatively\ndisplacing spin up and spin down atomic clouds in a trap using spin-dependent\ntemperature gradients. We compute the spin-Seebeck coefficient and related\nspin-heat transport coefficients as functions of temperature and interaction\nstrength. We find that when the inter-spin scattering length becomes larger\nthan the Fermi wavelength, the spin-Seebeck coefficient changes sign as a\nfunction of temperature, and hence so does the direction of the\nspin-separation. We compute this zero-crossing temperature as a function of\ninteraction strength and in particular in the unitary limit for the inter-spin\nscattering."
    },
    {
        "anchor": "A quantum storm in a teacup: The past decade has seen atomic Bose-Einstein condensates emerge as a\npromising prototype system to explore the quantum mechanical form of\nturbulence, buoyed by a powerful experimental toolbox to control and manipulate\nthe fluid, and the amenity to describe the system from first-principles. This\narticle presents an overview of quantum turbulence in atomic condensates, from\nits history and fundamental motivations, its characteristics and key results to\ndate, and finally to some promising future directions.",
        "positive": "Violation of the Wiedemann-Franz Law for ultracold atomic gases: We study energy and particle transport for one-dimensional strongly\ninteracting bosons through a single channel connecting two atomic reservoirs.\nWe show the emergence of particle- and energy- current separation, leading to\nthe violation of the Wiedemann-Franz law. As a consequence, we predict\ndifferent time scales for the equilibration of temperature and particle\nimbalances between the reservoirs. Going beyond the linear spectrum\napproximation, we show the emergence of ther- moelectric effects, which could\nbe controlled by either tuning interactions or the temperature. Our results\ndescribe in a unified picture fermions in condensed matter devices and bosons\nin ultracold atom setups. We conclude discussing the effects of a controllable\ndisorder."
    },
    {
        "anchor": "Two-Time Correlation Functions in Dissipative and Interacting\n  Bose-Hubbard Chains: A method is presented for the systematic derivation of a hierarchy of coupled\nequations for the computation of two-time correlation functions of operators\nfor open many-body quantum systems. We show how these systems of equations can\nbe closed in mean-field and beyond approximations. Results for the specific\nexample of the spectral weight functions are discussed. Our method allows one\nto access the full temporal evolution, not just the stationary solution, of\nnon-equilibrium open quantum problems described by a Markovian master equation.",
        "positive": "Collisionless spin dynamics in a magnetic field gradient: We study the collisionless spin dynamics of a harmonically trapped Fermi gas\nin a magnetic field gradient. In the absence of interactions, the system\nevolution is periodic: the magnetization develops twists, which evolve into a\nlongitudinal polarization. Recurrences follow. For weak interaction, the\nexchange interactions lead to beats in these oscillations. We present an array\nof analytic and numerical techniques for studying this physics."
    },
    {
        "anchor": "Mean-field scaling of the superfluid to Mott insulator transition in a\n  2D optical superlattice: The mean-field treatment of the Bose-Hubbard model predicts properties of\nlattice-trapped gases to be insensitive to the specific lattice geometry once\nsystem energies are scaled by the lattice coordination number $z$. We test this\nscaling directly by comparing coherence properties of $^{87}$Rb gases that are\ndriven across the superfluid to Mott insulator transition within optical\nlattices of either the kagome ($z=4$) or the triangular ($z=6$) geometries. The\ncoherent fraction measured for atoms in the kagome lattice is lower than for\nthose in a triangular lattice with the same interaction and tunneling energies.\nA comparison of measurements from both lattices agrees quantitatively with the\nscaling prediction. We also study the response of the gas to a change in\nlattice geometry, and observe the dynamics as a strongly interacting\nkagome-lattice gas is suddenly \"hole-doped\" by introducing the additional sites\nof the triangular lattice.",
        "positive": "Rotational pendulum dynamics of a vortex molecule in a channel geometry: A vortex molecule is a topological excitation in two coherently coupled\nsuperfluids consisting of a vortex in each superfluid connected by a domain\nwall of the relative phase, also known as a Josephson vortex. We investigate\nthe dynamics of this excitation in a quasi-two-dimensional geometry with slab\nor channel boundary conditions using an extended point vortex framework\ncomplemented by Gross-Pitaevskii simulations. Apart from translational motion\nalong the channel, the vortex molecule is found to exhibit intriguing internal\ndynamics including rotation and rotational-pendulum-like dynamics. Trajectories\nleading to a boundary-induced break-up of the vortex molecule are also\ndescribed qualitatively by the simplified model. We classify the stable and\nunstable fixed points as well as separatrices that characterize the vortex\nmolecule dynamics."
    },
    {
        "anchor": "Spectral properties and breathing dynamics of a few-body Bose-Bose\n  mixture in a 1D harmonic trap: We investigate a few-body mixture of two bosonic components, each consisting\nof two particles confined in a quasi one-dimensional harmonic trap. By means of\nexact diagonalization with a correlated basis approach we obtain the low-energy\nspectrum and eigenstates for the whole range of repulsive intra- and\ninter-component interaction strengths. We analyse the eigenvalues as a function\nof the inter-component coupling, covering hereby all the limiting regimes, and\ncharacterize the behaviour in-between these regimes by exploiting the\nsymmetries of the Hamiltonian. Provided with this knowledge we study the\nbreathing dynamics in the linear-response regime by slightly quenching the trap\nfrequency symmetrically for both components. Depending on the choice of\ninteractions strengths, we identify 1 to 3 monopole modes besides the breathing\nmode of the center of mass coordinate. For the uncoupled mixture each monopole\nmode corresponds to the breathing oscillation of a specific relative\ncoordinate. Increasing the inter-component coupling first leads to multi-mode\noscillations in each relative coordinate, which turn into single-mode\noscillations of the same frequency in the composite-fermionization regime.",
        "positive": "Emergence of a sharp quantum collective mode in a one-dimensional Fermi\n  polaron: The Fermi-polaron problem of a mobile impurity interacting with fermionic\nmedium emerges in various contexts, ranging from the foundations of Landau's\nFermi-liquid theory to electron-exciton interaction in semiconductors, to\nunusual properties of high-temperature superconductors. While classically the\nmedium provides only a dissipative environment to the impurity, quantum picture\nof polaronic dressing is more intricate and arises from the interplay of few-\nand many-body aspects of the problem. The conventional expectation for the\ndynamics of Fermi polarons is that it is dissipative in character, and any\nexcess energy is rapidly emitted away from the impurity as particle-hole\nexcitations. Here we report a strikingly different type of polaron dynamics in\na one-dimensional system of the impurity interacting repulsively with the\nfermions. When the total momentum of the system equals the Fermi momentum,\nthere emerges a sharp collective mode corresponding to long-lived oscillations\nof the polaronic cloud surrounding the impurity. This mode can be observed\nexperimentally with ultracold atoms using Ramsey interferometry and\nradio-frequency spectroscopy."
    },
    {
        "anchor": "Accelerating many-body entanglement generation by dipolar interactions\n  in the Bose-Hubbard model: The spin squeezing protocols allow the dynamical generation of massively\ncorrelated quantum many-body states, which can be utilized in\nentanglement-enhanced metrology and technologies. We study a quantum simulator\ngenerating twisting dynamics realized in a two-component Bose-Hubbard model\nwith dipolar interactions. We show that the interplay of contact and long-range\ndipolar interactions between atoms in the superfluid phase activates the\nanisotropic two-axis counter-twisting mechanism, accelerating the spin\nsqueezing dynamics and allowing the Heisenberg-limited accuracy in\nspectroscopic measurements.",
        "positive": "Floquet analysis of time-averaged trapping potentials: Time-averaged trapping potentials have played an important role in the\ndevelopment of the field of ultracold atoms. Despite their widespread\napplication, there is not yet a complete understanding of when a system can be\nconsidered time-averaged. Here we use Floquet theory to analyse the lowest\nenergy state of time-periodic trapping potentials, and characterise the\ntransition from a localised state in a slowly moving trap to a delocalised\nstate in a rapidly oscillating time-averaged potential. We investigate how the\ndriving parameters affect the density and phase of the Floquet ground state,\nand provide a quantitative measure of the degree to which they can be\nconsidered time-averaged. We study a number of simple representative systems,\nand comment on the features affecting the experimental realisation of\ntime-averaged trapping potentials."
    },
    {
        "anchor": "Ground and Low-Lying Collective States of Rotating Three-Boson System: The ground and low-lying collective states of a rotating system of $N=3$\nbosons harmonically confined in quasi-two-dimension and interacting via\nrepulsive finite-range Gaussian potential is studied in weakly to moderately\ninteracting regime. The $N$-body Hamiltonian matrix is diagonalized in\nsubspaces of quantized total angular momenta $0\\le L \\le 4N$ to obtain the\nground and low-lying eigenstates. Our numerical results show that breathing\nmodes with $N$-body eigenenergy spacing of $2\\hbar\\omega_{\\perp}$, known to\nexist in strictly 2D system with zero-range ($\\delta$-function) interaction\npotential, may as well exist in quasi-2D system with finite-range Gaussian\ninteraction potential. To gain an insight into the many-body states, the von\nNeumann entropy is calculated as a measure of quantum correlation and the\nconditional probability distribution is analyzed for the internal structure of\nthe eigenstates. In the rapidly rotating regime the ground state in angular\nmomentum subspaces $L=\\frac{q}{2}N\\left(N-1\\right)$ with $q=2, 4$ is found to\nexhibit the anticorrelation structure suggesting that it may variationally be\ndescribed by a Bose-Laughlin like state. We further observe that the first\nbreathing mode exhibits features similar to the Bose-Laughlin state in having\neigenenergy, von Neumann entropy and internal structure independent of\ninteraction for the three-boson system considered here. On the contrary, for\neigenstates lying between the Bose-Laughlin like ground state and the first\nbreathing mode, values of eigenenergy, von Neumann entropy and internal\nstructure are found to vary with interaction.",
        "positive": "Orbital physics of polar Fermi molecules: We study a system of polar dipolar fermions in a two-dimensional optical\nlattice and show that multi-band Fermi-Hubbard model is necessary to discuss\nsuch system. By taking into account both on-site, and long-range interactions\nbetween different bands, as well as occupation-dependent inter- and intra-band\ntunneling, we predict appearance of novel phases in the strongly-interacting\nlimit."
    },
    {
        "anchor": "Artificial spin-orbit coupling in ultra-cold Fermi superfluids: We develop a theory for interacting fermions in the presence of spin-orbit\ncoupling and Zeeman fields, and show that many new superfluids phases, which\nare topological in nature, emerge. Depending on values of spin-orbit coupling,\nZeeman fields, and interactions, initially gapped s-wave superfluids acquire\np-wave, d-wave, f-wave and higher angular momentum components, which produce\nzeros in the excitation spectrum, rendering the superfluid gapless. Several\nmulti-critical points, which separate topological superfluid phases from normal\nor non-uniform, are accessible depending on spin-orbit coupling, Zeeman fields\nor interactions, setting the stage for the study of tunable topological\nsuperfluids.",
        "positive": "Frustrated Quantum Magnetism with Bose Gases in Triangular Optical\n  Lattices at Negative Absolute Temperatures: Quantum antiferromagnets with geometrical frustration exhibit rich many-body\nphysics but are hard to simulate by means of classical computers. Although\nquantum-simulation studies for analyzing such systems are thus desirable, they\nare still limited to high temperature regions, where interesting quantum\neffects are smeared out. Here, we propose a feasible protocol to perform analog\nquantum simulation of frustrated antiferromagnetism with strong quantum\nfluctuations by using ultracold Bose gases in optical lattices at negative\nabsolute temperatures. Specifically, we show from numerical simulations that\nthe time evolution of a negative-temperature state subjected to a slow sweep of\nthe hopping energy simulates quantum phase transitions of a frustrated\nBose-Hubbard model with sign-inverted hoppings. Moreover, we quantitatively\npredict the phase boundary between the frustrated superfluid and Mott-insulator\nphases for triangular lattices with hopping anisotropy, which serves as a\nbenchmark for quantum simulation."
    },
    {
        "anchor": "Rotational properties of two-component Bose gases in the lowest Landau\n  level: We study the rotational (yrast) spectra of dilute two-component atomic Bose\ngases in the low angular momentum regime, assuming equal interspecies and\nintraspecies interaction. Our analysis employs the composite fermion (CF)\napproach including a pseudospin degree of freedom. While the CF approach is not\n{\\it a priori} expected to work well in this angular momentum regime, we show\nthat composite fermion diagonalization gives remarkably accurate approximations\nto low energy states in the spectra. For angular momenta $0 < L < M$ (where $N$\nand $M$ denote the numbers of particles of the two species, and $M \\geq N$), we\nfind that the CF states span the full Hilbert space and provide a convenient\nset of basis states which, by construction, are eigenstates of the symmetries\nof the Hamiltonian. Within this CF basis, we identify a subset of the basis\nstates with the lowest $\\Lambda$-level kinetic energy. Diagonalization within\nthis significally smaller subspace constitutes a major computational\nsimplification and provides very close approximations to ground states and a\nnumber of low-lying states within each pseudospin and angular momentum channel.",
        "positive": "Superfluid to Mott insulator transition in the one-dimensional\n  Bose-Hubbard model for arbitrary integer filling factors: We study the quantum phase transition between the superfluid and the Mott\ninsulator in the one-dimensional (1D) Bose-Hubbard model. Using the\ntime-evolving block decimation method, we numerically calculate the tunneling\nsplitting of two macroscopically distinct states with different winding\nnumbers. From the scaling of the tunneling splitting with respect to the system\nsize, we determine the critical point of the superfluid to Mott insulator\ntransition for arbitrary integer filling factors. We find that the critical\nvalues versus the filling factor in 1D, 2D, and 3D are well approximated by a\nsimple analytical function. We also discuss the condition for determining the\ntransition point from a perspective of the instanton method."
    },
    {
        "anchor": "Anisotropy-induced Coulomb phase and quasiparticle zoo in the atomic\n  monopole-spin hybrid system: Quantum simulation of a monopole-spin hybrid system is performed on basis of\na dipolar ultracold gas in a ladder lattice. The site-occupation states of the\ndipolar ladder lattice gas can spontaneously emulate both the monopole and spin\nexcitations. The hopping of the atoms induces a particle conversion process\nbetween spin and monopole pairs, and the dipole-dipole interaction determines\nthe spin-spin, spin-monopole and monopole-monopole interactions. The\nanisotropic nature of the dipole-dipole interaction allows hereby for a\nflexible engineering of the designed hybrid system, and for a significant\ntunability of the interaction strengths. As a result, we encounter a rich phase\ndiagram, and specifically a self-assembled Coulomb phase arises, in which\nmonopoles and spins coexist and are orderly arranged according to the local\nGauss's law. The Coulomb phase hosts a zoo of different types of\nquasiparticles, and provides the possibility to simulate various phenomena in\nparticle physics, such as a degenerate vacuum, particle decay and conversion\nprocesses. Our work provides a significant extension of the scope of quantum\nsimulations based on the anisotropy of dipolar interactions.",
        "positive": "Droplet Arrays in Doubly-Dipolar Bose-Einstein condensates: Gases of doubly-dipolar particles, with both magnetic and electric dipole\nmoments, offer intriguing novel possibilities. We show that the interplay\nbetween doubly-dipolar interactions, quantum stabilization, and external\nconfinement results in a rich ground-state physics of supersolids and\nincoherent droplet arrays in doubly-dipolar condensates. Our study reveals\nnovel possibilities for engineering quantum droplets and droplet supersolids,\nincluding supersolid-supersolid transitions and the realization of supersolid\narrays of pancake droplets."
    },
    {
        "anchor": "Thermalization of strongly interacting bosons after spontaneous\n  emissions in optical lattices: We study the out-of-equilibrium dynamics of bosonic atoms in a 1D optical\nlattice, after the ground-state is excited by a single spontaneous emission\nevent, i.e. after an absorption and re-emission of a lattice photon. This is an\nimportant fundamental source of decoherence for current experiments, and\nunderstanding the resulting dynamics and changes in the many-body state is\nimportant for controlling heating in quantum simulators. Previously it was\nfound that in the superfluid regime, simple observables relax to values that\ncan be described by a thermal distribution on experimental time-scales, and\nthat this breaks down for strong interactions (in the Mott insulator regime).\nHere we expand on this result, investigating the relaxation of the momentum\ndistribution as a function of time, and discussing the relationship to\neigenstate thermalization. For the strongly interacting limit, we provide an\nanalytical analysis for the behavior of the system, based on an effective\nlow-energy Hamiltonian in which the dynamics can be understood based on\ncorrelated doublon-holon pairs.",
        "positive": "Modelling of vorticity, sound and their interaction in two-dimensional\n  superfluids: Vorticity in two-dimensional superfluids is subject to intense research\nefforts due to its role in quantum turbulence, dissipation and the BKT phase\ntransition. Interaction of sound and vortices is of broad importance in\nBose-Einstein condensates and superfluid helium [1-4]. However, both the\nmodelling of the vortex flow field and of its interaction with sound are\ncomplicated hydrodynamic problems, with analytic solutions only available in\nspecial cases. In this work, we develop methods to compute both the vortex and\nsound flow fields in an arbitrary two-dimensional domain. Further, we analyse\nthe dispersive interaction of vortices with sound modes in a two-dimensional\nsuperfluid and develop a model that quantifies this interaction for any vortex\ndistribution on any two-dimensional bounded domain, possibly non-simply\nconnected, exploiting analogies with fluid dynamics of an ideal gas and\nelectrostatics. As an example application we use this technique to propose an\nexperiment that should be able to unambiguously detect single circulation\nquanta in a helium thin film."
    },
    {
        "anchor": "Microscopic origin of quantum supersonic phenomenon in one dimension: Using the Bethe ansatz (BA) solution, we rigorously determine non-equilibrium\ndynamics of quantum flutter and revival of an injected impurity with a large\ninitial momentum $Q$ into the one-dimensional (1D) interacting bosonic medium.\nWe show that two types of BA excited eigenstates drastically dominate the\noscillation nature of the quantum flutter with a periodicity which is simply\ngiven by the charge and spin dressed energies $\\varepsilon_{\\rm c,s}(0)$ at\nzero quasi-momentum $\\tau_{\\rm QF} = 2\\pi/(|\\varepsilon_{\\rm c}(0)|-\n|\\varepsilon_{\\rm s}(0)|)$. While we also determine quantum revival dynamics\nwith a larger periodicity $\\tau_{L} = L/\\left(v_{\\rm c}(Q-k^*)-v_{\\rm\ns}(k^*)\\right)$ than $\\tau_{\\rm QF}$, revealing the quantum reflection of\nexcitations induced by the periodic boundary conditions of a finite length $L$.\nHere $v_{\\rm c,s}$ are the sound velocities of charge and spin excitations,\nrespectively, and $k^*$ is determined by the rapidity of the impurity. Our\nresults reveals a microscopic origin of quantum supersonic phenomenon and shed\nlight on quantum magnon metrology for a measure of the gravitational force.",
        "positive": "Non-destructive cavity QED probe of Bloch oscillations in a gas of\n  ultracold atoms: We describe a scheme for probing a gas of ultracold atoms trapped in an\noptical lattice and moving in the presence of an external potential. The probe\nis non-destructive and uses the existing lattice fields as the measurement\ndevice. Two counter-propagating cavity fields simultaneously set up a\nconservative lattice potential and a weak quantum probe of the atomic motion.\nBalanced heterodyne detection of the probe field at the cavity output along\nwith integration in time and across the atomic cloud yield information about\nthe atomic dynamics in a single run. The scheme is applied to a measurement of\nthe Bloch oscillation frequency for atoms moving in the presence of the local\ngravitational potential. Signal-to-noise ratios are estimated to be as high as\n$10^4$."
    },
    {
        "anchor": "Superradiance induced particle flow via dynamical gauge coupling: We study fermions that are gauge-coupled to a cavity mode via Raman-assisted\nhopping in a one dimensional lattice. For an infinite lattice, we find a\nsuperradiant phase with infinitesimal pumping threshold which induces a\ndirected particle flow. We explore the fate of this flow in a finite lattice\nwith boundaries, studying the non-equilibrium dynamics including fluctuation\neffects. The short time dynamics is dominated by superradiance, while the long\ntime behaviour is governed by cavity fluctuations. We show that the steady\nstate in the finite lattice is not unique, and can be understood in terms of\ncoherent bosonic excitations above a Fermi surface in real space.",
        "positive": "Optical Flux Lattices for Ultracold Atomic Gases: We show that simple laser configurations can give rise to \"optical flux\nlattices\", in which optically dressed atoms experience a periodic effective\nmagnetic flux with high mean density. These potentials lead to narrow energy\nbands with non-zero Chern number. Optical flux lattices will greatly facilitate\nthe achievement of the quantum Hall regime for ultracold atomic gases."
    },
    {
        "anchor": "Discrete time crystals enforced by Floquet-Bloch scars: We analytically identify a new class of quantum scars protected by\nspatiotemporal translation symmetries, dubbed Floquet-Bloch scars. They\ndistinguish from previous (quasi-)static scars by a rigid spectral pairing only\npossible in Floquet systems, where strong interaction and drivings equalize the\nquasienergy corrections to all scars and maintain their spectral spacings\nagainst generic bilinear perturbations. Scars then enforce the spatial\nlocalization and rigid discrete time crystal (DTC) oscillations as verified\nnumerically in a trimerized kagome lattice model relevant to recent cold atom\nexperiments. Our analytical solutions offer a potential scheme to understand\nthe mechanisms for more generic translation-invariant DTCs.",
        "positive": "Collective modes of monolayer, bilayer, and multilayer fermionic dipolar\n  liquid: Motivated by recent experimental advances in creating polar molecular gases\nin the laboratory, we theoretically investigate the many body effects of\ntwo-dimensional dipolar systems with the anisotropic and $1/r^3$ dipole-dipole\ninteractions. We calculate collective modes of 2D dipolar systems, and also\nconsider spatially separated bilayer and multilayer superlattice dipolar\nsystems. We obtain the characteristic features of collective modes in quantum\ndipolar gases. We quantitatively compare the modes of these dipolar systems\nwith the modes of the extensively studied usual two-dimensional electron\nsystems, where the inter-particle interaction is Coulombic."
    },
    {
        "anchor": "Controlling integrability in a quasi-1D atom-dimer mixture: We analytically study the atom-dimer scattering problem in the\nnear-integrable limit when the oscillator length l_0 of the transverse\nconfinement is smaller than the dimer size, ~l_0^2/|a|, where a<0 is the\ninteratomic scattering length. The leading contributions to the atom-diatom\nreflection and break-up probabilities are proportional to a^6 in the bosonic\ncase and to a^8 for the up-(up-down) scattering in a two-component fermionic\nmixture. We show that by tuning a and l_0 one can control the \"degree of\nintegrability\" in a quasi-1D atom-dimer mixture in an extremely wide range\nleaving thermodynamic quantities unchanged. We find that the relaxation to\ndeeply bound states in the fermionic (bosonic) case is slower (faster) than\ntransitions between different Bethe ansatz states. We propose a realistic\nexperiment for detailed studies of the crossover from integrable to\nnonintegrable dynamics.",
        "positive": "Signatures of Many-Body Localization in a Controlled Open Quantum System: In the presence of disorder, an interacting closed quantum system can undergo\nmany-body localization (MBL) and fail to thermalize. However, over long times\neven weak couplings to any thermal environment will necessarily thermalize the\nsystem and erase all signatures of MBL. This presents a challenge for\nexperimental investigations of MBL, since no realistic system can ever be fully\nclosed. In this work, we experimentally explore the thermalization dynamics of\na localized system in the presence of controlled dissipation. Specifically, we\nfind that photon scattering results in a stretched exponential decay of an\ninitial density pattern with a rate that depends linearly on the scattering\nrate. We find that the resulting susceptibility increases significantly close\nto the phase transition point. In this regime, which is inaccessible to current\nnumerical studies, we also find a strong dependence on interactions. Our work\nprovides a basis for systematic studies of MBL in open systems and opens a\nroute towards extrapolation of closed system properties from experiments."
    },
    {
        "anchor": "Unitary dynamics of strongly-interacting Bose gases with time-dependent\n  variational Monte Carlo in continuous space: We introduce time-dependent variational Monte Carlo for continuous-space Bose\ngases. Our approach is based on the systematic expansion of the many-body\nwave-function in terms of multi-body correlations and is essentially exact up\nto adaptive truncation. The method is benchmarked by comparison to exact\nBethe-ansatz or existing numerical results for the integrable Lieb-Liniger\nmodel. We first show that the many-body wave-function achieves high precision\nfor ground-state properties, including energy and first-order as well as\nsecond-order correlation functions. Then, we study the out-of-equilibrium,\nunitary dynamics induced by a quantum quench in the interaction strength. Our\ntime-dependent variational Monte Carlo results are benchmarked by comparison to\nexact Bethe ansatz results available for a small number of particles, and also\ncompared to quench action results available for non-interacting initial states.\nMoreover, our approach allows us to study large particle numbers and general\nquench protocols, previously inaccessible beyond the mean-field level. Our\nresults suggest that it is possible to find correlated initial states for which\nthe long-term dynamics of local density fluctuations is close to the\npredictions of a simple Boltzmann ensemble.",
        "positive": "Exploring spin-squeezing in the Mott insulating regime: role of\n  anisotropy, inhomogeneity and hole doping: Spin-squeezing in systems with single-particle control is a well-established\nresource of modern quantum technology. Applied in an optical lattice clock can\nreduce the statistical uncertainty of spectroscopic measurements. Here, we\nconsider dynamic generation of spin-squeezing with ultra-cold bosonic atoms\nwith two internal states loaded into an optical lattice in the strongly\ninteracting regime as realized with state-of-the-art experiments using a\nquantum gas microscope. We show that anisotropic interactions and inhomogeneous\nmagnetic fields generate scalable spin-squeezing if their magnitudes are\nsufficiently small, but not negligible. The effect of non-uniform filling\ncaused by hole doping, non-zero temperature and external confinement is studied\nat a microscopic level demonstrating their limiting role in the dynamics and\nscaling of spin squeezing."
    },
    {
        "anchor": "Experimental realization of plaquette resonating valence bond states\n  with ultracold atoms in optical superlattices: The concept of valence bond resonance plays a fundamental role in the theory\nof the chemical bond and is believed to lie at the heart of many-body quantum\nphysical phenomena. Here we show direct experimental evidence of a\ntime-resolved valence bond quantum resonance with ultracold bosonic atoms in an\noptical lattice. By means of a superlattice structure we create a\nthree-dimensional array of independent four-site plaquettes, which we can fully\ncontrol and manipulate in parallel. Moreover, we show how small-scale plaquette\nresonating valence bond states with s- and d-wave symmetry can be created and\ncharacterized. We anticipate our findings to open the path towards the creation\nand analysis of many-body RVB states in ultracold atomic gases.",
        "positive": "Dynamics of a Mobile Impurity in a Two Leg Bosonic Ladder: We have analyzed the behavior of a mobile quantum impurity in a bath formed\nby a two-leg bosonic ladder by a combination of field theory\n(Tomonaga-Luttinger liquid) and numerical (Density Matrix Renormalization\nGroup) techniques. Computing the Green's function of the impurity as a function\nof time at different momenta, we find a power law decay at zero momentum, which\nsignals the breakdown of any quasi-particle description of the impurity motion.\nWe compute the exponent both for the limits of weak and strong impurity-bath\ninteractions. At small impurity-bath interaction, we find that the impurity\nexperiences the ladder as a single channel one-dimensional bath, but effective\ncoupling is reduced by a factor of $\\sqrt 2$, thus the impurity is less mobile\nin the ladder compared to a one dimensional bath. We compared the numerical\nresults for the exponent at zero momentum with a semi-analytical expression\nthat was initially established for the chain and find excellent agreement\nwithout adjustable parameters. We analyze the dependence of the exponent in the\ntransverse hopping in the bath and find surprisingly an increase of the\nexponent at variance with the naive extrapolation of the single channel regime.\nWe study the momentum dependence of the impurity Green's function and find\nthat, as for the single chain, two different regime of motion exist, one\ndominated by infrared metatrophy and a more conventional polaronic behavior. We\ncompute the critical momentum between these two regimes and compare with\nprediction based on the structure factor of the bath. In the polaronic regime\nwe also compute numerically the lifetime of the polaron. Finally we discuss how\nour results could be measured in cold atomic experiments."
    },
    {
        "anchor": "The Single Particle Excitation Spectrum of Degenerate Fermi gases in a\n  ring cavity: By considering a spin-$\\frac{1}{2}$ degenerate Fermi gases in a ring cavity\nwhere strong interaction between atoms and light gives rise to a superradiance,\nwe find the cavity dissipation could cause a severe broadening in some special\ncases, breaking down the quasi-particle picture which was constantly assumed in\nmean field theory studies. This broadening happens when the band gap resonant\nwith polariton excitation energy. Interestingly enough, this broadening is\nhighly spin selective depending on how the fermions are filled and the spectrum\nbecomes asymmetric due to dissipation. Further, a non-monotonous dependence of\nthe maximal broadening of the spectrum against cavity decay rate $\\kappa$ is\nfound and the largest broadening emerges at $\\kappa$ comparable to recoil\nenergy.",
        "positive": "Theory of \"magic\" optical traps for Zeeman-insensitive clock transitions\n  in alkalis: Precision measurements and quantum information processing with cold atoms may\nbenefit from trapping atoms with specially engineered, \"magic\" optical fields.\nAt the magic trapping conditions, the relevant atomic properties remain immune\nto strong perturbations by the trapping fields. Here we develop a theoretical\nanalysis of a recently observed magic trapping for especially valuable\nZeeman-insensitive clock transitions in alkali-metal atoms. The involved\nmechanism relies on applying \"magic\" bias B-field along circularly polarized\ntrapping laser field. We map out these B-fields as a function of trapping laser\nwavelength for all commonly-used alkalis."
    },
    {
        "anchor": "Anomalous Transport in the Superfluid Fluctuation Regime: Motivated by a recent experiment in ultracold atoms [ S. Krinner et al.,\nProc. Natl. Acad. Sci. U.S.A 113, 8144 (2016)], we analyze transport of\nattractively interacting fermions through a one-dimensional wire near the\nsuperfluid transition. We show that in a ballistic regime where the conductance\nis quantized in the absence of interaction, the conductance is renormalized by\nsuperfluid fluctuations in reservoirs. In particular, the particle conductance\nis strongly enhanced and the plateau is blurred by emergent bosonic pair\ntransport. For spin transport, in addition to the contact resistance the wire\nitself is resistive, leading to a suppression of the measured spin conductance.\nOur results are qualitatively consistent with the experimental observations.",
        "positive": "Density-wave ordering in a unitary Fermi gas with photon-mediated\n  interactions: A density wave (DW) is a fundamental type of long-range order in quantum\nmatter tied to self-organization into a crystalline structure. The interplay of\nDW order with superfluidity can lead to complex scenarios that pose a great\nchallenge to theoretical analysis. In the last decades, tunable quantum Fermi\ngases have served as model systems for exploring the physics of strongly\ninteracting fermions, including most notably magnetic ordering, pairing and\nsuperfluidity, and the crossover from a Bardeen-Cooper-Schrieffer (BCS)\nsuperfluid to a Bose-Einstein condensate (BEC). Here, we realize a Fermi gas\nfeaturing both strong, tunable contact interactions and photon-mediated,\nspatially structured long-range interactions in a transversely driven\nhigh-finesse optical cavity. Above a critical long-range interaction strength\nDW order is stabilized in the system, which we identify via its superradiant\nlight scattering properties. We quantitatively measure the variation of the\nonset of DW order as the contact interaction is varied across the BCS-BEC\ncrossover, in qualitative agreement with a mean-field theory. The atomic DW\nsusceptibility varies over an order of magnitude upon tuning the strength and\nthe sign of the long-range interactions below the self-ordering threshold,\ndemonstrating independent and simultaneous control over the contact and\nlong-range interactions. Therefore, our experimental setup provides a fully\ntunable and microscopically controllable platform for the experimental study of\nthe interplay of superfluidity and DW order."
    },
    {
        "anchor": "Species-selective confinement of atoms dressed with multiple\n  radiofrequencies: Methods to manipulate the individual constituents of an ultracold quantum gas\nmixture are essential tools for a number of applications, for example the\ndirect quantum simulation of impurity physics. We investigate a scheme in which\nspecies-selective control is achieved using magnetic potentials dressed with\nmultiple radiofrequencies, exploiting the different Land\\'e g-factors of the\nconstituent atomic species. We describe a mixture dressed with two frequencies,\nwhere atoms are confined in harmonic potentials with a controllable degree of\noverlap between the two atomic species. This is then extended to a four\nradiofrequency scheme in which a double well potential for one species is\noverlaid with a single well for the other. The discussion is framed with\nparameters that are suitable for a 85Rb and 87Rb mixture, but is readily\ngeneralised to other combinations.",
        "positive": "Observation of bound state self-interaction in a nano-eV atom collider: Quantum mechanical scattering resonances for colliding particles occur when a\ncontinuum scattering state couples to a discrete bound state between them. The\ncoupling also causes the bound state to interact with itself via the continuum\nand leads to a shift in the bound state energy, but, lacking knowledge of the\nbare bound state energy, measuring this self-energy via the resonance position\nhas remained elusive. Here, we report on the direct observation of\nself-interaction by using a nano-eV atom collider to track the position of a\nmagnetically-tunable Feshbach resonance through a parameter space spanned by\nenergy and magnetic field. Our system of potassium and rubidium atoms displays\na strongly non-monotonic resonance trajectory with an exceptionally large\nself-interaction energy arising from an interplay between the Feshbach bound\nstate and a different, virtual bound state at a fixed energy near threshold."
    },
    {
        "anchor": "Sigature of the universal super Efimov Effect: three-body contact in two\n  dimensional Fermi gases: A new class of universal \"three-body\" bound states has been recently\npredicted theoretically for identical fermions interacting at p-wave resonance\nin two dimensions. This phenomenon is called the super Efimov effect since the\nbinding energies of the states follow a intriguing double exponential scaling.\nHowever, experimental resolution of this scaling is expected to meet formidable\nchallenges. In this work, we introduce a new thermodynamic quantity, the\nthree-body contact $C_\\theta$, to quantify three-body correlations in a two\ndimensional gas composed of the resonantly interacting fermions; the contact\n$C_\\theta$ is the consequence of the underlying universal super Efimov effect\nin the many-body context. We show how $C_\\theta$ affects physical observables\nsuch as the radio-frequency spectrum, the momentum distribution and the atom\nloss rate. Signature of the elusive super Efimov effect in the thermodynamic\nsystem can be pinned down by the detection of the three-body contact $C_\\theta$\nvia these observables.",
        "positive": "Excitation dynamics in a lattice Bose gas within the time-dependent\n  Gutzwiller mean-field approach: The dynamics of the collective excitations of a lattice Bose gas at zero\ntemperature is systematically investigated using the time-dependent Gutzwiller\nmean-field approach. The excitation modes are determined within the framework\nof the linear-response theory as solutions of the generalized Bogoliubov-de\nGennes equations valid in the superfluid and Mott-insulator phases at arbitrary\nvalues of parameters. The expression for the sound velocity derived in this\napproach coincides with the hydrodynamic relation. We calculate the transition\namplitudes for the excitations in the Bragg scattering process and show that\nthe higher excitation modes give significant contributions. We simulate the\ndynamics of the density perturbations and show that their propagation velocity\nin the limit of week perturbation is satisfactorily described by the\npredictions of the linear-response analysis."
    },
    {
        "anchor": "Many-body effects in the excitation spectrum of weakly-interacting\n  Bose-Einstein condensates in one-dimensional optical lattices: In this work, we study many-body excitations of Bose-Einstein condensates\n(BECs) trapped in periodic one-dimensional optical lattices. In particular, we\ninvestigate the impact of quantum depletion onto the structure of the\nlow-energy spectrum and contrast the findings to the mean-field predictions of\nthe Bogoliubov-de Gennes (BdG) equations. Accurate results for the many-body\nexcited states are obtained by applying a linear-response theory atop the\nMCTDHB (multiconfigurational time-dependent Hartree method for bosons)\nequations of motion, termed LR-MCTDHB. We demonstrate for condensates in a\ntriple well that even weak ground-state depletion of around $1\\%$ leads to\nvisible many-body effects in the low-energy spectrum which deviate\nsubstantially from the corresponding BdG spectrum. We further show that these\neffects also appear in larger systems with more lattice sites and particles,\nindicating the general necessity of a full many-body treatment.",
        "positive": "Strong Anderson localization in cold atom quantum quenches: Signatures of strong Anderson localization in the momentum distribution of a\ncold atom cloud after a quantum quench are studied. We consider a quasi\none-dimensional cloud initially prepared in a well defined momentum state, and\nexpanding for some time in a disorder speckle potential. Anderson localization\nleads to a formation of a coherence peak in the \\emph{forward} scattering\ndirection (as opposed to the common weak localization backscattering peak). We\npresent a microscopic, and fully time resolved description of the phenomenon,\ncovering the entire diffusion--to--localization crossover. Our results should\nbe observable by present day technology."
    },
    {
        "anchor": "Beyond Thomas--Fermi analysis of the density profiles of a miscible\n  two-component Bose--Einstein condensate: We investigate a harmonically trapped two-component Bose--Einstein condensate\nwithin the miscible regime, close to its boundaries, for different ratios of\neffective intra- and inter-species interactions. We derive analytically a\nuniversal equation for the density around the different boundaries in one, two\nand three dimensions, for both the coexisting and spatially separated regimes.\nWe also present a general procedure to solve the Thomas--Fermi approximation in\nall three spatial dimensionalities, reducing the complexity of the\nThomas--Fermi problem for the spatially separated case in one and three\ndimensions to a single numerical inversion. Finally, we analytically determine\nthe frontier between the two different regimes of the system.",
        "positive": "Influence of quantum fluctuations on the superfluid critical velocity of\n  a one-dimensional Bose gas: The mean-field Gross-Pitaevskii equation with repulsive interactions exhibits\nfrictionless flow when stirred by an obstacle below a critical velocity. Here\nwe go beyond the mean-field approximation to examine the influence of quantum\nfluctuations on this threshold behaviour in a one-dimensional Bose gas in a\nring. Using the truncated Wigner approximation, we perform simulations of\nensembles of trajectories where the Bose gas is stirred with a repulsive\nobstacle below the mean-field critical velocity. We observe the probabilistic\nformation of grey solitons which subsequently decay, leading to an increase in\nthe momentum of the fluid. The formation of the first soliton leads to a\nsoliton cascade, such that the fluid rapidly accelerates to minimise the speed\ndifference with the obstacle. We measure the initial rate of momentum transfer,\nand relate it to macroscopic tunnelling between quantised flow states in the\nring."
    },
    {
        "anchor": "Energy response and spatial alignment of the perturbed electron gas: We present extensive new \\emph{ab initio} path integral Monte Carlo (PIMC)\nsimulations of the harmonically perturbed uniform electron gas (UEG) for\ndifferent densities and temperatures. This allows us to study the linear\nresponse of the UEG with respect to different contributions to the total energy\nfor different wave numbers. We find that the induced change in the interaction\nenergy exhibits a non-monotonic behaviour, and becomes negative for\nintermediate wave numbers. This effect is strongly dependent on the coupling\nstrength and can be traced back to the spatial alignment of electrons\nintroduced in earlier works [T.~Dornheim \\emph{et al.}, Communications Physics\n\\textbf{5}, 304 (2022)]. The observed quadratic dependence on the perturbation\namplitude in the limit of weak perturbations and the quartic dependence of the\nperturbation amplitude corrections are consistent with linear and non-linear\nversions of the density stifness theorem. All PIMC simulation results are\nfreely available online and can be used to benchmark new methods, or as input\nfor other calculations.",
        "positive": "Dynamics of order-disorder and complexity for interacting bosons in\n  optical lattice: The present work reports on the dynamical measures of order, disorder and\ncomplexity for the interacting bosons in optical lattice. We report results\nboth for the relaxed state as well as quench dynamics. Our key observations\nare: (1) Lattice depth can be taken as order-disorder parameter. (2) The\nsuperfluid to Mott insulator transition can be treated as `order-disorder'\ntransition. Our main motivation is to find how the system organize by itself\nduring quench and how it optimizes the complexity. We find dynamical measures\nof order and disorder are more sensitive tool than entropy measures. We\nspecifically calculate the time scale of entry and exit of different phases\nduring time evolution. Initially the system exhibits collapse revival trend,\nhowever gradually looses its ability to turn back to superfluid phase and\nfinally Settle to Mott insulator phase."
    },
    {
        "anchor": "Localization of ultracold atoms in incommensurate spin-orbit-coupling\n  and Zeeman lattices: We consider a particle governed by a one-dimensional Hamiltonian in which\nartificial periodic spin-orbit coupling and Zeeman lattice have incommensurate\nperiods. Using best rational approximations to such quasiperiodic Hamiltonian,\nthe problem is reduced to description of spinor states in a superlattice. In\nthe absence of a constant Zeeman splitting, the system acquires an additional\nsymmetry, which hinders the localization. However, if the lattices are deep\nenough, then localized states can appear even for Zeeman field with zero or\nsmall mean value. Spatial distribution of localized modes is nearly uniform and\nis directly related to the topological properties of the effective\nsuperlattice: center-of-mass coordinates of modes are determined by Zak phases\ncomputed from the superlattice band structure. The best rational approximations\nfeature the `memory' effect: each rational approximation holds the information\nabout the energies and spatial distribution of the modes obtained under\npreceding, less accurate approximations. Dispersion of low-energy initial\nwavepackets is characterized by the law $\\propto t^\\beta$ with $\\beta$ varying\nbetween $1/2$ at the initial stage and $1$ at longer, but still finite-time,\nevolution. The dynamics of initial wavepackets, exciting mainly localized\nmodes, manifests quantum revivals.",
        "positive": "Entanglement growth and correlation spreading with variable-range\n  interactions in spin and fermionic tunnelling models: We investigate the dynamics following a global parameter quench for two 1D\nmodels with variable-range power-law interactions: a long-range transverse\nIsing model, which has recently been realised in chains of trapped ions, and a\nlong-range lattice model for spinless fermions with long-range tunnelling. For\nthe transverse Ising model, the spreading of correlations and growth of\nentanglement are computed using numerical matrix product state techniques, and\nare compared with exact solutions for the fermionic tunnelling model. We\nidentify transitions between regimes with and without an apparent linear light\ncone for correlations, which correspond closely between the two models. For\nlong-range interactions (in terms of separation distance r, decaying slower\nthan 1/r), we find that despite the lack of a light-cone, correlations grow\nslowly as a power law at short times, and that -- depending on the structure of\nthe initial state -- the growth of entanglement can also be sublinear. These\nresults are understood through analytical calculations, and should be\nmeasurable in experiments with trapped ions."
    },
    {
        "anchor": "Dynamics of a massive superfluid vortex in $r^k$ confining potentials: We study the motion of a superfluid vortex in condensates having different\nbackground density profiles, ranging from parabolic to uniform. The resulting\neffective point-vortex model for a generic power-law potential $\\propto r^k$\ncan be experimentally realized with recent advances in optical-trapping\ntechniques. Our analysis encompasses both empty-core and filled-core vortices.\nIn the latter case, the vortex acquires a mass due to the presence of\ndistinguishable atoms located in its core. The axisymmetry allows us to reduce\nthe coupled dynamical equations of motion to a single radial equation with an\neffective potential $V_{\\rm eff}$. In many cases, $V_{\\rm eff}$ has a single\nminimum, where the vortex precesses uniformly. The dynamics of the vortex and\nthe localized massive core arises from the dependence of the energy on the\nradial position of the vortex and from the $r^k$ trap potential. We find that a\npositive vortex with small mass orbits in the positive direction, but the sense\nof precession can reverse as the core mass increases. Early experiments and\ntheoretical studies on two-component vortices found some qualitatively similar\nbehavior.",
        "positive": "Virial expansion of a harmonically trapped Fermi gas across a narrow\n  Feshbach resonance: We theoretically investigate the high-temperature thermodynamics of a\nharmonically trapped Fermi gas across a narrow Feshbach resonance, by using the\nsecond-order quantum virial expansion, and point out some new features compared\nto the broad resonance. The interatomic interaction is modeled by the\npseudopotential with an additional parameter, i.e., the effective range, to\ncharacterize the narrow resonance width. Deeply inside the width of a narrow\nFeshbach resonance, we find the second virial coefficient evolves with the\neffective range from the well-known universal value 1/4 in the broad-resonance\nlimit to one another value 1/2 in the narrow-resonance limit. This means the\nFermi gas is more strongly interacted at the narrow resonance. In addition, far\nbeyond the resonance width, we find the harmonically trapped Fermi gas still\nmanifests appreciable interaction effect across a narrow Feshbach resonance,\nwhich is contrary to our knowledge of the broad Feshbach resonance. All our\nresults can be directly tested in current narrow Feshbach resonance\nexperiments, which are generally carried out in a harmonic trap."
    },
    {
        "anchor": "Instabilities of a Bose-Einstein condensate with mixed nonlinear and\n  linear lattices: Bose-Einstein condensates (BECs) in periodic potentials generate interesting\nphysics on the instabilities of Bloch states. The lowest-energy Bloch states of\nBECs in pure nonlinear lattices are dynamically and Landau unstable, which\nbreaks down BEC superfluidity. In this paper we propose to use an out-of-phase\nlinear lattice to stabilize them. The stabilization mechanism is revealed by\nthe averaged interaction. We further incorporate a constant interaction into\nBECs with mixed nonlinear and linear lattices, and reveal its effect on the\ninstabilities of Bloch states in the lowest band.",
        "positive": "Generation and decay of Higgs mode in a strongly interacting Fermi gas: We investigate the life cycle of the large amplitude Higgs mode in strongly\ninteracting superfluid Fermi gas. Through numerical simulations with\ntime-dependent density-functional theory and the technique of the interaction\nquench, we verify the previous theoretical predictions on the mode's frequency.\nNext, we demonstrate that the mode is dynamically unstable against external\nperturbation and qualitatively examine the emerging state after the mode\ndecays. The post-decay state is characterized by spatial fluctuations of the\norder parameter and density at scales comparable to the superfluid coherence\nlength scale. We identify similarities with FFLO states, which become more\nprominent at higher dimensionalities and nonzero spin imbalances."
    },
    {
        "anchor": "Microscopy of many-body states in optical lattices: Ultracold atoms in optical lattices have proven to provide an extremely clean\nand controlled setting to explore quantum many-body phases of matter. Now,\nimaging of atoms in such lattice structures has reached the level of\nsingle-atom sensitive detection combined with the highest resolution down to\nthe level of individual lattice sites. This has opened up fundamentally new\nopportunities for the characterization and the control of quantum many-body\nsystems. Here we give a brief overview of this field and explore the\nopportunities offered for future research.",
        "positive": "Dynamics of quantum double dark-solitons and an exact finite-size\n  scaling of Bose-Einstein condensation: We show several novel aspects in the exact non-equilibrium dynamics of\nquantum double dark-soliton states in the Lieb-Liniger model for the\none-dimensional Bose gas with repulsive interactions. We also show an exact\nfinite-size scaling of the fraction of the Bose-Einstein condensation (BEC) in\nthe ground state, which should characterize the quasi-BEC in quantum double\ndark-soliton states that we assume to occur in the weak coupling regime. First,\nwe show the exact time evolution of the density profile in the quantum state\nassociated with a quantum double dark-soliton by the Bethe ansatz. Secondly, we\nderive a kind of macroscopic quantum wave-function effectively by exactly\nevaluating the square amplitude and phase profiles of the matrix element of the\nfield operator between the quantum double dark-soliton states. The profiles are\nclose to those of dark-solitons particularly in the weak-coupling regime. Then,\nthe scattering of two notches in the quantum double dark-soliton state is\nexactly demonstrated. It is suggested from the above observations that the\nquasi-BEC should play a significant role in the dynamics of quantum double\ndark-soliton states. If the condensate fraction is close to 1, the quantum\nstate should be well approximated by the quasi-BEC state where the mean-field\npicture is valid."
    },
    {
        "anchor": "Dissipative Luttinger liquids: We investigate a one dimensional quantum fluid coupled to a dissipative bath.\nThe quantum fluid is captured by the canonical Luttinger liquid; the bath is\ngiven by the model of Caldeira and Leggett, i.e. a tower of oscillators coupled\nlinearly to the fluid density, $\\rho$. The bath can be integrated out exactly,\nproducing an effective interaction for the fluid that is nonlocal in time; we\nargue that the form corresponding to Ohmic dissipation is generic. Compared to\nprevious works, we compute correlation functions for this minimal model without\napproximation, including at finite temperature $T>0$. From these and a Kubo\ncalculation, we conclude that arbitrary dissipation destroys the perfect\nconductivity of the Luttinger liquid via Zeno localization, even in the absence\nof a spatial potential; from RG analysis of harmonic terms, we also find that\nthe open Luttinger liquid is significantly more prone to localization by such\npotentials, in contrast to the usual intuition that baths make systems less\nlocalized.",
        "positive": "Structured hetero-symmetric quantum droplets: We predict that Lee-Huang-Yang effect makes it possible to create stable\nquantum droplets (QDs) in binary Bose-Einstein condensates with a\nhetero-symmetric or hetero-multipole structure, i.e., different vorticities or\nmultipolarities in their components. The QDs feature flat-top shapes when\neither chemical potential \\mu_1,2 of the droplet approaches an edge of a\ntriangular existence domain in the (\\mu_1,\\mu_2) plane. QDs with different\nvorticities of their components are stable against azimuthal perturbations,\nprovided that the norm of one component is large. We also present multipole\nstates, in which the interaction with a strong fundamental component balances\nthe repulsion between poles with opposite signs in the other component, leading\nto the formation of stable bound states. Extended stability domains are\nobtained for dipole QDs; tripole ones exist but are unstable, while quadrupoles\nare stable in a narrow region. The results uncover the existence of much richer\nfamilies of stable binary QDs in comparison to states with identical\ncomponents."
    },
    {
        "anchor": "Relativistic quantum effects of Dirac particles simulated by ultracold\n  atoms: Quantum simulation is a powerful tool to study a variety of problems in\nphysics, ranging from high-energy physics to condensed-matter physics. In this\narticle, we review the recent theoretical and experimental progress in quantum\nsimulation of Dirac equation with tunable parameters by using ultracold neutral\natoms trapped in optical lattices or subject to light-induced synthetic gauge\nfields. The effective theories for the quasiparticles become relativistic under\ncertain conditions in these systems, making them ideal platforms for studying\nthe exotic relativistic effects. We focus on the realization of one, two, and\nthree dimensional Dirac equations as well as the detection of some relativistic\neffects, including particularly the well-known Zitterbewegung effect and Klein\ntunneling. The realization of quantum anomalous Hall effects is also briefly\ndiscussed.",
        "positive": "Spin and density self-ordering in dynamic polarization gradients fields: We study the zero-temperature quantum phase diagram for a two-component\nBose-Einstein condensate in an optical cavity. The two atomic spin states are\nRaman coupled by two transverse orthogonally-polarized, blue detuned plane-wave\nlasers inducing a repulsive cavity potential. For weak pump the lasers favor a\nstate with homogeneous density and predefined uniform spin direction. When one\npump laser is polarized parallel to the cavity mode polarization, the photons\ncoherently scattered into the resonator induce a polarization gradient along\nthe cavity axis, which mediates long-range density-density, spin-density, and\nspin-spin interactions. We show that the coupled atom-cavity system implements\ncentral aspects of the $t$-$J$-$V$-$W$ model with a rich phase diagram. At the\nmean-field limit we identify at least four qualitatively distinct density- and\nspin-ordered phases including ferro- and anti-ferromagnetic order along the\ncavity axis, which can be controlled via the pump strength and detuning. A real\ntime observation of amplitude and phase of the emitted fields bears strong\nsignatures of the realized phase and allows for real-time determination of\nphase transition lines. Together with measurements of the population imbalance\nmost properties of the phase diagram can be reconstructed."
    },
    {
        "anchor": "Anomalous Expansion of Attractively Interacting Fermionic Atoms in an\n  Optical Lattice: Strong correlations can dramatically modify the thermodynamics of a quantum\nmany-particle system. Especially intriguing behaviour can appear when the\nsystem adiabatically enters a strongly correlated regime, for the interplay\nbetween entropy and strong interactions can lead to counterintuitive effects. A\nwell known example is the so-called Pomeranchuk effect, occurring when liquid\n3He is adiabatically compressed towards its crystalline phase. Here, we report\non a novel anomalous, isentropic effect in a spin mixture of attractively\ninteracting fermionic atoms in an optical lattice. As we adiabatically increase\nthe attraction between the atoms we observe that the gas, instead of\ncontracting, anomalously expands. This expansion results from the combination\nof two effects induced by pair formation in a lattice potential: the\nsuppression of quantum fluctuations as the attraction increases, which leads to\na dominant role of entropy, and the progressive loss of the spin degree of\nfreedom, which forces the gas to excite additional orbital degrees of freedom\nand expand to outer regions of the trap in order to maintain the entropy. The\nunexpected thermodynamics we observe reveal fundamentally distinctive features\nof pairing in the fermionic Hubbard model.",
        "positive": "Single-shot reconstruction of the density profile of a dense atomic gas: Partial transfer absorption imaging (PTAI) of ultracold atoms allows for\nrepeated and minimally-destructive measurements of an atomic ensemble. Here, we\npresent a reconstruction technique based on PTAI that can be used to piece\ntogether the non-uniform spatial profile of high-density atomic samples using\nmultiple measurements. We achieved a thirty-fold increase of the effective\ndynamic range of our imaging, and were able to image otherwise saturated\nsamples with unprecedented accuracy of both low- and high-density features."
    },
    {
        "anchor": "Three-body spin mixing in spin-1 Bose-Einstein condensates: We study zero-energy collisions between three identical bosons with spin $f =\n1$ interacting via pairwise potentials. We quantify the corresponding\nthree-body scattering hypervolumes, which parametrize the effective three-body\ninteraction strengths in a many-body description of spin-1 Bose-Einstein\ncondensates. Our results demonstrate universal behavior of the scattering\nhypervolumes for strong $s$- and $p$-wave two-body interactions. At weak\ninteractions we find that the real parts of the scattering hypervolumes are\npredominantly determined by hard-hyperspherelike collisions which we\ncharacterize by a simple formula. With this universal result we estimate that\nspin mixing via three-body collisions starts to dominate over two-body spin\nmixing at a typical particle density of $10^{17}~\\mathrm{cm}^{-3}$ for\n${}^{23}$Na and ${}^{41}$K spinor condensates. This density can be reduced by\ntuning the two-body interactions to an $s$- or $p$-wave dimer resonance or to a\npoint where two-body spin mixing effectively vanishes. Another possibility to\nobserve effects of three-body spin mixing involves the application of weak\nmagnetic fields to cancel out the effective two-body interaction strength in\nthe characteristic timescale describing the spin dynamics.",
        "positive": "Systematic vector solitary waves from their linear limits in\n  one-dimensional $n$-component Bose-Einstein condensates: We systematically construct a series of vector solitary waves in harmonically\ntrapped one-dimensional three-, four-, and five-component Bose-Einstein\ncondensates. These stationary states are continued in chemical potentials from\nthe analytically tractable low-density linear limit of respective states, as\nindependent linear quantum harmonic oscillator states, to the high-density\nnonlinear Thomas-Fermi regime. A systematic interpolation procedure is proposed\nto achieve this sequential continuation via a trajectory in the\nmulti-dimensional space of the chemical potentials. The Bogolyubov-de Gennes\n(BdG) spectra analysis shows that all of the states considered herein can be\nfully stabilized in suitable chemical potential intervals in the Thomas-Fermi\nregime. Finally, we present some typical $SU(n)$-rotation-induced and\ndriving-induced dynamics. This method can be extended to higher dimensions and\nshows significant promise for finding a wide range of solitary waves ahead."
    },
    {
        "anchor": "Strongly Correlated Quantum Gas Prepared by Direct Laser Cooling: We create a one-dimensional strongly correlated quantum gas of $^{133}$Cs\natoms with attractive interactions by direct laser cooling in 300~ms. After\ncompressing and cooling the optically trapped atoms to the vibrational ground\nstate along two tightly confined directions, the emergence of a non-Gaussian\ntime-of-flight distribution along the third, weakly confined direction reveals\nthat the system enters a quantum degenerate regime. We observe a strong\nreduction of two- and three-body spatial correlations and infer that the atoms\nare directly cooled into a highly correlated excited metastable state, known as\na super-Tonks-Girardeau gas.",
        "positive": "BCS-BEC crossover-like phenomena driven by quantum-size effects in\n  quasi-one-dimensional fermionic condensates: Quantum confinement is known to influence fermionic condensates, resulting in\nquantum-size oscillations of superfluid/superconducting properties. Here we\nshow that the impact of quantum-size effects is even more dramatic. Under\nrealistic conditions, a significant phase-space reconfiguration induced by\nquantum-size effects opens a quasi-molecule channel in the fermionic pairing so\nthat the condensed pairs exhibit features typical of a molecular state. As an\nillustration we consider a quasi-one-dimensional fermionic condensate, as\nrealized, e.g., in cigar-shaped atomic Fermi gases or superconducting quantum\nwires. In this case the transverse quantization of the particle motion favors\npairing through a coherent superposition of quantum channels that are formed\ndue to the grouping of single-particle levels into a series of well\ndistinguished subbands. Whenever the bottom of a subband approaches the Fermi\nlevel, the longitudinal spatial distribution of fermions in a condensed pair\nbecomes strongly localized within the corresponding quantum channel. The\nfermionic pairs in this channel resemble molecules with bosonic character."
    },
    {
        "anchor": "Low-momentum dynamic structure factor of a strongly interacting Fermi\n  gas at finite temperature: The Goldstone phonon and its Landau damping: We develop a microscopic theory of dynamic structure factor to describe the\nBogoliubov-Anderson-Goldstone phonon mode and its damping rate in a strongly\ninteracting Fermi gas at finite temperature. It is based on a density\nfunctional approach - the so-called superfluid local density approximation. The\naccuracy of the theory is quantitatively examined by comparing the theoretical\npredictions with the recent experimental measurements for the local dynamic\nstructure factor of a nearly homogeneous unitary Fermi gas at low transferred\nmomentum {[}S. Hoinka \\textit{et al.}, Nat. Phys. \\textbf{13}, 943 (2017){]},\nwithout any free parameters. We calculate the dynamic structure factor as\nfunctions of temperature and transferred momentum, and determine the\ntemperature evolution of the phonon damping rate, by considering the dominant\ndecay process of the phonon mode via scatterings off fermionic quasiparticles.\nThese predictions can be confronted with future Bragg scattering experiments on\na unitary Fermi gas near the superfluid transition.",
        "positive": "Glass-like Behavior in a System of One Dimensional Fermions after a\n  Quantum Quench: We investigate the non-equilibrium relaxation dynamics of a one dimensional\nsystem of interacting spinless fermions near the XXZ integrable point. We\nobserve two qualitatively different regimes: close to integrability and for low\nenergies the relaxation proceeds in two steps (prethermalization scenario),\nwhile for large energies and/or away from integrability the dynamics develops\nin a single step. When the integrability breaking parameter is below a certain\nfinite threshold and the energy of the system is sufficiently low the lifetime\nof the metastable states increases abruptly by several orders of magnitude,\nresembling the physics of glassy systems. This is reflected in a sudden jump in\nthe relaxation timescales. We present results for finite but large systems and\nfor large times compared to standard numerical methods. Our approach is based\non the construction of equations of motion for one- and two-particle\ncorrelation functions using projection operator techniques."
    },
    {
        "anchor": "Hydrodynamic model of BEC with anisotropic short range interaction and\n  the bright solitons in the repulsive BEC: The quantum hydrodynamic model is developed for the axial symmetric\nanisotropic short-range interaction. The quantum stress tensor presents the\ninteraction. It is derived up to the third order by the interaction radius. The\nfirst order by the interaction radius contains the isotropic part only. It\nleads to the interaction in the Gross-Pitaevskii approximation. Terms existing\nin the third order by the interaction radius are caused by the isotropic and\nnonisotropic parts of the interaction. Each of them introduces the interaction\nconstant. Therefore, three interaction constants are involved in the model.\nAtoms, except the alkali and alkali-earth atoms, can have anisotropic potential\nof interaction, particularly it is demonstrated for the lanthanides. The\nshort-wavelength instability caused by the nonlocal terms appears in the\nBogoliubov spectrum. Conditions for the stable and unstable behaviour are\ndescribed. Bright solitons in the repulsive BEC are studied under influence of\nthe anisotropic short-range interaction in the BEC of one species. Area of\nexistence of this bright solitons corresponds to the area of the instability of\nthe Bogoliubov spectrum. Approximate reduction of the nonlocal nonlinearity to\nthe quintic nonlinearity at the description of the bright solitons is\ndemonstrated either.",
        "positive": "Tunable anisotropic superfluidity in an optical kagome superlattice: We study the phase diagram of the Bose-Hubbard model on the kagome lattice\nwith a broken sublattice symmetry. Such a superlattice structure can naturally\nbe created and tuned by changing the potential offset of one sublattice in the\noptical generation of the frustrated lattice. The superstructure gives rise to\na rich quantum phase diagram, which is analyzed by combining Quantum Monte\nCarlo simulations with the Generalized Effective Potential Landau Theory. Mott\nphases with non-integer filling and a characteristic order along stripes are\nfound, which show a transition to a superfluid phase with an anisotropic\nsuperfluid density. Surprisingly, the direction of the superfluid anisotropy is\nchanging between different symmetry directions as a function of the particle\nnumber or the hopping strength. Finally, we discuss characteristic signatures\nof anisotropic phases in time-of-flight absorption measurements."
    },
    {
        "anchor": "Equilibration via Gaussification in fermionic lattice systems: In this work, we present a result on the non-equilibrium dynamics causing\nequilibration and Gaussification of quadratic non-interacting fermionic\nHamiltonians. Specifically, based on two basic assumptions - clustering of\ncorrelations in the initial state and the Hamiltonian exhibiting delocalizing\ntransport - we prove that non-Gaussian initial states become locally\nindistinguishable from fermionic Gaussian states after a short and well\ncontrolled time. This relaxation dynamics is governed by a power-law\nindependent of the system size. Our argument is general enough to allow for\npure and mixed initial states, including thermal and ground states of\ninteracting Hamiltonians on and large classes of lattices as well as certain\nspin systems. The argument gives rise to rigorously proven instances of a\nconvergence to a generalized Gibbs ensemble. Our results allow to develop an\nintuition of equilibration that is expected to be more generally valid and\nrelates to current experiments of cold atoms in optical lattices.",
        "positive": "Correlation function of weakly interacting bosons in a disordered\n  lattice: One of the most important issues in disordered systems is the interplay of\nthe disorder and repulsive interactions. Several recent experimental advances\non this topic have been made with ultracold atoms, in particular the\nobservation of Anderson localization, and the realization of the disordered\nBose-Hubbard model. There are however still questions as to how to\ndifferentiate the complex insulating phases resulting from this interplay, and\nhow to measure the size of the superfluid fragments that these phases entail.\nIt has been suggested that the correlation function of such a system can give\nnew insights, but so far little experimental investigation has been performed.\nHere, we show the first experimental analysis of the correlation function for a\nweakly interacting, bosonic system in a quasiperiodic lattice. We observe an\nincrease in the correlation length as well as a change in shape of the\ncorrelation function in the delocalization crossover from Anderson glass to\ncoherent, extended state. In between, the experiment indicates the formation of\nprogressively larger coherent fragments, consistent with a fragmented BEC, or\nBose glass."
    },
    {
        "anchor": "Topological Supersolidity of Dipolar Fermi Gases in a Spin-Dependent\n  Optical Lattice: We investigate topological supersolidity of dipolar Fermi gases in a\nspin-dependent 2D optical lattice. Numerical results show that the topological\nsupersolid states can be synthesized via the combination of topological\nsuperfluid states with the stripe order, where the topological superfluid\nstates generated with dipolar interaction possess the $\\Delta_{x}+i\\Delta_{y}$\norder, and it is of D class topological classification. By adjusting the ratio\nbetween hopping amplitude $t_{x}/t_{y}$ and interaction strength $U$ with\ndipole orientation $\\phi \\approx \\frac{\\pi}{4}$, the system will undergo phase\ntransitions among the $p_{x}+ip_{y}$-wave topological superfluid state, the\np-wave superfluid state, and the topological supersolid state. The topological\nsupersolid state is proved to be stable by the positive sign of the inverse\ncompressibility. We design an experimental protocol to realize the staggered\nnext-next-nearest-neighbour hopping via the laser assisted tunneling technique,\nwhich is the key to synthesize topological supersolid states.",
        "positive": "Dynamics and Quantum correlations in Two independently driven Rydberg\n  atoms with distinct laser fields: We study the population dynamics in a two-atom setup in which each atom is\ndriven independently by different light fields, but coupling the same Rydberg\nstate. In particular, we look at how an offset in the Rabi frequencies between\ntwo atoms influences the dynamics. We find novel features such as amplifying\nthe Rabi frequency of one atom, together with strong Rydberg-Rydberg\ninteractions freezes the dynamics in the second atom. We characterize the\nRydberg-biased freezing phenomenon in detail, with effective Hamiltonians\nobtained for various limits of the system parameters. In the absence of\nRabi-offset, the doubly excited state population exhibits a Lorentzian profile\nas a function of interaction, whereas for very small offsets it shows splitting\nand thus peaks. Using an effective Hamiltonian as well as the perturbation\ntheory for weak interactions, we show that the peak arises from a competition\nbetween Rabi-offset and Rydberg-Rydberg interactions when both are sufficiently\nsmall, together with the Rydberg blockade at large interactions. The effective\nHamiltonians provide us with analytical results which are in an excellent\nagreement with full numerical solutions. Also, we analyze the growth and the\ndynamics of quantum correlations such as entanglement entropy and quantum\ndiscord for the coherent dynamics. We extend our studies to the dissipative\ncase in which the spontaneous emission from the Rydberg state is taken into\naccount and in particular, we look at the purity and quantum discord of the\nsteady states. To conclude, our studies reveal that the local manipulation of\nan atom using Rabi-offset can be an ideal tool to control the quantum\ncorrelations and in general, quantum states of the composite two-qubit systems."
    },
    {
        "anchor": "Trapped ideal Bose gas with a few heavy impurities: We formulate a general scheme for calculation of thermodynamic properties of\nideal Bose gas with microscopic number of static impurities immersed, when the\nsystem is loaded in the harmonic trapping potential with quasi-1D and quasi-2D\nconfigurations. The binding energy of a single impurity and a detailed study of\nthe medium-induced Casimir-like forces between two impurities in trapped Bose\ngas are numerically calculated in wide range of temperatures and interaction\nstrengths.",
        "positive": "Supersolid Devil's Staircases of Spin-Orbit-Coupled Bosons in Optical\n  Lattices: We study the emergence of supersolid Devil's staircases of spin-orbit coupled\nbosons loaded in optical lattices. We consider two- and three-dimensional\nsystems of pseudo-spin-$1/2$ bosons interacting via local spin-dependent\ninteractions. These interactions together with spin-orbit coupling produce\nlength scales that are commensurate to the lattice spacing. This\ncommensurability leads to Devil's staircases of supersolids, with fractal\nHausdorff dimensions, which arise from uniform superfluid phases. We show that\numklapp processes are essential for the existence of commensurate supersolids,\nand that without them the Devil's staircase does not exist. Lastly, we\nemphasize the generality of our results, suggest experiments that can unveil\nthese unusual predictions, and discuss potential applications to the case of\n$^{87}$Rb."
    },
    {
        "anchor": "Collective pairing of resonantly coupled microcavity polaritons: We consider the possible phases of microcavity polaritons tuned near a\nbipolariton Feshbach resonance. We show that, as well as the regular polariton\nsuperfluid phase, a \"molecular\" superfluid exists, with (quasi-)long-range\norder only for pairs of polaritons. We describe the experimental signatures of\nthis state. Using variational approaches we find the phase diagram (critical\ntemperature, density and exciton-photon detuning). Unlike ultracold atoms, the\nmolecular superfluid is not inherently unstable, and our phase diagram suggests\nit is attainable in current experiments.",
        "positive": "Measure synchronization in quantum many-body systems: The concept of measure synchronization between two coupled quantum many-body\nsystems is presented. In general terms we consider two quantum many-body\nsystems whose dynamics gets coupled through the contact particle-particle\ninteraction. This coupling is shown to produce measure synchronization, a\ngeneralization of synchrony to a large class of systems which takes place in\nabsence of dissipation. We find that in quantum measure synchronization, the\nmany-body quantum properties for the two subsystems, e.g. condensed fractions\nand particle fluctuations, behave in a coordinated way. To illustrate the\nconcept we consider a simple case of two species of bosons occupying two\ndistinct quantum states. Measure synchronization can be readily explored with\nstate-of-the-art techniques in ultracold atomic gases and, if propertly\ncontrolled, be employed to share quantum correlations between different degrees\nof freedom."
    },
    {
        "anchor": "Currents algebra for the two-sites Bose-Hubbard model: I present a currents algebra for the two-sites Bose-Hubbard model, generalize\nthe Heisenberg equation of motion to write the second time derivative of the\ncurrents operators and use it to get the quantum dynamics of the currents. For\ndifferent choices of the Hamiltonian parameters I get different currents\ndynamics and determine the period of the oscillations in function of the\nparameters.",
        "positive": "Effect of Weak Disorder on the BCS-BEC crossover in a two-dimensional\n  Fermi Gas: In this article we study the two-dimensional (2D) ultracold Fermi gas with\nweak impurity in the framework of mean-field theory where the impurity is\nintroduced through Gaussian fluctuations. We have investigated the role of the\nimpurity by studying the experimentally accessible quantities such as\ncondensate fraction and equation of state of the ultracold systems. Our\nanalysis reveals that, at the crossover the disorder enhances superfluidity,\nwhich we attribute to the unique nature of the unitary region and to the\ndimensional effect."
    },
    {
        "anchor": "Holographic imaging of an array of submicron light scatterers at low\n  photon numbers: We experimentally test a recently proposed holographic method for imaging\ncoherent light scatterers which are distributed over a 2-dimensional grid. In\nour setup the scatterers consist of a back-illuminated, opaque mask with\nsubmicron-sized holes. We study how the imaging fidelity depends on various\nparameters of the set-up. We observe that a few hundred scattered photons per\nhole already suffice to obtain a fidelity of 96% to correctly determine whether\na hole is located at a given grid point. The holographic method demonstrated\nhere has a high potential for applications with ultracold atoms in optical\nlattices.",
        "positive": "Baryon squishing in synthetic dimensions by effective $SU(M)$ gauge\n  fields: We investigate few body physics in a cold atomic system with synthetic\ndimensions (Celi et al., PRL 112, 043001 (2014)) which realizes a Hofstadter\nmodel with long-ranged interactions along the synthetic dimension. We show that\nthe problem can be mapped to a system of particles (with $SU(M)$ symmetric\ninteractions) which experience an $SU(M)$ Zeeman field at each lattice site\n{\\em and} a non-Abelian $SU(M)$ gauge potential that affects their hopping from\none site to another. This mapping brings out the possibility of generating {\\em\nnon-local} interactions (interaction between particles at different physical\nsites). It also shows that the non-Abelian gauge field, which induces a\nflavor-orbital coupling, mitigates the \"baryon breaking\" effects of the Zeeman\nfield. For $M$ particles, the $SU(M)$ singlet baryon which is site localized,\nis \"deformed\" to be a nonlocal object (\"squished\" baryon) by the combination of\nthe Zeeman and the non-Abelian gauge potential, an effect that we conclusively\ndemonstrate by analytical arguments and exact (numerical) diagonalization\nstudies. These results not only promise a rich phase diagram in the many body\nsetting, but also suggests possibility of using cold atom systems to address\nproblems that are inconceivable in traditional condensed matter systems. As an\nexample, we show that the system can be adapted to realize Hamiltonians akin to\nthe $SU(M)$ random flux model."
    },
    {
        "anchor": "Breathing modes of repulsive polarons in Bose-Bose mixtures: We consider impurity atoms embedded in a two-component Bose-Einstein\ncondensate in a quasi-one dimensional regime. We study the effects of repulsive\ncoupling between the impurities and Bose species on the equilibrium of the\nsystem for both miscible and immiscible mixtures by numerically solving the\nunderlying coupled Gross-Pitaevskii equations. Our results reveal that the\npresence of impurities may lead to a miscible-immiscible phase transition due\nto the interaction of the impurities and the two condensates. Within the realm\nof the Bogoliubov-de Gennes equations we calculate the quantum fluctuations due\nto the different types of interactions. The breathing modes and the time\nevolution of harmonically trapped impurities in both homogeneous and\ninhomogeneous binary condensates are deeply discussed in the miscible case\nusing variational and numerical means. We show in particular that the\nself-trapping, the miscibility and the inhomogeneity of the trapped Bose\nmixture may strongly modify the low-lying excitations and the dynamical\nproperties of impurities. The presence of phonons in the homogeneous Bose\nmixture gives rise to the damping of breathing oscillations of impurities\nwidth.",
        "positive": "Exotic Pairing Structures in Population-Imbalanced Fermionic Systems:\n  Dynamics as a Probe: We investigate a population-imbalanced two-species fermionic system where the\nresonantly-paired fermions combine to form bosonic molecules via Feshbach\ninteraction. We study the dynamics of the intrinsic quantum fluctuations of the\nsystem. It is shown that the natural fluctuations of the condensate fraction\nconsists of a fixed number of periodic components : indicating that these\noscillations do not die out, and are sustained in the mean field dynamics of\nthe system. These frequency components bear distinct signatures of the nature\nof pairing present in the system. We describe how a time dependent external\nmagnetic field can be used to locate these oscillation frequencies, and thus to\nexplore the momentum space structure of the population imbalanced system. We\npropose that this method can be used as an indirect experimental probe for\ndetecting exotic phases like the breached pair state, FFLO state, and a\nphase-separated state comprising of BCS and normal regions."
    },
    {
        "anchor": "Collective Modes in a Two-band Superfluid of Ultracold Alkaline-earth\n  Atoms Close to an Orbital Feshbach Resonance: We discuss the collective modes in an alkaline-earth Fermi gas close to an\norbital Feshbach resonance. Unlike the usual Feshbach resonance, the orbital\nFeshbach resonance in alkaline-earth atoms realizes a two-band superfluid\nsystem where the fermionic nature of both the open and the closed channel has\nto be taken into account. We show that apart from the usual Anderson-Bogoliubov\nmode which corresponds to the oscillation of total density, there also appears\nthe long-sought Leggett mode corresponding to the oscillation of relative\ndensity between the two channels. The existence of the phonon and the Leggett\nmodes and their evolution are discussed in detail. We show how these collective\nmodes are reflected in the density response of the system.",
        "positive": "Nonlocal interactions in a BEC: an Analogue Gravity perspective: We add a minimal correction term to the local Gross-Pitaevskii equation to\nrepresent non-locality in the interactions. We show that the effective minimal\nnon-locality can make the healing length decrease more rapidly with the\nincrease of $s$-wave scattering length leaving the expression of the velocity\nof sound unaltered. We discuss the implication of this result for a\nBose-Einstein Condensate (BEC) being used as an analogue gravity system. The\npresented result is important in the context of condensed matter physics as\nwell because one can considerably change the size of a quantized vortex at\nfinite $s$-wave scattering length by tuning the healing length."
    },
    {
        "anchor": "Analytic solutions for the spatial character and coherence properties of\n  light scattered from two dipole-coupled atoms: Analytic solutions for steady-state expectation values of atomic quantities\nand second order correlations are obtained for a fully quantum treatment of two\nstationary dipole-coupled atoms driven in a standard geometric configuration by\na near resonant laser. Explicit expressions for the spatial and coherence\nproperties of the far-field scattered light intensity are derived, valid for\nthe full range of system parameters. A comprehensive survey of the steady-state\nscattering behaviour is given, with key features precisely characterised,\nincluding subradiant scattering, and the regime in which the dipole-dipole\ncoupling has significant effect. A regime is also found where the incoherent\nscattered light develops spatial interference fringes. We examine in detail a\ndecorrelation approximation that has potential application for larger systems\nof atoms that are intractable in a full quantum treatment. Finally, we\nintroduce the concept of an effective driving field and show that it can\nprovide a direct and intuitive physical interpretation of key aspects of the\nsystem behaviour, including subradiant scattering.",
        "positive": "Reaching Fermi degeneracy via universal dipolar scattering: We report on the creation of a degenerate dipolar Fermi gas of erbium atoms.\nWe force evaporative cooling in a fully spin-polarized sample down to\ntemperatures as low as 0.2 times the Fermi temperature. The strong magnetic\ndipole-dipole interaction enables elastic collisions between identical fermions\neven in the zero-energy limit. The measured elastic scattering cross section\nagrees well with the predictions from dipolar scattering theory, which follow a\nuniversal scaling law depending only on the dipole moment and on the atomic\nmass. Our approach to quantum degeneracy proceeds with very high cooling\nefficiency and provides large atomic densities, and it may be extended to\nvarious dipolar systems."
    },
    {
        "anchor": "Theoretical Analysis on Spectroscopy of Atomic Bose-Hubbard Systems: We provide a numerical method to calculate comprehensively the microwave and\nthe laser spectra of ultracold bosonic atoms in optical lattices at finite\ntemperatures. Our formulation is built up with the sum rules, up to the second\norder, derived from the general principle of spectroscopy. The sum rule\napproach allows us to discuss the physical origins of a spectral peak shift and\nalso a peak broadening. We find that a spectral broadening of superfluid atoms\ncan be determined from number fluctuations of atoms, while that of normal-state\natoms is mainly attributed to quantum fluctuations resulting from hopping of\natoms. To calculate spectra at finite temperatures, based on the sum rule\napproach, we provide a two-mode approximation assuming that spectra of the\nsuperfluid and normal state atoms can be calculated separately. Our method can\nproperly deal with multi-peak structures of spectra resulting from thermal\nfluctuations and also coexisting of the superfluid and the normal states. By\ncombining the two-mode approximation with a finite temperature Gutzwiller\napproximation, we calculate spectra at finite temperatures by considering\nrealistic systems, and the calculated spectra show nice agreements with those\nin experiments.",
        "positive": "Efficient generation of many-body singlet states of spin-1 bosons in\n  optical superlattices: We propose an efficient stepwise adiabatic merging (SAM) method to generate\nmany-body singlet states in antiferromagnetic spin-1 bosons in concatenated\noptical superlattices with isolated double-well arrays, by adiabatically\nramping up the double-well bias. With an appropriate choice of bias sweeping\nrate and magnetic field, the SAM protocol predicts a fidelity as high as 90%\nfor a sixteen-body singlet state and even higher fidelities for smaller\neven-body singlet states. During their evolution, the spin-1 bosons exhibit\ninteresting squeezing dynamics, manifested by an odd-even oscillation of the\nexperimentally observable squeezing parameter. The generated many-body singlet\nstates may find practical applications in precision measurement of magnetic\nfield gradient and in quantum information processing."
    },
    {
        "anchor": "Two-dimensional dynamics of expansion of a degenerate Bose gas: Expansion of a degenerate Bose gas released from a pancakelike trap is\nnumerically simulated under the assumption of separation of the motion in the\nplane of the loose initial trapping and the motion in the direction of the\ninitial tight trapping. The initial conditions for the phase fluctuations are\ngenerated using the extension to the two-dimensional case of the description of\nthe phase noise by the Ornstein-Uhlenbeck stochastic process. The numerical\nsimulations, taking into account both the finite size of the two-dimensional\nsystem and the atomic interactions, which cannot be neglected on the early\nstage of expansion, did not reproduce the scaling law for the peaks in the\ndensity fluctuation spectra experimentally observed by Choi, Seo, Kwon, and\nShin [Phys. Rev. Lett. 109, 125301 (2012)]. The latter experimental results may\nthus require an explanation beyond our current assumptions.",
        "positive": "Energies and widths of Efimov states in the three-boson continuum: Three-boson Efimov physics is well known in the bound-state regime, but far\nless in the three-particle continuum at negative two-particle scattering length\nwhere Efimov states evolve into resonances. They are studied solving rigorous\nthree-particle scattering equations for transition operators in the momentum\nspace. The dependence of the three-boson resonance energy and width on the\ntwo-boson scattering length is studied with several force models. The universal\nlimit is determined numerically considering highly excited states; simple\nparametrizations for the resonance energy and width in terms of the scattering\nlength are established. Decreasing the attraction, the resonances rise not much\nabove the threshold but broaden rapidly and become physically unobservable,\nevolving into subthreshold resonances. Finite-range effects are studied and\nrelated to those in the bound-state regime."
    },
    {
        "anchor": "Dynamical properties of hard-core anyons in one-dimensional optical\n  lattices: We investigate the dynamical properties of anyons confined in one-dimensional\noptical lattice combined with a weak harmonic trap using the exact numerical\nmethod based on a generalized Jordan-Wigner transformation. The density\nprofiles, momentum distribution, occupation distribution and occupations of the\nlowest natural orbital are obtained for different statistical parameters. The\ndensity profiles of anyons display the same behaviors irrespective of\nstatistical parameter in the full evolving period. While the behaviors\ndependent on statistical property are shown in the momentum distributions and\noccupations of natural orbitals.",
        "positive": "Mixtures of correlated bosons and fermions: Dynamical mean-field theory\n  for normal and condensed phases: We derive a dynamical mean-field theory for mixtures of interacting bosons\nand fermions on a lattice (BF-DMFT). The BF-DMFT is a comprehensive,\nthermodynamically consistent framework for the theoretical investigation of\nBose-Fermi mixtures and is applicable for arbitrary values of the coupling\nparameters and temperatures. It becomes exact in the limit of high spatial\ndimensions d or coordination number Z of the lattice. In particular, the\nBF-DMFT treats normal and condensed bosons on equal footing and thus includes\nthe effects caused by their dynamic coupling. Using the BF-DMFT we investigate\ntwo different interaction models of correlated lattice bosons and fermions, one\nwhere all particles are spinless (model I) and one where fermions carry a spin\none-half (model II). In model I the local, repulsive interaction between bosons\nand fermions can give rise to an attractive effective interaction between the\nbosons. In model II it can also lead to an attraction between the fermions."
    },
    {
        "anchor": "Study of Bose-Einstein condensation using generalized canonical\n  partition function: We open a new discussion of generalized canonical partition function in\nstandard statistical mechanics and apply it for the study of Bose-Einstein\ncondensation. We discuss the possible cases for the generalized canonical\npartition function and arrives at a conclusion that the system of trapped bose\ngas will not be existing at absolute zero. We analyse the present study with an\nexperimental result and point out the general difficulties in the analyses of\nexperimental observations, which can possibly suppress the effect of\ngeneralized canonical partition function over standard canonical partition\nfunction. We mention that the experimental studies with ideal condensates at\nabsolute zero with an unbiased approach towards the traditional Bose-Einstein\ncondensation theory can bring out the effect of generalized canonical partition\nfunction.",
        "positive": "Scattering length of composite bosons in the 3D BCS-BEC crossover: We study the zero-temperature grand potential of a three-dimensional\nsuperfluid made of ultracold fermionic alkali-metal atoms in the BCS-BEC\ncrossover. In particular, we analyze the zero-point energy of both fermionic\nsingle-particle excitations and bosonic collective excitations. The bosonic\nelementary excitations, which are crucial to obtain a reliable equation of\nstate in the BEC regime, are obtained with a low-momentum expansion up to the\nforth order of the quadratic (Gaussian) action of the fluctuating pairing\nfield. By performing a cutoff regularization and renormalization of Gaussian\nfluctuations, we find that the scattering length $a_B$ of composite bosons,\nbound states of fermionic pairs, is given by $a_B = (2/3) a_F$, where $a_F$ is\nthe scattering length of fermions."
    },
    {
        "anchor": "Two-dimensional spin-imbalanced Fermi gases at non-zero temperature:\n  Phase separation of a non-condensate: We study a trapped two-dimensional spin-imbalanced Fermi gas over a range of\ntemperatures. In the moderate temperature regime, associated with current\nexperiments, we find reasonable semi-quantitative agreement with the measured\ndensity profiles as functions of varying spin imbalance and interaction\nstrength. Our calculations show that, in contrast to the three-dimensional\ncase, the phase separation which appears as a spin balanced core, can be\nassociated with non-condensed fermion pairs. We present predictions at lower\ntemperatures where a quasi-condensate will first appear, based on the pair\nmomentum distribution and following the protocols of Jochim and collaborators.\nWhile these profiles also indicate phase separation, they exhibit distinctive\nfeatures which may aid in identifying the condensation regime.",
        "positive": "Bad metallic transport in a cold atom Fermi-Hubbard system: Charge transport is a revealing probe of the quantum properties of materials.\nStrong interactions can blur charge carriers resulting in a poorly understood\n\"quantum soup\". Here we study the conductivity of the Fermi-Hubbard model, a\ntesting ground for strong interaction physics, in a clean quantum system -\nultracold $^6$Li in a 2D optical lattice. We determine the charge diffusion\nconstant in our system by measuring the relaxation of an imposed density\nmodulation and modeling its decay hydrodynamically. The diffusion constant is\nconverted to a resistivity, which exhibits a linear temperature dependence and\nexceeds the Mott-Ioffe-Regel limit, two characteristic signatures of a bad\nmetal. The techniques we develop here may be applied to measurements of other\ntransport quantities, including the optical conductivity and thermopower."
    },
    {
        "anchor": "Thermometry for Laughlin States of Ultracold Atoms: Cooling atomic gases into strongly correlated quantum phases requires\nestimates of the entropy to perform thermometry and establish viability. We\nconstruct an ansatz partition function for models of Laughlin states of atomic\ngases by combining high temperature series expansions with exact\ndiagonalization. Using the ansatz we find that entropies required to observe\nLaughlin correlations with bosonic gases are within reach of current cooling\ncapabilities.",
        "positive": "Disentangling phonons from spins in ion-trap-based quantum spin\n  simulators: We compute how phonon creation affects the fidelity of the quantum spin\ndynamics in trapped ion simulators. A rigorous treatment of the quantum\ndynamics is made by employing an exact operator factorization of the evolution\noperator. Although it is often assumed that phonon creation modifies the\ndynamics of the spin evolution, for an Ising spin-spin interaction in an\nexternal magnetic field, phonons have \\textit{no effect} on the probabilities\nof spin product states measured in the direction of the Ising model axis.\nPhonons play a much more important role in influencing the effective spin\ndynamics for Heisenberg or XY model spin simulators or for other observables,\nlike witness operators in the Ising model."
    },
    {
        "anchor": "Universal three-body physics in ultracold KRb mixtures: Ultracold atomic gases have recently become a driving force in few-body\nphysics due to the observation of the Efimov effect. While initially observed\nin equal mass systems, one expects even richer few-body physics in the\nheteronuclear case. In previous experiments with ultracold mixtures of\npotassium and rubidium, an unexpected non-universal behavior of Efimov\nresonances was observed. In contrast, we measure the scattering length\ndependent three-body recombination coefficient in ultracold heteronuclear\nmixtures of $^{39}\\mathrm{K}$-\\87Rb and $^{41}\\mathrm{K}$-\\87Rb and do not\nobserve any signatures of Efimov resonances for accessible scattering lengths\nin either mixture. Our results show good agreement with our theoretical model\nfor the scattering dependent three-body recombination coefficient and\nreestablish universality across isotopic mixtures.",
        "positive": "Realizing distance-selective interactions in a Rydberg-dressed atom\n  array: Measurement-based quantum computing relies on the rapid creation of\nlarge-scale entanglement in a register of stable qubits. Atomic arrays are well\nsuited to store quantum information, and entanglement can be created using\nhighly-excited Rydberg states. Typically, isolating pairs during gate operation\nis difficult because Rydberg interactions feature long tails at large\ndistances. Here, we engineer distance-selective interactions that are strongly\npeaked in distance through off-resonant laser coupling of molecular potentials\nbetween Rydberg atom pairs. Employing quantum gas microscopy, we verify the\ndressed interactions by observing correlated phase evolution using many-body\nRamsey interferometry. We identify atom loss and coupling to continuum modes as\na limitation of our present scheme and outline paths to mitigate these effects,\npaving the way towards the creation of large-scale entanglement."
    },
    {
        "anchor": "Many-body Aharonov-Bohm caging in a lattice of rings: We study a system of a few ultracold bosons loaded into the states with\norbital angular momentum $l=1$ of a one-dimensional staggered lattice of rings.\nLocal eigenstates with winding numbers $+l$ and $-l$ form a Creutz ladder with\na real dimension and a synthetic one. States with opposite winding numbers in\nadjacent rings are coupled through complex tunnelings, which can be tuned by\nmodifying the central angle $\\phi$ of the lattice. We analyze both the\nsingle-particle case and the few boson bound-state subspaces for the regime of\nstrong interactions using perturbation theory, showing how the geometry of the\nsystem can be engineered to produce an effective $\\pi$-flux through the\nplaquettes. We find non-trivial topological band structures and many-body\nAharonov-Bohm caging in the $N$-particle subspaces even in the presence of a\ndispersive single-particle spectrum. Additionally, we study the family of\nmodels where the angle $\\phi$ is introduced at an arbitrary lattice periodicity\n$\\Gamma$. For $\\Gamma>2$, the $\\pi$-flux becomes non-uniform, which enlarges\nthe spatial extent of the Aharonov-Bohm caging as the number of flat bands in\nthe spectrum increases. All the analytical results are benchmarked through\nexact diagonalization.",
        "positive": "Rosen-Zener model in cold molecule formation: The Rosen-Zener model for association of atoms in a Bose-Einstein condensate\nis studied. Using a nonlinear Volterra integral equation, we obtain an analytic\nformula for final probability of the transition to the molecular state for weak\ninteraction limit. Considering the strong coupling limit of high field\nintensities, we show that the system reveals two different time-evolution\npictures depending on the detuning of the frequency of the associating field.\nFor both limit cases we derive highly accurate formulas for the molecular state\nprobability valid for the whole range of variation of time. Using these\nformulas, we show that at large detuning regime the molecule formation process\noccurs almost non-oscillatory in time and a Rosen-Zener pulse is not able to\nassociate more than one third of atoms at any time point. The system returns to\nits initial all-atomic state at the end of the process and the maximal\ntransition probability is achieved when the field intensity reaches its peak.\nIn contrast, at small detuning the evolution of the system displays\nlarge-amplitude oscillations between atomic and molecular populations. We find\nthat the shape of the oscillations in the first approximation is defined by the\nfield detuning only. Finally, a hidden singularity of the Rosen-Zener model due\nto the specific time-variation of the field amplitude at the beginning of the\ninteraction is indicated. It is this singularity that stands for many of the\nqualitative and quantitative properties of the model. The singularity may be\nviewed as an effective resonance-touching."
    },
    {
        "anchor": "A Novel Route to Reach a $p$-wave Superfluid Fermi Gas: We theoretically propose an idea to realize a $p$-wave superfluid Fermi gas.\nTo overcome the experimental difficulty that a $p$-wave pairing interaction to\nform $p$-wave Cooper pairs damages the system before the condensation growth,\nwe first prepare a $p$-wave pair amplitude ($\\Phi_{p}$) in a spin-orbit coupled\n$s$-wave superfluid Fermi gas, without any $p$-wave interaction. Then, by\nsuddenly changing the $s$-wave interaction with a $p$-wave one ($U_{p}$) by\nusing a Feshbach resonance, we reach the $p$-wave superfluid phase with the\n$p$-wave order parameter being symbolically written as $\\Delta_{p}\\sim\nU_{p}\\Phi_{p}$. In this letter, we assess this scenario within the framework of\na time-dependent Bogoliubov-de Gennes theory. Our results would contribute to\nthe study toward the realization of unconventional pairing states in an\nultracold Fermi gas.",
        "positive": "Efficient production of long-lived ultracold Sr$_2$ molecules: We associate Sr atom pairs on sites of a Mott insulator optically and\ncoherently into weakly-bound ground-state molecules, achieving an efficiency\nabove 80\\%. This efficiency is 2.5 times higher than in our previous work [S.\nStellmer, B. Pasquiou, R. Grimm, and F. Schreck, Phys. Rev. Lett. 109, 115302\n(2012)] and obtained through two improvements. First, the lifetime of the\nmolecules is increased beyond one minute by using an optical lattice wavelength\nthat is further detuned from molecular transitions. Second, we compensate\nundesired dynamic light shifts that occur during the stimulated Raman adiabatic\npassage (STIRAP) used for molecule association. We also characterize and model\nSTIRAP, providing insights into its limitations. Our work shows that\nsignificant molecule association efficiencies can be achieved even for atomic\nspecies or mixtures that lack Feshbach resonances suitable for\nmagnetoassociation."
    },
    {
        "anchor": "Simulation of time crystal behavior for a few boson chiral soliton model\n  in a ring: We present numerical simulations for a chiral soliton model with N=2,3 bosons\nin a ring, this being a few-particle version of our previous mean-field model\nfor a quantum time crystal. Following Syrwid, Kosior, and Sacha (SKS), the\nnotion is that a precise position measurement of one particle can lead to\nspontaneous formation of a bright soliton that in a time crystal should rotate\nintact for at least a few revolutions around the ring. In their work SKS find\nspontaneous formation of a soliton due to the position measurement, but quantum\nfluctuations cause the soliton to subsequently decay before it has a chance to\nperform even one revolution of the ring. Based on this they conclude that time\ncrystal dynamics are impossible. In contrast, for our few boson chiral soliton\nmodel, and allowing for imprecise (weak) measurements of the particle position,\nwe show that time crystal behavior is possible allowing for several revolutions\nof the spontaneously formed soliton around the ring. We therefore argue that\nour chiral soliton model can realize a quantum time crystal when weak position\nmeasurements are allowed for.",
        "positive": "Comment on the paper \"Electromagnetic Wave Dynamics in Matter-Wave\n  Superradiant Scattering\" by L. Deng, M.G. Payne, and E.W. Hagley: The paper by Deng et al. (Phys. Rev. Lett. 104, 050402 (2010)) presents an\nanalytic theoretical description of matter-wave superradiance (Phys. Rev. Lett.\n85, 4225-4228 (2000)) which claims to go beyond previous theoretical\nframeworks. I show here that the theory presented in this paper is not a\ndescription of superradiance per se, but rather an elegant perturbative\ndescription of a Raman amplifier far away from the superradiant threshold. As\nsuch, it merely is a limiting case of previously known treatments of\nsuperradiance. Two additional new findings of the paper are incorrect: (1) The\nclaim that adiabatic elimination of the excited state of the atoms is only\npossible when the probe pulse propagates slowly. (2) The prediction that\nsuperradiance has a dependence on the sign of the detuning of the pump laser\ndue to a phase-matching condition."
    },
    {
        "anchor": "Basis for time crystal phenomena in ultra-cold atoms bouncing on an\n  oscillating mirror: We consider classical dynamics of a 1D system of $N$ particles bouncing on an\noscillating mirror in the presence of gravitational field. The particles behave\nlike hard balls and they are resonantly driven by the mirror. We identify the\nmanifolds the particles move on and derive the effective secular Hamiltonian\nfor resonant motion of the particles. Proper choice of time periodic\noscillations of the mirror allows for engineering of the effective behaviour of\nthe particles. In particular, the system can behave like a $N$-dimensional\nfictitious particle moving in an $N$-dimensional crystalline structure. Our\nclassical analysis constitutes a basis for quantum research of novel time\ncrystal phenomena in ultra-cold atoms bouncing on an oscillating atom mirror.",
        "positive": "Shape and size measurements of nonequilibrium Bose-Einstein condensates\n  using image processing: Bose-Einstein condensates have been the subject of intense research in recent\nyears due to their potential applications in quantum computing and many other\nareas. However, measuring the shape and size of out-of-equilibrium\nBose-Einstein condensates is a challenging task that requires sophisticated\nimage processing techniques. We propose to study perturbed BEC based on general\nconcepts of analysis, which are widely used in the image processing community.\nThe mathematical basis underlying the algorithms is quite general and\nindependent of the type of image studied. The morphological changes observed in\nthe perturbed atomic clouds as a result of excitation amplitude were observed\nin a consistent manner. And the spatial expansion of the atomic clouds under\nfree fall shows some symmetry, but it was only observed under certain\nconditions"
    },
    {
        "anchor": "Comment on \"Interface tension of Bose-Einstein condensates\" by Bert Van\n  Schaeybroeck, Phys. Rev. A 78, 023624-9 (2008): The purpose of the comment is to point out that the leading term of the\nGinzburg-Landau nonanalytical correction to the interface tension of\nBose-Einstein condensates with strong segregation and the surface tension of\nextreme type-I superconductors are described by a common coefficient derived\nfrom the universal equation for the phase boundary. The agreement between the\nnumerical value of the coefficients gives a hint that this can be an exact\nresult which deserves to be checked. The outcome will be of interest for\nphysicists working in both fields.",
        "positive": "Mobile magnetic impurities in a Fermi superfluid: a route to designer\n  molecules: A magnetic impurity in a fermionic superfluid hosts bound quasiparticle\nstates known as Yu-Shiba-Rusinov (YSR) states. We argue here that, if the\nimpurity is mobile (i.e., has a finite mass), the impurity and its bound YSR\nquasiparticle move together as a midgap molecule, which has an unusual\n\"Mexican-hat\" dispersion that is tunable via the fermion density. We map out\nthe impurity dispersion, which consists of an \"atomic\" branch (in which the\nimpurity is dressed by quasiparticle pairs) and a \"molecular\" branch (in which\nthe impurity binds a quasiparticle). We discuss the experimental realization\nand detection of midgap Shiba molecules, focusing on lithium-cesium mixtures,\nand comment on the prospects they offer for realizing exotic many-body states."
    },
    {
        "anchor": "Anderson localization of a weakly interacting one dimensional Bose gas: We consider the phase coherent transport of a quasi one-dimensional beam of\nBose-Einstein condensed particles through a disordered potential of length L.\nAmong the possible different types of flow identified in [T. Paul et al., Phys.\nRev. Lett. 98, 210602 (2007)], we focus here on the supersonic stationary\nregime where Anderson localization exists. We generalize the diffusion\nformalism of Dorokhov-Mello-Pereyra-Kumar to include interaction effects. It is\nshown that interactions modify the localization length and also introduce a\nlength scale L* for the disordered region, above which most of the realizations\nof the random potential lead to time dependent flows. A Fokker-Planck equation\nfor the probability density of the transmission coefficient that takes this new\neffect into account is introduced and solved. The theoretical predictions are\nverified numerically for different types of disordered potentials. Experimental\nscenarios for observing our predictions are discussed.",
        "positive": "Aligned dipolar Bose-Einstein condensate in a double-well potential:\n  From cigar-shaped to pancake-shaped: We consider a Bose-Einstein condensate (BEC), which is characterized by\nlong-range and anisotropic dipole-dipole interactions and vanishing s-wave\nscattering length, in a double-well potential. The properties of this system\nare investigated as functions of the height of the barrier that splits the\nharmonic trap into two halves, the number of particles (or dipole-dipole\nstrength) and the aspect ratio $\\lambda$, which is defined as the ratio between\nthe axial and longitudinal trapping frequencies $\\omega_z$ and $\\omega_{\\rho}$.\nThe phase diagram is determined by analyzing the stationary mean-field\nsolutions. Three distinct regions are found: a region where the energetically\nlowest lying stationary solution is symmetric, a region where the energetically\nlowest lying stationary solution is located asymmetrically in one of the wells,\nand a region where the system is mechanically unstable. For sufficiently large\naspect ratio $\\lambda$ and sufficiently high barrier height, the system\nconsists of two connected quasi-two-dimensional sheets with density profiles\nwhose maxima are located either at $\\rho=0$ or away from $\\rho=0$. The\nstability of the stationary solutions is investigated by analyzing the\nBogoliubov de Gennes excitation spectrum and the dynamical response to small\nperturbations. These studies reveal unique oscillation frequencies and distinct\ncollapse mechanisms. The results derived within the mean-field framework are\ncomplemented by an analysis based on a two-mode model."
    },
    {
        "anchor": "Dimensional crossover in a Fermi gas from one to effective six\n  dimensions and a cross-dimensional Tomonaga-Luttinger model: We describe the dimensional crossover in a noninteracting Fermi gas in an\nanisotropic trap, obtained by populating various transverse modes of the trap.\nWe study the dynamical structure factor and drag force. Starting from a\ndimension $d$, the $(\\!d\\!+\\!1\\!)$-dimensional case is obtained to a good\napproximation with relatively few modes. We show that the dynamical structure\nfactor of a gas in a $d$-dimensional harmonic trap simulates an effective\n$2d$-dimensional box trap. We focus then on the experimentally relevant\nsituation when only a portion of the gas in harmonic confinement is probed and\ngive a condition to obtain the behavior of a $d$-dimensional gas in a box.\nFinally, we propose a generalized Tomonaga-Luttinger model for the multimode\nconfiguration and compare the dynamical structure factor in the 2D limit with\nthe exact result, finding that it is accurate in the backscattering region and\nat low energy.",
        "positive": "Liberating Efimov physics from three dimensions: When two particles attract via a resonant short-range interaction, three\nparticles always form an infinite tower of bound states characterized by a\ndiscrete scaling symmetry. It has been considered that this Efimov effect\nexists only in three dimensions. Here we review how the Efimov physics can be\nliberated from three dimensions by considering two-body and three-body\ninteractions in mixed dimensions and four-body interaction in one dimension. In\nsuch new systems, intriguing phenomena appear, such as confinement-induced\nEfimov effect, Bose-Fermi crossover in Efimov spectrum, and formation of\ninterlayer Efimov trimers. Some of them are observable in ultracold atom\nexperiments and we believe that this study significantly broadens our horizons\nof universal Efimov physics."
    },
    {
        "anchor": "Landau Damping in a Mixture of Bose and Fermi Superfluids: We study the Landau damping in Bose-Fermi superfluid mixture at finite\ntemperature. We find that at low temperature, the Landau damping rate will be\nexponentially suppressed at both the BCS side and the BEC side of Fermi\nsuperfluid. The momentum dependence of the damping rate is obtained, and it is\nquite different from the BCS side to the BEC side. The relations between our\nresult and collective mode experiment in the recently realized Bose-Fermi\nsuperfluid mixture are also discussed.",
        "positive": "Localization of weakly interacting Bose gas in quasiperiodic potential: We study the localization properties of weakly interacting Bose gas in a\nquasiperiodic potential commonly known as Aubry-Andr\\'e model. Effect of\ninteraction on localization is investigated by computing the `superfluid\nfraction' and `inverse participation ratio'. For interacting Bosons the inverse\nparticipation ratio increases very slowly after the localization transition due\nto `multisite localization' of the wave function. We also study the\nlocalization in Aubry-Andr\\'e model using an alternative approach of classical\ndynamical map, where the localization is manifested by chaotic classical\ndynamics. For weakly interacting Bose gas, Bogoliubov quasiparticle spectrum\nand condensate fraction are calculated in order to study the loss of coherence\nwith increasing disorder strength. Finally we discuss the effect of trapping\npotential on localization of matter wave."
    },
    {
        "anchor": "Spin-imbalanced ultracold Fermi gases in a two-dimensional array of\n  tubes: Motivated by a recent experiment [Revelle et al. Phys. Rev. Lett. 117, 235301\n(2016)] that characterized the one- to three-dimensional crossover in a\nspin-imbalanced ultracold gas of $^6$Li atoms trapped in a two-dimensional\narray of tunnel-coupled tubes, we calculate the phase diagram for this system\nusing Hartree-Fock Bogoliubov-de Gennes mean-field theory, and compare the\nresults with experimental data. Mean-field theory predicts fully spin-polarized\nnormal, partially spin-polarized normal, spin-polarized superfluid, and\nspin-balanced superfluid phases in a homogeneous system. We use the local\ndensity approximation to obtain density profiles of the gas in a harmonic trap.\nWe compare these calculations with experimental measurements in Revelle {\\em et\nal.} as well as previously unpublished data. Our calculations qualitatively\nagree with experimentally-measured densities and coordinates of the phase\nboundaries in the trap, and quantitatively agree with experimental measurements\nat moderate-to-large polarizations. Our calculations also reproduce the\nexperimentally-observed universal scaling of the phase boundaries for different\nscattering lengths at a fixed value of scaled inter-tube tunneling. However,\nour calculations have quantitative differences with experimental measurements\nat low polarization, and fail to capture important features of the one- to\nthree-dimensional crossover observed in experiments. These suggest the\nimportant role of physics beyond-mean-field theory in the experiments. We\nexpect that our numerical results will aid future experiments in narrowing the\nsearch for the FFLO phase.",
        "positive": "Selective distillation phenomenon in two-species Bose-Einstein\n  condensates in open boundary optical lattices: We investigate the formation of discrete breathers (DBs) and the dynamics of\nthe mixture of two-species Bose-Einstein condensates (BECs) in open boundary\noptical lattices using the discrete nonlinear Schr\\\"{o}dinger equations. The\nresults show that the coupling of intra- and interspecies interaction can lead\nto the existence of pure single-species DBs and symbiotic DBs (i.e.,\ntwo-species DBs). Furthermore, we find that there is a selective distillation\nphenomenon in the dynamics of the mixture of two-species BECs. One can\nselectively distil one species from the mixture of two-species BECs and can\neven control dominant species fraction by adjusting the intra- and interspecies\ninteraction in optical lattices. Our selective distillation mechanism may find\npotential application in quantum information storage and quantum information\nprocessing based on multi-species atoms."
    },
    {
        "anchor": "Quantum stochastic behaviour in cold Fermi gases: Phonon propagation: We examine the effect of quantum fluctuations in a tunable cold Fermi gas on\nthe propagation of phonons. We show that these fluctuations can be interpreted\nas inducing a stochastic (acoustic) space-time. The variation in times of\nflight induced by this stochastic behaviour can be significant in the\ntransition region between BEC and BCS regimes.",
        "positive": "Impact of photo-assisted collisions on superradiant light scattering\n  with Bose condensates: We present experimental evidence supporting the postulation that the\nsecondary effects of light-assisted collisions are the main reason that the\nsuperradiant light scattering efficiency in condensates is asymmetric with\nrespect to the sign of the pump-laser detuning. Contrary to the recent\nexperimental study, however, we observe severe and comparable heating with all\nthree pump-laser polarizations. We also perform two-color, double-pulse\nmeasurements to directly study the degradation of condensate coherence and the\nresulting impact on the superradiant scattering efficiency."
    },
    {
        "anchor": "Hydrodynamics of Quantum Vortices on a Closed Surface: We develop a neutral vortex fluid theory on closed surfaces with zero genus.\nThe theory describes collective dynamics of many well-separated quantum\nvortices in a superfluid confined on a closed surface. Comparing to the case on\na plane, the covariant vortex fluid equation on a curved surface contains an\nadditional term proportional to Gaussian curvature multiplying the circulation\nquantum. This term describes the coupling between topological defects and\ncurvature in the macroscopic level. For a sphere, the simplest nontrivial\nstationary vortex flow is obtained analytically and this flow is analogous to\nthe celebrated zonal Rossby-Haurwitz wave in classical fluids on a nonrotating\nsphere. For this flow the difference between the coarse-grained vortex velocity\nfield and the fluid velocity field generated by vortices is solely driven by\ncurvature and vanishes in the corresponding vortex flow on a plane when the\nradius of the sphere goes to infinity.",
        "positive": "Inducing vortices in a Bose-Einstein condensate using holographically\n  produced light beams: In this paper we demonstrate a technique that can create out-of-equilibrium\nvortex configurations with almost arbitrary charge and geometry in a\nBose-Einstein condensate. We coherently transfer orbital angular momentum from\na holographically generated light beam to a Rubidium 87 condensate using a\ntwo-photon stimulated Raman process. Using matter wave interferometry, we\nverify the phase pattern imprinted onto the atomic wave function for a single\nvortex and a vortex-antivortex pair. In addition to their phase winding, the\nvortices created with this technique have an associated hyperfine spin texture."
    },
    {
        "anchor": "Many-Body Echo: In this letter we propose a protocol to reverse a quantum many-body dynamical\nprocess. We name it \"many-body echo\" because the underlying physics is closely\nrelated to the spin echo effect in nuclear magnetic resonance systems. We\nconsider a periodical modulation of the interaction strength in a weakly\ninteracting Bose condensate, which resonantly excites quasi-particles from the\ncondensate. A dramatic phenomenon is that, after pausing the interaction\nmodulation for half a period and then continuing on with the same modulation,\nnearly all the excited quasi-particles in the resonance modes will be absorbed\nback into the condensate. During the intermediate half period, the free\nevolution introduces a $\\pi$ phase, which plays a role reminiscent of that\nplayed by the $\\pi$-pulse in the spin echo. Comparing our protocol with another\none implemented by the Chicago group in a recent experiment, we find that ours\nis more effective at reversing the many-body process. The difference between\nthese two schemes manifests the physical effect of the micro-motion in the\nFloquet theory. Our scheme can be generalised to other periodically driven\nmany-body systems.",
        "positive": "Unpaired topological triply degenerate point for\n  spin-tensor-momentum-coupled ultracold atoms: The realization of triply degenerate points (TDPs) with exotic fermionic\nexcitations has opened a new perspective for the understanding of our nature.\nHere we explore the coexistence of single unpaired TDP and multiple twofold\nWeyl points (WPs) and propose an experimental scheme with ultracold\npseudospin-1 atomic gases trapped in optical lattices. We show that the\npredicted single unpaired TDP emerged by the interplay of quadratic\nspin-vector- and spin-tensor-momentum-coupling could possess a topological\nnontrivial middle band. This exotic TDP with mirror symmetry breaking is\nessential different from the recently observed TDPs that must appear in pairs\ndue to the Nielsen-Ninomiya theorem and host the topological trivial middle\nband. Strikingly, the topologically protected Fermi-arc states directly connect\nthe unpaired TDP with additional WPs, in contrast to the conventional Fermi-arc\nstates that connect the same degeneracies of band degenerate points with\nopposite chirality. Furthermore, the different types of TDPs with unique\nlinking structure of Fermi arcs can be readily distinguished by measuring spin\ntexture along high-symmetry lines of the system. Our scheme provides a platform\nfor emerging new fermions with exotic physical phenomena and versatile device\napplications."
    },
    {
        "anchor": "Vortex Mass in a Superfluid: We consider the inertial mass of a vortex in a superfluid. We obtain a vortex\nmass that is well defined and is determined microscopically and\nself-consistently by the elementary excitation energy of the kelvon\nquasiparticle localised within the vortex core. The obtained result for the\nvortex mass is found to be consistent with experimental observations on\nsuperfluid quantum gases and vortex rings in water. We propose a method to\nmeasure the inertial rest mass and Berry phase of a vortex in superfluid Bose\nand Fermi gases.",
        "positive": "Reentrant Superfluidity and Pair Density Wave in Single Component\n  Dipolar Fermi Gases: We study the superfluidity of single component dipolar Fermi gases in three\ndimensions within a pairing fluctuation theory. The transition temperature\n$T_{c}$ for the dominant $p_z$ wave superfluidity exhibits a remarkable\nre-entrant behavior as a function of the pairing strength induced by the\ndipole-dipole interaction (DDI), which leads to an anisotropic pair dispersion.\nThe anisotropy and the long range nature of the DDI cause $T_c$ to vanish for a\nnarrow range of intermediate interaction strengths, where a pair density wave\nstate emerges as the ground state. The superfluid density and thermodynamics\nbelow $T_{c}$, along with the density profiles in a harmonic trap, are\ninvestigated as well, throughout the BCS-BEC crossover. Implications for\nexperiments are discussed."
    },
    {
        "anchor": "Polarized superfluid state in a three-dimensional fermionic optical\n  lattice: We study ultracold fermionic atoms trapped in a three dimensional optical\nlattice by combining the real-space dynamical mean-field approach with\ncontinuous-time quantum Monte Carlo simulations. For a spin-unpolarized system\nwe show results the density and pair potential profile in the trap for a range\nof temperatures. We discuss how a polarized superfluid state is spatially\nrealized in the spin-polarized system with harmonic confinement at low\ntemperatures and present the local particle density, local magnetization, and\npair potential.",
        "positive": "Imaging magnetic polarons in the doped Fermi-Hubbard model: Polarons are among the most fundamental quasiparticles emerging in\ninteracting many-body systems, forming already at the level of a single mobile\ndopant. In the context of the two-dimensional Fermi-Hubbard model, such\npolarons are predicted to form around charged dopants in an antiferromagnetic\nbackground in the low doping regime close to the Mott insulating state.\nMacroscopic transport and spectroscopy measurements related to high $T_{c}$\nmaterials have yielded strong evidence for the existence of such quasiparticles\nin these systems. Here we report the first microscopic observation of magnetic\npolarons in a doped Fermi-Hubbard system, harnessing the full single-site spin\nand density resolution of our ultracold-atom quantum simulator. We reveal the\ndressing of mobile doublons by a local reduction and even sign reversal of\nmagnetic correlations, originating from the competition between kinetic and\nmagnetic energy in the system. The experimentally observed polaron signatures\nare found to be consistent with an effective string model at finite\ntemperature. We demonstrate that delocalization of the doublon is a necessary\ncondition for polaron formation by contrasting this mobile setting to a\nscenario where the doublon is pinned to a lattice site. Our work paves the way\ntowards probing interactions between polarons, which may lead to stripe\nformation, as well as microscopically exploring the fate of polarons in the\npseudogap and bad metal phase."
    },
    {
        "anchor": "Multicriticality, Metastability, and Roton Feature in Bose-Einstein\n  Condensates with Three-Dimensional Spin-Orbit Coupling: We theoretically study homogeneously trapped atomic Bose-Einstein condensates\nwhere all three momentum components couple to a pseudo-spin-$1/2$ degree of\nfreedom. Tuning the anisotropies of spin-orbit coupling and the spin-dependent\ninteractions is shown to provide access to a rich phase diagram with a\ntetracritical point, first-order phase transitions, and multiple metastable\nphases of stripe and plane-wave character. The elementary excitation spectrum\nof the axial plane-wave phase features an anisotropic roton feature and can be\nused to probe the phase diagram. In addition to providing a versatile\nlaboratory for studying fundamental concepts in statistical physics, the\nemergence of metastable phases creates new opportunities for observing\nfalse-vacuum decay and bubble nucleation in ultra-cold-atom experiments.",
        "positive": "Improving the Gutzwiller Ansatz with Matrix Product States: The Gutzwiller variational wavefunction (GVW) is commonly employed to capture\ncorrelation effects in condensed matter systems such as ferromagnets, ultracold\nbosonic gases, correlated superconductors, etc. By noticing that the\ngrand-canonical and number-conserving Gutzwiller Ans\\\"atze are in fact the\nzero-order approximation of an expansion in the truncation parameter of a\nMatrix Product State (MPS), we argue that MPSs, and the algorithms used to\noperate on them, are not only flexible computational tools but also a unifying\ntheoretical framework that can be used to generalize and improve on the GVW. In\nfact, we show that a number-conserving GVW is less efficient in capturing the\nground state of a quantum system than a more general MPS which can be optimized\nwith comparable computational resources. Moreover, we suggest a corrected\ntime-dependent density matrix renormalization group algorithm that ensures the\nconservation of the expectation value of the number of particles when a GVW or\na MPS are not explicitly number-conserving. The GVW dynamics obtained with our\nalgorithm compares very well with the exact one in 1D. Most importantly, the\nalgorithm works in any dimension for a GVW. We thus expect it to be of great\nvalue in the study of the dynamics of correlated quantum systems."
    },
    {
        "anchor": "Engineering entanglement Hamiltonians with strongly interacting cold\n  atoms in optical traps: We present a proposal for the realization of entanglement Hamiltonians in\none-dimensional critical spin systems with strongly interacting cold atoms. Our\napproach is based on the notion that the entanglement spectrum of such systems\ncan be realized with a physical Hamiltonian containing a set of\nposition-dependent couplings. We focus on reproducing the universal ratios of\nthe entanglement spectrum for systems in two different geometries: a harmonic\ntrap, which corresponds to a partition embedded in an infinite system, and a\nlinear potential, which reproduces the properties of a half-partition with open\nboundary conditions. Our results demonstrate the possibility of measuring the\nentanglement spectra of the Heisenberg and XX models in a realistic cold-atom\nexperimental setting by simply using gravity and standard trapping techniques.",
        "positive": "Number Fluctuations of a Dipolar Condensate: Anisotropy and Slow\n  Approach to the Thermodynamic Regime: We present a theory for the number fluctuations of a quasi-two-dimensional\n(quasi-2D) dipolar Bose-Einstein condensate measured with finite resolution\ncells. We show that when the dipoles are tilted to have a component parallel to\nthe plane of the trap, the number fluctuations become anisotropic, i.e. depend\non the in-plane orientation of the measurement cell. We develop analytic\nresults for the quantum and thermal fluctuations applicable to the cell sizes\naccessible in experiments. We show that as cell size is increased the\nthermodynamic fluctuation result is approached much more slowly than in\ncondensates with short range interactions, so experiments would not require\nhigh numerical aperture imaging to observe the predicted effect."
    },
    {
        "anchor": "Elementary excitations of ultracold soft-core bosons across the\n  superfluid-supersolid phase transition: We investigate the zero-temperature excitation spectrum of two-dimensional\nsoft-core bosons for a wide range parameters and across the phase transition\nfrom a superfluid to a supersolid state. Based on mean field calculations and\nrecent Quantum Monte Carlo results, we demonstrate the applicability of the\nBogoliubov-de Gennes equations, even at high interaction strengths where the\nsystem forms an insulating cluster crystal. Interestingly, our study reveals\nthat the maximum energy of the longitudinal phonon band in the supersolid phase\nconnects to the maxon energy of the superfluid at the phase transition.",
        "positive": "Roton-maxon spectrum and instability for weakly interacting dipolar\n  excitons in a semiconductor layer: The formation of the roton-maxon excitation spectrum and the roton\ninstability effect for a weakly correlated Bose gas of dipolar excitons in a\nsemiconductor layer are predicted. The stability diagram is calculated.\nAccording to our numerical estimations, the threshold of the roton instability\nfor Bose-Einstein condensed exciton gas with roton-maxon spectrum is achievable\nexperimentally, e.g., in GaAs semiconductor layers."
    },
    {
        "anchor": "Phase diffusion in stationary state of nonequilibrium Bose gas: Properties of low energy spectrum of elementary excitations in nonequilibrium\nBose gas in stationary state with the dynamical equilibrium of outgoing and\nincoming of particles are studied. It is shown that due to the noise effect,\ntypical for nonequilibrium systems, this spectrum has a diffusion character, in\ncontradiction with the thermodynamically equilibrium systems, where this\nspectrum has a sound form.",
        "positive": "Quantum Elliptic Vortex in a Nematic-Spin Bose-Einstein Condensate: We find a novel topological defect in a spin-nematic superfluid\ntheoretically. A quantized vortex spontaneously breaks its axisymmetry, leading\nto an elliptic vortex in nematic-spin Bose-Einstein condensates with small\npositive quadratic Zeeman effect. The new vortex is considered the Joukowski\ntransform of a conventional vortex. Its oblateness grows when the Zeeman length\nexceeds the spin healing length. This structure is sustained by balancing the\nhydrodynamic potential and the elasticity of a soliton connecting two spin\nspots, which are observable by in situ magnetization imaging. The theoretical\nanalysis clearly defines the difference between half quantum vortices of the\npolar and antiferromagnetic phases in spin-1 condensates."
    },
    {
        "anchor": "Superfluid and magnetic states of an ultracold Bose gas with synthetic\n  three-dimensional spin-orbit coupling in an optical lattice: We study ultracold bosonic atoms with the synthetic three-dimensional\nspin-orbit (SO) coupling in a cubic optical lattice. In the superfluidity\nphase, the lowest energy band exhibits one, two or four pairs of degenerate\nsingle-particle ground states depending on the SO-coupling strengths, which can\ngive rise to the condensate states with spin-stripes for the weak atomic\ninteractions. In the deep Mott-insulator regime, the effective spin Hamiltonian\nof the system combines three-dimensional Heisenberg exchange interactions,\nanisotropy interactions and Dzyaloshinskii-Moriya interactions. Based on Monte\nCarlo simulations, we numerically demonstrate that the resulting Hamiltonian\nwith an additional Zeeman field has a rich phase diagram with spiral, stripe,\nvortex crystal, and especially Skyrmion crystal spin-textures in each xy-plane\nlayer. The obtained Skyrmion crystals can be tunable with square and hexagonal\nsymmetries in a columnar manner along the z axis, and moreover are stable\nagainst the inter-layer spin-spin interactions in a large parameter region.",
        "positive": "Universal behavior of two-dimensional bosonic gases at\n  Berezinskii-Kosterlitz-Thouless transitions: We study the universal critical behavior of two-dimensional (2D) lattice\nbosonic gases at the Berezinskii-Kosterlitz-Thouless (BKT) transition, which\nseparates the low-temperature superfluid phase from the high-temperature normal\nphase. For this purpose, we perform quantum Monte Carlo simulations of the\nhard-core Bose-Hubbard (BH) model at zero chemical potential. We determine the\ncritical temperature by using a matching method that relates finite-size data\nfor the BH model with corresponding data computed in the classical XY model. In\nthis approach, the neglected scaling corrections decay as inverse powers of the\nlattice size L, and not as powers of 1/lnL, as in more standard approaches,\nmaking the estimate of the critical temperature much more reliable. Then, we\nconsider the BH model in the presence of a trapping harmonic potential, and\nverify the universality of the trap-size dependence at the BKT critical point.\nThis issue is relevant for experiments with quasi-2D trapped cold atoms."
    },
    {
        "anchor": "Skyrmion Ground States of Rapidly Rotating Few-Fermion Systems: We show that ultracold fermions in an artificial magnetic field open up a new\nwindow to the physics of the spinful fractional quantum Hall effect. We\nnumerically study the lowest energy states of strongly interacting few-fermion\nsystems in rapidly rotating optical microtraps. We find that skyrmion-like\nground states with locally ferromagnetic, long-range spin textures emerge. To\nrealize such states experimentally, rotating microtraps with higher-order\nangular momentum components may be used to prepare fermionic particles in a\nlowest Landau level. We find parameter regimes in which skyrmion-like ground\nstates should be accessible in current experiments and demonstrate an adiabatic\npathway for their preparation in a rapidly rotating harmonic trap. The addition\nof long range interactions will lead to an even richer interplay between spin\ntextures and fractional quantum Hall physics.",
        "positive": "Interacting Floquet polaritons: Ordinarily, photons do not interact with one another. However, atoms can be\nused to mediate photonic interactions, raising the prospect of forming\nsynthetic materials and quantum information systems from photons. One promising\napproach uses electromagnetically-induced transparency with highly-excited\nRydberg atoms to generate strong photonic interactions. Adding an optical\ncavity shapes the available modes and forms strongly-interacting polaritons\nwith enhanced light-matter coupling. However, since every atom of the same\nspecies is identical, the atomic transitions available are only those\nprescribed by nature. This inflexibility severely limits their utility for\nmediating the formation of photonic materials in cavities, as the resonator\nmode spectrum is typically poorly matched to the atomic spectrum. Here we use\nFloquet engineering to redesign the spectrum of Rubidium and make it compatible\nwith the spectrum of a cavity, in order to explore strongly interacting\npolaritons in a customized space. We show that periodically modulating the\nenergy of an atomic level redistributes its spectral weight into\nlifetime-limited bands separated by multiples of the modulation frequency.\nSimultaneously generating bands resonant with two chosen spatial modes of an\noptical cavity supports \"Floquet polaritons\" in both modes. In the presence of\nRydberg dressing, we find that these polaritons interact strongly. Floquet\npolaritons thus provide a promising new path to quantum information\ntechnologies such as multimode photon-by-photon switching, as well as to\nordered states of strongly-correlated photons, including crystals and\ntopological fluids."
    },
    {
        "anchor": "Topologically protected pure helicity cascade in non-Abelian quantum\n  turbulence: By numerically studying non-Abelian quantum turbulence, we find that the\nhelicity cascade and the inverse energy cascade are topologically protected\nagainst reconnection of vortices and lead to the energy spectrum $E(k) \\propto\nk^{-7/3}$ for a large-scale energy injection and $E(k) \\propto k^{-5/3}$ for a\nsmall-scale energy injection with a large-scale web of non-Abelian vortices.\nOur prediction can be tested in the cyclic phase of a spin-2 spinor\nBose-Einstein condensate.",
        "positive": "Bosonic quantum Hall states in single-layer two-dimensional optical\n  lattices: Quantum Hall (QH) states of 2D single layer optical lattices are examined\nusing Bose-Hubbard model (BHM) in presence of artificial gauge field. We study\nthe QH states of both the homogeneous and inhomogeneous systems. For the\nhomogeneous case we use cluster Gutzwiller mean field (CGMF) theory with\ncluster sizes ranging from $2\\times 2$ to $5\\times 5$. We, then, consider the\ninhomogeneous case, which is relevant to experimental realization. In this\ncase, we use CGMF and exact diagonalization (ED). The ED studies are using\nlattice sizes ranging from $3\\times 3$ to $4\\times 12$. Our results show that\nthe geometry of the QH states are sensitive to the magnetic flux $\\alpha$ and\ncluster sizes. For homogeneous system, among various combinations of\n$1/5\\leqslant \\alpha\\leqslant 1/2$ and filling factor $\\nu$, only the QH state\nof $\\alpha=1/4$ with $\\nu=1/2$, $1$, $3/2$ and $2$ occur as ground states. For\nother combinations, the competing superfluid (SF) state is the ground state and\nQH state is metastable. For BHM with envelope potential all the QH states\nobserved in homogeneous system exist for box potentials, but none for the\nharmonic potential. The QH states also persist for very shallow Gaussian\nenvelope potential. As a possible experimental signature we study the two point\ncorrelations of the QH and SF states."
    },
    {
        "anchor": "Analog Kerr Black hole and Penrose effect in a Bose-Einstein Condensate: Analog physics allows simulating inaccessible objects, such as black holes,\nin the lab. We propose to implement an acoustic Kerr black hole with quantized\nangular momentum in a polariton Bose-Einstein condensate. We show that the\nmetric of the condensate is equivalent to the Kerr's one, exhibiting a horizon\nand an ergosphere. Using topological defects as test particles, we demonstrate\nan analog Penrose effect, extracting the rotation energy of the black hole. The\nparticle trajectories are well described by the time-like geodesics of the Kerr\nmetric, confirming the potential of analog gravity.",
        "positive": "Variational approach to the ground state of an impurity in Bose-Einstein\n  condensate: In this paper we consider the effect of self-localization of a quantum\nimpurity in Bose-Einstein condensate. Space correlation function of the\nimpurity is evaluated with the help of the imaginary-time path integral\napproach. Employing the Feynman's variational method we calculate the impurity\ncorrelation function as well as the energy of the system associated with the\nimpurity. The effect of self-localization predicted before within\nGross-Pitaevskii approach is recovered by our treatment. The strong coupling\nregime with negative ground state energy is reached by variational method, and\ncorresponding correlation function is calculated."
    },
    {
        "anchor": "Theory of a peristaltic pump for fermionic quantum fluids: Motivated by the recent developments in fermionic cold atoms and in\nnanostructured systems, we propose the model of a peristaltic quantum pump.\nDifferently from the Thouless paradigm, a peristaltic pump is a quantum device\nthat generates a particle flux as the effect of a sliding finite-size\nmicrolattice. A one-dimensional tight-binding Hamiltonian model of this quantum\nmachine is formulated and analyzed within a lattice Green's function formalism\non the Keldysh contour. The pump observables, as e.g. the pumped particles per\ncycle, are studied as a function of the pumping frequency, the width of the\npumping potential, the particles mean free path and system temperature. The\nproposed analysis applies to arbitrary peristaltic potentials acting on\nfermionic quantum fluids confined to one dimension. These confinement\nconditions can be realized in nanostructured systems or, in a more controllable\nway, in cold atoms experiments. In view of the validation of the theoretical\nresults, we describe the outcomes of the model considering a fermionic cold\natoms system as a paradigmatic example.",
        "positive": "Quantum Effects in the Aubry Transition: The Aubry transition between sliding and pinned phases, driven by the\ncompetition between two incommensurate length scales, represents a paradigm\nthat is applicable to a large variety of microscopically distinct systems.\nDespite previous theoretical studies, it remains an open question to what\nextent quantum effects modify the transition, or are experimentally observable.\nAn experimental platform that can potentially reach the quantum regime has\nrecently become available in the form of trapped laser-cooled ions subject to a\nperiodic optical potential [A. Bylinskii, D. Gangloff, I. Counts, and V.\nVuletic, Nature Materials 15, 717 (2016)]. Using Path-Integral Monte Carlo\n(PIMC) simulation methods, we analyze the impact of quantum tunneling on the\nsliding-to-pinned transition in this system, and determine the phase diagram in\nterms of incommensuration and potential strength. We propose new signatures of\nthe quantum Aubry transition that are robust against thermal and finite-size\neffects, and that can be observed in future experiments."
    },
    {
        "anchor": "Temperature and coupling dependence of the universal contact intensity\n  for an ultracold Fermi gas: Physical properties of an ultracold Fermi gas in the temperature-coupling\nphase diagram can be characterized by the contact intensity C, which enters the\npair-correlation function at short distances and describes how the two-body\nproblem merges into its surrounding. We show that the local order established\nby pairing fluctuations about the critical temperature Tc of the superfluid\ntransition considerably enhances the contact C in a temperature range where\npseudogap phenomena are maximal. Our ab initio results for C in a trap compare\nwell with recently available experimental data over a wide coupling range. An\nanalysis is also provided for the effects of trap averaging on C.",
        "positive": "Acoustic horizon as a phase-slip surface: A recent experiment has demonstrated formation of a supersonic region in a\nconvergent two-dimensional flow of a condensate of cesium atoms. Theoretical\ndescription of this effect has made use of stationary solutions to the\nGross-Pitaevskii equation with a 3-body dissipative term. Here, we further\ndevelop that description, focusing on a new stationary solution, linear\nstability analysis, and properties of the time-dependent \"resistive\" state."
    },
    {
        "anchor": "Tunable Spin-Orbit Coupling via Strong Driving in Ultracold Atom Systems: Spin-orbit coupling (SOC) is an essential ingredient in topological\nmaterials, conventional and quantum-gas based alike.~Engineered spin-orbit\ncoupling in ultracold atom systems --unique in their experimental control and\nmeasurement opportunities-- provides a major opportunity to investigate and\nunderstand topological phenomena.~Here we experimentally demonstrate and\ntheoretically analyze a technique for controlling SOC in a two component\nBose-Einstein condensate using amplitude-modulated Raman coupling.",
        "positive": "Three-vortex configurations in trapped Bose-Einstein condensates: We report on the creation of three-vortex clusters in a $^{87}Rb$\nBose-Einstein condensate by oscillatory excitation of the condensate. This\nprocedure can create vortices of both circulation, so that we are able to\ncreate several types of vortex clusters using the same mechanism. The\nthree-vortex configurations are dominated by two types, namely, an\nequilateral-triangle arrangement and a linear arrangement. We interpret these\nmost stable configurations respectively as three vortices with the same\ncirculation, and as a vortex-antivortex-vortex cluster. The linear\nconfigurations are very likely the first experimental signatures of predicted\nstationary vortex clusters."
    },
    {
        "anchor": "Phases, transitions, and boundary conditions in a model of interacting\n  bosons: We carry out an extensive study of the phase diagrams of the extended Bose\nHubbard model, with a mean filling of one boson per site, in one dimension by\nusing the density matrix renormalization group and show that it contains\nSuperfluid (SF), Mott-insulator (MI), density-wave (DW) and Haldane-insulator\n(HI) phases. We show that the critical exponents and central charges for the\nHI-DW, MI-HI and SF-MI transitions are consistent with those for models in the\ntwo-dimensional Ising, Gaussian, and Berezinskii-Kosterlitz-Thouless (BKT)\nuniversality classes, respectively; and we suggest that the SF-HI transition\nmay be more exotic than a simple BKT transition. We show explicitly that\ndifferent boundary conditions lead to different phase diagrams.",
        "positive": "Strong interactions and bi-excitons in a polariton mixture: We develop a many-body theory for the properties of exciton-polaritons\ninteracting strongly with a Bose-Einstein condensate (BEC) of\nexciton-polaritons in another spin state. Interactions lead to the presence of\na two-body bound state, the bi-exciton, giving rise to a Feshbach resonance in\nthe polariton spectrum when its energy is equal to that of two free polaritons.\nUsing the minimal set of terms to describe this resonance, our theory recovers\nthe main findings of two experiments probing interaction effects for upper and\nlower polaritons in a BEC. This strongly supports that Feshbach physics has\nindeed been realized, and we furthermore extract the energy and decay of\nbiexciton from the experimental data. The decay rate is predicted to be much\nlarger than that coming from its dissociation into two free polaritons\nindicating that other decay channels are important."
    },
    {
        "anchor": "Matter Wave Scattering from Ultracold Atoms in an Optical Lattice: We study matter wave scattering from an ultracold, many body atomic system\ntrapped in an optical lattice. We determine the angular cross section that a\nmatter wave probe sees and show that it is strongly affected by the many body\nphase, superfluid or Mott insulator, of the target lattice. We determine these\ncross sections analytically in the first Born approximation, and we examine the\nvariation at intermediate points in the phase transition by numerically\ndiagonalizing the Bose Hubbard Hamiltonian for a small lattice. We show that\nmatter wave scattering offers a convenient method for non-destructively probing\nthe quantum many body phase transition of atoms in an optical lattice.",
        "positive": "Engineering topological chiral transport in a flat-band lattice of\n  ultracold atoms: The manipulation of particle transport in synthetic quantum matter is an\nactive research frontier for its theoretical importance and potential\napplications. Here we experimentally demonstrate an engineered topological\ntransport in a synthetic flat-band lattice of ultracold $^{87}$Rb atoms. We\nimplement a quasi-one-dimensional rhombic chain with staggered flux in the\nmomentum space of the atomic condensate and observe biased local oscillations\nthat originate from the interplay of the staggered flux and flat-band\nlocalization under the mechanism of Aharonov-Bohm caging. Based on these\nfeatures, we design and experimentally confirm a state-dependent chiral\ntransport under the periodic modulation of the synthetic flux. We show that the\nphenomenon is topologically protected by the winding of the Floquet Bloch bands\nof a coarse-grained effective Hamiltonian. The observed chiral transport offers\na strategy for efficient quantum device design where topological robustness is\nensured by fast Floquet driving and flat-band localization."
    },
    {
        "anchor": "Counterflow and paired superfluidity in one-dimensional Bose mixtures in\n  optical lattices: We study the quantum phases of mixtures of ultra-cold bosonic atoms held in\nan optical lattice that confines motion or hopping to one spatial dimension.\nThe phases are found by using Tomonaga-Luttinger liquid theory as well as the\nnumerical method of time evolving block decimation (TEBD). We consider a binary\nmixture with repulsive intra-species interactions, and either repulsive or\nattractive inter-species interaction. For a homogeneous system, we find paired-\nand counterflow-superfluid phases at different filling and hopping energies. We\nalso predict parameter regions in which these types of superfluid order coexist\nwith charge density wave order. We show that the Tomonaga-Luttinger liquid\ntheory and TEBD qualitatively agree on the location of the phase boundary to\nsuperfluidity. We then describe how these phases are modified and can be\ndetected when an additional harmonic trap is present. In particular, we show\nhow experimentally measurable quantities, such as time-of-flight images and the\nstructure factor, can be used to distinguish the quantum phases. Finally, we\nsuggest applying a Feshbach ramp to detect the paired superfluid state, and a\n$\\pi/2$ pulse followed by Bragg spectroscopy to detect the counterflow\nsuperfluid phase.",
        "positive": "Self-trapping of a Fermi super-fluid in a double-well potential in the\n  BEC-unitarity crossover: We derive a generalized Gross-Pitaevskii density-functional equation\nappropriate to study the Bose-Einstein condensate (BEC) of dimers formed of\nsinglet spin-half Fermi pairs in the BEC-unitarity crossover while the\ndimer-dimer scattering length $a$ changes from 0 to $\\infty$. Using an\neffective one-dimensional form of this equation, we study the phenomenon of\ndynamical self-trapping of a cigar-shaped Fermi super-fluid in the entire\nBEC-unitarity crossover in a double-well potential. A simple two-mode model is\nconstructed to provide analytical insights. We also discuss the consequence of\nour study on the self-trapping of an atomic BEC in a double-well potential."
    },
    {
        "anchor": "Vortex patterns of atomic Bose-Einstein condensates in a\n  density-dependent gauge potential: We theoretically examine the vortex states of a gas of trapped\nquasi-two-dimensional ultracold bosons subject to a density-dependent gauge\npotential, realizing an effective nonlinear rotation of the atomic condensate,\nwhich we also show is within the reach of current experimental techniques with\nultracold atom experiments. The nonlinear rotation has a two-fold effect; as\nwell as distorting the shape of the condensate it also leads to an\ninhomogeneous vorticity resulting in novel morphological and topological\nstates, including ring vortex arrangements that do not follow the standard\nAbrikosov result. The dynamics of trapped vortices are also explored, which\ndiffers from the case of rigid-body rotation due to the absence of a global\nlaboratory reference frame.",
        "positive": "Stable knots in the trapped Bose-Einstein condensates: The knot of spin texture is studied within the two-component Bose-Einstein\ncondensates which are described by the nonlinear Gross-Pitaevskii equations. We\nstart from the non-interacting equations including an axisymmetric harmonic\ntrap to obtain an exact solution, which exhibits a non-trivial topological\nstructure. The spin-texture is a knot with an integral Hopf invariant. The\nstability of the knot is verified by numerically evolving the nonlinear\nGross-Pitaevskii equations along imaginary time."
    },
    {
        "anchor": "Entropy dependence of correlations in one-dimensional SU(N)\n  antiferromagnets: Motivated by the possibility to load multi-color fermionic atoms in optical\nlattices, we study the entropy dependence of the properties of the\none-dimensional antiferromagnetic SU(N) Heisenberg model, the effective model\nof the SU(N) Hubbard model with one particle per site (filling 1/N). Using\ncontinuous-time world line Monte Carlo simulations for N=2 to 5, we show that\ncharacteristic short-range correlations develop at low temperature as a\nprecursor of the ground state algebraic correlations. We also calculate the\nentropy as a function of temperature, and we show that the first sign of\nshort-range order appears at an entropy per particle that increases with N and\nalready reaches 0.8k_B at N=4, in the range of experimentally accessible\nvalues.",
        "positive": "Reduction of local velocity spreads by linear potentials: We study the spreading of the wave function of a Bose-Einstein condensate\naccelerated by a constant force both in the absence and in the presence of\natom-atom interactions. We show that, despite the initial velocity dispersion,\nthe local velocity dispersion defined at a given position downward can reach\nultralow values and be used to probe very narrow energetic structures. We\nexplain how one can define quantum mechanically and without ambiguities the\ndifferent velocity moments at a given position by extension of their classical\ncounterparts. We provide a common theoretical framework for interacting and\nnon-interacting regimes based on the Wigner transform of the initial wave\nfunction that encapsulates the dynamics in a scaling parameter. In the absence\nof interaction, our approach is exact. Using a numerical simulation of the 1D\nGross-Pitaevskii equation, we provide the range of validity of our scaling\napproach and find a very good agreement in the Thomas-Fermi regime. We apply\nthis approach to the study of the scattering of a matter wave packet on a\ndouble barrier potential. We show that a Fabry-Perot resonance in such a cavity\nwith an energy width below the pK range can be probed in this manner. We show\nthat our approach can be readily transposed to a large class of many-body\nquantum systems that exhibit self-similar dynamics."
    },
    {
        "anchor": "Crossover from adiabatic to sudden interaction quenches in the Hubbard\n  model: Prethermalization and nonequilibrium dynamics: The recent experimental implementation of condensed matter models in optical\nlattices has motivated research on their nonequilibrium behavior. Predictions\non the dynamics of superconductors following a sudden quench of the pairing\ninteraction have been made based on the effective BCS Hamiltonian; however,\ntheir experimental verification requires the preparation of a suitable excited\nstate of the Hubbard model along a twofold constraint: (i) a sufficiently\nnonadiabatic ramping scheme is essential to excite the nonequilibrium dynamics,\nand (ii) overheating beyond the critical temperature of superconductivity must\nbe avoided. For commonly discussed interaction ramps there is no clear\nseparation of the corresponding energy scales. Here we show that the matching\nof both conditions is simplified by the intrinsic relaxation behavior of\nultracold fermionic systems: For the particular example of a linear ramp we\nexamine the transient regime of prethermalization [M. Moeckel and S. Kehrein,\nPhys. Rev. Lett. 100, 175702 (2008)] under the crossover from sudden to\nadiabatic switching using Keldysh perturbation theory. A real-time analysis of\nthe momentum distribution exhibits a temporal separation of an early energy\nrelaxation and its later thermalization by scattering events. For long but\nfinite ramping times this separation can be large. In the prethermalization\nregime the momentum distribution resembles a zero temperature Fermi liquid as\nthe energy inserted by the ramp remains located in high energy modes. Thus\nultracold fermions prove robust to heating which simplifies the observation of\nnonequilibrium BCS dynamics in optical lattices.",
        "positive": "Observing Properties of an Interacting Homogeneous Bose--Einstein\n  Condensate: Heisenberg-Limited Momentum Spread, Interaction Energy and\n  Free-Expansion Dynamics: We study the properties of an atomic Bose--Einstein condensate produced in an\noptical-box potential, using high-resolution Bragg spectroscopy. For a range of\nbox sizes, up to $70~\\mu$m, we directly observe Heisenberg-limited momentum\nuncertainty of the condensed atoms. We measure the condensate interaction\nenergy with a precision of $k_B \\times 100$ pK and study, both experimentally\nand numerically, the dynamics of its free expansion upon release from the box\npotential. All our measurements are in good agreement with theoretical\nexpectations for a perfectly homogeneous condensate of spatial extent equal to\nthe size of the box, which also establishes the uniformity of our optical-box\nsystem on a sub-nK energy scale."
    },
    {
        "anchor": "Coexistence of superfluid gap and pseudogap in the BCS-BEC crossover\n  regime of a trapped Fermi gas below $T_{\\rm c}$: We investigate strong pairing fluctuations and effects of a harmonic trap in\nthe superfluid phase of an ultracold Fermi gas. Including amplitude and phase\nfluctuations of the inhomogeneous superfluid order parameter $\\Delta(r)$ in a\ntrap within a combined $T$-matrix theory with the local density approximation,\nwe examine local properties of single-particle excitations and a thermodynamic\nquantity in the BCS-BEC crossover region. Below the superfluid phase transition\ntemperature $T_{\\rm c}$, we show that inhomogeneous pairing fluctuations lead\nto a shell structure of the gas cloud in which the spatial region where the\nordinary BCS-type superfluid density of states appears is surrounded by the\nregion where the pseudogap associated with strong pairing fluctuations\ndominates single-particle excitations. The former spatial region enlarges to\neventually cover the whole gas cloud far below $T_{\\rm c}$. We also examine how\nthis shell structure affects the photoemission spectrum, as well as the local\npressure. Since a cold Fermi gas is always trapped in a harmonic potential, our\nresults would be useful for the study of strong-coupling superfluid physics,\nincluding this realistic situation.",
        "positive": "Crossover in the dynamical critical exponent of a quenched\n  two-dimensional Bose gas: We study the phase ordering dynamics of a uniform Bose gas in two dimensions\nfollowing a quench into the ordered phase. We explore the crossover between\ndissipative and conservative evolution by performing numerical simulations\nwithin the classical field methodology. Regardless of the dissipation strength,\nwe find clear evidence for universal scaling, with dynamical critical exponent\n$z$ characterising the growth of the correlation length. In the dissipative\nlimit we find growth consistent with the logarithmically corrected law\n$[t/\\log(t/t_0)]^{1/z}$, and exponent $z=2$, in agreement with previous\nstudies. Decreasing the dissipation towards the conservative limit, we find\nstrong numerical evidence for the expected growth law $t^{1/z}$. However, we\nobserve a smooth crossover in $z$ that converges to an anomalous value\ndistinctly lower than $2$ at a small finite dissipation strength. We show that\nthis lower exponent may be attributable to a power-law vortex mobility arising\nfrom vortex--sound interactions."
    },
    {
        "anchor": "Strong coupling Bose polarons in a BEC: We use a non-perturbative renormalization group approach to develop a unified\npicture of the Bose polaron problem, where a mobile impurity is strongly\ninteracting with a surrounding Bose-Einstein condensate (BEC). A detailed\ntheoretical analysis of the phase diagram is presented and the\npolaron-to-molecule transition is discussed. For attractive polarons we argue\nthat a description in terms of an effective Fr\\\"ohlich Hamiltonian with\nrenormalized parameters is possible. Its strong coupling regime is realized\nclose to a Feshbach resonance, where we predict a sharp increase of the\neffective mass. Already for weaker interactions, before the polaron mass\ndiverges, we predict a transition to a regime where states exist below the\npolaron energy and the attractive polaron is no longer the ground state. On the\nrepulsive side of the Feshbach resonance we recover the repulsive polaron,\nwhich has a finite lifetime because it can decay into low-lying molecular\nstates. We show for the entire range of couplings that the polaron energy has\nlogarithmic corrections in comparison with predictions by the mean-field\napproach. We demonstrate that they are a consequence of the polaronic mass\nrenormalization which is due to quantum fluctuations of correlated phonons in\nthe polaron cloud.",
        "positive": "Repulsively diverging gradient of the density functional in the Reduced\n  Density Matrix Functional Theory: The Reduced Density Matrix Functional Theory (RDMFT) is a remarkable tool for\nstudying properties of ground states of strongly interacting quantum many body\nsystems. As it gives access to the one-particle reduced density matrix of the\nground state, it provides a perfectly tailored approach to studying the\nBose-Einstein condensation or systems of strongly correlated electrons. In\nparticular, for homogeneous Bose-Einstein condensates as well as for the\nBose-Hubbard dimer it has been recently shown that the relevant density\nfunctional exhibits a repulsive gradient (called the Bose-Einstein condensation\nforce) which diverges when the fraction of non-condensed bosons tends to zero.\nIn this paper, we show that the existence of the Bose-Einstein condensation\nforce is completely universal for any type of pair-interaction and also in the\nnon-homogeneous gases. To this end, we construct a universal family of\nvariational trial states which allows us to suitably approximate the relevant\ndensity functional in a finite region around the set of the completely\ncondensed states. We also show the existence of an analogous repulsive gradient\nin the fermionic RDMFT for the $N$-fermion singlet sector in the vicinity of\nthe set of the Hartree-Fock states. Finally, we show that our approximate\nfunctional may perform well in electron transfer calculations involving low\nnumbers of electrons. This is demonstrated numerically in the Fermi-Hubbard\nmodel in the strongly correlated limit where some other approximate functionals\nare known to fail."
    },
    {
        "anchor": "Optically guided beam splitter for propagating matter waves: We study experimentally and theoretically a beam splitter setup for guided\natomic matter waves. The matter wave is a guided atom laser that can be tuned\nfrom quasi-monomode to a regime where many transverse modes are populated, and\npropagates in a horizontal dipole beam until it crosses another horizontal beam\nat 45$^{\\rm o}$. We show that depending on the parameters of this $X$\nconfiguration, the atoms can all end up in one of the two beams (the system\nbehaves as a perfect guide switch), or be split between the four available\nchannels (the system behaves as a beam splitter). The splitting regime results\nfrom a chaotic scattering dynamics. The existence of these different regimes\nturns out to be robust against small variations of the parameters of the\nsystem. From numerical studies, we also propose a scheme that provides a robust\nand controlled beam splitter in two channels only.",
        "positive": "Can angular oscillations probe superfluidity in dipolar supersolids?: Angular oscillations can provide a useful probe of the superfluid properties\nof a system. Such measurements have recently been applied to dipolar\nsupersolids, which exhibit both density modulation and phase coherence, and for\nwhich robust probes of superfluidity are particularly interesting. So far,\nthese investigations have been confined to linear droplet arrays. Here, we\nexplore angular oscillations in systems with 2D structure, which in principle\nhave greater sensitivity to superfluidity. Surprisingly, in both experiment and\nsimulation, we find that the frequency of angular oscillations remains nearly\nunchanged even when the superfluidity of the system is altered dramatically.\nThis indicates that angular oscillation measurements do not always provide a\nrobust experimental probe of superfluidity with typical experimental protocols."
    },
    {
        "anchor": "Antiferromagnetic Order and Bose-Einstein Condensation in\n  Strongly-Correlated Cold-Atom Systems: Bosonic t-J Model in the Double-CP^1\n  Representation: We study the three-dimensional bosonic t-J model, i.e., the t-J model of\n\"bosonic electrons\" at finite temperatures. This model describes a system of\ncold bosonic atoms with two species in an optical lattice. The model is derived\nfrom the Hubbard model for very large on-site repulsive interaction between\nbosons of same species (hard-core nature) and also strong correlations between\ndifferent species. The operator B_{x\\sigma} for an atom at the site x with a\ntwo-component (pseudo-) spin \\sigma (=1,2) is treated as a hard-core boson\noperator, and represented by a composite of two slave particles; a spinon\ndescribed by a CP^1 field (Schwinger boson) z_{x\\sigma} and a holon described\nby a hard-core-boson field \\phi_x as B_{x\\sigma}=\\phi^\\dag_x z_{x\\sigma}.\n\\phi_x is then expressed by a pseudo-spin, which is, in turn, represented by\nanother CP^1 (pseudo) spinon w_{x\\eta} as \\phi_x = w_{x2}^\\dag w_{x1}. We then\nhave a double-CP^1 representation of the model by z_{x\\sigma} and w_{x\\eta}. By\nmeans of Monte Carlo simulations of this bosonic t-J model, we study its phase\nstructure and the possible phenomena like appearance of antiferromagnetic\nlong-range order, Bose-Einstein condensation, phase separation, etc. They\nshould be compared with the possible experimental results of a recently studied\nboson-boson mixture like ^87Rb and ^41K in an optical lattice.",
        "positive": "Bose-Einstein condensation in a minimal inhomogeneous system: We study the effects of repulsive interaction and disorder on Bosons in a\ntwo-site Bose-Hubbard system, which provides a simple model of the dirty boson\nproblem. By comparison with exact numerical results, we demonstrate how a\nstraightforward application of the Bogoliubov approximation fails even to\ndeliver a qualitatively correct picture: It wrongly predicts an increase of the\ncondensate depletion due to disorder. We show that, in the presence of\ndisorder, the noncommutative character of the condensate operator has to be\nretained for a correct description of the system."
    },
    {
        "anchor": "Modulation instability in quasi two-dimensional spin-orbit coupled\n  Bose-Einstein condensates: We theoretically investigate the dynamics of modulation instability (MI) in\ntwo-dimensional spin-orbit coupled Bose-Einstein condensates (BECs). The\nanalysis is performed for equal densities of pseudo-spin components. Different\ncombination of the signs of intra- and inter-component interaction strengths\nare considered, with a particular emphasize on repulsive interactions. We\nobserve that the unstable modulation builds from originally miscible\ncondensates, depending on the combination of the signs of the intra- and\ninter-component interaction strengths. The repulsive intra- and inter-component\ninteractions admit instability and the MI immiscibility condition is no longer\nsignificant. Influence of interaction parameters such as spin-orbit and Rabi\ncoupling on MI are also investigated. The spin-orbit coupling (SOC) inevitably\ncontributes to instability regardless of the nature of the interaction. In the\ncase of attractive interaction, SOC manifest in enhancing the MI. Thus, a\ncomprehensive study of MI in two-dimensional spin-orbit coupled binary BECs of\npseudo-spin components is presented.",
        "positive": "Composite structure of vortices in two-component Bose-Einstein\n  condensate: In contrast to one-component Bose-Einstein condensate case, the vortices in\ntwo-component condensate can have various complicated structures. The vortices\nin a space-homogeneous Bose-Einstein condensate have been studied in this\npaper. It is shown that the vortex structure is described by three\ndimensionless parameters. This is totally different from the usual\none-component condensate case, where an isolated vortex is described by a\nparameter-less dimensionless equation. The two-component vortex structure\nstrongly depends on the sign of \"interaction\" constant of the components. A few\ntypes of vortices with different qualitative structure are explored. We show\nthat the super-density vortices can exist, when the \"interaction\" constant is\npositive. The super-density vortices have the near-axis density greater than\nthe equilibrium density of a homogeneous space Bose-Einstein condensate. We\nalso show that the vortices with opposite direction of the condensate component\nrotation near the axis and far off the axis can exist."
    },
    {
        "anchor": "Experimental realization of a superfluid stripe phase in a\n  spin-orbit-coupled Bose-Einstein condensate enabled by momentum-space hopping: In the past few decades, the search for supersolid-like phases has attracted\ngreat attention in condensed matter and ultracold atom communities. Here we\nexperimentally demonstrate a route for realizing a superfluid stripe-phase in a\nspin-orbit coupled Bose-Einstein condensate by employing a weak optical lattice\nto induce momentum-space hopping between two spin-orbit band minima. We\ncharacterize the striped ground state as a function of lattice coupling\nstrength and spin-orbit detuning and find good agreement with mean-field\nsimulations. We observe coherent Rabi oscillations in momentum space between\ntwo band minima and demonstrate a long lifetime of the ground state. Our work\noffers an exciting new and stable experimental platform for exploring\nsuperfluid stripe-phases and their exotic excitations, which may shed light on\nthe properties of supersolid-like states.",
        "positive": "Vortices in rotating Bose gas interacting via finite range Gaussian\n  potential in a quasi-two-dimensional harmonic trap: A system of harmonically trapped N=16 spin-$0$ bosons confined in quasi-$2$D\nsymmetrical $x-y$ plane interacting via a finite range repulsive Gaussian\npotential is studied under an externally impressed rotation to an over all\nangular velocity $\\Omega$ about the $z-$axis. The exact diagonalization (ED) of\n$n\\times n$ many-body Hamiltonian matrix in a given subspace of quantized total\nangular momentum $0\\le L_{z} \\le 4N$ is performed using Davidson algorithm. For\n$N=16 \\mbox{and}\\ L_{z}=32$, the dimensionality of the Hilbert space turns out\nto be $n=384559$. The trap velocity $\\Omega$ being the Langrange multiplier\nassociated with the angular momentum $L_{z}$ for the rotating systems, the\n$L_{z}-\\Omega$ phase diagram (or stability line) is drawn which determines the\ncritical angular velocities, $\\Omega_{\\bf c_{i}}, i=1,2..$, at which, for a\ngiven angular momentum $L_{z}$, the system goes through a quantum phase\ntransition. %condensate fraction, von-Neumann entropy exhibit abrupt %(quantum\nphase)jumps. Further with increase in interaction range $\\sigma$, the quantum\nmechanical coherence extends over more and more particles in the system\nresulting in an enhanced stability of the $i^{th}$ vortical state with angular\nmomentum $L_{z}\\left(\\Omega_{c_{i}}\\right)$ leading to a delayed onset of the\nthe next vortical state $L_{z}\\left(\\Omega_{c_{i+1}}\\right)$ at a higher value\nof the next critical angular velocity $\\Omega_{c_{i+1}}$. There is an increase\nin the critical angular velocity $\\left(\\Omega_{\\textbf{c}_{i}},\ni=1,2,3\\cdots\\right)$ and in the largest condensate fraction $\\lambda_{1}$,\ncalculated using single particle reduced density matrix(SPRDM) eigen-values\nwith increase in the interaction range $\\sigma$. We calculated the von-Neumann\nquantum entropy ($S_{1}$), degree of condensation ($C_{d}$) and the conditional\nprobability density (CPDs)."
    },
    {
        "anchor": "Vortex trimer in three-component Bose-Einstein condensates: Vortex trimer is predicted in three-component Bose-Einstein condensates with\ninternal coherent couplings. The molecule is made by three constituent vortices\nwhich are bounded by domain walls of the relative phases. We show that the\nshape and the size of the molecule can be controlled by changing the internal\ncoherent couplings.",
        "positive": "Dynamical excitations in the collision of 2D Bose-Einstein condensates: We carry out simulations of the collision of two components of an\nadiabatically divided, quasi-2D BEC. We identify under, over and critically\ndamped regimes in the dipole oscillations of the components according to the\nbalance of internal and centre-of-mass (c.m.) energies of the components and\ninvestigate the creation of internal excitations. We distinguish the behaviour\nof this system from previous studies of quasi-1D BEC's. In particular we note\nthat the nature of the internal excitations is only essentially sensitive to an\ninitial phase difference between the components in the overdamped regime."
    },
    {
        "anchor": "Polariton fluids for analogue gravity physics: Analogue gravity enables the study of fields on curved spacetimes in the\nlaboratory. There are numerous experimental platforms in which amplification at\nthe event horizon or the ergoregion has been observed. Here, we demonstrate how\noptically generating a defect in a polariton microcavity enables the creation\nof one- and two-dimensional, transsonic fluid flows. We show that this highly\ntuneable method permits the creation of sonic horizons. Furthermore, we present\na rotating geometry akin to the water-wave bathtub vortex. These experiments\nusher-in the possibility of observing stimulated as well as spontaneous\namplification by the Hawking, Penrose and Zeld'ovich effects in fluids of\nlight.",
        "positive": "Controlled Split-Recombination of 2D Matter-Wave Solitons in\n  Time-Dependent Trap: We propose a novel approach to manipulate two-dimensional bright matter-wave\nsolitons by tuning the frequency of the trap which is different from Feshbach\nresonance technique. The exact bright soliton solutions for two-dimensional\nGross-Pitaevskii (GP) equation with attractive interaction strength in a\ntime-dependent trap are constructed analytically and its dynamics show no\ncollapse while modulating the trap frequency. The two-soliton dynamics exhibits\nan interesting splitting and recombination phenomenon which generates\ninterference pattern in the process. This type of behaviour in two-dimensional\nBECs has wider ramifications and our approach opens new avenues in stabilizing\nbright solitons in higher dimensional regime. We have also explored the\nexperimental realization of this novel phenomenon."
    },
    {
        "anchor": "Observation of Pauli blocking in light scattering from quantum\n  degenerate fermions: The Pauli exclusion principle forbids indistinguishable fermions to occupy\nthe same quantum mechanical state. Its implications are profound and it for\nexample accounts for the electronic shell structure of atoms. Here we perform\nmeasurements on the scattering of off-resonant light from ultracold gasses of\nfermionic atoms. For Fermi gases in the quantum degenerate regime, we observe a\nmarked suppression in light scattering as compared to a similarly prepared\nthermal Bose gas. We attribute the observed increased transmission of light\nthrough the quantum degenerate Fermi gas to Pauli blocking, where Fermi-Dirac\nstatistics causes atoms to occupy a large region of the momentum space limiting\nthe number of accessible states for the scattered atom. Our work confirms a\nlongstanding fundamental result in the theory of the optical response of\nquantum gases and is an important step towards novel cooling and thermometry\nmechanisms for degenerate Fermi gases.",
        "positive": "Tensor networks for Lattice Gauge Theories and Atomic Quantum Simulation: We show that gauge invariant quantum link models, Abelian and non-Abelian,\ncan be exactly described in terms of tensor networks states. Quantum link\nmodels represent an ideal bridge between high-energy to cold atom physics, as\nthey can be used in cold-atoms in optical lattices to study lattice gauge\ntheories. In this framework, we characterize the phase diagram of a (1+1)-d\nquantum link version of the Schwinger model in an external classical background\nelectric field: the quantum phase transition from a charge and parity ordered\nphase with non-zero electric flux to a disordered one with a net zero electric\nflux configuration is described by the Ising universality class."
    },
    {
        "anchor": "Fortran programs for the time-dependent Gross-Pitaevskii equation in a\n  fully anisotropic trap: We develop simple numerical algorithms for both stationary and non-stationary\nsolutions of the time-dependent Gross-Pitaevskii (GP) equation describing the\nproperties of Bose-Einstein condensates at ultra low temperatures. In\nparticular, we consider algorithms involving real and imaginary-time\npropagation based on a split-step Crank-Nicolson method. In a\none-space-variable form of the GP equation we consider the one-dimensional\nlinear, two-dimensional circularly symmetric, and the three-dimensional\nspherically-symmetric traps. In the two-space-variable form we consider the GP\nequation in two-dimensional anisotropic and three-dimensional axially-symmetric\ntraps. The fully-anisotropic three-dimensional GP equation is also considered.\nNumerical results for the chemical potential and root-mean-square size of\nstationary states are reported using imaginary-time propagation programs for\nall the cases and compared with previously obtained results. Also presented are\nnumerical results of non-stationary oscillation for different trap symmetries\nusing real-time propagation programs. A set of convenient working codes\ndeveloped in Fortran 77 are also provided for all these cases (twelve programs\nin all). In the case of two or three space variables, {Fortran 90/95 versions\nprovide some simplification over the Fortran 77 programs}, and these programs\nare also included (six programs in all).",
        "positive": "Propagation of Second sound in a superfluid Fermi gas in the unitary\n  limit: We study sound propagation in a uniform superfluid gas of Fermi atoms in the\nunitary limit. The existence of normal and superfluid components leads to\nappearance of two sound modes in the collisional regime, referred to as first\nand second sound. The second sound is of particular interest as it is a clear\nsignal of a superfluid component. Using Landau's two-fluid hydrodynamic theory,\nwe calculate hydrodynamic sound velocities and these weights in the density\nresponse function. The latter is used to calculate the response to a sudden\nmodification of the external potential generating pulse propagation. The\namplitude of a pulse which is proportional to the weight in the response\nfunction, is calculated the basis of the approach of Nozieres and Schmitt-Rink\n(NSR) for the BCS-BEC crossover. We show that, in a superfluid Fermi gas at\nunitarity, the second sound pulse is excited with an appreciate amplitude by\ndensity perturbations."
    },
    {
        "anchor": "The Renormalised Bogoliubov-Fr\u00f6hlich Hamiltonian: The Bogoliubov-Fr\\\"ohlich Hamiltonian models the interaction of an impurity\nwith the excitations of a Bose-Einstein condensate. It has been observed that\nthe dependence of the ground state energy on the ultraviolet cutoff differs\nsignificantly from what would be expected from similar well-known models. We\ngive a detailed explanation of this UV behaviour, and provide an explicit\nrepresentation of the renormalised Hamiltonian.",
        "positive": "Quadratic fractional solitons: We introduce a system combining the quadratic self-attractive or composite\nquadratic-cubic nonlinearity, acting in the combination with the fractional\ndiffraction, which is characterized by its L\\'{e}vy index $\\alpha $. The model\napplies to a gas of quantum particles moving by L\\'{e}vy flights, with the\nquadratic term representing the Lee-Huang-Yang correction to the mean-field\ninteractions. A family of fundamental solitons is constructed in a numerical\nform, while the dependence of its norm on the chemical potential characteristic\nis obtained in an exact analytical form. The family of \\textit{quasi-Townes\nsolitons}, appearing in the limit case of $\\alpha =1/2$, is investigated by\nmeans of a variational approximation. A nonlinear lattice, represented by\nspatially periodical modulation of the quadratic term, is briefly addressed\ntoo. The consideration of the interplay of competing quadratic (attractive) and\ncubic (repulsive) terms with a lattice potential reveals families of single-,\ndouble-, and triple-peak gap solitons (GSs) in two finite bandgaps. The\ncompeting nonlinearity gives rise to alternating regions of stability and\ninstability of the GS, the stability intervals shrinking with the increase of\nthe number of peaks in the GS."
    },
    {
        "anchor": "Coherent excitation transport through ring-shaped networks: The coherent quantum transport of matter wave through a ring-shaped circuit\nattached to leads defines an iconic system in mesoscopic physics that has\nallowed both to explore fundamental questions in quantum science and to draw\nimportant avenues for conceiving devices of practical use.\n  Here we study the source-to-drain transport of excitations going through a\nring-network, without propagation of matter waves. We model the circuit in\nterms of a spin system with specific long-range interactions that are relevant\nfor quantum technology, such as Rydberg atoms trapped in optical tweezers or\nion traps. Inspired by the logic of rf- and dc-SQUIDs, we consider rings with\none and two local energy offsets, or detunings. As a combination of specific\nphase shifts in going though the localized detunings and as a result of\ncoherent tunneling, we demonstrate how the transport of excitations can be\ncontrolled, with a distinctive dependence on the range of interactions.",
        "positive": "Fermionic Superradiance in a Transversely Pumped Optical Cavity: Following the experimental realization of Dicke superradiance in Bose gases\ncoupled to cavity light fields, we investigate the behavior of ultra cold\nfermions in a transversely pumped cavity. We focus on the equilibrium phase\ndiagram of spinless fermions coupled to a single cavity mode and establish a\nzero temperature transition to a superradiant state. In contrast to the bosonic\ncase, Pauli blocking leads to lattice commensuration effects that influence\nself-organization in the cavity light field. This includes a sequence of\ndiscontinuous transitions with increasing atomic density and tricritical\nsuperradiance. We discuss the implications for experiment."
    },
    {
        "anchor": "Bloch oscillations in lattice potentials with controlled aperiodicity: We numerically investigate the damping of Bloch oscillations in a\none-dimensional lattice potential whose translational symmetry is broken in a\nsystematic manner, either by making the potential bichromatic or by introducing\nscatterers at distinct lattice sites. We find that the damping strongly depends\non the ratio of lattice constants in the bichromatic potential, and that even a\nsmall concentration of scatterers can lead to strong damping. Moreover,\nmean-field interactions are able to counteract aperiodicity-induced damping of\nBloch oscillations.",
        "positive": "Sound waves and modulational instabilities on continuous wave solutions\n  in spinor Bose-Einstein condensates: We analyze sound waves (phonons, Bogoliubov excitations) propagating on\ncontinuous wave (cw) solutions of repulsive $F=1$ spinor Bose-Einstein\ncondensates (BECs), such as $^{23}$Na (which is antiferromagnetic or polar) and\n$^{87}$Rb (which is ferromagnetic). Zeeman splitting by a uniform magnetic\nfield is included. All cw solutions to ferromagnetic BECs with vanishing\n$M_F=0$ particle density and non-zero components in both $M_F=\\pm 1$ fields are\nsubject to modulational instability (MI). MI increases with increasing particle\ndensity. MI also increases with differences in the components' wavenumbers;\nthis effect is larger at lower densities but becomes insignificant at higher\nparticle densities. CW solutions to antiferromagnetic (polar) BECS with\nvanishing $M_F=0$ particle density and non-zero components in both $M_F=\\pm 1$\nfields do not suffer MI if the wavenumbers of the components are the same. If\nthere is a wavenumber difference, MI initially increases with increasing\nparticle density, then peaks before dropping to zero beyond a given particle\ndensity. The cw solutions with particles in both $M_F=\\pm 1$ components and\nnonvanishing $M_F=0$ components do not have MI if the wavenumbers of the\ncomponents are the same, but do exhibit MI when the wavenumbers are different.\nDirect numerical simulations of a cw with weak white noise confirm that weak\nnoise grows fastest at wavenumbers with the largest MI, and shows some of the\nresults beyond small amplitude perturbations. Phonon dispersion curves are\ncomputed numerically; we find analytic solutions for the phonon dispersion in a\nvariety of limiting cases."
    },
    {
        "anchor": "Strongly correlated one-dimensional Bose-Fermi quantum mixtures:\n  symmetry and correlations: We consider multi-component quantum mixtures (bosonic, fermionic, or mixed)\nwith strongly repulsive contact interactions in a one-dimensional harmonic\ntrap. In the limit of infinitely strong repulsion and zero temperature, using\nthe class-sum method, we study the symmetries of the spatial wave function of\nthe mixture. We find that the ground state of the system has the most symmetric\nspatial wave function allowed by the type of mixture. This provides an example\nof the generalized Lieb-Mattis theorem. Furthermore, we show that the symmetry\nproperties of the mixture are embedded in the large-momentum tails of the\nmomentum distribution, which we evaluate both at infinite repulsion by an exact\nsolution and at finite interactions using a numerical DMRG approach. This\nimplies that an experimental measurement of the Tan's contact would allow to\nunambiguously determine the symmetry of any kind of multi-component mixture.",
        "positive": "REVIEW. Quantum optics with ultracold quantum gases: towards the full\n  quantum regime of the light-matter interaction: Although the study of ultracold quantum gases trapped by light is a prominent\ndirection of modern research, the quantum properties of light were widely\nneglected in this field. Quantum optics with quantum gases closes this gap and\naddresses phenomena, where the quantum statistical nature of both light and\nultracold matter play equally important roles. First, light can serve as a\nquantum nondemolition (QND) probe of the quantum dynamics of various ultracold\nparticles from ultracold atomic and molecular gases to nanoparticles and\nnanomechanical systems. Second, due to dynamic light-matter entanglement,\nprojective measurement-based preparation of the many-body states is possible,\nwhere the class of emerging atomic states can be designed via optical geometry.\nLight scattering constitutes such a quantum measurement with controllable\nmeasurement back-action. As in cavity-based spin squeezing, atom number\nsqueezed and Schroedinger cat states can be prepared. Third, trapping atoms\ninside an optical cavity one creates optical potentials and forces, which are\nnot prescribed but quantized and dynamical variables themselves. Ultimately,\ncavity QED with quantum gases requires a self-consistent solution for light and\nparticles, which enriches the picture of quantum many-body states of atoms\ntrapped in quantum potentials. This will allow quantum simulations of phenomena\nrelated to the physics of phonons, polarons, polaritons and other quantum\nquasiparticles."
    },
    {
        "anchor": "Jet Sub-structure in Fireworks Emission from Non-uniform and Rotating\n  Bose-Einstein Condensates: We show that jet emission from a Bose condensate with periodically driven\ninteractions, a.k.a. \"Bose fireworks\", contains essential information on the\ncondensate wavefunction, which is difficult to obtain using standard detection\nmethods. We illustrate the underlying physics with two examples. When\ncondensates acquire phase patterns from external potentials or from vortices,\nthe jets display novel sub-structure, such as oscillations or spirals, in their\ncorrelations. Through a comparison of theory, numerical simulations and\nexperiments, we show how one can quantitatively extract the phase and the\nhelicity of a condensate from the emission pattern. Our work demonstrating the\nstrong link between jet emission and the underlying quantum system, bears on\nthe recent emphasis on jet sub-structure in particle physics.",
        "positive": "Kubo formula for non-Hermitian systems and tachyon optical conductivity: Linear response theory plays a prominent role in various fields of physics\nand provides us with extensive information about the thermodynamics and\ndynamics of quantum and classical systems. Here we develop a general theory for\nthe linear response in non-Hermitian systems with non-unitary dynamics and\nderive a modified Kubo formula for the generalized susceptibility for arbitrary\n(Hermitian and non-Hermitian) system and perturbation. As an application, we\nevaluate the dynamical response of a non-Hermitian, one-dimensional Dirac model\nwith imaginary and real masses, perturbed by a time-dependent electric field.\nThe model has a rich phase diagram, and in particular, features a tachyon\nphase, where excitations travel faster than an effective speed of light.\nSurprisingly, we find that the dc conductivity of tachyons is finite, and the\noptical sum rule is exactly satisfied for all masses. Our results highlight the\npeculiar properties of the Kubo formula for non-Hermitian systems and are\napplicable for a large variety of settings."
    },
    {
        "anchor": "Penrose-Onsager Criterion Validation in a One-Dimensional Polariton\n  Condensate: We perform quantum tomography on one-dimensional polariton condensates,\nspontaneously occurring in linear disorder valleys in a CdTe planar microcavity\nsample. By the use of optical interferometric techniques, we determine the\nfirst-order coherence function and the amplitude and phase of the order\nparameter of the condensate, providing a full reconstruction of the single\nparticle density matrix for the polariton system. The experimental data are\nused as input to theoretically test the consistency of Penrose-Onsager\ncriterion for Bose-Einstein condensation in the framework of nonequilibrium\npolariton condensates. The results confirm the pertinence and validity of the\ncriterion for a non equilibrium condensed gas.",
        "positive": "Particle imbalanced weakly interacting quantum droplets in one-dimension: We explore the formation of one-dimensional two-component quantum droplets\nwith intercomponent particle imbalance using an ab-initio many-body method. It\nis shown that for moderate particle imbalance each component maintains its\ndroplet flat-top or Gaussian type character depending on the intercomponent\nattraction. Importantly, large particle imbalance leads to a flat-top shape of\nthe majority component with the minority exhibiting spatially localized\nconfigurations. The latter imprint modulations on the majority component which\nbecome more pronounced for increasing interspecies attraction. The same holds\nfor larger mass or increasing repulsion of the minority species. Such\nstructural transitions are also evident in the underlying two-body correlation\nfunctions. To interpret the origin and characteristics of these droplet states\nwe derive an effective model based on the established Lee-Huang-Yang theory\nproviding adequate qualitative analytical predictions even away from its\nexpected parametric region of validity. In contrast, the droplet character is\nfound to vanish in the presence of fermionic minority atoms. Our results pave\nthe way for unveiling complex droplet phases of matter."
    },
    {
        "anchor": "$p$ orbitals in 3D lattices; fermions, bosons and (exotic) models of\n  magnetism: We demonstrate how different types of $SU(3)$ Heisenberg models can be\nimplemented with the use of the $p$ orbitals of three dimensional optical\nlattices. By considering a Mott insulator with unit filling, the dynamics is\nwell described by an effective model derived from the perturbative treatment of\nthe tunneling elements relative to the onsite interaction terms. This yields\nsystems with degrees of freedom that are generators of the $SU(3)$ group, which\nextends the Heisenberg models frequently used to analyze quantum magnetism. Due\nto the different character of interactions in the bosonic and fermionic cases,\nthe choice of atom determines what type of anisotropies will appear in the\ncouplings of the corresponding effective Hamiltonians. Experimental schemes for\ndetection and manipulation of these systems are presented, and properties of\nthe ground states of selected examples are discussed.",
        "positive": "Correlated many-body calculation to study characteristics of Shannon\n  information entropy for ultracold trapped interacting bosons: A correlated many-body calculation is presented to characterize the Shannon\ninformation entropy of trapped interacting bosons. We reformulate the one-body\nShannon information entropy in terms of the one-body probability density. The\nminimum limit of the entropy uncertainty relation (EUR) is approached by making\n$N$ very small in our numerical work. We examine the effect of correlations in\nthe calculation of information entropy. Comparison with the mean-field result\nshows that the correlated basis function is indeed required to characterize the\nimportant features of the information entropies. We also accurately calculate\nthe point of critical instability of an attractive BEC, which is in close\nagreement with the experimental value. Next we calculate two-body entropies in\nposition and momentum spaces and study quantum correlations in the attractive\nBEC."
    },
    {
        "anchor": "Controlled Creation and Decay of Singly-Quantized Vortices in a Polar\n  Magnetic Phase: We experimentally and theoretically explore the creation and time evolution\nof vortex lines in the polar magnetic phase of a trapped spin-1 $^{87}$Rb\nBose-Einstein condensate. A process of phase-imprinting a nonsingular vortex,\nits decay into a pair of singular spinor vortices, and a rapid exchange of\nmagnetic phases creates a pair of three-dimensional, singular singly-quantized\nvortex lines with core regions that are filled with atoms in the ferromagnetic\nphase. Atomic interactions guide the subsequent vortex dynamics, leading to\ncore structures that suggest the decay of the singly-quantized vortices into\nhalf-quantum vortices.",
        "positive": "Giant increase of temporal coherence in optically trapped polariton\n  condensate: Coherent bosonic ensembles offer the promise of harnessing quantum effects in\nphotonic and quantum circuits. In the dynamic equilibrium regime, the\napplication of polariton condensates is hindered by exciton-polariton\nscattering induced de-coherence in the presence of a dark exciton reservoir. By\nspatially separating the condensate from the reservoir, we drive the system\ninto the weak interaction regime, where the ensemble coherence time exceeds the\nindividual particle lifetime by nearly three orders of magnitude. The observed\nnanosecond coherence provides an upper limit for polariton self-interactions.\nIn contrast to conventional photon lasers, we observe an increased contribution\nfrom the super-Poissonian component of the condensate to the overall particle\nnumber fluctuations. Coupled with the recent emergence of a quantum regime in\npolaritonics, coherence times extended to several nanoseconds favour the\nrealization of quantum information protocols."
    },
    {
        "anchor": "Three-dimensional solitons in Rydberg-Dressed cold atomic gases with\n  spin-orbit coupling: We present numerical results for three-dimensional (3D) solitons with\nsymmetries of the semi-vortex (SV) and mixed-mode (MM) types, which can be\ncreated in spinor Bose-Einstein condensates of Rydberg atoms under the action\nof the spin-orbit coupling (SOC). By means of systematic numerical\ncomputations, we demonstrate that the interplay of SOC and long-range\nspherically symmetric Rydberg interactions stabilize the 3D solitons, improving\ntheir resistance to collapse. We find how the stability range depends on the\nstrengths of the SOC and Rydberg interactions and the soft-core atomic radius.",
        "positive": "Geometric origin of superfluidity in the Lieb lattice flat band: The ground state and transport properties of the Lieb lattice flat band in\nthe presence of an attractive Hubbard interaction are considered. It is shown\nthat the superfluid weight can be large even for an isolated and strictly flat\nband. Moreover the superfluid weight is proportional to the interaction\nstrength and to the quantum metric, a band structure invariant obtained from\nthe flat-band Bloch functions. These predictions are amenable to verification\nwith ultracold gases and may explain the anomalous behaviour of the superfluid\nweight of high-Tc superconductors."
    },
    {
        "anchor": "Multimer formation in 1D two-component gases and trimer phase in the\n  asymmetric attractive Hubbard model: We consider two-component one-dimensional quantum gases at special imbalanced\ncommensurabilities which lead to the formation of multimer (multi-particle\nbound-states) as the dominant order parameter. Luttinger liquid theory supports\na mode-locking mechanism in which mass (or velocity) asymmetry is identified as\nthe key ingredient to stabilize such states. While the scenario is valid both\nin the continuum and on a lattice, the effects of umklapp terms relevant for\ndensities commensurate with the lattice spacing are also mentioned. These ideas\nare illustrated and confronted with the physics of the asymmetric\n(mass-imbalanced) fermionic Hubbard model with attractive interactions and\ndensities such that a trimer phase can be stabilized. Phase diagrams are\ncomputed using density-matrix renormalization group techniques, showing the\nimportant role of the total density in achieving the novel phase. The effective\nphysics of the trimer gas is as well studied. Lastly, the effect of a parabolic\nconfinement and the emergence of a crystal phase of trimers are briefly\naddressed. This model has connections with the physics of imbalanced\ntwo-component fermionic gases and Bose-Fermi mixtures as the latter gives a\ngood phenomenological description of the numerics in the strong-coupling\nregime.",
        "positive": "Grassmann phase space dynamics of strongly-correlated fermion: We discuss the numerical implementation of two related representations of\nfermionic density matrices which have been introduced in Annals of Physics 370,\n12 (2016). In both of them, the density matrix is expanded in a basis of\nBargmann coherent states with weights given by the two phase space\ndistributions. We derive the equations of motion for the distributions when\nimaginary time evolution is generated by the Hubbard Hamiltonian. One of them\nis a Grassmann Fokker-Planck equation that can be re-cast into a remarkably\nsimple It\\^{o} form involving solely complex variables. In spite of this simple\nform, we demonstrate that complications arise in numerically computing the\nexpectation value of any observable. These are due to exponential growth in the\nmatrix elements of the stochastic propagator, delicate numerical sensitivity in\nperforming primitive linear algebra operations, and the re-appearance of a sign\nproblem."
    },
    {
        "anchor": "The multiconfigurational time-dependent Hartree method for bosons with\n  internal degrees of freedom: Theory and composite fragmentation of\n  multi-component Bose-Einstein condensates: In this paper the multiconfigurational time-dependent Hartree for bosons\nmethod (MCTDHB) is derived for the case of $N$ identical bosons with internal\ndegrees of freedom. The theory for bosons with internal degrees of freedom\nconstitutes a generalization of the MCTDHB method that substantially enriches\nthe many-body physics that can be described. We demonstrate that the\nnumerically exact solution of the time-dependent many-body Schr\\\"odinger\nequation for interacting bosonic particles with internal degrees of freedom is\nnow feasible. We report on the MCTDHB equations of motion for bosons with\ninternal degrees of freedom and their implementation for a general many-body\nHamiltonian with one-body and two-body terms that, both, may depend on the\ninternal states of the considered particles. To demonstrate the capabilities of\nthe theory and its software implementation integrated in the MCTDH-X software,\nwe apply MCTDHB to the emergence of fragmentation of parabolically trapped\nbosons with two internal states: we study the groundstate of $N=100$\nparabolically confined bosons as a function of the splitting between the\nstate-dependent minima of the two parabolic potentials. To quantify the\ncoherence of the system we compute its normalized one-body correlation\nfunction. We find that the coherence within each internal state of the atoms is\nmaintained, while it is lost between the different internal states. This is a\nhallmark of a new kind of fragmentation which is absent in bosons without\ninternal structure. We term the emergent phenomenon \"composite fragmentation\".",
        "positive": "Critical velocity of superfluid flow through single barrier and periodic\n  potentials: We investigate the problem of an ultracold atomic gas in the superfluid phase\nflowing in the presence of a potential barrier or a periodic potential. We use\na hydrodynamic scheme in the local density approximation (LDA) to obtain an\nanalytic expression for the critical current as a function of the barrier\nheight or the lattice intensity, which applies to both Bose and Fermi\nsuperfluids. In this scheme, the stationary flow becomes energetically unstable\nwhen the local superfluid velocity is equal to the local sound velocity at the\npoint where the external potential is maximum. We compare this prediction with\nthe results of the numerical solutions of the Gross-Pitaevskii and\nBogoliubov-de Gennes equations. We discuss the role of long wavelength\nexcitations in determining the critical velocity. Our results allow one to\nidentify the different regimes of superfluid flow, namely, the LDA hydrodynamic\nregime, the regime of quantum effects beyond LDA for weak barriers and the\nregime of tunneling between weakly coupled superfluids for strong barriers. We\nfinally discuss the relevance of these results in the context of current\nexperiments with ultracold gases."
    },
    {
        "anchor": "Fermi-Bose mixture in mixed dimensions: One of the challenging goals in the studies of many-body physics with\nultracold atoms is the creation of a topological $p_{x} + ip_{y}$ superfluid\nfor identical fermions in two dimensions (2D). The expectations of reaching the\ncritical temperature $T_c$ through p-wave Feshbach resonance in spin-polarized\nfermionic gases have soon faded away because on approaching the resonance, the\nsystem becomes unstable due to inelastic-collision processes. Here, we consider\nan alternative scenario in which a single-component degenerate gas of fermions\nin 2D is paired via phonon-mediated interactions provided by a 3D BEC\nbackground. Within the weak-coupling regime, we calculate the critical\ntemperature $T_c$ for the fermionic pair formation, using Bethe-Salpeter\nformalism, and show that it is significantly boosted by higher-order\ndiagramatic terms, such as phonon dressing and vertex corrections. We describe\nin detail an experimental scheme to implement our proposal, and show that the\nlong-sought p-wave superfluid is at reach with state-of-the-art experiments.",
        "positive": "Charge Gaps at Fractional Fillings in Boson Hubbard Ladders: The Bose-Hubbard Hamiltonian describes the competition between superfluidity\nand Mott insulating behavior at zero temperature and commensurate filling as\nthe strength of the on-site repulsion is varied. Gapped insulating phases also\noccur at non-integer densities as a consequence of longer ranged repulsive\ninteractions. In this paper we explore the formation of gapped phases in\ncoupled chains due instead to anisotropies $t_x \\neq t_y$ in the bosonic\nhopping, extending the work of Crepin {\\it et al.} [Phys. Rev. B 84, 054517\n(2011)] on two coupled chains, where a gap was shown to occur at half filling\nfor arbitrarily small interchain hopping $t_y$. Our main result is that, unlike\nthe two-leg chains, for three- and four-leg chains, a charge gap requires a\nfinite nonzero critical $t_y$ to open. However, these finite values are\nsurprisingly small, well below the analogous values required for a fermionic\nband gap to open."
    },
    {
        "anchor": "Spin-Energy Correlation in Degenerate Weakly-Interacting Fermi Gases: Weakly interacting Fermi gases exhibit rich collective dynamics in\nspin-dependent potentials, arising from correlations between spin degrees of\nfreedom and conserved single atom energies, offering broad prospects for\nsimulating many-body quantum systems by engineering energy-space \"lattices,\"\nwith controlled energy landscapes and site to site interactions. Using quantum\ndegenerate clouds of $^6$Li, confined in a spin-dependent harmonic potential,\nwe measure complex, time-dependent spin-density profiles, varying on length\nscales much smaller than the cloud size. We show that a one-dimensional mean\nfield model, without additional simplifying approximations, quantitatively\npredicts the observed fine structure. We measure the magnetic fields where the\nscattering lengths vanish for three different hyperfine state mixtures to\nprovide new constraints on the collisional (Feshbach) resonance parameters.",
        "positive": "Establishing Conservation Laws in Pair Correlated Many Body theories: T\n  matrix Approaches: We address conservation laws associated with current, momentum and energy and\nshow how they can be satisfied within many body theories which focus on pair\ncorrelations. Of interest are two well known t-matrix theories which represent\nmany body theories which incorporate pairing in the normal state. The first of\nthese is associated with Nozieres Schmitt-Rink theory, while the second\ninvolves the t-matrix of a BCS-Leggett like state as identified by Kadanoff and\nMartin. T-matrix theories begin with an ansatz for the single particle self\nenergy and are to be distinguished from $\\Phi$-derivable theories which\nintroduce an ansatz for a particular contribution to the thermodynamical\npotential. Conservation laws are equivalent to Ward identities which we address\nin some detail here. Although $\\Phi$-derivable theories are often referred to\nas \"conserving theories\", a consequence of this work is the demonstration that\nthese two t-matrix approaches similarly can be made to obey all conservation\nlaws. Moreover, simplifying approximations in $\\Phi$-derivable theories,\nfrequently lead to results which are incompatible with conservation."
    },
    {
        "anchor": "Mode switching dynamics in organic polariton lasing: We study the dynamics of multimode polariton lasing in organic microcavities\nby using a second-order cumulant equation approach. By inspecting the time\nevolution of the photon mode occupations, we show that if multiple lasing peaks\nare observed in time-integrated mode occupations, the reason can be either\nbi-modal lasing or temporal switching between several modes. The former takes\nplace within a narrow range of parameters while the latter occurs more widely.\nWe find that the origin of the temporal switching is different in the weak- and\nstrong-coupling regimes. At weak coupling slope efficiency is the determining\nfactor, while for strong coupling it is changes in the eigenmodes and gain\nspectrum upon pumping. This difference is revealed by investigating the\nphotoluminescence and momentum-resolved gain spectra. Our results underscore\nthe importance of understanding the time evolution of the populations when\ncharacterizing the lasing behaviour of a multimode polariton system, and show\nhow these features differ between weak and strong coupling.",
        "positive": "Relaxation, chaos, and thermalization in a three-mode model of a BEC: We study the complex quantum dynamics of a system of many interacting atoms\nin an elongated anharmonic trap. The system is initially in a Bose-Einstein\ncondensed state, well described by Thomas-Fermi profile in the elongated\ndirection and the ground state in the transverse directions. After a sudden\nquench to a coherent superposition of the ground and lowest energy transverse\nmodes, quantum dynamics starts. We describe this process employing a three-mode\nmany-body model. The experimental realization of this system displays decaying\noscillations of the atomic density distribution. While a mean-field description\npredicts perpetual oscillations of the atomic density distribution, our quantum\nmany-body model exhibits a decay of the oscillations for sufficiently strong\natomic interactions. We associate this decay with the fragmentation of the\ncondensate during the evolution. The decay and fragmentation are also linked\nwith the approach of the many-body model to the chaotic regime. The approach to\nchaos lifts degeneracies and increases the complexity of the eigenstates,\nenabling the relaxation to equilibrium and the onset of thermalization. We\nverify that the damping time and quantum signatures of chaos show similar\ndependences on the interaction strength and on the number of atoms."
    },
    {
        "anchor": "Collective excitation frequencies and stationary states of trapped\n  dipolar Bose-Einstein condensates in the Thomas-Fermi regime: We present a general method for obtaining the exact static solutions and\ncollective excitation frequencies of a trapped Bose-Einstein condensate (BEC)\nwith dipolar atomic interactions in the Thomas-Fermi regime. The method\nincorporates analytic expressions for the dipolar potential of an arbitrary\npolynomial density profile, thereby reducing the problem of handling non-local\ndipolar interactions to the solution of algebraic equations.\n  We comprehensively map out the static solutions and excitation modes,\nincluding non-cylindrically symmetric traps, and also the case of negative\nscattering length where dipolar interactions stabilize an otherwise unstable\ncondensate. The dynamical stability of the excitation modes gives insight into\nthe onset of collapse of a dipolar BEC. We find that global collapse is\nconsistently mediated by an anisotropic quadrupolar collective mode, although\nthere are two trapping regimes in which the BEC is stable against quadrupole\nfluctuations even as the ratio of the dipolar to s-wave interactions becomes\ninfinite. Motivated by the possibility of fragmented BEC in a dipolar Bose gas\ndue to the partially attractive interactions, we pay special attention to the\nscissors modes, which can provide a signature of superfluidity, and identify a\nlong-range restoring force which is peculiar to dipolar systems. As part of the\nsupporting material for this paper we provide the computer program used to make\nthe calculations, including a graphical user interface.",
        "positive": "Open Quantum-System Simulation of Faraday's Induction Law via Dynamical\n  Instabilities: We propose a novel type of a Bose-Hubbard ladder model based on an open\nquantum-gas--cavity-QED setup to study the physics of dynamical gauge\npotentials. Atomic tunneling along opposite directions in the two legs of the\nladder is mediated by photon scattering from transverse pump lasers to two\ndistinct cavity modes. The resulting interplay between cavity photon\ndissipation and the optomechanical atomic back-action then induces an\naverage-density-dependent dynamical gauge field. The dissipation-stabilized\nsteady-state atomic motion along the legs of the ladder leads either to a pure\nchiral current, screening the induced dynamical magnetic field as in the\nMeissner effect, or generates simultaneously chiral and particle currents. For\nsufficiently strong pump the system enters into a dynamically unstable regime\nexhibiting limit-cycle and period-doubled oscillations. Intriguingly, an\nelectromotive force is induced in this dynamical regime as expected from an\ninterpretation based on Faraday's law of induction for the time-dependent\nsynthetic magnetic flux."
    },
    {
        "anchor": "General memory kernels and further corrections to the variational path\n  integral approach for the Bogoliubov-Fr\u00f6hlich Hamiltonian: The celebrated variational path integral approach to the polaron problem\nshows remarkable discrepancies with diagrammatic Monte Carlo for the\nBogoliubov-Fr\\\"{o}hlich Hamiltonian which describes an impurity weakly coupled\nto a Bose condensed atomic gas. It has been shown both via a renormalization\ngroup approach and by the method of correlated Gaussian wavefunctions that the\nmodel has a subtle UV divergence caused by quantum fluctuations, which are not\ncaptured within Feynman's approach. In this work we address the issues with\nFeynman's approach and show that by extending the model action to a more\ngeneral form, and by considering higher order corrections beyond the\nJensen-Feynman inequality, a good agreement with diagrammatic Monte Carlo can\nbe obtained.",
        "positive": "Interplay between exotic superfluidity and magnetism in a chain of\n  four-component ultracold atoms: We investigate the spin-polarized chain of ultracold fermionic atoms with\nspin-3/2 described by the fermionic Hubbard model with SU(4) symmetric\nattractive interaction. The competition of bound pairs, trions, quartets and\nunbound atoms is studied analytically and by density matrix renormalization\ngroup simulations. We find several distinct states where bound particles\ncoexist with the ferromagnetic state of unpaired fermions. In particular, an\nexotic inhomogeneous Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)-type superfluid of\nquartets in a magnetic background of uncorrelated atoms is found for weaker\ninteractions. We show that the system can be driven from this quartet-FFLO\nstate to a molecular state of localized quartets which is also reflected in the\nstatic structure factor. For strong enough coupling, spatial segregation\nbetween molecular crystals and ferromagnetic liquids emerges due to the large\neffective mass of the composite particles."
    },
    {
        "anchor": "Dynamics of rotating spin-orbit-coupled Bose-Einstein condensates in a\n  quasicrystalline optical lattice: We investigate the dynamics of rotating pseudo-spin-1/2 Bose-Einstein\ncondensates (BECs) with Rashba spin-orbit coupling (SOC) in a quasicrystalline\noptical lattice (QOL). For given parameters, the system evolves from an initial\nheliciform-stripe phase into a final visible vortex necklace with a giant\nvortex and a hidden vortex necklace. Simultaneously, the corresponding spin\ntexture undergoes a transition from a meron-antimeron pair to a\nhalf-antiskyrmion necklace. During the dynamic evolution process, the angular\nmomentum increases gradually, and then approaches to a convergent value.\nFurthermore, typical quantum phases of rotating two-component BECs with SOC in\ndifferent external potentials are summarized.",
        "positive": "Vortex Dynamics in Anisotropic Traps: We investigate the dynamics of linear vortex lattices in anisotropic traps in\ntwo-dimensions and show that the interplay between the rotation and the\nanisotropy leads to a rich but highly regular dynamics."
    },
    {
        "anchor": "Mediated interactions between Fermi polarons and the role of impurity\n  quantum statistics: The notion of quasi-particles is essential for understanding the behaviour of\ncomplex many-body systems. A prototypical example of a quasi-particle, a\npolaron, is an impurity strongly interacting with a surrounding medium. Fermi\npolarons, created in a Fermi sea, provide a paradigmatic realization of this\nconcept. As an inherent and important property such quasi-particles interact\nwith each other via modulation of the medium. While quantum simulation\nexperiments with ultracold atoms have significantly improved our understanding\nof individual polarons, the detection of their interactions has remained\nelusive in these systems. Here, we report the unambiguous observation of\nmediated interactions between Fermi polarons consisting of K impurities\nembedded in a Fermi sea of Li atoms. Our results confirm two landmark\npredictions of Landau's Fermi-liquid theory: the shift of the polaron energy\ndue to mediated interactions, linear in the concentration of impurities, and\nits sign inversion with impurity quantum statistics. For weak to moderate\ninteractions between the impurities and the medium, we find excellent agreement\nwith the static (zero-momentum and energy) predictions of Fermi-liquid theory.\nFor stronger impurity-medium interactions, we show that the observed behaviour\nat negative energies can be explained by a more refined many-body treatment\nincluding retardation and molecule formation",
        "positive": "Liquid crystal phases of ultracold dipolar fermions on a lattice: Motivated by the search for quantum liquid crystal phases in a gas of\nultracold atoms and molecules, we study the density wave and nematic\ninstabilities of dipolar fermions on the two-dimensional square lattice (in the\n$x-y$ plane) with dipoles pointing to the $z$ direction. We determine the phase\ndiagram using two complimentary methods, the Hatree-Fock mean field theory and\nthe linear response analysis of compressibility. Both give consistent results.\nIn addition to the staggered ($\\pi$, $\\pi$) density wave, over a finite range\nof densities and hopping parameters, the ground state of the system first\nbecomes nematic and then smectic, when the dipolar interaction strength is\nincreased. Both phases are characterized by the same broken four-fold (C$_4$)\nrotational symmetry. The difference is that the nematic phase has a closed\nFermi surface but the smectic does not. The transition from the nematic to the\nsmectic phase is associated with a jump in the nematic order parameter. This\njump is closely related to the van Hove singularities. We derive the kinetic\nequation for collective excitations in the normal isotropic phase and find that\nthe zero sound mode is strongly Landau damped and thus is not a well defined\nexcitation. Experimental implications of our results are discussed."
    },
    {
        "anchor": "Inhomogeneous Superfluid Phases in the Unitary Li6-K40 Mixture: We show that the ultracold three-dimensional ${}^6$Li-${}^{40}$K mixture at\nunitarity can exhibit the highly exotic Larkin-Ovchinnikov superfluid phase. We\ndetermine the phase diagram for majorities of ${}^{40}$K atoms within\nmean-field theory taking the inhomogeneities of the fermion states into account\nexactly. We find two different inhomogeneous superfluid phases in mixtures with\na majority of ${}^{40}$K atoms, namely the Larkin-Ovchinnikov (LO) phase with\none inhomogeneous direction and a cubic phase (LO$^3$) where three spatial\ntranslational symmetries are broken. We determine the transition between these\ntwo phases by solving the Bogoliubov-de Gennes equations in the superfluid LO\nphase. Subsequently, we calculate the atomic density modulation of the atoms in\nthe LO phase and show that it is sufficiently large to be visible in\nexperiment.",
        "positive": "Superfluid to Bose-glass transition of hard core bosons in\n  one-dimensional incommensurate optical lattice: We study superfluid to Anderson insulator transition of strongly repulsive\nBose gas in a one dimensional incommensurate optical lattice. In the hard core\nlimit, the Bose-Fermi mapping allows us to deal with the system exactly by\nusing the exact numerical method. Based on the Aubry-Andr\\'{e} model, we\nexploit the phase transition of the hard core boson system from superfluid\nphase with all the single particle states being extended to the Bose glass\nphase with all the single particle states being Anderson localized as the\nstrength of the incommensurate potential increasing relative to the amplitude\nof hopping. We evaluate the superfluid fraction, the one particle density\nmatrices, momentum distributions, the natural orbitals and their occupations.\nAll of these quantities show that there exists a phase transition from\nsuperfluid to insulator in the system."
    },
    {
        "anchor": "Quantum Walk in Degenerate Spin Environments: We study the propagation of a hole in degenerate (paramagnetic) spin\nenvironments. This canonical problem has important connections to a number of\nphysical systems, and is perfectly suited for experimental realization with\nultra-cold atoms in an optical lattice. At the short-to-intermediate timescale\nthat we can access using a stochastic-series-type numeric scheme, the\npropagation turns out to be distinctly non-diffusive with the proba- bility\ndistribution featuring minima in both space and time due to quantum\ninterference, yet the motion is not ballistic, except at the beginning. We\ndiscuss possible scenarios for long-term evolution that could be explored with\nan unprecedented degree of detail in experiments with single-atom resolved\nimaging.",
        "positive": "Isotropic vortex tangles in trapped atomic Bose-Einstein condensates via\n  laser stirring: The generation of isotropic vortex configurations in trapped atomic\nBose-Einstein condensates offers a platform to elucidate quantum turbulence on\nmesoscopic scales. We demonstrate that a laser-induced obstacle moving in a\nfigure-eight path within the condensate provides a simple and effective means\nto generate an isotropic three-dimensional vortex tangle due to its minimal net\ntransfer of angular momentum to the condensate. Our characterisation of vortex\nstructures and their isotropy is based on projected vortex lengths and velocity\nstatistics obtained numerically via the Gross-Pitaevskii equation. Our\nmethodology provides a possible experimental route for generating and\ncharacterising vortex tangles and quantum turbulence in atomic Bose-Einstein\ncondensates."
    },
    {
        "anchor": "Elementary modes of excitation caused by the quadratic Zeeman term and\n  the sensitivity of spin structures of small spin-2 condensates against the\n  magnetic field: The response of spin-2 small condensates to an external magnetic field $B$ is\nstudied. The parameters of the interaction are considered as variable. The\nemphasis is placed on clarifying the modes of excitation caused by the\nquadratic Zeeman term. The theoretical method used is beyond the mean field\ntheory. A set of eigenstates with the $U(5)\\supset SO(5)\\supset SO(3)$ symmetry\nis introduced to facilitate the analysis. To obtain a quantitative evaluation\non the response, the fidelity susceptibility and the $B$ -dependent average\npopulations of spin-components have been calculated. Mostly the particle number\nN=30 is assumed. The effect with a larger or smaller $N$ is also considered. It\nwas found that the sensitivity of the response depends strongly both on the\ninteraction and on the inherent symmetry.",
        "positive": "Unified statistical thermodynamics of quantum gases trapped under\n  generic power law potential in $d$ dimension and equivalence in $d=1$: A unified description for the Bose and Fermi gases trapped in an external\ngeneric power law potential $U=\\sum_{i=1} ^d c_i |\\frac{x_i}{a_i}|^{n_i}$ is\npresented using the grandpotential of the system in $d$ dimensional space. The\nthermodynamic quantities of the quantum gases are derived from the grand\npotential. An equivalence between the trapped Bose and Fermi gases is\nconstructed in one dimension ($d=1$) using the Landen relation. It is also\nfound that the established equivalence between the ideal free Bose and Fermi\ngases in $d=2$ (M. H. Lee, Phys. Rev. E 55, 1518 (1997)) is lost when external\npotential is applied."
    },
    {
        "anchor": "Energetic cooling below the BEC transition: a quantum kinetic\n  description within the Bogoliubov approximation: The dynamics of Bose-Einstein condensation in a three-dimensional harmonic\ntrap is studied explicitly including the Bogoliubov approximation for\ntemperatures below the critical one. To model the evolution towards equilibrium\nat each cooling step, we derive quantum kinetic equations that describe the\ndynamics of the gas for temperatures above and below the transition\ntemperature. These equations, valid in the Born and Markov approximations,\nconsider the essential role of the chemical potential as the main parameter\nthat signals the transition. The kinetic equation that describes the growth of\nthe condensate below the transition temperature is derived within the\nBogoliubov approximation. To illustrate our results we propose an energetic\ncooling protocol and simulate the whole sequence of the formation of a\ncondensate.",
        "positive": "Double-well ultracold-fermions computational microscopy: Wave-function\n  anatomy of attractive-pairing and Wigner-molecule entanglement and natural\n  orbitals: \"Bottom-up\" approaches to the many-body physics of fermions have demonstrated\nrecently precise number and site-resolved preparations with tunability of\ninterparticle interactions in single-well, SW, and double-well, DW, nano-scale\nconfinements created by manipulating ultracold fermionic atoms with optical\ntweezers. These experiments emulate an analogue-simulator mapping onto the\nrequisite microscopic hamiltonian, approaching realization of Feynman's vision\nof quantum simulators that \"will do exactly the same as nature\". Here we report\non exact benchmark configuration-interaction computational microscopy solutions\nof the hamiltonian, uncovering the spectral evolution, wave-function anatomy,\nand entanglement properties of the interacting fermions in the entire parameter\nrange, including crossover from a SW to a DW confinement and a controllable\nenergy imbalance between the wells. We demonstrate attractive pairing and\nformation of repulsive, highly-correlated, ultracold Wigner molecules,\nwell-described in the natural orbital representation. The agreement with the\nmeasurements affirms the henceforth gained deep insights into ultracold\nmolecules and opens access to the size-dependent evolution of nano-clustered\nand condensed-matter phases and ultracold-atoms quantum information."
    },
    {
        "anchor": "Flat-band-induced superconductivity in synthetic bilayer optical\n  lattices: Stacking two layers of graphene with a relative twist angle gives rise to\nmoir\\'e patterns, which can strongly modify electronic behavior and may lead to\nunconventional superconductivity. A synthetic version of twisted bilayers can\nbe engineered with cold atoms in optical lattices. Here, the bilayer structure\nis mimicked through coupling between atomic sublevels, and the twist is\nachieved by a spatial modulation of this coupling. In the present paper, we\ninvestigate the superconducting behavior of fermionic atoms in such a synthetic\ntwisted bilayer lattice. Attractive interactions between the atoms are treated\non the mean-field level, and the superconducting behavior is analyzed via the\nself-consistently determined pairing gap. A strong enhancement of the pairing\ngap is found, when a quasi-flat band structure occurs at the Fermi surface,\nreflecting the prominent role played by the twist on the superconductivity. The\ntunability of interactions allows for the switching of superconducting\ncorrelations from intra (synthetic) layer to inter (synthetic) layer. This\nincludes also the intermediate scenario, in which the competition between\ninter- and intra-layer coupling completely destroys the superconducting\nbehavior, resulting in re-entrant superconductivity upon tuning of the\ninteractions",
        "positive": "Dynamical disentangling and cooling of atoms in bilayer optical lattices: We show how experimentally available bilayer lattice systems can be used to\nprepare quantum many-body states with exceptionally low entropy in one layer,\nby dynamically disentangling the two layers. This disentangling operation moves\none layer - subsystem $A$ - into a regime where excitations in $A$ develop a\nsingle-particle gap. As a result, this operation maps directly to cooling for\nsubsystem $A$, with entropy being shuttled to the other layer. For both bosonic\nand fermionic atoms, we study the dynamics of this process, and show that\ndisentangling can be realised cleanly in ongoing optical lattice experiments.\nThe corresponding entanglement entropies are directly measurable with quantum\ngas microscopes, and as a tool for producing lower-entropy states, this\ntechnique opens a range of applications beginning with simplifying production\nof anti-ferromagnetically ordered states of fermions."
    },
    {
        "anchor": "On bifurcation of the four Liouville tori in one generalized integrable\n  model of the vortex dynamics: The article deals with a generalized mathematical model of the dynamics of\ntwo point vortices in the Bose-Einstein condensate enclosed in a harmonic trap,\nand of the dynamics of two point vortices in an ideal fluid bounded by a\ncircular region. In the case of a positive vortex pair, which is of interest\nfor physical experimental applications, a new bifurcation diagram is obtained,\nfor which the bifurcation of four tori into one is indicated. The presence of\nbifurcations of three and four tori in the integrable model of vortex dynamics\nwith positive intensities indicates a complex transition and the connection of\nbifurcation diagrams of both limit cases. Analytical results of this\npublication (the bifurcation diagram, the reduction to a system with one degree\nof freedom, the stability analysis) form the basis of computer simulation of\nabsolute dynamics of vortices in a fixed coordinate system in the case of\narbitrary values of the physical parameters of the model (the intensities, the\nvortex interaction and etc.)",
        "positive": "Quantum Transport of Bosonic Cold Atoms in Double Well Optical Lattices: We numerically investigate, using the time evolving block decimation\nalgorithm, the quantum transport of ultra-cold bosonic atoms in a double well\noptical lattice through slow and periodic modulation of the lattice parameters\n(intra- and inter-well tunneling, chemical potential, etc.). The transport of\natoms does not depend on the rate of change of the parameters (as along as the\nchange is slow) and can distribute atoms in optical lattices at the quantized\nlevel without involving external forces. The transport of atoms depends on the\natom filling in each double well and the interaction between atoms. In the\nstrongly interacting region, the bosonic atoms share the same transport\nproperties as non-interacting fermions with quantized transport at the half\nfilling and no atom transport at the integer filling. In the weakly interacting\nregion, the number of the transported atoms is proportional to the atom\nfilling. We show the signature of the quantum transport from the momentum\ndistribution of atoms that can measured in the time of flight image. A\nsemiclassical transport model is developed to explain the numerically observed\ntransport of bosonic atoms in the non-interacting and strongly interacting\nlimits. The scheme may serve as an quantized battery for atomtronics\napplications."
    },
    {
        "anchor": "Growth dynamics of a Bose-Einstein condensate in a dimple trap without\n  cooling: We study the formation of a Bose-Einstein condensate in a cigar-shaped\nthree-dimensional harmonic trap, induced by the controlled addition of an\nattractive \"dimple\" potential along the weak axis. In this manner we are able\nto induce condensation without cooling due to a localized increase in the phase\nspace density. We perform a quantitative analysis of the thermodynamic\ntransformation in both the sudden and adiabatic regimes for a range of dimple\nwidths and depths. We find good agreement with equilibrium calculations based\non self-consistent semiclassical Hartree-Fock theory describing the condensate\nand thermal cloud. We observe there is an optimal dimple depth that results in\na maximum in the condensate fraction. We also study the non-equilibrium\ndynamics of condensate formation in the sudden turn-on regime, finding good\nagreement for the observed time dependence of the condensate fraction with\ncalculations based on quantum kinetic theory.",
        "positive": "Magnetic polarons in two-component hard core bosons: We use a high-temperature expansion to explore spin correlations around a\nsingle hole in a two- dimensional lattice filled with a hard-core two component\nbose gas. We find that the spins around the hole develop ferromagnetic order\nand quantify the degree of polarization at temperatures of order the hopping\nenergy, finding a measurably nonzero polarization. We also discuss the effect\nof fixing the overall magnetization of the system for finite-sized systems."
    },
    {
        "anchor": "Thermometry by correlated dephasing of impurities in a 1D Fermi gas: We theoretically investigate the pure dephasing dynamics of two static\nimpurity qubits embedded within a common environment of ultracold fermionic\natoms, which are confined to one spatial dimension. Our goal is to understand\nhow bath-mediated interactions between impurities affect their performance as\nnonequilibrium quantum thermometers. By solving the dynamics exactly using a\nfunctional determinant approach, we show that the impurities become correlated\nvia retarded interactions of the Ruderman-Kittel-Kasuya-Yosida type. Moreover,\nwe demonstrate that these correlations can provide a metrological advantage,\nenhancing the sensitivity of the two-qubit thermometer beyond that of two\nindependent impurities. This enhancement is most prominent in the limit of low\ntemperature and weak collisional coupling between the impurities and the gas.\nWe show that this precision advantage can be exploited using standard Ramsey\ninterferometry, with no need to prepare correlated initial states nor to\nindividually manipulate or measure the impurities. We also quantitatively\nassess the impact of ignoring these correlations when constructing a\ntemperature estimate, finding that acceptable precision can still be achieved\nfrom a simplified model of independent impurities. Our results demonstrate the\nrich nonequilibrium physics of impurities dephasing in a common Fermi gas, and\nmay help to provide better temperature estimates at ultralow temperatures.",
        "positive": "Non-equilibrium Dynamics of Vortices in Two-Dimensional Quantum Gases:\n  Determining the Dynamical Scaling Region Using the Mahalanobis Distance: When a two-dimensional system undergoes a rapid quench from a disordered to\nan ordered phase, it does not order instantly but instead relaxes towards\nequilibrium over time. During this relaxation, the dynamical scaling hypothesis\npredicts that the length scale of ordered regions increases, with later\npatterns statistically similar to earlier ones except for a change in global\nscale. Quantum gases are one of many systems in which such out of equilibrium\nbehaviour is predicted to occur. Here we present a method for systematically\ntesting when dynamical scaling is taking place, by quantifying the similarity\nof the rescaled two-point correlation function over time using the Mahalanobis\ndistance. Data on the velocity field of a quantum fluid, generated from point\nvortex simulations, are used to illustrate the application of this method."
    },
    {
        "anchor": "Simulation of classical Ising-like magnetism with a Mott insulator of\n  paired atoms: Quantum simulation of the XXZ model with a two-component Bose or Fermi\nHubbard model based on a Mott insulator background has been widely used in the\ninvestigations of quantum magnetism with ultracold neutral atoms. In most\ncases, the diagonal spin-spin interaction is always accompanied by a large\nspin-exchange interaction which hinders the formation of long-range magnetic\norder at low temperature. Here we show that the spin-exchange interaction can\nbe strongly reduced in a Mott insulator of paired atoms, while the diagonal\nspin-spin interaction remains unaffected. Thus, the effective magnetic model is\nquite close to an exact classical Ising model in the textbook. And we analysed\nan experimentally achievable three-component Fermi-Hubbard model of\n$\\mathrm{{}^{6}Li}$ with two hyperfine levels of atoms paired in the lattice.\nWe find the long-range antiferromagnetic order of such a three-component\nFermi-Hubbard model can be much stronger than that of a typical two-component\nFermi-Hubbard model at low temperature. And we discussed the possiblity of\nsimulating an exact two-dimensional ferromagnetic Ising model in a Mott\ninsulator of paired bosonic atoms. Our results may be useful for experimental\ninvestigation of the long-range Ising-like magnetism with ultracold neutral\natoms under thermal equilibrium.",
        "positive": "Spontaneous Symmetry Breaking of Vortex Number in Binary Alternating\n  Current Countersuperflow: In binary superfluid counterflow systems, vortex nucleation arises as a\nconsequence of hydrodynamic instabilities when the coupling coefficient and\ncounterflow velocity exceed the critical value. When dealing with two identical\ncomponents, one might naturally anticipate that the number of vortices\ngenerated would remain equal. However, through the numerical experiments of the\nholographic model and the Gross-Pitaevskii equation, our investigation has\nunveiled a remarkable phenomenon: in Alternating Current counterflow systems,\nonce the coupling coefficient and frequency exceed certain critical values, a\nsurprising symmetry-breaking phenomenon occurs. This results in an asymmetry in\nthe number of vortices in the two components. We establish that this phenomenon\nrepresents a novel continuous phase transition, which, as indicated by the\nphase diagram, is exclusively observable in Alternating Current counterflow. We\nprovide an explanation for this intriguing phenomenon through soliton\nstructures, thereby uncovering the complex and unique characteristics of\nquantum fluid instabilities and their rich phenomena."
    },
    {
        "anchor": "Dissipation-engineered family of nearly dark states in many-body\n  cavity-atom systems: Three-level atomic systems coupled to light have the capacity to host dark\nstates. We study a system of V-shaped three-level atoms coherently coupled to\nthe two quadratures of a dissipative cavity. The interplay between the atomic\nlevel structure and dissipation makes the phase diagram of the open system\ndrastically different from the closed one. In particular, it leads to the\nstabilization of a continuous family of dark and nearly dark excited many-body\nstates with inverted atomic populations as the steady states. The\nmultistability of these states can be probed via their distinct fluctuations\nand excitation spectra, as well as the system's Liouvillian dynamics which are\nhighly sensitive to ramp protocols. Our model can be implemented experimentally\nby encoding the two higher-energy modes in orthogonal density-modulated states\nin a bosonic quantum gas. This implementation offers prospects for potential\napplications like the realization of quantum optical random walks and\nmicroscopy with subwavelength spatial resolution.",
        "positive": "Beyond mean-field dynamics in open Bose-Hubbard chains: We investigate the effects of phase noise and particle loss on the dynamics\nof a Bose-Einstein condensate in an optical lattice. Starting from the\nmany-body master equation, we discuss the applicability of generalized\nmean-field approximations in the presence of dissipation as well as methods to\nsimulate quantum effects beyond mean-field by including higher-order\ncorrelation functions. It is shown that localized particle dissipation leads to\nsurprising dynamics, as it can suppress decay and restore the coherence of a\nBose-Einstein condensate. These effects can be applied to engineer coherent\nstructures such as stable discrete breathers and dark solitons."
    },
    {
        "anchor": "Fisher zeros of a unitary Bose gas: For real inverse temperature beta, the canonical partition function is always\npositive, being a sum of positive terms. There are zeros, however, on the\ncomplex beta plane that are called Fisher zeros. In the thermodynamic limit,\nthe Fisher zeros coalesce into continuous curves. In case there is a phase\ntransition, the zeros tend to pinch the real-beta axis. For an ideal trapped\nBose gas in an isotropic three-dimensional harmonic oscillator, this tendency\nis clearly seen, signalling Bose-Einstein condensation (BEC). The calculation\ncan be formulated exactly in terms of the virial expansion with\ntemperature-dependent virial coefficients. When the second virial coefficient\nof a strongly interacting attractive unitary gas is included in the\ncalculation, BEC seems to survive, with the condensation temperature shifted to\na lower value for the unitary gas. This shift is consistent with a direct\ncalculation of the heat capacity from the canonical partition function of the\nideal and the unitary gas.",
        "positive": "Tunable axial gauge fields in engineered Weyl semimetals: Semiclassical\n  analysis and optical lattice implementations: In this work, we describe a toolbox to realize and probe synthetic axial\ngauge fields in engineered Weyl semimetals. These synthetic electromagnetic\nfields, which are sensitive to the chirality associated with Weyl nodes, emerge\ndue to spatially and temporally dependent shifts of the corresponding Weyl\nmomenta. First, we introduce two realistic models, inspired by recent cold-atom\ndevelopments, which are particularly suitable for the exploration of these\nsynthetic axial gauge fields. Second, we describe how to realize and measure\nthe effects of such axial fields through center-of-mass observables, based on\nsemiclassical equations of motion and exact numerical simulations. In\nparticular, we suggest realistic protocols to reveal an axial Hall response due\nto the axial electric field $\\mathbf{E}_5$, and also, the axial cyclotron\norbits and chiral pseudo-magnetic effect due to the axial magnetic field\n$\\mathbf{B}_5$."
    },
    {
        "anchor": "Onset time for energy oscillations in a two-dimensional trapped Bose gas\n  excited by a red laser potential: We explore the energy dynamics of a two dimensional (2D) harmonically trapped\nBose-Einstein condensate inside a box potential, excited by a moving\nred-detuned laser potential (RDLP). For an RDLP velocity $v$ less than a\ncritical value $v_c$, energy oscillations are observed to begin simultaneously\nwith the motion of the RDLP. For $v > v_c$, these oscillations are delayed\nthrough a transient in the energy. At the end of the delay time $t_{ons}$, the\nenergy oscillations are regenerated again, and $t_{ons}$ is found to depend on\n$v$ through universal relations for two cases: one for an RDLP depth sufficient\nto break off a BEC fragment, another for a depth insufficient to split the BEC.\nIn the case of splitting, $t_{ons}$ exactly equals the time it takes the BEC\nfragment (dragged by the RDLP trough) to reach the hard wall of the box\npotential.",
        "positive": "Site-resolved imaging of ultracold fermions in a triangular-lattice\n  quantum gas microscope: Quantum gas microscopes have expanded the capabilities of quantum simulation\nof Hubbard models by enabling the study of spatial spin and density\ncorrelations in square lattices. However, quantum gas microscopes have not been\nrealized for fermionic atoms in frustrated geometries. Here, we demonstrate the\nsingle-atom resolved imaging of ultracold fermionic $^{6}$Li atoms in a\ntriangular optical lattice with a lattice constant of 1003 nm. The optical\nlattice is formed by a recycled narrow-linewidth, high-power laser combined\nwith a light sheet to allow for Raman sideband cooling on the $D_1$ line. We\noptically resolve single atoms on individual lattice sites using a\nhigh-resolution objective to collect scattered photons while cooling them close\nto the two-dimensional ground vibrational level in each lattice site. By\nreconstructing the lattice occupation, we measure an imaging fidelity of ~98%.\nOur new triangular lattice microscope platform for fermions clears the path for\nstudying spin-spin correlations, entanglement and dynamics of geometrically\nfrustrated Hubbard systems which are expected to exhibit exotic emergent\nphenomena including spin liquids and kinetic frustration."
    },
    {
        "anchor": "Floquet Engineering of Haldane Chern Insulators and Chiral bosonic phase\n  transitions: The realization of synthetic gauge fields has attracted a lot of attention\nrecently in relation with periodically driven systems and the Floquet theory.\nIn ultra-cold atom systems in optical lattices and photonic networks, this\nallows to simulate exotic phases of matter such as quantum Hall phases,\nanomalous quantum Hall phases and analogs of topological insulators. In this\npaper, we apply the Floquet theory to engineer anisotropic Haldane models on\nthe honeycomb lattice and two-leg ladder systems. We show that these\nanisotropic Haldane models still possess a topologically non-trivial band\nstructure associated with chiral edge modes (without the presence of a net unit\nflux in a unit cell), then referring to the quantum anomalous Hall effect.\nFocusing on (interacting) boson systems in s-wave bands of the lattice, we show\nhow to engineer through the Floquet theory, a quantum phase transition between\na uniform superfluid and a BEC (Bose-Einstein Condensate) analog of FFLO\n(Fulde-Ferrell-Larkin-Ovchinnikov) states, where bosons condense at non-zero\nwave-vectors. We perform a Ginzburg-Landau analysis of the quantum phase\ntransition on the graphene lattice, and compute observables such as chiral\ncurrents and the momentum distribution. The results are supported by exact\ndiagonalization calculations and compared with those of the isotropic\nsituation. The validity of high-frequency expansion in the Floquet theory is\nalso tested using time-dependent simulations for various parameters of the\nmodel. Last, we show that the anisotropic choice for the effective vector\npotential allows a bosonization approach in equivalent ladder (strip)\ngeometries.",
        "positive": "Fast long-distance transport of cold cesium atoms: Transporting cold atoms between distant sections of a vacuum system is a\ncentral ingredient in many quantum simulation experiments, in particular in\nsetups, where a large optical access and precise control over magnetic fields\nis needed. In this work, we demonstrate optical transport of cold cesium atoms\nover a total transfer distance of about $43\\,$cm in less than $30\\,$ms. The\nhigh speed is facilitated by a moving lattice, which is generated via the\ninterference of a Bessel and a Gaussian laser beam. We transport about $3\\times\n10^6$ atoms at a temperature of a few $\\mu$K with a transport efficiency of\nabout $75\\%$. We provide a detailed study of the transport efficiency for\ndifferent accelerations and lattice depths and find that the transport\nefficiency is mainly limited by the potential depth along the direction of\ngravity. To highlight the suitability of the optical-transport setup for\nquantum simulation experiments, we demonstrate the generation of a pure\nBose-Einstein condensate with about $2\\times 10^4$ atoms. We find a robust\nfinal atom number within $2\\%$ over a duration of $2.5\\,$h with a standard\ndeviation of $<5\\%$ between individual experimental realizations."
    },
    {
        "anchor": "Quantum simulation of correlated-hopping models with fermions in optical\n  lattices: By using a modulated magnetic field in a Feshbach resonance for ultracold\nfermionic atoms in optical lattices, we show that it is possible to engineer a\nclass of models usually referred to as correlated-hopping models. These models\ndiffer from the Hubbard model in exhibiting additional density-dependent\ninteraction terms that affect the hopping processes. In addition to the\nspin-SU(2) symmetry, they also possess a charge-SU(2) symmetry, which opens the\npossibility of investigating the $\\eta$-pairing mechanism for superconductivity\nintroduced by Yang for the Hubbard model. We discuss the known solution of the\nmodel in 1D (where $\\eta$ states have been found in the degenerate manifold of\nthe ground state) and show that, away from the integrable point, quantum Monte\nCarlo simulations at half filling predict the emergence of a phase with\ncoexisting incommensurate spin and charge order.",
        "positive": "Observation of Solitonic Vortices in Bose-Einstein Condensates: We observe solitonic vortices in an atomic Bose-Einstein condensate after\nfree expansion. Clear signatures of the nature of such defects are the twisted\nplanar density depletion around the vortex line, observed in absorption images,\nand the double dislocation in the interference pattern obtained through\nhomodyne techniques. Both methods allow us to determine the sign of the\nquantized circulation. Experimental observations agree with numerical\nsimulations. These solitonic vortices are the decay product of phase defects of\nthe BEC order parameter spontaneously created after a rapid quench across the\nBEC transition in a cigar-shaped harmonic trap and are shown to have a very\nlong lifetime."
    },
    {
        "anchor": "Universal properties of dissipative Tomonaga-Luttinger liquids: Case\n  study of a non-Hermitian XXZ spin chain: We demonstrate the universal properties of dissipative Tomonaga-Luttinger\n(TL) liquids by calculating correlation functions and performing finite-size\nscaling analysis of a non-Hermitian XXZ spin chain as a prototypical model in\none-dimensional open quantum many-body systems. Our analytic calculation is\nbased on effective field theory with bosonization, finite-size scaling approach\nin conformal field theory, and the Bethe-ansatz solution. Our numerical\nanalysis is based on the density-matrix renormalization group generalized to\nnon-Hermitian systems (NH-DMRG). We uncover that the model in the massless\nregime with weak dissipation belongs to the universality class characterized by\nthe complex-valued TL parameter, which is related to the complex generalization\nof the $c=1$ conformal field theory. As the dissipation strength increases, the\nvalues of the TL parameter obtained by the NH-DMRG begin to deviate from those\nobtained by the Bethe-ansatz analysis, indicating that the model becomes\nmassive for strong dissipation. Our results can be tested with the\ntwo-component Bose-Hubbard system of ultracold atoms subject to two-body loss.",
        "positive": "Matter Wave Turbulence: Beyond Kinetic Scaling: Turbulent scaling phenomena are studied in an ultracold Bose gas away from\nthermal equilibrium. Fixed points of the dynamical evolution are characterized\nin terms of universal scaling exponents of correlation functions. The scaling\nbehavior is determined analytically in the framework of quantum field theory,\nusing a nonperturbative approximation of the two-particle irreducible effective\naction. While perturbative Kolmogorov scaling is recovered at higher energies,\nscaling solutions with anomalously large exponents arise in the infrared regime\nof the turbulence spectrum. The extraordinary enhancement in the momentum\ndependence of long-range correlations could be experimentally accessible in\ndilute ultracold atomic gases. Such experiments have the potential to provide\ninsight into dynamical phenomena directly relevant also in other present-day\nfocus areas like heavy-ion collisions and early-universe cosmology."
    },
    {
        "anchor": "Dynamics of Disordered States in the Bose-Hubbard Model with Confinement: Observations of center of mass dynamics offer a straightforward method to\nidentify strongly interacting quantum phases of atoms placed in optical\nlattices. We theoretically study the dynamics of states derived from the\ndisordered Bose-Hubbard model in a trapping potential. We find that the edge\nstates in the trap allow center of mass motion even with insulating states in\nthe center. We identify short and long-time scale mechanisms for edge state\ntransport in insulating phases. We also argue that the center of mass velocity\ncan aid in identifying a Bose-glass phase. Our zero temperature results offer\nimportant insights into mechanisms of transport of atoms in trapped optical\nlattices while putting bounds on center of mass dynamics expected at non-zero\ntemperature.",
        "positive": "Precision Many-Body Study of the Berezinskii-Kosterlitz-Thouless\n  Transition and Temperature-Dependent Properties in the Two-Dimensional Fermi\n  Gas: We perform large-scale, numerically exact calculations on the two-dimensional\ninteracting Fermi gas with a contact attraction. Reaching much larger lattice\nsizes and lower temperatures than previously possible, we determine\nsystematically the finite-temperature phase diagram of the\nBerezinskii-Kosterlitz-Thouless (BKT) transitions for interaction strengths\nranging from BCS to crossover to BEC regimes. The evolutions of the pairing\nwavefunctions and the fermion and Cooper pair momentum distributions with\ntemperature are accurately characterized. In the crossover regime, we find that\nthe contact has a non-monotonic temperature dependence, first increasing as\ntemperature is lowered, and then showing a slight decline below the BKT\ntransition temperature to approach the ground-state value from above."
    },
    {
        "anchor": "Higher order transmission resonances in above-barrier reflection of\n  ultra-cold atoms: The reflectionless transmission resonances in above-barrier reflection of\nBose-Einstein condensates by the Rosen-Morse potential are considered using the\nmean field Gross-Pitaevskii approach. Applying an exact third order nonlinear\ndifferential equation obeyed by the condensate's density, the exact solution of\nthe problem for the first resonance is derived. It is shown that in the\nnonlinear case the total transmission is possible for positive potential\nheights, i.e., for potential barriers. Further, it is shown that an appropriate\napproximation for higher-order resonances can be constructed using a limit\nsolution of the equation for the density written as a root of a polynomial\nequation of the third degree. Using this limit function and the solution for\nthe first resonance, a simple approximation for the shift of the nonlinear\nresonance potential's depth from the corresponding linear resonance's position\nis constructed for higher order resonances. The result is written as a linear\nfunction of the resonance order. This behavior notably differs from the case of\nthe rectangular barrier for which the nonlinear shift is approximately constant\nfor all the resonance orders.",
        "positive": "Energy functionals of single-particle densities: A unified view: Density functional theory is usually formulated in terms of the density in\nconfiguration space. Functionals of the momentum-space density have also been\nstudied, and yet other densities could be considered. We offer a unified view\nfrom a second-quantized perspective and introduce a version of density\nfunctional theory that treats all single-particle contributions to the energy\nexactly. An appendix deals with semiclassical eigenvalues."
    },
    {
        "anchor": "A Proposal for measuring Anisotropic Shear Viscosity in Unitary Fermi\n  Gases: We present a proposal to measure anisotropic shear viscosity in a strongly\ninteracting, ultra-cold, unitary Fermi gas confined in a harmonic trap. We\nintroduce anisotropy in this setup by strongly confining the gas in one of the\ndirections with relatively weak confinement in the remaining directions. This\nsystem has a close resemblance to anisotropic strongly coupled field theories\nstudied recently in the context of gauge-gravity duality. Computations in such\ntheories (which have gravity duals) revealed that some of the viscosity\ncomponents of the anisotropic shear viscosity tensor can be made much smaller\nthan the entropy density, thus parametrically violating the bound proposed by\nKovtun, Son and Starinets (KSS): $\\frac {\\eta} {s} \\geq \\frac{1}{4 \\pi}$. A\nBoltzmann analysis performed in a system of weakly interacting particles in a\nlinear potential also shows that components of the viscosity tensor can be\nreduced. Motivated by these exciting results, we propose two hydrodynamic modes\nin the unitary Fermi gas whose damping is governed by the component of shear\nviscosity expected to violate the KSS bound. One of these modes is the well\nknown scissor mode. We estimate trap parameters for which the reduction in the\nshear viscosity is of order unity and find that the trap geometry, the damping\ntimescales, and mode amplitudes are within the range of existing experimental\nsetups on ultra-cold Fermi gases.",
        "positive": "Thermalization in a Spin-Orbit coupled Bose gas by enhanced spin Coulomb\n  drag: An important component of the structure of the atom, the effects of\nspin-orbit coupling are present in many sub-fields of physics. Most of these\neffects are present continuously. We present a detailed study of the dynamics\nof changing the spin-orbit coupling in an ultra-cold Bose gas, coupling the\nmotion of the atoms to their spin. We find that the spin-orbit coupling greatly\nincreases the damping towards equilibrium. We interpret this damping as spin\ndrag, which is enhanced by spin-orbit coupling rate, scaled by a remarkable\nfactor of $8.9(6)$~s. We also find that spin-orbit coupling lowers the final\ntemperature of the Bose gas after thermalization."
    },
    {
        "anchor": "Universal dynamics of zero-momentum to plane-wave transition in\n  spin-orbit coupled Bose-Einstein condensates: We investigate the universal spatiotemporal dynamics in spin-orbit coupled\nBose-Einstein condensates which are driven from the zero-momentum phase to the\nplane-wave phase. The excitation spectrum reveals that, at the critical point,\nthe Landau critical velocity vanishes and the correlation length diverges.\nTherefore, according to the Kibble-Zurek mechanism, spatial domains will\nspontaneously appear in such a quench through the critical point. By simulating\nthe real-time dynamics, we numerically extract the static correlation length\ncritical exponent v and the dynamic critical exponent z from the scalings of\nthe temporal bifurcation delay and the spatial domain number. The numerical\nscalings consist well with the analytical ones obtained by analyzing the\nexcitation spectrum.",
        "positive": "Emergent glassy behavior in a kagome Rydberg atom array: We present large-scale quantum Monte Carlo simulation results on a realistic\nHamiltonian of kagome-lattice Rydberg atom arrays. Although the system has no\nintrinsic disorder, intriguingly, our analyses of static and dynamic properties\non large system sizes reveal \\textit{emergent} glassy behavior in a region of\nparameter space located between two valence bond solid phases. The extent of\nthis glassy region is demarcated using the Edwards-Anderson order parameter,\nand its phase transitions to the two proximate valence bond solids -- as well\nas the crossover towards a trivial paramagnetic phase -- are identified. We\ndemonstrate the intrinsically slow (imaginary) time dynamics deep inside the\nglassy phase and discuss experimental considerations for detecting such a\nquantum disordered phase with numerous nearly degenerate local minima. Our\nproposal paves a new route to the study of real-time glassy phenomena and\nhighlights the potential for quantum simulation of a distinct phase of quantum\nmatter beyond solids and liquids in current-generation Rydberg platforms."
    },
    {
        "anchor": "Universal subdiffusion in strongly tilted many-body systems: The quantum dynamics away from equilibrium is of fundamental interest for\ninteracting many-body systems. In this letter, we study tilted many-body\nsystems using the effective Hamiltonian derived from the microscopic\ndescription. We first give general arguments for the density relaxation rate\nsatisfying $1/\\tau\\propto k^4$ for a large class of systems, including the\nFermi Hubbard model case as observed in the the recent experiment [1]. Here $k$\nis the wave vector of the density wave. The main ingredients are the emergence\nof the reflection symmetry and dipole moment conservation to the leading\nnon-trivial order of the large tilted strength. To support our analysis, we\nthen construct a solvable model with large local Hilbert space dimension by\ncoupling sites discribed by the Sachdev-Ye-Kitaev models, where the density\nresponse can be computed explicitly. The the tilt strength and the temperature\ndependence of the subdiffusion constant are also discussed.",
        "positive": "Evolution of the unitary Bose gas for broad to narrow Feshbach\n  resonances: We study the post-quench dynamics of unitary Bose gases using a two-channel\nmodel, focusing on the effect of variations in the width of the Feshbach\nresonance due to density changes. We generally find that increasing the density\nleads to a corresponding increase in the production of closed channel\nmolecules, a decrease in the build up of quantum depletion and a transition\nfrom linear to quadratic early-time growth of the two-body contact as well as\nthe condensed pair fraction. Motivated by the presence of closed-channel\nmolecules in the unitary regime, we study the embedded two-body problem finding\na transition from open to closed-channel dominated dimers due to many-body\neffects."
    },
    {
        "anchor": "Equilibrium solutions of immiscible two-species Bose-Einstein\n  condensates in perturbed harmonic traps: We investigate the mean--field equilibrium solutions for a two--species\nimmiscible Bose--Einstein condensate confined by a harmonic confinement with\nadditional linear perturbations. We observe a range of equilibrium density\nstructures, including `ball and shell' formations and axially/radially\nseparated states, with a marked sensitivity to the potential perturbations and\nthe relative atom number in each species. Incorporation of linear trap\nperturbations, albeit weak, are found to be essential to match the range of\nequilibrium density profiles observed in a recent Rb-87 - Cs-133 Bose-Einstein\ncondensate experiment [D. J. McCarron et al., Phys. Rev. A, 84, 011603(R)\n(2011)]. Our analysis of this experiment demonstrates that sensitivity to\nlinear trap perturbations is likely to be important factor in interpreting the\nresults of similar experiments in the future.",
        "positive": "Inhomogeneous spin diffusion in traps with cold atoms: The spin diffusion and damped oscillations are studied in the collision of\ntwo spin polarized clouds of cold atoms with resonant interactions. The strong\ndensity dependence of the diffusion coefficient leads to inhomogeneous spin\ndiffusion that changes from central to surface spin flow as the temperature\nincreases. The inhomogeneity and the smaller finite trap size significantly\nreduce the spin diffusion rate at low temperatures. The resulting spin\ndiffusion rates, spin drag and initial damped oscillations are compatible with\nmeasurements at low to high temperatures for resonant attractive interactions\nbut are incompatible with a metastable ferromagnetic phase."
    },
    {
        "anchor": "Josephson effect in fermionic superfluids across the BEC-BCS crossover: We report on the observation of the Josephson effect between two strongly\ninteracting fermionic superfluids coupled through a thin tunneling barrier. We\nprove that the relative population and phase are canonically conjugate\ndynamical variables, coherently oscillating throughout the entire crossover\nfrom molecular Bose-Einstein condensates (BEC) to Bardeen-Cooper-Schrieffer\n(BCS) superfluids. We measure the plasma frequency and we extract the Josephson\ncoupling energy, both exhibiting a non-monotonic behavior with a maximum near\nthe crossover regime. We also observe the transition from coherent to\ndissipative dynamics, which we directly ascribe to the propagation of vortices\nthrough the superfluid bulk. Our results highlight the robust nature of\nresonant superfluids, opening the door to the study of the dynamics of\nsuperfluid Fermi systems in the presence of strong correlations and\nfluctuations.",
        "positive": "Dimer-atom scattering between two identical fermions and a third\n  particle: We use the diagrammatic $T$-matrix approach to analyze the three-body\nscattering problem between two identical fermions and a third particle (which\ncould be a different species of fermion or a boson). We calculate the s-wave\ndimer-atom scattering length for all mass ratios, and our results exactly match\nthe results of Petrov. In particular, we list the exact dimer-atom scattering\nlengths for all available two-species Fermi-Fermi and Bose-Fermi mixtures. In\naddition, unlike that of the equal-mass particles case where the three-body\nscattering $T$-matrix decays monotonically as a function of the outgoing\nmomentum, we show that, after an initial rapid drop, this function changes sign\nand becomes negative at large momenta and then decays slowly to zero when the\nmass ratio of the fermions to the third particle is higher than a critical\nvalue (around 6.5). As the mass ratio gets higher, modulations of the\n$T$-matrix become more apparent with multiple sign changes, related to the\n\"fall of a particle to the center\" phenomenon and to the emergence of\nthree-body Efimov bound states."
    },
    {
        "anchor": "Stability of the Breached Pair State for a Two-species Fermionic System\n  in the Presence of Feshbach Resonance: We investigate the phenomenon of fermionic pairing with mismatched Fermi\nsurfaces in a two-species system in the presence of Feshbach resonance, where\nthe resonantly-paired fermions combine to form bosonic molecules. We observe\nthat the Feshbach parameters control the critical temperature of the gapped BCS\nsuperfluid state, and also determine the range over which a gapless breached\npair state may exist. Demanding the positivity of the superfluid density, it is\nshown that although a breached pair state with two Fermi surfaces is always\nunstable, its single Fermi-surface counterpart can be stable if the chemical\npotentials of the two pairing species have opposite signs. This condition is\nsatisfied only over a narrow region in the BEC side, characterized by an upper\nand a lower limit for the magnetic field. We estimate these limits for a\nmixture of two hyperfine states of $^6$Li using recent experimental data.",
        "positive": "Trapping Centers at the Superfluid-Mott-insulator Criticality:\n  Transition between Charge-quantized States: Under the conditions of superfluid-Mott-insulator criticality in two\ndimensions, the trapping centers--i.e., local potential wells and bumps--are\ngenerically characterized by an integer charge corresponding to the number of\ntrapped particles (if positive) or holes (if negative). Varying the strength of\nthe center leads to a transition between two competing ground states with\ncharges differing by $\\pm 1$. The hallmark of the transition scenario is a\nsplitting of the number density distortion, $\\delta n(r)$, into a half-integer\ncore and a large halo carrying the complementary charge of $\\pm 1/2$. The sign\nof the halo changes across the transition and the radius of the halo, $r_0$,\ndiverges on the approach to the critical strength of the center, $V = V_c$, by\nthe law $r_0 \\propto |V-V_c|^{-\\tilde{\\nu}}$, with $\\tilde{\\nu} \\approx\n2.33(5)$."
    },
    {
        "anchor": "The Equation of State of a Low-Temperature Fermi Gas with Tunable\n  Interactions: Interacting fermions are ubiquitous in nature and understanding their\nthermodynamics is an important problem. We measure the equation of state of a\ntwo-component ultracold Fermi gas for a wide range of interaction strengths at\nlow temperature. A detailed comparison with theories including Monte-Carlo\ncalculations and the Lee-Huang-Yang corrections for low-density bosonic and\nfermionic superfluids is presented. The low-temperature phase diagram of the\nspin imbalanced gas reveals Fermi liquid behavior of the partially polarized\nnormal phase for all but the weakest interactions. Our results provide a\nbenchmark for many-body theories and are relevant to other fermionic systems\nsuch as the crust of neutron stars.",
        "positive": "Tonks-Girardeau gas, super-Tonks-Girardeau gas, and bound states of\n  one-dimensional bosons in a hard-wall trap: We investigate the Bose gas with repulsive or attractive interactions between\natoms in the scheme of Bethe Ansatz equation in a hard wall trap. Three typical\nquantum phases in the current research of 1D interacting cold atoms are\nclarified in terms of the energy spectrum, single particle density distribution\nand two-particle correlation function. We identify two matching points in the\nphase diagram, i.e. the TG and STG gas show the same profiles at the strongly\ninteracting point $-1/\\gamma=0$, and in the weakly interacting limit $\\gamma=0$\nthe ground states TG and BS join to each other smoothly."
    },
    {
        "anchor": "Condensed Matter Theory of Dipolar Quantum Gases: Recent experimental breakthroughs in trapping, cooling and controlling\nultracold gases of polar molecules, magnetic and Rydberg atoms have paved the\nway toward the investigation of highly tunable quantum systems, where\nanisotropic, long-range dipolar interactions play a prominent role at the\nmany-body level. In this article we review recent theoretical studies\nconcerning the physics of such systems. Starting from a general discussion on\ninteraction design techniques and microscopic Hamiltonians, we provide a\nsummary of recent work focused on many-body properties of dipolar systems,\nincluding: weakly interacting Bose gases, weakly interacting Fermi gases,\nmultilayer systems, strongly interacting dipolar gases and dipolar gases in 1D\nand quasi-1D geometries. Within each of these topics, purely dipolar effects\nand connections with experimental realizations are emphasized.",
        "positive": "Vortex Synchronization in Bose-Einstein Condensates: A Time-Dependent\n  Gross-Pitaevskii Equation Approach: In this work we consider vortex lattices in rotating Bose-Einstein\nCondensates composed of two species of bosons having different masses.\nPreviously [1] it was claimed that the vortices of the two species form bound\npairs and the two vortex lattices lock. Remarkably, the two condensates and the\nexternal drive all rotate at different speeds due to the disparity of the\nmasses of the constituent bosons. In this paper we study the system by solving\nthe full two-component Gross-Pitaevskii equations numerically. Using this\napproach we verify the stability of the putative locked state which is found to\nexist within a disk centered on the axis of rotation and which depends on the\nmass ratio of the two bosons. We also show that an analytic estimate of this\nlocking radius based on a two-body force calculation agrees well with the\nnumerical results."
    },
    {
        "anchor": "Hydrodynamics of the atomic Bose-Einstein condensate beyond the\n  mean-field approximation: a mini-review: Several hydrodynamic models the atomic Bose-Einstein condensate beyond the\nmean-field approximation are discussed together from one point of view. All\nthese models are derived from microscopic quantum description. The derivation\nis made within the many-particle quantum hydrodynamics method suggested by L.\nKuz'menkov. The derivation is demonstrated and discussed for the mean-field\nregime revealing the Gross-Pitaevskii equation as the simplest illustration. It\nappears in the first order by the interaction radius. Generalization of the\nhydrodynamic Euler equation obtained in the third order by the interaction\nradius are discussed. It includes the contribution of the isotropic short-range\ninteraction presented by the third space derivative of the square of\nconcentration. The Euler equation also includes the contribution of the\nanisotropic part of the short-range interaction proportional to the second\norder spherical function. Systematic account of the quantum fluctuations in\nterms of the many-particle quantum hydrodynamics method requires the extension\nof the set of hydrodynamic equations from the couple continuity and Euler\nequations to the set of four equations which also includes the pressure\nevolution equation and the evolution equation for the third rank analog of\npressure. The pressure evolution equation contains no interaction contribution\nin the first order by the interaction radius. The source of the quantum\nfluctuations is in the interaction caused term in the third rank tensor\nevolution equation which is obtained in the first order by the interaction\nradius.",
        "positive": "The Beliaev Broken Symmetry Description of Superfluidity vs the\n  Classical-Field Approach: The standard theoretical basis for understanding superfluidity in Bose\nsystems was formulated by Beliaev in 1957, based on splitting the quantum field\noperator into a macroscopically occupied condensate component and a\nnon-condensate component. This leads to a description of the condensate in\nterms of a 'single-particle state', the so-called macroscopic wavefunction.\nSince the discovery of Bose-condensed gases, an alternative theoretical picture\nhas been developed which is based on a 'coherent band' of classically occupied\nstates. This is often called the classical or c-field approach. The goal of\nthis chapter is to review the differences between the Beliaev broken symmetry\nand c-field approach, and to argue that the c-field concept of a coherent\ncondensate band of states has problems as a description of Bose superfluidity.\nHowever, the c-field idea of treating the lowest energy excitations classically\ncan be used to advantage to simplify calculations within the Beliaev\nbroken-symmetry formalism."
    },
    {
        "anchor": "Thermoelectricity in a junction between interacting cold atomic Fermi\n  gases: A gas of interacting ultracold fermions can be tuned into a strongly\ninteracting regime using a Feshbach resonance. Here we theoretically study\nquasiparticle transport in a system of two reservoirs of interacting ultracold\nfermions on the BCS side of the BCS-BEC crossover coupled weakly via a tunnel\njunction. Using the generalized BCS theory we calculate the time evolution of\nthe system that is assumed to be initially prepared in a non-equilibrium state\ncharacterized by a particle number imbalance or a temperature imbalance. A\nnumber of characteristic features like sharp peaks in quasiparticle currents,\nor transitions between the normal and superconducting states are found. We\ndiscuss signatures of the Seebeck and the Peltier effect and the resulting\ntemperature difference of the two reservoirs as a function of the interaction\nparameter $(k_Fa)^{-1}$. The Peltier effect may lead to an additional cooling\nmechanism for ultracold fermionic atoms.",
        "positive": "Atom-atom correlations in time-of-flight imaging of ultra-cold bosons in\n  optical lattices: We study the spatial correlations of strongly interacting bosons in a ground\nstate, confined in two-dimensional square and three-dimensional cubic lattice.\nUsing combined Bogoliubov method and the quantum rotor approach, we map the\nHamiltonian of strongly interacting bosons onto U(1) phase action in order to\ncalculate the atom-atom correlations decay along the principal axis and a\ndiagonal of the lattice plane direction as a function of distance. Lower\ntunneling rates lead to quicker decays of the correlations, which character\nbecomes exponential. Finally, correlation functions allow us to calculate\nquantities that are directly bound to experimental outcomes, namely\ntime-of-flight absorption images and resulting visibility. Our results contain\nall the characteristic features present in experimental data (transition from\nMott insulating blob to superfluid peaks, etc.), which emphasizes the usability\nof the proposed approach."
    },
    {
        "anchor": "Strongly Interacting Two-Dimensional Dirac Fermions: We show how strongly interacting two-dimensional Dirac fermions can be\nrealized with ultracold atoms in a two-dimensional optical square lattice with\nan experimentally realistic, inherent gauge field, which breaks time-reversal\nand inversion symmetries. We find remarkable phenomena in a temperature range\naround a tenth of the Fermi-temperature, accessible with present experimental\ntechniques: at zero chemical potential, besides a conventional s-wave\nsuperconducting phase, unconventional superconductivity with non-local bond\npairing arises. In a temperature versus doping phase diagram, the\nunconventional superconducting phase exhibits a dome structure, reminiscent of\nthe phase diagram for high-temperature superconductors and heavy fermions.",
        "positive": "Atomic twin-beams and violation of a motional-state Bell inequality from\n  a phase-fluctuating quasi-condensate source: We investigate the dynamics of atomic twin beams produced from a\nphase-fluctuating source, specifically a 1D Bose gas in the quasi-condensate\nregime, motivated by the experiment reported in Nature Physics 7, 608 (2011). A\nshort-time analytic model is constructed, which is a modified version of the\nundepleted pump approximation widely used in quantum and atom optics, except\nthat here we take into account the initial phase fluctuations of the pump\nsource as opposed to assuming long-range phase coherence. We use this model to\nmake quantitative and qualitative predictions of how phase-fluctuations of the\nsource impact the two-particle correlations of scattered atom-pairs. The model\nis benchmarked against detailed numerical simulations using stochastic\nphase-space methods, and is shown to validate the intuitive notion that the\nbroadening of momentum-space correlation functions between atoms scattered from\na quasi-condensate is driven by the broadened momentum width of the source\ncompared to a true phase coherent condensate. Finally, we combine these\ntheoretical tools and results to investigate the effect phase fluctuations of\nthe twin-beam source can have on a proposed demonstration of a violation of a\nBell inequality, which intrinsically relies on phase-sensitive pair\ncorrelations."
    },
    {
        "anchor": "Influence of Rashba spin-orbit and Rabi couplings on the miscibility and\n  ground state phases of binary Bose-Einstein condensates: We study the miscibility properties and ground state phases of two-component\nspin-orbit (SO) coupled Bose-Einstein condensates (BECs) in a harmonic trap\nwith strong axial confinement. By numerically solving the coupled\nGross-Pitaevskii equations in the two-dimensional setting, we analyze the\nSO-coupled BECs for two possible permutations of the intra- and interspecies\ninteractions, namely (i) weak intra- and weak interspecies interactions (W-W)\nand (ii) weak intra- and strong interspecies interactions (W-S). Considering\nthe density overlap integral as a miscibility order parameter, we investigate\nthe miscible-immiscible transition by varying the coupling parameters. We\nobtain various ground state phases, including plane wave, half quantum vortex,\nelongated plane wave, and different stripe wave patterns for W-W interactions.\nFor finite Rabi coupling, an increase in SO coupling strength leads to the\ntransition from the fully miscible to the partially miscible state. We also\ncharacterize different ground states in the coupling parameter space using the\nroot mean square sizes of the condensate. The spin density vector for the\nground state phases exhibits density, quadrupole and dipole like spin\npolarizations. For the W-S interaction, in addition to that observed in the W-W\ncase, we witness semi vortex, mixed mode, and shell-like immiscible phases. We\nnotice a wide variety of spin polarizations, such as density, dipole,\nquadrupole, symbiotic, necklace, and stripe-like patterns for the W-S case. A\ndetailed investigation in the coupling parameter space indicates immiscible to\nmiscible state phase transition upon varying the Rabi coupling for a fixed\nRashba SO coupling. The critical Rabi coupling for the immiscible-miscible\nphase transition decreases upon increasing the SO coupling strength.",
        "positive": "AtomECS: Simulate laser cooling and magneto-optical traps: AtomECS is a software package that efficiently simulates the motion of\nneutral atoms experiencing forces exerted by laser radiation, such as in\nmagneto-optical traps and Zeeman slowers. The program is implemented using the\nEntity-Component-System pattern, which gives excellent performance, flexibility\nand scalability to parallel computing resources. The simulation package has\nbeen verified by comparison to analytic results, and extensively unit tested."
    },
    {
        "anchor": "Exploring classically chaotic potentials with a matter wave quantum\n  probe: We study an experimental setup in which a quantum probe, provided by a\nquasi-monomode guided atom laser, interacts with a static localized attractive\npotential whose characteristic parameters are tunable. In this system,\nclassical mechanics predicts a transition from a regular to a chaotic behavior\nas a result of the coupling between the longitudinal and transverse degrees of\nfreedom. Our experimental results display a clear signature of this transition.\nOn the basis of extensive numerical simulations, we discuss the quantum versus\nclassical physics predictions in this context. This system opens new\npossibilities for investigating quantum scattering, provides a new testing\nground for classical and quantum chaos and enables to revisit the\nquantum-classical correspondence.",
        "positive": "Realization of a Laughlin state of two rapidly rotating fermions: We realize a Laughlin state of two rapidly rotating fermionic atoms in an\noptical tweezer. By utilizing a single atom and spin resolved imaging\ntechnique, we sample the Laughlin wavefunction, thereby revealing its\ndistinctive features, including a vortex distribution in the relative motion,\ncorrelations in the particles' relative angle, and suppression of the\ninter-particle interactions. Our work lays the foundation for atom-by-atom\nassembly of fractional quantum Hall states in rotating atomic gases."
    },
    {
        "anchor": "Phase contrast imaging of Bose condensed clouds: Phase contrast imaging is used to observe Bose-Einstein condensates (BECs) at\nfinite temperature in situ. The imaging technique is used to accurately derive\nthe absolute phase shift of a probe laser beam due to both the condensate and\nthe thermal cloud. The accuracy of the method is enhanced by using the\nperiodicity of the intensity signal as a function of the accumulated phase. The\nmeasured density profiles can be described using a two relevant parameter fit,\nin which only the chemical potential and the temperature are to be determined.\nThis allows us to directly compare the measured density profiles to different\nmean-field models in which the interaction between the condensed and thermal\natoms is taken into account to various degrees.",
        "positive": "Transition from Band insulator to Bose-Einstein Condensate superfluid\n  and Mott State of Cold Fermi Gases with Multiband Effects in Optical Lattices: We study two models realized by two-component Fermi gases loaded in optical\nlattices. We clarify that multi-band effects inevitably caused by the optical\nlattices generate a rich structure, when the systems crossover from the region\nof weakly bound molecular bosons to the region of strongly bound atomic bosons.\nHere the crossover can be controlled by attractive fermion interaction. One of\nthe present models is a case with attractive fermion interaction, where an\ninsulator-superfluid transition takes place. The transition is characterized as\nthe transition between a band insulator and a Bose-Einstein condensate (BEC)\nsuperfluid state. Differing from the conventional BCS superfluid transition,\nthis transition shows unconventional properties. In contrast to the one\nparticle excitation gap scaled by the superfluid order parameter in the\nconventional BCS transition, because of the multi-band effects, a large gap of\none-particle density of states is retained all through the transition although\nthe superfluid order grows continuously from zero. A reentrant transition with\nlowering temperature is another unconventionality. The other model is the case\nwith coexisting attractive and repulsive interactions. Within a mean field\ntreatment, we find a new insulating state, an orbital ordered insulator. This\ninsulator is one candidate for the Mott insulator of molecular bosons and is\nthe first example that the orbital internal degrees of freedom of molecular\nbosons appears explicitly. Besides the emergence of a new phase, a coexisting\nphase also appears where superfluidity and an orbital order coexist just by\ndoping holes or particles. The insulating and superfluid particles show\ndifferentiation in momentum space as in the high-Tc cuprate superconductors."
    },
    {
        "anchor": "Driven-dissipative Ising Model: An exact field-theoretical analysis: Driven-dissipative many-body systems are difficult to analyze analytically\ndue to their non-equilibrium dynamics, dissipation and many-body interactions.\nIn this paper, we consider a driven-dissipative infinite-range Ising model with\nlocal spontaneous emission, which naturally emerges from the open Dicke model\nin the large-detuning limit. Utilizing an adaptation of the Suzuki-Trotter\nquantum-to-classical mapping, we develop an exact field-theoretical analysis\nand a diagrammatic representation of the spin model that can be understood from\na simple scattering picture. With this representation, we are able to analyze\ncritical behavior, finite-size scaling and the effective temperature near the\nrespective phase transition. Our formalism further allows a detailed study of\nthe ordered phase where we find a \"heating\" region within which the effective\ntemperature becomes negative, thereby exhibiting a truly non-equilibrium\nbehavior. At the phase transition, we find two distinct critical behaviors with\noverdamped and underdamped critical dynamics at generic and weakly-dissipative\ncritical points, respectively. We further show that the underdamped critical\nbehavior is robust against short-range perturbations and is not an artifact of\nthe mean-field nature of the model. To treat such perturbations, we extend our\ndiagrammatic representation to include the coupling to spin waves due to the\nshort-range interactions. The field-theoretical approach and the diagrammatics\ndeveloped in this work should prove useful in applications to generic\nshort-range driven-dissipative spin systems.",
        "positive": "Unraveling the Excitation Spectrum of Many-Body Systems from Quantum\n  Quenches: Quenches are now routinely used in synthetic quantum systems to study a\nvariety of fundamental effects, including ergodicity breaking, light-cone-like\nspreading of information, and dynamical phase transitions. It was shown\nrecently that the dynamics of equal-time correlators may be related to\nground-state phase transitions and some properties of the system excitations.\nHere, we show that the full low-lying excitation spectrum of a generic\nmany-body quantum system can be extracted from the after-quench dynamics of\nequal-time correlators. We demonstrate it for a variety of one-dimensional\nlattice models amenable to exact numerical calculations, including Bose and\nspin models, with short- or long-range interactions. The approach also applies\nto higher dimensions, correlated fermions, and continuous models. We argue that\nit provides an alternative approach to standard pump-probe spectroscopic\nmethods and discuss its advantages."
    },
    {
        "anchor": "Spin-Orbit Coupled Exciton-Polariton Condensates in Lead Halide\n  Perovskites: Spin-orbit coupling (SOC) is responsible for a range of spintronic and\ntopological processes in condensed matter. Here we show photonic analogs of\nSOCs in exciton-polaritons and their condensates in microcavities composed of\nbirefringent lead halide perovskite single crystals. The presence of\ncrystalline anisotropy coupled with splitting in the optical cavity of the\ntransverse electric (TE) and transverse magnetic (TM) modes gives rise to a\nnon-Abelian gauge field, which can be described by the Rashba-Dresselhaus\nHamiltonian near the degenerate points of the two polarization modes. With\nincreasing density, the exciton polaritons with pseudospin textures undergo\nphase transitions to competing condensates with orthogonal polarizations.\nUnlike their pure photonic counterparts, these exciton polaritons and\ncondensates inherit nonlinearity from their excitonic components and may serve\nas quantum simulators of many-body SOC processes.",
        "positive": "Condensation and superfluidity of $SU(N)$ Bose gas: We perform the comprehensive comparison of properties of the condensate and\nsuperfluid densities for the $N$-component three-dimensional Bose gas with the\nsymmetric inter- and intraspecies short-range interaction between particles. In\nparticular, based on the large-$N$ expansion approach for many-boson systems we\nobtain general expression for density of the superfluid component that at very\nlow temperatures reproduce the well-know Landau's formula and non-trivially\nincludes the thermal fluctuations in the finite-temperature region, and compare\nit to the condensate density calculated previously. The numerically evaluated\ntemperature dependencies are in a qualitatively good agreement with the results\nof Monte Carlo simulations."
    },
    {
        "anchor": "Superfluid/Bose-glass transition in one dimension: We consider a one-dimensional system of interacting bosons in a random\npotential. At zero temperature, it can be either in the superfluid or in the\ninsulating phase. We study the transition at weak disorder and moderate\ninteraction. Using a systematic approach, we derive the renormalization group\nequations at two-loop order and discuss the phase diagram. We find the\nuniversal form of the correlation functions at the transitions and compute the\nlogarithmic corrections to the main universal power-law behavior. In order to\nmimic large density fluctuations on a single site, we study a simplified model\nof disordered two-leg bosonic ladders with correlated disorder across the rung.\nContrarily to the single-chain case, the latter system exhibits a transition\nbetween a superfluid and a localized phase where the exponents of the\ncorrelation functions at the transition do not take universal values.",
        "positive": "Dynamical generation of dark-bright solitons through the domain wall of\n  two immiscible Bose-Einstein condensates: We theoretically investigate the one-dimensional dynamics of a dark soliton\nin a two-component immiscible mixture of Bose-Einstein condensates with\nrepulsive interactions. We analyze the reflection and transmission of a soliton\nwhen it propagates through the domain wall, and we show that a dark-bright\nsoliton can be dynamically generated by the interaction of the dark soliton\nwith the domain wall, outside the regime of parameters where stationary\nsolutions are known to exist. The dynamics of this dark-bright soliton is\nharmonic like, with a numerical frequency that is in good agreement with the\npredictions of a semi-analytical model."
    },
    {
        "anchor": "Clustering of Four-Component Unitary Fermions: Ab initio nuclear physics tackles the problem of strongly interacting\nfour-component fermions. The same setting could foreseeably be probed\nexperimentally in ultracold atomic systems, where two- and three-component\nexperiments have led to major breakthroughs in recent years. Both due to the\nproblem's inherent interest and as a pathway to nuclear physics, in this Letter\nwe study four-component fermions at unitarity via the use of quantum Monte\nCarlo methods. We explore novel forms of the trial wave function and find one\nwhich leads to a ground state of the eight-particle system whose energy is\nalmost equal to that of two four-particle systems. We investigate the\nclustering properties involved and also extrapolate to the zero-range limit. In\naddition to being experimentally testable, our results impact the prospects of\ndeveloping nuclear physics as a perturbation around the unitary limit.",
        "positive": "Pomeranchuk effect and spin-gradient cooling of Bose-Bose mixtures in an\n  optical lattice: We theoretically investigate finite-temperature thermodynamics and\ndemagnetization cooling of two-component Bose-Bose mixtures in a cubic optical\nlattice, by using bosonic dynamical mean field theory (BDMFT). We calculate the\nfinite-temperature phase diagram, and remarkably find that the system can be\nheated from the superfluid into the Mott insulator at low temperature,\nanalogous to the Pomeranchuk effect in 3He. This provides a promising many-body\ncooling technique. We examine the entropy distribution in the trapped system\nand discuss its dependence on temperature and an applied magnetic field\ngradient. Our numerical simulations quantitatively validate the spin-gradient\ndemagnetization cooling scheme proposed in recent experiments."
    },
    {
        "anchor": "Entangled states of dipolar bosons generated in a triple-well potential: We study the generation of entangled states using a device constructed from\ndipolar bosons confined to a triple-well potential. Dipolar bosons possess\ncontrollable, long-range interactions. This property permits specific choices\nto be made for the coupling parameters, such that the system is integrable.\nIntegrability assists in the analysis of the system via an effective\nHamiltonian constructed through a conserved operator. Through computations of\nfidelity we establish that this approach, to study the time-evolution of the\nentanglement for a class of non-entangled initial states, yields accurate\napproximations given by analytic formulae.",
        "positive": "Topological interfaces crossed by defects and textures of continuous and\n  discrete point group symmetries in spin-2 Bose-Einstein condensates: We systematically and analytically construct a set of spinor wave functions\nrepresenting defects and textures that continuously penetrate interfaces\nbetween coexisting, topologically distinct magnetic phases in a spin-2\nBose-Einstein condensate. These include singular and nonsingular vortices\ncarrying mass or spin circulation that connect across interfaces between\nbiaxial- and uniaxial nematic, cyclic and ferromagnetic phases, as well as\nvortices terminating as monopoles on the interface (\"boojums\"). The\nbiaxial-nematic and cyclic phases exhibit discrete polytope symmetries\nfeaturing non-Abelian vortices and we investigate a pair of non-commuting line\ndefects within the context of a topological interface. By numerical\nsimulations, we characterize the emergence of non-trivial defect core\nstructures, including the formation of composite defects. Our results\ndemonstrate the potential of spin-2 Bose-Einstein condensates as experimentally\naccessible platforms for exploring interface physics, offering a wealth of\ncombinations of continuous and discrete symmetries."
    },
    {
        "anchor": "Quantum distillation: dynamical generation of low-entropy states of\n  strongly correlated fermions in an optical lattice: Correlations between particles can lead to subtle and sometimes\ncounterintuitive phenomena. We analyze one such case, occurring during the\nsudden expansion of fermions in a lattice when the initial state has a strong\nadmixture of double occupancies. We promote the notion of quantum distillation:\nduring the expansion, and in the presence of strongly repulsive interactions,\ndoublons group together, forming a nearly ideal band insulator, which is\nmetastable with a low entropy. We propose that this effect could be used for\ncooling purposes in experiments with two-component Fermi gases.",
        "positive": "Coexistence of photonic and atomic Bose-Einstein condensates in ideal\n  atomic gases: We have studied conditions of photon Bose-Einstein condensate formation that\nis in thermodynamic equilibrium with ideal gas of two-level Bose atoms below\nthe degeneracy temperature. Equations describing thermodynamic equilibrium in\nthe system were formulated; critical temperatures and densities of photonic and\natomic gas subsystems were obtained analytically. Coexistence conditions of\nthese photonic and atomic Bose-Einstein condensates were found. There was\npredicted the possibility of an abrupt type of photon condensation in the\npresence of Bose condensate of ground-state atoms: it was shown that the\nslightest decrease of the temperature could cause a significant gathering of\nphotons in the condensate. This case could be treated as a simple model of the\nsituation known as \"stopped light\" in cold atomic gas. We also showed how\npopulation inversion of atomic levels can be created by lowering the\ntemperature. The latter situation looks promising for light accumulation in\natomic vapor at very low temperatures."
    },
    {
        "anchor": "Phase separation of multicomponent excitonic Bose-Einstein condensates: For the observation of Bose-Einstein condensation, excitons in cuprous oxide\nare regarded as promising candidates due to their large binding energy and long\nlifetime. High particle densities may be achieved by entrapment in a stress\ninduced potential. We consider a multi-component gas of interacting para- and\northoexcitons in cuprous oxide confined in a three-dimensional potential trap.\nBased on the Hartree-Fock-Bogoliubov theory, we calculate density profiles as\nwell as decay luminescence spectra which exhibit signatures of the separation\nof the Bose-condensed phases.",
        "positive": "Excitation of atoms in an optical lattice driven by polychromatic\n  amplitude modulation: We investigate the mutiphoton process between different Bloch states in an\namplitude modulated optical lattice. In the experiment, we perform the\nmodulation with more than one frequency components, which includes a high\ndegree of freedom and provides a flexible way to coherently control quantum\nstates. Based on the study of single frequency modulation, we investigate the\ncollaborative effect of different frequency components in two aspects. Through\ndouble frequency modulations, the spectrums of excitation rates for different\nlattice depths are measured. Moreover, interference between two separated\nexcitation paths is shown, emphasizing the influence of modulation phases when\ntwo modulation frequencies are commensurate. Finally, we demonstrate the\napplication of the double frequency modulation to design a\nlarge-momentum-transfer beam splitter. The beam splitter is easy in practice\nand would not introduce phase shift between two arms."
    },
    {
        "anchor": "Macroscopic Matter Wave Quantum Tunnelling: Quantum tunneling is a phenomenon of non-equilibrium quantum dynamics and its\ndetailed process is largely unexplored. We report the experimental observation\nof macroscopic quantum tunneling of Bose-Einstein Condensate in a hybrid trap.\nBy exerting a non-adiabatic kick to excite a collective rotation mode of the\ntrapped condensate, a periodic pulse train, which remains as condensate, is\nthen out-coupled by quantum tunneling. This non-equilibrium dynamics is\nanalogue to tunneling ionization. The imaged tunneling process shows the\nsplitting of matter-wave packet by the potential barrier. The controversial\n\"tunneling time\" question is found inadequate, from the point of view of wave\npropagation. The realized matter-wave pulse train can also be a passive pulsed\natom laser for atom interferometer applications.",
        "positive": "Bright soliton to quantum droplet transition in a mixture of\n  Bose-Einstein condensates: Attractive Bose-Einstein condensates can host two types of macroscopic\nself-bound states of different nature: bright solitons and quantum liquid\ndroplets. Here, we investigate the connection between them with a Bose-Bose\nmixture confined in an optical waveguide. We develop a simple theoretical model\nto show that, depending on atom number and interaction strength, solitons and\ndroplets can be smoothly connected or remain distinct states coexisting only in\na bi-stable region. We experimentally measure their spin composition, extract\ntheir density for a broad range of parameters and map out the boundary of the\nregion separating solitons from droplets."
    },
    {
        "anchor": "Superfluid--Mott insulator transition of ultracold superradiant bosons\n  in a cavity: We investigate harmonically-trapped, laser-pumped bosons with infinite-range\ninteractions induced by a dissipative high-finesse red-detuned optical cavity\nwith numerical and analytical methods. We obtain multiple cavity and atomic\nobservables as well as the full phase diagram of the system using the\nmulticonfigurational time-dependent Hartree method for indistinguishable\nparticles (MCTDH-X) approach. Besides the transition from an unorganized normal\nphase to a superradiant phase where atoms self-organize, we focus on an\nin-depth investigation of the self-organized superfluid to self-organized Mott\ninsulator phase transition in the superradiant phase as a function of the\ncavity-atom coupling. The numerical results are substantiated by an analytical\nstudy of an effective Bose-Hubbard model. We numerically analyze cavity\nfluctuations and emergent strong correlations between atoms in the many-body\nstate across the Mott transition via the atomic density distributions and\nGlauber correlation functions. Unexpectedly, the weak harmonic trap leads to\nfeatures like a lattice switching between the two symmetry-broken\n$\\mathbb{Z}_2$ configurations of the untrapped system and a reentrance of\nsuperfluidity in the Mott insulating phase. Our analytical considerations\nquantitatively explain the numerically observed correlation features.",
        "positive": "Decay of a Quantum Knot: We experimentally study the dynamics of quantum knots in a uniform magnetic\nfield in spin-1 Bose-Einstein condensates. The knot is created in the polar\nmagnetic phase, which rapidly undergoes a transition towards the ferromagnetic\nphase in the presence of the knot. The magnetic order becomes scrambled as the\nsystem evolves, and the knot disappears. Strikingly, over long evolution times,\nthe knot decays into a polar-core spin vortex, which is a member of a class of\nsingular SO(3) vortices. The polar-core spin vortex is stable with an observed\nlifetime comparable to that of the condensate itself. The structure is similar\nto that predicted to appear in the evolution of an isolated monopole defect,\nsuggesting a possible universality in the observed topological transition."
    },
    {
        "anchor": "Interacting multi-component exciton gases in a potential trap: phase\n  separation and Bose-Einstein condensation: The system under consideration is a multi-component gas of interacting para-\nand orthoexcitons confined in a three dimensional potential trap. We calculate\nthe spatially resolved optical emission spectrum due to interband transitions\ninvolving weak direct and phonon mediated exciton-photon interactions. For each\ncomponent, the occurrence of a Bose-Einstein condensate changes the spectrum in\na characteristic way so that it directly reflects the constant chemical\npotential of the excitons and the renormalization of the quasiparticle\nexcitation spectrum. Moreover, the interaction between the components leads, in\ndependence on temperature and particle number, to modifications of the spectra\nindicating phase separation of the subsystems. Typical examples of density\nprofiles and luminescence spectra of ground-state para- and orthoexcitons in\ncuprous oxide are given.",
        "positive": "Photon blockade with ground-state neutral atoms: We show that induced dipole-dipole interactions allow for photon blockade in\nsubwavelength ensembles of two-level, ground-state neutral atoms. Our protocol\nrelies on the energy shift of the single-excitation, superradiant state of $N$\natoms, which can be engineered to yield an effective two-level system. A\ncoherent pump induces Rabi oscillation between the ground state and a\ncollective bright state, with at most a single excitation shared among all\natoms. The possibility of using clock transitions that are long-lived and\nrelatively robust against stray fields, alongside new prospects on experiments\nwith subwavelength lattices, makes our proposal a promising alternative for\nquantum information protocols."
    },
    {
        "anchor": "Comparison of strong-coupling theories for a two-dimensional Fermi gas: Understanding the formation of Cooper pairs and the resulting thermodynamic\nproperties of a low-dimensional Fermi gas is an important area of research,\nelucidating our understanding of high temperature superconductors. In lower\ndimensions quantum fluctuations are expected to play an increasingly important\nrole and the reliability of strong-coupling theories becomes questionable.\nHere, we present a comparison of recent thermodynamic measurements and\ntheoretical predictions from different many-body $T$-matrix theories for a\ntwo-dimensional strongly interacting Fermi gas in the normal state. We find\nthat the fully self-consistent $T$-matrix theory provides the best description\nof the experimental data over a wide range of temperatures and interatomic\ninteractions. Our comparison reveals the crucial role played by the\ninteractions between Cooper pairs and suggests that the future development of a\nquantitative strong-coupling theory for two-dimensional Fermi superfluids must\nexplicitly take into account the diagrams that are responsible for pair-pair\ninteractions.",
        "positive": "Hopf characterization of two-dimensional Floquet topological insulators: We present a topological characterization of time-periodically driven\ntwo-band models in 2+1 dimensions as Hopf insulators. The intrinsic periodicity\nof the Floquet system with respect to both time and the underlying\ntwo-dimensional momentum space constitutes a map from a three dimensional torus\nto the Bloch sphere. As a result, we find that the driven system can be\nunderstood by appealing to a Hopf map that is directly constructed from the\nmicromotion of the drive. Previously found winding numbers are shown to\ncorrespond to Hopf invariants, which are associated with linking numbers\ndescribing the topology of knots in three dimensions. Moreover, after being\ncast as a Hopf insulator, not only the Chern numbers, but also the winding\nnumbers of the Floquet topological insulator become accessible in experiments\nas linking numbers. We exploit this description to propose a feasible scheme\nfor measuring the complete set of their Floquet topological invariants in\noptical lattices."
    },
    {
        "anchor": "Quantum-enhanced multiparameter estimation and compressed sensing of a\n  field: We show that a significant quantum gain corresponding to squeezed or\nover-squeezed spin states can be obtained in multiparameter estimation by\nmeasuring the Hadamard coefficients of a 1D or 2D signal. The physical platform\nwe consider consists of twolevel atoms in an optical lattice in a squeezed-Mott\nconfiguration, or more generally by correlated spins distributed in spatially\nseparated modes. Our protocol requires the possibility to locally flip the\nspins, but relies on collective measurements. We give examples of applications\nto scalar or vector field mapping and compressed sensing.",
        "positive": "Dipolar Bose-Einstein Condensates with Weak Disorder: A homogeneous polarized dipolar Bose-Einstein condensate is considered in the\npresence of weak quenched disorder within mean-field theory at zero\ntemperature. By first solving perturbatively the underlying Gross-Pitaevskii\nequation and then performing disorder ensemble averages for physical\nobservables, it is shown that the anisotropy of the two-particle interaction is\npassed on to both the superfluid density and the sound velocity."
    },
    {
        "anchor": "A continuous model for bosonic hard spheres in quasi one-dimensional\n  optical lattices: By means of diffusion Monte Carlo calculations, we investigated the quantum\nphase transition between a superfluid and a Mott insulator for a system of\nhard-sphere bosons in a quasi one-dimensional optical lattice. For this\ncontinuous hamiltonian, we studied how the stability limits of the Mott phase\nchanged with the optical lattice depth and the transverse confinement width. A\ncomparison of these results to those of a one-dimensional homogeneous\nBose-Hubbard model indicates that this last model describes accurately the\nphase diagram only in the limit of deep lattices. For shallow ones, our results\nare comparable to those of the sine-Gordon model in its limit of application.\nWe provide an estimate of the critical parameters when none of those models are\nrealistic descriptions of a quasi one-dimensional optical lattice.",
        "positive": "Size and shape of Mott regions for fermionic atoms in a two-dimensional\n  optical lattice: We investigate the harmonic-trap control of size and shape of Mott regions in\nthe Fermi Hubbard model on a square optical lattice. The use of Lanczos\ndiagonalization on clusters with twisted boundary conditions, followed by an\naverage over 50-80 samples, drastically reduce finite-size effects in some\nground state properties; calculations in the grand canonical ensemble together\nwith a local-density approximation (LDA) allow us to simulate the radial\ndensity distribution. We have found that as the trap closes, the atomic cloud\ngoes from a metallic state, to a Mott core, and to a Mott ring; the coverage of\nMott atoms reaches a maximum at the core-ring transition. A `phase diagram' in\nterms of an effective density and the on-site repulsion is proposed, as a guide\nto maximize the Mott coverage. We also predict that the usual experimentally\naccessible quantities, the global compressibility and the average double\noccupancy (rather, its density derivative) display detectable signatures of the\ncore-ring transition. Some spin correlation functions are also calculated, and\npredict the existence N\\'eel ordering within Mott cores and rings."
    },
    {
        "anchor": "Phase-space distributions of Bose-Einstein condensates in an optical\n  lattice: Optimal shaping and reconstruction: We apply quantum optimal control to shape the phase-space distribution of\nBose-Einstein condensates in a one-dimensional optical lattice. By a\ntime-dependent modulation of the lattice position, determined from optimal\ncontrol theory, we prepare, in the phase space of each lattice site, translated\nand squeezed Gaussian states, and superpositions of Gaussian states. Complete\nreconstruction of these non-trivial states is performed through a maximum\nlikelihood state tomography. As a practical application of our method to\nquantum simulations, we initialize the atomic wavefunction in an optimal\nFloquet-state superposition to enhance dynamical tunneling signals.",
        "positive": "Bloch oscillations of bosonic lattice polarons: We consider a single impurity atom confined to an optical lattice and\nimmersed in a homogeneous Bose-Einstein condensate (BEC). Interaction of the\nimpurity with the phonon modes of the BEC leads to the formation of a stable\nquasiparticle, the polaron. We use a variational mean-field approach to study\ndispersion renormalization and derive equations describing non-equilibrium\ndynamics of polarons by projecting equations of motion into mean-field (MF)\ntype wavefunctions. As a concrete example, we apply our method to study\ndynamics of impurity atoms in response to a suddenly applied force and explore\nthe interplay of coherent Bloch oscillations and incoherent drift. We obtain a\nnon-linear dependence of the drift velocity on the applied force, including a\nsub-Ohmic dependence for small forces for dimensionality d>1 of the BEC. For\nthe case of heavy impurity atoms we derive a closed analytical expression for\nthe drift velocity. Our results show considerable differences with the commonly\nused phenomenological Esaki-Tsu model."
    },
    {
        "anchor": "Realization of a distributed Bragg reflector for propagating guided\n  matter waves: We report on the experimental realization of a Bragg reflector for guided\nmatter waves. A Bose-Einstein condensate with controlled velocity distribution\nimpinges onto an attractive optical lattice of finite length and directly\nprobes its band structure. We study the dynamics of the scattering by this\npotential and compare the results with simple one-dimensional models. We\nemphasize the importance of taking into account the gaussian envelope of the\noptical lattice which gives rise to Bragg cavity effects. Our results are a\nfurther step towards integrated atom optics setups for quasi-cw matter waves.",
        "positive": "Dynamical properties of the unitary Fermi gas: collective modes and\n  shock waves: We discuss the unitary Fermi gas made of dilute and ultracold atoms with an\ninfinite s-wave inter-atomic scattering length. First we introduce an efficient\nThomas-Fermi-von Weizsacker density functional which describes accurately\nvarious static properties of the unitary Fermi gas trapped by an external\npotential. Then, the sound velocity and the collective frequencies of\noscillations in a harmonic trap are derived from extended superfluid\nhydrodynamic equations which are the Euler-Lagrange equations of a\nThomas-Fermi-von Weizsacker action functional. Finally, we show that this\namazing Fermi gas supports supersonic and subsonic shock waves."
    },
    {
        "anchor": "Incommensurable matter-wave jets in quasi-1D geometry: We experimentally show the formation of incommensurable \"golden\"\n$\\frac{1+\\sqrt{5}}{2}$ matter-wave jets in a Bose-Einstein condensate (BEC)\nsubjected to single frequency interaction modulation. We study the formation of\nhigher order jets and the corresponding incommensurable density waves in quasi\none dimensional (1D) geometry with the help of numerical 1D Gross-Pitaevskii\nequation simulation. We explore the process of jet formation experimentally and\ntheoretically for a large range of modulation amplitudes and frequencies and\npresent a phase diagram for jet formation. In simulation, for large modulation\namplitudes, the distribution of jet velocities forms a supercontinuum, which\nemerges from the observed incommensurable matter-wave jets.",
        "positive": "Functional renormalization group approach to interacting bosons at zero\n  temperature: We investigate the single-particle spectral density of interacting bosons\nwithin the non-perturbative functional renormalization group technique. The\nflow equations for a Bose gas are derived in a scheme which treats the\ntwo-particle density-density correlations exactly but neglects irreducible\ncorrelations among three and more particles. These flow equations are solved\nwithin a truncation which allows to extract the complete frequency and momentum\nstructure of the normal and anomalous self-energies. Both the asymptotic small\nmomentum regime, where perturbation regime fails, as well as the perturbative\nregime at larger momenta are well described within a single unified approach.\nThe self-energies do not exhibit any infrared divergences, satisfy the U(1)\nsymmetry constraints, and are in accordance with the Nepomnyashchy relation\nwhich states that the anomalous self-energy vanishes at zero momentum and zero\nfrequency. From the self-energies we extract the single-particle spectral\ndensity of the two-dimensional Bose gas. The dispersion is found to be of the\nBogoliubov form and shows the crossover from linear Goldstone modes to the\nquadratic behavior of quasi-free bosons. The damping of the quasiparticles is\nfound to be in accordance with the standard Beliaev damping. We furthermore\nrecover the exact asymptotic limit of the propagators derived by Gavoret and\nNozieres and discuss the nature of the non-analyticities of the self-energies\nin the very small momentum regime."
    },
    {
        "anchor": "Spin-heat relaxation and thermo-spin diffusion in atomic Bose and Fermi\n  gases: We study spin-dependent heat transport in quantum gases, focusing on\ntransport phenomena related to pure spin currents and spin-dependent\ntemperatures. Using the Boltzmann equation, we compute the coupled spin and\nheat transport coefficients as a function of temperature and interaction\nstrength for energy dependent $s$-wave scattering. We address the issue of\nwhether spin-dependent temperatures can be sustained on a time and length scale\nrelevant for experiments by computing the spin-heat relaxation time and\ndiffusion length. We find that the time scale for spin-heat relaxation time\ndiverges at low temperatures for both bosons and fermions, indicating that the\nconcept of spin-heat accumulation is well defined for degenerate gases. For\nbosons, we find power-law behavior on approach to Bose condensation above the\ncritical temperature, as expected from the theory of dynamical critical\nphenomena.",
        "positive": "Supersolidity of lattice Bosons immersed in strongly correlated Rydberg\n  dressed atoms: Recent experiments have illustrated that long range two-body interactions can\nbe induced by laser coupling atoms to highly excited Rydberg states. Stimulated\nby this achievement, we study supersolidity of lattice bosons in an\nexperimentally relevant situation. In our setup, we consider two-component\natoms on a square lattice, where one species is weakly dressed to an\nelectronically high-lying (Rydberg) state, generating a tunable, soft-core\nshape long-range interaction. Interactions between atoms of the second species\nand between the two species are characterized by local inter- and intra-species\ninteractions. Using a dynamical mean-field calculation, we find that\ninterspecies onsite interactions can stabilize a pronounced region of\nsupersolid phases. This is characterized by two distinctive types of\nsupersolids, where the bare species forms supersolid phases that are immersed\nin strongly correlated quantum phases, i.e. a crystalline solid or supersolid\nof the dressed atoms. We show that the interspecies interaction leads to a\nroton-like instability in the bare species and therefore is crucially important\nto the supersolid formation. We provide a detailed calculation of the\ninteraction potential to show how our results can be explored under current\nexperimental conditions."
    },
    {
        "anchor": "Atom chips with two-dimensional electron gases: theory of near surface\n  trapping and ultracold-atom microscopy of quantum electronic systems: We show that current in a two-dimensional electron gas (2DEG) can trap\nultracold atoms $<1 \\mu$m away with orders of magnitude less spatial noise than\na metal trapping wire. This enables the creation of hybrid systems, which\nintegrate ultracold atoms with quantum electronic devices to give extreme\nsensitivity and control: for example, activating a single quantized conductance\nchannel in the 2DEG can split a Bose-Einstein condensate (BEC) for atom\ninterferometry. In turn, the BEC offers unique structural and functional\nimaging of quantum devices and transport in heterostructures and graphene.",
        "positive": "Flat band induced non-Fermi liquid behavior of multicomponent fermions: We investigate multicomponent fermions in a flat band and predict\nexperimental signatures of non-Fermi liquid behavior. We use dynamical\nmean-field theory to obtain the density, double occupancy and entropy in a Lieb\nlattice for $\\mathcal{N} = 2$ and $\\mathcal{N} = 4$ components. We derive a\nmean-field scaling relation between the results for different values of\n$\\mathcal{N}$, and study its breakdown due to beyond-mean field effects. The\npredicted signatures occur at temperatures above the N\\'eel temperature and\npersist in presence of a harmonic trapping potential, thus they are observable\nwith current ultracold gas experiments."
    },
    {
        "anchor": "Three-Dimensional Anderson Localization of Ultracold Matter: Anderson localization (AL) is a ubiquitous interference phenomenon in which\nwaves fail to propagate in a disordered medium. We observe three-dimensional AL\nof noninteracting ultracold matter by allowing a spin-polarized atomic Fermi\ngas to expand into a disordered potential. A two-component density distribution\nemerges consisting of an expanding mobile component and a nondiffusing\nlocalized component. We extract a mobility edge that increases with the\ndisorder strength, whereas the thermally averaged localization length is shown\nto decrease with disorder strength and increase with particle energy. These\nmeasurements provide a benchmark for more sophisticated theories of AL.",
        "positive": "Transition from the mean-field to the bosonic Laughlin state in a\n  rotating Bose-Einstein condensate: We consider a weakly-interacting Bose-Einstein condensate that rotates in\neither a harmonic, or a weakly-anharmonic trapping potential. Performing\nnumerical calculations, we investigate the behaviour of the gas in these two\ncases as the angular momentum, or equivalently as the rotational frequency of\nthe trap increases. While in the case of a purely-harmonic potential the gas\nmakes a transition from the mean-field regime to the correlated, \"Laughlin\",\nregime, in the case of anharmonic confinement the mean-field approximation\nremains always valid. We compare our derived results in these two cases, using\nboth the mean-field approximation, as well as the diagonalization of the\nmany-body Hamiltonian considering a small atom number."
    },
    {
        "anchor": "Mode bifurcation in the Rayleigh-Taylor instability of binary\n  condensates: We examine the generation and subsequent evolution of Rayleigh Taylor\ninstability in anisotropic binary Bose-Einstein condensates. Considering a\npancake-shaped geometry, to initiate the instability we tune the intraspecies\ninteraction and analytically study the normal modes of the interface in\nelliptic cylindrical coordinates. The normal modes are then Mathieu functions\nand undergoes bifurcation at particular values of anisotropy and ratio of\nnumber of atoms. We find that the analytical estimates of the bifurcation\nparameters are in good agreement with the numerical results.",
        "positive": "Giant Vortex Clusters in a Two-Dimensional Quantum Fluid: Adding energy to a system through transient stirring usually leads to more\ndisorder. In contrast, point-like vortices in a bounded two-dimensional fluid\nare predicted to reorder above a certain energy, forming persistent vortex\nclusters. Here we realize experimentally these vortex clusters in a planar\nsuperfluid: a $^{87}$Rb Bose-Einstein condensate confined to an elliptical\ngeometry. We demonstrate that the clusters persist for long times, maintaining\nthe superfluid system in a high energy state far from global equilibrium. Our\nexperiments explore a regime of vortex matter at negative absolute\ntemperatures, and have relevance to the dynamics of topological defects,\ntwo-dimensional turbulence, and systems such as helium films, nonlinear optical\nmaterials, fermion superfluids, and quark-gluon plasmas."
    },
    {
        "anchor": "Theory of the Normal/Superfluid interface in population imbalanced Fermi\n  gases: We present a series of theoretical studies of the boundary between a\nsuperfluid and normal region in a partially polarized gas of strongly\ninteracting fermions. We present mean-field estimates of the surface energy in\nthis boundary as a function of temperature and scattering length. We discuss\nthe structure of the domain wall, and use a previously introduced\nphenomonological model to study its influence on experimental observables.\n  Our microscopic mean-field calculations are not consistent with the magnitude\nof the surface tension found from our phenomonological modelling of data from\nthe Rice experiments. We conclude that one must search for novel mechanisms to\nexplain the experiments.",
        "positive": "Enhancement and sign change of magnetic correlations in a driven quantum\n  many-body system: Periodic driving can be used to coherently control the properties of a\nmany-body state and to realize new phases which are not accessible in static\nsystems. For example, exposing materials to intense laser pulses enables to\nprovoke metal-insulator transitions, control the magnetic order and induce\ntransient superconducting behaviour well above the static transition\ntemperature. However, pinning down the responsible mechanisms is often\ndifficult, since the response to irradiation is governed by complex many-body\ndynamics. In contrast to static systems, where extensive calculations have been\nperformed to explain phenomena such as high-temperature superconductivity,\ntheoretical analyses of driven many-body Hamiltonians are more demanding and\nnew theoretical approaches have been inspired by the recent observations. Here,\nwe perform an experimental quantum simulation in a periodically modulated\nhexagonal lattice and show that anti-ferromagnetic correlations in a fermionic\nmany-body system can be reduced or enhanced or even switched to ferromagnetic\ncorrelations. We first demonstrate that in the high frequency regime, the\ndescription of the many-body system by an effective Floquet-Hamiltonian with a\nrenormalized tunnelling energy remains valid, by comparing the results to\nmeasurements in an equivalent static lattice. For near-resonant driving, the\nenhancement and sign reversal of correlations is explained by a microscopic\nmodel, in which the particle tunnelling and magnetic exchange energies can be\ncontrolled independently. In combination with the observed sufficiently long\nlifetime of correlations, Floquet engineering thus constitutes an alternative\nroute to experimentally investigate unconventional pairing in strongly\ncorrelated systems."
    },
    {
        "anchor": "Variational theory of angulons and their rotational spectroscopy: The angulon, a quasiparticle formed by a quantum rotor dressed by the\nexcitations of a many-body bath, can be used to describe an impurity rotating\nin a fluid or solid environment. Here we propose a coherent state ansatz in the\nco-rotating frame which provides a comprehensive theoretical description of\nangulons. We reveal the quasiparticle properties, such as energies,\nquasiparticle weights and spectral functions, and show that our ansatz yields a\npersistent decrease in the impurity's rotational constant due to many-body\ndressing, consistent with experimental observations. From our study, a picture\nof the angulon emerges as an effective spin interacting with a magnetic field\nthat is self-consistently generated by the molecule's rotation. Moreover, we\ndiscuss rotational spectroscopy, which focuses on the response of rotating\nmolecules to a laser perturbation in the linear response regime. Importantly,\nwe take into account initial-state interactions that have been neglected in\nprior studies and reveal their impact on the excitation spectrum. To examine\nthe angulon instability regime, we use a single-excitation ansatz and obtain\nresults consistent with experiments, in which a broadening of spectral lines is\nobserved while phonon wings remain highly suppressed due to initial-state\ninteractions.",
        "positive": "Quantum Scattering in an Optical Collider for Ultracold Atoms: We report on experiments investigating the collisional properties of atoms at\nultralow collision energies using an all-optical atom collider. By using a pair\nof optical tweezers, we can manipulate two ultracold atom clouds and collide\nthem together at energies up to three orders of magnitude larger than their\nthermal energy. Our experiments measure the scattering of $\\rm ^{87}Rb$, $\\rm\n^{40}K$, and $\\rm ^{40}K$-$\\rm ^{87}Rb$ collisions. The versatility of our\ncollider allows us to probe both shape resonances and Feshbach resonances in\nany partial wave. As examples, we present experiments demonstrating p-wave\nscattering with indistinguishable fermions, inelastic scattering at non-zero\nenergies near a homonuclear Feshbach resonance, and partial wave interference\nin heteronuclear collisions."
    },
    {
        "anchor": "Dynamical quantum phase transitions in a spinor Bose-Einstein condensate\n  and criticality enhanced quantum sensing: Quantum phase transitions universally exist in the ground and excited states\nof quantum many-body systems, and they have a close relationship with the\nnonequilibrium dynamical phase transitions, which however are challenging to\nidentify. In the system of spin-1 Bose-Einstein condensates, though dynamical\nphase transitions with correspondence to equilibrium phase transitions in the\nground state and uppermost excited state have been probed, those taken place in\nintermediate excited states remain untouched in experiments thus far. Here we\nunravel that both the ground and excited-state quantum phase transitions in\nspinor condensates can be diagnosed with dynamical phase transitions. A\nconnection between equilibrium phase transitions and nonequilibrium behaviors\nof the system is disclosed in terms of the quantum Fisher information. We also\ndemonstrate that near the critical points parameter estimation beyond standard\nquantum limit can be implemented. This work not only advances the exploration\nof excited-state quantum phase transitions via a scheme that can immediately be\napplied to a broad class of few-mode quantum systems, but also provides new\nperspective on the relationship between quantum criticality and quantum\nenhanced sensing.",
        "positive": "Properties of the signal mode in the polariton OPO regime: Theoretical analyses of the polariton optical parametric oscillator (OPO)\nregime often rely on a mean field approach based on the complex\nGross-Pitaevskii equations in a three-mode approximation, where only three\nmomentum states, the signal, pump and idler, are assumed to be significantly\noccupied. This approximation, however, lacks a constraint to uniquely determine\nthe signal and idler momenta. In contrast, multimode numerical simulations and\nexperiments show a unique momentum structure for the OPO states. In this work\nwe show that an estimate for the signal momentum chosen by the system can be\nfound from a simple analysis of the pump-only configuration. We use this\nestimate to investigate how the chosen signal momentum depends on the\nproperties of the drive."
    },
    {
        "anchor": "One dimensional Bose-Einstein condensate under the effect of the\n  extended uncertainty principle: In this study, an analytical investigation was conducted to assess the\neffects of the extended uncertainty principle (EUP) on a Bose-Einstein\ncondensate (BEC) described by the deformed one-dimensional Gross-Pitaevskii\nequation (GPE). Analytical solutions were derived for null potential, while, we\nused variational and numerical methods for harmonic oscillator potential.\nSubsequently, we analyzed the probability density, position, and momentum\nuncertainties as functions of the deformation parameter $\\alpha$.",
        "positive": "Efimov resonance position near a narrow Feshbach resonance in\n  $^6$Li-$^{133}$Cs mixture: In the vicinity of a narrow Feshbach resonances Efimov features are expected\nto be characterized by the resonance's properties rather than the van der Waals\nlength of the interatomic potential. Although this theoretical prediction is\nwell-established by now, it still lacks experimental confirmation. Here, we\napply our recently developed three-channel model [Yudkin and Khaykovich, Phys.\nRev. A 103, 063303 (2021)] to the experimental result obtained in a\nmass-imbalanced $^6$Li-$^{133}$Cs mixture in the vicinity of the narrowest\nresonance explored to date [Johansen at. al. Nat. Phys. 13, 731 (2017)]. We\nconfirm that the observed position of the Efimov resonance is dictated mainly\nby the resonance physics while the influence of the van der Waals tail of the\ninteratomic potential is minor. We show that the resonance position is strongly\ninfluenced by the presence of another Feshbach resonance which significantly\nalters the effective background scattering length at the narrow resonance\nposition."
    },
    {
        "anchor": "Phase slips driven by acoustic waves in Bose-Einstein condensates with\n  ring topology: Rotational superradiance is one of the most fascinating phenomena in\nblack-hole physics. Here, with the aim of probing quantum properties of\nsuperradiance in the lab, we investigate the interaction of the acoustic waves\nwith quantum vortices in Bose-Einstein condensates (BEC) in the framework of\ndissipative mean-field model. We find the conditions of the acoustic-induced\nquantum phase slips in condensates with ring topology and discuss the\npossibility of observing an acoustic analogue of quantum superradiance in\nultracold atomic gases.",
        "positive": "Spin-orbit coupled interferometry with ring-trapped Bose--Einstein\n  condensates: We propose a method of atom-interferometry using a spinor Bose-Einstein\ncondensate (BEC) with a time-varying magnetic field acting as a coherent\nbeam-splitter. Our protocol creates long-lived superpositional counterflow\nstates, which are of fundamental interest and can be made sensitive to both the\nSagnac effect and magnetic fields on the sub-micro-G scale. We split a\nring-trapped condensate, initially in the $m_f=0$ hyperfine state, into\nsuperpositions of internal $m_f=\\pm1$ states and condensate superflow, which\nare spin-orbit coupled. After interrogation, relative phase accumulation can be\ninferred from a population transfer to the $m_f=\\pm1$ states. The counterflow\ngeneration protocol is adiabatically deterministic and does not rely on\ncoupling to additional optical fields or mechanical stirring techniques. Our\nprotocol can maximise the classical Fisher information for any rotation,\nmagnetic field, or interrigation time, and so has the maximum sensitivity\navailable to uncorrelated particles. Precision can increase with the\ninterrogation time, and so is limited only by the lifetime of the condensate."
    },
    {
        "anchor": "Photon BEC with Thermo-Optic Interaction at Dimensional Crossover: Since the advent of experiments with photon Bose-Einstein condensates in\ndye-filled microcavities in 2010, many investigations have focused upon the\nemerging effective photon-photon interaction. Despite its smallness, it can be\nidentified to stem from two physically distinct mechanisms. On the one hand, a\nKerr nonlinearity of the dye medium yields a photon-photon contact interaction.\nOn the other hand, a heating of the dye medium leads to an additional\nthermo-optic interaction, which is both delayed and non-local. The latter turns\nout to represent the leading contribution to the effective interaction for the\ncurrent 2D experiments. Here we analyse theoretically how the effective\nphoton-photon interaction increases when the system dimension is reduced from\n2D to 1D. To this end, we consider an anisotropic harmonic trapping potential\nand determine via a variational approach how the properties of the photon\nBose-Einstein condensate in general, and both aforementioned interaction\nmechanisms in particular, change with increasing anisotropy. We find that the\nthermo-optic interaction strength increases at first linearly with the trap\naspect ratio and lateron saturates at a certain value of the trap aspect ratio.\nFurthermore, in the strong 1D limit the roles of both interactions get reversed\nas the thermo-optic interaction remains saturated and the contact Kerr\ninteraction becomes the leading interaction mechanism. Finally, we discuss how\nthe predicted effects can be measured experimentally.",
        "positive": "Multi-wavelength holography with a single Spatial Light Modulator for\n  ultracold atom experiments: We demonstrate a method to create arbitrary intensity distributions of\nmultiple wavelengths of light, which can be useful for ultracold atom\nexperiments, by using regional phase-calculation algorithms to find a single\nhologram which is illuminated with overlapped laser beams. The regionality of\nthe algorithms is used to program spatially distinct features in the calculated\nintensity distribution, which then overlap in the Fourier plane due to the\ndependence of diffraction angle on wavelength. This technique is easily\nintegrated into cold atom experiments, requiring little optical access. We\ndemonstrate the method and two possible experimental scenarios by generating\nlight patterns with 670nm, 780nm and 1064nm laser light which are accurate to\nthe level of a few percent."
    },
    {
        "anchor": "Dissipation in a Finite Temperature Atomic Josephson Junction: We numerically demonstrate and characterize the emergence of distinct\ndynamical regimes of a finite temperature bosonic superfluid in an elongated\nJosephson junction generated by a thin Gaussian barrier over the entire\ntemperature range where a well-formed condensate can be clearly identified.\nAlthough the dissipation arising from the coupling of the superfluid to the\ndynamical thermal cloud increases with increasing temperature as expected, the\nimportance of this mechanism is found to depend on two physical parameters\nassociated (i) with the initial chemical potential difference, compared to some\ncharacteristic value, and (ii) the ratio of the thermal energy to the barrier\namplitude. The former determines whether the superfluid Josephson dynamics are\ndominated by gradually damped plasma-like oscillations (for relatively small\ninitial population imbalances), or whether dissipation at early times is\ninstead dominated by vortex- and sound-induced dissipation (for larger initial\nimbalances). The latter defines the effect of the thermal cloud on the\ncondensate dynamics, with a reversal of roles, i.e. the condensate being driven\nby the oscillating thermal cloud, being observed when the thermal particles\nacquire enough energy to overcome the barrier. Our findings are within current\nexperimental reach in ultracold superfluid junctions.",
        "positive": "Realizing the entanglement Hamiltonian of a topological quantum Hall\n  system: Topological quantum many-body systems, such as Hall insulators, are\ncharacterized by a hidden order encoded in the entanglement between their\nconstituents. Entanglement entropy, an experimentally accessible single number\nthat globally quantifies entanglement, has been proposed as a first signature\nof topological order. Conversely, the full description of entanglement relies\non the entanglement Hamiltonian, a more complex object originally introduced to\nformulate quantum entanglement in curved spacetime. As conjectured by Li and\nHaldane, the entanglement Hamiltonian of a many-body system appears to be\ndirectly linked to its boundary properties, making it particularly useful for\ncharacterizing topological systems. While the entanglement spectrum is commonly\nused to identify complex phases arising in numerical simulations, its\nmeasurement remains an outstanding challenge. Here, we perform a variational\napproach to realize experimentally, as a genuine Hamiltonian, the entanglement\nHamiltonian of a synthetic quantum Hall system. We use a synthetic dimension,\nencoded in the electronic spin of dysprosium atoms, to implement spatially\ndeformed Hall systems, as suggested by the Bisognano-Wichmann prediction. The\nspectrum of the optimal variational Hamiltonian exhibits a chiral dispersion\nakin to a topological edge mode, revealing the fundamental link between\nentanglement and boundary physics. Our variational procedure can be easily\ngeneralized to interacting many-body systems on various platforms, marking an\nimportant step towards the exploration of exotic quantum systems with\nlong-range correlations, such as fractional Hall states, chiral spin liquids\nand critical systems."
    },
    {
        "anchor": "Quench dynamics in disordered two-dimensional Gross-Pitaevskii Lattices: We numerically investigate the quench expansion dynamics of an initially\nconfined state in a two-dimensional Gross-Pitaevskii lattice in the presence of\nexternal disorder. The expansion dynamics is conveniently described in the\ncontrol parameter space of the energy and norm densities. The expansion can\nslow down substantially if the expected final state is a non-ergodic non-Gibbs\none, regardless of the disorder strength. Likewise stronger disorder delays\nexpansion. We compare our results with recent studies for quantum many body\nquench experiments.",
        "positive": "Momentum reconstruction and contact of the one-dimensional Bose-Fermi\n  mixture: We investigate the one-dimensional mixture of scalar bosons and spin\npolarized fermions interacting through a $\\delta$-function potential. Using a\nthermodynamic description derived by employing a lattice embedding of the\ncontinuum model and the quantum transfer matrix method we perform a detailed\nanalysis of the contact and quantum critical behaviour. We show that the\ncompressibility Wilson ratio presents anomalous enhancement at the quantum\ncritical points and that the boundaries of the quantum critical regions can be\nwell mapped by the maxima of the specific heat. As a function of the coupling\nstrength and temperature the contact presents nonmonotonic behavior. In the\nstrong coupling regime the local minimum exhibited by the contact as a function\nof temperature is accompanied by a significant momentum reconstruction at both\nlow and high momenta. This momentum reconstruction occurs as the system crosses\nthe boundary between the Tomonaga-Luttinger liquid phase to the spin-incoherent\nregime and provides an experimental signature of the transition."
    },
    {
        "anchor": "Confinement and precession of vortex pairs in coherently coupled\n  Bose-Einstein condensates: The dynamic behavior of vortex pairs in two-component coherently (Rabi)\ncoupled Bose-Einstein condensates is investigated in the presence of harmonic\ntrapping. We discuss the role of the surface tension associated with the domain\nwall connecting two vortices in condensates of atoms occupying different spin\nstates and its effect on the precession of the vortex pair. The results, based\non the numerical solution of the Gross-Pitaevskii equations, are compared with\nthe predictions of an analytical macroscopic model and are discussed as a\nfunction of the size of the pair, the Rabi coupling and the inter-component\ninteraction. We show that the increase of the Rabi coupling results in the\ndisintegration of the domain wall into smaller pieces, connecting vortices of\nnew-created vortex pairs. The resulting scenario is the analogue of quark\nconfinement and string breaking in quantum chromodynamics.",
        "positive": "Scissors mode of trapped dipolar gases: We study the scissors modes of dipolar boson and fermion gases trapped in a\nspherically symmetric potential. We use the harmonic oscillator states to solve\nthe time-dependent Gross-Pitaevskii equation for bosons and the time-dependent\nHartree-Fock equation for fermions. It is pointed out that the scissors modes\nof bosons and fermions can be of quite different nature."
    },
    {
        "anchor": "Incompressibility Estimates for the Laughlin Phase: This paper has its motivation in the study of the Fractional Quantum Hall\nEffect. We consider 2D quantum particles submitted to a strong perpendicular\nmagnetic field, reducing admissible wave functions to those of the Lowest\nLandau Level. When repulsive interactions are strong enough in this model,\nhighly correlated states emerge, built on Laughlin's famous wave function. We\ninvestigate a model for the response of such strongly correlated ground states\nto variations of an external potential. This leads to a family of variational\nproblems of a new type. Our main results are rigorous energy estimates\ndemonstrating a strong rigidity of the response of strongly correlated states\nto the external potential. In particular we obtain estimates indicating that\nthere is a universal bound on the maximum local density of these states in the\nlimit of large particle number. We refer to these as incompressibility\nestimates.",
        "positive": "Flowing bosonization in the nonperturbative functional\n  renormalization-group approach: Bosonization allows one to describe the low-energy physics of one-dimensional\nquantum fluids within a bosonic effective field theory formulated in terms of\ntwo fields: the \"density\" field $\\varphi$ and its conjugate partner, the phase\n$\\vartheta$ of the superfluid order parameter. We discuss the implementation of\nthe nonperturbative functional renormalization group in this formalism,\nconsidering a Luttinger liquid in a periodic potential as an example. We show\nthat in order for $\\vartheta$ and $\\varphi$ to remain conjugate variables at\nall energy scales, one must dynamically redefine the field $\\vartheta$ along\nthe renormalization-group flow. We derive explicit flow equations using a\nderivative expansion of the scale-dependent effective action to second order\nand show that they reproduce the flow equations of the sine-Gordon model\n(obtained by integrating out the field $\\vartheta$ from the outset) derived\nwithin the same approximation. Only with the scale-dependent (flowing)\nreparametrization of the phase field $\\vartheta$ do we obtain the standard\nphenomenology of the Luttinger liquid (when the periodic potential is\nsufficiently weak so as to avoid the Mott-insulating phase) characterized by\ntwo low-energy parameters, the velocity of the sound mode and the renormalized\nLuttinger parameter."
    },
    {
        "anchor": "Microwave control of coupling parameters in spinor alkali condensates: We propose a protocol which utilises radio frequency magnetic pulses in order\nto tune the effective two-particle scattering amplitudes for alkali atoms in\nthe $F=1$ hyperfine ground state. Unlike the Feshbach resonance method, the\nproposed protocol preserves with controllable accuracy the global rotational\nsymmetry in the spin space offering access to a broad region of the phase\ndiagram of the rotationally-symmetric spinor Bose condensate. Examples of\n$^{41}$K and $^{7}$Li are considered and it is shown that for these atoms\nsufficient variation in the effective coupling constants can be achieved in\norder to explore phase transitions between different symmetry-broken phases of\nthe condensate.",
        "positive": "New opportunites for interactions and control with ultracold lanthanides: Lanthanide atoms have an unusual electron configuration, with a partially\nfilled shell of $f$ orbitals. This leads to a set of characteristic properties\nthat enable enhanced control over ultracold atoms and their interactions: large\nnumbers of optical transitions with widely varying wavelengths and transition\nstrengths, anisotropic interaction properties between atoms and with light, and\na large magnetic moment and spin space present in the ground state. These\nfeatures in turn enable applications ranging from narrow-line laser cooling and\nspin manipulation to evaporative cooling through universal dipolar scattering,\nto the observation of a rotonic dispersion relation, self-bound liquid-like\ndroplets stabilized by quantum fluctuations, and supersolid states. In this\nshort review, we describe how the unusual level structure of lanthanide atoms\nleads to these key features, and provide a brief and necessarily partial\noverview of experimental progress in this rapidly developing field."
    },
    {
        "anchor": "Thermal Ising transition in two-dimensional SU(3) Fermi lattice gases\n  with population imbalance: We focus on three-component SU(3) Fermi gases loaded into a square optical\nlattice, with population imbalance between one component and the others. At\nstrong coupling the system is described by the SU(3) Heisenberg model with an\nexternal field that couples to the population imbalance. We discuss the ground\nstate at the mean-field level and then analyze the thermal fluctuations with\nthe semi-classical Monte Carlo method. The interplay of interactions,\npopulation imbalance and thermal fluctuations gives rise to a phase transition\nlinked to the breaking of an emergent Ising symmetry, despite the absence of\nfrustration. This represents a new scenario of discrete symmetry breaking in\nlow-dimensional systems with continuous symmetries. Possible implementations\nwith cold alkaline-earth(-like) atoms are discussed.",
        "positive": "Chiral edge states in position shaken finite-size honeycomb optical\n  lattice: The quantum anomalies at the edges correspond to the topological phases in\nthe system, and the chiral edge states can reflect bulk bands' topological\nproperties. In this paper, we demonstrate a simulation of Floquet system's\nchiral edge states in position shaken finite-size honeycomb optical lattice.\nThrough the periodical shaking, we break the time reversal symmetry of the\nsystem, and get the topological non-trivial states with non-zero Chen number.\nAt the topological non-trivial area, we find chiral edge states on different\nsides of the lattice, and the locations of chiral edge states change with the\ntopological phase. Further, gapless boundary excitations are found to appear at\nthe topological phase transition points. It provides a new scheme to simulate\nchiral edge states in the Floquet system, and promotes the study of gapless\nboundary excitations."
    },
    {
        "anchor": "d_{xy}-Density wave in fermion-fermion cold atom mixtures: We study density wave instabilities in a doubly-degenerate Fermi-Fermi\nmixture with $SU(2)\\times SU(2)$ symmetry on a square lattice. For sufficiently\nlarge on-site inter-species repulsion, when the two species of fermions are\nboth at half-filling, two conventional ($s$-wave) number density waves are\nformed with a $\\pi$-phase difference between them to minimize the inter-species\nrepulsion. Upon moving one species away from half-filling, an unconventional\ndensity wave with $d_{xy}$-wave symmetry emerges. When both species are away\nfrom the vicinity of half-filling, superconducting instabilities dominate. We\npresent results of a functional renormalization-group calculation that maps out\nthe phase diagram at weak couplings. Also, we provide a simple explanation for\nthe emergence of the $d_{xy}$-density wave phase based on a four-patch model.\nWe find a robust and general mechanism for $d_{xy}$-density-wave formation that\nis related to the shape and size of the Fermi surfaces. The density imbalance\nbetween the two species of fermions in the vicinity of half-filling leads to\nphase-space discrepancy for different inter-species Umklapp couplings. Using a\nphase space argument for leading corrections in the one-loop renormalization\ngroup approach to fermions, we show that the phase-space discrepancy in our\nsystem causes opposite flows for the two leading intra-species Umklapp\ncouplings and that this triggers the $d_{xy}$-density-wave instability.",
        "positive": "Pauli crystal melting in shaken optical traps: Pauli crystals are ordered geometric structures that emerge in trapped\nnoninteracting fermionic systems due to their underlying Pauli repulsion. The\ndeformation of Pauli crystals - often called melting - has been recently\nobserved in experiments, but the mechanism that leads to it remains unclear. We\naddress this question by studying the melting dynamics of N=6 fermions as a\nfunction of periodic driving and experimental imperfections in the trap\n(anisotropy and anharmonicity) by employing a combination of numerical\nsimulations and Floquet theory. Surprisingly, we reveal that the melting of\nPauli crystals is not simply a direct consequence of an increase in system\nenergy, but is instead related to the trap geometry and the population of the\nFloquet modes. We show that the melting is absent in traps without\nimperfections and triggered only by a sufficiently large shaking amplitude in\ntraps with imperfections."
    },
    {
        "anchor": "Undamped nonequilibrium dynamics of a nondegenerate Bose gas in a 3D\n  isotropic trap: We investigate anomalous damping of the monopole mode of a non-degenerate 3D\nBose gas under isotropic harmonic confinement as recently reported by the JILA\nTOP trap experiment [D. S. Lob- ser, A. E. S. Barentine, E. A. Cornell, and H.\nJ. Lewandowski (in preparation)]. Given a realistic confining potential, we\ndevelop a model for studying collective modes that includes the effects of\nanharmonic corrections to a harmonic potential. By studying the influence of\nthese trap anharmonicities throughout a range of temperatures and collisional\nregimes, we find that the damping is caused by the joint mechanisms of\ndephasing and collisional relaxation. Furthermore, the model is complimented by\nMonte Carlo simulations which are in fair agreement with data from the JILA\nexperiment.",
        "positive": "Nonequilibrium dynamics of an ultracold dipolar gas: We study the relaxation and damping dynamics of an ultracold, but not quantum\ndegenerate, gas consisting of dipolar particles. These simulations are\nperformed using a direct simulation Monte Carlo method and employing the highly\nanisotropic differential cross section of dipoles in the Wigner threshold\nregime. We find that both cross-dimensional relaxation and damping of breathing\nmodes occur at rates that are strongly dependent on the orientation of the\ndipole moments relative to the trap axis. The relaxation simulations are in\nexcellent agreement with recent experimental results in erbium. The results\ndirect our interest toward a less explored regime in dipolar gases where\ninteractions are dominated by collision processes rather than mean-field\ninteractions."
    },
    {
        "anchor": "Connecting Topological Anderson and Mott Insulators in Disordered\n  Interacting Fermionic Systems: The topological Anderson and Mott insulators are two phases that have so far\nbeen separately and widely explored beyond topological band insulators. Here we\ncombine the two seemingly different topological phases into a system of\nspin-1/2 interacting fermionic atoms in a disordered optical lattice. We find\nthat the topological Anderson and Mott insulators in the noninteracting and\nclean limits can be adiabatically connected without gap closing in the phase\ndiagram of our model. Lying between the two phases, we uncover a disordered\ncorrelated topological insulator, which is induced from a trivial band\ninsulator by the combination of disorder and interaction, as the generalization\nof topological Anderson insulators to the many-body interacting regime. The\nphase diagram is determined by computing various topological properties and\nconfirmed by unsupervised and automated machine learning. We develop an\napproach to provide a unified and clear description of topological phase\ntransitions driven by interaction and disorder. The topological phases can be\ndetected from disorder/interaction induced edge excitations and charge pumping\nin optical lattices.",
        "positive": "Violation of Cauchy-Schwarz inequalities by spontaneous Hawking\n  radiation in resonant boson structures: The violation of a classical Cauchy-Schwarz (CS) inequality is identified as\nan unequivocal signature of spontaneous Hawking radiation in sonic black holes.\nThis violation can be particularly large near the peaks in the radiation\nspectrum emitted from a resonant boson structure forming a sonic horizon. As a\nfunction of the frequency-dependent Hawking radiation intensity, we analyze the\ndegree of CS violation and the maximum violation temperature for a double\nbarrier structure separating two regions of subsonic and supersonic condensate\nflow. We also consider the case where the resonant sonic horizon is produced by\na space-dependent contact interaction. In some cases, CS violation can be\nobserved by direct atom counting in a time-of-flight experiment. We show that\nnear the conventional zero-frequency radiation peak, the decisive CS violation\ncannot occur."
    },
    {
        "anchor": "Quantum Many-Body Calculations using Body-Centered Cubic Lattices: It is often computationally advantageous to model space as a discrete set of\npoints forming a lattice grid. This technique is particularly useful for\ncomputationally difficult problems such as quantum many-body systems. For\nreasons of simplicity and familiarity, nearly all quantum many-body\ncalculations have been performed on simple cubic lattices. Since the removal of\nlattice artifacts is often an important concern, it would be useful to perform\ncalculations using more than one lattice geometry. In this work we show how to\nperform quantum many-body calculations using auxiliary-field Monte Carlo\nsimulations on a three-dimensional body-centered cubic (BCC) lattice. As a\nbenchmark test we compute the ground state energy of 33 spin-up and 33\nspin-down fermions in the unitary limit, which is an idealized limit where the\ninteraction range is zero and scattering length is infinite. As a fraction of\nthe free Fermi gas energy $E_{\\rm FG}$, we find that the ground state energy is\n$E_0/E_{\\rm FG}= 0.369(2), 0.371(2),$ using two different definitions of the\nfinite-system energy ratio. This is in excellent agreement with recent results\nobtained on a cubic lattice \\cite{He:2019ipt}. We find that the computational\neffort and performance on a BCC lattice is approximately the same as that for a\ncubic lattice with the same number of lattice points. We discuss how the\nlattice simulations with different geometries can be used to constrain the size\nlattice artifacts in simulations of continuum quantum many-body systems.",
        "positive": "$\\mathbb{Z}_n$ solitons in intertwined topological phases: Topological phases of matter can support fractionalized quasi-particles\nlocalized at topological defects. The current understanding of these exotic\nexcitations, based on the celebrated bulk-defect correspondence, typically\nrelies on crude approximations where such defects are replaced by a static\nclassical background coupled to the matter sector. In this work, we explore the\nstrongly-correlated nature of symmetry-protected topological defects by\nfocusing on situations where such defects arise spontaneously as dynamical\nsolitons in intertwined topological phases, where symmetry breaking coexists\nwith topological symmetry protection. In particular, we focus on the\n$\\mathbb{Z}_2$ Bose-Hubbard model, a one-dimensional chain of interacting\nbosons coupled to $\\mathbb{Z}_2$ fields, and show how solitons with\n$\\mathbb{Z}_n$ topological charges appear for particle/hole dopings about\ncertain commensurate fillings, extending the results of [1] beyond half\nfilling. We show that these defects host fractionalized bosonic\nquasi-particles, forming bound states that travel through the system unless\nexternally pinned, and repel each other giving rise to a fractional soliton\nlattice for sufficiently high densities. Moreover, we uncover the topological\norigin of these fractional bound excitations through a pumping mechanism, where\nthe quantization of the inter-soliton transport allows us to establish a\ngeneralized bulk-defect correspondence. This in-depth analysis of dynamical\ntopological defects bound to fractionalized quasi-particles, together with the\npossibility of implementing our model in cold-atomic experiments, paves the way\nfor further exploration of exotic topological phenomena in strongly-correlated\nsystems."
    },
    {
        "anchor": "Repulsively-bound exciton-biexciton states in high-spin fermions in\n  optical lattices: We show that the interplay between spin-changing collisions and quadratic\nZeeman coupling provides a novel mechanism for the formation of repulsively\nbound composites in high-spin fermions, which we illustrate by considering spin\nflips in an initially polarized hard-core 1D Mott insulator of spin-3/2\nfermions. We show that after the flips the dynamics is characterized by the\ncreation of two types of exciton-biexciton composites. We analyze the\nconditions for the existence of these bound states, and discuss their\nintriguing properties. In particular we show that the effective mass and\nstability of the composites depends non-trivially on spin-changing collisions,\non the quadratic Zeeman effect and on the initial exciton localization.\nFinally, we show that the composites may remain stable against inelastic\ncollisions, opening the possibility of novel quantum composite phases.",
        "positive": "Phase Separation of Superfluids in the Chain of Four-Component Ultracold\n  Atoms: We investigate the competition of various exotic superfluid states in a chain\nof spin-polarized ultracold fermionic atoms with hyperfine spin $F = 3/2$ and\ns-wave contact interactions. We show that the ground state is an exotic\ninhomogeneous mixture in which two distinct superfluid phases --- spin-carrying\npairs and singlet quartets --- form alternating domains in an extended region\nof the parameter space."
    },
    {
        "anchor": "Fermions on a torus knot: In this work, we investigate the effects of a nontrivial topology (and\ngeometry) of a system considering \\textit{interacting} and\n\\textit{noninteracting} particle modes, which are restricted to follow a closed\npath over the torus surface. In order to present a prominent thermodynamical\ninvestigation of this system configuration, we carry out a detailed analysis\nusing statistical mechanics within the grand canonical ensemble approach to\ndeal with \\textit{noninteracting} fermions. In an analytical manner, we study\nthe following thermodynamic functions in such context: the Helmholtz free\nenergy, the mean energy, the magnetization and the susceptibility. Further, we\ntake into account the behavior of Fermi energy of the thermodynamic system.\nFinally, we briefly outline how to proceed in case of \\textit{interacting}\nfermions.",
        "positive": "Vortex nucleation through fragmentation in a stirred resonant\n  Bose-Einstein condensate: Superfluids are distinguished from ordinary fluids by the quantized manner\nthe rotation is manifested in them. Precisely, quantized vortices are known to\nappear in the bulk of a superfluid subject to external rotation. In this work\nwe study a trapped ultracold Bose gas of $N=101$ atoms in two spatial\ndimensions that is stirred by a rotating beam. We use the multiconfigurational\nHartree method for bosons, that extends the mainstream mean-field theory, to\ncalculate the dynamics of the gas in real time. As the gas is rotated the\nwavefunction of the system changes symmetry and topology. We see a series of\nresonant rotations as the stirring frequency is increased. Fragmentation\naccompanies the resonances and change of symmetry of the wavefunction of the\ngas. We conclude that fragmentation of the gas appears hand-in-hand with\nresonant absorption of energy and angular momentum from the external agent of\nrotation."
    },
    {
        "anchor": "Ring model for trapped condensates with synthetic spin-orbit coupling: We derive an effective ring model in momentum space for trapped bosons with\nsynthetic spin-orbit coupling. This effective model is characterized by a\npeculiar form of the inter particle interactions, which is crucially modified\nby the external confinement. The ring model allows for an intuitive\nunderstanding of the phase diagram of trapped condensates with isotropic\nspin-orbit coupling, and in particular for the existence of skyrmion lattice\nphases. The model, which may be generally applied for spinor condensates of\narbitrary spin and spin-dependent interactions, is illustrated for the\nparticular cases of spin-1/2 and spin-1 condensates.",
        "positive": "Correlated Quantum Dynamics of a Single Atom Collisionally Coupled to an\n  Ultracold Finite Bosonic Ensemble: We explore the correlated quantum dynamics of a single atom, regarded as an\nopen system, with a spatio-temporally localized coupling to a finite bosonic\nenvironment. The single atom, initially prepared in a coherent state of low\nenergy, oscillates in a one-dimensional harmonic trap and thereby periodically\npenetrates an interacting ensemble of $N_A$ bosons, held in a displaced trap.\nWe show that the inter-species energy transfer accelerates with increasing\n$N_A$ and becomes less complete at the same time. System-environment\ncorrelations prove to be significant except for times when the excess energy\ndistribution among the subsystems is highly imbalanced. These correlations\nresult in incoherent energy transfer processes, which accelerate the early\nenergy donation of the single atom and stochastically favour certain energy\ntransfer channels depending on the instantaneous direction of transfer.\nConcerning the subsystem states, the energy transfer is mediated by\nnon-coherent states of the single atom and manifests itself in singlet and\ndoublet excitations in the finite bosonic environment. These comprehensive\ninsights into the non-equilibrium quantum dynamics of an open system are gained\nby ab-initio simulations of the total system with the recently developed\nMulti-Layer Multi-Configuration Time-Dependent Hartree Method for Bosons."
    },
    {
        "anchor": "Two-body and three-body contacts for three bosons in the unitary regime:\n  Analytic expressions and limiting forms: The two and three-body contacts are central to a set of univeral relations\nbetween microscopic few-body physics within an ultracold Bose gas and its\nthermodynamical properties. They may also be defined in trapped few-particle\nsystems, which is the subject of this work. In this work, we focus on the\nunitary three-body problem in a trap, where interactions are as strong as\nallowed by quantum mechanics. We derive analytic results for the two and\nthree-body contacts in this regime and compare with existing limiting\nexpressions and previous numerical studies.",
        "positive": "Criticality and Spin Squeezing in the Rotational Dynamics of a BEC on a\n  Ring Lattice: We examine the dynamics of circulating modes of a Bose-Einstein condensate\nconfined in toroidal lattice. Nonlinearity due to interactions leads to\ncriticality that separates oscillatory and self-trapped phases among\ncounter-propagating modes which however share the same physical space. In the\nmean-field limit, the criticality is found to substantially enhance sensitivity\nto rotation of the system. Analysis of the quantum dynamics reveals the\nfluctuations near criticality are significant, that we explain using\nspin-squeezing formalism visualized on a Bloch sphere. We utilize the squeezing\nto propose a Ramsey interferometric scheme that suppresses fluctuation in the\nrelevant quadrature sensitive to rotation."
    },
    {
        "anchor": "Quantum geometry and flat band Bose-Einstein condensation: We study the properties of a weakly interacting Bose-Einstein condensate\n(BEC) in a flat band lattice system by using multiband Bogoliubov theory, and\ndiscover fundamental connections to the underlying quantum geometry. In a flat\nband, the speed of sound and the quantum depletion of the condensate are\ndictated by the quantum geometry, and a finite quantum distance between the\ncondensed and other states guarantees stability of the BEC. Our results reveal\nthat a suitable quantum geometry allows one to reach the strong quantum\ncorrelation regime even with weak interactions.",
        "positive": "Collision dynamics of Skyrmions in a two-component Bose-Einstein\n  condensate: The dynamics of Skyrmions in a two-component Bose-Einstein condensate are\nnumerically investigated in the mean-field theory. When two Skyrmions collide\nwith each other, they are first united and then scattered into various states.\nFor head-on collisions, Skyrmions with unit winding number are scattered. The\ncollision dynamics with an impact parameter are shown to depend on the relative\nphase. These dynamic processes are characterized by integer winding numbers."
    },
    {
        "anchor": "Floquet engineering topological Dirac bands: We experimentally realized a time-periodically modulated 1D lattice for\nultracold atoms featuring a pair of linear bands, each associated with a\nFloquet winding number: a topological invariant. These bands are spin-momentum\nlocked and almost perfectly linear everywhere in the Brillouin zone (BZ),\nmaking this system a near-ideal realization of the 1D Dirac Hamiltonian. We\ncharacterized the Floquet winding number using a form of quantum state\ntomography, covering the BZ and following the micromotion through one Floquet\nperiod. Lastly, we altered the modulation timing to lift the topological\nprotection, opening a gap at the Dirac point that grew in proportion to the\ndeviation from the topological configuration.",
        "positive": "Self-localization of magnons and magnetoroton in a binary Bose-Einstein\n  condensate: We consider a two-component Bose-condensed mixture characterized by positive\ns-wave scattering lengths. We assume equal densities and intra-species\ninteractions. By doing the Bogoliubov transformation of an effective\nHamiltonian we obtain the lower energy magnon dispersion incorporating the\nsuperfluid entrainment between the components. We argue that p-wave pairing of\ndistinct bosons should be accompanied by self-localization of magnons and\nformation of a magnetoroton. We demonstrate the effect on a model system of\nparticles interacting via step potentials."
    },
    {
        "anchor": "Feedback-enhanced algorithm for aberration correction of holographic\n  atom traps: We show that a phase-only spatial light modulator can be used to generate\nnon-trivial light distributions suitable for trapping ultracold atoms, when the\nhologram calculation is included within a simple and robust feedback loop that\ncorrects for imperfect device response and optical aberrations. This correction\nreduces the discrepancy between target and experimental light distribution to\nthe level of a few percent (RMS error). We prove the generality of this\nalgorithm by applying it to a variety of target light distributions of\nrelevance for cold atomic physics.",
        "positive": "Realizing quantum Ising models in tunable two-dimensional arrays of\n  single Rydberg atoms: Spin models are the prime example of simplified manybody Hamiltonians used to\nmodel complex, real-world strongly correlated materials. However, despite their\nsimplified character, their dynamics often cannot be simulated exactly on\nclassical computers as soon as the number of particles exceeds a few tens. For\nthis reason, the quantum simulation of spin Hamiltonians using the tools of\natomic and molecular physics has become very active over the last years, using\nultracold atoms or molecules in optical lattices, or trapped ions. All of these\napproaches have their own assets, but also limitations. Here, we report on a\nnovel platform for the study of spin systems, using individual atoms trapped in\ntwo-dimensional arrays of optical microtraps with arbitrary geometries, where\nfilling fractions range from 60 to 100% with exact knowledge of the initial\nconfiguration. When excited to Rydberg D-states, the atoms undergo strong\ninteractions whose anisotropic character opens exciting prospects for\nsimulating exotic matter. We illustrate the versatility of our system by\nstudying the dynamics of an Ising-like spin-1/2 system in a transverse field\nwith up to thirty spins, for a variety of geometries in one and two dimensions,\nand for a wide range of interaction strengths. For geometries where the\nanisotropy is expected to have small effects we find an excellent agreement\nwith ab-initio simulations of the spin-1/2 system, while for strongly\nanisotropic situations the multilevel structure of the D-states has a\nmeasurable influence. Our findings establish arrays of single Rydberg atoms as\na versatile platform for the study of quantum magnetism."
    },
    {
        "anchor": "Quantum Entropic Effects in the Liquid Viscosities of Hydrogen,\n  Deuterium, and Neon: The extremely low temperatures have limited the availability and accuracy of\nexperimental thermophysical property measurements for cryogens, particularly\ntransport properties. Traditional scaling techniques such as corresponding\nstates theory have long been known to be inaccurate for fluids with strong\nquantum effects. To address this need, this paper investigates how quantum\neffects impact thermodynamics and momentum transfer (shear viscosity) in the\nfluid phases of hydrogen, deuterium, and neon. We utilize experimental\nviscosity measurements and reference empirical equations of state to show that\nconventional entropy scaling is inadequate for quantum-dominated systems. We\nthen provide a simple empirical correction to entropy scaling based on the\nratio of quantum to packing length scale that accounts for the deviations.",
        "positive": "Universal three-body parameter in ultracold 4He*: We have analyzed our recently-measured three-body loss rate coefficient for a\nBose-Einstein condensate of spin-polarized metastable triplet 4He atoms in\nterms of Efimov physics. The large value of the scattering length for these\natoms, which provides access to the Efimov regime, arises from a nearby\npotential resonance. We find the loss coefficient to be consistent with the\nthree-body parameter (3BP) found in alkali-metal experiments, where Feshbach\nresonances are used to tune the interaction. This provides new evidence for a\nuniversal 3BP, the first outside the group of alkali-metal elements. In\naddition, we give examples of other atomic systems without Feshbach resonances\nbut with a large scattering length that would be interesting to analyze once\nprecise measurements of three-body loss are available."
    },
    {
        "anchor": "Andreev-Bashkin effect in superfluid cold gases mixture: We study a mixture of two superfluids with density-density and\ncurrent-current (Andreev-Bashkin) interspecies interactions. The\nAndreev-Bashkin coupling gives rise to a dissipationless drag (or entrainment)\nbetween the two superfluids. Within the quantum hydrodynamics approximation, we\nstudy the relations between speeds of sound, susceptibilities and static\nstructure factors, in a generic model in which the density and spin dynamics\ndecouple. Due to translational invariance, the density channel does not feel\nthe drag. The spin channel, instead, does not satisfy the usual Bijl-Feynman\nrelation, since the f-sum rule is not exhausted by the spin phonons. The very\nsame effect on one dimensional Bose mixtures and their Luttinger liquid\ndescription is analysed within perturbation theory. Using diffusion quantum\nMonte Carlo simulations of a system of dipolar gases in a double layer\nconfiguration, we confirm the general results. Given the recent advances in\nmeasuring the counterflow instability, we also study the effect of the\nentrainment on the dynamical stability of a superfluid mixture with non-zero\nrelative velocity.",
        "positive": "Diagrammatic Monte Carlo study of the acoustic and the BEC polaron: We consider two large polaron systems that are described by a Fr\\\"{o}hlich\ntype of Hamiltonian, namely the Bose-Einstein condensate (BEC) polaron in the\ncontinuum and the acoustic polaron in a solid. We present ground-state energies\nof these two systems calculated with the Diagrammatic Monte Carlo (DiagMC)\nmethod and with a Feynman all-coupling approach. The DiagMC method evaluates up\nto very high order a diagrammatic series for the polaron Green's function. The\nFeynman all-coupling approach is a variational method that has been used for a\nwide range of polaronic problems. For the acoustic and BEC polaron both methods\nprovide remarkably similar non-renormalized ground-state energies that are\nobtained after introducing a finite momentum cutoff. For the renormalized\nground-state energies of the BEC polaron, there are relatively large\ndiscrepancies between the DiagMC and the Feynman predictions. These differences\ncan be attributed to the renormalization procedure for the contact interaction."
    },
    {
        "anchor": "Dynamics of a Lattice Gauge Theory with Fermionic Matter -- Minimal\n  Quantum Simulator with Time-Dependent Impurities in Ultracold Gases: We propose a minimal model to study the real-time dynamics of a\n$\\mathbb{Z}_2$ lattice gauge theory coupled to fermionic matter in a cold atom\nquantum simulator setup. We show that dynamical correlators of the gauge fields\ncan be measured in experiments studying the time-evolution of two pairs of\nimpurities, and suggest the protocol for implementing the model in cold atom\nexperiments. Further, we discuss a number of unexpected features found in the\nintegrable limit of the model, as well as its extensions to a non-integrable\ncase. A potential experimental implementation of our model in the latter regime\nwould allow one to simulate strongly-interacting lattice gauge theories beyond\ncurrent capabilities of classical computers.",
        "positive": "Decay of a quantum vortex: test of non-equilibrium theories for warm\n  Bose-Einstein condensates: The decay of a vortex from a non-rotating high temperature Bose-Einstein\ncondensate (BEC) is modeled using the stochastic projected Gross-Pitaevskii\nequation (SPGPE). In order to exploit the tunability of temperature in SPGPE\ntheory while maintaining the total atom number constant, we develop a simple\nand accurate Hartree-Fock method to estimate the SPGPE parameters for systems\nclose to thermal equilibrium. We then calculate the lifetime of a vortex using\nthree classical field theories that describe vortex decay in different levels\nof approximation. The SPGPE theory is shown to give the most complete\ndescription of the decay process, predicting significantly shorter vortex\nlifetimes than the alternative theories. Using the SPGPE theory to simulate\nvortex decay for a trapped gas of $5\\times 10^5$ $^{87}$Rb atoms, we calculate\na vortex lifetime $\\bar{t}$ that decreases linearly with temperature, falling\nin the range 20{\\rm s}$ >\\bar{t} >$1.5{\\rm s} corresponding to the temperature\nrange $0.78T_c\\leq T\\leq0.93T_c$. The vortex lifetimes calculated provide a\nlower bound for the lifetime of a persistent current with unit winding number\nin our chosen trap geometry, in the limit of vanishing vortex pinning\npotential."
    },
    {
        "anchor": "Bose-Einstein condensation in spherically symmetric traps: We present a pedagogical introduction to Bose-Einstein condensation in traps\nwith spherical symmetry, namely the spherical box and the thick shell,\nsometimes called bubble trap. In order to obtain the critical temperature for\nBose-Einstein condensation, we describe how to calculate the cumulative state\nnumber and density of states in these geometries, using numerical and\nanalytical (semi-classical) approaches. The differences in the results of both\nmethods are a manifestation of Weyl's theorem, i.e., they reveal how the\ngeometry of the trap (boundary condition) affects the number of the eigenstates\ncounted. Using the same calculation procedure, we analyzed the impact of going\nfrom three-dimensions to two-dimensions, as we move from a thick shell to a\ntwo-dimensional shell. The temperature range we obtained, for most commonly\nused atomic species and reasonable confinement volumes, is compatible with\ncurrent cold atom experiments, which demonstrates that these trapping\npotentials may be employed in experiments.",
        "positive": "Odd-frequency Two Particle Bose-Einstein Condensate: We introduce the concept of the {\\em odd-frequency} Bose Einstein Condensate\n(BEC), characterized by the odd frequency/time two-boson expectation value. To\nillustrate the concept of odd frequency BEC we present simple classification of\npair boson condensates that explicitly permits this state. We point qualitative\ndifferences of odd-frequency BEC with conventional BEC and introduce the order\nparameter and wave function for the odd-frequency BEC."
    },
    {
        "anchor": "Interaction-Range Effects and Universality in the BCS-BEC Crossover of\n  Spin-Orbit Coupled Fermi Gases: We explore the evolution of a ultracold quantum gas of interacting fermions\ncrossing from a Bardeen-Cooper-Schrieffer (BCS) superfluidity to a\nBose-Einstein condensation (BEC) of molecular bosons in the presence of a\ntunable-range interaction among the fermions and of an artificial magnetic\nfield, which can be used to simulate a pseudo-spin-orbit coupling (SOC) and to\nproduce topological states. We find that the crossover is affected by a\ncompetition between the finite range of the interaction and the SOC and that\nthe threshold $\\lambda_B$ for the topological transition is affected by the\ninteractions only in the small pair size, BEC-like, regime. Below $\\lambda_B$,\nwe find persistence of universal behavior in the critical temperature, chemical\npotential, and condensate fraction, provided that the pair correlation length\nis used as a driving parameter. Above threshold, universality is lost in the\nregime of large pair sizes. Here, the limiting ground state departs from a\nweakly-interacting BCS-like, so that a different description is required. Our\nresults can be relevant in view of current experiments with cold atoms in\noptical cavities, where tunable-range effective atomic interactions can be\nengineered.",
        "positive": "Chaos in the Bose-glass phase of a one-dimensional disordered Bose fluid: We show that the Bose-glass phase of a one-dimensional disordered Bose fluid\nexhibits a chaotic behavior, i.e., an extreme sensitivity to external\nparameters. Using bosonization, the replica formalism and the nonperturbative\nfunctional renormalization group, we find that the ground state is unstable to\nany modification of the disorder configuration (\"disorder\" chaos) or variation\nof the Luttinger parameter (\"quantum\" chaos, analog to the \"temperature\" chaos\nin classical disordered systems). This result is obtained by considering two\ncopies of the system, with slightly different disorder configurations or\nLuttinger parameters, and showing that inter-copy statistical correlations are\nsuppressed at length scales larger than an overlap length\n$\\xi_{\\mathrm{ov}}\\sim |\\epsilon|^{-1/\\alpha}$ ($|\\epsilon|\\ll 1$ is a measure\nof the difference between the disorder distributions or Luttinger parameters of\nthe two copies). The chaos exponent $\\alpha$ can be obtained by computing\n$\\xi_{\\mathrm{ov}}$ or by studying the instability of the Bose-glass fixed\npoint for the two-copy system when $\\epsilon\\neq 0$. The renormalized,\nfunctional, inter-copy disorder correlator departs from its fixed-point value\n-- characterized by cuspy singularities -- via a chaos boundary layer, in the\nsame way as it approaches the Bose-glass fixed point when $\\epsilon=0$ through\na quantum boundary layer. Performing a linear analysis of perturbations about\nthe Bose-glass fixed point, we find $\\alpha=1$."
    },
    {
        "anchor": "Measurement induced dynamics and stabilization of spinor condensate\n  domain walls: Weakly measuring many-body systems and allowing for feedback in real-time can\nsimultaneously create and measure new phenomena in strongly correlated quantum\nsystems. We study the dynamics of a continuously measured two-component\nBose-Einstein condensate (BEC) potentially containing a domain wall, and focus\non the trade-off between usable information obtained from measurement and\nquantum backaction. Each weakly measured system yields a measurement record\nfrom which we extract real-time dynamics of the domain wall. We show that\nquantum backaction due to measurement causes two primary effects: domain wall\ndiffusion and overall heating. The system dynamics and signal-to-noise ratio\ndepend on the choice of measurement observable. We describe a feedback protocol\nto create and stabilize a domain wall in the regime where domain walls are\nunstable, giving a prototype example of Hamiltonian engineering using\nmeasurement and feedback.",
        "positive": "Topological Bogoliubov quasiparticles from Bose-Einstein condensate in a\n  flat band system: For bosons with flat energy dispersion, condensation can occur in different\nsymmetry sectors. Here, we consider bosons in a Kagome lattice with $\\pi$-flux\nhopping, which in the presence of mean-field interactions exhibit degenerate\ncondensates in the $\\Gamma$- and the $K$-point. We analyze the excitation above\nboth condensates and find strikingly different properties: For the $K$-point\ncondensate, the Bogoliubov-de Gennes (BdG) Hamiltonian has broken particle-hole\nsymmetry (PHS) and exhibits a topologically trivial quasiparticle band\nstructure. However, band flatness plays a key role in breaking the time\nreversal symmetry (TRS) of the BdG Hamiltonian for a $\\Gamma$-point condensate.\nConsequently, its quasiparticle band structure exhibits non-trivial topology,\ncharacterized by non-zero Chern numbers and the presence of edge states.\nAlthough quantum fluctuations energetically favor the $K$-point condensate, the\ninteresting properties of the $\\Gamma$-point condensate become relevant for\nanisotropic hopping. The topological properties of the $\\Gamma$-point\ncondensate get even richer in the presence of extended Bose-Hubbard\ninteractions. We find a topological phase transition into a topological\ncondensate characterized by high Chern number and also comment on the\nrealization and detection of such excitations."
    },
    {
        "anchor": "Vortex generation in a superfluid gas of dipolar chains in crossed\n  electric and magnetic fields: Crossed electric and magnetic fields influence dipolar neutral particles in\nthe same way as the magnetic field influences charged particles. The effect of\ncrossed fields is proportional to the dipole moment of the particle (inherent\nor induced). We show that this effect is quite spectacular in a multilayer\nsystem of polar molecules. In this system molecules may bind in chains. At low\ntemperature the gas of chains becomes the superfluid one. The crossed fields\nthen induce vortices in the superfluid gas of chains. The density of vortices\nis proportional to the number of particles in the chain. The effect can be used\nfor monitoring the formation and destruction of chains in multilayer dipolar\ngases.",
        "positive": "Spin 1 condensates at thermal equilibrium : a $SU(3)$ coherent state\n  approach: We propose a theoretical framework based on $SU(3)$ coherent states as a\nconvenient tool to describe the collective state of a Bose-Einstein condensate\nof spin 1 atoms at thermal equilibrium. We work within the single-mode\napproximation, which assumes that all atoms condense in the same spatial mode.\nIn this system, the magnetization $m_z$ is conserved to a very good\napproximation. This conservation law is included by introducing a prior\ndistribution for $m_z$ and constructing a generalized statistical ensemble that\npreserves its first moments. In the limit of large particle numbers, we\nconstruct the partition function at thermal equilibrium and use it to compute\nvarious quantities of experimental interest, such as the probability\ndistribution function and moments of the population in each Zeeman state. When\n$N$ is large but finite (as in typical experiments, where $N\\sim 10^3-10^5$),\nwe find that fluctuations of the collective spin can be important."
    },
    {
        "anchor": "Non-exponential tunneling due to mean-field induced swallowtails: Typically, energy levels change without bifurcating in response to a change\nof a control parameter. Bifurcations can lead to loops or swallowtails in the\nenergy spectrum. The simplest quantum Hamiltonian that supports swallowtails is\na non-linear $2 \\times 2$ Hamiltonian with non-zero off-diagonal elements and\ndiagonal elements that depend on the population difference of the two states.\nThis work implements such a Hamiltonian experimentally using ultracold atoms in\na moving one-dimensional optical lattice. Self-trapping and non-exponential\ntunneling probabilities, a hallmark signature of band structures that support\nswallowtails, are observed. The good agreement between theory and experiment\nvalidates the optical lattice system as a powerful platform to study, e.g.,\nJosephson junction physics and superfluidity in ring-shaped geometries.",
        "positive": "Production of a degenerate Fermi-Fermi mixture of dysprosium and\n  potassium atoms: We report on the realization of a mixture of fermionic $^{161}$Dy and\nfermionic $^{40}$K where both species are deep in the quantum-degenerate\nregime. Both components are spin-polarized in their absolute ground states, and\nthe low temperatures are achieved by means of evaporative cooling of the\ndipolar dysprosium atoms together with sympathetic cooling of the potassium\natoms. We describe the trapping and cooling methods, in particular the final\nevaporation stage, which leads to Fermi degeneracy of both species. Analyzing\ncross-species thermalization we obtain an estimate of the magnitude of the\ninter-species $s$-wave scattering length at low magnetic field. We demonstrate\nmagnetic levitation of the mixture as a tool to ensure spatial overlap of the\ntwo components. The properties of the Dy-K mixture make it a very promising\ncandidate to explore the physics of strongly interacting mass-imbalanced\nFermi-Fermi mixtures."
    },
    {
        "anchor": "Non-Linear Interference Challenging Topological Protection of Chiral\n  Edge States: We report on a non-linear scattering effect that challenges the notion of\ntopological protection for wave packets propagating in chiral edge modes.\nSpecifically, in a Floquet topological system close to resonant driving and\nwith a non-linear potential, we demonstrate how a wave packet propagating in a\nchiral edge mode may be irreversibly deflected by scattering off a localized\nwave-packet, or pass the collision region virtually unaffected in an\napproximately linear fashion. An experimentally accessible knob to tune between\nthose two scenarios is provided by the relative phase between the involved\nwave-packets. This genuinely non-linear interference phenomenon is in stark\ncontrast to linear scattering off a static impurity, which cannot destroy a\ntopological edge state. Besides corroborating our findings with numerically\nexact simulations, we propose two physical platforms where our predictions may\nbe verified with state of the art experimental techniques: First, a coupled\nwaveguide setting where non-linearity has been engineered via an\nintensity-dependent optical index. Second, a Bose-Einstein condensate of cold\natoms in an optical Honeycomb lattice governed by a non-linear Gross-Pitaevskii\nequation that effectively accounts for many-body interactions.",
        "positive": "Fermionic Sign Structure of High-order Feynman diagrams in a\n  Many-fermion System: The sign cancellation between scattering amplitudes makes fermions different\nfrom bosons. We systematically investigate Feynman diagrams' fermionic sign\nstructure in a representative many-fermion system---a uniform Fermi gas with\nYukawa interaction. We analyze the role of the crossing symmetry and the global\ngauge symmetry in the fermionic sign cancellation. The symmetry arguments are\nthen used to identify the sign-canceled groups of diagrams. Sign-structure\nanalysis has two applications. Numerically, it leads to a cluster diagrammatic\nMonte Carlo algorithm for fast diagram evaluations. The new algorithm is about\n$10^5$ times faster than the conventional approaches in the sixth order.\nFurthermore, our analysis provides important hints in constructing the relevant\neffective field theory for many-fermion systems."
    },
    {
        "anchor": "Diagrammatic Monte Carlo study of mass-imbalanced Fermi-polaron system: We apply the diagrammatic Monte Carlo approach to three-dimensional\nFermi-polaron systems with mass-imbalance, where an impurity interacts\nresonantly with a noninteracting Fermi sea whose atoms have a different mass.\nThis method allows to go beyond frequently used variational techniques by\nstochastically summing all relevant impurity Feynman diagrams up to a maximum\nexpansion order limited by the sign problem. Polaron energy and quasiparticle\nresidue can be accurately determined over a broad range of impurity masses.\nFurthermore, the spectral function of an imbalanced polaron demonstrates the\nstability of the quasiparticle and allows to locate in addition also the\nrepulsive polaron as an excited state. The quantitative exactness of\ntwo-particle-hole wave-functions is investigated, resulting in a relative\nlowering of polaronic energies in the mass-imbalance phase diagram. Tan's\ncontact coefficient for the mass-balanced polaron system is found in good\nagreement with variational methods. Mass-imbalanced systems can be studied\nexperimentally by ultracold atom mixtures like $^6$Li-$^{40}$K.",
        "positive": "p-Wave stabilization of three-dimensional Bose-Fermi solitons: We explore bright soliton solutions of ultracold Bose-Fermi gases, showing\nthat the presence of p-wave interactions can remove the usual collapse\ninstability and support stable soliton solutions that are global energy minima.\nA variational model that incorporates the relevant s- and p-wave interactions\nin the system is established analytically and solved numerically to probe the\ndependencies of the solitons on key experimental parameters. Under attractive\ns-wave interactions, bright solitons exist only as meta-stable states\nsusceptible to collapse. Remarkably, the presence of repulsive p-wave\ninteractions alleviates this collapse instability. This dramatically widens the\nrange of experimentally-achievable soliton solutions and indicates greatly\nenhanced robustness. While we focus specifically on the boson-fermion pairing\nof 87Rb and 40K, the stabilization inferred by repulsive p-wave interactions\nshould apply to the wider remit of ultracold Bose-Fermi mixtures."
    },
    {
        "anchor": "Expansion dynamics of a spherical Bose-Einstein condensate: We experimentally and theoretically observe the expansion behaviors of a\nspherical Bose-Einstein condensate. A rubidium condensate is produced in an\nisotropic optical dipole trap with an asphericity of 0.037. We measure the\nvariation of the condensate size during the expansion process. The free\nexpansion of the condensate is isotropic, which is different from that of the\ncondensate usually produced in the anisotropic trap. The expansion in the short\ntime is speeding and then after a long time the expansion velocity\nasymptotically approaches a constant value. We derive an analytic solution of\nthe expansion behavior based on the spherical symmetry, allowing a quantitative\ncomparison with the experimental measurement. The interaction energy of the\ncondensate is gradually converted into the kinetic energy at the beginning of\nthe expansion and the kinetic energy dominates after a long-time expansion. We\nobtain the interaction energy of the condensate in the trap by probing the\nexpansion velocity, which is consistent with the theoretical prediction.",
        "positive": "Bosonic Topological Excitations from the Instability of a Quadratic Band\n  Crossing: We investigate the interaction-driven instability of a quadratic band\ncrossing arising for ultracold bosonic atoms loaded into a two-dimensional\noptical lattice. We consider the case when the degenerate point becomes a local\nminimum of both crossing energy bands such that it can support a stable\nBose-Einstein condensate. Repulsive contact interaction among the condensed\nbosons induces a spontaneously time-reversal symmetry broken superfluid phase\nand a topological gap is opened in the excitation spectrum. We propose two\nconcrete realizations of the desired quadratic band crossing in lattices with\neither fourfold or sixfold rotational symmetries via suitable tuning of the\nunit cell leading to reduced Brillouin zones and correspondingly folded bands.\nIn either case, topologically protected edge excitations are found for a finite\nsystem."
    },
    {
        "anchor": "Scaling Law for Three-body Collisions in Identical Fermions with\n  $p$-wave Interactions: We experimentally confirmed the threshold behavior and scattering length\nscaling law of the three-body loss coefficients in an ultracold spin-polarized\ngas of $^6$Li atoms near a $p$-wave Feshbach resonance. We measured the\nthree-body loss coefficients as functions of temperature and scattering volume,\nand found that the threshold law and the scattering length scaling law hold in\nlimited temperature and magnetic field regions. We also found that the\nbreakdown of the scaling laws is due to the emergence of the effective-range\nterm. This work is an important first step toward full understanding of the\nloss of identical fermions with $p$-wave interactions.",
        "positive": "Collectively pair-driven-dissipative bosonic arrays: exotic and\n  self-oscillatory condensates: Modern quantum platforms such as superconducting circuits provide exciting\nopportunities for the experimental exploration of driven-dissipative many-body\nsystems in unconventional regimes. One of such regimes occurs in bosonic\nsystems, where nowadays one can induce driving and dissipation through pairs of\nexcitations, rather than the conventional single-excitation processes.\nMoreover, modern platforms can be driven in a way in which the modes of the\nbosonic array decay collectively rather than locally, such that the pairs of\nexcitations recorded by the environment come from a coherent superposition of\nall sites. In this work we analyze the superfluid phases accessible to bosonic\narrays subject to these novel mechanisms more characteristic of quantum optics,\nwhich we prove to lead to remarkable spatiotemporal properties beyond the\ntraditional scope of pattern formation in condensed-matter systems or nonlinear\noptics alone. We show that, even in the presence of residual local loss, the\nsystem is stabilized into an exotic state with bosons condensed along the modes\nof a closed manifold in Fourier space, with a distribution of the population\namong these Fourier modes that can be controlled via a weak bias (linear)\ndrive. This gives access to a plethora of different patterns, ranging from\nperiodic and quasi-periodic ones with tunable spatial wavelength, to\nhomogeneously-populated closed-Fourier-manifold condensates that are thought to\nplay an important role in some open problems of condensed-matter physics.\nMoreover, we show that when any residual local linear dissipation is balanced\nwith pumping, new constants of motion emerge that can force the superfluid to\noscillate in time, similarly to the mechanism behind the recently discovered\nsuperfluid time crystals. We propose specific experimental implementations with\nwhich this rich and unusual spatiotemporal superfluid behavior can be explored."
    },
    {
        "anchor": "Quantum transport of strongly interacting fermions in one dimension at\n  far-out-of-equilibrium: In the study of quantum transport, much has been known for dynamics near\nthermal equilibrium. However, quantum transport far away from equilibrium is\nmuch less well understood--the linear response approximation does not hold for\nphysics far-out-of-equilibrium in general. In this work, motivated by recent\ncold atom experiments on probing quantum many-body dynamics of a\none-dimensional XXZ spin chain, we study the strong interaction limit of the\none-dimensional spinless fermion model, which is dual to the XXZ spin chain. We\ndevelop a highly efficient computation algorithm for simulating the\nnon-equilibrium dynamics of this system exactly, and examine the\nnon-equilibrium dynamics starting from a density modulation quantum state. We\nfind ballistic transport in this strongly correlated setting, and show a\nplane-wave description emerges at long-time evolution. We also observe sharp\ndistinction between transport velocities in short and long times as induced by\ninteraction effects, and provide a quantitative interpretation for the\nlong-time transport velocity.",
        "positive": "Interaction effects of pseudospin-based magnetic monopoles and kinks in\n  a doped dipolar superlattice gas: Magnetic monopoles and kinks are topological excitations extensively\ninvestigated in quantum spin systems, but usually they are studied in different\nsetups. We explore the conditions for the coexistence and the interaction\neffects of these quasiparticles in the pseudospin chain of the atomic dipolar\nsuperlattice gas. In this chain, the magnetic kink is the intrinsic\nquasiparticle, and the particle/hole defect takes over the role of the\nnorth/south magnetic monopole, exerting monopolar magnetic fields to\nneighboring spins. A confinement effect between the monopole and kink is\nrevealed, which renormalizes the dispersion of the kink. The corresponding\ndynamical deconfinement process is observed and arises due to the kink-antikink\nannihilation. The rich interaction effects of the two quasiparticles could\nstimulate corresponding investigations in bulk spin systems."
    },
    {
        "anchor": "The effect of light assisted collisions on matter wave coherence in\n  superradiant Bose-Einstein condensates: We investigate experimentally the effects of light assisted collisions on the\ncoherence between momentum states in Bose-Einstein condensates. The onset of\nsuperradiant Rayleigh scattering serves as a sensitive monitor for matter wave\ncoherence. A subtle interplay of binary and collective effects leads to a\nprofound asymmetry between the two sides of the atomic resonance and provides\nfar bigger coherence loss rates for a condensate bathed in blue detuned light\nthan previously estimated. We present a simplified quantitative model\ncontaining the essential physics to explain our experimental data and point at\na new experimental route to study strongly coupled light matter systems.",
        "positive": "Exploring out-of-equilibrium quantum magnetism and thermalization in a\n  spin-3 many-body dipolar lattice system: Understanding quantum thermalization through entanglement build-up in\nisolated quantum systems addresses fundamental questions on how unitary\ndynamics connects to statistical physics. Here, we study the spin dynamics and\napproach towards local thermal equilibrium of a macroscopic ensemble of S = 3\nspins prepared in a pure coherent spin state, tilted compared to the magnetic\nfield, under the effect of magnetic dipole-dipole interactions. The experiment\nuses a unit filled array of 104 chromium atoms in a three dimensional optical\nlattice, realizing the spin-3 XXZ Heisenberg model. The buildup of quantum\ncorrelation during the dynamics, especially as the angle approaches pi/2, is\nsupported by comparison with an improved numerical quantum phase-space method\nand further confirmed by the observation that our isolated system thermalizes\nunder its own dynamics, reaching a steady state consistent with the one\nextracted from a thermal ensemble with a temperature dictated from the system's\nenergy. This indicates a scenario of quantum thermalization which is tied to\nthe growth of entanglement entropy. Although direct experimental measurements\nof the Renyi entropy in our macroscopic system are unfeasible, the excellent\nagreement with the theory, which can compute this entropy, does indicate\nentanglement build-up."
    },
    {
        "anchor": "Coherent splitting of two-dimensional Bose gases in magnetic potentials: Investigating out-of-equilibrium dynamics with two-dimensional (2D) systems\nis of widespread theoretical interest, as these systems are strongly influenced\nby fluctuations and there exists a superfluid phase transition at a finite\ntemperature. In this work, we realise matter-wave interference for degenerate\nBose gases, including the first demonstration of coherent splitting of 2D Bose\ngases using magnetic trapping potentials. We improve the fringe contrast by\nimaging only a thin slice of the expanded atom clouds, which will be necessary\nfor subsequent studies on the relaxation of the gas following a quantum quench.",
        "positive": "Persistent superfluid flow arising from the He-McKellar-Wilkens effect\n  in molecular dipolar condensates: We show that the He-McKellar-Wilkens effect can induce a persistent flow in a\nBose-Einstein condensate of polar molecules confined in a toroidal trap, with\nthe dipolar interaction mediated via an electric dipole moment. For\nBose-Einstein condensates of atoms with a magnetic dipole moment, we show that\nalthough it is theoretically possible to induce persistent flow via the\nAharonov-Casher effect, the strength of electric field required is prohibitive.\nWe also outline an experimental geometry tailored specifically for observing\nthe He-McKellar-Wilkens effect in toroidally-trapped condensates."
    },
    {
        "anchor": "Realizing non-Abelian gauge potentials in optical square lattices:\n  Application to atomic Chern insulators: We describe a scheme to engineer non-Abelian gauge potentials on a square\noptical lattice using laser-induced transitions. We emphasize the case of\ntwo-electron atoms, where the electronic ground state g is laser coupled to a\nmetastable state e within a state-dependent optical lattice. In this scheme,\nthe alternating pattern of lattice sites hosting g and e states depict a\ncheckerboard structure, allowing for laser-assisted tunneling along both\nspatial directions. In this configuration, the nuclear spin of the atoms can be\nviewed as a \"flavor\" quantum number undergoing non-Abelian tunneling along\nnearest-neighbor links. We show that this technique can be useful to simulate\nthe equivalent of the Haldane quantum Hall model using cold atoms trapped in\nsquare optical lattices, offering an interesting route to realize Chern\ninsulators. The emblematic Haldane model is particularly suited to investigate\nthe physics of topological insulators, but requires, in its original form,\ncomplex hopping terms beyond nearest-neighboring sites. In general, this\ndrawback inhibits a direct realization with cold atoms, using standard\nlaser-induced tunneling techniques. We demonstrate that a simple mapping allows\nto express this model in terms of matrix hopping operators, that are defined on\na standard square lattice. This mapping is investigated for two models that\nlead to anomalous quantum Hall phases. We discuss the practical implementation\nof such models, exploiting laser-induced tunneling methods applied to the\ncheckerboard optical lattice.",
        "positive": "Dynamics of a vortex lattice in an expanding polariton quantum fluid: If a quantum fluid is driven with enough angular momentum, at equilibrium the\nground state of the system is given by a lattice of quantised vortices whose\ndensity is prescribed by the quantization of circulation. We report on the\nfirst experimental study of the Feynman-Onsager relation in a non-equilibrium\npolariton fluid, free to expand and rotate. Upon initially imprinting a lattice\nof vortices in the quantum fluid, we track the vortex core positions on\npicosecond time scales. We observe an accelerated stretching of the lattice and\nan outward bending of the linear trajectories of the vortices, due to the\nrepulsive polariton interactions. Access to the full density and phase fields\nallows us to detect a small deviation from the Feynman-Onsager rule in terms of\na transverse velocity component, due to the density gradient of the fluid\nenvelope acting on the vortex lattice."
    },
    {
        "anchor": "Excitation Spectrum and Momentum Distribution of Bose-Hubbard Model with\n  On-site Two- and Three-body Interaction: An effective action for Bose-Hubbard model with two- and three-body on-site\ninteraction in a square optical lattice is derived in the frame of a\nstrong-coupling approach developed by Sengupta and Dupuis. From this effective\naction, superfluid-Mott insulator (MI) phase transition, excitation spectrum\nand momentum distribution for two phases are calculated by taking into account\nGaussian fluctuation about the saddle-point approximation. In addition the\neffects of three-body interaction are also discussed.",
        "positive": "Fusing Quantum Hall States in Cold Atoms: Realizing quantum Hall states in a fast rotating Bose gas is a long sought\ngoal in cold atom research. The effort is very challenging because Bose\nstatistics fights against quantum Hall correlations. In contrast, Fermi\nstatistics does not cause such conflict. Here, we show that by sweeping the\ninteger quantum Hall states of a spin-1/2 Fermi gas across the Feshbach\nresonance from the BCS side to the BEC side at a \"projection\" rate similar to\nthat in the \"projection\" experiment of fermion superfluid, these states can be\n\"fused\" into a bosonic quantum Hall states. A projection sweep means the pair\nassociation is sufficiently fast so that the center of mass of the pair remains\nunchanged in the process. We show that the fusion of integer fermion states\nwith filling factor $\\nu_{\\uparrow}=\\nu_{\\downarrow}=n$ will result in a\nbosonic Laughlin state and Pfaffian state for $n=1$ and 2. The is due to a\nhidden property of the fermionic integer quantum Hall states -- for any\ngrouping of opposite spin into pairs, their centers of mass automatically\nassume a bosonic quantum Hall structure."
    },
    {
        "anchor": "Analytical results on quantum correlations of few bosons in a\n  double-well trap: We consider a finite number $N$ of interacting bosonic atoms at zero\ntemperature confined in a one-dimensional double-well trap and study this\nsystem by using the two-site Bose-Hubbard (BH) Hamiltonian. For systems with\n$N=2$ and $N=3$, and $N=4$ bosons we analytically solve the eigenproblem\nassociated to this Hamiltonian and find its lowest energetic state. We\ninvestigate the structure of the ground state by varying the strength of the\nboson-boson interaction from the strongly attractive regime to the deep\nrepulsive one. We characterize the ground state of the two-site BH Hamiltonian\nby calculating the Fisher information $F$, the coherence visibility $\\alpha$,\nand the entanglement entropy $S$. For these quantities we provide analytical\nformulas that we use to study $F$, $\\alpha$, and $S$ as functions of the\ninteraction between the particles. We discuss the difference existing, in the\ndeep repulsive regime, between the case with an even number of bosons and that\nwith an odd number of particles, both in the structure of the lowest energetic\nstate and in the behavior of the three above ground-state characterizing\nparameters",
        "positive": "Magnetic Quantum Phases of Ultracold Dipolar Gases in an Optical\n  Superlattice: We propose an effective Ising spin chain constructed with dipolar quantum\ngases confined in a one-dimensional optical superlattice. Mapping the motional\ndegrees of freedom of a single particle in the lattice onto a pseudo-spin\nresults in effective transverse and longitudinal magnetic fields. This\neffective Ising spin chain exhibits a quantum phase transition from a\nparamagnetic to a single-kink phase as the dipolar interaction increases.\nParticularly in the single-kink phase,a magnetic kink arises in the effective\nspin chain and behaves as a quasi-particle in a pinning potential exerted by\nthe longitudinal magnetic field. Being realizable with current experimental\ntechniques, this effective Ising chain presents a unique platform for emulating\nthe quantum phase transition as well as the magnetic kink effects in the\nIsing-spin chain and enriches the toolbox for quantum emulation of spin models\nby ultracold quantum gases."
    },
    {
        "anchor": "Weak and Strong Coupling Polarons in Binary Bose-Einstein Condensates: The Bose polaron is a quasiparticle that arises from the interaction between\nimpurities and Bogoliubov excitation in Bose-Einstein condensates, analogous to\nthe polaron formed by electrons and phonons in solid-state physics. In this\npaper, we investigate the effect of phase separation on weakly coupled and\nstrongly coupled Bose polarons. Our findings reveal that phase separation\ninduces a remarkable alteration in the properties of weakly coupled Bose\npolarons. However, in the case of strong coupling, phase separation cannot\ndestroy the polaron as a highly self-trapping state comes into existence.",
        "positive": "Dark solitons in atomic Bose-Einstein condensates: from theory to\n  experiments: This review paper presents an overview of the theoretical and experimental\nprogress on the study of matter-wave dark solitons in atomic Bose-Einstein\ncondensates. Upon introducing the general framework, we discuss the statics and\ndynamics of single and multiple matter-wave dark solitons in the quasi\none-dimensional setting, in higher-dimensional settings, as well as in the\ndimensionality crossover regime. Special attention is paid to the connection\nbetween theoretical results, obtained by various analytical approaches, and\nrelevant experimental observations."
    },
    {
        "anchor": "Bogoliubov excitation spectrum of an elongated condensate from\n  quasi-one-dimensional to three-dimensional transition: The quasiparticle excitation spectra of a Bose gas trapped in a highly\nanisotropic trap is studied with respect to varying total number of particles\nby numerically solving the effective one-dimensional (1D) Gross-Pitaevskii (GP)\nequation proposed recently by Mateo \\textit{et al.}. We obtain the static\nproperties and Bogoliubov spectra of the system in the high energy domain. This\nmethod is computationally efficient and highly accurate for a condensate system\nundergoing a 1D to three-dimensional (3D) cigar-shaped transition, as is shown\nthrough a comparison our results with both those calculated by the 3D-GP\nequation and analytical results obtained in limiting cases. We identify the\napplicable parameter space for the effective 1D-GP equation and find that this\nequation fails to describe a system with large number of atoms. We also\nidentify that the description of the transition from 1D Bose-Einstein\ncondensate (BEC) to 3D cigar-shaped BEC using this equation is not smooth,\nwhich highlights the fact that for a finite value of $a_\\perp/a_s$ the junction\nbetween the 1D and 3D crossover is not perfect.",
        "positive": "Observation of Dipole-Induced Spin Texture in an $^{87}$Rb Bose-Einstein\n  Condensate: We report the spin texture formation resulting from the magnetic\ndipole-dipole interaction in a spin-2 $^{87}$Rb Bose-Einstein condensate. The\nspinor condensate is prepared in the transversely polarized spin state and the\ntime evolution is observed under a magnetic field of 90 mG with a gradient of 3\nmG/cm using Stern-Gerlach imaging. The experimental results are compared with\nnumerical simulations of the Gross-Pitaevskii equation, which reveals that the\nobserved spatial modulation of the longitudinal magnetization is due to the\nspin precession in an effective magnetic field produced by the dipole-dipole\ninteraction. These results show that the dipole-dipole interaction has\nconsiderable effects even on spinor condensates of alkali metal atoms."
    },
    {
        "anchor": "Bound solitonic states in trapped multidimensional Bose-Einstein\n  condensates: We report on the existence and stability of multidimensional bound solitonic\nstates in harmonically-trapped scalar Bose-Einstein condensates. Their\nequilibrium separation, as a measure of the strength of the soliton-soliton or\nthe solitonic vortex-vortex interaction, is provided for varying chemical\npotential $\\mu$. Static bound dark solitons are shown to be dynamically stable\nin elongated condensates within a range of intermediate (repulsive)\ninterparticle-interaction strength. Beyond this range the snaking instability\nmanifests during the time evolution of the planar solitons and produces the\ndecay into non-stationary vortex states. A subsequent dynamical recurrence of\nsolitons and vortices can be observed at low $\\mu$. At equilibrium, the\nbifurcations of bound dark solitons are bound solitonic vortices. Among them,\nboth two-open and two-ring vortex lines are demonstrated to exist with both\ncounter- and co-rotating steady velocity fields. The latter flow configurations\nevolve, for high chemical potential, into a stationary 3D-chain-shaped vortex\nand a three vortex-antivortex-vortex ring sequence that arrest the otherwise\nincreasing angular or linear momentum respectively. As a common feature to the\nbifurcated vortex states, their excitation spectra present unstable modes with\nassociated oscillatory dynamics.",
        "positive": "Generation of dispersive shock waves by the flow of a Bose-Einstein\n  condensate past a narrow obstacle: We study the flow of a quasi-one-dimensional Bose-Einstein condensate\nincident onto a narrow obstacle. We consider a configuration in which a\ndispersive shock is formed and propagates upstream away from the obstacle while\nthe downstream flow reaches a supersonic velocity, generating a sonic horizon.\nConditions for obtaining this regime are explicitly derived and the accuracy of\nour analytical results is confirmed by numerical simulations."
    },
    {
        "anchor": "Synthetic Topological Vacua of Yang-Mills Fields in Bose-Einstein\n  Condensates: Topological vacua are a family of degenerate ground states of Yang-Mills\nfields with zero field strength but nontrivial topological structures. They\nplay a fundamental role in particle physics and quantum field theory, but have\nnot yet been experimentally observed. Here we report the first theoretical\nproposal and experimental realization of synthetic topological vacua with a\ncloud of atomic Bose-Einstein condensates. Our setup provides a promising\nplatform to demonstrate the fundamental concept that a vacuum, rather than\nbeing empty, has rich spatial structures. The Hamiltonian for the vacuum of\ntopological number n = 1 is synthesized and the related Hopf index is measured.\nThe vacuum of topological number n = 2 is also realized, and we find that vacua\nwith different topological numbers have distinctive spin textures and Hopf\nlinks. Our work opens up opportunities for exploring topological vacua and\nrelated long-sought-after instantons in tabletop experiments.",
        "positive": "Theory for Self-Bound States of Dipolar Bose-Einstein Condensates: We investigate the self-bound states of dipolar Dy condensates with the\nGaussian-state ansatz which improves the conventional coherent-state ansatz\nwith multimode squeezed coherent states. We show that the self-bound states\nconsist of the experimentally observed self-bound liquid phase and the\nunobserved self-bound gas phase. The numerically obtained gas-liquid boundary\nis in good agreement with experimental data. Our theory also allows one to\nextract the real part of the three-body coupling constant of the Dy atoms from\nthe particle number distribution of the condensates. In particular, we results\nshow that the self-bound states are stabilized by the short-range three-body\nrepulsion. Our study shed a different light to understand the self-bound\ndroplets of Bose-Einstein condensates."
    },
    {
        "anchor": "Spin-orbit coupled soliton in a random potential: We investigate theoretically the dynamics of a spin-orbit coupled soliton\nformed by a self- interacting Bose-Einstein condensate immersed in a random\npotential, in the presence of an artificial magnetic field. We find that due to\nthe anomalous spin-dependent velocity, the synthetic Zeeman coupling can play a\ncritical role in the soliton dynamics by causing its localization or\ndelocalization, depending on the coupling strength and on the parameters of the\nrandom potential. The observed effects of the Zeeman coupling qualitatively\ndepend on the type of self-interaction in the condensate since the spin state\nand the self-interaction energy of the condensate are mutually related if the\ninvariance of the latter with respect to the spin rotation is lifted.",
        "positive": "Classical and Quantum Gases on a Semiregular Mesh: The main objective of a statistical mechanical calculation is drawing the\nphase diagram of a many-body system. In this respect, discrete systems offer\nthe clear advantage over continuum systems of an easier enumeration of\nmicrostates, though at the cost of added abstraction. With this in mind, we\nexamine a system of particles living on the vertices of the (biscribed)\npentakis dodecahedron, using different couplings for first and second neighbor\nparticles to induce a competition between icosahedral and dodecahedral orders.\nAfter working out the phases of the model at zero temperature, we carry out\nMetropolis Monte Carlo simulations at finite temperature, highlighting the\nexistence of smooth transitions between distinct \"phases\", The sharpest of\nthese crossovers are characterized by hysteretic behavior near zero\ntemperature, which reveals a bottleneck issue for Metropolis dynamics in state\nspace. Next, we introduce the quantum (Bose-Hubbard) counterpart of the\nprevious model and calculate its phase diagram at zero and finite temperatures\nusing the decoupling approximation. We thus uncover, in addition to Mott\ninsulating \"solids\", also the existence of supersolid \"phases\" which\nprogressively shrink as the system is heated up. We argue that a quantum system\nof the kind described here can be realized with programmable holographic\noptical tweezers."
    },
    {
        "anchor": "Spin-orbit coupling in symmetric and mixed spin-symmetry: Synthetically spin-orbit coupling in cold atoms couples the pseudo-spin and\nspatial degrees of freedom, and therefore the inherent spin symmetry of the\nsystem plays an important role. In systems of two pseudo-spin degrees, two\nparticles configure symmetric states and anti-symmetric states, but the spin\nsymmetry can be mixed for more particles. We study the role of mixed spin\nsymmetry in the presence of spin-orbit coupling and consider the system of\nthree bosons with two hyper-fine states trapped in a harmonic potential. We\ninvestigate the ground state and the energy spectrum by implementing exact\ndiagonalization. It is found that the interplay between spin-orbit coupling and\nrepulsive interactions between anti-aligned pseudo-spins increases the\npopulation of the unaligned spin components in the ground state. The emergence\nof the mixed spin symmetric states compensates for the rise of the interaction\nenergy. With the aligned interaction on, the avoided crossing between the\nground state and the first excited state is observed only for small\ninteraction, and this causes shape changes in the spin populations.\nFurthermore, we find that the pair correlation of the ground state shows\nsimilarly to that of Tonks-Girardeau gas even for relatively small contact\ninteractions and such strong interaction feature is enhanced by the spin-orbit\ncoupling.",
        "positive": "Comment on \"Universal and Non-Universal Correction Terms of Bose Gases\n  in Dilute Region: A Quantum Monte Carlo Study'' [J. Phys. Soc. Jpn. 91,\n  024001 (2022)]: We comment on J. Phys. Soc. Jpn. 91, 024001 (2022) by Masaki-Kato et al. and\nshow that their results are in very good agreement with the semi-classical\nspin-wave approximation of Bose-Hubbard model in the hardcore limit. This\nallows for recovering the analytical formulae for both the s-wave scattering\nlength and the Lee-Huang-Yang correction."
    },
    {
        "anchor": "Spinor-Induced Instability of Kinks, Holes and Quantum Droplets: We address the existence and stability of one-dimensional (1D) holes and\nkinks and two-dimensional (2D) vortex-holes nested in extended binary Bose\nmixtures, which emerge in the presence of Lee-Huang-Yang (LHY) quantum\ncorrections to the mean-field energy, along with self-bound quantum droplets.\nWe consider both the symmetric system with equal intra-species scattering\nlengths and atomic masses, modeled by a single (scalar) LHY-corrected\nGross-Pitaevskii equation (GPE), and the general asymmetric case with different\nintra-species scattering lengths, described by two coupled (spinor) GPEs. We\nfound that in the symmetric setting, 1D and 2D holes can exist in a stable form\nwithin a range of chemical potentials that overlaps with that of self-bound\nquantum droplets, but that extends far beyond it. In this case, holes are found\nto be stable in 1D and they transform into pairs of stable out-of-phase kinks\nat the critical chemical potential at which localized droplets turn into\nflat-top states, thereby revealing the connection between localized and\nextended nonlinear states. In contrast, spinor nature of the asymmetric systems\nmay lead to instability of 1D holes, which tend to break into two gray states\nmoving in the opposite directions. Such instability arises due to spinor nature\nof the system and it affects only holes nested in extended\nmodulationally-stable backgrounds, while localized quantum droplet families\nremain completely stable, even in the asymmetric case, while 1D holes remain\nstable only close to the point where they transform into pairs of kinks. We\nalso found that symmetric systems allow fully stable 2D vortex-carrying\nsingle-charge states at moderate amplitudes, while unconventional instabilities\nappear also at high amplitudes. Symmetry also strongly inhibits instabilities\nfor double-charge vortex-holes, which thus exhibit unexpectedly robust\nevolutions at low amplitudes.",
        "positive": "Exploration of doped quantum magnets with ultracold atoms: In the last decade, quantum simulators, and in particular cold atoms in\noptical lattices, have emerged as a valuable tool to study strongly correlated\nquantum matter. These experiments are now reaching regimes that are numerically\ndifficult or impossible to access. In particular they have started to fulfill a\npromise which has contributed significantly to defining and shaping the field\nof cold atom quantum simulations, namely the exploration of doped and\nfrustrated quantum magnets and the search for the origins of high-temperature\nsuperconductivity in the fermionic Hubbard model. Despite many future\nchallenges lying ahead, such as the need to further lower the experimentally\naccessible temperatures, remarkable studies have already emerged. Among them,\nspin-charge separation in one-dimensional systems has been demonstrated,\nextended-range antiferromagnetism in two-dimensional systems has been observed,\nconnections to modern day large-scale numerical simulations were made, and\nunprecedented comparisons with microscopic trial wavefunctions have been\ncarried out at finite doping. In many regards, the field has acquired new\nrealms, putting old ideas to a new test and producing new insights and\ninspiration for the next generation of physicists. In the first part of this\npaper, we review the results achieved in cold atom realizations of the\nFermi-Hubbard model in recent years. In the second part of this paper, with the\nstage set and the current state of the field in mind, we propose a new\ndirection for cold atoms to explore: namely mixed-dimensional bilayer systems,\nwhere the charge motion is restricted to individual layers which remain coupled\nthrough spin-exchange. We propose a novel, strong pairing mechanism in these\nsystems, which puts the formation of hole pairs at experimentally accessible,\nelevated temperatures within reach."
    },
    {
        "anchor": "Coherence measurements of polaritons in thermal equilibrium reveal a new\n  power law for two-dimensional condensates: We have created a spatially homogeneous polariton condensate in thermal\nequilibrium, up to very high condensate fraction. Under these conditions, we\nhave measured the coherence as a function of momentum, and determined the total\ncoherent fraction of this boson system from very low density up to density well\nabove the condensation transition. These measurements reveal a consistent power\nlaw for the coherent fraction as a function total density over nearly three\norders of its magnitude. The same power law is seen in numerical simulations\nsolving the two-dimensional Gross-Pitaevskii equation for the equilibrium\ncoherence. This power law has not been predicted by prior analytical theories.",
        "positive": "Non-Hermitian Linear Response Theory: Linear response theory lies at the heart of quantum many-body physics because\nit builds up connections between the dynamical response to an external probe\nand correlation functions at equilibrium. Here we consider the dynamical\nresponse of a Hermitian system to a non-Hermitian probe, and we develop a\nnon-Hermitian linear response theory that can also relate this dynamical\nresponse to equilibrium properties. As an application of our theory, we\nconsider the real-time dynamics of momentum distribution induced by one-body\nand two-body dissipations. We find that, for many cases, the dynamics of\nmomentum occupation and the width of momentum distribution obey the same\nuniversal function, governed by the single-particle spectral function. We also\nfind that, for critical state with no well-defined quasi-particles, the\ndynamics are slower than normal state and our theory provides a model\nindependent way to extract the critical exponent. We apply our results to\nanalyze recent experiment on the Bose-Hubbard model and find surprising good\nagreement between theory and experiment. We also propose to further verify our\ntheory by carrying out a similar experiment on a one-dimensional Luttinger\nliquid."
    },
    {
        "anchor": "Structural change of vortex patterns in anisotropic Bose-Einstein\n  condensates: We study the changes in the spatial distribution of vortices in a rotating\nBose-Einstein condensate due to an increasing anisotropy of the trapping\npotential. Once the rotational symmetry is broken, we find that the vortex\nsystem undergoes a rich variety of structural changes, including the formation\nof zig-zag and linear configurations. These spatial re-arrangements are well\nsignaled by the change in the behavior of the vortex-pattern eigenmodes against\nthe anisotropy parameter. The existence of such structural changes opens up\npossibilities for the coherent exploitation of effective many-body systems\nbased on vortex patterns.",
        "positive": "Droplet under confinement: Competition and coexistence with soliton\n  bound state: We study the stability of quantum droplet and its associated phase\ntransitions in ultracold Bose-Bose mixtures uniformly confined in\nquasi-two-dimension. We show that the confinement-induced boundary effect can\nbe significant when increasing the atom number or reducing the confinement\nlength, which destabilizes the quantum droplet towards the formation of a\nsoliton bound state. In particular, as increasing the atom number we find the\nreentrance of soliton ground state, while the droplet is stabilized only within\na finite number window that sensitively depends on the confinement length. Near\nthe droplet-soliton transitions, they can coexist with each other as two local\nminima in the energy landscape. Take the two-species $^{39}$K bosons for\ninstance, we have mapped out the phase diagram for droplet-soliton transition\nand coexistence in terms of atom number and confinement length. The revealed\nintriguing competition between quantum droplet and soliton under confinement\ncan be readily probed in current cold atoms experiments."
    },
    {
        "anchor": "Twisted superfluid phase in the extended one-dimensional Bose-Hubbard\n  model: In one-dimensional systems a twisted superfluid phase is found which is\ninduced by a spontaneous breaking of the time-reversal symmetry. Using the\ndensity-matrix renormalization group allows us to show that the excitation\nenergy gap closes exponentially causing a quasi-degenerate ground state. The\ntwo degenerate ground states are connected by the time-reversal symmetry which\nmanifests itself in an alternating complex phase of the long-range correlation\nfunction. The quantum phase transition to the twisted superfluid is driven by\npair tunneling processes in an extended Bose-Hubbard model. The phase\nboundaries of several other phases are discussed including a supersolid, a pair\nsuperfluid, and a pair supersolid phase as well as a highly unconventional Mott\ninsulator with a degenerate ground state and a staggered pair correlation\nfunction.",
        "positive": "Mott Insulators of Ultracold Fermionic Alkaline Earth Atoms:\n  Underconstrained Magnetism and Chiral Spin Liquid: We study Mott insulators of fermionic alkaline earth atoms, described by\nHeisenberg spin models with enhanced SU(N) symmetry. In dramatic contrast to\nSU(2) magnetism, more than two spins are required to form a singlet. On the\nsquare lattice, the classical ground state is highly degenerate and magnetic\norder is thus unlikely. In a large-N limit, we find a chiral spin liquid ground\nstate with topological order and Abelian fractional statistics. We discuss its\nexperimental detection. Chiral spin liquids with non-Abelian anyons may also be\nrealizable with alkaline earth atoms."
    },
    {
        "anchor": "Spin squeezing in dipolar spinor condensates: We study the effect of dipolar interactions on the level of squeezing in\nspin-1 Bose-Einstein condensates by using the single mode approximation. We\nlimit our consideration to the $\\mathfrak{su}(2)$ Lie subalgebra spanned by\nspin operators. The biaxial nature of dipolar interactions allows for dynamical\ngeneration of spin-squeezed states in the system. We analyze the phase\nportraits in the reduced mean-filed space in order to determine positions of\nunstable fixed points. We calculate numerically spin squeezing parameter\nshowing that it is possible to reach the strongest squeezing set by the\ntwo-axis countertwisting model. We partially explain scaling with the system\nsize by using the Gaussian approach and the frozen spin approximation.",
        "positive": "Topological Floquet-bands in a circularly shaken dice lattice: The hoppings of non-interacting particles in the optical dice lattice result\nin the gapless dispersions in the band structure formed by the three lowest\nminibands. In our research, we find that once a periodic driving force is\napplied to this optical dice lattice, the original spectral characteristics\ncould be changed, forming three gapped quasi-energy bands in the quasi-energy\nBrillouin zone. The topological phase diagram containing the Chern number of\nthe lowest quasi-energy band shows that when the hopping strengths of the\nnearest-neighboring hoppings are isotropic, the system persists in the\ntopologically non-trivial phases with Chern number $C=2$ within a wide range of\nthe driving strength. Accompanied by the anisotropic nearest-neighboring\nhopping strengths, a topological phase transition occurs, making Chern number\nchange from $C=2$ to $C=1$. This transition is further verified by our\nanalytical method. Our theoretical work implies that it is feasible to realize\nthe non-trivially topological characteristics of optical dice lattices by\napplying the periodic shaking, and that topological phase transition can be\nobserved by independently tuning the strength of a type of nearest-neighbor\nhopping."
    },
    {
        "anchor": "Persistent currents in a bosonic mixture in the ring geometry: In this paper we analyze the possibility of persistent currents of a\ntwo-species bosonic mixture in the one-dimensional ring geometry. We extend the\narguments used by Bloch to obtain a criterion for the stability of persistent\ncurrents for the two-species system. If the mass ratio of the two species is a\nrational number, persistent currents can be stable at multiples of a certain\ntotal angular momenta. We show that the Bloch criterion can also be viewed as a\nLandau criterion involving the elementary excitations of the system. Our\nanalysis reveals that persistent currents at higher angular momenta are more\nstable for the two-species system than previously thought.",
        "positive": "The dominant scattering channel induced by two-body collision of D-band\n  atoms in triangular optical lattice: The mechanism of atomic collisions in excited bands plays an important role\nin the study of the orbital physics in optical lattices and simulation of\ncondensed matter physics. Atoms distributing in one excited bands of an optical\nlattice would collide and decay to other bands through different scattering\nchannels. In excited bands of one dimensional lattice, due to lack of geometry,\nthere is no significant difference between cross section of scattering\nchannels. Here, we investigate the collisional scattering channels for atoms in\nthe excited bands of a triangular optical lattice and demonstrate a dominant\nscattering channel in the experiment. A shortcut method is utilized to load\nBose-Einstein condensates of $^{87} {\\rm Rb}$ atoms into the first D band with\nzero quasi-momentum. After some time for evolution, the number of atoms\nscattering to S band due to two-body collisions is around four times more than\nthat to the second most band. We reveal that the scattering channel to $ss$\nband is dominant by theoretical calculation, which agrees with experimental\nmeasurements. The appearance of dominant scattering channels in triangular\noptical lattice is owing to geometric dimension coupling. This work is helpful\nfor the study of many-body systems and directional enhancement in optical\nlattices."
    },
    {
        "anchor": "Scale-invariant relaxation dynamics in two-component Bose-Einstein\n  condensates with large particle-number imbalance: We theoretically study the scale-invariant relaxation dynamics in segregating\ntwo-component Bose-Einstein condensates with large particle-number imbalance,\nand uncover that random walk of droplet for the minor component plays a\nfundamental role in the relaxation process. Our numerical simulations based on\nthe binary Gross-Pitaevskii model reveal the emergence of the dynamical scaling\nduring the relaxation, which is a hallmark of scale-invariant dynamics, in a\ncorrelation function for the minor condensate. Tracking exponents\ncharacterizing the dynamical scaling in time, we find out a crossover\nphenomenon that features the change in power exponents of the correlation\nlength. To understand the fundamental mechanism inherent in the scale-invariant\nrelaxation dynamics, we construct a random walk model for droplets. Employing\nthe model, we analytically derive the $1/3$ and $1/2$ power laws and predict\nthe crossover of the scaling. These exponents are in reasonable agreement with\nthe values obtained in the numerical calculations. We also discuss a possible\nexperimental setup for observing the scale-invariant dynamics.",
        "positive": "Dynamic high-resolution optical trapping of ultracold atoms: All light has structure, but only recently it has become possible to\nconstruct highly controllable and precise potentials so that most laboratories\ncan harness light for their specific applications. In this chapter, we review\nthe emerging techniques for high-resolution and configurable optical trapping\nof ultracold atoms. We focus on optical deflectors and spatial light modulators\nin the Fourier and direct imaging configurations. These optical techniques have\nenabled significant progress in studies of superfluid dynamics, single-atom\ntrapping, and underlie the emerging field of atomtronics. The chapter is\nintended as a complete guide to the experimentalist for understanding,\nselecting, and implementing the most appropriate optical trapping technology\nfor a given application. After introducing the basic theory of optical trapping\nand image formation, we describe each of the above technologies in detail,\nproviding a guide to the fundamental operation of optical deflectors, digital\nmicromirror devices, and liquid crystal spatial light modulators. We also\ndescribe the capabilities of these technologies for manipulation of trapped\nultracold atoms, where the potential is dynamically modified to enable\nexperiments, and where time-averaged potentials can realise more complex traps.\nThe key considerations when implementing time-averaged traps are described."
    },
    {
        "anchor": "Chaos and thermalization in small quantum systems: Chaos and ergodicity are the cornerstones of statistical physics and\nthermodynamics. While classically even small systems like a particle in a\ntwo-dimensional cavity, can exhibit chaotic behavior and thereby relax to a\nmicrocanonical ensemble, quantum systems formally can not. Recent theoretical\nbreakthroughs and, in particular, the eigenstate thermalization hypothesis\n(ETH) however indicate that quantum systems can also thermalize. In fact ETH\nprovided us with a framework connecting microscopic models and macroscopic\nphenomena, based on the notion of highly entangled quantum states. Such\nthermalization was beautifully demonstrated experimentally by A. Kaufman et.\nal. who studied relaxation dynamics of a small lattice system of interacting\nbosonic particles. By directly measuring the entanglement entropy of\nsubsystems, as well as other observables, they showed that after the initial\ntransient time the system locally relaxes to a thermal ensemble while globally\nmaintaining a zero-entropy pure state.",
        "positive": "Direct observation of the quantum-fluctuation driven amplitude mode in a\n  microcavity polariton condensate: The Higgs amplitude mode is a collective excitation studied and observed in a\nbroad class of matter, including superconductors, charge density waves,\nantiferromagnets, 3He p-wave superfluid, and ultracold atomic condensates. In\nall the observations reported thus far, the amplitude mode was excited by\nperturbing the condensate out of equilibrium. Studying an exciton-polariton\ncondensate, here we report the first observation of this mode purely driven by\nintrinsic quantum fluctuations without such perturbations. By using an\nultrahigh quality microcavity and a Raman spectrometer to maximally reject\nphotoluminescence from the condensate, we observe weak but distinct\nphotoluminescence at energies below the condensate emission. We identify this\nas the so-called ghost branches of the amplitude mode arising from quantum\ndepletion of the condensate into this mode. These energies, as well as the\noverall structure of the photoluminescence spectra, are in good agreement with\nour theoretical analysis."
    },
    {
        "anchor": "Interference effect of critical ultra-cold atomic Bose gases: For ultra-cold atomic gases close to the critical temperature, there is a\ndivergent correlation behavior within the critical regime. This divergent\ncorrelation behavior is the cornerstone of the universal behavior within the\ncritical regime, e.g. the universal critical exponent for the same class with\nvery different physical systems. It is still quite challenging to observe this\ndivergent correlation behavior in experiments with ultra-cold atomic gases.\nHere we consider theoretically the interference effect of the critical atomic\nBose gas by a Kapitza-Dirac scattering. We find that the Kapitza-Dirac\nscattering has the merit of enhancing the interference effect in the\nobservation of the correlation behavior. This provides a potential method to\nstudy the critical behavior of ultra-cold Bose gases. A simple rule is found by\nnumerical simulations to get the critical exponent and correlation amplitude\nratio from the interference fringes after the Kapitza-Dirac scattering.",
        "positive": "Two-dimensional dipolar Bose-Einstein condensate bright and vortex\n  solitons on one-dimensional optical lattice: By solving the three-dimensional Gross-Pitaevskii equation we generate\ntwo-dimensional axially-symmetric and anisotropic dipolar Bose-Einstein\ncondensate bright solitons, for repulsive atomic interaction, stabilized by\nonly a weak one-dimensional optical lattice (OL) aligned along and\nperpendicular, respectively, to the dipole polarization direction. In the\nformer case vortex solitons can also be created. We show that it is possible to\nmake a stable array of small interacting axially-symmetric dipolar solitons put\non alternate OL sites. Further, we demonstrate the elastic nature of the\ncollision of two such solitons."
    },
    {
        "anchor": "Thermodynamics of Strongly Correlated One-Dimensional Bose Gases: We investigate the thermodynamics of one-dimensional Bose gases in the\nstrongly correlated regime. To this end, we prepare ensembles of independent 1D\nBose gases in a two-dimensional optical lattice and perform high-resolution in\nsitu imaging of the column-integrated density distribution. Using an inverse\nAbel transformation we derive effective one-dimensional line-density profiles\nand compare them to exact theoretical models. The high resolution allows for a\ndirect thermometry of the trapped ensembles. The knowledge about the\ntemperature enables us to extract thermodynamic equations of state such as the\nphase-space density, the entropy per particle and the local pair correlation\nfunction.",
        "positive": "Topologically nontrivial states in one-dimensional nonlinear bichromatic\n  superlattices: We study topological properties of one-dimensional nonlinear bichromatic\nsuperlattices and unveil the effect of nonlinearity on topological states. We\nfind the existence of nontrivial edge solitions, which distribute on the\nboundaries of the lattice with their chemical potential located in the linear\ngap regime and are sensitive to the phase parameter of the superlattice\npotential. We further demonstrate that the topological property of the\nnonlinear Bloch bands can be characterized by topological Chern numbers defined\nin the extended two-dimensional parameter space. In addition, we discuss that\nthe composition relations between the nolinear Bloch waves and gap solitions\nfor the nonlinear superlattices. The stabilities of edge solitons are also\nstudied."
    },
    {
        "anchor": "Irreversible Work and Orthogonality Catastrophe in the Aubry-Andr\u00e9\n  model: We address the statistical orthogonality catastrophe induced by a local\nquench in the Aubry-Andr\\'e model from the perspective of nonequilibrium\nthermodynamics. We study the average work and the irreversible work production\nwhen quenching the impurity potential in proximity of an orthogonality event.\nWe show how this description is able to capture the level crossings generating\nthe orthogonality and the avoided crossings which causes the plateau-like\nstructures, signature of the Aubry-Andr\\'e spectrum, when considering the full\nstatistics of orthogonality events.",
        "positive": "Dark soliton oscillations in Bose-Einstein condensates with multi-body\n  interactions: We consider the dynamics of dark matter solitons moving through non-uniform\ncigar-shaped Bose-Einstein condensates described by the mean field\nGross-Pitaevskii equation with generalized nonlinearities, in the case when the\ncondition for the modulation stability of the Bose-Einstein condensate is\nfulfilled. The analytical expression for the frequency of the oscillations of a\ndeep dark soliton is derived for nonlinearities which are arbitrary functions\nof the density, while specific results are discussed for the physically\nrelevant case of a cubic-quintic nonlinearity modeling two- and three-body\ninteractions, respectively. In contrast to the cubic Gross-Pitaevskii equation\nfor which the frequencies of the oscillations are known to be independent of\nbackground density and interaction strengths, we find that in the presence of a\ncubic-quintic nonlinearity an explicit dependence of the oscillations frequency\non the above quantities appears. This dependence gives rise to the possibility\nof measuring these quantities directly from the dark soliton dynamics, or to\nmanage the oscillation via the changes of the scattering lengths by means of\nFeshbach resonance. A comparison between analytical results and direct\nnumerical simulations of the cubic-quintic Gross-Pitaevskii equation shows good\nagreement which confirms the validity of our approach."
    },
    {
        "anchor": "Meissner-like effect for synthetic gauge field in multimode cavity QED: Previous realizations of synthetic gauge fields for ultracold atoms do not\nallow the spatial profile of the field to evolve freely. We propose a scheme\nwhich overcomes this restriction by using the light in a multimode cavity, in\nconjunction with Raman coupling, to realize an artificial magnetic field which\nacts on a Bose-Einstein condensate of neutral atoms. We describe the evolution\nof such a system, and present the results of numerical simulations which show\ndynamical coupling between the effective field and the matter on which it acts.\nCrucially, the freedom of the spatial profile of the field is sufficient to\nrealize a close analogue of the Meissner effect, where the magnetic field is\nexpelled from the superfluid. This back-action of the atoms on the synthetic\nfield distinguishes the Meissner-like effect described here from the\nHess-Fairbank suppression of rotation in a neutral superfluid observed\nelsewhere.",
        "positive": "Quantum droplets in a dipolar Bose gas at a dimensional crossover: We study the beyond-mean-field corrections to the energy of a dipolar Bose\ngas confined to two dimensions by a box potential with dipoles oriented in\nplane. At a critical strength of the dipolar interaction the system becomes\nunstable on the mean field level. We find that the ground state of the gas is\nstrongly influenced by the corrections, leading to formation of a self-bound\ndroplet, in analogy to the free space case. Properties of the droplet state can\nbe found by minimizing the extended Gross-Pitaevskii energy functional. In the\nlimit of strong confinement we show analytically that the correction can be\ninterpreted as an effective three-body repulsion which stabilizes the gas at\nfinite density."
    },
    {
        "anchor": "Looking for \"avalanche-mechanism\" loss at an atom-molecule Efimov\n  resonance: The \"avalanche mechanism\" has been used to relate Efimov trimer states to\ncertain enhanced atom loss features observed in ultracold atom gas experiments.\nThese atom loss features are argued to be a signature of resonant atom-molecule\nscattering that occurs when an Efimov trimer is degenerate with the\natom-molecule scattering threshold. However, observation of these atom loss\nfeatures has yet to be combined with the direct observation of atom-molecule\nresonant scattering for any particular atomic species. In addition, recent\nMonte-Carlo simulations were unable to reproduce a narrow loss feature. We\nexperimentally search for enhanced atom loss features near an established\nscattering resonance between 40K87Rb Feshbach molecules and 87Rb atoms. Our\nmeasurements of both the three-body recombination rate in a gas of 40K and 87Rb\natoms and the ratio of the number loss for the two species do not show any\nbroad loss feature and are therefore inconsistent with theoretical predictions\nthat use the avalanche mechanism.",
        "positive": "D-brane solitons and boojums in field theory and Bose-Einstein\n  condensates: In certain field theoretical models, composite solitons consisting of a\ndomain wall and vortex lines attached to the wall have been referred to as\nD-brane solitons. We show that similar composite solitons can be realized in\nphase-separated two-component Bose-Einstein condensates. We discuss the\nsimilarities and differences between topological solitons in the Abelian-Higgs\nmodel and those in two-component Bose-Einstein condensates. Based on the\nformulation of gauge theory, we introduce the \"boojum charge\" to characterize\nthe \"D-brane soliton\" in Bose-Einstein condensates."
    },
    {
        "anchor": "Dynamics of the central-depleted-well regime in the open Bose-Hubbard\n  trimer: We study the quantum dynamics of the central-depleted-well (CDW) regime in a\nthree-mode Bose Hubbard model subject to a confining parabolic potential. By\nintroducing a suitable set of momentum-like modes we identify the microscopic\nvariables involved in the quantization process and the dynamical algebra of the\nmodel. We describe the diagonalization procedure showing that the model reduces\nto a double oscillator. Interestingly, we find that the parameter-space domain\nwhere this scheme entails a discrete spectrum well reproduces the two regions\nwhere the classical trimer excludes unstable oscillations. Spectral properties\nare examined in different limiting cases together with various delocalization\neffects. These are shown to characterize quantum states of the CDW regime in\nthe proximity of the borderline with classically-unstable domains.",
        "positive": "Magnetic Monopole Noise: Magnetic monopoles are hypothetical elementary particles exhibiting quantized\nmagnetic charge $m_0=\\pm(h/\\mu_0e)$ and quantized magnetic flux $\\Phi_0=\\pm\nh/e$. A classic proposal for detecting such magnetic charges is to measure the\nquantized jump in magnetic flux $\\Phi$ threading the loop of a superconducting\nquantum interference device (SQUID) when a monopole passes through it.\nNaturally, with the theoretical discovery that a plasma of emergent magnetic\ncharges should exist in several lanthanide-pyrochlore magnetic insulators,\nincluding Dy$_2$Ti$_2$O$_7$, this SQUID technique was proposed for their direct\ndetection. Experimentally, this has proven extremely challenging because of the\nhigh number density, and the generation-recombination (GR) fluctuations, of the\nmonopole plasma. Recently, however, theoretical advances have allowed the\nspectral density of magnetic-flux noise $S_{\\Phi}(\\omega,T)$ due to GR\nfluctuations of $\\pm m_*$ magnetic charge pairs to be determined. These\ntheories present a sequence of strikingly clear predictions for the\nmagnetic-flux noise signature of emergent magnetic monopoles. Here we report\ndevelopment of a high-sensitivity, SQUID based flux-noise spectrometer, and\nconsequent measurements of the frequency and temperature dependence of\n$S_{\\Phi}(\\omega,T)$ for Dy$_2$Ti$_2$O$_7$ samples. Virtually all the elements\nof $S_{\\Phi}(\\omega,T)$ predicted for a magnetic monopole plasma, including the\nexistence of intense magnetization noise and its characteristic frequency and\ntemperature dependence, are detected directly. Moreover, comparisons of\nsimulated and measured correlation functions $C_{\\Phi}(t)$ of the magnetic-flux\nnoise $\\Phi(t)$ imply that the motion of magnetic charges is strongly\ncorrelated because traversal of the same trajectory by two magnetic charges of\nsame sign is forbidden."
    },
    {
        "anchor": "Topology, edge states, and zero-energy states of ultracold atoms in 1D\n  optical superlattices with alternating onsite potentials or hopping\n  coefficients: One-dimensional superlattices with periodic spatial modulations of onsite\npotentials or tunneling coefficients can exhibit a variety of properties\nassociated with topology or symmetry. Recent developments of ring-shaped\noptical lattices allow a systematic study of those properties in superlattices\nwith or without boundaries. While superlattices with additional modulating\nparameters are shown to have quantized topological invariants in the augmented\nparameter space, we also found localized or zero-energy states associated with\nsymmetries of the Hamiltonians. Probing those states in ultracold-atoms is\npossible by utilizing recently proposed methods analyzing particle depletion or\nthe local density of states. Moreover, we summarize feasible realizations of\nconfigurable optical superlattices using currently available techniques.",
        "positive": "3/2-Body Correlations and Coherence in Bose-Einstein Condensates: We construct a variational wave function for the ground state of weakly\ninteracting bosons that gives a lower energy than the mean-field\nGirardeau-Arnowitt (or Hartree-Fock-Bogoliubov) theory. This improvement is\nbrought about by incorporating the dynamical 3/2-body processes where one of\ntwo colliding non-condensed particles drops into the condensate and vice versa.\nThe processes are also shown to transform the one-particle excitation spectrum\ninto a bubbling mode with a finite lifetime even in the long-wavelength limit.\nThese 3/2-body processes, which give rise to dynamical exchange of particles\nbetween the non-condensate reservoir and condensate absent in ideal gases, are\nidentified as a key mechanism for realizing and sustaining macroscopic\ncoherence in Bose-Einstein condensates."
    },
    {
        "anchor": "Bose-Hubbard model with occupation dependent parameters: We study the ground-state properties of ultracold bosons in an optical\nlattice in the regime of strong interactions. The system is described by a\nnon-standard Bose-Hubbard model with both occupation-dependent tunneling and\non-site interaction. We find that for sufficiently strong coupling the system\nfeatures a phase-transition from a Mott insulator with one particle per site to\na superfluid of spatially extended particle pairs living on top of the Mott\nbackground -- instead of the usual transition to a superfluid of single\nparticles/holes. Increasing the interaction further, a superfluid of particle\npairs localized on a single site (rather than being extended) on top of the\nMott background appears. This happens at the same interaction strength where\nthe Mott-insulator phase with 2 particles per site is destroyed completely by\nparticle-hole fluctuations for arbitrarily small tunneling. In another regime,\ncharacterized by weak interaction, but high occupation numbers, we observe a\ndynamical instability in the superfluid excitation spectrum. The new ground\nstate is a superfluid, forming a 2D slab, localized along one spatial direction\nthat is spontaneously chosen.",
        "positive": "Absence of the Twisted Superfluid State in a mean field model of bosons\n  on a Honeycomb Lattice: Motivated by recent observations (P. Soltan-Panahi {\\it et al.}, Nature\nPhysics {\\bf 8}, 71-75 (2012)), we study the stability of a Bose-Einstein\nCondensate within a spin-dependent honeycomb lattice towards forming a \"Twisted\nSuperfluid\" state. Our exhaustive numerical search fails to find this phase,\npointing to possible non-mean field physics."
    },
    {
        "anchor": "Interacting ultracold atomic kicked rotors: dynamical localization ?: We study the fate of dynamical localization of two quantum kicked rotors with\ncontact interaction. This interaction mimics experimental realizations with\nultracold atomic gases. Dynamical localization for a single rotor takes place\nin momentum space. The contact interaction affects the evolution of the\nrelative momentum $k$ of a pair of interacting rotors in a non-analytic way.\nConsequently the evolution operator $U$ is exciting large relative momenta with\namplitudes which decay only as a power law $1/k^4$. This is in contrast to the\ncenter-of-mass momentum $K$ for which the amplitudes excited by $U$ decay\nsuperexponentially fast. Therefore dynamical localization is preserved for the\ncenter-of-mass momentum, but destroyed for the relative momentum for any\nnonzero strength of interaction.",
        "positive": "Vortex lattices in three-component Bose-Einstein condensates under\n  rotation: simulating colorful vortex lattices in a color superconductor: We study vortex lattices in three-component BECs under rotation, where three\nkinds of fractional vortices winding one of three components are present.\nUnlike the cases of two-component BECs where the phases of square and\ntriangular lattices are present depending on the intercomponent coupling\nconstant and the rotation speed, we find triangular ordered \"colorful\" vortex\nlattices where three kind of fractional vortices are placed in order without\ndefects, in all parameter region where the inter-component coupling g' is less\nthan the intra-component coupling g. When g > g' on the other hand, we find the\nphase separation; In a region where one component is present, the other two\ncomponents must vanish, where we find ghost vortices in these two components\nwhose positions are separated. In the boundary g = g', the accidental U(3)\nsymmetry is present, in which case two vortices in different components are\nclose to each other in some regions."
    },
    {
        "anchor": "Instability of Bose-Einstein condensates in tilted lattices with\n  time-periodical modulation: We study the dynamical stability of Bose-Einstein condensates in an optical\nlattice with a time-periodic modulation potential and a constant acceleration\nforce simultaneously. We derive the explicit expressions of quasienergies and\nobtain the stability diagrams in the parameter space of the interaction\nstrength and the modulation amplitude. The ratio of the acceleration force to\nthe modulation frequency characterizes two cases: integer and non-integer\nresonances. For integer resonances, the critical interaction strength\n$g_{\\mathrm{c}}$ shows an alternate behavior where the completely unstable\nregions correspond to the negative effective tunneling strength. Among\nnon-integer resonances, we observe that $g_{\\mathrm{c}}$ peaks are centered\naround half-integer resonances for which the completely unstable regions\ndisappear, accompanied with a whole displacement of $g_{\\mathrm{c}}$. Compared\nwith integer and half-integer resonances, the crossovers between them show no\nexplicit dependence of $g_{\\mathrm{c}}$ on the modulation amplitude.",
        "positive": "Amplitude modulated phase in a Bose-Einstein condensate: the role of\n  non-local interactions: We consider a Gross-Pitaevskii model of BEC with non-local interactions of\nrange of the order of the s-wave scattering length. With this model, we study\nthe density modulated phase in 1D and 2D, which are solutions of this modified\nmodel along with the usual uniform density state. We find an exact free energy\nfunctional for our model and show that the 1D density modulated state can have\nlower energy than the uniform density state. Although, the density modulated\nstate can be made to be energetically favourable, we show also that, this state\nis inherently dynamically unstable due to the coupling of instabilities to the\nspatial order."
    },
    {
        "anchor": "Spatial tomography of individual atoms in a quantum gas microscope: We demonstrate a method to determine the position of single atoms in a\nthree-dimensional optical lattice. Atoms are sparsely loaded from a\nfar-off-resonant optical tweezer into a few vertical planes of a cubic optical\nlattice positioned near a high-resolution microscope objective. In a single\nrealization of the experiment, we pin the atoms in deep lattices and then\nacquire multiple fluorescence images with single-site resolution. The objective\nis translated between images, bringing different lattice planes of the lattice\ninto focus. The applicability of our method is assessed using simulated\nfluorescence images, where the atomic filling fraction in the lattice is\nvaried. This opens up the possibility of extending the domain of quantum\nsimulation using quantum gas microscopes from two to three dimensions.",
        "positive": "Correlation Effects in a Trapped Bose-Fermi Mixture: Exact Results: Many-body properties of a fermionic impurity embedded in a Bose-Einstein\ncondensate are analyzed analytically using a solvable model, the\nharmonic-interaction model for Bose-Fermi mixtures. The one-particle and\ntwo-particle densities, reduced density matrices, and correlation functions of\nthe fermions and bosons, both in position and momentum spaces, are prescribed\nin closed form. The various coherence lengths are analyzed. We show that the\nfirst-order coherence lengths in position and momentum spaces are equal whereas\nthe second-order quantities can differ substantially. Illustrative examples\nwhere the sole interaction is between the impurity and the condensate are\npresented. Implications are briefly discussed."
    },
    {
        "anchor": "Exact Solution of Bogoliubov Equations for Bosons in One-Dimensional\n  Piecewise Constant Potential: We show that Bogoliubov equations in one-dimensional systems with piecewise\nconstant potentials can be always solved. In particular, we analyze in detail\nthe case where the condensate wavefunction is a real-valued function, and give\nthe explicit expressions for wavefunctions of Bogoliubov excitations. By means\nof these solutions, we consider transmission and reflection properties of\nBogoliubov excitations for two types of potential, namely, a rectangular\nbarrier and a potential step. The results yield simple and exact examples of\nanomalous tunneling effect and quantum evaporation.",
        "positive": "Realizing discontinuous quantum phase transitions in a\n  strongly-correlated driven optical lattice: Discontinuous quantum phase transitions and the associated metastability play\ncentral roles in diverse areas of physics ranging from ferromagnetism to false\nvacuum decay in the early universe. Using strongly-interacting ultracold atoms\nin an optical lattice, we realize a driven many-body system whose quantum phase\ntransition can be tuned from continuous to discontinuous. Resonant shaking of a\none-dimensional optical lattice hybridizes the lowest two Bloch bands, driving\na novel transition from a Mott insulator to a $\\pi$-superfluid, i.e., a\nsuperfluid state with staggered phase order. For weak shaking amplitudes, this\ntransition is discontinuous (first-order) and the system can remain frozen in a\nmetastable state, whereas for strong shaking, it undergoes a continuous\ntransition toward a $\\pi$-superfluid. Our observations of this metastability\nand hysteresis are in good quantitative agreement with numerical simulations\nand pave the way for exploring the crucial role of quantum fluctuations in\ndiscontinuous transitions."
    },
    {
        "anchor": "Quasi-One-Dimensional Dipolar Quantum Gases: In this letter we consider dipolar quantum gases in a quasi-one-dimensional\ntube with dipole moment perpendicular to the tube direction. We deduce the\neffective one-dimensional interaction potential and show that this potential is\nnot purely repulsive, but rather has an attractive part due to high-order\nscattering processes through transverse excited states. The attractive part can\ninduce bound state and cause scattering resonances. This represents the dipole\ninduced resonance in low-dimension. We work out an unconventional behavior of\nlow-energy phase shift for this effective potential and show how it evolves\nacross a resonance. Based on the phase shift, the interaction energy of\nspinless bosons is obtained using asymptotic Bethe ansatz. Despite of\nlong-range nature of dipolar interaction, we find that a behavior similar as\nshort-range Lieb-Linger gas emerges at the resonance regime.",
        "positive": "Axial collective mode of a dipolar quantum droplet: In this work, we investigate the ground state properties and collective\nexcitations of a dipolar Bose-Einstein condensate that self-binds into a\nquantum droplet, stabilized by quantum fluctuations. We demonstrate that a sum\nrule approach can accurately determine the frequency of the low energy axial\nexcitation, using properties of the droplet obtained from the ground state\nsolutions. This excitation corresponds to an oscillation in the length of the\nfilament-shaped droplet. Additionally, we evaluate the static polarizabilities,\nwhich quantify change in the droplet dimensions in response to a change in\nharmonic confinement."
    },
    {
        "anchor": "Parametric resonance and spin-charge separation in 1D fermionic systems: We show that the periodic modulation of the Hamiltonian parameters for 1D\ncorrelated fermionic systems can be used to parametrically amplify their\nbosonic collective modes. Treating the problem within the Luttinger liquid\npicture, we show how charge and spin density waves with different momenta are\nsimultaneously amplified. We discuss the implementation of our predictions for\ncold atoms in 1D modulated optical lattices, showing that the fermionic\nmomentum distribution directly provides a clear signature of spin-charge\nseparation.",
        "positive": "Atomic number fluctuations in a mixture of two spinor condensates: We study particle number fluctuations in the quantum ground states of a\nmixture of two spin-1 atomic condensates when the interspecies spin-exchange\ncoupling interaction $c_{12}\\beta$ is adjusted. The two spin-1 condensates\nforming the mixture are respectively ferromagnetic and polar in the absence of\nan external magnetic (B-) field. We categorize all possible ground states using\nthe angular momentum algebra and compute their characteristic atom number\nfluctuations, focusing especially on the the AA phase (when $ c_{12}\\beta >0$),\nwhere the ground state becomes fragmented and atomic number fluctuations\nexhibit drastically different features from a single stand alone spin-1 polar\ncondensate. Our results are further supported by numerical simulations of the\nfull quantum many-body system."
    },
    {
        "anchor": "Temporal fluctuations in the bosonic Josephson junction as a probe for\n  phase space tomography: We study the long time coherence dynamics of a two-mode Bose-Hubbard model in\nthe Josephson interaction regime, as a function of the relative phase and\noccupation imbalance of an arbitrary coherent preparation. We find that the\nvariance of the long time fluctuations of the one-body coherence can be\nfactorized as a product of the inverse participation number 1/M that depends\nonly on the preparation, and a semi-classical function C(E) that reflects the\nphase space characteristics of the pertinent observable. Temporal fluctuations\ncan thus be used as a sensitive probe for phase space tomography of quantum\nmany-body states.",
        "positive": "Comment on \"Dispersive bottleneck delaying thermalization of turbulent\n  Bose-Einstein Condensates\" by Krstulovic and Brachet [arXiv:1007.4441]: We reveal the connection of the recent numerical observations of Krstulovic\nand Brachet [arXiv:1007.4441] with the general theory of relaxation kinetics of\nthe strongly non-equilibrium Bose-Einstein condensates."
    },
    {
        "anchor": "Floquet Dynamical Decoupling at Zero Bias: Dynamical decoupling (DD) is an efficient method to decouple systems from\nenvironmental noises and to prolong the coherence time of systems. In contrast\nto discrete and continuous DD protocols in the presence of bias field, we\npropose a Floquet DD at zero bias to perfectly suppress both the zeroth and\nfirst orders of noises according to the Floquet theory. Specifically, we\ndemonstrate the effectiveness of this Floquet DD protocol in two typical\nsystems including a spinor atomic Bose-Einstein condensate decohered by\nclassical stray magnetic fields and a semiconductor quantum dot electron spin\ncoupled to nuclear spins. Furthermore, our protocol can be used to sense\nhigh-frequency noises. The Floquet DD protocol we propose shines new light on\nlow-cost and high-portable DD technics without bias field and with low\ncontrolling power, which may have wide applications in quantum computing,\nquantum sensing, nuclear magnetic resonance and magnetic resonance imaging.",
        "positive": "Optomechanically-Based Probing of Spin-Charge Separation in Ultracold\n  Gases: We propose a new approach to investigate the spin-charge separation in 1D\nquantum liquids via the optomechanical coupled atom-cavity system. We show\nthat, one can realize an effective two-modes optomechanical model with the\nspin/charge modes playing the role of mechanical resonators. By tuning the weak\nprobe laser under a pump field, the signal of spin-charge separation could be\nprobed explicitly in the sideband regime via cavity transmissions. Moreover,\nthe spin/charge modes can be addressed separately by designing the probe field\nconfigurations, which may be beneficial for future studies of the atom-cavity\nsystems and quantum many-body physics."
    },
    {
        "anchor": "Path integral Monte Carlo simulation of global and local superfluidity\n  in liquid $^{4}$He reservoirs separated by nanoscale apertures: We present a path integral Monte Carlo study of the global superfluid\nfraction and local superfluid density in cylindrically-symmetric reservoirs of\nliquid $^{4}$He separated by nanoaperture arrays. The superfluid response to\nboth translations along the axis of symmetry (longitudinal response) and\nrotations about the cylinder axis (transverse response) are computed, together\nwith radial and axial density distributions that reveal the microscopic\ninhomogeneity arising from the combined effects of the confining external\npotential and the $^4$He-$^4$He interatomic potentials. We make a microscopic\ndetermination of the length-scale of decay of superfluidity at the radial\nboundaries of the system by analyzing the local superfluid density distribution\nto extract a displacement length that quantifies the superfluid mass\ndisplacement away from the boundary. We find that the longitudinal superfluid\nresponse is reduced in reservoirs separated by a septum containing sufficiently\nsmall apertures compared to a cylinder with no intervening aperture array, for\nall temperatures below $T_{\\lambda}$. For a single aperture in the septum, a\nsignificant drop in the longitudinal superfluid response is seen when the\naperture diameter is made smaller than twice the empirical\ntemperature-dependent $^4$He healing length, consistent with the formation of a\nweak link between the reservoirs. Increasing the diameter of a single aperture\nor the number of apertures in the array results in an increase of the\nsuperfluid density toward the expected bulk value.",
        "positive": "Mean-field description of pairing effects, BKT physics, and\n  superfluidity in 2D Bose gases: We derive a mean-field description for two-dimensional (2D) interacting Bose\ngases at arbitrary temperatures. We find that genuine Bose-Einstein\ncondensation with long-range coherence only survives at zero temperature. At\nfinite temperatures, many-body pairing effects included in our mean-field\ntheory introduce a finite amplitude for the pairing density, which results in a\nfinite superfluid density. We incorporate Berenzinskii-Kosterlitz-Thouless\n(BKT) physics into our model by considering the phase fluctuations of our\npairing field. This then leads to the result that the superfluid phase is only\nstable below the BKT temperature due to these phase fluctuations. In the weakly\ninteracting regime at low temperature we compare our theory to previous results\nfrom perturbative calculations, renormalization group calculations as well as\nMonte Carlo simulations. We present a finite-temperature phase diagram of 2D\nBose gases. One signature of the finite amplitude of the pairing density field\nis a two-peak structure in the single-particle spectral function, resembling\nthat of the pseudogap phase in 2D attractive Fermi gases."
    },
    {
        "anchor": "Hartree-Fock Analogue Theory of Thermo-Optic Interaction: Thermo-optic interaction significantly differs from the usual\nparticle-particle interactions in physics, as it is retarded in time. A\nprominent platform for realising this kind of interaction are photon\nBose-Einstein condensates, which are created in dye-filled microcavities. The\ndye solution continually absorbs and re-emits these photons, causing the photon\ngas to thermalise and to form a Bose-Einstein condensate. Because of a\nnon-ideal quantum efficiency, these cycles heat the dye solution, creating a\nmedium that provides an effective thermo-optic photon-photon interaction. So\nfar, only a mean-field description of this process exists. This paper goes\nbeyond by working out a quantum mechanical description of the effective\nthermo-optic photon-photon interaction. To this end, the self-consistent\nmodelling of the temperature diffusion builds the backbone of the modelling.\nFurthermore, the manyfold experimental timescales allow for deriving an\napproximate Hamiltonian. The resulting quantum theory is applied in the\nperturbative regime to both a harmonic and a box potential for investigating\nits prospect for precise measurements of the effective photon-photon\ninteraction strength.",
        "positive": "Bose - Einstein condensation of triplons with a weakly broken U(1)\n  symmetry: The low-temperature properties of certain quantum magnets can be described in\nterms of a Bose-Einstein condensation (BEC) of magnetic quasiparticles\n(triplons). Some mean-field approaches (MFA) to describe these systems, based\non the standard grand canonical ensemble, do not take the anomalous density\ninto account and leads to an internal inconsistency, as it has been shown by\nHohenberg and Martin, and may therefore produce unphysical results. Moreover,\nan explicit breaking of the U(1) symmetry as observed, for example, in TlCuCl3\nmakes the application of MFA more complicated. In the present work, we develop\na self-consistent MFA approach, similar to the Hartree-Fock-Bogolyubov\napproximation in the notion of representative statistical ensembles, including\nthe effect of a weakly broken U(1) symmetry. We apply our results on\nexperimental data of the quantum magnet TlCuCl3 and show that magnetization\ncurves and the energy dispersion can be well described within this\napproximation assuming that the BEC scenario is still valid. We predict that\nthe shift of the critical temperature Tc due to a finite exchange anisotropy is\nrather substantial even when the anisotropy parameter \\gamma is small, e.g.,\n\\Delta T_c \\approx 10%$ of Tc in H = 6T and for \\gamma\\approx 4 \\mu eV."
    },
    {
        "anchor": "Chaotic and regular dynamics in the three-site Bose-Hubbard model: We analyze the energy spectrum of the three-site Bose-Hubbard model. It is\nshown that this spectrum is a mixture of the regular and irregular spectra\nassociated with the regular and chaotic components of the classical\nBose-Hubbard model. We find relative volumes of these components by using the\npseudoclassical approach. Substituting these values in the Berry-Robnik\ndistribution for the level spacing statistics we obtain good agreement with the\nnumerical data.",
        "positive": "A compact and fast magnetic coil for the interaction manipulation of\n  quantum gases with Feshbach resonances: Cold atom experiments commonly use broad magnetic Feshbach resonances to\nmanipulate the interaction between atoms. In order to induce quantum dynamics\nby a change of the interaction strength, rapid ($\\sim\\mu s$) magnetic field\nchanges over several tens of Gauss are required. Here we present a compact\ndesign of a coil and its control circuit for a change of the magnetic field up\nto $36G$ in $3\\mu s$. The setup comprises two concentric solenoids with minimal\nspace requirements, which can be readily added to existing apparatuses. This\ndesign makes the observation of non-equilibrium physics with broad Feshbach\nresonances accessible."
    },
    {
        "anchor": "Cavity QED with Quantum Gases: New Paradigms in Many-Body Physics: We review the recent developments and the current status in the field of\nquantum-gas cavity QED. Since the first experimental demonstration of atomic\nself-ordering in a system composed of a Bose-Einstein condensate coupled to a\nquantized electromagnetic mode of a high-$Q$ optical cavity, the field has\nrapidly evolved over the past decade. The composite quantum-gas--cavity systems\noffer the opportunity to implement, simulate, and experimentally test\nfundamental solid-state Hamiltonians, as well as to realize non-equilibrium\nmany-body phenomena beyond conventional condensed-matter scenarios. This hinges\non the unique possibility to design and control in open quantum environments\nphoton-induced tunable-range interaction potentials for the atoms using\ntailored pump lasers and dynamic cavity fields. Notable examples range from\nHubbard-like models with long-range interactions exhibiting a\nlattice-supersolid phase, over emergent magnetic orderings and quasicrystalline\nsymmetries, to the appearance of dynamic gauge potentials and non-equilibrium\ntopological phases. Experiments have managed to load spin-polarized as well as\nspinful quantum gases into various cavity geometries and engineer versatile\ntunable-range atomic interactions. This led to the experimental observation of\nspontaneous discrete and continuous symmetry breaking with the appearance of\nsoft-modes as well as supersolidity, density and spin self-ordering, dynamic\nspin-orbit coupling, and non-equilibrium dynamical self-ordered phases among\nothers. In addition, quantum-gas--cavity setups offer new platforms for\nquantum-enhanced measurements. In this review, starting from an introduction to\nbasic models, we pedagogically summarize a broad range of theoretical\ndevelopments and put them in perspective with the current and near future\nstate-of-art experiments.",
        "positive": "The quantum ground state of self-organized atomic crystals in optical\n  resonators: Cold atoms, driven by a laser and simultaneously coupled to the quantum field\nof an optical resonator, can self-organize in periodic structures. These\nstructures are supported by the optical lattice, which emerges from the laser\nlight they scatter into the cavity mode, and form when the laser intensity\nexceeds a threshold value. We study theoretically the quantum ground state of\nthese structures above the pump threshold of self-organization, by mapping the\natomic dynamics of the self-organized crystal to a Bose-Hubbard model. We find\nthat the quantum ground state of the self-organized structure can be the one of\na Mott-insulator or a superfluid, depending on the pump strength of the driving\nlaser. For very large pump strengths, where the intracavity intensity is\nmaximum and one would expect a Mott-insulator state, we find intervals of\nparameters where the system is superfluid. These states could be realized in\nexisting experimental setups."
    },
    {
        "anchor": "Effective multi-body induced tunneling and interactions in the\n  Bose-Hubbard model of the lowest dressed band of an optical lattice: We construct the effective lowest-band Bose-Hubbard model incorporating\ninteraction-induced on-site correlations. The model is based on ladder\noperators for local correlated states, which deviate from the usual Wannier\ncreation and annihilation, allowing for a systematic construction of the most\nappropriate single-band low-energy description in the form of the extended\nBose-Hubbard model. A formulation of this model in terms of ladder operators\nnot only naturally contains the previously found effective multibody\ninteractions, but also contains multibody-induced single-particle tunneling,\npair tunneling, and nearest-neighbor interaction processes of higher orders. An\nalternative description of the same model can be formulated in terms of\noccupation-dependent Bose-Hubbard parameters. These multiparticle effects can\nbe enhanced using Feshbach resonances, leading to corrections which are well\nwithin experimental reach and of significance to the phase diagram of ultracold\nbosonic atoms in an optical lattice. We analyze the energy-reduction mechanism\nof interacting atoms on a local lattice site and show that this cannot be\nexplained only by a spatial broadening of Wannier orbitals on a single-particle\nlevel, which neglects correlations.",
        "positive": "Spin-Orbit Coupled Bose Gases at Finite Temperatures: Spin-orbit coupling is predicted to have dramatic effects on thermal\nproperties of a two-component atomic Bose gas. We show that in three spatial\ndimensions it lowers the critical temperature of condensation and enhances\nthermal depletion of the condensate fraction. In two dimensions we show that\nspin-orbit coupling destroys superfluidity at any finite temperature, modifying\ndramatically the cerebrated Berezinskii-Kosterlitz-Thouless scenario. We\nexplain this by the increase of the number of low energy states induced by\nspin-orbit coupling, enhancing the role of quantum fluctuations."
    },
    {
        "anchor": "Dynamical spin properties of confined Fermi and Bose systems in presence\n  of spin-orbit coupling: Due to the recent experimental progress, tunable spin-orbit (SO) interactions\nrepresent ideal candidates for the control of polarization and dynamical spin\nproperties in both quantum wells and cold atomic systems. A detailed\nunderstanding of spin properties in SO coupled systems is thus a compelling\nprerequisite for possible novel applications or improvements in the context of\nspintronics and quantum computers. Here we analyze the case of equal Rashba and\nDresselhaus couplings in both homogeneous and laterally confined\ntwo-dimensional systems. Starting from the single-particle picture and\nsubsequently introducing two-body interactions we observe that periodic spin\nfluctuations can be induced and maintained in the system. Through an analytical\nderivation we show that the two-body interaction does not involve decoherence\neffects in the bosonic dimer, and, in the repulsive homogeneous Fermi gas it\nmay be even exploited in combination with the SO coupling to induce and tune\nstanding currents. By further studying the effects of a harmonic lateral\nconfinement --a particularly interesting case for Bose condensates-- we\nevidence the possible appearance of non-trivial {\\it spin textures}, whereas\nthe further application of a small Zeeman-type interaction can be exploited to\nfine-tune the system polarizability.",
        "positive": "Fast generation of spin-squeezed states in bosonic Josephson junctions: We describe methods for fast production of highly coherent-spin-squeezed\nmany-body states in bosonic Josephson junctions (BJJs). We start from the known\nmapping of the two-site Bose-Hubbard (BH) Hamiltonian to that of a single\neffective particle evolving according to a Schr\\\"odinger-like equation in Fock\nspace. Since, for repulsive interactions, the effective potential in Fock space\nis nearly parabolic, we extend recently derived protocols for shortcuts to\nadiabatic evolution in harmonic potentials to the many-body BH Hamiltonian. The\nbest scaling of the squeezing parameter for large number of atoms N is \\xi^2_S\n~ 1/N."
    },
    {
        "anchor": "Universal spin dynamics in two-dimensional Fermi gases: Harnessing spins as carriers for information has emerged as an elegant\nextension to the transport of electrical charges. The coherence of such spin\ntransport in spintronic circuits is determined by the lifetime of spin\nexcitations and by spin diffusion. Fermionic quantum gases are a unique system\nto study the fundamentals of spin transport from first principles since\ninteractions can be precisely tailored and the dynamics is on time scales which\nare directly observable. In particular at unitarity, spin transport is dictated\nby diffusion and is expected to reach a universal, quantum-limited diffusivity\non the order of hbar/m. Here, we study the non-equilibrium dynamics of a\ntwo-dimensional Fermi gas following a quench into a metastable, transversely\npolarized spin state. Using the spin-echo technique, we measure the yet lowest\ntransverse spin diffusion constant of 0.25(3) hbar/m. For weak interactions, we\nobserve a coherent collective transverse spin-wave mode that exhibits mode\nsoftening when approaching the hydrodynamic regime.",
        "positive": "Collisions of matter-wave solitons: Solitons are localised wave disturbances that propagate without changing\nshape, a result of a nonlinear interaction which compensates for wave packet\ndispersion. Individual solitons may collide, but a defining feature is that\nthey pass through one another and emerge from the collision unaltered in shape,\namplitude, or velocity. This remarkable property is mathematically a\nconsequence of the underlying integrability of the one-dimensional (1D)\nequations, such as the nonlinear Schr\\\"odinger equation, that describe solitons\nin a variety of wave contexts, including matter-waves$^{1,2}$. Here we explore\nthe nature of soliton collisions using Bose-Einstein condensates of atoms with\nattractive interactions confined to a quasi-one-dimensional waveguide. We show\nby real-time imaging that a collision between solitons is a complex event that\ndiffers markedly depending on the relative phase between the solitons. Yet,\nthey emerge from the collision unaltered in shape or amplitude, but with a new\ntrajectory reflecting a discontinuous jump. By controlling the strength of the\nnonlinearity we shed new light on these fundamental features of soliton\ncollisional dynamics, and explore the implications of collisions that bring the\nwave packets out of the realm of integrability, where they may undergo\ncatastrophic collapse.\n  1. Zabusky, N.J. & Kruskal, M.D. Interaction of \"solitons\" in a collisionless\nplasma and the recurrence of initial states. Phys. Rev. Lett. 15, 240 (1965).\n  2. Zakharov, V.E. & Shabat, A.B. Exact theory of two-dimensional\nself-focusing and one-dimensional self-moduation of waves in nonlinear media.\nSov. Phys. JEPT. 34, 62 (1972)."
    },
    {
        "anchor": "Suppression and Control of Pre-thermalization in Multi-component Fermi\n  Gases Following a Quantum Quench: We investigate the mechanisms of control and suppression of\npre-thermalization in $N$-component alkaline earth gases. To this end, we\ncompute the short-time dynamics of the instantaneous momentum distribution and\nthe relative population for different initial conditions after an interaction\nquench, accounting for the 11 peffect of initial interactions. We find that\nswitching on an interaction that breaks the SU$(N)$ symmetry of the initial\nHamiltonian, thus allowing for the occurrence of spin-changing collisions, does\nnot necessarily lead to a suppression of pre-thermalization. However, the\nsuppression will be most effective in the presence of SU$(N)$-breaking\ninteractions provided the number of components $N \\ge 4$ and the initial state\ncontains a population imbalance that breaks the SU$(N)$ symmetry. We also find\nthe conditions on the imbalance initial state that allow for a pre-thermal\nstate to be stabilized for a certain time. Our study highlights the important\nrole played by the initial state in the pre-thermalization dynamics of\nmulticomponent Fermi gases. It also demonstrates that alkaline-earth Fermi\ngases provide an interesting playground for the study and control of\npre-thermalization.",
        "positive": "Entanglement and Localization of a Two-Mode Bose-Einstein Condensate: A simple second quantization model is used to describe a two-mode\nBose-Einstein condensate (BEC), which can be written in terms of the generators\nof a SU(2) algebra with three parameters. We study the behaviour of the\nentanglement entropy and localization of the system in the parameter space of\nthe model. The phase transitions in the parameter space are determined by means\nof the coherent state formalism and the catastrophe theory, which besides let\nus get the best variational state that reproduces the ground state energy. The\nentanglement entropy is determined for two recently proposed partitions of the\ntwo-mode BEC that are called separation by boxes and separation by modes of the\natoms. The entanglement entropy in the boxes partition is strongly correlated\nto the properties of localization in phase space of the model, which is given\nby the evaluation of the second moment of the Husimi function. To compare the\nfitness of the trial wavefunction its overlap with the exact quantum solution\nis evaluated. The entanglement entropy for both partitions, the overlap and\nlocalization properties of the system get singular values along the separatrix\nof the two-mode BEC, which indicates the phase transitions which remain in the\nthermodynamical limit, in the parameter space."
    },
    {
        "anchor": "Intrinsic phonon effects on analog quantum simulators with ultracold\n  trapped ions: Linear Paul traps have been used recently to simulate the transverse field\nIsing model with long-range spin-spin couplings. We study the intrinsic effects\nof phonon creation (from the initial phonon ground state) on the spin-state\nprobability and spin entanglement for such quantum spin simulators. While it\nhas often been assumed that phonon effects are benign because they play no role\nin the pure Ising model, they can play a significant role when a transverse\nfield is added to the model. We use a many-body factorization of the quantum\ntime-evolution operator of the system, adiabatic perturbation theory and exact\nnumerical integration of the Schr\\\"odinger equation in a truncated spin-phonon\nHilbert space followed by a tracing out of the phonon degrees of freedom to\nstudy this problem. We find that moderate phonon creation often makes the\nprobabilities of different spin states behave differently from the static spin\nHamiltonian. In circumstances in which phonon creation is minor, the spin\ndynamics state probabilities converge to the static spin Hamiltonian prediction\nat the cost of reducing the spin entanglement. We show how phonon creation can\nseverely impede the observation of kink transitions in frustrated spin systems\nwhen the number of ions increases. Many of our results also have implications\nfor quantum simulation in a Penning trap.",
        "positive": "Bose-Einstein Condensate on a Synthetic Topological Hall Cylinder: The interplay between matter particles and gauge fields in physical spaces\nwith nontrivial geometries can lead to novel topological quantum matter.\nHowever, detailed microscopic mechanisms are often obscure, and unconventional\nspaces are generally challenging to construct in solids. Highly controllable\natomic systems can quantum simulate such physics, even those inaccessible in\nother platforms. Here, we realize a Bose-Einstein condensate (BEC) on a\nsynthetic cylindrical surface subject to a net radial synthetic magnetic flux.\nWe observe a symmetry-protected topological band structure emerging on this\nHall cylinder but disappearing in the planar counterpart. BEC's transport\nobserved as Bloch oscillations in the band structure is analogous to traveling\non a M\\\"obius strip in the momentum space, revealing topological band crossings\nprotected by a nonsymmorphic symmetry. We demonstrate that breaking this\nsymmetry induces a topological transition manifested as gap opening at band\ncrossings, and further manipulate the band structure and BEC's transport by\ncontrolling the axial synthetic magnetic flux. Our work opens the door for\nusing atomic quantum simulators to explore intriguing topological phenomena\nintrinsic in unconventional spaces."
    },
    {
        "anchor": "Phase diagram of a non-Abelian Aubry-Andr\u00e9-Harper model with $p$-wave\n  superfluidity: We theoretically study a one-dimensional quasi-periodic Fermi system with\ntopological $p$-wave superfluidity, which can be deduced from a topologically\nnon-trivial tight-binding model on the square lattice in a uniform magnetic\nfield and subject to a non-Abelian gauge field. The system may be regarded a\nnon-Abelian generalization of the well-known Aubry-Andr\\'e-Harper model. We\ninvestigate its phase diagram as functions of the strength of the\nquasi-disorder and the amplitude of the $p$-wave order parameter, through a\nnumber of numerical investigations, including a multifractal analysis. There\nare four distinct phases separated by three critical lines, i.e., two phases\nwith all extended wave-functions (I and IV), a topologically trivial phase (II)\nwith all localized wave-functions and a critical phase (III) with all\nmultifractal wave-functions. The phase I is related to the phase IV by duality.\nIt also seems to be related to the phase II by duality. Our proposed phase\ndiagram may be observable in current cold-atom experiments, in view of\nsimulating non-Abelian gauge fields and topological insulators/superfluids with\nultracold atoms.",
        "positive": "N-body Efimov states from two-particle noise: The ground state energies of universal N-body clusters tied to Efimov\ntrimers, for N even, are shown to be encapsulated in the statistical\ndistribution of two particles interacting with a background auxiliary field at\nlarge Euclidean time when the interaction is tuned to the unitary point.\nNumerical evidence that this distribution is log-normal is presented, allowing\none to predict the ground-state energies of the N-body system."
    },
    {
        "anchor": "Dimensional crossover in self-organised super-radiant phases of ultra\n  cold atoms inside a cavity: We consider a condensate of ultra cold bosonic atoms in a linear optical\ncavity illuminated by a two-pump configuration where each pump is making\ndifferent angles with the direction of the cavity axis. We show such\nconfiguration allows a smooth transition from a one-dimensional quantum optical\nlattice configuration to a two-dimensional quantum optical lattice\nconfiguration induced by the cavity-atom interaction. Using a\nHolstein-Primakoff transformation, we find out the atomic density profile of\nsuch self-organised ground state in the super-radiant phase as a function of\nthe angular orientations of the pump in such dynamical quantum optical lattice,\nand, also provide an analysis of their structures in coordinate and momentum\nspace. In the later part of the paper, we show how the corresponding results\ncan also be qualitatively understood in terms of an Extended Bose-Hubbard model\nin such quantum optical lattice potential.",
        "positive": "Motion of a Solitonic Vortex in the BEC-BCS Crossover: We observe a long-lived solitary wave in a superfluid Fermi gas of $^6$Li\natoms after phase-imprinting. Tomographic imaging reveals the excitation to be\na solitonic vortex, oriented transverse to the long axis of the cigar-shaped\natom cloud. The precessional motion of the vortex is directly observed, and its\nperiod is measured as a function of the chemical potential in the BEC-BCS\ncrossover. The long period and the correspondingly large ratio of the inertial\nto the bare mass of the vortex are in good agreement with estimates based on\nsuperfluid hydrodynamics that we derive here using the known equation of state\nin the BEC-BCS crossover."
    },
    {
        "anchor": "Born-Oppenheimer study of two-component few-particle systems under\n  one-dimensional confinement: The energy spectrum, atom-dimer scattering length, and atom-trimer scattering\nlength for systems of three and four ultracold atoms with $\\delta$-function\ninteractions in one dimension are presented as a function of the relative mass\nratio of the interacting atoms. The Born-Oppenheimer approach is used to treat\nthree-body (\"HHL\") systems of one light and two heavy atoms, as well as\nfour-body (\"HHHL\") systems of one light and three heavy atoms. Zero-range\ninteractions of arbitrary strength are assumed between different atoms, but the\nheavy atoms are assumed to be noninteracting among themselves. Both fermionic\nand bosonic heavy atoms are considered.",
        "positive": "Controllable non-local interactions between dark solitons in dipolar\n  condensates: We study the family of static and moving dark solitons in\nquasi-one-dimensional dipolar Bose-Einstein condensates, exploring their\nmodified form and interactions. The density dip of the soliton acts as a giant\nanti-dipole which adds a non-local contribution to the conventional local\nsoliton-soliton interaction. We map out the stability diagram as a function of\nthe strength and polarization direction of the atomic dipoles, identifying both\nroton and phonon instabilities. Away from these instabilities, the solitons\ncollide elastically. Varying the polarization direction relative to the\ncondensate axis enables tuning of this non-local interaction between repulsive\nand attractive; the latter case supports unusual dark soliton bound states.\nRemarkably, these bound states are themselves shown to behave like solitons,\nemerging unscathed from collisions with each other."
    },
    {
        "anchor": "Experimental realization of a Dirac monopole through the decay of an\n  isolated monopole: We experimentally observe the decay dynamics of deterministically created\nisolated monopoles in spin-1 Bose-Einstein condensates. As the condensate\nundergoes a change between magnetic phases, the isolated monopole gradually\nevolves into a spin configuration hosting a Dirac monopole in its synthetic\nmagnetic field. We characterize in detail the Dirac monopole by measuring the\nparticle densities of the spin states projected along different quantization\naxes. Importantly, we observe the spontaneous emergence of nodal lines in the\ncondensate density that accompany the Dirac monopole. We also demonstrate that\nthe monopole decay accelerates in weaker magnetic field gradients.",
        "positive": "Vortices with massive cores in a binary mixture of Bose-Einstein\n  condensates: We analyze a notable class of states relevant to an immiscible bosonic binary\nmixture loaded in a rotating box-like circular trap, i.e. states where vortices\nin one species host the atoms of the other species, which thus play the role of\nmassive cores. Within a fully-analytical framework, we calculate the\nequilibrium distance distinguishing the motion of precession of two corotating\nmassive vortices, the angular momentum of each component, the vortices healing\nlength and the characteristic size of the cores. We then compare these\nprevisions with the measures extracted from the numerical solutions of the\nassociated coupled Gross-Pitaevskii equations. Interestingly, making use of a\nsuitable change of reference frame, we show that vortices drag the massive\ncores which they host thus conveying them their same motion of precession, but\nthat there is no evidence of tangential entrainment between the two fluids,\nsince the cores keep their orientation constant while orbiting."
    },
    {
        "anchor": "Spin-Orbit Coupled Bose-Einstein Condensate under Rotation: We examine the combined effects of Rashba spin-orbit (SO) coupling and\nrotation on trapped spinor Bose-Einstein condensates (BECs). Nature of single\nparticle states is thoroughly examined in the Landau level basis and is shown\nto support the formation of half-quantum vortex. In the presence of weak s-wave\ninteractions, the ground state at strong SO coupling develops ring-like\nstructures with domains whose number shows step behavior with increasing\nrotation. For fast rotation case, the vortex pattern favors triangular lattice,\naccompanied by the density depletion in the central region and weakened\nSkyrmionic character as the SO coupling is enhanced. Giant vortex formation is\nfacilitated when SO coupling and rotation are both strong.",
        "positive": "Strongly Interacting Atom Lasers in Three Dimensional Optical Lattices: We show that the dynamical melting of a Mott insulator in a three-dimensional\nlattice leads to condensation at nonzero momenta, a phenomenon that can be used\nto generate strongly interacting atom lasers in optical lattices. For infinite\nonsite repulsion, the case considered here, the momenta at which bosons\ncondense is determined analytically and found to have a simple dependence on\nthe hopping amplitudes. The occupation of the condensates is shown to scale\nlinearly with the total number of atoms in the initial Mott insulator. Our\nresults are obtained using a Gutzwiller-type mean-field approach, gauged\nagainst exact diagonalization solutions of small systems."
    },
    {
        "anchor": "Kink-like Solitons in Quantum Droplet: Solitonic excitations of the one-dimensional quantum droplets are obtained,\nwhich smoothly connect vacuum with the flat-top droplet, akin to compactons in\nclassical liquids. These solitons are of the kink type, necessarily residing on\na constant pedestal, determined by the mean-field repulsion and beyond mean\nfield quantum correction and having exactly one-third of the uniform condensate\namplitude. Akin to the kinks, the propagating modes occur in pairs and are\nphase-locked with the background. The lowest chemical potential and condensate\namplitude at the flat-top boundary matches with the self-trapped quantum\ndroplet. More general excitations of analogous kind are obtained through the\nM\\\"obius transform, which connect the required solutions to elliptic functions\nin general.",
        "positive": "Faraday patterns in spin-orbit coupled Bose-Einstein condensates: We study the Faraday patterns generated by spin-orbit-coupling induced\nparametric resonance in a spinor Bose-Einstein condensate with repulsive\ninteraction. The collective elementary excitations of the Bose-Einstein\ncondensate, including density waves and spin waves, are coupled as the result\nof the Raman-induced spin-orbit coupling and a quench of the relative phase of\ntwo Raman lasers without the modulation of any of the system's parameters. We\nobserved several higher parametric resonance tongues at integer multiples of\nthe driving frequency and investigated the interplay between Faraday\ninstabilities and modulation instabilities when we quench the\nspin-orbit-coupled Bose-Einstein condensate from zero-momentum phase to\nplane-wave phase. If the detuning is equal to zero, the wave number of\ncombination resonance barely changes as the strength of spin-orbit coupling\nincreases. If the detuning is not equal to zero after a quench, a single\ncombination resonance tongue will split into two parts."
    },
    {
        "anchor": "Keldysh approach for non-equilibrium phase transitions in quantum\n  optics: beyond the Dicke model in optical cavities: We investigate non-equilibrium phase transitions for driven atomic ensembles,\ninteracting with a cavity mode, coupled to a Markovian dissipative bath. In the\nthermodynamic limit and at low-frequencies, we show that the distribution\nfunction of the photonic mode is thermal, with an effective temperature set by\nthe atom-photon interaction strength. This behavior characterizes the static\nand dynamic critical exponents of the associated superradiance transition.\nMotivated by these considerations, we develop a general Keldysh path integral\napproach, that allows us to study physically relevant nonlinearities beyond the\nidealized Dicke model. Using standard diagrammatic techniques, we take into\naccount the leading-order corrections due to the finite number of atoms N. For\nfinite N, the photon mode behaves as a damped, classical non-linear oscillator\nat finite temperature. For the atoms, we propose a Dicke action that can be\nsolved for any N and correctly captures the atoms' depolarization due to\ndissipative dephasing.",
        "positive": "Quench-induced Floquet topological p-wave superfluids: Ultracold atomic gases in two dimensions tuned close to a p-wave Feshbach\nresonance were expected to exhibit topological superfluidity, but these were\nfound to be experimentally unstable. We show that one can induce a topological\nFloquet superfluid if weakly interacting atoms are brought suddenly close\n(\"quenched\") to such a resonance, in the time before the instability kicks in.\nThe resulting superfluid possesses Majorana edge modes, yet differs from a\nconventional Floquet system as it is not driven externally. Instead, the\nperiodic modulation is self-generated by the dynamics."
    },
    {
        "anchor": "Non-linear edge dynamics of an Integer Quantum Hall fluid: We report a theoretical study of the linear and nonlinear dynamics of edge\nexcitations of an integer quantum Hall state of non-interacting fermions. New\nfeatures beyond the chiral Luttinger liquid picture are anticipated to arise\nfrom the interplay of the curvature of the Landau level dispersion and of the\nPauli exclusion principle. For long-wavelength perturbations, the microscopic\nnumerical results are captured by a chiral nonlinear hydrodynamic equation\nincluding a density-dependent velocity term. In the wave-breaking regime, shock\nwaves are found to be regularized into a complex ripple pattern by dispersion\neffects. Our results are of specific relevance for experiments with synthetic\nquantum matter, in particular ultracold atomic gases.",
        "positive": "Onset of vortex clustering and inverse energy cascade in dissipative\n  quantum fluids: Turbulent phenomena are among the most striking effects that both classical\nand quantum fluids can exhibit. While classical turbulence is ubiquitous in\nnature, the observation of quantum turbulence requires the precise manipulation\nof quantum fluids such as superfluid helium or atomic Bose-Einstein\ncondensates. In this work we demonstrate the turbulent dynamics of a 2D quantum\nfluid of exciton-polaritons, hybrid light-matter quasiparticles, both by\nmeasuring the kinetic energy spectrum and showing the onset of vortex\nclustering. We demonstrate that the formation of clusters of quantum vortices\nis triggered by the increase of the incompressible kinetic energy per vortex,\nshowing the tendency of the vortex-gas towards highly excited configurations\ndespite the dissipative nature of our system. These results lay the basis for\nthe investigations of quantum turbulence in two-dimensional fluids of light."
    },
    {
        "anchor": "Frustration induced quasi-many-body localization without disorder: Motivated by the question of whether disorder is a prerequisite for\nlocalization to occur in quantum many-body systems, we study a frustrated\none-dimensional spin chain, which supports localized many-body eigenstates in\nthe absence of disorder. When the system is prepared in an initial state with\none domain wall, it exhibits characteristic signatures of quasi-many-body\nlocalization (quasi- MBL), including initial state memory retention, an\nexponentially increasing lifetime with enlarging the size of the system, a\nlogarithmic growth of entanglement entropy, and a logarithmic light cone of an\nout-of-time-ordered correlator. We further show that the localized many-body\neigenstates can be manipulated as pseudospin-1/2s and thus could potentially\nserve as qubits. Our findings suggest a new route of using frustration to\naccess quasi-MBL and preserve quantum coherence.",
        "positive": "Vortex-hole duality: a unified picture of weak and strong-coupling\n  regimes of bosonic ladders with flux: Two-leg bosonic ladders with flux harbor a remarkable vortex-hole duality\nbetween the weak-coupling vortex lattice superfluids and strong-coupling\ncharge-density-wave crystals. The strong-coupling crystalline states, which are\nrealized in the vicinity of $\\pi$-flux, are independent of particle statistics,\nand are related with the incompressible fractional quantum Hall states in the\nthin-cylinder limit. These fully gapped ground states, away of $\\pi$-flux,\ndevelop nonzero chiral (spin) currents. Contact-interacting quantum gases\npermit exploration of this vortex-hole duality in experiments."
    },
    {
        "anchor": "Quantized transport induced by topology transfer between coupled\n  one-dimensional lattice systems: We show that a topological pump in a one-dimensional (1D) insulator can\ninduce a strictly quantized transport in an auxiliary chain of non-interacting\nfermions weakly coupled to the first. The transported charge is determined by\nan integer topological invariant of the ficticious Hamiltonian of the\ninsulator, given by the covariance matrix of single-particle correlations. If\nthe original system consists of non-interacting fermions, this number is\nidentical to the TKNN (Thouless, Kohmoto, Nightinghale, den Nijs) invariant of\nthe original system and thus the coupling induces a transfer of topology to the\nauxiliary chain. When extended to particles with interactions, for which the\nTKNN number does not exist, the transported charge in the auxiliary chain\ndefines a topological invariant for the interacting system. In certain cases\nthis invariant agrees with the many-body generalization of the TKNN number\nintroduced by Niu, Thouless, and Wu (NTW). We illustrate the topology transfer\nto the auxiliary system for the Rice-Mele model of non-interacting fermions at\nhalf filling and the extended superlattice Bose-Hubbard model at quarter\nfilling. In the latter case the induced charge pump is fractional.",
        "positive": "Superfluid critical velocity of an elongated harmonically trapped\n  Bose-Einstein condensate: We numerically model experiments on the superfluid critical velocity of an\nelongated, harmonically trapped Bose-Einstein condensate as reported by [P.\nEngels and C. Atherton, Phys. Rev. Lett. 99, 160405 (2007)]. These experiments\nswept an obstacle formed by an optical dipole potential through the long axis\nof the condensate at constant velocity. Their results found an increase in the\nresulting density fluctuations of the condensate above an obstacle velocity of\n$v\\approx 0.3$ mm/s, suggestive of a superfluid critical velocity substantially\nless than the average speed of sound. However, our analysis shows that the that\nthe experimental observations of Engels and Atherton are in fact consistent\nwith a superfluid critical velocity equal to the local speed of sound. We\nconstruct a model of energy transfer to the system based on the local density\napproximation to explain the experimental observations, and propose and\nsimulate experiments that sweep potentials through harmonically trapped\ncondensates at a constant fraction of the local speed of sound. We find that\nthis leads to a sudden onset of excitations above a critical fraction, in\nagreement with the Landau criterion for superfluidity."
    },
    {
        "anchor": "Topology and its detection in a dissipative Aharonov-Bohm chain: In a recent experiment, a dissipative Aharaonov-Bohm (AB) chain was\nimplemented in the momentum space of a Bose-Einstein condensate. Formed by a\nseries of dissipative AB rings threaded by synthetic magnetic flux, the chain\nexhibits the non-Hermitian skin effect, necessitating the non-Bloch band theory\nto account for its topology. In this work, we systematically characterize\ntopological features of the dissipative AB chain, particularly beyond the\nexperimentally realized parameter regime. Further, we show that an\natom-injection spectroscopy is not only capable of revealing topological edge\nstates, as has been demonstrated in the experiment, but also the general band\nstructure of the system. We then discuss alternative dynamic detection schemes\nfor the topological edge states. Given the generality of the model and the\ndetection schemes, our work is helpful to future study of topological models\nwith non-Hermitian skin effects across a variety of quantum simulators.",
        "positive": "Breakdown of Anderson localization in the transport of Bose-Einstein\n  condensates through one-dimensional disordered potentials: We study the transport of an interacting Bose--Einstein condensate through a\n1D correlated disorder potential. We use for this purpose the truncated Wigner\nmethod, which is, as we show, corresponding to the diagonal approximation of a\nsemiclassical van Vleck-Gutzwiller representation of this many-body transport\nprocess. We also argue that semiclassical corrections beyond this diagonal\napproximation are vanishing under disorder average, thus confirming the\nvalidity of the truncated Wigner method in this context. Numerical calculations\nshow that, while for weak atom-atom interaction strength Anderson localization\nis preserved with a slight modification of the localization length, for larger\ninteraction strenghts a crossover to a delocalized regime exists due to\ninelastic scattering. In this case, the transport is fully incoherent."
    },
    {
        "anchor": "Dynamics of inertial vortices in multi-component Bose-Einstein\n  condensates: With use of the nonlinear Schr{\\\"o}dinger (or Gross-Pitaevskii) equation with\nstrong repulsive cubic nonlinearity, dynamics of multi-component Bose-Einstein\ncondensates (BECs) with a harmonic trap in 2 dimensions is investigated beyond\nthe Thomas-Fermi regime. In the case when each component has a single vortex,\nwe obtain an effective nonlinear dynamics for vortex cores (particles). The\nparticles here acquire the inertia, in marked contrast to the standard theory\nof point vortices widely known in the usual hydrodynamics. The effective\ndynamics is equivalent to that of charged particles under a strong spring force\nand in the presence of Lorentz force with the uniform magnetic field. The\ninter-particle (vortex-vortex) interaction is singularly-repulsive and\nshort-ranged with its magnitude decreasing with increasing distance of the\ncenter of mass from the trapping center. \"Chaos in the three-body problem\" in\nthe three vortices system can be seen, which is not expected in the\ncorresponding point vortices without inertia in 2 dimensions.",
        "positive": "Zero-temperature equation of state of mass-imbalanced resonant Fermi\n  gases: We calculate the zero-temperature equation of state of mass-imbalanced\nresonant Fermi gases in an ab initio fashion, by implementing the recent\nproposal of imaginary-valued mass difference to bypass the sign problem in\nlattice Monte Carlo calculations. The fully non-perturbative results thus\nobtained are analytically continued to real mass imbalance to yield the\nphysical equation of state, providing predictions for upcoming experiments with\nmass-imbalanced atomic Fermi gases. In addition, we present an exact relation\nfor the rate of change of the equation of state at small mass imbalances,\nshowing that it is fully determined by the energy of the mass-balanced system."
    },
    {
        "anchor": "Variance of a Trapped Bose-Einstein Condensate: The ground state of a Bose-Einstein condensate in a two-dimensional trap\npotential is analyzed numerically at the infinite-particle limit. It is shown\nthat the anisotropy of the many-particle position variance along the $x$ and\n$y$ axes can be opposite when computed at the many-body and mean-field levels\nof theory. This is despite the system being $100\\%$ condensed, and the\nrespective energies per particle and densities per particle to coincide.",
        "positive": "Finite size effect on Bose-Einstein condensate mixtures in improved\n  Hartree-Fock approximation: Using Cornwal-Jackiw-Tomboulis effective potential approach we found that at\nzero temperature, in improved Hartree-Fock approximation, the effective masses\nand order parameters of a two component Bose-Einstein condensates confined\nbetween two parallel plates strongly depend on the distance between two slabs.\nThe Casimir force is also considered in this approximation and shown that this\nforce differs from zero in limit of strong segregation."
    },
    {
        "anchor": "Fragmented condensation in Bose-Hubbard trimers with tunable tunnelling: We consider a Bose-Hubbard trimer, i.e. an ultracold Bose gas populating\nthree quantum states. The latter can be either different sites of a triple-well\npotential or three internal states of the atoms. The bosons can tunnel between\ndifferent states with variable tunnelling strength between two of them. This\nwill allow us to study; i) different geometrical configurations, i.e. from a\nclosed triangle to three aligned wells and ii) a triangular configuration with\na $\\pi$-phase, i.e. by setting one of the tunnellings negative. By solving the\ncorresponding three-site Bose-Hubbard Hamiltonian we obtain the ground state of\nthe system as a function of the trap topology. We characterise the different\nground states by means of the coherence and entanglement properties. For small\nrepulsive interactions, fragmented condensates are found for the $\\pi$-phase\ncase. These are found to be robust against small variations of the tunnelling\nin the small interaction regime. A low-energy effective many-body Hamiltonian\nrestricted to the degenerate manifold provides a compelling description of the\n$\\pi$-phase degeneration and explains the low-energy spectrum as excitations of\ndiscrete semifluxon states.",
        "positive": "Realization of Two-Dimensional Spin-orbit Coupling for Bose-Einstein\n  Condensates: Cold atoms with laser-induced spin-orbit (SO) interactions provide intriguing\nnew platforms to explore novel quantum physics beyond natural conditions of\nsolids. Recent experiments demonstrated the one-dimensional (1D) SO coupling\nfor boson and fermion gases. However, realization of 2D SO interaction, a much\nmore important task, remains very challenging. Here we propose and\nexperimentally realize, for the first time, 2D SO coupling and topological band\nwith $^{87}$Rb degenerate gas through a minimal optical Raman lattice scheme,\nwithout relying on phase locking or fine tuning of optical potentials. A\ncontrollable crossover between 2D and 1D SO couplings is studied, and the SO\neffects and nontrivial band topology are observed by measuring the atomic cloud\ndistribution and spin texture in the momentum space. Our realization of 2D SO\ncoupling with advantages of small heating and topological stability opens a\nbroad avenue in cold atoms to study exotic quantum phases, including the\nhighly-sought-after topological superfluid phases."
    },
    {
        "anchor": "Impurity Scattering in a Bose-Einstein Condensate at finite temperature: We consider the effects of finite temperature on the scattering of impurity\natoms in a BoseEinstein condensate, showing that the scattering rate is\nenhanced by the thermal atoms. Collisions can increase or decrease the impurity\nenergy. Below the Landau velocity only the first process occurs, i.e., the\ncollisions cool the condensate. Above the critical velocity the dissipative\ncollisions prevail over the cooling ones for sufficiently low temperatures.\nThese considerations are applied to a recent experiment.",
        "positive": "Limitation of the Lee-Huang-Yang interaction in forming a self-bound\n  state in Bose-Einstein condensates: The perturbative Lee-Huang-Yang (LHY) interaction proportional to $n^{3/2}$,\nwhere $n$ is the density, creates an infinitely repulsive potential at the\ncenter of a Bose-Einstein condensate (BEC) with net attraction, which stops the\ncollapse to form a self-bound state in a dipolar BEC and in a binary BEC.\nHowever, recent microscopic calculations of the non-perturbative\nbeyond-mean-field (BMF) interaction indicate that the LHY interaction %with the\n$n^{3/2}$ term is valid only for very small values of gas parameter $x$. We\nshow that a realistic non-perturbative BMF interaction can stop collapse and\nform a self-bound state only in a weakly attractive binary BEC with small $x$\nvalues ($x\\lessapprox 0.01$), whereas the perturbative LHY interaction stops\ncollapse for all attractions. We demonstrate these aspects using an analytic\nBMF interaction with appropriate weak-coupling LHY and strong coupling limits."
    },
    {
        "anchor": "Exact methods in analysis of nonequilibrium dynamics of integrable\n  models: application to the study of correlation functions in nonequilibrium\n  1D Bose gas: In this paper we study nonequilibrium dynamics of one dimensional Bose gas\nfrom the general perspective of dynamics of integrable systems. After outlining\nand critically reviewing methods based on inverse scattering transform,\nintertwining operators, q-deformed objects, and extended dynamical conformal\nsymmetry, we focus on the form-factor based approach. Motivated by possible\napplications in nonlinear quantum optics and experiments with ultracold atoms,\nwe concentrate on the regime of strong repulsive interactions. We consider\ndynamical evolution starting from two initial states: a condensate of particles\nin a state with zero momentum and a condensate of particles in a gaussian\nwavepacket in real space. Combining the form-factor approach with the method of\nintertwining operator we develop a numerical procedure which allows explicit\nsummation over intermediate states and analysis of the time evolution of\nnon-local density-density correlation functions. In both cases we observe a\ntendency toward formation of crystal-like correlations at intermediate time\nscales.",
        "positive": "Motional decoherence in ultracold Rydberg atom quantum simulators of\n  spin models: Ultracold Rydberg atom arrays are an emerging platform for quantum simulation\nand computing. However, decoherence in these systems remains incompletely\nunderstood. Recent experiments [Guardado-Sanchez et al. Phys. Rev. X 8, 021069\n(2018)] observed strong decoherence in the quench and longitudinal-field-sweep\ndynamics of two-dimensional Ising models realized with Lithium-6 Rydberg atoms\nin optical lattices. This decoherence was conjectured to arise from spin-motion\ncoupling. Here we show that spin-motion coupling indeed leads to decoherence in\nqualitative, and often quantitative, agreement with the experimental data,\ntreating the difficult spin-motion coupled problem using the discrete truncated\nWigner approximation method. We also show that this decoherence will be an\nimportant factor to account for in future experiments with Rydberg atoms in\noptical lattices and microtrap arrays, and discuss methods to mitigate the\neffect of motion, such as using heavier atoms or deeper traps."
    },
    {
        "anchor": "Quantum gas microscopy of an attractive Fermi-Hubbard system: The attractive Fermi-Hubbard model is the simplest theoretical model for\nstudying pairing and superconductivity of fermions on a lattice. Although its\ns-wave pairing symmetry excludes it as a microscopic model for high-temperature\nsuperconductivity, it exhibits much of the relevant phenomenology, including a\nshort-coherence length at intermediate coupling and a pseudogap regime with\nanomalous properties. Here we study an experimental realization of this model\nusing a two-dimensional (2D) atomic Fermi gas in an optical lattice. Our\nsite-resolved measurements on the normal state reveal checkerboard\ncharge-density-wave correlations close to half-filling. A \"hidden\" SU(2)\npseudo-spin symmetry of the Hubbard model at half-filling guarantees superfluid\ncorrelations in our system, the first evidence for such correlations in a\nsingle-band Hubbard system of ultracold fermions. Compared to the paired atom\nfraction, we find the charge-density-wave correlations to be a much more\nsensitive thermometer, useful for optimizing cooling into superfluid phases in\nfuture experiments.",
        "positive": "Thermalized Abrikosov lattices from decaying turbulence in rotating BECs: We study the long-time decay of rotating turbulence in Bose-Einstein\ncondensates (BECs). We consider the Gross-Pitaevskii equation in a rotating\nframe of reference, and review different formulations for the Hamiltonian of a\nrotating BEC. We discuss how the energy can be decomposed, and present a method\nto generate out-of-equilibrium initial conditions. We also present a method to\ngenerate finite-temperature states of rotating BECs compatible with the\nCanonical or the Grand canonical ensembles. Finally, we integrate numerically\nrotating BECs in cigar-shaped traps. A transition is found in the system\ndynamics as the rotation rate is increased, with a final state of the decay of\nthe turbulent flow compatible with an Abrikosov lattice in a finite-temperature\nthermalized state."
    },
    {
        "anchor": "Self-ordered Time Crystals: Periodic Temporal Order Under Quasiperiodic\n  Driving: A discrete time crystal is a remarkable non-equilibrium phase of matter\ncharacterized by persistent sub-harmonic response to a periodic drive.\nMotivated by the question of whether such time-crystalline order can persist\nwhen the drive becomes aperiodic, we investigate the dynamics of a\nLipkin-Meshkov-Glick model under quasiperiodic kicking. Intriguingly, this\ninfinite-range-interacting spin chain can exhibit long-lived periodic\noscillations when the kicking amplitudes are drawn from the Thue-Morse sequence\n(TMS). We dub this phase a ``self-ordered time crystal\" (SOTC), and demonstrate\nthat our model hosts at least two qualitatively distinct prethermal SOTC\nphases. These SOTCs are robust to various perturbations, and they originate\nfrom the interplay of long-range interactions and the recursive structure of\nthe TMS. Our results suggest that quasiperiodic driving protocols can provide a\npromising route for realizing novel non-equilibrium phases of matter in\nlong-range interacting systems.",
        "positive": "Transport measurement of the orbital Kondo effect with ultracold atoms: The Kondo effect in condensed-matter systems manifests itself most sharply in\ntheir transport measurements. Here we propose an analogous transport signature\nof the orbital Kondo effect realized with ultracold atoms. Our system consists\nof imbalanced Fermi seas of two components of fermions and an impurity atom of\ndifferent species which is confined by an isotropic potential. We first apply a\n\\pi/2 pulse to transform two components of fermions into two superposition\nstates. Their interactions with the impurity atom then cause a \"transport\" of\nfermions from majority to minority superposition states, whose numbers can be\nmeasured after applying another 3\\pi/2 pulse. In particular, when the\ninteraction of one component of fermions with the impurity atom is tuned close\nto a confinement-induced p-wave or higher partial-wave resonance, the resulting\nconductance is shown to exhibit the Kondo signature, i.e., universal\nlogarithmic growth by lowering the temperature. The proposed transport\nmeasurement will thus provide a clear evidence of the orbital Kondo effect\naccessible in ultracold atom experiments and pave the way for developing new\ninsights into Kondo physics."
    },
    {
        "anchor": "Homogeneous one-dimensional Bose-Einstein Condensate in the Bogoliubov's\n  Regime: We analyze the corrections caused by finite size effects upon the ground\nstate properties of a homogeneous one-dimensional Bose-Einstein condensate. We\nassume from the very beginning that the Bogoliubov's formalism is valid and\nconsequently we show that in order to obtain a well defined ground state\nproperties, finite size effects of the system must be taken into account.\nIndeed, the formalism described in the present work allows to recover the usual\nproperties related to the ground state of a homogeneous one-dimensional\nBose-Einstein condensate but corrected by finite size effects of the system.\nFinally, this scenario allows us to analyze the sensitivity of the system when\nthe Bogoliubov's regime is valid and when finite size effects are present.\nThese facts open the possibility to apply these ideas to more realistic\nscenarios, e.g., low-dimensional trapped Bose-Einstein condensates.",
        "positive": "Effects of interactions on Bose-Einstein condensation of an atomic gas: The phase transition to a Bose-Einstein condensate is unusual in that it is\nnot necessarily driven by inter-particle interactions but can occur in an ideal\ngas as a result of a purely statistical saturation of excited states. However,\ninteractions are necessary for any system to reach thermal equilibrium and so\nare required for condensation to occur in finite time. In this Chapter we\nreview the role of interactions in Bose-Einstein condensation, covering both\ntheory and experiment. We focus on measurements performed on harmonically\ntrapped ultracold atomic gases, but also discuss how these results relate to\nthe uniform-system case, which is more theoretically studied and also more\nrelevant for other experimental systems.\n  We first consider interaction strengths for which the system can be\nconsidered sufficiently close to equilibrium to measure thermodynamic\nbehaviour. In particular we discuss the effects of interactions both on the\nmechanism of condensation (namely the saturation of the excited states) and on\nthe critical temperature at which condensation occurs. We then discuss in more\ndetail the conditions for the equilibrium thermodynamic measurements to be\npossible, and the non-equilibrium phenomena that occur when these conditions\nare controllably violated by tuning the strength of interactions in the gas."
    },
    {
        "anchor": "Collisionally inhomogeneous Bose-Einstein condensates with a linear\n  interaction gradient: We study the evolution of a collisionally inhomogeneous matter wave in a\nspatial gradient of the interaction strength. Starting with a Bose-Einstein\ncondensate with weak repulsive interactions in quasi-one-dimensional geometry,\nwe monitor the evolution of a matter wave that simultaneously extends into\nspatial regions with attractive and repulsive interactions. We observe the\nformation and the decay of soliton-like density peaks, counter-propagating\nself-interfering wave packets, and the creation of cascades of solitons. The\nmatter-wave dynamics is well reproduced in numerical simulations based on the\nnonpolynomial Schroedinger equation with three-body loss, allowing us to better\nunderstand the underlying behaviour based on a wavelet transformation. Our\nanalysis provides new understanding of collapse processes for solitons, and\nopens interesting connections to other nonlinear instabilities.",
        "positive": "The Higgs mode in a superfluid of Dirac fermions: We study the Higgs amplitude mode in the s-wave superfluid state on the\nhoneycomb lattice inspired by recent cold atom experiments. We consider the\nattractive Hubbard model and focus on the vicinity of a quantum phase\ntransition between semi-metal and superfluid phases. On either side of the\ntransition, we find collective mode excitations that are stable against decay\ninto quasiparticle-pairs. In the semi-metal phase, the collective modes have\n\"Cooperon\" and exciton character. These modes smoothly evolve across the\nquantum phase transition, and become the Anderson-Bogoliubov mode and the Higgs\nmode of the superfluid phase. The collective modes are accommodated within a\nwindow in the quasiparticle-pair continuum, which arises as a consequence of\nthe linear Dirac dispersion on the honeycomb lattice, and allows for sharp\ncollective excitations. Bragg scattering can be used to measure these\nexcitations in cold atom experiments, providing a rare example wherein\ncollective modes can be tracked across a quantum phase transition."
    },
    {
        "anchor": "Feedback cooling Bose gases to quantum degeneracy: Degenerate quantum gases are instrumental in advancing many-body quantum\nphysics and underpin emerging precision sensing technologies. All\nstate-of-the-art experiments use evaporative cooling to achieve the ultracold\ntemperatures needed for quantum degeneracy, yet evaporative cooling is\nextremely lossy: more than 99.9% of the gas is discarded. Such final particle\nnumber limitations constrain imaging resolution, gas lifetime, and applications\nleveraging macroscopic quantum coherence. Here we show that atomic Bose gases\ncan be cooled to quantum degeneracy using real-time feedback, an entirely new\nmethod that does not suffer the same limitations as evaporative cooling.\nThrough novel quantum-field simulations and scaling arguments, we demonstrate\nthat an initial low-condensate-fraction thermal Bose gas can be cooled to a\nhigh-purity Bose-Einstein condensate (BEC) by feedback control, with\nsubstantially lower atomic loss than evaporative cooling. Advantages of\nfeedback cooling are found to be robust to imperfect detection, finite\nresolution of the control and measurement, time delay in the control loop, and\nspontaneous emission. Using feedback cooling to create degenerate sources with\nhigh coherence and low entropy enables new capabilities in precision\nmeasurement, atomtronics, and few- and many-body quantum physics.",
        "positive": "Vortices in spin-0 superfluids carry magnetic flux: Vortices in spin-$0$ superfluids generically carry magnetic fields inside\ntheir cores, so that even neutral superfluid vortices may be thought of as\nmagnetic flux tubes. We give a systematic analysis of this `vortex magnetic\neffect' using effective field theory, clarifying earlier literature on the\nsubject. Our analysis shows that in superfluid Helium-$4$ the vortex magnetic\neffect may be large enough to be experimentally detectable."
    },
    {
        "anchor": "Imaging trapped quantum gases by off-axis holography: We present a dispersive imaging method for trapped quantum gases based on\ndigital off-axis holography. Both phase delay and intensity of the probe field\nare determined from the same image. Due to the heterodyne gain inherent to the\nholographic method it is possible to retrieve the phase delay induced by the\natoms at probe beam doses two orders of magnitude lower than phase-contrast\nimaging methods. Using the full field of the probe beam we numerically correct\nfor image defocusing.",
        "positive": "Real-Time Ginzburg-Landau Theory for Bosons in Optical Lattices: Within the Schwinger-Keldysh formalism we derive a Ginzburg-Landau theory for\nthe Bose-Hubbard model which describes the real-time dynamics of the complex\norder parameter field. Analyzing the excitations in the vicinity of the quantum\nphase transitions it turns out that particle/hole dispersions in the Mott phase\nmap continuously onto corresponding amplitude/phase excitations in the\nsuperfluid phase. Furthermore, in the superfluid phase we find a sound mode,\nwhich is in accordance with recent Bragg spectroscopy measurements in the\nBogoliubov regime, as well as an additional gapped mode, which seems to have\nbeen detected via lattice modulation."
    },
    {
        "anchor": "Impurity in a Bose-Einstein condensate in a double well: We compare and contrast the mean-field and many-body properties of a\nBose-Einstein condensate trapped in a double well potential with a single\nimpurity atom. The mean-field solutions display a rich structure of\nbifurcations as parameters such as the boson-impurity interaction strength and\nthe tilt between the two wells are varied. In particular, we study a pitchfork\nbifurcation in the lowest mean-field stationary solution which occurs when the\nboson-impurity interaction exceeds a critical magnitude. This bifurcation,\nwhich is present for both repulsive and attractive boson-impurity interactions,\ncorresponds to the spontaneous formation of an imbalance in the number of\nparticles between the two wells. If the boson-impurity interaction is large,\nthe bifurcation is associated with the onset of a Schroedinger cat state in the\nmany-body ground state. We calculate the coherence and number fluctuations\nbetween the two wells, and also the entanglement entropy between the bosons and\nthe impurity. We find that the coherence can be greatly enhanced at the\nbifurcation.",
        "positive": "Geometric phases of a vortex in a superfluid: We consider geometric phases of mobile quantum vortices in superfluid\nBose-Einstein condensates. Haldane and Wu [Phys. Rev. Lett. 55, 2887 (1985)]\nshowed that the geometric phase, $\\gamma_{\\mathcal C}=2\\pi N_{\\mathcal C}$, of\nsuch a vortex is determined by the number of condensate atoms $N_{\\mathcal C}$\nenclosed by the vortex trajectory. Considering an experimentally realistic\nfreely orbiting vortex leads to an apparent disagreement with this prediction.\nWe resolve it using the superfluid electrodynamics picture, which allows us to\nidentify two additional contributions to the measured geometric phase; (i) a\ntopologically protected edge current of vortices at the condensate boundary,\nand (ii) a superfluid displacement current. Our results generalise to, and pave\nthe way for experimental measurements of vortex geometric phases using scalar\nand spinor Bose--Einstein condensates, and superfluid Fermi gases."
    },
    {
        "anchor": "Non-Bloch topological invariants in a non-Hermitian domain-wall system: We study non-Bloch bulk-boundary correspondence in a non-Hermitian\nSu-Schieffer-Heeger model in a domain-wall configuration where the left and\nright bulks have different parameters. Focusing on the case where chiral\nsymmetry is still conserved, we show that non-Hermitian skin effects of bulk\nstates persist in the system, while the definition of the non-Bloch winding\nnumber of either bulk depends on parameters on both sides of the boundary.\nUnder these redefined non-Bloch topological invariants, we confirm non-Bloch\nbulk-boundary correspondence under the domain-wall configuration, which\nexemplifies the impact of boundary conditions in non-Hermitian topological\nsystems.",
        "positive": "Generation of density waves in dipolar quantum gases by time-periodic\n  modulation of atomic interactions: We study the emergence of density waves in dipolar Bose-Einstein condensates\n(BEC) when the strength of dipole-dipole atomic interactions is periodically\nvaried in time. The proposed theoretical model, based on the evolution of small\nperturbations of the background density, allows to compute the growth rate of\ninstability (gain factor) for arbitrary set of input parameters, thus to\nidentify the regions of instability against density waves. We find that among\nother modes of the system the roton mode is most effectively excited due to the\ncontribution of sub-harmonics of the excitation frequency. The frequency of\ntemporal oscillations of emerging density waves coincides with the half of the\ndriving frequency, this being the hallmark of the parametric resonance, is\ncharacteristic to Faraday waves. The possibility to create density waves in\ndipolar BECs, which can persist after the emergence, has been demonstrated. The\nexistence of a stationary spatially periodic solution of the nonlocal\nGross-Pitaevskii equation has been discussed. The effect of three-body atomic\ninteractions, which is relevant to condensates with increased density, upon the\nproperties of emerging waves has been analyzed too. Significant modification of\nthe condensate's excitation spectrum owing to three-body effects is shown."
    },
    {
        "anchor": "Many-body physics in the classical-field description of a degenerate\n  Bose gas: The classical-field formalism has been widely applied in the calculation of\nnormal correlation functions, and the characterization of condensation, in\nfinite-temperature Bose gases. Here we discuss the extension of this method to\nthe calculation of more general correlations, including the so-called anomalous\ncorrelations of the field, without recourse to symmetry-breaking assumptions.\nOur method is based on the introduction of U(1)-symmetric classical-field\nvariables analogous to the modified quantum ladder operators of\nnumber-conserving approaches to the degenerate Bose gas, and allows us to\nrigorously quantify the anomalous and non-Gaussian character of the field\nfluctuations. We compare our results for anomalous correlation functions with\nthe predictions of mean-field theories, and demonstrate that the nonlinear\nclassical-field dynamics incorporate a full description of many-body processes\nwhich modify the effective mean-field potentials experienced by condensate and\nnoncondensate atoms. We discuss the role of these processes in shaping the\ncondensate mode, and thereby demonstrate the consistency of the Penrose-Onsager\ndefinition of the condensate orbital in the classical-field equilibrium. We\nconsider the contribution of various noncondensate-field correlations to the\noverall suppression of density fluctuations and interactions in the field, and\ndemonstrate the distinct roles of phase and density fluctuations in the\ntransition of the field to the normal phase.",
        "positive": "Energy, contact, and density profiles of one-dimensional fermions in a\n  harmonic trap via non-uniform lattice Monte Carlo: We determine the ground-state energy and Tan's contact of attractively\ninteracting few-fermion systems in a one-dimensional harmonic trap, for a range\nof couplings and particle numbers. Complementing those results, we show the\ncorresponding density profiles. The calculations were performed with a new\nlattice Monte Carlo approach based on a non-uniform discretization of space,\ndefined via Gauss-Hermite quadrature points and weights. This particular\ncoordinate basis is natural for systems in harmonic traps, and can be\ngeneralized to traps of other shapes. In all cases, it yields a\nposition-dependent coupling and a corresponding non-uniform\nHubbard-Stratonovich transformation. The resulting path integral is performed\nwith hybrid Monte Carlo as a proof of principle for calculations at finite\ntemperature and in higher dimensions. We present results for N=4,...,20\nparticles (although the method can be extended beyond that) to cover the range\nfrom few- to many-particle systems. This method is also exact up to statistical\nand systematic uncertainties, which we account for -- and thus also represents\nthe first ab initio calculation of this system, providing a benchmark for other\nmethods and a prediction for ultracold-atom experiments."
    },
    {
        "anchor": "Quantum gas mixtures in different correlation regimes: We present a many-body description for two-component ultracold bosonic gases\nwhen one of the species is in the weakly interacting regime and the other is\neither weakly or strongly interacting. In the one-dimensional limit the latter\ncase system is a hybrid in which a Tonks-Girardeau gas is immersed in a\nBose-Einstein condensate, which is an example of a new class of quantum system\ninvolving a tunable, superfluid environment. We describe the process of phase\nseparation microscopically and semiclassically in both situations and show that\nthe quantum correlations are maintained in the separated phase.",
        "positive": "Soliton-based matter wave interferometer: We consider a matter wave bright soliton interferometer composed of a\nharmonic potential trap with a Rosen--Morse barrier at its center on which an\nincident soliton collides and splits into two solitons. These two solitons\nrecombine after a dipole oscillation in the trap at the position of the\nbarrier. We focus on the characterization of the splitting process in the case\nin which the reflected and transmitted solitons have the same number of atoms.\nWe obtain that the velocity of the split solitons strongly depends on the\nnonlinearity and on the width of the barrier and that the reflected soliton is\nin general slower than the transmitted one. Also, we study the phase difference\nacquired between the two solitons during the splitting and we fit\nsemi-analytically the main dependences with the velocity of the incident\nsoliton, the nonlinearity and the width of the barrier. The implementation of\nthe full interferometer sequence is tested by means of the phase imprinting\nmethod."
    },
    {
        "anchor": "Aspects of Bose-Einstein condensation in a charged boson system over the\n  dielectric surface: We study theoretically a gas consisting of charged bosons (ions) over the\nflat dielectric surface at low temperatures and its tendency to form a state\nwith a Bose-Einstein condensate. For the stability of a system, an additional\nexternal electric field, which keeps charges at the dielectric surface, is\nintroduced. The formalism is developed in the framework of a\nself-consistent-field approach, which combines the quasiclassical description\nin terms of the Wigner distribution functions and the quantum-mechanical\napproach by employing the Gross-Pitaevskii equation. We predict a formation of\nthe state with a Bose-Einstein condensate and determine the near-critical\nphysical characteristics of the system. It is shown that the thermal and\ncondensate components become spatially separated under these conditions. We\ndiscuss the limitations of the developed semiclassical approach and prospects\nfor the pure quantum-mechanical treatment of the problem.",
        "positive": "Non-Abelian spin singlet states of two-component Bose gases in\n  artificial gauge fields: We study strongly correlated phases of a pseudo-spin-1/2 Bose gas in an\nartificial gauge field using the exact diagonalization method. The atoms are\nconfined in two dimensions and interact via a two-body contact potential. In\nAbelian gauge fields, pseudo-spin singlets are favored by pseudo-spin\nindependent interactions. We find a series of incompressible phases at fillings\n\\nu=2k/3. By comparison with the non-Abelian spin singlet (NASS) states,\nconstructed as zero-energy eigenstates of a (k+1)-body contact interaction, we\nclassify the non-trivial topology of the states. An additional spin-orbit\ncoupling is shown to switch between NASS-like states and spin-polarized phases\nfrom the Read-Rezayi series."
    },
    {
        "anchor": "Critical Energy Dissipation in a Binary Superfluid Gas by a Moving\n  Magnetic Obstacle: We study the critical energy dissipation in an atomic superfluid gas with two\nsymmetric spin components by an oscillating magnetic obstacle. Above a certain\ncritical oscillation frequency, spin-wave excitations are generated by the\nmagnetic obstacle, demonstrating the spin superfluid behavior of the system.\nWhen the obstacle is strong enough to cause density perturbations via local\nsaturation of spin polarization, half-quantum vortices (HQVs) are created for\nhigher oscillation frequencies, which reveals the characteristic evolution of\ncritical dissipative dynamics from spin-wave emission to HQV shedding. Critical\nHQV shedding is further investigated using a pulsed linear motion of the\nobstacle, and we identify two critical velocities to create HQVs with different\ncore magnetization.",
        "positive": "Finite-temperature quantum fluctuations in two-dimensional Fermi\n  superfluids: In two-dimensional systems with a continuous symmetry the\nMermin-Wagner-Hohenberg theorem precludes spontaneous symmetry breaking and\ncondensation at finite temperature. The Berezinskii-Kosterlitz-Thouless\ncritical temperature marks the transition from a superfluid phase characterized\nby quasi-condensation and algebraic long-range order to a normal phase, where\nvortex proliferation completely destroys superfluidity. As opposed to\nconventional off-diagonal long-range order typical of three-dimensional\nsuperfluid systems, algebraic long-range order is driven by quantum and thermal\nfluctuations strongly enhanced in reduced dimensionality. Motivated by this\nunique scenario and by the very recent experimental realization of trapped\nquasi-two-dimensional fermionic clouds, we include one-loop Gaussian\nfluctuations in the theoretical description of resonant Fermi superfluids in\ntwo dimensions demonstrating that first sound, second sound and also critical\ntemperature are strongly renormalized, away from their mean-field values. In\nparticular, we prove that in the intermediate and strong coupling regimes these\nquantities are radically different when Gaussian fluctuations are taken into\naccount. Our one-loop theory shows good agreement with very recent experimental\ndata on the Berezinskii-Kosterlitz-Thouless critical temperature [Phys. Rev.\nLett. 115, 010401 (2015)] and on the first sound velocity, giving novel\npredictions for the second sound as a function of interaction strength and\ntemperature, open for experimental verification."
    },
    {
        "anchor": "Vortex detection in atomic Bose-Einstein condensates using neural\n  networks trained on synthetic images: Quantum vortices in atomic Bose-Einstein condensates (BECs) are topological\ndefects characterized by quantized circulation of particles around them. In\nexperimental studies, vortices are commonly detected by time-of-flight imaging,\nwhere their density-depleted cores are enlarged. In this work, we describe a\nmachine learning-based method for detecting vortices in experimental BEC\nimages, particularly focusing on turbulent condensates containing irregularly\ndistributed vortices. Our approach employs a convolutional neural network (CNN)\ntrained solely on synthetic simulated images, eliminating the need for manual\nlabeling of the vortex positions as ground truth. We find that the CNN achieves\naccurate vortex detection in real experimental images, thereby facilitating\nanalysis of large experimental datasets without being constrained by specific\nexperimental conditions. This novel approach represents a significant\nadvancement in studying quantum vortex dynamics and streamlines the analysis\nprocess in the investigation of turbulent BECs.",
        "positive": "Density redistribution effects in fermionic optical lattices: We simulate a one dimensional fermionic optical lattice to analyse heating\ndue to non-adiabatic lattice loading. Our simulations reveal that, similar to\nthe bosonic case, density redistribution effects are the major cause of heating\nin harmonic traps. We suggest protocols to modulate the local density\ndistribution during the process of lattice loading, in order to reduce the\nexcess energy. Our numerical results confirm that linear interpolation of the\ntrapping potential and/or the interaction strength is an efficient method of\ndoing so, bearing practical applications relevant to experiments."
    },
    {
        "anchor": "Dynamics of spin and density fluctuations in strongly interacting\n  few-body systems: The decoupling of spin and density dynamics is a remarkable feature of\nquantum one-dimensional many-body systems. In a few-body regime, however,\nlittle is known about this phenomenon. To address this problem, we study the\ntime evolution of a small system of strongly interacting fermions after a\nsudden change in the trapping geometry. We show that, even at the few-body\nlevel, the excitation spectrum of this system presents separate signatures of\nspin and density dynamics. Moreover, we describe the effect of considering\nadditional internal states with SU(N) symmetry, which ultimately leads to the\nvanishing of spin excitations in a completely balanced system.",
        "positive": "Fluctuation assisted collapses of Bose-Einstein condensates: We study the collapse dynamics of a Bose-Einstein condensate subjected to a\nsudden change of the scattering length to a negative value by adopting the\nself-consistent Gaussian state theory for mixed states. Compared to the\nGross-Pitaevskii and the Hartree-Fock-Bogoliubov approaches, both fluctuations\nand three-body loss are properly treated in our theory. We find a new type of\ncollapse assisted by fluctuations which amplify the attractive interaction\nbetween atoms. Moreover, the calculation of the fluctuated atoms, the entropy,\nand the second-order correlation function showed that the collapsed gas was\nsignificantly deviated from a pure state."
    },
    {
        "anchor": "Emergent symmetries and slow quantum dynamics in a Rydberg-atom chain\n  with confinement: Rydberg atoms in optical tweezer arrays provide a playground for\nnonequilibrium quantum many-body physics. The PXP model describes the dynamics\nof such systems in the strongly interacting Rydberg blockade regime and notably\nexhibits weakly nonergodic dynamics due to quantum many-body scars. Here, we\nstudy the PXP model in a strong staggered external field, which has been\nproposed to manifest quasiparticle confinement in light of a mapping to a\nlattice gauge theory. We characterize this confining regime using both\nnumerical exact diagonalization and perturbation theory around the strong-field\nlimit. In addition to the expected emergent symmetry generated by the staggered\nfield, we find a second emergent symmetry that is special to the PXP model. The\ninterplay between these emergent symmetries and the Rydberg blockade constraint\ndramatically slows down the system's dynamics beyond naive expectations. We\ndevise a nested Schrieffer-Wolff perturbation theory to properly account for\nthe new emergent symmetry and show that this treatment is essential to\nunderstand the numerically observed relaxation time scales. We also discuss\nconnections to Hilbert space fragmentation and trace the origin of the new\nemergent symmetry to a \"nearly-$SU(2)$\" algebra discovered in the context of\nmany-body scarring.",
        "positive": "Raise and fall of a bright soliton in an optical lattice: We study an ultracold atomic gas with attractive interactions in a\none-dimensional optical lattice. We find that its excitation spectrum displays\na quantum soliton band, corresponding to $N$-particle bound states, and a\ncontinuum band of other, mostly extended, states. For a system of a finite\nsize, the two branches are degenerate in energy for weak interactions, while a\ngap opens above a threshold value for the interaction strength. We find that\nthe interplay between degenerate extended and bound states has important\nconsequences for both static and dynamical properties of the system. In\nparticular, the solitonic states turn out to be protected from spatial\nperturbations and random disorder. We discuss how such dynamics implies that\nour system effectively provides an example of a quantum many-body system that,\nwith the variation of the bosonic lattice filling, crosses over from integrable\nnon-ergodic to non-integrable ergodic dynamics, through non-integrable\nnon-ergodic regimes."
    },
    {
        "anchor": "Stable dilute supersolid of two-dimensional dipolar bosons: We consider two-dimensional bosonic dipoles oriented perpendicularly to the\nplane. On top of the usual two-body contact and long-range dipolar interactions\nwe add a contact three-body repulsion as expected, in particular, for dipoles\nin the bilayer geometry with tunneling. The three-body repulsion is crucial for\nstabilizing the system, and we show that our model allows for stable continuous\nspace supersolid states in the dilute regime and calculate the zero-temperature\nphase diagram.",
        "positive": "A Floquet-Rydberg quantum simulator for confinement in $\\mathbb{Z}_2$\n  gauge theories: Recent advances in the field of quantum technologies have opened up the road\nfor the realization of small-scale quantum simulators of lattice gauge theories\nwhich, among other goals, aim at improving our understanding on the\nnon-perturbative mechanisms underlying the confinement of quarks. In this work,\nconsidering periodically-driven arrays of Rydberg atoms in a tweezer ladder\ngeometry, we devise a scalable Floquet scheme for the quantum simulation of the\nreal-time dynamics in a $\\mathbb{Z}_2$ LGT. Resorting to an external magnetic\nfield to tune the angular dependence of the Rydberg dipolar interactions, and\nby a suitable tuning of the driving parameters, we manage to suppress the main\ngauge-violating terms, and show that an observation of gauge-invariant\nconfinement dynamics in the Floquet-Rydberg setup is at reach of current\nexperimental techniques. Depending on the lattice size, we present a thorough\nnumerical test of the validity of this scheme using either exact\ndiagonalization or matrix-product-state algorithms for the\nperiodically-modulated real-time dynamics."
    },
    {
        "anchor": "Core Structure and Non-Abelian Reconnection of Defects in a Biaxial\n  Nematic Spin-2 Bose-Einstein Condensate: We calculate the energetic structure of defect cores and propose controlled\nmethods to imprint a nontrivially entangled vortex pair that undergoes\nnon-Abelian vortex reconnection in a biaxial nematic spin-2 condensate. For a\nsingular vortex, we find three superfluid cores in addition to depletion of the\ncondensate density. These exhibit order parameter symmetries that are different\nfrom the discrete symmetry of the biaxial nematic phase, forming an interface\nbetween the defect and the bulk superfluid. We provide a detailed analysis of\nphase mixing in the resulting vortex cores and find an instability dependent\nupon the orientation of the order parameter. We further show that the spin-2\ncondensate is a promising system for observing spontaneous deformation of a\npoint defect into an \"Alice ring\" that has so far avoided experimental\ndetection.",
        "positive": "The study of random vorticity in quantum fluids through interference\n  fluctuations: We study the vortex dynamics of a quantum degenerate Bose gas through the\nintensity fluctuations of the interference from particles extracted at two\ndifferent positions. It is shown numerically with classical field simulations\nthat an interacting Bose gas with proliferating vortices exhibits long\ncorrelation times for these intensity fluctuations. This behavior is contrasted\nwith the case of a noninteracting gas, that we describe analytically, and with\nthe case of a well condensed Bose gas without vortices. We discuss the\nobservability of our predictions in quantum fluids of exciton-polaritons."
    },
    {
        "anchor": "Topological Fulde-Ferrell superfluid in spin-orbit coupled atomic Fermi\n  gases: We theoretically predict a new topological matter - topological inhomogeneous\nFulde-Ferrell superfluid - in one-dimensional atomic Fermi gases with equal\nRashba and Dresselhaus spin-orbit coupling near s-wave Feshbach resonances. The\nrealization of such a spin-orbit coupled Fermi system has already been\ndemonstrated recently by using a two-photon Raman process and the extra\none-dimensional confinement is easy to achieve using a tight two-dimensional\noptical lattice. The topological Fulde-Ferrell superfluid phase is\ncharacterized by a nonzero center-of-mass momentum and a non-trivial Berry\nphase. By tuning the Rabi frequency and the detuning of Raman laser beams, we\nshow that such an exotic topological phase occupies a significant part of\nparameter space and therefore it could be easily observed experimentally, by\nusing, for example, momentum-resolved and spatially resolved radio-frequency\nspectroscopy.",
        "positive": "Quantum signatures of self-trapping transition in attractive lattice\n  bosons: We consider the Bose-Hubbard model describing attractive bosonic particles\nhopping across the sites of a translation-invariant lattice, and compare the\nrelevant ground-state properties with those of the corresponding\nsymmetry-breaking semiclassical nonlinear theory. The introduction of a\nsuitable measure allows us to highlight many correspondences between the\nnonlinear theory and the inherently linear quantum theory, characterized by the\nwell-known self-trapping phenomenon. In particular we demonstrate that the\nlocalization properties and bifurcation pattern of the semiclassical\nground-state can be clearly recognized at the quantum level. Our analysis\nhighlights a finite-number effect."
    },
    {
        "anchor": "Material-barrier Tunneling in One-dimensional Few-boson Mixtures: We study the quantum dynamics of strongly interacting few-boson mixtures in\none-dimensional traps. If one species is strongly localized compared to the\nother (e.g., much heavier), it can serve as an effective potential barrier for\nthat mobile component. Near the limit of infinite localization, we map this to\na system of identical bosons in a double well. For realistic localization, the\nbackaction of the light species on the \"barrier\" atoms is explained--to lowest\norder--in terms of an induced attraction between these. Even in equilibrium,\nthis may outweigh the bare intra-species interaction, leading to unexpected\ncorrelated states. Remarkably, the backaction drastically affects the\ninter-species dynamics, such as the tunneling of an attractively bound pair of\nfermionized atoms.",
        "positive": "Occupation numbers of the harmonically trapped few-boson system: We consider a harmonically trapped dilute $N$-boson system described by a\nlow-energy Hamiltonian with pairwise interactions. We determine the condensate\nfraction, defined in terms of the largest occupation number, of the\nweakly-interacting $N$-boson system ($N \\ge 2$) by employing a perturbative\ntreatment within the framework of second quantization. The one-body density\nmatrix and the corresponding occupation numbers are compared with those\nobtained by solving the two-body problem with zero-range interactions exactly.\nOur expressions are also compared with high precision {\\em{ab initio}}\ncalculations for Bose gases with $N=2-4$ that interact through finite-range\ntwo-body model potentials. Non-universal corrections are identified to enter at\nsubleading order, confirming that different low-energy Hamiltonians,\nconstructed to yield the same energy, may yield different occupation numbers.\nLastly, we consider the strongly-interacting three-boson system under\nspherically symmetric harmonic confinement and determine its occupation numbers\nas a function of the three-body \"Efimov parameter\"."
    },
    {
        "anchor": "Quantum thermalization via percolation: We highlight a dynamical anomaly in which the rate of relaxation towards\nthermal equilibrium in a bi-partite quantum system violates the standard\nlinear-response (Kubo) formulation, even when the underlying dynamics is highly\nchaotic. This anomaly originates from an $\\hbar$-dependent sparsity of the\nunderlying quantum network of transitions. Using a minimal bi-partite\nBose-Hubbard model as an example, we find that the relaxation rate acquires an\nanomalous $\\hbar$ dependence that reflects percolation-like dynamics in energy\nspace.",
        "positive": "Selective insulators and anomalous responses in correlated fermions with\n  synthetic extra dimensions: We study a three-component fermionic fluid in an optical lattice in a regime\nof intermediate-to- strong interactions allowing for Raman processes connecting\nthe different components, similar to those used to create artificial gauge\nfields (AGF). Using Dynamical Mean-Field Theory we show that the combined\neffect of interactions and AGFs induces a variety of anomalous phases in which\ndifferent components of the fermionic fluid display qualitative differences,\ni.e., the physics is flavor-selective. Remarkably, the different components can\ndisplay huge differences in the correlation effects, measured by their\neffective masses and non-monotonic behavior of their occupation number as a\nfunction of the chemical potential, signaling a sort of selective instability\nof the overall stable quantum fluid."
    },
    {
        "anchor": "Experimental realization of fragmented models in tilted Fermi-Hubbard\n  chains: Quantum many-body systems may defy thermalization even without disorder.\nIntriguingly, non-ergodicity may be caused by a fragmentation of the many-body\nHilbert-space into dynamically disconnected subspaces. The tilted\none-dimensional Fermi-Hubbard model was proposed as a platform to realize\nfragmented models perturbatively in the limit of large tilt. Here, we\ndemonstrate the validity of this effective description for the transient\ndynamics using ultracold fermions. The effective analytic model allows for a\ndetailed understanding of the emergent microscopic processes, which in our case\nexhibit a pronounced doublon-number dependence. We study this experimentally by\ntuning the doublon fraction in the initial state.",
        "positive": "Skyrmion-string defects with arbitrary topological charges in spinor\n  Bose-Einstein condensates: Under the presence of external magnetic fields with cylindrical symmetry,\nSkyrmion-string defects with arbitrary topological charges are shown to appear\nin spinor $F = 1$ Bose-Einstein condensates. We show that, depending on the\nmagnetic field boundary condition, the topological spin texture, at the planes\nperpendicular to the cylindrical axis, can take zero, half integer, or\narbitrary values between $-1/2$ and $1/2$. We argue that these are true\ntopological defects since their charge is independent of the spatial location\nof the singularity and since the total Skyrmion charge is the sum of the\nindividual charges of the defects present. Our findings are obtained by\nnumerically solving the corresponding fully coupled Gross-Pitaevskii equations\nwithout any symmetry assumptions. We analyze, both, polar $^{23}$Na and\nferromagnetic $^{87}$Rb condensates."
    },
    {
        "anchor": "All Optical Scheme for Strongly Enhanced Production of Dipolar Molecules\n  in the Electro-Vibrational Ground State: We consider two-color heteronuclear photoassociation of atoms into dipolar\nmolecules in the J=1 electro-vibrational ground state, where a free-ground\nlaser couples atoms directly to the ground state and a free-bound laser couples\nthe atoms to an electronically-excited state. This problem raises an interest\nbecause heteronuclear photoassociation from atoms to near-ground state\nmolecules is limited by the small size of the target state. Nevertheless, the\naddition of the excited state creates a second pathway for creating ground\nstate molecules, leading to quantum interference between direct\nphotoassociation and photoassociation via the excited molecular state, as well\nas a dispersive-like shift of the free-ground resonance position. Using LiNa as\nan example, these results are shown to depend on the detuning and intensity of\nthe free-bound laser, as well as the semi-classical size of both molecular\nstates. Despite strong enhancement, coherent conversion to the LiNa\nelectro-vibrational ground state is possible only in a limited regime near the\nfree-bound resonance.",
        "positive": "Precision benchmark calculations for four particles at unitarity: The unitarity limit describes interacting particles where the range of the\ninteraction is zero and the scattering length is infinite. We present precision\nbenchmark calculations for two-component fermions at unitarity using three\ndifferent ab initio methods: Hamiltonian lattice formalism using iterated\neigenvector methods, Euclidean lattice formalism with auxiliary-field\nprojection Monte Carlo, and continuum diffusion Monte Carlo with fixed and\nreleased nodes. We have calculated the ground state energy of the unpolarized\nfour-particle system in a periodic cube as a dimensionless fraction of the\nground state energy for the non-interacting system. We obtain values 0.211(2)\nand 0.210(2) using two different Hamiltonian lattice representations, 0.206(9)\nusing Euclidean lattice, and an upper bound of 0.212(2) from fixed-node\ndiffusion Monte Carlo. Released-node calculations starting from the fixed-node\nresult yield a decrease of less than 0.002 over a propagation of 0.4/E_F in\nEuclidean time, where E_F is the Fermi energy. We find good agreement among all\nthree ab initio methods."
    },
    {
        "anchor": "The Nature and Properties of a Repulsive Fermi Gas in the \"Upper Branch\": We generalize the Nozi\\'eres-Schmitt-Rink (NSR) method to study the repulsive\nFermi gas in the absence of molecule formation, i.e., in the so-called \"upper\nbranch\". We find that the system remains stable except close to resonance at\nsufficiently low temperatures. With increasing scattering length, the energy\ndensity of the system attains a maximum at a positive scattering length before\nresonance. This is shown to arise from Pauli blocking which causes the bound\nstates of fermion pairs of different momenta to disappear at different\nscattering lengths. At the point of maximum energy, the compressibility of the\nsystem is substantially reduced, leading to a sizable uniform density core in a\ntrapped gas. The change in spin susceptibility with increasing scattering\nlength is moderate and does not indicate any magnetic instability. These\nfeatures should also manifest in Fermi gases with unequal masses and/or spin\npopulations.",
        "positive": "Two-orbital SU(N) magnetism with ultracold alkaline-earth atoms: Fermionic alkaline-earth atoms have unique properties that make them\nattractive candidates for the realization of novel atomic clocks and degenerate\nquantum gases. At the same time, they are attracting considerable theoretical\nattention in the context of quantum information processing. Here we demonstrate\nthat when such atoms are loaded in optical lattices, they can be used as\nquantum simulators of unique many-body phenomena. In particular, we show that\nthe decoupling of the nuclear spin from the electronic angular momentum can be\nused to implement many-body systems with an unprecedented degree of symmetry,\ncharacterized by the SU(N) group with N as large as 10. Moreover, the interplay\nof the nuclear spin with the electronic degree of freedom provided by a stable\noptically excited state allows for the study of spin-orbital physics. Such\nsystems may provide valuable insights into strongly correlated physics of\ntransition metal oxides, heavy fermion materials, and spin liquid phases."
    },
    {
        "anchor": "Quantum reflection of a Bose-Einstein condensate from a rapidly varying\n  potential: the role of dark soliton: We study the dynamic behavior of a Bose-Einstein condensate (BEC) containing\na dark soliton separately reflected from potential drops and potential\nbarriers. It is shown that for a rapidly varying potential and in a certain\nregime of incident velocity, the quantum reflection probability displays the\ncosine of the deflection angle between the incident soliton and the reflected\nsoliton, i.e., $R(\\theta) \\sim \\cos 2\\theta$. For a potential drop, $R(\\theta)$\nis susceptible to the widths of potential drop up to the length of the dark\nsoliton and the difference of the reflection rates between the orientation\nangle of the soliton $\\theta=0$ and $\\theta=\\pi/2$, $\\delta R_s$, displays\noscillating exponential decay with increasing potential widths. However, for a\nbarrier potential, $R(\\theta)$ is insensitive for the potential width less than\nthe decay length of the matter wave and $\\delta R_s$ presents an exponential\ntrend. This discrepancy of the reflectances in two systems is arisen from the\ndifferent behaviors of matter waves in the region of potential variation.",
        "positive": "Out-of-equilibrium dynamics of Bose-Bose mixtures in optical lattices: We examine the quench dynamics across quantum phase transitions from a Mott\ninsulator (MI) to a superfluid (SF) phase in a two-component bosonic mixture in\nan optical lattice. We show that two-component Bose mixtures exhibit\nqualitatively different quantum dynamics than one-component Bose gas. Besides\nsecond-order MI-SF transitions, we also investigate quench dynamics across a\nfirst-order MI-SF transition. The Bose mixtures show the critical slowing down\nof dynamics near the critical transition point, as proposed by the Kibble-Zurek\nmechanism. For MI-SF transitions with homogeneous lattice-site distributions in\nthe MI phase, the dynamical critical exponents extracted by the power-law\nscaling of the proposed quantities obtained via numerical simulations are in\nvery close agreement with the mean-field predictions."
    },
    {
        "anchor": "Matter Waves in Atomic Artificial Graphene: We present a new model to realize artificial 2D lattices with cold atoms\ninvestigating the atomic artificial graphene: a 2D-confined matter wave is\nscattered by atoms of a second species trapped around the nodes of a honeycomb\noptical lattice. The system allows an exact determination of the Green\nfunction, hence of the transport properties. The inter-species interaction can\nbe tuned via the interplay between scattering length and confinements. Band\nstructure and density of states of a periodic lattice are derived for different\nvalues of the interaction strength. Emergence and features of Dirac cones are\npointed out, together with the appearance of multiple gaps and a non-dispersive\nand isolated flat band. Robustness against finite-size and vacancies effects is\nnumerically investigated.",
        "positive": "Two Fermions in a double well: Exploring a fundamental building block of\n  the Hubbard model: We have prepared two ultracold fermionic atoms in an isolated double-well\npotential and obtained full control over the quantum state of this system. In\nparticular, we can independently control the interaction strength between the\nparticles, their tunneling rate between the wells and the tilt of the\npotential. By introducing repulsive (attractive) interparticle interactions we\nhave realized the two-particle analog of a Mott-insulating\n(charge-density-wave) state. We have also spectroscopically observed how\nsecond-order tunneling affects the energy of the system. This work realizes the\nfirst step of a bottom-up approach to deterministically create a single-site\naddressable realization of a ground-state Fermi-Hubbard system."
    },
    {
        "anchor": "Adiabatic preparation of vortex lattices: By engineering appropriate artificial gauge potentials, a Bose-Einstein\ncondensate can be adiabatically loaded into a current carrying state that\nresembles a vortex lattice of a rotating uniform Bose gas. We give two\nexplicit, experimentally feasible protocols by which vortex lattices can be\nsmoothly formed from a condensate initially at rest. In the first example we\nshow how this can be achieved by adiabatically loading a uniform BEC into an\noptical flux lattice, formed from coherent optical coupling of internal states\nof the atom. In the second example we study a tight binding model that is\ncontinuously manipulated in parameter space such that it smoothly transforms\ninto the Harper-Hofstadter model with 1/3 flux per plaquette.",
        "positive": "Quantum flutter of supersonic particles in one-dimensional quantum\n  liquids: The non-equilibrium dynamics of strongly correlated many-body systems\nexhibits some of the most puzzling phenomena and challenging problems in\ncondensed matter physics. Here we report on essentially exact results on the\ntime evolution of an impurity injected at a finite velocity into a\none-dimensional quantum liquid. We provide the first quantitative study of the\nformation of the correlation hole around a particle in a strongly coupled\nmany-body quantum system, and find that the resulting correlated state does not\ncome to a complete stop but reaches a steady state which propagates at a finite\nvelocity. We also uncover a novel physical phenomenon when the impurity is\ninjected at supersonic velocities: the correlation hole undergoes long-lived\ncoherent oscillations around the impurity, an effect we call quantum flutter.\nWe provide a detailed understanding and an intuitive physical picture of these\nintriguing discoveries, and propose an experimental setup where this physics\ncan be realized and probed directly."
    },
    {
        "anchor": "Equation of state of a laser cooled gas: We experimentally determine the equation of state of a laser cooled gas. By\nemploying the Lane-Emden formalism, widely used in astrophysics, we derive the\nequilibrium atomic profiles in large magneto optical traps where the\nthermodynamic effects are cast in a polytropic equation of state. The effects\nof multiple scattering of light are included, which results in a generalized\nLane-Emden equation for the atomic profiles. A detailed experimental\ninvestigation reveals an excellent agreement with the model, with a two-fold\nsignificance. In one hand, we can infer on the details of the equation of state\nof the system, from an ideal gas to a correlated phase due to an effective\nelectrical charge for the atoms, which is accurately described by a\nmicroscopical description of the effective electrostatic interaction. On the\nother hand, we are able map the effects of multiple scattering onto directly\ncontrollable experimental variables, which paves the way to subsequent\nexperimental investigations of this collective interaction.",
        "positive": "Atomtronics with a spin: statistics of spin transport and\n  non-equilibrium orthogonality catastrophe in cold quantum gases: We propose to investigate the full counting statistics of nonequilibrium spin\ntransport with an ultracold atomic quantum gas. The setup makes use of the spin\ncontrol available in atomic systems to generate spin transport induced by an\nimpurity atom immersed in a spin-imbalanced two-component Fermi gas. In\ncontrast to solid-state realizations, in ultracold atoms spin relaxation and\nthe decoherence from external sources is largely suppressed. As a consequence,\nonce the spin current is turned off by manipulating the internal spin degrees\nof freedom of the Fermi system, the nonequilibrium spin population remains\nconstant. Thus one can directly count the number of spins in each reservoir to\ninvestigate the full counting statistics of spin flips, which is notoriously\nchallenging in solid state devices. Moreover, using Ramsey interferometry, the\ndynamical impurity response can be measured. Since the impurity interacts with\na many-body environment that is out of equilibrium, our setup provides a way to\nrealize the non-equilibrium orthogonality catastrophe. Here, even for spin\nreservoirs initially prepared in a zero-temperature state, the Ramsey response\nexhibits an exponential decay, which is in contrast to the conventional\npower-law decay of Anderson's orthogonality catastrophe. By mapping our system\nto a multi-step Fermi sea, we are able to derive analytical expressions for the\nimpurity response at late times. This allows us to reveal an intimate\nconnection of the decay rate of the Ramsey contrast and the full counting\nstatistics of spin flips."
    },
    {
        "anchor": "Doublon production rate in modulated optical lattices: We study theoretically lattice modulation experiments with ultracold fermions\nin optical lattices. We focus on the regime relevant to current experiments\nwhen interaction strength is larger than the bandwidth and temperature is\nhigher than magnetic superexchange energy. We obtain analytical expressions for\nthe rate of doublon production as a function of modulation frequency, filling\nfactor, and temperature. We use local density approximation to average over\ninhomogeneous density for atoms in a parabolic trap and find excellent\nagreement with experimentally measured values. Our results suggest that lattice\nmodulation experiments can be used for thermometry of strongly interacting\nfermionic ensembles in optical lattices.",
        "positive": "Viscosity and scale invariance in the unitary Fermi gas: We compute the shear viscosity of the unitary Fermi gas above the superfluid\ntransition temperature, using a diagrammatic technique that starts from the\nexact Kubo formula. The formalism obeys a Ward identity associated with scale\ninvariance which guarantees that the bulk viscosity vanishes identically. For\nthe shear viscosity, vertex corrections and the associated Aslamazov-Larkin\ncontributions are shown to be crucial to reproduce the full Boltzmann equation\nresult in the high-temperature, low fugacity limit. The frequency dependent\nshear viscosity $\\eta(\\omega)$ exhibits a Drude-like transport peak and a\npower-law tail at large frequencies which is proportional to the Tan contact.\nThe weight in the transport peak is given by the equilibrium pressure, in\nagreement with a sum rule due to Taylor and Randeria. Near the superfluid\ntransition the peak width is of the order of $0.5 T_F$, thus invalidating a\nquasiparticle description. The ratio $\\eta/s$ between the static shear\nviscosity and the entropy density exhibits a minimum near the superfluid\ntransition temperature whose value is larger than the string theory bound\n$\\hbar/(4\\pi k_B)$ by a factor of about seven."
    },
    {
        "anchor": "Spectral response and contact of the unitary Fermi gas: We measure radiofrequency (rf) spectra of the homogeneous unitary Fermi gas\nat temperatures ranging from the Boltzmann regime through quantum degeneracy\nand across the superfluid transition. For all temperatures, a single spectral\npeak is observed. Its position smoothly evolves from the bare atomic resonance\nin the Boltzmann regime to a frequency corresponding to nearly one Fermi energy\nat the lowest temperatures. At high temperatures, the peak width reflects the\nscattering rate of the atoms, while at low temperatures, the width is set by\nthe size of fermion pairs. Above the superfluid transition, and approaching the\nquantum critical regime, the width increases linearly with temperature,\nindicating non-Fermi-liquid behavior. From the wings of the rf spectra, we\nobtain the contact, quantifying the strength of short-range pair correlations.\nWe find that the contact rapidly increases as the gas is cooled below the\nsuperfluid transition.",
        "positive": "Resonant excitations of a Bose Einstein condensate in an optical lattice: We investigate experimentally a Bose Einstein condensate placed in a 1D\noptical lattice whose phase or amplitude is modulated in a frequency range\nresonant with the first bands of the band structure. We study the combined\neffect of the strength of interactions and external confinement on the 1 and\n2-phonon transitions. We identify lines immune or sensitive to atom-atom\ninteractions. Experimental results are in good agreement with numerical\nsimulations. Using the band mapping technique, we get a direct access to the\npopulations that have undergone $n$-phonon transitions for each modulation\nfrequency."
    },
    {
        "anchor": "Quantum fluctuations on top of a $\\mathcal{PT}$-symmetric Bose-Einstein\n  Condensate: We investigate the effects of quantum fluctuations in a\nparity-time($\\mathcal{PT}$) symmetric two-species Bose-Einstein\nCondensate(BEC). It is found that the $\\mathcal{PT}$-symmetry, though preserved\nby the macroscopic condensate, can be spontaneously broken by its Bogoliubov\nquasi-particles under quantum fluctuations. The associated\n$\\mathcal{PT}$-breaking transitions in the Bogoliubov spectrum can be\nconveniently tuned by the interaction anisotropy in spin channels and the\nstrength of $\\mathcal{PT}$ potential. In the $\\mathcal{PT}$-unbroken regime,\nthe real Bogoliubov modes are generally gapped, in contrast to the gapless\nphonon mode in Hermitian case. Moreover, the presence of $\\mathcal{PT}$\npotential is found to enhance the mean-field collapse and thereby intrigue the\ndroplet formation after incorporating the repulsive force from quantum\nfluctuations. These remarkable interplay effects of $\\mathcal{PT}$-symmetry and\ninteraction can be directly probed in cold atoms experiments, which shed light\non related quantum phenomena in general $\\mathcal{PT}$-symmetric systems.",
        "positive": "Mean-field regime of trapped dipolar Bose-Einstein condensates in one\n  and two dimensions: We derive rigorous one- and two-dimensional mean-field equations for cigar-\nand pancake-shaped dipolar Bose-Einstein condensates with arbitrary\npolarization angle. We show how the dipolar interaction modifies the contact\ninteraction of the strongly confined atoms. In addition, our equations\nintroduce a nonlocal potential, which is anisotropic for pancake-shaped\ncondensates. We propose to observe this anisotropy via measurement of the\ncondensate aspect ratio. We also derive analytically approximate density\nprofiles from our equations. Both the numerical solutions of our reduced\nmean-field equations and the analytical density profiles agree well with\nnumerical solutions of the full Gross-Pitaevskii equation while being more\nefficient to compute."
    },
    {
        "anchor": "The BCS-BEC crossover: From ultra-cold Fermi gases to nuclear systems: This report adresses topics and questions of common interest in the fields of\nultra-cold gases and nuclear physics in the context of the BCS-BEC crossover.\nThe BCS-BEC crossover has recently been realized experimentally, and\nessentially in all of its aspects, with ultra-cold Fermi gases. This\nrealization, in turn, has raised the interest of the nuclear physics community\nin the crossover problem, since it represents an unprecedented tool to test\nfundamental and unanswered questions of nuclear many-body theory. Here, we\nfocus on the several aspects of the BCS-BEC crossover, which are of broad joint\ninterest to both ultra-cold Fermi gases and nuclear matter, and which will\nlikely help to solve in the future some open problems in nuclear physics\n(concerning, for instance, neutron stars). Similarities and differences\noccurring in ultra-cold Fermi gases and nuclear matter will then be emphasized,\nnot only about the relative phenomenologies but also about the theoretical\napproaches to be used in the two contexts. After an introduction to present the\nkey concepts of the BCS-BEC crossover, this report discusses the mean-field\ntreatment of the superfluid phase, both for homogeneous and inhomogeneous\nsystems, as well as for symmetric (spin- or isospin-balanced) and asymmetric\n(spin- or isospin-imbalanced) matter. Pairing fluctuations in the normal phase\nare then considered, with their manifestations in thermodynamic and dynamic\nquantities. The last two Sections provide a more specialized discussion of the\nBCS-BEC crossover in ultra-cold Fermi gases and nuclear matter, respectively.\nThe separate discussion in the two contexts aims at cross communicating to both\ncommunities topics and aspects which, albeit arising in one of the two fields,\nshare a strong common interest.",
        "positive": "Realization of an anomalous Floquet topological system with ultracold\n  atoms: Coherent control via periodic modulation, also known as Floquet engineering,\nhas emerged as a powerful experimental method for the realization of novel\nquantum systems with exotic properties. In particular, it has been employed to\nstudy topological phenomena in a variety of different platforms. In driven\nsystems, the topological properties of the quasienergy bands can often be\ndetermined by standard topological invariants, such as Chern numbers, which are\ncommonly used in static systems. However, due to the periodic nature of the\nquasienergy spectrum, this topological description is incomplete and new\ninvariants are required to fully capture the topological properties of these\ndriven settings. Most prominently, there exist two-dimensional anomalous\nFloquet systems that exhibit robust chiral edge modes, despite all Chern\nnumbers are equal to zero. Here, we realize such a system with bosonic atoms in\na periodically-driven honeycomb lattice and infer the complete set of\ntopological invariants from energy gap measurements and local Hall deflections."
    },
    {
        "anchor": "Microscopic description of anisotropic low-density dipolar Bose gases in\n  two dimensions: A microscopic description of the zero energy two-body ground state and\nmany-body static properties of anisotropic homogeneous gases of bosonic dipoles\nin two dimensions at low densities is presented and discussed. By changing the\npolarization angle with respect to the plane, we study the impact of the\nanisotropy, present in the dipole--dipole interaction, on the energy per\nparticle, comparing the results with mean field predictions. We restrict the\nanalysis to the regime where the interaction is always repulsive, although the\nstrength of the repulsion depends on the orientation with respect to the\npolarization field. We present a series expansion of the solution of the zero\nenergy two-body problem which allows us to find the scattering length of the\ninteraction and to build a suitable Jastrow factor that we use as a trial wave\nfunction for both a variational and diffusion Monte Carlo simulation of the\ninfinite system. We find that the anisotropy has an almost negligible impact on\nthe ground state properties of the many-body system in the universal regime\nwhere the scattering length governs the physics of the system. We also show\nthat scaling in the gas parameter persists in the dipolar case up to values\nwhere other isotropic interactions with the same scattering length yield\ndifferent predictions.",
        "positive": "Fast preparation of critical ground states using superluminal fronts: We propose a spatio-temporal quench protocol that allows for the fast\npreparation of ground states of gapless models with Lorentz invariance.\nAssuming the system initially resides in the ground state of a corresponding\nmassive model, we show that a superluminally-moving `front' that\n$\\textit{locally}$ quenches the mass, leaves behind it (in space) a state\n$\\textit{arbitrarily close}$ to the ground state of the gapless model.\nImportantly, our protocol takes time $\\mathcal{O} \\left( L \\right)$ to produce\nthe ground state of a system of size $\\sim L^d$ ($d$ spatial dimensions), while\na fully adiabatic protocol requires time $\\sim \\mathcal{O} \\left( L^2 \\right)$\nto produce a state with exponential accuracy in $L$. The physics of the\ndynamical problem can be understood in terms of relativistic rarefaction of\nexcitations generated by the mass front. We provide proof-of-concept by solving\nthe proposed quench exactly for a system of free bosons in arbitrary\ndimensions, and for free fermions in $d = 1$. We discuss the role of\ninteractions and UV effects on the free-theory idealization, before numerically\nillustrating the usefulness of the approach via simulations on the quantum\nHeisenberg spin-chain."
    },
    {
        "anchor": "Localization on a synthetic Hall cylinder: By engineering laser-atom interactions, both Hall ribbons and Hall cylinders\nas fundamental theoretical tools in condensed matter physics have recently been\nsynthesized in laboratories. Here, we show that turning a synthetic Hall ribbon\ninto a synthetic Hall cylinder could naturally lead to localization. Unlike a\nHall ribbon, a Hall cylinder hosts an intrinsic lattice, which arises due to\nthe periodic boundary condition in the azimuthal direction, in addition to the\nexternal periodic potential imposed by extra lasers. When these two lattices\nare incommensurate, localization may occur on a synthetic Hall cylinder. Near\nthe localization-delocalization transitions, the dependence of physical\nobservables on the axial magnetic flux allows us to tackle a fundamental\nquestion of determining the accuracy of rational approximation of irrational\nnumbers. In the irrational limit, physical observables are no longer affected\nby fluctuations of the axial flux.",
        "positive": "Quantum engineering of Majorana quasiparticles in one-dimensional\n  optical lattices: We propose a feasible way of engineering Majorana-type quasiparticles in\nultracold fermionic gases on a one-dimensional (1D) optical lattice. For this\npurpose, imbalanced ultracold atoms interacting by the spin-orbit coupling\nshould be hybridized with a three-dimensional Bose-Einstein condensate (BEC)\nmolecular cloud. By constraining the profile of an internal defect potential we\nshow that the Majorana-type excitations can be created or annihilated. This\nprocess is modelled within the Bogoliubov-de Gennes approach. This study is\nrelevant also to nanoscopic 1D superconductors where modification of the\ninternal defect potential can be obtained by electrostatic means."
    },
    {
        "anchor": "Spontaneous symmetry breaking and phase coherence of a photon\n  Bose-Einstein condensate coupled to a reservoir: We examine the phase evolution of a Bose-Einstein condensate of photons\ngenerated in a dye microcavity by temporal interference with a phase reference.\nThe photo-excitable dye molecules constitute a reservoir of variable size for\nthe condensate particles, allowing for grand canonical statistics with photon\nbunching, as in a lamp-type source. We directly observe phase jumps of the\ncondensate associated with the large statistical number fluctuations and find a\nseparation of correlation timescales. For large systems, our data reveals phase\ncoherence and a spontaneously broken symmetry, despite the statistical\nfluctuations.",
        "positive": "First order phase transitions in optical lattices with tunable\n  three-body onsite interaction: We study the two-dimensional Bose-Hubbard model in the presence of a\nthree-body interaction term, both at a mean field level and via quantum Monte\nCarlo simulations. The three-body term is tuned by coupling the triply occupied\nstates to a trapped universal trimer. We find that, for sufficiently attractive\nthree-body interaction the n = 2 Mott lobe disappears and the system displays\nfirst order phase transitions separating the n = 1 from the n = 3 lobes, and\nthe n = 1 and n = 3 Mott insulator from the superfluid. We have also analyzed\nthe effect of finite temperature and found that transitions are still of first\norder at temperatures T\\simJ where J is the hopping matrix element."
    },
    {
        "anchor": "Quantized Adiabatic Transport in Momentum Space: Though topological aspects of energy bands are known to play a key role in\nquantum transport in solid-state systems, the implications of Floquet band\ntopology for transport in momentum space (i.e., acceleration) are not explored\nso far. Using a ratchet accelerator model inspired by existing cold-atom\nexperiments, here we characterize a class of extended Floquet bands of\none-dimensional driven quantum systems by Chern numbers, reveal topological\nphase transitions therein, and theoretically predict the quantization of\nadiabatic transport in momentum space. Numerical results confirm our theory and\nindicate the feasibility of experimental studies.",
        "positive": "Higher-order topological quantum paramagnets: Quantum paramagnets are strongly-correlated phases of matter where competing\ninteractions frustrate magnetic order down to zero temperature. In certain\ncases, quantum fluctuations induce instead topological order, supporting, in\nparticular, fractionalized quasi-particle excitations. In this work, we\ninvestigate paradigmatic spin models and show how magnetic frustration can also\ngive rise to higher-order topological properties. We first study the frustrated\nHeisenberg model in a square lattice, where a plaquette valence bond solid\nappears through the spontaneous breaking of translational invariance. Despite\nthe amount of effort that has been devoted to study this phase, its topological\nnature has so far been overlooked. By means of tensor network simulations, we\nestablish how such state belongs to a higher-order symmetry-protected\ntopological phase, where long-range plaquette order and non-trivial topology\ncoexist. This interplay allows the system to support excitations that would be\nabsent otherwise, such as corner-like states in the bulk attached to dynamical\ntopological defects. Finally, we demonstrate how this higher-order topological\nquantum paramagnet can also be induced by dipolar interactions, indicating the\npossibility to directly observe this phase using atomic quantum simulators."
    },
    {
        "anchor": "Formation and quench of homonuclear and heteronuclear quantum droplets\n  in one dimension: We exemplify the impact of beyond Lee-Huang-Yang (LHY) physics, especially\ndue to intercomponent correlations, in the ground state and the quench dynamics\nof one-dimensional so-called quantum droplets using an ab-initio\nnonperturbative approach. It is found that the droplet Gaussian-shaped\nconfiguration arising for intercomponent attractive couplings becomes narrower\nfor stronger intracomponent repulsion and transits towards a flat-top structure\neither for larger particle numbers or weaker intercomponent attraction.\nAdditionally, a harmonic trap prevents the flat-top formation. At the balance\npoint where mean-field interactions cancel out, we show that a correlation hole\nis present in the few particle limit of these fluids as well as for flat-top\ndroplets. Introducing mass-imbalance, droplets experience intercomponent mixing\nand excitation signatures are identified for larger masses. Monitoring the\ndroplet expansion (breathing motion) upon considering interaction quenches to\nstronger (weaker) attractions we explicate that beyond LHY correlations result\nin a reduced velocity (breathing frequency). Strikingly, the droplets feature\ntwo-body anti-correlations (correlations) at the same position (longer\ndistances). Our findings pave the way for probing correlation-induced phenomena\nof droplet dynamics in current ultracold atom experiments.",
        "positive": "Condensates in annuli: Dimensionality of the variance: Static and dynamic properties of Bose-Einstein condensates in annular traps\nare investigated by solving the many-boson Schr\\\"odinger equation numerically\naccurately using the multiconfigurational time-dependent Hartree for bosons\nmethod. We concentrate on weakly-interacting bosons exhibiting low depletion.\nAnalysis of the mean-field position variance, which accounts for the shape of\nthe density only, and the many-body position variance, which incorporates a\ntiny amount of excitations through the reduced two-particle density matrix,\nshows that the former behaves essentially as a quasi-one-dimensional quantity\nwhereas the latter as a two-dimensional quantity. This brings another dimension\nto the physics of bosons in ring-shaped traps."
    },
    {
        "anchor": "A Cold-Atom Particle Collider: A major objective of the strong ongoing drive to realize quantum simulators\nof gauge theories is achieving the capability to probe collider-relevant\nphysics on them. In this regard, a highly pertinent and sought-after\napplication is the controlled collisions of elementary and composite particles,\nas well as the scattering processes in their wake. Here, we propose\nparticle-collision experiments in a cold-atom quantum simulator for a $1+1$D\n$\\mathrm{U}(1)$ lattice gauge theory with a tunable topological $\\theta$-term,\nwhere we demonstrate an experimentally feasible protocol to impart momenta to\nelementary (anti)particles and their meson composites. We numerically benchmark\nthe collisions of moving wave packets for both elementary and composite\nparticles, uncovering a plethora of rich phenomena, such as oscillatory string\ndynamics in the wake of elementary (anti)particle collisions due to\nconfinement. We also probe string inversion and entropy production processes\nacross Coleman's phase transition through far-from-equilibrium quenches. We\nfurther demonstrate how collisions of composite particles unveil their internal\nstructure. Our work paves the way towards the experimental investigation of\ncollision dynamics in state-of-the-art quantum simulators of gauge theories,\nand sets the stage for microscopic understanding of collider-relevant physics\nin these platforms.",
        "positive": "Spin-1 Atoms in Optical Superlattices: Single-Atom Tunneling and\n  Entanglement: We examine spinor Bose-Einstein condensates in optical superlattices\ntheoretically using a Bose-Hubbard Hamiltonian that takes spin effects into\naccount. Assuming that a small number of spin-1 bosons is loaded in an optical\npotential, we study single-particle tunneling that occurs when one lattice site\nis ramped up relative to a neighboring site. Spin-dependent effects modify the\ntunneling events in a qualitative and quantitative way. Depending on the\nasymmetry of the double well different types of magnetic order occur, making\nthe system of spin-1 bosons in an optical superlattice a model for mesoscopic\nmagnetism. We use a double-well potential as a unit cell for a one-dimensional\nsuperlattice. Homogeneous and inhomogeneous magnetic fields are applied and the\neffects of the linear and the quadratic Zeeman shifts are examined. We also\ninvestigate the bipartite entanglement between the sites and construct states\nof maximal entanglement. The entanglement in our system is due to both orbital\nand spin degrees of freedom. We calculate the contribution of orbital and spin\nentanglement and show that the sum of these two terms gives a lower bound for\nthe total entanglement."
    },
    {
        "anchor": "Stability of Bose-Einstein condensates in a circular array: The properties of the superfluid phase of ultra cold bosonic atoms loaded in\na circular array are investigated in the framework of the Bose-Hubbard model\nand the Bogoliubov theory. We derive and solve the Gross-Pitaevskii equation of\nthe model to find that the atoms condense in states of well-defined\nquasimomentum. A detailed analysis of the coupling structure in the effective\nquadratic grand-canonical Hamiltonian shows that only pairs of distinct and\nidentical quasimomenta are coupled. Solving the corresponding Bogoliubov-de\nGennes equations we see that each pair of distinct quasimomenta gives raise to\ndoublets in the excitation energy spectrum and that the quasimomenta of the\nzero-energy mode and of the occupied state in the condensates are identical.\nThe dynamical and energetic stabilities of the condensates are determined by\nstudying the behavior of the elementary excitations in the control parameters\nspace. Our investigation establishes that superflow condensates exists only in\nthe central region of the first Brillouin zone whereas there is none in the\nlast quarters since they are energetically unstable, independently of the\ncontrol parameters.",
        "positive": "Effects of classical stochastic webs on the quantum dynamics of cold\n  atomic gases in a moving optical lattice: We introduce and investigate a system that uses temporal resonance-induced\nphase space pathways to create strong coupling between an atomic Bose-Einstein\ncondensate and a traveling optical lattice potential. We show that these\npathways thread both the classical and quantum phase space of the atom cloud,\neven when the optical lattice potential is arbitrarily weak. The topology of\nthe pathways, which form web-like patterns, can by controled by changing the\namplitude and period of the optical lattice. In turn, this control can be used\nto increase and limit the BEC's center-of-mass kinetic energy to pre-specified\nvalues. Surprisingly, the strength of the atom-lattice interaction and\nresulting BEC heating of the center-of-mass motion is enhanced by the repulsive\ninter-atomic interactions."
    },
    {
        "anchor": "Statistical mechanics of one-dimensional quantum droplets: We study the statistical mechanics and the dynamical relaxation process of\nmodulationally unstable one-dimensional quantum droplets described by a\nmodified Gross-Pitaevskii equation. To determine the classical partition\nfunction thereof, we leverage the semi-analytical transfer integral operator\n(TIO) technique. The latter predicts a distribution of the observed wave\nfunction amplitudes and yields two-point correlation functions providing\ninsights into the emergent dynamics involving quantum droplets. We compare the\nensuing TIO results with the probability distributions obtained at large times\nof the modulationally unstable dynamics as well as with the equilibrium\nproperties of a suitably constructed Langevin dynamics. We find that the\ninstability leads to the spontaneous formation of quantum droplets featuring\nmultiple collisions and by which are found to coalesce at large evolution\ntimes. Our results from the distinct methodologies are in good agreement aside\nfrom the case of low temperatures in the special limit where the droplet\nwidens. In this limit, the distribution acquires a pronounced bimodal\ncharacter, exhibiting a deviation between the TIO solution and the Langevin\ndynamics.",
        "positive": "Absence of two-body delocalization transitions in the two-dimensional\n  Anderson-Hubbard model: We investigate Anderson localization of two particles moving in a\ntwo-dimensional (2D) disordered lattice and coupled by contact interactions.\nBased on transmission-amplitude calculations for relatively large strip-shaped\ngrids, we find that all pair states are localized in lattices of infinite size.\nIn particular, we show that previous claims of an interaction-induced mobility\nedge are biased by severe finite-size effects. The localization length of a\npair with zero total energy exhibits a nonmonotonic behavior as a function of\nthe interaction strength, characterized by an exponential enhancement in the\nweakly interacting regime. Our findings also suggest that the many-body\nmobility edge of the 2D Anderson-Hubbard model disappears in the zero-density\nlimit, irrespective of the (bosonic or fermionic) quantum statistics of the\nparticles."
    },
    {
        "anchor": "Damping of elementary excitations in one-dimensional dipolar Bose gases: In the presence of dipolar interactions the excitation spectrum of a Bose gas\ncan acquire a local minimum. The corresponding quasiparticles are known as\nrotons. They are gaped and do not decay at zero temperature. Here we study the\ndecay of rotons in one-dimensional Bose gases at low temperatures. It\npredominantly occurs due to the backscattering of thermal phonons on rotons.\nThe resulting rate scales with the third power of temperature and is inversely\nproportional to the sixth power of the roton gap near the solidification phase\ntransition. The hydrodynamic approach used here enables us to find the decay\nrate for quasiparticles at practically any momenta, with minimal assumptions on\nthe exact form of the interparticle interactions. Our results are an essential\nprerequisite for the description of all the dissipative phenomena in dipolar\ngases and have direct experimental relevance.",
        "positive": "Topological $p_{x}+ip_{y}$ Superfluid Phase of a Dipolar Fermi Gas in a\n  2D Optical Lattice: In a dipolar Fermi gas, the anisotropic interaction between electric dipoles\ncan be turned into an effectively attractive interaction in the presence of a\nrotating electric field. We show that the topological $p_{x}+ip_{y}$ superfluid\nphase can be realized in a single-component dipolar Fermi gas trapped in a 2D\nsquare optical lattice with this attractive interaction at low temperatures.\nThe $p_{x}+ip_{y}$ superfluid state has potential applications for topological\nquantum computing. We obtain the phase diagram of this system at zero\ntemperature. In the weak-coupling limit, the p-wave superfluid phase is stable\nfor all filling factors. As the interaction strength increases, it is stable\nclose to filling factors $n=0$ or $n=1$, and phase separation takes place in\nbetween. When the interaction strength is above a threshold, the system is\nphase separated for any $0<n<1$. The transition temperature of the\n$p_{x}+ip_{y}$ superfluid state is estimated and the implication for\nexperiments is discussed."
    },
    {
        "anchor": "Free Bosons with a Localized Source: We analyze the time evolution of an open quantum system driven by a localized\nsource of bosons. We consider non-interacting identical bosons that are\ninjected into a single lattice site and and perform a continuous time quantum\nwalks on a lattice. We show that the average number of bosons grows\nexponentially with time when the input rate exceeds a certain lattice-dependent\ncritical value. Below the threshold, the growth is quadratic in time, which is\nstill much faster than the naive linear in time growth. We compute the critical\ninput rate for hyper-cubic lattices and find that it is positive in all\ndimensions $d$ except for $d=2$ where the critical input rate vanishes---the\ngrowth is always exponential in two dimensions. To understand the exponential\ngrowth, we construct an explicit microscopic Hamiltonian model which gives rise\nto the open system dynamics once the bath is traced out. Exponential growth is\nidentified with a region of dynamic instability of the Hamiltonian system.",
        "positive": "Formation of matter-wave soliton molecules: We propose a method of forming matter-wave soliton molecules that is inspired\nby the recent experiment of Dris {\\it et al.}. In the proposed set-up we show\nthat if two solitons are initially prepared in phase and with a sufficiently\nsmall separation and relative velocity, a bound pair will always form. This is\nverified by direct numerical simulation of the Gross-Pitaevskii equation and by\nthe derivation of the exact interaction energy of two solitons, which takes the\nform of a Morse potential. This interaction potential depends not only on the\nseparation but also on the relative phase of the solitons and is essential for\nan analytical treatment of a host of other problems, such as the soliton gas\nand the Toda lattice of solitons."
    },
    {
        "anchor": "Antiferromagnetism and superfluidity of a dipolar Fermi gas in a 2D\n  optical lattice: In a dipolar Fermi gas, the dipole-dipole interaction between fermions can be\nturned into a dipolar Ising interaction between pseduospins in the presence of\nan AC electric field. When trapped in a 2D optical lattice, such a dipolar\nFermi gas has a very rich phase diagram at zero temperature, due to the\ncompetition between antiferromagnetism and superfluidity. At half filling, the\nantiferromagnetic state is the favored ground state. The superfluid state\nappears as the ground state at a smaller filling factor. In between there is a\nphase-separated region. The order parameter of the superfluid state can display\ndifferent symmetries depending on the filling factor and interaction strength,\nincluding d-wave ($d$), extend s-wave ($xs$), or their linear combination\n($xs+i\\times d$). The implication for the current experiment is discussed.",
        "positive": "Controlling atomic spin-mixing via multiphoton transitions in a cavity: We propose to control spin-mixing dynamics in a gas of spinor atoms, via the\ncombination of two off-resonant Raman transition pathways, enabled by a common\ncavity mode and a bichromatic pump laser. The mixing rate, which is\nproportional to the synthesized spin-exchange interaction strength, and the\neffective atomic quadratic Zeeman shift (QZS), can both be tuned by changing\nthe pump laser parameters. Quench and driving dynamics of the atomic collective\nspin are shown to be controllable on a faster time scale than in existing\nexperiments based on inherent spin-exchange collision interactions. The results\nwe present open a promising avenue for exploring spin-mixing physics of atomic\nensembles accessible in current experiments."
    },
    {
        "anchor": "Anomalous Casimir effect in an expanding ring: The Casimir effect is a macroscopic evidence of the quantum nature of the\nvacuum. On a ring, it leads to a finite size correction to the vacuum energy.\nIn this work, we show that this vacuum's energy and pressure acquire\nadditional, sizable corrections, when the ring's radius is increased fast\nenough, an experimentally accessible model of an expanding universe. This\neffect is distinct from the dynamical Casimir effect: it is a manifestation of\nthe conformal anomaly, originating from the spacetime curvature induced by the\nincrease of the ring's radius. This anomalous dynamical Casimir effect is\nmeasurable through the work necessary to increase the ring size, which becomes\nnon-monotonous in time.",
        "positive": "Weyl points and topological nodal superfluids in a face-centered cubic\n  optical lattice: We point out that a face-centered cubic (FCC) optical lattice, which can be\nrealised by a simple scheme using three lasers, provides one a highly\ncontrollable platform for creating Weyl points and topological nodal\nsuperfluids in ultracold atoms. In non-interacting systems, Weyl points\nautomatically arise in the Floquet band structure when shaking such FCC\nlattices, and sophisticated design of the tunnelling is not required. More\ninterestingly, in the presence of attractive interaction between two hyperfine\nspin states, which experience the same shaken FCC lattice, a three-dimensional\ntopological nodal superfluid emerges, and Weyl points show up as the gapless\npoints in the quasiparticle spectrum. One could either create a double Weyl\npoint of charge 2, or split it to two Weyl points of charge 1, which can be\nmoved in the momentum space by tuning the interactions. Correspondingly, the\nFermi arcs at the surface may be linked with each other or separated as\nindividual ones."
    },
    {
        "anchor": "Evolution of squeezed states under the Fock-Darwin Hamiltonian: We develop a complete analytical description of the time evolution of\nsqueezed states of a charged particle under the Fock-Darwin Hamiltonian and a\ntime-dependent electric field. This result generalises a relation obtained by\nInfeld and Pleba\\'nski for states of the one-dimensional harmonic oscillator.\nWe relate the evolution of a state-vector subjected to squeezing to that of\nstate which is not subjected to squeezing and for which the time-evolution\nunder the simple harmonic oscillator dynamics is known (e.g. an eigenstate of\nthe Hamiltonian). A corresponding relation is also established for the Wigner\nfunctions of the states, in view of their utility in the analysis of cold-ion\nexperiments. In an appendix, we compute the response functions of the FD\nHamiltonian to an external electric field, using the same techniques as in the\nmain text.",
        "positive": "Few-fermion systems in one dimension: Ground- and excited-state energies\n  and contacts: Using the lattice Monte Carlo method, we compute the energy and Tan's contact\nin the ground state as well as the first excited state of few- to many-fermion\nsystems in a one-dimensional periodic box. We focus on unpolarized systems of\nN=4,6,...,12 particles, with a zero-range interaction, and a wide range of\nattractive couplings. In addition, we provide extrapolations to the\ninfinite-volume and thermodynamic limits."
    },
    {
        "anchor": "Characteristic quantities for nonequilibrium Bose systems: The paper discusses what characteristic quantities could quantify\nnonequilibrium states of Bose systems. Among such quantities, the following are\nconsidered: effective temperature, Fresnel number, and Mach number. The\nsuggested classification of nonequilibrium states is illustrated by studying a\nBose-Einstein condensate in a shaken trap, where it is possible to distinguish\neight different nonequilibrium states: weak nonequilibrium, vortex germs,\nvortex rings, vortex lines, deformed vortices, vortex turbulence, grain\nturbulence, and wave turbulence. Nonequilibrium states are created\nexperimentally and modeled by solving the nonlinear Schr\\\"odinger equation.",
        "positive": "Nematic-orbit coupling and nematic density waves in spin-1 condensates: We propose the creation of artificial nematic-orbit coupling in spin-1\nBose-Einstein condensates, in analogy to spin-orbit coupling. Using a suitably\ndesigned microwave chip, the quadratic Zeeman shift, normally uniform in space,\ncan be made to be spatio-temporally varying, leading to a coupling between\nspatial and nematic degrees of freedom. A phase diagram is explored where three\nquantum phases with the nematic order emerge: easy-axis, easy-plane with\nsingle-well and easy-plane with double well structure in momentum space. By\nincluding spin-dependent and spin-independent interactions, we also obtain the\nlow energy excitation spectra in these three phases. Lastly, we show that the\nnematic-orbit coupling leads to a periodic nematic density modulation in\nrelation to the period $\\lambda_T$ of the cosinusoidal quadratic Zeeman term.\nOur results point to the rich possibilities for manipulation of tensorial\ndegrees of freedom in ultracold gases without requiring Raman lasers, and\ntherefore, obviating light-scattering induced heating."
    },
    {
        "anchor": "Many-Body Quantum Optics with Decaying Atomic Spin States: ($\u03b3$,\n  $\u03ba$) Dicke model: We provide a theory for quantum-optical realizations of the open Dicke model\nwith internal, atomic spin states subject to spontaneous emission with rate\n$\\gamma$. This introduces a second decay channel for excitations to\nirreversibly dissipate into the environment, in addition to the photon loss\nwith rate $\\kappa$, which is composed of individual atomic decay processes and\na collective atomic decay mechanism. The strength of the latter is determined\nby the cavity geometry. We compute the mean-field non-equilibrium steady states\nfor spin and photon observables in the long-time limit, $t\\rightarrow \\infty$.\nAlthough $\\gamma$ does not conserve the total angular momentum of the spin\narray, we argue that our solution is exact in the thermodynamic limit, for the\nnumber of atoms $N\\rightarrow \\infty$. In light of recent and upcoming\nexperiments realizing superradiant phase transitions using internal atomic\nstates with pinned atoms in optical lattices, our work lays the foundation for\nthe pursuit of a new class of open quantum magnets coupled to quantum light.",
        "positive": "Kolmogorov turbulence defeated by Anderson localization for a\n  Bose-Einstein condensate in a Sinai-oscillator trap: We study the dynamics of a Bose-Einstein condensate in a Sinai-oscillator\ntrap under a monochromatic driving force. Such a trap is formed by a harmonic\npotential and a repulsive disk located in the center vicinity corresponding to\nthe first experiments of condensate formation by Ketterle group in 1995. We\nargue that the external driving allows to model the regime of weak wave\nturbulence with the Kolmogorov energy flow from low to high energies. We show\nthat in a certain regime of weak driving and weak nonlinearity such a turbulent\nenergy flow is defeated by the Anderson localization that leads to localization\nof energy on low energy modes. A critical threshold is determined above which\nthe turbulent flow to high energies becomes possible. We argue that this\nphenomenon can be studied with ultra cold atoms in magneto-optical traps."
    },
    {
        "anchor": "Enhancing variational Monte Carlo using a programmable quantum simulator: Programmable quantum simulators based on Rydberg atom arrays are a\nfast-emerging quantum platform, bringing together long coherence times,\nhigh-fidelity operations, and large numbers of interacting qubits\ndeterministically arranged in flexible geometries. Today's Rydberg array\ndevices are demonstrating their utility as quantum simulators for studying\nphases and phase transitions in quantum matter. In this paper, we show that\nunprocessed and imperfect experimental projective measurement data can be used\nto enhance in silico simulations of quantum matter, by improving the\nperformance of variational Monte Carlo simulations. As an example, we focus on\ndata spanning the disordered-to-checkerboard transition in a $16 \\times 16$\nsquare lattice array [S. Ebadi et al. Nature 595, 227 (2021)] and employ\ndata-enhanced variational Monte Carlo to train powerful autoregressive\nwavefunction ans\\\"atze based on recurrent neural networks (RNNs). We observe\nuniversal improvements in the convergence times of our simulations with this\nhybrid training scheme. Notably, we also find that pre-training with\nexperimental data enables relatively simple RNN ans\\\"atze to accurately capture\nphases of matter that are not learned with a purely variational training\napproach. Our work highlights the promise of hybrid quantum--classical\napproaches for large-scale simulation of quantum many-body systems, combining\nautoregressive language models with experimental data from existing quantum\ndevices.",
        "positive": "Matter-wave lensing of shell-shaped Bose-Einstein condensates: Motivated by the recent experimental realization of ultracold quantum gases\nin shell topology, we propose a straightforward implementation of matter-wave\nlensing techniques for shell-shaped Bose-Einstein condensates. This approach\nallows to significantly extend the observation time of the condensate shell\nduring its free expansion and enables the study of novel quantum many-body\neffects on curved geometries. With both analytical and numerical methods we\nderive optimal parameters for realistic lensing schemes to conserve the shell\nshape of the condensate for times up to hundreds of milliseconds."
    },
    {
        "anchor": "Antiferromagnetic spinor condensates in a two-dimensional optical\n  lattice: We experimentally demonstrate that spin dynamics and the phase diagram of\nspinor condensates can be conveniently tuned by a two-dimensional optical\nlattice. Spin population oscillations and a lattice-tuned separatrix in phase\nspace are observed in every lattice where a substantial superfluid fraction\nexists. In a sufficiently deep lattice, we observe a phase transition from a\nlongitudinal polar phase to a broken-axisymmetry phase in steady states of\nlattice-confined spinor condensates. The steady states are found to depend\nsigmoidally on the lattice depth and exponentially on the magnetic field. We\nalso introduce a phenomenological model that semi-quantitatively describes our\ndata without adjustable parameters.",
        "positive": "Coherence Times of Bose-Einstein Condensates beyond the Shot-Noise Limit\n  via Superfluid Shielding: We demonstrate a new way to extend the coherence time of separated\nBose-Einstein condensates that involves immersion into a superfluid bath. When\nboth the system and the bath have similar scattering lengths, immersion in a\nsuperfluid bath cancels out inhomogeneous potentials either imposed by external\nfields or inherent in density fluctuations due to atomic shot noise. This\neffect, which we call superfluid shielding, allows for coherence lifetimes\nbeyond the projection noise limit. We probe the coherence between separated\ncondensates in different sites of an optical lattice by monitoring the contrast\nand decay of Bloch oscillations. Our technique demonstrates a new way that\ninteractions can improve the performance of quantum devices."
    },
    {
        "anchor": "Modified Bose-Einstein condensation in an optical quantum gas: Open quantum systems can be systematically controlled by making changes to\ntheir environment. A well-known example is the spontaneous radiative decay of\nan electronically excited emitter, such as an atom or a molecule, which is\nsignificantly influenced by the feedback from the emitter's environment, for\nexample, by the presence of reflecting surfaces. A prerequisite for a\ndeliberate control of an open quantum system is to reveal the physical\nmechanisms that determine the state of the system. Here, we investigate the\nBose-Einstein condensation of a photonic Bose gas in an environment with\ncontrolled dissipation and feedback realised by a potential landscape that\neffectively acts as a Mach-Zehnder interferometer. Our measurements offer a\nhighly systematic picture of Bose-Einstein condensation under non-equilibrium\nconditions. We show that the condensation process is an interplay between\nminimising the energy of the condensate, minimising particle losses and\nmaximising constructive feedback from the environment. In this way our\nexperiments reveal physical mechanisms involved in the formation of a\nBose-Einstein condensate, which typically remain hidden when the system is\nclose to thermal equilibrium. Beyond a deeper understanding of Bose-Einstein\ncondensation, our results open new pathways in quantum simulation with optical\nBose-Einstein condensates.",
        "positive": "Elastic collision rates of spin-polarized fermions in two dimensions: We study the $p$-wave elastic collision rates in a two-dimensional\nspin-polarized ultracold Fermi gas in the presence of a $p$-wave Feshbach\nresonance. We derive the analytical relation of the elastic collision rate\ncoefficient in the close vicinity of resonance when the effective range is\ndominant. The elastic collision rate is enhanced by an exponential scaling of\n$e^{-q_{r}^{2} / q_{T}^{2}}$ towards the resonance. Here, $q_{r}$ is the\nresonant momentum and $q_T$ is the thermal momentum. An analogous expression is\nderived for the case of three dimensions successfully explains the\nthermalization rates measurement in the recent experiment~[Phys. Rev. A 88,\n012710 (2013)]. In the zero-range limit where the effective range is\nnegligible, the elastic collision rate coefficient is proportional to\ntemperature $T^2$ and scattering area $A_{p}^2$. In this limit, energy transfer\nfrom high to low velocity through $p$-wave collision is approximately\n$\\sqrt{2}$ times faster compared to the three-dimensional case. We also discuss\nthe collisional stability in the presence of three-body losses in the\nbackground scattering limit. Our results suggest that $p$-wave evaporation may\nbe performed with improved efficiency and may provide insight into the dynamics\nof the system in experiments."
    },
    {
        "anchor": "Isothermal compressibility and effects of multi-body molecular\n  interactions in a strongly interacting ultracold Fermi gas: We theoretically investigate the isothermal compressibility $\\kappa_{T}$ in\nthe normal state of an ultracold Fermi gas. Including pairing fluctuations, as\nwell as preformed-pair formations, within the framework of the self-consistent\n$T$-matrix approximation (SCTMA), we evaluate the temperature dependence of\nthis thermodynamic quantity over the entire BCS (Bardeen-Cooper-Schrieffer)-BEC\n(Bose-Einstein condensation) crossover region. While $\\kappa_T$ in the\nweak-coupling BCS regime is dominated by Fermi atoms near the Fermi surface,\ncorrelations between tightly bound Cooper-pair molecules are found to play\ncrucial roles in the strong-coupling BEC regime. In the latter region, besides\na two-body molecular interaction, a three-body one is shown to sizably affect\n$\\kappa_T$ near the superfluid phase transition temperature. Our results\nindicate that the strong-coupling BEC regime of an ultracold Fermi gas would\nprovide a unique opportunity to study multi-body correlations between\nCooper-pair molecules.",
        "positive": "Single Particle Spectroscopies of $p$-wave and $d$-wave Interacting Bose\n  Gases in Normal Phase: Motivated by experiments of interacting quantum gases across high partial\nwave resonance, we investigated the thermodynamic properties as well as single\nparticle spectrums of Bose gases in normal phase for different interaction\nstrengths both for $p$-wave and $d$-wave interactions. The free energy, contact\ndensity, momentum distributions, and self-energies of single particle Green's\nfunctions are obtained in the spirit of ladder diagram approximations. Radio\nfrequency (RF) spectrum, as an important experimental approach to detect\nFeshbach molecules or interaction effect, is calculated at different\ntemperatures. A reversed temperature dependence on the BEC side and BCS side is\nidentified for both $p$-wave and $d$-wave interactions. An estimation for the\nsignal of RF spectra under typical experimental conditions is also provided."
    },
    {
        "anchor": "Signatures of Self-Organised Criticality in an Ultracold Atomic Gas: Self organisation provides an elegant explanation for how complex structures\nemerge and persist throughout nature. Surprisingly often, these structures\nexhibit remarkably similar scale-invariant properties. While this is sometimes\ncaptured by simple models that feature a critical point as an attractor for the\ndynamics, the connection to real-world systems is exceptionally hard to test\nquantitatively. Here we observe three key signatures of self-organised\ncriticality in the dynamics of a driven-dissipative gas of ultracold atoms: (i)\nself-organisation to a stationary state that is largely independent of the\ninitial conditions, (ii) scale-invariance of the final density characterised by\na unique scaling function, and (iii) large fluctuations of the number of\nexcited atoms (avalanches) obeying a characteristic power-law distribution.\nThis establishes a well-controlled platform for investigating self-organisation\nphenomena and non-equilibrium criticality with unprecedented experimental\naccess to the underlying microscopic details of the system.",
        "positive": "Can we swim in superfluids?: Numerical demonstration of self-propulsion\n  in a Bose-Einstein condensate: It is numerically investigated whether a deformable object can propel itself\nin a superfluid. Articulated bodies and multi-component condensates are\nexamined as swimmers. An articulated two-body swimmer cannot obtain locomotion\nwithout emitting excitations. More flexible swimmers can do so without the need\nto excite waves."
    },
    {
        "anchor": "Normal and anomalous densities in Bose-Einstein condensate with optical\n  lattices: We study the quantum phase transition from the superfluid to the Mott\ninsulator state in two and three dimensional Bose-Einstein condensate (BEC)\nwith optical lattices using Bose-Hubbard Hamiltonian within the Generalized\nHatree-Fock-Bogoliubov (GHFB) approximation. The behavior of the depletion and\nthe anomalous fraction has been investigated in the Mott insulator phase. We\nfound that at T = 0, these quantities become significant in two and three\ndimensions. It is shown also that the dimensionality of the lattice enhances\nthe anomalous density.",
        "positive": "On the existence of an energy gap in one-dimensional Lesanovsky's model: We study the quantum lattice gas model in one dimension introduced by\nLesanovsky, who showed that the exact ground state and a couple of excited\nstates can be obtained analytically. The Hamiltonian of the model depends\nsolely on the parameter $z$, the meaning of which is a fugacity in the\ncorresponding classical lattice gas model. For small $z$ ($0<z<1$), we prove\nthat there is an energy gap between the ground state and the excited states by\napplying Knabe's method."
    },
    {
        "anchor": "Confinement induced interlayer molecules: a route to strong interatomic\n  interactions: We study theoretically the interaction between two species of ultracold atoms\nconfined into two layers of a finite separation, and demonstrate the existence\nof new types of confinement-induced interlayer bound and quasi-bound molecules:\nthese novel exciton-like interlayer molecules appear for both positive and\nnegative scattering lengths, and exist even for layer separations many times\nlarger than the interspecies scattering length. The lifetime of the quasi-bound\nmolecules grows exponentially with increasing layer separation, and they can\ntherefore be observed in simple shaking experiments, as we demonstrate through\ndetailed many-body calculations. These quasi-bound molecules can also give rise\nto novel interspecies Feshbach resonances, enabling one to control\ngeometrically the interaction between the two species by changing the layer\nseparation. Rather counter-intuitively, the species can be made strongly\ninteracting, by increasing their spatial separation. The separation induced\ninterlayer resonances provide a powerful tool for the experimental control of\ninterspecies interactions and enables one to realize novel quantum phases of\nmulticomponent quantum gases.",
        "positive": "Symmetry-breaking thermally induced collapse of dipolar Bose-Einstein\n  condensates: We investigate a Bose-Einstein condensate with additional long-range dipolar\ninteraction in a cylindrically symmetric trap within a variational framework.\nCompared to the ground state of this system, little attention has as yet been\npayed to its unstable excited states. For thermal excitations, however, the\nlatter is of great interest, because it forms the \"activated complex\" that\nmediates the collapse of the condensate. For a certain value of the s-wave\nscatting length our investigations reveal a bifurcation in the transition\nstate, leading to the emergence of two additional and symmetry-breaking excited\nstates. Because these are of lower energy than their symmetric counterpart, we\npredict the occurrence of a symmetry-breaking thermally induced collapse of\ndipolar condensates. We show that its occurrence crucially depends on the trap\ngeometry and calculate the thermal decay rates of the system within leading\norder transition state theory with the help of a uniform rate formula near the\nrank-2 saddle which allows to smoothly pass the bifurcation."
    },
    {
        "anchor": "Topological flat band with higher winding number in a superradiance\n  lattice: A five-level M-type scheme in atomic ensembles is proposed to generate a\none-dimensional bipartite superradiance lattice in momentum space. By taking\nadvantage of this tunable atomic system, we show that various types of\nSu-Schrieffer-Heeger (SSH) model, including the standard SSH and extended SSH\nmodel, can be realized. Interestingly, it is shown that through changing the\nRabi frequencies and detunings in our proposed scheme, there is a topological\nphase transition from topological trivial regime with winding number being 0 to\ntopological non-trivial regime with winding number being 2. Furthermore, a\nrobust flat band with higher winding number (being 2) can be achieved in the\nabove topological non-trivial regime, where the superradiance spectra can be\nutilized as a tool for experimental detection. Our proposal would provide a\npromising approach to explore new physics, such as fractional topological\nphases, in the flat bands with higher topological number.",
        "positive": "Unexpectedly Slow Two Particle Decay of Ultra-Dense Excitons in Cuprous\n  Oxide: For an ultra-dense exciton gas in cuprous oxide (Cu$_2$O), exciton-exciton\ninteractions are the dominant cause of exciton decay. This study demonstrates\nthat the accepted Auger recombination model overestimates the exciton decay\nrate following intense two photon excitation. Two exciton decay is relevant to\nthe search for collective quantum behavior of excitons in bulk systems. These\nresults suggest the existence of a new high density regime of exciton behavior."
    },
    {
        "anchor": "Contact parameters in two dimensions for general three-body systems: We study the two dimensional three-body problem in the general case of three\ndistinguishable particles interacting through zero-range potentials. The\nFaddeev decomposition is used to write the momentum-space wave function. We\nshow that the large-momentum asymptotic spectator function has the same\nfunctional form as derived previously for three identical particles. We derive\nanalytic relations between the three different Faddeev components for three\ndistinguishable particles. We investigate the one-body momentum distributions\nboth analytically and numerically and analyze the tail of the distributions to\nobtain two- and three-body contact parameters. We specialize from the general\ncases to examples of two identical, interacting or non-interacting, particles.\nWe find that the two-body contact parameter is not a universal constant in the\ngeneral case and show that the universality is recovered when a subsystem is\ncomposed of two identical non-interacting particles. We also show that the\nthree-body contact parameter is negligible in the case of one non-interacting\nsubsystem compared to the situation where all subsystem are bound. As example,\nwe present results for mixtures of Lithium with two Cesium or two Potassium\natoms, which are systems of current experimental interest.",
        "positive": "Spin dynamics and structure formation in a spin-1 condensate in a\n  magnetic field: We study the dynamics of a trapped spin-1 condensate in a magnetic field.\nFirst, we analyze the homogeneous system, for which the dynamics can be\nunderstood in terms of orbits in phase space. We analytically solve for the\ndynamical evolution of the populations of the various Zeeman components of the\nhomogeneous system. This result is then applied via a local density\napproximation to trapped quasi-1D condensates. Our analysis of the trapped\nsystem in a magnetic field shows that both the mean-field and Zeeman regimes\nare simultaneously realized, and we argue that the border between these two\nregions is where spin domains and phase defects are generated. We propose a\nmethod to experimentally tune the position of this border."
    },
    {
        "anchor": "Thermodynamic limit of the free electron gas on a circle: We show that for the ground state of a one dimensional free electron gas on a\ncircle the analytic expression for the canonical ensemble partition function\ncan be easily derived from the density matrix by assuming that the\nthermodynamic limit coincides with the limit of the eigenfunction expansion of\nthe kinetic energy. This approximation fails to give the finite temperature\npartition function because those two limits cannot be chosen as coincident.",
        "positive": "Simulating Dirac fermions with Abelian and non-Abelian gauge fields in\n  optical lattices: In this work we present an optical lattice setup to realize a full Dirac\nHamiltonian in 2+1 dimensions. We show how all possible external potentials\ncoupled to the Dirac field can arise from perturbations of the existing\ncouplings of the honeycomb lattice model, without the need of additional laser\nfields. This greatly simplifies the proposed implementations, requiring only\nspatial modulations of the intensity of the laser beams. We finally suggest\nseveral experiments to observe the properties of the Dirac field in the setup."
    },
    {
        "anchor": "Strong spin-exchange recombination of three weakly interacting $^7$Li\n  atoms: We reveal a significant spin-exchange pathway in the three-body recombination\nprocess for ultracold lithium-7 atoms near a zero-crossing of the two-body\nscattering length. This newly discovered recombination pathway involves the\nexchange of spin between all three atoms, which is not included in many\ntheoretical approaches with restricted spin structure. Taking it into account,\nour calculation is in excellent agreement with experimental observations. To\ncontrast our findings, we predict the recombination rate around a different\nzero-crossing without strong spin-exchange effects to be two orders of\nmagnitude smaller, which gives a clear advantage to future many-body\nexperiments in this regime. This work opens new avenues to study elementary\nreaction processes governed by the spin degree of freedom in ultracold gases.",
        "positive": "Investigating polaron transitions with polar molecules: We determine the phase diagram of a polaron model with mixed breathing-mode\nand Su-Schrieffer-Heeger couplings and show that it has two sharp transitions,\nin contrast to pure models which exhibit one (for Su-Schrieffer-Heeger\ncoupling) or no (for breathing-mode coupling) transition. Our results indicate\nthat the physics of realistic mixed polaron models is much richer than that of\nsimplified models. We then show that ultracold molecules trapped in optical\nlattices can be used to study precisely this mixed Hamiltonian, and that the\nrelative contributions of the two couplings can be tuned with external electric\nfields. The parameters of current experimental set-ups place them in the region\nwhere one of the transitions occurs. We propose a scheme to measure the polaron\ndispersion using stimulated Raman spectroscopy."
    },
    {
        "anchor": "Generalized Higgs mechanism in long-range interacting quantum systems: The physics of long-range interacting quantum systems is currently living\nthrough a renaissance driven by the fast progress in quantum simulators. In\nthese systems many paradigms of statistical physics do not apply and also the\nuniversal long-wavelength physics gets substantially modified by the presence\nof long-ranged forces. Here we explore the low-energy excitations of several\nlong-range interacting quantum systems, including spin models and interacting\nBose gases, in the ordered phase associated with the spontaneous breaking of\nU(1) and SU(2) symmetries. Instead of the expected Goldstone modes, we find\nthree qualitatively different regimes, depending on the range of the\ninteraction. In one of these regimes the Goldstone modes are gapped, via a\ngeneralization of the Higgs mechanism. Moreover, we show how this effect is\nrealized in current experiments with ultracold atomic gases in optical\ncavities.",
        "positive": "Reentrant stability of BEC standing wave patterns: We describe standing wave patterns induced by an attractive finite-ranged\nexternal potential inside a large Bose-Einstein Condensate (BEC). As the\npotential depth increases, the time independent Gross-Pitaevskii equation\ndevelops pairs of solutions that have nodes in their wavefunction. We elucidate\nthe nature of these states and study their dynamical stability. Although we\nstudy the problem in a two-dimensional BEC subject to a cylindrically symmetric\nsquare-well potential of a radius that is comparable to the coherence length of\nthe BEC, our analysis reveals general trends, valid in two and three\ndimensions, independent of the symmetry of the localized potential well, and\nsuggestive of the behavior in general, short- and large-range potentials. One\nset of nodal BEC wavefunctions resembles the single particle n node bound state\nwavefunction of the potential well, the other wavefunctions resemble the n-1\nnode bound-state wavefunction with a kink state pinned by the potential. The\nsecond state, though corresponding to the lower free energy value of the pair\nof n node BEC states, is always unstable, whereas the first can be dynamically\nstable in intervals of the potential well depth, implying that the standing\nwave BEC can evolve from a dynamically unstable to stable, and back to unstable\nstatus as the potential well is adiabatically deepened, a phenomenon that we\nrefer to as \"reentrant dynamical stability\"."
    },
    {
        "anchor": "Light-cone like spreading of single-particle correlations in the\n  Bose-Hubbard model after a quantum quench in the strong coupling regime: We study the spreading of correlations in space and time after a quantum\nquench in the Bose Hubbard model. We derive equations of motion for the\nsingle-particle Green's function within the contour-time formalism, allowing us\nto study dynamics in the strong coupling regime. We discuss the numerical\nsolutions of these equations and calculate the single-particle density matrix\nfor quenches in the Mott phase. We demonstrate light-cone like spreading of\ncorrelations in the Mott phase in one, two, and three dimensions and calculate\npropagation velocities in each dimension.",
        "positive": "Dynamical crystal creation with polar molecules or Rydberg atoms in\n  optical lattices: We investigate the dynamical formation of crystalline states with systems of\npolar molecules or Rydberg atoms loaded into a deep optical lattice. External\nfields in these systems can be used to couple the atoms or molecules between\ntwo internal states: one that is weakly interacting and one that exhibits a\nstrong dipole-dipole interaction. By appropriate time variation of the external\nfields, we show that it is possible to produce crystalline states of the\nstrongly interacting states with high filling fractions chosen via the\nparameters of the coupling. We study the coherent dynamics of this process in\none dimension (1D) using a modified form of the time-evolving block decimation\n(TEBD) algorithm, and obtain crystalline states for system sizes and parameters\ncorresponding to realistic experimental configurations. For polar molecules\nthese crystalline states will be long-lived, assisting in a characterization of\nthe state via the measurement of correlation functions. We also show that as\nthe coupling strength increases in the model, the crystalline order is broken.\nThis is characterized in 1D by a change in density-density correlation\nfunctions, which decay to a constant in the crystalline regime, but show\ndifferent regions of exponential and algebraic decay for larger coupling\nstrengths."
    },
    {
        "anchor": "Super Efimov effect for mass-imbalanced systems: We study two species of particles in two dimensions interacting by isotropic\nshort-range potentials with the interspecies potential fine-tuned to a p-wave\nresonance. Their universal low-energy physics can be extracted by analyzing a\nproperly constructed low-energy effective field theory with the renormalization\ngroup method. Consequently, a three-body system consisting of two particles of\none species and one of the other is shown to exhibit the super Efimov effect,\nthe emergence of an infinite tower of three-body bound states with orbital\nangular momentum $l=\\pm1$ whose binding energies obey a doubly exponential\nscaling, when the two particles are heavier than the other by a mass ratio\ngreater than 4.03404 for identical bosons and 2.41421 for identical fermions.\nWith increasing the mass ratio, the super Efimov spectrum becomes denser which\nwould make its experimental observation easier. We also point out that the\nBorn-Oppenheimer approximation is incapable of reproducing the super Efimov\neffect, the universal low-energy asymptotic scaling of the spectrum.",
        "positive": "Effects of three-body scattering processes on BCS-BEC crossover: We investigate the BCS-BEC crossover taking into account an additional\nthree-body interaction, which is essentially the scattering between the Cooper\npairs and the newly formed bosons. We show that if the two-body interaction is\nattractive, the presence of this additional three-body term makes the crossover\nprocess a nonreversible one. Starting from a stable Bose-Einstein condensate\n(BEC) state, crossover to BCS can be achieved; but if the BCS state is the\nstarting point, instead of a stable BEC region, what the system crosses over to\nis a metastable condensed state."
    },
    {
        "anchor": "Ensemble master equation for a trapped-atom clock with one- and two-body\n  losses: An ensemble density matrix model that includes one- and two-body losses is\nderived for a trapped-atom clock. A trapped-atom clock is mainly affected by\none- and two-body losses, generally giving nonexponential decays of\npopulations; nevertheless, three-body recombination is also quantitatively\nanalyzed to demonstrate the boundaries of its practical relevance. The\nimportance of one-body losses is highlighted without which population trapping\nbehavior would be observed. The model is written with decay constants expressed\nthrough experimental parameters. It can complement, e.g., the ISRE (identical\nspin rotation effect) model to improve its predictions: ISRE dramatically\nincreases the ensemble coherence time, hence it enables one to observe the\ninfluence of two-body losses on the interferometry contrast envelope. The\npresented model is useful for Ramsey interferometry and is ready for immediate\nexperimental verification in existing systems.",
        "positive": "Ground state of weakly repulsive soft-core bosons on a sphere: We study a system of penetrable bosons embedded in a spherical surface. Under\nthe assumption of weak interaction between the particles, the ground state of\nthe system is, to a good approximation, a pure condensate. We employ\nthermodynamic arguments to investigate, within a variational ansatz for the\nsingle-particle state, the crossover between distinct finite-size \"phases\" in\nthe parameter space spanned by the sphere radius and the chemical potential. In\nparticular, for radii up to a few interaction ranges we examine the stability\nof the fluid phase with respect to a number of crystal-like arrangements having\nthe symmetry of a regular or semi-regular polyhedron. We find that, while\nquantum fluctuations keep the system fluid at low density, upon compression it\neventually becomes inhomogeneous, i.e., particles gather together in clusters.\nAs the radius increases, the nature of the high-density aggregate varies and we\nobserve a sequence of transitions between different cluster phases (\"solids\"),\nwhose underlying rationale is to maximize the coordination number of clusters,\nwhile ensuring at the same time the proper distance between each neighboring\npair. We argue that, at least within our mean-field description, every cluster\nphase is supersolid."
    },
    {
        "anchor": "Universal coarsening dynamics of a quenched ferromagnetic spin-1\n  condensate: We demonstrate that a quasi-two-dimensional spin-1 condensate quenched to a\nferromagnetic phase undergoes universal coarsening in its late time dynamics.\nThe quench can be implemented by a sudden change in the applied magnetic field\nand, depending on the final value, the ferromagnetic phase has easy-axis\n(Ising) or easy-plane (XY) symmetry, with different dynamical critical\nexponents. Our results for the easy-plane phase reveal a fractal domain\nstructure and the crucial role of polar-core spin vortices in the coarsening\ndynamics.",
        "positive": "Topological semimetal and superfluid of s-wave interacting fermionic\n  atoms in an orbital optical lattice: Recent advanced experimental implementations of optical lattices with highly\ntunable geometry open up new regimes for quantum many-body states of matter\nthat previously had not been accessible. Here we introduce a symmetry-based\nmethod of utilizing the geometry of optical lattice to systematically control\ntopologically non-trivial orbital hybridization. Such an orbital mixing leads\nto an unexpected and yet robust topological semimetal at single-particle level\nfor a gas of fermionic atoms. When considering s-wave attractive interaction\nbetween atoms as for instance tuned by Feshbach resonance, topological\nsuperfluid state with high Chern number is unveiled in the presence of on-site\nrotation. This state supports chiral edge excitations, manifesting its\ntopological nature. An experimental realization scheme is designed, which\nintroduces a systematic way of achieving a new universality class (such as\nChern number of 2) of orbital-hybridized topological phases beyond\ngeometrically standard optical lattices."
    },
    {
        "anchor": "Hidden Quantum Criticality and Entanglement in Quench Dynamics: Entanglement exhibits universal behavior near the ground-state critical point\nwhere correlations are long-ranged and the thermodynamic entropy is vanishing.\nOn the other hand, a quantum quench imparts extensive energy and results in a\nbuild-up of entropy, hence no critical behavior is expected at long times. In\nthis work, we present a new paradigm in the quench dynamics of integrable spin\nchains which exhibit a ground-state order-disorder phase transition at a\ncritical line. Specifically, we consider a quench along the critical line which\ndisplays a volume-law behavior of the entropy and exponentially decaying\ncorrelations; however, we show that quantum criticality is hidden in\nhigher-order correlations and becomes manifest via measures such as the mutual\ninformation and logarithmic negativity. Furthermore, we showcase the\nscale-invariance of the R\\'{e}nyi mutual information between disjoint regions\nas further evidence for genuine critical behavior. We attribute the emerging\nuniversality to the vanishing effective temperature of the soft mode in spite\nof the quench. Our results are amenable to an experimental realization on\ndifferent quantum simulator platforms, particularly the Rydberg simulators.",
        "positive": "Bosons with long range interactions on two-leg ladders in artificial\n  magnetic fields: Motivated by experiments exploring the physics of neutral atoms in artificial\nmagnetic fields, we study the ground state of bosons interacting with long\nrange dipolar interactions on a two-leg ladder. Using two complimentary\nvariational approaches, valid for weak interactions, we find rich physics\ndriven by the long range forces. Generically, long range interactions tend to\ndestroy the Meissner phase in favor of modulated density wave phases. Nearest\nneighbor interactions produce a novel interleg charge density wave phase, where\nthe total density remains uniform, but the density on each leg of the ladder is\nmodulating in space, out-of-phase with one another. At weak magnetic fields,\nnext nearest neighbor interactions lead to a fully modulated biased ladder\nphase, where all the particles are on one leg of the ladder, and the density is\nmodulating in space. This state simultaneously breaks $Z_{2}$ reflection\nsymmetry and $U(1)$ symmetry associated with translation in real space. For\nvalues of the flux near $\\phi = \\pi$, we find that a switching effect occurs\nfor arbitrarily weak interactions, where the density modulates in space, but\nthe chiral current changes sign on every plaquette. Arbitrarily weak attractive\ninteractions along the rungs destroy the Meissner phase completely, in favor of\na modulated density wave phase. Varying magnetic field produces a cascade of\nfirst order transitions between modulated density wave states with different\nwave-vectors, which manifests itself as discrete jumps in the chiral current.\nPolarizing the dipoles along the ladder direction yields a region of phase\nspace where a stable biased ladder phase occurs even at arbitrarily weak\nmagnetic fields. We discuss the experimental consequences of our work, in\nparticular, how the interleg charge density wave can manifest itself in recent\nexperiments on bosons in synthetic dimensions."
    },
    {
        "anchor": "Magnetic oscillations for neutral atoms subject to an electromagnetic\n  field: We show that the de Haas van Alphen effect can be induced in a two\ndimensional atomic gas by the He-McKellar-Wilkens interaction mediated via an\nelectric dipole moment. Under an appropriate field-dipole configuration, we\nshow that the neutral atoms subject to a synthetic magnetic field arrange\nthemselves in Landau levels. An experimental arrangement for observation of the\natomic analog of dHvA oscillations is proposed. In a strong effective magnetic\nfield regime we present the quantum oscillations in the energy and effective\nmagnetization of the two dimensional atomic gas. From the dHvA period we\ndetermine the area of the Fermi circle of the atomic cloud.",
        "positive": "Optical tweezers for vortex rings in Bose-Einstein condensates: We study formation and stabilization of vortex rings in atomic Bose-Einstein\ncondensates. We suggest a novel approach for generating and trapping of vortex\nrings by 'optical tweezers'--two blue-detuned optical beams forming a toroidal\nvoid in the bulk of a magnetically or optically confined condensate cloud. We\ndemonstrate that matter-wave vortex rings trapped within the void are\nenergetically and dynamically stable. Our theoretical findings suggest the\npossibility for generation, stabilization, and nondestructive manipulation of\nquantized vortex rings in experimentally feasible trapping configurations."
    },
    {
        "anchor": "Generation of uniform synthetic magnetic fields by split driving of an\n  optical lattice: We describe a method to generate a synthetic gauge potential for ultracold\natoms held in an optical lattice. Our approach uses a time-periodic driving\npotential based on two quickly alternating signals to engineer the appropriate\nAharonov-Bohm phases, and permits the simulation of a uniform tunable magnetic\nfield. We explicitly demonstrate that our split driving scheme reproduces the\nbehavior of a charged quantum particle in a magnetic field over the complete\nrange of field strengths, and obtain the Hofstadter butterfly band-structure\nfor the Floquet quasienergies at high fluxes.",
        "positive": "Tunable critical supercurrent and spin-asymmetric Josephson effect in\n  superlattices: Combining the Josephson effect with magnetism, or spin dependence in general,\ncreates novel physical phenomena. The spin-asymmetric Josephson effect is a\npredicted phenomenon where a spin-dependent potential applied across a\nJosephson junction induces a spin-polarized Josephson current. Here, we propose\nan approach to observe the spin-asymmetric Josephson effect with spin-dependent\nsuperlattices, realizable, e.g., in ultracold atomic gases. We show that\nobserving this effect is feasible by studying numerically the quantum dynamics\nof the system in one dimension. Furthermore, we show that the enhancement, or\ntunability, of the critical supercurrent in ferromagnetic Josephson junctions\n[F. S. Bergeret, A. F. Volkov, and K. B. Efetov, Phys. Rev. Lett. 86, 3140\n(2001)] can be explained by the spin-asymmetric Josephson effect."
    },
    {
        "anchor": "Topological Uniform Superfluid and FFLO Phases in 3D to 1D crossover of\n  spin-orbit coupled Fermi gases: We consider the quasi-one dimensional system realized by an array of weakly\ncoupled parallel one-dimensional \"tubes\" in a two-dimensional lattice which\npermits free motion of atoms in an axial direction in the presence of a Zeeman\nfield, Rashba type spin orbit coupling (SOC), and an s-wave attractive\ninteraction, while the radial motion is tightly confined. We solve the\nzero-temperature (T=0) Bogoliubov-de Gennes (BdG) equations for the quasi-1D\nFermi gas with the dispersion modified by tunneling between the tubes, and show\nthat the T=0 phase diagram hosts the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)\nphase with non-zero center of mass momentum Cooper pairs for small values of\nthe SOC while for larger values of the SOC and high Zeeman fields the uniform\nsuperfluid phase with zero center of mass momentum Cooper pairs has an\ninstability towards the topological uniform superfluid phase with Majorana\nfermions at the tube ends. Also, we show that tuning the two-dimensional\noptical lattice strength in this model allows one to explore the crossover\nbehaviors of the phases during the transition between the 3D and the 1D system\nand in general the FFLO (for small SOC) and the topological uniform superfluid\nphase (for large SOC) are favored as the system becomes more one-dimensional.\nWe also find evidence of the existence of a Zeeman tuned topological quantum\nphase transition (TQPT) within the FFLO phase itself and for large values of\nthe Zeeman field and small SOC the TQPT gives rise to a topologically distinct\nFFLO phase.",
        "positive": "Radial Fulde-Ferrell-Larkin-Ovchinnikov state in a population-imbalanced\n  Fermi gas: The possibility of a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state in a\npopulation imbalanced Fermi gas with a vortex is proposed. Employing the\nBogoliubov-de-Gennes formalism we self-consistently determine the superfluid\norder parameter and the particle number density in the presence of a vortex. We\nfind that as increasing population imbalance, the superfluid order parameter\nspatially oscillates around the vortex core in the radial direction, indicating\nthat the FFLO state becomes stable. We find that the radial FFLO states cover a\nwide region of the phase diagram in the weak-coupling regime at $T=0$ in\ncontrast to the conventional case without a vortex. We show that this\ninhomogeneous superfluidity can be detected as peak structures of the local\npolarization rate associated with the node structure of the superfluid order\nparameter. Since the vortex in the 3D Fermi gas with population imbalance has\nbeen already realized in experiments, our proposal is a promising candidate of\nthe FFLO state in cold atom physics."
    },
    {
        "anchor": "On the quantization of the Hall conductivity in the Harper-Hofstadter\n  model: We study the robustness of the quantization of the Hall conductivity in the\nHarper-Hofstadter model towards the details of the protocol with which a\nlongitudinal uniform driving force $F_x(t)$ is turned on. In the vector\npotential gauge, through Peierls substitution, this involves the switching-on\nof complex time-dependent hopping amplitudes\n$\\mathrm{e}^{-\\frac{i}{\\hbar}\\mathcal{A}_x(t)}$ in the\n$\\hat{\\mathbf{x}}$-direction such that $\\partial_t \\mathcal{A}_x(t)=F_x(t)$.\nThe switching-on can be sudden, $F_x(t)=\\theta(t) F$, where $F$ is the steady\ndriving force, or more generally smooth $F_x(t)=f(t/t_{0}) F$, where\n$f(t/t_{0})$ is such that $f(0)=0$ and $f(1)=1$. We investigate how the\ntime-averaged (steady-state) particle current density $j_y$ in the\n$\\hat{\\mathbf{y}}$-direction deviates from the quantized value $j_y \\, h/F = n$\ndue to the finite value of $F$ and the details of the switching-on protocol.\nExploiting the time-periodicity of the Hamiltonian $\\hat{H}(t)$, we use Floquet\ntechniques to study this problem. In this picture the (Kubo) linear response\n$F\\to 0$ regime corresponds to the adiabatic limit for $\\hat{H}(t)$. In the\ncase of a sudden quench $j_y \\, h/F$ shows $F^2$ corrections to the perfectly\nquantized limit. When the switching-on is smooth, the result depends on the\nswitch-on time $t_{0}$: for a fixed $t_{0}$ we observe a crossover force $F^*$\nbetween a quadratic regime for $F<F^*$ and a {\\em non-analytic} exponential\n$\\mathrm{e}^{-\\gamma/|F|}$ for $F>F^*$. The crossover $F^*$ decreases as\n$t_{0}$ increases, eventually recovering the topological robustness. These\neffects are in principle amenable to experimental tests in optical lattice cold\natomic systems with synthetic gauge fields.",
        "positive": "Dynamics of fermions in an amplitude modulated lattice: We study dynamics of fermions loaded in an optical lattice with a\nsuperimposed parabolic trap potential. In the recent Hamburg experiments\n[J.Heinze et.al., Phys. Rev. Lett. 110, 085302 (2013)] on quantum simulation of\nphotoconductivity, a modulation pulse on the optical lattice transferred part\nof the population of the lowest band to an excited band, leaving a hole in the\nparticle distribution of the lowest band. Subsequent intricate dynamics of both\nexcited particles and holes can be explained by a semiclassical approach based\non the evolution of Wigner function. Here we provide a more detailed analysis\nof the dynamics taking into account the dimensionality of the system and finite\ntemperature effects, aiming at reproducing experimental results on longer\ntimescales. A semiclassical wave packet is constructed more accurately than in\nthe previous theory. As a result, semiclassical dynamics indeed reproduces\nexperimental data and full quantum numerical calculations with much better\naccuracy. In particular, fascinating phenomenon of collapse and revival of\nholes is investigated in a more detail. We presume the experimental setup can\nbe used for deeper exploration of nonlinear waves in fermionic gases."
    },
    {
        "anchor": "Self trapping in the two-dimensional Bose-Hubbard model: We study the expansion of harmonically trapped bosons in a two-dimensional\nlattice after suddenly turning off the confining potential. We show that, in\nthe presence of multiple occupancies per lattice site and strong interactions,\nthe system exhibits a clear dynamical separation into slowly and rapidly\nexpanding clouds. We discuss how this effect can be understood within a simple\npicture by invoking doublons and Bose enhancement. This picture is corroborated\nby an analysis of the momentum distribution function in the regions with slowly\nand rapidly expanding bosons.",
        "positive": "Inflationary Dynamics and Particle Production in a Toroidal\n  Bose-Einstein Condensate: We present a theoretical study of the dynamics of a Bose-Einstein condensate\n(BEC) trapped inside an expanding toroid that can realize an analogue\ninflationary universe. As the system expands, we find that phonons in the BEC\nundergo redshift and damping due to quantum pressure effects. We predict that\nrapidly expanding toroidal BEC's can exhibit spontaneous particle creation, and\nstudy this phenomenon in the context of an initial coherent state wavefunction.\nWe show how particle creation would be revealed in the atom density and density\ncorrelations, and discuss connections to the cosmological theory of inflation."
    },
    {
        "anchor": "Relaxation dynamics of ultracold bosons in a double-well potential:\n  Thermalization and prethermalization in a nearly integrable model: We numerically investigate the relaxation dynamics in an isolated quantum\nsystem of interacting bosons trapped in a double-well potential after an\nintegrability breaking quench. Using the statistics of the spectrum, we\nidentify the postquench Hamiltonian as nonchaotic and close to integrability\nover a wide range of interaction parameters. We demonstrate that the system\nexhibits thermalization in the context of the eigenstate thermalization\nhypothesis (ETH). We also explore the possibility of an initial state to\ndelocalize with respect to the eigenstates of the postquench Hamiltonian even\nfor energies away from the middle of the spectrum. We observe distinct regimes\nof equilibration process depending on the initial energy. For low energies, the\nsystem rapidly relaxes in a single step to a thermal state. As the energy\nincreases towards the middle of the spectrum, the relaxation dynamics exhibits\nprethermalization and the lifetime of the metastable states grows. Time\nevolution of the occupation numbers and the von Neumann entropy in the\nmode-partitioned system underpins the analyses of the relaxation dynamics.",
        "positive": "Tunable topological phases with fermionic atoms in a one-dimensional\n  flux lattice: We present a simple scheme for implementing a one-dimensional (1D)\nmagnetic-flux lattice of ultracold fermionic spin-$1/2$ atoms. The resulting\ntight-binding model supports gapped and gapless topological phases, and chiral\ncurrents for Meissner and vortex phases. Its single-particle spectra exhibit\ntopological flat bands at small flux, and the flatness sensitively depends on\nhopping strength. An effective $p$-wave interaction arises in a $s$-wave paired\nsuperfluid. Treating atomic internal states as forming a synthetic dimension\nand balancing the interplay of magnetic flux and Zeeman field, our model\ndescribes a tunable topological Fermi superfluid, which paves the way towards\nexperimental explorations of non-Abelian topological matter in 1D atomic\nquantum gases."
    },
    {
        "anchor": "Hysteresis of noninteracting and spin-orbit coupled atomic Fermi gases\n  with relaxation: Hysteresis can be found in driven many-body systems such as magnets and\nsuperfluids. Rate-dependent hysteresis arises when a system is driven\nperiodically while relaxing towards equilibrium. A two-state paramagnet driven\nby an oscillating magnetic field in the relaxation approximation clearly\ndemonstrates rate-dependent hysteresis. A noninteracting atomic Fermi gas in an\noptical ring potential, when driven by a periodic artificial gauge field and\nsubjected to dissipation, is shown to exhibit hysteresis loops of atomic\ncurrent due to a competition of the driving time and the relaxation time. This\nis in contrast to electronic systems exhibiting equilibrium persistent current\ndriven by magnetic flux due to rapid relaxation. Universal behavior of the\ndissipated energy in one hysteresis loop is observed in both the magnetic and\natomic systems, showing linear and inverse-linear dependence on the relaxation\ntime in the strong and weak dissipation regimes. While interactions in general\ninvalidate the framework for rate-dependent hysteresis, an atomic Fermi gas\nwith artificial spin-orbit coupling exhibits hysteresis loops of atomic\ncurrents. Cold-atoms in ring-shape potentials are thus promising in\ndemonstrating rate-dependent hysteresis and its associated phenomena.",
        "positive": "Lattice Boltzmann simulations of a two-dimensional Fermi gas at\n  unitarity: We present fully nonlinear dissipative fluid dynamics simulations of a\ntrapped two-dimensional Fermi gas at unitarity using a Lattice Boltzmann\nalgorithm. We are able to simulate non-harmonic trapping potentials,\ntemperature-dependent viscosities as well as a discretized version of the\nballistic (non-interacting) behavior. Our approach lends itself to direct\ncomparison with experimental data, opening up the possibility of a precision\ndetermination of transport coefficients in the unitary Fermi gas. Furthermore,\nwe predict the presence of a non-hydrodynamic component in the quadrupole mode,\nwhich should be observable experimentally."
    },
    {
        "anchor": "Observation of topological phase with critical localization in a\n  quasi-periodic lattice: Disorder and localization have dramatic influence on the topological\nproperties of a quantum system. While strong disorder can close the band gap\nthus depriving topological materials of topological features, disorder may also\ninduce topology from trivial band structures, wherein topological invariants\nare shared by completely localized states in real space. Here we experimentally\ninvestigate a fundamentally distinct scenario where a topological phase is\nidentified in a critically localized regime, with eigenstates neither fully\nextended nor completely localized. Adopting the technique of momentum-lattice\nengineering for ultracold atoms, we implement a one-dimensional, generalized\nAubry-Andr\\'e model with off-diagonal quasi-periodic disorder in momentum\nspace, and characterize its localization and topological properties through\ndynamic observables. We then demonstrate the impact of interactions on the\ncritically localized topological state, as a first experimental endeavour\ntoward the clarification of many-body critical phase, the critical analogue of\nthe many-body localized state.",
        "positive": "Detecting topological transitions in two dimensions by Hamiltonian\n  evolution: We show that the evolution of two-component particles governed by a\ntwo-dimensional spin-orbit lattice Hamiltonian can reveal transitions between\ntopological phases. A kink in the mean width of the particle distribution\nsignals the closing of the band gap, a prerequisite for a quantum phase\ntransition between topological phases. Furthermore, for realistic and\nexperimentally motivated Hamiltonians the density profile in topologically\nnon-trivial phases displays characteristic rings in the vicinity of the origin\nthat are absent in trivial phases. The results are expected to have immediate\napplication to systems of ultracold atoms and photonic lattices."
    },
    {
        "anchor": "Correlation dynamics of strongly-correlated bosons in time-dependent\n  optical lattices: We analyze by means of Matrix-Product-State simulations the correlation\ndynamics of strongly-correlated superfluid Bose gases in one-dimensional\ntime-dependent optical lattices. We show that, as for the case of abrupt\nquenches, a quasi-adiabatic modulation of the lattice is characterized by a\nrelatively long transient regime for which quasi-local single-particle\ncorrelation functions have already converged to a new equilibrium, whereas\nlong-range correlations and particularly the quasi-condensate fraction may\nstill present a very significant dynamics well after the end of the lattice\nmodification. We also address the issue of adiabaticity by considering the\nfidelity between the time-evolved state and the ground-state of the final\nlattice.",
        "positive": "Introduction to the physics of artificial gauge fields: Simulating magnetic effects with cold gases of neutral atoms is a challenge.\nSince these atoms have no charge, one needs to create artificial gauge fields\nby taking advantage of the geometric phases that can result for instance from\natom-light interaction. We review here some schemes that lead to the desired\nHamiltonians, either in a bulk geometry or in a lattice configuration. We also\ndetail the relations between some general concepts of magnetism, such as gauge\ninvariance, Landau levels, topological bands, and the features that can be\ngenerated in cold atoms setups."
    },
    {
        "anchor": "Dynamics of spontaneous symmetry breaking in a space-time crystal: We present the theory of spontaneous symmetry breaking (SSB) of discrete time\ntranslations as recently realized in the space-time crystals of an atomic\nBose-Einstein condensate. The non-equilibrium physics related to such a\ndriven-dissipative system is discussed in both the Langevin as well as the\nFokker-Planck formulation. We consider a semi-classical and a fully quantum\napproach, depending on the dissipation being either frequency independent or\nlinearly dependent on frequency, respectively. For both cases, the Langevin\nequation and Fokker-Planck equation are derived, and the resulting equilibrium\ndistribution is studied. We also study the time evolution of the space-time\ncrystal and focus in particular on its formation and the associated dynamics of\nthe spontaneous breaking of a Z2 symmetry out of the symmetry unbroken phase,\ni.e., the equilibrium Bose-Einstein condensate before the periodic drive is\nturned on. Finally, we compare our results with experiments and conclude that\nour theory provides a solid foundation for the observations.",
        "positive": "Enhanced Fulde-Ferrell-Larkin-Ovchinnikov and Sarma superfluid states\n  near an orbital Feshbach resonance: We investigate the inhomogeneous Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) and\nhomogeneous Sarma superfluid states in alkaline-earth-like $^{173}$Yb atomic\ngases near an orbital Feshbach resonance at zero temperature with population\nimbalances in both the open and closed channels (or bands). We find that in\nhomogeneous space by adjusting the open-channel Zeeman energy $h_o$, both the\nSarma and Fulde-Ferrell superfluid states are greatly enhanced by the\nspin-exchange interaction while the closed-channel Zeeman energy $h_c$ remains\nsmall. In the presence of an external harmonic trap, the trapped gas features a\nshell structure of separated phases, where the Sarma phase leaves detectable\nvalley structure in the columnar-integrated momentum distribution, and the\nFulde-Ferrell state acquires enhanced spatial anisotropy. As both signatures\ncan be easily detected in time-of-flight images, our findings are helpful to\nrealize and detect the long-sought FFLO and Sarma superfluid states at the same\ntime in experiments."
    },
    {
        "anchor": "The strongly driven Fermi polaron: Quasiparticles are emergent excitations of matter that underlie much of our\nunderstanding of quantum many-body systems. Therefore, the prospect of\nmanipulating their properties with external fields -- or even destroying them\n-- has both fundamental and practical implications. However, in solid-state\nmaterials it is often challenging to understand how quasiparticles are modified\nby external fields owing to their complex interplay with other collective\nexcitations, such as phonons. Here, we take advantage of the clean setting of\nhomogeneous quantum gases and fast radio-frequency control to manipulate Fermi\npolarons -- quasiparticles formed by impurities interacting with a\nnon-interacting Fermi gas -- from weak to ultrastrong drives. Exploiting two\ninternal states of the impurity species, we develop a steady-state\nspectroscopy, from which we extract the energy of the driven polaron. We\nmeasure the decay rate and the quasiparticle residue of the driven polaron from\nthe Rabi oscillations between the two internal states. At large drive\nstrengths, the so-extracted quasiparticle residue exceeds unity, raising\nintriguing questions on the relationship between the Rabi oscillations and the\nimpurity's spectral functions. Our experiment establishes the driven Fermi\npolaron as a promising platform for studying controllable quasiparticles in\nstrongly driven quantum matter.",
        "positive": "Leading corrections to local approximations II (with turning points): Quantum corrections to Thomas-Fermi (TF) theory are investigated for\nnoninteracting one-dimensional fermions with known uniform semiclassical\napproximations to the density and kinetic energy. Their structure is analyzed,\nand contributions from distinct phase space regions (classically-allowed versus\nforbidden at the Fermi energy) are derived analytically. Universal formulas are\nderived for both particle numbers and energy components in each region. For\nexample, in the semiclassical limit, exactly 1/(6\\pi3^{1/2}) of a particle\nleaks into the evanescent region beyond a turning point. The correct\nnormalization of semiclassical densities is proven analytically in the\nsemiclassical limit. Energies and densities are tested numerically in a variety\nof one-dimensional potentials, especially in the limit where TF theory becomes\nexact. The subtle relation between the pointwise accuracy of the semiclassical\napproximation and integrated expectation values is explored. The limitations of\nthe semiclassical formulas are also investigated when the potential varies too\nrapidly. The approximations are shown to work for multiple wells, except right\nat the mid-phase point of the evanescent regions. The implications for density\nfunctional approximations are discussed."
    },
    {
        "anchor": "Collisional losses of ultracold molecules due to intermediate complex\n  formation: Understanding the sources of losses and chemical reactions of ultracold\nalkali-metal molecules is among the critical elements needed for their\napplication in precision measurements and quantum technologies. Recent\nexperiments with nonreactive systems have reported unexpectedly large loss\nrates, posing a challenge for theoretical explanation. Here, we examine the\ndynamics of intermediate four-atom complexes formed in bimolecular collisions.\nWe calculate the nuclear spin--rotation, spin--spin, and quadrupole coupling\nconstants for bialkali tetramers using ab intio quantum-chemical methods. We\nshow that the nuclear spin--spin and quadrupole couplings are strong enough to\ncouple different rotational manifolds to increase the density of states and\nlifetimes of the collision complexes, which is consistent with experimental\nresults. We propose further experiments to confirm our predictions.",
        "positive": "Three-body recombination of two-component cold atomic gases into deep\n  dimers in an optical model: We consider three-body recombination into deep dimers in a mass-imbalanced\ntwo-component atomic gas. We use an optical model where a phenomenological\nimaginary potential is added to the lowest adiabatic hyper-spherical potential.\nThe consequent imaginary part of the energy eigenvalue corresponds to the decay\nrate or recombination probability of the three-body system. The method is\nformulated in details and the relevant qualitative features are discussed as\nfunctions of scattering lengths and masses. We use zero-range model in analyses\nof recent recombination data. The dominating scattering length is usually\nrelated to the non-equal two-body systems. We account for temperature smearing\nwhich tends to wipe out the higher-lying Efimov peaks. The range and the\nstrength of the imaginary potential determine positions and shapes of the\nEfimov peaks as well as the absolute value of the recombination rate. The\nEfimov scaling between recombination peaks is calculated and shown to depend on\nboth scattering lengths. Recombination is predicted to be largest for\nheavy-heavy-light systems. Universal properties of the optical parameters are\nindicated. We compare to available experiments and find in general very\nsatisfactory agreement."
    },
    {
        "anchor": "Higgs mode in the quench dynamics of a confined ultracold Fermi gas in\n  the BCS regime: The Higgs amplitude mode of the order parameter of an ultracold confined\nFermi gas in the BCS regime after a quench of the coupling constant is analyzed\ntheoretically. Characteristic features are a damped oscillation which at a\ncertain transition time changes into a rather irregular dynamics. We compare\nthe numerical solution of the full set of nonlinear equations of motion for the\nnormal and anomalous Bogoliubov quasiparticle excitations with a linearized\napproximation. In doing so the transition time as well as the difference\nbetween resonant systems, i.e., systems where the Fermi energy is close to a\nsubband minimum, and off-resonant systems can be well understood and traced\nback to the system and geometry parameters.",
        "positive": "Anisotropic Weyl Fermions from Quasiparticle Excitation Spectrum of a 3D\n  Fulde-Ferrell Superfluid: Weyl fermions, first proposed for describing massless chiral Dirac fermions\nin particle physics, have not been observed yet in experiments. Recently, much\neffort has been devoted to explore Weyl fermions around band touching points of\nsingle particle energy dispersions in certain solid state materials (named\n\\textit{Weyl semimetals}), similar as graphene for Dirac fermions. Here we show\nthat such Weyl semimetals also exist in the quasiparticle excitation spectrum\nof a three-dimensional (3D) spin-orbit coupled Fulde-Ferrell (FF) superfluid.\nBy varying Zeeman fields, the properties of Weyl fermions, such as their\ncreation and annihilation, number and position, as well as anisotropic linear\ndispersions around band touching points, can be tuned. We study the\nmanifestation of anisotropic Weyl fermions in sound speeds of FF fermionic\nsuperfluids, which are detectable in experiments."
    },
    {
        "anchor": "Disorder Induced Vortex Lattice Melting in Bose-Einstein Condensate: We study the vortex lattice dynamics in presence of single impurity as well\nas random impurities or disorder. We show that in presence of a single impurity\nthe vortex lattice gets distorted and the distortion depends on the position of\nthe single impurity with respect to the positions of the vortices in the\nimpurity free Abrikosov vortex lattice and also the strength of the impurity\npotential. We then show that a new type of giant hole with hidden vortices\ninside it can be created in the vortex lattice by a cluster of impurities. In\npresence of random impurity potential or disorder the vortex lattice melts. We\nshow that the vortex lattice also melts in presence of pseudorandom potential\ngenerated by the superposition of two optical lattices. The absence of\nlong-range order in the melted vortex lattice is demonstrated from the\nstructure factor profile and the histogram of the distances between each pair\nof the vortices.",
        "positive": "Using polarons for sub-nK quantum non-demolition thermometry in a\n  Bose-Einstein condensate: We introduce a novel minimally-disturbing method for sub-nK thermometry in a\nBose-Einstein condensate (BEC). Our technique is based on the Bose-polaron\nmodel; namely, an impurity embedded in the BEC acts as the thermometer. We\npropose to detect temperature fluctuations from measurements of the position\nand momentum of the impurity. Crucially, these cause minimal back-action on the\nBEC and hence, realize a non-demolition temperature measurement. Following the\nparadigm of the emerging field of \\textit{quantum thermometry}, we combine\ntools from quantum parameter estimation and the theory of open quantum systems\nto solve the problem in full generality. We thus avoid \\textit{any}\nsimplification, such as demanding thermalization of the impurity atoms, or\nimposing weak dissipative interactions with the BEC. Our method is illustrated\nwith realistic experimental parameters common in many labs, thus showing that\nit can compete with state-of-the-art \\textit{destructive} techniques, even when\nthe estimates are built from the outcomes of accessible (sub-optimal)\nquadrature measurements."
    },
    {
        "anchor": "On the Stability of the Repulsive Fermi Gas with Contact Interactions: We report the creation and the study of the stability of a repulsive\nquasi-homogeneous spin-$1/2$ Fermi gas with contact interactions. For the range\nof scattering lengths $a$ explored, the dominant mechanism of decay is a\nuniversal three-body recombination towards a Feshbach bound state. We observe\nthat the recombination coefficient $K_3\\propto \\epsilon_\\text{kin} a^6$, where\nthe first factor, the average kinetic energy per particle\n$\\epsilon_\\text{kin}$, arises from a three-body threshold law, and the second\none from the universality of recombination. Both scaling laws are consequences\nof Pauli blocking effects in three-body collisions involving two identical\nfermions. As a result of the interplay between Fermi statistics and the\nmomentum dependence of the recombination process, the system exhibits\nnon-trivial temperature dynamics during recombination, alternatively heating or\ncooling depending on its initial quantum degeneracy. The measurement of $K_3$\nprovides an upper bound for the interaction strength achievable in equilibrium\nfor a uniform repulsive Fermi gas.",
        "positive": "Realizing arbitrary trapping potentials for light via direct laser\n  writing of mirror surface profiles: The versatility of quantum gas experiments greatly benefits from the ability\nto apply variable potentials. Here we describe a method which allows the\npreparation of potential structures for microcavity photons via spatially\nselective deformation of optical resonator geometries with a heat induced\nmirror surface microstructuring technique. We investigate the thermalization of\na two-dimensional photon gas in a dye-filled microcavity composed of the custom\nsurface-structured mirrors at wavelength-scale separation. Specifically, we\ndescribe measurements of the spatial redistribution of thermal photons in a\ncoupled double-ridge structure, where photons form a Bose-Einstein condensate\nin a spatially split ground state, as a function of different pumping\ngeometries."
    },
    {
        "anchor": "Nonuniform Bose-Einstein condensate. I. An improvement of the\n  Gross-Pitaevskii method: A nonuniform condensate is usually described by the Gross-Pitaevskii (GP)\nequation, which is derived with the help of the c-number ansatz $\\hat{\n\\Psi}(\\mathbf{r},t)=\\Psi (\\mathbf{r},t)$. Proceeding from a more accurate\noperator ansatz $\\hat{\\Psi}(\\mathbf{r},t)=\\hat{a}_{0}\\Psi (\\mathbf{r},t)\n\\sqrt{N}$, we find the equation $i\\hbar \\frac{\\partial \\Psi\n(\\mathbf{r},t)}{\\partial t}=-\\frac{\\hbar ^{2}}{2m}\\frac{\\partial ^{2}\\Psi\n(\\mathbf{r},t)}{\\partial \\mathbf{r}^{2}}+\\left( 1-\\frac{1}{N}\\right) 2c\\Psi\n(\\mathbf{r},t)|\\Psi(\\mathbf{r},t)|^{2}$ (the GP$_{N}$ equation). It differs\nfrom the GP equation by the factor $(1-1/N)$, where $N$ is the number of Bose\nparticles. We compare the accuracy of the GP and GP$_{N}$ equations by\nanalyzing the ground state of a one-dimensional system of point bosons with\nrepulsive interaction ($c>0$) and zero boundary conditions. Both equations are\nsolved numerically, and the system energy $E$ and the particle density profile\n$\\rho (x)$ are determined for various values of~$N$, the mean particle density\n$\\bar{\\rho}$, and the coupling constant $\\gamma =c/\\bar{\\rho}$. The solutions\nare compared with the exact ones obtained by the Bethe ansatz. The results show\nthat in the weak coupling limit ($N^{-2}\\ll \\gamma \\lesssim 0.1$), the GP and\nGP$_{N}$ equations describe the system equally well if $N\\gtrsim 100$. For\nfew-boson systems ($N\\lesssim 10$) with $\\gamma \\lesssim N^{-2}$ the solutions\nof the GP$_{N}$ equation are in excellent agreement with the exact ones. That\nis, the multiplier $(1-1/N)$ allows one to describe few-boson systems with high\naccuracy. This means that it is reasonable to extend the notion of\nBose-Einstein condensation to few-particle systems.",
        "positive": "Universality in rotating strongly interacting gases: We analytically determine the properties of two interacting particles in a\nharmonic trap subject to a rotation or a uniform synthetic magnetic field,\nwhere the spherical symmetry of the relative Hamiltonian is preserved.\nThermodynamic quantities such as the entropy and energy are calculated via the\nsecond order quantum cluster expansion. We find that in the strongly\ninteracting regime the energy is universal, however the entropy changes as a\nfunction of the rotation or synthetic magnetic field strength."
    },
    {
        "anchor": "Polariton-Enhanced Exciton Transport: The transport distance of excitons in exciton-polariton systems has\npreviously been assumed to be very small ($\\lesssim 1~\\mu$m). The sharp spatial\nprofiles observed when generating polaritons by non-resonant optical excitation\nshow that this assumption is generally true. In this paper, however, we show\nthat the transport distances of excitons in two-dimensional planar cavity\nstructures with even a slightly polaritonic character are much longer than\nexpected ($\\approx 20~\\mu$m). Although this population of slightly polaritonic\nexcitons is normally small compared to the total population of excitons, they\ncan substantially outnumber the population of the polaritons at lower energies,\nleading to important implications for the tailoring of potential landscapes and\nthe measurement of interactions between polaritons.",
        "positive": "Universal Loss Dynamics in a Unitary Bose Gas: The low temperature unitary Bose gas is a fundamental paradigm in few-body\nand many-body physics, attracting wide theoretical and experimental interest.\nHere we first present a theoretical model that describes the dynamic\ncompetition between two-body evaporation and three-body re-combination in a\nharmonically trapped unitary atomic gas above the condensation temperature. We\nidentify a universal magic trap depth where, within some parameter range,\nevaporative cooling is balanced by recombination heating and the gas\ntemperature stays constant. Our model is developed for the usual\nthree-dimensional evaporation regime as well as the 2D evaporation case.\nExperiments performed with unitary 133 Cs and 7 Li atoms fully support our\npredictions and enable quantitative measurements of the 3-body recombination\nrate in the low temperature domain. In particular, we measure for the first\ntime the Efimov inelasticity parameter $\\eta$ * = 0.098(7) for the 47.8-G\nd-wave Feshbach resonance in 133 Cs. Combined 133 Cs and 7 Li experimental data\nallow investigations of loss dynamics over two orders of magnitude in\ntemperature and four orders of magnitude in three-body loss. We confirm the 1/T\n2 temperature universality law up to the constant $\\eta$ *."
    },
    {
        "anchor": "Universal Tomonaga-Luttinger liquid phases in one-dimensional strongly\n  attractive SU(N) fermionic cold atoms: A simple set of algebraic equations is derived for the exact low-temperature\nthermodynamics of one-dimensional multi-component strongly attractive fermionic\natoms with enlarged SU(N) spin symmetry and Zeeman splitting. Universal\nmulti-component Tomonaga-Luttinger liquid (TLL) phases are thus determined. For\nlinear Zeeman splitting, the physics of the gapless phase at low temperatures\nbelongs to the universality class of a two-component asymmetric TLL\ncorresponding to spin-neutral N-atom composites and spin-(N-1)/2 single atoms.\nThe equation of states is also obtained to open up the study of multi-component\nTLL phases in 1D systems of N-component Fermi gases with population imbalance.",
        "positive": "Dynamics of phase defects trapped in optically imprinted orbits in\n  dissipative binary polariton condensate: We study the dynamics of phase defects trapped in a finite optically\nimprinted ring lattice in binary polariton condensates, under the influence of\nthe cross-interaction (CI) between the condensates in different spin components\nand the spin-orbit interaction (SOI). In this configuration, we find that a\nvortex circulates unidirectionally in optically induced orbits because of the\nMagnus force acting in the polariton fluid, and the vortex' angular velocity is\ninfluenced by the SOI and CI. Interestingly, in our system, these two\ninteractions can also lead to elongated and frozen phase defects, forming a\nfrozen dark solution with similarity to a dark soliton but with finite size in\nboth spin components. When the dark solution is stretched further to occupy the\nentire orbit of a condensate ring, the phase defect triggers a snake\ninstability and induces the decay of the dark ring solution. The circulation\ndirection of a single vortex is determined by the Magnus force. This situation\nis more complex for the group motion of multiple vortices because of\nsignificant vortex-antivortex interaction. The collective motion of such vortex\nconstellations, however, can be determined by the SOI."
    },
    {
        "anchor": "Schrieffer-Wolff Transformation for Periodically Driven Systems:\n  Strongly Correlated Systems with Artificial Gauge Fields: We generalize the Schrieffer-Wolff transformation to periodically driven\nsystems using Floquet theory. The method is applied to the periodically driven,\nstrongly interacting Fermi-Hubbard model, for which we identify two regimes\nresulting in different effective low-energy Hamiltonians. In the nonresonant\nregime, we realize an interacting spin model coupled to a static gauge field\nwith a nonzero flux per plaquette. In the resonant regime, where the Hubbard\ninteraction is a multiple of the driving frequency, we derive an effective\nHamiltonian featuring doublon association and dissociation processes. The\nground state of this Hamiltonian undergoes a phase transition between an\nordered phase and a gapless Luttinger liquid phase. One can tune the system\nbetween different phases by changing the amplitude of the periodic drive.",
        "positive": "Tunneling of polarized fermions in 3D double wells: We study the tunneling of a spin polarized Fermi gas in a three-dimensional\ndouble well potential, focusing on the time dynamics starting from an initial\nstate in which there is an imbalance in the number of particles in the two\nwells. Although fermions in different doublets of the double well tunnel with\ndifferent frequencies, we point out that (incoherent) oscillations of a large\nnumber of particles can arise, as a consequence of the presence of transverse\ndegrees of freedom. Estimates of the doublet structure and of the occupation of\ntransverse eigenstates for a realistic experimental setup are provided."
    },
    {
        "anchor": "Feshbach resonances in Cesium at Ultra-low Static Magnetic Fields: We have observed Feshbach resonances for 133Cs atoms in two different\nhyperfine states at ultra-low static magnetic fields by using an atomic\nfountain clock. The extreme sensitivity of our setup allows for high\nsignal-to-noise-ratio observations at densities of only 2*10^7 cm^{-3}. We have\nreproduced these resonances using coupled-channels calculations which are in\nexcellent agreement with our measurements. We justify that these are s-wave\nresonances involving weakly-bound states of the triplet molecular Hamiltonian,\nidentify the resonant closed channels, and explain the observed multi-peak\nstructure. We also describe a model which precisely accounts for the\ncollisional processes in the fountain and which explains the asymmetric shape\nof the observed Feshbach resonances in the regime where the kinetic energy\ndominates over the coupling strength.",
        "positive": "Absence of damping of low energy excitations in a quasi-2D dipolar Bose\n  gas: We develop a theory of damping of low energy, collective excitations in a\nquasi-2D, homogenous, dipolar Bose gas at zero temperature, via processes\nwhereby an excitation decays into two excitations with lower energy. We find\nthat owing to the nature of the low energy spectrum of a quasi-2D dipolar gas,\nsuch processes cannot occur unless the momentum of the incoming quasi-particle\nexceeds a critical value k_{crit}. We find that as the dipolar interaction\nstrength is increased, this critical value shifts to larger momenta. Our\npredictions can be directly verified in current experiments on dipolar Bose\ncondensates using Bragg spectroscopy, and provide valuable insight into the\nquantum many-body physics of dipolar gases."
    },
    {
        "anchor": "Phase-space mixing in dynamically unstable, integrable few-mode quantum\n  systems: Quenches in isolated quantum systems are currently a subject of intense\nstudy. Here, we consider quantum few-mode systems that are integrable in their\nclassical mean-field limit and become dynamically unstable after a quench of a\nsystem parameter. Specifically, we study a Bose-Einstein condensate (BEC) in a\ndouble-well potential and an antiferromagnetic spinor BEC constrained to a\nsingle spatial mode. We study the time dynamics after the quench within the\ntruncated Wigner approximation (TWA) and find that system relaxes to a steady\nstate due to phase-space mixing. Using the action-angle formalism and a\npendulum as an illustration, we derive general analytical expressions for the\ntime evolution of expectation values of observables and their long-time limits.\nWe find that the deviation of the long-time expectation value from its\nclassical value scales as $1/O(\\ln N )$, where $N$ is the number of atoms in\nthe condensate. Furthermore, the relaxation of an observable to its steady\nstate value is a damped oscillation and the damping is Gaussian in time. We\nconfirm our results with numerical TWA simulations.",
        "positive": "Quantum phases of constrained bosons on a two-leg Bose-Hubbard ladder: Bosons in periodic potentials with very strong local interactions, known as\nthe constrained bosons often exhibit interesting physical behavior. We\ninvestigate the ground state properties of a two-leg Bose-Hubbard ladder by\nimposing three-body constraint in one leg and hardcore constraint in the other.\nBy using the cluster-mean-field theory approximation and the density matrix\nrenormalization group method, we show that at unit filling, for strong two-body\nattraction among the three-body constrained bosons, the system becomes a gapped\npair-Mott insulator where all the bosons form strong bound pairs and occupy the\nleg with three-body constraint. With increase in hopping strength this\npair-Mott insulator phase undergoes a phase transition to the gapless\nsuperfluid phase for equal leg and rung hopping strengths. However, when the\nrung hopping is stronger compared to the leg hopping, we obtain a crossover to\nanother gapped phase which is called the rung-Mott insulator phase where the\nbosons prefer to delocalize on the rungs than the legs. By moving away from\nunit filling, the system remains in the superfluid phase except for a small\nregion below the gapped phase where a pair superfluid phase is stabilized in\nthe regime of strong attractive interaction. We further extend our studies by\nconsidering three-body constraint on both the legs and find that the crossover\nfrom the gapped to gapped phase does not occur rather the system undergoes a\ntransition from a pair-rung-Mott insulator phase to the superfluid phase at\nunit filling. Moreover, in this case we find the signature of the pair\nsuperfluid phase on either sides of this gapped phase."
    },
    {
        "anchor": "Many-body multi-valuedness of particle-current variance in closed and\n  open cold-atom systems: The quantum variance of an observable is a fundamental quantity in quantum\nmechanics, and the variance provides additional information other than the\naverage itself. By examining the relation between the particle-current variance\n$(\\delta J)^2$ and the average current $J$ in both closed and open interacting\nfermionic systems, we show the emergence of a multi-valued Lissajous curve\nbetween $\\delta J$ and $J$ due to interactions. As a closed system we\nconsidered the persistent current in a benzene-like lattice enclosing an\neffective magnetic flux and solved it by exact diagonalization. For the open\nsystem, the steady-state current flowing through a few lattice sites coupled to\ntwo particle reservoirs was investigated using a Lindblad equation. In both\ncases, interactions open a loop and change the topology of the corresponding\n$\\delta J$-$J$ Lissajous curve, showing that this effect is model-independent.\nWe finally discuss how the predicted phenomena can be observed in ultracold\natoms, thus offering an alternative way of probing the dynamics of many-body\nsystems.",
        "positive": "Superexchange Liquefaction of Strongly Correlated Lattice Dipolar Bosons: We propose a mechanism for liquid formation in strongly correlated lattice\nsystems. The mechanism is based on an interplay between long-range attraction\nand superexchange processes. As an example, we study dipolar bosons in\none-dimensional optical lattices. We present a perturbative theory and validate\nit in comparison with full density-matrix renormalization group simulations for\nthe energetic and structural properties of different phases of the system,\ni.e., self-bound Mott insulator, liquid, and gas. We analyze the nonequilibrium\nproperties and calculate the dynamic structure factor. Its structure differs in\ncompressible and insulating phases. In particular, the low-energy excitations\nin compressible phases are linear phonons. We extract the speed of sound and\nanalyze its dependence on dipolar interaction and density. We show that it\nexhibits a nontrivial behaviour owing to the breaking of Galilean invariance.\nWe argue that an experimental detection of this previously unknown quantum\nliquid could provide a fingerprint of the superexchange process and open\nintriguing possibilities for investigating non-Galilean invariant liquids."
    },
    {
        "anchor": "Engineering infinite-range SU($n$) interactions with spin-orbit-coupled\n  fermions in an optical lattice: We study multilevel fermions in an optical lattice described by the Hubbard\nmodel with on site SU($n$)-symmetric interactions. We show that in an\nappropriate parameter regime this system can be mapped onto a spin model with\nall-to-all SU($n$)-symmetric couplings. Raman pulses that address internal spin\nstates modify the atomic dispersion relation and induce spin-orbit coupling,\nwhich can act as a synthetic inhomogeneous magnetic field that competes with\nthe SU($n$) exchange interactions. We investigate the mean-field dynamical\nphase diagram of the resulting model as a function of $n$ and different initial\nconfigurations that are accessible with Raman pulses. Consistent with previous\nstudies for $n=2$, we find that for some initial states the spin model exhibits\ntwo distinct dynamical phases that obey simple scaling relations with $n$.\nMoreover, for $n>2$ we find that dynamical behavior can be highly sensitive to\ninitial intra-spin coherences. Our predictions are readily testable in current\nexperiments with ultracold alkaline-earth(-like) atoms.",
        "positive": "Crossover from 2D to 3D in a weakly interacting Fermi gas: We have studied the transition from two to three dimensions in a low\ntemperature weakly interacting $^6$Li Fermi gas. Below a critical atom number,\n$N_{2D}$, only the lowest transverse vibrational state of a highly anisotropic\noblate trapping potential is occupied and the gas is two-dimensional. Above\n$N_{2D}$ the Fermi gas enters the quasi-2D regime where shell structure\nassociated with the filling of individual transverse oscillator states is\napparent. This dimensional crossover is demonstrated through measurements of\nthe cloud size and aspect ratio versus atom number."
    },
    {
        "anchor": "Do phase fluctuations influence the Fulde-Ferrell-Larkin-Ovchinnikov\n  state in a 3D Fermi gas?: In ultracold Fermi gases, the effect of spin-imbalance on superfluidity has\nbeen the subject of intense study. One of the reasons for this is that\nspin-imbalance frustrates the Bardeen-Cooper-Schrieffer (BCS) superfluid\npairing mechanism, in which fermions in different spin states combine into\nCooper pairs with zero momentum. In 1964, it was proposed that an exotic\nsuperfluid state called the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, in\nwhich the Cooper pairs have nonzero momentum, could exist in a spin-imbalanced\nFermi gas. At the saddle-point (mean field) level, it has been shown that the\nFFLO state only occupies a very small sliver in the ground state phase diagram\nof a 3D Fermi gas. However, a question that remains to be investigated is: what\nis the influence of phase fluctuations around the saddle point on the FFLO\nstate? In this work we show that phase fluctuations only lead to relatively\nsmall quantitative corrections to the presence of the FFLO state in the\nsaddle-point phase diagram of a 3D spin-imbalanced Fermi gas. Starting from the\npartition function of the system, we calculate the effective action within the\npath-integral adiabatic approximation. The action is then expanded up to second\norder in the fluctuation field around the saddle point, leading to the\nfluctuation free energy. Using this free energy, we calculate corrections due\nto phase fluctuations to the BCS-FFLO transition in the saddle-point phase\ndiagram. At temperatures at which the FFLO state exists, we find only small\ncorrections to the size of the FFLO area. Our results suggest that fluctuations\nof the phase of the FFLO order parameter, which can be interpreted as an\noscillation of its momentum vector, do not cause an instability of the FFLO\nstate with respect to the BCS state.",
        "positive": "Localization of interacting Fermi gases in quasiperiodic potentials: We investigate the zero-temperature metal-insulator transition in a\none-dimensional two-component Fermi gas in the presence of a quasi-periodic\npotential resulting from the superposition of two optical lattices of equal\nintensity but incommensurate periods. A mobility edge separating (low energy)\nAnderson localized and (high energy) extended single-particle states appears in\nthis continuous-space model beyond a critical intensity of the quasi-periodic\npotential. In order to discern the metallic phase from the insulating phase in\nthe interacting many-fermion system, we employ unbiased quantum Monte Carlo\n(QMC) simulations combined with the many-particle localization length familiar\nfrom the modern theory of the insulating state. In the noninteracting limit,\nthe critical optical-lattice intensity for the metal-insulator transition\npredicted by the QMC simulations coincides with the Anderson localization\ntransition of the single-particle eigenstates. We show that weak repulsive\ninteractions induce a shift of this critical point towards larger intensities,\nmeaning that repulsion favors metallic behavior. This shift appears to be\nlinear in the interaction parameter, suggesting that even infinitesimal\ninteractions can affect the position of the critical point."
    },
    {
        "anchor": "Universal relations for spin-orbit coupled Fermi gas near an s-wave\n  resonance: The synthetic spin-orbit coupled quantum gases is widely studied both\nexperimentally and theoretically in recent years. As previous studies show,\nthis modification of single-body dispersion will in general couple different\npartial waves and thus distort the wave-function of bound states which\ndetermines the short-distance behavior of many-body wave function. In this\nwork, we focus on the two-component Fermi gas with one-dimensional or\nthree-dimensional spin-orbit coupling near an s-wave resonance. Using the\nmethod of effective field theory and the operator product expansion, we derive\nuniversal relations for both systems, and obtain the momentum distribution\nmatrix $\\left<\\psi^\\dagger_a(\\mathbf{q})\\psi_b(\\mathbf{q})\\right>$ at large\n$\\mathbf{q}$ ($a,b$ are spin index), which shows anisotropic features. We also\ndiscuss the experimental implication of these results depending on the\nrealization of the spin-orbit coupling.",
        "positive": "Formation of Feshbach molecules in the presence of artificial spin-orbit\n  coupling and Zeeman fields: We derive general conditions for the emergence of singlet Feshbach molecules\nin the presence of artificial Zeeman fields for arbritary mixtures of Rashba\nand Dresselhaus spin-orbit orbit coupling in two or three dimensions. We focus\non the formation of two-particle bound states resulting from interactions\nbetween ultra-cold spin-1/2 fermions, under the assumption that interactions\nare short-ranged and occur only in the s-wave channel. In this case, we\ncalculate explicitly binding energies of Feshbach molecules and analyze their\ndependence on spin-orbit couplings, Zeeman fields, interactions and center of\nmass momentum, paying particular attention to the experimentally relevant case\nof spin-orbit couplings with equal Rashba and Dresselhaus (ERD) amplitudes."
    },
    {
        "anchor": "Interaction Induced Topological Charge Pump: Based on a topological transition of the symmetry protected topological phase\n(SPT), an interaction induced topological charge pump (iTCP) is proposed with\nthe symmetry breaking parameter as a synthetic dimension. It implies that the\nphase boundary of the SPT is the topological obstruction although iTCP and the\ngap closing singularity is stable for symmetry breaking perturbations. We have\nconfirmed the bulk-edge correspondence for this iTCP using DMRG for the\nRice-Mele model with nearest-neighbor interactions. As for a realization in\noptical lattices, an interaction sweeping pump protocol is proposed as well.",
        "positive": "Sound propagation in cigar-shaped Bose liquids in the Thomas-Fermi\n  approximation: A comparative study between Gross-Pitaevskii and logarithmic\n  models: A comparative study is done of the propagation of sound pulses in elongated\nBose liquids and Bose-Einstein condensates in Gross-Pitaevskii and logarithmic\nmodels, by means of the Thomas-Fermi approximation. It is shown that in the\nlinear regime the propagation of small density fluctuations is essentially\none-dimensional in both models, in the direction perpendicular to the cross\nsection of a liquid's lump. Under these approximations, it is shown that the\nspeed of sound scales as a square root of particle density in the case of the\nGross-Pitaevskii liquid/condensate, but it is constant in a case of the\nhomogeneous logarithmic liquid."
    },
    {
        "anchor": "Mott Transition for Strongly-Interacting 1D Bosons in a Shallow Periodic\n  Potential: We investigate the superfluid-insulator transition of one-dimensional\ninteracting Bosons in both deep and shallow periodic potentials. We compare a\ntheoretical analysis based on Monte-Carlo simulations in continuum space and\nLuttinger liquid approach with experiments on ultracold atoms with tunable\ninteractions and optical lattice depth. Experiments and theory are in excellent\nagreement. It provides a quantitative determination of the critical parameter\nfor the Mott transition and defines the regime of validity of widely used\napproximate models, namely the Bose-Hubbard and sine-Gordon models",
        "positive": "Quantum phases of two-component bosons on the Harper-Hofstadter ladder: We study two-component bosons on the Harper-Hofstadter model with two legs.\nThe synthetic magnetic fields for the two types of bosons point to either the\nsame direction or opposite directions. The bosons have hardcore intra-species\ninteraction such that there can be no more than one boson of the same type on\neach lattice site. For certain filling factors in the absence of inter-species\ninteraction, each component realizes a vortex Mott insulator with rung current\nor a Meissner superfluid without rung current. The system undergoes phase\ntransitions to other phases as inter-species interaction is turned on, which\nare characterized numerically using the density matrix renormalization group\nmethod and supplemented with analytical studies when possible. The vortex Mott\ninsulator transits to a gapped Meissner phase without rung current and the\nMeissner superfluid transits to a gapped vortex phase with rung current. In\nboth cases, we observe gapped spin density wave states that break certain\n${\\mathbb Z}_{2}$ symmetries."
    },
    {
        "anchor": "Quantum-Enhanced Sensing Based on Time Reversal of Nonlinear Dynamics: We experimentally demonstrate a nonlinear detection scheme exploiting\ntime-reversal dynamics that disentangles continuous variable entangled states\nfor feasible readout. Spin-exchange dynamics of Bose-Einstein condensates is\nused as the nonlinear mechanism which not only generates entangled states but\ncan also be time reversed by controlled phase imprinting. For demonstration of\na quantum-enhanced measurement we construct an active atom SU(1,1)\ninterferometer, where entangled state preparation and nonlinear readout both\nconsist of parametric amplification. This scheme is capable of exhausting the\nquantum resource by detecting solely mean atom numbers. Controlled nonlinear\ntransformations widen the spectrum of useful entangled states for applied\nquantum technologies.",
        "positive": "Highly polarized Fermi gases in two dimensions: We investigate the highly polarized limit of a two-dimensional (2D) Fermi\ngas, where we effectively have a single spin-down impurity atom immersed in a\nspin-up Fermi sea. By constructing variational wave functions for the impurity,\nwe map out the ground state phase diagram as a function of mass ratio M/m and\ninteraction strength. In particular, we determine when it is favorable for the\ndressed impurity (polaron) to bind particles from the Fermi sea to form a\ndimer, trimer or even larger clusters. Similarly to 3D, we find that the Fermi\nsea favors the trimer state so that it exists for M/m less than the critical\nmass ratio for trimer formation in the vacuum. We also find a region where\ndimers have finite momentum in the ground state, a scenario which corresponds\nto the Fulde-Ferrell-Larkin-Ovchinnikov superfluid state in the limit of large\nspin imbalance. For equal masses (M=m), we compute rigorous bounds on the\npolaron-dimer transition, and we show that the polaron energy and residue is\nwell captured by the variational approach, with the former quantity being in\ngood agreement with experiment. When there is a finite density of impurities,\nwe find that this polaron-dimer transition is preempted by a first-order\nsuperfluid-normal transition at zero temperature, but it remains an open\nquestion what happens at finite temperature."
    },
    {
        "anchor": "Rectification in Nonequilibrium Steady States of Open Many-Body Systems: We study how translationally invariant couplings of many-particle systems and\nnonequilibrium baths can be used to rectify particle currents, for which we\nconsider minimal setups to realize bath-induced currents in nonequilibrium\nsteady states of one-dimensional open fermionic systems. We first analyze\ndissipative dynamics associated with a nonreciprocal Lindblad operator and\nidentify a class of Lindblad operators that are sufficient to acquire a\nunidirectional current. We show that unidirectional particle transport can in\ngeneral occur when a Lindblad operator is reciprocal provided that the\ninversion symmetry and the time-reversal symmetry of the microscopic\nHamiltonian are broken. We demonstrate this mechanism on the basis of both\nanalytical and numerical approaches including the Rashba spin-orbit coupling\nand the Zeeman magnetic field.",
        "positive": "Molecular branch of a small highly-elongated Fermi gas with an impurity:\n  Full three-dimensional versus effective one-dimensional description: We consider an impurity immersed in a small Fermi gas under highly-elongated\nharmonic confinement. The impurity interacts with the atoms of the Fermi gas\nthrough an isotropic short-range potential with three-dimensional free-space\ns-wave scattering length $a_{3\\text{d}}$. We investigate the energies of the\nmolecular branch, i.e., the energies of the state that corresponds to a gas\nconsisting of a weakly-bound diatomic molecule and \"unpaired\" atoms, as a\nfunction of the s-wave scattering length $a_{3\\text{d}}$ and the ratio $\\eta$\nbetween the angular trapping frequencies in the tight and weak confinement\ndirections. The energies obtained from our three-dimensional description that\naccounts for the dynamics in the weak and tight confinement directions are\ncompared with those obtained within an effective one-dimensional framework,\nwhich accounts for the dynamics in the tight confinement direction via a\nrenormalized one-dimensional coupling constant. Our theoretical results are\nrelated to recent experimental measurements."
    },
    {
        "anchor": "Interacting Hofstadter spectrum of atoms in an artificial gauge field: Motivated by experimental advances in the synthesis of gauge potentials for\nultracold atoms, we consider the superfluid phase of interacting bosons on a\nsquare lattice in the presence of a magnetic field. We show that superfluid\norder implies spatial symmetry breaking, and predict clear signatures of\nmany-body effects in time-of-flight measurements. By developing a Bogoliubov\nexpansion based on the exact Hofstadter spectrum, we find the dispersion of the\nquasiparticle modes within the superfluid phase, and describe the consequences\nfor Bragg spectroscopy measurements. The theory also provides an estimate of\nthe critical interaction strength at the transition to the Mott insulator\nphase.",
        "positive": "Dark Solitons with Majorana Fermions in Spin-Orbit-Coupled Fermi Gases: We show that a single dark soliton can exist in a spin-orbit-coupled Fermi\ngas with a high spin imbalance, where spin-orbit coupling favors uniform\nsuperfluids over non-uniform Fulde-Ferrell-Larkin-Ovchinnikov states, leading\nto dark soliton excitations in highly imbalanced gases. Above a critical spin\nimbalance, two topological Majorana fermions (MFs) without interactions can\ncoexist inside a dark soliton, paving a way for manipulating MFs through\ncontrolling solitons. At the topological transition point, the atom density\ncontrast across the soliton suddenly vanishes, suggesting a signature for\nidentifying topological solitons."
    },
    {
        "anchor": "Bistability of Bose-Fermi mixtures: We study the properties of the Bose-Fermi mixture from the perspective of\nreaching a state of a self-bound quantum droplet. The variational analysis\nshows that the system exhibits bistability. For weak repulsion between bosons,\none of the equilibrium states, smaller in size, spherically symmetric, and with\nnegative energy, corresponds to quantum droplet, the other with always positive\nenergy represents the elongated droplet-like state immersed in the sea of a\nfermionic cloud. For stronger repulsion between bosons the bifurcation is\nseized and only the former state is left. Now it represents an elongated object\nwhich, for strong enough boson-fermion attraction, gets negative energy. It\nbecomes an excited Bose-Fermi droplet when the trap is released, what is\ndemonstrated by solving the quantum hydrodynamics equations for the Bose-Fermi\nsystem. To depict our ideas we consider the $^{133}$Cs-$^6$Li mixture under\nideal conditions, i.e. we assume no losses.",
        "positive": "Reentrant behavior of the breathing-mode-oscillation frequency in a\n  one-dimensional Bose gas: We calculate the breathing mode frequency $\\omega$ in a one-dimensional Bose\ngas confined to a harmonic trap of frequency $\\omega_z$. We predict Exciting\ntemporal oscillations of the density distribution is a high-precision method\nfor probing ultracold trapped atomic gases. Interaction effects in their\nmany-body dynamics are particularly puzzling and counter-intuitive in one\nspatial dimension (1D) due to enhanced quantum correlations. We consider 1D\nquantum Bose gas in a parabolic trap at zero temperature and explain,\nanalytically and numerically, how oscillation frequency depends on the number\nof particles, their repulsion and the trap strength. We identify the frequency\nwith the energy difference between the ground state and a particular excited\nstate. This way we avoided resolving the dynamical evolution of the system,\nsimplifying the problem immensely. We find an excellent quantitative agreement\nof our results with the data from the Innsbruck experiment [Science 325, 1224\n(2009)]."
    },
    {
        "anchor": "Cooper Triples in Attractive Three-Component Fermions: Implication for\n  Hadron-Quark Crossover: We investigate many-body properties of equally populated three-component\nfermions with attractive three-body contact interaction in one dimension. A\ndiagrammatic approach suggests the possible occurrence of Cooper triples at low\ntemperature, which are three-body counterparts of Cooper pairs with a two-body\nattraction. We develop a minimal framework that bridges the crossover from\ntightly-bound trimers to Cooper triples with increasing chemical potential and\nshow how the formation of Cooper triples occurs in the grand-canonical phase\ndiagram. Moreover, we argue that this non-trivial crossover is similar to the\nhadron-quark crossover proposed in dense matter. A coexistence of\nmedium-induced triples and the underlying Fermi sea at positive chemical\npotential is analogous to quarkyonic matter consisting of baryonic excitations\nand the underlying quark Fermi sea. The comparison with the existing quantum\nMonte Carlo results implies that the emergence of these kinds of three-body\nstates can be a microscopic origin of the peak of the sound velocity along the\ncrossover.",
        "positive": "Lindhard function of a d-dimensional Fermi gas: We review in detail the derivation of the dielectric response function of a\nnoninteracting system of spin-1/2 fermions in the random-phase approximation.\nResults for the response function of a Fermi gas in one, two and three\ndimensions can be obtained in closed form, and represent the baseline for\ndeveloping a pedagogical understanding of the effect of correlations on the\nresponse functions in interacting systems of fermions."
    },
    {
        "anchor": "Wave chaos in the non-equilibrium dynamics of the Gross-Pitaevskii\n  equation: The Gross-Pitaevskii equation (GPE) plays an important role in the\ndescription of Bose-Einstein condensates (BECs) at the mean-field level. The\nGPE belongs to the class of non-linear Schr\\\"odinger equations which are known\nto feature dynamical instability and collapse for attractive non-linear\ninteractions. We show that the GPE with repulsive non-linear interactions\ntypical for BECs features chaotic wave dynamics. We find positive Lyapunov\nexponents for BECs expanding in periodic and aperiodic smooth external\npotentials as well as disorder potentials. Our analysis demonstrates that wave\nchaos characterized by the exponential divergence of nearby initial\nwavefunctions is to be distinguished from the notion of non-integrability of\nnon-linear wave equations. We discuss the implications of these observations\nfor the limits of applicability of the GPE, the problem of Anderson\nlocalization, and the properties of the underlying many-body dynamics.",
        "positive": "The band structure of the whole spectrum of an N-body cold system\n  containing atoms with arbitrary integer spin and dominated by singlet pairing\n  force: The spectra of $N$-boson systems with arbitrary nonzero spin $\\mathfrak{f}$\nhave been studied. Firstly, only the singlet pairing interaction is considered,\na set of eigenstates together with the eigenenergies are analytically obtained.\nThe completeness of this set is proved. The analytical expression allows us to\nsee clearly the spin structures of various states different in $N$ and/or\n$\\mathfrak{f}$, and to find out the similarity and relationship lying among\nthem. Secondly, the effect of other interactions is evaluated via exact\nnumerical calculations on the systems with a smaller $N$. Some features and\nnotable phenomena that might emerge in high-$\\mathfrak{f}$ systems, say, the\nground band might have extremely high level density, have been discussed."
    },
    {
        "anchor": "Magnetization Oscillation of a Spinor Condensate Induced by Magnetic\n  Field Gradient: We study the spin mixing dynamics of ultracold spin-1 atoms in a weak\nnon-uniform magnetic field with field gradient $G$, which can flip the spin\nfrom +1 to -1 so that the magnetization $m=\\rho_{+}-\\rho_{-}$ is not any more a\nconstant. The dynamics of $m_F=0$ Zeeman component $\\rho_{0}$, as well as the\nsystem magnetization $m$, are illustrated for both ferromagnetic and polar\ninteraction cases in the mean-field theory. We find that the dynamics of system\nmagnetization can be tuned between the Josephson-like oscillation similar to\nthe case of double well, and the interesting self-trapping regimes, i.e. the\nspin mixing dynamics sustains a spontaneous magnetization. Meanwhile the\ndynamics of $\\rho_0$ may be sufficiently suppressed for initially imbalanced\nnumber distribution in the case of polar interaction. A \"beat-frequency\"\noscillation of the magnetization emerges in the case of balanced initial\ndistribution for polar interaction, which vanishes for ferromagnetic\ninteraction.",
        "positive": "Bridging Effective Field Theories and Generalized Hydrodynamics: Generalized Hydrodynamics (GHD) has recently been devised as a method to\nsolve the dynamics of integrable quantum many-body systems beyond the\nmean-field approximation. In its original form, a major limitation is the\ninability to predict equal-time correlations. Here we present a new method to\ntreat thermal fluctuations of a 1D bosonic degenerate gas within the GHD\nframework. We show how the standard results using the thermodynmaic Bethe\nansatz can be obtained through sampling of collective bosonic excitations,\nrevealing the connection or duality between GHD and effective field theories\nsuch as the standard hydrodynamic equations. As an example, we study the\ndamping of a coherently excited density wave and show how equal-time phase\ncorrelation functions can be extracted from the GHD evolution. Our results\npresent a conceptually new way of treating fluctuations beyond the linearized\nregime of GHD."
    },
    {
        "anchor": "Quantized superfluid vortex dynamics on cylindrical surfaces and planar\n  annuli: Superfluid vortex dynamics on an infinite cylinder differs significantly from\nthat on a plane. The requirement that a condensate wave function be single\nvalued upon once encircling the cylinder means that such a single vortex cannot\nremain stationary. Instead, it acquires one of a series of quantized\ntranslational velocities around the circumference, the simplest being $\\pm\n\\hbar/(2MR)$, with $M$ the mass of the superfluid particles and $R$ the radius\nof the cylinder. A generalization to a finite cylinder automatically includes\nthese quantum-mechanical effects through the pairing of the single vortex and\nits image in either the top or bottom end of the surface. The dynamics of a\nsingle vortex on this surface provides a hydrodynamic analog of Laughlin\npumping. The interaction energy for two vortices on an infinite cylinder is\nproportional to the classical stream function $\\chi({\\bf r}_{12})$, and it\ncrosses over from logarithmic to linear when the intervortex separation ${\\bf\nr}_{12}$ becomes larger than the cylinder radius. An Appendix summarizes the\nconnection to an earlier study of Ho and Huang for one or more vortices on an\ninfinite cylinder. A second Appendix reviews the topologically equivalent\nplanar annulus, where such quantized vortex motion has no offset, but Laughlin\npumping may be more accessible to experimental observation.",
        "positive": "Second-order, number-conserving description of non-equilibrium dynamics\n  in finite-temperature Bose-Einstein condensates: While the Gross--Pitaevskii equation is well-established as the canonical\ndynamical description of atomic Bose-Einstein condensates (BECs) at\nzero-temperature, describing the dynamics of BECs at finite temperatures\nremains a difficult theoretical problem, particularly when considering\nlow-temperature, non-equilibrium systems in which depletion of the condensate\noccurs dynamically as a result of external driving. In this paper, we describe\na fully time-dependent numerical implementation of a second-order,\nnumber-conserving description of finite-temperature BEC dynamics. This\ndescription consists of equations of motion describing the coupled dynamics of\nthe condensate and non-condensate fractions in a self-consistent manner, and is\nideally suited for the study of low-temperature, non-equilibrium, driven\nsystems. The \\delta-kicked-rotor BEC provides a prototypical example of such a\nsystem, and we demonstrate the efficacy of our numerical implementation by\ninvestigating its dynamics at finite temperature. We demonstrate that the\nqualitative features of the system dynamics at zero temperature are generally\npreserved at finite temperatures, and predict a quantitative finite-temperature\nshift of resonance frequencies which would be relevant for, and could be\nverified by, future experiments."
    },
    {
        "anchor": "Interacting bosonic flux ladders with a synthetic dimension:\n  Ground-state phases and quantum quench dynamics: Flux ladders constitute the minimal setup enabling a systematic understanding\nof the rich physics of interacting particles subjected simultaneously to strong\nmagnetic fields and a lattice potential. In this paper, the ground-state phase\ndiagram of a flux-ladder model is mapped out using extensive density-matrix\nrenormalization-group simulations. The emphasis is put on parameters which can\nbe experimentally realized exploiting the internal states of potassium atoms as\na synthetic dimension. The focus is on accessible observables such as the\nchiral current and the leg-population imbalance. Considering a particle filling\nof one boson per rung, we report the existence of a Mott-insulating Meissner\nphase as well as biased-ladder phases on top of superfluids and Mott\ninsulators. Furthermore, we demonstrate that quantum quenches from suitably\nchosen initial states can be used to probe the equilibrium properties in the\ntransient dynamics. Concretely, we consider the instantaneous turning on of\nhopping matrix elements along the rungs or legs in the synthetic flux-ladder\nmodel, with different initial particle distributions. We show that clear\nsignatures of the biased-ladder phase can be observed in the transient\ndynamics. Moreover, the behavior of the chiral current in the transient\ndynamics is discussed. The results presented in this paper provide guidelines\nfor future implementations of flux ladders in experimental setups exploiting a\nsynthetic dimension.",
        "positive": "Two-point density correlations of quasicondensates in free expansion: We measure the two-point density correlation function of freely expanding\nquasicondensates in the weakly interacting quasi-one-dimensional (1D) regime.\nWhile initially suppressed in the trap, density fluctuations emerge gradually\nduring expansion as a result of initial phase fluctuations present in the\ntrapped quasicondensate. Asymptotically, they are governed by the thermal\ncoherence length of the system. Our measurements take place in an intermediate\nregime where density correlations are related to near-field diffraction effects\nand anomalous correlations play an important role. Comparison with a recent\ntheoretical approach described by Imambekov et al. yields good agreement with\nour experimental results and shows that density correlations can be used for\nthermometry of quasicondensates."
    },
    {
        "anchor": "Observation of hybrid Tamm-plasmon exciton-polaritons with GaAs quantum\n  wells and a MoSe2 monolayer: Strong light matter coupling between excitons and microcavity photons, as\ndescribed in the framework of cavity quantum electrodynamics, leads to the\nhybridization of light and matter excitations. The regime of collective strong\ncoupling arises, when various excitations from different host media are\nstrongly coupled to the same optical resonance. This leads to a\nwell-controllable admixture of various matter components in three hybrid\npolariton modes. Here, we study a cavity device with four embedded GaAs quantum\nwells hosting excitons that are spectrally matched to the A-valley exciton\nresonance of a MoSe2 monolayer. The formation of hybrid polariton modes is\nevidenced in momentum resolved photoluminescence and reflectivity studies. We\ndescribe the energy and k-vector distribution of exciton-polaritons along the\nhybrid modes by a thermodynamic model, which yields a very good agreement with\nthe experiment.",
        "positive": "Cavity optomechanical detection of persistent currents and solitons in a\n  bosonic ring condensate: We present numerical simulations of the cavity optomechanical detection of\npersistent currents and bright solitons in an atomic Bose-Einstein condensate\nconfined in a ring trap. This work describes a novel technique that measures\ncondensate rotation in situ, in real-time, and with minimal destruction, in\ncontrast to currently used methods, all of which destroy the condensate\ncompletely. For weakly repulsive inter-atomic interactions, the analysis of\npersistent currents extends our previous few-mode treatment of the condensate\n[P. Kumar et al. Phys. Rev. Lett. 127, 113601 (2021)] to a stochastic\nGross-Pitaevskii simulation. For weakly attractive atomic interactions, we\npresent the first analysis of optomechanical detection of matter-wave soliton\nmotion. We provide optical cavity transmission spectra containing signatures of\nthe condensate rotation, sensitivity as a function of the system response\nfrequency, and atomic density profiles quantifying the effect of the\nmeasurement backaction on the condensate. We treat the atoms at a mean-field\nlevel and the optical field classically, account for damping and noise in both\ndegrees of freedom, and investigate the linear as well as nonlinear response of\nthe configuration. Our results are consequential for the characterization of\nrotating matter waves in studies of atomtronics, superfluid hydrodynamics, and\nmatter-wave soliton interferometry."
    },
    {
        "anchor": "Gaussian impurity moving through a Bose-Einstein superfluid: In this paper a Gaussian impurity moving through an equilibrium Bose-Einstein\ncondensate at T = 0 is studied. The problem can be described by a\nGross-Pitaevskii equation, which is solved perturbatively. The analysis is done\nfor systems of 2 and 3 spatial dimensions and generalises the work by [G.E.\nAstrakharchik and L.P. Pitaevskii, Phys. Rev. A 70, 013608 (2004)]. The\nBogoliubov equation solutions for the condensate perturbed by a finite impurity\nare calculated in the co-moving frame, which are formally equivalent up to a\ndimension dependent form factor for general dimensions. From those solutions\nthe total energy of the perturbed system is determined as a function of the\nwidth and the amplitude of the moving Gaussian impurity and its velocity.\nFinally we derive the drag force the Gaussian impurity approximately\nexperiences as it moves through the superfluid, which proofs the existence of a\nsuperfluid phase for finite extensions of the impurities below the speed of\nsound and that the force increases monotonically with velocity until it\ndecreases again.",
        "positive": "Finite-temperature effects on a triatomic Efimov resonance in ultracold\n  cesium: We report a thorough investigation of finite-temperature effects on\nthree-body recombination near a triatomic Efimov resonance in an ultracold gas\nof cesium atoms. Our measurements cover a wide range from a near-ideal\nrealization of the zero-temperature limit to a strongly temperature-dominated\nregime. The experimental results are analyzed within a recently introduced\ntheoretical model based on a universal zero-range theory. The\ntemperature-induced shift of the resonance reveals a contribution that points\nto an energy-dependence of the three-body parameter. We interpret this\ncontribution in terms of the finite range of the van der Waals interaction in\nreal atomic systems and we quantify it in an empirical way based on length\nscale arguments. A universal character of the corresponding resonance shift is\nsuggested by observations related to other Efimov resonances and the comparison\nwith a theoretical finite-temperature approach that explicitly takes the van\nder Waals interaction into account. Our findings are of importance for the\nprecise determination of Efimov resonance positions from experiments at finite\ntemperatures."
    },
    {
        "anchor": "Transfer of BECs through discrete breathers in an optical lattice: We study the stability of a stationary discrete breather (DB) on a nonlinear\ntrimer in the framework of the discrete nonlinear Schr\\\"odinger equation\n(DNLS). In previous theoretical investigations of the dynamics of Bose-Einstein\ncondensates in leaking optical lattices, collisions between a DB and a lattice\nexcitation, e.g. a moving breather (MB) or phonon, were studied. These\ncollisions lead to the transmission of a fraction of the incident (atomic) norm\nof the MB through the DB, while the DB can be shifted in the direction of the\nincident lattice excitation. Here we show that there exists a total energy\nthreshold of the trimer, above which the lattice excitation can trigger the\ndestabilization of the DB and that this is the mechanism leading to the\nmovement of the DB. Furthermore, we give an analytic estimate of upper bound to\nthe norm that is transmitted through the DB. Our analysis explains the results\nof the earlier numerical studies and may help to clarify functional operations\nwith BECs in optical lattices such as blocking and filtering coherent (atomic)\nbeams.",
        "positive": "Microscopy of an ultranarrow Feshbach resonance using a laser-based atom\n  collider: A quantum defect theory analysis: We employ a quantum defect theory framework to provide a detailed analysis of\nthe interplay between a magnetic Feshbach resonance and a shape resonance in\ncold collisions of ultracold $\\rm ^{87}Rb$ atoms as captured in recent\nexperiments using a laser-based collider [Phys. Rev. Research 3, 033209\n(2021)]. By exerting control over a parameter space spanned by both collision\nenergy and magnetic field, the width of a Feshbach resonance can be tuned over\nseveral orders of magnitude. We apply a quantum defect theory specialized for\nultracold atomic collisions to fully describe of the experimental observations.\nWhile the width of a Feshbach resonance generally increases with collision\nenergy, its coincidence with a shape resonance leads to a significant\nadditional boost. By conducting experiments at a collision energy matching the\nshape resonance and using the shape resonance as a magnifying lens we\ndemonstrate a feature broadening to a magnetic width of 8 G compared to a\npredicted Feshbach resonance width $\\ll 0.1$~mG."
    },
    {
        "anchor": "Exchange interactions in the Hubbard-Stratonovich transformation for the\n  stability analysis of itinerant ferromagnetism: Itinerant ferromagnetism, i.e. spontaneous polarization of non-localized\nparticles, is expected to occur for strong repulsive interactions in a spin-1/2\nFermi system. However, this state has proven notoriously hard to find\nexperimentally, both in ultracold gases and in solids. This raises questions\nabout the stability of the itinerant ferromagnetic state itself. Here we\ndevelop a new approach to describe both the direct and exchange interactions\nfor a general interaction potential in the path-integral formalism and we apply\nthis method to itinerant ferromagnetism in three-dimensional ultracold Fermi\ngases. We show that the exchange interactions are lost in the\nHubbard-Stratonovich transformation and we propose to explicitly include the\nexchange effects in a new modified interaction potential. In the saddle-point\napproximation, the effect of interactions can be taken into account using only\nthree parameters. If the interactions become too strong, all saddle points\nbecome unstable to density fluctuations. This greatly restricts the area in the\nphase diagram where uniform itinerant ferromagnetism is expected to occur.",
        "positive": "Ultracold LiCr: a new pathway to quantum gases of paramagnetic polar\n  molecules: Quantum gases of doubly-polar molecules represent appealing frameworks for a\nvariety of cross-disciplinary applications, encompassing quantum simulation and\ncomputation, controlled quantum chemistry and precision measurements. Through a\njoint experimental and theoretical study, here we explore a novel class of\nultracold paramagnetic polar molecules combining lithium alkali and chromium\ntransition metal elements. Focusing on the specific bosonic isotopologue\n$^{6}$Li$^{53}$Cr, leveraging on the Fermi statistics of the parent atomic\nmixture and on suitable Feshbach resonances recently discovered, we produce up\nto $50\\times10^3$ ultracold LiCr molecules at peak phase-space densities\nexceeding 0.1, prepared within the least-bound rotationless level of the LiCr\nelectronic $sextet$ ground state $X^6\\Sigma^+$. We thoroughly characterize the\nmolecular gas, demonstrating the paramagnetic nature of LiCr dimers and the\nprecise control of their quantum state. We investigate their stability against\ninelastic processes and identify a parameter region where pure LiCr samples\nexhibit lifetimes exceeding 0.2 s. Parallel to this, we employ state-of-the-art\nquantum-chemical calculations to predict the properties of LiCr ground and\nexcited electronic states. We identify efficient paths to coherently transfer\nweakly-bound LiCr dimers to their absolute ground state, to deliver ultracold\ngases of doubly-polar molecules with significant electric (3.3 D) and magnetic\n($5\\,\\mu_\\text{B}$) dipole moments."
    },
    {
        "anchor": "Few-boson system with a single impurity: Universal bound states tied to\n  Efimov trimers: Small weakly-bound droplets determine a number of properties of ultracold\nBose and Fermi gases. For example, Efimov trimers near the atom-atom-atom and\natom-dimer thresholds lead to enhanced losses from bosonic clouds.\nGeneralizations to four- and higher-body systems have also been considered.\nMoreover, Efimov trimers have been predicted to play a role in the Bose polaron\nwith large boson-impurity scattering length. Motivated by these considerations,\nthe present work provides a detailed theoretical analysis of weakly-bound\n$N$-body clusters consisting of $N-1$ identical bosons (denoted by \"B\") of mass\n$m$ that interact with a single distinguishable impurity particle (denoted by\n\"X\") of mass $M$. The system properties are analyzed as a function of the mass\nratio $\\kappa$ (values from $\\kappa=1$ to $50$ are considered), where $\\kappa$\nis equal to $m/M$, and the two-body $s$-wave scattering length $a_{\\text{BX}}$\nbetween the bosons and the impurity. To reach the universal Efimov regime in\nwhich the size of the BBX trimer as well as those of larger clusters is much\nlarger than the length scales of the underlying interaction model, three\ndifferent approaches are considered: resonance states are determined in the\nabsence of BB and BBX interactions, bound states are determined in the presence\nof repulsive three-body boson-boson-impurity interactions, and bound states are\ndetermined in the presence of repulsive two-body boson-boson interactions. The\nuniversal regime, in which the details of the underlying interaction model\nbecome irrelevant, is identified.",
        "positive": "Origin of nonlinear optical processes in matter-wave superradiance: We study a highly efficient, matter-wave amplification mechanism in a\nlongitudinally-excited, Bose-Einstein condensate and reveal a very large\nenhancement due to nonlinear gain from a sixmatter- optical, wave-mixing\nprocess involving four photons. Under suitable conditions this\nopticallydegenerate, four-photon process can be stronger than the usual\ntwo-photon inelastic light scattering mechanism, leading to nonlinear growth of\nthe observed matter-wave scattering independent of any enhancement from bosonic\nstimulation. Our theoretical framework can be extended to encompass even\nhigher-order, nonlinear superradiant processes that result in higher-order\nmomentum transfer."
    },
    {
        "anchor": "Cavity-Assisted Dynamical Spin-Orbit Coupling in Cold Atoms: We consider ultracold atoms subjected to a cavity-assisted two-photon Raman\ntransition. The Raman coupling gives rise to effective spin-orbit interaction\nwhich couples atom's center-of-mass motion to its pseudospin degrees of\nfreedom. Meanwhile, the cavity photon is dynamically affected by the atom. This\nfeedback between atom and photon leads to a dramatic modification of the atomic\ndispersion relation, and further leads to dynamical instability of the system.\nWe propose to detect the change of cavity photon number as a direct way to\ndemonstrate dynamical instability.",
        "positive": "Crossover from collisionless to collisional spin dynamics of polarized\n  fermions: We study the transverse spin dynamics of trapped polarized Fermi gases in the\nhigh temperature limit. In the non-interacting collisionless regime, a magnetic\nfield gradient induces collective spin wave oscillations. In the strongly\ninteracting collisional regime, the dynamics are governed by spin diffusion.\nThese two limits have been extensively studied both experimentally and\ntheoretically, but the crossover between them has received less attention. In\nthis paper, we use a quantum Boltzmann equation to study transverse spin\ndynamics and show how the excitations evolve from dispersive to diffusive in\nthe high temperature limit. We provide analytical solutions in the two limiting\nregimes, which agree well with our numerical results."
    },
    {
        "anchor": "Particle-Hole Pair Coherence in Mott Insulator Quench Dynamics: We predict the existence of novel collapse and revival oscillations that are\na distinctive signature of the short-range off-diagonal coherence associated\nwith particle-hole pairs in Mott insulator states. Starting with an atomic Mott\nstate in a one-dimensional optical lattice, suddenly raising the lattice depth\nfreezes the particle-hole pairs in place and induces phase oscillations. The\npeak of the quasi-momentum distribution, revealed through time of flight\ninterference, oscillates between a maximum occupation at zero quasi-momentum\n(the $\\Gamma$ point) and the edge of the Brillouin zone. We show that the\npopulation enhancements at the edge of the Brillouin zone is due to coherent\nparticle-hole pairs, and we find similar effects for fermions and Bose-Fermi\nmixtures in a lattice. Our results open a new avenue for probing strongly\ncorrelated many-body states with short-range phase coherence that goes beyond\nthe familiar collapse and revivals previously observed in the long-range\ncoherent superfluid regime.",
        "positive": "The BCS-BEC Crossover: This chapter presents the crossover from the Bardeen-Cooper-Schrieffer (BCS)\nstate of weakly-correlated pairs of fermions to the Bose-Einstein condensation\n(BEC) of diatomic molecules in the atomic Fermi gas. Our aim is to provide a\npedagogical review of the BCS-BEC crossover, with an emphasis on the basic\nconcepts, particularly those that are not generally known or are difficult to\nfind in the literature. We shall not attempt to give an exhaustive survey of\ncurrent research in the limited space here; where possible, we will direct the\nreader to more extensive reviews."
    },
    {
        "anchor": "Two-dimensional pseudogap effects of an ultracold Fermi gas in the\n  BCS-BEC crossover region: We investigate pseudogap phenomena originating from pairing fluctuations in\nthe BCS-BEC crossover regime of a two-dimensional Fermi gas in a harmonic trap.\nIncluding pairing fluctuations within a $T$-matrix theory and effects of a trap\nwithin the local density approximation, we calculate the local density of\nstates (LDOS) at the superfluid phase transition temperature $T_{\\rm c}$. In\nthe weak-coupling regime, we show that the pseudogap already appears in LDOS\naround the trap center. The spatial region where the pseudogap can be seen in\nLDOS becomes wider for a strong pairing interaction. We also discuss how the\npseudogap affects the spectrum of the photoemission-type experiment developed\nby JILA group.",
        "positive": "Meron Ground State of Rashba Spin-Orbit-Coupled Dipolar Bosons: We study the effects of dipolar interactions on a Bose-Einstein condensate\nwith synthetically generated Rashba spin-orbit coupling. The dipolar\ninteraction we consider includes terms that couple spin and orbital angular\nmomentum in a way perfectly congruent with the single-particle Rashba coupling.\nWe show that this internal spin-orbit coupling plays a crucial role in the rich\nground-state phase diagram of the trapped condensate. In particular, we predict\nthe emergence of a thermodynamically stable ground state with a meron spin\nconfiguration."
    },
    {
        "anchor": "Universal Coarsening in a Homogeneous Two-Dimensional Bose Gas: Coarsening of an isolated far-from-equilibrium quantum system is a\nparadigmatic many-body phenomenon, relevant from subnuclear to cosmological\nlengthscales, and predicted to feature universal dynamic scaling. Here, we\nobserve universal scaling in the coarsening of a homogeneous two-dimensional\nBose gas, with exponents that match analytical predictions. For different\ninitial states, we reveal universal scaling in the experimentally accessible\nfinite-time dynamics by elucidating and accounting for the\ninitial-state-dependent prescaling effects. The methods we introduce establish\ndirect comparison between cold-atom experiments and non-equilibrium field\ntheory, and are applicable to any study of universality far from equilibrium.",
        "positive": "Efficient matter-wave lensing of ultracold atomic mixtures: Mixtures of ultracold quantum gases are at the heart of high-precision\nquantum tests of the weak equivalence principle, where extremely low expansion\nrates have to be reached with matter-wave lensing techniques. We propose to\nsimplify this challenging atom-source preparation by employing magic laser\nwavelengths for the optical lensing potentials which guarantee that all atomic\nspecies follow identical trajectories and experience common expansion dynamics.\nIn this way, the relative shape of the mixture is conserved during the entire\nevolution while cutting in half the number of required lensing pulses compared\nto standard approaches."
    },
    {
        "anchor": "Squeezing Out the Entropy of Fermions in Optical Lattices: At present, there is considerable interest in using atomic fermions in\noptical lattices to emulate the mathematical models that have been used to\nstudy strongly correlated electronic systems. Some of these models, such as the\ntwo dimensional fermion Hubbard model, are notoriously difficult to solve, and\ntheir key properties remain controversial despite decades of studies. It is\nhoped that the emulation experiments will shed light on some of these long\nstanding problems. A successful emulation, however, requires reaching\ntemperatures as low as $10^{-12}$K and beyond, with entropy per particle far\nlower than what can be achieved today. Achieving such low entropy states is an\nessential step and a grand challenge of the whole emulation enterprise. In this\npaper, we point out a method to literally squeeze the entropy out from a Fermi\ngas into a surrounding Bose-Einstein condensed gas (BEC), which acts as a heat\nreservoir. This method allows one to reduce the entropy per particle of a\nlattice Fermi gas to a few percent of the lowest value obtainable today.",
        "positive": "Comparative study for two-terminal transport through a lossy\n  one-dimensional quantum wire: Motivated by realization of the dissipative quantum point contact in\nultracold atomic gases, we investigate a two-terminal mesoscopic transport\nsystem in which a single-particle loss is locally present in a one-dimensional\nchain. By means of the Dyson equation approach in the Keldysh formalism that\ncan incorporate dissipative effects, we reveal analytic structures of the\nparticle and energy currents whose formal expressions correspond to ones in\ncertain three-terminal systems where the particle loss is absent. The obtained\nformulas are also consistent with non-hermitian and three-terminal\nLandauer-B\\\"{u}ttiiker analyses. The universality on the current expressions\nholds regardless of quantum statistics and may be useful for understanding\nlossy two-terminal transport in terms of three-terminal transport and vice\nversa."
    },
    {
        "anchor": "Elastic scattering of a quantum matter-wave bright soliton on a barrier: We consider a one-dimensional matter-wave bright soliton, corresponding to\nthe ground bound state of N particles of mass m having a binary attractive\ndelta potential interaction on the open line. For a full N-body quantum\ntreatment, we derive several results for the scattering of this quantum soliton\non a short-range, bounded from below, external potential, restricting to the\nlow energy, elastic regime where the centre-of-mass kinetic energy of the\nincoming soliton is lower than the internal energy gap of the soliton, that is\nthe minimal energy required to extract particles from the soliton.",
        "positive": "A coherent superposition of Feshbach dimers and Efimov trimers: A powerful experimental technique to study Efimov physics at positive\nscattering lengths is demonstrated. We use the Feshbach dimers as a local\nreference for Efimov trimers by creating a coherent superposition of both\nstates. Measurement of its coherent evolution provides information on the\nbinding energy of the trimers with unprecedented precision and yields access to\npreviously inaccessible parameters of the system such as the Efimov trimers'\nlifetime and the elastic processes between atoms and the constituents of the\nsuperposition state. We develop a comprehensive data analysis suitable for\nnoisy experimental data that confirms the trustworthiness of our demonstration."
    },
    {
        "anchor": "Numerical Realization of Dynamical Fermionization and Bethe Rapidities\n  in a cold quenched Bose gas: In this numerical investigation, we explore the non-equilibrium dynamics of a\ncold Lieb-Liniger (LL) Bose gas -- a well established integrable quantum system\nin one dimension exhibiting repulsive interactions. Our study involves the\npresence of a hard wall potential during the ballistic expansion of the Bose\ngas from its ground state within an infinite deep box of length L0 to a final\nlength L. The Quantum Monte Carlo method, based on the Generalized Feynman-Kac\napproach, serves as our computational tool. Given the integrability of the\nLieb-Liniger model, strongly correlated systems resist thermalization. To\ncapture the intricate dynamics we employ the concept of Bethe Rapidities(BRs),\na holistic function that extends beyond atomic or energy density\nconsiderations. Our thought experiment involves a box-to-box expansion,\nproviding a unique opportunity for direct numerical observation of Bethe\nRapidities and the phenomenon of Dynamical Fermionization(DF). This\ninvestigation aims to contribute insights into the behavior of strongly\ncorrelated quantum systems during non-equilibrium processes, offering a\ndetailed examination of Bethe Rapidities and the dynamic evolution of\nFermionization throughout the expansion.",
        "positive": "Vortex-core structure in a mixture of Bose and Fermi superfluids: We study a single quantized vortex in the fermionic component of a mixture of\nFermi superfluid and Bose-Einstein condensate. As the density ratio between the\nboson and the fermion components is tuned, we identify a transition in the\nvortex-core structure, across which fermions in the vortex core become\ncompletely depleted even in the weak-coupling Bardeen-Cooper-Schrieffer regime.\nThis is accompanied by changes in key properties of the vortex state, as well\nas by the localization of the Bose-Einstein condensate in the vortex core. The\ntransition in the vortex-core structure can be experimentally probed in\nBose-Fermi superfluid mixtures by detecting the size and visibility of the\nvortices."
    },
    {
        "anchor": "Study of a degenerate dipolar Fermi gas of 161Dy atoms: We study properties of a single-component (spin polarized) degenerate dipolar\nFermi gas of 161Dy atoms using a hydrodynamic description. Under\naxially-symmetric trapping we suggest reduced one- (1D) and two-dimensional\n(2D) description of the same for cigar and disk shapes, respectively. In\naddition to a complete numerical solution of the hydrodynamic model we also\nconsider a variational approximation of the same. For a trapped system under\nappropriate conditions, the variational approximation as well as the reduced 1D\nand 2D models are found to yield results for shape, size and chemical potential\nof the system in agreement with the full numerical solution of the\nthree-dimensional (3D) model. For the uniform system we consider anisotropic\nsound propagation in 3D. An analytical result for anisotropic sound propagation\nin uniform dipolar degenerate Fermi gas is found to be in agreement with\nresults of numerical simulation in 3D.",
        "positive": "Superfluidity in atomic Fermi gases: In a trapped atomic Fermi gas, one can tune continuously via a Feshbach\nresonance the effective pairing interaction between fermionic atoms from very\nweak to very strong. As a consequence, the low temperature superfluidity\nevolves continuously from the BCS type in the weak interaction limit to that of\nBose-Einstein condensation in the strong pairing limit, exhibiting a BCS-BEC\ncrossover. In this paper, we review recent experimental progress in atomic\nFermi gases which elucidates the nature of the superfluid phase as the\ninteraction is continuously tuned. Of particular interest is the intermediate\nor crossover regime where the $s$-wave scattering length diverges. We will\npresent an intuitive pairing fluctuation theory, and show that this theory is\nin quantitative agreement with existing experiments in cold atomic Fermi gases."
    },
    {
        "anchor": "Landau Levels in Lattices with Long Range Hopping: In the presence of a periodic potential Landau levels (LLs) are broadened,\nforming a barrier for accurate simulation of fractional quantum Hall effect\nusing cold atoms in optical lattices. Recently, it has been shown that the\ndegeneracy of the lowest Landau level (LLL) can be restored in a tight binding\nlattice, if a particular form of long range hopping is introduced [E. Kapit and\nE. J. Mueller, Phys. Rev. Lett. 105, 215303 (2010)]. In this paper, we\ninvestigate three problems related to such quantum Hall parent Hamiltonians in\nlattices. First, we show that there are infinitely many long range hopping\nmodels in which a massively degenerate manifold is formed by lattice\ndiscretizations of wavefunctions in the continuum LLL. We then give a general\nmethod to construct such models, which is applicable to not only the LLL but\nalso higher LLs. We use this method to give an analytic expression for the\nhoppings that restore the LLL, and an integral expression for the next LL. We\nalso consider whether the space spanned by discretized LL wavefunctions is as\nlarge as the space spanned by continuum wavefunctions and find the constraints\non magnetic field for this condition to be satisfied. Finally, using these\nconstraints and first Chern numbers, we identify the bands of the Hofstadter\nbutterfly that correspond to continuum LLs.",
        "positive": "Symmetries and Correlations in Strongly Interacting One-dimensional\n  Quantum Gases: The main focus of this thesis is the theoretical study of strongly\ninteracting quantum mixtures confined in one dimension and subjected to a\nharmonic external potential. Such strongly correlated systems can be realized\nand tested in ultracold atoms experiments. Their non-trivial permutational\nsymmetry properties are investigated, as well as their interplay with\ncorrelations. Exploiting an exact solution at strong interactions, we extract\ngeneral correlation properties encoded in the one-body density matrix and in\nthe associated momentum distributions, in fermionic and Bose-Fermi mixtures. In\nparticular, we obtain substantial results about the short-range behavior, and\ntherefore the high-momentum tails, which display typical $k^{-4}$ laws. The\nweights of these tails, denoted as Tan's contacts, are related to numerous\nthermodynamic properties of the systems such as the two-body correlations, the\nderivative of the energy with respect to the one-dimensional scattering length,\nor the static structure factor. We show that these universal Tan's contacts\nalso allow to characterize the spatial symmetry of the systems, and therefore\nis a deep connection between correlations and symmetries. Besides, the exchange\nsymmetry is extracted using a group theory method, namely the class-sum method,\nwhich comes originally from nuclear physics. Moreover, we show that these\nsystems follow a generalized version of the famous Lieb-Mattis theorem. Wishing\nto make our results as experimentally relevant as possible, we derive scaling\nlaws for Tan's contact as a function of the interaction, temperature and\ntransverse confinement. These laws display interesting effects related to\nstrong correlations and dimensionality."
    },
    {
        "anchor": "Non-equilibrium evolution of Bose-Einstein condensate deformation in\n  temporally controlled weak disorder: We consider a time-dependent extension of a perturbative mean-field approach\nto the dirty boson problem by considering how switching on and off a weak\ndisorder potential affects the stationary state of an initially equilibrated\nBose-Einstein condensate by the emergence of a disorder-induced condensate\ndeformation. We find that in the switch on scenario the stationary condensate\ndeformation turns out to be a sum of an equilibrium part, that actually\ncorresponds to adiabatic switching on the disorder, and a dynamically-induced\npart, where the latter depends on the particular driving protocol. If the\ndisorder is switched off afterwards, the resulting condensate deformation\nacquires an additional dynamically-induced part in the long-time limit, while\nthe equilibrium part vanishes. We also present an appropriate generalization to\ninhomogeneous trapped condensates. Our results demonstrate that the condensate\ndeformation represents an indicator of the generically non-equilibrium nature\nof steady states of a Bose gas in a temporally controlled weak disorder.",
        "positive": "Collective and single-particle excitations in 2D dipolar Bose gases: The Berezinskii-Kosterlitz-Thouless transition in 2D dipolar systems has been\nstudied recently by path integral Monte Carlo (PIMC) simulations [A. Filinov et\nal., PRL 105, 070401 (2010)]. Here, we complement this analysis and study\ntemperature-coupling strength dependence of the density (particle-hole) and\nsingle-particle (SP) excitation spectra both in superfluid and normal phases.\nThe dynamic structure factor, S(q,omega), of the longitudinal excitations is\nrigorously reconstructed with full information on damping. The SP spectral\nfunction, A(q,omega), is worked out from the one-particle Matsubara Green's\nfunction. A stochastic optimization method is applied for reconstruction from\nimaginary times. In the superfluid regime sharp energy resonances are observed\nboth in the density and SP excitations. The involved hybridization of both\nspectra is discussed. In contrast, in the normal phase, when there is no\ncoupling, the density modes, beyond acoustic phonons, are significantly damped.\nOur results generalize previous zero temperature analyses based on variational\nmany-body wavefunctions [F. Mazzanti et al., PRL 102, 110405 (2009), D. Hufnagl\net al., PRL 107, 065303 (2011)], where the underlying physics of the excitation\nspectrum and the role of the condensate has not been addressed."
    },
    {
        "anchor": "Quantum Hall effect with small numbers of vortices in Bose-Einstein\n  condensates: When vortices are displaced in Bose-Einstein condensates (BEC), the Magnus\nforce gives the system a momentum transverse in the direction to the\ndisplacement. We show that Bose-Einstein condensates (BEC) in long channels\nwith vortices exhibit a quantization of the current response with respect to\nthe spatial vortex distribution. The quantization originates from the\nwell-known topological property of the phase around a vortex --- it is an\ninteger multiple of $ 2 \\pi $. In a similar way to the integer quantum Hall\neffect, the current along the channel is related to this topological phase, and\ncan be extracted from two experimentally measurable quantities: the total\nmomentum of the BEC and the spatial distribution. The quantization is in units\nof $ m/2h $, where $ m $ is the mass of the atoms and $ h $ is Planck's\nconstant. We derive an exact vortex momentum-displacement relation for BECs in\nlong channels under general circumstances. Our results presents the possibility\nthat the configuration described here can be used as a novel way of measuring\nthe mass of the atoms in the BEC using a topological invariant of the system.\nIf an accurate determination of the plateaus are experimentally possible, this\ngives the possibility of a topological quantum mass standard and precise\ndetermination of the fine structure constant.",
        "positive": "Renormalization group approach to the normal phase of 2D Fermi gases: We present results on the effect of short-range, attractive interactions on\nthe properties of balanced 2D Fermi gases in the non-superfluid (normal) phase.\nOur approach combines the renormalization group (RG) with perturbation theory,\nyielding observables such as the equation of state and compressibility. We find\ngood agreement with recent experiments that measured the equation of state in\ntrapped gases in the balanced regime, showing that these results are consistent\nwith logarithmic corrections in the equation of state."
    },
    {
        "anchor": "Quantum de-mixing in binary mixtures of dipolar bosons: Quantum Monte Carlo simulations of a two-component Bose mixture of trapped\ndipolar atoms of identical masses and dipole moments, provide numerical\nevidence of de-mixing at low finite temperatures. De-mixing occurs as a\nconsequence of quantum statistics, which results in an effective attraction\nbetween like bosons. Spatial separation of two components takes place at low\ntemperature with the onset of long exchanges of identical particles, underlying\nBose-Einstein condensation of both components. Conversely, at higher\ntemperature the system is miscible due to the entropy of mixing. Exchanges are\nalso found to enhance de-mixing in the case of mixtures of non-identical and\ndistinguishable species.",
        "positive": "Holographic method for site-resolved detection of a 2D array of\n  ultracold atoms: We propose a novel approach to site-resolved detection of a 2D gas of\nultracold atoms in an optical lattice. A near resonant laser beam is coherently\nscattered by the atomic array and its interference pattern is holographically\nrecorded by superimposing it with a reference laser beam on a CCD chip. Fourier\ntransformation of the recorded intensity pattern reconstructs the atomic\ndistribution in the lattice with single-site resolution. The holographic\ndetection method requires only a few hundred scattered photons per atom in\norder to achieve a high reconstruction fidelity. Therefore, additional cooling\nduring detection might not be necessary even for light atomic elements such as\nlithium."
    },
    {
        "anchor": "Stability Window of Trapless Polariton Bose-Einstein condensates: We theoretically explore the possibility of stabilizing the trapless\npolariton Bose-Einstein condensates (pBECs). Exploiting the variational method,\nwe solve the associated nonlinear, complex Gross-Pitaevskii (cGP) equation and\nderive the equation of motion for the amplitude and width of the condensate.\nThese variational results described by ordinary differential equations are\nrewritten to perform a linear stability analysis to generate a stability window\nin the repulsive domain. A set of coupled nonlinear ordinary differential\nequations obtained through variational approach are then solved by numerical\nsimulations through the fourth order Runge-Kutta method, which are further\nsupported by split-step Crank-Nicholson method, thereby setting the platform\nfor stable pBECs. In particular, we generate a window containing system\nparameters in the $g_1-\\gamma_{eff}$ space within which the system can admit\nstable condensates. The highlight of the results is that one observes beating\neffects in the real time evolution of the condensates with attractive\ninteractions much similar to multicomponent BECs, and their periodicity can be\nvaried by manipulating linear and nonlinear loss/gain terms. For repulsive\ncondensates, one notices the stretching of the density.",
        "positive": "Functional Wigner representation of BEC quantum dynamics: We develop a method of simulating the full quantum field dynamics of\nmulti-mode multi-component Bose-Einstein condensates in a trap. We use the\ntruncated Wigner representation to obtain a probabilistic theory that can be\nsampled. This method produces c-number stochastic equations which may be solved\nusing conventional stochastic methods. The technique is valid for large mode\noccupation numbers. We give a detailed derivation of methods of functional\nWigner representation appropriate for quantum fields. Our approach describes\nspatial evolution of spinor components and properly accounts for nonlinear\nlosses. Such techniques are applicable to calculating the leading quantum\ncorrections, including effects like quantum squeezing, entanglement, EPR\ncorrelations and interactions with engineered nonlinear reservoirs. By using a\nconsistent expansion in the inverse density, we are able to explain an\ninconsistency in the nonlinear loss equations found by earlier authors."
    },
    {
        "anchor": "Interacting trapped bosons yield fragmented condensate states in low\n  dimensions: We investigate the level population statistics and degree of coherence\nencoded in the single-particle density matrix of harmonically trapped\nlow-dimensional [quasi-one-dimensional (quasi-1D) or quasi-two-dimensional\n(quasi-2D)] Bose gases with repulsive contact interactions. Using a variational\nanalysis, we derive fragmentation of the condensate in the weakly confining\ndirections into two (quasi-1D) respectively three (quasi-2D) mutually\nincoherent macroscopic pieces, upon increasing a dimensionless interaction\nmeasure beyond a critical value. Fragmented condensate many-body states in\nlow-dimensional systems therefore occur well before the thermodynamic limit of\ninfinite extension is reached, in which phase fluctuations of the matter wave\nfield create an infinite number of nonmacroscopic fragments.",
        "positive": "Universal and non-universal effective $N$-body interactions for\n  ultracold harmonically-trapped few-atom systems: We derive the ground-state energy for a small number of ultracold atoms in an\nisotropic harmonic trap using effective quantum field theory (EFT). Atoms are\nassumed to interact through pairwise energy-independent and energy-dependent\ndelta-function potentials with strengths proportional to the scattering length\n$a$ and effective range volume $V$, respectively. The calculations are\nperformed systematically up to order $l^{-4}$, where $l$ denotes the harmonic\noscillator length. The effective three-body interaction contains a logarithmic\ndivergence in the cutoff energy, giving rise to a non-universal three-body\ninteraction in the EFT. Our EFT results are confirmed by nonperturbative\nnumerical calculations for a Hamiltonian with finite-range two-body Gaussian\ninteractions. For this model Hamiltonian, we explicitly calculate the\nnon-universal effective three-body contribution to the energy."
    },
    {
        "anchor": "Macroscopic properties of triplon Bose-Einstein condensates: Magnetic insulators can be characterized by a gap separating the singlet\nground state from the lowest energy triplet, S=1 excitation. If the gap can be\nclosed by the Zeeman interaction in applied magnetic field, the resulting S=1\nquasiparticles, triplons, can have concentrations sufficient to undergo the\nBose-Einstein condensates transition. We consider macroscopic properties of the\ntriplon Bose-Einstein condensates in the Hartree-Fock-Bogoliubov approximation\ntaking into account the anomalous averages. We prove that these averages play\nthe qualitative role in the condensate properties. As a result, we show that\nwith the increase in the external magnetic field at a given temperature, the\ncondensate demonstrates an instability related to the appearance of nonzero\nphonon damping and a change in the characteristic dependence of the speed of\nsound on the magnetic field. The calculated magnetic susceptibility diverges\nwhen the external magnetic field approaches this instability threshold,\nproviding a tool for the experimental verification of this approach.",
        "positive": "Finite-temperature degenerate perturbation theory for bosons in optical\n  lattices: Bosonic atoms confined in optical lattices can exist in two different phases,\nMott-insulator and superfluid, depending on the strength of the system\nparameters, such as the on-site interaction between particles and the hopping\nparameter. This work is motivated by the fact that non-degenerate perturbation\ntheory applied to the mean-field approximation of the Bose-Hubbard Hamiltonian\nat zero and finite temperature fails to give consistent results in the vicinity\nof the Mott-insulator-superfluid phase transition, e.g., the order parameter\ncalculated via non-degenerate perturbation theory reveals an unphysical\nbehavior between neighboring Mott lobes, which is an explicit consequence of\ndegeneracy problems that artificially arise from such a treatment. Therefore,\nin order to fix this problem, we propose a finite-temperature degenerate\nperturbation theory approach based on a projection operator formalism which\nends up solving such degeneracy problems in order to obtain physically\nconsistent results for the order parameter near the phase transition."
    },
    {
        "anchor": "Non-equilibrium and local detection of the normal fraction of a trapped\n  two-dimensional Bose gas: We propose a method to measure the normal fraction of a two-dimensional Bose\ngas, a quantity that generally differs from the non-condensed fraction. The\nidea is based on applying a spatially oscillating artificial gauge field to the\natoms. The response of the atoms to the gauge field can be read out either\nmechanically from the deposited energy into the cloud, or optically from the\nmacroscopic optical properties of the atomic gas. The local nature of the\nproposed scheme allows one to reconstruct the spatial profile of the superfluid\ncomponent; furthermore, the proposed method does not require having established\nthermal equilibrium in the gas in the presence of the gauge field. The\ntheoretical description of the system is based on a generalization of the\nDum-Olshanii theory of artificial gauge fields to the interacting many-body\ncontext. The efficiency of the proposed measurement scheme is assessed by means\nof classical field numerical simulations. An explicit atomic level scheme\nminimizing disturbing effects such as spontaneous emission and light-shifts is\nproposed for Rb 87 atoms.",
        "positive": "Hilbert space shattering and disorder-free localization in polar lattice\n  gases: Emerging dynamical constraints resulting from inter-site interactions\nseverely limit particle mobility in polar lattice gases. Whereas in absence of\ndisorder hard-core Hubbard models with only strong nearest-neighbor\ninteractions present Hilbert space fragmentation but no many-body localization\nfor typical states, the $1/r^3$ tail of the dipolar interaction results in\nHilbert space shattering, as well as in a dramatically slowed down dynamics and\neventual disorder-free localization. Our results show that the study of the\nintriguing interplay between disorder- and interaction-induced many-body\nlocalization is within reach of future experiments with magnetic atoms and\npolar molecules."
    },
    {
        "anchor": "Charge density wave and charge pump of interacting fermions in\n  circularly shaken hexagonal optical lattices: We analyze strong correlation effects and topological properties of\ninteracting fermions with a Falicov-Kimball type interaction in circularly\nshaken hexagonal optical lattices, which can be effectively described by the\nHaldane-Falicov-Kimball model, using the real-space Floquet dynamical\nmean-field theory (DMFT). The Haldane model, a paradigmatic model of the Chern\ninsulator, is experimentally relevant, because it has been realized using\ncircularly shaken hexagonal optical lattices. We show that in the presence of\nstaggering a charge density wave emerges, which is affected by interactions and\nresonant tunneling. We demonstrate that interactions smear out the edge states\nby introducing a finite life time of quasiparticles. Even though a general\nmethod for calculating the topological invariant of a nonequilibrium steady\nstate is lacking, we extract the topological invariant using a Laughlin charge\npump set-up. We find and attribute to the dissipations into the bath connected\nto every lattice site, which is intrinsic to real-space Floquet DMFT methods,\nthat the pumped charge is not an integer even for the non-interacting case at\nvery low reservoir temperatures. Furthermore, using the rate equation based on\nthe Floquet-Born-Markov approximation, we calculate the charge pump from the\nrate equations for the non-interacting case to identify the role of the\nspectral properties of the bath. Starting from this approach we propose an\nexperimental protocol for measuring quantized charge pumping.",
        "positive": "Anyonic Haldane insulator in one dimension: We demonstrate numerically the existence of a nontrivial topological Haldane\nphase for the one-dimensional extended ($U$-$V$) Hubbard model with a mean\ndensity of one particle per site, not only for bosons but also for anyons,\ndespite a broken reflection parity symmetry. The Haldane insulator, surrounded\nby superfluid, Mott insulator and density-wave phases in the $V$-$U$ parameter\nplane, is protected by combined (modified) spatial-inversion and time-reversal\nsymmetries, which is verified within our matrix-product-state based infinite\ndensity-matrix renormalization group scheme by analyzing generalized transfer\nmatrices. With regard to an experimental verification of the anyonic Haldane\ninsulator state the calculated asymmetry of the dynamical density structure\nfactor should be of particular importance."
    },
    {
        "anchor": "Quantum Fluctuations of Vortex-Lattice State in Ultrafast Rotating Bose\n  Gas: Quantum fluctuations in an ultrafast rotating Bose gas at zero temperature\nare investigated. We calculate the condensate density perturbatively to show\nthat no condensate is present in the thermodynamic limit. The excitation from\nGaussian fluctuations around the mean field solution causes infrared\ndivergences in loop diagrams, nevertheless, in calculating the atom number\ndensity, the correlation functions and the free energy, we find the sum of the\ndivergences in the same loop order vanishes and obtain finite physical\nquantities. The long-range correlation is explored and the algebraic decay\nexponent for the single-particle correlation function is obtained. The atom\nnumber density distribution is obtained at the one-loop level, which\nillustrates the quantum fluctuation effects to melt the mean field\nvortex-lattice. By the non-perturbative Gaussian variational method, we locate\nthe spinodal point of the vortex-lattice state.",
        "positive": "Analogy of RKKY oscillations to the heat exchange in cold atoms: An oscillatory term is found in both the energy expectation and dynamics of a\nwave-packet in a time-varying harmonic trap and infinite potential well. They\nare proved to oscillate in coherence with the time lapse within each period\ndepending on both the cutoff in transition energies and the specific route via\nwhich the potential is being varied. This oscillatory term is general to\narbitrary potential forms since it derives from the interference between\ncrossed transition trajectories. Close analogy is made to the\nRuderman-Kittel-Kasuya-Yosida interaction for giant-magnetoresistance\ntrilayers, where many-body quantum interference among scattering states renders\nthe oscillation as a function of spacer width. This connection reveals the\ngenerality of quantum friction due to parasitic oscillations."
    },
    {
        "anchor": "BCS-BEC quantum phase transition and collective excitations in\n  two-dimensional Fermi gases with p- and d-wave pairings: It is generally believed that the BCS-BEC evolution in fermionic systems with\ns-wave pairing is a smooth crossover. However, for nonzero\norbital-angular-momentum pairing such as p- or d-wave pairing, the system\nundergoes a quantum phase transition at the point where the chemical potential\n$\\mu$ vanishes. In this paper, we study the BCS-BEC quantum phase transition\nand the collective excitations associated with the order-parameter fluctuations\nin two-dimensional fermionic systems with p- and d-wave pairings. We show that\nthe quantum phase transition in such systems can be generically traced back to\nthe infrared behavior of the fermionic excitation at $\\mu=0$: $E_{\\bf k}\\sim\nk^l$, where $l=1,2$ is the quantum number of the orbital angular momentum. The\nnonanalyticity of the thermodynamic quantities is due to the infrared\ndivergence caused by the fermionic excitation at $\\mu=0$. As a result, the\nevolution of the Anderson-Bogoliubov mode is not smooth: Its velocity is\nnonanalytical across the quantum phase transition.",
        "positive": "Strongly Correlated Quantum Walks in Optical Lattices: Full control over the dynamics of interacting, indistinguishable quantum\nparticles is an important prerequisite for the experimental study of strongly\ncorrelated quantum matter and the implementation of high-fidelity quantum\ninformation processing. Here we demonstrate such control over the quantum walk\n- the quantum mechanical analogue of the classical random walk - in the strong\ninteraction regime. Using interacting bosonic atoms in an optical lattice, we\ndirectly observe fundamental effects such as the emergence of correlations in\ntwo-particle quantum walks, as well as strongly correlated Bloch oscillations\nin tilted optical lattices. Our approach can be scaled to larger systems,\ngreatly extending the class of problems accessible via quantum walks"
    },
    {
        "anchor": "Cooling of a Bose-Einstein Condensate by spin distillation: We propose and experimentally demonstrate a new cooling mechanism leading to\npurification of a spinor Bose-Einstein Condensate (BEC). Our scheme starts with\na BEC polarized in the lowest energy spin state. Spin excited states are\nthermally populated by lowering the single particle energy gap set by the\nmagnetic field. Then these spin-excited thermal components are filtered out,\nwhich leads to an increase of the BEC fraction. We experimentally demonstrate\nsuch cooling for a spin 3 52Cr dipolar BEC. Our scheme should be applicable to\nNa or Rb, with perspective to reach temperatures below 1 nK.",
        "positive": "Approximate mean-field equations of motion for quasi-2D Bose-Einstein\n  condensate systems: We present a method for approximating the solution of the three-dimensional,\ntime-dependent Gross-Pitaevskii equation (GPE) for Bose-Einstein condensate\nsystems where the confinement in one dimension is much tighter than in the\nother two. This method employs a hybrid Lagrangian variational technique whose\ntrial wave function is the product of a completely unspecified function of the\ncoordinates in the plane of weak confinement and a gaussian in the strongly\nconfined direction having a time-dependent width and quadratic phase. The\nhybrid Lagrangian variational method produces equations of motion that consist\nof (1) a two-dimensional, effective GPE whose nonlinear coefficient contains\nthe width of the gaussian and (2) an equation of motion for the width that\ndepends on the integral of the fourth power of the solution of the 2D effective\nGPE. We apply this method to the dynamics of Bose-Einstein condensates confined\nin ring-shaped potentials and compare the approximate solution to the numerical\nsolution of the full 3D GPE."
    },
    {
        "anchor": "Interaction dependent temperature effects in Bose-Fermi mixtures in\n  optical lattices: We present a quantitative finite temperature analysis of a recent experiment\nwith Bose-Fermi mixtures in optical lattices, in which the dependence of the\ncoherence of bosons on the inter-species interaction was analyzed. Our theory\nreproduces the characteristics of this dependence and suggests that intrinsic\ntemperature effects play an important role in these systems. Namely, under the\nassumption that the ramping up of the optical lattice is an isentropic process,\nadiabatic temperature changes of the mixture occur that depend on the\ninteraction between bosons and fermions. Matching the entropy of two\nregimes---no lattice on the one hand and deep lattices on the other---allows us\nto compute the temperature in the lattice and the visibility of the\nquasi-momentum distribution of the bosonic atoms, which we compare to the\nexperiment. We briefly comment on the remaining discrepancy between theory and\nexperiment, speculating that it may in part be attributed to the dependence of\nthe Bose-Fermi scattering length on the confinement of the atoms.",
        "positive": "Thermalization and breakdown of thermalization in photon condensates: We examine in detail the mechanisms behind thermalization and Bose-Einstein\ncondensation of a gas of photons in a dye-filled microcavity. We derive a\nmicroscopic quantum model, based on that of a standard laser, and show how this\nmodel can reproduce the behavior of recent experiments. Using the rate equation\napproximation of this model, we show how a thermal distribution of photons\narises. We go on to describe how the non-equilibrium effects in our model can\ncause thermalization to break down as one moves away from the experimental\nparameter values. In particular, we examine the effects of changing cavity\nlength, and of altering the vibrational spectrum of the dye molecules. We are\nable to identify two measures which quantify whether the system is in thermal\nequilibrium. Using these we plot \"phase diagrams\" distinguishing BEC and\nstandard lasing regimes. Going beyond the rate equation approximation, our\nquantum model allows us to investigate both the second order coherence,\n$g^{(2)}$, and the linewidth of the emission from the cavity. We show how the\nlinewidth collapses as the system transitions to a Bose condensed state, and\ncompare the results to the Schawlow--Townes linewidth."
    },
    {
        "anchor": "Quantum fluctuations around black hole horizons in Bose-Einstein\n  condensates: We study several realistic configurations allowing to realize an acoustic\nhorizon in the flow of a one dimensional Bose-Einstein condensate. In each case\nwe give an analytical description of the flow pattern, of the spectrum of\nHawking radiation and of the associated quantum fluctuations. Our calculations\nconfirm that the non local correlations of the density fluctuations previously\nstudied in a simplified model provide a clear signature of Hawking radiation\nalso in realistic configurations. In addition we explain by direct computation\nhow this non local signal relates to short range modifications of the density\ncorrelations.",
        "positive": "Stability and dynamics of two-soliton molecules: The problem of soliton-soliton force is revisited. From the exact two\nsolitons solution of a nonautonomous Gross-Pitaevskii equation, we derive a\ngeneralized formula for the mutual force between two solitons. The force is\ngiven for arbitrary solitons amplitude difference, relative speed, phase, and\nseparation. The latter allows for the investigation of soliton molecules\nformation, dynamics, and stability. We reveal the role of the time-dependent\nrelative phase between the solitons in binding them in a soliton molecule. We\nderive its equilibrium bond length, spring constant, frequency, effective mass,\nand binding energy of the molecule. We investigate the molecule's stability\nagainst perturbations such as reflection from surfaces, scattering by barriers,\nand collisions with other solitons."
    },
    {
        "anchor": "Bose Einstein condensate as nonlinear block of a Machine Learning\n  pipeline: Physical systems can be used as an information processing substrate and with\nthat extend traditional computing architectures. For such an application the\nexperimental platform must guarantee pristine control of the initial state, the\ntemporal evolution and readout. All these ingredients are provided by modern\nexperimental realizations of atomic Bose Einstein condensates. By embedding the\nnonlinear evolution of a quantum gas in a Machine Learning pipeline, one can\nrepresent nonlinear functions while only linear operations on classical\ncomputing of the pipeline are necessary. We demonstrate successful regression\nand interpolation of a nonlinear function using a quasi one-dimensional cloud\nof potassium atoms and characterize the performance of our system.",
        "positive": "Functional renormalization for repulsive Bose-Bose mixtures at zero\n  temperature: We study weakly-repulsive Bose-Bose mixtures in two and three dimensions at\nzero temperature using the functional renormalization group (FRG). We examine\nthe RG flows and the role of density and spin fluctuations. We study the\ncondition for phase separation and find that this occurs at the mean-field\npoint within the range of parameters explored. Finally, we examine the energy\nper particle and condensation depletion. We obtain that our FRG calculations\ncompare favorably with known results from perturbative approaches for\nmacroscopic properties."
    },
    {
        "anchor": "High-resolution Internal State Control of Ultracold $^{23}$Na$^{87}$Rb\n  Molecules: We report the full control over the internal states of ultracold\n$^{23}$Na$^{87}$Rb molecules, including vibrational, rotational and hyperfine\ndegrees of freedom. Starting from a sample of weakly bound Feshbach molecules,\nwe realize the creation of molecules in single hyperfine levels of both the\nrovibrational ground and excited states with a high-efficiency and\nhigh-resolution stimulated Raman adiabatic passage. Starting from the\nrovibrational and hyperfine ground state, we demonstrate rotational and\nhyperfine control with one- and two-photon microwave spectroscopy. This\nachievement of fully controlling the molecular internal states paves the way to\nstudy state dependent molecular collisions and state controlled chemical\nreactions.",
        "positive": "Momentum isotropisation in random potentials: When particles are multiply scattered by a random potential, their momentum\ndistribution becomes isotropic on average. We study this quantum dynamics\nnumerically and with a master equation. We show how to measure the elastic\nscattering time as well as characteristic isotropisation times, which permit to\nreconstruct the scattering phase function, even in rather strong disorder."
    },
    {
        "anchor": "Suppression of the quantum collapse in binary bosonic gases: Attraction of the quantum particle to the center in the 3D space with\npotential V/r^2 gives rise to the quantum collapse, i.e., nonexistence of the\nground state (GS) when the attraction strength exceeds a critical value (V =\n1/8, in the present notation). Recently, we have demonstrated that the quantum\ncollapse is suppressed, and the GS is restored, if repulsive interactions\nbetween particles in the quantum gas are taken into account, in the mean-field\napproximation. This setting can be realized in a gas of dipolar molecules\nattracted to the central charge, with dipole-dipole interactions taken into\nregard too. Here we analyze this problem for a binary gas. GSs supported by the\nrepulsive interactions are constructed in a numerical form, as well as by means\nof analytical approximations for both miscible and immiscible binary systems.\nIn particular, the Thomas-Fermi (TF) approximation is relevant if V is large\nenough. It is found that the GS of the miscible binary gas, both balanced and\nimbalanced, features a weak phase transition at another critical value, V =\n1/2. The transition is characterized by an analyticity-breaking change in the\nstructure of the wave functions at small r. To illustrate the generic character\nof the present phenomenology, we also consider the binary system with the\nattraction between the species (rather than repulsion), in the case when the\ncentral potential pulls a single component only.",
        "positive": "Condensation Energy of a Spin-1/2 Strongly Interacting Fermi Gas: We report a measurement of the condensation energy of a two-component Fermi\ngas with tunable interactions. From the equation of state of the gas, we infer\nthe properties of the normal phase in the zero-temperature limit. By comparing\nthe pressure of the normal phase at T=0 to that of the low-temperature\nsuperfluid phase, we deduce the condensation energy, i.e. the energy gain of\nthe system in being in the superfluid rather than normal state. We compare our\nmeasurements to a ladder approximation description of the normal phase, and to\na fixed node Monte-Carlo approach, finding excellent agreement. We discuss the\nrelationship between condensation energy and pairing gap in the BEC-BCS\ncrossover."
    },
    {
        "anchor": "SU(N) magnetism in chains of ultracold alkaline-earth-metal atoms: Mott\n  transitions and quantum correlations: We investigate one dimensional SU$(N)$ Hubbard chains at zero temperature,\nwhich can be emulated with ultracold alkaline earth atoms, by using the density\nmatrix renormalization group (DMRG), Bethe ansatz (BA), and bosonization. We\ncompute experimental observables and use the DMRG to benchmark the accuracy of\nthe Bethe ansatz for $N>2$ where the BA is only approximate. In the worst case,\nwe find a relative error $\\epsilon \\lesssim 4%$ in the BA ground state energy\nfor $N \\leq 4$ at filling 1/N, which is due to the fact that BA improperly\ntreats the triply and higher occupied states. Using the DMRG for $N \\leq 4$ and\nthe BA for large $N$, we determine the regimes of validity of strong- and\nweak-coupling perturbation theory for all values of $N$ and in particular, the\nparameter range in which the system is well described by a SU$(N)$ Heisenberg\nmodel at filling 1/N. We find this depends only weakly on $N$. We investigate\nthe Berezinskii-Kosterlitz-Thouless phase transition from a Luttinger liquid to\na Mott-insulator by computing the fidelity susceptibility and the Luttinger\nparameter $K_\\rho$ at 1/N filling. The numerical findings give strong evidence\nthat the fidelity susceptibility develops a minimum at a critical interaction\nstrength which is found to occur at a finite positive value for $N>2$.",
        "positive": "Spontaneous emissions and thermalization of cold bosons in optical\n  lattices: We study the thermalization of excitations generated by spontaneous emission\nevents for cold bosons in an optical lattice. Computing the dynamics described\nby the many-body master equation, we characterize equilibration timescales in\ndifferent parameter regimes. For simple observables, we find regimes in which\nthe system relaxes rapidly to values in agreement with a thermal distribution,\nand others where thermalization does not occur on typical experimental\ntimescales. Because spontaneous emissions lead effectively to a local quantum\nquench, this behavior is strongly dependent on the low-energy spectrum of the\nHamiltonian, and undergoes a qualitative change at the Mott\nInsulator-superfluid transition point. These results have important\nimplications for the understanding of thermalization after localized quenches\nin isolated quantum gases, as well as the characterization of heating in\nexperiments."
    },
    {
        "anchor": "Many-body theories of density response for a strongly correlated Fermi\n  gas: Recent breakthroughs in the creation of ultra-cold atomic gases in the\nlaboratory have ushered in major changes in physical science. Many novel\nexperiments are now possible, with an unprecedented control of interaction,\ngeometry and purity. Quantum many-body theory is facing severe challenges in\nquantitatively understanding new experimental results. Here, we review some\nrecently developed theoretical techniques that provide successful predictions\nfor density response of a strongly correlated atomic Fermi gas. These include\nthe strong-coupling random-phase approximation theory, high-temperature quantum\nvirial expansion, and asymptotically exact Tan relations applicable at large\nmomentum.",
        "positive": "Localized phase structures growing out of quantum fluctuations in a\n  quench of tunnel-coupled atomic condensates: We investigate the relative phase between two weakly interacting 1D\ncondensates of bosonic atoms after suddenly switching on the tunnel-coupling.\nThe following phase dynamics is governed by the quantum sine-Gordon equation.\nIn the semiclassical limit of weak interactions, we observe the parametric\namplification of quantum fluctuations leading to the formation of breathers\nwith a finite lifetime. The typical lifetime and density of the these\n'quasibreathers' are derived employing exact solutions of the classical\nsine-Gordon equation. Both depend on the initial relative phase between the\ncondensates, which is considered as a tunable parameter."
    },
    {
        "anchor": "Floquet Spinor Bose Gases: We introduce a Floquet spinor Bose-Einstein condensate induced by a\nperiodically driven quadratic Zeeman coupling whose frequency is larger than\nany other energy scales. By examining a spin-1 system available in ultracold\natomic gases, we demonstrate that such an external driving field has great\neffect on the condensate through emergence of a unique spin-exchange\ninteraction. We uncover that the ferromagnetic condensate has several\nunconventional stationary states and thus exhibits rich continuous phase\ntransitions. On the other hand, the antiferromagnetic condensate is found to\npossess a nontrivial metastable region, which supports unusual elementary\nexcitations and hysteresis phenomena.",
        "positive": "Dynamical structure factors of a two-dimensional Fermi superfluid within\n  random phase approximation: Based on random phase approximation (RPA), we numerically calculate dynamical\nstructure factors of a balanced two-dimensional (2D) Fermi superfluid, and\ndiscuss their energy, momentum and interaction strength dependence in the 2D\nBEC-BCS crossover. At a small transferred momentum, a stable Higgs mode is\nobserved in the unitary 2D Fermi superfluid gas where the particle-hole\nsymmetry is not satisfied. Stronger interaction strength will make the\nvisibility of the dispersion of Higgs mode harder to be observed. We also\ndiscuss the dimension effect and find that the signal of the Higgs mode in two\ndimension is more obvious than that in 3D case. At a large transferred momentum\nregime, stronger interaction strength will induce the weight of the molecules\nexcitation increasing, while in verse the atomic one decreasing, which shows\nthe pairing information of Fermi superfluid. The theoretical results\nqualitatively agree with the corresponding Quantum Monte Carlo data."
    },
    {
        "anchor": "Prethermalization to thermalization crossover in a dilute Bose gas\n  following an interaction ramp: The dynamics of a weakly interacting Bose gas at low temperatures is close to\nintegrable due to the approximate quadratic nature of the many-body\nHamiltonian. While the short-time physics after an abrupt ramp of the\ninteraction constant is dominated by the integrable dynamics, integrability is\nbroken at longer times by higher-order interaction terms in the Bogoliubov\nHamiltonian, in particular by Beliaev-Landau scatterings involving three\nquasiparticles. The two-stage relaxation process is highlighted in the\nevolution of local observables such as the density-density correlation\nfunction: a dephasing mechanism leads the system to a prethermal stage,\nfollowed by true thermalization conveyed by quasiparticle collisions. Our\nresults bring the crossover from prethermalization to thermalization within\nreach of current experiments with ultracold atomic gases.",
        "positive": "Dynamical spin-orbit coupling of a quantum gas: We realize the dynamical 1D spin-orbit-coupling (SOC) of a Bose-Einstein\ncondensate confined within an optical cavity. The SOC emerges through\nspin-correlated momentum impulses delivered to the atoms via Raman transitions.\nThese are effected by classical pump fields acting in concert with the quantum\ndynamical cavity field. Above a critical pump power, the Raman coupling emerges\nas the atoms superradiantly populate the cavity mode with photons.\nConcomitantly, these photons cause a back-action onto the atoms, forcing them\nto order their spin-spatial state. This SOC-inducing superradiant Dicke phase\ntransition results in a spinor-helix polariton condensate. We observe emergent\nSOC through spin-resolved atomic momentum imaging. Dynamical SOC in quantum gas\ncavity QED, and the extension to dynamical gauge fields, may enable the\ncreation of Meissner-like effects, topological superfluids, and exotic quantum\nHall states in coupled light-matter systems."
    },
    {
        "anchor": "Three-level Haldane-like model on dice optical lattice: We consider ultracold atoms in a two-dimensional optical lattice of the dice\ngeometry in a tight-binding regime. The atoms experience a laser-assisted\ntunneling between the nearest neighbour sites of the dice lattice accompanied\nby the momentum recoil. This allows one to engineer staggered synthetic\nmagnetic fluxes over plaquettes, and thus pave a way towards a realization of\ntopologically nontrivial band structures. In such a lattice the real-valued\nnext-neighbour transitions are not needed to reach a topological regime. Yet,\nsuch transitions can increase a variety of the obtained topological phases. The\ndice lattice represents a triangular Bravais lattice with a three-site basis\nconsisting of a hub site connected to two rim sites. As a consequence, the dice\nlattice supports three dispersion bands. From this point of view, our model can\nbe interpreted as a generalization of the paradigmatic Haldane model which is\nreproduced if one of the two rim sub-lattices is eliminated. We demonstrate\nthat the proposed upgrade of the Haldane model creates a significant added\nvalue, including an easy access to topological semimetal phases relying only on\nthe nearest neighbour coupling, as well as enhanced topological band structures\nfeaturing Chern numbers higher than one. The numerical investigation is\nsupported and complemented by an analytical scheme based on the study of\nsingularities in the Berry connection.",
        "positive": "Determination of the density and temperature dependence of the shear\n  viscosity of a unitary Fermi gas based on hydrodynamic flow: We determine the shear viscosity of the ultracold Fermi gas at unitarity in\nthe normal phase using hydrodynamic expansion data. The analysis is based on a\ngeneralized fluid dynamic framework which ensures a smooth transition between\nthe fluid dynamic core of the cloud and the ballistic corona. We use expansion\ndata taken by Joseph et al. and measurements of the equation of state by Ku et\nal. We find that the shear viscosity to particle density ratio just above the\ncritical temperature is $\\eta/n|_{T_c}=0.41\\pm 0.11$. We also obtain evidence\nthat the shear viscosity to entropy density ratio has a minimum slightly above\n$T_c$ with $\\eta/s |_{\\it min}=0.50\\pm 0.10$."
    },
    {
        "anchor": "Feshbach Resonances in an Erbium-Dysprosium Dipolar Mixture: We report on the observation of heteronuclear magnetic Feshbach resonances in\nseveral isotope mixtures of the highly magnetic elements erbium and dysprosium.\nAmong many narrow features, we identify two resonances with a width greater\nthan one Gauss. We characterize one of these resonances, in a mixture of\n$^{168}$Er and $^{164}$Dy, in terms of loss rates and elastic cross section,\nand observe a temperature dependence of the on-resonance loss rate suggestive\nof a universal scaling associated with broad resonances. Our observations hold\npromise for the use of such a resonance for tuning the interspecies scattering\nproperties in a dipolar mixture. We further compare the prevalence of narrow\nresonances in an $^{168}$Er-$^{164}$Dy mixture to the single-species case, and\nobserve an increased density of resonances in the mixture.",
        "positive": "Maintaining supersolidity in one and two dimensions: We theoretically investigate supersolidity in three-dimensional dipolar\nBose-Einstein condensates. We focus on the role of trap geometry in determining\nthe dimensionality of the resulting droplet arrays, which range from\none-dimensional to zigzag, through to two-dimensional supersolids in circular\ntraps. Supersolidity is well established in one-dimensional arrays, and may be\njust as favorable in two-dimensional arrays provided that one appropriately\nscales the atom number to the trap volume. We develop a tractable variational\nmodel--which we benchmark against full numerical simulations--and use it to\nstudy droplet crystals and their excitations. We also outline how exotic ring\nand stripe states may be created with experimentally-feasible parameters. Our\nwork paves the way for future studies of two-dimensional dipolar supersolids in\nrealistic settings."
    },
    {
        "anchor": "Light scattering and dissipative dynamics of many fermionic atoms in an\n  optical lattice: We investigate the many-body dissipative dynamics of fermionic atoms in an\noptical lattice in the presence of incoherent light scattering. Deriving and\nsolving a master equation to describe this process microscopically for many\nparticles, we observe contrasting behaviour in terms of the robustness against\nthis type of heating for different many-body states. In particular, we find\nthat the magnetic correlations exhibited by a two-component gas in the Mott\ninsulating phase should be particularly robust against decoherence from light\nscattering, because the decoherence in the lowest band is suppressed by a\nlarger factor than the timescales for effective superexchange interactions that\ndrive coherent dynamics. Furthermore, the derived formalism naturally\ngeneralizes to analogous states with SU(N) symmetry. In contrast, for typical\natomic and laser parameters, two-particle correlation functions describing\nbound dimers for strong attractive interactions exhibit superradiant effects\ndue to the indistinguishability of off-resonant photons scattered by atoms in\ndifferent internal states. This leads to rapid decay of correlations describing\noff-diagonal long-range order for these states. Our predictions should be\ndirectly measurable in ongoing experiments, providing a basis for\ncharacterising and controlling heating processes in quantum simulation with\nfermions.",
        "positive": "Attractive Hubbard Model on a Honeycomb Lattice: We study the attractive fermionic Hubbard model on a honeycomb lattice using\ndeterminantal quantum Monte Carlo simulations. By increasing the interaction\nstrength U (relative to the hopping parameter t) at half-filling and zero\ntemperature, the system undergoes a quantum phase transition at 5.0 < U_c/t <\n5.1 from a semi-metal to a phase displaying simultaneously superfluid behavior\nand density order. Doping away from half-filling, and increasing the\ninteraction strength at finite but low temperature T, the system always appears\nto be a superfluid exhibiting a crossover between a BCS and a molecular regime.\nThese different regimes are analyzed by studying the spectral function. The\nformation of pairs and the emergence of phase coherence throughout the sample\nare studied as U is increased and T is lowered."
    },
    {
        "anchor": "Quantum trajectories for the variational description of closed systems:\n  a case study with Gaussian states: It is proposed to improve the quality of a variational description of a\nclosed quantum system by adding ficticious dissipation that reduces the\nentanglement. The proposal is implemented for a small Bose-Hubbard chain, which\nshows chaotic behavior and associated fast growth of quantum fluctuations. For\nappropriately chosen dissipation, good agreement with the truncated Wigner\napproximation (which is very accurate for the chosen system parameters) is\nfound.",
        "positive": "Collective modes and generation of a new vortex in a trapped Bose gas at\n  finite temperature: The dynamics of Bose-Einstein condensate (BEC) is studied at nonzero\ntemperatures using our variational time-dependent-HFB formalism. We have shown\nthat this approach is an efficient tool to study the expansion and collective\nexcitations of the condensate, the thermal cloud and the anomalous correlation\nfunction at nonzero temperatures. We have found that the condensate and the\nanomalous density have the same breathing oscillations. We have investigated,\non the other hand, the behavior of a single quantized vortex in a harmonically\ntrapped BEC at nonzero temperatures. Generalized expressions for vortex\nexcitations, vortex core size and Kelvin modes have been derived. An important\nand somehow surprising result is that the numerical solution of our equations\npredicts that the vortex core is partially filled by the thermal atoms at\nnonzero temperatures. We have shown that the effect of thermal fluctuations is\nimportant and it may lead to enhancing the size of the vortex core. The\nbehavior of the singly anomalous vortex has also been studied at nonzero\ntemperatures."
    },
    {
        "anchor": "Fermi polaron in a one-dimensional quasi-periodic optical lattice: the\n  simplest many-body localization challenge: We theoretically investigate the behavior of a moving impurity immersed in a\nsea of fermionic atoms that are confined in a quasi-periodic (bichromatic)\noptical lattice, within a standard variational approach. We consider both\nrepulsive and attractive contact interactions for such a simplest many-body\nlocalization problem of Fermi polarons. The variational approach enables us to\naccess relatively large systems and therefore may be used to understand\nmany-body localization in the thermodynamic limit. The energy and wave-function\nof the polaron states are found to be strongly affected by the quasi-random\nlattice potential and their experimental measurements (i.e., via\nradio-frequency spectroscopy or quantum gas microscope) therefore provide a\nsensitive way to underpin the localization transition. We determine a phase\ndiagram by calculating two critical quasi-random disorder strengths, which\ncorrespond to the onset of the localization of the ground-state polaron state\nand the many-body localization of all polaron states, respectively. Our\npredicted phase diagram could be straightforwardly examined in current\ncold-atom experiments.",
        "positive": "Effect of realistic interatomic interactions and two-body correlation on\n  the heat capacity of a trapped BEC: An approximate many-body theory has been used to calculate the heat capacity\nand the condensate fraction of a BEC with effective repulsive interaction. The\neffect of interactions has been analyzed and compared with the non-interacting\ncase. It has been found that the repulsive interaction lowers the critical\ntemperature from the value found in the non-interacting case. The difference\nbetween the critical temperatures increases with the increase in the total\nnumber of atoms in the trap."
    },
    {
        "anchor": "Persistent Current of SU(N) Fermions: We study the persistent current in a system of SU($N$) fermions with\nrepulsive interaction confined in a ring-shaped potential and pierced by an\neffective magnetic flux. By applying a combination of Bethe ansatz and\nnumerical analysis, we demonstrate that, as a combined effect of spin\ncorrelations, interactions and applied flux a specific phenomenon can occur in\nthe system: spinon creation in the ground state. As a consequence, peculiar\nfeatures in the persistent current arise. The elementary flux quantum, which\nfixes the persistent current periodicity, is observed to evolve from a single\nparticle one to an extreme case of fractional flux quantum, in which one\nquantum is shared by all the particles. We show that the persistent current\ndepends on the number of spin components $N$, number of particles and\ninteraction in a specific way that in certain physical regimes has universality\ntraits. At integer filling fractions, the persistent current is suppressed\nabove a threshold of the repulsive interaction by the Mott spectral gap.\nDespite its mesoscopic nature, the current displays a clear finite size scaling\nbehavior. Specific parity effects in the persistent current landscape hold.",
        "positive": "Observation of Cooper Pairs in a Mesoscopic 2D Fermi Gas: Pairing is the fundamental requirement for fermionic superfluidity and\nsuperconductivity. To understand the mechanism behind pair formation is an\nongoing challenge in the study of many strongly correlated fermionic systems.\nCooper pairs are the key ingredient to BCS theory as the microscopic\nexplanation of conventional superconductivity. They form between particles of\nopposite spin and momentum at the Fermi surface of the system. Here, we\ndirectly observe Cooper pairs in a mesoscopic two-dimensional Fermi gas. We\napply an imaging scheme that enables us to extract the full in-situ momentum\ndistribution of a strongly interacting Fermi gas with single particle and spin\nresolution. Our ultracold gas allows us to freely tune between a completely\nnon-interacting, unpaired system and weak attractions, where we find Cooper\npair correlations at the Fermi surface. When increasing the attractive\ninteractions even further, the pairs gradually turn into deeply bound molecules\nbreaking up the Fermi surface. Our mesoscopic system is closely related to the\nphysics of nuclei, superconducting grains or quantum dots. With the precise\ncontrol over interactions, particle number and potential landscape in our\nexperiment, the observables we establish in this work provide a new approach to\nlongstanding questions concerning not only such mesoscopic systems but also\ntheir connection to the macroscopic world."
    },
    {
        "anchor": "Self-trapped quantum balls in binary Bose-Einstein condensates: We study the formation of a stable self-trapped spherical quantum ball in a\nbinary Bose-Einstein condensate (BEC) with two-body inter-species attraction\nand intra-species repulsion employing the beyond-mean-field Lee-Huang-Yang and\nthe three-body interactions. We find that either of these interactions or a\ncombination of these can stabilize the binary BEC quantum ball with very\nsimilar stationary results, and for a complete description of the problem both\nthe terms should be considered. These interactions lead to higher-order\nnonlinearities, e.g. quartic and quintic, respectively, in a nonlinear\ndynamical equation compared to the cubic nonlinearity of the two-body contact\ninteraction in the mean-field Gross-Pitaevskii equation. The higher-order\nnonlinearity makes the energy infinitely large at the center of the binary ball\nand thus avoids its collapse. In addition to the formation of stationary binary\nballs, we also study a collision between two such balls. At large velocities,\nthe collision is found to be elastic, which turns out to be inelastic as the\nvelocity is lowered. We consider the numerical solution of a beyond-mean-field\nmodel for the binary ball as well as a single-mode variational approximation to\nit in this study.",
        "positive": "Long-range transverse Ising model built with dipolar condensates in\n  two-well arrays: Dipolar Bose-Einstein condensates in an array of double-well potentials\nrealize an effective transverse Ising model with peculiar inter-layer\ninteractions, that may result under proper conditions in an anomalous\nfirst-order ferromagnetic-antiferromagnetic phase transition, and nontrivial\nphases due to frustration. The considered setup as well allows the study of\nKibble-Zurek defect formation, whose kink statistics follows that expected from\nthe universality class of the mean-field transverse Ising model in 1D.\nFurthermore, random occupation of each layer of the stack leads to random\neffective Ising interactions and generation of local transverse fields, thus\nallowing the study of Anderson-like localization of imbalance perturbations in\nthe two-well stack under controllable conditions."
    },
    {
        "anchor": "From Narrow to Broad Feshbach Resonances: Condensate Fraction of Cooper\n  Pairs and Preformed Molecules: We extend our previous investigations of fermionic condensation in broad\nFeshbach resonances by using the two-channel model developed for narrow\nFeshbach resonances. We investigate two crossovers: the BCS-BEC crossover by\nchanging the s-wave scattering length and the crossover from a narrow to a\nbroad resonance by changing the atom-molecule coupling. At zero temperature we\nanalyze, as a function of both atom-molecule coupling and s-wave scattering\nlength, the chemical potential, the energy gap, and the condensate fraction of\natoms. In particular, we predict the contribution of Cooper pairs and preformed\nmolecules to the total condensate density along the two crossovers.",
        "positive": "Correlated spontaneous symmetry breaking induced by zero-point\n  fluctuations in a quantum mixture: We propose a form of spontaneous symmetry breaking driven by zero-point\nquantum fluctuations. To be specific, we consider the low-energy dynamics of a\nmixture of two species of spin-$1$ Bose gases. It is demonstrated that the\nquantum fluctuations lift a degeneracy regarding the relative orientations of\nthe spin directors of the two species, and result in correlation or locking\nbetween these macroscopic variables. This locking persists in the presence of\nthe trapping potential and weak magnetic fields, allowing, in principle, an\nexperimental probe of this correlated spontaneous symmetry breaking, as a\nmacroscopic manifestation of zero-point quantum fluctuations."
    },
    {
        "anchor": "Momentum Evolution Numerics of an Impurity in a Quantum Quench: A discussion on the momentum evolution of an impurity interacting via a\nfinite delta potential repulsion with a non-interacting fermionic background\ngas is presented. It has recently been shown that the momentum evolution of\nthis system displays two interesting features, namely a non-zero thermalised\nvalue and a long-lived quantum mechanical oscillation around this plateau named\n\"quantum flutter\" [Mathy, Zvonarev, Demler, Nat. Phys. 2012]. We discuss\nrevivals in the momentum of the impurity, which have been seen before but not\nyet thoroughly investigated. Subsequently it is shown the quantum flutter and\nrevivals are caused by disjoint sets of eigenstate transitions, and this fact\nis used to interpret some of their aspects. This attribution of momentum\nfeatures to different eigenstate subsets allows quantitative reproduction of\nthese features with much less computational expense than has so far been\npossible. Finally some results on the distribution of the momentum of\neigenstates and their relation to the momentum of the impurity once the system\nhas been thermalised are presented along with a discussion on the time averaged\ninfinite time value of the momentum and its comparison to different eigenstate\nsubsets.",
        "positive": "A Kapitza Pendulum for Ultracold Atoms: We report on the experimental realization of a Kapitza pendulum for ultracold\natoms. Using time-periodic attractive and repulsive Gaussian potentials, we\ncreate an effective trap for ultracold neutral atoms in a regime where the time\naverage of the potential is equal to zero. We analyze the role of experimental\nimperfections, the stability of the trapped atomic cloud, and the magnitude of\nthe effective potential. We find good agreement with the high-frequency\nexpansion of the underlying system dynamics. Our experimental approach opens up\nnew possibilities to study Floquet systems of neutral atoms."
    },
    {
        "anchor": "Nonperturbative renormalization group treatment of amplitude\n  fluctuations for $|\\varphi|^4$ topological phase transitions: The study of the Berezinskii-Kosterlitz-Thouless transition in\ntwo-dimensional $|\\varphi|^4$ models can be performed in several\nrepresentations, and the amplitude-phase (AP) Madelung parametrization is a\nnatural way to study the contribution of density fluctuations to nonuniversal\nquantities. We introduce a functional renormalization group scheme in AP\nrepresentation where amplitude fluctuations are integrated first to yield an\neffective sine-Gordon model with renormalized superfluid stiffness. By a\nmapping between the lattice XY and continuum $|\\varphi|^4$ models, our method\napplies to both on equal footing. Our approach correctly reproduces the\nexistence of a line of fixed points and of universal thermodynamics and it\nallows to estimate universal and nonuniversal quantities of the two models,\nfinding good agreement with available Monte Carlo results. The presented\napproach is flexible enough to treat parameter ranges of experimental\nrelevance.",
        "positive": "Spin-textures of the Bose-Einstein condensates with three kinds of\n  spin-1 atoms: We have performed a quantum mechanic calculation (including solving the\ncoupled Gross-Pitaevskii equations to obtain the spatial wave functions, and\ndiagonalizing the spin-dependent Hamiltonian in the spin-space to obtain the\ntotal spin state) together with an analytical analysis based on a classical\nmodel. Then, according to the relative orientations of the spins $S_A$, $S_B$\nand $S_C$ of the three species, the spin-textures of the ground state can be\nclassified into two types. In Type-I the three spins are either parallel or\nanti-parallel to each others, while in Type-II they point to different\ndirections but remain to be coplanar. Moreover, according to the magnitudes of\n$S_A$, $S_B$ and $S_C$ the spin-textures can be further classified into four\nkinds, namely, $p$+$p$+$p$ (all atoms of each species are in singlet-pairs),\none species in $f$ (fully polarized) and two species in $q$ (a mixture of\npolarized atoms and singlet-pairs), two in $f$ and one in $q$, and $f$+$f$+$f$.\nOther combinations are not allowed. The scopes of the parameters that supports\na specific spin-texture have been specified. A number of\nspin-texture-transitions have been found. For Type-I, the critical values at\nwhich a transition takes place are given by simple analytical formulae,\ntherefore these values can be predicted."
    },
    {
        "anchor": "Can the dipolar interaction suppress dipolar relaxation?: Magnetic atoms in a thin layer have repulsive interactions when their\nmagnetic moments are aligned perpendicular to the layer. We show experimentally\nand theoretically how this can suppress dipolar relaxation, the dominant loss\nprocess in spin mixtures of highly magnetic atoms. Using dysprosium, we observe\nan order of magnitude extension of the lifetime, and another factor of ten is\nwithin reach based on the models which we have validated with our experimental\nstudy. The loss suppression opens up many new possibilities for quantum\nsimulations with spin mixtures of highly magnetic atoms.",
        "positive": "Spectrum and quench-induced dynamics of spin-orbit coupled quantum\n  droplets: We investigate the ground state and dynamics of one-dimensional spin-orbit\ncoupled (SOC) quantum droplets within the extended Gross-Pitaevskii approach.\nAs the SOC wavenumber increases, stripe droplet patterns emerge, with a\nflat-top background, for larger particle numbers. The surface energy decays\nfollowing a power-law with respect to the interactions. At small SOC\nwavenumbers, a transition from Gaussian to flat-top droplets occurs for either\na larger number of atoms or reduced intercomponent attraction. The excitation\nspectrum shows that droplets for relatively small SOC wavenumbers are stable,\notherwise stripe droplets feature instabilities as a function of the particle\nnumber or the interactions. We also witness rich droplet dynamical features\nusing velocity imprinting and abrupt changes in the intercomponent interaction\nor the SOC parameters. Characteristic responses include breathing oscillations,\nexpansion, symmetric and asymmetric droplet fragmentation, admixtures of single\nand stripe droplet branches, and erratic spatial distributions suggesting the\ntriggering of relevant instabilities. Our results reveal the controlled\ndynamical generation and stability properties of stripe droplets that should be\ndetectable in current cold-atom experiments."
    },
    {
        "anchor": "Fortran and C programs for the time-dependent dipolar Gross-Pitaevskii\n  equation in an anisotropic trap: Many of the static and dynamic properties of an atomic Bose-Einstein\ncondensate (BEC) are usually studied by solving the mean-field Gross-Pitaevskii\n(GP) equation, which is a nonlinear partial differential equation for\nshort-range atomic interaction. More recently, BEC of atoms with long-range\ndipolar atomic interaction are used in theoretical and experimental studies.\nFor dipolar atomic interaction, the GP equation is a partial\nintegro-differential equation, requiring complex algorithm for its numerical\nsolution. Here we present numerical algorithms for both stationary and\nnon-stationary solutions of the full three-dimensional (3D) GP equation for a\ndipolar BEC, including the contact interaction. We also consider the simplified\none- (1D) and two-dimensional (2D) GP equations satisfied by cigar- and\ndisk-shaped dipolar BECs. We employ the split-step Crank-Nicolson method with\nreal- and imaginary-time propagations, respectively, for the numerical solution\nof the GP equation for dynamic and static properties of a dipolar BEC. The\natoms are considered to be polarized along the z axis and we consider ten\ndifferent cases, e.g., stationary and non-stationary solutions of the GP\nequation for a dipolar BEC in 1D (along x and z axes), 2D (in x-y and x-z\nplanes), and 3D, and we provide working codes in Fortran 90/95 and C for these\nten cases (twenty programs in all). We present numerical results for energy,\nchemical potential, root-mean-square sizes and density of the dipolar BECs and,\nwhere available, compare them with results of other authors and of variational\nand Thomas-Fermi approximations.",
        "positive": "Rapidity distribution within the defocusing non-linear Schr\u00f6dinger\n  equation model: We consider the classical field integrable system whose evolution equation is\nthe nonlinear Schr\\\"odinger equation with defocusing non-linearities, which is\nthe classical limit of the quantum Lieb-Liniger model. We propose a simple\nderivation of the relation between two sets of conserved quantities: on the one\nhand the trace of the monodromy matrix, parameterized by the spectral parameter\nand introduced in the inverse-scattering framework, and on the other hand the\nrapidity distribution, a concept imported from the Lieb-Liniger model. To do so\nwe use the definition of the rapidity distribution as the asymptotic momentum\ndistribution after an expansion. More precisely we use thought experiments\nimplementing an expansion and we present two different ways to derive our\nresult, based on different thought experiments which lead to different\ncalculations."
    },
    {
        "anchor": "Novel Polaron State for Single Impurity in a Bosonic Mott Insulator: We show that a single impurity embedded in a cold atom bosonic Mott insulator\nleads to a novel polaron that exhibits correlated motion with an effective mass\nand a linear size that nearly diverge at critical value of the on-site\nimpurity-boson interaction strength. Cold atom technology can tune the\npolaron's properties and break up the composite particle into a deconfined\nimpurity-hole and boson particle state at finite, controllable polaron\nmomentum.",
        "positive": "Minimally destructive, Doppler measurement of a quantized, superfluid\n  flow: The Doppler effect, the shift in the frequency of sound due to motion, is\npresent in both classical gases and quantum superfluids. Here, we perform an\nin-situ, minimally destructive measurement, of the persistent current in a\nring-shaped, superfluid Bose-Einstein condensate using the Doppler effect.\nPhonon modes generated in this condensate have their frequencies Doppler\nshifted by a persistent current. This frequency shift will cause a\nstanding-wave phonon mode to be \"dragged\" along with the persistent current. By\nmeasuring this precession, one can extract the background flow velocity. This\ntechnique will find utility in experiments where the winding number is\nimportant, such as in emerging `atomtronic' devices."
    },
    {
        "anchor": "Quantum geometry in superfluidity and superconductivity: We review the theoretical description of the role of quantum geometry in\nsuperfluidity and superconductivity of multiband systems, with focus on flat\nbands where quantum geometry is wholly responsible for supercurrents. This\nreview differs from previous ones in that it is based on the most recent\nunderstanding of the theory: the dependence of the self-consistent order\nparameter on the supercurrent is properly taken into account, and the\nsuperfluid weight in a flat band becomes proportional to the minimal quantum\nmetric. We provide a recap of basic quantum geometric quantities and the\nconcept of superfluid density. The geometric contribution of superconductivity\nis introduced via considering the two-body problem. The superfluid weight of a\nmultiband system is derived within mean-field theory, leading to a topological\nbound of flat band superconductivity. The physical interpretation of the flat\nband supercurrent in terms of Wannier function overlaps is discussed.",
        "positive": "Mixtures of Bose Gases Confined in a Ring Potential: The rotational properties of a mixture of two distinguishable Bose gases that\nare confined in a ring potential provide novel physical effects that we\ndemonstrate in this study. Persistent currents are shown to be stable for a\nrange of the population imbalance between the two components at low angular\nmomentum. At higher values of the angular momentum, even small admixtures of a\nsecond species of atoms make the persistent currents highly fragile."
    },
    {
        "anchor": "Suppression of Spontaneous Defect Formation in Inhomogeneous Bose Gases: In phase transition dynamics involving symmetry breaking, topological defects\ncan be spontaneously created but it is suppressed in a spatially inhomogeneous\nsystem due to the spreading of the ordered phase information. We demonstrate\nthe defect suppression effect in a trapped atomic Bose gas which is quenched\ninto a superfluid phase. The spatial distribution of created defects is\nmeasured for various quench times and it is shown that for slower quenches, the\nspontaneous defect production is relatively more suppressed in the sample's\nouter region with higher atomic density gradient. The power-law scaling of the\nlocal defect density with the quench time is enhanced in the outer region,\nwhich is consistent with the Kibble-Zurek mechanism including the causality\neffect due to the spatial inhomogeneity of the system. This work opens an\navenue in the study of nonequilibrium phase transition dynamics using the\ndefect position information.",
        "positive": "Density profile of a semi-infinite one-dimensional Bose gas and bound\n  states of the impurity: We study the effect of the boundary on a system of weakly interacting bosons\nin one dimension. It strongly influences the boson density which is completely\nsuppressed at the boundary position. Away from it, the density is depleted over\nthe distances on the order of the healing length at the mean-field level.\nQuantum fluctuations modify the density profile considerably. The local density\napproaches the average one as an inverse square of the distance from the\nboundary. We calculate an analytic expression for the density profile at\narbitrary separations from the boundary. We then consider the problem of\nlocalization of a foreign quantum particle (impurity) in the potential created\nby the inhomogeneous boson density. At the mean-field level, we find exact\nresults for the energy spectrum of the bound states, the corresponding wave\nfunctions, and the condition for interaction-induced localization. The quantum\ncontribution to the boson density gives rise to small corrections of the bound\nstate energy levels. However, it is fundamentally important for the existence\nof a long-range Casimir-like interaction between the impurity and the boundary."
    },
    {
        "anchor": "Dimensional crossover in non-relativistic effective field theory: Isotropic scattering in various spatial dimensions is considered for\narbitrary finite-range potentials using non-relativistic effective field\ntheory. With periodic boundary conditions, compactifications from a box to a\nplane and to a wire, and from a plane to a wire, are considered by matching\nS-matrix elements. The problem is greatly simplified by regulating the\nultraviolet divergences using dimensional regularization with minimal\nsubtraction. General relations among (all) effective-range parameters in the\nvarious dimensions are derived, and the dependence of bound states on changing\ndimensionality are considered. Generally, it is found that compactification\nbinds the two-body system, even if the uncompactified system is unbound. For\ninstance, compactification from a box to a plane gives rise to a bound state\nwith binding momentum given by $\\ln \\left({\\scriptstyle\n\\frac{1}{2}}\\left(3+\\sqrt{5} \\right) \\right)$ in units of the inverse\ncompactification length. This binding momentum is universal in the sense that\nit does not depend on the two-body interaction in the box. When the two-body\nsystem in the box is at unitarity, the S-matrices of the compactified two-body\nsystem on the plane and on the wire are given exactly as universal functions of\nthe compactification length",
        "positive": "Damping of the Higgs and Nambu-Goldstone modes of superfluid Bose gases\n  at finite temperatures: We study collective modes of superfluid Bose gases in optical lattices at\ncommensurate fillings. We focus on the vicinity of the quantum phase transition\nto the Mott insulator, where there exists the Higgs amplitude mode in addition\nto the Nambu-Goldstone phase mode associated with the spontaneous U(1) symmetry\nbreaking. We analyze finite-temperature effects on the damping of the\ncollective modes by using an effective spin-1 model and the field theoretical\nmethods based on the finite-temperature Green's function. We calculate the\ndamping rates up to 1-loop order and evaluate them analytically and\nnumerically. We show that the damping rate of the Higgs mode increases with\nincreasing the temperature but it remains underdamped up to a typical\ntemperature achieved in experiments. Moreover, we find that the Nambu-Goldstone\nmode attenuates via a Landau damping process resulting from interactions with\nthe Higgs mode and it can be overdamped at the typical temperature in a certain\nparameter region."
    },
    {
        "anchor": "Superfluid Phases of Dipolar Fermions in Harmonically Trapped Optical\n  Lattices: We describe the emergence of superfluid phases of ultracold dipolar fermions\nin optical lattices for two-dimensional systems. Considering the many-body\nscreening of dipolar interactions at intermediate and larger filling factors,\nwe show that several superfluid phases with distinct pairing symmetries\nnaturally arise in the singlet channel: local s-wave $(sl)$, extended s-wave\n$(se)$, d-wave $(d)$ or time-reversal-symmetry breaking $(sl + se \\pm\nid)$-wave. We obtain the temperature versus filling factor phase diagram and\nshow that d-wave pairing is favored near half-filling, that $(sl + se)$-wave is\nfavored near zero or full filling, and that time-reversal-breaking $(sl + se\n\\pm id)$-wave is favored in between. The inclusion of a harmonic trap reveals\nthat a sequence of phases can coexist in the cloud depending on the filling\nfactor at the center of the trap. Most notably in the spatial region where the\n$(sl + se \\pm id)$-wave superfluid occurs, spontaneous currents are generated,\nand may be detected using velocity sensitive Bragg spectroscopy.",
        "positive": "Vortex Nucleation in a Dissipative Variant of the Nonlinear\n  Schr\u00f6dinger Equation under Rotation: In the present work, we motivate and explore the dynamics of a dissipative\nvariant of the nonlinear Schr{\\\"o}dinger equation under the impact of external\nrotation. As in the well established Hamiltonian case, the rotation gives rise\nto the formation of vortices. We show, however, that the most unstable mode\nleading to this instability scales with an appropriate power of the chemical\npotential $\\mu$ of the system, increasing proportionally to $\\mu^{2/3}$. The\nprecise form of the relevant formula, obtained through our asymptotic analysis,\nprovides the most unstable mode as a function of the atomic density and the\ntrap strength. We show how these unstable modes typically nucleate a large\nnumber of vortices in the periphery of the atomic cloud. However, through a\npattern selection mechanism, prompted by symmetry-breaking, only few isolated\nvortices are pulled in sequentially from the periphery towards the bulk of the\ncloud resulting in highly symmetric stable vortex configurations with far fewer\nvortices than the original unstable mode. These results may be of relevance to\nthe experimentally tractable realm of finite temperature atomic condensates."
    },
    {
        "anchor": "Strongly anomalous non-thermal fixed point in a quenched two-dimensional\n  Bose gas: Universal scaling behavior in the relaxation dynamics of an isolated\ntwo-dimensional Bose gas is studied by means of semi-classical stochastic\nsimulations of the Gross-Pitaevskii model. The system is quenched far out of\nequilibrium by imprinting vortex defects into an otherwise phase-coherent\ncondensate. A strongly anomalous non-thermal fixed point is identified,\nassociated with a slowed decay of the defects in the case that the dissipative\ncoupling to the thermal background noise is suppressed. At this fixed point, a\nlarge anomalous exponent $\\eta \\simeq -3$ and, related to this, a large\ndynamical exponent $z \\simeq 5$ are identified. The corresponding power-law\ndecay is found to be consistent with three-vortex-collision induced loss. The\narticle discusses these aspects of non-thermal fixed points in the context of\nphase-ordering kinetics and coarsening dynamics, thus relating phenomenological\nand analytical approaches to classifying far-from-equilibrium scaling dynamics\nwith each other. In particular, a close connection between the anomalous\nscaling exponent $\\eta$, introduced in a quantum-field theoretic approach, and\nconservation-law induced scaling in classical phase-ordering kinetics is\nrevealed. Moreover, the relation to superfluid turbulence as well as to driven\nstationary systems is discussed.",
        "positive": "Many-body quantum chaos in stroboscopically-driven cold atoms: In quantum chaotic systems, the spectral form factor (SFF), defined as the\nFourier transform of the two-level spectral correlation function, is known to\nfollow random matrix theory (RMT), namely a 'ramp' followed by a 'plateau' in\nsufficiently late times. Recently, a generic early-time deviation from the RMT\nbehavior, which we call the 'bump', was shown to exist in random quantum\ncircuits and spin chains as toy models for many-body quantum chaotic systems.\nHere we demonstrate the existence of the 'bump-ramp-plateau' behavior in the\nSFF for a number of paradigmatic and stroboscopically-driven 1D cold atom\nmodels: (i) Bose-Hubbard model, (ii) spin$-1/2$ Bose-Hubbard model, and (iii)\nnonintegrable spin-$1$ condensate with contact or dipolar interactions. We find\nthat the scaling of the many-body Thouless time $t_{\\textrm{Th}}$ -- the onset\nof RMT -- , and the bump amplitude are more sensitive to variations in atom\nnumber than the lattice size regardless of the hyperfine structure, the\nsymmetry classes, or the choice of driving protocol. Moreover,\n$t_{\\textrm{Th}}$ scaling and the increase of the bump amplitude in atom number\nare significantly slower in spinor gases than interacting bosons in 1D optical\nlattices, demonstrating the role of locality. We obtain universal scaling\nfunctions of SFF which suggest power-law behavior for the bump regime in\nquantum chaotic cold-atom systems, and propose an interference measurement\nprotocol."
    },
    {
        "anchor": "Multi-band and nonlinear hopping corrections to the 3D Bose-Fermi\n  Hubbard model: Recent experiments revealed the importance of higher-band effects for the\nMott insulator (MI) -- superfluid transition (SF) of ultracold bosonic atoms or\nmixtures of bosons and fermions in deep optical lattices [Best \\emph{et al.},\nPRL \\textbf{102}, 030408 (2009); Will \\emph{et al.}, Nature \\textbf{465}, 197\n(2010)]. In the present work, we derive an effective lowest-band Hamiltonian in\n3D that generalizes the standard Bose-Fermi Hubbard model taking these effects\nas well as nonlinear corrections of the tunneling amplitudes mediated by\ninterspecies interactions into account. It is shown that a correct description\nof the lattice states in terms of the bare-lattice Wannier functions rather\nthan approximations such as harmonic oscillator states is essential. In\ncontrast to self-consistent approaches based on effective Wannier functions our\napproach provides a quantitative explanation of the observed reduction of the\nsuperfluid phase for repulsive interspecies interactions.",
        "positive": "Two and Three-body Contacts in the Unitary Bose Gas: In many-body systems governed by pairwise contact interactions, a wide range\nof observables is linked by a single parameter, the two-body contact, which\nquantifies two-particle correlations. This profound insight has transformed our\nunderstanding of strongly interacting Fermi gases. Here, using Ramsey\ninterferometry, we study coherent evolution of the resonantly interacting Bose\ngas, and show that it cannot be explained by only pairwise correlations. Our\nexperiments reveal the crucial role of three-body correlations arising from\nEfimov physics, and provide a direct measurement of the associated three-body\ncontact."
    },
    {
        "anchor": "Dynamics of Uniform Quantum Gases, II: Magnetic Susceptibility: A general expression for temperature-dependent magnetic susceptibility of\nquantum gases composed of particles possessing both charge and spin degrees of\nfreedom has been obtained within the framework of the generalized random-phase\napproximation. The conditions for the existence of dia-, para-, and\nferro-magnetism have been analyzed in terms of a parameter involving\nsingle-particle charge and spin. The zero-temperature limit retrieves the\nexpressions for the Landau and the Pauli susceptibilities for an electron gas.\nIt is found for a Bose gas that on decreasing the temperature, it passes either\nthrough a diamagnetic incomplete Meissner-effect regime or through a\nparamagnetic-ferromagnetic large magnetization fluctuation regime before going\nto the Meissner phase at BEC critical temperature.",
        "positive": "Control of Spin-Exchange Interaction between Alkali-Earth Atoms via\n  Confinement-Induced Resonances in a Quasi 1+0 Dimensional System: A nuclear-spin exchange interaction exists between two ultracold fermionic\nalkali-earth (like) atoms in the electronic $^{1}{\\rm S}_{0}$ state ($g$-state)\nand $^{3}{\\rm P}_{0}$ state ($e$-state), and is an essential ingredient for the\nquantum simulation of Kondo effect. We study the control of this spin-exchange\ninteraction for two atoms simultaneously confined in a quasi-one-dimensional\n(quasi-1D) tube, where the $g$-atom is freely moving in the axial direction\nwhile the $e$-atom is further localized by an additional axial trap and behaves\nas a quasi-zero-dimensional (quasi-0D) impurity. In this system, the two atoms\nexperience effective-1D spin-exchange interactions in both even and odd partial\nwave channels, whose intensities can be controlled by the characteristic\nlengths of the confinements via the confinement-induced-resonances (CIRs). In\ncurrent work, we go beyond that pure-1D approximation. We model the transverse\nand axial confinements by harmonic traps with finite characteristic lengths\n$a_\\perp$ and $a_z$, respectively, and exactly solve the \"quasi-1D + quasi-0D\"\nscattering problem between these two atoms. Using the solutions we derive the\neffective 1D spin-exchange interaction and investigate the locations and widths\nof the even/odd wave CIRs for our system.\n  It is found that when the ratio $a_z/a_\\perp$ is larger, the CIRs can be\ninduced by weaker confinements, which are easier to be realized experimentally.\n  The comparison between our results and the recent experiment shows that the\ntwo experimentally observed resonance branches of the spin-exchange effect are\ndue to an even-wave CIR and an odd-wave CIR, respectively. Our results are\nadvantageous for the control and description of either the effective\nspin-exchange interaction or other types of interactions between ultracold\natoms in quasi 1+0 dimensional systems."
    },
    {
        "anchor": "Emergent flux in a one-dimensional Bose-Fermi mixture: We find a novel chiral superfluid (CSF) phase in a chain of Bose-Fermi\nmixture, which has been validated using two unbiased numerical methods, density\nmatrix renormalization group and Grassmann multi-scale entanglement\nrenormalization ansatz. The system hosts the interplay between two types of\nfermions: bare spinless fermions and composite fermions, the latter consisting\nof a fermion and a boson. In the CSF phase, bosons condensate at non-zero\nmomentum $\\pm 2\\pi /L$ with chain length $L$. In essence, the local superfluid\norder parameter continuously rotates along the chain, indicating that the CSF\nphase spontaneously breaks time-reversal symmetry. This symmetry breaking gives\nrise to an emergent flux in the background, effectively optimizing the kinetic\nenergy of the composite fermions within the system. We provide a physical\nunderstanding at the mean-field level. Furthermore, we demonstrate that the 1D\nCSF phase can emerge in a more widely applicable extended Hubbard model. The\npotential realization of this phase in cold-atom experiments has also been\nexplored.",
        "positive": "Measuring the branching ratios from the $y^8 {\\rm P}_{9/2}$ state to\n  metastable states in europium: We measure the branching ratios from the $y^8{\\rm P}_{9/2}$ excited state to\nsix metastable states of europium through fluorescence spectroscopy of an\natomic beam. The sum of the six branching ratios is estimated to be\n$1.05(2)\\times 10^{-3}$. This research provides us with insightful information\nto determine the feasibility of using the $a^8{\\rm S}_{7/2} - y^8{\\rm P}_{9/2}$\ntransition in order to implement the Zeeman slowing for europium atoms in the\nground state. Based on this result, we also propose a scheme for Zeeman slowing\nand magneto-optical trapping, using a specific metastable state which has a\ncyclic transition."
    },
    {
        "anchor": "Supersolid and solitonic phases in one-dimensional Extended Bose-Hubbard\n  model: We report our findings on quantum phase transitions in cold bosonic atoms in\na one dimensional optical lattice using the finite size density matrix\nrenormalization group method in the framework of the extended Bose-Hubbard\nmodel. We consider wide ranges of values for the filling factors and the\nnearest neighbor interactions. At commensurate fillings, we obtain two\ndifferent types of charge density wave phases and a Mott insulator phase.\nHowever, departure from commensurate fillings yield the exotic supersolid phase\nwhere both the crystalline and the superfluid orders coexist. In addition, we\nobtain signatures for solitary waves and also superfluidity.",
        "positive": "Simulation of frustrated classical XY models with ultra-cold atoms in 3D\n  triangular optical lattices: Miscellaneous magnetic systems are being recently intensively investigated\nbecause of their potential applications in modern technologies. Nonetheless, a\nmany body dynamical description of complex magnetic systems may be cumbersome,\nespecially when the system exhibits a geometrical frustration. This paper deals\nwith simulations of the classical XY model on a three dimensional triangular\nlattice with anisotropic couplings, including an analysis of the phase diagram\nand a Bogoliubov description of the dynamical stability of mean-field\nstationary solutions. We also discuss the possibilities of the realization of\nBose-Hubbard models with complex tunneling amplitudes in shaken optical\nlattices without breaking the generalized time-reversal symmetry and the\nopposite, i.e. real tunneling amplitudes in systems with the time-reversal\nsymmetry broken."
    },
    {
        "anchor": "Quantum critical transport in the unitary Fermi gas: The thermodynamic and transport properties of the unitary Fermi gas at finite\ntemperature T are governed by a quantum critical point at T=0 and zero density.\nWe compute the universal shear viscosity to entropy ratio \\eta/s in the\nhigh-temperature quantum critical regime T>>|\\mu| and find that this strongly\ncoupled quantum fluid comes close to perfect fluidity \\eta/s=\\hbar/(4\\pi k_B).\nUsing a controlled large-N expansion we show that already at the first\nnon-trivial order the equation of state and the Tan contact density C agree\nwell with the most recent experimental measurements and theoretical\nLuttinger-Ward and Bold Diagrammatic Monte Carlo calculations.",
        "positive": "Collective modes and the speed of sound in the\n  Fulde-Ferrell-Larkin-Ovchinnikov state: We consider the density response of a spin-imbalanced ultracold Fermi gas in\nan optical lattice in the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. We\ncalculate the collective mode spectrum of the system in the generalised random\nphase approximation and find that though the collective modes are damped even\nat zero tempererature, the damping is weak enough to have well-defined\ncollective modes. We calculate the speed of sound in the gas and show that it\nis anisotropic due to the anisotropy of the FFLO pairing, which implies an\nexperimental signature for the FFLO state."
    },
    {
        "anchor": "Anderson localization of Bogoliubov excitations on quasi-1D strips: Anderson localization of Bogoliubov excitations is studied for disordered\nlattice Bose gases in planar quasi-one-dimensional geometries. The inverse\nlocalization length is computed as function of energy by a numerical\ntransfer-matrix scheme, for strips of different widths. These results are\ndescribed accurately by analytical formulas based on a weak-disorder expansion\nof backscattering mean free paths.",
        "positive": "Fast scrambling without appealing to holographic duality: Motivated by the question of whether all fast scramblers are holographically\ndual to quantum gravity, we study the dynamics of a non-integrable spin chain\nmodel composed of two ingredients - a nearest neighbor Ising coupling, and an\ninfinite range $XX$ interaction. Unlike other fast scrambling many-body\nsystems, this model is not known to be dual to a black hole. We quantify the\nspreading of quantum information using an out-of time-ordered correlator\n(OTOC), and demonstrate that our model exhibits fast scrambling for a wide\nparameter regime. Simulation of its quench dynamics finds that the rapid\ndecline of the OTOC is accompanied by a fast growth of the entanglement\nentropy, as well as a swift change in the magnetization. Finally, potential\nrealizations of our model are proposed in current experimental setups. Our work\nestablishes a promising route to create fast scramblers."
    },
    {
        "anchor": "Manipulation of a Bose-Einstein condensate by a time-averaged orbiting\n  potential using phase jumps of the rotating field: We report on the manipulation of the center-of-mass motion (`sloshing') of a\nBose Einstein condensate in a time-averaged orbiting potential (TOP) trap. We\nstart with a condensate at rest in the center of a static trapping potential.\nWhen suddenly replacing the static trap with a TOP trap centered about the same\nposition, the condensate starts to slosh with an amplitude much larger than the\nTOP micromotion. We show, both theoretically and experimentally, that the\ndirection of sloshing is related to the initial phase of the rotating magnetic\nfield of the TOP. We show further that the sloshing can be quenched by applying\na carefully timed and sized jump in the phase of the rotating field.",
        "positive": "Large-N ground state of the Lieb-Liniger model and Yang-Mills theory on\n  a two-sphere: We derive the large particle number limit of the Bethe equations for the\nground state of the attractive one-dimensional Bose gas (Lieb-Liniger model) on\na ring and solve it for arbitrary coupling. We show that the ground state of\nthis system can be mapped to the large-N saddle point of Euclidean Yang-Mills\ntheory on a two-sphere with a U(N) gauge group, and the phase transition that\ninterpolates between the homogeneous and solitonic regime is dual to the\nDouglas-Kazakov confimenent-deconfinement phase transition."
    },
    {
        "anchor": "Ultracold atoms and the Functional Renormalization Group: We give a self-contained introduction to the physics of ultracold atoms using\nfunctional integral techniques. Based on a consideration of the relevant length\nscales, we derive the universal effective low energy Hamiltonian describing\nultracold alkali atoms. We then introduce the concept of the effective action,\nwhich generalizes the classical action principle to full quantum status and\nprovides an intuitive and versatile tool for practical calculations. This\nframework is applied to weakly interacting degenerate bosons and fermions in\nthe spatial continuum. In particular, we discuss the related BEC and BCS\nquantum condensation mechanisms. We then turn to the BCS-BEC crossover, which\ninterpolates between both phenomena, and which is realized experimentally in\nthe vicinity of a Feshbach resonance. For its description, we introduce the\nFunctional Renormalization Group approach. After a general discussion of the\nmethod in the cold atoms context, we present a detailed and pedagogical\napplication to the crossover problem. This not only provides the physical\nmechanism underlying this phenomenon. More generally, it also reveals how the\nrenormalization group can be used as a tool to capture physics at all scales,\nfrom few-body scattering on microscopic scales, through the finite temperature\nphase diagram governed by many-body length scales, up to critical phenomena\ndictating long distance physics at the phase transition. The presentation aims\nto equip students at the beginning PhD level with knowledge on key physical\nphenomena and flexible tools for their description, and should enable to embark\nupon practical calculations in this field.",
        "positive": "An Aharonov-Bohm interferometer for determining Bloch band topology: The geometric structure of an energy band in a solid is fundamental for a\nwide range of many-body phenomena in condensed matter and is uniquely\ncharacterized by the distribution of Berry curvature over the Brillouin zone.\nIn analogy to an Aharonov-Bohm interferometer that measures the magnetic flux\npenetrating a given area in real space, we realize an atomic interferometer to\nmeasure Berry flux in momentum space. We demonstrate the interferometer for a\ngraphene-type hexagonal lattice, where it has allowed us to directly detect the\nsingular $\\pi$ Berry flux localized at each Dirac point. We show that the\ninterferometer enables one to determine the distribution of Berry curvature\nwith high momentum resolution. Our work forms the basis for a general framework\nto fully characterize topological band structures and can also facilitate\nholonomic quantum computing through controlled exploitation of the geometry of\nHilbert space."
    },
    {
        "anchor": "Non-Analytic Crossover Behavior of SU($\\mathcal{N}_c$) Fermi Liquid: We consider the thermodynamic potential of a dilute Fermi gas with a contact\ninteraction, at both finite temperature $T$ and non-zero effective magnetic\nfields $\\mathbf{H}$, and derive the equation of state analytically using second\norder perturbation theory. Special attention is paid to the non-analytic\ndependence of $\\Omega$ on temperature $T$ and (effective) magnetic field\n$\\mathbf{H}$, which exhibits a crossover behavior as the ratio of the two is\ncontinuously varied. This non-analyticity is due to the particle-hole pair\nexcitation being always gapless and long-ranged. The non-analytic crossover\nfound in this paper can therefore be understood as an analog of the\nGinzberg-Landau critical scaling, albeit only at the sub-leading order. We\nextend our results to an $\\mathcal{N}_c$- component Fermi gas with an\n$\\mathrm{SU}(\\mathcal{N}_c)$-symmetric interaction, and point out possible\nenhancement of the crossover behavior by a large $\\mathcal{N}_c$.",
        "positive": "Trapped Bose-Einstein condensates with nonlinear coherent modes: The review presents the methods of generation of nonlinear coherent\nexcitations in strongly nonequilibrium Bose-condensed systems of trapped atoms\nand their properties. Non-ground-state Bose-Einstein condensates are\nrepresented by nonlinear coherent modes. The principal difference of nonlinear\ncoherent modes from linear collective excitations is emphasized. Methods of\ngenerating nonlinear modes and the properties of the latter are described.\nMatter-wave interferometry with coherent modes is discussed, including such\neffects as interference patterns, internal Josephson current, Rabi\noscillations, Ramsey fringes, harmonic generation, and parametric conversion.\nDynamic transition between mode-locked and mode-unlocked regimes is shown to be\nanalogous to a phase transition. Atomic squeezing and entanglement in a lattice\nof condensed atomic clouds with coherent modes are considered. Nonequilibrium\nstates of trapped Bose-condensed systems, starting from weakly nonequilibrium\nstate, vortex state, vortex turbulence, droplet or grain turbulence, and wave\nturbulence, are classified by means of effective Fresnel and Mach numbers. The\ninverse Kibble-Zurek scenario is described. A method for the formation of\ndirected beams from atom lasers is reported."
    },
    {
        "anchor": "Effective Spin-2 Quasi-particles at Linear Dispersive Five-fold\n  Degenerate Points with Tunable Topological Chern Numbers: In this work, which is based on spin-2 vectors and traceless spin-2 tensors,\nan effective Hamiltonian is constructed with a linearly dispersive five-fold\ndegenerate point with spin-2 vector-momentum couplings. For the model without\nspin-2 vector-tensor coupling, the topological Chern numbers of five bands are\ncalculated as 4, 2, 0, -2, -4. After including spin-2 vector-tensor coupling,\nseparate topological Chern numbers are obtained for different couplings. A\ncubic lattice of atoms with five internal states is designed to realize two\nfive-fold degenerate points. The Chern numbers of the bands can be changed by\ntuning the coupling coefficient. In this work we propose a theoretical design\nto obtain spin-2 quasi-particles.",
        "positive": "Non-Hermitian skin effect in one-dimensional interacting Bose gas: Non-Hermitian skin effect (NHSE) is a unique feature studied extensively in\nnon-interacting non-Hermitian systems. In this work, we extend the NHSE\noriginally discovered in non-interacting systems to interacting many-body\nsystems by investigating an exactly solvable non-Hermitian model, i.e., the\nprototypical Lieb-Liniger Bose gas with imaginary vector potential. We show\nthat this non-Hermitian many-body model can also be exactly solved through\nBethe ansatz. By solving the Bethe ansatz equations accurately, the explicit\neigenfunction is obtained, and the model's density profiles and momentum\ndistributions are calculated to characterize the NHSE quantitatively. We find\nthat the NHSE is gradually suppressed on the repulsive side but does not vanish\nas the repulsive interaction strength increases. On the attractive side, the\nNSHE for bound-state solutions is enhanced as interaction strength grows. In\ncontrast, for the scattering state the NHSE shows a non-monotonic behavior in\nthe attractive side. Our work provides the first example of the NHSE in exactly\nsolvable many-body systems, and we envision that it can be extended to other\nnon-Hermitian many-body systems, especially to integrable models."
    },
    {
        "anchor": "Machine learning classification of two-dimensional vortex configurations: We consider computer generated configurations of quantised vortices in planar\nsuperfluid Bose-Einstein condensates. We show that unsupervised machine\nlearning technology can successfully be used for classifying such vortex\nconfigurations to identify prominent vortex phases of matter. The machine\nlearning approach could thus be applied for automatically classifying large\ndata sets of vortex configurations obtainable by experiments on two-dimensional\nquantum turbulence.",
        "positive": "Stability of persistent currents in open-dissipative quantum fluids: The phenomenon of stable persistent currents is central to the studies of\nsuperfluidity in a range of physical systems. While all of the previous\ntheoretical studies of superfluid flows in annular geometries concentrated on\nconservative systems, here we extend the stability analysis of persistent\ncurrents to open-dissipative exciton-polariton superfluids. By considering an\nexciton-polariton condensate in an optically-induced annular trap, we determine\nstability conditions for an initially imposed flow with a non-zero orbital\nangular momentum. We show, theoretically and numerically, that the system can\nsustain metastable persistent currents in a large parameter region, and\ndescribe scenarios of the supercurrent decay due to the dynamical instability."
    },
    {
        "anchor": "Extension of the Generalized Hydrodynamics to the Dimensional Crossover\n  Regime: In an effort to address integrability breaking in cold gas experiments, we\nextend the integrable hydrodynamics of the 1d Lieb-Liniger model with two\nadditional components representing the population of atoms in the first and\nsecond transverse excited states, thus enabling a description of quasi-1d\ncondensates. Collisions between different components are accounted for through\nthe inclusion of a Boltzmann-type collision integral in the hydrodynamic\nequation. Contrary to standard generalized hydrodynamics, our extended model\ncaptures thermalization of the condensate at a rate consistent with\nexperimental observations from a quantum Newton's cradle setup.",
        "positive": "FFLO- and N\u00e9el States in finite-size Systems: The general structure of the $s$-wave fermionic superfluid pairing order\nparameter is discussed for systems in thermal equilibrium. We demonstrate that\nfor finite-size systems with fixed boundary conditions the pairing-amplitude\nmay always be chosen as a {\\it real} function in space, in contrast to systems\nunderlying periodic boundary conditions, with drastical consequences for\nseveral postulated Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states. Using a\nsimple mapping, we also investigate the consequences of our results for\nantiferromagnetic equilibrium states in a repulsive Hubbard model."
    },
    {
        "anchor": "Resonant Matter Wave Amplification in Mean Field Theory: We develop a Green's function based mean-field theory for coherent mixing of\nmatter- and light-waves. To demonstrate the utility of this approach, we\nanalyse a co-propagating Raman matter-wave amplifier. We find that for a given\nlaser intensity, a significantly faster amplification process can be achieved\nemploying resonant rather than off-resonance driving. The ratio of the\nmatter-wave gain to atom loss-rate due to spontaneous emission is given by the\noptical depth of the sample, and is the same both on- and off-resonance.\nFurthermore, we show that for short-times, the single-mode approximation for\nthe matter-waves gives exact agreement with the full spatial dynamics. For long\ntimes, the off-resonant case shows suppressed amplification due to a spatially\ninhomogenous AC Stark shift associated with laser depletion. This suppression\nis absent on-resonance, where the AC Stark shift is absent.",
        "positive": "Quantum hydrodynamics for supersolid crystals and quasicrystals: Supersolids are theoretically predicted quantum states that break the\ncontinuous rotational and translational symmetries of liquids while preserving\nsuperfluid transport properties. Over the last decade, much progress has been\nmade in understanding and characterizing supersolid phases through numerical\nsimulations for specific interaction potentials. The formulation of an\nanalytically tractable framework for generic interactions still poses\ntheoretical challenges. By going beyond the usually considered quadratic\ntruncations, we derive a systematic higher-order generalization of the\nGross-Pitaevskii mean field model in conceptual similarity with the\nSwift-Hohenberg theory of pattern formation. We demonstrate the tractability of\nthis broadly applicable approach by determining the ground state phase diagram\nand the dispersion relations for the supersolid lattice vibrations in terms of\nthe potential parameters. Our analytical predictions agree well with numerical\nresults from direct hydrodynamic simulations and earlier quantum Monte-Carlo\nstudies. The underlying framework is universal and can be extended to\nanisotropic pair potentials with complex Fourier-space structure."
    },
    {
        "anchor": "Experimental Evidence for Inhomogeneous-Pumping and Energy-Dependent\n  Effects in Photon Bose-Einstein Condensation: Light thermalised at room temperature in an optically pumped, dye-filled\nmicrocavity resembles a model system of non-interacting Bose-Einstein\ncondensation in the presence of dissipation. We have experimentally\ninvestigated some of the steady-state properties of this unusual state of light\nand found features which do not match the available theoretical descriptions.\nWe have seen that the critical pump power for condensation depends on the pump\nbeam geometry, being lower for smaller pump beams. Far below threshold, both\nintracavity photon number and thermalised photon cloud size depend on pump beam\nsize, with optimal coupling when pump beam matches the thermalised cloud size.\nWe also note that the critical pump power for condensation depends on the\ncavity cutoff wavelength and longitudinal mode number, which suggests that\nenergy-dependent thermalisation and loss mechanisms are important.",
        "positive": "Many interacting fermions in a one-dimensional harmonic trap: a\n  quantum-chemical treatment: We employ \\textit{ab initio} methods of quantum chemistry to investigate\nspin-1/2 fermions interacting via a two-body contact potential in a\none-dimensional harmonic trap. The convergence of the total energy with the\nsize of the one-particle basis set is analytically investigated for the\ntwo-body problem and the same form of the convergence formula is numerically\nconfirmed to be valid for the many-body case. Benchmark calculations for two to\nsix fermions with the full configuration interaction method equivalent to the\nexact diagonalization approach, and the coupled cluster method including\nsingle, double, triple, and quadruple excitations are presented. The\nconvergence of the correlation energy with the level of excitations included in\nthe coupled cluster model is analyzed. The range of the interaction strength\nfor which single-reference coupled cluster methods work is examined. Next, the\ncoupled cluster method restricted to single, double, and noniterative triple\nexcitations, CCSD(T), is employed to study a two-component Fermi gas composed\nof 6 to 80 atoms in a one-dimensional harmonic trap. The density profiles of\ntrapped atomic clouds are also reported. Finally, a comparison with\nexperimental results for few-fermion systems is presented. Upcoming possible\napplications and extensions of the presented approach are discussed."
    },
    {
        "anchor": "Loss features in ultracold $^{162}$Dy gases: two- versus three-body\n  processes: Dipolar gases like erbium and dysprosium have a dense spectrum of resonant\nloss features associated with their strong anisotropic interaction potential.\nThese resonances display various behaviours with density and temperature,\nimplying diverse microscopic properties. Here, we quantitatively investigate\nthe low-field ($B < 6\\,\\text{G}$) loss features in ultracold thermal samples of\n$^{162}$Dy, revealing two- and three-body dominated loss processes. We\ninvestigate their temperature dependence and detect a feature compatible with a\n$d$-wave Fano-Feshbach resonance, which has not been observed before. We also\nanalyse the expansion of the dipolar Bose-Einstein condensate as a function of\nthe magnetic field and interpret the changes in size close to the resonances\nwith a variation in the scattering length.",
        "positive": "Dynamics of small trapped one-dimensional Fermi gas under oscillating\n  magnetic fields: Deterministic preparation of an ultracold harmonically trapped\none-dimensional Fermi gas consisting of a few fermions has been realized by the\nHeidelberg group. Using Floquet formalism, we study the time dynamics of two-\nand three-fermion systems in a harmonic trap under an oscillating magnetic\nfield. The oscillating magnetic field produces a time-dependent interaction\nstrength through a Feshbach resonance. We explore the dependence of these\ndynamics on the frequency of the oscillating magnetic field for\nnon-interacting, weakly interacting, and strongly interacting systems. We\nidentify the regimes where the system can be described by an effective\ntwo-state model and an effective three-state model. We find an unbounded\ncoupling to all excited states at the infinitely strong interaction limit and\nseveral simple relations that characterize the dynamics. Based on our findings,\nwe propose a technique for driving transition from the ground state to the\nexcited states using an oscillating magnetic field."
    },
    {
        "anchor": "On-demand generation of dark-bright soliton trains in Bose-Einstein\n  condensates: The controlled creation of dark-bright (DB) soliton trains in multi-component\nBose-Einstein condensates (BECs) is a topic of ongoing interest. In this work\nwe generalize earlier findings on the creation of dark soliton trains in\nsingle-component BECs [A. Romero-Ros et al., Phys. Rev. A 103, 023329 (2021)]\nto two-component BECs. By choosing suitable filled box-type initial\nconfigurations (FBTCs) and solving the direct scattering problem for the\ndefocusing vector nonlinear Schr\\\"odinger equation with nonzero boundary\nconditions we obtain analytical expressions for the DB soliton solutions\nproduced by a general FBTC. It is found that the size of the initial box and\nthe amount of filling directly affects the number, size, and velocity of the\nsolitons, while the initial phase determines the parity (even or odd) of the\nsolutions. Our analytical results are compared to direct numerical integration\nof the coupled Gross-Pitaevskii equations, both in the absence and in the\npresence of a harmonic trap, and an excellent agreement between the two is\ndemonstrated.",
        "positive": "A One-Dimensional Electron Gas Coupled to Light: The prospect of using light to probe or manipulate quantum materials has\nbecome an active area of interest. Here, we investigate a quantum wire --\ntreated as a finite-sized one-dimensional electron gas -- that is coupled to a\nsingle photonic mode. This work focuses on the radiative properties of the wire\nwhen it is prepared in some excited state. One of our key results addresses the\nphoton cascade initiated by the creation of a single electron-hole pair.\nRepeated photon emission leads to the generation of entanglement between the\nelectron and hole and the emission rates exhibit Dicke-like superradiance. In\ngeneral, the radiation is characterized by a competition between superradiance\nand Pauli blocking. We find that the one-dimensional electron gas represents an\nideal system for investigating quantum coherent phenomena and quantum\nentanglement. This work has direct relevance to applications in quantum\ncomputation and quantum transduction."
    },
    {
        "anchor": "Interaction-induced conducting-nonconducting transition of ultra-cold\n  atoms in 1D optical lattices: The study of time-dependent, many-body transport phenomena is increasingly\nwithin reach of ultra-cold atom experiments. We show that the introduction of\nspatially inhomogeneous interactions, e.g., generated by optically-controlled\ncollisions, induce negative differential conductance in the transport of atoms\nin 1D optical lattices. Specifically, we simulate the dynamics of interacting\nfermionic atoms via a micro-canonical transport formalism within both\nmean-field and a higher-order approximation, as well as with time-dependent\nDMRG. For weakly repulsive interactions, a quasi steady-state atomic current\ndevelops that is similar to the situation occurring for electronic systems\nsubject to an external voltage bias. At the mean-field level, we find that this\natomic current is robust against the details of how the interaction is switched\non. Further, a conducting-to-nonconducting transition exists when the\ninteraction imbalance exceeds some threshold from both our approximate and\ntime-dependent DMRG simulations. This transition is preceded by the atomic\nequivalent of negative differential conductivity observed in transport across\nsolid-state structures.",
        "positive": "Properties of phonon modes of ion trap quantum computer in the Aubry\n  phase: We study analytically and numerically the properties of phonon modes in an\nion quantum computer. The ion chain is placed in a harmonic trap with an\nadditional periodic potential which dimensionless amplitude $K$ determines\nthree main phases available for quantum computations: at zero $K$ we have the\ncase of Cirac-Zoller quantum computer, below a certain critical amplitude\n$K<K_c$ the ions are in the Kolmogorov-Arnold-Moser (KAM) phase, with\ndelocalized phonon modes and free chain sliding, and above the critical\namplitude $K>K_c$ ions are in the pinned Aubry phase with a finite frequency\ngap protecting quantum gates from temperature and other external fluctuations.\nFor the Aubry phase, in contrast to the Cirac-Zoller and KAM phases, the phonon\ngap remains independent of the number of ions placed in the trap keeping a\nfixed ion density around the trap center. We show that in the Aubry phase the\nphonon modes are much better localized comparing to the Cirac-Zoller and KAM\ncases. Thus in the Aubry phase the recoil pulses lead to local oscillations of\nions while in other two phases they spread rapidly over the whole ion chains\nmaking them rather sensible to external fluctuations. We argue that the\nproperties of localized phonon modes and phonon gap in the Aubry phase provide\nadvantages for the ion quantum computations in this phase with a large number\nof ions."
    },
    {
        "anchor": "Quantum dynamics of local phase differences between reservoirs of driven\n  interacting bosons separated by simple aperture arrays: We present a derivation of the effective action for the relative phase of\ndriven, aperture-coupled reservoirs of weakly-interacting condensed bosons from\na (3+1)-D microscopic model with local U(1) gauge symmetry. We show that\ninclusion of local chemical potential and driving velocity fields as a gauge\nfield allows derivation of the hydrodynamic equations of motion for the driven\nmacroscopic phase differences across simple aperture arrays. For a single\naperture, the current-phase equation for driven flow contains sinusoidal,\nlinear, and current-bias contributions. We compute the renormalization group\n(RG) beta function of the periodic potential in the effective action for small\ntunneling amplitudes and use this to analyze the temperature dependence of the\nlow-energy current-phase relation, with application to the transition from\nlinear to sinusoidal current-phase behavior observed in experiments by\nHoskinson et al. \\cite{packard} for liquid $^{4}$He driven through nanoaperture\narrays. Extension of the microscopic theory to a two-aperture array shows that\ninterference between the microscopic tunneling contributions for individual\napertures leads to an effective coupling between apertures which amplifies the\nJosephson oscillations in the array. The resulting multi-aperture current-phase\nequations are found to be equivalent to a set of equations for coupled pendula,\nwith microscopically derived couplings.",
        "positive": "Wigner crystal induced by dipole-dipole interaction in one-dimensional\n  optical lattices: We demonstrate that the static structure factor, momentum distribution and\ndensity distribution provide clear signatures of the emergence of Wigner\ncrystal for the fermionic dipolar gas with strongly repulsive dipole-dipole\ninteractions trapped in one-dimensional optical lattices. Our numerical\nevidences are based on the exact diagonalization of the microscopic effective\nlattice Hamiltonian of few particles interacting with long-range interactions.\nAs a comparison, we also study the system with only nearest-neighbor\ninteractions, which displays quite different behaviors from the dipolar system\nin the regime of strong repulsion."
    },
    {
        "anchor": "Second sound dipole mode in a partially Bose-Einstein condensed gas: We study the second sound dipole mode in a partially Bose-Einstein condensed\ngas. This mode is excited by spatially separating and releasing the\ncenter-of-mass of the Bose-Einstein condensate (BEC) with respect to the\nthermal cloud, after which the equilibration is observed. The oscillation\nfrequency and the damping rate of this mode is studied for different harmonic\nconfinements and temperatures. The measured damping rates close to the\ncollisionless regime are found to be in good agreement with Landau damping. For\nincreasing hydrodynamicity of the cloud we observe an increase of the damping.",
        "positive": "Turbulence in Binary Bose-Einstein Condensates Generated by Highly\n  Non-Linear Rayleigh-Taylor and Kelvin-Helmholtz Instabilities: Quantum turbulence (QT) generated by the Rayleigh-Taylor instability in\nbinary immiscible ultracold 87Rb atoms at zero temperature is studied\ntheoretically. We show that the quantum vortex tangle is qualitatively\ndifferent from previously considered superfluids, which reveals deep relations\nbetween QT and classical turbulence. The present QT may be generated at\narbitrarily small Mach numbers, which is a unique property not found in\npreviously studied superfluids. By numerical solution of the coupled\nGross-Pitaevskii equations we find that the Kolmogorov scaling law holds for\nthe incompressible kinetic energy. We demonstrate that the phenomenon may be\nobserved in the laboratory."
    },
    {
        "anchor": "Thermodynamics in expanding shell-shaped Bose-Einstein condensates: Inspired by investigations of Bose-Einstein condensates (BECs) produced in\nthe Cold Atom Laboratory (CAL) aboard the International Space Station, we\npresent a study of thermodynamic properties of shell-shaped BECs. Within the\ncontext of a spherically symmetric `bubble trap' potential, we study the\nevolution of the system from small filled spheres to hollow, large, thin shells\nvia the tuning of trap parameters. We analyze the bubble trap spectrum and\nstates, and track the distinct changes in spectra between radial and angular\nmodes across the evolution. This separation of the excitation spectrum provides\na basis for quantifying dimensional cross-over to quasi-2D physics at a given\ntemperature. Using the spectral data, for a range of trap parameters, we\ncompute the critical temperature for a fixed number of particles to form a BEC.\nFor a set of initial temperatures, we also evaluate the change in temperature\nthat would occur in adiabatic expansion from small filled sphere to large thin\nshell were the trap to be dynamically tuned. We show that the system cools\nduring this expansion but that the decrease in critical temperature occurs more\nrapidly, thus resulting in depletion of any initial condensate. We contrast our\nspectral methods with standard semiclassical treatments, which we find must be\nused with caution in the thin-shell limit. With regards to interactions, using\nenergetic considerations and corroborated through Bogoliubov treatments, we\ndemonstrate that they would be less important for thin shells due to reduced\ndensity but vortex physics would become more predominant. Finally, we apply our\ntreatments to traps that realistically model CAL experiments and borrow from\nthe thermodynamic insights found in the idealized bubble case during adiabatic\nexpansion.",
        "positive": "Loschmidt echo in one-dimensional interacting Bose gases: We explore Loschmidt echo in two regimes of one-dimensional (1D) interacting\nBose gases: the strongly interacting Tonks-Girardeau (TG) regime, and the\nweakly-interacting mean-field regime. We find that the Loschmidt echo of a TG\ngas decays as a Gaussian when small perturbations are added to the Hamiltonian\n(the exponent is proportional to the number of particles and the magnitude of a\nsmall perturbation squared). In the mean-field regime the Loschmidt echo decays\nfaster for larger interparticle interactions (nonlinearity), and it shows\nricher behavior than the TG Loschmidt echo dynamics, with oscillations\nsuperimposed on the overall decay."
    },
    {
        "anchor": "Itinerant ferromagnetism of a repulsive atomic Fermi gas: a quantum\n  Monte Carlo study: We investigate the phase diagram of a two-component repulsive Fermi gas at\nT=0 by means of quantum Monte Carlo simulations. For a given value of the\npositive s-wave scattering length, both purely repulsive and purely attractive\nmodel potentials are considered in order to analyze the limits of the universal\nregime where the details of interatomic forces can be neglected. The equation\nof state of both balanced and unbalanced systems is calculated as a function of\nthe interaction strength and the critical density for the onset of\nferromagnetism is determined. The energy per particle of the strongly polarized\ngas is calculated and parametrized in terms of the physical properties of\nrepulsive polarons, which are relevant for the stability of the fully\nmagnetized ferromagnetic state. Finally, we analyze the phase diagram in the\npolarization/interaction plane under the assumption that only phases with\nhomogeneous magnetization can be produced.",
        "positive": "Dynamical Detection of Topological Phase Transitions in Short-Lived\n  Atomic Systems: We demonstrate that dynamical probes provide direct means of detecting the\ntopological phase transition (TPT) between conventional and topological phases,\nwhich would otherwise be difficult to access because of loss or heating\nprocesses. We propose to avoid such heating by rapidly quenching in and out of\nthe short-lived topological phase across the transition that supports gapless\nexcitations. Following the quench, the distribution of excitations in the final\nconventional phase carries signatures of the TPT. We apply this strategy to\nstudy the TPT into a Majorana-carrying topological phase predicted in\none-dimensional spin-orbit-coupled Fermi gases with attractive interactions.\nThe resulting spin-resolved momentum distribution, computed by\nself-consistently solving the time-dependent Bogoliubov--de Gennes equations,\nexhibits Kibble-Zurek scaling and St\\\"{u}ckelberg oscillations characteristic\nof the TPT. We discuss parameter regimes where the TPT is experimentally\naccessible."
    },
    {
        "anchor": "Superconducting transition temperature of the Bose one-component plasma: We present results of first principle numerical simulations of the Bose\none-component plasma, i.e., a Bose gas with pairwise Coulomb interactions among\nparticles and a uniform neutralizing background. We compute the superconducting\ntransition temperature for a wide range of densities, in two and three\ndimensions, for both continuous and lattice versions of the model. Our results\nare of direct relevance to quantitative studies of bipolaron mechanisms of\n(high-temperature) superconductivity.",
        "positive": "Generalized TBA and generalized Gibbs: We consider the extension of the thermodynamic Bethe Ansatz (TBA) to cases in\nwhich additional terms involving higher conserved charges are added to the\nHamiltonian, or in which a distinction is made between the Hamiltonian used for\ntime evolution and that used for defining the density matrix. Writing down\nequations describing the saddle-point (pseudo-equilibrium) state of the\ninfinite system, we prove the existence and uniqueness of solutions for\nLieb-Liniger provided simple requirements are met. We show how a knowledge of\nthe saddle-point rapidity distribution is equivalent to that of all generalized\nchemical potentials, and how the standard equilibrium equations for e.g.\nexcitations are simply generalized."
    },
    {
        "anchor": "Functional renormalisation approach to driven dissipative dynamics: I investigate stationary scaling states of Burgers' and Gross-Pitaevskii\nequations (GPE).\n  The path integral representation of the steady state of the stochastic\nBurgers equation is used in order to investigate the scaling solutions of the\nsystem at renormalisation group (RG) fixed points. I employ the functional RG\nin order to access the non-perturbative regime. I devise an approximation that\nrespects Galilei invariance and is designed to resolve the frequency and\nmomentum dependence of low order correlation functions. I establish a set of RG\nfixed point equations for inverse propagators with an arbitrary frequency and\nmomentum dependence. In all spatial dimensions they yield a continuum of fixed\npoints as well as an isolated one. These results are fully compatible with the\nexisting literature for $d=1$. For $d\\neq1$ however results of the literature\nfocus almost exclusively on irrotational solutions while the solutions that my\napproximation can capture contain necessarily vorticity and are closer to\nNavier-Stokes turbulence.\n  Non-equilibrium steady states of ultra-cold Bose gases coupled to external\nbaths of energy and particles such as exciton-polariton condensates are related\nto Kardar-Parisi-Zhang (KPZ) dynamics. I postulate that the scaling that we\nobtain in this context applies as well to far-from-equilibrium quasi-stationary\nstates (non-thermal fixed points) of the closed system described by the GPE. I\ntranslate results found in the KPZ literature to their corresponding dual in\nthe ultra-cold Bose gas set-up. I find that this provides a new scaling\nrelation which can be used to analytically identify the classical Kolmogorov\n-5/3 exponent and its anomalous correction. Moreover I estimate the anomalous\ncorrection to the scaling exponent of the compressible part of the kinetic\nenergy spectrum of the Bose gas which is confirmed by numerical simulations of\nthe GPE.",
        "positive": "Observation of two-beam collective scattering phenomena in a\n  Bose-Einstein condensate: New phenomena of collective light scattering are observed when an elongated\nBose-Einstein condensate is pumped by two non-interfering beams\ncounterpropagating along its long axis. In the limit of small Rayleigh\nscattering rates, the presence of a second pump beam suppresses superradiance,\nwhereas at large Rayleigh scattering rates it lowers the effective threshold\npower for collective light scattering. In the latter regime, the quench\ndynamics of the two-beam system are oscillatory, compared to monotonic in the\nsingle-beam case. In addition, the dependence on power, detuning, and atom\nnumber is explored. The observed features of the two-beam system qualitatively\nagree with the recent prediction of a supersolid crystalline phase of light and\nmatter at large Rayleigh scattering rates [S. Ostermann, F. Piazza, and H.\nRitsch, Phys. Rev. X 6, 021026 (2016).]"
    },
    {
        "anchor": "Dual-species Bose-Einstein condensates of $^{23}$Na and $^{41}$K with\n  tunable interactions: We report the creation of dual-species Bose-Einstein condensates (BECs) of\n$^{23}$Na and $^{41}$K. Favorable background scattering lengths enable\nefficient sympathetic cooling of $^{41}$K via forced evaporative cooling of\n$^{23}$Na in a plugged magnetic trap and an optical dipole trap. The $1/e$\nlifetime of the thermal mixture in the stretched hyperfine state exceeds 5 s in\nthe presence of background scattering. At the end of evaporation, we create\ndual BECs in the immiscible phase, with about $3\\times10^5$ $^{23}$Na atoms\nsurrounding $5\\times10^4$ $^{41}$K atoms. To further enable the tuning of the\ninterspecies interaction strength, we locate multiple Feshbach resonances at\nmagnetic fields up to 100 G. The broadest $s$-wave resonance located at 73.4(3)\nG features a favorable width of 1.8(2) G. This work sets the stage for the\ncreation of ultracold gases of strongly dipolar bosonic $^{23}$Na$^{41}$K\nmolecules as well as the exploration of many-body physics in bosonic\n$^{23}$Na-$^{41}$K mixtures.",
        "positive": "Antiferromagnetic Heisenberg Spin Chain of a Few Cold Atoms in a\n  One-Dimensional Trap: We report on the deterministic preparation of antiferromagnetic Heisenberg\nspin chains consisting of up to four fermionic atoms in a one-dimensional trap.\nThese chains are stabilized by strong repulsive interactions between the two\nspin components without the need for an external periodic potential. We\nindependently characterize the spin configuration of the chains by measuring\nthe spin orientation of the outermost particle in the trap and by projecting\nthe spatial wave function of one spin component on single-particle trap levels.\nOur results are in good agreement with a spin-chain model for fermionized\nparticles and with numerically exact diagonalizations of the full few-fermion\nsystem."
    },
    {
        "anchor": "Three s-wave interacting fermions under anisotropic harmonic\n  confinement: Dimensional crossover of energetics and virial coefficients: We present essentially exact solutions of the Schroedinger equation for three\nfermions in two different spin states with zero-range s-wave interactions under\nharmonic confinement. Our approach covers spherically symmetric, strictly\ntwo-dimensional, strictly one-dimensional, cigar-shaped, and pancake-shaped\ntraps. In particular, we discuss the transition from quasi-one-dimensional to\nstrictly one-dimensional and from quasi-two-dimensional to strictly\ntwo-dimensional geometries. We determine and interpret the eigenenergies of the\nsystem as a function of the trap geometry and the strength of the zero-range\ninteractions. The eigenenergies are used to investigate the dependence of the\nsecond- and third-order virial coefficients, which play an important role in\nthe virial expansion of the thermodynamic potential, on the geometry of the\ntrap. We show that the second- and third-order virial coefficients for\nanisotropic confinement geometries are, for experimentally relevant\ntemperatures, very well approximated by those for the spherically symmetric\nconfinement for all s-wave scattering lengths.",
        "positive": "Realization of inverse Kibble-Zurek scenario with trapped Bose gases: We show that there exists the inverse Kibble-Zurek scenario, when we start\nwith an equilibrium system with broken symmetry and, by imposing perturbations,\ntransform it to a strongly nonequilibrium symmetric state through the sequence\nof states with spontaneously arising topological defects. We demonstrate the\ninverse Kibble-Zurek scenario both experimentally, by perturbing the\nBose-Einstein condensate of trapped $^{87}$Rb atoms, and also by accomplishing\nnumerical simulations for the same setup as in the experiment, the experimental\nand numerical results being in good agreement with each other."
    },
    {
        "anchor": "Conserving Approximation of Pairing theories in Fermionic superfluid\n  phase: Respecting the conservation laws of momentum and energy in a many body theory\nis very important for understanding the transport phenomena. The previous\nconserving approximation requires that the self-energy of a single particle can\nbe written as a functional derivative of a full dressed Green's function. This\ncondition can not be satisfied in the $G_0G$ t-matrix or pair fluctuation\ntheory which emphasizes the fermion pairing with a stronger than the\nBardeen-Cooper-Schrieffer (BCS) attraction. In the previous\nwork\\cite{stressWI}, we have shown that when the temperature is above the\nsuperfluid transition temperature $T_c$, the $G_0G$ t-matrix theory can be put\ninto a form that satisfies the stress tensor Ward identity (WI) or local form\nof conservation laws by introducing a new type of vertex correction. In this\npaper, we will extend the above conservation approximation to the superfluid\nphase in the BCS mean field level. To establish the stress tensor WI, we have\nto include the fluctuation of the order parameter or the contribution from the\nGoldstone mode. The result will be useful for understanding the transport\nproperties such as the behavior of the viscosity of Fermionic gases in the\nsuperfluid phases.",
        "positive": "Spin Solitons in Spin-1 Bose-Einstein Condensates: Solitons in multi-component Bose-Einstein condensates have been paid much\nattention, due to the stability and wide applications of them. The exact\nsoliton solutions are usually obtained for integrable models. In this paper, we\npresent four families of exact spin soliton solutions for non-integrable cases\nin spin-1 Bose-Einstein Condensates. The whole particle density is uniform for\nthe spin solitons, which is in sharp contrast to the previously reported\nsolitons of integrable models. The spectrum stability analysis and numerical\nsimulation indicate the spin solitons can exist stably. The spin density\nredistribution happens during the collision process, which depends on the\nrelative phase and relative velocity between spin solitons. The non-integrable\nproperties of the systems can bring spin solitons experience weak amplitude and\nlocation oscillations after collision. These stable spin soliton excitations\ncould be used to study the negative inertial mass of solitons, the dynamics of\nsoliton-impurity systems, and the spin dynamics in Bose-Einstein condensates."
    },
    {
        "anchor": "Steady-state phase diagram of quantum gases in a lattice coupled to a\n  membrane: In a recent experiment [Vochezer {\\it et al.,} Phys. Rev. Lett. \\textbf{120},\n073602 (2018)], a novel kind of hybrid atom-opto-mechanical system has been\nrealized by coupling atoms in a lattice to a membrane. While such system\npromises a viable contender in the competitive field of simulating\nnon-equilibrium many-body physics, its complete steady-state phase diagram is\nstill lacking. Here we study the phase diagram of this hybrid system based on\nan atomic Bose-Hubbard model coupled to a quantum harmonic oscillator. We take\nboth the expectation value of the bosonic operator and the mechanical motion of\nthe membrane as order parameters, and thereby identify four different quantum\nphases. Importantly, we find the atomic gas in the steady state of such\nnon-equilibrium setting undergoes a superfluid-Mott-insulator transition when\nthe atom-membrane coupling is tuned to increase. Such steady-state phase\ntransition can be seen as the non-equilibrium counterpart of the conventional\nsuperfluid-Mott-insulator transition in the ground state of Bose-Hubbard model.\nFurther, no matter which phase the quantum gas is in, the mechanic motion of\nthe membrane exhibits a transition from an incoherent vibration to a coherent\none when the atom-membrane coupling increases, agreeing with the experimental\nobservations. Our present study provides a simple way to study non-equilibrium\nmany-body physics that is complementary to ongoing experiments on the hybrid\natomic and opto-mechanical systems.",
        "positive": "Active Learning Approach to Optimization of Experimental Control: In this work we present a general machine learning based scheme to optimize\nexperimental control. The method utilizes the neural network to learn the\nrelation between the control parameters and the control goal, with which the\noptimal control parameters can be obtained. The main challenge of this approach\nis that the labeled data obtained from experiments are not abundant. The\ncentral idea of our scheme is to use the active learning to overcome this\ndifficulty. As a demonstration example, we apply our method to control\nevaporative cooling experiments in cold atoms. We have first tested our method\nwith simulated data and then applied our method to real experiments. We\ndemonstrate that our method can successfully reach the best performance within\nhundreds of experimental runs. Our method does not require knowledge of the\nexperimental system as a prior and is universal for experimental control in\ndifferent systems."
    },
    {
        "anchor": "Effective Action and Field Equation for BEC from Weak to Strong\n  Couplings: While free and weakly interacting nonrelativistic particles are described by\na Gross-Pitaevskii equation, which is a nonlinear self-interacting\nSchr\\\"odinger equation, the phenomena in the strong- coupling limit are\ngoverned by an effective action that is extremized by a double-fractional\ngeneralization of this equation. Its particle orbits perform L\\`evy walks\nrather than Gaussian random walks.",
        "positive": "Three-body recombination near the d-wave resonance in ultracold\n  $^{85}$Rb\\,-$^{87}$Rb mixtures: We have studied the three-body recombination rates on both sides of the\ninterspecies d-wave Feshbach resonance in the $^{85}$Rb\\,-$^{87}$Rb-$^{87}$Rb\nsystem using the $R$-matrix propagation method in the hyperspherical coordinate\nframe. Two different mechanisms of recombination rate enhancement for positive\nand negative $^{85}$Rb\\,-$^{87}$Rb d-wave scattering lengths are analyzed. On\nthe positive scattering length side, the recombination rate enhancement occurs\ndue to the existence of three-body shape resonance, while on the negative\nscattering length side, the coupling between the lowest entrance channel and\nthe highest recombination channel is crucial to the appearance of the\nenhancement. In addition, our study shows that the intraspecies interaction\nplays a significant role in determining the emergence of recombination rate\nenhancements. Compared to the case in which the three pairwise interactions are\nall in d-wave resonance, when the $^{87}$Rb-$^{87}$Rb interaction is near the\nd-wave resonance, the values of the interspecies scattering length that produce\nthe recombination enhancement shift. In particular, when the\n$^{87}$Rb-$^{87}$Rb interaction is away from the d-wave resonance, the\nenhancement disappears on the negative interspecies scattering length side."
    },
    {
        "anchor": "How creating one additional well can generate Bose-Einstein condensation: The realization of Bose-Einstein condensation in ultracold trapped gases has\nled to a revival of interest in that fascinating quantum phenomenon. This\nexperimental achievement necessitated both extremely low temperatures and\nsufficiently weak interactions. Particularly in reduced spatial dimensionality\neven an infinitesimal interaction immediately leads to a departure to\nquasi-condensation. We propose a system of strongly interacting bosons which\novercomes those obstacles by exhibiting a number of intriguing related\nfeatures: (i) The tuning of just a single control parameter drives a transition\nfrom quasi-condensation to complete condensation, (ii) the destructive\ninfluence of strong interactions is compensated by the respective increased\nmobility, (iii) topology plays a crucial role since a crossover from one- to\n`infinite'-dimensionality is simulated, (iv) a ground state gap opens which\nmakes the condensation robust to thermal noise. Remarkably, all these features\ncan be derived by analytical and exact numerical means despite the\nnon-perturbative character of the system.",
        "positive": "Dimensional crossover and cold-atom realization of topological Mott\n  insulators: We propose a cold-atom setup which allows for a dimensional crossover from a\ntwo-dimensional quantum spin Hall insulating phase to a three-dimensional\nstrong topological insulator by tuning the hopping between the layers. We\nfurther show that additional Hubbard onsite interactions can give rise to spin\nliquid-like phases: weak and strong topological Mott insulators. They represent\nthe celebrated paradigm of a quantum state of matter which merely exists\nbecause of the interplay of the non-trivial topology of the band structure and\nstrong interactions. While the theoretical understanding of this phase has\nremained elusive, our proposal shall help to shed some light on this exotic\nstate of matter by paving the way for a controlled experimental investigation\nin optical lattices."
    },
    {
        "anchor": "Polariton dynamics in strongly interacting quantum many-body systems: We develop a theory for light propagating in an atomic Bose-Einstein\ncondensate in the presence of strong interactions. The resulting many-body\ncorrelations are shown to have profound effects on the optical properties of\nthis interacting medium. For weak atom-light coupling, there is a well-defined\nquasiparticle, the polaron-polariton, supporting light propagation with\nspectral features differing significantly from the noninteracting case. The\ndamping of the polaron-polariton depends nonmonotonically on the light-matter\ncoupling strength, initially increasing and then decreasing. This gives rise to\nan interesting crossover between two quasiparticles: a bare polariton and a\npolaron-polariton, separated by a complex and lossy mixture of light and\nmatter.",
        "positive": "Observation of the Berezinskii-Kosterlitz-Thouless Phase Transition in\n  an Ultracold Fermi Gas: We experimentally investigate the first-order correlation function of a\ntrapped Fermi gas in the two-dimensional BEC-BCS crossover. We observe a\ntransition to a low-temperature superfluid phase with algebraically decaying\ncorrelations. We show that the spatial coherence of the entire trapped system\ncan be characterized by a single temperature-dependent exponent. We find the\nexponent at the transition to be constant over a wide range of interaction\nstrengths across the crossover. This suggests that the phase transitions in\nboth the bosonic regime and the strongly interacting crossover regime are of\nBerezinskii-Kosterlitz-Thouless-type and lie within the same universality\nclass. On the bosonic side of the crossover, our data are well-described by\nQuantum Monte Carlo calculations for a Bose gas. In contrast, in the strongly\ninteracting regime, we observe a superfluid phase which is significantly\ninfluenced by the fermionic nature of the constituent particles."
    },
    {
        "anchor": "Condensate density of interacting bosons: a functional renormalization\n  group approach: We calculate the temperature dependent condensate density $\\rho^0 (T)$ of\ninteracting bosons in three dimensions using the functional renormalization\ngroup (FRG). From the numerical solution of suitably truncated FRG flow\nequations for the irreducible vertices we obtain $\\rho^0 (T)$ for arbitrary\ntemperatures. We carefully extrapolate our numerical results to the critical\npoint and determine the order parameter exponent $\\beta \\approx 0.32$, in\nreasonable agreement with the expected value $ 0.345$ associated with the\nXY-universality class. We also calculate the condensate density in two\ndimensions at zero temperature using a truncation of the FRG flow equations\nbased on the derivative expansion including cubic and quartic terms in the\nexpansion of the effective potential in powers of the density. As compared with\nthe widely used quadratic approximation for the effective potential, the\ncoupling constants associated with the cubic and quartic terms increase the\nresult for the condensate density by a few percent. However, the cubic and\nquartic coupling constants flow to rather large values, which sheds some doubt\non FRG calculations based on a low order polynomial approximation for the\neffective potential.",
        "positive": "Oscillation and decay of particle current due to a quench and dephasing\n  in an interacting fermionic system: We study the response of a particle current to dissipative dephasing in an\ninteracting, few-body fermionic lattice system. The particles are prepared in\nthe ground state in presence of an artificial magnetic gauge field, which is\nsubsequently quenched to zero. The initial current decays non-trivially in the\ndissipative environment and we explore the emerging dynamics and its dependence\non various system parameters."
    },
    {
        "anchor": "Probing non-locality of interactions in a Bose-Einstein Condensate using\n  solitons: We consider a Bose-Einstein Condensate(BEC) with non-local inter-particle\ninteractions. The local Gross-Pitaevskii(GP) equation is valid for the gas\nparameter $\\nu =: a^{3} n_{0} << 1$, but for $\\nu \\rightarrow 1$, the BEC is\ndescribed by modified GP equation(MGPE). We study the exact solutions of the\nMGPE describing bright and dark solitons. It turns out that the width of these\nnon-local solitons has qualitatively similar behaviour as the modified healing\nlength due to the non-local interactions of the MGPE. We also study the effect\nof the non-locality and gas parameter({\\nu}) on the stability of the solitons\nusing the Vakhitov Kolokolov(VK) stability criterion. We show that these\nsoliton solutions are indeed stable. Further, the stability of these soliton\nsolutions gets enhanced due to the non-locality of interactions.",
        "positive": "Phase separation in a spin-orbit coupled Bose-Einstein condensate: We study a spin-orbit (SO) coupled hyperfine spin-1 Bose-Einstein condensate\n(BEC) in a quasi-one-dimensional trap. For a SO-coupled BEC in a\none-dimensional box, we show that in the absence of the Rabi term, any non-zero\nvalue of SO coupling will result in a phase separation among the components for\na ferromagnetic BEC, like $^{87}$Rb. On the other hand, SO coupling favors\nmiscibility in a polar BEC, like $^{23}$Na. In the presence of a harmonic trap,\nwhich favors miscibility, a ferromagnetic BEC phase separates, provided the\nSO-coupling strength and number of atoms are greater than some critical value.\nThe Rabi term favors miscibility irrespective of the nature of the spin\ninteraction: ferromagnetic or polar."
    },
    {
        "anchor": "Superfluidity and collective modes in Rashba spin-orbit coupled Fermi\n  gases: We present a theoretical study of the superfluidity and the corresponding\ncollective modes in two-component atomic Fermi gases with s-wave attraction and\nsynthetic Rashba spin-orbit coupling. The general effective action for the\ncollective modes is derived from the functional path integral formalism. By\ntuning the spin-orbit coupling from weak to strong, the system undergoes a\ncrossover from an ordinary BCS/BEC superfluid to a Bose-Einstein condensate of\nrashbons. We show that the properties of the superfluid density and the\nAnderson-Bogoliubov mode manifest this crossover. At large spin-orbit coupling,\nthe superfluid density and the sound velocity become independent of the\nstrength of the s-wave attraction. The two-body interaction among the rashbons\nis also determined. When a Zeeman field is turned on, the system undergoes\nquantum phase transitions to some exotic superfluid phases which are\ntopologically nontrivial. For the two-dimensional system, the nonanalyticities\nof the thermodynamic functions and the sound velocity across the phase\ntransition are related to the bulk gapless fermionic excitation which causes\ninfrared singularities. The superfluid density and the sound velocity behave\nnonmonotonically: they are suppressed by the Zeeman field in the normal\nsuperfluid phase, but get enhanced in the topological superfluid phase. The\nthree-dimensional system is also studied.",
        "positive": "Thermodynamic signatures of the polaron-molecule transition in a Fermi\n  gas: We consider the highly spin-imbalanced limit of a two-component Fermi gas,\nwhere there is a small density of $\\downarrow$ impurities attractively\ninteracting with a sea of $\\uparrow$ fermions. In the single-impurity limit at\nzero temperature, there exists the so-called polaron-molecule transition, where\nthe impurity sharply changes its character by binding a $\\uparrow$ fermion at\nsufficiently strong attraction. Using a recently developed variational\napproach, we calculate the thermodynamic properties of the impurity, and we\nshow that the transition becomes a smooth crossover at finite temperature due\nto the thermal occupation of excited states in the impurity spectral function.\nHowever, remnants of the single-impurity transition are apparent in the\nmomentum-resolved spectral function, which can in principle be probed with\nRaman spectroscopy. We furthermore show that the Tan contact exhibits a\ncharacteristic non-monotonic dependence on temperature that provides a\nsignature of the zero-temperature polaron-molecule transition. For a finite\nimpurity density, we argue that descriptions purely based on the behavior of\nthe Fermi polaron are invalid near the polaron-molecule transition, since\ncorrelations between impurities cannot be ignored. In particular, we show that\nthe spin-imbalanced system undergoes phase separation at low temperatures due\nto the strong attraction between $\\uparrow\\downarrow$ molecules induced by the\nFermi sea. Thus, we find that the impurity spectrum and the induced\nimpurity-impurity interactions are key to understanding the phase diagram of\nthe spin-imbalanced Fermi gas."
    },
    {
        "anchor": "Goldstone mode and pair-breaking excitations in atomic Fermi superfluids: Spontaneous symmetry breaking is a central paradigm of elementary particle\nphysics, magnetism, superfluidity and superconductivity. According to\nGoldstone's theorem, phase transitions that break continuous symmetries lead to\nthe existence of gapless excitations in the long-wavelength limit. These\nGoldstone modes generally dominate the low-energy excitations, showing that\nsymmetry breaking has a profound impact on the physical properties of matter.\nHere, we present the first comprehensive study of the elementary excitations in\na homogeneous strongly interacting Fermi gas through the crossover from a\nBardeen-Cooper-Schrieffer (BCS) superfluid to a Bose-Einstein condensate (BEC)\nof molecules using two-photon Bragg spectroscopy. The spectra exhibit a\ndiscrete Goldstone mode, associated with the broken symmetry superfluid phase,\nas well as pair breaking single-particle excitations. Our techniques yield a\ndirect determination of the superfluid pairing gap and speed of sound in close\nagreement with a strong-coupling theory.",
        "positive": "Quantum signature of analog Hawking radiation in momentum space: We consider a sonic analog of a black hole realized in the one-dimensional\nflow of a Bose-Einstein condensate. Our theoretical analysis demonstrates that\none- and two-body momentum distributions accessible by present-day experimental\ntechniques provide clear direct evidence (i) of the occurrence of a sonic\nhorizon, (ii) of the associated acoustic Hawking radiation and (iii) of the\nquantum nature of the Hawking process. The signature of the quantum behavior\npersists even at temperatures larger than the chemical potential."
    },
    {
        "anchor": "Universal scaling of Efimov resonance positions in cold atom systems: Recent cold atom experiments report a surprising universal scaling of the\nfirst Efimov resonance position a_{-}^1 by the two-body van der Waals length\nr_{vdW}. The ratio C=-a_{-}^1/r_{vdW}=8.5~9.5 for identical particles appears\nto be a constant regardless of the atomic spin configuration, the Feshbach\nresonance employed to tune the scattering length, and even the atomic species,\nwith K-39 being the only exception. This result indicates that the Efimov\nenergy structure is insensitive to the details of the short range potential. We\nsuggest that the universality results from the quantum reflection of the Efimov\nwavefunciton by the short-range molecular potential. Assuming Born-Oppenheimer\napproximation and strong quantum reflection, we obtain an analytic result of\nC=9.475... for three identical particles. We suspect the exceptional case of\nK-39 is a result of resonant coupling between the Efimov state and a\nshort-range molecular state.",
        "positive": "Analyzing non-equilibrium quantum states through snapshots with\n  artificial neural networks: Current quantum simulation experiments are starting to explore\nnon-equilibrium many-body dynamics in previously inaccessible regimes in terms\nof system sizes and time scales. Therefore, the question emerges which\nobservables are best suited to study the dynamics in such quantum many-body\nsystems. Using machine learning techniques, we investigate the dynamics and in\nparticular the thermalization behavior of an interacting quantum system which\nundergoes a dynamical phase transition from an ergodic to a many-body localized\nphase. A neural network is trained to distinguish non-equilibrium from thermal\nequilibrium data, and the network performance serves as a probe for the\nthermalization behavior of the system. We test our methods with experimental\nsnapshots of ultracold atoms taken with a quantum gas microscope. Our results\nprovide a path to analyze highly-entangled large-scale quantum states for\nsystem sizes where numerical calculations of conventional observables become\nchallenging."
    },
    {
        "anchor": "Shortcuts to adiabaticity in the strongly-coupled regime: nonadiabatic\n  control of a unitary Fermi gas: Coherent control of complex quantum systems is a fundamental requirement in\nquantum information processing and engineering. Recently developed notion of\nshortcut to adiabaticity (STA) has spawned intriguing prospects. So far, the\nmost experimental investigations of STA are implemented in the ideal thermal\ngas or the weakly interacting ultracold Bose gases. Here we report the first\ndemonstration of a many-body STA in a 3D anisotropically trapped unitary Fermi\ngas. A new dynamical scaling law is demonstrated on such a strongly interacting\nquantum gas. By simply engineering the frequency aspect ratio of a harmonic\ntrap, the dynamics of the gas can be manipulated and the many-body state can be\ntransferred adiabatically from one stationary state to another one in short\ntime scale without the excitation. The universal scaling both for\nnon-interacting and unitary Fermi gas is also verified. This could be very\nimportant for future many-body quantum engineering and the exploration of the\nfundamental law of the thermodynamics.",
        "positive": "Lower bound for ground state energy of BEC in a rotating optical lattice: We use the frustrated XY model approximation of BEC in a rotating optical\nlattice and formulate the problem of the ground state in terms of eigenvectors\nand eigenvalues of frustrated adjacency matrix (coupling matrix). By using this\nformulation, we show that there is a lower bound for ground state energy in\nterms of maximum eigenvalue of this matrix."
    },
    {
        "anchor": "Dynamics of Nonequilibrium Dicke Models: Motivated by experiments observing self-organization of cold atoms in optical\ncavities we investigate the collective dynamics of the associated\nnonequilibrium Dicke model. The model displays a rich semiclassical phase\ndiagram of long time attractors including distinct superradiant fixed points,\nbistable and multistable coexistence phases and regimes of persistent\noscillations. We explore the intrinsic timescales for reaching these asymptotic\nstates and discuss the implications for finite duration experiments. On the\nbasis of a semiclassical analysis of the effective Dicke model we find that\nsweep measurements over 200ms may be required in order to access the asymptotic\nregime. We briefly comment on the corrections that may arise due to quantum\nfluctuations and states outside of the effective two-level Dicke model\ndescription.",
        "positive": "Self-binding of one-dimensional fermionic mixtures with zero-range\n  interspecies attraction: For sufficiently large mass ratios the attractive exchange force caused by a\nsingle light atom interacting with a few heavy identical fermions can overcome\ntheir Fermi degeneracy pressure and bind them into an $N+1$ cluster. Here, by\nusing a mean-field approach valid for large $N$, we find that $N+1$ clusters\ncan attract each other and form a self-bound charge density wave, the\nproperties of which we fully characterize. Our work shows that there are no\nfundamental obstacles for having self-bound states in fermionic mixtures with\nzero-range interactions."
    },
    {
        "anchor": "Topological phases of shaken quantum Ising lattices: The quantum compass model consists of a two-dimensional square spin lattice\nwhere the orientation of the spin-spin interactions depends on the spatial\ndirection of the bonds. It has remarkable symmetry properties and the ground\nstate shows topological degeneracy. The implementation of the quantum compass\nmodel in quantum simulation setups like ultracold atoms and trapped ions is far\nfrom trivial, since spin interactions in those sytems typically are independent\nof the spatial direction. Ising spin interactions, on the contrary, can be\ninduced and controlled in atomic setups with state-of-the art experimental\ntechniques. In this work, we show how the quantum compass model on a\nrectangular lattice can be simulated by the use of the photon-assisted\ntunneling induced by periodic drivings on a quantum Ising spin model. We\ndescribe a procedure to adiabatically prepare one of the doubly-degenerate\nground states of this model by adiabatically ramping down a transverse magnetic\nfield, with surprising differences depending on the parity of the lattice size.\nExact diagonalizations confirm the validity of this approach for small\nlattices. Specific implementations of this scheme are presented with ultracold\natoms in optical lattices in the Mott insulator regime, as well as with Rydberg\natoms.",
        "positive": "Production of rubidium Bose-Einstein condensate in an optically-plugged\n  magnetic quadrupole trap: We have experimentally produced rubidium Bose-Einstein condensate in an\noptically-plugged magnetic quadrupole (OPQ) trap. A far blue-detuned focused\nlaser beam with a wavelength of 532 nm is plugged in the center of the magnetic\nquadrupole trap to increase the number of trapped atoms and suppress the\nheating. A radio frequency (RF) evaporative cooling in the magneto-optical\nhybrid trap is applied to decrease the atom temperature into degeneracy. The\natom number of the condensate is $1.2(0.4)\\times10^5$ and the temperature is\nbelow 100 nK. We have also studied characteristic behaviors of the condensate,\nsuch as phase space density (PSD), condensate fraction and anisotropic\nexpansion."
    },
    {
        "anchor": "Comment on: `Single-shot simulations of dynamic quantum many-body\n  systems' [arXiv:1501.03224]: In their recent paper [Nature Physics 15, 451 (2006)], Sakmann and Kasevich\nstudy the formation of fringe patterns in ultra-cold Bose gases and claim:\n`Here, we show how single shots can be simulated from numerical solutions of\nthe time-dependent many-body Schr\\\"odinger equation.' It would be remarkable if\nthey had solved this exponentially complex equation. Instead they solve\nnonlinear equations with the aim to approximate the solution of the\nSchr\\\"odinger equation. The authors proceed to criticize phase-space approaches\nto simulating quantum dynamics and claim the impossibility of interpreting\nsingle trajectories of the truncated Wigner (tW) method as single-shot\nexperimental outcomes. Here we aim to provide relevant context and elaborate\nwhy we disagree with the authors' claims.",
        "positive": "Asymmetric Conductivity of the Kondo Effect in Cold Atomic Systems: Motivated by recent theoretical and experimental advances in quantum\nsimulations using alkaline earth(AE) atoms, we put forward a proposal to detect\nthe Kondo physics in a cold atomic system. It has been demonstrated that the\nintrinsic spin-exchange interaction in AE atoms can be significantly enhanced\nnear a confinement-induced resonance(CIR), which facilitates the simulation of\nKondo physics. Since the Kondo effect appears only for antiferromagnetic\ncoupling, we find that the conductivity of such a system exhibits an asymmetry\nacross a resonance of spin-exchange interaction. The asymmetric conductivity\ncan serve as the smoking gun evidence for Kondo physics in the cold atom\ncontext. When an extra magnetic field ramps up, the spin-exchange process near\nthe Fermi surface is suppressed by Zeeman energy and the conductivity becomes\nmore and more symmetric. Our results can be verified in the current\nexperimental setup."
    },
    {
        "anchor": "Instability of superfluid Fermi gases induced by a roton-like density\n  mode in optical lattices: We study the stability of superfluid Fermi gases in deep optical lattices in\nthe BCS--Bose-Einstein condensation (BEC) crossover at zero temperature. Within\nthe tight-binding attractive Hubbard model, we calculate the spectrum of the\nlow-energy Anderson-Bogoliubov (AB) mode as well as the single-particle\nexcitations in the presence of superfluid flow in order to determine the\ncritical velocities. To obtain the spectrum of the AB mode, we calculate the\ndensity response function in the generalized random-phase approximation\napplying the Green's function formalism developed by C\\^ot\\'e and Griffin to\nthe Hubbard model. We find that the spectrum of the AB mode is separated from\nthe particle-hole continuum having the characteristic rotonlike minimum at\nshort wavelength due to the strong charge-density-wave fluctuations. The energy\nof the rotonlike minimum decreases with increasing the lattice velocity and it\nreaches zero at the critical velocity which is smaller than the pair breaking\nvelocity. This indicates that the superfluid state is energetically unstable\ndue to the spontaneous emission of the short-wavelength rotonlike excitations\nof the AB mode instead due to pair-breaking. We determine the critical\nvelocities as functions of the interaction strength across the BCS-BEC\ncrossover regime.",
        "positive": "Non-Local Order Parameters as a Probe for Phase Transitions in the\n  Extended Fermi-Hubbard Model: The Extended Fermi-Hubbard model is a rather studied Hamiltonian due to both\nits many applications and a rich phase diagram. Here we prove that all the\nphase transitions encoded in its one dimensional version are detectable via\nnon-local operators related to charge and spin fluctuations. The main advantage\nin using them is that, in contrast to usual local operators, their asymptotic\naverage value is finite only in the appropriate gapped phases. This makes them\npowerful and accurate probes to detect quantum phase transitions. Our results\nindeed confirm that they are able to properly capture both the nature and the\nlocation of the transitions. Relevantly, this happens also for conducting\nphases with a spin gap, thus providing an order parameter for the\nidentification of superconducting and paired superfluid phases"
    },
    {
        "anchor": "Observation of microscopic confinement dynamics by a tunable topological\n  $\u03b8$-angle: The topological $\\theta$-angle is central to the understanding of a plethora\nof phenomena in condensed matter and high-energy physics such as the strong CP\nproblem, dynamical quantum topological phase transitions, and the\nconfinement--deconfinement transition. Difficulties arise when probing the\neffects of the topological $\\theta$-angle using classical methods, in\nparticular through the appearance of a sign problem in numerical simulations.\nQuantum simulators offer a powerful alternate venue for realizing the\n$\\theta$-angle, which has hitherto remained an outstanding challenge due to the\ndifficulty of introducing a dynamical electric field in the experiment. Here,\nwe report on the experimental realization of a tunable topological\n$\\theta$-angle in a Bose--Hubbard gauge-theory quantum simulator, implemented\nthrough a tilted superlattice potential that induces an effective background\nelectric field. We demonstrate the rich physics due to this angle by the direct\nobservation of the confinement--deconfinement transition of $(1+1)$-dimensional\nquantum electrodynamics. Using an atomic-precision quantum gas microscope, we\ndistinguish between the confined and deconfined phases by monitoring the\nreal-time evolution of particle--antiparticle pairs, which exhibit constrained\n(ballistic) propagation for a finite (vanishing) deviation of the\n$\\theta$-angle from $\\pi$. Our work provides a major step forward in the\nrealization of topological terms on modern quantum simulators, and the\nexploration of rich physics they have been theorized to entail.",
        "positive": "Correlated Topological Phases and Exotic Magnetism with Ultracold\n  Fermions: Motivated by the recent progress in engineering artificial non-Abelian gauge\nfields for ultracold fermions in optical lattices, we investigate the\ntime-reversal-invariant Hofstadter-Hubbard model. We include an additional\nstaggered lattice potential and an artificial Rashba--type spin-orbit coupling\nterm available in experiment. Without interactions, the system can be either a\n(semi)-metal, a normal or a topological insulator, and we present the\nnon-Abelian generalization of the Hofstadter butterfly. Using a combination of\nreal-space dynamical mean-field theory (RDMFT), analytical arguments, and\nMonte-Carlo simulations we study the effect of strong on-site interactions. We\ndetermine the interacting phase diagram, and discuss a scenario of an\ninteraction-induced transition from normal to topological insulator. At\nhalf-filling and large interactions, the system is described by a quantum spin\nHamiltonian, which exhibits exotic magnetic order due to the interplay of\nRashba--type spin-orbit coupling and the artificial time-reversal-invariant\nmagnetic field term. We determine the magnetic phase diagram: both for the\nitinerant model using RDMFT and for the corresponding spin model in the\nclassical limit using Monte-Carlo simulations."
    },
    {
        "anchor": "Resonance Cascades and Number Theory: In this article, we are interested in situations where the existence of a\ncontiguous cascade of quantum resonant transitions is predicated on the\nvalidity of a particular statement in number theory. Unexpectedly, the\nprincipal challenge was posed by the design of the perturbation potential: as\nwe have reported elsewhere, a non-uniform distribution of the transition matrix\nelements leads to a localization that arrests mobility. A significant portion\nof our paper is devoted to ensuring that uniformity.\n  As a case study, we look at the following trivial statement: \"Any power of\n$3$ is an integer.\" Consequently, we \"test\" this statement in a numerical\nexperiment where we demonstrate an un-impeded upward mobility along an\nequidistant, $\\ln(3)$-spaced subsequence of the energy levels of a potential\nwith a log-natural spectrum, under a frequency $\\ln(3)$ time-periodic\nperturbation. We further show when we \"remove\" $9$ from the set of integers --\nby excluding the corresponding energy level from the spectrum -- the cascade\nhalts abruptly.",
        "positive": "Transport of dipolar Bose-Einstein condensates in a one-dimensional\n  optical lattice: We show that magnetic dipolar interactions can stabilize superfluidity in\natomic gases but the dipole alignment direction required to achieve this\nvaries, depending on whether the flow is oscillatory or continuous. If a\ncondensate is made to oscillate through a lattice, damping of the oscillations\ncan be reduced by aligning the dipoles perpendicular to the direction of\nmotion. However, if a lattice is driven continuously through the condensate,\nsuperfluid behavior is best preserved when the dipoles are aligned parallel to\nthe direction of motion. We explain these results in terms of the formation of\ntopological excitations and tunnel barrier heights between lattice sites."
    },
    {
        "anchor": "Resonant enhancement of particle emission from a parametrically driven\n  condensate in a one-dimensional lattice: Motivated by recent experiments, we investigate particle emission from a\nBose-Einstein condensate in a one-dimensional lattice, where the interaction\nstrength is periodically modulated. The modulated interactions parametrically\nexcite a collective mode, leading to density oscillations. These collective\noscillations in turn drive particle emission. This multistep process amplifies\nthe drive, producing larger particle jets. We find that the amplitude\ndependence of the emission rate has a characteristic threshold behavior, as\nseen in experiments.",
        "positive": "Superfluid pairing in a mixture of a spin-polarized Fermi gas and a\n  dipolar condensate: We consider a mixture of a spin-polarized Fermi gas and a dipolar\nBose-Einstein condensate in which s-wave scattering between fermions and the\nquasiparticles of the dipolar condensate can result in an effective attractive\nFermi-Fermi interaction anisotropic in nature and tunable by the dipolar\ninteraction. We show that such an interaction can significantly increase the\nprospect of realizing a superfluid with a gap parameter characterized with a\ncoherent superposition of all odd partial waves. We formulate, in the spirit of\nthe Hartree-Fock-Bogoliubov mean-field approach, a theory which allows us to\nestimate the critical temperature when the anisotropic Fock potential is taken\ninto consideration and to determine the system parameters that optimize the\ncritical temperature at which such a superfluid emerges before the system\nbegins to phase separate."
    },
    {
        "anchor": "Quantum Magnetism with Polar Alkali Dimers: We show that dipolar interactions between ultracold polar alkali dimers in\noptical lattices can be used to realize a highly tunable generalization of the\nt-J model, which we refer to as the t-J-V-W model. The model features\nlong-range spin-spin interactions J_z and J_perp of XXZ type, long-range\ndensity-density interaction V, and long-range density-spin interaction W, all\nof which can be controlled in both magnitude and sign independently of each\nother and of the tunneling t. The \"spin\" is encoded in the rotational degree of\nfreedom of the molecules, while the interactions are controlled by applied\nstatic electric and continuous-wave microwave fields. Furthermore, we show that\nnuclear spins of the molecules can be used to implement an additional (orbital)\ndegree of freedom that is coupled to the original rotational degree of freedom\nin a tunable way. The presented system is expected to exhibit exotic physics\nand to provide insights into strongly correlated phenomena in condensed matter\nsystems. Realistic experimental imperfections are discussed.",
        "positive": "An Ultracold Gas of Bosonic $^{23}\\textrm{Na}^{39}\\textrm{K}$\n  Ground-State Molecules: We report the creation of ultracold bosonic dipolar\n$^{23}\\textrm{Na}^{39}\\textrm{K}$ molecules in their absolute rovibrational\nground state. Starting from weakly bound molecules immersed in an ultracold\natomic mixture, we coherently transfer the dimers to the rovibrational ground\nstate using an adiabatic Raman passage. We analyze the two-body decay in a pure\nmolecular sample and in molecule-atom mixtures and find an unexpectedly low\ntwo-body decay coefficient for collisions between molecules and\n$^{39}\\textrm{K}$ atoms in a selected hyperfine state. The preparation of\nbosonic $^{23}\\textrm{Na}^{39}\\textrm{K}$ molecules opens the way for future\ncomparisons between fermionic and bosonic ultracold ground-state molecules of\nthe same chemical species."
    },
    {
        "anchor": "Localized modes in dense repulsive and attractive Bose-Einstein\n  condensates with spin-orbit and Rabi couplings: We consider a binary Bose-Einstein condensate with linear and nonlinear\ninteractions between its components, which emulate the spinor system with\nspin-orbit (SO) and Rabi couplings. For a relatively dense condensate, 1D\ncoupled equations with the nonpolynomial nonlinearity of both repulsive and\nattractive signs are derived from the 3D Gross-Pitaevskii equations. Profiles\nof modes confined in an external potential under the action of the\nself-repulsion, and self-trapped solitons in the case of the self-attraction,\nare found in a numerical form and by means of analytical approximations. In the\nformer case, the interplay of the SO and Rabi couplings with the repulsive\nnonlinearity strongly distorts shapes of the trapped modes, adding conspicuous\nside lobes to them. In the case of the attractive nonlinearity, the most\nessential result is reduction of the collapse threshold under the action of the\nSO and Rabi couplings.",
        "positive": "Moving perturbation in a one-dimensional Fermi gas: We simulate a balanced attractively interacting two-component Fermi gas in a\none-dimensional lattice perturbed with a moving potential well or barrier.\nUsing the time-evolving block decimation method, we study different velocities\nof the perturbation and distinguish two velocity regimes based on clear\ndifferences in the time evolution of particle densities and the pair\ncorrelation function. We show that, in the slow regime, the densities deform as\nparticles are either attracted by the potential well or repelled by the\nbarrier, and a wave front of hole or particle excitations propagates at the\nmaximum group velocity. Simultaneously, the initial pair correlations are\nbroken and coherence over different sites is lost. In contrast, in the fast\nregime, the densities are not considerably deformed and the pair correlations\nare preserved."
    },
    {
        "anchor": "Entanglement spectrum of one-dimensional extended Bose-Hubbard models: The entanglement spectrum provides crucial information about correlated\nquantum systems. We show that the study of the block-like nature of the reduced\ndensity matrix in number sectors and the partition dependence of the spectrum\nin finite systems leads to interesting unexpected insights, which we illustrate\nfor the case of a 1D extended Hubbard model. We show that block symmetry\nprovides an intuitive understanding of the spectral double degeneracy of the\nHaldane-insulator, revealing as well partial double degeneracy for the\nMott-insulator. Moreover, surprisingly, the partition dependence of the\nspectral degeneracy in the Haldane- and Mott-insulator is directly linked to\nthe, in principle unrelated, density-density correlations, and presents an\nintriguing periodic behavior in superfluid and supersolid phases.",
        "positive": "Quantum XY criticality in a two-dimensional Bose gas near the Mott\n  transition: We derive the equation of state of a two-dimensional Bose gas in an optical\nlattice in the framework of the Bose-Hubbard model. We focus on the vicinity of\nthe multicritical points where the quantum phase transition between the Mott\ninsulator and the superfluid phase occurs at fixed density and belongs to the\nthree-dimensional XY model universality class. Using a nonperturbative\nrenormalization-group approach, we compute the pressure $P(\\mu,T)$ as a\nfunction of chemical potential and temperature. Our results compare favorably\nwith a calculation based on the quantum O(2) model -- we find the same\nuniversal scaling function -- and allow us to determine the region of the phase\ndiagram in the vicinity of a quantum multicritical point where the equation of\nstate is universal. We also discuss the possible experimental observation of\nquantum XY criticality in a ultracold gas in an optical lattice."
    },
    {
        "anchor": "How to measure the free energy and partition function from atom-atom\n  correlations: We propose an experimental approach for determining thermodynamic properties\nof ultracold atomic gases with short-range interactions. As a test case, we\nfocus on the one-dimensional (1D) Bose gas described by the integrable\nLieb-Liniger model. The proposed approach relies on deducing the Helmholtz or\nLandau free energy directly from measurements of local atom-atom correlations\nby utilising the inversion of a finite-temperature version of the\nHellmann-Feynman theorem. We demonstrate this approach theoretically by\nderiving approximate analytic expressions for the free energies in specific\nasymptotic regimes of the 1D Bose gas and find excellent agreement with the\nexact results based on the thermodynamic Bethe ansatz available for this\nintegrable model.",
        "positive": "Pairing, Ferromagnetism, and Condensation of a normal spin-1 Bose gas: We theoretically study the stability of a normal, spin disordered, homogenous\nspin-1 Bose gas against ferromagnetism, pairing, and condensation through a\nRandom Phase Approximation which includes exchange (RPA-X). Repulsive\nspin-independent interactions stabilize the normal state against both\nferromagnetism and pairing, and for typical interaction strengths leads to a\ndirect transition from an unordered normal state to a fully ordered single\nparticle condensate. Atoms with much larger spin-dependent interaction may\nexperience a transition to a ferromagnetic normal state or a paired superfluid,\nbut, within the RPA-X, there is no instability towards a normal state with\nspontaneous nematic order. We analyze the role of the quadratic Zeeman effect\nand finite system size."
    },
    {
        "anchor": "i-SPin 2: An integrator for general spin-s Gross-Pitaevskii systems: We provide an algorithm for evolving general spin-$s$ Gross-Pitaevskii /\nnon-linear Schr\\\"odinger systems carrying a variety of interactions, where the\n$2s+1$ components of the `spinor' field represent the different\nspin-multiplicity states. We consider many nonrelativistic interactions up to\nquartic order in the Schr\\\"odinger field (both short and long-range, and\nspin-dependent and spin-independent interactions), including explicit\nspin-orbit couplings. The algorithm allows for spatially varying external\nand/or self-generated vector potentials that couple to the spin density of the\nfield. Our work can be used for scenarios ranging from laboratory systems such\nas spinor Bose-Einstein condensates (BECs), to cosmological/astrophysical\nsystems such as self-interacting bosonic dark matter. As examples, we provide\nresults for two different setups of spin-$1$ BECs that employ a varying\nmagnetic field and spin-orbit coupling, respectively, and also collisions of\nspin-$1$ solitons in dark matter. Our symplectic algorithm is second-order\naccurate in time, and is extensible to the known higher-order accurate methods.",
        "positive": "Emission of Spin-correlated Matter-wave Jets from Spinor Bose-Einstein\n  Condensates: We report the observation of matter-wave jet emission in a strongly\nferromagnetic spinor Bose-Einstein condensate of $^7$Li atoms. Directional\natomic beams with $|{F=1,m_F=1}\\rangle$ and $|{F=1,m_F=-1}\\rangle$ spin states\nare generated from $|{F=1,m_F=0}\\rangle$ state condensates, or vice versa. This\nresults from collective spin-mixing scattering events, where spontaneously\nproduced pairs of atoms with opposite momentum facilitates additional\nspin-mixing collisions as they pass through the condensates. The matter-wave\njets of different spin states ($|{F=1,m_F=\\pm1}\\rangle$) can be a macroscopic\nEinstein-Podolsky-Rosen state with spacelike separation. Its spin-momentum\ncorrelations are studied by using the angular correlation function for each\nspin state. Rotating the spin axis, the inter-spin and intra-spin momentum\ncorrelation peaks display a high contrast oscillation, indicating collective\ncoherence of the atomic ensembles. We provide numerical calculations that\ndescribe the experimental results at a quantitative level and can identify its\nentanglement after 100~ms of a long time-of-flight."
    },
    {
        "anchor": "Disorder-Free Localization in $2+1$D Lattice Gauge Theories with\n  Dynamical Matter: Disorder-free localization (DFL) has been established as a mechanism of\nstrong ergodicity breaking in $1+1$D lattice gauge theories (LGTs) with\ndynamical matter for quenches starting in homogeneous initial states that span\nan extensive number of gauge superselection sectors. Nevertheless, the fate of\nDFL in $2+1$D in the presence of dynamical matter has hitherto remained an open\nquestion of great interest in light of the instability of quenched-disorder\nmany-body localization in higher spatial dimensions. Using infinite matrix\nproduct state calculations, we show that DFL survives in $2+1$D LGTs, albeit it\nis generally less pronounced than in $1+1$D, and highly depends on the matter\nconfiguration of the initial state. Through suitable matter configurations, we\nare able to relate and compare the $1+1$D and $2+1$D cases, showing that the\nmain ingredient for the strength of DFL in our setup is the \\textit{propagation\ndirectionality} of matter. Our results suggest that, generically, DFL is\nweakened with increasing spatial dimension, although it can be made independent\nof the latter by minimizing the propagation directionality of matter in the\ninitial state.",
        "positive": "Bunching-antibunching crossover in harmonically trapped few-body\n  Bose-Fermi mixtures: We investigate the ground state of a few-body Bose-Fermi mixture in a\none-dimensional harmonic trap with varying interaction strengths and mass\nratio. A bunching-antibunching crossover of the bosonic species for increasing\ninterspecies' repulsion is observed within our fully correlated\n\\textit{ab~initio} studies. Interestingly, this crossover is suppressed if the\nbosonic repulsion exceeds a critical value which strongly depends on the mass\nratio. In order to unveil the physical origin of this crossover, we employ\ndifferent levels of approximations: while a species mean-field approach can\naccount for the antibunching, only the inclusion of the interspecies\ncorrelations can lead to the bunching. We show that these correlations\neffectively create an induced bosonic interaction, which in turn elucidates the\noccurrence of the bosonic bunching. Finally, we derive a two-site extended\nBose-Hubbard model which reveals the low-energy physics of the bosons for the\ncase of much heavier fermions."
    },
    {
        "anchor": "Suppression of collision-induced dephasing by periodic, erratic, or\n  noisy driving: We compare different driving scenarios for controlling the loss of single\nparticle coherence of an initially coherent preparation in the vicinity of the\nhyperbolic instability of the two-mode bose-Hubbard model. In particular we\ncontrast the quantum Zeno suppression of decoherence by broad-band erratic or\nnoisy driving, with the Kapitza effect obtained for high frequency periodic\nmonochromatic driving.",
        "positive": "Spin diffusion of lattice fermions in one dimension: We study long-time spin diffusion of harmonically trapped lattice fermions in\none dimension. Combining thermodynamic Bethe ansatz approach and local density\napproximation, we calculate spin current and spin diffusion coefficient driven\nby the population imbalance. We find spin current is driven by susceptibility\neffects rather than typical diffusion where magnetization would transport from\nregions of high magnetization to low. As expected, spin transport is zero\nthrough insulating regions and are only present in the metallic regions. In the\nweak coupling limit, the local spin diffusion coefficient shows maxima at all\nthe insulating regions. Further, we estimate damping rate of diffusion modes in\nthe weak coupling limit within the lower metallic portion of the cloud. The\npredicted spin current pattern can be probed via currently available\nexperimental techniques."
    },
    {
        "anchor": "Unitary work extraction from a Generalized Gibbs Ensemble using Bragg\n  scattering: We investigate work extraction from integrable quantum systems under unitary\noperations. As a model system, we consider non-interacting fermions in one\ndimension. Thanks to its integrability, this system does not thermalize after a\nperturbation, even though it does reach a steady state which can be described\nby a Generalized Gibbs Ensemble (GGE). Such a GGE has an excess free energy\ncompared to a thermal state and we propose to extract this energy by applying\nBragg pulses. We show how all the available work in the GGE can be extracted in\nthe adiabatic limit while some excess energy is left at finite times. The\nunextracted work reaches the adiabatic limit as a power law with exponent\n$z=-2$ for small systems and with $z=-1$ in the thermodynamic limit. Two\ndistinct protocols for combining the Bragg operations are compared, and in some\nsystems an extensive difference in efficiency arises. From the unextracted work\nand the entropy production, a notion of temperature is defined and compared to\nthe Boltzmann-Gibbs temperature of the system.",
        "positive": "Trimers, molecules and polarons in imbalanced atomic Fermi gases: We consider the ground state of a single \"spin-down\" impurity atom\ninteracting attractively with a \"spin-up\" atomic Fermi gas. By constructing\nvariational wave functions for polarons, molecules and trimers, we perform a\ndetailed study of the transitions between each of these dressed bound states as\na function of mass ratio $r=m_\\uparrow/m_\\downarrow$ and interaction strength.\nWe find that the presence of a Fermi sea enhances the stability of the $p$-wave\ntrimer, which can be viewed as a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)\nmolecule that has bound an additional majority atom. For sufficiently large\n$r$, we find that the transitions lie outside the region of phase separation in\nimbalanced Fermi gases and should thus be observable in experiment, unlike the\nwell-studied equal-mass case."
    },
    {
        "anchor": "Spin- and Momentum-Correlated Atom Pairs Mediated by Photon Exchange and\n  Seeded by Vacuum Fluctuations: Engineering pairs of massive particles that are simultaneously correlated in\ntheir external and internal degrees of freedom is a major challenge, yet\nessential for advancing fundamental tests of physics and quantum technologies.\nIn this Letter, we experimentally demonstrate a mechanism for generating pairs\nof atoms in well-defined spin and momentum modes. This mechanism couples atoms\nfrom a degenerate Bose gas via a superradiant photon-exchange process in an\noptical cavity, producing pairs via a single channel or two discernible\nchannels. The scheme is independent of collisional interactions, fast and\ntunable. We observe a collectively enhanced production of pairs and probe\ninterspin correlations in momentum space. We characterize the emergent pair\nstatistics and find that the observed dynamics is consistent with being\nprimarily seeded by vacuum fluctuations in the corresponding atomic modes.\nTogether with our observations of coherent many-body oscillations involving\nwell-defined momentum modes, our results offer promising prospects for\nquantum-enhanced interferometry and quantum simulation experiments using\nentangled matter waves.",
        "positive": "Excess energy of an ultracold Fermi gas in a trapped geometry: We have analytically explored finite size and interparticle interaction\ncorrections to the average energy of a harmonically trapped Fermi gas below and\nabove the Fermi temperature, and have obtained a better fitting for the excess\nenergy reported by DeMarco and Jin [Science $\\textbf{285}$, 1703 (1999)]. We\nhave presented a perturbative calculation within a mean field approximation."
    },
    {
        "anchor": "Resonant dipolar collisions of ultracold molecules induced by microwave\n  dressing: We demonstrate microwave dressing on ultracold, fermionic\n${}^{23}$Na${}^{40}$K ground-state molecules and observe resonant dipolar\ncollisions with cross sections exceeding three times the $s$-wave unitarity\nlimit. The origin of these collisions is the resonant alignment of the\napproaching molecules' dipoles along the intermolecular axis, which leads to\nstrong attraction. We explain our observations with a conceptually simple\ntwo-state picture based on the Condon approximation. Furthermore, we perform\ncoupled-channels calculations that agree well with the experimentally observed\ncollision rates. While collisions are observed here as laser-induced loss,\nmicrowave dressing on chemically stable molecules trapped in box potentials may\nenable the creation of strongly interacting dipolar gases of molecules.",
        "positive": "Ground State Geometry of Binary Condensates in Axisymmetric Traps: We show that the ground state interface geometry of binary condensates in the\nphase separated regime undergoes a smooth transition from planar to ellipsoidal\nto cylindrical geometry. This occurs for condensates with repulsive\ninteractions as the trapping potential is changed from prolate to oblate. The\ncorrect ground state geometry emerges when the interface energy is included in\nthe energy minimization. Where as energy minimization based on Thomas-Fermi\napproximation gives incorrect geometry."
    },
    {
        "anchor": "Quantum Mass Acquisition in Spinor Bose-Einstein Condensates: Quantum mass acquisition, in which a massless (quasi)particle becomes massive\ndue to quantum corrections, is predicted to occur in several subfields of\nphysics. However, its experimental observation remains elusive since the\nemergent energy gap is too small. We show that a spinor Bose-Einstein\ncondensate is an excellent candidate for the observation of such a peculiar\nphenomenon as the energy gap turns out to be 2 orders of magnitude larger than\nthe zero-point energy. This extraordinarily large energy gap is a consequence\nof the dynamical instability. The propagation velocity of the resultant massive\nexcitation mode is found to be decreased by the quantum corrections as opposed\nto phonons.",
        "positive": "Single-particle vs. pair superfluidity in a bilayer system of dipolar\n  bosons: We consider the ground state of a bilayer system of dipolar bosons, where\ndipoles are oriented by an external field in the direction perpendicular to the\nparallel planes. Quantum Monte Carlo methods are used to calculate the\nground-state energy, the one-body and two-body density matrix, and the\nsuperfluid response as a function of the separation between layers. We find\nthat by decreasing the interlayer distance for fixed value of the strength of\nthe dipolar interaction, the system undergoes a quantum phase transition from a\nsingle-particle to a pair superfluid. The single-particle superfluid is\ncharacterized by a finite value of both the atomic condensate and the\nsuper-counterfluid density. The pair superfluid phase is found to be stable\nagainst formation of many-body cluster states and features a gap in the\nspectrum of elementary excitations."
    },
    {
        "anchor": "Controllable Finite-Momenta Dynamical Quasicondensation in the\n  Periodically Driven One-Dimensional Fermi-Hubbard Model: In the strongly interacting limit of the Hubbard model localized\ndouble-occupancies form effective hard-core bosonic excitations, called a\ndoublons, which are long-lived due to energy conservation. Using time-dependent\ndensity-matrix renormalisation group we investigate numerically the dynamics of\ndoublons arising from the sudden expansion of a spatially confined\nband-insulating state in one spatial dimension. By analysing the occupation\nscaling of the natural orbitals within the many-body state, we show that\ndoublons dynamically quasicondense at the band edges, consistent with the\nspontaneous emergence of an eta-quasicondensate. Building on this, we study the\neffect of periodically driving the system during the expansion. Floquet\nanalysis reveals that doublon-hopping and doublon-repulsion are strongly\nrenormalised by the drive, breaking the eta-SU(2) symmetry of the Hubbard\nmodel. Numerical simulation of the driven expansion dynamics demonstrate that\nthe momentum in which doublons quasicondense can be controlled by the driving\namplitude. These results point to new pathways for engineering non-equilibrium\ncondensates in fermionic cold-atom experiments and are potentially relevant to\ndriven solid-state systems.",
        "positive": "Ultracold bosonic scattering dynamics off a repulsive barrier: coherence\n  loss at the dimensional crossover: We explore the impact of dimensionality on the scattering of a small bosonic\nensemble in an elongated harmonic trap off a centered repulsive barrier,\nthereby taking particle correlations into account. The loss of coherence as\nwell as the oscillation of the center of mass are studied and we analyze the\ninfluence of both particle and spatial correlations. Two different mechanisms\nof coherence losses in dependence of the aspect ratio are found. For small\naspect ratios, loss of coherence between the region close to the barrier and\nouter regions occurs, due to spatial correlations, and for large aspect ratios,\nincoherence between the two density fragments of the left and right side of the\nbarrier arises, due to particle correlations. Apart form the decay of the\ncenter of mass motion induced by the reflection and transmission, further\neffects due to the particle and spatial correlations are explored. For tight\ntransversal traps, the amplitude of the center of mass oscillation experiences\na weaker damping, which can be traced back to the population of a second\nnatural orbital, and for a weaker transversal confinement, we detect a strong\ndecay, due to the possibility of transferring energy to transversal excited\nmodes. These effects are enhanced if the aspect ratio is integer valued."
    },
    {
        "anchor": "Local quench spectroscopy of many-body quantum systems: Quench spectroscopy is a relatively new method which enables the\ninvestigation of spectral properties of many-body quantum systems by monitoring\nthe out-of-equilibrium dynamics of real-space observables after a quench. So\nfar the approach has been devised for global quenches or using local\nengineering of momentum-resolved excitations. Here, we extend the quench\nspectroscopy method to local quenches. We show that it allows us to extract\nquantitative information about global properties of the system, and in\nparticular the elementary excitation spectrum. Using state-of-the-art numerical\nmethods, we simulate the out-of-equilibrium dynamics of a variety of quantum\nsystems following various local quench protocols and demonstrate a general\nscheme for designing an appropriate local quench protocol for any chosen model.\nWe provide detailed examples of how the local quench protocol can be realised\nin realistic current generation experiments, including ultracold atomic gases\nand trapped ion systems.",
        "positive": "Phase characterization of spinor Bose-Einstein condensates: a Majorana\n  stellar representation approach: We study the variational perturbations for the mean-field solution of an\ninteracting spinor system with underlying rotational symmetries. An approach\nbased upon the Majorana stellar representation for mixed states and group\ntheory is introduced to this end. The method reduces significantly the unknown\ndegrees of freedom of the perturbation, allowing us a simplified and direct\nexploration on emergent physical phenomena. We apply it to characterize the\nphases of a spin-1 Bose-Einstein condensate and to study the behavior of these\nphases with entropy. The spin-2 phase diagram was also investigated within the\nHartree-Fock approximation, where a non-linear deviation of the cyclic-nematic\nphase boundary with temperature is predicted."
    },
    {
        "anchor": "Hole-induced anomaly in the thermodynamic behavior of a one-dimensional\n  Bose gas: We reveal an intriguing anomaly in the temperature dependence of the specific\nheat of a one-dimensional Bose gas. The observed peak holds for arbitrary\ninteraction and remembers a superfluid-to-normal phase transition in higher\ndimensions, but phase transitions are not allowed in one dimension. The\npresence of the anomaly signals a region of unpopulated states which behaves as\nan energy gap and is located below the hole branch in the excitation spectrum.\nThe anomaly temperature is found to be of the same order of the energy of the\nmaximum of the hole branch. We rely on the Bethe Ansatz to obtain the specific\nheat exactly and provide interpretations of the analytically tractable limits.\nThe dynamic structure factor is computed with the Path Integral Monte Carlo\nmethod for the first time. We notice that at temperatures similar to the\nanomaly threshold, the energy of the thermal fluctuations become comparable\nwith the maximal hole energy, leading to a qualitative change in the structure\nof excitations. This excitation pattern experiences the breakdown of the\nquasi-particle description for any value of the interaction strength at the\nanomaly, similarly to any superfluid phase transition at the critical\ntemperature. We provide indications for future observations and how the hole\nanomaly can be employed for in-situ thermometry, identifying different\ncollisional regimes and understanding other anomalies in atomic, solid-state,\nelectronic, spin-chain and ladder systems.",
        "positive": "Multichannel Molecular State and Rectified Short-range Boundary\n  Condition for Spin-orbit Coupled Ultracold Fermions Near p-wave Resonances: We study the interplay of spin-orbit coupling (SOC) and strong p-wave\ninteraction to the scattering property of spin-1/2 ultracold Fermi gases. Based\non a two-channel square-well potential generating p-wave resonance, we show\nthat the presence of an isotropic SOC, even for its length much longer than the\npotential range, can greatly modify the p-wave short-range boundary\ncondition(BC). As a result, the conventional p-wave BC cannot predict the\ninduced molecules near p-wave resonance, which can be fully destroyed to vanish\ndue to strong interference between s- and p-wave channels. By analyzing the\nintrinsic reasons for the breakdown of conventional BC, we propose a new p-wave\nBC that can excellently reproduce the exact molecule solutions and also equally\napply for a wide class of single-particle potentials besides SOC. This work\nreveals the significant effect of SOC to both the short- and long-range\nproperties of fermions near p-wave resonance, paving the way for future\nexploring interesting few- and many-body physics in such system."
    },
    {
        "anchor": "Spin-polarized vortices with reversed circulation: We present the analysis of the structure of fermionic vortices with the\nspin-polarized core from a weak coupling limit to the unitary regime. We show\nthe mechanism for the generation of the {\\it reversed circulation} in the\nvortex core induced by an excess of majority spin particles. We introduce the\nclassification of the polarized vortices based on the number of Fermi circles\nwhere the minigap vanishes. This provides a unique description of the vortex as\none cannot smoothly map wave functions into one another corresponding to\nvortices differing by the number of Fermi circles. The effective mass of\nquasiparticles along the vortex core is analyzed and its role in the\npropagation of spin-polarization along the vortex line is discussed.",
        "positive": "Effective theory for ultracold strongly interacting fermionic atoms in\n  two dimensions: We propose a minimal theoretical model for the description of a\ntwo-dimensional (2D) strongly interacting Fermi gas confined transversely in a\ntight harmonic potential, and present accurate predictions for its equation of\nstate and breathing mode frequency. We show that the minimal model Hamiltonian\nneeds at least two independent interaction parameters, the 2D scattering length\nand effective range of interactions, in order to quantitatively explain recent\nexperimental measurements at nonzero filling factor $N/N_{2D}$, where $N$ is\nthe total number of atoms and $N_{2D}$ is the threshold number to reach the 2D\nlimit. We therefore resolve in a satisfactory way the puzzling experimental\nobservations of reduced equations of state and reduced quantum anomaly in\nbreathing mode frequency, due to small yet non-negligible $N/N_{2D}$. We argue\nthat a conclusive demonstration of the much-anticipated quantum anomaly is\npossible at a filling factor of a few percent. Our establishment of the minimal\nmodel for 2D ultracold atoms could be crucial to understanding the fermionic\nBerezinskii-Kosterlitz-Thouless transition in the strongly correlated regime."
    },
    {
        "anchor": "Pattern formation in one-dimensional polaron systems and temporal\n  orthogonality catastrophe: Recent studies have demonstrated that higher than two-body bath-impurity\ncorrelations are not important for quantitatively describing the ground state\nof the Bose polaron. Motivated by the above, we employ the so-called Gross\nAnsatz (GA) approach to unravel the stationary and dynamical properties of the\nhomogeneous one-dimensional Bose-polaron for different impurity momenta and\nbath-impurity couplings. We explicate that the character of the equilibrium\nstate crossovers from the quasi-particle Bose polaron regime to the\ncollective-excitation stationary dark-bright soliton for varying impurity\nmomentum and interactions. Following an interspecies interaction quench the\ntemporal orthogonality catastrophe is identified, provided that bath-impurity\ninteractions are sufficiently stronger than the intraspecies bath ones, thus\ngeneralizing the results of the confined case. This catastrophe originates from\nthe formation of dispersive shock wave structures associated with the\nzero-range character of the bath-impurity potential. For initially moving\nimpurities, a momentum transfer process from the impurity to the dispersive\nshock waves via the exerted drag force is demonstrated, resulting in a final\npolaronic state with reduced velocity. Our results clearly demonstrate the\ncrucial role of non-linear excitations for determining the behavior of the\none-dimensional Bose polaron.",
        "positive": "Persistent current oscillations in a double-ring quantum gas: Vorticity in closed quantum fluid circuits is known to arise in the form of\npersistent currents. In this work, we develop a method to engineer transport of\nthe quantized vorticity between density-coupled ring-shaped atomic\nBose-Einstein condensates in experimentally accessible regimes. Introducing a\ntunable weak link between the rings, we observe and characterize the\ncontrollable periodic transfer of the current and investigate the role of\ntemperature on suppressing these oscillations via a range of complementary\nstate-of-the-art numerical methods. Our setup paves the way for precision\nmeasurements of local acceleration and rotation."
    },
    {
        "anchor": "Magnetic solitons in Rabi-coupled Bose-Einstein condensates: We study magnetic solitons, solitary waves of spin polarization (i.e.,\nmagnetization), in binary Bose-Einstein condensates in the presence of Rabi\ncoupling. We show that the system exhibits two types of magnetic solitons,\ncalled $2\\pi$ and $0\\pi$ solitons, characterized by a different behavior of the\nrelative phase between the two spin components. $2\\pi$ solitons exhibit a\n$2\\pi$ jump of the relative phase, independent of their velocity, the static\ndomain wall explored by Son and Stephanov being an example of such $2\\pi$\nsolitons with vanishing velocity and magnetization. $0\\pi$ solitons instead do\nnot exhibit any asymptotic jump in the relative phase. Systematic results are\nprovided for both types of solitons in uniform matter. Numerical calculations\nin the presence of a one-dimensional harmonic trap reveal that a $2\\pi$ soliton\nevolves in time into a $0\\pi$ soliton, and vice versa, oscillating around the\ncenter of the trap. Results for the effective mass, the Landau critical\nvelocity, and the role of the transverse confinement are also discussed.",
        "positive": "Polarizing the Medium: Fermion-Mediated Interactions between Bosons: We consider a homogeneous mixture of bosons and polarized fermions. We find\nthat long-range and attractive fermion-mediated interactions between bosons\nhave dramatic effects on the properties of the bosons. We construct the phase\ndiagram spanned by boson-fermion mass ratio and boson-fermion scattering\nparameter. It consists of stable region of mixing and unstable region toward\nphase separation. In stable mixing phase, the collective long-wavelength\nexcitations can either be well-behaved with infinite lifetime or be finite in\nlifetime suffered from the Landau damping. We examine the effects of the\ninduced interaction on the properties of weakly interacting bosons. It turns\nout that the induced interaction not only enhances the repulsion between the\nbosons against collapse but also enhances the stability of the superfluid state\nby suppressing quantum depletion."
    },
    {
        "anchor": "Phase and group velocities for correlation spreading in the Mott phase\n  of the Bose-Hubbard model in dimensions greater than one: Lieb-Robinson and related bounds set an upper limit on the rate of spreading\nof information in non-relativistic quantum systems. Experimentally, they have\nbeen observed in the spreading of correlations in the Bose-Hubbard model after\na quantum quench. Using a recently developed two particle irreducible (2PI)\nstrong coupling approach to out-of-equilibrium dynamics in the Bose-Hubbard\nmodel we calculate both the group and phase velocities for the spreading of\nsingle-particle correlations in one, two and three dimensions as a function of\ninteraction strength. Our results are in quantitative agreement with\nmeasurements of the velocities for the spreading of single particle\ncorrelations in both the one and two dimensional Bose-Hubbard model realized\nwith ultra-cold atoms. They also agree with the claim that the phase velocity\nrather than the group velocity was observed in recent experiments in two\ndimensions. We demonstrate that there can be large differences between the\nphase and group velocities for the spreading of correlations and also explore\nthe variation of the anisotropy in the velocity at which correlations spread\nacross the phase diagram of the Bose-Hubbard model. Our results establish the\n2PI strong coupling approach as a powerful tool to study out-of-equilibrium\ndynamics in the Bose-Hubbard model in dimensions greater than one.",
        "positive": "Roton immiscibility in a two-component dipolar Bose gas: We characterize the immiscibility-miscibility transition (IMT) of a\ntwo-component Bose-Einstein condensate (BEC) with dipole-dipole interactions.\nIn particular, we consider the quasi-two dimensional geometry, where a strong\ntrapping potential admits only zero-point motion in the trap direction, while\nthe atoms are more free to move in the transverse directions. We employ the\nBogoliubov treatment of the two-component system to identify both the\nwell-known long-wavelength IMT in addition to a roton-like IMT, where the\ntransition occurs at finite-wave number and is reminiscent of the roton\nsoftening in the single component dipolar BEC. Additionally, we verify the\nexistence of the roton IMT in the fully trapped, finite systems by direct\nnumerical simulation of the two-component coupled non-local Gross-Pitaevskii\nequations."
    },
    {
        "anchor": "Direct Observation of Fragmentation in a Disordered, Strongly\n  Interacting Fermi Gas: Describing the behaviour of strongly interacting particles in the presence of\ndisorder is among the most challenging problems in quantum many-body physics.\nThe controlled setting of cold atom experiments provides a new avenue to\naddress these challenges [1], complementing studies in solid state physics,\nwhere a number of puzzling findings have emerged in experiments using\nsuperconducting thin films [2,3]. Here we investigate a strongly interacting\nthin film of an atomic Fermi gas subject to a random potential. We use\nhigh-resolution in-situ imaging [4-7] to resolve the atomic density at the\nlength scale of a single impurity, which would require scanning probe\ntechniques in solid state physics [8]. This allows us to directly observe the\nfragmentation of the density profile and to extract its percolation properties.\nTransport measurements in a two-terminal configuration indicate that the\nfragmentation process is accompanied by a breakdown of superfluidity. Our\nresults suggest that percolation of paired atoms is responsible for the loss of\nsuperfluidity, and that disorder is able to increase the binding energy of\npairs.",
        "positive": "Lifetime of double occupancies in the Fermi-Hubbard model: We investigate the decay of artificially created double occupancies in a\nrepulsive Fermi-Hubbard system in the strongly interacting limit using\ndiagrammatic many-body theory and experiments with ultracold fermions on\noptical lattices. The lifetime of the doublons is found to scale exponentially\nwith the ratio of the on-site repulsion to the bandwidth. We show that the\ndominant decay process in presence of background holes is the excitation of a\nlarge number of particle hole pairs to absorb the energy of the doublon. We\nalso show that the strongly interacting nature of the background state is\ncrucial in obtaining the correct estimate of the doublon lifetime in these\nsystems. The theoretical estimates and the experimental data are in fair\nquantitative agreement."
    },
    {
        "anchor": "One-dimensional Bose gas in optical lattices of arbitrary strength: One-dimensional Bose gas with contact interaction in optical lattices at zero\ntemperature is investigated by means of the exact diffusion Monte Carlo\nalgorithm. The results obtained from the fundamental continuous model are\ncompared with those obtained from the lattice (discrete) Bose-Hubbard model,\nusing exact diagonalization, and from the quantum sine-Gordon model. We map out\nthe complete phase diagram of the continuous model and determine the regions of\napplicability of the Bose-Hubbard model. Various physical quantities\ncharacterizing the systems are calculated and it is demonstrated that the\nsine-Gordon model used for shallow lattices is inaccurate.",
        "positive": "Non-adiabatic quantum phase transition in a trapped spinor condensate: We study the effect of an external harmonic trapping potential on an outcome\nof the non-adiabatic quantum phase transition from an antiferromagnetic to a\nphase-separated state in a spin-1 atomic condensate. Previously, we\ndemonstrated that the dynamics of an untrapped system exhibits double\nuniversality with two different scaling laws appearing due to conservation of\nmagnetization. We show that in the presence of a trap double universality\npersists. However, the corresponding scaling exponents are strongly modified by\ntransfer of local magnetization across the system. The values of these\nexponents cannot be explained by the effect of causality alone, as in the\nspinless case. We derive the appropriate scaling laws based on a slow\ndiffusive-drift relaxation process in the local density approximation."
    },
    {
        "anchor": "Floquet operator engineering for quantum state stroboscopic\n  stabilization: Optimal control is a valuable tool for quantum simulation, allowing for the\noptimized preparation, manipulation, and measurement of quantum states. Through\nthe optimization of a time-dependent control parameter, target states can be\nprepared to initialize or engineer specific quantum dynamics. In this work, we\nfocus on the tailoring of a unitary evolution leading to the stroboscopic\nstabilization of quantum states of a Bose-Einstein condensate in an optical\nlattice. We show how, for states with space and time symmetries, such an\nevolution can be derived from the initial state-preparation controls; while for\na general target state we make use of quantum optimal control to directly\ngenerate a stabilizing Floquet operator. Numerical optimizations highlight the\nexistence of a quantum speed limit for this stabilization process, and our\nexperimental results demonstrate the efficient stabilization of a broad range\nof quantum states in the lattice.",
        "positive": "Complex scaling flows in the quench dynamics of interacting particles: Many-body systems driven out of equilibrium can exhibit scaling flows of the\nquantum state. For a sudden quench to resonant interactions between particles\nwe construct a new class of analytical scaling solutions for the time evolved\nwave function with a complex scale parameter. These solutions determine the\nexact dynamical scaling of observables such as the pair correlation function,\nthe contact and the fidelity. We give explicit examples of the nonequilibrium\ndynamics for two trapped fermions or bosons quenched to unitarity, for ideal\nBose polarons, and for resonantly interacting, Borromean three-body systems.\nThese solutions reveal universal scaling properties of interacting many-body\nsystems that arise from the buildup of correlations at short times after the\nquench."
    },
    {
        "anchor": "Appropriate conditions to realize a $p$-wave superfluid state starting\n  from a spin-orbit coupled $s$-wave superfluid Fermi gas: We theoretically investigate a spin-orbit coupled $s$-wave superfluid Fermi\ngas, to examine the time evolution of the system, after an $s$-wave pairing\ninteraction is replaced by a $p$-wave one at $t=0$. In our recent paper, we\nproposed that this manipulation may realize a $p$-wave superfluid Fermi gas,\nbecause the $p$-wave pair amplitude that is induced in the $s$-wave superfluid\nstate by a parity-broken antisymmetric spin-orbit interaction gives a\nnon-vanishing $p$-wave superfluid order parameter, immediately after the\n$p$-wave interaction is turned on. In this paper, using a time-dependent\nBogoliubov-de Gennes theory, we assess this idea under various conditions with\nrespect to the $s$-wave and $p$-wave interaction strengths, as well as the\nspin-orbit coupling strength. From these, we clarify that the momentum\ndistribution of Fermi atoms in the initial $s$-wave state ($t<0$) is a key to\nproduce a large $p$-wave superfluid order parameter. Since the realization of a\n$p$-wave superfluid state is one of the most exciting and difficult challenges\nin cold Fermi gas physics, our results may provide a possible way to accomplish\nthis.",
        "positive": "Realizing the Hayden-Preskill Protocol with Coupled Dicke Models: Hayden and Preskill proposed a thought experiment that Bob can recover the\ninformation Alice throws into a black hole if he has a quantum computer\nentangled with the black hole, and Yoshida and Kitaev recently proposed a\nconcrete decoding scheme. The parallel question is that after a small system is\nthermalized with a large system, how one can decode the initial state\ninformation with the help of two entangled many-body systems. Here we propose\nto realize this protocol in a physical system of two Dicke models, with two\ncavity fields prepared in a thermofield double state. We show that the\nYoshida-Kitaev protocol allows us to read out the initial spin information\nafter it is scrambled into the cavity. We show that the readout efficiency\nreaches a maximum when the model parameter is tuned to the regime where the\nsystem is the most chaotic, characterized by the shortest scrambling time in\nthe out-of-time-ordered correlation function. Our proposal opens up the\npossibility of discussing this profound thought experiment in a realistic\nsetting."
    },
    {
        "anchor": "Permutation cycles of hardcore Bose-Hubbard models on square and Kagome\n  lattices: In this paper, we study the statistics of permutation cycles of ground-state\nhardcore lattice bosons described by various two-dimensional Bose-Hubbard-type\nmodels on both square and Kagome lattices. We find that it is possible to\ndifferentiate quantum phases by the statistics of permutations cycles. Indeed,\nfeatures in the permutation cycles statistics can be used to uniquely identify\ncertain insulating phases, and are consistent with local resonances of\noccupation numbers in the ground-state expansion of the phase. We also confirm\nthat suitable quantities derived from the probability distribution of the\nlength of permutation cycles can be used to detect superfluid to insulator\nphase transitions.",
        "positive": "Universal four-component Fermi gas in one dimension: A four-component Fermi gas in one dimension with a short-range four-body\ninteraction is shown to exhibit a one-dimensional analog of the BCS-BEC\ncrossover. Its low-energy physics is governed by a Tomonaga-Luttinger liquid\nwith three spin gaps. The spin gaps are exponentially small in the weak\ncoupling (BCS) limit where they arise from the charge-density-wave instability,\nand become large in the strong coupling (BEC) limit because of the formation of\ntightly-bound tetramers. We investigate the ground-state energy, the sound\nvelocity, and the gap spectrum in the BCS-BEC crossover and discuss exact\nrelationships valid in our system. We also show that a one-dimensional analog\nof the Efimov effect occurs for five bosons while it is absent for fermions.\nOur work opens up a very rich new field of universal few-body and many-body\nphysics in one dimension."
    },
    {
        "anchor": "One-dimensional Bose-Hubbard model with pure three-body interactions: The extended Bose-Hubbard model with pure three-body local interactions is\nstudied using the Density Matrix Renormalization Group approach. The shapes of\nthe first two insulating lobes are discussed, and the values of the critical\ntunneling for which the system undergoes the quantum phase transition from\ninsulating to superfluid phase are predicted. It is shown that stability of\ninsulating phases, in contrast to the standard Bose-Hubbard model, is enhanced\nfor larger fillings. It is also shown that, on the tip of the boundary of the\ninsulating phase, the model under consideration belongs to the\nBerenzinskii-Kosterlitz-Thouless universality class.",
        "positive": "Atom number filter in an optical lattice: We present an efficient procedure to filter out from an optical lattice,\nhaving inhomogeneous site occupation number, only preselected number of bosonic\natoms per site and place them into another internal atomic state, creating\nthereby a lattice with desired site occupation number."
    },
    {
        "anchor": "Nonsmooth and level-resolved dynamics illustrated with the tight binding\n  model: We point out that in the first order time-dependent perturbation theory, the\ntransition probability may behave nonsmoothly in time and have kinks\nperiodically. Moreover, the detailed temporal evolution can be sensitive to the\nexact locations of the eigenvalues in the continuum spectrum, in contrast to\ncoarse-graining ideas. Underlying this nonsmooth and level-resolved dynamics is\na simple equality about the sinc function $\\sinc x \\equiv \\sin x / x$. These\nphysical effects appear in many systems with approximately equally spaced\nspectra, and is also robust for larger-amplitude coupling beyond the domain of\nperturbation theory. We use a one-dimensional periodically driven tight-binding\nmodel to illustrate these effects, both within and outside the perturbative\nregime.",
        "positive": "Classical Analog of Quantum Models in Synthetic Dimensions: We introduce a classical analog of quantum matter in ultracold molecule -- or\nRydberg atom -- synthetic dimensions, extending the Potts model to include\ninteractions J1 between atoms adjacent in both real and synthetic space and\nstudying its finite temperature properties. For intermediate values of J1, the\nresulting phases and phase diagrams are similar to those of the clock and\nVillain models, in which three phases emerge. There exists a sheet phase\nanalogous to that found in quantum synthetic dimension models between the high\ntemperature disordered phase and the low temperature ferromagnetic phase. We\nalso employ machine learning to uncover non-trivial features of the phase\ndiagram using the learning by confusion approach. The key result there is that\nthe method is able to discern several successive phase transitions."
    },
    {
        "anchor": "Efimov Trimers near the Zero-crossing of a Feshbach Resonance: Near a Feshbach resonance, the two-body scattering length can assume any\nvalue. When it approaches zero, the next-order term given by the effective\nrange is known to diverge. We consider the question of whether this divergence\n(and the vanishing of the scattering length) is accompanied by an anomalous\nsolution of the three-boson Schr\\\"odinger equation similar to the one found at\ninfinite scattering length by Efimov. Within a simple zero-range model, we find\nno such solutions, and conclude that higher-order terms do not support Efimov\nphysics.",
        "positive": "Attraction-induced dynamical stability of a Bose-Einstein condensate in\n  a nonlinear lattice: We study multiple-period Bloch states of a Bose-Einstein condensate with\nspatially periodic interactomic interaction. Solving the Gross-Pitaevskii\nequation for the continuum model, and also using a simplified discrete version\nof it, we investigate the energy-band structures and the corresponding\nstability properties. We observe a new \"attraction-induced dynamical stability\"\nmechanism caused by the localization of the density distribution in the\nattractive domains of the system and the isolation of these higher-density\nregions. This makes the superfluid stable near the zone boundary, and also\nenhances the stability of higher-periodic states if the nonlinear interaction\nstrength is sufficiently high."
    },
    {
        "anchor": "Polarization angle dependence of the breathing modes in confined\n  one-dimensional dipolar bosons: Probing the radial collective oscillation of a trapped quantum system is an\naccurate experimental tool to investigate interactions and dimensionality\neffects. We consider a fully polarized quasi-one dimensional dipolar quantum\ngas of bosonic dysprosium atoms in a parabolic trap at zero temperature. We\nmodel the dipolar gas with an effective quasi-one dimensional Hamiltonian in\nthe single-mode approximation, and derive the equation of state using a\nvariational approximation based on the Lieb-Liniger gas Bethe Ansatz\nwavefunction or perturbation theory. We calculate the breathing mode\nfrequencies while varying polarization angles by a sum-rule approach, and find\nthem in good agreement with recent experimental findings.",
        "positive": "Visibility and stability of superstripes in a spin-orbit-coupled\n  Bose-Einstein condensate: We consider a spin-$1/2$ Bose-Einstein condensate with equal Rashba and\nDresselhaus spin-orbit coupling. After reviewing some relevant features of the\nquantum phases of the system, we present a short study on how their properties\nare changed by the presence of non-zero magnetic detunings and spin-asymmetric\ninteractions. At small values of the Raman coupling and of the magnetic field\nthe so-called stripe phase occurs, which displays both superfluidity and\nperiodic density modulations, in analogy with supersolids. We finally review a\nrecent proposal (Phys. Rev. A 90, 041604) to improve the visibility of the\nfringes, based on the space separation of the two spin components into a 2D\nbi-layer configuration and on the application of a $\\pi/2$ Bragg pulse, and we\nshow that this new configuration also yields a sizable increase of the\nstability of the stripe phase against magnetic fluctuations."
    },
    {
        "anchor": "Ground-state pressure of quasi-2D Fermi and Bose gases: Using an ultracold gas of atoms, we have realized a quasi-two-dimensional\nFermi system with widely tunable s-wave interactions nearly in a ground state.\nPressure and density are measured. The experiment covers physically different\nregimes: weakly and strongly attractive Fermi gases and a Bose gas of tightly\nbound pairs of fermions. In the Fermi regime of weak interactions, the pressure\nis systematically above a Fermi-liquid-theory prediction, maybe due to\nmesoscopic effects. In the opposite Bose regime, the pressure agrees with a\nbosonic mean-field scaling in a range beyond simplest expectations. In the\nstrongly interacting regime, measurements disagree with a purely 2D model.\nReported data may serve for sensitive testing of theoretical methods applicable\nacross different quantum physics disciplines.",
        "positive": "A Non-Equilibrium Kinetic Theory for Trapped Binary Condensates: We derive a non-equilibrium finite-temperature kinetic theory for a binary\nmixture of two interacting atomic Bose-Einstein condensates and use it to\nexplore the degree of hydrodynamicity attainable in realistic experimental\ngeometries. Based on the standard separation of timescale argument of kinetic\ntheory, the dynamics of the condensates of the multi-component system are shown\nto be described by dissipative Gross-Pitaevskii equations, self-consistently\ncoupled to corresponding Quantum Boltzmann equations for the non-condensate\natoms: on top of the usual mean field contributions, our scheme identifies a\ntotal of eight distinct collisional processes, whose dynamical interplay is\nexpected to be responsible for the systems equilibration. In order to provide\ntheir first characterization, we perform a detailed numerical analysis of the\nrole of trap frequency and geometry on collisional rates for experimentally\naccessible mixtures of $^{87}$Rb-$^{41}$K and $^{87}$Rb-$^{85}$Rb, discussing\nthe extent to which the system may approach the hydrodynamic regime with regard\nto some of those processes, as a guide for future experimental investigations\nof ultracold Bose gas mixtures."
    },
    {
        "anchor": "Broad Feshbach resonance in the 6Li-40K mixture: We study the widths of interspecies Feshbach resonances in a mixture of the\nfermionic quantum gases 6Li and 40K. We develop a model to calculate the width\nand position of all available Feshbach resonances for a system. Using the model\nwe select the optimal resonance to study the 6Li/40K mixture. Experimentally,\nwe obtain the asymmetric Fano lineshape of the interspecies elastic cross\nsection by measuring the distillation rate of 6Li atoms from a potassium-rich\n6Li/40K mixture as a function of magnetic field. This provides us with the\nfirst experimental determination of the width of a resonance in this mixture,\nDelta B=1.5(5) G. Our results offer good perspectives for the observation of\nuniversal crossover physics using this mass-imbalanced fermionic mixture.",
        "positive": "Interaction-driven dynamical quantum phase transitions in a strongly\n  correlated bosonic system: We study dynamical quantum phase transitions (DQPTs) in the extended\nBose-Hubbard model after a sudden quench of the nearest-neighbor interaction\nstrength. Using the time-dependent density matrix renormalization group, we\ndemonstrate that interaction-driven DQPTs can appear after quenches between two\ntopologically trivial insulating phases -- a phenomenon that has so far only\nbeen studied between gapped and gapless phases. These DQPTs occur when the\ninteraction strength crosses a certain threshold value that does not coincide\nwith the equilibrium phase boundaries, which is in contrast to quenches that\ninvolve a change of topology. In order to elucidate the nonequilibrium\nexcitations during the time evolution, we define a new set of string and parity\norder parameters. We find a close connection between DQPTs and these newly\ndefined order parameters for both types of quenches. In the interaction-driven\ncase, the order parameter exhibits a singularity at the time of the DQPT only\nwhen the quench parameter is close to the threshold value. Finally, the\ntimescales of DQPTs are scrutinized and different kinds of power laws are\nrevealed for the topological and interaction-driven cases."
    },
    {
        "anchor": "First and second sound in a two-dimensional dilute Bose gas across the\n  Berezinskii-Kosterlitz-Thouless transition: We theoretically investigate first and second sound of a two-dimensional (2D)\natomic Bose gas in harmonic traps by solving Landau's two-fluid hydrodynamic\nequations. For an isotropic trap, we find that first and second sound modes\nbecome degenerate at certain temperatures and exhibit typical avoided crossings\nin mode frequencies. At these temperatures, second sound has significant\ndensity fluctuation due to its hybridization with first sound and has a\ndivergent mode frequency towards the Berezinskii-Kosterlitz-Thouless (BKT)\ntransition. For a highly anisotropic trap, we derive the simplified\none-dimensional hydrodynamic equations and discuss the sound-wave propagation\nalong the weakly confined direction. Due to the universal jump of the\nsuperfluid density inherent to the BKT transition, we show that the first sound\nvelocity exhibits a kink across the transition. Our predictions can be readily\nexamined in current experimental setups for 2D dilute Bose gases.",
        "positive": "Antiferromagnetic self-ordering of a Fermi gas in a ring cavity: We explore the density and spin self-ordering of driven spin-$1/2$\ncollisionless fermionic atoms coupled to the electromagnetic fields of a ring\nresonator. The two spin states are two-photon Raman-coupled via a pair of\ndegenerate counterpropagating cavity modes and two transverse pump fields. In\nthis one-dimensional configuration the coupled atom-field system possesses a\ncontinuous $U(1)$ translational symmetry and a discrete $\\mathbf{Z}_2$ spin\ninversion symmetry. At half filling for sufficiently strong pump strengths, the\ncombined $U(1)\\times \\mathbf{Z}_2$ symmetry is spontaneously broken at the\nonset of a superradiant phase transition to a state with self-ordered density\nand spin structures. We predominately find an antiferromagnetic lattice order\nat the cavity wavelength. The self-ordered states exhibit unexpected positive\nmomentum pair correlations between fermions with opposite spin. These strong\ncavity-mediated correlations vanish at higher pump strength."
    },
    {
        "anchor": "Polariton condensation into vortex states in the synthetic magnetic\n  field of a strained honeycomb lattice: Photonic materials are a rapidly growing platform for studying condensed\nmatter physics with light, where the exquisite control capability is allowing\nus to learn about the relation between microscopic dynamics and macroscopic\nproperties. One of the most interesting aspects of condensed matter is the\ninterplay between interactions and the effect of an external magnetic field or\nrotation, responsible for a plethora of rich phenomena -- Hall physics and\nquantized vortex arrays. At first sight, however, these effects for photons\nseem vetoed: they do not interact with each other and they are immune to\nmagnetic fields and rotations. Yet in specially devised structures these\neffects can be engineered. Here, we propose the use of a synthetic magnetic\nfield induced by strain in a honeycomb lattice of resonators to create a\nnon-equilibrium Bose-Einstein condensate of light-matter particles (polaritons)\nin a rotating state, without the actual need for external rotation nor\nreciprocity-breaking elements. We show that thanks to the competition between\ninteractions, dissipation and a suitably designed incoherent pump, the\ncondensate spontaneously becomes chiral by selecting a single Dirac valley of\nthe honeycomb lattice, occupying the lowest Landau level and forming a vortex\narray. Our results offer a new platform where to study the exciting physics of\narrays of quantized vortices with light and pave the way to explore the\ntransition from a vortex-dominated phase to the photonic analogue of the\nfractional quantum Hall regime.",
        "positive": "Impurity and soliton dynamics in a Fermi gas with nearest-neighbor\n  interactions: We study spinless fermions with repulsive nearest-neighbor interactions\nperturbed by an impurity particle or a local potential quench. Using the\nnumerical time-evolving block decimation method and a simplified analytic\nmodel, we show that the pertubations create a soliton-antisoliton pair. If\nsolitons are already present in the bath, the two excitations have a\ndrastically different dynamics: The antisoliton does not annihilate with the\nsolitons and is therefore confined close to its origin while the soliton\nexcitation propagates. We discuss the consequences for experiments with\nultracold gases."
    },
    {
        "anchor": "Bulk viscosity of resonantly interacting fermions in the quantum virial\n  expansion: We consider two-component fermions with a zero-range interaction both in two\nand three dimensions and calculate the bulk viscosity for an arbitrary\nscattering length in the high-temperature regime. We evaluate the Kubo formula\nfor the bulk viscosity using an expansion with respect to the fugacity, which\nacts as a small parameter at high temperatures. In the zero-frequency limit of\nthe Kubo formula, pinch singularities emerge that reduce the order of the\nfugacity by one. These singularities can turn higher-order vertex corrections\nat nonzero frequencies into the leading order at zero frequency, so that all\nsuch contributions have to be resummed. We present an exact microscopic\ncomputation for the bulk viscosity in the high-temperature regime by taking\ninto account these pinch singularities. For negative scattering lengths, we\nderive the complete bulk viscosity at second order in fugacity and show that a\nself-consistent equation to resum the vertex corrections is identical to a\nlinearized kinetic equation. For positive scattering lengths, a new type of\npinch singularity arises for bound pairs. We show that the pinch singularity\nfor bound pairs leads to a first-order contribution to the bulk viscosity,\nwhich is one order lower than that for negative scattering lengths, and that\nthe vertex corrections also provide first-order contributions. We propose a new\nkinetic equation for bound pairs that derives from a self-consistent equation\nto resum the vertex corrections.",
        "positive": "Stable controllable giant vortex in a trapped Bose-Einstein condensate: In a harmonically-trapped rotating Bose-Einstein condensate (BEC), a vortex\nof large angular momentum decays to multiple vortices of unit angular momentum\nfrom an energetic consideration. We demonstrate the formation of a robust and\ndynamically stable giant vortex of large angular momentum in a harmonically\ntrapped rotating BEC with a potential hill at the center, thus forming a\nMexican hat like trapping potential. For a small inter-atomic interaction\nstrength, a highly controllable stable giant vortex appears, whose angular\nmomentum slowly increases as the angular frequency of rotation is increased. As\nthe inter-atomic interaction strength is increased beyond a critical value,\nonly vortices of unit angular momentum are formed, unless the strength of the\npotential hill at the center is also increased: for a stronger potential hill\nat the center a giant vortex is again formed. The dynamical stability of the\ngiant vortex is demonstrated by real-time propagation numerically. These giant\nvortices of large angular momentum can be observed and studied experimentally\nin a highly controlled fashion."
    },
    {
        "anchor": "Quasi-one-dimensional flow of polariton condensate past an obstacle: Nonlinear wave patterns generated by the flow of polariton condensate past an\nobstacle are studied for quasi-one-dimensional microcavity geometry. It is\nshown that pumping and nonlinear damping play a crucial role in this process\nleading to sharp differences in subsonic and supersonic regimes. Subsonic flows\nresult in a smooth disturbance of the equilibrium condensate around the\nobstacle whereas supersonic flow generates a dispersive shock wave in the flow\nupstream the obstacle and a long smooth downstream tail. Main characteristics\nof the wave pattern are calculated analytically and analytical results are in\nexcellent agreement with the results of numerical simulations. The conditions\nfor existence of stationary wave patterns are determined numerically.",
        "positive": "The Vortex-Particle Magnus Effect: Experimentalists use particles as tracers in liquid helium. The intrusive\neffects of particles on the dynamics of vortices remain poorly understood. We\nimplement a study of how basic well understood vortex states, such as a\npropagating pair of oppositely signed vortices, change in the presence of\nparticles by using a simple model based on the Magnus force. We focus on the 2D\ncase, and compare the analytic and semi-analytic model with simulations of the\nGross-Pitaevskii (GP) equation with particles modelled by dynamic external\npotentials. The results confirm that the Magnus force model is an effective way\nto approximate vortex-particle motion either with closed-form simplified\nsolutions or with a more accurate numerically solvable ordinary differential\nequations (ODEs). Furthermore, we increase the complexity of the vortex states\nand show that the suggested semi-analytical model remains robust in capturing\nthe dynamics observed in the GP simulations."
    },
    {
        "anchor": "Dimensionless ratios: characteristics of quantum liquids and their phase\n  transitions: Dimensionless ratios of physical properties can characterize low-temperature\nphases in a wide variety of materials. As such, the Wilson ratio (WR), the\nKadowaki-Woods ratio and the Wiedemann\\--Franz law capture essential features\nof Fermi liquids in metals, heavy fermions, etc. Here we prove that the phases\nof many-body interacting multi-component quantum liquids in one dimension (1D)\ncan be described by WRs based on the compressibility, susceptibility and\nspecific heat associated with each component. These WRs arise due to additivity\nrules within subsystems reminiscent of the rules for multi-resistor networks in\nseries and parallel --- a novel and useful characteristic of multi-component\nTomonaga-Luttinger liquids (TLL) independent of microscopic details of the\nsystems. Using experimentally realised multi-species cold atomic gases as\nexamples, we prove that the Wilson ratios uniquely identify phases of TLL,\nwhile providing universal scaling relations at the boundaries between phases.\nTheir values within a phase are solely determined by the stiffnesses and sound\nvelocities of subsystems and identify the internal degrees of freedom of said\nphase such as its spin-degeneracy. This finding can be directly applied to a\nwide range of 1D many-body systems and reveals deep physical insights into\nrecent experimental measurements of the universal thermodynamics in ultracold\natoms and spins.",
        "positive": "Temporally resolved second-order photon correlations of\n  exciton-polariton Bose-Einstein condensate formation: Second-order time correlation measurements with a temporal resolution better\nthan 3 ps were performed on a CdTe microcavity where spontaneous Bose-Einstein\ncondensation is observed. After the laser pulse, the nonresonantly excited\nthermal polariton population relaxes into a coherent polariton condensate.\nPhoton statistics of the light emitted by the microcavity evidences a clear\nphase transition from the thermal state to a coherent state, which occurs\nwithin 3.2 ps after the onset of stimulated scattering. Following this very\nfast transition, we show that the emission possesses a very high coherence that\npersists for more than 100 ps after the build-up of the condensate."
    },
    {
        "anchor": "Thermal vs. Entanglement Entropy: A Measurement Protocol for Fermionic\n  Atoms with a Quantum Gas Microscope: We show how to measure the order-two Renyi entropy of many-body states of\nspinful fermionic atoms in an optical lattice in equilibrium and\nnon-equilibrium situations. The proposed scheme relies on the possibility to\nproduce and couple two copies of the state under investigation, and to measure\nthe occupation number in a site- and spin-resolved manner, e.g. with a quantum\ngas microscope. Such a protocol opens the possibility to measure entanglement\nand test a number of theoretical predictions, such as area laws and their\ncorrections. As an illustration we discuss the interplay between thermal and\nentanglement entropy for a one dimensional Fermi-Hubbard model at finite\ntemperature, and its possible measurement in an experiment using the present\nscheme.",
        "positive": "Gapless excitations of axially symmetric vortices in systems with\n  tensorial order parameter: We extend the results of previous work on the vortex order parameter in\nsystems similar to the Ginzburg-Landau description of superfluid $^3$He in the\nbulk B phase. Specifically, we consider vortices preserving an axial $U(1)$\nsymmetry. We determine the conditions required by the $\\beta_i$ parameters to\nallow for an energetically favorable development of the off-diagonal\nantisymmetric and symmetric-traceless elements satisfying the axial symmetry\nfrom the trace-only ansatz of the order parameter. The number and type of\ngapless moduli appearing on the classical low energy theory of axial vortices\nis determined. The time-dependent part of the Ginzburg-Landau free energy is\nthen considered to determine the number of quantized modes emerging from the\ngapless moduli fields."
    },
    {
        "anchor": "Clustered Superfluids in the One Dimensional Bose-Hubbard model with\n  extended correlated hopping: Bosonic lattice systems with non-trivial interactions represent an intriguing\nplatform to study exotic phases of matter. Here, we study the effects of\nextended correlated hopping processes in a system of bosons trapped in a\nlattice geometry. The interplay between single particle tunneling terms,\ncorrelated hopping processes and on-site repulsion is studied by means of a\ncombination of exact diagonalization, strong coupling expansion and cluster\nmean field theory. We identify a rich ground state phase diagram where, apart\nthe usual Mott and superfluid states, superfluid phases with interesting\nclustering properties occur.",
        "positive": "A Feshbach resonance in collisions between ultracold ground state\n  molecules: Collisional resonances are an important tool which has been used to modify\ninteractions in ultracold gases, for realizing novel Hamiltonians in quantum\nsimulations, for creating molecules from atomic gases and for controlling\nchemical reactions. So far, such resonances have been observed for atom-atom\ncollisions, atom-molecule collisions and collisions between Feshbach molecules\nwhich are very weakly bound. Whether such resonances exist for ultracold ground\nstate molecules has been debated due to the possibly high density of states\nand/or rapid decay of the resonant complex. Here we report a very pronounced\nand narrow (25 mG) Feshbach resonance in collisions between two ground state\nNaLi molecules. This molecular Feshbach resonance has two special\ncharacteristics. First, the collisional loss rate is enhanced by more than two\norders of magnitude above the background loss rate which is saturated at the\n$p$-wave universal value, due to strong chemical reactivity. Second, the\nresonance is located at a magnetic field where two open channels become nearly\ndegenerate. This implies the intermediate complex predominantly decays to the\nsecond open channel. We describe the resonant loss feature using a model with\ncoupled modes which is analogous to a Fabry-P\\'erot cavity. Our observations\nprove the existence of long-lived coherent intermediate complexes even in\nsystems without reaction barriers and open up the possibility of coherent\ncontrol of chemical reactions."
    },
    {
        "anchor": "Critical temperature of a Rashba spin-orbit coupled Bose gas in harmonic\n  traps: We investigate theoretically Bose-Einstein condensation of an ideal, trapped\nBose gas in the presence of Rashba spin-orbit coupling. Analytic results for\nthe critical temperature and condensate fraction are derived, based on a\nsemi-classical approximation to the single-particle energy spectrum and density\nof states, and are compared with exact results obtained by explicitly summing\ndiscrete energy levels for small number of particles. We find a significant\ndecrease of the critical temperature and of the condensate fraction due to a\nfinite spin-orbit coupling. For large coupling strength and finite number of\nparticles $N$, the critical temperature scales as $N^{2/5}$ and $N^{2/3}$ in\nthree and two dimensions, respectively, contrasted to the predictions of\n$N^{1/3}$ and $N^{1/2}$ in the absence of spin-orbit coupling. Finite size\ncorrections in three dimensions are also discussed.",
        "positive": "Quantum Many-Body Scarring in $2+1$D Gauge Theories with Dynamical\n  Matter: Quantum many-body scarring (QMBS) has emerged as an intriguing paradigm of\nweak ergodicity breaking in nonintegrable quantum many-body models,\nparticularly lattice gauge theories (LGTs) in $1+1$ spacetime dimensions.\nHowever, an open question is whether QMBS exists in higher-dimensional LGTs\nwith dynamical matter. Given that nonergodic dynamics in $d{=}1$ spatial\ndimension tend to vanish in $d{>}1$, it is important to probe this question.\nUsing matrix product state techniques for both finite and infinite systems, we\nshow that QMBS occurs in the $2{+}1$D $\\mathrm{U}(1)$ quantum link model (QLM),\nas evidenced in persistent coherent oscillations in local observables, a marked\nslowdown in the growth of the bipartite entanglement entropy, and revivals in\nthe fidelity. Interestingly, we see that QMBS is more robust when the matter\ndegrees of freedom are bosonic rather than fermionic. Our results further shed\nlight on the intimate connection between gauge invariance and QMBS, and\nhighlight the persistence of scarring in higher spatial dimensions. Our\nfindings can be tested in near-term analog and digital quantum simulators, and\nwe demonstrate their accessibility on a recently proposed cold-atom analog\nquantum simulator."
    },
    {
        "anchor": "Quantum droplets of dipolar mixtures: Recently achieved two-component dipolar Bose-Einstein condensates open\nexciting possibilities for the study of mixtures of ultra-dilute quantum\nliquids. While non-dipolar self-bound mixtures are necessarily miscible with an\napproximately fixed ratio between the two densities, the density ratio for the\ndipolar case is free. As a result, self-bound dipolar mixtures present\nqualitatively novel and much richer physics, characterized by three possible\nground-state phases: miscible, symmetric immiscible and asymmetric immiscible,\nwhich may in principle occur at any population imbalance. Self-bound immiscible\ndroplets are possible due to mutual non-local inter-component attraction, which\nresults in the formation of a droplet molecule. Moreover, our analysis of the\nimpurity regime, shows that quantum fluctuations in the majority component\ncrucially modify the miscibility of impurities. Our work opens intriguing\nperspectives for the exploration of spinor physics in ultra-dilute liquids,\nwhich should resemble to some extent that of 4He-3He droplets and\nimpurity-doped helium droplets.",
        "positive": "Vortex depinning in a two-dimensional superfluid: We employ the Gross--Pitaevskii theory to model a quantized vortex depinning\nfrom a small obstacle in a two-dimensional superfluid due to an imposed\nbackground superfluid flow. We find that, when the flow's velocity exceeds a\ncritical value, the vortex drifts orthogonally to the flow before subsequently\nmoving parallel to it away from the pinning site. The motion of the vortex\naround the pinning site is also accompanied by an emission of a spiral-shaped\nsound pulse. Through simulations, we present a phase diagram of the critical\nflow velocity for vortex depinning together with an empirical formula that\nillustrates how the critical velocity increases with the height and width of\nthe pinning site. By employing a variety of choices of initial and boundary\nconditions, we are able to obtain lower and upper bounds on the critical\nvelocity and demonstrate the robustness of these results."
    },
    {
        "anchor": "Topological semimetal in a fermionic optical lattice: Optical lattices play a versatile role in advancing our understanding of\ncorrelated quantum matter. The recent implementation of orbital degrees of\nfreedom in chequerboard and hexagonal optical lattices opens up a new thrust\ntowards discovering novel quantum states of matter, which have no prior analogs\nin solid state electronic materials. Here, we demonstrate that an exotic\ntopological semimetal emerges as a parity-protected gapless state in the\norbital bands of a two-dimensional fermionic optical lattice. The new quantum\nstate is characterized by a parabolic band-degeneracy point with Berry flux\n$2\\pi$, in sharp contrast to the $\\pi$ flux of Dirac points as in graphene. We\nprove that the appearance of this topological liquid is universal for all\nlattices with D$_4$ point group symmetry as long as orbitals with opposite\nparities hybridize strongly with each other and the band degeneracy is\nprotected by odd parity. Turning on inter-particle repulsive interactions, the\nsystem undergoes a phase transition to a topological insulator whose\nexperimental signature includes chiral gapless domain-wall modes, reminiscent\nof quantum Hall edge states.",
        "positive": "Comparison of time profiles for the magnetic transport of cold atoms: We have compared different time profiles for the trajectory of the centre of\na quadrupole magnetic trap designed for the transport of cold sodium atoms. Our\nexperimental observations show that a smooth profile characterized by an\nanalytical expression involving the error function minimizes the transport\nduration while limiting atom losses and heating of the trapped gas. Using\nnumerical calculations of single atom classical trajectories within the trap,\nwe show that this observation can be qualitatively interpreted as a trade-off\nbetween two types of losses: finite depth of the confinement and Majorana spin\nflips."
    },
    {
        "anchor": "Spin fragmentation of Bose-Einstein condensates with antiferromagnetic\n  interactions: We study spin fragmentation of an antiferromagnetic spin 1 condensate in the\npresence of a quadratic Zeeman (QZ) effect breaking spin rotational symmetry.\nWe describe how the QZ effect turns a fragmented spin state, with large\nfluctuations of the Zeemans populations, into a regular polar condensate, where\natoms all condense in the $m=0$ state along the field direction. We calculate\nthe average value and variance of the Zeeman state $m=0$ to illustrate clearly\nthe crossover from a fragmented to an unfragmented state. The typical width of\nthis crossover is $q \\sim k_B T/N$, where $q$ is the QZ energy, $T$ the spin\ntemperature and $N$ the atom number. This shows that spin fluctuations are a\nmesoscopic effect that will not survive in the thermodynamic limit\n$N\\rightarrow \\infty$, but are observable for sufficiently small atom number.",
        "positive": "A fully controllable Kondo system: Coupling a flux qubit and an\n  ultracold Fermi gas: We show that a composite spin-1/2 Kondo system can be formed by coupling a\nsuperconducting quantum interference device (SQUID) to the internal hyperfine\nstates of a trapped ultracold atomic Fermi gas. Here, the SQUID, or flux qubit,\nacts as an effective magnetic impurity that induces spin-flip scattering near\nthe Fermi energies of the trapped gas. Although the ultracold gas and SQUID are\nat vastly different temperatures, the formation of a strongly correlated Kondo\nstate between the two systems is found when the gas is cooled below the Kondo\ntemperature; this temperature regime is within current experimental limits.\nFurthermore, the momentum distribution of the trapped fermions is calculated.\nWe find that it clearly contains an experimental signature of this correlated\nstate and the associated Kondo screening length. In addition to probing Kondo\nphysics, the controllability of this system can be used to systematically\nexplore the relaxation and equilibration of a strongly correlated system that\nhas been initially prepared in a selected nonequilibrium state."
    },
    {
        "anchor": "Quantum Gas Mixtures and Dual-Species Atom Interferometry in Space: The capability to reach ultracold atomic temperatures in compact instruments\nhas recently been extended into space. Ultracold temperatures amplify quantum\neffects, while free-fall allows further cooling and longer interactions time\nwith gravity - the final force without a quantum description. On Earth, these\ndevices have produced macroscopic quantum phenomena such as Bose-Einstein\ncondensation (BECs), superfluidity, and strongly interacting quantum gases.\nQuantum sensors interfering the superposition of two ultracold atomic isotopes\nhave tested the Universality of Free Fall (UFF), a core tenet of Einstein's\nclassical gravitational theory, at the $10^{-12}$ level. In space, cooling the\nelements needed to explore the rich physics of strong interactions and\npreparing the multiple species required for quantum tests of the UFF has\nremained elusive. Here, utilizing upgraded capabilities of the multi-user Cold\nAtom Lab (CAL) instrument within the International Space Station (ISS), we\nreport the first simultaneous production of a dual species Bose-Einstein\ncondensate in space (formed from $^{87}$Rb and $^{41}$K), observation of\ninterspecies interactions, as well as the production of $^{39}$K ultracold\ngases. We have further achieved the first space-borne demonstration of\nsimultaneous atom interferometry with two atomic species ($^{87}$Rb and\n$^{41}$K). These results are an important step towards quantum tests of UFF in\nspace, and will allow scientists to investigate aspects of few-body physics,\nquantum chemistry, and fundamental physics in novel regimes without the\nperturbing asymmetry of gravity.",
        "positive": "Two-dimensional Fermi gases near a p-wave resonance: effect of quantum\n  fluctuations: We study the stability of p-wave superfluidity against quantum fluctuations\nin two-dimensional Fermi gases near a p-wave Feshbach resonance . An analysis\nis carried out in the limit when the interchannel coupling is strong. By\ninvestigating the effective potential for the pairing field via the standard\nloop expansion, we show that a homogeneous p-wave pairing state becomes\nunstable when two-loop quantum fluctuations are taken into account. This is in\ncontrast to the previously predicted $p + ip$ supefluid in the weak-coupling\nlimit [V. Gurarie et al., Phys. Rev. Lett. 94, 230403 (2005)]. It implies a\npossible onset of instability at certain intermediate interchannel coupling\nstrength. Alternatively, the instability can also be driven by lowering the\nparticle density. We also discuss the validity of our analysis."
    },
    {
        "anchor": "Polarons in Binary Bose-Einstein Condensates: Bose polarons are quasiparticles formed through the interaction between\nimpurities and Bose-Einstein condensates. In this paper, we derive an effective\nFr\\\"{o}hlich Hamiltonian using the generalized Bogoliubov transformation. The\neffective Fr\\\"{o}hlich Hamiltonian encompasses two types of effective\ninteractions: impurity-density (ID) coupling and impurity-spin (IS) coupling.\nFurthermore, we employ the Lee-Low-Pines variational approach to investigate\nthe relevant properties of Bose polarons induced by the ID and IS coupling.\nThese properties include the ground state energy, effective mass, and average\nnumber of virtual phonons. Our findings reveal that the contribution resulting\nfrom IS couplings to the ground energy decreases to zero near the\nmiscible-immiscible boundary. Additionally, the increase of the IS coupling\ninduces a greater number of virtual phonons, impeding the movement of\nimpurities and leading to a significant increase in the effective mass of Bose\npolarons.",
        "positive": "Pitchfork bifurcations in blood-cell shaped dipolar Bose-Einstein\n  condensates: We demonstrate that the method of coupled Gaussian wave packets is a\nfull-fledged alternative to direct numerical solutions of the Gross-Pitaevskii\nequation of condensates with electromagnetically induced attractive 1/r\ninteraction, or with dipole-dipole interaction. Moreover, Gaussian wave packets\nare superior in that they are capable of producing both stable and unstable\nstationary solutions, and thus of giving access to yet unexplored regions of\nthe space of solutions of the Gross-Pitaevskii equation. We apply the method to\nclarify the theoretical nature of the collapse mechanism of blood-cell shaped\ndipolar condensates: On the route to collapse the condensate passes through a\npitchfork bifurcation, where the ground state itself turns unstable, before it\nfinally vanishes in a tangent bifurcation."
    },
    {
        "anchor": "Few-body Bose gases in low dimensions -- a laboratory for quantum\n  dynamics: Cold atomic gases have become a paradigmatic system for exploring fundamental\nphysics, which at the same time allows for applications in quantum\ntechnologies. The accelerating developments in the field have led to a highly\nadvanced set of engineering techniques that, for example, can tune\ninteractions, shape the external geometry, select among a large set of atomic\nspecies with different properties, or control the number of atoms. In\nparticular, it is possible to operate in lower dimensions and drive atomic\nsystems into the strongly correlated regime. In this review, we discuss recent\nadvances in few-body cold atom systems confined in low dimensions from a\ntheoretical viewpoint. We mainly focus on bosonic systems in one dimension and\nprovide an introduction to the static properties before we review the\nstate-of-the-art research into quantum dynamical processes stimulated by the\npresence of correlations. Besides discussing the fundamental physical phenomena\narising in these systems, we also provide an overview of the calculational and\nnumerical tools and methods that are commonly used, thus delivering a balanced\nand comprehensive overview of the field. We conclude by giving an outlook on\npossible future directions that are interesting to explore in these correlated\nsystems.",
        "positive": "Higgs oscillations in a unitary Fermi superfluid: Symmetry-breaking phase transitions are central to our understanding of\nstates of matter. When a continuous symmetry is spontaneously broken, new\nexcitations appear that are tied to fluctuations of the order parameter. In\nsuperconductors and fermionic superfluids, the phase and amplitude can\nfluctuate independently, giving rise to two distinct collective branches.\nHowever, amplitude fluctuations are difficult to both generate and measure, as\nthey do not couple directly to the density of fermions and have only been\nobserved indirectly to date. Here, we excite amplitude oscillations in an\natomic Fermi gas with resonant interactions by an interaction quench.\nExploiting the sensitivity of Bragg spectroscopy to the amplitude of the order\nparameter, we measure the time-resolved response of the atom cloud, directly\nrevealing amplitude oscillations at twice the frequency of the gap. The\nmagnitude of the oscillatory response shows a strong temperature dependence,\nand the oscillations appear to decay faster than predicted by time-dependent\nBCS theory applied to our experimental setup."
    },
    {
        "anchor": "Recurrence times of the Lieb-Liniger model in the weak and strong\n  coupling regimes: Quantum systems exhibit recurrence phenomena after equilibration, but it is a\ndifficult task to evaluate the recurrence time of a quantum system because it\ndrastically increases as the system size increases (usually double-exponential\nin the number of particles) and strongly depends on the initial state. Here, we\nanalytically derive the recurrence times of the Lieb-Liniger model with\nrelatively small particle numbers for the weak and strong coupling regimes. It\nturns out that these recurrence times are independent of the initial state and\nincreases only polynomially in the system size.",
        "positive": "A mixed dimensional Bose polaron: A new generation of cold atom experiments trapping atomic mixtures in species\nselective optical potentials opens up the intriguing possibility to create\nsystems in which different atoms live in different spatial dimensions. Inspired\nby this, we investigate a mixed dimensional Bose polaron consisting of an\nimpurity particle moving in a two-dimensional (2D) layer immersed in a 3D\nBose-Einstein condensate (BEC), using a theory that includes the mixed\ndimensional vacuum scattering between the impurity and the bosons exactly. We\nshow that similarly to the pure 3D case, this system exhibits a well-defined\npolaron state for attractive boson-impurity interaction that evolves smoothly\ninto a mixed-dimensional dimer for strong attraction, as well as a well-defined\npolaron state for weak repulsive interaction, which becomes over-damped for\nstrong interaction. We furthermore find that the properties of the polaron\ndepend only weakly on the gas parameter of the BEC as long as the Bogoliubov\ntheory remains a valid description for the BEC. This indicates that higher\norder correlations between the impurity and the bosons are suppressed by the\nmixed dimensional geometry in comparison to a pure 3D system, and that the\nmixed dimensional polaron has universal properties in the unitarity limit of\nthe impurity-boson interaction."
    },
    {
        "anchor": "Disordered cold atoms in different symmetry classes: We consider an experimentally realizable model of non-interacting but\nrandomly coupled atoms in a two-dimensional optical lattice. By choosing\nappropriate real or complex-valued random fields and species-dependent energy\noffsets, this system can be used to analyze effects of disorder in four\ndifferent classes: The chiral BDI and AIII, and the A and AI symmetry classes.\nThese chiral classes are known to support a metallic phase at zero energy,\nwhich here, due to the inevitable finite size of the system, should also\npersist in a neighborhood of non-zero energies. As we discuss, this is of\nparticular interest for experiments involving quenches. Away from the centre of\nthe spectrum, we find that excitations appear as domain walls in the cases with\ntime-reversal symmetry, or as vortices in the cases where time-reversal\nsymmetry is absent. Therefore, a quench in a system with uniform density would\nlead to the formation of either vortices or domain walls depending on the\nsymmetry class. For the non-chiral models in the A and AI classes, a population\nimbalance between the two atomic species naturally occurs. In these cases, one\nof the two species is seen to favour a more uniform density. We also study the\nonset of localization as the disorder strength is increased for the different\nclasses, and by deriving an effective model for the non-chiral cases we show\nhow their eigenstates remain extended for larger values of the coupling with\nthe disorder, if compared to the non-chiral ones.",
        "positive": "Two-dimensional electron-hole system under the influence of the\n  Chern-Simons gauge field created by the quantum point vortices: In the present work the Chern-Simons(C-S) gauge field theory developed by\nJackiw and Pi [1] and widely used to explain the fractional quantum Hall\neffects, was applied to describe the two-dimensional (2D) electron-hole (e-h)\nsystem in a strong perpendicular magnetic field under the influence of the\nquantum point vortices creating the Chern-Simons(C-S) gauge field. The\ncomposite particles formed by electrons and by holes with equal integer\npositive numbers of the attached quantum point vortices are described by the\ndressed field operators, which obey to the Fermi or to the Bose statistics\ndepending on the even or odd numbers . It is shown that the phase operators as\nwell as the vector and the scalar potentials of the C-S gauge field depend on\nthe difference of the electron and of the hole density operators. They vanish\nin the mean field approximation, when the average values of the electron and of\nthe whole densities coincide. Nevertheless, even in this case, the quantum\nfluctuations of the C-S gauge field lead to new physics of the 2D e-h system."
    },
    {
        "anchor": "Breathing Oscillations in Bose - Fermi Mixing Gases with Yb atoms in the\n  Largely Prolate Deformed Traps: We study the breathing oscillations in bose-fermi mixtures with Yb isotopes\nin the largely prolate deformed trap, which are realized by Kyoto group. We\nchoose the three combinations of the Yb isotopes, Yb170-Yb171, Yb170-Yb173 and\nYb174-Yb173, whose boson-fermion interactions are weakly repulsive, strongly\nattractive and strongly repulsive. The collective oscillations in the deformed\ntrap are calculated in the dynamical time-development approach, which is\nformulated with the time-dependent Gross-Pitaevskii and the Vlasov equations.\nWe analyze the results in the time-development approach with the intrinsic\noscillation modes of the deformed system, which are obtained using the scaling\nmethod, and show that the damping and forced-oscillation effects of the\nintrinsic modes give time-variation of oscillations, especially, in the fermion\ntransverse mode.",
        "positive": "Bose-Einstein statistics for a finite number of particles: This article presents a study of the grand canonical Bose-Einstein (BE)\nstatistics for a finite number of particles in an arbitrary quantum system. The\nthermodynamical quantities that identify BE condensation -- namely, the\nfraction of particles in the ground state and the specific heat -- are\ncalculated here exactly in terms of temperature and fugacity. These\ncalculations are complemented by a numerical calculation of fugacity in terms\nof the number of particles, without taking the thermodynamic limit. The main\nadvantage of this approach is that it does not rely on approximations made in\nthe vicinity of the usually defined critical temperature, rather it makes\ncalculations with arbitrary precision possible, irrespective of temperature.\nGraphs for the calculated thermodynamical quantities are presented in\ncomparison to the results previously obtained in the thermodynamic limit. In\nparticular, it is observed that for the gas trapped in a 3-dimensional box the\nderivative of specific heat reaches smaller values than what was expected in\nthe thermodynamic limit -- here, this result is also verified with analytical\ncalculations. This is an important result for understanding the role of the\nthermodynamic limit in phase transitions and makes possible to further study BE\nstatistics without relying neither on the thermodynamic limit nor on\napproximations near critical temperature."
    },
    {
        "anchor": "Thermodynamics of a weakly interacting Bose gas above the transition\n  temperature: We study thermodynamic properties of weakly interacting Bose gases above the\ntransition temperature of Bose-Einstein condensation in the framework of a\nthermodynamic perturbation theory. Cases of local and non-local interactions\nbetween particles are analyzed both analytically and numerically. We obtain and\ncompare the temperature dependencies for the chemical potential, entropy,\npressure, and specific heat to those of noninteracting gases. The results set\nreliable benchmarks for thermodynamic characteristics and their asymptotic\nbehavior in dilute atomic and molecular Bose gases above the transition\ntemperature.",
        "positive": "Condensation to a strongly correlated dark fluid of two dimensional\n  dipolar excitons: Recently we reported on the condensation of cold, electrostatically trapped\ndipolar excitons in GaAs bilayer heterostructure into a new, dense and dark\ncollective phase. Here we analyze and discuss in detail the experimental\nfindings and the emerging evident properties of this collective liquid-like\nphase. We show that the phase transition is characterized by a sharp increase\nof the number of non-emitting dipoles, by a clear contraction of the fluid\nspatial extent into the bottom of the parabolic-like trap, and by spectral\nnarrowing. We extract the total density of the condensed phase which we find to\nbe consistent with the expected density regime of a quantum liquid. We show\nthat there are clear critical temperature and excitation power onsets for the\nphase transition and that as the power further increases above the critical\npower, the strong darkening is reduced down until no clear darkening is\nobserved. At this point another transition appears which we interpret as a\ntransition to a strongly repulsive yet correlated $e$-$h$ plasma. Based on the\nexperimental findings, we suggest that the physical mechanism that may be\nresponsible for the transition is a dynamical final-state stimulation of the\ndipolar excitons to their dark spin states, which have a long lifetime and thus\nsupport the observed sharp increase in density. Further experiments and\nmodeling will hopefully be able to unambiguously identify the physical\nmechanism behind these recent observations."
    },
    {
        "anchor": "Sub- and supercritical defect scattering in Schr\u00f6dinger chains with\n  higher-order hopping: We theoretically analyze a discrete Schr\\\"odinger chain with hopping to the\nfirst and second neighbors, as can be realized with zigzag arrangements of\noptical waveguides or lattice sites for cold atoms. Already at moderate values,\nthe second-neighbor hopping has a strong impact on the band structure, leading\nto the emergence of a new extremum located inside the band, accompanied by a\nvan Hove singularity in the density of states. The energy band is then divided\ninto a subcritical regime with the usual unique correspondence between wave\nnumber and energy of the travelling waves, and a supercritical regime, in which\nwaves of different wave number are degenerate in energy. We study the\nconsequences of these features in a scattering setup, introducing a defect that\nlocally breaks the translational invariance. The notion of a local probability\ncurrent is generalized beyond the nearest-neighbor approximation and bound\nstates with energies outside the band are discussed. At subcritical energies\ninside the band, an evanescent mode coexists with the travelling plane wave,\ngiving rise to resonance phenomena in scattering. At weak coupling to the\ndefect, we identify a prototypical Fano-Feshbach resonance of tunable shape and\nprovide analytical expressions for its profile parameters. At supercritical\nenergies, we observe coupling of the degenerate travelling waves, leading to an\nintricate wave packet fragmentation dynamics. The corresponding branching\nratios are analyzed.",
        "positive": "Symmetry-protected topological phase transitions and robust chiral order\n  on a tunable zigzag lattice: Symmetry fractionalization, generating a large amount of symmetry-protected\ntopological phases, provides scenarios for continuous phase transitions\ndifferent from spontaneous symmetry breaking. However, it is hard to detect\nthese symmetry-protected topological phase transitions experimentally.\nMotivated by the recent development of highly tunable ultracold polar\nmolecules, we show that the setup in a zigzag optical lattice of this system\nprovides a perfect platform to realize symmetry-protected topological phase\ntransitions. By using infinite time-evolving block decimation, we obtain the\nphase diagram in a large parameter regions and find another scheme to realize\nthe long-sought vector chiral phase, which is robust from quantum fluctuations.\nWe discuss the existence of the chiral phase by an effective field analysis."
    },
    {
        "anchor": "Cavity-induced chiral states of fermionic quantum gases: We investigate ultra-cold fermions placed into an optical cavity and\nsubjected to optical lattices which confine the atoms to ladder structures. A\ntransverse running-wave laser beam induces together with the dynamical cavity\nfield a two-photon Raman-assisted tunneling process with spatially dependent\nphase imprint along the rungs of the ladders. We identify the steady states\nwhich can occur by the feedback mechanism between the cavity field and the\natoms. We find the spontaneous emergence of a finite cavity field amplitude\nwhich leads to an artificial magnetic field felt by the fermionic atoms. These\nform a chiral insulating or chiral liquid state carrying a chiral current. We\nexplore the rich state diagram as a function of the power of the transverse\nlaser beam, the atomic filling, and the phase imprint during the cavity-induced\ntunneling. Both a sudden onset or a slow exponential activation with the\ntransverse laser power of the self-organized chiral states can occur.",
        "positive": "Temporal evolution of attractive Bose-Einstein condensate in a quasi 1D\n  cigar-shape trap modeled through the semiclassical limit of the focusing\n  Nonlinear Schroedinger Equation: One-dimensional (1D) Nonlinear Schroedinger Equaation (NLS) provides a good\napproximation to attractive Bose-Einshtein condensate (BEC) in a quasi 1D\ncigar-shaped optical trap in certain regimes. 1D NLS is an integrable equation\nthat can be solved through the inverse scattering method. Our observation is\nthat in many cases the parameters of the BEC correspond to the semiclassical\n(zero dispersion) limit of the focusing NLS. Hence, recent results about the\nstrong asymptotics of the semiclassical limit solutions can be used to describe\nsome interesting phenomena of the attractive 1D BEC. In general, the\nsemiclassical limit of the focusing NLS exibits very strong modulation\ninstability. However, in the case of an analytical initial data, the NLS\nevolution does displays some ordered structure, that can describe, for example,\nthe bright soliton phenomenon. We discuss some general features of the\nsemiclassical NLS evolution and propose some new observables."
    },
    {
        "anchor": "Chiral condensates in a polariton hexagonal ring: We model generation of vortex modes in exciton-polariton condensates in\nsemiconductor micropillars, arranged into a hexagonal ring molecule, in the\npresence of TE-TM splitting. This splitting lifts the degeneracy of azimuthally\nmodulated vortex modes with opposite topological charges supported by this\nstructure, so that a number of non-degenerate vortex states characterized by\ndifferent combinations of topological charges in two polarization components\nappears. We present a full bifurcation picture for such vortex modes and show\nthat because they have different energies, they can be selectively excited by\ncoherent pump beams with specific frequencies and spatial configurations. At\nhigh pumping intensity, polariton-polariton interactions give rise to the\ncoupling of different vortex resonances and a bistable regime is achieved.",
        "positive": "Quantum noise in three-dimensional BEC interferometry: We develop a theory of quantum fluctuations and squeezing in a\nthree-dimensional Bose-Einstein condensate atom interferometer with nonlinear\nlosses. We use stochastic equations in a truncated Wigner representation to\ntreat quantum noise. Our approach includes the multi-mode spatial evolution of\nspinor components and describes the many-body dynamics of a mesoscopic quantum\nsystem."
    },
    {
        "anchor": "Non-Fermi liquids from kinetic constraints in tilted optical lattices: We study Fermi-Hubbard models with kinetically constrained dynamics that\nconserves both total particle number and total center of mass, a situation that\narises when interacting fermions are placed in strongly tilted optical\nlattices. Through a combination of analytics and numerics, we show how the\nkinetic constraints stabilize an exotic non-Fermi liquid phase described by\nfermions coupled to a gapless bosonic field, which in many respects mimics a\ndynamical gauge field. This offers a novel route towards the study of non-Fermi\nliquid phases in the precision environments afforded by ultracold atom\nplatforms.",
        "positive": "Single-particle Excitations and Effects of Hetero-pairing Fluctuations\n  in a Bose-Fermi Mixture with a Feshbach Resonance: We theoretically investigate normal-state properties of a gas mixture of\nsingle-component bosons and fermions with a hetero-nuclear Feshbach resonance.\nIncluding strong hetero-pairing fluctuations associated with the Feshbach\nresonance, we calculate single-particle density of states, as well as the\nspectral weight at various interaction strengths. For this purpose, we employ\nan improved T-matrix approximation (TMA), where the bare Bose Green's function\nin the non-selfconsistent TMA self-energy is modified so as to satisfy the\nHugenholtz-Pines relation at the Bose-Einstein condensation (BEC) temperature\n$T_{\\rm BEC}$. In the unitary regime at $T_{\\rm BEC}$, we show that\nhetero-pairing fluctuations couple Fermi atomic excitations with Fermi\nmolecular excitations, as well as with Bose atomic excitations. Although a\nsimilar coupling phenomenon by pairing fluctuations is known to give a\npseudo-gapped density of states in the unitary regime of a two-component Fermi\ngas, such a dip structure is found to not appear even in the unitary limit of a\nBose-Fermi mixture. It only appears in the strong-coupling regime. Instead, a\nspectral peak along the molecular dispersion appears in the spectral weight.We\nalso clarify how this coupling phenomenon is seen in the Bose channel. Since a\nhetero-nuclear Feshbach resonance, as well as the formation of Bose-Fermi\nmolecules, have been realized, our results would be useful for the study of\nstrong-coupling properties of this unique quantum gas."
    },
    {
        "anchor": "Two-dimensional supersolidity in a dipolar quantum gas: Supersolidity -- a quantum-mechanical phenomenon characterized by the\npresence of both superfluidity and crystalline order -- was initially\nenvisioned in the context of bulk solid helium, as a possible answer to the\nquestion of whether a solid could have superfluid properties. While\nsupersolidity has not been observed in solid helium (despite much effort),\nultracold atomic gases have provided a fundamentally new approach, recently\nenabling the observation and study of supersolids with dipolar atoms. However,\nunlike the proposed phenomena in helium, these gaseous systems have so far only\nshown supersolidity along a single direction. By crossing a structural phase\ntransition similar to those occurring in ionic chains, quantum wires, and\ntheoretically in chains of individual dipolar particles, we demonstrate the\nextension of supersolid properties into two dimensions, providing an important\nstep closer to the bulk situation envisioned in helium. This opens the\npossibility of studying rich excitation properties, including vortex formation,\nas well as ground-state phases with varied geometrical structure in a highly\nflexible and controllable system.",
        "positive": "Dynamical Universal Behavior in Quantum Chaotic Systems: We discover numerically that a moving wave packet in a quantum chaotic\nbilliard will always evolve into a quantum state, whose density probability\ndistribution is exponential. This exponential distribution is found to be\nuniversal for quantum chaotic systems with rigorous proof. In contrast, for the\ncorresponding classical system, the distribution is Gaussian. We find that the\nquantum exponential distribution can smoothly change to the classical Gaussian\ndistribution with coarse graining."
    },
    {
        "anchor": "Vortices in dipolar condensates with dominant dipolar interactions: We present full three-dimensional numerical calculations of single vortex\nstates in rotating dipolar condensates. We consider a Bose-Einstein condensate\nof 52Cr atoms with dipole-dipole and s-wave contact interactions confined in an\naxially symmetric harmonic trap. We obtain the vortex states by numerically\nsolving the Gross-Pitaevskii equation in the rotating frame with no further\napproximations. We investigate the properties of a single vortex and calculate\nthe critical angular velocity for different values of the s-wave scattering\nlength. We show that, whereas the standard variational approach breaks down in\nthe limit of pure dipolar interactions, exact solutions of the Gross-Pitaevskii\nequation can be obtained for values of the s-wave scattering length down to\nzero. The energy barrier for the nucleation of a vortex is calculated as a\nfunction of the vortex displacement from the rotation axis for different values\nof the angular velocity of the rotating trap.",
        "positive": "Spontaneous increase of magnetic flux and chiral-current reversal in\n  bosonic ladders: Swimming against the tide: The interplay between spontaneous symmetry breaking in many-body systems, the\nwavelike nature of quantum particles and lattice effects produces an\nextraordinary behavior of the chiral current of bosonic particles in the\npresence of a uniform magnetic flux defined on a two-leg ladder. While\nnon-interacting as well as strongly interacting particles, stirred by the\nmagnetic field, circulate along the system's boundary in the counterclockwise\ndirection in the ground state, interactions stabilize vortex lattices. These\nstates break translational symmetry, which can lead to a reversal of the\ncirculation direction. Our predictions could readily be accessed in quantum gas\nexperiments with existing setups or in arrays of Josephson junctions."
    },
    {
        "anchor": "Fractional Excitations in Cold Atomic Gases: We study the behavior of excitations in the tilted one-dimensional\nBose-Hubbard model. In the phase with broken symmetry, fundamental excitations\nare domain-walls which show fractional statistics. Using perturbation theory,\nwe derive an analytic model for the time evolution of these fractional\nexcitations, and demonstrate the existence of a repulsively bound state above a\ncritical center of mass momentum. The validity of the perturbative analysis is\nconfirmed by the use of t- DMRG simulations. These findings open the path for\nexperimental detection of fractional particles in cold atomic gases.",
        "positive": "Clustered Wigner crystal phases of cold polar molecules in arrays of\n  one-dimensional tubes: We analyze theoretically polar molecules confined in planar arrays of one\ndimensional tubes. In the classical limit, if the number of tubes is finite,\nnew types of \"clustered Wigner crystals\" with increasingly many molecules per\nunit cell can be stabilized by tuning the in-plane angle between the dipolar\nmoments and the tube direction. Quantum mechanically, these phases melt into\ndistinct \"clustered Luttinger liquids.\" We calculate the phase diagram of the\nsystem and study the quantum melting of the clustered phases. We find that the\nrequirements for exploring these phases are reachable in current experiments\nand discuss possible experimental signatures."
    },
    {
        "anchor": "Symmetry breaking and physical properties of the bosonic single-impurity\n  Anderson model: We show how exact diagonalization of small clusters can be used as a fast and\nreliable impurity solver by determining the phase diagram and physical\nproperties of the bosonic single-impurity Anderson model. This is specially\nimportant for applications which require the solution of a large number of\ndifferent single-impurity problems, such as the bosonic dynamical mean field\ntheory of disordered systems. In particular, we investigate the connection\nbetween spontaneous global gauge symmetry breaking and the occurrence of\nBose-Einstein condensation (BEC). We show how BEC is accurately signaled by the\nappearance of broken symmetry, even when a fairly modest number of states is\nretained. The occurrence of symmetry breaking can be detected both by adding a\nsmall conjugate field or, as in generic quantum critical points, by the\ndivergence of the associated phase susceptibility. Our results show excellent\nagreement with the considerably more demanding numerical renormalization group\n(NRG) method. We also investigate the mean impurity occupancy and its\nfluctuations, identifying an asymmetry in their critical behavior across the\nquantum phase transitions between BEC and `Mott' phases.",
        "positive": "Spin-polarized hydrogen adsorbed on the surface of superfluid 4He: The experimental realization of a thin layer of spin-polarized hydrogen\nadsorbed on top of the surface of superfluid 4He provides one of the best\nexamples of a stable nearly two-dimensional quantum Bose gas. We report a\ntheoretical study of this system using quantum Monte Carlo methods in the limit\nof zero temperature. Using the full Hamiltonian of the system, composed of a\nsuperfluid 4He slab and the adsorbed hydrogen layer, we calculate the main\nproperties of its ground state using accurate models for the pair interatomic\npotentials. Comparing the results for the layer with the ones obtained for a\nstrictly two-dimensional (2D) setup, we analyze the departure from the 2D\ncharacter when the density increases. Only when the coverage is rather small\nthe use of a purely 2D model is justified. The condensate fraction of the layer\nis significantly larger than in 2D at the same surface density, being as large\nas $60\\%$ at the largest coverage studied."
    },
    {
        "anchor": "Anisotropic expansion of a thermal dipolar Bose gas: We report on the anisotropic expansion of ultracold bosonic dysprosium gases\nat temperatures above quantum degeneracy and develop a quantitative theory to\ndescribe this behavior. The theory expresses the post-expansion aspect ratio in\nterms of temperature and microscopic collisional properties by incorporating\nHartree-Fock mean-field interactions, hydrodynamic effects, and\nBose-enhancement factors. Our results extend the utility of expansion imaging\nby providing accurate thermometry for dipolar thermal Bose gases, reducing\nerror in expansion thermometry from tens of percent to only a few percent.\nFurthermore, we present a simple method to determine scattering lengths in\ndipolar gases, including near a Feshbach resonance, through observation of\nthermal gas expansion.",
        "positive": "Suppression of the quantum-mechanical collapse by repulsive interactions\n  in a quantum gas: The quantum-mechanical collapse (alias fall onto the center of particles\nattracted by potential -1/r^2), or \"quantum anomaly\", is a well-known issue in\nthe quantum theory. We demonstrate that the mean-field repulsive nonlinearity\nprevents the collapse and thus puts forward a solution to the quantum-anomaly\nproblem different from that previously developed in the framework of the linear\nquantum-field theory. This solution may be realized in the 3D or 2D gas of\ndipolar bosons attracted by a central charge, and in the 2D gas of magnetic\ndipoles attracted by a current filament. In the 3D setting, the dipole-dipole\ninteractions are also taken into regard, in the mean-field approximation. In\nlieu of the collapse, the cubic nonlinearity creates a 3D ground state (GS),\nwhich does not exist in the respective linear Schroedinger equation (SE). The\naddition of the harmonic trap gives rise to a tristability, in the case when\nthe SE still does not lead to the collapse. In the 2D setting, the cubic\nnonlinearity is not strong enough to prevent the collapse; however, the quintic\nterm does it, creating the GS, as well as its counterparts carrying the angular\nmomentum (vorticity). Counter-intuitively, such self-trapped 2D modes exist\neven in the case of a weakly repulsive potential 1/r^2. In the presence of the\nharmonic trap, the 2D quintic model with a weakly repulsive central potential\n1/r^2 gives rise to three confined modes, the middle one being unstable,\nspontaneously developing into a breather. In both the 3D and 2D cases, the GS\nwave functions are found in a numerical form, and also in the form of an\nanalytical approximation, which is asymptotically exact in the limit of the\nlarge norm."
    },
    {
        "anchor": "Interacting polariton fluids in a monolayer of tungsten disulfide: Atomically thin transition metal dichalcogenides (TMDs) possess a number of\nproperties that make them attractive for realizing room-temperature polariton\ndevices. An ideal platform for manipulating polariton fluids within monolayer\nTMDs is that of Bloch surface waves, which confine the electric field to a\nsmall volume near the surface of a dielectric mirror. Here we demonstrate that\nmonolayer tungsten disulfide ($\\text{WS}_2$) can sustain Bloch surface wave\npolaritons (BSWPs) with a Rabi splitting of 43 meV and propagation constants\nreaching 33 $\\mu$m. In addition, we evidence strong polariton-polariton\nnonlinearities within BSWPs, which manifest themselves as a reversible\nblueshift of the lower polariton resonance by up to 12.9$\\pm$0.5 meV. Such\nnonlinearities are at the heart of polariton devices and have not yet been\ndemonstrated in TMD polaritons. As a proof of concept, we use the nonlinearity\nto implement a nonlinear polariton source. Our results demonstrate that BSWPs\nusing TMDs can support long-range propagation combined with strong\nnonlinearities, enabling potential applications in integrated optical\nprocessing and polaritonic circuits.",
        "positive": "Quantum Emulation of Extreme Non-equilibrium Phenomena with Trapped\n  Atoms: Ultracold atomic physics experiments offer a nearly ideal context for the\ninvestigation of quantum systems far from equilibrium. We describe three\nrelated emerging directions of research into extreme non-equilibrium phenomena\nin atom traps: quantum emulation of ultrafast atom-light interactions, coherent\nphasonic spectroscopy in tunable quasicrystals, and realization of Floquet\nmatter in strongly-driven lattice systems. We show that all three should enable\nquantum emulation in parameter regimes inaccessible in solid-state experiments,\nfacilitating a complementary approach to open problems in non-equilibrium\ncondensed matter."
    },
    {
        "anchor": "Quasi-condensation in two-dimensional Fermi gases: In this paper we follow the analysis and protocols of recent experiments,\ncombined with simple theory, to arrive at a physical understanding of\nquasi-condensation in two dimensional Fermi gases. We find that\nquasi-condensation mirrors Berezinskii-Kosterlitz-Thouless behavior in many\nways, including the emergence of a strong zero momentum peak in the pair\nmomentum distribution. Importantly, the disappearance of this quasi-condensate\noccurs at a reasonably well defined crossover temperature. The resulting phase\ndiagram, pair momentum distribution, and algebraic power law decay are\ncompatible with recent experiments throughout the continuum from BEC to BCS.",
        "positive": "Localization by Dissipative Disorder: a Deterministic Approach to\n  Position Measurements: We propose an approach to position measurements based on the hypothesis that\nthe action of a position detector on a quantum system can be effectively\ndescribed by a dissipative disordered potential. We show that such kind of\npotential is able, via the dissipation-induced Anderson localization, to\ncontemporary localize the wavefunction of the system and to dissipate\ninformation to modes bounded to the detector. By imposing a diabaticity\ncondition we demonstrate that the dissipative dynamics between the modes of the\nsystem leads to a localized energy exchange between the detector and the rest\nof the environment -the \"click\" of the detector- thus providing a complete\ndeterministic description of a position measurement. We finally numerically\ndemonstrate that our approach is consistent with the Born probability rule."
    },
    {
        "anchor": "Collective excitations in two-dimensional harmonically trapped quantum\n  droplets: The collective excitation modes in quantum droplets trapped in a\ntwo-dimensional harmonic potential in the context of symmetric weakly\ninteracting binary bosonic mixtures are studied. By utilizing the linearization\ntechnique, the time-dependent extended Gross-Pitaevskii equation, and a\nsum-rule approach with a variational approximation, the ground state properties\nand collective excitations of such a two-dimensional quantum system are\ninvestigated for various system parameters. We present comprehensive analysis\nand calculations on the effect of the confinement strength and anisotropy of\nthe trapping potential, the number of atoms in the droplet, and the collective\nexcitation modes. The radius of the droplet, as well as the chemical potential,\nis non-monotonically related to the number of atoms in the droplet, and the\nconfinement tends to shift the minimum values towards the ideal gas limit. The\nexcitation frequency peaks, which are prominent in a self-bounded droplet,\nbecome less pronounced and smoother when subjected to a strong trapping\npotential. The sum-rule approach fails to reproduce the breathing mode\nfrequency for a moderate number of atoms in a weak trapping potential, however,\nworks perfectly well in a strong confinement. It was found that the anisotropy\nin the trap eliminates the degeneracy between the quadrupole and scissors modes\nthat occurs in an isotropic trap, causing the frequencies of these two modes to\nimmediately diverge from each other for any degree of anisotropy. These\nfindings provide valuable insights into the unique characteristics and behavior\nof quantum droplets, offering potential implications for future research and\napplications in the dynamic behaviors of intriguing quantum droplets.",
        "positive": "Rabi-coupling driven motion of a soliton in a Bose-Einstein condensate: We study the motion of a self-attractive Bose-Einstein condensate with\npseudo-spin 1/2 driven by a synthetic Rabi (Zeeman-like) field. This field\ntriggers the pseudo-spin dynamics resulting in a density redistribution between\nits components and, as a consequence, in changes of the overall density\ndistribution. In the presence of an additional external potential, the latter\nproduces a net force acting on the condensate and activates its displacement.\nAs an example, here we consider the case of a one-dimensional condensate in a\nrandom potential."
    },
    {
        "anchor": "Universal Relations of Ultracold Fermi Gases with Arbitrary Spin-Orbit\n  Coupling: We derive the universal relations for an ultracold two-component Fermi gas\nwith spin-orbit coupling (SOC)\n$\\sum_{\\alpha,\\beta=x,y,z}\\lambda_{\\alpha\\beta}\\sigma_{\\alpha}p_{\\beta}$, where\n$p_{x,y,z}$ and $\\sigma_{x,y,z}$ are the single-atom momentum and Pauli\noperators for pseudo spin, respectively, and the SOC intensity\n$\\lambda_{\\alpha\\beta}$ could take arbitrary value. We consider the system with\nan s-wave short-range interspecies interaction, and ignore the SOC-induced\nmodification for the value of the scattering length. Using the first-quantized\napproach developed by S. Tan (Phys. Rev. Lett. \\textbf{107}, 145302 (2011)), we\nobtain the short-range and high-momentum expansions for the one-body real-space\ncorrelation function and momentum distribution function, respectively. For our\nsystem these functions are $2\\times2$ matrix in the pseudo-spin basis. We find\nthat the leading-order ($1/k^{4}$) behavior of the diagonal elements of the\nmomentum distribution function (i.e., $n_{\\uparrow\\uparrow}({\\bf k})$ and\n$n_{\\downarrow\\downarrow}({\\bf k})$) are not modified by the SOC. However, the\nSOC can significantly modify the behavior of the \\textit{non-diagonal elements}\nof the momentum distribution function, i.e., $n_{\\uparrow\\downarrow}({\\bf k})$\nand $n_{\\downarrow\\uparrow}({\\bf k})$, in the large-$k$ limit. In the absence\nof the SOC, the leading order of these elements is ${\\cal O}(1/k^{6})$. When\nSOC appears, it can induce a term on the order of $1/k^{5}$. We further derive\nthe adiabatic relation and the energy functional. Our results show the SOC can\ninduce a new term in the energy functional, which simply describe the\ncontribution from the SOC to the total energy. The form of the adiabatic\nrelation for our system is not modified by the SOC.",
        "positive": "Quantum critical behavior of entanglement in lattice bosons with\n  cavity-mediated long-range interactions: We analyze the ground-state entanglement entropy of the extended Bose-Hubbard\nmodel with infinite-range interactions. This model describes the low-energy\ndynamics of ultracold bosons tightly bound to an optical lattice and\ndispersively coupled to a cavity mode. The competition between onsite repulsion\nand global cavity-induced interactions leads to a rich phase diagram, which\nexhibits superfluid, supersolid, and insulating (Mott and checkerboard) phases.\nWe use a slave-boson treatment of harmonic quantum fluctuations around the\nmean-field solution and calculate the entanglement entropy across the phase\ntransitions. At commensurate filling, the insulator-superfluid transition is\nsignalled by a singularity in the area-law scaling coefficient of the\nentanglement entropy, that is similar to the one reported for the standard\nBose-Hubbard model. Remarkably, at the continuous $\\mathbb{Z}_2$\nsuperfluid-to-supersolid transition we find a critical logarithmic term,\nregardless of the filling. This behavior originates from the appearance of a\nroton mode in the excitation and entanglement spectrum, becoming gapless at the\ncritical point, and it is characteristic of collective models."
    },
    {
        "anchor": "Boiling a Unitary Fermi Liquid: We study the thermal evolution of a highly spin-imbalanced, homogeneous Fermi\ngas with unitarity limited interactions, from a Fermi liquid of polarons at low\ntemperatures to a classical Boltzmann gas at high temperatures. Radio-frequency\nspectroscopy gives access to the energy, lifetime, and short-range correlations\nof Fermi polarons at low temperatures $T$. In this regime, we observe a\ncharacteristic $T^2$ dependence of the spectral width, corresponding to the\nquasiparticle decay rate expected for a Fermi liquid. At high $T$, the spectral\nwidth decreases again towards the scattering rate of the classical, unitary\nBoltzmann gas, $\\propto T^{-1/2}$. In the transition region between the quantum\ndegenerate and classical regime, the spectral width attains its maximum, on the\nscale of the Fermi energy, indicating the breakdown of a quasiparticle\ndescription. Density measurements in a harmonic trap directly reveal the\nmajority dressing cloud surrounding the minority spins and yield the\ncompressibility along with the effective mass of Fermi polarons.",
        "positive": "Dynamics of heat and mass transport in a quantum insulator: The real time evolution of two pieces of quantum insulators, initially at\ndifferent temperatures, is studied when they are glued together. Specifically,\neach subsystem is taken as a Bose-Hubbard model in a Mott insulator state. The\nprocess of temperature equilibration via heat transfer is simulated in real\ntime using the Minimally Entangled Typical Thermal States algorithm. The\nanalytic theory based on quasiparticles transport is also given."
    },
    {
        "anchor": "Suppression of polaron self-localization by correlations: We investigate self-localization of a polaron in a homogeneous Bose-Einstein\ncondensate in one dimension. This effect, where an impurity is trapped by the\ndeformation that it causes in the surrounding Bose gas, has been first\npredicted by mean field calculations, but has not been seen in experiments. We\nstudy the system in one dimension, where, according to the mean field\napproximation, the self-localization effect is particularly robust, and present\nfor arbitrarily weak impurity-boson interactions. We address the question\nwhether self-localization is a real effect by developing a variational method\nwhich incorporates impurity-boson correlations non-perturbatively and solving\nthe resulting inhomogeneous correlated polaron equations. We find that\ncorrelations inhibit self-localization except for very strongly repulsive or\nattractive impurity-boson interactions. Our prediction for the critical\ninteraction strength for self-localization agrees with a sharp drop of the\ninverse effective mass to almost zero found in quantum Monte Carlo simulations\nof polarons in one dimension.",
        "positive": "Variational and Parquet-diagram theory for strongly correlated normal\n  and superfluid systems: We develop the variational and correlated basis functions/parquet-diagram\ntheory of strongly interacting normal and superfluid systems. The first part of\nthis contribution is devoted to highlight the connections between the Euler\nequations for the Jastrow-Feenberg wave function on the one hand side, and the\nring, ladder, and self-energy diagrams of parquet-diagram theory on the other\nside. We will show that these subsets of Feynman diagrams are contained, in a\nlocal approximation, in the variational wave function.\n  In the second part of this work, we derive the fully optimized\nFermi-Hypernetted Chain (FHNC-EL) equations for a superfluid system. Close\nexamination of the procedure reveals that the na\\\"ive application of these\nequations exhibits spurious unphysical properties for even an infinitesimal\nsuperfluid gap. We will conclude that it is essential to go {\\em beyond\\/} the\nusual Jastrow-Feenberg approximation and to include the exact particle-hole\npropagator to guarantee a physically meaningful theory and the correct\nstability range.\n  We will then implement this method and apply it to neutron matter and low\ndensity Fermi liquids interacting via the Lennard-Jones model interaction and\nthe P\\\"oschl-Teller interaction. While the quantitative changes in the\nmagnitude of the superfluid gap are relatively small, we see a significant\ndifference between applications for neutron matter and the Lennard-Jones and\nP\\\"oschl-Teller systems. Despite the fact that the gap in neutron matter can be\nas large as half the Fermi energy, the corrections to the gap are relatively\nsmall. In the Lennard-Jones and P\\\"oschl-Teller models, the most visible\nconsequence of the self-consistent calculation is the change in stability range\nof the system."
    },
    {
        "anchor": "Edge binding of sine-Gordon solitons in spin-orbit coupled Bose-Einstein\n  condensates: In recent experiments with ultracold gases a Raman coupling scheme is used to\nproduce both spin-orbit (SO) and Zeeman-type couplings [Y.-J. Lin et al.,\nNature 471, 83 (2011)]. Their competition drives a phase transition to a\nmagnetized state with broken $Z_2$ symmetry. Using a hydrodynamic approach we\nstudy a confined binary condensate subject to both SO and Zeeman-type\ncouplings. We find that in the limit of small healing length and in the phase\nwith unbroken symmetry, the boundary magnetization profile has an analytical\nsolution in the form of a sine-Gordon soliton. The soliton is bound to the edge\nof the system by the nontrivial boundary condition resulting from the combined\neffect of the SO coupling and the drop in the particle density. The same\nboundary condition is important in the magnetized phase as well, where we\ncharacterize numerically the boundary spin structure. We further discuss how\nthe nontrivial magnetization structure affects the density profile near the\nboundary, yet another prediction that can be tested in current experiments of\nspin-orbit coupled condensates.",
        "positive": "Ground-state and Excitation spectra of Bose-Fermi Mixtures in a\n  Three-Dimensional Optical Lattice: Motivated by recent developments in the experimental study of Bose-Fermi\nmixtures, we investigate ground-state phase diagrams and excitation spectra for\nBose-Fermi mixtures in a three-dimensional (3D) optical lattice. The Gutzwiller\napproximation is used to identify a new phase in which both superfluid bosons\nand metal fermions coexist. As a useful probe to identify the quantum phases,\nwe also calculate the excitation spectra. In Mott insulator phase, two\nexcitation features appear in the spectra that correspond to particle and hole\nexcitations. In superfluid phase, there are Bogoliubov modes and amplitude\nmodes. In coexisting phase, two gapless dispersive modes are identified, which\nshift due to interaction between bosons and fermions."
    },
    {
        "anchor": "Characterization of Mott-insulating and superfluid phases in the\n  one-dimensional Bose--Hubbard model: We use strong-coupling perturbation theory, the variational cluster approach\n(VCA), and the dynamical density-matrix renormalization group (DDMRG) method to\ninvestigate static and dynamical properties of the one-dimensional\nBose--Hubbard model in both the Mott-insulating and superfluid phases. From the\nvon Neumann entanglement entropy we determine the central charge and the\ntransition points for the first two Mott lobes. Our DMRG results for the\nground-state energy, momentum distribution function, boson correlation function\ndecay, Mott gap, and single particle-spectral function are reproduced very well\nby the strong-coupling expansion to fifth order, and by VCA with clusters up to\n12 sites as long as the ratio between the hopping amplitude and on-site\nrepulsion, t/U, is smaller than 0.15 and 0.25, respectively. In addition, in\nthe superfluid phase VCA captures well the ground-state energy and the sound\nvelocity of the linear phonon modes. This comparison provides an authoritative\nestimate for the range of applicability of these methods. In strong-coupling\ntheory for the Mott phase, the dynamical structure factor is obtained from the\nsolution of an effective single-particle problem with an attractive potential.\nThe resulting resonances show up as double-peak structure close to the\nBrillouin zone boundary. These high-energy features also appear in the\nsuperfluid phase which is characterized by a pronounced phonon mode at small\nmomenta and energies, as predicted by Bogoliubov and field theory. In one\ndimension, there are no traces of an amplitude mode in the dynamical\nsingle-particle and two-particle correlation functions.",
        "positive": "Controlling the pair momentum of the FFLO state in a 3D Fermi gas\n  through a 1D periodic potential: The question whether a spin-imbalanced Fermi gas can accommodate the\nFulde-Ferrell-Larkin-Ovchinnikov (FFLO) state has been the subject of intense\nstudy. This state, in which Cooper pairs obtain a nonzero momentum, has\nhitherto eluded experimental observation. Recently, we demonstrated that the\nFFLO state can be stabilized in a 3D Fermi gas, by adding a 1D periodic\npotential. Until now it was assumed that the FFLO wave vector always lies\nparallel to this periodic potential (FFLO-P). In this contribution we show\nthat, surprisingly, the FFLO wave vector can also lie skewed with respect to\nthe potential (FFLO-S). Starting from the partition sum, the saddle-point free\nenergy of the system is derived within the path-integral formalism. Minimizing\nthis free energy allows us to study the different competing ground states of\nthe system. To qualitatively understand the underlying pairing mechanism, we\nvisualize the Fermi surfaces of the spin up and spin down particles. From this\nvisualization, we find that tilting the FFLO wave vector with respect to the\ndirection of the periodic potential, can result in a larger overlap between the\npairing bands of both spin species. This skewed FFLO state can provide an\nadditional experimental signature for observing FFLO superfluidity in a 3D\nFermi gas."
    },
    {
        "anchor": "Ground states of a Bose-Einstein Condensate in a one-dimensional\n  laser-assisted optical lattice: We study the ground-state behavior of a Bose-Einstein Condensate (BEC) in a\nRaman-laser-assisted one-dimensional (1D) optical lattice potential forming a\nmultilayer system. We find that, such system can be described by an effective\nmodel with spin-orbit coupling (SOC) of pseudospin $(N-1)/2$, where $N$ is the\nnumber of layers. Due to the intricate interplay between atomic interactions,\nSOC and laser-assisted tunnelings, the ground-state phase diagrams generally\nconsist of three phases -- a stripe, a plane wave and a normal phase with\nzero-momentum, touching at a quantum tricritical point. More important, even\nthough the single-particle states only minimize at zero-momentum for odd $N$,\nthe many-body ground states may still develop finite momenta. The underlying\nmechanisms are elucidated. Our results provide an alternative way to realize an\neffective spin-orbit coupling of Bose gas with the Raman-laser-assisted optical\nlattice, and would also be beneficial to the studies on SOC effects in spinor\nBose systems with large spin.",
        "positive": "Two-dimensional dipolar gap solitons in free space with spin-orbit\n  coupling: We present gap solitons (GSs) that can be created in free nearly\ntwo-dimensional (2D) space in dipolar spinor Bose-Einstein condensates with the\nspin-orbit coupling (SOC), subject to tight confinement, with size $a_{\\perp\n}$, in the third direction. For quasi-2D patterns, with lateral sizes $l\\gg\na_{\\perp }$, the kinetic-energy terms in the respective spinor Gross-Pitaevskii\nequations may be neglected in comparison with SOC. This gives rise to a bandgap\nin the system's spectrum, in the presence of the Zeeman splitting between the\nspinor components. While the present system with contact interactions does not\nproduce 2D solitons, stable gap solitons(GSs), with vorticities $0$ and $1$ in\nthe two components, are found, in quasi-analytical and numerical forms, under\nthe action of dipole-dipole interaction (DDI). Namely, isotropic and\nanisotropic 2D GSs are obtained when the dipoles are polarized, respectively,\nperpendicular or parallel to the 2D plane. The GS families extend, as\n\\textit{embedded solitons} (ESs), into spectral bands, a part of the ES branch\nbeing stable for isotropic solitons. The GSs remain stable if the competing\ncontact interaction, with the sign opposite to that of the DDI, is included,\nwhile the addition of the contact term with the same sign destabilizes the GSs,\nat first replacing them by breathers, and eventually leading to destruction of\nthe solitons. Mobility and collision of the GSs are studied too, revealing\nnegative and positive effective masses of the isotropic and anisotropic\nsolitons, respectively."
    },
    {
        "anchor": "Exploring Interacting Topological Insulators with Ultracold Atoms: the\n  Synthetic Creutz-Hubbard Model: Understanding the robustness of topological phases of matter in the presence\nof strong interactions, and synthesising novel strongly-correlated topological\nmaterials, lie among the most important and difficult challenges of modern\ntheoretical and experimental physics. In this work, we present a complete\ntheoretical analysis of the synthetic Creutz-Hubbard ladder, which is a\nparadigmatic model that provides a neat playground to address these challenges.\nWe put special attention to the competition of correlated topological phases\nand orbital quantum magnetism in the regime of strong interactions. These\nresults are furthermore confirmed and extended by extensive numerical\nsimulations. Moreover we propose how to experimentally realize this model in a\nsynthetic ladder, made of two internal states of ultracold fermionic atoms in a\none-dimensional optical lattice. Our work paves the way towards quantum\nsimulators of interacting topological insulators with cold atoms.",
        "positive": "Atom-dimer and dimer-dimer scatterings in a spin-orbit coupled Fermi gas: Using the diagrammatic approach, here we study how spin-orbit coupling (SOC)\naffects the fermion-dimer and dimer-dimer scattering lengths in the Born\napproximation, and benchmark their accuracy with the higher-order\napproximations. We consider both isotropic and Rashba couplings in three\ndimensions, and show that the Born approximation gives accurate results in the\n$1/(m \\alpha a_s) \\ll -1$ limit, where $m$ is the mass of the fermions,\n$\\alpha$ is the strength of the SOC, and $a_s$ is the $s$-wave scattering\nlength between fermions. This is because the higher-loop contributions form a\nperturbative series in the $1/(m \\alpha a_s) < 0$ region that is controlled by\nthe smallness of the residue $Z$ of the dimer propagator. In sharp contrast,\nsince $Z$ grows with the square-root of the binding energy of the dimer in the\n$1/(m \\alpha a_s) > 0$ region, all of the higher-loop contributions are of\nsimilar order."
    },
    {
        "anchor": "Rotational Response of Two-Component Bose-Einstein Condensates in Ring\n  Traps: We consider a two-component Bose-Einstein condensate (BEC) in a ring trap in\na rotating frame, and show how to determine the response of such a\nconfiguration to being in a rotating frame, via accumulation of a Sagnac phase.\nThis may be accomplished either through population oscillations, or the motion\nof spatial density fringes. We explicitly include the effect of interactions\nvia a mean-field description, and study the fidelity of the dynamics relative\nto an ideal configuration.",
        "positive": "Ultracold bosons with short-range interaction in regular optical\n  lattices: During the last decade, many exciting phenomena have been experimentally\nobserved and theoretically predicted for ultracold atoms in optical lattices.\nThis paper reviews these rapid developments concentrating mainly on the theory.\nDifferent types of the bosonic systems in homogeneous lattices of different\ndimensions as well as in the presence of harmonic traps are considered. An\noverview of the theoretical methods used for these investigations as well as of\nthe obtained results is given. Available experimental techniques are presented\nand discussed in connection with theoretical considerations. Eigenstates of the\ninteracting bosons in homogeneous lattices and in the presence of harmonic\nconfinement are analysed. Their knowledge is essential for understanding of\nquantum phase transitions at zero and finite temperature."
    },
    {
        "anchor": "The Fate of the Higgs Mode in a Trapped Dipolar Supersolid: We theoretically investigate the spectrum of elementary excitations of a\ntrapped dipolar quantum gas across the BEC-supersolid phase transition. Our\ncalculations reveal the existence of distinct Higgs and Nambu-Goldstone modes\nthat emerge from the softening roton modes of the dipolar BEC at the phase\ntransition point. On the supersolid side of the transition, the energy of the\nHiggs mode increases rapidly, leading to a strong coupling to higher-lying\nmodes. Our study highlights how the symmetry-breaking nature of the supersolid\nstate translates to finite-size systems.",
        "positive": "Gap solitons and nonlinear Bloch states in Bose-Einstein condensates\n  with current-dependent interactions: We show how the chiral properties of Bose Einstein condensates subject to\ncurrent-density interactions and loaded in optical lattices can be observed in\nthe realization of nonlinear Bloch states, whose spectrum lacks the usual\nperiodic structure. Chirality is also manifested by spatially localized states,\nor gap solitons, which are found for positive rotation rates of the lattice at\nthe energy gaps between the linear energy bands, whereas for negative rotations\nthey appear in the semi-infinite gap of the linear spectrum. The stability of\nextended and localized states is checked through the spectrum of linear\nexcitations and nonlinear time evolution of perturbed states, and the\nphenomenon of Bloch oscillations is explored. Our results are obtained in quasi\n1D ring geometries with feasible experimental parameters."
    },
    {
        "anchor": "Room-temperature superfluidity in a polariton condensate: Superfluidity---the suppression of scattering in a quantum fluid at\nvelocities below a critical value---is one of the most striking manifestations\nof the collective behaviour typical of Bose-Einstein condensates. This\nphenomenon, akin to superconductivity in metals, has until now only been\nobserved at prohibitively low cryogenic temperatures. For atoms, this limit is\nimposed by the small thermal de Broglie wavelength, which is inversely related\nto the particle mass. Even in the case of ultralight quasiparticles such as\nexciton-polaritons, superfluidity has only been demonstrated at liquid helium\ntemperatures. In this case, the limit is not imposed by the mass, but instead\nby the small exciton binding energy of Wannier-Mott excitons, which places the\nupper temperature limit. Here we demonstrate a transition from normal to\nsuperfluid flow in an organic microcavity supporting stable Frenkel\nexciton-polaritons at room temperature. This result paves the way not only to\ntable-top studies of quantum hydrodynamics, but also to room-temperature\npolariton devices that can be robustly protected from scattering.",
        "positive": "Formation and decay of Bose-Einstein condensates in an excited band of a\n  double-well optical lattice: We study the formation and collision-aided decay of an ultra-cold atomic\nBose-Einstein condensate in the first excited band of a double-well 2D-optical\nlattice with weak harmonic confinement in the perpendicular $z$ direction. This\nlattice geometry is based on an experiment by Wirth et al. The double well is\nasymmetric, with the local ground state in the shallow well nearly degenerate\nwith the first excited state of the adjacent deep well. We compare the band\nstructure obtained from a tight-binding (TB) model with that obtained\nnumerically using a plane wave basis. We find the TB model to be in\nquantitative agreement for the lowest two bands, qualitative for next two\nbands, and inadequate for even higher bands. The band widths of the excited\nbands are much larger than the harmonic oscillator energy spacing in the $z$\ndirection. We then study the thermodynamics of a non-interacting Bose gas in\nthe first excited band. We estimate the condensate fraction and critical\ntemperature, $T_c$, as functions of lattice parameters. For typical atom\nnumbers, the critical energy $k_BT_c$, with $k_B$ the Boltzmann constant, is\nlarger than the excited band widths and harmonic oscillator energy. Using\nconservation of total energy and atom number, we show that the temperature\nincreases after the lattice transformation. Finally, we estimate the time scale\nfor a two-body collision-aided decay of the condensate as a function of lattice\nparameters. The decay involves two processes, the dominant one in which both\ncolliding atoms decay to the ground band, and the second involving excitation\nof one atom to a higher band. For this estimate, we have used TB wave functions\nfor the lowest four bands, and numerical estimates for higher bands. The decay\nrate rapidly increases with lattice depth, but stays smaller than the tunneling\nrate between the $s$ and $p$ orbitals in adjacent wells."
    },
    {
        "anchor": "Incommensurability effects on dipolar bosons in optical lattices: We present a study that investigated a quantum dipolar gas in continuous\nspace where a potential lattice was imposed. Employing exact quantum Monte\nCarlo techniques, we analysed the ground state properties of the scrutinised\nsystem, varying the lattice depth and the dipolar interaction. For system\ndensities corresponding to a commensurate filling with respect to the optical\nlattice, we observed a simple crystal-to-superfluid quantum phase transition,\nbeing consistent with the physics of dipolar bosons in continuous space. In\ncontrast, an incommensurate density showed the presence of a supersolid phase.\nIndeed, such a result opens up the tempting opportunity to observe a\ndefect-induced supersolidity with dipolar gases in combination with a tunable\noptical lattice. Finally, the stability of the condensate was analysed at\nfinite temperature.",
        "positive": "Response to comment by Tin-Lun Ho on \"Itinerant Ferromagnetism in a\n  Strongly Interacting Fermi Gas of Ultracold Atoms\", Science 325, 1521 (2009): Ho claims in his comment that our experiment is direct evidence that\nitinerant ferromagnetism does not exist in ultracold Fermi gases. This claim is\nincorrect and based on an invalid estimate of relaxation times and an erroneous\ninterpretation of the detectability of ferromagnetic domains. We point out that\nthe experimental evidence is consistent with the existence of ferromagnetism,\nbut further experiments are needed to distinguish a ferromagnetic ground state\nfrom a non-magnetic ground state with ferromagnetic correlations."
    },
    {
        "anchor": "Quantum fluctuations and condensate fraction during the time-of-flight\n  expansion: The quantum fluctuation effects in the time-of-flight (TOF) experiment for a\ncondensate released from an optical lattice potential is studied within the\ntruncated Wigner approximation. By investigating both the spatial and momentum\ndensity distributions, we find that the condensate fraction decreases\nmonotonically in time and hence cannot be measured in the standard TOF image.\nWe then propose a semi-quantitative analysis for such dynamical quantum\ndepletion process. Our study shows a universal algebraic decay of the true\ncondensate fraction, and have a very good agreement with numerical results. We\nalso discuss possible methods to determine the condensate fraction inside the\noptical lattice, and its implication to the TOF experiments in higher\ndimensional systems.",
        "positive": "Expansion Dynamics of Two Dimensional Extended Bose-Hubbard Model: We study the expansion dynamics of harmonically trapped bosons in a\ntwo-dimensional lattice within the extended Bose-Hubbard model. We evaluate the\ndynamics of the system following a sudden removal of the confining potential,\nstarting with a cloud mostly in n = 1 Mott state. We show that the nearest\nneighbour interactions have a strong influence on the dynamics of ultracold\nbosons on an optical lattice. Also we conclude that validity of the widely used\ncontact potential approximation is questionable in the presence of Feschbach\nresonances."
    },
    {
        "anchor": "Chiral d-wave superfluid in periodically driven lattices: Chiral d-wave superfluid is a preliminary example of topological matters that\nintrinsically encodes interaction effects. It exhibits fascinating properties\nincluding a finite Chern number in the bulk and topologically protected edge\nstates, which have been invoking physicists for decades. However, unlike s-wave\nsuperfluids prevalent in nature, its existence requires a strong interaction in\nthe d-wave channel, a criterion that is difficult to access in ordinary\nsystems. So far, such an unconventional superfluid has not been discovered in\nexperiments. Here, we present a new principle for creating a two-dimensional\nchiral d-wave superfluid using periodically driven lattices. Due to an\nimprinted two-dimensional pseudospin-orbit coupling, where the sublattice index\nserves as the pseudospin, s-wave interaction between two hyperfine spin states\nnaturally creates a chiral d-wave superfluid. This scheme also allows\nphysicists to study the phase transition between the topologically distinct s-\nand d-wave superfluids by controlling the driving field or the particle\ndensity.",
        "positive": "Transport of Hubbard-Band Quasiparticles in Disordered Optical Lattices: Quantum degenerate gases trapped in optical lattices are ideal testbeds for\nfundamental physics because these systems are tunable, well characterized, and\nisolated from the environment. Controlled disorder can be introduced to explore\nsuppression of quantum diffusion in the absence of conventional dephasing\nmechanisms such as phonons, which are unavoidable in experiments on electronic\nsolids. Recent experiments use transport of degenerate Fermi gases in optical\nlattices (Kondov et al. Phys. Rev. Lett. 114, 083002 (2015)) to probe a\nparticularly extreme regime of strong interaction in what can be modeled as an\nAnderson-Hubbard model. These experiments find evidence for an intriguing\ninsulating phase where quantum diffusion is completely suppressed by strong\ndisorder. Quantitative interpretation of these experiments remains an open\nproblem that requires inclusion of non-zero entropy, strong interaction, and\ntrapping. We argue that the suppression of transport can be thought of as\nlocalization of Hubbard-band quasiparticles. We construct a theory of transport\nof Hubbard-band quasiparticles tailored to trapped optical lattice experiments.\nWe compare the theory directly with center-of-mass transport experiments of\nKondov et al. with no fitting parameters. The close agreement between theory\nand experiments shows that the suppression of transport is only partly due to\nfinite entropy effects. We argue that the complete suppression of transport is\nconsistent with Anderson localization of Hubbard-band quasiparticles. The\ncombination of our theoretical framework and optical lattice experiments offers\nan important platform for studying localization in isolated many-body quantum\nsystems."
    },
    {
        "anchor": "Onset of the Limit Cycle and Universal Three-Body Parameter in Efimov\n  Physics: The Efimov effect is the only experimentally realized universal phenomenon\nthat exhibits the renormalization-group limit cycle with the three-body\nparameter parametrizing a family of universality classes. Recent experiments in\nultracold atoms have unexpectedly revealed that the three-body parameter itself\nis universal when measured in units of an effective range. By performing an\nexact functional renormalization-group analysis with various finite-range\ninteraction potentials, we demonstrate that the onset of the\nrenormalization-group flow into the limit cycle is universal, regardless of\nshort-range details, which connects the missing link between the two\nuniversalities of the Efimov physics. A close connection between the\ntopological property of the limit cycle and few-body physics is also\ndelineated.",
        "positive": "Magnetic field induced band insulator to Mott insulator transformations\n  in 4-component alkali fermions at half-filling: Under the influence of an external magnetic field and spin-changing\ncollisions, the band insulator (BI) state of one-dimensional (1D) s-wave\nrepulsively interacting 4-component fermions at half-filling transforms into\nMott insulator (MI) states with spontaneously broken translational symmetry: a\ndimerized state for shallow lattices and a N{\\'e}el state for deep lattices via\nan intermediate topological state. Since a BI has vanishing entropy per\nparticle, these MI phases could be particularly inviting for experimental\nrealization under the similar conditions as those for $^{40}$K atoms [1],\nprovided the magnetic field is changed adiabatically."
    },
    {
        "anchor": "Signature of Quantum Criticality in the Density Profiles of Cold Atom\n  Systems: In recent years, there is considerable experimental effort using cold atoms\nto study strongly correlated many-body systems. One class of phenomena of\nparticularly interests is quantum critical (QC) phenomena. While prevalent in\nmany materials, these phenomena are notoriously difficult theoretical problems\ndue to the vanishing of energy scales in QC region. So far, there are no\nsystematic ways to deduce QC behavior of bulk systems from the data of trapped\natomic gases. Here, we present a simple algorithm to use the experimental\ndensity profile to determine the T=0 phase boundary of bulk systems, as well as\nthe scaling functions in QC regime. We also present another scheme for removing\nfinite size effects of the trap. We demonstrate the validity of our schemes\nusing exactly soluble models.",
        "positive": "Scattering tightly bound dimers off a scattering potential: The motion of two attractively interacting atoms in an optical lattice is\ninvestigated in the presence of a scattering potential. The initial\nwavefunction can be prepared by using tightly bound exact two-particle\neigenfunction for vanishing scattering potential. This allows to numerically\nsimulate the dynamics in the generation of two-particle Schrodinger cat states\nusing a scheme recently proposed for scattering of quantum matter wave\nsolitons."
    },
    {
        "anchor": "Consistent theory of self-bound quantum droplets with bosonic pairing: We revisit the Bogoliubov theory of quantum droplets proposed by Petrov\n{[}Phys. Rev. Lett. \\textbf{115}, 155302 (2015){]} for an ultracold Bose-Bose\nmixture, where the mean-field collapse is stabilized by the Lee-Huang-Yang\nquantum fluctuations. We show that a loophole in Petrov's theory, i.e., the\nignorance of the softening complex Bogoliubov spectrum, can be naturally\nremoved by the introduction of bosonic pairing. The pairing leads to weaker\nmean-field attractions, and also stronger Lee-Huang-Yang term in the case of\nunequal intraspecies interactions. As a result, the equilibrium density for the\nformation of self-bound droplets significantly decrease in the deep droplet\nregime, in agreement with a recent observation from diffusion Monte Carlo\nsimulations. Our construction of a consistent Bogoliubov theory paves the way\nto understand the puzzling low critical number of small quantum droplets\nobserved in the experiment {[}Science \\textbf{359}, 301 (2018){]}.",
        "positive": "Universality of Bose-Einstein Condensation and Quenched Formation\n  Dynamics: The emergence of macroscopic coherence in a many-body quantum system is a\nubiquitous phenomenon across different physical systems and scales. This\nChapter reviews key concepts characterizing such systems (correlation\nfunctions, condensation, quasi-condensation) and applies them to the study of\nemerging non-equilibrium features in the dynamical path towards such a\nhighly-coherent state: particular emphasis is placed on emerging universal\nfeatures in the dynamics of conservative and open quantum systems, their\nequilibrium or non-equilibrium nature, and the extent that these can be\nobserved in current experiments with quantum gases. Characteristic examples\ninclude symmetry-breaking in the Kibble-Zurek mechanism, coarsening and\nphase-ordering kinetics, and universal spatiotemporal scalings around\nnon-thermal fixed points and in the context of the Kardar- Parisi-Zhang\nequation; the Chapter concludes with a brief review of the potential relevance\nof some of these concepts in modelling the large-scale distribution of dark\nmatter in the universe."
    },
    {
        "anchor": "Evidence from on-site atom number fluctuations for a quantum\n  Berezinskii-Kosterlitz-Thouless transition in the one-dimensional\n  Bose-Hubbard model: We study the one-dimensional Bose-Hubbard model describing the\nsuperfluid-Mott insulator quantum phase transition of cold atoms in optical\nlattices. We show that derivatives of the variance of the on-site atom number\noccupation, computed with respect to the parameter driving the transition, have\nextrema that are located off the critical point even in the thermodynamic\nlimit. We discuss whether such extrema provide solid evidence of the quantum\nBerezinskii-Kosterlitz-Thouless transition taking place in this system. The\ncalculations are done for systems with the mean number of atoms per lattice\nsite equal to either one or two. They also characterize the nearest-neighbor\ncorrelation function, which is typically discussed in the context of\ntime-of-flight images of cold atoms.",
        "positive": "Adiabaticity when raising a uniform 3D optical lattice in a bimodal\n  Bose-Einstein condensate: Using the time-dependent Bogoliubov approach, we study adiabaticity for a\ntwo-component Bose-Einstein condensate in a 3D time-dependent optical lattice\nwith unit filling, in the superfluid and weakly interacting regime. We show\nthat raising the lattice potential height can couple the ground state of the\nBogoliubov Hamiltonian to excited states with two quasiparticles of opposite\nquasi-momenta. In the symmetric case for interactions and density in the two\ncomponents these represent sound waves where the two components oscillate out\nof phase. We find an analytic expression of the adiabatic time, its dependence\non the fraction of atoms in each component and its scaling with the system\nsize."
    },
    {
        "anchor": "Rabi-coupled Countersuperflow in Binary Bose-Einstein Condensates: We show theoretically that periodic density patterns are stabilized in two\ncounter-propagating Bose-Einstein condensates of atoms in different hyperfine\nstates under Rabi coupling. In the presence of coupling, the relative velocity\nbetween two components is localized around density depressions in\nquasi-one-dimensional systems. When the relative velocity is sufficiently\nsmall, the periodic pattern reduces to a periodic array of topological solitons\nas kinks of relative phase. According to our variational and numerical\nanalyses, the soliton solution is well characterized by the soliton width and\ndensity depression. We demonstrate the dependence of the depression and width\non the Rabi frequency and the coupling constant of inter-component\ndensity-density interactions. The periodic pattern of the relative phase\ntransforms continuously from a soliton array to a sinusoidal pattern as the\nperiod becomes smaller than the soliton width. These patterns become unstable\nwhen the localized relative velocity exceeds a critical value. The\nstability-phase diagram of this system is evaluated with a stability analysis\nof countersuperflow, by taking into account the finite-size-effect owing to the\ndensity depression.",
        "positive": "Faraday Waves in strongly interacting superfluids: We report on the observation of Faraday waves in a cigar-shaped Fermi\nsuperfluid of $^6$Li parametrically excited by modulating the radial trap\nfrequency. We characterize the phenomenon as a function of the interaction\nparameter by means of a Feshbach resonance. Starting from the BEC side of the\nresonance we observe a drop on the visibility of the Faraday pattern as we\napproach to unitarity, possibly due to the increased incompressibility of the\nsystem. We probe the superfluid excitation spectrum by extracting an effective\n1D speed of sound for different values of the interaction parameter, in good\nagreement with numerical simulations. Finally, we perform a stability analysis\nin the parameter space using a simplified model and we show the emergence of\nthe Faraday waves as unstable solutions to a Mathieu-like equation."
    },
    {
        "anchor": "Multivortex states and dynamics in nonequilibrium quantum fluids: In strongly nonequilibrium Bose-Einstein condensates described by the\ngeneralized Gross-Pitaevskii equation, vortex motion becomes self-accelerated\nwhile the long-range vortex-antivortex interaction appears to be repulsive. We\nnumerically study the impact of these rather unusual vortex properties on the\ndynamics of multivortex systems. We show that at strong nonequilibrium the\nrepulsion between vortices and antivortices leads to a dramatic slowdown of\ntheir annihilation. Moreover, in finite-size samples, relaxation of multivortex\nsystems can lead to the formation of metastable vortex-antivortex clusters,\nwhose shape and size depend, in particular, on the sample geometry, boundary\nconditions and deviations from equilibrium. We further demonstrate that at\nstrong nonequilibrium the interaction of self-accelerated vortices with\ninhomogeneous condensate flows can lead to generation of new vortex-antivortex\npairs.",
        "positive": "Active SU(1,1) atom interferometry: Active interferometers use amplifying elements for beam splitting and\nrecombination. We experimentally implement such a device by using spin exchange\nin a Bose-Einstein condensate. The two interferometry modes are initially empty\nspin states that get spontaneously populated in the process of parametric\namplification. This nonlinear mechanism scatters atoms into both modes in a\npairwise fashion and generates a nonclassical state. Finally, a matched second\nperiod of spin exchange is performed that nonlinearly amplifies the output\nsignal and maps the phase onto readily detectable first moments. Depending on\nthe accumulated phase this nonlinear readout can reverse the initial dynamics\nand deamplify the entangled state back to empty spin states. This sequence is\ndescribed in the framework of SU(1,1) mode transformations and compared to the\nSU(2) angular momentum description of passive interferometers."
    },
    {
        "anchor": "Floquet engineering spectral statistics in the Bose-Hubbard model: We study the spectral statistics of a one-dimensional Bose-Hubbard model\nsubjected to kinetic driving; a form of Floquet engineering where the kinetic\nenergy is periodically driven in time with a zero time-average. As the\namplitude of the driving is increased, the ground state of the resulting\nflat-band system passes from the Mott insulator regime to an exotic superfluid.\nWe show that this transition is associated with a change in the system's\nspectral statistics from Poisson to GOE-type. Remarkably, and unlike in the\nconventional Bose-Hubbard model, which we use as a benchmark, the details of\nthe GOE statistics are sensitive to the parity of both the particle number and\nthe lattice sites. We show how this effect arises from a hidden symmetry of the\nHamiltonian produced by this form of Floquet driving.",
        "positive": "Universality of miscible-immiscible phase separation dynamics in\n  two-component Bose-Einstein condensates: We investigate the non-equilibrium dynamics across the miscible-immiscible\nphase separation in a binary mixture of Bose-Einstein condensates.\n  The excitation spectra reveal that the Landau critical velocity vanishes at\nthe critical point, where the superfluidity spontaneously breaks down.\n  We analytically extract the dynamical critical exponent $z=2$ from the Landau\ncritical velocity.\n  Moreover, by simulating the real-time dynamics across the critical point, we\nfind the average domain number and the average bifurcation delay show universal\nscaling laws with respect to the quench time.\n  We then numerically extract the static correlation length critical exponent\n$v=1/2$ and the dynamical critical exponent $z=2$ according to Kibble-Zurek\nmechanism.\n  The scaling exponents $(v=1/2, z=2)$ in the phase separation driven by\nquenching the atom-atom interaction are different from the ones $(v=1/2, z=1)$\nin the phase separation driven by quenching the Rabi coupling strength [PRL\n\\textbf{102}, 070401 (2009); PRL \\textbf{107}, 230402 (2011)].\n  Our study explores the connections between the spontaneous superfluidity\nbreakdown and the spontaneous defect formation in the phase separation\ndynamics."
    },
    {
        "anchor": "Atom Cloud Detection Using a Deep Neural Network: We use a deep neural network to detect and place region-of-interest boxes\naround ultracold atom clouds in absorption and fluorescence images---with the\nability to identify and bound multiple clouds within a single image. The neural\nnetwork also outputs segmentation masks that identify the size, shape and\norientation of each cloud from which we extract the clouds' Gaussian\nparameters. This allows 2D Gaussian fits to be reliably seeded thereby enabling\nfully automatic image processing.",
        "positive": "Energetics and structural properties of two- and three-boson systems in\n  the presence of 1D spin-orbit coupling: It was shown recently that the discrete scaling symmetry, which underlies the\nEfimov effect in the three identical boson system with two-body short-range\ninteractions, survives when single-particle 1D spin-orbit coupling terms are\nadded to the Hamiltonian. Each three-body energy level in the ordinary Efimov\nscenario turns into an energy manifold that contains four energy levels in the\npresence of 1D spin-orbit coupling (equal mixture of Rashba-Dresselhaus\ncoupling). This work provides a detailed characterization of the energy levels\nin these manifolds. The two-boson energies, which enter into the three-boson\nscattering threshold, are analyzed in detail. Moreover, the structural\nproperties, e.g., momentum distributions of the two- and three-boson systems,\nare analyzed for various parameter combinations."
    },
    {
        "anchor": "Quantum phases of Bose-Bose mixtures on a triangular lattice: We investigate the zero temperature quantum phases of a Bose-Bose mixture on\na triangular lattice using Bosonic Dynamical Mean Field Theory (BDMFT). We\nconsider the case of total filling one where geometric frustration arises for\nasymmetric hopping. We map out a rich ground state phase diagram including\nxy-ferromagnetic, spin-density wave, superfluid, and supersolid phases. In\nparticular, we identify a stripe spin-density wave phase for highly asymmetric\nhopping. On top of the spin-density wave, we find that the system generically\nshows weak charge (particle) density wave order.",
        "positive": "Quantum information theoretic measures to distinguish fermionized bosons\n  from non-interacting fermions: We study the dynamical fermionization of strongly interacting one-dimensional\nbosons in Tonks-Girardeau limit by solving the time dependent many-boson\nSchr\\\"odinger equation numerically exactly. We establish that the one-body\nmomentum distribution approaches the ideal Fermi gas distribution at the time\nof dynamical fermionization. The analysis is further complemented by the\nmeasures on two-body level. Investigation on two-body momentum distribution,\ntwo-body local and non-local correlation clearly distinguish the fermionized\nbosons from non-interacting fermions. The magnitude of distinguishablity\nbetween the two systems is further discussed employing suitable measures of\ninformation theory, i.e., the well known Kullback-Leibler relative entropy and\nthe Jensen-Shannon divergence entropy. We also observe very rich structure in\nthe higher-body density for strongly correlated bosons whereas non-interacting\nfermions do not possess any higher order correlation beyond two-body."
    },
    {
        "anchor": "Hydrodynamic modes of partially condensed Bose mixtures: We generalize the Landau-Khalatnikov hydrodynamic theory for superfluid\nhelium to two-component (binary) Bose mixtures at arbitrary temperatures. In\nparticular, we include the spin-drag terms that correspond to viscous coupling\nbetween the clouds. Therefore, our theory not only describes the usual\ncollective modes of the individual components, e.g., first and second sound,\nbut also results in new collective modes, where both constituents participate.\nWe study these modes in detail and present their dispersions using\nthermodynamic quantities obtained within the Popov approximation.",
        "positive": "Density Dependent Spin-Orbit Coupling in Degenerate Quantum Gases: In this letter we propose a method to realize a kind of spin-orbit coupling\nin ultracold Bose and Fermi gases whose format and strength depend on density\nof atoms. Our method combines two-photon Raman transition and periodical\nmodulation of spin-dependent interaction, which gives rise to the direct Raman\nprocess and the interaction assisted Raman process, and the latter depends on\ndensity of atoms. These two processes have opposite effects in term of\nspin-momentum locking and compete with each other. As the interaction\nmodulation increases, the system undergoes a crossover from the direct Raman\nprocess dominated regime to the interaction assisted Raman process dominated\nregime. For this crossover, we show that for bosons, both the condensate\nmomentum and the chirality of condensate wave function change sign, and for\nfermions, the Fermi surface distortion is inverted. We highlight that there\nexists an emergent spatial reflection symmetry in the crossover regime, which\ncan manifest itself universally in both Bose and Fermi gases. Our method paves\na way to novel phenomena in a non-abelian gauge field with intrinsic dynamics."
    },
    {
        "anchor": "Superfluidity and dimerization in a multilayered system of fermionic\n  polar molecules: We consider a layered system of fermionic molecules with permanent dipole\nmoments aligned by an external field. The dipole interactions between fermions\nin adjacent layers are attractive and induce inter-layer pairing. Due to\ncompetition for pairing among adjacent layers, the mean-field ground state of\nthe layered system is a dimerized superfluid, with pairing only between\nevery-other layer. We construct an effective Ising-XY lattice model that\ndescribes the interplay between dimerization and superfluid phase fluctuations.\nIn addition to the dimerized superfluid ground state, and high temperature\nnormal state, at intermediate temperature, we find an unusual dimerized\n\"pseudogap\" state with only short-range phase coherence. We propose light\nscattering experiments to detect dimerization.",
        "positive": "Exactly solvable model of two interacting Rydberg-dressed atoms confined\n  in a two-dimensional harmonic trap: Exactly solvable model of two Rydberg-dressed atoms moving in a\nquasi-two-dimensional harmonic trap is introduced and its properties are\ninvestigated. Depending on the strength of inter-particle interactions and the\ncritical range of the potential, the two-particle eigenstates are classified\nwith respect to the excitations of the center-of-mass motion, relative angular\nmomentum, and relative distance variable. Having these solutions in hand, we\ndiscuss inter-particle correlations as functions of interaction parameters. We\nalso present a straightforward prescription of how to generalize obtained\nsolutions to higher dimensions."
    },
    {
        "anchor": "Soliton core filling in superfluid Fermi gases with spin-imbalance: In this paper the properties of dark solitons in superfluid Fermi gases with\nspin-imbalance are studied by means of a recently developed effective field\ntheory [S. N. Klimin, J. Tempere, G. Lombardi, J. T. Devreese, Eur. Phys. J. B\n88, 122 (2015)] suitable to describe the BEC-BCS crossover in ultracold gases\nin an extended range of temperatures as compared to the usual Ginzburg-Landau\ntreatments. The spatial profiles for the total density and for the density of\nthe excess-spin component, and the changes of their properties across the\nBEC-BCS crossover are examined in different conditions of temperature and\nimbalance. The presence of population imbalance is shown to strongly affect the\nstructure of the soliton excitation by filling its core with unpaired atoms.\nThis in turn influences the dynamical properties of the soliton since the\nadditional particles in the core have to be dragged along thus altering the\neffective mass.",
        "positive": "Numerical method for the stochastic projected Gross-Pitaevskii equation: We present a method for solving the stochastic projected Gross-Pitaevskii\nequation (SPGPE) for a three-dimensional Bose gas in a harmonic-oscillator\ntrapping potential. The SPGPE contains the challenge of both accurately\nevolving all modes in the low energy classical region of the system, and\nevaluating terms from the number-conserving scattering reservoir process. We\ngive an accurate and efficient procedure for evaluating the scattering terms\nusing a Hermite-polynomial based spectral-Galerkin representation, which allows\nus to precisely implement the low energy mode restriction. Stochastic\nintegration is performed using the weak semi-implicit Euler method. We\nextensively characterize the accuracy of our method, finding a faster than\nexpected rate of stochastic convergence. Physical consistency of the algorithm\nis demonstrated by considering thermalization of initially random states."
    },
    {
        "anchor": "Transverse spin dynamics in the anisotropic Heisenberg model realized\n  with ultracold atoms: In Heisenberg models with exchange anisotropy, transverse spin components are\nnot conserved and can decay not only by transport, but also by dephasing. Here\nwe utilize ultracold atoms to simulate the dynamics of 1D Heisenberg spin\nchains, and observe fast, local spin decay controlled by the anisotropy.\nAdditionally, we directly observe an effective magnetic field created by\nsuperexchange which causes an inhomogeneous decay mechanism due to variations\nof lattice depth between chains, as well as dephasing within each chain due to\nthe twofold reduction of the effective magnetic field at the edges of the\nchains and due to fluctuations of the effective magnetic field in the presence\nof mobile holes. The latter is a new coupling mechanism between holes and\nmagnons. All these dephasing mechanisms, corroborated by extensive numerical\nsimulations, have not been observed before with ultracold atoms and illustrate\nbasic properties of the underlying Hubbard model.",
        "positive": "Trapped Bose-Bose mixtures at finite temperature: a quantum Monte Carlo\n  approach: We study thermal properties of a trapped Bose-Bose mixture in a dilute regime\nusing quantum Monte Carlo methods. Our main aim is to investigate the\ndependence of the superfluid density and the condensate fraction on\ntemperature, for the mixed and separated phases. To this end, we use the\ndiffusion Monte Carlo method, in the zero-temperature limit, and the\npath-integral Monte Carlo method for finite temperatures. The results obtained\nare compared with solutions of the coupled Gross-Pitaevskii equations for the\nmixture at zero temperature. We notice the existence of an anisotropic\nsuperfluid density in some phase-separated mixtures. Our results also show that\nthe temperature evolution of the superfluid density and condensate fraction is\nslightly different, showing noteworthy situations where the superfluid fraction\nis smaller than the condensate fraction."
    },
    {
        "anchor": "Ground-State Ferromagnetic Transition in Strongly Repulsive\n  One-Dimensional Fermi Gases: We prove that as a one-dimensional Fermi gas is brought across the resonance\nadiabatically from large repulsion to large attraction, the singlet ground\nstate will give way to the maximum spin state, which is the lowest energy state\namong the states accessible to the system in this process. In the presence of\ntiny symmetry breaking fields that destroy spin conservation, the singlet\nground state can evolve to the ferromagnetic state or a spin segregated state.\nWe have demonstrated these effects by exact calculations on fermion cluster\nrelevant to current experiments, and have worked out the quantum mechanical\nwavefunction that exhibits phase separation.",
        "positive": "Observation of Light-Induced Dipole-Dipole Forces in Ultracold Atomic\n  Gases: We investigate an attractive force caused by light induced dipole-dipole\ninteractions in freely expanding ultracold 87Rb atoms. This collective,\nlight-triggered effect results in a self-confining potential with interesting\nfeatures: it exhibits nonlocal properties, is attractive for both red and\nblue-detuned light fields and induces a remarkably strong force that depends on\nthe gradient of the atomic density. The experimental data are discussed in the\nframework of a theoretical model based on a local-field approach for the light\nscattered by the atomic cloud."
    },
    {
        "anchor": "Collective modes of an imbalanced unitary Fermi gas: We study theoretically the collective mode spectrum of a strongly imbalanced\ntwo-component unitary Fermi gas in a cigar-shaped trap, where the minority\nspecies forms a gas of polarons. We describe the collective breathing mode of\nthe gas in terms of the Fermi liquid kinetic equation taking collisions into\naccount using the method of moments. Our results for the frequency and damping\nof the longitudinal in-phase breathing mode are in good quantitative agreement\nwith an experiment by Nascimb\\`ene et al. [Phys. Rev. Lett. 103, 170402 (2009)]\nand interpolate between a hydrodynamic and a collisionless regime as the\npolarization is increased. A separate out-of phase breathing mode, which for a\ncollisionless gas is sensitive to the effective mass of the polaron, however,\nis strongly damped at finite temperature, whereas the experiment observes a\nwell-defined oscillation.",
        "positive": "Multimode model for an atomic Bose-Einstein condensate in a ring-shaped\n  optical lattice: We study the population dynamics of a ring-shaped optical lattice with a high\nnumber of particles per site and a low, below ten, number of wells. Using a\nlocalized on-site basis defined in terms of stationary states, we were able to\nconstruct a multiple-mode model depending on relevant hopping and on-site\nenergy parameters. We show that in case of two wells, our model corresponds\nexactly to the latest improvement of the two-mode model. We derive a formula\nfor the self-trapping period, which turns out to be chiefly ruled by the\non-site interaction energy parameter. By comparing to time dependent\nGross-Pitaevskii simulations, we show that the multimode model results can be\nenhanced in a remarkable way over all the regimes by only renormalizing such a\nparameter. Finally, using a different approach which involves only the ground\nstate density, we derive an effective interaction energy parameter that shows\nto be in accordance with the renormalized one."
    },
    {
        "anchor": "Topological interface physics of defects and textures in spinor\n  Bose-Einstein condensates: We provide a detailed description of our previously proposed scheme for\ntopological interface engineering with constructed defects and textures\nperforating across coherent interfaces between different broken symmetries [M.\nO. Borgh and J. Ruostekoski, Phys. Rev. Lett. 109, 015302 (2012)]. We consider\na spin-1 Bose-Einstein condensate, in which polar and ferromagnetic phases are\nprepared in spatially separated regions. We show that a stable coherent\ninterface is established between the two phases, allowing defects of different\ntopology to connect continuously across the boundary. We provide analytic\nconstructions of interface-crossing defect solutions that could be\nexperimentally phase-imprinted using existing technology. By numerically\nminimizing the energy, we calculate the core structures of interface-crossing\ndefect configurations. We demonstrate nontrivial core deformations to\nconsiderably more complex structures, such as the formation of an arch-shaped\nhalf-quantum line defect, an Alice arch, at the interface, with the topological\ncharge of a point defect, whose emergence may be understood by the \"hairy ball\"\ntheorem. Another example of an energetically stable object is the connection of\na coreless vortex to a pair of half-quantum vortices. We show that rotation\nleads to spontaneous nucleation of defects in which a coreless vortex\ncontinuously transforms to a half-quantum vortex across the interface.",
        "positive": "Ballistic, diffusive, and arrested transport in disordered\n  momentum-space lattices: Ultracold atoms in optical lattices offer a unique platform for investigating\ndisorder-driven phenomena. While static disordered site potentials have been\nexplored in a number of optical lattice experiments, a more general control\nover site-energy and off-diagonal tunneling disorder has been lacking. The use\nof atomic quantum states as \"synthetic dimensions\" has introduced the\nspectroscopic, site-resolved control necessary to engineer new, more tailored\nrealizations of disorder. Here, by controlling laser-driven dynamics of atomic\npopulation in a momentum-space lattice, we extend the range of\nsynthetic-dimension-based quantum simulation and present the first explorations\nof dynamical disorder and tunneling disorder in an atomic system. By applying\nstatic tunneling phase disorder to a one-dimensional lattice, we observe\nballistic quantum spreading as in the case of uniform tunneling. When the\napplied disorder fluctuates on timescales comparable to intersite tunneling, we\ninstead observe diffusive atomic transport, signaling a crossover from quantum\nto classical expansion dynamics. We compare these observations to the case of\nstatic site-energy disorder, where we directly observe quantum localization in\nthe momentum-space lattice."
    },
    {
        "anchor": "Laser Cooling by Collisional Redistribution of Radiation: The general idea that optical radiation may cool matter was put forward by\nPringsheim already in 1929. Doppler cooling of dilute atomic gases is an\nextremely successful application of this concept, and more recently anti-Stokes\ncooling in multilevel systems has been explored, culminating in the optical\nrefrigeration of solids. Collisional redistribution of radiation is a proposed\ndifferent cooling mechanism that involves atomic two-level systems, though\nexperimental investigations in gases with moderate density have so far not\nreached the cooling regime.\n  Here we experimentally demonstrate laser cooling of an atomic gas based on\ncollisional redistribution of radiation, using rubidium atoms subject to 230\nbar of argon buffer gas pressure. The frequent collisions in the ultradense gas\ntransiently shift a far red detuned laser beam into resonance, while\nspontaneous decay occurs close to the unperturbed atomic resonance frequency.\nDuring each excitation cycle, a kinetic energy of order of the thermal energy\nk_B T is extracted from the dense atomic sample. In a proof of principle\nexperiment with a thermally non-isolated sample, we experimentally demonstrate\nrelative cooling by 66 K. The cooled gas has a density of more than 10 orders\nof magnitude above the typical values in Doppler cooling experiments, and the\ncooling power reaches 87 mW. Future prospects of the demonstrated effect\ninclude studies of supercooling beyond the homogeneous nucleation temperature\nand optical chillers.",
        "positive": "Direct observation of zitterbewegung in a Bose-Einstein condensate: Zitterbewegung, a force-free trembling motion first predicted for\nrelativistic fermions like electrons, was an unexpected consequence of the\nDirac equation's unification of quantum mechanics and special relativity.\nThough the oscillatory motion's large frequency and small amplitude have\nprecluded its measurement with electrons, zitterbewegung is observable via\nquantum simulation. We engineered an environment for 87Rb Bose-Einstein\ncondensates where the constituent atoms behaved like relativistic particles\nsubject to the one-dimensional Dirac equation. With direct imaging, we observed\nthe sub-micrometer trembling motion of these clouds, demonstrating the utility\nof neutral ultracold quantum gases for simulating Dirac particles."
    },
    {
        "anchor": "Direct observation of Dirac cones and a flatband in a honeycomb lattice\n  for polaritons: Two-dimensional lattices of coupled micropillars etched in a planar\nsemiconductor microcavity offer a workbench to engineer the band structure of\npolaritons. We report experimental studies of honeycomb lattices where the\npolariton low-energy dispersion is analogous to that of electrons in graphene.\nUsing energy-resolved photoluminescence we directly observe Dirac cones, around\nwhich the dynamics of polaritons is described by the Dirac equation for\nmassless particles. At higher energies, we observe p orbital bands, one of them\nwith the nondispersive character of a flatband. The realization of this\nstructure which holds massless, massive and infinitely massive particles opens\nthe route towards studies of the interplay of dispersion, interactions, and\nfrustration in a novel and controlled environment.",
        "positive": "Spin-orbit coupled Fermi liquid theory of ultra-cold magnetic dipolar\n  fermions: We investigate Fermi liquid states of the ultra-cold magnetic dipolar Fermi\ngases in the simplest two-component case including both thermodynamic\ninstabilities and collective excitations. The magnetic dipolar interaction is\ninvariant under the simultaneous spin-orbit rotation, but not under either the\nspin or the orbit one. Therefore, the corresponding Fermi liquid theory is\nintrinsically spin-orbit coupled. This is a fundamental feature of magnetic\ndipolar Fermi gases different from electric dipolar ones. The Landau\ninteraction matrix is calculated and is diagonalized in terms of the spin-orbit\ncoupled partial-wave channels of the total angular momentum J. The leading\nthermodynamic instabilities lie in the channels of ferromagnetism hybridized\nwith the ferronematic order with J = 1+ and the spin-current mode with J = 1-,\nwhere + and - represent even and odd parities, respectively. An exotic\npropagating collective mode is identified as spin-orbit coupled Fermi surface\noscillations in which spin distribution on the Fermi surface exhibits a\ntopologically nontrivial hedgehog configuration."
    },
    {
        "anchor": "Floquet Quantum Spin Hall Insulator in Cold Atomic Systems: For cold atomic systems, varying the optical lattice potential periodically\nprovides a general and simple way to drive the system into phases with\nnontrivial topology. Besides its simplicity, this driving approach, compared to\nthe usual driving approach by exerting an external electromagnetic field to the\nstatic system, has the merit that it does not break the original static\nsystem's time-reversal symmetry at any given time. Based on this approach, we\nfind that a trivial insulator with time-reversal symmetry can be driven into a\nFloquet quantum spin Hall insulator. This novel state of matter can stably host\none or two pair of gapless helical states on the same boundary, which suggests\nthis state is not a simple analog of the quantum spin Hall insulator. The\neffect of a time-reversal-symmetry-breaking periodic perturbation, the\nstability of the novel states, and this new driving approach to a system\nwithout time-reversal symmetry are discussed.",
        "positive": "The Bogoliubov inequality and the nature of Bose-Einstein condensates\n  for interacting atoms in spatial dimensions $D \\le 2$: We consider the restriction placed by the Bogoliubov inequality on the nature\nof the Bose-Einstein condensates (BECs) for interacting atoms in a spatial\ndimension D </- 2 and in the presence of an external arbitrary potential, which\nmay be a confining \"box\", a periodic, or a disordered potential. The atom-atom\ninteraction gives rise to a (gauge invariance) symmetry-breaking term that\nplaces further restrictions on BECs in the form of a consistency proviso. The\nnecessary condition for the existence of a BEC in D </- 2 in all cases is\nmacroscopic occupation of many single-particle momenta states with the origin a\nlimit point (or accumulation point) of condensates. It is shown that the nature\nof BECs for noninteracting atoms in a disordered potential is precisely the\nsame as that of BECs for interacting atoms in the absence of an external\npotential."
    },
    {
        "anchor": "Random Kronig-Penney-type potentials for ultracold atoms using dark\n  states: A construction of a quasi-random potential for cold atoms using dark states\nemerging in $\\Lambda$ {level configuration} is proposed. Speckle laser fields\nare used as a source of randomness.\n  Anderson localisation in such potentials is studied and compared with the\nknown results for the speckle potential itself. It is found out that the\nlocalisation length is greatly decreased due to the non-linear fashion in which\ndark-state potential is obtained. In effect, random dark state potentials\nresemble those occurring in random Kronig-Penney-type Hamiltonians.",
        "positive": "The temperature evolution of the shear viscosity in a unitary Fermi gas: We present an ab initio determination of the shear viscosity for the unitary\nFermi gas based on finite temperature quantum Monte Carlo (QMC) calculations\nand the Kubo linear-response formalism. The results are confronted with the\nbound for the shear viscosity originating from hydrodynamic fluctuations.\nAssuming smoothness of the frequency dependent shear viscosity eta(omega), we\nshow that the bound is violated in the low temperature regime and the violation\noccurs simultaneously with the onset of the Cooper paring in the system. In\norder to preserve the hydrodynamic bound in QMC eta(omega) has to possess a\nsharp structure located in the vicinity of zero frequency which is not resolved\nby an analytic continuation procedure."
    },
    {
        "anchor": "Dissipation assisted Thouless pumping in the Rice-Mele model: We investigate the effect of dissipation from a thermal environment on\ntopological pumping in the periodically-driven Rice-Mele model. We report that\ndissipation can improve the robustness of pumping quantisation in a regime of\nfinite driving frequencies. Specifically, in this regime, a low-temperature\ndissipative dynamics can lead to a pumped charge that is much closer to the\nThouless quantised value, compared to a coherent evolution. We understand this\neffect in the Floquet framework: dissipation increases the population of a\nFloquet band which shows a topological winding, where pumping is essentially\nquantised. This finding is a step towards understanding a potentially very\nuseful resource to exploit in experiments, where dissipation effects are\nunavoidable. We consider small couplings with the environment and we use a\nBloch-Redfield quantum master equation approach for our numerics: Comparing\nthese results with an exact MPS numerical treatment we find that the quantum\nmaster equation works very well also at low temperature, a quite remarkable\nfact.",
        "positive": "Critical entropies for magnetic ordering in bosonic mixtures on a\n  lattice: We perform a numeric study (worm algorithm Monte Carlo simulations) of\nultracold two-component bosons in two- and three-dimensional optical lattices.\nAt strong enough interactions and low enough temperatures the system features\nmagnetic ordering. We compute critical temperatures and entropies for the\ndisappearance of the Ising antiferromagnetic and the xy-ferromagnetic order and\nfind that the largest possible entropies per particle are ~0.5kB. We also\nestimate (optimistically) the experimental hold times required to reach\nequilibrium magnetic states to be on a scale of seconds. Low critical entropies\nand long hold times render the experimental observations of magnetic phases\nchallenging and call for increased control over heating sources."
    },
    {
        "anchor": "Non-equilibrium quasi-condensates in reduced dimensions: We develop a generic phenomenological model to describe the fluctuations on\ntop of a non-equilibrium Bose-Einstein condensate. Analytic expressions are\nobtained for the momentum distribution of the non-condensed cloud and for the\nlong-distance behavior of the spatial coherence in the different\ndimensionalities. Comparison of our predictions with available experimental\ndata on condensates of exciton-polaritons and on surface-emitting planar laser\ndevices is finally made.",
        "positive": "Geometric scaling of Efimov states in a\n  $^{6}\\textrm{Li}$-$^{133}\\textrm{Cs}$ mixture: In few-body physics, Efimov states are an infinite series of three-body bound\nstates that obey universal discrete scaling symmetry when pairwise interactions\nare resonantly enhanced. Despite abundant reports of Efimov states in recent\ncold atom experiments, direct observation of the discrete scaling symmetry\nremains an elusive goal. Here we report the observation of three consecutive\nEfimov resonances in a heteronuclear Li-Cs mixture near a broad interspecies\nFeshbach resonance. The positions of the resonances closely follow a geometric\nseries $1$, $\\lambda$, $\\lambda^2$. The observed scaling constant $\\lambda_{\\rm\nexp} = 4.9(4)$ is in good agreement with the predicted value of 4.88."
    },
    {
        "anchor": "Three-body and Coulomb interactions in a quasi two-dimensional dipolar\n  Bose condensed gas: In this paper, we studied a dilute quasi two-dimensional dipolar\nBose-condensed with two- and three-body contact, and Coulomb interactions using\nthe Hartree-Fock-Bogoliubov-Popov approximation. We analyze numerically the\neffects of three-body contact, and Coulomb interactions on the energy spectrum,\nthe quantum and thermal noncondensate fraction of the system. We show that\nincreasing the three-body contact and Coulomb interactions leads to the\nappearance of rotonization and condensate instability at stronger dipole-dipole\ninteraction. Also we find that the temperature dependence of the thermal\nnoncondensate fraction is linear at low temperature.",
        "positive": "Infinite Lattices of Vortex Molecules in Rabi-Coupled Condensates: Vortex molecules can form in a two component superfluid when a Rabi field\ndrives transitions between the two components. We study the ground state of an\ninfinite system of vortex molecules in 2D, using a numerical scheme which makes\nno use of the lowest Landau level approximation. We find the ground state\nlattice geometry for different values of inter-component interactions and\nstrength of the Rabi field. In the limit of large field when molecules are\ntightly bound, we develop a complimentary analytical description. The energy\ngoverning the alignment of molecules on a triangular lattice is found to\ncorrespond to that of an infinite system of 2D quadrupoles, which may be\nwritten in terms of an elliptic function $\\mathcal{Q}(z_{ij};\\omega_1 ,\n\\omega_2 )$. This allows for a numerical evaluation of the energy which enables\nus to find the ground state configuration of the molecules."
    },
    {
        "anchor": "Bogoliubov theory of a Bose-Einstein condensate of rigid rotor molecules: We consider a BEC of rigid rotor molecules confined to quasi-2d through\nharmonic trapping. The molecules are subjected to an external electric field\nwhich polarizes the gas, and the molecules interact via dipole-dipole\ninteractions. We present a description of the ground state and low-energy\nexcitations of the system including an analysis of the mean-field energy,\npolarization, and stability. Under large electric fields the gas becomes fully\npolarized and we reproduce a well known density-wave instability which arises\nin polar BECs. Under smaller applied electric fields the gas develops an\nin-plane polarization leading to the emergence of a new global instability as\nthe molecules \"tilt\". The character of these instabilities is clarified by\nmeans of momentum-space density-density structure factors. A peak at zero\nmomentum in the spin-spin structure factor for the in-plane component of the\npolarization indicates that the tilt instability is a global phonon-like\ninstability.",
        "positive": "Extracting atoms one by one from a small matter-wave soliton: Excitations of small one-dimensional matter-wave solitons are considered\nwithin a framework of the attractive Bose-Hubbard model. The initial\neigenstates of the system are found by exact diagonalization of the\nBose-Hubbard Hamiltonian. We drive transitions between the eigenstates by\ninducing a weak modulation of the tunnelling rate and show that a single atom\ncan be extracted while the remaining atoms stay localized despite the\npersistent external modulation. This scheme suggests the experimental\nrealization of small matter-wave solitons with deterministic number of atoms.\nIn addition, the knowledge of exact eigenstates allows identification of the\nselection rules for transitions between the different eigenstates of the\nHamiltonian. One selection rule is related to the translation symmetry of the\nsystem. Another one is strictly applicable only on a subspace of the total\nHilbert space and is related to the parity symmetry. We show that in the\nstrongly interacting limit this selection rule has implications on the entire\nHilbert space. We discuss its signatures on the system's dynamics and consider\nhow it can be observed experimentally with ultracold atoms."
    },
    {
        "anchor": "Matter wave switching in Bose-Einstein condensates via intensity\n  redistribution soliton interactions: Using time dependent nonlinear (s-wave scattering length) coupling between\nthe components of a weakly interacting two component Bose-Einstein condensate\n(BEC), we show the possibility of matter wave switching (fraction of atoms\ntransfer) between the components via shape changing/intensity redistribution\n(matter redistribution) soliton interactions. We investigate the exact\nbright-bright N-soliton solution of an effective one-dimensional (1D) two\ncomponent BEC by suitably tailoring the trap potential, atomic scattering\nlength and atom gain or loss. In particular, we show that the effective 1D\ncoupled Gross-Pitaevskii (GP) equations with time dependent parameters can be\ntransformed into the well known completely integrable Manakov model described\nby coupled nonlinear Schr\\\"odinger (CNLS) equations by effecting a change of\nvariables of the coordinates and the wave functions under certain conditions\nrelated to the time dependent parameters. We obtain the one-soliton solution\nand demonstrate the shape changing/matter redistribution interactions of two\nand three soliton solutions for the time independent expulsive harmonic trap\npotential, periodically modulated harmonic trap potential and kink-like\nmodulated harmonic trap potential. The standard elastic collision of solitons\noccur only for a specific choice of soliton parameters.",
        "positive": "Instability of the superfluid flow as black-hole lasing effect: We show that the instability leading to the decay of the one-dimensional\nsuperfluid flow through a penetrable barrier are due to the black-hole lasing\neffect. This dynamical instability is triggered by modes resonating in an\neffective cavity formed by two horizons enclosing the barrier. The location of\nthe horizons is set by $v(x)=c(x)$, with $v(x),c(x)$ being the local fluid\nvelocity and sound speed, respectively. We compute the critical velocity\nanalytically and show that it is univocally determined by the horizons\nconfiguration. In the limit of broad barriers, the continuous spectrum at the\norigin of the Hawking-like radiation and of the Landau energetic instability is\nrecovered."
    },
    {
        "anchor": "Hierarchical dimensional crossover of an optically-trapped quantum gas\n  with disorder: Dimensionality serves as an indispensable ingredient in any attempt to\nformulate the low-dimensional physics, and studying the dimensional crossover\nat a fundamental level is challenging. The purpose of this work is to study the\nhierarchical dimensional crossovers, namely the crossover from three dimensions\n(3D) to quasi-2D and then to 1D. Our system consists of a 3D Bose-Einstein\ncondensate (BEC) trapped in an anisotropic 2D optical lattice characterized by\nthe lattice depths $V_1$ along the $x$ direction and $V_2$ along the $y$\ndirection, respectively, where the hierarchical dimensional crossover is\ncontrolled via $V_1$ and $V_2$. We analytically derive the ground-state energy,\nquantum depletion and the superfluid density of the system. Our results\ndemonstrate the 3D-quasi-2D-1D dimensional crossovers in the behavior of\nquantum fluctuations. Conditions for possible experimental realization of our\nscenario are also discussed.",
        "positive": "Polaron-Depleton Transition in the Yrast Excitations of a\n  One-Dimensional Bose Gas with a Mobile Impurity: We present exact numerical data for the lowest-energy momentum eigenstates\n(yrast states) of a repulsive spin impurity in a one-dimensional Bose gas using\nfull configuration interaction quantum Monte Carlo (FCIQMC). As a stochastic\nextension to exact diagonalization it is well suited for the study of yrast\nstates of a lattice-renormalized model for a quantum gas. Yrast states carry\nvaluable information about the dynamic properties of slow-moving mobile\nimpurities immersed in a many-body system. Based on the energies and the first\nand second order correlation functions of yrast states, we identify different\ndynamical regimes and the transitions between them: The polaron regime, where\nthe impurity's motion is affected by the Bose gas through a renormalized\neffective mass; a regime of a gray soliton that is weakly correlated with a\nstationary impurity, and the depleton regime, where the impurity occupies a\ndark or gray soliton. Extracting the depleton effective mass reveals a super\nheavy regime where the magnitude of the (negative) depleton mass exceeds the\nmass of the finite Bose gas."
    },
    {
        "anchor": "Dysprosium dipolar Bose-Einstein condensate with broad Feshbach\n  resonances: We produce Bose-Einstein condensates of $^{162}$Dy atoms employing an\ninnovative technique based on a resonator-enhanced optical trap that allows\nefficient loading from the magneto-optical trap and fast evaporation. We\ncharacterize the scattering properties of the ultracold atoms for magnetic\nfields between 6 and 30 G. In addition to the typical chaotic distribution of\nnarrow Feshbach resonances in Lanthanides, we discover two rather isolated\nbroad features at around 22 G and 27 G. A characterization using the\ncomplementary measurements of losses, thermalization, anisotropic expansion and\nmolecular binding energy points towards resonances of predominant s-wave\ncharacter. Such resonances will ease the investigation of quantum phenomena\nrelying on the interplay between dipole and contact interactions.",
        "positive": "Pseudogap regime of a strongly interacting two-dimensional Fermi gas\n  with and without confinement-induced effect range of interactions: We investigate theoretically the many-body pairing of a strongly correlated\ntwo-dimensional Fermi gas with and without negative confinement-induced\neffective range. Using a strong-coupling effective field theory in the normal\nstate, we show that the specific heat at constant volume can be used as a\ncharacteristic indicator of the crossover from the normal Fermi liquid to the\npseudogap state in two dimensions. We calculate the pseudogap formation\ntemperature through the specific heat at constant volume, examining the role of\na negative confinement-induced effective range on many-body pairing above the\nsuperfluid transition. We compare our results with and without effective range\nto the recent experimental measurement performed with radio-frequency\nspectroscopy in Murthy et al.[Science359, 452-455 (2018)]. Although a good\nqualitative agreement is found, we are not able to discriminate the effect of\nthe confinement-induced effect range in the experimental data."
    },
    {
        "anchor": "Hartree-Fock treatment of Fermi polarons using the Lee-Low-Pine\n  transformation: We consider the Fermi polaron problem at zero temperature, where a single\nimpurity interacts with non-interacting host fermions. We approach the problem\nstarting with a Frohlich-like Hamiltonian where the impurity is described with\ncanonical position and momentum operators. We apply the Lee-Low-Pine (LLP)\ntransformation to change the fermionic Frohlich Hamiltonian into the fermionic\nLLP Hamiltonian which describes a many-body system containing host fermions\nonly. We adapt the self-consistent Hartree-Fock (HF) approach, first proposed\nby Edwards, to the fermionic LLP Hamiltonian in which a pair of host fermions\nwith momenta $\\mathbf{k}$ and $\\mathbf{k}'$ interact with a potential\nproportional to $\\mathbf{k}\\cdot\\mathbf{k}'$. We apply the HF theory, which has\nthe advantage of not restricting the number of particle-hole pairs, to\nrepulsive Fermi polarons in one dimension. When the impurity and host fermion\nmasses are equal our variational ansatz, where HF orbitals are expanded in\nterms of free-particle states, produces results in excellent agreement with\nMcGuire's exact analytical results based on the Bethe ansatz. This work raises\nthe prospect of using the HF ansatz and its time-dependent generalization as\nbuilding blocks for developing all-coupling theories for both equilibrium and\nnonequilibrium Fermi polarons in higher dimensions",
        "positive": "Pair correlations in the normal phase of an attractive Fermi gas: In a recent paper [Phys. Rev. A 99, 053617 (2019)], the total number of\nfermion pairs in a spin-balanced two-component Fermi gas of $^6$Li atoms was\nexperimentally probed in the normal phase above the superfluid critical\ntemperature, in order to investigate the sectors of pseudogap and\npreformed-pair in the temperature-coupling phase diagram. Here, we present a\ntheoretical account of these experimental results in terms of an ab-initio\nself-consistent $t$-matrix calculation, which emphasizes the role of the\npair-correlation function between opposite-spin fermions at equilibrium. Good\nagreement is found between the available experimental data and the theoretical\nresults obtained with no adjustable parameter."
    },
    {
        "anchor": "Dipoles on a Two-leg Ladder: We study polar molecules with long-range dipole-dipole interactions confined\nto move on a two-leg ladder for different orientations of the molecular dipole\nmoments with respect to the ladder. Matrix product states are employed to\ncalculate the many-body ground state of the system as function of lattice\nfilling fractions, perpendicular hopping between the legs, and dipole\ninteraction strength. We show that the system exhibits zig-zag ordering when\nthe dipolar interactions are predominantly repulsive. As a function of dipole\nmoment orientation with respect to the ladder, we find that there is a critical\nangle at which ordering disappears. This angle is slightly larger than the\nangle at which the dipoles are non-interacting along a single leg. This\nbehavior should be observable using current experimental techniques.",
        "positive": "Statistical periodicity in driven quantum systems: General formalism and\n  application to noisy Floquet topological chains: Much recent experimental effort has focused on the realization of exotic\nquantum states and dynamics predicted to occur in periodically driven systems.\nBut how robust are the sought-after features, such as Floquet topological\nsurface states, against unavoidable imperfections in the periodic driving? In\nthis work, we address this question in a broader context and study the dynamics\nof quantum systems subject to noise with periodically recurring statistics. We\nshow that the stroboscopic time evolution of such systems is described by a\nnoise-averaged Floquet superoperator. The eigenvectors and -values of this\nsuperoperator generalize the familiar concepts of Floquet states and\nquasienergies and allow us to describe decoherence due to noise efficiently.\nApplying the general formalism to the example of a noisy Floquet topological\nchain, we re-derive and corroborate our recent findings on the noise-induced\ndecay of topologically protected end states. These results follow directly from\nan expansion of the end state in eigenvectors of the Floquet superoperator."
    },
    {
        "anchor": "Time-Dependent Superfluid Local Density Approximation: The time-dependent superfluid local density approximation (TDSLDA) is an\nextension of the Hohenberg-Kohn density functional theory (DFT) to\ntime-dependent phenomena in superfluid fermionic systems. Unlike linear\nresponse theory, which is only valid for weak external fields, the (TDSLDA)\napproach allows one to study non-linear excitations in fermionic superfluids,\nincluding large amplitude collective modes, and the response to strong external\nprobes. Even in the case of weak external fields, the (TDSLDA) approach is\ntechnically easier to implement. We will illustrate the implementation of the\n(TDSLDA) for the unitary Fermi gas, where dimensional arguments and Galilean\ninvariance simplify the form of the functional, and ab initio input from (QMC)\nsimulations fix the coefficients to quite high precision.",
        "positive": "Overlapping Bose-Einstein Condensates of $^{23}$Na and $^{133}$Cs: We report on the creation of dual-species Bose-Einstein condensates (BECs) of\n$^{23}$Na atoms and $^{133}$Cs atoms. We demonstrate sympathetic cooling of Cs\nwith Na in a magnetic quadrupole trap and a crossed optical dipole trap,\nleading to Na BECs with $8 \\times 10^5$ atoms and Cs BECs with $3.5 \\times\n10^4$ atoms. Investigating cross-thermalization and lifetimes of the mixture,\nwe find that the Na and Cs BECs are miscible and overlapping, interacting with\na moderate interspecies scattering length of $18(4)\\,a_0$ at $23\\,$G and\n$29(4)\\,a_0$ at $894\\,$G and coexisting for tens of seconds. Overlapping\ncondensates of Na and Cs offer new possibilities for many-body physics with\nultracold bosonic mixtures and constitute an ideal starting point for the\ncreation of ultracold ensembles of NaCs ground state molecules."
    },
    {
        "anchor": "Properties of the one-dimensional Bose-Hubbard model from a high-order\n  perturbative expansion: We employ a high-order perturbative expansion to characterize the ground\nstate of the Mott phase of the one-dimensional Bose-Hubbard model. We compute\nfor different integer filling factors the energy per lattice site, the\ntwo-point and density-density correlations, and expectation values of powers of\nthe on-site number operator determining the local atom number fluctuations\n(variance, skewness, kurtosis). We compare these expansions to numerical\nsimulations of the infinite-size system to determine their range of\napplicability. We also discuss a new sum rule for the density-density\ncorrelations that can be used in both equilibrium and non-equilibrium systems.",
        "positive": "Quantum Simulation of Lattice Gauge Theories on Superconducting\n  Circuits: Quantum Phase Transition and Quench Dynamics: Recently, quantum simulation of low-dimensional lattice gauge theories (LGTs)\nhas attracted many interests, which may improve our understanding of strongly\ncorrelated quantum many-body systems. Here, we propose an implementation to\napproximate $\\mathbb{Z}_2$ LGT on superconducting quantum circuits, where the\neffective theory is a mixture of a LGT and a gauge-broken term. Using matrix\nproduct state based methods, both the ground state properties and quench\ndynamics are systematically investigated. With an increase of the transverse\n(electric) field, the system displays a quantum phase transition from a\ndisordered phase to a translational symmetry breaking phase. In the ordered\nphase, an approximate Gauss law of the $\\mathbb{Z}_2$ LGT emerges in the ground\nstate. Moreover, to shed light on the experiments, we also study the quench\ndynamics, where there is a dynamical signature of the spontaneous translational\nsymmetry breaking. The spreading of the single particle of matter degree is\ndiffusive under the weak transverse field, while it is ballistic with small\nvelocity for the strong field. Furthermore, due to the emergent Gauss law under\nthe strong transverse field, the matter degree can also exhibit confinement\ndynamics which leads to a strong suppression of the nearest-neighbor hopping.\nOur results pave the way for simulating the LGT on superconducting circuits,\nincluding the quantum phase transition and quench dynamics."
    },
    {
        "anchor": "Dissipative preparation of Chern insulators: Engineered dissipation can be employed to prepare interesting quantum many\nbody states in a non-equilibrium fashion. The basic idea is to obtain the state\nof interest as the unique steady state of a quantum master equation,\nirrespective of the initial state. Due to a fundamental competition of topology\nand locality, the dissipative preparation of gapped topological phases with a\nnon-vanishing Chern number has so far remained elusive. Here, we study the open\nquantum system dynamics of fermions on a two-dimensional lattice in the\nframework of a Lindblad master equation. In particular, we discover a mechanism\nto dissipatively prepare a topological steady state with non-zero Chern number\nby means of short-range system bath interaction. Quite remarkably, this gives\nrise to a stable topological phase in a non-equilibrium phase diagram. We\ndemonstrate how our theoretical construction can be implemented in a\nmicroscopic model that is experimentally feasible with cold atoms in optical\nlattices.",
        "positive": "Asymmetry and nonlinearity of current-bias characteristics in\n  superfluid-normal state junctions of weakly-interacting Bose gases: We uncover current-bias characteristics of superfluid-normal state junctions\nwith weakly-interacting Bose gases. It is shown that in the presence of a\nchemical potential bias the characteristics can strongly be asymmetric for\norigin. The salient feature that is absent in the fermionic counterpart arises\nfrom a tunneling process associated with a condensate and a bosonic Andreev\nreflection process. It turns out that such processes are intrinsically\nnonlinear and therefore do not obey Ohm's law even at a low bias. In addition,\nthe remaining processes are found to obey Ohm's law and become dominant for\ntransport driven by a temperature bias."
    },
    {
        "anchor": "Long-Lived Ultracold Molecules with Electric and Magnetic Dipole Moments: We create fermionic dipolar $^{23}$Na$^6$Li molecules in their triplet ground\nstate from an ultracold mixture of $^{23}$Na and $^6$Li. Using\nmagneto-association across a narrow Feshbach resonance followed by a two-photon\nSTIRAP transfer to the triplet ground state, we produce $3\\,{\\times}\\,10^4$\nground state molecules in a spin-polarized state. We observe a lifetime of\n$4.6\\,\\text{s}$ in an isolated molecular sample, approaching the $p$-wave\nuniversal rate limit. Electron spin resonance spectroscopy of the triplet state\nwas used to determine the hyperfine structure of this previously unobserved\nmolecular state.",
        "positive": "Quantum Monte Carlo study of strongly interacting Fermi gases: In recent years Quantum Monte Carlo techniques provided to be a valuable tool\nto study strongly interacting Fermi gases at zero temperature. We have used QMC\nmethods to investigate several properties of the two-components Fermi gas at\nunitarity and in the BCS-BEC crossover, both with equal and unequal masses\ncorresponding to the $Li-K$ Fermi mixture. In this paper we present several\nrecent QMC results, including the energy at zero and finite effective range,\nthe contact parameter and the static structure factor, which, at low momentum,\ndepends strongly on the phonons in the unitary Fermi gas."
    },
    {
        "anchor": "A supercritical superfluid and vortex unbinding following a quantum\n  quench: We study the dynamics of the relative phase of a bilayer of two-dimensional\nsuperfluids after the two superfluids have been decoupled, using truncated\nWigner approximation. On short time scales the relative phase shows \"light\ncone\" like thermalization and creates a metastable superfluid state, which can\nbe supercritical. On longer time scales this state relaxes to a disordered\nstate due to dynamical vortex unbinding. This scenario of dynamically\nsuppressed vortex proliferation constitutes a {\\it reverse-Kibble-Zurek\neffect}. We observe dynamics of creation of vortex anti-vortex pairs and their\nconsequent motion. Our predictions can be directly measured in interference\nexperiments, see Ref 1.",
        "positive": "Universality in Three- and Four-Body Bound States of Ultracold Atoms: Under certain circumstances, three or more interacting particles may form\nbound states. While the general few-body problem is not analytically solvable,\nthe so-called Efimov trimers appear for a system of three particles with\nresonant two-body interactions. The binding energies of these trimers are\npredicted to be universally connected to each other, independent of the\nmicroscopic details of the interaction. By exploiting a Feshbach resonance to\nwidely tune the interactions between trapped ultracold lithium atoms, we find\nevidence for two universally connected Efimov trimers and their associated\nfour-body bound states. A total of eleven precisely determined three- and\nfour-body features are found in the inelastic loss spectrum. Their relative\nlocations on either side of the resonance agree well with universal theory,\nwhile a systematic deviation from universality is found when comparing features\nacross the resonance."
    },
    {
        "anchor": "Quantum disorder in the spatially completely anisotropic triangular\n  lattice II: frustrated hard-core bosons: Spin liquids occuring in 2D frustrated spin systems were initially assumed to\nappear at strongest frustration, but evidence grows that they more likely\nintervene at transitions between two different types of order. To identify if\nthis is more general, we here analyze a generalization of the spatially\nanisotropic triangular lattice (SATL) with antiferromagnetic XY interactions,\nthe spatially \\emph{completely} anisotropic triangular lattice (SCATL). This\nmodel can be implemented in experiments with trapped ions, ultra-small\nJosephson junctions, or ultracold atoms in optical lattices. Using Takahashi's\nmodified spin-wave theory, we find indications that indeed two different kinds\nof order are always separated by phases without magnetic long-range order. Our\nresults further suggest that two gapped, magnetically-disordered phases,\nidentified as distinct in the SATL, are actually continuously connected via the\nadditional anisotropy of the SCATL. As these results indicate, this additional\nanisotropy -- allowing to approach quantum-disordered phases from different\nangles -- can give fundamental insight into the nature of quantum disordered\nphases. We complement our results by exact diagonalizations, which also\nindicate that in part of the gapped non-magnetic phase, chiral long-range\ncorrelations could survive.",
        "positive": "Fundamental Constraints on Linear Response Theories of Fermi Superfluids\n  Above and Below $T_c$: We present fundamental constraints required for a consistent linear response\ntheory of fermionic superfluids and address temperatures both above and below\nthe transition temperature $T_c$. We emphasize two independent constraints, one\nassociated with gauge invariance (and the related Ward identity) and another\nassociated with the compressibility sum rule, both of which are satisfied in\nstrict BCS theory. However, we point out that it is the rare many body theory\nwhich satisfies both of these. Indeed, well studied quantum Hall systems and\nrandom-phase approximations to the electron gas are found to have difficulties\nwith meeting these constraints. We summarize two distinct theoretical\napproaches which are, however, demonstrably compatible with gauge invariance\nand the compressibility sum rule. The first of these involves an extension of\nBCS theory to a mean field description of the BCS-Bose Einstein condensation\ncrossover. The second is the simplest Nozieres Schmitt- Rink (NSR) treatment of\npairing correlations in the normal state. As a point of comparison we focus on\nthe compressibility $\\kappa$ of each and contrast the predictions above $T_c$.\nWe note here that despite the compliance with sum rules, this NSR based scheme\nleads to an unphysical divergence in $\\kappa$ at the transition. Because of the\ndelicacy of the various consistency requirements, the results of this paper\nsuggest that avoiding this divergence may repair one problem while at the same\ntime introducing others."
    },
    {
        "anchor": "Anomalous charge pumping in a one-dimensional optical superlattice: We model atomic motion in a sliding superlattice potential to explore\ntopological \"charge pumping\" and to find optimal parameters for experimental\nobservation of this phenomenon. We analytically study the band-structure,\nfinding how the Wannier states evolve as two sinusoidal lattices are moved\nrelative to one-another, and relate this evolution to the center of mass motion\nof an atomic cloud. We pay particular attention to counterintuitive or\nanomalous regimes, such as when the atomic motion is opposite to that of the\nlattice.",
        "positive": "Cold atoms in cavity-generated dynamical optical potentials: We review state-of-the-art theory and experiment of the motion of cold and\nultracold atoms coupled to the radiation field within a high-finesse optical\nresonator in the dispersive regime of the atom-field interaction with small\ninternal excitation. The optical dipole force on the atoms together with the\nback-action of atomic motion onto the light field gives rise to a complex\nnonlinear coupled dynamics. As the resonator constitutes an open driven and\ndamped system, the dynamics is non-conservative and in general enables cooling\nand confining the motion of polarizable particles. In addition, the emitted\ncavity field allows for real-time monitoring of the particle's position with\nminimal perturbation up to sub-wavelength accuracy. For many-body systems, the\nresonator field mediates controllable long-range atom-atom interactions, which\nset the stage for collective phenomena. Besides correlated motion of distant\nparticles, one finds critical behavior and non-equilibrium phase transitions\nbetween states of different atomic order in conjunction with superradiant light\nscattering. Quantum degenerate gases inside optical resonators can be used to\nemulate opto-mechanics as well as novel quantum phases like supersolids and\nspin glasses. Non-equilibrium quantum phase transitions, as predicted by e.g.\nthe Dicke Hamiltonian, can be controlled and explored in real-time via\nmonitoring the cavity field. In combination with optical lattices, the cavity\nfield can be utilized for non-destructive probing Hubbard physics and tailoring\nlong-range interactions for ultracold quantum systems."
    },
    {
        "anchor": "Thermalization of isolated Bose-Einstein condensate under a PT-symmetric\n  environment: The postulates of the eigenstate thermalization hypothesis (ETH) express that\nthermalization occurs due to the individual eigenstate of the system's\nHamiltonian. But the ETH put no light on the dynamics that lead toward\nthermalization. In this paper, we observe the thermalization of a Bose-Einstein\nCondensate (BEC) confined in an optical lattice potential that is embedded in\nthe harmonic trap. Such optical lattice potential offers local friction to the\noscillating BEC. The spread in the temporal density plot of BEC shows the\nthermalization of the BEC. Moreover, we observe that the presence of a\nPT-symmetric potential greatly influences the BEC dynamics and the\nthermalization of the system. The presence of a PT-symmetric potential offers a\nway to manipulate the mean position of the BEC to the desired location and for\na desired length of time.",
        "positive": "Low-energy scattering of ultracold atoms by a dielectric nanosphere: We theoretically study the low-energy scattering of ultracold atoms by a\ndielectric nanosphere of silica glass levitated in a vacuum. The atom and\ndielectric surface interact via dispersion force of which strength sensitively\ndepends on the polarizability, dielectric function, and geometry. For cesium\nand rubidium atoms, respectively, we compute the atom-surface interaction\nstrength, and characterize the stationary scattering states by taking\nadsorption of the atoms onto the surface into account. As the energy of the\nincoming atoms is lowered, we find that differences between quantum and\nclassical scatterings emerge in two steps. First, the quantum-mechanical\ndifferential cross section of the elastic scattering starts to deviate from the\nclassical one at an energy scale comparable to a few microkelvin in units of\ntemperature due to the de Broglie matter-wave diffraction. Second, the\ndifferences are found in the cross sections in a regime lower than a few\nnanokelvin, where the classically forbidden reflection occurs associated with\nthe $s$-wave scattering, and the discrete nature of angular momentum. We also\nstudy the dependencies of quantum and classical scattering properties on the\nradius of the nanosphere. This paper paves the way to identify the quantum\nregime and to understand the physical origin of quantum effects in the\ncollisions between a nanoparticle and environmental gas over various\ntemperatures."
    },
    {
        "anchor": "Phase diagram, band structure and density of states in two-dimensional\n  attractive Fermi-Hubbard model with Rashba spin-orbit coupling: Based on the two-dimensional (2D) attractive Fermi-Hubbard model with Rashba\nspin-orbit coupling (SOC), the SOC strength and Zeeman field dependences of the\nphase diagram are investigated by calculating the pairing gap\nself-consistently. The results reveal that the phase transition from the BCS\nsuperfluid to the topological superfluid happens under proper Zeeman field\nstrength and SOC strength. In particular, in contrast to the BCS superfluid\ndecreasing monotonically as the SOC strength increasing, the topological\nsuperfluid region shows a dome with the SOC strength increasing. An optimal\nregion in the phase diagram to find the topological superfluid can be found,\nwhich is important to realize the topological superfluid in optical lattice\nexperimentally. Then we obtain the change of both band structure and density of\nstates (DOS) during the topological phase transition, and explain the four\npeaks of DOS in the topological superfluid by the topology change of the\nlow-energy branch of quasiparticle energy spectra. Moreover, the topological\nsuperfluid can be suppressed by the doping concentration.",
        "positive": "Formation of a spin texture in a quantum gas coupled to a cavity: We observe cavity mediated spin-dependent interactions in an off-resonantly\ndriven multi-level atomic Bose-Einstein condensate that is strongly coupled to\nan optical cavity. Applying a driving field with adjustable polarization, we\nidentify the roles of the scalar and the vectorial components of the atomic\npolarizability tensor for single and multi-component condensates. Beyond a\ncritical strength of the vectorial coupling, we observe a spin texture in a\ncondensate of two internal states, providing perspectives for global dynamic\ngauge fields and self-consistently spin-orbit coupled gases."
    },
    {
        "anchor": "Off-site trimer superfluid on a one-dimensional optical lattice: The Bose-Hubbard model with an effective off-site three-body tunneling,\ncharacterized by jumps towards one another, between one atom on a site and a\npair atoms on the neighborhood site, is studied systematically on a\none-dimensional lattice, by using the density matrix renormalization group\nmethod. The off-site trimer superfluid, condensing at momentum $k=0$, emerges\nin the softcore Bose-Hubbard model but it disappears in the hardcore\nBose-Hubbard model. Our results numerically verify that the off-site trimer\nsuperfluid phase derived in the momentum space from [Phys. Rev. A {\\bf 81},\n011601(R) (2010)] is stable in the thermodynamic limit. The off-site trimer\nsuperfluid phase, the partially off-site trimer superfluid phase and the Mott\ninsulator phase are found, as well as interesting phase transitions, such as\nthe continuous or first-order phase transition from the trimer superfluid phase\nto the Mott insulator phase. Our results are helpful in realizing this novel\noff-site trimer superfluid phase by cold atom experiments.",
        "positive": "Generalized nonpolynomial Schrodinger equations for matter waves under\n  anisotropic transverse confinement: Starting from the three-dimensional Gross-Pitaevskii equation we derive a 1D\ngeneralized nonpolynomial Schrodinger equation, which describes the dynamics of\nBose-Einstein condensates under the action of a generic potential in the\nlongitudinal axial direction and of an anisotropic harmonic potential in the\ntransverse radial direction. This equation reduces to the familiar 1D\nnonpolynomial Schrodinger equation [Phys. Rev. A 65, 043614 (2002)] in the case\nof isotropic transverse harmonic confinement. In addition, we show that if the\nlongitudinal potential models a periodic optical lattice the 3D GPE can be\nmapped into a 1D generalized discrete nonpolynomial Schrodinger equation."
    },
    {
        "anchor": "Holes and magnetic polarons in a triangular lattice antiferromagnet: The intricate interplay between charge motion and magnetic order in\ngeometrically frustrated lattices is central for the properties of many\ntwo-dimensional quantum materials. The triangular lattice antiferromagnet is a\ncanonical example of a frustrated system, and here we analyse the dynamics of a\nhole in such a lattice focusing on observables that have become accessible in a\nnew generation of experiments. Using the $t$-$J$ model, we solve the problem\nexactly within linear spin wave theory in the limit of strong magnetic\ninteractions, showing that the ground state is described by a coherent state of\nspin waves. The derivation highlights the crucial role played by the\ninteraction between a static hole and the neighboring spins, which originates\nin the geometric frustration and has often been omitted in earlier works.\nFurthermore, we show that the non-equilibrium dynamics after a hole has\nabruptly been inserted at a lattice site is given exactly by a coherent state\nwith time-dependent oscillatory coefficients. Physically, this describes a\nburst of magnetic frustration propagating through only two-thirds of the\nlattice sites, since a destructive interference of spin waves leaves spins\nparallel to that removed by the hole unperturbed. After the wave has propagated\nthrough the lattice, the magnetization relaxes to that of the ground state. We\nthen use our analytical solution to benchmark the widely used self-consistent\nBorn approximation (SCBA), showing that it is very accurate also for a\ntriangular lattice. The magnetic polaron spectrum is analysed for general\nmagnetic interactions using the SCBA, and we compare our results with those for\na square lattice.",
        "positive": "Fermi surface deformations and pairing in mixtures of dipolar and\n  non-dipolar fermions: We study mass-imbalanced two-component Fermi mixtures, where one of the\ncomponents consists of dipolar fermions. We specifically study the mass\nimbalances corresponding to the atomic ${}^{163}$Dy-${}^{40}$K and\n${}^{53}$Cr-${}^{6}$Li mixtures. We study the onset of the $s$-wave superfluid\nphase, as a function of population imbalance and the dipolar interaction\nstrength. We find the critical temperature and the Fermi surface deformations\nat the transition to depend on the dipolar interaction strength, where the\ncritical temperature increases (decreases) with dipolar interaction strength\nfor a majority (minority) of dipolar atoms. We present momentum distributions\nof both components where the Fermi surface deformations are visible."
    },
    {
        "anchor": "Dynamical tunnelling with ultracold atoms in magnetic microtraps: The study of dynamical tunnelling in a periodically driven anharmonic\npotential probes the quantum-classical transition via the experimental control\nof the effective Planck's constant for the system. In this paper we consider\nthe prospects for observing dynamical tunnelling with ultracold atoms in\nmagnetic microtraps on atom chips. We outline the driven anharmonic potentials\nthat are possible using standard magnetic traps, and find the Floquet spectrum\nfor one of these as a function of the potential strength, modulation, and\neffective Planck's constant. We develop an integrable approximation to the\nnon-integrable Hamiltonian and find that it can explain the behaviour of the\ntunnelling rate as a function of the effective Planck's constant in the regular\nregion of parameter space. In the chaotic region we compare our results with\nthe predictions of models that describe chaos-assisted tunnelling. Finally we\nexamine the practicality of performing these experiments in the laboratory with\nBose-Einstein condensates.",
        "positive": "A manifestly Hermitian semiclassical expansion for the one-particle\n  density matrix of a two-dimensional Fermi gas: The semiclassical $\\hbar$-expansion of the one-particle density matrix for a\ntwo-dimensional Fermi gas is calculated within the Wigner transform method of\nGrammaticos and Voros, originally developed in the context of nuclear physics.\nThe method of Grammaticos and Voros has the virture of preserving both the\nHermiticity and idempotency of the density matrix to all orders in the\n$\\hbar$-expansion. As a topical application, we use our semiclassical expansion\nto go beyond the local-density approximation for the construction of the total\ndipole-dipole interaction energy functional of a two-dimensional,\nspin-polarized dipolar Fermi gas. We find a {\\em finite}, second-order gradient\ncorrection to the Hartree-Fock energy, which takes the form $\\varepsilon\n(\\nabla \\rho)^2/\\sqrt{\\rho}$, with $\\varepsilon$ being small ($|\\varepsilon|\n\\ll1$) and negative. We test the quality of the corrected energy by comparing\nit with the exact results available for harmonic confinement. Even for small\nparticle numbers, the gradient correction to the dipole-dipole energy provides\na significant improvement over the local-density approximation."
    },
    {
        "anchor": "Topological origin of universal few-body clusters in Efimov physics: Efimov physics is renowned for the self-similar spectrum featuring the\nuniversal ratio of one eigenenergy to its neighbor. Even more esoteric is the\nnumerically unveiled fact that every Efimov trimer is accompanied by a pair of\ntetramers. Here we demonstrate that this hierarchy of universal few-body\nclusters has a topological origin by identifying the numbers of universal 3-\nand 4-body bound states with the winding numbers of the renormalization-group\nlimit cycle in theory space. The finding suggests a topological phase\ntransition in mass-imbalanced few-body systems which should be tested\nexperimentally.",
        "positive": "Flow enhanced pairing and other novel effects in Fermi gases in\n  synthetic gauge fields: Recent experiments on fermions in synthetic gauge fields result in systems\nwith a spin-orbit coupling along one spatial axis, a detuning field, and a\nZeeman field. We show theoretically that the presence of all three results in\ninteresting and unusual phenomena in such systems in the presence of a contact\nsinglet attraction between the fermions (described by a scattering length). For\ntwo particles, bound states appear over certain range of the centre of mass\nmomenta when a critical positive scattering length is attained, with the\ndeepest bound state appearing at a nonzero centre of mass momentum. For the\ncentre of mass momenta without a bound state, the gauge field induces a\nresonance like feature in the scattering continuum resulting in a large\nscattering phase shift. For many particles, we demonstrate that the system, in\na parameter range, shows flow enhanced pairing, i.e., a more robust superfluid\nat finite centre of mass momentum. Yet another regime of parameters offers the\nopportunity to study strongly interacting normal states of spin-orbit coupled\nfermionic systems utilizing the resonance like feature induced by the synthetic\ngauge field."
    },
    {
        "anchor": "Theory of a many-boson system with deformed Heisenberg algebra: We propose to consider nonlinear fluctuations in the theory of liquid\n$^{4}$He deforming the commutation relations between the generalized\ncoordinates and momenta. Generalized coordinates are coefficients of density\nfluctuations of Bose particles. The deformation parameter takes into account\nthe effects of three- and four-particle correlations in the behavior of a\nsystem. This parameter is defined from the experimental values of the\nelementary excitation spectrum and the structure factor extrapolated to $T=0$\nK. The numerical estimation of the ground state energy and the Bose condensate\nfraction is made. The elementary excitation spectrum and the potential of\ninteraction between the helium atoms are recovered.",
        "positive": "Topological superfluids with time-reversal symmetry from $s$-wave\n  interaction in a bilayer system: Topological superconducting phases with time-reversal (TR) symmetry have been\nwidely explored in recent years. However the involved unconventional pairings\nare generally implausible in realistic materials. Here we demonstrate via\ndetailed self-consistent calculation that these topological phases with TR\nsymmetry in DIII and BDI classes can be realized in a spin-orbit coupled\nbilayer system with only $s$-wave interaction. The bilayer freedom enables the\ndefinition of TR symmetry between the layers even in the presence of local\nZeeman fields, which we propose to be realized using four laser beams. The\ngapped phase in DIII class is characterized by $\\mathbb{Z}_2$, while all the\ngapless phases in these two classes are characterized by nontrivial winding\nnumbers and are also manifested from the Majorana flat bands. We also unveil\nthe intimate relation between TR symmetry and mirror symmetry due to phase\nlocking effect between the two layers, which harbors the mirror symmetry\nprotected topological phases. We finally demonstrate that these phases will not\nbe spoiled by interlayer pairings."
    },
    {
        "anchor": "Universal High-Frequency Behavior of Periodically Driven Systems: from\n  Dynamical Stabilization to Floquet Engineering: We give a general overview of the high-frequency regime in periodically\ndriven systems and identify three distinct classes of driving protocols in\nwhich the infinite-frequency Floquet Hamiltonian is not equal to the\ntime-averaged Hamiltonian. These classes cover systems, such as the Kapitza\npendulum, the Harper-Hofstadter model of neutral atoms in a magnetic field, the\nHaldane Floquet Chern insulator and others. In all setups considered, we\ndiscuss both the infinite-frequency limit and the leading finite-frequency\ncorrections to the Floquet Hamiltonian. We provide a short overview of Floquet\ntheory focusing on the gauge structure associated with the choice of\nstroboscopic frame and the differences between stroboscopic and\nnon-stroboscopic dynamics. In the latter case one has to work with dressed\noperators representing observables and a dressed density matrix. We also\ncomment on the application of Floquet Theory to systems described by static\nHamiltonians with well-separated energy scales and, in particular, discuss\nparallels between the inverse-frequency expansion and the Schrieffer-Wolff\ntransformation extending the latter to driven systems.",
        "positive": "Quantum fluctuations in quasi-one-dimensional dipolar Bose-Einstein\n  condensates: Recent experiments have revealed that beyond-mean-field corrections are much\nmore relevant in weakly-interacting dipolar condensates than in their\nnon-dipolar counterparts. We show that in quasi-one-dimensional geometries\nquantum corrections in dipolar and non-dipolar condensates are strikingly\ndifferent due to the peculiar momentum dependence of the dipolar interactions.\nThe energy correction of the condensate presents not only a modified density\ndependence, but it may even change from attractive to repulsive at a critical\ndensity due to the surprising role played by the transversal directions. The\nanomalous quantum correction translates into a strongly modified physics for\nquantum-stabilized droplets and dipolar solitons. Moreover, and for similar\nreasons, quantum corrections of three-body correlations, and hence of\nthree-body losses, are strongly modified by the dipolar interactions. This\nintriguing physics can be readily probed in current experiments with magnetic\natoms."
    },
    {
        "anchor": "Spontaneous creation of non-zero angular momentum modes in\n  tunnel-coupled two-dimensional degenerate Bose gases: We investigate the dynamics of two tunnel-coupled two-dimensional degenerate\nBose gases. The reduced dimensionality of the clouds enables us to excite\nspecific angular momentum modes by tuning the coupling strength, thereby\ncreating striking patterns in the atom density profile. The extreme sensitivity\nof the system to the coupling and initial phase difference results in a rich\nvariety of subsequent dynamics, including vortex production, complex\noscillations in relative atom number and chiral symmetry breaking due to\ncounter-rotation of the two clouds.",
        "positive": "The anomalous Floquet Anderson insulator in a continuously driven\n  optical lattice: The anomalous Floquet Anderson insulator (AFAI) has been theoretically\npredicted in step-wise periodically driven models, but its stability under more\ngeneral driving protocols hasn't been determined. We show that adding disorder\nto the anomalous Floquet topological insulator realized with a continuous\ndriving protocol in the experiment by K. Wintersperger et. al., Nat. Phys.\n$\\textbf{16}$, 1058 (2020), supports an AFAI phase, where, for a range of\ndisorder strengths, all the time averaged bulk states become localized, while\nthe pumped charge in a Laughlin pump setup remains quantized."
    },
    {
        "anchor": "Rotating Bose-Einstein condensate in an square optical lattice: vortex\n  configuration for ground state in Josephson junction arrays regime: We consider a rotating Bose-Einstein condensate in a square optical lattice\nin the regime in which the Hamiltonian of the system can be mapped onto a\nJosephson junction array. In an approximate scheme where the couplings are\nassumed uniform, the ground state energy is formulated in terms of the vortex\nconfiguration. The results are compared with experimental results and also\npreviously reported results for frustrated XY model. We also show that vortex\nconfiguration is robust with respect to change of couplings and therefore the\nresults remain valid when we consider more realistic model with non-uniform\ncouplings.",
        "positive": "Two-component spin mixtures: The high degree of control on ultracold gases allows us to precisely\nmanipulate their internal state. When the gas is made of atoms in two different\ninternal states, it can be considered as a two-component spin mixture. Below a\ncritical temperature, the gas becomes a superfluid mixture, never realized\nbefore with any other platform, and therefore interesting to study per se, but\nit also constitutes a promising and versatile platform for applications in\nspintronic devices or to study phenomena belonging to very different fields,\nsuch as magnetism, high-energy physics or gravitation. Here, I will revisit\nground-state properties and excitations of a binary bosonic superfluid, and\nthen introduce a coherent coupling between the states and treat the global\nstate of the atoms as a spin in the presence of a variable external field."
    },
    {
        "anchor": "Exploring quantum signatures of chaos on a Floquet synthetic lattice: Ergodicity and chaos play an integral role in the dynamical behavior of\nmany-particle systems and are crucial to the formulation of statistical\nmechanics. Still, a general understanding of how randomness and chaos emerge in\nthe dynamical evolution of closed quantum systems remains elusive. Here, we\ndevelop an experimental platform for the realization of canonical quantum\nchaotic Hamiltonians based on quantum simulation with synthetic lattices. We\nmap the angular momentum projection states of an effective quantum spin onto\nthe linear momentum states of a $^{87}$Rb Bose-Einstein condensate, which can\nalternatively be viewed as lattice sites in a synthetic dimension. This\nsynthetic lattice, with local and dynamical control of tight-binding lattice\nparameters, enables new capabilities related to the experimental study of\nquantum chaos. In particular, the capabilities of our system let us tune the\neffective size of our spin, allowing us to illustrate how classical chaos can\nemerge from a discrete quantum system. Moreover, spectroscopic control over our\nsynthetic lattice allows us to explore unique aspects of our spin's dynamics by\nmeasuring the out-of-time-ordered correlation function, and enables future\ninvestigations into entirely new classes of chaotic systems.",
        "positive": "Statics and dynamics of a self-bound matter-wave quantum ball: We study the statics and dynamics of a stable, mobile, three-dimensional\nmatter-wave spherical quantum ball created in the presence of an attractive\ntwo-body and a very small repulsive three-body interaction. The quantum ball\ncan propagate with a constant velocity in any direction in free space and its\nstability under a small perturbation is established numerically and\nvariationally. In frontal head-on and angular collisions at large velocities\ntwo quantum balls behave like quantum solitons. Such collision is found to be\nquasi elastic and the quantum balls emerge after collision without any change\nof direction of motion and velocity and with practically no deformation in\nshape. When reflected by a hard impenetrable plane, the quantum ball bounces\noff like a wave obeying the law of reflection without any change of shape or\nspeed. However, in a collision at small velocities two quantum balls coalesce\nto form a larger ball which we call a quantum-ball breather. We point out the\nsimilarity and difference between the collision of two quantum and classical\nballs. The present study is based on an analytic variational approximation and\na full numerical solution of the mean-field Gross-Pitaevskii equation using the\nparameters of $^7$Li atoms."
    },
    {
        "anchor": "Strong Interaction Effects in Superfluid Ising Quantum Phase Transition: We study the quantum phase transition between a normal Bose superfluid to one\nthat breaks additional Z_2 Ising symmetry. Using the recent shaken optical\nlattice experiment as an example, we first show that at mean-field level atomic\ninteraction can significantly shift the critical point. Near the critical\npoint, bosons can condense into a momentum state with high or even locally\nmaximum kinetic energies due to interaction effect. Then, we present a general\nlow-energy effective field theory that treats both the superfluid transition\nand the Ising transition in a uniform framework, and identify a quantum\ntricritical point separating normal superfluid, Z_2 superfluid and Mott\ninsulator. Using perturbative renormalization group method, we find that the\nquantum phase transition belongs to a unique universality class that is\ndifferent from that of a dilute Bose gas.",
        "positive": "On the relaxation towards equilibrium in an isolated strongly correlated\n  1D Bose gas: In this work we study the time evolution of soft core bosons on a\none-dimensional lattice, where the particles are initially quenched into a\natomic density wave. At time $t=0$ the particles are released from the quench\nand can evolve under the dynamics of a soft-core Bose-Hubbard Hamiltonian on a\nlattice including a confining trap."
    },
    {
        "anchor": "Oscillating superflow in multicomponent Bose-Einstein condensates: Conservation of angular momentum depends on the existence of rotational\nsymmetry. However, even in systems where this symmetry is broken, flipping\nbetween angular momentum eigenstates often requires an activation energy. Here\nwe discuss an example of superfluid flow in a toroidal potential, which shows\nsustained oscillations between two different rotation directions. The energy\nrequired to change the direction of rotation is taken out of and temporarily\nrestored into the rotational and intra-component interaction energies of the\nsystem.",
        "positive": "Geometrically Frustrated Coarsening Dynamics in Spinor Bose-Fermi\n  Mixtures: Coarsening dynamics theory has successfully described the equilibration of a\nbroad class of systems.By studying the relaxation of a periodic array of\nmicrocondensates immersed in a Fermi gas which can mediate long-range spin\ninteractions to simulate frustrated classical magnets, we show that coarsening\ndynamics can be suppressed by geometrical frustration. The system is found to\neventually approach a metastable state which is robust against random field\nnoise and characterized by finite correlation lengths with the emergence of\ntopologically stable Z2 vortices. We find universal scaling laws with no\nthermal-equilibrium analog that relate the correlation lengths and the number\nof vortices to the degree of frustration in the system."
    },
    {
        "anchor": "Long time rigidity to flux-induced symmetry breaking in quantum quench\n  dynamics: We investigate how the breaking of charge conjugation symmetry $\\mathcal{C}$\nimpacts on the dynamics of a half-filled fermionic lattice system after global\nquenches. We show that, when the initial state is insulating and the\n$\\mathcal{C}$-symmetry is broken non-locally by a constant magnetic flux, local\nobservables and correlations behave as if the symmetry were unbroken for a time\ninterval proportional to the system size $L$. In particular, the local particle\ndensity of a quenched dimerized insulator remains pinned to $1/2$ in each\nlattice site for an extensively long time, while it starts to significantly\nfluctuate only afterwards. Due to its qualitative resemblance to the sudden\narrival of rapidly rising ocean waves, we dub this phenomenon the ``tsunami\neffect\". Notably, it occurs even though the chiral symmetry is dynamically\nbroken right after the quench. Furthermore, we identify a way to quantify the\namount of symmetry breaking in the quantum state, showing that in insulators\nperturbed by a flux it is exponentially suppressed as a function of the system\nsize, while it is only algebraically suppressed in metals and in insulators\nwith locally broken $\\mathcal{C}$-symmetry. The robustness of the tsunami\neffect to weak disorder and interactions is demonstrated, and possible\nexperimental realizations are proposed.",
        "positive": "Quantum criticality of a one-dimensional Bose-Fermi mixture: The one-dimensional interacting Bose-Fermi mixtures, exhibiting quantum phase\ntransitions at zero temperature, are particularly valuable for the study of\nquantum critical phenomena. In the present paper, we analytically study quantum\nphase diagram, equation of state and quantum criticality of the Bose-Fermi\nmixture using the thermodynamic Bethe ansatz equations. We show that\nthermodynamical properties display universal scaling behaviour at quantum\ncriticality. Furthermore, quantum criticality of the Bose-Fermi mixture in an\nharmonic trap is also studied within the local density approximation. We thus\ndemonstrate that the phase diagram and critical properties of the bulk system\nprovide insights into understanding universal features of many-body critical\nphenomena."
    },
    {
        "anchor": "Von K\u00e1rm\u00e1n vortex street in a Bose-Einstein condensate: Vortex shedding from an obstacle potential moving in a Bose-Einstein\ncondensate is investigated. Long-lived alternately aligned vortex pairs are\nfound to form in the wake, as for the von K\\'arm\\'an vortex street in classical\nviscous fluids. Various patterns of vortex shedding are systematically studied\nand the drag force on the obstacle is calculated. It is shown that the\nphenomenon can be observed in a trapped system.",
        "positive": "Bloch dynamics in lattices with long range hoppings: We study a discrete Schr\\\"odinger equation with arbitrary long range hopping\nterms under the influence of an external force. The impact of long range\nhoppings on the single particle Bloch dynamics in the lattice is investigated.\nA closed expression for the propagator is given, based on which we analyze the\ndynamics of initially Gaussian wave packets. Our findings capture the\nanharmonic oscillations recently observed in zigzag lattices and furthermore\nprovide a detailed quantitative description of the crossover between center of\nmass Bloch oscillations for wide wave packets and left-right symmetric width\noscillations for narrow single site excitations. The analytical results are\nshown to be in agreement with numerical simulations. A helix lattice setup for\nultracold atoms is proposed where such hopping terms to far neighbors can be\nexperimentally tuned to sizable values."
    },
    {
        "anchor": "Creating and probing the Sachdev-Ye-Kitaev model with ultracold gases:\n  Towards experimental studies of quantum gravity: We suggest that the holographic principle, combined with recent technological\nadvances in atomic, molecular, and optical physics, can lead to experimental\nstudies of quantum gravity. As a specific example, we consider the\nSachdev-Ye-Kitaev (SYK) model, which consists of spin-polarized fermions with\nan all-to-all complex random two-body hopping and has been conjectured to be\ndual to a certain quantum gravitational system. Achieving low-temperature\nstates of the SYK model is interpreted as a realization of a stringy black\nhole, provided that the holographic duality is true. We introduce a variant of\nthe SYK model, in which the random two-body hopping is real. This model is\nequivalent to the origincal SYK model in the large-$N$ limit. We show that this\nmodel can be created in principle by confining ultracold fermionic atoms into\noptical lattices and coupling two atoms with molecular states via\nphoto-association lasers. This development serves as an important first step\ntowards an experimental realization of such systems dual to quantum black\nholes. We also show how to measure out-of-time-order correlation functions of\nthe SYK model, which allow for identifying the maximally chaotic property of\nthe black hole.",
        "positive": "Miscibility in coupled dipolar and non-dipolar Bose-Einstein condensates: We perform a full three-dimensional study on miscible-immiscible conditions\nfor coupled dipolar and non-dipolar Bose-Einstein condensates (BEC), confined\nwithin anisotropic traps. Without loosing general miscibility aspects that can\noccur for two-component mixtures, our main focus was on the atomic\nerbium-dysprosium ($^{168}$Er-$^{164}$Dy) and dysprosium-dysprosium\n($^{164}$Dy-$^{162}$Dy) mixtures. Our analysis for pure-dipolar BEC was limited\nto coupled systems confined in pancake-type traps, after considering a study on\nthe stability regime of such systems. In case of non-dipolar systems with\nrepulsive contact intneeractions we are able to extend the miscibility analysis\nto coupled systems with cigar-type symmetries. For a coupled condensate with\nrepulsive inter- and intra-species two-body interactions, confined by an\nexternal harmonic trap, the transition from a miscible to an immiscible phase\nis verified to be much softer than in the case the system is confined by a\nsymmetric hard-wall potential. Our results, presented by density plots, are\npointing out the main role of the trap symmetry and inter-species interaction\nfor the miscibility. A relevant parameter to measure the overlap between the\ntwo densities was defined and found appropriate to quantify the miscibility of\na coupled system."
    },
    {
        "anchor": "Bragg spectroscopy of clean and disordered lattice bosons in one\n  dimension: a spectral fingerprint of the Bose glass: We study the dynamic structure factor of a one-dimensional Bose gas confined\nin an optical lattice and modeled by the Bose-Hubbard Hamiltonian, using a\nvariety of numerical and analytical approaches. The dynamic structure factor,\nexperimentally measurable by Bragg spectroscopy, is studied in three relevant\ncases: in the clean regime, featuring either a superfluid or a Mott phase; and\nin the presence of two types of (quasi-)disordered external potentials: a\nquasi-periodic potential obtained from a bichromatic superlattice and a\nrandom-box disorder - both featuring a Bose glass phase. In the clean case, we\nshow the emergence of a gapped doublon mode (corresponding to a repulsively\nbound state) for incommensurate filling, well separated from the low-energy\nacoustic mode. In the disordered case, we show that the dynamic structure\nfactor provides a direct insight into the spatial structure of the excitations,\nunveiling their localized nature, which represents a fundamental signature of\nthe Bose glass phase. Furthermore, it provides a clear fingerprint of the very\nnature of the localization mechanism which differs for the two kinds of\ndisorder potentials we consider. In special cases, the dynamic structure factor\nmay provide an estimate of the position of the localization transition from\nsuperfluid to Bose glass, in a complementary manner to the information deduced\nfrom the momentum distribution.",
        "positive": "Harmonically trapped fermions in one dimension: A finite temperature\n  lattice Monte Carlo study: We study a one-dimensional two-component Fermi gas in a harmonic trapping\npotential using finite temperature lattice quantum Monte Carlo methods. We are\nable to compute observables in the canonical ensemble via an efficient\nprojective approach. Results for density profiles, correlations, as well as\nenergy-related observables are presented for systems with up to 80 particles\nand various temperatures. Our simulations reproduce known numerical results and\ncompare well against available experimental data close to the ground state,\nwhile at higher temperature they are benchmarked against the exact solution of\nthe two particle system. This provides an indication that a standard lattice\ndiscretization is sufficient to capture the physics of the trapped system. In\nthe special case of a spin-imbalanced gas, we find no sign problem in the\nparameter ranges studied, allowing access without the need of specialized\nmethods. This includes simulations close to the ground state and at large\npopulation imbalance, where we present results for density correlations,\nindicating pairing at finite total momentum."
    },
    {
        "anchor": "Ramsey interference in one dimensional systems: The full distribution\n  function of fringe contrast as a probe of many-body dynamics: We theoretically analyze Ramsey interference experiments in one dimensional\nquasi-condensates and obtain explicit expressions for the time evolution of\nfull distribution functions of fringe contrast. We show that distribution\nfunctions contain unique signatures of the many-body mechanism of decoherence.\nWe argue that Ramsey interference experiments provide a powerful tool for\nanalyzing strongly correlated nature of 1D interacting systems.",
        "positive": "Achieving ground-state polar molecular condensates by chainwise\n  atom-molecule adiabatic passage: We generalize the idea of chainwise stimulated Raman adiabatic passage\n(STIRAP) [Kuznetsova \\textit{et al.} Phys. Rev. A \\textbf{78}, 021402(R)\n(2008)] to a photoassociation-based chainwise atom-molecule system, with the\ngoal of directly converting two-species atomic Bose-Einstein condensates (BEC)\ninto a ground polar molecular BEC. We pay particular attention to the\nintermediate Raman laser fields, a control knob inaccessible to the usual\nthree-level model. We find that an appropriate exploration of both the\nintermediate laser fields and the stability property of the atom-molecule\nSTIRAP can greatly reduce the power demand on the photoassociation laser, a key\nconcern for STIRAPs starting from free atoms due to the small Franck-Condon\nfactor in the free-bound transition."
    },
    {
        "anchor": "Bogoliubov Theory for a Superfluid Bose Gas Flowing in a Random\n  Potential: Stability and Critical Velocity: We investigate the stability and critical velocity of a weakly interacting\nBose gas flowing in a random potential. By applying the Bogoliubov theory to a\ndisordered Bose system with a steady flow, the condensate density and the\nsuperfluid density are determined as functions of the disorder strength, flow\nvelocity, and temperature. The critical velocity, at which the steady flow\nbecomes unstable, is calculated from the spectrum of hydrodynamic excitation.\nWe also show that in two dimensions the critical velocity strongly depends on\nthe system size.",
        "positive": "Anisotropic sound and shock waves in dipolar Bose-Einstein condensate: We study the propagation of anisotropic sound and shock waves in dipolar\nBose-Einstein condensate in three dimensions (3D) as well as in quasi-two (2D,\ndisk shape) and quasi-one (1D, cigar shape) dimensions using the mean-field\napproach. In 3D, the propagation of sound and shock waves are distinct in\ndirections parallel and perpendicular to dipole axis with the appearance of\ninstability above a critical value corresponding to attraction. Similar\ninstability appears in 1D and not in 2D. The numerical anisotropic Mach angle\nagrees with theoretical prediction. The numerical sound velocity in all cases\nagrees with that calculated from Bogoliubov theory. A movie of the anisotropic\nwave propagation in a dipolar condensate is made available as supplementary\nmaterial."
    },
    {
        "anchor": "Dynamics of a dipolar Bose-Einstein condensate in the vicinity of a\n  superconductor: We study the dynamics of a dipolar Bose-Einstein condensate, like for example\na $^{52}$Cr or $^{164}$Dy condensate, interacting with a superconducting\nsurface. The magnetic dipole moments of the atoms in the Bose-Einstein\ncondensate induce eddy currents in the superconductor. The magnetic field\ngenerated by eddy currents modifies the trapping potential such that the\ncenter-of-mass oscillation frequency is shifted. We numerically solve the\nGross-Pitaevskii equation for this system and compare the results with\nanalytical approximations. We present an approximation that gives excellent\nagreement with the numerical results. The eddy currents give rise to anharmonic\nterms, which leads to the excitation of shape fluctuations of the condensate.\nWe discuss how the strength of the excitation of such modes can be increased by\nexploiting resonances, and we examine the strength of the resonances as a\nfunction of the center-of-mass oscillation amplitude of the condensate.\nFinally, we study different orientations of the magnetic dipoles and discuss\nfavorable conditions for the experimental observation of the eddy current\neffect.",
        "positive": "Phase diagrams of Bose-Hubbard model and Haldane-Bose-Hubbard model with\n  complex hopping amplitudes: In this paper, we study Bose-Hubbard models on the square and honeycomb\nlattices with complex hopping amplitudes, which are feasible by recent\nexperiments of cold atomic gases in optical lattices. To clarify phase\ndiagrams, we use an extended quantum Monte-Carlo simulations (eQMC). For the\nsystem on the square lattice, the complex hopping is realized by an artificial\nmagnetic field. We found that vortex-solid states form for certain set of\nmagnetic field, i.e., the magnetic field with the flux quanta per plaquette\n$f=p/q$, where $p$ and $q$ are co-prime natural numbers. For the system on the\nhoneycomb lattice, we add the next-nearest neighbor complex hopping. The model\nis a bosonic analog of the Haldane-Hubbard model. By means of the eQMC, we\nstudy the model with both weak and strong on-site repulsions. Numerical study\nshows that the model has a rich phase diagram. We also found that in the system\ndefined on the honeycomb lattice of the cylinder geometry, an interesting edge\nstate appears."
    },
    {
        "anchor": "Many-body localization of one-dimensional degenerate Fermi gases with\n  cavity-assisted non-local quasiperiodic interactions: The localization properties of one-dimensional degenerate Fermi gases with\ncavity-assisted non-local quasiperiodic interactions are numerically studied.\nAlthough the cavity-induced interaction is typically nonlocal, it is proved\nthat the eigenstate thermalization hypothesis (ETH) is still applicable in our\nsystem depending on the system parameters. We also find the segment of the\nspectrum corresponding to infinite effective temperature varies for different\nsystem parameters, which indicates the spectral range employed in the spectral\nstatistical analysis should be varied accordingly. The features of many-body\nlocalization (MBL) are numerically identified by analyzing the spectral\nstatistics and the entanglement entropy using exact diagonalization. These\nfeatures are further confirmed by our time evolution results. In addition, the\nnumber of cavity photons are found stable over long time dynamics in the MBL\nphase. Such a feature can not only be utilized to nondestructively diagnose the\nMBL phase by monitoring the number of leaking photons from the cavity, but\nleveraged for constructing a device to produce a stable number of photons.",
        "positive": "Itinerant magnetism in spin-orbit coupled Bose gases: Phases of matter are conventionally characterized by order parameters\ndescribing the type and degree of order in a system. For example, crystals\nconsist of spatially ordered arrays of atoms, an order that is lost as the\ncrystal melts. Like- wise in ferromagnets, the magnetic moments of the\nconstituent particles align only below the Curie temperature, TC. These two\nexamples reflect two classes of phase transitions: the melting of a crystal is\na first-order phase transition (the crystalline order vanishes abruptly) and\nthe onset of magnetism is a second- order phase transition (the magnetization\nincreases continuously from zero as the temperature falls below TC). Such\nmagnetism is robust in systems with localized magnetic particles, and yet rare\nin model itinerant systems where the particles are free to move about. Here for\nthe first time, we explore the itinerant magnetic phases present in a spin-1\nspin-orbit coupled atomic Bose gas; in this system, itinerant ferromagnetic\norder is stabilized by the spin-orbit coupling, vanishing in its absence. We\nfirst located a second-order phase transition that continuously stiffens until,\nat a tricritical point, it transforms into a first- order transition (with\nobserved width as small as h x 4 Hz). We then studied the long-lived metastable\nstates associated with the first-order transition. These measurements are all\nin agreement with theory."
    },
    {
        "anchor": "Noise-induced transition from superfluid to vortex state in\n  two-dimensional nonequilibrium polariton condensates: We study the Berezinskii-Kosterlitz-Thouless mechanism for vortex-antivortex\npair formation in two-dimensional superfluids for nonequilibrium condensates.\nOur numerical study is based on a classical field model for driven-dissipative\nquantum fluids that is applicable to polariton condensates. We investigate the\ncritical noise needed to create vortex-antivortex pairs in the systems,\nstarting from a state with uniform phase. The dependence of the critical noise\non the nonequilibrium and energy relaxation parameters is analyzed in detail.",
        "positive": "Observation of Nagaoka Polarons in a Fermi-Hubbard Quantum Simulator: Quantum interference can deeply alter the nature of many-body phases of\nmatter. In the paradigmatic case of the Hubbard model, Nagaoka famously proved\nthat introducing a single itinerant charge can transform a paramagnetic\ninsulator into a ferromagnet through path interference. However, a microscopic\nobservation of such kinetic magnetism induced by individually imaged dopants\nhas been so far elusive. Here we demonstrate the emergence of Nagaoka polarons\nin a Hubbard system realized with strongly interacting fermions in a triangular\noptical lattice. Using quantum gas microscopy, we reveal these polarons as\nextended ferromagnetic bubbles around particle dopants arising from the local\ninterplay of coherent dopant motion and spin exchange. In contrast, kinetic\nfrustration due to the triangular geometry promotes antiferromagnetic polarons\naround hole dopants, as proposed by Haerter and Shastry. Our work augurs the\nexploration of exotic quantum phases driven by charge motion in strongly\ncorrelated systems and over sizes that are challenging for numerical\nsimulation."
    },
    {
        "anchor": "Condensate Phase Microscopy: We show that the phase of a Bose-Einstein condensate wave-function of\nultra-cold atoms in an optical lattice potential in two-dimensions can be\ndetected. The time-of-flight images, obtained in a free expansion of initially\ntrapped atoms, are related to the initial distribution of atomic momenta but\nthe information on the phase is lost. However, the initial atomic cloud is\nbounded and this information, in addition to the time-of-flight images, is\nsufficient in order to employ the phase retrieval algorithms. We analyze the\nphase retrieval methods for model wave-functions in a case of a Bose-Einstein\ncondensate in a triangular optical lattice in the presence of artificial gauge\nfields.",
        "positive": "Observation of generalized Kibble-Zurek mechanism across a first-order\n  quantum phase transition in a spinor condensate: The Kibble-Zurek mechanism provides a unified theory to describe the\nuniversal scaling laws in the dynamics when a system is driven through a\nsecond-order quantum phase transition. However, for first-order quantum phase\ntransitions, the Kibble-Zurek mechanism is usually not applicable. Here, we\nexperimentally demonstrate and theoretically analyze a power-law scaling in the\ndynamics of a spin-1 condensate across a first-order quantum phase transition\nwhen a system is slowly driven from a polar phase to an antiferromagnetic\nphase. We show that this power-law scaling can be described by a generalized\nKibble-Zurek mechanism. Furthermore, by experimentally measuring the spin\npopulation, we show the power-law scaling of the temporal onset of spin\nexcitations with respect to the quench rate, which agrees well with our\nnumerical simulation results. Our results open the door for further exploring\nthe generalized Kibble-Zurek mechanism to understand the dynamics across\nfirst-order quantum phase transitions."
    },
    {
        "anchor": "Decay of polarons and molecules in a strongly polarized Fermi gas: The ground state of an impurity immersed in a Fermi sea changes from a\npolaron to a molecule as the interaction strength is increased.\n  We show here that the coupling between these two states is strongly\nsuppressed due to a combination of phase space effects and Fermi statistics,\nand that it vanishes much faster than the energy difference between the two\nstates, thereby confirming the first order nature of the polaron-molecule\ntransition. In the regime where each state is metastable, we find quasiparticle\nlifetimes which are much longer than what is expected for a usual Fermi liquid.\nOur analysis indicates that the decay rates are sufficiently slow to be\nexperimentally observable.",
        "positive": "Wave pattern induced by a localized obstacle in the flow of a\n  one-dimensional polariton condensate: Motivated by recent experiments on generation of wave patterns by a polariton\ncondensate incident on a localized obstacle, we study the characteristics of\nsuch flows under the condition that irreversible processes play a crucial role\nin the system. The dynamics of a non-resonantly pumped polariton condensate in\na quasi-one-dimensional quantum wire is modeled by a Gross-Pitaevskii equation\nwith additional phenomenological terms accounting for the dissipation and\npumping processes. The response of the condensate flow to an external potential\ndescribing a localized obstacle is considered in the weak-perturbation limit\nand also in the nonlinear regime. The transition from a viscous drag to a\nregime of wave resistance is identified and studied in detail."
    },
    {
        "anchor": "Quantum Monte Carlo Study of a Resonant Bose-Fermi Mixture: We study a resonant Bose-Fermi mixture at zero temperature by using the\nfixed-node diffusion Monte Carlo method. We explore the system from weak to\nstrong boson-fermion interaction, for different concentrations of the bosons\nrelative to the fermion component. We focus on the case where the boson density\n$n_B$ is smaller than the fermion density $n_F$, for which a first-order\nquantum phase transition is found from a state with condensed bosons immersed\nin a Fermi sea, to a Fermi-Fermi mixture of composite fermions and unpaired\nfermions. We obtain the equation of state and the phase diagram, and we find\nthat the region of phase separation shrinks to zero for vanishing $n_B$.",
        "positive": "Counterflow dynamics of two correlated impurities immersed in a bosonic\n  gas: The counterflow dynamics of two correlated impurities in a double-well\ncoupled to an one-dimensional bosonic medium is explored. We determine the\nground state phase diagram of the system according to the impurity-medium\nentanglement and the impurities two-body correlations. Specifically, bound\nimpurity structures reminiscent of bipolarons for strong attractive couplings\nas well as configurations with two clustered or separated impurities in the\nrepulsive case are identified. The interval of existence of these phases\ndepends strongly on the impurity-impurity interactions and external confinement\nof the medium. Accordingly the impurities dynamical response, triggered by\nsuddenly ramping down the central potential barrier, is affected by the\nmedium's trapping geometry. In particular, for a box-confined medium repulsive\nimpurity-medium couplings lead, due to attractive induced interactions, to the\nlocalization of the impurities around the trap center. In contrast, for a\nharmonically trapped medium the impurities perform a periodic collision and\nexpansion dynamics further interpreted in terms of a two-body effective model.\nOur findings elucidate the correlation aspects of the collisional physics of\nimpurities which should be accessible in recent cold atom experiments."
    },
    {
        "anchor": "Spin dependent inelastic collisions between metastable state\n  two-electron atoms and ground state alkali-atoms: Experimentally the spin dependence of inelastic collisions between ytterbium\n(Yb) in the metastable 3P0 state and lithium (Li) in the Li ground state\nmanifold is investigated at low magnetic fields. Using selective excitation all\nmagnetic sublevels mJ of 174Yb(3P0) are accessed and four of the six lowest\nlying magnetic sublevels of 6Li are prepared by optical pumping. On the one\nhand, mJ-independence of collisions involving Li(F=1/2) atoms is found. A\nsystematic mJ-dependence in collisions with Li(F=3/2) atoms, in particular\nsuppressed losses for stretched collisional states, is observed on the other\nhand. Further, mJ-changing processes are found to be of minor relevance. The\nspan of observed inelastic collision rates is between 1*10^{-11} cm^3/s and\n40*10^{-11} cm^3/s, and a possible origin of the observed behavior is\ndiscussed.",
        "positive": "Self-consistent perturbation expansion for Bose-Einstein condensates\n  satisfying Goldstone's theorem and conservation laws: Quantum-field-theoretic descriptions of interacting condensed bosons have\nsuffered from the lack of self-consistent approximation schemes satisfying\nGoldstone's theorem and dynamical conservation laws simultaneously. We present\na procedure to construct such approximations systematically by using either an\nexact relation for the interaction energy or the Hugenholtz-Pines relation to\nexpress the thermodynamic potential in a Luttinger-Ward form. Inspection of the\nself-consistent perturbation expansion up to the third order with respect to\nthe interaction shows that the two relations yield a unique identical result at\neach order, reproducing the conserving-gapless mean-field theory [T. Kita, J.\nPhys. Soc. Jpn. 74, 1891 (2005)] as the lowest-order approximation. The\nuniqueness implies that the series becomes exact when infinite terms are\nretained. We also derive useful expressions for the entropy and superfluid\ndensity in terms of Green's function and a set of real-time dynamical equations\nto describe thermalization of the condensate."
    },
    {
        "anchor": "The role of thermal fluctuations in sound propagation in a\n  two-dimensional Fermi gas: We numerically study the transport properties of a two-dimensional Fermi gas\nin a weakly and strongly interacting regimes, in the range of temperatures\nclose to the transition to a superfluid phase. For that we excite sound waves\nin a fermionic mixture by using the phase imprinting technique, follow their\nevolution, and finally determine both their speed and attenuation. Our\nformalism incorporates thermal fluctuations via the ground canonical ensemble\ndescription and with the help of Metropolis algoritm. From numerical\nsimulations we extract temperature dependence of the sound velocity and\ndiffusivity as well as the dependence on the interaction strength. We emphasize\nthe role of virtual vortex-antivortex pairs creation in the process of sound\ndissipation.",
        "positive": "Three-body problem in a two-dimensional Fermi gas: We investigate the three-body properties of two identical \"up\" fermions and\none distinguishable \"down\" atom interacting in a strongly confined\ntwo-dimensional geometry. We compute exactly the atom-dimer scattering\nproperties and the three-body recombination rate as a function of collision\nenergy and mass ratio m_up/m_down. We find that the recombination rate for\nfermions is strongly energy dependent, with significant contributions from\nhigher partial waves at low energies. For m_up < m_down, the s-wave atom-dimer\nscattering below threshold is completely described by the scattering length.\nFurthermore, we examine the \"up-up-down\" bound states (trimers) appearing at\nlarge m_up/m_down and find that the energy spectrum for the deepest bound\ntrimers resembles that of a hydrogen atom confined to two dimensions."
    },
    {
        "anchor": "Condensates Breaking Up Under Rotation: The ground state of a rotating Bose-Einstein condensate trapped in a\ntwo-dimensional anharmonic--anisotropic potential is analyzed numerically at\nthe limit of an infinite number of particles. We find that the density breaks\nup along the $x$ direction in position space and along the $p_y$ direction in\nmomentum space together with the acquisition of angular momentum. Side by side,\nthe anisotropies of the many-particle position variances along the $x$ and $y$\ndirections and of the many-particle momentum variances along the $p_y$ and\n$p_x$ directions become opposite when computed at the many-body and mean-field\nlevels of theory. All in all, the rotating bosons are found to possess unique\ncorrelations at the limit of an infinite number of particles, both in position\nand momentum spaces, although their many-body and mean-field energies per\nparticle and densities per particle coincide and the condensate fraction is\n100\\%. Implications are briefly discussed.",
        "positive": "Quantum time reflection and refraction of ultracold atoms: Time reflection and refraction are temporal analogies of the spatial boundary\neffects derived from Fermat's principle. They occur when classical waves strike\na time boundary where an abrupt change in the properties of the medium is\nintroduced. The main features of time-reflected and refracted waves are the\nshift of frequency and conservation of momentum, which offer a new degree of\nfreedom for steering extreme waves and controlling phases of matter. The\nconcept was originally proposed for manipulating optical waves more than five\ndecades ago. However, due to the extreme challenges in the ultrafast\nengineering of the optical materials, the experimental realization of the time\nboundary effects remains elusive. Here, we introduce a time boundary into a\nmomentum lattice of ultracold atoms and simultaneously demonstrate the time\nreflection and refraction experimentally. Through launching a\nGaussian-superposed state into the Su-Schrieffer-Heeger (SSH) atomic chain, we\nobserve the time-reflected and refracted waves when the input state strikes a\ntime boundary. Furthermore, we detect a transition from time\nreflection/refraction to localization with increasing strength of disorder and\nshow that the time boundary effects are robust against considerable disorder.\nOur work opens a new avenue for future exploration of time boundaries and\nspatiotemporal lattices, and their interplay with non-Hermiticity and many-body\ninteractions."
    },
    {
        "anchor": "Interaction-controlled impurity transport in trapped mixtures of\n  ultracold bosons: We explore the dynamical transport of an impurity between different embedding\nmajority species which are spatially separated in a double well. The transfer\nand storage of the impurity is triggered by dynamically changing the\ninteraction strengths between the impurity and the two majority species. We\nfind a simple but efficient protocol consisting of linear ramps of\nmajority-impurity interactions at designated times to pin or unpin the\nimpurity. Our study of this highly imbalanced few-body triple mixture is\nconducted with the multi-layer multi-configuration time-dependent Hartree\nmethod for atomic mixtures which accounts for all interaction-induced\ncorrelations. We analyze the dynamics in terms of single-particle densities,\nentanglement growth and provide an effective potential description involving\nmean-fields of the interacting components. The majority components remain\nself-trapped in their individual wells at all times, which is a crucial element\nfor the effectiveness of our protocol. During storage times each component\nperforms low-amplitude dipole oscillations in a single well. Unexpectedly, the\ninter-species correlations possess a stabilizing impact on the transport and\nstorage properties of the impurity particle.",
        "positive": "Prospects for thermalization of microwave-shielded ultracold molecules: We study anisotropic thermalization in dilute gases of microwave shielded\npolar molecular fermions. For collision energies above the threshold regime, we\nfind that thermalization is suppressed due to a strong preference for forward\nscattering and a reduction in total cross section with energy, significantly\nreducing the efficiency of evaporative cooling. We perform close-coupling\ncalculations on the effective potential energy surface derived by Deng et al.\n[Phys. Rev. Lett. 130, 183001 (2023)], to obtain accurate 2-body elastic\ndifferential cross sections across a range of collision energies. We use\nGaussian process regression to obtain a global representation of the\ndifferential cross section, over a wide range of collision angles and energies.\nThe route to equilibrium is then analyzed with cross-dimensional\nrethermalization experiments, quantified by a measure of collisional efficiency\ntoward achieving thermalization."
    },
    {
        "anchor": "Unstable Avoided Crossing in Coupled Spinor Condensates: We consider the dynamics of a Bose-Einstein condensate with two internal\nstates, coupled through a coherent drive. We focus on a specific quench\nprotocol, in which the sign of the coupling field is suddenly changed. At a\nmean-field level, the system is transferred from a minimum to a maximum of the\ncoupling energy and can remain dynamically stable, in spite of the development\nof negative- frequency modes. In the presence of a non-zero detuning between\nthe two states, the \"charge\" and \"spin\" modes couple, giving rise to an\nunstable avoided crossing. This phenomenon is generic to systems with two\ndispersing modes away from equilibrium and constitutes an example of\nclass-$I_o$ non-equilibrium pattern formation in quantum systems.",
        "positive": "Quantum state control of a Bose-Einstein condensate in an optical\n  lattice: We report on the efficient design of quantum optimal control protocols to\nmanipulate the motional states of an atomic Bose-Einstein condensate (BEC) in a\none-dimensional optical lattice. Our protocols operate on the momentum comb\nassociated with the lattice. In contrast to previous works also dealing with\ncontrol in discrete and large Hilbert spaces, our control schemes allow us to\nreach a wide variety of targets by varying a single parameter, the lattice\nposition. With this technique, we experimentally demonstrate a precise, robust\nand versatile control: we optimize the transfer of the BEC to a single or\nmultiple quantized momentum states with full control on the relative phase\nbetween the different momentum components. This also allows us to prepare the\nBEC in a given eigenstate of the lattice band structure, or superposition\nthereof."
    },
    {
        "anchor": "Ab-initio Quantum Monte Carlo study of ultracold atomic mixtures: In this thesis, the properties of mixtures of Bose-Einstein condensates at $T\n= 0$ have been investigated using quantum Monte Carlo (QMC) methods and Density\nFunctional Theory (DFT) with the aim of understanding physics beyond the\nmean-field theory in Bose-Bose mixtures.",
        "positive": "Probing the bond order wave phase transitions of the ionic Hubbard model\n  by superlattice modulation spectroscopy: An exotic phase, the bond order wave, characterized by the spontaneous\ndimerization of the hopping, has been predicted to exist sandwiched between the\nband and Mott insulators in systems described by the ionic Hubbard model.\nDespite growing theoretical evidences, this phase still evades experimental\ndetection. Given the recent realization of the ionic Hubbard model in ultracold\natomic gases, we propose here to detect the bond order wave using superlattice\nmodulation spectroscopy. We demonstrate, with the help of time-dependent\ndensity-matrix renormalization group and bosonization, that this spectroscopic\napproach reveals characteristics of both the Ising and Kosterlitz-Thouless\ntransitions signaling the presence of the bond order wave phase. This scheme\nalso provides insights into the excitation spectra of both the band and Mott\ninsulators."
    },
    {
        "anchor": "Artificial gauge potentials for neutral atoms: When a neutral atom moves in a properly designed laser field, its\ncenter-of-mass motion may mimic the dynamics of a charged particle in a\nmagnetic field, with the emergence of a Lorentz-like force. In this Colloquium\nwe present the physical principles at the basis of this artificial (synthetic)\nmagnetism and relate the corresponding Aharonov-Bohm phase to the Berry's phase\nthat emerges when the atom follows adiabatically one of its dressed states. We\nalso discuss some manifestations of artificial magnetism for a cold quantum\ngas, in particular in terms of vortex nucleation. We then generalise our\nanalysis to the simulation of non-Abelian gauge potentials and present some\nstriking consequences, such as the emergence of an effective spin-orbit\ncoupling. We address both the case of bulk gases and discrete systems, where\natoms are trapped in an optical lattice.",
        "positive": "Spin-twisted Optical Lattices: Tunable Flat Bands and Larkin-Ovchinnikov\n  Superfluids: Moir\\'{e} superlattices in twisted bilayer graphene and transition-metal\ndichalcogenides have emerged as a powerful tool for engineering novel band\nstructures and quantum phases of two-dimensional quantum materials. Here we\ninvestigate Moir\\'{e} physics emerging from twisting two independent hexagonal\noptical lattices of atomic (pseudo-)spin states (instead of bilayers), which\nexhibits remarkably different physics from twisted bilayer graphene. We employ\na momentum-space tight-binding calculation that includes all range real-space\ntunnelings, and show that all twist angles $\\theta \\lesssim 6^{\\circ }$ can\nbecome magic that support gapped flat bands. Due to greatly enhanced density of\nstates near the flat bands, the system can be driven to superfluid by weak\nattractive interaction. Strikingly, the superfluid phase corresponds to a\nLarkin-Ovchinnikov state with finite momentum pairing, resulting from the\ninterplay between flat bands and inter-spin interactions in the unique\nsingle-layer spin-twisted lattice. Our work may pave the way for exploring\nnovel quantum phases and twistronics in cold atomic systems."
    },
    {
        "anchor": "Precision Measurements of Atom-Dimer Interactions in a Uniform Planar\n  Bose Gas: Cold quantum gases, when acted upon by electromagnetic fields, can give rise\nto samples where isolated atoms coexist with dimers or trimers, which raises\nthe question of the interactions between these various constituents. Here we\nperform microwave photoassociation in a degenerate gas of $^{87}$Rb atoms to\ncreate weakly-bound dimers in their electronic ground state. From the\ndensity-induced shift of the photoassociation line, we measure the atom-dimer\nscattering length for the two least-bound states of the molecular potential. We\nalso determine the complete energy diagram of one hyperfine manifold of the\nleast-bound state, which we accurately reproduce with a simple model.",
        "positive": "Effect of Dimple Potential on Ultraslow Light in a Bose-Einstein\n  Condensate: We investigate the propagation of ultraslow optical pulse in atomic\nBose-Einstein condensate in a harmonic trap decorated with a dimple potential.\nThe role of dimple potential on the group velocity and time delay is studied.\nSince we consider the interatomic scattering interactions nonlinear Schrodinger\nequation or Gross-Pitaevskii equation is used in order to get the density\nprofile of the atomic system. We find large group delays of order 1 msec in an\natomic Bose-Einstein condensate in a harmonic trap with a deep dimple\npotential."
    },
    {
        "anchor": "Renormalization group study of Bose polarons: We study the properties of a single impurity in a dilute Bose gas, a Bose\npolaron, using the functional renormalization group. We use an ansatz for the\neffective action motivated by a derivative expansion, and we compute the\nenergies of the attractive and repulsive branches of excitations in both two\nand three spatial dimensions. Three-body correlations play an important role in\nthe attractive branch, and we account for those by including three-body\ncouplings between two bath bosons and the impurity. Our calculations compare\nvery favorably with state-of-the-art experimental measurements and numerical\nsimulations.",
        "positive": "Superfluidity and collective oscillations of trapped Bose-Einstein\n  condensates in a periodical potential: Based on a unified theoretical treatment of the 1D Bogoliubov-de Genes\nequations, the superfluidity phenomenon of the Bose-Einstein condensates (BEC)\nloaded into trapped optical lattice is studied. Within the perturbation regime,\nan all-analytical framework is presented enabling a straightforward\nphenomenological mapping of the collective excitation and oscillation character\nof a trapped BEC where the available experimental configurations also fit."
    },
    {
        "anchor": "Controlled state-to-state atom-exchange reaction in an ultracold\n  atom-dimer mixture: Ultracold molecules offer remarkable opportunities to study chemical\nreactions at nearly zero temperature. Although significant progresses have been\nachieved in exploring ultracold bimolecular reactions, the investigations are\nusually limited to measurements of the overall loss rates of the reactants.\nDetection of the reaction products will shed new light on understanding the\nreaction mechanism and provide a unique opportunity to study the state-to-state\nreaction dynamics. Here we report on the direct observation of an exoergic\natom-exchange reaction in an ultracold atom-dimer mixture. Both the atom and\nmolecule products are observed and the quantum states are characterized. By\nchanging the magnetic field, the reaction can be switched on or off, and the\nreaction rate can be controlled. The reaction is efficient and we have measured\na state-to-state reaction rate of up to $1.1(3)\\times10^{-9}$cm$^{3}/$s from\nthe time evolution of the reactants and products. Our work represents the\nrealization of a controlled quantum state selected/resolved ultracold reaction.\nThe atom-exchange reaction observed is also an effective spin-exchange\ninteraction between the Feshbach molecules and the fermionic atoms and may be\nexploited to implement quantum simulations of the Kondo effect with ultracold\natoms and molecules.",
        "positive": "Many-body and temperature effects in two-dimensional quantum droplets in\n  Bose-Bose mixtures: We study the equilibrium properties of self-bound droplets in two-dimensional\nBose mixtures employing the time-dependent Hartree-Fock-Bogoliubov theory. This\ntheory allows one to understand both the many-body and temperature effects\nbeyond the Lee-Huang-Yang description. We calculate higher-order corrections to\nthe excitations, the sound velocity, and the energy of the droplet. Our results\nfor the ground-state energy are compared with the diffusion Monte Carlo data\nand good agreement is found. The behavior of the depletion and anomalous\ndensity of the droplet is also discussed. At finite temperature, we show that\nthe droplet emerges at temperatures well below the\nBerezinskii-Kosterlitz-Thouless transition temperature. The critical\ntemperature strongly depends on the interspecies interactions. Our study is\nextended to the finite size droplet by numerically solving the generalized\nfinite-temperature Gross-Pitaevskii equation which is obtained\nself-consistently from our formalism in the framework of the local density\napproximation."
    },
    {
        "anchor": "Order-by-Disorder Degeneracy Lifting of Interacting Bosons on the Dice\n  Lattice: Motivated by recent experimental progress in the realization of synthetic\ngauge fields in systems of ultracold atoms, we consider interacting bosons on\nthe dice lattice with half flux per plaquette. All bands of the non-interacting\nspectrum of this system were previously found to have the remarkable property\nof being completely dispersionless. We show that degeneracies remain when\ninteractions are treated at the level of mean field theory, and the ground\nstate exhibits vortex lattice configurations already established in the simpler\nXY model in the same geometry. We argue that including quantum and thermal\nfluctuations will select a unique vortex lattice up to overall symmetries based\non the order-by-disorder mechanism. We verify the stability of the selected\nstate by analyzing the condensate depletion. The latter is shown to exhibit an\nunusual non-monotonic behavior as a function of the interaction parameters\nwhich can be understood as a consequence of the dispersionless nature of the\nnon-interacting spectrum. Finally, we comment on the role of domain walls which\nhave interactions mediated through fluctuations.",
        "positive": "Persistent Currents in Toroidal Dipolar Supersolids: We investigate the rotational properties of a dipolar Bose-Einstein\ncondensate trapped in a toroidal geometry. Studying the ground states in the\nrotating frame and at fixed angular momenta, we observe that the condensate\nacts in distinctly different ways depending on whether it is in the superfluid\nor in the supersolid phase. We find that intriguingly, the toroidal dipolar\ncondensate can support a supersolid persistent current which occurs at a local\nminimum in the ground state energy as a function of angular momentum, where the\nstate has a vortex solution in the superfluid component of the condensate. The\ndecay of this state is prevented by a barrier that in part consists of states\nwhere a fraction of the condensate mimics solid-body rotation in a direction\nopposite to that of the vortex. Furthermore, the rotating toroidal supersolid\nshows hysteretic behavior that is qualitatively different depending on the\nsuperfluid fraction of the condensate."
    },
    {
        "anchor": "Angular momentum Josephson effect between two isolated condensates: We demonstrate that the two degenerate energy levels in spin-orbit coupled\ntrapped Bose gases, coupled by a quenched Zeeman field, can be used for angular\nmomentum Josephson effect. In a static quenched field, we can realize a\nJosephson oscillation with period ranging from millisecond to hundreds of\nmilliseconds. Moreover, by a driven Zeeman field, we realize a new Josephson\noscillation, in which the population imbalance may have the same expression as\nthe current in the directed current (dc) Josephson effect. When the dynamics of\ncondensate can not follow up the modulation frequency, it the self-trapping\nregime. This new dynamics is understood from the time dependent evolution of\nthe constant-energy trajectory in phase space. This model has several salient\nadvantages as compared with the previous ones. The condensates are isolated\nfrom their excitations by a finite gap, thus can greatly suppress the damping\neffect induced by thermal atoms and Bogoliubov excitations. The oscillation\nperiod can be tuned by several order of magnitudes without influencing other\nparameters. In experiments, the dynamics can be mapped out from spin and\nmomentum spaces, thus is not limited by the spatial resolution in imaging. This\nsystem can serve as a promising platform for exploring of matter wave\ninterferometry.",
        "positive": "Superfluid Density of Weakly Interacting Bosons on a Lattice: We use a path integral approach to calculate the superfluid density of a Bose\nlattice gas in the limit where the number of atoms per site is large. Our\nanalytical expressions agree with numerical results on small systems for low\ntemperatures and relatively weak interactions. We also calculate the superfluid\ndensity and drag for two-component lattice bosons. To attain the correct\nresults we develop tools for calculating discrete time path integrals. These\ntools should be broadly applicable to a range of systems which are naturally\ndescribed within an overcomplete basis."
    },
    {
        "anchor": "Multidimensional Spectroscopy of Time-Dependent Impurities in Ultracold\n  Fermions: We investigate the system of a heavy impurity immersed in a degenerated Fermi\ngas, where the impurity's internal degree of freedom (pseudospin) is\nmanipulated by a series of radiofrequency (RF) pulses at several different\ntimes. Applying the functional determinant approach, we carry out an\nessentially exact calculation of the Ramsey-interference-type responses to the\nRF pulses. These responses are universal functions of the multiple time\nintervals between the pulses for all time and can be regarded as\nmultidimensional (MD) spectroscopy of the system in the time domain. A Fourier\ntransformation of the time intervals gives the MD spectroscopy in the frequency\ndomain, providing insightful information on the many-body correlation and\nrelaxation via the cross-peaks, e.g., the off-diagonal peaks in a\ntwo-dimensional spectrum. These features are inaccessible for the conventional,\none-dimensional absorption spectrum. Our scheme provides a new method to\ninvestigate many-body nonequilibrium physics beyond the linear response regime\nwith the accessible tools in cold atoms.",
        "positive": "Universal scaling of density and momentum distributions in Lieb-Liniger\n  gases: We present an exact numerical study of the scaling of density and momentum\ndistribution functions of harmonically trapped one-dimensional bosons with\nrepulsive contact interactions at zero and finite temperatures. We use path\nintegral quantum Monte Carlo with worm updates in our calculations at finite\ninteraction strengths, and the Bose-Fermi mapping in the Tonks-Girardeau\nregime. We discuss the homogeneous case and, within the local density\napproximation, use it to motivate the scaling in the presence of a harmonic\ntrap. For the momentum distribution function, we pay special attention to the\nhigh momentum tails and their $k^{-4}$ asymptotic behavior."
    },
    {
        "anchor": "Geometric squeezing into the lowest Landau level: The equivalence between neutral particles under rotation and charged\nparticles in a magnetic field relates phenomena as diverse as spinning atomic\nnuclei, weather patterns, and the quantum Hall effect. In their quantum\ndescriptions, translations along different directions do not commute, implying\na Heisenberg uncertainty relation between spatial coordinates. Here, we exploit\nthe ability to squeeze non-commuting variables to dynamically create a\nBose-Einstein condensate occupying a single Landau gauge wavefunction in the\nlowest Landau level. We directly resolve the extent of the zero-point cyclotron\norbits, and demonstrate geometric squeezing of the orbits' guiding centers by\nmore than ${7}~$dB below the standard quantum limit. The condensate attains an\nangular momentum of more than ${1000}\\,{\\hbar}$ per particle, and an\ninteratomic distance comparable to the size of the cyclotron orbits. This\noffers a new route towards strongly correlated fluids and bosonic quantum Hall\nstates.",
        "positive": "From single-particle excitations to sound waves in a box-trapped atomic\n  Bose-Einstein condensate: We experimentally and theoretically investigate the lowest-lying axial\nexcitation of an atomic Bose-Einstein condensate in a cylindrical box trap. By\ntuning the atomic density, we observe how the nature of the mode changes from a\nsingle-particle excitation (in the low-density limit) to a sound wave (in the\nhigh-density limit). Throughout this crossover the measured mode frequency\nagrees with Bogoliubov theory. Using approximate low-energy models we show that\nthe evolution of the mode frequency is directly related to the\ninteraction-induced shape changes of the condensate and the excitation.\nFinally, if we create a large-amplitude excitation, and then let the system\nevolve freely, we observe that the mode amplitude decays non-exponentially in\ntime; this nonlinear behaviour is indicative of interactions between the\nelementary excitations, but remains to be quantitatively understood."
    },
    {
        "anchor": "Universal energy-dependent pseudopotential for the two-body problem of\n  confined ultracold atoms: The two-body scattering amplitude and energy spectrum of confined ultracold\natoms are of fundamental importance for studies of ultracold atom physics. For\nmany systems, one can efficiently calculate these quantities via the zero-range\nHuang-Yang pseudopotential (HYP), in which the interatomic interaction is\ncharacterized by the scattering length $a$. Furthermore, when the scattering\nlength is dependent on the kinetic energy $\\varepsilon_{\\rm r}$ of two-atom\nrelative motion, the results are applicable for a broad energy region. However,\nwhen the free Hamiltonian of atomic internal state does not commute with the\ninter-atomic interaction, or the center-of-mass (c.m.) motion is coupled to the\nrelative motion, the generalization of this technique is still lacking. We\nsolve this problem and construct a reasonable energy-dependent multi-channel\nHYP, which is characterized by a \"scattering length operator\" ${\\hat a}_{\\rm\neff}$. Here ${\\hat a}_{\\rm eff}$ is an operator for atomic internal states and\nc.m. motion, and depends on both the total two-atom energy and the external\nfield as well as the trapping parameter. The effects from the internal-state or\nc.m.-relative motion coupling can be self-consistently taken into account by\n${\\hat a}_{\\rm eff}$. We further show a method based on the quantum defect\ntheory, with which ${\\hat a}_{\\rm eff}$ can be analytically derived for systems\nwith van der Waals inter-atomic interaction. To demonstrate our method, we\ncalculate the spectrum of two ultracold fermionic alkaline-earth-like atoms\nconfined in an optical lattice. By comparing our results with the recent\nexperimental measurements for two Yb173 atoms and two Yb171 atoms, we calibrate\nthe scattering lengths $a_{\\pm}$ with respect to anti-symmetric and symmetric\nnuclear-spin states to be $a_{+}=2012(19)a_{0}$ and $a_{-}=193(4)a_{0}$ for\nYb173, and $a_{+}=232(3)a_{0}$ and $a_{-}=372(1)a_{0}$ for Yb171.",
        "positive": "Quantum spin mixing in a binary mixture of spin-1 atomic condensates: We study quantum spin mixing in a binary mixture of spin-1 condensates\nincluding coherent interspecies mixing process, using the familiar spinor\ncondensates of $^{87}$Rb and $^{23}$Na atoms in the ground lower hyperfine F=1\nmanifolds as prototype examples. Within the single spatial mode approximation\nfor each of the two spinor condensates, the mixing dynamics reduce to that of\nthree coupled nonlinear pendulums with clear physical interpretations. Using\nsuitably prepared initial states, it is possible to determine the interspecies\nsinglet-pairing as well as spin-exchange interactions from the subsequent\nmixing dynamics."
    },
    {
        "anchor": "On the anomalous density for Bose gases at finite temperature: We analyze the behavior of the anomalous density as function of the radial\ndistance at different temperatures in a variational framework. We show that the\ntemperature dependence of the anomalous density agrees with the\nHartree-Fock-Bogoliubov (HFB) calculations. Comparisons between the normal and\nthe anomalous fractions at low temperature show that the latter remains higher\nand consequently the neglect of the anomalous density may destabilize the\ncondensate. These results are compatible with those of Yukalov. Surprisingly,\nthe study of the anomalous density in terms of the interaction parameter shows\nthat the dip in the central density is destroyed for sufficiently weak\ninteractions. We explain this effect.",
        "positive": "Dynamics of Macroscopic Tunneling in Elongated BEC: We investigate macroscopic tunneling from an elongated quasi 1-d trap,\nforming a 'cigar shaped' BEC. Using recently developed formalism we get the\nleading analytical approximation for the right hand side of the potential wall,\ni.e. outside the trap, and a formalism based on Wigner functions, for the left\nside of the potential wall, i.e. inside the BEC. We then present accomplished\nresults of numerical calculations, which show a 'blip' in the particle density\ntraveling with an asymptotic shock velocity, as resulted from previous works on\na dot-like trap, but with significant differences from the latter. Inside the\nBEC a pattern of a traveling dispersive shock wave is revealed. In the\nattractive case, we find trains of bright solitons frozen near the boundary."
    },
    {
        "anchor": "Tricriticalities and Quantum Phases in Spin-Orbit-Coupled Spin-$1$ Bose\n  Gases: We study the zero-temperature phase diagram of a spin-orbit-coupled\nBose-Einstein condensate of spin $1$, with equally weighted Rashba and\nDresselhaus couplings. Depending on the antiferromagnetic or ferromagnetic\nnature of the interactions, we find three kinds of striped phases with\nqualitatively different behaviors in the modulations of the density profiles.\nPhase transitions to the zero-momentum and the plane-wave phases can be induced\nin experiments by independently varying the Raman coupling strength and the\nquadratic Zeeman field. The properties of these transitions are investigated in\ndetail, and the emergence of tricritical points, which are the direct\nconsequence of the spin-dependent interactions, is explicitly discussed.",
        "positive": "Quasiparticle excitations in Bose-Fermi mixtures: We analyze the excitation spectrum of a three-dimensional(3D) Bose-Fermi\nmixture with tunable resonant interaction parameters and high hyperfine spin\nmultiplets. We focus on a 3-particle vertex describing fermionic and bosonic\natoms which can scatter to create fermionic molecules or disassociate. For a\nsingle molecular level, in analogy to the single magnetic impurity problem we\nargue that the low lying excitations of the mean-field theory are described by\nthe Fermi liquid picture with a quasiparticle weight and charge which is\njustified by a $1/N_\\psi$ expansion, expected to be exact in the limit of\ninfinite degeneracy (or very high fermionic spin) $N_\\psi \\to \\infty$. Our\nemphasis is placed on the novel conditions for chemical equilibrium and how\nmany-body chemical reactions renormalize the bosonic chemical potential,\nmodifying condensation and superfluid-insulator transitions."
    },
    {
        "anchor": "Dirac-Weyl fermions with arbitrary spin in two-dimensional optical\n  superlattices: Dirac-Weyl fermions are massless relativistic particles with a well-defined\nhelicity which arise in the context of high-energy physics. Here we propose a\nquantum simulation of these paradigmatic fermions using multicomponent\nultracold atoms in a two-dimensional square optical lattice. We find that\nlaser-assisted spin-dependent hopping, specifically tuned to the\n$(2s+1)$-dimensional representations of the $\\mathfrak{su}$(2) Lie algebra,\ndirectly leads to a regime where the emerging massless excitations correspond\nto Dirac-Weyl fermions with arbitrary pseudospin $s$. We show that this\nplatform hosts two different phases: a semimetallic phase that occurs for\nhalf-integer $s$, and a metallic phase that contains a flat zero-energy band at\ninteger $s$. These phases host a variety of interesting effects, such as a very\nrich anomalous quantum Hall effect and a remarkable multirefringent Klein\ntunneling. In addition we show that these effects are directly related to the\nnumber of underlying Dirac-Weyl species and zero modes.",
        "positive": "p-wave Superfluidity by Spin-Nematic Fermi Surface Deformation: We study attractively interacting fermions on a square lattice with\ndispersion relations exhibiting strong spin-dependent anisotropy. The resulting\nFermi surface mismatch suppresses the s-wave BCS-type instability, clearing the\nway for unconventional types of order. Unbiased sampling of the Feynman\ndiagrammatic series using Diagrammatic Monte Carlo methods reveals a rich phase\ndiagram in the regime of intermediate coupling strength. Instead of a proposed\nCooper-pair Bose metal phase [A. E. Feiguin and M. P. A. Fisher, Phys. Rev.\nLett. 103, 025303 (2009)] we find an incommensurate density wave at strong\nanisotropy and two different p-wave superfluid states with unconventional\nsymmetry at intermediate anisotropy."
    },
    {
        "anchor": "Majorana modes and $p$-wave superfluids for fermionic atoms in optical\n  lattices: We present a simple approach to create a strong $p$-wave interaction for\nfermions in an optical lattice. The crucial step is that the combination of a\nlattice setup with different orbital states and $s$-wave interactions can give\nrise to a strong induced $p$-wave pairing. We identify different topological\nphases and demonstrate that the setup offers a natural way to explore the\ntransition from Kitaev's Majorana wires to two-dimensional $p$-wave\nsuperfluids. We demonstrate how this design can induce Majorana modes at edge\ndislocations in the optical lattice, and we provide an experimentally feasible\nprotocol for the observation of the non-Abelian statistics.",
        "positive": "Extended Bose-Hubbard model in a shaken optical lattice: We study an extended Bose-Hubbard model with next-nearest-neighbor (NNN)\nhopping in a shaken optical lattice. We show how mean-field phase diagram\nevolves with the change of NNN hopping amplitude $t_{2}$, which can be easily\ntuned via shaking amplitude. As $t_{2}$ increases, a $Z_{2}$-symmetry-breaking\nsuperfluid ($Z_{2}$SF) phase emerges at the bottom of the Mott lobs. The\ntricritical points between normal superfluid, $Z_{2}$SF, and Mott insulator\n(MI) phases are identified. We further demonstrate the tricritical point can be\ntuned to the tip of the Mott lobe, in which case a new critical behavior has\nbeen predicted. Within random-phase approximation, excitation spectra in the\nthree phases are obtained, which indicate how the phase transitions occur."
    },
    {
        "anchor": "Kibble-Zurek mechanism in a trapped ferromagnetic Bose-Einstein\n  condensate: Spontaneous spin vortex formation in the magnetic phase transition of a\ntrapped spin-1 Bose-Einstein condensate is investigated using mean-field\ntheory. In a harmonic trapping potential, an inhomogeneous atomic density leads\nto spatial variations of the critical point, magnetization time scale, and spin\ncorrelation length. The Kibble-Zurek phenomena are shown to emerge even in such\ninhomogeneous systems, when the quench of the quadratic Zeeman energy is fast\nenough. For slow quench, the magnetized region gradually expands from the\ncenter of the trap pushing out spin vortices, which hinders the Kibble-Zurek\nmechanism from occurring. A harmonic trap with a plug potential is also taken\ninto account.",
        "positive": "Metastable criticality and the super Tonks-Girardeau gas: We consider a 1D Bose gas with attractive interactions in an\nout-of-equilibrium highly excited state containing no bound states. We show\nthat relaxation processes in the gas are suppressed, making the system\nmetastable on long timescales. We compute dynamical correlation functions,\nrevealing the structure of excitations, an enhancement of umklapp correlations\nand new branches due to intermediate bound states. These features give a clear\nindication of the attractive regime and can be probed experimentally. We\nobserve that, despite its out-of-equilibrium nature, the system displays\ncritical behaviour: correlation functions are characterised by asymptotic\npower-law decay described by the Luttinger liquid framework."
    },
    {
        "anchor": "Vortex Formations from Domain Wall Annihilations in Two-component\n  Bose-Einstein Condensates: We theoretically study the vortex formation from the collision of the domain\nwalls in phase-separated two-component Bose-Einstein condensates. The collision\nprocess mimics the tachyon condensation for the annihilation of D-brane and\nanti-D-brane in string theory. A pair annihilation leaves the quantized\nvortices with superflow along their core, namely `superflowing cosmic strings'.\nIt is revealed that the line density and the core size of the vortices depend\non the initial distance between the walls.",
        "positive": "Geometrically induced complex tunnelings for ultracold atoms carrying\n  orbital angular momentum: We investigate the dynamics of angular momentum states for a single ultracold\natom trapped in two dimensional systems of sided coupled ring potentials. The\nsymmetries of the system show that tunneling amplitudes between different ring\nstates with variation of the winding number are complex. In particular, we\ndemonstrate that in a triangular ring configuration the complex nature of the\ncross-couplings can be used to geometrically engineer spatial dark states to\nmanipulate the transport of orbital angular momentum states via quantum\ninterference."
    },
    {
        "anchor": "The stability of the low-dimensional mixtures of dilute quantum gases: We study the stability of the dilute Bose-Fermi and Bose-Bose mixtures with\nrepulsive interactions in one and two dimensions in terms of the\nrenormalization group. For the Bose-Fermi mixture, we show that the uniform\nmixture is stable against de-mixing in the dilute limit. For the Bose-Bose\nmixture, we give the stability conditions in the dilute limit. As a byproduct,\nwe also calculate the critical temperature for the superfluid phase of the\ntwo-dimensional Bose-Fermi mixture in the extremely dilute limit.",
        "positive": "On-demand dark soliton train manipulation in a spinor polariton\n  condensate: We theoretically demonstrate the generation of dark solitons trains in a\none-dimensional exciton- polariton condensate within an experimentally trivial\nscheme. In particular we show that the fre- quency of the train can be finely\ntuned either electrically of fully optically to provide a stable and efficient\noutput signal modulation. Taking the polarization degree of freedom into\naccount we elucidate the possibility to additionally form on-demand\nhalf-solitons trains."
    },
    {
        "anchor": "Frustrated Magnetism of Dipolar Molecules on a Square Optical Lattice:\n  Prediction of a Quantum Paramagnetic Ground State: Motivated by the experimental realization of quantum spin models of polar\nmolecule KRb in optical lattices, we analyze the spin 1/2 dipolar Heisenberg\nmodel with competing anisotropic, long-range exchange interactions. We show\nthat, by tilting the orientation of dipoles using an external electric field,\nthe dipolar spin system on square lattice comes close to a maximally frustrated\nregion similar, but not identical, to that of the $J_1$-$J_2$ model. This\nprovides a simple yet powerful route to potentially realize a quantum spin\nliquid without the need for a triangular or kagome lattice. The ground state\nphase diagrams obtained from Schwinger-boson and spin-wave theories\nconsistently show a spin disordered region between the N$\\acute{\\textrm{e}}$el,\nstripe, and spiral phase. The existence of a finite quantum paramagnetic region\nis further confirmed by an unbiased variational ansatz based on tensor network\nstates and a tensor renormalization group.",
        "positive": "The Gor'kov and Melik-Barkhudarov correction to the mean-field critical\n  field transition to Fulde-Ferrell-Larkin-Ovchinnikov states: The Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states, characterized by Cooper\npairs condensed at finite-momentum are, at the same time, exotic and elusive.\nIt is partially due to the fact that the FFLO states allow superconductivity to\nsurvive even in strong magnetic fields at the mean-field level. The effects of\ninduced interactions at zero temperature are calculated in both clean and dirty\ncases, and it is found that the critical field at which the quantum phase\ntransition to an FFLO state occurs at the mean-field level is strongly\nsuppressed in imbalanced Fermi gases. This strongly shrinks the phase space\nregion where the FFLO state is unstable and more exotic ground state is to be\nfound. In the presence of high level impurities, this shrinkage may destroy the\nFFLO state completely."
    },
    {
        "anchor": "Anisotropic excitation spectrum of a dipolar quantum Bose gas: We measure the excitation spectrum of a dipolar Chromium Bose Einstein\nCondensate with Raman-Bragg spectroscopy. The energy spectrum depends on the\norientation of the dipoles with respect to the excitation momentum,\ndemonstrating an anisotropy which originates from the dipole-dipole\ninteractions between the atoms. We compare our results with the Bogoliubov\ntheory based on the local density approximation, and, at large excitation\nwavelengths, with numerical simulations of the time dependent Gross-Pitaevskii\nequation. Our results show an anisotropy of the speed of sound",
        "positive": "Coherent Impurity Transport in an Attractive Binary Bose-Einstein\n  condensate: We study the dynamics of a soliton-impurity system modeled in terms of a\nbinary Bose-Einstein condensate. This is achieved by `switching off' one of the\ntwo self-interaction scattering lengths, giving a two component system where\nthe second component is trapped entirely by the presence of the first\ncomponent. It is shown that this system possesses rich dynamics, including the\nidentification of unusual `weak' dimers that appear close to the zero\ninter-component scattering length. It is further found that this system\nsupports quasi-stable trimers in regimes where the equivalent single-component\ngas does not, which is attributed to the presence of the impurity atoms which\ncan dynamically tunnel between the solitons, and maintain the required phase\ndifferences that support the trimer state."
    },
    {
        "anchor": "Ultracold Dipolar Gas of Fermionic $^{23}$Na$^{40}$K Molecules in their\n  Absolute Ground State: We report on the creation of an ultracold dipolar gas of fermionic\n$^{23}$Na$^{40}$K molecules in their absolute rovibrational and hyperfine\nground state. Starting from weakly bound Feshbach molecules, we demonstrate\nhyperfine resolved two-photon transfer into the singlet ${\\rm X}^1\\Sigma^+\n|v{=}0,J{=}0\\rangle$ ground state, coherently bridging a binding energy\ndifference of 0.65 eV via stimulated rapid adiabatic passage. The\nspin-polarized, nearly quantum degenerate molecular gas displays a lifetime\nlonger than 2.5 s, highlighting NaK's stability against two-body chemical\nreactions. A homogeneous electric field is applied to induce a dipole moment of\nup to 0.8 Debye. With these advances, the exploration of many-body physics with\nstrongly dipolar Fermi gases of $^{23}$Na$^{40}$K molecules is in experimental\nreach.",
        "positive": "Dynamical preparation of laser-excited anisotropic Rydberg crystals in\n  2D optical lattices: We describe the dynamical preparation of anisotropic crystalline phases\nobtained by laser-exciting ultracold Alkali atoms to Rydberg p-states where\nthey interact via anisotropic van der Waals interactions. We develop a time-\ndependent variational mean field ansatz to model large, but finite\ntwo-dimensional systems in experimentally accessible parameter regimes, and we\npresent numerical simulations to illustrate the dynamical formation of\nanisotropic Rydberg crystals."
    },
    {
        "anchor": "Effect of mediated interactions on a Hubbard chain in mixed-dimensional\n  fermionic cold atoms: Cold atom experiments can now realize mixtures where different components\nmove in different spatial dimensions. We investigate a fermion mixture where\none species is constrained to move along a one-dimensional lattice embedded in\na two-dimensional lattice populated by another species of fermions, and where\nall bare interactions are contact interactions. By focusing on the\none-dimensional fermions, we map this problem onto a model of fermions with\nnon-local interactions on a chain. The effective interaction is mediated by the\ntwo-dimensional fermions and is both attractive and retarded, the form of which\ncan be varied by changing the density of the two-dimensional fermions. By using\nthe functional renormalization group in the weak-coupling and adiabatic limit,\nwe show that the one-dimensional fermions can be controlled to be in various\ndensity-wave, or spin-singlet or triplet superconducting phases.",
        "positive": "Atomtronic superconducting quantum interference device in synthetic\n  dimensions: We propose atomtronic counterpart of superconducting quantum interference\ndevice (SQUID) in synthetic $2$-dimensional space. The system is composed of\nBose-Einstein condensate (BEC) in two neighboring optical wells which is\ncoupled to an external coherent light. Furthermore, availability of\ncontrollable atomtronic flux qubit in the synthetic dimensions is demonstrated\nwith this system. Control parameter for the qubit is naturally provided by\nartificial magnetic flux originated from the coherent atom-light coupling.\nComparing with traditional SQUID which requires at least $2$-dimensional\ncircuits, the synthetic dimensional SQUID can be realized only in\n$1$-dimensional circuits. It should be a great advantage for the scalability\nand integration feature of quantum logic gates."
    },
    {
        "anchor": "Bogoliubov theory of interacting bosons: new insights from an old\n  problem: In a gas of $N$ interacting bosons, the Hamiltonian $H_c$, obtained by\ndropping all the interaction terms between free bosons with moment\n$\\hbar\\mathbf{k}\\ne\\mathbf{0}$, is diagonalized exactly. The resulting\neigenstates $|\\:S,\\:\\mathbf{k},\\:\\eta\\:\\rangle$ depend on two discrete indices\n$S,\\:\\eta=0,\\:1,\\:\\dots$, where $\\eta$ numerates the \\emph{quasiphonons}\ncarrying a moment $\\hbar\\mathbf{k}$, responsible for transport or dissipation\nprocesses. $S$, in turn, numerates a ladder of \\textquoteleft\nvacua\\textquoteright$\\:|\\:S,\\:\\mathbf{k},\\:0\\:\\rangle$, with increasing\nequispaced energies, formed by boson pairs with opposite moment. Passing from\none vacuum to another ($S\\rightarrow S\\pm1$), results from\ncreation/annihilation of new momentless collective excitations, that we call\n\\emph{vacuons}. Exact quasiphonons originate from one of the vacua by\n\\textquoteleft creating\\textquoteright$\\:$an asymmetry in the number of\nopposite moment bosons. The well known Bogoliubov collective excitations (CEs)\nare shown to coincide with the exact eigenstates\n$|\\:0,\\:\\mathbf{k},\\:\\eta\\:\\rangle$, i.e. with the quasiphonons created from\nthe lowest-level vacuum ($S=0$). All this is discussed, in view of existing or\nfuture experimental observations of the vacuons (PBs), a sort of bosonic Cooper\npairs, which are the main factor of novelty beyond Bogoliubov theory.",
        "positive": "Dynamics of spin polarization in tilted polariton rings: We have observed the effect of pseudo magnetic field originating from the\npolaritonic analog of spin-orbit coupling (TE$-$TM splitting) on a polariton\ncondensate in a ring-shaped microcavity. The effect gives rise to a stable\nfour-leaf pattern around the ring as seen from the linear polarization\nmeasurements of the condensate photoluminescence. This pattern is found to\noriginate from the interplay of the cavity potential, energy relaxation, and\nTE-TM splitting in the ring. Our observations are compared to the dissipative\none-dimensional spinor Gross-Pitaevskii equation with the TE-TM splitting\nenergy which shows good qualitative agreement."
    },
    {
        "anchor": "Dynamical properties of a few mass-imbalanced ultra-cold fermions\n  confined in a double-well potential: A comprehensive analysis of the exact unitary dynamics of two-component\nmass-imbalanced fermions in a one-dimensional double-well potential is\naccomplished by considering the total number of particles maximum up to six.\nThe simultaneous effect of mass imbalance between the flavors and their mutual\ninteractions on the dynamics is scrutinized through the exact diagonalization.\nIn particular, we investigate the occupation dynamics of such systems being\ninitially prepared in experimentally accessible states in which opposite\ncomponents occupy opposite wells. Moreover, to capture the role of\ninteractions, we also inspect situations in which initial states contain an\nopposite-spin pair localized in a chosen well. Finally, to assess the amount of\nquantum correlations produced during the evolution, we analyze the behavior of\nthe von Neumann entanglement entropy between components.",
        "positive": "Entangling two Bose Einstein condensates in a double cavity system: We propose a scheme to transfer the quantum state of light fields to the\ncollective density excitations of a Bose Einstein condensate (BEC) in a cavity.\nThis scheme allows to entangle two BECs in a double cavity setup by\ntransferring the quantum entanglement of two light fields produced from a\nnondegenerate parametric amplifier (NOPA) to the collective density excitations\nof the two BECs. An EPR state of the collective density excitations can be\ncreated by a judicious choice of the system parameters."
    },
    {
        "anchor": "Elastic properties and thermodynamic anomalies of supersolids: We study a supersolid in the context of a Gross-Pitaevskii theory with a\nnon-local effective potential. We employ a homogenisation technique which\nallows us to calculate the elastic moduli, supersolid fraction and other state\nvariables of the system. Our methodology is verified against numerical\nsimulations of elastic deformations. We can also verify that the\nlong-wavelength Goldstone modes that emerge from this technique agree with\nBogoliubov theory. We find a thermodynamic anomaly that the supersolid does not\nobey the thermodynamic relation $\\partial P / \\partial V \\bigr|_N = - n \\,\n\\partial P / \\partial N \\bigr|_V$, which we claim is a feature unique to\nsupersolids.",
        "positive": "Enhancement of chiral edge currents in ($d$+1)-dimensional atomic\n  Mott-band hybrid insulators: We consider the effect of a local interatomic repulsion on synthetic\nheterostructures where a discrete synthetic dimension is created by Raman\nprocesses on top of $SU(N)$-symmetric two-dimensional lattice systems. At a\nfilling of one fermion per site, increasing the interaction strength, the\nsystem is driven towards a Mott state which is adiabatically connected to a\nband insulator. The chiral currents associated with the synthetic magnetic\nfield increase all the way to the Mott transition, where they reach the maximum\nvalue, and they remain finite in the whole insulating state. The transition\ntowards the Mott-band insulator is associated with the opening of a gap within\nthe low-energy quasiparticle peak, while a mean-field picture is recovered deep\nin the insulating state."
    },
    {
        "anchor": "Topologically protected boundary discrete time crystal for a solvable\n  model: Floquet time crystal, which breaks discrete time-translation symmetry, is an\nintriguing phenomenon in non-equilibrium systems. It is crucial to understand\nthe rigidity and robustness of discrete time crystal (DTC) phases in a\nmany-body system, and finding a precisely solvable model can pave a way for\nunderstanding of the DTC phase. Here, we propose and study a solvable spin\nchain model by mapping it to a Floquet superconductor through the Jordan-Wigner\ntransformation. The phase diagrams of Floquet topological systems are\ncharacterized by topological invariants and tell the existence of anomalous\nedge states. The sub-harmonic oscillation, which is the typical signal of the\nDTC, can be generated from such edge states and protected by topology. We also\nexamine the robustness of the DTC by adding symmetry-preserving and\nsymmetry-breaking perturbations. Our results on topologically protected DTC can\nprovide a deep understanding of the DTC when generalized to other interacting\nor dissipative systems.",
        "positive": "Quantum Monte Carlo simulations of antiferromagnetism in ultracold\n  fermions on optical lattices within real-space dynamical mean-field theory: We present a massively parallel quantum Monte Carlo based implementation of\nreal-space dynamical mean-field theory for general inhomogeneous correlated\nfermionic lattice systems. As a first application, we study magnetic order in a\nbinary mixture of repulsively interacting fermionic atoms harmonically trapped\nin an optical lattice. We explore temperature effects and establish signatures\nof the N\\'{e}el transition in observables directly accessible in cold-atom\nexperiments; entropy estimates are also provided. We demonstrate that the local\ndensity approximation (LDA) fails for ordered phases. In contrast, a \"slab\"\napproximation allows us to reach experimental system sizes with O(10^5) atoms\nwithout significant loss of accuracy."
    },
    {
        "anchor": "Collective excitations in cigar-shaped spin-orbit coupled spin-1\n  Bose-Einstein condensates: We theoretically study the collective excitations of a spin-orbit-coupled\nspin-1 Bose-Einstein condensate with antiferromagnetic spin-exchange\ninteractions in a cigar-shaped trapping potential at zero and finite\ntemperatures using the Hartree-Fock-Bogoliubov theory with Popov approximation.\nThe collective modes at zero temperature are corroborated by the real-time\nevolution of the ground state subjected to a perturbation suitable to excite a\ndensity or a spin mode. We have also calculated a few low-lying modes\nanalytically and found a very good agreement with the numerical results. We\nconfirm the presence of excitations belonging to two broad categories, namely\ndensity, and spin excitations, based on the calculation of dispersion. The\ndegeneracy between a pair of spin modes is broken by the spin-orbit coupling.\nAt finite temperature, spin and density excitations show qualitatively\ndifferent behavior as a function of temperature.",
        "positive": "Harnessing exciton-polaritons for digital computing, neuromorphic\n  computing, and optimization: Polaritons are quasiparticles resulting from strong quantum coupling of light\nand matter. Peculiar properties of polaritons are a mixture of physics usually\nrestricted to one of these realms, making them interesting for study not only\nfrom the fundamental point of view but also for applications. In recent years,\nmany studies have been devoted to the potential use of exciton-polaritons for\ncomputing. Very recently, it has been shown experimentally that they can be\nharnessed not only for digital computing, but also for optical neural networks\nand for optimization related to hard computational problems. Here, we provide a\nbrief review of recent studies and most important results in this area. We\nfocus our attention in particular on the emerging concepts of non-von-Neumann\ncomputing schemes and their realizations in exciton-polariton systems."
    },
    {
        "anchor": "Mass-imbalanced fermionic mixture in a harmonic trap: The mass-imbalanced fermionic mixture is studied, where $N\\le5$ identical\nfermions interact resonantly with an impurity, a distinguishable atom. The\nshell structure is explored, and the physics of a dynamic light-impurity is\nshown to be different from that of the static heavy-impurity case. The energies\nin a harmonic trap at unitarity are calculated and extrapolated to the\nzero-range limit. In doing so, the scaling factor of the ground state, as well\nas of a few excited states, is calculated. In the $2 \\le N \\le 4$ systems, pure\n$(N+1)$ Efimov states exist for large enough mass ratio. However, no sign for a\nsix-body Efimov state in the $(5+1)$ system is found in the mass ratio\nexplored, $M/m \\le 12$.",
        "positive": "Spontaneous formation of spin lattices in semimagnetic exciton-polariton\n  condensates: An exciton-polariton microcavity that incorporates magnetic ions can exhibit\na spontaneous self-trapping phenomenon which is an analog of the classical\npolaron effect. We investigate in detail the full model of a polariton\ncondensate that includes pumping and losses, the spin degree of freedom,\nexternal magnetic field and energy relaxation. In the quasi-one-dimensional\ncase, we show that the polaron effect can give rise to a spontaneous lattice of\nperfectly arranged polarization domains in an antiferromagnetic configuration.\nWe find that partial polarization of the condensate at moderate magnetic field\nstrengths facilitates the formation of such \"polaron lattices\", which are\nqualitatively different from self-trapped polarons that appear in a fully\npolarized condensate. Within the Bogoliubov-de Gennes approximation, we\ncalculate the instability condition which marks the appearance of the patterns.\nSurprisingly, we find that the stability condition displays a discontinuity at\nthe point of partial-full polarization threshold."
    },
    {
        "anchor": "Fast Frictionless Expansion of an Optical Lattice: We investigate fast frictionless expansion of an optical lattice with\ndynamically variable spacing (accordion lattice). We design an expansion\ntrajectory that yields a final state identical to the initial state up to an\nirrelevant phase factor. We discuss the effect of additional force and\nnonlinear interaction on the fast frictionless expansion.",
        "positive": "Two-Photon Pathway to Ultracold Ground State Molecules of\n  $^{23}$Na$^{40}$K: We report on high-resolution spectroscopy of ultracold fermionic\n\\nak~Feshbach molecules, and identify a two-photon pathway to the rovibrational\nsinglet ground state via a resonantly mixed \\Bcres intermediate state.\nPhotoassociation in a $^{23}$Na-$^{40}$K atomic mixture and one-photon\nspectroscopy on \\nak~Feshbach molecules reveal about 20 vibrational levels of\nthe electronically excited \\ctrip state. Two of these levels are found to be\nstrongly perturbed by nearby \\Bsing states via spin-orbit coupling, resulting\nin additional lines of dominant singlet character in the perturbed complex\n{${\\rm B}^1\\Pi |v{=}4\\rangle {\\sim} {\\rm c}^3\\Sigma^+ | v{=}25\\rangle$}, or of\nresonantly mixed character in {${\\rm B}^1\\Pi | v{=}12 \\rangle {\\sim}{\\rm\nc}^3\\Sigma^+ | v{=}35 \\rangle$}. The dominantly singlet level is used to locate\nthe absolute rovibrational singlet ground state ${\\rm X}^1\\Sigma^+ | v{=}0,\nJ{=}0 \\rangle$ via Autler-Townes spectroscopy. We demonstrate coherent\ntwo-photon coupling via dark state spectroscopy between the predominantly\ntriplet Feshbach molecular state and the singlet ground state. Its binding\nenergy is measured to be 5212.0447(1) \\cm, a thousand-fold improvement in\naccuracy compared to previous determinations. In their absolute singlet ground\nstate, \\nak~molecules are chemically stable under binary collisions and possess\na large electric dipole moment of $2.72$ Debye. Our work thus paves the way\ntowards the creation of strongly dipolar Fermi gases of NaK molecules."
    },
    {
        "anchor": "Advances in precision contrast interferometry with Yb Bose-Einstein\n  condensates: Using a three-path contrast interferometer (CI) geometry and laser-pulse\ndiffraction gratings, we create the first matter-wave interferometer with\nytterbium (Yb) atoms. We present advances in contrast interferometry relevant\nto high-precision measurements. By comparing to a traditional atom\ninterferometer, we demonstrate the immunity of the CI to vibrations for long\ninteraction times (> 20 ms). We characterize and demonstrate control over the\ntwo largest systematic effects for a high-precision measurement of the fine\nstructure constant via photon recoil with our interferometer: diffraction\nphases and atomic interactions. Diffraction phases are an important systematic\nfor most interferometers using large-momentum transfer beam splitters; atomic\ninteractions are a key concern for any BEC interferometer. Finally, we consider\nthe prospects for a future sub-part per billion photon recoil measurement using\na Yb CI.",
        "positive": "Snapshot-based detection of $\\frac{1}{2}$-Laughlin states: coupled\n  chains and central charge: Experimental realizations of topologically ordered states of matter, such as\nfractional quantum Hall states, with cold atoms are now within reach. In\nparticular, optical lattices provide a promising platform for the realization\nand characterization of such states, where novel detection schemes enable an\nunprecedented microscopic understanding. Here we show that the central charge\ncan be directly measured in current cold atom experiments using the number\nentropy as a proxy for the entanglement entropy. We perform density-matrix\nrenormalization-group simulations of Hubbard-interacting bosons on coupled\nchains subject to a magnetic field with $\\alpha=\\frac{1}{4}$ flux quanta per\nplaquette. Tuning the inter-chain hopping, we find a transition from a trivial\nquasi-one dimensional phase to the topologically ordered Laughlin state at\nmagnetic filling factor $\\nu=\\frac{1}{2}$ for systems of three or more chains.\nWe resolve the transition using the central charge, on-site correlations,\nmomentum distributions and the many-body Chern number. Additionally, we propose\na scheme to experimentally estimate the central charge from Fock basis\nsnapshots. The model studied here is experimentally realizable with existing\ncold atom techniques and the proposed observables pave the way for the\ndetection and classification of a larger class of interacting topological\nstates of matter."
    },
    {
        "anchor": "Thermometry of a deeply degenerate Fermi gas with a Bose-Einstein\n  condensate: We measure the temperature of a deeply degenerate Fermi gas, by using a\nweakly interacting sample of heavier bosonic atoms as a probe. This thermometry\nmethod relies on the thermalization between the two species and on the\ndetermination of the condensate fraction of the bosons. In our experimental\nimplementation, a small sample of 41K atoms serves as the thermometer for a 6Li\nFermi sea. We investigate the evaporative cooling of a 6Li spin mixture in a\nsingle-beam optical dipole trap and observe how the condensate fraction of the\nthermometry atoms depends on the final trap depth. From the condensate\nfraction, the temperature can be readily extracted. We show that the lowest\ntemperature of 6.3(5)% of the Fermi temperature is obtained, when the\ndecreasing trap depth closely approaches the Fermi energy. To understand the\nsystematic effects that may in uence the results, we carefully investigate the\nrole of the number of bosons and the thermalization dynamics between the two\nspecies. Our thermometry approach provides a conceptually simple, accurate, and\ngeneral way to measure the temperature of deeply degenerate Fermi gases. Since\nthe method is independent of the specific interaction conditions within the\nFermi gas, it applies to both weakly and strongly interacting Fermi gases.",
        "positive": "Topological phases with long-range interactions: Topological phases of matter are primarily studied in systems with\nshort-range interactions. In nature, however, non-relativistic quantum systems\noften exhibit long-range interactions. Under what conditions topological phases\nsurvive such interactions, and how they are modified when they do, is largely\nunknown. By studying the symmetry-protected topological phase of an\nantiferromagnetic spin-1 chain with $1/r^{\\alpha}$ interactions, we show that\ntwo very different outcomes are possible, depending on whether or not the\ninteractions are frustrated. While non-frustrated long-range interactions can\ndestroy the topological phase for $\\alpha\\lesssim3$, the topological phase\nsurvives frustrated interactions for all $\\alpha>0$. Our conclusions are based\non strikingly consistent results from large-scale matrix-product-state\nsimulations and effective-field-theory calculations, and we expect them to hold\nfor more general interacting spin systems. The models we study can be naturally\nrealized in trapped-ion quantum simulators, opening the prospect for\nexperimental investigation of the issues confronted here."
    },
    {
        "anchor": "Ramsey interferometry of non-Hermitian quantum impurities: We introduce a Ramsey pulse scheme which extracts the non-Hermitian\nHamiltonian associated to an arbitrary Lindblad dynamics. We propose a realted\nprotocol to measure via interferometry a generalised Loschmidt echo of a\ngeneric state evolving in time with the non-Hermitian Hamiltonian itself, and\nwe apply the scheme to a one-dimensional weakly interacting Bose gas coupled to\na stochastic atomic impurity. The Loschmidt echo is mapped into a functional\nintegral from which we calculate the long-time decohering dynamics at arbitrary\nimpurity strengths. For strong dissipation we uncover the phenomenology of a\nquantum many-body Zeno effect: corrections to the decoherence exponent\nresulting from the impurity self-energy becomes purely imaginary, in contrast\nto the regime of small dissipation where they instead enhance the decay of\nquantum coherences. Our results illustrate the prospects for experiments\nemploying Ramsey interferometry to study dissipative quantum impurities in\ncondensed matter and cold atoms systems.",
        "positive": "The imbalanced Fermi gas at unitarity: Lattice field theory is a useful tool for studying strongly interacting\ntheories in condensed matter physics. A prominent example is the unitary Fermi\ngas: a two-component system of fermions interacting with divergent scattering\nlength. With Monte Carlo methods this system can be studied from first\nprinciples. In the presence of an imbalance (unequal number of particles in the\ntwo components) a sign problem arises, which makes conventional algorithms\ninapplicable. We will show how to apply reweighting techniques to generalise\nthe recently developed worm algorithm to the imbalanced case, and present\nresults for the critical temperature, the energy per particle, the chemical\npotential and the contact density for equal, as well as unequal number of\nfermions in the two spin components."
    },
    {
        "anchor": "Evidence for the breakdown of momentum independent many-body t-matrix\n  approximation in the normal phase of Bosons: We revisit the momentum independent many-body t-matrix approach for boson\nsystems developed by Shi and Griffin~\\cite{sg} and Bijlsma and Stoof~\\cite{bs}.\nDespite its popularity, simplicity, and expected advantage of being its\napplicability to both normal and superfluid phases, we find that the theory\nbreaks down in the normal phase of bosons. We conjecture that this failure is\ndue to neglecting of momentum dependence on the t-matrix.",
        "positive": "Mott-insulator phases of spin-3/2 fermions in the presence of quadratic\n  Zeeman coupling: We study the influence of the quadratic Zeeman effect in the Mott-insulator\nphases of hard-core spin-3/2 fermions. We show that contrary to spinor bosons,\nany quadratic Zeeman coupling preserves a $SU(2)\\otimes SU(2)$ symmetry,\nleading for large-enough quadratic Zeeman coupling to an isotropic\npseudo-spin-1/2 Heisenberg antiferromagnet. Depending on the scattering\nlengths, on 1D lattices the quadratic Zeeman coupling can induce either a\nKosterlitz-Thouless transition between a gapped dimerized spin-3/2 phase and a\ngapless pseudo-spin-1/2 antiferromagnet, or a commensurate-incommensurate\ntransition from a gapless spin-liquid into the pseudo-spin-1/2 antiferromagnet.\nSimilar arguments allow to foresee corresponding transitions on ladder type and\nsquare lattices. We analyze various observables which should reveal in\nexperiments these phases."
    },
    {
        "anchor": "Emergent criticality and universality class of spin and charge density\n  wave transitions of two-component lattice Bose gases in optical cavities at\n  finite temperature: We investigate the finite temperature spin density wave (SDW) and charge\ndensity wave (CDW) transition of two-component lattice spinor Bose gases in\noptical lattices in the Mott-insulator limit. At the temperature scale around\nhalf of the on-site interaction energy, we find a new critical regime emerges\nand features, in particular, a new bicritical line and two critical lines\nassociated with the finite temperature SDW-CDW, homogeneous-SDW, and\nhomogeneous-CDW transition, respectively. Direct calculation of the critical\nexponents for the scaling behavior and investigating on the effective theory in\nthis critical regime show that they belong to the five-dimensional Ising\nuniversality class, clearly manifesting the long-range character of the\nsystem's interaction. Our prediction of the emergent criticality can be readily\nobserved by current experimental setups operated at the intermediate\ntemperature scale around half the on-site interaction energy.",
        "positive": "Observation of Attractive and Repulsive Polarons in a Bose-Einstein\n  Condensate: The problem of an impurity particle moving through a bosonic medium plays a\nfundamental role in physics. However, the canonical scenario of a mobile\nimpurity immersed in a Bose-Einstein condensate (BEC) has not yet been\nrealized. Here, we use radio frequency spectroscopy of ultracold bosonic\n$^{39}$K atoms to experimentally demonstrate the existence of a well-defined\nquasiparticle state of an impurity interacting with a BEC. We measure the\nenergy of the impurity both for attractive and repulsive interactions, and find\nexcellent agreement with theories that incorporate three-body correlations,\nboth in the weak-coupling limits and across unitarity. The spectral response\nconsists of a well-defined quasiparticle peak at weak coupling, while for\nincreasing interaction strength, the spectrum is strongly broadened and becomes\ndominated by the many-body continuum of excited states. Crucially, no\nsignificant effects of three-body decay are observed. Our results open up\nexciting prospects for studying mobile impurities in a bosonic environment and\nstrongly interacting Bose systems in general."
    },
    {
        "anchor": "Floquet-engineered pair and single particle filter in the Fermi Hubbard\n  model: We investigate the Fermi-Hubbard model with a Floquet-driven impurity in the\nform of a local time-oscillating potential. For strong attractive interactions\na stable formation of pairs is observed. These pairs show a completely\ndifferent transmission behavior than the transmission that is observed for the\nsingle unpaired particles. Whereas in the high frequency limit the single\nparticles show a maximum of the transition at low driving amplitudes, the pairs\ndisplay a pronounced maximum transmission when the amplitude of the driving\nlies close to the ratio of the interaction U and the driving frequency\n{\\omega}. We use the distinct transmission behaviour to design filters for\npairs or single particles, respectively. For example one can totally block the\ntransmission of single particles through the driven impurity and allow only for\nthe transmission of pairs. We quantify the quality of the designed filters.",
        "positive": "Connecting few-body inelastic decay to many-body correlations: a weakly\n  coupled impurity in a resonant Fermi gas: We study three-body recombination in an ultracold Bose-Fermi mixture. We\nfirst show theoretically that, for weak inter-species coupling, the loss rate\nis proportional to Tan's contact. Second, using a 7 Li/ 6 Li mixture we probe\nthe recombination rate in both the thermal and dual superfluid regimes. We find\nexcellent agreement with our model in the BEC-BCS crossover. At unitarity where\nthe fermion-fermion scattering length diverges, we show that the loss rate is\nproportional the 4/3 power of the fermionic density. Our results demonstrate\nthat impurity-induced losses can be used as a quantitative probe of many-body\ncorrelations."
    },
    {
        "anchor": "Polytropic equilibrium and normal modes in cold atomic traps: The compressibility limit of a cold gas confined in a magneto-optical trap\ndue to multiple scattering of light is a long-standing problem. This scattering\nmechanism induces long-range interactions in the system, which is responsible\nfor the occurrence of plasma-like phenomena. In the present paper, we\ninvestigate the importance of the long-range character of the mediated\natom-atom interaction in the equilibrium and dynamical features of a\nmagneto-optical trap. Making use of a hydrodynamical formulation, we derive a\ngeneralized Lane-Emden equation modeling the polytropic equilibirum of a\nmagneto-optical trap, allowing us to describe the cross-over between the two\nlimiting cases: temperature dominated and multiple-scattering dominated traps.\nThe normal collective modes of the system are also computed.",
        "positive": "Momentum-space correlations of a one-dimensional Bose gas: Analyzing the noise in the momentum profiles of single realizations of\none-dimensional Bose gases, we present the experimental measurement of the full\nmomentum-space density correlations $\\langle \\delta n_p \\delta n_{p'}\\rangle$,\nwhich are related to the two-body momentum correlation function. Our data span\nthe weakly interacting region of the phase diagram, going from the the ideal\nBose gas regime to the quasicondensate regime. We show experimentally that the\nbunching phenomenon, which manifests itself as super-Poissonian local\nfluctuations in momentum space, is present in all regimes. The quasicondensate\nregime is however characterized by the presence of negative correlations\nbetween different momenta, in contrast to Bogolyubov theory for Bose\ncondensates, predicting positive correlations between opposite momenta. Our\ndata are in good agreement with {\\it ab-initio} calculations."
    },
    {
        "anchor": "Incommensurate phases of a bosonic two-leg ladder under a flux: A boson two--leg ladder in the presence of a synthetic magnetic flux is\ninvestigated by means of bosonization techniques and Density Matrix\nRenormalization Group (DMRG). We follow the quantum phase transition from the\ncommensurate Meissner to the incommensurate vortex phase with increasing flux\nat different fillings. When the applied flux is $\\rho \\pi$ and close to it,\nwhere $\\rho$ is the filling per rung, we find a second incommensuration in the\nvortex state that affects physical observables such as the momentum\ndistribution, the rung-rung correlation function and the spin-spin and\ncharge-charge static structure factors.",
        "positive": "Competing regimes of motion in 1D mobile impurities: We show that a distinguishable mobile impurity inside a one-dimensional\nmany-body state at zero temperature generally does not behave like a\nquasiparticle (QP). Instead, both the impurities dynamics as well as the ground\nstate of the bath are fundamentally transformed by a diverging number of\nzero-energy excitations being generated, leading to what we call\ninfrared-dominated (ID) dynamics. Combining analytics and DMRG numerics we\nprovide a general formula for the power law governing ID dynamics at zero\nmomentum, discuss a threshold beyond which quasiparticle dynamics may occur\nagain, and study the competition between the ID and quasiparticle universality\nclasses at larger impurity momenta."
    },
    {
        "anchor": "Momentum-space engineering of gaseous Bose-Einstein condensates: We show how the momentum distribution of gaseous Bose--Einstein condensates\ncan be shaped by applying a sequence of standing-wave laser pulses. We present\na theory, whose validity for was demonstrated in an earlier experiment [L.\\\nDeng, et al., \\prl {\\bf 83}, 5407 (1999)], of the effect of a two-pulse\nsequence on the condensate wavefunction in momentum space. We generalize the\nprevious result to the case of $N$ pulses of arbitrary intensity separated by\narbitrary intervals and show how these parameters can be engineered to produce\na desired final momentum distribution. We find that several momentum\ndistributions, important in atom-interferometry applications, can be engineered\nwith high fidelity with two or three pulses.",
        "positive": "Isentropes of spin-1 bosons in an optical lattice: We analyze the effects of adiabatic ramping of optical lattices on the\ntemperature of spin-1 bosons in a homogeneous lattice. Using mean-field theory,\nwe present the isentropes in the temperature-interaction strength ($T,U_0$)\nplane for ferromagnetic, antiferromagnetic, and zero spin couplings. Following\nthe isentropic lines, temperature changes can be determined during adiabatic\nloading of current experiments. We show that the heating-cooling separatrix\nlies on the superfluid-Mott phase boundary with cooling occuring within the\nsuperfluid and heating in the Mott insulator, and quantify the effects of spin\ncoupling on the heating rate. We find that the mean-field isentropes for low\ninitial entropy terminate at the superfluid-Mott insulator phase boundary."
    },
    {
        "anchor": "Finite size effects in global quantum quenches: examples from free\n  bosons in an harmonic trap and the one-dimensional Bose-Hubbard model: We investigate finite size effects in quantum quenches on the basis of simple\nenergetic arguments. Distinguishing between the low-energy part of the\nexcitation spectrum, below a microscopic energy-scale, and the high-energy\nregime enables one to define a crossover number of particles that is shown to\ndiverge in the small quench limit. Another crossover number is proposed based\non the fidelity between the initial and final ground-states. Both criteria can\nbe computed using ground-state techniques that work for larger system sizes\nthan full spectrum diagonalization. As examples, two models are studied: one\nwith free bosons in an harmonic trap which frequency is quenched, and the\none-dimensional Bose-Hubbard model, that is known to be non-integrable and for\nwhich recent studies have uncovered remarkable non-equilibrium behaviors. The\ndiagonal weights of the time-averaged density-matrix are computed and\nobservables obtained from this diagonal ensemble are compared with the ones\nfrom statistical ensembles. It is argued that the \"thermalized\" regime of the\nBose-Hubbard model, previously observed in the small quench regime, experiences\nstrong finite size effects that render difficult a thorough comparison with\nstatistical ensembles. In addition, we show that the non-thermalized regime,\nemerging on finite size systems and for large interaction quenches, is not\nrelated to the existence of an equilibrium quantum critical point but to the\nhigh energy structure of the energy spectrum in the atomic limit. Its features\nare reminiscent of the quench from the non-interacting limit to the atomic\nlimit.",
        "positive": "Phases, instabilities and excitations in a two-component lattice model\n  with photon-mediated interactions: Engineering long-range interacting spin systems with ultra cold atoms offers\nthe possibility to explore exotic magnetically ordered phases in\nstrongly-correlated scenarios. Quantum gases in optical cavities provide a\nversatile experimental platform to further engineer photon-mediated\ninteractions and access the underlying microscopic processes by probing the\ncavity field. Here, we study a two-component spin Bose-Hubbard system with\ncavity-mediated interactions. We provide a comprehensive overview of its phase\ndiagram and transitions in experimentally relevant regimes. The interplay of\ndifferent energy scales yields a rich phase diagram with superfluid and\ninsulating phases exhibiting density modulation or spin ordering. In\nparticular, the combined effect of contact and global-range interactions gives\nrise to an antiferromagnetically ordered phase for arbitrarily small\nspin-dependent light-matter coupling, while long-range and inter-spin contact\ninteractions introduce regions of instability and phase separation in the phase\ndiagram. We further study the low energy excitations above the\nantiferrogmagnetic phase. Besides particle-hole branches, it hosts\nspin-exchange excitations with a tunable energy gap. The studied lattice model\ncan be readily realized in cold-atom experiments with optical cavities."
    },
    {
        "anchor": "Breathing mode frequency of a strongly interacting Fermi gas across the\n  2D-3D dimensional crossover: We address the interplay between dimension and quantum anomaly on the\nbreathing mode frequency of a strongly interacting Fermi gas harmonically\ntrapped at zero temperature. Using a beyond mean-field, Gaussian pair\nfluctuation theory, we employ periodic boundary conditions to simulate the\ndimensionality of the system and impose a local density approximation, with two\ndifferent schemes, to model different trapping potentials in the\ntightly-confined axial direction. By using a sum-rule approach, we compute the\nbreathing mode frequency associated with a small variation of the trapping\nfrequency along the weakly-confined transverse direction, and describe its\nbehavior as functions of the dimensionality, from two- to three-dimensions, and\nof the interaction strength. We compare our predictions with previous\ncalculations on the two-dimensional breathing mode anomaly and discuss their\npossible observation in ultracold Fermi gases of $^{6}$Li and $^{40}$K atoms.",
        "positive": "Relaxation dynamics of half-quantum vortices in a two-dimensional\n  two-component Bose-Einstein condensate: We study the relaxation dynamics of quantum turbulence in a two-component\nBose-Einstein condensate containing half-quantum vortices. We find a temporal\nscaling regime for the number of vortices and the correlation lengths that at\nearly times is strongly dependent on the relative strength of the inter-species\ninteraction. At later times we find that the scaling becomes universal,\nindependent of the inter-species interaction, and approaches that numerically\nobserved in a scalar Bose-Einstein condensate."
    },
    {
        "anchor": "Cavity-enhanced optical lattices for scaling neutral atom quantum\n  technologies to higher qubit numbers: We demonstrate a cavity-based solution to scale up experiments with ultracold\natoms in optical lattices by an order of magnitude over state-of-the-art free\nspace lattices. Our two-dimensional optical lattices are created by power\nenhancement cavities with large mode waists of 489(8) $\\mu$m and allow us to\ntrap ultracold strontium atoms at a lattice depth of 60 $\\mu$K by using only 80\nmW of input light per cavity axis. We characterize these lattices using\nhigh-resolution clock spectroscopy and resolve carrier transitions between\ndifferent vibrational levels. With these spectral features, we locally measure\nthe lattice potential envelope and the sample temperature with a spatial\nresolution limited only by the optical resolution of the imaging system. The\nmeasured ground-band and trap lifetimes are 18(3) s and 59(2) s, respectively,\nand the lattice frequency (depth) is long-term stable on the MHz (0.1\\%) level.\nOur results show that large, deep, and stable two-dimensional cavity-enhanced\nlattices can be created at any wavelength and can be used to scale up\nneutral-atom-based quantum simulators, quantum computers, sensors, and optical\nlattice clocks.",
        "positive": "Multi-orbital bosons in bipartite optical lattices: We study interacting bosons in a two dimensional bipartite optical lattice.\nBy focusing on the regime where the first three excited bands are nearly\ndegenerate we derive a three orbital tight-binding model which captures the\nmost relevant features of the bandstructure. In addition, we also derive a\ncorresponding generalized Bose-Hubbard model and solve it numerically under\ndifferent situations, both with and without a confining trap. It is especially\nfound that the hybridization between sublattices can strongly influence the\nphase diagrams and in a trap enable even appearances of condensed phases\nintersecting the same Mott insulating plateaus."
    },
    {
        "anchor": "Single-atom-resolved probing of lattice gases in momentum space: Measuring the full distribution of individual particles is of fundamental\nimportance to characterize many-body quantum systems through correlation\nfunctions at any order. Here we demonstrate the possibility to reconstruct the\nmomentum-space distribution of three-dimensional interacting lattice gases\natom-by-atom. This is achieved by detecting individual metastable Helium atoms\nin the far-field regime of expansion, when released from an optical lattice. We\nbenchmark our technique with Quantum Monte-Carlo calculations, demonstrating\nthe ability to resolve momentum distributions of superfluids occupying $10^5$\nlattice sites. It permits a direct measure of the condensed fraction across\nphase transitions, as we illustrate on the superfluid-to-normal transition. Our\nsingle-atom-resolved approach opens a new route to investigate interacting\nlattice gases through momentum correlations.",
        "positive": "Spatially-antisymmetric localization of matter wave in a bichromatic\n  optical lattice: By direct numerical simulation of the time-dependent Gross-Pitaevskii\nequation using the split-step Fourier spectral method we study the\ndouble-humped localization of a cigar-shaped Bose-Einstein condensate (BEC) in\na one-dimensional bichromatic quasi-periodic optical-lattice potential, as used\nin a recent experiment on the localization of a BEC [Roati et al., Nature 453,\n895 (2008)]. Such states are spatially antisymmetric and are excited modes of\nAnderson localization. Where possible, we have compared the numerical results\nwith a variational analysis. We also demonstrate the stability of the localized\ndouble-humped BEC states under small perturbation."
    },
    {
        "anchor": "Zero and First Sound in Normal Fermi Systems: On the basis of a moment method, general solutions of a linearized Boltzmann\nequation for a normal Fermi system are investigated. In particular, we study\nthe sound velocities and damping rates as functions of the temperature and the\ncoupling constant. In the extreme limits of collisionless and hydrodynamic\nregimes, eigenfrequency of sound mode obtained from the moment equations\nreproduces the well-known results of zero sound and first sound. In addition,\nthe moment method can describe crossover between those extreme limits at finite\ntemperatures. Solutions of the moment equations also involve a thermal\ndiffusion mode. From solutions of these equations, we discuss excitation\nspectra corresponding to the particle-hole continuum as well as collective\nexcitations. We also discuss a collective mode in a weak coupling case.",
        "positive": "Spontaneous breaking of spatial and spin symmetry in spinor condensates: Parametric amplification of quantum fluctuations constitutes a fundamental\nmechanism for spontaneous symmetry breaking. In our experiments, a spinor\ncondensate acts as a parametric amplifier of spin modes, resulting in a twofold\nspontaneous breaking of spatial and spin symmetry in the amplified clouds. Our\nexperiments permit a precise analysis of the amplification in specific spatial\nBessel-like modes, allowing for the detailed understanding of the double\nsymmetry breaking. On resonances that create vortex-antivortex superpositions,\nwe show that the cylindrical spatial symmetry is spontaneously broken, but\nphase squeezing prevents spin-symmetry breaking. If, however, nondegenerate\nspin modes contribute to the amplification, quantum interferences lead to\nspin-dependent density profiles and hence spontaneously-formed patterns in the\nlongitudinal magnetization."
    },
    {
        "anchor": "Quantum critical thermal transport in the unitary Fermi gas: Strongly correlated systems are often associated with an underlying quantum\ncritical point which governs their behavior in the finite temperature phase\ndiagram. Their thermodynamical and transport properties arise from critical\nfluctuations and follow universal scaling laws. Here, we develop a microscopic\ntheory of thermal transport in the quantum critical regime expressed in terms\nof a thermal sum rule and an effective scattering time. We explicitly compute\nthe characteristic scaling functions in a quantum critical model system, the\nunitary Fermi gas. Moreover, we derive an exact thermal sum rule for heat and\nenergy currents and evaluate it numerically using the nonperturbative\nLuttinger-Ward approach. For the thermal scattering times we find a simple\nquantum critical scaling form. Together, the sum rule and the scattering time\ndetermine the heat conductivity, thermal diffusivity, Prandtl number and sound\ndiffusivity from high temperatures down into the quantum critical regime. The\nresults provide a quantitative description of recent sound attenuation\nmeasurements in ultracold Fermi gases.",
        "positive": "Thermodynamics of Van der Waals Fluids with quantum statistics: We consider thermodynamics of the van der Waals fluid of quantum systems. We\nderive general relations of thermodynamic functions and parameters of any ideal\ngas and the corresponding van der Waals fluid. This provides unambiguous\ngeneralization of the classical van der Waals theory to quantum statistical\nsystems. As an example, we apply the van der Waals fluid with fermi statistics\nto characterize the liquid-gas critical point in nuclear matter. We also\nintroduce the Bose-Einstein condensation in the relativistic van der Waals\nboson gas, and argue, that it exhibits two-phase structure separated in space."
    },
    {
        "anchor": "Bose-Einstein condensates with localized spin-orbit coupling: soliton\n  complexes and spinor dynamics: Spin-orbit (SO) coupling can be introduced in a Bose--Einstein condensate\n(BEC) as a gauge potential acting only in a localized spatial domain. Effect of\nsuch a SO \"defect\" can be understood by transforming the system to the\nintegrable vector model. The properties of the SO-BEC change drastically if the\nSO defect is accompanied by the Zeeman splitting. In such a non-integrable\nsystem, the SO defect qualitatively changes the character of soliton\ninteractions and allows for formation of stable nearly scalar soliton complexes\nwith almost all atoms concentrated in only one dark state. These solitons exist\nonly if the number of particles exceeds a threshold value. We also report on\nthe possibility of transmission and reflection of a soliton upon its scattering\non the SO defect. Scattering strongly affects the pseudo-spin polarization and\ncan induce pseudo-spin precession. The scattering can also result in almost\ncomplete atomic transfer between the dark states.",
        "positive": "Vortex annihilation and inverse cascades in two dimensional superfluid\n  turbulence: We study two dimensional superfluid turbulence by employing an effective\ndescription valid in the limit where the density of superfluid vortices is\nparametrically small. At sufficiently low temperatures the effective\ndescription yields an inverse cascade with Kolmogorov energy spectrum $E(k)\n\\sim k^{-5/3}$. Denoting the number of vortices as a function of time by\n$N(t)$, we find that the vortex annihilation rate scales like $\\dot N \\sim\nN^{5/3}$ in states with an inverse cascade and $\\dot N \\sim N^2$ for laminar\nflow."
    },
    {
        "anchor": "Single-particle density matrix for a time-dependent strongly interacting\n  one-dimensional Bose gas: We derive a $1/c$-expansion for the single-particle density matrix of a\nstrongly interacting time-dependent one-dimensional Bose gas, described by the\nLieb-Liniger model ($c$ denotes the strength of the interaction). The formalism\nis derived by expanding Gaudin's Fermi-Bose mapping operator up to $1/c$-terms.\nWe derive an efficient numerical algorithm for calculating the density matrix\nfor time-dependent states in the strong coupling limit, which evolve from a\nfamily of initial conditions in the absence of an external potential. We have\napplied the formalism to study contraction dynamics of a localized wave packet\nupon which a parabolic phase is imprinted initially.",
        "positive": "Observation of confinement-induced resonances in a 3D lattice: We report on the observation of confinement-induced resonances for strong\nthree-dimensional (3D) confinement in a lattice potential. Starting from a\nMott-insulator state with predominantly single-site occupancy, we detect loss\nand heating features at specific values for the confinement length and the 3D\nscattering length. Two independent models, based on the coupling between the\ncenter-of-mass and the relative motion of the particles as mediated by the\nlattice, predict the resonance positions to a good approximation, suggesting a\nuniversal behavior. Our results extend confinement-induced resonances to any\ndimensionality and open up an alternative method for interaction tuning and\ncontrolled molecule formation under strong 3D confinement."
    },
    {
        "anchor": "Quantum density anomaly in optically trapped ultracold gases: We show that the Bose-Hubbard Model exhibits an increase in density with\ntemperature at fixed pressure in the regular fluid regime and in the superfluid\nphase. The anomaly at the Bose-Einstein condensate is the first density anomaly\nobserved in a quantum state. We propose that the mechanism underlying both the\nnormal phase and the superfluid phase anomalies is related to zero point\nentropies and ground state phase transitions. A connection with the typical\nexperimental scales and setups is also addressed. This key finding opens a new\npathway for theoretical and experimental studies of water-like anomalies in the\narea of ultracold quantum gases.",
        "positive": "Mesoscopic quantum superpositions in bimodal Bose-Einstein condensates:\n  decoherence and strategies to counteract it: We study theoretically the interaction-induced generation of mesoscopic\ncoherent spin state superpositions (small cat states) from an initial coherent\nspin state in bimodal Bose-Einstein condensates and the subsequent phase\nrevival, including decoherence due to particle losses and fluctuations of the\ntotal particle number. In a full multimode description, we propose a\npreparation procedure of the initial coherent spin state and we study the\neffect of preexisting thermal fluctuations on the phase revival, and on the\nspin and orbito-spinorial cat fidelities."
    },
    {
        "anchor": "Renyi Entropy Dynamics and Lindblad Spectrum for Open Quantum System: In this letter we point out that the Lindblad spectrum of a quantum many-body\nsystem displays a segment structure and exhibits two different energy scales in\nthe strong dissipation regime. One energy scale determines the separation\nbetween different segments, being proportional to the dissipation strength, and\nthe other energy scale determines the broadening of each segment, being\ninversely proportional to the dissipation strength. Ultilizing a relation\nbetween the dynamics of the second R\\'enyi entropy and the Lindblad spectrum,\nwe show that these two energy scales respectively determine the short- and the\nlong-time dynamics of the second R\\'enyi entropy starting from a generic\ninitial state. This gives rise to opposite behaviors, that is, as the\ndissipation strength increases, the short-time dynamics becomes faster and the\nlong-time dynamics becomes slower. We also interpret the quantum Zeno effect as\nspecific initial states that only occupy the Lindblad spectrum around zero, for\nwhich only the broadening energy scale of the Lindblad spectrum matters and\ngives rise to suppressed dynamics with stronger dissipation. We illustrate our\ntheory with two concrete models that can be experimentally verified.",
        "positive": "Strongly correlated phases in rapidly rotating Bose gases: We consider a system of trapped spinless bosons interacting with a repulsive\npotential and subject to rotation. In the limit of rapid rotation and small\nscattering length, we rigorously show that the ground state energy converges to\nthat of a simplified model Hamiltonian with contact interaction projected onto\nthe Lowest Landau Level. This effective Hamiltonian models the bosonic analogue\nof the Fractional Quantum Hall Effect (FQHE). For a fixed number of particles,\nwe also prove convergence of states; in particular, in a certain regime we show\nconvergence towards the bosonic Laughlin wavefunction. This is the first\nrigorous justification of the effective FQHE Hamiltonian for rapidly rotating\nBose gases. We review previous results on this effective Hamiltonian and\noutline open problems."
    },
    {
        "anchor": "Quantum swapping of immiscible Bose-Einstein condensates as an\n  alternative to the Rayleigh-Taylor instability: We consider a two-component Bose-Einstein condensate in a\nquasi-one-dimensional harmonic trap, where the immiscible components are\npressed against each other by an external magnetic force. The zero-temperature\nnon-stationary Gross-Pitaevskii equations are solved numerically; analytical\nmodels are developed for the key steps in the process. We demonstrate that if\nthe magnetic force is strong enough, then the condensates may swap their places\nin the trap due to dynamic quantum interpenetration of the nonlinear matter\nwaves. The swapping is accompanied by development of a modulational instability\nleading to quasi-turbulent excitations. Unlike the multidimensional\nRayleigh-Taylor instability in a similar geometry of two-component quantum\nfluid systems, quantum interpenetration has no classical analogue. A crossover\nbetween the Rayleigh-Taylor instability and the quantum interpenetration in a\ntwo-dimensional geometry is demonstrated.",
        "positive": "Stability of Emergent Kinetics in Optical Lattices with Artificial\n  Spin-Orbit Coupling: Artificial spin-orbit coupling in optical lattices can be engineered to tune\nband structure into extreme regimes where the single-particle band flattens\nleaving only inter-particle interactions to define many-body states of matter.\nLin et al. [Phys. Rev. Lett 112, 110404 (2014)] showed that under such\nconditions interactions lead to a Wigner crystal of fermionic atoms under\napproximate conditions: no bandwidth or band mixing. The excitations were shown\nto possess emergent kinetics with fractionalized charge derived entirely from\ninteractions. In this work we use numerical exact diagonalization to study a\nmore realistic model with non-zero bandwidth and band mixing. We map out the\nstability phase diagram of the Wigner crystal. We find that emergent properties\nof the Wigner crystal excitations remain stable for realistic experimental\nparameters. Our results validate the approximations made by Lin et al. and\ndefine parameter regimes where strong interaction effects generate emergent\nkinetics in optical lattices."
    },
    {
        "anchor": "R\u00e9nyi Entropy Singularities as Signatures of Topological Criticality\n  in Coupled Photon-Fermion Systems: We show that the topological phase transition for a Kitaev chain embedded in\na cavity can be identified by measuring experimentally accessible photon\nobservables such as the Fano factor and the cavity quadrature amplitudes.\nMoreover, based on density matrix renormalization group numerical calculations,\nendorsed by an analytical Gaussian approximation for the cavity state, we\npropose a direct link between those observables and quantum entropy\nsingularities. We study two bipartite entanglement measures, the von Neumann\nand R\\'enyi entanglement entropies, between light and matter subsystems. Even\nthough both display singularities at the topological phase transition points,\nremarkably only the R\\'enyi entropy can be analytically connected to the\nmeasurable Fano factor. Consequently, we show a method to recover the bipartite\nentanglement of the system from a cavity observable. Thus, we put forward a\npath to experimentally access the control and detection of a topological\nquantum phase transition via the R\\'enyi entropy, which can be measured by\nstandard low noise linear amplification techniques in superconducting circuits.\nIn this way, the main quantum information features of Majorana polaritons in\nphoton-fermion systems can be addressed in feasible experimental setups.",
        "positive": "Universality of internal correlations of strongly interacting p-wave\n  fermions in one-dimensional geometry: We consider the many-body ground state of polarized fermions interacting via\nzero-range $\\mathfrak{p}$-wave forces in a one-dimensional geometry. We\nrigorously prove that in the limit of infinite attractions spectral properties\nof any-order reduced density matrix describing arbitrary subsystem are\ncompletely independent of the shape of an external potential. It means that\nquantum correlations between any two subsystems are in this limit insensitive\nto the confinement. In addition, we show that the purity of these matrices\nquantifying the amount of quantum correlations can be obtained analytically for\nany number of particles without diagonalizing them. This observation may serve\nas a rigorous benchmark for other models and methods describing strongly\ninteracting p-wave fermions."
    },
    {
        "anchor": "Helicity in Superfluids: existence and the classical limit: In addition to mass, energy, and momentum, classical dissipationless flows\nconserve helicity, a measure of the topology of the flow. Helicity has\nfar-reaching consequences for classical flows from Newtonian fluids to plasmas.\nSince superfluids flow without dissipation, a fundamental question is whether\nsuch a conserved quantity exists for superfluid flows. We address the existence\nof a \"superfluid helicity\" using an analytical approach based on the the\nsymmetry underlying classical helicity conservation: the particle relabeling\nsymmetry. Furthermore, we use numerical simulations to study whether bundles of\nsuperfluid vortices which approximate the structure of a classical vortex,\nrecover the conservation of classical helicity and find dynamics consistent\nwith classical vortices in a viscous fluid.",
        "positive": "Two simple systems with cold atoms: quantum chaos tests and\n  nonequilibrium dynamics: This article is an attempt to provide a link between the quantum\nnonequilibrium dynamics of cold gases and fifty years of progress in the\nlowdimensional quantum chaos. We identify two atomic systems lying on the\ninterface: two interacting atoms in a harmonic multimode waveguide and an\ninteracting two-component Bose-Bose mixture in a double-well potential. In\nparticular, we study the level spacing distribution, the wavefunction\nstatistics, the eigenstate thermalization, and the ability to thermalize in a\nrelaxation process as such."
    },
    {
        "anchor": "Stability of a Fully Polarized Ultracold Fermi Gas near Zero-Crossing of\n  a p-wave Feshbach Resonance: We consider a fully polarized ultracold Fermi gas interacting through a\np-wave Feshbach resonance. Using a two-channel model, we find the effective\npotential at the point where the p-wave scattering length goes to zero. Here\nthe effective interaction provides attraction and one can therefore ask about\nthe stability of the system. We calculate the energy density of the system in\nthe Thomas-Fermi approximation, determine the profile of the gas, and the\ncritical number of particle in the system as function of the relevant\ninteraction parameters. The instability can be deduced from a simple breathing\nmode argument which explains the scaling found numerically. The critical\nparticle number turns out to be extremely large unless the external confinement\nis very tight. We therefore conclude that the effect is insignificant for\nstandard trapping potentials and that the magnetic dipole interaction is the\nimportant term at zero scattering length. However, for tight confinement as in\nan optical lattice higher-order corrections can become important.",
        "positive": "Quasi-One-Dimensional Few-Body Systems with Correlated Gaussians: The theoretical study of ultracold few-body systems is often done using an\nidealized 1D model with zero range interactions. Here we study these systems\nusing a more realistic 3D model with finite range interactions. We place\nthree-particles, two identical and one impurity, in an axial symmetric harmonic\ntrap and solve the corresponding stationary Schr\\\"odinger equation using the\ncorrelated Gaussian method for different particle types, aspect ratios and\ninteractions strength. We show that the idealized model is accurate for small\nand intermediate strength interactions at aspect ratios larger than four,\nindependently of the particle types. In the strongly interacting limit, the\nidealized model is acceptable for bosonic systems, but not for fermionic\nsystems even at large aspect ratios."
    },
    {
        "anchor": "Statistical models of nonequilibrium Bose gases: The idea is advanced that strong perturbations of an initially equilibrium\nBose-condensed gas lead to the sequence of nonequilibrium states whose order is\ninverse to the sequence of states arising in the process of the Bose-gas\nrelaxation from an initial nonequilibrium state. An approach is described for\nconstructing statistical models of nonequilibrium Bose gases. The method is\nbased on the averaging over heterogenous configurations of a nonequilibrium\nsystem. A statistical model of grain turbulence is suggested. A simple model is\nanalyzed consisting of a mixture of two phases, one gauge symmetric and the\nother with broken gauge symmetry.",
        "positive": "Quantum Hall phase diagram of two-component Bose gases: Intercomponent\n  entanglement and pseudopotentials: We study the ground-state phase diagram of two-dimensional two-component (or\npseudospin-1/2) Bose gases in a high synthetic magnetic field in the space of\nthe total filling factor and the ratio of the intercomponent coupling\n$g_{\\uparrow\\downarrow}$ to the intracomponent one $g>0$. Using exact\ndiagonalization, we find that when the intercomponent coupling is attractive\n($g_{\\uparrow\\downarrow}<0$), the product states of a pair of nearly\nuncorrelated quantum Hall states are remarkably robust and persist even when\n$|g_{\\uparrow\\downarrow}|$ is close to $g$. This contrasts with the case of an\nintercomponent repulsion, where a variety of spin-singlet quantum Hall states\nwith high intercomponent entanglement emerge for $g_{\\uparrow\\downarrow}\\approx\ng$. We interpret this marked dependence on the sign of $g_{\\uparrow\\downarrow}$\nin light of pseudopotentials on a sphere, and also explain recent numerical\nresults in two-component Bose gases in mutually antiparallel magnetic fields\nwhere a qualitatively opposite dependence on the sign of\n$g_{\\uparrow\\downarrow}$ is found. Our results thus unveil an intriguing\nconnection between multicomponent quantum Hall systems and quantum spin Hall\nsystems in minimal setups."
    },
    {
        "anchor": "Finite-Temperature Auxiliary-Field Quantum Monte Carlo for Bose-Fermi\n  Mixtures: We present a quantum Monte Carlo (QMC) technique for calculating the exact\nfinite-temperature properties of Bose-Fermi mixtures. The Bose-Fermi\nAuxiliary-Field Quantum Monte Carlo (BF-AFQMC) algorithm combines two methods,\na finite-temperature AFQMC algorithm for bosons and a variant of the standard\nAFQMC algorithm for fermions, into one algorithm for mixtures. We demonstrate\nthe accuracy of our method by comparing its results for the Bose-Hubbard and\nBose-Fermi-Hubbard models against those produced using exact diagonalization\nfor small systems. Comparisons are also made with mean-field theory and the\nworm algorithm for larger systems. As is the case with most fermion\nHamiltonians, a sign or phase problem is present in BF-AFQMC. We discuss the\nnature of these problems in this framework and describe how they can be\ncontrolled with well-studied approximations to expand BF-AFQMC's reach. The new\nalgorithm can serve as an essential tool for answering many unresolved\nquestions about many-body physics in mixed Bose-Fermi systems.",
        "positive": "Decay of Resonance Structure and Trapping Effect in Potential Scattering\n  Problem of Self-Focusing Wave Packet: Potential scattering problems governed by the time-dependent Gross-Pitaevskii\nequation are investigated numerically for various values of coupling constants.\nThe initial condition is assumed to have the Gaussian-type envelope, which\ndiffers from the soliton solution. The potential is chosen to be a box or well\ntype. We estimate the dependences of reflectance and transmittance on the width\nof the potential and compare these results with those given by the stationary\nSchr\\\"odinger equation. We attribute the behaviors of these quantities to the\nlimitation on the width of the nonlinear wave packet. The coupling constant and\nthe width of the potential play an important role in the distribution of the\nwaves appearing in the final state of scattering."
    },
    {
        "anchor": "Emergent eigenstate solution for generalized thermalization: Generalized thermalization is a process that occurs in integrable systems in\nwhich unitary dynamics, e.g., following a quantum quench, results in states in\nwhich observables after equilibration are described by generalized Gibbs\nensembles (GGEs). Here we discuss an emergent eigenstate construction that\nallows one to built emergent local Hamiltonians of which one eigenstate\ncaptures the entire generalized thermalization process following a global\nquantum quench. Specifically, we study the emergent eigenstate that describes\nthe quantum dynamics of hard-core bosons in one dimension (1D) for which the\ninitial state is a density wave and they evolve under a homogeneous\nHamiltonian.",
        "positive": "Observation of a dissipative time crystal in a strongly interacting\n  Rydberg gas: The notion of spontaneous symmetry breaking has been well established to\ncharacterize classical and quantum phase transitions of matter, such as in\ncondensation, crystallization or quantum magnetism. Generalizations of this\nparadigm to the time dimension can lead to an exotic dynamical phase, the time\ncrystal, which spontaneously breaks the time translation symmetry of the system\n[1]. While the existence of a continuous time crystal at equilibrium has been\nchallenged by no-go theorems [2-4], the difficulty can be circumvented by\ndissipation in an open system. Here, we report the experimental observation of\nsuch dissipative time crystalline order in a room-temperature atomic gas, where\nground-state atoms are continuously driven to Rydberg states. The emergent time\ncrystal is revealed by persistent oscillations of the photon transmission, with\nno observable damping during the measurement. We show that the observed limit\ncycles arise from the coexistence and competition between distinct Rydberg\ncomponents, in agreement with a mean-field analysis derived from the\nmicroscopic model. The nondecaying autocorrelation of the oscillation, together\nwith the robustness against temporal noises, indicates the establishment of\ntrue long-range temporal order and demonstrates the realization of a continuous\ntime crystal in our experiments."
    },
    {
        "anchor": "Unconventional superfluidity in Bose-Fermi Mixtures: Pairing between fermions that attract each other, reveal itself to the\nmacroscopic world in the form of superfluidity. Since the discovery of\nfermionic superfluidity, intense search has been going on to find various\nunconventional forms of fermion pairing as well as to increase the transition\ntemperature. Here, we show that a two dimensional mixture of single-component\nfermions and dipolar bosons allows to reach experimentally feasible superfluid\ntransition temperatures for non-standard pairing symmetries. Excitations in\nthese superfluids are anyonic and their statistics depends on the order of\ntheir permutations, i.e is non-Abelian. Our results provide for the first time\nan example of a highly tunable system which exhibits various kind of pairing\nsymmetry and high transition temperature. Additionally, they provide a\nplayground to observe anyonic excitations and their braiding properties.",
        "positive": "Interaction of a Bose-Einstein Condensate and a Superconductor via Eddy\n  Currents: We study center-of-mass oscillations of a dipolar Bose-Einstein condensate in\nthe vicinity of a superconducting surface. We show that the magnetic field of\nthe magnetic dipoles induces eddy currents in the superconductor, which act\nback on the Bose-Einstein condensate. This leads to a shift of its oscillation\nfrequency and to an anharmonic coupling of the Bose-Einstein condensate with\nthe superconductor. The anharmonicity creates a coupling to one of the\ncollective modes of the condensate that can be resonantly enhanced, if the\nparameters of the condensate are chosen properly. This provides a new physical\nmechanism to couple a Bose-Einstein condensate and a superconductor which\nbecomes significant for 52Cr, 168Er or 164Dy condensates in superconducting\nmircotraps."
    },
    {
        "anchor": "Collective modes of a strongly interacting Bose gas: probing the Mott\n  transition: We analyze the collective modes of a harmonically trapped, strongly\ninteracting Bose gas in an optical lattice in the vicinity of the Mott\ninsulator transition. For that aim we employ the dynamical Gutzwiller\nequations, by performing real-time evolution and by solving the equations in\nlinear response. We find a strong dependence on the spatial dimension of the\nsystem: while in one dimension the frequency of the dipole mode vanishes at the\nMott transition, in higher dimensions the dominant dipole mode is featureless\nand we find a signature only in the breathing mode. We discuss implications for\nexperiments with bosonic and fermionic atoms.",
        "positive": "Interacting Bose-condensed gases: We provide an overview of the effects of interactions in Bose-condensed\ngases. We focus on phenomena that have been explored in ultracold atom\nexperiments, covering both tuneable contact interactions and dipolar\ninteractions. Our discussion includes: modifications to the ground state and\nexcitation spectrum, critical behaviour near the Bose--Einstein condensation\ntemperature, the unitary regime where the interactions are as strong as allowed\nby quantum mechanics, quantum droplets in mixtures, and supersolids in dipolar\ngases."
    },
    {
        "anchor": "Fermionic Luttinger liquids from a microscopic perspective: We consider interacting one-dimensional, spinless Fermi gases, whose\nlow-energy properties are described by Luttinger liquid theory. We perform a\nsystematic, in-depth analysis of the relation between the macroscopic,\nphenomenological parameters of Luttinger liquid effective field theory, and the\nmicroscopic interactions of the Fermi gas. In particular, we begin by\nexplaining how to model effective interactions in one dimension, which we then\napply to the main forward scattering channel -- the interbranch collisions --\ncommon to these systems. We renormalise the corresponding interbranch\nphenomenological constants in favour of scattering phase shifts. Interestingly,\nour renormalisation procedure shows (i) how Luttinger's model arises in a\ncompletely natural way -- and not as a convenient approximation -- from\nTomonaga's model, and (ii) the reasons behind the interbranch coupling constant\nremaining unrenormalised in Luttinger's model. We then consider the so-called\nintrabranch processes, whose phenomenological coupling constant is known to be\nfixed by charge conservation, but whose microscopic origin is not well\nunderstood. We show that, contrary to general belief and common sense, the\nintrabranch interactions appearing in Luttinger liquid theory do not correspond\nto an intrabranch scattering channel, nor an energy shift due to intrabranch\ninteractions, in the microscopic theory. Instead, they are due to interbranch\nprocesses. We finally apply our results to a particular example of an exactly\nsolvable model, namely the fermionic dual to the Lieb-Liniger model in the\nTonks-Girardeau and super-Tonks-Girardeau regimes.",
        "positive": "Prethermal Floquet Steady States and Instabilities in the Periodically\n  Driven, Weakly Interacting Bose-Hubbard Model: We explore prethermal Floquet steady states and instabilities of the weakly\ninteracting two-dimensional Bose-Hubbard model subject to periodic driving. We\ndevelop a description of the nonequilibrium dynamics, at arbitrary drive\nstrength and frequency, using a weak-coupling conserving approximation. We\nestablish the regimes in which conventional (zero-momentum) and unconventional\n[$(\\pi,\\pi)$-momentum] condensates are stable on intermediate time scales. We\nfind that condensate stability is \\emph{enhanced} by increasing the drive\nstrength, because this decreases the bandwidth of quasiparticle excitations and\nthus impedes resonant absorption and heating. Our results are directly relevant\nto a number of current experiments with ultracold bosons."
    },
    {
        "anchor": "Polarons and Molecules in a Two-Dimensional Fermi Gas: We study an impurity atom in a two-dimensional Fermi gas using variational\nwave functions for (i) an impurity dressed by particle-hole excitations\n(polaron) and (ii) a dimer consisting of the impurity and a majority atom. In\ncontrast to three dimensions, where similar calculations predict a sharp\ntransition to a dimer state with increasing interspecies attraction, we show\nthat the polaron ansatz always gives a lower energy. However, the exact\nsolution for a heavy impurity reveals that both a two-body bound state and\ndistortions of the Fermi sea are crucial. This reflects the importance of\nparticle-hole pairs in lower dimensions and makes simple variational\ncalculations unreliable. We show that the energy of an impurity gives important\ninformation about its dressing cloud, for which both ans\\\"atze give inaccurate\nresults.",
        "positive": "Effective Field Theory for Few-Boson Systems: We study universal bosonic few-body systems within the framework of effective\nfield theory at leading order (LO). We calculate binding energies of systems of\nup to six particles and the atom-dimer scattering length. Convergence to the\nlimit of zero-range two- and three-body interactions is shown, indicating that\nno additional few-body interactions need to be introduced at LO.\nGeneralizations of the Tjon line are constructed, showing correlations between\nfew-body binding energies and the binding energy of the trimer, for a given\ndimer energy. As a specific example, we implement our theory for 4He atomic\nsystems, and show that the results are in surprisingly good agreement with\nthose of sophisticated 4He-4He potentials. Potential implications for the\nconvergence of the EFT expansion are discussed."
    },
    {
        "anchor": "Dynamics and thermalization of Bose-Einstein condensate in Sinai\n  oscillator trap: We study numerically the evolution of Bose-Einstein condensate in the Sinai\noscillator trap described by the Gross-Pitaevskii equation in two dimensions.\nIn the absence of interactions this trap mimics the properties of Sinai\nbilliards where the classical dynamics is chaotic and the quantum evolution is\ndescribed by generic properties of quantum chaos and random matrix theory. We\nshow that, above a certain border, the nonlinear interactions between atoms\nlead to the emergence of dynamical thermalization which generates the\nstatistical Bose-Einstein distribution over eigenmodes of the system without\ninteractions. Below the thermalization border the evolution remains\nquasi-integrable. Such a Sinai oscillator trap, formed by the oscillator\npotential and a repulsive disk located in the vicinity of the center, had been\nalready realized in rst experiments with the Bose-Einstein condensate formation\nby Ketterle group in 1995 and we argue that it can form a convenient test bed\nfor experimental investigations of dynamical of thermalization. Possible links\nand implications for Kolmogorov turbulence in absence of noise are also\ndiscussed.",
        "positive": "Variance of an anisotropic Bose-Einstein condensate: The anisotropy of a trap potential can impact the density and variance of a\nBose-Einstein condensate (BEC) in an opposite manner. We exemplify this effect\nfor both the ground state and out-of-equilibrium dynamics of structureless\nbosons interacting by a long-range inter-particle interaction and trapped in a\ntwo-dimensional single-well potential. We demonstrate that even when the\ndensity of the BEC is, say, wider along the $y$ direction and narrower along\nthe $x$ direction, its position variance can actually be smaller and momentum\nvariance larger in the $y$ direction than in the $x$ direction. This behavior\nof the variance in a many-particle system is counterintuitive. It suggests\nusing the variance as a tool to characterize the strength of correlations along\nthe $y$ and $x$ directions in a trapped BEC."
    },
    {
        "anchor": "Rotational dynamics induced by low energy binary collisions of quantum\n  droplets: A theoretical analysis of the rotational dynamics induced by off axis binary\ncollisions of quantum droplets constituted by ultracold atoms is reported. We\nfocus on quantum droplets formed by degenerate dilute Bose gases made up from\nbinary mixtures of alkaline atoms under feasible experimental conditions. The\nstability of the ground state is known to be longer for the chosen\nheteronuclear gases than for the homonuclear ones. In both cases, we find out\nthat the dynamics seems to privilege a high similarity of the density of each\natomic species. However, the evolution of the phase of the corresponding order\nparameter differs significantly for heteronuclear admixtures. We evaluate the\nfidelity as a figure of merit for the overlap between the order parameters of\neach atomic species. Dynamical evidence of the differences between the phase of\nthe order parameters are predicted to manifest in their corresponding linear\nand angular momenta. We numerically verify that the total angular and linear\nmomenta are conserved both during the collision. Some direct correlations\nbetween the Weber number and the impact parameter with the distribution of the\ndynamical variables are established.",
        "positive": "Static and dynamic properties of self-bound droplets of light in hot\n  vapours: The propagation of light in nonlinear media is well described by a $2$D\nnonlinear Schr\\\"odinger equation (NLSE) within the paraxial approximation,\nwhich is equivalent to the Gross-Pitaesvskii equation (GPE), the mean-field\ndescription for the dynamics of Bose-Einstein condensates (BECs). Due to this\nsimilarity, many theoretical and experimental investigations of phenomena which\nhave already been studied and realized in BECs have been recently analysed in\nalternative experimental platforms such as hot atomic vapours. In this work, we\nstudy the formation of droplets of light in these media, attempting to\nestablish a mapping between the experimental parameters normally used in BEC\nexperiments and those needed to observe the analogous phenomenon in hot atomic\nvapours. We obtain the energy functional for the susceptibility of the medium\nin the $\\chi^{(3)}$ , $\\chi^{(3)}+\\chi^{(5)}$ and saturating regimes for a\ntwo-level atomic configuration considering the focusing (attractive) regime. We\napply a Gaussian variational approach and check its predictions through\nnumerical simulations of the NLSE for each regime. Finally, we study the\nreal-time dynamics of the system for both the $\\chi^{(3)}+\\chi^{(5)}$ and\nsaturating nonlinearities, focusing our attention on the behaviour of the\nbreathing mode and on the analysis of droplet formation for realistic\nexperimental conditions."
    },
    {
        "anchor": "Rigorous mean-field dynamics of lattice bosons: Quenches from the Mott\n  insulator: We provide a rigorous derivation of Gutzwiller mean-field dynamics for\nlattice bosons, showing that it is exact on fully connected lattices. We apply\nthis formalism to quenches in the interaction parameter from the Mott insulator\nto the superfluid state. Although within mean-field the Mott insulator is a\nsteady state, we show that a dynamical critical interaction $U_d$ exists, such\nthat for final interaction parameter $U_f>U_d$ the Mott insulator is\nexponentially unstable towards emerging long-range superfluid order, whereas\nfor $U_f<U_d$ the Mott insulating state is stable. We discuss the implications\nof this prediction for finite-dimensional systems.",
        "positive": "Exploring vortex formation in rotating Bose-Einstein condensates beyond\n  mean-field regime: The production of quantized vortices having diverse structures is a\nremarkable effect of rotating Bose-Einstein condensates. Vortex formation\ndescribed by the mean-field theory is valid only in the regime of weak\ninteractions. The exploration of the rich and diverse physics of strongly\ninteracting BEC requires a more general approach. This study explores the\nvortex formation of strongly interacting and rapidly rotating BEC from a\ngeneral ab initio many-body perspective. We demonstrate that the quantized\nvortices form various structures that emerge from an intricate interplay\nbetween the angular momentum and many-body interaction. We examine the distinct\nimpact of the angular velocity and interaction energy on the vortex formation.\nOur analysis shows that, while the angular rotation generally augments the\nvortex formation, the interactions can enhance as well as impede the vortices\nproduction."
    },
    {
        "anchor": "Non-Hermitian Skin Effect In Periodically-Driven Dissipative Ultracold\n  Atoms: The non-Hermitian skin effect (NHSE), featured by the collapse of bulk-band\neigenstates into the localized boundary modes of the systems, is one of most\nstriking properties in the fields of non-Hermitian physics. Unique physical\nphenomena related to the NHSE have attracted a lot of interest, however, their\nexperimental realizations usually require nonreciprocal hopping, which faces a\ngreat challenge in ultracold-atom systems. In this work, we propose to realize\nthe NHSE in a 1D optical lattice by periodically-driven ultracold atoms in the\npresence of staggered atomic loss. By studying the effective Floquet\nHamiltonian in the high-frequency approximation, we reveal the underlying\nmechanism for the periodic-driving-induced the NHSE. We found that the robust\nNHSE can be tuned by driving phase, which is manifested by the dynamical\nlocalization. Most remarkably, we uncover the periodic-driving-induced critical\nskin effect for two coupled chains with different driving phases, accompanied\nby the appearance of size-dependent topological in-gap modes. Our studies\nprovide a feasible way for observing the NHSE and exploring corresponding\nunique physical phenomena due to the interplay of non-Hermiticity and many-body\nstatistics in ultracold-atom systems.",
        "positive": "Density functional theory of a trapped Bose gas with tunable scattering\n  length: from weak-coupling to unitarity: We study an interacting Bose gas at T=0 under isotropic harmonic confinement\nwithin Density Functional Theory in the Local Density approximation. The energy\ndensity functional, which spans the whole range of positive scattering lengths\nup to the unitary regime (infinite scattering length), is obtained by fitting\nthe recently calculated Monte Carlo bulk equation of state [Phys. Rev. A 89,\n041602(R) (2014)]. We compare the density profiles of the trapped gas with\nthose obtained by MC calculations. We solve the time-dependent Density\nFunctional equation to study the effect of increasing values of the interaction\nstrength on the frequencies of monopole and quadrupole oscillations of the\ntrapped gas. We find that the monopole breathing mode shows a non-monotonous\nbehavior as a function of the scattering length. We also consider the damping\neffect of three-body losses on such modes."
    },
    {
        "anchor": "Negative refraction in the relativistic electron gas: We show that a gas of relativistic electrons is a left-handed material at low\nfrequencies by computing the effective electric permittivity and effective\nmagnetic permeability that appear in Maxwell's equations in terms of the\nresponses appearing in the constitutive relations, and showing that the former\nare both negative below the {\\it same} frequency, which coincides with the\nzero-momentum frequency of longitudinal plasmons. We also show, by explicit\ncomputation, that the photonic mode of the electromagnetic radiation does not\ndissipate energy, confirming that it propagates in the gas with the speed of\nlight in vacuum, and that the medium is transparent to it. We then combine\nthose results to show that the gas has a negative effective index of refraction\n$n_{\\rm eff}=-1$. We illustrate the consequences of this fact for Snell's law,\nand for the reflection and transmission coefficients of the gas.",
        "positive": "Stability and Excitations of Spontaneous Vortices in Homogeneous\n  Polariton Condensates: We study the dynamics of spontaneously formed vortices in homogeneous\nmicrocavity-polariton condensates (MPCs). We find that vortices are stable and\nappear spontaneously without stirring or rotating MPCs. The dip of the vortex\ncore contains some background of reservoir polaritons and the visibility of a\nvortex is increasing with respect to the pump strength. The vortex radius is\ninversely proportional to the square root of the condensate density. Excitation\nenergies of vortices at high and low pump powers are finite and zero,\nrespectively. Vortices at low pump powers exhibit the short lifetime."
    },
    {
        "anchor": "Theory of Interacting Cavity Rydberg Polaritons: Photonic materials are an emerging platform to explore quantum matter and\nquantum dynamics. The development of Rydberg electromagnetically induced\ntransparency provided a clear route to strong interactions between individual\noptical photons. In conjunction with carefully designed optical resonators, it\nis now possible to achieve extraordinary control of the properties of\nindividual photons, introducing tunable gauge fields whilst imbuing the photons\nwith mass and embedding them on curved spatial manifolds. Building on work\nformalizing Rydberg-mediated interactions between propagating photons, we\ndevelop a theory of interacting Rydberg polaritons in multimode optical\nresonators, where the strong interactions are married with tunable\nsingle-particle properties to build and probe exotic matter. In the presence of\nstrong coupling between the resonator field and a Rydberg-dressed atomic\nensemble, a quasiparticle called the \"cavity Rydberg polariton\" emerges. We\ninvestigate its properties, finding that it inherits both the fast dynamics of\nits photonic constituents and the strong interactions of its atomic\nconstituents. We develop tools to properly renormalize the interactions when\npolaritons approach each other, and investigate the impact of atomic motion on\nthe coherence of multi-mode polaritons, showing that most channels for\natom-polariton cross-thermalization are strongly suppressed. Finally, we\npropose to harness the repeated diffraction and refocusing of the optical\nresonator to realize interactions which are local in momentum space. This work\npoints the way to efficient modeling of polaritonic quantum materials in\nproperly renormalized strongly interacting effective theories, thereby enabling\nexperimental studies of photonic fractional quantum Hall fluids and crystals,\nplus photonic quantum information processors and repeaters.",
        "positive": "Coupling of polaritons to vibrational modes of ultracold atoms in an\n  optical lattice: The coupling of internal electronic excitations to vibrational modes of the\nexternal motion of ultracold atoms in an optical lattice is studied here in\nusing a perturbation expansion in small atomic displacements. In the Mott\ninsulator case with one atom per site, the resonance dipole-dipole coupling\nbetween neighboring sites can induce emission and absorption of vibrational\nquanta. Within a cavity in the strong exciton-photon coupling regime such\ncoupling results in polariton-vibration interactions, which create a\nsignificant thermalization mechanism for polaritons toward their minimum\nenergy, and leading to motional heating of the lattice atoms."
    },
    {
        "anchor": "Large-$N$ properties of a non-ideal Bose gas: We rigorously discuss the large-$N$ thermodynamics of a Bose gas with a\nshort-range two-body potential. Considering the system as a mixture of $N$\nidentical components with symmetrical interaction we calculated numerically the\ntemperature dependence of the leading-order corrections to the depletion of\nBose-Einstein condensate and to the isothermal compressibility.",
        "positive": "Weakly interacting disordered Bose gases out of equilibrium: from\n  multiple scattering to superfluidity: We explore the quench dynamics of a two-dimensional, weakly interacting\ndisordered Bose gas for various relative strengths of interactions and\ndisorder. This allows us to identify two well distinct out-of-equilibrium\nregimes. When interactions are smaller than the disorder, the gas experiences\nmultiple scattering and exhibits a short-range spatial coherence. At short time\nthis coherence is only smoothly affected by interactions, via a diffusion\nprocess of the particles' energies. When interactions are larger than the\ndisorder, scattering ceases and the gas behaves more and more like a fluid,\nultimately like a superfluid at low energy. In the superfluid regime, the gas\nexhibits a long-range algebraic coherence, characteristic of a pre-thermal\nregime in disorder."
    },
    {
        "anchor": "Itinerant ferromagnetism of two-dimensional repulsive fermions with Rabi\n  coupling: We study a two-dimensional fermionic cloud of repulsive alkali-metal atoms\ncharacterized by two hyperfine states which are Rabi coupled. Within a\nvariational Hartree-Fock scheme, we calculate analytically the ground-state\nenergy of the system. Then we determine the conditions under which there is a\nquantum phase transition with spontaneous symmetry breaking from a\nspin-balanced configuration to a spin-polarized one, an effect known as\nitinerant ferromagnetism. Interestingly, we find that the transition appears\nwhen the interaction energy per particle exceedes both the kinetic energy per\nparticle and the Rabi coupling energy. The itinerant ferromagnetism of the\npolarized phase is analyzed, obtaining the population imbalance as a function\nof interaction strength, Rabi coupling, and number density. Finally, the\ninclusion of a external harmonic confinement is investigated by adopting the\nlocal density approximation. We predict that a single atomic cloud can display\npopulation imbalance near the center of the trap and a fully balanced\nconfiguration at the periphery.",
        "positive": "The third virial coefficient of a two-component unitary Fermi gas across\n  an Efimov-effect threshold: We consider a mixture of two single-spin-state fermions with an interaction\nof negligible range and infinite $s$-wave scattering length. By varying the\nmass ratio $\\alpha$ across $\\alpha\\_c\\simeq 13.6069$ one can switch on-and-off\nthe Efimov effect. We determine analytically the third cluster coefficient of\nthe gas. We show that it is a smooth function of $\\alpha$ across $\\alpha\\_c$\nsince, unexpectedly, the three-body parameter characterizing the interaction is\nrelevant even on the non-Efimovian side $\\alpha\\textless{}\\alpha\\_c$."
    },
    {
        "anchor": "Topological Superfluid and Majorana Zero Modes in Synthetic Dimension: Recently it has been shown that multicomponent spin-orbit-coupled fermions in\none-dimensional optical lattices can be viewed as spinless fermions moving in\ntwo-dimensional synthetic lattices with synthetic magnetic flux. The quantum\nHall edge states in these systems have been observed in recent experiments. In\nthis paper we study the effect of an attractive Hubbard interaction. Since the\nHubbard interaction is long-range in the synthetic dimension, it is able to\nefficiently induce Cooper pairing between the counterpropagating chiral edge\nstates. The topological class of the resultant one-dimensional superfluid is\ndetermined by the parity (even/odd) of the Chern number in the two-dimensional\nsynthetic lattice. We also show the presence of a chiral symmetry in our model,\nwhich implies ${\\rm Z}$ classification and the robustness of multiple zero\nmodes when this symmetry is unbroken.",
        "positive": "Momentum-resolved radio-frequency spectroscopy of a spin-orbit coupled\n  atomic Fermi gas near a Feshbach resonance in harmonic traps: We theoretically investigate the momentum-resolved radio-frequency\nspectroscopy of a harmonically trapped atomic Fermi gas near a Feshbach\nresonance in the presence of equal Rashba and Dresselhaus spin-orbit coupling.\nThe system is qualitatively modeled as an ideal gas mixture of atoms and\nmolecules, in which the properties of molecules, such as the wavefunction,\nbinding energy and effective mass, are determined from the two-particle\nsolution of two-interacting atoms. We calculate separately the radio-frequency\nresponse from atoms and molecules at finite temperatures by using the standard\nFermi golden rule, and take into account the effect of harmonic traps within\nlocal density approximation. The total radio-frequency spectroscopy is\ndiscussed, as functions of temperature and spin-orbit coupling strength. Our\nresults give a qualitative picture of radio-frequency spectroscopy of a\nresonantly interacting spin-orbit coupled Fermi gas and can be directly tested\nin atomic Fermi gases of K40 atoms at Shanxi University and of Li6 atoms at\nMIT."
    },
    {
        "anchor": "Unfolding multi-particle quantum correlations hidden in decoherence: Quantum coherence is a fundamental characteristic to distinguish quantum\nsystems from their classical counterparts. Though quantum coherence persists in\nisolated non-interacting systems, interactions inevitably lead to decoherence,\nwhich is in general believed to cause the lost of quantum correlations. Here,\nwe show that, accompanying to the single-particle decoherence, interactions\nbuild up quantum correlations on the two-, three-, and multi-particle levels.\nUsing the quantitative solutions of the quantum dynamics of a condensate\noccupying two modes, such as two bands of an optical lattice, we find out that\nsuch dynamically emergent multi-particle correlations not only reveal how\ninteractions control the quantum coherence of a many-body system in a highly\nintriguing means, but also evince the rise of exotic fragmented condensates,\nwhich are difficult to access at the ground state. We further develop a generic\ninterferometry that can be used in experiments to measure high order\ncorrelation functions directly.",
        "positive": "On the existence of steady-state black hole analogues in finite\n  quasi-one-dimensional Bose-Einstein condensates: We theoretically propose a finite-size quasi-one-dimensional Bose-Einstein\ncondensate with coherent source and drain placed at its two ends, which can in\nprinciple sustain a stationary sonic black hole with a single event horizon.\nOur analysis is focused on the condensate persistence against quantum\nfluctuations. We show that similar to white hole-black hole pairs, dynamical\ninstabilities occur. Investigating in detail the instabilities' dependence on\nthe system parameters, we also identify windows of formally infinite black hole\nlifetimes. By using quantum depletion of the condensate as a diagnostic tool,\nwe validate the usage of Bogoliubov theory to describe the analogue Hawking\nprocess, and establish novel signatures of Hawking radiation in the depleted\ncloud, both inside and outside the event horizon."
    },
    {
        "anchor": "On the ground state energy of the inhomogeneous Bose gas: Within the self-consistent Hartree-Fock approximation, an explicit expression\nfor the ground state energy of inhomogeneous Bose gas is derived as a\nfunctional of the inhomogeneous density of the Bose-Einstein condensate. The\nresults obtained are based on existence of the off-diagonal long-range order in\nthe single-particle density matrix for systems with a Bose-Einstein condensate.\nThis makes it possible to avoid the use of anomalous averages. The explicit\nform of the kinetic energy, which differs from one in the Gross-Pitaevski\napproach, is found. This form is valid beyond the Hartree-Fock approximation\nand can be applied for arbitrary strong interparticle interaction.",
        "positive": "Topological phases in pseudospin-1 Fermi gases with two-dimensional\n  spin-orbit coupling: The recent experimental realization of spin-orbit (SO) coupling for ultracold\nbosons and fermions opens an exciting avenue for engineering quantum matter\nthat may be challenging to realize in solid state materials such as SO coupled\nspin-1 fermions. While one-dimensional SO coupling for spin-1 bosons has been\nexperimentally realized, the generation of two-dimensional (2D) SO coupling and\nits topological properties are largely unexplored. Here we propose an\nexperimental scheme for realizing a 2D Dresselhaus-type SO coupling in a square\nlattice for spin-1 Fermi gases. Because of the extended spin degree of freedom,\nmany interesting topological phases could exist without relying on lattice\npoint group symmetries that are crucial in solid state materials. These exotic\nphases include triply-degenerate points, quadratic band touching, a large Chern\nnumber ($C=5$) superfluid with 5 Majorana modes, triple-Weyl fermions, etc. Our\nscheme can be generalized to larger spins and provides a new route for\nengineering topological quantum matter by utilizing large spin degrees of\nfreedom, instead of specific lattice symmetries."
    },
    {
        "anchor": "Optical Control of Exchange Interaction and Kondo Temperature in cold\n  Atom Gas: The relevance of magnetic impurity problems in cold atom systems depends\ncrucially on the nature of exchange interaction between itinerant fermionic\natoms and a localized impurity atom. In particular, Kondo physics occurs only\nif the exchange interaction is anti-ferromagnetic, and strong enough to yield\nhigh enough Kondo temperature ($T_K/T_F \\ge 0.1$). Focusing, as an example, on\nthe experimentally accessible system of ultra-cold $^{173}$Yb atoms, it is\nshown that the sign and strength of an exchange interaction between an\nitinerant Yb($^{1}$S$_{0}$) atom and a trapped Yb($^{3}$P$_{0}$) atom can be\noptically controlled. Explicitly, as the light intensity increases (from zero),\nthe exchange interaction changes from ferromagnetic to anti-ferromagnetic. When\nthe light intensity is just below a singlet Feshbach resonance, the singlet\nscattering length $a_S$ is large and negative, and the Kondo temperature\nincreases sharply.",
        "positive": "Analysis of Particle Transfer by Periodic Lattice Modulation for\n  Ultracold Fermionic Atom Systems in Three Dimensional Optical Lattice: We analyze a ultracold fermionic atom system in a three dimensional optical\nlattice with a confinement harmonic potential, using the Hubbard model, and\ntime-dependent Gutzwiller variational approach for numerical calculation. Our\nstudy is focused on the time evolution of the particle transfer when the\nlattice potential is modulated by adding a periodic one. The choice of the\nparameters such as the modulation frequency and amplitude and the particle\nnumber affects the particle transfer. We calculate the time evolution of the\nvariance in the particle distribution, and show its dependence on the\nparameters. The lattice modulation turns out to work effectively in order to\ncontrol the particle transfer, and will be a useful method in experiments for\nfermionic atom systems."
    },
    {
        "anchor": "Controlling Transport of Ultra-Cold Atoms in 1D Optical Lattices with\n  Artificial Gauge Fields: We show that the recently developed optical lattices with Peierls\nsubstitution -- which can be modeled as a lattice with a complex tunneling\ncoefficient -- may be used to induce controllable quantum transport of\nultra-cold atoms. In particular, we show that by ramping up the phase of the\ncomplex tunneling coefficient in a spatially uniform fashion, a finite quasi\nsteady-state current (QSSC) ensues from the exact dynamics of non-interacting\nfermions. The direction and magnitude of the current can be controlled by the\noverall phase difference but not the details of the ramp. The entanglement\nentropy does not increase when the QSSC lasts. Due to different spin\nstatistics, condensed non-interacting bosons do not support a finite QSSC under\nthe same setup. We also find that an approximate form of the QSSC survives when\nperturbative effects from interactions, weak harmonic background traps, and\nfinite-temperature are present, which suggests that our findings should be\nobservable with available experimental capabilities.",
        "positive": "The Planck distribution of phonons in a Bose-Einstein condensate: The Planck distribution of photons emitted by a black body led to the\ndevelopment of quantum theory. An analogous distribution of phonons should\nexist in a Bose-Einstein condensate. We observe this Planck distribution of\nthermal phonons in a 3D condensate. This observation provides an important\nconfirmation of the basic nature of the condensate's quantized excitations. In\ncontrast to the bunching effect, the density fluctuations are seen to increase\nwith increasing temperature. This is due to the non-conservation of the number\nof phonons. In the case of rapid cooling, the phonon temperature is out of\nequilibrium with the surrounding thermal cloud. In this case, a Bose-Einstein\ncondensate is not as cold as previously thought. These measurements are enabled\nby our in situ k-space technique."
    },
    {
        "anchor": "Universal Landau-Zener regimes in dynamical topological phase\n  transitions: In finite systems driven unitarily across topological phase transitions, the\nChern number and the Bott index have been found to exhibit different behaviors\ndepending on the boundary conditions and on the commensurability of the\nlattice. For periodic boundary conditions, the Chern number does not change for\nfinite commensurate lattices (or in the thermodynamic limit). On the other\nhand, the Chern number can change for incommensurate lattices with periodic\nboundary conditions and the Bott index can change for lattices with open\nboundary conditions. Here we show that the scalings of the fields at which\nthose two indices change exhibit Landau-Zener and near-adiabatic regimes\ndepending on the speed at which the strength of the drive is ramped up and on\nthe system size. Those regimes are preceded by a regime in which the\ntopological indices do not change. The latter is the only regime that, for\nnonvanishing ramp speeds, survives in the thermodynamic limit. We then show\nthat the dc Hall response can be used to detect topological phase transitions\nindependently of the behavior of the topological indices.",
        "positive": "Effective three-body interactions via photon-assisted tunneling in an\n  optical lattice: We present a simple, experimentally realizable method to make coherent\nthree-body interactions dominate the physics of an ultracold lattice gas. Our\nscheme employs either lattice modulation or laser-induced tunneling to reduce\nor turn off two-body interactions in a rotating frame, promoting three-body\ninteractions arising from multi-orbital physics to leading-order processes.\nThis approach provides a route to strongly-correlated phases of lattice gases\nthat are beyond the reach of previously proposed dissipative three-body\ninteractions. In particular, we study the mean-field phase diagram for spinless\nbosons with three- and two- body interactions, and provide a roadmap to dimer\nstates of varying character in 1D. This new toolset should be immediately\napplicable in state-of-the-art cold atom experiments."
    },
    {
        "anchor": "Polaron, molecule and pairing in one-dimensional spin-1/2 Fermi gas with\n  an attractive Delta-function interaction: Using solutions of the discrete Bethe ansatz equations, we study in detail\nthe quantum impurity problem of a spin-down fermion immersed into a fully\nploarized spin-up Fermi sea with weak attraction. We prove that this impurity\nfermion in the one-dimensional (1D) fermionic medium behaves like a polaron for\nweak attraction. However, as the attraction grows, the spin-down fermion binds\nwith one spin-up fermion from the fully-polarized medium to form a tightly bond\nmolecule. Thus it is seen that the system undergos a cross-over from a mean\nfield polaron-like nature into a mixture of excess fermions and a bosonic\nmolecule as the attraction changes from weak attraction into strong attraction.\nThis polaron-molecule cross-over is universal in 1D many-body systems of\ninteracting fermions. In thermodynamic limit, we further study the relationship\nbetween the Fredholm equations for the 1D spin-1/2 Fermi gas with weakly\nrepulsive and attractive delta-function interactions.",
        "positive": "A versatile ring trap for quantum gases: We report on the confinement of a Bose-Einstein condensate in an annular trap\nwith widely tunable parameters. The trap relies on a combination of magnetic,\noptical and radio-frequency fields. The loading procedure is discussed. We\npresent annular traps with radii adjusted between 20 and 150 micrometers. We\ndemonstrate the preparation of persistent flows both with a rotating laser\nstirrer and with a global quadrupole deformation of the ring.Our setup is well\nadapted for the study of superfluid dynamics."
    },
    {
        "anchor": "Chiral Bosonic Mott Insulator on the Frustrated Triangular Lattice: We study the superfluid and insulating phases of interacting bosons on the\ntriangular lattice with an inverted dispersion, corresponding to frustrated\nhopping between sites. The resulting single-particle dispersion has multiple\nminima at nonzero wavevectors in momentum space, in contrast to the unique\nzero-wavevector minimum of the unfrustrated problem. As a consequence, the\nsuperfluid phase is unstable against developing additonal chiral order that\nbreaks time reversal (T) and parity (P) symmetries by forming a condensate at\nnonzero wavevector. We demonstrate that the loss of superfluidity can lead to\nan even more exotic phase, the chiral Mott insulator, with nontrivial current\norder that breaks T, P. These results are obtained via variational estimates,\nas well as a combination of bosonization and DMRG of triangular ladders, which\ntaken together permit a fairly complete characterization of the phase diagram.\nWe discuss the relevance of these phases to optical lattice experiments, as\nwell as signatures of chiral symmetry breaking in time-of-flight images.",
        "positive": "Strong-coupling solution of the bosonic dynamical mean-field theory: We derive an approximate analytical solution of the self-consistency\nequations of the bosonic dynamical mean-field theory (B-DMFT) in the\nstrong-coupling limit. The approach is based on a linked-cluster expansion in\nthe hybridization function of normal bosons around the atomic limit. The\nsolution is used to compute the phase diagram of the bosonic Hubbard model for\ndifferent lattices. We compare our results with numerical solutions of the\nB-DMFT equations and numerically exact methods, respectively. The very good\nagreement with those numerical results demonstrates that our approach captures\nthe essential physics of correlated bosons both in the Mott insulator and in\nthe superfluid phase. Close to the transition into the superfluid phase the\nmomentum distribution function at zero momentum is found to be strongly\nenhanced already in the normal phase. The linked-cluster expansion also allows\nus to compute dynamical properties such as the spectral function of bosons. The\nevolution of the spectral function across the transition from the normal to the\nsuperfluid phase is seen to be characteristically different for the interaction\ndriven and density driven transition, respectively."
    },
    {
        "anchor": "Permanent variational wave functions for bosons: We study the performance of permanent states (the bosonic counterpart of the\nSlater determinant state) as approximating functions for bosons, with the\nintention to develop variational methods based upon them. For a system of $N$\nidentical bosons, a permanent state is constructed by taking a set of $N$\narbitrary (not necessarily orthonormal) single-particle orbitals, forming their\nproduct and then symmetrizing it. It is found that for the one-dimensional\nBose-Hubbard model with the periodic boundary condition and at unit filling,\nthe exact ground state can be very well approximated by a permanent state, in\nthat the permanent state has high overlap (at least 0.96 even for 12 particles\nand 12 sites) with the exact ground state and can reproduce both the ground\nstate energy and the single-particle correlators to high precision. For a\ngeneric model, we have devised a greedy algorithm to find the optimal set of\nsingle-particle orbitals to minimize the variational energy or maximize the\noverlap with a target state. It turns out that quite often the ground state of\na bosonic system can be well approximated by a permanent state by all the\ncriterions of energy, overlap, and correlation functions. And even if the error\nis apparent, it can often be remedied by including more configurations, i.e.,\nby allowing the variational wave function to be a combination of multiple\npermanent states. The algorithm is used to study the stability of a\ntwo-particle system, with great success. All these suggest that permanent\nstates are very effective as variational wave functions for bosonic systems,\nand hence deserve further studies.",
        "positive": "Kovtun-Son-Starinets Conjecture and Effects of Mass Imbalance in the\n  Normal State of an Ultracold Fermi Gas in the BCS-BEC Crossover Region: We theoretically assess the conjecture proposed by Kovtun, Son, and\nStarinets, stating that the ratio $\\eta/s$ of the shear viscosity $\\eta$ to the\nentropy density $s$ has the lower bound as $\\eta/s\\ge\\hbar/(4\\pi\nk_{\\mathrm{B}})$. In the normal state of a mass-imbalanced ultracold Fermi gas,\nconsistently including strong-coupling corrections to both $\\eta$ and $s$\nwithin the self-consistent $T$-matrix approximation, we evaluate $\\eta/s$ over\nthe entire BCS (Bardeen-Cooper-Schrieffer)-BEC (Bose-Einstein condensation)\ncrossover region, in the presence of mass imbalance. We find that $\\eta/s$\nachieves the minimum value $4.5\\times \\hbar/(4\\pi k_{\\mathrm{B}})$, not at the\nunitarity, but slightly in the BEC regime, $(k_{\\mathrm{F}}a_s)^{-1}\\simeq\n0.4>0$ (where $a_s$ is the $s$-wave scattering length, and $k_{\\mathrm{F}}$ is\nthe Fermi momentum). In contract to the previous expectation, we find that this\nlower bound is almost independent of mass imbalance: Our results predict that\nall the mass-balanced $^6$Li-$^6$Li and $^{40}$K-$^{40}$K mixtures and the\nmass-imbalanced $^{40}$K-$^{161}$Dy mixture give almost the same lower bound of\n$\\eta/s$. We also point out that the two quantum phenomena, Pauli blocking and\nbound-state formation, are crucial keys for the lower bound of $\\eta/s$."
    },
    {
        "anchor": "Correlated phases of bosons in tilted, frustrated lattices: We study the `tilting' of Mott insulators of bosons into metastable states.\nThese are described by Hamiltonians acting on resonant subspaces, and have rich\npossibilities for correlated phases with non-trivial entanglement of pseudospin\ndegrees of freedom encoded in the boson density. We extend a previous study\n(arXiv:cond-mat/0205169) of cubic lattices to a variety of lattices and tilt\ndirections in 2 dimensions: square, decorated square, triangular, and kagome.\nFor certain configurations three-body interactions are necessary to ensure that\nthe energy of the effective resonant subspace is bounded from below. We find\nquantum phases with Ising density wave order, with superfluidity transverse to\nthe tilt direction, and a quantum liquid state with no broken symmetry. The\nexistence of the quantum liquids state is shown by an exact solution for a\nparticular correlated boson model. We also find cases for which the resonant\nsubspace is described by effective quantum dimer models.",
        "positive": "Quantum Droplets in Imbalanced Atomic Mixtures: Quantum droplets are a quantum analogue to classical fluid droplets in that\nthey are self-bound and display liquid-like properties -- such as\nincompressibility and surface tension -- though their stability is the result\nof quantum fluctuations. One of the major systems for observing quantum\ndroplets is two-component Bose gases. Two-component droplets are typically\nconsidered to be balanced, having a fixed ratio between the densities of the\ntwo component. This work goes beyond the fixed density ratio by investigating\nspherical droplets in imbalanced mixtures. With increasing imbalance, the\ndroplet is able to lower its energy up to a limit, at which point the droplet\nbecomes saturated with the atoms of the majority component and any further\natoms added to this component cannot bind to the droplet. Analysing the\nbreathing mode dynamics of imbalanced droplets indicates that the droplet can\nemit particles, as in balanced mixtures, but the imbalance leads to an\nintricate superposition of multiple simultaneously decaying collective\noscillations."
    },
    {
        "anchor": "Measuring entanglement entropy through the interference of quantum\n  many-body twins: Entanglement is one of the most intriguing features of quantum mechanics. It\ndescribes non-local correlations between quantum objects, and is at the heart\nof quantum information sciences. Entanglement is rapidly gaining prominence in\ndiverse fields ranging from condensed matter to quantum gravity. Despite this\ngenerality, measuring entanglement remains challenging. This is especially true\nin systems of interacting delocalized particles, for which a direct\nexperimental measurement of spatial entanglement has been elusive. Here, we\nmeasure entanglement in such a system of itinerant particles using quantum\ninterference of many-body twins. Leveraging our single-site resolved control of\nultra-cold bosonic atoms in optical lattices, we prepare and interfere two\nidentical copies of a many-body state. This enables us to directly measure\nquantum purity, Renyi entanglement entropy, and mutual information. These\nexperiments pave the way for using entanglement to characterize quantum phases\nand dynamics of strongly-correlated many-body systems.",
        "positive": "Proposal for interferometric detection of topological defects in\n  modulated superfluids: Attractive interactions between fermions can produce a superfluid ground\nstate, in which pairs of up and down spins swirl together in a coordinated,\ncoherent dance. How is this dance affected by an imbalance in the population of\nup and down fermions? Do the extra fermions stand on the sides, or do they\ndisrupt the dance? The most intriguing possibility is the formation of a\nmodulated superfluid state, known as an LO phase, in which the excess fermions\nself-organize into domain walls where the pairing amplitude changes sign.\nDespite fifty years of theoretical and experimental work, there has so far been\nno direct observation of an LO phase. Here we propose an experiment in which\ntwo fermion clouds, prepared with unequal population imbalances, are allowed to\nexpand and interfere. A zipper pattern in the interference fringes is\nunequivocal evidence of LO physics. Furthermore, because the experiment is\nresolved in time and in two spatial directions, we expect an observable\nsignature even at finite temperatures (when thermal fluctuations destroy\nlong-range LO order averaged over time)."
    },
    {
        "anchor": "Phase randomization and typicality in the interference of two\n  condensates: Interference is observed when two independent Bose-Einstein condensates\nexpand and overlap. This phenomenon is typical, in the sense that the\noverwhelming majority of wave functions of the condensates, uniformly sampled\nout of a suitable portion of the total Hilbert space, display interference with\nmaximal visibility. We focus here on the phases of the condensates and their\n(pseudo) randomization, which naturally emerges when two-body scattering\nprocesses are considered. Relationship to typicality is discussed and analyzed.",
        "positive": "Quantum bright solitons in the Bose-Hubbard model with site-dependent\n  repulsive interactions: We introduce a one-dimensional (1D) spatially inhomogeneous Bose-Hubbard\nmodel (BHM) with the strength of the onsite repulsive interactions growing,\nwith the discrete coordinate $z_{j}$, as $|z_{j}|^{\\alpha }$ with $\\alpha >0$.\nRecently, the analysis of the mean-field (MF) counterpart of this system has\ndemonstrated self-trapping of robust unstaggered discrete solitons, under\ncondition $\\alpha >1$. Using the numerically implemented method of the density\nmatrix renormalization group (DMRG), we demonstrate that, in a certain range of\ninteraction, the BHM also self-traps, in the ground state, into a soliton-like\nconfiguration, at $\\alpha >1$, and remains weakly localized at $\\alpha <1$. An\nessential quantum feature is a residual density in the background surrounding\nthe soliton-like peak in the BHM ground state, while in the MF limit the\nfinite-density background is absent. Very strong onsite repulsion eventually\ndestroys soliton-like states, and, for integer densities, the system enters the\nMott phase with a spatially uniform density"
    },
    {
        "anchor": "Thermodynamics of dilute Bose gases: Beyond mean-field theory for binary\n  mixtures of Bose-Einstein condensate: We study the thermodynamic properties of binary Bose mixtures, by developing\na beyond mean-field Popov theory which properly includes the effects of quantum\nand thermal fluctuations in both the density and spin channels. Results for key\nthermodynamic quantities, such as the isothermal compressibility and the\nmagnetic susceptibility, are derived from a perturbative calculation of the\ngrand-canonical potential. We find that thermal fluctuations can play a crucial\nrole on the miscibility condition of a binary mixture, favoring phase\nseparation at finite temperature even if the mixture is soluble at zero\ntemperature, as already anticipated in a previous work [Ota et al., Phys. Rev.\nLett. 123, 075301 (2019)]. We further investigate the miscibility condition for\nbinary mixtures in the presence of asymmetry in the intra-species interactions,\nas well as in the masses of the two components. Furthermore, we discuss the\nsuperfluid behavior of the mixture and the temperature dependence of the\nAndreev-Bashkin effect.",
        "positive": "Modeling the adiabatic creation of ultracold, polar\n  $\\mathrm{^{23}Na^{40}K}$ molecules: In this work we model and realize stimulated Raman adiabatic passage (STIRAP)\nin the diatomic $\\mathrm{^{23}Na^{40}K}$ molecule from weakly bound Feshbach\nmolecules to the rovibronic ground state via the\n$\\left|v_d=5,J=\\Omega=1\\right\\rangle$ excited state in the $d^3\\Pi$ electronic\npotential. We demonstrate how to set up a quantitative model for polar molecule\nproduction by taking into account the rich internal structure of the molecules\nand the coupling laser phase noise. We find excellent agreement between the\nmodel predictions and the experiment, demonstrating the applicability of the\nmodel in the search of an ideal STIRAP transfer path. In total we produce 5000\nfermionic groundstate molecules. The typical phase-space density of the sample\nis 0.03 and induced dipole moments of up to 0.54 Debye could be observed."
    },
    {
        "anchor": "Antiferromagnetic Interorbital Spin-Exchange Interaction of $^{171}$Yb: We report on the investigation of the scattering properties between the\nground state $^1S_0$ and the metastable state $^3P_0$ of the fermionic isotope\nof $^{171}$Yb. We successfully measure the $s$-wave scattering lengths in the\ntwo-orbital collision channels as $a_{eg}^+=225(13)a_0$ and\n$a_{eg}^-=355(6)a_0$, using the clock transition spectroscopy in a\nthree-dimensional optical lattice. The result shows that the interorbital\nspin-exchange interaction is antiferromagnetic, indicating that $^{171}$Yb atom\nis a promising isotope for the quantum simulation of the Kondo effect with the\ntwo-orbital system.",
        "positive": "Boson gas in a periodic array of tubes: We report the thermodynamic properties of an ideal boson gas confined in an\ninfinite periodic array of channels modeled by two, mutually perpendicular,\nKronig-Penney delta-potentials. The particle's motion is hindered in the x-y\ndirections, allowing tunneling of particles through the walls, while no\nconfinement along the z direction is considered. It is shown that there exists\na finite Bose- Einstein condensation (BEC) critical temperature Tc that\ndecreases monotonically from the 3D ideal boson gas (IBG) value $T_{0}$ as the\nstrength of confinement $P_{0}$ is increased while keeping the channel's cross\nsection, $a_{x}a_{y}$ constant. In contrast, Tc is a non-monotonic function of\nthe cross-section area for fixed $P_{0}$. In addition to the BEC cusp, the\nspecific heat exhibits a set of maxima and minima. The minimum located at the\nhighest temperature is a clear signal of the confinement effect which occurs\nwhen the boson wavelength is twice the cross-section side size. This\nconfinement is amplified when the wall strength is increased until a\ndimensional crossover from 3D to 1D is produced. Some of these features in the\nspecific heat obtained from this simple model can be related, qualitatively, to\nat least two different experimental situations: $^4$He adsorbed within the\ninterstitial channels of a bundle of carbon nanotubes and\nsuperconductor-multistrand-wires Nb$_{3}$Sn."
    },
    {
        "anchor": "Weakly linked binary mixtures of F=1 87-Rb Bose-Einstein condensates: We present a study of binary mixtures of Bose-Einstein condensates confined\nin a double-well potential within the framework of the mean field\nGross-Pitaevskii equation. We reexamine both the single component and the\nbinary mixture cases for such a potential, and we investigate in which\nsituations a simpler two-mode approach leads to an accurate description of\ntheir dynamics. We also estimate the validity of the most usual dimensionality\nreductions used to solve the Gross-Pitaevskii equations. To this end, we\ncompare both the semi-analytical two-mode approaches and the numerical\nsimulations of the 1D reductions with the full 3D numerical solutions of the\nGross-Pitaevskii equation. Our analysis provides a guide to clarify the\nvalidity of several simplified models that describe mean field non-linear\ndynamics, using an experimentally feasible binary mixture of an F=1 spinor\ncondensate with two of its Zeeman manifolds populated, m=+1 and m=-1.",
        "positive": "Parity oscillations and photon correlation functions in the $ Z_2/U(1) $\n  Dicke model at a finite number of atoms or qubits: In this work, by using the strong coupling expansion and exact diagonization\n(ED), we study the $ Z_2/U(1) $ Dicke model with independent rotating wave (RW)\ncoupling $ g $ and counter-rotating wave (CRW) coupling $ g^{\\prime} $ at a\nfinite $ N $.\n  This model includes the four standard quantum optics model: Rabi, Dicke,\nJaynes-Cummings ( JC ) and Tavis-Cummings (TC) model as its various special\nlimits. We show that in the super-radiant phase, the system's energy levels are\ngrouped into doublets with even and odd parity.\n  Any anisotropy $ \\beta=g/g^{\\prime} \\neq 1 $ leads to the oscillation of\nparities in both the ground and excited doublets as the atom-photon coupling\nstrength increases.\n  The oscillations will be pushed to the infinite coupling strength in the\nisotropic $ Z_2 $ limit $ \\beta=1 $.\n  We find nearly perfect agreements between the strong coupling expansion and\nthe ED in the super-radiant regime.\n  We also compute the photon correlation functions, squeezing spectrum, number\ncorrelation functions which can be measured by various standard optical\ntechniques."
    },
    {
        "anchor": "Classifying the universal coarsening dynamics of a quenched\n  ferromagnetic condensate: Scale invariance and self-similarity in physics provide a unified framework\nto classify phases of matter and dynamical properties of near-equilibrium\nsystems. However, extending this framework to far-from-equilibrium quantum\nmany-body systems and categorizing their dynamics have remained a major\nchallenge in physics. Here, we report on the first classification of universal\ncoarsening dynamics in a quenched two-dimensional ferromagnetic spinor Bose\ngas. We observe spatiotemporal scaling of spin correlation functions with\ndistinguishable scaling exponents, $1/z=0.58(2)$ and $1/z=0.43(2)$,\ncharacteristic, respectively, of binary and diffusive fluids. We find the\nuniversality class of the coarsening dynamics are determined by the symmetry of\nthe order parameters and the annihilation dynamics of the topological defects.\nThese observations are in excellent agreement with many-body simulations. Our\nresults represent a paradigmatic example of categorizing far-from-equilibrium\ndynamics in quantum many-body systems.",
        "positive": "Topological Devil's staircase in atomic two-leg ladders: We show that a hierarchy of topological phases in one dimension -- a\ntopological Devil's staircase -- can emerge at fractional filling fractions in\ninteracting systems, whose single-particle band structure describes a\ntopological or a crystalline topological insulator. Focusing on a specific\nexample in the BDI class, we present a field-theoretical argument based on\nbosonization that indicates how the system, as a function of the filling\nfraction, hosts a series of density waves. Subsequently, based on a numerical\ninvestigation of the low-lying energy spectrum, Wilczek-Zee phases, and\nentanglement spectra, we show that they are symmetry protected topological\nphases. In sharp contrast to the non-interacting limit, these topological\ndensity waves do not follow the bulk-edge correspondence, as their edge modes\nare gapped. We then discuss how these results are immediately applicable to\nmodels in the AIII class, and to crystalline topological insulators protected\nby inversion symmetry. Our findings are immediately relevant to cold atom\nexperiments with alkaline-earth atoms in optical lattices, where the band\nstructure properties we exploit have been recently realized."
    },
    {
        "anchor": "Probing magnetic order in ultracold lattice gases: A forthcoming challenge in ultracold lattice gases is the simulation of\nquantum magnetism. That involves both the preparation of the lattice atomic gas\nin the desired spin state and the probing of the state. Here we demonstrate how\na probing scheme based on atom-light interfaces gives access to the order\nparameters of nontrivial quantum magnetic phases, allowing us to characterize\nunivocally strongly correlated magnetic systems produced in ultracold gases.\nThis method, which is also nondemolishing, yields spatially resolved spin\ncorrelations and can be applied to bosons or fermions. As a proof of principle,\nwe apply this method to detect the complete phase diagram displayed by a chain\nof (rotationally invariant) spin-1 bosons.",
        "positive": "Pseudopotential for the 2D contact interaction: We propose a smooth pseudopotential for the contact interaction acting\nbetween ultracold atoms confined to two dimensions. The pseudopotential\nreproduces the scattering properties of the repulsive contact interaction up to\n200 times more accurately than a hard disk potential, and in the attractive\nbranch gives a 10-fold improvement in accuracy over the square well potential.\nFurthermore, the new potential enables diffusion Monte Carlo simulations of the\nultracold gas to be run 15 times quicker than was previously possible."
    },
    {
        "anchor": "Dimensional crossover in a strongly interacting ultracold atomic Fermi\n  gas: We theoretically explore the crossover from three dimensions (3D) to two (2D)\nin a strongly interacting atomic Fermi superfluid through confining the\ntransverse spatial dimension. Using the gaussian pair fluctuation theory, we\ndetermine the zero-temperature equation of state and Landau critical velocity\nas functions of the spatial extent of the transverse dimension and interaction\nstrength. In the presence of strong interactions, we map out a dimensional\ncrossover diagram from the location of maximum critical velocity, which\nexhibits distinct dependence on the transverse dimension from 2D to quasi-2D,\nand to 3D. We calculate the dynamic structure factor to characterize the\nlow-energy excitations of the system and propose that the intermediate quasi-2D\nregime can be experimentally probed using Bragg spectroscopy.",
        "positive": "Free Fock parafermions in the tight-binding model with dissipation: Parafermions that generalize (Majorana or usual) fermions appear as\ninteracting quasi-particles because of their nature. Although attempts to\ndevelop models with free (non-interacting) parafermions have been undertaken,\nexisting proposals require unphysical conditions such as realizing purely\nnon-Hermitian systems. Here we present a way for the realization of free Fock\nparafermions in the tight-binding model with controlled dissipation of a very\nsimple form. Introducing dissipation transforms an originally non-integrable\nquantum model to an exactly solvable classical one."
    },
    {
        "anchor": "A primer on quantum fluids: This book introduces the theoretical description and properties of quantum\nfluids. The focus is on gaseous atomic Bose-Einstein condensates and, to a\nminor extent, superfluid helium, but the underlying concepts are relevant to\nother forms of quantum fluids such as polariton and photonic condensates. The\nbook is pitched at the level of advanced undergraduates and early postgraduate\nstudents, aiming to provide the reader with the knowledge and skills to develop\ntheir own research project on quantum fluids. Indeed, the content for this book\ngrew from introductory notes provided to our own research students. It is\nassumed that the reader has prior knowledge of undergraduate mathematics and/or\nphysics; otherwise, the concepts are introduced from scratch, often with\nreferences for directed further reading.",
        "positive": "Analytical and numerical study of dirty bosons in a\n  quasi-one-dimensional harmonic trap: The emergence of a Bose-glass region in a quasi one-dimensional\nBose-Einstein-condensed gas in a harmonic trapping potential with an additional\ndelta-correlated disorder potential at zero temperature is studied using three\napproaches. At first, the corresponding time-independent Gross-Pitaevskii\nequation is numerically solved for the condensate wave function, and disorder\nensemble averages are evaluated. In particular, we analyse quantitatively the\nemergence of mini-condensates in the local minima of the random potential,\nwhich occurs for weak disorder preferentially at the border of the condensate,\nwhile for intermediate disorder strength this happens in the trap centre.\nSecond, in view of a more detailed physical understanding of this phenomenon,\nwe extend a quite recent non-perturbative approach towards the weakly\ninteracting dirty boson problem, which relies on the Hartree-Fock theory and is\nworked out on the basis of the replica method, from the homogeneous case to a\nharmonic confinement. Finally, in the weak disorder regime we also apply the\nThomas-Fermi approximation, while in the intermediate disorder regime we\nadditionally use a variational ansatz in order to describe analytically the\nnumerically observed redistribution of the fragmented mini-condensates with\nincreasing disorder strength."
    },
    {
        "anchor": "Supersolid with nontrivial topological spin textures in\n  spin-orbit-coupled Bose gases: Supersolid is a long-sought exotic phase of matter, which is characterized by\nthe coexistence of a diagonal long-range order of solid and an off-diagonal\nlong-range order of superfluid. Possible candidates to realize such a phase\nhave been previously considered, including hard-core bosons with long-range\ninteraction and soft-core bosons. Here we demonstrate that an ultracold atomic\ncondensate of hard-core bosons with contact interaction can establish a\nsupersolid phase when simultaneously subjected to spin-orbit coupling and a\nspin-dependent periodic potential. This supersolid phase is accompanied by\ntopologically nontrivial spin textures, and is signaled by the separation of\nmomentum distribution peaks, which can be detected via time-of-flight\nmeasurements. We also discuss possibilities to produce and observe the\nsupersolid phase for realistic experimental situations.",
        "positive": "The rise and fall of patterns in driven-dissipative Rydberg polaritons: Spatial structures commonly emerge in interacting nonlinear systems. In this\nstudy, we focus on the out-of-equilibrium dynamics of the recently-established\nplatform of Rydberg exciton-polaritons, fueled by their characteristic\nlong-range non-local interactions, in the presence of an external drive and\ndissipation. Our work elucidates how modulational instability sets off\nspontaneous density pattern formations in a Rydberg polariton system with\ncharacteristic scales in the micron range. Under conditions of an unstable\nflattop state, we track the evolution of the polariton ensemble, showing the\nemergence of meta-stable patterns and their collapse in the long-time limit. We\ntrace this phenomenon back to the destructive interference between the\npolariton state and the pump in a driven ensemble. Finally, we map out\nconditions that allow stable patterns to form under incoherent pumping. These\nfindings provide new opportunities for exploring the emerging field of\nlong-range interacting gases through Rydberg exciton-polaritons."
    },
    {
        "anchor": "Ultracold spin-balanced fermionic quantum liquids with renormalized\n  $P$-wave interactions: We consider a spin-balanced degenerate gas of spin-1/2 fermions whose\ndynamics is governed by low-energy $P$-wave interactions, characterized by the\nscattering volume $a_1$ and effective momentum $r_1$. The energy per particle\n$\\bar{\\cal{E}}$ in the many-body system is calculated by resumming the ladder\ndiagrams comprising both particle-particle and hole-hole intermediate states,\nfollowing the novel advances recently developed by us in Ann.Phys.\n437,168741(2022). This allows to obtain a renormalized result for\n$\\bar{\\cal{E}}$ within generic cutoff regularization schemes, with\n$\\bar{\\cal{E}}$ directly expressed in terms of the scattering parameters $a_1$\nand $r_1$, once the cut off is sent to infinity. The whole set of possible\nvalues of $a_1$ and $r_1$ is explored for the first time in the literature\nlooking for minima in the energy per particle with $\\bar{\\cal{E}}$ given as\ndescribed. They are actually found, but a further inspection reveals that the\nassociated scattering parameters give rise to resonance poles in the complex\nmomentum-plane with positive imaginary part, which is at odds with the\nHermiticity of the Hamiltonian. We also determine that these conflictive poles,\nwith a pole-position momentum that is smaller in absolute value than the Fermi\nmomentum of the system, clearly impact the calculation of $\\bar{\\cal{E}}$. As a\nresult, we conclude that unpolarized spin-1/2 fermionic normal matter\ninteracting in $P$-wave is not stable. We also study three universal parameters\naround the unitary limit. Finally, the whole set of values for the parameters\n$a_1$, $r_1$ is characterized according to whether they give rise to unallowed\npoles and, if so, by attending to their pole positions relative to the Fermi\nmomentum of the system explored.",
        "positive": "A toy model for the dipolar-induced resonance in quasi-one-dimensional\n  systems: We discuss the properties of the effective dipolar interaction for two\nparticles tightly confined along a one-dimensional tube, stressing the\nemergence of a single dipolar-induced resonance in a regime for which two\nclassical dipoles would just repel each other. We present a toy-model potential\nreproducing the main features of the effective interaction: a non-zero-range\nrepulsive potential competing with an attractive contact term. The existence of\na single resonance is confirmed analytically. The toy model is than generalized\nto investigate the interplay between dipolar and contact interaction, giving an\nintuitive interpretation of the resonance mechanism."
    },
    {
        "anchor": "Traveling Dark Solitons in Superfluid Fermi Gases: Families of dark solitons exist in superfluid Fermi gases. The\nenergy-velocity dispersion and number of depleted particles completely\ndetermines the dynamics of dark solitons on a slowly-varying background\ndensity. For the unitary Fermi gas we determine these relations from general\nscaling arguments and conservation of local particle number. We find solitons\nto oscillate sinusoidally at the trap frequency reduced by a factor of\n$1/\\sqrt{3}$. Numerical integration of the time-dependent Bogoliubov-de Gennes\nequation determines spatial profiles and soliton dispersion relations across\nthe BEC-BCS crossover and proves consistent with the scaling relations at\nunitarity.",
        "positive": "Quantum dynamics of attractive versus repulsive bosonic Josephson\n  junctions: Bose-Hubbard and full-Hamiltonian results: The quantum dynamics of one-dimensional bosonic Josephson junctions with\nattractive and repulsive interparticle interactions is studied using the\nBose-Hubbard model and by numerically-exact computations of the full many-body\nHamiltonian. A symmetry present in the Bose-Hubbard Hamiltonian dictates an\nequivalence between the evolution in time of attractive and repulsive Josephson\njunctions with attractive and repulsive interactions of equal magnitude. The\nfull many-body Hamiltonian does not possess this symmetry and consequently the\ndynamics of the attractive and repulsive junctions are different."
    },
    {
        "anchor": "Free expansion of a Bose-Einstein condensate at the presence of a\n  thermal cloud: We investigate numerically the free-fall expansion of a $^{87}$Rb atoms\ncondensate at nonzero temperatures. The classical field approximation is used\nto separate the condensate and the thermal cloud during the expansion. We\ncalculate the radial and axial widths of the expanding condensate and find\nclear evidence that the thermal component changes the dynamics of the\ncondensate. Our results are confronted against the experimental data.",
        "positive": "Quantum phase transitions to superfluid state of chains in a polarized\n  gas of dipolar molecules: We analyze the nature of quantum phase transition to a superfluid state of\nflexible chains in a gas of polar bosonic molecules confined in a stack of $N$\nidentical 1d (\"cigar\" type) optical lattice layers and polarized\nperpendicularly to the layers. Monte Carlo simulations within the $J$-current\nmodel show that, in the absence of the inter-tube tunneling, the transition to\nthe $N$-layered superfluid is in the Berezinskii-Kosterlitz-Thouless\nuniversality class in the one-particle density matrix channel. The inter-layer\ntunneling changes it to the $q=N$ 2d Potts universality. The low energy field\ndescriptions of the transition are discussed in terms of conformal field\ntheories."
    },
    {
        "anchor": "Efficient Production of Large 39K Bose-Einstein Condensates: We describe an experimental setup and the cooling procedure for producing 39K\nBose-Einstein condensates of over 4x10^5 atoms. Condensation is achieved via a\ncombination of sympathetic cooling with 87Rb in a\nquadrupole-Ioffe-configuration (QUIC) magnetic trap, and direct evaporation in\na large volume crossed optical dipole trap, where we exploit the broad Feshbach\nresonance at 402 G to tune the 39K interactions from weak and attractive to\nstrong and repulsive. In the same apparatus we create quasi-pure 87Rb\ncondensates of over 8x10^5 atoms.",
        "positive": "Line of Dirac monopoles embedded in a Bose-Einstein condensate: The gauge field of a uniform line of magnetic monopoles is created using a\nsingle Laguerre-Gauss laser mode and a gradient in the physical magnetic field.\nWe study the effect of these monopoles on a Bose condensed atomic gas, whose\nvortex structure transforms when more than six monopoles are trapped within the\ncloud. Finally, we study this transition with the collective modes."
    },
    {
        "anchor": "Feshbach spectroscopy and analysis of the interaction potentials of\n  ultracold sodium: We have studied magnetic Feshbach resonances in an ultracold sample of Na\nprepared in the absolute hyperfine ground state. We report on the observation\nof three s-, eight d-, and three g-wave Feshbach resonances, including a more\nprecise determination of two known s-wave resonances, and one s-wave resonance\nat a magnetic field exceeding 200mT. Using a coupled-channels calculation we\nhave improved the sodium ground-state potentials by taking into account these\nnew experimental data, and derived values for the scattering lengths. In\naddition, a description of the molecular states leading to the Feshbach\nresonances in terms of the asymptotic-bound-state model is presented.",
        "positive": "Self-trapping dynamics in a 2D optical lattice: We describe theoretical models for the recent experimental observation of\nMacroscopic Quantum Self-Trapping (MQST) in the transverse dynamics of an\nultracold bosonic gas in a 2D lattice. The pure mean-field model based on the\nsolution of coupled nonlinear equations fails to reproduce the experimental\nobservations. It greatly overestimates the initial expansion rates at short\ntimes and predicts a slower expansion rate of the cloud at longer times. It\nalso predicts the formation of a hole surrounded by a steep square fort-like\nbarrier which was not observed in the experiment. An improved theoretical\ndescription based on a simplified Truncated Wigner Approximation (TWA), which\nadds phase and number fluctuations in the initial conditions, pushes the\ntheoretical results closer to the experimental observations but fails to\nquantitatively reproduce them. An explanation of the delayed expansion as a\nconsequence of a new type of self-trapping mechanism, where quantum\ncorrelations suppress tunneling even when there are no density gradients, is\ndiscussed and supported by numerical time-dependent Density Matrix\nRenormalization Group (t-DMRG) calculations performed in a simplified two\ncoupled tubes set-up."
    },
    {
        "anchor": "Laser-induced Kondo effect in ultracold alkaline-earth fermions: We demonstrate that laser excitations can coherently induce a novel Kondo\neffect in ultracold atoms in optical lattices. Using a model of alkaline-earth\nfermions with two orbitals, it is shown that the optically coupled two internal\nstates are dynamically entangled to form the Kondo-singlet state, overcoming\nthe heating effect due to the irradiation. Furthermore, a lack of SU($N$)\nsymmetry in the optical coupling provides a peculiar feature in the Kondo\neffect, which results in spin-selective renormalization of effective masses. We\nalso discuss effects of interorbital exchange interactions, and reveal that\nthey induce novel crossover or reentrant behavior of the Kondo effect owing to\ncontrol of the coupling anisotropy. The laser-induced Kondo effect is highly\ncontrollable by tuning the laser strength and the frequency, and thus offers a\nversatile platform to study the Kondo physics using ultracold atoms.",
        "positive": "Wigner Crystallization of Rotating Dipolar Fermions in the Fractional\n  Quantum Hall Regime: We show the possible existence of the Wigner crystal (WC) in the Fractional\nQuantum Hall (FQH) regime. We find that the Landau-level mixing (LLM) will\nlower the energy of the WC significantly in the high-density regime. The WC is\nlower in energy than the FQH liquid in the high-density regime. We conclude\nthat the crystal phase is expected at high density for rotating dipolar gases,\nwhich is consistent with non-rotating dipolar gases, but is inconsistent with\nthe low-density conclusion from Baranov et al. [Phys. Rev. Lett. 100, 200402\n(2008)], where the effect of LLM is ignored."
    },
    {
        "anchor": "Relaxation dynamics of interacting bosons in a flat band system: Quantum many-body systems are expected to relax to a thermal state over time,\nwith some exceptions such as systems with atypical eigenstates. In this study,\nwe investigate the effect of the existence of spatially localized eigenstates\non the relaxation dynamics of interacting bosons loaded into a one-dimensional\nsawtooth lattice, which exhibits a flat band in the single-particle spectrum by\ntuning the hopping rates. Using the time-evolving block decimation algorithm,\nwe simulate the time evolution of the local density profile based on the\nBose-Hubbard model with different initial conditions. Our results show the\npresence of the flat band leads to a significant slowing down of diffusion for\nweak interactions. Even for strong interaction, when the initial state includes\nan isolated localized single-particle eigenstate in the superposition, remnants\nof that state persist for a long time. This particular relaxation dynamics can\nbe tested using ultracold atoms in optical lattices.",
        "positive": "Effect of spin-orbit interaction on the critical temperature of an ideal\n  Bose gas: We consider Bose-Einstein condensation of an ideal bose gas with an equal\nmixture of `Rashba' and `Dresselhaus' spin-orbit interactions and study its\neffect on the critical temperature.\n  In uniform bose gas a `cusp' and a sharp drop in the critical temperature\noccurs due to the change in the density of states at a critical Raman coupling\nwhere the degeneracy of the ground states is lifted. Relative drop in the\ncritical temperature depends on the diluteness of the gas as well as on the\nspin-orbit coupling strength. In the presence of a harmonic trap, the cusp in\nthe critical temperature smoothened out and a minimum appears. Both the drop in\nthe critical temperature and lifting of `quasi-degeneracy' of the ground states\nexhibit crossover phenomena which is controlled by the trap frequency. By\nconsidering a 'Dicke' like model we extend our calculation to bosons with large\nspin and observe a similar minimum in the critical temperature near the\ncritical Raman frequency, which becomes deeper for larger spin. Finally in the\nlimit of infinite spin, the critical temperature vanishes at the critical\nfrequency, which is a manifestation of Dicke type quantum phase transition."
    },
    {
        "anchor": "Quench dynamics of dipolar fermions in a one-dimensional harmonic trap: We study a system of few fermions in a one-dimensional harmonic trap, and\nfocus on the case of dipolar majority particles in contact with a single\nimpurity. The impurity is used both for quenching the system, and for tracking\nthe system evolution after the quench. Employing exact diagonalization, we\ninvestigate relaxation and thermalization properties. In the absence of dipolar\ninteractions, the system is near integrability, and the dynamics remains\noscillatory even on long time scales. On the other hand, repulsive as well as\nattractive dipolar interactions lead to quick relaxation to the diagonal\nensemble average which is significantly different from corresponding thermal\naverages. A Wigner-shaped level spacing distribution indicates level repulsion\nand thus chaotic dynamical behavior due to the presence of dipolar\ninteractions.",
        "positive": "An ytterbium quantum gas microscope with narrow-line laser cooling: We demonstrate site-resolved imaging of individual bosonic\n$^{174}\\mathrm{Yb}$ atoms in a Hubbard-regime two-dimensional optical lattice\nwith a short lattice constant of 266 nm. To suppress the heating by probe light\nwith the $^1S_0$-$^1P_1$ transition of the wavelength $\\lambda$ = 399 nm for\nhigh-resolution imaging and preserve atoms at the same lattice sites during the\nfluorescence imaging, we simultaneously cool atoms by additionally applying\nnarrow-line optical molasses with the $^1S_0$-$^3P_1$ transition of the\nwavelength $\\lambda$ = 556 nm. We achieve a low temperature of $T = 7.4(1.3)\\\n\\mu\\mathrm{K}$, corresponding to a mean oscillation quantum number along the\nhorizontal axes of 0.22(4) during imaging process. We detect on average 200\nfluorescence photons from a single atom within 400 ms exposure time, and\nestimate the detection fidelity of 87(2)%. The realization of a quantum gas\nmicroscope with enough fidelity for Yb atoms in a Hubbard-regime optical\nlattice opens up the possibilities for studying various kinds of quantum\nmany-body systems such as Bose and Fermi gases, and their mixtures, and also\nlong-range-interacting systems such as Rydberg states."
    },
    {
        "anchor": "Pattern formation of correlated impurities subjected to an\n  impurity-medium interaction pulse: We study the correlated dynamics of few interacting bosonic impurities\nimmersed in a one-dimensional harmonically trapped bosonic environment. The\nmixture is exposed to a time-dependent impurity-medium interaction pulse moving\nit across the relevant phase separation boundary. For modulation frequencies\nsmaller than the trapping one, the system successively transits through the\nmiscible/immiscible phases according to the driving of the impurity-medium\ninteractions. For strong modulations, and driving from the miscible to the\nimmiscible regime, a significant fraction of the impurities is expelled to the\nedges of the bath. They exhibit a strong localization behavior and tend to\nequilibrate. Following the reverse driving protocol, the impurities perform a\nbreathing motion while featuring a two-body clustering and the bath is split\ninto two incoherent parts. Interestingly, in both driving scenarios,\ndark-bright solitons are nucleated in the absence of correlations. A\nlocalization of the impurities around the trap center for weak\nimpurity-impurity repulsions is revealed, which subsequently disperse into the\nbath for increasing interactions.",
        "positive": "Static impurities in a weakly-interacting Bose gas: We present a comprehensive discussion of the ground-state properties of\ndilute $D$-dimensional Bose gas interacting with a few static impurities.\nAssuming the short-ranged character of the boson-impurity interaction, we\ncalculate the energy of three- and two-dimensional Bose systems with one and\ntwo impurities immersed."
    },
    {
        "anchor": "Pseudo-gap pairing in ultracold Fermi atoms: The crossover from a BEC (Bose-Einstein condensation) to a BCS\n(Bardeen-Cooper-Schrieffer) superfluid in dilute gases of ultracold Fermi atoms\ncreates an ideal environment to enrich our knowledge of strongly correlated\nmany-body systems. These experiments are relevant to a wide range of fields\nfrom condensed matter to astrophysics. The nature of pairing in strongly\ninteracting Fermi gases can be readily studied, thus aiding our understanding\nof related problems in high-T_{c} superconductors, whose mechanism is still\nunder debate. These are not well-understood due to the large interaction\nparameter. Here, we calculate the dynamical properties of a normal, trapped,\nand strongly correlated Fermi gas, by developing a quantum cluster expansion.\nIn ultra-cold atomic physics one can measure the elementary excitations, using\nrf or Bragg spectroscopy. Our calculations for the single-particle spectral\nfunction agree with the recent measurements, and clearly demonstrate pseudogap\npairing in the strongly interacting regime.",
        "positive": "Spectroscopic observation of SU(N)-symmetric interactions in Sr orbital\n  magnetism: SU(N) symmetry can emerge in a quantum system with N single-particle spin\nstates when spin is decoupled from inter-particle interactions. So far, only\nindirect evidence for this symmetry exists, and the scattering parameters\nremain largely unknown. Here we report the first spectroscopic observation of\nSU(N=10) symmetry in Sr-87 using the state-of-the-art measurement precision\noffered by an ultra-stable laser. By encoding the electronic orbital degree of\nfreedom in two clock states, while keeping the system open to 10 nuclear spin\nsublevels, we probe the non-equilibrium two-orbital SU(N) magnetism via Ramsey\nspectroscopy of atoms confined in an array of two-dimensional optical traps. We\nstudy the spin-orbital quantum dynamics and determine all relevant interaction\nparameters. This work prepares for using alkaline-earth atoms as test-beds for\niconic orbital models."
    },
    {
        "anchor": "Ultra-cold bosons in zig-zag optical lattices: Ultra-cold bosons in zig-zag optical lattices present a rich physics due to\nthe interplay between frustration, induced by lattice geometry, two-body\ninteraction and three-body constraint. Unconstrained bosons may develop chiral\nsuperfluidity and a Mott-insulator even at vanishingly small interactions.\nBosons with a three-body constraint allow for a Haldane-insulator phase in\nnon-polar gases, as well as pair-superfluidity and density wave phases for\nattractive interactions. These phases may be created and detected within the\ncurrent state of the art techniques.",
        "positive": "Compressibility and the Equation of State of an Optical Quantum Gas in a\n  Box: The compressibility of a medium, quantifying its response to mechanical\nperturbations, is a fundamental property determined by the equation of state.\nFor gases of material particles, studies of the mechanical response are well\nestablished, in fields from classical thermodynamics to cold atomic quantum\ngases. Here we demonstrate a measurement of the compressibility of a\ntwo-dimensional quantum gas of light in a box potential and obtain the equation\nof state for the optical medium. The experiment is carried out in a\nnanostructured dye-filled optical microcavity. We observe signatures of\nBose-Einstein condensation at high phase-space densities in the finite-size\nsystem. Strikingly, upon entering the quantum degenerate regime, the measured\ndensity response to an external force sharply increases, hinting at the\npeculiar prediction of an infinite compressibility of the deeply degenerate\nBose gas."
    },
    {
        "anchor": "Bose-Einstein condensation temperature of weakly interacting atoms: The critical temperature of Bose-Einstein condensation essentially depends on\ninternal properties of the system as well as on the geometry of a trapping\npotential. The peculiarities of defining the phase transition temperature of\nBose-Einstein condensation for different systems are reviewed, including\nhomogenous Bose gas, trapped Bose atoms, and bosons in optical lattices. The\nmethod of self-similar approximants, convenient for calculating critical\ntemperature, is briefly delineated.",
        "positive": "Vortices in Bose-Einstein condensates - finite-size effects and the\n  thermodynamic limit: For a weakly-interacting Bose gas rotating in a harmonic trap we relate the\nyrast states of small systems (that can be treated exactly) to the\nthermodynamic limit (derived within the mean-field approximation). For a few\ndozens of atoms, the yrast line shows distinct quasi-periodic oscillations with\nincreasing angular momentum that originate from the internal structure of the\nexact many-body states. These finite-size effects disappear in the\nthermodynamic limit, where the Gross-Pitaevskii approximation provides the\nexact energy to leading order in the number of particles N. However, the exact\nyrast states reveal significant structure not captured by the mean-field\napproximation: Even in the limit of large N, the corresponding mean-field\nsolution accounts for only a fraction of the total weight of the exact quantum\nstate."
    },
    {
        "anchor": "Miscibility regimes in a $^{23}$Na-$^{39}$K quantum mixture: Effects of miscibility in interacting two-component classical fluids are\nrelevant in a broad range of daily applications. When considering quantum\nsystems, two-component Bose-Einstein condensates provides a well controlled\nplatform where the miscible-immiscible phase transition can be completely\ncharacterized. In homogeneous systems, this phase transition is governed only\nby the competition between intra- and inter-species interactions. However in\nmore conventional experiments dealing with trapped gases, the pressure of the\nconfinement increases the role of the kinetic energy and makes the system more\nmiscible. In the most general case, the miscibility phase diagram of unbalanced\nmixtures of different atomic species is strongly modified by the atom number\nratio and the different gravitational sags. Here, we numerically investigate\nthe ground-state of a $^{23}$Na-$^{39}$K quantum mixture for different\ninteraction strengths and atom number ratios considering realistic experimental\nparameters. Defining the spatial overlap between the resulting atomic clouds,\nwe construct the phase diagram of the miscibility transition which could be\ndirectly measured in real experiments.",
        "positive": "A note on Fermi energy of Fermi gas trapped under generic power law\n  potential in $d$-dimension: Average energy per fermion in case of Fermi gas with any kinematic\ncharacteristic, trapped under most general power law potential in $d$ dimension\nhas been calculated at zero temperature. In a previous paper (M. Acharyya, Eur.\nJ Phys. 31 L89 (2010)) it was shown, in case of free ideal Fermi gas as\ndimension increases average energy approaches to Fermi energy and in infinite\ndimension average energy becomes equal to Fermi energy at $T=0$. In this letter\nit is shown that, for trapped system at finite dimension the average energy\ndepends on power law exponent, but as dimension tends to infinity average\nenergy coincides with Fermi energy for any power law exponent. The result\nobtained in this manuscript is more general as we can describe free system as\nwell as any trapped system with appropriate choice of power law exponent and\ntrue for any kinematic parameter."
    },
    {
        "anchor": "Revisiting a stability problem of two-component droplets: We study the problem of the stability of a two-component droplet. The\nstandard solution known from the literature is based on a particular form of\nthe mean field energy functional, in particular on distinction of hard mode and\nsoft mode contributions. By imposing the constraint on densities of the two\nspecies which minimizes the hard mode energy, the problem is reduced to a\nstability analysis of a one component system. As opposed to this, we address\nthe issue in full generality. Our analysis is valid for arbitrary forms of\nenergy density. We formulate constraints which correspond to the physically\nrelevant situation of a system which has unconstrained volume and may evaporate\nparticles. For the specific case of a two component Bose-Bose droplet we find\napproximate analytic solutions and compare them to the standard result. We show\nthat the densities of both components of a stable droplet are limited to a\nrange depending on interaction strength, in contrast to the original unique\nsolution.",
        "positive": "Quantum states of dark solitons in the 1D Bose gas: We present a series of quantum states that are characterized by dark solitons\nof the nonlinear Schr\\\"{o}dinger equation (i.e. the Gross-Pitaevskii equation)\nfor the one-dimensional (1D) Bose gas interacting through the repulsive\ndelta-function potentials. The classical solutions satisfy the periodic\nboundary conditions and we call them periodic dark solitons. Through exact\nsolutions we show corresponding aspects between the states and the solitons in\nthe weak coupling case: the quantum and classical density profiles completely\noverlap with each other not only at an initial time but also at later times\nover a long period of time, and they move together with the same speed in time;\nthe matrix element of the bosonic field operator between the quantum states has\nexactly the same profiles of the square amplitude and the phase as the\nclassical complex scalar field of a periodic dark soliton not only at the\ninitial time but also at later times, and the corresponding profiles move\ntogether for a long period of time. We suggest that the corresponding\nproperties hold rigorously in the weak coupling limit. Furthermore, we argue\nthat the lifetime of the dark soliton-like density profile in the quantum state\nbecomes infinitely long as the coupling constant approaches zero, by comparing\nit with the quantum speed limit time. Thus, we call the quantum states quantum\ndark soliton states."
    },
    {
        "anchor": "Liouvillian gap and single spin-flip dynamics in the dissipative\n  Fermi-Hubbard model: Motivated by recent progress in cold-atom experiments, we analyze the SU($N$)\nFermi-Hubbard model on a $d$-dimensional hypercubic lattice with two-body loss.\nBy focusing on states near the ferromagnetic steady states, we obtain the\nLiouvillian gap in closed form for any $d$ and $N$. We also investigate the\ndynamics of a ferromagnetic initial state with a single spin flip both\nanalytically and numerically. In particular, we show that, by decreasing the\nstrength of the interaction and loss, the survival probability of the spin flip\nexhibits a crossover from the power-law decay to the exponential decay. We\nexpect that our findings can be tested experimentally with ultracold\nalkaline-earth-like atoms in an optical lattice.",
        "positive": "Two-body state with p-wave interaction in one-dimensional waveguides\n  under transversely anisotropic confinement: We theoretically study two atoms with $p$-wave interaction in a\none-dimensional waveguide, and investigate how the transverse anisotropy of the\nconfinement affects the two-body state, especially, the properties of the\nresonance. For bound-state solution, we find there are totally three two-body\nbound states due to the richness of the orbital magnetic quantum number of\n$p$-wave interaction, while only one bound state is supported by $s$-wave\ninteraction. Two of them become nondegenerate due to the breaking of the\nrotation symmetry under transversely anisotropic confinement. For scattering\nsolution, the effective one-dimensional scattering amplitude and scattering\nlength are derived. We find the position of the $p$-wave confinement-induced\nresonance shifts apparently as the transverse anisotropy increases. In\naddition, a two-channel mechanism for confinement-induced resonance in a\none-dimensional waveguide is generalized to $p$-wave interaction, which was\nproposed only for $s$-wave interaction before. All our calculations are based\non the parameterization of the $^{40}$K atom experiments, and can be confirmed\nin future experiments."
    },
    {
        "anchor": "Pairing Superfluidity in Spin-Orbit Coupled Ultracold Fermi Gases: We review some recent progresses on the study of ultracold Fermi gases with\nsynthetic spin-orbit coupling. In particular, we focus on the pairing\nsuperfluidity in these systems at zero temperature. Recent studies have shown\nthat different forms of spin-orbit coupling in various spatial dimensions can\nlead to a wealth of novel pairing superfluidity. A common theme of these\nvariations is the emergence of new pairing mechanisms which are direct results\nof spin-orbit-coupling-modified single-particle dispersion spectra. As\ndifferent configurations can give rise to single-particle dispersion spectra\nwith drastic differences in symmetry, spin dependence and low-energy density of\nstates, spin-orbit coupling is potentially a powerful tool of quantum control,\nwhich, when combined with other available control schemes in ultracold atomic\ngases, will enable us to engineer novel states of matter.",
        "positive": "Bogoliubov spectrum and the dynamic structure factor in a\n  quasi-two-dimensional spin-orbit coupled BEC: We compute the the Bogoliubov-de-Gennes excitation spectrum in a trapped\ntwo-component spin-orbit-coupled (SOC) Bose-Einstein condensate (BEC) in\nquasi-two-dimensions as a function of linear and angular momentum and analyse\nthem. The excitation spectrum exhibits a minima-like feature at finite momentum\nfor the immiscible SOC-BEC configuration. We augment these results by computing\nthe dynamic structure factor in the density and pseudo-spin sector, and discuss\nits interesting features that can be experimentally measured through Bragg\nspectroscopy of such ultra cold-condensate."
    },
    {
        "anchor": "Critical Trap Aspect Ratios For Dipolar BEC: We show that there exists critical trap aspect ratios for a trapped\nBose-Einstein condensate with dipole-dipole interactions. We discuss the role\nof critical trap aspect ratios on both the critical angular velocity above\nwhich a vortex is energetically favorable and the precession velocity of an\noff-axis vortex in TF regime. We show that the stability diagram for a purely\ndipolar gas depends crucially on the critical trap aspect ratios both for\npositive and negative strength of dipolar interaction. We prove that the\ncritical points can be changed by an anharmonic potential.",
        "positive": "Quantum gas magnifier for sub-lattice-resolved imaging of\n  three-dimensional quantum systems: Imaging is central for gaining microscopic insight into physical systems, but\ndirect imaging of ultracold atoms in optical lattices as modern quantum\nsimulation platform suffers from the diffraction limit as well as high optical\ndensity and small depth of focus. We introduce a novel approach to imaging of\nquantum many-body systems using matter wave optics to magnify the density\ndistribution prior to optical imaging, allowing sub-lattice spacing resolution\nin three-dimensional systems. Combining the site-resolved imaging with magnetic\nresonance techniques for local addressing of individual lattice sites, we\ndemonstrate full accessibility to local information and local manipulation in\nthree-dimensional optical lattice systems. The method opens the path for\nspatially resolved studies of new quantum many-body regimes including exotic\nlattice geometries."
    },
    {
        "anchor": "Rotating a Rashba-coupled Fermi gas in two dimensions: We analyze the interplay of adiabatic rotation and Rashba spin-orbit coupling\non the BCS-BEC evolution of a harmonically-trapped Fermi gas in two dimensions\nunder the assumption that vortices are not excited. First, by taking the\ntrapping potential into account via both the semi-classical and exact\nquantum-mechanical approaches, we firmly establish the parameter regime where\nthe non-interacting gas forms a ring-shaped annulus. Then, by taking the\ninteractions into account via the BCS mean-field approximation, we study the\npair-breaking mechanism that is induced by rotation, i.e., the Coriolis\neffects. In particular, we show that the interplay allows for the possibility\nof creating either an isolated annulus of rigidly-rotating normal particles\nthat is disconnected from the central core of non-rotating superfluid pairs or\nan intermediate mediator phase where the superfluid pairs and normal particles\ncoexist as a partially-rotating gapless superfluid.",
        "positive": "Engineering of Landau-Zener tunneling: Several ways are discussed how to control the Landau-Zener tunneling in the\nWannier-Stark system. We focus on a realization of this system with interacting\nand noninteracting ultracold bosons. The tunneling from the ground band to the\ncontinuum is shown to depend crucially on the initial condition and system\nparameters and, more interestingly, on added timedependent disorder -- noise --\non the lattice beams."
    },
    {
        "anchor": "Unconventional fermionic pairing states in a monochromatically tilted\n  optical lattice: We study the one-dimensional attractive Fermionic Hubbard model under the\ninfluence of periodic driving with the time-dependent density matrix\nrenormalization group method. We show that the system can be driven into an\nunconventional pairing state characterized by a condensate made of Cooper-pairs\nwith a finite center-of-mass momentum similar to a Fulde-Ferrell state. We\nobtain results both in the laboratory and the rotating reference frames\ndemonstrating that the momentum of the condensate can be finely tuned by\nchanging the ratio between the amplitude and the frequency of the driving. In\nparticular, by quenching this ratio to the value corresponding to suppression\nof the tunnelling and the Coulomb interaction strength to zero, we are able to\n\"freeze\" the condensate. We finally study the effects of different initial\nconditions, and compare our numerical results to those obtained from a\ntime-independent Floquet theory in the large frequency regime. Our work offers\nthe possibility of engineering and controlling unconventional pairing states in\nfermionic condensates.",
        "positive": "Thermal fluctuations and quantum phase transition in antiferromagnetic\n  Bose-Einstein condensates: We develop a method for investigating nonequilibrium dynamics of an ultracold\nsystem that is initially at thermal equilibrium. Our procedure is based on the\nclassical fields approximation with appropriately prepared initial state. As an\napplication of the method, we investigate the influence of thermal fluctuations\non the quantum phase transition from an antiferromagnetic to phase separated\nground state in a spin-1 Bose-Einstein condensate of ultracold atoms. We find\nthat at temperatures significantly lower than the critical condensation\ntemperature $T_c$ the scaling law for the number of created spin defects\nremains intact."
    },
    {
        "anchor": "Infrared behavior and spectral function of a Bose superfluid at zero\n  temperature: In a Bose superfluid, the coupling between transverse (phase) and\nlongitudinal fluctuations leads to a divergence of the longitudinal correlation\nfunction, which is responsible for the occurrence of infrared divergences in\nthe perturbation theory and the breakdown of the Bogoliubov approximation. We\nreport a non-perturbative renormalization-group (NPRG) calculation of the\none-particle Green function of an interacting boson system at zero temperature.\nWe find two regimes separated by a characteristic momentum scale $k_G$\n(\"Ginzburg\" scale). While the Bogoliubov approximation is valid at large\nmomenta and energies, $|\\p|,|\\w|/c\\gg k_G$ (with $c$ the velocity of the\nBogoliubov sound mode), in the infrared (hydrodynamic) regime $|\\p|,|\\w|/c\\ll\nk_G$ the normal and anomalous self-energies exhibit singularities reflecting\nthe divergence of the longitudinal correlation function. In particular, we find\nthat the anomalous self-energy agrees with the Bogoliubov result\n$\\Sigan(\\p,\\w)\\simeq\\const$ at high-energies and behaves as $\\Sigan(\\p,\\w)\\sim\n(c^2\\p^2-\\w^2)^{(d-3)/2}$ in the infrared regime (with $d$ the space\ndimension), in agreement with the Nepomnyashchii identity $\\Sigan(0,0)=0$ and\nthe predictions of Popov's hydrodynamic theory. We argue that the hydrodynamic\nlimit of the one-particle Green function is fully determined by the knowledge\nof the exponent $3-d$ characterizing the divergence of the longitudinal\nsusceptibility and the Ward identities associated to gauge and Galilean\ninvariances. The infrared singularity of $\\Sigan(\\p,\\w)$ leads to a continuum\nof excitations (coexisting with the sound mode) which shows up in the\none-particle spectral function.",
        "positive": "Fermions in Two Dimensions: Scattering and Many-Body Properties: Ultracold atomic Fermi gases in two-dimensions (2D) are an increasingly\npopular topic of research. The interaction strength between spin-up and\nspin-down particles in two-component Fermi gases can be tuned in experiments,\nallowing for a strongly interacting regime where the gas properties are yet to\nbe fully understood. We have probed this regime for 2D Fermi gases by\nperforming T=0 ab initio diffusion Monte Carlo calculations. The many-body\ndynamics are largely dependent on the two-body interactions, therefore we start\nwith an in-depth look at scattering theory in 2D. We show the partial-wave\nexpansion and its relation to the scattering length and effective range. Then\nwe discuss our numerical methods for determining these scattering parameters.\nWe close out this discussion by illustrating the details of bound states in 2D.\nTransitioning to the many-body system, we use variationally optimized wave\nfunctions to calculate ground-state properties of the gas over a range of\ninteraction strengths. We show results for the energy per particle and\nparametrize an equation of state. We then proceed to determine the chemical\npotential for the strongly interacting gas."
    },
    {
        "anchor": "Vortex nucleation as a case study of symmetry breaking in quantum\n  systems: Mean-field methods are a very powerful tool for investigating weakly\ninteracting many-body systems in many branches of physics. In particular, they\ndescribe with excellent accuracy trapped Bose-Einstein condensates. A generic,\nbut difficult question concerns the relation between the symmetry properties of\nthe true many-body state and its mean-field approximation. Here, we address\nthis question by considering, theoretically, vortex nucleation in a rotating\nBose-Einstein condensate. A slow sweep of the rotation frequency changes the\nstate of the system from being at rest to the one containing one vortex. Within\nthe mean-field framework, the jump in symmetry occurs through a turbulent phase\naround a certain critical frequency. The exact many-body ground state at the\ncritical frequency exhibits strong correlations and entanglement. We believe\nthat this constitutes a paradigm example of symmetry breaking in - or change of\nthe order parameter of - quantum many-body systems in the course of adiabatic\nevolution.",
        "positive": "Observation of shock waves in a large Bose-Einstein condensate: We observe the formation of shock waves in a Bose-Einstein condensate\ncontaining a large number of sodium atoms. The shock wave is initiated with a\nrepulsive, blue-detuned light barrier, intersecting the BEC, after which two\nshock fronts appear. We observe breaking of these waves when the size of these\nwaves approaches the healing length of the condensate. At this time, the wave\nfront splits into two parts and clear fringes appear. The experiment is modeled\nusing an effective 1D Gross-Pitaevskii-like equation and gives excellent\nquantitative agreement with the experiment, even though matter waves with\nwavelengths two orders of magnitude smaller than the healing length are\npresent. In these experiments, no significant heating or particle loss is\nobserved."
    },
    {
        "anchor": "Gr{\u00fc}neisen parameter of quantum magnets with spin gap: Using Hartree-Fock-Bogoliubov (HFB) approach we obtained analytical\nexpressions for thermodynamic quantities of the system of triplons in spin\ngapped quantum magnets such as magnetization, heat capacity and the magnetic\nGr{\\\"u}neisen parameter $\\Gamma_H$. Near the critical temperature, $\\Gamma_H$\nis discontinuous and changes its sign upon the Bose-Einstein condensation (BEC)\nof triplons. On the other hand, in the widely used Hartree-Fock-Popov (HFP)\napproach there is no discontinuity neither in the heat capacity nor in the\nGr{\\\"u}neisen parameter. We predict that in the low-temperature limit and near\nthe critical magnetic field $H_c$, $\\Gamma_H$ diverges as $\\Gamma_H\\sim\n1/T^{2}$, while it scales as $\\Gamma_H\\sim 1/(H-H_c)$ as the magnetic field\napproaches the quantum critical point at $H_c$.",
        "positive": "Quantum Criticality of one-dimensional multicomponent Fermi Gas with\n  Strongly Attractive Interaction: Quantum criticality of strongly attractive Fermi gas with $SU(3)$ symmetry in\none dimension is studied via the thermodynamic Bethe ansatz (TBA) equations.The\nphase transitions driven by the chemical potential $\\mu$, effective magnetic\nfield $H_1$, $H_2$ (chemical potential biases) are analyzed at the quantum\ncriticality. The phase diagram and critical fields are analytically determined\nby the thermodynamic Bethe ansatz equations in zero temperature limit. High\naccurate equations of state, scaling functions are also obtained analytically\nfor the strong interacting gases. The dynamic exponent $z=2$ and correlation\nlength exponent $\\nu=1/2$ read off the universal scaling form. It turns out\nthat the quantum criticality of the three-component gases involves a sudden\nchange of density of states of one cluster state, two or three cluster states.\nIn general, this method can be adapted to deal with the quantum criticality of\nmulti-component Fermi gases with $SU(N)$ symmetry."
    },
    {
        "anchor": "Disappearance of Quasiparticles in a Bose Lattice Gas: We use a momentum-space hole-burning technique implemented via stimulated\nRaman transitions to measure the momentum relaxation time for a gas of bosonic\natoms trapped in an optical lattice. By changing the lattice potential depth,\nwe observe a smooth crossover between relaxation times larger and smaller than\nthe bandwidth. The latter condition violates the Mott-Ioffe-Regal bound and\nindicates a breakdown of the quasi-particle picture. We produce a simple\nkinetic model that quantitatively predicts these relaxation times. Finally, we\nintroduce a cooling technique based upon our hole-burning technique.",
        "positive": "Dip-hump temperature dependence of Specific Heat and Effects of Pairing\n  Fluctuations in the Weak-coupling Side of a $p$-wave Interacting Fermi Gas: We investigate the specific heat $C_V$ at constant volume in the normal state\nof a $p$-wave interacting Fermi gas. Including $p$-wave pairing fluctuations\nwithin the strong-coupling theory developed by Nozi\\`eres and Schmitt-Rink, we\nshow that, in the weak-coupling side, $C_V$ exhibits a dip-hump behavior as a\nfunction of the temperature. While the dip is associated with the pseudogap\nphenomenon near $T_{\\rm c}$, the hump structure is found to come from the\nsuppression of Fermi quasiparticle scattering into a $p$-wave molecular state\nin the Fermi degenerate regime. Since the latter phenomenon does not occur in\nthe ordinary $s$-wave interacting Fermi gas, it may be viewed as a\ncharacteristic phenomenon associated with a $p$-wave pairing interaction."
    },
    {
        "anchor": "Exact ground state properties of the one-dimensional Coulomb gas: The ground state properties of a single-component one-dimensional Coulomb gas\nare investigated. We use Bose-Fermi mapping for the ground state wave function\nwhich permits to solve the Fermi sign problem in the following respects (i) the\nnodal surface is known, permitting exact calculations (ii) evaluation of\ndeterminants is avoided, reducing the numerical complexity to that of a bosonic\nsystem, thus allowing simulation of a large number of fermions. Due to the\nmapping the energy and local properties in one-dimensional Coulomb systems are\nexactly the same for Bose-Einstein and Fermi-Dirac statistics. The exact ground\nstate energy has been calculated in homogeneous and trapped geometries by using\nthe diffusion Monte Carlo method. We show that in the low-density Wigner\ncrystal limit an elementary low-lying excitation is a plasmon, which is to be\ncontrasted with the large-density ideal Fermi gas/Tonks-Girardeau limit, where\nlow lying excitations are phonons. Exact density profiles are confronted to the\nones calculated within the local density approximation which predicts a change\nfrom a semicircular to inverted parabolic shape of the density profile as the\nvalue of the charge is increased.",
        "positive": "Measuring Non-local Brane Order with Error-corrected Parity Snapshots: Exotic quantum many-body states, such as Haldane and spin liquid phases, can\nexhibit remarkable features like fractional excitations and non-abelian\nstatistics and offer new understandings of quantum entanglement in many-body\nquantum systems. These phases are classified by non-local correlators that can\nbe directly measured in atomic analog quantum simulating platforms, such as\noptical lattices and Rydberg atom arrays. However, characterizing these phases\nin large systems is experimentally challenging because they are sensitive to\nlocal errors like atom loss, which suppress its signals exponentially.\nAdditionally, protocols for systematically identifying and mitigating\nuncorrelated errors in analog quantum simulators are lacking. Here, we address\nthese challenges by developing an error correction method for large-scale\nneutral atom quantum simulators using optical lattices. Our error correction\nmethod can distinguish correlated particle-hole pairs from uncorrelated holes\nin the Mott insulator. After removing the uncorrelated errors, we observe a\ndramatic improvement in the non-local parity correlator and find the perimeter\nscaling law. Furthermore, the error model provides a statistical estimation of\nfluctuations in site occupation, from which we measure the generalized brane\ncorrelator and confirm that it can be an order parameter for Mott insulators in\ntwo dimensions. Our work provides a promising avenue for investigating and\ncharacterizing exotic phases of matters in large-scale quantum simulators."
    },
    {
        "anchor": "Spin-1 Bose Hubbard model with nearest neighbour extended interaction: We have studied a spinor (F = 1) Bose gas in presence of the density-density\ninteraction through the mean field approach and the perturbation theory for\neither sign of the spin dependent interaction, namely the antiferromagnetic\n(AF) and the ferromagnetic cases. In the AF case, the charge density wave (CDW)\nphase appears to be sandwiched between the Mott insulating (MI) and the\nsupersolid phases for small values of the extended interaction strength. But\nthe CDW phase completely occupies the MI lobe when the extended interaction\nstrength is larger than a certain critical value related to the width of the MI\nlobes and hence opens up the possibilities of spin singlet and nematic CDW\ninsulating phases. In the ferromagnetic case, the phase diagram shows similar\nfeatures as that of the AF case and are in complete agreement with a spin-0\nBose gas. The perturbation expansion calculations nicely corroborate the mean\nfield phase results in both these cases. Further, we extend our calculations in\npresence of a harmonic confinement and obtained the momentum distribution\nprofile that is related to the absorption spectra in order to distinguish\nbetween different phases.",
        "positive": "Finite-temperature trapped dipolar Bose gas: We develop a finite temperature Hartree theory for the trapped dipolar Bose\ngas. We use this theory to study thermal effects on the mechanical stability of\nthe system and density oscillating condensate states. We present results for\nthe stability phase diagram as a function of temperature and aspect ratio. In\noblate traps above the critical temperature for condensation we find that the\nHartree theory predicts significant stability enhancement over the\nsemiclassical result. Below the critical temperature we find that thermal\neffects are well described by accounting for the thermal depletion of the\ncondensate. Our results also show that density oscillating condensate states\noccur over a range of interaction strengths that broadens with increasing\ntemperature."
    },
    {
        "anchor": "Matter-waves in Bose-Einstein condensates with spin-orbit and Rabi\n  couplings: We investigate the one-dimensional (1D) and two-dimensional (2D)reduction of\na quantum field theory starting from the three-dimensional (3D) many-body\nHamiltonian of interacting bosons with spin-orbit (SO) and Rabi couplings. We\nobtain the effective time-dependent 1D and 2D nonpolynomial Heisenberg\nequations for both repulsive and attractive signs of the inter-atomic\ninteraction. Our findings show that in case in which the many-body state\ncoincides with the Glauber coherent state,the 1D and 2D Heisenberg equations\nbecome 1D and 2D nonpolynomial Schr\\\"odinger equations (NPSEs). These models\nwere derived in a mean-field approximation from 3D Gross-Pitaevskii equation\n(GPE), describing a Bose-Einstein condensate (BEC)with SO and Rabi couplings.\nIn the present work self-repulsive and self-attractive localized solutions of\nthe 1D NPSE and the 1D GPE are obtained in a numerical form. The combined\naction of SO and Rabi couplings produces conspicuous sidelobes on the density\nprofile, for both signs of the interaction. In the case of the attractive\nnonlinearity, an essential result is the possibility of getting an unstable\ncondensate by increasing of SO coupling.",
        "positive": "Universal probes for antiferromagnetic correlations and entropy in cold\n  fermions on optical lattices: We determine antiferromagnetic (AF) signatures in the half-filled Hubbard\nmodel at strong coupling on a cubic lattice and in lower dimensions. Upon\ncooling, the transition from the charge-excitation regime to the AF Heisenberg\nregime is signaled by a universal minimum of the double occupancy at entropy\ns=S/(N k_B)=s*=ln(2) per particle and a linear increase of the next-nearest\nneighbor (NNN) spin correlation function for s<s*. This crossover, driven by a\ngain in kinetic exchange energy, appears as the essential AF physics relevant\nfor current cold-atom experiments. The onset of long-range AF order (at low s\non cubic lattices) is hardly visible in nearest-neighbor spin correlations\nversus s, but could be detected in spin correlations at or beyond NNN\ndistances."
    },
    {
        "anchor": "Prethermalization in one-dimensional Bose gases: description by a\n  stochastic Ornstein-Uhlenbeck process: We experimentally study the relaxation dynamics of a coherently split\none-dimensional Bose gas using matterwave interference. Measuring the full\nprobability distributions of interference contrast reveals the\nprethermalization of the system to a non-thermal steady state. To describe the\nevolution of noise and correlations we develop a semiclassical effective\ndescription that allows us to model the dynamics as a stochastic\nOrnstein-Uhlenbeck process.",
        "positive": "Freezing of soft-core bosons at zero temperature: A variational theory: The properties of a macroscopic assembly of weakly-repulsive bosons at zero\ntemperature are well described by Gross-Pitaevskii mean-field theory. According\nto this formalism the system exhibits a quantum transition from superfluid to\ncluster supersolid as a function of pressure. We develop a thermodynamically\nrigorous treatment of the different phases of the system by adopting a\nvariational formulation of the condensate wave function --- represented as a\nsum of Gaussians --- that is amenable to exact manipulations. Not only is this\ndescription quantitatively accurate, but it is also capable to predict the\norder (and sometimes even the location) of the transition. We consider a number\nof crystal structures in two and three dimensions and determine the phase\ndiagram. Depending on the lattice, the transition from fluid to solid can be\nfirst-order or continuous, a lower coordination entailing a milder transition.\nIn two dimensions, crystallization would occur at the same pressure on three\ndistinct lattices (square, honeycomb, and stripes), all providing metastable\nphases with respect to the triangular crystal. A similar scenario holds in\nthree dimensions, where the simple-cubic and diamond crystals also share a\ncommon melting point; however, the stable crystal at low pressure is typically\nfcc. Upon compression and depending on the shape of the potential, the fcc\ncrystal may transform into hcp. We conclude by sketching a theory of the\nsolid-fluid interface and of quantum nucleation of the solid from the fluid."
    },
    {
        "anchor": "A Quantum Impurity Model for Anyons: One of the hallmarks of quantum statistics, tightly entwined with the concept\nof topological phases of matter, is the prediction of anyons. Although anyons\nare predicted to be realized in certain fractional quantum Hall systems, they\nhave not yet been unambiguously detected in experiment. Here we introduce a\nsimple quantum impurity model, where bosonic or fermionic impurities turn into\nanyons as a consequence of their interaction with the surrounding many-particle\nbath. A cloud of phonons dresses each impurity in such a way that it\neffectively attaches fluxes/vortices to it and thereby converts it into an\nAbelian anyon. The corresponding quantum impurity model, first, provides a new\napproach to the numerical solution of the many-anyon problem, along with a new\nconcrete perspective of anyons as emergent quasiparticles built from composite\nbosons or fermions. More importantly, the model paves the way towards realizing\nanyons using impurities in crystal lattices as well as ultracold gases. In\nparticular, we consider two heavy electrons interacting with a two-dimensional\nlattice crystal in a magnetic field, and show that when the impurity-bath\nsystem is rotated at the cyclotron frequency, impurities behave as anyons as a\nconsequence of the angular momentum exchange between the impurities and the\nbath. A possible experimental realization is proposed by identifying the\nstatistics parameter in terms of the mean square distance of the impurities and\nthe magnetization of the impurity-bath system, both of which are accessible to\nexperiment. Another proposed application are impurities immersed in a\ntwo-dimensional weakly interacting Bose gas.",
        "positive": "All-optical pump-and-probe detection of dynamical correlations in a\n  two-dimensional Fermi gas: We propose an all-optical scheme to probe the dynamical correlations of a\nstrongly-interacting gas of ultracold atoms. The proposed technique is based on\na pump-and-probe scheme: a coherent light pulse is initially converted into an\natomic coherence and later retrieved after a variable storage time. The\nefficiency of the proposed method to measure the one-particle Green function of\nthe gas is validated by numerical and analytical calculations of the expected\nsignal for the two cases of a normal Fermi gas and a BCS superfluid state.\nProtocols to extract the superfluid gap and the full quasi-particle dispersions\nare discussed."
    },
    {
        "anchor": "The Unitary Gas and its Symmetry Properties: The physics of atomic quantum gases is currently taking advantage of a\npowerful tool, the possibility to fully adjust the interaction strength between\natoms using a magnetically controlled Feshbach resonance. For fermions with two\ninternal states, formally two opposite spin states, this allows to prepare long\nlived strongly interacting three-dimensional gases and to study the BEC-BCS\ncrossover. Of particular interest along the BEC-BCS crossover is the so-called\nunitary gas, where the atomic interaction potential between the opposite spin\nstates has virtually an infinite scattering length and a zero range. This\nunitary gas is the main subject of the present chapter: It has fascinating\nsymmetry properties, from a simple scaling invariance, to a more subtle\ndynamical symmetry in an isotropic harmonic trap, which is linked to a\nseparability of the N-body problem in hyperspherical coordinates. Other\nanalytical results, valid over the whole BEC-BCS crossover, are presented,\nestablishing a connection between three recently measured quantities, the tail\nof the momentum distribution, the short range part of the pair distribution\nfunction and the mean number of closed channel molecules.",
        "positive": "Magnetization and collective excitations of a magnetic dipole fermion\n  gas: The ground states and collective excitations of trapped Fermion gases\nconsisting of atoms with magnetic dipole moment are studied using a\ntime-dependent density-matrix approach. The advantages of the density-matrix\napproach are that one-body and two-body observables are directly calculated\nusing one-body and two-body density matrices and that it has a clear relation\nto the Hartree-Fock (HF) and time-dependent HF theory. The HF calculations show\nthe magnetization of the gases when the dipole-dipole interaction is strong. It\nis shown that the tensor properties of the dipole-dipole interaction are\nrevealed in the excitation modes associated with spin degrees of freedom."
    },
    {
        "anchor": "High-momentum tails as magnetic structure probes for strongly-correlated\n  $SU(\u03ba)$ fermionic mixtures in one-dimensional traps: A universal $k^{-4}$ decay of the large-momentum tails of the momentum\ndistribution, fixed by Tan's contact coefficients, constitutes a direct\nsignature of strong correlations in a short-range interacting quantum gas. Here\nwe consider a repulsive multicomponent Fermi gas under harmonic confinement, as\nin the experiment of Pagano et al. [Nat. Phys. {\\bf 10}, 198 (2014)], realizing\na gas with tunable $SU(\\kappa)$ symmetry. We exploit an exact solution at\ninfinite repulsion to show a direct correspondence between the value of the\nTan's contact for each of the $\\kappa$ components of the gas and the Young\ntableaux for the $S_N$ permutation symmetry group identifying the magnetic\nstructure of the ground-state. This opens a route for the experimental\ndetermination of magnetic configurations in cold atomic gases, employing only\nstandard (spin-resolved) time-of-flight techniques. Combining the exact result\nwith matrix-product-states simulations, we obtain the Tan's contact at all\nvalues of repulsive interactions. We show that a local density approximation\n(LDA) on the Bethe-Ansatz equation of state for the homogeneous mixture is in\nexcellent agreement with the results for the harmonically confined gas. At\nstrong interactions, the LDA predicts a scaling behavior of the Tan's contact.\nThis provides a useful analytical expression for the dependence on the number\nof fermions, number of components and on interaction strength. Moreover, using\na virial approach in the limit of infinite interactions, we show that the\ncontact increases with the temperature and the number of components. At zero\ntemperature, we predict that the weight of the momentum distribution tails\nincreases with interaction strength and the number of components if the\npopulation per component is kept constant. This latter property was\nexperimentally observed in Ref.~[Nat. Phys. {\\bf 10}, 198 (2014)].",
        "positive": "Vortex stream generation and enhanced propagation in a polariton\n  superfluid: In this work, we implement a new experimental configuration which exploits\nthe specific properties of the optical bistability exhibited by the polariton\nsystem and we demonstrate the generation of a superfluid turbulent flow in the\nwake of a potential barrier. The propagation and direction of the turbulent\nflow are sustained by a support beam on distances an order of magnitude longer\nthan previously reported. This novel technique is a powerful tool for the\ncontrolled generation and propagation of quantum turbulences and paves the way\nto the study of the hydrodynamic of quantum turbulence in driven-dissipative 2D\npolariton systems."
    },
    {
        "anchor": "Anomalous scaling at non-thermal fixed points of the sine-Gordon model: We extend the theory of non-thermal fixed points to the case of anomalously\nslow universal scaling dynamics according to the sine-Gordon model. This\nentails the derivation of a kinetic equation for the momentum occupancy of the\nscalar field from a non-perturbative two-particle irreducible effective action,\nwhich re-sums a series of closed loop chains akin to a large-$N$ expansion at\nnext-to-leading order. The resulting kinetic equation is analyzed for possible\nscaling solutions in space and time that are characterized by a set of\nuniversal scaling exponents and encode self-similar transport to low momenta.\nAssuming the momentum occupancy distribution to exhibit a scaling form we can\ndetermine the exponents by identifying the dominating contributions to the\nscattering integral and power counting. If the field exhibits strong variations\nacross many wells of the cosine potential, the scattering integral is dominated\nby the scattering of many quasiparticles such that the momentum of each single\nparticipating mode is only weakly constrained. Remarkably, in this case, in\ncontrast to wave turbulent cascades, which correspond to local transport in\nmomentum space, our results suggest that kinetic scattering here is dominated\nby rather non-local processes corresponding to a spatial containment in\nposition space. The corresponding universal correlation functions in momentum\nand position space corroborate this conclusion. Numerical simulations performed\nin accompanying work yield scaling properties close to the ones predicted here.",
        "positive": "Enhancing nanomechanical squeezing by atomic interactions in a hybrid\n  atom-optomechanical system: In a hybrid atom-optomechanical system, the optical coupling of a mechanical\nmode of a nanomembrane in an optical cavity with a distant interacting atom gas\npermits highly non-classical quantum many-body states. We show that the\nmechanical mode can be squeezed by the back-action of internal excitations of\nthe atoms in the gas. A Bogoliubov approach reveals that these internal\nexcitations form a fluctuating environment of quasi-particle excitations for\nthe mechanical mode with a gaped spectral density. Nanomechanical squeezing\narises due to quasi-particle excitations in the interacting atom gas when the\nmechanical frequency is close to resonance with the internal atomic\ntransitions. Interestingly, nanomechanical squeezing is enhanced by atom-atom\ninteractions."
    },
    {
        "anchor": "Simulating Infinite Vortex Lattices in Superfluids: We present an efficient framework to numerically treat infinite periodic\nvortex lattices in rotating superfluids described by the Gross-Pitaevskii\ntheory. The commonly used split-step Fourier (SSF) spectral methods are\ninapplicable to such systems as the standard Fourier transform does not respect\nthe boundary conditions mandated by the magnetic translation group. We present\na generalisation of the SSF method which incorporates the correct boundary\nconditions by employing the so-called magnetic Fourier transform. We test the\nmethod and show that it reduces to known results in the lowest-Landau-level\nregime. While we focus on rotating scalar superfluids for simplicity, the\nframework can be naturally extended to treat multicomponent systems and systems\nunder more general `synthetic' gauge fields.",
        "positive": "Mott transition in a two-leg Bose-Hubbard ladder under an artificial\n  magnetic field: We consider the Bose-Hubbard model on a two-leg ladder under an artificial\nmagnetic field, and investigate the superfluid-to-Mott insulator transition in\nthis setting. Recently, this system has been experimentally realized [M.Atala\n\\textit{et al.}, Nature Physics \\textbf{10}, 588--593 (2014)], albeit in a\nparameter regime that is far from the Mott transition boundary. Depending on\nthe strength of the magnetic field, the single-particle spectrum has either a\nsingle ground state or two degenerate ground states. The transition between\nthese two phases is reflected in the many-particle properties. We first\ninvestigate these phases through the Bogoliubov approximation in the superfluid\nregime and calculate the transition boundary for weak interactions. For\nstronger interactions the system is expected to form a Mott insulator. We\ncalculate the Mott transition boundary as a function of the magnetic field and\ninterleg coupling with mean-field theory, strong-coupling expansion and density\nmatrix renormalization group (DMRG). Finally, using the DMRG, we investigate\nthe particle-hole excitation gaps of this system at different filling factors\nand find peaks at simple fractions indicating the possibility of correlated\nphases."
    },
    {
        "anchor": "Cold-atom quantum simulators of gauge theories: Gauge theories represent a fundamental framework underlying modern physics,\nconstituting the basis of the Standard Model and also providing useful\ndescriptions of various phenomena in condensed matter. Realizing gauge theories\non accessible and tunable tabletop quantum devices offers the possibility to\nstudy their dynamics from first principles time evolution and to probe their\nexotic physics, including that generated by deviations from gauge invariance,\nwhich is not possible, e.g., in dedicated particle colliders. Not only do\ncold-atom quantum simulators hold the potential to provide new insights into\noutstanding high-energy and nuclear-physics questions, they also provide a\nversatile tool for the exploration of topological phases and\nergodicity-breaking mechanisms relevant to low-energy many-body physics. In\nrecent years, cold-atom quantum simulators have demonstrated impressive\nprogress in the large-scale implementation of $1+1$D Abelian gauge theories. In\nthis Review, we chronicle the progress of cold-atom quantum simulators of gauge\ntheories, highlighting the crucial advancements achieved along the way in order\nto reliably stabilize gauge invariance and go from building blocks to\nlarge-scale realizations where \\textit{bona fide} gauge-theory phenomena can be\nprobed. We also provide a brief outlook on where this field is heading, and\nwhat is required experimentally and theoretically to bring the technology to\nthe next level by surveying various concrete proposals for advancing these\nsetups to higher spatial dimensions, higher-spin representations of the gauge\nfield, and non-Abelian gauge groups.",
        "positive": "Enhancement of the Bose glass phase in the presence of an artificial\n  gauge field: We examine the effects of an artificial gauge field and finite temperature in\na two-dimensional disordered Bose-Hubbard model. The disorder considered is\ndiagonal and quenched in nature. A signature of disorder in the Bose-Hubbard\nmodel is the Bose glass phase. Our work shows that the introduction of an\nartificial gauge field enhances the domain of the Bose glass phase in the phase\ndiagram. Most importantly, the size of the domain can be tuned with the\nstrength of the artificial gauge field. The introduction of the finite\ntemperature effects is essential to relate theoretical results with the\nexperimental realizations. For our studies we use the single site and cluster\nGutzwiller mean-field theories. The results from the latter are more reliable\nas it better describes the correlation effects. Our results show that the Bose\nglass phase has a larger domain with the latter method."
    },
    {
        "anchor": "Critical behavior at the spatial boundary of a trapped inhomogeneous\n  Bose-Einstein condensate: We investigate some aspects of the Bose-Einstein condensation (BEC) of\nquantum gases in the presence of inhomogeneous conditions. We consider\nthree-dimensional (3D) quantum gases trapped by an external potential when the\ntemperature is sufficiently low to show a BEC phase region around the center of\nthe trap. If the trap is sufficiently large, different phases may coexist in\ndifferent space regions, when moving from the center of the trap. We show that\nthe quantum gas develops a peculiar critical behavior at the boundary of the\nBEC region, whose scaling behavior is controlled by the universality class of\nthe homogenous BEC transition. We provide numerical evidence of this\nphenomenon, for lattice atomic gases modeled by the 3D Bose-Hubbard\nHamiltonian.",
        "positive": "Flemish Strings of Magnetic Solitons and a Non-Thermal Fixed Point in a\n  One-Dimensional Antiferromagnetic Spin-1 Bose Gas: Thermalization in a quenched one-dimensional antiferromagnetic spin-1 Bose\ngas is shown to proceed via a non-thermal fixed point through annihilation of\nFlemish-string bound states of magnetic solitons. A possible experimental\nsituation is discussed."
    },
    {
        "anchor": "Chaos and quantum scars in a coupled top model: We consider a coupled top model describing two interacting large spins, which\nis studied semiclassically as well as quantum mechanically. This model exhibits\nvariety of interesting phenomena such as quantum phase transition (QPT),\ndynamical transition and excited state quantum phase transitions above a\ncritical coupling strength. Both classical dynamics and entanglement entropy\nreveals ergodic behavior at the center of energy density band for an\nintermediate range of coupling strength above QPT, where the level spacing\ndistribution changes from Poissonian to Wigner-Dyson statistics. Interestingly,\nin this model we identify quantum scars as reminiscence of unstable collective\ndynamics even in presence of interaction. Statistical properties of such\nscarred states deviate from ergodic limit corresponding to random matrix theory\nand violate Berry's conjecture. In contrast to ergodic evolution, oscillatory\nbehavior in dynamics of unequal time commutator and survival probability is\nobserved as dynamical signature of quantum scar, which can be relevant for its\ndetection.",
        "positive": "Scattering Theory for Floquet-Bloch States: Motivated by recent experimental implementations of artificial gauge fields\nfor gases of cold atoms, we study the scattering properties of particles that\nare subjected to time-periodic Hamiltonians. Making use of Floquet theory, we\nfocus on translationally invariant situations in which the single-particle\ndynamics can be described in terms of spatially extended Floquet-Bloch waves.\nWe develop a general formalism for the scattering of these Floquet-Bloch waves.\nAn important role is played by the conservation of Floquet quasi-energy, which\nis defined only up to the addition of integer multiples of $\\hbar\\omega$ for a\nHamiltonian with period $T=2\\pi/\\omega$. We discuss the consequences of this\nfor the interpretation of \"elastic\" and \"inelastic\" scattering in cases of\nphysical interest. We illustrate our general results with applications to: the\nscattering of a single particle in a Floquet-Bloch state from a static\npotential; and, the scattering of two particles in Floquet-Bloch states through\ntheir interparticle interaction. We analyse examples of these scattering\nprocesses that are closely related to the schemes used to general artifical\ngauge fields in cold-atom experiments, through optical dressing of internal\nstates, or through time-periodic modulations of tight-binding lattices. We show\nthat the effects of scattering cannot, in general, be understood by an\neffective time-independent Hamiltonian, even in the limit $\\omega \\to \\infty$\nof rapid modulation. We discuss the relative sizes of the elastic scattering\n(required to stablize many-body phases) and of the inelastic scattering\n(leading to deleterious heating effects). In particular, we describe how\ninelastic processes that can cause significant heating in current experimental\nset-up can be switched off by additional confinement of transverse motion."
    },
    {
        "anchor": "The Josephson relation for the superfluid density and the connection to\n  the Goldstone theorem in dilute Bose atomic gasses: We derive the Josephson relation for a dilute Bose gas in the framework of an\nauxiliary-field resummation of the theory in terms of the normal- and\nanomalous-density condensates. The mean-field phase diagram of this theory\nfeatures two critical temperatures, T_c and $T^*, associated with the presence\nin the system of the Bose-Einstein condensate (BEC) and superfluid state,\nrespectively. In this context, the Josephson relation shows that the superfluid\ndensity is related to a second order parameter, the square of the\nanomalous-density condensate. This is in contrast with the corresponding result\nin the Bose gas theory without an anomalous condensate, which predicts that the\nsuperfluid density is proportional to the BEC condensate density. Our findings\nare consistent with the prediction that in the temperature range between T_c\nand T^* a fraction of the system is in the superfluid state in the absence of\nthe BEC condensate. This situation is similar to the case of dilute Fermi\ngases, where the superfluid density is proportional to the square of the gap\nparameter. The Josephson relation relies on the existence of zero energy and\nmomentum excitations showing the intimate relationship between superfluidity\nand the Goldstone theorem.",
        "positive": "Pattern Formation in Quantum Ferrofluids: from Supersolids to\n  Superglasses: Pattern formation is a ubiquitous phenomenon observed in nonlinear and\nout-of-equilibrium systems. In equilibrium, quantum ferrofluids formed from\nultracold atoms were recently shown to spontaneously develop coherent density\npatterns, manifesting a supersolid. We theoretically investigate the phase\ndiagram of such quantum ferrofluids in oblate trap geometries and find an even\nwider range of exotic states of matter. Two-dimensional supersolid crystals\nformed from individual ferrofluid quantum droplets dominate the phase diagram\nat low densities. For higher densities we find honeycomb and labyrinthine\nstates, as well as a pumpkin phase. We discuss scaling relations which allow us\nto find these phases for a wide variety of trap geometries, interaction\nstrengths, and atom numbers. Our study illuminates the origin of the various\npossible patterns of quantum ferrofluids and shows that their occurrence is\ngeneric of strongly dipolar interacting systems stabilized by beyond mean-field\neffects."
    },
    {
        "anchor": "Directed transport in driven optical lattices by phase generation: We examine the dynamics of ultracold atoms held in optical lattice\npotentials. By controlling the switching of a periodic driving potential we\nshow how a phase-induced renormalization of the intersite tunneling can be used\nto produce directed motion and control wavepacket spreading. We further show\nhow this generation of a synthetic gauge potential can be used to split and\nrecombine wavepackets, providing an attractive route to implementing quantum\ncomputing tasks.",
        "positive": "Average energy approximation of the ideal Bose-Einstein gas and\n  condensate: If the N bosons that compose an ideal Bose-Einstein gas with energy E and\nvolume V are each assumed to have the average energy of the system E/N, the\nentropy is easily expressed in terms of the number of bosons N and the number\nof single-particle microstates n they can occupy. Because the entropy derived\nis a function of only N and n, and the latter is a function of the extensive\nvariables, E, V, and N, this entropy describes all that can be known of the\nthermodynamics of this system. In particular, the entropy very simply recovers\nthe Sakur-Tetrode entropy in the classical limit and at sufficiently low\ntemperature describes an unstable system. A thermodynamic stability analysis\nrecovers the Bose-Einstein condensate and a two-phase region. Apart from\nnumerical factors of order one, results are identical with those derived via\nstandard, probabilistic methods."
    },
    {
        "anchor": "Quantum fluctuations in the BCS-BEC crossover of two-dimensional Fermi\n  gases: We present a theoretical study of the ground state of the BCS-BEC crossover\nin dilute two-dimensional Fermi gases. While the mean-field theory provides a\nsimple and analytical equation of state, the pressure is equal to that of a\nnoninteracting Fermi gas in the entire BCS-BEC crossover, which is not\nconsistent with the features of a weakly interacting Bose condensate in the BEC\nlimit and a weakly interacting Fermi liquid in the BCS limit. The inadequacy of\nthe 2D mean-field theory indicates that the quantum fluctuations are much more\npronounced than those in 3D. In this work, we show that the inclusion of the\nGaussian quantum fluctuations naturally recovers the above features in both the\nBEC and the BCS limits. In the BEC limit, the missing logarithmic dependence on\nthe boson chemical potential is recovered by the quantum fluctuations. Near the\nquantum phase transition from the vacuum to the BEC phase, we compare our\nequation of state with the known grand canonical equation of state of 2D Bose\ngases and determine the ratio of the composite boson scattering length $a_{\\rm\nB}$ to the fermion scattering length $a_{\\rm 2D}$. We find $a_{\\rm B}\\simeq\n0.56 a_{\\rm 2D}$, in good agreement with the exact four-body calculation. We\ncompare our equation of state in the BCS-BEC crossover with recent results from\nthe quantum Monte Carlo simulations and the experimental measurements and find\ngood agreements.",
        "positive": "Macroscopic quantum coherence in spinor condensates confined in an\n  anisotropic potential: We investigate the macroscopic quantum coherence of a spin-1 Rb condensate\nconfined in an anisotropic potential. Under the single-mode approximation, we\nshow that the system can be modeled as a biaxial quantum magnet due to the\ninterplay between the magnetic dipole-dipole interaction and the anisotropic\npotential. By applying a magnetic field along the hard-axis, we show that the\ntunneling splitting oscillates as a function of the field strength. We also\npropose an experimental scheme to detect the oscillatory behavior of the\ntunneling splitting by employing the Landau-Zener tunneling."
    },
    {
        "anchor": "Expansion of strongly interacting dipolar bosons in 1D optical lattices: We numerically study the expansion dynamics of initially localized dipolar\nbosons in a homogeneous 1D optical lattice for different initial states.\nComparison is made to interacting bosons with contact interaction. For shallow\nlattices the expansion is unimodal and ballistic, while strong lattices\nsuppress tunneling. However for intermediate lattice depths a strong interplay\nbetween dipolar interaction and lattice depth occurs. The expansion is found to\nbe bimodal, the central cloud expansion can be distinguished from the outer\nhalo structure. In the regime of strongly interactions dipolar bosons exhibit\ntwo time scales, with an initial diffusion and then arrested transport in the\nlong time; while strongly interacting bosons in the fermionized limit exhibit\nballistic expansion. Our study highlights how different lattice depths and\ninitial states can be manipulated to control tunneling dynamics.",
        "positive": "Fixed points and emergent topological phenomena in a\n  parity-time-symmetric quantum quench: We identify emergent topological phenomena such as dynamic Chern numbers and\ndynamic quantum phase transitions in quantum quenches of the non-Hermitian\nSu-Schrieffer-Heeger Hamiltonian with parity-time ($\\mathcal{PT}$) symmetry.\nTheir occurrence in the non-unitary dynamics are intimately connected with\nfixed points in the Brillouin zone, where the states do not evolve in time. We\nconstruct a theoretical formalism for characterizing topological properties in\nnon-unitary dynamics within the framework of biorthogonal quantum mechanics,\nand prove the existence of fixed points for quenches between distinct static\ntopological phases in the $\\mathcal{PT}$-symmetry-preserving regime. We then\nreveal the interesting relation between different dynamic topological phenomena\nthrough the momentum-time spin texture characterizing the dynamic process. For\nquenches involving Hamiltonians in the $\\mathcal{PT}$-symmetry-broken regime,\nthese topological phenomena are not ensured."
    },
    {
        "anchor": "Decay-dephasing-induced steady states in bosonic Rydberg-excited quantum\n  gases in an optical lattice: We investigate the possibility of realizing supersolid quantum phases in\nbosonic Rydberg-excited quantum lattice gases in the presence of non-unitary\nprocesses, by simulating the dynamical evolution starting from initial\npreparation in non-dissipative equilibrium states. Within Gutzwiller theory, we\nfirst analyze the many-body ground-state of a bosonic Rydberg-excited quantum\ngas in a two dimensional optical lattice for variable atomic hopping rates and\nRabi detunings. Furthermore, we perform time evolution of different supersolid\nphases using the Lindblad-master equation. With the inclusion of two different\nnon-unitary processes, namely spontaneous decay from a Rydberg state to the\nground state and dephasing of the addressed Rydberg state, we study the effect\nof non-unitary processes on those quantum phases and observe long-lived states\nin the presence of decay and dephasing. We find that long-lived supersolid\nquantum phases are observable within a range of realistic decay and dephasing\nrates, while high rates cause any initial configuration to homogenize quickly,\npreventing possible supersolid formation.",
        "positive": "Vortex nucleation in mesoscopic Bose superfluid and breaking of the\n  parity symmetry: We analyze vortex nucleation in mezoscopic 2D Bose superfluid in a rotating\ntrap. We explicitly include a weakly anisotropic stirring potential, breaking\nthus explicitly the axial symmetry. As the rotation frequency passes the\ncritical value $\\Omega_c$ the system undergoes an extra symmetry\nchange/breaking. Well below $\\Omega_c$ the ground state is properly described\nby the mean field theory with an even condensate wave function. Well above\n$\\Omega_c$ the MF solution works also well, but the order parameter becomes\nodd. This phenomenon involves therefore a discrete parity symmetry breaking. In\nthe critical region the MF solutions exhibit dynamical instability. The true\nmany body state is a strongly correlated entangled state involving two\nmacroscopically occupied modes (eigenstates of the single particle density\noperator). We characterize this state in various aspects: i) the eligibility\nfor adiabatic evolution; ii) its analytical approximation given by the\nmaximally entangled combination of two single modes; and finally iii) its\nappearance in particle detection measurements."
    },
    {
        "anchor": "Observation of interspecies Li-Cs Feshbach resonances: We report on the observation of nineteen interspecies Feshbach resonances in\nan optically trapped ultracold Bose-Fermi mixture of ^{133}Cs and ^{6}Li in the\ntwo energetically lowest spin states. We assign the resonances to s- and p-wave\nmolecular channels by a coupled-channels calculation, resulting in an accurate\ndetermination of LiCs ground state potentials. Fits of the resonance position\nbased on the undressed Asymptotic Bound State model do not provide the same\nlevel of accuracy as the coupled-channels calculation. Several broad s-wave\nresonances provide prospects to create fermionic LiCs molecules with a large\ndipole moment via Feshbach association followed by stimulated Raman passage.\nTwo of the s-wave resonances overlap with a zero crossing of the Cs scattering\nlength which offers prospects for the investigation of polarons in an ultracold\nLi-Cs mixture.",
        "positive": "Localization of a Bose-Einstein condensate in a bichromatic optical\n  lattice: By direct numerical simulation of the time-dependent Gross-Pitaevskii\nequation we study different aspects of the localization of a non-interacting\nideal Bose-Einstein condensate (BEC) in a one-dimensional bichromatic\nquasi-periodic optical-lattice potential. Such a quasi-periodic potential, used\nin a recent experiment on the localization of a BEC [Roati et al., Nature 453,\n895 (2008)], can be formed by the superposition of two standing-wave polarized\nlaser beams with different wavelengths. We investigate the effect of the\nvariation of optical amplitudes and wavelengths on the localization of a\nnon-interacting BEC. We also simulate the non-linear dynamics when a\nharmonically trapped BEC is suddenly released into a quasi-periodic potential,\n{as done experimentally in a laser speckle potential [Billy et al., Nature 453,\n891 (2008)]$ We finally study the destruction of the localization in an\ninteracting BEC due to the repulsion generated by a positive scattering length\nbetween the bosonic atoms."
    },
    {
        "anchor": "Coherent quench dynamics in the one-dimensional Fermi-Hubbard model: Recently, it has been shown that the momentum distribution of a metallic\nstate of fermionic atoms in a lattice Fermi-Bose mixture exhibits coherent\noscillations after a global quench that suppresses tunneling. The oscillation\nperiod is determined by the Fermi-Bose interaction strength. Here we show that\nsimilar dynamics occurs in the fermionic Hubbard model when we quench a\nnoninteracting metallic state by introducing a Hubbard interaction and\nsuppressing tunneling. The period is determined primarily by the interaction\nstrength. Conversely, we show that one can accurately determine the Hubbard\ninteraction strength from the oscillation period, taking into account\ncorrections from any small residual tunneling present in the final Hamiltonian.\nSuch residual tunneling shortens the period and damps the oscillations, the\nlatter being visible in the Fermi-Bose experiment.",
        "positive": "Ultracold atoms in an optical lattice with dynamically variable\n  periodicity: The use of a dynamic \"accordion\" lattice with ultracold atoms is\ndemonstrated. Ultracold atoms of $^{87}$Rb are trapped in a two-dimensional\noptical lattice, and the spacing of the lattice is then increased in both\ndirections from 2.2 to 5.5 microns. Atoms remain bound for expansion times as\nshort as a few milliseconds, and the experimentally measured minimum ramp time\nis found to agree well with numerical calculations. This technique allows an\nexperiment such as quantum simulations to be performed with a lattice spacing\nsmaller than the resolution limit of the imaging system, while allowing imaging\nof the atoms at individual lattice sites by subsequent expansion of the optical\nlattice."
    },
    {
        "anchor": "Comment on \"Phase separation in a two-species Bose mixture\": In an article in 2007, Mishra, Pai, and Das [Phys. Rev. A 76, 013604 (2007)]\ninvestigated the two-component Bose-Hubbard model using the numerical DMRG\nprocedure. In the regime of inter-species repulsion $U^{ab}$ larger than the\nintra-species repulsion $U$, they found a transition from a uniform miscible\nphase to phase-separation occurring at a finite value of $U$ , e.g., at around\n$U = 1.3$ for $\\Delta = U^{ab}/U = 1.05$ and $\\rho_{a} = \\rho_{b} = 1/2$. In\nthis comment, we show that this result is not correct and in fact the\ntwo-component Bose-Hubbard model is unstable to phase-separation for any\n$U^{ab} > U > 0$.",
        "positive": "Non-spreading matter-wave packets in a ring: Non-spreading wave packets and matter-wave packets in ring traps both have\nattracted great research interests due to their miraculous physical properties\nand tempting applications for quite a long time. Here, we proved that there\nexists only one set of non-spreading matter-wave packets in a free ring, and\nthis set of wave packets have been found analytically. These non-spreading\nmatter-wave packets can be realized in a toroidal trapped Bose-Einstein\ncondensate system with the help of Feshbach resonance to eliminate contact\ninteraction between atoms. Since experimentally residual interaction noise will\nalways exist, its effect on the stability of these non-spreading wave packets\nis also examined. Qualitatively, under weak residual interaction noise, these\nnon-spreading wave packets can preserve their shape for quite a long time,\nwhile a stronger interaction noise will induce shape breathing of the wave\npackets. Shape-keeping abilities of these wave packets are further studied\nquantitatively. We found that this set of wave packets have the same\nshape-keeping ability against interaction noise. And, the shape-keeping ability\nis linearly related to the interaction noise strength."
    },
    {
        "anchor": "Hard-core Bose-Fermi mixture in one-dimensional split traps: We consider a strongly interacting one-dimensional (1D) Bose-Fermi mixture\nconfined in a hard wall trap or a harmonic oscillator trap with a tunable\n$\\delta$-function barrier at the trap center. The mixture consists of 1D Bose\ngas with repulsive interactions and of 1D noninteracting spin-aligned Fermi\ngas, both species interacting through hard-core interactions. Using a\ngeneralized Bose-Fermi mapping, we calculated the reduced single-particle\ndensity matrix and the momentum distribution of the gas as a function of\nbarrier strength and the parity of particle number. The secondary peaks in the\nmomentum distribution show remarkable correlation between particles on the two\nsides of the split.",
        "positive": "Trapped Bose-Einstein condensates in synthetic magnetic field: Rotating properties of Bose-Einstein condensates in synthetic magnetic field\nare studied by numerically solving the Gross-Pitaevskii equation and compared\nwith condensates confined in the rotating trap. It seems that it is more\ndifficult to add large angular momentum to condensates spined up by the\nsynthetic magnetic field than by the rotating trap. However, strengthening the\nrepulsive interaction between atoms is an effective and realizable route to\novercome this problem and can at least generate vortex-lattice-like structures.\nIn addition, the validity of the Feynman rule for condensates in synthetic\nmagnetic field is verified."
    },
    {
        "anchor": "Multi-particle quantum walks and Fisher information in one-dimensional\n  lattices: Recent experiments on quantum walks (QWs) of a single and two particles\ndemonstrated subtle quantum statistics-dependent walks in one-dimensional (1D)\nlattices. However the roles of interaction and quantum statistics in such a\nkind of walks are little known at a many-body level. In this letter, using\ntime-evolving block decimation algorithm and many-body perturbation theory we\nrigorously study QWs, Bloch oscillations and quantum Fisher informations (FIs)\nfor three indistinguishable bosons and fermions in 1D lattices. We show that\nsuch strongly correlated many-body QWs not only give rise to\nstatistics-and-interaction-dependent ballistic transports of scattering states,\ntwo- and three-body bound states, but also present a quantum enhanced precision\nmeasurement of the gravitational force. It turns out that in contrast to the\nwalks of the fermions, the QWs of three bosons exhibit richer dynamics of\nco-walkings and competitive Bloch oscillations, which remarkably present a\nsurprising time scaling $t^3$ of FI below a characteristic time $t_0$ and\nsaturate to the fundamental limit of $t^2$ for $t>t_0$.",
        "positive": "Bogoliubov theory on the disordered lattice: Quantum fluctuations of Bose-Einstein condensates trapped in disordered\nlattices are studied by inhomogeneous Bogoliubov theory. Weak-disorder\nperturbation theory is applied to compute the elastic scattering rate as well\nas the renormalized speed of sound in lattices of arbitrary dimensionality.\nFurthermore, analytical results for the condensate depletion are presented,\nwhich are in good agreement with numerical data."
    },
    {
        "anchor": "Vibrational dressing in Kinetically Constrained Rydberg Spin Systems: Quantum spin systems with kinetic constraints have become paradigmatic for\nexploring collective dynamical behaviour in many-body systems. Here we discuss\na facilitated spin system which is inspired by recent progress in the\nrealization of Rydberg quantum simulators. This platform allows to control and\ninvestigate the interplay between facilitation dynamics and the coupling of\nspin degrees of freedom to lattice vibrations. Developing a minimal model, we\nshow that this leads to the formation of polaronic quasiparticle excitations\nwhich are formed by many-body spin states dressed by phonons. We investigate in\ndetail the properties of these quasiparticles, such as their dispersion\nrelation, effective mass and the quasiparticle weight. Rydberg lattice quantum\nsimulators are particularly suited for studying this phonon-dressed kinetically\nconstrained dynamics as their exaggerated length scales permit the\nsite-resolved monitoring of spin and phonon degrees of freedom.",
        "positive": "Many-body Landau-Zener Transition in Cold Atom Double Well Optical\n  Lattices: Ultra-cold atoms in optical lattices provide an ideal platform for exploring\nmany-body physics of a large system arising from the coupling among a series of\nsmall identical systems whose few-body dynamics is exactly solvable. Using\nLandau-Zener (LZ) transition of bosonic atoms in double well optical lattices\nas an experimentally realizable model, we investigate such few to many body\nroute by exploring the relation and difference between the small few-body (in\none double well) and the large many-body (in double well lattice)\nnon-equilibrium dynamics of cold atoms in optical lattices. We find the\nmany-body coupling between double wells greatly enhances the LZ transition\nprobability. The many-body dynamics in the double well lattice shares both\nsimilarity and difference from the few-body dynamics in one and two double\nwells. The sign of the on-site interaction plays a significant role on the\nmany-body LZ transition. Various experimental signatures of the many-body LZ\ntransition, including atom density, momentum distribution, and density-density\ncorrelation, are obtained."
    },
    {
        "anchor": "The Peierls substitution in an engineered lattice potential: Artificial gauge fields open new possibilities to realize quantum many-body\nsystems with ultracold atoms, by engineering Hamiltonians usually associated\nwith electronic systems. In the presence of a periodic potential, artificial\ngauge fields may bring ultracold atoms closer to the quantum Hall regime. Here,\nwe describe a one-dimensional lattice derived purely from effective\nZeeman-shifts resulting from a combination of Raman coupling and radiofrequency\nmagnetic fields. In this lattice, the tunneling matrix element is generally\ncomplex. We control both the amplitude and the phase of this tunneling\nparameter, experimentally realizing the Peierls substitution for ultracold\nneutral atoms.",
        "positive": "Formation and dynamics of anti-ferromagnetic correlations in tunable\n  optical lattices: We report on the observation of anti-ferromagnetic correlations of ultracold\nfermions in a variety of optical lattice geometries that are well described by\nthe Hubbard model, including dimers, 1D chains, ladders, isolated and coupled\nhoneycomb planes, as well as square and cubic lattices. The dependence of the\nstrength of spin correlations on the specific geometry is experimentally\nstudied by measuring the correlations along different lattice tunneling links,\nwhere a redistribution of correlations between the different lattice links is\nobserved. By measuring the correlations in a crossover between distinct\ngeometries, we demonstrate an effective reduction of the dimensionality for our\natom numbers and temperatures. We also investigate the formation and\nredistribution time of spin correlations by dynamically changing the lattice\ngeometry and studying the time-evolution of the system. Timescales ranging from\na sudden quench of the lattice geometry to an adiabatic evolution are probed."
    },
    {
        "anchor": "Entangled Dynamics in Macroscopic Quantum Tunneling of Bose-Einstein\n  Condensates: Tunneling of a quasibound state is a non-smooth process in the entangled\nmany-body case. Using time-evolving block decimation, we show that repulsive\n(attractive) interactions speed up (slow down) tunneling, which occurs in\nbursts. While the escape time scales exponentially with small interactions, the\nmaximization time of the von Neumann entanglement entropy between the remaining\nquasibound and escaped atoms scales quadratically. Stronger interactions\nrequire higher order corrections. Entanglement entropy is maximized when about\nhalf the atoms have escaped.",
        "positive": "Crossover between Kelvin-Helmholtz and counter-superflow instabilities\n  in two-component Bose-Einstein condensates: Dynamical instabilities at the interface between two Bose--Einstein\ncondensates that are moving relative to each other are investigated using\nmean-field and Bogoliubov analyses. Kelvin--Helmholtz instability is dominant\nwhen the interface thickness is much smaller than the wavelength of the\nunstable interface mode, whereas the counter-superflow instability becomes\ndominant in the opposite case. These instabilities emerge not only in an\nimmiscible system but also in a miscible system where an interface is produced\nby external potential. Dynamics caused by these instabilities are numerically\ndemonstrated in rotating trapped condensates."
    },
    {
        "anchor": "Universal and Non-Universal Correction Terms of Bose Gases in Dilute\n  Region: a Quantum Monte Carlo Study: We study dilute gases of interacting bosons at zero-temperature in the region\nwhere the system is characterized only by the s-wave scattering length. We\ncarry out quantum Monte Carlo simulation of the Bose Hubbard model and a\ncontinuous-space hard-core model. Fitting the extended Lee-Huang-Yang formula\nto the Monte Carlo results establishes the detailed mapping from the lattice\nmodel to the continuous field theory characterized only by the s-wave\nscattering length. Our estimate of the intrinsic s-wave scattering length $a_s$\nof the Bose-Hubbard model is $a_s/a_l = 0.316(2)$ where $a_l$ is the lattice\nconstant. It turned out that inclusion of the universal second correction term\nof $O(n \\log n)$ makes the fitting worse while it is restored by inclusion of\nthe non-universal third correction term, of which the existence was predicted\nanalytically.",
        "positive": "Color Superfluid and Trionic State of Attractive Three-Component Lattice\n  Fermionic Atoms at Finite Temperatures: We investigate the finite-temperature properties of attractive\nthree-component (colors) fermionic atoms in optical lattices using a\nself-energy functional approach. As the strength of the attractive interaction\nincreases in the low temperature region, a second-order transition occurs from\na Fermi liquid to a color superfluid (CSF). In the strong attractive region, a\nfirst-order transition occurs from a CSF to a trionic state. In the high\ntemperature region, a crossover between a Fermi liquid and a trionic state is\nobserved with increasing the strength of the attractive interaction. The\ncrossover region for fixed temperature is almost independent of filling."
    },
    {
        "anchor": "Vortex formation and quantum turbulence with rotating paddle potentials\n  in a two-dimensional binary Bose-Einstein condensate: We conduct a theoretical study of the creation and dynamics of vortices in a\ntwo-dimensional binary Bose-Einstein condensate with a mass imbalance between\nthe species. To initiate the dynamics, we use one or two rotating paddle\npotentials in one species, while the other species is influenced only via the\ninterspecies interaction. In both species, the number and the dominant sign of\nthe vortices are determined by the rotation frequency of the paddle potential.\nClusters of positive and negative vortices form at a low rotation frequency\ncomparable to that of the trap when using the single paddle potential. In\ncontrast, vortices of the same sign tend to dominate as the rotation frequency\nof the paddle increases, and the angular momentum reaches a maximum value at a\npaddle frequency, where the paddle velocity becomes equal to the sound velocity\nof the condensate. When the rotation frequency is sufficiently high, the rapid\nannihilation of vortex-antivortex pairs significantly reduces the number of\nvortices and antivortices in the system. For two paddle potentials rotating in\nthe same direction, the vortex dynamics phenomenon is similar to that of a\nsingle paddle. However, when the paddle potentials are rotated in the opposite\ndirection, both positive and negative signed vortices occur at all rotational\nfrequencies. At the low rotation frequencies, the cluster of like-signed\nvortices produces the $k^{-5/3}$ and $k^{-3}$ power laws in the incompressible\nkinetic energy spectrum at low and high wavenumbers, respectively, a hallmark\nof the quantum turbulent flows.",
        "positive": "Double transfer through Dirac points in a tunable honeycomb optical\n  lattice: We report on Bloch-Zener oscillations of an ultracold Fermi gas in a tunable\nhoneycomb lattice. The quasi-momentum distribution of the atoms is measured\nafter sequentially passing through two Dirac points. We observe a double-peak\nfeature in the transferred fraction to the second band, both as a function of\nthe band gap at the Dirac points and the quasi-momentum of the trajectory. Our\nresults are in good agreement with a simple analytical model based on two\nsuccessive Landau-Zener transitions. Owing to the variation of the potential\ngradient over the cloud size, coherent St\\\"uckelberg oscillations are not\nvisible in our measurements. This effect of the harmonic confinement is\nconfirmed by a numerical simulation of the dynamics of a trapped 2D system."
    },
    {
        "anchor": "Collisional stability of localized Yb(${}^3\\mathrm{P}_2$) atoms immersed\n  in a Fermi sea of Li: We establish an experimental method for a detailed investigation of inelastic\ncollisional properties between ytterbium (Yb) in the metastable\n${}^3\\mathrm{P}_2$ state and ground state lithium (Li). By combining an optical\nlattice and a direct excitation to the ${}^3\\mathrm{P}_2$ state we achieve high\nselectivity on the collisional partners. Using this method we determine\ninelastic loss coefficients in collisions between\n$^{174}$Yb(${}^3\\mathrm{P}_2$) with magnetic sublevels of $m_J=0$ and $-2$ and\nground state $^6$Li to be $(4.4\\pm0.3)\\times10^{-11}~\\mathrm{cm}^3/\\mathrm{s}$\nand $(4.7\\pm0.8)\\times10^{-11}~\\mathrm{cm}^3/\\mathrm{s}$, respectively. Absence\nof spin changing processes in Yb(${}^3\\mathrm{P}_2$)-Li inelastic collisions at\nlow magnetic fields is confirmed by inelastic loss measurements on the $m_J=0$\nstate. We also demonstrate that our method allows us to look into loss\nprocesses in few-body systems separately.",
        "positive": "Quantum phase transition of ultracold bosons in the presence of a\n  non-Abelian synthetic gauge field: We study the Mott phases and the superfluid-insulator transition of\ntwo-component ultracold bosons on a square optical lattice in the presence of a\nnon-Abelian synthetic gauge field, which renders a SU(2) hopping matrix for the\nbosons. Using a resummed hopping expansion, we calculate the excitation spectra\nin the Mott insulating phases and demonstrate that the superfluid-insulator\nphase boundary displays a non-monotonic dependence on the gauge field strength.\nWe also compute the momentum distribution of the bosons in the presence of the\nnon-Abelian field and show that they develop peaks at non-zero momenta as the\nsuperfluid-insulator transition point is approached from the Mott side.\nFinally, we study the superfluid phases near the transition and discuss the\ninduced spatial pattern of the superfluid density due to the presence of the\nnon-Abelian gauge potential."
    },
    {
        "anchor": "Non-destructive selective probing of phononic excitations in a cold Bose\n  gas using impurities: We introduce a detector that selectively probes the phononic excitations of a\ncold Bose gas. The detector is composed of a single impurity atom confined by a\ndouble-well potential, where the two lowest eigenstates of the impurity form an\neffective probe qubit that is coupled to the phonons via density-density\ninteractions with the bosons. The system is analogous to a two-level atom\ncoupled to photons of the radiation field. We demonstrate that tracking the\nevolution of the qubit populations allows probing both thermal and coherent\nexcitations in targeted phonon modes. The targeted modes are selected in both\nenergy and momentum by adjusting the impurity's potential. We show how to use\nthe detector to observe coherent density waves and to measure temperatures of\nthe Bose gas down to the nano-Kelvin regime. We analyze how our scheme could be\nrealized experimentally, including the possibility of using an array of\nmultiple impurities to achieve greater precision from a single experimental\nrun.",
        "positive": "Thermalization of a strongly interacting 1D Rydberg lattice gas: When Rydberg states are excited in a dense atomic gas the mean number of\nexcited atoms reaches a stationary value after an initial transient period. We\nshed light on the origin of this steady state that emerges from a purely\ncoherent evolution of a closed system. To this end we consider a\none-dimensional ring lattice, and employ the perfect blockade model, i.e. the\nsimultaneous excitation of Rydberg atoms occupying neighboring sites is\nforbidden. We derive an equation of motion which governs the system's evolution\nin excitation number space. This equation possesses a steady state which is\nstrongly localized. Our findings show that this state is to a good accuracy\ngiven by the density matrix of the microcanonical ensemble where the\ncorresponding microstates are the zero energy eigenstates of the interaction\nHamiltonian. We analyze the statistics of the Rydberg atom number count\nproviding expressions for the number of excited Rydberg atoms and the Mandel\nQ-parameter in equilibrium."
    },
    {
        "anchor": "Goos-H\u00e4nchen shifts in spin-orbit-coupled cold atoms: We consider a matter wave packet of cold atom gas impinging upon a step\npotential created by the optical light field. In the presence of spin-orbit\n(SO) coupling, the atomic eigenstates contain two types of evanescent states,\none of which is the ordinary evanescent state with pure imaginary wave vector\nwhile the other possesses complex wave vector and is recognized as oscillating\nevanescent state. We show that the presence and interplay of these two types of\nevanescent states can give rise to two different mechanisms for total internal\nreflection (TIR), and thus lead to unusual Goos-H\\\"anchen (GH) effect. As a\nresult, not only large positive but also large negative GH shift can be\nobserved in the reflected atomic beam. The dependence of the GH shift on the\nincident angle, energy and height of the step potential is studied numerically.",
        "positive": "Structure and dynamics of a rotating superfluid Bose-Fermi mixture: We investigate the structure and dynamics of a rotating superfluid Bose-Fermi\nmixture (SBFM) made of superfluid bosons and two-component (spin up and down)\nsuperfluid fermions. A ground-state phase diagram for the nonrotating case of a\nSBFM with specific parameters is given, where the ground-state configuration of\na nonrotating SBFM is mainly determined by the boson-fermion interaction. For\nthe rotating case of a SBFM with a sufficiently large rotation frequency, we\nshow that the system supports a mixed phase and three typical layer separated\nphases. In particular, the visible vortex formation in the fermionic superfluid\nexhibits a remarkable hysteresis effect during the dynamical evolution of a\nrotating SBFM, which is evidently different from the case of rotating\ntwo-component Bose-Einstein condensates."
    },
    {
        "anchor": "Zero sound in a quantum gas of spin-3/2 atoms with multipole exchange\n  interaction: In the context of quantum gases, we obtain a many-body Hamiltonian for\nspin-3/2 atoms with general multipole (spin, quadrupole, and octupole) exchange\ninteraction by employing the apparatus of irreducible spherical tensor\noperators. This Hamiltonian implies the finite-range interaction, whereas, for\nzero-range (contact) potentials parameterized by the $s$-wave scattering\nlength, the multipole exchange interaction becomes irrelevant. Following the\nreduced description method for quantum systems, we derive the quantum kinetic\nequation for spin-3/2 atoms in a magnetic field and apply it to examine the\nhigh-frequency oscillations known as zero sound.",
        "positive": "Morphology of an interacting three-dimensional trapped Bose-Einstein\n  condensate from many-particle variance anisotropy: The variance of the position operator is associated with how wide or narrow a\nwave-packet is, the momentum variance is similarly correlated with the size of\na wave-packet in momentum space, and the angular-momentum variance quantifies\nto what extent a wave-packet is non-spherically symmetric. We examine an\ninteracting three-dimensional trapped Bose-Einstein condensate at the limit of\nan infinite number of particles, and investigate its position, momentum, and\nangular-momentum anisotropies. Computing the variances of the three Cartesian\ncomponents of the position, momentum, and angular-momentum operators we present\nsimple scenarios where the anisotropy of a Bose-Einstein condensate is\ndifferent at the many-body and mean-field levels of theory, despite having the\nsame many-body and mean-field densities per particle. This suggests a way to\nclassify correlations via the morphology of 100\\% condensed bosons in a\nthree-dimensional trap at the limit of an infinite number of particles.\nImplications are briefly discussed."
    },
    {
        "anchor": "Unconventional magnetism in imbalanced Fermi systems with magnetic\n  dipolar interactions: We study the magnetic structure of the ground state of an itinerant Fermi\nsystem of spin-\\nicefrac{1}{2} particles with magnetic dipole-dipole\ninteractions. We show that, quite generally, the spin state of particles depend\non its momentum, i.e., spin and orbital degrees of freedom are entangled and\ntaken separately are not ``good'' quantum numbers. Specifically, we consider a\nuniform system with non-zero magnetization at zero temperature. Assuming the\nmagnetization is along $z$-axis, the quantum spin states are $\\v{k}$-dependent\nlinear combinations of eigenstates of the $\\sigma_z$ Pauli matrix. This leads\nto novel spin structures in \\textit{momentum space} and to the fact that the\nFermi surfaces for ``up'' and ``down'' spins are not well defined. The system\nstill has a cylindrical axis of symmetry along the magnetization axis. We also\nshow that the self energy has a universal structure which we determine based on\nthe symmetries of the dipolar interaction and we explicitly calculated it in\nthe Hartree-Fock approximation. We show that the bare magnetic moment of\nparticles is renormalized due to particle-particle interactions and we give\norder of magnitude estimates of this renormalization effect. We estimate that\nthe above mentioned dipolar effects are small but we discuss possible scenarios\nwhere this physics may be realized in future experiments.",
        "positive": "Nonlinear synthetic gauge potentials and sonic horizons in Bose-Einstein\n  condensates: Phonons in a Bose-Einstein condensate can be made to behave as if they\npropagate in curved spacetime by controlling the condensate flow speed.\nSeemingly disconnected to this, artificial gauge potentials can be induced in\ncharge neutral atomic condensates by for instance coupling two atomic levels to\na laser field. Here we connect these two worlds and show that synthetic\ninteracting gauge fields, i.e., density-dependent gauge potentials, induce a\nnon-trivial spacetime structure for the phonons. This allows for the creation\nof new spacetime geometries which depend not on the flow speed of the\ncondensate but on an easily controlled transverse laser phase. Using this, we\nshow how to create artificial black holes in a stationary condensate, we\nsimulate charge in a Reissner-Nordstr\\\"om black hole and induce cosmological\nhorizons by creating de Sitter spacetimes. We then show how to combine this de\nSitter spacetime with a black hole, which also opens up the possibility to\nstudy in experiments its quantum stability."
    },
    {
        "anchor": "Condensate deformation and quantum depletion of Bose-Einstein\n  condensates in external potentials: The one-body density matrix of weakly interacting, condensed bosons in\nexternal potentials is calculated using inhomogeneous Bogoliubov theory. We\ndetermine the condensate deformation caused by weak external potentials on the\nmean-field level. The momentum distribution of quantum fluctuations around the\ndeformed ground state is obtained analytically, and finally the resulting\nquantum depletion is calculated. The depletion due to the external potential,\nor potential depletion for short, is a small correction to the homogeneous\ndepletion, validating our inhomogeneous Bogoliubov theory. Analytical results\nare derived for weak lattices and spatially correlated random potentials, with\nsimple, universal results in the Thomas-Fermi limit of very smooth potentials.",
        "positive": "The `Higgs' Amplitude Mode at the Two-Dimensional Superfluid-Mott\n  Insulator Transition: Spontaneous symmetry breaking plays a key role in our understanding of\nnature. In a relativistic field theory, a broken continuous symmetry leads to\nthe emergence of two types of fundamental excitations: massless Nambu-Goldstone\nmodes and a massive `Higgs' amplitude mode. An excitation of Higgs type is of\ncrucial importance in the standard model of elementary particles and also\nappears as a fundamental collective mode in quantum many-body systems. Whether\nsuch a mode exists in low-dimensional systems as a resonance-like feature or\nbecomes over-damped through coupling to Nambu-Goldstone modes has been a\nsubject of theoretical debate. Here we reveal and study a Higgs mode in a\ntwo-dimensional neutral superfluid close to the transition to a Mott insulating\nphase. We unambiguously identify the mode by observing the expected softening\nof the onset of spectral response when approaching the quantum critical point.\nIn this regime, our system is described by an effective relativistic field\ntheory with a two-component quantum-field, constituting a minimal model for\nspontaneous breaking of a continuous symmetry. Additionally, all microscopic\nparameters of our system are known from first principles and the resolution of\nour measurement allows us to detect excited states of the many-body system at\nthe level of individual quasiparticles. This allows for an in-depth study of\nHiggs excitations, which also addresses the consequences of reduced\ndimensionality and confinement of the system. Our work constitutes a first step\nin exploring emergent relativistic models with ultracold atomic gases."
    },
    {
        "anchor": "Three-component soliton states in spinor $F=1$ Bose-Einstein condensates: Dilute-gas Bose-Einstein condensates are an exceptionally versatile testbed\nfor the investigation of novel solitonic structures. While matter-wave solitons\nin one- and two-component systems have been the focus of intense research\nefforts, an extension to three components has never been attempted in\nexperiments, to the best of our knowledge. Here, we experimentally demonstrate\nthe existence of robust dark-bright-bright (DBB) and dark-dark-bright (DDB)\nsolitons in a spinor $F=1$ condensate. We observe lifetimes on the order of\nhundreds of milliseconds for these structures. Our theoretical analysis, based\non a multiscale expansion method, shows that small-amplitude solitons of these\ntypes obey universal long-short wave resonant interaction models, namely\nYajima-Oikawa systems. Our experimental and analytical findings are\ncorroborated by direct numerical simulations highlighting the persistence of,\ne.g., the DBB states, as well as their robust oscillations in the trap.",
        "positive": "An Analytical Window into the World of Ultracold Atoms: We review the recent developments which had taken place in the domain of\nquasi one dimensional BECs from the viewpoint of integrability. To start with,\nwe consider the dynamics of scalar BECs in a time independent harmonic trap and\nobserve that the scattering length (SL) can be suitably manipulated either to\ncompress the bright solitons to attain peak matter wave density without causing\ntheir explosion or to broaden the width of the condensates without diluting\nthem. When the harmonic trap frequency becomes time dependent, we notice that\none can stabilize the condensates in the confining domain while the density of\nthe condensates continue to increase in the expulsive region. We also observe\nthat the trap frequency and the temporal SL can be maneuvered to generate\nmatter wave interference patterns indicating the coherent nature of the atoms\nin the condensates. We also notice that a small repulsive three body\ninteraction when reinforced with attractive binary interaction can extend the\nregion of stability of the condensates in the quasi-one dimensional regime. On\nthe other hand, the investigation of two component BECs in a time dependent\nharmonic trap suggests that it is possible to switch matter wave energy from\none mode to the other confirming the fact that vector BECs are long lived\ncompared to scalar BECs. The Feshbach resonance management of vector BECs\nindicates that the two component BECs in a time dependent harmonic trap are\nmore stable compared to the condensates in a time independent trap. The\nintroduction of weak time dependent Rabi coupling rapidly compresses the bright\nsolitons which however can be again stabilized through Feshbach resonance or by\nfinetuning the Rabi coupling while the spatial coupling of vector BECs\nintroduces a phase difference between the condensates which subsequently can be\nexploited to generate interference pattern in the bright or dark solitons."
    },
    {
        "anchor": "Superfluidity of pure spin current in ultracold Bose gases: We study the superfluidity of a pure spin current that is a spin current\nwithout mass current. We examine two types of pure spin currents, planar and\ncircular, in spin-1 Bose gas. For the planar current, it is usually unstable,\nbut can be stabilized by the quadratic Zeeman effect. The circular current can\nbe generated with spin-orbit coupling. When the spin-orbit coupling strength is\nweak, we find that the circular pure spin current is the ground state of the\nsystem and thus a super-flow. We discuss the experimental schemes to realize\nand detect a pure spin current.",
        "positive": "The large coordination number expansion of a lattice Bose gas at finite\n  temperature: The expansion of the partition function for large coordination number $Z$ is\na long standing method and has formerly been used to describe the Ising model\nat finite temperatures. We extend this approach and study the interacting Bose\ngas at finite temperatures. An analytical expression for the free energy is\nderived which is valid for weakly interacting and strongly interacting bosons.\nThe transition line which separates the superfluid phase from Mott\ninsulating/normal gas phase is shown for fillings $\\langle\\hat n\\rangle=1$ and\n$\\langle\\hat n\\rangle=2$. For unit filling, our findings agree qualitatively\nwith Quantum Monte-Carlo results. Contrary to the well-known mean-field result,\nthe shift of the critical temperature in the weakly interacting regime is\napparent."
    },
    {
        "anchor": "Collective excitations and the gap in spectrum of the degenerated Bose\n  gas: Model of the degenerated weakly non-ideal Bose gas is considered without\nsuggestion on C-number representation of the creation and annihilation\noperators with zero momentum. The \"density-density\" correlation function and\nthe one-particle Green function are calculated on basis of the suggestion about\nC-number representation of the operator of particle density in the Bose\ncondensate. It is shown, that the pole in the \"density-density\" Green function\ndetermines the Bogolyubov's spectrum of the collective excitations, which have\nthe phonon-roton form. At the same time the spectrum of the one-particle\nexcitations possesses a gap, whose value is connected with the density of\nparticles in the Bose condensate.",
        "positive": "Thermodynamics, spin-charge separation and correlation functions of\n  spin-1/2 fermions with repulsive interaction: We investigate the low temperature thermodynamics and correlation functions\nof one-dimensional spin-1/2 fermions with strong repulsion in an external\nmagnetic field via the thermodynamic Bethe ansatz method. The exact\nthermodynamics of the model in a weak magnetic field is derived with the help\nof Wiener-Hopf techniques. It turns out that the low energy physics can be\ndescribed by spin-charge separated conformal field theories of an effective\nTomonaga-Luttinger liquid and an antiferromagnetic SU(2) Heisenberg spin chain.\nHowever, these two types of conformally invariant low-lying excitations may\nbreak down as excitations take place far away from the Fermi points. The long\ndistance asymptotics of the correlation functions and the critical exponents\nfor the model in the presence of a magnetic field at zero temperature are\nderived in detail by solving dressed charge equations and by conformal mapping.\nFurthermore, we calculate the conformal dimensions for particular cases of\ncorrelation functions. The leading terms of these correlation functions are\ngiven explicitly for a weak magnetic field $H\\ll 1$ and for a magnetic field\nclose to the critical field $H\\rightarrow H_{c}$. Our analytical results\nprovide insights into universal thermodynamics and criticality in\none-dimensional many-body physics."
    },
    {
        "anchor": "Condensed Groundstates of Frustrated Bose-Hubbard Models: We study theoretically the groundstates of two-dimensional Bose-Hubbard\nmodels which are frustrated by gauge fields. Motivated by recent proposals for\nthe implementation of optically induced gauge potentials, we focus on the\nsituation in which the imposed gauge fields give rise to a pattern of staggered\nfluxes, of magnitude $\\alpha$ and alternating in sign along one of the\nprincipal axes. For $\\alpha=1/2$ this model is equivalent to the case of\nuniform flux per plaquette $n_\\phi=1/2$, which, in the hard-core limit,\nrealizes the \"fully frustrated\" spin-1/2 XY model. We show that the mean-field\ngroundstates of this frustrated Bose-Hubbard model typically break\ntranslational symmetry. We introduce a general numerical technique to detect\nbroken symmetry condensates in exact diagonalization studies. Using this\ntechnique we show that, for all cases studied, the groundstate of the\nBose-Hubbard model with staggered flux $\\alpha$ is condensed, and we obtain\nquantitative determinations of the condensate fraction. We discuss the\nexperimental consequences of our results. In particular, we explain the meaning\nof gauge-invariance in ultracold atom systems subject to optically induced\ngauge potentials, and show how the ability to imprint phase patterns prior to\nexpansion can allow very useful additional information to be extracted from\nexpansion images.",
        "positive": "Emergent devil's staircase without particle-hole symmetry in Rydberg\n  quantum gases with competing attractive and repulsive interactions: The devil's staircase is a fractal structure that characterizes the ground\nstate of one-dimensional classical lattice gases with long-range repulsive\nconvex interactions. Its plateaus mark regions of stability for specific\nfilling fractions which are controlled by a chemical potential. Typically such\nstaircase has an explicit particle-hole symmetry, i.e., the staircase at more\nthan half-filling can be trivially extracted from the one at less than half\nfilling by exchanging the roles of holes and particles. Here we introduce a\nquantum spin chain with competing short-range attractive and long-range\nrepulsive interactions, i.e. a non-convex potential. In the classical limit the\nground state features generalized Wigner crystals that --- depending on the\nfilling fraction --- are either composed of dimer particles or dimer holes\nwhich results in an emergent complete devil's staircase without explicit\nparticle-hole symmetry of the underlying microscopic model. In our system the\nparticle-hole symmetry is lifted due to the fact that the staircase is\ncontrolled through a two-body interaction rather than a one-body chemical\npotential. The introduction of quantum fluctuations through a transverse field\nmelts the staircase and ultimately makes the system enter a paramagnetic phase.\nFor intermediate transverse field strengths, however, we identify a region,\nwhere the density-density correlations suggest the emergence of quasi\nlong-range order. We discuss how this physics can be explored with\nRydberg-dressed atoms held in a lattice."
    },
    {
        "anchor": "Detecting quantum phase transitions in the quasi-stationary regime of\n  Ising chains: Recently, single-site observables have been shown to be useful for the\ndetection of dynamical criticality due to an emergence of a universal\ncritically-prethermal temporal regime in the magnetization [arXiv:2105.05986].\nHere, we explore the potential of single-site observables as probes of quantum\nphase transitions in integrable and nonintegrable transverse-field Ising chains\n(TFIC). We analytically prove the requirement of zero modes for a\nquasi-stationary temporal regime to emerge at a bulk probe site, and show how\nthis regime gives rise to a non-analytic behavior in the dynamical order\nprofiles. Our $t$-DMRG calculations verify the results of the quench mean-field\ntheory for near-integrable TFIC both with finite-size and finite-time scaling\nanalyses. We find that both finite-size and finite-time analyses suggest a\ndynamical critical point for a strongly nonintegrable and locally connected\nTFIC. We finally demonstrate the presence of a quasi-stationary regime in the\npower-law interacting TFIC, and extract local dynamical order profiles for TFIC\nin the long-range Ising universality class with algebraic light cones.",
        "positive": "Measurement of collective excitations in a spin-orbit-coupled\n  Bose-Einstein condensate: We measure the collective excitation spectrum of a spin-orbit coupled\nBose-Einstein condensate using Bragg spectroscopy. The spin-orbit coupling is\ngenerated by Raman dressing of atomic hyperfine states. When the Raman detuning\nis reduced, mode softening at a finite momentum is revealed, which provides\ninsight towards a supersolid-like phase transition. We find that for the\nparameters of our system, this softening stops at a finite excitation gap and\nis symmetric under a sign change of the Raman detuning. Finally, using a moving\nbarrier that is swept through the BEC, we also show the effect of the\ncollective excitation on the fluid dynamics."
    },
    {
        "anchor": "Supersolidity of dipolar Bose-Einstein condensates induced by coupling\n  to fermions: We study a mixture of a dipolar condensate and a degenerate Fermi gas in a\nquasi-one-dimensional geometry. We demonstrate that the presence of fermions\nmay drastically change the behavior of a dipolar condensate. For strong enough\nboson-fermion attraction a dipolar Bose-Fermi droplet appears in the mixture\nand a roton excitation develops in the Bogoliubov excitations spectrum. As\nshown analytically and by solving numerically the coupled set of extended\nGross-Pitaevski and Hartree-Fock equations for bosonic and fermionic\ncomponents, respectively, roton instability mechanism leads to the formation of\nsupersolid phase in a Bose-Einstein condensate. Scaling arguments show that\nalthough the dysprosium atoms are considered to demonstrate the appearance of\nthe supersolid phase, such a phase can be observed with less magnetic atoms\nlike chromium and even rubidium.",
        "positive": "Time-dependent entropy of a cooling Bose gas: Exact analytic solutions of a nonlinear boson diffusion equation with\nsuitable initial conditions that account for evaporative cooling of ultracold\natoms, plus boundary conditions at the singularity $\\epsilon=\\mu<0$ are\npresented, and used to calculate the time-dependent entropy of a cold quantum\ngas."
    },
    {
        "anchor": "Universality of the three-body Efimov parameter at narrow Feshbach\n  resonances: We measure the critical scattering length for the appearance of the first\nthree-body bound state, or Efimov three-body parameter, at seven different\nFeshbach resonances in ultracold 39K atoms. We study both intermediate and\nnarrow resonances, where the three-body spectrum is expected to be determined\nby the non-universal coupling of two scattering channels. We observe instead\napproximately the same universal relation of the three-body parameter with the\ntwo-body van der Waals radius already found for broader resonances, which can\nbe modeled with a single channel. This unexpected observation suggests the\npresence of a new regime for three-body scattering at narrow resonances.",
        "positive": "Strong-coupling limit in cold-molecule formation via photoassociation or\n  Feshbach resonance through Nikitin exponential resonance crossing: The strong-coupling limit of molecule formation in an atomic Bose-Einstein\ncondensate via two-mode one-color photoassociation or sweep across a Feshbach\nresonance is examined using a basic nonlinear time-dependent two-state model.\nFor the general class of term-crossing models with constant coupling, a common\nstrategy for attacking the problem is developed based on the reduction of the\ninitial system of semiclassical equations for atom-molecule amplitudes to a\nthird order nonlinear differential equation for the molecular state\nprobability. This equation provides deriving exact solution for a class of\nperiodic level-crossing models. These models reveal much in common with the\nRabi problem. Discussing the strong-coupling limit for the general case of\nvariable detuning, the equation is further truncated to a limit first-order\nnonlinear equation. Using this equation, the strong nonlinearity regime for the\nfirst Nikitin exponential-crossing model is analyzed and accurate asymptotic\nexpressions for the nonlinear transition probability to the molecular state are\nderived. It is shown that, because of a finite final detuning involved, this\nmodel displays essential deviations from the Landau-Zener behavior. In\nparticular, it is shown that in the limit of strong coupling the final\nconversion probability tends to 1/6. Thus, in this case the strong interaction\nlimit is not optimal for molecule formation. We have found that if optimal\nfield intensity is applied the molecular probability is increased up to 1/4\n(i.e., the half of the initial atomic population)."
    },
    {
        "anchor": "Spin-orbit coupling and perpendicular Zeeman field for fermionic cold\n  atoms: observation of the intrinsic anomalous Hall effect: We propose a scheme for generating Rashba spin-orbit coupling and\nperpendicular Zeeman field simultaneously for cold fermionic atoms in a\nharmonic trap through the coupling between atoms and laser fields. The\nrealization of Rashba spin-orbit coupling and perpendicular Zeeman field\nprovides opportunities for exploring many topological phenomena using cold\nfermionic atoms. We focus on the intrinsic anomalous Hall effect and show that\nit may be observed through the response of atomic density to a rotation of the\nharmonic trap.",
        "positive": "Generation of vortex dipoles in superfluid Fermi gas in BCS limit: We theoretically investigate the generation of the vortex dipoles in\nsuperfluid Fermi gas in the BCS limit. The vortex dipoles are generated in\nsuperfluid either by moving an obstacle above a critical speed or due to the\ndecay of the shock waves obtained on the sudden mixing of two superfluid\nfragments. We observe that in pancake-shaped traps, the shock waves can lead to\nthe formation of density ripples, which decay into vortex dipoles due to the\nonset of snake instability."
    },
    {
        "anchor": "Dynamical studies of macroscopic superposition states: Phase engineering\n  of controlled entangled number states of Bose-Einstein condensate in multiple\n  wells: We provide a scheme for the generation of entangled number states of\nBose-Einstein condensates in multiple wells with cyclic pairwise connectivity.\nThe condensate ground state in a multiple well trap can self-evolve, when phase\nengineered with specific initial phase differences between the neighboring\nwells, to a macroscopic superposition state with controllable entanglement --\nto multiple well generalization of double well NOON states. We demonstrate\nthrough numerical simulations the creation of entangled states in three and\nfour wells and then explore the creation of \"larger\" entangled states where\nthere are either a larger number of particles in each well or a larger number\nof wells. The type of entanglement produced as the particle numbers, or\ninteraction strength, increases changes in a novel and initially unexpected\nmanner.",
        "positive": "Medium-induced Interaction Between Impurities in a Bose-Einstein\n  Condensate: We consider two heavy particles immersed in a Bose-Einstein condensate in\nthree dimensions and compute their mutual interaction induced by excitations of\nthe medium. For an ideal Bose gas, the induced interaction is Newtonian up to a\nshift in distance which depends on the coupling strength between impurities and\nBosons. For a real BEC, we find that on short distances, the induced potential\nis dominated by three-body physics of a single Boson bound to the impurities,\nleading to an Efimov potential. At large distances of the order of the healing\nlength, a Yukawa potential emerges instead. In particular, we find that both\nregimes are realized for all impurity-boson couplings and determine the\ncorresponding crossover scales. The transition from the real to the ideal\ncondensate at low gas parameters is investigated."
    },
    {
        "anchor": "Particle creation in Bose--Einstein condensates: Theoretical formulation\n  based on conserving gapless mean field theory: We formulate particle creation phenomena in Bose--Einstein condensates in\nterms of conserving gapless mean field theory for weakly interacting Bose\ngases. The particle creation spectrum is calculated by rediagonalizing the\nBogoliubov--de Gennes (BdG) Hamiltonian in mean field theory. The conservation\nimplies that quasiparticle creation is accompanied by quantum backreaction to\nthe condensates. Particle creation in this mean field theory is found to be\nequivalent to that in quantum field theory (QFT) in curved spacetime. An\nexpression is obtained for an effective metric affected by quantum\nbackreaction. The formula for the particle creation spectrum obtained in terms\nof QFT in curved spacetime is shown to be the same as that given by\nrediagonalizing the BdG Hamiltonian.",
        "positive": "Optical excitation of nonlinear spin waves: We demonstrate a technique for exciting spin waves in an ultracold gas of\nRb-87 atoms based on tunable AC Stark potentials. This technique allows us to\nexcite normal modes of spin waves with arbitrary amplitudes in the trapped gas,\nincluding dipole, quadrupole, octupole, and hexadecapole modes. These modes\nexhibit strong nonlinearities, which manifest as amplitude dependence of the\nexcitation frequencies and departure from sinusoidal behavior. Our results are\nin good agreement with a full treatment of a quantum Boltzmann transport\nequation."
    },
    {
        "anchor": "High-field instability of field-induced triplon Bose-Einstein condensate: We study properties of magnetic field-induced Bose-Einstein condensate of\ntriplons as a function of temperature and the field within the\nHartree-Fock-Bogoliubov approach including the anomalous density. We show that\nthe magnetization is continuous across the transition, in agreement with the\nexperiment. In sufficiently strong fields the condensate becomes unstable due\nto triplon-triplon repulsion. As a result, the system is characterized by two\ncritical magnetic fields: one producing the condensate and the other destroying\nit. We show that nonparabolic triplon dispersion arising due to the gapped bare\nspectrum and the crystal structure has a strong influence on the phase diagram.",
        "positive": "Dynamical formation of two-fold fragmented many-body state induced by an\n  impurity in a double-well: We unravel the correlated quantum quench dynamics of a single impurity\nimmersed in a bosonic environment confined in an one-dimensional double-well\npotential. A particular emphasis is placed on the structure of the time-evolved\nmany-body wave function by relying on a Schmidt decomposition whose\ncoefficients directly quantify the number of configurations that are\nmacroscopically populated. For a non-interacting bosonic bath and weak\npostquench impurity-bath interactions, we observe the dynamical formation of a\ntwo-fold fragmented many-body state which is related to intra-band excitation\nprocesses of the impurity and manifests as a two-body phase separation\n(clustering) between the two species for repulsive (attractive) interactions.\nIncreasing the postquench impurity-bath coupling strength leads to the\ndestruction of the two-fold fragmentation since the impurity undergoes\nadditional inter-band excitation dynamics. By contrast, a weakly interacting\nbath suppresses excitations of the bath particles and consequently the system\nattains a weakly fragmented many-body state. Our results explicate the\ninterplay of intra- and inter-band impurity excitations for the dynamical\ngeneration of fragmented many-body states in multi-well traps and for designing\nspecific entangled impurity states."
    },
    {
        "anchor": "Taming the entanglement in the dynamical theory of weakly interacting\n  Bose gases: I show that the dynamics of the weakly interacting bose gas can be described\nby a modified time dependent Bogoliubov theory. The novelty of the approach is\nto include decoherence steps that gradually transform the entanglement entropy\nof the pure state into the von Neumann entropy of a statistical mixture. This\napproximation drastically reduces the entanglement that is needed in order to\nrepresent the system's state while becoming exponentially accurate in the mean\nfield limit. I argue that this scheme can be extended to all quantum systems\nwhose ground state can be well approximated by a variational wave function. The\nupshot is that the dynamics of almost all quantum systems can be reduced to\nstochastic classical motion supplemented with small quantum fluctuations.",
        "positive": "Interaction for the trapped fermi gas from a unitary transformation of\n  the exact two-body spectrum: We study systems of few two-component fermions interacting in a Harmonic\nOscillator trap. The fermion-fermion interaction is generated in a finite basis\nwith a unitary transformation of the exact two-body spectrum given by the Busch\nformula. The few-body Schr\\\"odinger equation is solved with the formalism of\nthe No-Core Shell Model. We present results for a system of three fermions\ninteracting at unitarity as well as for finite values of the S-wave scattering\nlength $a_2$ and effective range $r_2$. Unitary systems with four and five\nfermions are also considered. We show that the many-body energies obtained in\nthis approach are in excellent agreement with exact solutions for the\nthree-body problem, and results obtained by other methods in the other cases."
    },
    {
        "anchor": "Entangling many-body bound states with propagative modes in Bose-Hubbard\n  systems: The quantum evolution of a cloud of bosons initially localized on part of a\none dimensional optical lattice and suddenly subjected to a linear ramp is\nstudied, realizing a quantum analog of the \"Galileo ramp\" experiment. The main\nremarkable effects of this realistic setup are revealed using analytical and\nnumerical methods. Only part of the particles are ejected for a high enough\nramp, while the others remain self-trapped. Then, the trapped density profile\ndisplays rich dynamics with Josephson-like oscillations around a plateau. This\nsetup, by coupling bound states to propagative modes, creates two diverging\ncondensates for which the entanglement is computed and related to the\nequilibrium one. Further, we address the role of integrability on the\nentanglement and on the damping and thermalization of simple observables.",
        "positive": "Many body population trapping in ultracold dipolar gases: A system of interacting dipoles is of paramount importance for understanding\nof many-body physics. The interaction between dipoles is {\\it anisotropic} and\n{\\it long-range}. While the former allows to observe rich effects due to\ndifferent geometries of the system, long-range ($1/r^3$) interactions lead to\nstrong correlations between dipoles and frustration. In effect, interacting\ndipoles in a lattice form a paradigmatic system with strong correlations and\nexotic properties with possible applications in quantum information\ntechnologies, and as quantum simulators of condensed matter physics, material\nscience, etc. Notably, such a system is extremely difficult to model due to a\nproliferation of interaction induced multi-band excitations for sufficiently\nstrong dipole-dipole interactions. In this article we develop a consistent\ntheoretical model of interacting polar molecules in a lattice by applying the\nconcepts and ideas of ionization theory which allows us to include highly\nexcited Bloch bands. Additionally, by involving concepts from quantum optics\n(population trapping), we show that one can induce frustration and engineer\nexotic states, such as Majumdar-Ghosh state, or vector-chiral states in such a\nsystem."
    },
    {
        "anchor": "The dynamics of coherence between coupled and decoupled one-dimensional\n  quasicondensates: We reproduce the sub-exponential decoherence of one-dimensional\nquasicondensates observed in recent experiments. Counter-intuitively, the\nquasicondensates may decohere even when stongly coupled, if the temperature is\nlarge enough or the peak density is low enough to allow significant density\nfluctuations. We also propose an experiment to investigate the growth of\ncoherence between two initially incoherent quasicondensates. We predict that\nthe coherence will rise on a much slower timescale, and the final coherence\nagain depends strongly on the density fluctuations.",
        "positive": "Collective Modes in a Unitary Fermi Gas across the Superfluid Phase\n  Transition: We provide a joint theoretical and experimental investigation of the\ntemperature dependence of the collective oscillations of first sound nature\nexhibited by a highly elongated harmonically trapped Fermi gas at unitarity,\nincluding the region below the critical temperature for superfluidity.\nDifferently from the lowest axial breathing mode, the hydrodynamic frequencies\nof the higher nodal excitations show a temperature dependence, which is\ncalculated starting from Landau two-fluid theory and using the available\nexperimental knowledge of the equation of state. The experimental results agree\nwith high accuracy with the predictions of theory and provide the first\nevidence for the temperature dependence of the collective frequencies near the\nsuperfluid phase transition."
    },
    {
        "anchor": "Manipulation of an elongated internal Josephson junction of bosonic\n  atoms: We report on the experimental characterization of a spatially extended\nJosephson junction realized with a coherently-coupled two-spin-component\nBose-Einstein condensate. The cloud is trapped in an elongated potential such\nthat that transverse spin excitations are frozen. We extract the non-linear\nparameter with three different manipulation protocols. The outcomes are all\nconsistent with a simple local density approximation of the spin hydrodynamics,\ni.e., of the so-called Bose-Josephson junction equations. We also identify a\nmethod to produce states with a well defined uniform magnetization.",
        "positive": "Fast generation of time-stationary spin-1 squeezed states by\n  non-adiabatic control: A protocol for the creation of time-stationary squeezed states in a spin-1\nBose condensate is proposed. The method consists of a pair of controlled\nquenches of an external magnetic field, which allows tuning of the system\nHamiltonian in the vicinity of a phase transition. The quantum fluctuations of\nthe system are well described by quantum harmonic oscillator dynamics in the\nlimit of large system size, and the method can be applied to a spin-1 gas\nprepared in the low or high energy polar states."
    },
    {
        "anchor": "Ground state and excitation properties of soft-core bosons: We study the physics of soft-core bosons at zero temperature in two\ndimensions for a class of potentials that could be realised in experiments with\nRydberg dressed Bose-Einstein condensates. We analyze the ground state\nproperties of the system in detail and provide a complete description of the\nexcitation spectra in both superfluid, supersolid and crystalline phase for a\nwide range of interaction strengths and densities. In addition we describe a\nmethod to extract the transverse gapless excitation modes in the phases with\nbroken translational symmetry within the framework of path integral Monte Carlo\nmethods.",
        "positive": "Strings of ultracold molecules in a synthetic dimension: We consider ultracold polar molecules trapped in a unit-filled\none-dimensional chain in real space created with an optical lattice or a\ntweezer array and illuminated by microwaves that resonantly drive transitions\nwithin a chain of rotational states. We describe the system by a\ntwo-dimensional lattice model, with the first dimension being a lattice in real\nspace and the second dimension being a lattice in a synthetic direction\ncomposed of rotational states. We calculate this system's ground-state phase\ndiagram. We show that as the dipole interaction strength is increased, the\nmolecules undergo a phase transition from a two-dimensional gas to a phase in\nwhich the molecules bind together and form a string that resembles a\none-dimensional object living in the two-dimensional (i.e, one real and one\nsynthetic dimensional) space. We demonstrate this with two complementary\ntechniques: numerical calculations using matrix product state techniques and an\nanalytic solution in the limit of infinitely strong dipole interaction. Our\ncalculations reveal that the string phase at infinite interaction is\neffectively described by emergent particles living on the string and that this\nleads to a rich spectrum with excitations missed in earlier mean-field\ntreatments."
    },
    {
        "anchor": "Degeneracy of Many-body Quantum States in an Optical Lattice with a\n  Uniform Magnetic Field: We prove a theorem that shows the degeneracy of many-body states depends on\ntotal particle number and flux filling ratio, for particles in a periodic\nlattice and under a uniform magnetic field. Non-interacting fermions and weakly\ninteracting bosons are given as two examples. For the later case, this\nphenomena can also be understood in terms of destructive quantum interferences\nof multiple symmetry related tunneling paths between classical energy minima,\nwhich is reminiscent of the spin-parity effect discovered in magnetic molecular\ncluster. We also show that the quantum ground state of a mesoscopic number of\nbosons in this system is not a simple mean-field state but a fragmented state\neven for very weak interactions.",
        "positive": "Vortex dynamics and turbulence in dipolar Bose-Einstein condensates: Quantum turbulence indicators in dipolar Bose-Einstein condensed fluids,\nfollowing emissions of vortex-antivortex pairs generated by a circularly moving\ndetuned laser, are being provided by numerical simulations of the corresponding\nquasi-two-dimensional Gross-Pitaevskii formalism with repulsive contact\ninteractions combined with tunable dipole-dipole strength. The critical\nvelocities of two variants of a circularly moving obstacle are determined and\nanalyzed for vortex-antivortex nucleation in the form of regular and cluster\nemissions. The turbulent dynamical behavior is predicted to follow closely the\ninitial emission of vortex-antivortex pairs, relying on the expected\nKolmogorov's classical scaling law, which is verified by the spectral analysis\nof the incompressible part of the kinetic energy. Within our aim to provide\nfurther support in the up-to-now investigations of quantum turbulence, which\nhave been focused on non-dipolar Bose-Einstein condensates, we emphasize the\nrole of dipole-dipole interactions in the fluid dynamics."
    },
    {
        "anchor": "Testing the nonlocal kinetic energy functional of an inhomogeneous,\n  two-dimensional degenerate Fermi gas within the average density approximation: In a recent paper [Phys.~Rev.~A {\\bf 89}, 022503 (2014)], the average density\napproximation (ADA) was implemented to develop a parameter-free, nonlocal\nkinetic energy functional to be used in the orbital-free density-functional\ntheory of an inhomogenous, two-dimensional (2D), Fermi gas. In this work, we\nprovide a detailed comparison of self-consistent calculations within the ADA\nwith the exact results of the Kohn-Sham density-functional theory, and the\nelementary Thomas-Fermi (TF) approximation. We demonstrate that the ADA for the\n2D kinetic energy functional works very well under a wide variety of\nconfinement potentials, even for relatively small particle numbers. Remarkably,\nthe TF approximation for the kinetic energy functional, {\\em without any\ngradient corrections}, also yields good agreement with the exact kinetic energy\nfor all confining potentials considered, although at the expense of the spatial\nand kinetic energy densities exhibiting poor point-wise agreement, particularly\nnear the TF radius. Our findings illustrate that the ADA kinetic energy\nfunctional yields accurate results for {\\em both} the local and global\nequilibrium properties of an inhomogeneous 2D Fermi gas, without the need for\nany fitting parameters.",
        "positive": "Echo-Ramsey Interferometry with Motional Quantum States: Ramsey interferometers (RIs) using internal electronic or nuclear states find\nwide applications in science and engineering. We develop a matter wave Ramsey\ninterferometer for motional quantum states exploiting the S- and D-bands of an\noptical lattice and identify the different de-phasing and de-coherence\nmechanisms. We implement a band echo technique, employing repeated\n$\\pi$-pulses. This suppresses the de-phasing evolution and significantly\nincrease the coherence time of the motional state interferometer by one order\nof magnitude. We identify thermal fluctuations as the main mechanism for the\nremaining decay contrast. Our demonstration of an echo-Ramsey interferometer\nwith motional quantum states in an optical lattice has potential application in\nthe study of quantum many body lattice dynamics, and motional qubits\nmanipulation."
    },
    {
        "anchor": "Ground-State Dirac Monopole: We show theoretically that a monopole defect, analogous to the Dirac magnetic\nmonopole, may exist as the ground state of a dilute spin-1 Bose-Einstein\ncondensate. The ground-state monopole is not attached to a single semi-infinite\nDirac string, but forms a point where the circulation of a single vortex line\nis reversed. Furthermore, the three-dimensional dynamics of this monopole\ndefect are studied after the magnetic field pinning the monopole is removed and\nthe emergence of antimonopoles is observed. Our scheme is experimentally\nrealizable with the present-day state of the art.",
        "positive": "Ground state properties of trapped boson system with finite-range\n  Gaussian repulsion: Exact diagonalization study: We use exact diagonalization to study an interacting system of $N$ spinless\nbosons with finite-range Gaussian repulsion, confined in a\nquasi-two-dimensional harmonic trap with and without an introduced rotation.\nThe diagonalization of the Hamiltonian matrix using Davidson algorithm in\nsubspaces of quantized total angular momentum $L_{z}$ is carried out to obtain\nthe $N$-body lowest eigenenergy and eigenstate. To bring out the effect of\nquantum (Bose) statistics and consequent phase stiffness (rigidity) of the\nvariationally obtained many-body wavefunction on various physical quantities,\nour study spans from few-body ($N=2$) to many-body ($N=16$) systems. Further,\nto examine the finite-range effect of the repulsive Gaussian potential on\nmany-body ground state properties of the Bose-condensate, we obtain the lowest\neigenstate, the critical angular velocity of single vortex state and the\nquantum correlation (measured) in terms of von Neumann entanglement entropy and\ndegree of condensation. It is found that for small values of the range\n(measured by the parameter $\\sigma$) of Gaussian potential, the ground state\nenergy increases for few-boson ($2\\le N\\le 8$) systems but decreases for\nmany-boson ($N>8$) systems. On the other hand for relatively large values of\nthe range of Gaussian potential, the ground state energy exhibits a monotonic\ndecrease, regardless of the number of bosons $N$. For a given $N$, there is\nfound an optimal value of the range of Gaussian potential for which the first\nvortex (with $L_{z}=N$) nucleates at a lower value of the rotational angular\nvelocity $\\Omega_{\\bf c1}$ compared to the zero-range ($\\delta$-function)\npotential. Further, we observe that the inter-particle interaction and the\nintroduced rotation are competing effects with latter being dominant over the\nformer."
    },
    {
        "anchor": "Functional renormalisation group approach to the finite-temperature Bose\n  polaron: The non-perturbative functional renormalisation group (FRG) approach is\nemployed to study the Bose polaron problem at finite temperatures in the regime\nof strong attractive bath-impurity interactions. Both two- and\nthree-dimensional configurations are considered. The appearance of two polaron\nquasiparticle branches at finite temperatures is revealed, consistent with\nrecent findings by other analytical techniques. Then, ground-state polaron\nenergies are reported for selected interactions and temperatures within the gas\nsuperfluid phase.",
        "positive": "Spin squeezing in Bose-Einstein condensates: Limits imposed by\n  decoherence and non-zero temperature: We consider dynamically generated spin squeezing in interacting bimodal\ncondensates. We show that particle losses and non-zero temperature effects in a\nmultimode theory completely change the scaling of the best squeezing for large\natom numbers. We present the new scalings and we give approximate analytical\nexpressions for the squeezing in the thermodynamic limit. Besides reviewing our\nrecent theoretical results, we give here a simple physical picture of how\ndecoherence acts to limit the squeezing. We show in particular that under\ncertain conditions the decoherence due to losses and non-zero temperatureacts\nas a simple dephasing."
    },
    {
        "anchor": "Many-body Matter-wave Dark Soliton: The Gross-Pitaevskii equation - which describes interacting bosons in the\nmean-field approximation - possesses solitonic solutions in dimension one. For\nrepulsively interacting particles, the stationary soliton is dark, i.e. is\nrepresented by a local density minimum. Many-body effects may lead to filling\nof the dark soliton. Using quasi-exact many-body simulations, we show that, in\nsingle realizations, the soliton appears totally dark although the single\nparticle density tends to be uniform.",
        "positive": "Influence of a dark-soliton on the reflection of a Bose-Einstein\n  condensate by a square barrier: We study the quantum reflection of a two-dimensional disk-shaped\nBose-Einstein condensate with a dark-soliton excitation by a square potential\nbarrier. For the giving geometry, the dark-soliton initially located at the\ncentre of the condensate cloud survive long enough for investigating the\nreflection process. We show the time evolution of the reflection probability\nwith respect to various width of the barrier. The asymptotic value of the\nreflection probability is decreased by the existence of a dark-soliton, and is\nhighly sensitive to the initial orientation of the dark-soliton which also\naffects the excitation properties during the process of condensate and barrier\ninteraction."
    },
    {
        "anchor": "Core sizes and dynamical instabilities of giant vortices in dilute\n  Bose-Einstein condensates: Motivated by a recent demonstration of cyclic addition of quantized vorticity\ninto a Bose-Einstein condensate, the vortex pump, we study dynamical\ninstabilities and core sizes of giant vortices. The core size is found to\nincrease roughly as a square-root function of the quantum number of the vortex,\nwhereas the strength of the dynamical instability either saturates to a fairly\nlow value or increases extremely slowly for large quantum numbers. Our studies\nsuggest that giant vortices of very high angular momenta may be achieved by\ngradually increasing the operation frequency of the vortex pump.",
        "positive": "Binary Quantum Turbulence Arising from Countersuperflow Instability in\n  Two-Component Bose-Einstein Condensates: We theoretically study the development of quantum turbulence from two\ncounter-propagating superfluids of miscible Bose-Einstein condensates by\nnumerically solving the coupled Gross-Pitaevskii equations. When the relative\nvelocity exceeds a critical value, the counter-superflow becomes unstable and\nquantized vortices are nucleated, which leads to isotropic quantum turbulence\nconsisting of two superflows. It is shown that the binary turbulence can be\nrealized experimentally in a trapped system."
    },
    {
        "anchor": "Pseudogap effects in the strongly correlated regime of the\n  two-dimensional Fermi gas: The two-species Fermi gas with attractive short-range interactions in two\nspatial dimensions provides a paradigmatic system for the understanding of\nstrongly correlated Fermi superfluids in two dimensions. It is known to exhibit\na BEC-BCS crossover as a function of $\\ln(k_F a)$, where $a$ is the scattering\nlength, and to undergo a Berezinskii-Kosterlitz-Thouless superfluid transition\nbelow a critical temperature $T_c$. However, the extent of a pseudogap regime\nin the strongly correlated regime of $\\ln(k_F a)\\sim 1$, in which pairing\ncorrelations persist above $T_c$, remains largely unexplored with controlled\ntheoretical methods. Here we use finite-temperature auxiliary-field quantum\nMonte Carlo (AFMC) methods on discrete lattices in the canonical ensemble\nformalism to calculate thermodynamical observables in the strongly correlated\nregime. We extrapolate to continuous time and the continuum limit to eliminate\nsystematic errors and present results for particle numbers ranging from $N=42$\nto $N=162$. We estimate $T_c$ by a finite-size scaling analysis, and observe\nclear pseudogap signatures above $T_c$ and below a temperature $T^*$ in both\nthe spin susceptibility and free-energy gap. We also present results for the\ncontact, a fundamental thermodynamic property of quantum many-body systems with\nshort-range interactions.",
        "positive": "Vortex spin in a superfluid: General relativity predicts that the curvature of spacetime induces spin\nrotations on a parallel transported particle. We deploy Unruh's analogue\ngravity picture and consider a quantised vortex embedded in a two-dimensional\nsuperfluid Bose--Einstein condensate. We show that such a vortex behaves\ndynamically like a charged particle with a spin in a gravitational field. The\nexistence of a vortex spin in a superfluid complements Onsager's prediction of\nthe quantisation of circulation, and is suggestive of potential quantum\ntechnology applications of rotating superfluids."
    },
    {
        "anchor": "Two-dimensional short-range interacting attractive and repulsive Fermi\n  gases at zero temperature: We study a two-dimensional two-component Fermi gas with attractive or\nrepulsive short-range interactions at zero temperature. We use Diffusion Monte\nCarlo with Fixed Node approximation in order to calculate the energy per\nparticle and the opposite-spin pair distribution functions. We show the\nrelevance of beyond mean field effects and verify the consistency of our\napproach by using Tan's Contact relations.",
        "positive": "Spreading of correlations and Loschmidt echo after quantum quenches of a\n  Bose gas in the Aubry-Andr\u00e9 potential: We study the spreading of density-density correlations and the Loschmidt\necho, after different sudden quenches in an interacting one dimensional Bose\ngas on a lattice, also in the presence of a superimposed aperiodic potential.\nWe use a time dependent Bogoliubov approach to calculate the evolution of the\ncorrelation functions and employ the linked cluster expansion to derive the\nLoschmidt echo."
    },
    {
        "anchor": "Using off-diagonal confinement as a cooling method: In a recent letter [Phys. Rev. Lett. 104, 167201 (2010)] we proposed a new\nconfining method for ultracold atoms on optical lattices, based on off-diagonal\nconfinement (ODC). This method was shown to have distinct advantages over the\nconventional diagonal confinement (DC) that makes use of a trapping potential,\nincluding the existence of pure Mott phases and highly populated condensates.\nIn this paper we show that the ODC method can also lead to temperatures that\nare smaller than with the conventional DC method, depending on the control\nparameters. We determine these parameters using exact diagonalizations for the\nhard-core case, then we extend our results to the soft-core case by performing\nquantum Monte Carlo (QMC) simulations for both DC and ODC systems at fixed\ntemperatures, and analysing the corresponding entropies. We also propose a\nmethod for measuring the entropy in QMC simulations.",
        "positive": "Broken scale-invariance in time-dependent trapping potentials: The response of a cold atom gas with contact interactions to a smoothly\nvarying external harmonic confinement in the non-adiabatic regime is studied.\nThe time variation of the angular frequency is varied such that the system is,\nfor vanishing or infinitely strong contact interactions, scale invariant. The\ntime evolution of the system with broken scale invariance (i.e., the time\nevolution of the system with finite interaction strength), is contrasted with\nthat for a scale invariant system, which exhibits Efimovian-like expansion\ndynamics that is characterized by log-periodic oscillations with unique period\nand amplitude. It is found that the breaking of the scale invariance by the\nfiniteness of the interactions leads to a time dependence of the oscillation\nperiod and amplitude. It is argued, based on analytical considerations for\natomic gases of arbitrary size and numerical results for two one-dimensional\nparticles, that the oscillation pe riod approaches that of the scale-invariant\nsystem at large times. The role of the time-dependent contact in the expansion\ndynamics is analyzed."
    },
    {
        "anchor": "Subcritical temperature in Bose-Einstein condensates of chiral molecules: Bose-Einstein condensation of a sample of non-interacting chiral molecules\nleads to a non zero optical activity of the condensate and also to a\nsubcritical temperature in the heat capacity. This is due to the internal\nstructure of the molecule which, in our model, is considered as a simple\ntwo-state system, characterized by tunneling and parity violation. The\npredicted singular behavior found for the specific heat, below the condensation\ntemperature, sheds some light on the existence of the so far elusive parity\nviolation energy difference between enantiomers.",
        "positive": "Generalized Gross-Pitaevskii equation adapted to the $U(5)\\supset\n  SO(5)\\supset SO(3)$ symmetry for spin-2 condensates: A generalized Gross-Pitaevskii equation adapted to the $U(5)\\supset\nSO(5)\\supset SO(3)$ symmetry has been derived and solved for the spin-2\ncondensates. The spin-textile and the degeneracy of the ground state (g.s.)\ntogether with the factors affecting the stability of the g.s., such as the gap\nand the level density in the neighborhood of the g.s., have been studied. Based\non a rigorous treatment of the spin-degrees of freedom, the spin-textiles can\nbe understood in a $N$-body language. In addition to the ferro-, polar, and\ncyclic phases, the g,s, might in a mixture of them when $0< M< 2N$ ($M$ is the\ntotal magnetization). The great difference in the stability and degeneracy of\nthe g.s. caused by varying $\\varphi $ (which marks the features of the\ninteraction) and $M$ is notable.\n  Since the root mean square radius $R_{rms}$ is an observable, efforts have\nbeen made to derive a set of formulae to relate $R_{rms}$ and $% N$, $\\omega\n$(frequency of the trap), and $\\varphi $. These formulae provide a way to check\nthe theories with experimental data."
    },
    {
        "anchor": "Observation of the Meissner effect with ultracold atoms in bosonic\n  ladders: We report on the observation of the Meissner effect in bosonic flux ladders\nof ultracold atoms. Using artificial gauge fields induced by laser-assisted\ntunneling, we realize arrays of decoupled ladder systems that are exposed to a\nuniform magnetic field. By suddenly decoupling the ladders and projecting into\nisolated double wells, we are able to measure the currents on each side of the\nladder. For large coupling strengths along the rungs of the ladder, we find a\nsaturated maximum chiral current corresponding to a full screening of the\nartificial magnetic field. For lower coupling strengths, the chiral current\ndecreases in good agreement with expectations of a vortex lattice phase. Our\nwork marks the first realization of a low-dimensional Meissner effect and,\nfurthermore, it opens the path to exploring interacting particles in low\ndimensions exposed to a uniform magnetic field.",
        "positive": "Topologically quantized current in quasiperiodic Thouless pumps: Thouless pumps are topologically nontrivial states of matter with quantized\ncharge transport, which can be realized in atomic gases loaded into an optical\nlattice. This topological state is analogous to the quantum Hall state.\nHowever, contrarily to the exact, extremely precise, and robust quantization of\nthe Hall conductance, the pumped charge is strictly quantized only when the\npumping time is a multiple of a characteristic timescale, i.e., the pumping\ncycle duration. Here, we show instead that the pumped current becomes exactly\nquantized, independently from the pumping time, if the system is led into a\nquasiperiodic, incommensurate regime. In this quasiperiodic and topologically\nnontrivial state, the Bloch bands and the Berry curvature become flat, the\npumped charge becomes linear in time, while the current becomes steady,\ntopologically quantized, and proportional to the Chern number. The quantization\nof the current is exact up to exponentially small corrections. This has to be\ncontrasted with the case of the commensurate (nonquasiperiodic) regime, where\nthe current is not constant, and the pumped charge is quantized only at integer\nmultiples of the pumping cycle."
    },
    {
        "anchor": "Collective phenomena in quasi-two-dimensional fermionic polar molecules:\n  band renormalization and excitons: We theoretically analyze a quasi-two-dimensional system of fermionic polar\nmolecules in a harmonic transverse confining potential. The renormalized energy\nbands are calculated by solving the Hartree-Fock equation numerically for\nvarious trap and dipolar interaction strengths. The inter-subband excitations\nof the system are studied in the conserving time-dependent Hartree-Fock (TDHF)\napproximation from the perspective of lattice modulation spectroscopy\nexperiments. We find that the excitation spectrum consists of both\ninter-subband particle-hole excitation continuums and anti-bound excitons,\narising from the anisotropic nature of dipolar interactions. The excitonic\nmodes capture the majority of the spectral weight. We also evaluate the\ninter-subband transition rates in order to investigate the nature of the\nexcitonic modes and find that they are anti-bound states formed from\nparticle-hole excitations arising from several subbands. Our results indicate\nthat the excitonic effects are present for interaction strengths and\ntemperatures accessible in current experiments with polar molecules.",
        "positive": "Dynamic structure factor of a strongly correlated Fermi superfluid\n  within a density functional theory approach: We theoretically investigate the dynamic structure factor of a strongly\ninteracting Fermi gas at the crossover from Bardeen-Cooper-Schrieffer\nsuperfluids to Bose-Einstein condensates, by developing an improved random\nphase approximation within the framework of a density functional theory - the\nso-called superfluid local density approximation. Compared with the previous\nrandom-phase-approximation studies based on the standard Bogoliubov-de Gennes\nequations, the use of the density functional theory greatly improves the\naccuracy of the equation of state at the crossover, and leads to a better\ndescription of both collective Bogoliubov-Anderson-Goldstone phonon mode and\nsingle-particle fermionic excitations at small transferred momentum. Near\nunitarity, where the s-wave scattering length diverges, we show that the\nsingle-particle excitations start to significantly contribute to the spectrum\nof dynamic structure factor once the frequency is above a threshold of the\nenergy gap at $2\\Delta$. The sharp rise in the spectrum at this threshold can\nbe utilized to measure the pairing gap $\\Delta$. Together with the sound\nvelocity determined from the phonon branch, the dynamic structure factor\nprovides us some key information of the crossover Fermi superfluid. Our\npredictions could be examined in experiments with $^{6}$Li or $^{40}$K atoms\nusing Bragg spectroscopy."
    },
    {
        "anchor": "Quantum Computation and Quantum Simulation with Ultracold Molecules: Ultracold molecules confined in optical lattices or tweezer traps can be used\nto process quantum information and simulate the behaviour of many-body quantum\nsystems. Molecules offer several advantages for these applications. They have a\nlarge set of stable states with strong transitions between them and long\ncoherence times. They can be prepared in a chosen state with high fidelity, and\nthe state populations can be measured efficiently. They have controllable\nlong-range dipole-dipole interactions that can be used to entangle pairs of\nmolecules and generate interesting many-body states. We review the advances\nthat have been made and the challenges still to overcome, and describe the new\nideas that will unlock the full potential of the field.",
        "positive": "On the strong influence of boundaries on the bulk microstructure of a\n  uniform interacting Bose gas: It is usually assumed that the boundaries do not affect the bulk\nmicrostructure of an interacting uniform Bose gas.\n  Therefore, the models use the most convenient cyclic boundary conditions. We\nshow that, in reality, the boundaries affect strongly the bulk microstructure,\nby changing the ground-state energy E_0 and the energy of quasiparticles E(k).\nFor the latter, we obtain the formula E^2 =(h^2 k^{2}/2m)^2 + 2^{-f}n\\nu(k)(h^2\nk^2/m) differing from the well-known Bogolyubov formula by the factor 2^{-f},\nwhere f is the number of noncyclic coordinates.\n  The Bogolyubov solution is also possible in the presence of boundaries, but\nit has a larger value of $E_{0}$ and should be unstable. The influence of\nboundaries is related to the topology."
    },
    {
        "anchor": "Parametric triggering of vortices in toroidally trapped rotating\n  Bose-Einstein condensates: We study the creation of vortices by triggering the rotating Bose-Einstein\ncondensates in a toroidal trap with trap parameters such as laser beam waist\nand Gaussian potential depth. By numerically solving the time-dependent\nGross-Pitaevskii equation in two dimensions, we observe a change in vortex\nstructure and a considerable increase in the number of vortices when the waist\nof the irradiated laser beam is in consonance with the area of the condensate\nas we vary the Gaussian potential depth. By computing the root mean square\nradius of the condensate, we confirm the variation in the number of vortices\ngenerated as a function of the ratio between the root-mean-square radius of the\ncondensate and the laser beam waist. In particular, the number of hidden\nvortices reaches the maximum value when the above ratio is close to the value\n0.7. We find the variation in the number of vortices is rapid for deeper\nGaussian potentials, and we conclude that the larger beam waist and deeper\nGaussian potentials generate more vortices. Further, we calculate the number of\nvortices using the Feynman rule with Thomas Fermi approximation and compare\nthem with the numerical results. We also observe that the critical rotation\nfrequency decreases with an increase in depth of Gaussian potential.",
        "positive": "Tailoring quantum gases by Floquet engineering: Floquet engineering is the concept of tailoring a system by a periodic drive.\nIt has been very successful in opening new classes of Hamiltonians to the study\nwith ultracold atoms in optical lattices, such as artificial gauge fields,\ntopological band structures and density-dependent tunneling. Furthermore,\ndriven systems provide new physics without static counterpart such as anomalous\nFloquet topological insulators. In this review article, we provide an overview\nof the exciting developments in the field and discuss the current challenges\nand perspectives."
    },
    {
        "anchor": "Persistent oscillations versus thermalization in the quench dynamics of\n  quantum gases with long-range interactions: Searching for nonthermalized dynamics in interacting quantum systems is not\nonly of fundamental theoretical interest in nonequilibrium quantum physics, but\nalso of immense practical significance in quantum information processing. In\nthis paper, we study quantum quench dynamics in an hard-core bosonic model with\ninfinite-range interactions, which have been realized in recent high-finesse\ncavity experiments. We show the long-time dynamics of this model can exhibit\neither undamped oscillations or thermalization depending on the choice of\ninitial states. The long-range nature of the interactions rather than conserved\nquantities are responsible for such nonergodic dynamical behaviors.",
        "positive": "Wilson Fermions and Axion Electrodynamics in Optical Lattices: The formulation of massless relativistic fermions in lattice gauge theories\nis hampered by the fundamental problem of species doubling, namely, the rise of\nspurious fermions modifying the underlying physics. A suitable tailoring of the\nfermion masses prevents such abundance of species, and leads to the so-called\nWilson fermions. Here we show that ultracold atoms provide us with the first\ncontrollable realization of these paradigmatic fermions, thus generating a\nquantum simulator of fermionic lattice gauge theories. We describe a novel\nscheme that exploits laser-assisted tunneling in a cubic optical superlattice\nto design the Wilson fermion masses. The high versatility of this proposal\nallows us to explore a variety of interesting phases in three-dimensional\ntopological insulators, and to test the remarkable predictions of axion\nelectrodynamics."
    },
    {
        "anchor": "Inter-band tunneling near the merging transition of Dirac cones: Motivated by a recent experiment in a tunable graphene analog [L. Tarruell et\nal., Nature 483, 302 (2012)], we consider a generalization of the Landau-Zener\nproblem to the case of a quadratic crossing between two bands in the vicinity\nof the merging transition of Dirac cones. The latter is described by the\nso-called universal hamiltonian. In this framework, the inter-band tunneling\nproblem depends on two dimensionless parameters: one measures the proximity to\nthe merging transition and the other the adiabaticity of the motion. Under the\ninfluence of a constant force, the probability for a particle to tunnel from\nthe lower to the upper band is computed numerically in the whole range of these\ntwo parameters and analytically in different limits using (i) the Stueckelberg\ntheory for two successive linear band crossings, (ii) diabatic perturbation\ntheory, (iii) adiabatic perturbation theory and (iv) a modified Stueckelberg\nformula. We obtain a complete phase diagram and explain the presence of\nunexpected probability oscillations in terms of interferences between two poles\nin the complex time plane. We also compare our results to the above mentioned\nexperiment.",
        "positive": "Violation of single-length scaling dynamics via spin vortices in an\n  isolated spin-1 Bose gas: We consider the phase ordering dynamics of an isolated quasi-two-dimensional\nspin-1 Bose gas quenched into an easy-plane ferromagnetic phase. Preparing the\ninitial system in an unmagnetized anti-ferromagnetic state the subsequent\nordering involves both polar core and Mermin-Ho spin vortices, with the ratio\nbetween the different vortices controllable by the quench parameter.\nFerromagnetic domain growth occurs as these vortices annihilate. The distinct\ndynamics of the two types of vortices means that the domain growth law is\ndetermined by two macroscopic length scales, violating the standard dynamic\nscaling hypothesis. Nevertheless we find that universality of the ordering\nprocess manifests in the decay laws for the spin vortices."
    },
    {
        "anchor": "Finite-temperature dynamics of a single vortex in a Bose-Einstein\n  condensate: Equilibrium precession and rotational symmetry breaking: We consider a finite-temperature Bose-Einstein condensate in a\nquasi-two-dimensional trap containing a single precessing vortex. We find that\nsuch a configuration arises naturally as an ergodic equilibrium of the\nprojected Gross-Pitaevskii equation, when constrained to a finite conserved\nangular momentum. In an isotropic trapping potential the condensation of the\nclassical field into an off-axis vortex state breaks the rotational symmetry of\nthe system. We present a methodology to identify the condensate and the\nGoldstone mode associated with the broken rotational symmetry in the\nclassical-field model. We also examine the variation in vortex trajectories and\nthermodynamic parameters of the field as the energy of the microcanonical field\nsimulation is varied.",
        "positive": "Phase operators and blurring time of a pair-condensed Fermi gas: Due to atomic interactions and dispersion in the total atom number, the order\nparameter of a pair-condensed Fermi gas experiences a collapse in a time that\nwe derive microscopically. As in the bosonic case, this blurring time depends\non the derivative of the gas chemical potential with respect to the atom number\nand on the variance of that atom number. The result is obtained first using\nlinearized time-dependent Bogoliubov-de Gennes equations, then in the Random\nPhase Approximation, and then it is generalized to beyond mean field. In this\nframework, we construct and compare two phase operators for the paired\nfermionic field: The first one, issued from our study of the dynamics, is the\ninfinitesimal generator of adiabatic translations in the total number of pairs.\nThe second one is the phase operator of the amplitude of the field of pairs on\nthe condensate mode. We explain that these two operators differ due to the\ndependence of the condensate wave function on the atom number."
    },
    {
        "anchor": "Superfluid phases of fermions with hybridized $s$ and $p$ orbitals: We explore the superfluid phases of a two-component Fermi mixture with\nhybridized orbitals in optical lattices. We show that there exists a general\nmapping of this system to the Lieb lattice. By using simple multiband models\nwith hopping between $s$ and $p$-orbital states, we show that superfluid order\nparameters can have a $\\pi$-phase difference between lattice sites, which is\ndistinct from the case with hopping between $s$-orbitals. If the population\nimbalance between the two spin species is tuned, the superfluid phase may\nevolve through various phases due to the interplay between hopping,\ninteractions and imbalance. We show that the rich behavior is observable in\nexperimentally realizable systems.",
        "positive": "Three-component Bose-Einstein condensates and wetting without walls: From Gross-Pitaevskii (GP) theory for ultracold gases it is predicted that\nphase-segregated three-component Bose-Einstein condensates (BEC) feature a\nwetting phase diagram that depends only on atomic masses and scattering\nlengths. This is unique in theories of surface and interfacial phase\ntransitions and provides a new opportunity for experimental observation of\nwetting phenomena in BEC mixtures. Previous GP theory for two-component BEC\nrelied on an {\\it ad hoc} optical wall boundary condition, on which the\ncharacter and location of the wetting phase transitions depend sensitively.\nThis boundary condition dependence is eliminated by adding a third component\nand treating the three phases on equal footing. An unequivocal wetting phase\ndiagram is captured, with phase boundaries calculated analytically using an\nextension of the established double-parabola approximation."
    },
    {
        "anchor": "Multimode N00N states in driven atomtronic circuits: We propose a method to generate multi-mode N00N states with arrays of\nultracold atoms. Our protocol requires a strong relative offset among the wells\nand a drive of the interparticle interaction at a frequency resonant with the\noffsets. The proposal is demonstrated by a numerical and a Floquet analysis of\nthe quantum dynamics of a ring-shaped atomtronics circuit made of M weakly\ncoupled optical traps. We generate a hierarchy of energy scales down to very\nfew low-energy states where N00N dynamics takes place, making multi-mode N00N\nstates appear at nearly regular time intervals. The production of multi-mode\nN00N states can be probed by time-of-flight imaging. Such states may be used to\nbuild a multiple beam splitter.",
        "positive": "Signatures of quantum chaos of Rydberg dressed bosons in a triple-well\n  potential: We study signatures of quantum chaos in dynamics of Rydberg dressed bosonic\natoms held in a one dimensional triple-well potential. Long-range\nnearest-neighbor and next-nearest-neighbor interactions, induced by laser\ndressing atoms to strongly interacting Rydberg states, affect drastically mean\nfield and quantum many-body dynamics. By analyzing the mean field dynamics,\nclassical chaos regions with positive and large Lyapunov exponents are\nidentified as a function of the potential well tilting and dressed\ninteractions. In the quantum regime, it is found that level statistics of the\neigen-energies gains a Wigner-Dyson distribution when the Lyapunov exponents\nare large, giving rise to signatures of strong quantum chaos. We find that both\nthe time averaged entanglement entropy and survival probability of the initial\nstate have distinctively large values in the quantum chaos regime. We further\nshow that population variances could be used as an indicator of the emergence\nof quantum chaos. This might provide a way to directly probe quantum chaotic\ndynamics through analyzing population dynamics in individual potential wells."
    },
    {
        "anchor": "FFLO or Majorana superfluids: The fate of fermionic cold atoms in\n  spin-orbit coupled optical lattices: The recent experimental realization of spin-orbit coupling (SOC) for\nultra-cold atoms opens a completely new avenue for exploring new quantum\nmatter. In experiments, the SOC is implemented simultaneously with a Zeeman\nfield. Such spin-orbit coupled Fermi gases are predicted to support Majorana\nfermions with non-Abelian exchange statistics in one dimension (1D). However,\nas shown in recent theory and experiments for 1D spin-imbalanced Fermi gases,\nthe Zeeman field can lead to the long-sought Fulde-Ferrell-Larkin-Ovchinnikov\n(FFLO) superfluids with non-zero momentum Cooper pairings, in contrast to the\nzero momentum pairing in Majorana superfluids. Therefore a natural question to\nask is which phase, FFLO or Majorana superfluids, will survive in spin-orbit\ncoupled Fermi gases in the presence of a large Zeeman field. In this paper, we\naddress this question by studying the mean field quantum phases of 1D\n(quasi-1D) spin-orbit coupled fermionic cold atom optical lattices.",
        "positive": "Particle creation in the spin modes of a dynamically oscillating\n  two-component Bose-Einstein condensate: We investigate the parametric amplification of the zero-point fluctuations in\nthe spin modes of a two-component Bose-Einstein condensate, triggered by the\ndynamical evolution of the condensate density. We first make use of a\nThomas-Fermi approximation to develop a tractable theoretical model of the\nquantum dynamics of the Bogoliubov excitations in a harmonically trapped\ncondensate with a time-dependent trapping frequency. The predictions of this\nmodel are then compared to an ab-initio numerical study of the correlation\nfunctions of density and spin fluctuations for general spatially inhomogeneous\nconfigurations. Results are shown for the two cases of expanding and\noscillating condensates: while the quantum excitation of spin modes remains\nweak and relatively featureless in the case of an expanding condensate, clear\nand experimentally promising signatures of particle creation are anticipated\nfor the oscillating case under suitable resonance conditions between the\ndensity and the spin modes."
    },
    {
        "anchor": "Ultradilute low-dimensional liquids: We calculate the energy of one- and two-dimensional weakly interacting\nBose-Bose mixtures analytically in the Bogoliubov approximation and by using\nthe diffusion Monte Carlo technique. We show that in the case of attractive\ninter- and repulsive intraspecies interactions the energy per particle has a\nminimum at a finite density corresponding to a liquid state. We derive the\nGross-Pitaevskii equation to describe droplets of such liquids and solve it\nanalytically in the one-dimensional case.",
        "positive": "Ballistic quench-induced correlation waves in ultracold gases: We investigate the wave packet dynamics of a pair of particles that undergoes\na rapid change of scattering length. The short-range interactions are modeled\nin the zero-range limit, where the quench is accomplished by switching the\nboundary condition of the wave function at vanishing particle separation. This\ngenerates a correlation wave that propagates rapidly to nonzero particle\nseparations. We have derived universal, analytic results for this process that\nlead to a simple phase-space picture of the quench-induced scattering.\nIntuitively, the strength of the correlation wave relates to the initial\ncontact of the system. We find that, in one spatial dimension, the $k^{-4}$\ntail of the momentum distribution contains a ballistic contribution that does\nnot originate from short-range pair correlations, and a similar conclusion can\nhold in other dimensionalities depending on the quench protocol. We examine the\nresultant quench-induced transport in an optical lattice in 1D, and a\nsemiclassical treatment is found to give quantitatively accurate estimates for\nthe transport probabilities."
    },
    {
        "anchor": "Quantum Monte Carlo method for pairing phenomena: Super-counter-fluid of\n  two-species Bose gases in optical lattices: We study the super-counter-fluid(SCF) states in the two-component hardcore\nBose-Hubbard model on the square lattice, using the quantum Monte Carlo method\nbased on the worm(directed loop) algorithm. Since the SCF state is a state of a\npair-condensation characterized by $< a^{\\dagger} b > \\neq 0, < a > = 0$, and\n$< b > = 0$, where $a$ and $b$ are the order parameters of the two components,\nit is important to study behaviors of the pair-correlation function $< a_{i}\nb_{i}^{\\dagger} a_{j}^{\\dagger} b_{j} >$. For this purpose, we propose a choice\nof the worm head for calculating the pair-correlation function. From this\npair-correlation, we confirm the Kosterlitz-Thouless(KT) charactor of the SCF\nphase. The simulation efficiency is also improved in the SCF phase.",
        "positive": "Aspects of Floquet Bands and Topological Phase Transitions in a\n  Continuously Driven Superlattice: Recently the creation of novel topological states of matter by a periodic\ndriving field has attracted great attention. To motivate further experimental\nand theoretical studies, we investigate interesting aspects of Floquet bands\nand topological phase transitions in a continuously driven Harper model. In\nsuch a continuously driven system with an odd number of Floquet bands, the\nbands are found to have nonzero Chern numbers in general and topological phase\ntransitions take place as we tune various system parameters, such as the\namplitude or the period of the driving field. The nontrivial Floquet band\ntopology results in a quantized transport of Wannier states in the lattice\nspace. For certain parameter choices, very flat yet topologically nontrivial\nFloquet bands may also emerge, a feature that is potentially useful for the\nsimulation of physics of strongly correlated systems. Some cases with an even\nnumber of Floquet bands may also have intriguing Dirac cones in the spectrum.\nUnder open boundary conditions, anomalous counter-propagating chiral edge modes\nand degenerate zero modes are also found as the system parameters are tuned.\nThese results should be of experimental interest because a continuously driven\nsystem is easier to realize than a periodically kicked system."
    },
    {
        "anchor": "Gross-Neveu-Wilson model and correlated symmetry-protected topological\n  phases: We show that a Wilson-type discretization of the Gross-Neveu model, a\nfermionic N-flavor quantum field theory displaying asymptotic freedom and\nchiral symmetry breaking, can serve as a playground to explore correlated\nsymmetry-protected phases of matter using techniques borrowed from high-energy\nphysics. A large- N study, both in the Hamiltonian and Euclidean formalisms,\nyields a phase diagram with trivial, topological, and symmetry-broken phases\nseparated by critical lines that meet at a tri-critical point. We benchmark\nthese predictions using tools from condensed matter and quantum information\nscience, which show that the large-N method captures the essence of the phase\ndiagram even at N = 1. Moreover, we describe a cold-atom scheme for the quantum\nsimulation of this lattice model, which would allow to explore the\nsingle-flavor phase diagram.",
        "positive": "Topological fractional pumping with alkaline-earth(-like) ultracold\n  atoms: Alkaline-earth(-like) ultracold atoms, trapped in optical lattices and in the\npresence of an external gauge field, can stabilise Mott insulating phases\ncharacterised by density and magnetic order. We show that this property can be\nused to realise a topological fractional pump. Our analysis is based on a\nmany-body adiabatic expansion and on time-dependent matrix-product-states\nnumerical simulations. We characterise the pumping protocol by including both\nfinite-size and non-adiabatic corrections. For a specific form of atom-atom\ninteraction, we present an exactly-solvable model of a fractional pump.\nFinally, the numerical simulations allow us to thoroughly study a realistic\nsetup amenable of an experimental realisation."
    },
    {
        "anchor": "Phase diagram of dipolar hard-core bosons on honeycomb lattice: In this paper, we study phase diagrams of dipolar hard-core boson gases on\nthe honeycomb lattice. The system is described by the Haldane-Bose-Hubbard\nmodel with complex hopping amplitudes and the nearest neighbor repulsion. By\nusing the slave-particle representation of the hard-core bosons and also the\npath-integral quantum Monte-Carlo simulations, we investigate the system and to\nshow that the systems have a rich phase diagram. There are Mott, superfluid,\nchiral superfluid, and sublattice chiral superfluid phases as well as the\ndensity-wave phase. We also found that there exists a coexisting phase of\nsuperfluid and chiral superfluid. Critical behaviors of the phase transitions\nare also clarified.",
        "positive": "Topological stripe state in an extended Fermi-Hubbard model: Interaction-induced topological systems have attracted a growing interest for\ntheir exotic properties going beyond the single-particle picture of topological\ninsulators. In particular, the interplay between strong correlations and finite\ndoping can give rise to nonhomogeneous solutions that break the translational\nsymmetry. In this work, we report the appearance of a topological stripe state\nin an interaction-induced Chern insulator around half-filling. In contrast to\nsimilar stripe phases in nontopological systems, here we observe the appearance\nof chiral edge states on top of the domain wall. Furthermore, we characterize\ntheir topological nature by analyzing the quantized transferred charge of the\ndomains in a pumping scheme. Finally, we focus on aspects relevant to observing\nsuch phases in state-of-the-art quantum simulators of ultracold atoms in\noptical lattices. In particular, we propose an adiabatic state preparation\nprotocol and a detection scheme of the topology of the system in real space."
    },
    {
        "anchor": "Resonant Superfluidity in an Optical Lattice: We study a system of ultracold fermionic Potassium (40K) atoms in a\nthree-dimensional optical lattice in the vicinity of an s-wave Feshbach\nresonance. Close to resonance, the system is described by a multi-band\nBose-Fermi Hubbard Hamiltonian. We derive an effective lowest-band Hamiltonian\nin which the effect of the higher bands is incorporated by a self-consistent\nmean-field approximation. The resulting model is solved by means of Generalized\nDynamical Mean-Field Theory. In addition to the BEC/BCS crossover we find a\nphase transition to a fermionic Mott insulator at half filling, induced by the\nrepulsive fermionic background scattering length. We also calculate the\ncritical temperature of the BEC/BCS-state and find it to be minimal at\nresonance.",
        "positive": "Probing the circulation of ring-shaped Bose-Einstein condensates: This paper reports the results of a theoretical and experimental study of how\nthe initial circulation of ring-shaped Bose-Einstein condensates (BECs) can be\nprobed by time-of-flight (TOF) images. We have studied theoretically the\ndynamics of a BEC after release from a toroidal trap potential by solving the\n3D Gross-Pitaevskii (GP) equation. The trap and condensate characteristics\nmatched those of a recent experiment. The circulation, experimentally imparted\nto the condensate by stirring, was simulated theoretically by imprinting a\nlinear azimuthal phase on the initial condensate wave function. The theoretical\nTOF images were in good agreement with the experimental data. We find that upon\nrelease the dynamics of the ring--shaped condensate proceeds in two distinct\nphases. First, the condensate expands rapidly inward, filling in the initial\nhole until it reaches a minimum radius that depends on the initial circulation.\nIn the second phase, the density at the inner radius increases to a maximum\nafter which the hole radius begins slowly to expand. During this second phase a\nseries of concentric rings appears due to the interference of ingoing and\noutgoing matter waves from the inner radius. The results of the GP equation\npredict that the hole area is a quadratic function of the initial circulation\nwhen the condensate is released directly from the trap in which it was stirred\nand is a linear function of the circulation if the trap is relaxed before\nrelease. These scalings matched the data. Thus, hole size after TOF can be used\nas a reliable probe of initial condensate circulation. This connection between\ncirculation and hole size after TOF will facilitate future studies of\natomtronic systems that are implemented in ultracold quantum gases."
    },
    {
        "anchor": "Spin-orbit coupled Bose-Einstein condensates in a one-dimensional\n  optical lattice: The realization of artificial gauge fields and spin-orbit coupling for\nultra-cold quantum gases promises new insight into paradigm solid state\nsystems. Here we experimentally probe the dispersion relation of a spin-orbit\ncoupled Bose-Einstein condensate loaded into a translating optical lattice by\nobserving its dynamical stability, and develop an effective band structure that\nprovides a theoretical understanding of the locations of the band edges. This\nsystem presents exciting new opportunities for engineering condensed-matter\nanalogs using the flexible toolbox of ultra-cold quantum gases.",
        "positive": "Robust sub-shot-noise measurement via Rabi-Josephson oscillations in\n  bimodal Bose-Einstein condensates: Mach-Zehnder atom interferometry requires hold-time phase-squeezing to attain\nreadout accuracy below the standard quantum limit. This increases its\nsensitivity to phase-diffusion, restoring shot-noise scaling of the optimal\nsignal-to-noise ratio, $s_o$, in the presence of interactions. The\ncontradiction between the preparations required for readout accuracy and\nrobustness to interactions, is removed by monitoring Rabi-Josephson\noscillations instead of relative-phase oscillations during signal acquisition.\nOptimizing $s_o$ with a Gaussian squeezed input, we find that hold-time number\nsqueezing satisfies both demands and that sub-shot-noise scaling is retained\neven for strong interactions."
    },
    {
        "anchor": "Matter-wave interferometers with trapped strongly interacting Feshbach\n  molecules: We implement two types of matter wave interferometers using trapped\nBose-condensed Feshbach molecules, from weak to strong interactions. In each\ncase, we focus on investigating interaction effects and their implications for\nthe performance. In the Ramsey-type interferometer where the interference\nbetween the two motional quantum states in an optical lattice is observed,\ninter-particle interactions are found to induce energy shifts in the states.\nConsequently, this results in a reduction of the interferometer frequency and\nintroduces a phase shift during the lattice pulses used for state manipulation.\nFurthermore, non-uniformity leads to dephasing and collisional losses of\ncondensate contribute to the degradation of contrast. In the Michelson-type\ninterferometer, where matter waves are spatially split and recombined in a\nwaveguide, interference is observed in the presence of significant interaction,\nhowever coherence degrades with increasing interaction strength. Notably,\ncoherence is also observed in thermal clouds, indicating the white-color nature\nof the implemented Michelson interferometer.",
        "positive": "Kinetic theory for a mobile impurity in a degenerate Tonks-Girardeau gas: A kinetic theory describing the motion of an impurity particle in a\ndegenerate Tonks-Girardeau gas is presented. The theory is based on the\none-dimensional Boltzmann equation. An iterative procedure for solving this\nequation is proposed, leading to the exact solution in number of special cases\nand to an approximate solution with the explicitly specified precision in a\ngeneral case. Previously we have reported that the impurity reaches a\nnon-thermal steady state, characterized by an impurity momentum $p_\\infty$\ndepending on its initial momentum $p_0$. In the present paper the detailed\nderivation of $p_\\infty(p_0)$ is provided. We also study the motion of an\nimpurity under the action of a constant force $F$. It is demonstrated that if\nthe impurity is heavier than the host particles, $m_i>m_h$, damped oscillations\nof the impurity momentum develop, while in the opposite case, $m_i<m_h$,\noscillations are absent. The steady state momentum as a function of the applied\nforce is determined. In the limit of weak force it is found to be force\nindependent for a light impurity and proportional to $\\sqrt{F}$ for a heavy\nimpurity."
    },
    {
        "anchor": "Persistent currents in two-component condensates in a toroidal trap: The stability of persistent currents in a two-component Bose-Einstein\ncondensate in a toroidal trap is studied both in the miscible and immiscible\nregimes. In the miscible regime we show that superflow decay is related to\nlinear instabilities of the spin-density Bogoliubov mode. We find a region of\npartial stability, where the flow is stable in the majority component while it\ndecays in the minority component. We also characterize the dynamical\ninstability appearing for a large relative velocity between the two components.\nIn the immiscible regime the stability criterion is modified and depends on the\nspecific density distribution of the two components. The effect of a coherent\ncoupling between the two components is also discussed.",
        "positive": "Temperature-dependent periodicity of the persistent current in strongly\n  interacting systems: The persistent current in small isolated rings enclosing magnetic flux is the\ncurrent circulating in equilibrium in the absence of an external excitation.\nWhile initially studied in superconducting and normal metals, recently, atomic\npersistent currents have been generated in ultracold gases spurring a new wave\nof theoretical investigations. Nevertheless, our understanding of the\npersistent currents in interacting systems is far from complete, especially at\nfinite temperatures. Here we consider the fermionic one-dimensional Hubbard\nmodel and show that in the strong-interacting limit, the current can change its\nflux period and sign (diamagnetic or paramagnetic) as a function of\ntemperature, features that cannot be explained within the single-particle or\nLuttinger liquid techniques. Also, the magnitude of the current can\ncounterintuitively increase with temperature, in addition to presenting\ndifferent rates of decay depending on the polarization of the system. Our work\nhighlights the properties of the strongly-interacting multi-component systems\nwhich are missed by conventional approximation techniques, but can be important\nfor the interpretation of experiments on persistent currents in ultracold\ngases."
    },
    {
        "anchor": "Floquet-Band Engineering of Shaken Bosonic Condensates: Optical control and manipulation of cold atoms has become an important topic\nin condensed matter. Widely employed are optical lattice shaking experiments\nwhich allow the introduction of artificial gauge fields, the design of\ntopological bandstructures, and more general probing of quantum critical\nphenomena. Here we develop new numerical methods to simulate these periodically\ndriven systems by implementing lattice shaking directly. As a result we avoid\nthe usual assumptions associated with a simplified picture based on Floquet\ndynamics. A demonstrable success of our approach is that it yields quantitative\nagreement with experiment, including Kibble-Zurek scaling. Importantly, we\nargue that because their dynamics corresponds to an effective non-linear\nSchr\\\"{o}dinger equation, these particular superfluid studies present a unique\nopportunity to address how general Floquet band engineering is affected by\ninteractions. In particular, interactions cause instabilities at which the\nbehavior of the system changes dramatically.",
        "positive": "Path-Integral Fujikawa's Approach to Anomalous Virial Theorems and\n  Equations of State for Systems with $SO(2, 1)$ Symmetry: We derive anomalous equations of state for nonrelativistic 2D complex bosonic\nfields with contact interactions, using Fujikawa's path-integral approach to\nanomalies and scaling arguments. In the process, we derive an anomalous virial\ntheorem for such systems. The methods used are easily generalizable for other\n2D systems, including fermionic ones, and of different spatial dimensionality,\nall of which share a classical $SO(2,1)$ Schrodinger symmetry. The discussion\nis of a more formal nature and is intended mainly to shed light on the\nstructure of anomalies in 2D many-body systems. The anomaly corrections to the\nvirial theorem and equation of state - pressure relationship - may be\nidentified as the Tan contact term. The practicality of these ideas rests upon\nbeing able to compute in detail the Fujikawa Jacobian that contains the\nanomaly. This and other conceptual issues, as well as some recent developments,\nare discussed at the end of the paper."
    },
    {
        "anchor": "Exact solutions to the four Goldstone modes around a dark soliton of the\n  nonlinear Schroedinger equation: This article is concerned with the linearisation around a dark soliton\nsolution of the nonlinear Schr\\\"odinger equation. Crucially, we present\nanalytic expressions for the four linearly-independent zero eigenvalue\nsolutions (also known as Goldstone modes) to the linearised problem. These\nsolutions are then used to construct a Greens matrix which gives the\nfirst-order spatial response due to some perturbation. Finally we apply this\nGreens matrix to find the correction to the dark-soliton wavefunction of a\nBose-Einstein condensate in the presence of fluctuations.",
        "positive": "Magnetically Controlled Exchange Process in an Ultracold Atom-Dimer\n  Mixture: We report on the observation of an elementary exchange process in an\noptically trapped ultracold sample of atoms and Feshbach molecules. We can\nmagnetically control the energetic nature of the process and tune it from\nendoergic to exoergic, enabling the observation of a pronounced threshold\nbehavior. In contrast to relaxation to more deeply bound molecular states, the\nexchange process does not lead to trap loss. We find excellent agreement\nbetween our experimental observations and calculations based on the solutions\nof three-body Schr\\\"odinger equation in the adiabatic hyperspherical\nrepresentation. The high efficiency of the exchange process is explained by the\nhalo character of both the initial and final molecular states."
    },
    {
        "anchor": "Quantized vortices in a rotating Bose-Einstein condensate with\n  spatiotemporally modulated interaction: We present theoretical analysis and numerical studies of the quantized\nvortices in a rotating Bose-Einstein condensate with spatiotemporally modulated\ninteraction in harmonic and anharmonic potentials, respectively. The exact\nquantized vortex and giant vortex solutions are constructed explicitly by\nsimilarity transformation. Their stability behavior has been examined by\nnumerical simulation, which shows that a new series of stable vortex states\n(defined by radial and angular quantum numbers) can be supported by the\nspatiotemporally modulated interaction in this system. We find that there exist\nstable quantized vortices with large topological charges in repulsive\ncondensates with spatiotemporally modulated interaction. We also give an\nexperimental protocol to observe these vortex states in future experiments.",
        "positive": "Multiple polaron quasiparticles with dipolar fermions in a bilayer\n  geometry: We study the Fermi polaron problem with dipolar fermions in a bilayer\ngeometry, where a single dipolar particle in one layer interacts with a Fermi\nsea of dipolar fermions in the other layer. By evaluating the polaron spectrum,\nwe obtain the appearance of a series of attractive branches when the distance\nbetween the layers diminishes. We relate these to the appearance of a series of\nbound two-dipole states when the interlayer dipolar interaction strength\nincreases. By inspecting the orbital angular momentum component of the polaron\nbranches, we observe an interchange of orbital character when system parameters\nsuch as the gas density or the interlayer distance are varied. Further, we\nstudy the possibility that the lowest energy two-body bound state spontaneously\nacquires a finite center of mass momentum when the density of fermions exceeds\na critical value, and we determine the dominating orbital angular momenta that\ncharacterize the pairing. Finally, we propose to use the tunneling rate from\nand into an auxiliary layer as an experimental probe of the impurity spectral\nfunction."
    },
    {
        "anchor": "Relevance of Bose-Einstein Condensation to the Interference of Two\n  Independent Bose Gases: Interference of two independently prepared ideal Bose gases is discussed, on\nthe basis of the idea of measurement-induced interference: even if the number\nof each gas is individually fixed finite and the symmetry of the system is not\nbroken, an interference pattern is observed on each single snapshot. The key\nrole is played by the Hanbury Brown and Twiss effect, which leads to an\noscillating pattern of the cloud of identical atoms. Then, how essential is the\nBose-Einstein condensation to the interference? We describe the ideal Bose\ngases trapped respectively in two spatially separated 3D harmonic traps at a\nfinite temperature as canonical ensembles with fixed numbers of atoms, and\ncompute the full statistics of the snapshot profiles of the expanding and\noverlapping gases released from the traps. We obtain a simple formula, which\nshows that the average fringe spectrum (average fringe contrast) is given by\nthe purity of each gas. The purity is known to be a good measure of\ncondensation, and this result clarifies the relevance of the condensation to\nthe interference. The fluctuation of the interference spectrum is also studied,\nand it is shown that the fluctuation is vanishingly small below the critical\ntemperature, while it is nonvanishing above. This implies that interference\npattern is certainly observed on every snapshot below the critical temperature.\nThe fact that the number of atoms is fixed in the canonical ensemble is crucial\nto this vanishing fluctuation.",
        "positive": "Optical-plug-assisted spin vortex in a $^{87}$Rb dipolar spinor\n  Bose-Einstein condensate: Generating a spin vortex in a $^{87}$Rb dipolar spinor Bose-Einstein\ncondensate in a controllable way is still experimentally challenging. We\npropose an experimentally easy and tunable way to produce spin vortex by\nvarying the potential barrier height and the width of an additionally applied\noptical plug. A topological phase transition occurs from the trivial single\nmode approximation phase to the optical-plug-assisted-vortex one, as the\nbarrier height increases and the width lies in an appropriate range. The\noptical plug causes radial density variation thus the spin vortex is favored by\nsignificantly lowering the intrinsic magnetic dipolar energy. A type of\ncoreless spin vortex, different from the conventional polar core vortex, is\npredicted by our numerical results. Our proposal removes a major obstacle to\ninvestigate the topological phase transition in a $^{87}$Rb dipolar spinor BEC."
    },
    {
        "anchor": "Feshbach Loss Spectroscopy in an Ultracold $^{23}$Na and $^{40}$K\n  Mixture: We perform Feshbach spectroscopy in an ultracold mixture of $^{23}$Na and\n$^{40}$K with different spin-state combinations. We have observed 24 new\ninterspecies Feshbach resonances at magnetic field up to 350 G. A full\ncoupled-channel calculation is performed to assign these resonances. Among\nthem, 12 resonances are identified as d-wave Feshbach resonances. These d-wave\nFeshbach resonances are about 5 G systematically smaller than the predications\nbased on previous model potential. Taking into account these new experimental\nresults, we improve the Born-Oppenheimer potentials between Na and K, and\nachieve good agreement between the theory and experiment for all the observed\nFeshbach resonances.",
        "positive": "Quantum dynamics of impurities in a Bose-Einstein condensate: We study the quantum dynamics of the two impurities in a trapped\nquasi-one-dimensional Bose-Einstein condensate (BEC). We explore the effect of\nimpurity-BEC and impurity-impurity interaction strengths on the dynamics of\nimpurities inside the Bose-Einstein condensate. By studying the\nauto-correlation function of impurities and the BEC, we analyze and quantify\nthe trapping of impurities inside the BEC. We find out that for the small value\nof inter-species coupling strength the BEC starts to oscillate inside the trap.\nFor mild coupling strengths, attractive and repulsive impurities are captured\nafter a few cycles of oscillation inside the BEC. In the strong interaction\nstrength regime, the to-and-fro motion of impurities is suppressed quite fast.\nOur conclusion indicates that quench dynamics can be a tool for studying\nimpurity BEC interactions or impurity-impurity interactions. Our analysis shows\nthat the generation of phonon, shock waves, soliton trains, and self-trapping\nis strongly dependent on the impurity-BEC coupling coefficient."
    },
    {
        "anchor": "A Wavefunction Microscope for Ultracold Atoms: Quantum simulations with ultracold atoms typically create atomic\nwavefunctions with structures at optical length scales, where direct imaging\nsuffers from the diffraction limit. In analogy to advances in optical\nmicroscopy for biological applications, we use a non-linear atomic response to\nsurpass the diffraction limit. Exploiting quantum interference, we demonstrate\nimaging with super-resolution of $\\lambda/100$ and excellent temporal\nresolution of 500 ns. We characterize our microscope's performance by measuring\nthe ensemble averaged wavefunction of atoms within the unit cells of an optical\nlattice, and observe the dynamics of atoms excited into periodic motion. This\napproach can be readily applied to image any atomic or molecular system, as\nlong as it hosts a three-level system.",
        "positive": "False vacuum decay in an ultracold spin-1 Bose gas: We propose an ultracold atom analogue of early universe vacuum decay using\nall three states of a spin-1 Bose gas. We consider a one-dimensional system\nwith both radio frequency and optical Raman coupling between internal states.\nAn advantage of our proposal is the lack of a time-modulated coupling, which\ncan lead to instabilities. Within the elaborate phase structure of the system\nwe identify an effective Klein-Gordon field and use Gross-Pitaevskii\nsimulations within the truncated Wigner approximation to model the decay of its\nfalse vacuum. We examine the dependence of the rate of vacuum decay on particle\ndensity for $^{7}$Li and $^{41}$K and find reasonable agreement with instanton\nmethods."
    },
    {
        "anchor": "Applications of fidelity measures to complex quantum systems: We revisit the fidelity as a measure for the stability and the complexity of\nthe quantum motion of single and many-body systems. Within the context of cold\natoms, we present on overview of applications of two fidelities which we call\nstatic and dynamical fidelity, respectively. The static fidelity applies to\nquantum problems which can be diagonalized since it is defined via the\neigenfunctions. In particular, we show that the static fidelity is a highly\neffective practical detector of avoided crossings characterizing the complexity\nof the systems and their evolutions. The dynamical fidelity is defined via the\ntime-dependent wave functions. Focussing on the quantum kicked rotor system, we\nhighlight a few practical applications of fidelity measurements in order to\nbetter understand the large variety of dynamical regimes of this paradigm of a\nlow-dimensional system with mixed regular-chaotic phase space.",
        "positive": "Fluctuations and stochastic processes in one-dimensional many-body\n  quantum systems: We study the fluctuation properties of a one-dimensional many-body quantum\nsystem composed of interacting bosons, and investigate the regimes where\nquantum noise or, respectively, thermal excitations are dominant. For the\nlatter we develop a semiclassical description of the fluctuation properties\nbased on the Ornstein-Uhlenbeck stochastic process. As an illustration, we\nanalyze the phase correlation functions and the full statistical distributions\nof the interference between two one-dimensional systems, either independent or\ntunnel-coupled and compare with the Luttinger-liquid theory."
    },
    {
        "anchor": "Organic polariton lasing and the weak- to strong-coupling crossover: Following experimental realizations of room temperature polariton lasing with\norganic molecules, we present a microscopic model that allows us to explore the\ncrossover from weak to strong matter-light coupling. We consider a\nnon-equilibrium Dicke-Holstein model, including both strong coupling to\nvibrational modes and strong matter-light coupling, providing the phase diagram\nof this model in the thermodynamic limit. We discuss the mechanism of polariton\nlasing, uncovering a process of self-tuning, and identify the relation and\ndistinction between regular dye lasers and organic polariton lasers.",
        "positive": "Analytic Harmonic Approach to the N-body problem: We consider an analytic way to make the interacting N-body problem tractable\nby using harmonic oscillators in place of the relevant two-body interactions.\nThe two body terms of the N-body Hamiltonian are approximated by considering\nthe energy spectrum and radius of the relevant two-body problem which gives\nfrequency, center position, and zero point energy of the corresponding harmonic\noscillator. Adding external harmonic one-body terms, we proceed to solve the\nfull quantum mechanical N-body problem analytically for arbitrary masses.\nEnergy eigenvalues, eigenmodes, and correlation functions like density matrices\ncan then be computed analytically. As a first application of our formalism, we\nconsider the N-boson problem in two- and three dimensions where we fit the\ntwo-body interactions to agree with the well-known zero-range model for two\nparticles in a harmonic trap. Subsequently, condensate fractions, spectra,\nradii, and eigenmodes are discussed as function of dimension, boson number N,\nand scattering length obtained in the zero-range model. We find that energies,\nradii, and condensate fraction increase with scattering length as well as boson\nnumber, while radii decrease with increasing boson number. Our formalism is\ncompletely general and can also be applied to fermions, Bose-Fermi mixtures,\nand to more exotic geometries."
    },
    {
        "anchor": "Equation of State of a Strongly Interacting many-Boson System from an\n  Effective Interaction: A contact potential describing an effective interaction between atomic $^4$He\nreproducing the results obtained with the HFDHE2 potential by Aziz et al. is\nemployed to study the resulting equation of state by means of Quantum Monte\nCarlo calculations. \\cblack The energy per particle and the pair distribution\nfunctions were investigated as a function of the ultraviolet cutoff $\\Lambda$.\nThe results suggest that not only the mean field properties of the system, such\nas the energy and the saturation density, are correctly reproduced, but also\nvery microscopic quantities such as the pair distribution function are seen to\nconverge towards the exact results when extrapolating for\n$\\Lambda\\rightarrow\\infty$.",
        "positive": "Probing the relaxation towards equilibrium in an isolated strongly\n  correlated 1D Bose gas: The problem of how complex quantum systems eventually come to rest lies at\nthe heart of statistical mechanics. The maximum entropy principle put forward\nin 1957 by E. T. Jaynes suggests what quantum states one should expect in\nequilibrium but does not hint as to how closed quantum many-body systems\ndynamically equilibrate. A number of theoretical and numerical studies\naccumulate evidence that under specific conditions quantum many-body models can\nrelax to a situation that locally or with respect to certain observables\nappears as if the entire system had relaxed to a maximum entropy state. In this\nwork, we report the experimental observation of the non-equilibrium dynamics of\na density wave of ultracold bosonic atoms in an optical lattice in the regime\nof strong correlations. Using an optical superlattice, we are able to prepare\nthe system in a well-known initial state with high fidelity. We then follow the\ndynamical evolution of the system in terms of quasi-local densities, currents,\nand coherences. Numerical studies based on the time-dependent density-matrix\nrenormalization group method are in an excellent quantitative agreement with\nthe experimental data. For very long times, all three local observables show a\nfast relaxation to equilibrium values compatible with those expected for a\nglobal maximum entropy state. We find this relaxation of the quasi-local\ndensities and currents to initially follow a power-law with an exponent being\nsignificantly larger than for free or hardcore bosons. For intermediate times\nthe system fulfills the promise of being a dynamical quantum simulator, in that\nthe controlled dynamics runs for longer times than present classical algorithms\nbased on matrix product states can efficiently keep track of."
    },
    {
        "anchor": "Observation of interspecies Feshbach resonances in an ultracold\n  $^{39}$K-$^{133}$Cs mixture and refinement of interaction potentials: We observe interspecies Feshbach resonances due to s-wave bound states in\nultracold $^{39}$K-$^{133}$Cs scattering for three different spin mixtures. The\nresonances are observed as joint atom loss and heating of the K sample. We\nperform least-squares fits to obtain improved K-Cs interaction potentials that\nreproduce the observed resonances, and carry out coupled-channel calculations\nto characterize the scattering and bound-state properties for $^{39}$K-Cs,\n$^{40}$K-Cs and $^{41}$K-Cs. Our results open up the possibilities of tuning\ninteractions in K-Cs atomic mixtures and of producing ultracold KCs molecules.",
        "positive": "Microscopic observation of magnon bound states and their dynamics: More than eighty years ago, H. Bethe pointed out the existence of bound\nstates of elementary spin waves in one-dimensional quantum magnets. To date,\nidentifying signatures of such magnon bound states has remained a subject of\nintense theoretical research while their detection has proved challenging for\nexperiments. Ultracold atoms offer an ideal setting to reveal such bound states\nby tracking the spin dynamics after a local quantum quench with single-spin and\nsingle-site resolution. Here we report on the direct observation of two-magnon\nbound states using in-situ correlation measurements in a one-dimensional\nHeisenberg spin chain realized with ultracold bosonic atoms in an optical\nlattice. We observe the quantum walk of free and bound magnon states through\ntime-resolved measurements of the two spin impurities. The increased effective\nmass of the compound magnon state results in slower spin dynamics as compared\nto single magnon excitations. In our measurements, we also determine the decay\ntime of bound magnons, which is most likely limited by scattering on thermal\nfluctuations in the system. Our results open a new pathway for studying\nfundamental properties of quantum magnets and, more generally, properties of\ninteracting impurities in quantum many-body systems."
    },
    {
        "anchor": "Reference frame-independent model of a collective excitation atom\n  interferometer: We theoretically analyze the operating principles of a proposed matter-wave\nSagnac interferometer utilizing Bose-Einstein condensate (BEC) phonon modes as\nan interference medium. Previous work found that the orbital angular momentum\nphonon modes of a ring-trapped BEC are split in frequency by rotations, leading\nto a measurable rotation signal. We develop an alternate description in which\nan imbalance in the counter-propagating modes' amplitudes (populations) is\ninduced by the rotation of the system during condensation. This description\ngives analytic forms for the interferometric phase shift in 1D and is readily\ngeneralized to include mean-field interactions. To validate our findings, we\nsimulate a ring-trapped BEC Sagnac interferometer in one dimension and\ndemonstrate that measurement of an unknown rotation rate can be performed using\na modified analysis. Our simulation data show strong agreement with our\nanalytic results, and we further employ simulations to explore and clarify the\nrole of superfluidity in this matter-wave Sagnac interferometer.",
        "positive": "Emergent hydrodynamic behaviour of few strongly interacting fermions: Hydrodynamics provides a successful framework to effectively describe the\ndynamics of complex many-body systems ranging from subnuclear to cosmological\nscales by introducing macroscopic quantities such as particle densities and\nfluid velocities. According to textbook knowledge, it requires coarse graining\nover microscopic constituents to define a macroscopic fluid cell, which is\nlarge compared to the interparticle spacing and the mean free path. In\naddition, the entire system must consist of many such fluid cells. The latter\nrequirement on the system size has been challenged by experiments on\nhigh-energy heavy-ion collisions, where collective particle emission, typically\nassociated with the formation of a hydrodynamic medium, has been observed with\nfew tens of final-state particles. Here, we demonstrate emergence of\nhydrodynamics in a system with significantly less constituents. Our observation\nchallenges the requirements for a hydrodynamic description, as in our system\nall relevant length scales, i.e. the system size, the inter-particle spacing,\nand the mean free path are comparable. The single particle resolution,\ndeterministic control over particle number and interaction strength in our\nexperiment allow us to explore the boundaries between a microscopic description\nand a hydrodynamic framework in unprecedented detail."
    },
    {
        "anchor": "Bogoliubov excitations in the quasiperiodic kicked rotor: stability of a\n  kicked condensate and the quasi-insulator-metal transition: We study the dynamics of a Bose-Einstein condensate in the quasiperiodic\nkicked rotor described by a Gross-Pitaevskii equation with periodic boundary\nconditions. As the interactions are increased, Bogoliubov excitations appear\nand deplete the condensate; we characterize this instability by considering the\npopulation of the first Bogoliubov mode, and show that it does not prevent, for\nsmall enough interaction strengths, the observation of the transition. However,\nthe predicted subdiffusive behavior is not observed in the stable region. For\nhigher interaction strengths, the condensate may be strongly depleted before\nthis dynamical regimes set in.",
        "positive": "Monte Carlo Simulations of the Unitary Bose Gas: We investigate the zero-temperature properties of a diluted homogeneous Bose\ngas made of $N$ particles interacting via a two-body square-well potential by\nperfor ming Monte Carlo simulations. We tune the interaction strength to\nachieve arbitrary positive values of the scattering length and compute by Monte\nCarlo quadrature the energy per particle $E/N$ and the condensate fraction\n$N_0/N$ of this system by using a Jastrow ansatz for the many-body wave\nfunction which avoids the formation of the self-bound ground-state and\ndescribes instead a (metastable) gaseous state with uniform den sity. In the\nunitarity limit, where the scattering length diverges while the range of the\ninter-atomic potential is much smaller than the average distance between atoms,\nwe find a finite energy per particle ($E/N=0.70\\ \\hbar^2(6\\pi^2n)^{2/3}/2m$,\nwith $n$ th e number density) and a quite large condensate fraction\n($N_0/N=0.83$)."
    },
    {
        "anchor": "Comment on \"Direct Mapping of the Finite Temperature Phase Diagram of\n  Strongly Correlated Quantum Models\" by Q. Zhou, Y. Kato, N. Kawashima, and N.\n  Trivedi, Phys. Rev. Lett. 103, 085701 (2009): In their Letter, Zhou, Kato, Kawashima, and Trivedi claim that\nfinite-temperature critical points of strongly correlated quantum models\nemulated by optical lattice experiments can generically be deduced from kinks\nin the derivative of the density profile of atoms in the trap with respect to\nthe external potential, $\\kappa = -dn(r)/dV(r)$. In this comment we demonstrate\nthat the authors failed to achieve their goal: to show that under realistic\nexperimental conditions critical densities $n_c(T,U)$ can be extracted from\ndensity profiles with controllable accuracy.",
        "positive": "Controlled hole doping of a Mott insulator of ultracold fermionic atoms: Considering a system of ultracold atoms in an optical lattice, we propose a\nsimple and robust implementation of a quantum simulator for the homogeneous t-J\nmodel with a well-controlled fraction of holes x. The proposed experiment can\nprovide valuable insight into the physics of cuprate superconductors. A similar\nscheme applied to bosons, moreover, allows one to investigate experimentally\nthe subtle role of inhomogeneity when a system passes from one quantum phase to\nanother."
    },
    {
        "anchor": "Shear viscosity of p-wave superfluid Fermi gas with weak interaction at\n  low temperatures: The shear viscosity tensor of the superfluid Fermi gas in p-wave state with\nweak interaction is calculated at low temperatures, by using the Boltzmann\nequation approach. We consider the transition probabilities for the binary,\ndecay and coalescence processes. We show that only the binary processes are\ndominated at low temperatures and the components of shear viscosity {\\eta}_xy,\n{\\eta}_xx, {\\eta}_yy are proportional to (1/T)^2, and {\\eta}_xz, {\\eta}_yz and\n{\\eta}_zz are proportional to (1/T)^4 and (1/T)^6, respectively.",
        "positive": "Heavy polarons in ultracold atomic Fermi superfluids at the BEC-BCS\n  crossover: formalism and applications: We investigate the system of a heavy impurity embedded in a paired\ntwo-component Fermi gas at the crossover from a Bose-Einstein condensate (BEC)\nto a Bardeen--Cooper--Schrieffer (BCS) superfluid via an extension of the\nfunctional determinant approach (FDA). FDA is an exact numerical approach\napplied to study manifestations of Anderson\\textquoteright s orthogonality\ncatastrophe (OC) in the system of a static impurity immersed in an ideal Fermi\ngas. Here, we extend the FDA to a strongly correlated superfluid background\ndescribed by a BCS mean-field wavefunction. In contrast to the ideal Fermi gas\ncase, the pairing gap in the BCS superfluid prevents the OC and leads to\ngenuine polaron signals in the spectrum. Thus, our exactly solvable model can\nprovide a deeper understanding of polaron physics. In addition, we find that\nthe polaron spectrum can be used to measure the superfluid pairing gap, and in\nthe case of a magnetic impurity, the energy of the sub-gap Yu-Shiba-Rusinov\n(YSR) bound state. Our theoretical predictions can be examined with\nstate-of-art cold-atom experiments."
    },
    {
        "anchor": "Topological phase transitions in the repulsively interacting\n  Haldane-Hubbard model: Using dynamical mean-field theory and exact diagonalization we study the\nphase diagram of the repulsive Haldane-Hubbard model, varying the interaction\nstrength and the sublattice potential difference. In addition to the quantum\nHall phase with Chern number $C=2$ and the band insulator with $C=0$ present\nalready in the noninteracting model, the system also exhibits a $C=0$ Mott\ninsulating phase, and a $C=1$ quantum Hall phase. We explain the latter phase\nby a spontaneous symmetry breaking where one of the spin-components is in the\nHall state and the other in the band insulating state.",
        "positive": "Quantum simulations of the early universe: A procedure is described whereby a linearly coupled spinor Bose condensate\ncan be used as a physically accessible quantum simulator of the early universe.\nIn particular, an experiment to generate an analog of an unstable vacuum in a\nrelativistic scalar field theory is proposed. This is related to quantum\ntheories of the inflationary phase of the early universe. There is an unstable\nvacuum sector whose dynamics correspond to the quantum sine-Gordon equations in\none, two or three space dimensions. Numerical simulations of the expected\nbehavior are reported using a truncated Wigner phase-space method, giving\nevidence for the dynamical formation of complex spatial clusters. Preliminary\nresults showing the dependence on coupling strength, condensate size and\ndimensionality are obtained."
    },
    {
        "anchor": "Formation of Solitonic Bound State via Light-Matter Interaction: Exchange of energy by means of light-matter interaction provides a new\ndimension to various nonlinear dynamical systems. Here, the effects of\nlight-matter interaction are investigated for a situation, where two\ncounter-propagating, orthogonally polarized laser pulses are incident on the\natomic condensate. It's observed that a localized laser pulse profile can\ninduce localized modes in Bose-Einstein condensate. A stability analysis\nperformed using Vakhitov-Kolokolov-like criterion has established that these\nlocalized modes are stable, when the atom-atom interaction is repulsive. The\ncooperative effects of light-matter interactions and atom-atom interactions on\nthe Lieb-mode have been studied in the stable region through atomic dispersion,\nrevealing the signature of bound state formation when the optical potential is\nP\\\"oschl-Teller type. The energy diagram also indicates a continuous transfer\nof energy from the laser pulses to the atoms as the light-matter interaction\nchanges its sign.",
        "positive": "Analytical coupled-channels treatment of two-body scattering in the\n  presence of three-dimensional isotropic spin-orbit coupling: It is shown that the single-particle spin-orbit coupling terms, which---in\nthe cold atom context---are associated with synthetic gauge fields, can\nsignificantly and non-trivially modify the phase accumulation at small\ninterparticle distances even if the length scale $(k_{\\text{so}})^{-1}$\nassociated with the spin-orbit coupling term is significantly larger than the\nvan der Waals length $r_{\\text{vdW}}$ that characterizes the two-body\ninteraction potential. A theoretical framework, which utilizes a generalized\nlocal frame transformation and accounts for the phase accumulation\nanalytically, is developed. Comparison with numerical coupled-channels\ncalculations demonstrates that the phase accumulation can, to a very good\napproximation, be described over a wide range of energies by the free-space\nscattering phase shifts---evaluated at a scattering energy that depends on\n$k_{\\text{so}}$---and the spin-orbit coupling strength $k_{\\text{so}}$."
    },
    {
        "anchor": "Two-body repulsive bound pairs in multi-body interacting Bose-Hubbard\n  model: We study the system of multi-body interacting bosons on a two dimensional\noptical lattice and analyze the formation of bound bosonic pairs in the context\nof the Bose-Hubbard model. Assuming a repulsive two-body interaction we obtain\nthe signatures of pair formation in the regions between the Mott insulator\nlobes of the phase diagram for different choices of higher order local\ninteractions. Considering the most general Bose-Hubbard model involving local\nmulti-body interactions we investigate the ground state properties utilizing\nthe cluster mean-field theory approach and further confirm the results by means\nof sophisticated infinite Projected Entangled Pair States calculations. By\nusing various order parameters, we show that the choice of higher-order\ninteraction can lead to pair superfluid phase in the system between two\ndifferent Mott lobes. We also analyze the effect of temperature and\ndensity-dependent tunneling to establish the stability of the PSF phase.",
        "positive": "Non-equilibrium dynamics of an ultracold Bose gas under a multi-pulsed\n  quantum quench in interaction: We investigate the nonequilibrium dynamical properties of a\nweakly-interacting Bose gas at zero temperature under the multi-pulsed quantum\nquench in interaction by calculating one-body, two-body correlation functions\nand Tan's contact of the model system. The multi-pulsed quench is represented\nas follows: first suddenly quenching the interatomic interaction from $g_{i}$\nto $g_{f}$ at time $t=0$, holding time $t$, and then suddenly quenching\ninteraction from $g_{f}$ back to $g_{i}$, holding the time $t$ sequence $n$\ntimes. In particular, two typical kinds of quenching parameters are chosen,\ncorresponding to $(g_{i}/g_{f}>1)$ and $(g_{i}/g_{f}<1)$ respectively. We find\nthat the more the quenching times of $n$ are, the more the excitations are\nexcited, which suggests that the multi-pulsed QQ is more powerful way of\nstudying the non-equilibrium dynamics of many-body quantum system than the\n`one-off' quantum quench. Finally, we discuss the ultra-short-range properties\nof the two-body correlation function after the $n$th quenching, which can be\nused to probe the `Tan'scontact' in experiments. All our calculations can be\ntested in current cold atom experiments."
    },
    {
        "anchor": "Structural properties of bosonic He clusters with N=2-10 for different\n  potential models at the physical point and at unitarity: Since the $^4$He dimer supports only one weakly bound state with an average\ninteratomic distance much larger than the van der Waals length and no deeply\nbound states, $^4$He$_N$ clusters with $N>2$ are a paradigmatic model system\nwith which to explore foundational concepts such as large $s$-wave scattering\nlength universality, van der Waals universality, Efimov physics, and effective\nfield theories. This work presents structural properties such as the pair and\ntriple distribution functions, the hyperradial density, the probability to find\nthe $N$th particle at a given distance from the center of mass of the other\n$N-1$ atoms, and selected contacts. The kinetic energy release, which can be\nmeasured via Coulomb explosion in dedicated size-selected molecular beam\nexperiments -- at least for small $N$ -- , is also presented. The structural\nproperties are determined for three different realistic $^4$He-$^4$He\ninteraction potentials and contrasted with those for an effective low-energy\npotential model from the literature that reproduces the energies of $^4$He$_N$\nclusters in the ground state for $N=2$ to $N=\\infty$ at the $\\gtrsim\n95$~percent level with just four input parameters. The study is extended to\nunitarity (infinite $s$-wave scattering length) by artificially weakening the\ninteraction potentials. In addition to contributing to the characterization of\nsmall bosonic helium quantum droplets, our study provides insights into the\neffective low-energy theory's predictability of various structural properties.",
        "positive": "Engineering a flux-dependent mobility edge in disordered zigzag chains: There has been great interest in realizing quantum simulators of charged\nparticles in artificial gauge fields. Here, we perform the first quantum\nsimulation explorations of the combination of artificial gauge fields and\ndisorder. Using synthetic lattice techniques based on parametrically-coupled\natomic momentum states, we engineer zigzag chains with a tunable homogeneous\nflux. The breaking of time-reversal symmetry by the applied flux leads to\nanalogs of spin-orbit coupling and spin-momentum locking, which we observe\ndirectly through the chiral dynamics of atoms initialized to single lattice\nsites. We additionally introduce precisely controlled disorder in the site\nenergy landscape, allowing us to explore the interplay of disorder and large\neffective magnetic fields. The combination of correlated disorder and\ncontrolled intra- and inter-row tunneling in this system naturally supports\nenergy-dependent localization, relating to a single-particle mobility edge. We\nmeasure the localization properties of the extremal eigenstates of this system,\nthe ground state and the most-excited state, and demonstrate clear evidence for\na flux-dependent mobility edge. These measurements constitute the first direct\nevidence for energy-dependent localization in a lower-dimensional system, as\nwell as the first explorations of the combined influence of artificial gauge\nfields and engineered disorder. Moreover, we provide direct evidence for\ninteraction shifts of the localization transitions for both low- and\nhigh-energy eigenstates in correlated disorder, relating to the presence of a\nmany-body mobility edge. The unique combination of strong interactions,\ncontrolled disorder, and tunable artificial gauge fields present in this\nsynthetic lattice system should enable myriad explorations into intriguing\ncorrelated transport phenomena."
    },
    {
        "anchor": "Quantum-fluctuation-driven crossover from a dilute Bose-Einstein\n  condensate to a macro-droplet in a dipolar quantum fluid: In a joint experimental and theoretical effort, we report on the formation of\na macro-droplet state in an ultracold bosonic gas of erbium atoms with strong\ndipolar interactions. By precise tuning of the s-wave scattering length below\nthe so-called dipolar length, we observe a smooth crossover of the ground state\nfrom a dilute Bose-Einstein condensate (BEC) to a dense macro-droplet state of\nmore than $10^4$ atoms. Based on the study of collective excitations and loss\nfeatures, we quantitative prove that quantum fluctuations stabilize the\nultracold gas far beyond the instability threshold imposed by mean-field\ninteractions. Finally, we perform expansion measurements, showing the evolution\nof the normal BEC towards a three-dimensional self-bound state and show that\nthe interplay between quantum stabilization and three-body losses gives rise to\na minimal expansion velocity at a finite scattering length.",
        "positive": "Persistent, controllable circulation of a polariton ring condensate: Persistent circulation is a canonical effect of superfluidity. In previous\nexperiments, quantized circulation has been observed in polariton condensates,\nusually far from equilibrium, but persistent current in the absence of any\nstirring has not been seen. We report here the direct observation of persistent\ncirculation of a polariton condensate with no driving force and with no\nobservable change in time. We can cause the condensate to circulate in either\ndirection on demand using a short laser pulse, after which the condensate\ncontinues to circulate for dozens to hundreds of rotations around a ring trap\nwithout any further stimulation. Our theoretical model successfully shows how\nthe pulse, despite not carrying any angular momentum, causes the circulation."
    },
    {
        "anchor": "Topological order-by-disorder in orbitally degenerate dipolar bosons in\n  zig-zag lattice: Spinor bosons offer conceptually simple picture of macroscopic quantum\nbehavior of topological order-by-disorder: Paramagnetic state of two-component\ndipolar bosons in orbitally degenerate zig-zag lattice is unstable against\ninfinitezimal quantum fluctuations of orbitals towards developing non-local\nhidden order. Adjacent to the topological state locally correlated exact ground\nstate with spontaneously quadrupoled lattice constant is realized for the broad\nparameter regime.",
        "positive": "Tunable dipolar resonances and Einstein-de Haas effect in a Rb-87 atoms\n  condensate: We study a spinor condensate of Rb-87 atoms in F = 1 hyperfine state confined\nin an optical dipole trap. Putting initially all atoms in mF = 1 component we\nobserve a significant transfer of atoms to other, initially empty Zeeman states\nexclusively due to dipolar forces. Because of conservation of a total angular\nmomentum the atoms going to other Zeeman components acquire an orbital angular\nmomentum and circulate around the center of the trap. This is a realization of\nEinstein-de Haas effect in a system of cold gases. We show that the transfer of\natoms via dipolar interaction is possible only when the energies of the initial\nand the final sates are equal. This condition can be fulfilled utilizing a\nresonant external magnetic field, which tunes energies of involved states via\nthe linear Zeeman effect. We found that there are many final states of\ndifferent spatial density which can be tuned selectively to the initial state.\nWe show a simple model explaining high selectivity and controllability of weak\ndipolar interactions in the condensate of Rb-87 atoms."
    },
    {
        "anchor": "Interaction-Dependent Photon-Assisted Tunneling in Optical Lattices: A\n  Quantum Simulator of Strongly-Correlated Electrons and Dynamical Gauge Fields: We introduce a scheme that combines photon-assisted tunneling by a moving\noptical lattice with strong Hubbard interactions, and allows for the quantum\nsimulation of paradigmatic quantum many-body models. We show that, in a certain\nregime, this quantum simulator yields an effective Hubbard Hamiltonian with\ntunable bond-charge interactions, a model studied in the context of\nstrongly-correlated electrons. In a different regime, we show how to exploit a\ncorrelated destruction of tunneling to explore Nagaoka ferromagnetism at finite\nHubbard repulsion. By changing the photon-assisted tunneling parameters, we can\nalso obtain a $t$-$J$ model with independently controllable tunneling $t$,\nsuper-exchange interaction $J$, and even a Heisenberg-Ising anisotropy. Hence,\nthe full phase diagram of this paradigmatic model becomes accessible to\ncold-atom experiments, departing from the region $t\\gg J$ allowed by standard\nsingle-band Hubbard Hamiltonians in the strong-repulsion limit. We finally show\nthat, by generalizing the photon-assisted tunneling scheme, the quantum\nsimulator yields models of dynamical Gauge fields, where atoms of a given\nelectronic state dress the tunneling of the atoms with a different internal\nstate, leading to Peierls phases that mimic a dynamical magnetic field.",
        "positive": "Counterflow superfluid of polaron pairs in Bose-Fermi mixtures in\n  optical lattices: We study the quantum phases of one-dimensional Bose-Fermi mixtures in optical\nlattices. Assuming repulsive interparticle interactions, equal mass, and unit\ntotal filling, we calculate the ground-state phase diagram by means of both\nTomonaga-Luttinger liquid theory and time-evolving block decimation method. We\ndemonstrate the existence of a counterflow superfluid (CFSF) phase of polaron\npairs, which are composite particles consisting of two fermions and two bosonic\nholes, in a broad range of the parameter space. We find that this phase\nnaturally emerges in $^{174}$Yb-$^{173}$Yb mixtures, realized in recent\nexperiments, at low temperatures."
    },
    {
        "anchor": "Three-dimensional droplets of swirling superfluids: A new method for the creation of 3D solitary topological modes, corresponding\nto vortical droplets of a two-component dilute superfluid, is presented. We use\nthe recently introduced system of nonlinearly coupled Gross-Pitaevskii\nequations, which include contact attraction between the components, and quartic\nrepulsion stemming from the Lee-Huang-Yang correction to the mean-field energy.\nSelf-trapped vortex tori, carrying the topological charges m1=m2=1 or m1=m2=2\nin their components, are constructed by means of numerical and approximate\nanalytical methods. The analysis reveals stability regions for the vortex\ndroplets (in broad and relatively narrow parameter regions for m1=m2=1 and\nm1=m2=2, respectively). The results provide the first example of stable 3D\nself-trapped states with the double vorticity, in any physical setting. The\nstable modes are shaped as flat-top ones, with the space between the inner\nhole, induced by the vorticity, and the outer boundary filled by a nearly\nconstant density. On the other hand, all modes with hidden vorticity, i.e.,\ntopological charges of the two components m1=-m2=1, are unstable. The stability\nof the droplets with m1=m2=1 against splitting (which is the main scenario of\npossible instability) is explained by estimating analytically the energy of the\nsplit and un-split states. The predicted results may be implemented, exploiting\ndilute quantum droplets in mixtures of Bose-Einstein condensates.",
        "positive": "Bosonic Mott Insulator with Meissner Currents: We introduce a generic bosonic model exemplifying that (spin) Meissner\ncurrents can persist in insulating phases of matter. We consider two species of\ninteracting bosons on a lattice. Our model exhibits separation of charge (total\ndensity) and spin (relative density): The charge sector is gapped in a bosonic\nMott insulator phase with total density one, while the spin sector remains\nsuperfluid due to interspecies conversion. Coupling the spin sector to the\ngauge fields yields a spin Meissner effect reflecting the long-range spin\nsuperfluid coherence. We investigate the resulting phase diagram and describe\nother possible spin phases of matter in the Mott regime possessing chiral\ncurrents as well as a spin-density wave phase. The model presented here is\nrealizable in Josephson junction arrays and in cold atom experiments."
    },
    {
        "anchor": "Harmonically trapped two-atom systems: Interplay of short-range s-wave\n  interaction and spin-orbit coupling: The coupling between the spin degrees of freedom and the orbital angular\nmomentum has a profound effect on the properties of nuclei, atoms and condensed\nmatter systems. Recently, synthetic gauge fields have been realized\nexperimentally in neutral cold atom systems, giving rise to a spin-orbit\ncoupling term with \"strength\" $k_{\\text{so}}$. This paper investigates the\ninterplay between the single-particle spin-orbit coupling term of Rashba type\nand the short-range two-body $s$-wave interaction for cold atoms under external\nconfinement. Specifically, we consider two different harmonically trapped\ntwo-atom systems. The first system consists of an atom with spin-orbit coupling\nthat interacts with a structureless particle through a short-range two-body\npotential. The second system consists of two atoms that both feel the\nspin-orbit coupling term and that interact through a short-range two-body\npotential. Treating the spin-orbit term perturbatively, we determine the\ncorrection to the ground state energy for various generic parameter\ncombinations. Selected excited states are also treated. An important aspect of\nour study is that the perturbative treatment is not limited to small $s$-wave\nscattering lengths but provides insights into the system behavior over a wide\nrange of scattering lengths, including the strongly-interacting unitary regime.\nOur perturbative results are confirmed by numerical calculations that expand\nthe eigenfunctions of the two-particle Hamiltonian in terms of basis functions\nthat contain explicitly correlated Gaussians.",
        "positive": "Tunable Single-Ion Anisotropy in Spin-1 Models Realized with Ultracold\n  Atoms: Mott insulator plateaus in optical lattices are a versatile platform to study\nspin physics. Using sites occupied by two bosons with an internal degree of\nfreedom, we realize a uniaxial single-ion anisotropy term proportional to\n$(S^z)^2$, which plays an important role in stabilizing magnetism for\nlow-dimensional magnetic materials. Here we explore non-equilibrium spin\ndynamics and observe a resonant effect in the spin anisotropy as a function of\nlattice depth when exchange coupling and on-site anisotropy are similar. Our\nresults are supported by many-body numerical simulations and are captured by\nthe analytical solution of a two-site model."
    },
    {
        "anchor": "Degenerate Fermi Gas of $^{87}$Sr: We report quantum degeneracy in a gas of ultra-cold fermionic $^{87}$Sr\natoms. By evaporatively cooling a mixture of spin states in an optical dipole\ntrap for 10.5\\,s, we obtain samples well into the degenerate regime with\n$T/T_F=0.26^{+.05}_{-.06}$. The main signature of degeneracy is a change in the\nmomentum distribution as measured by time-of-flight imaging, and we also\nobserve a decrease in evaporation efficiency below $T/T_F \\sim 0.5$.",
        "positive": "One-dimensional Bose-Einstein condensation of photons in a microtube: This paper introduces a quasiequilibrium one-dimensional Bose-Einstein\ncondensation of photons trapped in a microtube. Light modes with a cut-off\nfrequency (a photon's \"mass\") interact through different processes of\nabsorption, emission, and scattering on molecules and atoms. In this paper, we\nstudy the conditions for the one-dimensional condensation of light and the role\nof photon-photon interactions in the system. The technique in use is the\nMatsubara's Green's functions formalism modified for the quasiequilibrium\nsystem under study."
    },
    {
        "anchor": "Supersolidity around a critical point in dipolar Bose Einstein\n  condensates: We explore spatial symmetry breaking of a dipolar Bose Einstein condensate in\nthe thermodynamic limit and reveal a critical point in the phase diagram at\nwhich crystallization occurs via a second order phase transition. This behavior\nis traced back to the significant effects of quantum fluctuations in dipolar\ncondensates, which moreover stabilize a new supersolid phase, namely a regular\nhoneycomb pattern with maximal modulational contrast and near-perfect\nsuperfluidity.",
        "positive": "Nonlinear Eigenmodes of a Polariton Harmonic Oscillator: We investigate theoretically the quantum oscillator-like states recently\nobserved experimentally in polariton condensates (Nat. Phys. 8, 190 (2012)). We\nconsider a complex Gross-Pitaevskii type model which includes the effects of\nself-interactions, and creation and decay of exciton-polaritons. We develop a\nperturbation theory for approximate solutions to this non-equilibrium\ncondensate model and compare the results with numerically calculated solutions\nfor both repulsive and attractive polariton-polariton interactions. While the\nnonlinearity has a weak effect on the mode selection their density profiles are\nmodified at moderate gain strengths and becomes more dominant when a very large\ngain of polaritons implies an extended cloud with high condensate densities.\nFinally, we identify the relation of the observed patterns to the input pump\nconfiguration, and suggest this may serve as a generalized NOR gate in the\ntradition of optical computing."
    },
    {
        "anchor": "Quantum dark solitons in the 1D Bose gas: From single to double\n  dark-solitons: We study quantum double dark-solitons by constructing corresponding quantum\nstates in the Lieb-Liniger model for the one-dimensional Bose gas. Here we\nexpect that the Gross-Pitaevskii (GP) equation should play a central role in\nthe long distance mean-field behavior of the 1D Bose gas. We first introduce\nnovel quantum states of a single dark soliton with a nonzero winding number. We\nshow them by exactly evaluating not only the density profile but also the\nprofiles of the square amplitude and phase of the matrix element of the field\noperator between the $N$-particle and $(N-1)$-particle states. For elliptic\ndouble dark-solitons, the density and phase profiles of the corresponding\nstates almost perfectly agree with those of the classical solutions,\nrespectively, in the weak coupling regime. We then show that the scheme of the\nmean-field product state is quite effective for the quantum states of double\ndark solitons. Assigning the ideal Gaussian weights to a sum of the excited\nstates with two particle-hole excitations we obtain double dark-solitons of\ndistinct narrow notches with different depths. We suggest that the mean-field\nproduct state should be well approximated by the ideal Gaussian weighted sum of\nthe low excited states with a pair of particle-hole excitations. The results of\ndouble dark-solitons should be fundamental and useful for constructing quantum\nmultiple dark-solitons.",
        "positive": "Atomic Josephson junction with two bosonic species: We study an atomic Josephson junction (AJJ) in presence of two interacting\nBose-Einstein condensates (BECs) confined in a double well trap. We assume that\nbosons of different species interact with each other. The macroscopic wave\nfunctions of the two components obey to a system of two 3D coupled\nGross-Pitaevskii equations (GPE). We write the Lagrangian of the system, and\nfrom this we derive a system of coupled ordinary differential equations (ODE),\nfor which the coupled pendula represent the mechanic analogous. These\ndifferential equations control the dynamical behavior of the fractional\nimbalance and of the relative phase of each bosonic component. We perform the\nstability analysis around the points which preserve the symmetry and get an\nanalytical formula for the oscillation frequency around the stable points. Such\na formula could be used as an indirect measure of the inter-species s-wave\nscattering length. We also study the oscillations of each fractional imbalance\naround zero and non zero - the macroscopic quantum self-trapping (MQST) - time\naveraged values. For different values of the inter-species interaction\namplitude, we carry out this study both by directly solving the two GPE and by\nsolving the corresponding coupled pendula equations. We show that, under\ncertain conditions, the predictions of these two approaches are in good\nagreement. Moreover, we calculate the crossover value of the inter-species\ninteraction amplitude which signs the onset of MQST."
    },
    {
        "anchor": "Quantum entangled ground states of two spinor Bose-Einstein condensates: We revisit in detail the non-mean-field ground-state phase diagram for a\nbinary mixture of spin-1 Bose-Einstein condensates including quantum\nfluctuations. The non-commuting terms in the spin-dependent Hamiltonian under\nsingle spatial mode approximation make it difficult to obtain exact\neigenstates. Utilizing the spin z-component conservation and the total spin\nangular momentum conservation, we numerically derive the information of the\nbuilding blocks and evaluate von Neumann entropy to quantify the ground states.\nThe mean-field phase boundaries are found to remain largely intact, yet the\nground states show fragmented and entangled behaviors within large parameter\nspaces of interspecies spin-exchange and singlet-pairing interactions.",
        "positive": "Complete devil's staircase and crystal--superfluid transitions in a\n  dipolar XXZ spin chain: A trapped ion quantum simulation: Systems with long-range interactions show a variety of intriguing properties:\nthey typically accommodate many meta-stable states, they can give rise to\nspontaneous formation of supersolids, and they can lead to counterintuitive\nthermodynamic behavior. However, the increased complexity that comes with\nlong-range interactions strongly hinders theoretical studies. This makes a\nquantum simulator for long-range models highly desirable. Here, we show that a\nchain of trapped ions can be used to quantum simulate a one-dimensional model\nof hard-core bosons with dipolar off-site interaction and tunneling, equivalent\nto a dipolar XXZ spin-1/2 chain. We explore the rich phase diagram of this\nmodel in detail, employing perturbative mean-field theory, exact\ndiagonalization, and quasiexact numerical techniques (density-matrix\nrenormalization group and infinite time evolving block decimation). We find\nthat the complete devil's staircase -- an infinite sequence of crystal states\nexisting at vanishing tunneling -- spreads to a succession of lobes similar to\nthe Mott-lobes found in Bose--Hubbard models. Investigating the melting of\nthese crystal states at increased tunneling, we do not find (contrary to\nsimilar two-dimensional models) clear indications of supersolid behavior in the\nregion around the melting transition. However, we find that inside the\ninsulating lobes there are quasi-long range (algebraic) correlations, opposed\nto models with nearest-neighbor tunneling which show exponential decay of\ncorrelations."
    },
    {
        "anchor": "Vortex patterns in rotating dipolar Bose-Einstein condensate mixtures\n  with squared optical lattices: Vortex lattice patterns with transitions from regular to other variety vortex\nshapes are predicted in rotating binary mixtures of dipolar Bose-Einstein\ncondensates loaded in squared optical lattice. We focus our investigation in\nthe experimentally accessible dipolar isotopes of dysprosium ($^{162,164}$Dy),\nerbium ($^{168}$Er), chromium ($^{52}$Cr), and rubidium ($^{87}$Rb), by\nconsidering the binary mixtures ($^{164}$Dy-$^{162}$Dy, $^{168}$Er-$^{164}$Dy,\n$^{164}$Dy-$^{52}$Cr and $^{164}$Dy-$^{87}$Rb), which are confined in strong\npancake-shaped trap and loaded in squared two-dimensional optical lattices,\nwhere we vary the polarization angle of dipoles, the inter-species contact\ninteractions and the rotation frequency. The ratio between inter- to\nintra-species contact interaction is used for altering the miscibility\nproperties; with the polarization of the dipolar species used for tuning to\nrepulsive or attractive the dipole-dipole interactions. For enough higher\nrotation, of particular interest is the regime when the inter- to intra-species\nscattering length is larger than one, in which a richer variety of\nvortex-lattice patterns are predicted, including vortex sheets and\ntwo-dimensional rotating droplet formations. The patterns can be controlled by\nchanging the optical lattice parameters, as shown for the symmetric\n$^{164}$Dy-$^{162}$Dy dipolar mixture. For mixtures with stronger differences\nin the dipole moments, as $^{164}$Dy-$^{52}$Cr and $^{164}$Dy-$^{87}$Rb, only\nhalf quantum vortices and circular ones have been observed, which will depend\non the dipole orientations.",
        "positive": "Quench in 1D Bose-Hubbard Model: Topological Defects and Excitations\n  from Kosterlitz-Thouless Phase Transition Dynamics: Kibble-Zurek mechanism (KZM) uses critical scaling to predict density of\ntopological defects and other excitations created in second order phase\ntransitions. We point out that simply inserting asymptotic critical exponents\ndeduced from the immediate vicinity of the critical point to obtain KZM\npredictions can lead to results that are inconsistent with a more careful\nKZM-like analysis based on causality -- on the comparison of the relaxation\ntime of the order parameter with the time \"distance\" from the critical point.\nAs a result, scaling of quench-generated excitations with quench rates can\nexhibit behavior that is locally (i.e., in the neighborhood of any given quench\nrate) well approximated by the power law, but with exponents that depend on\nthat rate, and that are quite different from the naive prediction based on the\ncritical exponents relevant for asymptotically long quench times.\nKosterlitz-Thouless scaling (that governs e.g. Mott insulator to superfluid\ntransition in the Bose-Hubbard model in one dimension) is investigated as an\nexample of this phenomenon."
    },
    {
        "anchor": "Entanglement Spectroscopy using Quantum Monte Carlo: We present a numerical scheme to reconstruct a subset of the entanglement\nspectrum of quantum many body systems using quantum Monte Carlo. The approach\nbuilds on the replica trick to evaluate particle number resolved traces of the\nfirst n of powers of a reduced density matrix. From this information we\nreconstruct n entanglement spectrum levels using a polynomial root solver. We\nillustrate the power and limitations of the method by an application to the\nextended Bose-Hubbard model in one dimension where we are able to resolve the\nquasi-degeneracy of the entanglement spectrum in the Haldane-Insulator phase.\nIn general the method is able to reconstruct the largest few eigenvalues in\neach symmetry sector and typically performs better when the eigenvalues are not\ntoo different.",
        "positive": "Spatial structure of the pair wavefunction and the density correlation\n  functions at the BEC-BCS crossover: By an exact numerical calculation of the BCS pair wavefunction and the\ndensity correlation functions both between atoms in the same and in different\nspin states, we extract the spatial large distance behavior of the respective\nfunctions. After different initial transients, those distributions show an\nalgebraic dependence accompanied with their own exponential decay and a well\ndefined periodic oscillatory behavior. While in general, in the BCS side there\nare long-range correlations and in the BEC region the behavior is dominated by\ntight pairs formation, each distribution shows its own overall behavior. We\nderive analytic expressions for the mean pair size and the correlation lengths\nof the same and different density correlation functions. The whole analysis\nyields a quite complete description of the spatial structure of the superfluid\nalong the crossover."
    },
    {
        "anchor": "Resonant wavepackets and shock waves in an atomtronic SQUID: The fundamental dynamics of ultracold atomtronic devices are reflected in\ntheir phonon modes of excitation. We probe such a spectrum by applying a\nharmonically driven potential barrier to a $^{23}$Na Bose-Einstein condensate\nin a ring-shaped trap. This perturbation excites phonon wavepackets. When\nexcited resonantly, these wavepackets display a regular periodic structure. The\nresonant frequencies depend upon the particular configuration of the barrier,\nbut are commensurate with the orbital frequency of a Bogoliubov sound wave\ntraveling around the ring. Energy transfer to the condensate over many cycles\nof the periodic wavepacket motion causes enhanced atom loss from the trap at\nresonant frequencies. Solutions of the time-dependent Gross-Pitaevskii equation\nexhibit quantitative agreement with the experimental data. We also observe the\ngeneration of supersonic shock waves under conditions of strong excitation, and\ncollisions of two shock wavepackets.",
        "positive": "Floquet solitons and dynamics of periodically driven matter waves with\n  negative effective mass: We experimentally study the dynamics of weakly interacting Bose-Einstein\ncondensates of cesium atoms in a 1D optical lattice with a periodic driving\nforce. After a sudden start of the driving we observe the formation of stable\nwave packets at the center of the first Brillouin zone (BZ) in momentum space,\nand we interpret these as Floquet solitons in periodically driven systems. The\nwave packets become unstable when we add a trapping potential along the lattice\ndirection leading to a redistribution of atoms within the BZ. The concept of a\nnegative effective mass and the resulting changes to the interaction strength\nand effective trapping potential are used to explain the stability and the time\nevolution of the wave packets. We expect that similar states of matter waves\nexist for discrete breathers and other types of lattice solitons in\nperiodically driven systems."
    },
    {
        "anchor": "Fluctuations of the order parameter of a mesoscopic Floquet condensate: We suggest that nonequilibrium Bose-Einstein condensates may occur in\ntime-periodically driven interacting Bose gases. Employing the model of a\nperiodically forced bosonic Josephson junction, we demonstrate that\nresonance-induced ground state-like many-particle Floquet states possess an\nalmost perfect degree of coherence, as corresponding to a mesoscopically\noccupied, explicitly time-dependent single-particle orbital. In marked contrast\nto the customary time-independent Bose-Einstein condensates, the order\nparameter of such systems is destroyed by violent fluctuations when the\nparticle number becomes too large, signaling the non-existence of a proper mean\nfield limit.",
        "positive": "Influence of the particle number on the spin dynamics of ultracold atoms: We study the dependency of the quantum spin dynamics on the particle number\nin a system of ultracold spin-1 atoms within the single-spatial-mode\napproximation. We find, for all strengths of the spin-dependent interaction,\nconvergence towards the mean-field dynamics in the thermodynamic limit. The\nconvergence is, however, particularly slow when the spin-changing collisional\nenergy and the quadratic Zeeman energy are equal, i.e. deviations between\nquantum and mean-field spin dynamics may be extremely large under these\nconditions. Our estimates show, that quantum corrections to the mean-field\ndynamics may play a relevant role in experiments with spinor Bose-Einstein\ncondensates. This is especially the case in the regime of few atoms, which may\nbe accessible in optical lattices. Here, spin dynamics is modulated by a beat\nnote at large magnetic fields due to the significant influence of correlated\nmany-body spin states."
    },
    {
        "anchor": "Lattice Polaron in a Bose-Einstein Condensate of Hard-Core Bosons: Lattice polarons, quasiparticles arising from the interaction between an\nimpurity and its surrounding bosonic environment confined to a lattice system,\nhave emerged as a platform for generating complex few-body states, probing\nmany-body phenomena, and addressing long-standing problems in physics. In this\nstudy, we employ a variational ansatz to investigate the quasiparticle and\nspectral properties of an impurity coupled to a condensate gas of hard-core\nbosons in a two-dimensional optical lattice. Our findings demonstrate that the\npolaron features can be tuned by adjusting the filling factor of the bath,\nrevealing intriguing polaron characteristics in the strongly interacting\nregime. These results offer valuable insights for lattice polaron experiments\nwith ultracold gases and can serve as a guide for new experiments in emergent\nquantum devices, such as moir\\'e materials, where optical excitations can be\ndescribed in terms of hard-core bosons.",
        "positive": "Effects of disorder on quantum fluctuations and superfluid density of a\n  Bose-Einstein condensate in a two-dimensional optical lattice: We investigate a Bose-Einstein condensate trapped in a 2D optical lattice in\nthe presence of weak disorder within the framework of the Bogoliubov theory. In\nparticular, we analyze the combined effects of disorder and an optical lattice\non quantum fluctuations and superfluid density of the BEC system. Accordingly,\nthe analytical expressions of the ground state energy and quantum depletion of\nthe system are obtained. Our results show that the lattice still induces a\ncharacteristic 3D to 1D crossover in the behavior of quantum fluctuations,\ndespite the presence of weak disorder. Furthermore, we use the linear response\ntheory to calculate the normal fluid density of the condensate induced by\ndisorder. Our results in the 3D regime show that the combined presence of\ndisorder and lattice induce a normal fluid density that asymptotically\napproaches 4/3 of the corresponding condensate depletion. Conditions for\npossible experimental realization of our scenario are also proposed."
    },
    {
        "anchor": "Interaction of half-quantized vortices in two-component Bose-Einstein\n  condensates: We study the asymptotic interaction between two half-quantized vortices in\ntwo-component Bose-Einstein condensates. When two vortices in different\ncomponents are placed at distance 2R, the leading order of the force between\nthem is found to be (log R/\\xi-1/2)/R^3, in contrast to 1/R between vortices\nplaced in the same component. We derive it analytically using the Abrikosov\nansatz and the profile functions of the vortices, confirmed numerically with\nthe Gross-Pitaevskii model. We also find that the short-range cutoff of the\ninter-vortex potential linearly depends on the healing length.",
        "positive": "Integral equations for the four-body problem: We consider the four-boson and 3+1 fermionic problems with a model\nHamiltonian which encapsulates the mechanism of the Feshbach resonance\ninvolving the coherent coupling of two atoms in the open channel and a molecule\nin the closed channel. The model includes also the pair-wise direct interaction\nbetween atoms in the open channel and in the bosonic case, the direct\nmolecule-molecule interaction in the closed channel. Interactions are modeled\nby separable potentials which makes it possible to reduce the four-body problem\nto the study of a single integral equation. We take advantage of the rotational\nsymmetry and parity invariance of the Hamiltonian to reduce the general\neigenvalue equation in each angular momentum sector to an integral equation for\nfunctions of three real variables only. A first application of this formalism\nin the zero-range limit is given elsewhere [Y. Castin, C. Mora, L. Pricoupenko,\nPhys. Rev. Lett. 105, 223201 (2010)]."
    },
    {
        "anchor": "Quasiparticle lifetime of the repulsive Fermi polaron: We investigate the metastable repulsive branch of a mobile impurity coupled\nto a degenerate Fermi gas via short-range interactions. We show that the\nquasiparticle lifetime of this repulsive Fermi polaron can be experimentally\nprobed by driving Rabi oscillations between weakly and strongly interacting\nimpurity states. Using a time-dependent variational approach, we find that we\ncan accurately model the impurity Rabi oscillations that were recently measured\nfor repulsive Fermi polarons in both two and three dimensions. Crucially, our\ntheoretical description does not include relaxation processes to the\nlower-lying attractive branch. Thus, the theory-experiment agreement\ndemonstrates that the quasiparticle lifetime is determined by many-body\ndephasing within the upper repulsive branch rather than by the metastability of\nthe upper branch itself. Our findings shed light on recent experimental\nobservations of persistent repulsive correlations, and have important\nconsequences for the nature and stability of the strongly repulsive Fermi gas.",
        "positive": "Thermalisation of Local Observables in Small Hubbard Lattices: We present a study of thermalisation of a small isolated Hubbard lattice\ncluster prepared in a pure state with a well-defined energy. We examine how a\ntwo-site subsystem of the lattice thermalises with the rest of the system as\nits environment. We explore numerically the existence of thermalisation over a\nrange of system parameters, such as the interaction strength, system size and\nthe strength of the coupling between the subsystem and the rest of the lattice.\nWe find thermalisation over a wide range of parameters and that interactions\nare crucial for efficient thermalisation of small systems. We relate this\nthermalisation behaviour to the eigenstate thermalisation hypothesis and\nquantify numerically the extent to which eigenstate thermalisation holds. We\nalso verify our numerical results theoretically with the help of previously\nestablished results from random matrix theory for the local density of states,\nparticularly the finite-size scaling for the onset of thermalisation."
    },
    {
        "anchor": "Reversal of quantised Hall drifts at non-interacting and interacting\n  topological boundaries: The transport properties of gapless edge modes at boundaries between\ntopologically distinct domains are of fundamental and technological importance.\nTherefore, it is crucial to gain a better understanding of topological edge\nstates and their response to interparticle interactions. Here, we\nexperimentally study long-distance quantised Hall drifts in a harmonically\nconfined topological pump of non-interacting and interacting ultracold\nfermionic atoms. We find that quantised drifts halt and reverse their direction\nwhen the atoms reach a critical slope of the confining potential, revealing the\npresence of a topological boundary. The drift reversal corresponds to a band\ntransfer between a band with Chern number $C = +1$ and a band with $C = -1$ via\na gapless edge mode, in agreement with the bulk-edge correspondence for\nnon-interacting particles. We establish that a non-zero repulsive Hubbard\ninteraction leads to the emergence of an additional edge in the system, relying\non a purely interaction-induced mechanism, in which pairs of fermions are\nsplit.",
        "positive": "Effect of Pauli blocking on coherent states of composite bosons: The quantum nature of elementary bosons can be completely erased by using\ncoherent states known as Glauber states. Here, we consider composite bosons\n(cobosons) made of two fermions and look for the possibility to erase the\nbosonic quantum nature of the field and the fermionic quantum nature of its\nconstituents, when the distribution of the coboson Schmidt decomposition is\neither flat like Frenkel excitons, or localized like Wannier excitons. We show\nthat for Frenkel-like cobosons, complete erasure of the field quantum nature is\npossible up to a density which corresponds to a sizable fraction of the number\nof fermion-pair states making the coboson at hand. At higher density, the Pauli\nexclusion principle between fermionic constituents shows up dramatically. It\ninduces: (i) the decrease of number-operator eigenvalues down to 1 and the\nincrease of the number-state second-order correlation function up to 2; (ii)\nthe disappearance of the usual sharp peak in the coherent-state distribution\nand the increase of the coherent-state second-order correlation function up to\n2. It also is possible to construct number states and coherent states for\nWannier-like cobosons, but their forms are far more complex. Finally, we show\nthat Pauli blocking makes the coboson coherent states qualitatively different\nfrom the Anderson's ansatz."
    },
    {
        "anchor": "Optimized fringe removal algorithm for absorption images: Optical absorption imaging is a basic detection technique for obtaining\ninformation from matter waves, in which the absorption signal can be obtained\nby comparing the recorded detection light field with the light field in the\npresence of absorption, thereby giving the spatial distribution of the atoms.\nThe noise in detection arises mainly from differences between the two recorded\nlight field distributions, which is difficult to avoid in experiments. In this\nwork, we present an optimized fringe removal algorithm, developing a method to\ngenerate an ideal reference light field, avoiding the noise generated by the\nlight field difference, and suppressing the noise signal to the theoretical\nlimit. Using principal component analysis, we explore the optimal calculation\narea and how to remove noise information from the basis to allow optimal\nperformance and speed. As an example, we consider scattering atomic peaks with\na small number of atoms in a triangular lattice. Compared with the conventional\nprocessing method, our algorithm can reduce the measured atomic temperature\nvariance by more than three times, giving a more reliable result.",
        "positive": "Kaleidoscopes of Hofstadter Butterflies and Aharonov-Bohm caging from\n  $2^n$-root topology in decorated square lattices: Square-root topology describes models whose topological properties can be\nrevealed upon squaring the Hamiltonian, which produces their respective parent\ntopological insulators. This concept has recently been generalized to\n$2^n$-root topology, characterizing models where $n$ squaring operations must\nbe applied to the Hamiltonian in order to arrive at the topological source of\nthe model. In this paper, we analyze the Hofstadter regime of\nquasi-one-dimensional (quasi-1D) and two-dimensional (2D) $2^n$-root models,\nthe latter of which has the square lattice (SL) (known for the Hofstadter\nButterfly) as the source model. We show that upon increasing the root-degree of\nthe model, there appear multiple magnetic flux insensitive flat bands, and\nanalytically determine corresponding eigenstates. These can be recast as\ncompact localized states (CLSs) occupying a finite region of the lattice. For a\nfinite flux, these CLSs correspond to different harmonics contained within the\nsame Aharonov-Bohm (AB) cage. Furthermore, as the root-degree increases, a\nkaleidoscope of butterflies is seen to appear in the Hofstadter diagram, with\neach butterfly constituting a topologically equivalent replica of the original\none of the SL. As such, the index $n$, which uniquely identifies the\nroot-degree of the model, can be seen as an additional fractal dimension of the\n$2^n$-root model present in its Hofstadter diagram. We discuss how these\ndynamics could be realized in experiments with ultracold atoms, and measured by\nBragg spectroscopy or through observing dynamics of initially localized atoms\nin a quantum gas microscope."
    },
    {
        "anchor": "Polar molecules in frustrated triangular ladders: Polar molecules in geometrically frustrated lattices may result in a very\nrich landscape of quantum phases, due to the non-trivial interplay between\nfrustration, and two- and possibly three-body inter-site interactions. In this\npaper, we illustrate this intriguing physics for the case of hard-core polar\nmolecules in frustrated triangular ladders. Whereas commensurate lattice\nfillings result in gapped phases with bond-order and/or density-wave order, at\nincommensurate fillings we find chiral-, two-component-, and pair-superfluids.\nWe show as well that, remarkably, polar molecules in frustrated lattices allow,\nfor the first time to our knowledge, for the observation of bond-ordered\nsupersolids.",
        "positive": "Quantum Quench of an Atomic Mott Insulator: We study quenches across the Bose-Hubbard Mott-insulator-to-superfluid\nquantum phase transition using an ultra-cold atomic gas trapped in an optical\nlattice. Quenching from the Mott insulator to superfluid phase is accomplished\nby continuously tuning the ratio of Hubbard tunneling to interaction energy.\nExcitations of the condensate formed after the quench are measured using\ntime-of-flight imaging. We observe that the degree of excitation is\nproportional to the fraction of atoms that cross the phase boundary, and that\nthe quantity of excitations and energy produced during the quench have a\npower-law dependence on the quench rate. These phenomena suggest an excitation\nprocess analogous to the Kibble-Zurek (KZ) mechanism for defect generation in\nnon-equilibrium classical phase transitions."
    },
    {
        "anchor": "Interaction-induced anomalous transport behavior in one dimensional\n  optical lattice: The non-equilibrium dynamics of spin impurity atoms in a strongly interacting\none-dimensional (1D) Bose gas under the gravity field is studied. We show that\ndue to the non-equilibrium preparation of the initial state as well as the\ninteraction between the impurity atoms and other bosons, a counterintuitive\nphenomenon may emerge: the impurity atoms could propagate upwards automatically\nin the gravity field . The effects of the strength of interaction, the gradient\nof the gravity field, as well as the different configurations of the initial\nstate are investigated by studying the time-dependent evolution of the 1D\nstrongly interacting bosonic system using time-evolving block decimation (TEBD)\nmethod. A profound connection between this counterintuitive phenomenon and the\nrepulsive bound pair is also revealed.",
        "positive": "Boosting the Rotational Sensitivity of Matter-wave Interferometry with\n  Nonlinearity: We propose a mechanism to use nonlinearity arising from inter-particle\ninteractions to significantly enhance rotation sensitivity of matter-wave\ninterferometers. The method relies on modifying Sagnac interferometers by\nintroducing a weak circular lattice potential that couples modes with opposite\norbital angular momenta (OAM). The primary observable comprises of the modal\npopulation distributions measured at particular times. This provides an\nalternate mechanism for rotation sensing that requires substantially smaller\nring size, even in the linear non-interacting regime. Nonlinearity can improve\nthe sensitivity, as well as operation timescales, by several orders of\nmagnitude."
    },
    {
        "anchor": "Nonlinear Dynamics of Ultra-Cold Gas: Collapse of Bose Gas With\n  Attractive Interaction: Solutions for the Nonlinear Schr\u007fodinger equation for collapsing Bose gas\nwith attraction. This is a copy of the paper published in 1992 in Proceedings\nof NATO Advanced Research workshop on Singularities in Fluids, Plasmas and\nOptics (Heraklion, Greece) edited by R.E. Caflisch and G.C. Papanicolaou\n(Kluwer Academic).",
        "positive": "Quantum lock-in detection of a vector light shift: We demonstrate detection of a vector light shift (VLS) using the quantum\nlock-in method. The method offers precise and accurate VLS measurement without\nbeing affected by real magnetic field fluctuations. We detect a VLS on a\nBose--Einstein condensate (BEC) of $^{87}$Rb atoms caused by an optical trap\nbeam with a resolution less than 1 Hz. We also demonstrate elimination of a VLS\nby controlling the beam polarization to realize a long coherence time of a\ntransversally polarized $F$ = 2 BEC. Quantum lock-in VLS detection should find\nwide application, including the study of spinor BECs, electric-dipole moment\nsearches, and precise magnetometry."
    },
    {
        "anchor": "Matter-wave localization in a weakly perturbed optical lattice: By numerical solution and variational approximation of the Gross-Pitaevskii\nequation, we studied the localization of a noninteracting and\nweakly-interacting Bose-Einstein condensate in a weakly perturbed optical\nlattice in one and three dimensions. The perturbation achieved through a weak\ndelocalizing expulsive or a linear potential as well as a weak localizing\nharmonic potential removes the periodicity of the optical lattice and leads to\nlocalization. We also studied some dynamics of the localized state confirming\nits stability.",
        "positive": "Measuring entanglement growth in quench dynamics of bosons in an optical\n  lattice: We discuss a scheme to measure the many-body entanglement growth during\nquench dynamics with bosonic atoms in optical lattices. By making use of a 1D\nor 2D setup in which two copies of the same state are prepared, we show how\narbitrary order Renyi entropies can be extracted using tunnel-coupling between\nthe copies and measurement of the parity of on-site occupation numbers, as has\nbeen performed in recent experiments. We illustrate these ideas for a\nSuperfluid-Mott insulator quench in the Bose-Hubbard model, and also for\nhard-core bosons, and show that the scheme is robust against imperfections in\nthe measurements."
    },
    {
        "anchor": "P-wave contacts of quantum gases in quasi-one-dimensional and\n  quasi-two-dimensional traps: The length scale separation in dilute quantum gases in quasi-one-dimensional\nor quasi-two-dimensional traps has spatially divided the system into two\ndistinct regimes. Whereas universal relations defined in strict one or two\ndimensions apply in a scale that is much larger than the characteristic length\nof the transverse confinements, physical observables in the short distances are\ninevitably governed by three-dimensional contacts. Here, we show that p-wave\ncontacts defined in different length scales are intrinsically connected by a\nuniversal relation, which depends on a simple geometric factor of the\ntransverse confinements. While this universal relation is derived for one of\nthe p-wave contacts, it establishes a concrete example of how dimensional\ncrossover interplays with contacts and universal relations for arbitrary\npartial wave scatterings.",
        "positive": "Elastic collision and molecule formation of spatiotemporal light bullets\n  in a cubic-quintic nonlinear medium: We consider the statics and dynamics of a stable, mobile three-dimensional\n(3D) spatiotemporal light bullet in a cubic-quintic nonlinear medium with a\nfocusing cubic nonlinearity above a critical value and any defocusing quintic\nnonlinearity. The 3D light bullet can propagate with a constant velocity in any\ndirection. Stability of the light bullet under a small perturbation is\nestablished numerically.We consider frontal collision between two light bullets\nwith different relative velocities. At large velocities the collision is\nelastic with the bullets emerge after collision with practically no distortion.\nAt small velocities two bullets coalesce to form a bullet molecule. At a small\nrange of intermediate velocities the localized bullets could form a single\nentity which expands indefinitely leading to a destruction of the bullets after\ncollision. The present study is based on an analytic Lagrange variational\napproximation and a full numerical solution of the 3D nonlinear Schr\\\"odinger\nequation."
    },
    {
        "anchor": "Signatures of the BCS-BEC crossover in the yrast spectra of Fermi\n  quantum rings: We study properties of the lowest energy states at non-zero total momentum\n(yrast states) of the Hubbard model for spin-1/2 fermions in the quantum ring\nconfiguration with attractive on-site interaction at low density. In the\none-dimensional (1D) case we solve the Hubbard model using the Bethe ansatz,\nwhile for the crossover into the 2D regime we use the\nFull-Configuration-Interaction Quantum Monte-Carlo method (FCIQMC) to obtain\nthe yrast states for the spin-balanced Fermi system. We show how the yrast\nexcitation spectrum changes from the 1D to the 2D regime and how pairing\naffects the yrast spectra. We also find signatures of fragmented condensation\nfor certain yrast states usually associated with dark solitons.",
        "positive": "Spontaneous time-reversal symmetry breaking for spinless fermions on a\n  triangular lattice: As a minimal fermionic model with kinetic frustration, we study a system of\nspinless fermions in the lowest band of a triangular lattice with long-range\nrepulsion. We find that the combination of interactions and kinetic frustration\nleads to spontaneous symmetry breaking in various ways. Time-reversal symmetry\ncan be broken by two types of loop current patterns, a chiral one and one that\nbreaks the translational lattice symmetry. Moreover, the translational symmetry\ncan also be broken by a density wave forming a kagome pattern or by a\nPeierls-type trimerization characterized by enhanced correlations among the\nsites of certain triangular plaquettes (giving a plaquette-centered density\nwave). We map out the phase diagram as it results from leading order\nGinzburg-Landau mean-field theory. Several experimental realizations of the\ntype of system under study are possible with ultracold atoms in optical\nlattices."
    },
    {
        "anchor": "Magnetic phases of orbital bipartite optical lattices: In the Hamburg cold atom experiment with orbital states in an optical\nlattice, $s$- and $p$-orbital atomic states hybridize between neighbouring\nsites. In this work we show how this alternation of sites hosting $s$- and\n$p$-orbital states gives rise to a plethora of different magnetic phases,\nquantum and classical. We focus on phases whose properties derive from\nfrustration originating from a competition between nearest and next nearest\nneighbouring exchange interactions. The physics of the Mott insulating phase\nwith unit filling is described by an effective spin-1/2 Hamiltonian showing\ngreat similarities with the $J_1$-$J_2$ model. Based on the knowledge of the\n$J_1$-$J_2$ model, together with numerical simulations, we discuss the\npossibility of realising a quantum spin liquid phase in the present optical\nlattice system. In the superfluid regime we consider the parameter regime where\nthe $s$-orbital states can be adiabatically eliminated to give an effective\nmodel for the $p$-orbital atoms. At the mean-field level we derive a\ngeneralized classical $XY$ model, and show that it may support maximum\nfrustration. When quantum fluctuations can be disregarded, the ground state is\nexpected to be a spin glass. Even with quantum fluctuations present it has been\ndebated whether a spin liquid may persist at the point of full frustration.",
        "positive": "Magnetostriction and exchange effects in trapped dipolar Bose and Fermi\n  gases: We examine the magnetostrictive position and momentum space distortions that\noccur in harmonically confined dipolar Bose and Fermi gases. Direct\ninteractions give rise to position space magnetostriction and exchange\ninteractions give rise to momentum space magnetostriction. While the position\nspace magnetostriction is similar in Bose and Fermi systems, the momentum space\nmagnetostriction is markedly different: the Bose gas momentum distribution\ndistorts in the opposite sense to that of the Fermi gas. By relating exchange\neffects to short range correlations between the particles we discuss the\nenergetic origin of this difference. Our main calculations are based on\nHartree-Fock theory, but we also provide analytic approximations for the\nmagnetostriction effects at zero and finite temperature. Our predictions should\nbe verifiable in current experiments with ultra-cold polar molecules."
    },
    {
        "anchor": "Spontaneous Four-Wave Mixing of de Broglie Waves: Beyond Optics: We investigate the atom-optical analog of degenerate four-wave mixing of\nphotons by colliding two Bose-Einstein condensates (BECs) of metastable helium\nand measuring the resulting momentum distribution of the scattered atoms with a\ntime and space resolved detector. For the case of photons, phase matching\nconditions completely define the final state of the system, and in the case of\ntwo colliding BECs, simple analogy implies a spherical momentum distribution of\nscattered atoms. We find, however, that the final momenta of the scattered\natoms instead lie on an ellipsoid whose radii are smaller than the initial\ncollision momentum. Numerical and analytical calculations agree well with the\nmeasurements, and reveal the interplay between many-body effects, mean-field\ninteraction, and the anisotropy of the source condensate.",
        "positive": "Chiral Prethermalization in supersonically split condensates: We study the dynamics of phase relaxation between a pair of one-dimensional\ncondensates created by a supersonic unzipping of a single condensate. We use\nthe Lorentz invariance of the low energy sector of such systems to show that\ndephasing results in an unusual prethermal state, in which right- and\nleft-moving excitations have different, Doppler-shifted temperatures. The\nchirality of these modes can be probed experimentally by measuring the\ninterference fringe contrasts with the release point of the split condensates\nmoving at another supersonic velocity. Further, an accelerated motion of the\nrelease point can be used to observe a space-like analogue of the Unruh effect.\nA concrete experimental realization of the quantum zipper for a BEC of trapped\natoms on a atom chip is outlined. We interpret these results in the context of\nthe general question of the Lorentz transformation of temperature, and the\nclose analogy with the dipolar anisotropy of the Cosmic Microwave Background."
    },
    {
        "anchor": "A pathway to ultracold bosonic $^{23}\\textrm{Na}^{39}\\textrm{K}$ ground\n  state molecules: We spectroscopically investigate a pathway for the conversion of\n$^{23}\\textrm{Na}^{39}\\textrm{K}$ Feshbach molecules into rovibronic ground\nstate molecules via STImulated Raman Adiabatic Passage (STIRAP). Using\nphotoassociation spectroscopy from the diatomic scattering threshold in the\n$a^3\\Sigma^+$ potential, we locate the resonantly mixed electronically excited\nintermediate states $|B^1\\Pi, v=8\\rangle$ and $|c^3\\Sigma^+, v=30\\rangle$\nwhich, due to their singlet-triplet admixture, serve as an ideal bridge between\npredominantly $a^3\\Sigma^+$ Feshbach molecules and pure $X^1\\Sigma^+$ ground\nstate molecules. We investigate their hyperfine structure and present a simple\nmodel to determine the singlet-triplet coupling of these states. Using\nAutler-Townes spectroscopy, we locate the rovibronic ground state of the\n$^{23}\\textrm{Na}^{39}\\textrm{K}$ molecule ($|X^1\\Sigma^+, v=0, N=0\\rangle$)\nand the second rotationally excited state $N=2$ to unambiguously identify the\nground state. We also extract the effective transition dipole moment from the\nexcited to the ground state. Our investigations result in a fully characterized\nscheme for the creation of ultracold bosonic $^{23}\\textrm{Na}^{39}\\textrm{K}$\nground state molecules.",
        "positive": "Non-linear stationary solutions in realistic models for analog\n  black-hole lasers: From both a theoretical and an experimental point of view, Bose-Einstein\ncondensates are good candidates for studying gravitational analogues of black\nholes and black-hole lasers. In particular, a recent experiment has shown that\na black-hole laser configuration can be created in the laboratory. However, the\nmost considered theoretical models for analog black-hole lasers are quite\ndifficult to implement experimentally. In order to fill this gap, we devote\nthis work to present more realistic models for black-hole lasers. For that\npurpose, we first prove that, by symmetrically extending every black-hole\nconfiguration, one can obtain a black-hole laser configuration with an\narbitrarily large supersonic region. Based on this result, we propose the use\nof an attractive square well and a double delta-barrier, which can be\nimplemented using standard experimental tools, for studying black-hole lasers.\nWe also compute the different stationary states of these setups, identifying\nthe true ground state of the system and discussing the relation between the\nobtained solutions and the appearance of dynamical instabilities."
    },
    {
        "anchor": "Polarons, Dressed Molecules, and Itinerant Ferromagnetism in ultracold\n  Fermi gases: In this review, we discuss the properties of a few impurity atoms immersed in\na gas of ultracold fermions, the so-called Fermi polaron problem. On one side,\nthis many-body system is appealing because it can be described almost exactly\nwith simple diagrammatic and/or variational theoretical approaches. On the\nother, it provides quantitatively reliable insight into the phase diagram of\nstrongly interacting population imbalanced quantum mixtures. In particular, we\nshow that the polaron problem can be applied to study itinerant ferromagnetism,\na long standing problem in quantum mechanics.",
        "positive": "Self-interference of a toroidal Bose-Einstein condensate: We demonstrate the role played by a ring trap and the associated ring\ngeometry in inducing self-interference of a toroidal Bose-Einstein condensate.\nWe start by showing how the existence of the self-interference can be inferred\nfrom the Wigner function representation of the ring. Then, using analytical\nexpressions for the time-evolution of a freely expanding ring condensate with\nand without a persistent current, we show that the self-interference of the\nring condensate is possible only in the absence of the persistent current. We\nconclude by proposing an experimental protocol for the creation of ring dark\nsolitons using the toroidal self-interference."
    },
    {
        "anchor": "Emergence of dark soliton signatures in a one-dimensional unpolarized\n  attractive Fermi gas on a ring: The two-component Fermi gas with contact attractive interactions between\ndifferent spin components can be described by the Yang-Gaudin model. Applying\nthe Bethe ansatz approach, one finds analytical formulae for the system\neigenstates that are uniquely parametrized by the solutions of the\ncorresponding Bethe equations. Recent numerical studies of the so-called yrast\neigenstates, i.e. lowest energy eigenstates at a given non-zero total momentum,\nin the Yang-Gaudin model show that their spectrum resembles yrast dispersion\nrelation of the Lieb-Liniger model which in turn matches the dark soliton\ndispersion relation obtained within the nonlinear Schr\\\"{o}dinger equation. It\nwas shown that such conjecture in the case of the Lieb-Liniger model was not\naccidental and that dark soliton features emerged in the course of measurement\nof positions of particles, when the system was initially prepared in an yrast\neigenstate. Here, we demonstrate that, starting with yrast eigenstates in the\nYang-Gaudin model, the key soliton signatures are revealed by the measurement\nof pairs of fermions. We study soliton signatures in a wide range of the\ninteraction strength.",
        "positive": "Two-fluid theory for superfluid system with anisotropic effective masses: In this work, we generalize the two-fluid theory to a superfluid system with\nanisotropic effective masses along different principal axis directions. As a\nspecific example, such a theory can be applied to spin-orbit coupled\nBose-Einstein condensate (BEC) at low temperature. The normal density from\nphonon excitations and the second sound velocity are obtained analytically.\nNear the phase transition from the plane wave to zero-momentum phases, due to\nthe effective mass divergence, the normal density from phonon excitation\nincreases greatly, while the second sound velocity is suppressed significantly.\nWith quantum hydrodynamic formalism, we give unified derivations for suppressed\nsuperfluid density and Josephson relation. At last, the momentum distribution\nfunction and fluctuation of phase for the long wave length are also discussed."
    },
    {
        "anchor": "Few vs many-body physics of an impurity immersed in a superfluid of spin\n  1/2 attractive fermions: In this article we investigate the properties of an impurity immersed in a\nsuperfluid of strongly correlated spin 1/2 fermions. For resonant interactions,\nwe first relate the stability diagram of dimer and trimer states to the\nthree-body problem for an impurity interacting with a pair of fermions. Then we\ncalculate the beyond-mean-field corrections to the energy of a weakly\ninteracting impurity. We show that these corrections are divergent and have to\nbe regularized by properly accounting for three-body physics in the problem.",
        "positive": "Visibility of ultra-cold Bose system in triangular optical lattices: In this paper, by treating the hopping parameter in Bose-Hubbard model as a\nperturbation, with the help of the re-summed Green's function method and\ncumulants expansion, the momentum distribution function of the ultra-cold Bose\nsystem in triangular optical lattice is calculated analytically. By utilizing\nit, the time-of-flight absorption picture is plotted and the corresponding\nvisibility is determined. The comparison between our analytical results and the\nexperimental data from Ref.[4] exhibits a qualitative agreement."
    },
    {
        "anchor": "Observation of wall-vortex composite defects in a spinor Bose-Einstein\n  condensate: We report the observation of spin domain walls bounded by half-quantum\nvortices (HQVs) in a spin-1 Bose-Einstein condensate with antiferromagnetic\ninteractions. A spinor condensate is initially prepared in the easy-plane polar\nphase, and then, suddenly quenched into the easy-axis polar phase. Domain walls\nare created via the spontaneous $\\mathbb{Z}_2$ symmetry breaking in the phase\ntransition and the walls dynamically split into composite defects due to snake\ninstability. The end points of the defects are identified as HQVs for the polar\norder parameter and the mass supercurrent in their proximity is demonstrated\nusing Bragg scattering. In a strong quench regime, we observe that singly\ncharged quantum vortices are formed with the relaxation of free wall-vortex\ncomposite defects. Our results demonstrate a nucleation mechanism for composite\ndefects via phase transition dynamics.",
        "positive": "A spinor Bose-Einstein condensate phase-sensitive amplifier for SU(1,1)\n  interferometry: The SU(1,1) interferometer was originally conceived as a Mach-Zehnder\ninterferometer with the beam-splitters replaced by parametric amplifiers. The\nparametric amplifiers produce states with correlations that result in enhanced\nphase sensitivity. $F=1$ spinor Bose-Einstein condensates (BECs) can serve as\nthe parametric amplifiers for an atomic version of such an interferometer by\ncollisionally producing entangled pairs of $\\left<F=1,m=\\pm1\\right|$ atoms. We\nsimulate the effect of single and double-sided seeding of the inputs to the\namplifier using the truncated-Wigner approximation. We find that single-sided\nseeding degrades the performance of the interferometer exactly at the phase the\nunseeded interferometer should operate the best. Double-sided seeding results\nin a phase-sensitive amplifier, where the maximal sensitivity is a function of\nthe phase relationship between the input states of the amplifier. In both\nsingle and double-sided seeding we find there exists an optimal phase shift\nthat achieves sensitivity beyond the standard quantum limit. Experimentally, we\ndemonstrate a spinor phase-sensitive amplifier using a BEC of $^{23}$Na in an\noptical dipole trap. This configuration could be used as an input to such an\ninterferometer. We are able to control the initial phase of the double-seeded\namplifier, and demonstrate sensitivity to initial population fractions as small\nas 0.1\\%."
    },
    {
        "anchor": "Normal mode oscillations of a nonlocal composite matter wave soliton: The existence of stable bound states of three solitons in a Bose-Einstein\ncondensate with nonlocal interactions is demonstrated by means of variational\napproach (VA) and numerical simulations. The potential of interaction between\nsolitons derived from VA is shown to be of molecular type, i.e. attractive at\nlong distances and repulsive at short distances. Normal modes of a\nthree-soliton molecule are investigated by computing small amplitude\noscillations of individual solitons near their equilibrium positions. Symmetric\nand asymmetric stretched states of the molecule are prepared and used as\ninitial conditions in numerical simulations of the nonlocal Gross-Pitaevskii\nequation. As opposed to usual triatomic molecules, we find that the frequency\nof the asymmetric mode of a three-soliton molecule is smaller than the one of\nthe symmetric mode. Possible experimental settings for the observation of these\nresults are briefly discussed.",
        "positive": "Algebraic order and the Berezinskii-Kosterlitz-Thouless transition in an\n  exciton-polariton gas: We observe quasi-long range coherence in a two-dimensional condensate of\nexciton-polaritons. Our measurements are the first to confirm that the spatial\ncorrelation algebraically decays with a slow power-law, whose exponent\nquantitatively behaves as predicted by the Berezinskii-Kosterlitz-Thouless\ntheory. The exciton-polaritons are created by non-resonant optical pumping of a\nmicro-cavity sample with embedded GaAs quantum-wells at liquid helium\ntemperature. Michelson interference is used to measure the coherence of the\nphotons emitted by decaying exciton-polaritons."
    },
    {
        "anchor": "One-dimensional hard-core anyon gas in a harmonic trap at finite\n  temperature: We investigate the strongly interacting hard-core anyon gases in a one\ndimensional harmonic potential at finite temperature by extending thermal\nBose-Fermi mapping method to thermal anyon-ferimon mapping method. With thermal\nanyon-fermion mapping method we obtain the reduced one-body density matrix and\ntherefore the momentum distribution for different statistical parameters and\ntemperatures. At low temperature hard-core anyon gases exhibit the similar\nproperties as those of ground state, which interpolate between Bose-like and\nFermi-like continuously with the evolution of statistical properties. At high\ntemperature hard-core anyon gases of different statistical properties display\nthe same reduced one-body density matrix and momentum distribution as those of\nspin-polarized fermions. The Tan's contact of hard-core anyon gas at finite\ntemperature is also evaluated, which take the simple relation with that of\nTonks-Girardeau gas $C_b$ as $C=\\frac12(1-cos\\chi\\pi)C_b$.",
        "positive": "All-optical control of superradiance and matter waves using a dispersive\n  cavity: Cavity quantum electrodynamics (CQED) plays an elegant role of studying\nstrong coupling between light and matter. However, a non-mechanical, direct and\ndynamical control of the used mirrors is still unavailable. Here we\ntheoretically investigate a novel type of dynamically controllable cavity\ncomposed of two atomic mirrors. Based on the electromagnetically induced\ntransparency (EIT), the reflectance of atomic mirror is highly controllable\nthrough its dispersive properties by varying the intensity of applied coupling\nfields or the optical depth of atomic media. To demonstrate the uniqueness of\nthe present cavity, we further show the possibility of manipulating\nvacuum-induced diffraction of a binary Bose-Einstein condensate (BEC) when\nloading it into a dispersive cavity and experiencing superradiant scatterings.\nOur results may provide a novel all-optical element for atom optics and shine\nnew light on controlling light-matter interaction."
    },
    {
        "anchor": "Three-phonon and four-phonon interaction processes in a pair-condensed\n  Fermi gas: We study the interactions among phonons and the phonon lifetime in a\npair-condensed Fermi gas in the BEC-BCS crossover in the collisionless regime.\nTo compute the phonon-phonon coupling amplitudes we use a microscopic model\nbased on a generalized BCS Ansatz including moving pairs, which allows for a\nsystematic expansion around the mean field BCS approximation of the ground\nstate. We show that the quantum hydrodynamic expression of the amplitudes\nobtained by Landau and Khalatnikov apply only on the energy shell, that is for\nresonant processes that conserve energy. The microscopic model yields the same\nexcitation spectrum as the Random Phase Approximation, with a linear (phononic)\nstart and a concavity at low wave number that changes from upwards to downwards\nin the BEC-BCS crossover. When the concavity of the dispersion relation is\nupwards at low wave number, the leading damping mechanism at low temperature is\nthe Beliaev-Landau process 2 phonons $\\leftrightarrow$ 1 phonon while, when the\nconcavity is downwards, it is the Landau-Khalatnikov process 2 phonons\n$\\leftrightarrow$ 2 phonons. In both cases, by rescaling the wave vectors to\nabsorb the dependence on the interaction strength, we obtain a universal\nformula for the damping rate. This universal formula corrects and extends the\noriginal analytic results of Landau and Khalatnikov [ZhETF {\\bf 19}, 637\n(1949)] for the $2\\leftrightarrow2$ processes in the downward concavity case.\nIn the upward concavity case, for the Beliaev 1$\\leftrightarrow$ 2 process for\nthe unitary gas at zero temperature, we calculate the damping rate of an\nexcitation with wave number $q$ including the first correction proportional to\n$q^7$ to the $q^5$ hydrodynamic prediction, which was never done before in a\nsystematic way.",
        "positive": "Helical Floquet Channels in 1D Lattices: We show how dispersionless channels exhibiting perfect spin-momentum locking\ncan arise in a 1D lattice model. While such spectra are forbidden by fermion\ndoubling in static 1D systems, here we demonstrate their appearance in the\nstroboscopic dynamics of a periodically driven system. Remarkably, this\nphenomenon does not rely on any adiabatic assumptions, in contrast to the well\nknown Thouless pump and related models of adiabatic spin pumps. The proposed\nsetup is shown to be experimentally feasible with state of the art techniques\nused to control ultracold alkaline earth atoms in optical lattices."
    },
    {
        "anchor": "Unravelling Interaction and Temperature Contributions in Unpolarized\n  Trapped Fermionic Atoms in the BCS Regime: In the BCS limit density profiles for unpolarized trapped fermionic clouds of\natoms are largely featureless. Therefore, it is a delicate task to analyze them\nin order to quantify their respective interaction and temperature\ncontributions. Temperature measurements have so far been mostly considered in\nan indirect way, where one sweeps isentropically from the BCS to the BEC limit.\nInstead we suggest here a direct thermometry, which relies on measuring the\ncolumn density and comparing the obtained data with a Hartree-Bogoliubov\nmean-field theory combined with a local density approximation. In case of an\nattractive interaction between two-components of $^{6}$Li atoms trapped in a\ntri-axial harmonic confinement we show that minimizing the error within such an\nexperiment-theory collaboration turns out to be a reasonable criterion for\nanalyzing in detail measured densities and, thus, for ultimately determining\nthe sample temperatures. The findings are discussed in view of various possible\nsources of errors.",
        "positive": "Shell-shaped condensates with gravitational sag: contact and dipolar\n  interactions: We investigate Bose-Einstein condensates in bubble trap potentials in the\npresence of a small gravity. In particular, we focus on thin shells and study\nboth contact and dipolar interacting condensates. We first analyze the effects\nof the anisotropic nature of the dipolar interactions, which already appear in\nthe absence of gravity and are enhanced when the polarization axis of the\ndipoles and the gravity are slightly misaligned. Then, in the small gravity\ncontext, we investigate the dynamics of small oscillations of these thin,\nshell-shaped condensates triggered either by an instantaneous tilting of the\ngravity direction or by a sudden change of the gravity strength. This system\ncould be a preliminary stage for realizing a gravity sensor in space\nlaboratories."
    },
    {
        "anchor": "Finite size effects and Hofstadter butterfly in a bosonic Mott insulator\n  with relativistic dispersion background: Gauge potentials with different configurations have been recently realized in\nthe optical lattice experiments. It is remarkable that one of the simplest\ngauge can generate particle energy spectrum with the self-similar structure\nknown as a Hofstadter butterfly. We investigate theoretically the impact of\nstrong on-site interaction on such a spectrum. In particular, it is shown that\nthe fractal structure is encoded in the quasi-particle and hole bosonic\nbranches. A square lattice and other structures (brick-wall and staggered\nmagnetic flux lattice) with relativistic energy dispersions which are currently\naccessible in the experiments are considered. Moreover, although in brick-wall\nand staggered flux lattices the quasi-particle densities of states looks\nqualitatively similar, the corresponding Hofstadter butterfly assumes different\nforms. In particular, we use a superposition of two different synthetic gauge\nfields which appears to be a generator of non-trivial phenomena in the optical\nlattice systems. The analysis is carried out within the strong coupling\nexpansion method on the finite size lattices and also at finite temperatures\nwhich are relevant for the currently made experiments.",
        "positive": "Momentum-dependent quasiparticle properties of the Fermi polaron from\n  the functional renormalization group: We study theoretically the lifetimes of attractive and repulsive Fermi\npolarons, as well as the molecule at finite momentum in three dimensions. To\nthis end, we develop a new technique that allows for the computation of Green's\nfunctions in the whole complex frequency plane using exact analytical\ncontinuation within the functional renormalization group. The improved\nnumerical stability and reduced computational cost of this method yield access\nto previously inaccessible momentum-dependent quasiparticle properties of\nlow-lying excited states. While conventional approaches like the\nnon-selfconsistent $T$-matrix approximation method cannot determine these\nlifetimes, we are able to find the momentum-dependent lifetime at different\ninteraction strengths of both the attractive and repulsive polaron as well as\nthe molecule. At weak coupling our results confirm predictions made from\neffective Fermi liquid theory regarding the decay of the attractive polaron,\nand we demonstrate that Fermi liquid-like behavior extends far into the\nstrong-coupling regime where attractive polaron and molecule exhibit a $p^4$\nmomentum scaling in their decay widths. Our results offer an intriguing insight\ninto the momentum-dependent quasiparticle properties of the Fermi polaron\nproblem, which can be measured using techniques such as Raman transfer and\nRamsey interferometry."
    },
    {
        "anchor": "Disorder-Driven Density and Spin Self-Ordering of a Bose-Einstein\n  Condensate in a Cavity: We study spatial spin and density self-ordering of a two-component\nBose-Einstein condensate via collective Raman scattering into a linear cavity\nmode. The onset of the Dicke superradiance phase transition is marked by a\nsimultaneous appearance of a crystalline density order and a spin-wave order.\nThe latter spontaneously breaks the discrete $\\mathbf{Z}_2$ symmetry between\neven and odd sites of the cavity optical potential. Moreover, in the\nsuperradiant state the continuous $U(1)$ symmetry of the relative phase of the\ntwo condensate wavefunctions is explicitly broken by the cavity-induced\nposition-dependent Raman coupling with a zero spatial average. Thus, the\nspatially-averaged relative condensate phase is locked at either $\\pi/2$ or\n$-\\pi/2$. This continuous symmetry breaking and relative condensate phase\nlocking by a zero-average Raman field can be considered as a generic\norder-by-disorder process similar to the random-field-induced order in the\ntwo-dimensional classical ferromagnetic $XY$ spin model. However, the seed of\nthe random field in our model stems from quantum fluctuations in the cavity\nfield and is a dynamical entity affected by self-ordering. The spectra of\nelementary excitations exhibit the typical mode softening at the superradiance\nthreshold.",
        "positive": "Suppression of Bogoliubov momentum pairing and emergence of non-Gaussian\n  correlations in ultracold interacting Bose gases: Strongly correlated quantum matter -- such as interacting electron systems or\ninteracting quantum fluids -- possesses properties that cannot be understood in\nterms of linear fluctuations and free quasi-particles. Quantum fluctuations in\nthese systems are indeed large and generically exhibit non-Gaussian statistics\n-- a property captured only by inspecting high-order correlations, whose\nquantitative reconstruction poses a formidable challenge to both experiments\nand theory alike. A prime example of correlated quantum matter is the strongly\ninteracting Bose fluid, realized by superfluid Helium and, more recently,\nultra-cold atoms. Here, we experimentally study interacting Bose gases from the\nweakly to the strongly interacting regime through single-atom-resolved\ncorrelations in momentum space. We observe that the Bogoliubov pairing among\nmodes of opposite momenta, emblematic of the weakly interacting regime, is\nsuppressed as interactions become stronger. This departure from the predictions\nof Bogoliubov theory signals the onset of the strongly correlated regime, as\nconfirmed by numerical simulations that highlight the role of non-linear\nquantum fluctuations in our system. Additionally, our measurements unveil a\nnon-zero four-operator cumulant at even stronger interactions, which is a\ndirect signature of non-Gaussian correlations. These results shed light on the\nemergence and physical origin of non-Gaussian correlations in ensembles of\ninteracting bosons."
    },
    {
        "anchor": "Ultracold Lattice Gases with Periodically Modulated Interactions: We show that a time-dependent magnetic field inducing a periodically\nmodulated scattering length may lead to interesting novel scenarios for cold\ngases in optical lattices, characterized by a nonlinear hopping depending on\nthe number difference at neighboring sites. We discuss the rich physics\nintroduced by this hopping, including pair superfluidity, exactly defect-free\nMott-insulator states for finite hopping, and pure holon and doublon\nsuperfluids. We also address experimental detection, showing that the\nintroduced nonlinear hopping may lead in harmonically trapped gases to abrupt\ndrops in the density profile marking the interface between different superfluid\nregions.",
        "positive": "Infrared behavior of interacting bosons at zero temperature: We review the infrared behavior of interacting bosons at zero temperature.\nAfter a brief discussion of the Bogoliubov approximation and the breakdown of\nperturbation theory due to infrared divergences, we show how the\nnon-perturbative renormalization group enables to obtain the exact infrared\nbehavior of the correlation functions."
    },
    {
        "anchor": "Local-field Theory of the BCS-BEC Crossover: We develop a self-consistent theory unifying the description of a quantum\nFermi gas in the presence of a Fano-Feshbach resonance in the whole phase\ndiagram ranging from BCS to BEC type of superfluidity and from narrow to broad\nresonances, including the fluctuations beyond mean field. Our theory covers a\npart of the phase diagram which is not easily accessible by Quantum Monte Carlo\nsimulations and is becoming interesting for a new class of experiments in cold\natoms.",
        "positive": "Control of the vortex lattice formation in coupled atom-molecular\n  Bose-Einstein condensate in a double well potential: Role of atom-molecule\n  coupling, trap rotation frequency and detuning: We study the vortex formation in coupled atomic and molecular condensates in\na rotating double well trap by numerically solving the coupled Gross-Pitaevskii\nlike equations. Starting with the atomic condensate in the double well\npotential we considered two-photon Raman photoassociation for coherent\nconversion of atoms to molecules. It is shown that the competition between\natom-molecule coupling strength and repulsive atom-molecule interaction\ncontrols the spacings between atomic and molecular vortices and the rotation\nfrequency of the trap is the key player for controlling the number of visible\natomic and molecular vortices. Whereas the Raman detuning controls the spacing\nbetween atomic and molecular vortices as well as the number of atomic and\nmolecular vortices in the trap. We have shown by considering the molecular\nlattices the distance between two molecular vortices can be controlled by\nvarying the Raman detuning. In addition we have found that the Feynman rule\nrelating the total number of vortices and average angular momentum both for\natoms and molecules can be satisfied by considering the atomic and molecular\nvortices those are hidden in density distribution and seen as singularities in\nphase distribution of the coupled system except for the lattice structure where\nmolecular vortices are overlapped with each other. It is found that although\nthe number of visible/core vortices in atomic and molecular vortex lattices\ndepends significantly on the system parameters the number of atomic and\nmolecular hidden vortices remains constant in most of the cases."
    },
    {
        "anchor": "Dephasing in coherently-split quasicondensates: We numerically model the evolution of a pair of coherently split\nquasicondensates. A truly one-dimensional case is assumed, so that the loss of\nthe (initially high) coherence between the two quasicondensates is due to\ndephasing only, but not due to the violation of integrability and subsequent\nthermalization (which are excluded from the present model). We confirm the\nsubexponential time evolution of the coherence between two quasicondensates\n$\\propto \\exp [-(t/t_0)^{2/3}]$, experimentally observed by S. Hofferberth {\\em\net. al.}, Nature {\\bf 449}, 324 (2007). The characteristic time $t_0$ is found\nto scale as the square of the ratio of the linear density of a quasicondensate\nto its temperature, and we analyze the full distribution function of the\ninterference contrast and the decay of the phase correlation.",
        "positive": "Nonlinear waves of Bose-Einstein condensates in rotating ring lattice\n  potentials: We analyze the dynamics of Bose-Einstein condensates loaded in rotating ring\nlattices made of a few sites, and show how rotation maps the states found in\nthis finite system into those belonging to a static infinite lattice. Ring\ncurrents and soliton states in the absence of a lattice find their continuation\nin the presence of the lattice as nonlinear Bloch waves and soliton-like states\nconnecting them. Both bright gap solitons and dark-soliton trains are shown to\nconnect continuously to linear solutions. The existence of adiabatic paths upon\nvarying rotation frequency between states with quantized supercurrents suggests\nhighly controllable methods for the experimental generation of persistent\ncurrents."
    },
    {
        "anchor": "Two-mode effective interaction in a double-well condensate: We investigate the origin of a disagreement between the two-mode model and\nthe exact Gross-Pitaevskii dynamics applied to double-well systems. In general\nthis model, even in its improved version, predicts a faster dynamics and\nunderestimates the critical population imbalance separating Josephson and\nself-trapping regimes. We show that the source of this mismatch in the dynamics\nlies in the value of the on-site interaction energy parameter. Using simplified\nThomas-Fermi densities, we find that the on-site energy parameter exhibits a\nlinear dependence on the population imbalance, which is also confirmed by\nGross-Pitaevskii simulations. When introducing this dependence in the two-mode\nequations of motion, we obtain a reduced interaction energy parameter which\ndepends on the dimensionality of the system. The use of this new parameter\nsignificantly heals the disagreement in the dynamics and also produces better\nestimates of the critical imbalance.",
        "positive": "Chiral currents in one-dimensional fractional quantum Hall states: We study bosonic and fermionic quantum two-leg ladders with orbital magnetic\nflux. In such systems, the ratio, $\\nu$, of particle density to magnetic flux\nshapes the phase-space, as in quantum Hall effects. In fermionic (bosonic)\nladders, when $\\nu$ equals one over an odd (even) integer, Laughlin fractional\nquantum Hall (FQH) states are stabilized for sufficiently long ranged repulsive\ninteractions. As a signature of these fractional states, we find a unique\ndependence of the chiral currents on particle density and on magnetic flux.\nThis dependence is characterized by the fractional filling factor $\\nu$, and\nforms a stringent test for the realization of FQH states in ladders, using\neither numerical simulations or future ultracold-atom experiments. The two-leg\nmodel is equivalent to a single spinful chain with spin-orbit interactions and\na Zeeman magnetic field, and results can thus be directly borrowed from one\nmodel to the other."
    },
    {
        "anchor": "Probing the FFLO phase by double occupancy modulation spectroscopy: We propose here that for a spin-imbalanced two-component attractive Fermi gas\nloaded in a 1D optical lattice in presence of an harmonic confining potential,\nthe observation of the change in the double occupancy after a lattice depth\nmodulation can provide clear evidence of the Fulde-Ferrell-Larkin-Ovchinnikov\n(FFLO) phase. Simulating the time evolution of the system, we can characterize\nthe double occupancy spectrum for different initial conditions, relating its\nfeatures to the FFLO wavevector $q$. In particular, the narrowing of the width\nof the spectrum can be related, through Bethe-ansatz equations in the strongly\ninteracting limit, to the FFLO wavevector $q$.",
        "positive": "Symmetry protected skyrmions in 3D spin-orbit coupled Bose gases: We present a variational study of pseudo-spin $1/2$ Bose gases in a harmonic\ntrap with weak 3D spin-orbit coupling of $\\bmsigma\\cdot\\mathbf{p}$ type. This\nspin-orbit coupling mixes states with different parities, which inspires us to\napproximate the single particle state with the eigenstates of the total angular\nmomentum, i.e. superposition of harmonic $s$-wave and $p$-wave states. As the\ntime reversal symmetry is protected by two-body interaction, we set the\nvariational order parameter as the combination of two mutually time reversal\nsymmetric eigenstates of the total angular momentum. The variational results\nessentially reproduce the 3D skyrmion-like ground state recently identified by\nKawakami {\\it et al.}. We show that these skyrmion-like ground states emerging\nin this model are primarily caused by $p$ wave spatial mode involving in the\nvariational order parameter that drives two spin components spatially\nseparated. We find the ground state of this system falls into two phases with\ndifferent density distribution symmetries depending on the relative magnitude\nof intraspecies and interspecies interaction: Phase I has parity symmetric and\naxisymmetric density distributions, while Phase II is featured with special\njoint symmetries of discrete rotational and time reversal symmetry. With the\nincreasing interaction strength the transition occurs between two phases with\ndistinct density distributions, while the topological 3D skyrmion-like spin\ntexture is symmetry protected."
    },
    {
        "anchor": "Bragg spectroscopic interferometer and quantum measurement-induced\n  correlations in atomic Bose-Einstein condensates: We theoretically analyze the Bragg spectroscopic interferometer of two\nspatially separated atomic Bose-Einstein condensates that was experimentally\nrealized by Saba et al. [Science 2005 v307 p1945] by continuously monitoring\nthe relative phase evolution. Even though the atoms in the light-stimulated\nBragg scattering interact with intense coherent laser beams, we show that the\nphase is created by quantum measurement-induced back-action on the homodyne\nphoto-current of the lasers, opening possibilities for quantum-enhanced\ninterferometric schemes. We identify two regimes of phase evolution: a running\nphase regime which was observed in the experiment of Saba et al., that is\nsensitive to an energy offset and suitable for an interferometer, and a trapped\nphase regime, that can be insensitive to applied forces and detrimental to\ninterferometric applications.",
        "positive": "Measuring Hopf links and Hopf invariants in a quenched topological Raman\n  lattice: In a recent experimental work [Z. Wu et al., Science 354, 83 (2016)], the\nPKU-USTC group realized a two-dimensional two-band quantum anomalous Hall model\non a square Raman lattice. By quenching the atom-laser detuning of such a Raman\nlattice, the time-dependent Bloch vectors for each quasimomentum points define\na Hopf mapping from quasimomentum-time space $(k_x,k_y,t)\\in T^3$ to the Bloch\nsphere $S^2$. The Hopf links between the preimages of any two Bloch vectors on\n$S^2$ can be measured experimentally through Bloch state tomography using\nspin-resolved time-of-flight measurement together with suitable radio-frequency\nmanipulations. The dynamical Hopf invariants, which are quasimomentum-time\nintegrations of Chern-Simons densities, can also be extracted experimentally\nthrough certain quench processes. As the Hopf invariant equals the Chern number\nof the post-quench Hamiltonian, the measurements of Hopf links and Hopf\ninvariants provide an alternative way of understanding the topological phase\ndiagram of the equilibrium system."
    },
    {
        "anchor": "Bound states of an ultracold atom interacting with a set of stationary\n  impurities: In this manuscript we analyse properties of bound states of an atom\ninteracting with a set of static impurities. We begin with the simplest system\nof a single atom interacting with two static impurities. We consider two types\nof atom-impurity interaction: (i) zero-range potential represented by\nregularized delta, (ii) more realistic polarization potential, representing\nlong-range part of the atom-ion interaction. For the former we obtain\nanalytical results for energies of bound states. For the latter we perform\nnumerical calculations based on the application of finite element method. Then,\nwe move to the case of a single atom interacting with one-dimensional (1D)\ninfinite chain of static ions. Such a setup resembles Kronig-Penney model of a\n1D crystalline solid, where energy spectrum exhibits band structure behaviour.\nFor this system, we derive analytical results for the band structure of bound\nstates assuming regularized delta interaction, and perform numerical\ncalculations, considering polarization potential to model atom-impurity\ninteraction. Both approaches agree quite well when separation between\nimpurities is much larger than characteristic range of the interaction\npotential.",
        "positive": "Mobile impurity in a Fermi sea from the functional renormalization group\n  analytically continued to real time: Motivated by experiments with cold atoms, we investigate a mobile impurity\nimmersed in a Fermi sea in three dimensions at zero temperature by means of the\nfunctional renormalization group. We first perform the derivative expansion of\nthe effective action to calculate the ground state energy and Tan's contact\nacross the polaron-molecule transition for several mass imbalances. Next we\nstudy quasiparticle properties of the impurity by using a real-time method\nrecently developed in nuclear physics, which allows one to go beyond the\nderivative expansion. We obtain the spectral function of the polaron, the\neffective mass and quasiparticle weight of attractive and repulsive polarons,\nand clarify how they are affected by mass imbalances."
    },
    {
        "anchor": "Anomalous Behavior of Spin Systems with Dipolar Interactions: We study the properties of spin systems realized by cold polar molecules\ninteracting via dipole-dipole interactions in two dimensions. Using a spin wave\ntheory, that allows for the full treatment of the characteristic long-distance\ntail of the dipolar interaction, we find several anomalous features in the\nground state correlations and the spin wave excitation spectrum, which are\nabsent in their counterparts with short range interaction. The most striking\nconsequence is the existence of true long-range order at finite temperature for\na two-dimensional phase with a broken U(1) symmetry.",
        "positive": "Spin-1 spin-orbit- and Rabi-coupled Bose-Einstein condensate solver: We present OpenMP versions of FORTRAN programs for solving the\nGross-Pitaevskii equation for a harmonically trapped three-component spin-1\nspinor Bose-Einstein condensate (BEC) in one (1D) and two (2D) spatial\ndimensions with or without spin-orbit (SO) and Rabi couplings. Several\ndifferent forms of SO coupling are included in the programs. We use the\nsplit-step Crank-Nicolson discretization for imaginary- and real-time\npropagation to calculate stationary states and BEC dynamics, respectively. The\nimaginary-time propagation programs calculate the lowest-energy stationary\nstate. The real-time propagation programs can be used to study the dynamics.\nThe simulation input parameters are provided at the beginning of each program.\nThe programs propagate the condensate wave function and calculate several\nrelevant physical quantities. Outputs of the programs include the wave\nfunction, energy, root-mean-square sizes, different density profiles (linear\ndensity for the 1D program, linear and surface densities for the 2D program).\nThe imaginary- or real-time propagation can start with an analytic wave\nfunction or a pre-calculated numerical wave function. The imaginary-time\npropagation usually starts with an analytic wave function, while the real-time\npropagation is often initiated with the previously calculated converged\nimaginary-time wave function."
    },
    {
        "anchor": "Full counting statistics of the interference contrast from independent\n  Bose-Einstein condensates: We show that the visibility in interference experiments with Bose-Einstein\ncondensates is directly related to the condensate fraction. The probability\ndistribution of the contrast over many runs of an interference experiment thus\ngives the full counting statistics of the condensed atom number. For\ntwo-dimensional Bose gases, we discuss the universal behavior of the\nprobability distribution in the superfluid regime and provide analytical\nexpressions for the distributions for both homogeneous and harmonically trapped\nsamples. They are non-Gaussian and unimodal with a variance that is directly\nrelated to the superfluid density. In general, the visibility is a\nself-averaging observable only in the presence of long range phase coherence.\nClose to the transition temperature, the visibility distribution reflects the\nuniversal order parameter distribution in the vicinity of the critical point.",
        "positive": "Dynamics and symmetries of a repulsively bound atom pair in an infinite\n  optical lattice: We investigate the dynamics of two bosons trapped in an infinite\none-dimensional optical lattice potential within the framework of the\nBose-Hubbard model and derive an exact expression for the wavefunction at\nfinite time. As initial condition we chose localized atoms that are separated\nby a distance of $d$ lattice sites and carry a center of mass quasi-momentum.\nAn initially localized pair ($d=0$) is found to be more stable as quantified by\nthe pair probability (probability to find two atoms at the same lattice site)\nwhen the interaction and/or the center of mass quasi-momentum is increased. For\ninitially separated atoms ($d \\neq 0$) there exists an optimal interaction\nstrength for pair formation. Simple expressions for the wavefunction, the pair\nprobability and the optimal interaction strength for pair formation are\ncomputed in the limit of infinite time. Whereas the time-dependent wavefunction\ndiffers for values of the interaction strength that differ only by the sign,\nimportant observables like the density and the pair probability do not. With a\nsymmetry analysis this behavior is shown to extend to the $N$-particle level\nand to fermionic systems. Our results provide a complementary understanding of\nthe recently observed [Winkler \\textit{et al.}, Nature (London) \\textbf{441},\n853 (2006)] dynamical stability of atom pairs in a repulsively interacting\nlattice gas."
    },
    {
        "anchor": "Improving Mean-Field Theory for Bosons in Optical Lattices via\n  Degenerate Perturbation Theory: The objective of this paper is the theoretical description of the\nMott-insulator to superfluid quantum phase transition of a Bose gas in an\noptical lattice. In former works the Rayleigh-Schr\\\"odinger perturbation theory\nwas used within a mean-field approach, which yields partially non-physical\nresults since the degeneracy between two adjacent Mott lobes is not taken into\naccount. In order to correct such non-physical results we apply the\nBrillouin-Wigner perturbation theory to the mean-field approximation of the\nBose-Hubbard model. Detailed explanations of how to use the Brillouin-Wigner\ntheory are presented, including a graphical approach that allows to efficiently\nkeep track of the respective analytic terms. To prove the validity of this\ncomputation, the results are compared with other works. Besides the analytic\ncalculation of the phase boundary from Mott-insulator to superfluid phase, the\ncondensate density is also determined by simultaneously solving two algebraic\nequations. The analytical and numerical results turn out to be physically\nmeaningful and can cover a region of system parameters inaccessible until now.\nOur results are of particular interest provided an harmonic trap is added to\nthe former calculations in an homogeneous system, in view of describing an\nexperiment within the local density approximation. Thus, the paper represents\nan essential preparatory work for determining the experimentally observed\nwedding-cake structure of particle-density profile at both finite temperature\nand hopping.",
        "positive": "Signatures of Bose-Einstein condensation in an optical lattice: We discuss typical experimental signatures for the Bose-Einstein condensation\n(BEC) of an ultracold Bose gas in an inhomogeneous optical lattice at finite\ntemperature. Applying the Hartree-Fock-Bogoliubov-Popov formalism, we calculate\nquantities such as the momentum-space density distribution, visibility and peak\nwidth as the system is tuned through the superfluid to normal phase transition.\nDifferent from previous studies, we consider systems with fixed total particle\nnumber, which is of direct experimental relevance. We show that the onset of\nBEC is accompanied by sharp features in all these signatures, which can be\nprobed via typical time-of-flight imaging techniques. In particular, we find a\ntwo-platform structure in the peak width across the phase transition. We show\nthat the onset of condensation is related to the emergence of the higher\nplatform, which can be used as an effective experimental signature."
    },
    {
        "anchor": "Extended flat-bands, entanglement and topological properties in a Creutz\n  ladder: In this work, we study the entanglement and topological properties of an\nextended flat-band Creutz ladder by considering a compacted localized state\n(CLS). Based on the CLS picture, we find a multiple flat-band extension from\nthe conventional two flat-band Creutz ladder. A simple vertical inter-chain\ncoupling leads to a four complete flat-band system and creates an additive\n$\\pi$-flux pattern on the Creutz ladder. Interestingly, the strong coupling\ninduces a topological phase transition where the distribution of CLSs is\nmodified: upper and lower flat-band CLSs are paired up. This pairing leads to\nthe destruction of the CLS' entanglement and, hence, to a vanishing edge mode\n(i.e., the breakdown of non-trivial topological phase). Finally, we study the\nlocalization dynamics induced by the presence of complete flat bands in this\nextended flat-band system.",
        "positive": "Layer-by-layer assembly of multilayer optical lattices: Application to\n  displaced dice lattice: We propose methods for synthesizing multilayer optical lattices of cold atoms\nin a layer-by-layer manner, to unlock the potential of optical lattices in\nsimulating the fascinating physics of multilayer systems. Central to the\napproach is to compress the beam profile of a red-detuned Gaussian laser beam\nfrom disklike to a thin line by a telescope with two cylindrical lenses. A\nhighly tunable multilayer optical lattice is obtained by passing the compressed\nGaussian beam through an optical device consisting of beam splitters, mirrors,\nand glass plates. We illustrate the proposal with the displaced dice lattice,\nwhich is a trilayer lattice that maps to the dice lattice when projected to the\nsame layer. Both the dice model and its interesting variants may be realized.\nFor a model of fermionic cold atoms, featuring an isolated flat band between\ntwo dispersive bands, we find valley-contrasting interband transitions\ninvolving the flat band."
    },
    {
        "anchor": "Fermion production at the boundary of an expanding universe: a cold-atom\n  gravitational analogue: We study the phenomenon of cosmological particle production of Dirac fermions\nin a Friedman-Robertson-Walker spacetime, focusing on a (1+1)-dimensional case\nin which the evolution of the scale factor is set by the equations of\nJackiw-Teitelboim gravity. As a first step towards a quantum simulation of this\nphenomenon, we consider two possible lattice regularizations, which allow us to\nexplore the interplay of particle production and topological phenomena in\nspacetimes with a boundary. In particular, for a Wilson-type discretization of\nthe Dirac field, the asymptotic Minkowski vacua connected by the intermediate\nexpansion corresponds to symmetry-protected topological groundstates, and have\na boundary manifestation in the form of zero-modes exponentially localized to\nthe spatial boundaries. We show that particle production can also populate\nthese zero modes, which contrasts with the situation with a na\\\"ive-fermion\ndiscretization, in which conformal zero-mass fields exhibit no particle\nproduction. We present a scheme for the quantum simulation of this\ngravitational analogue by means of ultra-cold atoms in Raman optical lattices,\nwhich requires real-time control of the Raman-beam detuning according to the\nscale factor of the simulated spacetime, as well as band-mapping measurements.",
        "positive": "Spin turbulence with small spin magnitude in spin-1 spinor Bose-Einstein\n  condensates: We theoretically and numerically study spin turbulence (ST) with small spin\nmagnitude in spin-1 spinor Bose-Einstein condensates by using the spin-1 spinor\nGross-Pitaevskii (GP)equations. This kind of ST is realized in two cases: (i)\nwith antiferromagnetic interaction and (ii) with ferromagnetic interaction\nunder a static magnetic field. The ST with small spin magnitude can exhibit two\ncharacteristic power laws in the spectrum of the spin-dependent interaction\nenergy: -1 and -7/3 power laws in the low- and high-wave-number regions,\nrespectively. These power laws are derived from a Kolmogorov-type dimensional\nscaling analysis for the equations of motion of the spin vector and nematic\ntensor. To confirm these power laws, we perform a numerical calculation of the\nspin-1 spinor GP equations in a two-dimensional uniform system. In case (i),\nthe -7/3 power law appears in the high-wave-number region, but the spectrum in\nthe low-wave-number region deviates from the -1 power law. In contrast, both -1\nand -7/3 power laws are found to clearly appear in case (ii)."
    },
    {
        "anchor": "Superfluidity of a Raman spin-orbit-coupled Bose gas at finite\n  temperature: We investigate the superfluidity of a three-dimensional weakly interacting\nBose gas with a one-dimensional Raman-type spin-orbit coupling at both zero and\nfinite temperatures. Using the imaginary-time Green's function within the\nBogoliubov approximation, we explicitly derive analytic expressions of the\ncurrent-current response functions in the plane-wave and zero-momentum phases,\nfrom which we extract the superfluid density in the limits of long wavelength\nand zero frequency. At zero temperature, we check that the resultant superfluid\ndensity agrees exactly with our previous analytic prediction obtained from a\nphase-twist approach. Both results also satisfy a generalized Josephson\nrelation in the presence of spin-orbit coupling. At finite temperature, we find\na significant non-monotonic temperature dependence of superfluid density near\nthe transition from the plane-wave phase to the zero-momentum phase. We show\nthat this non-trivial behavior might be understood from the sound velocity,\nwhich has a similar temperature dependence. The non-monotonic temperature\ndependence is also shared by Landau critical velocity, above which the\nspin-orbit-coupled Bose gas loses its superfluidity. Our results would be\nuseful for further theoretical and experimental studies of superfluidity in\nexotic spin-orbit coupled quantum gases.",
        "positive": "Diagnosing a two-body state of ultracold atoms with light: An absorption of a weak pulse by two identical atoms moving in a trap is\ninvestigated. Based on atom-light interactions we present a microscopic model\nof a two-body wave function diagnosis. We study the influence of pulse\nproperties on the results. We show that a pulse duration impact a resulting\none-photon and two-photons absorption probabilities significantly."
    },
    {
        "anchor": "Quantum simulation of non-trivial topology: We propose several designs to simulate quantum many-body systems in manifolds\nwith a non-trivial topology. The key idea is to create a synthetic lattice\ncombining real-space and internal degrees of freedom via a suitable use of\ninduced hoppings. The simplest example is the conversion of an open spin-ladder\ninto a closed spin-chain with arbitrary boundary conditions. Further\nexploitation of the idea leads to the conversion of open chains with internal\ndegrees of freedom into artificial tori and M\\\"obius strips of different kinds.\nWe show that in synthetic lattices the Hubbard model on sharp and scalable\nmanifolds with non-Euclidean topologies may be realized. We provide a few\nexamples of the effect that a change of topology can have on quantum systems\namenable to simulation, both at the single-particle and at the many-body level.",
        "positive": "Emergent periodic and quasiperiodic lattices on surfaces of synthetic\n  Hall tori and synthetic Hall cylinders: Synthetic spaces allow physicists to bypass constraints imposed by certain\nphysical laws in experiments. Here, we show that a synthetic torus, which\nconsists of a ring trap in the real space and internal states of ultracold\natoms cyclically coupled by Laguerre-Gaussian Raman beams, could be threaded by\na net effective magnetic flux through its surface---an impossible mission in\nthe real space. Such synthetic Hall torus gives rise to a periodic lattice in\nthe real dimension, in which the periodicity of density modulation of atoms\nfractionalizes that of the Hamiltonian. Correspondingly, the energy spectrum is\nfeatured by multiple bands grouping into clusters with nonsymmorphic symmetry\nprotected band crossings in each cluster, leading to braidings of wavepackets\nin Bloch oscillations. Our scheme allows physicists to glue two synthetic Hall\ntori such that localization may emerge in a quasicrystalline lattice. If the\nLaguerre-Gaussian Raman beams and ring traps were replaced by linear Raman\nbeams and ordinary traps, a synthetic Hall cylinder could be realized and\ndeliver many of the aforementioned phenomena."
    },
    {
        "anchor": "Internal Josephson Oscillations for Distinct Momenta Bose-Einstein\n  Condensates: The internal Josephson oscillations between an atomic Bose-Einstein\ncondensate (BEC) and a molecular one are studied for atoms in a square optical\nlattice subjected to a staggered gauge field. The system is described by a\nBose-Hubbard model with complex and anisotropic hopping parameters that are\ndifferent for each species, i.e., atoms and molecules. When the flux per\nplaquette for each species is small, the system oscillates between two\nconventional zero-momentum condensates. However, there is a regime of\nparameters in which Josephson oscillations between a vortex-carrying atomic\ncondensate (finite momentum BEC) and a conventional zero-momentum molecular\ncondensate may be realized. The experimental observation of the oscillations\nbetween these qualitatively distinct BEC's is possible with state-of-the-art\nRamsey interference techniques.",
        "positive": "Modified Bethe-Peierls boundary condition for ultracold atoms with\n  Spin-Orbit coupling: We show that the Bethe-Peierls (BP) boundary condition should be modified for\nultracold atoms with spin-orbit (SO) coupling. Moreover, we derive a general\nform of the modified BP boundary condition, which is applicable to a system\nwith arbitrary kind of SO coupling. In the modified BP condition, an\nanisotropic term appears and the inter-atomic scattering length is normally\nSO-coupling dependent. For the special system in the current experiments,\nhowever, it can be proved that the scattering length is SO-coupling\nindependent, and takes the same value as in the case without SO coupling. Our\nresult is helpful for the study of both few-body and many-body physics in\nSO-coupled ultracold gases."
    },
    {
        "anchor": "Phase Diagram for Magnon Condensate in Yttrium Iron Garnet Film: Recently, magnons, which are quasiparticles describing the collective motion\nof spins, were found to undergo Bose-Einstein condensation (BEC) at room\ntemperature in films of Yttrium Iron Garnet (YIG). Unlike other quasiparticle\nBEC systems, this system has a spectrum with two degenerate minima, which makes\nit possible for the system to have two condensates in momentum space. Recent\nBrillouin Light scattering studies for a microwave-pumped YIG film of thickness\nd=5 $\\mu$m and field H=1 kOe find a low-contrast interference pattern at the\ncharacteristic wavevector $Q$ of the magnon energy minimum. In this report, we\nshow that this modulation pattern can be quantitatively explained as due to\nnon-symmetric but coherent Bose-Einstein condensation of magnons into the two\nenergy minima. Our theory predicts a transition from a high-contrast symmetric\nphase to a low-contrast non-symmetric phase on varying the $d$ and $H$, and a\nnew type of collective oscillations.",
        "positive": "Chiral f-wave Topological Superuid in Triangular Optical Lattices: We demonstrate that an exotically chiral f-wave topological superfluid can be\ninduced in coldfermionic-atom triangular optical lattices through the\nlaser-field-generated effective non-Abelian gauge field, controllable Zeeman\nfields and s-wave Feshbach resonance. We find that the chiral f-wave\ntopological superfluid is characterized by three gapless Majorana edge states\nlocated on the boundary of the system. More interestingly, these Majorana edge\nstates degenerate into one Majorana fermion bound to each vortex in the\nsuperfluid. Our proposal enlarges topological superfluid family and specifies a\nunique experimentally controllable system to study the Majorana fermion\nphysics."
    },
    {
        "anchor": "Bell Soliton in Ultra-cold Atomic Fermi Gas: We demonstrate the existence of supersonic bell soliton in the\nBardeen-Cooper-Schrieffer-Bose-Einstein condensate (BCS-BEC) crossover regime.\nStarting from the extended Thomas-Fermi density functional theory of superfluid\norder parameter, a density transformation is used to map the hydrodynamic mean\nfield equation to a Lienard type equation. As a result, bell solitons are\nobtained as exact solutions, which is further verified by the numerical\nsolution of the dynamical equation. The stability of the soliton is established\nand its behaviour in the entire crossover domain is obtained. It is found that,\nakin to the case of vortices, the bell solitons yield highest contrast in the\nBEC regime.",
        "positive": "Tuning Dissipation and Excitations in Superfluid Fermi Gases with a\n  Moving Impurity: We develop a method to extract the dissipation for a heavy moving impurity\nimmersed in superfluid Fermi gases. The drag force is derived analytically. As\na reward, we are able to extract the dynamical structure factor, from which\ndensity excitations of the system is carefully examined. We show that\ndissipations through drag force is associated with two types of excitations,\none being single-particle and the other being collective. We map out the\ncritical velocity for dissipation across the BEC-BCS crossover, consistent with\nexisting experiments. For a magnetic impurity, we show that the dissipation is\nimmune to collective excitations. Our study clearly manifests that dissipation\nand associated excitations can be controlled by coupling superfluid Fermi gases\nwith a moving impurity, and paves the way for further exploring intriguing\nrealm of nonequilibrium phenomena and dissipation dynamics."
    },
    {
        "anchor": "Thermally activated phase slips of one-dimensional Bose gases in shallow\n  optical lattices: We study the decay of superflow via thermally activated phase slips in\none-dimensional Bose gases in a shallow optical lattice. By using the Kramers\nformula, we numerically calculate the nucleation rate of a thermally activated\nphase slip for various values of the filling factor and flow velocity in the\nabsence of a harmonic trapping potential. Within the local density\napproximation, we derive a formula connecting the phase-slip nucleation rate\nwith the damping rate of a dipole oscillation of the Bose gas in the presence\nof a harmonic trap. We use the derived formula to directly compare our theory\nwith the recent experiment done by the LENS group [L. Tanzi, et al., Sci. Rep.\n{\\bf 6}, 25965 (2016)]. From the comparison, the observed damping of dipole\noscillations in a weakly correlated and small velocity regime is attributed\ndominantly to thermally activated phase slips rather than quantum phase slips.",
        "positive": "Mapping between Hamiltonians with attractive and repulsive potentials on\n  a lattice: Through a simple and exact analytical derivation, we show that for a particle\non a lattice, there is a one-to-one correspondence between the spectra in the\npresence of an attractive potential $\\hat{V}$ and its repulsive counterpart\n$-\\hat{V}$. For a Hermitian potential, this result implies that the number of\nlocalized states is the same in both, attractive and repulsive, cases although\nthese states occur above (below) the band-continnum for the repulsive\n(attractive) case. For a $\\mP\\mT$-symmetric potential that is odd under parity,\nour result implies that in the $\\mP\\mT$-unbroken phase, the energy eigenvalues\nare symmetric around zero, and that the corresponding eigenfunctions are\nclosely related to each other."
    },
    {
        "anchor": "The Realization and Dectection of Weyl Semimetals and Chiral Anomaly in\n  Cold Atomic Systems: In this work, we describe a method to realize 3D Weyl semimetal by coupling\nmultilayers of honeycomb optical lattice in the presence of a pair of Raman\nlasers. The Raman lasers render each isolated honeycomb layer a Chern\ninsulator. With finite interlayer coupling, the bulk gap of the system closes\nat certain out-of-plane momenta due to Raman assisted tunnelling and result in\nthe Weyl semimetal phase. Using experimentally relevant parameters, we show\nthat both one and two pairs of Weyl points can be realized by tuning the\ninterlayer coupling strength. We suggest that Landau-Zener tunnelling can be\nused to detect Weyl points and show that the transition probability increases\ndramatically when Weyl point emerges. The realization of chiral anomaly by\nusing a magnetic field gradient is also discussed.",
        "positive": "Soliton localization in Bose-Einstein condensates with time-dependent\n  harmonic potential and scattering length: We derive exact solitonic solutions of a class of Gross-Pitaevskii equations\nwith time-dependent harmonic trapping potential and interatomic interaction. We\nfind families of exact single-solitonic, multi-solitonic, and solitary wave\nsolutions. We show that, with the special case of an oscillating trapping\npotential and interatomic interaction, a soliton can be localized indefinitely\nat an arbitrary position. The localization is shown to be experimentally\npossible for sufficiently long time even with only an oscillating trapping\npotential and a constant interatomic interaction."
    },
    {
        "anchor": "Validity of single-channel model for a spin-orbit coupled atomic Fermi\n  gas near Feshbach resonances: We theoretically investigate a Rashba spin-orbit coupled Fermi gas near\nFeshbach resonances, by using mean-field theory and a two-channel model that\ntakes into account explicitly Feshbach molecules in the close channel. In the\nabsence of spin-orbit coupling, when the channel coupling $g$ between the\nclosed and open channels is strong, it is widely accepted that the two-channel\nmodel is equivalent to a single-channel model that excludes Feshbach molecules.\nThis is the so-called broad resonance limit, which is well-satisfied by\nultracold atomic Fermi gases of $^{6}$Li atoms and $^{40}$K atoms in current\nexperiments. Here, with Rashba spin-orbit coupling we find that the condition\nfor equivalence becomes much more stringent. As a result, the single-channel\nmodel may already be insufficient to describe properly an atomic Fermi gas of\n$^{40}$K atoms at a moderate spin-orbit coupling. We determine a characteristic\nchannel coupling strength $g_{c}$ as a function of the spin-orbit coupling\nstrength, above which the single-channel and two-channel models are\napproximately equivalent. We also find that for narrow resonance with small\nchannel coupling, the pairing gap and molecular fraction is strongly suppressed\nby SO coupling. Our results can be readily tested in $^{40}$K atoms by using\noptical molecular spectroscopy.",
        "positive": "Bulk viscosity of dual Bose and Fermi gases in one dimension: One-dimensional Bose and Fermi gases with contact interactions are known to\nexhibit the weak-strong duality, where the equilibrium thermodynamic properties\nof one system at weak coupling are identical to those of the other system at\nstrong coupling. Here, we show that such duality extends beyond the\nthermodynamics to the frequency-dependent complex bulk viscosity, which is\nprovided by the contact-contact response function. In particular, we confirm\nthat the bulk viscosities of the Bose and Fermi gases agree in the\nhigh-temperature limit, where the systematic expansion in terms of fugacity is\navailable at arbitrary coupling. We also compute their bulk viscosities\nperturbatively in the weak-coupling limit at arbitrary temperature, which via\nthe duality serve as those of the Fermi and Bose gases in the strong-coupling\nlimit."
    },
    {
        "anchor": "Optically driven rotation of exciton-polariton condensates: The rotational response of quantum condensed fluids is strikingly distinct\nfrom rotating classical fluids, especially notable for the excitation and\nordering of quantized vortex ensembles. Although widely studied in conservative\nsystems, the dynamics of rotating open-dissipative superfluids such as\nexciton-polariton condensates remain largely unexplored, as it requires\nhigh-frequency rotation whilst avoiding resonantly driving the condensate. We\ncreate a rotating polariton condensate at GHz frequencies by off-resonantly\npumping with a rotating optical stirrer composed of the time-dependent\ninterference of two frequency-offset, structured laser modes. Acquisition of\nangular momentum exceeding the critical $1\\hbar$/particle is directly measured,\naccompanied by the deterministic nucleation and capture of quantized vortices\nwith a handedness controlled by the pump rotation direction. The demonstration\nof controlled optical rotation of a spontaneously formed polariton condensate\nenables new opportunities for the study of open-dissipative superfluidity,\nordering of non-Hermitian quantized vortex matter, and topological states in a\nhighly non-linear, photonic platform.",
        "positive": "Observation of \"broad\" d-wave Feshbach resonances with a triplet\n  structure: High partial-wave ($l\\ge2$) Feshbach resonance (FR) in an ultracold mixture\nof $^{85}$Rb-$^{87}$Rb atoms is investigated experimentally aided by a\npartial-wave insensitive analytic multichannel quantum-defect theory (MQDT).\nTwo \"broad\" resonances from coupling between d-waves in both the open and\nclosed channels are observed and characterized. One of them shows a fully\nresolved triplet structure with splitting ratio well explained by the\nperturbation to the closed channel due to interatomic spin-spin interaction.\nThese tunable \"broad\" d-wave resonances, especially the one in the\nlowest-energy open channel, could find important applications in simulating\nd-wave coupling dominated many-body systems. In addition, we find that there is\ngenerally a time and temperature requirement, associated with tunneling through\nthe angular momentum barrier, to establish and observe resonant coupling in\nnonzero partial waves."
    },
    {
        "anchor": "Universal few-body physics and cluster formation: A recent rejuvenation of experimental and theoretical interest in the physics\nof few- body systems has provided deep, fundamental insights into a broad range\nof problems. Few-body physics is a cross-cutting discipline not restricted to\nconventional subject ar- eas such as nuclear physics or atomic or molecular\nphysics. To a large degree, the recent explosion of interest in this subject\nhas been sparked by dramatic enhancements of experimental capabilities in\nultracold atomic systems over the past decade, which now permit atoms and\nmolecules to be explored deep in the quantum mechanical limit with controllable\ntwo-body interactions. This control, typically enabled by magnetic or\nelectromagnetically-dressed Fano-Feshbach resonances, allows in particular\naccess to the range of universal few-body physics, where two-body scattering\nlengths far exceed all other length scales in the problem. The Efimov effect,\nwhere 3 particles experienc- ing short-range interactions can\ncounterintuitively exhibit an infinite number of bound or quasi-bound energy\nlevels, is the most famous example of universality. Tremendous progress in the\nfield of universal Efimov physics has taken off, driven particularly by a\ncombination of experimental and theoretical studies in the past decade, and\nprior to the first observation in 2006, by an extensive set of theoretical\nstudies dating back to 1970. Because experimental observations of Efimov\nphysics have usually relied on resonances or interference phenomena in\nthree-body recombination, this connects naturally with the processes of\nmolecule formation in a low temperature gas of atoms or nucleons, and more\ngenerally with N-body recombination processes. Some other topics not closely\nrelated to the Efimov effect are also reviewed in this article, including ...",
        "positive": "Accelerating analysis of Boltzmann equations using Gaussian mixture\n  models: Application to quantum Bose-Fermi mixtures: The Boltzmann equation is a powerful theoretical tool for modeling the\ncollective dynamics of quantum many-body systems subject to external\nperturbations. Analysis of the equation gives access to linear response\nproperties including collective modes and transport coefficients, but often\nproves intractable due to computational costs associated with multidimensional\nintegrals describing collision processes. Here, we present a method to resolve\nthis bottleneck, enabling the study of a broad class of many-body systems that\nappear in fundamental science contexts and technological applications.\nSpecifically, we demonstrate that a Gaussian mixture model can accurately\nrepresent equilibrium distribution functions, thereby allowing efficient\nevaluation of collision integrals. Inspired by cold atom experiments, we apply\nthis method to investigate the collective behavior of a quantum Bose-Fermi\nmixture of cold atoms in a cigar-shaped trap, a system that is particularly\nchallenging to analyze. We focus on monopole and quadrupole collective modes\nabove the Bose-Einstein transition temperature, and find a rich phenomenology\nthat spans interference effects between bosonic and fermionic collective modes,\ndampening of these modes, and the emergence of hydrodynamics in various\nparameter regimes. These effects are readily verifiable experimentally."
    },
    {
        "anchor": "Steady states of a driven dissipative dipolar XXZ chain: We study theoretically a driven dissipative one-dimensional XXZ spin$-1/2$\nchain with dipole coupling and a tunable strength of the Ising and XY\ninteraction. Within a mean-field approximation, we find a rich phase diagram\nwith uniform, spin density wave, antiferromagnetic and oscillatory phases, as\nwell as regions of phase bistability. We study the phase diagram of small\nquantum systems using exact diagonalisation, and compare the results to the\nmean-field theory. We find that while expectation values only capture the\nuniform phases of the mean-field theory, fluctuations about these expectation\nvalues give signatures of spatially non-uniform phases and bistabilities. We\nfind these signatures for all ratios of the Ising to XY interaction, showing\nthat they appear to be general features of spin$-1/2$ systems",
        "positive": "Width and shift of Fano-Feshbach resonances for van der Waals\n  interactions: We revisit the basic properties of Fano-Feshbach resonances in two-body\nsystems with van der Waals tail interactions, such as ultracold neutral atoms.\nUsing a two-channel model and two different methods, we investigate the\nrelationship between the width and shift of the resonances and their dependence\non the low-energy parameters of the system. Unlike what was previously believed\n[Rev. Mod. Phys. 82, 1225 (2010)] for magnetic resonances, we find that the\nratio between the width and the shift of a resonance does not depend only on\nthe background scattering length, but also on a closed-channel scattering\nlength. We obtain different limits corresponding to different cases of optical\nand magnetic resonances. Although the generalisation of the theory to the\nmulti-channel case remains to be done, we found that our two-channel\npredictions are verified for a specific resonance of lithium-6."
    },
    {
        "anchor": "Stabilization of trapless dipolar Bose-Einstein condensates by temporal\n  modulation of the contact interaction: We theoretically study the stability of a trapless dipolar Bose-Einstein\ncondensate (BEC) with temporal modulation of short-range contact interaction.\nFor this aim, through both analytical and numerical methods, we solve a\nGross-Pitaevskii equation with both constant and oscillatory form of\nshort-range contact interaction along with long-range, nonlocal, dipole-dipole\n(DD) interaction terms. Using variational method, we discuss the stability of\nthe trapless dipolar BEC with presence and absence of both constant and\noscillatory contact interactions. We show that the oscillatory contact\ninteraction prevents the collapse of the trapless dipolar BEC. We confirm the\nanalytical prediction through numerical simulations. We have also studied the\ncollective excitations in the system induced by the effective potential due to\noscillating interaction.",
        "positive": "Spanning the full Poincar\u00e9 sphere with polariton Rabi oscillations: We propose theoretically and demonstrate experimentally a generation of light\npulses whose polarization varies temporally to cover selected areas of the\nPoincar\\'e sphere with tunable swirling speed and total duration (1 ps and 10\nps respectively in our implementation). The effect relies on the Rabi\noscillations of two polarized fields in the strong coupling regime, excited by\ntwo counter-polarized and delayed pulses. The interferences of the oscillating\nfields result in the precession of the Stokes vector of the emitted light while\npolariton lifetime imbalance results in its drift from a circle on the sphere\nof controllable radius to a single point at long times. The positioning of the\ninitial and final states allows to engineer the type of polarization spanning,\nincluding a full sweeping of the Poincar\\'e sphere. The universality and\nsimplicity of the scheme should allow for the deployment of time varying\npolarization fields at a technologically exploitable level."
    },
    {
        "anchor": "Mode softening in time-crystalline transitions of open quantum systems: In this work, we generalize the concept of roton softening mechanism of\nspatial crystalline transition to time crystals in open quantum systems. We\nstudy a dissipative Dicke model as a prototypical example, which exhibits both\ncontinuous time crystal and discrete time crystal phases.We found that on\napproaching the time crystalline transition, the response function diverges at\na finite frequency, which determines the period of the upcoming time crystal.\nThis divergence can be understood as softening of the relaxation rate of the\ncorresponding collective excitation, which can be clearly seen by the poles of\nthe response function on the complex plane. Using this mode softening analysis,\nwe predict a time quasi-crystal phase in our model, in which the self-organized\nperiod and the driving period are incommensurate.",
        "positive": "Bump-on-tail instability of twisted excitations in rotating cold atomic\n  clouds: We develop a kinetic theory for twisted density waves (phonons), carrying a\nfinite amount of orbital angular momentum, in large magneto optical traps,\nwhere the collective processes due to the exchange of scattered photons are\nconsidered. Explicit expressions for the dispersion relation and for the\nkinetic (Landau) damping are derived and contributions from the orbital angular\nmomentum are discussed. We show that for rotating clouds, exhibiting\nring-shaped structures, phonons carrying orbital angular momentum can cross the\ninstability threshold and grow out of noise, while the usual plane wave\nsolutions are kinetically damped."
    },
    {
        "anchor": "Classical dynamics of the optomechanical modes of a Bose-Einstein\n  condensate in a ring cavity: We consider a cavity optomechanical system consisting of a Bose-Einstein\ncondensate (BEC) interacting with two counterpropagating traveling-wave modes\nin an optical ring cavity. In contrast to the more familiar case where the\ncondensate is driven by the standing-wave field of a high-$Q$ Fabry-P{\\'e}rot\ncavity we find that both symmetric and antisymmetric collective density side\nmodes of the BEC are mechanically excited by the light field. In the\nsemiclassical, mean-field limit where the light field and the zero-momentum\nmode of the condensate are treated classically the system is found to exhibit a\nrich multistable behavior, including the appearance of isolated branches of\nsolutions (isolas). We also present examples of the dynamics of the system as\ninput parameters such as the frequency of the driving lasers are varied.",
        "positive": "Dissipative cooling of spin chains by a bath of dipolar particles: We consider a spin chain of fermionic atoms in an optical lattice,\ninteracting with each other by super-exchange interactions. We theoretically\ninvestigate the dissipative evolution of the spin chain when it is coupled by\nmagnetic dipole-dipole interaction to a bath consisting of atoms with a strong\nmagnetic moment. Dipolar interactions with the bath allow for a dynamical\nevolution of the collective spin of the spin chain. Starting from an\nuncorrelated thermal sample, we demonstrate that the dissipative cooling\nproduces highly entangled low energy spin states of the chain in a timescale of\na few seconds. In practice, the lowest energy singlet state driven by\nsuper-exchange interactions is efficiently produced. This dissipative approach\nis a promising alternative to cool spin-full atoms in spin-independent\nlattices. It provides direct thermalization of the spin degrees of freedom,\nwhile traditional approaches are plagued by the inherently long timescale\nassociated to the necessary spatial redistribution of spins under the effect of\nsuper-exchange interactions."
    },
    {
        "anchor": "Synthetic Gauge Fields for Lattices with Multi-Orbital Unit Cells:\n  Routes towards a $\u03c0$-flux Dice Lattice with Flat Bands: We propose a general strategy for generating synthetic magnetic fields in\ncomplex lattices with non-trivial connectivity based on light-matter coupling\nin cold atomic gases. Our approach starts from an underlying optical flux\nlattice in which flux arises by coupling several internal states. Starting from\na high symmetry optical flux lattice, we superpose a scalar potential with a\nsuper- or sublattice period in order to eliminate links between the original\nlattice sites. As an alternative to changing connectivity, the approach can\nalso be used to create or remove lattice sites from the underlying parent\nlattice. To demonstrate our concept, we consider the dice lattice geometry as\nan explicit example, and construct a dice lattice with a flux density of half a\nflux quantum per plaquette, providing a pathway to flat bands with a large band\ngap. While the intuition for our proposal stems from analysis of deep optical\nlattices, we demonstrate that the approach is robust even for shallow optical\nflux lattices far from the tight-binding limit. We also provide an alternative\nexperimental proposal to realize a synthetic gauge field in a fully frustrated\ndice lattice based on laser-induced hoppings along individual bonds of the\nlattice, again involving a superlattice potential. In this approach, atoms with\na long-lived excited state are trapped using an 'anti-magic' wavelength of\nlight, allowing the desired complex hopping elements to be induced in a\nspecific laser coupling scheme for the dice lattice geometry. We conclude by\ncomparing the complexity of these alternative approaches, and advocate that\ncomplex optical flux lattices provide the more elegant and easily generalisable\nstrategy.",
        "positive": "Interacting Stark localization dynamics in a three-dimensional lattice\n  Bose gas: We measure the thermalization dynamics of a lattice Bose gas that is Stark\nlocalized by a parabolic potential. A non-equilibrium thermal density\ndistribution is created by quickly removing an optical barrier. The resulting\nspatio-temporal dynamics are resolved using Mardia's $B$ statistic, which is a\nmeasure sensitive to the shape of the entire density distribution. We conclude\nthat equilibrium is achieved for all lattice potential depths that we sample,\nincluding the strongly interacting and localized regime. However,\nthermalization is slow and non-exponential, requiring up to 500 tunneling\ntimes. We show that the Hubbard $U$ term is not responsible for thermalization\nvia comparison to an exact diagonalization calculation, and we rule out\nequilibration driven by lattice-light heating by varying the laser wavelength.\nThe thermalization timescale is comparable to the next-nearest-neighbor\ntunneling time, which suggests that a continuum, strongly interacting theory\nmay be needed to understand equlibration in this system."
    },
    {
        "anchor": "Variations of the Kibble-Zurek scaling exponents of trapped Bose gases: We study the vortex nucleation dynamics in inhomogeneous atomic Bose gases\nquenched into a superfluid phase and investigate the dependence of the\nKibble-Zurek (KZ) scaling exponent on the underlying trap configuration. For\nsamples in a number of different inhomogeneous traps, we observe the\ncharacteristic power-law scaling of the vortex number with the thermal quench\nrate, as well as an enhanced vortex suppression in the outer regions with lower\nparticle density, in agreement with the causality effect as encapsulated in the\ninhomogeneous Kibble-Zurek mechanism (IKZM). However, the measured KZ scaling\nexponents show significant differences from the theoretical estimates, and\nfurthermore their trends as a function of the underlying trap configuration\ndeviate from the IKZM prediction. We also investigate the early-time coarsening\neffect using a two-step quench protocol as proposed in a recent study and show\nthat the interpretation of the measurement results without including the\ncausality effect might be misleading. This paper provides a comprehensive study\nof vortex formation dynamics in quenched Bose gases confined in inhomogeneous\ntrapping potentials and calls for a refined theoretical framework for\nquantitative understanding of the phase transition and defect formation\nprocesses in such inhomogeneous systems.",
        "positive": "A variational approach to Bogoliubov excitations and dynamics of dipolar\n  Bose-Einstein condensates: We investigate the stability properties and the dynamics of Bose-Einstein\ncondensates with axial symmetry, especially with dipolar long-range\ninteraction, using both simulations on grids and variational calculations. We\npresent an extended variational ansatz which is applicable for axial symmetry\nand show that this ansatz can reproduce the lowest eigenfrequencies of the\nBogoliubov spectrum, and also the corresponding eigenfunctions. Our variational\nansatz is capable of describing the roton instability of pancake-shaped dipolar\ncondensates for arbitrary angular momenta. After investigating the linear\nregime we apply the ansatz to determine the dynamics and show how the angular\ncollapse is correctly described within the variational framework."
    },
    {
        "anchor": "Bose-Einstein condensates in the presence of Weyl spin-orbit coupling: We consider two-component Bose-Einstein condensates subject to Weyl\nspin-orbit coupling. We obtain mean-field ground state phase diagram by\nvariational method. In the regime where interspecies coupling is larger than\nintraspecies coupling, the system is found to be fully polarized and condensed\nat a finite momentum lying along the quantization axis. We characterize this\nphase by studying the excitation spectrum, the sound velocity, the quantum\ndepletion of condensates, the shift of ground state energy, and the static\nstructure factor. We find that spin-orbit coupling and interspecies coupling\ngenerally leads to competing effects.",
        "positive": "Projective phase measurements in one-dimensional Bose gases: We consider time-of-flight measurements in split one-dimensional Bose gases.\nIt is well known that the low-energy sector of such systems can be described in\nterms of two compact phase fields $\\hat{\\phi}_{a,s}(x)$. Building on existing\nresults in the literature we discuss how a single projective measurement of the\nparticle density after trap release is in a certain limit related to the\neigenvalues of the vertex operator $e^{i\\hat{\\phi}_a(x)}$. We emphasize the\ntheoretical assumptions underlying the analysis of \"single-shot\" interference\npatterns and show that such measurements give direct access to multi-point\ncorrelation functions of $e^{i\\hat{\\phi}_a(x)}$ in a substantial parameter\nregime. For experimentally relevant situations, we derive an expression for the\nmeasured particle density after trap release in terms of convolutions of the\neigenvalues of vertex operators involving both sectors of the two-component\nLuttinger liquid that describes the low-energy regime of the split condensate.\nThis opens the door to accessing properties of the symmetric sector via an\nappropriate analysis of existing experimental data."
    },
    {
        "anchor": "Excitonic states of an impurity in a Fermi gas: We study excitonic states of an atomic impurity in a Fermi gas, i.e., bound\nstates consisting of the impurity and a hole. Previous studies considered bound\nstates of the impurity with particles from the Fermi sea where the holes only\nformed part of the particle-hole dressing. Within a two-channel model, we find\nthat, for a wide range of parameters, excitonic states are not ground but\nmetastable states. We further calculate the decay rates of the excitonic states\nto polaronic and dimeronic states and find they are long lived, scaling as\n$\\Gamma^{\\rm{Exc}}_ {\\rm{Pol}} \\propto ( \\Delta\\omega)^{5.5}$ and\n$\\Gamma^{\\rm{Exc}}_ {\\rm{Dim}} \\propto (\\Delta\\omega)^{4}$. We also find that a\nnew continuum of exciton-particle states should be considered alongside the\npreviously known dimeron-hole continuum in spectroscopic measurements. Excitons\nmust therefore be considered as a new ingredient in the study of metastable\nphysics currently being explored experimentally.",
        "positive": "Effective super Tonks-Girardeau gases as ground states of strongly\n  attractive multi-component fermions: In the strong interaction limit, attractive fermions with $N$-component\nhyperfine states in a one-dimensional waveguide form unbreakable bound cluster\nstates. We demonstrate that the ground state of strongly attractive SU($N$)\nFermi gases can be effectively described by a super Tonks-Girardeau gas-like\nstate composed of bosonic cluster states with strongly attractive\ncluster-cluster interaction for even $N$, and a Fermi duality of a super\nTonks-Girardeau gas-like state composed of fermionic cluster states with weakly\ninteracting cluster-cluster p-wave interaction for odd $N$."
    },
    {
        "anchor": "Continuous Loading of a Conservative Trap from an Atomic Beam: We demonstrate the fast accumulation of Cr atoms in a conservative potential\nfrom a magnetically guided atomic beam. Without laser cooling on a cycling\ntransition, a single dissipative step realized by optical pumping allows to\nload atoms at a rate of 2*10^7 1/s in the trap. Within less than 100 ms we\nreach the collisionally dense regime, from which we directly produce a\nBose-Einstein condensate with subsequent evaporative cooling. This constitutes\na new approach to degeneracy where, provided a slow beam of particles can be\nproduced by some means, Bose-Einstein condensation can be reached for species\nwithout a cycling transition.",
        "positive": "Tachyon Condensation Due to Domain-Wall Annihilation in Bose-Einstein\n  Condensates: We show theoretically that a domain-wall annihilation in two-component\nBose-Einstein condensates causes tachyon condensation accompanied by\nspontaneous symmetry breaking in a two-dimensional subspace. Three-dimensional\nvortex formation from domain-wall annihilations is considered a kink formation\nin subspace. Numerical experiments reveal that the subspatial dynamics obey the\ndynamic scaling law of phase-ordering kinetics. This model is experimentally\nfeasible and provides insights into how the extra dimensions influence\nsubspatial phase transition in higher-dimensional space."
    },
    {
        "anchor": "Optimizing Quantum Gas Production by an Evolutionary Algorithm: We report on the application of an evolutionary algorithm (EA) to enhance\nperformance of an ultra-cold quantum gas experiment. The production of a\n$^{87}$Rubidium Bose-Einstein condensate (BEC) can be divided into fundamental\ncooling steps, specifically magneto optical trapping of cold atoms, loading of\natoms to a far detuned crossed dipole trap and finally the process of\nevaporative cooling. The EA is applied separately for each of these steps with\na particular definition for the feedback the so-called fitness. We discuss the\nprinciples of an EA and implement an enhancement called differential evolution.\nAnalyzing the reasons for the EA to improve \\eg, the atomic loading rates and\nincrease the BEC phase-space density, yields an optimal parameter set for the\nBEC production and enables us to reduce the BEC production time significantly.\nFurthermore, we focus on how additional information about the experiment and\noptimization possibilities can be extracted and how the correlations revealed\nallow for further improvement. Our results illustrate that EAs are powerful\noptimization tools for complex experiments and exemplify that the application\nyields useful information on the dependence of these experiments on the\noptimized parameters.",
        "positive": "Quantisation and its breakdown in a Hubbard-Thouless pump: Geometric properties of waves and wave functions can explain the appearance\nof integer-valued observables throughout physics. For example, these\n'topological' invariants describe the plateaux observed in the quantised Hall\neffect and the pumped charge in its dynamic analogon, the Thouless pump.\nHowever, the presence of interparticle interactions can profoundly affect the\ntopology of a material, invalidating the idealised formulation in terms of\nBloch waves. Despite pioneering experiments in solid state systems, photonic\nwaveguides, and optical lattices, the study of topological insulators under\nvariation of inter-particle interactions has proven challenging. Here, we\nexperimentally realise a topological Thouless pump with tuneable Hubbard\ninteractions in an optical lattice and observe regimes with robust pumping, as\nwell as an interaction-induced breakdown. We confirm the pump's robustness\nagainst interactions that are smaller than the protecting gap, which holds true\nfor both repulsive and attractive Hubbard $U$. Furthermore, we identify that\nbound pairs of fermions are responsible for quantised transport at strongly\nattractive $U$, supported by measurements of pair fraction and adiabaticity.\nFor strong repulsive interactions, on the contrary, topological pumping breaks\ndown. Yet, we can reinstate quantised pumping by modifying the pump trajectory\nwhile starting from the same initial state. Our experiments pave the way for\ninvestigating interacting topological insulators, including edge effects and\ninteraction-induced topological phases."
    },
    {
        "anchor": "Self-bound ultra dilute Bose mixtures within Local Density Approximation: We have investigated self-bound binary ultra dilute bosonic mixtures at zero\ntemperature within Density Functional Theory using a Local Density\nApproximation. We provide the explicit expression of the Lee-Huang-Yang\ncorrection in the general case of heteronuclear mixtures, and investigate the\ngeneral thermodynamic conditions which lead to the formation of self-bound\nsystems. We have determined the conditions for stability against the\nevaporation of one component, as well as the mechanical and diffusive spinodal\nlines. We have also calculated the surface tension of the self-bound state as a\nfunction of the inter-species interaction strength. We find that relatively\nmodest changes of the latter result in order-of-magnitude changes in the\ncalculated surface tension. We suggest experimental realizations which might\ndisplay the metastability and phase separation of the mixture when entering\nregions of the phase diagram characterized by negative pressures. Finally, we\nshow that these droplets may sustain stable vortex and vortex dimers.",
        "positive": "Experimental realization of double Bragg diffraction: robust\n  beamsplitters, mirrors, and interferometers for Bose-Einstein condensates: We present the experimental implementation of double Bragg diffraction of\nBose-Einstein condensates (BECs) as proposed in [E. Giese, A. Roura, G.\nTackmann, E. M. Rasel, and W. P. Schleich, Phys. Rev. A \\textbf{88}, 053608\n(2013)]. We excite Rabi oscillations between the three coupled momentum states\n$\\left| 0 \\hbar k \\right\\rangle$ and $\\left| \\pm 2 \\hbar k \\right\\rangle$. By\nselecting appropriate interaction times we generate highly efficient\nbeamsplitters and mirrors for Bose-Einstein condensates. In addition, we\ndemonstrate higher-order double Bragg diffraction and display beamsplitters\nwith up to $ \\pm 6 \\hbar k$ momentum transfer. We compare double Bragg\ndiffraction to several other experimental realizations of beamsplitters.\nFinally, we show that double Bragg diffraction is well suited for matter wave\ninterferometry by realizing a Ramsey-type interferometer in a quasi\none-dimensional waveguide."
    },
    {
        "anchor": "Superfluid-Mott insulator transition in spin-orbit coupled Bose-Hubbard\n  Model: We consider a square optical lattice in two dimensions and study the effects\nof both the strength and symmetry of spin-orbit-coupling (SOC) and Zeeman field\non the ground-state, i.e., Mott insulator (MI) and superfluid (SF), phases and\nphase diagram, i.e., MI-SF phase transition boundary, of the two-component\nBose-Hubbard model. In particular, based on a variational Gutzwiller ansatz,\nour numerical calculations show that the spin-orbit coupled SF phase is a\nnonuniform (twisted) one with its phase (but not the magnitude) of the order\nparameter modulating from site to site. Fully analytical insights into the\nnumerical results are also given.",
        "positive": "Topologically driven Rabi-oscillating interference dislocation: Quantum vortices are the quantized version of classical vortices. Their\ncenter is a phase singularity or vortex core around which the flow of particles\nas a whole circulates and is typical in superfluids, condensates and optical\nfields. However, the exploration of the motion of the phase singularities in\ncoherently-coupled systems is still underway. We theoretically analyze the\npropagation of an interference dislocation in the regime of strong coupling\nbetween light and matter, with strong mass imbalance, corresponding to the case\nof microcavity exciton-polaritons. To this end, we utilize combinations of\nvortex and tightly focused Gaussian beams, which are introduced through\nresonant pulsed pumping. We show that a dislocation originates from\nself-interference fringes, due to the non-parabolic dispersion of polaritons\ncombined with moving Rabi-oscillating vortices. The morphology of singularities\nis analyzed in the Poincar\\'{e} space for the pseudospin associated to the\npolariton states. The resulting beam carries orbital angular momentum with\ndecaying oscillations due to the loss of overlap between the normal modes of\nthe polariton system."
    },
    {
        "anchor": "Population imbalanced lattice fermions near the BCS-BEC crossover: I.The\n  breached pair and metastable FFLO phases: We study s-wave superconductivity in the two dimensional attractive Hubbard\nmodel in an applied magnetic field, assume the extreme Pauli limit, and examine\nthe role of spatial fluctuations in the coupling regime corresponding to\nBCS-BEC crossover. We use a decomposition of the interaction in terms of an\nauxiliary pairing field, retain the static mode, and sample the pairing field\nvia Monte Carlo. The method requires iterative solution of the\nBogoliubov-de-Gennes (BdG) equations for amplitude and phase fluctuating\nconfigurations of the pairing field. We establish the full thermal phase\ndiagram of this strong coupling problem, revealing $T_c$ scales an order of\nmagnitude below the mean field estimate, highlight the spontaneous\ninhomogeneity in the field induced magnetization, and discover a strong non\nmonotonicity in the temperature dependence of the low energy density of states.\nWe compare our results to the experimental phase diagram of the imbalanced\nFermi gas at unitarity. This paper focuses on the magnetized but homogeneous\n(breached pair) superconducting state, a companion paper deals with the\nFulde-Ferrell-Larkin-Ovchinnikov (FFLO) regime.",
        "positive": "Relaxation dynamics of two coherently coupled one-dimensional bosonic\n  gases: In this work we consider the non-equilibrium dynamics of two tunnel coupled\nbosonic gases which are created from the coherent splitting of a\none-dimensional gas. The consequences of the tunneling both in the\nnon-stationary regime as well as at large time are investigated and compared\nwith equilibrium results. In particular, within a semiclassical approximation,\nwe compute correlation functions for the relative phase which are\nexperimentally measurable and we observe a transient regime displaying\noscillations as a function of the distance. The steady regime is very well\napproximated by a thermal state with a temperature independent of the tunneling\nstrength."
    },
    {
        "anchor": "Berezinskii-Kosterlitz-Thouless transition in the\n  time-reversal-symmetric Hofstadter-Hubbard model: Assuming that two-component Fermi gases with opposite artificial magnetic\nfields on a square optical lattice are well-described by the so-called\ntime-reversal-symmetric Hofstadter-Hubbard model, we explore the thermal\nsuperfluid properties along with the critical Berezinskii-Kosterlitz-Thouless\n(BKT) transition temperature in this model over a wide-range of its parameters.\nIn particular, since our self-consistent BCS-BKT approach takes the multi-band\nbutterfly spectrum explicitly into account, it unveils how dramatically the\ninter-band contribution to the phase stiffness dominates the intra-band one\nwith an increasing interaction strength for any given magnetic flux.",
        "positive": "Universality in Ultra-Cold Few- and Many-Boson Systems: This dissertation presents theoretical investigations of universality and\nfinite-range corrections in few- and many-boson systems. The main focus is on\nultra-cold atomic gases seen both from the three-body, many-body, and\nmean-field perspective. Topics include corrections to Efimov physics, the\nN-body Efimov effect, two-body correlations in condensates and higher-order\ninteractions in mean-field BECs."
    },
    {
        "anchor": "Theory of real supersolids: We review the main properties of a supersolid. We describe first the\nmacroscopic equation that satisfies a supersolid based on general arguments and\nsymmetries and show that such solids might exhibit simultaneously or\nindependently both elastic behavior and superfluidity. We then explain why a\nsupersolid state should exist for solids at very low temperature but with a\nvery small superfluid fraction. Finally, we propose a mean-field model, based\non the Gross-Pitaevski\\u{\\i} equation, which presents the general properties\nexpected for a supersolid and should therefore provide a consistent framework\nto study its dynamical properties.",
        "positive": "Coupling ultracold matter to dynamical gauge fields in optical lattices:\n  From flux-attachment to Z2 lattice gauge theories: Artificial magnetic fields and spin-orbit couplings have been recently\ngenerated in ultracold gases in view of realizing topological states of matter\nand frustrated magnetism in a highly-controllable environment. Despite being\ndynamically tunable, such artificial gauge fields are genuinely classical and\nexhibit no back-action from the neutral particles. Here we go beyond this\nparadigm, and demonstrate how quantized dynamical gauge fields can be created\nin mixtures of ultracold atoms in optical lattices. Specifically, we propose a\nprotocol by which atoms of one species carry a magnetic flux felt by another\nspecies, hence realizing an instance of flux-attachment. This is obtained by\ncombining coherent lattice modulation techniques with strong Hubbard\ninteractions. We demonstrate how this setting can be arranged so as to\nimplement lattice models displaying a local Z2 gauge symmetry, both in one and\ntwo dimensions. We also provide a detailed analysis of a ladder toy model,\nwhich features a global Z2 symmetry, and reveal the phase transitions that\noccur both in the matter and gauge sectors. Mastering flux-attachment in\noptical lattices envisages a new route towards the realization of\nstrongly-correlated systems with properties dictated by an interplay of\ndynamical matter and gauge fields."
    },
    {
        "anchor": "Observation of Transient Momentum-Space Interference During Scattering\n  of a Condensate From an Optical Barrier: Scattering theory traditionally deals with the asymptotic behaviour of a\nsystem far removed from the actual scattering event. Here we present an\nexperimental study of the one-dimensional scattering of a non-interacting\ncondensate of 87-Rb atoms from a potential barrier in the non-asymptotic\nregime, for which the collision dynamics are still ongoing. We show that for\nnear-transparent barriers, there are two distinct transient scattering effects\nthat arise and dramatically change the momentum distribution during the\ncollision: a deceleration of wavepacket components in mid-collision, and an\ninterference between incident and transmitted portions of the wavepacket. Both\neffects lead to the re-distribution of momenta giving rise to a rich\ninterference pattern that can be used to perform reconstruction of the\nsingle-particle phase profile.",
        "positive": "Strongly correlated states of a small cold atomic cloud from geometric\n  gauge fields: Using exact diagonalization for a small system of cold bosonic atoms, we\nanalyze the emergence of strongly correlated states in the presence of an\nartificial magnetic field. This gauge field is generated by a laser beam that\ncouples two internal atomic states, and it is related to Berry's geometrical\nphase that emerges when an atom follows adiabatically one of the two\neigenstates of the atom--laser coupling. Our approach allows us to go beyond\nthe adiabatic approximation, and to characterize the generalized Laughlin wave\nfunctions that appear in the strong magnetic field limit."
    },
    {
        "anchor": "Strong-Coupling and Finite Temperature Effects on $p$-wave Contacts: We theoretically investigate strong-coupling and finite temperature effects\non the p-wave contacts, as well as the asymptotic behavior of the momentum\ndistribution in large momentum region in a one-component Fermi gas with a\ntunable p-wave interaction. Including p-wave pairing fluctuations within a\nstrong-coupling theory, we calculate the p-wave contacts above the superfluid\ntransition temperature $T_{\\rm c}$ from the adiabatic energy relations. We show\nthat while the p-wave contacts related to the scattering volume monotonically\nincreases with increasing the interaction strength, one related to the\neffective range non-monotonically depends on interaction strength and its sign\nchanges in the intermediate-coupling regime. The non-monotonic interaction\ndependence of these quantities is shown to originate from the competition\nbetween the increase of the cutoff momentum and the decrease of the coupling\nconstant of the p-wave interaction with increasing the effective range. We also\nanalyze the asymptotic form of the momentum distribution in large momentum\nregion. In contrast to the conventional s-wave case, we show that the\nasymptotic behavior cannot be completely described by only the p-wave contacts,\nand the extra terms, which is not related to the thermodynamic properties,\nappear. Furthermore, in high temperature region, we find that the extra terms\ndominate the sub-leading term of the large-momentum distribution. We also\ndirectly compare our results with the recent experimental measurement, by\nincluding the effects of a harmonic trap potential within the local density\napproximation. We show that our model explains the dependence on the\ninteraction strength of the p-wave contacts.",
        "positive": "Quantum dimer models emerging from large-spin ultracold atoms: We propose an experimental protocol for using cold atoms to create and probe\nquantum dimer models, thereby exploring the Pauling-Anderson vision of a\nmacroscopic collection of resonating bonds. This process can allow the study of\nexotic crystalline phases, fractionalization, topological spin liquids, and the\nrelationship between resonating dimers and superconductivity subjects which\nhave been challenging to address in solid-state experiments. Our key technical\ndevelopment is considering the action of an off-resonant photoassociation laser\non large spin atoms localized at the sites of a deep optical lattice. The\nresulting superexchange interaction favors nearest-neighbor singlets. We derive\nan effective Hamiltonian in terms of these dimer degrees of freedom, finding\nthat it is similar to well-known quantum dimer models, which boast a rich\nvariety of valence bond crystal and spin liquid phases. We numerically study\nthe ground state, explain how to tune the parameters, and develop a protocol to\ndirectly measure the dimers and their resonating patterns."
    },
    {
        "anchor": "Signatures of the orthogonality catastrophe in a coherently driven\n  impurity: We consider a fixed impurity immersed in a Fermi gas at finite temperature.\nWe take the impurity to have two internal spin states, where the $\\uparrow$\nstate is assumed to interact with the medium such that it exhibits the\northogonality catastrophe, while the $\\downarrow$ state is a bare\nnoninteracting particle. Introducing a Rabi coupling between the impurity\nstates therefore allows us to investigate the coupling between a discrete\nspectral peak and the Fermi-edge singularity, i.e., between states with and\nwithout a quasiparticle residue. Combining an exact treatment of the uncoupled\nimpurity Green's functions with a variational approach to treat the Rabi driven\ndynamics, we find that the system features Rabi oscillations whose frequency\nscales as a non-trivial power of the Rabi drive at low temperatures. This\nreflects the power law of the Fermi-edge singularity and, importantly, this\nbehavior is qualitatively different from the case of a mobile impurity\nquasiparticle where the scaling is linear. We therefore argue that the scaling\nlaw serves as an experimentally implementable probe of the orthogonality\ncatastrophe. We additionally simulate rf spectroscopy beyond linear response,\nfinding a remarkable agreement with an experiment using heavy impurities\n[Kohstall $\\textit{et al.}$, Nature $\\textbf{485}$, 615 (2012)], thus\ndemonstrating the power of our approach.",
        "positive": "Realization of a Townes soliton in a two-component planar Bose gas: Most experimental observations of solitons are limited to one-dimensional\n(1D) situations, where they are naturally stable. For instance, in 1D cold Bose\ngases, they exist for any attractive interaction strength $g$ and particle\nnumber $N$. By contrast, in two dimensions, solitons appear only for discrete\nvalues of $gN$, the so-called Townes soliton being the most celebrated example.\nHere, we use a two-component Bose gas to prepare deterministically such a\nsoliton: Starting from a uniform bath of atoms in a given internal state, we\nimprint the soliton wave function using an optical transfer to another state.\nWe explore various interaction strengths, atom numbers and sizes, and confirm\nthe existence of a solitonic behaviour for a specific value of $gN$ and\narbitrary sizes, a hallmark of scale invariance."
    },
    {
        "anchor": "Ground-state densities of repulsive two-component Fermi gases: We investigate separations of trapped balanced two-component atomic Fermi\ngases with repulsive contact interaction. Candidates for ground-state densities\nare obtained from the imaginary-time evolution of a nonlinear\npseudo-Schr\\\"odinger equation in three dimensions, rather than from the\ncumbersome variational equations. With the underlying hydrodynamical approach,\ngradient corrections to the Thomas-Fermi approximation are conveniently\nincluded and are shown to be vital for reliable density profiles. We provide\ncritical repulsion strengths that mark the onset of phase transitions in a\nharmonic trap. We present transitions from identical density profiles of the\ntwo fermion species towards isotropic and anisotropic separations for various\nconfinements, including harmonic and double-well-type traps. Our proposed\nmethod is suited for arbitrary trap geometries and can be straightforwardly\nextended to study dynamics in the light of ongoing experiments on degenerate\nFermi gases.",
        "positive": "Minimizing rf-induced excess micromotion of a trapped ion with the help\n  of ultracold atoms: We report on the compensation of excess micromotion due to parasitic\nrf-electric fields in a Paul trap. The parasitic rf-electric fields stem from\nthe Paul trap drive but cause excess micromotion, e.g. due to imperfections in\nthe setup of the Paul trap. We compensate these fields by applying rf-voltages\nof the same frequency but adequate phases and amplitudes to Paul trap\nelectrodes. The magnitude of micromotion is probed by studying elastic\ncollision rates of the trapped ion with a gas of ultracold neutral atoms.\nFurthermore, we demonstrate that also reactive collisions can be used to\nquantify micromotion. We achieve compensation efficiencies of about\n1$\\:\\text{Vm}^{-1}$, which is comparable to other conventional methods."
    },
    {
        "anchor": "Trapped-ion quantum simulation of tunable-range Heisenberg chains: Quantum-optical techniques allow for generating controllable spin-spin\ninteractions between ions, making trapped ions an ideal quantum simulator of\nHeisenberg chains. A single parameter, the detuning of the Raman coupling,\nallows to switch between ferromagnetic and antiferromagnetic chains, and to\nmodify the range of the interactions. On the antiferromagnetic side, the system\ncan be tuned from an extreme long-range limit, in which any pair of ions\ninteracts with almost equal strength, to interactions with a $1/r^3$ decay. By\nexact diagonalization, we study how a system of up to 20 ions behaves upon\ntuning the interactions. We find that it undergoes a transition from a\ndimerized state with extremely short-ranged correlations towards a state with\nquasi long-range order, that is, algebraically decaying correlations. On the\nferromagnetic side of the system, we demonstrate the feasibility of witnessing\nnon-locality of quantum correlations.",
        "positive": "Bogoliubov Excitations of Disordered Bose-Einstein Condensates: We describe repulsively interacting Bose-Einstein condensates in spatially\ncorrelated disorder potentials of arbitrary dimension. The first effect of\ndisorder is to deform the mean-field condensate. Secondly, the quantum\nexcitation spectrum and condensate population are affected. By a saddle-point\nexpansion of the many-body Hamiltonian around the deformed mean-field ground\nstate, we derive the fundamental quadratic Hamiltonian of quantum fluctuations.\nImportantly, a basis is used such that excitations are orthogonal to the\ndeformed condensate. Via Bogoliubov-Nambu perturbation theory, we compute the\neffective excitation dispersion, including mean free paths and localization\nlengths. Corrections to the speed of sound and average density of states are\ncalculated, due to correlated disorder in arbitrary dimensions, extending to\nthe case of weak lattice potentials."
    },
    {
        "anchor": "Imbalanced Feshbach-resonant Fermi gases: We present an overview of recent developments in species-imbalanced\n(\"polarized\") Feshbach-resonant Fermi gases. We summarize the current status of\nthermodynamics of these systems in terms of a phase diagram as a function of\nthe Feshbach resonance detuning, polarization and temperature. We review\ninstabilities of the s-wave superfluidity across the BEC-BCS crossover to phase\nseparation, FFLO states, polarized molecular superfluidity and the normal\nstate, driven by the species imbalance. We discuss different models and\napproximations of this system and compare their predictions to current\nexperiments.",
        "positive": "Effects of Interactions and Temperature in Disordered Ultra-Cold Bose\n  Gases: We simulate ultra-cold interacting Bosons in quasi-one-dimensional,\nincommensurate optical lattices. In the tight-binding limit, these lattices\nhave pseudo-random on-site energies and thus can potentially lead to Anderson\nlocalization. We explore the parameter regimes that lead to Anderson\nlocalization and investigate the role of repulsive interactions, harmonic\nconfinement and finite temperature. We find that interactions can obscure the\nexponential localization characteristic of Anderson localization, thus impeding\nthe direct observation of this phenomenon when interactions are present."
    },
    {
        "anchor": "Density ripples in expanding low-dimensional gases as a probe of\n  correlations: We investigate theoretically the evolution of the two-point density\ncorrelation function of a low-dimensional ultracold Bose gas after release from\na tight transverse confinement. In the course of expansion thermal and quantum\nfluctuations present in the trapped systems transform into density\nfluctuations. For the case of free ballistic expansion relevant to current\nexperiments, we present simple analytical relations between the spectrum of\n``density ripples'' and the correlation functions of the original confined\nsystems. We analyze several physical regimes, including weakly and strongly\ninteracting one-dimensional (1D) Bose gases and two-dimensional (2D) Bose gases\nbelow the Berezinskii-Kosterlitz-Thouless (BKT) transition. For weakly\ninteracting 1D Bose gases, we obtain an explicit analytical expression for the\nspectrum of density ripples which can be used for thermometry. For 2D Bose\ngases below the BKT transition, we show that for sufficiently long expansion\ntimes the spectrum of the density ripples has a self-similar shape controlled\nonly by the exponent of the first-order correlation function. This exponent can\nbe extracted by analyzing the evolution of the spectrum of density ripples as a\nfunction of the expansion time.",
        "positive": "Attractive and repulsive Fermi polarons in two dimensions: The dynamics of a single impurity in an environment is a fundamental problem\nin many-body physics. In the solid state, a well-known case is an impurity\ncoupled to a bosonic bath, for example lattice vibrations. Here the impurity\ntogether with its accompanying lattice distortion form a new entity, a polaron.\nThis quasiparticle plays an important role in the spectral function of high-Tc\nsuperconductors as well as in colossal-magnetoresistance in manganites. For\nimpurities in a fermionic bath, the attention so far has been mostly on heavy\nor immobile impurities which exhibit Anderson's orthogonality catastrophe and\nthe Kondo effect. Only recently, mobile impurities have moved into the focus of\nresearch and they have been found to form new quasiparticles, so called Fermi\npolarons. The Fermi polaron problem constitutes the extreme, but conceptually\nsimple, limit of two important quantum many-body problems: the BEC-BCS\ncrossover with spin-imbalance for attractive interactions and Stoner's\nitinerant ferromagnetism for repulsive interactions. It has been proposed that\nthis and other yet elusive exotic quantum phases might become realizable in\nFermi gases confined to two dimensions. Their stability and observability is\nintimately related to the theoretically debated properties of the Fermi polaron\nin two dimensional Fermi gas. Here we create and investigate these Fermi\npolarons and measure their spectral function using momentum-resolved\nphotoemission spectroscopy. For attractive interactions we find evidence for\nthe disputed pairing transition between polarons and tightly bound dimers,\nwhich provides insight into the elementary pairing mechanism of imbalanced,\nstrongly-coupled two-dimensional Fermi gases. Additionally, for repulsive\ninteractions we study novel quasiparticles, repulsive polarons, whose lifetime\ndetermine the possibility of stabilizing repulsively interacting Fermi systems."
    },
    {
        "anchor": "Comment on \"Negative Differential Conductivity in an Interacting Quantum\n  Gas.\": Labouvie \\etal (\\prl {\\bf 115}, 050601, (20015)) recently demonstrated\nnegative differential conductivity (NDC) in a multi-well Bose-Einstein\ncondensate. They stated \"we demonstrate that NDC originates from a nonlinear,\natom number dependent tunneling coupling in combination with fast collisional\ndecoherence.\" We show theoretically how the essential feature of NDC, a\nreduction in atomic current caused by an increase in chemical potential, is\npresent in unitary dynamics through the well-known mechanism of macroscopic\nself-trapping (MST), and that the collisional decoherence merely serves as a\nquantitative modification of this.",
        "positive": "Evolution of the Normal State of a Strongly Interacting Fermi Gas from a\n  Pseudogap Phase to a Molecular Bose Gas: Wave-vector resolved radio frequency (rf) spectroscopy data for an ultracold\ntrapped Fermi gas are reported for several couplings at Tc, and extensively\nanalyzed in terms of a pairing-fluctuation theory. We map the evolution of a\nstrongly interacting Fermi gas from the pseudogap phase into a fully gapped\nmolecular Bose gas as a function of the interaction strength, which is marked\nby a rapid disappearance of a remnant Fermi surface in the single-particle\ndispersion. We also show that our theory of a pseudogap phase is consistent\nwith a recent experimental observation as well as with Quantum Monte Carlo data\nof thermodynamic quantities of a unitary Fermi gas above Tc."
    },
    {
        "anchor": "Many-body localization in Ising models with random long-range\n  interactions: We theoretically investigate the many-body localization phase transition in a\none-dimensional Ising spin chain with random long-range spin-spin interactions,\n$V_{ij}\\propto\\left|i-j\\right|^{-\\alpha}$, where the exponent of the\ninteraction range $\\alpha$ can be tuned from zero to infinitely large. By using\nexact diagonalization, we calculate the half-chain entanglement entropy and the\nenergy spectral statistics and use them to characterize the phase transition\ntowards the many-body localization phase at infinite temperature and at\nsufficiently large disorder strength. We perform finite-size scaling to extract\nthe critical disorder strength and the critical exponent of the divergent\nlocalization length. With increasing $\\alpha$, the critical exponent\nexperiences a sharp increase at about $\\alpha=1$ and then gradually decreases\nto a value found earlier in a disordered short-ranged interacting spin chain.\nFor $\\alpha<1$, we find that the system is mostly localized and the increase in\nthe disorder strength may drive a transition between two many-body localized\nphases. In contrast, for $\\alpha>1$, the transition is from a thermalized phase\nto the many-body localization phase. Our predictions could be experimentally\ntested with ion-trap quantum emulator with programmable random long-range\ninteractions, or with randomly distributed Rydberg atoms or polar molecules in\nlattices.",
        "positive": "Acoustic analogue of Hawking radiation in quantized circular superflows\n  of Bose-Einstein condensates: We propose emulation of Hawking radiation (HR) by means of acoustic\nexcitations propagating on top of persistent current in an atomic Bose-Einstein\ncondensate (BEC) loaded in an annular confining potential. The setting is\ninitially created as a spatially uniform one, and then switches into a\nnonuniform configuration, while maintaining uniform BEC density. The eventual\nsetting admits the realization of sonic black and white event horizons with\ndifferent slopes of the local sound speed. A smooth slope near the white-hole\nhorizon suppresses instabilities in the supersonic region. It is found that\ntongue-shaped patterns of the density-density correlation function, which\nrepresent the acoustic analog of HR, are strongly affected by the radius of the\nring-shaped configuration and number of discrete acoustic modes admitted by it.\nThere is a minimum radius that enables the emulation of HR. We also briefly\ndiscuss a possible similarity of properties of the matter-wave sonic black\nholes to the known puzzle of the stability of Planck-scale primordial black\nholes in quantum gravity."
    },
    {
        "anchor": "On the thermalization of a Luttinger liquid after a sequence of sudden\n  interaction quenches: We present a comprehensive analysis of the relaxation dynamics of a Luttinger\nliquid subject to a sequence of sudden interaction quenches. We express the\ncritical exponent $\\beta$ governing the decay of the steady-state propagator as\nan explicit functional of the switching protocol. At long distances $\\beta$\ndepends only on the initial state while at short distances it is also history\ndependent. Continuous protocols of arbitrary complexity can be realized with\ninfinitely long sequences. For quenches of finite duration we prove that there\nexist no protocol to bring the initial non-interacting system in the ground\nstate of the Luttinger liquid. Nevertheless memory effects are washed out at\nshort-distances. The adiabatic theorem is then investigated with\nramp-switchings of increasing duration, and several analytic results for both\nthe propagator and the excitation energy are derived.",
        "positive": "Non-Galilean response of Rashba coupled Fermi gases: We consider the effect of a momentum kick on the ground state of a\nnon-interacting two-dimensional Fermi gas subject to Rashba spin-orbit\ncoupling. Although the total momentum is a constant of motion, the gas does not\nobey the rules of Galilean relativity. Upon imprinting a small overall velocity\nto the non-interacting gas, we find that the Fermi sea is deformed in a\nnon-trivial way. We also consider a weakly repulsive Fermi gas, and find, from\nits Hartree shift, that the total ground state of the system may change into a\ndeformed, finite momentum ground state as the repulsion is increased beyond a\ncritical value, without the need of any external Zeeman fields. We also discuss\npossible experimental signatures of these effects."
    },
    {
        "anchor": "Quantum phase transitions of the spin-boson model within\n  multi-coherent-states: A variational approach based on the multi-coherent-state ansatz with\nasymmetric parameters is employed to study the ground state of the spin-boson\nmodel. Without any artificial approximations except for the finite number of\nthe coherent states, we find the robust Gaussian critical behavior in the whole\nsub-Ohmic bath regime. The converged critical coupling strength can be\nestimated with the $1/N$ scaling, where $N $ is the number of the coherent\nstates. It is strongly demonstrated the breakdown of the well-known\nquantum-to-classical mapping for $1/2<s<1$. In addition, the entanglement\nentropy displays more steep jump around the critical points for the Ohmic bath\nthan the sub-Ohmic bath.",
        "positive": "Lee-Yang cluster expansion approach to the BCS-BEC crossover: BCS and\n  BEC limits: It is shown that a cluster expansion technique, which is usually applied in\nthe high-temperature regime to calcutate virial coefficients, can be applied to\nevaluate the superfluid transition temperature of the BCS-BEC crossover \\`a la\nLee and Yang. The transition temperature is identified with the emergence of\nthe singularity in the sum of a certain infinite series of cluster functions.\nIn the weak-coupling limit, we reproduce the Thouless criterion and the number\nequation of Nozi\\`eres and Schmitt-Rink, and hence the transition temperature\nof the BCS theory. In the strong-coupling limit, we reproduce the transition\ntemperature of Bose-Einstein condensation of non-interacting tightly bound\ndimers."
    },
    {
        "anchor": "Excitation spectrum of a mixture of two Bose gases confined in a ring\n  potential with interaction asymmetry: We study the rotational properties of a two-component Bose-Einstein condensed\ngas of distinguishable atoms which are confined in a ring potential using both\nthe mean-field approximation, as well as the method of diagonalization of the\nmany-body Hamiltonian. We demonstrate that the angular momentum may be given to\nthe system either via single-particle, or \"collective\" excitation. Furthermore,\ndespite the complexity of this problem, under rather typical conditions the\ndispersion relation takes a remarkably simple and regular form. Finally, we\nargue that under certain conditions the dispersion relation is determined via\ncollective excitation. The corresponding many-body state, which, in addition to\nthe interaction energy minimizes also the kinetic energy, is dictated by\nelementary number theory.",
        "positive": "Pseudo-time-reversal-symmetry-protected topological Bogoliubov\n  excitations of Bose-Einstein condensates in optical lattices: Bogoliubov excitations of Bose-Einstein condensates in optical lattices may\npossess band topology in analogous to topological insulators in class AII of\nfermions. Using the language of the Krein-space theory, this topological\nproperty is shown to be protected by a pseudo-time-reversal symmetry that is\npseudo-antiunitary and squares to $-1$, with the associated bulk topological\ninvariant also being a $\\mathbb Z_2$ index. We construct three equivalent\nexpressions for it, relating to the Pfaffian, the pseudo-time-reversal\npolarization, and most practically, the Wannier center flow, all adopted from\nthe fermionic case, defined here with respect to the pseudo inner product. In\nthe presence of an additional pseudo-unitary and pseudo-Hermitian inversion\nsymmetry, a simpler expression is derived. We then study two toy models\nfeasible on cold atom platforms to numerically confirm the bulk-boundary\ncorrespondence. The Krein-space approach developed in this work is a universal\nformalism to study all kinds of symmetry-protected topological bosonic\nBogoliubov bands."
    },
    {
        "anchor": "Induced pairing of fermionic impurities in a one-dimensional strongly\n  correlated Bose gas: We investigate numerically the problem of few (one, two) noninteracting\nspin$-1/2$ fermions in a shallow harmonic trap coupled via contact repulsive\ninteractions to a uniform one-dimensional bath of lattice bosons, described by\nthe Bose-Hubbard model. Through extensive density-matrix renormalization group\ncalculations, we extract the binding energy and the effective mass of\nquasiparticles, including dressed impurities (polarons) and their two-body\nbound states (bipolarons), emerging from the effective non-local Casimir\ninteraction between the impurities. We show that the mixture exhibits rather\ndifferent pairing behaviors depending on the singlet \\textit{vs}.~triplet spin\nstate configurations of the two fermions. For opposite spin states, bipolarons\nare found for any finite value of the impurity-bath coupling. In particular, in\nthe strong coupling regime their binding energy reduces to that of a single\npolaron, provided the boson-boson repulsion is not too weak. For equal spin\nstates, we show that bipolarons emerge only beyond a critical strength of the\nBose-Fermi interaction and their effective mass grows rapidly approaching the\nstrong coupling regime.",
        "positive": "Spin Josephson vortices in two tunnel coupled spinor Bose gases: We study topological excitations in spin-1 Bose-Einstein condensates trapped\nin an elongated double-well optical potential. This system hosts a new\ntopological defect, the spin Josephson vortex (SJV), which forms due to the\ncompetition between the inter-well atomic tunneling and short-range\nferromagnetic two-body interaction. We identify the spin structure and\nformation dynamics of the SJV and determine the phase diagram of the system. By\nexploiting the intrinsic stability of the SJV, we propose a dynamical method to\ncreate SJVs under realistic experimental conditions."
    },
    {
        "anchor": "Breaking of Josephson junction oscillations and onset of quantum\n  turbulence in Bose--Einstein condensates: We analyse the formation and the dynamics of quantum turbulence in a\ntwo-dimensional Bose-Einstein condensate with a Josephson junction barrier\nmodelled using the Gross-Pitaevskii equation. We show that a sufficiently high\ninitial superfluid density imbalance leads to randomisation of the dynamics and\ngeneration of turbulence, namely, the formation of a quasi-1D dispersive shock\nconsisting of a train of grey solitons that eventually breakup into chains of\ndistinct quantised vortices of alternating vorticity followed by random\nturbulent flow. The Josephson junction barrier allows us to create two\nturbulent regimes: acoustic turbulence on one side and vortex turbulence on the\nother. Throughout the dynamics, a key mechanism for mixing these two regimes is\nthe transmission of vortex dipoles through the barrier: we analyse this\nscattering process in terms of the barrier parameters, sound emission and\nvortex annihilation. Finally, we discuss how the vortex turbulence evolves for\nlong times, presenting the optimal configurations for the density imbalance and\nbarrier height in order to create the desired turbulent regimes which last as\nlong as possible.",
        "positive": "Stable multidimensional soliton stripes in two-component Bose-Einstein\n  condensates: We discuss how to construct stable multidimensional extensions of\none-dimensional dark solitons, the so-called soliton stripes, in two-species\nBose-Einstein condensates in the immiscible regime. We show how using a second\ncomponent to fill the core a dark soliton stripe leads to reduced instabilities\nwhile propagating in homogeneous media. We also discuss how in the presence of\na trap arbitrarily long-lived dark soliton stripes can be constructed by\nincreasing the filling of the dark stripe core. Numerical evidences of the\nrobustness of the dark soliton stripes in collision scenarios are also\nprovided."
    },
    {
        "anchor": "Thermodynamics of a dilute Bose gas: A path-integral Monte Carlo study: We present precise path-integral Monte-Carlo results for the thermodynamics\nof a homogeneous dilute Bose gas. Pressure and energy are calculated as a\nfunction of temperature both below and above the Bose-Einstein transition.\nSpecifically, we address interaction effects, focusing on deviations from the\nideal gas law in the thermodynamic limit. We also calculate the isothermal\ncompressibility and the contact parameter, which provide a clear signature of\nthe role played by interactions. In particular, we show that the\ncompressibility exhibits a discontinuity at the transition point. To gain\nphysical insight, numerical results are systematically compared with the\npredictions of first-order Hartree-Fock and second-order Popov theories, both\ngiving an approximate description of the gas thermodynamics. The comparison\nshows the extension of the critical region around the transition point, where\nthe inaccuracies of the perturbative expansions are more pronounced.",
        "positive": "Orbital many-body dynamics of bosons in the second Bloch band of an\n  optical lattice: A Bose-Einstein condensate (BEC) of rubidium atoms is prepared in one of two\ndegenerate energy minima in the second Bloch band of an optical square lattice.\nA subsequent oscillation of the BEC between the two energy minima is observed,\nwhich is driven by two distinct collision processes: the conventional\nHubbard-type on-site collision and a collision process that changes the orbital\nflavor. The oscillation frequency scales with the relative strength of these\ncollisional interactions, which can be readily tuned via an experimentally well\ncontrolled distortion of the unit cell. The observations are compared to a\nquantum model of two single-particle modes and to a semi-classical multi-band\ntight-binding simulation of 12x12 tubular sites of the lattice. Both models\nreproduce the observed oscillatory quantum many-body dynamics and show the\ncorrect dependence of the oscillation frequency on the ratio between the\nstrengths of the on-site and flavor-changing collision processes."
    },
    {
        "anchor": "Approximating Steady States in Equilibrium and Nonequilibrium\n  Condensates: We obtain approximations for the time-independent Gross-Pitaevskii (GP) and\ncomplex GP equation in two and three spatial dimensions by generalizing the\ndivergence-free WKB method. The results include an explicit expression of a\nuniformly valid approximation for the condensate density of an ultracold Bose\ngas confined in a harmonic trap that extends into the classically forbidden\nregion. This provides an accurate approximation of the condensate density that\nincludes healing effects at leading order that are missing in the widely\nadopted Thomas-Fermi approximation. The results presented herein allow us to\nformulate useful approximations to a range of experimental systems including\nthe equilibrium properties of a finite temperature Bose gas and the\nsteady-state properties of a 2D nonequilibrium condensate. Comparisons between\nour asymptotic and numerical results for the conservative and\nforced-dissipative forms of the GP equations as applied to these systems show\nexcellent agreement between the two sets of solutions thereby illustrating the\naccuracy of these approximations.",
        "positive": "Quantized Quasi-Two Dimensional Bose-Einstein Condensates with Spatially\n  Modulated Nonlinearity: We investigate the localized nonlinear matter waves of the quasi-two\ndimensional Bose-Einstein condensates with spatially modulated nonlinearity in\nharmonic potential. It is shown that the whole Bose-Einstein condensates,\nsimilar to the linear harmonic oscillator, can have an arbitrary number of\nlocalized nonlinear matter waves with discrete energies, which are\nmathematically exact orthogonal solutions of the Gross-Pitaevskii equation.\nTheir novel properties are determined by the principle quantum number n and\nsecondary quantum number l: the parity of the matter wave functions and the\ncorresponding energy levels depend only on n, and the numbers of density\npackets for each quantum state depend on both n and l which describe the\ntopological properties of the atom packets. We also give an experimental\nprotocol to observe these novel phenomena in future experiments."
    },
    {
        "anchor": "Dynamics in spinor condensates controlled by a microwave dressing field: We experimentally study spin dynamics in a sodium antiferromagnetic spinor\ncondensate with off-resonant microwave pulses. In contrast to a magnetic field,\na microwave dressing field enables us to explore rich spin dynamics under the\ninfluence of a negative net quadratic Zeeman shift $q_{\\rm net}$. We find an\nexperimental signature to determine the sign of $q_{\\rm net}$, and observe\nharmonic spin population oscillations at every $q_{\\rm net}$ except near each\nseparatrix in phase space where spin oscillation period diverges. In the\nnegative and positive $q_{\\rm net}$ regions, we also observe a remarkably\ndifferent relationship between each separatrix and the magnetization. Our data\nconfirms an important prediction derived from the mean-field theory:\nspin-mixing dynamics in spin-1 condensates substantially depends on the sign of\nthe ratio of $q_{\\rm net}$ and the spin-dependent interaction energy. This work\nmay thus be the first to use only one atomic species to reveal mean-field spin\ndynamics, especially the separatrix, which are predicted to appear differently\nin spin-1 antiferromagnetic and ferromagnetic spinor condensates.",
        "positive": "Parametrized path integral formulation for large fermion systems: The exchange antisymmetry between identical fermions gives rise to the well\nknown fermion sign problem, in the form of large cancellation between positive\nand negative contribution to the partition function, making any simulation\nmethods which directly sample this partition function exponentially difficult\nto converge. In this work, we employ path integral molecular dynamics (PIMD)\nand build upon the recently discovered fictitious particle model to investigate\nthe fermion sign problem further. We consider the validity and invalidity\ncondition for the method of parametrized path integral formulation of the\npartition function and extrapolation to circumvent the fermion sign problem.\nFor the valid region of our method, our simulation shows that we may give\naccurate prediction of the energy for large fermion systems, which is much\nbeyond the capability of the direct sampling in the traditional method. In\nparticular, we find and verify a simple universal relation for high temperature\nnoninteracting particles or strongly repulsive interacting particles at low\ntemperatures."
    },
    {
        "anchor": "Non-Hermitian Ferromagnetism in an Ultracold Fermi Gas: We develop a non-Hermitian effective theory for a repulsively interacting\nFermi gas in the excited branch. The on-shell $T$-matrix is employed as a\ncomplex-valued interaction term, which describes a repulsive interaction\nbetween atoms in the excited branch and a two-body inelastic decay to the\nattractive branch. To see the feature of this model, we have addressed, in the\nweak coupling regime, the excitation properties of a repulsive Fermi polaron as\nwell as the time-dependent number density. The analytic expressions obtained\nfor these quantities qualitatively show a good agreement with recent\nexperiments. By calculating the dynamical transverse spin susceptibility in the\nrandom phase approximation, we show that a ferromagnetic system with nonzero\npolarization undergoes a dynamical instability and tends towards a\nheterogeneous phase.",
        "positive": "Lattice-Ramp Induced Dynamics in an Interacting Bose-Bose Mixture: We investigate a bosonic quantum gas consisting of two interacting species in\nan optical lattice at zero and finite temperature. The equilibrium properties\nand dynamics of this system are obtained by means of the Gutzwiller mean-field\nmethod. In particular we model recent experiments where the ramp-up of the\noptical lattice occurs on a time scale comparable to the tunneling time of the\nbosons. We demonstrate the violation of adiabaticity of this process with\nrespect to the many-body quantum states, and reproduce and explain the\noscillations of the visibility as a function of ramp-up time, as seen in\nexperiments."
    },
    {
        "anchor": "Multimode dynamics and emergence of a characteristic length-scale in a\n  one-dimensional quantum system: We study the non-equilibrium dynamics of a coherently split one-dimensional\n(1d) Bose gas by measuring the full probability distribution functions of\nmatter-wave interference. Observing the system on different length scales\nallows us to probe the dynamics of excitations on different energy scales,\nrevealing two distinct length-scale dependent regimes of relaxation. We measure\nthe crossover length-scale separating these two regimes and identify it with\nthe prethermalized phase-correlation length of the system. Our approach enables\na direct observation of the multimode dynamics characterizing one-dimensional\nquantum systems.",
        "positive": "Three-dimensional vortex-bright solitons in a spin-orbit coupled\n  spin-$1$ condensate: We demonstrate stable and metastable vortex-bright solitons in a\nthree-dimensional spin-orbit-coupled three-component hyperfine spin-1\nBose-Einstein condensate (BEC) using numerical solution and variational\napproximation of a mean-field model. The spin-orbit coupling provides\nattraction to form vortex-bright solitons in both attractive and repulsive\nspinor BECs. The ground state of these vortex-bright solitons is axially\nsymmetric for weak polar interaction. For a sufficiently strong ferromagnetic\ninteraction, we observe the emergence of a fully asymmetric vortex-bright\nsoliton as the ground state. We also numerically investigate moving solitons.\nThe present mean-field model is not Galilean invariant, and we use a\nGalilean-transformed mean-field model for generating the moving solitons."
    },
    {
        "anchor": "Production of dual species Bose-Einstein condensates of $^{39}$K and\n  $^{87}$Rb: We report the production of $^{39}$K and $^{87}$Rb Bose-Einstein condensates\n(BECs) in the lowest hyperfine states $| F=1,m_{F}=1 \\rangle$ simultaneously.\nWe collect atoms in bright/dark magneto-optical traps (MOTs) of\n$^{39}$K/$^{87}$Rb to overcome the light-assisted losses of $^{39}$K atoms.\nGray molasses cooling on the D1 line of the $^{39}$K is used to effectively\nincrease the phase density, which improves the loading efficiency of $^{39}$K\ninto the quadrupole magnetic trap. Simultaneously, the normal molasses are\nemployed for $^{87}$Rb. After the microwave evaporation cooling on $^{87}$Rb in\nthe optically plugged magnetic trap, the atoms mixture is transferred to a\ncrossed optical dipole trap, where the collisional properties of the two\nspecies in different combinations of the hyperfine states are studied. The dual\nspecies BECs of $^{39}$K and $^{87}$Rb are obtained by further evaporative\ncooling in optical dipole trap at a magnetic field of 372.6 G with the\nbackground repulsive interspecies scattering length $a_{KRb}$ = 34 $a_{0}$\n($a_{0}$ is the Bohr radius) and the intraspecies scattering length $a_{K}$ =\n20.05 $a_{0}$.",
        "positive": "Collision dynamics and reactions of fractional vortex molecules in\n  coherently coupled Bose-Einstein condensates: Coherently coupled two-component Bose-Einstein condensates (BEC) exhibit\nvortex confinement resembling quark confinement in Quantum Chromo Dynamics\n(QCD). Fractionally quantized vortices winding only in one of two components\nare attached by solitons, and they cannot stably exist alone. Possible stable\nstates are \"hadrons\" either of mesonic type, i.e., molecules made of a vortex\nand anti-vortex in the same component connected by a soliton, or of baryonic\ntype, i.e., molecules made of two vortices winding in two different components\nconnected by a soliton. Mesonic molecules move straight with a constant\nvelocity while baryonic molecules rotate. We numerically simulate collision\ndynamics of mesonic and baryonic molecules and find that the molecules swap a\npartner in collisions in general like chemical and nuclear reactions, summarize\nall collisions as vortex reactions, and describe those by Feynman diagrams. We\nfind a selection rule for final states after collisions of vortex molecules,\nanalogous to that for collisions of hadrons in QCD."
    },
    {
        "anchor": "Controllable high-speed polariton waves in a PT-symmetric lattice: Parity-time (PT) symmetry gives rise to unusual phenomena in many physical\nsystems, presently attracting a lot of attention. One essential and non-trivial\ntask is the fabrication and design of the PT-symmetric lattices in different\nsystems. Here we introduce a method to realize such a lattice in an\nexciton-polariton condensate in a planar semiconductor microcavity. We\ntheoretically demonstrate that in the regime, where lattice profile is nearly\nPT-symmetric, a polariton wave can propagate at very high velocity resulting\nfrom the beating of a ground state condensate created in the lowest energy band\nat very small momentum and a condensate simultaneously created in higher energy\nstates with large momentum. The spontaneous excitation of these two states in\nthe nonlinear regime due to competition between multiple eigenmodes becomes\npossible since the spectrum of nearly PT-symmetric structure reveals\npractically identical amplification for Bloch waves from the entire Brillouin\nzone. There exists a wide velocity range for the resulting polariton wave. This\nvelocity can be controlled by an additional coherent pulse carrying a specific\nmomentum. We also discuss the breakup of the PT-symmetry when the polariton\nlifetime exceeds a certain threshold value.",
        "positive": "Critical relaxation with overdamped quasiparticles in open quantum\n  systems: We study the late-time relaxation following a quench in a driven-dissipative\nquantum many-body system. We consider the open Dicke model, describing the\ninfinite-range interactions between $N$ atoms and a single, lossy\nelectromagnetic mode. We show that the dynamical phase transition at a critical\natom-light coupling is characterized by the interplay between reservoir-driven\nand intrinsic relaxation processes. Above the critical coupling, small\nfluctuations in the occupation of the dominant quasiparticle-mode start to grow\nin time while the quasiparticle lifetime remains finite due to losses. Near the\ncritical interaction strength we observe a crossover between exponential and\npower-law $1/\\tau$ relaxation, the latter driven by collisions between\nquasiparticles. For a quench exactly to the critical coupling, the power-law\nrelaxation extends to infinite times, but the finite lifetime of quasiparticles\nprevents ageing to appear. We predict our results to be accessible to quench\nexperiments with ultracold bosons in optical resonators."
    },
    {
        "anchor": "Phase diagram of a quantum Coulomb wire: We report the quantum phase diagram of a one-dimensional Coulomb wire\nobtained using the path integral Monte Carlo (PIMC) method. The exact knowledge\nof the nodal points of this system permits us to find the energy in an exact\nway, solving the sign problem which spoils fermionic calculations in higher\ndimensions. The results obtained allow for the determination of the stability\ndomain, in terms of density and temperature, of the one-dimensional Wigner\ncrystal. At low temperatures, the quantum wire reaches the quantum-degenerate\nregime, which is also described by the diffusion Monte Carlo method. Increasing\nthe temperature the system transforms to a classical Boltzmann gas which we\nsimulate using classical Monte Carlo. At large enough density, we identify a\none-dimensional ideal Fermi gas which remains quantum up to higher temperatures\nthan in two- and three-dimensional electron gases. The obtained phase diagram\nas well as the energetic and structural properties of this system are relevant\nto experiments with electrons in quantum wires and to Coulomb ions in\none-dimensional confinement.",
        "positive": "Repulsive polarons and itinerant ferromagnetism in strongly polarized\n  Fermi gases: We analyze the properties of a single impurity immersed in a Fermi sea. At\npositive energy and scattering lengths, we show that the system possesses a\nwell-defined but metastable excitation, the repulsive polaron, and we calculate\nits energy, quasiparticle residue and effective mass. From a thermodynamic\nargument we obtain the number of particles in the dressing cloud, illustrating\nthe repulsive character of the polaron. Identifying the important 2- and 3-body\ndecay channels, we furthermore calculate the lifetime of the repulsive polaron.\nThe stability conditions for the formation of fully spin polarized\n(ferromagnetic) domains are then examined for a binary mixture of atoms with a\ngeneral mass ratio. Our results indicate that mass imbalance lowers the\ncritical interaction strength for phase-separation, but that very short\nquasiparticle decay times will complicate the experimental observation of\nitinerant ferromagnetism. Finally, we present the spectral function of the\nimpurity for various coupling strengths and momenta."
    },
    {
        "anchor": "The normal state of attractive Fermi gases from coupled-cluster theory: We introduce coupled-cluster (CC) theory for the numerical study of the\nnormal state of two-component, dilute Fermi gases with attractive, short-range\ninteractions at zero temperature. We focus on CC theory with double excitations\n(CCD) and discuss its close relationship with -- and improvement upon -- the\nt-matrix approximation, i.e., the resummation of ladder diagrams via a\nrandom-phase approximation. We further discuss its relationship with Chevy's\nvariational wavefunction ansatz for the Fermi polaron and argue that CCD is its\nnatural extension to nonzero minority species concentrations. Studying normal\nstate energetics for a range of interaction strengths below and above\nunitarity, we find that CCD yields good agreement with fixed-node diffusion\nMonte Carlo. We find that CCD does not converge for small polarizations and\nlarge interaction strengths, which we speculatively attribute to the nascent\ninstability to a superfluid state.",
        "positive": "The Efimov effect in lithium 6: We analyse the recent experiments investigating the low-energy physics of\nthree lithium 6 atoms in different internal states with resonant two-body\nscattering lengths. All observed features are qualitatively consistent with the\nexpected Efimov effect, i.e. the effective universal three-body attraction that\narises for large values of the scattering lengths. However, we find that a\nquantitative description at negative energy requires non-universal two- and\nthree-body corrections due to presently unknown behaviour at short distance. An\nattempt to implement these corrections is made through energy-dependent\nparameters fitted to the experimental data."
    },
    {
        "anchor": "Stationary vortex flows and macroscopic Zeno effect in Bose-Einstein\n  condensates with localized dissipation: We theoretically demonstrate a possibility to observe the macroscopic Zeno\neffect in an effectively two-dimensional (pancake-shaped) repulsive\nBose--Einstein condensate subjected to a strong narrow dissipation. We show\nthat the dissipation can generate stable stationary nonlinear flows which bear\neither zero or non-zero topological charge (vorticity). The superfluid flows\ntowards the dissipative defect compensate the atomic losses. The macroscopic\nZeno effect manifests itself in a nonmonotonous dependence of the inward\ncurrent density on the strength of the dissipation.",
        "positive": "Dynamic response of strongly correlated Fermi gases in the quantum\n  virial expansion: By developing a quantum virial expansion theory, we quantitatively calculate\nthe dynamic density response function of a trapped strongly interacting Fermi\ngas at high temperatures near unitarity. A clear transition from atomic to\nmolecular responses is identified in the spectra when crossing from the BCS to\nBEC regimes, in qualitative agreement with recent Bragg spectroscopy\nobservations. Our virial expansion method provides a promising way to solve the\nchallenging strong-coupling problems and is applicable to other dynamical\nproperties of strongly correlated Fermi gases."
    },
    {
        "anchor": "Two-Dimensional Bose-Hubbard Model for Helium on Graphene: An exciting development in the field of correlated systems is the possibility\nof realizing two-dimensional (2D) phases of quantum matter. For a systems of\nbosons, an example of strong correlations manifesting themselves in a 2D\nenvironment is provided by helium adsorbed on graphene. We construct the\neffective Bose-Hubbard model for this system which involves hard-core bosons\n$(U\\approx\\infty)$, repulsive nearest-neighbor $(V>0)$ and small attractive\n$(V'<0)$ next-nearest neighbor interactions. The mapping onto the Bose-Hubbard\nmodel is accomplished by a variety of many-body techniques which take into\naccount the strong He-He correlations on the scale of the graphene lattice\nspacing. Unlike the case of dilute ultracold atoms where interactions are\neffectively point-like, the detailed microscopic form of the short range\nelectrostatic and long range dispersion interactions in the helium-graphene\nsystem are crucial for the emergent Bose-Hubbard description. The result places\nthe ground state of the first layer of $^4$He adsorbed on graphene deep in the\ncommensurate solid phase with $1/3$ of the sites on the dual triangular lattice\noccupied. Because the parameters of the effective Bose-Hubbard model are very\nsensitive to the exact lattice structure, this opens up an avenue to tune\nquantum phase transitions in this solid-state system.",
        "positive": "Observation of quantum phase transition in spin-orbital-angular-momentum\n  coupled Bose-Einstein condensate: Orbital angular momentum (OAM) of light represents a fundamental optical\nfreedom that can be exploited to manipulate quantum state of atoms. In\nparticular, it can be used to realize spin-orbital-angular-momentum (SOAM)\ncoupling in cold atoms by inducing an atomic Raman transition using two laser\nbeams with differing OAM. Rich quantum phases are predicted to exist in\nmany-body systems with SOAM coupling. Their observations in laboratory,\nhowever, are often hampered by the limited control of the system parameters. In\nthis work we report, for the first time, the experimental observation of the\nground-state quantum phase diagram of the SOAM coupled Bose-Einstein condensate\n(BEC). The discontinuous variation of the spin polarization as well as the\nvorticity of the atomic wave function across the phase boundaries provides\nclear evidence of first-order phase transitions. Our results open up a new way\nto the study of phase transitions and exotic quantum phases in quantum gases."
    },
    {
        "anchor": "Estimating strong correlations in optical lattices: Ultra-cold atoms in optical lattices provide one of the most promising\nplatforms for analog quantum simulations of complex quantum many-body systems.\nLarge-size systems can now routinely be reached and are already used to probe a\nlarge variety of different physical situations, ranging from quantum phase\ntransitions to artificial gauge theories. At the same time, measurement\ntechniques are still limited and full tomography for these systems seems out of\nreach. Motivated by this observation, we present a method to directly detect\nand quantify to what extent a quantum state deviates from a local Gaussian\ndescription, based on available noise correlation measurements from in-situ and\ntime-of-flight measurements. This is an indicator of the significance of strong\ncorrelations in ground and thermal states, as Gaussian states are precisely the\nground and thermal states of non-interacting models. We connect our findings,\naugmented by numerical tensor network simulations, to notions of equilibration,\ndisordered systems and the suppression of transport in Anderson insulators.",
        "positive": "Ballistic transport of a polariton ring condensate with spin precession: It is now routine to make Bose-Einstein condensates of polaritons with long\nenough lifetime and low enough disorder to travel ballistically for hundreds of\nmicrons in quasi-one-dimensional (1D) wires. We present observations of a\npolariton condensate injected at one point in a quasi-1D ring, with a\nwell-defined initial velocity and direction. A clear precession of the circular\npolarization is seen, which arises from an effective spin-orbit coupling term\nin the Hamiltonian. Our theoretical model accurately predicts the\nexperimentally observed behavior, and shows that \"zitterbewegung\" behavior\nplays a role in the motion of the polaritons."
    },
    {
        "anchor": "Optical signature of quantum coherence in fully dark exciton condensates: We predict that the collision of two fully dark exciton condensates produces\ninterference fringes which are not only dark but also bright. So, quite\nsurprisingly, the collision of coherent states made of dark excitons produces\nlight. This remarkable effect, which is many-body in essence, comes from the\ncomposite boson nature of excitons, through the fermion exchanges they can have\nwhich transform dark states into bright states. The possibility of optically\ndetecting quantum coherence in a regime where the system is hidden by its total\ndarkness, was up to now considered as hopeless.",
        "positive": "Probing nearest-neighbor correlations of ultracold fermions in an\n  optical lattice: We demonstrate a probe for nearest-neighbor correlations of fermionic quantum\ngases in optical lattices. It gives access to spin and density configurations\nof adjacent sites and relies on creating additional doubly occupied sites by\nperturbative lattice modulation. The measured correlations for different\nlattice temperatures are in good agreement with an ab initio calculation\nwithout any fitting parameters. This probe opens new prospects for studying the\napproach to magnetically ordered phases."
    },
    {
        "anchor": "Spatial Dependence of Entropy in Trapped Ultracold Bose Gases: We find a new physical regime in the trapped Bose-Hubbard Hamiltonian using\ntime-evolving block decimation. Between Mott-insulating and superfluid phases,\nthe latter induced by trap compression, a spatially self-organized state\nappears in which non-local entropy signals entanglement between spatially\ndistant superfluid shells. We suggest a linear rather than harmonic potential\nas an ideal way to observe such a self-organized system. We also explore both\nquantum information and thermal entropies in the superfluid regime, finding\nthat while the former follows the density closely the latter can be strongly\nmanipulated with the mean field.",
        "positive": "Bosonic Kondo-Hubbard model: We study, using quantum Monte-Carlo simulations, the bosonic Kondo-Hubbard\nmodel in a two dimensional square lattice. We explore the phase diagram and\nanalyse the mobility of particles and magnetic properties. At unit filling, the\ntransition from a paramagnetic Mott insulator to a ferromagnetic superfluid\nappears continuous, contrary to what was predicted with mean field. For double\noccupation per site, both the Mott insulating and superfluid phases are\nferromagnetic and the transition is still continuous. Multiband tight binding\nHamiltonians can be realized in optical lattice experiments, which offer not\nonly the possibility of tuning the different energy scales over wide ranges,\nbut also the option of loading the system with either fermionic or bosonic\natoms."
    },
    {
        "anchor": "Finite-temperature effects on the superfluid Bose-Einstein condensation\n  of confined ultracold atoms in three-dimensional optical lattices: We discuss the finite-temperature phase diagram in the three-dimensional\nBose-Hubbard (BH) model in the strong correlation regime, relevant for\nBose-Einstein condensates in optical lattices, by employing a quantum rotor\napproach. In systems with strong on site repulsive interactions, the rotor U(1)\nphase variable dual to the local boson density emerges as an important\ncollective field. After establishing the connection between the rotor\nconstruction and the the on--site interaction in the BH model the robust\neffective action formalism is developed which allows us to study the superfluid\nphase transition in various temperature--interaction regimes.",
        "positive": "Observation of Topologically Stable 2D Skyrmions in an Antiferromagnetic\n  Spinor Bose-Einstein Condensate: We present the creation and time evolution of two-dimensional Skyrmion\nexcitations in an antiferromagnetic spinor Bose-Einstein condensate. Using a\nspin rotation method, the Skyrmion spin textures were imprinted on a sodium\ncondensate in a polar phase, where the two-dimensional Skyrmion is\ntopologically protected. The Skyrmion was observed to be stable on a short time\nscale of a few tens of ms but to have dynamical instability to deform its shape\nand eventually decay to a uniform spin texture. The deformed spin textures\nreveal that the decay dynamics involves breaking the polar phase inside the\ncondensate without having topological charge density flow through the boundary\nof the finite-sized sample. We discuss the possible formation of half-quantum\nvortices in the deformation process."
    },
    {
        "anchor": "Energy shift of magnons in a ferromagnetic spinor-dipolar Bose-Einstein\n  condensate: Motivated by the recent experiment performed by the Berkeley group [G. E.\nMarti {\\it et al.}, Phys. Rev. Lett. {\\bf 113}, 155302 (2014)], we consider the\ndynamics of magnons in a spin-1 spinor-dipolar Bose-Einstein condensate, using\nmean-field theory. We show that the effective mass of a magnon is increased by\nthe magnetic dipole-dipole interaction, as observed in the experiment. The\nmagnon mass is also decreased by changing the direction of the magnetic field.\nThe increase and decrease in the magnon mass manifest themselves in the\nacceleration of the magnons.",
        "positive": "MCTDH-X: The multiconfigurational time-dependent Hartree method for\n  indistinguishable particles software: We introduce and describe the multiconfigurational time-depenent Hartree for\nindistinguishable particles (MCTDH-X) software. This powerful tool allows the\ninvestigation of ground state properties and dynamics of interacting quantum\nmany-body systems in different spatial dimensions. The MCTDH-X software is a\nset of programs and scripts to compute, analyze, and visualize solutions for\nthe time-dependent and time-independent many-body Schr\\\"{o}dinger equation for\nindistinguishable quantum particles. As the MCTDH-X software represents a\ngeneral solver for the Schr\\\"{o}dinger equation, it is applicable to a wide\nrange of problems in the fields of atomic, optical, molecular physics as well\nas condensed matter systems. In particular, it can be used to study\nlight-matter interactions, correlated dynamics of electrons, as well as some\naspects related to quantum information and computing. The MCTDH-X software\nsolves a set of non-linear coupled working equations based on the application\nof the variational principle to the Schr\\\"{o}dinger equation. These equations\nare obtained by using an ansatz for the many-body wavefunction that is a\ntime-dependent expansion in a set of time-dependent many-body basis states. The\ntime-dependence of the basis set enables MCTDH-X to deal with quantum dynamics\nat a superior accuracy as compared to, for instance, exact diagonalization\napproaches. Herein, we give an introduction to the MCTDH-X software via an\neasy-to-follow tutorial with a focus on accessibility. We use the double well\nto illustrate the fermionization of bosonic particles, the crystallization of\nfermionic particles, characteristics of the superfluid and Mott-insulator\nquantum phases in Hubbard models, and even dynamical quantum phase transitions.\nOur tutorial guides the potential user to apply the MCTDH-X software also to\nmore complex systems."
    },
    {
        "anchor": "Topological Fulde-Ferrell states in alkaline-earth-metal-like atoms near\n  an orbital Feshbach resonance: We study the effects of synthetic spin-orbit coupling on the pairing physics\nin quasi-one-dimensional ultracold Fermi gases of alkaline-earth-metal-like\natoms near an orbital Feshbach resonance (OFR). The interplay between\nspin-orbit coupling and pairing interactions near the OFR leads to an\ninteresting topological Fulde-Ferrell state, where the nontrivial topology of\nthe state is solely encoded in the closed channel with a topologically trivial\nFulde-Ferrell pairing in the open channel. We confirm the topological property\nof the system by characterizing the Zak phase and the edge states. The\ntopological Fulde-Ferrell state can be identified by the momentum-space density\ndistribution obtained from time-of-flight images.",
        "positive": "Superfluid transport dynamics in a capacitive atomtronic circuit: We simulate transport in an atomtronic circuit of a Bose-Einstein condensate\nthat flows from a source region into a drain through a gate channel. The\ntime-dependent Gross-Pitaevskii equation (GPE) solution matches the data of a\nrecent experiment. The atomtronic circuit is found to be similar to a\nvariable-resistance RLC circuit, which is critically damped at early times and\nshows LC oscillations later. The GPE also predicts atom loss from the drain.\nStudies of the dependence of condensate transport upon gate parameters suggest\nthe utility of the GPE for investigation of atomtronic circuits."
    },
    {
        "anchor": "Temperatures are not useful to characterise bright-soliton experiments\n  for ultra-cold atoms: Contrary to many other translationally invariant one-dimensional models, the\nlow-temperature phase for an attractively interacting one-dimensional Bose-gas\n(a quantum bright soliton) is stable against thermal fluctuations. However,\ntreating the thermal properties of quantum bright solitons within the canonical\nensemble leads to anomalous fluctuations of the total energy that indicate that\ncanonical and micro-canonical ensembles are not equivalent. State-of-the-art\nexperiments are best described by the micro-canonical ensemble, within which we\npredict a co-existence between single atoms and solitons even in the\nthermodynamic limit - contrary to strong predictions based on both the Landau\nhypothesis and the canonical ensemble. This questions the use of temperatures\nto describe state-of-the-art bright soliton experiments that currently load\nBose-Einstein condensates into quasi-one-dimensional wave guides without adding\ncontact to a heat bath.",
        "positive": "Crossover polarons in a strongly interacting Fermi superfluid: We investigate the zero-temperature quasiparticle properties of a mobile\nimpurity immersed in a strongly interacting Fermi superfluid at the crossover\nfrom a Bose-Einstein condensate (BEC) to a Bardeen--Cooper--Schrieffer (BCS)\nsuperfluid, by using a many-body $T$-matrix approach that excludes Efimov\ntrimer bound states. Termed BEC-BCS crossover polaron, or crossover polaron in\nshort, this quasiparticle couples to elementary excitations of a many-body\nbackground and therefore could provide a useful probe of the underlying\nstrongly interacting Fermi superfluid. Due to the existence of a significant\npairing gap $\\Delta$, we find that the repulsive polaron branch becomes less\nwell-defined. In contrast, the attractive polaron branch is protected by the\npairing gap and becomes more robust at finite momentum. It remains as a\ndelta-function peak in the impurity spectral function below a threshold\n$2\\Delta$. Above the threshold, the attractive polaron enters the particle-hole\ncontinuum and starts to get damped. We predict the polaron energy, residue and\neffective mass for realistic Bose-Fermi mixtures, where the minority bosonic\natoms play the role of impurity. These results are practically useful for\nfuture cold-atom experiments on crossover polarons."
    },
    {
        "anchor": "Extended Bose-Hubbard Model with dipolar and contact interactions: We study the phase diagram of the one-dimensional boson gas trapped inside an\noptical lattice with contact and dipolar interaction taking into account\nnext-nearest terms for both tunneling and interaction. Using the density matrix\nrenormalization group, we calculate how the locations of phase transitions\nchange with increasing dipolar interaction strength for average density $\\rho =\n1$. Furthermore, we show an emergence of pair-correlated phases for a large\ndipolar interaction strength and $\\rho \\geq 2$, including a supersolid phase\nwith an incommensurate density wave ordering manifesting the corresponding\nspontaneous breaking of the translational symmetry.",
        "positive": "Tuning the Quantum Phase Transition of Bosons in Optical Lattices via\n  Periodic Modulation of s-Wave Scattering Length: We consider interacting bosons in a 2D square and a 3D cubic optical lattice\nwith a periodic modulation of the s-wave scattering length. At first we map the\nunderlying periodically driven Bose-Hubbard model for large enough driving\nfrequencies approximately to an effective time-independent Hamiltonian with a\nconditional hopping. Combining different analytical approaches with quantum\nMonte Carlo simulations then reveals that the superfluid-Mott insulator quantum\nphase transition still exists despite the periodic driving and that the\nlocation of the quantum phase boundary turns out to depend quite sensitively on\nthe driving amplitude. A more detailed quantitative analysis shows even that\nthe effect of driving can be described within the usual Bose-Hubbard model\nprovided that the hopping is rescaled appropriately with the driving amplitude.\nThis finding indicates that the Bose-Hubbard model with a periodically driven\ns-wave scattering length and the usual Bose-Hubbard model belong to the same\nuniversality class from the point of view of critical phenomena."
    },
    {
        "anchor": "Multifractals Competing with Solitons on Fibonacci Optical Lattice: We study the stationary states for the nonlinear Schr\\\"odinger equation on\nthe Fibonacci lattice which is expected to be realized by Bose-Einstein\ncondensates loaded into an optical lattice. When the model does not have a\nnonlinear term, the wavefunctions and the spectrum are known to show fractal\nstructures. Such wavefunctions are called critical. We present a phase diagram\nof the energy spectrum for varying the nonlinearity. It consists of three\nportions, a forbidden region, the spectrum of critical states, and the spectrum\nof stationary solitons. We show that the energy spectrum of critical states\nremains intact irrespective of the nonlinearity in the sea of a large number of\nstationary solitons.",
        "positive": "Medium effects close to s- and p-wave Feshbach resonances in atomic\n  Fermi gases: Many-body effects may influence properties, such as scattering parameters,\nnature of pairing, etc., close to a Feshbach resonance in the fermion BEC-BCS\ncrossover problem. We study effects such as these using a tractable\ncrossing-symmetric approach. This method allow us to include quantum\nfluctuations, such as, density, current, spin, spin-current and the\nhigher-order fluctuations in a self-consistent fashion. The underlying fermion\ninteraction is reflected in the \"driving\" term. We perform calculations here on\nboth Bose-Einstein condensate (BEC) and BCS sides, and taking the driving term\nto be finite range, and of arbitrary strength. These are related to two-body\nsinglet and triplet scattering parameters, and can be connected with\nexperimental s- and p-wave Feshbach resonances. We include the $\\ell=0$ density\nand spin fluctuations, as well as $\\ell=1$ current and spin-current\nfluctuations. We calculate renormalized scattering amplitudes, pairing\namplitudes, nature of pairing, etc., on both the BEC and BCS sides. We then\ncompare our results qualitatively with experiments."
    },
    {
        "anchor": "Enhancing Kondo Coupling in Alkaline-Earth Atomic Gases with\n  Confinement-induced Resonances in Mixed Dimensions: The Kondo effect describes the spin-exchanging interaction between localized\nimpurity and the itinerant fermions. The ultracold alkaline-earth atomic gas\nprovides a natural platform for quantum simulation of the Kondo model,\nutilizing its long-lived clock state and the nuclear-spin exchanging\ninteraction between the clock state and the ground state. One of the key issue\nnow is whether the Kondo temperature can be high enough to be reached in\ncurrent experiment, for which we have proposed using a transverse confinement\nto confine atoms into a one-dimensional tube and to utilize the\nconfinement-induced resonance to enhance the Kondo coupling. In this work, we\nfurther consider the $1+0$ dimensional scattering problem when the clock state\nis further confined by an axial harmonic confinement. We show that this axial\nconfinement for the clock state atoms not only plays a role for localizing\nthem, but also can act as an additional control knob to reach the\nconfinement-induced resonance. We show that by combining both the transverse\nand the axial confinements, the confinement-induced resonance can be reached in\nthe practical conditions and the Kondo effect can be attainable in this system.",
        "positive": "Efficient three-body calculations with a two-body mapped grid method: We investigate the prospects of combining a standard momentum space approach\nfor ultracold three-body scattering with efficient coordinate space schemes to\nsolve the underlying two-body problem. In many of those schemes the two-body\nproblem is numerically restricted up to a finite interparticle distance\n$r_\\mathrm{b}$. We analyze effects of this two-body restriction on the two- and\nthree-body level using pairwise square-well potentials that allow for analytic\ntwo-body solutions and more realistic Lennard-Jones van der Waals potentials to\nmodel atomic interactions. We find that the two-body $t$-operator converges\nexponentially in $r_\\mathrm{b}$ for the square-well interaction. Setting\n$r_\\mathrm{b}$ to 2000 times the range of the interaction, the three-body\nrecombination rate can be determined accurately up to a few percent when the\nmagnitude of the scattering length is small compared to $r_\\mathrm{b}$, while\nthe position of the lowest Efimov features is accurate up to the percent level.\nIn addition we find that with the introduction of a momentum cut-off, it is\npossible to determine the three-body parameter in good approximation even for\ndeep van der Waals potentials."
    },
    {
        "anchor": "Reactions Between Layer-Resolved Molecules Mediated by Dipolar Exchange: Microscopic control over polar molecules with tunable interactions would\nenable realization of novel quantum phenomena. Using an applied electric field\ngradient, we demonstrate layer-resolved state preparation and imaging of\nultracold potassium-rubidium molecules confined to two-dimensional planes in an\noptical lattice. The coherence time of rotational superpositions in individual\nlayers is maximized by rotating the electric field relative to the optical trap\npolarization to achieve state-insensitive trapping. Molecules in adjacent\nlayers interact via dipolar exchange of rotational angular momentum; by\nadjusting the interaction strength between spatially separated ensembles of\nmolecules, we regulate the local chemical reaction rate. The observed resonance\nwidth of the exchange process vastly exceeds the dipolar interaction energy, an\neffect we attribute to the thermal energy. This work realizes precise control\nof interacting molecules, enabling electric field microscopy on subwavelength\nlength scales and allowing access to unexplored physics in two-dimensional\nsystems.",
        "positive": "Effective self-similar expansion of a Bose-Einstein condensate: Free\n  space vs confined geometries: We compare the exact evolution of an expanding three-dimensional\nBose-Einstein condensate with that obtained from the effective scaling approach\nintroduced in D. Gu\\'ery-Odelin [Phys. Rev. A 66, 033613 (2002)]. This\napproach, which consists in looking for self-similar solutions to be satisfied\non average, is tested here in different geometries and configurations. We find\nthat, in case of almost isotropic traps, the effective scaling reproduces with\nhigh accuracy the exact evolution dictated by the Gross-Pitaevskii equation for\narbitrary values of the interactions, in agreement with the proof-of-concept of\nM. Modugno, G. Pagnini, and M. A. Valle-Basagoiti [Phys. Rev. A 97, 043604\n(2018)]. Conversely, it is shown that the hypothesis of universal\nself-similarity breaks down in case of strong anisotropies and trapped\ngeometries."
    },
    {
        "anchor": "Trapped Ultracold Bosons in Periodically Modulated Lattices: Motivated by the recent rapid development of the field of quantum gases in\noptical lattices, we present a comprehensive study of the spectrum of ultracold\natoms in a one-dimensional optical lattice subjected to a periodic lattice\nmodulation. Using the time-dependent density-matrix renormalization group\nmethod, we study the dynamical response due to lattice modulations in different\nquantum phases of the system with varying density. For the Mott insulating\nstate, we identify several excitation processes, which provide important\ninformation about the density profile of the gases. For the superfluid, the\ndynamical response can be well described in a local density approximation. This\nsimplification can be valuable in understanding the strong-correlated\nsuperfluid in a slow-varying harmonic potential. All these spectroscopic\nfeatures of an inhomogeneous system can be used as a test for the validity of\nthe Bose-Hubbard model in a parabolic trapping potential.",
        "positive": "Energy spectrum and phase diagrams of two-sublattice hard-core boson\n  model: The energy spectrum, spectral density and phase diagrams have been obtained\nfor two-sublattice hard-core boson model in frames of random phase\napproximation approach. Reconstruction of boson spectrum at the change of\ntemperature, chemical potential and energy difference between local positions\nin sublattices is studied. The phase diagrams illustrating the regions of\nexistence of a normal phase which can be close to Mott-insulator (MI) or\ncharge-density (CDW) phases as well as the phase with the Bose-Einstein\ncondensate (SF phase) are built."
    },
    {
        "anchor": "Momentum relaxation of a mobile impurity in a one-dimensional quantum\n  gas: We investigate the time evolution of the momentum of an impurity atom\ninjected into a degenerate Tonks-Girardeau gas. We establish that given an\ninitial momentum $p_0$ the impurity relaxes to a steady state with a\nnon-vanishing momentum $p_\\infty.$ The nature of the steady state is found to\ndepend drastically on whether the masses of the impurity and the host are equal\nor not. This is due to multiple coherent scattering processes leading to a\nresonant interaction between the impurity and the host in the case of equal\nmasses. The dependence of $p_\\infty$ on $p_0$ remains non-trivial even in the\nlimit of vanishing interaction between the impurity and host particles. In this\nlimit $p_\\infty(p_0)$ is found explicitly.",
        "positive": "Quantum Phase Transition of Bosons in a Shaken Optical Lattice: Recently, the lattice shaking technique has been used to couple different\nBloch bands resonantly. For the one-dimensional (1D) case, in which shaking is\nalong only one direction, experimental observation of domain-wall formation has\nbeen explained by superfluid Ising transition. Inspired by these, we generalize\nto a 2D case in which shaking is along two orthogonal directions. Analogous to\nthe 1D case, we find three different phases, the normal superfluid (NSF) phase,\nthe $D_4$ symmetry-breaking superfluid ($D_4$SF) phase and the Mott insulator\n(MI) phase. Furthermore, we demonstrate that the interaction effect induced by\ninhomogeneous band mixing can modify the critical shaking amplitude. Unlike in\nthe 1D case, shaking types also can modify the critical shaking amplitude.\nUnlike in the 1D case, shaking types also can modify the critical shaking\namplitude. We also construct a low-energy effective field theory to study the\nquantum criticality of bosons near the tricritical point of NSF, $D_4$SF and MI\nphases. Moreover, we find a Bose liquid with anisotropically algebraic order\nand propose to change the Bose-Einstein condensation (BEC) into a non-condensed\nBose liquid by tuning the shaking amplitude approaching the critical value."
    },
    {
        "anchor": "Dark solitons in the unitary Bose gas: We study the dilute and ultracold unitary Bose gas, which is characterized by\na universal equation of state due to the diverging s-wave scattering length,\nunder a transverse harmonic confinement. From the hydrodynamic equations of\nsuperfluids we derive an effective one-dimensional nonpolynomial Schr\\\"odinger\nequation (1D NPSE) for the axial dynamics which, however, takes also into\naccount the transverse dynamics. Finally, by solving the 1D NPSE we obtain\nmeaningful analytical formulas for the dark (gray and black) solitons of the\nbosonic system.",
        "positive": "Classical crystal formation of dipoles in two dimensions: We consider a two-dimensional layer of dipolar particles in the regime of\nstrong dipole moments. Here we can describe the system using classical methods\nand determine the crystal structure that minimizes the total energy. The\ndipoles are assumed to be aligned by an external field and we consider\ndifferent orientations of the dipolar moments with respect to the\ntwo-dimensional plane of motion. We observe that when the orientation angle\nchanges away from perpendicular and towards the plane, the crystal structure\nwill change from a hexagonal form to one that has the dipoles sitting in\nequidistant rows, i.e. a striped configuration. In addition to calculating the\ncrystal unit cell, we also consider the phonon spectrum and the speed of sound.\nAs the orientation changes away from perpendicular the phonon spectrum develops\nlocal minima that are a result of the deformation to the crystal structure."
    },
    {
        "anchor": "Transport of ultracold atoms in superpositions of S- and D-band states\n  in a moving optical lattice: The ultracold atoms in a moving optical lattice with its high controllability\nis a feasible platform to research the transport phenomenon. Here, we study the\ntransport process of ultracold atoms at the D band in a one-dimensional optical\nlattice, and perform the manipulation of atomic transport by modulating the\npopulation proportion of S band and D band. In the experiment, we first load\nultracold atoms into the optical lattice using shortcut method, and then\naccelerate the optical lattice by scanning the phase of lattice beams. The\natomic transport in D band and S band is demonstrated respectively. We find the\ngroup velocity of atoms in D band is opposite to that in S band. By doping\natoms of D band into that of S band, group velocity of the atomic superposition\nstate is modulated, and the manipulation of atomic group velocity from positive\nto negative is realized. Furthermore, the influence of lattice depth and\nacceleration on the transport distance are studied. The calculations with\nmulti-orbital simulation are coincident with the experimental results. Our work\nprovides a useful method to manipulate the atomic transport in higher or mixed\norbits.",
        "positive": "Role of disorder in super- and subradiance of cold atomic clouds: The presence of superradiance and subradiance in microscopic and mean-field\napproaches to light scattering in atomic media is investigated. We show that\nthese phenomena are present in both descriptions, with only minor quantitative\ndifferences, so neither rely on disorder. In particular, they are most\nprominent in media with high resonant optical depth yet far-detuned light,\ni.e.. in the single--scattering regime."
    },
    {
        "anchor": "Dissipative shock waves generated by a quantum-mechanical piston: The piston shock problem is a prototypical example of strongly nonlinear\nfluid flow that enables the experimental exploration of fluid dynamics in\nextreme regimes. Here we investigate this problem for a nominally\ndissipationless, superfluid Bose-Einstein condensate and observe rich dynamics\nincluding the formation of a plateau region, a non-expanding shock front, and\nrarefaction waves. Many aspects of the observed dynamics follow predictions of\nclassical dissipative---rather than superfluid dispersive---shock theory. The\nemergence of dissipative-like dynamics is attributed to the decay of large\namplitude excitations at the shock front into turbulent vortex excitations\nwhich allow us to invoke an eddy viscosity hypothesis. Our experimental\nobservations are accompanied by numerical simulations of the mean field,\nGross-Pitaevskii equation that exhibit quantitative agreement with no fitting\nparameters. This work provides an avenue for the investigation of quantum shock\nwaves and turbulence in channel geometries, which are currently the focus of\nintense research efforts.",
        "positive": "Dynamical and Steady State Properties of a Bose-Hubbard Chain with\n  Bond-Dissipation: A Study based on Matrix Product Operators: We study a dissipative Bose-Hubbard chain subject to an engineered bath using\na superoperator approach based on matrix product operators. The dissipation is\nengineered to stabilize a BEC condensate wave function in its steady state. We\nthen characterize the steady state emerging from the interplay between\nincompatible Hamiltonian and dissipative dynamics. While it is expected that\ninteractions lead to this competition, even the kinetic energy in an open\nboundary condition setup competes with the dissipation, leading to a\nnon-trivial steady state. We also present results for the transient dynamics\nand probe the relaxation time revealing the closing of the dissipative gap in\nthe thermodynamic limit."
    },
    {
        "anchor": "Energy and contact of the one-dimensional Fermi polaron at zero and\n  finite temperature: We use the T-matrix approach for studying highly polarized homogeneous Fermi\ngases in one dimension with repulsive or attractive contact interactions. Using\nthis approach, we compute ground state energies and values for the contact\nparameter that show excellent agreement with exact and other numerical methods\nat zero temperature, even in the strongly interacting regime. Furthermore, we\nderive an exact expression for the value of the contact parameter in one\ndimension at zero temperature. The model is then extended and used for studying\nthe temperature dependence of ground state energies and the contact parameter.",
        "positive": "Boltzmann equation with double-well potentials: We study the dynamics of an interacting classical gas trapped in a\ndouble-well potential at finite temperature. Two model potentials are\nconsidered: a cubic box with a square barrier in the middle, and a harmonic\ntrap with a gaussian barrier along one direction. The study is performed using\nthe Boltzmann equation, solved numerically via the test-particle method. We\nintroduce and discuss a simple analytical model that allows to provide\nestimates of the relaxation time, which are compared with numerical results.\nFinally, we use our findings to make numerical and analytical predictions for\nthe case of a fermionic mixture in the normal-fluid phase in a realistic\ndouble-well potential relevant for experiments with cold atoms."
    },
    {
        "anchor": "Two-species Bose-Einstein condensate in an optical lattice: analytical\n  approximate formul\u00e6: Employing a general variational method and perturbation theory, we derived\nexplicit solutions for the description of one-dimensional two species\nBose-Einstein condensates confined by a harmonic trap potential in an optical\nlattice. We consider the system of two coupled Gross-Pitaevkii equations (GPE)\nand derive explicit expressions for the chemical potentials and wavefunctions\nin terms of the atom-atom interaction parameters and laser intensity. We have\ncompared our results with the numerical solutions of the GPE and performed a\nquantitative analysis for the both considered methods. We underline the\nimportance of the obtained explicit solutions to characterize the density\nprofile or degree of miscibility of the two components.",
        "positive": "Unitary $p$-wave Fermi gas in one dimension: We elucidate universal many-body properties of a one-dimensional,\ntwo-component ultracold Fermi gas near the $p$-wave Feshbach resonance. The\nlow-energy scattering in this system can be characterized by two parameters,\nthat is, $p$-wave scattering length and effective range. At the unitarity limit\nwhere the $p$-wave scattering length diverges and the effective range is\nreduced to zero without conflicting with the causality bound, the system obeys\nuniversal thermodynamics as observed in a unitary Fermi gas with contact\n$s$-wave interaction in three dimensions. It is in contrast to a Fermi gas with\nthe $p$-wave resonance in three dimensions in which the effective range is\ninevitably finite. We present the universal equation of state in this unitary\n$p$-wave Fermi gas within the many-body $T$-matrix approach as well as the\nvirial expansion method. Moreover, we examine the single-particle spectral\nfunction in the high-density regime where the virial expansion is no longer\nvalid. On the basis of the Hartree-like self-energy shift at the divergent\nscattering length, we conjecture that the equivalence of the Bertsch parameter\nacross spatial dimensions holds even for a one-dimensional unitary $p$-wave\nFermi gas."
    },
    {
        "anchor": "$p$-band stability of ultracold atom gas in anharmonic optical lattice\n  potential with large energy scales: Using an optical potential with subwavelength resolution in the form of sharp\n$\\delta$-like peaks, new potential landscapes are created with increased\nanharmonicity in placement of lattice band energies and more favorable energy\nscales. In particular, this makes the ultracold atom p-band gas more stable.\nThe article outlines the details of the construction and discusses the p-band\nstability in canonical cosine optical lattice potential, double well potential,\nand a combination of a classical cosine potential with dark state peaked\npotential.",
        "positive": "A single fermion in a Bose Josephson Junction: We consider the tunneling properties of a single fermionic impurity immersed\nin a Bose-Einstein condensate in a double-well potential. For strong\nboson-fermion interaction, we show the existence of a tunnel resonance where a\nlarge number of bosons and the fermion tunnel simultaneously. We give\nanalytical expressions for the lineshape of the resonance using degenerate\nBrillouin-Wigner theory. We finally compute the time-dependent dynamics of the\nmixture. Using the fermionic tunnel resonances as beam splitter for\nwave-functions, we construct a Mach-Zehnder interferometer that allows complete\npopulation transfer from one well to the other by tilting the double-well\npotential and only taking into account the fermion's tunnel properties."
    },
    {
        "anchor": "Dynamics of spin-orbit coupled Bose-Einstein condensates in a random\n  potential: Disorder plays a crucial role in spin dynamics in solids and condensed matter\nsystems. We demonstrate that for a spin-orbit coupled Bose-Einstein condensate\nin a random potential two mechanisms of spin evolution, that can be\ncharacterized as \"precessional\" and \"anomalous\", are at work simultaneously.\nThe precessional mechanism, typical for solids, is due to the condensate\ndisplacement. The unconventional \"anomalous\" mechanism is due to the\nspin-dependent velocity producing the distribution of the condensate spin\npolarization. The condensate expansion is accompanied by a random displacement\nand fragmentation, where it becomes sparse, as clearly revealed in the spin\ndynamics. Thus, different stages of the evolution can be characterized by\nlooking at the condensate spin.",
        "positive": "Inhomogeneous spin domain induced by the quadratic Zeeman effect in\n  spin-1 Bose-Einstein condensate: We show two kinds of inhomogeneous spin domain possessing N\\'{e}el-like\ndomain walls in spin-1 Bose-Einstein condensate, which are induced by the\npositive and negative quadratic Zeeman effect (QZE) respectively. In both\ncases, the spin density distribution is inhomogeneous and has zeros where the\nmagnetization vanishes. For positive and negative QZE, the spin patterns and\ntopological structures are remarkably different. Such phenomena are due to the\npointwise different axisymmetry-breaking caused by the pointwise different\npopulation exchange between the sublevels, arising uniquely from the QZE. We\nanalyze in detail the inhomogeneous domain formation and related experimental\nobservations for the spin-1 $^{87}$Rb and $^{23}$Na condensate."
    },
    {
        "anchor": "Self-trapping of exciton-polariton condensates: The self-trapping of exciton-polariton condensates is demonstrated and\nexplained by the formation of a new polaron-like state. Above the polariton\nlasing threshold, local variation of the lattice temperature provides the\nmechanism for an attractive interaction between polaritons. Due to this\nattraction, the condensate collapses into a small bright spot. Its position and\nmomentum variances approach the Heisenberg quantum limit. The self-trapping\ndoes not require either a resonant driving force or a presence of defects. The\ntrapped state is stabilized by the phonon-assisted stimulated scattering of\nexcitons into the polariton condensate. While the formation mechanism of the\nobserved self-trapped state is similar to the Landau-Pekar polaron model, this\nstate is populated by several thousands of quasiparticles, in a strike contrast\nto the conventional single-particle polaron state.",
        "positive": "Large-Scale $2+1$D $\\mathrm{U}(1)$ Gauge Theory with Dynamical Matter in\n  a Cold-Atom Quantum Simulator: A major driver of quantum-simulator technology is the prospect of probing\nhigh-energy phenomena in synthetic quantum matter setups at a high level of\ncontrol and tunability. Here, we propose an experimentally feasible realization\nof a large-scale $2+1$D $\\mathrm{U}(1)$ gauge theory with dynamical matter and\ngauge fields in a cold-atom quantum simulator with spinless bosons. We present\nthe full mapping of the corresponding Gauss's law onto the bosonic\ncomputational basis. We then show that the target gauge theory can be\nfaithfully realized and stabilized by an emergent gauge protection term in a\ntwo-dimensional single-species Bose--Hubbard optical Lieb superlattice with two\nspatial periods along either direction, thereby requiring only moderate\nexperimental resources already available in current cold-atom setups. Using\ninfinite matrix product states, we calculate numerical benchmarks for adiabatic\nsweeps and global quench dynamics that further confirm the fidelity of the\nmapping. Our work brings quantum simulators of gauge theories a significant\nstep forward in terms of investigating particle physics in higher spatial\ndimensions, and is readily implementable in existing cold-atom platforms."
    },
    {
        "anchor": "Antiferromagnetic spin correlation of SU($\\mathcal{N}$) Fermi gas in an\n  optical super-lattice: Large-spin cold atomic systems can exhibit unique phenomena that do not\nappear in spin-1/2 systems. We report the observation of nearest-neighbor\nantiferromagnetic spin correlations of a Fermi gas with SU($\\mathcal{N}$)\nsymmetry trapped in an optical lattice. The precise control of the spin degrees\nof freedom provided by an optical pumping technique enables us a\nstraightforward comparison between the cases of SU(2) and SU(4). Our important\nfinding is that the antiferromagnetic correlation is enhanced for the\nSU(4)-spin system compared with SU(2) as a consequence of a Pomeranchuk cooling\neffect. This work is an important step towards the realization of novel\nSU($\\mathcal{N}>2$) quantum magnetism.",
        "positive": "Role of spatial inhomogeneity in dissociation of trapped molecular\n  condensates: We theoretically analyze dissociation of a harmonically trapped Bose-Einstein\ncondensate of molecular dimers and examine how the spatial inhomogeneity of the\nmolecular condensate affects the conversion dynamics and the atom-atom pair\ncorrelations in the short-time limit. Both fermionic and bosonic statistics of\nthe constituent atoms are considered. Using the undepleted molecular-field\napproximation, we obtain explicit analytic results for the asymptotic behavior\nof the second-order correlation functions and for the relative number squeezing\nbetween the dissociated atoms in one, two and three spatial dimensions.\nComparison with the numerical results shows that the analytic approach employed\nhere captures the main underlying physics and provides useful insights into the\ndynamics of dissociation for conversion efficiencies up to 10%. The results\nshow explicitly how the strength of atom-atom correlations and relative number\nsqueezing degrade with the reduction of the size of the molecular condensate."
    },
    {
        "anchor": "Quantum-limited thermometry of a Fermi gas with a charged spin particle: We investigate the sensitivity of an ion sensor in determining the\ntemperature of an atomic Fermi gas. Our study extends to charged impurities the\nproposal by M. T. Mitchison et al. Phys. Rev. Lett. 125, 080402 (2020), where\natomic neutral impurities were used as an in situ thermometer of the quantum\ngas. We find that the long-range character of the atom-ion interaction enhances\nthe thermometer's sensitivity for certain system parameters. In addition, we\ninvestigate the impact of the ion quantum motional state on the sensitivity by\nassuming that it is confined in a harmonic trap. We observe that the\ntemperature sensitivity of the ion is noticeably influenced by its spatial\nextension, making the latter a versatile tool to be manipulated for improving\nthe thermometer performance. We finally discuss our findings in the context of\ncurrent experimental atom-ion mixtures.",
        "positive": "Correlation Energy for Elementary Bosons: Physics of the Singularity: We propose a compact perturbative approach that reveals the physical origin\nof the singularity occurring in the density dependence of correlation energy:\nlike fermions, elementary bosons have a singular correlation energy which comes\nfrom the accumulation, through Feynman \"bubble\" diagrams, of the same non-zero\nmomentum transfer excitations from the free particle ground state, that is, the\nFermi sea for fermions and the Bose-Einstein condensate for bosons. This\nunderstanding paves the way toward deriving the correlation energy of composite\nbosons like atomic dimers and semiconductor excitons, by suggesting Shiva\ndiagrams that have similarity with Feynman \"bubble\" diagrams, the previous\nelementary boson approaches, which hide this physics, being difficult to do so."
    },
    {
        "anchor": "Adiabatic preparation of fractional Chern insulators from an effective\n  thin-torus limit: We explore the quasi one-dimensional (thin torus, or TT) limit of fractional\nChern insulators (FCIs) as a starting point for their adiabatic preparation in\nquantum simulators. Our approach is based on tuning the hopping amplitude in\none direction as an experimentally amenable knob to dynamically change the\neffective aspect ratio of the system. Similar to the TT limit of fractional\nquantum Hall (FQH) systems in the continuum, we find that the hopping-induced\nTT limit adiabatically connects the FCI state to a trivial charge density wave\n(CDW) ground state. This adiabatic path may be harnessed for state preparation\nschemes relying on the initialization of a CDW state followed by the adiabatic\ndecrease of a hopping anisotropy. Our findings are based on the calculation of\nthe excitation gap in a number of FCI models, both on a lattice and consisting\nof coupled wires. By analytical calculation of the gap in the limit of strongly\nanisotropic hopping, we show that its scaling is compatible with the\npreparation of large size FCIs for sufficiently large hopping anisotropy. Our\nnumerical simulations in the framework of exact diagonalization explore the\nfull anisotropy range to corroborate these results.",
        "positive": "Quantum critical dynamics in a spinor Hubbard model quantum simulator: Three-dimensional (3D) strongly correlated many-body systems, especially\ntheir dynamics across quantum phase transitions, are prohibitively difficult to\nbe numerically simulated. We experimentally demonstrate that such complex\nmany-body dynamics can be efficiently studied in a 3D spinor Bose-Hubbard model\nquantum simulator, consisting of antiferromagnetic spinor Bose-Einstein\ncondensates confined in cubic optical lattices. We find novel dynamics and\nscaling effects beyond the scope of existing theories at superfluid-insulator\nquantum phase transitions and highlight spin populations as a new observable to\nprobe the quantum critical dynamics. Our data indicate that the scaling\nexponents are independent of the nature of the quantum phase transitions. We\nalso conduct numerical simulations in lower dimensions using time-dependent\nGutzwiller approximations, which qualitatively describe our observations."
    },
    {
        "anchor": "Frequency beating and damping of breathing oscillations of a\n  harmonically trapped one-dimensional quasicondensate: We study the breathing (monopole) oscillations and their damping in a\nharmonically trapped one-dimensional (1D) Bose gas in the quasicondensate\nregime using a finite-temperature classical field approach. By characterising\nthe oscillations via the dynamics of the density profile's rms width over long\ntime, we find that the rms width displays beating of two distinct frequencies.\nThis means that 1D Bose gas oscillates not at a single breathing mode\nfrequency, as found in previous studies, but as a superposition of two distinct\nbreathing modes, one oscillating at frequency close to $\\simeq\\!\\sqrt{3}\\omega$\nand the other at $\\simeq\\!2\\omega$, where $\\omega$ is the trap frequency. The\nbreathing mode at $\\sim\\!\\sqrt{3}\\omega$ dominates the beating at lower\ntemperatures, deep in the quasicondensate regime, and can be attributed to the\noscillations of the bulk of the density distribution comprised of particles\npopulating low-energy, highly-occupied states. The breathing mode at\n$\\simeq\\!2\\omega$, on the other hand, dominates the beating at higher\ntemperatures, close to the nearly ideal, degenerate Bose gas regime, and is\nattributed to the oscillations of the tails of the density distribution\ncomprised of thermal particles in higher energy states. The two breathing modes\nhave distinct damping rates, with the damping rate of the bulk component being\napproximately four times larger than that of the tails component.",
        "positive": "Control of spin current in a Bose gas by bang-bang pulses: We generate spin currents in an $^{87}$Rb spin-2 Bose-Einstein condensate by\napplication of a magnetic field gradient. The spin current destroys the spin\npolarization, leading to a sudden onset of two-body collisions. In addition,\nthe spin coherence, as measured by the fringe contrast using Ramsey\ninterferometry, is reduced drastically but experiences a weak revival due to\nin-trap oscillations. The spin current can be controlled using periodic $\\pi$\npulses (bang-bang control), producing longer spin coherence times. Our results\nshow that spin coherence can be maintained even in the presence of spin\ncurrents, with applications to quantum sensing in noisy environments."
    },
    {
        "anchor": "Criticality in the Bose-Hubbard model with three-body repulsion: We study the attractive Bose-Hubbard model with a tunable, on-site three-body\nconstraint. It is shown that the critical behavior of the system undergoing a\nphase transition from pair-superfluid to superfluid at unit filling depends on\nthe value of the three-body repulsion. In particular, we calculate critical\nexponents and the central charge governing the quantum phase transition.",
        "positive": "Topological Fulde-Ferrell Superfluids of a Spin-Orbit Coupled Fermi Gas: Topological Fermi superfluids have played the central role in various fields\nof physics. However, all previous studies focus on the cases where Cooper pairs\nhave zero center-of-mass momenta (i.e. normal superfluids). The topology of\nFulde-Ferrell superfluids with nonzero momentum pairings have never been\nexplored until recent findings that Fulde-Ferrell superfluids in a spin-orbit\ncoupled Fermi gas can accommodate Majorana fermions in real space in low\ndimensions and Weyl fermions in momentum space in three dimension. In this\nreview, we first discuss the mechanism of pairings in spin-orbit coupled Fermi\ngases in optical lattices subject to Zeeman fields, showing that spin-orbit\ncoupling as well as Zeeman fields enhance Fulde-Ferrell states while suppress\nLarkin-Ovchinnikov states. We then present the low temperature phase diagram\nincluding both FF superfluids and topological FF superfluids phases in both two\ndimension and three dimension. In one dimension, Majorana fermions as well as\nphase dependent order parameter are visualized. In three dimension, we show the\nproperties of Weyl fermions in momentum space such as anisotropic linear\ndispersion, Fermi arch, and gaplessness away from $k_{\\perp}=0$. Finally, we\ndiscuss some possible methods to probe FF superfluids and topological FF\nsuperfluids in cold atom systems."
    },
    {
        "anchor": "Anomalous phase ordering of a quenched ferromagnetic superfluid: Coarsening dynamics, the canonical theory of phase ordering following a\nquench across a symmetry breaking phase transition, is thought to be driven by\nthe annihilation of topological defects. Here we show that this understanding\nis incomplete. We simulate the dynamics of an isolated spin-1 condensate\nquenched into the easy-plane ferromagnetic phase and find that the mutual\nannihilation of spin vortices does not take the system to the equilibrium\nstate. A nonequilibrium background of long wavelength spin waves remain at the\nBerezinskii-Kosterlitz-Thouless temperature, an order of magnitude hotter than\nthe equilibrium temperature. The coarsening continues through a second much\nslower scale invariant process with a length scale that grows with time as\n$t^{1/3}$. This second regime of coarsening is associated with spin wave energy\ntransport from low to high wavevectors, bringing about the the eventual\nequilibrium state. Because the relevant spin waves are noninteracting, the\ntransport occurs through a dynamic coupling to other degrees of freedom of the\nsystem. The transport displays features of a spin wave energy cascade,\nproviding a potential profitable connection with the emerging field of spin\nwave turbulence. Strongly coupling the system to a reservoir destroys the\nsecond regime of coarsening, allowing the system to thermalise following the\nannihilation of vortices.",
        "positive": "Dipolar evaporation of reactive molecules to below the Fermi temperature: Molecules are the building blocks of matter and their control is key to the\ninvestigation of new quantum phases, where rich degrees of freedom can be used\nto encode information and strong interactions can be precisely tuned. Inelastic\nlosses in molecular collisions, however, have greatly hampered the engineering\nof low-entropy molecular systems. So far, the only quantum degenerate gas of\nmolecules has been created via association of two highly degenerate atomic\ngases. Here, we use an external electric field along with optical lattice\nconfinement to create a two-dimensional (2D) Fermi gas of spin-polarized\npotassium-rubidium (KRb) polar molecules, where elastic, tunable dipolar\ninteractions dominate over all inelastic processes. Direct thermalization among\nthe molecules in the trap leads to efficient dipolar evaporative cooling,\nyielding a rapid increase in phase-space density. At the onset of quantum\ndegeneracy, we observe the effects of Fermi statistics on the thermodynamics of\nthe molecular gas. These results demonstrate a general strategy for achieving\nquantum degeneracy in dipolar molecular gases to explore strongly interacting\nmany-body phases."
    },
    {
        "anchor": "Exact spectral function of the Tonks-Girardeau gas at finite temperature: We report on the derivation of determinant representations for the Green's\nfunctions and spectral function of the trapped Tonks-Girardeau gas on the\nlattice and in the continuum. Our results are valid for any type of statistics\nof the constituent particles, at zero and finite temperature and arbitrary\nconfining potentials, including nonequilibrium scenarios induced by sudden\nchanges of the external potential. In addition, they are also extremely\nefficient and easy to implement numerically with the main computational effort\nbeing represented by the calculation of partial overlaps of the dynamically\nevolved single particle wavefunctions. In the lattice case we show that the\nspectral function of a system with a strong harmonic potential presents only\ntwo singular lines compared with three singular lines in the case of a\nhomogeneous system.",
        "positive": "Observing the emergence of a quantum phase transition -- shell by shell: Many-body physics describes phenomena which cannot be understood looking at a\nsystems' constituents alone. Striking manifestations are broken symmetry, phase\ntransitions, and collective excitations. Understanding how such collective\nbehaviour emerges when assembling a system from individual particles has been a\nvision in atomic, nuclear, and solid-state physics for decades. Here, we\nobserve the few-body precursor of a quantum phase transition from a normal to a\nsuperfluid phase. The transition is signalled by the softening of the mode\nassociated with amplitude vibrations of the order parameter, commonly referred\nto as a Higgs mode. We achieve exquisite control over ultracold fermions\nconfined to two-dimensional harmonic potentials and prepare closed-shell\nconfigurations of 2, 6 and 12 fermionic atoms in the ground state with high\nfidelity. Spectroscopy is then performed on our mesoscopic system while tuning\nthe pair energy from zero to being larger than the shell spacing. Using full\natom counting statistics, we find the lowest resonance to consist of coherently\nexcited pairs only. The distinct non-monotonic interaction dependence of this\nmany-body excitation as well as comparison with numerical calculations allows\nus to identify it as the precursor of the Higgs mode. Our atomic simulator\nopens new pathways to systematically unravel the emergence of collective\nphenomena and the thermodynamic limit particle by particle."
    },
    {
        "anchor": "Nonlinear dynamics of coupled superfluids: Following recent experiments on ultracold dual superflows, we model in this\nwork the dynamics of two harmonically trapped counterflowing superfluids. Using\ncomplementary analytical and numerical approaches, we study the shedding of\nelementary excitations triggered by the relative motion of the two species. We\nexhibit two different excitation mechanisms leading to distinct threshold\nvelocities for the onset of dissipation: in addition to the parametric pair\nproduction present in homogeneous , galilean-invariant systems, we show that\nnon-uniform motion and density inhomogeneities allow for a Landau-like decay\nmechanism where single excitations are produced.",
        "positive": "Triplet pair amplitude in a trapped $s$-wave superfluid Fermi gas with\n  broken spin rotation symmetry: We investigate the possibility that the broken spatial inversion symmetry by\na trap potential induces a spin-triplet Cooper-pair amplitude in an $s$-wave\nsuperfluid Fermi gas. Being based on symmetry considerations, we clarify that\nthis phenomenon may occur, when a spin rotation symmetry of the system is also\nbroken. We also numerically confirm that a triplet pair amplitude is really\ninduced under this condition, using a simple model. Our results imply that this\nphenomenon is already present in a trapped $s$-wave superfluid Fermi gas with\nspin imbalance. As an interesting application of this phenomenon, we point out\nthat one may produce a $p$-wave superfluid Fermi gas, by suddenly changing the\n$s$-wave pairing interaction to a $p$-wave one by using the Feshbach resonance\ntechnique. Since a Cooper pair is usually classified into the spin-singlet (and\neven-parity) state and the spin-triplet (and odd-parity) state, our results\nwould be useful in considering how to mix them with each other in a superfluid\nFermi gas. Such admixture has recently attracted much attention in the field of\nnon-centrosymmetric superconductivity, so that our results would also\ncontribute to the further development of this research field, on the viewpoint\nof cold Fermi gas physics."
    },
    {
        "anchor": "Experimental Results Related to Discrete Nonlinear Schr\u00f6dinger\n  Equations: In this chapter, we discuss experiments that realize the discrete nonlinear\nSchr\\\"odinger (DNLS) equations. The relevance of such descriptions arises from\nthe competition of three common features: nonlinearity, dispersion, and a\nmedium to large level of (periodic, quasiperiodic, or random) discreteness in\nspace. DNLS equations have been especially prevalent in atomic and molecular\nphysics in the study of Bose-Einstein condensates in optical lattices or\nsuperlattices; and in nonlinear optics in the description of pulse propagation\nin waveguide arrays and photorefractive crystals. New experiments in both\nnonlinear optics and Bose-Einstein condensation provide new challenges for DNLS\nmodels, and DNLS and related equations have also recently been used to make\nimportant predictions in novel physical settings such as the study of composite\nmetamaterials and arrays of superconducting devices.",
        "positive": "The confinement induced resonance in spin-orbit coupled cold atoms with\n  Raman coupling: We investigate the confinement induced resonance in spin-orbit coupled cold\natoms with Raman coupling. We find that the quasi-bound levels induced by the\nspin-orbit coupling and Raman coupling result in the Feshbach-type resonances.\nFor sufficiently large Raman coupling, the bound states in one dimension exist\nonly for sufficiently strong attractive interaction. Furthermore, the bound\nstates in quasi-one dimension exist only for sufficient large ratio of the\nlength scale of confinement to three dimensional s-wave scattering length. The\nRaman coupling substantially changes the confinement-induced resonance\nposition. We give a proposal to realize confinement induced resonance by\nincreasing the Raman coupling strength in experiments."
    },
    {
        "anchor": "Noise correlations of two-dimensional Bose gases: We analyze density-density correlations of expanding clouds of weakly\ninteracting two-dimensional Bose gases below and above the\nBerezinskii-Kosterlitz-Thouless transition, with particular focus on short-time\nexpansions. During time-of-flight expansion, phase fluctuations of the trapped\nsystem translate into density fluctuations, in addition to the density\nfluctuations that exist in in-situ. We calculate the correlations of these\nfluctuations both in real space and in momentum space, and derive analytic\nexpressions in momentum space. Below the transition, the correlation functions\nshow an oscillatory behavior, controlled by the scaling exponent of the\nquasi-condensed phase, due to constructive interference. We argue that this can\nbe used to extract the scaling exponent of the quasi-condensate experimentally.\nAbove the transition, the interference is rapidly suppressed when the atoms\ntravel an average distance beyond the correlation length. This can be used to\ndistinguish the two phases qualitatively.",
        "positive": "Floquet integrability and long-range entanglement generation in the\n  one-dimensional quantum Potts model: We develop a Floquet protocol for long-range entanglement generation in the\none-dimensional quantum Potts model, which generalizes the transverse-filed\nIsing model by allowing each spin to have $n>2$ states. We focus on the case of\n$n=3$, so that the model describes a chain of qutrits. The suggested protocol\ncreates qutrit Bell-like pairs with non-local long-range entanglement that\nspans over the entire chain. We then conjecture that the proposed Floquet\nprotocol is integrable and explicitly construct a few first non-trivial\nconserved quantities that commute with the stroboscopic evolution operator. Our\nanalysis of the Floquet integrability relies on the deep connection between the\nquantum Potts model and a much broader class of models described by the\nTemperley-Lieb algebra. We work at the purely algebraic level and our results\non Floquet integrability are valid for any representation of the Temperley-Lieb\nalgebra. We expect that our findings can be probed with present experimental\nfacilities using Rydberg programmable quantum simulators and can find various\napplications in quantum technologies."
    },
    {
        "anchor": "Simulating Z_2 topological insulators with cold atoms in a\n  one-dimensional optical lattice: We propose an experimental scheme to simulate and detect the properties of\ntime-reversal invariant topological insulators, using cold atoms trapped in\none-dimensional bichromatic optical lattices. This system is described by a\none-dimensional Aubry-Andre model with an additional SU(2) gauge structure,\nwhich captures the essential properties of a two-dimensional Z2 topological\ninsulator. We demonstrate that topologically protected edge states, with\nopposite spin orientations, can be pumped across the lattice by sweeping a\nlaser phase adiabatically. This process constitutes an elegant way to transfer\ntopologically protected quantum states in a highly controllable environment. We\ndiscuss how density measurements could provide clear signatures of the\ntopological phases emanating from our one-dimensional system.",
        "positive": "Dynamical Spectral Response of Fractonic Quantum Matter: Quantum many-body systems with fractonic excitations can realize fascinating\nphases of matter. Here, we study the low-energy excitations of a constrained\nBose-Hubbard model in one dimension, which conserves the center of mass or,\nequivalently, the dipole moment in addition to the particle number. This model\nis known to realize fractonic phases, including a dipole Mott insulator, a\ndipole Luttinger liquid, and a metastable dipole supersolid. We use tensor\nnetwork methods to compute spectral functions from the dynamical response of\nthe system and verify predictions from low-energy field theories of the\ncorresponding ground state phases. We demonstrate the existence of gapped\nexcitations compatible with strong coupling results in a dipole Mott insulator,\nlinear sound modes characteristic of a Luttinger liquid of dipoles, and soft\nquadratic modes at both zero and finite momenta in a supersolid state with\ncharge density wave order and phase coherence at non-integer filling."
    },
    {
        "anchor": "Persistent currents in spinor condensates: We create and study persistent currents in a toroidal two-component Bose gas,\nconsisting of $^{87}$Rb atoms in two different spin states. For a large\nspin-population imbalance we observe supercurrents persisting for over two\nminutes. However we find that the supercurrent is unstable for spin\npolarisation below a well defined critical value. We also investigate the role\nof phase coherence between the two spin components and show that only the\nmagnitude of the spin-polarisation vector, rather than its orientation in spin\nspace, is relevant for supercurrent stability.",
        "positive": "Equilibration Dynamics of Strongly Interacting Bosons in 2D Lattices\n  with Disorder: Motivated by recent optical lattice experiments [J.-y. Choi et al., Science\n352, 1547 (2016)], we study the dynamics of strongly interacting bosons in the\npresence of disorder in two dimensions. We show that Gutzwiller mean-field\ntheory (GMFT) captures the main experimental observations, which are a result\nof the competition between disorder and interactions. Our findings highlight\nthe difficulty in distinguishing glassy dynamics, which can be captured by\nGMFT, and many-body localization, which cannot be captured by GMFT, and\nindicate the need for further experimental studies of this system."
    },
    {
        "anchor": "Observation of a partially rotating superfluid of exciton-polariton: Rotation of a container holding a viscous fluid forms a vortex which grows\nwith increasing angular velocity. A superfluid, however, is intrinsically\ndifferent from these normal fluids because its rotation is quantized. Even if a\ncontainer of superfluid is rotating, the fluid itself remains still until a\ncritical velocity is reached. Beyond the critical velocity, all the particles\nconspire to suddenly pick up an angular momentum of $\\hbar$ each and forms a\nquantized vortex. As a result, a superfluid is known to increase its rotation\nby a total angular momentum of $N\\hbar$. In this letter, we show that\nexciton-polariton superfluid can split into an irrotational part and a\nrotational part. The relative ratio between the two states can be controlled by\neither pump beam's power or spot size. Consequently, angular momentum of\nexciton-polariton superfluid can be tuned from zero to $N\\hbar$ continuously.\nThis striking observation sets the stage for studying non-equilibrium\nproperties of a superfluid with exciton-polaritons.",
        "positive": "Collective many-body bounce in the breathing-mode oscillations of a\n  Tonks-Girardeau gas: We analyse the breathing-mode oscillations of a harmonically quenched\nTonks-Giradeau (TG) gas using an exact finite-temperature dynamical theory. We\npredict a striking collective manifestation of impenetrability---a collective\nmany-body bounce effect. The effect, while being invisible in the evolution of\nthe in-situ density profile of the gas, can be revealed through a nontrivial\nperiodic narrowing of its momentum distribution, taking place at twice the rate\nof the fundamental breathing-mode frequency. We identify physical regimes for\nobserving the many-body bounce and construct the respective nonequilibrium\nphase diagram as a function of the quench strength and the initial temperature\nof the gas. We also develop a finite-temperature hydrodynamic theory of the TG\ngas, wherein the many-body bounce is explained by an increased thermodynamic\npressure of the gas during the isentropic compression, which acts as a\npotential barrier at the inner turning points of the breathing cycle."
    },
    {
        "anchor": "Interaction blockade for bosons in an asymmetric double well: The interaction blockade phenomenon isolates the motion of a single quantum\nparticle within a multi-particle system, in particular for coherent\noscillations in and out of a region affected by the blockade mechanism. For\nidentical quantum particles with Bose statistics, the presence of the other\nparticles is still felt by a bosonic stimulation factor $\\sqrt{N}$ that speeds\nup the coherent oscillations, where $N$ is the number of bosons. Here we\npropose an experiment to observe this enhancement factor with a small number of\nbosonic atoms. The proposed protocol realises an asymmetric double well\npotential with multiple optical tweezer laser beams. The ability to adjust bias\nindependently of the coherent coupling between the wells allows the potential\nto be loaded with different particle numbers while maintaining the resonance\ncondition needed for coherent oscillations. Numerical simulations with up to\nthree bosons in a realistic potential generated by three optical tweezers\npredict that the relevant avoided level crossing can be probed and the expected\nbosonic enhancement factor observed.",
        "positive": "Emergence of fluctuating hydrodynamics in chaotic quantum systems: A fundamental principle of chaotic quantum dynamics is that local subsystems\neventually approach a thermal equilibrium state. Large subsystems thermalize\nslower: their approach to equilibrium is limited by the hydrodynamic build-up\nof large-scale fluctuations. For classical out-of-equilibrium systems, the\nframework of macroscopic fluctuation theory (MFT) was recently developed to\nmodel the hydrodynamics of fluctuations. We perform large-scale quantum\nsimulations that monitor the full counting statistics of particle-number\nfluctuations in hard-core boson ladders, contrasting systems with ballistic and\nchaotic dynamics. We find excellent agreement between our results and MFT\npredictions, which allows us to accurately extract diffusion constants from\nfluctuation growth. Our results suggest that large-scale fluctuations of\nisolated quantum systems display emergent hydrodynamic behavior, expanding the\napplicability of MFT to the quantum regime."
    },
    {
        "anchor": "Detecting Fermi Surface Nesting Effect for Fermionic Dicke Transition by\n  Trap Induced Localization: Recently, the statistical effect of fermionic superradiance is approved by\nseries of experiments both in free space and in a cavity. The Pauli blocking\neffect can be visualized by a 1/2 scaling of Dicke transition critical pumping\nstrength against particle number Nat for fermions in a trap. However, the Fermi\nsurface nesting effect, which manifests the enhancement of superradiance by\nFermi statistics is still very hard to be identified. Here we studied the\ninfluence of localized fermions on the trap edge when both pumping optical\nlattice and the trap are presented. We find due to localization, the\nstatistical effect in superradiant transition is enhanced. Two new scalings of\ncritical pumping strength are observed as 4/3, and 2/3 for mediate particle\nnumber, and the Pauli blocking scaling 1/3 (2d case) in large particle number\nlimit is unaffected. Further, we find the 4/3 scaling is subject to a power law\nincreasing with rising ratio between recoil energy and trap frequency in\npumping laser direction. The divergence of this scaling of critical pumping\nstrength against $N_{\\rm at}$ in $E_R/\\omega_x\\rightarrow+\\infty$ limit can be\nidentified as the Fermi surface nesting effect. Thus we find a practical\nexperimental scheme for visualizing the long-desired Fermi surface nesting\neffect with the help of trap induced localization in a two-dimensional Fermi\ngas in a cavity.",
        "positive": "Measuring quantized circular dichroism in ultracold topological matter: The topology of two-dimensional materials traditionally manifests itself\nthrough the quantization of the Hall conductance, which is revealed in\ntransport measurements. Recently, it was predicted that topology can also give\nrise to a quantized spectroscopic response upon subjecting a Chern insulator to\na circular drive: Comparing the frequency-integrated depletion rates associated\nwith drives of opposite orientations leads to a quantized response dictated by\nthe topological Chern number of the populated Bloch band. Here we\nexperimentally demonstrate this intriguing topological effect for the first\ntime, using ultracold fermionic atoms in topological Floquet bands. In\naddition, our depletion-rate measurements also provide a first experimental\nestimation of the Wannier-spread functional, a fundamental geometric property\nof Bloch bands. Our results establish topological spectroscopic responses as a\nversatile probe, which could be applied to access the geometry and topology of\nmany-body quantum systems, such as fractional Chern insulators."
    },
    {
        "anchor": "Quantum simulation of a lattice Schwinger model in a chain of trapped\n  ions: We discuss how a lattice Schwinger model can be realized in a linear ion\ntrap, allowing a detailed study of the physics of Abelian lattice gauge\ntheories related to one-dimensional quantum electrodynamics. Relying on the\nrich quantum-simulation toolbox available in state-of-the-art trapped-ion\nexperiments, we show how one can engineer an effectively gauge-invariant\ndynamics by imposing energetic constraints, provided by strong Ising-like\ninteractions. Applying exact diagonalization to ground-state and time-dependent\nproperties, we study the underlying microscopic model, and discuss undesired\ninteraction terms and other imperfections. As our analysis shows, the proposed\nscheme allows for the observation in realistic setups of spontaneous parity-\nand charge-symmetry breaking, as well as false-vacuum decay. Besides an\nimplementation aimed at larger ion chains, we also discuss a minimal setting,\nconsisting of only four ions in a simpler experimental setup, which enables to\nprobe basic physical phenomena related to the full many-body problem. The\nproposal opens a new route for analog quantum simulation of high-energy and\ncondensed-matter models where gauge symmetries play a prominent role.",
        "positive": "Entanglement prethermalization: Locally thermal but non-locally\n  non-thermal states in a one-dimensional Bose gas: A well-isolated system often shows relaxation to a quasi-stationary state\nbefore reaching thermal equilibrium. Such a prethermalization has attracted\nconsiderable interest recently in association with closely related fundamental\nproblems of relaxation and thermalization of isolated quantum systems.\nMotivated by the recent experiment in ultracold atoms, we study the dynamics of\na one-dimensional Bose gas which is split into two subsystems, and find that\nindividual subsystems relax to Gibbs states, yet the entire system does not due\nto quantum entanglement. In view of recent experimental realization on a small\nwell-defined number of ultracold atoms, our prediction based on exact few-body\ncalculations is amenable to experimental test."
    },
    {
        "anchor": "Quartet Superfluid in Two-dimensional Mass-imbalanced Fermi Mixtures: Quartet superfluid (QSF) is a distinct type of fermion superfluidity that\nexhibits high-order correlation beyond the conventional BCS pairing paradigm.\nIn this Letter, we report the emergent QSF in 2D mass-imbalanced Fermi mixtures\nwith two-body contact interactions. This is facilitated by the formation of\nquartet bound state in vacuum that consists of a light atom and three heavy\nfermions. For an optimized heavy-light number ratio $3:1$, we identify QSF as\nthe ground state in a considerable parameter regime of mass imbalance and 2D\ncoupling strength. Its unique high-order correlation can be manifested in the\nmomentum-space crystallization of pairing field and density distribution of\nheavy fermions. Our results can be readily detected in Fermi-Fermi mixtures\nnowadays realized in cold atoms laboratories, and meanwhile shed light on\nexotic superfluidity in a broad context of mass-imbalanced fermion mixtures.",
        "positive": "The dynamics of dark solitons in a trapped superfluid Fermi gas: We study soliton oscillations in a trapped superfluid Fermi gas across the\nBose-Einstein condensate to Bardeen-Cooper-Schrieffer (BEC-BCS) crossover. We\nderive an exact equation relating the phase jump across the soliton to its\nenergy, and hence obtain an expression for the soliton period. Our analytic\napproach is supported by simulations of the time-dependent Bogoliubov-de Gennes\nequations, which show that the period dramatically increases as the soliton\nbecomes shallower on the BCS side of the resonance. Finally, we propose an\nexperimental protocol to test our predictions."
    },
    {
        "anchor": "Dynamics of a nonlinear quantum oscillator under non-Markovian pumping: We consider dynamics of a quantum nonlinear oscillator subjected to\nnon-Markovian pumping. Models of this kind can describe formation of\nexciton-polariton Bose-Einstein condensates in course of stimulated scattering\nand relaxation of reservoir excitons. Using the Markovian embedding techniques,\nwe obtain stochastic differential equations of motion with an additional degree\nof freedom corresponding to dynamical memory. It is shown that the oscillator\nasymptotically tends to the intrinsically non-Markovian stable fixed point\ncorresponding to constant product of oscillator amplitude and modulo of the\nmemory variable. The state corresponding to this point exhibits unlimited\ngrowth of population, with the growth rate that decreases with time. Our\nresults show that the Markovian behavior could be observed only within some\nlimited early stage of oscillator evolution provided that decay of dynamical\nmemory is sufficiently fast. Transition from the Markovian regime to\nnon-Markovian one with increasing time is linked to phase shift of the pumping\nterm. Coherence properties of the oscillator are studied. It was found that\ninteraction between particles delimits growth of condensate population, thereby\nimpeding formation of Bose-Einstein condensate.",
        "positive": "The nonlinear Dirac equation: Preparation and stability of relativistic\n  vortices in Bose-Einstein condensates: We propose a detailed experimental procedure for preparing relativistic\nvortices, governed by the nonlinear Dirac equation, in a two-dimensional\nBose-Einstein condensate (BEC) in a honeycomb optical lattice. Our setup\ncontains Dirac points, in direct analogy to graphene. We determine a range of\npractical values for all relevant physical parameters needed to realize\nrelativistic vortices in a BEC of $^{87}\\mathrm{Rb}$ atoms. Seven distinct\nvortex types, including Anderson-Toulouse and Mermin-Ho skyrmion textures and\nhalf-quantum vortices, are obtained, and their discrete spectra and stability\nproperties are calculated in a weak harmonic trap. We predict that most\nvortices are stable with a lifetime between $1$ and $10$ seconds."
    },
    {
        "anchor": "Preparing and probing Chern bands with cold atoms: The present Chapter discusses methods by which topological Bloch bands can be\nprepared in cold-atom setups. Focusing on the case of Chern bands for\ntwo-dimensional systems, we describe how topological properties can be\ntriggered by driving atomic gases, either by dressing internal levels with\nlight or through time-periodic modulations. We illustrate these methods with\nconcrete examples, and we discuss recent experiments where geometrical and\ntopological band properties have been identified.",
        "positive": "Double-peak specific heat anomaly and correlations in the Bose-Hubbard\n  model: Considering the thermodynamics of bosons in a lattice described by the\nBose-Hubbard Hamiltonian, we report the occurrence of anomalous double peaks in\ntheir specific heat dependence on temperature. This feature, usually associated\nwith a high geometrical frustration, can also be a consequence of a purely\nenergetic competition. By employing self-energy functional calculations\ncombined with finite-temperature perturbation theory, we propose a mechanism\nbased on ground-state degeneracies expressed as residual entropies. A general\ndecomposition of the specific heat regarding all possible transitions between\nthe system's eingenvalues provides an insight into the nature of each maximum.\nFurthermore, we address how the model parameters modify the structure of these\npeaks based on its spectral properties and atom-atom correlation function."
    },
    {
        "anchor": "Regulating atomic imbalance in double-well lattices: An insulating optical lattice with double-well sites is considered. In the\ncase of the unity filling factor, an effective Hamiltonian in the pseudospin\nrepresentation is derived. A method is suggested for manipulating the\nproperties of the system by varying the shape of the double-well potential. In\nparticular, it is shown that the atomic imbalance can be varied at will and a\nkind of the Morse-alphabet sequences can be created.",
        "positive": "Local atom-number fluctuations in quantum gases at finite temperature: We investigate the number fluctuations in small cells of quantum gases\npointing out important deviations from the thermodynamic limit fixed by the\nisothermal compressibility. Both quantum and thermal fluctuations in weakly as\nwell as highly compressible fluids are considered. For the two-dimensional (2D)\nsuperfluid Bose gas we find a significant quenching of fluctuations with\nrespect to the thermodynamic limit, in agreement with recent experimental\nfindings. An enhancement of the thermal fluctuations is instead predicted for\nthe 2D dipolar superfluid Bose gas, which becomes dramatic when the size of the\nsample cell is of the order of the wavelength of the rotonic excitation induced\nby the interaction."
    },
    {
        "anchor": "Spin Caloritronics in Noncondensed Bose Gases: We consider coupled spin and heat transport in a two-component, atomic Bose\ngas in the noncon- densed state. We find that the transport coefficients show a\ntemperature dependence reflecting the bosonic enhancement of scattering, and\ndiscuss experimental signatures of the spin-heat coupling in spin accumulation\nand total dissipation. Inside the critical region of Bose-Einstein\ncondensation, we find anomalous behavior of the transport coefficients, and in\nparticular, an enhancement for the spin caloritronics figure of merit that\ndetermines the thermodynamic efficiency of spin-heat conversion.",
        "positive": "Inhomogeneous Fulde-Ferrell superfluidity in spin-orbit coupled atomic\n  Fermi gases: Inhomogeneous superfluidity lies at the heart of many intriguing phenomena in\nquantum physics. It is believed to play a central role in unconventional\norganic or heavy-fermion superconductors, chiral quark matter, and neutron star\nglitches. However, so far even the simplest form of inhomogeneous\nsuperfluidity, the Fulde-Ferrell (FF) pairing state with a single\ncentre-of-mass momentum, is not conclusively observed due to the intrinsic\ncomplexibility of any realistic Fermi systems in nature. Here we theoretically\npredict that the controlled setting of ultracold fermionic atoms with synthetic\nspin-orbit coupling induced by a two-photon Raman process, demonstrated\nrecently in cold-atom laboratories, provides a promising route to realize the\nlong-sought FF superfluidity. At experimentally accessible low temperatures\n(i.e., $0.05T_{F}$, where $T_{F}$ is the Fermi temperature), the FF superfluid\nstate dominates the phase diagram, in sharp contrast to the conventional case\nwithout spin-orbit coupling. We show that the finite centre-of-mass momentum\ncarried by Cooper pairs is directly measurable via momentum-resolved\nradio-frequency spectroscopy. Our work opens the way to direct observation and\ncharacterization of inhomogeneous superfluidity."
    },
    {
        "anchor": "Equilibration and GGE for hard wall boundary conditions: In this work we present an analysis of a quench for the repulsive\nLieb-Liniger gas confined to a large box with hard wall boundary conditions. We\nstudy the time average of local correlation functions and show that both the\nquench action approach and the GGE formalism are applicable for the long time\naverage of local correlation functions. We find that the time average of the\nsystem corresponds to an eigenstate of the Lieb-Liniger Hamiltonian and that\nthis eigenstate is related to an eigenstate of a Lieb-Liniger Hamiltonian with\nperiodic boundary conditions on an interval of twice the length and with twice\nas many particles (a doubled system). We further show that local operators with\nsupport far away from the boundaries of the hard wall have the same expectation\nvalues with respect to this eigenstate as corresponding operators for the\ndoubled system. We present an example of a quench where the gas is initially\nconfined in several moving traps and then released into a bigger container, an\napproximate description of the Newton cradle experiment. We calculate the time\naverage of various correlation functions for long times after the quench.",
        "positive": "Quantum knots in Bose-Einstein condensates created by counterdiabatic\n  control: We theoretically study the creation of knot structures in the polar phase of\nspin-1 BECs using the counterdiabatic protocol in an unusual fashion. We\nprovide an analytic solution to the evolution of the external magnetic field\nthat is used to imprint the knots. As confirmed by our simulations using the\nfull three-dimensional spin-1 Gross-Pitaevskii equation, our method allows for\nthe precise control of the Hopf charge as well as the creation time of the\nknots. The knots with Hopf charge exceeding unity display multiple nested Hopf\nlinks."
    },
    {
        "anchor": "Spatiotemporal coherence of non-equilibrium multimode photon condensates: We report on the observation of quantum coherence of Bose-Einstein condensed\nphotons in an optically-pumped, dye-filled microcavity. We find that coherence\nis long-range in space and time above condensation threshold, but short-range\nbelow threshold, compatible with thermal-equilibrium theory. Far above\nthreshold, the condensate is no longer at thermal equilibrium and is fragmented\nover non-degenerate, spatially overlapping modes. A microscopic theory\nincluding cavity loss, molecular structure and relaxation shows that this\nmultimode condensation is similar to multimode lasing induced by imperfect gain\nclamping.",
        "positive": "Temperature dependence of an Efimov resonance in $^{39}\\mathrm{K}$: Ultracold atomic gases are an important testing ground for understanding\nfew-body physics. In particular, these systems enable a detailed study of the\nEfimov effect. We use ultracold $^{39}\\mathrm{K}$ to investigate the\ntemperature dependence of an Efimov resonance. The shape and position of the\nobserved resonance are analyzed by employing an empirical fit, and universal\nfinite-temperature zero-range theory. Both procedures suggest that the\nresonance position shifts towards lower absolute scattering lengths when\napproaching the zero-temperature limit. We extrapolate this shift to obtain an\nestimate of the three-body parameter at zero temperature. A surprising finding\nof our study is that the resonance becomes less prominent at lower\ntemperatures, which currently lacks a theoretical description and implies\nphysical effects beyond available models. Finally, we present measurements\nperformed near the Feshbach resonance center and discuss the prospects for\nobserving the second Efimov resonance in $^{39}\\mathrm{K}$."
    },
    {
        "anchor": "Correlation in Momentum Space of Tonks-Girardeau Gas: We investigate the correlation properties of the ground state of\nTonks-Gigrardeal gases in the momentum space. With Bose-Fermi mapping method\nthe exact ground state wavefunction in coordinate space can be obtained basing\non the wavefunction of spin-polarized Fermions. By Fourier transformation we\nobtain the ground state wavefunction in momentum space, and therefore the\nmomentum distribution, pair correlation and the reduced one-body density matrix\n(ROBDM) in momentum space. The ROBDM in momentum space is the Fourier\ntransformation of the ROBDM in coordinate space and the pair correlation in\nmomentun space is the Fourier transformation of the reduced two-body density\nmatrix in coordinate space. The correlations in momentum space display larger\nvalues only in small momentum region and vanish in most other regions. The\nlowest natural orbital and occupation distribution are also obtained.",
        "positive": "Cesium bright matter-wave solitons and soliton trains: A study of bright matter-wave solitons of a cesium Bose-Einstein condensate\n(BEC) is presented. Production of a single soliton is demonstrated and\ndependence of soliton atom number on the interatomic interaction is\ninvestigated. Formation of soliton trains in the quasi one-dimensional\nconfinement is shown. Additionally, fragmentation of a BEC has been observed\noutside confinement, in free space. In the end a double BEC production setup\nfor studying soliton collisions is described."
    },
    {
        "anchor": "Soliton interferometry with very narrow barriers obtained from spatially\n  dependent dressed states: Bright solitons in atomic Bose--Einstein condensates are strong candidates\nfor high precision matter-wave interferometry, as their inherent stability\nagainst dispersion supports long interrogation times. An analog to a beam\nsplitter is then a narrow potential barrier. A very narrow barrier is desirable\nfor interferometric purposes, but in a typical realisation using a blue-detuned\noptical dipole potential, the width is limited by the laser wavelength. We\ninvestigate a soliton interferometry scheme using the geometric scalar\npotential experienced by atoms in a spatially dependent dark state to overcome\nthis limit. We propose a possible implementation and numerically probe the\neffects of deviations from the ideal configuration.",
        "positive": "Temporal coherence of one-dimensional non-equilibrium quantum fluids: We theoretically investigate the time dependence of the first order coherence\nfunction for a one-dimensional driven dissipative non-equilibrium condensate.\nSimulations on the generalized Gross-Pitaevskii equation (GGPE) show that the\ncharacteristic time scale of exponential decay agrees with the linearized\nBogoliubov theory in the regime of large interaction energy. For very weak\ninteractions, the temporal correlation deviates from the linear theory, and\ninstead respects the dynamic scaling of the Kardar-Parisi-Zhang universality\nclass. This nonlinear dynamics is found to be quantitatively captured by a\nnoisy Kuramoto-Sivashinsky equation for the phase dynamics."
    },
    {
        "anchor": "Finite-temperature dynamics of a bosonic Josephson junction: In the framework of the stochastic projected Gross-Pitaevskii equation we\ninvestigate finite-temperature dynamics of a bosonic Josephson junction (BJJ)\nformed by a Bose-Einstein condensate of atoms in a two-well trapping potential.\nWe extract the characteristic properties of the BJJ from the stationary\nfinite-temperature solutions and compare the dynamics of the system with the\nresistively shunted Josephson model. Analyzing the decay dynamics of the\nrelative population imbalance we estimate the effective normal conductance of\nthe junction induced by thermal atoms. The calculated normal conductance at\nvarious temperatures is then compared with predictions of the noise-less model\nand the model of ballistic transport of thermal atoms.",
        "positive": "Dissipative Preparation of Many-Body Spin Steady States Using Trapped\n  Ultracold Atoms: This article presents a dissipative method of creating a spin steady state,\nor a state whose spin expectation values approaches a fixed value over time,\nusing a trapped gas of ultracold atoms coupled to a background BEC. The\nultracold atoms are trapped in a double potential well embedded in a wide\nharmonic trap, which has a higher energy level than the double wells. The\ntrapped atoms are then excited out of the double well trap into the harmonic\ntrap using Raman lasers. Due to the coupling of the system to the background\nBEC, the atoms are then able to return to the double potential well by emitting\nan excitation into the background BEC, which serves as a reservoir of these\nexcitations. By repeatedly coupling and uncoupling the trapped ultracold atoms\nand the background BEC over fixed intervals of time, the expectation value of\nthe total spin of these atoms will, over time, reach a steady - state value."
    },
    {
        "anchor": "SU(N) Fermions in a One-Dimensional Harmonic Trap: We conduct a theoretical study of SU(N) fermions confined by a\none-dimensional harmonic potential. Firstly, we introduce a new numerical\napproach for solving the trapped interacting few-body problem, by which one may\nobtain accurate energy spectra across the full range of interaction strengths.\nIn the strong-coupling limit, we map the SU(N) Hamiltonian to a spin-chain\nmodel. We then show that an existing, extremely accurate ansatz - derived for a\nHeisenberg SU(2) spin chain - is extendable to these N-component systems.\nLastly, we consider balanced SU(N) Fermi gases that have an equal number of\nparticles in each spin state for N=2, 3, 4. In the weak- and strong-coupling\nregimes, we find that the ground-state energies rapidly converge to their\nexpected values in the thermodynamic limit with increasing atom number. This\nsuggests that the many-body energetics of N-component fermions may be\naccurately inferred from the corresponding few-body systems of N\ndistinguishable particles.",
        "positive": "Weak ergodicity breaking through the lens of quantum entanglement: Recent studies of interacting systems of quantum spins, ultracold atoms and\ncorrelated fermions have shed a new light on how isolated many-body systems can\navoid rapid equilibration to their thermal state. It has been shown that many\nsuch systems can \"weakly\" break ergodicity: they possess a small number of\nnon-thermalising eigenstates and/or display slow relaxation from certain\ninitial conditions, while majority of other initial states equilibrate fast,\nlike in conventional thermalising systems. In this chapter, we provide a\npedagogical introduction to weak ergodicity breaking phenomena, including\nHilbert space fragmentation and quantum many-body scars. Central to these\ndevelopments have been the tools based on quantum entanglement, in particular\nmatrix product states and tangent space techniques, which have allowed to\nanalytically construct non-thermal eigenstates in various non-integrable\nquantum models, and to explore semiclassical quantisation of such systems in\nthe absence of a large-N or mean field limit. We also discuss recent\nexperimental realisations of weak ergodicity breaking phenomena in systems of\nRydberg atoms and tilted optical lattices."
    },
    {
        "anchor": "Glitches in rotating supersolids: Glitches, spin-up events in neutron stars, are of prime interest as they\nreveal properties of nuclear matter at subnuclear densities. We numerically\ninvestigate the glitch mechanism due to vortex unpinning using analogies\nbetween neutron stars and dipolar supersolids. We explore the vortex and\ncrystal dynamics during a glitch and its dependence on the supersolid quality,\nproviding a tool to study glitches from different radial depths of a neutron\nstar. Benchmarking our theory against neutron star observations, our work will\nopen a new avenue for the quantum simulation of stellar objects from Earth.",
        "positive": "Ultrafast tristable spin memory of a coherent polariton gas: Nonlinear interactions in coherent gases are not only at the origin of of\nbright and dark solitons and superfluids. At the same time, they give rise to\nphenomena such as multistability, which hold great promise for the development\nof advanced photonic and spintronic devices. In particular, spinor\nmultistability in strongly-coupled semiconductor microcavities shows that the\nspin of hundreds of exciton-polaritons can be coherently controlled, opening\nthe route to spin-optronic devices such as ultrafast spin memories, gates or\neven neuronal communication schemes. Here, we demonstrate that switching\nbetween the stable spin states of a driven polariton gas can be controlled by\nultrafast optical pulses. While such a long-lived spin memory necessarily\nrelies on strong and anisotropic spinor interactions within the coherent\npolariton gas, we also highlight the crucial role of nonlinear losses and\nformation of a non-radiative particle reservoir for ultrafast spin-switching."
    },
    {
        "anchor": "Bessel Vortices in Spin-Orbit Coupled Spin-1 Bose-Einstein Condensates: We investigate the stationary vortex solutions in two-dimensional (2D) Rashba\nspin-orbit (SO) coupled spin-1 Bose-Einstein condensate (BEC). By introducing\nthe generalized momentum operator, the linear version of the system can be\nsolved exactly and its solutions are a set of the Bessel vortices. Based on the\nlinear version solutions, the stationary vortex solutions of the full nonlinear\nsystem are constructed and determined entirely by the variational\napproximation. The results show that the variational results are in good\nagreement with the numerical ones. By means of the variational results, the\nvortex ground state phase-transition between the stationary vortex solutions,\nstability, and the unit Bloch vector textures are discussed in detail. The\nresults have the potential to be realized in experiment.",
        "positive": "Thermal suppression of phase separation in condensate mixtures: We examine the role of thermal fluctuations in binary condensate mixtures of\ndilute atomic gases. In particular, we use Hartree-Fock-Bogoliubov with Popov\napproximation to probe the impact of non-condensate atoms to the phenomenon of\nphase-separation in two-component Bose-Einstein condensates. We demonstrate\nthat, in comparison to $T=0$, there is a suppression in the phase-separation of\nthe binary condensates at $T\\neq0$. This arises from the interaction of the\ncondensate atoms with the thermal cloud. We also show that, when $T\\neq0$ it is\npossible to distinguish the phase-separated case from miscible from the trends\nin the correlation function. However, this is not the case at $T=0$."
    },
    {
        "anchor": "Single atom counting in a two-color magneto-optical trap: Recording the fluorescence of a magneto-optical trap (MOT) is a standard tool\nfor measuring atom numbers in experiments with ultracold atoms. When trapping\nfew atoms in a small MOT, the emitted fluorescence increases with the atom\nnumber in discrete steps, which allows to measure the atom number with\nsingle-particle resolution. Achieving such single particle resolution requires\nstringent minimization of stray light from the MOT beams, which is very\ndifficult to achieve in experimental setups that require in-vacuum components\nclose to the atoms. Here, we present a modified scheme that addresses this\nissue: Instead of collecting the fluorescence on the MOT (D2) transition, we\nscatter light on an additional probing (D1) transition and collect this\nfluorescence with a high-resolution microscope while filtering out the intense\nMOT light. Using this scheme, we are able to reliably distinguish up to 17\n$^{40}$K atoms with an average classification fidelity of 95 \\%.",
        "positive": "Optimal configurations and \"Pauli crystals\" of quantum clusters: Broken rotational and translational symmetries are the hallmarks of solid\nstate materials. In contrast, quantum liquids and gases do not exhibit such\nproperties. However, if we regard the logarithm of the absolute square of a\nquantum liquid as an energy ${\\cal E}= -{\\rm ln}|\\Psi|^2$, a geometric pattern\nnaturally occurs at the minimum, i.e. the optimal configuration. Such geometric\npatterns have recently been studied for non-interacting fermions, and have been\nnamed \"Pauli crystals\". However, such patterns exist in all interacting gases\n(Bose or Fermi), independent of statistics. Here, we present an algorithm to\ndetermine the optimal configurations of quantum clusters solely from the images\nof their densities and without theoretical inputs. We establish its validity by\nrecovering a number of exact results, showing that it can identify the changes\nin the cluster's ground state which corresponds to phase transitions in bulk\nsystems."
    },
    {
        "anchor": "Studying Superfluid Transition of a Dilute Bose Gas by Conserving\n  Approximations: We consider the Bose-Einstein transition of homogeneous weakly interacting\nspin-0 particles based on the normal-state Phi-derivable approximation.\nSelf-consistent calculations of Green's function and the chemical potential\nwith several approximate Phi's are performed numerically as a function of\ntemperature near Tc, which exhibit qualitatively different results. The ladder\napproximation apparently shows a continuous transition with the prefactor\nc=2.94 for the transition-temperature shift given in terms of the scattering\nlength a and density n. In contrast, the second-order, particle-hole, and\nfluctuation-exchange approximations yield a first-order transition. The fact\nthat some standard Phi's predict a first-order transition challenges us to\nclarify whether or not the transition is really continuous.",
        "positive": "Dynamical response of ultracold interacting fermion-boson mixtures: We analyze the dynamical response of a ultracold binary gas mixture in\npresence of strong boson-fermion couplings. Mapping the problem onto that of\nthe optical response of a metal/semiconductor electronic degrees of freedom to\nelectromagnetic perturbation we calculate the corresponding dynamic linear\nresponse susceptibility in the non-perturbative regimes of strong boson-fermion\ncoupling using diagrammatic resummation technique as well as quantum Monte\nCarlo simulations. We evaluate the Bragg spectral function as well as the\noptical conductivity and find a pseudogap, which forms in certain parameter\nregimes."
    },
    {
        "anchor": "Mott transition in a cavity-boson system: A quantitative comparison\n  between theory and experiment: The competition between short-range and cavity-mediated infinite-range\ninteractions in a cavity-boson system leads to the existence of a superfluid\nphase and a Mott-insulator phase within the self-organized regime. In this\nwork, we quantitatively compare the steady-state phase boundaries of this\ntransition measured in experiments and simulated using the Multiconfigurational\nTime-Dependent Hartree Method for Indistinguishable Particles. To make the\nproblem computationally feasible, we represent the full system by the exact\nmany-body wave function of a two-dimensional four-well potential. We argue that\nthe validity of this representation comes from the nature of both the\ncavity-atomic system and the Bose-Hubbard physics. Additionally we show that\nthe chosen representation only induces small systematic errors, and that the\nexperimentally measured and theoretically predicted phase boundaries agree\nreasonably. We thus demonstrate a new approach for the quantitative numerical\ndetermination of the superfluid--Mott-insulator phase boundary.",
        "positive": "The Bose-Hubbard model with localized particle losses: We consider the Bose-Hubbard model with particle losses at one lattice site.\nFor the non-interacting case, we find that half of the bosons of an initially\nhomogeneous particle distribution, are not affected by dissipation that only\nacts on one lattice site in the center of the lattice. A physical\ninterpretation of this result is that the surviving particles interfere\ndestructively when they tunnel to the location of the dissipative defect and\ntherefore never reach it. Furthermore we find for a one-dimensional model that\na fraction of the particles can propagate across the dissipative defect even if\nthe rate of tunneling between adjacent lattice sites is much slower than the\nloss rate at the defect. In the interacting case, the phase coherence is\ndestroyed and all particles eventually decay. We thus analyze the effect of\nsmall interactions and small deviations from the perfectly symmetric setting on\nthe protection of the particles against the localized losses. A possible\nexperimental realization of our setup is provided by ultracold bosonic atoms in\nan optical lattice, where an electron beam on a single lattice site ionizes\natoms that are then extracted by an electrostatic field."
    },
    {
        "anchor": "Soliton Instabilities and Vortex Streets Formation in a Polariton\n  Quantum Fluid: Exciton-polaritons have been shown to be an optimal system in order to\ninvestigate the properties of bosonic quantum fluids. We report here on the\nobservation of dark solitons in the wake of engineered circular obstacles and\ntheir decay into streets of quantized vortices. Our experiments provide a\ntime-resolved access to the polariton phase and density, which allows for a\nquantitative study of instabilities of freely evolving polaritons. The decay of\nsolitons is quantified and identified as an effect of disorder-induced\ntransverse perturbations in the dissipative polariton gas.",
        "positive": "Doppler Shift of the de Broglie Waves- Some New Results from Very Old\n  Concepts: The Doppler shift of de Broglie wave is obtained for fermions and massive\nbosons using the conventional form of Lorentz transformations for momentum and\nenergy of the particles. A formalism is developed to obtain the variation of\nwave length for de Broglie waves with temperature for individual particles\nusing the classic idea of Wien in a many body Fermi gas or massive Bose gas."
    },
    {
        "anchor": "Simulating and detecting artificial magnetic fields in trapped atoms: A Bose-Einstein condensate exhibiting a nontrivial phase induces an\nartificial magnetic field in immersed impurity atoms trapped in a stationary,\nring-shaped optical lattice. We present an effective Hamiltonian for the\nimpurities for two condensate setups: the condensate in a rotating ring and in\nan excited rotational state in a stationary ring. We use Bogoliubov theory to\nderive analytical formulas for the induced artificial magnetic field and the\nhopping amplitude in the limit of low condensate temperature where the impurity\ndynamics is coherent. As methods for observing the artificial magnetic field we\ndiscuss time of flight imaging and mass current measurements. Moreover, we\ncompare the analytical results of the effective model to numerical results of a\ncorresponding two-species Bose-Hubbard model. We also study numerically the\nclustering properties of the impurities and the quantum chaotic behavior of the\ntwo-species Bose-Hubbard model.",
        "positive": "Quantum Joule-Thomson Effect in a Saturated Homogeneous Bose Gas: We study the thermodynamics of Bose-Einstein condensation in a weakly\ninteracting quasi-homogeneous atomic gas, prepared in an optical-box trap. We\ncharacterise the critical point for condensation and observe saturation of the\nthermal component in a partially condensed cloud, in agreement with Einstein's\ntextbook picture of a purely statistical phase transition. Finally, we observe\nthe quantum Joule-Thomson effect, namely isoenthalpic cooling of an\n(essentially) ideal gas. In our experiments this cooling occurs spontaneously,\ndue to energy-independent collisions with the background gas in the vacuum\nchamber. We extract a Joule-Thomson coefficient $\\mu_{\\rm JT} > 10^9$ K/bar,\nabout ten orders of magnitude larger than observed in classical gases."
    },
    {
        "anchor": "Functional Theory for Bose-Einstein Condensates: One-particle reduced density matrix functional theory would potentially be\nthe ideal approach for describing Bose-Einstein condensates. It namely replaces\nthe macroscopically complex wavefunction by the simple one-particle reduced\ndensity matrix, therefore provides direct access to the degree of condensation\nand still recovers quantum correlations in an exact manner. We eventually\ninitiate and establish this novel theory by deriving the respective universal\nfunctional $\\mathcal{F}$ for general homogeneous Bose-Einstein condensates with\narbitrary pair interaction. Most importantly, the successful derivation\nnecessitates a particle-number conserving modification of Bogoliubov theory and\na solution of the common phase dilemma of functional theories. We then\nillustrate this novel approach in several bosonic systems such as homogeneous\nBose gases and the Bose-Hubbard model. Remarkably, the general form of\n$\\mathcal{F}$ reveals the existence of a universal Bose-Einstein condensation\nforce which provides an alternative and more fundamental explanation for\nquantum depletion.",
        "positive": "Asymmetric Tunneling of Bose-Einstein Condensates: In his celebrated textbook, \\textit{Quantum Mechanics: Nonrelativistic\nTheory}, Landau argued that, for single particle systems in 1D, tunneling\nprobability remains the same for a particle incident from the left or the right\nof a barrier. This left-right symmetry of tunneling probability holds\nregardless of the shape of the potential barrier. However, there are a variety\nof known cases that break this symmetry, e.g. when observing composite\nparticles. We computationally (and analytically, in the simplest case) show\nthis breaking of the left-right tunneling symmetry for Bose-Einstein\ncondensates (BEC) in 1D, modelled by the Gross-Pitaevskii equation (GPE). By\nvarying $g$, the parameter of inter-particle interaction in the BEC, we\ndemonstrate that the transition from symmetric ($g=0$) to asymmetric tunneling\nis a threshold phenomenon. Our computations employ experimentally feasible\nparameters such that these results may be experimentally demonstrated in the\nnear future. We conclude by suggesting applications of the phenomena to design\natomtronic diodes, synthetic gauge fields, Maxwell's demons, and black-hole\nanalogues."
    },
    {
        "anchor": "Bright solitons and self-trapping with a BEC of cold atoms in driven\n  tilted optical lattices: We suggest a method for creating bright matter solitons by loading a BEC of\natoms in a driven tilted optical lattice. It is shown that one can realize the\nself-focussing regime for the wave-packet dynamics by properly adjusting the\nphase of the driving field with respect to the phase of Bloch oscillations. If\natom-atom interactions are larger than some critical value $g_{min}$, this\nself-focussing regime is followed by the formation of bright solitons.\nIncreasing the interactions above another critical value $g_{max}$ makes this\nprocess unstable. Instead of soliton formation one now meets the phenomenon of\nincoherent self-trapping. In this regime a fraction of atoms is trapped in\nincoherent localized wave-packets, while the remaining atoms spread\nballistically.",
        "positive": "Ergodicity Breaking Under Confinement in Cold-Atom Quantum Simulators: The quantum simulation of gauge theories on synthetic quantum matter devices\nhas gained a lot of traction in the last decade, making possible the\nobservation of a range of exotic quantum many-body phenomena. In this work, we\nconsider the spin-$1/2$ quantum link formulation of $1+1$D quantum\nelectrodynamics with a topological $\\theta$-angle, which can be used to tune a\nconfinement-deconfinement transition. Exactly mapping this system onto a PXP\nmodel with mass and staggered magnetization terms, we show an intriguing\ninterplay between confinement and the ergodicity-breaking paradigms of quantum\nmany-body scarring and Hilbert-space fragmentation. We map out the rich\ndynamical phase diagram of this model, finding an ergodic phase at small values\nof the mass $\\mu$ and confining potential $\\chi$, an emergent integrable phase\nfor large $\\mu$, and a fragmented phase for large values of both parameters. We\nalso show that the latter hosts resonances that lead to a vast array of\neffective models. We propose experimental probes of our findings, which can be\ndirectly accessed in current cold-atom setups."
    },
    {
        "anchor": "Observation of transverse condensation via Hanbury Brown--Twiss\n  correlations: A fundamental property of a three-dimensional Bose-Einstein condensate (BEC)\nis long-range coherence, however, in systems of lower dimensionality, not only\nis the long range coherence destroyed, but additional states of matter are\npredicted to exist. One such state is a `transverse condensate', first\npredicted by van Druten and Ketterle [Phys. Rev. Lett. 79, 549 (1997)], in\nwhich the gas condenses in the transverse dimensions of a highly anisotropic\ntrap while remaining thermal in the longitudinal dimension. Here we detect the\ntransition from a three-dimensional thermal gas to a gas undergoing transverse\ncondensation by probing Hanbury Brown--Twiss correlations.",
        "positive": "Damping of phase fluctuations in superfluid Bose gases: Using Popov's hydrodynamic approach we derive an effective Euclidean action\nfor the long-wavelength phase fluctuations of superfluid Bose gases in D\ndimensions. We then use this action to calculate the damping of phase\nfluctuations at zero temperature as a function of D. For D >1 and wavevectors |\nk | << 2 mc (where m is the mass of the bosons and c is the sound velocity) we\nfind that the damping in units of the phonon energy E_k = c | k | is to leading\norder gamma_k / E_k = A_D (k_0^D / 2 pi rho) (| k | / k_0)^{2 D -2}, where rho\nis the boson density and k_0 =2 mc is the inverse healing length. For D -> 1\nthe numerical coefficient A_D vanishes and the damping is proportional to an\nadditional power of |k | /k_0; a self-consistent calculation yields in this\ncase gamma_k / E_k = 1.32 (k_0 / 2 pi rho)^{1/2} |k | / k_0. In one dimension,\nwe also calculate the entire spectral function of phase fluctuations."
    },
    {
        "anchor": "OpenMP Fortran and C programs for solving the time-dependent\n  Gross-Pitaevskii equation in an anisotropic trap: We present new version of previously published Fortran and C programs for\nsolving the Gross-Pitaevskii equation for a Bose-Einstein condensate with\ncontact interaction in one, two and three spatial dimensions in imaginary and\nreal time, yielding both stationary and non-stationary solutions. To reduce the\nexecution time on multicore processors, new versions of parallelized programs\nare developed using Open Multi-Processing (OpenMP) interface. The input in the\nprevious versions of programs was the mathematical quantity nonlinearity for\ndimensionless form of Gross-Pitaevskii equation, whereas in the present\nprograms the inputs are quantities of experimental interest, such as, number of\natoms, scattering length, oscillator length for the trap, etc. New output files\nfor some integrated one- and two-dimensional densities of experimental interest\nare given. We also present speedup test results for the new programs.",
        "positive": "Comparative study of quantum dynamics of a few bosons in a\n  one-dimensional split hard-wall trap: exact results versus Bose-Hubbard-model\n  approximations: We study the dynamical properties of a few bosons confined in an\none-dimensional split hard wall trap with the interaction strength varying from\nthe weakly to strongly repulsive regime. The system is initially prepared in\none side of the double well by setting the barrier strength of the split trap\nto be infinity and then the barrier strength is suddenly changed to a finite\nvalue. Both exact diagonalization method and Bose-Hubbard model (BHM)\napproximation are used to study the dynamical evolution of the initial system.\nThe exact results based on exact diagonaliztion verify the enhancement of\ncorrelated tunneling in the strongly interacting regime. Comparing results\nobtained by two different methods, we conclude that one-band BHM approximation\ncan well describe the dynamics in the weakly interacting regime, but is not\nefficient to give quantitatively consistent results in the strongly interacting\nregime. Despite of the quantitative discrepancy, we validate that the form of\ncorrelated tunneling gives an important contribution to tunneling in the large\ninteraction regime. To get a quantitative description for the dynamics of\nbosons in the strongly interacting regime, we find that a multi-band BHM\napproximation is necessary."
    },
    {
        "anchor": "Bose-Einstein condensation in multilayers: The critical BEC temperature $T_{c}$ of a non interacting boson gas in a\nlayered structure like those of cuprate superconductors is shown to have a\nminimum $T_{c,m}$, at a characteristic separation between planes $a_{m}$. It is\nshown that for $a<a_{m}$, $T_{c}$ increases monotonically back up to the ideal\nBose gas $T_{0}$ suggesting that a reduction in the separation between planes,\nas happens when one increases the pressure in a cuprate, leads to an increase\nin the critical temperature. For finite plane separation and penetrability the\nspecific heat as a function of temperature shows two novel crests connected by\na ridge in addition to the well-known BEC peak at $T_{c}$ associated with the\n3D behavior of the gas. For completely impenetrable planes the model reduces to\nmany disconnected infinite slabs for which just one hump survives becoming a\npeak only when the slab widths are infinite.",
        "positive": "Polarons and their induced interactions in highly imbalanced triple\n  mixtures: We unravel the polaronic properties of impurities immersed in a correlated\ntrapped one-dimensional (1D) Bose-Bose mixture. This setup allows for the\nimpurities to couple either attractively or repulsively to a specific host,\nthus offering a highly flexible platform for steering the emergent polaronic\nproperties. Specifically, the polaronic residue peak and strength of induced\ninteractions can be controlled by varying the coupling of the impurities to the\nindividual bosonic components. In particular, it is possible to maintain the\nquasiparticle character for larger interaction strengths as compared to the\ncase of impurities immersed in a single bosonic species. We explicate a\nhierarchy of the polaron binding energies in terms of the impurity-medium\ninteractions, thereby elucidating the identification of the polaronic\nresonances in recent experimental radiofrequency schemes. For strong attractive\nimpurity-medium couplings bipolaron formation is captured. Our findings pave\nthe way for continuously changing the quasiparticle character, under the impact\nof trap effects, while exposing the role of correlations in triple mixture\nsettings."
    },
    {
        "anchor": "Generation of atypical hopping and interactions by kinetic driving: We study the effect of time-periodically varying the hopping amplitude in a\none-dimensional Bose-Hubbard model, such that its time-averaged value is zero.\nEmploying Floquet theory, we derive a static effective Hamiltonian in which\nnearest-neighbor single-particle hopping processes are suppressed, but all even\nhigher-order processes are allowed. Unusual many-body features arise from the\ncombined effect of nonlocal interactions and correlated tunneling. At a\ncritical value of the driving, the system passes from a Mott insulator to a\nsuperfluid formed by two quasi-condensates with opposite nonzero momenta. This\nwork shows how driving of the hopping energy provides a novel form of Floquet\nengineering, which enables atypical Hamiltonians and exotic states of matter to\nbe produced and controlled.",
        "positive": "Does an isolated quantum system relax?: Statistical mechanics is one of the most comprehensive theories in physics.\nFrom a boiling pot of water to the complex dynamics of quantum many-body\nsystems it provides a successful connection between the microscopic dynamics of\natoms and molecules and the macroscopic properties of matter. However,\nstatistical mechanics only describes the thermal equilibrium situation of a\nsystem, and there is no general framework to describe how equilibrium is\nreached or under which circumstances it can be reached at all. This problem is\nparticularly challenging in quantum mechanics, where unitarity appears to\nrender the very concept of thermalization counterintuitive. With the rapid\nexperimental progress in the control and probing of ultracold quantum gases\nthis question has become within reach of detailed experimental investigations.\nIn these notes we present a series of experiments with ultracold\none-dimensional Bose gases, which provide novel insights into this fundamental\nquestion."
    },
    {
        "anchor": "Rotons in interacting ultracold Bose gases: In three dimensions, non-interacting bosons undergo Bose-Einstein\ncondensation at a critical temperature, $T_{c}$, which is slightly shifted by\n$\\Delta T_{\\mathrm{c}}$, if the particles interact. We calculate the excitation\nspectrum of interacting Bose-systems, \\sup{4}He and \\sup{87}Rb, and show that a\nroton minimum emerges in the spectrum above a threshold value of the gas\nparameter. We provide a general theoretical argument for why the roton minimum\nand the maximal upward critical temperature shift are related. We also suggest\ntwo experimental avenues to observe rotons in condensates. These results, based\nupon a Path-Integral Monte-Carlo approach, provide a microscopic explanation of\nthe shift in the critical temperature and also show that a roton minimum does\nemerge in the excitation spectrum of particles with a structureless,\nshort-range, two-body interaction.",
        "positive": "Quantum phase transition of cold atoms in the bilayer hexagonal optical\n  lattices: We propose a scheme to investigate the quantum phase transition of cold atoms\nin the bilayer hexagonal optical lattices. Using the quantum Monte Carlo\nmethod, we calculate the ground state phase diagrams which contain an\nantiferromagnet, a solid, a superfluid, a fully polarized state and a\nsupersolid. We find there is a supersolid emerging in a proper parameter space,\nwhere the diagonal long range order coexists with off-diagonal long range\norder. We show that the bilayer optical lattices can be realized by coupling\ntwo monolayer optical lattices and give an experimental protocol to observe\nthose novel phenomena in the real experiments."
    },
    {
        "anchor": "Emergent Spin Liquids in the Hubbard Model on the Anisotropic Honeycomb\n  Lattice: We study the repulsive Hubbard model on an anisotropic honeycomb lattice\nwithin a mean-field and a slave-rotor treatment. In addition to the known\nsemi-metallic and band-insulating phases, obtained for very weak interactions,\nand the anti-ferromagnetic phase at large couplings, various insulating\nspin-liquid phases develop at intermediate couplings. Whereas some of these\nspin liquids have gapless spinon excitations, a gapped one occupies a large\nregion of the phase diagram and becomes the predominant phase for large hopping\nanisotropies. This phase can be understood in terms of weakly-coupled strongly\ndimerized states.",
        "positive": "Phase Space Crystals: A New Way to Create a Quasienergy Band Structure: A novel way to create a band structure of the quasienergy spectrum for driven\nsystems is proposed based on the discrete symmetry in phase space. The system,\ne.g., an ion or ultracold atom trapped in a potential, shows no spatial\nperiodicity, but it is driven by a time-dependent field coupling highly\nnonlinearly to one of its degrees of freedom (e.g., ~ q^n). The band structure\nin quasienergy arises as a consequence of the n-fold discrete periodicity in\nphase space induced by this driving field. We propose an explicit model to\nrealize such a phase space crystal and analyze its band structure in the frame\nof a tight-binding approximation. The phase space crystal opens new ways to\nengineer energy band structures, with the added advantage that its properties\ncan be changed in situ by tuning the driving field's parameters."
    },
    {
        "anchor": "Entangling two distinguishable quantum bright solitons via collisions: The generation of mesoscopic Bell states via collisions of distinguishable\nbright solitons has been suggested in Phys. Rev. Lett. 111, 100406 (2013).\nHere, we extend our former proposal to two hyperfine states of 85Rb instead of\ntwo different atomic species, thus simplifying possible experimental\nrealisations. A calculation of the $s$-wave scattering lengths for the\nhyperfine states $(f,m_f)=(2,+2)$ and $(3,+2)$ identifies parameter regimes\nsuitable for the creation of Bell states with an advantageously broad Feshbach\nresonance. We show the generation of Bell states using the truncated Wigner\nmethod for the soliton's centre of mass and demonstrate the validity of this\napproach by a comparison to a mathematically rigorous effective potential\ntreatment of the quantum many-particle problem.",
        "positive": "Universality in fermionic dimer-dimer scattering: Collisions of two fermionic dimers near the unitary limit are studied using\nexact four-particle equations for transition operators in momentum space.\nUniversal properties of dimer-dimer phase shifts and effective range expansion\n(ERE) parameters are determined. The inclusion of the fourth-order momentum\nterm in the ERE significantly extends its validity to higher collision\nenergies. The dimer-dimer scattering length and effective range are determined\nin the unitary limit as well as their corrections arising due to the finite\nrange of the two-fermion interaction. These results are of considerably higher\naccuracy as compared to previous works, but confirm most of the previous\nresults except for the lattice effective field theory calculations."
    },
    {
        "anchor": "Convergence Properties of the Effective Theory for Trapped Bosons: We investigate few-boson systems with resonant interactions in a narrow\nharmonic trap within an effective theory framework. The size of the model space\nis identified with the effective theory cutoff. In the universal regime, the\ninteractions of the bosons can be approximated by contact interactions. We\ninvestigate the convergence properties of genuine and smeared contact\ninteractions as the size of the model space is increased and present a detailed\nerror analysis. The spectra for few-boson systems with up to 6 identical\nparticles are calculated by combining extrapolations in the cutoff and in the\nsmearing parameter.",
        "positive": "Dynamical Equilibration Across a Quenched Phase Transition in a Trapped\n  Quantum Gas: The formation of an equilibrium quantum state from an uncorrelated thermal\none through the dynamical crossing of a phase transition is a central question\nof non-equilibrium many-body physics. During such crossing, the system breaks\nits symmetry by establishing numerous uncorrelated regions separated by\nspontaneously-generated defects, whose emergence obeys a universal scaling law\nwith the quench duration. Much less is known about the ensuing re-equilibrating\nor \"coarse-graining\" stage, which is governed by the evolution and interactions\nof such defects under system-specific and external constraints. In this work we\nperform a detailed numerical characterization of the entire non-equilibrium\nprocess, addressing subtle issues in condensate growth dynamics and\ndemonstrating the quench-induced decoupling of number and coherence growth\nduring the re-equilibration process. Our unique visualizations not only\nreproduce experimental measurements in the relevant regimes, but also provide\nvaluable information in currently experimentally-inaccessible regimes."
    },
    {
        "anchor": "The fate of quantum many-body scars in the presence of disorder: Experiments performed on strongly interacting Rydberg atoms have revealed\nsurprising persistent oscillations of local observables. These oscillations\nhave been attributed to a special set of non-ergodic states, referred to as\nquantum many-body scars. Although a significant amount of research has been\ninvested to understand these special states, it has remained unclear how stable\nscar states are against disorder. We address this question by studying\nnumerically and analytically the magnetization and spatio-temporal correlators\nof a model of interacting Rydberg atoms in the presence of disorder. While the\noscillation amplitudes of these observables decay with time as the disorder\nstrength is increased, their oscillation frequency remains remarkably constant.\nWe show that this stability stems from resonances in the disordered spectrum\nthat are approximately centered at the same scar energies of the clean system.\nWe also find that multiple additional sets of scar resonances become accessible\ndue to the presence of disorder and further enhance the oscillation amplitudes.\nOur results show the robustness of non-ergodic dynamics in scar systems, and\nopens the door to understanding the behavior of experimentally realistic\nsystems.",
        "positive": "Association of Efimov trimers from a three-atom continuum: We develop an experimental technique for rf-association of Efimov trimers\nfrom three-atoms continuum. We apply it to probe the lowest accessible Efimov\nenergy level in bosonic lithium in the region where strong deviations from the\nuniversal behavior are expected, and provide quantitative study of this effect.\nPosition of the Efimov resonance at the atom-dimer threshold, measured with a\ndifferent experimental technique, concurs with the rf-association results."
    },
    {
        "anchor": "Backaction-Driven Transport of Bloch Oscillating Atoms in Ring Cavities: We predict that an atomic Bose-Einstein condensate strongly coupled to an\nintracavity optical lattice can undergo resonant tunneling and directed\ntransport when a constant and uniform bias force is applied. The bias force\ninduces Bloch oscillations, causing amplitude and phase modulation of the\nlattice which resonantly modifies the site-to-site tunneling. For the right\nchoice of parameters a net atomic current is generated. The transport velocity\ncan be oriented oppositely to the bias force, with its amplitude and direction\ncontrolled by the detuning between the pump laser and the cavity. The transport\ncan also be enhanced through imbalanced pumping of the two counter-propagating\nrunning wave cavity modes. Our results add to the cold atoms quantum simulation\ntoolbox, with implications for quantum sensing and metrology.",
        "positive": "The nonlinear Dirac equation in Bose-Einstein condensates: Superfluid\n  fluctuations and emergent theories from relativistic linear stability\n  equations: We present the theoretical and mathematical foundations of stability analysis\nfor a Bose-Einstein condensate (BEC) at Dirac points of a honeycomb optical\nlattice. The combination of s-wave scattering for bosons and lattice\ninteraction places constraints on the mean-field description, and hence on\nvortex configurations in the Bloch-envelope function near the Dirac point. A\nfull derivation of the relativistic linear stability equations (RLSE) is\npresented by two independent methods to ensure veracity of our results.\nSolutions of the RLSE are used to compute fluctuations and lifetimes of vortex\nsolutions of the nonlinear Dirac equation, which include Mermin-Ho and\nAnderson-Toulouse skyrmions, with lifetime $\\approx 4$ seconds. Beyond vortex\nstabilities the RLSE provide insight into the character of collective\nsuperfluid excitations, which we find to encode several established theories of\nphysics. In particular, the RLSE reduce to the Andreev equations, in the\nnonrelativistic and semiclassical limits, the Majorana equation, inside vortex\ncores, and the Dirac-Bogoliubov-de Gennes equations, when nearest-neighbor\ninteractions are included. Furthermore, by tuning a mass gap, relative\nstrengths of various spinor couplings, for the small and large quasiparticle\nmomentum regimes, we obtain weak-strong Bardeen-Cooper-Schrieffer\nsuperconductivity, as well as fundamental wave equations such as Schr\\\"odinger,\nDirac, Klein-Gordon, and Bogoliubov-de Gennes equations. Our results apply\nequally to a strongly spin-orbit coupled BEC in which the Laplacian\ncontribution can be neglected."
    },
    {
        "anchor": "Universal clusters as building blocks of stable quantum matter: We present an exploratory study that suggests that Efimov physics, a leading\nresearch theme in few-body quantum physics, can also induce stable many-body\nground states whose building blocks are universal clusters. We identify a range\nof parameters in a mass-and-density imbalanced two-species fermionic mixture\nfor which the ground state is a gas of Efimov-related universal trimers. An\nexplicit calculation of the trimer-trimer interaction reveals that the trimer\nphase is an SU$(3)$ Fermi liquid stable against recombination losses. We\npropose to experimentally observe this phase in a fermionic $^6$Li-$^{53}$Cr\nmixture.",
        "positive": "Quantum correlations and degeneracy of identical bosons in a 2D harmonic\n  trap: We consider a few number of identical bosons trapped in a 2D isotropic\nharmonic potential and also the $N$-boson system when it is feasible. The\natom-atom interaction is modelled by means of a finite-range Gaussian\ninteraction. The spectral properties of the system are scrutinized, in\nparticular, we derive analytic expressions for the degeneracies and their\nbreaking for the lower-energy states at small but finite interactions. We\ndemonstrate that the degeneracy of the low-energy states is independent of the\nnumber of particles in the noninteracting limit and also for sufficiently weak\ninteractions. In the strongly interacting regime, we show how the many-body\nwave function develops holes whenever two particles are at the same position in\nspace to avoid the interaction, a mechanism reminiscent of the Tonks-Girardeau\ngas in 1D. The evolution of the system as the interaction is increased is\nstudied by means of the density profiles, pair correlations and fragmentation\nof the ground state for $N=2$, $3$, and $4$ bosons."
    },
    {
        "anchor": "Influence of magnetic quantum confined Stark effect on the spin lifetime\n  of indirect excitons: We report on the unusual and counter-intuitive behaviour of spin lifetime of\nexcitons in coupled semiconductor quantum wells (CQWs) in the presence of\nin-plane magnetic field. Instead of conventional acceleration of spin\nrelaxation due to the Larmor precession of electron and hole spins we observe a\nstrong increase of the spin relaxation time at low magnetic fields followed by\nsaturation and decrease at higher fields. We argue that this non-monotonic spin\nrelaxation dynamics is a fingerprint of the magnetic quantum confined Stark\neffect. In the presence of electric field along the CQW growth axis, an applied\nmagnetic field efficiently suppresses the exciton spin coherence, due to\ninhomogeneous broadening of the $g$-factor distribution.",
        "positive": "Decay of an isolated monopole into a Dirac monopole configuration: We study numerically the detailed structure and decay dynamics of isolated\nmonopoles in conditions similar to those of their recent experimental\ndiscovery. We find that the core of a monopole in the polar phase of a spin-1\nBose-Einstein condensate contains a small half-quantum vortex ring. Well after\nthe creation of the monopole, we observe a dynamical quantum phase transition\nthat destroys the polar phase. Strikingly, the resulting ferromagnetic order\nparameter exhibits a Dirac monopole in its synthetic magnetic field."
    },
    {
        "anchor": "Energy fluctuation of ideal Fermi gas trapped under generic power law\n  potential $U=\\sum_{i=1} ^d c_i |\\frac{x_i}{a_i}|^{n_i}$ in d dimension: Energy fluctuation of ideal Fermi gas trapped under generic power law\npotential $U=\\sum_{i=1} ^d c_i |\\frac{x_i}{a_i}|^{n_i}$ have been calculated in\narbitrary dimension. Energy fluctuation is scrutinized further in the\ndegenerate limit $\\mu>> K_BT$ with the help of Sommerfeld expansion. The\ndependence of energy fluctuation on dimensionality and power law potential is\nstudied in detail. Most importantly our general result can exactly reproduce\nthe recently published result regarding free and harmonically trapped ideal\nFermi gas in d=3 (S Biswas, J Mitra, S Bhattacharyya, J. Stat. Mech. P03013,\n2015.)",
        "positive": "Gauge-spin-space rotation invariant vortices in spin-orbit coupled\n  Bose-Einstein condensates: We revisit ground states of spinor Bose-Einstein condensates with a Rashba\nspin-orbit coupling, and find that votices show up as a direct consequence of\nspontaneous symmetry breaking into a combined gauge, spin, and space rotation\nsymmetry, which determines the vortex-core spin state at the rotating center.\nFor the continuous combined symmetry, the total spin rotation about the\nrotating axis is restricted to $2\\pi$, whereas for the discrete combined\nsymmetry, we further need 2F quantum numbers to characterize the total spin\nrotation for the spin-$F$ system. For lattice phases we find that in the ground\nstate the topological charge for each unit cell vanishes. However, we find two\ntypes of highly symmetric lattices with a nontrivial topological charge in the\nspin-$\\frac{1}{2}$ system based on the symmetry classification, and show that\nthey are skyrmion crystals."
    },
    {
        "anchor": "Collective Dynamics and Atom Loss in Bright Soliton Matter Waves: Motivated by recent experiments, we model the dynamics of bright solitons\nformed by cold gases in quasi-1D traps. A dynamical variational ansatz captures\nthe far-from equilibrium excitations of these solitons. Due to a separation of\nscales, the radial and axial modes decouple, allowing for closed-form\napproximations for the dynamics. We explore how soliton dynamics influence atom\nloss, and find that the time-averaged loss is largely insensitive to the degree\nof excitation. The variational approach enables us to perform high precision\ncalculations of the critical atom number (ie. the maximum number of atoms that\ncan exist in a single soliton before the attractive forces overwhelm quantum\npressure, leading to collapse).",
        "positive": "Quench Dynamics of the Ideal Bose Polaron at Zero and Nonzero\n  Temperatures: We give a detailed account of a stationary impurity in an ideal Bose-Einstein\ncondensate, which we call the ideal Bose polaron, at both zero and non-zero\ntemperatures and arbitrary strength of the impurity-boson coupling. The time\nevolution is solved exactly and it is found that, surprisingly, many of the\nfeatures that have been predicted for the real BEC are already present in this\nsimpler setting and can be understood analytically therein. We obtain explicit\nformulae for the time evolution of the condensate wave function at $T=0$ and of\nthe one-particle density matrix at $T>0$. For negative scattering length, the\nsystem is found to thermalize even though the dynamics are perfectly coherent.\nThe time evolution and thermal values of the Tan contact are derived and\ncompared to a recent experiment. We find that contrary to the Fermi polaron,\nthe contact is not bounded at unitarity as long as a condensate exists. An\nexplicit formula for the dynamical overlap at $T=0$ allows us to compute the rf\nspectrum which can be understood in detail by relating it to the two-body\nproblem of one boson and the impurity."
    },
    {
        "anchor": "Universal Relations for Identical Bosons from 3-Body Physics: Systems consisting of identical bosons with a large scattering length satisfy\nuniversal relations determined by 2-body physics that are similar to those for\nfermions with two spin states. They require the momentum distribution to have a\nlarge-momentum 1/k^4 tail and the radio-frequency transition rate to have a\nhigh-frequency 1/omega^{3/2} tail, both of which are proportional to the 2-body\ncontact. Identical bosons also satisfy additional universal relations that are\ndetermined by 3-body physics and involve the 3-body contact, which measures the\nprobability of 3 particles being very close together. The coefficients of the\n3-body contact in the 1/k^5 tail of the momentum distribution and in the\n1/omega^2 tail of the radio-frequency transition rate are log-periodic\nfunctions of k and omega that depend on the Efimov parameter.",
        "positive": "Prethermalization and universal dynamics in near-integrable quantum\n  systems: We review the recent progress in the understanding of the relaxation of\nisolated near-integrable quantum many-body systems. Focusing on\nprethermalization and universal dynamics following a quench, we describe the\nexperiments with ultracold atomic gases that illustrate these phenomena and\nsummarize the essential theoretical concepts employed to interpret them. Our\ndiscussion highlights the key topics that link the different approaches to this\ninterdisciplinary field, including the generalized Gibbs ensemble, non-thermal\nfixed points, critical slowing and universal scaling. Finally, we point to new\nexperimental challenges demonstrating these fundamental features of many-body\nquantum systems out of equilibrium."
    },
    {
        "anchor": "Perfect transmission of Higgs modes via antibound states: We study tunneling properties of Higgs modes in superfluid Bose gases in\noptical lattices in the presence of a potential barrier introduced by local\nmodulation of hopping amplitude. Solving the time-dependent Ginzburg-Landau\nequation, Higgs modes are found to exhibit perfect transmission through a\npotential barrier if the barrier strength is weak. There exists, on the other\nhand, localized Higgs bound states in the presence of a strong potential\nbarrier. We find that the perfect transmission disappears at the critical\nbarrier strength above which one of the odd antibound state turns into a true\nbound state. We demonstrate that the perfect transmission of Higgs modes is\nmediated by resonance with the antibound states of Higgs modes.",
        "positive": "Dirac fields in curved spacetime as Fermi-Hubbard model with non unitary\n  tunnelings: In this article we show that a Dirac Hamiltonian in a curved background\nspacetime can be interpreted, when discretized, as a tight binding\nFermi-Hubbard model with non unitary tunnelings. We find the form of the\nnonunitary tunneling matrices in terms of the metric tensor. The main\nmotivation behind this exercise is the feasibility of such Hamiltonians by\nmeans of laser assisted tunnelings in cold atomic experiments. The mapping thus\nprovide a physical interpretation of such Hamiltonians. We demonstrate the use\nof the mapping on the example of time dependent metric in 2+1 dimensions.\nStudying the spin dynamics, we find qualitative agreement with known\ntheoretical predictions, namely the particle pair creation in expanding\nuniverse."
    },
    {
        "anchor": "Long-distance supercurrent transport in a room-temperature Bose-Einstein\n  magnon condensate: The term supercurrent relates to a macroscopic dissipation-free collective\nmotion of a quantum condensate and is commonly associated with such famous\nlow-temperature phenomena as superconductivity and superfluidity. Another type\nof motion of quantum condensates is second sound - a wave of the density of a\ncondensate. Recently, we reported on an enhanced decay of a parametrically\ninduced Bose-Einstein condensate (BEC) of magnons caused by a supercurrent\noutflow of the BEC phase from the locally heated area of a room temperature\nmagnetic film. Here, we present the direct experimental observation of a\nlong-distance spin transport in such a system. The condensed magnons being\npushed out from the potential well within the heated area form a density wave,\nwhich propagates through the BEC many hundreds of micrometers in the form of a\nspecific second sound pulse - Bogoliubov waves - and is reflected from the\nsample edge. The discovery of the long distance supercurrent transport in the\nmagnon BEC further advances the frontier of the physics of quasiparticles and\nallows for the application of related transport phenomena for low-loss data\ntransfer in perspective magnon spintronics devices.",
        "positive": "Static density response of one-dimensional soft bosons across the\n  clustering transition: One-dimensional bosons interacting via a soft-shoulder potential are\ninvestigated at zero temperature. The flatness of the potential at short\ndistances introduces a typical length, such that, at relatively high densities\nand sufficiently strong interactions, clusters are formed, even in the presence\nof a completely repulsive potential. We evaluate the static density response\nfunction of this system across the transition from the liquid to the cluster\nliquid phases. Such quantity reveals the density modulations induced by a weak\nperiodic external potential, and is maximal at the clustering wavevector. It is\nknown that this response function is proportional to the static structure\nfactor in the classical regime at high temperature, while for this\nzero-temperature quantum systems, we extract it from the dynamical structure\nfactor evaluated with quantum Monte Carlo methods."
    },
    {
        "anchor": "Gauge transformations and Galilean covariance in nonlinear gauge-coupled\n  quantum fluids: We investigate certain invariance properties of quantum fluids subject to a\nnonlinear gauge potential. In particular, we derive the covariant\ntransformation laws for the nonlinear potentials under a space-time Galilean\nboost and consider U(1) gauge transformations. We find that the hydrodynamic\ncanonical field equations are form-invariant in the case of external gauge\nfunctions, but not for nonlinear gauge functionals. Hence, nonlinear gauge\npotentials are non-trivial potentials which may not be \"gauged-away\". Notably,\nfor a 1D superfluid, attempting to do so generates the gauge-pressure of the\nfluid in the Hamiltonian density. Further, we investigate how the field\nequations transform under arbitrary Galilean transformations. We find that the\nimmediate lack of Galilean covariance is restored under a suitably chosen\ntransformation rule set for the potentials, which is identical in form to that\nof a Schr\\\"odinger particle coupled to external scalar and vector potentials.",
        "positive": "Global superfluid phase diagram of three component fermions with\n  magnetic ordering: We investigate a three component fermion mixture in the presence of weak\nattractive interactions. We use a combination of the equation of motion and the\nGaussian variational mean-field approaches, which both allow for simultaneous\nsuperfluid and magnetic ordering in an unbiased way, and capture the interplay\nbetween the two order parameters. This interplay significantly modifies the\nphase diagram, especially the superfluid-normal phase boundaries. In the close\nvicinity of the critical temperature and for small chemical potential\nimbalances, strong particle-hole symmetry breaking leads to a phase diagram\nsimilar to the one predicted by Cherng et al. [Phys. Rev. Lett. 99, 130406\n(2007)], however, the overall phase diagram is markedly different: new chemical\npotential-driven first and second order transitions and triple points emerge as\nwell as more exotic second order multicritical points, and bicritical lines\nwith O(2,2) symmetry. We identify the terms which are necessary to capture this\ncomplex phase diagram in a Ginzburg-Landau approach, and determine the\ncorresponding coefficients."
    },
    {
        "anchor": "Rotating binary Bose-Einstein condensates and vortex clusters in quantum\n  droplets: Quantum droplets may form out of a gaseous Bose-Einstein condensate,\nstabilized by quantum fluctuations beyond mean field. We show that multiple\nsingly-quantized vortices may form in these droplets at moderate angular\nmomenta in two dimensions. Droplets carrying these precursors of an Abrikosov\nlattice remain self-bound for certain timescales after switching off an initial\nharmonic confinement. Furthermore, we examine how these vortex-carrying\ndroplets can be formed in a more pertubation-resistant setting, by starting\nfrom a rotating binary Bose-Einstein condensate and inducing a metastable\npersistent current via a non-monotonic trapping potential.",
        "positive": "Fusion channels of non-Abelian anyons from angular-momentum and\n  density-profile measurements: We present a method to characterize non-Abelian anyons that is based only on\nstatic measurements and that does not rely on any form of interference. For\ngeometries where the anyonic statistics can be revealed by rigid rotations of\nthe anyons, we link this property to the angular momentum of the initial state.\nWe test our method on the paradigmatic example of the Moore-Read state, that is\nknown to support excitations with non-Abelian statistics of Ising type. As an\nexample, we reveal the presence of different fusion channels for two such\nexcitations, a defining feature of non-Abelian anyons. This is obtained by\nmeasuring density-profile properties, like the mean square radius of the system\nor the depletion generated by the anyons. Our study paves the way to novel\nmethods for characterizing non-Abelian anyons, both in the experimental and\ntheoretical domains."
    },
    {
        "anchor": "Phase Diagram of Bosons in a 2D Optical Lattice with infinite-range\n  Cavity-mediated Interactions: High-finesse optical cavity allows the establishment of long-range\ninteractions between bosons in an optical lattice when most cold atoms\nexperiments are restricted to short-range interactions. Supersolid phases have\nrecently been experimentally observed in such systems. Using both exact quantum\nMonte Carlo simulations and Gutzwiller approximation, we study the ground state\nphase diagrams of a two-dimensional Bose-Hubbard model with infinite-range\ninteractions which describes such experiments. In addition to superfluid and\ninsulating Mott phases, the infinite-range checkerboard interactions introduce\ncharge density waves and supersolid phases. We study here the system at various\nparticle densities, elucidate the nature of the phases and quantum phase\ntransitions, and discuss the stability of the phases with respect to phase\nseparation. In particular we confirm the existence and stability of a\nsupersolid phase detected experimentally.",
        "positive": "Viscosity of a Multi-channel One-Dimensional Fermi Gas: Many one-dimensional systems of experimental interest possess multiple bands\narising from shallow confining potentials. In this work, we study a gas of\nweakly interacting fermions and show that the bulk viscosity is dramatically\naltered by the occupation of more than one band. The reasons for this are\ntwo-fold: a multichannel system is more easily displaced from equilibrium and\nthe associated relaxation processes lead to more rapid equilibration than in\nthe single channel case. We estimate the bulk viscosity in terms of the\nunderlying microscopic interactions. The experimental relevance of this physics\nis discussed in the context of quantum wires and trapped cold atomic gases."
    },
    {
        "anchor": "Unconventional superfluid order in the $F$-band of a bipartite optical\n  square lattice: We report on the first observation of bosons condensed into the energy minima\nof an $F$-band of a bipartite square optical lattice. Momentum spectra indicate\nthat a truly complex-valued staggered angular momentum superfluid order is\nestablished. The corresponding wave function is composed of alternating local\n$F_{2x^3-3x} + i F_{2y^3-3y}$-orbits and local $S$-orbits residing in the deep\nand shallow wells of the lattice, which are arranged as the black and white\nareas of a checkerboard. A pattern of staggered vortical currents arises, which\nbreaks time reversal symmetry and the translational symmetry of the lattice\npotential. We have measured the populations of higher order Bragg peaks in the\nmomentum spectra for varying relative depths of the shallow and deep lattice\nwells and find remarkable agreement with band calculations.",
        "positive": "Inserting single Cs atoms into an ultracold Rb gas: We report on the controlled insertion of individual Cs atoms into an\nultracold Rb gas at about 400 nK. This requires to combine the techniques\nnecessary for cooling, trapping and manipulating single laser cooled atoms\naround the Doppler temperature with an experiment to produce ultracold\ndegenerate quantum gases. In our approach, both systems are prepared in\nseparated traps and then combined. Our results pave the way for coherent\ninteraction between a quantum gas and a single or few neutral atoms of another\nspecies."
    },
    {
        "anchor": "Time-of-flight expansion of binary Bose-Einstein condensates at finite\n  temperature: Ultracold quantum gases provide a unique setting for studying and\nunderstanding the properties of interacting quantum systems. Here, we\ninvestigate a multi-component system of $^{87}$Rb--$^{39}$K Bose-Einstein\ncondensates (BECs) with tunable interactions both theoretically and\nexperimentally. Such multi-component systems can be characterized by their\nmiscibility, where miscible components lead to a mixed ground state and\nimmiscible components form a phase-separated state. Here we perform the first\nfull simulation of the dynamical expansion of this system including both BECs\nand thermal clouds, which allows for a detailed comparison with experimental\nresults. In particular we show that striking features emerge in time-of-flight\nfor BECs with strong interspecies repulsion, even for systems which were\nseparated in situ by a large gravitational sag. An analysis of the center of\nmass positions of the BECs after expansion yields qualitative agreement with\nthe homogeneous criterion for phase-separation, but reveals no clear transition\npoint between the mixed and the separated phases. Instead one can identify a\ntransition region, for which the presence of a gravitational sag is found to be\nadvantageous. Moreover we analyze the situation where only one component is\ncondensed and show that the density distribution of the thermal component also\nshow some distinct features. Our work sheds new light on the analysis of\nmulti-component systems after time-of-flight and will guide future experiments\non the detection of miscibility in these systems.",
        "positive": "Non-equilibrium time evolution and rephasing in the quantum sine-Gordon\n  model: We discuss the non-equilibrium time evolution of the phase field in the\nsine-Gordon model using two very different approaches: the truncated Wigner\napproximation and the truncated conformal space approach. We demonstrate that\nthe two approaches agree for a period covering the first few oscillations,\nthereby giving a solid theoretical prediction in the framework of sine-Gordon\nmodel, which is thought to describe the dynamics of two bosonic condensates in\nquasi-one-dimensional traps coupled via a Josephson tunneling term. We\nconclude, however, that the recently observed phase-locking behavior cannot be\nexplained in terms of homogeneous sine-Gordon dynamics, which hints at the role\nof other degrees of freedom or inhomogeneity in the experimental system."
    },
    {
        "anchor": "Fermi polaron in a dissipative bath with spin-orbit coupling: We study the polaron problem of an impurity immersed in a dissipative\nspin-orbit coupled Fermi gas via a non-self-consistent T-matrix method. We\nfirst propose an experimental scheme to realize a spin-orbit coupled Fermi bath\nwith dissipation, and show that such a system can be described by a\nnon-Hermitian Hamiltonian that contains an imaginary spin-flip term and an\nimaginary constant shift term. We find that the non-Hermiticity will change the\nsingle particle dispersion of the bath gas, and modify the properties of\nattractive and repulsive polarons such as energy, quasi-particle residue,\neffective mass, and decay rate. We also investigate the Thouless criteria\ncorresponding to the instability of the polaron molecule transition, which\nsuggests a molecule state is more facilitated with stronger bath dissipation.\nFinally, we consider the case with finite impurity density and calculate the\ninteraction between polarons. Our result extends the study of polaron physics\nto non-Hermitian systems and may be realized in future experiment.",
        "positive": "Coherent Forward Scattering Peak Induced by Anderson Localization: Numerical simulations show that, at the onset of Anderson localization, the\nmomentum distribution of a coherent wave packet launched inside a random\npotential exhibits, in the forward direction, a novel interference peak that\ncomplements the coherent backscattering peak. An explanation of this phenomenon\nin terms of maximally crossed diagrams predicts that the signal emerges around\nthe localization time and grows on the scale of the Heisenberg time associated\nwith the localization volume. Together, coherent back and forward scattering\nprovide evidence for the occurrence of Anderson localization."
    },
    {
        "anchor": "Time evolution of coherent wave propagation and spin relaxation in\n  spin-orbit coupled systems: We investigate, both numerically and analytically, the time evolution of a\nparticle in an initial plane wave state as it is subject to elastic scattering\nin a two-dimensional disordered system with Rashba spin-orbit coupling (SOC).\nIn the analytic calculation, we treat the SOC non-perturbatively, and the\ndisorder perturbatively using the Diffuson and the Cooperon. We calculate the\ntime dependence of coherent backscattering (CBS) as a function of the strength\nof the SOC. We identify weak and strong SOC regimes, and give the relevant time\nand energy scales in each case. By studying the time dependence of the\nanisotropy of the disorder-averaged momentum distribution we identify the spin\nrelaxation time. We find a crossover from D'yakonov-Perel' spin relaxation for\nweak SOC to Elliot-Yafet like behaviour for strong SOC.",
        "positive": "Higher-order topological Peierls insulator in a two-dimensional\n  atom-cavity system: In this work, we investigate a two-dimensional system of ultracold bosonic\natoms inside an optical cavity, and show how photon-mediated interactions give\nrise to a plaquette-ordered bond pattern in the atomic ground state. The latter\ncorresponds to a 2D Peierls transition, generalizing the spontaneous bond\ndimmerization driven by phonon-electron interactions in the 1D\nSu-Schrieffer-Heeger (SSH) model. Here the bosonic nature of the atoms plays a\ncrucial role to generate the phase, as similar generalizations with fermionic\nmatter do not lead to a plaquette structure. Similar to the SSH model, we show\nhow this pattern opens a non-trivial topological gap in 2D, resulting in a\nhigher-order topological phase hosting corner states, that we characterize by\nmeans of a many-body topological invariant and through its entanglement\nstructure. Finally, we demonstrate how this higher-order topological Peierls\ninsulator can be readily prepared in atomic experiments through adiabatic\nprotocols. Our work thus shows how atomic quantum simulators can be harnessed\nto investigate novel strongly-correlated topological phenomena beyond those\nobserved in natural materials."
    },
    {
        "anchor": "Dynamics of quasi-one-dimensional bright and vortex solitons of a\n  dipolar Bose-Einstein condensate with repulsive atomic interaction: By numerical and variational analysis of the three-dimensional\nGross-Pitaevskii equation we study the formation and dynamics of bright and\nvortex-bright solitons in a cigar-shaped dipolar Bose-Einstein condensate for\nlarge repulsive atomic interactions. Phase diagram showing the region of\nstability of the solitons is obtained. We also study the dynamics of breathing\noscillation of the solitons as well as the collision dynamics of two solitons\nat large velocities. Two solitons placed side-by-side at rest coalesce to form\na stable bound soliton molecule due to dipolar attraction.",
        "positive": "Dynamical Scaling of Surface Roughness and Entanglement Entropy in\n  Disordered Fermion Models: Localization is one of the most fundamental interference phenomena caused by\nrandomness, and its universal aspects have been extensively explored from the\nperspective of one-parameter scaling mainly for static properties. We\nnumerically study dynamics of fermions on disordered onedimensional potentials\nexhibiting localization and find dynamical one-parameter scaling for surface\nroughness, which represents particle-number fluctuations at a given\nlengthscale, and for entanglement entropy when the system is in delocalized\nphases. This dynamical scaling corresponds to the Family-Vicsek scaling\noriginally developed in classical surface growth, and the associated scaling\nexponents depend on the type of disorder. Notably, we find that partially\nlocalized states in the delocalized phase of the random-dimer model lead to\nanomalous scaling, where destructive interference unique to quantum systems\nleads to exponents unknown for classical systems and clean systems."
    },
    {
        "anchor": "Bound and scattering states in harmonic waveguides in the vicinity of\n  free space Feshbach resonances: The two-body bound and scattering properties in an one-dimensional harmonic\nwaveguide close to free space magnetic Feshbach resonances are investigated\nbased on the local frame transformation approach within a single partial wave\napproximation. An energy and magnetic field dependent free space phase shift is\nadopted in the current theoretical framework. For both $s$- and $p$-wave\ninteraction, the least bound state in the waveguide dissociates into the\ncontinuum at the resonant magnetic field where the effective one-dimensional\nscattering length $a_{\\rm 1D}$ diverges. Consequently, the association of atoms\ninto molecules in the waveguide occurs when the magnetic field is swept\nadiabatically across the pole of $a_{\\rm 1D}$. In the vicinity of broad\n$s$-wave resonances, the resonant magnetic field is nearly independent on the\ntransverse confining frequency $\\omega_{\\perp}$ of the waveguide. Close to\n$p$-wave and narrow $s$-wave resonances, the resonant magnetic field changes as\n$\\omega_{\\perp}$ varies.",
        "positive": "Generating nonequilibrium stationary state from ground state condensate\n  through an almost-adiabatic cycle: It is shown that the ground state of weakly interacting Bose particles in a\nquasi one-dimensional box trap can be converted into an excited stationary\nstate by an adiabatic cyclic operation that involves a quench of interaction\nstrength: A sharp impurity potential is applied and its strength is varied\nduring the cycle, which induces a nonequilibrium stationary state exhibiting\nthe inversion of population. This process is robust in the sense that the\nresultant stationary state is almost independent of the details of the cycle,\nsuch as the position of the impurity as long as the cycle is far enough from\ncritical regions. The case of the failure of the population inversion due to\nthe strong interparticle interactions is also examined."
    },
    {
        "anchor": "Strong coupling Bose polarons out of equilibrium: Dynamical RG approach: When a mobile impurity interacts with a surrounding bath of bosons, it forms\na polaron. Numerous methods have been developed to calculate how the energy and\nthe effective mass of the polaron are renormalized by the medium for\nequilibrium situations. Here we address the much less studied non-equilibrium\nregime and investigate how polarons form dynamically in time. To this end, we\ndevelop a time-dependent renormalization group approach which allows\ncalculations of all dynamical properties of the system and takes into account\nthe effects of quantum fluctuations in the polaron cloud. We apply this method\nto calculate trajectories of polarons following a sudden quench of the\nimpurity-boson interaction strength, revealing how the polaronic cloud around\nthe impurity forms in time. Such trajectories provide additional information\nabout the polaron's properties which are challenging to extract directly from\nthe spectral function measured experimentally using ultracold atoms. At strong\ncouplings, our calculations predict the appearance of trajectories where the\nimpurity wavers back at intermediate times as a result of quantum fluctuations.\nOur method is applicable to a broader class of non-equilibrium problems. We\nalso apply it to calculate the spectral function and find good agreement with\nexperimental results. At very strong couplings, we predict that quantum\nfluctuations lead to the appearance of a dark continuum with strongly\nsuppressed spectral weight at low energies. While our calculations start from\nan effective Fr\\\"ohlich Hamiltonian describing impurities in a\nthree-dimensional Bose-Einstein condensate, we also calculate the effects of\nadditional terms in the Hamiltonian beyond the Fr\\\"ohlich paradigm. We\ndemonstrate that the main effect of these additional terms on the attractive\nside of a Feshbach resonance is to renormalize the coupling strength of the\neffective Fr\\\"ohlich model.",
        "positive": "Dark-bright solitons in Bose-Einstein condensates at finite temperatures: We study the dynamics of dark-bright solitons in binary mixtures of Bose\ngases at finite temperature using a system of two coupled dissipative\nGross-Pitaevskii equations. We develop a perturbation theory for the\ntwo-component system to derive an equation of motion for the soliton centers\nand identify different temperature-dependent damping regimes. We show that the\neffect of the bright (\"filling\") soliton component is to partially stabilize\n\"bare\" dark solitons against temperature-induced dissipation, thus providing\nlonger lifetimes. We also study analytically thermal effects on dark-bright\nsoliton \"molecules\" (i.e., two in- and out-of-phase dark-bright solitons),\nshowing that they undergo expanding oscillations while interacting. Our\nanalytical findings are in good agreement with results obtained via a\nBogoliubov-de Gennes analysis and direct numerical simulations."
    },
    {
        "anchor": "Interaction of solitons in dipolar Bose-Einstein condensates and\n  formation of soliton molecules: The interaction between two bright solitons in a dipolar Bose-Einstein\ncondensate (BEC) has been investigated aiming at finding the regimes when they\nform a stable bound state, known as soliton molecule. To study soliton\ninteractions in BEC we employed a method similar to that used in experimental\ninvestigation of the interaction between solitons in optical fibers. The idea\nconsists in creating two solitons at some spatial separation from each other at\ninitial time $t_0$, and then measuring the distance between them at a later\ntime $t_1 > t_0$. Depending on whether the distance between solitons has\nincreased, decreased or remained unchanged, compared to its initial value at\n$t_0$, we conclude that soliton interaction was repulsive, attractive or\nneutral, respectively. We propose an experimentally viable method for\nestimating the binding energy of a soliton molecule, based on its dissociation\nat critical soliton velocity. Our theoretical analysis is based on the\nvariational approach, which appears to be quite accurate in describing the\nproperties of soliton molecules in dipolar BEC, as reflected in good agreement\nbetween the analytical and numerical results.",
        "positive": "Renormalization group, dimer-dimer scattering, and three-body forces: We study the ratio between the fermion-fermion scattering length and the\ndimer-dimer scattering length for systems of nonrelativistic fermions, using\nthe same functional renormalisation technique as previously applied to\nfermionic matter. We find a strong dependence on the cutoff function used in\nthe renormalisation flow for a two-body truncation of the action. Adding a\nsimple three-body term substantially reduces this dependence."
    },
    {
        "anchor": "Spin exchange-induced spin-orbit coupling in a superuid mixture: We investigate the ground-state properties of a dual-species spin-1/2\nBose-Einstein condensate. One of the species is subjected to a pair of Raman\nlaser beams that induces spin-orbit (SO) coupling, whereas the other species is\nnot coupled to the Raman laser. In certain limits, analytical results can be\nobtained. It is clearly shown that, through the inter-species spin-exchange\ninteraction, the second species also exhibits SO coupling. This mixture system\ndisplays a very rich phase diagram, with many of the phases not present in an\nSO coupled single-species condensate. Our work provides a new way of creating\nSO coupling in atomic quantum gases, and opens up a new avenue of research in\nSO coupled superfluid mixtures. From a practical point of view, the spin\nexchange-induced SO coupling may overcome the heating issue for certain atomic\nspecies when subjected to the Raman beams.",
        "positive": "Non-Universal Equation of State of the Two-Dimensional Bose Gas: For a dilute two-dimensional Bose gas the universal equation of state has a\nlogarithmic dependence on the s-wave scattering length. Here we derive\nnon-universal corrections to this equation of state taking account finite-range\neffects of the inter-atomic potential. Our beyond-mean-field analytical results\nare obtained performing dimensional regularization of divergent zero-point\nquantum fluctuations within the finite-temperature formalism of functional\nintegration. In particular, we find that in the grand canonical ensemble the\npressure has a nonpolynomial dependence on the finite- range parameter and it\nis a highly nontrivial function of chemical potential and temperature."
    },
    {
        "anchor": "Crossover between integer and fractional vortex lattices in coherently\n  coupled two-component Bose-Einstein condensates: We study effects of the internal coherent (Rabi) coupling in vortex lattices\nin two-component BECs under rotation. We find how the vortex lattices without\nthe Rabi coupling known before are connected to the Abrikosov lattice of\ninteger vortices with increasing the Rabi coupling. We find that 1) for small\nRabi couplings, fractional vortices in triangular or square lattice for small\nor large inter-component coupling constitute hexamers or tetramers, namely\nmulti-dimer bound states made of six or four vortices, respectively, 2) these\nbound states are broken into a set of dimers at intermediate Rabi couplings,\nand 3) vortices change their partners in various ways depending on the\ninter-component coupling to organize themselves for constituting the Abrikosov\nlattice of integer vortices at strong Rabi couplings.",
        "positive": "Suppression and Revival of Weak Localization through Control of\n  Time-Reversal Symmetry: We report on the observation of suppression and revival of coherent\nbackscattering of ultra-cold atoms launched in an optical disorder and\nsubmitted to a short dephasing pulse, as proposed in a recent paper of T.\nMicklitz \\textit{et al.} [arXiv:1406.6915]. This observation, in a quasi-2D\ngeometry, demonstrates a novel and general method to study weak localization by\nmanipulating time reversal symmetry in disordered systems. In future\nexperiments, this scheme could be extended to investigate higher order\nlocalization processes at the heart of Anderson (strong) localization."
    },
    {
        "anchor": "Correlation properties of a one-dimensional repulsive Bose gas at finite\n  temperature: We present a comprehensive study shedding light on how thermal fluctuations\naffect correlations in a Bose gas with contact repulsive interactions in one\nspatial dimension. The pair correlation function, the static structure factor,\nand the one-body density matrix are calculated as a function of the interaction\nstrength and temperature with the exact ab-initio Path Integral Monte Carlo\nmethod. We explore all possible gas regimes from weak to strong interactions\nand from low to high temperatures. We provide a detailed comparison with a\nnumber of theories, such as perturbative (Bogoliubov and decoherent classical),\neffective (Luttinger liquid) and exact (ground-state and thermal Bethe Ansatz)\nones. Our Monte Carlo results exhibit an excellent agreement with the tractable\nlimits and provide a fundamental benchmark for future observations which can be\nachieved in atomic gases, cavity quantum-electrodynamic and\nsuperconducting-circuit platforms.",
        "positive": "Modified spin-wave theory with ordering vector optimization I:\n  frustrated bosons on the spatially anisotropic triangular lattice: We investigate a system of frustrated hardcore bosons, modeled by an XY\nantiferromagnet on the spatially anisotropic triangular lattice, using\nTakahashi's modified spin-wave (MSW) theory. In particular we implement\nordering vector optimization on the ordered reference state of MSW theory,\nwhich leads to significant improvement of the theory and accounts for quantum\ncorrections to the classically ordered state. The MSW results at zero\ntemperature compare favorably to exact diagonalization (ED) and projected\nentangled-pair state (PEPS) calculations. The resulting zero-temperature phase\ndiagram includes a 1D quasi-ordered phase, a 2D Neel ordered phase, and a 2D\nspiraling ordered phase. We have strong indications that the various ordered or\nquasi-ordered phases are separated by spin-liquid phases with short-range\ncorrelations, in analogy to what has been predicted for the Heisenberg model on\nthe same lattice. Within MSW theory we also explore the finite-temperature\nphase diagram. We find that the zero-temperature long-range-ordered phases turn\ninto quasi-ordered phases (up to a Berezinskii-Kosterlitz-Thouless\ntemperature), while zero-temperature quasi-ordered phases become short-range\ncorrelated at finite temperature. These results show that modified spin-wave\ntheory is very well suited for describing ordered and quasi-ordered phases of\nfrustrated XY spins (or, equivalently, of frustrated lattice bosons) both at\nzero and finite temperatures. While MSW theory, just as other theoretical\nmethods, cannot describe spin-liquid phases, its breakdown provides a fast\nmethod for singling out Hamiltonians which may feature these intriguing quantum\nphases. We thus suggest a tool for guiding our search for interesting systems\nwhose properties are necessarily studied with a physical quantum simulator."
    },
    {
        "anchor": "Irreversible entropy transport enhanced by fermionic superfluidity: The nature of the flow between two superfluids, as in the Josephson and\nfountain effects, is often understood in terms of reversible flow carried by an\nentropy-free, macroscopic wavefunction. While this wavefunction is responsible\nfor many intriguing properties of superfluids and superconductors, its\ninterplay with excitations in non-equilibrium situations is more subtle and\nless understood. Here, we observe large concurrent flows--not only of particles\nbut also entropy--through a ballistic channel connecting two strongly\ninteracting fermionic superfluids, both showing similar nonlinear responses to\nbiases in chemical potential and temperature. We find that the entropy\ntransported per particle is much larger than the local entropy of the\nequilibrium superfluid and is robust to changes in the channel's geometry. In\ncontrast, the timescales of advective and diffusive entropy transport vary\nsignificantly with the channel geometry. In our setting, superfluidity\ncounterintuitively increases the speed of irreversible entropy transport. We\ndevelop a phenomenological model describing the nonlinear dynamics within the\nframework of generalised gradient dynamics, an extension of Onsager's theory of\nirreversible processes. The presented approach to measure entropy currents may\nhelp uncover novel mechanisms of heat transfer in superfluids and\nsuperconducting devices.",
        "positive": "Lindblad Equation for the Inelastic Loss of Ultracold Atoms: The loss of ultracold trapped atoms due to deeply inelastic reactions has\npreviously been taken into account in effective field theories for low-energy\natoms by adding local anti-Hermitian terms to the effective Hamiltonian. Here\nwe show that when multi-atom systems are considered, an additional modification\nis required in the equation governing the density matrix. We define an\neffective density matrix by tracing over the states containing high-momentum\natoms produced by deeply inelastic reactions. We show that it satisfies a\nLindblad equation, with local Lindblad operators determined by the local\nanti-Hermitian terms in the effective Hamiltonian. We use the Lindblad equation\nto derive the universal relation for the two-atom inelastic loss rate for\nfermions with two spin states and the universal relation for the three-atom\ninelastic loss rate for identical bosons."
    },
    {
        "anchor": "Quantum dilute droplets of dipolar bosons at finite temperature: We systematically study the properties of dipolar Bose gases with two- and\nthree-body contact interactions at finite temperature using the\nHartree-Fock-Bogoliubov-Popov approximation. In uniform case, we obtain an\nexciting new extension of the seminal Lee-Huang-Yang corrected equation of\nstate that depends explicitly on the thermal fluctuations and on the coupling\nconstant of the three-body interaction. We investigate, on the other hand, the\neffects of thermal fluctuations on the occurrence and stability of a droplet\nstate in a Bose-Einstein condensate with strong dipole-dipole interactions. We\nfind that at finite temperature, the droplet phase appears as a narrow peak\nsurrounded by a broader thermal halo. We show that the number of particles\ninside the droplet decays with increasing temperature.",
        "positive": "Modulation instability associated nonlinear dynamics of spin-orbit\n  coupled Bose-Einstein condensates: We study pattern-forming nonlinear dynamics starting from a continuous wave\nstate of quasi-one-dimensional two-component Bose-Einstein condensates with\nsynthetic spin-orbit coupling induced by Raman lasers. Modulation instability\ncan occur even when the miscibility condition due to the interatomic\ninteractions is satisfied. We find that the initial stage of the nonlinear\ndevelopment is consistent with the prediction of modulation instability, where\nthe two primary and secondary instability bands lead to the spontaneous growth\nof the modulation and the subsequent complicated dynamics of pattern formation.\nAt later stages of the evolution, the wave functions undergo clear separation\nin the momentum space, reflected in the dispersion of the single particle\nHamiltonian."
    },
    {
        "anchor": "Enhanced visibility of the Fulde-Ferrell-Larkin-Ovchinnikov state in one\n  dimensional Bose-Fermi mixtures near the immiscibility point: Based on the matrix product states method, we investigate numerically the\nground state properties of one-dimensional mixtures of repulsive bosons and\nspin-imbalanced attractive fermions, the latter being in the\nFulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, where Cooper pairs condense at a\nfinite momentum $k=k_{FFLO}$. We find that the visibility of such a state is\ndramatically enhanced as the repulsive Bose-Fermi mixture is brought close to\nthe phase-separation point. In particular, large amplitude self-induced\noscillations with wave-vector $2k_{FFLO}$ appear in both the fermion total\ndensity and the boson density profiles, leaving sharp fingerprints in the\ncorresponding static structure factors. We show that these features remain well\nvisible in cold atoms systems trapped longitudinally by a smooth flat-bottom\npotential. Hence bosons can be used to directly reveal the modulated Fermi\nsuperfluid in experiments.",
        "positive": "Hyperbolic Bloch equations: atom-cluster kinetics of an interacting Bose\n  gas: Experiments with ultracold Bose gases can already produce so strong\natom--atom interactions that one can observe intriguing many-body dynamics\nbetween the Bose-Einstein condensate (BEC) and the normal component. The\nexcitation picture is applied to uniquely express the many-body state uniquely\nin terms of correlated atom clusters within the normal component alone.\nImplicit notation formalism is developed to {\\it explicitly} derive the quantum\nkinetics of {\\it all} atom clusters. The clusters are shown to build up\nsequentially, from smaller to larger ones, which is utilized to\nnonperturbatively describe the interacting BEC with as few clusters as\npossible. This yields the hyperbolic Bloch equations (HBEs) that not only\ngeneralize the Hartree-Fock Bogoliubov approach but also are analogous to the\nsemiconductor Bloch equations (SBEs). This connection is utilized to apply\nsophisticated many-body techniques of semiconductor quantum optics to BEC\ninvestigations. Here, the HBEs are implemented to determine how a strongly\ninteracting Bose gas reacts to a fast switching from weak to strong\ninteractions, often referred to as unitarity. The computations for $^{35}$Rb\ndemonstrate that molecular states (dimers) depend on atom density, and that the\nmany-body interactions create coherent transients on a 100$\\mu$s time scale\nconverting BEC into normal state via quantum depletion."
    },
    {
        "anchor": "Phase space monitoring of exciton-polariton multistability: Dynamics of exciton-polariton multistability is theoretically investigated.\nPhase portraits are used as a tool to enlighten the microscopic phenomena which\ninfluence spin multistability of a confined polariton field as well as\nultrafast reversible spin switching. The formation of a non-radiative\nreservoir, due to polariton pairing into biexcitons is found to play the lead\nrole in the previously reported spin switching experiments. Ways to tailor this\nreservoir formation are discussed in order to obtain optimal spin switching\nreliability.",
        "positive": "Motional Coherence of Fermions Immersed in a Bose Gas: We prepare a superposition of two motional states by addressing lithium atoms\nimmersed in a Bose-Einstein condensate of sodium with a species-selective\npotential. The evolution of the superposition state is characterized by the\npopulations of the constituent states as well as their coherence. The latter we\nextract employing a novel scheme analogous to the spin-echo technique.\nComparing the results directly to measurements on freely-evolving fermions\nallows us to isolate the decoherence effects induced by the bath. In our\nsystem, the decoherence time is close to the maximal possible value since the\ndecoherence is dominated by population relaxation processes. The measured data\nare in good agreement with a theoretical model based on Fermi's golden rule."
    },
    {
        "anchor": "Spatially inhomogeneous phase evolution of a two-component Bose-Einstein\n  condensate: We investigate the spatially dependent relative phase evolution of an\nelongated two-component Bose-Einstein condensate. The pseudospin-1/2 system is\ncomprised of the |F=1,m_F=-1> and |F=2,m_F=+1> hyperfine ground states of 87Rb,\nwhich we magnetically trap and interrogate with radio-frequency and microwave\nfields. We probe the relative phase evolution with Ramsey interferometry and\nobserve a temporal decay of the interferometric contrast well described by a\nmean-field formalism. Inhomogeneity of the collective relative phase dominates\nthe loss of interferometric contrast, rather than decoherence or phase\ndiffusion. We demonstrate a technique to simultaneously image each state,\nyielding subpercent variations in the measured relative number while preserving\nthe spatial mode of each component. In addition, we propose a spatially\nsensitive interferometric technique to image the relative phase.",
        "positive": "Dynamics of Uniform Quantum Gases, I: Density and Current Correlations: A unified approach valid for any wavenumber, frequency, and temperature is\npresented for uniform ideal quantum gases allowing for a comprehensive study of\nnumber density and particle-current density response functions. Exact\nanalytical expressions are obtained for spectral functions in terms of\npolylogarithms. Also, particle-number and particle-current static\nsusceptibilities are presented which, for fugacity less than unity,\nadditionally involve Kummer functions. The wavenumber and temperature dependent\ntransverse-current static susceptibility is used to show explicitly that\ncurrent correlations are of a long range in a Bose-condensed uniform ideal gas\nbut for bosons above the critical temperature and for Fermi and Boltzmann gases\nat all temperatures these correlations are of short range. Contact repulsive\ninteractions for systems of neutral quantum particles are considered within the\nrandom-phase approximation. The expressions for particle-number and\ntransverse-current susceptibilities are utilized to discuss the existence or\nnonexistence of superfluidity in the systems under consideration."
    },
    {
        "anchor": "Effective triangular ladders with staggered flux from spin-orbit\n  coupling in 1D optical lattices: Light-induced spin-orbit coupling is a flexible tool to study quantum\nmagnetism with ultracold atoms. In this work we show that spin-orbit coupled\nBose gases in a one-dimensional optical lattice can be mapped into a two-leg\ntriangular ladder with staggered flux following a lowest-band truncation of the\nHamiltonian. The effective flux and the ratio of the tunneling strengths can be\nindependently adjusted to a wide range of values. We identify a certain regime\nof parameters where a hard-core boson approximation holds and the system\nrealizes a frustrated triangular spin ladder with tunable flux. We study the\nproperties of the effective spin Hamiltonian using the density-matrix\nrenormalization-group method and determine the phase diagram at half-filling.\nIt displays two phases: a uniform superfluid and a bond-ordered insulator. The\nlatter can be stabilized only for low Raman detuning. Finally, we provide\nexperimentally feasible trajectories across the parameter space of the SOC\nsystem that cross the predicted phase transition.",
        "positive": "Saturation of black hole lasers in Bose-Einstein condensates: To obtain the end-point evolution of the so-called black hole laser\ninstability, we study the set of stationary solutions of the Gross-Pitaevskii\nequation for piecewise constant potentials which admit a homogeneous solution\nwith a supersonic flow in the central region between two discontinuities. When\nthe distance between them is larger than a critical value, we recover that the\nhomogeneous solution is unstable, and we identify the lowest energy state. We\nshow that it can be viewed as determining the saturated value of the first\n(node-less) complex frequency mode which drives the instability. We also\nclassify the set of stationary solutions and establish their relation both with\nthe set of complex frequency modes and with known soliton solutions. Finally,\nwe adopt a procedure \\`a la Pitaevski-Baym-Pethick to construct the effective\nfunctional which governs the transition from the homogeneous to non-homogeneous\nsolutions."
    },
    {
        "anchor": "High Chern number topological superfluids and new class of topological\n  phase transitions of Rashba spin-orbit coupled fermions on a lattice: Searching for the first topological superfluid (TSF) remains a primary goal\nof modern science. Here we study the system of attractively interacting\nfermions hopping in a square lattice with any linear combinations of Rashba or\nDresselhaus spin-orbit coupling (SOC) in a normal Zeeman field. By imposing\nself-consistence equations at half filling, we find there are 3 phases: Band\ninsulator ( BI ), Superfluid (SF) and Topological superfluid (TSF) with a Chern\nnumber $ C=2 $. The $ C=2 $ TSF happens in small Zeeman fields and weak\ninteractions which is in the experimentally most easily accessible regime. The\ntransition from the BI to the SF is a first order one due to the multi-minima\nstructure of the ground state energy landscape. There is a new class of\ntopological phase transition from the SF to the $ C=2 $ TSF at the low critical\nfield $ h_{c1} $, then another one from the $ C=2 $ TSF to the BI at the upper\ncritical field $ h_{c2} $. We derive effective actions to describe the two new\nclasses of topological phase transitions, then use them to study the Majorana\nedge modes and the zero modes inside the vortex core of the $ C=2 $ TSF near\nboth $ h_{c1} $ and $ h_{c2} $, especially explore their spatial and spin\nstructures. We find the edge modes decay into the bulk with oscillating\nbehaviors and determine both the decay and oscillating lengths. We compute the\nbulk spectra and map out the Berry Curvature distribution in momentum space\nnear both $ h_{c1} $ and $ h_{c2} $. We also elaborate some intriguing\nbulk-Berry curvature-edge-vortex correspondences. Experimental implications in\nboth 2d non-centrosymmetric materials under a periodic substrate and cold atoms\nin an optical lattice are given.",
        "positive": "Self-bound droplet clusters in laser-driven Bose-Einstein condensates: We investigate a two-dimensional Bose-Einstein condensate that is optically\ndriven via a retro-reflecting mirror, forming a single optical feedback loop.\nThis induces a peculiar type of long-range atomic interaction with highly\noscillatory behavior, and we show here how the sign of the underlying\ninteraction potential can be controlled by additional optical elements and\nexternal fields. This additional tunability enriches the behavior of the system\nsubstantially, and gives rise to a surprising range of new ground states of the\ncondensate. In particular, we find the emergence of self-bound crystals of\nquantum droplets with various lattice structures, from simple and familiar\ntriangular arrays to complex superlattice structures and crystals with entirely\nbroken rotational symmetry. This includes mesoscopic clusters composed of small\nnumbers of quantum droplets as well as extended crystalline structures.\nImportantly, such ordered states are entirely self-bound and stable without any\nexternal in-plane confinement, having no counterpart to other quantum-gas\nsettings with long-range atomic interactions."
    },
    {
        "anchor": "Coarsening dynamics of binary Bose condensates: We study the dynamics of domain formation and coarsening in a binary\nBose-Einstein condensate that is quenched across a miscible-immiscible phase\ntransition. The late-time evolution of the system is universal and governed by\nscaling laws for the correlation functions. We numerically determine the\nscaling forms and extract the critical exponents that describe the growth rate\nof domain size and autocorrelations. Our data is consistent with inviscid\nhydrodynamic domain growth, which is governed by a universal dynamical critical\nexponent of $1/z = 0.68(2)$. In addition, we analyze the effect of domain wall\nconfigurations which introduce a nonanalytic term in the short-distance\nstructure of the pair correlation function, leading to a high-momentum\n\"Porod\"-tail in the static structure factor, which can be measured\nexperimentally.",
        "positive": "Probing entanglement in a many-body-localized system: An interacting quantum system that is subject to disorder may cease to\nthermalize due to localization of its constituents, thereby marking the\nbreakdown of thermodynamics. The key to our understanding of this phenomenon\nlies in the system's entanglement, which is experimentally challenging to\nmeasure. We realize such a many-body-localized system in a disordered\nBose-Hubbard chain and characterize its entanglement properties through\nparticle fluctuations and correlations. We observe that the particles become\nlocalized, suppressing transport and preventing the thermalization of\nsubsystems. Notably, we measure the development of non-local correlations,\nwhose evolution is consistent with a logarithmic growth of entanglement entropy\n- the hallmark of many-body localization. Our work experimentally establishes\nmany-body localization as a qualitatively distinct phenomenon from localization\nin non-interacting, disordered systems."
    },
    {
        "anchor": "Diagrammatic Monte Carlo approach to angular momentum in quantum\n  many-particle systems: We introduce a Diagrammatic Monte Carlo (DiagMC) approach to angular momentum\nproperties of quantum many-particle systems possessing a macroscopic number of\ndegrees of freedom. The treatment is based on a diagrammatic expansion that\nmerges the usual Feynman diagrams with the angular momentum diagrams known from\natomic and nuclear structure theory, thereby incorporating the non-Abelian\nalgebra inherent to quantum rotations. Our approach is applicable at arbitrary\ncoupling, is free of systematic errors and of finite size effects, and\nnaturally provides access to the impurity Green function. We exemplify the\ntechnique by obtaining an all-coupling solution of the angulon model, however,\nthe method is quite general and can be applied to a broad variety of systems in\nwhich particles exchange quantum angular momentum with their many-body\nenvironment.",
        "positive": "Universality of the unitary Fermi gas: A few-body perspective: We revisit the properties of the two-component Fermi gas with short-range\ninteractions in three dimensions, in the limit where the s-wave scattering\nlength diverges. Such a unitary Fermi gas possesses universal thermodynamic and\ndynamical observables that are independent of any interaction length scale.\nFocusing on trapped systems of N fermions, where N$\\leq10$, we investigate how\nwell we can determine the zero-temperature behavior of the many-body system\nfrom published few-body data on the ground-state energy and the contact. For\nthe unpolarized case, we find that the Bertsch parameters extracted from\ntrapped few-body systems all lie within 15% of the established value.\nFurthermore, the few-body values for the contact are well within the range of\nvalues determined in the literature for the many-body system. In the limit of\nlarge spin polarization, we obtain a similar accuracy for the polaron energy,\nand we estimate the polaron's effective mass from the dependence of its energy\non N. We also compute an upper bound for the squared wave-function overlap\nbetween the unitary Fermi system and the non-interacting ground state, both for\nthe trapped and uniform cases. This allows us to prove that the trapped\nunpolarised ground state at unitarity has zero overlap with its non-interacting\ncounterpart in the many-body limit N$\\to \\infty$."
    },
    {
        "anchor": "Preparing and Analyzing Solitons in the sine-Gordon Model with Quantum\n  Gas Microscopes: The sine-Gordon model emerges as a low-energy theory in a plethora of quantum\nmany-body systems. Here, we theoretically investigate tunnel-coupled\nBose-Hubbard chains with strong repulsive interactions as a realization of the\nsine-Gordon model deep in the quantum regime. We propose protocols for quantum\ngas microscopes of ultracold atoms to prepare and analyze solitons, that are\nthe fundamental topological excitations of the emergent sine-Gordon theory.\nWith numerical simulations based on matrix product states we characterize the\npreparation and detection protocols and discuss the experimental requirements.",
        "positive": "Phase transition dimensionality crossover from two to three dimensions\n  in a trapped ultracold atomic Bose gas: The equilibrium properties of a weakly interacting atomic Bose gas across the\nBerezinskii-Kosterlitz-Thouless (BKT) and Bose-Einstein condensation (BEC)\nphase transitions are numerically investigated through a dimensionality\ncrossover from two to three dimensions. The crossover is realised by confining\nthe gas in an experimentally feasible hybridised trap which provides\nhomogeneity along the planar xy-directions through a box potential in tandem\nwith a harmonic transverse potential along the transverse z-direction. The\ndimensionality is modified by varying the frequency of the harmonic trap from\ntight to loose transverse trapping. Our findings, based on a stochastic\n(projected) Gross-Pitaevskii equation, showcase a continuous shift in the\ncharacter of the phase transition from BKT to BEC, and a monotonic increase of\nthe identified critical temperature as a function of dimensionality, with the\nstrongest variation exhibited for small chemical potential values up to\napproximately twice the transverse confining potential"
    },
    {
        "anchor": "Superfluidity of Bosons in Kagome Lattices with Frustration: In this letter we consider spinless bosons in a Kagome lattice with\nnearest-neighbor hopping and on-site interaction, and the sign of hopping is\ninverted by insetting a {\\pi} flux in each triangle of Kagome lattice so that\nthe lowest single particle band is perfectly flat. We show that in the high\ndensity limit, despite of the infinite degeneracy of the single particle ground\nstates, interaction will select out the Bloch state at the K point of Brillouin\nzone for boson condensation at the lowest temperature. As temperature\nincreases, the single boson superfluid order can be easily destroyed, while an\nexotic triple-boson paired superfluid order will remain. We establish that this\ntrion superfluid exists in a broad temperature regime until the temperature is\nincreased to the same order of hopping and then the system turns into normal\nphases. Finally we show that time of flight measurement of momentum\ndistribution and its noise correlation can be used to distinguish these three\nphases.",
        "positive": "Critical temperature of noninteracting bosonic gases in cubic optical\n  lattices at arbitrary integer fillings: We have shown that the critical temperature of a Bose-Einstein condensate to\na normal phase transition of noninteracting bosons in cubic optical lattices\nhas a linear dependence on the filling factor, especially at large densities.\nThe condensed fraction exhibits a linear power law dependence on temperature in\ncontrast to the case of ideal homogeneous Bose gases."
    },
    {
        "anchor": "Spontaneous symmetry breaking in a spin-orbit coupled $f=2$ spinor\n  condensate: We study the ground-state density profile of a spin-orbit coupled $f=2$\nspinor condensate in a quasi-one-dimensional trap. The Hamiltonian of the\nsystem is invariant under time reversal but not under parity. We identify\ndifferent parity- and time-reversal-symmetry-breaking states. The\ntime-reversal-symmetry breaking is possible for degenerate states. A phase\nseparation among densities of different components is possible in the domain of\ntime-reversal-symmetry breaking. Different types of parity- and\ntime-reversal-symmetry-breaking states are predicted analytically and studied\nnumerically. We employ numerical and approximate analytic solutions of a\nmean-field model in this investigation to illustrate our findings.",
        "positive": "Optical Feshbach resonances and ground state molecule production in the\n  RbHg system: We present the prospects for photoassociation, optical control of\ninterspecies scattering lengths and finally, the production of ultracold\nabsolute ground state molecules in the Rb+Hg system. We use the \"gold standard\"\nab initio methods for the calculations of ground (CCSD(T)) and excited state\n(EOM-CCSD) potential curves. The RbHg system, thanks to the wide range of\nstable Hg bosonic isotopes, offers possibilities for mass-tuning of ground\nstate interactions. The optical lengths describing the strengths of optical\nFeshbach resonances near the Rb transitions are favorable even at large laser\ndetunings. Ground state RbHg molecules can be produced with efficiencies\nranging from about 20% for deeply bound to at least 50% for weakly bound states\nclose to the dissociation limit. Finally, electronic transitions with favorable\nFranck-Condon factors can be found for the purposes of a STIRAP transfer of the\nweakly bound RbHg molecules to the absolute ground state using commercially\navailable lasers."
    },
    {
        "anchor": "Stability of resonantly interacting heavy-light Fermi mixtures: We investigate a two-component mixture of resonantly interacting Fermi gases\nas a function of the ratio \\kappa of the heavy to the light mass of the two\nspecies. The diffusion Monte Carlo method is used to calculate the ground-state\nenergy and the pair correlation function starting from two different guiding\nwave functions, which describe respectively the superfluid and the normal state\nof the gas. Results show that the mixture is stable and superfluid for mass\nratios smaller than the critical value \\kappa_c = 13 +/- 1. For larger values\nof \\kappa simulations utilizing the wave function of the normal state are\nunstable towards cluster formation. The relevant cluster states driving the\ninstability appear to be formed by one light particle and two or more heavy\nparticles within distances on the order of the range of the interatomic\npotential. The small overlap between the wave function of the trimer bound\nstate and the guiding wave function used to describe the superfluid state\nproduces the unphysical stability of the superfluid gas above \\kappa_c.",
        "positive": "Bright matter-wave soliton collisions at narrow barriers: We study fast-moving bright solitons in the focusing nonlinear Schr\\\"odinger\nequation perturbed by a narrow Gaussian potential barrier. In particular, we\npresent a general and comprehensive analysis of the case where two fast-moving\nbright solitons collide at the location of the barrier. In the limiting case of\na delta-function barrier, we use a quasi-analytic method to show that the\nrelative norms of the outgoing waves depends sinusoidally on the relative phase\nof the incoming waves, and to determine whether one, or both, of the outgoing\nwaves are bright solitons. We show using numerical simulations that this\nquasi-analytic result is valid in the high velocity limit: outside this limit\nnonlinear effects introduce a skew to the phase-dependence, which we quantify.\nFinally, we numerically explore the effects of introducing a finite-width\nGaussian barrier. Our results are particularly relevant, as they can be used to\ndescribe a range of interferometry experiments using bright solitary\nmatter-waves."
    },
    {
        "anchor": "Detecting $\u03c0$-phase superfluids with $p$-wave symmetry in a quasi-1D\n  optical lattice: We propose an experimental protocol to study $p$-wave superfluidity in a\nspin-polarized cold Fermi gas tuned by an $s$-wave Feshbach resonance. A\ncrucial ingredient is to add a quasi-1D optical lattice and tune the fillings\nof two spins to the $s$ and $p$ band, respectively. The pairing order parameter\nis confirmed to inherit $p$-wave symmetry in its center-of-mass motion. We find\nthat it can further develop into a state of unexpected $\\pi$-phase modulation\nin a broad parameter regime. Measurable quantities are calculated, including\ntime-of-flight distributions, radio-frequency spectra, and in situ\nphase-contrast imaging in an external trap. The $\\pi$-phase $p$-wave superfluid\nis reminiscent of the $\\pi$-state in superconductor-ferromagnet\nheterostructures but differs in symmetry and origin. If observed, it would\nrepresent another example of $p$-wave pairing, first discovered in He-3\nliquids.",
        "positive": "Quantum quenches in the anisotropic spin-1/2 Heisenberg chain: different\n  approaches to many-body dynamics far from equilibrium: Recent experimental achievements in controlling ultracold gases in optical\nlattices open a new perspective on quantum many-body physics. In these\nexperimental setups it is possible to study coherent time evolution of isolated\nquantum systems. These dynamics reveal new physics beyond the low-energy\nproperties usually relevant in solid-state many-body systems. In this paper we\nstudy the time evolution of antiferromagnetic order in the Heisenberg chain\nafter a sudden change of the anisotropy parameter, using various numerical and\nanalytical methods. As a generic result we find that the order parameter, which\ncan show oscillatory or non-oscillatory dynamics, decays exponentially except\nfor the effectively non-interacting case of the XX limit. For weakly ordered\ninitial states we also find evidence for an algebraic correction to the\nexponential law. The study is based on numerical simulations using a numerical\nmatrix product method for infinite system sizes (iMPS), for which we provide a\ndetailed description and an error analysis. Additionally, we investigate in\ndetail the exactly solvable XX limit. These results are compared to\napproximative analytical approaches including an effective description by the\nXZ-model as well as by mean-field, Luttinger-liquid and sine-Gordon theories.\nThis reveals which aspects of non-equilibrium dynamics can as in equilibrium be\ndescribed by low-energy theories and which are the novel phenomena specific to\nquantum quench dynamics. The relevance of the energetically high part of the\nspectrum is illustrated by means of a full numerical diagonalization of the\nHamiltonian."
    },
    {
        "anchor": "Detection of Pair-Superfluidity for bosonic mixtures in optical lattices: We consider a mixture of two bosonic species with tunable interspecies\ninteraction in a periodic potential and discuss the advantages of low filling\nfactors on the detection of the pair-superfluid phase. We show how the\nemergence of such a phase can be put dramatically into evidence by looking at\nthe interference pictures and density correlations after expansion and by\nchanging the interspecies interaction from attractive to repulsive.",
        "positive": "Phase separation of binary condensates in harmonic and lattice\n  potentials: We propose a modified Gaussian ansatz to study binary condensates, trapped in\nharmonic and optical lattice potentials, both in miscible and immiscible\ndomains. The ansatz is an apt one as it leads to the smooth transition from\nmiscible to immiscible domains without any {\\em a priori} assumptions. In\noptical lattice potentials, we analyze the squeezing of the density profiles\ndue to the increase in the depth of the optical lattice potential. For this we\ndevelop a model with three potential wells, and define the relationship between\nthe lattice depth and profile of the condensate."
    },
    {
        "anchor": "Propagation front of correlations in an interacting Bose gas: We analyze the quench dynamics of a one-dimensional bosonic Mott insulator\nand focus on the time evolution of density correlations. For these we identify\na pronounced propagation front, the velocity of which, once correctly\nextrapolated at large distances, can serve as a quantitative characteristic of\nthe many-body Hamiltonian. In particular, the velocity allows the weakly\ninteracting regime, which is qualitatively well described by free bosons, to be\ndistinguished from the strongly interacting one, in which pairs of distinct\nquasiparticles dominate the dynamics. In order to describe the latter case\nanalytically, we introduce a general approximation to solve the Bose-Hubbard\nHamiltonian based on the Jordan-Wigner fermionization of auxiliary particles.\nThis approach can also be used to determine the ground-state properties. As a\ncomplement to the fermionization approach, we derive explicitly the\ntime-dependent many-body state in the noninteracting limit and compare our\nresults to numerical simulations in the whole range of interactions of the\nBose-Hubbard model.",
        "positive": "Collisional Stability of 40K Immersed in a Strongly Interacting Fermi\n  Gas of 6Li: We investigate the collisional stability of a sample of 40K atoms immersed in\na tunable spin mixture of 6Li atoms. In this three-component Fermi-Fermi\nmixture, we find very low loss rates in a wide range of interactions as long as\nmolecule formation of 6Li is avoided. The stable fermionic mixture with two\nresonantly interacting spin states of one species together with another species\nis a promising system for a broad variety of phenomena in few- and many-body\nquantum physics."
    },
    {
        "anchor": "Pairing correlations across the superfluid phase transition in the\n  unitary Fermi gas: In the two-component Fermi gas with a contact interaction, a pseudogap regime\ncan exist at temperatures between the superfluid critical temperature $T_c$ and\na temperature $T^* > T_c$. This regime is characterized by pairing correlations\nwithout superfluidity. However, in the unitary limit of infinite scattering\nlength, the existence of this regime is still debated. To help address this, we\nhave applied finite-temperature auxiliary-field quantum Monte Carlo (AFMC) to\nstudy the thermodynamics of the superfluid phase transition and signatures of\nthe pseudogap in the spin-balanced homogeneous unitary Fermi gas. We present\nresults at finite filling factor $\\nu \\simeq 0.06$ for the condensate fraction,\nan energy-staggering pairing gap, the spin susceptibility, and the heat\ncapacity, and compare them to experimental data when available. In contrast to\nprevious AFMC simulations, our model space consists of the complete first\nBrillouin zone of the lattice, and our calculations are performed in the\ncanonical ensemble of fixed particle number. The canonical ensemble AFMC\nframework enables the calculation of a model-independent gap, providing direct\ninformation on pairing correlations without the need for numerical analytic\ncontinuation. We use finite-size scaling to estimate $T_c$ at the corresponding\nfilling factor. We find that the energy-staggering pairing gap vanishes above\n$T_c$, showing no pseudogap effects, and that the spin susceptibility shows a\nsubstantially reduced signature of a spin gap compared to previously reported\nAFMC simulations.",
        "positive": "Dynamics of Bright Soliton Under Cubic-Quartic Interactions in Quasi\n  One-Dimensional Geometry: Recent inspection of liquid-like state in ultracold atomic gases due to the\nstabilization mechanism through the delicate balance between effective\nmean-field and beyond mean-field (BMF) interactions, has motivated us to study\nthe modified/extended Gross-Pitaevskii (eGP) equation which includes the BMF\ncontribution. In this article, we focus on variational analysis of solitonic\nregime with eGP equation while the soliton is subjected to an obstacle. This\nreveals different scattering scenarios of the soliton with explicit dependence\nof the BMF interaction. The results show the existence of tunneling, partial\nand complete trappings, in different parameter domains. These observations are\nfurther corroborated by the fast-Fourier transform method. In the later part we\nalso extend our analysis to trapped systems. The controlled trapping in defect\npotential and its release can be potentially useful for quantum information\nstorage."
    },
    {
        "anchor": "Edge states and topological phases in one-dimensional optical\n  superlattices: We show that one-dimensional quasi-periodic optical lattice systems can\nexhibit edge states and topological phases which are generally believed to\nappear in two-dimensional systems. When the Fermi energy lies in gaps, the\nFermi system on the optical superlattice is a topological insulator\ncharacterized by a nonzero topological invariant. The topological nature can be\nrevealed by observing the density profile of a trapped fermion system, which\ndisplays plateaus with their positions uniquely determined by the ration of\nwavelengths of the bichromatic optical lattice. The butterfly-like spectrum of\nthe superlattice system can be also determined from the finite-temperature\ndensity profiles of the trapped fermion system. This finding opens an\nalternative avenue to study the topological phases and Hofstadter-like spectrum\nin one-dimensional optical lattices.",
        "positive": "Quantum Hall phases of two-component bosons: The recent production of synthetic magnetic fields acting on electroneutral\nparticles, like atoms or photons, has boosted the interest in the quantum Hall\nphysics of bosons. Adding pseudospin-1/2 to the bosons greatly enriches the\nscenario, as it allows them to form an interacting integer quantum Hall (IQH)\nphase with no fermionic counterpart. Here we show that, for a small\ntwo-component Bose gas on a disk, the complete strongly correlated regime,\nextending from the integer phase at filling factor $\\nu=2$ to the Halperin\nphase at filling factor $\\nu=2/3$, is well described by composite\nfermionization of the bosons. Moreover we study the edge excitations of the IQH\nstate, which, in agreement with expectations from topological field theory, are\nfound to consist of forward-moving charge excitations and backward-moving spin\nexcitations. Finally, we demonstrate how pair-correlation functions allow one\nto experimentally distinguish the IQH state from competing states, like\nnon-Abelian spin singlet (NASS) states."
    },
    {
        "anchor": "Ground-state and dynamical properties of two-dimensional dipolar Fermi\n  liquids: We study the ground-state properties of a two-dimensional spin-polarized\nfluid of dipolar fermions within the Euler-Lagrange Fermi-hypernetted-chain\napproximation. Our method is based on the solution of a scattering\nSchr\\\"odinger equation for the \"pair amplitude\" $\\sqrt{g(r)}$, where $g(r)$ is\nthe pair distribution function. A key ingredient in our theory is the effective\npair potential, which includes a bosonic term from Jastrow-Feenberg\ncorrelations and a fermionic contribution from kinetic energy and exchange,\nwhich is tailored to reproduce the Hartree-Fock limit at weak coupling. Very\ngood agreement with recent results based on quantum Monte Carlo simulations is\nachieved over a wide range of coupling constants up to the liquid-to-crystal\nquantum phase transition (QPT). Using a certain approximate model for the\ndynamical density-density response function, we furthermore demonstrate that:\ni) the liquid phase is stable towards the formation of density waves up to the\nliquid-to-crystal QPT and ii) an undamped zero-sound mode exists for any value\nof the interaction strength, down to infinitesimally weak couplings.",
        "positive": "Collapse and revival of oscillations in a parametrically excited\n  Bose-Einstein condensate in combined harmonic and optical lattice trap: In this work, we study parametric resonances in an elongated cigar-shaped BEC\nin a combined harmonic trap and a time dependent optical lattice by using\nnumerical and analytical techniques. We show that there exists a relative\ncompetition between the harmonic trap which tries to spatially localize the BEC\nand the time varying optical lattice which tries to delocalize the BEC. This\ncompetition gives rise to parametric resonances (collapse and revival of the\noscillations of the BEC width). Parametric resonances disappear when one of the\ncompeting factors i.e strength of harmonic trap or the strength of optical\nlattice dominates. Parametric instabilities (exponential growth of Bogoliubov\nmodes) arise for large variations in the strength of the optical lattice."
    },
    {
        "anchor": "Simulating and exploring Weyl semimetal physics with cold atoms in a\n  two-dimensional optical lattice: We propose a scheme to simulate and explore Weyl semimetal physics with\nultracold fermionic atoms in a two-dimensional square optical lattice subjected\nto experimentally realizable spin-orbit coupling and an artificial dimension\nfrom an external parameter space, which may increase experimental feasibility\ncompared with the cases in three dimensional optical lattices. It is shown that\nthis system with a tight-binding model is able to describe essentially\nthree-dimensional Weyl semimetals with tunable Weyl points. The relevant\ntopological properties are also addressed by means of the Chern number and the\ngapless edge states. Furthermore, we illustrate that the mimicked Weyl points\ncan be experimentally detected by measuring the atomic transfer fractions in a\nBloch-Zener oscillation, and the characteristic topological invariant can be\nmeasured with the particle pumping approach.",
        "positive": "One-loop renormalization group study of boson-fermion mixtures: A weakly interacting boson-fermion mixture model was investigated using\nWisonian renormalization group analysis. This model includes one boson-boson\ninteraction term and one boson-fermion interaction term. The scaling dimensions\nof the two interaction coupling constants were calculated as 2-D at tree level\nand the Gell-Mann-Low equations were derived at one-loop level. We find that in\nthe Gell-Mann-Low equations the contributions from the fermion loops go to zero\nas the length scale approaches infinity. After ignoring the fermion loop\ncontributions two fixed points were found in 3 dimensional case. One is the\nGaussian fixed point and the other one is Wilson-Fisher fixed point. We find\nthat the boson-fermion interaction decouples at the Wilson-Fisher fixed point.\nWe also observe that under RG transformation the boson-fermion interaction\ncoupling constant runs to negative infinity with a small negative initial\nvalue, which indicates a boson-fermion pairing instability. Furthermore, the\npossibility of emergent supersymmetry in this model was discussed."
    },
    {
        "anchor": "Spin-orbit-coupled Bose-Einstein condensates held under toroidal trap: We study a quasispin-$1/2$ Bose-Einstein condensate with synthetically\ngenerated spin-orbit coupling in a toroidal trap, and show that the system has\na rich variety of ground and metastable states. As the central hole region\nincreases, i.e., the potential changes from harmonic-like to ring-like, the\ncondensate exhibits a variety of structures, such as triangular stripes,\nflower-petal patterns, and counter-circling states. We also show that the\nrotating systems have exotic vortex configurations. In the limit of a quasi-one\ndimensional ring, the quantum many-body ground state is obtained, which is\nfound to be the fragmented condensate.",
        "positive": "Universal Spin Transport and Quantum Bounds for Unitary Fermions: We review recent advances in experimental and theoretical understanding of\nspin transport in strongly interacting Fermi gases. The central new phenomenon\nis the observation of a lower bound on the (bare) spin diffusivity in the\nstrongly interacting regime. Transport bounds are of broad interest for the\ncondensed matter community, with a conceptual similarity to observed bounds in\nshear viscosity and charge conductivity. We discuss the formalism of spin\nhydrodynamics, how dynamics are parameterized by transport coefficients, the\neffect of confinement, the role of scale invariance, the quasi-particle\npicture, and quantum critical transport. We conclude by highlighting open\nquestions, such as precise theoretical bounds, relevance to other phases of\nmatter, and extensions to lattice systems."
    },
    {
        "anchor": "Coreless vorticity in multicomponent Bose and Fermi superfluids: We consider quantized vortices in two-component Bose-Einstein condensates and\nthree-component Fermi gases with attractive interactions. In these systems, the\nvortex core can be either empty (normal in the fermion case) or filled with\nanother superfluid. We determine critical values of the parameters -- chemical\npotentials, scattering lengths and, for Fermi gases, temperature -- at which a\nphase transition between the two types of vortices occurs. Population imbalance\ncan lead to superfluid core (coreless) vorticity in multicomponent superfluids\nwhich otherwise support only usual vortices. For multicomponent Fermi gases, we\nconstruct the phase diagram including regions of coreless vorticity. We extend\nour results to trapped bosons and fermions using an appropriate local\napproximation, which goes beyond the usual Thomas-Fermi approximation for\ntrapped bosons.",
        "positive": "From optical lattices to quantum crystals: Optical lattices can be loaded with atoms which can have strong interactions,\nsuch that the interaction of atoms at different lattice sites cannot be\nneglected. Moreover, the intersite interactions can be so strong that it can\nforce the atoms to form a self-organized lattice, such that exists in crystals.\nWith increasing intersite interactions, there can appear several lattice\nstates, including conducting optical lattices, insulating optical lattices,\ndelocalized quantum crystals, and localized quantum crystals."
    },
    {
        "anchor": "Symmetry Classification of Spinor Bose-Einstein Condensates: We propose a method for systematically finding ground states of spinor\nBose-Einstein condensates by utilizing symmetry properties of the system. By\nthis method, we can find not only an inert state, whose symmetry is maximal in\nthe manifold under consideration, but also a non-inert state, which has lower\nsymmetry and depends on the parameters in the Hamiltonian. We establish the\nsymmetry-classification method for the spin-1, 2 and 3 cases at zero magnetic\nfield, and find a new phase in the last case. Properties of vortices in the\nspin-3 system are also discussed.",
        "positive": "Antiferromagnetic noise correlations in optical lattices: We analyze how noise correlations probed by time-of-flight (TOF) experiments\nreveal antiferromagnetic (AF) correlations of fermionic atoms in\ntwo-dimensional (2D) and three-dimensional (3D) optical lattices. Combining\nanalytical and quantum Monte Carlo (QMC) calculations using experimentally\nrealistic parameters, we show that AF correlations can be detected for\ntemperatures above and below the critical temperature for AF ordering. It is\ndemonstrated that spin-resolved noise correlations yield important information\nabout the spin ordering. Finally, we show how to extract the spin correlation\nlength and the related critical exponent of the AF transition from the noise."
    },
    {
        "anchor": "Exotic Superconductivity Through Bosons in a Dynamical Cluster\n  Approximation: We study the instabilities towards (exotic) superconductivity of mixtures of\nspin-$1/2$ fermions coupled to scalar bosons on a two-dimensional square\nlattice with the Dynamical-Cluster-Approximation (DCA) using a numerically\nexact continuous-time Monte-Carlo solver. The Bogoliubov bosons provide an\neffective phononic bath for the fermions and induce a non-local retarded\ninteraction between the fermions, which can lead to (exotic) superconductivity.\nBecause of the sign problem the biggest clusters we can study are limited to $2\n\\times 2$ in size, but this nevertheless allows us to study the pairing\ninstablilities, and their possible divergence, in the $s$- and $d$ -wave\nchannels as well as the competition with antiferromagnetic fluctuations. At\nfermionic half-filling we find that $d$-wave is stable when the mediated\ninteraction by the bosons is of the same order as the bare fermionic repulsion.\nIts critical temperature can be made as high as the maximum one for $s$-wave,\nwhich opens perspectives for its detection in a cold atom experiment.",
        "positive": "Defect Saturation in a Rapidly Quenched Bose Gas: We investigate the saturation of defect density in an atomic Bose gas rapidly\ncooled into a superfluid phase. The number of quantum vortices, which are\nspontaneously created in the quenched gas, exhibits a Poissonian distribution\nnot only for a slow quench in the Kibble-Zurek (KZ) scaling regime but also for\na fast quench in which case the mean vortex number is saturated. This shows\nthat the saturation is not caused by destructive vortex collisions, but by the\nearly-time coarsening in an emerging condensate, which is further supported by\nthe observation that the condensate growth lags the quenching in the saturation\nregime. Our results demonstrate that the defect saturation is an effect beyond\nthe KZ mechanism, opening a path for studying critical phase transition\ndynamics using the defect number distribution."
    },
    {
        "anchor": "Harmonically trapped fermions in two dimensions: ground-state energy and\n  contact of SU(2) and SU(4) systems via nonuniform lattice Monte Carlo: We study harmonically trapped, unpolarized fermion systems with attractive\ninteractions in two spatial dimensions with spin degeneracies Nf = 2 and 4 and\nN/Nf = 1, 3, 5, and 7 particles per flavor. We carry out our calculations using\nour recently proposed quantum Monte Carlo method on a nonuniform lattice. We\nreport on the ground-state energy and contact for a range of couplings, as\ndetermined by the binding energy of the two-body system, and show explicitly\nhow the physics of the Nf-body sector dominates as the coupling is increased.",
        "positive": "Braiding and fusion of non-Abelian vortex anyons: We demonstrate that certain vortices in spinor Bose-Einstein condensates are\nnon-Abelian anyons and may be useful for topological quantum computation. We\nperform numerical experiments of controllable braiding and fusion of such\nvortices, implementing the actions required for manipulating topological\nqubits. Our results suggest that a new platform for topological quantum\ninformation processing could potentially be developed by harnessing non-Abelian\nvortex anyons in spinor Bose-Einstein condensates."
    },
    {
        "anchor": "Realizing unconventional quantum magnetism with symmetric top molecules: We demonstrate that ultracold symmetric top molecules loaded into an optical\nlattice can realize highly tunable and unconventional models of quantum\nmagnetism, such as an XYZ Heisenberg spin model. We show that anisotropic\ndipole-dipole interactions between molecules can lead to effective spin-spin\ninteractions which exchange spin and orbital angular momentum. This exchange\nproduces effective spin models which do not conserve magnetization and feature\ntunable degrees of spatial and spin-coupling anisotropy. In addition to\nderiving pure spin models when molecules are pinned in a deep optical lattice,\nwe show that models of itinerant magnetism are possible when molecules can\ntunnel through the lattice. Additionally, we demonstrate rich tunability of the\neffective models' parameters using only a single microwave frequency, in\ncontrast to proposals with $^1\\Sigma$ diatomic molecules, which often require\nmany microwave frequencies. Our results are germane not only for experiments\nwith polyatomic symmetric top molecules, such as methyl fluoride (CH$_3$F), but\nalso diatomic molecules with an effective symmetric top structure, such as the\nhydroxyl radical OH.",
        "positive": "Macroscopic Klein Tunneling in spin-orbit coupled Bose-Einstein\n  Condensates: We propose an experimental scheme to detect macroscopic Klein tunneling with\nspin-orbit coupled Bose-Einstein condensates (BECs). We show that a nonlinear\nDirac equation with tunable parameters can be realized with such BECs. %in a\nsimple configuration to generate the artificial spin-orbit coupling. Through\nnumerical calculations, we demonstrate that macroscopic Klein tunneling can be\nclearly detected under realistic conditions. Macroscopic quantum coherence in\nsuch relativistic tunneling is clarified and a BEC with a negative energy is\nshown to be able to transmit transparently through a wide Gaussian potential\nbarrier."
    },
    {
        "anchor": "Schmidt gap in random spin chains: We numerically investigate the low-lying entanglement spectrum of the ground\nstate of random one-dimensional spin chains obtained after partition of the\nchain into two equal halves. We consider two paradigmatic models: the spin-1/2\nrandom transverse field Ising model, solved exactly, and the spin-1 random\nHeisenberg model, simulated using the density matrix renormalization group. In\nboth cases we analyze the mean Schmidt gap, defined as the difference between\nthe two largest eigenvalues of the reduced density matrix of one of the two\npartitions, averaged over many disorder realizations. We find that the Schmidt\ngap detects the critical point very well and scales with universal critical\nexponents.",
        "positive": "Finite-Temperature Quantum Matter with Rydberg or Molecule Synthetic\n  Dimensions: Synthetic dimension platforms offer unique pathways for engineering quantum\nmatter. We compute the phase diagram of a many-body system of ultracold atoms\n(or polar molecules) with a set of Rydberg states (or rotational states) as a\nsynthetic dimension, where the particles are arranged in real space in optical\nmicrotrap arrays and interact via dipole-dipole exchange interaction. Using\nmean-field theory, we find three ordered phases - two are localized in the\nsynthetic dimension, predicted as zero-temperature ground states in Refs. [Sci.\nRep., 8, 1 (2018) and Phys. Rev. A 99, 013624 (2019)], and a delocalized phase.\nWe characterize them by identifying the spontaneously broken discrete\nsymmetries of the Hamiltonian. We also compute the phase diagram as a function\nof temperature and interaction strength, for both signs of the interaction. For\nsystem sizes with more than six synthetic sites and attractive interactions, we\nfind that the thermal phase transitions can be first or second order, which\nleads to a tri-critical point on the phase boundary. By examining the\ndependence of the tri-critical point and other special points of the phase\nboundary on the synthetic dimension size, we shed light on the physics for\nthermodynamically large synthetic dimension."
    },
    {
        "anchor": "Perturbative behaviour of a vortex in a trapped Bose-Einstein condensate: We derive a set of equations that describe the shape and behaviour of a\nsingle perturbed vortex line in a Bose-Einstein condensate. Through the use of\na matched asymptotic expansion and a unique coordinate transform a relation for\na vortex's velocity, anywhere along the line, is found in terms of the\ntrapping, rotation, and distortion of the line at that location. This relation\nis then used to find a set of differential equations that give the line's\nspecific shape and motion. This work corrects a previous similar derivation by\nAnatoly A. Svidzinsky and Alexander L. Fetter [Phys. Rev. A \\textbf{62}, 063617\n(2000)], and enables a comparison with recent numerical results.",
        "positive": "Two-dimensional supersolidity in a planar dipolar Bose gas: We investigate the crystalline stationary states of a dipolar Bose-Einstein\ncondensate in a planar trapping geometry. Our focus is on the ground state\nphase diagram in the thermodynamic limit, where triangular, honeycomb and\nstripe phases occur. We quantify the superfluid fraction by calculating the\nnon-classical translational inertia, which allows us to identify favorable\nparameter regimes for observing supersolid ground states. We develop two\nsimplified theories to approximately describe the ground states, and consider\nthe relationship to roton softening in the uniform ground state. This also\nallows us to extend the phase diagram to the low density regime. While the\ntriangular and honeycomb states have an isotropic superfluid response tensor,\nthe stripe state exhibits anisotropic superfluidity."
    },
    {
        "anchor": "The phase diagram of ultra quantum liquids: We discuss the dependence of the phase diagram of a hypothetical isotope of\nhelium with nuclear mass less than 4 atomic mass units. We argue that with\ndecreasing nucleus mass, the temperature of the superfluid phase transition\n(about 2.2 K in real He-4) increases, while that of the liquid-gas critical\npoint (about 5.2 K in real He-4) decreases. We discuss various scenarios that\nmay occur when the two temperatures approach each other and the order\nparameters of the superfluid and the liquid-gas phase transitions interact with\neach other. The simplest scenario, in which both order parameters become\ncritical at particular values of the nuclear mass, temperature, and pressure,\ncan be ruled out through on an analysis of the Landau theory. We argue that in\nthe most likely scenario, as the nuclear mass decreases, first, a tricritical\npoint appears on the line separating the superfluid and the normal fluid phase,\nthen the critical point disappears under the first-order part of superfluid\nphase transition line, and in the end the tricritical point disappears. The\nlast change in the phase diagram occurs when the two-body scattering length\ncrosses zero, which corresponds to the nuclear mass of about 1.55 u. We develop\na quantitative theory that allows one to determine the phase diagram in the\nvicinity of this point. Finally, we discuss several ways to physically realize\nsuch liquids.",
        "positive": "Phase diagram of Rydberg atoms with repulsive van der Waals interaction: We report a quantum Monte Carlo calculation of the phase diagram of bosons\ninteracting with a repulsive inverse sixth power pair potential, a model for\nassemblies of Rydberg atoms in the local van der Waals blockade regime. The\nmodel can be parametrized in terms of just two parameters, the reduced density\nand temperature. Solidification happens to the fcc phase. At zero temperature\nthe transition density is found with the diffusion Monte Carlo method at\ndensity $\\rho = 3.9 (\\hbar^2/m C_6)^{3/4} $, where $C_6$ is the strength of the\ninteraction. The solidification curve at non-zero temperature is studied with\nthe path integral Monte Carlo approach and is compared with transitions in\ncorresponding harmonic and classical crystals. Relaxation mechanisms are\nconsidered in relation to present experiments, especially pertaining to hopping\nof the Rydberg excitation."
    },
    {
        "anchor": "Nonequilibrium Kinetics of One-Dimensional Bose Gases: We study cold dilute gases made of bosonic atoms, showing that in the\nmean-field one-dimensional regime they support stable out-of-equilibrium\nstates. Starting from the 3D Boltzmann-Vlasov equation with contact\ninteraction, we derive an effective 1D Landau-Vlasov equation under the\ncondition of a strong transverse harmonic confinement. We investigate the\nexistence of out-of-equilibrium states, obtaining stability criteria similar to\nthose of classical plasmas.",
        "positive": "Superfluid-supersolid phase transition of elongated dipolar\n  Bose-Einstein Condensates at finite temperatures: We analyse the finite-temperature phase diagram of a dipolar Bose Einstein\nCondensate confined in a tubular geometry. The effect of thermal fluctuations\nis accounted for by means of Bogoliubov theory employing the local density\napproximation. In the considered geometry, the superfluid-supersolid phase\ntransition can be of first- and second-order. We discuss how the corresponding\ntransition point is affected by the finite temperature of the system."
    },
    {
        "anchor": "A smooth polaron-molecule crossover in a Fermi system: The problem of a single down spin particle interacting with a Fermi sea of up\nspin particles is of current interest in the field of cold atoms. The Hubbard\nmodel, appropriate to atoms in an optical lattice potential, is considered in\nparallel with a gas model. As the strength of an attractive short-range\ninteraction is increased there is a crossover from \"polaron\" behaviour, in\nwhich the Fermi sea is weakly perturbed, to \"molecule\" behaviour in which the\ndown spin particle is bound to a single up spin particle. It is shown that this\nis a smooth crossover, not a sharp transition as claimed by many authors.",
        "positive": "Hyperfine state entanglement of spinor BEC and scattering atom: Condensate of spin-1 atoms frozen in a unique spatial mode may possess large\ninternal degrees of freedom. The scattering amplitudes of polarized cold atoms\nscattered by the condensate are obtained with the method of fractional\nparentage coefficients that treats the spin degrees of freedom rigorously.\nChannels with scattering cross sections enhanced by square of atom number of\nthe condensate are found. Entanglement between the condensate and the\npropagating atom can be established by the scattering. The entanglement entropy\nis analytically obtained for arbitrary initial states. Our results also give\nhint for the establishment of quantum thermal ensembles in the hyperfine space."
    },
    {
        "anchor": "Universal low energy physics in one-dimensional multicompnent Fermi\n  gases with a strongly repulsive $\u03b4$-function interaction: It was shown [Chin. Phys. Lett. 28, 020503 (2011)] that at zero temperature\nthe ground state of the one-dimensional (1D) $w$-component Fermi gas coincides\nwith that of the spinless Bose gas in the limit $\\omega\\to \\infty$. This\nbehaviour was experimentally evidenced through a quasi-1D tightly trapping\nultracold ${}^{173}$Yb atoms in the recent paper [Nature Physics 10, 198\n(2014)]. However, understanding of low temperature behaviour of the Fermi gases\nwith a repulsive interaction acquires spin-charge separated conformal field\ntheories of an effective Tomonaga-Luttinger liquid and an antiferromagnetic\n$SU(w)$ Heisenberg spin chain. Here we analytically derive universal\nthermodynamics of 1D strongly repulsive fermionic gases with $SU(w)$ symmetry\nvia the Yang-Yang thermodynamic Bethe ansatz method. The analytical free energy\nand magnetic properties of the systems at low temperatures in a weak magnetic\nfield are obtained through the Wiener-Hopf method. In particular, the free\nenergy essentially manifests the spin-charge separated conformal field theories\nfor the high symmetry systems with arbitrary repulsive interaction strength. We\nalso find that the sound velocity of the Fermi gases in the large $w$ limit\ncoincides with that for the spinless Bose gas, whereas the spin velocity\nvanishes quickly as $w$ becomes large. This indicates a strong suppression of\nthe Fermi exclusion statistics by the commutativity feature among the\n$w$-component fermions with different spin states in the Tomonaga-Luttinger\nliquid phase. Moreover, the equations of state and critical behaviour of\nphysical quantities at finite temperatures are analytically derived in terms of\nthe polylogarithm functions in the quantum critical region.",
        "positive": "Persistent currents in Bose gases confined in annular traps: We examine the problem of stability of persistent currents in a mixture of\ntwo Bose gases trapped in an annular potential. We evaluate the critical\ncoupling for metastability in the transition from quasi-one to two-dimensional\nmotion. We also evaluate the critical coupling for metastability in a mixture\nof two species as function of the population imbalance. The stability of the\ncurrents is shown to be sensitive to the deviation from one-dimensional motion."
    },
    {
        "anchor": "First-order, continuous, and multicritical Bose-Einstein condensation in\n  Bose mixtures: We address the possibility of realizing Bose-Einstein condensation as a\nfirst-order phase transition by admixture of particles of different species. To\nthis aim we perform a comprehensive analysis of phase diagrams of two-component\nmixtures of bosons at finite temperatures. As a prototype model, we analyze a\nbinary mixture of Bose particles interacting via an infinite-range (Kac-scaled)\ntwo-body potential. We obtain a rich phase diagram, where the transition\nbetween the normal and Bose-Einstein condensed phases may be either continuous\nor first-order. The phase diagram hosts lines of triple points, tricritical\npoints, as well as quadruple points. We address the structure of the phase\ndiagram depending on the relative magnitudes of the inter- and intra-species\ninteraction couplings. In addition, even for purely repulsive interactions, we\nidentify a first-order liquid-gas type transition between non-condensed phases\ncharacterized by different particle concentrations. In the obtained phase\ndiagram, a surface of such first-order transitions terminates with a line of\ncritical points.",
        "positive": "Collective excitations in two-dimensional SU($N$) Fermi gases with\n  tunable spin: We measure collective excitations of a harmonically trapped two-dimensional\n(2D) SU($N$) Fermi gas of $^{173}$Yb confined to a stack of layers formed by a\none-dimensional optical lattice. Quadrupole and breathing modes are excited and\nmonitored in the collisionless regime $\\lvert\\ln(k_F a_{2D})\\rvert\\gg 1$ with\ntunable spin. We observe that the quadrupole mode frequency decreases with\nincreasing number of spin components due to the amplification of the\ninteraction effect by $N$ in agreement with a theoretical prediction based on\n2D kinetic equations. The breathing mode frequency, however, is measured to be\ntwice the dipole oscillation frequency regardless of $N$. We also follow the\nevolution of collective excitations in the dimensional crossover from two to\nthree dimensions and characterize the damping rate of quadrupole and breathing\nmodes for tunable SU($N$) fermions, both of which reveal the enhanced\ninter-particle collisions for larger spin. Our result paves the way to\ninvestigate the collective property of 2D SU($N$) Fermi liquid with enlarged\nspin."
    },
    {
        "anchor": "Making an ultracold gas: We provide an introduction to the experimental physics of quantum gases. At\nthe low densities of ultracold quantum gases, confinement can be understood\nfrom single-particle physics, and interactions can be understood from two-body\nphysics. The structure of atoms provides resonances both in the optical domain\nand in the radio-frequency domain. Atomic structure data is given for the 27\natomic isotopes that had been brought to quantum degeneracy at the time this\nchapter was written. We discuss the motivations behind choosing among these\nspecies. We review how static and oscillatory fields are treated\nmathematically. An electric dipole moment can be induced in a neutral atom, and\nis the basis for optical manipulation as well as short-range interactions. Many\natoms have permanent magnetic dipole moments, which can be used for trapping or\nlong-range interactions. The Toronto $^{40}$K/$^{87}$Rb lattice experiment\nprovides an illustration of how these tools are combined to create an\nultracold, quantum-degenerate gas.",
        "positive": "Josephson vortices in a long Josephson junction formed by phase twist in\n  a polariton superfluid: Quantum fluids of light are an emerging platform for energy efficient signal\nprocessing, ultra-sensitive interferometry and quantum simulators at elevated\ntemperatures. Here we demonstrate the optical control of the topological\nexcitations induced in a large polariton condensate, realising the bosonic\nanalog of a long Josephson junction and reporting the first observation of\nbosonic Josephson vortices. When a phase difference is imposed at the\nboundaries of the condensate, two extended regions become separated by a sharp\n$\\pi$-slippage of the phase and a solitonic depletion of the density, forming\nan insulating barrier with a suppressed order parameter. The superfluid\nbehavior, that is a smooth phase gradient across the system instead of the\nsharp phase jump, is recovered at higher polariton densities and it is mediated\nby the nucleation of Josephson vortices within the barrier. Our results\ncontribute to the understanding of dissipation and stability of elementary\nexcitations in macroscopic quantum systems."
    },
    {
        "anchor": "Scrambled Mean Field Approach to the Quantum Dynamics of Degenerate Bose\n  Gases: We present a novel approach to modeling dynamics of trapped, degenerate,\nweakly interacting Bose gases beyond the mean field limit. We transform a\nmany-body problem to the interaction representation with respect to a suitably\nchosen part of the Hamiltonian and only then apply a multimode coherent-state\nansatz. The obtained equations are almost as simple as the Gross--Pitaevskii\nequation, but our approach captures essential features of the quantum dynamics\nsuch as the collapse of coherence.",
        "positive": "Observation of Many-body Dynamical Delocalization in a Kicked Ultracold\n  Gas: Contrary to a driven classical system that exhibits chaos phenomena and\ndiffusive energy growth, a driven quantum system can exhibit dynamical\nlocalization that features energy saturation. However, the evolution of the\ndynamically localized state in the presence of many-body interactions has long\nremained an open question. Here we experimentally study an interacting 1D\nultracold gas periodically kicked by a pulsed optical lattice, and observe the\ninteraction-driven emergence of dynamical delocalization and many-body quantum\nchaos. The observed dynamics feature a sub-diffusive energy growth manifest\nover a broad parameter range of interaction and kick strengths, and shed light\non an area where theoretical approaches are extremely challenging."
    },
    {
        "anchor": "Thermalization measurements on an ultracold mixture of metastable $^4$He\n  and $^{87}$Rb atoms in a quadrupole magnetic trap: Recently we have reported (Knoop et al. [arXiv:1404.4826]) on an experimental\ndetermination of metastable triplet $^4$He+$^{87}$Rb scattering length by\nperforming thermalization measurements for an ultracold mixture in a quadrupole\nmagnetic trap. Here we present our experimental apparatus and elaborate on\nthese thermalization measurements. In particular we give a theoretical\ndescription of interspecies thermalization rate for a quadrupole magnetic trap,\ni. e. in the presence of Majorana heating, and a general procedure to extract\nthe scattering length from the elastic cross section at finite temperature\nbased on knowledge of the $C_6$ coefficient alone. In addition, from our\nthermalization data we obtain an upper limit of the total interspecies two-body\nloss rate coefficient of $1.5\\times 10^{-12}$ cm$^3$s$^{-1}$.",
        "positive": "Phase Diagram of Two-dimensional Polarized Fermi Gas With Spin-Orbit\n  Coupling: We investigate the ground state of the two-dimensional polarized Fermi gas\nwith spin-orbit coupling and construct the phase diagram at zero temperature.\nWe find there exist phase separation when the binding energy is low. As the\nbinding energy increasing, the topological nontrivial superfluid phase coexist\nwith topologically trivial superfluid phase which is topological phase\nseparation. The spin-orbit coupling interaction enhance the triplet pairing and\ndestabilize the phase separation against superfluid phase."
    },
    {
        "anchor": "Hydrodynamics of Normal Atomic Gases with Spin-orbit Coupling: Successful realization of spin-orbit coupling in atomic gases by the NIST\nscheme opens the prospect of studying the effects of spin-orbit coupling on\nmany-body physics in an unprecedentedly controllable way. Here we derive the\nlinearized hydrodynamic equations for the normal atomic gases of the spin-orbit\ncoupling by the NIST scheme with zero detuning. We show that the hydrodynamics\nof the system crucially depends on the momentum susceptibilities which can be\nmodified by the spin-orbit coupling. We reveal the effects of the spin-orbit\ncoupling on the sound velocities and the dipole mode frequency of the gases by\napplying our formalism to the ideal Fermi gas. We also discuss the\ngeneralization of our results to other situations.",
        "positive": "Vortex solitons in two-dimensional spin-orbit coupled Bose-Einstein\n  condensates: effects of the Rashba-Dresselhaus coupling and the Zeeman\n  splitting: We present an analysis of two-dimensional (2D) matter-wave solitons, governed\nby the pseudo-spinor system of Gross-Pitaevskii equations with self- and\ncross-attraction, which includes the spin-orbit coupling (SOC) in the general\nRashba-Dresselhaus form, and, separately, the Rashba coupling and the Zeeman\nsplitting. Families of semi-vortex (SV) and mixed-mode (MM) solitons are\nconstructed, which exist and are stable in free space, as the SOC terms prevent\nthe onset of the critical collapse and create the otherwise missing ground\nstates in the form of the solitons. The Dresselhaus SOC produces a destructive\neffect on the vortex solitons, while the Zeeman term tends to convert the MM\nstates into the SV ones, which eventually suffer delocalization. Existence\ndomains and stability boundaries are identified for the soliton families. For\nphysically relevant parameters of the SOC system, the number of atoms in the 2D\nsolitons is limited by $\\sim 1.5\\times 10^{4}$. The results are obtained by\nmeans of combined analytical and numerical methods."
    },
    {
        "anchor": "Bose-Fermi Mapping and Multi-Branch Spin Chain Model for Strongly\n  Interacting Quantum Gases in One-Dimension: Dynamics and Collective\n  Excitations: We show that the wave function of a one dimensional spinor gas with contact\n$s$-wave interaction, either bosonic or fermionic, can be mapped to the direct\nproduct of the wave function of a spinless Fermi gas with short-range $p$-wave\ninteraction and that of a spin system governed by spin parity projection\noperators. Applying this mapping to strongly interacting spinor gases, we\nobtain a generalized spin chain model that captures both the static and\ndynamics properties of the system. Using this spin chain model, we investigate\nthe breathing mode frequency and the quench dynamics of strongly interacting\nharmonically trapped spinor gases.",
        "positive": "Weakly nonadditive Polychronakos statistics: A two-parametric fractional statistics is proposed, which can be used to\nmodel a weakly-interacting Bose-system. It is shown that the parameters of the\nintroduced weakly nonadditive Polychronakos statistics can be linked to effects\nof interactions as well as finite-size corrections. The calculations of the\nspecific heat and condensate fraction of the model system corresponding to\nharmonically trapped Rb-87 atoms are made. The behavior of the specific heat of\nthree-dimensional isotropic harmonic oscillators with respect to the values of\nthe statistics parameters is studied in the temperature domain including the\nBEC-like phase transition point."
    },
    {
        "anchor": "Bose-Einstein Condensation on the Surface of a Sphere: Motivated by the recent achievement of space-based Bose-Einstein condensates\n(BEC) with ultracold alkali-metal atoms under microgravity and by the proposal\nof bubble traps which confine atoms on a thin shell, we investigate the BEC\nthermodynamics on the surface of a sphere. We determine analytically the\ncritical temperature and the condensate fraction of a noninteracting Bose gas.\nThen we consider the inclusion of a zero-range interatomic potential, extending\nthe noninteracting results at zero and finite temperature. Both in the\nnoninteracting and interacting cases the crucial role of the finite radius of\nthe sphere is emphasized, showing that in the limit of infinite radius one\nrecovers the familiar two-dimensional results. We also investigate the\nBerezinski-Kosterlitz-Thouless transition driven by vortical configurations on\nthe surface of the sphere, analyzing the interplay of condensation and\nsuperfluidity in this finite-size system.",
        "positive": "Accuracy of quantum simulators with ultracold dipolar molecules: a\n  quantitative comparison between continuum and lattice descriptions: With rapid progress in control and manipulation of ultracold magnetic atoms\nand dipolar molecules, the quantum simulation of lattice models with strongly\ninteracting dipole-dipole interactions (DDI) and high densities is now within\nexperimental reach. This rapid development raises the issue about the validity\nof quantum simulation in such regimes. In this study, we address this question\nby performing a full quantitative comparison between the continuum description\nof a one-dimensional gas of dipolar bosons in an optical lattice, and the\nsingle-band Bose-Hubbard lattice model that it quantum simulates. By comparing\nenergies and density distributions, and by calculating direct overlaps between\nthe continuum and lattice many-body wavefunctions, we demonstrate that in\nregimes of strong DDI and high densities the continuum system fails to recreate\nthe desired lattice model. Two-band Hubbard models become necessary to reduce\nthe discrepancy observed between continuum and lattice descriptions, but\nappreciable deviations in the density profile still remain. Our study\nelucidates the role of strong DDI in generating physics beyond lowest-band\ndescriptions and should offer a guideline for the calibration of near-term\ndipolar quantum simulators."
    },
    {
        "anchor": "Effective preparation and collisional decay of atomic condensate in\n  excited bands of an optical lattice: We present a method for the effective preparation of a Bose-Einstein\ncondensate (BEC) into the excited bands of an optical lattice via a\nstanding-wave pulse sequence. With our method, the BEC can be prepared in\neither a single Bloch state in a excited-band, or a coherent superposition of\nstates in different bands. Our scheme is experimentally demonstrated by\npreparing a $^{87}$Rb BEC into the $d$-band and the superposition of $s$- and\n$d$-band states of a one-dimensional optical lattice, within a few tens of\nmicroseconds. We further measure the decay of the BEC in the $d$-band state,\nand carry an analytical calculation for the collisional decay of atoms in the\nexcited-band states. Our theoretical and experimental results consist well.",
        "positive": "Hard-core bosons in flat band systems above the critical density: We investigate the behaviour of hard-core bosons in one- and two-dimensional\nflat band systems, the chequerboard and the kagom\\'e lattice and\none-dimensional analogues thereof. The one dimensional systems have an exact\nlocal reflection symmetry which allows for exact results. We show that above\nthe critical density an additional particle forms a pair with one of the other\nbosons and that the pair is localised. In the two-dimensional systems exact\nresults are not available but variational results indicate a similar physical\nbehaviour."
    },
    {
        "anchor": "Stable nonlinear modes sustained by gauge fields: We reveal the universal effect of gauge fields on the existence, evolution,\nand stability of solitons in the spinor multidimensional nonlinear\nSchr\\\"{o}dinger equation. Focusing on the two-dimensional case, we show that\nwhen gauge field can be split in a pure gauge and a \\rtext{non-pure gauge}\ngenerating \\rtext{effective potential}, the roles of these components in\nsoliton dynamics are different: the \\btext{localization characteristics} of\nemerging states are determined by the curvature, while pure gauge affects the\nstability of the modes. Respectively the solutions can be exactly represented\nas the envelopes independent of the pure gauge, modulating stationary\ncarrier-mode states, which are independent of the curvature. Our central\nfinding is that nonzero curvature can lead to the existence of unusual modes,\nin particular, enabling stable localized self-trapped fundamental and\nvortex-carrying states in media with constant repulsive interactions without\nadditional external confining potentials and even in the expulsive external\ntraps.",
        "positive": "Scattering of mesons in quantum simulators: Simulating real-time evolution in theories of fundamental interactions\nrepresents one of the central challenges in contemporary theoretical physics.\nCold-atom platforms stand as promising candidates to realize quantum\nsimulations of non-perturbative phenomena in gauge theories, such as vacuum\ndecay and hadron collisions, in prohibitive conditions for direct experiments.\nIn this work, we demonstrate that present-day quantum simulators can imitate\nlinear particle accelerators, giving access to S-matrix measurements of elastic\nand inelastic meson collisions in low-dimensional Abelian gauge theories.\nConsidering for definiteness a $(1+1)$-dimensional $\\mathbb{Z}_2$-lattice gauge\ntheory realizable with Rydberg-atom arrays, we present protocols to observe and\nmeasure selected meson-meson scattering processes. We provide a benchmark\ntheoretical study of scattering amplitudes in the regime of large fermion mass,\nincluding an exact solution valid for arbitrary coupling strength. This allows\nus to discuss the occurrence of inelastic scattering channels, featuring the\nproduction of new mesons with different internal structures. We present\nnumerical simulations of realistic wavepacket collisions, which reproduce the\npredicted cross section peaks. This work highlights the potential of quantum\nsimulations to give unprecedented access to real-time scattering dynamics."
    },
    {
        "anchor": "Collisions of solitary waves in condensates beyond mean-field theory: Bright solitary waves in a Bose-Einstein condensate contain thousands of\nidentical atoms held together despite their only weakly attractive contact\ninteractions. They nonetheless behave like a compound object, staying whole in\ncollisions, with their collision properties strongly affected by inter-soliton\nquantum coherence. We show that separate solitary waves decohere due to phase\ndiffusion, dependent on their effective ambient temperature, after which their\ninitial mean-field relative phases are no longer well defined or relevant for\ncollisions. In this situation, collisions occur predominantly repulsively and\ncan no longer be described within mean field theory. When considering the\ntime-scales involved in recent solitary wave experiments where non-equilibrium\nphenomena play an important role, these features could explain the\npredominantly repulsive collision dynamics observed in most condensate soliton\ntrain experiments.",
        "positive": "Non-equilibrium steady states and critical slowing down in the\n  dissipative Bose-Hubbard model: Motivated by recent experiments, we study the properties of large\nBose-Hubbard chains with single-particle losses at one site using classical\nfield methods. We construct and validate a compact effective model that reduces\ncomputations to only a few sites. We show that in the mean-field approach the\ndescription captures the stationary states of the dissipative mode very well.\nNot only is there a good quantitative agreement in the hysteresis loop, the\ndark soliton state can be reproduced as well due to the the preservation of the\n$U(1)$ symmetry. Bimodality of the steady states, observed on longer\ntimescales, is studied using the truncated Wigner method. We compare the\nswitching statistics and derive the effective Liouvillian gap in function of\nthe tunneling, showing that the effective description underestimates\nfluctuations."
    },
    {
        "anchor": "Thermodynamics of two-dimensional bosons in the lowest Landau level: We study the thermodynamics of short-range interacting, two-dimensional\nbosons constrained to the lowest Landau level. When the temperature is higher\nthan other energy scales of the problem, the partition function reduces to a\nmultidimensional complex integral that can be handled by classical Monte Carlo\ntechniques. This approach takes the quantization of the lowest Landau level\norbits fully into account. We observe that the partition function can be\nexpressed in terms of a function of a single combination of thermodynamic\nvariables, which allows us to derive exact thermodynamic relations. We\ndetermine the asymptotic behavior of this function and compute some\nthermodynamic observables numerically.",
        "positive": "Asymptotic temperature of a lossy condensate: We monitor the time evolution of the temperature of phononic collective modes\nin a one-dimensional quasicondensate submitted to losses. At long times the\nratio between the temperature and the energy scale $mc^2$, where $m$ is the\natomic mass and $c$ the sound velocity takes, within a precision of 20\\%, an\nasymptotic value. This asymptotic value is observed while $mc^2$ decreases in\ntime by a factor as large as 2.5. Moreover this ratio is shown to be\nindependent on the loss rate and on the strength of interactions. These results\nconfirm theoretical predictions and the measured stationary ratio is in\nquantitative agreement with the theoretical calculations."
    },
    {
        "anchor": "Numerical method for the projected Gross--Pitaevskii equation in an\n  infinite rotating 2D Bose gas: We present a method for evolving the projected Gross-Pitaevskii equation in\nan infinite rotating Bose-Einstein condensate, the ground state of which is a\nvortex lattice. We use quasi-periodic boundary conditions to investigate the\nbehaviour of the bulk superfluid in this system, in the absence of boundaries\nand edge effects. We also give the Landau gauge expression for the phase of a\nBEC subjected to these boundary conditions. Our spectral representation uses\nthe eigenfunctions of the one-body Hamiltonian as basis functions. Since there\nis no known exact quadrature rule for these basis functions we approximately\nimplement the projection associated with the energy cut-off, but show that by\nchoosing a suitably fine spatial grid the resulting error can be made\nnegligible. We show how the convergence of this model is affected by simulation\nparameters such as the size of the spatial grid and the number of Landau\nlevels. Adding dissipation, we use our method to find the lattice ground state\nfor $N$ vortices. We can then perturb the ground-state, in order to investigate\nthe melting of the lattice.",
        "positive": "Superstripes and quasicrystals in bosonic systems with hard-soft corona\n  interactions: The search for spontaneous pattern formation in equilibrium phases with\ngenuine quantum properties is a leading direction of current research. In this\nwork we investigate the effect of quantum fluctuations - zero point motion and\nexchange interactions - on the phases of an ensemble of bosonic particles with\nisotropic hard-soft corona interactions. We perform extensive path-integral\nMonte Carlo simulations to determine their ground state properties. A rich\nphase diagram, parametrized by the density of particles and the interaction\nstrength of the soft-corona potential, reveals supersolid stripes, kagome and\ntriangular crystals in the low-density regime. In the high-density limit we\nobserve patterns with 12-fold rotational symmetry compatible with periodic\napproximants of quasicrystalline phases. We characterize these quantum phases\nby computing the superfluid density and the bond-orientational order parameter.\nFinally, we highlight the qualitative and quantitative differences of our\nfindings with the classical equilibrium phases for the same parameter regimes."
    },
    {
        "anchor": "Ginzburg-Landau effective action approach to disordered Bose-Hubbard\n  Model: We study the phase transition from Mott insulator (MI) to Bose glass (BG) of\na disordered Bose-Hubbard model within the framework of Ginzburg-Landau\neffective action approach. By treating MI as unperturbed ground state and\nperforming a systematic expansion with respect to tunneling matrix element, we\nextend such a field-theoretic method into the disordered lattice Bose systems.\nTo the lowest order, a second order phase transition is confirmed to happen\nhere and the corresponding phase boundary equation coincides with the previous\nmean-field approximation result. Keeping all the terms second order in hopping\nparameter, we obtain the beyond mean-field results of MI-BG phase boundary of\n2D and 3D disordered Bose-Hubbard models. Our analytic predictions are in\nagreement with recent semianalytic results.",
        "positive": "Dynamics of strongly interacting Fermi gases with time-dependent\n  interactions: Consequence of conformal symmetry: In this Letter, we investigate the effects of a time-dependent, short-ranged\ninteraction on the long-time expansion dynamics of Fermi gases. We show that\nthe effects of the interaction on the dynamics is dictated by how it changes\nunder a conformal transformation, and derive an explicit criterion for the\nrelevancy of time-dependent interactions in both the strongly and\nnon-interacting nearly scale invariant quantum gases. In addition, we show that\nit is possible to engineer interactions that give rise to non-exponential\nthermalization dynamics in trapped Fermi gases. To supplement the symmetry\nanalysis, we also perform hydrodynamic simulations to show that the moment of\ninertia of the trapped gas indeed follows a universal time-dependence\ndetermined jointly by the conformal symmetry and time-dependent scattering\nlength $a(t)$. Our results should also be relevant to the dynamics of other\nsystems that are nearly scale invariant and that are governed by a\nnon-relativistic conformal symmetry."
    },
    {
        "anchor": "Self-stabilized Bose polarons: The mobile impurity in a Bose-Einstein condensate (BEC) is a paradigmatic\nmany-body problem. For weak interaction between the impurity and the BEC, the\nimpurity deforms the BEC only slightly and it is well described within the\nFr\\\"ohlich model and the Bogoliubov approximation. For strong local attraction\nthis standard approach, however, fails to balance the local attraction with the\nweak repulsion between the BEC particles and predicts an instability where an\ninfinite number of bosons is attracted toward the impurity. Here we present a\nsolution of the Bose polaron problem beyond the Bogoliubov approximation which\nincludes the local repulsion between bosons and thereby stabilizes the Bose\npolaron even near and beyond the scattering resonance. We show that the Bose\npolaron energy remains bounded from below across the resonance and the size of\nthe polaron dressing cloud stays finite. Our results demonstrate how the\ndressing cloud replaces the attractive impurity potential with an effective\nmany-body potential that excludes binding. We find that at resonance, including\nthe effects of boson repulsion, the polaron energy depends universally on the\neffective range. Moreover, while the impurity contact is strongly peaked at\npositive scattering length, it remains always finite. Our solution highlights\nhow Bose polarons are self-stabilized by repulsion, providing a mechanism to\nunderstand quench dynamics and nonequilibrium time evolution at strong\ncoupling.",
        "positive": "Localization in spin chains with facilitation constraints and disordered\n  interactions: Quantum many-body systems with kinetic constraints exhibit intriguing\nrelaxation dynamics. Recent experimental progress in the field of cold atomic\ngases offers a handle for probing collective behavior of such systems, in\nparticular for understanding the interplay between constraints and disorder.\nHere we explore a spin chain with facilitation constraints --- a feature which\nis often used to model classical glass formers --- together with disorder that\noriginates from spin-spin interactions. The specific model we study, which is\nrealized in a natural fashion in Rydberg quantum simulators, maps onto an\nXX-chain with non-local disorder. Our study shows that the combination of\nconstraints and seemingly unconventional disorder may lead to interesting\nnon-equilibrium behaviour in experimentally relevant setups."
    },
    {
        "anchor": "Floquet analysis of the modulated two-mode Bose-Hubbard model: We study the tunneling dynamics in a time-periodically modulated two-mode\nBose-Hubbard model using Floquet theory. We consider situations where the\nsystem is in the self-trapping regime and either the tunneling amplitude, the\ninteraction strength, or the energy difference between the modes is modulated.\nIn the former two cases, the tunneling is enhanced in a wide range of\nmodulation frequencies, while in the latter case the resonance is narrow. We\nexplain this difference with the help of Floquet analysis. If the modulation\namplitude is weak, the locations of the resonances can be found using the\nspectrum of the non-modulated Hamiltonian. Furthermore, we use Floquet analysis\nto explain the coherent destruction of tunneling (CDT) occurring in a\nlarge-amplitude modulated system. Finally, we present two ways to create a NOON\nstate (a superposition of $N$ particles in mode 1 with zero particles in mode 2\nand vice versa). One is based on a coherent oscillation caused by detuning from\na partial CDT. The other makes use of an adiabatic variation of the modulation\nfrequency. This results in a Landau-Zener type of transition between the ground\nstate and a NOON-like state.",
        "positive": "Interrelated Thermalization and Quantum Criticality in a Lattice Gauge\n  Simulator: Gauge theory and thermalization are both foundations of physics and nowadays\nare both topics of essential importance for modern quantum science and\ntechnology. Simulating lattice gauge theories (LGTs) realized recently with\nultracold atoms provides a unique opportunity for carrying out a correlated\nstudy of gauge theory and thermalization in the same setting. Theoretical\nstudies have shown that an Ising quantum phase transition exists in this\nimplemented LGT, and quantum thermalization can also signal this phase\ntransition. Nevertheless, it remains an experimental challenge to accurately\ndetermine the critical point and controllably explore the thermalization\ndynamics in the quantum critical regime due to the lack of techniques for\nlocally manipulating and detecting matter and gauge fields. Here, we report an\nexperimental investigation of the quantum criticality in the LGT from both\nequilibrium and non-equilibrium thermalization perspectives by equipping the\nsingle-site addressing and atom-number-resolved detection into our LGT\nsimulator. We accurately determine the quantum critical point agreed with the\npredicted value. We prepare a $|Z_{2}\\rangle$ state deterministically and study\nits thermalization dynamics across the critical point, leading to the\nobservation that this $|Z_{2}\\rangle$ state thermalizes only in the critical\nregime. This result manifests the interplay between quantum many-body scars,\nquantum criticality, and symmetry breaking."
    },
    {
        "anchor": "Effective interaction in an unbalanced Fermion mixture: A one dimensional Fermi mixture with delta--interaction is investigated in\nthe limit of extreme imbalance. In particular we consider the cases of only one\nor two minority Fermions which interact with the Fermi-sea of the majority\nFermions. We calculate dispersion relation and polaron mass for the minority\nFermions as well as equal time density-density correlators. Within a cluster\nexpansion we derive an expression for the effective interaction potential\nbetween minority Fermions. For our calculations we use a reformulation of the\nexact wave functions, originally obtained by Yang and Gaudin by a nested Bethe\nansatz, in terms of determinants.",
        "positive": "Distinguishing mesoscopic quantum superpositions from statistical\n  mixtures in periodically shaken double wells: For Bose-Einstein condensates in double wells, N-particle Rabi-like\noscillations often seem to be damped. Far from being a decoherence effect, the\napparent damping can indicate the emergence of quantum superpositions in the\nmany-particle quantum dynamics. However, in an experiment it would be difficult\nto distinguish the apparent damping from decoherence effects. The present paper\nsuggests using controlled periodic shaking to quasi-instantaneously switch the\nsign of an effective Hamiltonian, thus implementing an `echo' technique which\ndistinguishes quantum superpositions from statistical mixtures. The scheme for\nthe effective time-reversal is tested by numerically solving the time-dependent\nN-particle Schrodinger equation."
    },
    {
        "anchor": "A study of one-dimensional transport of Bose-Einstein condensates using\n  exterior complex scaling: We numerically investigate the one-dimensional transport of Bose-Einstein\ncondensates in the context of guided atom lasers using a mean-field description\nof the condensate in terms of a spatially discretized Gross-Pitaevskii\nequation. We specifically consider a waveguide configuration in which spatial\ninhomogeneities and nonvanishing atom-atom interactions are restricted to a\nspatially localized scattering region of finite extent. We show how the method\nof smooth exterior complex scaling can be implemented for this particular\nconfiguration in order to efficiently absorb the outgoing flux within the\nwaveguide. A numerical comparison with the introduction of a complex absorbing\npotential as well as with the analytically exact elimination of the dynamics of\nthe free non-interacting motion outside the scattering region, giving rise to\ntransparent boundary conditions, clearly confirms the accuracy and efficiency\nof the smooth exterior complex scaling method.",
        "positive": "Landau's criterion for an anisotropic Bose-Einstein condensate: In this work, we discuss the Landau's criterion for anisotropic\nsuperfluidity. To this end, we consider a point-like impurity moving in a\nuniform Bose-Einstein condensate with either interparticle dipole-dipole\ninteraction or Raman induced spin-orbit coupling. In both cases, we find that\nthe Landau critical velocity $v_{\\rm c}$ is generally smaller than the sound\nvelocity in the moving direction. Beyond $v_{\\rm c}$, the energy dissipation\nrate is explicitly calculated via a perturbation approach. In the plane-wave\nphase of a spin-orbit coupled Bose gas, the dissipationless motion is\nsuppressed by the Raman coupling even in the direction orthogonal to the recoil\nmomentum. Our predictions can be tested in the experiments with ultracold\natoms."
    },
    {
        "anchor": "Exact solution of the Bose-Hubbard model on the Bethe lattice: The exact solution of a quantum Bethe lattice model in the thermodynamic\nlimit amounts to solve a functional self-consistent equation. In this paper we\nobtain this equation for the Bose-Hubbard model on the Bethe lattice, under two\nequivalent forms. The first one, based on a coherent state path integral, leads\nin the large connectivity limit to the mean field treatment of Fisher et al.\n[Phys. Rev. B {\\bf 40}, 546 (1989)] at the leading order, and to the bosonic\nDynamical Mean Field Theory as a first correction, as recently derived by\nByczuk and Vollhardt [Phys. Rev. B {\\bf 77}, 235106 (2008)]. We obtain an\nalternative form of the equation using the occupation number representation,\nwhich can be easily solved with an arbitrary numerical precision, for any\nfinite connectivity. We thus compute the transition line between the superfluid\nand Mott insulator phases of the model, along with thermodynamic observables\nand the space and imaginary time dependence of correlation functions. The\nfinite connectivity of the Bethe lattice induces a richer physical content with\nrespect to its infinitely connected counterpart: a notion of distance between\nsites of the lattice is preserved, and the bosons are still weakly mobile in\nthe Mott insulator phase. The Bethe lattice construction can be viewed as an\napproximation to the finite dimensional version of the model. We show indeed a\nquantitatively reasonable agreement between our predictions and the results of\nQuantum Monte Carlo simulations in two and three dimensions.",
        "positive": "Unconventional Bose-Einstein Condensation in a System of Two-species\n  Bosons in the $p$-orbital Bands of a Bipartite Lattice: In the context of Gross-Pitaevskii theory, we investigate the unconventional\nBose-Einstein condensations in the two-species mixture with $p$-wave symmetry\nin the second band of a bipartite optical lattice. A new imaginary-time\npropagation method is developed to numerically determine the $p$-orbital\ncondensation. Different from the single-species case, the two-species boson\nmixture exhibits two non-equivalent complex condensates in the\nintraspecies-interaction-dominating regime, exhibiting the vortex-antivortex\nlattice configuration in the charge and spin channels, respectively. When the\ninterspecies interaction is tuned across the SU(2) invariant point, the system\nundergoes a quantum phase transition toward a checkerboard-like spin density\nwave state with a real-valued condensate wavefunction. The influence of lattice\nasymmetry on the quantum phase transition is addressed. Finally, we present a\nphase-sensitive measurement scheme for experimentally detecting the UBEC in our\nmodel."
    },
    {
        "anchor": "Quantum correlations at infinite temperature: the dynamical Nagaoka\n  effect: Do quantum correlations play a role in high temperature dynamics of many-body\nsystems? A common expectation is that thermal fluctuations lead to fast\ndecoherence and make dynamics classical. In this paper, we provide a striking\nexample of a single particle created in a featureless, infinite temperature\nspin bath which not only exhibits non-classical dynamics but also induces\nstrong long-lived correlations between the surrounding spins. We study the\nnon-equilibrium dynamics of a hole created in a fermionic or bosonic Mott\ninsulator in the atomic limit, which corresponds to a degenerate spin system.\nIn the absence of interactions, the spin correlations arise purely from quantum\ninterference, and the correlations are both antiferromagnetic and\nferromagnetic, in striking contrast to the equilibrium Nagaoka effect. These\nresults are relevant for several condensed matter spin systems, and should be\nobservable using state of the art bosonic or fermionic quantum gas microscopes.",
        "positive": "Observation of vortex-antivortex pairing in decaying 2D turbulence of a\n  superfluid gas: In a two-dimensional (2D) classical fluid, a large-scale flow structure\nemerges out of turbulence, which is known as the inverse energy cascade where\nenergy flows from small to large length scales. An interesting question is\nwhether this phenomenon can occur in a superfluid, which is inviscid and\nirrotational by nature. Atomic Bose-Einstein condensates (BECs) of highly\noblate geometry provide an experimental venue for studying 2D superfluid\nturbulence, but their full investigation has been hindered due to a lack of the\ncirculation sign information of individual quantum vortices in a turbulent\nsample. Here, we demonstrate a vortex sign detection method by using Bragg\nscattering, and we investigate decaying turbulence in a highly oblate BEC at\nlow temperatures, with our lowest being $\\sim 0.5 T_c$, where $T_c$ is the\nsuperfluid critical temperature. We observe that weak spatial pairing between\nvortices and antivortices develops in the turbulent BEC, which corresponds to\nthe vortex-dipole gas regime predicted for high dissipation. Our results\nprovide a direct quantitative marker for the survey of various 2D turbulence\nregimes in the BEC system."
    },
    {
        "anchor": "Atomic boson-fermion mixtures in 1D box potentials: Few-body and\n  mean-field many-body analyses: We study binary atomic boson-fermion mixtures confined in one dimensional box\npotentials by few-body theory with contact interactions and mean-field\nmany-body theory with density-density interactions. A variety of correlations\nand structures arise as the inter- and intra- species interactions are tuned.\nBoth few-body and many-body results show that miscible phase and three-chunk\nphase separation are directly observable in the density profiles. Meanwhile,\ntwo-chunk phase separation can be inferred from the few-body correlations and\nmany-body density profiles. We present phase diagrams of selected types of\natomic mixtures to show where different structures survive. The few-body\nanalysis demonstrates that two-body correlation functions can reveal\ninformation relevant to the results from many-body calculations or experiments.\nFrom the many-body density profiles in the phase-separation regime, we extract\nthe healing lengths of each species and explain the scaling behavior by an\nenergy-competition argument.",
        "positive": "Mean-field study of itinerant ferromagnetism in trapped ultracold Fermi\n  gases: Beyond the local density approximation: We theoretically investigate the itinerant ferromagnetic transition of a\nspherically trapped ultracold Fermi gas with spin imbalance under strongly\nrepulsive interatomic interactions. Our study is based on a self-consistent\nsolution of the Hartree-Fock mean-field equations beyond the widely used local\ndensity approximation. We demonstrate that, while the local density\napproximation holds in the paramagnetic phase, after the ferromagnetic\ntransition it leads to a quantitative discrepancy in various thermodynamic\nquantities even with large atom numbers. We determine the position of the phase\ntransition by monitoring the shape change of the free energy curve with\nincreasing the polarization at various interaction strengths."
    },
    {
        "anchor": "Bifurcation of time crystals in driven and dissipative Rydberg atomic\n  gas: A time crystal is an exotic phase of matter where time-translational symmetry\nis broken; this phase differs from the spatial symmetry breaking induced in\ncrystals in space. Lots of experiments report the transition from a thermal\nequilibrium phase to time crystal phase. However, there is no experimental\nmethod to probe the bifurcation effect of distinct time crystals in quantum\nmany-body systems. Here, in a driven and dissipative many-body Rydberg atom\nsystem, we observe multiple continuous dissipative time crystals and emergence\nof more complex temporal symmetries beyond the single time crystal phase.\nBifurcation of time crystals in strongly interacting Rydberg atoms is observed;\nthe process manifests as a transition from a time crystal state of long\ntemporal order to one of short temporal order, or vice versa. By manipulating\nthe driving field parameters, we observe the time crystal's bistability and a\nhysteresis loop. These investigations indicate new possibilities for control\nand manipulation of the temporal symmetries of non-equilibrium systems.",
        "positive": "Effective equations for matter-wave gap solitons in higher-order\n  transversal states: We demonstrate that an important class of nonlinear stationary solutions of\nthe three-dimensional (3D) Gross-Pitaevskii equation (GPE) exhibiting\nnontrivial transversal configurations can be found and characterized in terms\nof an effective one-dimensional (1D) model. Using a variational approach we\nderive effective equations of lower dimensionality for BECs in $(m,n_{r})$\ntransversal states (states featuring a central vortex of charge $m$ as well as\n$n_{r}$ concentric zero-density rings at every $z$ plane) which provides us\nwith a good approximate solution of the original 3D problem. Since the\nspecifics of the transversal dynamics can be absorbed in the renormalization of\na couple of parameters, the functional form of the equations obtained is\nuniversal. The model proposed finds its principal application in the study of\nthe existence and classification of 3D gap solitons supported by 1D optical\nlattices, where in addition to providing a good estimate for the 3D wave\nfunctions it is able to make very good predictions for the $\\mu(N)$ curves\ncharacterizing the different fundamental families. We have corroborated the\nvalidity of our model by comparing its predictions with those from the exact\nnumerical solution of the full 3D GPE."
    },
    {
        "anchor": "On quantum melting of superfluid vortex crystals: from Lifshitz scalar\n  to dual gravity: Despite a long history of studies of vortex crystals in rotating superfluids,\ntheir melting due to quantum fluctuations is poorly understood. Here we develop\na fracton-elasticity duality to investigate a two-dimensional vortex lattice\nwithin the fast rotation regime, where the Lifshitz model of the collective\nTkachenko mode serves as the leading-order low-energy effective theory. We\nincorporate topological defects and discuss several quantum melting scenarios\ntriggered by their proliferation. Furthermore, we lay the groundwork for a dual\nnon-linear emergent gravity description of the superfluid vortex crystals.",
        "positive": "Three Dimensional Raman Cooling using Velocity Selective Rapid Adiabatic\n  Passage: We present a new and efficient implementation of Raman cooling of trapped\natoms. It uses Raman pulses with an appropriate frequency chirp to realize a\nvelocity selective excitation through a rapid adiabatic passage. This method\nallows to address in a single pulse a large number of non zero atomic velocity\nclasses and it produces a nearly unity transfer efficiency. We demonstrate this\ncooling method using cesium atoms in a far-detuned crossed dipole trap.\nThree-dimensional cooling of $1 \\times 10^{5}$ atoms down to $2 \\mu$K is\nperformed in 100 ms. In this preliminary experiment the final atomic density is\n$1.3\\times 10^{12}$ at/cm$^3$ (within a factor of 2) and the phase-space\ndensity increase over the uncooled sample is 20. Numerical simulations indicate\nthat temperatures below the single photon recoil temperature should be\nachievable with this method."
    },
    {
        "anchor": "Propagation of electromagnetic waves in Bose-Einstein condensate of\n  atoms with dipole moments: We study the propagation of electromagnetic waves in the Bose-Einstein\ncondensate of atoms with both intrinsic dipole moments and those induced by the\nelectric field. The modified Gross--Pitaevskii equation is used, which takes\ninto account relaxation and interaction with the electromagnetic field. Two\ncases are considered: 1) when the dispersion curves of the electromagnetic wave\nand of the condensate excitations do not intercross and 2) when the condensate\nexcitations' spectrum has a gap and the two dispersion curves do intercross. In\nthe second case the two branches hybridize. It is shown that propagation of\nsound waves can be accompanied by oscillation of the electromagnetic field. The\nimpact is studied of the dipole-dipole interaction on the character of\nelectromagnetic and acoustic waves' propagation in the Bose-Einstein\ncondensate.",
        "positive": "Population trapping and inversion in ultracold Fermi gases by excitation\n  of the optical lattice - Non-equilibrium Floquet-Keldysh description: A gas of ultracold interacting quantum degenerate Fermions is considered in a\nthree dimensional optical lattice which is externally modulated in the fre-\nquency and the amplitude. This theoretical study utilizes the Keldysh formalism\nto account for the system being out of thermodynamical equilibrium. A dynamical\nmean field theory, extended to non-equilibrium, is presented to calculate\ncharacteristic quantities such as the local density of states and the\nnon-equilibrium distribution function. A dynamics Franz-Keldysh splitting is\nfound which accounts for the non-equilibrium modification of the underlying\nbandstructure. The found characteristic Floquet-fan like bandstructure accounts\nfor the quantized nature of the effect over all frequency space."
    },
    {
        "anchor": "Efficient production of a narrow-line erbium magneto-optical trap with\n  two-stage slowing: We describe an experimental setup for producing a large cold erbium (Er)\nsample in a narrow-line magneto-optical trap (MOT) in a simple and efficient\nway. We implement a pair of angled slowing beams with respect to the Zeeman\nslower axis, and further slow down atoms exiting from the Zeeman slower. The\nsecond-stage slowing beams enable the narrow-line MOT to trap atoms exiting\nfrom the Zeeman slower with higher velocity. This scheme is particularly useful\nwhen the Zeeman slower is at low optical power without the conventional\ntransverse cooling between an oven and a Zeeman slower, in which case we\nsignificantly improve the loading efficiency into the MOT and are able to trap\nmore than $10^8$ atoms in the narrow-line MOT of $^{166}$Er. This work\nhighlights our implementation, which greatly simplifies laser cooling and\ntrapping of Er atoms and also should benefit other similar elements.",
        "positive": "A lattice pairing-field approach to ultracold Fermi gases: We develop a pairing-field formalism for ab initio studies of\nnon-relativistic two-component fermions on a $(d\\!+\\!1)$-dimensional spacetime\nlattice. More specifically, we focus on theories where the interaction between\nthe two components can be described by the exchange of a corresponding pairing\nfield. The introduction of a pairing field may indeed be convenient for studies\nof, e.g., the finite-temperature phase structure and critical behavior of,\ne.g., ultracold atomic Fermi gases. Moreover, such a formalism allows to\ndirectly compute the momentum and frequency dependence of the pair propagator,\nfrom which the pair-correlation function can be extracted. For a first\nillustration of the application of our formalism, we compute the density\nequation of state and the superfluid order parameter for a gas of unpolarized\nfermions in $(0\\!+\\!1)$ dimensions by employing the complex Langevin approach\nto surmount the sign problem."
    },
    {
        "anchor": "Dynamics of the modified Kibble-\u017burek mechanism in antiferromagnetic\n  spin-1 condensates: We investigate the dynamics and outcome of a quantum phase transition from an\nantiferromagnetic to phase separated ground state in a spin-1 Bose-Einstein\ncondensate of ultracold atoms. We explicitly demonstrate double universality in\ndynamics within experiments with various quench time. Furthermore, we show that\nspin domains created in the nonequilibrium transition constitute a set of\nmutually incoherent quasicondensates. The quasicondensates appear to be\npositioned in a semi-regular fashion, which is a result of the conservation of\nlocal magnetization during the post-selection dynamics.",
        "positive": "Vortex lattices in dipolar two-component Bose-Einstein condensates: We consider a rapidly rotating two-component Bose-Einstein condensate with\nshort-range s-wave interactions as well as dipolar coupling. We calculate the\nphase diagram of vortex lattice structures as a function of the intercomponent\ns-wave interaction and the strength of the dipolar interaction. We find that\nthe long-range interactions cause new vortex lattice structures to be stable\nand lead to a richer phase diagram. Our results reduce to the previously found\nlattice structures for short-range interactions and single-component dipolar\ngases in the corresponding limits."
    },
    {
        "anchor": "Non-Hermitian $p$-wave superfluid and effects of the inelastic\n  three-body loss in a one-dimensional spin-polarized Fermi gas: We theoretically investigate non-Hermitian $p$-wave Fermi superfluidity in\none-dimensional spin-polarized Fermi gases which is relevant to recent\nultracold atomic experiments. Considering an imaginary atom-dimer coupling\nresponsible for the three-body recombination process in the Lindblad formalism,\nwe discuss the stability of the superfluid state against the atomic loss\neffect. Within the two-channel non-Hermitian BCS-Leggett theory, the atomic\nloss is characterized by the product of the imaginary atom-dimer coupling and\nthe $p$-wave effective range. Our results indicate that for a given imaginary\natom-dimer coupling, a smaller magnitude of the effective ranges of $p$-wave\ninteraction is crucial for reaching the non-Hermitian $p$-wave Fermi superfluid\nstate.",
        "positive": "Effective interaction and condensation of dipolaritons in coupled\n  quantum wells: Dipolaritons are a three-way superposition of photon, a direct exciton, and\nan indirect exciton that are formed in coupled quantum well microcavities. As\nis the case with exciton-polaritons, dipolaritons have a self-interaction due\nto direct and exchange effects of the underlying electrons and holes. Here we\npresent a theoretical description of dipolaritons and derive simple formulas\nfor their basic parameters. In particular, we derive the effective\ndipolariton-dipolariton interaction taking into account of exchange effects\nbetween the excitons. We obtain a simple relation to describe the effective\ninteraction at low densities. We find that dipolaritons should condense under\nsuitable conditions, described by a dissipative Gross-Pitaevskii equation.\nWhile the parameters for condensation are promising, we find that the level of\ntunability of the interactions is limited."
    },
    {
        "anchor": "Emergence of isotropy in rotating turbulence of Bose-Einstein\n  condensates: We present a study on the development of rotating turbulence in Bose-Einstein\ncondensates with a dissipative Gross-Pitaevskii model. Turbulence is generated\nby driving the lattice of quantized vortices in a harmonic potential with a\nrandom forcing potential. As the turbulence progressed, the initial alignment\nof vortices underwent slight disruptions, thereby increasing the\nhigh-wavenumber components of the kinetic energy. In the turbulent state, the\ndistribution of incompressible kinetic energy exhibits milder anisotropy than\nthat in the initial lattice state and demonstrates a scaling behavior of\n$k_z^{-2.5}$ in the direction parallel to the rotation axis. In contrast, the\ncompressible kinetic energy exhibits an isotropic scaling behavior at high\nwavenumbers.",
        "positive": "The effects of disorder in dimerized quantum magnets in mean field\n  approximations: We study theoretically the effects of disorder on Bose-Einstein condensates\n(BEC) of bosonic triplon quasiparticles in doped dimerized quantum magnets. The\ncondensation occurs in a strong enough magnetic field Hc, where the\nconcentration of bosons in the random potential is sufficient to form the\ncondensate. The effect of doping is partly modeled by delta - correlated\ndisorder potential, which (i) leads to the uniform renormalization of the\nsystem parameters and (ii) produces disorder in the system with renormalized\nparameters. These approaches can explain qualitatively the available\nmagnetization data in the Tl_(1-x)K_(x)CuCl_3 compound taken as an example. In\naddition to the magnetization, we found that the speed of the Bogoliubov mode\nhas a peak as a function of doping parameter, x. No evidence of the pure Bose\nglass phase has been obtained in the BEC regime."
    },
    {
        "anchor": "Attractive dipolar coupling between stacked exciton fluids: The interaction between aligned dipoles is long-ranged and highly\nanisotropic: it changes from repulsive to attractive depending on the relative\npositions of the dipoles. We report on the observation of the attractive\ncomponent of the dipolar coupling between excitonic dipoles in stacked\nsemiconductor bilayers. We show that the presence of a dipolar exciton fluid in\none bilayer modifies the spatial distribution and increases the binding energy\nof excitonic dipoles in a vertically remote layer. The binding energy changes\nare explained by a many-body polaron model describing the deformation of the\nexciton cloud due to its interaction with a remote dipolar exciton. The results\nopen the way for the observation of theoretically predicted new and exotic\ncollective phases, the realization of interacting dipolar lattices in\nsemiconductor systems as well as for engineering and sensing their collective\nexcitations.",
        "positive": "A simple and efficient numerical method for computing the dynamics of\n  rotating Bose-Einstein condensates via a rotating Lagrangian coordinate: We propose a simple, efficient and accurate numerical method for simulating\nthe dynamics of rotating Bose-Einstein condensates (BECs) in a rotational frame\nwith/without a long-range dipole-dipole interaction. We begin with the\nthree-dimensional (3D) Gross-Pitaevskii equation (GPE) with an angular momentum\nrotation term and/or long-range dipole-dipole interaction, state the\ntwo-dimensional (2D) GPE obtained from the 3D GPE via dimension reduction under\nanisotropic external potential and review some dynamical laws related to the 2D\nand 3D GPE. By introducing a rotating Lagrangian coordinate system, the\noriginal GPEs are re-formulated to GPEs without the angular momentum rotation\nwhich is replaced by a time-dependent potential in the new coordinate system.\nWe then cast the conserved quantities and dynamical laws in the new rotating\nLagrangian coordinates. Based on the new formulation of the GPE for rotating\nBECs in the rotating Lagrangian coordinates, a time-splitting spectral method\nis presented for computing the dynamics of rotating BECs. The new numerical\nmethod is explicit, simple to implement, unconditionally stable and very\nefficient in computation. It is spectral order accurate in space and\nsecond-order accurate in time, and conserves the mass in the discrete level.\nExtensive numerical results are reported to demonstrate the efficiency and\naccuracy of the new numerical method. Finally, the numerical method is applied\nto test the dynamical laws of rotating BECs such as the dynamics of condensate\nwidth, angular momentum expectation and center-of-mass, and to investigate\nnumerically the dynamics and interaction of quantized vortex lattices in\nrotating BECs without/with the long-range dipole-dipole interaction."
    },
    {
        "anchor": "Shapiro steps in driven atomic Josephson junctions: We study driven atomic Josephson junctions realized by coupling two\ntwo-dimensional atomic clouds with a tunneling barrier. By moving the barrier\nat a constant velocity, dc and ac Josephson regimes are characterized by a zero\nand nonzero atomic density difference across the junction, respectively. Here,\nwe monitor the dynamics resulting in the system when, in addition to the above\nconstant velocity protocol, the position of the barrier is periodically driven.\nWe demonstrate that the time-averaged particle imbalance features a step-like\nbehavior that is the analog of Shapiro steps observed in driven superconducting\nJosephson junctions. The underlying dynamics reveals an intriguing interplay of\nthe vortex and phonon excitations, where Shapiro steps are induced via\nsuppression of vortex growth. We study the system with a classical-field\ndynamics method, and benchmark our findings with a driven circuit dynamics.",
        "positive": "Generating and detecting topological phases with higher Chern number: Topological phases with broken time-reversal symmetry and Chern number |C|>=2\nare of fundamental interest, but it remains unclear how to engineer the desired\ntopological Hamiltonian within the paradigm of spin-orbit-coupled particles\nhopping only between nearest neighbours of a static lattice. We show that\nphases with higher Chern number arise when the spin-orbit coupling satisfies a\ncombination of spin and spatial rotation symmetries. We leverage this result\nboth to construct minimal two-band tight binding Hamiltonians that exhibit\n|C|=2,3 phases, and to show that the Chern number of one of the energy bands\ncan be inferred from the particle spin polarization at the high-symmetry\ncrystal momenta in the Brillouin zone. Using these insights, we provide a\ndetailed experimental scheme for the specific realization of a\ntime-reversal-breaking topological phase with |C|=2 for ultracold atomic gases\non a triangular lattice subject to spin-orbit coupling. The Chern number can be\ndirectly measured using Zeeman spectroscopy; for fermions the spin amplitudes\ncan be measured directly via time of flight, while for bosons this is preceded\nby a short Bloch oscillation. Our results provide a pathway to the realization\nand detection of novel topological phases with higher Chern number in ultracold\natomic gases."
    },
    {
        "anchor": "Expansion of harmonically trapped interacting particles and time\n  dependence of the contact: We study the expansion of an interacting atomic system at zero temperature,\nfollowing its release from an isotropic three-dimensional harmonic trap and\ncalculate the time dependence of its density and momentum distribution, with\nspecial focus on the behavior of the contact parameter. We consider different\nquantum systems, including the unitary Fermi gas of infinite scattering length,\nthe weakly interacting Bose gas, and two interacting particles with highly\nasymmetric mass imbalance. In all cases analytic results can be obtained, which\nshow that the initial value of the contact, fixing the $1/k^4$ tail of the\nmomentum distribution, disappears for large expansion times. Our results raise\nthe problem of understanding the recent experiment of Chang \\textit{et al.}\n[Phys. Rev. Lett. \\textbf{117}, 235303 (2016)] carried out on a weakly\ninteracting Bose gas of metastable $^4$He atoms, where a $1/r^4$ tail in the\ndensity distribution was observed after a large expansion time, implying the\nexistence of the $1/k^4$ tail in the asymptotic momentum distribution.",
        "positive": "Antiferromagnetism with Ultracold Atoms: We use ultracold spin--1/2 atomic fermions ($^6$Li) to realize the Hubbard\nmodel on a three-dimensional (3D) optical lattice. At relatively high\ntemperatures and at densities near half-filling, we show that the gas forms a\nMott insulator with unordered spins. To observe antiferromagnetic order that is\npredicted to occur at lower temperatures, we developed the compensated optical\nlattice method to evaporatively cool atoms in the lattice. This cooling has\nenabled the detection of short-range magnetic order by spin-sensitive Bragg\nscattering of light."
    },
    {
        "anchor": "Two-dimensional polaron spectroscopy of Fermi superfluids: Multidimensional spectroscopy is becoming an increasingly popular tool and\nthere is an ongoing effort to access electronic transitions and many-body\ndynamics in correlated materials. We apply the protocol recently proposed by\nWang to extract two-dimensional polaron spectra in a Fermi superfluid with an\nimpurity. The bath is descibed by a BCS ansatz and it assumed that the impurity\ncan scatter at most one quasiparticle pair. The spectral response contains a\nsymmetric contribution, which carries the same information as Ramsey spectra,\nand an asymmetric one. While {\\it a priori} it may seem promising to probe the\nquasiparticle gap from the asymmetric contribution, we show explicitly that\nthis is not the case and, in the absence of incoherent processes,\nmultidimensional spectroscopy does not bring much additional information. Our\ncalculation is suitable for 3D ultracold gases, but we discuss implications for\nexciton-polarons in 2D materials.",
        "positive": "A route to non-Abelian quantum turbulence in spinor Bose-Einstein\n  condensates: We have studied computationally the collision dynamics of spin-2\nBose--Einstein condensates initially confined in a triple-well trap. Depending\non the intra- and inter-component relative phases of the initial state spinor\nwave function, the collision of the three condensate segments produces one of\nmany possible vortex-antivortex lattices after which the system transitions to\nquantum turbulence. We find that the emerging vortex lattice structures can be\ndescribed in terms of multi-wave interference. We show that the three-segment\ncollisions can be used to systematically produce staggered vortex-antivortex\nhoneycomb lattices of fractional-charge vortices, whose collision dynamics are\nknown to be non-Abelian. Such condensate collider experiments could potentially\nbe used as a controllable pathway to generating non-Abelian superfluid\nturbulence with networks of vortex rungs."
    },
    {
        "anchor": "Single-particle spectral density of the unitary Fermi gas: Novel\n  approach based on the operator product expansion, sum rules and the maximum\n  entropy method: Making use of the operator product expansion, we derive a general class of\nsum rules for the imaginary part of the single-particle self-energy of the\nunitary Fermi gas. The sum rules are analyzed numerically with the help of the\nmaximum entropy method, which allows us to extract the single-particle spectral\ndensity as a function of both energy and momentum. These spectral densities\ncontain basic information on the properties of the unitary Fermi gas, such as\nthe dispersion relation and the superfluid pairing gap, for which we obtain\nreasonable agreement with the available results based on quantum Monte-Carlo\nsimulations.",
        "positive": "Superfluidity with disorder in a quantum gas thin film: We investigate the properties of a strongly interacting, superfluid gas of\n6Li2 Feshbach molecules forming a thin film confined in a quasi two-dimensional\nchannel with a tunable random potential, creating a microscopic disorder. We\nmeasure the atomic current and extract the resistance of the film in a\ntwo-terminal configuration, and identify a superfluid state at low disorder\nstrength, which evolves into a normal, poorly conducting state for strong\ndisorder. The transition takes place when the chemical potential reaches the\npercolation threshold of the disorder. The evolution of the conduction\nproperties contrasts with the smooth behavior of the density and\ncompressibility across the transition, measured in-situ at equilibrium. These\nfeatures suggest the emergence of a glass-like phase at strong disorder."
    },
    {
        "anchor": "Quantum Many-Body Adiabaticity, Topological Thouless Pump and Driven\n  Impurity in a One-Dimensional Quantum Fluid: When it comes to applying the adiabatic theorem in practice, the key question\nto be answered is how slow \"slowly enough\" is. This question can be an\nintricate one, especially for many-body systems, where the limits of slow\ndriving and large system size may not commute. Recently we have shown how the\nquantum adiabaticity in many-body systems is related to the generalized\northogonality catastrophe [Phys. Rev. Lett. 119, 200401 (2017)]. We have proven\na rigorous inequality relating these two phenomena and applied it to establish\nconditions for the quantized transport in the topological Thouless pump. In the\npresent contribution we (i) review these developments and (ii) apply the\ninequality to establish the conditions for adiabaticity in a one-dimensional\nsystem consisting of a quantum fluid and an impurity particle pulled through\nthe fluid by an external force. The latter analysis is vital for the correct\nquantitative description of the phenomenon of quasi Bloch oscillations in a\none-dimensional translation invariant impurity-fluid system.",
        "positive": "Cumulant theory of the unitary Bose gas: Prethermal and Efimovian\n  dynamics: We study the quench of a degenerate ultracold Bose gas to the unitary regime,\nwhere interactions are as strong as allowed by quantum mechanics. We lay the\nfoundations of a cumulant theory able to capture simultaneously the three-body\nEfimov effect and ergodic evolution. After an initial period of rapid quantum\ndepletion, a universal prethermal stage is established characterized by a\nkinetic temperature and an emergent Bogoliubov dispersion law while the\nmicroscopic degrees of freedom remain far-from-equilibrium. Integrability is\nthen broken by higher-order interaction terms in the many-body Hamiltonian,\nleading to a momentum-dependent departure from power law to decaying\nexponential behavior of the occupation numbers at large momentum. We find also\nsignatures of the Efimov effect in the many-body dynamics and make a precise\nidentification between the observed beating phenomenon and the binding energy\nof an Efimov trimer. Throughout the work, our predictions for a uniform gas are\nquantitatively compared with experimental results for quenched unitary Bose\ngases in uniform potentials."
    },
    {
        "anchor": "Physical dipoles and second order perturbation theory for dipolar\n  fermions in two dimensions: In two dimensions the Fourier transform of the interaction between two point\ndipoles has a term which grows linearly in the modulus $| \\mathbf{\\textit{q}}\n|$ of the momentum . As a consequence, in second order perturbation theory the\nself-energy of two-dimensional dipolar fermions is ultraviolet divergent. We\nshow that for electric dipoles this divergence can be avoided if one takes into\naccount that physical dipoles consist of two opposite charges which are\nseparated by a finite distance. Using this regularization, we calculate the\nself-energy, the renormalized chemical potential, and the renormalized Fermi\nsurface of dipolar fermions in two dimensions in second order perturbation\ntheory. We find that in the Fermi liquid phase the second order corrections\nweaken first order effects.",
        "positive": "Splitting of topological charge pumping in an interacting two-component\n  fermionic Rice-Mele Hubbard model: A Thouless pump transports an integer amount of charge when pumping\nadiabatically around a singularity. We study the splitting of such a critical\npoint into two separate critical points by adding a Hubbard interaction.\nFurthermore, we consider extensions to a spinful Rice-Mele model, namely a\nstaggered magnetic field or an Ising-type spin coupling, further reducing the\nspin symmetry. The resulting models additionally allow for the transport of a\nsingle charge in a two-component system of spinful fermions, whereas in the\nabsence of interactions, zero or two charges are pumped. In the SU(2)-symmetric\ncase, the ionic Hubbard model is visited once along pump cycles that enclose a\nsingle singularity. Adding a staggered magnetic field additionally transports\nan integer amount of spin while the Ising term realizes a pure charge pump. We\nemploy real-time simulations in finite and infinite systems to calculate the\nadiabatic charge and spin transport, complemented by the analysis of gaps and\nthe many-body polarization to confirm the adiabatic nature of the pump. The\nresulting charge pumps are expected to be measurable in finite-pumping speed\nexperiments in ultra-cold atomic gases, for which the SU(2) invariant version\nis the most promising path. We discuss the implications of our results for a\nrelated quantum-gas experiment by Walter et al. [arXiv:2204.06561]."
    },
    {
        "anchor": "Fingering instabilities and pattern formation in a two-component dipolar\n  Bose-Einstein condensate: We study fingering instabilities and pattern formation at the interface of an\noppositely polarized two-component Bose-Einstein condensate with strong\ndipole-dipole interactions in three dimensions. It is shown that the rotational\nsymmetry is spontaneously broken by fingering instability when the\ndipole-dipole interactions are strengthened. Frog-shaped and mushroom-shaped\npatterns emerge during the dynamics due to the dipolar interactions. We also\ndemonstrate the spontaneous density modulation and domain growth of a\ntwo-component dipolar BEC in the dynamics. Bogoliubov analyses in the\ntwo-dimensional approximation are performed, and the characteristic lengths of\nthe domains are estimated analytically. Patterns resembling those in magnetic\nclassical fluids are modulated when the number ratio of atoms, the trap ratio\nof the external potential, or tilted polarization with respect to the z\ndirection is varied.",
        "positive": "Nonlinear interferometry beyond classical limit facilitated by cyclic\n  dynamics: Time-reversed evolution has substantial implications in physics, including\nprominent applications in refocusing of classical waves or spins and\nfundamental researches such as quantum information scrambling. In quantum\nmetrology, nonlinear interferometry based on time reversal protocols supports\nentanglement-enhanced measurements without requiring low-noise detection.\nDespite the broad interest in time reversal, it remains challenging to reverse\nthe quantum dynamics of an interacting many-body system as is typically\nrealized by an (effective) sign-flip of the system's Hamiltonian. Here, we\npresent an approach that is broadly applicable to cyclic systems for\nimplementing nonlinear interferometry without invoking time reversal. Inspired\nby the observation that the time-reversed dynamics drives a system back to its\nstarting point, we propose to accomplish the same by slaving the system to\ntravel along a 'closed-loop' instead of explicitly tracing back its antecedent\npath. Utilizing the quasi-periodic spin mixing dynamics in a three-mode\n$^{87}$Rb atom spinor condensate, we implement such a 'closed-loop' nonlinear\ninterferometer and achieve a metrological gain of $3.87_{-0.95}^{+0.91}$\ndecibels over the classical limit for a total of 26500 atoms. Our approach\nunlocks the high potential of nonlinear interferometry by allowing the dynamics\nto penetrate into deep nonlinear regime, which gives rise to highly entangled\nnon-Gaussian state. The idea of bypassing time reversal may open up new\nopportunities in the experimental investigation of researches that are\ntypically studied by using time reversal protocols."
    },
    {
        "anchor": "Many-body bound states and induced interactions of charged impurities in\n  a bosonic bath: Induced interactions and bound states of charge carriers immersed in a\nquantum medium are crucial for the investigation of quantum transport.\nUltracold atom-ion systems can provide a convenient platform for studying this\nproblem. Here, we investigate the static properties of one and two ionic\nimpurities in a bosonic bath using quantum Monte Carlo methods. We identify\nthree bipolaronic regimes depending on the strength of the atom-ion potential\nand the number of its two-body bound states: a perturbative regime resembling\nthe situation of a pair of neutral impurities, a non-perturbative regime that\nloses the quasi-particle character of the former, and a many-body bound state\nregime that can arise only in the presence of a bound state in the two-body\npotential. We further reveal strong bath-induced interactions between the two\nionic polarons. Our findings show that numerical simulations are indispensable\nfor describing highly correlated impurity models.",
        "positive": "Density, spin, and pairing instabilities in polarized ultracold Fermi\n  gases: We study the influence of population imbalance on the pairing, spin, and\ndensity instabilities of a two component ideal Fermi gas after a sudden quench\nof interactions near a Feshbach resonance. Over a large region of parameters\nthe pairing instability is dominated by finite momentum pairing, suggesting the\npossibility of observing FFLO-like states in the unstable initial dynamics.\nLong-wavelength density instabilities are found on the BCS side of the\nresonance, and are interpreted as a precursor of the phase separation expected\nat equilibrium. On the BEC side of the resonance, the pairing instability is\npresent for scattering lengths that are larger than a critical value that is\nonly weakly dependent on population imbalance and always smaller than the\nscattering length at which the Stoner-like spin instability occurs."
    },
    {
        "anchor": "Topologically non-trivial Hofstadter bands on the kagome lattice: We investigate how the multiple bands of fermions on a crystal lattice evolve\nif a magnetic field is added which does not increase the number of bands. The\nkagome lattice is studied as generic example for a lattice with loops of three\nbonds. Finite Chern numbers occur as non-trivial topological property in\npresence of the magnetic field. The symmetries and periodicities as function of\nthe applied field are discussed. Strikingly, the dispersions of the edge states\ndepend crucially on the precise shape of the boundary. This suggests that\nsuitable design of the boundaries helps to tune physical properties which may\neven differ between upper and lower edge. Moreover, we suggest a promising\ngauge to realize this model in optical lattices.",
        "positive": "Clock shift in a strongly interacting two-dimensional Fermi gas: We derive universal relations for the radio-frequency (rf) spectroscopy of a\ntwo-dimensional Fermi gas consisting of two spin states with a resonant S-wave\ninteraction. The rf transition rate has a high-frequency tail that is\nproportional to the contact and displays logarithmic scaling violations,\ndecreasing asymptotically like $1/(\\omega^2 \\ln^2 \\omega)$. Its coefficient is\nproportional to $\\ln^2(a_{2D}'/a_{2D})$, where $a_{2D}$ and $a_{2D}'$ are the\n2-dimensional scattering lengths associated with initial-state and final-state\ninteractions. The clock shift is proportional to the contact and to\n$\\ln(a_{2D}'/a_{2D})$. If $|\\ln(a_{2D}'/a_{2D})| \\gg 1$, the clock shift arises\nas a cancellation between much larger contributions proportional to\n$\\ln^2(a_{2D}'/a_{2D})$ from bound-bound and bound-free rf transitions."
    },
    {
        "anchor": "Bloch oscillations of spin-orbit-coupled cold atoms in an optical\n  lattice and spin current generation: We study the Bloch oscillation dynamics of a spin-orbit-coupled cold atomic\ngas trapped inside a one-dimensioanl optical lattice. The eigenspectra of the\nsystem is identified as two interpenetrating Wannier-Stark ladder. Based on\nthat, we carefully analyzed the Bloch oscillation dynamics and found out that\nintraladder coupling between neighboring rungs of Wannier-Stark ladder give\nrise to ordinary Bloch oscillation while interladder coupling lead to small\namplitude high frequency oscillation superimposed on it. Specifically\nspin-orbit interaction breaks Galilean invariance, which can be reflected by\nout-of-phase oscillation of the two spin components in the accelerated frame.\nThe possibility of generating spin current in this system are also explored.",
        "positive": "Observation of collective atomic recoil motion in a momentum-squeezed,\n  ultra-cold, degenerate fermion gas: We demonstrate clear collective atomic recoil motion in a dilute,\nmomentum-squeezed, ultra-cold degenerate fermion gas by circumventing the\neffects of Pauli blocking. Although gain from bosonic stimulation is\nnecessarily absent because the quantum gas obeys Fermi-Dirac statistics,\ncollective atomic recoil motion from the underlying wave-mixing process is\nclearly visible. With a single pump pulse of the proper polarization, we\nobserve two mutually-perpendicular wave-mixing processes occurring\nsimultaneously. Our experiments also indicate that the red-blue pump detuning\nasymmetry observed with Bose-Einstein condensates does not occur with fermions."
    },
    {
        "anchor": "Spin-flip induced superfluidity in a ring of spinful hard-core bosons: The t - J Hamiltonian of the spinful hard-core bosonic ring in the Nagaoka\nlimit is solved. The energy spectrum becomes quantized due to presence of spin,\nwhere each energy level corresponds to a cyclic permutation state of the spin\nchains. The ground state is true ferromagnetic when the ring contains N = 2, 3\nspinful hard-core bosons; for all other N it is a mixture of the ferromagnetic\nand non-ferromagnetic states. This behaviour is different from the fermionic\nring, where ground state is true ferromagnetic only for N = 3. It is shown that\nthe intrinsic spin generated gauge fields are analogous to the synthetic gauge\nfields generated by rotation of either the condensate or the confining\npotential. It is argued that the low lying excited levels of the spin flipped\nstates intrinsically support the superfluidity. Possible ways to experimentally\nverify these results are also discussed.",
        "positive": "Topological superfluid of spinless Fermi gases in p-band honeycomb\n  optical lattices with on-site rotation: In this paper, we put forward to another route realizing topological\nsuperfluid (TS). In contrast to conventional method, spin-orbit coupling and\nexternal magnetic field are not requisite. Introducing an experimentally\nfeasible technique called on-site rotation (OSR) into p-band honeycomb optical\nlattices for spinless Fermi gases and considering CDW and pairing on the same\nfooting, we investigate the effects of OSR on superfluidity. The results\nsuggest that when OSR is beyond a critical value, where CDW vanishes, the\nsystem transits from a normal superfluid (NS) with zero TKNN number to TS\nlabeled by a non-zero TKNN number. In addition, phase transitions between\ndifferent TS are also possible."
    },
    {
        "anchor": "Breakdown of the Peierls substitution for the Haldane model with\n  ultracold atoms: We present two independent calculations of the tight-binding parameters for a\nspecific realization of the Haldane model with ultracold atoms. The tunneling\ncoefficients up to next-to-nearest neighbors are computed ab-initio by using\nthe maximally localized Wannier functions, and compared to analytical\nexpressions written in terms of gauge invariant, measurable properties of the\nspectrum. The two approaches present a remarkable agreement and evidence the\nbreakdown of the Peierls substitution: (i) the phase acquired by the\nnext-to-nearest tunneling amplitude $t_{1}$ presents quantitative and\nqualitative differences with respect to that obtained by the integral of the\nvector field A, as considered in the Peierls substitution, even in the regime\nof low amplitudes of A; (ii) for larger values, also $|t_{1}|$ and the\nnearest-neighbor tunneling $t_{0}$ have a marked dependence on A. The origin of\nthis behavior and its implications are discussed.",
        "positive": "Quantum turbulence by vortex stirring in a spinor Bose-Einstein\n  condensate: We introduce a novel mechanism to develop a turbulent flow in a spinor\nBose-Einstein condensate, consisting in the stirring of a single line vortex by\nmeans of an external magnetic field. We find that density and velocity\nfluctuations have white-noise power spectra at large frequencies and that\nKolmogorov 5/3 law is obeyed in the turbulent region. As the stirring is turned\noff, the flow decays to an agitated non-equilibrium state that shows an energy\nbottleneck crossover at small length scales. We demonstrate our findings by\nnumerically solving two-state spinor coupled 3D Gross-Pitaevskii equations. We\nsuggest that this mechanism may be experimentally implemented in spinor\nultracold gases confined by optical traps."
    },
    {
        "anchor": "Effects of finite temperature on the robustness of the Mott insulator\n  phase in pseudo one-dimensional Bose-Hubbard Model: We study the superfluid-Mott insulator (SF-MI) transition in an\none-dimensional optical lattice system, and employ the Bose-Hubbard model in\ntwo dimension with a combined potential of an optical lattice in one direction\nand a confining harmonic trap in the other direction, which we refer to as the\npseudo one-dimension Bose-Hubbard model. There some excited states with respect\nto the harmonic trap are considered. The Mott lobes shrink in the $\\mu$ and $J$\ndirections of the $\\mu$-$J$ phase diagram. The shrinkage occurs because the\ninteractions involving the excited states become weaker than that between\nparticles in the ground state. The dispersion of the in-site particle increases\nbecause the energy spacing between the eigenstates of the Hamiltonian decreases\nat finite temperature. The excited states significantly affect the robustness\nof the MI phase at finite temperate.",
        "positive": "Thouless pumping and topology: Thouless pumping provides one of the simplest manifestations of topology in\nquantum systems, and has attracted a lot of recent interest, both theoretically\nand experimentally. Since the seminal works by Thouless and Niu in 1983 and\n1984, it is argued that the quantization of the pumped charge is robust against\nweak disorder, but a clear characterization of the localization properties of\nthe relevant states, and the breakdown of quantized transport in the presence\nof interaction or out of the adiabatic approximation, has been long debated.\nThouless pumping is also the first example of a topological phase emerging in a\nperiodically-driven system. Driven systems can exhibit exotic topological\nphases without any static analogue and have been the subject of many recent\nproposals both in fermionic and bosonic systems in diverse platforms ranging\nfrom cold atoms to photonics and condensed matter systems. In this respect,\nthis review has a twofold purpose: On the one hand, it serves as a basis to\nunderstand the robustness of the topology of slowly-driven systems per se; On\nthe other hand, it highlights the rich properties of topological pumps and\ntheir diverse range of applications, for instance, in systems with synthetic\ndimensions or for understanding higher-order topological phases. These examples\nunderline the relevance of topological pumping for the fast growing field of\ntopological quantum matter."
    },
    {
        "anchor": "Inducing Resonant Interactions in Ultracold Atoms with a Modulated\n  Magnetic Field: In systems of ultracold atoms, pairwise interactions can be resonantly\nenhanced by a new mechanism which does not rely upon a magnetic Feshbach\nresonance. In this mechanism, interactions are controlled by tuning the\nfrequency of an oscillating parallel component of the magnetic field close to\nthe transition frequency between the scattering atoms and a two-atom bound\nstate. The real part of the resulting s-wave scattering length $a$ is\nresonantly enhanced when the oscillation frequency is close to the transition\nfrequency. The resonance parameters can be controlled by varying the amplitude\nof the oscillating field. The amplitude also controls the imaginary part of $a$\nwhich arises because the oscillating field converts atom pairs into molecules.\nThe real part of $a$ can be made much larger than the background scattering\nlength without introducing catastrophic atom losses from the imaginary part.\nFor the case of a shallow bound state in the scattering channel, the\ndimensionless resonance parameters are universal functions of the dimensionless\noscillation amplitude.",
        "positive": "Spin turbulence in spinor Bose-Einstein condensates: We summarize the recent theoretical and numerical works on spin turbulence\n(ST) in spin-1 spinor Bose-Einstein condensates. When the system is excited\nfrom the ground state, it goes through hy- drodynamic instability to ST in\nwhich the spin density vector has various disordered direction. The properties\nof ST depend on whether the spin-dependent interaction is ferromagnetic or\nantiferro- magnetic. ST has some characteristics different from other kinds of\nturbulence in quantum fluids. Firstly, the spectrum of the spin-dependent\ninteraction energy exhibits the characteristic power law different from the\nusual Kolmogorov -5/3 law. Secondly, ST can show the spin-glass-like behavior;\nthe spin density vectors are spatially random but temporally frozen."
    },
    {
        "anchor": "Observation of resonant scattering between ultracold heteronuclear\n  Feshbach molecules: We report the observation of a dimer-dimer inelastic collision resonance for\nultracold Feshbach molecules made of bosonic sodium and rubidium atoms. This\nresonance, which we attribute to the crossing of the dimer-dimer threshold with\na heteronuclear tetramer state, manifests itself as a pronounced inelastic loss\npeak of dimers when the interspecies scattering length between the constituent\natoms is tuned. Near this resonance, a strong modification of the temperature\ndependence of the dimer-dimer scattering is observed. Our result provides\ninsight into the heteronuclear four-body system consisting of heavy and light\nbosons and offers the possibility of investigating ultracold molecules with\ntunable interactions.",
        "positive": "Life and death of the Bose polaron: Spectroscopic and interferometric measurements complement each other in\nextracting the fundamental properties of quantum many-body systems. While\nspectroscopy provides precise measurements of equilibrated energies,\ninterferometry can elucidate the dynamical evolution of the system. For an\nimpurity immersed in a bosonic medium, both are equally important for\nunderstanding the quasiparticle physics of the Bose polaron. Here, we compare\nthe interferometric and spectroscopic timescales to the underlying dynamical\nregimes of the impurity dynamics and the polaron lifetime, highlighting the\ncapability of the interferometric approach to clearly resolve polaron dynamics.\nIn particular, interferometric measurements of the coherence amplitude at\nstrong interactions reveal faster quantum dynamics at large repulsive\ninteraction strengths than at unitarity. These observations are in excellent\nagreement with a short-time theoretical prediction including both the continuum\nand the attractive polaron branch. For longer times, qualitative agreement with\na many-body theoretical prediction which includes both branches is obtained.\nMoreover, the polaron energy is extracted from interferometric measurements of\nthe observed phase velocity in agreement with previous spectroscopic results\nfrom weak to strong attractive interactions. Finally, the phase evolution\nallows for the measurement of an energetic equilibration timescale, describing\nthe initial approach of the phase velocity to the polaron energy.\nTheoretically, this is shown to lie within the regime of universal dynamics\nrevealing a fast initial evolution towards the formation of polarons. Our\nresults give a comprehensive picture of the many-body physics governing the\nBose polaron and thus validates the quasiparticle framework for further\nstudies."
    },
    {
        "anchor": "Nonlinear standing waves in an array of coherently coupled Bose-Einstein\n  condensates: Stationary solitary waves are studied in an array of $M$ linearly-coupled\none-dimensional Bose-Einstein condensates (BECs) by means of the\nGross-Pitaevskii equation. Solitary wave solutions with the character of\noverlapping dark solitons, Josephson vortex - antivortex arrays, and arrays of\nhalf-dark solitons are constructed for $M>2$ from known solutions for two\ncoupled BECs. Additional solutions resembling vortex dipoles and rarefaction\npulses are found numerically. Stability analysis of the solitary waves reveals\nthat overlapping dark solitons can become unstable and susceptible to decay\ninto arrays of Josephson vortices. The Josephson vortex arrays have mixed\nstability but for all parameters we find at least one stationary solitary wave\nconfiguration that is dynamically stable. The different families of nonlinear\nstanding waves bifurcate from one another. In particular we demonstrate that\nJosephson-vortex arrays bifurcate from dark soliton solutions at instability\nthresholds. The stability thresholds for dark soliton and Josephson-vortex type\nsolutions are provided, suggesting the feasibility of realization with optical\nlattice experiments.",
        "positive": "Contour-time approach to the disordered Bose-Hubbard model in the strong\n  coupling regime: There has been considerable interest in the disordered Bose Hubbard model\n(BHM) in recent years, particularly in the context of thermalization and\nmany-body localization. We develop a two-particle irreducible (2PI)\nstrong-coupling approach to the disordered BHM that allows us to treat both\nequilibrium and out-of-equilibrium situations. We obtain equations of motion\nfor spatio-temporal correlations and explore their equilibrium solutions. We\nstudy the equilibrium phase diagram as a function of disorder strength and\ndiscuss applications of the formalism to out-of-equilibrium situations. We also\nnote that the disorder strengths where the emergence of non-ergodic dynamics\nwas observed in a recent experiment [Choi $et \\,al.$, Science $\\bf{352}$, 1547\n(2016)] appear to correspond to the Mott insulator -- Bose glass phase\nboundary."
    },
    {
        "anchor": "Interactions between Rydberg excitons in Cu$_2$O: Highly-excited states of excitons in cuprous oxide have recently been\nobserved at a record quantum number of up to $n=25$. Here, we evaluate the\nlong-range interactions between pairs of Rydberg excitons in Cu$_2$O, which are\ndue to direct Coulomb forces rather than short-range collisions typically\nconsidered for ground state excitons. A full numerical analysis is supplemented\nby the van der Waals asymptotics at large exciton separations, including the\nangular dependence of the potential surfaces.",
        "positive": "Distribution of eigenfrequencies for oscillations of the ground state in\n  the Thomas--Fermi limit: In this work, we present a systematic derivation of the distribution of\neigenfrequencies for oscillations of the ground state of a repulsive\nBose-Einstein condensate in the semi-classical (Thomas-Fermi) limit. Our\ncalculations are performed in 1-, 2- and 3-dimensional settings. Connections\nwith the earlier work of Stringari, with numerical computations, and with\ntheoretical expectations for invariant frequencies based on symmetry principles\nare also given."
    },
    {
        "anchor": "Observability of Higgs Mode in a system without Lorentz invariance: We study the observability of the Higgs mode in BEC-BCS crossover. The\nobservability of Higgs mode is investigated by calculating the spectral weight\nfunctions of the amplitude fluctuation below the critical transition\ntemperature. At zero temperature, we find that there are two sharp peaks on the\nspectral function of the amplitude fluctuation attributed to Goldstone and\nHiggs modes respectively. As the system goes from BCS to BEC side, there is\nstrong enhancement of spectral weight transfer from the Higgs to Goldstone\nmode. However, even at the unitary regime where the Lorentz invariance is lost,\nthe sharp feature of Higgs mode still exists. We specifically calculate the\nfinite temperature spectral function of amplitude fluctuation at the unitary\nregime and show that the Higgs mode is observable at the temperature that\npresent experiments can reach.",
        "positive": "Strongly interacting mesoscopic systems of anyons in one dimension: Using the fractional statistical properties of so-called anyonic particles,\nwe present exact solutions for up to six strongly interacting particles in\none-dimensional confinement that interpolate the usual bosonic and fermionic\nlimits. Specifically, we consider two-component mixtures of anyons and use\nthese to eludicate the mixing-demixing properties of both balanced and\nimbalanced systems. Importantly, we demonstrate that the degree of demixing\ndepends sensitively on the external trap in which the particles are confined.\nWe also show how one may in principle probe the statistical parameter of an\nanyonic system by injection a strongly interacting impurity and doing spectral\nor tunneling measurements."
    },
    {
        "anchor": "A method for the dynamics of vortices in a Bose-Einstein condensate:\n  analytical equations of the trajectories of phase singularities: We present a method to study the dynamics of a quasi-two dimensional\nBose-Einstein condensate which contains initially many vortices at arbitrary\nlocations. We present first the analytical solution of the dynamics in a\nhomogeneous medium and in a parabolic trap for the ideal non-interacting case.\nFor the homogeneous case this was introduced in the context of photonics. Here\nwe discuss this case in the context of Bose-Einstein condensates and extend the\nanalytical solution to the trapped case, for the first time. This linear case\nallows one to obtain the trajectories of the position of phase singularities\npresent in the initial condensate along with time. Also, it allows one to\npredict some quantities of interest, such as the time at which a vortex and an\nantivortex contained in the initial condensate will merge. Secondly, the method\nis complemented with numerical simulations of the non-linear case. We use a\nnumerical split-step simulation of the non-linear Gross-Pitaevskii equation to\ndetermine how these trajectories and quantities of interest are changed by the\npresence of interactions. We illustrate the method with several simple cases of\ninterest both in the homogeneous and parabolically trapped systems.",
        "positive": "Synthetic magnetic field effects on neutral bosonic condensates in quasi\n  three-dimensional anisotropic layered structures: We discuss a system of dilute Bose gas confined in a layered structure of\nstacked square lattices (slab geometry). A derived phase diagram reveals a\nnon-monotonic dependence of the ratio of tunneling to on-site repulsion on the\nartificial magnetic field applied to the system. The effect is reduced when\nmore layers are added, which mimics a two- to quasi-three-dimensional geometry\ncrossover. Furthermore, we establish a correspondence between anisotropic\ninfinite (quasi three-dimensional) and isotropic finite (slab geometry) systems\nthat share exactly the same critical values, which can be an important clue for\nchoosing experimental setups that are less demanding, but still leading to the\nidentical results. Finally, we show that the properties of the ideal Bose gas\nin a three-dimensional optical lattice can be closely mimicked by finite (slab)\nsystems, when the number of two-dimensional layers is larger than ten for\nisotropic interactions or even less, when the layers are weakly coupled."
    },
    {
        "anchor": "First and second sound in a dilute Bose gas across the BKT transition: We study the propagation of the two sound modes in two-dimensional Bose gases\nacross the Berezinksii-Kosterlitz-Thouless (BKT) transition using\nclassical-field dynamics, which is motivated by recent measurements of\nChristodoulou et al. Nature 594, 191 (2021). Based on the dynamic structure\nfactor, we identify the two sound modes as the Bogoliubov (B) and the\nnon-Bogoliubov (NB) sound mode below the transition, and as the diffusive and\nthe normal sound mode above the transition. The NB sound mode velocity is\nhigher than the B sound mode velocity, which we refer to as the weak-coupling\nregime of the sound modes. We excite the sound modes by driving the system as\nin the experiment and by perturbing the density with a step-pulse perturbation,\nas a secondary comparison. The driven response depends on the driving strength\nand results in higher velocities for the B sound mode at high temperatures near\nthe transition, compared to the sound results of the dynamic structure factor\nand step-pulse excitation. We show that the higher mode velocity has a weak\ntemperature dependence across the transition, which is consistent with the\nexperimental observation.",
        "positive": "BCS-BEC crossover of atomic Fermi superfluid in a spherical bubble trap: We present a theory of a two-component atomic Fermi gas with tunable\nattractive contact interactions on a spherical shell going through the\nBardeen-Cooper-Schrieffer (BCS) - Bose Einstein condensation (BEC) crossover,\ninspired by the realizations of spherical bubble traps for ultracold atoms in\nmicrogravity. The derivation follows the BCS-Leggett theory to obtain the gap\nand number equations. The BCS-BEC crossover can be induced by tuning the\ninteraction, and the properly normalized gap and chemical potential exhibit\nuniversal behavior regardless of the planar or spherical geometry.\nNevertheless, the spherical-shell geometry introduces another way of inducing\nthe crossover by the curvature. The curvature-induced BCS-BEC crossover is made\npossible by fixing the particle number and interaction strength while shrinking\nthe sphere, causing a reduction to the ratio of the pairing and kinetic\nenergies and pushing the system towards the BCS limit. The saturation of the\nsuperfluid density further confirms the ground state is a Fermi superfluid."
    },
    {
        "anchor": "Rotation of cold molecular ions inside a Bose-Einstein condensate: We use recently developed angulon theory [Phys. Rev. Lett. 114, 203001\n(2015)] to study the rotational spectrum of a cyanide molecular anion immersed\ninto Bose-Einstein condensates of rubidium and strontium. Based on $\\textit {ab\ninitio}$ potential energy surfaces, we provide a detailed study of the\nrotational Lamb shift and many-body-induced fine structure which arise due to\ndressing of molecular rotation by a field of phonon excitations. We demonstrate\nthat the magnitude of these effects is large enough in order to be observed in\nmodern experiments on cold molecular ions. Furthermore, we introduce a novel\nmethod to construct pseudopotentials starting from the $\\textit {ab initio}$\npotential energy surfaces, which provides a means to obtain effective coupling\nconstants for low-energy polaron models.",
        "positive": "Crystallisation of a dilute atomic dipolar condensate: We present a theory that explains the experimentally observed crystallisation\nof a dilute dysprosium condensate into a lattice of droplets. The key\ningredient of our theory is a conservative three-body interaction which\nstabilises the droplets against collapse to high density spikes. Our theory\nreproduces the experimental observations, and provides insight into the\nmanybody properties of this new phase of matter. Notably, we show that it is\nunlikely that a supersolid was obtained in experiments, however our results\nsuggest a strategy to realize this phase."
    },
    {
        "anchor": "Mid-range order in trapped quasi-condensates of bosonic atoms: Finite Bose systems cannot display a genuine Bose-Einstein condensate with\ninfinite long-range order. But, if the number of trapped atoms is sufficiently\nlarge, a kind of Bose-Einstein condensation does occur, with the properties of\nthe arising quasi-condensate being very close to the genuine condensate.\nAlthough the quasi-condensate does not enjoy long-range order, it has mid-range\norder. This paper shows that the level of mid-range order in finite Bose\nsystems can be characterized by order indices of density matrices.",
        "positive": "Correlations and dynamics of tunnel-coupled one-dimensional Bose gases: We present a series of experiments performed with two ultracold\none-dimensional Bose gases (rubidium atoms) in a double well potential.\nEmploying matter-wave interference, we can measure the spatially resolved phase\ndifference between the two gases and consequently investigate spatial\ncorrelations. By investigating whether higher order correlation functions can\nbe factorized into correlations of lower order, we can investigate the\ninteraction properties of the system. For a non-interacting system, all\ncorrelation functions with orders greater than two factorize and one observes\nGaussian fluctuations.\n  Here, we present the measurement of non-factorizing fourth-order correlation\nfunctions, leading to an experimental characterization of the interactions\nbetween the collective excitations of the quantum many-body system. The degree\nof non-factorizibility, i.e., the degree of non-Gaussianity of the phase\nfluctuations, depends on the tuneable tunneling strength between the wells.\n  Starting from such a non-Gaussian state, we are able to observe the dynamical\nevolution towards a state with factorizing correlation functions (Gaussian\nfluctuations). We start in a double well with tunneling and then abruptly\ndecouple the two subsystems. Subsequently, we observe how the initially\nnon-Gaussian phase fluctuations become Gaussian.\n  Moreover, we discuss the dynamical emergence of phase coherence in a double\nwell potential with tunneling. We experimentally investigate the evolution\nstarting from two different initial states. In one case, we split a cloud of\natoms into two and trigger global oscillations in their relative phase. The\noscillations subsequently damp and phase coherence sets in. In the other case,\ntwo independent clouds are suddenly coupled by tunneling. Again, phase\ncoherence emerges between the two subsystems."
    },
    {
        "anchor": "Ferromagnetism in an extended coherently-coupled atomic superfluid: Ferromagnetism is an iconic example of a first-order phase transition taking\nplace in spatially extended systems and is characterized by hysteresis and the\nformation of domain walls. In this paper we demonstrate that an extended atomic\nsuperfluid in the presence of a coherent coupling between two internal states\nexhibits a quantum phase transition from a para- to a ferromagnetic state. The\nnature of the transition is experimentally assessed by looking at the phase\ndiagram as a function of the control parameters, at hysteresis phenomena, at\nthe magnetic susceptibility and the magnetization fluctuations around the\ncritical point. We show that the observed features are in good agreement with\nmean-field calculations. Additionally, we develop experimental protocols to\ndeterministically generate domain walls that separate spatial regions of\nopposite magnetization in the ferromagnetic state. Thanks to the enhanced\ncoherence properties of our atomic superfluid system compared to standard\ncondensed matter systems, our results open the way towards the study of\ndifferent aspects of the relaxation dynamics in isolated coherent many-body\nquantum systems.",
        "positive": "Quantum Field Theory of Correlated Bose-Einstein condensates: II.\n  Ward-Takahashi Identities and Correlation Functions: We derive Ward-Takahashi identities for correlated Bose-Einstein condensates\nbased on the expressions of the first-order variations $(\\delta\\Psi,\\delta G)$\ndue to perturbations obtained in the preceding paper [T. Kita, J. Phys. Soc.\nJpn. $\\bf 90$, 024001 (2021)] for the condensate wave function $\\Psi$ and\nGreen's function $G$. They enable us to obtain several exact results on the\ndensity and current correlation functions $K_{\\nu\\nu'}^{}$, and also express\n$K_{\\nu\\nu'}^{}$ in terms of low-energy Green's functions and vertices. The\nlatter expressions open up the possibility of constructing theory of superfluid\nBose liquids in the same way as that for fermions at low temperatures. The\nvertices are found to have different limits depending on which of frequency\n$\\omega$ and wavenumber $q$ is set equal to zero first."
    },
    {
        "anchor": "Continuous Symmetry Breaking in a Two-dimensional Rydberg Array: Spontaneous symmetry breaking underlies much of our classification of phases\nof matter and their associated transitions. The nature of the underlying\nsymmetry being broken determines many of the qualitative properties of the\nphase; this is illustrated by the case of discrete versus continuous symmetry\nbreaking. Indeed, in contrast to the discrete case, the breaking of a\ncontinuous symmetry leads to the emergence of gapless Goldstone modes\ncontrolling, for instance, the thermodynamic stability of the ordered phase.\nHere, we realize a two-dimensional dipolar XY model -- which exhibits a\ncontinuous spin-rotational symmetry -- utilizing a programmable Rydberg quantum\nsimulator. We demonstrate the adiabatic preparation of correlated\nlow-temperature states of both the XY ferromagnet and the XY antiferromagnet.\nIn the ferromagnetic case, we characterize the presence of long-range XY order,\na feature prohibited in the absence of long-range dipolar interaction. Our\nexploration of the many-body physics of XY interactions complements recent\nworks utilizing the Rydberg-blockade mechanism to realize Ising-type\ninteractions exhibiting discrete spin rotation symmetry.",
        "positive": "Reducing number fluctuations of ultracold atomic gases via dispersive\n  interrogation: We have used nondestructive laser probing to follow the central density\nevolution of a trapped atomic cloud during forced evaporative cooling. This was\nachieved in a heterodyne dispersive detection scheme. We propose to use this as\na precursor measurement for predicting the atom number subsequent to\nevaporation and provide a simple experimental demonstration of the principle\nleading to a conditional reduction of classical number fluctuations."
    },
    {
        "anchor": "Controlled preparation of phases in two-dimensional time crystals: The study of phases is useful for understanding novel states of matter. One\nsuch state of matter are time crystals which constitute periodically driven\ninteracting many-body systems that spontaneously break time translation\nsymmetry. Time crystals with arbitrary periods (and dimensions) can be realized\nusing the model of Bose-Einstein condensates bouncing on periodically-driven\nmirror(s). In this work, we identify the different phases that characterize the\ntwo-dimensional time crystal. By determining the optimal initial conditions and\nvalue of system parameters, we provide a practical route to realize a specific\nphase of the time crystal. These different phases can be mapped to the\nmany-body states existing on a two-dimensional Hubbard lattice model, thereby\nopening up interesting opportunities for quantum simulation of many-body\nphysics in time lattices.",
        "positive": "Dispersive and dissipative effects in quantum field theory in curved\n  space-time to model condensed matter systems: The two main predictions of quantum field theory in curved space-time, namely\nHawking radiation and cosmological pair production, have not been directly\ntested and involve ultra high energy configurations. As a consequence, they\nshould be considered with caution. Using the analogy with condensed matter\nsystems, their analogue versions could be tested in the lab. Moreover, the high\nenergy behavior of these systems is known and involves dispersion and\ndissipation, which regulate the theory at short distances. When considering\nexperiments which aim to test the above predictions, there will also be a\ncompetition between the stimulated emission from thermal noise and the\nspontaneous emission out of vacuum. In order to measure these effects, one\nshould thus compute the consequences of UV dispersion and dissipation, and\nidentify observables able to establish that the spontaneous emission took\nplace. In this thesis, we first analyze the effects of dispersion and\ndissipation on both Hawking radiation and pair particle production. To get\nexplicit results, we work in the context of de Sitter space. Using the extended\nsymmetries of the theory in such a background, exact results are obtained.\nThese are then transposed to the context of black holes using the\ncorrespondence between de Sitter space and the black hole near horizon region.\nTo introduce dissipation, we consider an exactly solvable model producing any\ndecay rate. We also study the quantum entanglement of the particles so\nproduced. In a second part, we consider explicit condensed matter systems,\nnamely Bose Einstein condensates and exciton-polariton systems. We analyze the\neffects of dissipation on entanglement produced by the dynamical Casimir\neffect. As a final step, we study the entanglement of Hawking radiation in the\npresence of dispersion for a generic analogue system."
    },
    {
        "anchor": "BCS-BEC crossover in a trapped Fermi super-fluid using a\n  density-functional equation: We derive a generalized time-dependent Galilean-invariant density-functional\n(DF) equation appropriate to study the stationary and non-stationary properties\nof a trapped Fermi super-fluid in the Bardeen-Cooper-Schrieffer (BCS) to\nBose-Einstein condensation (BCS) crossover. This equation is equivalent to a\nquantum hydrodynamical equation for a Fermi super-fluid. The bulk chemical\npotential of this equation has the proper (model-independent) dependence on the\nFermi-Fermi scattering length in the BCS and BEC limits. We apply this DF\nequation to the study of stationary density profile and size of a cigar-shaped\nFermi super-fluid of $^6$Li atoms and the results are in good agreement with\nthe experiment of Bartenstein {\\it et al.} in the BCS-BEC crossover. We also\napply the DF equation to the study of axial and radial breathing oscillation\nand our results for these frequencies are in good agreement with experiments in\nthe BCS-BEC crossover.",
        "positive": "Tonks-Girardeau and Super Tonks-Girardeau States of a Trapped 1D Spinor\n  Bose Gas: A harmonically trapped ultracold 1D spin-1 Bose gas with strongly repulsive\nor attractive 1D even-wave interactions induced by a 3D Feshbach resonance is\nstudied. The exact ground state, a hybrid of Tonks-Girardeau (TG) and ideal\nFermi gases, is constructed in the TG limit of infinite even-wave repulsion by\na spinor Fermi-Bose mapping to a spinless ideal Fermi gas. It is then shown\nthat in the limit of infinite even-wave attraction this same state remains an\nexact many-body eigenstate, now highly excited relative to the collapsed\ngeneralized McGuire cluster ground state, showing that the hybrid TG state is\ncompletely stable against collapse to this cluster ground state under a sudden\nswitch from infinite repulsion to infinite attraction. It is shown to be the TG\nlimit of a hybrid super Tonks-Girardeau (STG) state which is metastable under a\nsudden switch from finite but very strong repulsion to finite but very strong\nattraction. It should be possible to create it experimentally by a sudden\nswitch from strongly repulsive to strongly attractive interaction, as in the\nrecent Innsbruck experiment on a spin-polarized bosonic STG gas. In the case of\nstrong attraction there should also exist another STG state of much lower\nenergy, consisting of strongly bound dimers, a bosonic analog of a recently\npredicted STG gas which is an ultracold gas of strongly bound bosonic dimers of\nfermionic atoms, but it is shown that this STG state cannot be created by such\na switch from strong repulsion to strong attraction."
    },
    {
        "anchor": "Two-body and Three-body Contacts for Identical Bosons near Unitarity: In a recent experiment with ultracold trapped Rb-85 atoms, Makotyn et al.\nhave studied a quantum-degenerate Bose gas in the unitary limit where its\nscattering length is infinitely large. We show that the observed momentum\ndistributions are compatible with a universal relation that expresses the\nhigh-momentum tail in terms of the 2-body and the 3-body contacts. We determine\nthe 2- and 3-body contact densities for the unitary Bose gas with number\ndensity n to be approximately 20n^{4/3} and 2n^{5/3}, respectively. We also\nshow that the observed atom loss rate is compatible with that from 3-atom\ninelastic collisions, which gives a contribution proportional to the 3-body\ncontact, but the loss rate is not compatible with that from 2-atom inelastic\ncollisions, which gives a contribution proportional to the 2-body contact. We\npoint out that the contacts could be measured independently by using the virial\ntheorem near and at unitarity.",
        "positive": "Normal-state Properties of a Unitary Bose-Fermi Mixture: A Combined\n  Strong-coupling Approach with Universal Thermodynamics: We theoretically investigate normal-state properties of a unitary Bose-Fermi\nmixture. Including strong hetero-pairing fluctuations, we evaluate the Bose and\nFermi chemical potential, internal energy, pressure, entropy, as well as\nspecific heat at constant volume $C_V$, within the framework of a combined\nstrong-coupling theory with exact thermodynamic identities. We show that\nhetero-pairing fluctuations at the unitarity cause non-monotonic temperature\ndependence of $C_V$, being qualitatively different from the monotonic behavior\nof this quantity in the weak- and strong-coupling limit. On the other hand,\nsuch an anomalous behavior is not seen in the other quantities. Our results\nindicate that the specific heat $C_V$, which has recently become observable in\ncold atom physics, is a useful quantity for understanding strong-coupling\naspects of this quantum system."
    },
    {
        "anchor": "Exact Solutions for Solitary Waves in a Bose-Einstein Condensate under\n  the Action of a Four-Color Optical Lattice: We address dynamics of Bose-Einstein condensates (BECs) loaded into a\none-dimensional four-color optical lattice (FOL) potential with commensurate\nwavelengths and tunable intensities. This configuration lends system-specific\nsymmetry properties. The analysis identifies specific multi-parameter forms of\nthe FOL potential which admits exact solitary-wave solutions. This newly found\nclass of potentials includes more particular species, such as frustrated\ndouble-well superlattices, and bi-chromatic and three-color lattices, which are\nsubject to respective symmetry constraints. Our exact solutions provide options\nfor controllable positioning of density maxima of the localized patterns, and\ntunable Anderson-like localization in the frustrated potential. A numerical\nanalysis is performed to establish dynamical stability and structural stability\nof the obtained solutions, which makes them relevant for experimental\nrealization. The newly found solutions offer applications to the design of\nschemes for quantum simulations and processing quantum information.",
        "positive": "The weakening of fermionization of one dimensional spinor Bose gases\n  induced by spin-exchange interaction: We investigate the ground state density distributions of anti-ferromagnetic\nspin-1 Bose gases in one dimensional harmonic potential in the full interacting\nregimes. The ground state is obtained by diagonalizing the Hamiltonian in the\nHilbert space composed of the lowest eigenstates of noninteracting Bose gas and\nspin components. The study reveals that in the situation of weak spin-dependent\ninteraction the total density profiles evolve from Gaussian-like distribution\nto a Fermi-like shell structure of $N$ peaks with the increasing of\nspin-independent interaction. While the increasing spin-exchange interaction\nalways weaken the fermionization of density distribution such that the total\ndensity profiles show shell structure of less peaks and even show single peak\nstructure in the limit of strong spin-exchange interaction. The weakening of\nfermionization results from the formation of composite atoms induced by\nspin-exchange interaction. It is also shown that phase separation occurs for\nthe spinor Bose gas with weak spin-exchange interaction, meanwhile strong\nspin-independent interaction."
    },
    {
        "anchor": "Beyond-mean-field stochastic corrections to the blueshift of a\n  driven-dissipative exciton-polariton condensate: In the absence of vortices or phase slips, the phase dynamics of\nexciton-polariton condensates was shown to map onto the Kardar-Parisi-Zhang\n(KPZ) equation, which describes the stochastic growth of a classical interface.\nThis implies that the coherence of such non-equilibrium quasi-condensates\ndecays in space and time following stretched exponentials, characterized by KPZ\nuniversal critical exponents. In this work, we focus on the time evolution of\nthe average phase of a one-dimensional exciton-polariton condensate in the KPZ\nregime and determine the frequency of its evolution, which is given by the\nblueshift, i.e. the non-equilibrium analog of the chemical potential. We\ndetermine the stochastic corrections to the blueshift within Bogoliubov\nlinearized theory and find that while this correction physically originates\nfrom short scale effects, and depends both on density and phase fluctuations,\nit can still be related to the effective large-scale KPZ parameters. Using\nnumerical simulations of the full dynamics, we investigate the dependence of\nthese blueshift corrections on both noise and interaction strength, and compare\nthe results to the Bogoliubov prediction. Our finding contributes both to the\nclose comparison between equilibrium and non-equilibrium condensates, and to\nthe theoretical understanding of the KPZ mapping.",
        "positive": "Fractional quantization of charge and spin in topological quantum pumps: Topological quantum pumps are topologically equivalent to the quantum Hall\nstate: In these systems, the charge pumped during each pumping cycle is\nquantized and coincides with the Chern invariant. However, differently from\nquantum Hall insulators, quantum pumps can exhibit novel phenomena such as the\nfractional quantization of the charge transport, as a consequence of their\ndistinctive symmetries in parameter space. Here, we report the analogous\nfractional quantization of the spin transport in a topological spin pump\nrealized in a one-dimensional lattice via a periodically modulated Zeeman\nfield. In the proposed model, which is a spinfull generalization of the\nHarper-Hofstadter model, the amount of spin current pumped during well-defined\nfractions of the pumping cycle is quantized as fractions of the spin Chern\nnumber. This fractional quantization of spin is topological, and is a direct\nconsequence of the additional symmetries ensuing from the commensuration of the\nperiodic field with the underlying lattice."
    },
    {
        "anchor": "Static and dynamic properties of shell-shaped condensates: Static, dynamic, and topological properties of hollow systems differ from\nthose that are fully filled as a result of the presence of a boundary\nassociated with an inner surface. Hollow Bose-Einstein condensates (BECs)\nnaturally occur in various ultracold atomic systems and possibly within neutron\nstars but have hitherto not been experimentally realized in isolation on Earth\nbecause of gravitational sag. Motivated by the expected first realization of\nfully closed BEC shells in the microgravity conditions of the Cold Atomic\nLaboratory aboard the International Space Station, we present a comprehensive\nstudy of spherically symmetric hollow BECs as well as the hollowing transition\nfrom a filled sphere BEC into a thin shell through central density depletion.\nWe employ complementary analytic and numerical techniques in order to study\nequilibrium density profiles and the collective mode structures of condensate\nshells hosted by a range of trapping potentials. We identify concrete and\nrobust signatures of the evolution from filled to hollow structures and the\neffects of the emergence of an inner boundary, inclusive of a dip in\nbreathing-mode-type collective mode frequencies and a restructuring of surface\nmode structure across the transition. By extending our analysis to a\ntwo-dimensional transition of a disk to a ring, we show that the collective\nmode signatures are an essential feature of hollowing, independent of the\nspecific geometry. Finally, we relate our work to past and ongoing experimental\nefforts and consider the influence of gravity on thin condensate shells. We\nidentify the conditions under which gravitational sag is highly destructive and\nstudy the mode-mixing effects of microgravity on the collective modes of these\nshells.",
        "positive": "Laser Control of Singlet-Pairing Process in an Ultracold Spinor Mixture: In the mixture of ultracold spin-1 atoms of two different species A and B\n(e.g., $^{23}$Na (A) and $^{87}$Rb (B)), inter-species singlet-pairing process\n${\\rm A}_{+1}+{\\rm B}_{-1}\\rightleftharpoons {\\rm A}_{-1}+{\\rm B}_{+1}$, can be\ninduced by the spin-dependent inter-atomic interaction, where subscript $\\pm 1$\ndenotes the magnetic quantum number. Nevertheless, one cannot isolate this\nprocess from other spin-changing processes by tuning the bias real magnetic\nfield. As a result, so far the singlet-pairing process have not been clearly\nobserved in the experiments, and the measurement of the corresponding\ninteraction strength becomes difficult. In this work we propose to control the\nsinglet-pairing process via combining the real magnetic field and a\nlaser-induced species-dependent synthetic magnetic field. With our approach one\ncan significantly enhance this process and simultaneously supperess all other\nspin-changing processes. We illustrate our approach for both a confined\ntwo-atom system and a binary mixture of spinor Bose-Einstein condensates. Our\ncontrol scheme is helpful for the precise measurement of the weakly\nsinglet-pairing interaction strength and the entanglement generation of two\ndifferent atoms."
    },
    {
        "anchor": "Tight binding models for ultracold atoms in honeycomb optical lattices: We discuss how to construct tight-binding models for ultra cold atoms in\nhoneycomb potentials, by means of the maximally localized Wannier functions\n(MLWFs) for composite bands introduced by Marzari and Vanderbilt [1]. In\nparticular, we work out the model with up to third-nearest neighbors, and\nprovide explicit calculations of the MLWFs and of the tunneling coefficients\nfor the graphene-lyke potential with two degenerate minima per unit cell.\nFinally, we discuss the degree of accuracy in reproducing the exact Bloch\nspectrum of different tight-binding approximations, in a range of typical\nexperimental parameters.",
        "positive": "Strongly interacting ultracold polar molecules: This paper reviews recent advances in the study of strongly interacting\nsystems of dipolar molecules. Heteronuclear molecules feature large and tunable\nelectric dipole moments, which give rise to long-range and anisotropic\ndipole-dipole interactions. Ultracold samples of dipolar molecules with\nlong-range interactions offer a unique platform for quantum simulations and the\nstudy of correlated many-body physics. We provide an introduction to the\nphysics of dipolar quantum gases, both electric and magnetic, and summarize the\nmultipronged efforts to bring dipolar molecules into the quantum regime. We\ndiscuss in detail the recent experimental progress in realizing and studying\nstrongly interacting systems of polar molecules trapped in optical lattices,\nwith particular emphasis on the study of interacting spin systems and\nnon-equilibrium quantum magnetism. Finally, we conclude with a brief discussion\nof the future prospects for studies of strongly interacting dipolar molecules."
    },
    {
        "anchor": "Sub-Poissonian fluctuations in a 1D Bose gas: from the quantum\n  quasi-condensate to the strongly interacting regime: We report on local measurements of atom number fluctuations in slices of a\nsingle 1D Bose gas with repulsive interactions. For weakly interacting gases,\nthe fluctuations are super-Poissonian at intermediate atomic densities and\nbecome sub-Poissonian at high densities once the gas enters into the quantum\nquasi-condensate regime. At stronger interactions, when approaching the\nfermionization regime, we no longer observe super-Poissonian statistics; the\nfluctuations go from Poissonian to sub-Poissonian as the density is increased,\nas those in a Fermi gas.",
        "positive": "Bose-Einstein condensates in a homogeneous gravitational field: The behavior of a Bose--Einstein condensate in a homogeneous gravitational\nfield is analyzed. We consider two different trapping potentials. Firstly, the\ngas is inside a finite container. The effects of the finiteness of the height\nof the container in connection with the presence of a homogeneous gravitational\nfield are mathematically analyzed and the resulting energy eigenvalues are\ndeduced and used to obtain the corresponding partition function and the ensuing\nthermodynamical properties. Secondly, the trapping potential is an anisotropic\nharmonic oscillator and the effects of the gravitational field and of the\nzero--point energy on the condensation temperature are also considered. These\nresults are employed in order to put forward an experiment which could test the\nso called Einstein Equivalence Principle."
    },
    {
        "anchor": "Cooling and state preparation in an optical lattice via Markovian\n  feedback control: We propose and investigate a scheme based on Markovian feedback control that\nallows for the preparation of single targeted eigenstates of a system of\nbosonic atoms in a one-dimensional optical lattice with high fidelity. It can\nbe used for in-situ cooling the interacting system without particle loss, both\nfor weak and strong interactions, and for experimentally preparing and probing\nindividual excited eigenstates. For that purpose the system is assumed to be\nprobed weakly via homodyne detection of photons that are scattered\noff-resonantly by the atoms from a structured probe beam into a cavity mode. By\napplying an inertial force to the system that is proportional to the measured\nsignal, the system is then guided into a pure target state. The scheme is found\nto be robust against reduced measurement efficiencies.",
        "positive": "Dynamic Phase Diagram for the Quantum Phase Model: We address the stability of superfluid currents in a system of interacting\nlattice bosons. We consider various Gutzwiller trial states for the quantum\nphase model which provides a good approximation for the Bose-Hubbard model in\nthe limit of large interactions and boson populations. We thoroughly analyze\nthe current-carrying stationary states of the dynamics ensuing from a Gaussian\nansatz, and derive analytical results for the critical lines signaling their\nmodulational and energetic instability, as well as the maximum of the carried\ncurrent. We show that these analytical results are in good qualitative\nagreement with those obtained numerically in previous works on the Bose-Hubbard\nmodel, and in the present work for the quantum phase model."
    },
    {
        "anchor": "Phase transitions and elementary excitations in spin-1 Bose gases with\n  Raman-induced spin-orbit coupling: We study the ground state phase diagram and the quantum phase transitions in\nspin-1 Bose gases with Raman induced spin-orbit coupling. In addition to the\nBose-Einstein condensates with uniform density, three types of stripe\ncondensation phases that simultaneously break the U(1) symmetry and the\ntranslation symmetry are identified. The transitions between these phases are\ninvestigated, and the occurrences of the various tricritical points are\npredicted. The excitation spectra in the plane-wave phase and the zero-momentum\nphase show rich roton-maxon structures, and their instabilities indicate the\ntendency to develop the crystalline order. We propose the atomic gas of\n$^{23}$Na could be a candidate for observing the stripe condensate with high\ncontrast fringes.",
        "positive": "Zero sound in a two-dimensional dipolar Fermi gas: We study zero sound in a weakly interacting 2D gas of single-component\nfermionic dipoles (polar molecules or atoms with a large magnetic moment)\ntilted with respect to the plane of their translational motion. It is shown\nthat the propagation of zero sound is provided by both mean field and many-body\n(beyond mean field) effects, and the anisotropy of the sound velocity is the\nsame as the one of the Fermi velocity. The damping of zero sound modes can be\nmuch slower than that of quasiparticle excitations of the same energy. One thus\nhas wide possibilities for the observation of zero sound modes in experiments\nwith 2D fermionic dipoles, although the zero sound peak in the structure\nfunction is very close to the particle-hole continuum."
    },
    {
        "anchor": "Continuous symmetry breaking and a new universality class in 1D\n  long-range interacting quantum systems: Continuous symmetry breaking (CSB) in low-dimensional systems, forbidden by\nthe Mermin-Wagner theorem for short-range interactions, may take place in the\npresence of slowly decaying long-range interactions. Nevertheless, there is no\nstringent bound on how slowly interactions should decay to give rise to CSB in\n1D quantum systems at zero temperature. Here, we study a long-range interacting\nspin chain with $U(1)$ symmetry and power-law interactions\n$V(r)\\sim1/r^\\alpha$, directly relevant to ion-trap experiments. Using\nbosonization and renormalization group theory, we find CSB for $\\alpha$ smaller\nthan a critical exponent $\\alpha_c(\\le 3)$ depending on the microscopic\nparameters of the model. Furthermore, the transition from the gapless XY phase\nto the gapless CSB phase is mediated by the breaking of conformal symmetry due\nto long-range interactions, and is described by a new universality class akin\nto the Berezinskii-Kosterlitz-Thouless transition. Our analytical findings are\nin good agreement with a numerical calculation. Signatures of the CSB phase\nshould be accessible in existing trapped-ion experiments.",
        "positive": "Skin superfluid, topological Mott insulators, and asymmetric dynamics in\n  interacting non-Hermitian Aubry-Andre-Harper models: Non-Hermitian quantum many-body systems are a fascinating subject to be\nexplored. Using the generalized density matrix renormalisation group method and\ncomplementary exact diagonalization, we elucidate the many-body ground states\nand dynamics of a 1D interacting non-Hermitian Aubry-Andre-Harper model for\nbosons. We find stable ground states in the superfluid and Mott insulating\nregimes under wide range of conditions in this model. We reveal a skin\nsuperfluid state induced by the non-Hermiticity from the nonreciprocal hopping.\nWe investigate the topology of the Mott insulating phase and find its\nindependence of the non-Hermiticity. The topological Mott insulators in this\nnon-Hermitian system are characterized by four equal Chern numbers and a\nquantized shift of biorthogonal many-body polarizations. Furthermore, we show\ngeneric asymmetric expansion and correlation dynamics in the system."
    },
    {
        "anchor": "Temporal correlations of elongated Bose gases at finite temperature: Temporal correlations in the harmonically trapped finite temperature Bose gas\nare studied through the calculation of appropriate phase correlation functions.\nA wide parameter regime is covered to ascertain the role that temperature\nfluctuations and trap geometry play in the temporal coherence of the 1D to 3D\ncrossover region. Bogoliubov analysis is used to establish results in the 1D\nand spherical limits. Formalism is then developed using the projected\nGross-Pitaevskii equation to calculate correlation functions in 3D simulations\nof varying trap elongation and temperature.",
        "positive": "Bosonic fractional quantum Hall states in driven optical lattices: Strong synthetic magnetic fields have been successfully implemented in\nperiodically driven optical lattices. However, the interplay of the driving and\ninteractions introduces detrimental heating, and for this reason it is still\nchallenging to reach a fractional quantum Hall state in cold-atom setup. By\nperforming a numerical study, we investigate stability of a bosonic Laughlin\nstate in a small atomic sample exposed to driving. We identify an optimal\nregime of microscopic parameters, in particular interaction strength $U$ and\nthe driving frequency $\\omega$, such that the stroboscopic dynamics supports\nthe basic $\\nu = 1/2$ Laughlin state. Moreover, we explore slow ramping of a\ndriving term and show that the considered protocol allows for the preparation\nof the Laughlin state on experimentally realistic time scales."
    },
    {
        "anchor": "Quantum simulation of small-polaron formation with trapped ions: We propose a quantum simulation of small-polaron physics using a\none-dimensional system of trapped ions acted upon by off-resonant standing\nwaves. This system, envisioned as an array of microtraps, in the\nsingle-excitation case allows the realization of the anti-adiabatic regime of\nthe Holstein model. We show that the strong excitation-phonon coupling regime,\ncharacterized by the formation of small polarons, can be reached using\nrealistic values of the relevant system parameters. Finally, we propose\nmeasurements of the quasiparticle residue and the average number of phonons in\nthe ground state, experimental probes validating the polaronic character of the\nphonon-dressed excitation.",
        "positive": "Thermodynamic Properties of Rashba Spin-Orbit-Coupled Fermi Gas: We investigate the thermodynamic properties of a superfluid Fermi gas subject\nto Rashba spin-orbit coupling and effective Zeeman field. We adopt a T-matrix\nscheme that takes beyond-mean-field effects, which are important for strongly\ninteracting systems, into account. We focus on the calculation of two important\nquantities: the superfluid transition temperature and the isothermal\ncompressibility. Our calculation shows very distinct influences of the\nout-of-plane and the in-plane Zeeman fields on the Fermi gas. We also confirm\nthat the in-plane Zeeman field induces a Fulde-Ferrell superfluid below the\ncritical temperature and an exotic finite-momentum pseudo-gap phase above the\ncritical temperature."
    },
    {
        "anchor": "Nonlinear Quantum Hall effects in Rarita-Schwinger gas: Emergence of higher spin relativistic fermionic materials becomes a new\nfavorite in the study of condensed matter physics. Massive Rarita-Schwinger\n3/2-spinor was known owning very exotic properties, such as the superluminal\nfermionic modes and even being unstable in an external magnetic field. Due to\nthe superluminal modes and the non-trivial constraints on the Rarita-Schwinger\ngas, we exposit anomalous properties of the Hall effects in (2+1)-dimensions\nwhich subvert the well-known quantum Hall paradigms. First, the Hall\nconductance of a pure Rarita-Schwinger gas is step-like but not\nplateau-quantized, instead of the linear dependence on the filling factor for a\npure spin-1/2 Dirac gas. In reality, the Hall conductance of the Dirac gas is\nof quantized integer plateaus with the unit $\\frac{e^2}h$ due to the\nlocalization away from the Landau level centers. If the general localization\nrule is applicable to the disordered Rarita-Schwinger gas, the Hall plateaus\nare also expected to appear but they are nonlinearly dependent on the Landau\nlevel index. Furthermore, there is a critical magnetic field beyond which\nhigher Landau levels become unstable. This confines the filling factor of the\nsystem. We also show that the non-hermitness of the effective Hamiltonian is\nnot crucial to the nonlinearity of the quantum Hall conductance.",
        "positive": "Time-dependent variational Monte Carlo study of the dynamic response of\n  bosons in an optical lattice: We study the dynamics of a one-dimensional Bose gas at unit filling in both\nshallow and deep optical lattices and obtain the dynamic structure factor\n${S(k,\\omega)}$ by monitoring the linear response to a weak probe pulse. We\nintroduce a new procedure, based on the time-dependent variational Monte Carlo\nmethod (tVMC), which allows to evolve the system in real time, using as a\nvariational model a Jastrow-Feenberg wave function that includes pair\ncorrelations. Comparison with exact diagonalization results of ${S(k,\\omega)}$\nobtained on a lattice in the Bose-Hubbard limit shows good agreement of the\ndispersion relation for sufficiently deep optical lattices, while for shallow\nlattices we observe the influence of higher Bloch bands. We also investigate\nnon-linear response to strong pulses. From the power spectrum of the density\nfluctuations we obtain the excitation spectrum, albeit broadened, by higher\nharmonic generation after a strong pulse with a single low wave number. As a\nremarkable feature of our simulations we furthermore demonstrate that the full\nexcitation spectrum can be retrieved from the power spectrum of the density\nfluctuations due to the stochastic noise inherent in any Monte Carlo method,\nwithout applying an actual perturbation."
    },
    {
        "anchor": "First and second sound in a strongly interacting Fermi gas: Using a variational approach, we solve the equations of two-fluid\nhydrodynamics for a uniform and trapped Fermi gas at unitarity. In the uniform\ncase, we find that the first and second sound modes are remarkably similar to\nthose in superfluid Helium, a consequence of strong interactions. In the\npresence of harmonic trapping, first and second sound become degenerate at\ncertain temperatures. At these points, second sound hybridizes with first sound\nand is strongly coupled with density fluctuations, giving a promising way of\nobserving second sound. We also discuss the possibility of exciting second\nsound by generating local heat perturbations.",
        "positive": "Collective modes of a harmonically trapped one-dimensional Bose gas: the\n  effects of finite particle number and nonzero temperature: Following the idea of the density functional approach, we develop a\ngeneralized Bogoliubov theory of an interacting Bose gas confined in a\none-dimensional harmonic trap, by using a local chemical potential - calculated\nwith the Lieb-Liniger exact solution - as the exchange energy. At zero\ntemperature, we use the theory to describe collective modes of a\nfinite-particle system in all interaction regimes from the ideal gas limit, to\nthe mean-field Thomas-Fermi regime, and to the strongly interacting\nTonks-Girardeau regime. At finite temperature, we investigate the temperature\ndependence of collective modes in the weak-coupling regime by means of a\nHartree-Fock-Bogoliubov theory with Popov approximation. By emphasizing the\neffects of finite particle number and nonzero temperature on collective mode\nfrequencies, we make comparisons of our results with the recent experimental\nmeasurement [E. Haller et al., Science 325, 1224 (2009)] and some previous\ntheoretical predictions. We show that the experimental data are still not fully\nexplained within current theoretical framework."
    },
    {
        "anchor": "Ground-state phases of ultracold bosons with Rashba-Dresselhaus\n  spin-orbit coupling: We study ultracold bosons in three dimensions with an anisotropic\nRashba-Dresselhaus spin-orbit coupling. We first carry out the exact summation\nof ladder diagrams for the two-boson t-matrix at zero energy. Then, with the\nt-matrix as the effective interaction, we find the ground-state phase diagrams\nof bosons in mean field as a function of the spin-orbit coupling, the\nanisotropy, and the scattering lengths between particles in the same and in\ndifferent pseudospin states. The resulting phase diagrams have much richer\nstructures than those obtained using mean-field couplings, exhibiting three\ndifferent phases: a plane-wave condensate, a striped condensate, and an\nunstable phase. The differences between the present approach using the t-matrix\ncompared to using mean-field couplings is significant for large scattering\nlengths, large spin-orbit-coupling strength, or small anisotropy.",
        "positive": "Effects of spatially inhomogeneous atomic interactions on Bose-Einstein\n  condensates in optical lattices: An interplay of optical lattices and nonlinear impurities in controlling the\ndynamics of Bose-Einstein condensate bright solitons is investigated using\neffective potential approach. The ability of pushing the solitons into or away\nfrom the impurity region by changing both lattice and impurity parameters is\nsuggested. A possibility for the existence of stable fundamental gap solitons,\nwhich appear to satisfy an inverted Vakhitov-Kolokolov criterion, is examined."
    },
    {
        "anchor": "Notes on the Cluster Gutzwiller Method: Inhomogeneous Lattices,\n  Excitations, and Cluster Time Evolution: Several perspectives of the cluster Gutzwiller method are briefly discussed.\nI show that the cluster mean-field method can be used for large inhomogeneous\nlattices, for computing local excitations, and for the time evolution of\ncorrelated quantum systems.",
        "positive": "Stable and mobile two-dimensional dipolar ring-dark-in-bright\n  Bose-Einstein condensate soliton: We demonstrate robust, stable, mobile two-dimensional (2D) dipolar\nring-dark-in-bright (RDB) Bose-Einstein condensate (BEC) solitons for repulsive\ncontact interaction, subject to a harmonic trap along the $y$ direction\nperpendicular to the polarization direction $z$. Such a RDB soliton has a\nring-shaped notch (zero in density) imprinted on a 2D bright soliton free to\nmove in the $x-z$ plane. At medium velocity the head-on collision of two such\nsolitons is found to be quasi elastic with practically no deformation. The\npossibility of creating the RDB soliton by phase imprinting is demonstrated.\nThe findings are illustrated using numerical simulation employing realistic\ninteraction parameters in a dipolar $^{164}$Dy BEC."
    },
    {
        "anchor": "Evaporative cooling to a Rydberg crystal close to its ground state: We theoretically show how to obtain a long one-dimensional crystal near its\nquantum ground state. We rely on an evaporative cooling scheme applicable to\nmany-body systems with nonzero-ranged interactions. Despite the absence of\nperiodic potentials, the final state is a crystal which exhibits long-range\nspatial order. We describe the scheme thermodynamically, applying the truncated\nBoltzmann distribution to the collective excitations of the chain, and show\nthat it leads to a novel quasi-equilibrium many-body state. For longer chains,\ncomprising about 1000 atoms, we emphasize the quasi-universality of the\nevaporation curve. Such exceptionally long 1D crystals are only accessible deep\nin the quantum regime. We perform our analysis on the example of an initially\nthermal chain of circular Rydberg atoms confined to a one-dimensional (1D)\ngeometry. Our scheme may be applied to other quantum systems with long-ranged\ninteractions such as polar molecules.",
        "positive": "Total Energy Dynamics and Asymptotics of the Momentum Distribution\n  Following an Interaction Quench in a Two-component Fermi Gas: The absence of a characteristic momentum scale in the pseudo-potential\ndescription of atomic interaction in ultracold (two-component Fermi) gases is\nknown to lead to divergence in perturbation theory. Here we show that they also\nplague the calculation of the dynamics of the total energy following a quantum\nquench. A procedure to remove the divergence is devised, which provides finite\nanswers for the time-evolution of the total energy after a quench in which the\ninteraction strength is ramped up according to an arbitrary protocol. An\nimportant result of this analysis is the time evolution of the asymptotic tail\nof the momentum distribution (related to Tan's contact) and the contact for a\nlinear interaction ramp are obtained, as a function of the interaction ramp\ntime in the crossover from the sudden quench to the adiabatic limit are\nreported. In sudden quench limit, the contact, following a rapid oscillation,\nreaches a stationary value which is different from the equilibrium one. In the\nadiabatic limit, the contact grows quadratically in time and later saturates to\nits equilibrium value for the final value of the scattering length."
    },
    {
        "anchor": "Quantum bright soliton in a disorder potential: At very low temperature, a quasi-one-dimensional ensemble of atoms with\nattractive interactions tend to form a bright soliton. When exposed to a\nsufficiently weak external potential, the shape of the soliton is not modified,\nbut its external motion is affected. We develop in detail the Bogoliubov\napproach for the problem, treating, in a non-perturbative way, the motion of\nthe center of mass of the soliton. Quantization of this motion allows us to\ndiscuss its long time properties. In particular, in the presence of a\ndisordered potential, the quantum motion of the center of mass of a bright\nsoliton may exhibit Anderson localization, on a localization length which may\nbe much larger than the soliton size and could be observed experimentally.",
        "positive": "Aberrations in (3+1)D Bragg diffraction using pulsed Gaussian laser\n  beams: We analyze the transfer function of a three-dimensional atomic Bragg\nbeamsplitter formed by two counterpropagating pulsed Gaussian laser beams. Even\nfor ultracold atomic ensembles, the transfer efficiency depends significantly\non the residual velocity of the particles as well as on losses into higher\ndiffraction orders. Additional aberrations are caused by the spatial intensity\nvariation and wavefront curvature of the Gaussian beam envelope, studied with\n(3+1)D numerical simulations. The temporal pulse shape also affects the\ntransfer efficiency significantly. Thus, we consider the practically important\nrectangular-, Gaussian-, Blackman- and hyperbolic secant pulses. For the\nlatter, we can describe the time-dependent response analytically with the\nDemkov-Kunike method. The experimentally observed stretching of the $\\pi$-pulse\ntime is explained from a renormalization of the simple Pendell\\\"osung\nfrequency. Finally, we compare the analytical predictions for the\nvelocity-dependent transfer function with effective (1+1)D numerical\nsimulations for pulsed Gaussian beams, as well as experimental data and find\nvery good agreement, considering a mixture of Bose-Einstein condensate and\nthermal cloud."
    },
    {
        "anchor": "Dynamic generation of spin-squeezed states in bosonic Josephson\n  junctions: We analyze the formation of squeezed states in a condensate of ultracold\nbosonic atoms confined by a double-well potential. The emphasis is set on the\ndynamical formation of such states from initially coherent many-body quantum\nstates. Two cases are described: the squeezing formation in the evolution of\nthe system around the stable point, and in the short time evolution in the\nvicinity of an unstable point. The latter is shown to produce highly squeezed\nstates on very short times. On the basis of a semiclassical approximation to\nthe Bose-Hubbard Hamiltonian, we are able to predict the amount of squeezing,\nits scaling with $N$ and the speed of coherent spin formation with simple\nanalytical formulas which successfully describe the numerical Bose-Hubbard\nresults. This new method of producing highly squeezed spin states in systems of\nultracold atoms is compared to other standard methods in the literature.",
        "positive": "Finite temperature Dicke phase transition of a Bose-Einstein condensate\n  in an optical cavity: Dicke model predicts a quantum phase transition from normal to superradiant\nphases for a two-level atomic ensemble coupled with an optical cavity at zero\ntemperature. In a recent pioneer experiment [Nature 464, 1301 (2010)], such a\nphase transition has been observed using a Bose-Einstein condensate (BEC) in an\noptical cavity. Compared with the original Dicke model, the experimental system\nfeatures finite temperature and strong atom-photon nonlinear interaction in\nBEC. In this Letter, we develop a finite temperature theory for the Dicke phase\ntransition of a BEC in an optical cavity, taking into account the atom-photon\nnonlinear interaction. In addition to explaining the experimentally observed\ntransition from normal to superradiant phases at finite-temperature, we point\nit out that a new phase, the coexistence of normal and superradient phases, was\nalso observed in the experiment. We show rich finite temperature phase diagrams\nexisting in the experimental system by tuning various experimental parameters.\nWe find that the specific heat of the BEC can serve as a powerful tool for\nprobing various phases."
    },
    {
        "anchor": "Artificial magnetic field induced by an evanescent wave: Cold atomic gases are perfect laboratories for realization of quantum\nsimulators. In order to simulate solid state systems in the presence of\nmagnetic fields special effort has to be made because atoms are charge neutral.\nThere are different methods for realization of artificial magnetic fields, that\nis the creation of specific conditions so that the motion of neutral particles\nmimics the dynamics of charged particles in an effective magnetic field. Here,\nwe consider adiabatic motion of atoms in the presence of an evanescent wave.\nTheoretical description of the adiabatic motion involves artificial vector and\nscalar potentials related to the Berry phases. Due to the large gradient of the\nevanescent field amplitude, the potentials can be strong enough to induce\nmeasurable effects in cold atomic gases. We show that the resulting artificial\nmagnetic field is able to induce vortices in a Bose-Einstein condensate trapped\nclose to a surface of a prism where the evanescent wave is created. We also\nanalyze motion of an atomic cloud released from a magneto-optical trap that\nfalls down on the surface of the prism. The artificial magnetic field is able\nto reflect falling atoms that can be observed experimentally.",
        "positive": "Heating dynamics of bosonic atoms in a noisy optical lattice: We analyze the heating of interacting bosonic atoms in an optical lattice due\nto intensity fluctuations of the lasers forming the lattice. We focus in\nparticular on fluctuations at low frequencies below the band gap frequency,\nsuch that the dynamics is restricted to the lowest band. We derive stochastic\nequations of motion, and analyze the effects on different many-body states,\ncharacterizing heating processes in both strongly and weakly interacting\nregimes. In the limit where the noise spectrum is flat at low frequencies, we\ncan derive an effective Master equation describing the dynamics. We compute\nheating rates and changes to characteristic correlation functions both in the\nperturbation theory limit, and using a full time-dependent calculation of the\nstochastic many-body dynamics in 1D based on time-dependent\ndensity-matrix-renormalization-group methods."
    },
    {
        "anchor": "Trimer liquids and crystals of polar molecules in coupled wires: We investigate the pairing and crystalline instabilities of bosonic and\nfermionic polar molecules confined to a ladder geometry. By means of analytical\nand quasi-exact numerical techniques, we show that gases of composite molecular\ndimers as well as trimers can be stabilized as a function of the density\ndifference between the wires. A shallow optical lattice can pin both liquids,\nrealizing crystals of composite bosons or fermions. We show that these exotic\nquantum phases should be realizable under current experimental conditions in\nfinite-size confining potentials.",
        "positive": "Strongly interacting bosons on a three-leg ladder in the presence of a\n  homogeneous flux: We perform a density-matrix renormalization-group study of strongly\ninteracting bosons on a three-leg ladder in the presence of a homogeneous flux.\nFocusing on one-third filling, we explore the phase diagram in dependence of\nthe magnetic flux and the inter-leg tunneling strength. We find several phases\nincluding a Meissner phase, vortex liquids, a vortex lattice, as well as a\nstaggered-current phase. Moreover, there are regions where the chiral current\nreverses its direction, both in the Meissner and in the staggered-current\nphase. While the reversal in the latter case can be ascribed to spontaneous\nbreaking of translational invariance, in the first it stems from an effective\nflux increase in the rung direction. Interactions are a necessary ingredient to\nrealize either type of chiral-current reversal."
    },
    {
        "anchor": "Symmetry breaking in binary Bose-Einstein condensates in the presence of\n  an inhomogeneous artificial gauge field: We study a two component Bose-Einstein condensate in the presence of an\ninhomogeneous artificial gauge field. In response to this field, the condensate\nforms a localised vortex lattice structure that leads to a non-trivial symmetry\nbreaking in the phase separated regime. The underlying physical mechanism can\nbe understood by considering the energy landscape and we present a simplified\nmodel that is capable of reproducing the main features of the phase separation\ntransition. The intuition gained by numerically solving this simplified model\nis then corroborated using the analytical Thomas-Fermi model.",
        "positive": "Anisotropic Superfluid Behavior of a Dipolar Bose-Einstein Condensate: We present transport measurements on a dipolar superfluid using a\nBose-Einstein condensate of Dy-162 with strong magnetic dipole-dipole\ninteractions. By moving an attractive laser beam through the condensate we\nobserve an anisotropy in superfluid flow. This observation is compatible with\nan anisotropic critical velocity for the breakdown of dissipationless flow,\nwhich, in the spirit of the Landau criterion, can directly be connected to the\nanisotropy of the underlying dipolar excitation spectrum. In addition, the\nheating rate above this critical velocity reflects the same anisotropy. Our\nobservations are in excellent agreement with simulations based on the\nGross-Pitaevskii equation and highlight the effect of dipolar interactions on\nmacroscopic transport properties, rendering dissipation anisotropic."
    },
    {
        "anchor": "A two-dimensional Fermi liquid with attractive interactions: We realize and study an attractively interacting two-dimensional Fermi\nliquid. Using momentum resolved photoemission spectroscopy, we measure the\nself-energy, determine the contact parameter of the short-range interaction\npotential, and find their dependence on the interaction strength. We\nsuccessfully compare the measurements to a theoretical analysis, properly\ntaking into account the finite temperature, harmonic trap, and the averaging\nover several two-dimensional gases with different peak densities.",
        "positive": "Pseudopotentials for Two-dimentional Ultracold Scattering in the\n  Presence of Synthetic Spin-orbit-coupling: We derive a pseudopotential in two dimensions (2D) with the presence of a 2D\nRashba spin-orbit-coupling (SOC), following the same spirit of frame\ntransformation in {[}Phys. Rev. A 95, 020702(R) (2017){]}. The frame\ntransformation correctly describes the non-trivial phase accumulation and\npartial wave couplings due to the presence of SOC and gives rise to a different\npseudopotential than the free-space one, even when the length scale of SOC is\nsignificantly larger than the two-body potential range. As an application, we\napply our pseudopotential with the Lippmann-Schwinger equation to obtain an\nanalytical scattering matrix. To demonstrate the validity, we compare our\nresults with a numerical scattering calculation of finite-range potential and\nshow perfect agreement over a wide range of scattering energy and SOC strength.\nOur results also indicate that the differences between our pseudopotential and\nthe original free-space pseudopotential are essential to reproduce scattering\nobservables correctly."
    },
    {
        "anchor": "Spectroscopy of elementary excitations from quench dynamics in a dipolar\n  XY Rydberg simulator: We use a Rydberg quantum simulator to demonstrate a new form of spectroscopy,\ncalled quench spectroscopy, which probes the low-energy excitations of a\nmany-body system. We illustrate the method on a two-dimensional simulation of\nthe spin-1/2 dipolar XY model. Through microscopic measurements of the spatial\nspin correlation dynamics following a quench, we extract the dispersion\nrelation of the elementary excitations for both ferro- and anti-ferromagnetic\ncouplings. We observe qualitatively different behaviors between the two cases\nthat result from the long-range nature of the interactions, and the frustration\ninherent in the antiferromagnet. In particular, the ferromagnet exhibits\nelementary excitations behaving as linear spin waves. In the anti-ferromagnet,\nspin waves appear to decay, suggesting the presence of strong nonlinearities.\nOur demonstration highlights the importance of power-law interactions on the\nexcitation spectrum of a many-body system.",
        "positive": "Non-equilibrium dynamics of interacting Fermi systems in quench\n  experiments: We describe the dynamics of two component non-interacting ultracold Fermions\nwhich are initially in thermal equilibrium and undergo a rapid quench to either\nthe repulsive or attractive side of a Feshbach resonance. The short time\ndynamics is dominated by the exponentially growing collective modes. We study\nthe Stoner instability and formation of ferromagnetic textures on the repulsive\nside, and the pairing instability towards BCS or FFLO-like states (determined\nby the population imbalance) on the attractive side. In each case, we evaluate\nthe growth rate of unstable modes and predict the typical lengthscale of\ntextures to be formed."
    },
    {
        "anchor": "BCS-BCS crossover between atomic and molecular superfluids in a\n  Bose-Fermi mixture: We theoretically examine a continuity between atomic and molecular Fermi\nsuperfluids in a Bose-Fermi mixture near the Feshbach resonance. Considering a\ntwo-channel model describing the Feshbach resonance between Fermi and Bose\natoms, we have constructed the mean-field framework based on the perturbative\nexpansion of the Feshbach atom-dimer coupling. The resulting effective\nHamiltonian exhibits not only the continuity between atom-atom to\nmolecule-molecule Cooper pairings but also becomes equivalent to the\ntwo-band-superconductor model with Suhl-Matthias-Walker type pair-exchange\ncoupling. We demonstrate how these atomic and molecular Fermi superfluids\ncoexist within the two-band-like superfluid theory. The pair-exchange coupling\nand resulting superfluid gaps are found to be strongly enhanced near the\nFeshbach resonance due to the interplay between the infrared singularity of\nBogoliubov phonons and their Landau damping arising from the coupling with\nfermions. The pair-exchange coupling can be probed via the observation of the\nintrinsic Josephson effect between atomic and molecular superfluids.",
        "positive": "Hybrid quantum systems of ions and atoms: In this chapter we review the progress in experiments with hybrid systems of\ntrapped ions and ultracold neutral atoms. We give a theoretical overview over\nthe atom-ion interactions in the cold regime and give a summary of the most\nimportant experimental results. We conclude with an overview of remaining open\nchallenges and possible applications in hybrid quantum systems of ions and\nneutral atoms."
    },
    {
        "anchor": "Scrambling dynamics and many-body chaos in a random dipolar spin model: Is there a quantum many-body system that scrambles information as fast as a\nblack hole? The Sachev-Ye-Kitaev model can saturate the conjectured bound for\nchaos, but it requires random all-to-all couplings of Majorana fermions that\nare hard to realize in experiments. Here we examine a quantum spin model of\nrandomly oriented dipoles where the spin exchange is governed by dipole-dipole\ninteractions. The model is inspired by recent experiments on dipolar spin\nsystems of magnetic atoms, dipolar molecules, and nitrogen-vacancy centers. We\nmap out the phase diagram of this model by computing the energy level\nstatistics, spectral form factor, and out-of-time-order correlation (OTOC)\nfunctions. We find a broad regime of many-body chaos where the energy levels\nobey Wigner-Dyson statistics and the OTOC shows distinctive behaviors at\ndifferent times: Its early-time dynamics is characterized by an exponential\ngrowth, while the approach to its saturated value at late times obeys a power\nlaw. The temperature scaling of the Lyapunov exponent $\\lambda_L$ shows that\nwhile it is well below the conjectured bound $2\\pi T$ at high temperatures,\n$\\lambda_L$ approaches the bound at low temperatures and for large number of\nspins.",
        "positive": "Quantum Degenerate Fermi Gas with Spin-orbit Coupling and Crossed Zeeman\n  Fields: We study quantum degenerate ultra-cold Fermi gases in the presence of\nartificial spin-orbit coupling and crossed Zeeman fields. We emphasize the case\nwhere parity is violated in the excitation spectrum and compare it with the\nsimpler situation where parity is preserved. We investigate in detail\nspectroscopic properties such as the excitation spectrum, the spectral\nfunction, momentum distribution and density of states for the cases where\nparity is preserved or violated. Similarly, we show that thermodynamic\nproperties such as pressure, chemical potential, entropy, specific heat,\nisothermal compressibility and induced spin polarization become anisotropic as\na function of Zeeman field components, when parity is violated. Lastly, we\ndiscuss the effects of interactions and present results for the pairing\ntemperature as the precursor for the transition to a superfluid state. In\nparticular, we find that the pairing temperature is dramatically reduced in the\nweak interaction regime as parity violation gets stronger, and that the\nmomentum dependence of the order parameter for superfluidity violates parity\nwhen crossed Zeeman fields are present for finite spin-orbit coupling."
    },
    {
        "anchor": "Phase Retrieval of Vortices in Bose-Einstein Condensates: We propose and demonstrate numerically a measurement scheme for complete\nreconstruction of the quantum wavefunctions of Bose-Einstein condensates,\namplitude and phase, from a time of flight measurement. We identify a\nfundamental ambiguity present in the measurement of vortices and show how to\novercome it by augmenting the measurement to allow reconstruction of\nmatter-wave vortices and arrays of vortices.",
        "positive": "Competition between Normal Superfluidity and Larkin-Ovchinnikov Phases\n  of Polarized Fermi Gases in Elongated Traps: By applying the recently proposed antisymmetric superfluid local density\napproximation (ASLDA) to strongly interacting polarized atomic gases at\nunitarity in very elongated traps, we find families of Larkin-Ovchinnikov (LO)\ntype of solutions with prominent transversal oscillation of pairing potential.\nThese LO states coexist with a superfluid state having a smooth pairing\npotential. We suggest that the LO phase could be accessible experimentally by\nincreasing adiabatically the trap aspect ratio. We show that the local\nasymmetry effects contained in ASLDA do not support a deformed superfluid core\npredicted by previous Bogoliubov-de Gennes treatments."
    },
    {
        "anchor": "Bose-Einstein Condensation versus Dicke-Hepp-Lieb Transition in an\n  Optical Cavity: We provide an exact solution for the interplay between Bose-Einstein\ncondensation and the Dicke-Hepp-Lieb self-organization transition of an ideal\nBose gas trapped inside a single-mode optical cavity and subject to a\ntransverse laser drive. Based on an effective action approach, we determine the\nfull phase diagram at arbitrary temperature, which features a bi-critical point\nwhere the transitions cross. We calculate the dynamically generated band\nstructure of the atoms and the associated supression of the critical\ntemperature for Bose-Einstein condensation in the phase with a spontaneous\nperiodic density modulation. Moreover, we determine the evolution of the\npolariton spectrum due to the coupling of the cavity photons and the atomic\nfield near the self-organization transition, which is quite different above or\nbelow the Bose-Einstein condensation temperature. At low temperatures, the\ncritical value of the Dicke-Hepp-Lieb transition decreases with temperature and\nthus thermal fluctuations can enhance the tendency to a periodic arrangement of\nthe atoms.",
        "positive": "Observation of dipolar splittings in high-resolution atom-loss\n  spectroscopy of $^6$Li $p$-wave Feshbach resonances: We report on the observation of dipolar splitting in 6Li p-wave Feshbach\nresonances by highresolution atom-loss spectroscopy. The Feshbach resonances at\n159 G and 215 G exhibit a doublet structure of 10 mG and 13 mG, respectively,\nassociated with different projections of the orbital angular momentum. The\nobserved splittings agree very well with coupled-channel calculations. We map\nout the temperature dependence of the atom-loss spectrum allowing us to\nextrapolate resonance positions and the corresponding widths to zero\ntemperature. The observed dipolar splitting in fermionic lithium might be\nuseful for the realization of the quantum phase transition between the polar\nand axial p-wave superfluid phases."
    },
    {
        "anchor": "1D topological chains with Majorana fermions in 2D non-topological\n  optical lattices: The recent experimental realization of 1D equal Rashba-Dresselhaus spin-orbit\ncoupling (ERD-SOC) for cold atoms provide a disorder-free platform for the\nimplementation and observation of Majorana fermions (MFs), similar to the well\nstudied solid state nanowire/superconductor heterostructures. However, the\ncorresponding 1D chains of cold atoms possess strong quantum fluctuation, which\nmay destroy the superfluids and MFs. In this Letter, we show that such 1D\ntopological chains with MFs may be on demand generated in a 2D non-topological\noptical lattice with 1D ERD-SOC by modifying local potentials on target\nlocations using experimentally already implemented atomic gas microscopes or\npatterned (e.g., double or triple well) optical lattices. All ingredients in\nour scheme have been experimentally realized and the combination of them may\npave the way for the experimental observation of MFs in a clean system.",
        "positive": "Exploring multi-band excitations of interacting Bose gases in a 1D\n  optical lattice by coherent scattering: We use a coherent Bragg diffraction method to impart an external momentum to\nultracold bosonic atoms trapped in a one-dimensional optical lattice. This\nmethod is based on the application of a single light pulse, with conditions\nwhere scattering of photons can be resonantly amplified by the atomic density\ngrating. An oscillatory behavior of the momentum distribution resulting from\nthe time evolution in the lattice potential is then observed. By measuring the\noscillating frequencies, we extract multi-band energy structures of\nsingle-particle excitations with zero pseudo-momentum transfer for a wide range\nof lattice depths. The excitation energy structures reveal the interaction\neffect through the whole range of lattice depth."
    },
    {
        "anchor": "Quantum phases of dipolar bosons in one-dimensional optical lattices: We theoretically analyze the phase diagram of a quantum gas of bosons that\ninteract via repulsive dipolar interactions. The bosons are tightly confined by\nan optical lattice in a quasi one-dimensional geometry. In the single-band\napproximation, their dynamics is described by an extended Bose-Hubbard model\nwhere the relevant contributions of the dipolar interactions consist of\ndensity-density repulsion and correlated tunneling terms. We evaluate the phase\ndiagram for unit density using numerical techniques based on the density-matrix\nrenormalization group algorithm. Our results predict that correlated tunneling\ncan significantly modify the parameter range of the topological insulator\nphase. At vanishing values of the onsite interactions, moreover, correlated\ntunneling promotes the onset of a phase with a large number of low energy\nmetastable configurations.",
        "positive": "Non-exponential decay in Floquet-Bloch bands: Exponential decay laws describe systems ranging from unstable nuclei to\nfluorescent molecules, in which the probability of jumping to a lower-energy\nstate in any given time interval is static and history-independent. These\ndecays, involving only a metastable state and fluctuations of the quantum\nvacuum, are the most fundamental nonequilibrium process, and provide a\nmicroscopic model for the origins of irreversibility. Despite the fact that the\napparently universal exponential decay law has been precisely tested in a\nvariety of physical systems, it is a surprising truth that quantum mechanics\nrequires that spontaneous decay processes have non-exponential time dependence\nat both very short and very long times. Cold-atom experiments both classic and\nrecent have proven to be powerful probes of fundamental decay processes; in\nthis paper, we propose the use of Bose condensates in Floquet-Bloch bands as a\nprobe of long-time non-exponential decay in single isolated emitters. We\nidentify a range of parameters that should enable observation of long-time\ndeviations, and experimentally demonstrate a key element of the scheme: tunable\ndecay between quasienergy bands in a driven optical lattice."
    },
    {
        "anchor": "Josephson oscillations of chirality and identity in two-dimensional\n  solitons in spin-orbit-coupled condensates: We investigate dynamics of two-dimensional chiral solitons of semi-vortex\n(SV) and mixed-mode (MM) types in spin-orbit-coupled Bose-Einstein condensates\nwith the Manakov nonlinearity, loaded in a dual-core (double-layer) trap. The\nsystem supports two novel manifestations of Josephson phenomenology: one in the\nform of persistent oscillations between SVs or MMs with opposite chiralities in\nthe two cores, and another one demonstrating robust periodic switching\n(identity oscillations) between SV in one core and MM in the other, provided\nthat the strength of the inter-core coupling exceeds a threshold value. Below\nthe threshold, the system creates composite states, which are asymmetric with\nrespect to the two cores, or suffer the collapse. Robustness of the chirality\nand identity oscillations against deviations from the Manakov nonlinearity is\ninvestigated too. These dynamical regimes are possible only in the nonlinear\nsystem. In the linear one, exact stationary and dynamical solutions for SVs and\nMMs of the Bessel type are found. They sustain Josephson self-oscillations in\ndifferent modes, with no interconversion between them.",
        "positive": "Observation of Efimov Resonances in a Mixture with Extreme Mass\n  Imbalance: We observe two consecutive heteronuclear Efimov resonances in an ultracold\nLi-Cs mixture by measuring three-body loss coefficients as a function of\nmagnetic field near a Feshbach resonance. The first resonance is detected at a\nscattering length of $a_-^{(1)}=-320(10)~a_0$ corresponding to $\\sim 7 $ ($\\sim\n3$) times the Li-Cs (Cs-Cs) van der Waals range. The second resonance appears\nat $5.8(1.0) a_-^{(1)}$ close to the unitarity-limited regime at the sample\ntemperature of 450 nK. Indication of a third resonance is found in the atom\nloss spectra. The scaling of the resonance positions is close to the universal\nscaling value of 4.9 predicted for zero temperature. Deviations from\nuniversality might be caused by finite-range and temperature effects, as well\nas magnetic field dependent Cs-Cs interactions."
    },
    {
        "anchor": "Frustration- and doping-induced magnetism in a Fermi-Hubbard simulator: Geometrical frustration in strongly correlated systems can give rise to a\nplethora of novel ordered states and intriguing magnetic phases, such as\nquantum spin liquids. Promising candidate materials for such phases can be\ndescribed by the Hubbard model on an anisotropic triangular lattice, a\nparadigmatic model capturing the interplay between strong correlations and\nmagnetic frustration. However, the fate of frustrated magnetism in the presence\nof itinerant dopants remains unclear, as well as its connection to the doped\nphases of the square Hubbard model. Here we investigate the local spin order of\na Hubbard model with controllable frustration and doping, using ultracold\nfermions in anisotropic optical lattices continuously tunable from a square to\na triangular geometry. At half-filling and strong interactions $U/t \\sim 9$, we\nobserve at the single-site level how frustration reduces the range of magnetic\ncorrelations and drives a transition from a collinear N\\'eel antiferromagnet to\na short-range correlated 120$^{\\circ}$ spiral phase. Away from half-filling,\nthe triangular limit shows enhanced antiferromagnetic correlations on the\nhole-doped side and a reversal to ferromagnetic correlations at particle\ndopings above 20%, hinting at the role of kinetic magnetism in frustrated\nsystems. This work paves the way towards exploring possible chiral ordered or\nsuperconducting phases in triangular lattices and realizing t-t' square lattice\nHubbard models that may be essential to describe superconductivity in cuprate\nmaterials.",
        "positive": "Comparison between the numerical solutions and the Thomas-Fermi\n  approximation for atomic-molecular Bose-Einstein condensates: We study the stationary solution of an atomic Bose-Einstein condensate\ncoupled coherently to a molecular condensate with both repulsive and attractive\ninterspecies interactions confined in an isotropic harmonic trap. We use the\nThomas-Fermi approximation and find four kinds of analytical solution for the\ncases. These analytical solutions are adopted as trial function for the\ndiffusive numerical solution of the Gross-Pitaevskii equations. For the\nrepulsive interspecies interaction, the case in which the atomic and molecular\nwavefunctions are out-phase, the densities have similar profiles for both\nmethods, however, the case where the wavefunctions are in-phase, there are\nconsiderable difference between the density profiles. For the attractive\ninterspecies interaction, there are two cases in the Thomas Fermi approximation\nwhere the wavefunctions are in-phase. One of them has numerical solution that\nagree with the approximation and the other does not have corresponding\nnumerical solution."
    },
    {
        "anchor": "Atomic matter-wave revivals with definite atom number in an optical\n  lattice: We study the collapse and revival of interference patterns in the momentum\ndistribution of atoms in optical lattices, using a projection technique to\nproperly account for the fixed total number of atoms in the system. We consider\nthe common experimental situation in which weakly interacting bosons are loaded\ninto a shallow lattice, which is suddenly made deep. The collapse and revival\nof peaks in the momentum distribution is then driven by interactions in a\nlattice with essentially no tunnelling. The projection technique allows to us\nto treat inhomogeneous (trapped) systems exactly in the case that\nnon-interacting bosons are loaded into the system initially, and we use\ntime-dependent density matrix renormalization group techniques to study the\nsystem in the case of finite tunnelling in the lattice and finite initial\ninteractions. For systems of more than a few sites and particles, we find good\nagreement with results calculated via a naive approach, in which the state at\neach lattice site is described by a coherent state in the particle occupation\nnumber. However, for systems on the order of 10 lattice sites, we find\nexperimentally measurable discrepancies to the results predicted by this\nstandard approach.",
        "positive": "Are Quasiparticles and Phonons Identical in Bose--Einstein Condensates?: We study an interacting spinless Bose-Einstein condensate to clarify\ntheoretically whether the spectra of its quasiparticles (one-particle\nexcitations) and collective modes (two-particle excitations) are identical, as\nconcluded by Gavoret and Nozi\\`eres [Ann. Phys. 28, 349 (1964)]. We derive\nanalytic expressions for their first and second moments so as to extend the\nBijl-Feynman formula for the peak of the collective-mode spectrum to its width\n(inverse lifetime) and also to the one-particle channel. The obtained formulas\nindicate that the width of the collective-mode spectrum manifestly vanishes in\nthe long-wavelength limit, whereas that of the quasiparticle spectrum\napparently remains finite. We also evaluate the peaks and widths of the two\nspectra numerically for a model interaction potential in terms of the Jastrow\nwave function optimized by a variational method. It is thereby found that the\nwidth of the quasiparticle spectrum increases towards a constant as the\nwavenumber decreases. This marked difference in the spectral widths implies\nthat the two spectra are distinct. In particular, the lifetime of the\nquasiparticles remains finite even in the long-wavelength limit."
    },
    {
        "anchor": "Dymamical Casimir emission from polariton condensates: We study theoretically the dynamical Casimir effect in an exciton-polariton\ncondensate that is suddenly created by an ultrashort laser pulse at normal\nincidence. As a consequence of the abrupt change of the quantum vacuum,\nBogoliubov excitations are generated. The subsequent evolution, governed by\npolariton interactions and losses, is studied within a linearized truncted\nWigner approximation. We focus in particular on the momentum distribution and\nspatial coherence. The limiting behavior at large and small momenta is\ndetermined analytically. A simple scaling relation for the final condensate\ndepletion as a function of the system parameters is found and the correlation\nlength is shown to depend linearly on the condensate depletion.",
        "positive": "High temperature thermodynamics of fermionic alkaline earth atoms in\n  optical lattices: We calculate experimentally relevant properties of trapped fermionic alkaline\nearth atoms in an optical lattice, modeled by the SU(N) Hubbard model. Our\ncalculation is accurate when the temperature is much larger than the tunneling\nrate, similar to current regimes in ultracold atom experiments. In addition to\nexploring the Mott insulator-metal crossover, we calculate final temperatures\nachieved by the standard experimental protocol of adiabatically ramping from a\nnon-interacting gas, as a function of initial gas temperature and final state\nlattice parameters. Of particular experimental interest, we find that\nincreasing $N$ gives substantially \\textit{colder} Mott insulators, up to more\nthan a factor of five for relevant parameters. This cooling happens for all\n$N$, fixing the initial entropy, or for all $N \\lsim 20$ (the exact value\ndepends on dimensionality), fixing the initial temperature."
    },
    {
        "anchor": "Tunable topological Weyl semimetal from simple cubic lattices with\n  staggered fluxes: Three-dimensional Weyl fermions are found to emerge from simple cubic\nlattices with staggered fluxes. The mechanism is to gap the quadratic band\ntouching by time-reversal-symmetry-breaking hoppings. The system exhibits rich\nphase diagrams where the number of Weyl fermions and their topological charge\nare tunable via the plaquette fluxes. The Weyl semimetal state is shown to be\nthe intermediate phase between non-topological semimetal and quantum anomalous\nHall insulator. The transitions between those phases can be understood through\nthe evolution of the Weyl points as Berry flux insertion processes. As the Weyl\npoints move and split (or merge) through tuning the plaquette fluxes, the Fermi\narcs and surface states undergo significant manipulation. We also propose a\npossible scheme to realize the model in ultracold fermions in optical lattices\nwith artificial gauge fields.",
        "positive": "Designing Topological Bands in Reciprocal Space: Motivated by new capabilities to realise artificial gauge fields in ultracold\natomic systems, and by their potential to access correlated topological phases\nin lattice systems, we present a new strategy for designing topologically\nnon-trivial band structures. Our approach is simple and direct: it amounts to\nconsidering tight-binding models directly in reciprocal space. These models\nnaturally cause atoms to experience highly uniform magnetic flux density and\nlead to topological bands with very narrow dispersion, without fine-tuning of\nparameters. Further, our construction immediately yields instances of optical\nChern lattices, as well as band structures of higher Chern number, |C|>1."
    },
    {
        "anchor": "Uncertainty product of an out-of-equilibrium Bose-Einstein condensate: The variance and uncertainty product of the position and momentum\nmany-particle operators of structureless bosons interacting by a long-range\ninter-particle interaction and trapped in a single-well potential are\ninvestigated. In the first example, of an out-of-equilibrium interaction-quench\nscenario, it is found that, despite the system being fully condensed, already\nwhen a fraction of a particle is depleted differences with respect to the\nmean-field quantities emerge. In the second example, of the pathway from\ncondensation to fragmentation of the ground state, we find out that, although\nthe cloud's density broadens while the system's fragments, the position\nvariance actually decreases, the momentum variance increases, and the\nuncertainty product is not a monotonous function but has a maximum. Implication\nare briefly discussed.",
        "positive": "A binary mixture of Bose-Einstein-condensates in a double-well\n  potential: Berry phase and two-mode entanglement: A binary mixtures of Bose-Einstein condensate structures exhibit an\nincredible richness in terms of holding different kinds of phases. Depending on\nthe ratio of the inter- and intra-atomic interactions, the transition from\nmixed to separated phase, which is also known as the miscibility-immiscibility\ntransition, has been reported in different setups and by different groups.\nHere, we describe such type of quantum phase transition in an effective\nHamiltonian approach, by applying Holstein-Primakoff transformation in the\nlimit of large number of particles. We demonstrate that non-trivial geometric\nphase near the critical coupling is present, which confirms the connection\nbetween Berry phase and quantum phase transition. We also show that, by using\nthe spin form of Hillery & Zubairy criterion, a two mode entanglement\naccompanies this transition in the limit of large, but not infinite number of\nparticles."
    },
    {
        "anchor": "The critical velocity in the BEC-BCS crossover: We map out the critical velocity in the crossover from Bose-Einstein\ncondensation (BEC) to Bardeen-Cooper-Schrieffer superfluidity with ultracold\n$^{6}$Li gases. A small attractive potential is dragged along lines of constant\ncolumn density. The rate of the induced heating increases steeply above a\ncritical velocity $v_c$. In the same samples, we measure the speed of sound\n$v_s$ by exciting density waves and compare the results to the measured values\nof $v_c$. We perform numerical simulations in the BEC regime and find very good\nagreement, validating the approach. In the strongly correlated regime, where\ntheoretical predictions only exist for the speed of sound, our measurements of\n$v_c$ provide a testing ground for theoretical approaches.",
        "positive": "Twisted Phonons in Bose-Einstein condensates: We consider elementary excitations in a Bose Einstein condensate, carrying a\nfinite amount of angular momentum. We show that these elementary excitations\nare modified Bogoliubov oscillations, or phonons with an helical wave\nstructure. These twisted phonon modes can contribute to the total vorticity in\na quantum fluid, thus complementing the contribution of the traditional quantum\nvortices. Linear and nonlinear versions of twisted phonon modes will be\ndiscussed. New envelope soliton solutions are shown to exist in a condensate."
    },
    {
        "anchor": "Pathway to chaos through hierarchical superfluidity in a cavity-BEC\n  system: We explore the role of atomic correlations in a harmonically trapped\nBose-Einstein condensate coupled to a dissipative cavity, where both the atoms\nand the cavity are blue detuned from the external pumping laser. Using a\ngenuine many-body approach that goes beyond mean-field, we extract density\ndistributions and many-body correlations to unveil a pathway to chaos at large\npump power through a hierarchical self-organization of the atoms, where the\natoms transition from a single-well optical lattice to a double-well optical\nlattice. Correlated states of the atoms emerge and are characterized by local\nsuperfluid correlations in phases which are globally superfluid or Mott\ninsulating. Local superfluid-Mott transitions are precluded by a dynamical\ninstability to chaos which occurs via quasiperiodic attractors. Our results\nexplain the mechanism behind the dynamical instabilities observed in\nexperiments.",
        "positive": "Coupled Ferromagnetic and Nematic Ordering of Fermions in an Optical\n  Flux Lattice: Ultracold atoms in Raman-dressed optical lattices allow for effective\nmomentum-dependent interactions among single-species fermions originating from\nshort-range s-wave interactions. These dressed-state interactions combined with\nvery flat bands encountered in the recently introduced optical flux lattices\npush the Stoner instability towards weaker repulsive interactions, making it\naccessible with current experiments. As a consequence of the coupling between\nspin and orbital degrees of freedom, the magnetic phase features Ising nematic\norder."
    },
    {
        "anchor": "Band-gap structure and chiral discrete solitons in optical lattices with\n  artificial gauge fields: We study three-leg-ladder optical lattices loaded with repulsive atomic\nBose-Einstein condensates and subjected to artificial gauge fields. By\nemploying the plane-wave analysis and variational approach, we analyze the\nband-gap structure of the energy spectrum and reveal the exotic swallow-tail\nloop structures in the energy-level anti-crossing regions due to an interplay\nbetween the atom-atom interaction and artificial gauge field. Also, we discover\nstable discrete solitons residing in a semi-infinite gap above the highest\nband, these discrete solitons are associated with the chiral edge currents.",
        "positive": "Distributed vorticity model for vortex molecule dynamics: We analyze the effect of a hard wall trapping potential on the dynamics of a\nvortex molecule in a two-component Bose-Einstein condensate with linear\ncoherent coupling. A vortex molecule consists of a vortex of the same charge in\neach component condensate connected by a domain wall of the relative phase. In\na previous paper Ref.[Phys. RevA. 106,043319(2022)] we described the\ninteraction of a vortex molecule with the boundary using the method of images\nby separately treating each component vortex as a point vortex, in addition to\na Magnus force effect from the surface tension of the domain wall. Here we\nextend the model by considering a continuous distribution of image vorticity\nreflecting the effect of the domain wall on the vortex molecule phase\nstructure. In the case of a precessing centered vortex molecule in an isotropic\ntrap, distributing the image vorticity weakens its contribution to the\nprecession frequency. We test the model predictions against numerical\nsimulations of the coupled Gross-Pitaevskii equations in a two-dimensional\ncircular disc and find support for the improved model."
    },
    {
        "anchor": "Synthesizing the Quantum Spin Hall Phase for Ultracold Atoms in\n  Bichromatic Chiral Optical Ladders: Realizing the topological bands of helical states poses a challenge in\nstudying ultracold atomic gases. Motivated by the recent experimental success\nin realizing chiral optical ladders, here we present a scheme for synthesizing\ntopological quantum matter, especially the quantum spin Hall phase, in the\nchiral optical ladders. More precisely, we first establish the synthetic\npseudo-spin-orbit coupling and Zeeman splitting in the chiral ladders. We\nanalyze the band structure of the ladders exposed to the bichromatic optical\npotentials and report the existence of quantum spin Hall phase. We further\nidentify a rich phase diagram of the bichromatic chiral ladders, illustrating\nthat our proposal features a large space of system parameters exhibiting a\nvariety of quantum phase transitions. Our scheme can be readily implemented in\nthe existing experimental systems and hence provides a new method to engineer\nthe sophisticated topological bands for cold atomic gases.",
        "positive": "Critical velocity for a toroidal Bose-Einstein condensate flowing\n  through a barrier: We consider the setup employed in a recent experiment (Ramanathan et al 2011\nPhys. Rev. Lett. 106 130401) devoted to the study of the instability of the\nsuperfluid flow of a toroidal Bose-Einstein condensate in presence of a\nrepulsive optical barrier. Using the Gross-Pitaevskii mean-field equation, we\nobserve, consistently with what we found in Piazza et al (2009 Phys. Rev. A 80\n021601), that the superflow with one unit of angular momentum becomes unstable\nat a critical strength of the barrier, and decays through the mechanism of\nphase slippage performed by pairs of vortex-antivortex lines annihilating.\nWhile this picture qualitatively agrees with the experimental findings, the\nmeasured critical barrier height is not very well reproduced by the\nGross-Pitaevskii equation, indicating that thermal fluctuations can play an\nimportant role (Mathey et al 2012 arXiv:1207.0501). As an alternative\nexplanation of the discrepancy, we consider the effect of the finite resolution\nof the imaging system. At the critical point, the superfluid velocity in the\nvicinity of the obstacle is always of the order of the sound speed in that\nregion, $v_{\\rm barr}=c_{\\rm l}$. In particular, in the hydrodynamic regime\n(not reached in the above experiment), the critical point is determined by\napplying the Landau criterion inside the barrier region. On the other hand, the\nFeynman critical velocity $v_{\\rm f}$ is much lower than the observed critical\nvelocity. We argue that this is a general feature of the Gross-Pitaevskii\nequation, where we have $v_{\\rm f}=\\epsilon\\ c_{\\rm l}$ with $\\epsilon$ being a\nsmall parameter of the model. Given these observations, the question still\nremains open about the nature of the superfluid instability."
    },
    {
        "anchor": "Bipartite and tripartite entanglement in a Bose-Einstein acoustic black\n  hole: We investigate quantum entanglement in an analogue black hole realized in the\nflow of a Bose-Einstein condensate. The system is described by a three-mode\nGaussian state and we construct the corresponding covariance matrix at zero and\nfinite temperature. We study associated bipartite and tripartite entanglement\nmeasures and discuss their experimental observation. We identify a simple\noptical setup equivalent to the analogue Bose-Einstein black hole which\nsuggests a new way of determining the Hawking temperature and grey-body factor\nof the system.",
        "positive": "Universal relations for spin-orbit-coupled Fermi gases in two and three\n  dimensions: We present a comprehensive derivation of a set of universal relations for\nspin-orbit-coupled Fermi gases in three or two dimension, which follow from the\nshort-range behavior of the two-body physics. Besides the adiabatic energy\nrelations, the large-momentum distribution, the grand canonical potential and\npressure relation derived in our previous work for three-dimensional systems\n{[}Phys. Rev. Lett. 120, 060408 (2018){]}, we further derive high-frequency\ntail of the radio-frequency spectroscopy and the short-range behavior of the\npair correlation function. In addition, we also extend the derivation to\ntwo-dimensional systems with Rashba type of spin-orbit coupling. To simply\ndemonstrate how the spin-orbit-coupling effect modifies the two-body\nshort-range behavior, we solve the two-body problem in the sub-Hilbert space of\nzero center-of-mass momentum and zero total angular momentum, and\nperturbatively take the spin-orbit-coupling effect into account at short\ndistance, since the strength of the spin-orbit coupling should be much smaller\nthan the corresponding scale of the finite range of interatomic interactions.\nThe universal asymptotic forms of the two-body wave function at short distance\nare then derived, which do not depend on the short-range details of interatomic\npotentials. We find that new scattering parameters need to be introduced\nbecause of spin-orbit coupling, besides the traditional $s$- and $p$-wave\nscattering length (volume) and effective ranges. This is a general and unique\nfeature for spin-orbit-coupled systems. We show how these two-body parameters\ncharacterize the universal relations in the presence of spin-orbit coupling.\nThis work probably shed light for understanding the profound properties of the\nmany-body quantum systems in the presence of the spin-orbit coupling."
    },
    {
        "anchor": "Dynamics of a trapped ion in a quantum gas: effects of particle\n  statistics: We study the quantum dynamics of an ion confined in a radiofrequency trap in\ninteraction with either a Bose or spin-polarized Fermi gas. To this end, we\nderive quantum optical master equations in the limit of weak coupling and the\nLamb-Dicke approximations. For the bosonic bath, we also include the so-called\n\"Lamb-shift\" correction to the ion trap due to the coupling to the quantum gas\nas well as the extended Fr\\\"ohlich interaction within the Bogolyubov\napproximation that have been not considered in previous studies. We calculate\nthe ion kinetic energy for various atom-ion scattering lengths as well as gas\ntemperatures by considering the intrinsic micromotion and we analyse the\ndamping of the ion motion in the gas as a function of the gas temperature. We\nfind that the ion's dynamics depends on the quantum statistics of the gas and\nthat a fermionic bath enables to attain lower ionic energies.",
        "positive": "Family-Vicsek Scaling of Roughness Growth in a Strongly Interacting Bose\n  Gas: Family-Vicsek scaling is one of the most essential scale-invariant laws\nemerging in surface-roughness growth of classical systems. In this Letter, we\ntheoretically elucidate the emergence of the Family-Vicsek scaling even in a\nstrongly interacting quantum bosonic system by introducing a surface-height\noperator. This operator is comprised of a summation of local particle-number\noperators at a simultaneous time, and thus the observation of the surface\nroughness in the quantum many-body system and its scaling behavior are\naccessible to current experiments of ultracold atoms."
    },
    {
        "anchor": "Gutzwiller study of extended Hubbard models with fixed boson densities: We studied all possible ground states, including supersolid (SS) phases and\nphase separations of hard-core- and soft-core-extended Bose--Hubbard models\nwith fixed boson densities by using the Gutzwiller variational wave function\nand the linear programming method. We found that the phase diagram of the\nsoft-core model depends strongly on its transfer integral. Furthermore, for a\nlarge transfer integral, we showed that an SS phase can be the ground state\neven below or at half filling against the phase separation. We also found that\nthe density difference between nearest-neighbor sites, which indicates the\ndensity order of the SS phase, depends strongly on the boson density and\ntransfer integral.",
        "positive": "Tunneling dynamics of $^{164}$Dy supersolids and droplets: The tunneling dynamics of a magnetic $^{164}$Dy quantum gas in an elongated\nor circular skewed double-well trap is investigated with a time-dependent\nextended Gross-Pitaevskii approach. Upon lifting the energy offset, different\ntunneling regimes can be identified. In the elongated trap and for sufficiently\nlarge offset, the different configurations exhibit collective macroscopic\ntunneling. For smaller offset, partial reflection from and transmission through\nthe barrier lead to density accumulation in both wells, and eventually to\ntunneling-locking. One can also reach the macroscopic self-trapping regime for\nincreasing relative dipolar interaction strength, while tunneling vanishes for\nlarge barrier heights. A richer dynamical behavior is observed for the circular\ntrap. For instance, the supersolid maintains its shape, while the superfluid\ndensity gets distorted signifying the emergence of peculiar excitation patterns\nin the macroscopic tunneling regime. The findings reported here may offer new\nways to probe distinctive dynamical features in the supersolid and droplet\nregimes."
    },
    {
        "anchor": "Metastable spin textures and Nambu-Goldstone modes of a ferromagnetic\n  spin-1 Bose-Einstein condensate confined in a ring trap: We investigate the metastability of a ferromagnetic spin-1 Bose-Einstein\ncondensate confined in a quasi-one-dimensional rotating ring trap by solving\nthe spin-1 Gross-Pitaevskii equation. We find analytical solutions that exhibit\nspin textures. By performing linear stability analysis, it is shown that the\nsolutions can become metastable states. We also find that the number of\nNambu-Goldstone modes changes at a certain rotation velocity without changing\nthe continuous symmetry of the order parameter.",
        "positive": "Resonances in non-universal dipolar collisions: Scattering resonances due to the dipole-dipole interaction between ultracold\nmolecules, induced by static or microwave fields, are studied theoretically. We\ndevelop a method for coupled-channel calculations that can efficiently impose\nmany short-range boundary conditions, defined by a short-range phase shift and\nloss probability as in quantum-defect theory. We study how resonances appear as\nthe short-range loss probability is lowered below the universal unit\nprobability. This may become realizable for nonreactive ultracold molecules in\nblue-detuned box potentials."
    },
    {
        "anchor": "Phasonic Spectroscopy of a Quantum Gas in a Quasicrystalline Lattice: Phasonic degrees of freedom are unique to quasiperiodic structures, and play\na central role in poorly-understood properties of quasicrystals from excitation\nspectra to wavefunction statistics to electronic transport. However, phasons\nare challenging to access dynamically in the solid state due to their complex\nlong-range character and the effects of disorder and strain. We report phasonic\nspectroscopy of a quantum gas in a one-dimensional quasicrystalline optical\nlattice. We observe that strong phasonic driving produces a nonperturbative\nhigh-harmonic plateau strikingly different from the effects of standard dipolar\ndriving. Tuning the potential from crystalline to quasicrystalline, we identify\nspectroscopic signatures of quasiperiodicity and interactions and map the\nemergence of a multifractal energy spectrum, opening a path to direct imaging\nof the Hofstadter butterfly.",
        "positive": "Harmonic and Subharmonic Association and Dissociation of Universal\n  Dimers in a Thermal Gas: In a gas of ultracold atoms whose scattering length is controlled by a\nmagnetic Feshbach resonance, atoms can be associated into universal dimers by\nan oscillating magnetic field. In addition to the harmonic resonance with\nfrequency near that determined by the dimer binding energy, there is a\nsubharmonic resonance with half that frequency. If the thermal gas contains\ndimers, they can be dissociated into unbound atoms by the oscillating magnetic\nfield. We show that the transition rates for association and dissociation can\nbe calculated by treating the oscillating magnetic field as a sinusoidal\ntime-dependent perturbation proportional to the contact operator. Many-body\neffects are taken into account through transition matrix elements of the\ncontact operator. We calculate both the harmonic and subharmonic transition\nrates analytically for association in a thermal gas of atoms and dissociation\nin a thermal gas of dimers."
    },
    {
        "anchor": "Quantum and thermal fluctuations in a Raman spin-orbit coupled Bose gas: We theoretically study a three-dimensional weakly-interacting Bose gas with\nRaman-induced spin-orbit coupling at finite temperature. By employing a\ngeneralized Hartree-Fock-Bogoliubov theory with Popov approximation, we\ndetermine a complete finite-temperature phase diagram of three exotic\ncondensation phases (i.e., the stripe, plane-wave and zero-momentum phases),\nagainst both quantum and thermal fluctuations. We find that the plane-wave\nphase is significantly broadened by thermal fluctuations. The phonon mode and\nsound velocity at the transition from the plane-wave phase to the zero-momentum\nphase are thoughtfully analyzed. At zero temperature, we find that quantum\nfluctuations open an unexpected gap in sound velocity at the phase transition,\nin stark contrast to the previous theoretical prediction of a vanishing sound\nvelocity. At finite temperature, thermal fluctuations continue to significantly\nenlarge the gap, and simultaneously shift the critical minimum. For a Bose gas\nof $^{87}$Rb atoms at the typical experimental temperature, $T=0.3T_{0}$, where\n$T_{0}$ is the critical temperature of an ideal Bose gas without spin-orbit\ncoupling, our results of gap opening and critical minimum shifting in the sound\nvelocity, are qualitatively consistent with the recent experimental observation\n{[}S.-C. Ji \\textit{et al.}, Phys. Rev. Lett. \\textbf{114}, 105301 (2015){]}.",
        "positive": "Spinor Bose-Einstein gases: In a spinor Bose-Einstein gas, the non-zero hyperfine spin of the gas becomes\nan accessible degree of freedom. At low temperature, such a gas shows both\nmagnetic and superfluid order, and undergoes both density and spin dynamics.\nThese lecture notes present a general overview of the properties of spinor\nBose-Einstein gases. The notes are divided in five sections. In the first, we\nsummarize basic properties of multi-component quantum fluids, focusing on the\nspecific case of spinor Bose-Einstein gases and the role of rotational symmetry\nin defining their properties. Second, we consider the magnetic state of a\nspinor Bose-Einstein gas, highlighting effects of thermodynamics and\nBose-Einstein statistics and also of spin-dependent interactions between atoms.\nIn the third section, we discuss methods for measuring the properties of\nmagnetically ordered quantum gases and present newly developed schemes for\nspin-dependent imaging. We then discuss the dynamics of spin mixing in which\nthe spin composition of the gas evolves through the spin-dependent interactions\nwithin the gas. We discuss spin mixing first from a microscopic perspective,\nand then advance to discussing collective and beyond-mean-field dynamics. The\nfifth section reviews recent studies of the magnetic excitations of\nquantum-degenerate spinor Bose gases. We conclude with some perspectives on\nfuture directions for research."
    },
    {
        "anchor": "Excitations and stability of weakly interacting Bose gases with\n  multi-body interactions: We consider weakly interacting bosonic gases with local and non-local\nmulti-body interactions. By using the Bogoliubov approximation, we first\ninvestigate contact interactions, studying the case in which the interparticle\npotential can be written as a sum of N-body {\\delta}-interactions, and then\nconsidering general contact potentials. Results for the quasi-particle spectrum\nand the stability are presented. We then examine non-local interactions,\nfocusing on two different cases of 3-body non-local interactions. Our results\nare used for systems with 2- and 3-body {\\delta}-interactions and applied for\nrealistic values of the trap parameters. Finally, the effect of conservative\n3-body terms in dipolar systems and soft-core potentials (that can be simulated\nwith Rydberg dressed atoms) is also studied.",
        "positive": "Exploring the Kibble-Zurek mechanism with homogeneous Bose gases: Out-of-equilibrium phenomena is a subject of considerable interest in many\nfields of physics. Ultracold quantum gases, which are extremely clean,\nwell-isolated and highly controllable systems, offer ideal platforms to\ninvestigate this topic. The recent progress in tailoring trapping potentials\nnow allows the experimental production of homogeneous samples in custom\ngeometries, which is a key advance for studies of the emergence of coherence in\ninteracting quantum systems. Here we review recent experiments in which\ntemperature quenches have been performed across the Bose-Einstein condensation\n(BEC) phase transition in an annular geometry and in homogeneous 3D and\nquasi-2D gases. Combined, these experiments give a comprehensive picture of the\nKibble-Zurek (KZ) scenario through complementary measurements of correlation\nfunctions and topological defects density. They also allow the measurement of\nKZ scaling laws, the direct confirmation of the \"freeze-out\" hypothesis that\nunderlies the KZ theory, and the extraction of critical exponents of the\nBose-Einstein condensation transition."
    },
    {
        "anchor": "Probing Phases and Quantum Criticality using Deviations from the Local\n  Fluctuation-Dissipation Theorem: Introduction Cold atomic gases in optical lattices are emerging as excellent\nlaboratories for testing models of strongly interacting particles in condensed\nmatter physics. Currently, one of the major open questions is how to obtain the\nfinite temperature phase diagram of a given quantum Hamiltonian directly from\nexperiments. Previous work in this direction required quantum Monte Carlo\nsimulations to directly model the experimental situation in order to extract\nquantitative information, clearly defeating the purpose of an optical lattice\nemulator. Here we propose a new method that utilizes deviations from a local\nfluctuation dissipation theorem to construct a finite temperature phase\ndiagram, for the first time, from local observables accessible by in situ\nexperimental observations. Our approach extends the utility of the\nfluctuation-dissipation theorem from thermometry to the identification of\nquantum phases, associated energy scales and the quantum critical region. We\ntest our ideas using state-of-the-art large-scale quantum Monte Carlo\nsimulations of the two-dimensional Bose Hubbard model.",
        "positive": "Damping-free collective oscillations of a driven two-component Bose gas\n  in optical lattices: We explore quantum many-body physics of a driven Bose-Einstein condensate in\noptical lattices. The laser field induces a gap in the generalized Bogoliubov\nspectrum proportional to the effective Rabi frequency. The lowest lying modes\nin a driven condensate are characterized by zero group velocity and non-zero\ncurrent. Thus, the laser field induces roton modes, which carry interaction in\na driven condensate. We show that collective excitations below the energy of\nthe laser-induced gap remain undamped, while above the gap they are\ncharacterized by a significantly suppressed Landau damping rate."
    },
    {
        "anchor": "Andreev bound states at boundaries of polarized 2D Fermi superfluids\n  with s-wave pairing and spin-orbit coupling: A topological superfluid phase characterized by an emergent chiral-p-wave\npair potential is expected to form in a two-dimensional Fermi superfluid\nsubject to s-wave pairing, spin-orbit coupling and a large-enough Zeeman\nsplitting. Andreev bound states appear at phase boundaries, including Majorana\nzero modes whose existence is assured by the bulk-boundary correspondence\nprinciple. Here we study the physical properties of these subgap-energy bound\nstates at step-like interfaces using the spin-resolved Bogoliubov-deGennes\nmean-field formalism and assuming small spin-orbit coupling. Extending a\nrecently developed spin-projection technique based on Feshbach partitioning\n[SciPost Phys. 5, 016 (2018)] combined with the Andreev approximation allows us\nto obtain remarkably simple analytical expressions for the bound-state energies\nas well as the majority and minority spin components of their wave functions.\nBesides the vacuum boundary, where a majority-spin Majorana excitation is\nencountered, we also consider the boundary between the topological and a\nnontopological superfluid phase that can appear in a coexistence scenario due\nto the first-order topological phase transition predicted for this system. At\nthis superfluid-superfluid interface, we find a localized chiral Majorana mode\nhosted by the minority-spin sector. Our theory further predicts majority-spin\nsubgap-energy bound states similar to those found at a Josephson junction\nbetween same-chirality p-wave superfluids. Their presence affects the Majorana\nmode due to a coupling of minority and majority spin sectors only in the small\nenergy range where their spectra overlap. Our results may inform experimental\nefforts aimed at realizing and characterizing unconventional Majorana\nquasiparticles.",
        "positive": "Feshbach molecule formation in a Bose-Fermi mixture: We investigate magnetoassociation of ultracold fermionic Feshbach molecules\nin a mixture of $^{40}$K and $^{87}$Rb atoms, where we can create as many as\n$7\\times 10^4$ $^{40}$K$^{87}$Rb molecules with a conversion efficiency as high\nas 45%. In the perturbative regime, we find that the conversion efficiency\ndepends linearly on the density overlap of the two gases, with a slope that\nmatches a parameter-free model that uses only the atom masses and the known\nFeshbach resonance parameters. In the saturated regime, we find that the\nmaximum number of Feshbach molecules depends on the atoms' phase-space density.\nAt higher temperatures, our measurements agree with a phenomenological model\nthat successfully describes the formation of bosonic molecules from either Bose\nor Fermi gases. However, for quantum degenerate atom gas mixtures, we measure\nsignificantly fewer molecules than this model predicts."
    },
    {
        "anchor": "Bosons in a two-dimensional bichromatic quasiperiodic potential:\n  Analysis of the disorder in the Bose-Hubbard parameters and phase diagrams: Experimental realizations of disorder in optical lattices generate a\ndistribution of the Bose-Hubbard (BH) parameters, like on-site potentials,\nhopping strengths, and interaction energies. We analyze this distribution for\nbosons in a bichromatic quasi-periodic potential by determining the generalized\nWannier functions and calculating the corresponding BH parameters. Using a\nlocal mean-field cluster analysis, we study the effect of the corresponding\ndisorder on the phase diagrams. We find a substantial amount of disorder in the\nhopping strengths, which produces strong deviations from the phase diagram of\nthe disordered BH model with solely random on-site potentials.",
        "positive": "Dark soliton in quasi-one-dimensional Bose-Einstein condensates with a\n  Gaussian trap: In this paper we study dark solitons in quasi-one-dimensional Bose-Einstein\ncondensates (BECs) in presence of an anharmonic external potential. The\ntheoretical model is based on the Mu\\~noz-Mateo and Delgado (MMD) equation that\ndescribes cigar-shaped BECs with repulsive interatomic interactions. Since MMD\nequation presents a nonpolynomial form, the soliton-sound recombination cannot\ndisplay the same pattern presented in the cubic model. We perform numerical\nsimulations to compare both cases."
    },
    {
        "anchor": "Phase separation of a repulsive two-component Fermi gas at the two- to\n  three-dimensional crossover: We present a theoretical analysis of phase separations between two\nrepulsively interacting components in an ultracold fermionic gas, occurring at\nthe dimensional crossover in a harmonic trap with varying aspect ratios. A\ntailored kinetic energy functional is derived and combined with a\ndensity-potential functional approach to develop a framework that is\nbenchmarked with the orbital-based method. We investigate the changes in the\ndensity profile of the phase-separated gas under different interaction\nstrengths and geometries. The analysis reveals the existence of small,\npartially polarized domains in certain parameter regimes, which is similar to\nthe purely two-dimensional limit. However, the density profile is further\nenriched by a shell structure found in anisotropic traps. We also track the\ntransitions that can be driven by either a change in interaction strength or\ntrap geometry. The developed framework is noted to have applications for other\nsystems with repulsive interactions that combine continuous and discrete\ndegrees of freedom.",
        "positive": "Realization of Fractional Chern Insulators in the Thin-Torus-Limit with\n  Ultracold Bosons: Topological states of interacting many-body systems are at the focus of\ncurrent research due to the exotic properties of their elementary excitations.\nIn this paper we suggest a realistic experimental setup for the realization of\na simple version of such a phase. We show how delta-interacting bosons hopping\non the links of a one-dimensional (1D) ladder can be used to simulate the\nthin-torus-limit of the two-dimensional (2D) Hofstadter-Hubbard model at\none-quarter magnetic flux per plaquette. Bosons can be confined to ladders by\noptical superlattices, and synthetic magnetic fields can be realized by far\noff-resonant Raman beams. We show that twisted boundary conditions can be\nimplemented, enabling the realization of a fractionally quantized Thouless\npump. Using numerical density-matrix-renormalization-group (DMRG) calculations\nwe show that the groundstate of our model is an incompressible\nsymmetry-protected topological charge density wave (CDW) phase at average\nfilling $\\rho = 1/8$ per lattice site, related to the 1/2 Laughlin-type state\nof the corresponding 2D model."
    },
    {
        "anchor": "Comment on \"Quantum entangled dark solitons formed by ultracold atoms in\n  optical lattices\": We demonstrate that knowledge of two body correlation functions like g2(x) is\ninsufficient to draw conclusions about whether solitons fill in or not in\nindividual experimental runs. In our example, g2 is filled in, while the\nsoliton is not.",
        "positive": "Fourier's law on a one-dimensional optical random lattice: We study the transport properties of a one-dimensional hard-core bosonic\nlattice gas coupled to two particle reservoirs at different chemical potentials\nwhich generate a current flow through the system. In particular, the influence\nof random fluctuations of the underlying lattice on the stationary-state\nproperties is investigated. We show analytically that the steady-state density\npresents a linear profile. The local steady-state current obeys the Fourier law\n$j=-\\kappa(\\tau)\\nabla n $ where $\\tau$ is a typical timescale of the lattice\nfluctuations and $\\nabla n$ the density gradient imposed by the reservoirs."
    },
    {
        "anchor": "Onsager vortex clusters on a sphere: We study Onsager vortex clustered states in a shell-shaped superfluid\ncontaining a large number of quantum vortices. In the incompressible limit and\nat low temperatures, the relevant problem can be boiled down to the statistical\nmechanics of neutral point vortices confined on a sphere. We analyze rotation\nfree vortex clustered states within the mean field theory in the microcanonical\nensemble. We find that the sandwich state, which involves the separating of\nvortices with opposite circulation and the clustering of vortices with same\ncirculation around the poles and the equator, is the maximum entropy vortex\ndistribution, subject to zero angular momentum constraint. The dipole momentum\nvanishes for the sandwich state and the quadrupole tensor serves as an order\nparameter to characterize the vortex cluster structure. For given finite\nangular momentum, the equilibrium vortex distribution forms a dipole structure,\ni.e., vortices with opposite sign are separated and are accumulated around the\nsouth and north pole, respectively. The conditions for the onset of clustering,\nand the exponents associated with the quadrupole moment and the dipole moment\nas functions of energy, are obtained within the mean field theory. At large\nenergies, we obtain asymptotically exact vortex density distributions using the\nstereographic projection method, which give rise the parameter bounds for the\nvortex clustered states. The analytical predictions are in excellent agreement\nwith microcanonical Monte Carlo simulations.",
        "positive": "Bosonic and fermionic dipoles on a ring: We show that dipolar bosons and fermions confined in a quasi-one-dimensional\nring trap exhibit a rich variety of states because their interaction is\ninhomogeneous. For purely repulsive interactions, with increasing strength of\nthe dipolar coupling there is a crossover from a gas-like state to an\ninhomogeneous crystal-like one. For small enough angles between the dipoles and\nthe plane of the ring, there are regions with attractive interactions, and\nclustered states can form."
    },
    {
        "anchor": "Controlling spin motion and interactions in a one-dimensional Bose gas: Experiments on ultracold gases offer unparalleled opportunities to explore\nquantum many-body physics, with excellent control over key parameters including\ntemperature, density, interactions and even dimensionality. In some systems,\natomic interactions can be adjusted by means of magnetic Feshbach resonances,\nwhich have played a crucial role in realizing new many-body phenomena. However,\nsuitable Feshbach resonances are not always available, and they offer limited\nfreedom since the magnetic field strength is the only control parameter. Here\nwe show a new way to tune interactions in one-dimensional quantum gases using\nstate-dependent dressed potentials, enabling control over non-equilibrium spin\nmotion in a two-component gas of 87Rb. The accessible range includes the point\nof spin-independent interactions where exact quantum many-body solutions are\navailable and the point where spin motion is frozen. This versatility opens a\nnew route to experiments on spin waves, spin-\"charge\" separation and the\nrelation between superfluidity and magnetism in low-dimensional quantum gases.",
        "positive": "Phase diagram of the 3D Anderson model for uncorrelated speckle\n  potentials: We investigate the localization properties of atoms moving in a\nthree-dimensional optical lattice in the presence of an uncorrelated disorder\npotential having the same probability distribution $P(V)$ as laser speckles. We\nfind that the disorder-averaged (single-particle) Green's function, calculated\nvia the coherent potential approximation, is in very good agreement with exact\nnumerics. Using the transfer-matrix method, we compute the phase diagram in the\nenergy-disorder plane and show that its peculiar shape can be understood from\nthe self-consistent theory of localization. In particular, we recover the large\nasymmetry in the position of the mobility edge for blue and red speckles, which\nwas recently observed numerically for correlated speckle potentials."
    },
    {
        "anchor": "Correlation engineering via non-local dissipation: Controlling the spread of correlations in quantum many-body systems is a key\nchallenge at the heart of quantum science and technology. Correlations are\nusually destroyed by dissipation arising from coupling between a system and its\nenvironment. Here, we show that dissipation can instead be used to engineer a\nwide variety of spatio-temporal correlation profiles in an easily tunable\nmanner. We describe how dissipation with any translationally-invariant spatial\nprofile can be realized in cold atoms trapped in an optical cavity. A uniform\nexternal field and the choice of spatial profile can be used to design when and\nhow dissipation creates or destroys correlations. We demonstrate this control\nby preferentially generating entanglement at a desired wavevector. We thus\nestablish non-local dissipation as a new route towards engineering the\nfar-from-equilibrium dynamics of quantum information, with potential\napplications in quantum metrology, state preparation, and transport.",
        "positive": "Bloch bound state of spin-orbit-coupled fermions in an optical lattice: Understanding fundamentals of few-body physics provides an interesting\nbottom-up approach for the clarification of many-body properties. The\nremarkable experimental progress in realizing spin-orbit coupling (SOC) in\noptical Raman lattices offers a renewed thrust towards discovering novel\nfew-body features induced by the interplay between SOC and optical lattices.\nUsing the Wilson renormalization method to account for high-band effects, we\nstudy the low-energy two-body scattering processes of spin-$1/2$ fermions in\nspin-orbit coupled optical lattices. We demonstrate that, under weak SOC,\nadding a small lattice potential would destabilize shallow two-body bound\nstates, contrary to conventional wisdom. On the other hand, when lattice is\nsufficiently deep, two-body bound states are always stabilized by increasing\nthe lattice depth. This intriguing non-monotonic behavior of the bound-state\nstability derives from the competition between SOC and optical lattices, and\ncan be explained by analyzing the low-energy density of states. We also discuss\nthe impact of high-band effects on such a behavior, as well as potential\nexperimental detections."
    },
    {
        "anchor": "Quantized Rabi Oscillations and Circular Dichroism in Quantum Hall\n  Systems: The dissipative response of a quantum system upon a time-dependent drive can\nbe exploited as a probe of its geometric and topological properties. In this\nwork, we explore the implications of such phenomena in the context of\ntwo-dimensional gases subjected to a uniform magnetic field. It is shown that a\nfilled Landau level exhibits a quantized circular dichroism, which can be\ntraced back to its underlying non-trivial topology. Based on selection rules,\nwe find that this quantized circular dichroism can be suitably described in\nterms of Rabi oscillations, whose frequencies satisfy simple quantization laws.\nMoreover, we discuss how these quantized dissipative responses can be probed\nlocally, both in the bulk and at the boundaries of the quantum Hall system.\nThis work suggests alternative forms of topological probes in quantum systems\nbased on circular dichroism.",
        "positive": "New cross-phase modulated localized solitons in coupled atomic-molecular\n  BEC: The interacting atom-molecule BEC (AMBEC) dynamics is investigated in the\nmean field ap- proach. The presence of atom-atom, atom-molecule and\nmolecule-molecule interactions, coupled with a characteristically different\ninteraction representing atom-molecule interconversion, endows this system with\nnonlinearities, which differ significantly from the standard Gross-Pitaevskii\n(GP) equation. Exact localized solutions are found to belong to two distinct\nclasses. The first ones are analogous to the soliton solutions of the weakly\ncoupled GP equation, whereas the second non- equivalent class is related to the\nsolitons of the strongly coupled BEC. Distinct parameter domains characterize\nthese solitons, some of which are analogous to the complex profile Bloch\nsolitons in magnetic systems. These localized solutions are found to represent\na variety of phenomena, which include co-existence of both atom-molecule\ncomplex and miscible-immiscible phases. Numerical sta- bility is explicitly\nchecked, as also the stability analysis based on the study of quantum\nuctuations around our solutions. We also find out the domain of modulation\ninstability in this system."
    },
    {
        "anchor": "The dipolar Bose-Hubbard model: We study a simple model of interacting bosons on a d-dimensional cubic\nlattice whose dynamics conserves both total boson number and total boson dipole\nmoment. This model provides a simple framework in which several remarkable\nconsequences of dipole conservation can be explored. As a function of chemical\npotential and hopping strength, the model can be tuned between gapped Mott\ninsulating phases and various types of gapless condensates. The condensed phase\nrealized at large hopping strengths, which we dub a Bose-Einstein insulator, is\nparticularly interesting: despite having a Bose condensate, it is insulating,\nand despite being an insulator, it is compressible.",
        "positive": "A regular Hamiltonian halting ratchet for matter wave transport: We report on the design of a Hamiltonian ratchet exploiting periodically at\nrest integrable trajectories in the phase space of a modulated periodic\npotential, leading to the linear non-diffusive transport of particles. Using\nBose-Einstein condensates in a modulated one-dimensional optical lattice, we\nmake the first observations of this new spatial ratchet transport. In the\nsemiclassical regime, the quantum transport strongly depends on the effective\nPlanck constant due to Floquet state mixing. We also demonstrate the interest\nof quantum optimal control for efficient initial state preparation into the\ntransporting Floquet states to enhance the transport periodicity."
    },
    {
        "anchor": "Three-dimensional Gross-Pitaevskii solitary waves in optical lattices:\n  stabilization using the artificial quartic kinetic energy induced by lattice\n  shaking: In this Letter, we show that a three-dimensional Bose-Einstein solitary wave\ncan become stable if the dispersion law is changed from quadratic to quartic.\nWe suggest a way to realize the quartic dispersion, using shaken optical\nlattices. Estimates show that the resulting solitary waves can occupy as little\nas $\\sim 1/20$-th of the Brillouin zone in each of the three directions and\ncontain as many as $N = 10^{3}$ atoms, thus representing a \\textit{fully\nmobile} macroscopic three-dimensional object.",
        "positive": "Criticality-enhanced quantum sensing in ferromagnetic Bose-Einstein\n  condensates: role of readout measurement and detection noise: We theoretically investigate estimation of the control parameter in a\nferromagnetic Bose-Einstein condensate near second order quantum phase\ntransitions. We quantify sensitivity by quantum and classical Fisher\ninformation and using the error-propagation formula. For these different\nmetrics, we find the same, beyond-standard-quantum-limit (SQL) scaling with\natom number near critical points, and SQL scaling away from critical points. We\nfind that both depletion of the $m_f=0$ Zeeman sub-level and transverse\nmagnetization provide signals of sufficient quality to saturate the sensitivity\nscaling. To explore the effect of experimental imperfections, we study the\nscaling around criticality at nonzero temperature and with nonzero detection\nnoise. Our results suggest the feasibility of sub-SQL sensing in ferromagnetic\ncondensates with current experimental capabilities."
    },
    {
        "anchor": "Emergent Non-Eulerian Hydrodynamics of Quantum Vortices in Two\n  Dimensions: We develop a coarse-grained description of the point-vortex model, finding\nthat a large number of planar vortices and antivortices behave as an inviscid\nnon-Eulerian fluid at large scales. The emergent binary vortex fluid is subject\nto anomalous stresses absent from Euler's equation, caused by the singular\nnature of quantum vortices. The binary vortex fluid is compressible, and has an\nasymmetric Cauchy stress tensor allowing orbital angular momentum exchange with\nthe vorticity and vortex density. An analytic solution for vortex shear flow\ndriven by anomalous stresses is in excellent agreement with numerical\nsimulations of the point-vortex model.",
        "positive": "Making two dysprosium atoms rotate - Einstein-de Haas effect revisited: We present a numerical study of the behaviour of two magnetic dipolar atoms\ntrapped in a harmonic potential and exhibiting the standard Einstein-de Haas\neffect while subject to a time dependent homogeneous magnetic field. Using a\nsimplified description of the short range interaction and the full expression\nfor the dipole-dipole forces we show, that under experimentally realisable\nconditions two dysprosium atoms may be pumped to a high ($l>20$) value of the\nrelative orbital angular momentum."
    },
    {
        "anchor": "Spin-Orbit Coupled Degenerate Fermi Gases: Spin-orbit coupling plays an increasingly important role in the modern\ncondensed matter physics. For instance, it gives birth to topological\ninsulators and topological superconductors. Quantum simulation of spin-orbit\ncoupling using ultracold Fermi gases will offer opportunities to study these\nnew phenomena in a more controllable setting. Here we report the first\nexperimental study of a spin-orbit coupled Fermi gas. We observe spin dephasing\nin spin dynamics and momentum distribution asymmetry in the equilibrium state\nas hallmarks of spin-orbit coupling. We also observe evidences of Lifshitz\ntransition where the topology of Fermi surfaces change. This serves as an\nimportant first step toward finding Majorana fermions in this system.",
        "positive": "Coherence dynamics of kicked Bose-Hubbard dimers: Interferometric\n  signatures of chaos: We study the coherence dynamics of a kicked two-mode Bose-Hubbard model\nstarting with an arbitrary coherent spin preparation. For preparations in the\nchaotic regions of phase-space we find a generic behavior with Flouquet\nparticipation numbers that scale as the entire $N$-particle Hilbert space,\nleading to a rapid loss of single particle coherence. However, the chaotic\nbehavior is not uniform throughout the chaotic sea, and unique statistics is\nfound for preparations at the vicinity of hyperbolic points that are embedded\nin it. This is contrasted with the low log(N) participation that is responsible\nfor the revivals at the vicinity of isolated hyperbolic instabilities."
    },
    {
        "anchor": "Striped Ultradilute Liquid of Dipolar Bosons in Two Dimensions: We investigate the phases of a Bose-Einstein condensate of dipolar atoms\nrestricted to move in a two-dimensional plane. The dipole moments are all\naligned in a direction tilted with respect to the plane normal. As a result of\nthe attractive and repulsive components of the dipole-dipole interaction, the\ndipolar gas has a self-bound phase, which is stabilized by quantum\nfluctuations. Furthermore, tilting the dipoles tunes the anisotropy of the\ndipole-dipole interaction, which can trigger a spatial density modulation. In\nthis work we study these two aspects and investigate the conditions for the\nformation of a self-bound and striped phase, which has been realized in\nexperiments with dipolar droplets. We use a variational method based on the\nhypernetted-chain Euler-Lagrange optimization of a Jastrow-Feenberg ansatz for\nthe many-body wave function to study the ground state properties. This method\ntakes into account quantum fluctuations in a non-perturbative way and thus can\nbe used also for strongly correlated systems.",
        "positive": "Cavity Optomechanics with a Bose-Einstein Condensate: Normal Mode\n  Splitting: We study the normal mode splitting in a system consisting of a Bose Einstein\ncondensates (BECs) trapped inside a Fabry Perot cavity driven by a single mode\nlaser field. We analyze the variations in frequency and damping rate of the\ncollective density excitation of a BEC imparted by the optical field. We study\nthe occurrence of normal mode splitting which appears as consequences of the\nhybridization of the fluctuations of the intracavity field and the condensate\nmode. It is shown that normal mode splitting vanishes for weak coupling between\nthe condensate mode and the intracavity field. Moreover, we investigate the\nnormal mode splitting in the transmission spectrum of the cavity field."
    },
    {
        "anchor": "Exact Dynamical Correlations of Hard-Core Anyons in One-Dimensional\n  Lattices: The dynamical correlations of a strongly correlated system is an essential\ningredient to describe its non-equilibrium properties. We present a general\nmethod to calculate exactly the dynamical correlations of hard-core anyons in\none-dimensional lattices, valid for any type of confining potential and any\ntemperature. We obtain exact explicit expressions of the Green's function, the\nspectral function, and the out-of-time-ordered correlators (OTOCs). We find\nthat the anyonic spectral function displays three main singularity lines which\ncan be explained as a double spectrum in analogy to the Lieb-Liniger gas. The\ndispersion relations of these lines can be given explicitly and they cross at a\n\\emph{hot point} $(q_m,\\omega_m)$, which induces a peak in the momentum\ndistribution function at $q_m$ and a power-law singularity in the local\nspectral function at $\\omega_m$. We also find that the anyonic statistics can\ninduces spatial asymmetry in the Green's function, its spectrum, and the OTOC.\nMoreover, the information spreading characterized by the OTOCs shows light-cone\ndynamics, asymmetric for general statistics and low temperatures, but symmetric\nat infinite temperature. Our results pave the way toward studying the\nnon-equilibrium dynamics of hard-core anyons and experimentally probing anyonic\nstatistics through spectral functions.",
        "positive": "Theory of Bose-Einstein Condensation of Light in a Microcavity: A theory of Bose-Einstein condensation (BEC) of light in a dye microcavity is\ndeveloped. The photon polarization degeneracy and the interaction between dye\nmolecules and photons in all of the cavity modes are taken into account. The\ntheory goes beyond the grand canonical approximation and allows one to\ndetermine the statistical properties of the photon gas for all numbers of dye\nmolecules and photons at all temperatures, thus describing the microscopic,\nmesoscopic, and macroscopic light BEC from a general perspective. A universal\nrelation between the degrees of second-order coherence for the photon\ncondensate and the polarized photon condensate is obtained. The photon\nBose-Einstein condensate can be used as a new source of nonclassical light."
    },
    {
        "anchor": "Self-bound droplets in quasi-two-dimensional dipolar condensates: We study the ground-state properties of self-bound dipolar droplets in\nquasi-two-dimensional geometry by using the Gaussian state theory. We show that\nthere exist two quantum phases corresponding to the macroscopic squeezed vacuum\nand squeezed coherent states. We further show that the radial size versus atom\nnumber curve exhibits a double-dip structure, as a result of the multiple\nquantum phases. In particular, we find that the critical atom number for the\nself-bound droplets is determined by the quantum phases, which allows us to\ndistinguish the quantum state and validates the Gaussian state theory.",
        "positive": "Interaction-induced excited-band condensate in a double-well optical\n  lattice: We show theoretically that interaction effects in a double-well optical\nlattice can induce condensates in an excited band. For a symmetric double-well\nlattice, bosons condense into the bottom of the excited band at the edge of the\nBrillouin Zone if the chemical potential is above a critical value. For an\nasymmetric lattice, a condensate with zero momentum is automatically induced in\nthe excited band by the condensate in the lowest band. This is due to a\ncombined effect of interaction and lattice potential, which reduces the band\ngap and breaks the inversion symmetry. Our work can be generalized to a\nsuperlattice composed of multiple-well potentials at each lattice site, where\ncondensates can be induced in even higher bands."
    },
    {
        "anchor": "Tuning the Drude weight of Dirac-Weyl fermions in one-dimensional ring\n  traps: We study the response to an applied flux of an interacting system of\nDirac-Weyl fermions confined in a one-dimensional (1D) ring. Combining\nanalytical calculations with density-matrix renormalization group results, we\nshow that tuning of interactions leads to a unique many-body system that\ndisplays either a suppression or an enhancement of the Drude weight - the\nzero-frequency peak in the ac conductivity - with respect to the\nnon-interacting value. An asymmetry in the interaction strength between same-\nand different-pseudospin Dirac-Weyl fermions leads to Drude weight enhancement.\nViceversa, symmetric interactions lead to Drude weight suppression. Our\npredictions can be tested in mixtures of ultracold fermions in 1D ring traps.",
        "positive": "Rotons and Bose condensation in Rydberg-dressed Bose Gases: We investigate the ground-state properties and excitations of Rydberg-dressed\nbosons in both three and two dimensions, using the hypernetted-chain\nEuler-Lagrange approximation, which accounts for correlations and thus goes\nbeyond the mean field approximation. The short-range behavior of the pair\ndistribution function signals the instability of the homogeneous system towards\nthe formation of droplet crystals at strong couplings and large soft-core\nradius. This tendency to spatial density modulation coexists with off-diagonal\nlong-range order. The contribution of the correlation energy to the\nground-state energy is significant at large coupling strengths and intermediate\nvalues of the soft-core radius while for a larger soft-core radius the\nground-state energy is dominated by the mean-field (Hartree) energy. We have\nalso performed path integral Monte Carlo simulations to verify the performance\nof our hypernetted-chain Euler-Lagrange results in three dimensions. In the\nhomogeneous phase, the two approaches are in very good agreement. Moreover,\nMonte Carlo simulations predict a first-order quantum phase transition from a\nhomogeneous superfluid phase to the quantum droplet phase with face-centered\ncubic symmetry for Rydberg-dressed bosons in three dimensions."
    },
    {
        "anchor": "Dynamics of spin-polarized impurity in ultracold Fermi gas: We show that the motion of spin-polarized impurity (ferron) in ultracold\natomic gas is characterized by a certain critical velocity which can be traced\nback to the amount of spin imbalance inside the impurity. We have calculated\nthe effective mass of ferron in two dimensions. We show that the effective mass\nscales with the surface of the ferron. We discuss the impact of these findings;\nin particular, we demonstrate that ferrons become unstable in the vicinity of a\nvortex.",
        "positive": "Nematic ordering dynamics of an anti-ferromagnetic spin-1 condensate: We consider the formation of order in a quasi-two-dimensional (quasi-2D)\nanti-ferromagnetic spin-1 condensate quenched from an easy-axis (EA) to an\neasy-plane (EP) nematic phase. We define the relevant order parameter to\nquantify the spin-nematic degrees of freedom and study the evolution of the\nspin-nematic and superfluid order during the coarsening dynamics using\nnumerical simulations. We observe dynamical scaling in the late time dynamics\nwith both types of order extending across the system with a diffusive growth\nlaw. We identify half-quantum vortices (HQVs) as the relevant topological\ndefects of the ordering dynamics, and demonstrate that the growth of both types\nof order is determined by the mutual annihilation of these vortices."
    },
    {
        "anchor": "Theory of the Rotating Polaron: Spectrum and Self-Localization: We study a quantum impurity possessing both translational and internal\nrotational degrees of freedom interacting with a bosonic bath. Such a system\ncorresponds to a `rotating polaron', which can be used to model, e.g., a\nrotating molecule immersed in an ultracold Bose gas or superfluid Helium. We\nderive the Hamiltonian of the rotating polaron and study its spectrum in the\nweak- and strong-coupling regimes using a combination of variational,\ndiagrammatic, and mean-field approaches. We reveal how the coupling between\nlinear and angular momenta affects stable quasiparticle states, and demonstrate\nthat internal rotation leads to an enhanced self-localization in the\ntranslational degrees of freedom.",
        "positive": "Kinetic Theory for Interacting Luttinger Liquids: We derive a closed set of equations for the kinetics and non-equilibrium\ndynamics of interacting Luttinger Liquids with cubic resonant interactions. In\nthe presence of these interactions, the Luttinger phonons become dressed but\nstill well defined quasi-particles, characterized by a life-time much larger\nthen the inverse energy. This enables the separation of forward time dynamics\nand relative time dynamics into slow and fast dynamics and justifies the\nso-called Wigner approximation, which can be seen as a \"local-time\napproximation\" for the relative dynamics. Applying field theoretical methods in\nthe Keldysh framework, i.e. kinetic and Dyson-Schwinger equations, we derive a\nclosed set of dynamic equations, describing the kinetics of normal and\nanomalous phonon densities, the phonon self-energy and vertex corrections for\nan arbitrary non-equilibrium initial state. In the limit of low phonon\ndensities, the results from self-consistent Born approximation are recaptured,\nincluding Andreev's scaling solution for the quasi-particle life-time in a\nthermal state. As an application, we compute the relaxation of an excited state\nto its thermal equilibrium. \\red{ While the intermediate time dynamics displays\nexponentially fast relaxation, the last stages of thermalization are governed\nby algebraic laws. This can be traced back to the importance of energy and\nmomentum conservation at the longest times, which gives rise to dynamical slow\nmodes."
    },
    {
        "anchor": "$N$-coherence vs. $t$-coherence: An alternative route to the\n  Gross-Pitaevskii equation: We show how a candidate mean-field amplitude can be constructed from the\nexact wave function of an externally forced $N$-Boson system. The construction\nmakes use of subsidiary $(N-1)$-particle states which are propagated in time in\naddition to the true $N$-particle state, but does not involve spontaneous\nbreaking of the $U(1)$ symmetry associated with particle number conservation.\nProvided the flow in Fock space possesses a property which we call maximum\nstiffness, or $t$-coherence, the candidate amplitude actually satisfies the\ntime-dependent Gross-Pitaevskii equation, and then serves as macroscopic wave\nfunction of the forced $N$-particle system. The general procedure is\nillustrated in detail by numerical calculations performed for the model of a\ndriven bosonic Josephson junction, which allows one to keep track of all\ncontributions which usually are subject to uncontrolled assumptions. These\ncalculations indicate that macroscopic wave functions can persist even under\nconditions of strong forcing, but are rapidly destroyed upon entering a regime\nof chaotic dynamics. Our results provide a foundation for future attempts to\nmanipulate, and actively control, macroscopic wave functions by means of\npurposefully designed force protocols.",
        "positive": "Large Chern numbers in a dissipative dice model: For decades, the topological phenomena in quantum systems have always been\ncatching our attention. Recently, there are many interests on the systems where\ntopologically protected edge states exist, even in the presence of\nnon-Hermiticity. Motivated by these researches, the topological properties of a\nnon-Hermitian dice model are studied in two non-Hermitian cases, viz. in the\nimbalanced and the balanced dissipations. Our results suggest that the\ntopological phases are protected by the real gaps and the bulk-edge\ncorrespondence readily seen in the real edge-state spectra. Besides, we show\nthat the principle of the bulk-edge correspondence in Hermitian case is still\neffective in analyzing the three-band non-Hermitian system. We find that there\nare topological non-trivial phases with large Chern numbers $C=-3$ robust\nagainst the dissipative perturbations."
    },
    {
        "anchor": "Description of ion motion in a Paul trap immersed in a cold atomic gas: We investigate the problem of a single ion in a radio-frequency trap and\nimmersed in an ultracold Bose gas either in a condensed or a non-condensed\nphase. We develop master equation formalism describing the sympathetic cooling\nand we determine the cooling rates of ions. We show that cold atomic reservoir\nmodifies the stability diagram of the ion in the Paul trap creating the regions\nwhere the ion is either cooled or heated due to the energy quanta exchanged\nwith the time-dependent potential.",
        "positive": "Effects of Smooth Boundaries on Topological Edge Modes in Optical\n  Lattices: Since the experimental realization of synthetic gauge fields for neutral\natoms, the simulation of topologically non-trivial phases of matter with\nultracold atoms has become a major focus of cold atom experiments. However,\nseveral obvious differences exist between cold atom and solid state systems,\nfor instance the finite size of the atomic cloud and the smooth confining\npotential. In this article we show that sharp boundaries are not required to\nrealize quantum Hall or quantum spin Hall physics in optical lattices and, on\nthe contrary, that edge states which belong to a smooth confinement exhibit\nadditional interesting properties, such as spatially resolved splitting and\nmerging of bulk bands and the emergence of robust auxiliary states in bulk gaps\nto preserve the topological quantum numbers. In addition, we numerically\nvalidate that these states are robust against disorder. Finally, we analyze\npossible detection methods, with a focus on Bragg spectroscopy, to demonstrate\nthat the edge states can be detected and that Bragg spectroscopy can reveal how\ntopological edge states are connected to the different bulk bands."
    },
    {
        "anchor": "Spin-Orbit Coupling Induced Resonance in an Ultracold Bose Gas: We study a two-component Bose gas with artificial spin-orbit coupling (SOC)\nwhich couples the center-of-mass momentum of atom to its internal states. We\nshow that in this system resonance can be induced by tuning SOC strength. With\na two-dimensional SOC, resonances in two scattering channels can be induced by\ntuning the aspect ratio of SOC strengths. With a three-dimensional SOC,\nresonance in all scattering channels can be induced by tuning the appropriate\nSOC strength. Similarly, we also find that in a Fermi gas with two- or\nthree-dimensional SOC resonance can be induced by tuning SOC strength.",
        "positive": "Rotating Bose gas dynamically entering the lowest Landau level: Motivated by recent experiments, we model the dynamics of a condensed Bose\ngas in a rotating anisotropic trap, where the equations of motion are analogous\nto those of charged particles in a magnetic field. As the rotation rate is\nramped from zero to the trapping frequency, the condensate stretches along one\ndirection and is squeezed along another, becoming long and thin. When the trap\nanisotropy is slowly switched off on a particular timescale, the condensate is\nleft in the lowest Landau level. We use a time dependent variational approach\nto quantify these dynamics and give intuitive arguments about the structure of\nthe condensate wavefunction. This preparation of a lowest Landau level\ncondensate can be an important first step in realizing bosonic analogs of\nquantum Hall states."
    },
    {
        "anchor": "Signature of the FFLO phase in the collective modes of a trapped\n  ultracold Fermi gas: We study theoretically the collective modes of a two-component Fermi gas with\nattractive interactions in a quasi-one-dimensional harmonic trap. We focus on\nan imbalanced gas in the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase. Using a\nmean-field theory, we study the response of the ground state to time-dependent\npotentials. For potentials with short wavelengths, we find dramatic signatures\nin the large-scale response of the gas which are characteristic of the FFLO\nphase. This response provides an effective way to detect the FFLO state in\nexperiments.",
        "positive": "Spin-orbit coupling induced fractionalized Skyrmion excitations in\n  rotating and rapidly quenched spin-1 Bose-Einstein condensates: We investigate the fractionalized Skyrmion excitations induced by spin-orbit\ncoupling in rotating and rapidly quenched spin-1 Bose-Einstein condensates. Our\nresults show that the fractionalized Skyrmion excitation depends on the\ncombination of spin-orbit coupling and rotation, and it originates from a\ndipole structure of spin which is always embedded in three vortices constructed\nby each condensate component respectively. When spin-orbit coupling is larger\nthan a critical value, the fractionalized Skyrmions encircle the center with\none or several circles to form a radial lattice, which occurs even in the\nstrong ferromagnetic/antiferromagnetic condensates. We can use both the\nspin-orbit coupling and the rotation to adjust the radial lattice. The\nrealization and the detection of the fractionalized Skyrmions are compatible\nwith current experimental technology."
    },
    {
        "anchor": "Metastable supersolid in spin-orbit coupled Bose-Einstein condensates: Supersolid is a special state of matter with both superfluid properties and\nspontaneous modulation of particle density. In this paper, we focus on the\nsupersolid stripe phase realized in a spin-orbit coupled Bose-Einstein\ncondensate and explore the properties of a class of metastable supersolids. In\nparticular, we study a one-dimensional supersolid whose characteristic wave\nnumber $k$ (magnitude of wave vector) deviates from $k_{m}$, i.e., the one at\nground state. In other words, the period of density modulation is shorter or\nlonger than the one at ground state. We find that this class of supersolids can\nstill be stable if their wave numbers fall in the range $k_{c1}<k<k_{c2}$, with\ntwo thresholds $k_{c1}$ and $k_{c2}$. Stripes with $k$ outside this range\nsuffer from dynamical instability with complex Bogoliubov excitation spectrum\nat long wavelength. Experimentally, these stripes with $k$ away from $k_m$ are\naccessible by exciting the longitudinal spin dipole mode, resulting in temporal\noscillation of stripe period as well as $k$. Within the mean-field\nGross-Pitaevskii theory, we numerically confirm that for a large enough\namplitude of spin dipole oscillation, the stripe states become unstable through\nbreaking periodicity, in qualitative agreement with the existence of thresholds\nof $k$ for stable stripes. Our work extends the concept of supersolid and\nuncovers a new class of metastable supersolids to explore.",
        "positive": "Anisotropic Fermi liquid theory of the ultra cold fermionic polar\n  molecules: Landau parameters and collective modes: We study the Fermi liquid properties of the cold atomic dipolar Fermi gases\nwith the explicit dipolar anisotropy using perturbative approaches. Due to the\nexplicit dipolar anisotropy, Fermi surfaces exhibit distortions of the\n$d_{r^2-3z^2}$-type in three dimensions and of the $d_{x^2-y^2}$-type in two\ndimensions. The fermion self-energy, effective mass, and Fermi velocity develop\nthe same anisotropy at the Hartree-Fock level proportional to the interaction\nstrength. The Landau interaction parameters in the isotropic Fermi liquids\nbecome the tri-diagonal Landau interaction matrices in the dipolar Fermi\nliquids which renormalize thermodynamic susceptibilities. With large dipolar\ninteraction strength, the Fermi surface collapses along directions\nperpendicular to the dipole orientation. The dynamic collective zero sound\nmodes exhibit an anisotropic dispersion with the largest sound velocity\npropagating along the polar directions. Similarly, the longitudinal p-wave\nchannel spin mode becomes a propagating mode with an anisotropic dispersion in\nmulti-component dipolar systems."
    },
    {
        "anchor": "Supersolidity and crystallization of a dipolar Bose gas in an infinite\n  tube: We calculate the ground states of a dipolar Bose gas confined in an infinite\ntube potential. We use the extended Gross-Pitaevskii equation theory and\npresent a novel numerical method to efficiently obtain solutions. A key feature\nof this method is an analytic result for a truncated dipole-dipole interaction\npotential that enables the long-ranged interactions to be accurately evaluated\nwithin a unit cell. Our focus is on the transition of the ground state to a\ncrystal driven by dipole-dipole interactions as the short ranged interaction\nstrength is varied. We find that the transition is continuous or discontinuous\ndepending upon average system density. These results give deeper insight into\nthe supersolid phase transition observed in recent experiments, and validate\nthe utility of the reduced three-dimensional theory developed in [Phys. Rev.\nRes. 2, 043318 (2020)] for making qualitatively accurate predictions.",
        "positive": "From vortices to solitonic vortices in trapped atomic Bose-Einstein\n  condensates: Motivated by recent experiments we study theoretically the dynamics of\nvortices in the crossover from two to one-dimension in atomic condensates in\nelongated traps. We explore the transition from the dynamics of a vortex to\nthat of a dark soliton as the one-dimensional limit is approached, mapping this\ntransition out as a function of the key system parameters. Moreover, we probe\nthis transition dynamically through the hysteresis under time-dependent\ndeformation of the trap at the dimensionality crossover. When the solitonic\nregime is probed during the hysteresis, significant angular momentum is lost\nfrom the system but, remarkably, the vortex can re-emerge."
    },
    {
        "anchor": "Nonlinear Waves in an Experimentally Motivated Ring-shaped Bose-Einstein\n  Condensate Setup: We systematically construct stationary soliton states in a one-component,\ntwo-dimensional, repulsive, Gross-Pitaevskii equation with a ring-shaped\ntarget-like trap similar to the potential used to confine a Bose-Einstein\ncondensate in a recent experiment [Eckel, et al.\\ {\\em Nature} {\\bf 506}, 200\n(2014)]. In addition to the ground state configuration, we identify a wide\nvariety of excited states involving phase jumps (and associated dark solitons)\ninside the ring. These configurations are obtained from a systematic\nbifurcation analysis starting from the linear, small atom density, limit. We\nstudy the stability, and when unstable, the dynamics of the most basic\nconfigurations. Often these lead to vortical dynamics inside the ring\npersisting over long time scales in our numerical experiments. To illustrate\nthe relevance of the identified states, we showcase how such dark-soliton\nconfigurations (even the unstable ones) can be created in laboratory\ncondensates by using phase-imprinting techniques.",
        "positive": "Stationary and dynamical properties of two harmonically trapped bosons\n  in the crossover from two dimensions to one: We unravel the stationary properties and the interaction quench dynamics of\ntwo bosons, confined in a two-dimensional anisotropic harmonic trap. A\ntranscendental equation is derived giving access to the energy spectrum and\nrevealing the dependence of the energy gaps on the anisotropy parameter. The\nrelation between the two and the one dimensional scattering lengths as well as\nthe Tan contacts is established. The contact, capturing the two-body short\nrange correlations, shows an increasing tendency for a larger anisotropy.\nSubsequently, the interaction quench dynamics from attractive to repulsive\nvalues and vice versa is investigated for various anisotropies. A closed\nanalytical form of the expansion coefficients of the two-body wavefunction,\nduring the time evolution is constructed. The response of the system is studied\nby means of the time-averaged fidelity, the spectra of the spatial extent of\nthe cloud in each direction and the one-body density. It is found that as the\nanisotropy increases, the system becomes less perturbed independently of the\ninteractions while for fixed anisotropy quenches towards the non-interacting\nregime perturb the system in the most efficient manner. Furthermore, we\nidentify that in the tightly confined direction more frequencies are involved\nin the dynamics stemming from higher-lying excited states."
    },
    {
        "anchor": "Effective two-mode description of a few ultra-cold bosons in a\n  double-well potential: We present a construction of an improved two-mode model for modeling the\ndynamics of interacting ultra-cold bosons confined in a one-dimensional double\nwell trap. Unlike in the typically used two-mode model based on the lowest\nsingle-particle eigenstates of the external potential, the improved model uses\na basis of properly chosen effective wave functions originating in the\nmany-body model. Accuracy of the improved model is examined and it is shown\nthat within a certain limit of inter-particle interaction strength, the model\nrecovers an exact evolution of the wells' populations much more closely than\nthe traditional two-mode model.",
        "positive": "Density-induced processes in quantum gas mixtures in optical lattices: We show that off-site processes and multi-orbital physics have a crucial\nimpact on the phase diagram of quantum gas mixtures in optical lattices. In\nparticular, we discuss Bose-Fermi mixtures where the intra- and interspecies\ninteractions induce competing density-induced hopping processes, the so-called\nbond-charge interactions. Furthermore, higher bands strongly influence\ntunneling and on-site interactions. We apply a multi-orbital\ninteraction-induced dressing of the lowest band which leads to renormalized\nhopping processes. These corrections give rise to an extended Hubbard model\nwith intrinsically occupation-dependent parameters. The resulting decrease of\nthe tunneling competes with a decrease of the total on-site interaction energy\nboth affecting the critical lattice depth of the superfluid to Mott insulator\ntransition. In contrast to the standard Bose-Fermi-Hubbard model, we predict a\nlarge shift of the transition to shallower lattice depths with increasing\nBose-Fermi attraction. The applied theoretical model allows an accurate\nprediction of the modified tunneling amplitudes and the critical lattice depth\nboth recently observed experimentally."
    },
    {
        "anchor": "Dissipative dynamics of a harmonically confined Bose-Einstein condensate: We study the dissipation of the centre of mass oscillation of a harmonically\nconfined condensate in the presence of a disorder potential. An extension of\nthe Generalized Harmonic Theorem allows one to formulate the dynamics from the\npoint of view of an oscillating disorder potential. This formulation leads to a\nrigorous result for the damping rate in the limit of weak disorder.",
        "positive": "Evolution of Coherence During Ramps Across the Mott-Superfluid Phase\n  Boundary: We calculate how correlations in a Bose lattice gas grow during a finite\nspeed ramp from the Mott to the Superfluid regime. We use an interacting\ndoublon-holon model, applying a mean-field approach for implementing hard-core\nconstraints between these degrees of freedom. Our solutions are valid in any\ndimension, and agree with experimental results and with DMRG calculations in\none dimension. We find that the final energy density of the system drops\nquickly with increased ramp time for ramps shorter than one hopping time,\n$J\\tau_{ramp}\\lesssim 1$. For longer ramps, the final energy density depends\nonly weakly on ramp speed. We calculate the effects of inelastic light\nscattering during such ramps."
    },
    {
        "anchor": "Experimental realisation of the topological Haldane model: The Haldane model on the honeycomb lattice is a paradigmatic example of a\nHamiltonian featuring topologically distinct phases of matter. It describes a\nmechanism through which a quantum Hall effect can appear as an intrinsic\nproperty of a band-structure, rather than being caused by an external magnetic\nfield. Although an implementation in a material was considered unlikely, it has\nprovided the conceptual basis for theoretical and experimental research\nexploring topological insulators and superconductors. Here we report on the\nexperimental realisation of the Haldane model and the characterisation of its\ntopological band-structure, using ultracold fermionic atoms in a periodically\nmodulated optical honeycomb lattice. The model is based on breaking\ntime-reversal symmetry as well as inversion symmetry. The former is achieved\nthrough the introduction of complex next-nearest-neighbour tunnelling terms,\nwhich we induce through circular modulation of the lattice position. For the\nlatter, we create an energy offset between neighbouring sites. Breaking either\nof these symmetries opens a gap in the band-structure, which is probed using\nmomentum-resolved interband transitions. We explore the resulting\nBerry-curvatures of the lowest band by applying a constant force to the atoms\nand find orthogonal drifts analogous to a Hall current. The competition between\nboth broken symmetries gives rise to a transition between topologically\ndistinct regimes. By identifying the vanishing gap at a single Dirac point, we\nmap out this transition line experimentally and quantitatively compare it to\ncalculations using Floquet theory without free parameters. We verify that our\napproach, which allows for dynamically tuning topological properties, is\nsuitable even for interacting fermionic systems. Furthermore, we propose a\ndirect extension to realise spin-dependent topological Hamiltonians.",
        "positive": "Topology by Dissipation: Transport properties: Topological phases of matter are the center of much current interest, with\npromising potential applications in, e.g., topologically-protected transport\nand quantum computing. Traditionally such states are prepared by tuning the\nsystem Hamiltonian while coupling it to a generic bath at very low\ntemperatures; This approach is often ineffective, especially in cold-atom\nsystems. It was recently shown that topological phases can emerge much more\nefficiently even in the absence of a Hamiltonian, by properly engineering the\ninteraction of the system with its environment, to directly drive the system\ninto the desired state. Here we concentrate on dissipatively-induced 2D Chern\ninsulator (lattice quantum Hall) states. We employ open quantum systems tools\nto explore their transport properties, such as persistent currents and the\nconductance in the steady state, in the presence of various Hamiltonians. We\nfind that, in contrast with equilibrium systems, the usual relation between the\nChern topological number and the Hall conductance is broken. We explore the\nintriguing edge behaviors and elucidate under which conditions the Hall\nconductance is quantized."
    },
    {
        "anchor": "Light-cone effect and supersonic correlations in one- and\n  two-dimensional bosonic superfluids: We study the spreading of density-density correlations in Bose-Hubbard models\nafter a quench of the interaction strength, using time-dependent variational\nMonte Carlo simulations. It gives access to unprecedented long propagation\ntimes and to dimensions higher than one. In both one and two dimensions, we\nfind ballistic light-cone spreading of correlations and extract accurate values\nof the light-cone velocity in the superfluid regime. We show that the spreading\nof correlations is generally supersonic, with a light-cone propagating faster\nthan sound modes but slower than the maximum group velocity of density\nexcitations, except at the Mott transition, where all the characteristic\nvelocities are equal. Further, we show that in two dimensions the correlation\nspreading is highly anisotropic and presents nontrivial interference effects.",
        "positive": "Phase Diagram of Bosons in Two-Color Superlattices from Experimental\n  Parameters: We study the zero-temperature phase diagram of a gas of bosonic 87-Rb atoms\nin two-color superlattice potentials starting directly from the experimental\nparameters, such as wavelengths and intensities of the two lasers generating\nthe superlattice. In a first step, we map the experimental setup to a\nBose-Hubbard Hamiltonian with site-dependent parameters through explicit\nband-structure calculations. In the second step, we solve the many-body problem\nusing the density-matrix renormalization group (DMRG) approach and compute\nobservables such as energy gap, condensate fraction, maximum number\nfluctuations and visibility of interference fringes. We study the phase diagram\nas function of the laser intensities s_2 and s_1 as control parameters and show\nthat all relevant quantum phases, i.e. superfluid, Mott-insulator, and quasi\nBose-glass phase, and the transitions between them can be investigated through\na variation of these intensities alone."
    },
    {
        "anchor": "Itinerant Ferromagnetism in SU(N)-Symmetric Fermi Gases at Finite\n  Temperature: First Order Phase Transitions and Time-Reversal Symmetry: At temperatures well below the Fermi temperature $T_F$, the coupling of\nmagnetic fluctuations to particle-hole excitations in a two-component Fermi gas\nmakes the transition to itinerant ferromagnetism a first order phase\ntransition. This effect is not described by the paradigm of Landau's theory of\nphase transitions, which assumes the free energy is an analytic function of the\norder parameter and predicts a second order phase transition. On the other\nhand, despite that larger symmetry often introduces larger degeneracies in the\nlow-lying states, here we show that for a Fermi gas with SU($N > 2$)-symmetry\nin three space dimensions the ferromangetic phase transition is first order in\nagreement with the predictions of Landau's theory [M. A. Cazalilla \\emph{et\nal}. New J. of Phys. {\\bf 11} 103033 (2009)]. By performing unrestricted\nHartree-Fock calculations for an SU($N > 2$)-symmetric Fermi gas with short\nrange interactions, we find the order parameter undergoes a finite jump across\nthe transition. In addition, we do not observe any tri-critical point up to\ntemperatures $T \\simeq 0.5\\: T_F$, for which the thermal smearing of the Fermi\nsurface is subtantial. Going beyond mean-field, we find that the coupling of\nmagnetic fluctuations to particle-hole excitations makes the transition more\nabrupt and further enhances the tendency of the gas to become fully polarized\nfor smaller values of $N$ and the gas parameter $k_F a_s$. In our study, we\nalso clarify the role of time reversal symmetry in the microscopic Hamiltonian\nand obtain the temperature dependence of Tan's contact. For the latter, the\npresence of the tri-critical point for $N = 2$ leads to a more pronounced\ntemperature dependence around the transition than for SU($N > 2$)-symmetric\ngases.",
        "positive": "Path-integral approach to the thermodynamics of bosons with memory:\n  Density and correlation functions: Expanding upon previous work, using the path-integral formalism we derive\nexpressions for the one-particle reduced density matrix and the two-point\ncorrelation function for a quadratic system of bosons that interact through a\ngeneral class of memory kernels. The results are applied to study the density,\ncondensate fraction and pair correlation function of trapped bosons\nharmonically coupled to external distinguishable masses."
    },
    {
        "anchor": "The Operator Product Expansion Beyond Leading Order for Two-Component\n  Fermions: We consider a homogeneous, balanced gas of strongly interacting fermions in\ntwo spin states interacting through a large scattering length. Finite range\ncorrections are needed for a quantitative description of data which experiments\nand numerical simulations have provided. We use a perturbative field\ntheoretical framework and a tool called the Operator Product Expansion (OPE),\nwhich together allow for the expression of finite range corrections to the\nuniversal relations and momentum distribution. Using the OPE, we derive the\n$1/k^6$ part of the momentum tail, which is related to the sum of the\nderivative of the energy with respect to the finite range and the averaged\nkinetic energy of opposite spin pairs. By comparing the $1/k^4$ term and the\n$1/k^6$ correction in the momentum distribution to provided Quantum Monte Carlo\n(QMC) data, we show that including the $1/k^6$ part offers marked improvements.\nOur field theoretical approach allows for a clear understanding of the role of\nthe scattering length and finite effective range in the universal relations and\nthe momentum distribution.",
        "positive": "Superfluidity of Interacting Bosonic Mixtures in Optical Lattices: We report the observation of many-body interaction effects for a homonuclear\nbosonic mixture in a three-dimensional optical lattice with variable state\ndependence along one axis. Near the superfluid-to-Mott insulator transition for\none component, we find that the presence of a second component can reduce the\napparent superfluid coherence, most significantly when it either experiences a\nstrongly localizing lattice potential or none at all. We examine this effect by\nvarying the relative populations and lattice depths, and discuss the observed\nbehavior in view of recent proposals for scattering from impurities and of\natom-phonon coupling for atoms immersed in a superfluid."
    },
    {
        "anchor": "High-precision multiband spectroscopy of ultracold fermions in a\n  nonseparable optical lattice: Spectroscopic tools are fundamental for the understanding of complex quantum\nsystems. Here we demonstrate high-precision multi-band spectroscopy in a\ngraphene-like lattice using ultracold fermionic atoms. From the measured band\nstructure, we characterize the underlying lattice potential with a relative\nerror of 1.2 10^(-3). Such a precise characterization of complex lattice\npotentials is an important step towards precision measurements of quantum\nmany-body systems. Furthermore, we explain the excitation strengths into the\ndifferent bands with a model and experimentally study their dependency on the\nsymmetry of the perturbation operator. This insight suggests the excitation\nstrengths as a suitable observable for interaction effects on the eigenstates.",
        "positive": "Dissipative phase transitions in the fully-connected Ising model with\n  $p$-spin interaction: In this paper, we study the driven-dissipative p-spin models for $p\\geq 2$.\nIn thermodynamics limit, the equation of motion is derived by using a\nsemiclassical approach. The long-time asymptotic states are obtained\nanalytically, which exhibit multi-stability in some regions of the parameter\nspace. The steady state is unique as the number of spins is finite. But the\nthermodynamic limit of the steady-state magnetization displays nonanalytic\nbehavior somewhere inside the semiclassical multi-stable region. We find both\nthe first-order and continuous dissipative phase transitions. As the number of\nspins increases, both the Liouvillian gap and magnetization variance vanish\naccording to a power law at the continuous transition. At the first-order\ntransition, the gap vanishes exponentially accompanied by a jump of\nmagnetization in thermodynamic limit. The properties of transitions depend on\nthe symmetry and semiclassical multistability, being qualitatively different\namong $p=2$, odd $p$ ($p\\geq 3$) and even $p$ ($p\\geq 4$)."
    },
    {
        "anchor": "Many-Body Entanglement in Short-Range Interacting Fermi Gases for\n  Metrology: We explore many-body entanglement in spinful Fermi gases with short-range\ninteractions, for metrology purposes. We characterize the emerging quantum\nphases via Density-Matrix Renormalization Group simulations and quantify their\nentanglement content for metrological usability via the Quantum Fisher\nInformation (QFI). Our study establishes a method, promoting the QFI to be an\norder parameter. Short-range interactions reveal to build up metrologically\npromising entanglement in the XY-ferromagnetic and cluster ordering, the\ncluster physics being unexplored so far.",
        "positive": "Nonlinear localized modes in dipolar Bose-Einstein condensates in\n  optical lattices: The modulational instability and discrete matter wave solitons in dipolar\nBEC, loaded into a deep optical lattice, are investigated analytically and\nnumerically. The process of modulational instability of nonlinear plane matter\nwaves in a dipolar nonlinear lattice is studied and the regions of instability\nare established. The existence and stability of bulk discrete solitons are\nanalyzed analytically and confirmed by numerical simulations. In a marked\ncontrast with the usual DNLS behavior (no dipolar interactions), we found a\nregion where the two fundamental modes are simultaneously unstable allowing\nenhanced mobility across the lattice for large norm values. To study the\nexistence and properties of surface discrete solitons, an analysis of the dimer\nconfiguration is performed. The properties of symmetric and antisymmetric modes\nincluding the stability diagrams and bifurcations are investigated in closed\nform. For the case of a bulk medium, properties of fundamental on-site and\ninter-site localized modes are analyzed. On-site and inter-site surface\nlocalized modes are studied finding that they do not exist when nonlocal\ninteractions predominate with respect to local ones."
    },
    {
        "anchor": "Thermal effects on the spin domain phases of high spin-f Bose-Einstein\n  condensates with rotational symmetries: Spinor Bose Einstein condensates (BEC) can be realized nowadays using\ndifferent atomic species of several spin values, offering unprecedented\nopportunities to scrutinize the underlying physics of its spin phase domains\nand of its quantum phase transitions. At sufficient low temperatures, lower\nthan the critical temperature, a fraction of thermally excited atoms of the\ncondensate can still interact with the whole system leading to spin-dependent\ninteractions that can modify the nature of its phase domains. In this work, we\ncharacterize the thermal fraction of atoms of a spinorial BEC of general\nspin-$f$ value, provided that its ground state lies in a given spin phase with\nrotational symmetry. To that end, we use the Hartree-Fock approximation and a\nmethod based on the Majorana stellar representation for mixed quantum states\nand symmetry arguments. We consider the spin phases with usual point group\nsymmetries, including those with some exotic phases associated to the platonic\nsolids. The method leads to useful analytical expressions of the eigenspectrum\nof the thermal cloud allowing us to study the admissible regions and multipolar\nmagnetic moments of the spin phases as a function of the temperature for\ngeneral spin values.",
        "positive": "Finite temperature dynamics of vortices in Bose-Einstein condensates: We study the dynamics of a single and a pair of vortices in quasi\ntwo-dimensional Bose-Einstein condensates at finite temperatures. We use the\nstochastic Gross-Pitaevskii equation, which is the Langevin equation for the\nBose-Einstein condensate, to this end. For a pair of vortices, we study the\ndynamics of both the vortex-vortex and vortex-antivortex pairs, which are\ngenerated by rotating the trap and moving the Gaussian obstacle potential,\nrespectively. Due to thermal fluctuations, the constituent vortices are not\nsymmetrically generated with respect to each other at finite temperatures. This\ninitial asymmetry coupled with the presence of random thermal fluctuations in\nthe system can lead to different decay rates for the component vortices of the\npair, especially in the case of two corotating vortices."
    },
    {
        "anchor": "Spin Localization of a Fermi Polaron in a Quasirandom Optical Lattice: Recently, the topics of many-body localization (MBL) and one-dimensional\nstrongly interacting few-body systems have received a lot of interest. These\ntwo topics have been largely developed separately. However, the generality of\nthe latter as far as external potentials are concerned -- including random and\nquasirandom potentials -- and their shared spatial dimensionality, makes it an\ninteresting way of dealing with MBL in the strongly interacting regime.\nUtilising tools developed for few-body systems we look to gain insight into the\nlocalization properties of the spin in a Fermi gas with strong interactions. We\nobserve a delocalized--localized transition over a range of fillings of a\nquasirandom lattice. We find this transition to be of a different nature for\nlow and high fillings, due to the diluteness of the system for low fillings.",
        "positive": "Dynamical evolutions in non-Hermitian triple-well system with complex\n  potential: We investigate the dynamical properties for non-Hermitian triple-well system\nwith a loss in the middle well. When chemical potentials in two end wells are\nuniform and nonlinear interactions are neglected, there always exists a dark\nstate, whose eigenenergy becomes zero, and the projections onto which do not\nchange over time and the loss factor. The increasing of loss factor only makes\nthe damping form from the oscillating decay to over-damping decay. However,\nwhen the nonlinear interaction is introduced, even interactions in the two end\nwells are also uniform, the projection of the dark state will be obviously\ndiminished. Simultaneously the increasing of loss factor will also aggravate\nthe loss. In this process the interaction in the middle well plays no role.\nWhen two chemical potentials or interactions in two end wells are not uniform\nall disappear with time. In addition, when we extend the triple-well system to\na general (2n + 1)-well, the loss is reduced greatly by the factor 1=2n in the\nabsence of the nonlinear interaction."
    },
    {
        "anchor": "High-energy side-peak emission of exciton-polariton condensates in high\n  density regime: In a standard semiconductor laser, electrons and holes recombine via\nstimulated emission to emit coherent light, in a process that is far from\nthermal equilibrium. Exciton-polariton condensates -- sharing the same basic\ndevice structure as a semiconductor laser, consisting of quantum wells coupled\nto a microcavity -- have been investigated primarily at densities far below the\nMott density for signatures of Bose-Einstein condensation. At high densities\napproaching the Mott density, exciton-polariton condensates are generally\nthought to revert to a standard semiconductor laser, with the loss of strong\ncoupling. Here, we report the observation of a photoluminescence sideband at\nhigh densities that cannot be accounted for by conventional semiconductor\nlasing. This also differs from an upper-polariton peak by the observation of\nthe excitation power dependence in the peak-energy separation. Our\ninterpretation as a persistent coherent electron-hole-photon coupling captures\nseveral features of this sideband whereas many remain elusive. Understanding\nthe observation will lead to a development in non-equilibrium many-body\nphysics.",
        "positive": "Non-monotonic response and light-cone freezing in gapless-to-(partially)\n  gapped quantum quenches of fermionic systems: The properties of prototypical examples of one-dimensional fermionic systems\nundergoing a sudden quantum quench from a gapless state to a (partially) gapped\nstate are analyzed. By means of a Generalized Gibbs Ensemble analysis or by\nnumerical solutions in the interacting cases, we observe an anomalous,\nnon-monotonic response of steady state correlation functions as a function of\nthe strength of the mechanism opening the gap. In order to interpret this\nresult, we calculate the full dynamical evolution of these correlation\nfunctions, which shows a freezing of the propagation of the quench information\n(light cone) for large quenches. We argue that this freezing is responsible for\nthe non-monotonous behaviour of observables. In continuum non-interacting\nmodels, this freezing can be traced back to a Klein-Gordon equation in the\npresence of a source term. We conclude by arguing in favour of the robustness\nof the phenomenon in the cases of non-sudden quenches and higher\ndimensionality."
    },
    {
        "anchor": "Dynamics of kicked spin-orbit-coupled Bose-Einstein condensates: We investigate the dynamics of kicked pseudo-spin-1/2 Bose-Einstein\ncondensates (BECs) with spin-orbit coupling (SOC) in a tightly confined\ntoroidal trap. The system exhibits different dynamical behaviors depending on\nthe competition among SOC, kick strength, kick period and interatomic\ninteraction. For weak kick strength, with the increase of SOC the density\nprofiles of two components evolve from overlapped symmetric distributions into\nstaggered antisymmetric distributions, and the evolution of energy experiences\na transition from quasiperiodic motion to modulated quantum beating. For large\nkick strength, when the SOC strength increases, the overlapped symmetric\ndensity distributions become staggered irregular patterns, and the energy\nevolution undergoes a transition from quasiperiodic motion to dynamical\nlocalization. Furthermore, in the case of weak SOC, the increase of kick period\nleads to a transition of the system from quantum beating to Rabi oscillation,\nwhile for the case of strong SOC the system demonstrates complex quasiperiodic\nmotion.",
        "positive": "Quantum quenches, sonic horizons and the Hawking radiation in a class of\n  exactly solvable models: Taking advantage of the known exact mapping of the one-dimensional Hard Core\nBose (HCB) fluid onto a non-interacting spinless fermion gas, we examine in\nfull detail a thought experiment on cold atoms confined in a\nquasi-one-dimensional trap, in order to investigate the emergence of the\nanalogue Hawking radiation. The dynamics of a gas of interacting bosons\nimpinging on an external potential is exactly tracked up to the reach of a\nstationary state. Under few strict conditions on the experimental parameters,\nthe stationary state is shown to be described asymptotically by a thermal\ndistribution, precisely at the expected (analogue) Hawking temperature.\nHowever, we find that in most experimental conditions the emerging\n`Hawking-like radiation' is not thermal. This analysis provides a novel\nmany-body microscopic interpretation of the Hawking mechanism, together with\nuseful limits and conditions for the design of future experiments in\nBose-Einstein condensates."
    },
    {
        "anchor": "Correlation effects and collective excitations in bosonic bilayers: role\n  of quantum statistics, superfluidity and dimerization transition: A two-component two-dimensional (2D) dipolar bosonic system in the bilayer\ngeometry is considered. By performing quantum Monte Carlo simulations in a wide\nrange of layer spacings we analyze in detail the pair correlation functions,\nthe static response function, the kinetic and interaction energies. By reducing\nthe layer spacing we observe a transition from weakly to strongly bound dimer\nstates. The transition is accompanied by the onset of short-range correlations,\nsuppression of the superfluid response, and rotonization of the excitation\nspectrum. A dispersion law and a dynamic structure factor for the {\\em\nin-phase} (symmetric) and {\\em out-of-phase} (antisymmetric) collective modes,\nduring the dimerization, is studied in detail with the stochastic\nreconstruction method and the method of moments. The antisymmetric mode\nspectrum is most strongly influenced by suppression of the inlayer\nsuperfluidity (specified by the superfluid fraction $\\gamma_s=\\rho_s/\\rho$). In\na pure superfluid/normal phase only an acoustic/optical(gapped) mode is\nrecovered. In a partially superfluid phase, both are present simultaneously,\nand the dispersion splits into two branches corresponding to a normal and a\nsuperfluid component. The spectral weight of the acoustic mode scales linearly\nwith $\\gamma_s$. This weight transfers to the optical branch when $\\gamma_s$ is\nreduced due to formation of dimer states. In summary, we demonstrate how the\ninterlayer dimerization in dipolar bilayers can be uniquely identified by\nstatic and dynamic properties.",
        "positive": "Many Body Approach for Quartet Condensation in Strong Coupling: The theory for condensation of higher fermionic clusters is developed. Fully\nselfconsistent nonlinear equations for the quartet order parameter in strongly\ncoupled fermionic systems are established and solved. The breakdown of the\nquasiparticle picture is pointed out. Derivation of numerically tractable\napproximation is described. The momentum projected factorisation ansatz of Ref.\n\\cite{slr09} for the order parameter is employed again. As a definite example\nthe condensation of $\\alpha$ particles in nuclear matter is worked out."
    },
    {
        "anchor": "Phase Estimation With Interfering Bose-Condensed Atomic Clouds: We investigate how to estimate from atom-position measurements the relative\nphase of two Bose-Einstein condensates released from a double-well potential.\nWe demonstrate that the phase estimation sensitivity via the fit of the average\ndensity to the interference pattern is fundamentally bounded by shot noise.\nThis bound can be overcome by estimating the phase from the measurement of\n$\\sqrt N$ (or higher) correlation function. The optimal estimation strategy\nrequires the measurement of the $N$-th order correlation function. We also\ndemonstrate that a second estimation method -- based on the detection of the\ncenter of mass of the interference pattern -- provides sub shot-noise\nsensitivity. Yet, the implementation of both protocols might be experimentally\nchallenging.",
        "positive": "Hydrodynamic stabilization of self-organized criticality in a driven\n  Rydberg gas: Signatures of self-organized criticality (SOC) have recently been observed in\nan ultracold atomic gas under continuous laser excitation to\nstrongly-interacting Rydberg states [S. Helmrich et al., Nature, 577, 481--486\n(2020)]. This creates a unique possibility to study this intriguing dynamical\nphenomenon, e.g., to probe its robustness and universality, under controlled\nexperimental conditions. Here we examine the self-organizing dynamics of a\ndriven ultracold gas and identify an unanticipated feedback mechanism, which is\nespecially important for systems coupled to thermal baths. It sustains an\nextended critical region in the trap center for a notably long time via\nhydrodynamic transport of particles from the flanks of the cloud toward the\ncenter. This compensates the avalanche-induced atom loss and leads to a\ncharacteristic flat-top density profile, providing an additional experimental\nsignature for SOC and minimizing effects of inhomogeneity on the SOC features."
    },
    {
        "anchor": "Superfluidity of Bose-Einstein condensates in ultracold atomic gases: Liquid helium 4 had been the only bosonic superfluid available in experiments\nfor a long time. This situation was changed in 1995, when a new superfluid was\nborn with the realization of the Bose-Einstein condensation in ultracold atomic\ngases. The liquid helium 4 is strongly interacting and has no spin; there is\nalmost no way to change its parameters, such as interaction strength and\ndensity. The new superfluid, Bose-Einstein condensate (BEC), offers various\naspects of advantages over liquid helium. On the one hand, BEC is weakly\ninteracting and has spin degrees of freedom. On the other hand, it is\nconvenient to tune almost all the parameters of a BEC, for example, the kinetic\nenergy by spin-orbit coupling, the density by the external potential, and the\ninteraction by Feshbach resonance. Great efforts have been devoted to studying\nthese new aspects of superfluidity, and the results have greatly enriched our\nunderstanding of superfluidity. Here we review these developments by focusing\non the stability and critical velocity of various superfluids. The BEC systems\nconsidered include a uniform superfluid in free space, a superfluid with its\ndensity periodically modulated, a superfluid with artificially engineered\nspin-orbit coupling, and a superfluid of pure spin current. Due to the weak\ninteraction, these BEC systems can be well described by the mean field\nGross-Pitaevskii theory and their superfluidity, in particular critical\nvelocities, can be examined with Landau's theory of superfluid. Experimental\nproposals to observe these new aspects of superfluidity are discussed.",
        "positive": "Equilibration of a finite temperature binary Bose gas formed by\n  population transfer: We consider an equilibrium single-species homogeneous Bose gas from which a\nproportion of the atoms are instantaneously and coherently transferred to a\nsecond species, thereby forming a binary Bose gas in a non-equilibrium initial\nstate. We study the ensuing evolution towards a new equilibrium, mapping the\ndynamics and final equilibrium state out as a function of the population\ntransfer and the interspecies interactions by means of classical field methods.\nWhile in certain regimes, the condensate fractions are largely unaffected by\nthe population transfer process, in others, particularly for immiscible\ninteractions, one or both condensate fractions are vastly reduced to a new\nequilibrium value."
    },
    {
        "anchor": "From localization to anomalous diffusion in the dynamics of coupled\n  kicked rotors: We study the effect of many-body quantum interference on the dynamics of\ncoupled periodically kicked systems whose classical dynamics is chaotic and\nshows an unbounded energy increase. We specifically focus on a $N$ coupled\nkicked rotors model: we find that the interplay of quantumness and interactions\ndramatically modifies the system dynamics inducing a transition between energy\nsaturation and unbounded energy increase. We discuss this phenomenon both\nnumerically and analytically, through a mapping onto a $N$-dimensional Anderson\nmodel. The thermodynamic limit $N\\to\\infty$, in particular, always shows\nunbounded energy growth. This dynamical delocalization is genuinely quantum and\nvery different from the classical one: using a mean field approximation we see\nthat the system self-organizes so that the energy per site increases in time as\na power law with exponent smaller than one. This wealth of phenomena is a\ngenuine effect of quantum interference: the classical system for $N\\geq 2$\nalways behaves ergodically with an energy per site linearly increasing in time.\nOur results show that quantum mechanics can deeply alter the\nregularity/ergodicity properties of a many body driven system.",
        "positive": "Mott criticality and pseudogap in Bose-Fermi mixtures: We study the Mott transition of a mixed Bose-Fermi system of ultracold atoms\nin an optical lattice, where the number of (spinless) fermions and bosons adds\nup to one atom per lattice, n_F+n_B=1. For weak interactions, a Fermi surface\ncoexists with a Bose-Einstein condensate while for strong interaction the\nsystem is incompressible but still characterized by a Fermi surface of\ncomposite fermions. At the critical point, the spectral function of the\nfermions, A(k,w), exhibits a pseudo-gapped behavior, rising as |w| at the Fermi\nmomentum, while in the Mott phase it is fully gapped. Taking into account the\ninteraction between the critical modes leads at very low temperatures either to\np-wave pairing or the transition is driven weakly first order. The same\nmechanism should also be important in antiferromagnetic metals with a small\nFermi surface."
    },
    {
        "anchor": "Bogoliubov Theory of acoustic Hawking radiation in Bose-Einstein\n  Condensates: We apply the microscopic Bogoliubov theory of dilute Bose-Einstein\ncondensates to analyze quantum and thermal fluctuations in a flowing atomic\ncondensate in the presence of a sonic horizon. For the simplest case of a\nstep-like horizon, closed-form analytical expressions are found for the\nspectral distribution of the analog Hawking radiation and for the density\ncorrelation function. The peculiar long-distance density correlations that\nappear as a consequence of the Hawking emission features turns out to be\nreinforced by a finite initial temperature of the condensate. The analytical\nresults are in good quantitative agreement with first principle numerical\ncalculations.",
        "positive": "Spin-orbit-coupled topological Fulde-Ferrell states of fermions in a\n  harmonic trap: Motivated by recent experimental breakthroughs in generating spin-orbit\ncoupling in ultracold Fermi gases using Raman laser beams, we present a\nsystematic study of spin-orbit-coupled Fermi gases confined in a\nquasi-one-dimensional trap in the presence of an in-plane Zeeman field (which\ncan be realized using a finite two-photon Raman detuning). We find that a\ntopological Fulde-Ferrell state will emerge, featuring finite-momentum Cooper\npairing and zero-energy Majorana excitations localized near the edge of the\ntrap based on the self-consistent Bogoliubov-de Genes (BdG) equations. We find\nanalytically the wavefunctions of the Majorana modes. Finally using the\ntime-dependent BdG we show how the finite-momentum pairing field manifests\nitself in the expansion dynamics of the atomic cloud."
    },
    {
        "anchor": "Strong-Coupling Bose-Einstein Condensation: We extend the theory of Bose-Einstein condensation from Bogoliubov's\nweak-coupling regime to arbirarily strong couplings.",
        "positive": "Bosonic Pfaffian State in the Hofstadter-Bose-Hubbard Model: Topological states of matter, such as fractional quantum Hall states, are an\nactive field of research due to their exotic excitations. In particular,\nultracold atoms in optical lattices provide a highly controllable and adaptable\nplatform to study such new types of quantum matter. However, finding a clear\nroute to realize non-Abelian quantum Hall states in these systems remains\nchallenging. Here we use the density-matrix renormalization-group (DMRG) method\nto study the Hofstadter-Bose-Hubbard model at filling factor $\\nu = 1$ and find\nstrong indications that at $\\alpha=1/6$ magnetic flux quanta per plaquette the\nground state is a lattice analog of the continuum non-Abelian Pfaffian. We\nstudy the on-site correlations of the ground state, which indicate its paired\nnature at $\\nu = 1$, and find an incompressible state characterized by a charge\ngap in the bulk. We argue that the emergence of a charge density wave on thin\ncylinders and the behavior of the two- and three-particle correlation functions\nat short distances provide evidence for the state being closely related to the\ncontinuum Pfaffian. The signatures discussed in this letter are accessible in\ncurrent cold atom experiments and we show that the Pfaffian-like state is\nreadily realizable in few-body systems using adiabatic preparation schemes."
    },
    {
        "anchor": "Generation of optical potentials for ultracold atoms using a\n  superluminescent diode: We report on the realization and characterisation of optical potentials for\nultracold atoms using a superluminescent diode. The light emitted by this class\nof diodes is characterised by high spatial coherence but low temporal\ncoherence. On the one hand, this implies that it follows Gaussian propagation\nsimilar to lasers, allowing for high intensities and well-collimated beams. On\nthe other, it significantly reduces those interference effects that lead to\nsevere distortions in imaging. By using a high-resolution optical setup, we\nproduce patterned optical potentials with a digital micromirror device and\ndemonstrate that the quality of the patterns produced by our superluminescent\ndiode is consistently and substantially higher than those produced by our\nlaser. We show that the resulting optical potentials can be used to arrange the\natoms in arbitrary structures and manipulate them dynamically. Our results can\nopen new opportunities in the fields of quantum simulations and atomtronics.",
        "positive": "Bose-Einstein condensation in a frustrated triangular optical lattice: The recent experimental condensation of ultracold atoms in a triangular\noptical lattice with negative effective tunneling energies paves the way to\nstudy frustrated systems in a controlled environment. Here, we explore the\ncritical behavior of the chiral phase transition in such a frustrated lattice\nin three dimensions. We represent the low-energy action of the lattice system\nas a two-component Bose gas corresponding to the two minima of the dispersion.\nThe contact repulsion between the bosons separates into intra- and\ninter-component interactions, referred to as $V_{0}$ and $V_{12}$,\nrespectively. We first employ a Huang-Yang-Luttinger approximation of the free\nenergy. For $V_{12}/V_{0} = 2$, which corresponds to the bare interaction, this\napproach suggests a first order phase transition, at which both the U$(1)$\nsymmetry of condensation and the $\\mathbb{Z}_2$ symmetry of the emergent chiral\norder are broken simultaneously. Furthermore, we perform a renormalization\ngroup calculation at one-loop order. We demonstrate that the coupling regime\n$0<V_{12}/V_0\\leq1$ shares the critical behavior of the Heisenberg fixed point\nat $V_{12}/V_{0}=1$. For $V_{12}/V_0>1$ we show that $V_{0}$ flows to a\nnegative value, while $V_{12}$ increases and remains positive. This results in\na breakdown of the effective quartic field theory due to a cubic anisotropy,\nand again suggests a discontinuous phase transition."
    },
    {
        "anchor": "Intertwined Space-Time Symmetry, Orbital Magnetism and Dynamical Berry\n  Curvature in a Circularly Shaken Optical Lattice: We study the circular shaking of a two dimensional optical lattice, which is\nessentially a (2+1) dimensional space-time lattice exhibiting periodicities in\nboth spatial and temporal dimensions. The near-resonant optical shaking\nconsidered here dynamically couples the low-lying $s$ band and the first\nexcited $p$ bands by transferring a photon of shaking frequency. The\nintertwined space-time symmetries are further uncovered to elucidate the\ndegeneracy in the spectrum solved with the generalized Bloch-Floquet theorem.\nSetting the chirality of circular shaking explicitly breaks time reversal\nsymmetry and lifts the degeneracy of $p_\\pm = p_x \\pm ip_y$ orbitals, leading\nto the local circulation of orbital magnetism, i.e the imbalanced occupation in\n$p_\\pm$ orbitals. Moreover, the dynamics of Berry connection is revealed by the\ntime evolution of the Berry curvature and the polarization, which have physical\nobservable effects in experiments. Interestingly, the dynamics is found\ncharacterized by a universal phase shift, governed by the time screw rotational\nsymmetry involving a fractional translation of time. These findings suggest\nthat the present lattice-shaking scheme provides a versatile platform for the\ninvestigation of the orbital physics and the symmetry-protected dynamics.",
        "positive": "Magnetic Impurity in a Tonks Gas of Fermions: In this letter we consider a magnetic impurity in a one-dimensional\nspin-$1/2$ Fermi gas with infinitely strong repulsive interaction between\nfermions. We rigorously prove that, independent of whether the magnetic\ncoupling between impurity and fermions is ferromagnetic or anti-ferromagnetic,\nthe ground state is always a fully polarized ferromagnetic state for the\nitinerant fermions. This ferromagnetism can be understood as a cooperative\neffect of avoiding frustration of magnetic coupling during fermion hopping and\nthe large spin degeneracy of a fermion Tonks gas. By numerically diagonalizing\na finite size system, we show that the spin gap first increases linearly with\nmagnetic coupling strength in the weak coupling regime, while decreases in the\nstrong coupling regime. Our results show that a magnetic impurity in a strongly\ncorrelated gas can exhibit effect different from the Kondo effect as in a\nweakly correlated Fermi liquid."
    },
    {
        "anchor": "High-energy Bragg scattering measurements of a dipolar supersolid: We present an experimental and theoretical study of the high-energy\nexcitation spectra of a dipolar supersolid. Using Bragg spectroscopy, we study\nthe scattering response of the system to a high-energy probe, enabling\nmeasurements of the dynamic structure factor. We experimentally observe a\ncontinuous reduction of the response when tuning the contact interaction from\nan ordinary Bose-Einstein condensate to a supersolid state. Yet the observed\nreduction is faster than the one theoretically predicted by the\nBogoliubov-de-Gennes theory. Based on an intuitive semi-analytic model and\nreal-time simulations, we primarily attribute such a discrepancy to the\nout-of-equilibrium phase dynamics, which although not affecting the system\nglobal coherence, reduces its response.",
        "positive": "Characterization of the magnetic field through the three-body loss near\n  a narrow Feshbach resonance: The narrow s-wave Feshbach resonance of a $^6$Li Fermi gas shows strong\nthree-body loss, which is proposed to be used to measure the minute change of a\nmagnetic field around the resonance. However, the eddy current will cause\nultracold atom experiencing a magnetic field delayed to the desired magnetic\nfield from the current of the magnetic coils. The elimination of the eddy\ncurrent effect will play a key role in any experiments that motivated to\nmeasure the magnetic field to the precision of a part per million stability.\nHere, we apply a method to correct the eddy current effect for precision\nmeasurement of the magnetic field. We first record the three-body loss\ninfluenced by the effect of induced eddy current, then use a certain model to\nobtain the time constant of the actual magnetic field by fitting the atom loss.\nThis precisely determines the actual magnetic field according to the time\nresponse of the three-body loss. After that, we implement the desired magnetic\nfield to the atoms so that we can analyze the three-body loss across the whole\nnarrow Feshbach resonance. The results show that the three-body recombination\nis the dominated loss mechanism near the resonance. We expect this practical\nmethod of correcting the eddy current error of the magnetic field can be\nfurther applied to the future studies of quantum few- and many-body physics\nnear a narrow Feshbach resonance."
    },
    {
        "anchor": "Fast thermalization and Helmholtz oscillations of an ultracold Bose gas: We analyze theoretically the transport properties of a weakly-interacting\nultracold Bose gas enclosed in two reservoirs connected by a constriction. We\nassume that the transport of the superfluid part is hydrodynamic, and we\ndescribe the ballistic transport of the normal part using the Landauer-Buttiker\nformalism. Modeling the coupled evolution of the phase, atom number, and\ntemperature mismatches between the reservoirs, we predict that Helmholtz\n(plasma) oscillations, induced by an initial imbalance in atom numbers, can be\nobserved at non-zero temperatures below Tc. We show that, because of its strong\ncompressibility, the ultracold Bose gas is characterized by a fast\nthermalization compared to the damping time for plasma oscillations,\naccompanied by a fast transfer of the normal component through the\nconstriction. This fast thermalization also affects the gas above Tc, where we\npresent an explicit comparison to the ideal fermionic case.",
        "positive": "Topological superradiance in a degenerate Fermi gas: We predict the existence of a topological superradiant state in a\ntwo-component degenerate Fermi gas in a cavity. The superradiant light\ngeneration in the transversely driven cavity mode induces a cavity-assisted\nspin-orbit coupling in the system and opens a bulk gap at half-filling. This\nmechanism can simultaneously drive a topological phase transition in the\nsystem, yielding a topological superradiant phase. We map out the steady-state\nphase diagram of the system in the presence of an effective Zeeman field, and\nidentify a critical quadracritical point beyond which the topological and the\nconventional superraidiant phase boundaries separate. We also propose to detect\nthe topological phase transitions based on the unique signatures in the\nmomentum-space density distribution."
    },
    {
        "anchor": "Functional Determinant Approach Investigations of Heavy Impurity Physics: In this brief review, we report some new development in the functional\ndeterminant approach (FDA), an exact numerical method, in the studies of a\nheavy quantum impurity immersed in Fermi gases and manipulated with\nradio-frequency pulses. FDA has been successfully applied to investigate the\nuniversal dynamical responses of a heavy impurity in an ultracold ideal Fermi\ngas in both the time and frequency domain, which allows the exploration of the\nrenowned Anderson's orthogonality catastrophe (OC). In such a system, OC is\ninduced by the multiple particle-hole excitations of the Fermi sea, which is\nbeyond a simple perturbation picture and manifests itself as the absence of\nquasiparticles named polarons. More recently, two new directions for studying\nheavy impurity with FDA have been developed. One is to extend FDA to a strongly\ncorrelated background superfluid background, a Bardeen-Cooper-Schrieffer (BCS)\nsuperfluid. In this system, Anderson's orthogonality catastrophe is prohibited\ndue to the suppression of multiple particle-hole excitations by the superfluid\ngap, which leads to the existence of genuine polaron. The other direction is to\ngeneralize the FDA to the case of multiple RF pulses scheme, which extends the\nwell-established 1D Ramsey spectroscopy in ultracold atoms into\nmultidimensional, in the same spirit as the well-known multidimensional nuclear\nmagnetic resonance and optical multidimensional coherent spectroscopy.\nMultidimensional Ramsey spectroscopy allows us to investigate correlations\nbetween spectral peaks of an impurity-medium system that is not accessible in\nthe conventional one-dimensional spectrum.",
        "positive": "BEC-BCS Crossover with Feshbach Resonance for Three-Hyperfine-Species\n  Model: In a Feshbach resonance, the effective s-wave scattering length grows when\none moves toward the resonance point, and eventually diverges at this point.\nThere is one characteristic energy scale, $\\delta_c$, defined as, in the\nnegative side of the resonance point, the detuning energy at which the weight\nof the bound state shifts from predominatedly in the open-channel to\npredominated in the closed-channel. When the many-body energy scale (e.g. the\nFermi energy, $E_{F}$) is larger than $\\delta_c$, the closed-channel weight is\nsignificant and has to be included in the many-body theory. Furthermore, when\ntwo channels share a hyperfine species, the Pauli exclusion between fermions\nfrom two channels also needs to be taken into consideration in the many-body\ntheory.\n  The current thesis addresses the above problem in detail. A set of gap\nequations and number equations are derived at the mean-field level. The\nfermionic and bosonic excitation spectra are then derived. Assuming that the\nuncoupled bound-state of the closed-channel in resonance is much smaller than\nthe inter-particle distance, as well as the s-wave scattering length, $a_s$, we\nfind that the basic equations in the single-channel crossover model are still\nvalid. The correction first comes from the existing of the finite chemical\npotential and additional counting complication due to the closed-channel. These\ntwo corrections need to be included into the mean-field equations, i.e. the gap\nequations and the number equations, and be solved self-consistently. Then the\ncorrection due to the inter-channel Pauli exclusion is in the order of the\nratio of the Fermi energy and the Zeeman energy difference between two\nchannels, $E_F/\\eta$, which can be analyzed perturbatively over the previous\ncorrections.\n  Fermionic and bosonic excitation modes are studied."
    },
    {
        "anchor": "Local Chern marker of smoothly confined Hofstadter fermions: The engineering of topological non-trivial states of matter, using cold\natoms, has made great progress in the last decade. Driven by experimental\nsuccesses, it has become of major interest in the cold atom community. In this\nwork we investigate the time-reversal invariant Hofstadter model with an\nadditional confining potential. By calculating a local spin Chern marker we\nfind that topologically non-trivial phases can be observed in all considered\ntrap geometries. This holds also for spin-orbit coupled fermions, where the\nmodel exhibits a quantum spin Hall regime at half filling. Using dynamical\nmean-field theory, we find that interactions compete against the confining\npotential and induce a topological phase transition depending on the filling of\nthe system. Strong interactions furthermore yield a magnetic edge, which is\nlocalized through the interplay of the density distribution and the underlying\ntopological band structure.",
        "positive": "Robustness of gauge-invariant dynamics against defects in ultracold-atom\n  gauge theories: Recent years have seen strong progress in quantum simulation of gauge-theory\ndynamics using ultracold-atom experiments. A principal challenge in these\nefforts is the certification of gauge invariance, which has recently been\nrealized in [B.~Yang et al., arXiv:2003.08945]. One major but poorly\ninvestigated experimental source of gauge-invariance violation is an imperfect\npreparation of the initial state. Using the time-dependent density-matrix\nrenormalization group, we analyze the robustness of gauge-invariant dynamics\nagainst potential preparation defects in the above ultracold-atom\nimplementation of a $\\mathrm{U}(1)$ gauge theory. We find defects related to an\nerroneous initialization of matter fields to be innocuous, as the associated\ngauge-invariance violation remains strongly localized throughout the time\nevolution. A defect due to faulty initialization of the gauge field leads to a\nmild proliferation of the associated violation. Furthermore, we characterize\nthe influence of immobile and mobile defects by monitoring the spread of\nentanglement entropy. Overall, our results indicate that the aforementioned\nexperimental realization exhibits a high level of fidelity in the gauge\ninvariance of its dynamics at all evolution times. Our work provides strong\nevidence that ultracold-atom setups can serve as an extremely reliable\nframework for the quantum simulation of gauge-theory dynamics."
    },
    {
        "anchor": "Topological Higgs Amplitude Modes in Strongly Interacting Superfluids: By studying the 2-dimensional Su-Schrieffer-Heeger-Bose-Hubbard model, we\nshow the existence of topological Higgs amplitude modes in the strongly\ninteracting superfluid phase. Using the slave boson approach, we find that, in\nthe large filling limit, the Higgs excitations and the Goldstone excitations\nabove the ground state are well decoupled, and both of them exhibit nontrivial\ntopology inherited from the underlying noninteracting bands. At finite\nfillings, they become coupled at high energies; nevertheless, the topology of\nthese modes are unchanged. Moreover, based on an effective action analysis, we\nfurther provide a universal physical picture for the topological character of\nHiggs and Goldstone modes. Our discovery of the first realization of the\ntopological Higgs mode opens the path to novel investigations in various\nsystems such as superconductors and quantum magnetism.",
        "positive": "Rubidium-87 Bose-Einstein condensate in an optically plugged quadrupole\n  trap: We describe an experiment to produce 87Rb Bose-Einstein condensates in an\noptically plugged magnetic quadrupole trap, using a blue-detuned laser. Due to\nthe large detuning of the plug laser with respect to the atomic transition, the\nevaporation has to be carefully optimized in order to efficiently overcome the\nMajorana losses. We provide a complete theoretical and experimental study of\nthe trapping potential at low temperatures and show that this simple model\ndescribes well our data. In particular we demonstrate methods to reliably\nmeasure the trap oscillation frequencies and the bottom frequency, based on\nperiodic excitation of the trapping potential and on radio-frequency\nspectroscopy, respectively. We show that this hybrid trap can be operated in a\nwell controlled regime that allows a reliable production of degenerate gases."
    },
    {
        "anchor": "Non-integral form of the Gross-Pitaevskii equation for polarized\n  molecules: The Gross-Pitaevskii equation for polarized molecules is an\nintegro-differential equation, consequently it is complicated for solving. We\nfind a possibility to represent it as a non-integral nonlinear Schrodinger\nequation, but this equation should be coupled with two linear equations\ndescribing electric field. These two equations are the Maxwell equations. We\nrecapture the dispersion of collective excitations in the three dimensional\nelectrically polarized BEC with no evolution of the electric dipole moment\ndirections. We trace the contribution of the electric dipole moment. We\nexplicitly consider the contribution of the electric dipole moment in the\ninteraction constant for the short-range interaction. We show that the spectrum\nof dipolar BEC reveals no instability at repulsive short-range interaction.\nNonlinear excitations are also considered. We present dependence of the bright\nsoliton characteristics on the electric dipole moment.",
        "positive": "Momentum distribution of Vinen turbulence in trapped atomic\n  Bose-Einstein condensates: The decay of multicharged vortices in trapped Bose-Einstein condensates may\nlead to a disordered vortex state consistent with the Vinen regime of\nturbulence, characterized by an absence of large-scale flow and an\nincompressible kinetic energy spectrum $E\\propto k^{-1}$. In this work, we\nstudy numerically the dynamics of a three-dimensional harmonically trapped\nBose-Einstein condensate excited to a Vinen regime of turbulence through the\ndecay of two doubly-charged vortices. First, we study the momentum distribution\nand observe the emergence of a power-law behavior $n(k)\\propto k^{-3}$\nconsistent with the coexistence of wave turbulence. We also study the kinetic\nenergy and particle fluxes, which allows us to identify a direct particle\ncascade associated with the turbulent stage."
    },
    {
        "anchor": "Universal behavior of pair correlations in a strongly interacting Fermi\n  gas: We show that short-range pair correlations in a strongly interacting Fermi\ngas follow a simple universal law described by Tan's relations. This is\nachieved through measurements of the static structure factor which displays a\nuniversal scaling proportional to the ratio of Tan's contact to the momentum\n$C/q$. Bragg spectroscopy of ultracold $^6$Li atoms from a periodic optical\npotential is used to measure the structure factor for a wide range of momenta\nand interaction strengths, providing broad confirmation of this universal law.\nWe calibrate our Bragg spectra using the $f$-sum rule, which is found to\nimprove the accuracy of the structure factor measurement.",
        "positive": "Matter-wave bright solitons in spin-orbit coupled Bose-Einstein\n  condensates: We study matter-wave bright solitons in spin-orbit (SO) coupled Bose-Einstein\ncondensates (BECs) with attractive interatomic interactions. We use a\nmultiscale expansion method to identify solution families for chemical\npotentials in the semi-infinite gap of the linear energy spectrum. Depending on\nthe linear and spin-orbit coupling strengths, the solitons may resemble either\nstandard bright nonlinear Schr\\\"{o}dinger solitons or exhibit a modulated\ndensity profile, reminiscent of the stripe phase of SO-coupled repulsive BECs.\nOur numerical results are in excellent agreement with our analytical findings,\nand demonstrate the potential robustness of such solitons for experimentally\nrelevant conditions through stability analysis and direct numerical\nsimulations."
    },
    {
        "anchor": "Adiabatic Control of Atomic Dressed States for Transport and Sensing: We describe forms of adiabatic transport that arise for dressed-state atoms\nin optical lattices. Focussing on the limit of weak tunnel-coupling between\nnearest-neighbour lattice sites, we explain how adiabatic variation of optical\ndressing allows control of atomic motion between lattice sites: allowing\nadiabatic particle transport in a direction that depends on the internal state,\nand force measurements via spectroscopic preparation and readout. For uniformly\nfilled bands these systems display topologically quantised particle transport.",
        "positive": "Dynamics of single neutral impurity atoms immersed in an ultracold gas: We report on controlled doping of an ultracold Rb gas with single neutral Cs\nimpurity atoms. Elastic two-body collisions lead to a rapid thermalization of\nthe impurity inside the Rb gas, representing the first realization of an\nultracold gas doped with a precisely known number of impurity atoms interacting\nvia s-wave collisions. Inelastic interactions are restricted to a single\nthree-body recombination channel in a highly controlled and pure setting, which\nallows to determine the Rb-Rb-Cs three-body loss rate with unprecedented\nprecision. Our results pave the way for a coherently interacting hybrid system\nof individually controllable impurities in a quantum many-body system."
    },
    {
        "anchor": "Simulating cosmological supercooling with a cold atom system: We perform an analysis of the supercooled state in an analogue to an early\nuniverse phase transition based on a one dimensional, two-component Bose gas.\nWe demonstrate that the thermal fluctuations in the relative phase between the\ncomponents are characteristic of a relativistic thermal system. Furthermore, we\ndemonstrate the equivalence of two different approaches to the decay of the\nmetastable state: specifically a non-perturbative thermal instanton calculation\nand a stochastic Gross--Pitaevskii simulation.",
        "positive": "Floquet Engineering of a Dynamical $Z_{2}$ Lattice Gauge Field with\n  Ultracold Atoms: In this paper, we propose that a simple model, in which fermions coupled to a\ndynamical lattice gauge field, can be engineered via the Floquet approach. The\nmodel possess both a independent Maxwell term and the local $Z_{2}$ gauge\nsymmetry. Our proposal relies on a species dependent optical lattice, and can\nbe achieved in one, two or three dimension. By an unitary transformation, this\nmodel can be mapped into a non-interacting composite Fermion system with\nfluctuating back ground charge. With the help of this composite Fermion\npicture, two characteristic observations are predicted. One is the\nradio-frequency spectroscopy, which exhibits no dispersion in all parameter\nregimes. Second is the the dynamical localization, which depends on the\nstructure of the initial states."
    },
    {
        "anchor": "Single particle polariton properties in doped quantum well\n  microcavities: role of the Fermi edge singularity and Anderson orthogonality\n  catastrophe: A theoretical investigation of the single particle polariton properties for a\nmicrocavity embedding a charged quantum well is presented. The electron gas\noptical susceptibility is calculated numerically using the method devised by\nCombescot and Nozi\\`eres. The role of many-body effects, such as the Fermi edge\nsingularity and Anderson orthogonality catastrophe, in the polariton formation\nis elucidated. By tuning the light-matter coupling the short time behaviour of\nthe electron gas response function is probed and comparison with earlier\nresults only using the long time response are made. Various single particle\npolariton properties such as the Rabi splitting, line shape, Hopfield\ncoefficients and effective mass are discussed. These are experimentally\naccessible quantities and thus allow for a comparison with the presented\ntheory.",
        "positive": "Analytically solvable model to the spin Hall effect with Rashba and\n  Dresselhaus spin-orbit couplings: When the Rashba and Dresslhaus spin-orbit coupling are both presented for a\ntwo-dimensional electron in a perpendicular magnetic field, a striking\nresemblance to anisotropic quantum Rabi model in quantum optics is found. We\nperform a generalized Rashba coupling approximation to obtain a solvable\nHamiltonian by keeping the nearest-mixing terms of Laudau states, which is\nreformulated in the similar form to that with only Rashba coupling. Each Landau\nstate becomes a new displaced-Fock state with a displacement shift instead of\nthe original Harmonic oscillator Fock state, yielding eigenstates in closed\nform. Analytical energies are consistent with numerical ones in a wide range of\ncoupling strength even for a strong Zeeman splitting. In the presence of an\nelectric field, the spin conductance and the charge conductance obtained\nanalytically are in good agreements with the numerical results. As the\ncomponent of the Dresselhaus coupling increases, we find that the spin Hall\nconductance exhibits a pronounced resonant peak at a larger value of the\ninverse of the magnetic field. Meanwhile, the charge conductance exhibits a\nseries of plateaus as well as a jump at the resonant magnetic field. Our method\nprovides an easy-to-implement analytical treatment to two-dimensional electron\ngas systems with both types of spin-orbit couplings."
    },
    {
        "anchor": "Role of the intraspecies scattering length in the Efimov scenario with\n  large mass difference: We experimentally and theoretically study the effect of the intraspecies\nscattering length onto the heteronuclear Efimov scenario, following up on our\nearlier observation of Efimov resonances in an ultracold Cs-Li mixture for\nnegative [Pires et al., Phys. Rev. Lett. 112, 250404 (2014)] and positive Cs-Cs\nscattering length [Ulmanis et al., Phys. Rev. Lett. 117, 153201 (2016)]. Three\ntheoretical models of increasing complexity are employed to quantify its\ninfluence on the scaling factor and the three-body parameter: a simple\nBorn-Oppenheimer picture, a zero-range theory, and a spinless van der Waals\nmodel. These models are compared to Efimov resonances observed in an ultracold\nmixture of bosonic $^{133}$Cs and fermionic $^6$Li atoms close to two Cs-Li\nFeshbach resonances located at 843 G and 889 G, characterized by different sign\nand magnitude of the Cs-Cs interaction. By changing the sign and magnitude of\nthe intraspecies scattering length different scaling behaviors of the\nthree-body loss rate are identified, in qualitative agreement with theoretical\npredictions. The three-body loss rate is strongly influenced by the\nintraspecies scattering length.",
        "positive": "Infrared behavior in systems with a broken continuous symmetry:\n  classical O(N) model vs interacting bosons: In systems with a spontaneously broken continuous symmetry, the perturbative\nloop expansion is plagued with infrared divergences due to the coupling between\ntransverse and longitudinal fluctuations. As a result the longitudinal\nsusceptibility diverges and the self-energy becomes singular at low energy. We\nstudy the crossover from the high-energy Gaussian regime, where perturbation\ntheory remains valid, to the low-energy Goldstone regime characterized by a\ndiverging longitudinal susceptibility. We consider both the classical linear\nO($N$) model and interacting bosons at zero temperature, using a variety of\ntechniques: perturbation theory, hydrodynamic approach (i.e., for bosons,\nPopov's theory), large-$N$ limit and non-perturbative renormalization group. We\nemphasize the essential role of the Ginzburg momentum scale $p_G$ below which\nthe perturbative approach breaks down. Even though the action of\n(non-relativistic) bosons includes a first-order time derivative term, we find\nremarkable similarities in the weak-coupling limit between the classical O($N$)\nmodel and interacting bosons at zero temperature."
    },
    {
        "anchor": "Production of large Bose-Einstein condensates in a\n  magnetic-shield-compatible hybrid trap: We describe the production of large ${}^{23} \\mathrm{Na}$ Bose-Einstein\ncondensates in a hybrid trap characterized by a weak magnetic field quadrupole\nand a tightly focused infrared beam. The use of small magnetic field gradients\nmakes the trap compatible with the state-of-the-art magnetic shields. By taking\nadvantage of the deep cooling and high efficiency of gray molasses to improve\nthe initial trap loading conditions, we produce condensates composed of as much\nas $7$ million atoms in less than $30 \\; \\mathrm{s}$.",
        "positive": "Bose-Einstein Condensation of Strontium: We report on the attainment of Bose-Einstein condensation with ultracold\nstrontium atoms. We use the 84Sr isotope, which has a low natural abundance but\noffers excellent scattering properties for evaporative cooling. Accumulation in\na metastable state using a magnetic-trap, narrowline cooling, and\nstraightforward evaporative cooling in an optical trap lead to pure condensates\ncontaining 1.5x10^5 atoms. This puts 84Sr in a prime position for future\nexperiments on quantum-degenerate gases involving atomic two-electron systems."
    },
    {
        "anchor": "Vortex reconnections in atomic condensates at finite temperature: The study of vortex reconnections is an essential ingredient of understanding\nsuperfluid turbulence, a phenomenon recently also reported in trapped atomic\nBose-Einstein condensates. In this work we show that, despite the established\ndependence of vortex motion on temperature in such systems, vortex\nreconnections are actually temperature independent on the typical length/time\nscales of atomic condensates. Our work is based on a dissipative\nGross-Pitaevskii equation for the condensate, coupled to a semiclassical\nBoltzmann equation for the thermal cloud (the Zaremba-Nikuni-Griffin\nformalism). Comparison to vortex reconnections in homogeneous condensates\nfurther show reconnections to be insensitive to the inhomogeneity in the\nbackground density.",
        "positive": "Non-perturbative predictions for cold atom Bose gases with tunable\n  interactions: We derive a theoretical description for dilute Bose gases as a loop expansion\nin terms of composite-field propagators by rewriting the Lagrangian in terms of\nauxiliary fields related to the normal and anomalous densities. We demonstrate\nthat already in leading order this non-perturbative approach describes a large\ninterval of coupling-constant values, satisfies Goldstone's theorem, yields a\nBose-Einstein transition that is second-order, and is consistent with the\ncritical temperature predicted in the weak-coupling limit by the\nnext-to-leading order large-N expansion."
    },
    {
        "anchor": "Dynamic Hysteresis Across a Dissipative Multi-Mode Phase Transition: Dissipative phase transitions are characteristic features in open quantum\nsystems. Key signatures are the dynamical switching between different states in\nthe vicinity of the phase transition and the appearance of hysteresis. Here, we\nexperimentally study dynamic sweeps across a first order dissipative phase\ntransition in a multi-mode driven-dissipative system. In contrast to previous\nstudies, we perform sweeps of the dissipation strength instead of the driving\nstrength. We extract exponents for the scaling of the hysteresis area in\ndependence of the sweep time and study the $g^{(2)}(0)$ correlations, which\nshow non-trivial behavior. Due to the multi-mode nature of the system, we can\nalso study the influence of the temperature on the hysteresis area. We compare\nour results to numerical calculations done for a single mode variant of the\nsystem, and find surprisingly good agreement. Furthermore, we identify and\ndiscuss the differences between a scan of the dissipation strength and a scan\nof the driving strength.",
        "positive": "Adiabatic Perturbation Theory and Geometry of Periodically-Driven\n  Systems: We give a systematic review of the adiabatic theorem and the leading\nnon-adiabatic corrections in periodically-driven (Floquet) systems. These\ncorrections have a two-fold origin: (i) conventional ones originating from the\ngradually changing Floquet Hamiltonian and (ii) corrections originating from\nchanging the micro-motion operator. These corrections conspire to give a\nHall-type linear response for non-stroboscopic (time-averaged) observables\nallowing one to measure the Berry curvature and the Chern number related to the\nFloquet Hamiltonian, thus extending these concepts to periodically-driven\nmany-body systems. The non-zero Floquet Chern number allows one to realize a\nThouless energy pump, where one can adiabatically add energy to the system in\ndiscrete units of the driving frequency. We discuss the validity of Floquet\nAdiabatic Perturbation Theory (FAPT) using five different models covering\nlinear and non-linear few and many-particle systems. We argue that in\ninteracting systems, even in the stable high-frequency regimes, FAPT breaks\ndown at ultra slow ramp rates due to avoided crossings of photon resonances,\nnot captured by the inverse-frequency expansion, leading to a counter-intuitive\nstronger heating at slower ramp rates. Nevertheless, large windows in the ramp\nrate are shown to exist for which the physics of interacting driven systems is\nwell captured by FAPT."
    },
    {
        "anchor": "Quantum degenerate Bose-Fermi mixture of chemically different atomic\n  species with widely tunable interactions: We have created a quantum degenerate Bose-Fermi mixture of 23Na and 40K with\nwidely tunable interactions via broad interspecies Feshbach resonances. Twenty\nFeshbach resonances between 23Na and 40K were identified. The large and\nnegative triplet background scattering length between 23Na and 40K causes a\nsharp enhancement of the fermion density in the presence of a Bose condensate.\nAs explained via the asymptotic bound-state model (ABM), this strong background\nscattering leads to a series of wide Feshbach resonances observed at low\nmagnetic fields. Our work opens up the prospect to create chemically stable,\nfermionic ground state molecules of 23Na-40K where strong, long-range dipolar\ninteractions will set the dominant energy scale.",
        "positive": "Critical Temperature of Interacting Bose Gases in Periodic Potentials: The superfluid transition of a repulsive Bose gas in the presence of a\nsinusoidal potential which represents a simple-cubic optical lattice is\ninvestigate using quantum Monte Carlo simulations. At the average filling of\none particle per well the critical temperature has a nonmonotonic dependence on\nthe interaction strength, with an initial sharp increase and a rapid\nsuppression at strong interactions in the vicinity of the Mott transition. In\nan optical lattice the positive shift of the transition is strongly enhanced\ncompared to the homogenous gas. By varying the lattice filling we find a\ncrossover from a regime where the optical lattice has the dominant effect to a\nregime where interactions dominate and the presence of the lattice potential\nbecomes almost irrelevant."
    },
    {
        "anchor": "Propagation of collective modes in non-overlapping dipolar Bose-Einstein\n  condensates: We investigate long-range effects of the dipolar interaction in Bose-Einstein\ncondensates by solving the time-dependent 3D Gross-Pitaevskii equation. We\nstudy the propagation of excitations between non-overlapping condensates when a\ncollective mode is excited in one of the condensates. We obtain the frequency\nshifts due to the long-range character of the dipolar coupling for the bilayer\nand also the trilayer system when the dipolar mode is excited in one\ncondensate. The propagation of the monopolar and quadrupolar modes are also\ninvestigated. The coupled-pendulum model is proposed to qualitatively explain\nthe long range effects of the dipolar coupling.",
        "positive": "Quantum holonomy in Lieb-Liniger model: We examine a parametric cycle in the N-body Lieb-Liniger model that starts\nfrom the free system and goes through Tonks-Girardeau and super-Tonks-Girardeau\nregimes and comes back to the free system. We show the existence of exotic\nquantum holonomy, whose detailed workings are analysed with the specific sample\nof two- and three body systems. The classification of eigenstates based on\nclustering structure naturally emerges from the analysis."
    },
    {
        "anchor": "Inversion of coherent backscattering with interacting Bose-Einstein\n  condensates in two-dimensional disorder : a Truncated Wigner approach: We theoretically study the propagation of an interacting Bose-Einstein\ncondensate in a two-dimensional disorder potential, following the principle of\nan atom laser. The constructive interference between time-reversed scattering\npaths gives rise to coherent backscattering, which may be observed under the\nform of a sharp cone in the disorder-averaged angular backscattered current. As\nis found by the numerical integration of the Gross-Pitaevskii equation, this\ncoherent backscattering cone is inversed when a non-vanishing interaction\nstrength is present, indicating a crossover from constructive to destructive\ninterferences. Numerical simulations based on the Truncated Wigner method allow\none to go beyond the mean-field approach and show that dephasing renders this\nsignature of antilocalisation hidden behind a structureless and dominant\nincoherent contribution as the interaction strength is increased and the\ninjected density decreased, in a regime of parameters far away from the\nmean-field limit. However, despite a partial dephasing, we observe that this\nweak antilocalisation scenario prevails for finite interaction strengths,\nopening the way for an experimental observation with $^{87}$Rb atoms.",
        "positive": "Vortex properties in the extended supersolid phase of dipolar\n  Bose-Einstein condensates: We study the properties of singly-quantized linear vortices in the supersolid\nphase of a dipolar Bose-Einstein condensate at zero temperature modeling\n$^{164}$Dy atoms. The system is extended in the $x-y$ plane and confined by a\nharmonic trap in the the polarization direction $z$. Our study is based on a\ngeneralized Gross-Pitaevskii equation. We characterize the ground state of the\nsystem in terms of spatial order and superfluid fraction and compare the\nproperties of a single vortex and of a vortex dipole in the superfluid phase\n(SFP) and in the supersolid phase (SSP). At variance with a vortex in the SFP,\nwhich is free to move in the superfluid, a vortex in the SSP is localized at\nthe interstitial sites and does not move freely. We have computed the energy\nbarrier for motion from an equilibrium site to another. The fact that the\nvortex is submitted to a periodic potential has a dramatic effect on the\ndynamics of a vortex dipole made of two counter rotating parallel vortices;\ninstead of rigidly translating as in the SFP, the vortex and anti-vortex\napproach each other by a series of jumps from one site to another until they\nannihilate in a very short time and their energy is transferred to bulk\nexcitations."
    },
    {
        "anchor": "Spontaneous formation of Kagom\u00e9 lattice in two-dimensional Rydberg\n  atoms: Two-dimensional Rydberg atoms are modeled at low temperatures by means of the\nclassical Monte Carlo method. The Coulomb repulsion of charged ions competing\nwith the repulsive van der Waals long-range tail is modeled by a number of\ninteraction potentials. We find that under specific conditions the usual\ntriangular crystal becomes unstable with respect to more exotic lattices such\nas Kagom\\'e, flower, molecular crystal and rectangular chain packings.\nGround-state configurations are obtained by means of the annealing procedure\nand their stability is additionally studied by the normal modes analysis. While\ncommonly the square lattice is mechanically unstable due to softening of the\nshear modulus, we were able to find a specific set of parameters for which the\nsquare lattice can be made stable.",
        "positive": "Lattice bosons in a quasi-disordered environment: The effects of a\n  superlattice potential on single particle and many particle properties: In this paper we present a theoretical investigation of the effect of a\nsuperlattice potential on some properties of non-interacting bosons in one\ndimensional lattices with Aubry-And\\'re disorder potential. In the first part,\nwe investigate the single particle localization properties. We find a\nre-entrant localization-delocalization transition and the development of\nmultiple mobility edges for a range of superlattice potential strengths. In the\nsecond part, we study the Bose-Einstein condensation with an additional\nharmonic trapping potential. We find that an increase in the superlattice\npotential leads to an increase in the depletion of the condensate in the low\ntemperature limit."
    },
    {
        "anchor": "Superfluid fraction of interacting bosonic gases: The superfluid fraction $f$ of a quantum fluid is defined in terms of the\nresponse of the system to a weak and constant drag. Notably, Leggett long ago\nderived two simple expressions providing a rigorous upper bound and a heuristic\nlower bound for $f$. Here we study the superfluid fraction of bosonic gases in\nvarious two-dimensional potentials, such as regular optical lattices and\ndisordered speckles, by solving the Gross-Pitaevskii equation and performing\nDiffusion Monte Carlo simulations. We show that under conditions relevant for\nmost ultracold experiments the bounds proposed by Leggett provide a\nsurprisingly narrow bracketing of the exact value of the superfluid fraction.",
        "positive": "Steady-state theory of electron drag on polariton condensates: We present a general theory of drag on a condensate due to interactions with\na moving thermal bath of non-condensate particles, adapted from previous theory\nof equilibration of a condensate in a trap. This theory can be used to model\nthe polariton drag effect observed previously, in which an electric current\npassing through a polariton condensate gives a measurable momentum transfer to\nthe condensate, and an effective potential energy shift."
    },
    {
        "anchor": "High order exceptional points in ultracold Bose gases: We show that arbitrarily high-order exceptional points (EPs) can be achieved\nin a repulsively interacting two-species Bose gas in one dimension. By exactly\nsolving the non-Hermitian two-boson problem, we demonstrate the existence of\nthird-order EPs when the system is driven across the parity-time symmetry\nbreaking transition. We further address the fourth-order EPs with three bosons\nand generalize the results to $N$-body system, where the EP order can be as\nhigh as $N+1$. Physically, such high order originates from the intrinsic\nferromagnetic correlation in spinor bosons, which renders the entire system\ncollectively behave as a single huge spin. Moreover, we show how to create\nultra-sensitive spectral response around EPs via an interaction anisotropy in\ndifferent spin channels. Our work puts forward the possibility of atomic\nsensors made from highly controllable ultracold gases.",
        "positive": "Time-resolved density correlations as probe of squeezing in toroidal\n  Bose-Einstein condensates: I study the evolution of mean field and linear quantum fluctuations in a\ntoroidal Bose-Einstein condensate, whose interaction strength is quenched from\na finite (repulsive) value to zero. The azimuthal equal-time density-density\ncorrelation function is calculated and shows temporal oscillations with twice\nthe (final) excitation frequencies after the transition. These oscillations are\na direct consequence of positive and negative frequency mixing during\nnon-adiabatic evolution. I will argue that a time-resolved measurement of the\nequal-time density correlator might be used to calculate the moduli of the\nBogoliubov coefficients and thus the amount of squeezing imposed on a mode,\ni.e., the number of atoms excited out of the condensate."
    },
    {
        "anchor": "Full counting statistics of time of flight images: Inspired by recent advances in cold atomic systems and non-equilibrium\nphysics, we introduce a novel characterization scheme, the time of flight full\ncounting statistics. We benchmark this method on an interacting one dimensional\nBose gas, and show that there the time of flight image displays several\nuniversal regimes. Finite momentum fluctuations are observed at larger\ndistances, where a crossover from exponential to Gamma distribution occurs upon\ndecreasing momentum resolution. Zero momentum particles, on the other hand,\nobey a Gumbel distribution in the weakly interacting limit, characterizing the\nquantum fluctuations of the former quasi-condensate. Time of flight full\ncounting statistics is demonstrated to capture thermalization processes after a\nquantum quench, and can be useful for characterizing exotic quantum states such\nas many-body localized systems or models of holography.",
        "positive": "Dynamics of bubbles in a two-component Bose-Einstein condensate: The dynamics of a phase-separated two-component Bose-Einstein condensate are\ninvestigated, in which a bubble of one component moves through the other\ncomponent. Numerical simulations of the Gross--Pitaevskii equation reveal a\nvariety of dynamics associated with the creation of quantized vortices. In two\ndimensions, a circular bubble deforms into an ellipse and splits into fragments\nwith vortices, which undergo the Magnus effect. The B\\'enard--von K\\'arm\\'an\nvortex street is also generated. In three dimensions, a spherical bubble\ndeforms into toruses with vortex rings. When two rings are formed, they exhibit\nleapfrogging dynamics."
    },
    {
        "anchor": "Hartree shift in unitary Fermi gases: The Hartree energy shift is calculated for a unitary Fermi gas. By including\nthe momentum dependence of the scattering amplitude explicitly, the Hartree\nenergy shift remains finite even at unitarity. Extending the theory also for\nspin-imbalanced systems allows calculation of polaron properties. The results\nare in good agreement with more involved theories and experiments.",
        "positive": "Itinerant ferromagnetism in a Fermi gas with contact interaction:\n  Magnetic properties in a dilute Hubbard model: Ground state properties of the repulsive Hubbard model on a cubic lattice are\ninvestigated by means of the auxiliary-field quantum Monte Carlo method. We\nfocus on low-density systems with varying on-site interaction $U/t$, as a model\nrelevant to recent experiments on itinerant ferromagnetism in a dilute Fermi\ngas with contact interaction. Twist-average boundary conditions are used to\neliminate open-shell effects and large lattice sizes are studied to reduce\nfinite-size effects. The sign problem is controlled by a generalized\nconstrained path approximation. We find no ferromagnetic phase transition in\nthis model. The ground-state correlations are consistent with those of a\nparamagnetic Fermi liquid."
    },
    {
        "anchor": "Entanglement spectrum: Identification of the transition from\n  vortex-liquid to vortex-lattice state in a weakly interacting rotating\n  Bose-Einstein condensate: We use entanglement to investigate the transition from vortex liquid phase to\nvortex lattice phase in weakly interacting rotating Bose-Einstein condensate\n(BEC). Ground state entanglement spectrum is analyzed to distinguish these two\ndifferent phases. For the torus geometry, the low-lying part of ground state\nentanglement spectrum, as well as the behavior of its lowest level change\nclearly when the transition occurs. For the sphere geometry, the disappearance\nof entanglement gap in the conformal limit (CL) can indicate this transition.\nWe also show that the decrease of entanglement between particles can be\nregarded as a signal of the transition.",
        "positive": "From quantum to thermal topological-sector fluctuations of strongly\n  interacting bosons in a ring lattice: Inspired by recent experiments on Bose-Einstein condensates in ring traps, we\ninvestigate the topological properties of the phase of a one-dimensional Bose\nfield in the presence of both thermal and quantum fluctuations -- the latter\nones being tuned by the depth of an optical lattice applied along the ring. In\nthe regime of large filling of the lattice, quantum Monte Carlo simulations\ngive direct access to the full statistics of fluctuations of the Bose-field\nphase, and of its winding number $W$ along the ring. At zero temperature the\nwinding-number (or topological-sector) fluctuations are driven by quantum phase\nslips localized around a Josephson link between two lattice wells, and their {\nsusceptibility} is found to jump at the superfluid-Mott insulator transition.\nAt finite (but low) temperature, on the other hand, the winding number\nfluctuations are driven by thermal activation of nearly uniform phase twists,\nwhose activation rate is governed by the superfluid fraction. A\nquantum-to-thermal crossover in winding number fluctuations is therefore\nexhibited by the system, and it is characterized by a conformational change in\nthe topologically non-trivial configurations, from localized to uniform phase\ntwists, which can be experimentally observed in ultracold Bose gases via\nmatter-wave interference."
    },
    {
        "anchor": "Spinor Bose-Einstein Condensates of Rotating Polar Molecules: We propose a scheme to realize a pseudospin-$1/2$ model of the\n$^{1}\\Sigma(v=0)$ bialkali polar molecules with the spin states corresponding\nto two sublevels of the first excited rotational level. We show that the\neffective dipole-dipole interaction between two spin-$1/2$ molecules couples\nthe rotational and orbital angular momenta and is highly tunable via a\nmicrowave field. We also investigate the ground state properties of a\nspin-$1/2$ molecular condensate. A variety of nontrivial quantum phases,\nincluding the doubly-quantized vortex states, are discovered. Our scheme can\nalso be used to create spin-$1$ model of polar molecules. Thus, we show that\nthe ultracold gases of bialkali polar molecules provide a unique platform for\nstudying the spinor condensates of rotating molecules.",
        "positive": "Dipolar Gases in Coupled One-Dimensional Lattices: We consider dipolar bosons in two tubes of one-dimensional lattices, where\nthe dipoles are aligned to be maximally repulsive and the particle filling\nfraction is the same in each tube. In the classical limit of zero inter-site\nhopping, the particles arrange themselves into an ordered crystal for any\nrational filling fraction, forming a complete devil's staircase like in the\nsingle tube case. Turning on hopping within each tube then gives rise to a\ncompetition between the crystalline Mott phases and a liquid of defects or\nsolitons. However, for the two-tube case, we find that solitons from different\ntubes can bind into pairs for certain topologies of the filling fraction. This\nprovides an intriguing example of pairing that is purely driven by correlations\nclose to a Mott insulator."
    },
    {
        "anchor": "Stability of $(N+1)$-body fermion clusters in multiband Hubbard model: We start with a variational approach and derive a set of coupled integral\nequations for the bound states of $N$ identical spin-$\\uparrow$ fermions and a\nsingle spin-$\\downarrow$ fermion in a generic multiband Hubbard Hamiltonian\nwith an attractive onsite interaction. As an illustration we apply our integral\nequations to the one-dimensional sawtooth lattice up to $N \\le 3$, i.e., to the\n$(3+1)$-body problem, and reveal not only the presence of tetramer states in\nthis two-band model but also their quasi-flat dispersion when formed in a flat\nband. Furthermore, for $N = \\{4, 5, \\cdots, 10 \\}$, our DMRG simulations and\nexact diagonalization suggest the presence of larger and larger multimers with\nlower and lower binding energies, conceivably without an upper bound on $N$.\nThese peculiar $(N+1)$-body clusters are in sharp contrast with the exact\nresults on the single-band linear-chain model where none of the $N \\ge 2$\nmultimers appear. Hence their presence must be taken into account for a proper\ndescription of the many-body phenomena in flat-band systems, e.g., they may\nsuppress superconductivity especially when there exists a large spin imbalance.",
        "positive": "Fractional Local Moment and High Temperature Kondo Effect in\n  Rashba-Fermi Gases: We investigate the new physics that arises when a correlated quantum impurity\nhybridizes with Fermi gas with a generalized Rashba spin-orbit coupling\nproduced via a uniform synthetic non-Abelian gauge field. We show that the\nimpurity develops a {\\it fractional} local moment which couples\nanti-ferromagnetically to the Rashba-Fermi gas. This results in a concomitant\n{\\it Kondo effect with a high temperature scale} that can be tuned by the\nstrength of the Rashba spin-orbit coupling."
    },
    {
        "anchor": "Ultracold coherent control of molecular collisions at a F\u00f6rster\n  resonance: We show that the precise preparation of a quantum superposition between three\nrotational states of an ultracold dipolar molecule generates controllable\ninterferences in their two-body scattering dynamics and collisional rate\ncoefficients, at an electric field that produces a F\\\"orster resonance. This\nproposal represents a feasible protocol to achieve coherent control on\nultracold molecular collisions in current experiments. It sets the basis for\nfuture studies in which one can think to control the amount of each produced\npairs, including trapped entangled pairs of reactants, individual pairs of\nproducts in a chemical reaction, and measuring each of their scattering\nphase-shifts that could envision ``complete chemical experiments\" at ultracold\ntemperatures.",
        "positive": "Few-body collective excitations beyond Kohn's theorem in quantum Hall\n  systems: A relative coordinate breathing mode in the quantum Hall system is predicted\nto exist with different behavior under either Coulomb or dipole-dipole\ninteractions. While Kohn's theorem predicts that any relative coordinate\ninteraction will fail to alter the center of mass energy spectrum, it can\naffect excitations in the relative coordinates. One such collective excitation,\nwhich we call the hyperradial breathing mode, emerges naturally from a\nfew-body, hyperspherical representation of the problem and depends on the\ninter-particle interactions, the ground state wave function, and the number of\nparticles participating in the excitation. Possible observations of this\nexcitation will be discussed in the context of both cold rotating atomic\nsimulations and conventional quantum Hall experiments."
    },
    {
        "anchor": "A quantum moat barrier, realized with a finite square well: The notion of a double well potential typically involves two regions of space\nseparated by a repulsive potential barrier. The solution is a wave function\nthat is suppressed in the barrier region and localized in the two surrounding\nregions. Remarkably, we illustrate that similar solutions can be achieved using\nan attractive \"barrier\" potential (a \"quantum moat\") instead of a repulsive one\n(a \"quantum wall\"). The reason this works is intimately connected to the\nconcepts of \"orthogonalized plane waves\" and the pseudopotential method, both\noriginally used to understand electronic band structures in solids. While the\nmain goal of this work is to use a simple model to demonstrate the barrier-like\nattribute of a quantum moat, we also show how the pseudopotential method is\nused to greatly improve the efficiency of constructing wave functions for this\nsystem using matrix diagonalization.",
        "positive": "Quasiparticle spectra of supersolid lattice gases at near-resonant\n  Rydberg-dressing: One of the major challenges in realizing a strongly interacting lattice gas\nusing Rydberg states is the occurrence of avalanche loss processes. As these\nare directly proportional to the total Rydberg fraction, the commonly suggested\nsolution is using far off-resonantly excited Rydberg states. We instead propose\nthe realization of a correlated bosonic lattice gas at near-resonant\nexcitation, where the total Rydberg fraction in the bulk is low due to the\nstrong, interaction-driven effective detuning. Using real-space dynamical\nmean-field theory we show that its reduced effect at the boundary of a system\ncan easily be compensated by considering a tailored beam-waist of the driving\nRabi-laser. In this geometry we discuss the spectral properties at the\ncrossover between the supersolid and the superfluid state and present the\nmomentum resolved spectral properties of the supersolid bulk. The latter\nresults are obtained within an extended quasiparticle method which also yields\na correction of the mean-field phase transition."
    },
    {
        "anchor": "Analytical study on parameter regions of dynamical instability for\n  two-component Bose--Einstein condensates with coaxial quantized vortices: The dynamical instability of weakly interacting two-component Bose--Einstein\ncondensates with coaxial quantized vortices is analytically investigated in a\ntwo-dimensional isotopic harmonic potential. We examine whether complex\neigenvalues appear on the Bogoliubov--de Gennes equation, implying dynamical\ninstability. Rather than solving the Bogoliubov--de Gennes equation\nnumerically, we rely on a perturbative expansion with respect to the coupling\nconstant which enables a simple, analytic approach. For each pair of winding\nnumbers and for each magnetic quantum number, the ranges of inter-component\ncoupling constant where the system is dynamically unstable are exhaustively\nobtained. Co-rotating and counter-rotating systems show distinctive behaviors.\nThe latter is much more complicated than the former with respect to dynamical\ninstability, particularly because radial excitations contribute to complex\neigenvalues in counter-rotating systems.",
        "positive": "Phase diagrams and multistep condensations of spin-1 bosonic gases in\n  optical lattices: Motivated by recent experimental processes, we systemically investigate\nstrongly correlated spin-1 ultracold bosons trapped in a three-dimensional\noptical lattice in the presence of an external magnetic field. Based on a\nrecently developed bosonic dynamical mean-field theory (BDMFT), we map out\ncomplete phase diagrams of the system for both antiferromagnetic and\nferromagnetic interactions, where various phases are found as a result of the\ninterplay of spin-dependent interaction and quadratic Zeeman energy. For\nantiferromagnetic interactions, the system demonstrates competing magnetic\norders, including nematic, spin-singlet and ferromagnetic insulating phase,\ndepending on longitudinal magnetization, whereas, for ferromagnetic case, a\nferromagnetic-to-nematic-insulating phase transition is observed for small\nquadratic Zeeman energy, and the insulating phase demonstrates the nematic\norder for large Zeeman energy. Interestingly, at low magnetic field and finite\ntemperature, we find an abnormal multi-step condensation of the strongly\ncorrelated superfluid, i.e. the critical condensing temperature of the $m_F=-1$\ncomponent with antiferromagnetic interactions demonstrates an increase with\nlongitudinal magnetization, while, for ferromagnetic case, the Zeeman component\n$m_F = 0$ demonstrates a local minimum for the critical condensing temperature,\nin contrast to weakly interacting cases."
    },
    {
        "anchor": "Controllable fusion of electromagnetic bosons in two-dimensional\n  semiconductors: We propose a physical principle for implementation of controllable\ninteractions of identical electromagnetic bosons (excitons or polaritons) in\ntwo-dimensional (2D) semiconductors. The key ingredients are tightly bound\nbiexcitons and in-plane anisotropy of the host structure due to, e.g., a\nuniaxial strain. We show that anisotropy-induced splitting of the radiative\nexciton doublet couples the biexciton state to continua of boson scattering\nstates. As a result, two-body elastic scattering of bosons may be resonantly\namplified when energetically tuned close to the biexciton by applying a\ntransverse magnetic field or tuning the coupling with the microcavity photon\nmode. At the resonance, bosonic fields undergo quantum reaction of fusion\naccompanied by their squeezing. For excitons, we predict giant molecules\n(Feshbach dimers) which can be obtained from a biexciton via rapid adiabatic\nsweeping of the magnetic field across the resonance. The molecules possess\nnon-trivial entanglement properties. Our proposal holds promise for the\nstrongly-correlated photonics and quantum chemistry of light.",
        "positive": "Many-body density and coherence of trapped cold bosons: Many-body densities and correlation functions are of paramount importance for\nunderstanding quantum many-body physics. Here, we present a method to compute\nthem; our approach is general and based on the action of bosonic or fermionic\nannihilation field operators on the many-body wavefunction. We analyze $N = 6$\nquasi-one-dimensional harmonically-trapped bosons with weak to strong contact\ninteraction strength up to the Tonks-Girardeau limit with infinite repulsion\nusing the MultiConfigurational Time-Dependent Hartree method for\nindistinguishable particles (MCTDH-X). We compare our MCTDH-X solutions to the\nanalytical ones in the infinite repulsion regime as well as to the so-called\ncorrelated pair wavefunction approach and find a good agreement. Since\nnumerical approximations are not bound to the cases where analytical solutions\nare known, we thus demonstrate a general method to investigate high-order\nreduced density matrices and correlation functions in systems for which\nanalytical solutions are unknown. We trace the build-up of correlation features\nin the crossover from weak interactions to the Tonks-Girardeau limit and find\nthat the higher-order correlation functions and densities resemble those in the\nTonks-Girardeau limit for way smaller interactions than anticipated from just\nthe one-body density."
    },
    {
        "anchor": "Hydrodynamics with spacetime-dependent scattering length: Hydrodynamics provides a concise but powerful description of long-time and\nlong-distance physics of correlated systems out of thermodynamic equilibrium.\nHere we construct hydrodynamic equations for nonrelativistic particles with a\nspacetime-dependent scattering length and show that it enters constitutive\nrelations uniquely so as to represent the fluid expansion and contraction in\nboth normal and superfluid phases. As a consequence, we find that a leading\ndissipative correction to the contact density due to the spacetime-dependent\nscattering length is proportional to the bulk viscosity ($\\zeta_2$ in the\nsuperfluid phase). Also, when the scattering length is slowly varied over time\nin a uniform system, the entropy density is found to be produced even without\nfluid flows in proportion to the bulk viscosity, which may be useful as a novel\nprobe to measure the bulk viscosity in ultracold-atom experiments.",
        "positive": "Observation of self-patterned defect formation in atomic superfluids --\n  from ring dark solitons to vortex dipole necklaces: Unveiling nonequilibrium dynamics of solitonic and topological defect\nstructures in a multidimensional nonlinear medium is a current frontier across\ndiverse fields. One of the quintessential objects is a ring dark soliton (RDS),\nwhose dynamics are expected to display remarkable interplay between symmetry\nand self-patterned topological defect formation from a transverse (snake)\ninstability, but it has thus far evaded full experimental observations. Here,\nwe report an experimental realization of RDS generation in a two-dimensional\natomic superfluid trapped in a circular box. By quenching the confining box\npotential, we observe an RDS emitted from the edge and its peculiar signature\nin the radial motion. As an RDS evolves, we observe transverse modulations at\ndiscrete azimuthal angles, which clearly result in a patterned formation of a\ncircular vortex dipole array. Through collisions of the vortex dipoles with the\nbox trap, we observe vortex unbinding, vortex pinning to the edge, and emission\nof rarefaction pulses. Our box-quench protocol opens a new way to study\nmultidimensional dark solitons, structured formation of topological defects,\nand potentially the dynamics of ordered quantum vortex matter."
    },
    {
        "anchor": "Probe for bound states of SU(3) fermions and colour deconfinement: Fermionic artificial matter realized with cold atoms grants access to an\nunprecedented degree of control on sophisticated many-body effects with an\nenhanced flexibility of the operating conditions. We consider three-component\nfermions with attractive interactions to study the formation of complex bound\nstates whose nature goes beyond the standard fermion pairing occurring in\nquantum materials. Such systems display clear analogies with quark matter.\nHere, we address the nature of the bound states of a three-component fermionic\nsystem in a ring-shaped trap through the persistent current. In this way, we\ndemonstrate that we can distinguish between color superfluid and trionic bound\nstates. By analyzing finite temperature effects, we show how finite temperature\ncan lead to the deconfinement of bound states. For weak interactions the\ndeconfinement occurs because of scattering states. In this regime, the\ndeconfinement depends on the trade-off between interactions and thermal\nfluctuations temperature. For strong interactions the features of the\npersistent current result from the properties of a suitable gas of bound\nstates.",
        "positive": "Ab initio calculation of Hubbard parameters for Rydberg-dressed atoms in\n  an one-dimensional optical lattice: We obtain ab initio the Hubbard parameters for Rydberg-dressed atoms in an\none-dimensional sinusoidal optical lattice in the basis of maximally localized\nwannier states. Finite range, soft-core inter-atomic interactions become the\ntrait of Rydberg admixed atoms, which can be extended over many neighbouring\nlattice sites. On contrary to dipolar gases, where the interactions follow an\ninverse cubic law, the key feature of Rydberg-dressed interactions being the\npossibility of making neighbouring couplings to the same magnitude as that of\nthe onsite ones. The maximally localized Wannier functions are typically\ncalculated via spread minimization procedure [Phys. Rev. B 56, 12847 (1997)]\nand always found to be real functions apart from a trivial global phase when\nconsidering an isolated set of Bloch bands. For an isolated single Bloch band,\nthe above procedure reduces to a simple quasi-momentum dependent unitary phase\ntransformation. Here, in stead of minimizing the spread, we employ a diagonal\nphase transformation which eliminates the imaginary part of the Wannier\nfunctions. The resulting Wannier states are found to be maximally localized and\nin exact agreement with those obtained via spread minimization procedure. Using\nthat we calculate the Hubbard couplings from the Rydberg-admixed interactions,\nincluding dominant density assisted tunnelling coefficients. In the end we\nprovide realistic lattice parameters for the state of the art experimental\nRydberg dressed Rubidium setup."
    },
    {
        "anchor": "Macroscopic Quantum Tunneling of Solitons in Bose-Einstein Condensates: We study the quantum tunneling dynamics of many-body entangled solitons\ncomposed of ultracold bosonic gases in 1D optical lattices. A bright soliton,\nconfined by a potential barrier, is allowed to tunnel out of confinement by\nreducing the barrier width and for varying strengths of attractive\ninteractions. Simulation of the Bose Hubbard Hamiltonian is performed with\ntime-evolving block decimation. We find the characteristic $1/e$ time for the\nescape of the soliton, substantially different from the mean field prediction,\nand address how many-body effects like quantum fluctuations, entanglement, and\nnonlocal correlations affect macroscopic quantum tunneling; number fluctuations\nand second order correlations are suggested as experimental signatures. We find\nthat while the escape time scales exponentially in the interactions, the time\nat which both the von Neumann entanglement entropy and the slope of number\nfluctuations is maximized scale only linearly.",
        "positive": "Quantum collision theory in flat bands: We consider quantum scattering of particles in media exhibiting strong\ndispersion degeneracy. In particular, we study flat-banded lattices and\nlinearly dispersed energy bands. The former constitute a prime example of\nsingle-particle frustration while the latter show degeneracy at the few- and\nmany-particle level. We investigate both impurity and two-body scattering and\nshow that, quite generally, scattering does not occur, which we relate to the\nfact that transition matrices vanish on the energy shell. We prove that\nscattering is instead replaced by projections onto band-projected eigenstates\nof the interaction potential. We then use the general results to obtain\nlocalised flat band states that are eigenstates of impurity potentials with\nvanishing eigenvalues in one-dimensional flat bands and study the particular\ncase of a sawtooth lattice. We also uncover the relation between certain\nsolutions of one-dimensional systems that have been categorised as \"strange\",\nand the scattering states in linearly dispersed continuum systems."
    },
    {
        "anchor": "Ising Deconfinement Transition Between Feshbach-Resonant Superfluids: We investigate the phase diagram of bosons interacting via Feshbach-resonant\npairing interactions in a one-dimensional lattice. Using large scale density\nmatrix renormalization group (DMRG) and field theory techniques we explore the\natomic and molecular correlations in this low-dimensional setting. We provide\ncompelling evidence for an Ising deconfinement transition occurring between\ndistinct superfluids and extract the Ising order parameter and correlation\nlength of this unusual superfluid transition. This is supported by results for\nthe entanglement entropy which reveal both the location of the transition and\ncritical Ising degrees of freedom on the phase boundary.",
        "positive": "Bose-Einstein Condensate in Weak 3d Isotropic Speckle Disorder: The effect of a weak three-dimensional (3d) isotropic laser speckle disorder\non various thermodynamic properties of a dilute Bose gas is considered at zero\ntemperature. First, we summarize the derivation of the autocorrelation function\nof laser speckles in 1d and 2d following the seminal work of Goodman. The goal\nof this discussion is to show that a Gaussian approximation of this function,\nproposed in some recent papers, is inconsistent with the general background of\nlaser speckle theory. Then we propose a possible experimental realization for\nan isotropic 3d laser speckle potential and derive its corresponding\nautocorrelation function. Using a Fourier transform of that function, we\ncalculate both condensate depletion and sound velocity of a Bose-Einstein\ncondensate as disorder ensemble averages of such a weak laser speckle potential\nwithin a perturbative solution of the Gross-Pitaevskii equation. By doing so,\nwe reproduce the expression of the normalfluid density obtained earlier within\nthe treatment of Landau. This physically transparent derivation shows that\ncondensate particles, which are scattered by disorder, form a gas of\nquasiparticles which is responsible for the normalfluid component."
    },
    {
        "anchor": "Observation of universal behaviour of ultracold quantum critical gases: Quantum critical matter has already been studied in many systems, including\ncold atomic gases. We report the observation of a universal behaviour of\nultracold quantum critical Bose gases in a one-dimensional optical lattice. In\nthe quantum critical region above the Berezinskii-Kosterlitz-Thouless\ntransition, the relative phase fluctuations between neighboring subcondensates\nand spatial phase fluctuations of quasi-2D subcondensates coexist. We study the\ndensity probability distribution function when both these two phase\nfluctuations are considered. A universal exponential density probability\ndistribution is demonstrated experimentally, which agrees well with a simple\ntheoretical model by considering these two phase fluctuations.",
        "positive": "Breathing mode in the Bose-Hubbard chain with a harmonic trapping\n  potential: We investigate the breathing mode of harmonically trapped bosons in an\noptical lattice at small site occupancies. The Bose-Hubbard model with a\ntrapping potential is used to describe the breathing-mode dynamics initiated\nthrough weak quenches of the trap strength. We connect to results for continuum\nbosons (Lieb-Liniger and Gross-Pitaevskii results) and also present deviations\nfrom continuum physics. We take a spectral perspective, identifying the\nbreathing mode frequency with a particular energy gap in the spectrum of the\ntrapped Bose-Hubbard Hamiltonian. We present the low energy eigenspectrum of\nthe trapped many-boson system, and study overlaps of the initial state with\neigenstates of the quenched Hamiltonian. There is an intermediate interaction\nregime, between a \"free-boson\" limit and a \"free-fermion\" limit, in which the\nBose-Hubbard breathing mode frequency approaches the Gross-Pitaevskii\nprediction. In addition, we present a striking failure of the time-dependent\nGutzwiller approximation for describing breathing modes."
    },
    {
        "anchor": "Detecting antiferromagnetism of atoms in an optical lattice via optical\n  Bragg scattering: Antiferromagnetism of ultracold fermions in an optical lattice can be\ndetected by Bragg diffraction of light, in analogy to the diffraction of\nneutrons from solid state materials. A finite sublattice magnetization will\nlead to a Bragg peak from the (1/2 1/2 1/2) crystal plane with an intensity\ndepending on details of the atomic states, the frequency and polarization of\nthe probe beam, the direction and magnitude of the sublattice magnetization,\nand the finite optical density of the sample. Accounting for these effects we\nmake quantitative predictions about the scattering intensity and find that with\nexperimentally feasible parameters the signal can be readily measured with a\nCCD camera or a photodiode and used to detect antiferromagnetic order.",
        "positive": "Shape effects of localized losses in quantum wires: dissipative\n  resonances and nonequilibrium universality: We study the effects of the spacial structure of localized losses in\nweakly-interacting fermionic quantum wires. We show that multiple dissipative\nimpurities give rise to resonant effects visible in the transport properties\nand the particles' momentum distribution. These resonances can enhance or\nsuppress the effective particle losses in the wire. Moreover, we investigate\nthe interplay between interactions and the impurity shape and find that,\ndifferently from the coherent scatterer case, the impurity shape modifies the\nscaling of the scattering probabilities close to the Fermi momentum. We show\nthat, while the fluctuation-induced quantum Zeno effect is robust against the\nshape of the impurities, the fluctuation-induced transparency is lifted\ncontinuously. This is reflected in the emergence of a continuous line of fixed\npoints in the renormalization group flow of the scattering probabilities."
    },
    {
        "anchor": "Self trapping of a dipolar Bose-Einstein condensate in a double well: We study the Josephson oscillation and self trapping dynamics of a\ncigar-shaped dipolar Bose-Einstein condensate of $^{52}$Cr atoms polarized\nalong the symmetry axis of an axially-symmetric double-well potential using the\nnumerical solution of a mean-field model, for dominating repulsive contact\ninteraction (large positive scattering length a) over an anisotropic dipolar\ninteraction. Josephson-type oscillation emerges for small and very large number\nof atoms, whereas self trapping is noted for an intermediate number of atoms.\nThe dipolar interaction pushes the system away from self trapping towards\nJosephson oscillation. We consider a simple two-mode description for a\nqualitative understanding of the dynamics.",
        "positive": "Creation of p-wave Feshbach molecules in the selected angular momentum\n  states using an optical lattice: We selectively create p-wave Feshbach molecules in the $m_{l}=\\pm 1$ orbital\nangular momentum projection state of $^{6}$Li. We use an optical lattice\npotential to restrict the relative momentum of the atoms such that only the\n$m_{l}=\\pm 1$ molecular state couples to the atoms at the Feshbach resonance.\nWe observe the hollow-centered dissociation profile, which is a clear\nindication of the selective creation of p-wave molecules in the $m_{l}=\\pm1$\nstates. We also measure the dissociation energy of the p-wave molecules created\nin the optical lattice and develop a theoretical formulation to explain the\ndissociation energy as a function of the magnetic field ramp rate for\ndissociation. The capability of selecting one of the two closely-residing\np-wave Feshbach resonances is useful for the precise characterization of the\np-wave Feshbach resonances."
    },
    {
        "anchor": "Dimensional coupling induced current reversal in two-dimensional driven\n  lattices: We show that the direction of directed particle transport in a two\ndimensional ac-driven lattice can be dynamically reversed by changing the\nstructure of the lattice in the direction perpendicular to the applied driving\nforce. These structural changes introduce dimensional coupling effects, the\nstrength of which governs the timescale of the current reversals. The\nunderlying mechanism is based on the fact that dimensional coupling allows the\nparticles to explore regions of phase space which are inaccessible otherwise.\nThe experimental realization for cold atoms in ac-driven optical lattices is\ndiscussed.",
        "positive": "Quantum transport in the black-hole configuration of an atom condensate\n  outcoupled through an optical lattice: The outcoupling of a Bose-Einstein condensate through an optical lattice\nprovides an interesting scenario to study quantum transport phenomena or the\nanalog Hawking effect as the system can reach a quasi-stationary black-hole\nconfiguration. We devote this work to characterize the quantum transport\nproperties of quasi-particles on top of this black-hole configuration by\ncomputing the corresponding scattering matrix. We find that most of the\nfeatures can be understood in terms of the usual Schr\\\"odinger scattering. In\nparticular, a transmission band appears in the spectrum, with the normal-normal\ntransmission dominating over the anomalous-normal one. We show that this\npicture still holds in a realistic experimental situation where the actual\nGaussian envelope of the optical lattice is considered. A peaked resonant\nstructure is displayed near the upper end of the transmission band, which\nsuggests that the proposed setup is a good candidate to provide a clear signal\nof spontaneous Hawking radiation."
    },
    {
        "anchor": "Quantum simulation of hadronic states with Rydberg-dressed atoms: The phenomenon of confinement is well known in high-energy physics and can\nalso be realized for low-energy domain-wall excitations in one-dimensional\nquantum spin chains. A bound state consisting of two domain-walls can behave\nlike a meson, and in a recent work of Vovrosh et al. [PRX Quantum 3, 040309\n(2022)] , it was demonstrated that a pair of mesons could dynamically form a\nmeta-stable confinement-induced bound state (consisting of four domain-walls)\nakin to a hadronic state. However, the protocol discussed in Vovrosh et al.\n[PRX Quantum 3, 040309 (2022)] involving the use of interactions with\ncharacteristically non-monotonic distance dependence is not easy to come by in\nnature, thus, posing a challenge for its experimental realization. In this\nregard, Rydberg atoms can provide the required platform for simulating\nconfinement-related physics. We exploit the flexibility offered by interacting\nRydberg-dressed atoms to engineering modified spin-spin interactions for the\none-dimensional transverse field Ising model. Our numerical simulations show\nhow Rydberg-dressed interactions can give rise to a variety of effective\npotentials that are suitable for hadron formation, which opens the possibility\nof simulating confinement physics with Rydberg platforms as a viable\nalternative to current trapped-ion experiments.",
        "positive": "Fluctuation-induced forces in confined ideal and imperfect Bose gases: Fluctuation-induced forces are investigated for ideal and imperfect Bose\ngases confined to $d$-dimensional films of size $\\infty^{d-1}\\times D$ under\nperiodic (P), antiperiodic (A), Dirichlet-Dirichlet (DD), Neumann-Neumann (NN),\nand Robin (R) boundary conditions (BCs). The full scaling functions\n$\\Upsilon^{\\text{BC}}_d(x_\\lambda=D/\\lambda_{th},{x_\\xi=D/\\xi})$ of the\nresidual reduced grand potential per area,\n$\\varphi_{\\text{res},d}^{\\text{BC}}(T,\\mu,D)=D^{-(d-1)}\\Upsilon_d^{\\text{BC}}(x_\\lambda,x_\\xi)$,\nare determined for the ideal gas case with these BCs, where $\\lambda_{th}$ and\n$\\xi$ are the thermal de-Broglie wavelength and the bulk correlation length,\nrespectively. The scaling functions $\\Theta^{\\text{BC}}_d(x_\\xi)\\equiv\n\\Upsilon_d^{\\text{BC}}(\\infty,x_\\xi)$ describing the critical behavior at the\nbulk condensation transition are shown to agree with those previously\ndetermined from a massive free $O(2)$ theory for\n$\\text{BC}=\\text{P},\\text{A},\\text{DD},\\text{DN},\\text{NN}$. For $d=3$, they\nare expressed in closed analytical form. The analogous functions\n$\\Upsilon_d^{\\text{BC}}(x_\\lambda,x_\\xi,c_1D,c_2D)$ and\n$\\Theta^{\\text{R}}_d(x_\\xi,c_1D,c_2D)$ under the RBCs\n$(\\partial_z-c_1)\\phi|_{z=0}=(\\partial_z+c_2)\\phi|_{z=D}=0$ with $c_1\\ge 0$ and\n$c_2\\ge 0$ are also determined. The functions\n$\\Upsilon_{\\infty,d}^{\\text{P}}(x_\\lambda,x_\\xi)$ and\n$\\Phi_{\\infty,d}^{\\text{P}}(x_\\xi)$ for the imperfect Bose gas are shown to\nagree with those of the interacting Bose gas with $n\\to\\infty$ internal degrees\nof freedom. Hence for ${d=3}$, $\\Phi_{\\infty,d}^{\\text{P}}(x_\\xi)$ is known\nexactly in closed analytic form. A modified imperfect Bose-gas model with free\nBC is introduced that corresponds to the limit $n\\to\\infty$ of this interacting\nBose gas. Exact results for the function\n$\\Theta_{\\infty,3}^{\\mathbb{DD}}(x_\\xi)$ therefore follow from those of the\n$O(2n)$ $\\phi^4$ model for $n\\to\\infty$."
    },
    {
        "anchor": "Observation of an Efimov resonance in an ultracold mixture of atoms and\n  weakly bound dimers: We discuss our recent observation of an atom-dimer Efimov resonance in an\nultracold mixture of Cs atoms and Cs_2 Feshbach molecules [Nature Phys. 5, 227\n(2009)]. We review our experimental procedure and present additional data\ninvolving a non-universal g-wave dimer state, to contrast our previous results\non the universal s-wave dimer. We resolve a seeming discrepancy when\nquantitatively comparing our experimental findings with theoretical results\nfrom effective field theory.",
        "positive": "Thermodynamic measurement of the sound velocity of a Bose gas across the\n  transition to Bose-Einstein condensation: We present an alternative method for determining the sound velocity in atomic\nBose-Einstein condensates, based on thermodynamic global variables. The total\nnumber of trapped atoms was as a function of temperature carefully studied\nacross the phase transition, at constant volume. It allowed us to evaluate the\nsound velocity resulting in consistent values from the quantum to classical\nregime, in good agreement with previous results found in literature. We also\nprovide some insight about the dominant sound mode (thermal or superfluid)\nacross a wide temperature range."
    },
    {
        "anchor": "Particle partition entanglement of bosonic Luttinger liquids: We consider the R\\'{e}nyi entanglement entropy of bosonic Luttinger liquids\nunder a particle bipartition and demonstrate that the leading order finite-size\nscaling is logarithmic in the system size with a prefactor equal to the inverse\nLuttinger parameter. While higher order corrections involve a microscopic\nlength scale, the leading order scaling depends only on this sole dimensionless\nparameter which characterizes the low energy quantum hydrodynamics. This result\ncontrasts the leading entanglement entropy scaling under a spatial bipartition,\nfor which the coefficient is universal and independent of the Luttinger\nparameter. Using quantum Monte Carlo calculations, we explicitly confirm the\nscaling predictions of Luttinger liquid theory for the Lieb-Liniger model of\n$\\delta$-function interacting bosons in the one dimensional spatial continuum.",
        "positive": "High-temperature limit of the resonant Fermi gas: We use the virial expansion to investigate the behavior of the two-component,\nattractive Fermi gas in the high-temperature limit, where the system smoothly\nevolves from weakly attractive fermions to weakly repulsive bosonic dimers as\nthe short-range attraction is increased. We present a new formalism for\ncomputing the virial coefficients that employs a diagrammatic approach to the\ngrand potential and allows one to easily include an effective range $R^*$ in\nthe interaction. In the limit where the thermal wavelength $\\lambda \\ll R^*$,\nthe calculation of the virial coefficients is perturbative even at unitarity\nand the system resembles a weakly interacting Bose-Fermi mixture for all\nscattering lengths $a$. By interpolating from the perturbative limits\n$\\lambda/|a| \\gg 1$ and $R^*/\\lambda \\gg 1$, we estimate the value of the\nfourth virial coefficient at unitarity for $R^*=0$ and we find that it is close\nto the value obtained in recent experiments. We also derive the equations of\nstate for the pressure, density and entropy, as well as the spectral function\nat high temperatures."
    },
    {
        "anchor": "Fluctuations of squeezing fields beyond the Tomonaga--Luttinger liquid\n  paradigm: The concept of Tomonaga--Luttinger liquids (TLL) on the basis of the\nfree-boson models is ubiquitous in theoretical descriptions of low-energy\nproperties in one-dimensional quantum systems. In this work, we develop a\nsqueezed-field path-integral description for gapless one-dimensional systems\nbeyond the free-boson picture of the TLL paradigm. In the squeezed-field\ndescription, the parameter of the Bogoliubov transformation for the TL\nHamiltonian becomes a dynamical squeezing field, and its fluctuations give rise\nto corrections to the free-boson results. We derive an effective nonlinear\nLagrangian describing the dispersion relation of the squeezing field, and\ninteractions between the excitations of the TLL and the squeezing modes. Using\nthe effective Lagrangian, we analyze the imaginary-time correlation function of\na vertex operator in the non-interacting limit. We show that a side-band branch\nemerges due to the fluctuation of the squeezing field, in addition to the\nstandard branch of the free-boson model of the TLL paradigm. Furthermore, we\nperturbatively analyze the spectral function of the density fluctuations for an\nultracold Bose gas in one dimension. We evaluate the renormalized values of the\nphase velocities and spectral weights of the TLL and side-band branches due to\nthe interaction between the TLL and the squeezing modes. At zero temperature,\nthe renormalized dispersion relations are linear in the momentum, but at\nnonzero temperatures, these acquire a nonlinear dependence on the momentum due\nto the thermal population of the excitation branches.",
        "positive": "Rotating quantum droplets confined in an anharmonic potential: We investigate the rotational properties of quantum droplets, which form in a\nmixture of two Bose-Einstein condensates, in the presence of an anharmonic\ntrapping potential. We identify various phases as the atom number and the\nangular momentum/angular velocity of the trap vary. These phases include\ncenter-of-mass-like excitation (without, or with vortices), vortices of single\nand multiple quantization, etc. Finally, we compare our results with those of\nthe single-component problem."
    },
    {
        "anchor": "Quantum phase transitions in an interacting atom-molecule boson model: We study the quantum phase transitions of a model that describes the\ninterconversion of interacting bosonic atoms and molecules. Using a classical\nanalysis, we identify a threshold coupling line separating a molecular phase\nand a mixed phase. Through studies of the energy gap, von Neumann entanglement\nentropy, and fidelity, we give evidence that this line is associated to a\nboundary line in the ground-state phase diagram of the quantum system.",
        "positive": "Enhanced transport of spin-orbit coupled Bose gases in disordered\n  potentials: Anderson localization is a single particle localization phenomena in\ndisordered media that is accompanied by an absence of diffusion. Spin-orbit\ncoupling (SOC) describes an interaction between a particle's spin and its\nmomentum that directly affects its energy dispersion, for example creating\ndispersion relations with gaps and multiple local minima. We show theoretically\nthat combining one-dimensional spin-orbit coupling with a transverse Zeeman\nfield suppresses the effects of disorder, thereby increasing the localization\nlength and conductivity. This increase results from a suppression of back\nscattering between states in the gap of the SOC dispersion relation. Here, we\nfocus specifically on the interplay of disorder from an optical speckle\npotential and SOC generated by two-photon Raman processes in quasi-1D\nBose-Einstein condensates. We first describe back-scattering using a Fermi's\ngolden rule approach, and then numerically confirm this picture by solving the\ntime-dependent 1D Gross Pitaevskii equation for a weakly interacting\nBose-Einstein condensate with SOC and disorder. We find that on the 10's of\nmillisecond time scale of typical cold atom experiments moving in harmonic\ntraps, initial states with momentum in the zero-momentum SOC gap evolve with\nnegligible back-scattering, while without SOC these same states rapidly\nlocalize."
    },
    {
        "anchor": "Evaporative cooling of a small number of atoms in a single-beam\n  microscopic dipole trap: We demonstrate experimentally the evaporative cooling of a few hundred\nrubidium 87 atoms in a single-beam microscopic dipole trap. Starting from 800\natoms at a temperature of 125microKelvins, we produce an unpolarized sample of\n40 atoms at 110nK, within 3s. The phase-space density at the end of the\nevaporation reaches unity, close to quantum degeneracy. The gain in phase-space\ndensity after evaporation is 10^3. We find that the scaling laws used for much\nlarger numbers of atoms are still valid despite the small number of atoms\ninvolved in the evaporative cooling process. We also compare our results to a\nsimple kinetic model describing the evaporation process and find good agreement\nwith the data.",
        "positive": "Stability and Tunneling Dynamics of a Dark-Bright Soliton Pair in a\n  Harmonic Trap: We consider a binary repulsive Bose-Einstein condensate in a harmonic trap in\none spatial dimension and investigate particular solutions consisting of two\ndark-bright (DB) solitons. There are two different stationary solutions\ncharacterized by the phase difference in the bright component, in-phase and\nout-of-phase states. We show that above a critical particle number in the\nbright component, a symmetry breaking bifurcation of the pitchfork type occurs\nthat leads to a new asymmetric solution whereas the parental branch, i.e., the\nout-of-phase state becomes unstable. These three different states support\ndifferent small amplitude oscillations, characterized by an almost stationary\ndensity of the dark component and a tunneling of the bright component between\nthe two dark solitons. Within a suitable effective double-well picture, these\ncan be understood as the characteristic features of a Bosonic Josephson\nJunction (BJJ), and we show within a two-mode approach that all characteristic\nfeatures of the BJJ phase space are recovered. For larger deviations from the\nstationary states, the simplifying double-well description breaks down due to\nthe feedback of the bright component onto the dark one, causing the solitons to\nmove. In this regime we observe intricate anharmonic and aperiodic dynamics,\nexhibiting remnants of the BJJ phase space."
    },
    {
        "anchor": "Bose-Fermi dualities for arbitrary one-dimensional quantum systems in\n  the universal low energy regime: I consider general interacting systems of quantum particles in one spatial\ndimension. These consist of bosons or fermions, which can have any number of\ncomponents, arbitrary spin or a combination thereof, featuring low-energy two-\nand multiparticle interactions. The single-particle dispersion can be Galilean\n(non-relativistic), relativistic, or have any other form that may be relevant\nfor the continuum limit of lattice theories. Using an algebra of generalized\nfunctions, statistical transmutation operators that are genuinely unitary are\nobtained, putting bosons and fermions in a one-to-one correspondence without\nthe need for a short-distance hard core. In the non-relativistic case,\nlow-energy interactions for bosons yield, order by order, fermionic dual\ninteractions that correspond to the standard low-energy expansion for fermions.\nIn this way, interacting fermions and bosons are fully equivalent to each other\nat low energies. While the Bose-Fermi mappings do not depend on microscopic\ndetails, the resulting statistical interactions heavily depend on the kinetic\nenergy structure of the respective Hamiltonians. These statistical interactions\nare obtained explicitly for a variety of models, and regularized and\nrenormalized in the momentum representation, which allows for theoretically and\ncomputationally feasible implementations of the dual theories. The mapping is\nrewritten as a gauge interaction, and one-dimensional anyons are also\nconsidered.",
        "positive": "Intermittent emission of particles from a Bose-Einstein condensate in a\n  one-dimensional lattice: We investigate particle emission from a Bose-Einstein condensate with\nperiodically modulated interactions in a one-dimensional lattice. Within\nperturbative analysis, which leads to instabilities for discrete modes, we\nobtain the main regimes where the system can emit a large particle jet, and\nfind that the emission is distinctly intermittent rather than continuous. The\ntime evolution of the trapped particles exhibits a stair-like decay, and a\nlarger drive induces a more significant intermittency. We further shed light on\nthe dynamics of the stimulating process, and demonstrate that instead of a real\nsuspension, the intermittency represents a build-up stage of the system. The\ntheoretical framework might be generalized to the explorations on multiple-site\nsystems with analogous configurations and couplings, and offer new insights\ninto other fundamental nonequilibrium problems."
    },
    {
        "anchor": "Strongly correlated quantum droplets in quasi-1D dipolar Bose gas: We exploit a few- to many-body approach to study strongly interacting dipolar\nbosons in the quasi-one-dimensional system. The dipoles attract each other\nwhile the short range interactions are repulsive. Solving numerically the\nmulti-atom Schr\\\"{o}dinger equation, we discover that such systems can exhibit\nnot only the well known bright soliton solutions but also novel quantum\ndroplets for a strongly coupled case. For larger systems, basing on microscopic\nproperties of the found few-body solution, we propose a new equation for a\ndensity amplitude of atoms. It accounts for fermionization for strongly\nrepelling bosons by incorporating the Lieb-Liniger energy in a local density\napproximation and approaches the standard Gross-Pitaevskii equation (GPE) in\nthe weakly interacting limit. Not only does such a framework provide an\nalternative mechanism of the droplet stability, but it also introduces means to\nfurther analyze this previously unexplored quantum phase. In the limiting\nstrong repulsion case, yet another simple multi-atom model is proposed. We\nstress that the celebrated Lee-Huang-Yang term in the GPE is not applicable in\nthis case.",
        "positive": "Modulation of a quantized vortex street with a vibrating obstacle: Dynamics of a superfluid flow past an obstacle are investigated by solving\nthe Gross-Pitaevskii equation numerically. For an appropriate velocity and size\nof the obstacle, quantized vortices are periodically generated in the wake,\nwhich form a Benard-von Karman vortex street. It is found that vibration of an\nobstacle modulates the vortex street breaking a symmetry."
    },
    {
        "anchor": "Quantum Adsorption of an Electron to Porous Silicon: Using the theory of Zhang and Clougherty [Phys. Rev. Lett. 108, 173202\n(2012)], we provide detailed supporting information concerning the numerical\ncalculations of the probability ${\\it s}(E)$ for a low-energy electron with\nincident energy E adsorbing to the surface of nanoporous silicon.",
        "positive": "Mean-field description of dipolar bosons in triple-well potentials: We investigate the ground state properties of a polarized dipolar\nBose-Einstein condensate trapped in a triple-well potential. By solving the\ndipolar Gross-Pitaevskii equation numerically for different geometries we\nidentify states which reveal the non-local character of the interaction.\nDepending on the strength of the contact and dipolar interaction we depict the\nstable and unstable regions in parameter space."
    },
    {
        "anchor": "Evanescent Modes and Step-like Acoustic Black Holes: We consider a model of an acoustic black hole formed by a quasi-one\ndimensional Bose-Einstein condensate with a step-like horizon. This system is\nanalyzed by solving the corresponding Bogoliubov-de Gennes equation with an\nappropriate matching condition at the jump. When the step is between a subsonic\nand supersonic flow, a sonic horizon develops and in addition to the scattering\ncoefficients we compute the distribution of the accompanying analogue Hawking\nradiation. Additionally, in response to the abrupt variation in flow and\nnon-linear Bogoliubov dispersion relation, evanescent solutions of the\nBogoliubov-de Gennes equation also appear and decay out from the horizon. We\nbound this decay length and show that these modes produce a modulation of\nobservables outside the event horizon by their interference with outgoing\nHawking flux. We go further and find specific superpositions of ingoing\neigenmodes which exhibit coherent cancellation of the Hawking flux outside the\nhorizon but nevertheless have evanescent support outside the black hole. We\nconclude by speculating that when quasiparticle interactions are included,\nevanescent modes may yield a leakage of information across the event horizon\nvia interactions between the real outgoing Hawking flux and the virtual\nevanescent modes, and that we may expect this as a generic feature of models\nwhich break Lorentz invariance at the UV (Planck) scale.",
        "positive": "Rydberg impurity in a Fermi gas: Quantum statistics and rotational\n  blockade: We consider the quench of an atomic impurity via a single Rydberg excitation\nin a degenerate Fermi gas. The Rydberg interaction with the background gas\nparticles induces an ultralong-range potential that binds particles to form\ndimers, trimers, tetramers, etc. Such oligomeric molecules were recently\nobserved in atomic Bose-Einstein condensates. In this work, we demonstrate with\na functional determinant approach that quantum statistics and fluctuations have\nobservable spectral consequences. We show that the occupation of molecular\nstates is predicated on the Fermi statistics, which suppresses molecular\nformation in an emergent molecular shell structure. At large gas densities this\nleads to spectral narrowing, which can serve as a probe of the quantum gas\nthermodynamic properties."
    },
    {
        "anchor": "Dark quantum droplets and solitary waves in beyond-mean-field\n  Bose-Einstein condensate mixtures: Quantum liquid-like states of matter have been realized in an ongoing series\nof experiments with ultracold Bose gases. Using a combination of analytical and\nnumerical methods we identify the specific criteria for the existence of dark\nsolitons in beyond-mean-field binary condensates, revealing how these\nexcitations exist for both repulsive and attractive interactions, the latter\nleading to dark quantum droplets with properties intermediate between a dark\nsoliton and a quantum droplet. The phenomenology of the these excitations are\nexplored within the full parameter space of the model, revealing the novel\nspatial profile of the excitation that differs significantly from the\nZakharov-Shabat (ZS) soliton; leading to a negative effective mass that is\nenhanced in the presence of the quantum fluctuations. Finally the dynamics of\npairs of the excitations are explored, showing non-integrable dynamics and dark\nsoliton bound-states in the attractive regime.",
        "positive": "Ginzburg-Landau theory of a trapped Fermi gas with a BEC-BCS crossover: The Ginzburg-Landau theory of a trapped Fermi gas with a BEC-BCS crossover is\nderived by the path-integral method. In addition to the standard\nGinzburg-Landau equation, a second equation describing the total atom density\nis obtained. These two coupled equations are necessary to describe both\nhomogeneous and inhomogeneous systems. The Ginzburg-Landau theory is valid near\nthe transition temperature $T_c$ on both sides of the crossover. In the\nweakly-interacting BEC region, it is also accurate at zero temperature where\nthe Ginzburg-Landau equation can be mapped onto the Gross-Pitaevskii (GP)\nequation. The applicability of GP equation at finite temperature is discussed.\nOn the BEC side, the fluctuation of the order parameter is studied and the\nrenormalization to the molecule coupling constant is obtained."
    },
    {
        "anchor": "Non-Markovian master equation for quantum transport of fermionic\n  carriers: We propose a simple, yet feasible, model for quantum transport of fermionic\ncarriers across tight-binding chain connecting two reservoirs maintained at\narbitrary temperatures and chemical potentials. The model allows for elementary\nderivation of the master equation for the reduced single particle density\nmatrix in a closed form in both Markov and Born approximations. In the Markov\napproximation the master equation is solved analytically, whereas in the Born\napproximation the problem is reduced to an algebraic equation for the single\nparticle density matric in the Redfield form. The non-Markovian equation is\nshown to lead to resonant transport similar to Landauer's conductance.",
        "positive": "Tunneling transport of unitary fermions across the superfluid transition: We investigate the transport of a Fermi gas with unitarity-limited\ninteractions across the superfluid phase transition, probing its response to a\ndirect current (dc) drive through a tunnel junction. As the superfluid critical\ntemperature is crossed from below, we observe the evolution from a highly\nnonlinear to an Ohmic conduction characteristics, associated with the critical\nbreakdown of the Josephson dc current induced by pair condensate depletion.\nMoreover, we reveal a large and dominant anomalous contribution to resistive\ncurrents, which reaches its maximum at the lowest attained temperature,\nfostered by the tunnel coupling between the condensate and phononic\nBogoliubov-Anderson excitations. Increasing the temperature, while the zeroing\nof supercurrents marks the transition to the normal phase, the conductance\ndrops considerably but remains much larger than that of a normal, uncorrelated\nFermi gas tunneling through the same junction. We attribute such enhanced\ntransport to incoherent tunneling of sound modes, which remain weakly damped in\nthe collisional hydrodynamic fluid of unpaired fermions at unitarity."
    },
    {
        "anchor": "Strong parity effect of particle number in the interference fringes of\n  Bose-Einstein condensates released from a double-well potential: We study the parity effect of the particle number in the interference fringes\nof a Bose-Einstein condensate released from a double-well potential. For a\ncoherently splitting condensate in the double-well potential, with a decoupled\ntwo-mode Bose-Hubbard model, there is well-known phase diffusion because of\ninteratomic interactions. After a specific holding time of the double-well\npotential, the phase diffusion will make the interference patterns in the\ndensity distribution depend strongly on the parity of the total particle number\nby further overlapping two condensates. This parity effect originates from the\nquantized relative phase about the total particle number. The experimental\nscheme to observe this \"even-odd\" effect of the particle number is discussed.",
        "positive": "Quantum phases of quadrupolar Fermi gases in optical lattices: We introduce a new platform for quantum simulation of many-body systems based\non nonspherical atoms or molecules with zero dipole moment but possessing a\nsignificant value of electric quadrupole moment. We consider a quadrupolar\nFermi gas trapped in a 2D square optical lattice, and show that the peculiar\nsymmetry and broad tunability of the quadrupole-quadrupole interaction results\nin a rich phase diagram encompassing unconventional BCS and charge density wave\nphases, and opens up a perspective to create topological superfluid.\nQuadrupolar species, such as metastable alkaline-earth atoms and homonuclear\nmolecules, are stable against chemical reactions and collapse and are readily\navailable in experiment at high densities."
    },
    {
        "anchor": "Steady-state many-body entanglement of hot reactive fermions: Entanglement is typically created via systematic intervention in the time\nevolution of an initially unentangled state, which can be achieved by coherent\ncontrol, carefully tailored non-demolition measurements, or dissipation in the\npresence of properly engineered reservoirs. In this paper we show that\ntwo-component Fermi gases at ~\\mu K temperatures naturally evolve, in the\npresence of reactive two-body collisions, into states with highly entangled\n(Dicke-type) spin wavefunctions. The entanglement is a steady-state property\nthat emerges---without any intervention---from uncorrelated initial states, and\ncould be used to improve the accuracy of spectroscopy in experiments with\nfermionic alkaline earth atoms or fermionic groundstate molecules.",
        "positive": "Non-Hamiltonian Dynamics of Quantized Vortices in Bose-Einstein\n  Condensates: The dynamics of quantized vortices in weakly interacting superfluids are\noften modeled by a nonlinear Schr\\\"odinger equation. In contrast, we show that\nquantized vortices in fact obey a non-Hamiltonian evolution equation, which\nenhances dispersion along the vortex line while introducing a gain mechanism.\nThis allows the vortex medium to support a helical shock front propagating\nahead of a dissipative soliton. This dynamic relaxes localized curvature events\ninto Kelvin wave packets. Consequently, a beyond local induction model provides\na pathway for decay in low-temperature quantum turbulence."
    },
    {
        "anchor": "Stable Collective Dynamics of Two-Level Systems Coupled by Dipole\n  Interactions: We study the dynamics of a set of two-level systems coupled by dipolar\ninteractions under a resonant external Rabi drive. The two-level systems are\nprepared initially in a coherent product state, and we ask how the\nnon-equilibrium conditions caused by the drive affect this coherence. We study\nthe full non-linear dynamics of the coupled two-level systems within a\nclassical approximation by analysing numerically the equations of motion and\ndetermining the stability of the collective coherent state within classical\nFloquet theory. We establish the behaviour analytically in the high Rabi\ncoupling limit by employing a Magnus expansion and spin wave analysis. Our\nresults show that, typically, the dipole interactions between the two-level\nsystems lead to instabilities that cause a breakdown of the collective Rabi\noscillations. However, we identify parameter regimes for which the two-level\nsystems undergo collective coherent Rabi oscillations even in the presence of\nthe dipole interactions.",
        "positive": "Overlap of exact and Gross-Pitaevskii wavefunctions in Bose-Einstein\n  condensates of dilute gases: It has been proven theoretically for bosons with two-body repulsive\ninteraction potentials in the dilute limit that the Gross-Pitaevskii equation\nprovides the exact energy and density per particle as does the basic\nmany-particle Schroedinger equation [Lieb and Seiringer, Phys. Rev. Lett. 88,\n170409 (2002)]. Here, we investigate the overlap of the Gross-Pitaevskii and\nexact ground state wavefunctions. It is found that this overlap is always\nsmaller than unity and may even vanish in spite of the fact that both\nwavefunctions provide the same energy and density per particle. Consequences\nare discussed."
    },
    {
        "anchor": "Measurement of an Efimov trimer binding energy in a three-component\n  mixture of 6Li: The binding energy of an Efimov trimer state was precisely determined via\nradio-frequency association. It is found that the measurement results\nsignificantly shift with temperature, but that the shift can be made negligible\nat the lowest temperature in our experiment. The obtained trimer binding energy\nreveals a significant deviation from the nonuniversal theory prediction based\non a three-body parameter with a monotonic energy dependence.",
        "positive": "Interference induced anisotropy in a two-dimensional dark state optical\n  lattice: We describe a two-dimensional optical lattice for ultracold atoms with\nspatial features below the diffraction limit created by a bichromatic optical\nstanding wave. At every point in space these fields couple the internal atomic\nstates in a three-level Lambda coupling configuration. Adiabatically following\nthe local wavefunction of the resulting dark state yields a spatially uniform\nBorn-Oppenheimer potential augmented by geometric scalar and vector potentials\nappearing due to spatially rapid changes of the wavefunction. Depending on\nsystem parameters, we find that the geometric scalar potential can interpolate\nfrom a 2D analogue of the Kronig-Penney lattice, to an array of tubes with a\nzig-zag shaped barrier. The geometric vector potential induces a spatially\nperiodic effective magnetic field (the Berry's curvature) that can be tuned to\ncause destructive interference between neighboring tubes, thereby decoupling\nthem at a critical point in parameter space. We numerically investigate the\nenergy spectrum including decay from the excited state, and find that the\nadiabatic approximation is sound for strong coupling strengths, leading to\nnegligible loss in the dark state manifold. Furthermore, the spectrum is\nwell-described by a non-Hermitian tight binding model with on-site losses, and\nhopping characterized by both loss and, surprisingly, gain."
    },
    {
        "anchor": "Incoherent excitation and switching of spin states in exciton-polariton\n  condensates: We investigate, theoretically and numerically, the spin dynamics of a\ntwo-component exciton-polariton condensate created and sustained by\nnon-resonant spin-polarized optical pumping of a semiconductor microcavity.\nUsing the open-dissipative mean-field model, we show that the existence of well\ndefined phase-locked steady states of the condensate may lead to efficient\nswitching and control of spin (polarization) states with a non-resonant\nexcitation. Spatially inhomogeneous pulsed excitations can cause symmetry\nbreaking in the pseudo-spin structure of the condensate and lead to formation\nof non-trivial spin textures. Our model is universally applicable to two weakly\ncoupled polariton condensates, and therefore can also describe the behaviour of\ncondensate populations and phases in 'double-well' type potentials.",
        "positive": "Few-body precursor of the Higgs mode in a superfluid Fermi gas: We demonstrate that an undamped few-body precursor of the Higgs mode can be\ninvestigated in a harmonically trapped Fermi gas. Using exact diagonalisation,\nthe lowest monopole mode frequency is shown to depend non-monotonically on the\ninteraction strength, having a minimum in a crossover region. The minimum\ndeepens with increasing particle number, reflecting that the mode is the\nfew-body analogue of a many-body Higgs mode in the superfluid phase, which has\na vanishing frequency at the quantum phase transition point to the normal\nphase. We show that this mode mainly consists of coherent excitations of\ntime-reversed pairs, and that it can be selectively excited by modulating the\ninteraction strength, using for instance a Feshbach resonance in cold atomic\ngases."
    },
    {
        "anchor": "Microscopic model for Feshbach interacting fermions in an optical\n  lattice with arbitrary scattering length and resonance width: We numerically study the problem of two fermions in a three dimensional\noptical lattice interacting via a zero-range Feshbach resonance, and display\nthe dispersions of the bound states as a two-particle band structure with\nunique features compared to typical single-particle band structures. We show\nthat the exact two-particle solutions of a projected Hamiltonian may be used to\ndefine an effective two-channel, few-band model for the low energy, low density\nphysics of many fermions at arbitrary s-wave scattering length. Our method\napplies to resonances of any width, and can be adapted to multichannel\nsituations or higher-$\\ell$ pairing. In strong contrast to usual Hubbard\nphysics, we find that pair hopping is significantly altered by strong\ninteractions and the presence of the lattice, and the lattice induces multiple\nmolecular bound states.",
        "positive": "Exact result for the polaron mass in a one-dimensional Bose gas: We study the polaron quasiparticle in a one-dimensional Bose gas. In the\nintegrable case described by the Yang-Gaudin model, we derive an exact result\nfor the polaron mass in the thermodynamic limit. It is expressed in terms of\nthe derivative with respect to the density of the ground-state energy per\nparticle of the Bose gas without the polaron. This enables us to find\nhigh-order power series for the polaron mass in the regimes of weak and strong\ninteraction."
    },
    {
        "anchor": "Wave-packet Dynamics in Synthetic Non-Abelian Gauge Fields: It is generally admitted that in quantum mechanics, the electromagnetic\npotentials have physical interpretations otherwise absent in classical physics\nas illustrated by the Aharonov-Bohm effect. In 1984, Berry interpreted this\neffect as a geometrical phase factor. The same year, Wilczek and Zee\ngeneralized the concept of Berry phases to degenerate levels and showed that a\nnon-Abelian gauge field arises in these systems. In sharp contrast with the\nAbelian case, spatially uniform non-Abelian gauge fields can induce particle\nnoninertial motion. We explore this intriguing phenomenon with a degenerated\nFermionic atomic gas subject to a two-dimensional synthetic SU(2) non-Abelian\ngauge field. We reveal the spin Hall nature of the noninertial dynamic as well\nas its anisotropy in amplitude and frequency due to the spin texture of the\nsystem. We finally draw the similarities and differences of the observed wave\npacket dynamic and the celebrated Zitterbewegung effect of the relativistic\nDirac equation.",
        "positive": "Exact Soliton-like Solutions of the Radial Gross-Pitaevskii Equation: We construct exact ring soliton-like solutions of the cylindrically symmetric\n(i.e., radial) Gross- Pitaevskii equation with a potential, using the\nsimilarity transformation method. Depending on the choice of the allowed free\nfunctions, the solutions can take the form of stationary dark or bright rings\nwhose time dependence is in the phase dynamics only, or oscillating and\nbouncing solutions, related to the second Painlev\\'e transcendent. In each case\nthe potential can be chosen to be time-independent."
    },
    {
        "anchor": "Spin-squeezed states for metrology: Spin-squeezing is a well-established \"quantum technology\", where\nwell-designed correlations in an ensemble of two-level systems reduce the\nstatistical uncertainty of spectroscopic experiments. This paper reviews some\nimportant advances in the field, with emphasis on the author's contributions\nconcerning in particular the fundamental limits imposed by decoherence.\nBuilding on the material presented in the first part, new ideas and some\npromising developments are outlined in the last section.",
        "positive": "Density distribution of a trapped two-dimensional strongly interacting\n  Fermi gas: We calculate and measure the density distribution and cloud size of a trapped\ntwo-dimensional $^{6}$Li Fermi gas near a Feshbach resonance at low\ntemperatures. Density distributions and cloud sizes are calculated for a wide\nrange of interaction parameters using a local density approximation (LDA) and a\nzero-temperature equation of state obtained from quantum Monte Carlo\nsimulations reported by G. Bertaina and S. Giorgini, Phys. Rev. Lett.\n\\textbf{106}, 110403 (2011). We find that LDA predictions agree well with\nexperimental measurements across a Feshbach resonance. Theoretical results for\nTan's contact parameter in a trapped gas are reported along with predictions\nfor static structure factor at large momentum which could be measured in future\nBragg spectroscopy experiments on two-dimensional Fermi gases."
    },
    {
        "anchor": "Static properties of two linearly coupled discrete circuits: Bosonic two-ring ladders constitute an important class of atomtronic\ncircuits, where coherent current flows not only can offer a new insight into\nmany-body physics, but also can play the role of actual degrees of freedom, and\nhence allow for a viable implementation of cold-atom based devices and qubit\nsystems. In this work, we exhaustively investigate the ground state properties\nand the low-lying energy spectrum of two linearly coupled Bose-Hubbard rings.\nWe show that the competition among interactions, intra- and inter-ring hopping\nprocesses gives place to a rather rich physical scenario, where Mott-like\nstates and (different kinds of) superfluid-like states emerge. The latter ones\ndepend also on the (in)commensurate filling of the atoms. Our analysis, carried\nout within a simple analytical framework and by means of the exact numerical\ndiagonalization of the system Hamiltonian, provides one with a rather complete\ncharacterization of the static properties of the two-ring ladder, including,\nbut not limited to, coherence, fragmentation, correlations, and entanglement.\nWe complement our investigation by studying how these indicators depend on the\ncommensurability of the total number of bosons with respect to the total number\nof sites and show that the two stacked rings are always entangled for an odd\nnumber of atoms.",
        "positive": "Two-point momentum correlations of few ultracold quasi-one-dimensional\n  trapped fermions: Diffraction patterns: Spatial and momentum correlations are important in the analysis of the\nquantum states and different phases of trapped ultracold atom systems as a\nfunction of the strength of interatomic interactions. Identification and\nunderstanding of spin-resolved patterns exhibited in two-point correlations,\naccessible directly by experiments, are key for uncovering the symmetry and\nstructure of the many-body wave functions of the trapped system. Using the\nconfiguration interaction method for exact diagonalization of the many-body\nHamiltonian of $N=2-4$ fermionic atoms trapped in single, double, triple, and\nquadruple wells, we analyze both two-point momentum and space correlations, as\nwell as associated noise distributions, for a broad range of interparticle\ncontact repulsion strengths and interwell separations, unveiling\ncharacteristics allowing insights into the transition, via an intermediate\nphase, from the non-interacting Bose-Einstein condensate to the weakly\ninteracting quasi-Bose-Einstein regime, and from the latter to the\nstrong-repulsion Tonks-Girardeau (TG) one. The ab-initio numerical predictions\nare shown to agree well with the results of a constructed analytical model\nemploying localized displaced Gaussian functions to represent the $N$ fermions.\nThe two-point momentum correlations are found to exhibit damped oscillatory\ndiffraction behavior. This diffraction behavior develops fully for atoms\ntrapped in a single well with strong interatomic repulsion in the TG regime, or\nfor atoms in well-separated multi-well traps. Additionally, the two-body\nmomentum correlation and noise distributions are found to exhibit\n\"shortsightedness\", with the main contribution coming from nearest-neighboring\nparticles."
    },
    {
        "anchor": "Semiclassical descriptions of dissipative dynamics of strongly\n  interacting Bose gases in optical lattices: We develop semiclassical methods for describing real-time dynamics of\ndissipative Bose-Hubbard systems in a strongly interacting regime, which can be\nrealized in experiments with ultracold gases. Specifically, we present two\nkinds of SU(3) truncated Wigner approximation (TWA) for solving an effective\nLindblad master equation of the systems. The first one employs the discrete TWA\nfor finite levels or spin systems and is based on a classical equation of\nmotion in which the onsite dissipation term, as well as the onsite interaction\nterm, is linearized in the phase space variables. The other approach utilizes a\nstochastic Langevin equation, including decoherence effects in terms of\nnonlinear drift force and stochastic force terms, in which the initial\nconditions of trajectories are weighted with a quasiprobability distribution\nfor a typical initial quantum state. We apply these methods to the systems with\ntwo-body losses and compare their results with the exact numerical solutions\nfor a small system. We show that the former approach can simulate correctly\nlonger-time dynamics than the latter one. We also calculate the time evolution\nfor a large size setup that is comparable to experiments. We numerically\ndemonstrate that the discrete TWA approach is able to qualitatively capture the\ncontinuous quantum Zeno effect on dynamics subjected to a gradual change of the\nratio between the hopping amplitude and the onsite interaction across the\nsuperfluid-Mott insulator crossover, which has been observed experimentally.",
        "positive": "Yang-Yang thermometry and momentum distribution of a trapped\n  one-dimensional Bose gas: We describe the use of the exact Yang-Yang solutions for the one-dimensional\nBose gas to enable accurate kinetic-energy thermometry based on the\nroot-mean-square width of an experimentally measured momentum distribution.\nFurthermore, we use the stochastic projected Gross-Pitaevskii theory to provide\nthe first quantitative description of the full momentum distribution\nmeasurements of Van Amerongen et al., Phys. Rev. Lett. 100, 090402 (2008). We\nfind the fitted temperatures from the stochastic projected Gross-Pitaevskii\napproach are in excellent agreement with those determined by Yang-Yang\nkinetic-energy thermometry."
    },
    {
        "anchor": "Solving the quantum many-body problem via correlations measured with a\n  momentum microscope: In quantum many-body theory, all physical observables are described in terms\nof correlation functions between particle creation/annihilation operators.\nMeasurement of such correlation functions can therefore be regarded as an\noperational solution to the quantum many-body problem. Here we demonstrate this\nparadigm by measuring multi-particle momentum correlations up to third order\nbetween ultracold helium atoms in an s-wave scattering halo of colliding\nBose-Einstein condensates, using a quantum many-body momentum microscope. Our\nmeasurements allow us to extract a key building block of all higher-order\ncorrelations in this system|the pairing field amplitude. In addition, we\ndemonstrate a record violation of the classical Cauchy-Schwarz inequality for\ncorrelated atom pairs and triples. Measuring multi-particle momentum\ncorrelations could provide new insights into effects such as unconventional\nsuperconductivity and many-body localisation.",
        "positive": "Effective self-similar expansion for the Gross-Pitaevskii equation: We consider an effective scaling approach for the free expansion of a\none-dimensional quantum wave packet, consisting in a self-similar evolution to\nbe satisfied on average, i.e. by integrating over the coordinates. A direct\ncomparison with the solution of the Gross-Pitaevskii equation shows that the\neffective scaling reproduces with great accuracy the exact evolution - the\nactual wave function is reproduced with a fidelity close to unity - for\narbitrary values of the interactions. This result represents a proof-of-concept\nof the effectiveness of the scaling ansatz, which has been used in different\nforms in the literature but never compared with the exact evolution."
    },
    {
        "anchor": "Itinerant Ferromagnetism in ultracold Fermi gases: Itinerant ferromagnetism in cold Fermi gases with repulsive interactions is\nstudied applying the Jastrow-Slater approximation generalized to finite\npolarization and temperature. For two components at zero temperature a second\norder transition is found at $ak_F\\simeq0.90$ compatible with QMC.\nThermodynamic functions and observables such as the compressibility and spin\nsusceptibility and the resulting fluctuations in number and spin are\ncalculated. For trapped gases the resulting cloud radii and kinetic energies\nare calculated and compared to recent experiments. Spin polarized systems are\nrecommended for effective separation of large ferromagnetic domains. Collective\nmodes are predicted and tri-critical points are calculated for multi-component\nsystems.",
        "positive": "Using dark solitons from a Bose-Einstein condensate necklace to imprint\n  soliton states in the spectral memory of a free boson gas: A possible use of matter-wave dark-soliton crystal produced by a\nBose-Einstein condensate with ring geometry, to store soliton states in the\nquantum memory of a free boson gas, is explored. A self-defocusing nonlinearity\ncombined with dispersion and the finite size of the Bose-Einstein condensate,\nfavor the creation of dark-soliton crystals that imprint quantum states with\nJacobi elliptic-type soliton wavefunctions in the spectrum of the free boson\ngas. The problem is formulated by considering the Gross-Pitaevskii equation\nwith a positive scattering length, coupled to a linear Schr\\\"odinger equation\nfor the free boson gas. With the help of the matter-wave dark soliton-crystal\nsolution, the spectrum of bound states created in the free boson gas is shown\nto be determined by the Lam\\'e eigenvalue problem. This spectrum consists of\n$\\vert \\nu, \\mathcal{L} \\rangle$ quantum states whose wave functions and energy\neigenvalues can be unambiguously identified. Among these eigenstates some have\ntheir wave functions that are replicas of the generating dark soliton crystal."
    },
    {
        "anchor": "Non Degenerate Dual Atomic Parametric Amplifier: Entangled Atomic Fields: In this paper, we investigate the dynamics of two coupled quantum degenerate\natomic fields (BEC) interacting with two classical optical fields in the\nnonlinear atom optics regime. Two photon interaction produces entangled\natom-atom pairs which exhibit nonclassical correlations. Since the system\ninvolves the creation of two correlated atom pairs, we call it the\nnondegenerate dual atomic parametric amplifier.",
        "positive": "Ultracold Fermi Gases with Emergent SU(N) Symmetry: We review recent experimental and theoretical progress on ultracold\nalkaline-earth Fermi gases with emergent SU$(N)$ symmetry. Emphasis is placed\non describing the ground-breaking experimental achievements of recent years.\nThe latter include the cooling to below quantum degeneracy of various isotopes\nof ytterbium and strontium, the demonstration of optical Feshbach resonances\nand the optical Stern-Gerlach effect, the realization of a Mott insulator of\n$^{173}$Yb atoms, the creation of various kinds of Fermi-Bose mixtures and the\nobservation of many-body physics in optical lattice clocks. On the theory side,\nwe survey the zoo of phases that have been predicted for both gases in a trap\nand loaded into an optical lattice, focusing on two and three-dimensional\nsystems. We also discuss some of the challenges that lie ahead for the\nrealization of such phases, such as reaching the temperature scale required to\nobserve magnetic and more exotic quantum orders, and dealing with collisional\nrelaxation of excited electronic levels."
    },
    {
        "anchor": "Thermodynamic properties of ideal Bose gas trapped in different external\n  power-law potentials under generalized uncertainty principle*: Significant evidence is available to support the quantum effects of gravity\nthat leads to the generalized uncertainty principle (GUP) and the minimum\nobservable length. Usually quantum mechanics, statistical physics doesn't take\ngravity into account. Thermodynamic properties of ideal Bose gases in different\nexternal power-law potentials are studied under GUP with statistical physical\nmethod. Critical temperature, internal energy, heat capacity, entropy,\nparticles number of ground state and excited state are calculated analytically\nto ideal Bose gases in the external potentials under GUP. Below the critical\ntemperature, taking rubidium and sodium atoms ideal Bose gases whose particle\ndensities are under standard and experimental conditions, respectively, as\nexamples, the relations of internal energy, heat capacity and entropy with\ntemperature are analyzed numerically. Theoretical and numerical calculations\nshow that: GUP leads to an increase in the critical temperature. When the\ntemperature is lower than the critical temperature and slightly higher than\nzero Kelvin, GUP's amendments to internal energy, heat capacity and entropy are\npositive; As the temperature increases to a certain value, these amendments\nbecome negative. The external potentials can increase or decrease the influence\nof GUP on thermodynamic properties. Under the initial experimental conditions\nwhen Bose-Einstein condensation was first verified by sodium atomic gas, the\ninfluence of GUP can be completely ignored. Under certain conditions, GUP may\nbecome the dominant factor governing the thermodynamic properties of the\nsystem.",
        "positive": "Precise measurements on a quantum phase transition in antiferromagnetic\n  spinor Bose-Einstein condensates: We investigate, both experimentally and theoretically, the quench dynamics of\nantiferromagnetic spinor Bose-Einstein condensates in the vicinity of a zero\ntemperature quantum phase transition at zero quadratic Zeeman shift q. Both the\nrate of instability and the associated finite wavevector of the unstable modes\n- show good agreement with predictions based upon numerical solutions to the\nBogoliubov de-Gennes equations. A key feature of this work is inclusion of\nmagnetic field inhomogeneities that smooth the phase transition. Once these\nwere removed, we observed a dramatic sharpening of the transition point, which\ncould then be resolved within a quadratic Zeeman shift of only 1-2 Hz. Our\nresults point to the use of dynamics, rather than equilibrium quantities for\nhigh precision measurements of phase transitions in quantum gases."
    },
    {
        "anchor": "Absence of Bose condensation on lattices with moat bands: We study hard-core bosons on a class of frustrated lattices with the lowest\nBloch band having a degenerate minimum along a closed contour, the moat, in the\nreciprocal space. We show that at small density the ground state of the system\nis given by a noncondensed state, which may be viewed as a state of fermions\nsubject to Chern-Simons gauge field. At fixed density of bosons, such a state\nexhibits domains of incompressible liquids. Their fixed densities are given by\nfractions of the reciprocal-space area enclosed by the moat.",
        "positive": "Dissipative fluid dynamics for the dilute Fermi gas at unitarity:\n  Anisotropic fluid dynamics: We consider the time evolution of a dilute atomic Fermi gas after release\nfrom a trapping potential. A common difficulty with using fluid dynamics to\nstudy the expansion of the gas is that the theory is not applicable in the\ndilute corona, and that a naive treatment of the entire cloud using fluid\ndynamics leads to unphysical results. We propose to remedy this problem by\nincluding certain non-hydrodynamic degrees of freedom, in particular\nanisotropic components of the pressure tensor, in the theoretical description.\nWe show that, using this method, it is possible to describe the crossover from\nfluid dynamics to ballistic expansion locally. We illustrate the use of\nanisotropic fluid dynamics by studying the expansion of the dilute Fermi gas at\nunitarity using different functional forms of the shear viscosity, including a\nshear viscosity which is solely a function of temperature, $\\eta\\sim\n(mT)^{3/2}$, as predicted by kinetic theory in the dilute limit."
    },
    {
        "anchor": "Massless Dirac-Weyl Fermions in a T_3 Optical Lattice: We propose an experimental setup for the observation of quasi-relativistic\nmassless Fermions. It is based on a T_3 optical lattice, realized by three\npairs of counter-propagating lasers, filled with fermionic cold atoms. We show\nthat in the long wavelength approximation the T_3 Hamiltonian generalizes the\nDirac-Weyl Hamiltonian for the honeycomb lattice, however, with a larger value\nof the pseudo-spin S=1. In addition to the Dirac cones, the spectrum includes a\ndispersionless branch of localized states producing a finite jump in the atomic\ndensity. Furthermore, implications for the Landau levels are discussed.",
        "positive": "Rotating BEC in an optical lattice in Uniformly frustrated Josephson\n  Junction arrays regime: Vortex configuration formulation for ground state: We consider a rotating BEC in an optical lattices in a regime which can be\nmapped to the Joseohson junction arrays. In this regime, we formulate the\nground state energy in terms of vortex configuration. This method give us the\nvortex lattice in the ground state in a natural way. We apply our result for an\napproximation scheme of the problem which we suppose that the coupling of the\nJosephson junctions are uniform. Application of method for ladder case\npresented and the results compared with Monte-Carlo method numerically.We\ndiscuss about restriction of method and suggest improvement for it."
    },
    {
        "anchor": "Nonlinear corrections in the quantization of a weakly nonideal Bose gas\n  at zero temperature: In the present paper, quantization of a weakly nonideal Bose gas at zero\ntemperature along the lines of the well-known Bogolyubov approach is performed.\nThe analysis presented in this paper is based, in addition to the steps of the\noriginal Bogolyubov approach, on the use of nonoscillation modes (which are\nalso solutions of the linearized Heisenberg equation) for recovering the\ncanonical commutation relations in the linear approximation, as well as on the\ncalculation of the first nonlinear correction to the solution of the linearized\nHeisenberg equation which satisfies the canonical commutation relations at the\nnext order. It is shown that, at least in the case of free quasi-particles,\nconsideration of the nonlinear correction automatically solves the problem of\nnonconserved particle number, which is inherent to the original approach.",
        "positive": "Designer Spatial Control of Interactions in Ultracold Gases: Designer optical control of interactions in ultracold atomic gases has wide\napplication, from creating new quantum phases to modeling the physics of black\nholes. We demonstrate spatial control of interactions in a two-component cloud\nof $^6$Li fermions, using electromagnetically induced transparency (EIT) to\ncreate a \"sandwich\" of resonantly and weakly interacting regions. Interaction\ndesigns are imprinted on the trapped cloud by two laser beams and manipulated\nwith just MHz changes in the frequency of one beam. We employ radio-frequency\nspectroscopy to measure the imprinted 1D spatial profiles of the local\nmean-field interactions and to demonstrate that the tuning range of the\nscattering length is the same for both optical and magnetic control. All of the\ndata are in excellent agreement with our continuum-dressed state theoretical\nmodel of optical control, which includes both the spatial and momentum\ndependence of the interactions."
    },
    {
        "anchor": "A Scaling Function for the Particle Entanglement Entropy of Fermions: Entanglement entropy under a particle bipartition provides complementary\ninformation to mode entanglement as it is sensitive to interactions and\nparticle statistics at leading order and does not depend on any externally\nimposed length scale. In this paper, we investigate the particle entanglement\nentropy in a system of $N$ interacting spinless lattice fermions in one spatial\ndimension by combining bosonization techniques with exact and approximate\nnumerical methods. We introduce a general scaling form for the fermionic\nparticle entanglement entropy captured by a shape function that enters as a\nextensive interaction induced correction to a known free fermion result. A\ngeneral asymptotic expansion in the total number of particles demonstrates that\nits form is robust for different values of the R\\'enyi index and highlights how\nquantum correlations are encoded in the $n$-particle density matrix of a pure\nmany-body quantum state.",
        "positive": "Mixtures of ultra-cold atoms in 1D disordered potentials: We study interacting 1D two-component mixtures of cold atoms in a random\npotential, and extend the results reported earlier [{\\it Phys. Rev. Lett.} {\\bf\n105}, 115301 (2010)]. We construct the phase diagram of a disordered Bose-Fermi\nmixture as a function of the strength of the Bose-Bose and Bose-Fermi\ninteractions, and the ratio of the bosonic sound velocity and the Fermi\nvelocity. Performing renormalization group and variational calculations, three\nphases are identified: (i) a fully delocalized two-component Luttinger liquid\nwith superfluid bosons and fermions (ii) a fully localized phase with both\ncomponents pinned by disorder, and (iii) an intermediate phase where fermions\nare localized but bosons are superfluid. Within the variational approach, each\nphase corresponds to a different level of replica symmetry breaking. In the\nfully localized phase we find that the bosonic and fermionic localization\nlengths can largely differ. We also compute the momentum distribution as well\nas the structure factor of the atoms (both experimentally accessible), and\ndiscuss how the three phases can be experimentally distinguished."
    },
    {
        "anchor": "Topological stirring of two-dimensional atomic Bose-Einstein condensates: We stir vortices into a trapped quasi two-dimensional atomic Bose-Einstein\ncondensate by moving three laser stirrers. We apply stirring protocols\nintroduced by Boyland et. al. (2000) that efficiently build in topological\nchaos in classical fluids and are classified as Pseudo-Anosov stirring\nprotocols. These are compared to their inefficient mixing counterparts,\nfinite-order stirring protocols. We investigate if inefficient stirring\nprotocols result in a more clustered distribution of vortices. The efficiency\nwith which vortices are 'mixed' or distributed in a condensate is important for\ninvestigating dynamics of continuously forced quantum turbulence and the\nexistence of the inverse cascade in turbulent two-dimensional superfluids.",
        "positive": "Berry Phase of Nonlinear Correction: We investigate the geometric phase or Berry phase of adiabatic quantum\nevolution in the Bose-Einstein condensate (BEC) systems governed by nonlinear\nGross-Pitaevskii(GP) equations. We study how this phase is modified by the\nnonlinearity and find that the Bogoliubov fluctuations around the eigenstates\nare accumulated during the nonlinear adiabatic evolution and contribute a\nfinite phase of geometric nature. A two-mode BEC model is used to illustrate\nour theory. Our theory is applicable to other nonlinear systems such as\nparaxial wave equation for nonlinear optics and Ginzburg-Landau equations for\ncomplex order parameters in condensed-matter physics."
    },
    {
        "anchor": "Path integral Monte Carlo ground state approach: Formalism,\n  implementation, and applications: Monte Carlo techniques have played an important role in understanding\nstrongly-correlated systems across many areas of physics, covering a wide range\nof energy and length scales. Among the many Monte Carlo methods applicable to\nquantum mechanical systems, the path integral Monte Carlo approach with its\nvariants has been employed widely. Since semi-classical or classical approaches\nwill not be discussed in this review, path integral based approaches can for\nour purposes be divided into two categories: approaches applicable to quantum\nmechanical systems at zero temperature and approaches applicable to quantum\nmechanical systems at finite temperature. While these two approaches are\nrelated to each other, the underlying formulation and aspects of the algorithm\ndiffer. This paper reviews the path integral Monte Carlo ground state (PIGS)\napproach, which solves the time-independent Schroedinger equation.\nSpecifically, the PIGS approach allows for the determination of expectation\nvalues with respect to eigen states of the few- or many-body Schroedinger\nequation provided the system Hamiltonian is known. The theoretical framework\nbehind the PIGS algorithm, implementation details, and sample applications for\nsermonic systems are presented.",
        "positive": "Many-body perturbation theory for strongly correlated effective\n  Hamiltonians using effective field theory methods: Introducing low-energy effective Hamiltonians is usual to grasp most\ncorrelations in quantum many-body problems. For instance, such effective\nHamiltonians can be treated at the mean-field level to reproduce some physical\nproperties of interest. Employing effective Hamiltonians that contain many-body\ncorrelations renders the use of perturbative many-body techniques difficult\nbecause of the overcounting of correlations. In this work, we develop a\nstrategy to apply an extension of the many-body perturbation theory, starting\nfrom an effective interaction that contains correlations beyond the mean field\nlevel. The goal is to re-organize the many-body calculation to avoid the\novercounting of correlations originating from the introduction of correlated\neffective Hamiltonians in the description. For this purpose, we generalize the\nformulation of the Rayleigh-Schr\\\"odinger perturbation theory by including free\nparameters adjusted to reproduce the appropriate limits. In particular, the\nexpansion in the bare weak-coupling regime and the strong-coupling limit serves\nas a valuable input to fix the value of the free parameters appearing in the\nresulting expression. This method avoids double counting of correlations using\nbeyond-mean-field strategies for the description of many-body systems. The\nground state energy of various systems relevant for ultracold atomic, nuclear,\nand condensed matter physics is reproduced qualitatively beyond the domain of\nvalidity of the standard many-body perturbation theory. Finally, our method\nsuggests interpreting the formal results obtained as an effective field theory\nusing the proposed reorganization of the many-body calculation. The results,\nlike ground state energies, are improved systematically by considering higher\norders in the extended many-body perturbation theory while maintaining a\nstraightforward polynomial expansion."
    },
    {
        "anchor": "Superfluid, staggered state, and Mott insulator of repulsively\n  interacting three-component fermionic atoms in optical lattices: We review our theoretical analysis of repulsively interacting three-component\nfermionic atoms in optical lattices. We discuss quantum phase transitions at\naround half filling with a balanced population by focusing on Mott transitions,\nstaggered ordering, and superfluidity. At half filling (with 3/2 atoms per\nsite), characteristic Mott transitions are induced by the anisotropic\ninteractions, where two-particle repulsions between any two of the three colors\nhave different strengths. At half filling, two types of staggered ordered\nstates appear at low temperatures depending on the anisotropy of the\ninteractions. As the temperature increases, phase transitions occur from the\nstaggered ordered states to the unordered Mott states. Deviating from half\nfilling, an exotic superfluid state appears close to a regime in which the Mott\ntransition occurs. We explain the origin of these phase transitions and present\nthe finite-temperature phase diagrams.",
        "positive": "Supersolid in Bose-Bose-Fermi Mixtures subjected to a Square Lattice: Two-component Bose condensates with repulsive interaction are stable when\n$g_{\\rm \\scriptscriptstyle 1} g_{\\rm \\scriptscriptstyle 2}<g_{\\rm\n\\scriptscriptstyle 12}^{2}$ is satisfied. By tuning the interactions, we show\nthat the instability corresponding to bose-bose phase separation always happens\nat a higher temperature than corresponding to bose-fermi phase separation\nhappens. Moreover, we find both the transition temperature $T_{\\rm\n\\scriptscriptstyle DW}$ of supersolid and the coherence peak at $k_{\\rm\n\\scriptscriptstyle DW}$ are enhanced in the mixtures studied. These will make\nthe observation of supersolid in experiments more reachable."
    },
    {
        "anchor": "Mott Insulator-Superfluid Transition in a Generalized Bose-Hubbard Model\n  with Topologically Non-trivial Flat-Band: In this paper, we studied a generalized Bose-Hubbard model on a checkerboard\nlattice with topologically nontrivial flat-band. We used mean-field method to\ndecouple the model Hamiltonian and obtained phase diagram by Landau theory of\nsecond-order phase transition. We further calculate the energy gap and the\ndispersion of quasi-particle or quasi-hole in Mott insulator state and found\nthat in strong interaction limit the quasi-particles or the quasi-holes also\nhave flat bands.",
        "positive": "Dynamical quantum phase transitions in discrete time crystals: Discrete time crystals are related to non-equilibrium dynamics of\nperiodically driven quantum many-body systems where the discrete time\ntranslation symmetry of the Hamiltonian is spontaneously broken into another\ndiscrete symmetry. Recently, the concept of phase transitions has been extended\nto non-equilibrium dynamics of time-independent systems induced by a quantum\nquench, i.e. a sudden change of some parameter of the Hamiltonian. There, the\nreturn probability of a system to the ground state reveals singularities in\ntime which are dubbed dynamical quantum phase transitions. We show that the\nquantum quench in a discrete time crystal leads to dynamical quantum phase\ntransitions where the return probability of a periodically driven system to a\nFloquet eigenstate before the quench reveals singularities in time. It\nindicates that dynamical quantum phase transitions are not restricted to\ntime-independent systems and can be also observed in systems that are\nperiodically driven. We discuss how the phenomenon can be observed in\nultra-cold atomic gases."
    },
    {
        "anchor": "Observation of nodal-line semimetal with ultracold fermions in an\n  optical lattice: Observation of topological phases beyond two-dimension (2D) has been an open\nchallenge for ultracold atoms. Here, we realize for the first time a 3D\nspin-orbit coupled nodal-line semimetal in an optical lattice and observe the\nbulk line nodes with ultracold fermions. The realized topological semimetal\nexhibits an emergent magnetic group symmetry. This allows to detect the nodal\nlines by effectively reconstructing the 3D topological band from a series of\nmeasurements of integrated spin textures, which precisely render spin textures\non the parameter-tuned magnetic-group-symmetric planes. The detection technique\ncan be generally applied to explore 3D topological states of similar\nsymmetries. Furthermore, we observe the band inversion lines from topological\nquench dynamics, which are bulk counterparts of Fermi arc states and connect\nthe Dirac points, reconfirming the realized topological band. Our results\ndemonstrate the first approach to effectively observe 3D band topology, and\nopen the way to probe exotic topological physics for ultracold atoms in high\ndimensions.",
        "positive": "Realization of Qi-Wu-Zhang model in spin-orbit-coupled ultracold\n  fermions: Based on the optical Raman lattice technique, we experimentally realize the\nQi-Wu-Zhang model for quantum anomalous Hall phase in ultracold fermions with\ntwo-dimensional (2D) spin-orbit (SO) coupling. We develop a novel protocol of\npump-probe quench measurement to probe, with minimal heating, the resonant spin\nflipping on particular quasi-momentum subspace called band-inversion surfaces.\nWith this protocol we demonstrate the first Dirac-type 2D SO coupling in a\nfermionic system, and detect non-trivial band topology by observing the change\nof band-inversion surfaces as the two-photon detuning varies. The non-trivial\nband topology is also observed by slowly loading the atoms into optical Raman\nlattices and measuring the spin textures. Our results show solid evidence for\nthe realization of the minimal SO-coupled quantum anomalous Hall model, which\ncan provide a feasible platform to investigate novel topological physics\nincluding the correlation effects with SO-coupled ultracold fermions."
    },
    {
        "anchor": "Cavity-quantum-electrodynamical toolbox for quantum magnetism: The recent experimental observation of spinor self-ordering of ultracold\natoms in optical resonators has set the stage for the exploration of emergent\nmagnetic orders in quantum-gas--cavity systems. Based on this platform, we\nintroduce a generic scheme for the implementation of long-range quantum spin\nHamiltonians composed of various types of couplings, including Heisenberg and\nDzyaloshinskii-Moriya interactions. Our model is comprised of an effective\ntwo-component Bose-Einstein condensate, driven by two classical pump lasers and\ncoupled to a single dynamic mode of a linear cavity in a double $\\Lambda$\nscheme. Cavity photons mediate the long-range spin-spin interactions with\nspatially modulated coupling coefficients, where the latter ones can be tuned\nby modifying spatial profiles of the pump lasers. As experimentally relevant\nexamples, we demonstrate that by properly choosing the spatial profiles of the\npump lasers achiral domain-wall antiferromagnetic and chiral spin-spiral orders\nemerge beyond critical laser strengths. The transition between these two phases\ncan be observed in a single experimental setup by tuning the reflectivity of a\nmirror. We also discuss extensions of our scheme for the implementation of\nother classes of spin Hamiltonians.",
        "positive": "Detecting degenerate bands topological invariants in optical lattice: In this paper, we present a novel experimental approach for simulating and\ndetecting topological invariants using ultracold fermions confined in\ntwo-dimensional hexagonal optical lattices. We propose achieving two-fold\ndegenerate four-band models with non-trivial topologies in both the AII and A\nclasses by introducing additional inertial forces, Raman processes, or periodic\ndriving. By implementing various quench sequences and observing the evolution\nof the time-of-flight pattern, we can gather comprehensive information about\nthe ground states and determine the topology of the valence bands. Through the\nanalysis of tomographic results, we are able to extract and calculate the spin\nChern number for both spin-conserving and spin-nonconserving cases.\nAdditionally, we demonstrate the robustness of the quantized topological\ninvariants and discuss the effects of various experimental parameters."
    },
    {
        "anchor": "Reentrant Fulde-Ferrell-Larkin-Ovchinnikov superfluidity in the\n  honeycomb lattice: We study superconducting properties of population-imbalanced ultracold Fermi\nmixtures in the honeycomb lattice that can be effectively described by the\nspin-imbalanced attractive Hubbard model in the presence of a Zeeman magnetic\nfield. We use the mean-field theory approach to obtain ground state phase\ndiagrams including some unconventional superconducting phases such as the\nFulde--Ferrell--Larkin--Ovchinnikov (FFLO) phase. We show that this phase is\ncharacterized by atypical behaviour of the Cooper pairs total momentum in the\nexternal magnetic field. We show that the momentum changes its value as well as\ndirection with change of the system parameters. We discuss the influence of van\nHove singularities on the possibility of the reentrant FFLO phase occurrence,\nwithout a BCS precursor.",
        "positive": "Simple waves in a two-component Bose-Einstein condensate: We consider dynamics of simple waves in a two-component Bose-Einstein\ncondensates. The evolution of the condensate is described by the\nGross-Pitaevskii equations which can be reduced for simple wave solutions to a\nsystem of ordinary differential equations which coincide with those derived by\nOvsyannikov for the two-layer fuid dynamics. We solve the Ovsyannikov system\nfor two typical situations of large and small difference between inter-species\nand intra-species nonlinear interaction constants. Our analytic results are\nconfirmed by numerical simulations."
    },
    {
        "anchor": "Nontrivially Topological Phase Structure of Ideal Bose Gas System within\n  Different Boundary Conditions: The phase structure of ideal Bose gas system within different boundary\nconditions, i.e., the periodic boundary condition and Dirichlet boundary\ncondition in this work, in an infinite volume, is investigated. It is found\nthat the ground states of ideal Bose gas within those two boundary conditions\nare both topologically nontrivial, which can not be classified by the\ntraditional symmetry breaking theory. The ground states are different\ntopological phases corresponding to those two boundary conditions, which can be\ndistinguished by the off--diagonal particle number susceptibility. Moreover,\nthis result is universal. The boundary condition may play an important role in\npining the critical endpoint of QCD diagram on the approach of the lattice\nsimulations and the computation of some solvable statistical models .",
        "positive": "Supersolid in a one-dimensional model of hard-core bosons: We study a system of hardcore boson on a one-dimensional lattice with\nfrustrated next-nearest neighbor hopping and nearest neighbor interaction. At\nhalf filling, for equal magnitude of nearest and next-nearest neighbor hopping,\nthe ground state of this system exhibits a first order phase transition from a\nBond-Ordered (BO) solid to a Charge-Density-Wave(CDW) solid as a function of\nthe nearest neighbor interaction. Moving away from half filling we investigate\nthe system at incommensurate densities, where we find a SuperSolid (SS) phase\nwhich has concurrent off-diagonal long range order and density wave order which\nis unusual in a system of hardcore bosons in one dimension. Using the\nfinite-size Density-Matrix Renormalization Group (DMRG) method, we obtain the\ncomplete phase diagram for this model."
    },
    {
        "anchor": "Fermi Edge Resonances in Non-equilibrium States of Fermi Gases: We formulate the problem of the Fermi Edge Singularity in non-equilibrium\nstates of a Fermi gas as a matrix Riemann-Hilbert problem with an integrable\nkernel. This formulation is the most suitable for studying the singular\nbehavior at each edge of non-equilibrium Fermi states by means of the method of\nsteepest descent, and also reveals the integrable structure of the problem. We\nsupplement this result by extending the familiar approach to the problem of the\nFermi Edge Singularity via the bosonic representation of the electronic\noperators to non-equilibrium settings. It provides a compact way to extract the\nleading asymptotes.",
        "positive": "Challenges and constraints of dynamically emerged source and sink in\n  atomtronic circuits: From closed-system to open-system approaches: While batteries offer electronic source and sink in electronic devices,\natomic analogues of source and sink and their theoretical descriptions have\nbeen a challenge in cold-atom systems. Here we consider dynamically emerged\nlocal potentials as controllable source and sink for bosonic atoms. Although a\nsink potential can collect bosons in equlibrium and indicate its usefulness in\nthe adiabatic limit, sudden switching of the potential exhibits low\neffectiveness in pushing bosons into it. This is due to conservation of energy\nand particle in isolated systems such as cold atoms. By varying the potential\ndepth and interaction strength, the systems can further exhibit averse\nresponse, where a deeper emerged potential attracts less bosonic atoms into it.\nTo explore possibilities for improving the effectiveness, we investigate what\ntypes of system-environment coupling can help bring bosons into a dynamically\nemerged sink, and a Lindblad operator corresponding to local cooling is found\nto serve the purpose."
    },
    {
        "anchor": "Diagrammatic Monte Carlo study of the Fermi polaron in two dimensions: We study the properties of the two-dimensional Fermi polaron model in which\nan impurity attractively interacts with a Fermi sea of particles in the\nzero-range limit. We use a diagrammatic Monte Carlo (DiagMC) method which\nallows us to sample a Feynman diagrammatic series to very high order. The\nconvergence properties of the series and the role of multiple particle-hole\nexcitations are discussed. We study the polaron and molecule energy as a\nfunction of the coupling strength, revealing a transition from a polaron to a\nmolecule in the ground state. We find a value for the critical interaction\nstrength which complies with the experimentally measured one and predictions\nfrom variational methods. For all considered interaction strengths, the polaron\n$Z$ factor from the full diagrammatic series almost coincides with the\none-particle-hole result. We also formally link the DiagMC and the variational\napproaches for the polaron problem at hand.",
        "positive": "Signatures of quantum chaos in low-energy mixtures of few fermions: The low energy dynamics of mesoscopic systems strongly depends on the\npresence of internal equilibration. For this reason, a better interpretation of\nultracold atom experiments requires a more accurate understanding of how\nquantum chaos manifests itself in these systems. In this paper, we consider a\nsimple but experimentally relevant one-dimensional system of a few ultracold\nfermions moving in a double-well potential. We analyze its many-body spectral\nproperties, which are commonly used to trace quantum chaos. We observe some\nsignatures of quantum chaos already in the system with three particles.\nGenerally, these signatures become more pronounced when fermions are evenly\nadded to both components. On the contrary, they become suppressed when the\nparticle imbalance is increased."
    },
    {
        "anchor": "Strong Coupling Effects on the Specific Heat of an Ultracold Fermi Gas\n  in the Unitarity Limit: We investigate strong-coupling corrections to the specific heat $C_V$ in the\nnormal state of an ultracold Fermi gas in the BCS-BEC crossover region. A\nrecent experiment on a $^6$Li unitary Fermi gas [M. J. H. Ku, {\\it et. al.},\nScience {\\bf 335}, 563 (2012)] shows that $C_V$ is remarkably amplified near\nthe superfluid phase transition temperature $T_{\\rm c}$, being similar to the\nwell-known $\\lambda$-structure observed in liquid $^4$He. Including pairing\nfluctuations within the framework of the strong-coupling theory developed by\nNozi\\`eres and Schmitt-Rink, we show that strong pairing fluctuations are\nsufficient to explain the anomalous behavior of $C_V$ observed in a $^6$Li\nunitary Fermi gas near $T_{\\rm c}$. We also show that there is no contribution\nfrom {\\it stable} preformed Cooper pairs to $C_V$ at the unitarity. This\nindicates that the origin of the observed anomaly is fundamentally different\nfrom the case of liquid $^{4}$He, where {\\it stable} $^4$He Bose atoms induce\nthe $\\lambda$-structure in $C_V$ near the superfluid instability. Instead, the\norigin is the suppression of the entropy $S$, near $T_{\\rm c}$, due to the\nincrease of {\\it metastable} preformed Cooper pairs. Our results indicate that\nthe specific heat is a useful quantity to study the effects of pairing\nfluctuations on the thermodynamic properties of an ultracold Fermi gas in the\nBCS-BEC crossover region.",
        "positive": "Momentum-Space Josephson Effects: The Josephson effect is a prominent phenomenon of quantum supercurrents that\nhas been widely studied in superconductors and superfluids. Typical Josephson\njunctions consist of two real-space superconductors (superfluids) coupled\nthrough a weak tunneling barrier. Here we propose a momentum-space Josephson\njunction in a spin-orbit coupled Bose-Einstein condensate, where states with\ntwo diffferent momenta are coupled through Raman-assisted tunneling. We show\nthat Josephson currents can be induced not only by applying the equivalent of\n\"voltages\", but also by tuning tunneling phases. Such tunneling-phase-driven\nJosephson junctions in momentum space are characterized through both full mean\nfield analysis and a concise two-level model, demonstrating the important role\nof interactions between atoms. Our scheme provides a platform for\nexperimentally realizing momentum-space Josephson junctions and exploring their\napplications in quantum-mechanical circuits."
    },
    {
        "anchor": "Tunneling of ultracold atoms in time-independent potentials: We present theoretical as well as experimental results on resonantly enhanced\nquantum tunneling of Bose-Einstein condensates in optical lattices both in the\nlinear case of single particle dynamics and in the presence of atom-atom\ninteractions. Our results demonstrate the usefulness of condensates in optical\nlattices for the dynamical control of tunneling and for simulating Hamiltonians\noriginally used for describing solid state phenomena.",
        "positive": "Phase diagrams of the extended Bose-Hubbard model in one dimension by\n  Monte-Carlo simulation with the help of a stochastic-series expansion: In this paper, we study phase diagrams of the extended Bose-Hubbard model\n(EBHM) in one dimension by means of the quantum Monte-Carlo (QMC) simulation\nusing the stochastic-series expansion (SSE).In the EBHM, there exists a\nnearest-neighbor repulsion as well as the on-site repulsion. In the SSE-QMC\nsimulation, the highest particle number at each site, $n_c$, is also a\ncontrollable parameter, and we found that the phase diagrams depend on the\nvalue of $n_c$. It is shown that in addition to the Mott insulator, superfluid,\ndensity wave, the phase so-called Haldane insulator and supersolid appear in\nthe phase diagrams, and their locations in the phase diagrams are clarified."
    },
    {
        "anchor": "Wavelet representation of hardcore bosons: We consider the 1D Tonks-Girardeau gas with a space-dependent potential out\nof equilibrium. We derive the exact dynamics of the system when divided into\n$n$ boxes and decomposed into energy eigenstates within each box. It is a\nrepresentation of the wave function that is mixed between real space and\nmomentum space, whose basis elements are plane waves localized in a box,\nmotivating the word \"wavelet\". In this representation we derive the emergence\nof generalized hydrodynamics in appropriate limits without assuming local\nrelaxation. We emphasize in particular that a generalized hydrodynamic\nbehaviour emerges in a high-momentum and short-time limit, besides the more\ncommon large-space and late-time limit, which is akin to a semi-classical\nexpansion. In this limit, conserved charges do not require a large number of\nparticles to be described by generalized hydrodynamics. Besides, we show that\nthis wavelet representation provides an efficient numerical algorithm for a\ncomplete description of out-of-equilibrium dynamics of hardcore bosons.",
        "positive": "Pairing patterns in polarized unitary Fermi gases above the superfluid\n  transition: We non-perturbatively study pairing in the high-temperature regime of\npolarized unitary two-component Fermi gases by extracting the pair-momentum\ndistribution and shot-noise correlations. Whereas the pair-momentum\ndistribution allows us to analyze the propagation of pairs composed of one\nspin-up and one spin-down fermion, shot-noise correlations provide us with a\ntomographic insight into pairing correlations around the Fermi surfaces\nassociated with the two species. Assuming that the dominant pairing patterns\nright above the superfluid transition also govern the formation of condensates\nin the low-temperature regime, our analysis suggests that the superfluid ground\nstate is homogeneous and of the Bardeen-Cooper-Schrieffer-type over a wide\nrange of polarizations."
    },
    {
        "anchor": "Effect of interactions on harmonically confined Bose-Fermi mixtures in\n  optical lattices: We investigate a Bose-Fermi mixture in a three-dimensional optical lattice,\ntrapped in a harmonic potential. Using Generalized Dynamical Mean-Field theory,\nwhich treats the Bose-Bose and Bose-Fermi interaction in a fully\nnon-perturbative way, we show that for experimentally relevant parameters a\npeak in the condensate fraction close to the point of vanishing Bose-Fermi\ninteraction is reproduced within a single band framework. We identify two\nphysical mechanisms contributing to this effect: the spatial redistribution of\nparticles when the interspecies interaction is changed and the reduced phase\nspace for strong interactions, which results in a higher temperature at fixed\nentropy.",
        "positive": "Thermal Conductivity and Sound Attenuation in Dilute Atomic Fermi Gases: We compute the thermal conductivity and sound attenuation length of a dilute\natomic Fermi gas in the framework of kinetic theory. Above the critical\ntemperature for superfluidity, T_c, the quasi-particles are fermions, whereas\nbelow T_c, the dominant excitations are phonons. We calculate the thermal\nconductivity in both cases. We find that at unitarity the thermal conductivity\n\\kappa in the normal phase scales as \\kappa ~ T^{3/2}. In the superfluid phase\nwe find \\kappa ~ T^{2}. At high temperature the Prandtl number, the ratio of\nthe momentum and thermal diffusion constants, is 2/3. The ratio increases as\nthe temperature is lowered. As a consequence we expect sound attenuation in the\nnormal phase just above T_c to be dominated by shear viscosity. We comment on\nthe possibility of extracting the shear viscosity of the dilute Fermi gas at\nunitarity using measurements of the sound absorption length."
    },
    {
        "anchor": "Long-time averaged dynamics of a Bose-Einstein condensate in a\n  bichromatic optical lattice with external harmonic confinement: The dynamics of a Bose-Einstein condensate are examined numerically in the\npresence of a one-dimensional bichromatic optical lattice with external\nharmonic confinement. The condensate is excited by a focusing red laser. For\nthis purpose, the time-dependent Gross Pitaevskii equation is solved using the\nCrank Nicolson method in real time. Two realizations of the optical lattice are\nconsidered, one with a rational and the other with an irrational ratio of the\ntwo constituting wave lengths. For a weak bichromatic optical lattice, the\nlong-time averaged physical observables of the condensate respond only very\nweakly (or not at all) to changes in the secondary optical lattice depth.\nHowever, for a much larger strength of the latter optical lattice, the response\nis stronger. It is found that qualitatively there is no difference between the\ndynamics of the condensate resulting from the use of a rational or irrational\nratio of the optical lattice wavelengths since the external harmonic trap\nwashes it out. It is further found that in the presence of an external harmonic\ntrap, the bichromatic optical lattice acts in favor of superflow.",
        "positive": "Beyond mean-field dynamics of ultra-cold bosonic atoms in higher\n  dimensions: facing the challenges with a multi-configurational approach: Exploring the impact of dimensionality on the quantum dynamics of interacting\nbosons in traps including particle correlations is an interesting but\nchallenging task. Due to the different participating length scales the\nmodelling of the short-range interactions in three dimensions plays a special\nrole. We review different approaches for the latter and elaborate that for\nmulti-configurational computational strategies finite range potentials are\nadequate resulting in the need of large grids to resolve the relevant length\nscales. This results in computational challenges which include also the\nexponential scaling of complexity with the number of atoms. We show that the\nrecently developed ab-initio Multi-Layer Multi-Configurational Time- Dependent\nHartee method for Bosons (ML-MCTDHB) [J. Chem. Phys. 139, 134103 (2013)] can\nface both numerical challenges and present an efficient numerical\nimplementation of ML-MCTDHB in three spatial dimensions, particularly suited to\ndescribe the quantum dynamics for elongated traps.\n  The beneficial scaling of our approach is demonstrated by studying the\ntunnelling dynamics of bosonic ensembles in a double well. Comparing\nthree-dimensional with quasi-one dimensional simulations, we find\ndimensionality-induced effects in the density. Furthermore, we study the\ncrossover from weak transversal confinement, where a mean-field description of\nthe system is sufficient, towards tight transversal confinement, where particle\ncorrelations and beyond mean-field effects are pronounced."
    },
    {
        "anchor": "Quantum-geometric contribution to the Bogoliubov modes in a two-band\n  Bose-Einstein condensate: We consider a weakly-interacting Bose-Einstein condensate (BEC) that is\nloaded into an optical lattice with a two-point basis, and described by a\ntwo-band Bose-Hubbard model with generic one-body and two-body terms. By first\nprojecting the system to the lower Bloch band and then applying the Bogoliubov\napproximation to the resultant Hamiltonian, we show that the inverse\neffective-mass tensor of the superfluid carriers in the Bogoliubov spectrum has\ntwo physically distinct contributions. In addition to the usual inverse\nband-mass tensor that is originating from the intraband processes within the\nlower Bloch band, there is also a quantum-geometric contribution that is\ninduced by the two-body interactions through the interband processes. We also\ndiscuss the conditions under which the latter contribution is expressed in\nterms of the quantum-metric tensor of the Bloch states, i.e., the natural\nFubini-Study metric on the Bloch sphere.",
        "positive": "Creation, manipulation and detection of Majorana fermions with cold\n  atoms in optical lattice: We propose an experimental scheme to simulate the transverse field Ising\nmodel with cold atoms trapped in one-dimensional optical lattice. Majorana\nfermions are created at the ends of the optical lattice segment in topological\nphase. By controlling the addressing lasers, one can move, fuse and braid them.\nWe also show that the non-Abelian braiding statistics of Majorana fermions can\nbe demonstrated unambiguously through the construction of two braiding\noperations and distinguishing the resulting two output orthogonal collective\nspin states. A nice feature of the scheme is that the strong fluorescence\nprovided by the collective spin state can be readily detected in experiment."
    },
    {
        "anchor": "Nonlinear Dynamics in a Trapped Atomic Bose--Einstein Condensate Induced\n  by an Oscillating Gaussian Potential: We consider a trapped atomic Bose--Einstein condensate penetrated by a\nrepulsive Gaussian potential and theoretically investigate the dynamics induced\nby oscillating the Gaussian potential. Our study is based on the numerical\ncalculation of the two-dimensional Gross--Pitaevskii equation. Our calculation\nreveals the dependence of the characteristic behavior of the condensate on the\namplitude and frequency of the oscillating potential. These dynamics are deeply\nrelated to the nucleation and dynamics of quantized vortices and solitons. When\nthe potential oscillates with a large amplitude, it nucleates many vortex pairs\nthat move away from the potential. When the amplitude of the oscillation is\nsmall, it nucleates solitons through annihilation of vortex pairs. We discuss\nthree issues concerning the nucleation of vortices. The first is the phase\ndiagram for the nucleation of vortices and solitons near the oscillating\npotential. The second is the mechanism and critical velocity of the nucleation.\nThe critical velocity of the nucleation is an important issue in quantum\nfluids, and we propose a new expression for the velocity containing both the\ncoherence length and the size of the potential. The third is the divergence of\nthe nucleation time, which is the time it takes for the potential to nucleate\nvortices, near the critical parameters for vortex nucleation.",
        "positive": "Hybridization of first and second sound in a weakly-interacting Bose gas: Using Landau's theory of two-fluid hydrodynamics we investigate the sound\nmodes propagating in a uniform weakly-interacting superfluid Bose gas for\nvalues of temperature, up to the critical point. In order to evaluate the\nrelevant thermodynamic functions needed to solve the hydrodynamic equations,\nincluding the temperature dependence of the superfluid density, we use\nBogoliubov theory at low temperatures and the results of a perturbative\napproach based on Beliaev diagrammatic technique at higher temperatures.\nSpecial focus is given on the hybridization phenomenon between first and second\nsound which occurs at low temperatures of the order of the interaction energy\nand we discuss explicitly the behavior of the two sound velocities near the\nhybridization point."
    },
    {
        "anchor": "Topological lattice using multi-frequency radiation: We describe a novel technique for creating an artificial magnetic field for\nultra-cold atoms using a periodically pulsed pair of counter propagating Raman\nlasers that drive transitions between a pair of internal atomic spin states: a\nmulti-frequency coupling term. In conjunction with a magnetic field gradient,\nthis dynamically generates a rectangular lattice with a non-staggered magnetic\nflux. For a wide range of parameters, the resulting Bloch bands have\nnon-trivial topology, reminiscent of Landau levels, as quantified by their\nChern numbers.",
        "positive": "Quantum decay of dark solitons in one dimensional Bose systems: Unless protected by the exact integrability, solitons are subject to\ndissipative forces, originating from a thermally fluctuating background. At low\nenough temperatures $T$ background fluctuations should be considered as being\nquantized which enables us to calculate finite lifetime of the solitons\n$\\tau\\sim T^{-4}$. We also find that the coherent nature of the quantum\nfluctuations leads to long-range interactions between the solitons mediated by\nthe superradiation. Our results are of relevance to current experiments with\nultracold atoms, while the approach may be extended to solitons in other media."
    },
    {
        "anchor": "Emergence of nonlinear behavior in the dynamics of ultracold bosons: We study the evolution of a system of interacting ultracold bosons, which\npresents nonlinear, chaotic, behaviors in the limit of very large number of\nparticles. Using the spectral entropy as an indicator of chaos and three\ndifferent numerical approaches : Exact diagonalization, truncated Husimi method\nand mean-field (Gross-Pitaevskii) approximation, we put into evidence the\ndestructive impact of quantum noise on the emergence of the nonlinear dynamics.",
        "positive": "Soft quantum vibrations of PT-symmetric nonlinear ion chain: We theoretically study the quantum dynamics of transverse vibrations of a\none-dimensional chain of trapped ions in harmonic potentials interacting via a\nReggeon-type cubic nonlinearity that is nonunitary but preserves PT symmetry.\nWe propose the notion of quantum fragility for the dissipative structural phase\ntransition that spontaneously breaks the PT symmetry. In the quantum fragile\nregime, the nonlinearity dominates the response to mechanical perturbations and\nthe chain supports neither the ordinary quantum phonons of a Luttinger liquid,\nnor the supersonic solitons that arise in classical fragile critical points in\nthe absence of fluctuations. Quantum fluctuations, approximately captured\nwithin a one-loop renormalization group, give rise to mechanical excitations\nwith a strongly momentum-dependent phonon velocity and dissipative spectral\nbehavior. Observable signatures of the quantum fragile chain in trapped ion\nsystems are discussed."
    },
    {
        "anchor": "Quantum thermodynamic properties of a cold atom coupled to a heat bath\n  in non-Abelian gauge potentials: In this work, we study different quantum thermodynamic functions (QTFs) of a\ncold atom subjected to an artificial non-Abelian uniform magnetic field and\nlinearly coupled to a quantum heat bath through either usual\ncoordinate-coordinate coupling or through momentum variables. The bath is\nmodelled as a collection of independent quantum harmonic oscillators. In each\nof the coupling scheme, the effect of the non-Abelian magnetic field on\ndifferent QTFs are explicitly demonstrated for a U(2) gauge transformation. In\neach case, we show that the free energy has a different expression than that\nfor the Abelian case. We consider two illustrative heat bath spectrum (Ohmic\nbath and Drude model) to evaluate explicit closed form expressions of free\nenergy (F), specific heat (C), and entropy (S) in the low temperature limit for\neach of the above mentioned coupling scheme. The dependence of different QTFs\non the non-Abelian magnetic field are pointed out even if the gauge potential\nis uniform in space.",
        "positive": "Robust storage qubits in ultracold polar molecules: Quantum states with long-lived coherence are essential for quantum\ncomputation, simulation and metrology. The nuclear spin states of ultracold\nmolecules prepared in the singlet rovibrational ground state are an excellent\ncandidate for encoding and storing quantum information. However, it is\nimportant to understand all sources of decoherence for these qubits, and then\neliminate them, in order to reach the longest possible coherence times. Here,\nwe fully characterise the dominant mechanisms for decoherence of a storage\nqubit in an optically trapped ultracold gas of RbCs molecules using\nhigh-resolution Ramsey spectroscopy. Guided by a detailed understanding of the\nhyperfine structure of the molecule, we tune the magnetic field to where a pair\nof hyperfine states have the same magnetic moment. These states form a qubit,\nwhich is insensitive to variations in magnetic field. Our experiments reveal an\nunexpected differential tensor light shift between the states, caused by weak\nmixing of rotational states. We demonstrate how this light shift can be\neliminated by setting the angle between the linearly polarised trap light and\nthe applied magnetic field to a magic angle of\n$\\arccos{(1/\\sqrt{3})}\\approx55^{\\circ}$. This leads to a coherence time\nexceeding 6.9 s (90% confidence level). Our results unlock the potential of\nultracold molecules as a platform for quantum computation."
    },
    {
        "anchor": "Describing many-body bosonic waveguide scattering with the truncated\n  Wigner method: We consider quasi-stationary scattering of interacting bosonic matter waves\nin one-dimensional waveguides, as they arise in guided atom lasers. We show how\nthe truncated Wigner (tW) method, which corresponds to the semiclassical\ndescription of the bosonic many-body system on the level of the diagonal\napproximation, can be utilized in order to describe such many-body bosonic\nscattering processes. Special emphasis is put on the discretization of space at\nthe exact quantum level, in order to properly implement the semiclassical\napproximation and the tW method, as well as on the discussion of the results to\nbe obtained in the continuous limit.",
        "positive": "From Cosmology to Cold Atoms: Observation of Sakharov Oscillations in\n  Quenched Atomic Superfluids: Sakharov oscillations, conventionally discussed in the context of early\nuniverse evolution and the anisotropy of cosmic microwave background radiation,\nis the manifestation of interfering acoustic waves synchronously generated in\nan ideal fluid. Here we report the laboratory demonstration of Sakharov\noscillations in a quenched atomic superfluid. We quench the sample by Feshbach\ntuning and monitor the subsequent density fluctuations at different time and\nlength scales by in situ imaging. Sakharov oscillations are identified as the\nmulti-peak structure in the atomic density power spectrum, resembling that of\nthe cosmic microwave background. We also observe Sakharov oscillations in the\ntime domain, from which we extract the energy dispersion of the superfluid, and\ndetermine the sonic horizon of the excitations."
    },
    {
        "anchor": "Observing the two-dimensional Bose glass in an optical quasicrystal: The combined effect of disorder and interactions is central to the richness\nof condensed matter physics and can lead to novel quantum states such as the\nBose glass phase in disordered bosonic systems. Here, we report on the\nexperimental realisation of the two-dimensional Bose glass using ultra-cold\natoms in an eight-fold symmetric quasicrystalline optical lattice. By probing\nthe coherence properties of the system, we observe a Bose glass to superfluid\ntransition and map out the phase diagram in the weakly interacting regime.\nMoreover, we reveal the non-ergodic nature of the Bose glass by probing the\ncapability to restore coherence. Our observations are in good agreement with\nrecent quantum Monte Carlo predictions and pave the way for experimentally\ntesting the connection between the Bose glass, many-body localisation, and\nglassy dynamics more generally.",
        "positive": "Phase diagrams of polarized ultra-cold gases on attractive-U Hubbard\n  ladders: We consider a quasi-one-dimensional model of a two-component Fermi gas at\nzero temperature on one, two and three-leg attractive-U Hubbard ladders. We\nconstruct the grand canonical phase diagram of a two-component spin-polarized\ngas. We find that the structure of the phase diagram of the attractive-U\nHubbard model for two and three leg ladders significantly differs q from the\nstructure of the phase diagram of a single chain. We argue that the single\nchain model is a special case, and that multichain ladders display qualitative\nfeatures of the 1D-to-3D crossover, observed in experiments with trapped\nultracold gases."
    },
    {
        "anchor": "Equation of state of a polarized Fermi gas in the Bose-Einstein\n  Condensate limit: We present a theoretical study of the BEC-BCS crossover in the\nBose-Einstein-Condensate regime (BEC), in the case of an unequal number of\nfermions of two species. We take full account of the composite nature of the\ndimers made of fermions. In the limit of low densities, we calculate the ground\nstate energy of the system, or equivalentely the chemical potentials of each\nspecies as well as the one-particle gap and the energy of an \"impurity\"\nimmersed in a Fermi sea. For the chemical potentials we go up to order\n(density)^{4/3}.The results found involve the exact atom-dimer a_{AD} and\ndimer-dimer a_{DD} scattering lengths and therefore include the 3 and 4-body\nproblems in the manybody problem. We briefly comment on the importance of the\ndifferent mean-field corrections for recent experiments.",
        "positive": "Effects of an attractive three body interaction on a spin-1 Bose Hubbard\n  model: We study the effects of an attractive three body interaction potential on a\nspin-1 ultracold Bose gas using mean field approach (MFA). For an\nantiferromagnetic (AF) interaction, the third MI lobe is predominantly\naffected, where it completely engulfs the second and the fourth MI lobes at\nlarge values of the interaction strength. Albeit no significant change is\nobserved beyond the fourth MI lobe. The formation of the spin singlet (nematic)\nMI phase and the different order of phase transitions to the SF phase have been\ncarefully scrutinized with the help of spin eigenvalues and spin nematic order\nparameter. In the ferromagnetic case, the phase diagram shows similar features\nas that of a scalar Bose gas. We have compared our results on the MFA phase\ndiagrams for both types of the interaction potential via a perturbation\nexpansion in both the cases."
    },
    {
        "anchor": "Anharmonicity-Induced Criticality of Collective Excitation in a Trapped\n  Bose-Einstein Condensate: We investigate the low energy excitations of a dilute atomic Bose gas\nconfined in a anharmonic trap interacting with repulsive forces. The dispersion\nlaw of both surface and compression modes are derived and analyzed for large\nnumbers of atoms in the trap, which show two branches of excitation and appear\na two critical value. For a upper limit, BEC can be unstable with respect to\nsome specific collective excitation, while for the lower limit, the frequency\nof collective excitation under anharmonic influence can be effectively lower\nthan that without anharmonicity. Our work reveals the key role played by the\nanharmonicity and interatomic forces which introduce a rich structure in the\ndynamic behavior of these new many-body systems.",
        "positive": "Parity effect in a mesoscopic Fermi gas: We develop a quantitative analytic theory that accurately describes the\nodd-even effect observed experimentally in a one-dimensional, trapped Fermi gas\nwith a small number of particles [G. Z\\\"urn et al., Phys. Rev. Lett. 111,\n175302 (2013)]. We find that the underlying physics is similar to the parity\neffect known to exist in ultrasmall mesoscopic superconducting grains and\natomic nuclei. However, in contrast to superconducting nanograins, the density\n(Hartree) correction dominates over the superconducting pairing fluctuations\nand leads to a much more pronounced odd-even effect in the mesoscopic, trapped\nFermi gas. We calculate the corresponding parity parameter and separation\nenergy using both perturbation theory and a path integral framework in the\nmesoscopic limit, generalized to account for the effects of the trap, pairing\nfluctuations, and Hartree corrections. Our results are in an excellent\nquantitative agreement with experimental data and exact diagonalization.\nFinally, we discuss a few-to-many particle crossover between the perturbative\nmesoscopic regime and non-perturbative many-body physics that the system\napproaches in the thermodynamic limit."
    },
    {
        "anchor": "Atom transistor from the point of view of quantum nonequilibrium\n  dynamics: We analyze the atom field-effect transistor scheme [J. A. Stickney, D. Z.\nAnderson and A. A. Zozulya, Phys. Rev. A 75, 013608 (2007)] using the standard\ntools of nonequlilibrium dynamics. In particular, we study the deviations from\nthe Eigenstate Thermalization Hypothesis, quantum fluctuations, and the density\nof states, both ab initio and using their mean-field analogues. Having fully\nestablished the quantum vs. mean-field correspondence for this system, we\nattempt, using a mean-field model, to interpret the off-on threshold in our\ntransistor as the onset of ergodicity---a point where the system becomes able\nto visit the thermal values of the former integrals of motion in principle,\nalbeit not being fully thermalized yet.",
        "positive": "Exploring phonon-like interactions in one-dimensional Bose-Fermi\n  mixtures: With the objective of simulating the physical behavior of electrons in a\ndynamic background, we investigate a cold atomic Bose-Fermi mixture confined in\nan optical lattice potential solely affecting the bosons. The bosons, residing\nin the deep superfluid regime, inherit the periodicity of the optical lattice,\nsubsequently serving as a dynamic potential for the polarized fermions. Owing\nto the atom-phonon interaction between the fermions and the condensate, the\ncoupled system exhibits a Berezinskii-Kosterlitz-Thouless transition from a\nLuttinger liquid to a Peierls phase. However, under sufficiently strong\nBose-Fermi interaction, the Peierls phase loses stability, leading to either a\ncollapsed or a separated phase. We find that the primary function of the\noptical lattice is to stabilize the Peierls phase. Furthermore, the presence of\na confining harmonic trap induces a diverse physical behavior, surpassing what\nis observed for either bosons or fermions individually trapped. Notably, under\nattractive Bose-Fermi interaction, the insulating phase may adopt a fermionic\nwedding-cake-like configuration, reflecting the dynamic nature of the\nunderlying lattice potential. Conversely, for repulsive interaction, the trap\ndestabilizes the Peierls phase, causing the two species to separate."
    },
    {
        "anchor": "Ferromagnetism in a Repulsive Atomic Fermi Gas with Correlated Disorder: We investigate the zero-temperature ferromagnetic behavior of a two-component\nrepulsive Fermi gas in the presence of a correlated random field that\nrepresents an optical speckle pattern. The density is tuned so that the\n(noninteracting) Fermi energy is close to the mobility edge of the Anderson\nlocalization transition. We employ quantum Monte Carlo simulations to determine\nvarious ground-state properties, including the equation of state, the magnetic\nsusceptibility, and the energy of an impurity immersed in a polarized Fermi gas\n(repulsive polaron). In the weakly interacting limit, the magnetic\nsusceptibility is found to be suppressed by disorder. However, it rapidly\nincreases with the interaction strength, and it diverges at a much weaker\ninteraction strength compared to the clean gas. Both the transition from the\nparamagnetic phase to the partially ferromagnetic phase, and the one from the\npartially to the fully ferromagnetic phase are strongly favored by disorder,\nindicating a case of order induced by disorder.",
        "positive": "Three-dimensional Isotropic Droplets in Rydberg-dressed Bose Gases: We predict a scheme for the creation of isotropic three-dimensional droplets\nin Rydbeg-dressed Bose gases, which contain both repulsive contact interactions\nand attractive van der Waals interactions causing the quantum fluctuation\neffect non-negligible. We present detailed beyond mean-field calculations with\nLee-Huang-Yang correction and demonstrate the existence of isotropic droplets\nunder realistic experimental conditions. Stable droplets possess flat-top\ndensity distribution, and their chemical potentials decrease with the particle\nnumber expansion towarding a critical value. We distinguish droplets from\nbright solitons through peak density, width of condensate and quantum depletion\ncalculations. We summarize a phase diagram of realizing droplets, and\nsubsequently highlight the stability of droplets by real time evolution as well\nas collisions. Our work provides a novel platform for investigating excitation\nspectrum and superfluid nature of droplets."
    },
    {
        "anchor": "Dipolar Stabilization of an Attractive Bose Gas in a One Dimensional\n  Lattice: We experimentally show that dipolar interaction can stabilize otherwise\nunstable many-body systems like an attractive Bose gas. In a one dimensional\nlattice the repulsive dipolar on-site interaction balances negative scattering\nlengths up to -17 Bohr radii and stabilizes the chromium Bose-Einstein\ncondensate. For reduced lattice depths, the dipolar stabilization turns into\ndestabilization. We probe the full cross-over between the two regimes and our\nresults are in excellent agreement with theoretical calculations, which reveal\nsignificant dipolar inter-site interactions.",
        "positive": "Calibration of Interaction Energy between Bose and Fermi Superfluids: In this letter we study the interaction energy in a mixture of Bose and Fermi\nsuperfluids realized in recent cold atom experiment. On the\nBose-Einstein-condensate (BEC) side of a Feshbach resonance between fermionic\natoms, this interaction energy can be directly related to the scattering length\nbetween a bosonic atom and a dimer composed of fermions. We calculate the\natom-dimer scattering length from a three-body analysis with both a zero-range\nmodel and a separable model including the van der Waals length scale, and we\nfind significant deviation from the result given by a mean-field approach. We\nalso find that the multiple scattering between atom and dimer can account for\nsuch a deviation. Our results provide a calibration to the mean-field\ninteraction energy, which can be verified by measuring the shift of collective\noscillation frequency."
    },
    {
        "anchor": "Dynamics of polaron formation in 1D Bose gases in the strong-coupling\n  regime: We discuss the dynamics of the formation of a Bose polaron when an impurity\nis injected into a weakly interacting one-dimensional Bose condensate. While\nfor small impurity-boson couplings this process can be described within the\nFroehlich model as generation, emission and binding of Bogoliubov phonons, this\nis no longer adequate if the coupling becomes strong. To treat this regime we\nconsider a mean-field approach beyond the Froehlich model which accounts for\nthe backaction to the condensate, complemented with Truncated Wigner\nsimulations to include quantum fluctuation. For the stationary polaron we find\nan energy-momentum relation that displays a smooth crossover from a convex to a\nconcave dependence associated with a non-monotonous relation between impurity\nvelocity and polaron momentum. For larger momenta the energy is a periodic\nfunction including regions of negative impurity velocity. Studying the polaron\nformation after turning on the impurity-boson coupling quasi adiabatically and\nin a sudden quench, we find a very rich scenario of dynamical regimes. Due to\nthe build-up of an effective mass, the impurity is slowed down even if its\ninitial velocity is below the Landau critical value. For larger initial\nvelocities we find deceleration and even backscattering caused by emission of\ndensity waves or grey solitons and subsequent formation of stationary polaron\nstates in different momentum sectors. In order to analyze the effect of quantum\nfluctuations we consider a trapped condensate to avoid 1D infrared\ndivergencies. Using Truncated Wigner simulations in this case we show under\nwhat conditions the influence of quantum fluctuations is small.",
        "positive": "Quantum phases of constrained dipolar bosons in coupled one-dimensional\n  optical lattices: We investigate a system of two- and three-body constrained dipolar bosons in\na pair of one-dimensional optical lattices coupled to each other by the\nnon-local dipole-dipole interactions. Assuming attractive dipole-dipole\ninteractions, we obtain the ground state phase diagram of the system by\nemploying the cluster mean-field theory. The competition between the repulsive\non-site and attractive nearest-neighbor interactions between the chains yields\nthree kinds of superfluids; namely the trimer superfluid, pair superfluid and\nthe usual single particle superfluid along with the insulating Mott phase at\nthe commensurate density. Besides, we also realize simultaneous existence of\nMott insulator and superfluid phases for the two- and three-body constrained\nbosons, respectively. We also analyze the stability of these quantum phases in\nthe presence of a harmonic trap potential."
    },
    {
        "anchor": "Dynamics and kinetics of quasiparticle decay in a nearly-one-dimensional\n  degenerate Bose gas: We consider decay of a quasiparticle in a nearly-one-dimensional\nquasicondensate of trapped atoms, where virtual excitations of transverse modes\nbreak down one-dimensionality and integrability, giving rise to effective\nthree-body elastic collisions. We calculate the matrix element for the process\nthat involves one incoming quasiparticle and three outgoing quasiparticles.\nScattering that involves low-frequency modes with high thermal population\nresults in a diffusive dynamics of a bunch of quasiparticles created in the\nsystem.",
        "positive": "Hidden Magnetism in Periodically Modulated One Dimensional Dipolar\n  Fermions: The experimental realization of time dependent ultracold lattice systems has\npaved the way towards the implementation of new Hubbard-like Hamiltonians. We\nshow that in a one dimensional two components lattice dipolar Fermi gas the\ncompetition between long range repulsion and correlated hopping induced by\nperiodically modulated on-site interaction allows for the formation of exotic\nhidden magnetic phases. The magnetism, characterized solely by string-like\nnonlocal order parameters, manifests itself both in the charge and, noticeably,\nin the spin degrees of freedom. Such behavior is enlighten by employing both\nLuttinger theory and numerical methods. Crucially the range of parameters for\nwhich hidden magnetism is present can be reached by means of the currently\navailable experimental setups and probes."
    },
    {
        "anchor": "Momentum-resolved study of an array of 1D strongly phase-fluctuating\n  Bose gases: We investigate the coherence properties of an array of one-dimensional Bose\ngases with short-scale phase fluctuations. The momentum distribution is\nmeasured using Bragg spectroscopy and an effective coherence length of the\nwhole ensemble is defined. In addition, we propose and demonstrate that\ntime-of-flight absorption imaging can be used as a simple probe to directly\nmeasure the coherence-length of 1D gases in the regime where phase-fluctuations\nare strong. This method is suitable for future studies such as investigating\nthe effect of disorder on the phase coherence.",
        "positive": "Lattice bosons in a quasi-disordered environment: The effects of\n  next-nearest-neighbor hopping on localization and Bose-Einstein condensation: We present a theoretical study of the effects of the next-nearest-neighbor\n(NNN) hopping ($t_2$) on the properties of non-interacting bosons in optical\nlattices in the presence of an Aubry-Andr\\'{e} quasi-disorder. First we\ninvestigate, employing exact diagonalization, the effects of $t_2$ on the\nlocalization properties of a single boson. The localization is monitored using\nan entanglement measure as well as with inverse participation ratio. We find\nthat the sign of $t_2$ has a significant influence on the localization effects.\nWe also provide analytical results in support of the trends found in the\nlocalization behavior. Further, we extend these results including the effects\nof a harmonic potential which obtains in experiments. Next, we study the\neffects of $t_2$ on Bose-Einstein condensation. We find that, a positive $t_2$\nstrongly enhances the low temperature thermal depletion of the condensate while\na negative $t_2$ reduces it. It is also found that, for a fixed temperature,\nincreasing the quasi-disorder strength reduces the condensate fraction in the\nextended regime while enhancing it in the localized regime. We also investigate\nthe effects of boundary conditions and that of the phase of the AA potential on\nthe condensate. These are found to have significant effects on the condensate\nfraction in the localization transition region."
    },
    {
        "anchor": "Dynamics of Vector Solitons in Bose-Einstein Condensates: We analyze the dynamics of two-component vector solitons, namely\nbright-in-dark solitons, via the variational approximation in Bose-Einstein\ncondensates. The system is described by a vector nonlinear Schr\\\"odinger\nequation appropriate to multi-component Bose-Einstein condensates (BECs). The\nvariational approximation is based on hyperbolic secant (hyperbolic tangent)\nfor the bright (dark) component, which leads to a system of coupled ordinary\ndifferential equations for the evolution of the ansatz parameters. We obtain\nthe oscillation dynamics of two-component dark-bright vector solitons.\nAnalytical calculations are performed for same-width components in the vector\nsoliton and numerical calculations extend the results to arbitrary widths. We\ncalculate the binding energy of the system and find it proportional to the\nintercomponent coupling interaction, and numerically demonstrate the break up\nor unbinding of a dark-bright soliton. Our calculations explore observable\neigenmodes, namely the internal oscillation eigenmode and the Goldstone\neigenmode. We find analytically that the density of the bright component is\nrequired to be less than the density of the dark component in order to find the\ninternal oscillation eigenmode of the vector soliton and support the existence\nof the dark-bright soliton. This outcome is confirmed by numerical results.\nNumerically, we find that the oscillation frequency is amplitude independent.\nFor dark-bright vector solitons in $^{87}$Rb we find that the oscillation\nfrequency range is 90 to 405 Hz, and therefore observable in multi-component\nBEC experiments.",
        "positive": "Decoherence and momentum relaxation in Fermi-polaron Rabi dynamics: a\n  kinetic equation approach: Despite the paradigmatic nature of the Fermi-polaron model, the theoretical\ndescription of its nonlinear dynamics poses challenges. Here, we apply a\nquantum kinetic theory of driven polarons to recent experiments with ultracold\natoms, where Rabi oscillations between a Fermi-polaron state and a\nnon-interacting level were reported. The resulting equations separate\ndecoherence from momentum relaxation, with the corresponding rates showing a\ndifferent dependence on microscopic scattering processes and quasi-particle\nproperties. We describe both the polaron ground state and the excited\nrepulsive-polaron state and we find a good quantitative agreement between our\npredictions and the available experimental data without any fitting parameter.\nOur approach not only takes into account collisional phenomena, but also it can\nbe used to study the different roles played by decoherence and the collisional\nintegral in the strongly interacting highly-imbalanced mixture of Fermi gases."
    },
    {
        "anchor": "High-momentum oscillating tails of strongly interacting 1D gases in a\n  box: We study the momentum distribution of strongly interacting one-dimensional\nmixtures of particles at zero temperature in a box potential. We find that the\nmagnitude of the $1/k^4$ tail of the momentum distribution is not only due to\nshort-distance correlations, but also to the presence of the rigid walls,\nbreaking the Tan's relation relating this quantity to the adiabatic derivative\nof the energy with respect to the inverse of the interaction strength. The\nadditional contribution is a finite-size effect that includes a $k$-independent\nand an oscillating part. This latter, surprisingly, encodes information on\nlong-range spin correlations.",
        "positive": "Spin-rotation coupling in p-wave Feshbach resonances: We report evidence for spin-rotation coupling in $p$-wave Feshbach resonances\nin an ultracold mixture of fermionic $^6$Li and bosonic $^{133}$Cs lifting the\ncommonly observed degeneracy of states with equal absolute value of\norbital-angular-momentum projection on the external magnetic field. By\nemploying magnetic field dependent atom-loss spectroscopy we find triplet\nstructures in $p$-wave resonances. Comparison with coupled-channel\ncalculations, including contributions from both spin-spin and spin-rotation\ninteractions, yields a spin-rotation coupling parameter\n$|\\gamma|=0.566(50)\\times10^{-3}$. Our findings highlight the potential of\nFeshbach resonances in revealing subtle molecular couplings and providing\nprecise information on electronic and nuclear wavefunctions, especially at\nshort internuclear distance. The existence of a non-negligible spin-rotation\nsplitting may have consequences for future classifications of $p$-wave\nsuperfluid phases in spin-polarized fermions."
    },
    {
        "anchor": "Order by Disorder in Spin-Orbit Coupled Bose-Einstein Condensates: Motivated by recent experiments, we investigate the system of\nisotropically-interacting bosons with Rashba spin-orbit coupling. At the\nnon-interacting level, there is a macroscopic ground-state degeneracy due to\nthe many ways bosons can occupy the Rashba spectrum. Interactions treated at\nthe mean-field level restrict the possible ground-state configurations, but\nthere remains an accidental degeneracy not corresponding to any symmetry of the\nHamiltonian, indicating the importance of fluctuations. By finding analytical\nexpressions for the collective excitations in the long-wavelength limit and\nthrough numerical solution of the full Bogoliubov- de Gennes equations, we show\nthat the system condenses into a single momentum state of the Rashba spectrum\nvia the mechanism of order by disorder. We show that in 3D the quantum\ndepletion for this system is small, while the thermal depletion has an infrared\nlogarithmic divergence, which is removed for finite-size systems. In 2D, on the\nother hand, thermal fluctuations destabilize the system.",
        "positive": "Breathing mode of two-dimensional atomic Fermi gases in harmonic traps: For two-dimensional (2D) atomic Fermi gases in harmonic traps, the SO(2,1)\nsymmetry is broken by the interatomic interaction explicitly via the contact\ncorrelation operator. Consequently the frequency of the breathing mode\n$\\omega_B$ of the 2D Fermi gas can be different from $2\\omega_0$, with\n$\\omega_0$ the trapping frequency of harmonic potentials. At zero temperature,\nwe use the sum rules of density correlation functions to yield upper bounds for\n$\\omega_B$. We further calculate $\\omega_B$ through the Euler equations in the\nhydrodynamic regime. The obtained value of $\\omega_B$ satisfies the upper\nbounds and shows deviation from $2\\omega_0$ which can be as large as about 8%."
    },
    {
        "anchor": "Distinguishing Quantum Phases through Cusps in Full Counting Statistics: Measuring physical observables requires averaging experimental outcomes over\nnumerous identical measurements. The complete distribution function of possible\noutcomes or its Fourier transform, known as the full counting statistics,\nprovides a more detailed description. This method captures the fundamental\nquantum fluctuations in many-body systems and has gained significant attention\nin quantum transport research. In this letter, we propose that cusp\nsingularities in the full counting statistics are a novel tool for\ndistinguishing between ordered and disordered phases. As a specific example, we\nfocus on the superfluid-to-Mott transition in the Bose-Hubbard model and\nintroduce $Z_A(\\alpha)=\\langle \\exp({i\\alpha \\sum_{i\\in\nA}(\\hat{n}_i}-\\overline{n}))\\rangle $ with $\\overline{n}=\\langle n_i \\rangle$.\nThrough both analytical analysis and numerical simulations, we demonstrate that\n$\\partial_\\alpha \\log Z_A(\\alpha)$ exhibits a discontinuity near $\\alpha=\\pi$\nin the superfluid phase when the subsystem size is sufficiently large, while it\nremains smooth in the Mott phase. This discontinuity can be interpreted as a\nfirst-order transition between different semi-classical configurations of\nvortices. We anticipate that our discoveries can be readily tested using\nstate-of-the-art ultracold atom and superconducting qubit platforms.",
        "positive": "Swallowtail Structure in Fermi Superfluids with Periodically Modulated\n  Interactions: We study the superfluid flow in a quasi-one-dimensional Fermi gas with\nspatially modulated interactions induced by an optical Feshbach resonance. Due\nto the competition between the periodicity of the modulated interaction and the\nnonlinearity of the background interaction, an interesting swallowtail\nstructure emerges in the energy spectrum under appropriate parameters. As the\ninteraction strengths are tuned, the swallowtail structure may disappear,\ngiving rise to various different states on a rich phase diagram. We investigate\nthe spatial distribution of the order parameter and the particle density under\nvarious parameters, which are useful for the experimental detection of the\ninteresting phases in these systems."
    },
    {
        "anchor": "Shear viscosity of a universal Fermi gas near the superfluid phase\n  transition: We precisely measure the shear viscosity for a resonantly interacting Fermi\ngas as a function of temperature, from nearly the ground state through the\nsuperfluid phase transition at a critical temperature $T_c$. Using an iterative\nmethod to invert the data, we extract the {\\it local} shear viscosity\ncoefficient $\\alpha_S(\\theta)$ versus reduced temperature $\\theta$, revealing\npreviously hidden features. We find that $\\alpha_S$ begins to decrease rapidly\nwith decreasing $\\theta$ well above $T_c$, suggesting that preformed pairs play\nan important role. Further, we observe that the derivative $\\alpha_S'(\\theta)$\nhas a maximum at $T_c$. We compare the local data to several microscopic\ntheories. Finally, we determine the local ratio of the shear viscosity to the\nentropy density.",
        "positive": "Phase diagram of a rapidly-rotating two-component Bose gas: We derive analytically the phase diagram of a two-component Bose gas confined\nin an anharmonic potential, which becomes exact and universal in the limit of\nweak interactions and small anharmonicity of the trapping potential. The\ntransitions between the different phases, which consist of vortex states of\nsingle and multiple quantization, are all continuous because of the addition of\nthe second component."
    },
    {
        "anchor": "Quantum Engineering of a Low-Entropy Gas of Heteronuclear Bosonic\n  Molecules in an Optical Lattice: We demonstrate a generally applicable technique for mixing two-species\nquantum degenerate bosonic samples in the presence of an optical lattice, and\nwe employ it to produce low-entropy samples of ultracold 87Rb133Cs Feshbach\nmolecules with a lattice filling fraction exceeding 30%. Starting from two\nspatially separated Bose-Einstein condensates of Rb and Cs atoms, Rb-Cs atom\npairs are efficiently produced by using the superfluid-to-Mott insulator\nquantum phase transition twice, first for the Cs sample, then for the Rb\nsample, after nulling the Rb-Cs interaction at a Feshbach resonance's zero\ncrossing. We form molecules out of atom pairs and characterize the mixing\nprocess in terms of sample overlap and mixing speed. The dense and ultracold\nsample of more than 5000 RbCs molecules is an ideal starting point for\nexperiments in the context of quantum many-body physics with long-range dipolar\ninteractions.",
        "positive": "Confinement-induced Resonance of Alkaline-earth-metal-like Atoms in\n  Anisotropic Quasi-one-dimensional Traps: We study the confinement-induced resonance (CIR) of $^{173}$Yb atoms near an\norbital Feshbach resonance in a quasi-one-dimensional tube with transversal\nanisotropy. By solving the two-body scattering problem, we obtain the location\nof CIR for various anisotropy ratio and magnetic field. Our results show that\nthe anisotropy of the trapping potential can serve as an additional knob to\ntune the location of CIR. In particular, one can shift the location of CIR to\nthe region attainable in current experiment. We also study the energy spectrum\nof the system and analyze the properties of CIR from the perspective of bound\nstates. We find that as the orbital Feshbach resonance acquires two nearly\ndegenerate scattering channels, which in general have different threshold\nenergies, CIR takes place when the closed channel bound state energy becomes\ndegenerate with one of the thresholds."
    },
    {
        "anchor": "Efficient many-body non-Markovian dynamics of organic polaritons: We show how to simulate a model of many molecules with both strong coupling\nto many vibrational modes and collective coupling to a single photon mode. We\ndo this by combining process tensor matrix product operator methods with a\nmean-field approximation which reduces the dimension of the problem. We analyze\nthe steady-state of the model under incoherent pumping to determine the\ndependence of the polariton lasing threshold on cavity detuning, light-matter\ncoupling strength, and environmental temperature. Moreover, by measuring\ntwo-time correlations, we study quadratic fluctuations about the mean-field to\ncalculate the photoluminescence spectrum. Our method enables one to simulate\nmany-body systems with strong coupling to multiple environments, and to extract\nboth static and dynamical properties.",
        "positive": "Faster State Preparation across Quantum Phase Transition Assisted by\n  Reinforcement Learning: An energy gap develops near quantum critical point of quantum phase\ntransition in a finite many-body (MB) system, facilitating the ground state\ntransformation by adiabatic parameter change. In real application scenarios,\nhowever, the efficacy for such a protocol is compromised by the need to balance\nfinite system life time with adiabaticity, as exemplified in a recent\nexperiment that prepares three-mode balanced Dicke state near deterministically\n[PNAS {\\bf 115}, 6381 (2018)]. Instead of tracking the instantaneous ground\nstate as unanimously required for most adiabatic crossing, this work reports a\nfaster sweeping policy taking advantage of excited level dynamics. It is\nobtained based on deep reinforcement learning (DRL) from a multi-step training\nscheme we develop. In the absence of loss, a fidelity $\\ge 99\\%$ between\nprepared and the target Dicke state is achieved over a small fraction of the\nadiabatically required time. When loss is included, training is carried out\naccording to an operational benchmark, the interferometric sensitivity of the\nprepared state instead of fidelity, leading to better sensitivity in about half\nof the previously reported time. Implemented in a Bose-Einstein condensate of\n$\\sim 10^4$ $^{87}$Rb atoms, the balanced three-mode Dicke state exhibiting an\nimproved number squeezing of $13.02\\pm0.20$ dB is observed within 766 ms,\nhighlighting the potential of DRL for quantum dynamics control and quantum\nstate preparation in interacting MB systems."
    },
    {
        "anchor": "Reliable equation of state for composite bosons in the 2D BCS-BEC\n  crossover: We briefly discuss recent experiments on the BCS-BEC crossover with ultracold\nalkali-metal atoms both in three-dimensional configurations and two-dimensional\nones. Then we analyze the quantum-field-theory formalism used to describe an\nattractive $D$-dimensional Fermi gas taking into account Gaussian fluctuations.\nFinally, we apply this formalism to obtain a reliable equation of state of the\n2D system at low temperaratures in the BEC regime of the crossover by\nperforming a meaningful dimensional regularization of the divergent zero-point\nenergy of collective bosonic excitations.",
        "positive": "Nonlinear quantum interferometry with Bose condensed atoms: In quantum interferometry, it is vital to control and utilize nonlinear\ninteractions for achieving high-precision measurements. Attribute to their long\ncoherent time and high controllability, ultracold atoms including Bose\ncondensed atoms have been widely used for implementing quantum interferometry.\nHere, we review the recent progresses in theoretical studies of quantum\ninterferometry with Bose condensed atoms. In particular, we focus on the\nnonlinear phenomena induced by the atom-atom interaction and how to control and\nutilize these nonlinear phenomena. Under the mean-field description, due to the\natom-atom interaction, matter-wave solitons appear in the interference\npatterns, and macroscopic quantum self-trapping exists in the Bose-Josephson\njunctions. Under the many-body description, the atom-atom interaction can\ngenerate non-classical entanglement, which may be utilized to achieve\nhigh-precision measurements beyond the standard quantum limit."
    },
    {
        "anchor": "Observation of a dynamical sliding phase superfluid with P-band bosons: Sliding phases have been long sought after in the context of coupled\nXY-models, as they are of relevance to various many-body systems such as\nlayered superconductors, freestanding liquid-crystal films, and cationic\nlipid-DNA complexes. Here we report an observation of a dynamical sliding phase\nsuperfluid that emerges in a nonequilibrium setting from the quantum dynamics\nof a three-dimensional ultracold atomic gas loaded into the P-band of a\none-dimensional optical lattice. A shortcut loading method is used to transfer\natoms into the P-band at zero quasimomentum within a very short time duration.\nThe system can be viewed as a series of \"pancake\"-shaped atomic samples. For\nthis far-out-of-equilibrium system, we find an intermediate time window with a\nlifetime around tens of milliseconds, where the atomic ensemble exhibits robust\nsuperfluid phase coherence in the pancake directions, but no coherence in the\nlattice direction, which implies a dynamical sliding phase superfluid. The\nemergence of the sliding phase is attributed to a mechanism of\ncross-dimensional energy transfer in our proposed phenomenological theory,\nwhich is consistent with experimental measurements. This experiment potentially\nopens up a novel venue to search for exotic dynamical phases by creating\nhigh-band excitations in optical lattices.",
        "positive": "Generic regimes of quantum many-body dynamics of trapped bosonic systems\n  with strong repulsive interactions: Two generically different but universal dynamical quantum many-body behaviors\nare discovered by probing the stability of trapped fragmented bosonic systems\nwith strong repulsive finite/long range inter-particle interactions. We use\ndifferent time-dependent processes to destabilize the systems -- a sudden\ndisplacement of the trap is accompanied by a sudden quench of the strength of\nthe inter-particle repulsion. A rather moderate non-violent evolution of the\ndensity in the first \"topology-preserved\" scenario is contrasted with a\nhighly-non-equilibrium dynamics characterizing an explosive changes of the\ndensity profiles in the second scenario. The many-body physics behind is\nidentified and interpreted in terms of self-induced time-dependent barriers\ngoverning the respective under- and over-a-barrier dynamical evolutions. The\nuniversality of the discovered scenarios is explicitly confirmed in 1D, 2D and\n3D many-body computations in (a)symmetric traps and repulsive finite/long range\ninter-particle interaction potentials of different shapes. Implications are\nbriefly discussed."
    },
    {
        "anchor": "Vortex states and spin textures of rotating spin-orbit-coupled\n  Bose-Einstein condensates in a toroidal trap: We consider the ground-state properties of Rashba spin-orbit-coupled\npseudo-spin-1/2 Bose-Einstein condensates (BECs) in a rotating two-dimensional\n(2D) toroidal trap. In the absence of spin-orbit coupling (SOC), the increasing\nrotation frequency enhances the creation of giant vortices for the initially\nmiscible BECs, while it can lead to the formation of semiring density patterns\nwith irregular hidden vortex structures for the initially immiscible BECs.\nWithout rotation, strong 2D isotropic SOC yields a heliciform-stripe phase for\nthe initially immiscible BECs. Combined effects of rotation, SOC, and\ninteratomic interactions on the vortex structures and typical spin textures of\nthe ground state of the system are discussed systematically. In particular, for\nfixed rotation frequency above the critical value, the increasing isotropic SOC\nfavors a visible vortex ring in each component which is accompanied by a hidden\ngiant vortex plus a (several) hidden vortex ring(s) in the central region. In\nthe case of 1D anisotropic SOC, large SOC strength results in the generation of\nhidden linear vortex string and the transition from initial phase separation\n(phase mixing) to phase mixing (phase separation). Furthermore, the peculiar\nspin textures including skyrmion lattice, skyrmion pair and skyrmion string are\nrevealed in this system.",
        "positive": "Spatial Landau-Zener-St\u00fcckelberg interference in spinor\n  Bose-Einstein condensates: We investigate the St\\\"{u}ckelberg oscillations of a spin-1 Bose-Einstein\ncondensate subject to a spatially inhomogeneous transverse magnetic field and a\nperiodic longitudinal field. We show that the time-domain St\\\"{u}ckelberg\noscillations result in interference fringes in the density profiles of all spin\ncomponents due to the spatial inhomogeneity of the transverse field. This\nphenomenon represents the Landau-Zener-St\\\"{u}ckelberg interference in the\nspace-domain. Since the magnetic dipole-dipole interaction between spin-1 atoms\ninduces an inhomogeneous effective magnetic field, interference fringes also\nappear if a dipolar spinor condensate is driven periodically. We also point out\nsome potential applications of this spatial Landau-Zener-St\\\"{u}kelberg\ninterference."
    },
    {
        "anchor": "Edge-state instabilities of bosons in a topological band: In this work, we consider the dynamics of bosons in bands with non-trivial\ntopological structure. In particular, we focus on the case where bosons are\nprepared in a higher-energy band and allowed to evolve. The Bogoliubov theory\nabout the initial state can have a dynamical instability, and we show that it\nis possible to achieve the interesting situation where the topological edge\nmodes are unstable while all bulk modes are stable. Thus, after the initial\npreparation, the edge modes will become rapidly populated. We illustrate this\nwith the Su-Schrieffer-Heeger model which can be realized with a double-well\noptical lattice and is perhaps the simplest model with topological edge states.\nThis work provides a direct physical consequence of topological bands whose\nproperties are often not of immediate relevance for bosonic systems.",
        "positive": "Propagation of collective pair excitations in disordered Bose\n  superfluids: We study the effect of disorder on the propagation of collective excitations\nin a disordered Bose superfluid. We incorporate local density depletion induced\nby strong disorder at the meanfield level, and formulate the transport of the\nexcitations in terms of a screened scattering problem. We show that the\ncompetition of disorder, screening, and density depletion induces a strongly\nnon-monotonic energy dependence of the disorder parameter. In three dimensions,\nit results in a rich localization diagram with four different classes of\nmobility spectra, characterized by either no or up to three mobility edges.\nImplications on experiments with disordered ultracold atoms are discussed."
    },
    {
        "anchor": "Local equilibration of fermions and bosons: Local kinetic equilibration is a prerequisite for hydrodynamics to be valid.\nHere it is described through a nonlinear diffusion equation for finite systems\nof fermions and bosons. The model is solved exactly for constant transport\ncoefficients in both cases. It has the proper Fermi-Dirac and Bose-Einstein\nequilibrium limits and can replace the relaxation-time approximation (RTA). The\nmicroscopic transport coefficients are determined through the macroscopic\nvariables temperature and local equilibration time. Applications to the\ntransverse energy of quarks and gluons in the initial stages of central\nrelativistic heavy-ion collisions, and to bosonic and fermionic atoms at low\nenergies appropriate for cold quantum gases are discussed.",
        "positive": "Tight-binding models for ultracold atoms in optical lattices: general\n  formulation and applications: Tight-binding models for ultracold atoms in optical lattices can be properly\ndefined by using the concept of maximally localized Wannier functions for\ncomposite bands. The basic principles of this approach are reviewed here, along\nwith different applications to lattice potentials with two minima per unit\ncell, in one and two spatial dimensions. Two independent methods for computing\nthe tight-binding coefficients - one ab initio, based on the maximally\nlocalized Wannier functions, the other through analytic expressions in terms of\nthe energy spectrum - are considered. In the one dimensional case, where the\ntight-binding coefficients can be obtained by designing a specific gauge\ntransformation, we consider both the case of quasi resonance between the two\nlowest bands, and that between s and p orbitals. In the latter case, the role\nof the Wannier functions in the derivation of an effective Dirac equation is\nalso reviewed. Then, we consider the case of a two dimensional honeycomb\npotential, with particular emphasis on the Haldane model, its phase diagram,\nand the breakdown of the Peierls substitution. Tunable honeycomb lattices,\ncharacterized by movable Dirac points, are also considered. Finally, general\nconsiderations for dealing with the interaction terms are presented."
    },
    {
        "anchor": "Stroboscopic observation of quantum many-body dynamics: Recent experiments have demonstrated single-site resolved observation of cold\natoms in optical lattices. Thus, in the future it may be possible to take\nrepeated snapshots of an interacting quantum many-body system during the course\nof its evolution. Here we address the impact of the resulting Quantum\n(anti-)Zeno physics on the many-body dynamics. We use the time-dependent\ndensity-matrix renormalization group to obtain the time evolution of the full\nmany-body wave function, which is then periodically projected in order to\nsimulate realizations of stroboscopic measurements. For the example of a\none-dimensional lattice of spin-polarized fermions with nearest-neighbor\ninteractions, we find regimes for which many-particle configurations are\nstabilized and destabilized depending on the interaction strength and the time\nbetween observations.",
        "positive": "Current production in ring condensates with a weak link: We consider attractive and repulsive condensates in a ring trap stirred by a\nweak link, and analyze the spectrum of solitonic trains dragged by the link, by\nmeans of analytical expressions for the wave functions, energies and currents.\nThe precise evolution of current production and destruction in terms of defect\nformation in the ring and in terms of stirring is studied. We find that any\nexcited state can be coupled to the ground state through two proposed methods:\neither by adiabatically tuning the link's strength and velocity through precise\ncycles which avoid the critical velocities and thus unstable regions, or by\nkeeping the link still while setting an auxiliary potential and imprinting a\nnonlinear phase as the potential is turned off. We also analyze hysteresis\ncycles through the spectrum of energies and currents."
    },
    {
        "anchor": "Low-energy collective oscillations and Bogoliubov sound in an\n  exciton-polariton condensate: We report the observation of low-energy, low-momenta collective oscillations\nof an excitonpolariton condensate in a round \"box\" trap. The oscillations are\ndominated by the dipole and breathing modes, and the ratio of the frequencies\nof the two modes is consistent with that of a weakly interacting\ntwo-dimensional trapped Bose gas. The speed of sound extracted from the dipole\noscillation frequency is smaller than the Bogoliubov sound, which can be partly\nexplained by the influence of the incoherent reservoir. These results pave the\nway for understanding the effects of reservoir, dissipation, energy relaxation,\nand finite temperature on the superfluid properties of exciton-polariton\ncondensates and other two-dimensional open-dissipative quantum fluids.",
        "positive": "A simple model for interactions and corrections to the Gross-Pitaevskii\n  Equation: One of the assumptions leading to the Gross-Pitaevskii Equation (GPE) is that\nthe interaction between atom pairs can be written effectively as a \\delta\n-function so that the interaction range of the particles is assumed to vanish.\nA simple model that takes into account the extension of the inter-particle\npotential is introduced. The correction to the GPE predictions for the energy\nof a condensate confined by a harmonic trap in the Thomas-Fermi (TF) regime is\nestimated. Although it is found to be small, we believe that in some situations\nit can be measured using its dependance on the frequency of the confining trap.\nDue to the simplicity of the model, it may have a wide range of applications."
    },
    {
        "anchor": "Thermodynamics and magnetism in the 2D-3D crossover of the Hubbard model: The realization of antiferromagnetic (AF) correlations in ultracold fermionic\natoms on an optical lattice is a significant achievement. Experiments have been\ncarried out in one, two, and three dimensions, and have also studied\nanisotropic configurations with stronger tunneling in some lattice directions.\nSuch anisotropy is relevant to the physics of cuprate superconductors and other\nstrongly correlated materials. Moreover, this anisotropy might be harnessed to\nenhance AF order. Here we numerically investigate, using Determinant Quantum\nMonte Carlo, a simple realization of anisotropy in the 3D Hubbard model in\nwhich the tunneling between planes, $t_\\perp$, is unequal to the intraplane\ntunneling $t$. This model interpolates between the three-dimensional isotropic\n($t_\\perp = t$) and two-dimensional ($t_\\perp =0$) systems. We show that at\nfixed interaction strength to tunneling ratio ($U/t$), anisotropy can enhance\nthe magnetic structure factor relative to both 2D and 3D results. However, this\nenhancement occurs at interaction strengths below those for which the N\\'eel\ntemperature $T_{\\rm N\\acute{e}el}$ is largest, in such a way that the structure\nfactor cannot be made to exceed its value in isotropic 3D systems at the\noptimal $U/t$. We characterize the 2D-3D crossover in terms of the magnetic\nstructure factor, real space spin correlations, number of doubly-occupied\nsites, and thermodynamic observables. An interesting implication of our results\nstems from the entropy's dependence on anisotropy. As the system evolves from\n3D to 2D, the entropy at a fixed temperature increases. Correspondingly, at\nfixed entropy, the temperature will decrease going from 3D to 2D. This suggests\na cooling protocol in which the dimensionality is adiabatically changed from 3D\nto 2D.",
        "positive": "Optical Control of the Scattering Length and Effective Range for\n  Magnetically Tunable Feshbach Resonances in Ultracold Gases: We describe two-field optical techniques to control interactions in Feshbach\nresonances for two-body scattering in ultra-cold gases. These techniques create\na molecular dark state in the closed channel of a magnetically tunable Feshbach\nresonance, greatly suppressing optical scattering compared to single optical\nfield methods. The dark-state method enables control of the effective range, by\ncreating narrow features that modify the energy dependence of the scattering\nphase shift, as well as control of the elastic and inelastic parts of the\nzero-energy s-wave scattering amplitude. We determine the scattering length and\nthe effective range from an effective range expansion, by calculating the\nmomentum-dependent scattering phase shift from the two-body scattering state."
    },
    {
        "anchor": "Higher-order effective interactions for bosons near a two-body zero\n  crossing: We develop the perturbation theory for bosons interacting via a two-body\npotential $V$ of vanishing mean value. We find that the leading nonpairwise\ncontribution to the energy emerges in the third order in $V$ and represents an\neffective three-body interaction, the sign of which in most cases (although not\nin general) is anticorrelated with the sign of the long-range tail of $V$.\nExplicit results are obtained for a few particular two-body interaction\npotentials and we perform a detailed perturbative analysis of tilted dipoles in\nquasi-low-dimensional geometries.",
        "positive": "Collisionless sound in a uniform two-dimensional Bose gas: Using linear response theory within the Random Phase Approximation, we\ninvestigate the propagation of sound in a uniform two dimensional (2D) Bose gas\nin the collisionless regime. We show that the sudden removal of a static\ndensity perturbation produces a damped oscillatory behavior revealing that\nsound can propagate also in the absence of collisions, due to mean-field\ninteraction effects. Our analysis points out the crucial role played by Landau\ndamping. We support our predictions by performing numerical simulations with\nthe stochastic (projected) Gross-Pitaevskii equation. The results are\nconsistent with the recent experimental observation of sound in a weakly\ninteracting 2D Bose gas both below and above the superfluid\nBerezinskii-Kosterlitz-Thouless transition."
    },
    {
        "anchor": "Study of Efimov physics in two nuclear-spin sublevels of 7Li: Efimov physics in two nuclear-spin sublevels of bosonic lithium is studied\nand it is shown that the positions and widths of recombination minima and\nEfimov resonances are identical for both states within the experimental errors\nwhich indicates that the short-range physics is nuclear-spin independent. We\nalso find that the Efimov features are universally related across Feshbach\nresonances. These results crucially depend on careful mapping between the\nscattering length and the applied magnetic field which we achieve by\ncharacterization of the two broad Feshbach resonances in the different states\nby means of rf-spectroscopy of weakly bound molecules. By fitting the binding\nenergies numerically with a coupled channels calculation we precisely determine\nthe absolute positions of the Feshbach resonances and the values of the singlet\nand triplet scattering lengths.",
        "positive": "Non-Hermitian Stark Many-Body Localization: Utilizing exact diagonalization (ED) techniques, we investigate a\none-dimensional, non-reciprocal, interacting hard-core boson model under a\nStark potential with tail curvature. By employing the non-zero imaginary\neigenenergies ratio, half-chain entanglement entropy, and eigenstate\ninstability, we numerically confirm that the critical points of spectral\nreal-complex (RC) transition and many-body localization (MBL) phase transition\nare not identical, and an examination of the phase diagrams reveals that the\nspectral RC transition arises before the MBL phase transition, which suggests\nthe existence of a novel non-MBL-driven spectral RC transition. These findings\nare quite unexpected, and they are entirely different from observations in\ndisorder-driven interacting non-Hermitian systems. This work provides a useful\nreference for further research on phase transitions in disorder-free\ninteracting non-Hermitian systems."
    },
    {
        "anchor": "Ground state of spin-1 Bose-Einstein condensates with spin-orbit\n  coupling in a Zeeman field: We systematically investigate the weakly trapped spin-1 Bose-Einstein\ncondensates with spin-orbit coupling in an external Zeeman field. We find that\nthe mean-field ground state favors either a magnetized standing wave phase or\nplane wave phase when the strength of Zeeman field is below a critical value\nrelated to the strength of spin-orbit coupling. Zeeman field can induce the\nphase transition between standing wave and plane wave phases, and we determine\nthe phase boundary analytically and numerically. The magnetization of these two\nphases responds to the external magnetic field in a very unique manner, the\nlinear Zeeman effect magnetizes the standing wave phase along the direction of\nthe magnetic field, but the quadratic one demagnetizes the plane wave phase.\nWhen the strength of Zeeman field surpasses the critical value, the system is\ncompletely polarized to a ferromagnetic state or polar state with zero\nmomentum.",
        "positive": "Landau versus Spin Superfluidity in Spinor Bose-Einstein Condensates: We consider a spin-1/2 Bose-Einstein condensate prepared initially in a\nsingle spin projection. The two channels of excitations existing in such a\nsystem (namely density and spin waves) are discussed and we show how pure spin\nwaves can be excited in the presence of local magnetic defects. We analyze the\nrole played by spin excitations on the Landau superfluidity criterion and\ndemonstrate the absence of absolute superfluidity for the antiferromagnetic\ncondensate. In the ferromagnetic case, we identify two critical velocities for\nthe breakdown of superfluidity."
    },
    {
        "anchor": "Artificial magnetic field for synthetic quantum matter without dynamical\n  modulation: We propose an all-static method to realize an artificial magnetic field for\ncharge neutral particles without introducing any time modulation. Our proposal\nconsists of one-dimensional tubes subject to harmonic trapping potentials with\nshifted centers. We show that this setup realizes an artificial magnetic field\nin a hybrid real-momentum space. We discuss how characteristic features of\nparticles in a magnetic field, such as chiral edge states and the quantized\nHall response, can be observed in this setup. We find that the mean-field\nground state of bosons in this setup in the presence of long-range interactions\nin physical real space can have quantized vortices in the hybrid real-momentum\nspace; such a state with vortices exhibits a supersolid structure in the\nphysical real space. Our method can be applied to a variety of synthetic\nquantum matter, including ultracold atomic gases, coupled photonic cavities,\ncoupled waveguides, and exciton-polariton lattices.",
        "positive": "Ground-state Properties of Tonks-Girardeau Gas in One Dimensional\n  Periodic Potential: The relations among the occupation number of the lowest natural orbital\n(ONLNO), momentum distributions (MD) and off-diagonal long-range element\n(ODLRE) of the reduced single-particle density matrix (RSPDM) are studied while\nTonks-Girardeau gas in one dimensional periodic potential is in the ground\nstate. For $N$-body systems of large enough, RSPDM and its lowest natural\norbital do not vary with $N$ in overlapped areas in commensurate and\nincommensurate cases correspondingly. In commensurate case, the ODLRE is\nexponential attenuation with $N$, which results in that the ONLNO and MD are\ninvariant with $N$. While in contrast, in incommensurate case, the off-diagonal\nelements are inversely proportional to $\\sqrt{N}$, which results in the\ndifferent behavior of the ONLNO and MD."
    },
    {
        "anchor": "Bosonic bright soliton in the mixture of repulsive Bose-Einstein\n  condensate and polarized ultracold fermions under influence of the pressure\n  evolution: Repulsive Bose-Einstein condensate, where the short-range interaction is\nincluded up to the third order by the interaction radius, demonstrates\nexistence of a bright soliton in a narrow interval of parameters. This soliton\nis studied here for the boson-fermion mixture, where spin-1/2 fermions are\nconsider in the regime of full spin polarization. Influence of fermions via the\nboson-fermion interaction is considered up to the third order by the\ninteraction radius. Fermions themselves are considered by hydrodynamic model\nincluding the pressure evolution equation. Interaction between fermions is\nconsidered. The first order by the interaction radius gives zero contribution\nin the Euler equation and the pressure evolution equation, but the third order\nby the interaction radius provides nonzero contributions in both equations.\nRepulsive (attractive) boson-fermion interaction leads to the bright (dark)\nfermionic soliton.",
        "positive": "Self-trapping in an array of coupled 1D Bose gases: We study the transverse expansion of arrays of ultracold $^{87}$Rb atoms\nweakly confined in tubes created by a 2D optical lattice, and observe that\ntransverse expansion is delayed because of mutual atom interactions. A\nmean-field model of a coupled array shows that atoms become localized within a\nroughly square fort-like self-trapping barrier with time-evolving edges. But\nthe observed dynamics is poorly described by the mean-field model. Theoretical\nintroduction of random phase fluctuations among tubes improves the agreement\nwith experiment, but does not correctly predict the density at which the atoms\nstart to expand with larger lattice depths. Our results suggest a new type of\nself-trapping, where quantum correlations suppress tunneling even when there\nare no density gradients."
    },
    {
        "anchor": "Soliton creation during a Bose-Einstein condensation: We use stochastic Gross-Pitaevskii equation to study dynamics of\nBose-Einstein condensation. We show that cooling into a Bose-Einstein\ncondensate (BEC) can create solitons with density given by the cooling rate and\nby the critical exponents of the transition. Thus, counting solitons left in\nits wake should allow one to determine the critical exponents z and nu for a\nBEC phase transition. The same information can be extracted from two-point\ncorrelation functions.",
        "positive": "Quantum theory of bright matter wave solitons in harmonic confinement: This paper investigates bright quantum-matter-wave solitons beyond the\nGross-Pitaevskii equation (GPE). As proposals for interferometry and creating\nnonlocal quantum superpositions have been formed, it has become necessary to\ninvestigate effects not present in mean-field models. We investigate the effect\nof harmonic confinement on the internal degrees of freedom, as the ratio of\nzero-point harmonic oscillator length to classical soliton length, for\ndifferent numbers of atoms. We derive a first-order energy correction for the\naddition of a harmonic potential to the many-body wave function and use this to\ncreate a variational technique based on energy minimization of this wave\nfunction for an arbitrary number of atoms, and include numerics based on\ndiagonalization of the Hamiltonian in a basis of harmonic oscillator Fock\nstates. Finally we compare agreement between a Hartree product ground state and\nthe Bethe ansatz solution with a Gaussian envelope localizing the center of\nmass and show a region of good agreement."
    },
    {
        "anchor": "Reducing number fluctuations in an ultracold atomic sample using Faraday\n  rotation and iterative feedback: We demonstrate a method to reduce number fluctuations in an ultracold atomic\nsample using real-time feedback. By measuring the Faraday rotation of an\noff-resonant probe laser beam with a pair of avalanche photodetectors in a\npolarimetric setup we produce a proxy for the number of atoms in the sample. We\niteratively remove a fraction of the excess atoms from the sample to converge\non a target proxy value in a way that is insensitive to environmental\nperturbations and robust to errors in light polarization. Using absorption\nimaging for out-of-loop verification, we demonstrate a reduction in the number\nfluctuations from $3\\%$ to $0.45\\%$ for samples at a temperature of 16.4 $\\mu$K\nover the time-scale of several hours which is limited by temperature\nfluctuations, beam pointing noise, and photon shot noise.",
        "positive": "Metal-insulator transition and magnetism of SU(3) fermions in the square\n  lattice: We study the SU(3) symmetric Fermi-Hubbard model (FHM) in the square lattice\nat $1/3$-filling using numerically exact determinant quantum Monte Carlo (DQMC)\nand numerical linked-cluster expansion (NLCE) techniques. We present the\ndifferent regimes of the model in the $T-U$ plane, which are characterized by\nlocal and short-range correlations, and capture signatures of the\nmetal-insulator transition and magnetic crossovers. These signatures are\ndetected as the temperature scales characterizing the rise of the\ncompressibility, and an interaction-dependent change in the sign of the\ndiagonal spin-spin correlation function. The analysis of the compressibility\nestimates the location of the metal-insulator quantum critical point at $U_c/t\n\\sim 6$, and provides a temperature scale for observing Mott physics at\nfinite-$T$. Furthermore, from the analysis of the spin-spin correlation\nfunction we observe that for $U/t \\gtrsim6$ and $T \\sim J = 4t^2/U$ there is a\ndevelopment of a short-range two sublattice (2-SL) antiferromagnetic structure,\nas well as an emerging three sublattice (3-SL) antiferromagnetic structure as\nthe temperature is lowered below $T/J \\lesssim 0.57$. This crossover from 2-SL\nto 3-SL magnetic ordering agrees with Heisenberg limit predictions, and has\nobservable effects on the density of on-site pairs. Finally, we describe how\nthe features of the regimes in the $T$-$U$ plane can be explored with\nalkaline-earth-like atoms in optical lattices with currently-achieved\nexperimental techniques and temperatures. The results discussed in this\nmanuscript provide a starting point for the exploration of the SU(3) FHM upon\ndoping."
    },
    {
        "anchor": "Strongly Correlated Bosons on a Dynamical Lattice: We study a one-dimensional system of strongly correlated bosons on a\ndynamical lattice. To this end, we extend the standard Bose-Hubbard Hamiltonian\nto include extra degrees of freedom on the bonds of the lattice. We show that\nthis minimal model exhibits phenomena reminiscent of fermion-phonon models. In\nparticular, we discover a bosonic analog of the Peierls transition, where the\ntranslational symmetry of the underlying lattice is spontaneously broken. This\nprovides a dynamical mechanism to obtain a topological insulator in the\npresence of interactions, analogous to the Su-Schrieffer-Heeger model for\nelectrons. We characterize the phase diagram numerically, showing different\ntypes of bond order waves and topological solitons. Finally, we study the\npossibility of implementing the model using atomic systems.",
        "positive": "Non-linear fluctuating hydrodynamics for KPZ scaling in isotropic spin\n  chains: Finite temperature spin transport in integrable isotropic spin chains is\nknown to be superdiffusive, with dynamical spin correlations that are\nconjectured to fall into the Kardar-Parisi-Zhang (KPZ) universality class.\nHowever, integrable spin chains have time-reversal and parity symmetries that\nare absent from the KPZ/stochastic Burgers equation, which force higher-order\nspin fluctuations to deviate from standard KPZ predictions. We put forward a\nnon-linear fluctuating hydrodynamic theory consisting of two coupled stochastic\nmodes: the local spin magnetization and its effective velocity. Our theory\nfully explains the emergence of anomalous spin dynamics in isotropic chains: it\npredicts KPZ scaling for the spin structure factor but with a symmetric,\nquasi-Gaussian, distribution of spin fluctuations. We substantiate our results\nusing matrix-product states calculations."
    },
    {
        "anchor": "Finite-density corrections to the Unitary Fermi gas: A lattice\n  perspective from Dynamical Mean-Field Theory: We investigate the approach to the universal regime of the dilute unitary\nFermi gas as the density is reduced to zero in a lattice model. To this end we\nstudy the chemical potential, superfluid order parameter and internal energy of\nthe attractive Hubbard model in three different lattices with densities of\nstates (DOS) which share the same low-energy behavior of fermions in\nthree-dimensional free space: a cubic lattice, a \"Bethe lattice\" with a\nsemicircular DOS, and a \"lattice gas\" with parabolic dispersion and a sharp\nenergy cut-off that ensures the normalization of the DOS. The model is solved\nusing Dynamical Mean-Field Theory, that treats directly the thermodynamic limit\nand arbitrarily low densities, eliminating finite-size effects. At densities of\nthe order of one fermion per site the lattice and its specific form dominate\nthe results. The evolution to the low-density limit is smooth and it does not\nallow to define an unambiguous low-density regime. Such finite-density effects\nare significantly reduced using the lattice gas, and they are maximal for the\nthree-dimensional cubic lattice. Even though dynamical mean-field theory is\nbound to reduce to the more standard static mean field in the limit of zero\ndensity due to the local nature of the self-energy and of the vertex functions,\nit compares well with accurate Monte Carlo simulations down to the lowest\ndensities accessible to the latter.",
        "positive": "Capturing the Feshbach-induced Pairing Physics in the BEC-BCS Crossover: By including the effect of a trap with characteristic energy given by the\nFermi temperature $T_F$ in a two-body two-channel model for Feshbach\nresonances, we reproduce the experimental closed-channel fraction $Z$ across\nthe BEC-BCS crossover and into the BCS regime of a $^6$Li atomic Fermi gas. We\nobtain the expected behavior $Z \\propto \\sqrt{T_F}$ at unitarity, together with\nthe recently measured proportionality constant. Our results are also in\nagreement with recent measurements of the $Z$ dependency on $T_F$ on the BCS\nside, where a significant discrepancy between experiments and theory has been\nrepeatedly reported."
    },
    {
        "anchor": "Manipulating the momentum state of a condensate by sequences of standing\n  wave pulses: We analyze the effects of sequences of standing wave pulses on a\nBose-Einstein condensate (BEC). Experimental observations are in good agreement\nwith a numerical simulation based on the band structure theory in the optical\nlattice. We also demonstrate that a coherent control method based on such\nsequences of pulses is very efficient for experimentally designing specific\nmomentum states.",
        "positive": "A note on the calculation of the long-wavelength limit of the bosonic\n  excitation spectrum: An approach is proposed to analyze an interacting bosonic system using\ntwo-time temperature Green's functions on the collective variables. Two systems\nare studied: liquid helium-4 and the Yukawa Bose-liquid being a model of the\nnuclear matter. The suggested decoupling in the equations of motion for Green's\nfunctions yields a good description of the elementary excitation spectrum in\nthe long-wavelength limit."
    },
    {
        "anchor": "Large-momentum distribution of a polarized Fermi gas and p-wave contacts: We present a derivation of the adiabatic energy relations as well as the\nlarge momentum distribution of a polarized Fermi gas near p-wave Feshbach\nresonances. The leading asymptotic behavior ($k^{-2}$) and subleading behavior\n($k^{-4}$) of the large momentum distribution have recently been predicted by\nYu et al. [Phys. Rev. Lett. 115, 135304 (2015)] and by He et al. [Phys. Rev.\nLett. 116, 045301 (2016)] using two different approaches. Here, we show that\nthe subleading asymptotic behavior ($\\sim k^{-4}$) can not fully be captured by\nthe contact defined from the adiabatic energy relation related to the p-wave\neffective range, and there should be an extra term resulted from the\ncenter-of-mass motion of the pairs. The omission of this extra term is perhaps\na reasonable approximation at zero temperature. However, it should be taken\ninto account at finite temperature and should be of significant importance to\nunderstand the recently measured momentum distribution in a resonant p-wave\nFermi gas of ultracold $^{40}$K atoms [Luciuk et al., Nature Phys. 12, 599\n(2016)].",
        "positive": "Quantum Hall and Synthetic Magnetic-Field Effects in Ultra-Cold Atomic\n  Systems: In this Chapter, we give a brief review of the state of the art of\ntheoretical and experimental studies of synthetic magnetic fields and quantum\nHall effects in ultracold atomic gases. We focus on integer, spin, and\nfractional Hall effects, indicate connections to topological matter, and\ndiscuss prospects for the realization of full-fledged gauge field theories\nwhere the synthetic magnetic field has its own dynamics. The advantages of\nthese systems over traditional electronic systems are highlighted. Finally,\ninterdisciplinary comparisons with other synthetic matter platforms based on\nphotonic and trapped-ion systems are drawn. We hope this chapter to illustrate\nthe exciting progress that the field has experienced in recent years."
    },
    {
        "anchor": "Properties of Bose Gases with Raman-Induced Spin-Orbit Coupling: In this paper we investigate the properties of Bose gases with Raman-induced\nspin-orbit(SO) coupling. It is found that the SO coupling can greatly modify\nthe single particle density-of-state, and thus lead to non-monotonic behavior\nof the condensate depletion, the Lee-Huang-Yang correction of ground-state\nenergy and the transition temperature of a non-interacting Bose-Einstein\ncondensate. The presence of the SO coupling also breaks the Galilean\ninvariance, and this gives two different critical velocities, corresponding to\nthe movement of the condensate and the impurity respectively. Finally, we show\nthat with SO coupling, the interactions modify the BEC transition temperature\neven at Hartree-Fock level, in contrast to the ordinary Bose gas without SO\ncoupling. All results presented here can be directly verified in the current\ncold atom experiments using Raman laser-induced gauge field.",
        "positive": "Thermodynamic properties of two-component fermionic atoms trapped in a\n  two-dimensional optical lattice: We study the finite temperature properties of two-component fermionic atoms\ntrapped in a two-dimensional optical lattice. We apply the self-energy\nfunctional approach to the two-dimensional Hubbard model with a harmonic\ntrapping potential, and systematically investigate the thermodynamic properties\nof this system. We find that entropy and grand potential provide evidence of a\ncrossover between the Mott insulating and metallic phases at certain\ntemperatures. In addition, we find that entropy exhibits a cusp-like anomaly at\nlower temperatures, suggesting a second or higher order antiferromagnetic\ntransition. We estimate the antiferromagnetic transition temperatures, and\nclarify how the trapping potential affects this magnetic transition."
    },
    {
        "anchor": "Breakdown of universality for unequal-mass Fermi gases with infinite\n  scattering length: We treat small trapped unequal-mass two-component Fermi gases at unitarity\nwithin a non-perturbative microscopic framework and investigate the system\nproperties as functions of the mass ratio $\\kappa$, and the numbers $N_{1}$ and\n$N_2$ of heavy and light fermions. While equal-mass Fermi gases with infinitely\nlarge interspecies s-wave scattering length $a_s$ are universal, we find that\nunequal mass Fermi gases are, for sufficiently large $\\kappa$ and in the regime\nwhere Efimov physics is absent, not universal. In particular, the\n$(N_1,N_2)=(2,1)$ and $(3,1)$ systems exhibit three-body (3b) and four-body\n(4b) resonances at $\\kappa = 12.314(2)$ and $10.4(2)$, respectively, as well as\nsurprisingly large finite-range (FR) effects. These findings have profound\nimplications for ongoing experimental efforts and quantum simulation proposals\nthat utilize unequal-mass atomic Fermi gases.",
        "positive": "Equation of state of the two-dimensional Hubbard model: Understanding the phases of strongly correlated quantum matter is challenging\nbecause they arise from the subtle interplay between kinetic energy,\ninteractions, and dimensionality. In this quest it has turned out that even\nconceptually simple models of strongly correlated fermions, which often only\napproximately represent the physics of the solid state, are very hard to solve.\nSince the conjecture by P. W. Anderson that the two-dimensional Hubbard model\ndescribes the main features of high-T$_c$ superconductivity in the cuprates,\nthere has been a major, yet inconclusive, research effort on determining its\nfundamental thermodynamic properties. Here we present an experimental\ndetermination of the equation of state of the repulsive two-dimensional Hubbard\nmodel over a broad range of interactions, $0\\leq U/t \\lesssim 20$, and\ntemperatures, down to $k_BT/t=0.63(2)$, using high-resolution imaging of\nultracold atoms in optical lattices. The equation of state fully characterizes\nthe thermodynamics of the Hubbard model, and our results constitute benchmarks\nfor state-of-the-art theoretical approaches."
    },
    {
        "anchor": "On the information entropy of matter-waves in quasi-disorder potentials: We consider ultracold Bose gases in quasi-random potentials and quantify\nlocalization of matter waves by means of Shannon information entropy. We\nexplicitly examine the role of quasi-random potentials in producing localized\nstates in the linear and nonlinear regimes. It is seen that the information\nentropic-based approach can be more useful to quantify localization of\ndifferent types of states observed in Bose-Einstein condensates.",
        "positive": "Supersolid induced by dislocations with superfluid cores (Review\n  article): Dislocation model of the supersolid state of $^4$He was proposed in 1987 by\none of the authors of the review. The model obtained strong support by numerous\nexperimental and theoretical investigations from 2007 to date. In these\ninvestigations the validity of the idea put forward in 1987 was confirmed, and\nnew conceptions of superclimb of dislocations and of the giant isochoric\ncompressibility or the syringe effect were proposed. In this paper we review\nmain achievements of theoretical and experimental studies of\ndislocation-induced supersolid and present current understanding of this\nphenomenon."
    },
    {
        "anchor": "Realization of 1D Anyons with Arbitrary Statistical Phase: Low-dimensional quantum systems can host anyons, particles with exchange\nstatistics that are neither bosonic nor fermionic. Despite indications of a\nwealth of exotic phenomena, the physics of anyons in one dimension (1D) remains\nlargely unexplored. Here, we realize Abelian anyons in 1D with arbitrary\nexchange statistics using ultracold atoms in an optical lattice, where we\nengineer the statistical phase via a density-dependent Peierls phase. We\nexplore the dynamical behavior of two anyons undergoing quantum walks, and\nobserve the anyonic Hanbury Brown-Twiss effect, as well as the formation of\nbound states without on-site interactions. Once interactions are introduced, we\nobserve spatially asymmetric transport in contrast to the symmetric dynamics of\nbosons and fermions. Our work forms the foundation for exploring the many-body\nbehavior of 1D anyons.",
        "positive": "Quenched Magneto-association of Ultracold Feshbach Molecules: We study enhanced magneto-association of atoms into weakly-bound molecules\nnear a Feshbach resonance using a quench preparatory stage. In anticipation of\nexperiments with NASA's Cold Atom Laboratory aboard the International Space\nStation, we assume as a baseline a dual-species ($^{87}$Rb and $^{41}$K) gas in\na parameter regime enabled by a microgravity environment. This includes\nsubnanokelvin temperatures and dual-species gases at densities as low as\n10$^8$/cm$^3$. Our studies indicate that, in such a regime, traditional\nmagneto-association schemes are inefficient due to the weak coupling between\natomic and molecular states at low-densities, thus requiring extremely long\nmagnetic field sweeps. To address this issue we propose a modified scheme where\natoms are quenched to unitarity before proceeding with magneto-association.\nThis substantially improves molecular formation, allowing for up to $80\\%$\nefficiency, and within time-scales much shorter than those associated to atomic\nand molecular losses. We show that this scheme also applies at higher\ndensities, therefore proving to be of interest to ground-based experiments as\nwell."
    },
    {
        "anchor": "Non-equilibrium dynamics induced by miscible-immiscible transition in\n  binary Bose-Einstein condensates: The non-equilibrium spatial dynamics in a two-component Bose-Einstein\ncondensate were excited by controlled miscible-immiscible transition, in which\nimmiscible condensates with domain structures are transferred to the miscible\ncondensates by changing the internal state of 87Rb atoms. The subsequent\nevolution exhibits the oscillation of spatial structures involving component\nmixing and separation. We show that the larger total energy of the miscible\nsystem results in a higher oscillation frequency. This investigation introduces\na new technique to control the miscibility and the spatial degrees of freedom\nin atomic Bose-Einstein condensates.",
        "positive": "Dissipative Bose-Josephson junction coupled to bosonic baths: We investigate the effect of dissipation in a Bose-Josephson junction (BJJ)\ncoupled to bath of bosons at two sites. Apart from the dynamical transition due\nto repulsive interactions, the BJJ undergoes a quantum phase transition by\nincreasing the coupling strength with the bath modes. We analyze this system by\nmapping to an equivalent spin model coupled to the bosonic modes. The\nexcitation energies and fluctuation of number imbalance are obtained within\nHolstein-Primakoff approximation, which exhibit vanishing of energy gap and\nenhanced quantum fluctuations at the critical coupling. We study the dynamics\nof BJJ using time dependent variational method and analyze stability of\ndifferent types of steady states. As a special case we study in details the\nphase space dynamics of BJJ coupled to a single mode, which reveals diffusive\nand incoherent behaviour with increasing coupling to the bath mode. The\ndynamical steady states corresponding to the Pi-oscillation and self-trapped\nstate become unstable in the region where their oscillation frequencies are in\nresonance with the bath modes. We investigate the time evolution of number\nimbalance and relative phase in presence of Ohmic bath with Gaussian noise to\nincorporate thermal fluctuations. Apart from damping of Josephson oscillations\nand transition to symmetry broken state for strong coupling we observe decay of\nPi-oscillation and self-trapped state to the ground state as a result of\ndissipation. Variation of phase fluctuation with temperature of the bath shows\nsimilar behaviour as observed in experiment. Finally we discuss the\nexperimental setup to study the observable effects of dissipation in BJJ."
    },
    {
        "anchor": "Parton theory of magnetic polarons: Mesonic resonances and signatures in\n  dynamics: When a mobile hole is moving in an anti-ferromagnet it distorts the\nsurrounding Neel order and forms a magnetic polaron. Such interplay between\nhole motion and anti-ferromagnetism is believed to be at the heart of high-Tc\nsuperconductivity in cuprates. We study a single hole described by the t-Jz\nmodel with Ising interactions between the spins in 2D. This situation can be\nexperimentally realized in quantum gas microscopes. When the hole hopping is\nmuch larger than couplings between the spins, we find strong evidence that\nmagnetic polarons can be understood as bound states of two partons, a spinon\nand a holon carrying spin and charge quantum numbers respectively. We introduce\na microscopic parton description which is benchmarked by comparison with\nresults from advanced numerical simulations. Using this parton theory, we\npredict a series of excited states that are invisible in the spectral function\nand correspond to rotational excitations of the spinon-holon pair. This is\nreminiscent of mesonic resonances observed in high-energy physics, which can be\nunderstood as rotating quark antiquark pairs. We also apply the strong coupling\nparton theory to study far-from equilibrium dynamics of magnetic polarons\nobservable in current experiments with ultracold atoms. Our work supports\nearlier ideas that partons in a confining phase of matter represent a useful\nparadigm in condensed-matter physics and in the context of high-Tc\nsuperconductivity. While direct observations of spinons and holons in real\nspace are impossible in traditional solid-state experiments, quantum gas\nmicroscopes provide a new experimental toolbox. We show that, using this\nplatform, direct observations of partons in and out-of equilibrium are\npossible. Extensions of our approach to the t-J model are also discussed. Our\npredictions in this case are relevant to current experiments with quantum gas\nmicroscopes for ultracold atoms.",
        "positive": "Periodic shedding of vortex dipoles from a moving penetrable obstacle in\n  a Bose-Einstein condensate: We investigate vortex shedding from a moving penetrable obstacle in a highly\noblate Bose-Einstein condensate. The penetrable obstacle is formed by a\nrepulsive Gaussian laser beam that has the potential barrier height lower than\nthe chemical potential of the condensate. The moving obstacle periodically\ngenerates vortex dipoles and the vortex shedding frequency $f_v$ linearly\nincreases with the obstacle velocity $v$ as $f_v=a(v-v_c)$, where $v_c$ is a\ncritical velocity. Based on periodic shedding behavior, we demonstrate\ndeterministic generation of a single vortex dipole by applying a short linear\nsweep of a laser beam. This method will allow further controlled vortex\nexperiments such as dipole-dipole collisions."
    },
    {
        "anchor": "Shear Viscosity of Uniform Fermi Gases with Population Imbalance: The shear viscosity plays an important role in studies of transport phenomena\nin ultracold Fermi gases and serves as a diagnostic of various microscopic\ntheories. Due to the complicated phase structures of population-imbalanced\nFermi gases, past works mainly focus on unpolarized Fermi gases. Here we\ninvestigate the shear viscosity of homogeneous, population-imbalanced Fermi\ngases with tunable attractive interactions at finite temperatures by using a\npairing fluctuation theory for thermodynamical quantities and a gauge-invariant\nlinear response theory for transport coefficients. In the unitary and BEC\nregimes, the shear viscosity increases with the polarization because the excess\nmajority fermions cause gapless excitations acting like a normal fluid. In the\nweak BEC regime the excess fermions also suppress the noncondensed pairs at low\npolarization, and we found a minimum in the ratio of shear viscosity and\nrelaxation time. To help constrain the relaxation time from linear response\ntheory, we derive an exact relation connecting some thermodynamic quantities\nand transport coefficients at the mean-field level for unitary Fermi\nsuperfluids with population imbalance. An approximate relation beyond\nmean-field theory is proposed and only exhibits mild deviations from numerical\nresults.",
        "positive": "Dynamics of correlations in a dilute Bose gas following an interaction\n  quench: We calculate the dynamics of the one and two body correlation functions in a\nhomogeneous Bose gas at zero temperature following a sudden change in the\ninteraction strength, with and without an underlying lattice. We focus on\nconceptually simple examples that highlight the features arising separately\nfrom interactions and band structure. In the continuum, we show that the\nBogoliubov spectrum leads to a diffusive evolution of density correlations for\nshort times, and ballistic at long times. In the lattice we find that the\ncorrelation functions develop additional oscillations. Moreover, the lattice\ndispersion induces an additional velocity scale, and some features instead\npropagate with that velocity. Finally, we discuss the time-evolution of the\ncontact following a quench. Our predictions, which can be readily tested in\nexperiments, serve as a benchmark for considering the dynamics of more\ncomplicated systems."
    },
    {
        "anchor": "Internal Oscillations of a Dark-Bright Soliton in a Harmonic Potential: We investigate the dynamics of a dark-bright soliton in a harmonic potential\nusing a mean-field approach via coupled nonlinear Schr\\\"odinger equations\nappropriate to multicomponent Bose-Einstein condensates. We use a modified\nperturbed dynamical variational Lagrangian approximation, where the\nperturbation is due to the trap, taken as a Thomas-Fermi profile. The\nwavefunction ansatz is taken as the correct hyperbolic tangent and secant\nsolutions in the scalar case for the dark and bright components of the soliton,\nrespectively. We also solve the problem numerically with psuedo-spectral\nRunge-Kutta methods. We find, analytically and numerically, for weak trapping\nthe internal modes are nearly independent of center of mass motion of the\ndark-bright soliton. In contrast, in tighter traps the internal modes couple\nstrongly to the center of mass motion, showing that for dark-bright solitons in\na harmonic potential the center of mass and relative degrees of freedom are not\nindependent. This result is robust against noise in the initial condition and\nshould, therefore, be experimentally observable.",
        "positive": "Gap Solitons in Spin-Orbit-Coupled Bose-Einstein Condensates in Optical\n  Lattices: While different ways to realize spin-orbit coupling in Bose-Einstein\ncondensates exist, not all are currently experimentally implementable. Here we\npresent a detailed study of gap solitons in a Bose- Einstein condensate with\nexperimentally realizable spin-orbit coupling and discuss two cases relating to\na spin-dependent parity symmetry. In the parity symmetric case, two families of\nfundamental gap solitons in second linear energy gap are demonstrated with\nopposite sign of the parity, with one family having single humped densities and\nthe other double humped ones. In the case of broken parity symmetry, the\nfundamental modes manifest spin-polarization. Both families possess an opposite\nsign of the spin-polarization."
    },
    {
        "anchor": "Double Weyl points and Fermi arcs of topological semimetals in\n  non-Abelian gauge potentials: We study the effect of a non-Abelian SU(2) gauge potential on the topological\nsemimetal induced by a magnetic field having {\\pi}-flux per plaquette and\nacting on fermions in a cubic lattice. The Abelian {\\pi}-flux term gives rise\nto a spectrum characterized by Weyl points. When the non-Abelian part is turned\non, due to the presence of a C4 rotation symmetry, the Weyl points assume a\nquadratic dispersion along two directions and constitute double monopoles for\nthe Berry curvature. We examine both analytically and numerically the main\nfeatures of this system, focusing on its gapless surface modes, the so-called\nFermi arcs. We discuss the stability of the system under confining hard-wall\nand harmonic potentials, relevant for the implementation in ultracold atom\nsettings, and the effect of rotation symmetry breaking.",
        "positive": "Functional building blocks for scalable multipartite entanglement in\n  optical lattices: Featuring excellent coherence and operated parallelly, ultracold atoms in\noptical lattices form a competitive candidate for quantum computation. For\nthis, a massive number of parallel entangled atom pairs have been realized in\nsuperlattices. However, the more formidable challenge is to scale-up and detect\nmultipartite entanglement due to the lack of manipulations over local atomic\nspins in retro-reflected bichromatic superlattices. Here we developed a new\narchitecture based on a cross-angle spin-dependent superlattice for\nimplementing layers of quantum gates over moderately-separated atoms\nincorporated with a quantum gas microscope for single-atom manipulation. We\ncreated and verified functional building blocks for scalable multipartite\nentanglement by connecting Bell pairs to one-dimensional 10-atom chains and\ntwo-dimensional plaquettes of $2\\times4$ atoms. This offers a new platform\ntowards scalable quantum computation and simulation."
    },
    {
        "anchor": "Short-time universal scaling in an isolated quantum system after a\n  quench: Renormalization-group methods provide a viable approach for investigating the\nemergent collective behavior of classical and quantum statistical systems in\nboth equilibrium and nonequilibrium conditions. Within this approach we\ninvestigate here the dynamics of an isolated quantum system represented by a\nscalar $\\phi^4$ theory after a global quench of the potential close to a\ndynamical critical point. We demonstrate that, within a pre-thermal regime, the\ntime dependence of the relevant correlations is characterized by a short-time\nuniversal exponent, which we calculate at the lowest order in a dimensional\nexpansion.",
        "positive": "Stability of quantum degenerate Fermi gases of tilted polar molecules: A recent experimental realization of quantum degenerate gas of\n$^{40}$K$^{87}$Rb molecules opens up prospects of exploring strong dipolar\nFermi gases and many-body phenomena arising in that regime. Here we derive a\nmean-field variational approach based on the Wigner function for the\ndescription of ground-state properties of such systems. We show that the\nstability of dipolar fermions in a general harmonic trap is universal as it\nonly depends on the trap aspect ratios and the dipoles' orientation. We\ncalculate the species-independent stability diagram and the deformation of the\nFermi surface (FS) for polarized molecules, whose electric dipoles are oriented\nalong a preferential direction. Compared to atomic magnetic species, the\nstability of a molecular electric system turns out to strongly depend on its\ngeometry and the FS deformation significantly increases."
    },
    {
        "anchor": "Fermionization of two distinguishable fermions: In this work we study a system of two distinguishable fermions in a 1D\nharmonic potential. This system has the exceptional property that there is an\nanalytic solution for arbitrary values of the interparticle interaction. We\ntune the interaction strength via a magnetic offset field and compare the\nmeasured properties of the system to the theoretical prediction. At the point\nwhere the interaction strength diverges, the energy and square of the wave\nfunction for two distinguishable particles are the same as for a system of two\nidentical fermions. This is referred to as fermionization. We have observed\nthis phenomenon by directly comparing two distinguishable fermions with\ndiverging interaction strength with two identical fermions in the same\npotential. We observe good agreement between experiment and theory. By adding\none or more particles our system can be used as a quantum simulator for more\ncomplex few-body systems where no theoretical solution is available.",
        "positive": "Resonant collisional shielding of reactive molecules using electric\n  fields: Full control of molecular interactions, including reactive losses, would open\nnew frontiers in quantum science. Here, we demonstrate extreme tunability of\nchemical reaction rates by using an external electric field to shift excited\ncollision channels of ultracold molecules into degeneracy with the initial\ncollision channel. In this situation, resonant dipolar interactions mix the\nchannels at long range, dramatically altering the intermolecular potential. We\nprepare fermionic potassium-rubidium (KRb) molecules in their first excited\nrotational state and observe a three orders-of-magnitude modulation of the\nchemical reaction rate as we tune the electric field strength by a few percent\nacross resonance. In a quasi-two-dimensional geometry, we accurately determine\nthe contributions from the three lowest angular momentum projections of the\ncollisions. Using the resonant features, we shield the molecules from loss and\nsuppress the reaction rate by up to an order of magnitude below the background\nvalue, realizing a long-lived sample of polar molecules in large electric\nfields."
    },
    {
        "anchor": "Polaronic effects in one- and two-band quantum systems: In this work we study the formation and dynamics of polarons in a system with\na few impurities in a lattice immersed in a Bose-Einstein condensate (BEC).\nThis system has been experimentally realized using ultracold atoms and optical\nlattices. Here we consider a two-band model for the impurity atoms, along with\na Bogoliubov approximation for the BEC, with phonons coupled to impurities via\nboth intra- and inter-band transitions. We decouple this Fr\\\"ohlich-like term\nby an extended two-band Lang-Firsov polaron transformation using a variational\nmethod. The new effective Hamiltonian with two (polaron) bands differs from the\noriginal Hamiltonian by modified coherent transport, polaron energy shifts and\ninduced long-range interaction. A Lindblad master equation approach is used to\ntake into account residual incoherent coupling between polaron and bath. This\npolaronic treatment yields a renormalized inter-band relaxation rate compared\nto Fermi's Golden Rule. For a strongly coupled two-band Fr\\\"ohlich Hamiltonian,\nthe polaron is tightly dressed in each band and can not tunnel between them,\nleading to an inter-band self-trapping effect.",
        "positive": "Cavity Optomechanics with Ultra Cold Atoms in Synthetic Abelian and\n  Non-Abelian Gauge Field: In this article we present a pedagogical discussion of some of the\noptomechanical properties of a high finesse cavity loaded with ultracold atoms\nin laser induced synthetic gauge fields of different types. Essentially, the\nsubject matter of this article is an amalgam of two sub-fields of atomic\nmolecular and optical (AMO) physics namely, the cavity optomechanics with\nultracold atoms and ultracold atoms in synthetic gauge field. After providing a\nbrief introduction to either of these fields we shall show how and what\nproperties of these trapped ultracold atoms can be studied by looking at the\ncavity (optomechanical or transmission) spectrum. In presence of abelian\nsynthetic gauge field we discuss the cold-atom analogue of Shubnikov de Haas\noscillation and its detection through cavity spectrum. Then, in the presence of\na non-abelian synthetic gauge field (spin-orbit coupling), we see when the\nelectromagnetic field inside the cavity is quantized, it provides a quantum\noptical lattice for the atoms, leading to the formation of different quantum\nmagnetic phases. We also discuss how these phases can be explored by studying\nthe cavity transmission spectrum."
    },
    {
        "anchor": "Three-Boson Bound States in Two Dimensions: We investigate the possible existence of the bound state in the system of\nthree bosons interacting with each other via zero-radius potentials in two\ndimensions (it can be atoms confined in two dimensions or tri-exciton states in\nheterostructures or dihalogenated materials). The bosons are classified in two\nspecies (a,b) such that a-a and b-b pairs repel each other and a-b attract each\nother, forming the two-particle bound state with binding energy\n$\\epsilon_b^{(2)}$ (such as bi-exciton). We developed an efficient routine\nbased on the proper choice of basis for analytic and numerical calculations.\nFor zero-angular momentum we found the energies of the three-particle bound\nstates $\\epsilon^{(3)}_b$ for wide ranges of the scattering lengths, and found\na universal curve of $\\epsilon^{(3)}_b/\\epsilon^{(2)}_b$ which depends only on\nthe scattering lengths but not the microscopic details of the interactions,\nthis is in contrast to the three-dimensional Efimov effect, where a\nnon-universal three-body parameter is needed.",
        "positive": "Spectral density, Levinson's theorem, and the extra term in the second\n  virial coefficient for 1D delta-function potential: In contrast with the 3D result, the Beth-Uhlenbeck (BU) formula in 1D\ncontains an extra -1/2 term. The origin of this -1/2 term is explained using a\nspectral density approach. To be explicit, a delta-function potential is used\nto show that the correction term arises from a pole of the density of states at\nzero energy. The spectral density method shows that this term is actually an\nartifact of the non-normalizability of the scattering states and an infrared\ncutoff regularization scheme has to be used to get the correct result in 1D.\nThe formal derivation of the BU formula would miss this term since it ignores\nthe effects of the boundary terms. While the result is shown for the\ndelta-function potential, the method and result are valid for more general\npotentials. Additionally, the 1D Levinson's theorem can be extracted from the\nspectral density method using the asymptotic form of general potentials. The\nimportance of the result lies in the fact that all these correction terms in 1D\nhave a universal source: a pole at zero energy. Similar calculations using\nquantum field theoretical approaches (without explicit infrared cutoff\nregularization schemes) also show the same subtleties with the correction term\noriginating from the zero energy scattering states (appendix A)."
    },
    {
        "anchor": "Single-particle-exact density functional theory: We introduce 'single-particle-exact density functional theory' (1pEx-DFT), a\nnovel density functional approach that represents all single-particle\ncontributions to the energy with exact functionals. Here, we parameterize\ninteraction energy functionals by utilizing two new schemes for constructing\ndensity matrices from 'participation numbers' of the single-particle states of\nquantum many-body systems. These participation numbers play the role of the\nvariational variables akin to the particle densities in standard orbital-free\ndensity functional theory. We minimize the total energies with the help of\nevolutionary algorithms and obtain ground-state energies that are typically\naccurate at the one-percent level for our proof-of-principle simulations that\ncomprise interacting Fermi gases as well as the electronic structure of atoms\nand ions, with and without relativistic corrections. We thereby illustrate the\ningredients and practical features of 1pEx-DFT and reveal its potential of\nbecoming an accurate, scalable, and transferable technology for simulating\nmesoscopic quantum many-body systems.",
        "positive": "Inhomogeneous Topological Superfluidity in One-Dimensional\n  Spin-Orbit-Coupled Fermi Gases: We theoretically predict an exotic topological superfluid state with\nspatially modulated pairing gap in one-dimensional spin-orbit-coupled Fermi\ngases. This inhomogeneous topological superfluidity is induced by applying\nsimultaneously a perpendicular Zeeman magnetic field and an equally weighted\nRashba and Dresselhaus spin-orbit coupling in one-dimensional optical lattices.\nBased on the self-consistent Bogoliubov--de Gennes theory, we confirm that this\nnovel topological phase is a unique condensation of Cooper pairs, which\nmanifests the interplay between the inhomogeneity of superfluid and its\nnontrivial topological structure. The properties of the emergent Majorana bound\nstates are investigated in detail by examining the associated $\\mathbb{Z}_{2}$\ntopological number, the eigenenergy and density of states spectra, as well as\nthe wave functions of the localized Majorana end modes. Experimental\nfeasibility of observing this new topological state of matter is also\ndiscussed."
    },
    {
        "anchor": "Turning the BEC-BCS crossover into a transition by radiation: We show that the Bardeen-Cooper-Schrieffer state (BCS) and the Bose-Einstein\ncondensation (BEC) sides of the BCS-BEC crossover can be rigorously\ndistinguished from each other by the extrema of the spectrum of the fermionic\nexcitations. Moreover, we demonstrate that this formal distinction is realized\nas a non-equilibrium phase transition under radio frequency radiation. The BEC\nphase remains translationally invariant, whereas the BCS phase transforms into\nthe supersolid phase. For a two-dimensional system this effect occurs at\narbitrary small amplitude of the radiation field.",
        "positive": "Superfluidity of Bose-Einstein condensates in toroidal traps with\n  nonlinear lattices: Superfluid properties of Bose-Einstein condensates (BEC) in toroidal\nquasi-one-dimensional traps are investigated in the presence of periodic\nscattering length modulations along the ring. The existence of several types of\nstable periodic waves, ranging from almost uniform to very fragmented chains of\nweakly interacting and equally spaced solitons, is demonstrated. We show that\nthese waves may support persistent atomic currents and sound waves with spectra\nof Bogoliubov type. Fragmented condensates can be viewed as arrays of Josephson\njunctions and the current as a BEC manifestation of the dc-Josephson effect.\nThe influence of linear defects on BEC superfluidity has been also\ninvestigated. We found that for subcritical velocities, linear defects that are\nstatic with respect to the lattice (while the condensate moves in respect to\nboth the optical lattice and the defect) preserve the BEC superfluidity."
    },
    {
        "anchor": "Tunable boson-assisted finite-range interaction and engineering Majorana\n  corner modes in optical lattices: Nonlocal interaction between ultracold atoms trapped in optical lattices can\ngive rise to interesting quantum many-body phenomena. However, its realization\nusually demands unconventional techniques, for example the artificial gauge\nfields or higher-orbit Feshbach resonances, and is not highly controllable.\nHere, we propose a valid and feasible scheme for realizing a tunable\nfinite-range interaction for spinless fermions immersed into the bath of\nbosons. The strength of the effective interaction for the fermionic subsystem\nis artificially tunable by manipulating bosons, ranging from the repulsive to\nattractive regime. And the interaction distance is locked to the hopping of\nbosons, making the finite-range interaction perfectly clean for the fermionic\nsubsystem. Specifically we find that, by introducing an additional staggered\nhopping of bosons, the proposal is readily applied to search the Majorana\ncorner modes in such a spinless system, without implementation of complex\nartificial gauge fields, which is totally distinct from existing results\nreported in spinful systems. Therefore this scheme provides a potential\nplatform for exploring the unconventional topological superfluids and other\nnontrivial phases induced by long-range interactions in ultracold atoms.",
        "positive": "Excitations in the Yang-Gaudin Bose gas: We study the excitation spectrum of two-component delta-function interacting\nbosons confined to a single spatial dimension, the Yang-Gaudin Bose gas. We\nshow that there are pronounced finite-size effects in the dispersion relations\nof excitations, perhaps best illustrated by the spinon single particle\ndispersion which exhibits a gap at $2k_F$ and a finite-momentum roton minimum.\nSuch features occur at energies far above the finite volume excitation gap,\nvanish slowly as $1/L$ for fixed spinon number, and can persist to the\nthermodynamic limit at fixed spinon density. Features such as the $2k_F$ gap\nalso persist to multi-particle excitation continua. Our results show that\nexcitations in the finite system can behave in a qualitatively different manner\nto analogous excitations in the thermodynamic limit.\n  The Yang-Gaudin Bose gas is also host to multi-spinon bound states, known as\n$\\Lambda$-strings. We study these excitations both in the thermodynamic limit\nunder the string hypothesis and in finite size systems where string deviations\nare taken into account. In the zero-temperature limit we present a simple\nrelation between the length $n$ $\\Lambda$-string dressed energies\n$\\epsilon_n(\\lambda)$ and the dressed energy $\\epsilon(k)$. We solve the\nYang-Yang-Takahashi equations numerically and compare to the analytical\nsolution obtained under the strong couple expansion, revealing that the length\n$n$ $\\Lambda$-string dressed energy is Lorentzian over a wide range of real\nstring centers $\\lambda$ in the vicinity of $\\lambda = 0$. We then examine the\nfinite size effects present in the dispersion of the two-spinon bound states by\nnumerically solving the Bethe ansatz equations with string deviations."
    },
    {
        "anchor": "Topological Superfluids and BEC-BCS Crossover in Attractive\n  Haldane-Hubbard Model: Motivated by the recent realization of the Haldane model in shaking optical\nlattice, we investigate the effects of attractive interaction and BEC-BCS\ncrossover in this model at and away from half filling. We show that, contrary\nto the usual s-wave BEC-BCS crossover in the lattice, a topological superfluid\nwith Chern number C=2 appears in an extended region of phase space for\nintermediate strength of the attractive interaction in the interaction-density\nplane. When inversion symmetry is broken, a new gapless topological state is\nrealized. We also investigate the fluctuations in these superfluid phases and\nshow that the Anderson-Bogoliubov mode is quadratic due to time-reversal\nsymmetry breaking and the existence of an undamped Leggett mode in the strong\ncoupling limit.",
        "positive": "Phase Space Crystal Vibrations: Chiral Edge States with Preserved\n  Time-reversal Symmetry: It was recently discovered that atoms subject to a time-periodic drive can\ngive rise to a crystal structure in phase space. In this work, we point out the\natom-atom interactions give rise to collective phonon excitations of\nphase-space crystal via a pairing interaction with intrinsically complex phases\nthat can lead to a phonon Chern insulator, accompanied by topologically robust\nchiral transport along the edge of the phase-space crystal. This topological\nphase is realized even in scenarios where the time-reversal transformation is a\nsymmetry, which is surprising because the breaking of time-reversal symmetry is\na strict precondition for topological chiral transport in the standard setting\nof real-space crystals. Our work has also important implications for the\ndynamics of 2D charged particles in a strong magnetic field."
    },
    {
        "anchor": "Quantum Chaos of Unitary Fermi Gases in Strong Pairing Fluctuation\n  Region: The growth rate of the out-of-time-ordered correlator in a N-flavor Fermi gas\nis investigated and the Lyapunove exponent $\\lambda_L$ is calculated to the\norder of $1/N$. We find that the Lyapunove exponent monotonically increases as\nthe the interaction strength increases from the BCS limit to the unitary\nregion. At the unitarity the Lyapunove exponent increases while the temperature\ndrops and it can reach to the order of $\\lambda_L\\sim T$ around the critical\ntemperature for the $N=1$ case. The system scrambles faster for stronger\npairing fluctuations. At the BCS limit, the Lyapunov exponent behaviors as\n$\\lambda_L\\propto e^{\\mu/T} a^2_s T^2/N$.",
        "positive": "Spin and Charge Resolved Quantum Gas Microscopy of Antiferromagnetic\n  Order in Hubbard Chains: The repulsive Hubbard Hamiltonian is one of the foundational models\ndescribing strongly correlated electrons and is believed to capture essential\naspects of high temperature superconductivity. Ultracold fermions in optical\nlattices allow for the simulation of the Hubbard Hamiltonian with a unique\ncontrol over kinetic energy, interactions and doping. A great challenge is to\nreach the required low entropy and to observe antiferromagnetic spin\ncorrelations beyond nearest neighbors, for which quantum gas microscopes are\nideal. Here we report on the direct, single-site resolved detection of\nantiferromagnetic correlations extending up to three sites in spin-$1/2$\nHubbard chains, which requires an entropy well below $s^*=\\ln(2)$. Finally, the\nsimultaneous detection of spin and density opens the route towards the study of\nthe interplay between magnetic ordering and doping in various dimensions."
    },
    {
        "anchor": "Flat Band Quantum Scar: We show that a quantum scar state, an atypical eigenstate breaking eigenstate\nthermalization hypothesis embedded in a many-body energy spectrum, can be\nconstructed in flat band systems. The key idea of our construction is to make\nuse of orthogonal compact localized states. We concretely discuss our\nconstruction scheme, taking a saw-tooth flat lattice system as an example, and\nnumerically demonstrate the presence of a quantum scar state. Examples of\nhigher-dimensional systems are also addressed. Our construction method of\nquantum scar has broad applications to various flat band systems.",
        "positive": "Narrow-line magneto-optical trap for dysprosium atoms: We present our technique to create a magneto-optical trap for dysprosium\natoms using the narrow-line cooling transition at 626$\\,$nm to achieve suitable\nconditions for direct loading into an optical dipole trap. The magneto-optical\ntrap is loaded from an atomic beam via a Zeeman slower using the strongest\natomic transition at 421$\\,$nm. With this combination of two cooling\ntransitions we can trap up to $2.0\\cdot10^8$ atoms at temperatures down to 6$\\,\n\\mu$K. This cooling approach is simpler than present work with ultracold\ndysprosium and provides similar starting conditions for a transfer to an\noptical dipole trap."
    },
    {
        "anchor": "Synthetic magnetic fields for ultracold neutral atoms: Neutral atomic Bose condensates and degenerate Fermi gases have been used to\nrealize important many-body phenomena in their most simple and essential forms,\nwithout many of the complexities usually associated with material systems.\nHowever, the charge neutrality of these systems presents an apparent limitation\n- a wide range of intriguing phenomena arise from the Lorentz force for charged\nparticles in a magnetic field, such as the fractional quantum Hall states in\ntwo-dimensional electron systems. The limitation can be circumvented by\nexploiting the equivalence of the Lorentz force and the Coriolis force to\ncreate synthetic magnetic fields in rotating neutral systems. This was\ndemonstrated by the appearance of quantized vortices in pioneering experiments\non rotating quantum gases, a hallmark of superfluids or superconductors in a\nmagnetic field. However, because of technical issues limiting the maximum\nrotation velocity, the metastable nature of the rotating state and the\ndifficulty of applying stable rotating optical lattices, rotational approaches\nare not able to reach the large fields required for quantum Hall physics. Here,\nwe experimentally realize an optically synthesized magnetic field for ultracold\nneutral atoms, made evident from the appearance of vortices in our\nBose-Einstein condensate. Our approach uses a spatially-dependent optical\ncoupling between internal states of the atoms, yielding a Berry's phase\nsufficient to create large synthetic magnetic fields, and is not subject to the\nlimitations of rotating systems; with a suitable lattice configuration, it\nshould be possible to reach the quantum Hall regime, potentially enabling\nstudies of topological quantum computation.",
        "positive": "Bulk density signatures of a lattice quasihole with very few particles: Motivated by the recent experimental realization of a two-particle fractional\nquantum Hall state of ultracold atoms in a small optical lattice [Nature 619,\n495 (2023)], we propose a minimal setup to create and observe a quasihole in\nsuch a system. We find that clear signatures of a quasihole state with two or\nthree atoms can be obtained through a standard site-resolved density\nmeasurement provided that the system is appropriately modified with simple\nadditional potential profiles. By adding a single-site repulsive potential to\npin the quasihole and superimposing a harmonic trap on top of the optical\nlattice to keep the particles away from the system edge, we determine via exact\ndiagonalization an optimal range for system parameters such as the magnetic\nflux and the strengths of the additional potentials that would favour the\ncreation of the quasihole state. We hope that our results will be a useful\nguide for a possible proof-of-principle experiment that will demonstrate the\nfirst controllable creation of a simple quasihole state in a condensed matter\nsystem, which will pave the way for the observation of the anyonic statistics\nof quasiholes in a more complex system."
    },
    {
        "anchor": "Reconciling the Classical-Field Method with the Beliaev Broken Symmetry\n  Approach: We present our views on the issues raised in the chapter by Griffin and\nZaremba [A. Griffin and E. Zaremba, in Quantum Gases: Finite Temperature and\nNon-Equilibrium Dynamics, N. P. Proukakis, S. A. Gardiner, M. J. Davis, and M.\nH. Szymanska, eds., Imperial College Press, London (in press)]. We review some\nof the strengths and limitations of the Bose symmetry-breaking assumption, and\nexplain how such an approach precludes the description of many important\nphenomena in degenerate Bose gases. We discuss the theoretical justification\nfor the classical-field (c-field) methods, their relation to other\nnon-perturbative methods for similar systems, and their utility in the\ndescription of beyond-mean-field physics. Although it is true that present\nimplementations of c-field methods cannot accurately describe certain\ncollective oscillations of the partially condensed Bose gas, there is no\nfundamental reason why these methods cannot be extended to treat such\nscenarios. By contrast, many regimes of non-equilibrium dynamics that can be\ndescribed with c-field methods are beyond the reach of generalised mean-field\nkinetic approaches based on symmetry-breaking, such as the ZNG formalism.",
        "positive": "Observation of Spin Superfluidity in a Bose Gas Mixture: The spin dynamics of a harmonically trapped Bose-Einstein condensed binary\nmixture of sodium atoms is experimentally investigated at finite temperature.\nIn the collisional regime the motion of the thermal component is shown to be\ndamped because of spin drag, while the two condensates exhibit a counter flow\noscillation without friction, thereby providing direct evidence for spin\nsuperfluidity. Results are also reported in the collisionless regime where the\nspin components of both the condensate and thermal part oscillate without\ndamping, their relative motion being driven by a mean field effect. We also\nmeasure the static polarizability of the condensed and thermal parts and we\nfind a large increase of the condensate polarizability with respect to the T=0\nvalue, in agreement with the predictions of theory."
    },
    {
        "anchor": "Modulational instability, inter-component asymmetry and formation of\n  quantum droplets in one-dimensional binary Bose gases: Quantum droplets are ultradilute liquid states which emerge from the\ncompetitive interplay of two Hamiltonian terms, the mean-field energy and\nbeyond-mean-field correction, in a weakly interacting binary Bose gas. We\nrelate the formation of droplets in symmetric and asymmetric two-component\none-dimensional boson systems to the modulational instability of a spatially\nuniform state driven by the beyond-mean-field term. Asymmetry between the\ncomponents may be caused by their unequal populations or unequal\nintra-component interaction strengths. Stability of both symmetric and\nasymmetric droplets is investigated. Robustness of the symmetric solutions\nagainst symmetry-breaking perturbations is confirmed.",
        "positive": "Time-of-flight expansion of trapped dipolar Fermi gases: From the\n  collisionless to the hydrodynamic regime: A recent time-of-flight (TOF) expansion experiment with polarized fermionic\nerbium atoms measured a Fermi surface deformation from a sphere to an ellipsoid\ndue to dipole-dipole interaction, thus confirming previous theoretical\npredictions. Here we perform a systematic study of the ground-state properties\nand TOF dynamics for trapped dipolar Fermi gases from the collisionless to the\nhydrodynamic regime at zero temperature. To this end we solve analytically the\nunderlying Boltzmann-Vlasov equation within the relaxation-time approximation\nin the vicinity of equilibrium by using a suitable rescaling of the equilibrium\ndistribution. The resulting ordinary differential equations for the respective\nscaling parameters are then solved numerically for experimentally realistic\nparameters and relaxation times that correspond to the collisionless,\ncollisional, and hydrodynamic regime. The equations for the collisional regime\nare first solved in the approximation of a fixed relaxation time, and then this\napproach is extended to include a self-consistent determination of the\nrelaxation time. The presented analytical and numerical results are relevant\nfor a detailed quantitative understanding of ongoing experiments and the design\nof future experiments with ultracold fermionic dipolar atoms and molecules. In\nparticular, the obtained results are relevant for systems with strong\ndipole-dipole interaction, which turn out to affect significantly the aspect\nratios during the TOF expansion."
    },
    {
        "anchor": "Symmetry breaking in a localized interacting binary BEC in a\n  bi-chromatic optical lattice: By direct numerical simulation of the time-dependent Gross-Pitaevskii\nequation using the split-step Fourier spectral method we study different\naspects of the localization of a cigar-shaped interacting binary\n(two-component) Bose-Einstein condensate (BEC) in a one-dimensional\nbi-chromatic quasi-periodic optical-lattice potential, as used in a recent\nexperiment on the localization of a BEC [Roati et al., Nature 453, 895 (2008)].\nWe consider two types of localized states: (i) when both localized components\nhave a maximum of density at the origin x=0, and (ii) when the first component\nhas a maximum of density and the second a minimum of density at x=0. In the\nnon-interacting case the density profiles are symmetric around x=0. We\nnumerically study the breakdown of this symmetry due to inter-species and\nintra-species interaction acting on the two components. Where possible, we have\ncompared the numerical results with a time-dependent variational analysis. We\nalso demonstrate the stability of the localized symmetry-broken BEC states\nunder small perturbation.",
        "positive": "Collective, Coherent, and Ultrastrong Coupling of 2D Electrons with\n  Terahertz Cavity Photons: Nonperturbative coupling of light with condensed matter in an optical cavity\nis expected to reveal a host of coherent many-body phenomena and states. In\naddition, strong coherent light-matter interaction in a solid-state environment\nis of great interest to emerging quantum-based technologies. However, creating\na system that combines a long electronic coherence time, a large dipole moment,\nand a high cavity quality ($Q$) factor has been a challenging goal. Here, we\nreport collective ultrastrong light-matter coupling in an ultrahigh-mobility\ntwo-dimensional electron gas in a high-$Q$ terahertz photonic-crystal cavity in\na quantizing magnetic field, demonstrating a cooperativity of $\\sim$360. The\nsplitting of cyclotron resonance (CR) into the lower and upper polariton\nbranches exhibited a $\\sqrt{n_\\mathrm{e}}$-dependence on the electron density\n($n_\\mathrm{e}$), a hallmark of collective vacuum Rabi splitting. Furthermore,\na small but definite blue shift was observed for the polariton frequencies due\nto the normally negligible $A^2$ term in the light-matter interaction\nHamiltonian. Finally, the high-$Q$ cavity suppressed the superradiant decay of\ncoherent CR, which resulted in an unprecedentedly narrow intrinsic CR linewidth\nof 5.6 GHz at 2 K. These results open up a variety of new possibilities to\ncombine the traditional disciplines of many-body condensed matter physics and\ncavity-based quantum optics."
    },
    {
        "anchor": "Slow Thermalization Between a Lattice and Free Bose Gas: Using a 3D spin-dependent optical lattice, we study thermalization and energy\nexchange between two ultracold Bose gases, one of which is bound to the lattice\nand another that is free from the lattice potential. Disruption of\ninter-species thermalization is revealed through measurements of condensate\nfraction after the lattice is superimposed on the parabolic confining\npotential. By selectively heating the lattice-bound species and measuring the\nrate of heat transfer to the free state, suppression of energy exchange is\nobserved. Comparison with a Fermi's golden rule prediction confirms that this\neffect is caused by a dispersion mismatch that reduces the phase space\navailable for elastic collisions. This result has critical implications for\nmethods proposed to cool strongly correlated lattice gases.",
        "positive": "Quantum self-bound droplets in Bose-Bose mixtures: Effects of\n  higher-order quantum and thermal fluctuations: We systematically study the effects of higher-order quantum and thermal\nfluctuations on the stabilization of self-bound droplets in Bose mixtures\nemploying the time-dependent Hartree-Fock-Bogoliubov theory. We calculate the\nground-state energy, the droplet equilibrium density, the depletion and\nanomalous density of the droplets as well as the critical temperature as a\nfunction of the relevant parameters. Our findings are compared with previous\nanalytical predictions and diffusion Monte Carlo simulations. We employ our\ntheory together with the local density approximation for quantum and thermal\nfluctuations to obtain an extended finite-temperature Gross-Pitaevskii\nequation. The density profiles and breathing modes of the droplet are deeply\nexamined in terms of the interaction strength and the temperature by\nnumerically solving the developed generalized Gross-Pitaevskii equation."
    },
    {
        "anchor": "Visualizing edge states with an atomic Bose gas in the quantum Hall\n  regime: We engineered a two-dimensional magnetic lattice in an elongated strip\ngeometry, with effective per-plaquette flux ~4/3 times the flux quanta. We\nimaged the localized edge and bulk states of atomic Bose-Einstein condensates\nin this strip, with single lattice-site resolution along the narrow direction.\nFurther, we observed both the skipping orbits of excited atoms traveling down\nour system's edges, analogues to edge magnetoplasmons in 2-D electron systems,\nand a dynamical Hall effect for bulk excitations. Our lattice's long direction\nconsisted of the sites of an optical lattice and its narrow direction consisted\nof the internal atomic spin states. Our technique has minimal heating, a\nfeature that will be important for spectroscopic measurements of the Hofstadter\nbutterfly and realizations of Laughlin's charge pump.",
        "positive": "Spin dynamics and domain formation of a spinor Bose-Einstein condensate\n  in an optical cavity: We consider a ferromagnetic spin-1 Bose-Einstein condensate (BEC)\ndispersively coupled to a unidirectional ring cavity. We show that the ability\nof a cavity to modify, in a highly nonlinear fashion, matter-wave phase shifts\nadds a new dimension to the study of spinor condensates both within and beyond\nthe single-mode approximation. In addition to demonstrating strong matter-wave\nbistability as in our earlier publication [L. Zhou et al., Phys. Rev. Lett.\n103, 160403 (2009)], we show that the interplay between atomic and cavity\nfields can greatly enrich both the physics of critical slowing down in spin\nmixing dynamics and the physics of spin-domain formation in spinor condensates."
    },
    {
        "anchor": "Trimer and Tetramer Bound States in Heteronuclear Systems: The Efimov effect in heteronuclear cold atomic systems is experimentally more\neasily accessible than the Efimov effect for identical atoms, because of the\npotentially smaller scaling factor. We focus on the case of two or three heavy\nidentical bosons and another atom. The former case was recently observed in a\nmixture of 133Cs and 6Li atoms. We employ the Gaussian Expansion Method as\ndeveloped by Hiyama, Kino et al.. This is a variational method that uses\nGaussians that are distributed geometrically over a chosen range. Supplemental\ncalculations are performed using the Skorniakov-Ter-Martirosian equation. Blume\net al. previously investigated the scaling properties of heteronuclear systems\nin the unitary limit and at the three-body breakup threshold. We have completed\nthis picture by calculating the behaviour on the positive scattering length\nside of the Efimov plot, focussing on the dimer threshold.",
        "positive": "Persistent currents in a strongly interacting multicomponent Bose gas on\n  a ring: We consider a two-component Bose-Bose mixture at strong repulsive\ninteractions in a tightly confining, one-dimensional ring trap and subjected to\nan artificial gauge field. By employing the Bethe Ansatz exact solution for the\nmany-body wavefunction, we obtain the ground state energy and the persistent\ncurrents. For each value of the applied flux, we then determine the symmetry of\nthe state under particles exchange. We find that the ground-state energy and\nthe persistent currents display a reduced periodicity with respect to the case\nof non-interacting particles, corresponding to reaching states with fractional\nangular momentum per particle. We relate this effect to the change of symmetry\nof the ground state under the effect of the artificial gauge field. Our results\ngeneralize the ones previously reported for fermionic mixtures with both\nattractive and repulsive interactions and highlight the role of symmetry in\nthis effect"
    },
    {
        "anchor": "Self-Bound Quantum Droplet with Internal Stripe Structure in 1D\n  Spin-Orbit-Coupled Bose Gas: We study the quantum-droplet state in a 3-dimensional (3D) Bose gas in the\npresence of 1D spin-orbit-coupling and Raman coupling, especially the stripe\nphase with density modulation, by numerically computing the ground state energy\nincluding the mean-field energy and Lee-HuangYang correction. In this droplet\nstate, the stripe can exist in a wider range of Raman coupling, compared with\nthe BEC-gas state. More intriguingly, both spin-orbit-coupling and Raman\ncoupling strengths can be used to tune the droplet density.",
        "positive": "Topological bands with Chern number C=2 by dipolar exchange interactions: We demonstrate the realization of topological band structures by exploiting\nthe intrinsic spin-orbit coupling of dipolar interactions in combination with\nbroken time-reversal symmetry. The system is based on polar molecules trapped\nin a deep optical lattice, where the dynamics of rotational excitations follows\na hopping Hamiltonian which is determined by the dipolar exchange interactions.\nWe find topological bands with Chern number $C=2$ on the square lattice, while\na very rich structure of different topological bands appears on the honeycomb\nlattice. We show that the system is robust against missing molecules. For\ncertain parameters we obtain flat bands, providing a promising candidate for\nthe realization of hard-core bosonic fractional Chern insulators."
    },
    {
        "anchor": "Mapping trapped atomic gas with spin-orbit coupling to quantum Rabi-like\n  model: We construct a connection of the ultracold atomic system in a harmonic trap\nwith Raman-induced spin-orbit coupling to the quantum Rabi-like model. By\nmapping the trapped atomic system to a Rabi-like model, we can get the exact\nsolution of the Rabi-like model following the methods to solve the quantum Rabi\nmodel. The existence of such a mapping implies that we can study the basic\nmodel in quantum optics by using trapped atomic gases with spin-orbit coupling.",
        "positive": "Emergent non-trivial lattices for topological insulators: Materials with non-trivial lattice geometries allow for the creation of\nexotic states of matter like topologically insulating states. Therefore\nsearching for such materials is an important aspect of current research in\nsolid-state physics. In the field of ultracold gases there are ongoing studies\naiming to create non-trivial lattices using optical means. In this paper we\nstudy two species of fermions trapped in a square optical lattice and show how\nnon-trivial lattices can emerge due to strong interaction between atoms. We\ntheoretically investigate regimes of tunable parameters in which such\nself-assembly may take place and describe the necessary experimental\nconditions. Moreover we discuss the possibility of such emergent lattices\nhosting topologically insulating states."
    },
    {
        "anchor": "Chaotic Einstein-Podolsky-Rosen pairs, measurements and time reversal: We consider a situation when evolution of an entangled\nEinstein-Podolsky-Rosen (EPR) pair takes place in a regime of quantum chaos\nbeing chaotic in the classical limit. This situation is studied on an example\nof chaotic pair dynamics described by the quantum Chirikov standard map. The\ntime evolution is reversible even if a presence of small errors breaks time\nreversal of classical dynamics due to exponential growth of errors induced by\nexponential chaos instability. However, the quantum evolution remains\nreversible since a quantum dynamics instability exists only on a\nlogarithmically short Ehrenfest time scale. We show that due to EPR pair\nentanglement a measurement of one particle at the moment of time reversal\nbreaks exact time reversal of another particle which demonstrates only an\napproximate time reversibility. This result is interpreted in the framework of\nthe Schmidt decomposition and Feynman path integral formulation of quantum\nmechanics. The time reversal in this system has already been realized with cold\natoms in kicked optical lattices in absence of entanglement and measurements.\nOn the basis of the obtained results we argue that the experimental\ninvestigations of time reversal of chaotic EPR pairs is within reach of present\ncold atom capabilities.",
        "positive": "Topological Phase Transition and Charge Pumping in a One-Dimensional\n  Periodically Driven Optical Lattice: Experimental realizations of topological quantum systems and detections of\ntopological invariants in ultracold atomic systems have been a greatly\nattractive topic. In this work, we propose a scheme to realize topologically\ndifferent phases in a bichromatic optical lattice subjected to a periodically\ndriven tilt harmonic oscillation, which can be effectively described by a\nsuperlattice model with tunable long-range hopping processes. By tuning the\nratio of nearest-neighbor (NN) and next-nearest-neighbor (NNN) hopping\namplitudes, the system undergoes a topological phase transition accompanied by\nthe change of topological numbers of the lowest band from -1 to 2. Using a\nslowly time-periodic modulation, the system emerges distinct quantized\ntopological pumped charges (TPCs) of atoms in the filled band for different\ntopological phases. Our scheme is realizable in current cold atomic technique."
    },
    {
        "anchor": "Super-Tonks-Girardeau gas of spin-1/2 interacting fermions: Fermi gases confined in tight one-dimensional waveguides form two-particle\nbound states of atoms in the presence of a strongly attractive interaction.\nBased on the exact solution of the one-dimensional spin-1/2 interacting Fermi\ngas, we demonstrate that a stable excited state with no pairing between\nattractive fermionic atoms can be realized by a sudden switch of interaction\nfrom strongly repulsive regime to the strongly attractive regime. Such a state\nis an exact fermionic analog of the experimentally observed\nsuper-Tonks-Girardeau state of bosonic Cesium atoms [Science 325, 1224 (2009)]\nand should be possible to be observed by the experiment. The frequency of\nlowest breathing mode of the fermionic super-Tonks-Girardeau gas is calculated\nas a function of the interaction strength, which could be used as a detectable\nsignature for the experimental observation.",
        "positive": "Coherent insulator at arbitrary frequency in a driven atomtronic\n  transistor: We use numerical approach to study non-equilibrium transport of atomic gas in\na driven optical lattice atomtronic transistor. The shaken optical lattice\ntransistor displays a property of insulator within some regions of shaking\nfrequency and shaking strength. It is proved that appearance of the insulation\nis directly connected to coherence of the system. Coherence of the system is\naccompanied by coherent trapping of non-equilibrium atomic gas in one of the\noptical wells, which stops atomic currents. Comparing with the effective\nHamiltonian approach in Floquet engineering, the time-dependent Hamiltonian\napproach could be used in any frequency regime of periodically driven quantum\nsystem."
    },
    {
        "anchor": "Quench dynamics of neutral atoms in out-equilibrium one dimensional\n  optical lattices: A quantum simulator is proposed for nucleation and growth dynamics using an\nout-of equilibrium optical lattice. We calculate the density of neutral atoms\nin the lattice and we establish the connection with the\nKolmogorov-Mehl-Johnson-Avrami model. Here we show that a Avrami equation can\ndescribe most of the evolution in time of the population growth in the lattice,\ncoherence between neutral atoms leads a complex growth rate.",
        "positive": "Bose-Einstein Condensation in the presence of an artificial spin-orbit\n  interaction: Bose-Einstein condensation in the presence of a synthetic spin-momentum\ninteraction is considered, focusing on the case where a Dirac or Rashba\npotential is generated via a tripod scheme. We found that the ground states can\nbe either plane wave states or superpositions of them, each characterized by\ntheir unique density distributions."
    },
    {
        "anchor": "Fractal Quasicondensation in One Dimension: We unveil a novel mechanism for quasicondensation of hard-core bosons in the\npresence of quasiperiodicity-induced multifractal single-particle states. The\nnew critical state, here dubbed fractal quasicondensate, is characterized by\nnatural orbitals with multifractal properties and by an occupancy of the lowest\nnatural orbital, {\\lambda}0 ~ L{\\gamma}, which grows with system size but with\na nonuniversal scaling exponent, {\\gamma} < 1/2. In contrast to fractal\nquasicondensates obtained when the chemical potential lies in a region of\nmultifractal single-particle states, placing the chemical potential in regions\nof localized or delocalized states yields, respectively, no condensation or the\nusual 1D quasicondensation with {\\gamma} = 1/2. Our findings are established by\nstudying one-dimensional hardcore bosons subjected to various quasiperiodic\npotentials, including the well-known Aubry-Andre model, employing a mapping to\nnon-interacting fermionics that allows for numerically exact results. We\ndiscuss how to test our findings in state-of-the-art ultracold atom\nexperiments.",
        "positive": "Localization transition in weakly-interacting Bose superfluids in\n  one-dimensional quasiperdiodic lattices: We study the localization of collective pair excitations in\nweakly-interacting Bose superfluids in one-dimensional quasiperiodic lattices.\nThe localization diagram is first determined numerically. For intermediate\ninteraction and quasiperiodic amplitude we find a sharp localization\ntransition, with extended low-energy states and localized high-energy states.\nWe then develop an analytical treatment, which allows us to quantitatively map\nthe localization transition into that of an effective multiharmonic\nquasiperiodic system."
    },
    {
        "anchor": "Formation, dynamics and stability of coreless vortex dipoles in\n  phase-separated binary condensates: We study the motion of the Gaussian obstacle potential created by blue\ndetuned laser beam through a phase-separated binary condensate in\npancake-shaped traps. For the velocity of the obstacle above a critical\nvelocity, we observe the generation of vortex dipoles in the outer component\nwhich can penetrate the inner component. This is equivalent to finite, although\nsmall, transport of outer component across the inner component. In the inner\ncomponent, the same method can lead to the formation of coreless vortex\ndipoles.",
        "positive": "Supplementary information to \"Efimov-driven phase transitions of the\n  unitary Bose gas\": In quantum physics, Efimov trimers are bound states of three particles that\nfall apart like Borromean rings when one of them is removed. Initially\npredicted in nuclear physics, these striking bosonic states are hard to\nobserve, but the \"unitary\" interactions at which they form is commonly realized\nin current cold atoms experiments. There, they set the stage for a new class of\nuniversal physics: Two-body interactions are all but invisible, but three-body\neffects allow the emergence of a largely uncharted new world of many-particle\nbound states. Three-particle systems were characterized theoretically, and the\nground-state properties of small unitary clusters computed numerically, but the\nmacroscopic many-body behaviour has remained unknown. Here we show, using a\nPath-Integral Monte Carlo algorithm backed up by theoretical arguments, that\nthe unitary Bose gas presents a first-order phase transition from a normal gas\nto a superfluid Efimov liquid. The normal gas is very well described by the\navailable virial coefficients. At unitarity, the phase diagram of the bosonic\nsystem is universal in rescaled pressure and temperature. A triple point\nseparates the normal gas, the superfluid Efimov liquid, and a third phase, the\nconventional superfluid gas. These two superfluid phases are separated by a\ncritical line that ends in a critical point at high temperature. This rich\nphase diagram should allow for a number of experimental protocols that would\nprobe these universal transitions between the normal gas, the superfluid gas,\nand the superfluid Efimov liquid."
    },
    {
        "anchor": "Effects of heterogeneity in site-site couplings for tight-binding models\n  on scale-invariant structures: We studied the thermodynamic behaviors of non-interacting bosons and fermions\ntrapped by a scale-invariant branching structure of adjustable degree of\nheterogeneity. The full energy spectrum in tight-binding approximation was\nanalytically solved . We found that the log-periodic oscillation of the\nspecific heat for Fermi gas depended on the heterogeneity of hopping. Also, low\ndimensional Bose-Einstein condensation occurred only for non-homogeneous setup.",
        "positive": "Center-of-mass-momentum-dependent interaction between ultracold atoms: We show that a type of two-body interaction, which depends on the momentum of\nthe center of mass (COM) of these two particles, can be realized in ultracold\natom gases with a laser-modulated magnetic Feshbach resonance (MFR). Here the\nMFR is modulated by two laser beams propagating along different directions,\nwhich can induce Raman transition between two-body bound states. The Doppler\neffect causes the two-atom scattering length to be strongly dependent on the\nCOM momentum of these two atoms. As a result, the effective two-atom\ninteraction is COM-momentum dependent, while the one-atom free Hamiltonian is\nstill the simple kinetic energy p^2/(2m)."
    },
    {
        "anchor": "Scattering Hypervolume of Spin-Polarized Fermions: We analyze the collision of three identical spin-polarized fermions at zero\ncollision energy, assuming arbitrary finite-range potentials, and define the\ncorresponding three-body scattering hypervolume $D_F$. The scattering\nhypervolume $D$ was first defined for identical bosons in 2008 by one of us. It\nis the three-body analog of the two-body scattering length. We solve the\nthree-body Schr\\\"{o}dinger equation asymptotically when the three fermions are\nfar apart or one pair and the third fermion are far apart, deriving two\nasymptotic expansions of the wave function. Unlike the case of bosons for which\n$D$ has the dimension of length to the fourth power, here the $D_F$ we define\nhas the dimension of length to the eighth power. We then analyze the\ninteraction energy of three such fermions with momenta $\\hbar\\mathbf{k}_1$,\n$\\hbar\\mathbf{k}_2$ and $\\hbar\\mathbf{k}_3$ in a large periodic cubic box. The\nenergy shift due to $D_F$ is proportional to $D_F/\\Omega^2$, where $\\Omega$ is\nthe volume of the box. We also calculate the shifts of energy and pressure of\nspin-polarized Fermi gases due to a nonzero $D_F$ and the three-body\nrecombination rate of spin-polarized ultracold atomic Fermi gases at finite\ntemperatures.",
        "positive": "Ground-state properties of few dipolar bosons in a quasi-one-dimensional\n  harmonic trap: We study the ground state of few bosons with repulsive dipole-dipole\ninteraction in a quasi-one-dimensional harmonic trap by means of the exact\ndiagonalization method. Up to three interaction regimes are found depending on\nthe strength of the dipolar interaction and the ratio of transverse to axial\noscillator lengths: a regime where the dipolar Bose gas resembles a system of\nweakly delta-interacting bosons, a second regime where the bosons are\nfermionized, and a third regime where the bosons form a Wigner crystal. In the\nfirst two regimes, the dipole-dipole potential can be replaced by a delta\npotential. In the crystalline state, the overlap between the localized wave\npackets is strongly reduced and all the properties of the boson system equal\nthose of its fermionic counterpart. The transition from the Tonks-Girardeau gas\nto the solidlike state is accompanied by a rapid increase of the interaction\nenergy and a considerable change of the momentum distribution, which we trace\nback to the different short-range correlations in the two interaction regimes."
    },
    {
        "anchor": "Matter, Energy, and Heat Transfer in a Classical Ballistic Atom Pump: A ballistic atom pump is a system containing two reservoirs of neutral atoms\nor molecules and a junction connecting them containing a localized time-varying\npotential. Atoms move through the pump as independent particles. Under certain\nconditions, these pumps can create net transport of atoms from one reservoir to\nthe other. While such systems are sometimes called \"quantum pumps,\" they are\nalso models of classical chaotic transport, and their quantum behavior cannot\nbe understood without study of the corresponding classical behavior. Here we\nexamine classically such a pump's effect on energy and temperature in the\nreservoirs, in addition to net particle transport. We show that the changes in\nparticle number, of energy in each reservoir, and of temperature in each\nreservoir vary in unexpected ways as the incident particle energy is varied.",
        "positive": "Heat transport in an optical lattice via Markovian feedback control: Ultracold atoms offer a unique opportunity to study many-body physics in a\nclean and well-controlled environment. However, the isolated nature of quantum\ngases makes it difficult to study transport properties of the system, which are\namong the key observables in condensed matter physics. In this work, we employ\nMarkovian feedback control to synthesize two effective thermal baths that\ncouple to the boundaries of a one-dimensional Bose-Hubbard chain. This allows\nfor the realization of a heat-current-carrying state. We investigate the\nsteady-state heat current, including its scaling with system size and its\nresponse to disorder. In order to study large systems, we use semi-classical\nMonte-Carlo simulation and kinetic theory. The numerical results from both\napproaches show, as expected, that for non- and weakly interacting systems with\nand without disorder one finds the same scaling of the heat current with\nrespect to the system size as it is found for systems coupled to thermal baths.\nFinally, we propose and test a scheme for measuring the energy flow. Thus, we\nprovide a route for the quantum simulation of heat-current-carrying steady\nstates of matter in atomic quantum gases."
    },
    {
        "anchor": "Fermion pairing in mixed-dimensional atomic mixtures: We investigate the quantum phases of mixed-dimensional cold atom mixtures. In\nparticular, we consider a mixture of a Fermi gas in a two-dimensional lattice,\ninteracting with a bulk Fermi gas or a Bose-Einstein condensate in a\nthree-dimensional lattice. The effective interaction of the two-dimensional\nsystem mediated by the bulk system is determined. We perform a functional\nrenormalization group analysis, and demonstrate that by tuning the properties\nof the bulk system, a subtle competition of several superconducting orders can\nbe controlled among $s$-wave, $p$-wave, $d_{x^2-y^2}$-wave, and\n$g_{xy(x^2-y^2)}$-wave pairing symmetries. Other instabilities such as a\ncharge-density wave order are also demonstrated to occur. In particular, we\nfind that the critical temperature of the $d$-wave pairing induced by the\nnext-nearest-neighbor interactions can be an order of magnitude larger than\nthat of the same pairing induced by doping in the simple Hubbard model. We\nexpect that by combining the nearest-neighbor interaction with the\nnext-nearest-neighbor hopping (known to enhance $d$-wave pairing), an even\nhigher critical temperature may be achieved.",
        "positive": "Exotic quantum spin models in spin-orbit-coupled Mott insulators: We study cold atoms in an optical lattice with synthetic spin-orbit coupling\nin the Mott-insulator regime. We calculate the parameters of the corresponding\ntight-binding model using Peierls substitution and \"localized Wannier states\nmethod\" and derive the low-energy spin Hamiltonian for fermions and bosons. The\nspin Hamiltonian is a combination of Heisenberg model, quantum compass model\nand Dzyaloshinskii-Moriya interactions and it has a rich classical phase\ndiagram with collinear, spiral and vortex phases."
    },
    {
        "anchor": "A two-dimensional programmable tweezer array of fermions: We prepare high-filling two-component arrays of up to fifty fermionic atoms\nin optical tweezers, with the atoms in the ground motional state of each\ntweezer. Using a stroboscopic technique, we configure the arrays in various\ntwo-dimensional geometries with negligible Floquet heating. Full spin- and\ndensity-resolved readout of individual sites allows us to post-select near-zero\nentropy initial states for fermionic quantum simulation. We prepare a\ncorrelated state in a two-by-two tunnel-coupled Hubbard plaquette,\ndemonstrating all the building blocks for realizing a programmable fermionic\nquantum simulator.",
        "positive": "Inelastic collisions in radiofrequency-dressed mixtures of ultracold\n  atoms: Radiofrequency (RF)-dressed potentials are a promising technique for\nmanipulating atomic mixtures, but so far little work has been undertaken to\nunderstand the collisions of atoms held within these traps. In this work, we\ndress a mixture of 85Rb and 87Rb with RF radiation, characterize the inelastic\nloss that occurs, and demonstrate species-selective manipulations. Our\nmeasurements show the loss is caused by two-body 87Rb+85Rb collisions, and we\nshow the inelastic rate coefficient varies with detuning from the RF resonance.\nWe explain our observations using quantum scattering calculations, which give\nreasonable agreement with the measurements. The calculations consider magnetic\nfields both perpendicular to the plane of RF polarization and tilted with\nrespect to it. Our findings have important consequences for future experiments\nthat dress mixtures with RF fields."
    },
    {
        "anchor": "Interference of longitudinal and transversal fragmentations in the\n  Josephson dynamics of Bose-Einstein condensates: A set-up to investigate Josephson dynamics of interacting bosons in the\npresence of interference between longitudinal fragmentation, developed during\nthe quantum dynamics, and transversal fragmentation, produced by the geometry\nof the trap, is proposed. We find and explain how this interference speeds up\nthe collapse of density oscillations and slows down the revival process by\nanalyzing the survival probability along the junction, fluctuations of particle\npositions across the junction, and the occupancy of the lowest single-particle\nstates. The interference mechanism is always accompanied by a non-trivial\ntransition from loss of coherence to build up of coherence in the first excited\nsingle-particle state. Moreover, it is found that a fully fragmented state\nsignificantly accelerates the revival process compared to the conventional\nBose-Einstein condensate. All in all, we show that the interference of\nlongitudinal and transversal fragmentations establishes new rules for\nmacroscopic tunneling phenomena.",
        "positive": "Systematic solitary waves from their linear limits in two-component\n  Bose-Einstein condensates with unequal dispersion coefficients: We systematically construct vector solitary waves in harmonically trapped\none-dimensional two-component Bose-Einstein condensates with unequal dispersion\ncoefficients by a numerical continuation in chemical potentials from the\nrespective analytic low-density linear limits to the high-density nonlinear\nThomas-Fermi regime. The main feature of the linear states herein is that the\ncomponent with the larger quantum number has instead a smaller linear\neigenenergy, enabled by suitable unequal dispersion coefficients, leading to\nnew series of solutions compared with the states similarly obtained in the\nequal dispersion setting. Particularly, the lowest-lying series gives the\nwell-known dark-anti-dark waves, and the second series yields the\ndark-multi-dark states, and the following series become progressively more\ncomplex in their wave structures. The Bogoliubov-de Gennes spectra analysis\nshows that most of these states are typically unstable, but they can be\nlong-lived and most of them can be fully stabilized in suitable parameter\nregimes."
    },
    {
        "anchor": "Orbital hybridized topological Fulde-Ferrel superfluidity in a\n  noncentrosymmetric optical lattice: Topological phases like topological insulators or superconductors are\nfascinating quantum states of matter, featuring novel properties such as\nemergent chiral edge states or Majorana fermions with non-Abelian braiding\nstatistics. The recent experimental implementation of optical lattices with\nhighly tunable geometry in cold gases opens up a new thrust on exploring these\nnovel quantum states. Here we report that the topological non-trivial Bloch\nbands can arise naturally in a noncentrosymmetric lattice. It induces a\ncontrollable orbital hybridization, producing the topological band structure.\nIn such bands, when considering attractive fermionic atoms, we find a\ntopological Fulde-Ferrell superfluid state with finite center-of-mass momentum\nin the presence of onsite rotation. This topological superfluid supports\nMajorana fermions on its edges. Experimental signatures are predicted for cold\ngases in radio-frequency spectroscopy.",
        "positive": "Dynamical many-body phases of the parametrically driven, dissipative\n  Dicke model: The dissipative Dicke model exhibits a fascinating out-of-equilibrium\nmany-body phase transition as a function of a coupling between a driven\nphotonic cavity and numerous two-level atoms. We study the effect of a\ntime-dependent parametric modulation of this coupling, and discover a rich\nphase diagram as a function of the modulation strength. We find that in\naddition to the established normal and super-radiant phases, a new phase with\npulsed superradiance which we term dynamical normal phase appears when the\nsystem is parametrically driven. Employing different methods, we characterize\nthe different phases and the transitions between them. Specific heed is paid to\nthe role of dissipation in determining the phase boundaries. Our analysis paves\nthe road for the experimental study of dynamically stabilized phases of\ninteracting light and matter."
    },
    {
        "anchor": "Spin-orbit coupled Bose-Einstein condensate in a tilted optical lattice: Bloch oscillations appear for a particle in a weakly tilted periodic\npotential. The intrinsic spin Hall effect is an outcome of a spin-orbit\ncoupling. We demonstrate that both these phenomena can be realized\nsimultaneously in a gas of weakly interacting ultracold atoms exposed to a\ntilted optical lattice and to a set of spatially dependent light fields\ninducing an effective spin-orbit coupling. It is found that both the spin Hall\nas well as the Bloch oscillation effects may coexist, showing, however, a\nstrong correlation between the two. These correlations are manifested as a\ntransverse spin current oscillating in-phase with the Bloch oscillations.",
        "positive": "Superfluid light in propagating geometries: We review how the paraxial approximation naturally leads to a hydrodynamic\ndescription of light propagation in a Kerr nonlinear medium analogous to the\nGross-Pitaevskii equation for the temporal evolution of the order parameter of\na superfluid. The main features of the many-body collective dynamics of these\nfluids of light in a propagating geometry are discussed: Generation and\nobservation of Bogoliubov sound waves on top of the fluid is first described.\nExperimentally accessible manifestations of superfluidity are then highlighted.\nPerspectives in view of realizing analog models of gravity are finally given."
    },
    {
        "anchor": "Temperature Dependent Density Profiles of Dipolar Droplets: Recently, trapped dipolar gases were observed to form high density droplets\nin a regime where mean field theory predicts collapse. These droplets present a\nnovel form of equilibrium where quantum fluctuations are critical for\nstability. So far, the effect of quantum fluctuations have only been considered\nat zero temperature through the local chemical potential arising from the\nLee--Huang--Yang correction. Here, we extend the theory of dipolar droplets to\nnon-zero temperatures using Hartree--Fock--Bogoliubov theory (HFBT), and show\nthat the equilibrium is strongly affected by temperature fluctuations. HFBT,\ntogether with local density approximation for excitations, reproduces the zero\ntemperature results, and predict that the condensate density can change\ndramatically even at low temperatures where the total depletion is small.\nParticularly, we find that typical experimental temperatures ($T \\sim $ 100 nK)\ncan significantly modify the transition between low density and droplet phases.",
        "positive": "Truncated correlation hierarchy schemes for driven-dissipative multimode\n  quantum systems: We present a method to describe driven-dissipative multi-mode systems by\nconsidering a truncated hierarchy of equations for the correlation functions.\nWe consider two hierarchy truncation schemes with a global cutoff on the\ncorrelation order, which is the sum of the exponents of the operators involved\nin the correlation functions: a 'hard' cutoff corresponding to an expansion\naround the vacuum, which applies to a regime where the number of excitations\nper site is small; a 'soft' cutoff which corresponds to an expansion around\ncoherent states, which can be applied for large excitation numbers per site.\nThis approach is applied to describe the bunching-antibunching transition in\nthe driven-dissipative Bose-Hubbard model for photonic systems. The results\nhave been successfully benchmarked by comparison with calculations based on the\ncorner-space renormalization method in 1D and 2D systems. The regime of\nvalidity and strengths of the present truncation methods are critically\ndiscussed."
    },
    {
        "anchor": "A thermoelectric heat engine with ultracold atoms: Thermoelectric effects, such as the generation of a particle current by a\ntemperature gradient, have their origin in a reversible coupling between heat\nand particle flows. These effects are fundamental probes for materials and have\napplications to cooling and power generation. Here we demonstrate\nthermoelectricity in a fermionic cold atoms channel, ballistic or diffusive,\nconnected to two reservoirs. We show that the magnitude of the effect and the\nefficiency of energy conversion can be optimized by controlling the geometry or\ndisorder strength. Our observations are in quantitative agreement with a\ntheoretical model based on the Landauer-Bu ttiker formalism. Our device\nprovides a controllable model-system to explore mechanisms of energy conversion\nand realizes a cold atom based heat engine.",
        "positive": "Critical behavior of order parameter at the nonequilibrium phase\n  transition of the Ising model: After a quench of transverse field, the asymptotic long-time state of Ising\nmodel displays a transition from a ferromagnetic phase to a paramagnetic phase\nas the post-quench field strength increases, which is revealed by the vanishing\nof the order parameter defined as the averaged magnetization over time. We\nestimate the critical behavior of the magnetization at this nonequilibrium\nphase transition by using mean-field approximation. In the vicinity of the\ncritical field, the magnetization vanishes as the inverse of a logarithmic\nfunction, which is significantly distinguished from the critical behavior of\norder parameter at the corresponding equilibrium phase transition, i.e. a\npower-law function."
    },
    {
        "anchor": "Soliton collisions in Bose-Einstein condensates with current-dependent\n  interactions: We study general collisions between chiral solitons in Bose-Einstein\ncondensates subject to combined attractive and current-dependent interatomic\ninteractions. A simple analysis based on the linear superposition of the\nsolitons allows us to determine the relevant time and space scales of the\ndynamics, which is illustrated by extensive numerical simulations. By varying\nthe differential amplitude, the relative phase, the average velocity, and the\nrelative velocity of the solitons, we characterize the different dynamical\nregimes that give rise to oscillatory and interference phenomena. Apart from\nthe known inelastic character of the collisions, we show that the chiral\ndynamics involves an amplitude reduction with respect to the case of regular\nsolitons. To compare with feasible ultracold gas experiments, the influence of\nharmonic confinement is analyzed in both the emergence and the interaction of\nchiral solitons.",
        "positive": "Nonequilibrium noise as a probe of pair-tunneling transport in the\n  BCS--BEC Crossover: The detection of elementary carriers in transport phenomena is one of the\nmost important keys to understand non-trivial properties of strongly-correlated\nquantum matter. Here we propose a method to identify the tunneling current\ncarrier in strongly interacting fermions from nonequilibrium noise in the\nBardeen-Cooper-Schrieffer to Bose--Einstein condensate crossover. The\nnoise-to-current ratio, the Fano factor, can be a crucial probe for the current\ncarrier. Bringing strongly-correlated fermions into contact with a dilute\nreservoir produces a tunneling current in between. The associated Fano factor\nincreases from one to two as the interaction becomes stronger, reflecting the\nfact that the dominant conduction channel changes from the quasiparticle\ntunneling to the pair tunneling."
    },
    {
        "anchor": "Dipolar Drag in Bilayer Harmonically Trapped Gases: We consider two separated pancake-shaped trapped gases interacting with a\ndipolar (either magnetic or electric) force. We study how the center of mass\nmotion propagates from one cloud to the other as a consequence of the\nlong-range nature of the interaction. The corresponding dynamics is fixed by\nthe frequency difference between the in-phase and the out-of-phase center of\nmass modes of the two clouds, whose dependence on the dipolar interaction\nstrength and the cloud separation is explicitly investigated. We discuss Fermi\ngases in the degenerate as well as in the classical limit and comment on the\ncase of Bose-Einsten condensed gases.",
        "positive": "The Multi-component Correlated Basis Function Method and its Application\n  to Multilayered Dipolar Bose Gases: We present a method for calculating the dynamics of a bosonic mixture, the\nmulti-component correlated basis function (CBF) method. For single components,\nCBF results for the excitation energies agree quite well with experimental\nresults, even for highly correlated systems like $^4$He, and recent systematic\nimprovements of CBF achieve perfect agreement. We give a full derivation of\nmulti-component CBF, and apply the method to a dipolar Bose gas cut into\ntwo-dimensional layers by a deep optical lattice, with coupling between layers\ndue to the long-ranged dipole-dipole interaction. We consider the case of\nstrong coupling, leading to large positive interlayer correlations. We\ncalculate the spectrum for a system of 8 layers and show that the strong\ncoupling can lead to a simpler spectrum than in the uncoupled case, with a\nsingle peak carrying most of the spectral weight."
    },
    {
        "anchor": "Coherent inflationary dynamics for Bose-Einstein condensates crossing a\n  quantum critical point: Quantum phase transitions, transitions between many-body ground states, are\nof extensive interest in research ranging from condensed matter physics to\ncosmology. Key features of the phase transitions include a stage with rapidly\ngrowing new order, called inflation in cosmology, followed by the formation of\ntopological defects. How inflation is initiated and evolves into topological\ndefects remains a hot debate topic. Ultracold atomic gas offers a pristine and\ntunable platform to investigate quantum critical dynamics. We report the\nobservation of coherent inflationary dynamics across a quantum critical point\nin driven Bose-Einstein condensates. The inflation manifests in the exponential\ngrowth of density waves and populations in well-resolved momentum states. After\nthe inflation stage, extended coherent dynamics is evident in both real and\nmomentum space. We present an intuitive description of the quantum critical\ndynamics in our system and demonstrate the essential role of phase fluctuations\nin the formation of topological defects.",
        "positive": "Complex Langevin and other approaches to the sign problem in quantum\n  many-body physics: We review the theory and applications of complex stochastic quantization to\nthe quantum many-body problem. Along the way, we present a brief overview of a\nnumber of ideas that either ameliorate or in some cases altogether solve the\nsign problem, including the classic reweighting method, alternative\nHubbard-Stratonovich transformations, dual variables (for bosons and fermions),\nMajorana fermions, density-of-states methods, imaginary asymmetry approaches,\nand Lefschetz thimbles. We discuss some aspects of the mathematical\nunderpinnings of conventional stochastic quantization, provide a few\npedagogical examples, and summarize open challenges and practical solutions for\nthe complex case. Finally, we review the recent applications of complex\nLangevin to quantum field theory in relativistic and nonrelativistic quantum\nmatter, with an emphasis on the nonrelativistic case."
    },
    {
        "anchor": "Propagation and jamming dynamics in Heisenberg spin ladders: We investigate the propagation dynamics of initially localized excitations in\nspin-1/2 Heisenberg ladders. We consider initial states with two overturned\nspins, either on neighboring sites on the same leg or on the two sites of a\nsingle rung, in an otherwise polarized (ferromagnetic) background. Compared to\nthe corresponding dynamics in a chain (single leg), we observe several\nadditional modes of propagation. We connect these propagation modes to features\nof the spectrum of the ladder system, and to different effective models\ncorresponding to different segments of the spectrum. In addition to the regular\npropagation modes, we observe for one mode a peculiar `jamming' dynamics where\ncomponents of the excitations remain localized in an unusual manner. A\ncomparison with the spin-1 bilinear-biquadratic chain is developed and\nexplored, where a similar phenomenon is shown to occur.",
        "positive": "Two-fluid model of a Bose-Einstein condensate in the cavity\n  optomechanical regime: We analyze an atomic Bose-Einstein condensate trapped in a high-Q optical\ncavity driven by a feeble optical field, a situation formally analogous to the\ncentral paradigm of cavity optomechanics [Brennecke et al., Science, 322, 235\n(2008)]. We account for two-body interactions via a two-fluid model that\nretains the intuitive appeal of the optomechanical two-mode description. The\nBogoliubov excitation spectrum of this system comprises a gapped upper branch\nand a lower branch that can include an unstable excitation mode."
    },
    {
        "anchor": "Synchronization in disordered oscillatory media: a nonequilibrium phase\n  transition for driven-dissipative bosons: We show that a lattice of phase oscillators with random natural frequencies,\ndescribed by a generalization of the nearest-neighbor Kuramoto model with an\nadditional cosine coupling term, undergoes a phase transition from a\ndesynchronized to a synchronized state. This model may be derived from the\ncomplex Ginzburg-Landau equations describing a disordered lattice of\ndriven-dissipative Bose-Einstein condensates of exciton polaritons. We derive\nphase diagrams that classify the desynchronized and synchronized states that\nexist in both one and two dimensions. This is achieved by outlining the\nconnection of the oscillator model to the quantum description of localization\nof a particle in a random potential through a mapping to a modified\nKardar-Parisi-Zhang equation. Our results indicate that long-range order in\npolariton condensates, and other systems of coupled oscillators, is not\ndestroyed by randomness in their natural frequencies.",
        "positive": "Exact dynamics of two holes in two-leg antiferromagnetic ladders: We study the motion of holes in a mixed-dimensional setup of an\nantiferromagnetic ladder, featuring nearest neighbor hopping $t$ along the\nladders and Ising-type spin interactions along, $J_\\parallel$, and across,\n$J_\\perp$, the ladder. We determine exact solutions for the low-energy one- and\ntwo-hole eigenstates. The presence of the trans-leg spin coupling, $J_\\perp$,\nleads to a linear confining potential between the holes. As a result, holes on\nseparate legs feature a super-linear binding energy scaling as $(J_\\perp /\nt)^{2/3}$ in the strongly correlated regime of $J_\\perp,J_\\parallel \\leq t$.\nThis behavior is linked to an emergent length scale $\\lambda \\propto\n(t/J_\\perp)^{1/3}$, stemming from the linear confining potential, and which\ndescribes how the size of the two-hole molecular state diverges for\n$J_\\perp,J_\\parallel \\ll t$. On the contrary, holes on the same leg unbind at\nsufficiently low spin couplings. This is a consequence of the altered\nshort-range boundary condition for holes on the same leg, yielding an effective\nPauli repulsion between them, limiting their kinetic energy and making binding\nunfavorable. Finally, we determine the exact nonequilibrium quench dynamics\nfollowing the sudden immersion of initially localized nearest neigbhor holes.\nThe dynamics is characterized by a crossover from an initial ballistic quantum\nwalk to an aperiodic oscillatory motion around a finite average distance\nbetween the holes due to the confining potential between them. In the strongly\ncorrelated regime of low spin couplings, $J_\\perp, J_\\parallel \\leq t$, we find\nthis asymptotic distance to diverge as $t / J_\\perp$, showing a much stronger\nscaling than the eigenstates. The predicted results should be amenable to\nstate-of-the-art quantum simulation experiments using currently implemented\nexperimental techniques."
    },
    {
        "anchor": "Triangular vortex lattices and giant vortices in rotating bubble\n  Bose-Einstein condensates: We show that three-dimensional spherical-shell condensates respond to\nrotation by forming two aligned triangular Abrikosov-like vortex lattices on\neach hemispherical surface. The centrifugal force due to rotation causes an\nelliptical deformation of the spherical shell condensate shape and for faster\nrotation rates, drives the formation of a central multi-charged\nvortex-antivortex pair at the poles surrounded by a ring of singly charged\nvortices in the bulk density. The vortex distributions observed in each\nhemisphere take a similar form to those found in rotating harmonic plus quartic\ntraps.",
        "positive": "Dynamics of the Mott Insulator to Superfluid quantum phase transition in\n  the truncated Wigner approximation: The quantum phase transition from the Mott insulator state to the superfluid\nin the Bose-Hubbard model is investigated. We research one, two and three\ndimensional lattices in the truncated Wigner approximation. We compute both\nkinetic and potential energy and they turn out to have a power law behaviour as\na function of the transition rate, with the power equal to 1/3. The same\napplies to the total energy in a system with a harmonic trap, which is usually\npresent in the experimental set-up. These observations are in agreement with\nthe experiment of [8], where such scalings were also observed and the power of\nthe decay was numerically close to 1/3. The results confirm the Kibble-Zurek\n(adiabatic-impulse-adiabatic approximation) scenario for this transition."
    },
    {
        "anchor": "Hydrodynamic generation of skyrmions in a two-component Bose-Einstein\n  condensate: When an obstacle is moved in a superfluid faster than a critical velocity,\nquantized vortices are generated behind the obstacle. Here we propose a method\nto create more complicated topological excitations, three-dimensional\nskyrmions, behind a moving obstacle. We numerically show that, in a\ntwo-component Bose-Einstein condensate, component-dependent obstacle potentials\ncan generate skyrmions in the wake, made up of quantized vortex rings in\ndifferent components that are linked with each other. The lifetime of generated\nskyrmions can be prolonged by a guiding potential, which enables the formation\nof a skyrmion train.",
        "positive": "Observation of Bose-Einstein Condensation in a Strong Synthetic Magnetic\n  Field: Extensions of Berry's phase and the quantum Hall effect have led to the\ndiscovery of new states of matter with topological properties. Traditionally,\nthis has been achieved using gauge fields created by magnetic fields or spin\norbit interactions which couple only to charged particles. For neutral\nultracold atoms, synthetic magnetic fields have been created which are strong\nenough to realize the Harper-Hofstadter model. Despite many proposals and major\nexperimental efforts, so far it has not been possible to prepare the ground\nstate of this system. Here we report the observation of Bose-Einstein\ncondensation for the Harper-Hofstadter Hamiltonian with one-half flux quantum\nper lattice unit cell. The diffraction pattern of the superfluid state directly\nshows the momentum distribution on the wavefuction, which is gauge-dependent.\nIt reveals both the reduced symmetry of the vector potential and the twofold\ndegeneracy of the ground state. We explore an adiabatic many-body state\npreparation protocol via the Mott insulating phase and observe the superfluid\nground state in a three-dimensional lattice with strong interactions."
    },
    {
        "anchor": "Dissipative Transport of Trapped Bose-Einstein Condensates through\n  Disorder: After almost half a century since the work of Anderson [Phys. Rev. {\\bf 109},\n1492 (1958)], at present there is no well established theoretical framework for\nunderstanding the dynamics of interacting particles in the presence of\ndisorder. Here, we address this problem for interacting bosons near $T=0$, a\nsituation that has been realized in trapped atomic experiments with an optical\nspeckle disorder. We develop a theoretical model for understanding the\nhydrodynamic transport of \\emph{finite-size} Bose-Einstein condensates through\ndisorder potentials. The goal has been to set up a simple model that will\nretain all the richness of the system, yet provide analytic expressions,\nallowing deeper insight into the physical mechanism. Comparison of our\ntheoretical predictions with the experimental data on large-amplitude dipole\noscillations of a condensate in an optical-speckle disorder shows striking\nagreement. We are able to quantify various dissipative regimes of slow and fast\ndamping. Our calculations provide a clear evidence of reduction in disorder\nstrength due to interactions. The analytic treatment presented here allows us\nto predict the power law governing the interaction dependance of damping. The\ncorresponding exponents are found to depend sensitively on the dimensionality\nand are in excellent agreement with experimental observations. Thus, the\nadeptness of our model, to correctly capture the essential physics of\ndissipation in such transport experiments, is established.",
        "positive": "Spin-orbit-coupled dipolar Bose-Einstein condensates: We propose an experimental scheme to create spin-orbit coupling in spin-3 Cr\natoms using Raman processes. Employing linear Zeeman effect and optical Stark\nshift, two spin states within the ground electronic manifold are selected,\nwhich results in a pseudo-spin-1/2 model. We further study the ground state\nstructures of a spin-orbit-coupled Cr condensate. We show that, in addition to\nthe stripe structures induced by the spin-orbit coupling, the magnetic\ndipole-dipole interaction gives rise to the vortex phase, in which spontaneous\nspin vortex is formed."
    },
    {
        "anchor": "Variational Monte Carlo study of soliton excitations in hard-sphere Bose\n  gases: By using a full many-body approach, we calculate the excitation energy, the\neffective mass and the density profile of soliton states in a three dimensional\nBose gas of hard spheres at zero temperature. The many-body wave function used\nto describe the soliton contains a one-body term, derived from the solution of\nthe Gross-Pitaevskii equation, and a two-body Jastrow term which accounts for\nthe repulsive correlations between atoms. We optimize the parameters in the\nmany-body wave function via a Variational Monte Carlo procedure, calculating\nthe grand-canonical energy and the canonical momentum of the system in a moving\nreference frame where the soliton is stationary. As the density of the gas is\nincreased, significant deviations from the mean-field predictions are found for\nthe excitation energy and the density profile of both dark and grey solitons.\nIn particular, the soliton effective mass $m^\\ast$ and the mass $m\\Delta N$ of\nmissing particles in the region of the density depression are smaller than the\nresult from the Gross-Pitaevskii equation, their ratio being however well\nreproduced by this theory up to large values of the gas parameter. We also\ncalculate the profile of the condensate density around the soliton notch\nfinding good agreement with the prediction of the local density approximation.",
        "positive": "Bose-Einstein Condensation of 84-Sr: We report Bose-Einstein condensation of 84-Sr in an optical dipole trap.\nEfficient laser cooling on the narrow intercombination line and an ideal s-wave\nscattering length allow creation of large condensates (N0 ~ 3x10^5) even though\nthe natural abundance of this isotope is only 0.6%. Condensation is heralded by\nthe emergence of a low-velocity component in time-of-flight images."
    },
    {
        "anchor": "Transport in Floquet-Bloch bands: We report Floquet band engineering of long-range transport and direct imaging\nof Floquet-Bloch bands in an amplitude-modulated optical lattice. In one\nvariety of Floquet-Bloch band we observe tunable rapid long-range high-fidelity\ntransport of a Bose condensate across thousands of lattice sites. Quenching\ninto an opposite-parity Floquet-hybridized band allows Wannier-Stark\nlocalization to be controllably turned on and off using modulation. A central\nresult of this work is the use of transport dynamics to demonstrate direct\nimaging of a Floquet-Bloch band structure. These results demonstrate that\ntransport in dynamical Floquet-Bloch bands can be mapped to transport in\nquasi-static effective bands, opening a path to cold atom quantum emulation of\nultrafast multi-band electronic dynamics.",
        "positive": "Photon Counting for Bragg Spectroscopy of Quantum Gases: We demonstrate a photon-counting technique for detecting Bragg excitation of\nan ultracold gas of atoms. By measuring the response of the light field to the\natoms, we derive a signal independent of traditional time-of-flight\natom-imaging techniques. With heterodyne detection we achieve photon shot-noise\nlimited detection of the amplification or depletion of one of the Bragg laser\nbeams. Photon counting for Bragg spectroscopy will be useful for strongly\ninteracting gases where atom-imaging detection fails. In addition, this\ntechnique provides the ability to resolve the evolution of excitations as a\nfunction of pulse duration."
    },
    {
        "anchor": "Interaction energy and itinerant ferromagnetism in a strongly\n  interacting Fermi gas in the absence of molecule formation: We investigate the interaction energy and the possibility of itinerant\nferromagnetism in a strongly interacting Fermi gas at zero temperature in the\nabsence of molecule formation. The interaction energy is obtained by summing\nthe perturbative contributions of Galitskii-Feynman type to all orders in the\ngas parameter. It can be expressed by a simple phase space integral of an\nin-medium scattering phase shift. In both three and two dimensions (3D and 2D),\nthe interaction energy shows a maximum before reaching the resonance from the\nBose-Einstein condensate side, which provides a possible explanation of the\nexperimental measurements of the interaction energy. This phenomenon can be\ntheoretically explained by the qualitative change of the nature of the binary\ninteraction in the medium. The appearance of an energy maximum has significant\neffects on the itinerant ferromagnetism. In 3D, the ferromagnetic transition is\nreentrant and itinerant ferromagnetism exists in a narrow window around the\nenergy maximum. In 2D, the present theoretical approach suggests that itinerant\nferromagnetism does not exist, which reflects the fact that the energy maximum\nbecomes much lower than the energy of the fully polarized state.",
        "positive": "BCS-BEC Crossover in 2D Fermi Gases with Rashba Spin-Orbit Coupling: We present a systematic theoretical study of the BCS-BEC crossover in\ntwo-dimensional Fermi gases with Rashba spin-orbit coupling (SOC). By solving\nthe exact two-body problem in the presence of an attractive short-range\ninteraction we show that the SOC enhances the formation of the bound state: the\nbinding energy $E_{\\text B}$ and effective mass $m_{\\text B}$ of the bound\nstate grows along with the increase of the SOC. For the many-body problem, even\nat weak attraction, a dilute Fermi gas can evolve from a BCS superfluid state\nto a Bose condensation of molecules when the SOC becomes comparable to the\nFermi momentum. The ground-state properties and the\nBerezinskii-Kosterlitz-Thouless (BKT) transition temperature are studied, and\nanalytical results are obtained in various limits. For large SOC, the BKT\ntransition temperature recovers that for a Bose gas with an effective mass\n$m_{\\text B}$. We find that the condensate and superfluid densities have\ndistinct behaviors in the presence of SOC: the condensate density is generally\nenhanced by the SOC due to the increase of the molecule binding, the superfluid\ndensity is suppressed because of the non-trivial molecule effective mass\n$m_{\\text B}$."
    },
    {
        "anchor": "Vortex Lattice Formation in Spin-Orbit-Coupled Spin-2 Bose-Einstein\n  Condensate Under Rotation: We investigate the vortex lattice configuration in a rotating spin\norbit-coupled spin-2 Bose-Einstein condensate confined in a\nquasi-two-dimensional harmonic trap. By considering the interplay between\nrotation frequency, spin-orbit couplings, and inter atomic interactions, we\nexplore a variety of vortex lattice structures emerging as a ground state\nsolution. Our study focuses on the combined effects of spin-orbit coupling and\nrotation, analyzed by using the variational method for the single-particle\nHamiltonian. We observe that the interplay between rotation and Rashba\nspin-orbit coupling gives rise to different effective potentials for the\nbosons. Specifically, at higher rotation frequencies, isotropic spin-orbit\ncoupling leads to an effective toroidal potential, while fully anisotropic\nspin-orbit coupling results in a symmetric double-well potential. To obtain\nthese findings, we solve the five coupled Gross-Pitaevskii equations for the\nspin-2 BEC with spin-orbit coupling under rotation. Notably, we find that the\nantiferromagnetic, cyclic, and ferromagnetic phases exhibit similar behavior at\nhigher rotation.",
        "positive": "Bose-Einstein Condensates in Non-abelian Gauge Fields: The recent success of the NIST group in generating abelian gauge field in\ncold atoms has created opportunities to simulate electronic transports in\nsolids using atomic gases. Very recently, the NIST group has also announced in\na DARPA Meeting the creation of non-abelian gauge fields in a pseudo spin-1/2\nBose gas. While there have been considerable theoretical activities in\nsynthetic gauge fields, non-abelian fields have not been generated until now.\nHere, we show that in a non-abelian gauge field, a spinor condensate will\ndevelop a spontaneous stripe structure in each spin component, reflecting a\nground state made up of two non-orthogonal dressed states with different\nmomenta. Depending on interactions, this ground state can reduce back to a\nsingle dressed state. These momentum carrying stripes are the {\\em macroscopic}\nbosonic counterpart of the spin-orbit phenomena in fermions that are being\nactively studied in electron physics today."
    },
    {
        "anchor": "Subdiffusion and heat transport in a tilted 2D Fermi-Hubbard system: Using quantum gas microscopy we study the late-time effective hydrodynamics\nof an isolated cold-atom Fermi-Hubbard system subject to an external linear\npotential (a \"tilt\"). The tilt is along one of the principal directions of the\ntwo-dimensional (2D) square lattice and couples mass transport to local heating\nthrough energy conservation. We study transport and thermalization in our\nsystem by observing the decay of prepared initial density waves as a function\nof wavelength $\\lambda$ and tilt strength and find that the associated decay\ntime $\\tau$ crosses over as the tilt strength is increased from\ncharacteristically diffusive to subdiffusive with $\\tau\\propto\\lambda^4$. In\norder to explain the underlying physics we develop a hydrodynamic model that\nexhibits this crossover. For strong tilts, the subdiffusive transport rate is\nset by a thermal diffusivity, which we are thus able to measure as a function\nof tilt in this regime. We further support our understanding by probing the\nlocal inverse temperature of the system at strong tilts, finding good agreement\nwith our theoretical predictions. Finally, we discuss the relation of the\nstrongly tilted limit of our system to recently studied 1D models which may\nexhibit nonergodic dynamics.",
        "positive": "Critical Behavior and Fractality in Shallow One-Dimensional\n  Quasiperiodic Potentials: Quasiperiodic systems offer an appealing intermediate between long-range\nordered and genuine disordered systems, with unusual critical properties.\nOne-dimensional models that break the so-called self-dual symmetry usually\ndisplay a mobility edge, similarly as truly disordered systems in dimension\nstrictly higher than two. Here, we determine the critical localization\nproperties of single particles in shallow, one-dimensional, quasiperiodic\nmodels and relate them to the fractal character of the energy spectrum. On the\none hand, we determine the mobility edge and show that it separates the\nlocalized and extended phases, with no intermediate phase. On the other hand,\nwe determine the critical potential amplitude and find the universal critical\nexponent $\\nu \\simeq 1/3$. We also study the spectral Hausdorff dimension and\nshow that it is nonuniversal but always smaller than unity, hence showing that\nthe spectrum is nowhere dense. Finally, applications to ongoing studies of\nAnderson localization, Bose-glass physics, and many-body localization in\nultracold atoms are discussed."
    },
    {
        "anchor": "Single-shot simulations of dynamics of quantum dark solitons: Eigenstates of Bose particles with repulsive contact interactions in\none-dimensional space with periodic boundary conditions can be found with the\nhelp of the Bethe ansatz. The type~II excitation spectrum identified by E. H.\nLieb, reproduces the dispersion relation of dark solitons in the mean-field\napproach. The corresponding eigenstates possess translational symmetry which\ncan be broken in measurements of positions of particles. We analyze emergence\nof single and double solitons in the course of the measurements and investigate\ndynamics of the system. In the weak interaction limit, the system follows the\nmean-field prediction for a short period of time. Long time evolution reveals\nmany-body effects that are related to an increasing uncertainty of soliton\npositions. In the strong interaction regime particles behave like impenetrable\nbosons. Then, the probability densities in the configuration space become\nidentical to the probabilities of non-interacting fermions but the\nwave-functions themselves remember the original Bose statistics. Especially,\nthe phase flips that are key signatures of the solitons in the weak interaction\nlimit, can be observed in the time evolution of the strongly interacting\nbosons.",
        "positive": "Ground state properties of interacting Bose polarons: We theoretically investigate the role of multiple impurity atoms on the\nground state properties of Bose polarons. The Bogoliubov approximation is\napplied for the description of the condensate resulting in a Hamiltonian\ncontaining terms beyond the Fr\\\"ohlich approximation. The many-body nature of\nthe impurity atoms is taken into account by extending the many-body description\nfor multiple Fr\\\"ohlich polarons, revealing the static structure factor of the\nimpurities as the key quantity. Within this formalism various experimentally\naccessible polaronic properties are calculated such as the energy and the\neffective mass. These results are examined for system parameters corresponding\nto two recent experimental realizations of the Bose polaron, one with fermionic\nimpurities and one with bosonic impurities."
    },
    {
        "anchor": "Macroscopic superposition states of ultracold bosons in a double-well\n  potential: We present a thorough description of the physical regimes for ultracold\nbosons in double wells, with special attention paid to macroscopic\nsuperpositions (MSs). We use a generalization of the Lipkin-Meshkov-Glick\nHamiltonian of up to eight single particle modes to study these MSs, solving\nthe Hamiltonian with a combination of numerical exact diagonalization and\nhigh-order perturbation theory. The MS is between left and right potential\nwells; the extreme case with all atoms simultaneously located in both wells and\nin only two modes is the famous NOON state, but our approach encompasses much\nmore general MSs. Use of more single particle modes brings dimensionality into\nthe problem, allows us to set hard limits on the use of the original two-mode\nLMG model commonly treated in the literature, and also introduces a new mixed\nJosephson-Fock regime. Higher modes introduce angular degrees of freedom and MS\nstates with different angular properties.",
        "positive": "Propagating wave-packets and quantised currents in coherently driven\n  polariton superfluids: We study the properties of propagating polariton wave-packets and their\nconnection to the stability of doubly charged vortices. Wave-packet propagation\nand related photoluminescence spectra exhibit a rich behaviour dependent on the\nexcitation regime. We show that, because of the non-quadratic polariton\ndispersion, doubly charged vortices are stable only when initiated in\nwave-packets propagating at small velocities. Vortices propagating at larger\nvelocities, or those imprinted directly into the polariton optical parametric\noscillator (OPO) signal and idler are always unstable to splitting."
    },
    {
        "anchor": "Quantum crystal growing: Adiabatic preparation of a bosonic\n  antiferromagnet in the presence of a parabolic inhomogeneity: We theoretically study the adiabatic preparation of an antiferromagnetic\nphase in a mixed Mott insulator of two bosonic atom species in a\none-dimensional optical lattice. In such a system one can engineer a tunable\nparabolic inhomogeneity by controlling the difference of the trapping\npotentials felt by the two species. Using numerical simulations we predict that\na finite parabolic potential can assist the adiabatic preparation of the\nantiferromagnet. The optimal strength of the parabolic inhomogeneity depends\nsensitively on the number imbalance between the two species. We also find that\nduring the preparation finite size effects will play a crucial role for a\nsystem of realistic size. The experiment that we propose can be realized, for\nexample, using atomic mixtures of Rubidium 87 with Potassium 41 or Ytterbium\n168 with Ytterbium 174.",
        "positive": "Schwinger pair production with ultracold atoms: We consider a system of ultracold atoms in an optical lattice as a quantum\nsimulator for electron-positron pair production in quantum electrodynamics\n(QED). For a setup in one spatial dimension, we investigate the nonequilibrium\nphenomenon of pair production including the backreaction leading to plasma\noscillations. Unlike previous investigations on quantum link models, we focus\non the infinite-dimensional Hilbert space of QED and show that it may be well\napproximated by experiments employing Bose-Einstein condensates interacting\nwith fermionic atoms. The calculations based on functional integral techniques\ngive a unique access to the physical parameters required to realize the QED\nphenomena in a cold atom experiment. In particular, we use our approach to\nconsider quantum link models in a yet unexplored parameter regime and give\nbounds for their ability to capture essential features of the physics. The\nresults suggest a paradigmatic change towards realizations using coherent\nmany-body states rather than single atoms for quantum simulations of\nhigh-energy particle physics phenomena."
    },
    {
        "anchor": "Exciting the Goldstone Modes of a Supersolid Spin-Orbit-Coupled Bose Gas: Supersolidity is deeply connected with the emergence of Goldstone modes,\nreflecting the spontaneous breaking of both phase and translational symmetry.\nHere, we propose accessible signatures of these modes in harmonically trapped\nspin-orbit-coupled Bose-Einstein condensates, where supersolidity appears in\nthe form of stripes. By suddenly changing the trapping frequency, an axial\nbreathing oscillation is generated, whose behavior changes drastically at the\ncritical Raman coupling. Above the transition, a single mode of hybridized\ndensity and spin nature is excited, while below it, we predict a beating effect\nsignaling the excitation of a Goldstone spin-dipole mode. We further provide\nevidence for the Goldstone mode associated with the translational motion of\nstripes. Our results open up new perspectives for probing supersolid properties\nin experimentally relevant configurations with both symmetric as well as highly\nasymmetric intraspecies interactions.",
        "positive": "Roton Instabilities and Wigner Crystallization of Rotating Dipolar\n  Fermions in the Fractional Quantum Hall Regime: We point out the possibility of occurring instabilities in Laughlin liquids\nof rotating dipolar fermions with zero thickness. Previously such a system was\npredicted to be the Laughlin liquid for filling factors being greater and equal\nto 1/7. However, from intra-Landau-level excitations of the liquid in the\nsingle-mode approximation, the roton minima become negative and Laughlin\nliquids are unstable for filling factors being less and equal to 1/7. We then\nconclude that there are correlated Wigner crystals for filling factors being\nless and equal to 1/7."
    },
    {
        "anchor": "Slow scrambling in sonic black holes: We study from the perspective of quantum information scrambling an acoustic\nblack hole modelled by two semi-infinite, stationary, one dimensional\ncondensates, connected by a spatial step-like discontinuity, and flowing\nrespectively at subsonic and supersonic velocities. We develop a simple\nanalytical treatment based on Bogolyubov theory of quantum fluctuations which\nis sufficient to derive analogue Hawking emission, and we compute out-of-time\norder correlations (OTOCs) of the Bose density field. We find that sonic black\nholes are slow scramblers contrary to their astrophysical counterparts: this\nmanifests in a power law growth $\\propto t^2$ of OTOCs in contrast to the\nexponential increase in time expected for fast scramblers.",
        "positive": "Fluctuation-damping of isolated, oscillating Bose-Einstein condensates: Experiments on the nonequilibrium dynamics of an isolated Bose-Einstein\ncondensate (BEC) in a magnetic double-well trap exhibit a puzzling divergence:\nWhile some show dissipation-free Josephson oscillations, others find strong\ndamping. Such damping in isolated BECs cannot be understood on the level of the\ncoherent Gross-Pitaevskii dynamics. Using the Keldysh functional-integral\nformalism, we describe the time-dependent system dynamics by means of a\nmulti-mode BEC coupled to fluctuations (single-particle excitations) beyond the\nGross-Pitaevskii saddle point. We find that the Josephson oscillations excite\nan excess of fluctuations when the effective Josephson frequency,\n$\\tilde{\\omega}_J$, is in resonance with the effective fluctuation energy,\n$\\tilde{\\varepsilon}_m$, where both, $\\tilde{\\omega}_J$ and\n$\\tilde{\\varepsilon}_m$, are strongly renormalized with respect to their\nnoninteracting values. Evaluating and using the model parameters for the\nrespective experiments describes quantitatively the presence or absence of\ndamping."
    },
    {
        "anchor": "Evaporation of microwave-shielded polar molecules to quantum degeneracy: Ultracold polar molecules offer strong electric dipole moments and rich\ninternal structure, which makes them ideal building blocks to explore exotic\nquantum matter, implement novel quantum information schemes, or test\nfundamental symmetries of nature. Realizing their full potential requires\ncooling interacting molecular gases deeply into the quantum degenerate regime.\nHowever, the complexity of molecules which makes their collisions intrinsically\nunstable at the short range, even for nonreactive molecules, has so far\nprevented the cooling to quantum degeneracy in three dimensions. Here, we\ndemonstrate evaporative cooling of a three-dimensional gas of fermionic\nsodium-potassium molecules to well below the Fermi temperature using microwave\nshielding. The molecules are protected from reaching short range with a\nrepulsive barrier engineered by coupling rotational states with a blue-detuned\ncircularly polarized microwave. The microwave dressing induces strong tunable\ndipolar interactions between the molecules, leading to high elastic collision\nrates that can exceed the inelastic ones by at least a factor of 460. This\nlarge elastic-to-inelastic collision ratio allows us to cool the molecular gas\ndown to 21 nanokelvin, corresponding to 0.36 times the Fermi temperature. Such\nunprecedentedly cold and dense samples of polar molecules open the path to the\nexploration of novel many-body phenomena, such as the long-sought topological\np-wave superfluid states of ultracold matter.",
        "positive": "Geometry-induced entanglement in a mass-imbalanced few-fermion system: Many-body systems undergoing quantum phase transitions reveal substantial\ngrowth of non-classical correlations between different parties of the system.\nThis behavior is manifested by characteristic divergences of the von Neumann\nentropy. Here we show, that very similar features may be observed in\none-dimensional systems of a few strongly interacting atoms when the structural\ntransitions between different spatial orderings are driven by a varying shape\nof an external potential. When the appropriate adaptation of the finite-size\nscaling approach is performed in the vicinity of the transition point,\nfew-fermion systems display a characteristic power-law invariance of divergent\nquantities."
    },
    {
        "anchor": "Zero Sound in Dipolar Fermi Gases: We study the propagation of sound in a homogeneous dipolar gas at zero\ntemperature, known as zero sound. We find that undamped sound propagation is\npossible only in a range of solid angles around the direction of polarization\nof the dipoles. Above a critical dipole moment, we find an unstable mode, by\nwhich the gas collapses locally perpendicular to the dipoles' direction.",
        "positive": "Spectral functions of the strongly interacting 3D Fermi gas: Computing dynamical properties of strongly interacting quantum many-body\nsystems poses a major challenge to theoretical approaches. Usually, one has to\nresort to numerical analytic continuation of results on imaginary frequencies,\nwhich is a mathematically ill-defined procedure. Here, we present an efficient\nmethod to compute the spectral functions of the two-component Fermi gas near\nthe strongly interacting unitary limit directly in real frequencies. To this\nend, we combine the Keldysh path integral that is defined in real time with the\nself-consistent T-matrix approximation. The latter is known to predict\nthermodynamic and transport properties in good agreement with experimental\nobservations in ultracold atoms. We validate our method by comparison with\nthermodynamic quantities obtained from imaginary time calculations and by\ntransforming our real-time propagators to imaginary time. By comparison with\nstate-of-the-art numerical analytic continuation of the imaginary time results,\nwe show that our real-time results give qualitative improvements for dynamical\nquantities. Moreover, we show that no significant pseudogap regime exists in\nthe self-consistent T-matrix approximation above the critical temperature\n$T_c$, an issue that has been under significant debate. We close by pointing\nout the versatile nature of our method as it can be extended to other systems,\nlike the spin- or mass-imbalanced Fermi gas, other Bose-Fermi models, 2D\nsystems as well as systems out of equilibrium."
    },
    {
        "anchor": "A ring of BEC pools as a trap for persistent flow: Mott insulator - superfluid transition in a periodic lattice of Josephson\njunctions can be driven by tunneling rate increase. Resulting winding numbers\n$W$ of the condensate wavefunction decrease with increasing quench time in\naccord with the Kibble-Zurek mechanism (KZM). However, in very slow quenches\nBose-Hubbard dynamics rearranges wavefunction phase so that its random walk\ncools, $\\bar{W^2}$ decreases and eventually the wavefunction becomes too cold\nto overcome potential barriers separating different $W$. Thus, in contrast with\nKZM, in very slow quenches $\\bar{W^2}$ is set by random walk with \"critical\"\nstep size, independently of $\\tau_Q$.",
        "positive": "Quasiperiodic and periodic extended Hatano-Nelson model: Anomalous\n  complex-real transition and non-Hermitian skin effect: We study the effect of quasiperiodic and periodic onsite potentials in a\nHatano-Nelson model with next-nearest-neighbour hopping. By considering a\nnon-reciprocal next-nearest-neighbour hopping and a quasiperiodic onsite\npotential under periodic boundary conditions, we show a breakdown of the\ntypical correspondence between the delocalization-localization and complex-real\ntransitions as a function of the potential strength. Moreover, we reveal that\nin the delocalized regime, when the potential strength increases, the\neigenstates under open boundary conditions exhibit a bidirectional\nnon-Hermitian skin effect, i.e., they tend to localize on both the edges\ninstead of localizing on either of the edges. However, when a periodic onsite\npotential is considered, the system not only exhibits a bidirectional skin\neffect but also shows a complete direction reversal of the skin effect as a\nfunction of the onsite periodic potential."
    },
    {
        "anchor": "Analytical theory of enhanced Bose-Einstein condensation in thin films: We present an analytically solvable theory of Bose-Einstein condensation in\nthin film geometries. Analytical closed-form expressions for the critical\ntemperature are obtained in both the low-to-moderate confinement regime (where\nthe film thickness $L$ is in the order of microns) as well as in the strong\nconfinement regime where the thickness is in the order of few nanometers or\nlower. The possibility of high-temperature BEC is predicted in the strong\nconfinement limit, with a square-root divergence of the critical temperature\n$T_{c} \\sim L^{-1/2}$. For cold Bose gases, this implies an enhancement up to\ntwo orders of magnitude in $T_{c}$ for films on the nanometer scale. Analytical\npredictions are also obtained for the heat capacity and the condensate\nfraction. A new law for the heat capacity of the condensate, i.e. $C \\sim\nT^{2}$, is predicted for nano-scale films, which implies a different $\\lambda$\npoint behaviour with respect to bulk systems, while the condensate fraction is\npredicted to follow a $[1- (T/T_{c})^{2}]$ law.",
        "positive": "Thermodynamics and renormalized quasi-particles in the vicinity of the\n  dilute Bose gas quantum critical point in two dimensions: We use the functional renormalization group (FRG) to derive analytical\nexpressions for thermodynamic observables (density, pressure, entropy, and\ncompressibility) as well as for single-particle properties (wavefunction\nrenormalization and effective mass) of interacting bosons in two dimensions as\na function of temperature $T$ and chemical potential $\\mu$. We focus on the\nquantum disordered and the quantum critical regime close to the dilute Bose gas\nquantum critical point. Our approach is based on a truncated vertex expansion\nof the hierarchy of FRG flow equations and the decoupling of the two-body\ncontact interaction in the particle-particle channel using a suitable\nHubbard-Stratonovich transformation. Our analytic FRG results extend previous\nanalytical renormalization group calculations for thermodynamic observables at\n$\\mu =0$ to finite values of $\\mu$. To confirm the validity of our FRG\napproach, we have also performed quantum Monte Carlo simulations to obtain the\nmagnetization, the susceptibility, and the correlation length of the\ntwo-dimensional spin-$1/2$ quantum $XY$ model with coupling $J$ in a regime\nwhere its quantum critical behavior is controlled by the dilute Bose gas\nquantum critical point. We find that our analytical results describe the Monte\nCarlo data for $\\mu \\leq 0$ rather accurately up to relatively high\ntemperatures $T \\lesssim 0.1 J$."
    },
    {
        "anchor": "Quantum phases of tilted dipolar bosons in two-dimensional optical\n  lattice: We consider a minimal model to describe the quantum phases of ultracold\ndipolar bosons in two-dimensional (2D) square optical lattices. The model is a\nvariation of the extended Bose-Hubbard model and apt to study the quantum\nphases arising from the variation in the tilt angle $\\theta$ of the dipolar\nbosons. At low tilt angles $0^{\\circ}\\leqslant\\theta\\apprle25^{\\circ}$, the\nground state of the system are phases with checkerboard order, which could be\neither checkerboard supersolid or checkerboard density wave. For high tilt\nangles $55^{\\circ}\\apprge\\theta\\apprge35^{\\circ}$, phases with striped order of\nsupersolid or density wave are preferred. In the intermediate domain\n$25^{\\circ}\\apprle\\theta\\apprle35^{\\circ}$ an emulsion or SF phase intervenes\nthe transition between the checkerboard and striped phases. The attractive\ninteraction dominates for $\\theta\\apprge55^{\\circ}$, which renders the system\nunstable and there is a density collapse. For our studies we use Gutzwiller\nmean-field theory to obtain the quantum phases and the phase boundaries. In\naddition, we calculate the phase boundaries between an incompressible and a\ncompressible phase of the system by considering second order perturbation\nanalysis of the mean-field theory. The analytical results, where applicable,\nare in excellent agreement with the numerical results.",
        "positive": "Experimental observation of one-dimensional superradiance lattices in\n  ultracold atoms: We measure the superradiant emission in a one-dimensional (1D) superradiance\nlattice (SL) in ultracold atoms. Resonantly excited to a superradiant state,\nthe atoms are further coupled to other collectively excited states, which form\na 1D SL. The directional emission of one of the superradiant excited states in\nthe 1D SL is measured. The emission spectra depend on the band structure, which\ncan be controlled by the frequency and intensity of the coupling laser fields.\nThis work provides a platform for investigating the collective Lamb shift of\nresonantly excited superradiant states in Bose-Einstein condensates and paves\nthe way for realizing higher dimensional superradiance lattices."
    },
    {
        "anchor": "State engineering of Bose-Einstein condensate in the optical lattice by\n  a periodic sublattice of dissipative sites: We introduce the notion of dissipative periodic lattice as an optical lattice\nwith periodically distributed dissipative sites and argue that it allows to\nengineer unconventional Bose-Einstein superfluids with the complex-valued order\nparameter. We consider two examples, the one-dimensional dissipative optical\nlattice, where each third site is dissipative, and the dissipative honeycomb\noptical lattice, where each dissipative lattice site neighbors three\nnon-dissipated sites. The tight-binding approximation is employed, which allows\none to obtain analytical results. In the one-dimensional case the condensate is\ndriven to a coherent Bloch-like state with non-zero quasimomentum, which breaks\nthe translational periodicity of the dissipative lattice. In the\ntwo-dimensional case the condensate is driven to a zero quasimomentum\nBloch-like state, which is a coherent superposition of four-site discrete\nvortices of alternating vorticity with the vortex centers located at the\ndissipative sites.",
        "positive": "Emergence of isotropy and dynamic scaling in 2D wave turbulence in a\n  homogeneous Bose gas: We realise a turbulent cascade of wave excitations in a homogeneous 2D Bose\ngas, and probe on all relevant time and length scales how it builds up from\nsmall to large momenta, until the system reaches a steady state with matching\nenergy injection and dissipation. This all-scales view directly reveals the two\ntheoretically expected cornerstones of turbulence formation -- the emergence of\nstatistical momentum-space isotropy under anisotropic forcing, and the\nspatiotemporal scaling of the momentum distribution at times before any energy\nis dissipated."
    },
    {
        "anchor": "Relaxation of the collective magnetization of a dense 3D array of\n  interacting dipolar S=3 atoms: We report on measurements of the dynamics of the collective spin length\n(total magnetization) and spin populations in an almost unit filled lattice\nsystem comprising about 10^4 spin S=3 chromium atoms, under the effect of\ndipolar interactions. The observed spin population dynamics is unaffected by\nthe use of a spin echo, and fully consistent with numerical simulations of the\nS=3 XXZ spin model. On the contrary, the observed spin length decays slower\nthan in simulations, and surprisingly reaches a small but nonzero asymptotic\nvalue within the longest timescale. Our findings show that spin coherences are\nsensitive probes to systematic effects affecting quantum many-body behavior\nthat cannot be diagnosed by merely measuring spin populations.",
        "positive": "The three-body pseudo-potential for atoms confined in one dimension: Following a strong analogy with two-dimensional physics, the three-body\npseudo-potential in one dimension is derived. The Born approximation is then\nconsidered in the context of ultracold atoms in a linear harmonic waveguide. In\nthe vicinity of the dimer threshold a direct connection is made between the\nzero-range potential and the dimensional reduction of the three-body\nSchr{\\\"o}dinger equation."
    },
    {
        "anchor": "Localization driven superradiant instability: The prominent Dicke superradiant phase arises from coupling an ensemble of\natoms to cavity optical field when external optical pumping exceeds a threshold\nstrength. Here we report a prediction of the superrandiant instability driven\nby Anderson localization, realized with a hybrid system of Dicke and\nAubry-Andre (DAA) model for bosons trapped in a one-dimensional (1D)\nquasiperiodic optical lattice and coupled to a cavity. Our central finding is\nthat for bosons condensed in localized phase given by the DAA model, the\nresonant superradiant scattering is induced, for which the critical optical\npumping of superradiant phase transition approaches zero, giving an instability\ndriven by Anderson localization. The superradiant phase for the DAA model with\nor without a mobility edge is investigated, showing that the localization\ndriven superradiant instability is in sharp contrast to the superradiance as\nwidely observed for Bose condensate in extended states, and should be\ninsensitive to temperature of the system. This study unveils an insightful\neffect of localization on the Dicke superradiance, and is well accessible based\non the current experiments.",
        "positive": "Dimensionally Induced Phase Transition of the Weakly Interacting\n  Ultracold Bose Gas: We investigate the dimensionally induced phase transition from the normal to\nthe Bose-Einstein-condensed phase for a weakly interacting Bose gas in an\noptical lattice. To this end we make use of the Hartree-Fock-Bogoliubov-Popov\ntheory, where we include numerically exact hopping energies and effective\ninteraction strengths. At first we determine the critical chemical potential,\nwhere we find a much better agreement with recent experimental data than a pure\nHartree-Fock treatment. This finding is in agreement with the dominant role of\nquantum fluctuations in lower dimensions, as they are explicitly included in\nour theory. Furthermore, we determine for the 1D-3D-transition the power-law\nexponent of the critical temperature for two different non-interacting Bose gas\nmodels yielding the same value of 1/2, which indicates that they belong to the\nsame universality class. For the weakly interacting Bose gas we find for both\nmodels that this exponent is robust with respect to finite interaction\nstrengths."
    },
    {
        "anchor": "Spatial coherence and stability in a disordered organic polariton\n  condensate: Although only a handful of organic materials have shown polariton\ncondensation, their study is rapidly becoming more accessible. The spontaneous\nappearance of long-range spatial coherence is often recognized as a defining\nfeature of such condensates. In this work, we study the emergence of spatial\ncoherence in an organic microcavity and demonstrate a number of unique features\nstemming from the peculiarities of this material set. Despite its disordered\nnature, we find that correlations extend over the entire spot size and we\nmeasure $g^{(1)}(r,r')$ values of nearly unity at short distances and of 50%\nfor points separated by nearly 10 $\\mu$m. We show that for large spots, strong\nshot to shot fluctuations emerge as varying phase gradients and defects,\nincluding the spontaneous formation of vortices. These are consistent with the\npresence of modulation instabilities. Furthermore, we find that measurements\nwith flat-top spots are significantly influenced by disorder and can, in some\ncases, lead to the formation of mutually incoherent localized condensates.",
        "positive": "Synthetic U(1) Gauge Invariance in a Spin-1 Bose Gas: Recent experimental realizations of the lattice Schwinger model [Nature 587,\n392 (2020) and Science 367, 1128 (2020)] open a door for quantum simulation of\nelementary particles and their interactions using ultracold atoms, in which the\nmatter and gauge fields are constrained by a local U(1) gauge invariance known\nas the Gauss's law. Stimulated by such exciting progress, we propose a new\nscenario in simulating the lattice Schwinger model in a spin-1 Bose-Einstein\ncondensate. It is shown that our model naturally contains an interaction of the\nmatter fields which respects the U(1) gauge symmetry but has no counterpart in\nthe conventional Schwinger model. In addition to the Z2-ordered phase\nidentified in the previous work, this additional interaction leads to a new\nZ3-ordered phase. We map out a rich phase diagram and identify that the\ncontinuous phase transitions from the disordered to the Z2-ordered and the\nZ3-ordered phases belong to the Ising and the 3-state Potts universality\nclasses, respectively. Furthermore, the two ordered phases each possess a set\nof quantum scars which give rise to anomalous quantum dynamics when quenched to\na special point in the phase diagram. Our proposal provides a novel platform\nfor extracting emergent physics in cold-atom-based quantum simulators with\ngauge symmetries."
    },
    {
        "anchor": "Collisions of three-component vector solitons in Bose-Einstein\n  condensates: Ultracold gases provide an unprecedented level of control for the\ninvestigation of soliton dynamics and collisions. We present a scheme for\ndeterministically preparing pairs of three-component solitons in a\nBose-Einstein condensate. Our method is based on local spin rotations which\nsimultaneously imprint suitable phase and density distributions. This enables\nus to observe striking collisional properties of the vector degree of freedom\nwhich naturally arises for the coherent nature of the emerging multi-component\nsolitons. We find that the solitonic properties in the quasi-one-dimensional\nsystem are quantitatively described by the integrable repulsive three-component\nManakov model.",
        "positive": "Dynamical revival of phase coherence in a many-boson system: We study the quantum dynamics of cold Bose atoms in a double well. It is\nshown that self-trapping, as well as population oscillations are common\nphenomena associated to nonlinear interactions. For larger $U/t$,\nmulti-particle tunneling is damped and the quantum dynamics is dominated by the\nsingle-particle tunneling. The many-body system can be effectively described in\na truncated Fock space. It exhibits coherence-decoherence oscillations in the\ntemporal evolution. We predict a novel phenomenon of dynamical revival and\ncollapse of matter wave fields in optical lattices in regimes near the\nsuperfluid-Mott insulator phase boundary."
    },
    {
        "anchor": "Shortcut to adiabaticity in spinor condensates: We devise a method to shortcut the adiabatic evolution of a spin-1 Bose gas\nwith an external magnetic field as the control parameter. An initial many-body\nstate with almost all bosons populating the Zeeman sublevel $m=0$, is evolved\nto a final state very close to a macroscopic spin-singlet condensate, a\nfragmented state with three macroscopically occupied Zeeman states. The\nshortcut protocol, obtained by an approximate mapping to a harmonic oscillator\nHamiltonian, is compared to linear and exponential variations of the control\nparameter. We find a dramatic speedup of the dynamics when using the shortcut\nprotocol.",
        "positive": "Phase diagram of vortices in the polar phase of spin-1 Bose-Einstein\n  condensates: The phase diagram of lowest-energy vortices in the polar phase of spin-1\nBose--Einstein condensates is investigated theoretically. Singly quantized\nvortices are categorized by the local ordered state in the vortex core and\nthree types of vortices are found as lowest-energy vortices, which are elliptic\nAF-core vortices, axisymmetric F-core vortices, and N-core vortices. These\nvortices are named after the local ordered state, ferromagnetic (F),\nantiferromagnetic (AF), broken-axisymmetry (BA), and normal (N) states apart\nfrom the bulk polar (P) state. The N-core vortex is a conventional vortex, in\nthe core of which the superfluid order parameter vanishes. The other two types\nof vortices are stabilized when the quadratic Zeeman energy is smaller than a\ncritical value. The axisymmetric F-core vortex is the lowest-energy vortex for\nferromagnetic interaction, and it has an F core surrounded by a BA skin that\nforms a ferromagnetic-spin texture, as exemplified by the localized Mermin--Ho\ntexture. The elliptic AF-core vortex is stabilized for antiferromagnetic\ninteraction; the vortex core has both nematic-spin and ferromagnetic orders\nlocally and is composed of the AF-core soliton spanned between two BA edges.\nThe phase transition from the N-core vortex to the other two vortices is\ncontinuous, whereas that between the AF-core and F-core vortices is\ndiscontinuous. The critical point of the continuous vortex-core transition is\ncomputed by the perturbation analysis of the Bogoliubov theory and the\nGinzburg--Landau formalism describes the critical behavior. The influence of\ntrapping potential on the core structure is also investigated."
    },
    {
        "anchor": "Dynamics of correlation spreading in low-dimensional transverse-field\n  Ising models: We investigate the dynamical spreading of spatial correlations after a\nquantum quench starting from a magnetically disordered state in the\ntransverse-field Ising model at one (1D) and two spatial dimensions (2D). We\nanalyze specifically the longitudinal and transverse spin-spin correlation\nfunctions at equal time with use of several methods. From the comparison of the\nresults in 1D obtained by the linear spin-wave approximation (LSWA) and those\nobtained by the rigorous analytical approach, we show that the LSWA can\nasymptotically reproduce the exact group velocity in the limit of strong\ntransverse fields while it fails to capture the detailed time dependence of the\ncorrelation functions. By applying the LSWA to the 2D case, in which the\nrigorous analytical approach is unavailable, we estimate the propagation\nvelocity to be $Ja/(2\\hbar)$ at the strong-field limit, where $J$ is the Ising\ninteraction and $a$ is the lattice spacing. We also utilize the tensor-network\nmethod based on the projected-entangled pair states for 2D and quantitatively\ncompute the time evolution of the correlation functions for a relatively short\ntime. Our findings provide useful benchmarks for quantum simulation experiments\nof correlation spreading and theoretical refinement of the Lieb-Robinson bound\nin the future.",
        "positive": "Three-dimensional localization of ultracold atoms in an optical\n  disordered potential: We report a study of three-dimensional (3D) localization of ultracold atoms\nsuspended against gravity, and released in a 3D optical disordered potential\nwith short correlation lengths in all directions. We observe density profiles\ncomposed of a steady localized part and a diffusive part. Our observations are\ncompatible with the self-consistent theory of Anderson localization, taking\ninto account the specific features of the experiment, and in particular the\nbroad energy distribution of the atoms placed in the disordered potential. The\nlocalization we observe cannot be interpreted as trapping of particles with\nenergy below the classical percolation threshold."
    },
    {
        "anchor": "Many-body quantum dynamics of an asymmetric bosonic Josephson junction: The out-of-equilibrium quantum dynamics of an interacting Bose gas trapped in\na 1D asymmetric double-well potential is studied by solving the many-body\nSchr\\\"odinger equation numerically accurately. We examine how the loss of\nsymmetry of the confining trap affects the macroscopic quantum tunneling\ndynamics of the system between the two wells. In an asymmetric DW, the two\nwells are not equivalent anymore -the left well is deeper than the right one.\nAccordingly, we analyze the dynamics by initially preparing the condensate in\nboth the left and the right well. We examined the frequencies and amplitudes of\nthe oscillations of the survival probabilities, the time scale for the\ndevelopment of fragmentation and its degree, and the growth and oscillatory\nbehavior of the many-body position and momentum variances. There is an overall\nsuppression of the oscillations of the survival probabilities in an asymmetric\ndouble well. However, depending on whether the condensate is initially prepared\nin the left or right well, the repulsive inter-atomic interactions affect the\nsurvival probabilities differently. The degree of fragmentation depends both on\nthe asymmetry of the trap and the initial well in which the condensate is\nprepared in a non-trivial manner. Overall, the many-body position and momentum\nvariances bear the prominent signatures of the density oscillations of the\nsystem in the asymmetric double well as well as a breathing-mode oscillation.\nFinally, a universality of fragmentation for systems made of different numbers\nof particles but the same interaction parameter is also found. The phenomenon\nis robust despite the asymmetry of the junction and admits a\nmacroscopically-large fragmented condensate characterized by a diverging\nmany-body position variance.",
        "positive": "Free Expansion of a Weakly-interacting Dipolar Fermi Gas: We theoretically investigate a polarized dipolar Fermi gas in free expansion.\nThe inter-particle dipolar interaction deforms phase-space distribution in trap\nand also in the expansion. We exactly predict the minimal quadrupole\ndeformation in the expansion for the high-temperature Maxwell-Boltzmann and\nzero-temperature Thomas-Fermi gases in the Hartree-Fock and Landau-Vlasov\napproaches. In conclusion, we provide a proper approach to develop the\ntime-of-flight method for the weakly-interacting dipolar Fermi gas and also\nreveal a scaling law associated with the Liouville's theorem in the long-time\nbehaviors of the both gases."
    },
    {
        "anchor": "Controlling quantum coherence of a two-component Bose-Einstein\n  condensate via an impurity atom: We propose a scheme to control quantum coherence of a two-component\nBose-Einstein condensate (BEC) by a single impurity atom immersed in the BEC.\nWe show that the single impurity atom can act as a single atom valve (SAV) to\ncontrol quantum coherence of the two-component BEC. It is demonstrated that the\nSAV can realize the on-demand control over quantum coherence at an arbitrary\ntime. Specially, it is found that the SAV can also control higher-order quantum\ncoherence of two-component BEC. We investigate the long-time evolution of\nquantum coherence of the two-component BEC. It is indicated that the single\nimpurity atom can induce collapse and revival phenomenon of quantum coherence\nof the two-component BEC. Collapse-revival configurations of quantum coherence\ncan be manipulated by the initial-state parameters of the impurity atom and the\nimpurity-BEC interaction strengths.",
        "positive": "The time-domain Landau-Zener-Stuckelberg-Majorana interference in\n  optical lattice clock: The interference between a sequence of Landau-Zener (LZ) transitions can\nproduce Rabi oscillations(LZROs). This phenomenon is a kind of time-domain\nLandau-Zener-Stuckelberg-Majorana (LZSM) interference. However, experimental\ndemonstrations of this LZSM interference induced Rabi oscillation are extremely\nhard due to the short coherence time of the driven quantum system. Here, we\nstudy theoretically the time-domain LZSM interference between the clock\ntransition in one-dimensional (1D) Sr-87 optical lattice clock (OLC) system.\nWith the help of both the adiabatic-impulse model and Floquet numerical\nsimulation method, the LZROs with special step-like structure are clearly found\nboth in fast- and slow-passage limit in the real experiment parameter regions.\nIn addition, the dephasing effect caused by the system temperature can be\nsuppressed with destructive interference in the slow-passage limit. Finally, we\ndiscuss the possible Bloch-Siegert shift while the pulse time is away from the\nhalf-integer and integer periods. Our work provides a clear roadmap to observe\nthe LZROs on the OLC platform."
    },
    {
        "anchor": "Quench dynamics of a confined ultracold Fermi gas: Direct visibility of\n  the Goldstone mode in the single-particle excitations: We present a numerical study of a confined ultracold Fermi gas showing that\nthe Goldstone mode of the BCS gap is directly visible in the dynamics of the\nsingle-particle excitations. To this end, we investigate the low-energy dynamic\nresponse of a confined Fermi gas to a rapid change of the scattering length\n(i.e., an interaction quench). Based on a fully microscopic time-dependent\ndensity-matrix approach within the Bogoliubov-de Gennes formalism that includes\na 3D harmonic confinement we simulate and identify the emergence of the\nGoldstone mode in a cigar-shaped $^6$Li gas. We show that the quench leads to a\nlow-frequency in-phase oscillation of the single-particle occupations. Complete\ninversion is achieved for occupations corresponding to the lowest-lying\nsingle-particle states.",
        "positive": "Thermal spin fluctuations in spinor Bose-Einstein condensates: We study the thermal activation of spin fluctuations in dynamically-stable\nspinor Bose-Einstein condensates. We analyze the specific cases of a\nnon-dipolar spin-1 condensate in m = 0, where thermal activation results from\nspin-changing collisions, and of a Chromium condensate in the maximally\nstretched state m = -3, where thermal spin fluctuations are due to\ndipole-induced spin- relaxation. In both cases, we show that the low energy\nassociated to the spinor physics may be employed for thermometry purposes down\nto extremely low temperatures, typically impossible to measure in BECs with\nusual thermometric techniques. Moreover, the peculiar dependence of the\nsystem's entropy with the applied Zeeman energy opens a possible route for\nadiabatic cooling."
    },
    {
        "anchor": "Variational analysis of flat-top solitons in Bose-Einstein condensates: Static and dynamic properties of matter-wave solitons in dense Bose-Einstein\ncondensates, where three-body interactions play a significant role, have been\nstudied by a variational approximation (VA) and numerical simulations. For\nexperimentally relevant parameters, matter-wave solitons may acquire a flat-top\nshape, which suggests employing a super-Gaussian trial function for VA.\nComparison of the soliton profiles, predicted by VA and those found from\nnumerical solution of the governing Gross-Pitaevskii equation shows good\nagreement, thereby validating the proposed approach.",
        "positive": "Observation of a Modulational Instability in Bose-Einstein condensates: We observe the breakup dynamics of an elongated cloud of condensed $^{85}$Rb\natoms placed in an optical waveguide. The number of localized spatial\ncomponents observed in the breakup is compared with the number of solitons\npredicted by a plane-wave stability analysis of the nonpolynomial nonlinear\nSchr\\\"odinger equation, an effective one-dimensional approximation of the\nGross-Pitaevskii equation for cigar-shaped condensates. It is shown that the\nnumbers predicted from the fastest growing sidebands are consistent with the\nexperimental data, suggesting that modulational instability is the key\nunderlying physical mechanism driving the breakup."
    },
    {
        "anchor": "Exploring competing density order in the ionic Hubbard model with\n  ultracold fermions: We realize and study the ionic Hubbard model using an interacting\ntwo-component gas of fermionic atoms loaded into an optical lattice. The\nbipartite lattice has honeycomb geometry with a staggered energy-offset that\nexplicitly breaks the inversion symmetry. Distinct density-ordered phases are\nidentified using noise correlation measurements of the atomic momentum\ndistribution. For weak interactions the geometry induces a charge density wave.\nFor strong repulsive interactions we detect a strong suppression of doubly\noccupied sites, as expected for a Mott insulating state, and the externally\nbroken inversion symmetry is not visible anymore in the density distribution.\nThe local density distributions in different configurations are characterized\nby measuring the number of doubly occupied lattice sites as a function of\ninteraction and energy-offset. We further probe the excitations of the system\nusing direction dependent modulation spectroscopy and discover a complex\nspectrum, which we compare with a theoretical model.",
        "positive": "Rashba-type Spin-orbit Coupling in Bilayer Bose-Einstein Condensates: We explore a new way of producing the Rashba spin-orbit coupling (SOC) for\nultracold atoms by using a two-component (spinor) atomic Bose-Einstein\ncondensate (BEC) confined in a bilayer geometry. The SOC of the Rashba type is\ncreated if the atoms pick up a {\\pi} phase after completing a cyclic transition\nbetween four combined spin-layer states composed of two spin and two layer\nstates. The cyclic coupling of the spin-layer states is carried out by\ncombining an intralayer Raman coupling and an interlayer laser assisted\ntunneling. We theoretically determine the ground-state phases of the\nspin-orbit-coupled BEC for various strengths of the atom-atom interaction and\nthe laser-assisted coupling. It is shown that the bilayer scheme provides a\ndiverse ground-state phase diagram. In an intermediate range of the atom-light\ncoupling two interlacing lattices of half- skyrmions and half-antiskyrmions are\nspontaneously created. In the strong-coupling regime, where the SOC of the\nRashba-type is formed, the ground state represents plane-wave or standing-wave\nphases depending on the interaction between the atoms. A variational analysis\nis shown to be in a good agreement with the numerical results."
    },
    {
        "anchor": "Bose condensation of squeezed light: Light with a chemical potential and no mass is shown to possess a general\nphase-transition curve to Bose-Einstein condensation. This limiting density and\ntemperature range is found by the diverging in-medium potential range of\neffective interaction. The inverse expansion series of the effective\ninteraction from Bethe-Salpeter equation is employed exceeding the ladder\napproximation. While usually the absorption and emission with Dye molecules is\nconsidered, here it is proposed that squeezing can create also such a mean\ninteraction leading to a chemical potential. The equivalence of squeezed light\nwith a complex Bogoliubov transformation of interacting Bose system with finite\nlifetime is established with the help of which an effective gap is deduced\nwhere the squeezing parameter is related to an equivalent gap by\n$|\\Delta(\\omega)|={\\hbar \\omega/( \\coth {2|z(\\omega)|}-1)}$. This gap phase\ncreates a finite condensate in agreement with the general limiting density and\ntemperature range. In this sense it is shown that squeezing induces the same\neffect on light as an interaction leading to possible condensation. The phase\ndiagram for condensation is presented due to squeezing and the appearance of\ntwo gaps is discussed.",
        "positive": "Functional renormalization and ultracold quantum gases: The method of functional renormalization is applied to the theoretical\ninvestigation of ultracold quantum gases. Flow equations are derived for a Bose\ngas with approximately pointlike interaction, for a Fermi gas with two\n(hyperfine) spin components in the Bardeen-Cooper-Schrieffer (BCS) to\nBose-Einstein condensation (BEC) crossover and for a Fermi gas with three\ncomponents. The solution of the flow equations determine the properties of\nthese systems both in the few-body regime and in thermal equilibrium.\n  For the Bose gas this covers the quantum phase diagram, the condensate and\nsuperfluid fraction, the critical temperature, the correlation length, the\nspecific heat or sound propagation. The properties are discussed both for three\nand two spatial dimensions. The discussion of the Fermi gas in the BCS-BEC\ncrossover concentrates on the effect of particle-hole fluctuations but\naddresses the complete phase diagram. For the three component fermions, the\nflow equations in the few-body regime show a limit-cycle scaling and the Efimov\ntower of three-body bound states. Applied to the case of Lithium they explain\nrecently observed three-body loss features. Extending the calculations by\ncontinuity to nonzero density, it is found that a new trion phase separates a\nBCS and a BEC phase for three component fermions close to a common resonance.\n  More formal is the derivation of a new exact flow equation for scale\ndependent composite operators. This equation allows for example a better\ntreatment of bound states."
    },
    {
        "anchor": "Non-equilibrium dynamics of Bosonic Mott insulators in an electric field: We study the non-equilibrium dynamics of one-dimensional Mott insulating\nbosons in the presence of a tunable effective electric field E which takes the\nsystem across a quantum critical point (QCP) separating a disordered and a\ntranslation symmetry broken ordered phase. We provide an exact numerical\ncomputation of the residual energy Q, the log-fidelity F, the excess defect\ndensity D, and the order parameter correlation function for a linear-in-time\nvariation of E with a rate v. We discuss the temporal and spatial variation of\nthese quantities for a range of v and for finite system sizes as relevant to\nrealistic experimental setups [J. Simon et al., Nature 472, 307 (2011)]. We\nshow that in finite-sized systems Q, F, and D obey Kibble-Zurek scaling, and\nsuggest further experiments within this setup to test our theory.",
        "positive": "Locating the quantum critical point of the Bose-Hubbard model through\n  singularities of simple observables: We show that the critical point of the two-dimensional Bose-Hubbard model can\nbe easily found through studies of either on-site atom number fluctuations or\nthe nearest-neighbor two-point correlation function (the expectation value of\nthe tunnelling operator). Our strategy to locate the critical point is based on\nthe observation that the derivatives of these observables with respect to the\nparameter that drives the superfluid-Mott insulator transition are singular at\nthe critical point in the thermodynamic limit. Performing the quantum Monte\nCarlo simulations of the two-dimensional Bose-Hubbard model, we show that this\ntechnique leads to the accurate determination of the position of its critical\npoint. Our results can be easily extended to the three-dimensional Bose-Hubbard\nmodel and different Hubbard-like models. They provide a simple\nexperimentally-relevant way of locating critical points in various cold atomic\nlattice systems."
    },
    {
        "anchor": "Bright sink-type localized states in exciton-polariton condensates: The family of one-dimensional localized solutions to dissipative nonlinear\nequations includes a variety of objects such as sources, sinks, shocks (kinks),\nand pulses. These states are in general accompanied by nontrivial density\ncurrents, which are not necessarily related to the movement of the object\nitself. We investigate the existence and physical properties of sink-type\nsolutions in nonresonantly pumped exciton-polariton condensates modeled by an\nopen-dissipative Gross-Pitaevskii equation. While sinks possess density\nprofiles similar to bright solitons, they are qualitatively different objects\nas they exist in the case of repulsive interactions and represent a\nheteroclinic solution. We show that sinks can be created in realistic systems\nwith appropriately designed pumping profiles. We also conclude that in\ntwo-dimensional configurations, due to the proliferation of vortices, sinks do\nnot appear.",
        "positive": "The transition and coexistence of quantum droplets and solitons in\n  quasi-1D dipolar Bose gas: In our study, we investigated bright solitons, dark solitons, and quantum\ndroplets in quasi-one-dimensional dipolar Bose gases, and further validated the\ncrossover and coexistence of quantum droplets and solitons using the\nLieb-Liniger energy within the framework of local density approximation.\nIncreasing the particle number N transforms the bright dipolar soliton state\ninto a stable self-bound quantum droplet state, with further increases in N\nleading to a broader quantum droplet that enables the presence of dark solitons\nwithin it."
    },
    {
        "anchor": "New type of crossover physics in three-component Fermi gases: A three-component Fermi gas near a broad Feshbach resonance does not have a\nuniversal ground state due to the Thomas collapse, while it does near a narrow\nFeshbach resonance. We explore its universal phase diagram in the plane of the\ninverse scattering length 1/akF and the resonance range RkF. For a large RkF,\nthere exists a Lifshitz transition between superfluids with and without an\nunpaired Fermi surface as a function of 1/akF. With decreasing RkF, the Fermi\nsurface coexisting with the superfluid can change smoothly from that of atoms\nto trimers (\"atom-trimer continuity\"), corresponding to the quark-hadron\ncontinuity in a dense nuclear matter. Eventually, there appears a finite window\nin 1/akF where the superfluid is completely depleted by the trimer Fermi gas,\nwhich gives rise to a pair of quantum critical points. The boundaries of these\nthree quantum phases are determined in regions where controlled analyses are\npossible and are also evaluated based on a mean-field plus trimer model.",
        "positive": "Semiclassical dynamics of a dark soliton in a one-dimensional bosonic\n  superfluid in an optical lattice: We study quantum dynamics of a dark soliton in a one-dimensional Bose gas in\nan optical lattice within the truncated Wigner approximation. A previous work\nhas revealed that in the absence of quantum fluctuations, dynamical stability\nof the dark soliton significantly depends on whether its phase kink is located\nat a lattice site or a link of two neighboring sites. It has also shown that\nthe dark soliton is unstable in a regime of strong quantum fluctuations\nregardless of the phase-kink position. To bridge the gap between the classical\nand strongly quantum regimes, we investigate the dynamical stability of the\ndark soliton in a regime of weak quantum fluctuations. We find that the\nposition dependence of the dynamical stability gradually diminishes and\neventually vanishes as the strength of quantum fluctuations increases. This\nclassical-to-quantum crossover of the soliton stability remains even in the\npresence of a parabolic trapping potential. We suggest that the crossover\nbehavior can be used for experimentally diagnosing whether the instability of a\ndark soliton is due to quantum fluctuations or classical dynamical instability."
    },
    {
        "anchor": "Time crystals in a shaken atom-cavity system: We demonstrate the emergence of a time crystal of atoms in a high-finesse\noptical cavity driven by a phase-modulated transverse pump field, resulting in\na shaken lattice. This shaken system exhibits macroscopic oscillations in the\nnumber of cavity photons and order parameters at noninteger multiples of the\ndriving period, which signals the appearance of an incommensurate time crystal.\nThe subharmonic oscillatory motion corresponds to dynamical switching between\nsymmetry-broken states, which are nonequilibrium bond ordered density wave\nstates. Employing a semiclassical phase-space representation for the\ndriven-dissipative quantum dynamics, we confirm the rigidity and persistence of\nthe time crystalline phase. We identify experimentally relevant parameter\nregimes for which the time crystal phase is long-lived, and map out the\ndynamical phase diagram. We compare and contrast the incommensurate time\ncrystal with the commensurate Dicke time crystal in the amplitude-modulated\ncase.",
        "positive": "Far-Away-From-Equilibrium Quantum Critical Conformal Dynamics:\n  Reversibility, Thermalization, and Hydrodynamics: Generic far-away-from-equilibrium many-body dynamics involve entropy\nproduction, and hence are thermodynamically irreversible. Near quantum critical\npoints, an emergent conformal symmetry can impose strong constraints on entropy\nproduction rates, and in some cases completely forbid entropy production, which\nusually occurs for systems that deviate from quantum critical points. In this\narticle, we illustrate how the vanishing entropy production near a quantum\ncritical point results in reversible far-away-from-equilibrium dynamics at\nfinite temperatures that are otherwise irreversible. Away from the quantum\ncritical point, the quantum dynamics are damped, and our analysis directly\nrelates the thermalization time scale to the hydrodynamic viscosity near\nquantum critical points with dynamical critical exponent $z=2$. We demonstrate\nhow both controllable reversible and irreversible dynamics can be potentially\nstudied in cold gas experiments using Feshbach resonances."
    },
    {
        "anchor": "Energy and momentum transfer in one-dimensional trapped gases by\n  stimulated light scattering: In ultracold atoms settings, inelastic light scattering is a preeminent\ntechnique to reveal static and dynamic properties at nonzero momentum. In this\nwork, we investigate an array of one-dimensional trapped Bose gases, by\nmeasuring both the energy and the momentum imparted to the system via light\nscattering experiments. The measurements are performed in the weak perturbation\nregime, where these two quantities - the energy and momentum transferred - are\nexpected to be related to the dynamical structure factor of the system. We\ndiscuss this relation, with special attention to the role of in-trap dynamics\non the transferred momentum.",
        "positive": "Thermalisation of a two-dimensional photonic gas in a 'white-wall'\n  photon box: Bose-Einstein condensation, the macroscopic accumulation of bosonic particles\nin the energetic ground state below a critical temperature, has been\ndemonstrated in several physical systems. The perhaps best known example of a\nbosonic gas, blackbody radiation, however exhibits no Bose-Einstein\ncondensation at low temperatures. Instead of collectively occupying the lowest\nenergy mode, the photons disappear in the cavity walls when the temperature is\nlowered - corresponding to a vanishing chemical potential. Here we report on\nevidence for a thermalised two-dimensional photon gas with freely adjustable\nchemical potential. Our experiment is based on a dye filled optical\nmicroresonator, acting as a 'white-wall' box for photons. Thermalisation is\nachieved in a photon number-conserving way by photon scattering off the\ndye-molecules, and the cavity mirrors both provide an effective photon mass and\na confining potential - key prerequisites for the Bose-Einstein condensation of\nphotons. As a striking example for the unusual system properties, we\ndemonstrate a yet unobserved light concentration effect into the centre of the\nconfining potential, an effect with prospects for increasing the efficiency of\ndiffuse solar light collection."
    },
    {
        "anchor": "Magnetic properties and strong-coupling corrections in an ultracold\n  Fermi gas with population imbalance: We investigate magnetic properties of an ultracold Fermi gas with population\nimbalance. In the presence of population imbalance, the strong-coupling theory\ndeveloped by Nozieres and Schmitt-Rink (which is frequently referred to as the\nNSR theory, or Gaussian fluctuation theory) is known to give unphysical results\nin the BCS-BEC crossover region. We point out that this problem comes from how\nto treat pseudogap effects originating from pairing fluctuations and many-body\ncorrections to the spin susceptibility. We also clarify how to overcome this\nproblem by including higher order fluctuations beyond the ordinary T-matrix\ntheory. Calculated spin susceptibility based on our extended T-matrix theory\nagrees well with the recent experiment on a 6Li Fermi gas.",
        "positive": "Searching for Magnetostatic Modes in Spin-Polarized Atomic Hydrogen: We consider a possibility of the magnetostatic type spin waves driven by a\nlong-range magnetic dipole interactions, to account for the peaks in the ESR\nspectra observed in our previous work. The Walker equation for magnetostatic\nmodes is solved for a cylinder of atomic hydrogen, first in a uniform magnetic\nfield and second in a linearly decreasing magnetic field. The frequency\nbehavior of the solved modes with length of the cylinder and density of the gas\nis compared to experimental data. We conclude that magnetostatic modes are\nunlikely to account for the observed modulations of ESR spectra."
    },
    {
        "anchor": "Symmetry classification of spin-orbit coupled spinor Bose-Einstein\n  condensates: We develop a symmetry classification scheme to find ground states of pseudo\nspin-1/2, spin-1, and spin-2 spin-orbit coupled spinor Bose-Einstein\ncondensates, and show that as the SO(2) symmetry of simultaneous spin and space\nrotations is broken into discrete cyclic groups, various types of lattice\nstructures emerge in the absence of a lattice potential, examples include two\ndifferent kagaome lattices for pseudo spin-1/2 condensates and a nematic vortex\nlattice in which uniaxial and biaxial spin textures align alternatively for\nspin-2 condensates. For the pseudo spin-1/2 system, although mean-field states\nalways break time-reversal symmetry, there exists a time-reversal invariant\nmany-body ground state, which is fragmented and expected to be observed in a\nmicro-condensate.",
        "positive": "Frustrated quantum Ising spins simulated by spinless bosons in a tilted\n  lattice: from a quantum liquid to antiferromagnetic order: We study spinless bosons in a decorated square lattice with a near-diagonal\ntilt. The resonant subspace of the tilted Mott insulator is described by an\neffective Hamiltonian of frustrated quantum Ising spins on a non-bipartite\nlattice. This generalizes an earlier proposal for the unfrustrated quantum\nIsing model in one dimension which was realized in a recent experiment on\nultracold $^{87}$Rb atoms in an optical lattice. Very close to diagonal tilt,\nwe find a quantum liquid state which is continuously connected to the\nparamagnet. Frustration can be reduced by increasing the tilt angle away from\nthe diagonal, and the system undergoes a transition to an antiferromagnetically\nordered state. Using quantum Monte Carlo simulations and exact diagonalization,\nwe find that for realistic system sizes the antiferromagnetic order appears to\nbe quasi-one-dimensional; however, in the thermodynamic limit the order is\ntwo-dimensional."
    },
    {
        "anchor": "Corrections to Local Density Approximation for superfluid trapped\n  fermionic atoms from the Wigner-Kirkwood $\\hbar$ expansion: A semiclassical second-order differential equation for the inhomogeneous\nlocal gap $\\Delta(r)$ is derived from a strict second-order $\\hbar$ expansion\nof the anomalous pairing tensor and compared with a similar equation given by\nSimonucci et al. The second-order normal density matrix is given as well.\nSeveral extra gradient terms are revealed. Second-order expressions at finite\ntemperature are given for the first time. The corresponding Ginzburg-Landau\nequation is presented and it is shown that, compared to the equation of Baranov\nand Petrov, an extra second-order gradient term is present. Applications to the\npairing gap in cold atoms in a harmonic trap are presented.",
        "positive": "Dimensional reduction of a binary Bose-Einstein condensate in mixed\n  dimensions: We present effective reduced equations for the study of a binary\nBose-Einstein condensate (BEC), where the confining potentials of the two BEC\ncomponents have distinct asymmetry so that the components belong to different\nspace dimensions as in a recent experiment [G. Lamporesi et al., Phys. Rev.\nLett. 104, 153202 (2010)]. Starting from a binary three-dimensional (3D)\nGross-Pitaevskii equation (GPE) and using a Lagrangian variational approach we\nderive a binary effective nonlinear Schroedinger equation with components in\ndifferent reduced dimensions, e. g., the first component in one dimension and\nthe second in two dimensions as appropriate to represent a cigar-shaped BEC\ncoupled to a disk-shaped BEC. We demonstrate that the effective reduced binary\nequation, which depend on the geometry of the system, is quite reliable when\ncompared with the binary 3D GPE and can be efficiently used to perform\nnumerical simulation and analytical calculation for the investigation of static\nand dynamic properties of a binary BEC in mixed dimensions."
    },
    {
        "anchor": "Universal scattering phase shift in the presence of spin-orbit coupling: Scattering phase shift, as a key parameter in scattering theory, plays an\nimportant role in characterizing low-energy collisions between ultracold atoms.\nIn this work, we theoretically investigate the universal low-energy behavior of\nthe scattering phase shifts for cold atoms in the presence of spin-orbit\ncoupling. We first construct the asymptotic form of the two-body wave function\nwhen two fermions get as close as the interaction range, and consider\nperturbatively the correction of the spin-orbit coupling up to the second\norder, in which new scattering parameters are introduced. Then for elastic\ncollisions, the scattering phase shifts are defined according to the unitary\nscattering $S$ matrix. We show how the low-energy behavior of the scattering\nphase shifts is modified by these new scattering parameters introduced by\nspin-orbit coupling. The universality of the scattering phase shifts is\nmanifested as the independence of the specific form of the interatomic\npotential. The explicit forms of the new scattering parameters are analytically\nderived within a model of the spherical-square-well potential. Our method\nprovides a unified description of the low-energy properties of scattering phase\nshifts in the presence of spin-orbit coupling.",
        "positive": "Thermodynamics in the vicinity of a relativistic quantum critical point\n  in 2+1 dimensions: We study the thermodynamics of the relativistic quantum O($N$) model in two\nspace dimensions. In the vicinity of the zero-temperature quantum critical\npoint (QCP), the pressure can be written in the scaling form\n$P(T)=P(0)+N(T^3/c^2)\\calF_N(\\Delta/T)$ where $c$ is the velocity of the\nexcitations at the QCP and $\\Delta$ is a characteristic zero-temperature energy\nscale. Using both a large-$N$ approach to leading order and the nonperturbative\nrenormalization group, we compute the universal scaling function $\\calF_N$. For\nsmall values of $N$ ($N\\lesssim 10$) we find that $\\calF_N(x)$ is nonmonotonous\nin the quantum critical regime ($|x|\\lesssim 1$) with a maximum near $x=0$. The\nlarge-$N$ approach -- if properly interpreted -- is a good approximation both\nin the renormalized classical ($x\\lesssim -1$) and quantum disordered\n($x\\gtrsim 1$) regimes, but fails to describe the nonmonotonous behavior of\n$\\calF_N$ in the quantum critical regime. We discuss the renormalization-group\nflows in the various regimes near the QCP and make the connection with the\nquantum nonlinear sigma model in the renormalized classical regime. We compute\nthe Berezinskii-Kosterlitz-Thouless transition temperature in the quantum O(2)\nmodel and find that in the vicinity of the QCP the universal ratio\n$\\Tkt/\\rho_s(0)$ is very close to $\\pi/2$, implying that the stiffness\n$\\rho_s(\\Tkt^-)$ at the transition is only slightly reduced with respect to the\nzero-temperature stiffness $\\rho_s(0)$. Finally, we briefly discuss the\nexperimental determination of the universal function $\\calF_2$ from the\npressure of a Bose gas in an optical lattice near the\nsuperfluid--Mott-insulator transition."
    },
    {
        "anchor": "Exact edge, bulk and bound states of finite topological systems: Finite topologically non-trivial systems are often characterised by the\npresence of bound states at their physical edges. These topological edge modes\ncan be distinguished from usual Shockley waves energetically, as their energies\nremain finite and in-gap. On a clean 1D or reducible 2D model, in either the\ncommensurate or semi-infinite case, the edge modes can be obtained\nanalytically, as shown in [PRL 71, 3697 (1993)] and [PRA 89, 023619 (2014)]. We\nput forward a method for obtaining the spectrum and wave functions of\ntopological edge modes for arbitrary finite lattices, including the\nincommensurate case. A small number of parameters are easily determined\nnumerically, with the form of the eigenstates remaining fully analytical. We\nalso obtain the bulk modes in the finite system analytically and their\neigenenergies, which lie within the infinite-size limit continuum. Our method\nis general and can be easily applied to obtain the properties of\nnon-topological models and/or extended to include impurities. As an example, we\nconsider the case of an impurity located next to one edge of a 1D system,\nequivalent to a softened boundary in a separable 2D model. We show that a\nlocalised impurity can have a drastic effect on the edge modes of the system.\nUsing the periodic Harper and Hofstadter models to illustrate our method, we\nfind that, on increasing the impurity strength, edge states can enter or exit\nthe continuum, and a trivial Shockley state bound to the impurity may appear.\nThe fate of the topological edge modes in the presence of impurities can be\naddressed by quenching the impurity strength. We find that at certain critical\nimpurity strengths, the transition probability for a particle initially\nprepared in an edge mode to decay into the bulk exhibits discontinuities that\nmark the entry and exit points of edge modes from and into the bulk spectrum.",
        "positive": "Bardeen-Cooper-Schrieffer--type pairing in a spin-$\\frac{1}{2}$ Bose gas\n  with spin-orbit coupling: We apply the functional path-integral approach to analyze how the presence of\na spin-orbit coupling (SOC) affects the basic properties of a BCS-type paired\nstate in a two-component Bose gas. In addition to a mean-field theory that is\nbased on the saddle-point approximation for the inter-component pairing, we\nderive a Ginzburg-Landau theory by including the Gaussian fluctuations on top,\nand use them to reveal the crucial roles played by the momentum-space structure\nof an arbitrary SOC field in the stability of the paired state at finite\ntemperatures. For this purpose, we calculate the critical transition\ntemperature for the formation of paired bosons, and that of the gapless\nquasiparticle excitations for a broad range of interaction and SOC strengths.\nIn support of our results for the many-body problem, we also benchmark our\nnumerical calculations against the analytically-tractable limits, and provide a\nfull account of the two-body limit including its non-vanishing binding energy\nfor arbitrarily weak interactions and the anisotropic effective mass tensor."
    },
    {
        "anchor": "Three and Four Harmonically Trapped Particles in an Effective Field\n  Theory Framework: We study systems of few two-component fermions interacting via short-range\ninteractions within a harmonic-oscillator trap. The dominant interactions,\nwhich are two-body, are organized according to the number of derivatives and\ndefined in a two-body truncated model space made from a bound-state basis.\nLeading-order (LO) interactions are solved for exactly using the formalism of\nthe No-Core Shell Model, whereas corrections are treated as many-body\nperturbations. We show explicitly that next-to-LO and next-to-next-to-LO\ninteractions improve convergence as the model space increases. We present\nresults at unitarity for three- and four-fermion systems, which show excellent\nagreement with the exact solution (for the three-body problem) and results\nobtained by others methods (in the four-body case). We also present results for\nfinite scattering lengths and non-zero range of the interaction, including (at\npositive scattering length) observation of a change in the structure of the\nthree-body ground state and extraction of the atom-dimer scattering length.",
        "positive": "Generalized Berry phase for a bosonic Bogoliubov system with exceptional\n  points: We discuss the topology of Bogoliubov excitation bands from a Bose-Einstein\ncondensate in an optical lattice. Since the Bogoliubov equation for a bosonic\nsystem is non-Hermitian, complex eigenvalues often appear and induce dynamical\ninstability. As a function of momentum, the onset of appearance and\ndisappearance of complex eigenvalues is an exceptional point (EP), which is a\npoint where the Hamiltonian is not diagonalizable and hence the Berry\nconnection and curvature are ill-defined, preventing defining topological\ninvariants. In this paper, we propose a systematic procedure to remove EPs from\nthe Brillouin zone by introducing an imaginary part of the momentum. We then\ndefine the Berry phase for a one-dimensional bosonic Bogoliubov system.\nExtending the argument for Hermitian systems, the Berry phase for an\ninversion-symmetric system is shown to be $Z_2$. As concrete examples, we\nnumerically investigate two toy models and confirm the bulk-edge correspondence\neven in the presence of complex eigenvalues. The $Z_2$ invariant associated\nwith particle-hole symmetry and the winding number for a\ntime-reversal-symmetric system are also discussed."
    },
    {
        "anchor": "Synthetic gauge field in two interacting ultracold atomic gases without\n  an optical lattice: A 2D Fock-state lattice (FSL is constructed from the many-body states of two\ninteracting two-mode quantum gases. By periodically driving the interspecies\ninteractions and pulsing the tunneling between the two modes of each gas, a\nsynthetic gauge field is generated. We derive an effective Hamiltonian in the\nshort pulse limit which resembles the Harper-Hofstadter Hamiltonian where the\nmagnetic flux per plaquette is controlled by the ratio of the interaction\nenergy and the driving frequency. The quasispectrum of the Floquet operator of\nthe driving sequence shows the celebrated Hofstadter's butterfly pattern as\nwell as the existence of edge states. From the calculation of the local Chern\nmarker, we establish that the FSL has non-trivial topology and by simulating\nthe dynamics of the edge states, show that they exhibit chirality. Finally, the\ninclusion of the intraspecies interactions creates an overall harmonic trap in\nthe lattice and introduces the nonlinear effect of macroscopic quantum\nself-trapping which is shown to hinder the movement along the edge of the\nlattice. This work introduces a new avenue to explore synthetic gauge fields\nand provides a link between non-trivial condensed matter systems and quantum\ngases.",
        "positive": "Phase diagram of disordered Bose-Hubbard model based on mean-field and\n  percolation analysis in two dimensions and at fixed $n=1$ filling: We present a phase diagram of Bose-Hubbard model with on-site chemical\npotential disorder at two dimensions within the scope of mean-field theory. The\nphase diagram in the disorder strength ($\\Delta$) and the on-site repulsion\n($U$) for disordered BHM at fixed filling $\\langle{n\\rangle}=1$, show\ninteresting re-entrance of superfluid phase, sandwiched between Bose-glass\nphases, as observed by the previous QMC results. We probe the Bose-glass to\nsuperfluid transition, as a percolation transition, based on the mean-field\nresults at various parts of the phase diagram using both $\\Delta$ and $U$ as\nthe tuning parameter. We argue the robustness of the re-entrant superfluid."
    },
    {
        "anchor": "One Dimensional 1H, 2H and 3H: The ground-state properties of one-dimensional electron-spin-polarized\nhydrogen $^1$H, deuterium $^2$H, and tritium $^3$H are obtained by means of\nquantum Monte Carlo methods. The equations of state of the three isotopes are\ncalculated for a wide range of linear densities. The pair correlation function\nand the static structure factor are obtained and interpreted within the\nframework of the Luttinger liquid theory. We report the density dependence of\nthe Luttinger parameter and use it to identify different physical regimes:\nBogoliubov Bose gas, super-Tonks-Girardeau gas, and quasi-crystal regimes for\nbosons; repulsive, attractive Fermi gas, and quasi-crystal regimes for\nfermions. We find that the tritium isotope is the one with the richest\nbehaviour. Our results show unambiguously the relevant role of the isotope mass\nin the properties of this quantum system.",
        "positive": "Multiple-quantized vortices in rotating LOFF state of ultracold Fermi\n  superfluid gas: A rotating ultracold S-wave superfluid Fermi gas is considered, when the\npopulation imbalance (or equivalently the mismatch in chemical potentials)\ncorresponds to the Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) state in the\nvicinity of the Lifshitz critical point. It is shown that under these\nconditions the critical angular velocity in two-dimensional systems is an\noscillating function of temperature and population imbalance giving rise to\nreentrant superfluid phases. This leads to vortex lattices with\nmultiple-quantized circulation quanta. The reason for this behavior is the\npopulation by Cooper pairs of the Landau levels above the lowest one."
    },
    {
        "anchor": "Realising Type II Weyl Points in an Optical Lattice: The recent discovery of the Lorentz symmetry-violating 'Type II' Weyl\nsemimetal phase has renewed interest in the study of Weyl physics in condensed\nmatter systems. However, tuning the exceptional properties of this novel state\nhas remained a challenge. Optical lattices, created using standing laser beams,\nprovide a convenient platform to tune tunnelling parameters continuously in\ntime. In this paper, we propose a generalised two level system exhibiting type\nII Weyl points that can be realised using ultra-cold atoms in an optical\nlattice. The system is engineered using a three-dimensional lattice with\ncomplex $\\pi$ phase tunnelling amplitudes. Various unique properties of the\ntype II Weyl semimetal such as open Fermi surface, anomalous chirality and\ntopological Fermi arcs can be probed using the proposed optical lattice scheme.",
        "positive": "Gauge theory description of Rydberg atom arrays with a tunable blockade\n  radius: We discuss a Rydberg atom chain with a tunable blockade radius from the gauge\ntheoretic perspective. When the blockade radius is one lattice spacing, this\nsystem can be formulated in terms of the PXP model, and there is a\n$\\mathbb{Z}_2$ Ising phase transition known to be equivalent to a\nconfinement-deconfinement transition in a gauge theory, the lattice Schwinger\nmodel. Further increasing the blockade radius, one can add a next-nearest\nneighbor (NNN) interaction into the PXP model. We discuss the interpretation of\nNNN interaction in terms of the gauge theory and how finite NNN interaction\nalters the deconfinement behavior and propose a corresponding experimental\nprotocol. When the blockade radius reaches two lattice spacing, the model\nreduces to the PPXPP model. A novel gauge theory equivalent to the PPXPP model\nis formulated, and the phases in the two formulations are delineated. These\nresults are readily explored experimentally in Rydberg quantum simulators."
    },
    {
        "anchor": "Breakdown of Anderson localization of interacting quantum bright\n  solitons in a disorder potential: The center of mass of a bright soliton in a Bose-Einstein condensate may\nreveal Anderson localization in the presence of a weak disorder potential. We\nanalyze the effects of interactions between two bright solitons on the Anderson\nlocalization phenomenon. Perturbation calculus shows that even very weak\ninteractions modify localization properties of the system eigenstates. For\nstronger interactions, i.e. when the solitons are close to each other, the\nlocalization is totally broken. It implies that in order to experimentally\nobserve the Anderson localization effects, a single bright soliton has to be\nprepared and excitation of soliton trains must be avoided.",
        "positive": "Creating a Quantum Degenerate Gas of Stable Molecules via Weak\n  Photoassociation: Quantum degenerate molecules represent a new paradigm for fundamental studies\nand practical applications. Association of already quantum degenerate atoms\ninto molecules provides a crucial shortcut around the difficulty of cooling\nmolecules to ultracold temperatures. Whereas association can be induced with\neither laser or magnetic fields, photoassociation requires impractical laser\nintensity to overcome poor overlap between the atom pair and molecular\nwavefunctions, and experiments are currently restricted to magnetoassociation.\nHere we model realistic production of a quantum degenerate gas of stable\nmolecules via two-photon photoassociation of Bose-condensed atoms. An adiabatic\nchange of the laser frequency converts the initial atomic condensate almost\nentirely into stable molecular condensate, even for low-intensity lasers.\nResults for dipolar LiNa provide an upper bound on the necessary\nphotoassociation laser intensity for alkali-metal atoms ~30 W/cm^2, indicating\na feasible path to quantum degenerate molecules beyond magnetoassociation."
    },
    {
        "anchor": "Mean-field and stability analysis of two-dimensional flowing soft-core\n  bosons modeling a supersolid: The soft-core boson system is one of the simplest models of supersolids,\nwhich have both off-diagonal long-range order (Bose-Einstein condensation) and\ndiagonal long-range order (crystalline order). Although this model has been\nstudied from various points of view, studies of the stability of\ncurrent-flowing states are lacking. Solving the Gross-Pitaevskii and Bogoliubov\nequations, we obtain excitation spectra in superfluid, supersolid, and stripe\nphases. On the basis of the results of the excitation spectra, we present a\nstability phase diagram that shows the region of the metastable superflow\nstates for each phase.",
        "positive": "Direct absorption imaging of ultracold polar molecules: We demonstrate a scheme for direct absorption imaging of an ultracold\nground-state polar molecular gas near quantum degeneracy. A challenge in\nimaging molecules is the lack of closed optical cycling transitions. Our\ntechnique relies on photon shot-noise limited absorption imaging on a strong\nbound-bound molecular transition. We present a systematic characterization of\nthis imaging technique. Using this technique combined with time-of-flight (TOF)\nexpansion, we demonstrate the capability to determine momentum and spatial\ndistributions for the molecular gas. We anticipate that this imaging technique\nwill be a powerful tool for studying molecular quantum gases."
    },
    {
        "anchor": "Effect of optically-induced potential on the energy of trapped\n  exciton-polaritons below the condensation threshold: Exciton-polaritons (polaritons herein) offer a unique nonlinear platform for\nstudies of collective macroscopic quantum phenomena in a solid state system.\nShaping of polariton flow and polariton confinement via potential landscapes\ncreated by nonresonant optical pumping has gained considerable attention due to\nthe degree of flexibility and control offered by optically-induced potentials.\nRecently, large density-dependent energy shifts (blueshifts) exhibited by\noptically trapped polaritons at low densities, below the bosonic condensation\nthreshold, were interpreted as an evidence of strong polariton-polariton\ninteractions [Nat. Phys. 13, 870 (2017)]. In this work, we further investigate\nthe origins of these blueshifts in optically-induced circular traps and present\nevidence of significant blueshift of the polariton energy due to reshaping of\nthe optically-induced potential with laser pump power. Our work demonstrates\nstrong influence of the effective potential formed by an optically-injected\nexcitonic reservoir on the energy blueshifts observed below and up to the\npolariton condensation threshold and suggests that the observed blueshifts\narise due to interaction of polaritons with the excitonic reservoir, rather\nthan due to polariton-polariton interaction.",
        "positive": "Atomic quantum gases in periodically driven optical lattices: Time periodic forcing in the form of coherent radiation is a standard tool\nfor the coherent manipulation of small quantum systems like single atoms. In\nthe last years, periodic driving has more and more also been considered as a\nmeans for the coherent control of many-body systems. In particular, experiments\nwith ultracold quantum gases in optical lattices subjected to periodic driving\nin the lower kilohertz regime have attracted a lot of attention. Milestones\ninclude the observation of dynamic localization, the dynamic control of the\nquantum phase transition between a bosonic superfluid and a Mott insulator, as\nwell as the dynamic creation of strong artificial magnetic fields and\ntopological band structures. This article reviews these recent experiments and\ntheir theoretical description. Moreover, fundamental properties of periodically\ndriven many-body systems are discussed within the framework of Floquet theory,\nincluding heating, relaxation dynamics, anomalous topological edge states, and\nthe response to slow parameter variations."
    },
    {
        "anchor": "A Two-dimensional Algebraic Quantum Liquid Produced by an Atomic\n  Simulator of the Quantum Lifshitz Model: Bosons have a natural instinct to condense at zero temperature. It is a\nlong-standing challenge to create a high-dimensional quantum liquid that does\nnot exhibit long-range order at the ground state, as either extreme\nexperimental parameters or sophisticated designs of microscopic Hamiltonian are\nrequired for suppressing the condensation. Here, we show that ultra cold atoms\nwith synthetic spin-orbit coupling provide physicists a simple and practical\nscheme to produce a two-dimensional algebraic quantum liquid at the ground\nstate. This quantum liquid arises at a critical Lifshitz point, where the\nsingle-particle ground state shrinks to a point from a circle in the momentum\nspace, and many fundamental properties of two-dimensional bosons are changed in\nits proximity. Such an ideal simulator of the quantum Lifshitz model allows\nexperimentalists to directly visualize and explore the deconfinement transition\nof topological excitations, an intriguing phenomenon that is difficult to\naccess in other systems.",
        "positive": "Elastic scattering of a Bose-Einstein condensate at a potential\n  landscape: We investigate the elastic scattering of Bose-Einstein condensates at shallow\nperiodic and disorder potentials. We show that the collective scattering of the\nmacroscopic quantum object couples to internal degrees of freedom of the\nBose-Einstein condensate such that the Bose-Einstein condensate gets depleted.\nAs a precursor for the excitation of the Bose-Einstein condensate we observe\nwave chaos within a mean-field theory."
    },
    {
        "anchor": "Characteristic temperatures of a triplon system of dimerized quantum\n  magnets: Exploiting the analogy between ultracold atomic gases and the system of\ntriplons, we study magneto-thermodynamic properties of dimerized quantum\nmagnets in the framework of Bose -Einstein condensation (BEC). Particularly,\nintroducing the inversion (or Joule - Thomson) temperature $T_{JT}$ as the\npoint where Joule - Thomson coefficient of an isenthalpic process changes its\nsign, we show that for a simple paramagnet, this temperature is infinite, while\nfor three-dimensional (3D) dimerized quantum magnets it is finite and always\nlarger than the critical temperature $T_c$ of BEC. Below the inversion\ntemperature $T<T_{JT}$ the system of triplons may be in a liquid phase, which\nundergoes a transition into a superfluid phase at $T\\le T_c<T_{JT}$. The\ndependence of the inversion temperature on the external magnetic field $T_{JT}\n(H)$ has been calculated for quantum magnets of TlCuCl$_3$ and\nSr$_3$Cr$_2$O$_8$.",
        "positive": "Electric-field induced helium-helium resonances: The tunability of the helium-helium interaction through an external electric\nfield is investigated. For a static external field, electric-field induced\nresonances and associated electric-field induced bound states are calculated\nfor the $^4$He-$^4$He, $^3$He-$^4$He, and $^3$He-$^3$He systems. Qualitative\nagreement is found with the literature for the $^3$He-$^4$He and $^3$He-$^3$He\nsystems [E. Nielsen, D. V. Fedorov, and A. S. Jensen, Phys. Rev. Lett.\n{\\bf{82}}, 2844 (1999)]. The implications of the predicted electric-field\ninduced resonances for $^4$He-$^4$He on the wave packet dynamics, initiated by\nintense laser pulses, are investigated. Our results are expected to guide next\ngeneration experiments."
    },
    {
        "anchor": "Droplet formation in a Bose-Einstein condensate with strong\n  dipole-dipole interaction: Motivated by the recent experiment [H. Kadau \\textit{et al.},\narXiv:1508.05007 (2015)], we study roton instability and droplet formation in a\nBose-Einstein condensate of $^{164}$Dy atoms with strong magnetic dipole-dipole\ninteraction. We numerically solve the cubic-quintic Gross-Pitaevskii equation\nwith dipole-dipole interaction, and show that the three-body interaction plays\na significant role in the formation of droplet patterns. We numerically\ndemonstrate the formation of droplet patterns and crystalline structures, decay\nof droplets, and hysteresis behavior, which are in good agreement with the\nexperiment. Our numerical simulations provide the first prediction on the\nvalues of the three-body interaction in a $^{164}$Dy Bose-Einstein condensate.\nWe also predict that the droplets remain stable during the time-of-flight\nexpansion. From our results, further experiments investigating the three-body\ninteraction in dipolar quantum gases are required.",
        "positive": "Emergence of Quintet Superfluidity in the Chain of Partially Polarized\n  Spin-3/2 Ultracold Atom: The system of ultracold atoms with hyperfine spin $F=3/2$ might be unstable\nagainst the formation of quintet pairs if the interaction is attractive in the\nquintet channel. We have investigated the behavior of correlation functions in\na model including only s-wave interactions at quarter filling by large-scale\ndensity-matrix renormalization-group simulations. We show that the correlations\nof quintet pairs become quasi-long-ranged, when the system is partially\npolarized, leading to the emergence of various mixed superfluid phases in which\nBCS-like pairs carrying different magnetic moment coexist."
    },
    {
        "anchor": "Quasiparticle properties of an impurity in a Fermi gas: We report on a study of a spin-down impurity strongly coupled to a spin-up\nFermi sea (a so-called Fermi polaron) with the diagrammatic Monte-Carlo\n(DiagMC) technique. Conditions of zero temperature and three dimensions are\nconsidered for an ultracold atomic gas with resonant interactions in the\nzero-range limit. A Feynman diagrammatic series is developed for the one-body\nand two-body propagators providing information about the polaron and molecule\nchannel respectively. The DiagMC technique allows us to reach diagram orders\nthat are high enough for extrapolation to infinite order. The robustness of the\nextracted results is examined by checking various resummation techniques and by\nrunning the simulations with various choices for the propagators and vertex\nfunctions. It turns out that dressing the lines in the diagrams as much as\npossible is not always the optimal choice. We also identify classes of dominant\ndiagrams for the one-body and two-body self-energy in the region of strong\ninteraction. These dominant diagrams turn out to be the leading processes of\nthe strong-coupling limit. The quasiparticle energies and $Z$-factor are\nobtained as a function of the interaction strength. We find that the DiagMC\nresults for the molecule and polaron properties are very similar to those\nobtained with a variational ansatz. Surprisingly, this variational ansatz gives\nvery good predictions for the quasiparticle residue even when this residue is\nsignificantly smaller than one.",
        "positive": "Non classical velocity statistics in a turbulent atomic Bose Einstein\n  condensate: In a recent experiment Paoletti et al (Phys. Rev. Lett. 101, 154501, 2008)\nmonitored the motion of tracer particles in turbulent superfluid helium and\ninferred that the velocity components do not obey the Gaussian statistics\nobserved in ordinary turbulence. Motivated by their experiment, we create a\nsmall turbulent state in an atomic Bose-Einstein condensate, which enables us\nto compute directly the velocity field, and we find similar non-classical\npower-law tails. Our result thus suggests that non-Gaussian turbulent velocity\nstatistics describe a fundamental property of quantum fluids. We also track the\ndecay of the vortex tangle in the presence of the thermal cloud."
    },
    {
        "anchor": "Efficiency for preforming molecules from mixtures of light Fermi and\n  heavy Bose atoms in optical lattices: the strong-coupling-expansion method: We discuss the application of a strong-coupling expansion (perturbation\ntheory in the hopping) for studying light-Fermi-heavy-Bose (like\n$^{40}$K-$^{87}$Rb) mixtures in optical lattices. We use the strong-coupling\nmethod to evaluate the efficiency for pre-forming molecules, the entropy per\nparticle and the thermal fluctuations. We show that within the strong\ninteraction regime (and at high temperature), the strong-coupling expansion is\nan economical way to study this problem. In some cases, it remains valid even\ndown to low temperatures. Because the computational effort is minimal, the\nstrong-coupling approach allows us to work with much larger system sizes, where\nboundary effects can be eliminated, which is particularly important at higher\ntemperatures. Since the strong-coupling approach is so efficient and accurate,\nit allows one to rapidly scan through parameter space in order to optimize the\npre-forming of molecules on a lattice (by choosing the lattice depth and\ninterspecies attraction). Based on the strong-coupling calculations, we test\nthe thermometry scheme based on the fluctuation-dissipation theorem and find\nthe scheme gives accurate temperature estimation even at very low temperature.\nWe believe this approach and the calculation results will be useful in the\ndesign of the next generation of experiments, and will hopefully lead to the\nability to form dipolar matter in the quantum degenerate regime.",
        "positive": "Amplitude and phase mode in a Bose Einstein condensate: We show that starting from the Heisenberg equations of motion for Bose\nannihilation and creation operators and using an appropriate transformation, we\ncan split the Bogoliubov mode into a free particle mode and the amplitude mode.\nWe show this for both the free Bose gas as well as the Bose gas in an optical\nlattice."
    },
    {
        "anchor": "Polaron in almost ideal molecular Bose-Einstein condensate: We discuss properties of a single impurity atom immersed in the spin-$1/2$\ndilute Fermi gas with equal populations of two species in the deep\nBose-Einstein condensate (BEC) phase. In this limit, when an almost undepleted\nBEC of the tightly bound molecules of spin-up and spin-down fermions is formed,\nwe calculate the parameters of an impurity spectrum. It is justified that the\nleading-order contribution to the impurity energy, while being determined by\nthe two- and three-body scattering processes, is dominated by the former ones.",
        "positive": "The liquid state of one-dimensional Bose mixtures: a quantum Monte-Carlo\n  study: By using exact quantum Monte-Carlo methods we calculate the ground-state\nproperties of the liquid phase in one-dimensional Bose mixtures with contact\ninteractions. We find that the liquid state can be formed if the ratio of\ncoupling strengths between inter-species attractive and intraspecies repulsive\ninteractions exceeds a critical value. As a function of this ratio we determine\nthe density where the energy per particle has a minimum and the one where the\ncompressibility diverges, thereby identifying the equilibrium density and the\nspinodal point in the phase diagram of the homogeneous liquid. Furthermore, in\nthe stable liquid state, we calculate the chemical potential, the speed of\nsound, as well as structural and coherence properties such as the pair\ncorrelation function, the static structure factor and the one-body density\nmatrix, thus providing a detailed description of the bulk region in self-bound\ndroplets."
    },
    {
        "anchor": "The Gross-Pitaevskii-Poisson model for an ultracold plasma: density\n  waves and solitons: We introduce 1D and 2D models of a degenerate bosonic gas composed of ions\nwith positive and negative charges (cations and anions). The system may exist\nin the mean-field condensate state, enabling the competition of the Coulomb\ncoupling, contact repulsion, and kinetic energy of the particles, provided that\ntheir effective mass is reduced by means of a lattice potential. The model\ncombines the Gross-Pitaevskii (GP) equations for the two-component wave\nfunction of the cations and anions, coupled to the Poisson equation for the\nelectrostatic potential mediating the Coulomb coupling. The contact interaction\nin the GP system can be derived, in the Thomas-Fermi approximation, from a\nsystem of three GP equations, which includes the wave function of heavy neutral\natoms. In the system with fully repulsive contact interactions, we construct\nstable spatially periodic patterns (density waves, DWs). The transition to DWs\nis identified by analysis of the modulational instability of a uniformly mixed\nneutral state. The DW pattern, which represents the system's ground state (GS),\nis predicted by a variational approximation. In 2D, a stable pattern is\nproduced too, with a quasi-1D shape. The 1D system with contact self-attraction\nin each component produces bright solitons of three types: neutral ones, with\nfully mixed components; dipoles, with the components separated by the\ninter-species contact repulsion; and quadrupoles, with a layer of one component\nsandwiched between side lobes formed by the other. The transition from the\nneutral solitons to dipoles is accurately modeled analytically. A chart of the\nGSs of the different types (neutral solitons, dipoles, or quadrupoles) is\nproduced. Different soliton species do not coexist as stable states. Collisions\nbetween traveling solitons are elastic for dipole-dipole pairs, while\ndipole-antidipole ones merge into stable quadrupoles via multiple collisions.",
        "positive": "Resistivity of the two-dimensional Bose-Hubbard model at weak coupling: We calculate the weak-coupling resistivity of the two-dimensional Bose\nHubbard model, comparing with the more familiar fermionic case. At high\ntemperature the resistivity is linear in $T$, while in the low temperature\nnormal state it is exponentially suppressed. We explore the density dependence\nand calculate the momentum relaxation rate."
    },
    {
        "anchor": "BCS-BEC crossover in a quasi-two-dimensional Fermi superfluid: We study the crossover from the Bardeen-Cooper-Shrieffer (BCS) regime to the\nBose-Einstein-condensation (BEC) regime in a quasi-two-dimensional quantum gas\nof ultracold fermionic atoms. Using an effective two-dimensional Hamiltonian\nwith renormalized interactions between atoms and dressed molecules within a\nGaussian pair fluctuation theory, we investigate how Fermi superfluidity is\naffected by reduced dimensionality at zero temperature in a wide range of\ncrossover. We observe that the order parameter and pair size show universal\nrelations with the chemical potential on the BCS side, irrespective of\ndimensionality. However, such universal dependences break down towards the BEC\nlimit with increasing interaction strength. This results reveal the notable\neffect of reduced dimenionality on pairing physics, which can also be observed\nin the sound velocity and convexity parameter of the Goldstone mode. We compare\nour results with the latest experiments in both ${}^{6}$Li atomic gases and\nlayered nitrides LixZrNCl and find good agreements.",
        "positive": "The optimal frequency window for Floquet engineering in optical lattices: The concept of Floquet engineering is to subject a quantum system to\ntime-periodic driving in such a way that it acquires interesting novel\nproperties. It has been employed, for instance, for the realization of\nartificial magnetic fluxes in optical lattices and, typically, it is based on\ntwo approximations. First, the driving frequency is assumed to be low enough to\nsuppress resonant excitations to high-lying states above some energy gap\nseparating a low energy subspace from excited states. Second, the driving\nfrequency is still assumed to be large compared to the energy scales of the\nlow-energy subspace, so that also resonant excitations within this space are\nnegligible. Eventually, however, deviations from both approximations will lead\nto unwanted heating on a time scale $\\tau$. Using the example of a\none-dimensional system of repulsively interacting bosons in a shaken optical\nlattice, we investigate the optimal frequency (window) that maximizes $\\tau$.\nAs a main result, we find that, when increasing the lattice depth, $\\tau$\nincreases faster than the experimentally relevant time scale given by the\ntunneling time $\\hbar/J$, so that Floquet heating becomes suppressed."
    },
    {
        "anchor": "Scalar quantum kinetic theory for spin-1/2 particles: mean field theory: Starting from the Pauli Hamiltonian operator, we derive a scalar quantum\nkinetic equations for spin-1/2 systems. Here the regular Wigner two-state\nmatrix is replaced by a scalar distribution function in extended phase space.\nApart from being a formulation of principal interest, such scalar quantum\nkinetic equation makes the comparison to classical kinetic theory\nstraightforward, and lends itself naturally to currently available numerical\nVlasov and Boltzmann schemes. Moreover, while the quasi-distribution is a\nWigner function in regular phase space, it is given by a Q-function in spin\nspace. As such, nonlinear and dynamical quantum plasma problems are readily\nhandled. Moreover, the issue of gauge invariance is treated. Applications (e.g.\nultra-dense laser compressed targets and their diagnostics), possible\nextensions, and future improvements of the presented quantum statistical model\nare discussed.",
        "positive": "Nearly order from quantum disorder phenomena and its observation in a\n  bosonic quantum anomalous Hall system: We report a new many body phenomena called \" Nearly order from quantum\ndisorder phenomena\" (NOFQD). We demonstrate the NOFQD in the experimentally\nrealized weakly interacting Quantum Anomalous Hall system of spinor bosons in\nan optical lattice. We establish intrinsic connections between the\nphenomenological GL theory and the microscopic calculations on the effective\npotential. Connections with the bilayer quantum Hall system with a total\nfilling factor $ \\nu_T=1 $ are made. Some insightful analogy with $\nNAdS_2/NCFT_1 $ ( where $ N $ also means nearly ) correspondence in the context\nof Sachdev-Ye-Kitaev models are hinted. Two types of OFQDs are classified, one\nresponse trivially, another non-trivially to a small deformation to the\nHamiltonian leading to NOFQD. The NOFQD can be detected in the current cold\natom bosonic quantum anomalous Hall experiments and may also appear in many\nother frustrated systems."
    },
    {
        "anchor": "Competing valence bond and symmetry breaking Mott states of spin-3/2\n  fermions on a honeycomb lattice: We investigate magnetic properties of strongly interacting four component\nspin-3/2 ultracold fermionic atoms in the Mott insulator limit with one\nparticle per site in an optical lattice with honeycomb symmetry. In this limit,\natomic tunneling is virtual, and only the atomic spins can exchange. We find a\ncompetition between symmetry breaking and liquid like disordered phases.\nParticularly interesting are valence bond states with bond centered\nmagnetizations, situated between the ferromagnetic and conventional valence\nbond phases. In the framework of a mean-field theory, we calculate the phase\ndiagram and identify an experimentally relevant parameter region where a\nhomogeneous SU(4) symmetric Affleck-Kennedy-Lieb-Tasaki-like valence bond state\nis present.",
        "positive": "Transport of the repulsive Bose-Einstein condensate in a double-well\n  trap: interaction impact and relation to Josephson effect: Two aspects of the transport of the repulsive Bose-Einstein condensate (BEC)\nin a double-well trap are inspected: impact of the interatomic interaction and\nanalogy to the Josephson effect. The analysis employs a numerical solution of\n3D time-dependent Gross-Pitaevskii equation for a total order parameter\ncovering all the trap. The population transfer is driven by a time-dependent\nshift of a barrier separating the left and right wells. Sharp and soft profiles\nof the barrier velocity are tested. Evolution of the relevant characteristics,\ninvolving phase differences and currents, is inspected. It is shown that the\nrepulsive interaction substantially supports the transfer making it possible i)\nin a wide velocity interval and ii) three orders of magnitude faster than in\nthe ideal BEC. The transport can be approximately treated as the d.c. Josephson\neffect. A dual origin of the critical barrier velocity (break of adiabatic\nfollowing and d.c.-a.c. transition) is discussed. Following the calculations,\nrobustness of the transport (d.c.) crucially depends on the interaction and\nbarrier velocity profile. Only soft profiles which minimize undesirable dipole\noscillations are acceptable."
    },
    {
        "anchor": "Condensation temperature of strongly interacting $^{39}K$ condensates in\n  the mean-field and semi-classical approximations: We consider the effect of inter-atom interactions on the condensation\ntemperature $T_c$ of an atomic Bose-Einstein condensate. We find an analytic\nexpression of the shift in $T_c$ induced by interactions with respect the ideal\nnon-interacting case, in the mean-field and semi-classical approximations. Such\na shift is expressed in terms of the ratio $a/\\lambda_{T_c}$ between the s-wave\nscattering length $a$ and the thermal wavelength $\\lambda_{T_c}$. This result\nis used to discuss the tension between mean-field predictions and observations\nin strongly interacting $^{39}K$ condensates. It is shown that such a tension\nis solved taking into account the details of the Feshbach resonance used to\ntune $a$ in the experiments.",
        "positive": "Negative quench induced excitation dynamics for ultracold bosons in\n  one-dimensional lattices: The nonequilibrium dynamics following a quench of strongly repulsive bosonic\nensembles in one-dimensional finite lattices is investigated by employing\ninteraction quenches and/or a ramp of the lattice potential. Both sudden and\ntime-dependent quenches are analyzed in detail. For the case of interaction\nquenches we address the transition from the strong repulsive to the\nweakly-interacting regime, suppressing in this manner the heating of the\nsystem. The excitation modes such as the cradle process and the local breathing\nmode are examined via local density observables. In particular, the cradle mode\nis inherently related to the initial delocalization and, following a negative\ninteraction quench, can be excited only for incommensurate setups with filling\nlarger than unity. Alternatively, a negative quench of the lattice depth which\nfavors the spatial delocalization is used to access the cradle mode for setups\nwith filling smaller than unity. Our results shed light on possible schemes to\ncontrol the cradle and the breathing modes. Finally, employing the notion of\nfidelity we study the dynamical response of the system after a diabatic or\nadiabatic parameter modulation for short and long evolution times. The\nevolution of the system is obtained numerically using the ab-initio multi-layer\nmulti-configuration time-dependent Hartree method for bosons which permits to\nfollow non-equilibrium dynamics including the corresponding investigation of\nhigher-band effects."
    },
    {
        "anchor": "Interaction induced mergence of Dirac points in Non-Abelian optical\n  lattices: We study the properties of an ultracold Fermi gas loaded in a square optical\nlattice and subjected to an external and classical non-Abelian gauge field. We\ncalculate the energy spectrum of the system and show that the Dirac points in\nthe energy spectrum will remain quite stable under onsite interaction of\ncertain strength. Once the on-site interaction grows stronger than a critical\nvalue, the Dirac points will no longer be stable and merge into a single hybrid\npoint. This mergence implies a quantum phase transition from a semimetallic\nphase to a band insulator. The on-site interaction between ultracold fermions\ncould be conveniently controlled by Feshbach resonances in current experiments.\nWe proposed that this remarkable interaction induced mergence of Dirac points\nmay be observed in the ultracold fermi gas experiments.",
        "positive": "$\u03b7$-pairing superfluid in periodically-driven fermionic Hubbard model\n  with strong attraction: We propose a novel possibility of dynamically changing the pairing of\nsuperconductors from $s$ wave to $\\eta$ pairing (where the pairs condense at\nthe Brillouin-zone corner momenta) by driving the system with ac fields. We\nconsider a periodically-driven attractive Hubbard model in the strong-coupling\nregime, and show that the pair-hopping and pair-repulsion terms in the\neffective Hamiltonian in the Floquet formalism are drastically renormalized in\ndifferent manners between the two terms, which can change the ground states\nfrom an $s$-wave superconductivity to an $\\eta$-pairing superconductivity or a\ncharge-ordered phase. While in isolated systems such as cold atoms a simple\nquench scheme would not realize the dynamical phase transition into $\\eta$\npairing, we show that there are pathways that realize the dynamical transition,\nwhere the field amplitude is varied via a charge-ordered phase as an\nintermediate state."
    },
    {
        "anchor": "Harmonically Trapped Atoms with Spin-Orbit Coupling: We study harmonically trapped one-dimensional atoms subjected to an equal\ncombination of Rashba and Dresselhaus spin-orbit coupling induced by Raman\ntransition. We first examine the wave function and the degeneracy of the\nsingle-particle ground state, followed by a study of two weakly interacting\nbosons or fermions. For the two-particle ground state, we focus on the effects\nof the interaction on the degeneracy, the spin density profiles, and the\ndensity-density correlation functions. Finally we show how these studies help\nus to understand the many-body properties of the system.",
        "positive": "Radiofrequency spectroscopy of $^6$Li p-wave molecules: towards\n  photoemission spectroscopy of a p-wave superfluid: Understanding superfluidity with higher order partial waves is crucial for\nthe understanding of high-$T_c$ superconductivity. For the realization of a\nsuperfluid with anisotropic order parameter, spin-polarized fermionic lithium\natoms with strong p-wave interaction are the most promising candidates to date.\nWe apply rf-spectroscopy techniques that do not suffer from severe final-state\neffects \\cite{Perali08} with the goal to perform photoemission spectroscopy on\na strongly interacting p-wave Fermi gas similar to that recently applied for\ns-wave interactions \\cite{Stewart08}. Radiofrequency spectra of both quasibound\np-wave molecules and free atoms in the vicinity of the p-wave Feshbach\nresonance located at 159.15\\,G \\cite{Schunck05} are presented. The observed\nrelative tunings of the molecular and atomic signals in the spectra with\nmagnetic field confirm earlier measurements realized with direct rf-association\n\\cite{Fuchs08}. Furthermore, evidence of bound molecule production using\nadiabatic ramps is shown. A scheme to observe anisotropic superfluid gaps, the\nmost direct proof of p-wave superfluidity, with 1d-optical lattices is\nproposed."
    },
    {
        "anchor": "A trapped single ion inside a Bose-Einstein condensate: Improved control of the motional and internal quantum states of ultracold\nneutral atoms and ions has opened intriguing possibilities for quantum\nsimulation and quantum computation. Many-body effects have been explored with\nhundreds of thousands of quantum-degenerate neutral atoms and coherent\nlight-matter interfaces have been built. Systems of single or a few trapped\nions have been used to demonstrate universal quantum computing algorithms and\nto detect variations of fundamental constants in precision atomic clocks. Until\nnow, atomic quantum gases and single trapped ions have been treated separately\nin experiments. Here we investigate whether they can be advantageously combined\ninto one hybrid system, by exploring the immersion of a single trapped ion into\na Bose-Einstein condensate of neutral atoms. We demonstrate independent control\nover the two components within the hybrid system, study the fundamental\ninteraction processes and observe sympathetic cooling of the single ion by the\ncondensate. Our experiment calls for further research into the possibility of\nusing this technique for the continuous cooling of quantum computers. We also\nanticipate that it will lead to explorations of entanglement in hybrid quantum\nsystems and to fundamental studies of the decoherence of a single, locally\ncontrolled impurity particle coupled to a quantum environment.",
        "positive": "Mesoscopic dynamics of fermionic cold atoms ---Quantitative analysis of\n  transport coefficients and relaxation times---: We give a quantitative analysis of the dynamical properties of fermionic cold\natomic gases in normal phase, such as the shear viscosity, heat conductivity,\nand viscous relaxation times, using the novel microscopic expressions derived\nby the renormalization group (RG) method, where the Boltzmann equation is\nfaithfully solved to extract the hydrodynamics without recourse to any ansatz.\nIn particular, we examine the quantum statistical effects, temperature\ndependence, and scattering-length dependence of the transport coefficients and\nthe viscous relaxation times. The numerical calculation shows that the relation\n$\\tau_\\pi=\\eta/P$, which is derived in the relaxation-time approximation (RTA)\nand is used in most of the literature, turns out to be satisfied quite well,\nwhile the similar relation for the viscous relaxation time $\\tau_J$ of the heat\nconductivity is satisfied only approximately with a considerable error."
    },
    {
        "anchor": "Phases of supersolids in confined dipolar Bose-Einstein condensates: Dipolar Bose-Einstein condensates represent a powerful platform for the\nexploration of quantum many-body phenomena arising from long-range\ninteractions. A series of recent experiments has demonstrated the formation of\nsupersolid states of matter. Subsequent theoretical works have shown that\nquantum fluctuations can affect the underlying phase transition and may lead to\nthe emergence of supersolids with various lattice structures in dipolar\ncondensates. In this work we explore the signatures of such different\ngeometries in confined finite condensates. In addition to previously found\ntriangular lattices, our analysis reveals a rich spectrum of states, from\nhoneycomb patterns and ring structures to striped supersolids. By optimizing\nrelevant parameters we show that transitions between distinct supersolids\nshould be observable in current experiments.",
        "positive": "Shape oscillations in non-degenerate Bose gases - transition from the\n  collisionless to the hydrodynamic regime: We investigate collective oscillations of non-degenerate clouds of Rb-87\natoms as a function of density in an elongated magnetic trap. For the low-lying\nM=0 monopole-quadrupole shape oscillation we measure the oscillation\nfrequencies and damping rates. At the highest densities the mean-free-path is\nsmaller than the axial dimension of the sample, which corresponds to\ncollisionally hydrodynamic conditions. This allows us to cover the cross-over\nfrom the collisionless to the hydrodynamic regime. The experimental results\nshow good agreement with theory. We also analyze the influence of trap\nanharmonicities on the oscillations in relation to observed temperature\ndependencies of the dipole and quadrupole oscillation frequencies. We present\nconvenient expressions to quantify these effects."
    },
    {
        "anchor": "Mean-field equations for cigar- and disk-shaped Bose and Fermi\n  superfluids: Starting from the three-dimensional (3D) time-dependent nonlinear\nGross-Pitaevskii equation for a Bose-Einstein condensate (BEC) and density\nfunctional (DF) equation for a Fermi superfluid at the unitarity and\nBardeen-Cooper-Schrieffer (BCS) limits, we derive effective one- (1D) and\ntwo-dimensional (2D) mean-field equations, respectively, for the dynamics of a\ntrapped cigar- and disk-shaped BEC and Fermi superfluid by using the adiabatic\napproximation. The reduced 1D and 2D equations for a cigar- and disk-shaped\nFermi superfluid have simple analytic nonlinear terms and at unitarity produce\nresults for stationary properties and non-stationary breathing oscillation and\nfree expansion in excellent agreement with the solution of the full 3D\nequation.",
        "positive": "Light self-trapping in a large cloud of cold atoms: We show that, for a near-resonant propagating beam, a large cloud of cold\n87Rb atoms acts as a saturable Kerr medium and produces self-trapping of light.\nBy side fluorescence imaging we monitor the transverse size of the beam and,\ndepending on the sign of the laser detuning with respect to the atomic\ntransition, we observe self-focusing or -defocusing, with the waist remaining\nstationary for an appropriate choice of parameters. We analyze our observations\nby using numerical simulations based on a simple 2-level atom model."
    },
    {
        "anchor": "Many-Body Quantum Dynamics of a Bosonic Josephson Junction with a\n  Finite-Range Interaction: The out-of-equilibrium quantum dynamics of a Bose gas trapped in an\nasymmetric double well and interacting with a finite-range interaction has been\nstudied in real space by solving the time-dependent many-body Schr\\\"odinger\nequation numerically accurately using the multiconfigurational time-dependent\nHartree method for bosons (MCTDHB). We have focused on the weakly interacting\nlimit where the system is essentially condensed. We have examined the impact of\nthe range of the interaction on the dynamics of the system, both at the\nmean-field and many-body levels. Explicitly, we have studied the maximal and\nthe minimal values of the many-body position variance in each cycle of\noscillation, and the overall pace of its growth. We find that the range of the\ninteraction affects the dynamics of the system differently for the right well\nand the left well. We have also examined the infinite-particle limit and find\nthat even there, the impact of the range of the interaction can only be\ndescribed by a many-body theory such as MCTDHB.",
        "positive": "Classification of topological ladder models: Ladder architectures are fruitful systems to realize topological phases of\nmatter. Here we present a classification of ladder models giving rise to\ntopological insulators. We identify six different types of topological ladder\nmodels, three in the BDI symmetry class, and three in the AIII symmetry class.\nThey correspond to six distinct configurations of Wilson fermions. The six\ntypes are manifested in distinctive momentum distributions of the corresponding\ntopological edge modes. The number of Wilson fermions, their chirality and\nmass, are directly manifested in the number, momentum and height of the peaks\nof the momentum distribution of the corresponding topological edge modes. We\nidentify a canonical ladder geometry, the {\\em bowtie ladder}, from which any\nother topological ladder model can be obtained by a unitary transformation. We\nidentify, classify and list all possible topological ladder geometries,\ndetermining the parameter regimes in which each of the six types of topological\nedge modes can be realized. Our results open a route for the experimental\nrealization and detection of topological insulators in novel symmetry classes\nwith ladder architectures."
    },
    {
        "anchor": "Loop current states and their stability in small fractal lattices of\n  Bose-Einstein condensates: We consider a model of interacting Bose-Einstein condensates on small\nSierpinski gaskets. We study eigenstates which are characterised by cyclic\nsupercurrents per each triangular plaquette (\"loop\" states). For noninteracting\nsystems we find at least three classes of loop eigenmodes: standard; chaotic\nand periodic. Standard modes are those inherited from the basic three-site ring\nof condensates with phase differences locked to $2\\pi/3$. Standard modes become\nunstable in the interacting system but only when interaction exceeds a certain\ncritical value $u_c$. Chaotic modes are characterised by very different\ncircular currents per plaquette, so that the usual symmetry of loop currents is\nbroken. Circular supercurrents associated with chaotic modes become chaotic for\nany finite interaction, signalling the loss of coherence between the\ncondensates. Periodic modes are described by alternating populations and two\ndifferent phase differences. The modes are self-similar and are present in all\ngenerations of Sierpinskii gasket. When interaction is included, circular\ncurrent of such a mode becomes periodic in time with the amplitude growing\nlinearly with interaction. Above a critical interaction the amplitude saturates\nsignalling a transition to a macroscopic self-trapping state originally known\nfrom a usual Bose Josephson junction. We perform a systematic analysis of this\nnovel and rich physics.",
        "positive": "Multiple-scale analysis for resonance reflection by a one-dimensional\n  rectangular barrier in the Gross-Pitaevskii problem: We consider a quantum above-barrier reflection of a Bose-Einstein condensate\nby a one-dimensional rectangular potential barrier, or by a potential well, for\nnonlinear Schroedinger equation (Gross-Pitaevskii equation) with a small\nnonlinearity. The most interesting case is realized in resonances when the\nreflection coefficient is equal to zero for the linear Schroedinger equation.\nThen the reflection is determined only by small nonlinear term in the\nGross-Pitaevskii equation. A simple analytic expression has been obtained for\nthe reflection coefficient produced only by the nonlinearity. An analytical\ncondition is found when common action of potential barrier and nonlinearity\nproduces a zero reflection coefficient. The reflection coefficient is derived\nanalytically in the vicinity of resonances which are shifted by nonlinearity."
    },
    {
        "anchor": "Snell's Law for a vortex dipole in a Bose-Einstein condensate: A quantum vortex dipole, comprised of a closely bound pair of vortices of\nequal strength with opposite circulation, is a spatially localized travelling\nexcitation of a planar superfluid that carries linear momentum, suggesting a\npossible analogy with ray optics. We investigate numerically and analytically\nthe motion of a quantum vortex dipole incident upon a step-change in the\nbackground superfluid density of an otherwise uniform two-dimensional\nBose-Einstein condensate. Due to the conservation of fluid momentum and energy,\nthe incident and refracted angles of the dipole satisfy a relation analogous to\nSnell's law, when crossing the interface between regions of different density.\nThe predictions of the analogue Snell's law relation are confirmed for a wide\nrange of incident angles by systematic numerical simulations of the\nGross-Piteavskii equation. Near the critical angle for total internal\nreflection, we identify a regime of anomalous Snell's law behaviour where the\nfinite size of the dipole causes transient capture by the interface.\nRemarkably, despite the extra complexity of the surface interaction, the\nincoming and outgoing dipole paths obey Snell's law.",
        "positive": "Quantum quench dynamics of the Luttinger model: The dynamics of the Luttinger model after a quantum quench is studied. We\ncompute in detail one and two-point correlation functions for two types of\nquenches: from a non-interacting to an interacting Luttinger model and\nvice-versa. In the former case, the non-interacting Fermi gas features in the\nmomentum distribution and other correlation functions are destroyed as time\nevolves. In the infinite-time limit, equal-time correlations are power-laws but\nthe critical exponents are found to differ from their equilibrium values. In\nall cases, we find that these correlations are well described by a generalized\nGibbs ensemble [M. Rigol et al., Phys. Rev. Lett. 98, 050405 (2007)], which\nassigns a momentum dependent temperature to each eigenmode."
    },
    {
        "anchor": "Precise determination of the structure factor and contact in a unitary\n  Fermi gas: We present a high-precision determination of the universal contact parameter\nin a strongly interacting Fermi gas. In a trapped gas at unitarity we find the\ncontact to be $3.06 \\pm 0.08$ at a temperature of 0.08 of the Fermi temperature\nin a harmonic trap. The contact governs the high-momentum (short-range)\nproperties of these systems and this low temperature measurement provides a new\nbenchmark for the zero temperature homogeneous contact. The experimental\nmeasurement utilises Bragg spectroscopy to obtain the dynamic and static\nstructure factors of ultracold Fermi gases at high momentum in the unitarity\nand molecular Bose-Einstein condensate (BEC) regimes. We have also performed\nquantum Monte Carlo calculations of the static properties, extending from the\nweakly coupled Bardeen-Cooper-Schrieffer (BCS) regime to the strongly coupled\nBEC case, which show agreement with experiment at the level of a few percent.",
        "positive": "Leading-Order Auxiliary Field Theory of the Bose-Hubbard Model: We discuss the phase diagram of the Bose-Hubbard (BH) model in the\nleading-order auxiliary field (LOAF) theory. LOAF is a conserving\nnon-perturbative approximation that treats on equal footing the normal and\nanomalous density condensates. The mean-field solutions in LOAF correspond to\nfirst-order and second-order phase transition solutions with two critical\ntemperatures corresponding to a vanishing Bose-Einstein condensate, $T_c$, and\na vanishing diatom condensate, $T^\\star$. The \\emph{second-order} phase\ntransition solution predicts the correct order of the transition in continuum\nBose gases. For either solution, the superfluid state is tied to the presence\nof the diatom condensate related to the anomalous density in the system. In\nultracold Bose atomic gases confined on a three-dimensional lattice, the\ncritical temperature $T_c$ exhibits a quantum phase transition, where $T_c$\ngoes to zero at a finite coupling. The BH phase diagram in LOAF features a line\nof first-order transitions ending in a critical point beyond which the\ntransition is second order while approaching the quantum phase transition. We\nidentify a region where a diatom condensate is expected for temperatures higher\nthan $T_c$ and less than $T_0$, the critical temperature of the non-interacting\nsystem. The LOAF phase diagram for the BH model compares qualitatively well\nwith existing experimental data and results of \\emph{ab initio} Monte Carlo\nsimulations."
    },
    {
        "anchor": "Quantum entanglement and phase transition in a two-dimensional\n  photon-photon pair model: We propose a two-dimensional model consisting of photons and photon pairs. In\nthe model, the mixed gas of photons and photon pairs is formally equivalent to\na two-dimensional system of massive bosons with non-vanishing chemical\npotential, which implies the existence of two possible condensate phases. Using\nthe variational method, we discuss the quantum phase transition of the mixed\ngas and obtain the critical coupling line analytically. Moreover, we also find\nthat the phase transition of the photon gas can be interpreted as second\nharmonic generation. We then discuss the entanglement between photons and\nphoton pairs. Additionally, we also illustrate how the entanglement between\nphotons and photon pairs can be associated with the phase transition of the\nsystem.",
        "positive": "Long lifetime supersolid in a two-component dipolar Bose-Einstein\n  condensate: Recent studies on supersolidity in a single-component Bose-Einstein\ncondensate (BEC) have relied on the Lee-Huang-Yang (LHY) correction for\nstabilization of self-bound droplets, which however involves a high density\ninside the droplets, limiting the lifetime of the supersolid. Here we propose a\ntwo-component mixture of dipolar and nondipolar BECs, such as an\n$^{166}$Er-$^{87}$Rb mixture, to create and stabilize a supersolid without the\nLHY correction, which can suppress the atomic loss and may allow observation of\nthe long-time dynamics of the supersolid. In such a system, supersolidity can\nbe controlled by the difference in the trap centers between the two components."
    },
    {
        "anchor": "Theory of Fermionic superfluid with SU(2)xSU(6) symmetry: We study theoretically interspecies Cooper pairing in a fermionic system with\nSU(2)xSU(6) sym- metry. We show that, with suitable unitary transformations,\nthe order parameter for the ground state can be reduced to only two\nnon-vanishing complex components. The ground state has a large degeneracy. We\nfind that while some Goldstone modes have linear dispersions, others are\nquadratic at low frequencies. We compare our results with the case of SU(N).",
        "positive": "Topological Rice-Mele model in an emergent lattice: Exact\n  diagonalization approach: Using exact diagonalization methods we study possible phases in a one\ndimensional model of two differently populated fermionic species in a\nperiodically driven optical lattice. The shaking amplitude and frequency are\nchosen to resonantly drive $s-p$ transition while minimizing the standard\nintraband tunnelings. We numerically verify that in the vicinity of vanishing\nintraband tunnelings the system, for an appropriate filling, shows an emergent\ndensity wave configuration of composites. The majority fermions moving in such\na lattice mimic the celebrated Rice-Mele model. Far away from that region\nstructure changes to clustered phase, with intermediate phase abundantly\npopulated by defects of the density wave. These defects lead to loclaized modes\ncarrying fractional particle charge. The results obtained are compared with\nearlier mean field approximation predictions."
    },
    {
        "anchor": "FORTRESS: FORTRAN programs for solving coupled Gross-Pitaevskii\n  equations for spin-orbit coupled spin-1 Bose-Einstein condensate: Here, we present simple and efficient numerical scheme to study static and\ndynamic properties of spin-1 Bose-Einstein condensates (BECs) with spin-orbit\n(SO) coupling by solving three coupled Gross-Pitaevskii equations (CGPEs) in\nthree-, quasi-two and quasi-one dimensional systems. We provide a set of three\ncodes developed in FORTRAN 90/95 programming language with user defined '{\\em\noption}' of imaginary and real-time propagation. We present the numerical\nresults for energy, chemical potentials, and component densities for the ground\nstate and compare with the available results from the literature. The results\nare presented for both the ferromagnetic and antiferromagnetic spin-1 BECs with\nand without SO coupling. To improve the computational speed, all the codes have\nthe option of OpenMP parallelization. We have also presented the results for\nspeedup and efficiency of OpenMP parallelization for the three codes with both\nimaginary and real-time propagation.",
        "positive": "Type-II Weyl Points in Three-Dimensional Cold Atom Optical Lattices: Topological Lifshitz phase transition characterizes an abrupt change of the\ntopology of the Fermi surface through a continuous deformation of parameters.\nRecently, Lifshitz transition has been predicted to separate two types of Weyl\npoints: type-I and type-II (or called structured Weyl points), which has\nattracted considerable attention in various fields. Although recent\nexperimental investigation has seen a rapid progress on type-II Weyl points, it\nstill remains a significant challenge to observe their characteristic Lifshitz\ntransition. Here, we propose a scheme to realize both type-I and type-II Weyl\npoints in three-dimensional ultracold atomic gases by introducing an\nexperimentally feasible configuration based on current spin-orbit coupling\ntechnology. In the resultant Hamiltonian, we find three degenerate points: two\nWeyl points carrying a Chern number $-1$ and a four-fold degenerate point\ncarrying a Chern number $2$. Remarkably, by continuous tuning of a convenient\nexperimental knob, all these degenerate points can transition from type-I to\ntype-II, thereby providing an ideal platform to study different types of Weyl\npoints and directly probe their Lifshitz phase transition."
    },
    {
        "anchor": "Controlling directed atomic motion and second-order tunneling of a\n  spin-orbit-coupled atom in optical lattices: We theoretically explore the tunneling dynamics for the tight-binding (TB)\nmodel of a single spin-orbit-coupled atom trapped in an optical lattice\nsubjected to lattice shaking and to time-periodic Zeeman field. By means of\nanalytical and numerical methods, we demonstrate that the spin-orbit (SO)\ncoupling adds some new results to the tunneling dynamics in both multiphoton\nresonance and far-off-resonance parameter regimes. When the driving frequency\nis resonant with the static Zeeman field (multi-photon resonances), we obtain\nan unexpected new dynamical localization (DL) phenomenon where the single\nSO-coupled atom is restricted to making perfect two-site Rabi oscillation\naccompanied by spin flipping.By using the unconventional DL phenomenon, we are\nable to generate a ratchetlike effect which enables directed atomic motion\ntowards different directions and accompanies periodic spin-flipping under the\naction of SO coupling. For the far-off-resonance case, we show that by\nsuppressing the usual inter-site tunneling alone, it is possible to realize a\ntype of spin-conserving second-order tunneling between next-nearest-neighboring\nsites, which is not accessible in the conventional lattice system without SO\ncoupling. We also show that simultaneous controls of the usual inter-site\ntunneling and the SO-coupling-related second-order-tunneling are necessary for\nquasienergies flatness (collapse) and completely frozen dynamics to exist.\nThese results may be relevant to potential applications such as spin-based\nquantum information processing and design of novel spintronics devices.",
        "positive": "Doublon dynamics and polar molecule production in an optical lattice: Ultracold polar molecules provide an excellent platform to study quantum\nmany-body spin dynamics, which has become accessible in the recently realized\nlow entropy quantum gas of polar molecules in an optical lattice. To obtain a\ndetailed understanding for the molecular formation process in the lattice, we\nprepare a density distribution where lattice sites are either empty or occupied\nby a doublon composed of a bosonic atom interacting with a fermionic atom. By\nletting this disordered, out-of-equilibrium system evolve from a well-defined\ninitial condition, we observe clear effects on pairing that arise from\ninter-species interactions, a higher partial wave Feshbach resonance, and\nexcited Bloch-band population. When only the lighter fermions are allowed to\ntunnel in the three-dimensional (3D) lattice, the system dynamics can be well\ndescribed by theory. However, in a regime where both fermions and bosons can\ntunnel, we encounter correlated dynamics that is beyond the current capability\nof numerical simulations. Furthermore, we show that we can probe the\nmicroscopic distribution of the atomic gases in the lattice by measuring the\ninelastic loss of doublons. These techniques realize tools that are generically\napplicable to heteronuclear diatomic systems in optical lattices and can shed\nlight on molecule production as well as dynamics of a Bose-Fermi mixture."
    },
    {
        "anchor": "Strong-Coupling Effects and Single-Particle Properties in an Ultracold\n  Fermi Gas with Mass Imbalance: We investigate single-particle properties of a strongly interacting ultracold\nFermi gas with mass imbalance. Using an extended $T$-matrix theory, we\ncalculate the density of states, as well as the single-particle spectral\nweight, in the unitarity limit above the superfluid phase transition\ntemperature $T_{\\rm c}$. We show that the momentum regions where pairing\nfluctuations strongly affect single-particle excitations are different between\nlight fermions and heavy fermions, reflecting the difference of the Pauli\nblocking effects between them. In addition, we obtain different pseudogap\nphenomena associated with pairing fluctuations in between the two components.\nSince the realization of a mass-imbalanced superfluid Fermi gas is an important\nchallenge in this field, our results would contribute to the understanding of\nphysical properties of the hetero-pairing state.",
        "positive": "Anisotropic 2D diffusive expansion of ultra-cold atoms in a disordered\n  potential: We study the horizontal expansion of vertically confined ultra-cold atoms in\nthe presence of disorder. Vertical confinement allows us to realize a situation\nwith a few coupled harmonic oscillator quantum states. The disordered potential\nis created by an optical speckle at an angle of 30{\\deg} with respect to the\nhorizontal plane, resulting in an effective anisotropy of the correlation\nlengths of a factor of 2 in that plane. We observe diffusion leading to\nnon-Gaussian density profiles. Diffusion coefficients, extracted from the\nexperimental results, show anisotropy and strong energy dependence, in\nagreement with numerical calculations."
    },
    {
        "anchor": "Models for a multimode bosonic tunneling junction: We discuss the relaxation dynamics for a bosonic tunneling junction with two\nmodes in the central potential well. We use a master equation description for\nultracold bosons tunneling in the presence of noise and incoherent coupling\nprocesses into the two central modes. Whilst we cannot quantitatively reproduce\nthe experimental data of the setup reported in [Phys. Rev. Lett. {\\bf 115},\n050601 (2015)], we find a reasonable qualitative agreement of the refilling\nprocess of the initially depleted central site. Our results may pave the way\nfor the control of bosonic tunneling junctions by the simultaneous presence of\ndecoherence processes and atom-atom interaction.",
        "positive": "Harmonic trap resonance enhanced synthetic atomic spin-orbit coupling: Spin-orbit coupling (SOC) plays an essential role in many exotic and\ninteresting phenomena in condensed matter physics. In neutral-atom-based\nquantum simulations, synthetic SOC constitutes a key enabling element. The\nstrength of SOC realized so far is limited by various reasons or constraints.\nThis work reports tunable SOC synthesized with a gradient magnetic field (GMF)\nfor atoms in a harmonic trap. Nearly ten-fold enhancement is observed when the\nGMF is modulated near the harmonic-trap resonance in comparison with free-space\natoms. A theory is developed that well explains the experimental results. Our\nwork offers a clear physical insight into and analytical understanding of how\nto tune the strength of atomic SOC synthesized with GMF using harmonic trap\nresonance."
    },
    {
        "anchor": "Tunneling control in an integrable model for Bose-Einstein Condensate in\n  a triple well potential: In this work we show the simplest and integrable model for Bose-Einstein\ncondensates loaded in a triple well potential where the tunneling between two\nwells can be controlled by the other well showing a behavior similar to an\nelectronic field effect transistor. Using a classical analysis, the Hamilton's\nequation are obtained, a threshold indicating a discontinuous phase transition\nis presented and the classical dynamics is computed. Then, the quantum dynamics\nis investigated using direct diagonalisation. We find well agreement in both\nthese analysis. Based on our results, the switching scheme for tunneling is\nshown and the experimental feasibility is discussed.",
        "positive": "Observation of the universal jump across the\n  Berezinskii-Kosterlitz-Thouless transition in two-dimensional Bose gases: The physics in two-dimensional (2D) systems is very different from what we\nobserve in three-dimensional (3D) systems. Thermal fluctuations in 2D systems\nare enhanced, and they prevent the conventional Bose-Einstein condensation\n(BEC) at non-zero temperatures by destroying the long-range order. However, a\nphase transition to a superfluid phase is still expected to occur in a 2D\nsystem along with an emergence of a quasi-long-range order, explained by the\nBerezinskii-Kosterlitz-Thouless (BKT) mechanism. Within the BKT mechanism, a\nuniversal jump of the superfluid density in a 2D Bosonic system was\ntheoretically predicted by Nelson and Kosterlitz, and was first observed in 2D\n\\textsuperscript{4}He films by Bishop and Reppy. Recent experiments in trapped\nultracold 2D Bose gas systems have shown signatures of the BKT transition, and\nits superfluidity. However, the universal jump in the superfluid density was\nnot observed in these systems. Here we report the first observation of the\nuniversal jump in the superfluid density using an optically trapped ultracold\n2D Bose gas. The measured superfluid phase space density at the BKT transition\nagrees well with the predicted value within our measurement uncertainty.\nAdditionally, we measure the phase fluctuations in our density profiles to show\nthat the BKT transition occurs first, followed by the BEC transition."
    },
    {
        "anchor": "Dipolar fermions in a two-dimensional lattice at non-zero temperature: We examine density ordered and superfluid phases of fermionic dipoles in a\ntwo-dimensional square lattice at non-zero temperature. The critical\ntemperature of the density ordered phases is determined and is shown to be\nproportional to the coupling strength for strong coupling. We calculate the\nsuperfluid fraction and demonstrate that the Berezinskii-Kosterlitz-Thouless\ntransition temperature of the superfluid phase is proportional to the hopping\nmatrix element in the strong coupling limit. We finally analyze the effects of\nan external harmonic trapping potential.",
        "positive": "Cross-over to quasi-condensation: mean-field theories and beyond: We analyze the cross-over of a homogeneous one-dimensional Bose gas from the\nideal gas into the dense quasi-condensate phase. We review a number of\nmean-field theories, perturbative or self-consistent, and provide accurate\nevaluations of equation of state, density fluctuations, and correlation\nfunctions. A smooth crossover is reproduced by classical-field simulations\nbased on the stochastic Gross-Pitaevskii equation, and the Yang-Yang solution\nto the one-dimensional Bose gas."
    },
    {
        "anchor": "Luttinger theorem and imbalanced Fermi systems: The proof of the Luttinger theorem, which was originally given for a normal\nFermi liquid with equal spin populations formally described by the exact\nmany-body theory at zero temperature, is here extended to an approximate theory\ngiven in terms of a \"conserving\" approximation also with spin imbalanced\npopulations. The need for this extended proof, whose underlying assumptions are\nhere spelled out in detail, stems from the recent interest in superfluid\ntrapped Fermi atoms with attractive inter-particle interaction, for which the\ndifference between two spin populations can be made large enough that\nsuperfluidity is destroyed and the system remains normal even at zero\ntemperature. In this context, we will demonstrate the validity of the Luttinger\ntheorem separately for the two spin populations for any \"$\\Phi$-derivable\"\napproximation, and illustrate it in particular for the self-consistent\n$t$-matrix approximation.",
        "positive": "Identifying insulating states of ultra cold atoms with cavity\n  transmission spectrum: In this paper, we consider the transmission characteristics of an optical\ncavity loaded with ultra cold atoms in a one dimensional optical lattice at\nabsolute zero temperature. In particular, we consider the situation when the\nmany body quantum state of the ultra cold atoms is an insulating state with\nfixed number of atoms at each site, which can be either density wave (DW) or\nMott insulator (MI) phase, each showing different type of discrete lattice\ntranslational symmetry. We provide a general framework of understanding the\ntransmission spectrum from a single and two cavities/modes loaded with such\ninsulating phases. Further, we also discuss how such a transmission spectrum\nchanges when these insulating phases make a cross over to the superfluid (SF)\nphase with the changing depth of the optical lattice potential."
    },
    {
        "anchor": "Probing few-particle Laughlin states of photons via correlation\n  measurements: We propose methods to create and observe Laughlin-like states of photons in a\nstrongly nonlinear optical cavity. Such states of strongly interacting photons\ncan be prepared by pumping the cavity with a Laguerre-Gauss beam, which has a\nwell-defined orbital angular momentum per photon. The Laughlin-like states\nappear as sharp resonances in the particle-number-resolved transmission\nspectrum. Power spectrum and second-order correlation function measurements\nyield unambiguous signatures of these few-particle strongly-correlated states.",
        "positive": "Emergent criticality and universality class of the finite temperature\n  charge density wave transition in lattice Bose gases within optical cavities: We investigate the finite temperature charge density wave (CDW) transition of\nlattice Bose gases within optical cavities in the deep Mott-insulator limit. We\nfind a new critical regime emerges at a temperature around one-half of the\non-site interaction energy, where the first order CDW transition at low\ntemperatures terminates at a critical point and changes to a second order one.\nBy directly calculating the critical exponents and constructing the effective\ntheory in the corresponding critical regime, we find the emergent criticality\nbelongs to the five-dimensional Ising universality class. Direct experimental\nobservation of the emergent criticality can be readily performed by current\nexperimental set-ups operated in the temperature regime around half the on-site\ninteraction energy."
    },
    {
        "anchor": "Self-consistent tight-binding description of Dirac points moving and\n  merging in two dimensional optical lattices: We present an accurate ab initio tight-binding model, capable of describing\nthe dynamics of Dirac points in tunable honeycomb optical lattices following a\nrecent experimental realization [L. Tarruell et al., Nature 483, 302 (2012)].\nOur scheme is based on first-principle maximally localized Wannier functions\nfor composite bands. The tunneling coefficients are calculated for different\nlattice configurations, and the spectrum properties are well reproduced with\nhigh accuracy. In particular, we show which tight binding description is needed\nin order to accurately reproduce the position of Dirac points and the\ndispersion law close to their merging, for different laser intensities.",
        "positive": "Universal shock-wave propagation in one-dimensional Bose fluids: We propose a protocol for creating moving, robust dispersive shock waves in\ninteracting one-dimensional Bose fluids. The fluid is prepared in a moving\nstate by phase imprinting and sent against the walls of a box trap. We\ndemonstrate that the thus formed shock wave oscillates for several periods and\nis robust against thermal fluctuations. We show that this large amplitude\ndynamics is universal across the whole spectrum of the interatomic interaction\nstrength, from weak to strong interactions, and it is fully controlled by the\nsound velocity inside the fluid. Our work provides a generalization of the\ndispersive-shock-wave paradigm to the many-body regime. The shock waves we\npropose are within reach for ultracold atom experiments."
    },
    {
        "anchor": "Thermodynamics and spin-charge separation of one-dimensional strongly\n  repulsive three-component fermions: The low temperature thermodynamics of one-dimensional strongly repulsive\nSU(3) fermions in the presence of a magnetic field is investigated via the\nYang-Yang thermodynamic Bethe ansatz method. The analytical free energy and\nmagnetic properties of the model at low temperatures in a weak magnetic field\nare derived via the Wiener-Hopf method. It is shown that the low energy physics\ncan be described by spin-charge separated conformal field theories of an\neffective Tomonaga-Luttinger liquid and an antiferromagnetic SU(3) Heisenberg\nspin chain. Beyond the Tomonaga-Luttinger liquid regime, the equation of state\nis given in terms of the polylog function for a weak external field. The\nresults obtained are essential for further study of quantum criticality in\nstrongly repulsive three-component fermions.",
        "positive": "Self-bound supersolid stripe phase in binary Bose-Einstein condensates: Supersolidity - a coexistence of superfluidity and crystalline or amorphous\ndensity variations - has been vividly debated ever since its conjecture. While\nthe initial focus was on helium-4, recent experiments uncovered supersolidity\nin ultra-cold dipolar quantum gases. Here, we propose a new self-bound\nsupersolid phase in a binary mixture of Bose gases with short-range\ninteractions, making use of the non-trivial properties of spin-orbit coupling.\nWe find that a first-order phase transition from a self-bound supersolid stripe\nphase to a zero-minimum droplet state of the Bose gas occurs as a function of\nthe Rabi coupling strength. These phases are characterized using the momentum\ndistribution, the transverse spin polarization and the superfluid fraction. The\ncritical point of the transition is estimated in an analytical framework. The\npredicted density-modulated supersolid stripe and zero-minimum droplet phase\nshould be experimentally observable in a binary mixture of $^{39}$K with\nspin-orbit coupling."
    },
    {
        "anchor": "Driving Dipolar Fermions into the Quantum Hall Regime by Spin-Flip\n  Induced Insertion of Angular Momentum: A new method to drive a system of neutral dipolar fermions into the lowest\nLandau level regime is proposed. By employing adiabatic spin-flip processes in\ncombination with a diabatic transfer, the fermions are pumped to higher orbital\nangular momentum states in a repeated scheme that allows for the precise\ncontrol over the final angular momentum. A simple analytical model is derived\nto quantify the transfer and compare the approach to rapidly rotating systems.\nNumerical simulations of the transfer process have been performed for small,\ninteracting systems.",
        "positive": "Quantum phase-space analysis of population equilibration in multi-well\n  ultracold atomic systems: We examine the medium time quantum dynamics and population equilibration of\ntwo, three and four-well Bose-Hubbard models using stochastic integration in\nthe truncated Wigner phase-space representation. We find that all three systems\nwill enter at least a temporary state of equilibrium, with the details\ndepending on both the classical initial conditions and the initial quantum\nstatistics. We find that classical integrability is not necessarily a good\nguide as to whether equilibration will occur. We construct an effective\nsingle-particle reduced density matrix for each of the systems, using the\nexpectation values of operator moments, and use this to calculate an effective\nentropy. Knowing the expected maximum values of this entropy for each system,\nwe are able to quantify the different approaches to equilibrium."
    },
    {
        "anchor": "Simulating cosmological supercooling with a cold atom system II: We perform an analysis of the supercooled state in an analogue of an early\nuniverse phase transition based on a one dimensional, two-component Bose gas\nwith time-dependent interactions. We demonstrate that the system behaves in the\nsame way as a thermal, relativistic Bose gas undergoing a first order phase\ntransition. We propose a way to prepare the state of the system in the\nmetastable phase as an analogue to supercooling in the early universe. While we\nshow that parametric resonances in the system can be suppressed by thermal\ndamping, we find that the theoretically estimated thermal damping in our model\nis too weak to suppress the resonances for realistic experimental parameters.\nHowever, we propose that experiments to investigate the effective damping rate\nin experiments would be worthwhile.",
        "positive": "Quantum gray solitons in confining potentials: We define and study hole-like excitations (the Lieb II mode) in a weakly\ninteracting Bose liquid subject to external confinement. These excitations are\nobtained by semiclassical quantization of gray solitons propagating on top of a\nThomas-Fermi background. Radiation of phonons by an accelerated gray soliton\nleads to a finite life-time for the trapped Lieb II mode. It is shown that, for\na large number of trapped atoms, most of the Lieb II levels can be\nexperimentally resolved."
    },
    {
        "anchor": "Bosonic Double Ring Lattice Under Artificial Gauge Fields: We consider a system of weakly interacting bosons confined on a planar double\nring lattice subjected to two artificial gauge fields. We determine its ground\nstate by solving coupled discrete non-linear Schr\\\"odinger equations at mean\nfield level. At varying inter-ring tunnel coupling, flux and interactions we\nidentify the vortex, Meissner and biased-ladder phases also predicted for a\nbosonic linear ladder by a variational Ansatz. We also find peculiar features\nassociated to the ring geometry, in particular parity effects in the number of\nvortices, and the appearance of a single vortex in the Meissner phase. We show\nthat the persistent currents on the rings carry precise information on the\nvarious phases. Finally, we propose a way of observing the Meissner and vortex\nphases via spiral interferogram techniques.",
        "positive": "Soliton Dimer-soliton scattering in coupled Quasi-one-dimensional\n  Dipolar Bose-Einstein Condensates: We discuss scattering between a bright soliton and a soliton dimer in coupled\nquasi-one-dimensional dipolar Bose-Einstein condensates. The dimer is formed by\neach soliton from both tubes due to the attractive inter-layer dipole-dipole\ninteraction. The dipoles within each tube repel each other, and a stable,\nbright soliton is stabilized via attractive contact interactions. In general,\nthe scattering is inelastic, transferring the kinetic energy into internal\nmodes of both soliton dimer and single soliton. Our studies reveal rich\nscattering scenarios, including dimer-soliton repulsion at small initial\nvelocities, exchange of atoms between dimer and single soliton and soliton\nfusion at intermediate velocities. Interestingly, for some particular initial\nvelocities, the dimer-soliton scattering results in a state of two dimers. At\nlarge initial velocities, the scattering is elastic as expected."
    },
    {
        "anchor": "Stability of High-Density Two-Dimensional Excitons against a Mott\n  Transition in High Magnetic Fields Probed by Coherent Terahertz Spectroscopy: We have performed time-resolved terahertz absorption measurements on\nphotoexcited electron-hole pairs in undoped GaAs quantum wells in magnetic\nfields. We probed both unbound- and bound-carrier responses via cyclotron\nresonance and intraexciton resonance, respectively. The stability of excitons,\nmonitored as the pair density was systematically increased, was found to\ndramatically increase with increasing magnetic field. Specifically, the\n1$s$-2$p_-$ intraexciton transition at 9 T persisted up to the highest density,\nwhereas the 1$s$-2$p$ feature at 0 T was quickly replaced by a free-carrier\nDrude response. Interestingly, at 9 T, the 1$s$-2$p_-$ peak was replaced by\nfree-hole cyclotron resonance at high temperatures, indicating that 2D\nmagnetoexcitons do dissociate under thermal excitation, even though they are\nstable against a density-driven Mott transition.",
        "positive": "Multi-stability in an optomechanical system with two-component\n  Bose-Einstein condensate: We investigate a system consisting of a two-component Bose-Einstein\ncondensate interacting dispersively with a Fabry-Perot optical cavity where the\ntwo components of the condensate are resonantly coupled to each other by\nanother classical field. The key feature of this system is that the atomic\nmotional degrees of freedom and the internal pseudo-spin degrees of freedom are\ncoupled to the cavity field simultaneously, hence an effective spin-orbital\ncoupling within the condensate is induced by the cavity. The interplay among\nthe atomic center- of-mass motion, the atomic collective spin and the cavity\nfield leads to a strong nonlinearity, resulting in multi- stable behavior in\nboth matter wave and light wave at the few-photon level."
    },
    {
        "anchor": "Fermi polaron revisited: polaron-molecule transition and coexistence: We revisit the polaron-molecule transition in three-dimensional(3D) fermion\nsystems using the well-established variational approach. The molecule is found\nto be intrinsically unstable against lowest-order particle-hole excitations,\nand it can only approximate the ground state of impurity system with finite\ntotal momentum in the strong coupling regime. The polaron-molecule transition\ncan therefore be reinterpreted as a first-order transition between single\nimpurity systems with different total momenta. Within certain interaction\nwindow near their transition, both states appear as local minima in the\ndispersion curve, indicating they can coexist in a realistic system. We have\nfurther confirmed the polaron-molecule coexistence in the presence of a finite\nimpurity concentration and at low temperature, which directly leads to a smooth\npolaron-molecule transition as observed in recent experiments of 3D ultracold\nFermi gases. Our results have provided an unambiguous physical picture for the\ncompetition and conversion between polaron and molecule, and also shed light on\nFermi polaron properties in low dimensions.",
        "positive": "Anomalous loss behavior in a single-component Fermi gas close to a\n  $p$-Wave Feshbach resonance: We theoretically investigate three-body losses in a single-component Fermi\ngas near a $p$-wave Feshbach resonance in the interacting, non-unitary regime.\nWe extend the cascade model introduced by Waseem \\textit{et al.} [M. Waseem, J.\nYoshida, T. Saito, and T. Mukaiyama, Phys. Rev. A \\textbf{99}, 052704 (2019)]\nto describe the elastic and inelastic collision processes. We find that the\nloss behavior exhibits a $n^3$ and an anomalous $n^2$ density dependence for a\nratio of elastic-to-inelastic collision rate larger and smaller than 1,\nrespectively. The corresponding evolutions of the energy distribution show\ncollisional cooling or evolution toward low-energetic non-thermalized steady\nstates, respectively. These findings are particularly relevant for\nunderstanding atom loss and energetic evolution of ultracold gases of fermionic\nlithium atoms in their ground state."
    },
    {
        "anchor": "Extracting the Chern number from the dynamics of a Fermi gas:\n  Implementing a quantum Hall bar for cold atoms: We propose a scheme to measure the quantized Hall conductivity of an\nultracold Fermi gas initially prepared in a topological (Chern) insulating\nphase, and driven by a constant force. We show that the time evolution of the\ncenter of mass, after releasing the cloud, provides a direct and clear\nsignature of the topologically invariant Chern number. We discuss the validity\nof this scheme, highlighting the importance of driving the system with a\nsufficiently strong force to displace the cloud over measurable distances while\navoiding band-mixing effects. The unusual shapes of the driven atomic cloud are\nqualitatively discussed in terms of a semi-classical approach.",
        "positive": "Spin drag and fast response in a quantum mixture of atomic gases: By applying a sudden perturbation to one of the components of a mixture of\ntwo quantum fluids, we explore the effect on the motion of the second component\non a short time scale. By implementing perturbation theory, we prove that for\nshort times the response of the second component is fixed by the energy\nweighted moment of the crossed dynamic structure factor (crossed f-sum rule).\nWe also show that by properly monitoring the time duration of the perturbation\nit is possible to identify peculiar fast spin drag regimes, which are sensitive\nto the interaction effects in the Hamiltonian. Special focus is given to the\ncase of coherently coupled Bose-Einstein condensates, interacting Bose mixtures\nexhibiting the Andreev-Bashkin effect, normal Fermi liquids and the polaron\nproblem. The relevant excitations of the system contributing to the spin drag\neffect are identified and the contribution of the low frequency gapless\nexcitations to the f-sum rule in the density and spin channels is explicitly\ncalculated employing the proper macroscopic dynamic theories. Both spatially\nperiodic and Galilean boost perturbations are considered."
    },
    {
        "anchor": "Periodic driving control of Raman-induced spin-orbit coupling in\n  Bose-Einstein condensates: the heating mechanisms: We focus on a technique recently implemented for controlling the magnitude of\nsynthetic spin-orbit coupling (SOC) in ultra-cold atoms in the Raman-coupling\nscenario. This technique uses a periodic modulation of the Raman-coupling\namplitude to tune the SOC. Specifically, it has been shown that the effect of a\nhigh-frequency sinusoidal modulation of the Raman-laser intensity can be\nincorporated into the undriven Hamiltonian via effective parameters, whose\nadiabatic variation can then be used to steer the SOC. Here, we characterize\nthe heating mechanisms that can be relevant to this method. We identify the\nmain mechanism responsible for the heating observed in the experiments as\nbasically rooted in driving-induced transfer of population to excited states.\nCharacteristics of that process determined by the harmonic trapping, the decay\nof the excited states, and the technique used for preparing the system are\ndiscussed. Additional heating, rooted in departures from adiabaticity in the\nvariation of the effective parameters, is also described. Our analytical study\nprovides some clues that may be useful in the design of strategies for curbing\nthe effects of heating on the efficiency of the control methods.",
        "positive": "Extending rotational coherence of interacting polar molecules in a\n  spin-decoupled magic trap: Superpositions of rotational states in polar molecules induce strong,\nlong-range dipolar interactions. Here we extend the rotational coherence by\nnearly one order of magnitude to 8.7(6) ms in a dilute gas of polar\n$^{23}$Na$^{40}$K molecules in an optical trap. We demonstrate spin-decoupled\nmagic trapping, which cancels first-order and reduces second-order differential\nlight shifts. The latter is achieved with a dc electric field that decouples\nnuclear spin, rotation and trapping light field. We observe density-dependent\ncoherence times, which can be explained by dipolar interactions in the bulk\ngas."
    },
    {
        "anchor": "Radiofrequency spectroscopy of a linear array of Bose-Einstein\n  condensates in a magnetic lattice: We report site-resolved radiofrequency spectroscopy measurements of\nBose-Einstein condensates of 87Rb atoms in about 100 sites of a one-dimensional\n10 micron-period magnetic lattice produced by a grooved magnetic film plus bias\nfields. Site-to-site variations of the trap bottom, atom temperature,\ncondensate fraction and chemical potential indicate that the magnetic lattice\nis remarkably uniform, with variations in trap bottoms of only +/- 0.4 mG. At\nthe lowest trap frequencies (radial and axial frequencies 1.5 kHz and 260 Hz,\nrespectively), temperatures down to 0.16 microkelvin are achieved in the\nmagnetic lattice and at the smallest trap depths (50 kHz) condensate fractions\nup to 80% are observed. With increasing radial trap frequency (up to 20 kHz, or\naspect ratio up to about 80) large condensate fractions persist and the highly\nelongated clouds approach the quasi-1D Bose gas regime. The temperature\nestimated from analysis of the spectra is found to increase by a factor of\nabout five which may be due to suppression of rethermalising collisions in the\nquasi-1D Bose gas. Measurements for different holding times in the lattice\nindicate a decay of the atom number with a half-life of about 0.9 s due to\nthree-body losses and the appearance of a high temperature (about 1.5\nmicrokelvin) component which is attributed to atoms that have acquired energy\nthrough collisions with energetic three-body decay products.",
        "positive": "A finite temperature study of ideal quantum gases in the presence of one\n  dimensional quasi-periodic potential: We study the thermodynamics of ideal Bose gas as well as the transport\nproperties of non interacting bosons and fermions in a one dimensional\nquasi-periodic potential, namely Aubry-Andr\\'e (AA) model at finite\ntemperature. For bosons in finite size systems, the effect of quasi-periodic\npotential on the crossover phenomena corresponding to Bose-Einstein\ncondensation (BEC), superfluidity and localization phenomena at finite\ntemperatures are investigated. From the ground state number fluctuation we\ncalculate the crossover temperature of BEC which exhibits a non monotonic\nbehavior with the strength of AA potential and vanishes at the self-dual\ncritical point following power law. Appropriate rescaling of the crossover\ntemperatures reveals universal behavior which is studied for different\nquasi-periodicity of the AA model. Finally, we study the temperature and flux\ndependence of the persistent current of fermions in presence of a\nquasi-periodic potential to identify the localization at the Fermi energy from\nthe decay of the current."
    },
    {
        "anchor": "Separation of Timescales in a Quantum Newton's Cradle: For strongly repulsive bosons in one dimension, we provide detailed modeling\nof the Bragg pulse used in quantum Newton's cradle-like settings or in Bragg\nspectroscopy experiments. By employing the Fermi-Bose mapping for a finite\nharmonically trapped gas and the Quench Action approach for a thermodynamic\nsystem on a ring, we reconstruct the exact post-pulse many-body time evolution\nof Lieb-Liniger gases in the Tonks-Girardeau limit, together with their\nchanging local density profile and momentum distribution. Our results display a\nclear separation of timescales between rapid and trap-insensitive relaxation\nimmediately after the pulse, followed by slow in-trap periodic behaviour.",
        "positive": "Finite-size effects in a bosonic Josephson junction: We investigate finite-size quantum effects in the dynamics of $N$ bosonic\nparticles which are tunneling between two sites adopting the two-site\nBose-Hubbard model. By using time-dependent atomic coherent states (ACS) we\nextend the standard mean-field equations of this bosonic Josephson junction,\nwhich are based on time-dependent Glauber coherent states. In this way we find\n$1/N$ corrections to familiar mean-field (MF) results: the frequency of\nmacroscopic oscillation between the two sites, the critical parameter for the\ndynamical macroscopic quantum self trapping (MQST), and the attractive critical\ninteraction strength for the spontaneous symmetry breaking (SSB) of the ground\nstate. To validate our analytical results we perform numerical simulations of\nthe quantum dynamics. In the case of Josephson oscillations around a balanced\nconfiguration we find that also for a few atoms the numerical results are in\ngood agreement with the predictions of time-dependent ACS variational approach,\nprovided that the time evolution is not too long. Also the numerical results of\nSSB are better reproduced by the ACS approach with respect to the MF one.\nInstead the onset of MQST is correctly reproduced by ACS theory only in the\nlarge $N$ regime and, for this phenomenon, the $1/N$ correction to the MF\nformula is not reliable."
    },
    {
        "anchor": "Acceleration of spin-orbit coupled Bose-Einstein condensates: analytical\n  description of the emergence of Landau-Zener transitions: We analytically study the effect of gravitational and harmonic forces on\nultra-cold atoms with synthetic spin-orbit coupling (SOC). In particular, we\nfocus on the recently observed transitions between internal states induced by\nacceleration of the external modes. Our description corresponds to a\ngeneralized version of the Landau-Zener (LZ) model: the dimensionality is\nenlarged to combine the quantum treatment of the external variables with the\ninternal-state characterization; additionally, atomic-interaction effects are\nconsidered. The emergence of the basic model is analytically traced. Namely, by\nusing a sequence of unitary transformations and a subsequent reduction to the\nspin space, the SOC Hamiltonian, with the gravitational potential incorporated,\nis exactly converted into the primary LZ scenario. Moreover, the transitions\ninduced by harmonic acceleration are approximately cast into the framework of\nthe basic LZ model through a complete analytical procedure. We evaluate how the\nvalidity of our picture depends on the system preparation and on the magnitude\nof atomic-interaction effects. The identification of the regime of\napplicability and the rigorous characterization of the parameters of the\neffective model provide elements to control the transitions.",
        "positive": "Entangled Collective Spin States of Two Species Ultracold atoms in a\n  Ring: We study the general quantum Hamiltonian that can be realized with two\nspecies of mutually interacting degenerate ultracold atoms in a ring-shaped\ntrap, with the options of rotation and an azimuthal lattice. We examine the\nspectrum and the states with a collective spin picture in a Dicke state basis.\nThe system can generate states with a high degree of entanglement gauged by the\nvon Neumann entropy. The Hamiltonian has two components, a linear part that can\nbe controlled and switched on via rotation or the azimuthal lattice, and an\ninteraction-dependent quadratic part. Exact solutions are found for the\nquadratic part for equal strengths of intra-species and the inter-species\ninteractions, but for generally different particle numbers in the two species.\nThe quadratic Hamiltonian has a degenerate ground state when the two species\nhave unequal number of particles, but non-degenerate when equal. We determine\nthe impact on the entanglement entropy of deviations from equal particle\nnumbers as well as deviations from the assumption of equal interaction\nstrengths. Limiting cases are shown to display features of a beam-splitter and\nspin-squeezing that can find utility in interferometry. The density of states\nfor the full Hamiltonian shows features as of phase transition in varying\nbetween linear and quadratic limits."
    },
    {
        "anchor": "Interaction-induced Bloch Oscillation in a Harmonically Trapped and\n  Fermionized Quantum Gas in One Dimension: Motivated by a recent experiment by F. Meinert et al, arxiv:1608.08200, we\nstudy the dynamics of an impurity moving in the background of a harmonically\ntrapped one-dimensional Bose gas in the hard-core limit. We show that due to\nthe hidden \"lattice\" structure of background bosons, the impurity effectively\nfeels a quasi-periodic potential via impurity-boson interactions that can drive\nthe Bloch oscillation under an external force, even in the absence of real\nlattice potentials. Meanwhile, the inhomogeneous density of trapped bosons\nimposes an additional harmonic potential to the impurity, resulting in a\nsimilar oscillation dynamics but with different periods and amplitudes. We show\nthat the sign and the strength of impurity-boson coupling can significantly\naffect above two potentials so as to determine the impurity dynamics.",
        "positive": "Miscibility and stability of dipolar bosonic mixtures: Combining two Bose-Einstein condensates (BECs) may result in a miscible or\nimmiscible mixture, or even a violent implosion. We theoretically demonstrate\nthat dipolar two-component BECs produce far richer physics than their\nnondipolar counterparts. Intriguingly, when both components have equivalent\ndipoles, the transition to immiscibility is largely unaffected by dipolar\nphysics, yet the dipoles maximally affect stability. Conversely, antiparallel\ndipoles strongly affect miscibility but have little effect on stability. By\nperforming three-dimensional calculations of the ground states and their\nexcitations, we find strong dependencies on the confinement geometry. We\nexplore and elucidate the various phononic and rotonic phase transitions, as\nwell as symmetry preserving crossovers."
    },
    {
        "anchor": "Rotating Dipolar Spin-1 Bose-Einstein Condensates: We have computed phase diagrams for rotating spin-1 Bose-Einstein condensates\nwith long-range magnetic dipole-dipole interactions. Spin textures including\nvortex sheets, staggered half-quantum- and skyrmion vortex lattices and higher\norder topological defects have been found. These systems exhibit both\nsuperfluidity and magnetic crystalline ordering and they could be realized\nexperimentally by imparting angular momentum in the condensate.",
        "positive": "Staggered superfluid phases of dipolar bosons in two-dimensional square\n  lattices: We study the quantum ground state of ultracold bosons in a two-dimensional\nsquare lattice. The bosons interact via the repulsive dipolar interactions and\ns-wave scattering. The dynamics is described by the extended Bose-Hubbard model\nincluding correlated hopping due to the dipolar interactions, the coefficients\nare found from the second quantized Hamiltonian using the Wannier expansion\nwith realistic parameters. We determine the phase diagram using the Gutzwiller\nansatz in the regime where the coefficients of the correlated hopping terms are\nnegative and can interfere with the tunneling due to single-particle effects.\nWe show that this interference gives rise to staggered superfluid and\nsupersolid phases at vanishing kinetic energy, while we identify parameter\nregions at finite kinetic energy where the phases are incompressible. We\ncompare the results with the phase diagram obtained with the cluster Gutzwiller\napproach and with the results found in one dimension using DMRG."
    },
    {
        "anchor": "Two-dimensional boson-fermion mixtures: Using mean-field theory, we study the equilibrium properties of boson-fermion\nmixtures confined in a harmonic pancake-shaped trap at zero temperature. When\nthe modulus of the s-wave scattering lengths are comparable to the mixture\nthickness, two-dimensional scattering events introduce a logarithmic dependence\non density in the coupling constants, greatly modifying the density profiles\nthemselves. We show that for the case of a negative boson-fermion\nthree-dimensional s-wave scattering length, the dimensional crossover\nstabilizes the mixture against collapse and drives it towards spatial demixing.",
        "positive": "Quantum Monte Carlo study of a two dimensional dipolar Bose gas in a\n  harmonic trap: We present a Quantum Monte Carlo study of the ground state properties of a\ntwo dimensional system of Bose particle with dipole moment in a harmonic trap.\nThe direction of the dipoles is assumed to be fixed by an external field. We\nstudy how the system behaves when the direction of the dipole moments is\nchanged. Our analysis is made using Path Integral Monte Carlo simulations in\nthe Grand Canonical ensemble, using the Worm Algorithm. We study systems of\nincreasing size, focusing on the spatial distribution of the atoms inside the\ntrap and on the superfluid fraction of the sample. We find that vertical\ndipoles form a crystal, characterized by a shell structure, while tilting the\ndipoles has the effect of inducing a striped structure. We find that similar\nbehaviour can be found in the analogue classical system. Vertical dipoles\ndisplay nonclassical inertia while a strong tilting decreases superfluidity."
    },
    {
        "anchor": "Pseudogap phenomena in a two-dimensional ultracold Fermi gas near the\n  Berezinskii-Kosterlitz-Thouless transition: We investigate single-particle excitations and strong-coupling effects in a\ntwo-dimensional Fermi gas. Including pairing fluctuations within a Gaussian\nfluctuation theory, we calculate the density of states $\\rho(\\omega)$ near the\nBerezinskii-Kosterlitz-Thouless (BKT) transition temperature $T_{\\rm BKT}$.\nNear $T_{\\rm BKT}$, we show that superfluid fluctuations induce a pseudogap in\n$\\rho(\\omega)$. The pseudogap structure is very similar to the BCS superfluid\ndensity of states, although the superfluid order parameter is absent in the\npresent two-dimensional case. Since a two-dimensional $^{40}$K Fermi gas has\nrecently been realized, our results would contribute to the understanding of\nsingle-particle properties near the BKT instability.",
        "positive": "Moving obstacle potential in a spin-orbit-coupled Bose-Einstein\n  condensate: We investigate the dynamics around an obstacle potential moving in the\nplane-wave state of a pseudospin-$1/2$ Bose-Einstein condensate with Rashba\nspin-orbit coupling. We numerically investigate the dynamics of the system and\nfind that it depends not only on the velocity of the obstacle but also\nsignificantly on the direction of obstacle motion, which are verified by a\nBogoliubov analysis. The excitation diagram with respect to the velocity and\ndirection is obtained. The dependence of the critical velocity on the strength\nof the spin-orbit coupling and the size of the obstacle is also investigated."
    },
    {
        "anchor": "Creation and robustness of quantized vortices in a dipolar supersolid\n  when crossing the superfluid-to-supersolid transition: Experiments on dipolar Bose-Einstein condensates have recently reported the\nobservation of supersolidity. Although quantized vortices constitute a key\nprobe of superfluidity, their observability in dipolar supersolids is largely\nprevented by the strong density depletion caused by the formation of droplets.\nWe present a novel approach to the nucleation of vortices and their\nobservation, based on the quenching of the s-wave scattering length across the\nsuperfluid-supersolid transition. Starting from a slowly rotating, vortex-free,\nconfiguration in the superfluid phase, we predict vortex nucleation as the\nsystem enters the supersolid phase, due to the strong reduction of the critical\nangular velocity in the supersolid. Once a vortex is created, we show that it\nis robustly preserved when the condensate is brought back to the superfluid\nphase, where it may be readily observed.",
        "positive": "Simulating quantum magnets with symmetric top molecules: We establish a correspondence between the electric dipole matrix elements of\na polyatomic symmetric top molecule in a state with nonzero projection of the\ntotal angular momentum on the symmetry axis of the molecule and the magnetic\ndipole matrix elements of a magnetic dipole associated with an elemental spin\n$F$. It is shown that this correspondence makes it possible to perform quantum\nsimulation of the single-particle spectrum and the dipole-dipole interactions\nof magnetic dipoles in a static external magnetic field $\\bf{B}$ with symmetric\ntop molecules subject to a static external electric field\n$\\bf{E}_{\\mathrm{DC}}$. We further show that no such correspondence exists for\n$^1\\Sigma$ molecules in static fields, such as the alkali metal dimers. The\neffective spin angular momentum of the simulated magnetic dipole corresponds to\nthe rotational angular momentum of the symmetric top molecule, and so quantum\nsimulation of arbitrarily large integer spins is possible. Further, taking the\nmolecule CH$_3$F as an example, we show that the characteristic dipole-dipole\ninteraction energies of the simulated magnetic dipole are a factor of 620, 600,\nand 310 larger than for the highly magnetic atoms Chromium, Erbium, and\nDysprosium, respectively. We present several applications of our correspondence\nfor many-body physics, including long-range and anisotropic spin models with\narbitrary integer spin $S$ using symmetric top molecules in optical lattices,\nquantum simulation of molecular magnets, and spontaneous demagnetization of\nBose-Einstein condensates due to dipole-dipole interactions. Our results are\nexpected to be relevant as cold symmetric top molecules reach quantum\ndegeneracy through Stark deceleration and opto-electrical cooling."
    },
    {
        "anchor": "Transition region properties of a trapped quasi-two-dimensional\n  degenerate Bose gas: The c-field simulation technique is used to study a trapped quasi-two\ndimensional Bose gas. We calculate the central curvature of the system density\nand fluctuations of the condensate mode in the degenerate regime. These results\nprovide new understanding of the system behavior in the region of the\nsuperfluid transition.",
        "positive": "Universal Three-Body Parameter of Heavy-Heavy-Light systems with\n  negative intraspecies scattering length: The Three-Body Parameter(3BP)\n$a^{\\scriptscriptstyle(1)}_{\\scriptscriptstyle-}$ is crucial to understanding\nEfimov physics, and a universal 3BP has been shown in experiments and theory in\nultracold homonuclear gases. The 3BP of heteronuclear systems was predicted to\npossess much richer properties than the homonuclear counterparts for the large\nparameter space. In this work, we investigate the universal properties of\n$a^{\\scriptscriptstyle(1)}_{\\scriptscriptstyle-}$ for the\nHeavy-Heavy-Light(HHL) system with negative intraspecies scattering length\n$a_{\\scriptscriptstyle HH}$. We find that\n$a^{\\scriptscriptstyle(1)}_{\\scriptscriptstyle-}$ follows a universal behavior\ndetermined by the van der Waals(vdW) interaction and the mass ratio. An\nanalytic formula of $a^{\\scriptscriptstyle(1)}_{\\scriptscriptstyle-}$ is given\nas a function of $a_{\\scriptscriptstyle HH}$, which allows an intuitive\nunderstanding of how does $a^{\\scriptscriptstyle(1)}_{\\scriptscriptstyle-}$\ndepend on the mass ratio and the vdW length $r_{\\scriptscriptstyle vdW}$. In a\nspecial case, when the two heavy atoms are in resonance,\n$a^{\\scriptscriptstyle(1)}_{\\scriptscriptstyle-}$ is approximately a constant:\n$a^{\\scriptscriptstyle(1)}_{\\scriptscriptstyle-} = -(6.3\\pm0.6)\\,\nr_{\\scriptscriptstyle vdW,HL}$."
    },
    {
        "anchor": "Excited spin states and phase separation in spinor Bose-Einstein\n  condensates: We analyze the structure of spin-1 Bose-Einstein condensates in the presence\nof a homogenous magnetic field. We classify the homogenous stationary states\nand study their existence, bifurcations, and energy spectra. We reveal that the\nphase separation can occur in the ground state of polar condensates, while the\nspin components of the ferromagnetic condensates are always miscible and no\nphase separation occurs. Our theoretical model, confirmed by numerical\nsimulations, explains that this phenomenon takes place when the energy of the\nlowest homogenous state is a concave function of the magnetization. In\nparticular, we predict that phase separation can be observed in a $^{23}$Na\ncondensate confined in a highly elongated harmonic trap. Finally, we discuss\nthe phenomena of dynamical instability and spin domain formation.",
        "positive": "Spectral functions of a time-periodically driven Falicov-Kimball model:\n  real-space Floquet DMFT study: We present a systematic study of spectral functions of a time-periodically\ndriven Falicov-Kimball Hamiltonian. In the high-frequency limit, this system\ncan be effectively described as a Harper-Hofstadter-Falicov-Kimball model.\nUsing real-space Floquet dynamical mean-field theory (DMFT), we take into\naccount interaction effects and contributions from higher Floquet bands in a\nnon-perturbative way. Our calculations show a high degree of similarity between\nthe interacting driven system and its effective static counterpart with respect\nto spectral properties. However, as also illustrated by our results, one should\nbear in mind that Floquet DMFT describes a non-equilibrium steady state (NESS),\nwhile an effective static Hamiltonian describes an equilibrium state. We\nfurther demonstrate the possibility of using real-space Floquet DMFT to study\nedge states on a cylinder geometry."
    },
    {
        "anchor": "Emergent Infrared Conformal Dynamics in Strongly Interacting Quantum\n  Gases: Conformal dynamics can appear in quantum gases when the interactions are fine\ntuned to be scale symmetric. One well-known example of such a system is a\nthree-dimensional Fermi gas at a Feshbach resonance. In this letter, we\nillustrate how conformal dynamics can also emerge in the infrared limit in\none-dimensional harmonically trapped Fermi gases, even though the system may\nnot have exactly scale symmetric interactions. The conformal dynamics are\ninduced by strong renormalization effects due to the nearby infrared stable\nscale invariant interaction. When the system approaches the infrared limit, or\nwhen the external harmonic trapping frequency $\\omega_f \\rightarrow 0$, the\ndynamics are characterized by a unique vanishingly small dissipation rate,\n$\\Gamma \\propto \\omega_f$, rather than a constant as in generic interacting\nsystems. We also examine the work done in a two-quench protocol, $W$, and the\naverage power $\\mathcal{P}$. In one dimension, the average power, $\\mathcal{P}\n\\propto \\omega_f$, becomes vanishingly small in the infrared limit, a signature\nof emergent conformal dynamics.",
        "positive": "Absence of Landau damping in driven three-component Bose-Einstein\n  condensate in optical lattices: We explore the quantum many-body physics of a three-component Bose-Einstein\ncondensate (BEC) in an optical lattices driven by laser fields in $V$ and\n$\\Lambda$ configurations. We obtain exact analytical expressions for the energy\nspectrum and amplitudes of elementary excitations, and discover symmetries\namong them. We demonstrate that the applied laser fields induce a gap in the\notherwise gapless Bogoliubov spectrum. We find that Landau damping of the\ncollective modes above the energy of the gap is carried by laser-induced roton\nmodes and is considerably suppressed compared to the phonon-mediated damping\nendemic to undriven scalar BECs."
    },
    {
        "anchor": "Three-dimensional vortex structures in a rotating dipolar Bose-Einstein\n  condensate: We study the three-dimensional ground state vortex lattice structures of\npurely dipolar Bose-Einstein condensate (BEC). By using the mean-field model we\nobtain a stability diagram for the vortex states in purely dipolar BECs as a\nfunction of harmonic trap aspect ratio ($\\lambda$) and dipole-dipole\ninteraction strength ($D$) under rotation. Rotating the condensate within the\nunstable region leads to collapse, while in the stable region furnishes stable\nvortex lattices of dipolar BECs. We analyse stable vortex lattice structures by\nsolving three-dimensional time dependent Gross-Pitaevskii equation in imaginary\ntime. Further, the stability of vortex states is examined by evolution in\nreal-time. We also investigate distribution of vortices in fully anisotropic\ntrap by increasing eccentricity of the external trapping potential. Breaking up\nof the condensate in two parts has been observed with equally shared vortices\non each when the trap is sufficiently weak and the rotation frequency is high.",
        "positive": "Large-Amplitude Superexchange of High-Spin Fermions in Optical Lattices: We show that fermionic high-spin systems with spin-changing collisions allow\nto monitor superexchange processes in optical superlattices with large\namplitudes and strong spin fluctuations. By investigating the non-equilibrium\ndynamics, we find a superexchange dominated regime at weak interactions. The\nunderlying mechanism is driven by an emerging tunneling-energy gap in shallow\nfew-well potentials. As a consequence, the interaction-energy gap that is\nexpected to occur only for strong interactions in deep lattices is\nreestablished. By tuning the optical lattice depth, a crossover between two\nregimes with negligible particle number fluctuations is found: first, the\ncommon regime with vanishing spin-fluctuations in deep lattices and, second, a\nnovel regime with strong spin fluctuations in shallow lattices. We discuss the\npossible experimental realization with ultracold 40K atoms and observable\nquantities in double wells and two-dimensional plaquettes."
    },
    {
        "anchor": "Dimensional Crossover in a Quantum Gas of Light: The dimensionality of a system profoundly influences its physical behaviour,\nleading to the emergence of different states of matter in many-body quantum\nsystems. In lower dimensions, fluctuations increase and lead to the suppression\nof long-range order. For example, in bosonic gases, Bose-Einstein condensation\n(BEC) in one dimension requires stronger confinement than in two dimensions. We\nexperimentally study the properties of a harmonically trapped photon gas\nundergoing Bose-Einstein condensation along the dimensional crossover from one\nto two dimensions. The photons are trapped in a dye microcavity where polymer\nnanostructures provide the trapping potential for the photon gas. By varying\nthe aspect ratio of the harmonic trap, we tune from an isotropic\ntwo-dimensional confinement to an anisotropic, highly elongated one-dimensional\ntrapping potential. Along this transition we determine the caloric properties\nof the photon gas and find a softening of the second-order Bose-Einstein\ncondensation phase transition observed in two dimensions to a crossover\nbehaviour in one dimension.",
        "positive": "Fluctuation-Induced Quantum Zeno Effect: An isolated quantum gas with a localized loss features a non-monotonic\nbehavior of the particle loss rate as an incarnation of the quantum Zeno\neffect, as recently shown in experiments with cold atomic gases. While this\neffect can be understood in terms of local, microscopic physics, we show that\nnovel many-body effects emerge when non-linear gapless quantum fluctuations\nbecome important. To this end, we investigate the effect of a local dissipative\nimpurity on a one-dimensional gas of interacting fermions. We show that the\nescape probability for modes close to the Fermi energy vanishes for an\narbitrary strength of the dissipation. In addition, transport properties across\nthe impurity are qualitatively modified, similarly to the Kane-Fisher barrier\nproblem. We substantiate these findings using both a microscopic model of\nspinless fermions and a Luttinger liquid description."
    },
    {
        "anchor": "Virial expansion for a strongly correlated Fermi gas with imbalanced\n  spin populations: Quantum virial expansion provides an ideal tool to investigate the\nhigh-temperature properties of a strongly correlated Fermi gas. Here, we\nconstruct the virial expansion in the presence of spin population imbalance. Up\nto the third order, we calculate the high-temperature free energy of a unitary\nFermi gas as a function of spin imbalance, with infinitely large, attractive or\nrepulsive interactions. In the latter repulsive case, we show that there is no\nitinerant ferromagnetism when quantum virial expansion is applicable. We\ntherefore estimate an upper bound for the ferromagnetic transition temperature\n$T_{c}$. For a harmonically trapped Fermi gas at unitarity, we find that\n$(T_{c})_{uppper}<T_{F}$, where $T_{F}$ is the Fermi temperature at the center\nof the trap. Our result for the high-temperature equations of state may\nconfront future high-precision thermodynamic measurements.",
        "positive": "Critical behavior of Tan's contact for bosonic systems with a fixed\n  chemical potential: The temperature dependence of Tan's contact parameter $C$ and its derivatives\nfor spin gapped quantum magnets are investigated. We use the paradigm of\nBose-Einstein condensation (BEC) to describe the low temperature properties of\nquasiparticles in the system known as triplons. Since the number of particles\nand the condensate fraction are not fixed we use the $\\mu VT$ ensemble to\ncalculate the thermodynamic quantities. The interactions are treated at the\nHartree-Fock-Bogoliubov approximation level. We obtained the temperature\ndependence of $C$ and its derivative with respect to temperature and applied\nmagnetic field both above and below $T_c$ of the phase transition from the\nnormal phase to BEC. We have shown that $C$ is regular, while its derivatives\nare discontinuous at $T_c$ in accordance with Ehrenfest's classification of\nphase transitions. Moreover, we have found a sign change in $\\partial\nC/\\partial T$ close to the critical temperature. As to the quantum critical\npoint, $C$ and its derivatives are regular as a function of the control\nparameter $r$, which induces the quantum phase transition. At very low\ntemperatures, one may evaluate $C$ simply from the expression $C=m^2\\mu^2/{\\bar\na}^{4}$, where the only parameter effective mass of quasiparticles should be\nestimated. We propose a method for measuring of Tan's contact for spin gapped\ndimerized magnets."
    },
    {
        "anchor": "Quench dynamics of spin-imbalanced Fermi-Hubbard model in one dimension: We study a nonequilibrium dynamics of a one-dimensional spin-imbalanced\nFermi-Hubbard model following a quantum quench of on-site interaction,\nrealizable, for example, in Feshbach-resonant atomic Fermi gases. We focus on\nthe post-quench evolution starting from the initial BCS and\nFuldeFerrell-Larkin-Ovchinnikov (FFLO) ground states and analyze the\ncorresponding spin-singlet, spin-triplet, density-density, and\nmagnetization-magnetization correlation functions. We find that beyond a\nlight-cone crossover time, rich post-quench dynamics leads to thermalized and\npre-thermalized stationary states that display strong dependence on the initial\nground state. For initially gapped BCS state, the long-time stationary state\nresembles thermalization with the effective temperature set by the initial\nvalue of the Hubbard interaction. In contrast, while the initial gapless FFLO\nstate reaches a stationary pre-thermalized form, it remains far from\nequilibrium. We suggest that such post-quench dynamics can be used as a\nfingerprint for identification and study of the FFLO phase.",
        "positive": "Universal scaling at non-thermal fixed points of a two-component Bose\n  gas: Quasi-stationary far-from-equilibrium critical states of a two-component Bose\ngas are studied in two spatial dimensions. After the system has undergone an\ninitial dynamical instability it approaches a non-thermal fixed point. At this\ncritical point the structure of the gas is characterised by ensembles of\n(quasi-)topological defects such as vortices, skyrmions and solitons which give\nrise to universal power-law behaviour of momentum correlation functions. The\nresulting power-law spectra can be interpreted in terms of\nstrong-wave-turbulence cascades driven by particle transport into\nlong-wave-length excitations. Scaling exponents are determined on both sides of\nthe miscible-immiscible transition controlled by the ratio of the intra-species\nto inter-species couplings. Making use of quantum turbulence methods, we\nexplain the specific values of the exponents from the presence of transient\n(quasi-)topological defects."
    },
    {
        "anchor": "Massive particle interferometry with lattice solitons: We discuss an interferometric scheme employing interference of bright\nsolitons formed as specific bound states of attracting bosons on a lattice. We\nrevisit the proposal of Castin and Weiss [Phys. Rev. Lett. vol. 102, 010403\n(2009)] for using the scattering of a quantum matter-wave soliton on a barrier\nin order to create a coherent superposition state of the soliton being entirely\nto the left of the barrier and being entirely to the right of the barrier. In\nthat proposal, it was assumed that the scattering is perfectly elastic, i.e.\\\nthat the center-of-mass kinetic energy of the soliton is lower than the\nchemical potential of the soliton. Here we relax this assumption: By employing\na combination of Bethe ansatz and DMRG based analysis of the dynamics of the\nappropriate many-body system, we find that the interferometric fringes persist\neven when the center-of-mass kinetic energy of the soliton is above the energy\nneeded for its complete dissociation into constituent atoms.",
        "positive": "Driven-dissipative Rydberg blockade in optical lattices: While dissipative Rydberg gases exhibit unique possibilities to tune\ndissipation and interaction properties, very little is known about the quantum\nmany-body physics of such long-range interacting open quantum systems. We\ntheoretically analyze the steady state of a van der Waals interacting Rydberg\ngas in an optical lattice based on a variational treatment that also includes\nlong-range correlations necessary to describe the physics of the Rydberg\nblockade, i.e., the inhibition of neighboring Rydberg excitations by strong\ninteractions. In contrast to the ground state phase diagram, we find that the\nsteady state undergoes a single first order phase transition from a blockaded\nRydberg gas to a facilitation phase where the blockade is lifted. The first\norder line terminates in a critical point when including sufficiently strong\ndephasing, enabling a highly promising route to study dissipative criticality\nin these systems. In some regimes, we also find good quantitative agreement\nwith effective short-range models despite the presence of the Rydberg blockade,\njustifying the wide use of such phenomenological descriptions in the\nliterature."
    },
    {
        "anchor": "Two-leg fermionic Hubbard ladder system in the presence of\n  state-dependent hopping: We study a two-leg fermionic Hubbard ladder model with a state-dependent\nhopping. We find that, contrary to the case without a state-dependent hopping,\nfor which the system has a superfluid nature regardless of the sign of the\ninteraction at incommensurate filling, in the presence of such a hopping a\nspin-triplet superfluid, spin- density wave and charge-density wave phases\nemerge. We examine our results in the light of recent experiments on\nperiodically-driven optical lattices in cold atoms. We give protocols allowing\nus to realize the spin-triplet superfluid elusive in the cold atoms.",
        "positive": "Chiral edge dynamics and quantum Hall physics in synthetic dimensions\n  with an atomic erbium Bose-Einstein condensate: Quantum Hall physics is at the heart of research on both matter and\nartificial systems, such as cold atomic gases, with non-trivial topological\norder. We report on the observation of a chiral edge current by transferring\natomic wavepackets simultaneously to opposite edges of a synthetic Hall system\nrealized in the two-dimensional state space formed by one spatial and one\nsynthetic dimension encoded in the J=6 electronic spin of erbium atoms. To\ncharacterize the system, the Hall drift of the employed atomic Bose-Einstein\ncondensate in the lowest Landau-like level is determined. The topological\nproperties are verified by determining the local Chern marker, and upon\nperforming low-lying excitations both cyclotron and skipping orbits are\nobserved in the bulk and edges respectively. Future prospects include studies\nof novel topological phases in cold atom systems."
    },
    {
        "anchor": "Supersolid edge and bulk phases of a dipolar quantum gas in a box: We investigate the novel density distributions acquired by a dipolar\nBose-Einstein condensed gas confined in a box potential, with special focus on\nthe effects of supersolidity. Differently from the case of harmonic trapping,\nthe ground state density reveals a strong depletion in the bulk region and an\naccumulation of atoms near the walls, well separated from the bulk, as a\nconsequence of the competition between the attractive and the repulsive nature\nof the dipolar force. In a quasi two-dimensional geometry characterized by\ncylindrical box trapping, we observe the emergence of a ring-like configuration\nnear the boundary of the box, reveling peculiar supersolid and crystal effects\nin a useful range of parameters. In the case of square box trapping the density\noscillations along the edges, caused by the enhanced accumulation of atoms near\nthe vertices, exhibit interesting analogies with the case of box trapped one\ndimensional configurations. For sufficiently large values of the atom number\nalso the bulk region can exhibit supersolidity, the resulting geometry\nreflecting the symmetry of the confining potential even for large systems.",
        "positive": "Direct Measurement of the Zak phase in Topological Bloch Bands: Geometric phases that characterize the topological properties of Bloch bands\nplay a fundamental role in the modern band theory of solids. Here we report on\nthe direct measurement of the geometric phase acquired by cold atoms moving in\none-dimensional optical lattices. Using a combination of Bloch oscillations and\nRamsey interferometry, we extract the Zak phase - the Berry phase acquired\nduring an adiabatic motion of a particle across the Brillouin zone - which can\nbe viewed as an invariant characterizing the topological properties of the\nband. For a dimerized optical lattice, which models polyacetylene, we measure a\ndifference of the Zak phase equal to phi_Zak=0.97(2)pi for the two possible\npolyacetylene phases with different dimerization. This indicates that the two\ndimerized phases belong to different topological classes, such that for a\nfilled band, domain walls have fractional quantum numbers. Our work establishes\na new general approach for probing the topological structure of Bloch bands in\noptical lattices."
    },
    {
        "anchor": "Quantum Defect Theory for Orbital Feshbach Resonance: In the ultracold gases of alkali-earth (like) atoms, a new type of Feshbach\nresonance, i.e., the orbital Feshbach resonance (OFR), has been proposed and\nexperimentally observed in ultracold $^{173}$Yb atoms. When the OFR of the\n$^{173}$Yb atoms occurs, the energy gap between the open and closed channels is\nsmaller by two orders of magnitudes than the van der Waals energy. As a result,\nquantitative accurate results for the low-energy two-body problems can be\nobtained via multi-channel quantum defect theory (MQDT), which is based on the\nexact solution of the Schr$\\ddot{{\\rm o}}$dinger equation with the van der\nWaals potential. In this paper we use the MQDT to calculate the two-atom\nscattering length, effective range, and the binding energy of two-body bound\nstates for the systems with OFR. With these results we further study the\nclock-transition spectrum for the two-body bound states, which can be used to\nexperimentally measure the binding energy. Our results are helpful for the\nquantitative theoretical and experimental researches for the ultracold gases of\nalkali-earth (like) atoms with OFR.",
        "positive": "Mass imbalance effect in resonant Bose-Fermi mixtures: We consider a homogeneous Bose-Fermi mixture, with the boson-fermion\ninteraction tuned by a Fano-Feshbach resonance, in the presence of mass and\ndensity imbalance between the two species. By using many-body diagrammatic\nmethods, we first study the finite-temperature phase diagram for the specific\ncase of the mass-imbalanced mixture $^{87}$Rb $-^{40}$K for different values of\nthe density imbalance. We then analyse the quantum phase transition associated\nwith the disappearance at zero temperature of the boson condensate above a\ncritical boson-fermion coupling. We find a pronounced dependence of the\ncritical coupling on the mass ratio and a weak dependence on the density\nimbalance. For a vanishingly small boson density, we derive, within our\napproximation, the asymptotic expressions for the critical coupling in the\nlimits of small and large mass ratios. These expressions are relevant also for\nthe polaron-molecule transition in a Fermi mixture at small and large mass\nratios. The analysis of the momentum distribution functions at sufficiently\nlarge density imbalances shows an interesting effect in the bosonic momentum\ndistribution due to the simultaneous presence of composite fermions and\nunpaired fermions."
    },
    {
        "anchor": "Fluctuations of imbalanced fermionic superfluids in two dimensions\n  induce continuous quantum phase transitions and non-Fermi liquid behavior: We study the nature of superfluid pairing in imbalanced Fermi mixtures in two\nspatial dimensions. We present evidence that the combined effect of Fermi\nsurface mismatch and order parameter fluctuations of the superfluid condensate\ncan lead to continuous quantum phase transitions from a normal Fermi mixture to\nan intermediate Sarma-Liu-Wilczek superfluid with two gapless Fermi surfaces --\neven when mean-field theory (incorrectly) predicts a first order transition to\na phase-separated \"Bardeen-Cooper-Schrieffer plus excess fermions\" ground\nstate. We propose a mechanism for non-Fermi liquid behavior from repeated\nscattering processes between the two Fermi surfaces and fluctuating Cooper\npairs. Prospects for experimental observation with ultracold atoms are\ndiscussed.",
        "positive": "Damping of the quadrupole mode in a two-dimensional Fermi gas: In a recent experiment [E. Vogt et al., Phys. Rev. Lett. 108, 070404 (2012)],\nquadrupole and breathing modes of a two-dimensional Fermi gas were studied. We\nmodel these collective modes by solving the Boltzmann equation via the method\nof phase-space moments up to fourth order, including in-medium effects on the\nscattering cross section. In our analysis, we use a realistic Gaussian\npotential deformed by the presence of gravity and magnetic field gradients. We\nconclude that the origin of the experimentally observed damping of the\nquadrupole mode, especially in the weakly interacting (or even non-interacting)\ncase, cannot be explained by these mechanisms."
    },
    {
        "anchor": "Measuring entropy and mutual information in the two-dimensional Hubbard\n  model: We measure pressure and entropy of ultracold fermionic atoms in an optical\nlattice for a range of interaction strengths, temperatures and fillings. Our\nmeasurements demonstrate that, for low enough temperatures, entropy-rich\nregions form locally in the metallic phase which are in contact with a\nMott-insulating phase featuring lower entropy. In addition, we also measure the\nreduced density matrix of a single lattice site, and from the comparison\nbetween the local and thermodynamic entropies we determine the mutual\ninformation between a single lattice site and the rest of the system. For low\nlattice fillings, we find the mutual information to be independent of\ninteraction strength, however, for half filling we find that strong\ninteractions suppress the correlations between a single site and the rest of\nthe system.",
        "positive": "Observation of Laughlin states made of light: Much of the richness in nature emerges because the same simple constituents\ncan form an endless variety of ordered states. While many such states are fully\ncharacterized by their symmetries, interacting quantum systems can also exhibit\ntopological order, which is instead characterized by intricate patterns of\nentanglement. A paradigmatic example of such topological order is the Laughlin\nstate, which minimizes the interaction energy of charged particles in a\nmagnetic field and underlies the fractional quantum Hall effect. Broad efforts\nhave arisen to enhance our understanding of these orders by forming Laughlin\nstates in synthetic quantum systems, such as those composed of ultracold atoms\nor photons. In spite of these efforts, electron gases remain essentially the\nonly physical system in which topological order has appeared. Here, we present\nthe first observation of optical photon pairs in the Laughlin state. These\npairs emerge from a photonic analog of a fractional quantum Hall system, which\ncombines strong, Rydberg-mediated interactions between photons and synthetic\nmagnetic fields for light, induced by twisting an optical resonator. Photons\nentering this system undergo collisions to form pairs in an angular momentum\nsuperposition consistent with the Laughlin state. Characterizing the same pairs\nin real space reveals that the photons avoid each other, a hallmark of the\nLaughlin state. This work heralds a new era of quantum many-body optics, where\nstrongly interacting and topological photons enable exploration of quantum\nmatter with wholly new properties and unique probes."
    },
    {
        "anchor": "Longitudinal spin diffusion in a nondegenerate trapped $^{87}$Rb gas: Longitudinal spin diffusion of two pseudo-spin domains is studied in a\ntrapped $^{87}$Rb sample above quantum degeneracy, and the effect of coherence\nin the domain wall on the dynamics of the system is investigated. Coherence in\na domain wall leads to transverse-spin-mediated longitudinal spin diffusion\nthat is slower than classical predictions, as well as altering the domains'\noscillation frequency. The system also shows an instability in the longitudinal\nspin dynamics as longitudinal and transverse spin components couple, and a\nconversion of longitudinal spin to transverse spin is observed, resulting in an\nincrease in the total amount of coherence in the system.",
        "positive": "Loading and detecting a three-dimensional Fermi gas in one-dimensional\n  optical superlattice: We investigate the procedures of loading and detecting three-dimensional\nfermionic quantum gases in a one-dimensional optical superlattice potential\nsubjected to a trapping potential. Additionally, we consider the relaxation\ndynamics after a sudden change of the superlattice potential. We numerically\nsimulate the time-dependent evolution of the continuous system using exact\ndiagonalization of non-interacting fermions. During the loading procedure we\nanalyze the occupation of the instantaneous energy levels and compare the\nsituation in a homogeneous system with the trapped one. Strong differences are\nfound in particular in the evolution of excitations which we trace back to the\ndistinct global density distribution. Starting from an imbalanced state in the\nsuperlattice potential, we consider the relaxation dynamics of fermions after a\nslow change of the superlattice potential and find a bimodule distribution of\nexcitations. To be able to compare with the experimental results we also\nsimulate the measurement sequence of the even and odd local density and find a\nstrong dependence of the outcome on the actual ramp procedure. We suggest how\nthe loading and detecting procedure can be optimized."
    },
    {
        "anchor": "Hyperfine Spin-Two (F=2) Atoms in Three-Dimensional Optical Lattices:\n  Phase Diagrams and Phase Transitions: We consider ultracold matter of spin-2 atoms in optical lattices. We derive\nan effective Hamiltonian for the studies of spin ordering in Mott states and\ninvestigate hyperfine spin correlations. Particularly, we diagonalize the\nHamiltonian in an on-site Hilbert space taking into account spin-dependent\ninteractions and exchange between different sites. We obtain phase diagrams and\nquantum phase transitions between various magnetic phases.",
        "positive": "Anderson localization of solitons: At low temperature, a quasi-one-dimensional ensemble of atoms with attractive\ninteraction forms a bright soliton. When exposed to a weak and smooth external\npotential, the shape of the soliton is hardly modified, but its center-of-mass\nmotion is affected. We show that in a spatially correlated disordered\npotential, the quantum motion of a bright soliton displays Anderson\nlocalization. The localization length can be much larger than the soliton size\nand could be observed experimentally."
    },
    {
        "anchor": "Dynamics of Ultracold Quantum Gases in the Dissipative Fermi-Hubbard\n  Model: We employ metastable ultracold $^{173}$Yb atoms to study dynamics in the 1D\ndissipative Fermi-Hubbard model experimentally and theoretically, and observe a\ncomplete inhibition of two-body losses after initial fast transient dynamics.\nWe attribute the suppression of particle loss to the dynamical generation of a\nhighly entangled Dicke state. For several lattice depths and for two- and\nsix-spin component mixtures we find very similar dynamics, showing that the\ncreation of strongly correlated states is a robust and universal phenomenon.\nThis offers interesting opportunities for precision measurements.",
        "positive": "Spin-superflow turbulence in spin-1 ferromagnetic spinor Bose-Einstein\n  condensates: Spin-superflow turbulence (SST) in spin-1 ferromagnetic spinor Bose-Einstein\ncondensates is theoretically and numerically studied by using the spinor\nGross-Pitaevskii (GP) equations. SST is turbulence in which the disturbed spin\nand superfluid velocity fields are coupled. Applying the Kolmogorov-type\ndimensional scaling analysis to the hydrodynamic equations of spin and velocity\nfields, we theoretically find that the -5/3 and -7/3 power laws appear in\nspectra of the superflow kinetic and the spin-dependent interaction energy,\nrespectively. Our numerical calculation of the GP equations confirms SST with\nthe coexistence of disturbed spin and superfluid velocity field with two power\nlaws."
    },
    {
        "anchor": "Collective excitations of a BCS superfluid in the presence of two\n  sublattices: We consider a generic Hamiltonian that is suitable for describing a uniform\nBCS superfluid on a lattice with a two-point basis, and study its collective\nexcitations at zero temperature. For this purpose, we first derive an\neffective-Gaussian action for the pairing fluctuations, and then extract the\nlow-energy dispersion relations for the in-phase Goldstone and out-of-phase\nLeggett modes along with the corresponding amplitude (i.e., the so-called\nHiggs) ones. We find that while the Goldstone mode is gapless at zero momentum\nand propagating in general, the Leggett mode becomes undamped only with\nsufficiently strong interactions. Furthermore, we show that, in addition to the\nconventional contribution that is controlled by the energy of the Bloch bands,\nthe velocity of the Goldstone mode has a geometric contribution that is\ngoverned by the quantum metric tensor of the Bloch states. Our results suggest\nthat the latter contribution dominates the velocity when the former one becomes\nnegligible for a narrow- or a flat-band.",
        "positive": "Expansion Dynamics of a Two-Component Quasi-One-Dimensional\n  Bose-Einstein Condensate: Phase Diagram, Self-Similar Solutions, and\n  Dispersive Shock Waves: We investigate the expansion dynamics of a Bose-Einstein condensate that\nconsists of two components and is initially confined in a quasi-one-dimensional\ntrap. We classify the possible initial states of the two-component condensate\nby taking into account the non-uniformity of the distributions of its\ncomponents and construct the corresponding phase diagram in the plane of\nnonlinear interaction constants. The differential equations that describe the\ncondensate evolution are derived by assuming that the condensate density and\nvelocity depend on the spatial coordinate quadratically and linearly,\nrespectively, what reproduces the initial equilibrium distribution of the\ncondensate in the trap in the Thomas-Fermi approximation. We obtained\nself-similar solutions of these differential equations for several important\nspecial cases and wrote out asymptotic formulas describing the condensate\nmotion on long time scales, when the condensate density becomes so low that the\ninteraction between atoms can be neglected. The problem on the dynamics of\nimmiscible components with the formation of dispersive shock waves was also\nconsidered. We compare the numerical solutions of the Gross-Pitaevskii\nequations with their approximate analytical solutions and study numerically the\nsituations when the analytical method admits no exact solutions."
    },
    {
        "anchor": "Creating vortons and three-dimensional skyrmions from domain wall\n  annihilation with stretched vortices in Bose-Einstein condensates: We propose a mechanism to create a vorton or three-dimensional skyrmion in\nphase-separated two-component BECs with the order parameters Psi_1 and Psi_2 of\nthe two condensates. We consider a pair of a domain wall (brane) and an\nanti-domain wall (anti-brane) stretched by vortices (strings), where the Psi_2\ncomponent with a vortex winding is sandwiched by two domains of the Psi_1\ncomponent. The vortons appear when the domain wall pair annihilates.\nExperimentally, this can be realized by preparing the phase separation in the\norder Psi_1, Psi_2 and Psi_1 components, where the nodal plane of a dark\nsoliton in Psi_1 component is filled with the Psi_2 component with vorticity.\nBy selectively removing the filling Psi_2 component gradually with a resonant\nlaser beam, the collision of the brane and anti-brane can be made, creating\nvortons.",
        "positive": "Entangling lattice-trapped bosons with a free impurity: impact on\n  stationary and dynamical properties: We address the interplay of few lattice trapped bosons interacting with an\nimpurity atom in a box potential. For the ground state, a classification is\nperformed based on the fidelity allowing to quantify the susceptibility of the\ncomposite system to structural changes due to the intercomponent coupling. We\nanalyze the overall response at the many-body level and contrast it to the\nsingle-particle level. By inspecting different entropy measures we capture the\ndegree of entanglement and intraspecies correlations for a wide range of intra-\nand intercomponent interactions and lattice depths. We also spatially resolve\nthe imprint of the entanglement on the one- and two-body density distributions\nshowcasing that it accelerates the phase separation process or acts against\nspatial localization for repulsive and attractive intercomponent interactions\nrespectively. The many-body effects on the tunneling dynamics of the individual\ncomponents, resulting from their counterflow, are also discussed. The tunneling\nperiod of the impurity is very sensitive to the value of the impurity-medium\ncoupling due to its effective dressing by the few-body medium. Our work\nprovides implications for engineering localized structures in correlated\nimpurity settings using species selective optical potentials."
    },
    {
        "anchor": "Identifying strongly correlated supersolid states on the optical lattice\n  by quench-induced \u03c0-states: We consider the rapid quench of a one-dimensional strongly correlated\nsupersolid to a localized density wave (checkerboard) phase, and calculate the\nfirst-order coherence signal following the quench. It is shown that unique\ncoherence oscillations between the even and odd sublattice sites of the\ncheckerboard are created by the quench, which are absent when the initial state\nis described by a Gutzwiller product state. This is a striking manifestation of\nthe versatility of the far-from-equilbrium and nonperturbative collapse and\nrevival phenomenon as a microscope for quantum correlations in complex\nmany-body states. For the present example, this opens up the possibility to\ndiscriminate experimentally between mean-field and many-body origins of\nsupersolidity.",
        "positive": "Variational Monte-Carlo investigation of SU($N$) Heisenberg chains: Motivated by recent experimental progress in the context of ultra-cold\nmulti-color fermionic atoms in optical lattices, we have investigated the\nproperties of the SU($N$) Heisenberg chain with totally antisymmetric\nirreducible representations, the effective model of Mott phases with $m < N$\nparticles per site. These models have been studied for arbitrary $N$ and $m$\nwith non-abelian bosonization [I. Affleck, Nuclear Physics B 265, 409 (1986);\n305, 582 (1988)], leading to predictions about the nature of the ground state\n(gapped or critical) in most but not all cases. Using exact diagonalization and\nvariational Monte-Carlo based on Gutzwiller projected fermionic wave functions,\nwe have been able to verify these predictions for a representative number of\ncases with $N \\leq 10$ and $m \\leq N/2$, and we have shown that the opening of\na gap is associated to a spontaneous dimerization or trimerization depending on\nthe value of m and N. We have also investigated the marginal cases where\nabelian bosonization did not lead to any prediction. In these cases,\nvariational Monte-Carlo predicts that the ground state is critical with\nexponents consistent with conformal field theory."
    },
    {
        "anchor": "Variational ansatz for the nonlinear Landau-Zener problem for cold atom\n  association: We present a rigorous analysis of the Landau-Zener linear-in-time term\ncrossing problem for quadratic-nonlinear systems relevant to the coherent\nassociation of ultracold atoms in degenerate quantum gases. Our treatment is\nbased on an exact third-order nonlinear differential equation for the molecular\nstate probability. Applying a variational two-term ansatz, we construct a\nsimple approximation that accurately describes the whole-time dynamics of\ncoupled atom-molecular system for any set of involved parameters. Ensuring an\nabsolute error less than for the final transition probability, the resultant\nsolution improves by several orders of magnitude the accuracy of the previous\napproximations by A. Ishkhanyan et al. developed separately for the weak\ncoupling [J. Phys. A 38, 3505 (2005)] and strong interaction [J. Phys. A 39,\n14887 (2006)] limits. In addition, the constructed approximation covers the\nwhole moderate-coupling regime, providing for this intermediate regime the same\naccuracy as for the two mentioned limits. The obtained results reveal the\nremarkable observation that for the strong-coupling limit the resonance\ncrossing is mostly governed by the nonlinearity, while the coherent\natom-molecular oscillations arising soon after the resonance has been crossed\nare basically of linear nature. This observation is supposed to be of a general\ncharacter due to the basic attributes of the resonance crossing processes in\nthe nonlinear quantum systems of the discussed type of involved quadratic\nnonlinearity.",
        "positive": "Angle-resolved photoemission spectroscopy of a Fermi-Hubbard system: Angle-resolved photoemission spectroscopy (ARPES) measures the\nsingle-particle excitations of a many-body quantum system with both energy and\nmomentum resolution, providing detailed information about strongly interacting\nmaterials. ARPES is a direct probe of fermion pairing, and hence a natural\ntechnique to study the development of superconductivity in a variety of\nexperimental systems ranging from high temperature superconductors to unitary\nFermi gases. In these systems a remnant gap-like feature persists in the normal\nstate, which is referred to as a pseudogap. A quantitative understanding of\npseudogap regimes may elucidate details about the pairing mechanisms that lead\nto superconductivity, but developing this is difficult in real materials partly\nbecause the microscopic Hamiltonian is not known. Here we report on the\ndevelopment of ARPES to study strongly interacting fermions in an optical\nlattice using a quantum gas microscope. We benchmark the technique by measuring\nthe occupied single-particle spectral function of an attractive Fermi-Hubbard\nsystem across the BCS-BEC crossover and comparing to quantum Monte Carlo\ncalculations. We find evidence for a pseudogap in our system that opens well\nabove the expected critical temperature for superfluidity. This technique may\nalso be applied to the doped repulsive Hubbard model which is expected to\nexhibit a pseudogap at temperatures close to those achieved in recent\nexperiments."
    },
    {
        "anchor": "Finite-size effects on the Bose-Einstein condensation critical\n  temperature in a harmonic trap: We obtain second and higher order corrections to the shift of the\nBose-Einstein critical temperature due to finite-size effects. The confinement\nis that of a harmonic trap with general anisotropy. Numerical work shows the\nhigh accuracy of our expressions. We draw attention to a subtlety involved in\nthe consideration of experimental values of the critical temperature in\nconnection with analytical expressions for the finite-size corrections.",
        "positive": "Jet-like tunneling from a trapped vortex: We analyze the tunneling of vortex states from elliptically shaped traps.\nUsing the hydrodynamic representation of the Gross-Pitaevskii (Nonlinear\nSchr\\\"odinger) equation, we derive analytically and demonstrate numerically a\nnovel type of quantum fluid flow: a jet-like singularity formed by the\ninteraction between the vortex and the nonhomogenous field. For strongly\nelongated traps, the ellipticity overwhelms the circular rotation, resulting in\nthe ejection of field in narrow, well-defined directions. These jets can also\nbe understood as a formation of caustics since they correspond to a convergence\nof trajectories starting from the top of the potential barrier and meeting at a\ncertain point on the exit line. They will appear in any coherent wave system\nwith angular momentum and non-circular symmetry, such as superfluids,\nBose-Einstein condensates, and light."
    },
    {
        "anchor": "Perfect transmission and perfect reflection of Bogoliubov quasiparticles\n  in a dynamically unstable Bose-Einstein condensate: The Nambu-Goldstone (NG) mode in a Bose-Einstein condensate (BEC) transmits a\npotential barrier with probability 1 in the zero-energy limit, which is known\nas the anomalous tunneling. In this paper, we investigate the tunneling\nproperties of quasiparticles in a dynamically unstable BEC. We prepare a\nmulti-component BEC (binary and spin-1 BEC) in a dynamically unstable state and\nsolve the tunneling problem of the spin-wave excitation from the condensate. We\nfind that the perfect transmission occurs even when the BEC is dynamically\nunstable if the spin-wave is the NG mode. Here, the mode that exhibits the\nperfect transmission is the dynamically unstable spin-wave mode, which is a\npure-imaginary-eigenvalue solution of the Bogoliubov-de Gennes equation. Hence,\nwe should take the zero-energy limit along not the real axis but the imaginary\naxis. We also demonstrate the existence of the perfect reflection of a\ndynamically unstable mode at the point where the imaginary part of the\neigenvalue takes its maximum. In this case, the incident and reflected waves\ndestructively interfere, and the amplitude of the quasiparticle wave function\nis strongly suppressed. We numerically confirm that the perfect reflection is a\ngeneric nature of dynamically unstable modes and not related to the NG mode.",
        "positive": "Damping of Bloch oscillations: Variational solutions of the Boltzmann\n  equation beyond linear response: Variational solutions of the Boltzmann equation usually rely on the concept\nof linear response. We extend the variational approach for tight-binding models\nat high entropies to a regime far beyond linear response. We analyze both\nweakly interacting fermions and incoherent bosons on a lattice. We consider a\ncase where the particles are driven by a constant force, leading to the\nwell-known Bloch oscillations, and we consider interactions that are weak\nenough not to overdamp these oscillations. This regime is computationally\ndemanding and relevant for ultracold atoms in optical lattices. We derive a\nsimple theory in terms of coupled dynamic equations for the particle density,\nenergy density, current and heat current, allowing for analytic solutions. As\nan application, we identify damping coefficients for Bloch oscillations in the\nHubbard model at weak interactions and compute them for a one-dimensional toy\nmodel. We also approximately solve the long-time dynamics of a weakly\ninteracting, strongly Bloch-oscillating cloud of fermionic particles in a\ntilted lattice, leading to a subdiffusive scaling exponent."
    },
    {
        "anchor": "Dipolar Bose-Einstein condensate for large scattering length: A uniform dilute Bose gas of known density has a universal behavior as the\natomic scattering length tends to infinity at unitarity while most of its\nproperties are determined by a universal parameter $\\xi$ relating the energies\nof the noninteracting and unitary gases. The usual mean-field equation is not\nvalid in this limit and beyond mean-field corrections become important. We use\na dynamical model including such corrections to investigate a trapped\ndisk-shaped dipolar Bose-Einstein condensate (BEC) and a dipolar BEC vortex for\nlarge scattering length. We study the sensitivity of our results on the\nparameter $\\xi$ and discuss the possibility of extracting the value of this\nparameter from experimental observables.",
        "positive": "Causality and defect formation in the dynamics of an engineered quantum\n  phase transition in a coupled binary Bose-Einstein condensate: Continuous phase transitions occur in a wide range of physical systems, and\nprovide a context for the study of non-equilibrium dynamics and the formation\nof topological defects. The Kibble-Zurek (KZ) mechanism predicts the scaling of\nthe resulting density of defects as a function of the quench rate through a\ncritical point, and this can provide an estimate of the critical exponents of a\nphase transition. In this work we extend our previous study of the\nmiscible-immiscible phase transition of a binary Bose-Einstein condensate (BEC)\ncomposed of two hyperfine states in which the spin dynamics are confined to one\ndimension [J. Sabbatini et al., Phys. Rev. Lett. 107, 230402 (2011)]. The\ntransition is engineered by controlling a Hamiltonian quench of the coupling\namplitude of the two hyperfine states, and results in the formation of a random\npattern of spatial domains. Using the numerical truncated Wigner phase space\nmethod, we show that in a ring BEC the number of domains formed in the phase\ntransitions scales as predicted by the KZ theory. We also consider the same\nexperiment performed with a harmonically trapped BEC, and investigate how the\ndensity inhomogeneity modifies the dynamics of the phase transition and the KZ\nscaling law for the number of domains. We then make use of the symmetry between\ninhomogeneous phase transitions in anisotropic systems, and an inhomogeneous\nquench in a homogeneous system, to engineer coupling quenches that allow us to\nquantify several aspects of inhomogeneous phase transitions. In particular, we\nquantify the effect of causality in the propagation of the phase transition\nfront on the resulting formation of domain walls, and find indications that the\ndensity of defects is determined during the impulse to adiabatic transition\nafter the crossing of the critical point."
    },
    {
        "anchor": "Response function of strongly interacting Fermi gas in a virial\n  expansion: The dynamic response functions of strongly interacting fermion gas in\nhomogeneous space are investigated in a virial expansion to second order. The\ndensity response function exhibits transition from atomic to molecular\nresponse, as the interaction strength increases and the system undergoes\nBCS-BEC crossover. The qualitative features of density and spin response agree\nwith measurements from the Bragg spectroscopy experiments. The virial response\nis exact at low density and high temperature, therefore providing a benchmark\nfor many-body response.",
        "positive": "Resonant Scattering and Microscopic Model of Spinless Fermi Gases in\n  One-dimensional Optical Lattices: We study the effective Bloch-wave scattering of a spinless Fermi gas in\none-dimensional (1D) optical lattices. By tuning the odd-wave scattering\nlength, we find multiple resonances of Bloch-waves scattering at the bottom\n(and the top) of the lowest band, beyond which an attractive (and a repulsive)\ntwo-body bound state starts to emerge. These resonances exhibit comparable\nwidths in the deep lattice limit, and the finite interaction range plays an\nessential role in determining their locations. Based on the exact two-body\nsolutions, we construct an effective microscopic model for the low-energy\nscattering of fermions. The model can reproduce not only the scattering\namplitudes of Bloch-waves at the lowest band bottom/top, but also the\nattractive/repulsive bound states within a reasonably large energy range\nbelow/above the band. These results lay the foundation for quantum simulating\ntopological states in cold Fermi gases confined in 1D optical lattices."
    },
    {
        "anchor": "Hamilton's equations of motion of a vortex filament in the rotating\n  Bose-Einstein condensate and their \"soliton\" solutions: The equation of motion of a quantized vortex filament in a trapped\nBose-Einstein condensate [A. A. Svidzinsky and A. L. Fetter, Phys. Rev. A {\\bf\n62}, 063617 (2000)] has been generalized to the case of an arbitrary anharmonic\nanisotropic rotating trap and presented in a variational form. For condensate\ndensity profiles of the form $\\rho=f(x^2+y^2+\\mbox{Re\\,}\\Psi(x+iy))$ in the\npresence of the plane of symmetry $y=0$, the solutions $x(z)$ describing\nstationary vortices of U and S types coming to the surface and solitary waves\nhave been found in quadratures. Analogous three-dimensional configurations of\nthe vortex filament uniformly moving along the $z$ axis have also been found in\nstrictly cylindrical geometry. The dependence of solutions on the form of the\nfunction $f(q)$ has been analyzed.",
        "positive": "Quantum-statistics-induced flow patterns in driven ideal Fermi gases: While classical or quantum interacting liquids become turbulent under\nsufficiently strong driving, it is not obvious what flow pattern an ideal\nquantum gas develops under similar conditions. Unlike classical noninteracting\nparticles which exhibit rather trivial flow, ideal fermions have to satisfy the\nexclusion principle, which acts as a form of collective repulsion. We thus\nstudy the flow of an ideal Fermi gas as it is driven out of a narrow orifice of\nwidth comparable to the Fermi wavelength, employing both a microcanonical\napproach to transport, and solving a Lindblad equation for Markovian driving\nleads. Both methods are in good agreement and predict an outflowing current\ndensity with a complex microscopic pattern of vorticity in the steady state.\nApplying a bias of the order of the chemical potential results in a short-range\ncorrelated antiferromagnetic vorticity pattern, corresponding to local moments\nof the order of a tenth of a magneton, $e\\hbar/2m$, if the fermions are\ncharged. The latter may be detectable by magnetosensitive spectroscopy in\nstrongly driven cold gases (atoms) or clean electronic nanostructures\n(electrons)."
    },
    {
        "anchor": "Kelvin-Tkachenko waves of few-vortex arrays in trapped Bose-Einstein\n  condensates: We have calculated the low-lying elementary excitations of three-dimensional\nfew-vortex arrays in trapped Bose-Einstein condensates. The number of different\nKelvin-Tkachenko vortex wave branches matches the number of vortices in the\ncondensate. The lowest odd-parity modes exhibit superfluid gyroscopic vortex\nmotion. Experimentally, these modes could be excited and observed individually\nor in connection with the formation and decay of quantum turbulence.",
        "positive": "Interband heating processes in a periodically driven optical lattice: We investigate multi-\"photon\" interband excitation processes in an optical\nlattice that is driven periodically in time by a modulation of the lattice\ndepth. Assuming the system to be prepared in the lowest band, we compute the\nexcitation spectrum numerically. Moreover, we estimate the effective coupling\nparameters for resonant interband excitation processes analytically, employing\ndegenerate perturbation theory in Floquet space. We find that below a threshold\ndriving strength, interband excitations are suppressed exponentially with\nrespect to the inverse driving frequency. For sufficiently low frequencies,\nthis leads to a rather sudden onset of interband heating, once the driving\nstrength reaches the threshold. We argue that this behavior is rather generic\nand should also be found in lattice systems that are driven by other forms of\nperiodic forcing. Our results are relevant for Floquet engineering, where a\nlattice system is driven periodically in time in order to endow it with novel\nproperties like the emergence of a strong artificial magnetic field or a\ntopological band structure. In this context, interband excitation processes\ncorrespond to detrimental heating."
    },
    {
        "anchor": "Quantum Control by Imaging : The Zeno effect in an ultracold lattice gas: We demonstrate the control of quantum tunneling in an ultracold lattice gas\nby the measurement backaction imposed by an imaging process. A {\\em in situ}\nimaging technique is used to acquire repeated images of an ultracold gas\nconfined in a shallow optical lattice. The backaction induced by these position\nmeasurements modifies the coherent quantum tunneling of atoms within the\nlattice. By smoothly varying the rate at which spatial information is extracted\nfrom the atomic ensemble, we observe the continuous crossover from the 'weak\nmeasurement regime' where position measurements have little influence on the\ntunneling dynamics, to the 'strong measurement regime' where\nmeasurement-induced localization causes a large suppression of tunneling. This\nsuppression of coherent tunneling is a manifestation of the Quantum Zeno\neffect. Our study realizes an experimental demonstration of the paradigmatic\nHeisenberg microscope in a lattice gas and sheds light on the implications of\nquantum measurement on the coherent evolution of a mesoscopic quantum system.\nIn addition, this demonstrates a powerful technique for the control of an\ninteracting many-body quantum system via spatially resolved measurement\nbackaction.",
        "positive": "Symmetry breaking, Josephson oscillation and self-trapping in a\n  self-bound three-dimensional quantum ball: We study spontaneous symmetry breaking (SSB), Josephson oscillation, and\nself-trapping in a stable, mobile, three-dimensional matter-wave spherical\nquantum ball self-bound by attractive two-body and repulsive three-body\ninteractions. The SSB is realized by a parity-symmetric (a) one-dimensional\n(1D) double-well potential and (b) a 1D Gaussian potential, both along the $z$\naxis and no potential along the $x$ and $y$ axes. In the presence of each of\nthese potentials, the symmetric ground state dynamically evolves into a\ndoubly-degenerate SSB ground state. If the SSB ground state in the double well,\npredominantly located in the first well ($z>0$), is given a small displacement,\nthe quantum ball oscillates with a self-trapping in the first well. For a\nmedium displacement one encounters an asymmetric Josephson oscillation. The\nasymmetric oscillation is a consequence of SSB. The study is performed by a\nvariational and numerical solution of a non-linear mean-field model with 1D\nparity-symmetric perturbations."
    },
    {
        "anchor": "BCS-BEC crossover with unequal mass fermions: We investigate the crossover from BCS pairing to molecular BEC in an atomic\ngas with two fermion species with masses $m_\\up \\ne m_\\dn$ tuned through a\nFeshbach resonance. We present results for the T=0 equation of state as a\nfunction of the scattering length including the effects of Gaussian\nfluctuations about the mean field ground state. We compute the ground state\nenergy as a function of $m_\\up/m_\\dn$ at unitarity and find excellent agreement\nwith the quantum Monte Carlo result for $m_\\up/m_\\dn = 6.67$ for a\n$^{40}$K-$^6$Li mixture. We show that the dimer scattering length in the BEC\nlimit as a function of $m_\\up/m_\\dn$ compares well with exact four-body results\nof Petrov {\\it et al}. We also derive the condition for trapping frequencies to\nobtain an unpolarized gas in a harmonic trap.",
        "positive": "Multiple phase separation in one-dimensional mixtures of mass- and\n  population-imbalanced attractive Fermi gases: We study the attractive Fermi mixture of a\n${}^{6}\\mathrm{Li}$-${}^{40}\\mathrm{K}$ gas in one dimension using the\ncontinuous matrix product states variational ansatz and obtain the $T=0$ phase\ndiagram. We predict an axial density profile that contains four distinct phases\ntrapped induced along one-dimensional (1D) tubes, which is more intricate than\nthose observed in 1D mass-balanced systems or in higher-dimensional gas clouds.\nThe parameter regimes explored are realistic in view of possible future\nexperiments. This an application of continuous matrix product states to a\nnonintegrable fermionic system."
    },
    {
        "anchor": "Fractional photon-assisted tunneling in an optical superlattice: large\n  contribution to particle transfer: Fractional photon-assisted tunneling is investigated both analytically and\nnumerically for few interacting ultra-cold atoms in the double-wells of an\noptical superlattice. This can be realized experimentally by adding periodic\nshaking to an existing experimental setup [Phys. Rev. Lett. 101, 090404\n(2008)]. Photon-assisted tunneling is visible in the particle transfer between\nthe wells of the individual double wells. In order to understand the physics of\nthe photon-assisted tunneling, an effective model based on the rotating wave\napproximation is introduced. The validity of this effective approach is tested\nfor wide parameter ranges which are accessible to experiments in double-well\nlattices. The effective model goes well beyond previous perturbation theory\napproaches and is useful to investigate in particular the fractional\nphoton-assisted tunneling resonances. Analytic results on the level of the\nexperimentally realizable two-particle quantum dynamics show very good\nagreement with the numerical solution of the time-dependent Schr\\\"odinger\nequation. Far from being a small effect, both the one-half-photon and the\none-third-photon resonance are shown to have large effects on the particle\ntransfer.",
        "positive": "Off-diagonal long-range order in arrays of dipolar droplets: We report quantum Monte Carlo results of harmonically confined quantum Bose\ndipoles within a range of interactions covering the evolution from a gas phase\nto the formation of an array of droplets. Scaling the experimental setup to a\ncomputationally accessible domain we characterize that evolution in qualitative\nagreement with experiments. Our microscopic approach generates ground-state\nresults free from approximations, albeit with some controlled statistical\nnoise. The simultaneous estimation of the static structure factor and the\none-body density matrix allows for a better knowledge of the quantum coherence\nbetween droplets. Our results show a narrow window of interaction strengths\nwhere diagonal and off-diagonal long-range order can coexist. This domain,\nwhich is the key signal of a supersolid state, is reduced with respect to the\none predicted by the extended Gross-Pitaevskii equation. Differences are\nprobably due to an increase of attraction in our model, observed previously in\nthe calculation of critical atom numbers for single dipolar drops."
    },
    {
        "anchor": "Shape of a sound wave in a weakly-perturbed Bose gas: We employ the Gross-Pitaevskii equation to study acoustic emission generated\nin a uniform Bose gas by a static impurity. The impurity excites a sound-wave\npacket, which propagates through the gas. We calculate the shape of this wave\npacket in the limit of long wave lengths, and argue that it is possible to\nextract properties of the impurity by observing this shape. We illustrate here\nthis possibility for a Bose gas with a trapped impurity atom -- an example of a\nrelevant experimental setup. Presented results are general for all\none-dimensional systems described by the nonlinear Schr\\\"odinger equation and\ncan also be used in nonatomic systems, e.g., to analyze light propagation in\nnonlinear optical media. Finally, we calculate the shape of the sound-wave\npacket for a three-dimensional Bose gas assuming a spherically symmetric\nperturbation.",
        "positive": "Cooling through optimal control of quantum evolution: Nonadiabatic unitary evolution with tailored time-dependent Hamiltonians can\nprepare systems of cold atomic gases with various desired properties. For a\nsystem of two one-dimensional quasicondensates coupled with a time-varying\ntunneling amplitude, we show that the optimal protocol, for maximizing any\nfigure of merit in a given time, is bang-bang, i.e., the coupling alternates\nbetween only two values through a sequence of sudden quenches. Minimizing the\nenergy of one of the quasicondensates with such nonadiabatic protocols, and\nthen decoupling it at the end of the process, can result in effective cooling\nbeyond the current state of the art. Our cooling method can be potentially\napplied to arbitrary systems through an integration of the experiment with\nsimulated annealing computations."
    },
    {
        "anchor": "Stationary entanglement entropies following an interaction quench in 1D\n  Bose gas: We analyze the entanglement properties of the asymptotic steady state after a\nquench from free to hard-core bosons in one dimension. The R\\'enyi and von\nNeumann entanglement entropies are found to be extensive, and the latter\ncoincides with the thermodynamic entropy of the Generalized Gibbs Ensemble\n(GGE). Computing the spectrum of the two-point function, we provide exact\nanalytical results both for the leading extensive parts and the subleading\nterms for the entropies as well as for the cumulants of the particle number\nfluctuations. We also compare the extensive part of the entanglement entropy\nwith the thermodynamic ones, showing that the GGE entropy equal the\nentanglement one and it is the double of the diagonal entropy.",
        "positive": "Unified description of dynamics of a repulsive two-component Fermi gas: We study a binary spin-mixture of a zero-temperature repulsively interacting\n$^6$Li atoms using both the atomic-orbital and the density functional\napproaches. The gas is initially prepared in a configuration of two magnetic\ndomains and we determine the frequency of the spin-dipole oscillations which\nare emerging after the repulsive barrier, initially separating the domains, is\nremoved. We find, in agreement with recent experiment (G. Valtolina et al.,\narXiv:1605.07850 (2016)), the occurrence of a ferromagnetic instability in an\natomic gas while the interaction strength between different spin states is\nincreased, after which the system becomes ferromagnetic. The ferromagnetic\ninstability is preceded by the softening of the spin-dipole mode."
    },
    {
        "anchor": "Beyond effective Hamiltonians: micromotion of Bose Einstein condensates\n  in periodically driven optical lattices: We investigate a Bose Einstein condensate held in a 1D optical lattice whose\nphase undergoes a fast oscillation using a statistical analysis. The averaged\npotential experienced by the atoms boils down to a periodic potential having\nthe same spatial period but with a renormalized depth. However, the atomic\ndynamics also contains a \\emph{micromotion} whose main features are revealed by\na Kolmorogov-Smirnov analysis of the experimental momentum distributions. We\nfurthermore discuss the impact of the micromotion on a quench process\ncorresponding to a proper sudden change of the driving amplitude which reverses\nthe curvature of the averaged potential.",
        "positive": "The nonlinear Dirac equation in Bose-Einstein condensates: I.\n  Relativistic solitons in armchair nanoribbon optical lattices: We present a thorough analysis of soliton solutions to the\nquasi-one-dimensional nonlinear Dirac equation (NLDE) for a Bose-Einstein\ncondensate in a honeycomb lattice with armchair geometry. Our NLDE corresponds\nto a quasi-one-dimensional reduction of the honeycomb lattice along the zigzag\ndirection, in direct analogy to graphene nanoribbons. Excitations in the\nremaining large direction of the lattice correspond to the linear subbands in\nthe armchair nanoribbon spectrum. Analytical as well as numerical soliton Dirac\nspinor solutions are obtained. We analyze the solution space of the\nquasi-one-dimensional NLDE by finding fixed points, delineating the various\nregions in solution space, and through an invariance relation which we obtain\nas a first integral of the NLDE. We obtain spatially oscillating multi-soliton\nsolutions as well as asymptotically flat single soliton solutions using five\ndifferent methods: by direct integration; an invariance relation; parametric\ntransformation; a series expansion; and by numerical shooting. By tuning the\nratio of the chemical potential to the nonlinearity for a fixed value of the\nenergy-momentum tensor, we can obtain both bright and dark solitons over a\nnonzero density background."
    },
    {
        "anchor": "Fermi gas with attractive potential and arbitrary spin in\n  one-dimensional trap: A gas of ultracold $^6$Li atoms (effective spin 1/2) confined to an elongated\ntrap with one-dimensional properties is a candidate to display three different\nphases: (i) fermions bound in Cooper-pair-like states, (ii) unbound\nspin-polarized particles, and (iii) a mixed phase which is believed to have\nsome resemblance to the FFLO pairing. It is of great interest to extend these\nstudies to fermionic atoms with higher spin, e.g., for neutral $^{40}$K,\n$^{43}$Ca, $^{87}$Sr or $^{173}$Yb atoms. Within the grand-canonical ensemble\nwe investigated the $\\mu$ vs. $H$ phase diagram for $S=3/2$ ($\\mu$ is the\nchemical potential and $H$ the external magnetic field) for the ground state\nusing the exact Bethe {\\it ansatz} solution of the one-dimensional Fermi gas\ninteracting with an attractive $\\delta$-function potential. There are four\nfundamental states: The particles can be either unpaired or clustered in bound\nstates of two, three and four fermions. The rich phase diagram consists of\nthese four states and various mixed phases in which combinations of the\nfundamental states coexist. Bound states of four fermions are not favorable in\nhigh magnetic fields, but always present if the field is low. Working within\nthe grand-canonical ensemble has the following advantages: (1) A universal\nphase diagram is obtained by scaling with respect to the interaction strength\nand (2) possible scenarios for phase separation are explored within the local\ndensity approximation. The phase diagram for the superposition of a Zeeman and\na quadrupolar splitting is also discussed.",
        "positive": "Symmetry breaking and entropy production during the evolution of spinor\n  Bose-Einstein condensate driven by coherent atom beam: The spinor condensate with spin states degenerated in the ground spin-space\nprovides a unique platform for investigating the edge of quantum mechanics and\nstatistical physics. We study the evolution of the condensate under the\nscattering of a coherent atom beam. The time-dependent magnetization,\nentanglement entropy, thermal entropy and the entropy production rate are\ncalculated. A novel spontaneous symmetry breaking is found during the\nevolution, It is shown that the stationary spin distribution can be controlled\nby the incoming coherent spin state of the incident atom beam, therefore the\natom-condensate scattering provides a new way to probe the spin distribution of\nthe condensate"
    },
    {
        "anchor": "Interacting atomic interferometry for rotation sensing approaching the\n  Heisenberg Limit: Atom interferometers provide exquisite measurements of the properties of\nnon-inertial frames. While atomic interactions are typically detrimental to\ngood sensing, efforts to harness entanglement to improve sensitivity remain\ntantalizing. Here we explore the role of interactions in an analogy between\natomic gyroscopes and SQUIDs, motivated by recent experiments realizing ring\nshaped traps for ultracold atoms. We explore the one-dimensional limit of these\nring systems with a moving weak barrier, such as that provided by a\nblue-detuned laser beam. In this limit, we employ Luttinger liquid theory and\nfind an analogy with the superconducting phase-slip qubit, in which the\ntopological charge associated with persistent currents can be put into\nsuperposition. In particular, we find that strongly-interacting atoms in such a\nsystem could be used for precision rotation sensing. We compare the performance\nof this new sensor to an equivalent non-interacting atom interferometer, and\nfind improvements in sensitivity and bandwidth beyond the atomic shot-noise\nlimit.",
        "positive": "The phase diagram of 2D polar condensates in a magnetic field: Spin one condensates in the polar (antiferromagnetic) phase in two dimensions\nare shown to undergo a transition of the Ising type, in addition to the\nexpected Kosterlitz--Thouless (KT) transition of half vortices, due to the\nquadratic Zeeman effect. We establish the phase diagram in terms of temperature\nand the strength of the Zeeman effect using Monte Carlo simulations. When the\nZeeman effect is sufficiently strong the Ising and KT transitions merge. For\nvery strong Zeeman field the remaining transition is of the familiar integer KT\ntype."
    },
    {
        "anchor": "Quantum fluctuations beyond the Gutzwiller approximation in the\n  Bose-Hubbard model: Taking inspiration from the state-of-the art knowledge of the Bose-Hubbard\n(BH) model and recent methodological developments in its fermionic counterpart,\nthis work deals with the study of the collective dynamics of a lattice Bose gas\nbeyond the mean-field picture through a quantum description of its elementary\nexcitations. The Hamiltonian quantization, performed via a Bogoliubov\nquadratization of the BH action within the Gutzwiller approach, allows to\nexpand the effective action of the theory up to second order in the\nfluctuations around the mean-field solution, as well as to prefigure the\npossibility of identifying the main decay vertices of the collective modes and\nother effects that are not evident at the second-order level. This quantum\ndescription extends the standard Bogoliubov approach to the study of superfluid\nBose systems for comprising higher excitation branches, including the Higgs\nmode in the superfluid phase, and identifies their physical meaning together\nwith appropriate observables which could be taken into consideration for their\nexperimental characterization. The ultimate aim of the quantization procedure\nis the determination of fundamental quantities as the depletion of the\ncondensate and the effective superfluid fraction, which are not accessible by a\nmean-field description or not completely characterized in the regime of strong\ninteractions.",
        "positive": "Collective modes of trapped spinor Bose condensates: We study the richer structures of quasi-one-dimensional Bogoliubov-de Genes\ncollective excitations of F = 1 spinor Bose-Einstein condensate in a harmonic\ntrap potential loaded in an optical lattice. Employing a perturbative method we\nreport general analytical expressions for the confined collective polar and\nferromagnetic Goldstone modes. In both cases the excited eigenfrequencies are\ngiven as function of the 1D effective coupling constants, trap frequency and\noptical lattice parameters. It is shown that the main contribution of the\noptical lattice laser intensity is to shift the confined phonon frequencies.\nMoreover, for high intensities, the excitation spectrum becomes independent of\nthe self-interaction parameters. We reveal some features of the evolution for\nthe Goldstone modes as well as the condensate densities from the ferromagnetic\nto the polar phases."
    },
    {
        "anchor": "Roton-Maxon Excitation Spectrum of Bose Condensates in a Shaken Optical\n  Lattice: We present experimental evidence showing that an interacting Bose condensate\nin a shaken optical lattice develops a roton-maxon excitation spectrum, a\nfeature normally associated with superfluid helium. The roton-maxon feature\noriginates from the double-well dispersion in the shaken lattice, and can be\ncontrolled by both the atomic interaction and the lattice shaking amplitude. We\ndetermine the excitation spectrum using Bragg spectroscopy and measure the\ncritical velocity by dragging a weak speckle potential through the condensate -\nboth techniques are based on a digital micromirror device. Our dispersion\nmeasurements are in good agreement with a modified-Bogoliubov model.",
        "positive": "The Haldane Model with Chiral Edge States using a Synthetic Dimension: We explicitly show that the differences, with respect to the appearance of\ntopological phases, between the traditional Haldane model, which utilises a\nhoneycomb lattice structure, to that of the Haldane model imbued onto a\nbrick-wall lattice geometry, are inconsequential. A proposal is then put\nforward to realise the Haldane model by exploiting the internal degrees of\nfreedom of atoms as a synthetic dimension. This leads to a convenient platform\nfor the investigation of chiral edge states due to the hard boundaries provided\nby the hyperfine manifold. We make some cursory comments on the effects of\ninteractions in the system."
    },
    {
        "anchor": "Dissipative two-dimensional Raman lattice: We show that a dissipative two-dimensional Raman lattice can be engineered in\na two-component ultracold atomic gas, where the interplay of the\ntwo-dimensional spin-orbit coupling and lightinduced atom loss gives rise to a\ndensity flow diagonal to the underlying square lattice. The flow is driven by\nthe non-Hermitian corner skin effect, under which eigenstates localize toward\none corner of the system. We illustrate that the topological edge states of the\nsystem can only be accounted for by the non-Bloch band theory where the\ndeformation of the bulk eigenstates are explicitly considered. The directional\nflow can be detected through the dynamic evolution of an initially localized\ncondensate in the lattice, or by introducing an immobile impurity species that\ninteract spin-selectively with a condensate in the ground state of the Raman\nlattice.",
        "positive": "Phase spreading and temporal coherence of a pair-condensed Fermi gas at\n  low temperature: A condensate of pairs in an isolated, homogeneous, unpolarised, finite-size\nspin 1/2 Fermi gas at low nonzero temperature T, undergoes with time a phase\nchange with a random component, due to coupling to the gas thermal phonons.\nWith the quantum second Josephson relation relating the derivative of the\ncondensate phase operator to the phonon occupation numbers, and linearised\nkinetic equations giving the evolution of occupation number fluctuations, we\naccess the behaviour of the phase change variance at times much longer than the\nphonon collision time. The case of a convex phonon branch is similar to the\nBose gas case: the leading collisional processes are the Beliaev-Landau\n3-phonons processes, and the variance is the sum of a ballistic term and of a\ndelayed diffusive term, whose analytical expressions are given in the\nthermodynamic limit. The concave case is more exotic. It is analysed at time\nscales $T^{-9}$, allowing one to restrict to 2 phonons $\\rightarrow$ 2 phonons\nsmall-angle Landau-Khalatnikov processes. The total number of phonons is\nconserved and the phonon mean occupation numbers at equilibrium can exhibit a\nnegative chemical potential, assumed isotropic. The phase change variance is\nthen the sum of a ballistic term, of a diffusive term, of exotic subsubleading\nterms and of a constant term. The analytic expression of some of the\ncorresponding coefficients is obtained, as well as the diverging leading\nbehavior of the other ones when the phonon chemical potential tends to 0. When\nthis chemical potential is 0, the variance sub-ballistic part becomes\nsuperdiffusive, with an exponent 5/3 and an exactly-known coefficient. For a\nnonzero infinitesimal phonon chemical potential, a law is found, interpolating\nbetween superdiffusive and diffusive phase spreading. Also new results are\nobtained on the phonon Landau-Khalatnikov damping rate, in particular at\nnegative phonon chemical potential."
    },
    {
        "anchor": "Quantum chaos in SU_3 models with trapped ions: A scheme to generate long-range spin-spin interactions between three-level\nions in a chain is presented, providing a feasible experimental route to the\nrich physics of well-known $SU_3$ models. In particular, we demonstrate\ndifferent signatures of quantum chaos which can be controlled and observed in\nexperiments with trapped ions.",
        "positive": "Dropping an impurity into a Chern insulator: a polaron view on\n  topological matter: We investigate the properties of an impurity particle interacting with a\nFermi gas in a Chern-insulating state. The interaction leads to the formation\nof an exotic polaron, which consists of a coherent superposition of the\ntopologically-trivial impurity and the surrounding topological cloud. We\ncharacterize this intriguing topologically-composite object by calculating its\ntransverse (Hall) conductivity, using diagrammatic as well as variational\nmethods. The \"polaronic Hall conductivity\" is shown to be non-zero whenever the\nsurrounding cloud is prepared in a non-trivial Chern insulating state, which we\nattribute to the transverse drag exerted by the dressing cloud on the impurity.\nIn this way, the polaron partially inherits the topological properties of the\nChern insulator through genuine interaction effects. This is also analysed at\nthe microscopic level of wave functions, by identifying a \"composite Berry\ncurvature\" for the polaron, which closely mimics the Berry curvature of the\nChern insulator's band structure. Finally, we discuss how this interplay\nbetween topology and many-body correlations can be studied in cold-atom\nexperiments, using available technologies."
    },
    {
        "anchor": "Density-wave steady-state phase of dissipative ultracold fermions with\n  nearest-neighbor interactions: In this work we investigate the effect of local dissipation on the presence\nof density-wave ordering in spinful fermions with both local and\nnearest-neighbor interactions as described by the extended Hubbard model. We\nfind density-wave order to be robust against decoherence effects up to a\ncritical point where the system becomes homogeneous with no spatial ordering.\nOur results will be relevant for future cold-atom experiments using fermions\nwith non-local interactions arising from the dressing by highly-excited Rydberg\nstates, which have finite lifetimes due to spontaneous emission processes.",
        "positive": "Scale Invariance in the Lowest Landau Level: We show that the discrete set of pair amplitudes $A_m$ introduced by Haldane\nare an angular-momentum resolved generalization of the Tan two-body contact,\nwhich parametrizes universal short-range correlations in atomic quantum gases.\nThe pair amplitudes provide a complete description of translation-invariant and\nrotation-invariant states in the lowest Landau level (LLL), both compressible\nand incompressible. To leading nontrivial order beyond the non-interacting\nhigh-temperature limit, they are determined analytically in terms of the\nHaldane pseudopotential parameters $V_m$, which provides a qualitative\ndescription of the crossover towards incompressible ground states for different\nfilling factors. Moreover, we show that for contact interactions $\\sim g_2\n\\delta^{(2)}({\\bf x})$, which are scale invariant at the classical level, the\nnon-commutativity of the guiding center coordinates gives rise to a quantum\nanomaly in the commutator $i [\\hat{H}_{\\rm LLL}, \\hat{D}_R] = (2 + \\ell\n\\partial_\\ell) \\hat{H}_{\\rm LLL}$ with the dilatation operator $\\hat{D}_R$ in\nthe LLL, which replaces the trace anomaly in the absence of a magnetic field.\nThe interaction-induced breaking of scale invariance gives rise to a finite\nfrequency shift of the breathing mode in a harmonic trap, which describes\ntransitions between different Landau levels, the strength of which is estimated\nin terms of the relevant dimensionless coupling constant $\\tilde{g}_2$."
    },
    {
        "anchor": "Excitation picture of an interacting Bose gas: Atomic Bose-Einstein condensates (BECs) can be viewed as macroscopic objects\nwhere atoms form correlated atom clusters to all orders. Therefore, the\npresence of a BEC makes the direct use of the cluster-expansion approach ---\nlucrative e.g. in semiconductor quantum optics --- inefficient when solving the\nmany-body kinetics of a strongly interacting Bose. An excitation picture is\nintroduced with a nonunitary transformation that exclusively describes the\nsystem in terms of atom clusters within the normal component alone. The\nnontrivial properties of this transformation are systematically studied, which\nyields a cluster-expansion friendly formalism for a strongly interacting Bose\ngas. Its connections and corrections to the standard Hartree-Fock Bogoliubov\napproach are discussed and the role of the order parameter and the Bogoliubov\nexcitations are identified. The resulting interaction effects are shown to\nvisibly modify number fluctuations of the BEC. Even when the BEC has a nearly\nperfect second-order coherence, the BEC number fluctuations can still resolve\ninteraction-generated non-Poissonian fluctuations.",
        "positive": "Observation of Dynamical Fermionization: We observe dynamical fermionization, where the momentum distribution of a\nTonks-Girardeau (T-G) gas of strongly interacting bosons in 1D evolves from\nbosonic to fermionic after its axial confinement is removed. The asymptotic\nmomentum distribution after expansion in 1D is the distribution of rapidities,\nwhich are the conserved quantities associated with many-body integrable\nsystems. Rapidities have not previously been measured in any interacting\nmany-body quantum system. Our measurements agree well with T-G gas theory. We\nalso study momentum evolution after the trap depth is suddenly changed to a new\nnon-zero value. We observe the predicted bosonic-fermionic oscillations and see\ndeviations from the theory outside of the T-G gas limit."
    },
    {
        "anchor": "Probing the exchange statistics of one-dimensional anyon models: We propose feasible scenarios for revealing the modified exchange statistics\nin one-dimensional anyon models in optical lattices based on an extension of\nthe multicolor lattice-depth modulation scheme introduced in [{Phys. Rev. A 94,\n023615 (2016)}]. We show that the fast modulation of a two-component fermionic\nlattice gas in the presence a magnetic field gradient, in combination with\nadditional resonant microwave fields, allows for the quantum simulation of\nhardcore anyon models with periodic boundary conditions. Such a semi-synthetic\nring set-up allows for realizing an interferometric arrangement sensitive to\nthe anyonic statistics. Moreover, we show as well that simple expansion\nexperiments may reveal the formation of anomalously bound pairs resulting from\nthe anyonic exchange.",
        "positive": "Period-doubled Bloch states in a Bose-Einstein condensate: We study systematically the period-doubled Bloch states for a weakly\ninteracting Bose-Einstein condensate in a one-dimensional optical lattice. This\nkind of state is of form $\\psi_k=e^{ikx}\\phi_k(x)$, where $\\phi_k(x)$ is of\nperiod twice the optical lattice constant. Our numerical results show how these\nnonlinear period-doubled states grow out of linear period-doubled states at a\nquarter away from the Brillouin zone center as the repulsive interatomic\ninteraction increases. This is corroborated by our analytical results. We find\nthat all nonlinear period-doubled Bloch states have both Landau instability and\ndynamical instability."
    },
    {
        "anchor": "Finite Range Effects in Energies and Recombination Rates of Three\n  Identical Bosons: We investigate finite-range effects in systems with three identical bosons.\nWe calculate recombination rates and bound state spectra using two different\nfinite-range models that have been used recently to describe the physics of\ncold atomic gases near Feshbach resonances where the scattering length is\nlarge. The models are built on contact potentials which take into account\nfinite range effects; one is a two-channel model and the other is an effective\nrange expansion model implemented through the boundary condition on the\nthree-body wave function when two of the particles are at the same point in\nspace. We compare the results with the results of the ubiquitous\nsingle-parameter zero-range model where only the scattering length is taken\ninto account. Both finite range models predict variations of the well-known\ngeometric scaling factor 22.7 that arises in Efimov physics. The threshold\nvalue at negative scattering length for creation of a bound trimer moves to\nhigher or lower values depending on the sign of the effective range compared to\nthe location of the threshold for the single-parameter zero-range model. Large\neffective ranges, corresponding to narrow resonances, are needed for the\nreduction to have any noticeable effect.",
        "positive": "Singularities in the Loschmidt echo of quenched topological\n  superconductors: We study the Loschmidt echo in the quenched two-dimensional $p$-wave\ntopological superconductor. We find that if this superconductor is quenched out\nof the critical point separating its topological and non-topological phases\ninto either of the two gapful phases, its Loschmidt echo features singularities\noccurring periodically in time where the second derivative of the Loschmidt\necho over time diverges logarithmically. Conversely, we give arguments towards\n$s$-wave superconductors not having singularities in their Loschmidt echo\nregardless of the quench. We also demonstrate that the conventional mean field\ntheory calculates classical echo instead of its quantum counterpart, and show\nhow it should be modified to capture the full quantum Loschmidt echo."
    },
    {
        "anchor": "Bosonic superfluid-insulator transition in continuous space: We investigate the zero-temperature phase diagram of interacting Bose gases\nin the presence of a simple cubic optical lattice, going beyond the regime\nwhere the mapping to the single-band Bose-Hubbard model is reliable. Our\ncomputational approach is a new hybrid quantum Monte Carlo method which\ncombines algorithms used to simulate homogeneous quantum fluids in continuous\nspace with those used for discrete lattice models of strongly correlated\nsystems. We determine the critical interaction strength and optical lattice\nintensity where the superfluid-to-insulator transition takes place, considering\nalso the regime of shallow optical lattices and strong inter-atomic\ninteractions. The implications of our findings for the super-solid state of\nmatter are discussed.",
        "positive": "Spontaneous pattern formation in an anti-ferromagnetic quantum gas: Spontaneous pattern formation is a phenomenon ubiquitous in nature, examples\nranging from Rayleigh-Benard convection to the emergence of complex organisms\nfrom a single cell. In physical systems, pattern formation is generally\nassociated with the spontaneous breaking of translation symmetry and is closely\nrelated to other symmetry-breaking phenomena, of which (anti-)ferromagnetism is\na prominent example. Indeed, magnetic pattern formation has been studied\nextensively in both solid-state materials and classical liquids. Here, we\nreport on the spontaneous formation of wave-like magnetic patterns in a spinor\nBose-Einstein condensate, extending those studies into the domain of quantum\ngases. We observe characteristic modes across a broad range of the magnetic\nfield acting as a control parameter. Our measurements link pattern formation in\nthese quantum systems to specific unstable modes obtainable from linear\nstability analysis. These investigations open new prospects for controlled\nstudies of symmetry breaking and the appearance of structures in the quantum\ndomain."
    },
    {
        "anchor": "Direct and inverse cascades of spin-wave turbulence in spin-1\n  ferromagnetic spinor Bose-Einstein condensates: We theoretically and numerically study spin-wave turbulence in spin-1\nferromagnetic spinor Bose-Einstein condensates, finding direct and inverse\ncascades with power-law behavior. To derive these power exponents analytically,\nthe conventional weak wave turbulence theory is applied to the spin-1 spinor\nGross-Pitaevskii equation. Thus, we obtain the $-7/3$ and $-5/3$ power laws in\nthe transverse spin correlation function for the direct and inverse cascades,\nrespectively. To confirm these power laws, numerical calculations are performed\nthat obtain results consistent with these power laws.",
        "positive": "Spin-orbit coupling in organic microcavities: Lower polariton splitting,\n  triplet polaritons, and disorder-induced dark-states relaxation: Using an extended Tavis-Cummings model, we study the effect of the spin-orbit\ncoupling between the singlet and the triplet molecular excitons in organic\nmicrocavities in the strong coupling regime. The model is solved in the single\nexcitation space for polaritons, which contains the bright (permutation\nsymmetric) singlet and triplet excitons, as well as the dark bands consisting\nof the nonsymmetric excitons of either type. We find that the spin-orbit\ncoupling splits the lower polariton into two branches, and also creates a\ntriplet polariton when the cavity mode is in resonance with the triplet\nexcitons. The optical absorption spectrum of the system that can reveal this\nsplitting in experiments is presented and the effect of disorder in exciton\nenergies and couplings is explored. An important consequence of the disorder in\nthe spin-orbit coupling -- a weak coupling between the otherwise decoupled\nbright and dark sectors -- is explored and detailed calculations of the squared\ntransition matrix elements between the dark bands and polaritons are presented\nalong with derivation of some approximate yet quite accurate analytical\nexpressions. This relaxation channel for the dark states contains an\ninterference between two transition paths that, for a given polariton state,\nsuppresses the relaxation of one dark band and enhances it for the other."
    },
    {
        "anchor": "Realizing Altermagnetism in Fermi-Hubbard Models with Ultracold Atoms: Altermagnetism represents a new type of collinear magnetism distinct from\nferromagnetism and conventional antiferromagnetism. In contrast to the latter,\nsublattices of opposite spin are related by spatial rotations and not only by\ntranslations and inversions. As a result, altermagnets have spin split bands\nleading to unique experimental signatures. Here, we show theoretically how a\nd-wave altermagnetic phase can be realized with ultracold fermionic atoms in\noptical lattices. We propose an altermagnetic Hubbard model with anisotropic\nnext-nearest neighbor hopping and obtain the Hartree-Fock phase diagram. The\naltermagnetic phase separates in a metallic and an insulating phase and is\nrobust over a large parameter regime. We show that one of the defining\ncharacteristics of altermagnetism, the anisotropic spin transport, can be\nprobed with trap-expansion experiments.",
        "positive": "Modified interactions in a Floquet topological system on a square\n  lattice and their impact on a bosonic fractional Chern insulator state: We propose a simple scheme for the realization of a topological quasienergy\nband structure with ultracold atoms in a periodically driven optical square\nlattice. It is based on a circular lattice shaking in the presence of a\nsuperlattice that lowers the energy on every other site. The topological band\ngap, which separates the two bands with Chern numbers $\\pm 1$, is opened in a\nway characteristic to Floquet topological insulators, namely, by terms of the\neffective Hamiltonian that appear in subleading order of a high-frequency\nexpansion. These terms correspond to processes where a particle tunnels several\ntimes during one driving period. The interplay of such processes with particle\ninteractions also gives rise to new interaction terms of several distinct\ntypes. For bosonic atoms with on-site interactions, they include nearest\nneighbor density-density interactions introduced at the cost of weakened\non-site repulsion as well as density-assisted tunneling. Using exact\ndiagonalization, we investigate the impact of the individual induced\ninteraction terms on the stability of a bosonic fractional Chern insulator\nstate at half filling of the lowest band."
    },
    {
        "anchor": "Quantum Simulation Meets Nonequilibrium Dynamical Mean Field Theory:\n  Exploring the Periodically Driven, Strongly Correlated Fermi-Hubbard Model: We perform an ab-initio comparison between nonequilibrium dynamical\nmean-field theory and optical lattice experiments by studying the time\nevolution of double occupations in the periodically driven Fermi-Hubbard model.\nFor off-resonant driving, the range of validity of a description in terms of an\neffective static Hamiltonian is determined and its breakdown due to energy\nabsorption close to resonance is demonstrated. For near-resonant driving, we\ninvestigate the response to a change in driving amplitude and discover an\nasymmetric excitation spectrum with respect to the detuning. In general, we\nfind good agreement between experiment and theory, which cross-validates the\nexperimental and numerical approaches in a strongly-correlated nonequilibrium\nsystem.",
        "positive": "Isentropic Curves at Magnetic Phase Transitions: Experiments on cold atom systems in which a lattice potential is ramped up on\na confined cloud have raised intriguing questions about how the temperature\nvaries along isentropic curves, and how these curves intersect features in the\nphase diagram. In this paper, we study the isentropic curves of two models of\nmagnetic phase transitions- the classical Blume-Capel Model (BCM) and the Fermi\nHubbard Model (FHM). Both Mean Field Theory (MFT) and Monte Carlo (MC) methods\nare used. The isentropic curves of the BCM generally run parallel to the phase\nboundary in the Ising regime of low vacancy density, but intersect the phase\nboundary when the magnetic transition is mainly driven by a proliferation of\nvacancies. Adiabatic heating occurs in moving away from the phase boundary. The\nisentropes of the half-filled FHM have a relatively simple structure, running\nparallel to the temperature axis in the paramagnetic phase, and then curving\nupwards as the antiferromagnetic transition occurs. However, in the doped case,\nwhere two magnetic phase boundaries are crossed, the isentrope topology is\nconsiderably more complex."
    },
    {
        "anchor": "Hanle model of a spin-orbit coupled Bose-Einstein condensate of excitons\n  in semiconductor quantum wells: We present a theoretical model of a driven-dissipative spin-orbit coupled\nBose-Einstein condensate of indirect excitons in semiconductor quantum wells\n(QW's). Our steady-state solution of the problem shares analogies with the\nHanle effect in an optical orientation experiment. The role of the spin pump in\nour case is played by boson stimulated scattering into the linearly-polarized\nground state and the depolarization occurs as a result of long-range exchange\ninteraction between electrons and holes. Our theory agrees with the recent\nexperiment [A. A. High et al., Phys. Rev. Lett. 110, 246403 (2013)], where\nspontaneous emergence of spatial coherence and polarization texture have been\nobserved. As a complementary test, we discuss a configuration where an external\nmagnetic field is applied in the structure plane.",
        "positive": "Dynamics of large samples of repulsive Fermi gases at nonzero\n  temperatures: We develop a model of a binary fermionic mixture, consisting of large number\nof atoms, applicable at nonzero temperatures, in the normal phase. We use this\napproach to study dynamics of degenerate Fermi systems under various\nperturbations. For example, we analyze spin-dipole oscillations of a\ntwo-component fermionic mixture, demonstrating that the ferromagnetic phase\nshows up at stronger repulsion between components while the temperature raises.\nWe study as well the radial oscillations of weakly interacting repulsive Fermi\ngases. We obtain a good agreement with experimental data when available.\nOtherwise, we compare our results with the outcome of the Hartree-Fock orbital\ncalculations done for the system with small number of fermions."
    },
    {
        "anchor": "Non-perturbative renormalization-group approach to the Bose-Hubbard\n  model: We present a non-perturbative renormalization-group approach to the\nBose-Hubbard model. By taking as initial condition of the RG flow the (local)\nlimit of decoupled sites, we take into account both local and long-distance\nfluctuations in a nontrivial way. This approach yields a phase diagram in very\ngood quantitative agreement with the quantum Monte Carlo results and reproduces\nthe two universality classes of the superfluid--Mott-insulator transition with\na good estimate of the critical exponents. Furthermore, it reveals the crucial\nrole of the \"Ginzburg length\" as a crossover length between a weakly- and a\nstrongly-correlated superfluid phase.",
        "positive": "Direct observation of chiral currents and magnetic reflection in atomic\n  flux lattices: The prospect of studying topological matter with the precision and control of\natomic physics has driven the development of many techniques for engineering\nartificial magnetic fields and spin-orbit interactions. Recently, the idea of\nintroducing nontrivial topology through the use of internal (or external)\natomic states as effective \"synthetic dimensions\" has garnered attraction for\nits versatility and possible immunity from heating. Here, we directly engineer\ntunable artificial gauge fields through the local control of tunneling phases\nin an effectively two-dimensional manifold of discrete atomic momentum states.\nWe demonstrate the ability to create homogeneous gauge fields of arbitrary\nvalue, directly imaging the site-resolved dynamics of induced chiral currents.\nWe furthermore engineer the first inhomogeneous artificial gauge fields for\ncold atoms, observing the magnetic reflection of atoms incident upon a\nstep-like variation of an artificial vector potential. These results open up\nnew possibilities for the study of topological phases and localization\nphenomena in atomic gases."
    },
    {
        "anchor": "Chladni solitons and the onset of the snaking instability for dark\n  solitons in confined superfluids: Complex solitary waves composed of intersecting vortex lines are predicted in\na channeled superfluid. Their shapes in a cylindrical trap include a cross,\nspoke wheels, and Greek $\\Phi$, and trace the nodal lines of unstable vibration\nmodes of a planar dark soliton in analogy to Chladni's figures of membrane\nvibrations. The stationary solitary waves extend a family of solutions that\ninclude the previously known solitonic vortex and vortex rings. Their\nbifurcation points from the dark soliton indicating the onset of new unstable\nmodes of the snaking instability are predicted from scale separation for\nBose-Einstein condensates (BECs) and superfluid Fermi gases across the BEC--BCS\ncrossover, and confirmed by full numerical calculations. Chladni solitons could\nbe observed in ultra-cold gas experiments by seeded decay of dark solitons.",
        "positive": "Rotation Sensitive Quench and Revival of Coherent Oscillations in a Ring\n  Lattice: We consider ultracold atoms trapped in a toroidal trap with an azimuthal\nlattice for utility as a macroscopic simulator of quantum optics phenomena. We\nexamine the dynamics induced by the adiabatic introduction of the lattice that\nserves to couple the normal modes, as an analog of a laser field coupling\nelectronic states. The system is found to display two distinct behaviors,\nmanifest in the angular momentum - coherent oscillation and self-trapping -\nreminiscent of non-linear dynamics, yet not requiring interatomic interactions.\nThe choice is set by the interplay of discrete parameters, the specific initial\nmode and the periodicity of the lattice. However, rotation can cause continuous\ntransition between the two regimes, causing periodic quenches and revivals in\nthe oscillations as a function of the angular velocity. Curiously, the impact\nof rotation is determined entirely by the energy spectrum in the absence of the\nlattice, a feature that can be attributed to adiabaticity. We assess the\neffects of varying the lattice parameters, and consider applications in\nrotation sensing."
    },
    {
        "anchor": "Generating multiparticle entangled states by self-organization of driven\n  ultracold atoms: We describe a mechanism for guiding the dynamical evolution of ultracold\natomic motional degrees of freedom toward multiparticle entangled\nDicke-squeezed states, via nonlinear self-organization under external driving.\nTwo examples of many-body models are investigated. In the first model, the\nexternal drive is a temporally oscillating magnetic field leading to\nself-organization by interatomic scattering. In the second model, the drive is\na pump laser leading to transverse self organization by photon-atom scattering\nin a ring cavity. We numerically demonstrate the generation of multiparticle\nentangled states of atomic motion and discuss prospective experimental\nrealizations of the models. For the cavity case, the calculations with\nadiabatically eliminated photonic sidebands show significant momentum\nentanglement generation can occur even in the \"bad cavity\" regime. The results\nhighlight the potential for using self-organization of atomic motion in quantum\ntechnological applications.",
        "positive": "Exact results for persistent currents of two bosons in a ring lattice: We study the ground state of two interacting bosonic particles confined in a\nring-shaped lattice potential and subjected to a synthetic magnetic flux. The\nsystem is described by the Bose-Hubbard model and solved exactly through a\nplane-wave Ansatz of the wave function. We obtain energies and correlation\nfunctions of the system both for repulsive and attractive interactions. In\ncontrast with the one-dimensional continuous theory described by the\nLieb-Liniger model, in the lattice case we prove that the center of mass of the\ntwo particles is coupled with its relative coordinate. Distinctive features\nclearly emerge in the persistent current of the system. While for repulsive\nbosons the persistent current displays a periodicity given by the standard flux\nquantum for any interaction strength, in the attractive case the flux quantum\nbecomes fractionalized in a manner that depends on the interaction. We also\nstudy the density after the long time expansion of the system which provides an\nexperimentally accessible route to detect persistent currents in cold atom\nsettings. Our results can be used to benchmark approximate schemes for the\nmany-body problem."
    },
    {
        "anchor": "Bosons in a double-well potential: Understanding the interplay between\n  disorder and interaction in a simple model: We propose an exactly solvable model to reveal the physics of the interplay\nbetween interaction and disorder in bosonic systems. Considering interacting\nbosons in a double-well potential, in which disorder is mimicked by taking the\nenergy level mismatch between the two wells to be randomly distributed, we find\n\"two negatives make a positive\" effect. While disorder or interaction by itself\nsuppresses the phase coherence between the two wells, both together enhance the\nphase coherence. This model also captures several striking features of the\ndisordered Bose-Hubbard model found in recent numerical simulations. Results at\nfinite temperatures may help explain why a recent experiment did not find any\nevidence for the enhancement of phase coherence in a disordered bosonic system.",
        "positive": "Correcting inconsistencies in the conventional superfluid path integral\n  scheme: In this paper we show how to redress a shortcoming of the path integral\nscheme for fermionic superfluids and superconductors. This approach is built\naround a simultaneous calculation of electrodynamics and thermodynamics. An\nimportant sum rule, the compressibility sum rule, fails to be satisfied in the\nusual calculation of the electromagnetic and thermodynamic response at the\nGaussian fluctuation level. Here we present a path integral scheme to address\nthis inconsistency. Specifically, at the leading order we argue that the\nsuperconducting gap should be calculated using a different saddle point\ncondition modified by the presence of an external vector potential. This leads\nto the well known gauge-invariant BCS electrodynamic response and is associated\nwith the usual (mean field) expression for thermodynamics. In this way the\ncompressibility sum rule is satisfied at the BCS level. Moreover, this scheme\ncan be readily extended to address arbitrary higher order fluctuation theories.\nAt any level this approach will lead to a gauge invariant and compressibility\nsum rule consistent treatment of electrodynamics and thermodynamics."
    },
    {
        "anchor": "The Gor'kov and Melik-Barkhudarov correction to an imbalanced Fermi gas\n  in the presence of impurities: The effects of induced interactions are calculated in both clean and dirty\nsituations, for balanced and imbalanced Fermi gases. We investigate the effects\nof nonmagnetic impurities on the induced interactions corrections to the\ntransition temperature in the case of a balanced gas, and to the tricritical\npoint in the case of an imbalanced Fermi gas at unitarity. We find that\nimpurities act in detriment of the induced interactions, or particle-hole\nfluctuations, for the transition temperature and the tricritical point. For\nlarge impurity parameter, the particle-hole fluctuations are strongly\nsuppressed. We have also found the Chandrasekhar-Clogston limit of an\nimbalanced Fermi gas at unitarity considering the effects of the induced\ninteractions, both in the pure and impurity regimes.",
        "positive": "Ion solvation in atomic baths: from snowballs to polarons: Solvation, the result of the complicated interplay between solvent-solute and\nsolvent-internal interactions, is one of the most important chemical processes.\nConsequently, a complete theoretical understanding of solvation seems a heroic\ntask. However, it is possible to elucidate fundamental solvation mechanisms by\nlooking into simpler systems, such as ion solvation in atomic baths. In this\nwork, we study ion solvation by calculating the ground state properties of a\nsingle ion in a neutral bath from the high-density regime to the low-density\nregime, finding common ground for these two, in principle, disparate regimes.\nOur results indicate that a single $^{174}$Yb$^+$ ion in a bath of $^{7}$Li\natoms forms a coordination complex at high densities with a coordination number\nof 8, with strong electrostriction, characteristic of the snowball effect. On\nthe contrary, treating the atomic bath as a dilute quantum gas at low\ndensities, we find that the ion-atom interaction's short-range plays a\nsignificant role in the physics of many-body bound states and polarons.\nFurthermore, in this regime, we explore the role of a putative ion trap, which\ndrastically affects the binding mechanism of the ion and atoms from a quantum\ngas. Therefore, our results give a novel insight into the universality of\nion-neutral systems in the ultracold regime and the possibilities of observing\nexotic many-body effects."
    },
    {
        "anchor": "Observation of brane parity order in programmable optical lattices: The Mott-insulating phase of the two-dimensional (2d) Bose-Hubbard model is\nexpected to be characterized by a non-local brane parity order. Parity order\ncaptures the presence of microscopic particle-hole fluctuations and\nentanglement, whose properties depend on the underlying lattice geometry. We\nrealize 2d Bose-Hubbard models in dynamically tunable lattice geometries, using\nneutral atoms in a novel passively phase-stable tunable optical lattice in\ncombination with programmable site-blocking potentials. We benchmark the\nperformance of our system by single-particle quantum walks in the square,\ntriangular, kagome and Lieb lattice. In the strongly correlated regime, we\nmicroscopically characterize the geometry dependence of the quantum\nfluctuations and experimentally validate the brane parity as a proxy for the\nnon-local order parameter signaling the superfluid-to-Mott insulating phase\ntransition.",
        "positive": "Phase fluctuations and first-order correlation functions of dissipative\n  Bose-Einstein condensates: We investigate the finite lifetime effects on first-order correlation\nfunctions of dissipative Bose-Einstein condensates. By taking into account the\nphase fluctuations up to all orders, we show that the finite lifetime effects\nare neglible for the spatial first-order correlation functions, but have an\nimportant effect on the temporal correlations. As an application, we calculate\nthe one-particle density matrix of a quasi-condensate of photons. Finally, we\nalso consider the photons in the normal state and we demonstrate that the\nfinite lifetime effects decrease both the spatial and temporal first-order\ncorrelation functions."
    },
    {
        "anchor": "Tail-free self-accelerating solitons and vortices: Self-accelerating waves in conservative systems, which usually feature slowly\ndecaying tails, such as Airy waves, have drawn great interest in studies of\nquantum and classical wave dynamics. They typically appear in linear media,\nwhile nonlinearities tend to deform and eventually destroy them. We\ndemonstrate, by means of analytical and numerical methods, the existence of\nrobust one- and two-dimensional (1D and 2D) self-accelerating tailless solitons\nand solitary vortices in a model of two-component Bose-Einstein condensates,\ndressed by a microwave (MW) field, whose magnetic component mediates long-range\ninteraction between the matter-wave constituents, with the feedback of the\nmatter waves on the MW field taken into account. In particular,\nself-accelerating 2D solitons may move along a curved trajectory in the\ncoordinate plane. The system may also include the spin-orbit coupling between\nthe components, leading to similar results for the self-acceleration. The\neffect persists if the contact cubic nonlinearity is included. A similar\nmechanism may generate 1D and 2D self-accelerating solitons in optical media\nwith thermal nonlinearity.",
        "positive": "General features and contact modeling of $N$-body isolated resonances\n  near threshold: $N$-body non efimovian bound or quasi-bound states for particles with short\nrange interactions are considered in arbitrary dimensions. The different\nresonance regimes near the threshold are depicted by using a generalization of\nthe effective range approximation. This two-parameter description can be used\nin various contexts from ultra-cold to hadronic physics. The universal\ncharacter of these states makes it possible a formulation in terms of a contact\nmodel. The singularity at the contact imposes the introduction of a modified\nscalar product to solve the normalization catastrophe and to restore the\nself-adjoint character of the model. An equivalence with the standard scalar\nproduct used for realistic finite range models is derived."
    },
    {
        "anchor": "Particle-hole pairs and density-density correlations in the Lieb-Liniger\n  model: We review the recently introduced thermodynamic form factors for pairs of\nparticle-hole excitations on finite-entropy states in the Lieb-Liniger model.\nWe focus on the density operator and we show how the form factors can be used\nfor analytic computations of dynamical correlation functions. We derive a new\nrepresentation for the form factors and we discuss some aspects of their\nstructure. We rigorously show that in the small momentum limit (or\nequivalently, on hydrodynamic scales) a single particle-hole excitation fully\nsaturates the spectral sum and we also discuss the contribution from two\nparticle-hole pairs. Finally we show that thermodynamic form factors can be\nalso used to study the ground state correlations and to derive the edge\nexponents.",
        "positive": "Viscosity-entropy ratio of the unitary Fermi gas from zero-temperature\n  elementary excitations: We investigate the low-temperature behavior of the ratio between the shear\nviscosity \\eta and the entropy density s in the unitary Fermi gas by using a\nmodel based on the zero-temperature spectra of both bosonic collective modes\nand fermonic single-particle excitations. Our theoretical curve of \\eta/s as a\nfunction of the temperature T is in qualitative agreement with the experimental\ndata of trapped ultracold 6Li atomic gases. We find the minimum value \\eta/s\n\\simeq 0.44 (in units of \\hbar/k_B) at the temperature T/T_F \\simeq 0.27, with\nT_F the Fermi temperature."
    },
    {
        "anchor": "Numerical study of localized impurity in a Bose-Einstein condensate: Motivated by recent experiments, we investigate a single $^{133}\\text{Cs}$\nimpurity in the center of a trapped $^{87}\\text{Rb}$ Bose-Einstein condensate.\nWithin a zero-temperature mean-field description we provide a one-dimensional\nphysical intuitive model which involves two coupled differential equations for\nthe condensate and the impurity wave function, which we solve numerically. With\nthis we determine within the equilibrium phase diagram spanned by the intra-\nand inter-species coupling strength, whether the impurity is localized at the\ntrap center or expelled to the condensate border. In the former case we find\nthat the impurity induces a bump or dip on the condensate for an attractive or\na repulsive Rb-Cs interaction strength, respectively. Conversely, the\ncondensate environment leads to an effective mass of the impurity which\nincreases quadratically for small interspecies interaction strength.\nAfterwards, we investigate how the impurity imprint upon the condensate wave\nfunction evolves for two quench scenarios. At first we consider the case that\nthe harmonic confinement is released. During the resulting time-of-flight\nexpansion it turns out that the impurity-induced bump in the condensate wave\nfunction starts decaying marginally, whereas the dip decays with a\ncharacteristic time scale which decreases with increasing repulsive\nimpurity-BEC interaction strength. Secondly, once the attractive or repulsive\ninterspecies coupling constant is switched off, we find that white-shock waves\nor bi-solitons emerge which both oscillate within the harmonic confinement with\na characteristic frequency.",
        "positive": "Symmetry breaking in dipolar matter-wave solitons in dual-core couplers: We study effects of the spontaneous symmetry-breaking (SSB) in solitons built\nof the dipolar Bose-Einstein condensate (BEC), trapped in a dual-core system\nwith the dipole-dipole interactions (DDIs) and hopping between the cores. Two\nrealizations of such a matter-wave coupler are introduced, weakly- and\nstrongly-coupled. The former one in based on two parallel pipe-shaped traps,\nwhile the latter one is represented by a single pipe sliced by an external\nfield into parallel layers. The dipoles are oriented along axes of the pipes.\nIn these systems, the dual-core solitons feature the SSB of the supercritical\ntype and subcritical types, respectively. Stability regions are identified for\nsymmetric and asymmetric solitons, and, in addition, for non-bifurcating\nantisymmetric ones, as well as for symmetric flat states, which may also be\nstable in the strongly-coupled system, due to competition between the\nattractive and repulsive intra- and inter-core DDIs. Effects of the contact\ninteractions are considered too. Collisions between moving asymmetric solitons\nin the weakly-symmetric system feature elastic rebound, merger into a single\nbreather, and passage accompanied by excitation of intrinsic vibrations of the\nsolitons, for small, intermediate, and large collision velocities,\nrespectively. A PT-symmetric version of the weakly-coupled system is briefly\nconsidered too, which may be relevant for matter-wave lasers. Stability\nboundaries for PT-symmetric and antisymmetric solitons are identified."
    },
    {
        "anchor": "Tunneling vortex dynamics in linearly coupled Bose-Hubbard rings: The quantum dynamics of population-balanced fractional vortices and\npopulation-imbalanced vortices in an effective two-state bosonic system, made\nof two coupled discrete circuits with few sites, is addressed within the\nBose-Hubbard model. % We show that for low on-site interaction, the tunneling\nof quantized vortices between the rings performs a coherent, oscillating\ndynamics connecting current states with chiral symmetry. The vortex-flux\ntransfer dually follows the usual sinusoidal particle current of the Josephson\neffect, in good agreement with a mean-field approximation. Within such regime,\nthe switch of persistent currents in the rings resembles flux-qubit features,\nand is feasible to experimental realization. On the contrary, strong\ninteratomic interactions suppress the chiral current and lead the system into\nfragmented condensation.",
        "positive": "Correlated dynamics of collective droplet excitations in a\n  one-dimensional harmonic trap: We address the existence and dynamics of one-dimensional harmonically\nconfined quantum droplets, appearing in two-component mixtures by deploying a\nnonperturbative approach. We find that, in symmetric homonuclear settings,\nbeyond Lee-Huang-Yang correlations result in flat-top droplet configurations\nfor either decreasing intercomponent attraction or larger atom number.\nAsymmetric mixtures feature spatial mixing among the involved components with\nthe more strongly interacting or heavier one exhibiting flat-top structures.\nApplying quenches on the harmonic trap we trigger the lowest-lying collective\ndroplet excitations. The interaction-dependent breathing frequency, being\nslightly reduced in the presence of correlations, shows a decreasing trend for\nstronger attractions. Semi-analytical predictions are also obtained within the\nLee-Huang-Yang framework. For relatively large quench amplitudes the droplet\nprogressively delocalizes and higher-lying motional excitations develop in its\ncore. Simultaneously, enhanced intercomponent entanglement and long-range\ntwo-body intracomponent correlations arise. In sharp contrast, the dipole\nmotion remains robust irrespectively of the system parameters. Species\nselective quenches lead to a correlation-induced dephasing of the droplet or to\nirregular dipole patterns due to intercomponent collisions."
    },
    {
        "anchor": "Sound propagation in a uniform superfluid two-dimensional Bose gas: In superfluid systems several sound modes can be excited, as for example\nfirst and second sound in liquid helium. Here, we excite propagating and\nstanding waves in a uniform two-dimensional Bose gas and we characterize the\npropagation of sound in both the superfluid and normal regime. In the\nsuperfluid phase, the measured speed of sound is well described by a two-fluid\nhydrodynamic model, and the weak damping rate is well explained by the\nscattering with thermal excitations. In the normal phase the sound becomes\nstrongly damped due to a departure from hydrodynamic behavior.",
        "positive": "Universal high-momentum asymptote and thermodynamic relations in a\n  spinless Fermi gas with a resonant $p$-wave interaction: We investigate universal relations in a spinless Fermi gas near a $p$-wave\nFeshbach resonance. We show that the momentum distribution $n_{\\vec{k}}$ has an\nasymptote proportional to $k^{-2}$ with the proportionality constant--the\n$p$-wave contact-- scaling with the number of closed-channel molecules. We\nprove the adiabatic sweep theorem for a $p$-wave resonance which reveals the\nphysical meaning of the $p$-wave contact in thermodynamics. In contrast to the\nunitary Fermi gas in which Tan's contact is universal, the $p$-wave contact\ndepends on the short-range details of the interaction."
    },
    {
        "anchor": "Thermodynamics of Trapped Photon Gases at Dimensional Crossover from 2D\n  to 1D: Photon Bose-Einstein condensates are characterised by a quite weak\ninteraction, so they behave nearly as an ideal Bose gas. Moreover, since the\ncurrent experiments are conducted in a microcavity, the longitudinal motion is\nfrozen out and the photon gas represents effectively a two-dimensional trapped\ngas of massive bosons. In this paper we focus on a harmonically confined ideal\nBose gas in two dimensions, where the anisotropy of the confinement allows for\na dimensional crossover. If the confinement in one direction is strong enough\nso that this squeezed direction is frozen out, then only one degree of freedom\nsurvives and the system can be considered to be quasi-one dimensional. In view\nof an experimental set-up we work out analytically the thermodynamic properties\nfor such a system with a finite number of photons. In particular, we focus on\nexamining the dimensional information which is contained in the respective\nthermodynamic quantities.",
        "positive": "Observation of Dynamical Quantum Phase Transition with Correspondence in\n  Excited State Phase Diagram: Dynamical quantum phase transitions are closely related to equilibrium\nquantum phase transitions for ground states. Here, we report an experimental\nobservation of a dynamical quantum phase transition in a spinor condensate with\ncorrespondence in an excited state phase diagram, instead of the ground state\none. We observe that the quench dynamics exhibits a non-analytical change with\nrespect to a parameter in the final Hamiltonian in the absence of a\ncorresponding phase transition for the ground state there. We make a connection\nbetween this singular point and a phase transition point for the highest energy\nlevel in a subspace with zero spin magnetization of a Hamiltonian. We further\nshow the existence of dynamical phase transitions for finite magnetization\ncorresponding to the phase transition of the highest energy level in the\nsubspace with the same magnetization. Our results open a door for using\ndynamical phase transitions as a tool to probe physics at higher energy\neigenlevels of many-body Hamiltonians."
    },
    {
        "anchor": "Conformal-invariance of 2D quantum turbulence in an exciton-polariton\n  fluid of light: The similarities of quantum turbulence with classical hydrodynamics allow\nquantum fluids to provide essential models of their classical analogue, paving\nthe way for fundamental advances in physics and technology. Recently,\nexperiments on 2D quantum turbulence observed the clustering of same-sign\nvortices in strong analogy with the inverse energy cascade of classical fluids.\nHowever, self-similarity of the turbulent flow, a fundamental concept in the\nstudy of classical turbulence, has so far remained largely unexplored in\nquantum systems. Here, thanks to the unique features of exciton-polaritons, we\nmeasure the scale invariance of velocity circulations and show that the cascade\nprocess follows the universal scaling of critical phenomena in 2D. We\ndemonstrate this behaviour from the statistical analysis of the experimentally\nmeasured incompressible velocity field and the microscopic imaging of the\nquantum fluid. These results can find wide application in both quantum and\nclassical 2D turbulence.",
        "positive": "Tight-binding models in a quasiperiodic optical lattice: This paper describes how one can use four standing wave laser fields to\nrealize a two dimensional optical quasicrystal with eight-fold symmetry,\nclosely related to the well-known octagonal or Ammann-Beenker tiling\nquasicrystal. We describe the structure and its properties, and the effective\ntight-binding model for atoms in this optical quasicrystal. Such a system, if\nrealized experimentally, should provide valuable insights into the quantum\nproperties of quasicrystals."
    },
    {
        "anchor": "Displaced dynamics of binary mixtures in linear and nonlinear optical\n  lattices: The dynamical behavior of matter wave solitons of two-component Bose-Einstein\ncondensates (BEC) in combined linear and nonlinear optical lattices (OLs) is\ninvestigated. In particular, the dependence of the frequency of the oscillating\ndynamics resulting from initially slightly displaced components is investigated\nboth analytically, by means of a variational effective potential approach for\nthe reduced collective coordinate dynamics of the soliton, and numerically, by\ndirect integrations of the mean field equations of the BEC mixture. We show\nthat for small initial displacements binary solitons can be viewed as point\nmasses connected by elastic springs of strengths related to the amplitude of\nthe OL and to the intra and inter-species interactions. Analytical expressions\nof symmetric and anti-symmetric mode frequencies, are derived and occurrence of\nbeatings phenomena in the displaced dynamics is predicted. These expressions\nare shown to give a very good estimation of the oscillation frequencies for\ndifferent values of the intra-species interatomic scattering length, as\nconfirmed by direct numerical integrations of the mean field Gross-Pitaevskii\nequations (GPE) of the mixture. The possibility to use displaced dynamics for\nindirect measurements of BEC mixture characteristics such as number of atoms\nand interatomic interactions is also suggested.",
        "positive": "Efficient production of an 87Rb F = 2, mF = 2 Bose-Einstein condensate\n  in a hybrid trap: We have realized Bose-Einstein condensation (BEC) of 87Rb in the F=2, m_F=2\nhyperfine substate in a hybrid trap, consisting of a quadrupole magnetic field\nand a single optical dipole beam. The symmetry axis of the quadrupole magnetic\ntrap coincides with the optical beam axis, which gives stronger axial\nconfinement than previous hybrid traps. After loading 2x10^6 atoms at 14 muK\nfrom a quadrupole magnetic trap into the hybrid trap, we perform efficient\nforced evaporation and reach the onset of BEC at a temperature of 0.5 muK and\nwith 4x10^5 atoms. We also obtain thermal clouds of 1x10^6 atoms below 1 muK in\na pure single beam optical dipole trap, by ramping down the magnetic field\ngradient after evaporative cooling in the hybrid trap."
    },
    {
        "anchor": "Reply to \"Comment on 'Kinetic theory for a mobile impurity in a\n  degenerate Tonks-Girardeau gas'\": In our recent paper [Phys. Rev. E 90, 032132 (2014)] we have studied the\ndynamics of a mobile impurity particle weakly interacting with the\nTonks-Girardeau gas and pulled by a small external force, $F$. Working in the\nregime when the thermodynamic limit is taken prior to the small force limit, we\nhave found that the Bloch oscillations of the impurity velocity are absent in\nthe case of a light impurity. Further, we have argued that for a light impurity\nthe steady state drift velocity, $V_D$, remains finite in the limit\n$F\\rightarrow 0$. These results are in contradiction with earlier works by\nGangardt, Kamenev and Schecter [Phys. Rev. Lett. 102, 070402 (2009), Annals of\nPhysics 327, 639 (2012)]. One of us (OL) has conjectured [Phys. Rev. A 91,\n040101 (2015)] that the central assumption of these works - the adiabaticity of\nthe dynamics - can break down in the thermodynamic limit. In the preceding\nComment [Phys. Rev. E 92, 016101 (2015)] Schecter, Gangardt and Kamenev have\nargued against this conjecture and in support of the existence of Bloch\noscillations and linearity of $V_D(F)$. They have suggested that the ground\nstate of the impurity-fluid system is a quasi-bound state and that this is\nsufficient to ensure adiabaticity in the thermodynamic limit. Their analytical\nargument is based on a certain truncation of the Hilbert space of the system.\nWe argue that extending the results and intuition based on their truncated\nmodel on the original many-body problem lacks justification.",
        "positive": "Quantum Chaos for the Unitary Fermi Gas from the Generalized Boltzmann\n  Equations: In this paper, we study the chaotic behavior of the unitary Fermi gas in both\nhigh and low temperature limits by calculating the Quantum Lyapunov exponent\ndefined in terms of the out-of-time-order correlator. We take the method of\ngeneralized Boltzmann equations derived from the augmented Keldysh approach\n\\cite{augKeldysh}. At high temperature, the system is described by weakly\ninteracting fermions with two spin components and the Lyapunov exponent is\nfound to be $\\lambda_L=21\\frac{n}{T^{1/2}}$. Here $n$ is the density of\nfermions for a single spin component. In the low temperature limit, the system\nis a superfluid and can be described by phonon modes. Using the effective\naction derived in \\cite{Son}, we find $\\lambda_L=9\\times\n10^3\\left(\\frac{T}{T_F}\\right)^4T$ where $T_F$ is the Fermi energy. By\ncomparing these to existing results of heat conductivity, we find that $D_E\\ll\nv^2 /\\lambda_L$ where $D_E$ is the energy diffusion constant and $v$ is some\ntypical velocity. We argue that this is related to the conservation law for\nsuch systems with quasi-particles."
    },
    {
        "anchor": "Measuring Chern numbers in Hofstadter strips: Topologically non-trivial Hamiltonians with periodic boundary conditions are\ncharacterized by strictly quantized invariants. Open questions and fundamental\nchallenges concern their existence, and the possibility of measuring them in\nsystems with open boundary conditions and limited spatial extension. Here, we\nconsider transport in Hofstadter strips, that is, two-dimensional lattices\npierced by a uniform magnetic flux which extend over few sites in one of the\nspatial dimensions. As we show, an atomic wavepacket exhibits a transverse\ndisplacement under the action of a weak constant force. After one Bloch\noscillation, this displacement approaches the quantized Chern number of the\nperiodic system in the limit of vanishing tunneling along the transverse\ndirection. We further demonstrate that this scheme is able to map out the Chern\nnumber of ground and excited bands, and we investigate the robustness of the\nmethod in presence of both disorder and harmonic trapping. Our results prove\nthat topological invariants can be measured in Hofstadter strips with open\nboundary conditions and as few as three sites along one direction.",
        "positive": "The second critical point for the Perfect Bose gas in\n  quasi-one-dimensional traps: We present a new model of quasi-one-dimensional trap with some unknown\nphysical predictions about a second transition, including about a change in\nfractions of condensed coherence lengths due to the existence of a second\ncritical temperature Tm < Tc. If this physical model is acceptable, we want to\nchallenge experimental physicists in this regard."
    },
    {
        "anchor": "Specific Heat and Effects of Uniaxial Anisotropy of a $p$-wave Pairing\n  Interaction in a Strongly Interacting Ultracold Fermi Gas: We investigate the specific heat $C_V$ at constant volume and effects of\nuniaxial anisotropy of a $p$-wave attractive interaction in the normal state of\nan ultracold Fermi gas. Within the framework of the strong-coupling theory\ndeveloped by Nozi\\`eres and Schmitt-Rink, we evaluate this thermodynamic\nquantity as a function of temperature, in the whole interaction regime. While\nthe uniaxial anisotropy is not crucial for $C_V$ in the weak-coupling regime,\n$C_V$ is found to be sensitive to the uniaxial anisotropy in the\nstrong-coupling regime. This originates from the population imbalance among\n$p_i$-wave molecules ($i=x,y,z$), indicating that the specific heat is a useful\nobservable to see which kinds of $p$-wave molecules dominantly exist in the\nstrong-coupling regime when the $p$-wave interaction has uniaxial anisotropy.\nUsing this strong point, we classify the strong-coupling regime into some\ncharacteristic regions. Since a $p$-wave pairing interaction with uniaxial\nanisotropy has been discovered in a $^{40}$K Fermi gas, our results would be\nuseful in considering strong-coupling properties of a $p$-wave interacting\nFermi gas, when the interaction is uniaxially anisotropic.",
        "positive": "Creation and dynamics of remote spin-entangled pairs in the expansion of\n  strongly correlated fermions in an optical lattice: We consider the nonequilibrium dynamics of an interacting spin-1/2 fermion\ngas in a one-dimensional optical lattice after switching off the confining\npotential. In particular, we study the creation and the time evolution of\nspatially separated, spin-entangled fermionic pairs. The time-dependent\ndensity-matrix renormalization group is used to simulate the time evolution and\nevaluate the two-site spin correlation functions, from which the concurrence is\ncalculated. We find that the typical distance between entangled fermions\ndepends crucially on the onsite interaction strength, and that a time-dependent\nmodulation of the tunneling amplitude can enhance the production of\nspin-entanglement. Moreover, we discuss the prospects of experimentally\nobserving these phenomena using spin-dependent single-site detection."
    },
    {
        "anchor": "Evolution of Higgs mode in a Fermion Superfluid with Tunable\n  Interactions: In this letter we present a coherent picture for the evolution of Higgs mode\nin both neutral and charged $s$-wave fermion superfluids, as the strength of\nattractive interaction between fermions increases from the BCS to the BEC\nregime. In the case of neutral fermionic superfluid, such as ultracold\nfermions, the Higgs mode is pushed to higher energy while at the same time,\ngradually loses its spectral weight as interaction strength increases toward\nthe BEC regime, because the system is further tuned away from Lorentz\ninvariance. On the other hand, when damping is taken into account, Higgs mode\nis significantly broadened due to coupling to phase mode in the whole BEC-BCS\ncrossover. In the charged case of electron superconductor, the Anderson-Higgs\nmechanism gaps out the phase mode and suppresses the coupling between the Higgs\nand the phase modes, and consequently, stabilizes the Higgs mode.",
        "positive": "First-order superfluid to Mott-insulator phase transitions in spinor\n  condensates: We observe evidence of first-order superfluid to Mott-insulator quantum phase\ntransitions in a lattice-confined antiferromagnetic spinor Bose-Einstein\ncondensate. The observed signatures include hysteresis effect and significant\nheatings across the phase transitions. The nature of the phase transitions is\nfound to strongly depend on the ratio of the quadratic Zeeman energy to the\nspin-dependent interaction. Our observations are qualitatively understood by\nthe mean field theory, and in addition suggest tuning the quadratic Zeeman\nenergy is a new approach to realize superfluid to Mott-insulator phase\ntransitions."
    },
    {
        "anchor": "Classical versus quantum dynamics of the atomic Josephson junction: We compare the classical (mean-field) dynamics with the quantum dynamics of\natomic Bose-Einstein condensates in double-well potentials. The quantum\ndynamics are computed using a simple scheme based upon the Raman-Nath\nequations. Two different methods for exciting a non-equilbrium state are\nconsidered: an asymmetry between the wells which is suddenly removed, and a\nperiodic time oscillating asymmetry. The first method generates wave packets\nthat lead to collapses and revivals of the expectation values of the\nmacroscopic variables, and we calculate the time scale for these revivals. The\nsecond method permits the excitation of a single energy eigenstate of the\nmany-particle system, including Schroedinger cat states. We also discuss a band\ntheory interpretation of the energy level structure of an asymmetric\ndouble-well, thereby identifying analogies to Bloch oscillations and Bragg\nresonances. Both the Bloch and Bragg dynamics are purely quantum and are not\ncontained in the mean-field treatment.",
        "positive": "The Aharonov-Bohm effect in mesoscopic Bose-Einstein condensates: Ultra-cold atoms in light-shaped potentials open up new ways to explore\nmesoscopic physics: Arbitrary trapping potentials can be engineered with only a\nchange of the laser field. Here, we propose using ultracold atoms in\nlight-shaped potentials to feasibly realize a cold atom device to study one of\nthe fundamental problems of mesoscopic physics, the Aharonov-Bohm effect: The\ninteraction of particles with a magnetic field when traveling in a closed loop.\nSurprisingly, we find that the Aharonov-Bohm effect is washed out for\ninteracting bosons, while it is present for fermions. We show that our atomic\ndevice has possible applications as quantum simulator, Mach-Zehnder\ninterferometer and for tests of quantum foundation."
    },
    {
        "anchor": "Density profiles and density oscillations of an interacting\n  three-component normal Fermi gas: We use a semiclassical approximation to investigate density variations and\ndipole oscillations of an interacting three-component normal Fermi gas in a\nharmonic trap. We consider both attractive and repulsive interactions between\ndifferent pairs of fermions and study the effect of population imbalance on\ndensities. We find that the density profiles significantly deviate from those\nof non-interacting profiles and extremely sensitive to interactions and\npopulation imbalance. Unlike for a two-component Fermi system, we find density\nimbalance even for balanced populations. For some range of parameters, one\ncomponent completely repels from the trap center giving rise a donut shape\ndensity profile. Further, we find that the in-phase dipole oscillation\nfrequency is consistent with Kohn's theorem and other two dipole mode\nfrequencies are strongly effected by the interactions and the number of atoms\nin the harmonic trap.",
        "positive": "Spin rotons and supersolids in binary antidipolar condensates: We present a theoretical study of a mixture of antidipolar and nondipolar\nBose-Einstein condensates confined to an infinite tube. We predict the presence\nof a spin roton and its associated instability, which triggers a continuous\nunmodulated--to--supersolid phase transition. We characterize the phase diagram\nof the binary system, ranging from the quasi-1D to the radial Thomas-Fermi\n(elongated 3D) regimes. We also present the dynamic formation of supersolids\nfollowing a quench from the uniform miscible phase, which maintains phase\ncoherence across the system."
    },
    {
        "anchor": "Spontaneous solitons in the thermal equilibrium of a\n  quasi-one-dimensional Bose gas: Solitons, or non-destructible local disturbances, are important features of\nmany one-dimensional (1D) nonlinear wave phenomena, from water waves in narrow\ncanals to light pulses in optical fibers. In ultra-cold gases, they have long\nbeen sought, and were first observed to be generated by phase-imprinting. More\nrecently, their spontaneous formation in 1D gases was predicted as a result of\nthe Kibble-Zurek mechanism, rapid evaporative cooling, and dynamical processes\nafter a quantum quench. Here we show that they actually occur generically in\nthe thermal equilibrium state of a weakly-interacting elongated Bose gas,\nwithout the need for external forcing or perturbations. This reveals a major\nnew quality to the experimentally widespread quasicondensate state. It can be\nunderstood via thermal occupation of the famous and somewhat elusive Type II\nexcitations in the Lieb-Liniger model of a uniform 1D gas.",
        "positive": "Engineered Nearest-Neighbour Interactions with Doubly Modulated Optical\n  Lattices: Optical lattice systems provide exceptional platforms for quantum simulation\nof many-body systems. We focus on the doubly modulated Bose-Hubbard model\ndriven by both time-dependent on-site energy and interaction, and predict the\nemergence of the nearest neighbour interaction and density-assisted tunnelling.\nBy specifically designing a bi-chromatic driving pattern for a one dimensional\nlattice, we demonstrate that the doubly modulated fields can be tuned to\nrealize desired quantum phases, e.g. the Mott insulator phase with selective\ndefects, and density wave phase."
    },
    {
        "anchor": "Quantum stabilization of photonic spatial correlations: The driven, dissipative Bose-Hubbard model (BHM) provides a generic\ndescription of collective phases of interacting photons in cavity arrays. In\nthe limit of strong optical nonlinearities (hard-core limit), the BHM maps on\nthe dissipative, transverse-field XY model (XYM). The steady-state of the XYM\ncan be analyzed using mean-field theory, which reveals a plethora of\ninteresting dynamical phenomena. For example, strong hopping combined with a\nblue-detuned drive, leads to an instability of the homogeneous steady-state\nwith respect to antiferromagnetic fluctuations. In this paper, we address the\nquestion whether such an antiferromagnetic instability survives in the presence\nof quantum correlations beyond the mean-field approximation. For that purpose,\nwe employ a self-consistent $1/z$ expansion for the density matrix, where $z$\nis the lattice coordination number, i.e., the number of nearest neighbours for\neach site. We show that quantum fluctuations stabilize a new homogeneous\nsteady-state with antiferromagnetic correlations in agreement with exact\nnumerical simulations for finite lattices. The latter manifests itself as\nshort-ranged oscillations of the first and second-order spatial coherence\nfunctions of the photons emitted by the array.",
        "positive": "Variational study of polarons and bipolarons in a 1D Bose lattice gas in\n  both superfluid and Mott regimes: We use variational methods to study a spin impurity in a 1D Bose lattice gas.\nBoth in the strongly interacting superfluid regime and the Mott regime we find\nthat the impurity binds with a hole, forming a polaron. Our calculations for\nthe dispersion of the polaron are consistent with recent experiments by\nFukuhara et. al. [Nature Phys. 9, 235 (2013)] and give a better understanding\nof their numerical simulations. We find that for sufficiently weak interactions\nthere are ranges of momentum for which the polaron is unstable. We propose\nexperimentally studying the stability of the polaron by measuring the\ncorrelation between the impurity and holes. We also study two interacting\nimpurities, finding stable bipolarons for sufficiently strong interactions."
    },
    {
        "anchor": "An ansatz for the nonlinear Demkov-Kunike problem for cold molecule\n  formation: We study nonlinear mean-field dynamics of ultracold molecule formation in the\ncase when the external field configuration is defined by the level-crossing\nDemkov-Kunike model, characterized by a bell-shaped coupling and finite\nvariation of the detuning. Analyzing the fast sweep rate regime of the strong\ninteraction limit, which models a situation when the peak value of the coupling\nis large enough and the resonance crossing is sufficiently fast, we construct a\nhighly accurate ansatz to describe the temporal dynamics of the molecule\nformation in the mentioned interaction regime. The absolute error of the\nconstructed approximation is less than 3*10^-6 for the final transition\nprobability while at certain time points it might increase up to 10^-3.\nExamining the role of the different terms in the constructed approximation, we\nprove that in the fast sweep rate regime of the strong interaction limit the\ntemporal dynamics of the atom-molecule conversion effectively consists of the\nprocess of resonance crossing, which is governed by a nonlinear equation,\nfollowed by atom-molecular coherent oscillations which are basically described\nby a solution of the linear problem, associated with the considered nonlinear\none.",
        "positive": "Few-Body Route to One-Dimensional Quantum Liquids: Gapless many-body quantum systems in one spatial dimension are universally\ndescribed by the Luttinger liquid effective theory at low energies.\nEssentially, only two parameters enter the effective low-energy description,\nnamely the speed of sound and the Luttinger parameter. These are highly system\ndependent and their calculation requires accurate non-perturbative solutions of\nthe many-body problem. Here, we present a simple method that only uses\ncollisional information to extract the low-energy properties of these systems.\nOur results are in remarkable agreement with available results for integrable\nmodels and from large scale Monte Carlo simulations of one-dimensional helium\nand hydrogen isotopes. Moreover, we estimate theoretically the critical point\nfor spinodal decomposition in one-dimensional helium-4, and show that the\nexponent governing the divergence of the Luttinger parameter near the critical\npoint is exactly 1/2, in excellent agreement with Monte Carlo simulations."
    },
    {
        "anchor": "Dissipative Josephson vortices in annular polariton fluids: We consider two concentric rings formed by bosonic condensates of\nexciton-polaritons. A circular superfluid flow of polaritons in one of the\nrings can be manipulated by acting upon the second annular polariton\ncondensate. The complex coupling between the rings with different topological\ncharges triggers nucleation of stable Josephson vortices (JVs) which are\nrevealed as topological defects of the angular dependence of the relative phase\nbetween rings. Being dependent on the coupling strength, the structure of the\nJV governs the difference of the mean angular momenta of the inner and the\nouter rings. At the vanishing coupling the condensates rotate independently\ndemonstrating no correlations of their winding numbers. At the moderate\ncoupling, the interaction between two condensates tends to equalize their mean\nangular momenta despite of the mismatch of the winding numbers demonstrating\nthe phenomenology of a drag effect. Above the critical coupling strength the\nsynchronous rotation is established via the phase slip events.",
        "positive": "Ground state phase diagram of ultrasoft bosons: In 2D bosonic systems ultra-soft interactions develop an interesting\nphenomenology that ultimately leads to the appearance of supersolid phases in\nfree space conditions. While suggested in early theoretical works and despite\nmany further analytical efforts, the appearance of these exotic phases as well\nas the detailed shape of the ground-state phase diagrams have not been\nestablished yet. Here we develop a variational mean-field calculation for a\ngeneric quantum system with cluster-forming interactions. We show that by\nincluding the restriction of a fixed integer number of particles per cluster\nthe ground-state phase diagram can be obtained in great detail. The latter\nincludes the determination of coexistence regimes of crystals of different\noccupancy as well as crystals with super-fluid phases. To illustrate the\napplication of the method we consider an ultrasoft potential for which the\ncomputational phase diagram is known. Our results show very good quantitative\nagreement with the simulations and suggest that the solid-superfluid\ncoexistence could be a reliable marker to locate supersolidity."
    },
    {
        "anchor": "Characteristic features of the Shannon information entropy of dipolar\n  Bose-Einstein condensates: Calculation of the Shannon information entropy (S) and its connection with\nthe order-disorder transition, and with inter-particle interaction provide a\nchallenging research area in the field of quantum information. Experimental\nprogress with cold trapped atoms has corroborated this interest. In the present\nwork, S is calculated for the Bose-Einstein condensate (BEC) with dominant\ndipolar interaction for different dipole strengths, trap aspect ratio and\nnumber of particles (N). Trapped dipolar bosons in an anisotropic trap provide\nan example of system where the effective interaction is strongly determined by\nthe trap geometry. The main conlcusion of the present calculation is that the\nanisotropic trap reduces the number of degrees of freedom, resulting in more\nordered configurations. The Landsberg's order parameter exhibits quick\nsaturation with the increase in scattering length in both prolate and oblate\ntraps. We also define the threshold scattering length which makes the system\ncompletely disordered. Unlike non-dipolar BEC in a spherical trap, we do not\nfind a universal linear relation between S and ln N, and we, therefore,\nintroduce a general quintic polynomial fit rather well working for a wide range\nof particle number.",
        "positive": "Bond-Order Density Wave Phases in Dimerized Extended Bose-Hubbard Models: The Bose-Hubbard model (BHM) has been widely explored to develop a profound\nunderstanding of the strongly correlated behavior of interacting bosons.\nQuantum simulators not only allow the exploration of the BHM but also extend it\nto models with interesting phenomena such as gapped phases with multiple orders\nand topological phases. In this work, an extended Bose-Hubbard model involving\na dimerized one-dimensional model of long-range interacting hard-core bosons is\nstudied. Bond-order density wave phases (BODW) are characterized in terms of\ntheir symmetry breaking and topological properties. At certain fillings,\ninteractions combined with dimerized hoppings give rise to an emergent\nsymmetry-breaking leading to BODW phases, which differs from the case of\nnon-interacting models that require an explicit breaking of the symmetry.\nSpecifically, the BODW phase at filling $\\rho=1/3$ possesses no analogue in the\nnon-interacting model in terms of its symmetry-breaking properties and the unit\ncell structure. Upon changing the dimerization pattern, the system realizes\ntopologically trivial BODW phases. At filling $\\rho=1/4$, on-site density\nmodulations are shown to stabilize the topological BODW phase. Our work\nprovides the bridge between interacting and non-interacting BODW phases and\nhighlights the significance of long-range interactions in a dimerized lattice\nby showing unique BODW phases that do not exist in the non-interacting model."
    },
    {
        "anchor": "Reanalysis of experimental determinations of polariton-polariton\n  interactions in microcavities: The polariton-polariton interaction strength is an important parameter for\nall kinds of applications using the nonlinear properties of polaritons, such as\noptical switching and single-photon blockade devices. In this paper, we review\nand compare the results of a series of experiments on polariton-polariton\ninteractions in GaAs/Al$_x$Ga$_{-1x}$As microcavity polariton structures, and\npresent new theoretical analysis of these experiments. We show that not just\nthe energy shift of the spectral lines, but also the results of measurements\nsensitive to the polariton scattering rate are important for the calibration of\nthe interaction parameter at low excitation density. We find that when\nadjustments are made to correct for new understanding of the experiments, the\nvalue of the interaction parameter at low density is lower than previous\nreported, but still significantly higher than theoretically predicted.",
        "positive": "Trojan quasiparticles: We argue that a time-periodically driven bosonic Josephson junction supports\nstable, quasi-particle-like collective response modes which are $N$-particle\nanalogs of the nonspreading Trojan wave packets known from microwave-driven\nRydberg atoms. Similar to their single-particle counterparts, these collective\nmodes, dubbed \"flotons\", are well described by a Floquet-Mathieu approximation,\nand possess a well-defined discrete set of excitations. In contrast to other,\n\"chaotic\" modes of response, the nonheating Trojan modes conform to a\nmean-field description, and thus may be of particular interest for the more\ngeneral question under which conditions the reduction of quantum $N$-particle\ndynamics to a strongly simplified mean-field evolution is feasible. Our\nreasoning is supported by phase-space portraits which reveal the degree of\ncorrespondence beween the $N$-particle dynamics und the mean-field picture in\nan intuitive manner."
    },
    {
        "anchor": "Influence of global features of a Bose-Einstein condensate on the vortex\n  velocity: We study the way in which the geometry of the trapping potential affects the\nvortex velocity in a Bose-Einstein condensate confined by a toroidal trap. We\ncalculate the vortex precession velocity through a simple relationship between\nsuch a velocity and the gradient of the numerically obtained vortex energy. We\nobserve that our results correspond very closely to the velocity calculated\nthrough time evolution simulations. However, we find that the estimates derived\nfrom available velocity field formulas present appreciable differences. To\nresolve such discrepancies, we further study the induced velocity field,\nanalyzing the effect of global features of the condensate on such a field and\non the precession velocity.",
        "positive": "Orbital Feshbach Resonance in Alkali-Earth Atoms: For a mixture of alkali-earth atomic gas in the long-lived excited state\n${}^3P_0$ and ground state ${}^1S_0$, in addition to nuclear spin, another\n\"orbital\" index is introduced to distinguish these two internal states. In this\nletter we propose a mechanism to induce Feshbach resonance between two atoms\nwith different orbital and nuclear spin quantum numbers. Two essential\ningredients are inter-orbital spin-exchanging scattering and orbital dependence\nof the Land\\'e g-factors. Here the orbital degrees of freedom plays similar\nrole as electron spin degree of freedom in magnetic Feshbach resonance in\nalkali-metal atoms. This resonance is particularly accessible for ${}^{173}$Yb\nsystem. The BCS-BEC crossover in this system requires two fermion pairing order\nparameters, and displays significant difference comparing to that in\nalkali-metal system."
    },
    {
        "anchor": "SU(6) Heisenberg model on the honeycomb lattice: competition between\n  plaquette and chiral order: We revisit the SU(6) Heisenberg model on the honeycomb lattice, which has\nbeen predicted to be a chiral spin liquid by mean-field theory [G. Szirmai et\nal., Phys. Rev. A 84, 011611 (2011)]. Using exact diagonalizations of finite\nclusters, infinite projected entangled pair states simulations, and variational\nMonte Carlo simulations based on Gutzwiller projected wave functions, we\nprovide strong evidence in favour of the competing plaquette state, which was\nreported to be higher but close by in energy according to mean-field theory.\nThis is further confirmed by the investigation of the model with a ring\nexchange term, which shows that there is a transition between the plaquette\nstate and the chiral state at a finite value of the ring exchange term.",
        "positive": "Anomalous Hall conductivity from the dipole mode of spin-orbit-coupled\n  cold-atom systems: Motivated by recent experiments [Lin {\\it et al.}, Nature {\\bf 417}, 83\n(2011)] that engineered spin-orbit coupling in ultra-cold mixtures of bosonic\natoms, we study the dipole oscillation of trapped spin-orbit-coupled\nnon-condensed Bose and Fermi gases. We find that different directions of\noscillation are coupled by the spin-orbit interactions. The phase difference\nbetween oscillatory motion in orthogonal directions and the trapping\nfrequencies of the modes are shown to be related to the anomalous Hall\nconductivity. Our results can be used to experimentally determine the anomalous\nHall conductivity for cold-atom systems."
    },
    {
        "anchor": "Long-range sound-mediated dark soliton interactions in trapped atomic\n  condensates: A long-range soliton interaction is discussed whereby two or more dark\nsolitons interact in an inhomogeneous atomic condensate, modifying their\nrespective dynamics via the exchange of sound waves without ever coming into\ndirect contact. An idealized double well geometry is shown to yield perfect\nenergy transfer and complete periodic identity reversal of the two solitons.\nTwo experimentally relevant geometries are analyzed which should enable the\nobservation of this long-range interaction.",
        "positive": "Information theoretic approach to effects of spin-orbit coupling in\n  Bose-Einstein condensates: We make use of Shannon entropy ($S$) and Fisher information ($I$) to study\nthe response of atomic density profiles of a spin-orbit coupled Bose-Einstein\ncondensate to changes in the wave number ($\\kappa_L$) of the Raman laser that\ncouples two hyperfine states of atoms in the condensate. The choice for values\nof $\\kappa_L$, the so-called spin-orbit parameter, and Rabi frequency\n($\\Omega$) leads to two distinct regions in the system's energy spectrum with\ndifferent order parameters and/or probability densities. In addition, we can\nhave a spatially modulated density profile, reminiscent of the so called stripe\nphase. Our numbers for $S$ and $I$ demonstrate that for $\\kappa_L^2<\\Omega$\n(region 1) the density profile becomes localized as $\\kappa_L$ increases while\nwe observe delocalization in the density distribution for $\\kappa_L^2>\\Omega$\n(region 2) for increasing values of $\\kappa_L$. In the stripe phase the nature\nof $S$ and $I$ to changes in $\\kappa_L$ is similar to that found for the\ncondensate in region 2. The results for information theoretic quantities in the\nstripe phase are, in general, augmented compared to those of region 2. In\nparticular, the highly enhanced values of position-space Fisher information\nimply an extremely concentrated atomic density distribution to provide an\nevidence for supersolid properties of Bose-Einstein condensates in the presence\nof spin-orbit coupling."
    },
    {
        "anchor": "The cold-atom elevator: From edge-state injection to the preparation of\n  fractional Chern insulators: Optical box traps for cold atoms offer new possibilities for quantum-gas\nexperiments. Building on their exquisite spatial and temporal control, we\npropose to engineer system-reservoir configurations using box traps, in view of\npreparing and manipulating topological atomic states in optical lattices.\nFirst, we consider the injection of particles from the reservoir to the system:\nthis scenario is shown to be particularly well suited to activate\nenergy-selective chiral edge currents, but also, to prepare fractional Chern\ninsulating ground states. Then, we devise a practical evaporative-cooling\nscheme to effectively cool down atomic gases into topological ground states.\nOur open-system approach to optical-lattice settings provides a new path for\nthe investigation of ultracold quantum matter, including strongly-correlated\nand topological phases.",
        "positive": "Spatiotemporal vortex rings in atomic Bose-Einstein condensates: We investigate spatiotemporal vortex rings with phase dislocation both in\nspace and time. It is demonstrated that these structures naturally appear as a\nperiodical in time edge phase dislocation at the low-density region of a\nperturbed atomic Bose-Einstein condensate. The condition of formation, dynamics\nand stability of the spatiotemporal vortex rings are investigated for repulsive\nand attractive interatomic interactions. These theoretical findings open up a\nperspective for experimental observation of novel type of topological coherent\nstructures in ultracold gases."
    },
    {
        "anchor": "Ergodicity breaking from Rydberg clusters in a driven-dissipative\n  many-body system: It is challenging to probe ergodicity breaking trends of a quantum many-body\nsystem when dissipation inevitably damages quantum coherence originated from\ncoherent coupling and dispersive two-body interactions. Rydberg atoms provide a\ntest bed to detect emergent exotic many-body phases and non-ergodic dynamics\nwhere the strong Rydberg atom interaction competes with and overtakes\ndissipative effects even at room temperature. Here we report experimental\nevidence of a transition from ergodic towards ergodic breaking dynamics in\ndriven-dissipative Rydberg atomic gases. The broken ergodicity is featured by\nthe long-time phase oscillation, which is attributed from the formation of\nRydberg excitation clusters in limit cycle phases. The broken symmetry in the\nlimit cycle is a direct manifestation of many-body interactions, which is\nverified by tuning atomic densities in our experiment. The reported result\nreveals that Rydberg many-body systems are a promising candidate to probe\nergodicity breaking dynamics, such as limit cycles, and enable the benchmark of\nnon-equilibrium phase transition.",
        "positive": "Single-particle momentum distribution of Efimov states in noninteger\n  dimensions: We studied the single-particle momentum distribution of mass-imbalanced\nEfimov states embedded in noninteger dimensions. The contact parameters, which\ncan be related to the thermodynamic properties of the gas, were calculated from\nthe high momentum tail of the single particle densities. We studied the\ndependence of the contact parameters with the progressive change of the\nnoninteger dimension, ranging from three (D=3) to two (D=2) dimensions. Within\nthis interval, we move from the (D=3) regime where the Efimov discrete scale\nsymmetry drives the physics, until close to the critical dimension, which\ndepends on the mass imbalance, where the continuum scale symmetry takes place.\nWe found that the two- and three-body contacts grow significantly in magnitude\nwith the decrease of the noninteger dimension towards the critical dimension,\nimpacting observables of resonantly interacting trapped Bose gases."
    },
    {
        "anchor": "Analytical results for Josephson dynamics of ultracold Bosons: We study the dynamics of ultracold Bosons in a double-well potential within\nthe two-mode Bose-Hubbard model by means of semiclassical methods. By applying\na WKB quantization we find analytical results for the energy spectrum, which\nare in excellent agreement with numerical exact results. They are valid in the\nenergy range of plasma oscillations, both in the Rabi and the Josephson regime.\nAdopting the reflection principle and the Poisson summation formula we derive\nan analytical expression for the dynamics of the population imbalance depending\non the few relevant parameters of the system only. This allows us to discuss\nits characteristic dynamics, especially the oscillation frequency, and the\ncollapse- and revival time, as a function of the model parameters, leading to a\ndeeper understanding of Josephson physics. We find that our fomulae match\nprevious experimental observations.",
        "positive": "Surface excitations, shape deformation and the long-time behavior in a\n  stirred Bose-Einstein condensate: The surface excitations, shape deformation and the formation of persistent\ncurrent for a Gaussian obstacle potential rotating in an highly oblate\nBose-Einstein condensate(BEC)are investigated. Vortex dipole can be produced\nand trapped in the center of the stirrer even for slow motion of the stirring\nbeam. When the barrier angular velocity is above some critical value, the\ncondensate shape can be deformed remarkably according to the rotation frequency\ndue to the existence of plenty of surface wave excitations. After a long enough\ntime, a few vortices are found to be left either trapped in the condensate or\npinned by the obstacle, a vortex dipole or several vortices can be trapped at\nthe beam center, which enables the possibility of vortex manipulation."
    },
    {
        "anchor": "Ultracold Spin-Orbit Coupled Bose-Einstein Condensate in a Cavity: Route\n  to Magnetic Phases Through Cavity Transmission: We study the spin orbit coupled ultra cold Bose-Einstein condensate placed in\na single mode Fabry-P\\'erot cavity. The cavity introduces a quantum optical\nlattice potential which dynamically couples with the atomic degrees of freedom\nand realizes a generalized extended Bose Hubbard model whose zero temperature\nphase diagram can be controlled by tuning the cavity parameters. In the\nnon-interacting limit, where the atom-atom interaction is set to zero, the\nresulting atomic dispersion shows interesting features such as bosonic analogue\nof Dirac points, cavity controlled Hofstadter spectrum which bears the hallmark\nof pseudo-spin-1/2 bosons in presence of Abelian and non-Abelian gauge field\n(the later due to spin-orbit coupling) in a cavity induced optical lattice\npotential. In the presence of atom-atom interaction, using a mapping to a\ngeneralized Bose Hubbard model of spin-orbit coupled bosons in classical\noptical lattice, we show that the system realizes a host of quantum magnetic\nphases whose magnetic order can be be detected from the cavity transmission.\nThis provides an alternative approach for detecting quantum magnetism in ultra\ncold atoms. We discuss the effect of cavity induced optical bistability on this\nphases and their experimental consequences.",
        "positive": "Stable multi-peak vector solitons in spin-orbit coupled spin-1 polar\n  condensates: We demonstrate the formation of multi-peak three-component stationary stripe\nvector solitons in a quasi-one-dimensional spin-orbit-coupled hyper-fine spin\n$F = 1$ polar Bose-Einstein condensate. The present investigation is carried\nout through a numerical solution by imaginary-time propagation and an analytic\nvariational approximation of the underlying mean-field Gross-Pitaevskii\nequation. Simple analytic results for energy and component densities were found\nto be in excellent agreement with the numerical results for solitons with more\nthan 100 pronounced maxima and minima. The vector solitons are one of the two\ntypes: dark-bright-dark or bright-dark-bright. In the former a maximum density\nin component $ F_z = 0 $ at the center is accompanied by a zero in components\n$F_z = \\pm 1$. The opposite happens in the latter case. The vector solitons are\ndemonstrated to be mobile and dynamically stable. The collision between two\nsuch vector solitons is found to be quasi elastic at large velocities with the\nconservation of total density of each vector soliton. However, at very small\nvelocity, the collision is inelastic with a destruction of the initial vector\nsolitons. It is possible to observe and study the predicted SO-coupled vector\nsolitons in a laboratory."
    },
    {
        "anchor": "Topological quantum phase transitions of attractive spinless fermions in\n  a honeycomb lattice: We investigate a spinless Fermi gas trapped in a honeycomb optical lattice\nwith attractive nearest-neighbor interactions. At zero temperature, mean-field\ntheory predicts three quantum phase transitions, two being topological. At low\ninteractions, the system is semi-metallic. Increasing the interaction further,\nthe semi-metal destabilizes into a fully gapped superfluid. At larger\ninteractions, a topological transition occurs and this superfluid phase becomes\ngapless, with Dirac-like dispersion relations. Finally, increasing again the\ninteraction, a second topological transition occurs and the gapless superfluid\nis replaced by a different fully gapped superfluid phase. We analyze these\ndifferent quantum phases as the temperature and the lattice filling are varied.",
        "positive": "Quantum phases of strongly-interacting bosons on a two-leg Haldane\n  ladder: We study the ground-state physics of a single-component Haldane model on a\nhexagonal two-leg ladder geometry with a particular focus on strongly\ninteracting bosonic particles. We concentrate our analysis on the regime of\nless than one particle per unit-cell. As a main result, we observe several\nMeissner-like and vortex-fluid phases both for a superfluid as well as a\nMott-insulating background. Furthermore, we show that for strongly interacting\nbosonic particles an unconventional vortex-lattice phase emerges, which is\nstable even in the regime of hardcore bosons. We discuss the mechanism for its\nstabilization for finite interactions by a means of an analytical\napproximation. We show how the different phases may be discerned by measuring\nthe nearest- and next-nearest-neighbor chiral currents as well as their\ncharacteristic momentum distributions."
    },
    {
        "anchor": "Extended Bose-Hubbard model with pair hopping on the triangular lattice: We study systematically an extended Bose-Hubbard model on the triangular\nlattice by means of a meanfield method based on the Gutzwiller ansatz. Pair\nhopping terms are explicitly included and a three-body constraint is applied.\nThe ground-state phase diagram and a variety of quantum phase transitions are\ninvestigated in great detail. In particular, we show the existence and\nstability of the pair supersolid phase.",
        "positive": "Prethermalization in a quenched one-dimensional quantum fluid of light:\n  Intrinsic limits to the coherent propagation of a light beam in a nonlinear\n  optical fiber: We study the coherence properties of a laser beam after propagation along a\none-dimensional lossless nonlinear optical waveguide. Within the paraxial,\nslowly-varying-envelope, and single-transverse-mode approximations, the quantum\npropagation of the light field in the nonlinear medium is mapped onto a quantum\nGross-Pitaevskii-type evolution of a closed one-dimensional system of many\ninteracting photons. Upon crossing the entrance and the back faces of the\nwaveguide, the photon-photon interaction parameter undergoes two sudden jumps,\nresulting in a pair of quantum quenches of the system's Hamiltonian. In the\nweak-interaction regime, we use the modulus-phase Bogoliubov theory of dilute\nBose gases to describe the quantum fluctuations of the fluid of light and\npredict that correlations typical of a prethermalized state emerge locally in\ntheir final form and propagate in a light-cone way at the Bogoliubov speed of\nsound in the photon fluid. This peculiar relaxation dynamics, visible in the\nlight exiting the waveguide, results in a loss of long-lived coherence in the\nbeam of light."
    },
    {
        "anchor": "Bound states and expansion dynamics of interacting bosons on a\n  one-dimensional lattice: The expansion dynamics of bosonic gases in optical lattices has recently been\nthe focus of increasing attention, both experimental and theoretical. We\nconsider, by means of numerical Bethe ansatz, the expansion dynamics of\ninitially confined wave packets of two interacting bosons on a lattice. We show\nthat a correspondence between the asymptotic expansion velocities and the\nprojection of the evolved wave function over the bound states of the system\nexists, clarifying the existing picture for such situations. Moreover, we\ninvestigate the role of the lattice in this kind of evolution.",
        "positive": "BCS-BEC crossover in relativistic Fermi systems: We review the BCS-BEC crossover in relativistic Fermi systems, including the\nQCD matter at finite density. In the first part we study the BCS-BEC crossover\nin a relativistic four-fermion interaction model and show how the relativistic\neffect affects the BCS-BEC crossover. In the second part, we investigate both\ntwo-color QCD at finite baryon density and pion superfluid at finite isospin\ndensity, by using an effective Nambu--Jona-Lasinio model. We will show how the\nmodel describes the weakly interacting diquark and pion condensates at low\ndensity and the BEC-BCS crossover at high density."
    },
    {
        "anchor": "Dipolar confinement-induced resonances of ultracold gases in waveguides: We develop a non-perturbative theoretical framework to treat collisions with\ngeneric anisotropic interactions in quasi-one-dimensional geometries. Our\nmethod avoids the limitations of pseudopotential theory allowing to include\naccurately long-range anisotropic interactions. Analyzing ultracold dipolar\ncollisions in a harmonic waveguide we predict dipolar confinement-induced\nresonances (DCIRs) which are attributed to different angular momentum states.\nThe analytically derived resonance condition reveals in detail the interplay of\nthe confinement with the anisotropic nature of the dipole-dipole interactions.\nThe results are in excellent agreement with ab initio numerical calculations\nconfirming the robustness of the presented approach. The exact knowledge of the\npositions of DCIRs may pave the way for the experimental realization e.g.\nTonks-Girardeau-like or super-Tonks-Girardeau-like phases in effective\none-dimensional dipolar gases.",
        "positive": "Proposal for simulating quantum spin models with Dzyaloshinskii-Moriya\n  interaction using Rydberg atoms, and construction of asymptotic quantum\n  many-body scar states: We propose a method to realize tunable quantum spin models with\nDzyaloshinskii-Moriya interaction (DMI) in Rydberg atom quantum simulators. Our\nscheme uses a two-photon Raman transition and transformation to the\nspin-rotating frame. We investigate the properties of the model including only\nthe DMI and Zeeman energy, which can be experimentally realized in our scheme.\nWe show that the model accommodates exact and asymptotic quantum many-body\nscars exhibiting nonergodic dynamics."
    },
    {
        "anchor": "Itinerant ferromagnetism in the repulsive Hubbard chain with anisotropic\n  odd-wave attraction: The ground-state properties of the Hubbard chain with on-site repulsion and\nanisotropic nearest-neighbor attraction are investigated by means of density\nmatrix renormalization group calculations. The non-local attraction acts\nbetween fermions of one spin component only, mimicking the effect of p-wave\nFeshbach resonances in cold-atom systems. We analyze the onset of itinerant\nferromagnetism, pinpointing the critical attraction strength where partially\nand fully ferromagnetic states occur. In the cold-atom setup, where the two\n(pseudo) spin populations are separately conserved, ferromagnetism occurs with\nthe nucleation of a fully imbalanced band-insulating domain hosting the\nattractive component only. The size of this domain grows with the attraction\nstrength, therefore increasing the (opposite) imbalance of the other domain,\nuntil the two spin components are fully separated. In the presence of a\nharmonic trap, the ferromagnetic state hosts a partially imbalanced domain in\nthe center with an excess of the attractive component and filling lower than\none. This central region is surrounded by fully imbalanced domains, located in\nthe trap tails, hosting only fermions belonging to the other component.",
        "positive": "Superradiant Solid in Cavity QED Coupled to a Lattice of Rydberg Gas: We study an optical cavity coupled to a lattice of Rydberg atoms, which can\nbe represented by a generalized Dicke model. We show that the competition\nbetween the atomic interaction and atom-light coupling induces a rich phase\ndiagram. A novel \"superradiant solid\" (SRS) phase is found, where both the\nsuperradiance and crystalline orders coexist. Different from the normal second\norder superradiance (SR) transition, here both the Solid-1/2 and SRS to SR\nphase transitions are first order. These results are confirmed by the large\nscale quantum Monte Carlo simulations."
    },
    {
        "anchor": "Phase sensitive measurements of order parameters for ultracold atoms\n  through two particles interferometry: Nontrivial symmetry of order parameters is crucial in some of the most\ninteresting quantum many-body states of ultracold atoms and condensed matter\nsystems. Examples in cold atoms include p-wave Feshbach molecules and d-wave\npaired states of fermions that could be realized in optical lattices in the\nHubbard regime. Identifying these states in experiments requires measurements\nof the relative phase of different components of the entangled pair\nwavefunction.\n  We propose and discuss two schemes for such phase sensitive measurements,\nbased on two-particle interference revealed in atom-atom or atomic density\ncorrelations. Our schemes can also be used for relative phase measurements for\nnon-trivial particle-hole order parameters, such as d-density wave order.",
        "positive": "Nonequilibrium properties of an atomic quantum dot coupled to a\n  Bose-Einstein condensate: We study nonequilibrium properties of an atomic quantum dot (AQD) coupled to\na Bose-Einstein condensate (BEC) within Keldysh-Green's function formalism when\nthe AQD level is varied harmonically in time. Nonequilibrium features in the\nAQD energy absorption spectrum are the side peaks that develop as an effect of\nphoton absorption and emission. We show that atoms can be efficiently\ntransferred from the BEC into the AQD for the parameter regime of current\nexperiments with cold atoms."
    },
    {
        "anchor": "Statistics of orthogonality catastrophe events in localised disordered\n  lattices: We address the phenomenon of statistical orthogonality catastrophe in\ninsulating disordered systems. More in detail, we analyse the response of a\nsystem of non-interacting fermions to a local perturbation induced by an\nimpurity. By inspecting the overlap between the pre and post-quench many-body\nground states we fully characterise the emergent statistics of orthogonality\nevents as a function of both the impurity position and the coupling strength.\nWe consider two well-known one-dimensional models, namely the Anderson and the\nAubry- Andr\\'e insulators, highlighting the arising differences. Particularly,\nin the Aubry-Andr\\'e model the highly correlated nature of the quasi periodic\npotential produces unexpected features in how the orthogonality catastrophe\noccurs. We provide a quantitative explanation of such features via a simple,\neffective model. We further discuss the incommensurate ratio approximation and\nsuggest a viable experimental verification in terms of charge transfer\nstatistics and interferometric experiments using quantum probes.",
        "positive": "Three-component Fermi gas with SU(3) symmetry: BCS-BEC crossover in\n  three and two dimensions: We analyze the BCS-BEC crossover for a Fermi gas made of neutral atoms in\nthree hyperfine states with a SU(3) invariant attractive interaction. By\nsolving the extended BCS equations for the total number of particles and the\npairing gap, we calculate at zero temperature the pairing gap, the population\nimbalance, the condensate fraction and the first sound velocity of the uniform\nsystem as a function of the interaction strength in both three and two\ndimensions. Contrary to the three-dimensional case, in two dimensions the\ncondensate fraction approaches the value 1 only for an extremely large\ninteraction strength and, moreover, the sound velocity gives a clear signature\nof the disappearance of one of the three hyperfine components."
    },
    {
        "anchor": "Supersolid phases of dipolar bosons in optical lattices with a staggered\n  flux: We present the theoretical mean-field zero-temperature phase diagram of a\nBose-Einstein condensate (BEC) with dipolar interactions loaded into an optical\nlattice with a staggered flux. Apart from uniform superfluid, checkerboard\nsupersolid and striped supersolid phases, we identify several supersolid phases\nwith staggered vortices, which can be seen as combinations of supersolid phases\nfound in earlier work on dipolar BECs and a staggered-vortex phase found for\nbosons in optical lattices with staggered flux. By allowing for different\nphases and densities on each of the four sites of the elementary plaquette,\nmore complex phase patterns are found.",
        "positive": "Doublon relaxation in the Bose-Hubbard model: Decay of a high-energy double occupancy state, doublon, in a narrow-band\nlattice requires creation of a coherent many-particle excitation. This leads to\nan exponentially long relaxation time of such a state. We show that, if the\naverage occupation number is sufficiently small, the corresponding exponent may\nbe evaluated exactly. To this end we develop the quasiclassical approach to\ncalculation of the high-order tree-level decay amplitudes."
    },
    {
        "anchor": "Modulation stabilization of Bloch oscillations of two-component\n  Bose-Einstein condensates in optical lattices: We study the Bloch oscillations (BOs) of two-component Bose-Einstein\ncondensates (BECs) trapped in spin-dependent optical lattices. Based on the\nderived equations of motion of the wave packet in the basis of localized wave\nfunctions of the lattice sites, the damping effect induced by the\nintercomponent and intracomponent interactions to the BOs is explored\nanalytically and numerically. We also show that such damping of the BOs can be\nsuppressed entirely if all the atom-atom interactions are modulated\nsynchronously and harmonically in time with suitable frequency via the Feshbach\nresonance. When the intercomponent and the intracomponent interactions have\ninverse signs, we find that the long-living BOs and even the revival of the BOs\ncan be achieved via only statically modulating the configuration of optical\nlattices. The results provide a valuable guidance for achieving long-living BOs\nin the two-component BEC system by the Feshbach resonances and manipulating the\nconfiguration of the optical lattices.",
        "positive": "Density-dependent hopping for ultracold atoms immersed in a\n  Bose-Einstein-condensate vortex lattice: Both mixtures of atomic Bose-Einstein condensates and systems with atoms\ntrapped in optical lattices have been intensely explored theoretically, mainly\ndue to the exceptional developments on the experimental side. We investigate\nthe properties of ultracold atomic impurities (bosons) immersed in a vortex\nlattice of a second Bose-condensed species. In contrast to the static\noptical-lattice configuration, the vortex lattice presents intrinsic dynamics\ngiven by its Tkachenko modes. These excitations induce additional correlations\nbetween the impurities, which consist in a long-range attractive potential and\nin a density-dependent hopping, described here in the framework of an extended\nBose-Hubbard model. We compute the quantum phase diagram of the impurity\nspecies through a Gutzwiller ansatz and through the mean-field approach, and\nseparately identify the effects of the two additional terms, i.e., the shift\nand the deformation of the Mott insulator lobes. The long-range attraction, in\nparticular, induces the existence of a triple point in the phase diagram, in\nagreement with previous quantum Monte Carlo calculations [Chaviguri \\emph{et\nal.}, Phys. Rev. A \\textbf{95}, 053639 (2017)]."
    },
    {
        "anchor": "Trapped two-dimensional condensates with synthetic spin-orbit coupling: We study trapped 2D atomic Bose-Einstein condensates with spin-independent\ninteractions in the presence of an isotropic spin-orbit coupling, showing that\na rich physics results from the non-trivial interplay between spin-orbit\ncoupling, confinement and inter-atomic interactions. For low interactions two\ntypes of half-vortex solutions with different winding occur, whereas\nstrong-enough repulsive interactions result in a stripe-phase similar to that\npredicted for homogeneous condensates. Intermediate interaction regimes are\ncharacterized for large enough spin-orbit coupling by an hexagonally-symmetric\nphase with a triangular lattice of density minima similar to that observed in\nrapidly rotating condensates.",
        "positive": "Realistic scheme for quantum simulation of $\\mathbb{Z}_2$ lattice gauge\n  theories with dynamical matter in $(2+1)$D: Gauge fields coupled to dynamical matter are ubiquitous in many disciplines\nof physics, ranging from particle to condensed matter physics, but their\nimplementation in large-scale quantum simulators remains challenging. Here we\npropose a realistic scheme for Rydberg atom array experiments in which a\n$\\mathbb{Z}_2$ gauge structure with dynamical charges emerges on experimentally\nrelevant timescales from only local two-body interactions and one-body terms in\ntwo spatial dimensions. The scheme enables the experimental study of a variety\nof models, including $(2+1)$D $\\mathbb{Z}_2$ lattice gauge theories coupled to\ndifferent types of dynamical matter and quantum dimer models on the honeycomb\nlattice, for which we derive effective Hamiltonians. We discuss ground-state\nphase diagrams of the experimentally most relevant effective $\\mathbb{Z}_2$\nlattice gauge theories with dynamical matter featuring various confined and\ndeconfined, quantum spin liquid phases. Further, we present selected probes\nwith immediate experimental relevance, including signatures of disorder-free\nlocalization and a thermal deconfinement transition of two charges."
    },
    {
        "anchor": "Transition to quantum turbulence in a finite size superfluid: A novel concept of quantum turbulence in finite size superfluids, such as\ntrapped bosonic atoms, is discussed. We have used an atomic $^{87}\\mathrm{Rb}$\nBEC to study the emergence of this phenomenon. In our experiment, the\ntransition to the quantum turbulent regime is characterized by a tangled vortex\nlines formation, controlled by the amplitude and time duration of the\nexcitation produced by an external oscillating field. A simple model is\nsuggested to account for the experimental observations. The transition from the\nnon-turbulent to the turbulent regime is a rather gradual crossover. But it\ntakes place in a sharp enough way, allowing for the definition of an effective\ncritical line separating the regimes. Quantum turbulence emerging in a\nfinite-size superfluid may be a new idea helpful for revealing important\nfeatures associated to turbulence, a more general and broad phenomenon.",
        "positive": "Coexistence of the \"bogolons\" and the one-particle spectrum of\n  excitations with a gap in the degenerated Bose gas: Properties of the weakly non-ideal Bose gas are considered without suggestion\non C-number representation of the creation and annihilation operators with zero\nmomentum. The \"density-density\" correlation function and the one-particle Green\nfunction of the degenerated Bose gas are calculated on the basis of the\nself-consistent Hartree-Fock approximation. It is shown that the spectrum of\nthe one-particle excitations possesses a gap whose value is connected with the\ndensity of particles in the \"condensate\". At the same time, the pole in the\n\"density-density\" Green function determines the phonon-roton spectrum of\nexcitations which exactly coincides with one discovered by Bogolyubov for the\ncollective excitations (the \"bogolons\")."
    },
    {
        "anchor": "Non-perturbative theoretical description of two atoms in an optical\n  lattice with time-dependent perturbations: A theoretical approach for a non-perturbative dynamical description of two\ninteracting atoms in an optical lattice potential is introduced. The approach\nbuilds upon the stationary eigenstates found by a procedure described in\nGrishkevich et al. [Phys. Rev. A 84, 062710 (2011)]. It allows presently to\ntreat any time-dependent external perturbation of the lattice potential up to\nquadratic order. Example calculations of the experimentally relevant cases of\nan acceleration of the lattice and the turning-on of an additional harmonic\nconfinement are presented.",
        "positive": "Production of quantum degenerate mixtures of ytterbium and lithium with\n  controllable inter-species overlap: Quantum degenerate mixtures of alkali and spin-singlet atoms form the\nstarting point for studying few- and many-body physics of mass-imbalanced pairs\nas well as the production of paramagnetic polar molecules. We recently reported\nthe achievement of dual-species quantum degeneracy of a mixture of lithium and\nytterbium atoms. Here we present details of the key experimental steps for the\nall-optical preparation of these mixtures. Further we demonstrate the use of\nthe magnetic field gradient tool to compensate for the differential\ngravitational sag of the two species and control their spatial overlap."
    },
    {
        "anchor": "Direct measurement of polariton-polariton interaction strength in the\n  Thomas-Fermi regime of exciton-polariton condensation: Bosonic condensates of exciton polaritons (light-matter quasiparticles in a\nsemiconductor) provide a solid-state platform for studies of non-equilibrium\nquantum systems with a spontaneous macroscopic coherence. These driven,\ndissipative condensates typically coexist and interact with an incoherent\nreservoir, which undermines measurements of key parameters of the condensate.\nHere, we overcome this limitation by creating a high-density exciton-polariton\ncondensate in an optically-induced \"box\" trap. In this so-called Thomas-Fermi\nregime, the condensate is fully separated from the reservoir and its behaviour\nis dominated by interparticle interactions. We use this regime to directly\nmeasure the polariton-polariton interaction strength, and reduce the existing\nuncertainty in its value from four orders of magnitude to within three times\nthe theoretical prediction. The Thomas-Fermi regime has previously been\ndemonstrated only in ultracold atomic gases in thermal equilibrium. In a\nnon-equilibrium exciton-polariton system, this regime offers a novel\nopportunity to study interaction-driven effects unmasked by an incoherent\nreservoir.",
        "positive": "Dissipation in 2D degenerate gases with non-vanishing rest mass: The complete set of transport coefficients for two dimensional relativistic\ndegenerate gases is derived within a relaxation approximation in kinetic\ntheory, by considering both the particle and energy frames. A thorough\ncomparison between Marle and Anderson-Witting's models is carried out, pointing\nout the drawbacks of the former when compared both to the latter and to the\nfull Boltzmann equation results in the non-degenerate limit. Such task is\naccomplished by solving the relativistic Uehling-Uhlenbeck equation, in both\nthe particle and energy frames, in order to establish the constitutive\nequations for the heat flux and the Navier tensor together with analytical\nexpressions for the transport coefficients in such representations. In\nparticular, the temperature dependence of the thermal conductivity (associated\nwith a generalized thermal force) and the bulk and shear viscosities are\nanalyzed and compared within both models and with the non-degenerate,\nnon-relativistic and ultra-relativistic limits."
    },
    {
        "anchor": "New States of Matter Suggested by New Topological Structures: We extend the well-known Borromean and Brunnian rings to new higher order\nversions. Then we suggest an extension of the connection between Efimov states\nin cold gases and Borromean and Brunnian rings to these new higher order links.\nThis gives rise to a whole new hierarchy of possible states with Efimov states\nat the bottom.",
        "positive": "Rebound-through transition of bright-bright solitons collision in two\n  species condensates with repulsive interspecies interactions: We study the dynamical properties of bright-bright solitons in two species\nBose-Einstein condensates with the repulsive interspecies interactions under\nthe external harmonic potentials by using a variational approach combined with\nnumerical simulation. It is found that the interactions between bright-bright\nsolitons vary from repulsive to attractive interactions with the increasing of\ntheir separating distances. And the bright-bright solitons can be localized at\nequilibrium positions, different from the periodic oscillation of bright\nsoliton in the single species condensates. Especially, a through-collision is\nnewly observed from the bright-bright solitons collisions with the increasing\nof the initial velocity. The collisional type of bright-bright solitons, either\nrebound - or through -collision, depends on the modulation of the initial\nconditions. These results will be helpful for the experimental manipulating\nsuch solitons."
    },
    {
        "anchor": "Anharmonicity Induced Supersolidity In Spin-Orbit Coupled Bose-Einstein\n  Condensates: Supersolid, a fascinating quantum state of matter, features novel phenomena\nsuch as the non-classical rotational inertia and transport anomalies. It is a\nlong standing issue of the coexistence of superfluidity and broken\ntranslational symmetry in condensed matter physics. By recent experimental\nadvances to create tunable synthetic spin-orbit coupling in ultracold gases,\nsuch highly controllable atomic systems would provide new possibilities to\naccess supersolidity with no counterpart in solids. Here we report that the\ncombination of anharmonicity of trapping potential and spin-orbit coupling will\nprovide a new paradigm to achieve supersolids. By means of imaginary time\nevolution of the Gross-Pitaevskii equation, we demonstrate that a supersolid\nstate can be found when considering a trapped Rashba-type spin-orbit coupled\nbosonic atoms loaded in a one-dimensional optical lattice. Furthermore, a\nskyrmion-anti-skyrmion lattice is associated with the appearance of such\nsupersoildity, indicating the topological nontrivial properties of our proposed\nsupersolids.",
        "positive": "Ab-initio phase diagram of ultracold 87-Rb in an one-dimensional\n  two-color superlattice: We investigate the ab-initio phase diagram of ultracold 87-Rb atoms in an\none-dimensional two-color superlattice. Using single-particle band structure\ncalculations we map the experimental setup onto the parameters of the\nBose-Hubbard model. This ab-initio ansatz allows us to express the phase\ndiagrams in terms of the experimental control parameters, i.e., the intensities\nof the lasers that form the optical superlattice. In order to solve the\nmany-body problem for experimental system sizes we adopt the density-matrix\nrenormalization-group algorithm. A detailed study of convergence and\nfinite-size effects for all observables is presented. Our results show that all\nrelevant quantum phases, i.e., superfluid, Mott-insulator, and quasi\nBose-glass, can be accessed through intensity variation of the lasers alone.\nHowever, it turns out that the phase diagram is strongly affected by the\nlongitudinal trapping potential."
    },
    {
        "anchor": "Finite-rate quenches of site bias in the Bose-Hubbard dimer: For a Bose-Hubbard dimer, we study quenches of the site energy imbalance,\ntaking a highly asymmetric Hamiltonian to a fully symmetric one. The ramp is\ncarried out over a finite time that interpolates between the instantaneous and\nadiabatic limits. We provide results for the excess energy of the final state\ncompared to the ground state energy of the final Hamiltonian, as a function of\nthe quench rate. This excess energy serves as the analog of the defect density\nthat is considered in the Kibble-Zurek picture of ramps across phase\ntransitions. We also examine the fate of quantum `self-trapping' when the ramp\nis not instantaneous.",
        "positive": "Behavior of heat capacity of an attractive Bose-Einstein Condensate\n  approaching collapse: We report calculation of heat capacity of an attractive Bose-Einstein\ncondensate, with the number N of bosons increasing and eventually approaching\nthe critical number Ncr for collapse, using the correlated potential harmonics\n(CPH) method. Boson pairs interact via the realistic van der Waals potential.\nIt is found that the transition temperature Tc increases initially slowly, then\nrapidly as N becomes closer to Ncr . The peak value of heat capacity for a\nfixed N increases slowly with N, for N far away from Ncr . But after reaching a\nmaximum, it starts decreasing when N approaches Ncr . The effective potential\ncalculated by CPH method provides an insight into this strange behavior."
    },
    {
        "anchor": "Hardcore bosons in a zig-zag optical superlattice: We study a system of hard-core bosons at half-filling in a one-dimensional\noptical superlattice. The bosons are allowed to hop to nearest and next-nearest\nneighbor sites producing a zig-zag geometry and we obtain the ground state\nphase diagram as a function of microscopic parameters using the finite-size\ndensity matrix renormalization group (FS-DMRG) method. Depending on the sign of\nthe next-nearest neighbor hopping and the strength of the superlattice\npotential the system exhibits three different phases, namely the bond-order\n(BO) solid, the superlattice induced Mott insulator (SLMI) and the superfluid\n(SF) phase. When the signs of both hopping amplitudes are the same (the\n\"unfrustrated\" case), the system undergoes a transition from the SF to the SLMI\nat a non-zero value of the superlattice potential. On the other hand, when the\ntwo amplitudes differ in sign (the \"frustrated\" case), the SF is unstable to\nswitching on a superlattice potential and also exists only up to a finite value\nof the next nearest neighbor hopping. This part of the phase diagram is\ndominated by the BO phase which breaks translation symmetry spontaneously even\nin the absence of the superlattice potential and can thus be characterized by a\nbond order parameter. The transition from BO to SLMI appears to be first order.",
        "positive": "Energy-space random walk in a driven disordered Bose gas: Motivated by the experimental observation [1] that driving a non-interacting\nBose gas in a 3D box with weak disorder leads to power-law energy growth, $E\n\\propto t^{\\eta}$ with $\\eta=0.46(2)$, and compressed-exponential momentum\ndistributions that show dynamic scaling, we perform systematic numerical and\nanalytical studies of this system. Schr\\\"odinger-equation simulations reveal a\ncrossover from $\\eta \\approx 0.5$ to $\\eta \\approx 0.4$ with increasing\ndisorder strength, hinting at the existence of two different dynamical regimes.\nWe present a semi-classical model that captures the simulation results and\nallows an understanding of the dynamics in terms of an energy-space random\nwalk, from which a crossover from $E \\propto t^{1/2}$ to $E \\propto t^{2/5}$\nscaling is analytically obtained. The two limits correspond to the random walk\nbeing limited by the rate of the elastic disorder-induced scattering or the\nrate at which the drive can change the system's energy. Our results provide the\ntheoretical foundation for further experiments."
    },
    {
        "anchor": "Two-dimensional crystals of Rydberg excitations in a resonantly driven\n  lattice gas: The competition between resonant optical excitation of Rydberg states of\natoms and their strong, long-range van der Waals interaction results in spatial\nordering of Rydberg excitations in a two-dimensional lattice gas, as observed\nin a recent experiment of Schau{\\ss} et al. [Nature 491, 87 (2012)]. Here we\nuse semiclassical Monte Carlo simulations to obtain stationary states for\nhundreds of atoms in finite-size lattices. We show the formation of regular\nspatial structures of Rydberg excitations in a system of increasing size, and\nfind highly sub-Poissonian distribution of the number of Rydberg excitations\ncharacterized by a large negative value of the Mandel Q parameter which is\nnearly independent of the system size.",
        "positive": "Emergent Pauli blocking in a weakly interacting Bose gas: The relationship between many-body interactions and dimensionality is\nintegral to numerous emergent quantum phenomena. A striking example is the Bose\ngas, which upon confinement to one dimension (1D) obeys an infinite set of\nconservation laws, prohibiting thermalization and constraining dynamics. In our\nexperiment, we demonstrate that such 1D behavior can extend much farther into\nthe dimensional crossover towards 3D than expected. Starting from a weakly\ninteracting Bose gas trapped in a highly elongated potential, we perform a\nquench to instigate dynamics of a single density mode. Employing the theory of\nGeneralized Hydrodynamics, we identify the dominant relaxation mechanism as the\n1D dephasing of the relevant collective excitations of the system, the\nrapidities. Surprisingly, the dephasing remains dominant even for temperatures\nfar exceeding conventional limits of one-dimensionality where thermalization\nshould occur. We attribute our observations to an emergent Pauli blocking of\ntransverse excitations, caused by the rapidities assuming fermionic statistics,\ndespite the gas being purely bosonic. Thus, our study suggests that 1D physics\nis less fragile than previously thought, as it can persist even in the presence\nof significant perturbations. More broadly, by employing the exact Bethe ansatz\nsolutions of the many-body system, we facilitate an interpretation of how the\nemergent macroscopic behavior arises from the microscopic interactions."
    },
    {
        "anchor": "State diagram and the phase transition of $p$-bosons in a square\n  bi-partite optical lattice: It is shown that, in a reasonable approximation, the quantum state of\n$p$-bosons in a bi-partite square two-dimensional optical lattice is governed\nby the nonlinear boson model describing tunneling of \\textit{boson pairs}\nbetween two orthogonal degenerate quasi momenta on the edge of the first\nBrillouin zone. The interplay between the lattice anisotropy and the atomic\ninteractions leads to the second-order phase transition between the\nnumber-squeezed and coherent phase states of the $p$-bosons. In the isotropic\ncase of the recent experiment, Nature Physicis 7, 147 (2011), the $p$-bosons\nare in the coherent phase state, where the relative global phase between the\ntwo quasi momenta is defined only up to mod($\\pi$): $\\phi=\\pm\\pi/2$. The\nquantum phase diagram of the nonlinear boson model is given.",
        "positive": "Superfluidity and pairing phenomena in ultracold atomic Fermi gases in\n  one-dimensional optical lattices, Part II: Effects of population imbalance: In this paper, we study the effect of population imbalance and its interplay\nwith pairing strength and lattice effect in atomic Fermi gases in a\none-dimensional optical lattice. We compute various phase diagrams as the\nsystem undergoes BCS-BEC crossover, using the same pairing fluctuation theory\nas in Part I. We find widespread pseudogap phenomena beyond the BCS regime and\nintermediate temperature superfluid states for relatively low population\nimbalances. The Fermi surface topology plays an important role in the behavior\nof $T_\\text{c}$. For large $d$ and/or small $t$, which yield an open Fermi\nsurface, superfluidity can be readily destroyed by a small amount of population\nimbalance $p$. The superfluid phase, especially in the BEC regime, can exist\nonly for a highly restricted volume of the parameter space. Due to the\ncontinuum-lattice mixing, population imbalance gives rise to a new mechanism\nfor pair hopping, as assisted by excessive majority fermions, which may lead to\nsignificant enhancement of $T_\\text{c}$ on the BEC side of the Feshbach\nresonance, and also render $T_\\text{c}$ approaching a constant asymptote in the\nBEC limit, when it exists. Furthermore, we find that not all minority fermions\nwill be paired up in BEC limit, unlike the 3D continuum case. These predictions\ncan be tested in future experiments."
    },
    {
        "anchor": "Persistent currents with non-quantized angular momentum: We analyze the generation of persistent currents in Bose-Einstein condensates\nof ultracold gases confined in a ring. This phenomenon has been recently\ninvestigated in an experiment [Nature \\textbf{506}, 200 (2014)], where\nhysteresis loops have been observed in the activation of quantized persistent\ncurrents by rotating weak links. In this work, we demonstrate the existence of\n3D stationary currents with non-quantized angular momentum. They are generated\nby families of solitary waves that show a continuous variation in the angular\nmomentum, and provide a bridge between different winding numbers. We show that\nthe size of hysteresis loops is determined by the range of existence within the\nweak link region of solitary waves which configure the energy barrier\npreventing phase slips. The barrier vanishes when the critical rotation leads\nwinding numbers and solitonic states to a matching configuration. At this\npoint, Landau and Feynman criteria for phase slips meet: the fluid flow reaches\nthe local speed of sound, and stationary vortex lines (which are the building\nblocks of solitons) can be excited inside the system.",
        "positive": "High-temperature expansion of the viscosity in interacting quantum gases: We compute the frequency-dependent shear and bulk viscosity spectral\nfunctions of an interacting Fermi gas in a quantum virial expansion up to\nsecond quadratic order in the fugacity parameter $z=e^{\\beta \\mu}$, which is\nsmall at high temperatures. Calculations are carried out using a diagrammatic\nfinite-temperature field-theoretic framework, in which the analytic\ncontinuation from Matsubara to real frequencies is carried out in closed\nanalytic form. Besides a possible zero-frequency Drude peak, our results for\nthe spectral functions show a broad continuous spectrum at all frequencies with\nan additional bound-state contribution for frequencies larger than the\ndimer-breaking energy. Our results are consistent with various sum rules and\nuniversal high-frequency tails. In the low-frequency limit, the shear viscosity\nspectral function is recast as a collision integral, which reproduces known\nresults for the static shear viscosity from kinetic theory. Our findings for\nthe static bulk viscosity of a Fermi gas near unitarity, however, show a\nnonanalytic dependence on the scattering length, at variance with kinetic\ntheory."
    },
    {
        "anchor": "Interplay between binary and three-body interactions and enhancement of\n  stability in trapless dipolar Bose-Einstein condensates: We investigate the nonlocal Gross-Pitaevskii (GP) equation with long-range\ndipole-dipole and contact interactions (including binary and three-body\ncollisions). We address the impact of the three-body interaction on stabilizing\ntrapless dipolar Bose-Einstein condensates (BECs). It is found that the dipolar\nBECs exhibit stability not only for the usual combination of attractive binary\nand repulsive three-body interactions, but also for the case when these terms\nhave opposite signs. The trapless stability of the dipolar BECs may be further\nenhanced by time-periodic modulation of the three-body interaction imposed by\nmeans of Feshbach resonance. The results are produced analytically using the\nvariational approach and confirmed by numerical simulations.",
        "positive": "Droplets of trapped quantum dipolar bosons: Strongly interacting systems of dipolar bosons in three dimensions confined\nby harmonic traps are analyzed using the exact Path Integral Ground State Monte\nCarlo method. By adding a repulsive two-body potential, we find a narrow window\nof interaction parameters leading to stable ground- state configurations of\ndroplets in a crystalline arrangement. We find that this effect is entirely due\nto the interaction present in the Hamiltonian without resorting to additional\nstabilizing mechanisms or specific three-body forces. We analyze the number of\ndroplets formed in terms of the Hamiltonian parameters, relate them to the\ncorresponding s-wave scattering length, and discuss a simple scaling model for\nthe density profiles. Our results are in qualitative agreement with recent\nexperiments showing a quantum Rosensweig instability in trapped Dy atoms."
    },
    {
        "anchor": "Driving interactions efficiently in a composite few-body system: We study how to efficiently control an interacting few-body system consisting\nof three harmonically trapped bosons. Specifically we investigate the process\nof modulating the interparticle interactions to drive an initially\nnon-interacting state to a strongly interacting one, which is an eigenstate of\na chosen Hamiltonian. We also show that for unbalanced subsystems, where one\ncan individually control the different inter- and intra-species interactions,\ncomplex dynamics originates when the symmetry of the ground state is broken by\nphase separation. However, as driving the dynamics too quickly can result in\nunwanted excitations of the final state, we optimize the driven processes using\nshortcuts to adiabaticity, which are designed to reduce these excitations at\nthe end of the interaction ramp ensuring that the target eigenstate is reached.",
        "positive": "Observation of broad p-wave Feshbach resonances in ultracold\n  $^{85}$Rb-$^{87}$Rb mixtures: We observe new Feshbach resonances in ultracold mixtures of $^{85}$Rb and\n$^{87}$Rb atoms in the $^{85}$Rb$|2, +2\\rangle$+$^{87}$Rb$|1, +1\\rangle$ and\n$^{85}$Rb$|2, -2\\rangle$+$^{87}$Rb$|1, -1\\rangle$ scattering channels. The\npositions and properties of the resonances are predicted and characterized\nusing the semi-analytic multichannel quantum-defect theory by Gao. Of\nparticular interest, a number of broad entrance-channel dominated p-wave\nresonances are identified, implicating exciting opportunities for studying a\nvariety of p-wave interaction dominated physics."
    },
    {
        "anchor": "Fractonic Luttinger Liquids and Supersolids in a Constrained\n  Bose-Hubbard Model: Quantum many-body systems with fracton constraints are widely conjectured to\nexhibit unconventional low-energy phases of matter. In this work, we\ndemonstrate the existence of a variety of such exotic quantum phases in the\nground states of a dipole-moment conserving Bose-Hubbard model in one\ndimension. For integer boson fillings, we perform a mapping of the system to a\nmodel of microscopic local dipoles, which are composites of fractons. We apply\na combination of low-energy field theory and large-scale tensor network\nsimulations to demonstrate the emergence of a dipole Luttinger liquid phase. At\nnon-integer fillings our numerical approach shows an intriguing compressible\nstate described by a quantum Lifshitz model in which charge density-wave order\ncoexists with dipole long-range order and superfluidity - a `dipole\nsupersolid'. While this supersolid state may eventually be unstable against\nlattice effects in the thermodynamic limit, its numerical robustness is\nremarkable. We discuss potential experimental implications of our results.",
        "positive": "Direct imaging of topological edge states in cold-atom systems: Detecting topological order in cold-atom experiments is an ongoing challenge,\nthe resolution of which offers novel perspectives on topological matter. In\nmaterial systems, unambiguous signatures of topological order exist for\ntopological insulators and quantum Hall devices. In quantum Hall systems, the\nquantized conductivity and the associated robust propagating edge modes -\nguaranteed by the existence of non-trivial topological invariants - have been\nobserved through transport and spectroscopy measurements. Here, we show that\noptical-lattice-based experiments can be tailored to directly visualize the\npropagation of topological edge modes. Our method is rooted in the unique\ncapability for initially shaping the atomic gas, and imaging its time-evolution\nafter suddenly removing the shaping potentials. Our scheme, applicable to an\nassortment of atomic topological phases, provides a method for imaging the\ndynamics of topological edge modes, directly revealing their angular velocity\nand spin structure."
    },
    {
        "anchor": "Emergent Mott-insulators at non-integer fillings and devil's staircase\n  induced by attractive interaction in many-body polarons: We investigate the ground state properties of an ultracold atom system\nconsisting of many-body polarons, quasiparticles formed by impurity atoms in\noptical lattices immersing in a Bose-Einstein condensate. We find the\nnearest-neighbor attractive interaction between polarons can give rise to rich\nphysics that is peculiar to this system. In a relatively shallow optical\nlattice, the attractive interaction can drive the system being in a self-bound\nsuperfluid phase with its particle density distribution manifesting a\nself-concentrated structure. While in a relatively deep optical lattice, the\nattractive interaction can drive the system forming the Mott-insulator phase\neven though the global filling factor is not integer. Interestingly, in the\nMott-insulator regime, the system can support a series of different\nMott-insulators with their effective density manifesting a devil's staircase\nstructure with respect to the strength of attractive interaction. Detailed\nestimation on relevant experimental parameters shows that these rich physics\ncan be readily observed in current experimental setups.",
        "positive": "Dipolar particles in a double-trap confinement: Response to tilting the\n  dipolar orientation: We analyze the microscopic few-body properties of dipolar particles confined\nin two parallel quasi-one-dimensional harmonic traps. In particular, we show\nthat an adiabatic rotation of the dipole orientation about the trap axes can\ndrive an initially non-localized few-fermion state into a localized state with\nstrong inter-trap pairing. For an instant, non-adiabatic rotation, however,\nlocalization is inhibited and a highly excited state is reached. This state may\nbe interpreted as the few-body analog of a super-Tonks-Girardeau state, known\nfrom one-dimensional systems with contact interactions."
    },
    {
        "anchor": "Bond order solid of two-dimensional dipolar fermions: Recent experimental realization of dipolar Fermi gases near or below quantum\ndegeneracy provides opportunity to engineer Hubbard-like models with long range\ninteractions. Motivated by these experiments, we chart out the theoretical\nphase diagram of interacting dipolar fermions on the square lattice at zero\ntemperature and half filling. We show that in addition to p-wave superfluid and\ncharge density wave order, two new and exotic types of bond order emerge\ngenerically in dipolar fermion systems. These phases feature homogeneous\ndensity but periodic modulations of the kinetic hopping energy between nearest\nor next-nearest neighbors. Similar, but manifestly different, phases of\ntwo-dimensional correlated electrons have previously only been hypothesized and\ntermed \"density waves of nonzero angular momentum\". Our results suggest that\nthese phases can be constructed flexibly with dipolar fermions, using currently\navailable experimental techniques.",
        "positive": "Thermal instability, evaporation and thermodynamics of one-dimensional\n  liquids in weakly-interacting Bose-Bose mixtures: We study the low-temperature thermodynamics of weakly-interacting uniform\nliquids in one-dimensional attractive Bose-Bose mixtures.~The Bogoliubov\napproach is used to simultaneously describe quantum and thermal fluctuations.\nFirst, we investigate in detail two different thermal mechanisms driving the\nliquid-to-gas transition, the dynamical instability and the evaporation, and we\ndraw the phase diagram. Then, we compute the main thermodynamic quantities of\nthe liquid, such as the chemical potential, the Tan's contact, the adiabatic\nsound velocity and the specific heat at constant volume. The strong dependence\nof the thermodynamic quantities on the temperature may be used as a precise\ntemperature probe for experiments on quantum liquids."
    },
    {
        "anchor": "Quantum Coherent States of Interacting Bose-Fermi Mixtures in One\n  Dimension: We study two-component atomic gas mixtures in one dimension involving both\nbosons and fermions. When the inter-species interaction is attractive, we\nreport a rich variety of coherent ground-state phases that vary with the\nintrinsic and relative strength of the interactions. We avoid any artifacts of\nlattice discretization by developing a novel implementation of a continuous\nmatrix product state ansatz for mixtures and priorly demonstrate the validity\nof our approach on the integrable point that exists for mixtures with equal\nmasses and interactions (Lai-Yang model) where we find that the ansatz\ncorrectly and systematically converges towards the exact results.",
        "positive": "Stabilization of the chiral phase of the SU($6m$) Heisenberg model on\n  the honeycomb lattice with $m$ particles per site for $m$ larger than 1: We show that, when $N$ is a multiple of 6 ($N=6m$, $m$ integer), the \\SU{N}\nHeisenberg model on the honeycomb lattice with $m$ particles per site has a\nclear tendency toward chiral order as soon as $m\\geq 2$. This conclusion has\nbeen reached by a systematic variational Monte Carlo investigation of\nGutzwiller projected wave-functions as a function of $m$ between the case of\none particle per site ($m=1$), for which the ground state has recently been\nshown to be in a plaquette singlet state, and the $m\\rightarrow \\infty$ limit,\nwhere a mean-field approach has established that the ground state has chiral\norder. This demonstrates that the chiral phase can indeed be stabilized for not\ntoo large values of $m$, opening the way to its experimental realisations in\nother lattices."
    },
    {
        "anchor": "Effects of Gapless Bosonic Fluctuations on Majorana Fermions in Atomic\n  Wire Coupled to a Molecular Reservoir: We discuss the effects of quantum and thermal fluctuations on the Majorana\nedge states in a topological atomic wire coupled to a superfluid molecular gas\nwith gapless excitations. We find that the coupling between the Majorana edge\nstates remains exponentially decaying with the length of the wire, even at\nfinite temperatures smaller than the energy gap for bulk excitations in the\nwire. This exponential dependence is controlled solely by the localization\nlength of the Majorana states. The fluctuations, on the other hand, provide the\ndominant contribution to the preexponential factor, which increases with\ntemperature and the length of the wire. More important is that thermal\nfluctuations give rise to a decay of an initial correlation between Majorana\nedge states to its stationary value after some thermalization time. This\nstationary value is sensitive to the temperature and to the length of the wire,\nand, although vanishing in the thermodynamic limit, can still be feasible in a\nmesoscopic system at sufficiently low temperatures. The thermalization time, on\nthe other hand, is found to be much larger than the typical time scales in the\nwire, and is sufficient for quantum operations with Majorana fermions before\nthe temperature-induced decoherence sets in.",
        "positive": "On-Demand Entanglement of Molecules in a Reconfigurable Optical Tweezer\n  Array: Entanglement is crucial to many quantum applications including quantum\ninformation processing, simulation of quantum many-body systems, and\nquantum-enhanced sensing. Molecules, because of their rich internal structure\nand interactions, have been proposed as a promising platform for quantum\nscience. Deterministic entanglement of individually controlled molecules has\nnevertheless been a long-standing experimental challenge. Here we demonstrate,\nfor the first time, on-demand entanglement of individually prepared molecules.\nUsing the electric dipolar interaction between pairs of molecules prepared\nusing a reconfigurable optical tweezer array, we realize an entangling\ntwo-qubit gate, and use it to deterministically create Bell pairs. Our results\ndemonstrate the key building blocks needed for quantum information processing,\nsimulation of quantum spin models, and quantum-enhanced sensing. They also open\nup new possibilities such as using trapped molecules for quantum-enhanced\nfundamental physics tests and exploring collisions and chemical reactions with\nentangled matter."
    },
    {
        "anchor": "Anderson localization in optical lattices with correlated disorder: We study the Anderson localization of atomic gases exposed to simple-cubic\noptical lattices with a superimposed disordered speckle pattern. The two\nmobility edges in the first band and the corresponding critical filling factors\nare determined as a function of the disorder strength, ranging from vanishing\ndisorder up to the critical disorder intensity where the two mobility edges\nmerge and the whole band becomes localized. Our theoretical analysis is based\nboth on continuous-space models which take into account the details of the\nspatial correlation of the speckle pattern, and also on a simplified\ntight-binding model with an uncorrelated distribution of the on-site energies.\nThe mobility edges are computed via the analysis of the energy-level\nstatistics, and we determine the universal value of the ratio between\nconsecutive level spacings at the mobility edge. We analyze the role of the\nspatial correlation of the disorder, and we also discuss a qualitative\ncomparison with available experimental data for interacting atomic Fermi gases\nmeasured in the moderate interaction regime.",
        "positive": "Efimov three-body states on top of a Fermi sea: The stabilization of Cooper pairs of bound electrons in the background of a\nFermi sea is the origin of superconductivity and the paradigmatic example of\nthe striking influence of many-body physics on few-body properties. In the\nquantum-mechanical three-body problem the famous Efimov effect yields\nunexpected scaling relations among a tower of universal states. These seemingly\nunrelated problems can now be studied in the same setup thanks to the success\nof ultracold atomic gas experiments. In light of the tremendous effect of a\nbackground Fermi sea on two-body properties, a natural question is whether a\nbackground can modify or even destroy the Efimov effect. Here we demonstrate\nhow the generic problem of three interacting particles changes when one\nparticle is embedded in a background Fermi sea, and show that Efimov scaling\npersists. It is found in a scaling that relates the three-body physics to the\nbackground density of fermionic particles."
    },
    {
        "anchor": "Confinement induced resonances in anharmonic waveguides: We develop the theory of anharmonic confinement-induced resonances (ACIR).\nThese are caused by anharmonic excitation of the transverse motion of the\ncenter of mass (COM) of two bound atoms in a waveguide. As the transverse\nconfinement becomes anisotropic, we find that the COM resonant solutions split\nfor a quasi-1D system, in agreement with recent experiments. This is not found\nin harmonic confinement theories. A new resonance appears for repulsive\ncouplings ($a_{3D}>0$) for a quasi-2D system, which is also not seen with\nharmonic confinement. After inclusion of anharmonic energy corrections within\nperturbation theory, we find that these ACIR resonances agree extremely well\nwith anomalous 1D and 2D confinement induced resonance positions observed in\nrecent experiments. Multiple even and odd order transverse ACIR resonances are\nidentified in experimental data, including up to N=4 transverse COM quantum\nnumbers.",
        "positive": "Seeing spin dynamics in atomic gases: The dynamics of internal spin, electronic orbital, and nuclear motion states\nof atoms and molecules have preoccupied the atomic and molecular physics\ncommunity for decades. Increasingly, such dynamics are being examined within\nmany-body systems composed of atomic and molecular gases. Our findings\nsometimes bear close relation to phenomena observed in condensed-matter\nsystems, while on other occasions they represent truly new areas of\ninvestigation. I discuss several examples of spin dynamics that occur within\nspinor Bose-Einstein gases, highlighting the advantages of spin-sensitive\nimaging for understanding and utilizing such dynamics."
    },
    {
        "anchor": "Few strongly interacting fermions of different mass driven in the\n  vicinity of a critical point: It was recently argued that one-dimensional systems of several strongly\ninteracting fermions of different mass undergo critical transitions between\ndifferent spatial orderings when the external confinement adiabatically changes\nits shape. In this work, we explore their dynamical properties when finite-time\ndrivings are considered. By detailed analysis of many-body spectra, we show\nthat the dynamics is typically guided only by the lowest eigenstates and may be\nwell-understood in the language of the generalized Landau-Zener mechanism. In\nthis way, we can capture precisely the dynamical response of the system to the\nexternal driving. As consequence, we show that by appropriate tailoring\nparameters of the driving one can target desired many-body state in a\nnon-infinite time. Our theoretical predictions can be straightforwardly\nutilized in upcoming state-of-the-art experiments with ultracold atoms.",
        "positive": "Quantum algorithm for Bose-Einstein condensate quantum fluid dynamics: The dynamics of vortex solitons in a BEC superfluid is studied. A quantum\nlattice-gas algorithm (localization-based quantum computation) is employed to\nexamine the dynamical behavior of vortex soliton solutions of the\nGross-Pitaevskii equation (phi^4 interaction nonlinear Schroedinger equation).\nQuantum turbulence is studied in large grid numerical simulations: Kolmogorov\nspectrum associated with a Richardson energy cascade occurs on large flow\nscales. At intermediate scales a k^{-6} power law emerges, in a\nclassical-quantum transition from vortex filament reconnections to Kelvin\nwave-acoustic wave coupling. The spontaneous exchange of intermediate vortex\nrings is observed. Finally, at very small spatial scales a k^{-3} power law\nemerges, characterizing fluid dynamics occurring within the scale size of the\nvortex cores themselves, a characteristic Kelvin wave cascade region. Poincare\nrecurrence is studied: in the free non-interacting system, a fast Poincare\nrecurrence occurs for regular arrays of line vortices. The recurrence period is\nused to demarcate dynamics driving the nonlinear quantum fluid towards\nturbulence, since fast recurrence is an approximate symmetry of the nonlinear\nquantum fluid at early times. This class of quantum algorithms is useful for\nstudying BEC superfluid dynamics over a broad range of wave numbers, from\nquantum flow to a pseudo-classical inviscid flow regime to a Kolmogorov\ninertial subrange."
    },
    {
        "anchor": "Finite temperature phases and excitations of bosons on a square lattice:\n  A cluster mean field study: We study the finite temperature phases and collective excitations of hardcore\nas well as softcore bosons on a square lattice with nearest and next nearest\nneighbor interactions, focusing on the formation of various types of supersolid\n(SS) phases and their stability under thermal fluctuations. The interplay\nbetween the on-site, nearest, and next nearest neighbor interactions leads to\nvarious density ordering and structural transitions, which we have plotted out.\nThermodynamic properties and phase diagrams are obtained by cluster mean field\ntheory at finite temperatures, which includes quantum effects systematically,\nand they are compared with the single-site mean field results. We investigate\nthe melting process of the SS phase to normal fluid (NF), which can occur in at\nleast two steps due to the presence of two competing orders in the SS. A\ntetra-critical point exists at finite temperature and exhibits intriguing\nbehavior, which is analyzed for different regimes of interactions. The phase\ndiagrams reveal the different pathways of the thermal transition of SSs to the\nNF phase, for different interaction regimes, which can be accessible by thermal\nquench protocols used in recent experiments. We show how the phases and the\ntransitions between them can be identified from the characteristic features of\nthe excitation spectrum. We analyze the appearance of a low-energy gapped mode\napart from the gapless sound mode in the SS phase, which is analogous to the\ngapped mode recently studied for dipolar SS phases. Finally, we discuss the\nrelevance of the results of the present work in the context of ongoing\nexperiments on ultracold atomic gases and newly observed SS phases.",
        "positive": "Capillary wave dynamics and interface structure modulation in binary\n  Bose-Einstein condensate mixtures: The localized low-energy interfacial excitations, or Nambu-Goldstone modes,\nof phase-segregated binary mixtures of Bose-Einstein condensates are\ninvestigated analytically by means of a double-parabola approximation (DPA) to\nthe Lagrangian density in Gross-Pitaevskii theory for a system in a uniform\npotential. Within this model analytic expressions are obtained for the\nexcitations underlying capillary waves or \"ripplons\" for arbitrary strength\n$K\\,(>1)$ of the phase segregation. The dispersion relation $\\omega \\propto\nk^{3/2}$ is derived directly from the Bogoliubov-de Gennes equations in limit\nthat the wavelength $2\\pi/k$ is much larger than the healing length $\\xi $. The\nproportionality constant in the dispersion relation provides the static\ninterfacial tension. A correction term in $\\omega (k)$ of order $k^{5/2}$ is\ncalculated analytically, entailing a finite-wavelength correction factor\n$(1+\\frac{\\sqrt{K-1} \\,k\\xi}{4\\sqrt{2}\\,(\\sqrt{2}+\\sqrt{K-1})})$. This\nprediction may be tested experimentally using (quasi-)uniform optical-box\ntraps. Explicit expressions are obtained for the structural deformation of the\ninterface due to the passing of the capillary wave. It is found that the\namplitude of the wave is enhanced by an amount that is quadratic in the ratio\nof the phase velocity $\\omega/k$ to the sound velocity $c$. For generic\nasymmetric mixtures consisting of condensates with unequal healing lengths an\nadditional modulation is predicted of the common value of the condensate\ndensities at the interface."
    },
    {
        "anchor": "Phase Estimation from Atom Position Measurements: We study the measurement of the position of atoms as a means to estimate the\nrelative phase between two Bose-Einstein condensates. First, we consider $N$\natoms released from a double-well trap, forming an interference pattern, and\nshow that a simple least-squares fit to the density gives a shot-noise limited\nsensitivity. The shot-noise limit can instead be overcome by using correlation\nfunctions of order $\\sqrt{N}$ or larger. The measurement of the\n$N\\mathrm{th}$-order correlation function allows to estimate the relative phase\nat the Heisenberg limit. Phase estimation through the measurement of the\ncenter-of-mass of the interference pattern can also provide sub-shot-noise\nsensitivity. Finally, we study the effect of the overlap between the two clouds\non the phase estimation, when Mach-Zehnder interferometry is performed in a\ndouble-well.",
        "positive": "Topological phases of lattice bosons with a dynamical gauge field: Optical lattices with a complex-valued tunnelling term have become a standard\nway of studying gauge-field physics with cold atoms. If the complex phase of\nthe tunnelling is made density-dependent, such system features even a\nself-interacting or dynamical magnetic field. In this paper we study the\nscenario of a few bosons in either a static or a dynamical gauge field by means\nof exact diagonalization. The topological structures are identified computing\ntheir Chern number. Upon decreasing the atom-atom contact interaction, the\neffect of the dynamical gauge field is enhanced, giving rise to a phase\ntransition between two topologically non-trivial phases."
    },
    {
        "anchor": "Vortices and vortex lattices in quantum ferrofluids: The experimental realization of quantum-degenerate Bose gases made of atoms\nwith sizeable magnetic dipole moments has created a new type of fluid, known as\na quantum ferrofluid, which combines the extraordinary properties of\nsuperfluidity and ferrofluidity. A hallmark of superfluids is that they are\nconstrained to rotate through vortices with quantized circulation. In quantum\nferrofluids the long-range dipolar interactions add new ingredients by inducing\nmagnetostriction and instabilities, and also affect the structural properties\nof vortices and vortex lattices. Here we give a review of the theory of\nvortices in dipolar Bose-Einstein condensates, exploring the interplay of\nmagnetism with vorticity and contrasting this with the established behaviour in\nnon-dipolar condensates. We cover single vortex solutions, including structure,\nenergy and stability, vortex pairs, including interactions and dynamics, and\nalso vortex lattices. Our discussion is founded on the mean-field theory\nprovided by the dipolar Gross-Pitaevskii equation, ranging from analytic\ntreatments based on the Thomas-Fermi (hydrodynamic) and variational approaches\nto full numerical simulations. Routes for generating vortices in dipolar\ncondensates are discussed, with particular attention paid to rotating\ncondensates, where surface instabilities drive the nucleation of vortices, and\nlead to the emergence of rich and varied vortex lattice structures. We also\npresent an outlook, including potential extensions to degenerate Fermi gases,\nquantum Hall physics, toroidal systems and the Berezinskii-Kosterlitz-Thouless\ntransition.",
        "positive": "Effective field theory for dilute Fermi systems at fourth order: We discuss high-order calculations in perturbative effective field theory for\nfermions at low energy scales. The Fermi-momentum or $k_{\\rm F} a_s$ expansion\nfor the ground-state energy of the dilute Fermi gas is calculated to fourth\norder, both in cutoff regularization and in dimensional regularization. For the\ncase of spin one-half fermions we find from a Bayesian analysis that the\nexpansion is well-converged at this order for ${| k_{\\rm F} a_s | \\lesssim\n0.5}$. Further, we show that Pad{\\'e}-Borel resummations can improve the\nconvergence for ${| k_{\\rm F} a_s | \\lesssim 1}$. Our results provide important\nconstraints for nonperturbative calculations of ultracold atoms and dilute\nneutron matter."
    },
    {
        "anchor": "Texture control in a pseudospin Bose-Einstein condensate: We describe a wavefunction engineering approach to the formation of textures\nin a two-component nonrotated Bose-Einstein condensate. By controlling the\nphases of wavepackets that combine in a three-wave interference process, a\nballistically-expanding regular lattice-texture is generated, in which the\nphases determine the component textures. A particular example is presented of a\nlattice-texture composed of half-quantum vortices and spin-2 textures. We\ndemonstrate the lattice formation with numerical simulations of a viable\nexperiment, identifying the textures and relating their locations to a linear\ntheory of wavepacket interference.",
        "positive": "Efimov Physics and the Three-Body Parameter within a Two-Channel\n  Framework: We calculate shallow three-body bound states in the universal regime, defined\nby Efimov, with inclusion of both scattering length and effective range\nparameters. The universal spectrum is recovered for the least bound states,\nwhereas for larger binding energies we find corrections to the universal\nscaling laws. We recover known results for broad Feshbach resonances with small\neffective range, whereas in the case of narrow resonances we find a distinct\nnon-monotonic behavior of the threshold at which the lowest Efimov trimer\nmerges with the three-body continuum. To address the issue of the physical\norigin of the three-body parameter we provide a physically clear model for the\nrelation between three-body physics and typical two-body atom-atom\ninteractions. Our results demonstrate that experimental information from narrow\nFeshbach resonances and/or mixed systems are of vital importance to pin down\nthe relation of two- and three-body physics in atomic systems."
    },
    {
        "anchor": "Correlation energy of a homogeneous dipolar Fermi gas: We study the normal state of a 3-$d$ homogeneous dipolar Fermi gas beyond the\nHartree-Fock approximation. The correlation energy is found of the same order\nas the Fock energy, unusually strong for a Fermi-liquid system. As a result,\nthe critical density of mechanical collapse is smaller than that estimated in\nthe Hartree-Fock approximation. With the correlation energy included, a new\nenergy functional is proposed for the trapped system, and its property is\nexplored.",
        "positive": "Persistent current formation in a high-temperature Bose-Einstein\n  condensate: an experimental test for c-field theory: Experimental stirring of a toroidally trapped Bose-Einstein condensate at\nhigh temperature generates a disordered array of quantum vortices that decays\nvia thermal dissipation to form a macroscopic persistent current [T. W. Neely\nem et al. arXiv:1204.1102 (2012)]. We perform 3D numerical simulations of the\nexperimental sequence within the Stochastic Projected Gross-Pitaevskii equation\nusing ab initio determined reservoir parameters. We find that both damping and\nnoise are essential for describing the dynamics of the high-temperature Bose\nfield. The theory gives a quantitative account of the formation of a persistent\ncurrent, with no fitted parameters."
    },
    {
        "anchor": "Stochastic longevity of a dark soliton in a finite-temperature\n  Bose-Einstein condensate: We study the decay of a dark soliton in a homogeneous Bose-Einstein\ncondensate. We give an analytical treatment of a decaying soliton, deriving an\nexpression for the soliton velocity and decay time in the absence of thermal\nnoise. We test the result against numerical simulations of a spatially confined\nsystem and find good agreement in the regime of low temperature ($k_BT\\ll\n\\mu$). Thermal fluctuations are found to slow the escape of the soliton,\nextending its lifetime beyond the predictions of the noise-free theory; the\neffect becomes significant at a characteristic temperature $k_BT\\sim \\mu$. This\nstabilization by noise allows us to infer an analytical lower bound for the\ndark soliton decay time.",
        "positive": "Order indices of density matrices for finite systems: The definition of order indices for density matrices is extended to finite\nsystems. This makes it possible to characterize the level of ordering in such\nfinite systems as macromolecules, nanoclusters, quantum dots, or trapped atoms.\nThe general theory is exemplified by explicit calculations of the order index\nfor the first-order density matrix of bosonic atoms confined in a finite box at\nzero temperature."
    },
    {
        "anchor": "Derivation of the effective action of a dilute Fermi gas in the unitary\n  limit of the BCS-BEC crossover: The effective action describing the gapless Nambu-Goldstone, or\nAnderson-Bogoliubov, mode of a zero-temperature dilute Fermi gas at unitarity\nis derived up to next-to-leading order in derivatives from the microscopic\ntheory. Apart from a next-to-leading order term that is suppressed in the BCS\nlimit, the effective action obtained in the strong-coupling unitary limit is\nproportional to that in the weak-coupling BCS limit.",
        "positive": "Spin-driven stationary turbulence in spinor Bose-Einstein condensates: We report the observation of stationary turbulence in antiferromagnetic\nspin-1 Bose-Einstein condensates driven by a radio-frequency magnetic field.\nThe magnetic driving injects energy into the system by spin rotation and the\nenergy is dissipated via dynamic instability, resulting in the emergence of an\nirregular spin texture in the condensate. Under continuous driving, the spinor\ncondensate evolves into a nonequilibrium steady state with characteristic spin\nturbulence, while the low energy scale of spin excitations ensures that the\nsample's lifetime is minimally affected. When the driving strength is on par\nwith the system's spin interaction energy and the quadratic Zeeman energy,\nremarkably, the stationary turbulent state exhibits spin-isotropic features in\nspin composition and spatial spin texture. We numerically show that ambient\nfield fluctuations play a crucial role in sustaining the turbulent state within\nthe system. These results open up new avenues for exploring quantum turbulence\nin spinor superfluid systems."
    },
    {
        "anchor": "Entanglement and particle correlations of Fermi gases in harmonic traps: We investigate quantum correlations in the ground state of noninteracting\nFermi gases of N particles trapped by an external space-dependent harmonic\npotential, in any dimension. For this purpose, we compute one-particle\ncorrelations, particle fluctuations and bipartite entanglement entropies of\nextended space regions, and study their large-N scaling behaviors. The\nhalf-space von Neumann entanglement entropy is computed for any dimension,\nobtaining S_HS = c_l N^(d-1)/d ln N, analogously to homogenous systems, with\nc_l=1/6, 1/(6\\sqrt{2}), 1/(6\\sqrt{6}) in one, two and three dimensions\nrespectively. We show that the asymptotic large-N relation S_A\\approx \\pi^2\nV_A/3, between the von Neumann entanglement entropy S_A and particle variance\nV_A of an extended space region A, holds for any subsystem A and in any\ndimension, analogously to homogeneous noninteracting Fermi gases.",
        "positive": "Temperature-driven crossover in the Lieb-Liniger model: The large-distance behavior of the density-density correlation function in\nthe Lieb-Liniger model at finite temperature is investigated by means of the\nrecently derived nonlinear integral equations characterizing the correlation\nlengths. We present extensive numerical results covering all the physical\nregimes fromweak to strong interaction and all temperatures. We find that the\nleading term of the asymptotic expansion becomes oscillatory at a critical\ntemperature which decreases with the strength of the interaction. As we\napproach the Tonks-Girardeau limit the asymptotic behavior becomes more complex\nwith a double crossover of the largest and next-largest correlation lengths.\nThe crossovers exist only for intermediate couplings and vanish for $\\gamma=0$\nand $\\gamma=\\infty$."
    },
    {
        "anchor": "Control of dipolar relaxation in external fields: We study dipolar relaxation in both ultra-cold thermal and Bose-condensed\nchromium atom gases. We show three different ways to control dipolar\nrelaxation, making use of either a static magnetic field, an oscillatory\nmagnetic field, or an optical lattice to reduce the dimensionality of the gas\nfrom 3D to 2D. Although dipolar relaxation generally increases as a function of\na static magnetic field intensity, we find a range of non-zero magnetic field\nintensities where dipolar relaxation is strongly reduced. We use this resonant\nreduction to accurately determine the S=6 scattering length of chromium atoms:\n$a_6 = 103 \\pm 4 a_0$. We compare this new measurement to another new\ndetermination of $a_6$, which we perform by analysing the precise spectroscopy\nof a Feshbach resonance in d-wave collisions, yielding $a_6 = 102.5 \\pm 0.4\na_0$. These two measurements provide by far the most precise determination of\n$a_6$ to date. We then show that, although dipolar interactions are long-range\ninteractions, dipolar relaxation only involves the incoming partial wave $l=0$\nfor large enough magnetic field intensities, which has interesting consequences\non the stability of dipolar Fermi gases. We then study ultra-cold chromium\ngases in a 1D optical lattice resulting in a collection of independent 2D\ngases. We show that dipolar relaxation is modified when the atoms collide in\nreduced dimensionality at low magnetic field intensities, and that the\ncorresponding dipolar relaxation rate parameter is reduced by a factor up to 7\ncompared to the 3D case. Finally, we study dipolar relaxation in presence of\nradio-frequency (rf) oscillating magnetic fields, and we show that both the\noutput channel energy and the transition amplitude can be controlled by means\nof rf frequency and Rabi frequency.",
        "positive": "Haldane phase in the sawtooth lattice: Edge states, entanglement\n  spectrum and the flat band: Using density matrix renormalization group numerical calculations, we study\nthe phase diagram of the half filled Bose-Hubbard system in the sawtooth\nlattice with strong frustration in the kinetic energy term. We focus in\nparticular on values of the hopping terms which produce a flat band and show\nthat, in the presence of contact and near neighbor repulsion, three phases\nexist: Mott insulator (MI), charge density wave (CDW), and the topological\nHaldane insulating (HI) phase which displays edge states and particle imbalance\nbetween the two ends of the system. We find that, even though the entanglement\nspectrum in the Haldane phase is not doubly degenerate, it is in excellent\nagreement with the entanglement spectrum of the Affleck-Kennedy-Lieb-Tasaki\n(AKLT) state built in the Wannier basis associated with the flat band. This\nemphasizes that the absence of degeneracy in the entanglement spectrum is not\nnecessarily a signature of a non-topological phase, but rather that the\n(hidden) protecting symmetry involves non-local states. Finally, we also show\nthat the HI phase is stable against small departure from flatness of the band\nbut is destroyed for larger ones."
    },
    {
        "anchor": "Density correlation functions and the spatial structure of the\n  two-dimensional BEC-BCS crossover: The spatial structure of a two-dimensional homogeneous mixture of fermionic\natoms in two hyperfine states is analyzed throughout the BEC-BCS crossover.\nWithin the BCS-Leggett mean-field model we consider three functions: the pair\nwave function and the density-density correlation functions between atoms of\nthe same and of different hyperfine states. For the correlation functions we\nderive analytical expressions which allow to unveil the rich spatial structure\nof the superfluid. Mainly, we are able to study the large-distance behavior of\nthe three functions, which exhibits an exponential decay and a well-defined\noscillatory behavior. We report closed-form expressions for the correlation\nlengths and mean pair radius. Differences and similarities emerge when\ncomparing with the three dimensional case. Particularly, we find an expression\nfor the large-distance correlation length, in terms of the chemical potential\nand the gap, valid in two and three dimensions, but whose dependence on the\ncorresponding scattering lengths differ significantly.",
        "positive": "Time-domain Ramsey interferometry with interacting Rydberg atoms: We theoretically investigate the dynamics of a gas of strongly interacting\nRydberg atoms subject to a time-domain Ramsey interferometry protocol. The\nmany-body dynamics is governed by an Ising-type Hamiltonian with long range\ninteractions of tunable strength. We analyze and model the contrast degradation\nand phase accumulation of the Ramsey signal and identify scaling laws for\nvarying interrogation times, ensemble densities, and ensemble dimensionalities."
    },
    {
        "anchor": "Deformation Dependence of Breathing Oscillations in Bose - Fermi\n  Mixtures at Zero Temperature: We study the breathing oscillations in bose-fermi mixtures in the\naxially-symmetric deformed trap of prolate, spherical and oblate shapes, and\nclarify the deformation dependence of the frequencies and the characteristics\nof collective oscillations. The collective oscillations of the mixtures in\ndeformed traps are calculated in the scaling method. In largely-deformed\nprolate and oblate limits and spherical limit, we obtain the analytical\nexpressions of the collective frequencies. The full calculation shows that the\ncollective oscillations become consistent with the analytically-obtained\nfrequencies when the system is deformed into both prolate and oblate regions.\nThe complicated changes of oscillation characters are shown to occur in the\ntranscendental regions around the spherically-deformed region. We find that\nthese critical changes of oscillation characters are explained by the level\ncrossing behaviors of the intrinsic oscillation modes. The approximate\nexpressions are obtained for the level crossing points that determine the\ntranscendental regions. We also compare the results of the scaling methods with\nthose of the dynamical approach.",
        "positive": "Theory of correlations in strongly interacting fluids of two-dimensional\n  dipolar bosons: Ground-state properties of a two-dimensional fluid of bosons with repulsive\ndipole-dipole interactions are studied by means of the Euler-Lagrange\nhypernetted-chain approximation. We present a self-consistent semi-analytical\ntheory of the pair distribution function $g(r)$ and ground-state energy of this\nsystem. Our approach is based on the solution of a zero-energy scattering\nSchr\\\"{o}dinger equation for the \"pair amplitude\" $\\sqrt{g(r)}$ with an\neffective potential from Jastrow-Feenberg correlations. We find excellent\nagreement with quantum Monte Carlo results over a wide range of coupling\nstrength, nearly up to the critical coupling for the liquid-to-crystal quantum\nphase transition. We also calculate the one-body density matrix and related\nquantities, such as the momentum distribution function and the condensate\nfraction."
    },
    {
        "anchor": "Beliaev technique for a weakly interacting Bose gas: Aiming for simplicity of explicit equations and at the same time controllable\naccuracy of the theory we present results for all thermodynamic quantities and\ncorrelation functions for the weakly interacting Bose gas at\nshort-to-intermediate distances obtained within an improved version of\nBeliaev's diagrammatic technique. With a small symmetry breaking term Beliaev's\ndiagrammatic technique becomes regular in the infrared limit. Up to\nhigher-order terms (for which we present order-of-magnitude estimates), the\npartition function and entropy of the system formally correspond to those of a\nnon-interacting bosonic (pseudo-)Hamiltonian with a temperature dependent\nBogoliubov-type dispersion relation. Away from the fluctuation region, this\napproach provides the most accurate--in fact, the best possible within the\nBogoliubov-type pseudo-Hamiltonian framework--description of the system with\ncontrolled accuracy. It produces accurate answers for the off-diagonal\ncorrelation functions up to distances where the behaviour of correlators is\ncontrolled by generic hydrodynamic relations, and thus can be accurately\nextrapolated to arbitrarily large scales. In the fluctuation region, the\nnon-perturbative contributions are given by universal (for all weakly\ninteracting U(1) systems) constants and scaling functions, which can be\nobtained separately--by simulating classical U(1) models--and then used to\nextend the description of the weakly interacting Bose gas to the fluctuation\nregion. The theory works in all spatial dimensions and we explicitly check its\nvalidity against first-principle Monte Carlo simulations for various\nthermodynamic properties and the single-particle density matrix.",
        "positive": "Density Distribution of a Bose-Einstein Condensate of Photons in a\n  Dye-Filled Microcavity: The achievement of Bose-Einstein condensation of photons (phBEC) in a\ndye-filled microcavity has led to a renewed interest in the density\ndistribution of the ideal Bose gas in a two-dimensional harmonic oscillator. We\npresent measurements of the radial profile of photons inside the microcavity\nbelow and above the critical point for phBEC with a good signal-to-noise ratio.\nWe obtain a good agreement with theoretical profiles obtained using exact\nsummation of eigenstates."
    },
    {
        "anchor": "Solitary waves and yrast states in Bose-Einstein condensed gases of\n  atoms: Considering a Bose-Einstein condensed gas confined in one dimension with\nperiodic boundary conditions, we demonstrate that, very generally,\nsolitary-wave and rotational excitations coincide. This exact equivalence\nallows us to establish connections between a number of effects that are present\nin these two problems, many of which have been studied using the mean-field\napproximation.",
        "positive": "Homogeneous and domain wall topological Haldane conductors with dressed\n  Rydberg atoms: The interplay between antiferromagnetic interaction and hole motion is\ncapable of inducing intriguing conducting topological Haldane phases described\nby a finite non-local string order parameter. Here we show that these states of\nmatter are captured by the one dimensional $t-J_z$ model which can be\nexperimentally realized with dressed Rydberg atoms trapped onto a one\ndimensional optical lattice. In the sector with vanishing total magnetization\nexact Bethe ansatz calculations associated to bosonization technique allow to\npredict that both metallic and superconducting topological Haldane states can\nbe achieved. With the addition of an appropriate magnetic field the system\nenters in a domain wall structure with finite total magnetization. In this\nregime conducting topological Haldane states are confined in domains separated\nby regions where fully polarized Luttinger liquid occurs. A procedure to\ndynamically stabilize such Haldane topological phases starting from a confined\nIsing state is also described"
    },
    {
        "anchor": "Ab initio transport results for strongly correlated fermions: Quantum transport of strongly correlated fermions is of central interest in\ncondensed matter physics. Here, we present first-principle nonequilibrium Green\nfunctions results using $T$-matrix selfenergies for finite Hubbard clusters of\ndimension $1,2,3$. We compute the expansion dynamics following a potential\nquench and predict its dependence on the interaction strength and particle\nnumber. We discover a universal scaling, allowing an extrapolation to\ninfinite-size systems, which shows excellent agreement with recent cold atom\ndiffusion experiments [Schneider et al., Nat. Phys. 8, 213 (2012)].",
        "positive": "Properties of strongly dipolar Bose gases beyond the Born approximation: Strongly dipolar Bose gases can form liquid droplets stabilized by quantum\nfluctuations. In theoretical description of this phenomenon, low energy\nscattering amplitude is utilized as an effective potential. We show that for\nmagnetic atoms corrections with respect to Born approximation arise, and derive\nmodified pseudopotential using realistic interaction model. We discuss the\nresulting changes in collective mode frequencies and droplet stability diagram.\nOur results are relevant for recent experiments with erbium and dysprosium\natoms."
    },
    {
        "anchor": "Positive and negative mass solitons in spin-orbit coupled Bose-Einstein\n  condensates: We present a unified description of different types of matter-wave solitons\nthat can emerge in quasi one-dimensional spin-orbit coupled (SOC) Bose-Einstein\ncondensates (BECs). This description relies on the reduction of the original\ntwo-component Gross-Pitaevskii SOC-BEC model to a single nonlinear\nSchr\\\"{o}dinger equation, via a multiscale expansion method. This way, we find\napproximate bright and dark soliton solutions, for attractive and repulsive\ninteratomic interactions respectively, for different regimes of the SOC\ninteractions. Beyond this, our approach also reveals \"negative mass\" regimes,\nwhere corresponding \"negative mass\" bright or dark solitons can exist for\nrepulsive or attractive interactions, respectively. Such a unique opportunity\nstems from the structure of the excitation spectrum of the SOC-BEC. Numerical\nresults are found to be in excellent agreement with our analytical predictions.",
        "positive": "Observation of first and second sound in a BKT superfluid: Superfluidity in its various forms has fascinated scientists since the\nobservation of frictionless flow in liquid helium II. In three spatial\ndimensions (3D), it is conceptually associated with the emergence of long-range\norder (LRO) at a critical temperature $T_{\\text{c}}$. One of its hallmarks,\npredicted by the highly successful two-fluid model and observed in both liquid\nhelium and ultracold atomic gases, is the existence of two kinds of sound\nexcitations, the first and second sound. In 2D systems, thermal fluctuations\npreclude LRO, but superfluidity nevertheless emerges at a nonzero\n$T_{\\text{c}}$ via the infinite-order Berezinskii-Kosterlitz-Thouless (BKT)\ntransition, which is associated with a universal jump in the superfluid density\n$n_{\\text{s}}$ without any discontinuities in the fluid's thermodynamic\nproperties. BKT superfluids are also predicted to support two sounds, but the\nobservation of this has remained elusive. Here we observe first and second\nsound in a homogeneous 2D atomic Bose gas, and from the two\ntemperature-dependent sound speeds extract its superfluid density. Our results\nagree with BKT theory, including the prediction for the universal\nsuperfluid-density jump."
    },
    {
        "anchor": "Giant vortex phase transition in rapidly rotating trapped Bose-Einstein\n  condensates: A Bose-Einstein condensate of cold atoms is a superfluid and thus responds to\nrotation of its container by the nucleation of quantized vortices. If the\ntrapping potential is su ciently strong, there is no theoretical limit to the\nrotation frequency one can impose to the fluid, and several phase transitions\ncharacterized by the number and distribution of vortices occur when it is\nincreased from zero to infinity. In this note we focus on a regime of very\nlarge rotation velocity where vortices disappear from the bulk of the fluid,\ngathering in a central hole of low matter density induced by the centrifugal\nforce.",
        "positive": "Strongly Interacting p-wave Fermi Gas in Two-Dimensions: Universal\n  Relations and Breathing Mode: The contact is an important concept that characterizes the universal\nproperties of a strongly interacting quantum gas. It appears in both\nthermodynamic (energy, pressure, etc.) and dynamic quantities (radio-frequency\nand Bragg spectroscopies, etc.) of the system. Very recently, the concept of\ncontact has been extended to higher partial waves, in particular, the p-wave\ncontacts have been experimentally probed in recent experiment. So far\ndiscussions on p-wave contacts have been limited to three-dimensions. In this\npaper, we generalize the p-wave contacts to two-dimensions and derive a series\nof universal relations, including the adiabatic relations, high momentum\ndistribution, virial theorem and pressure relation. At high temperature and low\ndensity limit, we calculated the p-wave contacts explicitly using virial\nexpansion. A formula which directly connects the shift of the breathing mode\nfrequency and the p-wave contacts are given in a harmonically trapped system.\nFinally, we also derive the relationships between interaction parameters in\nthree and two dimensional Fermi gas and discuss possible experimental\nrealization of two dimensional Fermi gas with p-wave interactions."
    },
    {
        "anchor": "Feshbach Resonance in a Tight-Binding Model: The physics of Feshbach resonance is analyzed using an analytic expression\nfor the $s$-wave scattering phase-shift and the scattering length $a$ which we\nderive within a two-channel tight-binding model. Employing a unified treatment\nof bound states and resonances in terms of the Jost function, it is shown that\nfor strong inter-channel coupling, Feshbach resonance can occur even when the\nclosed channel does not have a bound state. This may extend the range of\nultra-cold atomic systems that can be manipulated by Feshbach resonance. The\ndependence of the sign of $a$ on the coupling strength in the unitary limit is\nelucidated. As a by-product, analytic expressions are derived for the\nbackground scattering length, the external magnetic field at which resonance\noccurs, and the energy shift $\\varepsilon-\\varepsilon_B$, where $\\varepsilon$\nis the scattering energy and $\\varepsilon_B$ is the bound state energy in the\nclosed channel (when there is one).",
        "positive": "Parametric resonance of capillary waves at the interface between two\n  immiscible Bose-Einstein condensates: We study parametric resonance of capillary waves on the interface between two\nimmiscible Bose-Einstein condensates pushed towards each other by an\noscillating force. Guided by analytical models, we solve numerically the\ncoupled Gross-Pitaevskii equations for two-component Bose-Einstein condensate\nat zero temperature. We show that, at moderate amplitudes of the driving force,\nthe instability is stabilized due to non-linear modifications of the\noscillation frequency. When the amplitude of the driving force is large enough,\nwe observe detachment of droplets from the Bose-Einstein condensates, resulting\nin generation of quantum vortices (skyrmions). We analytically investigate the\nvortex dynamics, and conditions of quantized vortex generation."
    },
    {
        "anchor": "Quantum simulation of lattice gauge theories using Wilson fermions: Quantum simulators have the exciting prospect of giving access to real-time\ndynamics of lattice gauge theories, in particular in regimes that are difficult\nto compute on classical computers. Future progress towards scalable quantum\nsimulation of lattice gauge theories, however, hinges crucially on the\nefficient use of experimental resources. As we argue in this work, due to the\nfundamental non-uniqueness of discretizing the relativistic Dirac Hamiltonian,\nthe lattice representation of gauge theories allows for an optimization that up\nto now has been left unexplored. We exemplify our discussion with lattice\nquantum electrodynamics in two-dimensional space-time, where we show that the\nformulation through Wilson fermions provides several advantages over the\npreviously considered staggered fermions. Notably, it enables a strongly\nsimplified optical lattice setup and it reduces the number of degrees of\nfreedom required to simulate dynamical gauge fields. Exploiting the optimal\nrepresentation, we propose an experiment based on a mixture of ultracold atoms\ntrapped in a tilted optical lattice. Using numerical benchmark simulations, we\ndemonstrate that a state-of-the-art quantum simulator may access the Schwinger\nmechanism and map out its non-perturbative onset.",
        "positive": "Optically Induced Monopoles, Knots, and Skyrmions in Quantum Gases: We propose, and theoretically analyze, a practical protocol for the creation\nof topological monopole configurations, quantum knots, and skyrmions in\nBose--Einstein condensates by employing fictitious magnetic fields induced by\nthe interaction of the atomic cloud with coherent light fields. It is observed\nthat a single coherent field is not enough for this purpose, but instead we\nfind incoherent superpositions of several coherent fields that introduce\ntopological point charges. We numerically estimate the experimentally\nachievable strengths and gradients of the induced fictitious magnetic fields\nand find them to be adjustable at will to several orders of magnitude greater\nthan those of the physical magnetic fields employed in previous experimental\nstudies. This property together with ultrafast control of the optical fields\npaves the way for advanced engineering of topological defects in quantum gases."
    },
    {
        "anchor": "Pairing correlations in a trapped one-dimensional Fermi gas: We use a BCS-type variational wavefunction to study attractively-interacting\nquasi one-dimensional (1D) fermionic atomic gases, motivated by cold-atom\nexperiments that access the 1D regime using an anisotropic harmonic trapping\npotential (with trapping frequencies $\\omega_x = \\omega_y \\gg \\omega_z$) that\nconfines the gas to a cigar-shaped geometry. To handle the presence of the trap\nalong the $z$-direction, we construct our variational wavefunction from the\nharmonic oscillator Hermite functions that are the eigenstates of the\nsingle-particle problem. Using an analytic determination of the effective\ninteraction among harmonic oscillator states along with a numerical solution of\nthe resulting variational equations, we make specific experimental predictions\nfor how pairing correlations would be revealed in experimental probes like the\nlocal density and the momentum correlation function.",
        "positive": "Out-of-Time-Order Correlation for Many-Body Localization: In this paper we first compute the out-of-time-order correlators (OTOC) for\nboth a phenomenological model and a random-field XXZ model in the many-body\nlocalized phase. We show that the OTOC decreases in power law in a many-body\nlocalized system at the scrambling time. We also find that the OTOC can also be\nused to distinguish a many-body localized phase from an Anderson localized\nphase, while a normal correlator cannot. Furthermore, we prove an exact theorem\nthat relates the growth of the second R\\'enyi entropy in the quench dynamics to\nthe decay of the OTOC in equilibrium. This theorem works for a generic quantum\nsystem. We discuss various implications of this theorem."
    },
    {
        "anchor": "Phase-diagram and dynamics of Rydberg-dressed fermions in two-dimensions: We investigate the ground-state properties and the collective modes of a\ntwo-dimensional two-component Rydberg-dressed Fermi liquid in the\ndipole-blockade regime. We find instability of the homogeneous system toward\nphase separated and density ordered phases, using the Hartree-Fock and\nrandom-phase approximations, respectively. The spectral weight of collective\ndensity oscillations in the homogenous phase also signals the emergence of\ndensity-wave instability. We examine the effect of exchange-hole on the\ndensity-wave instability and on the collective mode dispersion using the\nHubbard local-field factor.",
        "positive": "Non-Abelian geometric potentials and spin-orbit coupling for\n  periodically driven systems: We demonstrate the emergence of the non-Abelian geometric potentials and thus\nthe three-dimensional (3D) spin-orbit coupling (SOC) for ultracold atoms\nwithout using the laser beams. This is achieved by subjecting an atom to a\nperiodic perturbation which is the product of a position-dependent Hermitian\noperator $\\hat{V}\\left(\\mathbf{r}\\right)$ and a fast oscillating periodic\nfunction $f\\left(\\omega t\\right)$ with a zero average. To have a significant\nspin-orbit coupling (SOC), we analyze a situation where the characteristic\nenergy of the periodic driving is not necessarily small compared to the driving\nenergy $\\hbar\\omega$. Applying a unitary transformation to eliminate the\noriginal periodic perturbation, we arrive at a non-Abelian (non-commuting)\nvector potential term describing the 3D SOC. The general formalism is\nillustrated by analyzing the motion of an atom in a spatially inhomogeneous\nmagnetic field oscillating in time. A cylindrically symmetric magnetic field\nprovides the SOC involving the coupling between the spin $\\mathbf{F}$ and all\nthree components of the orbital angular momentum (OAM) $\\mathbf{L}$. In\nparticular, the spherically symmetric monopole-type synthetic magnetic field\n$\\mathbf{B}\\propto\\mathbf{r}$ generates the 3D SOC of the $\\mathbf{L}\\cdot\n\\mathbf{F}$ form, which resembles the fine-structure interaction of hydrodgen\natom. However, the strength of the SOC here goes as $1/r^{2}$ for larger\ndistances, instead of $1/r^3$ as in atomic fine structure. Such a longer-ranged\nSOC significantly affects not only the lower states of the trapped atom, but\nalso the higher ones. Furthermore, by properly tailoring the external trapping\npotential, the ground state of the system can occur at finite OAM, while the\nground state of hydrogen atom has zero OAM."
    },
    {
        "anchor": "Ferromagnetism and Skyrmions in the Hofstadter-Fermi-Hubbard Model: Strongly interacting fermionic systems host a variety of interesting quantum\nmany-body states with exotic excitations. For instance, the interplay of strong\ninteractions and the Pauli exclusion principle can lead to Stoner\nferromagnetism, but the fate of this state remains unclear when kinetic terms\nare added. While in many lattice models the fermions' dispersion results in\ndelocalization and destabilization of the ferromagnet, flat bands can restore\nstrong interaction effects and ferromagnetic correlations. To reveal this\ninterplay, here we propose to study the Hofstadter-Fermi-Hubbard model using\nultracold atoms. We demonstrate, by performing large-scale DMRG simulations,\nthat this model exhibits a lattice analog of the quantum Hall ferromagnet at\nmagnetic filling factor $\\nu=1$. We reveal the nature of the low energy\nspin-singlet states around $\\nu\\approx1$ and find that they host\nquasi-particles and quasi-holes exhibiting spin-spin correlations reminiscent\nof skyrmions. Finally, we predict the breakdown of flat-band ferromagnetism at\nlarge fields. Our work paves the way towards experimental studies of lattice\nquantum Hall ferromagnetism, including prospects to study many-body states of\ninteracting skyrmions and explore the relation to high-$T_{\\rm c}$\nsuperconductivity.",
        "positive": "Spontaneous spatial order in two-dimensional ferromagnetic spin-orbit\n  coupled uniform spin-1 condensate solitons: We demonstrate spontaneous spatial order in stripe and super-lattice solitons\nin a Rashba spin-orbit (SO) coupled spin-1 uniform quasi-two-dimensional\n(quasi-2D) ferromagnetic Bose-Einstein condensate. For weak SO coupling, the\nsolitons are of the $(- 1,0,+ 1)$ or $(0,+ 1,+ 2)$ type with intrinsic\nvorticity, where the numbers in the parentheses denote angular momentum in spin\ncomponents $F_z=+1,0,-1$, respectively. For intermediate SO coupling, three\ntypes of solitons are found: (a) circularly-asymmetric solitons, (b)\ncircularly-symmetric $(- 1,0,+ 1)$- and (c) $(0,+ 1,+ 2)$-type multi-ring\nsolitons maintaining the above-mentioned vortices in respective components. For\nlarge SO coupling, quasi-degenerate stripe and super-lattice solitons are found\nin addition to the circularly-asymmetric solitons. A super-lattice soliton\nforms a 2D square lattice structure in the total density as in a super-solid;\nin component densities it may have either (i) a 1D stripe pattern or (ii) a 2D\nsquare lattice structure."
    },
    {
        "anchor": "Realizing the Frenkel-Kontorova model with Rydberg-dressed atoms: We propose a method to realize the Frenkel-Kontorova model using an array of\nRydberg dressed atoms. Our platform can be used to study this model with a\nrange of realistic interatomic potentials. In particular, we concentrate on two\ntypes of interaction potentials: a springlike potential and a repulsive\nlong-range potential. We numerically calculate the phase diagram for such\nsystems and characterize the Aubry-like and commensurate-incommensurate phase\ntransitions. Experimental realizations of this system that are possible to\nachieve using current technology are discussed.",
        "positive": "Spontaneous patterns in coherently driven polariton microcavities: We consider a polariton microcavity resonantly driven by two external lasers\nwhich simultaneously pump both lower and upper polariton branches at normal\nincidence. In this setup, we study the occurrence of instabilities of the\npump-only solutions towards the spontaneous formation of patterns. Their\nappearance is a consequence of the spontaneous symmetry breaking of\ntranslational and rotational invariance due to interaction induced parametric\nscattering. We observe the evolution between diverse patterns which can be\nclassified as single-pump, where parametric scattering occurs at the same\nenergy as one of the pumps, and as two-pump, where scattering occurs at a\ndifferent energy. For two-pump instabilities, stripe and chequerboard patterns\nbecome the dominant steady-state solutions because cubic parametric scattering\nprocesses are forbidden. This contrasts with the single-pump case, where\nhexagonal patterns are the most common arrangements. We study the possibility\nof controlling the evolution between different patterns. Our results are\nobtained within a linear stability analysis and are confirmed by finite size\nfull numerical calculations."
    },
    {
        "anchor": "Tan relations in one dimension: We derive exact relations that connect the universal $C/k^4$-decay of the\nmomentum distribution at large $k$ with both thermodynamic properties and\ncorrelation functions of two-component Fermi gases in one dimension with\ncontact interactions. The relations are analogous to those obtained by Tan in\nthe three-dimensional case and are derived from an operator product expansion\nof the one- and two-particle density matrix. They extend earlier results by\nOlshanii and Dunjko [Phys. Rev. Lett. 91, 090401 (2003)] for the bosonic\nLieb-Liniger gas. As an application, we calculate the pair distribution\nfunction at short distances and the dimensionless contact in the limit of\ninfinite repulsion. The ground state energy approaches a universal constant in\nthis limit, a behavior that also holds in the three-dimensional case. In both\none and three dimensions, a Stoner instability to a saturated ferromagnet for\nrepulsive fermions with zero range interactions is ruled out at any finite\ncoupling.",
        "positive": "Anderson localization in an interacting fermionic system: In the present article, we discuss the role played by the interaction in the\nAnderson localization problem, for a system of interacting fermions in a\none-dimensional disordered lattice, described by the Fermi Hubbard Hamiltonian,\nin presence of an on-site random potential. We show that, given the proper\nidentification of the elementary excitations of the system described in terms\nof doublons and unpaired particles, the Anderson localization picture survives.\nEnsuing a \"global quench\", we show that the system exhibits a rich localization\nscenario, which can be ascribed to the nearly-free dynamics of the elementary\nexcitations of the Hubbard Hamiltonian."
    },
    {
        "anchor": "Nonequilibrium quantum dynamics of atomic dark solitons: We study quantum dynamics of bosonic atoms that are excited to form a phase\nkink, or several kinks, by an imprinting potential in a one-dimensional trap.\nWe calculate dissipation due to quantum and thermal fluctuations in soliton\ntrajectories, collisions and the core structure. Single-shot runs show weak\nfilling of a soliton core, typically deeper solitons in the case of stronger\nfluctuations and spreading/disappearing solitons due to collisions. We also\nanalyze a soliton system in an optical lattice that shows especially strong\nfluctuation-induced phenomena.",
        "positive": "Localization from quantum interference in one-dimensional disordered\n  potentials: We show that the tails of the asymptotic density distribution of a quantum\nwave packet that localizes in the the presence of random or quasiperiodic\ndisorder can be described by the diagonal term of the projection over the\neingenstates of the disordered potential. This is equivalent of assuming a\nphase randomization of the off-diagonal/interference terms. We demonstrate\nthese results through numerical calculations of the dynamics of ultracold atoms\nin the one-dimensional speckle and quasiperiodic potentials used in the recent\nexperiments that lead to the observation of Anderson localization for matter\nwaves [Billy et al., Nature 453, 891 (2008); Roati et al., Nature 453, 895\n(2008)]. For the quasiperiodic case, we also discuss the implications of using\ncontinuos or discrete models."
    },
    {
        "anchor": "Fate of the Bose polaron at finite temperature: We consider an impurity immersed in a Bose-Einstein condensate with tunable\nboson-impurity interactions. Such a Bose polaron has recently been predicted to\nexhibit an intriguing energy spectrum at finite temperature, where the\nground-state quasiparticle evenly splits into two branches as the temperature\nis increased from zero [Guenther et al., Phys. Rev. Lett. 120, 050405 (2018)].\nTo investigate this theoretical prediction, we employ a recently developed\nvariational approach that systematically includes multi-body correlations\nbetween the impurity and the finite-temperature medium, thus allowing us to go\nbeyond previous finite-temperature methods. Crucially, we find that the number\nof quasiparticle branches is simply set by the number of hole excitations of\nthe thermal cloud, such that including up to one hole yields one splitting, two\nholes yields two splittings, and so on. Moreover, this effect is independent of\nthe impurity mass. We thus expect that the exact ground-state quasiparticle\nwill evolve into a single broad peak for temperatures $T>0$, with a broadening\nthat scales as $T^{3/4}$ at low temperatures and sufficiently weak boson-boson\ninteractions. In the zero-temperature limit, we show that our calculated\nground-state polaron energy is in excellent agreement with recent quantum Monte\nCarlo results and with experiments.",
        "positive": "Phase separation in binary Bose mixtures at finite temperature: We investigate the magnetic behavior of finite-temperature repulsive\ntwo-component Bose mixtures by means of exact path-integral Monte-Carlo\nsimulations. Novel algorithms are implemented for the free energy and the\nchemical potential of the two components. Results on the magnetic\nsusceptibility suggest that the conditions for phase separation are not\nmodified from the zero temperature case. This contradicts previous predictions\nbased on approximate theories. We also determine the temperature dependence of\nthe chemical potential and the contact parameters for experimentally relevant\nbalanced mixtures."
    },
    {
        "anchor": "Heating a dipolar quantum fluid into a solid: Raising the temperature of a material enhances the thermal motion of\nparticles. Such an increase in thermal energy commonly leads to the melting of\na solid into a fluid and eventually vaporises the liquid into a gaseous phase\nof matter. Here, we study the finite-temperature physics of dipolar quantum\nfluids and find surprising deviations from this general phenomenology. In\nparticular, we describe how heating a dipolar superfluid from near-zero\ntemperatures can induce a phase transition to a supersolid state with a broken\ntranslational symmetry. The predicted effect agrees with experimental\nmeasurements on ultracold dysprosium atoms, which opens the door for exploring\nthe unusual thermodynamics of dipolar quantum fluids.",
        "positive": "Modeling Rydberg Gases using Random Sequential Adsorption on Random\n  Graphs: The statistics of strongly interacting, ultracold Rydberg gases are governed\nby the interplay of two factors: geometrical restrictions induced by blockade\neffects, and quantum mechanical effects. To shed light on their relative roles\nin the statistics of Rydberg gases, we compare three models in this paper: a\nquantum mechanical model describing the excitation dynamics within a Rydberg\ngas, a Random Sequential Adsorption (RSA) process on a Random Geometric Graph\n(RGG), and a RSA process on a Decomposed Random Intersection Graph (DRIG). The\nlatter model is new, and refers to choosing a particular subgraph of a mixture\nof two other random graphs. Contrary to the former two models, it lends itself\nfor a rigorous mathematical analysis; and it is built specifically to have\nparticular structural properties of a RGG. We establish for it a fluid limit\ndescribing the time-evolution of number of Rydberg atoms, and show numerically\nthat the expression remains accurate across a wider range of particle densities\nthan an earlier approach based on an RSA process on an Erdos-Renyi Random Graph\n(ERRG). Finally, we also come up with a new heuristic using random graphs that\ngives a recursion to describe a normalized pair-correlation function of a\nRydberg gas. Our results suggest that even without dissipation, on long time\nscales the statistics are affected most by the geometrical restrictions induced\nby blockade effects, while on short time scales the statistics are affected\nmost by quantum mechanical effects."
    },
    {
        "anchor": "The Condensation of Ideal Dunkl-Bose Gas in Power-Law Traps: We explore the phenomenon of Bose-Einstein condensation in two and\none-dimensional Dunkl-boson gases confined within a power-law potential,\nemploying the framework of Dunkl-deformed boson theory. Our investigation\ninvolves the calculation of particle numbers and phase transition temperatures\nusing the Dunkl formalism. To assess the validity of our findings, we compare\nthem with the corresponding results obtained from the standard approach. We\nfind that the impact of the Dunkl-formalism on the condensate fractions is\nsimilar in one and two-dimensional cases. However, we see that this conclusion\nis not fully valid for the phase transition temperature.",
        "positive": "On-shell approximation for the s-wave scattering theory: We investigate the scattering theory of two particles in a generic\n$D$-dimensional space. For the s-wave problem, by adopting an on-shell\napproximation for the $T$-matrix equation, we derive analytical formulas which\nconnect the Fourier transform ${\\tilde V}(k)$ of the interaction potential to\nthe s-wave phase shift. In this way we obtain explicit expressions of the\nlow-momentum parameters ${\\tilde g}_0$ and ${\\tilde g}_2$ of ${\\tilde\nV}(k)={\\tilde g}_0+{\\tilde g}_2k^2 +...$ in terms of the s-wave scattering\nlength $a_s$ and the s-wave effective range $r_s$ for $D=3$, $D=2$, and $D=1$.\nOur results, which are strongly dependent on the spatial dimension $D$, are a\nuseful benchmark for few-body and many-body calculations. As a specific\napplication, we derive the zero-temperature pressure of a 2D uniform\ninteracting Bose gas with a beyond-mean-field correction which includes both\nscattering length and effective range."
    },
    {
        "anchor": "Correlation dynamics during a slow interaction quench in a\n  one-dimensional Bose gas: We investigate the response of a one-dimensional Bose gas to a slow increase\nof its interaction strength. We focus on the rich dynamics of equal-time\nsingle-particle correlations treating the Lieb-Liniger model within a\nbosonization approach and the Bose-Hubbard model using the time-dependent\ndensity-matrix renormalization group method. For short distances, correlations\nfollow a power-law with distance with an exponent given by the adiabatic\napproximation. In contrast, for long distances, correlations decay\nalgebraically with an exponent understood within the sudden quench\napproximation. This long distance regime is separated from an intermediate\ndistance one by a generalized Lieb-Robinson criterion. At long times, in this\nintermediate regime, bosonization predicts that single-particle correlations\ndecay following a stretched exponential. This latter regime is unconventional\nas, for one-dimensional interacting systems, the decay of single-particle\ncorrelations is usually algebraic within the Luttinger liquid picture. We\ndevelop here an intuitive understanding for the propagation of correlations, in\nterms of a generalized light-cone, applicable to a large variety of systems and\nquench forms.",
        "positive": "Fluctuations of spinor Bose-Einstein condensates: We develop theory for fluctuations in atom number and spin within\nfinite-sized cells of a spinor Bose-Einstein condensate. This theory provides a\nmodel of measurements that can be performed in current experiments using finite\nresolution in situ imaging. We develop analytic results for quantum and\nthermodynamic limits of the fluctuations and apply our theory to the four\nequilibrium phases of a spin-1 condensate. We then validate these limits and\nexamine the behaviour over a wide parameter regime using numerical calculations\nspecialised to the case of a spinor condensate confined to be\nquasi-two-dimensional (quasi-2D)."
    },
    {
        "anchor": "Spontaneous condensation of exciton polaritons in the single-shot regime: Bose-Einstein condensate of exciton polaritons in a semiconductor microcavity\nis a macroscopically populated coherent quantum state subject to concurrent\npumping and decay. Debates about the fundamental nature of the condensed phase\nin this open quantum system still persist. Here, we gain a new insight into the\nspontaneous condensation process by imaging long-lifetime exciton polaritons in\na high-quality inorganic microcavity in the single-shot optical excitation\nregime, without averaging over multiple condensate realisations. In this highly\nnon-stationary regime, a condensate is strongly influenced by the `hot'\nincoherent reservoir, and reservoir depletion is critical for the transition to\nthe ground energy and momentum state. Condensates formed by more photonic\nexciton polaritons exhibit dramatic reservoir-induced density filamentation and\nshot-to-shot fluctuations. In contrast, condensates of more excitonic\nquasiparticles display smooth density and are second-order coherent. Our\nobservations show that the single-shot measurements offer a unique opportunity\nto study formation of macroscopic phase coherence during a quantum phase\ntransition in a solid state system.",
        "positive": "Dispersive and dissipative coupling of photon Bose-Einstein condensates: The synchronization of coherent states of light has long been an important\nsubject of basic research and technology. Recently, a new concept for analog\ncomputers has emerged where this synchronization process can be exploited to\nsolve computationally hard problems - potentially faster and more\nenergy-efficient than what can be achieved with conventional computer\ntechnology today. The unit cell of such systems consists of two coherent\ncenters that are coupled to one another in a controlled manner. Here, we\nexperimentally characterize and analyze the synchronization process of two\nphoton Bose-Einstein condensates, which are coupled to one another, either\ndispersively or dissipatively. We show that both types of coupling are robust\nagainst a detuning of the condensate frequencies and show similar time\nconstants in establishing mutual coherence. Significant differences between\nthese couplings arise in the behaviour of the condensate populations under\nimbalanced optical pumping. The combination of these two types of coupling\nextends the class of physical models that can be investigated using analog\nsimulations."
    },
    {
        "anchor": "Bose Hubbard model far from equilibrium: We study the nonequilibrium steady state of the Bose Hubbard model coupled to\nLindblad reservoirs, using the density matrix renormalization group in operator\nspace. We observe a transition from a flat particle density profile in the\nnoninteracting limit to the linear profile with onset of the interparticle\ninteraction. Analyzing the effect of coherent pumping on the nonequilibrium\nsteady state we find a subspace which remains unaffected by the pumping in the\nnoninteracting limit with the protection gradually diminishing due to\ninterparticle interaction. In the equilibrium situation with one or more\nsymmetric reservoirs we show analytically that the steady state of the system\nis a product state for any interaction strength. We also provide analytical\nresults in the noninteracting limits, using the method of the third\nquantization in operator space.",
        "positive": "Quantum transport in an environment parametrized by dispersive bosons: We generalize the two-channel (Edwards) fermion-boson model describing\nquantum transport in a background medium to the more realistic case of\ndispersive bosons. Using the variational exact diagonalization technique, we\nnumerically solve the extended model in a one-dimensional setting, for both\ndownward and upward curved boson dispersion, and show that going away from the\nprevious Einstein-boson assumption has profound consequences for the particle\ntransport. Specifically, we analyze the ground-state and spectral properties\nand demonstrate the renormalization of the particle's coherent band, effective\nmass, photoemission spectra and fermion-boson correlation functions due to the\ninterplay of fluctuations and correlations in a dispersive environment."
    },
    {
        "anchor": "Dimer, trimer and FFLO liquids in mass- and spin-imbalanced trapped\n  binary mixtures in one dimension: We present a systematic investigation of attractive binary mixtures in\npresence of both spin- and mass-imbalance in one dimensional setups described\nby the Hubbard model. After discussing typical cold atomic experimental\nrealizations and the relation between microscopic and effective parameters, we\nstudy several many-body features of trapped Fermi-Fermi and Bose-Bose mixtures\nsuch as density profiles, momentum distributions and correlation functions by\nmeans of numerical density-matrix-renormalization-group and Quantum Monte Carlo\nsimulations. In particular, we focus on the stability of\nFulde-Ferrell-Larkin-Ovchinnikov, dimer and trimer fluids in inhomogeneous\nsituations, as typically realized in cold gas experiments due to the harmonic\nconfinement. We finally consider possible experimental signatures of these\nphases both in the presence of a finite polarization and of a finite\ntemperature.",
        "positive": "Spontaneous formation of bright solitons in self-localized impurities in\n  Bose-Einstein condensate: We study the formation of bright solitons in the impurity component of\nBose-Einstein condensate (BEC)-impurity mixture by using the time-dependent\nHartree-Fock-Bogoliubov theory. While we assume the boson-boson and\nimpurity-boson interactions to be effectively repulsive, their character can be\nchanged spontaneously from repulsive to attractive in the presence of strong\nanomalous correlations. In such a regime the impurity component becomes a\nsystem of effectively attractive atoms leading automatically to the generation\nof bright solitons. We find that this soliton decays at higher temperatures due\nto the dissipation induced by the impurity-host and host-host interactions. We\nshow that after a sudden increase of the impurity-boson strength a train of\nbright solitons is produced and this can be interpreted in terms of the\nmodulational instability (MI) of the time-dependent impurity wave function."
    },
    {
        "anchor": "Stability and metastability of trapless Bose-Einstein condensates and\n  quantum liquids: Various kinds of Bose-Einstein condensates are considered, which evolve\nwithout any geometric constraints or external trap potentials including\ngravitational. For studies of their collective oscillations and stability,\nincluding the metastability and macroscopic tunneling phenomena, both the\nvariational approach and the Vakhitov-Kolokolov criterion are employed,\ncalculations are done for condensates of an arbitrary spatial dimension. It is\ndetermined that that the trapless condensate described by the logarithmic wave\nequation is essentially stable, regardless of its dimensionality, while the\ntrapless condensates described by wave equations of a polynomial type with\nrespect to the wavefunction, such as the Gross-Pitaevskii (cubic),\ncubic-quintic, and so on, are at best metastable. This means that trapless\n\"polynomial\" condensates are unstable against spontaneous delocalization caused\nby fluctuations of their width, density and energy, leading to a finite\nlifetime.",
        "positive": "Viscous Drude weight of dual Bose and Fermi gases in one dimension: We continue to study frequency-dependent complex bulk viscosities of\none-dimensional Bose and Fermi gases with contact interactions, which exhibit\nthe weak-strong duality according to our recent work. Here we show that they\nare contributed to by Drude peaks divergent at zero frequency as typical for\ntransport coefficients of quantum integrable systems in one dimension. In\nparticular, their Drude weights are evaluated based on the Kubo formula in the\nhigh-temperature limit at arbitrary coupling as well as in the weak-coupling\nand strong-coupling limits at arbitrary temperature, where systematic\nexpansions in terms of small parameters are available. In all three limits, the\nDrude peaks are found at higher orders compared to the finite regular parts."
    },
    {
        "anchor": "Vortex pairing in two-dimensional Bose gases: Recent experiments on ultracold Bose gases in two dimensions have provided\nevidence for the existence of the Berezinskii-Kosterlitz-Thouless (BKT) phase\nvia analysis of the interference between two independent systems. In this work\nwe study the two-dimensional quantum degenerate Bose gas at finite temperature\nusing the projected Gross-Pitaevskii equation classical field method. While\nthis describes the highly occupied modes of the gas below a momentum cutoff, we\nhave developed a method to incorporate the higher momentum states in our model.\nWe concentrate on finite-sized homogeneous systems in order to simplify the\nanalysis of the vortex pairing. We determine the dependence of the condensate\nfraction on temperature and compare this to the calculated superfluid fraction.\nBy measuring the first order correlation function we determine the boundary of\nthe Bose-Einstein condensate and BKT phases, and find it is consistent with the\nsuperfluid fraction decreasing to zero. We reveal the characteristic unbinding\nof vortex pairs above the BKT transition via a coarse-graining procedure.\nFinally, we model the procedure used in experiments to infer system\ncorrelations [Hadzibabic et al., Nature 441, 1118 (2006)], and quantify its\nlevel of agreement with directly calculated in situ correlation functions.",
        "positive": "Controlling collisional loss and scattering lengths of ultracold dipolar\n  molecules with static electric fields: Trapped samples of ultracold molecules are often short-lived, because close\ncollisions between them result in trap loss. We investigate the use of\nshielding with static electric fields to create repulsive barriers between\npolar molecules to prevent such loss. Shielding is very effective even for\nRbCs, with a relatively low dipole moment, and even more effective for\nmolecules such as NaK, NaRb and NaCs, with progressively larger dipoles.\nVarying the electric field allows substantial control over the scattering\nlength, which will be crucial for the stability or collapse of molecular\nBose-Einstein condensates. This arises because the dipole-dipole interaction\ncreates a long-range attraction that is tunable with electric field. For RbCs,\nthe scattering length is positive across the range where shielding is\neffective, because the repulsion responsible for shielding dominates. For NaK,\nthe scattering length can be tuned across zero to negative values. For NaRb and\nNaCs, the attraction is strong enough to support tetraatomic bound states, and\nthe scattering length passes through resonant poles where these states cross\nthreshold. For KAg and CsAg, there are multiple bound states and multiple\npoles. For each molecule, we calculate the variation of scattering length with\nfield and comment on the possibilities for exploring new physics."
    },
    {
        "anchor": "Feshbach resonances in potassium Bose-Bose mixtures: We present a detailed study of the scattering properties of ultracold\nmixtures of bosonic potassium atoms. We locate 20 previously unobserved\nFeshbach resonances in isotopic 39K-41K mixtures. These are assigned to s-wave\nmolecular channels by comparison to an asymptotic bound state model and coupled\nchannels calculations. Additional Feshbach resonances are studied in spin\nmixtures of a single potassium isotope, both in 39K and 41K. In particular, we\ncharacterize the parameters of a selected 39K Feshbach resonance by\nradio-frequency association of Feshbach molecules. Our results could be\nexploited to refine the model potentials for potassium scattering. Furthermore,\nthese new Feshbach resonances enlarge the range of experiments possible with\ndegenerate Bose-Bose mixtures.",
        "positive": "Faraday and Resonant Waves in Dipolar Cigar-Shaped Bose-Einstein\n  Condensates: Faraday and resonant density waves emerge in Bose-Einstein condensates as a\nresult of harmonic driving of the system. They represent nonlinear excitations\nand are generated due to the interaction-induced coupling of collective\noscillation modes and the existence of parametric resonances. Using a\nmean-field variational and a full numerical approach, we studied density waves\nin dipolar condensates at zero temperature, where breaking of the symmetry due\nto anisotropy of the dipole-dipole interaction (DDI) plays an important role.\nWe derived variational equations of motion for the dynamics of a driven dipolar\nsystem and identify the most unstable modes that correspond to the Faraday and\nresonant waves. Based on this, we derived the analytical expressions for\nspatial periods of both types of density waves as functions of the contact and\nthe DDI strength. We compared the obtained variational results with the results\nof extensive numerical simulations that solve the dipolar Gross-Pitaevskii\nequation in 3D, and found a very good agreement."
    },
    {
        "anchor": "Einstein-Bose condensation of Onsager vortices: We have studied statistical mechanics of a gas of vortices in two dimensions.\nWe introduce a new observable---a condensate fraction of Onsager vortices---to\nquantify the emergence of the vortex condensate. The condensation of Onsager\nvortices is most transparently observed in a single vortex species system and\noccurs due to a competition between solid body rotation (c.f. vortex lattice)\nand potential flow (c.f. multiple quantum vortex state). We propose an\nexperiment to observe the condensation transition of the vortices in such a\nsingle vortex species system.",
        "positive": "First and second sound in a compressible 3D Bose fluid: The two-fluid model is fundamental for the description of superfluidity. In\nthe nearly-incompressible-liquid regime, it successfully describes first and\nsecond sound, corresponding, respectively, to density and entropy waves, in\nboth liquid helium and unitary Fermi gases. Here, we study the two sounds in\nthe opposite regime of a highly compressible fluid, using an ultracold $^{39}$K\nBose gas in a three-dimensional box trap. We excite the longest-wavelength mode\nof our homogeneous gas, and observe two distinct resonant oscillations below\nthe critical temperature, of which only one persists above it. In a microscopic\nmode-structure analysis, we find agreement with the hydrodynamic theory, where\nfirst and second sound involve density oscillations dominated by, respectively,\nthermal and condensed atoms. Varying the interaction strength, we explore the\ncrossover from hydrodynamic to collisionless behavior in a normal gas."
    },
    {
        "anchor": "Interacting bosons in two-dimensional lattices with localized\n  dissipation: Motivated by the recent experiment [Takafumi Tomita \\emph{et al.}, Sci. Adv.\n{\\bf 3}, (2017)], we study the dynamics of interacting bosons in a\ntwo-dimensional optical lattice with local dissipation. Together with the\nGutzwiller mean-field theory for density matrices and Lindblad master equation,\nwe show how the onsite interaction between bosons affects the particle loss for\nvarious strengths of dissipation. For moderate dissipation, the trend in\nparticle loss differs significantly near the superfluid-Mott boundary than the\ndeep superfluid regime. While the loss is suppressed for stronger dissipation\nin the deep superfluid regime, revealing the typical quantum Zeno effect, the\nloss near the phase boundary shows non-monotonic dependence on the dissipation\nstrength. We furthermore show that close to the phase boundary, the long-time\ndynamics is well contrasted with the dissipative dynamics deep into the\nsuperfluid regime. Thus the loss of particle due to dissipation may act as a\nprobe to differentiate strongly-correlated superfluid regime from its\nweakly-correlated counterpart.",
        "positive": "Zero density limit extrapolation of the superfluid transition\n  temperature in a unitary atomic Fermi gas on a lattice: The superfluid transition temperature $T_c$ of a unitary Fermi gas on a\nthree-dimensional isotropic lattice with an attractive on-site interaction is\ninvestigated as a function of density $n$, from half filling down to $5.0\\times\n10^{-7}$ per unit cell, using a pairing fluctuation theory. We show that except\nat very low densities ($n^{1/3} <0.2$), where $T_c/E_F$ is linear in $n^{1/3}$,\n$T_c/E_F$ exhibits significant higher order nonlinear dependence on $n^{1/3}$.\nTherefore, linear extrapolation using results at intermediate densities such as\nin typical quantum Monte Carlo simulations leads to a significant underestimate\nof the zero density limit of $T_c/E_F$. Our result, $T_c/E_F=0.256$, at $n=0$\nis subject to reduction from particle-hole fluctuations and incoherent single\nparticle self energy corrections."
    },
    {
        "anchor": "Collective modes of p-wave superfluid Fermi gases in BEC phase: The low-energy modes of a superfluid atomic Fermi gas at zero temperature are\ninvestigated. The Bose-Einstein-condensate (BEC) side of the superfluid phase\nis studied in detail. The atoms are assumed to be in only one internal state,\nso that for a sufficiently diluted gas the pairing of fermions can be\nconsidered effective in the l=1 channel only. In agreement with previous works\non p-wave superfluidity in Fermi systems, it is found that the $p_x+ip_y$ phase\nrepresents the lowest energy state in both the Bardeen-Cooper-Schrieffer (BCS)\nand BEC sides. Our calculations show that at low energy three branches of\ncollective modes can emerge, with different species of dispersion relations: a\nphonon-like mode, a single-particle-like mode and a gapped mode. A comparison\nwith the Bogoliubov excitations of the corresponding spinor Bose condensate is\nmade. They reproduce the dispersion relations of the excitation modes of the\np-wave superfluid Fermi gas to a high accuracy.",
        "positive": "Demkov-Kunike model for cold atom association: weak interaction regime: We study the nonlinear mean-field dynamics of molecule formation at coherent\nphoto- and magneto-association of an atomic Bose-Einstein condensate for the\ncase when the external field configuration is defined by the quasi-linear level\ncrossing Demkov-Kunike model, characterized by a bell-shaped pulse and finite\nvariation of the detuning. We present a general approach to construct an\napproximation describing the temporal dynamics of the molecule formation in the\nweak interaction regime and apply the developed method to the nonlinear\nDemkov-Kunike problem. The presented approximation, written as a scaled\nsolution to the linear problem associated to the nonlinear one we treat,\ncontains fitting parameters which are determined through a variational\nprocedure. Assuming that the parameters involved in the solution of the linear\nproblem are not modified, we suggest an analytical expression for the scaling\nparameter."
    },
    {
        "anchor": "Supersolid phases of dipolar fermions in a two-dimensional-lattice\n  bilayer array: Supersolid phases as a result of a coexistence of superfluid and density\nordered checkerboard phases are predicted to appear in ultracold Fermi\nmolecules confined in a bilayer array of two-dimensional square optical\nlattices. We demonstrate the existence of these phases within the inhomogeneous\nmean-field approach. In particular, we show that tuning the interlayer\nseparation distance at a fixed value of the chemical potential produces\ndifferent fractions of superfluid, density ordered, and supersolid phases.",
        "positive": "Thermodynamic characteristics of ideal quantum gases in harmonic\n  potentials within exact and semiclassical approaches: We theoretically examine equilibrium properties of the harmonically trapped\nideal Bose and Fermi gases in the quantum degeneracy regime. We analyze\nthermodynamic characteristics of gases with a finite number of atoms by means\nof the known semiclassical approach and perform comparison with exact numerical\nresults. For a Fermi gas, we demonstrate deviations in the Fermi energy values\noriginating from a discrete level structure and show that these are observable\nonly for a small number of particles. For a Bose gas, we observe characteristic\nsoftening of phase transition features, which contrasts to the semiclassical\npredictions and related approximations. We provide a more accurate methodology\nof determining corrections to the critical temperature due to finite number of\nparticles."
    },
    {
        "anchor": "Bosonic superfluid transport in a quantum point contact: We present a microscopic theory of heat and particle transport of an\ninteracting, low temperature Bose-Einstein condensate in a quantum point\ncontact. We show that, in contrast to charged, fermionic superconductors,\nbosonic systems feature tunneling processes of condensate elements, leading to\nthe presence of odd-order harmonics in the AC Josephson current. A crucial role\nis played by an anomalous tunneling process where condensate elements are\ncoherently converted into phonon excitations, leading to even-order harmonics\nin the AC currents as well as a DC contribution. At low bias, we find\ndissipative components obeying Ohm's law, and bias-independent nondissipative\ncomponents, in sharp contrast to fermionic superconductors. Analyzing the DC\ncontribution, we find zero thermopower and Lorenz number at zero temperature, a\nbreakdown of the bosonic Wiedemann-Franz law. These results highlight\nimportance of the anomalous tunneling process inherent to charge neutral\nsuperfluids. The consequences could readily be observed in existing cold-atom\ntransport setups.",
        "positive": "Finite temperature vortices in a rotating Fermi gas: Vortices and vortex arrays have been used as a hallmark of superfluidity in\nrotated, ultracold Fermi gases. These superfluids can be described in terms of\nan effective field theory for a macroscopic wave function representing the\nfield of condensed pairs, analogous to the Ginzburg-Landau theory for\nsuperconductors. Here, we have established how rotation modifies this effective\nfield theory, by rederiving it starting from the action of Fermi gas in the\nrotating frame of reference. The rotation leads to the appearance of an\neffective vector potential, and the coupling strength of this vector potential\nto the macroscopic wave function depends on the interaction strength between\nthe fermions, due to a renormalization of the pair effective mass in the\neffective field theory. The mass renormalization derived here is in agreement\nwith results of functional renormalization group theory. In the extreme BEC\nregime, the pair effective mass tends to twice the fermion mass, in agreement\nwith the physical picture of a weakly interacting Bose gas of molecular pairs.\nThen, we use our macroscopic wave function description to study vortices and\nthe critical rotation frequencies to form them. Equilibrium vortex state\ndiagrams are derived, and they are in good agreement with available results of\nthe Bogoliubov - De Gennes theory and with experimental data."
    },
    {
        "anchor": "Clusters in Separated Tubes of Tilted Dipoles: A few-body cluster is a building block of a many-body system in a gas phase\nprovided the temperature at most is of the order of the binding energy of this\ncluster. Here we illustrate this statement by considering a system of tubes\nfilled with dipolar distinguishable particles. We calculate the partition\nfunction, which determines the probability to find a few-body cluster at a\ngiven temperature. The input for our calculations -- the energies of few-body\nclusters -- is estimated using the harmonic approximation. We first describe\nand demonstrate the validity of our numerical procedure. Then we discuss the\nresults featuring melting of the zero-temperature many-body state into a gas of\nfree particles and few-body clusters. For temperature higher than its binding\nenergy threshold, the dimers overwhelmingly dominate the ensemble, where the\nremaining probability is in free particles. At very high temperatures free\n(harmonic oscillator trap-bound) particle dominance is eventually reached. This\nstructure evolution appears both for one and two particles in each layer\nproviding crucial information about the behavior of ultracold dipolar gases.\nThe investigation addresses the transition region between few and many-body\nphysics as a function of temperature using a system of ten dipoles in five\ntubes.",
        "positive": "Generation of Josephson vortices in stacked toroidal Bose-Einstein\n  condensates: Coupled coaxially stacked toroidal condensates with persistent currents\nsuggest an appealing physical platform for the investigation of various\nphenomena related to interacting superflows from Josephson effects in the\nregime of weak interactions to the quantum Kelvin-Helmholtz instability for\nmerging rings. We suggest experimentally accessible methods to prepare states\nwith different topological charges in two coupled coaxial ring-shaped atomic\nBose-Einstein condensates. Our results open up the way to direct observation of\nrotational Josephson vortices in atomic Bose-Einstein condensates."
    },
    {
        "anchor": "Temporal and spatio-temporal correlation functions for trapped Bose\n  gases: Density correlations unambiguously reveal the quantum nature of matter. Here,\nwe study correlations between measurements of density in cold-atom clouds at\ndifferent times at one position, and also at two separated positions. We take\ninto account the effects of finite-size and -duration measurements made by\nlight beams passing through the atom cloud. We specialise to the case of Bose\ngases in harmonic traps above critical temperature, for weakly-perturbative\nmeasurements. For overlapping measurement regions, shot-noise correlations\nrevive after a trap oscillation period. For non-overlapping regions, bosonic\ncorrelations dominate at long times, and propagate at finite speeds. Finally,\nwe give a realistic measurement protocol for performing such experiments.",
        "positive": "Time-dependent study of a black-hole laser in a flowing atomic\n  condensate: We numerically study the temporal evolution of a black-hole laser\nconfiguration displaying a pair of black and white hole horizons in a flowing\natomic condensate. This configuration is initially prepared starting from a\nhomogeneous flow via a suitable space-dependent change of the interaction\nconstant and the evolution is then followed up to long times. Depending on the\nvalues of the system parameters, the system typically either converges to the\nlowest energy solution by evaporating away the horizons or displays a\ncontinuous and periodic coherent emission of solitons. By making a physical\ncomparison with optical laser devices, we identify the latter regime of\ncontinuous emission of solitons as the proper black-hole laser effect. We\ninclude some movies of the temporal evolution of the spatial density and\nvelocity profiles in the most significant cases."
    },
    {
        "anchor": "A mesoscopic Rydberg impurity in an atomic quantum gas: Giant impurity excitations with large binding energies are powerful probes\nfor exploring new regimes of far out of equilibrium dynamics in few- and\nmany-body quantum systems, as well as for in-situ observations of correlations.\nMotivated by recent experimental progress in spectroscopic studies of Rydberg\nexcitations in ensembles of ultracold atoms, we develop a new theoretical\napproach for describing multiscale dynamics of Rydberg excitations in quantum\nBose gases. We find that the crossover from few- to many-body dynamics\nmanifests in a dramatic change in spectral profile from resolved molecular\nlines to broad Gaussian distributions representing a superpolaronic state in\nwhich many atoms bind to the Rydberg impurity. We discuss signatures of this\ncrossover in the temperature and density dependence of the spectra.",
        "positive": "Phase coherence in out-of-equilibrium supersolid states of ultracold\n  dipolar atoms: A supersolid is a fascinating phase of matter, combining the global phase\ncoherence of a superfluid with hallmarks of solids, e.g. a spontaneous breaking\nof the translational symmetry. Recently, states with such counter-intuitive\nproperties have been realized in experiments using ultracold quantum gases with\nstrong dipolar interactions. Here, we investigate the response of a supersolid\nstate to phase excitations which shatter the global phase coherence. After the\ncreation of those excitations, we observe a rapid re-establishment of a global\nphase coherence, suggesting the presence of a superfluid flow across the whole\nsample and an efficient dissipation mechanism. We are able to identify a\nwell-defined region where rephasing occurs, indicating the phase boundary\nbetween the solid-like and the supersolid phase. Our observations call for the\ndevelopment of theoretical descriptions able to capture the non-equilibrium\ndynamics in the recently discovered supersolid states of quantum matter."
    },
    {
        "anchor": "Finite Temperature Properties of Three-Component Fermion Systems in\n  Optical Lattice: We investigate finite temperature properties in the half-filled\nthree-component (colors) fermion systems. It is clarified that a color\ndensity-wave (CDW) state is more stable than a color-selective\n\"antiferromagnetic\" (CSAF) state against thermal fluctuations. The reentrant\nbehavior in the phase boundary for the CSAF state is found. We also address the\nmaximum critical temperature of the translational symmetry breaking states in\nthe multicomponent fermionic systems.",
        "positive": "Optical spin conductivity in ultracold quantum gases: We show that the optical spin conductivity being a small AC response of a\nbulk spin current and elusive in condensed matter systems can be measured in\nultracold atoms. We demonstrate that this conductivity contains rich\ninformation on quantum states by analyzing experimentally achievable systems\nsuch as a spin-1/2 superfluid Fermi gas, a spin-1 Bose-Einstein condensate, and\na Tomonaga-Luttinger liquid. The obtained conductivity spectra being absent in\nthe Drude conductivity reflect quasiparticle excitations and non-Fermi liquid\nproperties. Accessible physical quantities include the superfluid gap and the\ncontact for the superfluid Fermi gas, gapped and gapless spin excitations as\nwell as quantum depletion for the Bose-Einstein condensate, and the spin part\nof the Tomonaga-Luttinger liquid parameter elusive in cold-atom experiments.\nUnlike its mass transport counterpart, the spin conductivity serves as a probe\napplicable to clean atomic gases without disorder and lattice potentials. Our\nformalism can be generalized to various systems such as spin-orbit coupled and\nnonequilibrium systems."
    },
    {
        "anchor": "Analogues of D-branes in Bose-Einstein condensates: We demonstrate theoretically that analogues of D-branes in string theory can\nbe realized in rotating, phase-separated, two-component Bose-Einstein\ncondensates and that they are observable using current experimental techniques.\nThis study raises the possibility of simulating D-branes in the laboratory.",
        "positive": "Quantum phases and collective excitations of a spin-orbit-coupled\n  Bose-Einstein condensate in a one-dimensional optical lattice: The ground state of a spin-orbit-coupled Bose gas in a one-dimensional\noptical lattice is known to exhibit a mixed regime, where the condensate wave\nfunction is given by a superposition of multiple Bloch-wave components, and an\nunmixed one, in which the atoms occupy a single Bloch state. The unmixed regime\nfeatures two unpolarized Bloch-wave phases, having quasimomentum at the center\nor at the edge of the first Brillouin zone, and a polarized Bloch-wave phase at\nintermediate quasimomenta. By calculating the critical values of the Raman\ncoupling and of the lattice strength at the transitions among the various\nphases, we show the existence of a tricritical point where the mixed, the\npolarized and the edge-quasimomentum phases meet, and whose appearance is a\nconsequence of the spin-dependent interaction. Furthermore, we evaluate the\nexcitation spectrum in the unmixed regime and we characterize the behavior of\nthe phonon and the roton modes, pointing out the instabilities occurring when a\nphase transition is approached."
    },
    {
        "anchor": "Second Josephson excitations beyond mean field as a toy model for\n  thermal pressure: exact quantum dynamics and the quantum phase model: A simple four-mode Bose-Hubbard model with intrinsic time scale separation\ncan be considered as a paradigm for mesoscopic quantum systems in thermal\ncontact. In our previous work we showed that in addition to coherent particle\nexchange, a novel slow collective excitation can be identified by a series of\nHolstein-Primakoff transformations. This resonant energy exchange mode is not\npredicted by linear Bogoliubov theory, and its frequency is sensitive to\ninteractions among Bogoliubov quasi-particles; it may be referred to as a\nsecond Josephson oscillation, in analogy to the second sound mode of liquid\nHelium II. In this paper we will explore this system beyond the\nGross-Pitaevskii mean field regime. We directly compare the classical mean\nfield dynamics to the exact full quantum many-particle dynamics and show good\nagreement over a large range of the system parameters. The second Josephson\nfrequency becomes imaginary for stronger interactions, however, indicating\ndynamical instability of the symmetric state. By means of a generalized quantum\nphase model for the full four-mode system, we then show that, in this regime,\nhigh-energy Bogoliubov quasiparticles tend to accumulate in one pair of sites,\nwhile the actual particles preferentially occupy the opposite pair. We\ninterpret this as a simple model for thermal pressure.",
        "positive": "Effect of Inter-Well Interactions on Non-Linear Beam Splitters for\n  Matter-Wave Interferometers: We study the non-linear beam splitter in matter-wave interferometers using\nultracold quantum gases in a double-well configuration in presence of non-local\ninteractions inducing inter-well density-density coupling, as they can be\nrealized, e.g., with dipolar gases. We explore this effect after considering\ndifferent input states, in the form of either coherent, or Twin-Fock, or NOON\nstates. We first review the non-interacting limit and the case in which only\nthe local interaction is present, including the study of sensitivity near the\nself-trapping threshold. Then, we consider the two-mode model in the presence\nof inter-well interactions and consider the scaling of the sensitivity as a\nfunction of the non-local coupling strength. Our analysis clearly shows that\nnon-local interactions can compensate the degradation of the sensitivity\ninduced by local interactions, so that they may be used to restore optimal\nsensitivity."
    },
    {
        "anchor": "Nonlocal pair correlations in Lieb-Liniger gases: A unified\n  nonperturbative approach from weak degeneracy to high temperatures: We present analytical results for the nonlocal pair correlations in\none-dimensional bosonic systems with repulsive contact interactions that are\nuniformly valid from the classical regime of high temperatures down to weak\nquantum degeneracy entering the regime of ultralow temperatures. By using the\ninformation contained in the short-time approximations of the full many-body\npropagator, we derive results that are nonperturbative in the interaction\nparameter while covering a wide range of temperatures and densities. For the\ncase of three particles we give a simple formula for arbitrary couplings that\nis exact in the dilute limit while remaining valid up to the regime where the\nthermal de Broglie wavelength $\\lambda_T$ is of the order of the characteristic\nlength $L$ of the system. We then show how to use this result to find\nanalytical expressions for the nonlocal correlations for arbitrary but fixed\nparticle numbers $N$ including finite-size corrections. Neglecting the latter\nin the thermodynamic limit provides an expansion in the quantum degeneracy\nparameter $N\\lambda_T/L$. We compare our analytical results with numerical\nBethe ansatz calculations, finding excellent agreement.",
        "positive": "Quantum fluctuations and Gross-Pitaevskii theory: Using the linearized version of the time dependent Gross-Pitaevskii equation\nwe calculate the dynamic response of a Bose-Einstein condensed gas to periodic\ndensity and particle perturbations. The zero temperature limit of the\nfluctuation-dissipation theorem is used to evaluate the corresponding quantum\nfluctuations induced by the elementary excitations in the ground state. In\nuniform conditions the predictions of Bogoliubov theory, including the infrared\ndivergency of the particle distribution function and the quantum depletion of\nthe condensate, are exactly reproduced by Gross-Pitaevskii theory. Results are\nalso given for the crossed particle-density response function and the extension\nof the formalism to non uniform systems is discussed. The generalization of the\nGross-Pitaevskii equation to include beyond mean field effects is finally\nconsidered and an explicit result for the chemical potential is found, in\nagreement with the prediction of Lee-Huang-Yang theory."
    },
    {
        "anchor": "Materia cu\u00e1ntica y din\u00e1mica por mediciones: This article discusses some details of the course on \"Quantum matter and\nmeasurement induced dynamics\" given in the Summer School of Physics XXIX at\nUNAM in 2022. The notes describe useful concepts to study the dynamics induced\nby photon losses, the method for simulation (quantum trajectories) is\nsummarized and details of models in optical lattices and high-Q cavities are\ngiven. The notes are in Spanish.\n  En este art\\'iculo se discuten algunos detalles del curso sobre \"Materia\ncu\\'antica y din\\'amica inducida por medici\\'on\" de la escuela de verano de\nF\\'isica XXIX (2022) en la UNAM. Las notas describen conceptos \\'utiles para\nestudiar la din\\'amica emergente por efectos de medici\\'on de fotones, se\nresume el m\\'etodo para simulaci\\'on (trayectorias cu\\'anticas) y se dan\ndetalles de modelos de materia cu\\'antica y cavidades de alta reflectancia.",
        "positive": "The Connection of Polaritons and Vacuum Rabi Splitting: Polaritons, in particular microcavity exciton-polaritons, have attracted much\nattention in recent years, as the phenomena of Bose-Einstein condensation and\nsuperfluidity have been observed for these quasiparticles. While the basic\nphysics of these systems is well understood, there has been confusion over the\nconnection of these systems to other phenomena, namely the Jaynes-Cummings\nHamiltonian, Rabi flopping, and the vacuum Rabi splitting of atoms in a cavity.\nThis paper reviews the basic theory of polaritons and shows these connections\nexplicitly."
    },
    {
        "anchor": "Two-dimensional imbalanced Fermi gas in antiparallel magnetic fields: We study a two-dimensional Fermi gas with an attractive interaction subjected\nto synthetic magnetic fields, which are assumed to be mutually antiparallel for\ntwo different spin components with population imbalance. By employing the\nmean-field approximation, we show that the Fulde-Ferrell state is energetically\nfavored over the Larkin-Ovchinnikov state in the weak-coupling limit. We then\nelucidate the zero-temperature phase diagram in the space of attraction and two\nchemical potentials analytically at weak coupling as well as numerically beyond\nit. Rich structures consisting of quantum Hall insulator, unpolarized\nsuperfluid, and Fulde-Ferrell phases separated by various second-order and\nfirst-order quantum phase transitions are found.",
        "positive": "Magnetic domain growth in a ferromagnetic Bose-Einstein condensate:\n  Effects of current: Magnetic domain patterns in a ferromagnetic Bose-Einstein condensate (BEC)\nshow different properties depending on the quadratic Zeeman effect and\ndissipation. Another important factor that affects domain patterns and domain\ngrowth is superfluid flow of atoms. Domain growth in a ferromagnetic BEC with\nnegative quadratic Zeeman energy is characterized by the same growth law as\n(classical) binary fluid in the inertial hydrodynamic regime. In the absence of\nthe superfluid flow, the domain growth law for negative quadratic Zeeman energy\nis the same as that of scalar conserved fields such as binary alloys."
    },
    {
        "anchor": "Transport coefficients from the Boson Uehling-Uhlenbeck Equation: We derive microscopic expressions for the bulk viscosity, shear viscosity and\nthermal conductivity of a quantum degenerate Bose gas above $T_C$, the critical\ntemperature for Bose-Einstein condensation. The gas interacts via a contact\npotential and is described by the Uehling-Uhlenbeck equation. To derive the\ntransport coefficients, we use Rayleigh-Schrodinger perturbation theory rather\nthan the Chapman-Enskog approach. This approach illuminates the link between\ntransport coefficients and eigenvalues of the collision operator. We find that\na method of summing the second order contributions using the fact that the\nrelaxation rates have a known limit improves the accuracy of the computations.\nWe numerically compute the shear viscosity and thermal conductivity for any\nboson gas that interacts via a contact potential. We find that the bulk\nviscosity remains identically zero as it is for the classical case.",
        "positive": "Magnetic phases of spin-3/2 fermions on a spatially anisotropic square\n  lattice: We study the magnetic phase diagram of spin-3/2 fermions in a spatially\nanisotropic square optical lattice at quarter filling (corresponding to one\nparticle per lattice site). In the limit of the large on-site repulsion the\nsystem can be mapped to the so-called Sp(N) Heisenberg spin model with N=4. We\nanalyze the Sp(N) spin model with the help of the large-N field-theoretical\napproach and show that the effective theory corresponds to the Sp(N) extension\nof the CP^{N-1} model, with the Lorentz invariance generically broken. We\nobtain the renormalization flow of the model couplings and show that although\nthe Sp(N) terms are seemingly irrelevant, their presence leads to a\nrenormalization of the CP^{N-1} part of the action, driving a phase transition.\nWe further consider the influence of the external magnetic field (the quadratic\nZeeman effect), and present the qualitative analysis of the ground state phase\ndiagram."
    },
    {
        "anchor": "Efimov correlations in strongly interacting Bose gases: We compute the virial coefficients, the contact parameters, and the momentum\ndistribution of a strongly interacting three-dimensional Bose gas by means of a\nvirial expansion up to third order in the fugacity, which takes into account\nthree-body correlations exactly. Our results characterize the nondegenerate\nregime of the interacting Bose gas, where the thermal wavelength is smaller\nthan the interparticle spacing but the scattering length may be arbitrarily\nlarge. We observe a rapid variation of the third virial coefficient as the\nscattering length is tuned across the three-atom and the atom-dimer thresholds.\nThe momentum distribution at unitarity displays a universal high-momentum tail\nwith a log-periodic momentum dependence, which is a direct signature of Efimov\nphysics. We provide a quantitative description of the momentum distribution at\nhigh momentum as measured by P. Makotyn et al. [Nat. Phys. 10, 116 (2014)], and\nour calculations indicate that the lowest trimer state might not be occupied in\nthe experiment. Our results allow for a spectroscopy of Efimov states in the\nunitary limit.",
        "positive": "Observation of an Efimov spectrum in an atomic system: In 1970 V. Efimov predicted a puzzling quantum-mechanical effect that is\nstill of great interest today. He found that three particles subjected to a\nresonant pairwise interaction can join into an infinite number of loosely bound\nstates even though each particle pair cannot bind. Interestingly, the\nproperties of these aggregates, such as the peculiar geometric scaling of their\nenergy spectrum, are universal, i.e. independent of the microscopic details of\ntheir components. Despite an extensive search in many different physical\nsystems, including atoms, molecules and nuclei, the characteristic spectrum of\nEfimov trimer states still eludes observation. Here we report on the discovery\nof two bound trimer states of potassium atoms very close to the Efimov\nscenario, which we reveal by studying three-particle collisions in an ultracold\ngas. Our observation provides the first evidence of an Efimov spectrum and\nallows a direct test of its scaling behaviour, shedding new light onto the\nphysics of few-body systems."
    },
    {
        "anchor": "Excitations of a vortex line in an elongated dipolar condensate: We characterise the properties of a vortex line in an elongated dipolar\nBose-Einstein condensate. Increasing the strength of the dipole-dipole\ninteractions (DDIs) relative to the short ranged contact interactions we find\nthat the system crosses over to a self-bound vortex droplet stabilized from\ncollapse by quantum fluctuations. We calculate the quasiparticle excitation\nspectrum of the vortex state, which is important in characterizing the vortex\nresponse, and assessing its stability. When the DDIs are sufficiently strong we\nfind that the vortex is dynamically unstable to quadrupolar modes.",
        "positive": "Coexistence of phase transitions and hysteresis near BEC: Multiple phases occurring in a Bose gas with finite-range interaction are\ninvestigated. In the vicinity of the onset of Bose-Einstein condensation (BEC)\nthe chemical potential and the pressure show a van-der-Waals like behavior\nindicating a first-order phase transition although there is no long-range\nattraction. Furthermore the equation of state becomes multivalued near the BEC\ntransition. For a Hartree-Fock or Popov (Hartree-Fock-Bogoliubov) approximation\nsuch a multivalued region can be avoided by the Maxwell construction. For\nsufficiently weak interaction the multivalued region can also be removed using\na many-body \\mbox{T-matrix} approximation. However, for strong interactions\nthere remains a multivalued region even for the \\mbox{T-matrix} approximation\nand after the Maxwell construction, what is interpreted as a density\nhysteresis. This unified treatment of normal and condensed phases becomes\npossible due to the recently found scheme to eliminate self-interaction in the\n\\mbox{T-matrix} approximation, which allows to calculate properties below and\nabove the critical temperature."
    },
    {
        "anchor": "Interference of parametrically driven one-dimensional ultracold gases: We theoretically analyze interference patterns of parametrically driven one\ndimensional ultracold atomic gases. By modulating the interaction strength\nperiodically in time, we propose to excite collective modes in a pair of\nindependent one dimensional gases at energies corresponding to the drive\nfrequency. The excited collective modes lead to spatial oscillations in the\ncorrelations of the interference pattern, which can be analyzed to obtain the\nsound velocity of the collective modes. We discuss both bosonic and fermionic\nsystems, and how such experiments could be used to probe spin charge\nseparation.",
        "positive": "Enhanced stripe phases in spin-orbit-coupled Bose-Einstein condensates\n  in ring cavities: The coupled dynamics of the atom and photon fields in optical ring cavities\nwith two counter-propagating modes give rise to both spin-orbit interactions as\nwell as long-ranged interactions between atoms of a many-body system. At zero\ntemperature, the interplay between the two-body and cavity-mediated\ninteractions determines the ground state of a Bose-Einstein condensate. In this\nwork, we find that cavity quantum electrodynamics in the weak-coupling regime\nfavors a stripe-phase state over a plane-wave phase as the strength of\ncavity-mediated interactions increases. Indeed, the stripe phase is\nenergetically stabilized even for condensates with attractive intra- and\ninter-species interactions for sufficiently large cavity interactions. The\nelementary excitation spectra in both phases correspond to linear dispersion\nrelation at long wavelengths, indicating that both phases exhibit\nsuperfluidity, though the plane-wave phase also displays a characteristic\nroton-type feature. The results suggest that even in the weak coupling regime\ncavities can yield interesting new physics in ultracold quantum gases."
    },
    {
        "anchor": "Equilibrating dynamics in quenched Bose gases: characterizing multiple\n  time regimes: We address the physics of equilibration in ultracold atomic gases following a\nquench of the interaction parameter. We focus on the momentum distribution of\nthe excitations, $n_{\\mathbf k}$, and observe that larger ${\\mathbf k}$ modes\nwill equilibrate faster, as has been claimed in recent experimental work. We\nidentify three time regimes. At short times $n_{\\mathbf k}$ exhibits\noscillations; these are damped out at intermediate times where the system\nappears to be in a false-equilibrium. Finally, at longer times, full\nequilibration occurs. This false-equilibrium is associated with the necessarily\nslower relaxation of the condensate which sufficiently high ${\\mathbf\nk}$-states (of the excitation response) will then quasi-adiabatically follow.\nOur work bears on the recent literature focus on interaction quench\nexperiments. We take issue with the fact that theories to date assume that the\noscillatory regime is adequate for addressing experiments.",
        "positive": "Holographic power-law traps for the efficient production of\n  Bose-Einstein condensates: We use a phase-only spatial light modulator to generate light distributions\nin which the intensity decays as a power law from a central maximum, with order\nranging from 2 (parabolic) to 0.5. We suggest that a sequence of these can be\nused as a time-dependent optical dipole trap for all-optical production of\nBose-Einstein condensates in two stages: efficient evaporative cooling in a\ntrap with adjustable strength and depth, followed by an adiabatic\ntransformation of the trap order to cross the BEC transition in a reversible\nway. Realistic experimental parameters are used to verify the capability of\nthis approach in producing larger Bose-Einstein condensates than by evaporative\ncooling alone."
    },
    {
        "anchor": "Resonant three-body physics in two spatial dimensions: We discuss the three-body properties of identical bosons exhibiting large\nscattering length in two spatial dimensions. Within an effective field theory\nfor resonant interactions, we calculate the leading non-universal corrections\nfrom the two-body effective range to bound-state and scattering observables. In\nparticular, we compute the three-body binding energies, the boson-dimer\nscattering properties, and the three-body recombination rate for finite\nenergies. We find significant effective range effects in the vicinity of the\nunitary limit. The implications of this result for future experiments are\nbriefly discussed.",
        "positive": "Correlated Spin-Flip Tunneling in a Fermi Lattice Gas: We report the realization of correlated, density-dependent tunneling for\nfermionic 40K atoms trapped in an optical lattice. By appropriately tuning the\nfrequency difference between a pair of Raman beams applied to a spin-polarized\ngas, simultaneous spin transitions and tunneling events are induced that depend\non the relative occupations of neighboring lattice sites. Correlated spin-flip\ntunneling is spectroscopically resolved using gases prepared in opposite spin\nstates, and the inferred Hubbard interaction energy is compared with a\ntight-binding prediction. We show that the laser-induced correlated tunneling\nprocess generates doublons via loss induced by light-assisted collisions.\nFurthermore, by controllably introducing vacancies to a spin-polarized gas, we\ndemonstrate that correlated tunneling is suppressed when neighboring lattice\nsites are unoccupied."
    },
    {
        "anchor": "Proper phase imprinting method for a dark soliton excitation in a\n  superfluid Fermi mixture: It is common knowledge that a dark soliton can be excited in an ultra-cold\natomic gas by means of the phase imprinting method. We show that, for a\nsuperfluid fermionic mixture, the standard phase imprinting procedure applied\nto both components fails to create a state with symmetry properties identical\nto those of the dark soliton solution of the Bogoliubov-de Gennes equations. To\nproduce a dark soliton in the BCS regime, a single component of the Fermi\nmixture should be phase imprinted only.",
        "positive": "Universal Hall Response in Synthetic Dimensions: We theoretically study the Hall effect on interacting $M$-leg ladder systems,\ncomparing different measures and properties of the zero temperature Hall\nresponse in the limit of weak magnetic fields. Focusing on $SU(M)$ symmetric\ninteracting bosons and fermions, as relevant for e.g. typical synthetic\ndimensional quantum gas experiments, we identify an extensive regime in which\nthe Hall imbalance $\\Delta_{\\rm H}$ is universal and corresponds to a classical\nHall resistivity $R_{\\rm H}=-1/n$ for a large class of quantum phases. Away\nfrom this high symmetry point we observe interaction driven phenomena such as\nsign reversal and divergence of the Hall response."
    },
    {
        "anchor": "Formation of Matter-Wave Polaritons in an Optical Lattice: The polariton, a quasiparticle formed by strong coupling of a photon to a\nmatter excitation, is a fundamental ingredient of emergent photonic quantum\nsystems ranging from semiconductor nanophotonics to circuit quantum\nelectrodynamics. Exploiting the interaction between polaritons has led to the\nrealization of superfluids of light as well as of strongly correlated phases in\nthe microwave domain, with similar efforts underway for microcavity\nexciton-polaritons. Here, we develop an ultracold-atom analogue of an\nexciton-polariton system in which interacting polaritonic phases can be studied\nwith full tunability and without dissipation. In our optical-lattice system,\nthe exciton is replaced by an atomic excitation, while an atomic matter wave is\nsubstituted for the photon under a strong dynamical coupling. We access the\nband structure of the matter-wave polariton spectroscopically by coupling the\nupper and lower polariton branches, and explore polaritonic many-body transport\nin the superfluid and Mott-insulating regimes, finding quantitative agreement\nwith our theoretical expectations. Our work opens up novel possibilities for\nstudies of polaritonic quantum matter.",
        "positive": "Feshbach resonances of large mass-imbalance Er-Li mixtures: We report on the experimental observation of Feshbach resonances in large\nmass-imbalance mixtures of Erbium (Er) and Lithium (Li). All combinations\nbetween ${}^{168}$Er, ${}^{166}$Er and ${}^7$Li, ${}^6$Li are cooled to\ntemperatures of a few microkelvin, partially by means of sympathetic cooling\ntogether with Ytterbium (Yb) as a third mixture component. The Er-Li inelastic\ninterspecies collisional properties are studied for magnetic fields up to 680\nG. In all cases resonant interspecies loss features, indicative of Feshbach\nresonances, have been observed. While most resonances have sub-Gauss widths, a\nfew of them are broad and feature widths of several Gauss. Those broad\nresonances are a key to the realization of ultracold Er-Li quantum gas mixtures\nwith tunable interactions."
    },
    {
        "anchor": "Supersolidity of cold-atom Bose-Fermi mixtures in optical lattices: We investigate a cold atomic mixture of spinless bosons and fermions in\ntwo-dimensional optical lattices. In the presence of a nested Fermi surface,\nthe bosons may develop a fascinating supersolid behavior characterized by a\nfinite superfluid density as well as a spatial density wave order. Focusing on\nthe triangular lattice geometry and combining a general Landau-Ginzburg-Wilson\napproach with microscopically derived mean-field theory, we find an exotic\nsupersolid phase at a fermionic band-filling of $n_f = 3/4$ with a Kagome-type\ncrystalline order. We also address the case of anisotropic hopping amplitudes,\nand show that striped supersolid phases emerge on the square and triangular\nlattices. For weak interactions, the supersolid competes with phase separation.\nFor strong intra- and inter-species interactions, with the total number of\nfermions and bosons corresponding to one particle per site, the bosons form an\nalternating Mott insulator ground state. Finally, for a mixture of\n$^{87}\\text{Rb}^{40}\\text{K}$ and $^{23}\\text{Na}^6\\text{Li}$, we show that\nsupersolidity can be observed in the range of accessible temperatures in the\nsquare lattice geometry.",
        "positive": "Optimized Configuration Interaction Approach for Trapped Multiparticle\n  Systems Interacting Via Contact Forces: For one-dimensional systems with delta-contact interactions, the convergence\nof the exact-diagonalization method is tested with a basis of harmonic\noscillator eigenfunctions with frequency $\\Omega$ optimized through the\nminimization of the eigenenergy of the desired level. It is shown that within\nthe framework of this approach the well-converged results can be achieved at\nmuch smaller dimensions of the Hamiltonian matrix than with the standard\napproach that uses $\\Omega=1$. We present calculations for model systems of\nidentical bosons with harmonic and double-well potentials. Our results show\npromising potential for diminishing the computational cost of numerical\nsimulations of various systems of trapped ultracold atoms."
    },
    {
        "anchor": "Quasi-condensation of bilayer excitons in a periodic potential: We study two-dimensional excitons confined in a lattice potential, for high\nfillings of the lattice sites. We show that a quasi-condensate is possibly\nformed for small values of the lattice depth, but for larger ones the critical\nphase-space density for quasi-condensation rapidly exceeds our experimental\nreach, due to the increase of the excitons effective mass. On the other hand,\nin the regime of a deep lattice potential where excitons are strongly localised\nat the lattice sites, we show that an array of phase-independent\nquasi-condensates, different from a Mott insulating phase, is realised.",
        "positive": "Supersolidity in Two-Dimensional Trapped Dipolar Droplet Arrays: We theoretically investigate the ground states and the spectrum of elementary\nexcitations across the superfluid to droplet crystallization transition of an\noblate dipolar Bose-Einstein condensate. We systematically identify regimes\nwhere spontaneous rotational symmetry breaking leads to the emergence of a\nsupersolid phase with characteristic collective excitations, such as the Higgs\namplitude mode. Furthermore, we study the dynamics across the transition and\nshow how these supersolids can be realized with standard protocols in\nstate-of-the-art experiments."
    },
    {
        "anchor": "Pair tunneling of two atoms out of a trap: A simple theory for the tunneling of two cold atoms out of a trap in the\npresence of an attractive contact force is developed. Two competing decay\nchannels, respectively for single-atom and bound-pair tunneling, contribute\nindependently to the decay law of the mean atom number in the trap. The\nsingle-atom tunneling rate is obtained through the quasiparticle wave function\nformalism. For pair tunneling an effective equation for the center-of-mass\nmotion is derived, so the calculation of the corresponding tunneling rate is\nagain reduced to a simpler one-body problem. The predicted dependence of\ntunneling rates on the interaction strength qualitatively agrees with a recent\nmeasurement of the two-atom decay time [G. Zuern, A. N. Wenz, S. Murmann, T.\nLompe, and S. Jochim, arXiv:1307.5153].",
        "positive": "Turbulent cascade induced persistent current of cold atomic superfluids: Dissipating of disorder quantum vortices in an annular two-dimensional\nBose-Einstein condensate can form a macroscopic persistent flow of atoms. We\npropose a protocol to create persistent flow with high winding number based on\na double concentric ring-shaped configuration. We find that a sudden geometric\nquench of the trap from single ring-shape into double concentric ring-shape\nwill enhance the circulation flow in the outer ring-shaped region of the trap\nwhen the initial state of the condensate is with randomly distributed vortices\nof the same charge. The circulation flows that we created are with high\nstability and good uniformity free from topological excitations. Our study is\npromising for new atomtronic designing, and is also helpful for quantitatively\nunderstanding quantum tunneling and interacting quantum systems driven far from\nequilibrium."
    },
    {
        "anchor": "Phase diagram of spin 1 antiferromagnetic Bose-Einstein condensates: We study experimentally the equilibrium phase diagram of a spin 1\nBose-Einstein condensate with antiferromagnetic interactions, in a regime where\nspin and spatial degrees of freedom are decoupled. For a given total\nmagnetization mz, we observe for low magnetic fields an \"antiferromagnetic\"\nphase where atoms condense in the m=+/-1 Zeeman states, and occupation of the\nm=0 state is suppressed. Conversely, for large enough magnetic fields, a phase\ntransition to a \"broken axisymmetry\" phase takes place: The m=0 component\nbecomes populated and rises sharply above a critical field Bc(mz). This\nbehavior results from the competition between antiferromagnetic spin-dependent\ninteractions (dominant at low fields) and the quadratic Zeeman energy (dominant\nat large fields). We compare the measured Bc as well as the global shape of the\nphase diagram with mean-field theory, and find good quantitative agreement.",
        "positive": "Atoms in a spin-dependent optical lattice potential as a topological\n  insulator with broken time-reversal symmetry: We investigate fermionic $^{6}$Li $F= 1/2$ atoms in a 2D spin-dependent\noptical lattice potential (SDOLP) generated by intersecting laser beams with a\nsuperposition of polarizations. The effective interaction of a Li atom with the\nelectromagnetic field contains a scalar and vector (called as fictitious\nmagnetic field, ${\\bf B}_\\mathrm{fic}$) contribution. We calculate the band\nstructure of Li atoms in the SDOLP as a function of the laser intensity and an\nexternal magnetic field ${\\bf B}_{\\mathrm{ext}} = B_{\\mathrm{ext}} {\\hat {\\bf\nz}}$. We also calculate the Chern numbers of the SDOLP and show that depending\non $B_{\\mathrm{ext}}$, the system is an ordinary insulator, an Abeliean\ntopological insulator (TI), or a non-Abelian TI. Introducing a blue-detuned\nlaser potential, $V_{\\mathrm{BD}}(y) = V_{\\mathrm{BD},0}(y) \\Theta (|y| -\nL_y/2)$, results in edges for the SDOL. We calculate the resulting edge states\n(some of which are topological) and study their density, current density,\nspin-current density and correlate the edge states with the Chern numbers."
    },
    {
        "anchor": "Loading a quantum gas from an hybrid dimple trap to a shell trap: Starting from a degenerate Bose gas in an hybrid trap combining a magnetic\nquadrupole trap and an attractive optical trap resulting from a focused laser\nbeam, we demonstrate the efficient loading of this quantum gas into a\nshell-shaped trap. The shell trap is purely magnetic and relies on adiabatic\npotentials for atoms in an inhomogeneous magnetic field dressed by a\nradiofrequency (rf) field. We show that direct rf evaporation in the hybrid\ntrap enables an efficient and simple preparation of the cold sample, well\nadapted to the subsequent loading procedure. The transfer into the shell trap\nis adiabatic and limits the final excitation of the center-of-mass motion to\nbelow 2 micrometres.",
        "positive": "Lieb's soliton-like excitations in harmonic trap: We study the solitonic Lieb II branch of excitations in one-dimensional\nBose-gas in homogeneous and trapped geometry. Using Bethe-ansatz Lieb's\nequations we calculate the \"effective number of atoms\" and the \"effective mass\"\nof the excitation. The equations of motion of the excitation are defined by the\nratio of these quantities. The frequency of oscillations of the excitation in a\nharmonic trap is calculated. It changes continuously from its \"soliton-like\"\nvalue \\omega_h/\\sqrt{2} in the high density mean field regime to \\omega_h in\nthe low density Tonks-Girardeau regime with \\omega_h the frequency of the\nharmonic trapping. Particular attention is paid to the effective mass of a\nsoliton with velocity near the speed of sound."
    },
    {
        "anchor": "Confocal shift interferometry of coherent emission from trapped dipolar\n  excitons: We introduce a confocal shift-interferometer based on optical fibers. The\npresented spectroscopy allows measuring coherence maps of luminescent samples\nwith a high spatial resolution even at cryogenic temperatures. We apply the\nspectroscopy onto electrostatically trapped, dipolar excitons in a\nsemiconductor double quantum well. We find that the measured spatial coherence\nlength of the excitonic emission coincides with the point spread function of\nthe confocal setup. The results are consistent with a temporal coherence of the\nexcitonic emission down to temperatures of 250 mK.",
        "positive": "Nonlinear Bloch-Zener oscillations for Bose-Einstein condensates in a\n  Lieb optical lattice: We investigate Bloch-Zener oscillations and mean-field Bloch bands of a\nBose-Einstein condensate (BEC) in a Lieb optical lattice. We find that the\natomic interaction will break the point group symmetry of the system, leading\nto the destruction of the Dirac cone structure, while the flat band is\npreserved on the highly symmetric lines. Due to the nonlinear effect, a tubular\nband structure with a flat band will appear in the system. Furthermore,\ncomparing with that the tight-binding (TB) model fails to describe the\ninteracting bosonic systems in the honeycomb lattice, we show that the TB model\nis applicable to study the nonlinear energy band structures for the Lieb\nlattice. In addition, we show that the loop structure can be determined by the\nobservation of the chaos of the state in the Bloch-Zener oscillations."
    },
    {
        "anchor": "Some applications of the Faddeev-Yakubovsky equations to the cold-atom\n  physics: We present some recent applications of the Faddeev--Yakubovsky equations in\ndescribing atomic bound and scattering problems. We consider the scattering of\na charged particle $X$ by atomic hydrogen with special interest in\n$X=p,e^{\\pm}$, systems of cold bosonic molecules and the bound and scattering\nproperties of N=3 and N=4 atomic $^4$He multimers.",
        "positive": "Effect of one-, two-, and three-body atom loss processes on\n  superpositions of phase states in Bose-Josephson junctions: In a two-mode Bose-Josephson junction formed by a binary mixture of ultracold\natoms, macroscopic superpositions of phase states are produced during the time\nevolution after a sudden quench to zero of the coupling amplitude. Using\nquantum trajectories and an exact diagonalization of the master equation, we\nstudy the effect of one-, two-, and three-body atom losses on the\nsuperpositions by analyzing separately the amount of quantum correlations in\neach subspace with fixed atom number. The quantum correlations useful for atom\ninterferometry are estimated using the quantum Fisher information. We identify\nthe choice of parameters leading to the largest Fisher information, thereby\nshowing that, for all kinds of loss processes, quantum correlations can be\npartially protected from decoherence when the losses are strongly asymmetric in\nthe two modes."
    },
    {
        "anchor": "Localization of solitons: linear response of the mean-field ground state\n  to weak external potentials: Two aspects of bright matter-wave solitons in weak external potentials are\ndiscussed. First, we briefly review recent results on the Anderson localization\nof an entire soliton in disordered potentials [Sacha et al. PRL 103, 210402\n(2009)], as a paradigmatic showcase of genuine quantum dynamics beyond simple\nperturbation theory. Second, we calculate the linear response of the mean-field\nsoliton shape to a weak, but otherwise arbitrary external potential, with a\ndetailed application to lattice potentials.",
        "positive": "From many-body oscillations to thermalization in an isolated spinor gas: The dynamics of a many-body system can take many forms, from a purely\nreversible evolution to fast thermalization. Here we show experimentally and\nnumerically that an assembly of spin 1 atoms all in the same spatial mode\nallows one to explore this wide variety of behaviors. When the system can be\ndescribed by a Bogoliubov analysis, the relevant energy spectrum is linear and\nleads to undamped oscillations of many-body observables. Outside this regime,\nthe non-linearity of the spectrum leads to irreversibity, characterized by a\nuniversal behavior. When the integrability of the Hamiltonian is broken, a\nchaotic dynamics emerges and leads to thermalization, in agreement with the\nEigenstate Thermalization Hypothesis paradigm."
    },
    {
        "anchor": "Direct observation of the Fermi surface in an ultracold atomic gas: The ideal (i.e. noninteracting), homogeneous Fermi gas, with its\ncharacteristic sharp Fermi surface in the momentum distribution, is a\nfundamental concept relevant to the behavior of many systems. With trapped\nFermi gases of ultracold atoms, one can realize and probe a nearly ideal Fermi\ngas, however these systems have a nonuniform density due to the confining\npotential. We show that the effect of the density variation, which typically\nwashes out any semblance of a Fermi surface step in the momentum distribution,\ncan be mitigated by selectively probing atoms near the center of a trapped gas.\nWith this approach, we have directly measured a Fermi surface in momentum space\nfor a nearly ideal gas, where the average density and temperature of the probed\nportion of the gas can be determined from the location and sharpness of the\nFermi surface.",
        "positive": "Interaction-induced dynamical phase locking of Bose-Einstein condensates: We show that interactions result in the emergence of a {\\it definite}\nrelative-phase between two initially incoherent Bose-Einstein condensates. The\nmany-realization interference fringe visibility is universal at\n$g_{12}^{(1)}\\sim1/3$ throughout the Josephson interaction regime, as evident\nfrom a semiclassical picture. Other types of incoherent preparation yield\nqualitatively different coherence dynamics."
    },
    {
        "anchor": "Analog spacetimes from nonrelativistic Goldstone modes in spinor\n  condensates: It is well established that linear dispersive modes in a flowing quantum\nfluid behave as though they are coupled to an Einstein-Hilbert metric and\nexhibit a host of phenomena coming from quantum field theory in curved space,\nincluding Hawking radiation. We extend this analogy to any nonrelativistic\nGoldstone mode in a flowing spinor Bose-Einstein condensate. In addition to\nshowing the linear dispersive result for all such modes, we show that the\nquadratically dispersive modes couple to a special nonrelativistic spacetime\ncalled a Newton-Cartan geometry. The kind of spacetime (Einstein-Hilbert or\nNewton-Cartan) is intimately linked to the mean-field phase of the condensate.\nTo illustrate the general result, we further provide the specific theory in the\ncontext of a pseudo-spin-1/2 condensate where we can tune between relativistic\nand nonrelativistic geometries. We uncover the fate of Hawking radiation upon\nsuch a transition: it vanishes and remains absent in the Newton-Cartan geometry\ndespite the fact that any fluid flow creates a horizon for certain wave\nnumbers. Finally, we use the coupling to different spacetimes to compute and\nrelate various energy and momentum currents in these analog systems. While this\nresult is general, present day experiments can realize these different\nspacetimes including the magnon modes for spin-1 condensates such as $^{87}$Rb,\n$^{7}$Li, $^{41}$K (Newton-Cartan), and $^{23}$Na (Einstein-Hilbert).",
        "positive": "A Full Configuration Interaction Perspective on the Homogeneous Electron\n  Gas: Highly accurate results for the homogeneous electron gas (HEG) have only been\nachieved to date within a diffusion Monte Carlo (DMC) framework. Here, we\nintroduce a newly developed stochastic technique, Full Configuration\nInteraction Quantum Monte Carlo (FCIQMC), which samples the exact wavefunction\nexpanded in plane wave Slater determinants. Despite the introduction of a basis\nset incompleteness error, we obtain a finite-basis energy which is\nsignificantly, and variationally lower than any previously published work for\nthe 54-electron HEG at $r_s$ = 0.5 a.u., in a Hilbert space of $10^{108}$\nSlater determinants. At this value of $r_s$, as well as of 1.0 a.u., we remove\nthe remaining basis set incompleteness error by extrapolation, yielding results\ncomparable or better than state-of-the-art DMC backflow energies. In doing so,\nwe demonstrate that it is possible to yield highly accurate results with the\nFCIQMC method in sizable periodic systems."
    },
    {
        "anchor": "Ground-state properties of anyons in a one-dimensional lattice: Using the Anyon-Hubbard Hamiltonian, we analyze the ground-state properties\nof anyons in a one-dimensional lattice. To this end we map the hopping dynamics\nof correlated anyons to an occupation-dependent hopping Bose-Hubbard model\nusing the fractional Jordan-Wigner transformation. In particular, we calculate\nthe quasi-momentum distribution of anyons, which interpolates between\nBose-Einstein and Fermi-Dirac statistics. Analytically, we apply a modified\nGutzwiller mean-field approach, which goes beyond a classical one by including\nthe influence of the fractional phase of anyons within the many-body\nwavefunction. Numerically, we use the density-matrix renormalization group by\nrelying on the ansatz of matrix product states. As a result it turns out that\nthe anyonic quasi-momentum distribution reveals both a peak-shift and an\nasymmetry which mainly originates from the nonlocal string property. In\naddition, we determine the corresponding quasi-momentum distribution of the\nJordan-Wigner transformed bosons, where, in contrast to the hard-core case, we\nalso observe an asymmetry for the soft-core case, which strongly depends on the\nparticle number density.",
        "positive": "Tomography of correlation functions for ultracold atoms via\n  time-of-flight images: We propose to utilize density distributions from a series of time-of-flight\nimages of an expanding cloud to reconstruct single-particle correlation\nfunctions of trapped ultra-cold atoms. In particular, we show how this\ntechnique can be used to detect off-diagonal correlations of atoms in a\nquasi-one-dimensional trap, where both real- and momentum- space correlations\nare extracted at a quantitative level. The feasibility of this method is\nanalyzed with specific examples, taking into account finite temporal and\nspatial resolutions in experiments."
    },
    {
        "anchor": "Optimal control of quantum superpositions in a bosonic Josephson\n  junction: We show how to optimally control the creation of quantum superpositions in a\nbosonic Josephson junction within the two-site Bose-Hubbard model framework.\nBoth geometric and purely numerical optimal control approaches are used, the\nformer providing a generalization of the proposal of Micheli et al [Phys. Rev.\nA 67, 013607 (2003)]. While this method is shown not to lead to significant\nimprovements in terms of time of formation and fidelity of the superposition, a\nnumerical optimal control approach appears more promising, as it allows to\ncreate an almost perfect superposition, within a time short compared to other\nexisting protocols. We analyze the robustness of the optimal solution against\natom number variations. Finally, we discuss to which extent these optimal\nsolutions could be implemented with the state of art technology.",
        "positive": "Dynamics of vortex quadrupoles in nonrotating trapped Bose-Einstein\n  condensate: Dynamics of vortex clusters is essential for understanding diverse superfluid\nphenomena. In this paper, we examine the dynamics of vortex quadrupoles in a\ntrapped two-dimensional (2D) Bose-Einstein condensate. We find that the\nmovement of these vortex-clusters fall into three distinct regimes which are\nfully described by the radial positions of the vortices in a 2D isotropic\nharmonic trap, or by the major radius (minor radius) of the elliptical\nequipotential lines decided by the vortex positions in a 2D anisotropic\nharmonic trap. In the \"recombination\" and \"exchange\" regimes the quadrupole\nstructure maintains, while the vortices annihilate each other permanently in\nthe \"annihilation\" regime. We find that the mechanism of the charge flipping in\nthe \"exchange\" regime and the disappearance of the quadrupole structure in the\n\"annihilation\" regime are both through an intermediate state where two vortex\ndipoles connected through a soliton ring. We give the parameter ranges for\nthese three regimes in coordinate space for a specific initial configuration\nand phase diagram of the vortex positions with respect to the Thomas-Fermi\nradius of the condensate. We show that the results are also applicable to\nsystems with quantum fluctuations for the short-time evolution."
    },
    {
        "anchor": "Quasiequilibrium Mixture of Itinerant and Localized Bose Atoms in\n  Optical Lattice: Conditions are studied under which there can exist a quasiequilibrium mixture\nof itinerant and localized bosonic atoms in an optical lattice, even at zero\ntemperature and at integer filling factor, when such a coexistence is\nimpossible for an equilibrium lattice. The consideration is based on a model\nhaving the structure of a two-band, or two-component, boson Hubbard\nHamiltonian. The minimal value for the ratio of on-site repulsion to tunneling\nparameter, necessary for the occurrence of such a mixture, is found.",
        "positive": "The Role of the Effective Range in Resonantly Interacting Fermi Gases:\n  How Breaking Scale Symmetry Affects the Bulk Viscosity: We investigate the role of the effective range on the bulk viscosity of $s$-\nand $p$-wave Fermi gases. At resonance, the presence of the effective range\nbreaks the scale invariance of the system, and hence results in a non-zero bulk\nviscosity. However, we show that the effective range plays a very different\nrole in the two cases. In the $s$-wave case, the role of the effective range is\nperturbative, and its contribution to the bulk viscosity vanishes in the limit\nof zero effective range. On the other hand, the effective range in $p$-wave\nFermi gases leads to a non-zero bulk viscosity, even in the zero-range limit.\nWe setup the general diagrammatic approach to compute the bulk viscosity\nspectral function that includes the effects of the effective range. We then\ncompute the analytic expressions for the spectral function in the high\ntemperature limit, at low- and high-frequencies. We also derive the sum rules\nfor the bulk viscosity spectral function for both $s$- and $p$-wave gases."
    },
    {
        "anchor": "Quantum hexatic order in two-dimensional dipolar and charged fluids: Recent advances in cold atom experimentation suggest that studies of quantum\ntwo-dimensional melting of dipolar molecules, with dipoles aligned\nperpendicular to ordering plane, may be on the horizon. An intriguing aspect of\nthis problem is that two-dimensional \\emph{classical} aligned dipoles (already\nstudied in great detail in soft matter experiments on magnetic colloids) are\nknown to melt via a two-stage process, with an intermediate hexatic phase\nseparating the usual crystal and isotropic fluid phases. We estimate here the\neffect of quantum fluctuations on this hexatic phase, for both dipolar systems\nand charged Wigner crystals. Our approximate phase diagrams rely on a pair of\nLindemann criteria, suitably adapted to deal with effects of thermal\nfluctuations in two dimensions. As part of our analysis, we determine the\nphonon spectra of quantum particles on a triangular lattice interacting with\nrepulsive $1/r^3$ and $1/r$ potentials. A large softening of the transverse and\nlongitudinal phonon frequencies, due to both lattice effects and quantum\nfluctuations, plays a significant role in our analysis. The hexatic phase is\npredicted to survive down to very low temperatures.",
        "positive": "Finite range and upper branch effects on itinerant ferromagnetism in\n  repulsive Fermi gases: Bethe-Goldstone ladder resummation approach: We investigate the ferromagnetic transition in repulsive Fermi gases at zero\ntemperature with upper branch and effective range effects. Based on a general\neffective Lagrangian that reproduces precisely the two-body $s$-wave scattering\nphase shift, we obtain a nonperturbative expression of the energy density as a\nfunction of the polarization by using the Bethe-Goldstone ladder resummation.\nFor hard sphere potential, the predicted critical gas parameter $k_{\\rm\nF}a=0.816$ and the spin susceptibility agree well with the results from\nfixed-node diffusion Monte Carlo calculations. In general, positive and\nnegative effective ranges have opposite effects on the critical gas parameter\n$k_{\\rm F}a$: While a positive effective range reduces the critical gas\nparameter, a negative effective range increases it. For attractive potential or\nFeshbach resonance model, the many-body upper branch exhibits an energy maximum\nat $k_{\\rm F}a=\\alpha$ with $\\alpha=1.34$ from the Bethe-Goldstone ladder\nresummation, which is qualitatively consistent with experimental results. The\nmany-body T-matrix has a positive-energy pole for $k_{\\rm F}a>\\alpha$ and it\nbecomes impossible to distinguish the bound state and the scattering state.\nThese positive-energy bound states become occupied and therefore the upper\nbranch reaches an energy maximum at $k_{\\rm F}a=\\alpha$. In the zero range\nlimit, there exists a narrow window ($0.86<k_{\\rm F}a<1.56$) for the\nferromagnetic phase. At sufficiently large negative effective range, the\nferromagnetic phase disappears. On the other hand, the appearance of\npositive-energy bound state resonantly enhances the two-body decay rate around\n$k_{\\rm F}a=\\alpha$ and may prevent the study of equilibrium phases and\nferromagnetism of the upper branch Fermi gas."
    },
    {
        "anchor": "Dark-dark solitons and modulational instability in miscible,\n  two-component Bose-Einstein condensates: We investigate the dynamics of two miscible superfluids experiencing fast\ncounterflow in a narrow channel. The superfluids are formed by two\ndistinguishable components of a trapped dilute-gas Bose-Einstein condensate\n(BEC). The onset of counterflow-induced modulational instability throughout the\ncloud is observed and shown to lead to the proliferation of dark-dark vector\nsolitons. These solitons, which we observe for the first time in a BEC, do not\nexist in single-component systems, exhibit intriguing beating dynamics and can\nexperience a transverse instability leading to vortex line structures.\nExperimental results and multi-dimensional numerical simulations are presented.",
        "positive": "Weak three-dimensional mediators of two-dimensional triplet pairing: Recent experiments demonstrate the ability to construct cold atom mixtures\nwith species selective optical lattices. This allows for the possibility of a\nmixed-dimension system, where one fermionic atomic species is confined to a two\ndimensional lattice, while another species is confined to a three dimensional\nlattice that contains the two-dimensional one. We show that by tuning the\ndensity of an arbitrary number of three-dimensional atomic species, we can\nengineer an arbitrary, rotationally-symmetric, density-density, effective\ninteraction for the two-dimensional particles. This possibility allows for an\neffective interaction that favours triplet pairing for two-dimensional, $SU(2)$\nsymmetric particles. Using a functional renormalization-group analysis for the\ntwo-dimensional particles, we derive and numerically confirm that the critical\ntemperature for triplet pairing depends exponentially on the effective\ninteraction strength. We then analyse how the stability of this phase is\naffected by the particle densities and the fine tuning of interaction\nparameters. We conclude by briefly discussing experimental considerations and\nthe potential to study triplet pairing physics, including Majorana fermions and\nspin textures, with cold atoms on optical lattices."
    },
    {
        "anchor": "Spin-Nematic Squeezed Vacuum in a Quantum Gas: Using squeezed states it is possible to surpass the standard quantum limit of\nmeasurement uncertainty by reducing the measurement uncertainty of one property\nat the expense of another complementary property. Squeezed states were first\ndemonstrated in optical fields and later with ensembles of pseudo spin-1/2\natoms using non-linear atom-light interactions. Recently, collisional\ninteractions in ultracold atomic gases have been used to generate a large\ndegree of quadrature spin squeezing in two-component Bose condensates. For\npseudo spin-1/2 systems, the complementary properties are the different\ncomponents of the total spin vector <S>, which fully characterize the state on\nan SU(2) Bloch sphere. Here, we measure squeezing in a spin-1 Bose condensate,\nan SU(3) system, which requires measurement of the rank-2 nematic or quadrupole\ntensor <Q_ij> as well to fully characterize the state. Following a quench\nthrough a nematic to ferromagnetic quantum phase transition, squeezing is\nobserved in the variance of the quadratures up to -8.3(-0.7 +0.6) dB\n(-10.3(-0.9 +0.7) dB corrected for detection noise) below the standard quantum\nlimit. This spin-nematic squeezing is observed for negligible occupation of the\nsqueezed modes and is analogous to optical two-mode vacuum squeezing. This work\nhas potential applications to continuous variable quantum information and\nquantum-enhanced magnetometry.",
        "positive": "Reactive collisions in confined geometries: We consider low energy threshold reactive collisions of particles interacting\nvia a van der Waals potential at long range in the presence of external\nconfinement and give analytic formulas for the confinement modified scattering\nin such circumstances. The reaction process is described in terms of the short\nrange reaction probability. Quantum defect theory is used to express elastic\nand inelastic or reaction collision rates analytically in terms of two\ndimensionless parameters representing phase and reactivity. We discuss the\nmodifications to Wigner threshold laws for quasi-one-dimensional and\nquasi-two-dimensional geometries. Confinement-induced resonances are suppressed\ndue to reactions and are completely absent in the universal limit where the\nshort-range loss probability approaches unity."
    },
    {
        "anchor": "Probing site-resolved correlations in a spin system of ultracold\n  molecules: Synthetic quantum systems with interacting constituents play an important\nrole in quantum information processing and in elucidating fundamental phenomena\nin many-body physics. Following impressive advances in cooling and trapping\ntechniques, ensembles of ultracold polar molecules have emerged as a promising\nsynthetic system that combines several advantageous properties. These include a\nlarge set of internal states for encoding quantum information, long nuclear and\nrotational coherence times and long-range, anisotropic interactions. The latter\nare expected to allow the exploration of intriguing phases of correlated\nquantum matter, such as topological superfluids, quantum spin liquids,\nfractional Chern insulators and quantum magnets. Probing correlations in these\nphases is crucial to understand their microscopic properties, necessitating the\ndevelopment of new experimental techniques. Here we use quantum gas microscopy\nto measure the site-resolved dynamics of quantum correlations in a gas of polar\nmolecules in a two-dimensional optical lattice. Using two rotational states of\nthe molecules, we realize a spin-1/2 system where the particles are coupled via\ndipolar interactions, producing a quantum spin-exchange model. Starting with\nthe synthetic spin system prepared far from equilibrium, we study the evolution\nof correlations during the thermalization process for both spatially isotropic\nand anisotropic interactions. Furthermore, we study the correlation dynamics in\na spin-anisotropic Heisenberg model engineered from the native spin-exchange\nmodel using Floquet techniques. These experiments push the frontier of probing\nand controlling interacting systems of ultracold molecules, with prospects for\nexploring new regimes of quantum matter and characterizing entangled states\nuseful for quantum computation and metrology.",
        "positive": "Strong-coupling expansion for ultracold bosons in an optical lattice at\n  finite temperatures in the presence of superfluidity: We develop a strong-coupling ($t \\ll U$) expansion technique for calculating\nthe density profile for bosonic atoms trapped in an optical lattice with an\noverall harmonic trap at finite temperature and finite on site interaction in\nthe presence of superfluid regions. Our results match well with quantum Monte\nCarlo simulations at finite temperature. We also show that the superfluid order\nparameter never vanishes in the trap due to proximity effect. Our calculations\nfor the scaled density in the vacuum to superfluid transition agree well with\nthe experimental data for appropriate temperatures. We present calculations for\nthe entropy per particle as a function of temperature which can be used to\ncalibrate the temperature in experiments. We also discuss issues connected with\nthe demonstration of universal quantum critical scaling in the experiments."
    },
    {
        "anchor": "Fluctuation theorem anomaly in a point-vortex fluid: The second law of thermodynamics posits that in closed macroscopic systems\nthe rate of entropy production must be positive. However, small systems can\nexhibit negative entropy production over short timescales, seemingly in\ncontradiction with this law. The fluctuation theorem quantitatively connects\nthese two limits, predicting that entropy producing trajectories become\nexponentially dominant as the system size and measurement time are increased.\nHere we explore the predictions of the fluctuation theorem for a fluid of\npoint-vortices, where the long-range interactions and existence of negative\nabsolute temperature states provide an intriguing test bed for the theorem. Our\nresults suggest that while the theorem broadly holds even at negative absolute\ntemperatures, the long-range interactions inherent to the vortex matter lead to\nanomalously large entropy production over short time intervals. The predictions\nof the fluctuation theorem are only fully recovered when sufficient noise is\nintroduced to the dynamics to overwhelm the vortex-vortex interactions.",
        "positive": "Kinetic theory of dark solitons with tunable friction: We study controllable friction in a system consisting of a dark soliton in a\none-dimensional Bose-Einstein condensate coupled to a non-interacting Fermi\ngas. The fermions act as impurity atoms, not part of the original condensate,\nthat scatter off of the soliton. We study semi-classical dynamics of the dark\nsoliton, a particle-like object with negative mass, and calculate its friction\ncoefficient. Surprisingly, it depends periodically on the ratio of interspecies\n(impurity-condensate) to intraspecies (condensate-condensate) interaction\nstrengths. By tuning this ratio, one can access a regime where the friction\ncoefficient vanishes. We develop a general theory of stochastic dynamics for\nnegative mass objects and find that their dynamics are drastically different\nfrom their positive mass counterparts - they do not undergo Brownian motion.\nFrom the exact phase space probability distribution function (i.e. in position\nand velocity), we find that both the trajectory and lifetime of the soliton are\naltered by friction, and the soliton can only undergo Brownian motion in the\npresence of friction and a confining potential. These results agree\nqualitatively with experimental observations by Aycock, et. al. (PNAS, 2017) in\na similar system with bosonic impurity scatterers."
    },
    {
        "anchor": "Bosonic Josephson effect in the Fano-Anderson model: We investigate the coherent dynamics of a non-interacting Bose-Einstein\ncondensate in a system consisting of two bosonic reservoirs coupled via a\nspatially localized mode. We describe this system by a two-terminal\nFano-Anderson model and investigate analytically the time evolution of\nobservables such as the bosonic Josephson current. In doing so, we find that\nthe Josephson current sensitively depends on the on-site energy of the\nlocalized mode. This facilitates to use this setup as a transistor for a\nBose-Einstein condensate. We identify two regimes. In one regime, the system\nexhibits well-behaved long-time dynamics with a slowly oscillating and undamped\nJosephson current. In a second regime, the Josephson current is a superposition\nof an extremely weakly damped slow oscillation and an undamped fast\noscillation. Our results are confirmed by finite-size simulations.",
        "positive": "Observation and uses of position-space Bloch oscillations in an\n  ultracold gas: We report the direct observation and characterization of position-space Bloch\noscillations using an ultracold gas in a tilted optical lattice. While Bloch\noscillations in momentum space are a common feature of optical lattice\nexperiments, the real-space center-of-mass dynamics are typically too small to\nresolve. Tuning into the regime of rapid tunneling and weak force, we observe\nreal-space Bloch oscillation amplitudes of hundreds of lattice sites, in both\nground and excited bands. We demonstrate two unique capabilities enabled by\ntracking of Bloch dynamics in position space: measurement of the full\nposition-momentum phase-space evolution during a Bloch cycle, and direct\nimaging of the lattice band structure. These techniques, along with the ability\nto exert long-distance coherent control of quantum gases without modulation,\nmay open up new possibilities for quantum control and metrology."
    },
    {
        "anchor": "Flat band effects on the ground-state BCS-BEC crossover in atomic Fermi\n  gases in a quasi-two-dimensional Lieb lattice: The ground-state superfluid behavior of ultracold atomic Fermi gases with an\non-site attractive interaction in a quasi-two-dimensional Lieb lattice is\nstudied using BCS mean-field theory, within the context of BCS-BEC crossover.\nWe find that the flat band leads to nontrivial exotic effects. As the Fermi\nlevel enters the flat band, both the pairing gap and the in-plane superfluid\ndensity exhibit an unusual power law as a function of interaction, with\nstrongly enhanced quantum geometric effects, in addition to a dramatic increase\nof compressibility as the interaction approaches the BCS limit. As the Fermi\nlevel crosses the van Hove singularities, the character of pairing changes from\nparticle-like to hole-like or vice versa. We present the computed phase\ndiagram, in which a pair density wave state emerges at high densities with\nrelatively strong interaction strength.",
        "positive": "Trap effects and continuum limit of the Hubbard model in the presence of\n  a harmonic potential: We give a prescription to perform the continuum limit of the $d$-dimensional\nHubbard model in the presence of a harmonic trap at zero temperature. We\nperform the continuum limit at fixed number of particles. In $d\\geq3$ the\nlattice system of spin-1/2 particles is mapped into a non-interacting\ntwo-component Fermi gas in a harmonic trap. In $d=1$ and $d=2$ the particles\nwith opposite spin interact via a Dirac delta interaction. We show that the\nproperties of this continuum limit can be put in correspondence with those\nderived applying the Trap-Size scaling (TSS) formalism to the confined Hubbard\nmodel in the so called Dilute Regime (fixed number of particles and weak\nconfinement). The correspondence in $d=1$ and $d=2$ has been tested comparing\nthe numerical results obtained for lattice system with those of the continuum\nlimit in the case of two-particle and in absence of spin-polarization\n($N=2$,$N_{\\uparrow}=N_{\\downarrow}=1$)."
    },
    {
        "anchor": "Modified spin-wave theory and spin liquid behavior of cold bosons on an\n  inhomogeneous triangular lattice: Ultracold bosons in a triangular lattice are a promising candidate for\nobserving quantum spin liquid behavior. Here we investigate, for such system,\nthe role of a harmonic trap giving rise to an inhomogeneous density. We\nconstruct a modified spin-wave theory for arbitrary filling, and predict the\nbreakdown of order for certain values of the lattice anisotropy. These regimes,\nidentified with the spin liquid phases, are found to be quite robust upon\nchanges in the filling factor. This result is backed by an exact\ndiagonalization study on a small lattice.",
        "positive": "Mixed state topological order parameters for symmetry protected fermion\n  matter: We construct an observable mixed state topological order parameter for\nsymmetry-protected free fermion matter. It resolves the entire table of\ntopological insulators and superconductors, relying exclusively on the symmetry\nclass, but not on unitary symmetries. It provides a robust, quantized signal\nnot only for pure ground states, but also for mixed states in- or out of\nthermal equilibrium. Key ingredient is a unitary probe operator, whose phase\ncan be related to spectral asymmetry, in turn revealing the topological\nproperties of the underlying state. This is demonstrated analytically in the\ncontinuum limit, and validated numerically on the lattice. The order parameter\nis experimentally accessible via either interferometry or full counting\nstatistics, for example, in cold atom experiments."
    },
    {
        "anchor": "Structure and stability of quasi-two-dimensional boson-fermion mixtures\n  with vortex-antivortex superposed states: We investigate the equilibrium properties of a quasi-two-dimensional\ndegenerate boson-fermion mixture (DBFM) with a bosonic vortex-antivortex\nsuperposed state (VAVSS) using a quantum-hydrodynamic model. We show that,\ndepending on the choice of parameters, the DBFM with a VAVSS can exhibit rich\nphase structures. For repulsive boson-fermion (BF) interaction, the\nBose-Einstein condensate (BEC) may constitute a petal-shaped \"core\" inside the\nhoneycomb-like fermionic component, or a ring-shaped joint \"shell\" around the\nonion-like fermionic cloud, or multiple segregated \"islands\" embedded in the\ndisc-shaped Fermi gas. For attractive BF interaction just below the threshold\nfor collapse, an almost complete mixing between the bosonic and fermionic\ncomponents is formed, where the fermionic component tends to mimic a bosonic\nVAVSS. The influence of an anharmonic trap on the density distributions of the\nDBFM with a bosonic VAVSS is discussed. In addition, a stability region for\ndifferent cases of DBFM (without vortex, with a bosonic vortex, and with a\nbosonic VAVSS) with specific parameters is given.",
        "positive": "Finite temperature study of bosons in a two dimensional optical lattice: We use quantum Monte Carlo (QMC) simulations to study the combined effects of\nharmonic confinement and temperature for bosons in a two dimensional optical\nlattice. The scale invariant, finite temperature, state diagram is presented\nfor the Bose-Hubbard model in terms of experimental parameters -- the particle\nnumber, confining potential and interaction strength. To distinguish the nature\nof the spatially separated superfluid, Mott Insulator and normal Bose liquid\nphases, we examine the local density, compressibility, superfluid density and\nGreen's function. In the annular superfluid rings, as the width of the ring\ndecreases, the long range superfluid correlations start to deviate from an\nequivalent homogeneous 2D system. At zero temperature, the correlation decay is\nintermediate between 1D and 2D, while at finite temperature, the decay is\nsimilar to that in 1D at a much lower temperature. The calculations reveal\nshortcomings of the local density approximation (LDA) in describing superfluid\nproperties of trapped bosons. We also present the finite temperature phase\ndiagram for the homogeneous two dimensional Bose-Hubbard model. We compare our\nstate diagram with the results of a recent experiment at NIST on a harmonically\ntrapped 2D lattice [Phys. Rev. Lett. 105, 110401 (2010)], and identify a finite\ntemperature effect in the experiment."
    },
    {
        "anchor": "Universal dynamic structure factor of a strongly correlated Fermi gas: Universality of strongly interacting fermions is a topic of great interest in\ndiverse fields. Here we investigate theoretically the universal dynamic density\nresponse of resonantly interacting ultracold Fermi atoms in the limit of either\nhigh temperature or large frequency: (1) At high temperature, we use quantum\nvirial expansion to derive universal, non-perturbative expansion functions of\ndynamic structure factor; (2) At large momentum, we identify that the\nsecond-order expansion function gives the Wilson coefficient used in the\noperator expansion product method. The dynamic structure factor is therefore\ndetermined by its second-order expansion function with an overall normalization\nfactor given by Tan's contact parameter. We show that the spin parallel and\nantiparallel dynamic structure factors have respectively a tail of the form\n$\\sim \\pm \\omega^{-5/2}$ for $\\omega\\rightarrow\\infty$, decaying slower than\nthe total dynamic structure factor found previously ($\\sim \\omega^{-7/2}$). Our\npredictions for dynamic structure factor at high temperature or large frequency\nare testable using Bragg spectroscopy for ultracold atomic Fermi gases.",
        "positive": "Spin-orbit-coupling induced localization in the expansion of an\n  interacting Bose-Einstein condensate: By developing a hydrodynamic formalism, we investigate the expansion dynamics\nof the single-minimum phase of a binary spin-orbit coupled Bose-Einstein\ncondensate, after releasing from an external harmonic trap. We find that the\nexpansion of the condensate along the direction of the spin-orbit coupling is\ndramatically slowed down near the transition between the single-minimum phase\nand the plane-wave phase. Such a slow expansion, resembling a form of an\neffective localization, is due to the quenching of the superfluid motion which\nresults in a strong increase of the effective mass. In the single-minimum phase\nthe anisotropic expansion of the Bose gas, which is spin balanced at\nequilibrium, is accompanied by the emergence of a local spin polarization. Our\nanalytic scaling solutions emerging from hydrodynamic picture are compared with\na full numerical simulation based on the coupled Gross-Pitaevskii equations."
    },
    {
        "anchor": "Effective-range corrections to the ground-state energy of the\n  weakly-interacting Bose gas in two dimensions: Nonuniversal effects due to leading effective-range corrections are computed\nfor the ground-state energy of the weakly-coupled repulsive Bose gas in two\nspatial dimensions. Using an effective field theory of contact interactions,\nthese corrections are computed first by considering fluctuations around the\nmean-field free energy of a system of interacting bosons. This result is then\nconfirmed by an exact calculation in which the energy of a finite number of\nbosons interacting in a square with period boundary conditions is computed and\nthe thermodynamic limit is explicitly taken.",
        "positive": "Phase structure of spin-imbalanced unitary Fermi gases: We investigate the phase structure of spin-imbalanced unitary Fermi gases\nbeyond mean-field theory by means of the Functional Renormalization Group. In\nthis approach, quantum and thermal fluctuations are resolved in a systematic\nmanner. The discretization of the effective potential on a grid allows us to\naccurately account for both first- and second-order phase transitions that are\npresent on the mean-field level. We compute the full phase diagram in the plane\nof temperature and spin-imbalance and discuss the existence of other\nconjectured phases such as the Sarma phase and a precondensation region. In\naddition, we explain on a qualitative level how we expect that in-situ density\nimages are affected by our findings and which experimental signatures may\npotentially be used to probe the phase structure."
    },
    {
        "anchor": "Antiferromagnetic Spatial Ordering in a Quenched One-dimensional Spinor\n  Gas: We have experimentally observed the emergence of spontaneous\nantiferromagnetic spatial order in a sodium spinor Bose-Einstein condensate\nthat was quenched through a magnetic phase transition. For negative values of\nthe quadratic Zeeman shift, a gas initially prepared in the F = 1, mF = 0 state\ncollapsed into a dynamically evolving superposition of all 3 spin projections,\nmF = 0, +/-1. The quench gave rise to rich, nonequilibrium behavior where both\nnematic and magnetic spin waves were generated. We characterized the\nspatiotemporal evolution through two particle correlations between atoms in\neach pair of spin states. These revealed dramatic differences between the\ndynamics of the spin correlations and those of the spin populations.",
        "positive": "Evolution from few- to many-body physics in one-dimensional Fermi\n  systems: One- and two-body density matrices, and particle-partition\n  entanglement: We study the evolution from few- to many-body physics of fermionic systems in\none spatial dimension with attractive pairwise interactions. We determine the\ndetailed form of the momentum distribution, the structure of the one-body\ndensity matrix, and the pairing properties encoded in the two-body density\nmatrix. From the low- and high-momentum scaling behavior of the single-particle\nmomentum distribution we estimate the speed of sound and Tan's contact,\nrespectively. Both quantities are found to be in agreement with previous\ncalculations. Based on our calculations of the one-body density matrices, we\nalso present results for the particle-partition entanglement entropy, for which\nwe find a logarithmic dependence on the total particle number."
    },
    {
        "anchor": "Dynamic localization in optical and Zeeman lattices in the presence of\n  spin-orbit coupling: The dynamic localization of a two-level atom in a periodic potential under\nthe action of spin-orbit coupling and a weak harmonically-varying linear force\nis studied. We consider optical and Zeeman potentials that are either in-phase\nor out-of-phase in two spinor components, respectively. The expectation value\nfor the position of the atom after one oscillation period of the linear force\nis recovered in authentic resonances or in pseudo-resonances. The frequencies\nof the linear force corresponding to authentic resonances are determined by the\nband structure of the periodic potential and are affected by the spin-orbit\ncoupling. The width/dispersion of the wavepacket in authentic resonances is\nusually minimal. The frequencies corresponding to pseudo-resonances do not\ndepend on the type of potential and on the strength of the spin-orbit coupling,\nwhile the evolution of excitations at the corresponding frequencies is usually\naccompanied by significant dispersion. Pseudo-resonances are determined by the\ninitial phase of the linear force and by the quasi-momentum of the wavepacket.\nDue to the spinor nature of the system, the motion of the atom is accompanied\nby periodic, but not harmonic, spin oscillations. Under the action of\nspin-orbit coupling the oscillations of the wavepacket can be nearly completely\nsuppressed in optical lattices. Dynamic localization in Zeeman lattices is\ncharacterized by doubling of the resonant oscillation periods due to band\ncrossing at the boundary of the Brillouin zone. We also show that higher\nharmonics in the Fourier expansion of the energy band lead to effective\ndispersion, which can be strong enough to prevent dynamic localization of the\nBloch wavepacket.",
        "positive": "Fractional energy states of strongly-interacting bosons in one dimension: We study two-component bosonic systems with strong inter-species and\nvanishing intra-species interactions. A new class of exact eigenstates is found\nwith energies that are {\\it not} sums of the single-particle energies with wave\nfunctions that have the characteristic feature that they vanish over extended\nregions of coordinate space. This is demonstrated in an analytically solvable\nmodel for three equal mass particles, two of which are identical bosons, which\nis exact in the strongly-interacting limit. We numerically verify our results\nby presenting the first application of the stochastic variational method to\nthis kind of system. We also demonstrate that the limit where both inter- and\nintra-component interactions become strong must be treated with extreme care as\nthese limits do not commute. Moreover, we argue that such states are generic\nalso for general multi-component systems with more than three particles. The\nstates can be probed using the same techniques that have recently been used for\nfermionic few-body systems in quasi-1D."
    },
    {
        "anchor": "Twonniers: Interaction-induced effects on Bose-Hubbard parameters: We study the effects of the repulsive on-site interactions on the broadening\nof the localized Wannier functions used for calculating the parameters to\ndescribe ultracold atoms in optical lattices. For this, we replace the common\nsingle-particle Wannier functions, which do not contain any information about\nthe interactions, by two-particle Wannier functions (\"Twonniers\") obtained from\nan exact solution which takes the interactions into account. We then use these\ninteraction-dependent basis functions to calculate the Bose--Hubbard model\nparameters, showing that they are substantially different both at low and high\nlattice depths, from the ones calculated using single-particle Wannier\nfunctions. Our results suggest that density effects are not negligible for many\nparameter ranges and need to be taken into account in metrology experiments.",
        "positive": "Vortex Nucleation in a Bose-Einstein Condensate: From the Inside Out: We observed a new mechanism for vortex nucleation in Bose-Einstein\ncondensates (BECs) subject to synthetic magnetic fields. We made use of a\nstrong synthetic magnetic field initially localized between a pair of merging\nBECs to rapidly create vortices in the bulk of the merged condensate. Unlike\nprevious implementations and in agreement with our Gross-Pitaevskii equation\nsimulations, our dynamical process rapidly injects vortices into our system's\nbulk, and with initial number in excess of the system's equilibrium vortex\nnumber."
    },
    {
        "anchor": "Vortex lattices in binary Bose-Einstein condensates: Collective modes,\n  quantum fluctuations, and intercomponent entanglement: We study binary Bose-Einstein condensates subject to synthetic magnetic\nfields in mutually parallel or antiparallel directions. Within the mean-field\ntheory, the two types of fields have been shown to give the same vortex-lattice\nphase diagram. We develop an improved effective field theory to study\nproperties of collective modes and ground-state intercomponent entanglement.\nHere, we point out the importance of introducing renormalized coupling\nconstants for coarse-grained densities. We show that the low-energy excitation\nspectra for the two kindsof fields are related to each other by suitable\nrescaling using the renormalized constants. By calculating the entanglement\nentropy, we find that for an intercomponent repulsion (attraction), the two\ncomponents are more strongly entangled in the case of parallel (antiparallel)\nfields, in qualitative agreement with recent studies for a quantum (spin) Hall\nregime. We also find that the entanglement spectrum exhibits an anomalous\nsquare-root dispersion relation, which leads to a subleading logarithmic term\nin the entanglement entropy. All of these are confirmed by numerical\ncalculations based on the Bogoliubov theory with the lowest-Landau-level\napproximation. Finally, we investigate the effects of quantum fluctuations on\nthe phase diagrams by calculating the correction to the ground-state energy due\nto zero-point fluctuations in the Bogoliubov theory. We find that the\nboundaries between rhombic-, square-, and rectangular-lattice phases shift\nappreciably with a decrease in the filling factor.",
        "positive": "Metastable Quantum Phase Transitions in a One-Dimensional Bose Gas: This is a chapter for a book. The first paragraph of this chapter is as\nfollows: \"Ultracold quantum gases offer a wonderful playground for quantum many\nbody physics, as experimental systems are widely controllable, both statically\nand dynamically. One such system is the one-dimensional (1D) Bose gas on a\nring. In this system binary contact interactions between the constituent\nbosonic atoms, usually alkali metals, can be controlled in both sign and\nmagnitude; a recent experiment has tuned interactions over seven orders of\nmagnitude, using an atom-molecule resonance called a Feshbach resonance. Thus\none can directly realize the Lieb-Liniger Hamiltonian, from the weakly- to the\nstrongly-interacting regime. At the same time there are a number of experiments\nutilizing ring traps. The ring geometry affords us the opportunity to study\ntopological properties of this system as well; one of the main properties of a\nsuperfluid is the quantized circulation in which the average angular momentum\nper particle, L/N, is quantized under rotation. Thus we focus on a tunable 1D\nBose system for which the main control parameters are interaction and rotation.\nWe will show that there is a critical boundary in the interaction-rotation\ncontrol-parameter plane over which the topological properties of the system\nchange. This is the basis of our concept of \\textit{metastable quantum phase\ntransitions} (QPTs). Moreover, we will show that the finite domain of the ring\nis necessary for the QPT to occur at all because the zero-point kinetic\npressure can induce QPTs, i.e., the system must be finite; we thus seek to\ngeneralize the concept of QPTs to inherently finite, mesoscopic or nanoscopic\nsystems.\""
    },
    {
        "anchor": "Realization of an atomic quantum Hall system in four dimensions: Topological states of matter lie at the heart of our modern understanding of\ncondensed matter systems. In two-dimensional (2D) quantum Hall insulators, the\nnon-trivial topology, defined by the first Chern number, manifests as a\nquantized Hall conductance and protected ballistic edge modes. Besides\ntopological insulators and Weyl semi-metals experimentally realized in 3D\nmaterials, a large variety of topological systems, theoretically predicted in\ndimensions $D > 3$, remains unexplored - among them a generalization of the\nquantum Hall effect in 4D. So far, topological properties linked with the 4D\nHall effect have been revealed via geometrical charge pump experiments in 2D\nsystems. A truly 4D Hall system has also been realized using electronic\ncircuits - however, no direct evidence of topological quantization has been\nreported. Here, we engineer an atomic quantum Hall system evolving in 4D, by\ncoupling with light fields two spatial dimensions and two synthetic ones\nencoded in the electronic spin $J = 8$ of dysprosium atoms. We measure the\ncharacteristic properties of a 4D quantum Hall system, namely the quantization\nof its electromagnetic non-linear response by a second Chern number, and the\nspecial nature of its 3D hyperedge modes, which combine ballistic motion along\none orientation and insulating behaviour in the two remaining directions. We\nalso probe low-lying excitations, revealing non-planar cyclotron orbits in\ncontrast with their circular equivalents in $D\\leq3$. Our findings pave the way\nto the exploration of interacting quantum Hall systems in 4D, from the\ninvestigation of strongly-correlated liquids to the simulation of high-energy\nmodels in link with quantum gravity and Yang-Mills field theory.",
        "positive": "Fast trimers in one-dimensional extended Fermi-Hubbard model: We consider a one-dimensional two component extended Fermi-Hubbard model with\nnearest neighbor interactions and mass imbalance between the two species. We\nstudy the stability of trimers, various observables for detecting them, and\nexpansion dynamics. We generalize the definition of the trimer gap to include\nthe formation of different types of clusters originating from nearest neighbor\ninteractions. Expansion dynamics reveal rapidly propagating trimers, with\nspeeds exceeding doublon propagation in strongly interacting regime. We present\na simple model for understanding this unique feature of the movement of the\ntrimers, and we discuss the potential for experimental realization."
    },
    {
        "anchor": "Perpetual motion and driven dynamics of a mobile impurity in a quantum\n  fluid: We study the dynamics of a mobile impurity in a quantum fluid at zero\ntemperature. Two related settings are considered. In the first setting the\nimpurity is injected in the fluid with some initial velocity ${\\mathbf v}_0$,\nand we are interested in its velocity at infinite time, ${\\mathbf v}_\\infty$.\nWe derive a rigorous upper bound on $|{\\mathbf v}_0-{\\mathbf v}_\\infty|$ for\ninitial velocities smaller than the generalized critical velocity. In the limit\nof vanishing impurity-fluid coupling this bound amounts to ${\\mathbf\nv}_\\infty={\\mathbf v}_0$ which can be regarded as a rigorous proof of the\nLandau criterion of superfluidity. In the case of a finite coupling the\nvelocity of the impurity can drop, but not to zero; the bound quantifies the\nmaximal possible drop. In the second setting a small constant force is exerted\nupon the impurity. We argue that two distinct dynamical regimes exist --\nbackscattering oscillations of the impurity velocity and saturation of the\nvelocity without oscillations. For fluids with $v_{c {\\rm L}}=v_s$ (where $v_{c\n{\\rm L}}$ and $v_s$ are the Landau critical velocity and sound velocity,\nrespectively) the latter regime is realized. For fluids with $v_{c {\\rm L}} <\nv_s$ both regimes are possible. Which regime is realized in this case depends\non the mass of the impurity, a nonequilibrium quantum phase transition\noccurring at some critical mass. Our results are equally valid in one, two and\nthree dimensions.",
        "positive": "Quantum magnetism of bosons with synthetic gauge fields in\n  one-dimensional optical lattices: a Density Matrix Renormalization Group\n  study: In this paper, we provide a comprehensive study of the quantum magnetism in\nthe Mott insulating phases of the 1D Bose-Hubbard model with abelian or\nnon-abelian synthetic gauge fields, using the Density Matrix Renormalization\nGroup (DMRG) method. We focus on the interplay between the synthetic gauge\nfield and the asymmetry of the interactions, which give rise to a very general\neffective magnetic model: a XYZ model with various Dzyaloshinskii-Moriya (DM)\ninteractions. The properties of the different quantum magnetic phases and\nphases transitions of this model are investigated."
    },
    {
        "anchor": "Dynamic stabilization of a quantum many-body spin system: We demonstrate dynamic stabilization of an unstable strongly interacting\nquantum many-body system by periodic manipulation of the phase of the\ncollective states. The experiment employs a spin-1 atomic Bose condensate\ninitialized to an unstable (hyperbolic) fixed point of the spin-nematic phase\nspace, where subsequent free evolution gives rise to squeezing and quantum spin\nmixing. To stabilize the system, periodic microwave pulses are applied that\nmanipulate the spin-nematic many-body fluctuations and limit their growth. The\nrange of pulse periods and phase shifts for which the condensate can be\nstabilized is measured and the resulting stability diagram compares well with a\nlinear stability analysis of the problem.",
        "positive": "Chaotic delocalization of two interacting particles in the classical\n  Harper model: We study the problem of two interacting particles in the classical Harper\nmodel in the regime when one-particle motion is absolutely bounded inside one\ncell of periodic potential. The interaction between particles breaks\nintegrability of classical motion leading to emergence of Hamiltonian dynamical\nchaos. At moderate interactions and certain energies above the mobility edge\nthis chaos leads to a chaotic propulsion of two particles with their diffusive\nspreading over the whole space both in one and two dimensions. At the same time\nthe distance between particles remains bounded by one or two periodic cells\ndemonstrating appearance of new composite quasi-particles called chaons. The\neffect of chaotic delocalization of chaons is shown to be rather general being\npresent for Coulomb and short range interactions. It is argued that such\ndelocalized chaons can be observed in experiments with cold atoms and ions in\noptical lattices."
    },
    {
        "anchor": "Stability of the Fulde-Ferrell-Larkin-Ovchinnikov states in anisotropic\n  systems and critical behavior at thermal $m$-axial Lifshitz points: We revisit the question concerning stability of nonuniform superfluid states\nof the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) type to thermal and quantum\nfluctuations. Invoking the properties of the putative phase diagram of\ntwo-component Fermi mixtures, on general grounds we argue, that for isotropic,\ncontinuum systems the phase diagram hosting a long-range-ordered FFLO-type\nphase envisaged by the mean-field theory cannot be stable to fluctuations at\nany temperature $T>0$ in any dimensionality $d<4$. In contrast, in layered\nunidirectional systems the lower critical dimension for the onset of FFLO-type\nlong-range order accompanied by a Lifshitz point at $T>0$ is $d=5/2$. In\nconsequence, its occurrence is excluded in $d=2$, but not in $d=3$. We propose\na relatively simple method, based on nonperturbative renormalization group to\ncompute the critical exponents of the thermal $m$-axial Lifshitz point\ncontinuously varying $m$, spatial dimensionality $d$ and the number of order\nparameter components $N$. We point out the possibility of a robust, fine-tuning\nfree occurrence of a quantum Lifshitz point in the phase diagram of imbalanced\nFermi mixtures.",
        "positive": "Synthetic Dimensions for Cold Atoms from Shaking a Harmonic Trap: We introduce a simple scheme to implement synthetic dimensions in ultracold\natomic gases, which only requires two basic and ubiquitous ingredients: the\nharmonic trap, which confines the atoms, combined with a periodic shaking. In\nour approach, standard harmonic oscillator eigenstates are reinterpreted as\nlattice sites along a synthetic dimension, while the coupling between these\nlattice sites is controlled by the applied time-modulation. The phase of this\nmodulation enters as a complex hopping phase, leading straightforwardly to an\nartificial magnetic field upon adding a second dimension. We show that this\nartificial gauge field has important consequences, such as the counterintuitive\nreduction of average energy under resonant driving, or the realisation of\nquantum Hall physics. Our approach offers significant advantages over previous\nimplementations of synthetic dimensions, providing an intriguing route towards\nhigher-dimensional topological physics and strongly-correlated states."
    },
    {
        "anchor": "Resonant control of cold-atom transport through two optical lattices\n  with a constant relative speed: We show theoretically that the dynamics of cold atoms in the lowest energy\nband of a stationary optical lattice can be transformed and controlled by a\nsecond, weaker, periodic potential moving at a constant speed along the axis of\nthe stationary lattice. The atom trajectories exhibit complex behavior, which\ndepends sensitively on the amplitude and speed of the propagating lattice. When\nthe speed and amplitude of the moving potential are low, the atoms are dragged\nthrough the static lattice and perform drifting orbits with frequencies an\norder of magnitude higher than that corresponding to the moving potential.\nIncreasing either the speed or amplitude of the moving lattice induces\nBloch-like oscillations within the energy band of the static lattice, which\nexhibit complex resonances at critical values of the system parameters. In some\ncases, a very small change in these parameters can reverse the atom's direction\nof motion. In order to understand these dynamics we present an analytical\nmodel, which describes the key features of the atom transport and also\naccurately predicts the positions of the resonant features in the atom's phase\nspace. The abrupt controllable transitions between dynamical regimes, and the\nassociated set of resonances, provide a mechanism for transporting atoms\nbetween precise locations in a lattice: as required for using cold atoms to\nsimulate condensed matter or as a stepping stone to quantum information\nprocessing. The system also provides a direct quantum simulator of acoustic\nwaves propagating through semiconductor nanostructures in sound analogs of the\noptical laser (SASER).",
        "positive": "Critical properties of weakly interacting Bose gases as modified by a\n  harmonic confinement: The critical properties of the phase transition from a normal gas to a BEC\n(superfluid) of a harmonically confined Bose gas are addressed with the\nknowledge of an equation of state of the underlying homogeneous Bose fluid. It\nis shown that while the presence of the confinement trap arrests the usual\ndivergences of the isothermal compressibility and heat capacities, the critical\nbehavior manifests itself now in the divergence of derivatives of the mentioned\nsusceptibilities. This result is illustrated with a mean-field like model of an\nequation of state for the homogeneous particle density as a function of the\nchemical potential and temperature of the gas. The model assumes the form of an\nideal Bose gas in the normal fluid while in the superfluid state a function is\nproposed such that, both, asymptotically reaches the Thomas-Fermi solution of a\nweakly interacting Bose gas at large densities and low temperatures and, at the\ntransition, matches the critical properties of the ideal Bose gas. With this\nmodel we obtain the {\\it global} thermodynamics of the harmonically confined\ngas, from which we analyze its critical properties. We discuss how these\nproperties can be experimentally tested."
    },
    {
        "anchor": "Modified Fermi-sphere, pairing gap and critical temperature for the\n  BCS-BEC crossover: We investigate the phase diagram of two-component fermions in the BCS-BEC\ncrossover. Using functional renormalization group equations we calculate the\neffect of quantum fluctuations on the fermionic self-energy parametrized by a\nwavefunction renormalization, an effective Fermi radius and the gap. This\nallows us to follow the modifications of the Fermi surface and the dispersion\nrelation for fermionic excitations throughout the whole crossover region. We\nalso determine the critical temperature of the second order phase transition to\nsuperfluidity. Our results are in agreement with BCS theory including Gorkov's\ncorrection for small negative scattering length a and with an interacting Bose\ngas for small positive a. At the unitarity point the result for the gap at zero\ntemperature agrees well with Quantum-Monte-Carlo simulations while the critical\ntemperature differs.",
        "positive": "Weakly Bound Cluster States of Efimov Character: We study the behavior of weakly bound clusters and their relation to the\nwell-known three-body Efimov states. We adopt a model to describe universal\nbehavior of strongly interacting bosonic systems, and we test its validity by\nreproducing predictions of three- and four-body universal states. Then, we\nextend our study to larger systems and identify a series of universal cluster\nstates that can be qualitatively interpreted as adding one particle at a time\nto an Efimov trimer. The properties of these cluster states and their\nexperimental signatures are discussed."
    },
    {
        "anchor": "Third- and fourth-order virial coefficients of harmonically trapped\n  fermions in a semiclassical approximation: Using a leading-order semiclassical approximation, we calculate the third-\nand fourth-order virial coefficients of nonrelativistic spin-1/2 fermions in a\nharmonic trapping potential in arbitrary spatial dimensions, and as functions\nof temperature, trapping frequency and coupling strength. Our simple, analytic\nresults for the interaction-induced changes $\\Delta b_3$ and $\\Delta b_4$ agree\nqualitatively, and in some regimes quantitatively, with previous numerical\ncalculations for the unitary limit of three-dimensional Fermi gases.",
        "positive": "Quantum gas of polar molecules ensembles at ultralow temperatures:\n  f-wave superfluids: We investigate novel f-wave superfluids of fermionic polar molecules in a\ntwo-dimensional bilayer system with dipole moments polarized perpendicular to\nthe layers and in opposite directions in different layers. The solution of the\nBCS gap equation reveals that these unconventional superfluids emerge at\ntemperatures on the level of femtokelvin which opens up new possibilities to\nexplore the topological f+i f phase, quantum interferometry and Majorana\nfermions in experiments with ultracold polar molecules. The experimental\nrealization of such interesting novel f-wave pairings is discussed."
    },
    {
        "anchor": "Borromean droplet in three-component ultracold Bose gases: Borromean ring refers to a peculiar structure where three rings are linked\ntogether while any two of them are unlinked. Here we propose the realization of\nits quantum mechanical analog in a many-body system of three-component\nultracold bosons. Namely, we identify the {\\it Borromean droplet}, where only\nthe ternary bosons can form a self-bound droplet while any binary subsystems\ncannot. Its formation is facilitated by an additional attractive force induced\nby the density fluctuation of a third component, which enlarges the mean-field\ncollapse region in comparison to the binary case and renders the formation of\nBorromean droplet after incorporating the repulsive force from quantum\nfluctuations. Outside the Borromean regime, the competition between ternary and\nbinary droplets leads to an interesting phenomenon of droplet phase separation,\nmanifested by double plateaus in the density profile. We further show that the\ntransition between different droplets and gas phase can be conveniently tuned\nby boson numbers and interaction strengths. The study reveals the possibility\nof Borromean binding in the many-body world and sheds light on more intriguing\nmany-body bound state formed in multi-component systems.",
        "positive": "Cooling Atomic Gases With Disorder: Cold atomic gases have proven capable of emulating a number of fundamental\ncondensed matter phenomena including Bose-Einstein condensation, the Mott\ntransition, Fulde-Ferrell-Larkin-Ovchinnikov pairing and the quantum Hall\neffect. Cooling to a low enough temperature to explore magnetism and exotic\nsuperconductivity in lattices of fermionic atoms remains a challenge. We\npropose a method to produce a low temperature gas by preparing it in a\ndisordered potential and following a constant entropy trajectory to deliver the\ngas into a non-disordered state which exhibits these incompletely understood\nphases. We show, using quantum Monte Carlo simulations, that we can approach\nthe Ne\\'el temperature of the three-dimensional Hubbard model for\nexperimentally achievable parameters. Recent experimental estimates suggest the\nrandomness required lies in a regime where atom transport and equilibration are\nstill robust."
    },
    {
        "anchor": "Observations of $\u03bb/4$ structure in a low-loss\n  radiofrequency-dressed optical lattice: We load a Bose-Einstein condensate into a one-dimensional (1D) optical\nlattice altered through the use of radiofrequency (rf) dressing. The rf\nresonantly couples the three levels of the $^{87}$Rb $F=1$ manifold and\ncombines with a spin-dependent \"bare\" optical lattice to result in adiabatic\npotentials of variable shape, depth, and spatial frequency content. We choose\ndressing parameters such that the altered lattice is stable over lifetimes\nexceeding tens of ms at higher depths than in previous work. We observe\nsignificant differences between the BEC momentum distributions of the dressed\nlattice as compared to the bare lattice, and find general agreement with a 1D\nband structure calculation informed by the dressing parameters. Previous work\nusing such lattices was limited by very shallow dressed lattices and strong\nLandau-Zener tunnelling loss between adiabatic potentials, equivalent to\nfailure of the adiabatic criterion. In this work we operate with significantly\nstronger rf coupling (increasing the avoided-crossing gap between adiabatic\npotentials), observing dressed lifetimes of interest for optical lattice-based\nanalogue solid-state physics.",
        "positive": "Quantum Monte Carlo simulations of thermodynamic properties of\n  attractive SU($3$) Dirac fermions: We employ the determinant quantum Monte Carlo method to study the\nfinite-temperature properties of the half-filled attractive SU($3$) Hubbard\nmodel on a honeycomb lattice. We calculate the phase diagram in which the phase\nboundary separates the disordered phase and the charge-density-wave (CDW) phase\nand the transition temperature $T_{\\text{tr}}(|U|)$ varies non-monotonically\nwith attractive Hubbard interaction $|U|$. As the Hubbard $|U|$ increases at\nconstant temperature $T<\\text{max}(T_{\\text{tr}}(|U|))$, the system first\nundergoes a transition from thermal Dirac semimetal phase to CDW phase, and\neventually the CDW state is thermally melted at a strong Hubbard $|U|$ where\nthe system enters a trion liquid phase. In between the two transition points\nthe non-monotonic $|U|$ dependence of CDW order strength is strikingly\ndifferent from the zero-temperature monotonic behavior. In the trion CDW state\nwhere off-site trions arise from quantum fluctuations (a fermion inside an\non-site trion hops to a nearest-neighbor site), the simulated triple occupancy\nat constant Hubbard $|U|$ surprisingly increases with temperature, implying\nthat the formation of off-site trions is suppressed by the thermal\ndelocalization of on-site trions. We have also calculated the\nentropy-temperature relations for various attractive Hubbrad interactions,\nwhich exhibit the prominent characteristic of the Pomeranchuk effect. Our work\nhas revealed that the formation of on-site and off-site trions has significant\nconsequences for thermodynamic properties of SU(3) Dirac fermions."
    },
    {
        "anchor": "Unique signatures for Bose-Einstein condensation in the decay\n  luminescence lineshape of weakly interacting excitons in a potential trap: We calculate the spatially resolved optical emission spectrum of a weakly\ninteracting Bose gas of excitons confined in a three dimensional potential trap\ndue to interband transitions involving weak direct and phonon mediated\nexciton-photon interactions. Applying the local density approximation, we show\nthat for a non-condensed system the spatio-spectral lineshape of the direct\nprocess reflects directly the shape of the potential. The existence of a\nBose-Einstein condensate changes the spectrum in a characteristic way so that\nit directly reflects the constant chemical potential of the excitons and the\nrenormalization of the quasiparticle excitation spectrum. Typical examples are\ngiven for parameters of the lowest yellow excitons in cuprous oxide.",
        "positive": "Effective dipole-dipole interactions in multilayered dipolar\n  Bose-Einstein condensates: We propose a two-dimensional model for a multilayer stack of dipolar\nBose-Einstein condensates formed by a strong optical lattice. We derive\neffective intra- and interlayer dipole-dipole interaction potentials and\nprovide simple analytical approximations for a given number of lattice sites at\narbitrary polarization. We find that the interlayer dipole-dipole interaction\nchanges the transverse aspect ratio of the ground state in the central layers\ndepending on its polarization and the number of lattice sites. The changing\naspect ratio should be observable in time of flight images. Furthermore, we\nshow that the interlayer dipole-dipole interaction reduces the excitation\nenergy of local perturbations, affecting the development of a roton minimum."
    },
    {
        "anchor": "Polarized entangled Bose-Einstein condensation: We consider a mixture of two distinct species of atoms of pseudospin-1/2 with\nboth intraspecies and Interspecies spin-exchange interactions, and find all the\nground stats in a general case of the parameters in the effective Hamiltonian.\nIn general, corresponding to the two species and two pseudo-spin states, there\nare four orbital wave functions into which the atoms condense. We find that in\ncertain parameter regimes, the ground state is the so-called polarized\nentangled Bose-Einstein condensation, i.e. in addition to condensation of\ninterspecies singlet pairs, there are unpaired atoms with spins polarized in\nthe same direction. The interspecies entanglement and polarization\nsignificantly affect the generalized Gross-Pitaevskii equations governing the\nfour orbital wave functions into which the atoms condense, as an interesting\ninterplay between spin and orbital degrees of freedom.",
        "positive": "Quantum dark solitons in Bose gas confined in a hard wall box: Schr\\\"odinger equation for Bose gas with repulsive contact interactions in\none-dimensional space may be solved analytically with the help of the Bethe\nansatz if we impose periodic boundary conditions. It was shown that in such a\nsystem there exist many-body eigenstates directly corresponding to dark soliton\nsolutions of the mean-field equation. The system is still integrable if one\nswitches from the periodic boundary conditions to an infinite square well\npotential. The corresponding eigenstates were constructed by M. Gaudin. We\nanalyze weak interaction limit of Gaudin's solutions and identify\nparametrization of eigenstates strictly connected with single and multiple dark\nsolitons. Numerical simulations of detection of particle's positions reveal\ndark solitons in the weak interaction regime and their quantum nature in the\npresence of strong interactions."
    },
    {
        "anchor": "Effective time-reversal via periodic shaking: For a periodically shaken optical lattice, effective time-reversal is\ninvestigated numerically. For interacting ultra-cold atoms, the scheme of [J.\nPhys. B 45, 021002 (2012)] involves a quasi-instantaneous change of both the\nshaking-amplitude and the sign of the interaction. As the wave function returns\nto its initial state with high probability, time-reversal is ideal to\ndistinguish pure quantum dynamics from the dynamics described by statistical\nmixtures.",
        "positive": "Spin susceptibility and effects of inhomogeneous strong pairing\n  fluctuations in a trapped ultracold Fermi gas: We theoretically investigate magnetic properties of a unitary Fermi gas in a\nharmonic trap. Including strong pairing fluctuations within the framework of an\nextended $T$-matrix approximation (ETMA), as well as effects of a trap\npotential within the local density approximation (LDA), we calculate the local\nspin susceptibility $\\chi(T,r)$ above the superfluid phase transition\ntemperature $T_{\\rm c}$. We show that the formation of preformed singlet Cooper\npairs anomalously suppresses $\\chi(T,r)$ in the trap center near $T_{\\rm c}$.\nWe also point out that, in the unitarity limit, the spin-gap temperature in a\nuniform Fermi gas can be evaluated from the observation of the spatial\nvariation of $\\chi(T,r)$. Since a real ultracold Fermi gas is always in a trap\npotential, our results would be useful for the study of how this spatial\ninhomogeneity affects thermodynamic properties of an ultracold Fermi gas in the\nBCS-BEC crossover region."
    },
    {
        "anchor": "Giant spin Meissner effect in a non-equilibrium exciton-polariton gas: The suppression of Zeeman energy splitting due to spin-dependent interactions\nwithin a Bose-Einstein condensate (the spin Meissner effect) was predicted to\noccur up to a certain value of magnetic field strength. We report a clear\nobservation of this effect in semimagnetic microcavities which exhibit the\ngiant Zeeman energy splitting between two spin-polarised polariton states as\nhigh as 2 meV, and demonstrate that partial suppression of energy difference\noccurs already in the uncondensed phase in a striking similarity to the\nup-critical superconductors in the fluctuation dominated regime. These\nobservations are explained quantitatively by a kinetic model accounting for\nboth the condensed and uncondensed polaritons and taking into account the\nnon-equilibrium character of the system.",
        "positive": "Fluctuation indices for atomic systems with Bose-Einstein condensate: The notion of fluctuation indices, characterizing thermodynamic stability of\nstatistical systems, is advanced. These indices are especially useful for\ninvestigating the stability of nonuniform and trapped atomic assemblies. The\nfluctuation indices are calculated for several systems with Bose-Einstein\ncondensate. It is shown that: the ideal uniform Bose-condensed gas is\nthermodynamically unstable; trapped ideal gases are stable for the confining\ndimension larger than two; trapped gases, under the confining dimension two,\nare weakly unstable; harmonically trapped gas is stable only for the spatial\ndimension three; one-dimensional harmonically trapped gas is unstable;\ntwo-dimensional gas in a harmonic trap represents a marginal case, being weakly\nunstable; interacting nonuniform three-dimensional Bose-condensed gas is\nstable. There are no thermodynamically anomalous particle fluctuations in\nstable Bose-condensed systems."
    },
    {
        "anchor": "High-Contrast Interference of Ultracold Fermions: Many-body interference between indistinguishable particles can give rise to\nstrong correlations rooted in quantum statistics. We study such Hanbury\nBrown-Twiss-type correlations for number states of ultracold massive fermions.\nUsing deterministically prepared $^6$Li atoms in optical tweezers, we measure\nmomentum correlations using a single-atom sensitive time-of-flight imaging\nscheme. The experiment combines on-demand state preparation of highly\nindistinguishable particles with high-fidelity detection, giving access to two-\nand three-body correlations in fields of fixed fermionic particle number. We\nfind that pairs of atoms interfere with a contrast close to 80%. We show that\nsecond-order density correlations arise from contributions from all\ntwo-particle pairs and detect intrinsic third-order correlations.",
        "positive": "Dissipative Preparation of Spatial Order in Rydberg-Dressed\n  Bose-Einstein Condensates: We propose a technique for engineering momentum-dependent dissipation in\nBose-Einstein condensates with non-local interactions. The scheme relies on the\nuse of momentum-dependent dark-states in close analogy to velocity-selective\ncoherent population trapping. During the short-time dissipative dynamics, the\nsystem is driven into a particular finite-momentum phonon mode, which in real\nspace corresponds to an ordered structure with non-local density-density\ncorrelations. Dissipation-induced ordering can be observed and studied in\npresent-day experiments using cold atoms with dipole-dipole or off-resonant\nRydberg interactions. Due to its dissipative nature, the ordering does not\nrequire artificial breaking of translational symmetry by an opticallattice or\nharmonic trap. This opens up a perspective of direct cooling of quantum gases\ninto strongly-interacting phases."
    },
    {
        "anchor": "Stochastic precession of the polarization in a polariton laser: Microcavity polaritons in the lasing regime undergo a spontaneous symmetry\nbreaking transition resulting in coherent emission with a well defined\npolarization. The order parameter is thus a vector describing both the laser\nglobal phase and polarization. Using an ultrafast single-shot detection\ntechnique we show that polariton lasing in GaAs-based microcavities presents a\nhigh degree of second order coherence ($g^{(2)}(\\tau=0) \\approx 1$) above\nthreshold, and that the initial polarization is stochastic, taking any possible\ndirection in the Poincar\\'e sphere (linear, elliptical or circular). Once the\npolarization direction is established, subsequent oscillations of the emission\nprobability witness the presence of an intrinsic polarization splitting. Our\nresults show the negligible role of polariton interactions in the total\nemission statistics and in the establishment of the initial polarization.",
        "positive": "Parametrically excited star-shaped patterns at the interface of binary\n  Bose-Einstein condensates: A Faraday-wave-like parametric instability is investigated via mean-field and\nFloquet analysis in immiscible binary Bose-Einstein condensates. The\ncondensates form a so-called \\textit{ball-shell} structure in a two-dimensional\nharmonic trap. To trigger the dynamics, the scattering length of the core\ncondensate is periodically modulated in time. We reveal that in the dynamics\nthe interface becomes unstable towards the formation of oscillating patterns.\nThe interface oscillates sub-harmonically exhibiting an $m$-fold rotational\nsymmetry that can be controlled by maneuvering the amplitude and the frequency\nof the modulation. Using Floquet analysis we are able to predict the generated\ninterfacial tension of the mixture and derive a dispersion relation for the\nnatural frequencies of the emergent patterns. A heteronuclear system composed\nof $^{87}$Rb-$^{85}$Rb atoms can be used for the experimental realization of\nthe phenomenon, yet our results are independent of the specifics of the\nemployed atomic species {and of the parameter at which the driving is applied."
    },
    {
        "anchor": "From Non-Hermitian Linear Response to Dynamical Correlations and\n  Fluctuation-Dissipation Relations in Quantum Many-Body Systems: Quantum many-body systems are characterized by their correlations. While\nequal-time correlators and unequal-time commutators between operators are\nstandard observables, the direct access to unequal-time anti-commutators poses\na formidable experimental challenge. Here, we propose a general technique for\nmeasuring unequal-time anti-commutators using the linear response of a system\nto a non-Hermitian perturbation. We illustrate the protocol at the example of a\nBose-Hubbard model, where the approach to thermal equilibrium in a closed\nquantum system can be tracked by measuring both sides of the\nfluctuation-dissipation relation. We relate the scheme to the quantum Zeno\neffect and weak measurements, and illustrate possible implementations at the\nexample of a cold-atom system. Our proposal provides a way of characterizing\ndynamical correlations in quantum many-body systems with potential applications\nin understanding strongly correlated matter as well as for novel quantum\ntechnologies.",
        "positive": "Transition from spin-orbit to hyperfine dominated spin relaxation in a\n  cold fluid of dipolar excitons: We measure the spin-resolved transport of dipolar excitons in a biased GaAs\ndouble quantum well structure. From these measurements we extract both spin\nlifetime and mobility of the excitons. We find that below a temperature of\n$4.8$K, there is a sharp increase in the spin lifetime of the excitons,\ntogether with a sharp reduction in their mobility. Below a critical power the\nspin lifetime increases with increasing mobility and density, while above the\ncritical power the opposite trend is observed. We interpret this transition as\nan evidence of the interplay between two different spin dephasing mechanisms:\nat low mobility the dephasing is dominated by the hyperfine interaction with\nthe lattice nuclei spins, while at higher mobility the spin-orbit interaction\ndominates, and a Dyakonov-Perel spin relaxation takes over. The excitation\npower and temperature regime where the hyperfine interaction induced spin\ndephasing is observed correlates with the regime where a dark dipolar quantum\nliquid was reported recently on a similar sample."
    },
    {
        "anchor": "Interferometric determination of the s- and d-wave scattering amplitudes\n  in $^{87}$Rb: We demonstrate an interference method to determine the low-energy elastic\nscattering amplitudes of a quantum gas. We linearly accelerate two ultracold\natomic clouds up to energies of 1.2 mK and observe the collision halo by direct\nimaging in free space. From the interference between $s$- and $d$- partial\nwaves in the differential scattering pattern we extract the corresponding phase\nshifts. The method does not require knowledge of the atomic density. This\nallows us to infer accurate values for the $s$- and d-wave scattering\namplitudes from the zero-energy limit up to the first Ramsauer minimum using\nonly the Van der Waals $C_{6}$ coefficient as theoretical input. For the\n$^{87}$Rb triplet potential, the method reproduces the scattering length with\nan accuracy of 6%.",
        "positive": "Dynamical structure factor of a fermionic supersolid on an optical\n  lattice: Interfacing unbiased quantum Monte Carlo simulations with state-of-art\nanalytic continuation techniques, we obtain exact numerical results for\ndynamical density and spin correlations in the attractive Hubbard model,\ndescribing a spin-balanced two-dimensional cold Fermi gas on an optical\nlattice. We focus on half-filling, where on average one fermion occupies each\nlattice site, and the system displays an intriguing supersolid phase: a\nsuperfluid with a checkerboard density modulation. The coexistence of $U(1)$\nbroken symmetry and the density modulations makes this regime very challenging\nand interesting for the calculation of dynamical properties. We compare our\nunbiased results with state-of-the-art Generalized Random Phase Approximation\ncalculations: both approaches agree on a well-defined low-energy\nNambu-Goldstone collective mode in the density correlations, while the higher\nenergy structures appear to differ significantly. We also observe an\ninteresting high-energy spin mode. We argue that our results provide a robust\nbenchmark for Generalized Random Phase Approximation techniques, which are\nwidely considered to be the method of choice for dynamical correlations in\nFermi gases. Also, our calculations yield new physical insight in the\nhigh-energy behavior of the dynamical structure factor of the attractive\nHubbard model, which is a well known prototype lattice model for\nsuperconductors and is a fertile field to target the observation of collective\nmodes in strongly correlated systems."
    },
    {
        "anchor": "Tan's adiabatic sweep theorem from the variational theorem for the\n  scattering length: It is shown that variation of the one-particle dispersion in a universal\nmany-body system enables us to obtain Tan's adiabatic sweep theorem and its\ngeneralization. The derivation is based on the Hellmann-Feynman theorem and the\nvariational theorem for the scattering length suggested in our previous paper\n[Cherny and Shanenko, Phys. Rev. E 62, 1646 (2000)]. As an example, the\nuniversal effects in the system of spinless bosons are considered. With the\nhelp of the variational theorem, we obtain the mean kinetic and interaction\nenergies and derive the virial theorem for the homogeneous and trapped bosons.\nThe results can easily be generalized to the two-component fermions with\ninteractions between opposite spins.",
        "positive": "Majorana fermions in one-dimensional spin-orbit coupled Fermi gases: We theoretically study trapped one-dimensional Fermi gases in the presence of\nspin-orbit coupling induced by Raman lasers. The gas changes from a\nconventional (non-topological) superfluid to a topological superfluid as one\nincreases the intensity of the Raman lasers above a critical chemical-potential\ndependent value. Solving the Bogoliubov-de Gennes equations self-consistently,\nwe calculate the density of states in real and momentum space at finite\ntemperatures. We study Majorana fermions (MFs) which appear at the boundaries\nbetween topologically trivial and topologically non-trivial regions. We\nlinearize the trap near the location of a MF, finding an analytic expression\nfor the localized MF wavefunction and the gap between the MF state and other\nedge states."
    },
    {
        "anchor": "A Quantum Gas Microscope for Fermionic Atoms: Strongly interacting fermions define the properties of complex matter at all\ndensities, from atomic nuclei to modern solid state materials and neutron\nstars. Ultracold atomic Fermi gases have emerged as a pristine platform for the\nstudy of many-fermion systems. Here we realize a quantum gas microscope for\nfermionic $^{40}$K atoms trapped in an optical lattice, which allows one to\nprobe strongly correlated fermions at the single atom level. We combine 3D\nRaman sideband cooling with high-resolution optics to simultaneously cool and\nimage individual atoms with single lattice site resolution at a detection\nfidelity above $95\\%$. The imaging process leaves each atom predominantly in\nthe 3D ground state of its lattice site, inviting the implementation of a\nMaxwell's demon to assemble low-entropy many-body states. Single site resolved\nimaging of fermions enables the direct observation of magnetic order, time\nresolved measurements of the spread of particle correlations, and the detection\nof many-fermion entanglement.",
        "positive": "Non-equilibrium Quantum Many-Body Dynamics: Functional Integral\n  Approaches: We discuss functional-integral approaches to far-from-equilibrium quantum\nmany-body dynamics. Specific techniques considered include the\ntwo-particle-irreducible effective action and the real-time flow-equation\napproach. Different applications, including equilibration after a sudden\nparameter change and non-equilibrium critical phenomena, illustrate the\npotential of these methods."
    },
    {
        "anchor": "Interorbital Interactions in an SU(2)xSU(6)-Symmetric Fermi-Fermi\n  Mixture: We characterize inter- and intraisotope interorbital interactions between\natoms in the 1S0 ground state and the 3P0 metastable state in interacting\nFermi-Fermi mixtures of 171Yb and 173Yb. We perform high-precision clock\nspectroscopy to measure interaction-induced energy shifts in a deep 3D optical\nlattice and determine the corresponding scattering lengths. We find the elastic\ninteraction of the interisotope mixtures 173Yb_e-171Yb_g and 173Yb_g-171Yb_e to\nbe weakly attractive and very similar, while the corresponding two-body loss\ncoefficients differ by more than two orders of magnitude. By comparing\ndifferent spin mixtures we experimentally demonstrate the SU(2)xSU(6) symmetry\nof all elastic and inelastic interactions. Furthermore, we measure the\nspin-exchange interaction in 171Yb and confirm its previously observed\nantiferromagnetic nature.",
        "positive": "High-fidelity contact pseudopotentials and p-wave superconductivity: We develop ultratransferable pseudopotentials for the contact interaction\nthat are 100 times more accurate than contemporary approximations. The\npseudopotential offers scattering properties very similar to the contact\npotential, has a smooth profile to accelerate numerics by a factor of up to\n4,000, and, for positive scattering lengths, does not support an unwanted bound\nstate. We demonstrate these advantages in a Diffusion Monte Carlo study of\nfermions with repulsive interactions, delivering the first numerical evidence\nfor the formation of a p-wave superconducting state."
    },
    {
        "anchor": "General relations for quantum gases in two and three dimensions. II.\n  Bosons and mixtures: We derive exact general relations between various observables for N bosons\nwith zero-range interactions, in two or three dimensions, in an arbitrary\nexternal potential. Some of our results are analogous to relations derived\npreviously for two-component fermions, and involve derivatives of the energy\nwith respect to the two-body s-wave scattering length a. Moreover, in the\nthree-dimensional case, where the Efimov effect takes place, the interactions\nare characterized not only by a, but also by a three-body parameter R\\_t. We\nthen find additional relations which involve the derivative of the energy with\nrespect R\\_t. In short, this derivative gives the probability to find three\nparticles close to each other. Although it is evaluated for a totally loss-less\nmodel, it remarkably also gives the three-body loss rate always present in\nexperiments (due to three-body recombination to deeply bound diatomic\nmolecules), at least in the limit where the so-called inelasticity parameter\neta is small enough. As an application, we obtain, within the zero-range model\nand to first order in eta, an analytic expression for the three-body loss rate\nconstant for a non-degenerate Bose gas with infinite scattering length. We also\ndiscuss the generalization to arbitrary mixtures of bosons and/or fermions.",
        "positive": "Conserving and Gapless Hartree-Fock-Bogoliubov theory for 3D dilute Bose\n  gas at finite temperature: The energy spectrum for the three dimensional Bose gas in Bose-Einstein\nCondensation phase is calculated with Modified Hartree-Fock-Bogoliubov theory,\nwhich is both conserving and gapless. From Improved $\\Phi -$% derivable theory,\nthe diagrams needed to preserve Ward-Takahashi Identity are resummed in a\nsystematic and nonperturbative way. The results show significant discrepancies\nwith Popov theory at finite temperature. It is valid up to the critical\ntemperature where the dispersion relation of the low energy excitation spectrum\nchanges from linear to quadratic. Because of the repulsive interaction, the\ncritical temperature has a positive shift from that of idea gas, which is in\naccordance with the result from the previous calculations in the uncondensed\nphase."
    },
    {
        "anchor": "Observation of the Sign Reversal of the Magnetic Correlation in a\n  Driven-Dissipative Fermi Gas in Double Wells: We report the observation of the sign reversal of the magnetic correlation\nfrom antiferromagnetic to ferromagnetic in a dissipative Fermi gas in double\nwells, utilizing the dissipation caused by on-site two-body losses in a\ncontrolled manner. We systematically measure dynamics of the nearest-neighbor\nspin correlation in an isolated double-well optical lattice, as well as a\ncrossover from an isolated double-well lattice to a one-dimensional uniform\nlattice. In a wide range of lattice configurations over an isolated double-well\nlattice, we observe a ferromagnetic spin correlation, which is consistent with\na Dicke type of correlation expected in the long-time limit. This work\ndemonstrates the control of quantum magnetism in open quantum systems with\ndissipation.",
        "positive": "Tan's universal contact and collective oscillations of strongly\n  interacting Fermi gases: We study strongly interacting two component Fermi gas near a Feshbach\nresonance. By using a ground state energy functional constructed based on\nasymptotic limits and Monte Carlo calculations, we calculate the contact,\nstructure factor, and collective oscillation frequencies in the BCS-BEC\ncrossover region. The calculated contact and structure factor show excellent\nagreements with recent experiments. We compare these results with a standard\nmean-field theory and find that the contact is proportional to the square of\nsuperfluid order parameter. Further, we present the chemical potential and the\npolytropic index in terms of homogenous energy and the contact."
    },
    {
        "anchor": "Chern numbers and chiral anomalies in Weyl butterflies: The Hofstadter butterfly of lattice electrons in a strong magnetic field is a\ncornerstone of condensed matter physics, exploring the competition between\nperiodicities imposed by the lattice and the field. In this work we introduce\nand characterize the Weyl butterfly, which emerges when a large magnetic field\nis applied to a three-dimensional Weyl semimetal. Using an experimentally\nmotivated lattice model for cold atomic systems, we solve this problem\nnumerically. We find that Weyl nodes reemerge at commensurate fluxes and\npropose using wavepackets dynamics to reveal their chirality and location.\nMoreover, we show that the chiral anomaly -- a hallmark of the topological Weyl\nsemimetal -- does not remain proportional to magnetic field at large fields,\nbut rather inherits a fractal structure of linear regimes as a function of\nexternal field. The slope of each linear regime is determined by the difference\nof two Chern numbers in gaps of the Weyl butterfly and can be measured\nexperimentally in time of flight.",
        "positive": "Experimental control of transport resonances in a coherent quantum\n  rocking ratchet: The ratchet phenomenon is a means to get directed transport without net\nforces. Originally conceived to rectify stochastic motion and describe\noperational principles of biological motors, the ratchet effect can be used to\nachieve controllable coherent quantum transport. This transport is an\ningredient of several perspective quantum devices including atomic chips. Here\nwe examine coherent transport of ultra-cold atoms in a rocking quantum ratchet.\nThis is realized by loading a rubidium atomic Bose-Einstein condensate into a\nperiodic optical potential subjected to a biharmonic temporal drive. The\nachieved long-time coherence allows us to resolve resonance enhancement of the\natom transport induced by avoided crossings in the Floquet spectrum of the\nsystem. By tuning the strength of the temporal modulations, we observe a\nbifurcation of a single resonance into a doublet. Our measurements reveal the\nrole of interactions among Floquet eigenstates for quantum ratchet transport."
    },
    {
        "anchor": "Mean-field transport of a Bose-Einstein condensate: The expansion of an initially confined Bose-Einstein condensate into either\nfree space or a tilted optical lattice is investigated in a mean-field\napproach. The effect of the interactions is to enhance or suppress the\ntransport depending on the sign and strength of the interactions. These effects\nare discusses in detail in view of recent experiments probing non-equilibrium\ntransport of ultracold quantum gases.",
        "positive": "An ultra-cold, molecular Rydberg plasma with exceptionally long lifetime\n  and strongly-coupled properties formed by threshold laser excitation in the\n  expansion region of a supersonic jet: An ultra-cold molecular plasma with extraordinarily long lifetime (~0.5 ms)\nis generated under strong collisional cooling conditions in the expansion\nregion of a seeded supersonic jet expansion close to the nozzle. A resonant\ntwo-photon one-color laser process excites para-difluorobenzene molecules into\nthe high-n Rydberg threshold region. Disorder heating during plasma formation\nis quenched by the high collision rate in the expansion, which keeps the ions\nat the translational jet temperature of 0.2K-0.7K. The Coulomb coupling\nparameter \\Gammai for the ions is expected to be ca. 230-820."
    },
    {
        "anchor": "Fractional quantum Hall phases of bosons with tunable interactions: From\n  the Laughlin liquid to a fractional Wigner crystal: Highly tunable platforms for realizing topological phases of matter are\nemerging from atomic and photonic systems, and offer the prospect of designing\ninteractions between particles. The shape of the potential, besides playing an\nimportant role in the competition between different fractional quantum Hall\nphases, can also trigger the transition to symmetry-broken phases, or even to\nphases where topological and symmetry-breaking order coexist. Here, we explore\nthe phase diagram of an interacting bosonic model in the lowest Landau level at\nhalf-filling as two-body interactions are tuned. Apart from the well-known\nLaughlin liquid, Wigner crystal phase, stripe, and bubble phases, we also find\nevidence of a phase that exhibits crystalline order at fractional filling per\ncrystal site. The Laughlin liquid transits into this phase when pairs of bosons\nstrongly repel each other at relative angular momentum $4\\hbar$. We show that\nsuch interactions can be achieved by dressing ground-state cold atoms with\nmultiple different-parity Rydberg states.",
        "positive": "Protected cat states from kinetic driving of a boson gas: We investigate the behavior of a one-dimensional Bose-Hubbard gas in both a\nring and a hard-wall box, whose kinetic energy is made to oscillate with zero\ntime-average, which suppresses first-order particle hopping. For intermediate\nand large driving amplitudes the system in the ring has similarities to the\nRichardson model, but with a peculiar type of pairing and an attractive\ninteraction in momentum space. This analogy permits an understanding of some\nkey features of the interacting boson problem. The ground state is a\nmacroscopic quantum superposition, or cat state, of two many-body states\ncollectively occupying opposite momentum eigenstates. Interactions give rise to\na reduction (or modified depletion) cloud that is common to both\nmacroscopically distinct states. Symmetry arguments permit a precise\nidentification of the two orthonormal macroscopic many-body branches which\ncombine to yield the ground state. In the ring, the system is sensitive to\nvariations of the effective flux but in such a way that the macroscopic\nsuperposition is preserved. We discuss other physical aspects that contribute\nto protect the cat-like nature of the ground state."
    },
    {
        "anchor": "Bloch oscillations in supersolids: We show that the motion of an accelerated atomic impurity immersed in a\nspin-orbit coupled Bose-Einstein condensate in the supersolid stripe phase\nundergoes oscillations, similar to the well-known phenomenon of Bloch\noscillations in solids. While the back-action of the oscillatory movement onto\nthe condensate excites phonon modes inside the supersolid, it does not affect\nthe position of the roton minimum and therefore not the periodicity of the\nmatter wave lattice. The ultimate decay of the oscillations is mostly due to\nthe dispersion of the wavepacket and we show that this can be counteracted to a\nlarge extent by assuming that the impurity is a bright soliton.",
        "positive": "Efficient all-optical production of large $^6$Li quantum gases using\n  D$_1$ gray-molasses cooling: We use a gray molasses operating on the D$_1$ atomic transition to produce\ndegenerate quantum gases of $^{6}$Li with a large number of atoms. This\nsub-Doppler cooling phase allows us to lower the initial temperature of 10$^9$\natoms from 500 to 40 $\\mu$K in 2 ms. We observe that D$_1$ cooling remains\neffective into a high-intensity infrared dipole trap where two-state mixtures\nare evaporated to reach the degenerate regime. We produce molecular\nBose-Einstein condensates of up to 5$\\times$10$^{5}$ molecules and\nweakly-interacting degenerate Fermi gases of $7\\times$10$^{5}$ atoms at\n$T/T_{F}<0.1$ with a typical experimental duty cycle of 11 seconds."
    },
    {
        "anchor": "Mott transitions in ternary flavor mixtures of ultracold fermions on\n  optical lattices: Ternary flavor mixtures of ultracold fermionic atoms in an optical lattice\nare studied in the case of equal, repulsive on-site interactions U>0. The\ncorresponding SU(3) invariant Hubbard model is solved numerically exactly\nwithin dynamical mean-field theory using multigrid Hirsch-Fye quantum Monte\nCarlo simulations. We establish Mott transitions close to integer filling at\nlow temperatures and show that the associated signatures in the compressibility\nand pair occupancy persist to high temperatures, i.e., should be accessible to\nexperiments. In addition, we present spectral functions and discuss the\nproperties of a ``semi-compressible'' state observed for large U near half\nfilling.",
        "positive": "A continuum of compass spin models on the honeycomb lattice: Quantum spin models with spatially dependent interactions, known as compass\nmodels, play an important role in the study of frustrated quantum magnetism.\nOne example is the Kitaev model on the honeycomb lattice with spin-liquid\nground states and anyonic excitations. Another example is the geometrically\nfrustrated quantum $120^\\circ$ model on the same lattice whose ground state has\nnot been unambiguously established. To generalize the Kitaev model beyond the\nexactly solvable limit and connect it with other compass models, we propose a\nnew model, dubbed \"the tripod model\", which contains a continuum of\ncompass-type models. It smoothly interpolates the Ising model, the Kitaev\nmodel, and the quantum $120^\\circ$ model by tuning a single parameter\n$\\theta'$, the angle between the three legs of a tripod in the spin space.\nHence it not only unifies three paradigmatic spin models, but also enables the\nstudy of their quantum phase transitions. We obtain the phase diagram of the\ntripod model numerically by tensor networks in the thermodynamic limit. We show\nthat the ground state of the quantum $120^\\circ$ model has long-range dimer\norder. Moreover, we find an extended spin-disordered (spin-liquid) phase\nbetween the dimer phase and an antiferromagnetic phase. The unification and\nsolution of a continuum of frustrated spin models as outline here may be useful\nto exploring new domains of other quantum spin or orbital models."
    },
    {
        "anchor": "Collective excitations of superfluid Fermi gases near the transition\n  temperature: Studying the collective pairing phenomena in a two-component Fermi gas, we\npredict the appearance near the transition temperature $T_c$ of a well-resolved\ncollective mode of quadratic dispersion. The mode is visible both above and\nbelow $T_c$ in the system's response to a driving pairing field. When\napproaching $T_c$ from below, the phononic and pair-breaking branches,\ncharacteristic of the zero temperature behavior, reduce to a very low\nenergy-momentum region when the pair correlation length reaches its critical\ndivergent behavior $\\xi_{\\rm pair}\\propto|T_c-T|^{-1/2}$; elsewhere, they are\nreplaced by the quadratically-dispersed pairing resonance, which thus acts as a\nprecursor of the phase transition. In the strong-coupling and Bose-Einstein\nCondensate regime, this mode is a weakly-damped propagating mode associated to\na Lorentzian resonance. Conversely, in the BCS limit it is a relaxation mode of\npure imaginary eigenenergy. At large momenta, the resonance disappears when it\nis reabsorbed by the lower-edge of the pairing continuum. At intermediate\ntemperatures between 0 and $T_c$, we unify the newly found collective phenomena\nnear $T_c$ with the phononic and pair-breaking branches predicted from previous\nstudies, and we exhaustively classify the roots of the analytically continued\ndispersion equation, and show that they provided a very good summary of the\npair spectral functions.",
        "positive": "Mode interference in quantum joint probabilities for multimode\n  Bose-condensed systems: The method of defining quantum joint probabilities of two events is applied\nto a multimode system of trapped Bose-condensed atoms. The coherent modes are\ngenerated by modulating the trapping potential with an alternating field with a\nfrequency in resonance with a transition frequency between two coherent modes.\nThe system is subjected to nondestructive measurements randomly influencing the\nphase difference of the modes. The joint probability of observing two events,\ncorresponding to the observation of two states, is calculated by employing the\nchannel-state duality. The interference term in the joint probability can arise\nwhen the composite events form an entangled prospect and the system state is\nalso entangled. This interference is due to the uncertainty induced by\nnondestructive measurements."
    },
    {
        "anchor": "Trap Frequency Measurement with a Pulsed Atom Laser: We describe a novel method of single-shot trap frequency measurement for a\nconfined Bose-Einstein Condensate, which uses an atom laser to repeatedly\nsample the mean velocity of trap oscillations as a function of time. The method\nis able to determine the trap frequency to an accuracy of 39~ppm (16~mHz) in a\nsingle experimental realization, improving on the literature by a factor of\nthree. Further, we show that by employing a reconstructive aliasing approach\nour method can be applied to trap frequencies more than a factor of 3 greater\nthan the sampling frequency.",
        "positive": "Hydrodynamic theory of motion of quantized vortex rings in trapped\n  superfluid gases: I study vortex ring oscillations in a superfluid, trapped in an elongated\ntrap, under the conditions of the Local Density Approximation. On the basis of\nthe Hamiltonian formalism I develop a hydrodynamic theory, which is valid for\nan arbitrary superfluid and depends only on the equation of state. The problem\nis reduced to an ordinary differential equation for the ring radius. The cases\nof the dilute BEC and the Fermi gas at unitarity are investigated in detail.\nSimple analytical equations for the periods of small oscillations are obtained\nand the equations of non-linear dynamics are solved in quadratures. The results\nagree with available numerical calculations. Experimental possibilities to\ncheck the predictions are discussed."
    },
    {
        "anchor": "Self-bound clusters of one-dimensional fermionic mixtures: Diffusion Monte Carlo calculations on the possibility of having self-bound\none-dimen\\-sional droplets of SU(6) $\\times$ SU(2) ultracold fermionic mixtures\nare presented. We found that, even though arrangements with attractive\ninteractions with only two spin types are not self-bound, mixtures with at\nleast three kinds of fermions form stable small drops. However, that\nstabilization decreases for very tight confinements, where a universal behavior\nis found for Fermi-Fermi and Fermi-Boson clusters including attractive and\nrepulsive interactions.",
        "positive": "One-Dimensional Integrable Spinor BECs Mapped to Matrix Nonlinear\n  Schr\u00f6dinger Equation and Solution of Bogoliubov Equation in These Systems: In this short note, we construct mappings from one-dimensional integrable\nspinor BECs to matrix nonlinear Schr\\\"odinger equation, and solve the\nBogoliubov equation of these systems. A map of spin-$n$ BEC is constructed from\nthe $2^n$-dimensional spinor representation of irreducible tensor operators of\n$so(2n+1)$. Solutions of Bogoliubov equation are obtained with the aid of the\ntheory of squared Jost functions."
    },
    {
        "anchor": "Quantum-granularity effect in the formation of supermixed solitons in\n  ring lattices: We investigate a notable class of states peculiar to a bosonic binary mixture\nfeaturing repulsive intraspecies and attractive interspecies couplings. We\nevidence that, for small values of the hopping amplitudes, one can access\nparticular regimes marked by the fact that the interwell boson transfer occurs\nin a jerky fashion. This property is shown to be responsible for the emergence\nof a staircase-like structure in the phase diagram of a mixture confined in a\nring trimer and to strongly resemble the mechanism of the superfluid-Mott\ninsulator transition. Under certain conditions, in fact, we show that it is\npossible to interpret the interspecies attraction as an effective chemical\npotential and the supermixed soliton as an effective particle reservoir. Our\ninvestigation is developed both within a fully quantum approach based on the\nanalysis of several quantum indicators and by means of a simple analytical\napproximation scheme capable of capturing the essential features of this\nultraquantum effect.",
        "positive": "Structural and quantum properties of van der Waals cluster near the\n  unitary regime: We study the structural and several quantum properties of three-dimensional\nbosonic cluster interacting through van der Waals potential at large scattering\nlength. We use Faddeev-type decomposition of the many-body wave function which\nincludes all possible two-body correlations. At large scattering length, we\nobserve spatially extended states which exhibit the exponential dependence on\nthe state number. The cluster ground state energy shows universal nature at\nlarge negative scattering length. We also find the existence of generalized\nTjon lines for $N$- body clusters. Signature of universal behaviour of weakly\nbound clusters can be observed in experiments of ultracold Bose gases. We also\nstudy the spectral statistics of the system. We calculate both the short-range\nfluctuation and long-range.correlation and observe semi-Poisson distribution\nwhich interpolates the Gaussian Orthogonal Ensemble (GOE) and Poisson\nstatistics of random matrix theory. It indicates that the van der Waal cluster\nnear the unitary becomes highly complex and correlated. However additional\nstudy of $P(r)$ distribution (without unfolding of energy spectrum) reveals the\npossibility of chaos for larger cluster."
    },
    {
        "anchor": "Dynamical Phase Diagram of Ultracold Josephson Junctions: We provide a complete study of the phase diagram characterising the distinct\ndynamical regimes emerging in a three-dimensional Josephson junction in an\nultracold quantum gas. Considering trapped ultracold superfluids separated into\ntwo reservoirs by a barrier of variable height and width, we analyse the\npopulation imbalance dynamics following a variable initial population mismatch.\nWe demonstrate that as the chemical potential difference is increased, the\nsystem transitions from Josephson plasma oscillations to either a dissipative\n(in the limit of low and narrow barriers) or a self-trapped regime (for large\nand wider barriers), with a crossover between the dissipative and the\nself-trapping regimes which we explore and characterize for the first time.\nThis work, which extends beyond the validity of the standard two-mode model,\nconnects the role of the barrier width, vortex rings and associated acoustic\nemission with different regimes of the superfluid dynamics across the junction,\nestablishing a framework for its experimental observation, which is found to be\nwithin current experimental reach.",
        "positive": "Semiclassical dynamics of quasi-one-dimensional, attractive\n  Bose-Einstein condensates: The strongly interacting regime for attractive Bose-Einstein condensates\n(BECs) tightly confined in an extended cylindrical trap is studied. For\nappropriately prepared, non-collapsing BECs, the ensuing dynamics are found to\nbe governed by the one-dimensional focusing Nonlinear Schr\\\"odinger equation\n(NLS) in the semiclassical (small dispersion) regime. In spite of the\nmodulational instability of this regime, some mathematically rigorous results\non the strong asymptotics of the semiclassical limiting solutions were obtained\nrecently. Using these results, \"implosion-like\" and \"explosion-like\" events are\npredicted whereby an initial hump focuses into a sharp spike which then expands\ninto rapid oscillations. Seemingly related behavior has been observed in\nthree-dimensional experiments and models, where a BEC with a sufficient number\nof atoms undergoes collapse. The dynamical regimes studied here, however, are\nnot predicted to undergo collapse. Instead, distinct, ordered structures,\nappearing after the \"implosion\", yield interesting new observables that may be\nexperimentally accessible."
    },
    {
        "anchor": "Quantum phase transition in an atom-molecule conversion system with\n  atomic hopping: The quantum phase transition in an atom-molecule conversion system with\natomic hopping between different hyperfine states is studied. In mean field\napproximation, we give the phase diagram whose phase boundary only depends on\nthe atomic hopping strength and the atom-molecule energy detuning but not on\nthe atomic interaction. Such a phase boundary is further confirmed by the\nfidelity of the ground state and the energy gap between the first-excited state\nand the ground one. In comparison to mean field approximation, we also study\nthe quantum phase transition in full quantum method, where the phase boundary\ncan be affected by the particle number of the system. Whereas, with the help of\nfinite-size scaling behaviors of energy gap, fidelity susceptibility and the\nfirst-order derivative of entanglement entropy, we show that one can obtain the\nsame phase boundary by the MFA and full quantum methods in the limit of\n$N\\rightarrow \\infty$. Additionally, our results show that the quantum phase\ntransition can happens at the critical value of the atomic hopping strength\neven if the atom-molecule energy detuning is fixed on a certain value, which\nprovides one a new way to control the quantum phase transition.",
        "positive": "Finite-range effects in the two-dimensional repulsive Fermi polaron: We study the repulsive Fermi polaron in a two-component, two-dimensional\nsystem of fermionic atoms inspired by the results of a recent experiment with\n$^{173}$Yb atoms [N. Darkwah Oppong \\textit{et al.}, Phys. Rev. Lett.\n\\textbf{122}, 193604 (2019)]. We use the diffusion Monte Carlo method to report\nproperties such as the polaron energy and the quasi-particle residue that have\nbeen measured in that experiment. To provide insight on the quasi-particle\ncharacter of the problem, we also report results for the effective mass. We\nshow that the effective range, together with the scattering length, is needed\nin order to reproduce the experimental results. Using different model\npotentials for the interaction between the Fermi sea and the impurity, we show\nthat it is possible to establish a regime of universality, in terms of these\ntwo parameters, that includes the whole experimental regime. This illustrates\nthe relevance of quantum fluctuations and beyond mean-field effects to\ncorrectly describe the Fermi polaron problem."
    },
    {
        "anchor": "Competition between pairing and ferromagnetic instabilities in ultracold\n  Fermi gases near Feshbach resonances: We study the quench dynamics of a two-component ultracold Fermi gas from the\nweak into the strong interaction regime, where the short time dynamics are\ngoverned by the exponential growth rate of unstable collective modes. We obtain\nan effective interaction that takes into account both Pauli blocking and the\nenergy dependence of the scattering amplitude near a Feshbach resonance. Using\nthis interaction we analyze the competing instabilities towards Stoner\nferromagnetism and pairing.",
        "positive": "Bosonic hard spheres in quasi-one dimensional bichromatic optical\n  lattices: We calculated the phase diagram of a continuous system of hard spheres loaded\nin a quasi-one dimensional bichromatic optical lattice. The wavelengths of both\nlattice-defining lasers were chosen to model an incommensurate arrangement.\nDensities of one particle and half a particle per potential well were\nconsidered. Our results can be compared directly to those of the experimental\nsystem [Fallani et al. PRL, {\\bf 98} 130404 (2007)] from which our initial\nparameters were taken. The phase diagrams for both densities are\nsignificatively different to those obtained by describing the same experimental\nsetup with a Bose-Hubbard model."
    },
    {
        "anchor": "Improved characterization of Feshbach resonances and interaction\n  potentials between $^{23}$Na and $^{87}$Rb atoms: The ultracold mixture of \\Na and \\Rb atoms has become an important system for\ninvestigating physics in Bose-Bose atomic mixtures and for forming ultracold\nground-state polar molecules. In this work, we provide an improved\ncharacterization of the most commonly used Feshbach resonance near 347.64 G\nbetween \\Na and \\Rb in their absolute ground states. We form Feshbach molecules\nusing this resonance and measure their binding energies by dissociating them\nvia magnetic field modulation. We use the binding energies to refine the\nsinglet and triplet potential energy curves, using coupled-channel bound-state\ncalculations. We then use coupled-channel scattering calculations on the\nresulting potentials to produce a high-precision mapping between magnetic field\nand scattering length. We also observe 10 additional $s$-wave Feshbach\nresonances for \\Na and \\Rb in different combinations of Zeeman sublevels of the\n$F = 1$ hyperfine states. Some of the resonances show 2-body inelastic decay\ndue to spin exchange. We compare the resonance properties with coupled-channel\nscattering calculations that full take account of inelastic properties.",
        "positive": "Entanglement and spin-squeezing without infinite-range interactions: Infinite-range interactions are known to facilitate the production of highly\nentangled states with applications in quantum information and metrology.\nHowever, many experimental systems have interactions that decay with distance,\nand the achievable benefits in this context are much less clear. Combining\nrecent exact solutions with a controlled expansion in the system size, we\nanalyze quench dynamics in Ising models with power-law ($1/r^{\\alpha}$)\ninteractions in $D$ dimensions, thereby expanding the understanding of spin\nsqueezing into a broad and experimentally relevant context. In spatially\nhomogeneous systems, we show that for small $\\alpha$ the scaling of squeezing\nwith system size is identical to the infinite-range ($\\alpha=0$) case. This\nindifference to the interaction range persists up to a critical value\n$\\alpha=2D/3$, above which squeezing degrades continuously. Boundary-induced\ninhomogeneities present in most experimental systems modify this picture, but\nit nevertheless remains qualitatively correct for finite-sized systems."
    },
    {
        "anchor": "Limit of Spin Squeezing in Finite Temperature Bose-Einstein Condensates: We show that, at finite temperature, the maximum spin squeezing achievable\nusing interactions in Bose-Einstein condensates has a finite limit when the\natom number $N\\to \\infty$ at fixed density and interaction strength. We\ncalculate the limit of the squeezing parameter for a spatially homogeneous\nsystem and show that it is bounded from above by the initial non-condensed\nfraction.",
        "positive": "Interaction induced ferro-electricity in the rotational states of polar\n  molecules: We show that a ferro-electric quantum phase transition can be driven by the\ndipolar interaction of polar molecules in the presence a micro-wave field. The\nobtained ferro-electricity crucially depends on the harmonic confinement\npotential, and the resulting dipole moment persists even when the external\nfield is turned off adiabatically. The transition is shown to be second order\nfor fermions and for bosons of a smaller permanent dipole moment, but is first\norder for bosons of a larger moment. Our results suggest the possibility of\nmanipulating the microscopic rotational state of polar molecules by tuning the\ntrap's aspect ratio (and other mesoscopic parameters), even though the later's\nenergy scale is smaller than the former's by six orders of magnitude."
    },
    {
        "anchor": "Strong coupling phases of the spin-orbit-coupled spin-1 Bose-Hubbard\n  chain: odd integer Mott lobes and helical magnetic phases: We study the odd integer filled Mott phases of a spin-1 Bose-Hubbard chain\nand determine their fate in the presence of a Raman induced spin-orbit coupling\nwhich has been achieved in ultracold atomic gases; this system is described by\na quantum spin-1 chain with a spiral magnetic field. The spiral magnetic field\ninitially induces helical order with either ferromagnetic or dimer order\nparameters, giving rise to a spiral paramagnet at large field. The spiral\nferromagnet-to-paramagnet phase transition is in a novel universality class,\nwith critical exponents associated with the divergence of the correlation\nlength $\\nu \\approx 2/3$ and the order parameter susceptibility $\\gamma \\approx\n1/2$. We solve the effective spin model exactly using the density matrix\nrenormalization group, and compare with both a large-$S$ classical solution and\na phenomenological Landau theory. We discuss how these exotic bosonic magnetic\nphases can be produced and probed in ultracold atomic experiments in optical\nlattices.",
        "positive": "Rapid production of $^{87}$Rb BECs in a combined magnetic and optical\n  potential: We describe an apparatus for quickly and simply producing $\\Rb87$\nBose-Einstein condensates. It is based on a magnetic quadrupole trap and a red\ndetuned optical dipole trap. We collect atoms in a magneto-optical trap (MOT)\nand then capture the atom in a magnetic quadrupole trap and force rf\nevaporation. We then transfer the resulting cold, dense cloud into a spatially\nmode-matched optical dipole trap by lowering the quadrupole field gradient to\nbelow gravity. This technique combines the efficient capture of atoms from a\nMOT into a magnetic trap with the rapid evaporation of optical dipole traps;\nthe approach is insensitive to the peak quadrupole gradient and the precise\ntrapping beam waist. Our system reliably produces a condensate with\n$N\\approx2\\times10^6$ atoms every $16\\second$."
    },
    {
        "anchor": "Composite Boson Mapping for Lattice Boson Systems: We present a canonical mapping transforming physical boson operators into\nquadratic products of cluster composite bosons that preserves matrix elements\nof operators when a physical constraint is enforced. We map the 2D lattice\nBose-Hubbard Hamiltonian into $2\\times 2$ composite bosons and solve it at mean\nfield. The resulting Mott insulator-superfluid phase diagram reproduces well\nQuantum Monte Carlo results. The Higgs boson behavior along the particle-hole\nsymmetry line is unraveled and in remarkable agreement with experiment. Results\nfor the properties of the ground and excited states are competitive with other\nstate-of-the-art approaches, but at a fraction of their computational cost. The\ncomposite boson mapping here introduced can be readily applied to frustrated\nmany-body systems where most methodologies face significant hurdles.",
        "positive": "Quantum phase transitions and quantum chaos in generalized Dicke and\n  Jahn-Teller polaron model and finite-size effects: The Dicke model extended to two bosons of different frequencies or equivalent\ngeneralized Jahn-Teller lattice model are shown to exhibit a spontaneous\nquantum phase transition between the polaron-modified \"quasi-normal\" and\nsqueezed \"radiation\" phase with the transition point dependent on the\nfrequencies. In a finite lattice a mixed domain of coexistence of the\nquasi-normal and modified radiation phase is created within the quasi-normal\nphase domain. There occurs a field-directed oscillation-assisted tunneling\n(hopping). The field is driven by simultaneous squeezing and polaron-dressing\nof the collective boson level mode due to the additional boson mode. In a\nfinite lattice in the radiation domain there occurs a sequence of local\ntunnelings (oscillations) between two minima of a local potential weakly\ncoupled to two assisting oscillations. The \"radiation\" phase reveals itself as\nan almost ideal instanton--anti-instanton gas phase. The correlations among the\nenergy levels mediated by the additional mode in the mixed domain considerably\nreduce the level repulsions. As a consequence, the Wigner level spacing\nprobability distribution of the two-boson Dicke model is non-universally\nreduced from the Wigner to the semi-Poisson and asymptotically to the Poisson\ndistribution of level spacings. The correlations cause a suppression of the\ncoherence of the radiation phase as finite-size effect. Possible applications\nof the present theory are suggested."
    },
    {
        "anchor": "Relaxation dynamics of the Lieb-Liniger gas following an interaction\n  quench: A coordinate Bethe-ansatz analysis: We investigate the relaxation dynamics of the integrable Lieb-Liniger model\nof contact-interacting bosons in one dimension following a sudden quench of the\ncollisional interaction strength. The system is initially prepared in its\nnoninteracting ground state and the interaction strength is then abruptly\nswitched to a positive value, corresponding to repulsive interactions between\nthe bosons. We calculate equal-time correlation functions of the nonequilibrium\nBose field for small systems of up to five particles via symbolic evaluation of\ncoordinate Bethe-ansatz expressions for operator matrix elements between\nLieb-Liniger eigenstates. We characterize the relaxation of the system by\ncomparing the time-evolving correlation functions following the quench to the\nequilibrium correlations predicted by the diagonal ensemble and relate the\nbehavior of these correlations to that of the quantum fidelity between the\nmany-body wave function and the initial state of the system. Our results for\nthe asymptotic scaling of local second-order correlations with increasing\ninteraction strength agree with the predictions of recent generalized\nthermodynamic Bethe-ansatz calculations. By contrast, third-order correlations\nobtained within our approach exhibit a markedly different power-law dependence\non the interaction strength as the Tonks-Girardeau limit of infinitely strong\ninteractions is approached.",
        "positive": "Counterflow of spontaneous mass currents in trapped spin-orbit coupled\n  Fermi gases: We use the Bogoliubov-de Gennes formalism and study the ground-state phases\nof trapped spin-orbit coupled Fermi gases in two dimensions. Our main finding\nis that the presence of a symmetric (Rashba type) spin-orbit coupling\nspontaneously induces counterflowing mass currents in the vicinity of the trap\nedge, i.e. $\\uparrow$ and $\\downarrow$ particles circulate in opposite\ndirections with equal speed. These currents flow even in noninteracting\nsystems, but their strength decreases toward the molecular BEC limit, which can\nbe achieved either by increasing the spin-orbit coupling or the interaction\nstrength. These currents are also quite robust against the effects of\nasymmetric spin-orbit couplings in $x$ and $y$ directions, gradually reducing\nto zero as the spin-orbit coupling becomes one dimensional. We compare our\nresults with those of chiral p-wave superfluids/superconductors."
    },
    {
        "anchor": "Resonant Hawking radiation in Bose-Einstein condensates: We study double-barrier interfaces separating regions of asymptotically\nsubsonic and supersonic flow of Bose condensed atoms. These setups contain at\nleast one black hole sonic horizon from which the analog of Hawking radiation\nshould be generated and emitted against the flow in the subsonic region.\nMultiple coherent scattering by the double-barrier structure strongly modulates\nthe transmission probability of phonons, rendering it very sensitive to their\nfrequency. As a result, resonant tunneling occurs with high probability within\na few narrow frequency intervals. This gives rise to highly non-thermal spectra\nwith sharp peaks. We find that these peaks are mostly associated to decaying\nresonances and only occasionally to dynamical instabilities. Even at achievable\nnonzero temperatures, the radiation peaks can be dominated by the spontaneous\nemission, i.e. enhanced zero-point fluctuations, and not, as often in analog\nmodels, by stimulated emission.",
        "positive": "Experimental realization of spin-tensor momentum coupling in ultracold\n  Fermi gases: We experimentally realize the spin-tensor momentum coupling (STMC) using the\nthree ground Zeeman states coupled by three Raman laser beams in ultracold\natomic system of $^{40}$K Fermi atoms. This new type of STMC consists of two\nbright-state bands as a regular spin-orbit coupled spin-1/2 system and one\ndark-state middle band. Using radio-frequency spin-injection spectroscopy, we\ninvestigate the energy band of STMC. It is demonstrated that the middle state\nis a dark state in the STMC system. The realized energy band of STMC may open\nthe door for further exploring exotic quantum matters."
    },
    {
        "anchor": "Flow-Induced Charge Modulation in Superfluid Atomic Fermions Loaded into\n  an Optical Kagome Lattice: We study the superfluid state of atomic fermions in a tunable optical kagome\nlattice motivated by recent experiments. We show that imposed superflow induces\nspatial modulations in the density and order parameter of the pair condensate\nand leads to a charge modulated superfluid state analogous to a supersolid\nstate. The spatial modulations in the superfluid emerge due to the geometric\neffect of the kagome lattice that introduces anisotropy in hopping amplitudes\nof fermion pairs in the presence of superflow. We also study superflow\ninstabilities and find that the critical current limited by the dynamical\ninstability is quite enhanced due to the large density of states associated\nwith the flatband. The charge modulated superfluid state can sustain high\ntemperatures close to the transition temperature that is also enhanced due to\nthe flatband, and is therefore realizable in experiments.",
        "positive": "Excitation spectrum of a trapped dipolar supersolid and its experimental\n  evidence: We study the spectrum of elementary excitations of a dipolar Bose gas in a\nthree-dimensional anisotropic trap across the superfluid-supersolid phase\ntransition. Theoretically, we show that, when entering the supersolid phase,\ntwo distinct excitation branches appear, respectively associated with\ndominantly crystal and superfluid excitations. These results confirm\ninfinite-system predictions, showing that finite-size effects play only a small\nqualitative role, and connect the two branches to the simultaneous occurrence\nof crystal and superfluid orders. Experimentally, we probe compressional\nexcitations in an Er quantum gas across the phase diagram. While in the\nBose-Einstein condensate regime the system exhibits an ordinary quadrupole\noscillation, in the supersolid regime we observe a striking two-frequency\nresponse of the system, related to the two spontaneously broken symmetries."
    },
    {
        "anchor": "Quantum Phases and Correlations Drive the Dynamics of Macroscopic\n  Quantum Tunneling Escape in Quantum Simulators: Quantum tunneling remains unexplored in many regimes of many-body quantum\nphysics, including the effect of quantum phase transitions on tunneling\ndynamics. In general, the quantum phase is a statement about the ground state\nand has no relation to far-from-equilibrium dynamics. Although tunneling is a\nhighly dynamical process involving many excited states, we find that the\nquantum phase of the Bose-Hubbard model determines phase-dependent tunneling\noutcomes for the quantum tunneling escape, or quasi-bound problem. Superfluid\nand Mott insulator correlations lead to a new quantum tunneling rate, the\nquantum fluctuation rate. This rate shows surprising and highly dynamical\nfeatures, such as oscillatory interference between trapped and escaped atoms\nand a completely different macroscopic quantum tunneling behavior for\nsuperfluid and Mott insulator phases. In the superfluid phase we find that\nescape dynamics are wave-like and coherent, leading to interference patterns in\nthe density with a rapid decay process which is non-exponential. Quantum\nentropy production peaks when about half the atoms have escaped. In the Mott\nphase, despite stronger repulsive interactions, tunneling is significantly\nslowed by the presence of a Mott gap, creating an effective extra barrier to\novercome. Only one atom can tunnel at a time, yet the decay process is nearly\nlinear, completely defying the single-particle exponential model. Moreover,\nquantum entropy peaks when only about one quarter of the atoms have escaped.\nThese and many other such effects go beyond the usual notions of\nsingle-particle quantum tunneling, quantum statistical effects on tunneling,\nand well-known semi-classical approaches from WKB to instanton theory. These\nresults thus open up a new regime of exploration of far-from-equilibrium\ndynamics for quantum simulators and quantum dynamics.",
        "positive": "ATUS-PRO: A FEM-based solver for the time-dependent and stationary\n  Gross-Pitaevskii equation: ATUS-PRO is a solver-package written in C++ designed for the calculation of\nnumerical solutions of the stationary- and the time dependent Gross--Pitaevskii\nequation for local two-particle contact interaction utilising finite element\nmethods. These are implemented by means of the deal.II library. The code can be\nused in order to perform simulations of Bose-Einstein condensates in\ngravito-optical surface traps, isotropic and full anisotropic harmonic traps,\nas well as for arbitrary trap geometries. A special feature of this package is\nthe possibility to calculate non-ground state solutions (topological modes,\nexcited states) for an arbitrarily high non-linearity term. The solver- package\nis designed to run on parallel distributed machines and can be applied to\nproblems in one, two, or three spatial dimensions with axial symmetry or in\nCartesian coordinates. The time dependent Gross--Pitaevskii equation is solved\nby means of the fully implicit Crank- Nicolson method, whereas stationary\nstates are obtained with a modified version based on our own constrained Newton\nmethod. The latter method enables to find the excited state solutions."
    },
    {
        "anchor": "Microscopic derivation of Hubbard parameters for cold atomic gases: We study the exact solution for two atomic particles in an optical lattice\ninteracting via a Feshbach resonance. The analysis includes the influence of\nall higher bands, as well as the proper renormalization of molecular energy in\nthe closed channel. Using an expansion in Bloch waves, we show that the problem\nreduces to a simple matrix equation, which can be solved numerically very\nefficient. This exact solution allows for the precise determination of the\nparameters in the Hubbard model and the two-particle bound state energy. We\nidentify the regime, where a single band Hubbard model fails to describe the\nscattering of the atoms as well as the bound states.",
        "positive": "Parallel dark soliton pair in a bistable 2D exciton-polariton superfluid: Collective excitations, such as vortex-antivortex and dark solitons, are\namong the most fascinating effects of macroscopic quantum states. However, 2D\ndark solitons are unstable and collapse into vortices due to snake\ninstabilities. Making use of the optical bistability in exciton-polariton\nmicrocavities, we demonstrate that a pair of dark solitons can be formed in the\nwake of an obstacle in a polariton flow resonantly supported by a homogeneous\nlaser beam. Unlike the purely dissipative case where the solitons are grey and\nspatially separate, here the two solitons are fully dark, rapidly align at a\nspecific separation distance and propagate parallel as long as the flow is in\nthe bistable regime. Remarkably, the use of this regime allows to avoid the\nphase fixing arising in resonant pumping regime and to circumvent the polariton\ndecay. Our work opens very wide perspectives of studying new classes of\nphase-density defects which can form in driven-dissipative quantum fluids of\nlight."
    },
    {
        "anchor": "Universal Properties of a Strongly Interacting Fermi Gas at a $p$-wave\n  Resonance: In this letter, we investigate the properties of a strongly interacting\nspinless Fermi gas close to a $p$-wave resonance. We show that the universal\nproperties at a $p$-wave resonance are captured by two contacts, which are\nrelated respectively to the variation of energy with the $p$-wave scattering\nvolume $v$ and with the effective range $R$ in the two adiabatic theorems\nderived. We show how the two contacts determine the leading and sub-leading\nasymptotic behavior of the momentum distribution ($\\sim 1/k^2$ and $\\sim\n1/k^4$) and how they can be measured experimentally by radio-frequency, Bragg,\nand photo-association spectroscopies. Finally, we evaluate the two contacts at\nhigh temperature via the virial expansion.",
        "positive": "Topological superfluid in a Fermi-Bose mixture with a high critical\n  temperature: We show that a two-dimensional (2D) spin-polarised Fermi gas immersed in a 3D\nBose-Einstein condensate (BEC) constitutes a very promising system to realise a\n$p_x+ip_y$ superfluid. The fermions attract each other via an induced\ninteraction mediated by the bosons, and the resulting pairing is analysed with\nretardation effects fully taken into account. This is further combined with\nBerezinskii-Kosterlitz-Thouless (BKT) theory to obtain reliable results for the\nsuperfluid critical temperature. We show that both the strength and the range\nof the induced interaction can be tuned experimentally, which can be used to\nmake the critical temperature approach the maximum value allowed by general BKT\ntheory. Moreover, this is achieved while keeping the Fermi-Bose interaction\nweak so that three-body losses are small. Our results show that realising a\ntopological superfluid with atomic Fermi-Bose mixtures is within experimental\nreach."
    },
    {
        "anchor": "Stability and Dynamics of Atom-Molecule Superfluids Near a Narrow\n  Feshbach Resonance: The recent observations of a stable molecular condensate emerging from a\ncondensate of bosonic atoms and related ``super-chemical\" dynamics have raised\nan intriguing set of questions. Here we provide a microscopic understanding of\nthis unexpected stability and dynamics in atom-molecule superfluids; we show\none essential element behind these phenomena is an extremely narrow Feshbach\nresonance in $^{133}$Cs at 19.849G. Comparing theory and experiment we\ndemonstrate how this narrow resonance enables the dynamical creation of a large\nclosed-channel molecular fraction superfluid, appearing in the vicinity of\nunitarity. Theoretically the observed superchemistry (\\textit{i.e.}, Bose\nenhanced reactions of atoms and molecules), is found to be assisted by the\nformation of Cooper pairs of bosonic atoms having opposite momenta.\nImportantly, this narrow resonance opens the possibility to explore the quantum\ncritical point of a molecular Bose superfluid and related phenomena which would\nnot be possible near a more typically broad Feshbach resonance.",
        "positive": "The spin evolution of spin-3 $^{52}$Cr Bose-Einstein condensate: The spin evolution of a Bose-Einstein condensate starting from a mixture of\ntwo or three groups of $^{52}$Cr (spin-3) atoms in an optical trap has been\nstudied theoretically. The initial state is so chosen that the system does not\ndistinguish up and down. In this choice, the deviation caused by the\nsingle-mode approximation is reduced. Moreover, since the particle number is\ngiven very small (N=20), the deviation caused by the neglect of the long-range\ndipole force is also reduced. Making use of these two simplifications, a\ntheoretical calculation beyond the mean field theory is performed. The\nnumerical results are help to evaluate the unknown strength $g_0$."
    },
    {
        "anchor": "Quantum solitons in spin-orbit-coupled Bose-Bose mixtures: Recent experimental and theoretical results show that weakly interacting\natomic Bose-Bose mixtures with attractive interspecies interaction are\nstabilized by beyond-mean-field effects. Here we consider the peculiar\nproperties of these systems in a strictly one-dimensional configuration, taking\nalso into account the nontrivial role of spin-orbit and Rabi couplings. We show\nthat when the value of inter- and intraspecies interaction strengths are such\nthat mean-field contributions to the energy cancel, a self-bound bright soliton\nfully governed by quantum fluctuations exists. We derive the phase diagram of\nthe phase transition between a single-peak soliton and a multipeak (striped)\nsoliton, produced by the interplay between spin-orbit, Rabi couplings and\nbeyond-mean-field effects, which also affect the breathing mode frequency of\nthe atomic cloud. Finally, we prove that a phase imprinting of the single-peak\nsoliton leads to a self-confined propagating solitary wave even in the presence\nof spin-orbit coupling.",
        "positive": "Scattering of matter wave solitons on localized potentials: We present numerical and analytical results for the reflection and\ntransmission properties of matter wave solitons impinging on localized\nscattering potentials in one spatial dimension. Our mean field analysis\nidentifies regimes where the solitons behave more like waves or more like\nparticles as a result of the interplay between the dispersive wave propagation\nand the attractive interactions between the atoms. For a bright soliton\npropagating together with a dark soliton void in a two-species Bose-Einstein\ncondensate of atoms with repulsive interactions, we find different reflection\nand transmission properties of the dark and the bright components."
    },
    {
        "anchor": "Self-bound many-body states of quasi-one-dimensional dipolar Fermi\n  gases: Exploiting Bose-Fermi mappings for generalized contact interactions: Using a combination of results from exact mappings and from mean-field theory\nwe explore the phase diagram of quasi-one-dimensional systems of identical\nfermions with attractive dipolar interactions. We demonstrate that at low\ndensity these systems provide a realization of a single-component\none-dimensional Fermi gas with a generalized contact interaction. Using an\nexact duality between one-dimensional Fermi and Bose gases, we show that when\nthe dipole moment is strong enough, bound many-body states exist, and we\ncalculate the critical coupling strength for the emergence of these states. At\nhigher densities, the Hartree-Fock approximation is accurate, and by combining\nthe two approaches we determine the structure of the phase diagram. The\nmany-body bound states should be accessible in future experiments with\nultracold polar molecules.",
        "positive": "Rashba spin-orbit coupled atomic Fermi gases: We investigate theoretically BEC-BCS crossover physics in the presence of a\nRashba spin-orbit coupling in a system of two-component Fermi gas with and\nwithout a Zeeman field that breaks the population balance between the two\ncomponents. A new bound state (Rashba pair) emerges because of the spin-orbit\ninteraction. We study the properties of Rashba pairs using a standard pair\nfluctuation theory. At zero temperature, the Rashba pairs condense into a\nmacroscopic mixed spin state. We discuss in detail the experimental signatures\nfor observing the condensation of Rashba pairs by calculating various physical\nobservables which characterize the properties of the system and can be measured\nin experiment."
    },
    {
        "anchor": "Effective Hamiltonians for quasi-one-dimensional Fermi gases with\n  spin-orbit coupling: We derive one-dimensional effective Hamiltonians for spin-orbit coupled Fermi\ngases confined in quasi-one-dimensional trapping potentials. For energy regime\naround the two-body bound state energy, the effective Hamiltonian takes a\ntwo-channel form, where the population in transverse excited levels are\ndescribed by dressed molecules in the closed channel. For energy regime\nslightly above the continuum threshold, the effective Hamiltonian takes a\nsingle-channel form, where low-energy physics is governed by the\none-dimensional interacting strength determined by three-dimensional scattering\nlength and transverse confinement. We further discuss the effect of spin-orbit\ncoupling and effective Zeeman field on the position of confinement-induced\nresonances, and show that these resonances can be understood as Feshbach\nresonances between the threshold of the transverse ground state and the\ntwo-body bound state associated with the transverse excited states. We expect\nthat the shift of confinement-induced resonances can be observed under present\nexperimental technology at attainable temperatures.",
        "positive": "Spin gradient demagnetization cooling of ultracold atoms: A major goal of ultracold atomic physics is quantum simulation of spin\nHamiltonians in optical lattices. Progress towards this goal requires the\nattainment of extremely low temperatures. Here we demonstrate a new cooling\nmethod which consists of applying a time-varying magnetic field gradient to a\nspin mixture of ultracold atoms. We have used this method to prepare isolated\nspin distributions at positive and negative spin temperatures of +/-50\npicokelvin. The spin system can also be used to cool other degrees of freedom,\nand we have used this coupling to reduce the temperature of an apparently\nequilibrated sample of rubidium atoms in a Mott insulating state to 350\npicokelvin. These are the lowest temperatures ever measured in any system."
    },
    {
        "anchor": "Thermodynamic Properties of Universal Fermi Gases: We develop a simple, mean-field-like theory for the normal phase of a unitary\nFermi gas by deriving a self-consistent equation for its self-energy via a\nmomentum-dependent coupling constant for both attractive and repulsive\nuniversal fermions. For attractive universal fermions in the lower branch of a\nFeshbach resonance, we use zero-temperature Monte Carlo results as a starting\npoint for one-step iteration in order to derive an analytical expression for\nthe momentum-dependent self-energy. For repulsive universal fermions in the\nupper branch of a Feshbach resonance, we iteratively calculate the\nmomentum-dependent self-energy via our self-consistent equation. Lastly, for\nthe case of population imbalance, we propose an ansatz for higher order virial\nexpansion coefficents. Overall, we find that our theory is in good agreement\nwith currently available, high temperature experimental data.",
        "positive": "Single particle momentum distributions for three-bosons in two and three\n  dimensions and dimensional crossover: In this paper, we revise our main results involving the single particle\nmomentum distribution of bosonic trimer states in two and three dimensions. A\nsummary table makes easier the comparison between the matrix elements and the\ndifferent terms of the momentum distributions. We also show a practical method\nto continuously interpolate between different dimensions."
    },
    {
        "anchor": "Competition of superfluid phases in low-dimensional spin-$1\\over 2$\n  fermions with $s$- and $p$-wave interactions: The ground state of spin-$1\\over 2$ fermions with contact $s$-wave inter- and\n$p$-wave intra-species interactions is discussed. Particularly, we formulate\nthe mean field scheme for calculating thermodynamic properties of the system in\narbitrary dimension $D<2$ and discuss in detail the phase diagram in 1D case.\nExcept clean phases with either singlet or triplet Cooper pairings, we have\nidentified two mixed phases (one stable and another metastable) of the\none-dimensional two-component fermions where both pairing mechanisms coexist.",
        "positive": "Chaos-assisted tunneling resonances in a synthetic Floquet superlattice: The field of quantum simulation, which aims at using a tunable quantum system\nto simulate another, has been developing fast in the past years as an\nalternative to the all-purpose quantum computer. In particular, the use of\ntemporal driving has attracted a huge interest recently as it was shown that\ncertain fast drivings can create new topological effects, while a strong\ndriving leads to e.g. Anderson localization physics. In this work, we focus on\nthe intermediate regime to observe a quantum chaos transport mechanism called\nchaos-assisted tunneling which provides new possibilities of control for\nquantum simulation. Indeed, this regime generates a rich classical phase space\nwhere stable trajectories form islands surrounded by a large sea of unstable\nchaotic orbits. This mimics an effective superlattice for the quantum states\nlocalized in the regular islands, with new controllable tunneling properties.\nBesides the standard textbook tunneling through a potential barrier,\nchaos-assisted tunneling corresponds to a much richer tunneling process where\nthe coupling between quantum states located in neighboring regular islands is\nmediated by other states spread over the chaotic sea. This process induces\nsharp resonances where the tunneling rate varies by orders of magnitude over a\nshort range of parameters. We experimentally demonstrate and characterize these\nresonances for the first time in a quantum system. This opens the way to new\nkinds of quantum simulations with long-range transport and new types of control\nof quantum systems through complexity."
    },
    {
        "anchor": "Enhancement of condensate depletion due to spin-orbit coupling: We show that spin-orbit coupling (SOC) significantly enhances the depletion\nof a homogeneous Bose-Einstein condensate in three dimensions. With decreasing\nanisotropy of the SOC, both the quantum and thermal depletion increase. In\nparticular, different types of SOC give rise to qualitatively different\ndependences of the condensate depletion on microscopic variables including the\nscattering length, the strength of the SOC, and the temperature, which can be\ndirectly observed once these types of SOC are realized in experiments.\nMoreover, we point out that thermal depletion in three dimensions becomes\nlogarithmically divergent at any given finite temperature when both the SOC and\nthe interaction approach the isotropic limit.",
        "positive": "Short-distance and short-time structure of a unitary Fermi gas: We consider the operator product expansions for unitarity fermions. We\ncompute the dynamic structure factor S(q,w) at large frequency and wavenumber\naway from the one-particle peak. The overall normalization of S(q,w) is\ndetermined by Tan's contact parameter, and the dependence on q and w is\nobtained in closed analytic form. We also find energy deposited into the system\nby small, rapid variations of the inverse scattering length."
    },
    {
        "anchor": "Aharonov-Bohm caging in spin-orbit coupled exciton-polariton lattices: We study the Aharonov-Bohm (AB) caging effect in rhombic exciton-polariton\nlattices, with the Rashba-Dresselhaus spin-orbit coupling (RDSOC) in acting a\nsynthetic gauge field. The effective magnetic flux through each plaquette is\ncontrolled by the orientation of the RDSOC and geometry of the rhombic lattice.\nThe results show that the interplay of lattice geometry and the RDSOC will\ndramatically influence the energy band structure, furthermore, determining the\ntransportation properties of exciton-polariton condensates. Non-Hermitian\neffects, which arise from the polariton intrinsic loss mechanism, on the AB\ncaging is also discussed in detail. Meanwhile, the effect of disorder on the\ndynamics of AB caging is investigated, and we find that the disorder will lead\nto the inverse Anderson localization. We propose that using the AB caging\neffect allows to trap and steer the propagation of polaritons in a given\nparameter regime. Considering the specific example of a photonic liquid crystal\nmicrocavity to achieve our theoretical predictions, the AB caging could be\nswitched on and off by applying an external voltage.",
        "positive": "Fast and selective inter-band transfer of ultracold atoms in bichromatic\n  lattices permitting Dirac points: An experimental group at Beijing[Yueyang Zhai, ${\\it et. al.}$, Phys. Rev. A\n${\\bf 87}$, 063638 (2013)] introduced the method of standing-wave pulse\nsequence for efficiently preparing ultracold bosonic atoms into a specific\nexcited band in a 1-dimensional optical lattice. Here, we report a theoretical\nextension of their work to the problem of 1-dimensional bichromatic\nsuperlattice. We find that varying the lattice parameters leads to the\nso-called Dirac point where a pair of excited bands crosses. This paper thus\ndiscusses ${\\it simultaneously}$ the efficient excitation of the wave packet to\nthe proximity of the Dirac point and its subsequent dynamics in the force field\nof a parabolic trap. With the aid of a toy model, we theoretically unravel the\nmechanism of the efficient preparation, and then numerically explore optimal\npulse-sequence parameters for a realistic situation. We find an optimized\nsequence of a bichromatic optical lattice that excites more than 99% of the\natoms to the 1st and 2nd excited bands within 100 $\\mu$s without the harmonic\ntrap. Our main finding is that the system permitting the Dirac point possesses\na region of parameters where the excited energy bands become nearly parabolic,\nconducive to robust coherence and isochronicity. We also provide an appropriate\ndata set for future experimentation, including effects of the atom-atom\ninteraction by way of the mean-field nonlinear term."
    },
    {
        "anchor": "Ground States of the Spin-1 Bose-Hubbard Model: We prove basic theorems about the ground states of the S=1 Bose-Hubbard\nmodel. The results are quite universal and depend only on the coefficient U_2\nof the spin-dependent interaction. We show that the ground state exhibits\nsaturated ferromagnetism if U_2<0, is spin-singlet if U_2>0, and exhibits\n\"SU(3)-ferromagnetism\" if U_2=0, and completely determine the degeneracy in\neach region.",
        "positive": "Counter-rotating vortices in miscible two-component Bose-Einstein\n  condensates: Counter-rotating vortices in miscible two-component Bose-Einstein\ncondensates, in which superflows counter-rotate between the two components\naround the overlapped vortex cores, are studied theoretically in a\npancake-shaped potential. In a linear stability analysis with the Bogoliubov-de\nGennes model, we show that counter-rotating vortices are dynamically unstable\nagainst splitting into multiple vortices. The instability shows characteristic\nbehaviors as a result of countersuperflow instability, which causes relaxation\nof relative flows between the two components in binary condensates. The\ncharacteristic behaviors are completely different from those of multiquantum\nvortices in single-component Bose-Einstein condensates; the number of vortices\ngenerated by the instability can become larger than the initial winding number\nof the counter-rotating vortex. We also investigate the nonlinear dynamics of\nthe instability by numerically solving the Gross-Pitaevskii equations. The\nnonlinear dynamics drastically changes when the winding number of\ncounter-rotating vortices becomes larger, which lead to nucleation of vortex\npairs outside of the vortex core. The instability eventually develops into\nturbulence after the relaxation of the relative rotation between the two\ncomponents."
    },
    {
        "anchor": "Quantum turbulence in quantum gases: Turbulence is characterized by a large number of degrees of freedom,\ndistributed over several length scales, that result into a disordered state of\na fluid. The field of quantum turbulence deals with the manifestation of\nturbulence in quantum fluids, such as liquid helium and ultracold gases. We\nreview, from both experimental and theoretical points of view, advances in\nquantum turbulence focusing on atomic Bose-Einstein condensates. We also\nexplore the similarities and differences between quantum and classical\nturbulence. Lastly, we present challenges and possible directions for the\nfield. We summarize questions that are being asked in recent works, which need\nto be answered in order to understand fundamental properties of quantum\nturbulence, and we provide some possible ways of investigating them.",
        "positive": "Dynamics of a Nonequilibrium Discontinuous Quantum Phase Transition in a\n  Spinor Bose-Einstein Condensate: Symmetry-breaking quantum phase transitions lead to the production of\ntopological defects or domain walls in a wide range of physical systems. In\nsecond-order transitions, these exhibit universal scaling laws described by the\nKibble-Zurek mechanism, but for first-order transitions a similarly universal\napproach is still lacking. Here we propose a spinor Bose-Einstein condensate as\na testbed system where critical scaling behavior in a first-order quantum phase\ntransition can be understood from generic properties. We generalize the\nKibble-Zurek mechanism to determine the critical exponents for: (1) the onset\nof the decay of the metastable state on short times scales, and (2) the number\nof resulting phase-separated ferromagnetic domains at longer times, as a\none-dimensional spin-1 condensate is ramped across a first-order quantum phase\ntransition. The predictions are in excellent agreement with mean-field\nnumerical simulations and provide a paradigm for studying the decay of\nmetastable states in experimentally accessible systems."
    },
    {
        "anchor": "Optical Lattice Emulators: Bose and Fermi Hubbard Models: This chapter is a pedagogical review of the Hubbard model for bosons with\nrepulsion and for fermions with attraction and repulsion primarily using two\nmethods, one chosen for its simplicity and insights (mean field theory) and the\nother chosen for its accuracy and reliability (quantum Monte Marlo methods).\nFrom a comparison of the two methods we glean valuable information into the\neffects of fluctuations that dominate quantum phase transitions. The chapter\nincludes an in-depth comparison with experiments. We conclude with a discussion\nof future developments where the technical methods expounded on here, mean\nfield theory and quantum Monte Carlo, could be useful.",
        "positive": "Topologically protected edge gap solitons of interacting Bosons in\n  one-dimensional superlattices: We comprehensively investigate the nontrivial states of interacting Bose\nsystem in one-dimensional optical superlattices under the open boundary\ncondition. Our results show that there exists a kind of stable localized\nstates: edge gap solitons. We argue that the states originate from the\neigenstates of independent edge parabolas. In particular, the edge gap solitons\nexhibit a nonzero topological invariant. The topological nature is due to the\nconnection of the present model to the quantized adiabatic particle transport\nproblem. In addition, the composition relations between the gap solitons and\nthe extend states under the open boundary condition are discussed."
    },
    {
        "anchor": "Bose-Fermi Pairs in a Mixture and the Luttinger Theorem within a\n  Nozieres-Schmitt-Rink like Approach: Bose-Fermion pair correlations in a mixture are considered at zero\ntemperature in the T-matrix approximation. Special attention is paid to the\nLuttinger theorem. In a strict RPA variant of the Nozieres-Schmitt-Rink\napproach, it is shown that this theorem is respected also in the homogeneous\ninfinite matter case. We calculate the corresponding occupation numbers of\nfermions and bosons and the condensate depletion. We also show that in the\nlimit of very small boson density, our results are in good agreement with the\nresults found in the literature for the Fermi polaron in strongly imbalanced\nFermi-Fermi mixtures.",
        "positive": "Observing the loss and revival of long-range phase coherence through\n  disorder quenches: Relaxation of quantum systems is a central problem in nonequilibrium physics.\nIn contrast to classical systems, the underlying quantum dynamics results not\nonly from atomic interactions but also from the long-range coherence of the\nmany-body wave function. Experimentally, nonequilibrium states of quantum\nfluids are usually created using moving objects or laser potentials, directly\nperturbing and detecting the system's density. However the fate of long-range\nphase coherence for hydrodynamic motion of disordered quantum systems is less\nexplored, especially in three dimension. Here, we unravel how the density and\nphase coherence of a Bose-Einstein condensate of $^6$Li$_2$ molecules respond\nupon quenching on or off an optical speckle potential. We find that, as the\ndisorder is switched on, long-range phase coherence breaks down one order of\nmagnitude faster than the density of the quantum gas responds. After removing\nit, the system needs two orders of magnitude longer times to reestablish\nquantum coherence, compared to the density response. We compare our results\nwith numerical simulations of the Gross-Pitaevskii equation on large\nthree-dimensional grids, finding an overall good agreement. Our results shed\nlight on the importance of long-range coherence and possibly long-lived phase\nexcitations for the relaxation of nonequilibrium quantum many-body systems."
    },
    {
        "anchor": "Spatial Adiabatic Passage of Massive Quantum Particles: By adiabatically manipulating tunneling amplitudes of cold atoms in a\nperiodic potential with a multiple sublattice structure, we are able to\ncoherently transfer atoms from a sublattice to another without populating the\nintermediate sublattice, which can be regarded as a spatial analogue of\nstimulated Raman adiabatic passage. A key is the existence of dark eigenstates\nforming a flat band in a Lieb-type optical lattice. We also successfully\nobserve a matter-wave analogue of Autler-Townes doublet using the same setup.\nThis work shed light on a novel kind of coherent control of cold atoms in\noptical potentials.",
        "positive": "A New Non-Abelian Topological Phase of Cold Fermi Gases in Anisotropic\n  and Spin-Dependent Optical Lattices: To realize non-Abelian s-wave topological superfluid (TS) of cold Fermi\ngases, generally a Zeeman magnetic field larger than superfluid pairing gap is\nnecessary. In this paper we find that using an anisotropic and spin-dependent\noptical lattice (ASDOL) to trap gases, a new non-Abelian TS phase appears, in\ncontrast to an isotropic and spin-independent optical lattice. A characteristic\nof this new non-Abelian TS is that Zeeman magnetic field can be smaller than\nthe superfluid pairing gap. By self-consistently solving pairing gap equation\nand considering the competition against normal state and phase separation, this\nnew phase is also stable. Thus an ASDOL supplies a convenient route to realize\nTS. We also investigate edge states and the effects of a harmonic trap\npotential."
    },
    {
        "anchor": "On the theory of inhomogeneous Bose-Einstein condensation of magnons in\n  yttrium garnet: The Bose-Einstein condensation (BEC) of magnons created by a strong pumping\nin ferromagnetic thin films of yttrium iron garnet used as systems of finite\nsize is considered analytically. Such a peculiarity, typical for this magnetic\nmaterial, as the presence of a minimum in the spectrum of spin waves at a\nfinite value of the wave vector is taken into account. The definition of\nhightemperature BEC is introduced and its characteristics are discussed. A role\nof boundary conditions for spin variables is analyzed, and it is shown that in\nthe case of free spins on the boundary the magnon lattice can form in the\nsystem. The factors responsible for its appearance are discussed.",
        "positive": "Rayleigh-Taylor instability of binary condensates: We propose a scheme to initiate and examine Rayleigh-Taylor instability in\nthe two species Bose-Einstein condensates. We identify $^{85}$Rb-$^{87}$Rb\nmixture as an excellent candidate to observe it experimentally. The instability\nis initiated by tuning the $^{85}$Rb-$^{85}$Rb interaction through magnetic\nFeshbach resonance. We show that the observable signature of the instability is\nthe damping of the radial oscillation. This would perhaps be one of the best\ncontrolled experiments on Rayleigh-Taylor instability. We also propose a semi\nanalytic scheme to determinate stationary state of binary condensates with the\nThomas-Fermi approximation for the axis symmetric traps."
    },
    {
        "anchor": "Quantum phase transitions in attractive extended Bose-Hubbard Model with\n  three-body constraint: The effect of nearest-neighbor repulsion on the ground-state phase diagrams\nof three-body constrained attractive Bose lattice gases is explored\nnumerically. When the repulsion is turned on, in addition to the uniform Mott\ninsulating state and two superfluid phases (the atomic and the dimer\nsuperfluids), a dimer checkerboard solid state appears at unit filling, where\nboson pairs form a solid with checkerboard structure. We find also that the\nfirst-order transitions between the uniform Mott insulating state and the\natomic superfluid state can be turned into the continuous ones as the repulsion\nis increased. Moreover, the stability regions of the dimer superfluid phase can\nbe extended to modest values of the hopping parameter by tuning the strength of\nthe repulsion. Our conclusions hence shed light on the search of the dimer\nsuperfluid phase in real ultracold Bose gases in optical lattices.",
        "positive": "Phase separation and multistability of two-component Bose-Einstein\n  condensate in an optical cavity: We examine the multistability associated with miscibility-immiscibility\nconditions for a two-component Bose-Einstein condensate coupled to the light\nfield in an optical cavity. For a strongly immiscible condition, the system\nexhibits a variety of density structures, including separated state, stripe\nstate, and their coexistence. The multistability arises from these spatial\nstructures of the two-component condensate, which significantly alter the\nhysteresis curve with respect to the intensity of cavity pumping. We present a\nvariational approach to confirm our numerical results."
    },
    {
        "anchor": "Even-Odd Correlation Functions on an Optical Lattice: We study how different many body states appear in a quantum gas microscope,\nsuch as the one developed at Harvard [Bakr et al. Nature 462, 74 (2009)], where\nthe site-resolved parity of the atom number is imaged. We calculate the spatial\ncorrelations of the microscope images, corresponding to the correlation\nfunction of the parity of the number of atoms at each site. We produce analytic\nresults for a number of well-known models: noninteracting bosons, the large U\nBose-Hubbard model, and noninteracting fermions. We find that these parity\ncorrelations tend to be less strong than density-density correlations, but they\ncarry similar information.",
        "positive": "Spin conductivity spectrum and spin superfluidity in a binary Bose\n  mixture: We investigate the spectrum of spin conductivity for a miscible two-component\nBose-Einstein condensate (BEC) that exhibits spin superfluidity. By using the\nBogoliubov theory, the regular part being the spin conductivity at finite ac\nfrequency and the spin Drude weight characterizing the delta-function peak at\nzero frequency are analytically computed. We demonstrate that the spectrum\nexhibits a power-law behavior at low frequency, reflecting gapless density and\nspin modes specific to the binary BEC. At the phase transition points into\nimmiscible and quantum-droplet states, the change in quasiparticle dispersion\nrelations modifies the power law. In addition, the spin Drude weight becomes\nfinite, indicating zero spin resistivity due to spin superfluidity. Our results\nalso suggest that the Andreev-Bashkin drag density is accessible by measuring\nthe spin conductivity spectrum."
    },
    {
        "anchor": "Universal dynamics and non-thermal fixed points in quantum fluids far\n  from equilibrium: Closed quantum systems far from thermal equilibrium can show universal\ndynamics near attractor solutions, known as non-thermal fixed points,\ngenerically in the form of scaling behavior in space and time. A systematic\nclassification and comprehensive understanding of such scaling solutions are\ntasks of future developments in non-equilibrium quantum many-body theory. In\nthis tutorial review, we outline several analytical approaches to non-thermal\nfixed points and summarize corresponding numerical and experimental results.\nThe analytic methods include a non-perturbative kinetic theory derived within\nthe two-particle irreducible effective-action formalism, as well as a\nlow-energy effective field theory framework. As one of the driving forces of\nthis research field are numerical simulations, we summarize the main results of\nexemplary cases of universal dynamics in ultracold Bose gases. This encompasses\nquantum vortex ensembles in turbulent superfluids as well as recently observed\nreal-time instanton solutions in one-dimensional spinor condensates.",
        "positive": "Correlated Pair Approach to Composite Boson Scattering Lengths: We derive the scattering length of composite bosons (cobosons) within the\nframework of the composite boson many-body formalism that uses correlated-pair\nstates as a basis, instead of free fermion states. The integral equation\nconstructed from this physically relevant basis makes transparent the role of\nfermion exchange in the coboson-coboson effective scattering. Three potentials\nused for Cooper pairs, fermionic-atom dimers, and semiconductor excitons are\nconsidered. While the s-wave scattering length for the BCS-like potential is\njust equal to its Born value, the other two are substantially smaller. For\nfermionic-atom dimers and semiconductor excitons, our results, calculated\nwithin a restricted correlated-pair basis, are in good agreement with those\nobtained from procedures numerically more demanding. We also propose model\ncoboson-coboson scatterings that are separable and thus easily workable, and\nthat produce scattering lengths which match quantitatively well with the\nnumerically-obtained values for all fermion mass ratios. These separable model\nscatterings can facilitate future works on many-body effects in coboson gases."
    },
    {
        "anchor": "Shear Viscosity of a Unitary Fermi Gas: We present the first ab initio determination of the shear viscosity eta of\nthe Unitary Fermi Gas, based on finite temperature quantum Monte Carlo\ncalculations and the Kubo linear-response formalism. We determine the\ntemperature dependence of the shear viscosity to entropy density ratio eta/s.\nThe minimum of eta/s appears to be located above the critical temperature for\nthe superfluid-to-normal phase transition with the most probable value being\neta/s approx 0.2 hbar/kB, which almost saturates the Kovtun-Son-Starinets\nuniversal value hbar/(4 pi kB).",
        "positive": "Fractional quantum Hall states of photons in an array of dissipative\n  coupled cavities: We report a theoretical study of the collective optical response of a\ntwo-dimensional array of nonlinear cavities in the impenetrable photon regime\nunder a strong artificial magnetic field. Taking advantage of the\nnon-equilibrium nature of the photon gas, we propose an experimentally viable\nall-optical scheme to generate and detect strongly correlated photon states\nwhich are optical analogs of the Laughlin states of fractional quantum Hall\nphysics."
    },
    {
        "anchor": "Transparent, Non-local, Species-selective Transport in an Optical\n  Superlattice Containing Two Interacting Atom Species: In an optical superlattice of triple wells, containing two mutually\ninteracting atom species in adjacent wells, we show that one species can be\ntransported through the positions of the other species, yet avoiding\nsignificant overlap and direct interaction. The transfer protocol is optimized\nto be robust against missing atoms of either species in any lattice site, as\nwell as against lattice fluctuations. The degree and the duration of the\ninter-species overlap during passage can be tuned, making possible controlled\nlarge-scale interaction-induced change of internal states.",
        "positive": "Periodically-driven quantum matter: the case of resonant modulations: Quantum systems can show qualitatively new forms of behavior when they are\ndriven by fast time-periodic modulations. In the limit of large driving\nfrequency, the long-time dynamics of such systems can often be described by a\ntime-independent effective Hamiltonian, which is generally identified through a\nperturbative treatment. Here, we present a general formalism that describes\ntime-modulated physical systems, in which the driving frequency is large, but\nresonant with respect to energy spacings inherent to the system at rest. Such a\nsituation is currently exploited in optical-lattice setups, where superlattice\n(or Wannier-Stark-ladder) potentials are resonantly modulated so as to control\nthe tunneling matrix elements between lattice sites, offering a powerful method\nto generate artificial fluxes for cold-atom systems. The formalism developed in\nthis work identifies the basic ingredients needed to generate interesting flux\npatterns and band structures using resonant modulations. Additionally, our\napproach allows for a simple description of the micro-motion underlying the\ndynamics; we illustrate its characteristics based on diverse dynamic-lattice\nconfigurations. It is shown that the impact of the micro-motion on physical\nobservables strongly depends on the implemented scheme, suggesting that a\ntheoretical description in terms of the effective Hamiltonian alone is\ngenerally not sufficient to capture the full time-evolution of the system."
    },
    {
        "anchor": "Collective modes of a two-dimensional Fermi gas at finite temperature: In this work we examine the breathing mode of a strongly interacting\ntwo-dimensional Fermi gas and the role of temperature on the anomalous breaking\nof scale invariance. By calculating the equation of state with different\nmany-body $T$-matrix theories and the virial expansion approach, we obtain a\nhydrodynamic equation of the harmonically trapped Fermi gas (with trapping\nfrequency $\\omega_{0}$) through the local density approximation. By solving the\nhydrodynamic equation we determine the breathing mode frequencies as functions\nof interaction strength and temperature. We find that the breathing mode\nanomaly depends sensitively on both interaction strength and temperature. In\nparticular, in the strongly interacting regime we predict a significant\ndown-shift of the breathing mode frequency, below the scale invariant value of\n$2\\omega_{0}$ for temperatures of order the Fermi temperature.",
        "positive": "Experimentally accessible invariants encoded in interparticle\n  correlations of harmonically trapped ultra-cold few-fermion mixtures: System of a two-flavor mixture of ultra-cold fermions confined in a\none-dimensional harmonic trap is studied in the frame of the center of mass. We\npresent a numerical method of obtaining energetic spectra in this frame for an\narbitrary mass ratio of fermionic species. We identify a specific invariant\nencoded in many-body correlations which enable one to determine an eigenstate\nof the Hamiltonian and to label excitations of the center of mass. The tool\npresented may be particularly useful in experimental analysis of the\ninterparticle interactions which do not affect the center of mass excitations\nin a harmonic potential."
    },
    {
        "anchor": "Effects of quantum fluctuations on the low-energy collective modes of\n  two-dimensional superfluid Fermi gases from the BCS to the Bose Limit: We investigate the effects of quantum fluctuations on the low-energy\ncollective modes of two-dimensional (2D) $s$-wave Fermi superfluids from the\nBCS to the Bose limit. We compare our results to recent Bragg scattering\nexperiments in 2D box potentials, with very good agreement. We show that\nquantum fluctuations in the phase and modulus of the pairing order parameter\nare absolutely necessary to give physically acceptable chemical potential and\ndispersion relation of the low-energy collective mode throughout the BCS to\nBose evolution. Furthermore, we demonstrate that the dispersion of the\ncollective modes change from concave to convex as interactions are tuned from\nthe BCS to the Bose regime, and never crosses the two-particle continuum,\nbecause arbitrarily small attractive interactions produce bound states in 2D.",
        "positive": "Vortex nucleation in rotating Bose-Einstein condensates with\n  density-dependent gauge potential: We study numerically the vortex dynamics and vortex-lattice formation in a\nrotating density-dependent Bose-Einstein condensate (BEC), characterized by the\npresence of nonlinear rotation. By varying the strength of nonlinear rotation\nin density-dependent BECs, we calculate the critical frequency,\n$\\Omega_{\\text{cr}}$, for vortex nucleation both in adiabatic and sudden\nexternal trap rotations. The nonlinear rotation modifies the extent of\ndeformation experienced by the BEC due to the trap and shifts the\n$\\Omega_{\\text{cr}}$ values for vortex nucleation. The critical frequencies and\nthereby, the transition to vortex-lattices in an adiabatic rotation ramp,\ndepend on conventional $\\textit{s}$-wave scattering lengths through the\nstrength of nonlinear rotation, $\\mathit{C}$, such that\n$\\Omega_{\\text{cr}}(\\mathit{C}>0) < \\Omega_{\\text{cr}}(\\mathit{C}=0) <\n\\Omega_{\\text{cr}}(\\mathit{C}<0)$. In an analogous manner, the critical\nellipticity ($\\epsilon_{\\text{cr}}$) for vortex nucleation during an adiabatic\nintroduction of trap ellipticity ($\\epsilon$) depends on the nature of\nnonlinear rotation besides trap rotation frequency. The nonlinear rotation\nadditionally affects the vortex-vortex interactions and the motion of the\nvortices through the condensate by altering the strength of Magnus force on\nthem. The combined result of these nonlinear effects is the formation of the\nnon-Abrikosov vortex-lattices and ring-vortex arrangements in the\ndensity-dependent BECs."
    },
    {
        "anchor": "Antiferromagnetic phase transition in a nonequilibrium lattice of\n  Rydberg atoms: We study a driven-dissipative system of atoms in the presence of laser\nexcitation to a Rydberg state and spontaneous emission. The atoms interact via\nthe blockade effect, whereby an atom in the Rydberg state shifts the Rydberg\nlevel of neighboring atoms. We use mean-field theory to study how the Rydberg\npopulation varies in space. As the laser frequency changes, there is a\ncontinuous transition between the uniform and antiferromagnetic phases. The\nnonequilibrium nature also leads to a novel oscillatory phase and bistability\nbetween the uniform and antiferromagnetic phases.",
        "positive": "Slow interaction ramps in trapped many-particle systems: universal\n  deviations from adiabaticity: For harmonic-trapped atomic systems, we report system-independent\nnon-adiabatic features in the response to interaction ramps. We provide results\nfor several different systems in one, two, and three dimensions: bosonic and\nfermionic Hubbard models realized through optical lattices, a Bose-Einstein\ncondensate, a fermionic superfluid and a fermi liquid. The deviation from\nadiabaticity is characterized through the heating or excitation energy produced\nduring the ramp. We find that the dependence of the heat on the ramp time is\nsensitive to the ramp protocol but has aspects common to all systems\nconsidered. We explain these common features in terms of universal dynamics of\nthe system size or cloud radius."
    },
    {
        "anchor": "Mass-imbalanced Bose-Einstein condensed mixtures in rotating perturbed\n  trap: We consider the mass-imbalanced sensibility for the emergence of vortex\npatterns in the Bose-Einstein condensed binary mixture of rubidium-cesium\n($^{85}$Rb-$^{133}$Cs), confined in quasi-two-dimensional harmonic traps, with\none species linearly perturbed in one direction. Non-dipolar coupled species\nare chosen to highlight mass symmetry effects. We first analyze the condensed\nmixture in the unperturbed non-rotating regime, where radial phase separation\nis verified in the immiscible regime, which occurs for large ratio between\ninter- and intra-species repulsive interactions. By going to the linear\nperturbed regime, the radial phase separation that occurs in the immiscible\ncondition splits up with the two densities having their maxima at distinct\npositions. In the rotating regime of both unperturbed and perturbed cases, the\nminimum rotation is determined in terms of the inter-species interaction to\nobserve vortex structures. In the immiscible regime a dramatic spatial\ninterchange between the species is verified by increasing the rotation.",
        "positive": "Cold Atom Quantum Simulator for Dilute Neutron Matter: The internal structure of neutron stars and the physical properties of nuclei\ndepend on the equation of state (EOS) of neutron matter. Dilute neutron matter\nis a quantum system of spin-1/2 Fermi particles interacting via s-wave\nscattering. Although a nuclear system and an ultracold atomic system have\nlength scales and energy scales that differ by several orders of magnitude,\nboth systems follow a common universal EOS considering their non-dimensional\nuniversal interaction parameters. In this study, we determine the EOS of\nneutron matter in the dilute region, where the influence of the s-wave\nscattering length is dominant but that of the effective range is small, by\nutilizing a quantum simulator of ultracold $^6$Li atoms with Feshbach\nresonance."
    },
    {
        "anchor": "Testing the universality of the many-body metal-insulator transition by\n  time evolution of a disordered one-dimensional ultracold fermionic gas: It is now possible to study experimentally the combined effect of disorder\nand interactions in cold atom physics. Motivated by these developments we\ninvestigate the dynamics around the metal-insulator transition (MIT) in a\none-dimensional (1D) Fermi gas with short-range interactions in a quasiperiodic\npotential by the time-dependent density-matrix renormalization group (tDMRG)\ntechnique. By tuning disorder and interactions we study the MIT from the weakly\nto the strongly interacting limit. The MIT is not universal as time evolution,\nwell described by a process of anomalous diffusion, depends qualitatively on\nthe interaction strength. By using scaling ideas we relate the parameter that\ncontrols the diffusion process with the critical exponent that describes the\ndivergence of the localization length. In the limit of strong interactions\ntheoretical arguments suggest that the motion at the MIT tends to ballistic and\ncritical exponents approach mean-field predictions.",
        "positive": "Synthetic magneto-hydrodynamics in Bose-Einstein condensates and routes\n  to vortex nucleation: Engineering of synthetic magnetic flux in Bose-Einstein condensates [Lin et\nal., Nature {\\bf 462}, 628 (2009)] has prospects for attaining the high vortex\ndensities necessary to emulate the fractional quantum Hall effect. We\nanalytically establish the hydrodynamical behaviour of a condensate in a\nuniform synthetic magnetic field, including its density and velocity profile.\nImportantly, we find that the onset of vortex nucleation observed\nexperimentally corresponds to a dynamical instability in the hydrodynamical\nsolutions and reveal other routes to instability and anticipated vortex\nnucleation."
    },
    {
        "anchor": "Conductivity of strongly correlated bosons in optical lattices in an\n  Abelian synthetic magnetic field: Topological phase engineering of neutral bosons loaded in an optical lattice\nopens a new window for manipulating of transport phenomena in such systems.\nExploiting the Bose Hubbard model and using the magnetic Kubo formula proposed\nin this paper we show that the optical conductivity abruptly changes for\ndifferent flux densities in the Mott phase. Especially, when the frequency of\nthe applied field corresponds to the on-site boson interaction energy, we\nobserve insulator or metallic behavior for a given Hofstadter spectrum. We also\nprove, that for different synthetic magnetic field configurations, the critical\nconductivity at the tip of the lobe is non-universal and depends on the energy\nminima of the spectrum. In the case of $1/2$ and $1/3$ flux per plaquette, our\nresults are in good agreement with those of the previous Monte Carlo (MC)\nstudy. Moreover, we show that for half magnetic-flux through the cell the\ncritical conductivity suddenly changes in the presence of a superlattice\npotential with uniaxial periodicity.",
        "positive": "Fragmentation and correlations in a rotating Bose-Einstein condensate\n  undergoing breakup: The theoretical investigation of rotating Bose-Einstein condensates has\nmainly focused on the emergence of quantum vortex states and the condensed\nproperties of such systems. In the present work, we concentrate on other facets\nby examining the impact of rotation on the ground state of weakly interacting\nbosons confined in anharmonic potentials computed both at the mean-field level\nand particularly at the many-body level of theory. For the many-body\ncomputations, we employ the well-established many-body method known as the\nmulticonfigurational time-dependent Hartree method for bosons (MCTDHB). We\npresent how various degrees of fragmentation can be generated following the\nbreakup of the ground state densities in anharmonic traps without ramping up a\npotential barrier for strong rotations. The breakup of the densities is found\nto be associated with the acquisition of angular momentum in the condensate due\nto the rotation. In addition to fragmentation, the presence of many-body\ncorrelations is examined by computing the variances of the many-particle\nposition and momentum operators. For strong rotations, the many-body variances\nbecome smaller than their mean-field counterparts, and one even finds a\nscenario with opposite anisotropies of the mean-field and many-body variances.\nFurther, it is observed that for higher discrete symmetric systems of order k,\nnamely three-fold and four-fold symmetry, breakup to k sub-clouds and emergence\nof k-fold fragmentation take place. All in all, we provide a thorough many-body\ninvestigation of how and which correlations build up when a trapped\nBose-Einstein condensate breaks up under rotation."
    },
    {
        "anchor": "Expansion of a matter wave packet in a one-dimensional disordered\n  potential in the presence of a uniform bias force: We study numerically the expansion dynamics of an initially confined quantum\nwave packet in the presence of a disordered potential and a uniform bias force.\nFor white-noise disorder, we find that the wave packet develops asymmetric\nalgebraic tails for any ratio of the force to the disorder strength. The\nexponent of the algebraic tails decays smoothly with that ratio and no evidence\nof a critical behavior on the wave density profile is found. Algebraic\nlocalization features a series of critical values of the force-to-disorder\nstrength where the m-th position moment of the wave packet diverges. Below the\ncritical value for the m-th moment, we find fair agreement between the\nasymptotic long-time value of the m-th moment and the predictions of\ndiagrammatic calculations. Above it, we find that the m-th moment grows\nalgebraically in time. For correlated disorder, we find evidence of systematic\ndelocalization, irrespective to the model of disorder. More precisely, we find\na two-step dynamics, where both the center-of-mass position and the width of\nthe wave packet show transient localization, similar to the white-noise case,\nat short time and delocalization at sufficiently long time. This\ncorrelation-induced delocalization is interpreted as due to the decrease of the\neffective de Broglie wave length, which lowers the effective strength of the\ndisorder in the presence of finite-range correlations.",
        "positive": "Flipping-shuttle oscillations of bright one- and two-dimensional\n  solitons in spin-orbit-coupled Bose-Einstein condensates with Rabi mixing: We analyze a possibility of macroscopic quantum effects in the form of\ncoupled structural oscillations and shuttle motion of bright two-component\nspin-orbit-coupled striped (one-dimensional, 1D) and semi-vortex\n(two-dimensional, 2D) matter-wave solitons, under the action of linear mixing\n(Rabi coupling) between the components. In 1D, the intrinsic oscillations\nmanifest themselves as flippings between spatially even and odd components of\nstriped solitons, while in 2D the system features periodic transitions between\nzero-vorticity and vortical components of semi-vortex solitons. The\nconsideration is performed by means of a combination of analytical and\nnumerical methods."
    },
    {
        "anchor": "Freed by interaction kinetic states in the Harper model: We study the problem of two interacting particles in a one-dimensional\nquasiperiodic lattice of the Harper model. We show that a short or long range\ninteraction between particles leads to emergence of delocalized pairs in the\nnon-interacting localized phase. The properties of these Freed by Interaction\nKinetic States (FIKS) are analyzed numerically including the advanced Arnoldi\nmethod. We find that the number of sites populated by FIKS pairs grows\nalgebraically with the system size with the maximal exponent $b=1$, up to a\nlargest lattice size $N=10946$ reached in our numerical simulations, thus\ncorresponding to a complete delocalization of pairs. For delocalized FIKS pairs\nthe spectral properties of such quasiperiodic operators represent a deep\nmathematical problem. We argue that FIKS pairs can be detected in the framework\nof recent cold atom experiments [M.~Schreiber {\\it et al.} Science {\\bf 349},\n842 (2015)] by a simple setup modification. We also discuss possible\nimplications of FIKS pairs for electron transport in the regime of\ncharge-density wave and high $T_c$ superconductivity.",
        "positive": "Thermodynamics and structural transition of binary atomic Bose-Fermi\n  mixtures in box or harmonic potentials: A path-integral study: Experimental realizations of a variety of atomic binary Bose-Fermi mixtures\nhave brought opportunities for studying composite quantum systems with\ndifferent spin-statistics. The binary atomic mixtures can exhibit a structural\ntransition from a mixture into phase separation as the boson-fermion\ninteraction increases. By using a path-integral formalism to evaluate the grand\npartition function and thermodynamic grand potential, we obtain the effective\npotential of binary Bose-Fermi mixtures. Thermodynamic quantities in a broad\nrange of temperatures and interactions are also derived. The structural\ntransition can be identified as a loop of the effective potential curve, and\nthe volume fraction of phase separation can be determined by the lever rule.\nFor $^6$Li-$^7$Li and $^6$Li-$^{41}$K mixtures, we present the phase diagrams\nof the mixtures in a box potential at zero and finite temperatures. Due to the\nflexible densities of atomic gases, the construction of phase separation is\nmore complicated when compared to conventional liquid or solid mixtures where\nthe individual densities are fixed. For harmonically trapped mixtures, we use\nthe local density approximation to map out the finite-temperature density\nprofiles and present typical trap structures, including the mixture, partially\nseparated phases, and fully separated phases."
    },
    {
        "anchor": "Many-body properties of quasi-one dimensional Boson gas across a narrow\n  CIR: We study strong interaction effects in a one-dimensional (1D) Boson gas\nacross a narrow confinement induced resonance (CIR). In contrast to the zero\nrange potential, the 1D two-body interaction in the narrow CIR can be written\nas a polynomial of derivative $\\delta$-function interaction on many-body level.\nUsing the asymptotic Bethe ansatz, we find that the low energy physics of this\nmany-body problem is described by the Tomonaga-Luttinger liquid where the\nLuttinger parameters are essentially modified by an effective finite range\nparameter $v$. This parameter drastically alters quantum criticality and\nuniversal thermodynamics of the gas. In particular, it drives the\nTonks-Girardeau (TG) gas from non-mutual Fermi statistics to mutual statistics\nor to a more exclusive super TG gas. This novel feature is further discussed in\nterms of the breathing mode which is experimentally measurable.",
        "positive": "Spin diffusion in Fermi gases: We examine spin diffusion in a two-component homogeneous Fermi gas in the\nnormal phase. Using a variational approach, analytical results are presented\nfor the spin diffusion coefficient and the related spin relaxation time as a\nfunction of temperature and interaction strength. For low temperatures, strong\ncorrelation effects are included through the Landau parameters which we extract\nfrom Monte Carlo results. We show that the spin diffusion coefficient has a\nminimum for a temperature somewhat below the Fermi temperature with a value\nthat approaches the quantum limit $\\sim\\hbar/m$ in the unitarity regime where\n$m$ is the particle mass. We finally derive a value for the low temperature\nshear viscosity in the normal phase from the Landau parameters."
    },
    {
        "anchor": "Loss-induced phase separation and pairing for 3-species atomic lattice\n  fermions: We study the physics of a three-component Fermi gas in an optical lattice, in\nthe presence of a strong three-body constraint arising due to three-body loss.\nUsing analytical and numerical techniques, we show that an atomic color\nsuperfluid phase is formed in this system and undergoes phase separation\nbetween unpaired fermions and superfluid pairs. This phase separation survives\nwell above the critical temperature, giving a clear experimental signature of\nthe three-body constraint.",
        "positive": "Fermi gas throughout the BCS-BEC crossover: Comparative study of\n  t-matrix approaches with various degrees of self-consistency: The diagrammatic t-matrix approximation has often been adopted to describe a\ndilute Fermi gas. This approximation, originally considered by Galitskii for a\nrepulsive inter-particle interaction (Galitskii-1958), has later been widely\nutilized for an attractive Fermi gas to describe the BCS-BEC crossover from\nstrongly overlapping Cooper pairs in weak coupling to non-overlapping composite\nbosons in strong coupling. Several variants of the $t$-matrix approximation\nhave been considered in the literature, which are distinguished by the degree\nof self-consistency allowed in the building blocks of the diagrammatic\nstructure. Here, we perform a systematic and comparative study of all possible\nvariants on the degree of self-consistency for the $t$-matrix approximation in\nan attractive Fermi gas, which enables us to confront their outcomes for\nthermodynamic and dynamical quantities on the same footing in an unbiased way.\nFor definiteness, only the normal phase above the superfluid critical\ntemperature is considered. The dispute that can be raised in this context,\nabout the adequateness of introducing progressive degrees of self-consistency\nover and above the non-self-consistent $t$-matrix approximation for an\nattractive Fermi gas, parallels the recent interest in the literature on\nassessing the importance of various degrees of self-consistency in the context\nof semiconductors and insulators."
    },
    {
        "anchor": "Extended hydrodynamics of the degenerate partially spin polarized\n  fermions with the short-range interaction up to the third order by the\n  interaction radius approximation: A possibility of the hydrodynamic description of ultracold fermions via the\nmicroscopic derivation of the model is described. Differently truncated\nhydrodynamic models are derived and compared. All models are based on the\nmicroscopic many-particle Schr\\\"{o}dinger equation. Minimal coupling model\nbased on the continuity and Euler equations are considered. The extended\nhydrodynamic model including the independent dynamics of the momentum flux (the\npressure evolution) is derived. Influence of the spin polarization is\ndescribed. The short-range interaction is considered in the isotropic limit.\nThe interaction is considered up to the third order by the interaction radius.\nTherefore, the single fluid model of spin-1/2 fermions and the two fluid model\nof spin-1/2 fermions are under consideration in this paper. Spectra of bulk\ncollective excitations are derived and compared in terms of different models.",
        "positive": "Thermodynamic properties of rotating trapped ideal Bose gases: Ultracold atomic gases can be spined up either by confining them in rotating\nframe, or by introducing ``synthetic\" magnetic field. In this paper,\nthermodynamics of rotating ideal Bose gases are investigated within\ntruncated-summation approach which keeps to take into account the discrete\nnature of energy levels, rather than to approximate the summation over\nsingle-particle energy levels by an integral as does in semi-classical\napproximation. Our results show that Bose gases in rotating frame exhibit much\nstronger dependence on rotation frequency than those in ``synthetic\" magnetic\nfield. Consequently, BEC can be more easily suppressed in rotating frame than\nin ``synthetic\" magnetic field."
    },
    {
        "anchor": "Two-dimensional Bose-Einstein condensate under pressure: Evading the Mermin-Wagner-Hohenberg no-go theorem and revisiting with rigor\nthe ideal Bose gas confined in a square box, we explore a discrete phase\ntransition in two spatial dimensions. Through both analytic and numerical\nmethods we verify that thermodynamic instability emerges if the number of\nparticles is sufficiently yet finitely large: specifically $N\\geq 35131$. The\ninstability implies that the isobar of the gas zigzags on the\ntemperature-volume plane, featuring supercooling and superheating phenomena.\nThe Bose-Einstein condensation then can persist from absolute zero to the\nsuperheating temperature. Without necessarily taking the large $N$ limit, under\nconstant pressure condition, the condensation takes place discretely both in\nthe momentum and in the position spaces. Our result is applicable to a harmonic\ntrap. We assert that experimentally observed Bose-Einstein condensations of\nharmonically trapped atomic gases are a first-order phase transition which\ninvolves a discrete change of the density at the center of the trap.",
        "positive": "Exploring complex phenomena using ultracold atoms in bichromatic\n  lattices: With an underlying common theme of competing length scales, we study the\nmany-body Schr\\\"{o}dinger equation in a quasiperiodic potential and discuss its\nconnection with the Kolmogorov-Arnold-Moser (KAM) problem of classical\nmechanics. We propose a possible visualization of such connection in\nexperimentally accessible many-body observables. Those observables are useful\nprobes for the three characteristic phases of the problem: the metallic,\nAnderson and band insulator phases. In addition, they exhibit fingerprints of\nnon-linear phenomena such as Arnold tongues, bifurcations and devil's\nstaircases. Our numerical treatment is complemented with a perturbative\nanalysis which provides insight on the underlying physics. The perturbation\ntheory approach is particularly useful in illuminating the distinction between\nthe Anderson insulator and the band insulator phases in terms of paired sets of\ndimerized states."
    },
    {
        "anchor": "Coupled Hydrodynamics in Dipole-Conserving Quantum Systems: We investigate the coupled dynamics of charge and energy in interacting\nlattice models with dipole conservation. We formulate a generic hydrodynamic\ntheory for this combination of fractonic constraints and numerically verify its\napplicability to the late-time dynamics of a specific bosonic quantum system by\ndeveloping a microscopic non-equilibrium quantum field theory. Employing a\nself-consistent $1/N$ approximation in the number of field components, we\nextract all entries of a generalized diffusion matrix and determine their\ndependence on microscopic model parameters. We discuss the relation of our\nresults to experiments in ultracold atom quantum simulators.",
        "positive": "Rashbon bound states associated with a spherical spin-orbit coupling in\n  an ultracold Fermi gas with an $s$-wave interaction: We investigate the formation of rashbon bound states and strong-coupling\neffects in an ultracold Fermi gas with a spherical spin-orbit interaction,\n$H_{\\rm so}=\\lambda{\\bf p}\\cdot{\\bf \\sigma}$ (where ${\\bf\n\\sigma}=(\\sigma_x,\\sigma_y,\\sigma_z)$ are Pauli matrices). Extending the\nstrong-coupling theory developed by Nozi\\`eres and Schmitt-Rink (NSR) to\ninclude this spin-orbit coupling, we determine the superfluid phase transition\ntemperature $T_{\\rm c}$, as functions of the strength of a pairing interaction\n$U_s$, as well as the spin-orbit coupling strength $\\lambda$. Evaluating poles\nof the NSR particle-particle scattering matrix describing fluctuations in the\nCooper channel, we clarify the region where rashbon bound states dominate the\nsuperfluid phase transition in the $U_{s}$-$\\lambda$ phase diagram. Since the\nantisymmetric spin-orbit interaction $H_{\\rm so}$ breaks the inversion symmetry\nof the system, rashbon bound states naturally have, not only a spin-singlet and\neven-parity symmetry, but also a spin-triplet and odd-parity symmetry. Thus,\nour results would be also useful for the study of this parity mixing effect in\nthe BCS-BEC crossover regime of a spin-orbit coupled Fermi gas."
    },
    {
        "anchor": "Magnetic supersolid phases of two-dimensional extended Bose-Hubbard\n  model with spin-orbit coupling: The study of ultracold atomic spin systems with long-range interaction\nprovides the possibility of searching for magnetic supersolid phases in quantum\nmany-body scenarios. In this paper, we consider two-species Bose gases with\nspin-orbit coupling and nearest-neighbor interaction confined in a\ntwo-dimensional optical lattice. The competition between spin-orbit coupling\nand interactions creates rich ground-state diagrams with supersolid phases\nexhibiting phase modulations or magnetic orderings. We obtain the phase-twisted\nand phase-striped pair checkboard supersolid phases that are generated by the\ncombination of spin-orbit coupling and intraspecies nearest-neighbor\ninteraction. The introduction of interspecies nearest-neighbor interaction\nenriches the quantum phases of the system. It leads to the appearance of the\nphase-twisted and phase-striped lattice supersolid phases. In addition to the\nlattice supersolid phase, we find the emergence of nontrivial supersolid phases\nthat depend on the interspecies on-site interaction strength. The\nlattice-insulated supersolid phase with supersolidility in one species but\ninsulation in the other exists in the miscible domain, while the pair striped\nsupersolid phase with stripe structures in each species is in the immiscible\ndomain. Finally, to further characterize each phase, we discuss their\nspin-dependent momentum distributions and spin textures. The magnetic textures,\nsuch as antiferromagnetic, spiral and stripe orders, are shown in SS phases.\nThe results here could help in the observe for these magnetic supersolid phases\nin ultracold atomic experiments with nearest-neighbor interaction and\nspin-orbit coupling in optical lattice.",
        "positive": "Fermi-Liquid Behavior of the Normal Phase of a Strongly Interacting Gas\n  of Cold Atoms: We measure the magnetic susceptibility of a Fermi gas with tunable\ninteractions in the low-temperature limit and compare it to quantum Monte Carlo\ncalculations. Experiment and theory are in excellent agreement and fully\ncompatible with the Landau theory of Fermi liquids. We show that these measure-\nments shed new light on the nature of the excitations of the normal phase of a\nstrongly interacting Fermi gas."
    },
    {
        "anchor": "Orbital-driven melting of a bosonic Mott insulator in a shaken optical\n  lattice: In order to study the interplay between localized and dispersive orbital\nstates in a system of ultracold atoms in an optical lattice, we investigate the\npossibility to coherently couple the lowest two Bloch bands by means of\nresonant periodic forcing. Considering bosons in one dimension, it is shown\nthat a strongly interacting Floquet system can be realized, where at every\nlattice site two (and only two) near-degenerate orbital states are relevant. By\nsmoothly tuning both states into resonance we find that the system can undergo\nan orbital-driven Mott-insulator-to-superfluid transition. As an intriguing\nconsequence of the kinetic frustration in the system, this transition can be\neither continuous or first-order, depending on parameters such as lattice depth\nand filling.",
        "positive": "Lattice control of non-ergodicity in a polar lattice gas: Inter-site interactions in polar lattice gases may result, due to\nHilbert-space fragmentation, in a lack of ergodicity even in absence of\ndisorder. We show that the inter-site interaction in a one-dimensional dipolar\ngas in an optical lattice departs from the usually considered $1/r^3$\ndependence, acquiring a universal form that depends on the transversal\nconfinement and the lattice depth. Due to the crucial role played by the\nnearest- and next-to-nearest neighbors, the Hilbert-space fragmentation and\nparticle dynamics are very similar to that of a power-law model\n$1/r^{\\beta_{\\mathrm{eff}}<3}$, where $\\beta_{\\mathrm{eff}}$ is experimentally\ncontrollable by properly tailoring the transversal confinement. Our results are\nof direct experimental relevance for experiments on dipolar gases in optical\nlattices, and show that the particle dynamics may be remarkably different if\nthe quasi-1D lattice model is realized in a strong 3D lattice, or by means of a\nstrong transversal harmonic confinement."
    },
    {
        "anchor": "The improved Gaussian approximation Calculation of Bogoliubov Mode in\n  One Dimensional Bosonic Gas: In this paper, we study the homogeneous one-dimensional bosonic gas\ninteracting via a repulsive contact potential by using the improved Gaussian\napproximation. We obtain the gapless excitation spectrum of Bogoliubov mode.\nOur result is in good agreement with the exact numerical calculation based on\nthe Bethe ansatz. We speculate that the improved Gaussian approximation could\nbe a quantitatively good approximation for higher dimensional systems.",
        "positive": "Collective excitations across the BCS-BEC crossover induced by a\n  synthetic Rashba spin-orbit coupling: Synthetic non-Abelian gauge fields in cold atom systems produce a Rashba\nspin-orbit interaction described by a vector $\\blam = (\\lambda_x, \\lambda_y,\n\\lambda_z)$. It was recently shown [Phys. Rev. B 84, 014512 (2011)] that on\nincreasing $\\lambda = |\\blam|$, fermions at a finite density $\\rho\\approx\\kf^3$\nevolve to a BEC like state even in the presence of a weak attractive\ninteraction (described by a scattering length $\\as$). The BEC obtained at large\nspin-orbit coupling ($\\lambda \\gg k_F$) is a condensate of rashbons -- novel\nbosonic bound pairs of fermions whose properties are determined solely by the\ngauge field. Here we study the collective excitations of such superfluids by\nconstructing a Gaussian theory using functional integral methods. We derive\nexplicit expressions for superfluid phase stiffness, sound speed and mass of\nthe Anderson-Higgs boson that are valid for any $\\blam$ and scattering length.\nWe find that at finite $\\lambda$, the phase stiffness is always lower than that\nset by the density of particles, consistent with earlier work[arXiv:1110.3565]\nwhich attributed this to the lack of Galilean invariance of the system at\nfinite $\\lambda$. We show that there is an emergent Galilean invariance at\nlarge $\\lambda$, and the phase stiffness is determined by the rashbon density\nand mass, consistent with Leggett's theorem. We further demonstrate that the\nrashbon BEC state is a superfluid of anisotropic rashbons interacting via a\ncontact interaction characterized by a rashbon-rashbon scattering length $a_R$.\nWe show that $a_R$ goes as $\\lambda^{-1}$ and is essentially {\\em independent}\nof the scattering length between the fermions as long as it is nonzero.\nAnalytical results are presented for a rashbon BEC obtained in a spherical\ngauge field with $\\lambda_x = \\lambda_y = \\lambda_z =\n\\frac{\\lambda}{\\sqrt{3}}$."
    },
    {
        "anchor": "Beyond-mean-field corrections for dipolar bosons in an optical lattice: Recent experiments with ultracold lanthanide atoms which are characterized by\na large magnetic moment have revealed the crucial importance of\nbeyond-mean-field corrections in understanding the dynamics of the gas. We\nstudy how the presence of an external optical lattice modifies the structure of\nthe corrections. We find that deep in the superfluid regime the equation of\nstate is well described by introducing an anisotropic effective mass. However,\nfor a deep lattice we find terms with anomalous density dependence which do not\narise in free space. For a one-dimensional lattice, the relative orientation of\nthe dipole axis with respect to the lattice plays a crucial role and the\nbeyond-mean-field corrections can be either enhanced or suppressed.",
        "positive": "Deriving density-matrix functionals for excited states: We initiate the recently proposed $\\boldsymbol{w}$-ensemble one-particle\nreduced density matrix functional theory ($\\boldsymbol{w}$-RDMFT) by deriving\nthe first functional approximations and illustrate how excitation energies can\nbe calculated in practice. For this endeavour, we first study the symmetric\nHubbard dimer, constituting the building block of the Hubbard model, for which\nwe execute the Levy-Lieb constrained search. Second, due to the particular\nsuitability of $\\boldsymbol{w}$-RDMFT for describing Bose-Einstein condensates,\nwe demonstrate three conceptually different approaches for deriving the\nuniversal functional in a homogeneous Bose gas for arbitrary pair interaction\nin the Bogoliubov regime. Remarkably, in both systems the gradient of the\nfunctional is found to diverge repulsively at the boundary of the functional's\ndomain, extending the recently discovered Bose-Einstein condensation force to\nexcited states. Our findings highlight the physical relevance of the\ngeneralized exclusion principle for fermionic and bosonic mixed states and the\ncurse of universality in functional theories."
    },
    {
        "anchor": "Induced supersolidity in a normal and hardcore boson mixture: It is well known that the supersolid form of matter can arise in a single\nspecies of cold bosonic atoms in an optical lattice due to long range\ninteractions. We present a scenario where a supersolid is induced in one of the\ncomponents of a mixture of two species bosonic atoms where there is no long\nrange interactions. We study a system of normal and hardcore boson mixture with\nonly the former possessing long range interactions. We consider three cases:\nthe first where the total density is commensurate and the other two where they\nare incommensurate . By suitable choices of the densities and the interaction\nstrengths of the atoms, we predict that the charge density wave and the\nsupersolid orders can be induced in the hardcore species as a result of the\ncompeting interatomic interactions.",
        "positive": "Interspecies entanglement with impurity atoms in a lattice gas: The dynamics of impurity atoms introduced into bosonic gases in an optical\nlattice have generated a lot of recent interest, both in theory and experiment.\nWe investigate to what extent measurements on either the impurity species or\nthe majority species in these systems are affected by their interspecies\nentanglement. This arises naturally in the dynamics and plays an important role\nwhen we measure only one species. We explore the corresponding effects in\nstrongly interacting regimes, using a combination of few-particle analytical\ncalculations and Density Matrix Renormalisation group methods in one dimension.\nWe identify how the resulting effects on impurities can be used to probe the\nmany-body states of the majority species, and separately ask how to enter\nregimes where this entanglement is small, so that the impurities can be used as\nprobes that do not significantly affect the majority species. The results are\naccessible in current experiments, and provide important considerations for the\nmeasurement of complex systems with using few probe atoms."
    },
    {
        "anchor": "Superfluid filaments of dipolar bosons in free space: We systematically investigate the zero temperature phase diagram of bosons\ninteracting via dipolar interactions in three dimensions in free space via path\nintegral Monte Carlo simulations with few hundreds of particles and periodic\nboundary conditions based on the worm algorithm. Upon increasing the strength\nof the dipolar interaction and at sufficiently high densities we find a wide\nregion where filaments are stabilized along the direction of the external\nfield. Most interestingly by computing the superfluid fraction we conclude that\nsuperfluidity is anisotropic and is greatly suppressed along the orthogonal\nplane. Finally we perform simulations at finite temperature confirming the\nstability of filaments against thermal fluctuations and provide an estimate of\nthe superfluid fraction in the weak coupling limit in the framework of the\nLandau two-fluid model.",
        "positive": "Impurity induced quantum chaos for an ultracold bosonic ensemble in a\n  double-well: We demonstrate that an ultracold many-body bosonic ensemble confined in a\none-dimensional (1D) double-well (DW) potential can exhibit chaotic dynamics\ndue to the presence of a single impurity. The non-equilibrium dynamics is\ntriggered by a quench of the impurity-Bose interaction and is illustrated via\nthe evolution of the population imbalance for the bosons between the two wells.\nWhile the increase of the post-quench interaction strength always facilitates\nthe irregular motion for the bosonic population imbalance, it becomes regular\nagain when the impurity is initially populated in the highly excited states.\nSuch an integrability to chaos (ITC) transition is fully captured by the\ntransient dynamics of the corresponding linear entanglement entropy, whose\ninfinite-time averaged value additionally characterizes the edge of the chaos\nand implies the existence of an effective Bose-Bose attraction induced by the\nimpurity. In order to elucidate the physical origin for the observed ITC\ntransition, we perform a detailed spectral analysis for the mixture with\nrespect to both the energy spectrum as well as the eigenstates. Specifically,\ntwo distinguished spectral behaviors upon a variation of the interspecies\ninteraction strength are observed. While the avoided level-crossings take place\nin the low-energy spectrum, the energy levels in the high-energy spectrum\npossess a band-like structure and are equidistant within each band. This leads\nto a significant delocalization of the low-lying eigenvectors which, in turn,\naccounts for the chaotic nature of the bosonic dynamics. By contrast, those\nhighly excited states bear a high resemblance to the non-interacting integrable\nbasis, which explains for the recovery of the integrability for the bosonic\nspecies. Finally, we discuss the induced Bose-Bose attraction as well as its\nimpact on the bosonic dynamics."
    },
    {
        "anchor": "Measuring the topological phase transition via the single-particle\n  density matrix: We discuss the topological phase transition of the spin-$\\frac{1}{2}$\nfermionic Haldane model with repulsive on-site interaction. We show that the\nBerry curvature of the topological Hamiltonian, the first Chern number, and the\ntopological phase transition point can be extracted from the single-particle\ndensity matrix for this interacting system. Furthermore, we design a tomography\nscheme for the single-particle density matrix of interacting fermionic two-band\nmodels in experimental realizations with cold atoms in optical lattices.",
        "positive": "The creation of two-dimensional composite solitons in spin-orbit-coupled\n  self-attractive Bose-Einstein condensates in free space: It is commonly known that two-dimensional mean-field models of optical and\nmatter waves with the cubic self-attraction cannot produce stable solitons in\nfree space because of the occurrence of the collapse in the same setting. By\nmeans of the numerical analysis and variational approximation, we demonstrate\nthat the two-component model of the Bose-Einstein condensate, with the\nspin-orbit Rashba coupling and cubic attractive interactions, gives rise to\nsolitary-vortex complexes of two types: semi-vortices (SVs, with a vortex in\none component and a fundamental soliton in the other), and mixed modes (MMs,\nwith topological charges 0 and +1/-1 mixed in both components). These two-\ndimensional composite modes can be created using the trapping\nharmonic-oscillator (HO) potential, but remain stable in the free space, if the\ntrap is gradually removed. The SVs and MMs realize the ground state of the\nsystem, provided that the self-attraction in the two components is,\nrespectively, stronger or weaker than the cross-attraction between them. The\nSVs and MMs which are not the ground state are subject to a drift instability.\nIn the free space (in the absence of the HO trap), modes of both types\ndegenerate into unstable Townes solitons when their norms attain the respective\ncritical values, while there is no lower existence threshold for the stable\nmodes. Moving free-space stable solitons are also found in the present\nnon-Galilean-invariant system, up to a critical velocity. Collisions between\ntwo moving solitons lead to their merger into a single one."
    },
    {
        "anchor": "Phase Transitions of Repulsive Two-Component Fermi Gases in Two\n  Dimensions: We predict the phase separations of two-dimensional Fermi gases with\nrepulsive contact-type interactions between two spin components. Using\ndensity-potential functional theory with systematic semiclassical\napproximations, we address the long-standing problem of itinerant\nferromagnetism in realistic settings. We reveal a universal transition from the\nparamagnetic state at small repulsive interactions towards ferromagnetic\ndensity profiles at large interaction strengths, with intricate particle-number\ndependent phases in between. Building on quantum Monte Carlo results for\nuniform systems, we benchmark our simulations against Hartree-Fock calculations\nfor a small number of trapped fermions. We thereby demonstrate that our\nemployed corrections to the mean-field interaction energy and especially to the\nThomas-Fermi kinetic energy functional are necessary for reliably predicting\nproperties of trapped mesoscopic Fermi gases. The density patterns of the\nground state survive at low finite temperatures and confirm the Stoner-type\npolarization behavior across a universal interaction parameter, albeit with\nsubstantial quantitative differences that originate in the trapping potential\nand the quantum-corrected kinetic energy. We also uncover a zoo of metastable\nconfigurations that are energetically comparable to the ground-state density\nprofiles and are thus likely to be observed in experiments. We argue that our\ndensity-functional approach can be easily applied to interacting\nmulti-component Fermi gases in general.",
        "positive": "Spin-orbit-induced bound state and molecular signature of the degenerate\n  Fermi gas in a narrow Feshbach resonance: In this paper we explore the spin-orbit-induced bound state and molecular\nsignature of the degenerate Fermi gas in a narrow Feshbach resonance based on a\ngeneralized two-channel model. Without the atom-atom interactions, only one\nbound state can be found even if spin-orbit coupling exists. Moreover, the\ncorresponding bound-state energy depends strongly on the strength of spin-orbit\ncoupling, but is influenced slightly by its type. In addition, we find that\nwhen increasing the strength of spin-orbit coupling, the critical point at\nwhich the molecular fraction vanishes shifts from zero to the negative\ndetuning. In the weak spin-orbit coupling, this shifting is proportional to the\nsquare of its strength. Finally, we also show that the molecular fraction can\nbe well controlled by spin-orbit coupling."
    },
    {
        "anchor": "Optical control of a magnetic Feshbach resonance in ultracold Fermi\n  gases: We use laser light near-resonant with a molecular bound-to-bound transition\nto control a magnetic Feshbach resonance in ultracold Fermi gases of $^{40}$K\natoms. The spectrum of excited molecular states is measured by applying a laser\nfield that couples the ground Feshbach molecular state to electronically\nexcited molecular states. Nine strong bound-to-bound resonances are observed\nbelow the $^{2}P_{1/2}+^{2}S_{1/2}$ threshold. We use radio-frequency\nspectroscopy to characterize the laser-dressed bound state near a specific\nbound-to-bound resonance and show clearly the shift of the magnetic Feshbach\nresonance using light with negligible atomic loss. The demonstrated technology\ncould be used to modify interatomic interactions with high spatial and temporal\nresolutions in the crossover regime from a Bose-Einstein condensate (BEC) to a\nBardeen-Cooper-Schrieffer (BCS) superfluid.",
        "positive": "Phonon Stability and Sound Velocity of Quantum Droplets in a Boson\n  Mixture: Quantum droplets have been realized in experiments on binary boson mixtures\nand dipolar Bose gases. In these systems, the mean-field energy of the\nBose-Einstein condensation is attractive, and the repulsive Lee-Huang-Yang\nenergy is crucial for stability. The Bogoliubov theory incorrectly predicts\nthat the phonon mode is dynamically unstable in the long-wavelength limit. In\nthis work, we go beyond the Bogoliubov theory to study how the phonon mode is\nstabilized in the quantum droplet of a binary boson mixture. Similar to\nBeliaev's approach to a single-component Bose gas, we compute higher-order\ncontributions to the self-energy of the boson propagator. We find that the\ninteraction between spin and phonon excitations is the key for the phonon\nstability. We obtain the sound velocity which can be tested by measuring the\nsuperfluid critical velocity of the droplet in experiments. Beliaev damping of\nthis quantum droplet is also discussed."
    },
    {
        "anchor": "Universal Aspects of Vortex Reconnections across the BCS-BEC Crossover: Reconnecting vortices in a superfluid allow for the energy transfer between\ndifferent length scales and its subsequent dissipation. The present picture\nassumes that the dynamics of a reconnection is driven mostly by the phase of\nthe order parameter, and this statement can be justified in the case of\nBose-Einstein Condensates (BECs), where vortices have a simple internal\nstructure. Therefore, it is natural to postulate that the reconnection dynamics\nin the vicinity of the reconnection moment is universal. This expectation has\nbeen confirmed in numerical simulations for BECs and experimentally for the\nsuperfluid ${}^4$He. Not much has been said about this relation in the context\nof Fermi superfluids. In this article we aim at bridging this gap, and we\nreport our findings, which reveal that the reconnection dynamics conforms with\nthe predicted universal behaviour across the entire BCS-BEC crossover. The\nuniversal scaling also survives for spin-imbalanced systems, where unpaired\nfermions induce a complex structure of the colliding vortices.",
        "positive": "Penetration of a vortex dipole across an interface of Bose-Einstein\n  condensates: The dynamics of a vortex dipole in a quasi-two dimensional two-component\nBose-Einstein condensate are investigated. A vortex dipole is shown to\npenetrate the interface between the two components when the incident velocity\nis sufficiently large. A vortex dipole can also disappear or disintegrate at\nthe interface depending on its velocity and the interaction parameters."
    },
    {
        "anchor": "Dynamical spin-density waves in a spin-orbit-coupled Bose-Einstein\n  condensate: Synthetic spin-orbit (SO) coupling, an important ingredient for quantum\nsimulation of many exotic condensed matter physics, has recently attracted\nconsiderable attention. The static and dynamic properties of a SO coupled\nBose-Einstein condensate (BEC) have been extensively studied in both theory and\nexperiment. Here we numerically investigate the generation and propagation of a\n\\textit{dynamical} spin-density wave (SDW) in a SO coupled BEC using a fast\nmoving Gaussian-shaped barrier. We find that the SDW wavelength is sensitive to\nthe barrier's velocity while varies slightly with the barrier's peak potential\nor width. We qualitatively explain the generation of SDW by considering a\nrectangular barrier in a one dimensional system. Our results may motivate\nfuture experimental and theoretical investigations of rich dynamics in the SO\ncoupled BEC induced by a moving barrier.",
        "positive": "Quantum gas microscopy of Kardar-Parisi-Zhang superdiffusion: The Kardar-Parisi-Zhang (KPZ) universality class describes the coarse-grained\nbehavior of a wealth of classical stochastic models. Surprisingly, it was\nrecently conjectured to also describe spin transport in the one-dimensional\nquantum Heisenberg model. We test this conjecture by experimentally probing\ntransport in a cold-atom quantum simulator via the relaxation of domain walls\nin spin chains of up to 50 spins. We find that domain-wall relaxation is indeed\ngoverned by the KPZ dynamical exponent $z = 3/2$, and that the occurrence of\nKPZ scaling requires both integrability and a non-abelian SU(2) symmetry.\nFinally, we leverage the single-spin-sensitive detection enabled by the\nquantum-gas microscope to measure a novel observable based on spin-transport\nstatistics, which yields a clear signature of the non-linearity that is a\nhallmark of KPZ universality."
    },
    {
        "anchor": "Effective dynamics of a tracer particle in a dense homogeneous quantum\n  gas: We investigate the mean field regime of the dynamics of a tracer particle in\na homogenous quantum gas. For a bosonic gas, we show that this regime is\nconstrained by the well known requirement of an appropriate mean field scaling\nof the interaction. For fermions, however, we find an important qualitative\ndifference. Not only are fermions much more homogeneously distributed than\nbosons but also deviations from the mean are due only to fast degrees of\nfreedom in the gas. This observation leads to an explanation of why a tracer\nparticle behaves freely in the dense homogeneous fermion gas despite of a\nnon-scaled interaction, i.e., despite of non-vanishing statistical\nfluctuations. Finally, we indicate how the gained insight can be rigorously\njustified.",
        "positive": "Phase diagrams of tunable spin-orbit coupled Bose-Einstein condensates: We analytically calculate phase boundaries of tunable spin-orbit coupled BECs\nwith effective two-body interactions by using variational method. Phase\ndiagrams for periodically driving $^{87}\\rm{Rb}$ and $^{23}\\rm{Na}$ systems are\npresented, respectively, which display several characteristic features contrast\nwith those of undriven systems. In the $^{87}\\rm{Rb}$ BECs, the critical\ndensity $n_{c}$ (density at quantum tricritical point) can be dramatically\nreduced in some parameter regions, thus the prospect of observing this\nintriguing quantum tricritical point is greatly enlarged. Moreover, a series of\nquantum tricritical points emerge quasi-periodically with increasing the Raman\ncoupling strength for fixed $^{87}\\rm{Rb}$ density. In the $^{23}\\rm{Na}$ BECs,\ntwo hyperfine states of $^{23}\\rm{Na}$ atoms can be miscible due to driving\nunder proper parameters. As a result, $^{23}\\rm{Na}$ systems can stay in the\nstripe phase with small Raman frequency at typical density. This expands the\nregion of stripe phase in the phase diagram. In addition, there is no quantum\ntricritical point in such $^{23}\\rm{Na}$ system , which is different from\n$^{87}\\rm{Rb}$ system."
    },
    {
        "anchor": "Engineering photon statistics in a spinor polariton condensate: We implement full polarization tomography on the photon correlations in a\nspinor exciton-polariton condensate. Our measurements reveal condensate\npseudospin mean-field dynamics spanning from stochastic switching between\nlinear polarization components, limit cycles, and stable fixed points, and\ntheir intrinsic relation to the condensate photon statistics. We optically\nharness the cavity birefringence, polariton interactions, and the optical\norientation of the photoexcited exciton background to engineer photon\nstatistics with precise control. Our results demonstrate a smooth transition\nfrom a highly coherent to a super-thermal state of the condensate polarization\ncomponents.",
        "positive": "Densities probabilities of a Bose-Fermi Mixture in 1D Double well\n  potential: We use the two mode approximation for a interacting one-dimensional spinless\nsoft core bosons and one half spin fermions in a double-well potential with a\nlarge central barrier. We include all the on-site boson-boson, fermion-fermion\nand boson-fermion repulsive contact potential represented by delta-function and\nconsidered bosonic and fermionic isotopes of ytterbium(Yb) $^{170}Yb$ and\n$^{171}Yb$ respectively. By means of the approximation, we find that in the\nregime $U_{BF}>U_{BB}$ give rise to a immiscible phase and in the regime\n$U_{BB}\\geq U_{BF}$ give rise to a miscible phase, that is characterized by a\ntemporal overlap of the bosonic and fermionic probability densities. We also\nreport that due to the Bose-Fermi interaction, the system presents an apparent\ndestruction of the collapse-revival oscillation of boson density probability at\nleast in the ranges investigated."
    },
    {
        "anchor": "Modeling Particle Loss in Open Systems using Keldysh Path Integral and\n  Second Order Cumulant Expansion: For open quantum systems, integration of the bath degrees of freedom using\nthe second order cumulant expansion in the Keldysh path integral provides an\nalternative derivation of the effective action for systems coupled to general\nbaths. The baths can be interacting and not necessarily Markovian. Using this\nmethod in the Markovian limit, we compute the particle loss dynamics in various\nmodels of ultra-cold atomic gases including a one-dimensional Bose-Hubbard\nmodel with two-particle losses and a multi-component Fermi gas with\ninteractions tuned by an optical Feshbach resonance. We explicitly demonstrate\nthat the limit of strong two-body losses can be treated by formulating an\nindirect loss scheme to describe the bath-system coupling. The particle-loss\ndynamics thus obtained is valid at all temperatures. For the one-dimensional\nBose-Hubbard model, we compare it to solutions of the phenomenological rate\nequations. The latter are shown to be accurate at high temperatures.",
        "positive": "Stable Topological Superfluid Phase of Ultracold Polar Fermionic\n  Molecules: We show that single-component fermionic polar molecules confined to a 2D\ngeometry and dressed by a microwave field, may acquire an attractive $1/r^3$\ndipole-dipole interaction leading to superfluid p-wave pairing at sufficiently\nlow temperatures even in the BCS regime. The emerging state is the topological\n$p_x+ip_y$ phase promising for topologically protected quantum information\nprocessing. The main decay channel is via collisional transitions to dressed\nstates with lower energies and is rather slow, setting a lifetime of the order\nof seconds at 2D densities $\\sim 10^8$ cm$^{-2}$."
    },
    {
        "anchor": "Polar molecules in bilayers with high population imbalance: We investigate a dilute Fermi gas of polar molecules confined into a bilayer\nsetup with dipole moments polarized perpendicular to the layers. In particular,\nwe consider the extreme case of population imbalance, where we have only one\nparticle in one layer and many particles in the other one. The single molecule\nis attracted by the dilute Fermi-gas through the inter-layer dipole-dipole\nforce presenting an interesting impurity problem with longrange anistropic\ninteraction. We calulate the chemical potential of the impurity, in second\norder perturbation theory and in ladder approximation with a\nBrueckner-Hartree-Fock approach. Moreover, we determine the momentum relaxation\nrate of the impurity, which is related to the \"dipolar\" drag effect. For a\nconfined system we relate the results for the chemical potential with the\nmeasurement of the collective modes of the impurity. The momentum relaxation\nrate provide instead an estimate on how quickly the oscillations are damped.",
        "positive": "Atom-number squeezing and bipartite entanglement of two-component\n  Bose-Einstein condensates: analytical results: We investigate spin dynamics of a two-component Bose-Einstein condensates\nwith weak Josephson coupling. Analytical expressions of atom-number squeezing\nand bipartite entanglement are presented for atom-atom repulsive interactions.\nFor attractive interactions, there is no number squeezing; however, the\nsqueezing parameter is still useful to recognize the appearance of\nSchr\\\"{o}dinger's cat state."
    },
    {
        "anchor": "Density profile of interacting Fermions in a one-dimensional optical\n  trap: The density distribution of the one-dimensional Hubbard model in a harmonic\ntrapping potential is investigated in order to study the effect of the\nconfining trap. Strong superimposed oscillations are always present on top of a\nuniform density cloud, which show universal scaling behavior as a function of\nincreasing interactions. An analytical formula is proposed on the basis of\nbosonization, which describes the density oscillations for all interaction\nstrengths. The wavelength of the dominant oscillation changes with interaction,\nwhich indicates the crossover to a spin-incoherent regime. Using the Bethe\nansatz the shape of the uniform fermion cloud is analyzed in detail, which can\nbe described by a universal scaling form.",
        "positive": "Measuring the single-particle density matrix for fermions and hard-core\n  bosons in an optical lattice: Ultracold atoms in optical lattices provide clean, tunable, and well-isolated\nrealizations of paradigmatic quantum lattice models. With the recent advent of\nquantum-gas microscopes, they now also offer the possibility to measure the\noccupations of individual lattice sites. What, however, has not yet been\nachieved is to measure those elements of the single-particle density matrix,\nwhich are off-diagonal in the occupation basis. Here, we propose a scheme to\naccess these basic quantities both for fermions as well as hard-core bosons and\ninvestigate its accuracy and feasibility. The scheme relies on the engineering\nof a large effective tunnel coupling between distant lattice sites and a\nprotocol that is based on measuring site occupations after two subsequent\nquenches."
    },
    {
        "anchor": "Intertwined orders from symmetry projected wavefunctions of repulsively\n  interacting Fermi gases in optical lattices: Unconventional strongly correlated phases of the repulsive Fermi-Hubbard\nmodel, which could be emulated by ultracold vapors loaded in optical lattices,\nare investigated by means of energy minimizations with quantum number\nprojection before variation and without any assumed order parameter. In a\ntube-like geometry of optical plaquettes to realize the four-leg ladder Hubbard\nHamiltonian, we highlight the intertwining of spin-, charge-, and pair-density\nwaves embedded in a uniform d-wave superfluid background. As the lattice\nfilling increases, this phase emerges from homogenous states exhibiting spiral\nmagnetism and evolves towards a doped antiferromagnet. A concomitant\nenhancement of long-ranged d-wave pairing correlations is also found. Numerical\ntests of the approach for two-dimensional clusters are carried out, too.",
        "positive": "Two-body quench dynamics of harmonically trapped interacting particles: We consider the quantum evolution of a pair of interacting atoms in a three\ndimensional isotropic trap where the interaction strength is quenched from one\nvalue to another. Using exact solutions of the static problem we are able to\nevaluate time-dependent observables such as the overlap between initial and\nfinal states and the expectation value of the separation between the two atoms.\nIn the case where the interaction is quenched from the non-interacting regime\nto the strongly interacting regime, or vice versa, we are able to obtain\nanalytic results. Examining the overlap between the initial and final states we\nshow that when the interaction is quenched from the non-interacting to strongly\ninteracting regimes the early time dependence dynamics are consistent with\ntheoretical work in the single impurity many-body limit. When the system is\nquenched from the strongly to non-interacting regime we predict large\noscillations in the separation between the two atoms, which arises from a\nlogarithmic divergence due to the zero-range nature of the interaction\npotential."
    },
    {
        "anchor": "Interaction effects on dynamic correlations in non-condensed Bose gases: We consider dynamic, i.e., frequency-dependent, correlations in non-condensed\nultracold atomic Bose gases. In particular, we consider the single-particle\ncorrelation function and its power spectrum. We compute this power spectrum for\na one-component Bose gas, and show how it depends on the interatomic\ninteractions that lead to a finite single-particle relaxation time. As another\nexample, we consider the power spectrum of spin-current fluctuations for a\ntwo-component Bose gas and show how it is determined by the spin-transport\nrelaxation time.",
        "positive": "Self-consistent theory of Bose-Einstein condensate with impurity at\n  finite temperature: We study the properties of Bose-Einstein condensate (BEC)-impurity mixtures\nat finite temperature employing the Balian-V\\'en\\'eroni (BV) variational\nprinciple. The method leads to a set of coupled nonlinear equations of motion\nfor the condensate and its normal and anomalous fluctuations on the one hand,\nand for the impurity on the other. We show that the obtained equations satisfy\nthe energy and number conserving laws. Useful analytic expressions for the\nchemical potential and the radius of both condensate and anomalous components\nare derived in the framework of the Thomas-Fermi (TF) approximation in\n$d$-dimensional regime. Effects of the impurity on these quantities are\ndiscussed."
    },
    {
        "anchor": "Excitations of a binary supersolid: We predict a rich excitation spectrum of a binary dipolar supersolid in a\nlinear crystal geometry, where the ground state consists of two partially\nimmiscible components with alternating, interlocking domains. We identify three\nGoldstone branches, each with first-sound, second-sound or spin-sound\ncharacter. In analogy with a diatomic crystal, the resulting lattice has a\ntwo-domain primitive basis and we find that the crystal (first-sound-like)\nbranch is split into optical and acoustic phonons. We also find a spin-Higgs\nbranch that is associated with the supersolid modulation amplitude.",
        "positive": "Asymptotic behavior of correlation functions of one-dimensional\n  polar-molecules on optical lattices: We combine a slave-spin approach with a mean-field theory to develop an\napproximate theoretical scheme to study the density, spin, and, pairing\ncorrelation functions of fermionic polar molecules. We model the polar\nmolecules subjected to a one-dimensional periodic optical lattice potential\nusing a generalized $t-J$ model, where the long-range part of the interaction\nis included through the exchange interaction parameter. For this model, we\nderive a set of self-consistent equations for the correlation functions, and\nevaluate them numerically for the long-distance behaviour. We find that the\npairing correlations are related to spin correlations through the density and\nthe slave-spin correlations. Further, our calculations indicates that the\nlong-range character of the interaction can be probed through these correlation\nfunctions. In the absence of exact solutions for the one-dimensional $t-J$\nmodel, our approximate theoretical treatment can be treated as a useful tool to\nstudy one dimensional long-range correlated fermions."
    },
    {
        "anchor": "Many-body Multifractality throughout Bosonic Superfluid and Mott\n  Insulator Phases: We demonstrate many-body multifractality of the Bose-Hubbard Hamiltonian's\nground state in Fock space, for arbitrary values of the interparticle\ninteraction. Generalized fractal dimensions unambiguously signal, even for\nsmall system sizes, the emergence of a Mott insulator, that cannot, however, be\nnaively identified with a localized phase in Fock space. We show that the\nscaling of the derivative of any generalized fractal dimension with respect to\nthe interaction strength encodes the critical point of the superfluid to Mott\ninsulator transition, and provides an efficient way to accurately estimate its\nposition. We further establish that the transition can be quantitatively\ncharacterized by one single wavefunction amplitude from the exponentially large\nFock space.",
        "positive": "Crossover between snake instability and Josephson instability of dark\n  solitons in superfluid Fermi gases: Dark solitons in superfluid Bose gases decay through the snake instability\nmechanism, unless they are strongly confined. Recent experiments in superfluid\nFermi gases have also interpreted soliton decay via this mechanism. However, we\nshow using both an effective field numerical simulation and a perturbative\nanalysis that there is a qualitative difference between soliton decay in the\nBEC- and BCS-regimes. On the BEC-side of the interaction domain, the\ncharacteristic snaking deformations are induced by fluctuations of the\namplitude of the order parameter, while on the BCS-side, fluctuations of the\nphase destroy the soliton core through the formation of local Josephson\ncurrents. The latter mechanism is qualitatively different from the snaking\ninstability and this difference should be experimentally detectable."
    },
    {
        "anchor": "Estimation of phase diffusion rates in a condensate interferometer using\n  the Gross-Pitaevskii Equation: Atom interferometers using Bose-Einstein condensates are fundamentally\nlimited by a phase diffusion process that arises from atomic interactions. The\nGross-Pitaevskii equation is here used to accurately calculate the diffusion\nrate for a Bragg interferometer. It is seen to agree with a Thomas-Fermi\napproximation at large atom numbers and a perturbative approximation at low\natom numbers. The diffusion times obtained are generally longer than the\ncoherence times observed in experiments to date.",
        "positive": "Dimensional crossover of a boson gas in multilayers: We obtain the thermodynamic properties for a non-interacting Bose gas\nconstrained on multilayers modeled by a periodic Kronig-Penney delta potential\nin one direction and allowed to be free in the other two directions. We report\nBose-Einstein condensation (BEC) critical temperatures, chemical potential,\ninternal energy, specific heat, and entropy for different values of a\ndimensionless impenetrability $P\\geqslant 0$ between layers. The BEC critical\ntemperature $T_{c}$ coincides with the ideal gas BEC critical temperature\n$T_{0}$ when $P=0$ and rapidly goes to zero as $P$ increases to infinity for\nany finite interlayer separation. The specific heat $C_{V}$ \\textit{vs} $T$ for\nfinite $P$ and plane separation $a$ exhibits one minimum and one or two maxima\nin addition to the BEC, for temperatures larger than $T_{c}$ which highlights\nthe effects due to particle confinement. Then we discuss a distinctive\ndimensional crossover of the system through the specific heat behavior driven\nby the magnitude of $P$. For $T<T_{c}$ the crossover is revealed by the change\nin the slope of $\\log C_{V}(T)$ and when $T>T_{c}$, it is evidenced by a broad\nminimum in $C_{V}(T)$."
    },
    {
        "anchor": "Dynamic freezing of strongly correlated ultracold bosons: We study the non-equilibrium dynamics of ultracold bosons in an optical\nlattice with a time dependent hopping amplitude J(t)=J_0 +\\delta J \\cos(\\omega\nt) which takes the system from a superfluid phase near the Mott-superfluid\ntransition (J= J_0+\\delta J) to a Mott phase (J=J_0-\\delta J) and back through\na quantum critical point (J=J_c) and demonstrate dynamic freezing of the boson\nwavefunction at specific values of \\omega. At these values, the wavefunction\noverlap F (defect density P=1-F) approaches unity (zero). We provide a\nqualitative explanation of the freezing phenomenon, show it's robustness\nagainst quantum fluctuations and the presence of a trap, compute residual\nenergy and superfluid order parameter for such dynamics, and suggest\nexperiments to test our theory.",
        "positive": "Asymptotically perfect efficient quantum state transfer across uniform\n  chains with two impurities: The ability to transfer quantum information from one location to another with\nhigh fidelity is of central importance to quantum information science.\nUnfortunately for the simplest system of a uniform chain (a spin chain or a\nparticle in a one-dimensional lattice), the state transfer time grows\nexponentially in the chain length $N$ at fixed fidelity. In this work we show\nthat the addition of an impurity near each endpoint, coupled to the uniform\nchain with strength $w$, is sufficient to ensure efficient and high-fidelity\nstate transfer. An eigenstate localized in the vicinity of the impurity can be\ntuned into resonance with chain extended states by tuning $w(N)\\propto\nN^{1/2}$; the resulting avoided crossing yields resonant eigenstates with large\namplitudes on the chain endpoints and approximately equidistant eigenvalues.\nThe state transfer time scales as $t\\propto N^{3/2}$ and its fidelity $F$\napproaches unity in the thermodynamic limit $N\\to\\infty$; the error scales as\n$1-F\\propto N^{-1}$. Thus, with the addition of two impurities, asymptotically\nperfect state transfer with a uniform chain is possible even in the absence of\nexternal control."
    },
    {
        "anchor": "Reaching the quantum Hall regime with rotating Rydberg-dressed atoms: Despite the striking progress in the field of quantum gases, one of their\nmuch anticipated application -- the simulation of quantum Hall states --\nremains elusive: all experimental approaches so far failed in reaching a\nsufficiently small ratio between atom and vortex densities. In this paper we\nconsider rotating Rydberg--dressed atoms in magnetic traps: these gases offer\nstrong and tunable non-local repulsive interactions and very low densities;\nhence they provide an exceptional platform to reach the quantum Hall regime.\nBased on the Lindemann criterion and the analysis of the interplay of the\nlength scales of the system, we show that there exists an optimal value of the\ndressing parameters that minimizes the ratio between the filling factor of the\nsystem and its critical value to enter the Hall regime, thus making it possible\nto reach this strongly--correlated phase for more than 1000 atoms under\nrealistic conditions.",
        "positive": "Entanglement entropy in low-energy field theories at finite chemical\n  potential: We investigate the leading area-law contribution to entanglement entropy in a\nsystem described by a general Lagrangian with O(2) symmetry containing first-\nand second-order time derivatives, namely breaking the Lorentz-invariance. We\nestablish a connection between the Higgs gap present in a symmetry-broken phase\nand the area-law term for the entanglement entropy in the general,\nnon-relativistic case. Our predictions for the entanglement entropy and\ncorrelation length are successfully compared to numerical results in two\nparadigmatic systems: the Mott insulator to superfluid transition for ultracold\nlattice bosons, and the ground state of ferrimagnetic systems."
    },
    {
        "anchor": "Observation of 2D fermionic Mott insulators of $^{40}$K with single-site\n  resolution: We report on the site-resolved observation of characteristic states of the\ntwo-dimensional repulsive Fermi-Hubbard model, using ultracold $^{40}$K atoms\nin an optical lattice. By varying the tunneling, interaction strength, and\nexternal confinement, we realize metallic, Mott-insulating, and band-insulating\nstates. We directly measure the local moment, which quantifies the degree of\non-site magnetization, as a function of temperature and chemical potential.\nEntropies per particle as low as $0.99(6)\\,k_B$ indicate that nearest-neighbor\nantiferromagnetic correlations should be detectable using spin-sensitive\nimaging.",
        "positive": "Pseudopotentials for an ultracold dipolar gas: A gas of ultracold molecules interacting via the long-range dipolar potential\noffers a highly controlled environment in which to study strongly correlated\nphases. However, at particle coalescence the divergent $1/r^3$ dipolar\npotential and associated pathological wavefunction hinder computational\nanalysis. For a dipolar gas constrained to two dimensions we overcome these\nnumerical difficulties by proposing a pseudopotential that is explicitly smooth\nat particle coalescence, resulting in a 2000-times speedup in diffusion Monte\nCarlo calculations. The pseudopotential delivers the scattering phase shifts of\nthe dipolar interaction with an accuracy of $10^{-5}$ and predicts the energy\nof a dipolar gas to an accuracy of $10^{-4}E_\\mathrm{F}$ in a diffusion Monte\nCarlo calculation."
    },
    {
        "anchor": "Efficient conversion of closed-channel dominated Feshbach molecules of\n  $^{23}$Na$^{40}$K to their absolute ground state: We demonstrate the transfer of $^{23}$Na$^{40}$K molecules from a\nclosed-channel dominated Feshbach-molecule state to the absolute ground state.\nThe Feshbach molecules are initially created from a gas of sodium and potassium\natoms via adiabatic ramping over a Feshbach resonance at 78.3$\\,$G. The\nmolecules are then transferred to the absolute ground state using stimulated\nRaman adiabatic passage with an intermediate state in the spin-orbit-coupled\ncomplex $|c^3 \\Sigma^+, v=35, J=1 \\rangle \\sim |B^1\\Pi, v=12, J=1\\rangle$. Our\nmeasurements show that the pump transition dipole moment linearly increases\nwith the closed-channel fraction. Thus, the pump-beam intensity can be two\norders of magnitude lower than is necessary with open-channel dominated\nFeshbach molecules. We also demonstrate that the phase noise of the Raman\nlasers can be reduced by filter cavities, significantly improving the transfer\nefficiency.",
        "positive": "Exactly Solvable Points and Symmetry-Protected Topological Phases of\n  Quantum Spins on a Zig-Zag Lattice: A large number of symmetry-protected topological (SPT) phases have been\nhypothesized for strongly interacting spin-1/2 systems in one dimension.\nRealizing these SPT phases, however, often demands fine-tunings hard to reach\nexperimentally. And the lack of analytical solutions hinders the understanding\nof their many-body wave functions. Here we show that two kinds of SPT phases\nnaturally arise for ultracold polar molecules confined in a zigzag optical\nlattice. This system, motivated by recent experiments, is described by a spin\nmodel whose exchange couplings can be tuned by an external field to reach\nparameter regions not studied before for spin chains or ladders. Within the\nenlarged parameter space, we find the ground state wave function can be\nobtained exactly along a line and at a special point, for these two phases\nrespectively. These exact solutions provide a clear physical picture for the\nSPT phases and their edge excitations. We further obtain the phase diagram by\nusing infinite time-evolving block decimation, and discuss the phase\ntransitions between the two SPT phases and their experimental signatures."
    },
    {
        "anchor": "Simulating the Palmer-Chalker state in an orbital superfluid: We consider a bosonic $s$ and $p$ orbital system in a face-centered cubic\n(FCC) optical lattice, and predict a fluctuation-induced instability towards\nthe orbital analogue of Palmer-Chalker state, which is originally proposed in\nan electronic spin system. For bosons loaded in the FCC optical lattice, the\nsingle-particle spectrum has four degenerate band minima with their crystal\nmomenta forming a tetrahedron in Brillouin zone. In the weakly interacting\nregime, the ensuing many-particle ground state, at the classical level,\nunderlies a four-sublattice tetrahedral supercell of spontaneously generated\n$p$-orbital angular momenta through the Bravias-Bloch duality between real and\nmomentum space, and is macroscopically degenerate originating from the\ngeometric frustration. The fluctuations on top of the classical ground state\nlift its degeneracy and select the Palmer-Chalker ordering of $p$-orbital\nangular momenta as the quantum ground state through order-by-disorder\nmechanism. These findings raise the exciting possibility of simulating the\nPalmer-Chalker state with its orbital counterpart in ultracold atomic gases.",
        "positive": "Exact calculation of phonon effects on spin squeezing: Theoretical models of spins coupled to bosons provide a simple setting for\nstudying a broad range of important phenomena in many-body physics, from\nvirtually mediated interactions to decoherence and thermalization. In many\natomic, molecular, and optical systems, such models also underlie the most\nsuccessful attempts to engineer strong, long-ranged interactions for the\npurpose of entanglement generation. Especially when the coupling between the\nspins and bosons is strong---such that it cannot be treated\nperturbatively---the properties of such models are extremely challenging to\ncalculate theoretically. Here, exact analytical expressions for nonequilibrium\nspin-spin correlation functions are derived for a specific model of spins\ncoupled to bosons. The spatial structure of the coupling between spins and\nbosons is completely arbitrary, and thus the solution can be applied to systems\nin any number of dimensions. The explicit and nonperturbative inclusion of the\nbosons enables the study of entanglement generation (in the form of spin\nsqueezing) even when the bosons are driven strongly and near-resonantly, and\nthus provides a quantitative view of the breakdown of adiabatic elimination\nthat inevitably occurs as one pushes towards the fastest entanglement\ngeneration possible. The solution also helps elucidate the effect of finite\ntemperature on spin squeezing. The model considered is relevant to a variety of\natomic, molecular, and optical systems, such as atoms in cavities or trapped\nions. As an explicit example, the results are used to quantify phonon effects\nin trapped ion quantum simulators, which are expected to become increasingly\nimportant as these experiments push towards larger numbers of ions."
    },
    {
        "anchor": "Reply to Comment by Wolfgang Ketterle on \"Electromagnetic Wave Dynamics\n  in Matter-Wave Superradiant Scattering\" (see arXiv:1010.3915): The Comment by Wolfgang Ketterle (Ref.[1]) purports to present a viable model\nof superradiance in condensates. However, Ref.[1] is not able to explain the\nred/blue pump detuning asymmetry that was first observed recently by us\n(Ref.[2]). It is clear from our original paper (Ref.[3]) that the\nrate-equation-based theories of Ref.[1] are incomplete since they only model\nthe final growth stage of the process when a red-detuned pump is used. Our\ntheoretical framework (Ref.[3]), on the other hand, also treats the initial\ngrowth stage of superradiance and is therefore also capable of explaining the\ngenesis of the red/blue detuning asymmetry (Ref.[2]). This is the key message\nof our response, which we frame in terms of reference to the specific points\nraised in Ref. [1].",
        "positive": "State-to-state endothermic and nearly thermoneutral reactions in an\n  ultracold atom-dimer mixture: Chemical reactions at ultracold temperature provide an ideal platform to\nstudy chemical reactivity at the fundamental level, and to understand how\nchemical reactions are governed by quantum mechanics. Recent years have\nwitnessed the remarkable progress in studying ultracold chemistry with\nultracold molecules. However, these works were limited to exothermic reactions.\nThe direct observation of state-to-state ultracold endothermic reaction remains\nelusive. Here we report on the investigation of endothermic and nearly\nthermoneutral atom-exchange reactions in an ultracold atom-dimer mixture. By\ndeveloping an indirect reactant-preparation method based on a molecular\nbound-bound transition, we are able to directly observe a universal endothermic\nreaction with tunable energy threshold and study the state-to-state reaction\ndynamics. The reaction rate coefficients show a strikingly threshold\nphenomenon. The influence of the reverse reaction on the reaction dynamics is\nobserved for the endothermic and nearly thermoneutral reactions. We carry out\nzero-range quantum mechanical scattering calculations to obtain the reaction\nrate coefficients, and the three-body parameter is determined by comparison\nwith the experiments. The observed endothermic and nearly thermoneutral\nreaction may be employed to implement collisional Sisyphus cooling of\nmolecules, study the chemical reactions in degenerate quantum gases and conduct\nquantum simulation of Kondo effect with ultracold atoms."
    },
    {
        "anchor": "Local spectral density of an interacting one-dimensional Bose gas with\n  an impurity: A weakly interacting Bose gas with a single static impurity is studied in one\ndimension. The local spectral density is evaluated and an analytic expression\nvalid for positive strengths of the impurity coupling to the bosons, at all\ndistances and at all frequencies is obtained using the Bogoliubov-de Gennes\napproximation.",
        "positive": "Deviation from Universality in Collisions of Ultracold $^6$Li$_2$\n  Molecules: Collisions of $^6$Li$_2$ molecules with free $^6$Li atoms reveal a striking\ndeviation from universal predictions based on long-range van der Waals\ninteractions. Li$_2$ closed-channel molecules are formed in the highest\nvibrational state near a narrow Feshbach resonance, and decay via two-body\ncollisions with Li$_2$, Li, and Na. For Li$_2$+Li$_2$ and Li$_2$+Na, the decay\nrates agree with the universal predictions of the quantum Langevin model. In\ncontrast, the rate for Li$_2$+Li is exceptionally small, with an upper bound\nten times smaller than the universal prediction. This can be explained by the\nlow density of available decay states in systems of light atoms [G.\nQu\\'em\\'ener, J.-M. Launay, and P. Honvault, Phys. Rev. A \\textbf{75}, 050701\n(2007)], for which such collisions have not been studied before."
    },
    {
        "anchor": "Collective excitations of a charged Fermi superfluid in the BCS-BEC\n  crossover: We consider collective excitations in the superfluid state of Fermi condensed\ncharged gases. The dispersion and damping of collective excitations at nonzero\ntemperatures are examined, and the coexistence and interaction of different\nbranches of collective excitations: plasma oscillations, pair-breaking Higgs\nmodes, and Carlson-Goldman phonon-like excitations are taken into account. The\npath integral methods for superfluid Fermi gases and for Coulomb gas are\ncombined into a unified formalism that extends the Gaussian fluctuation\napproximation to account for plasmonic modes. This approximation of Gaussian\npair and density fluctuations is able to describe all branches of collective\nexcitations existing in a charged superfluid. The spectra of collective\nexcitations are determined in two ways: from the spectral functions and from\nthe complex poles of the fluctuation propagator. A resonant avoided crossing of\ndifferent modes is shown. It is accompanied by resonant enhancement of the\nresponse provided by the pair-breaking modes due to their interaction with\nplasma oscillations. This may facilitate the experimental observation of the\npair-breaking modes.",
        "positive": "Interplay of interaction and disorder in the steady state of an open\n  quantum system: Many types of dissipative processes can be found in nature or be engineered,\nand their interplay with a system can give rise to interesting phases of\nmatter. Here we study the interplay among interaction, tunneling, and disorder\nin the steady state of a spin chain coupled to a tailored bath. We consider a\ndissipation which, in contrast to disorder, tends to generate a homogeneously\npolarized steady state. We find that the steady state can be highly sensitive\neven to weak disorder. We also establish that, in the presence of such\ndissipation, even in the absence of interaction, a finite amount of disorder is\nneeded for localization. Last, we show that for strong disorder the system\nreveals signatures of localization both in the weakly and strongly interacting\nregimes."
    },
    {
        "anchor": "Lack of a genuine time crystal in a chiral soliton model: In a recent publication [Phys. Rev. Lett. {\\bf 124}, 178902] \\\"Ohberg and\nWright claim that in a chiral soliton model it is possible to realize a genuine\ntime crystal which corresponds to a periodic evolution of an inhomogeneous\nprobability density in the lowest energy state. We show that this result is\nincorrect and present a solution which possesses lower energy with the\ncorresponding probability density that does not reveal any motion. It implies\nthat the authors' conclusion that a genuine time crystal can exist in the\nsystem they consider is not true.",
        "positive": "Composite-boson formalism applied to strongly bound fermion pairs in a\n  one-dimensional trap: We analyze a system of fermions in a one-dimensional harmonic trap with\nattractive delta-interactions between different fermions species, as an\napproximate description of experiments involving atomic dimers. We solve the\nproblem of two fermion pairs numerically using the so-called ''coboson\nformalism'' as an alternative to techniques which are based on the\nsingle-particle basis. This allows us to explore the strongly bound regime,\napproaching the limit of infinite attraction in which the composite particles\nbehave as hard-core bosons. Our procedure is computationally inexpensive and\nillustrates how the coboson toolbox is useful for ultracold atom systems even\nin absence of condensation."
    },
    {
        "anchor": "The Universality and stability for a dilute Bose gas with a Feshbach\n  resonance: We study the bosonic atoms with a wide Feshbach resonance at zero temperature\nin terms of the renormalization group. We indicate that this system will always\ncollapse in the dilute limit. On the side with a positive scattering length,\nthe atomic superfluid is an unstable local minimum in the dilute limit and it\ndetermines the thermodynamics of this system within its lifetime. We calculate\nthe equilibrium properties at zero temperature in the unitary regime. They\nexhibit universal scaling forms in the dilute limit due to the presence of a\nnontrivial zero temperature, zero density fixed point. Moreover, we find that\nthe T=0 thermodynamics of this system in the unitary limit is exactly identical\nto the one for an ideal Fermi gas.",
        "positive": "Dimensional Crossover in a Spin-imbalanced Fermi gas: We model the one-dimension (1D) to three-dimension (3D) crossover in a\ncylindrically trapped Fermi gas with attractive interactions and\nspin-imbalance. We calculate the mean-field phase diagram, and study the\nrelative stability of exotic superfluid phases as a function of interaction\nstrength and temperature. For weak interactions and low density, we find\n1D-like behavior, which repeats as a function of the chemical potential as new\nchannels open. For strong interactions, mixing of single-particle levels gives\n3D-like behavior at all densities. Furthermore, we map the system to an\neffective 1D model, finding significant density dependence of the effective 1D\nscattering length."
    },
    {
        "anchor": "Capillary Flotation in a System of Two Immiscible Bose-Einstein\n  Condensates: A spatially inhomogeneous, trapped two-component Bose-Einstein condensate of\ncold atoms in the phase separation mode has been numerically simulated. It has\nbeen demonstrated for the first time that the surface tension between the\ncomponents makes possible the existence of drops of a denser phase floating on\nthe surface of a less dense phase. Depending on the harmonic trap anisotropy\nand other system parameters, a stable equilibrium of the drop is achieved\neither at the poles or at the equator. The drop flotation sometimes persists\neven in the presence of an attached quantized vortex.",
        "positive": "Detecting chiral pairing and topological superfluidity using circular\n  dichroism: Realising and probing topological superfluids is a key goal for fundamental\nscience, with exciting technological promises. Here, we show that chiral\n$p_x+ip_y$ pairing in a two-dimensional topological superfluid can be detected\nthrough circular dichroism, namely, as a difference in the excitation rates\ninduced by a clockwise and counter-clockwise circular drive. For weak pairing,\nthis difference is to a very good approximation determined by the Chern number\nof the superfluid, whereas there is a non-topological contribution scaling as\nthe superfluid gap squared that becomes signifiant for stronger pairing. This\ngives rise to a competition between the experimentally driven goal to maximise\nthe critical temperature of the superfluid, and observing a signal given by the\nunderlying topology. Using a combination of strong coupling Eliashberg and\nBerezinskii-Kosterlitz-Thouless theory, we analyse this tension for an atomic\nBose-Fermi gas, which represents a promising platform for realising a chiral\nsuperfluid. We identify a wide range of system parameters where both the\ncritical temperature is high and the topological contribution to the dichroic\nsignal is dominant."
    },
    {
        "anchor": "Bound vortex states and exotic lattices in multi-component Bose-Einstein\n  condensates: The role of vortex-vortex interaction: We numerically study the vortex-vortex interaction in multi-component\nhomogeneous Bose-Einstein condensates within the realm of the Gross-Pitaevskii\ntheory. We provide strong evidences that pairwise vortex interaction captures\nthe underlying mechanisms which determine the geometric configuration of the\nvortices, such as different lattices in many-vortex states, as well as the\nbound vortex states with two (dimer) or three (trimer) vortices. Specifically,\nwe discuss and apply our theoretical approach to investigate intra- and\ninter-component vortex-vortex interactions in two- and three-component\nBose-Einstein condensates, thereby shedding light on the formation of the\nexotic vortex configurations. These results correlate with current experimental\nefforts in multi-component Bose-Einstein condensates, and the understanding of\nthe role of vortex interactions in multiband superconductors.",
        "positive": "Vortex interactions in the collision of Bose-Einstein condensates: We investigate the effects of vortex interaction on the formation of\ninterference patterns in a coherent pair of two-dimensional Bose condensed\nclouds of ultra-cold atoms traveling in opposite directions subject to a\nharmonic trapping potential. We identify linear and nonlinear regimes in the\ndipole oscillations of the condensates according to the balance of internal and\ncentre-of-mass energies of the clouds. Simulations of the collision of two\nclouds each containing a vortex with different winding number (charge) were\ncarried out in these regimes in order to investigate the creation of varying\ninterference patterns. The interaction between different vortex type can be\nclearly distinguished by those patterns."
    },
    {
        "anchor": "Capture Dynamics of Ultracold Atoms in the Presence of an Impurity Ion: We explore the quantum dynamics of a one-dimensional trapped ultracold\nensemble of bosonic atoms triggered by the sudden creation of a single ion. The\nnumerical simulations are performed by means of the ab initio\nmulticonfiguration time-dependent Hartree method for bosons which takes into\naccount all correlations. The dynamics is analyzed via a cluster expansion\napproach, adapted to bosonic systems of fixed particle number, which provides a\ncomprehensive understanding of the occurring many-body processes. After a\ntransient during which the atomic ensemble separates into fractions which are\nunbound and bound with respect to the ion, we observe an oscillation in the\natomic density which we attribute to the additional length and energy scale\ninduced by the attractive long-range atom-ion interaction. This oscillation is\nshown to be the main source of spatial coherence and population transfer\nbetween the bound and the unbound atomic fraction. Moreover, the dynamics\nexhibits collapse and revival behavior caused by the dynamical build-up of\ntwo-particle correlations demonstrating that a beyond mean-field description is\nindispensable.",
        "positive": "Feshbach resonances in a nonseparable trap: We consider a pair of atoms in an arbitrary trapping potential in the\npresence of magnetically tunable Feshbach resonance. We find the energy levels\nand occupation of the bound molecular states taking into account possible\ncoupling between center of mass and relative motion induced by the trap. As a\nspecific example we discuss the case of different atomic species in harmonic\npotential, where each atom feels different trapping frequency."
    },
    {
        "anchor": "Synthetic charge-flux quantum liquids: We apply rotating optical flux lattices to spinor Bose-Einstein condensates.\nDistinct quantum states emerge for fractional ratios of vortex charge density\nto optical flux density. We exhibit the calculated charge-flux states and\ndiscuss their topological structure and experimental signatures.",
        "positive": "Thermodynamics of Attractive and Repulsive Fermi Gases in Two Dimensions: We study the attractive and repulsive two-component Fermi gas with spin\nimbalance in two dimensions. Using a generalized $T$-matrix approximation, we\nexamine the thermodynamic properties of both attractive and repulsive contact\ninteracting Fermi gases. The interaction strength, which is characterized by\nthe bound state energy $E_b=\\hbar^2/m a_{2d}^2$ in vacuum, can be adjusted\nthrough a Feshbach resonance. We calculate the interaction energy,\ncompressibility and spin susceptibility of the two branches of the Fermi gas.\nFor the repulsive branch, we also find a critical strength of interaction\n$a_{2d}^{(c)}$ above which this metastable thermodynamic state becomes\nunstable. This critical value depends on the temperature and the spin imbalance\n(the \"magnetization\") of the system."
    },
    {
        "anchor": "Pairing correlations of cold fermionic gases at overflow from a narrow\n  to a wide harmonic trap: Within the context of Hartree-Fock-Bogoliubov theory, we study the behavior\nof superfluid Fermi systems when they pass from a small to a large container.\nSuch systems can be now realized thanks to recent progress in experimental\ntechniques. It will allow to better understand pairing properties at overflow\nand in general in rapidly varying external potentials.",
        "positive": "Impurity in a zero-temperature three-dimensional Fermi gas: We consider an impurity in a sea of zero-temperature fermions uniformly\ndistributed throughout the space. The impurity scatters on fermions. On\naverage, the momentum of impurity decreases with time as $t^{-1/(d+1)}$ in $d$\ndimensions, and the momentum distribution acquires a scaling form in the long\ntime limit. We solve the Lorentz-Boltzmann equation for the scaled momentum\ndistribution of the impurity in three dimensions. The solution is a combination\nof confluent hypergeometric functions. In two spatial dimensions, the\nLorentz-Boltzmann equation is analytically intractable, so we merely extract a\nfew exact predictions about asymptotic behaviors when the scaled momentum of\nthe impurity is small or large."
    },
    {
        "anchor": "Rashbon condensation in a Bose gas with Rashba spin-orbit coupling: We show that in a two-component Bose gas with Rashba spin-orbit coupling\n(SOC) two atoms can form bound states (Rashbons) with any intra-species\nscattering length. At zero center-of-mass momentum there are two degenerate\nRashbons due to time-reversal symmetry, but the degeneracy is lifted at finite\nin-plane momentum with two different effective masses. A stable Rashbon\ncondensation can be created in a dilute system with weakly attractive\nintra-species and repulsive inter-species interactions. The critical\ntemperature of Rashbon condensation is about six times smaller than the BEC\ntransition temperature of an ideal Bose gas. Due Rashba SOC, excitations in the\nRashbon condensation phase are anisotropic in momentum space.",
        "positive": "Evolution of the Pseudogap in a polarized Fermi gas: We calculate the single particle spectral density of a normal\n(non-superfluid) two component gas of fermions in the BCS-BEC crossover within\na T-matrix approximation. We review how non-condensed pairs lead to a spectral\ndensity reminiscent of the ordered state, and explore how a gap-like feature in\nthe spectrum evolves as one changes the polarization of the gas. As the gas is\npolarized we find that this pseudogap becomes more diffuse and moves away from\nthe Fermi level, reflecting the fact that fewer pairs are present but that they\nstill play an important role in the excitations."
    },
    {
        "anchor": "Curved vortex surfaces in four-dimensional superfluids: II.\n  Equal-frequency double rotations: As is well-known, two-dimensional and three-dimensional superfluids under\nrotation can support topological excitations such as quantized point vortices\nand line vortices respectively. Recently, we have studied how, in a\nhypothetical four-dimensional (4D) superfluid, such excitations can be\ngeneralised to vortex planes and surfaces. In this paper, we continue our\nanalysis of skewed and curved vortex surfaces based on the 4D Gross-Pitaevskii\nequation, and show that certain types of such states can be stabilised by\nequal-frequency double rotations for suitable parameters. This work extends the\nrich phenomenology of vortex surfaces in 4D, and raises interesting questions\nabout vortex reconnections and the competition between various vortex\nstructures which have no direct analogue in lower dimensions.",
        "positive": "Potential and Feshbach $s$-wave resonances in coupled atomic collision\n  channels: We discuss $s$-wave scattering in an atomic binary collision with two coupled\nchannels, tunable by an external magnetic field, one channel open and the other\nclosed for the incident energies considered. The analysis is performed with a\nstylized model of square-well potentials. This simplification allows for a\npedagogically thorough discussion of the different scattering resonances that\nappear in coupled channels. One of the them, the potential resonances at\nvanishing energy, occur as a bound state of the coupled system emerges, in\nturned tuned at a very precise value of the external field. The other\nresonances, described by Feshbach theory, occur when the incident energy is\nnear a bound state of the closed channel, as if it were decoupled from the open\nchannel. These resonances exist for values of the external field above a\nparticular threshold value. Besides the potential intrinsic value of this study\nin a quantum mechanics course, as the analysis can be performed with minor\nnumerical calculations, it is also an aid for the understanding of current\nresearch advances in the exciting field of ultracold gases."
    },
    {
        "anchor": "Fermionization of a Few-Body Bose System Immersed into a Bose-Einstein\n  Condensate: We study the recently introduced self-pinning transition [Phys. Rev. Lett.\n128, 053401 (2022)] in a quasi-one-dimensional two-component quantum gas in the\ncase where the component immersed into the Bose-Einstein condensate has a\nfinite intraspecies interaction strength. As a result of the matter-wave\nbackaction, the fermionization in the limit of infinite intraspecies repulsion\noccurs via a first-order phase transition to the self-pinned state, which is in\ncontrast to the asymptotic behavior in static trapping potentials. The system\nalso exhibits an additional superfluid state for the immersed component if the\ninterspecies interaction is able to overcome the intraspecies repulsion. We\napproximate the superfluid state in an analytical model and derive an\nexpression for the phase transition line that coincides with well-known phase\nseparation criteria in binary Bose systems. The full phase diagram of the\nsystem is mapped out numerically for the case of two and three atoms in the\nimmersed component.",
        "positive": "Robust and Ultrafast State Preparation by Ramping Artificial Gauge\n  Potentials: The implementation of static artificial magnetic fields in ultracold atomic\nsystems has become a powerful tool, e.g. for simulating quantum-Hall physics\nwith charge-neutral atoms. Taking an interacting bosonic flux ladder as a\nminimal model, we investigate protocols for adiabatic state preparation via\nmagnetic flux ramps. Considering the fact that it is actually the artificial\nvector potential (in the form of Peierls phases) that can be experimentally\nengineered in optical lattices, rather than the magnetic field, we find that\nthe time required for adiabatic state preparation dramatically depends on which\npattern of Peierls phases is used. This can be understood intuitively by noting\nthat different patterns of time-dependent Peierls phases that all give rise to\nthe same magnetic field ramp, generally lead to different artificial electric\nfields during the ramp. Remarkably, we find that an optimal choice allows for\npreparing the ground state almost instantaneously. We relate this observation\nto shortcuts to adiabaticity via counterdiabatic driving. Our findings open new\npossibilities for robust state preparation in atomic quantum simulators."
    },
    {
        "anchor": "Rapidly Rotating Fermions in an Anisotropic Trap: We consider a cold gas of non-interacting fermions in a two dimensional\nharmonic trap with two different trapping frequencies $\\omega_x \\leq \\omega_y$,\nand discuss the effect of rotation on the density profile. Depending on the\nrotation frequency $\\Omega$ and the trap anisotropy $\\omega_y/\\omega_x$, the\ndensity profile assumes two qualitatively different shapes. For small\nanisotropy ($\\omega_y/\\omega_x \\ll \\sqrt{1+4 \\Omega^2/\\omega_x^2}$), the\ndensity consists of elliptical plateaus of constant density, corresponding to\nLandau levels and is well described by a two dimensional local density\napproximation. For large anisotropy ($\\omega_y/\\omega_x \\gg \\sqrt{1+4\n\\Omega^2/\\omega_x^2}$), the density profile is Gaussian in the strong confining\ndirection and semicircular with prominent Friedel oscillations in the weak\ndirection. In this regime, a one dimensional local density approximation is\nwell suited to describe the system. The crossover between the two regimes is\nsmooth where the step structure between the Landau level edges turn into\nFriedel oscillations. Increasing the temperature causes the step structure or\nthe Friedel oscillations to wash out leaving a Boltzmann gas density profile.",
        "positive": "Hydrodynamic signatures and spectral properties of the quantum vortex: We characterize the low-lying excitations of a quantum vortex in a\nquasi-two-dimensional Bose-Einstein condensate (BEC) using the standard\ndefinition of the density of states (DOS) and a modified version that is\nsensitive to complementary aspects of the excitation's spectrum. The latter\nproves to be particularly relevant to studying the polaronic state realized\nwhen an impurity is embedded in a quantum vortex. We establish that the\nimpurity becomes sensitive to the transversal fluctuations of the vortex, via\nits remnant kelvon mode, and to the phase fluctuations of the BEC\nNambu-Goldstone mode. The presence of the vortex yields an anomalous excitation\nspectrum with a finite energy gap and non-linear DOS at low energies. We find\nthat the high sensitivity of the kelvon mode to external potentials provides a\nchannel of quantum-level control over impurities trapped in a vortex. This\nextra control channel may be of practical use for the proposal of using\nvortex-trapped impurities as qubit units for quantum information processing."
    },
    {
        "anchor": "Route to observing topological edge modes in ultracold fermions: We show how to exploit the rich hyperfine structure of fermionic alkali atoms\nto produce a quasi-1D topological superfluid while avoiding excessive heating\nfrom off-resonant scattering. We model interacting fermions where four\nhyperfine states are coupled by a variety of optical and microwave fields. We\ncalculate the local density of states in a trap, finding regimes with zero\nenergy topological edge modes. Heating rates in this system are significantly\nsuppressed compared to simple Raman-induced spin-orbit coupling approaches.",
        "positive": "Theoretical confirmation of Feynman's hypothesis on the creation of\n  circular vortices in Bose-Einstein condensates: III: In two preceding papers (Infeld and Senatorski 2003 J. Phys.: Condens. Matter\n15 5865, and Senatorski and Infeld 2004 J. Phys.: Condens. Matter 16 6589) the\nauthors confirmed Feynman's hypothesis on how circular vortices can be created\nfrom oppositely polarized pairs of linear vortices (first paper), and then gave\nexamples of the creation of several different circular vortices from one linear\npair (second paper). Here in part III, we give two classes of examples of how\nthe vortices can interact. The first confirms the intuition that the\nreconnection processes which join two interacting vortex lines into one,\npractically do not occur. The second shows that new circular vortices can also\nbe created from pairs of oppositely polarized coaxial circular vortices. This\nseems to contradict the results for such pairs given in Koplik and Levine 1996\nPhys. Rev. Lett. 76 4745."
    },
    {
        "anchor": "Evidence of Potts-Nematic Superfluidity in a Hexagonal $sp^2$ Optical\n  Lattice: As in between liquid and crystal phases lies a nematic liquid crystal, which\nbreaks rotation with preservation of translation symmetry, there is a nematic\nsuperfluid phase bridging a superfluid and a supersolid. The nematic order also\nemerges in interacting electrons and has been found to largely intertwine with\nmulti-orbital correlation in high-temperature superconductivity, where Ising\nnematicity arises from a four-fold rotation symmetry $C_4$ broken down to\n$C_2$. Here we report an observation of a three-state ($\\mathbb{Z}_3$) quantum\nnematic order, dubbed \"Potts-nematicity\", in a system of cold atoms loaded in\nan excited band of a hexagonal optical lattice described by an $sp^2$-orbital\nhybridized model. This Potts-nematic quantum state spontaneously breaks a\nthree-fold rotation symmetry of the lattice, qualitatively distinct from the\nIsing nematicity. Our field theory analysis shows that the Potts-nematic order\nis stabilized by intricate renormalization effects enabled by strong\ninter-orbital mixing present in the hexagonal lattice. This discovery paves a\nway to investigate quantum vestigial orders in multi-orbital atomic\nsuperfluids.",
        "positive": "Current-Phase Relation of a Bose-Einstein Condensate Flowing Through a\n  Weak Link: We study the current-phase relation of a Bose-Einstein condensate flowing\nthrough a repulsive square barrier by solving analytically the one dimensional\nGross-Pitaevskii equation. The barrier height and width fix the current-phase\nrelation $j(\\delta\\phi)$, which tends to $j\\sim\\cos(\\delta\\phi/2)$ for weak\nbarriers and to the Josephson sinusoidal relation $j\\sim\\sin(\\delta\\phi)$ for\nstrong barriers. Between these two limits, the current-phase relation depends\non the barrier width. In particular, for wide enough barriers, we observe two\nfamilies of multivalued current-phase relations. Diagrams belonging to the\nfirst family, already known in the literature, can have two different positive\nvalues of the current at the same phase difference. The second family, new to\nour knowledge, can instead allow for three different positive currents still\ncorresponding to the same phase difference. Finally, we show that the\nmultivalued behavior arises from the competition between hydrodynamic and\nnonlinear-dispersive components of the flow, the latter due to the presence of\na soliton inside the barrier region."
    },
    {
        "anchor": "Strongly Interacting Two-component Coupled Bose Gas in Optical Lattices: Two-component coupled Bose gas in a 1D optical lattice is examined. In\naddition to the postulated Mott insulator and superfluid phases, multiple\nbosonic components manifest spin degrees of freedom. Coupling of the components\nin the Bose gas leads to substantial change in the previously observed spin\nphases, giving rise to new effective spin Hamiltonian and unraveling remarkable\nspin correlations. The system exhibiting ferromagnetic and non-ferromagnetic\nspin phases for on-site intra-component interaction stronger than\ninter-component interaction switches from first-order to second-order phase\ntransition between the spin phases upon introduction of coupling, on which is\ndependent the transition width. For comparable on-site inter- and intra-\ncomponent interaction, with coupling, instead of one, two spin phases emerge\nwith a second-order phase transition. Exact diagonalization and Variational\nMonte Carlo (VMC) with stochastic minimization on Entangled Plaquette State\n(EPS) bestow a unique and enhanced perspective into the system beyond the scope\nof a mean-field treatment.",
        "positive": "Quantized vortices in interacting gauge theories: We consider a two-dimensional weakly interacting ultracold Bose gas whose\nconstituents are two-level atoms. We study the effects of a synthetic\ndensity-dependent gauge field that arises from laser-matter coupling in the\nadiabatic limit with a laser configuration such that the single-particle\nzero-order vector potential corresponds to a constant synthetic magnetic field.\nWe find a new exotic type of current non-linearity in the Gross-Pitaevskii\nequation which affects the dynamics of the order parameter of the condensate.\nWe investigate the rotational properties of this system, focusing in particular\non the physical conditions that make the nucleation of a quantized vortex in\nthe system energetically favourable with respect to the non rotating solution.\nWe point out that two different physical interpretations can be given to this\nnew non linearity: firstly it can be seen as a local modification of the mean\nfield coupling constant, whose value depends on the angular momentum of the\ncondensate. Secondly, it can be interpreted as a density modulated angular\nvelocity given to the cloud. Looking at the problem from both of these\nviewpoints, we analyze the physical conditions that make a single vortex state\nenergetically favourable. In the Thomas-Fermi limit, we show that the effect of\nthe new nonlinearity is to induce a rotation to the condensate, where the\ntransition from non-rotating to rotating states depends on the density of the\ncloud."
    },
    {
        "anchor": "Virial coefficients of trapped and un-trapped three-component fermions\n  with three-body forces in arbitrary spatial dimensions: Using a coarse temporal lattice approximation, we calculate the first few\nterms of the virial expansion of a three-species fermion system with a\nthree-body contact interaction in $d$ spatial dimensions, both in homogeneous\nspace as well as in a harmonic trapping potential of frequency $\\omega$. Using\nthe three-body problem to renormalize, we report analytic results for the\nchange in the fourth- and fifth-order virial coefficients $\\Delta b_4$ and\n$\\Delta b_5$ as functions of $\\Delta b_3$. Additionally, we argue that in the\n$\\omega \\to 0$ limit the relationship $b_n^\\text{T} = n^{-d/2} b_n$ holds\nbetween the trapped (T) and homogeneous coefficients for arbitrary temperature\nand coupling strength (not merely in scale-invariant regimes). Finally, we\npoint out an exact, universal (coupling- and frequency-independent)\nrelationship between $\\Delta b_3^\\text{T}$ in 1D with three-body forces and\n$\\Delta b_2^\\text{T}$ in 2D with two-body forces.",
        "positive": "Finite-temperature dynamics of a Tonks-Girardeau gas in a\n  frequency-modulated harmonic trap: We study the out-of-equilibrium dynamics of a finite-temperature harmonically\ntrapped Tonks-Girardeau gas induced by periodic modulation of the trap\nfrequency. We give explicit exact solutions for the real-space density and\nmomentum distributions of this interacting many-body system and characterize\nthe stability diagram of the dynamics by mapping the many-body solution to the\nsolution and stability diagram of Mathieu's differential equation. The mapping\nallows one to deduce the exact structure of parametric resonances in the\nparameter space characterized by the driving amplitude and frequency of the\nmodulation. Furthermore, we analyze the same problem within the\nfinite-temperature hydrodynamic approach and show that the respective solutions\nto the hydrodynamic equations can be mapped to the same Mathieu equation.\nAccordingly, the stability diagram and the structure of resonances following\nfrom the hydrodynamic approach is exactly the same as those obtained from the\nexact many-body solution."
    },
    {
        "anchor": "Sub-second production of a quantum degenerate gas: Realizing faster experimental cycle times is important for the future of\nquantum simulation. The cycle time determines how often the many-body\nwave-function can be sampled, defining the rate at which information is\nextracted from the quantum simulation. We demonstrate a system which can\nproduce a Bose-Einstein condensate of $8 \\times 10^4$ $^{168}\\text{Er}$ atoms\nwith approximately 85% condensate fraction in 800 ms and a degenerate Fermi gas\nof $^{167}\\text{Er}$ in 4 seconds, which are unprecedented times compared to\nmany existing quantum gas experiments. This is accomplished by several novel\ncooling techniques and a tunable dipole trap. The methods used here for\naccelerating the production of quantum degenerate gases should be applicable to\na variety of atomic species and are promising for expanding the capabilities of\nquantum simulation.",
        "positive": "The approach to vortex reconnection: We present numerical solutions of the Gross--Pitaevskii equation\ncorresponding to reconnecting vortex lines. We determine the separation of\nvortices as a function of time during the approach to reconnection, and study\nthe formation of pyramidal vortex structures. Results are compared with\nanalytical work and numerical studies based on the vortex filament method."
    },
    {
        "anchor": "Fate of the Higgs mode near quantum criticality: We study the relativistic O(N) field theory near the quantum critical point\nin 2+1 dimensions for N=2 and N=3. The scalar susceptibility is evaluated by\nMonte Carlo simulation. We show that the spectrum contains a peak associated\nwith the Higgs mode, which remains well-defined all the way to the critical\npoint. The fidelity of this peak and the amplitude ratio between the critical\nenergy scales on both sides of the transition are computed.",
        "positive": "Weyl Bogoliubov excitations in Bose-Hubbard extension of Weyl semimetal: In this paper, a Bose-Hubbard extension of a Weyl semimetal is proposed that\ncan be realized for ultracold atoms using laser assisted tunneling and Feshbach\nresonance technique in three dimensional optical lattices. The global phase\ndiagram is obtained consisting of a superfluid phase and various Mott insulator\nphases by using Landau theory. The Bogoliubov excitation modes for the weakly\ninteracting case have nontrivial properties (Weyl nodes, bosonic surface arc,\netc.) analogs of those in Weyl semimetals of electronic systems, which are\nsmoothly carried over to that of Bloch bands for the noninteracting case. The\nproperties of the insulating phases for the strongly interacting case are\nexplored by calculating both the quasiparticle and quasihole dispersion\nrelation, which shows two quasiparticle spectra touch at Weyl nodes."
    },
    {
        "anchor": "Non-equilibrium $8\u03c0$ Josephson Effect in Atomic Kitaev Wires: We theoretically study a Kitaev wire interrupted by an extra site which gives\nrise to super exchange coupling between two Majorana bound states. We show that\nthis system hosts a tunable, non-equlibrium Josephson effect with a\ncharacteristic $8\\pi$ periodicity of the Josephson current. We elucidate the\nphysical mechanism deriving a minimal model for the junction and confirm its\nquantitative accuracy by comparison to the numerical solution of the full\nmodel. The visibility of the $8\\pi$ periodicity of the Josephson current is\nthen studied using time-dependent simulations including the effects of\ndephasing and particle losses. Our findings provide a novel signature of\nMajorana quasi-particles which is qualitatively different form the behavior of\na conventional superconductor, and can be experimentally verified in cold atom\nsystems using alkaline-earth-like atoms.",
        "positive": "Bright dipolar Bose-Einstein condensate soliton mobile in a direction\n  perpendicular to polarization: We demonstrate stable, robust, bright dipolar Bose-Einstein condensate (BEC)\nsolitons, moving in a direction perpendicular to the polarization direction,\nformed due to dipolar interaction for repulsive contact interaction. At medium\nvelocity the head on collision of two such solitons is found to be quasi\nelastic with practically no deformation. Upon small perturbation the solitons\nare found to exhibit sustained breathing oscillation. The findings are\nillustrated by numerical simulation using the 3D mean-field Gross-Pitaevskii\nequation and a reduced 2D model in three and two spatial dimensions employing\nrealistic interaction parameters for a dipolar $^{164}$Dy BEC."
    },
    {
        "anchor": "Precise measurements on a quantum phase transition in antiferromagnetic\n  spinor Bose-Einstein condensates: We have experimentally investigated the quench dynamics of antiferromagnetic\nspinor Bose-Einstein condensates in the vicinity of a zero temperature quantum\nphase transition at zero quadratic Zeeman shift $q$. The rate of instability\nshows good agreement with predictions based upon solutions to the Bogoliubov\nde-Gennes equations. A key feature of this work was removal of magnetic field\ninhomogeneities, resulting in a steep change in behavior near the transition\npoint. The quadratic Zeeman shift at the transition point was resolved to 250\nmilliHertz uncertainty, equivalent to an energy resolution of $k_B \\times 12$\npicoKelvin. To our knowledge, this is the first demonstration of sub-Hz\nprecision measurement of a phase transition in quantum gases. Our results point\nto the use of dynamics, rather than equilibrium studies for high precision\nmeasurements of phase transitions in quantum gases.",
        "positive": "Berry phase, entanglement entropy, and algebraic properties of ground\n  states of BCS and BEC superfluids: By using Bogoliubov transformations to construct the ground states of\nfermionic Bardeen-Cooper-Schrieffer (BCS) superfluids and weakly-interacting\nBose gases supporting Bose Einstein Condensation (BEC), their algebraic\nstructures and implications can be analyzed in detail. Both ground states are\ngeneralized squeezed coherent states saturating a generalized Heisenberg\nuncertainty relation, and they acquire quantized Berry phases when the\ncorresponding systems are transported along a closed path in their parameter\nspaces. While the Berry phase of the BCS ground state depends on the total\nparticle number, the Berry phase of the BEC ground state depends only on the\nparticles outside the BEC. The Berry phases are associated with magnetic\nmonopoles in the parameter spaces and we found that the Dirac quantization\ncondition is satisfied. Moreover, both ground states are entangled states of\nthe fermion or boson quanta and we found the entanglement entropy quantifying\nthe internal correlations. A fixed particle-number approach of fermionic\nsuperfluids does not saturate the generalized uncertainty relation, exhibits\ninternal entanglement, and gives corresponding Berry phase. In addition, the\nalgebraic structures of the ground states can be classified by the $q$-deformed\nHopf algebra, $\\bigoplus_{\\mathbf{k}}h_{q_{\\mathbf{k}}}(1)$ for bosons and\n$q$-deformed Hopf superalgebra $\\bigoplus_{\\mathbf{k}}h_{q_{\\mathbf{k}}}(1|1)$\nfor fermions, respectively."
    },
    {
        "anchor": "Emergent Quasicrystalline Symmetry in Light-Induced Quantum Phase\n  Transitions: The discovery of quasicrystals with crystallographically forbidden rotational\nsymmetries has changed the notion of the ordering in materials, yet little is\nknown about the dynamical emergence of such exotic forms of order. Here we\ntheoretically study a nonequilibrium cavity-QED setup realizing a\nzero-temperature quantum phase transition from a homogeneous Bose-Einstein\ncondensate to a quasicrystalline phase via collective superradiant light\nscattering. Across the superradiant phase transition, collective light\nscattering creates a dynamical, quasicrystalline optical potential for the\natoms. Remarkably, the quasicrystalline potential is \"emergent\" as its\neight-fold rotational symmetry is not present in the Hamiltonian of the system,\nrather appears solely in the low-energy states. For sufficiently strong\ntwo-body contact interactions between atoms, a quasicrystalline order is\nstabilized in the system, while for weakly interacting atoms the condensate is\nlocalized in one or few of the deepest minima of the quasicrystalline\npotential.",
        "positive": "Dipole excitons in coupled quantum wells: toward an equilibrium exciton\n  condensate: In recent years, experiments by several groups have demonstrated spontaneous\ncoherence in polariton systems, which can be viewed as a type of nonequilibrium\nBose-Einstein condensation. In these systems, the polariton lifetime is longer\nthan, but not much longer than, the polariton-polariton scattering time which\nleads to the thermalization. By contrast, over the past twenty years several\ngroups have pursued experiments in a different system, which has very long\nexciton lifetime, up to 30 microseconds or more, essentially infinite compared\nto the thermalization time of the excitons. Thermal equilibrium of this type of\nexciton in a trap has been demonstrated experimentally. In this system, the\ninteractions between the excitons are not short-range contact interactions, but\ninstead are dipole-dipole interactions, with the force at long range going as\n$1/r^{3}$. Up to now there has not been a universally accepted demonstration of\nBEC in this type of system, and the way forward will require better\nunderstanding of the many-body effects of the excitons. I review what has been\nlearned and accomplished in the past two decades in the search for an\nequilibrium BEC in this promising system."
    },
    {
        "anchor": "Fourth- and fifth-order virial expansion of harmonically trapped\n  fermions at unitarity: By generalizing our automated algebra approach from homogeneous space to\nharmonically trapped systems, we have calculated the fourth- and fifth-order\nvirial coefficients of universal spin-1/2 fermions in the unitary limit,\nconfined in an isotropic harmonic potential. We present results for said\ncoefficients as a function of trapping frequency (or, equivalently,\ntemperature), which compare favorably with previous Monte Carlo calculations\n(available only at fourth order) as well as with our previous estimates in the\nuntrapped limit (high temperature, low frequency). We use our estimates of the\nvirial expansion, together with resummation techniques, to calculate the\ncompressibility and spin susceptibility.",
        "positive": "Dark soliton collisions in superfluid Fermi gases: In this work dark soliton collisions in a one-dimensional superfluid Fermi\ngas are studied across the BEC-BCS crossover by means of a recently developed\nfinite-temperature effective field theory [S. N. Klimin, J. Tempere, G.\nLombardi, J. T. Devreese, Eur. Phys. J. B 88, 122 (2015)] . The evolution of\ntwo counter-propagating solitons is simulated numerically based on the theory's\nnonlinear equation of motion for the pair field. The resulting collisions are\nobserved to introduce a spatial shift into the trajectories of the solitons.\nThe magnitude of this shift is calculated and studied in different conditions\nof temperature and spin-imbalance. When moving away from the BEC-regime, the\ncollisions are found to become inelastic, emitting the lost energy in the form\nof small-amplitude density oscillations. This inelasticity is quantified and\nits behavior analyzed and compared to the results of other works. The\ndispersion relation of the density oscillations is calculated and is\ndemonstrated to show a good agreement with the spectrum of collective\nexcitations of the superfluid."
    },
    {
        "anchor": "Field-induced long-lived supermolecules: We demonstrate that the long-lived bound states (super-molecules) can exist\nin the dilute limit when we tune the shape of effective potential between polar\nmolecules by an external microwave field. Binding energies, average sizes, and\nphase diagrams for both s-orbital (bosons) and p-orbital (fermions) dimers are\nstudied, together with bosonic trimer states. We explicitly show that the non-\nadiabatic transition rate can be easily tuned small for such ground state\nsuper-molecules, so that the system can be stable from collapse even near the\nassociated potential resonance. Our results, therefore, suggest a feasible cold\nmolecule system to investigate both novel few-body and many-body physics (for\nexample, the p-wave BCS-BEC crossover for fermions and the paired condensate\nfor bosons) that can not be easily accessed in single species atomic gases.",
        "positive": "Model for two-body collisions between ultracold dipolar molecules around\n  a F\u00f6rster resonance in an electric field: We propose a one-channel, simple model to describe the dynamics of ultracold\ndipolar molecules around a F\\\"orster resonance. Slightly above a specific\nelectric field, a collisional shielding can take place, suppressing the\nmolecular losses in a gas. The overall description of the quantum physical\nmechanism comes back to the dynamics on a unique energy surface, which depends\non the relative distance and angular approach of the molecules. This surface\nenables to interpret how the dipole moments of the molecules are induced and\ninterlocked by the electric field and the dipole-dipole interaction during the\nprocess, especially when the shielding is triggered. Averaging the relative\nangular motion over a unique partial wave (the lowest one when the ultracold\nregime is reached), the model reproduces well the behaviour of the rate\ncoefficients observed experimentally and predicted theoretically [Matsuda et\nal., Science 370, 1324 (2020); Li et al., Nat. Phys. 17, 1144 (2021)]. This\neconomic model encapsulates the main physics of the quantum process. Therefore,\nit can be used as an alternative to a full quantum dynamical treatment and is\npromising for future studies of collisions involving more bodies."
    },
    {
        "anchor": "Emergence of the Unconventional Type-II Nambu-Goldstone Modes with\n  Topological Origin in Bose Superfluids: The Nambu-Goldstone (NG) modes in a nonrelativistic system can be classified\ninto two types from their characteristic features: being of either an odd (type\nI) or an even (type II) power energy-momentum dispersion. Conventionally, the\ntype-II NG modes may universally arise from spontaneous breaking of\nnoncommutative symmetry pairs. Here, we predict a novel type of quadratically\ndispersed NG modes that emerges in mixed $s$ and $p$ band Bose superfluids in\nan optical lattice and, unlike the conventional type-II NG modes, cannot be\nsolely interpreted with the celebrated symmetry-based argument. Instead, we\nshow that the existence of such modes has a profound connection to the\ntopological transition on projective complex order-parameter space. The\ndetection scheme is also proposed. Our Letter reveals a new universal mechanism\nfor emergence of type-II NG modes, which bridges intrinsically the Landau\nsymmetry-breaking and topological theories.",
        "positive": "Numerical generation of a vortex ring cascade in quantum turbulence: A symmetric anti-parallel quantum pair of vortices is simulated using the\nthree-dimensional Gross-Pitaevski equations. The initial development before\ncores interact directly demonstrates the traditional vortex dynamics of\nstretching, curvature and torsion in a manner consistent with a filament\ncalculation and simulations of the classical, ideal Euler equations. Once the\ncores begin to interact, reconnection develops in the vacuum that forms between\nthe pair. Out of the reconnection region, vortex waves are emitted with\nproperties similar to waves in the local induction approximation. These waves\npropagate down the initial vortex and deepen. When they deepen far enough,\nsecondary reconnections occur and vortex rings form. Near this time, spectra\nhave a $k^{-3}$ regime. As the vortex rings fully separate, the high wavenumber\nspectra grow until, at the final time simulated, spectra in two directions\ndevelop nearly -5/3 subranges. This occurs without the dissipation of energy.\nPreliminary analysis of the flow of energies in spectral scale and physical\nspace is discussed."
    },
    {
        "anchor": "Large time and long distance asymptotics of the thermal correlators of\n  the impenetrable anyonic lattice gas: We study thermal correlation functions of the one-dimensional impenetrable\nlattice anyons. These correlation functions can be presented as a difference of\ntwo Fredholm determinants. To describe large time and long distance behavior of\nthese objects we use effective form factor approach. The asymptotic behavior is\ndifferent in the space-like and time-like regions. In particular, in the\ntime-like region we observe the additional power factor on top of the\nexponential decay. We argue that this result is universal as it is related to\nthe discontinuous behavior of the phase shift function of the effective\nfermions. At particular values of the anyonic parameter we recover asymptotics\nof spin-spin correlation functions in XXO quantum chain.",
        "positive": "Long-lived direct and indirect interlayer excitons in van der Waals\n  heterostructures: We investigate the photoluminescence of interlayer excitons in\nheterostructures consisting of monolayer MoSe2 and WSe2 at low temperatures.\nSurprisingly, we find a doublet structure for such interlayer excitons. Both\npeaks exhibit long photoluminescence lifetimes of several ten nanoseconds up to\n100 ns at low temperatures, which verifies the interlayer nature of both. The\npeak energy and linewidth of both show unusual temperature and power\ndependences. In particular, we observe a blue-shift of their emission energy\nfor increasing excitation powers. At a low excitation power and low\ntemperatures, the energetically higher peak shows several spikes. We explain\nthe findings by two sorts of interlayer excitons; one that is indirect in real\nspace but direct in reciprocal space, and the other one being indirect in both\nspaces. Our results provide fundamental insights into long-lived interlayer\nstates in van der Waals heterostructures with possible bosonic many-body\ninteractions"
    },
    {
        "anchor": "Real-space collapse of a polariton condensate: Polaritons in microcavities are versatile quasi-2D bosonic particles with a\nhigh degree of coherence and strong nonlinearities, thanks to their hybrid\nlight-matter character. In their condensed form, they display striking quantum\nhydrodynamic features analogous to atomic Bose-Einstein condensates, such as\nlong-range order coherence, superfluidity and quantized vorticity. Their\nvariegated dispersive and dissipative properties, however, set significant\ndifferences from their atomic counterpart. In this work, we report the unique\nphenomenology that is observed when a pulse of light impacts the polariton\nvacuum: the condensate that is instantaneously formed does not splash in real\nspace but instead coheres into an enigmatic structure, featuring concentric\nrings and, most notably, a sharp and bright peak at the center. Using a\nstate-of-the-art ultrafast imaging with 50 fs time steps, we are able to track\nthe dynamics of the polariton mean-field wavefunction in both real and\nreciprocal space. The observation of the real-space collapse of the condensate\ninto an extremely localized---resolution limited---peak is at odd with the\nrepulsive interactions of polaritons and their positive effective mass. An\nunconventional mechanism is therefore at play to account for our observations.\nOur modeling suggests that self-trapping due to a local heating of the crystal\nlattice---that can be described as a collective polaron formed by a polariton\ncondensate---could be involved. These observations hint at the fascinating\nfluid dynamics of polaritons in conditions of extreme intensities and ultrafast\ntimes.",
        "positive": "The effect of atomic collisions on the quantum phase transition of a\n  Bose-Einstein condensate inside an optical cavity: In this paper, we investigate the effect of atomic collisions on the phase\ntransition form the normal to the superradiant phase in a one-dimensional\nBose-Einstein condensate (BEC) trapped inside an optical cavity. Specifically,\nwe show that driving the atoms from the side of the cavity leads to the\nexcitation of modes in the edges of the first Brillouin zone of every energy\nband, which results in the two-mode approximation of the BEC matter field in\nthe limit of weak coupling regime. The nonlinear effect of atom-atom\ninteraction shifts the threshold of the quantum phase transition of the BEC and\nalso affect the power low behavior of quantum fluctuations in the total\nparticle number. Besides, we show the possibility of controlling the quantum\nphase transition of the system through the s-wave scattering frequency when the\nthe strength of the transverse pumping has been fixed."
    },
    {
        "anchor": "Superfluid state in the periodic Anderson model with attractive\n  interactions: We investigate the periodic Anderson model with attractive interactions by\nmeans of dynamical mean-field theory (DMFT). Using a continuous-time quantum\nMonte Carlo impurity solver, we study the competition between the superfluid\nstate and the paramagnetic Kondo insulating state, and determine the phase\ndiagram. At the chemical potential-induced phase transition from the Kondo\ninsulating state to the superfluid state, a low-energy peak characteristic of\nthe superfluid state appears inside the hybridization gap. We also address the\neffect of the confining potential in optical lattice systems by means of\nreal-space DMFT calculations.",
        "positive": "Quantum simulation of the Hubbard model with ultracold fermions in\n  optical lattices: Ultracold atomic gases provide a fantastic platform to implement quantum\nsimulators and investigate a variety of models initially introduced in\ncondensed matter physics or other areas. One of the most promising applications\nof quantum simulation is the study of strongly-correlated Fermi gases, for\nwhich exact theoretical results are not always possible with state-of-the-art\napproaches. Here, we review recent progress of the quantum simulation of the\nemblematic Fermi-Hubbard model with ultracold atoms. After introducing the\nFermi-Hubbard model in the context of condensed matter, its implementation in\nultracold atom systems, and its phase diagram, we review landmark experimental\nachievements, from the early observation of the onset of quantum degeneracy and\nsuperfluidity to demonstration of the Mott insulator regime and the emergence\nof long-range anti-ferromagnetic order. We conclude by discussing future\nchallenges, including the possible observation of high-Tc superconductivity,\ntransport properties, and the interplay of strong correlations and disorder or\ntopology."
    },
    {
        "anchor": "Generation of ring dark solitons by phase engineering and their\n  oscillations in spin-1 Bose-Einstein condensates: The ring dark solitons in spin-1 $^{23}$Na and $^{87}$Rb Bose-Einstein\ncondensates are studied numerically in the framework of the time-dependent\nGross-Pitaevskii equations. By simulating the phase engineering technique in\nreal experiments, we explore the roles of the parameters characterizing the\nfar-off resonant laser pulse which can be used to generate the ring dark\nsolitons. The variations of these parameters have dramatic effect on the\nlifetime and the decay profiles of the ring dark solitons. If only one ring\ndark soliton is generated in one component of the condensate, ring dark\nsolitons in other components are inclined to be induced, resulting in a\ncoexistence state composed of interdependent ring dark solitons coming from\ndifferent components of the condensate. Ring dark solitons in this coexistence\nstate exhibit dynamical oscillations for hundreds of milliseconds. By studying\nthe lifetime and decaying profiles of ring dark solitons, we explore the\nsimilarities and differences of $^{23}$Na and $^{87}$Rb condensates. Besides,\ntaking into account the fact that the center of the ring may not be coincide\nwith that of the trap, we study the dynamics and decaying profiles of the\noff-centered ring dark solitons in the presence of symmetry breaking effect.",
        "positive": "Chirp Control of Sinusoidal Lattice Modes in Bose-Einstein Condensate: A parametrically forced Bose-Einstein condensate (BEC) is studied in the mean\nfield approach for the case of a general moving optical lattice. The\ninteraction between the atoms in the condensate and the time dependent lattice\npotential leads to a novel propagating superfluid matter wave, which can be\ncontrolled through chirp management. This system, when placed in a trap,\naccelerates and undergoes rapid nonlinear compression, controlled by the chirp.\nThe density achieves its maximum, precisely when the matter wave changes\ndirection. A dynamical phase transition is identified, which takes the\nsuperfluid phase to an insulating state. The exact expression for energy is\nobtained and analyzed in detail to gain physical understanding of the chirp\nmanagement of the sinusoidal excitations and also the dynamical phase\ntransition."
    },
    {
        "anchor": "Aharonov-Bohm Caging and Inverse Anderson transition in Ultracold Atoms: Aharonov-Bohm (AB) caging, a special flat-band localization mechanism, has\nspurred great interest in different areas of physics. AB caging can be\nharnessed to explore the rich and exotic physics of quantum transport in\nflatband systems, where geometric frustration, disorder and correlations act in\na synergetic and distinct way than in ordinary dispersive band systems. In\ncontrast to the ordinary Anderson localization, where disorder induces\nlocalization and prevents transport, in flat band systems disorder can induce\nmobility, a phenomenon dubbed inverse Anderson transition. Here, we report on\nthe experimental realization of the AB cage using a synthehtic lattice in the\nmomentum space of ultracold atoms with tailored gauge fields, demonstrate the\ngeometric localization due to the flat band and the inverse Anderson transition\nwhen correlated binary disorder is added to the system. Our experimental\nplatform in a many-body environment provides a fashiinating quantum simulator\nwhere the interplay between engineered gauge fields, localization, and\ntopological properties of flat band systems can be finely explored.",
        "positive": "Study on Cooling of Positronium for Bose-Einstein Condensation: A new method of cooling positronium down is proposed to realize Bose-Einstein\ncondensation of positronium. We perform detail studies about three processes\n(1) thermalization processes between positronium and silica walls of a cavity,\n(2) Ps-Ps scatterings and (3) Laser cooling. The thermalization process is\nshown to be not sufficient for BEC. Ps-Ps collision is also shown to make a big\neffect on the cooling performance. We combine both methods and establish an\nefficient cooling for BEC. We also propose a new optical laser system for the\ncooling."
    },
    {
        "anchor": "Observation of self-amplifying Hawking radiation in an analog black hole\n  laser: It has been proposed that a black hole horizon should generate Hawking\nradiation. In order to test this theory, we have created a narrow, low density,\nvery low temperature atomic Bose-Einstein condensate, containing an analog\nblack hole horizon and an inner horizon, as in a charged black hole. We observe\nHawking radiation emitted by the black hole. This is the output of the black\nhole laser. We also observe the exponential growth of a standing wave between\nthe horizons. The latter results from interference between the negative energy\npartners of the Hawking radiation and the negative energy particles reflected\nfrom the inner horizon. We thus observe self-amplifying Hawking radiation.",
        "positive": "Observation of phonon parametric down-conversion in a spherical\n  Bose-Einstein condensate: We report the observation of parametric down-conversion of phonons in a\nspherical Bose-Einstein condensate. The spherical symmetry, which is crucial\nfor observing this phenomenon, is experimentally demonstrated by measuring the\ncollective mode and expansion behavior of the condensate. The low-energy\nmonopole mode is excited by coupling with a high-energy mode with a nearly\ntwice eigen-frequency. The population of the low-energy mode becomes maximum\nonly when the high-energy mode is resonantly excited. Furthermore, we directly\nobserve the parametric down-conversion process in the driving process, through\nsimultaneously probing the two coupling modes. The experimental observation is\nconsistent with the perturbation theory including the gravity effect. This work\nopens the challenge in related study of the condensate beyond mean-field theory\nand has potential applications in quantum information."
    },
    {
        "anchor": "A spin-orbit coupled Bose-Einstein condensate: Spin-orbit (SO) coupling -- the interaction between a quantum particle's spin\nand its momentum -- is ubiquitous in nature, from atoms to solids. In condensed\nmatter systems, SO coupling is crucial for the spin-Hall effect and topological\ninsulators, which are of extensive interest; it contributes to the electronic\nproperties of materials such as GaAs, and is important for spintronic devices.\nUltracold atoms, quantum many-body systems under precise experimental control,\nwould seem to be an ideal platform to study these fascinating SO coupled\nsystems. While an atom's intrinsic SO coupling affects its electronic\nstructure, it does not lead to coupling between the spin and the center-of-mass\nmotion of the atom. Here, we engineer SO coupling (with equal Rashba and\nDresselhaus strengths) in a neutral atomic Bose-Einstein condensate by dressing\ntwo atomic spin states with a pair of lasers. Not only is this the first SO\ncoupling realized in ultracold atomic gases, it is also the first ever for\nbosons. Furthermore, in the presence of the laser coupling, the interactions\nbetween the two dressed atomic spin states are modified, driving a quantum\nphase transition from a spatially spin-mixed state (lasers off) to a phase\nseparated state (above a critical laser intensity). The location of this\ntransition is in quantitative agreement with our theory. This SO coupling --\nequally applicable for bosons and fermions -- sets the stage to realize\ntopological insulators in fermionic neutral atom systems.",
        "positive": "Quantum magnetism in strongly interacting one-dimensional spinor Bose\n  systems: Strongly interacting one-dimensional quantum systems often behave in a manner\nthat is distinctly different from their higher-dimensional counterparts. When a\nparticle attempts to move in a one-dimensional environment it will unavoidably\nhave to interact and 'push' other particles in order to execute a pattern of\nmotion, irrespective of whether the particles are fermions or bosons. A present\nfrontier in both theory and experiment are mixed systems of different species\nand/or particles with multiple internal degrees of freedom. Here we consider\ntrapped two-component bosons with short-range inter-species interactions much\nlarger than their intra-species interactions and show that they have novel\nenergetic and magnetic properties. In the strongly interacting regime, these\nsystems have energies that are fractions of the basic harmonic oscillator trap\nquantum and have spatially separated ground states with manifestly\nferromagnetic wave functions. Furthermore, we predict excited states that have\nperfect antiferromagnetic ordering. This holds for both balanced and imbalanced\nsystems, and we show that it is a generic feature as one crosses from few- to\nmany-body systems."
    },
    {
        "anchor": "Dark-soliton molecules in an exciton-polariton superfluid: The general theory of dark solitons relies on repulsive interactions and\ntherefore predicts the impossibility to form dark-soliton bound states. One\nimportant exception to this prediction is the observation of bound solitons in\nnon-local nonlinear media. Here, we report that exciton-polariton superfluids\ncan also sustain dark-soliton molecules although the interactions are fully\nlocal. With a novel all optical technique, we create two dark solitons and bind\nthem to each other to form an unconventional dark-soliton molecule. We\ndemonstrate that the stability of this structure and the separation distance\nbetween two dark-solitons is tightly connected to the driven-dissipative nature\nof the polariton fluid.",
        "positive": "Synergy Dynamics of Vortices and Solitons in Atomic Bose-Einstein\n  Condensate Excited by an Oscillating Potential: The hydrodynamics of quantized vortices and solitons in an atomic\nBose-Einstein condensate excited by an oscillating potential are studied by\nnumerically solving the two-dimensional Gross-Pitaevskii equation. The\noscillating potential keeps nucleating vortex dipoles, whose impulses\nalternatively change their direction synchronously with the oscillation of the\npotential. This leads to synergy dynamics of vortices and solitons which have\nnot been previously reported in quantum fluids."
    },
    {
        "anchor": "Quantum anomaly and 2D-3D crossover in strongly interacting Fermi gases: We present an experimental investigation of collective oscillations in\nharmonically trapped Fermi gases through the crossover from two to three\ndimensions. Specifically, we measure the frequency of the radial monopole or\nbreathing mode as a function of dimensionality in Fermi gases with tunable\ninteractions. The frequency of this mode is set by the adiabatic\ncompressibility and probes the thermodynamic equation of state. In 2D, a\ndynamical scaling symmetry for atoms interacting via a {\\delta}-potential\npredicts the breathing mode to occur at exactly twice the harmonic confinement\nfrequency. However, a renormalized quantum treatment introduces a new length\nscale which breaks this classical scale invariance resulting in a so-called\nquantum anomaly. Our measurements deep in the 2D regime lie above the\nscale-invariant prediction for a range of interaction strengths indicating the\nbreakdown of a {\\delta}-potential model for atomic interactions. As the\ndimensionality is tuned from 2D to 3D we see the breathing oscillation\nfrequency evolve smoothly towards the 3D limit.",
        "positive": "Universal Sound Diffusion in a Strongly Interacting Fermi Gas: Transport of strongly interacting fermions governs modern materials -- from\nthe high-$T_c$ cuprates to bilayer graphene --, but also nuclear fission, the\nmerging of neutron stars and the expansion of the early universe. Here we\nobserve a universal quantum limit of diffusivity in a homogeneous, strongly\ninteracting Fermi gas of atoms by studying sound propagation and its\nattenuation via the coupled transport of momentum and heat. In the normal\nstate, the sound diffusivity ${D}$ monotonically decreases upon lowering the\ntemperature $T$, in contrast to the diverging behavior of weakly interacting\nFermi liquids. As the superfluid transition temperature is crossed, ${D}$\nattains a universal value set by the ratio of Planck's constant ${h}$ and the\nparticle mass ${m}$. This finding of quantum limited sound diffusivity informs\ntheories of fermion transport, with relevance for hydrodynamic flow of\nelectrons, neutrons and quarks."
    },
    {
        "anchor": "Spin Superfluidity versus Solidity of Ultracold Polar Molecules: We present a technique for engineering quantum magnets via ultracold polar\nmolecules in optical lattices and explore exotic interplay between its spin\nsuperfluidity and solidity. The molecular ground and first excited rotational\nstates are resonantly coupled by a linearly polarized microwave field. The\nspin-up (spin-down) states are presented by molecular rotational states of\nelectric dipole moment along (against) the coupling field. By controlling the\nangle between the lattice direction and the coupling field, the inter-site\ninteraction can be tuned from antiferromagnetic to ferromagnetic. Furthermore,\nthe dipole-dipole interaction induces an exotic interplay between spin\nsuperfluidity and solidity, and spin supersolid phases may appear in mediate\nregions.",
        "positive": "A two-species five-beam magneto-optical trap for highly magnetic Er and\n  Dy atoms: We report on the first realization of a two-species magneto-optical trap\n(MOT) for erbium and dysprosium. The MOT operates on an intercombination line\nfor the respective species. Owing to the narrow-line character of such a\ncooling transition and the action of gravity, we demonstrate a novel trap\ngeometry employing only five beams in orthogonal configuration. We observe that\nthe mixture is cooled and trapped very efficiently, with up to \\num{5e8} Er\natoms and \\num{e9} Dy atoms at temperatures of about $10\\,\\mu K$. Our results\noffer an ideal starting condition for the creation of a dipolar quantum mixture\nof highly magnetic atoms."
    },
    {
        "anchor": "Short-range correlations and entropy in ultracold atomic Fermi gases: We relate short-range correlations in ultracold atomic Fermi gases to the\nentropy of the system over the entire temperature, $T$, vs. coupling strength,\n$-1/k_Fa$, plane. In the low temperature limit the entropy is dominated by\nphonon excitations and the correlations increase as $T^4$. In the BEC limit, we\ncalculate a boson model within the Bogoliubov approximation to show explicitly\nhow phonons enhance the fermion correlations. In the high temperature limit, we\nshow from the virial expansion that the correlations decrease as $1/T$. The\ncorrelations therefore reach a maximum at a finite temperature. We infer the\ngeneral structure of the isentropes of the Fermi gas in the $T,-1/k_Fa$ plane,\nand the temperature dependence of the correlations in the unitary, BEC, and BCS\nlimits. Our results compare well with measurements of the correlations via\nphotoassociation experiments at higher temperatures.",
        "positive": "Non-Thermal Fixed Points in Bose Gas Experiments: One of the most challenging tasks in physics has been understanding the route\nan out-of-equilibrium system takes to its thermalized state. This problem can\nbe particularly overwhelming when one considers a many-body quantum system.\nHowever, several recent theoretical and experimental studies have indicated\nthat some far-from-equilibrium systems display universal dynamics when close to\na so-called non-thermal fixed point (NTFP), following a rescaling of both space\nand time. This opens up the possibility of a general framework for studying and\ncategorizing out-of-equilibrium phenomena into well-defined universality\nclasses. This paper reviews the recent advances in observing NTFPs in\nexperiments involving Bose gases. We provide a brief introduction to the theory\nbehind this universal scaling, focusing on experimental observations of NTFPs.\nWe present the benefits of NTFP universality classes by analogy with\nrenormalization group theory in equilibrium critical phenomena."
    },
    {
        "anchor": "Quantum soliton-trains of strongly correlated impurities in\n  Bose-Einstein condensates: Strongly correlated impurities immersed in a Bose-Einstein condensate (BEC)\ncan form a periodic structure of tightly localized single atoms due to\ncompeting inter- and intra-species interactions, leading to a self-organized\npinned state. In this work, we show numerically that the impurities in the\nself-pinned state form a soliton-train, as a consequence of a BEC-mediated\nattractive self-interaction and ordering due to the exclusion principle. The\ndynamics of the impurities possess similar characteristics to bright\nmatter-wave solitons as they appear in attractive BECs, however in the few\nimpurities case, the detailed nature of collisions is determined by their\nquantum statistics.",
        "positive": "Density-potential functional theory for fermions in one dimension: We showcase the advantages of orbital-free density-potential functional\ntheory (DPFT), a more flexible variant of Hohenberg-Kohn density functional\ntheory. DPFT resolves the usual trouble with the gradient-expanded kinetic\nenergy functional by facilitating systematic semiclassical approximations in\nterms of an effective potential energy that incorporates all interactions. With\nthe aid of two systematic approximation schemes we demonstrate that DPFT is not\nonly scalable, universally applicable in both position and momentum space, and\nallows kinetic and interaction energy to be approximated consistently, but can\nalso compete with highly accurate, yet restricted, methods. As two- and\nthree-dimensional geometries are extensively covered elsewhere, our focus here\nis on one-dimensional settings, with semiclassical observables systematically\nderived from both the Wigner function formalism and a split-operator approach.\nThe high quality of our results for Fermi gases in Morse potentials invites the\nuse of DPFT for describing more exotic systems, such as trapped large-spin\nfermion mixtures with contact or dipole-dipole interactions."
    },
    {
        "anchor": "Scaling law for three-body collisions near a narrow s-wave Feshbach\n  resonance: Ultracold atomic gases provide a controllable system to study the inelastic\nprocesses for three-body systems, where the three-body recombination rate\ndepends on the scattering length scaling. Such scalings have been confirmed in\nbosonic systems with various interaction strengths, but their existence with\nfermionic atoms remains elusive. In this work, we report on an experimental\ninvestigation of the scaling law for the three-body atomic loss rate $L_3$ in a\ntwo-component $^6$Li Fermi gas with the scattering length $a<0$. The scaling\nlaw is validated within a certain range of $a$ near the narrow $s$-wave\nFeshbach resonance, where $L_3\\propto T|a|^{2.60(5)}$, and $T$ is the gas\ntemperature. The scaling law is observed to have an upper and a lower bound in\nterms of the scattering length. For the upper bound, when $a\\rightarrow\n\\infty$, the power-law scaling is suppressed by the unitary behavior of the\nresonance caused by the strong three-body collisions. For the lower bound,\n$a\\rightarrow 0$, the finite range effect modifies the scaling law by the\neffective scattering length $L_e$. These results indicate that the three-body\nrecombination rate in a fermionic system could be characterized by the scaling\nlaw associated with the generalized Efimov physics.",
        "positive": "Propagating Ferrodark Solitons in a Superfluid: Exact Solutions and\n  Anomalous Dynamics: Exact propagating topological solitons are found in the easy-plane phase of\nferromagnetic spin-1 Bose-Einstein condensates, manifesting themselves as kinks\nin the transverse magnetization. Propagation is only possible when the\nsymmetry-breaking longitudinal magnetic field is applied. Such solitons have\ntwo types: a low energy branch with positive inertial mass and a higher branch\nsolution with negative inertial mass. Both types become identical at the\nmaximum speed, a new speed bound that is different from speed limits set by the\nelementary excitations. The physical mass, which accounts for the number\ndensity dip, is negative for both types. In a finite one-dimensional system\nsubject to a linear potential, the soliton undergoes oscillations caused by\ntransitions between the two types occurring at the maximum speed."
    },
    {
        "anchor": "Theory of domain formation in inhomogeneous ferromagnetic dipolar\n  condensates: Recent experimental studies of $^{87}$Rb spinor Bose Einstein condensates\nhave shown the existence of a magnetic field driven quantum phase transition\naccompanied by structure formation on the ferromagnetic side of the transition.\nIn this theoretical study we examine the dynamics of the unstable modes\nfollowing the transition taking into account the effects of the trap,\nnon-linearities, finite temperature and dipole-dipole interactions. Starting\nfrom an initial state which includes quantum fluctuations, we attempt to make\nquantitative comparisons with recent experimental data on this system and\nestimate the contribution of quantum zero-point fluctuations to the domain\nformation. Finally, using the strong anisotropy of the trap, we propose ways to\nobserve directly the effects of dipole-dipole interactions on the spinor\ncondensate dynamics.",
        "positive": "Asymptotic Floquet states of open quantum systems: The role of\n  interaction: We investigate the asymptotic state of a periodically driven many-body\nquantum system which is weakly coupled to an environment. The combined action\nof the modulations and the environment steers the system towards a state being\ncharacterized by a time-periodic density operator. To resolve this asymptotic\nnon-equilibrium state at stroboscopic instants of time, we introduce the\ndissipative Floquet map, evaluate the stroboscopic density operator as its\neigen-element and elucidate how particle interactions affect properties of the\ndensity operator. We illustrate the idea with a periodically modulated\nBose-Hubbard dimer and discuss the relations between the interaction-induced\nbifurcations in a mean-field dynamics and changes in the characteristics of the\ngenuine quantum many-body state. We argue that Floquet maps provide insight\ninto the system relaxation towards its asymptotic state and may help to\nunderstand whether it is possible (or not) to construct a stroboscopic\ntime-independent generator mimicking the action of the original time-dependent\none."
    },
    {
        "anchor": "Two-dimensional quantum droplets in binary quadrupolar condensates: We study the stability and characteristics of two-dimensional (2D)\nquasi-isotropic quantum droplets (QDs) of fundamental and vortex types, formed\nby binary Bose-Einstein condensate with magnetic quadrupole-quadrupole\ninteractions (MQQIs). The magnetic quadrupoles are built as pairs of dipoles\nand antidipoles polarized along the x-axis. The MQQIs are induced by applying\nan external magnetic field that varies along the x-axis. The system is modeled\nby the Gross-Pitaevskii equations including the MQQIs and Lee-Huang-Yang\ncorrection to the mean-field approximation. Stable 2D fundamental QDs and\nquasi-isotropic vortex QDs with topological charges S<4 are produced by means\nof the imaginary-time-integration method for configurations with the\nquadrupoles polarized parallel to the systems two-dimensional plane. Effects of\nthe norm and MQQI strength on the QDs are studied in detail. Some results,\nincluding an accurate prediction of the effective area, chemical potential, and\npeak density of QDs, are obtained in an analytical form by means of the\nThomas-Fermi approximation. Collisions between moving QDs are studied by means\nof systematic simulations.",
        "positive": "Exploring interacting topological insulator of extended\n  Su-Schrieffer-Heeger model: Exploring topological phases in interacting systems is a challenging task. We\ninvestigate many-body topological physics of interacting fermions in an\nextended Su-Schrieffer-Heeger (SSH) model, which extends the two sublattices of\nSSH model into four sublattices and thus is dubbed SSH4 model, based on the\ndensity-matrix renormalization-group numerical method. The interaction-driven\nphase transition from topological insulator to charge density wave (CDW) phase\ncan be identified by analyzing the variations of entanglement spectrum,\nentanglement entropies, energy gaps, CDW order parameter, and fidelity. We map\nthe global phase diagram of the many-body ground state, which contains\nnontrivial topological insulator, trivial insulator and CDW phases,\nrespectively. In contrast to interacting SSH model, in which the phase\ntransitions to the CDW phase are argued to be first-order phase transitions,\nthe phase transitions between the CDW phase and topologically\ntrivial/nontrivial phases are shown to be continuous phase transitions.\nFinally, we {also} show the phase diagram of interacting spinful SSH4 model,\nwhere the attractive (repulsive) on-site spin interaction amplifies\n(suppresses) the CDW phase. The models analyzed here can be implemented with\nultracold atoms on optical superlattices."
    },
    {
        "anchor": "p-Wave Resonant Bose Gas: A Finite-Momentum Spinor Superfluid: We show that a degenerate gas of two-species bosonic atoms interacting\nthrough a p-wave Feshbach resonance (as realized in, e.g., a 85Rb-87Rb mixture)\nexhibits a finite-momentum atomic-molecular superfluid (AMSF), sandwiched by a\nmolecular p-wave (orbital spinor) superfluid and by an s-wave atomic superfluid\nat large negative and positive detunings, respectively. The magnetic field can\nbe used to tune the modulation wave vector of the AMSF state, as well as to\ndrive quantum phase transitions in this rich system.",
        "positive": "Pfaffian State Generation by Strong 3-Body Dissipation: We propose a scheme for preparing and stabilizing the Pfaffian state with\nhigh fidelity in rapidly rotating 2D traps containing a small number of bosons.\nThe goal is achieved by strongly increasing 3-body loss processes, which\nsuppress superpositions of three particles while permitting pairing. This\nfiltering mechanism gives rise to reasonably small losses if the system is\ninitialized with the right angular momentum. We discuss some methods for tuning\n3-body interactions independently of 2-body collisions."
    },
    {
        "anchor": "Observation of a space-time crystal in a superfluid quantum gas: Time crystals are a phase of matter, for which the discrete time symmetry of\nthe driving Hamiltonian is spontaneously broken. The breaking of discrete time\nsymmetry has been observed in several experiments in driven spin systems. Here,\nwe show the observation of a space-time crystal using ultra-cold atoms, where\nthe periodic structure in both space and time are directly visible in the\nexperimental images. The underlying physics in our superfluid can be described\nab initio and allows for a clear identification of the mechanism that causes\nthe spontaneous symmetry breaking. Our results pave the way for the usage of\nspace-time crystals for the discovery of novel nonequilibrium phases of matter.",
        "positive": "Rotation of a Bose-Einstein Condensate held under a toroidal trap: The aim of this paper is to perform a numerical and analytical study of a\nrotating Bose Einstein condensate placed in a harmonic plus Gaussian trap,\nfollowing the experiments of \\cite{bssd}. The rotational frequency $\\Omega$ has\nto stay below the trapping frequency of the harmonic potential and we find that\nthe condensate has an annular shape containing a triangular vortex lattice. As\n$\\Omega$ approaches $\\omega$, the width of the condensate and the circulation\ninside the central hole get large. We are able to provide analytical estimates\nof the size of the condensate and the circulation both in the lowest Landau\nlevel limit and the Thomas-Fermi limit, providing an analysis that is\nconsistent with experiment."
    },
    {
        "anchor": "Effect of disorder close to the superfluid transition in a\n  two-dimensional Bose gas: We experimentally study the effect of disorder on trapped quasi\ntwo-dimensional (2D) 87Rb clouds in the vicinity of the\nBerezinskii-Kosterlitz-Thouless (BKT) phase transition. The disorder\ncorrelation length is of the order of the Bose gas characteristic length scales\n(thermal de Broglie wavelength, healing length) and disorder thus modifies the\nphysics at a microscopic level. We analyze the coherence properties of the\ncloud through measurements of the momentum distributions, for two disorder\nstrengths, as a function of its degeneracy. For moderate disorder, the\nemergence of coherence remains steep but is shifted to a lower entropy. In\ncontrast, for strong disorder, the growth of coherence is hindered. Our study\nis an experimental realization of the dirty boson problem in a well controlled\natomic system suitable for quantitative analysis.",
        "positive": "Phases of driven two-level systems with nonlocal dissipation: We study an array of two-level systems arranged on a lattice and illuminated\nby an external plane wave which drives a dipolar transition between the two\nenergy levels. In this set up, the two-level systems are coupled by dipolar\ninteractions and subject to nonlocal dissipation, so behave as an open\nmany-body quantum system. We investigate the long-time dynamics of the system\nat the mean-field level, and use this to determine a phase diagram as a\nfunction of external drive and detuning. We find a multitude of phases\nincluding antiferromagnetism, spin density waves, oscillations and phase\nbistabilities. We investigate these phases in more detail and explain how\nnonlocal dissipation plays a role in the long-time dynamics. Furthermore, we\ndiscuss what features would survive in the full quantum description."
    },
    {
        "anchor": "Universal quantum computation and quantum error correction with\n  ultracold atomic mixtures: Quantum information platforms made great progress in the control of many-body\nentanglement and the implementation of quantum error correction, but it remains\na challenge to realize both in the same setup. Here, we propose a mixture of\ntwo ultracold atomic species as a platform for universal quantum computation\nwith long-range entangling gates, while providing a natural candidate for\nquantum error-correction. In this proposed setup, one atomic species realizes\nlocalized collective spins of tunable length, which form the fundamental unit\nof information. The second atomic species yields phononic excitations, which\nare used to entangle collective spins. Finally, we discuss a finite-dimensional\nversion of the Gottesman-Kitaev-Preskill code to protect quantum information\nencoded in the collective spins, opening up the possibility to universal\nfault-tolerant quantum computation in ultracold atom systems.",
        "positive": "Exact Diagonalization Study of Bose-Condensed Gas with Finite-Range\n  Gaussian Interaction: We investigate a system of $N$ spinless bosons confined in\nquasi-two-dimensional harmonic trap with repulsive two-body finite-range\nGaussian interaction potential of large $s$-wave scattering length. Exact\ndiagonalization of the Hamiltonian matrix is carried out to obtain the $N$-body\nground state as well as low-lying excited states, using Davidson algorithm in\nbeyond lowest-Landau-level approximation. We examine the finite-range effects\nof the interaction potential on the many-body ground state energy as also the\ndegree of condensation of the Bose-condensed gas. The results obtained indicate\nthat the finite-range Gaussian interaction potential enhances the degree of\ncondensation compared to the zero-range interaction potential. We further\nanalyze the effect of finite-range interaction potential on the breathing mode\ncollective excitation. Our theoretical results may be relevant for experiments\ncurrently conducted on quasi-two-dimensional Bose gas with more realistic\ninteraction potential."
    },
    {
        "anchor": "Ground state and rotational properties of two-dimensional self-bound\n  quantum droplets: We consider a two-dimensional self-bound quantum droplet, which consists of a\nmixture of two Bose-Einstein condensates. We start with the ground state, and\nthen turn to the rotational response of this system, in the presence of an\nexternal (harmonic) potential. We identify various phases, depending on the\natom number, the strength of the external confinement and the angular momentum.\nThese include center of mass excitation, ghost vortices, as well as vortices of\nsingle and multiple quantization. According to our results, this is an\nexcellent system for the study of superfluid states.",
        "positive": "Two-body collisions in the time-of-flight dynamics of lattice Bose\n  superfluids: We investigate two-body collisions occurring during the time-of-flight\nexpansion of interacting three-dimensional lattice Bose superfluids. The number\nof collisions is extracted from the observed s-wave scattering halos located\nbetween the diffraction peaks of the superfluids. These faint halos can be\nmonitored thanks to the large dynamical range in densities associated with\ndetecting individual metastable Helium atoms. We monitor the number of\ncollisions as a function of the total atom number and of the amplitude of the\nlattice, in a regime where the number of trapped atoms per lattice site is\nlarge. In addition, we introduce a classical model of collisions that\nquantitatively describes the experiment without adjustable parameters. Finally,\nthe present work validates quantitatively the assumption of a ballistic\nexpansion when investigating the Bose-Hubbard Hamiltonian with a unity\noccupation of the lattice."
    },
    {
        "anchor": "Expansion of a one-dimensional Bose gas: the role of interactions and\n  kinetic-energy driving: We study the expansion of a one-dimensional boson gas by suddenly increasing\nthe length of the chain where it resides. We consider three initial\nground-state configurations: the Mott insulator, the conventional superfluid\nclumped around zero momentum, and the cat-like state with peaks at momenta $\\pm\n\\pi/2$, resulting from rapid kinetic driving. In turn, we consider three types\nof expansion: spectroscopic (with interactions tuned to zero), dynamic (with\nstandard short-range repulsive interactions) and under kinetic driving. The\nnumerical calculations are exact. We compute the momentum- and real-space\none-particle densities as well as the two-particle momentum correlations. The\nspectroscopic time-of-flight experiment faithfully reflects the initial\nmomentum distribution. For the dynamic expansion starting from an insulator, we\nreproduce the non-equilibrium quasi-condensation into momenta $\\pm \\pi/2$ while\nnoticing correlations in the momentum distribution, and provide an intuitive\nphysical picture. A discussion of various measures of the momentum correlations\nis also presented.",
        "positive": "Control of unstable macroscopic oscillations in the dynamics of three\n  coupled Bose condensates: We study the dynamical stability of the macroscopic quantum oscillations\ncharacterizing a system of three coupled Bose-Einstein condensates arranged\ninto an open-chain geometry. The boson interaction, the hopping amplitude and\nthe central-well relative depth are regarded as adjustable parameters. After\nderiving the stability diagrams of the system, we identify three mechanisms to\nrealize the transition from an unstable to stable behavior and analyze specific\nconfigurations that, by suitably tuning the model parameters, give rise to\nmacroscopic effects which are expected to be accessible to experimental\nobservation. Also, we pinpoint a system regime that realizes a\nJosephson-junction-like effect. In this regime the system configuration do not\ndepend on the model interaction parameters, and the population oscillation\namplitude is related to the condensate-phase difference. This fact makes\npossible estimating the latter quantity, since the measure of the oscillating\namplitudes is experimentally accessible."
    },
    {
        "anchor": "Exploring helical phases of matter in bosonic ladders: Ladder models of ultracold atoms offer a versatile platform for the\nexperimental and theoretical study of different phenomena and phases of matter\nlinked to the interplay between artificial gauge fields and interactions.\nStrongly correlated helical states are known to appear for specific ratios of\nthe particle and magnetic flux densities and they can often be interpreted as a\none-dimensional limit of fractional quantum Hall states, thus being called\npretopological. Their signatures, however, are typically hard to observe due to\nthe small gaps characterizing these states. Here we investigate bosonic ladder\nmodels at filling factor 1. Based on bosonization, renormalization group and\nmatrix product state simulations we pinpoint two strongly correlated helical\nphases appearing at this resonance. We show that one of them can be accessed in\nsystems with two-species hardcore bosons and on-site repulsions only, thus\namenable for optical lattice experiments. Its signatures are sizable and stable\nover a broad range of parameters for realistic system sizes.",
        "positive": "The Rhombi-Chain Bose-Hubbard Model: geometric frustration and\n  interactions: We explore the effects of geometric frustration within a one-dimensional\nBose-Hubbard model using a chain of rhombi subject to a magnetic flux. The\ncompetition of tunnelling, self-interaction and magnetic flux gives rise to the\nemergence of a pair-superfluid (pair-Luttinger liquid) phase besides the more\nconventional Mott-insulator and superfluid (Luttinger liquid) phases. We\ncompute the complete phase diagram of the model by identifying characteristic\nproperties of the pair-Luttinger liquid phase such as pair correlation\nfunctions and structure factors and find that the pair-Luttinger liquid phase\nis very sensitive to changes away from perfect frustration (half-flux). We\nprovide some proposals to make the model more resilient to variants away from\nperfect frustration. We also study the bipartite entanglement properties of the\nchain. We discover that, while the scaling of the block entropy pair-superfluid\nand of the single-particle superfluid leads to the same central charge, the\nproperties of the low-lying entanglement spectrum levels reveal their\nfundamental difference."
    },
    {
        "anchor": "Kohn-Sham theory of rotating dipolar Fermi gas in two dimensions: A two-dimensional dipolar Fermi gas in harmonic trap under rotation is\nstudied by solving \"ab initio\" Kohn-Sham equations. The physical parameters\nused match those of ultracold gas of fermionic $^{23}Na^{40}K$ molecules, a\nprototype system of strongly interacting dipolar quantum matter, which has been\ncreated very recently. We find that, as the critical rotational frequency is\napproached and the system collapses into the lowest Landau level, an array of\ntightly packed quantum vortices develops, in spite of the non-superfluid\ncharacter of the system. In this state the system looses axial symmetry, and\nthe fermionic cloud boundaries assume an almost perfect square shape. At higher\nvalues of the filling factor the vortex lattice disappears, while the system\nstill exhibits square-shaped boundaries. At lower values of the filling factor\nthe fermions become instead localized in a \"Wigner cluster\" structure.",
        "positive": "Quantum droplets with magnetic vortices in spinor dipolar Bose-Einstein\n  condensates: Motivated by the recent experimental realization of a Bose-Einstein\ncondensate (BEC) of europium atoms, we investigate the self-bound droplet state\nof a europium BEC with spin degrees of freedom. Under a sufficiently weak\nmagnetic field, the droplet has a torus shape with circulating spin vectors,\nwhich is referred to as a magnetic vortex. The ground state transforms from the\ntorus to cigar shape through bistability with an increase in the magnetic\nfield. Dynamical change of the magnetic field causes the torus to rotate due to\nthe Einstein-de Haas effect. The magnetic vortices form a supersolid in a\nconfined system."
    },
    {
        "anchor": "Supersolid Phase of Cold Fermionic Polar Molecules in 2D Optical\n  Lattices: We study a system of ultra-cold fermionic polar molecules in a\ntwo-dimensional square lattice interacting via both the long-ranged\ndipole-dipole interaction and a short-ranged on-site attractive interaction.\nSinglet superfluid, charge density wave, and supersolid phases are found to\nexist in the system. We map out the zero temperature phase diagram and find\nthat the supersolid phase is considerably stabilized by the dipole-dipole\ninteraction and thus can exist over a large region of filling factors. We study\nthe melting of the supersolid phase with increasing temperature, map out a\nfinite temperature phase diagram of the system at fixed filling, and determine\nthe parameter region where the supersolid phase can possibly be observed in\nexperiments.",
        "positive": "Topological edge and corner states in coupled wave lattices in nonlinear\n  polariton condensates: Topological states have been widely investigated in different types of\nsystems and lattices. In the present work, we report on topological edge states\nin double-wave (DW) chains, which can be described by a generalized\nAubry-Andr\\'e-Harper (AAH) model. For the specific system of a\ndriven-dissipative exciton polariton system we show that in such potential\nchains, different types of edge states can form. For resonant optical\nexcitation, we further find that the optical nonlinearity leads to a\nmultistability of different edge states. This includes topologically protected\nedge states evolved directly from individual linear eigenstates as well as\nadditional edge states that originate from nonlinearity-induced localization of\nbulk states. Extending the system into two dimensions (2D) by stacking\nhorizontal DW chains in the vertical direction, we also create 2D multi-wave\nlattices. In such 2D lattices multiple Su-Schrieffer-Heeger (SSH) chains appear\nalong the vertical direction. The combination of DW chains in the horizontal\nand SSH chains in the vertical direction then results in the formation of\nhigher-order topological insulator corner states. Multistable corner states\nemerge in the nonlinear regime."
    },
    {
        "anchor": "Vector Dark-Antidark Solitary Waves in Multi-Component Bose-Einstein\n  condensates: Multi-component Bose-Einstein condensates exhibit an intriguing variety of\nnonlinear structures. In recent theoretical work, the notion of magnetic\nsolitons has been introduced. Here we generalize this concept to vector\ndark-antidark solitary waves in multi-component Bose-Einstein condensates. We\nfirst provide concrete experimental evidence for such states in an atomic BEC\nand subsequently illustrate the broader concept of these states, which are\nbased on the interplay between miscibility and inter-component repulsion. Armed\nwith this more general conceptual framework, we expand the notion of such\nstates to higher dimensions presenting the possibility of both vortex-antidark\nstates and ring-antidark-ring (dark soliton) states. We perform numerical\ncontinuation studies, investigate the existence of these states and examine\ntheir stability using the method of Bogolyubov-de Gennes analysis.\nDark-antidark and vortex-antidark states are found to be stable for broad\nparametric regimes. In the case of ring dark solitons, where the\nsingle-component ring state is known to be unstable, the vector entity appears\nto bear a progressively more and more stabilizing role as the inter-component\ncoupling is increased.",
        "positive": "Techniques to measure quantum criticality in cold atoms: Attempts to understand zero temperature phase transitions have forced\nphysicists to consider a regime where the standard paradigms of condensed\nmatter physics break down [1-4]. These quantum critical systems lack a simple\ndescription in terms of weakly interacting quasiparticles, but over the past 20\nyears physicists have gained deep insights into their properties. Most\ndramatically, theory predicts that universal scaling relationships describe\ntheir finite temperature thermodynamics up to remarkably high temperatures.\nUnfortunately, these universal functions are hard to calculate: for example\nthere are no reliable general techniques [4,5] to calculate the scaling\nfunctions for dynamics. Viewing a cold atom experiment as a quantum simulator\n[6], we show how to extract universal scaling functions from (non-universal)\natomic density profiles or spectroscopic measurements. Such experiments can\nresolve important open questions about the Mott-Metal crossover [7,8] and the\ndynamics of the finite density O(2) rotor model [1,9], with direct impact on\ntheories of, for example, high temperature superconducting cuprates [10,11],\nheavy fermion materials [12], and graphene [13]."
    },
    {
        "anchor": "Vortex patterns in moderately rotating Bose-condensed gas: Using exact diagonalization, we investigate the many-body ground state for\nvortex patterns in a rotating Bose-condensed gas of $N$ spinless particles,\nconfined in a quasi-two-dimensional harmonic trap and interacting repulsively\nvia finite-range Gaussian potential. The $N$-body Hamiltonian matrix is\ndiagonalized in given subspaces of quantized total angular momentum $L_{z}$, to\nobtain the lowest-energy eigenstate. Further, the internal structure of these\neigenstates is analyzed by calculating the corresponding conditional\nprobability distribution. Specifically, the quantum mechanically stable as well\nas unstable states in a co-rotating frame are examined in the moderately\nrotating regime corresponding to angular momenta $4N \\le L_{z} < 5N$ for $N=16$\nbosons. In response to externally impressed rotation, patterns of singly\nquantized vortices are formed, shaping into canonical polygons with a central\nvortex at the trap center. The internal structure of unstable states reveals\nthe mechanism of entry, nucleation and pattern formation of vortices with\nstructural phase transition, as the condensate goes from one stable vortical\nstate to the other. The stable polygonal vortex patterns having discrete\n$p$-fold rotational symmetry with $p=5$ and $p=6$ are observed. The hexagonal\nvortex pattern with $p=6$ symmetry is a precursor to the triangular vortex\nlattice of singly quantized vortices in the thermodynamic limit. For unstable\nstates, quantum melting of vortex patterns due to uncertainty in positions of\nindividual vortices, is also briefly discussed.",
        "positive": "Half-Vortex Unbinding and Ising Transition in Constrained Superfluids: We analyze the thermodynamics of the atomic and (nematic) pair superfluids\nappearing in the attractive two-dimensional Bose-Hubbard model with a\nthree-body hard-core constraint that has been derived as an effective model for\ncold atoms subject to strong three-body losses in optical lattices. We show\nthat the thermal disintegration of the pair superfluidity is governed by the\nproliferation of fractional half-vortices leading to a\nBerezinskii-Kosterlitz-Thousless transition with unusual jump in the helicity\nmodulus. In addition to the (conventional) Berezinskii-Kosterlitz-Thousless\ntransition out of the atomic superfluid, we furthermore identify a direct\nthermal phase transition separating the pair and the atomic superfluid phases,\nand show that this transition is continuous with critical scaling exponents\nconsistent with those of the two-dimensional Ising universality class. We\nexhibit a direct connection between the partial loss of quasi long-range order\nat the Ising transition between the two superfluids and the parity selection in\nthe atomic winding number fluctuations that distinguish the atomic from the\npair superfluid."
    },
    {
        "anchor": "Dependence of structure factor and correlation energy on the width of\n  electron wires: The structure factor and correlation energy of a quantum wire of thickness\n$b\\ll a_B$ are studied in random phase approximation and for the less\ninvestigated region $r_s<1$. Using the single-loop approximation, analytical\nexpressions of the structure factor have been obtained. The exact expressions\nfor the exchange energy are also derived for a cylindrical and harmonic wire.\nThe correlation energy $\\epsilon_c$ is found to be represented by $\\epsilon_c\n(b,r_s)= \\frac{\\alpha(r_s)}{b} + \\beta(r_s)\\; ln(b) + \\eta(r_s)$, for small $b$\nand high densities. For a pragmatic width of the wire, the correlation energy\nis in agreement with the quantum Monte Carlo simulation data.",
        "positive": "Coupled-cluster theory for trapped bosonic mixtures: We develop a coupled-cluster theory for bosonic mixtures of binary species in\nexternal traps, providing a promising theoretical approach to demonstrate\nhighly accurately the many-body physics of mixtures of Bose-Einstein\ncondensates. The coupled-cluster wavefunction for the binary species is\nobtained when an exponential cluster operator $e^T$, where\n$T=T^{(1)}+T^{(2)}+T^{(12)}$ and $T^{(1)}$ accounts for excitations in\nspecies-1, $T^{(2)}$ for excitations in species-2, and $T^{(12)}$ for combined\nexcitations in both species, acts on the ground state configuration prepared by\naccumulating all bosons in a single orbital for each species. We have\nexplicitly derived the working equations for the bosonic mixtures by truncating\nthe cluster operator upto the single and double excitations and using an\narbitrary sets of orthonormal orbitals for each of the species. Further, the\ncomparatively simplified version of the working equations are formulated using\nthe Fock-like operators. Finally, using an exactly solvable many-body model for\nbosonic mixtures that exists in the literature allows us to implement and test\nthe performance and accuracy of the coupled-cluster theory for situations with\nbalanced as well as imbalanced boson numbers and for weak to moderately strong\nintra- and inter-species interaction strengths. The comparison between our\ncomputed results using coupled-cluster theory with the respective analytical\nexact results displays remarkable agreement exhibiting excellent success of the\ncoupled-cluster theory for bosonic mixtures. All in all, the correlation\nexhaustive coupled-cluster theory shows encouraging results and it could be a\npromising approach in paving the way for high-accuracy modelling of various\nbosonic mixture systems."
    },
    {
        "anchor": "Multimode Trapped Interferometer with Ideal Bose-Einstein Condensates: We experimentally demonstrate a multi-mode interferometer comprising a\nBose-Einstein condensate of $^{39}$K atoms trapped in a harmonic potential,\nwhere the interatomic interaction can be cancelled exploiting Feshbach\nresonances. Kapitza-Dirac diffraction from an optical lattice coherently splits\nthe BEC in multiple momentum components equally spaced that form different\ninterferometric paths, closed by the trapping harmonic potential. We\ninvestigate two different interferometric schemes, where the recombination\npulse is applied after a full or half oscillation in the confining potential.\nWe find that the relative amplitudes of the momentum components at the\ninterferometer output are sensitive to external forces, through the induced\ndisplacement of the harmonic potential with respect to the optical lattice. We\nshow how to calibrate the interferometer, fully characterize its output and\ndiscuss perspective improvements.",
        "positive": "Quantum Spin Dynamics in a Normal Bose Gas with Spin-orbit Coupling: In this Letter, we investigate spin dynamics of a two-component Bose gas with\nspin-orbit coupling realised in cold atom experiments. We derive coupled\nhydrodynamic equations for number and spin densities as well as their\nassociated currents. Specialising to quasi-one-dimensional situation, we obtain\nanalytic solutions of the spin helix structure and its dynamics in both\nadiabatic and diabatic regimes. In the adiabatic regime, the transverse spin\ndecays parabolically in the short-time limit and exponentially in the long time\nlimit, depending on initial polarisation. In contrast, in the diabatic regime,\ntransverse spin density and current oscillate in a way similar to the\ncharge-current oscillation in an undamped LC circuit. The effects of Rabi\ncoupling on the short-time spin dynamics is also discussed. Finally, using\nrealistic experimental parameters for $^{87}$Rb, we show that the time scales\nfor spin dynamics is of order of milliseconds to a few seconds and can be\nobserved experimentally."
    },
    {
        "anchor": "Small two-component Fermi gases in a cubic box with periodic boundary\n  conditions: The properties of two-component Fermi gases become universal if the\ninterspecies s-wave scattering length $a_s$ and the average interparticle\nspacing are much larger than the range of the underlying two-body potential.\nUsing an explicitly correlated Gaussian basis set expansion approach, we\ndetermine the eigen energies of two-component Fermi gases in a cubic box with\nperiodic boundary conditions as functions of the interspecies s-wave scattering\nlength and the effective range of the two-body potential. The universal\nproperties of systems consisting of up to four particles are determined by\nextrapolating the finite-range energies to the zero-range limit. We determine\nthe eigen energies of states with vanishing and finite momentum. In the\nweakly-attractive BCS regime, we analyze the energy spectra and degeneracies\nusing first-order degenerate perturbation theory. Excellent agreement between\nthe perturbative energy shifts and the numerically determined energies is\nobtained. For the infinitely large scattering length case, we compare our\nresults - where available - with those presented in the literature.",
        "positive": "Transition state theory for wave packet dynamics. II. Thermal decay of\n  Bose-Einstein condensates with long-range interaction: We apply transition state theory to coupled Gaussian wave packets and\ncalculate thermal decay rates of Bose-Einstein condensates with additional\nlong-range interaction. The ground state of such a condensate is metastable if\nthe contact interaction is attractive and a sufficient thermal excitation may\nlead to its collapse. The use of transition state theory is made possible by\ndescribing the condensate within a variational framework and locally mapping\nthe variational parameters to classical phase space as has been demonstrated in\nthe preceding paper [A. Junginger, J. Main, and G. Wunner, submitted to J.\nPhys. A]. We apply this procedure to Gaussian wave packets and present results\nfor condensates with monopolar 1/r-interaction comparing decay rates obtained\nby using different numbers of coupled Gaussian trial wave functions as well as\ndifferent normal form orders."
    },
    {
        "anchor": "Quantum bright solitons in a quasi-one-dimensional optical lattice: We study a quasi-one-dimensional attractive Bose gas confined in an optical\nlattice with a superimposed harmonic potential by analyzing the effective\none-dimensional Bose-Hubbard Hamiltonian of the system. In order to have a\nreliable description of the ground-state, that we call quantum bright soliton,\nwe use the Density-Matrix-Renormalization-Group (DMRG) technique. By comparing\nDMRG results with mean-field (MF) ones we find that beyond-mean-field effects\nbecome relevant by increasing the attraction between bosons or by decreasing\nthe frequency of the harmonic confinement. In particular we discover that,\ncontrary to the MF predictions based on the discrete nonlinear Schr\u007f\\\"odinger\nequation, quantum bright solitons are not self-trapped. We also use the\ntime-evolving-block-decimation (TEBD) method to investigate dynamical\nproperties of bright solitons when the frequency of the harmonic potential is\nsuddenly increased. This quantum quench induces a breathing mode whose period\ncrucially depends on the final strength of the super-imposed harmonic\nconfinement.",
        "positive": "Adiabatic Formation of Rydberg Crystals with Chirped Laser Pulses: Ultracold atomic gases have been used extensively in recent years to realize\ntextbook examples of condensed matter phenomena. Recently, phase transitions to\nordered structures have been predicted for gases of highly excited, 'frozen'\nRydberg atoms. Such Rydberg crystals are a model for dilute metallic solids\nwith tunable lattice parameters, and provide access to a wide variety of\nfundamental phenomena. We investigate theoretically how such structures can be\ncreated in four distinct cold atomic systems, by using tailored\nlaser-excitation in the presence of strong Rydberg-Rydberg interactions. We\nstudy in detail the experimental requirements and limitations for these\nsystems, and characterize the basic properties of small crystalline Rydberg\nstructures in one, two and three dimensions."
    },
    {
        "anchor": "Quantum phases in spin-orbit-coupled Floquet spinor Bose gases: We propose a spin-orbit-coupled Floquet spinor Bose-Einstein condensate (BEC)\nwhich can be implemented by Floquet engineering of a quadratic Zeeman field.\nThe Floquet spinor BEC has a Bessel-function-modulated Rabi frequency and a\nFloquet-induced spin-exchange interaction. The quantum phase diagram of the\nspin-orbit-coupled Floquet spinor BEC is investigated by considering\nantiferromagnetic or ferromagnetic spin-spin interactions. In comparison with\nthe usual spin-orbit-coupled spin-1 BEC, we find that a stripe phase for\nantiferromagnetic interactions can exist in a large quadratic Zeeman field\nregime, and a different stripe phase with an experimentally favorable contrast\nfor ferromagnetic interactions is uncovered.",
        "positive": "Commensurate-incommensurate transition in frustrated Wigner crystals: Geometric frustration in systems with long-range interactions is a largely\nunexplored phenomenon. In this work we analyse the ground state emerging from\nthe competition between a periodic potential and a Wigner crystal in one\ndimension, consisting of a selforganized chain of particles with the same\ncharge. This system is a paradigmatic realization of the Frenkel-Kontorova\nmodel with Coulomb interactions. We derive the action of a Coulomb soliton in\nthe continuum limit and demonstrate the mapping to a massive (1+1) Thirring\nmodel with long-range interactions. Here, the solitons are charged fermionic\nexcitations over an effective Dirac sea. The mismatch between the periodicities\nof potential and chain, giving rise to frustration, is a chemical potential\nwhose amplitude is majorly determined by the Coulomb self-energy. The\nmean-field limit is a long-range antiferromagnetic spin chain with uniform\nmagnetic field and predicts that the commensurate, periodic structures form a\ncomplete devil's staircase as a function of the charge density. Each step of\nthe staircase correspond to the interval of stability of a stable commensurate\nphase and scales with the number $N$ of charges as $1/\\ln N$. This implies that\nthere is no commensurate-incommensurate phase transition in the thermodynamic\nlimit. For finite systems, however, the ground state has a fractal structure\nthat could be measured in experiments with laser-cooled ions in traps."
    },
    {
        "anchor": "Quench-produced solitons in a box-trapped Bose-Einstein condensate: We describe a protocol to prepare solitons in a quasi-1d box-trapped\nBose-Einstein condensate using only a quench of the isotropic s-wave scattering\nlength. A quench to exactly four times the initial 1d coupling strength creates\none soliton at each boundary of the box, which then propagate in a uniform\nbackground density and collide with one another. No nonsolotonic excitations\nare created during the quench. The procedure is robust against imperfections in\nthe scattering length ramp rate and a mismatch of the final scattering length.",
        "positive": "Direct observation of coherent inter-orbital spin-exchange dynamics: We report on the first direct observation of fast spin-exchange coherent\noscillations between different long-lived electronic orbitals of ultracold\n$^{173}$Yb fermions. We measure, in a model-independent way, the strength of\nthe exchange interaction driving this coherent process. This observation allows\nus to retrieve important information on the inter-orbital collisional\nproperties of $^{173}$Yb atoms and paves the way to novel quantum simulations\nof paradigmatic models of two-orbital quantum magnetism."
    },
    {
        "anchor": "Tensor-network study of correlation-spreading dynamics in the\n  two-dimensional Bose-Hubbard model: Recent developments in analog quantum simulators based on cold atoms and\ntrapped ions call for cross-validating the accuracy of quantum-simulation\nexperiments with use of quantitative numerical methods; however, it is\nparticularly challenging for dynamics of systems with more than one spatial\ndimension. Here we demonstrate that a tensor-network method running on\nclassical computers is useful for this purpose. We specifically analyze\nreal-time dynamics of the two-dimensional Bose-Hubbard model after a sudden\nquench starting from the Mott insulator by means of the tensor-network method\nbased on infinite projected entangled pair states. Calculated single-particle\ncorrelation functions are found to be in good agreement with a recent\nexperiment. By estimating the phase and group velocities from the\nsingle-particle and density-density correlation functions, we predict how these\nvelocities vary in the moderate interaction region, which serves as a\nquantitative benchmark for future experiments and numerical simulations.",
        "positive": "Response to comment on \"Quantum time crystals and interacting gauge\n  theories in atomic Bose-Einstein condensates\" by Syrwid, Kosior, and Sacha: In a recent comment [1] on our paper [2] Syrwid, Kosior, and Sacha (SKS)\nasserted that we did not correctly calculate the chiral soliton energy ${\\cal\nE}_{LAB}$ in the lab frame, and further that the system we proposed is not\ncapable of supporting a genuine quantum time crystal. We concede that we did\nnot correctly calculate ${\\cal E}_{LAB}$ but we illustrate below that our\nsystem can nonetheless display time crystal behavior with a ground state that\nis spatially localized and rotating."
    },
    {
        "anchor": "Stable and unstable vortex knots in a trapped Bose-Einstein condensate: The dynamics of a quantum vortex torus knot ${\\cal T}_{P,Q}$ and similar\nknots in an atomic Bose-Einstein condensate at zero temperature in the\nThomas-Fermi regime has been considered in the hydrodynamic approximation. The\ncondensate has a spatially nonuniform equilibrium density profile $\\rho(z,r)$\ndue to an external axisymmetric potential. It is assumed that $z_*=0$, $r_*=1$\nis a maximum point for function $r\\rho(z,r)$, with $\\delta\n(r\\rho)\\approx-(\\alpha-\\epsilon) z^2/2 -(\\alpha+\\epsilon) (\\delta r)^2/2$ at\nsmall $z$ and $\\delta r$. Configuration of knot in the cylindrical coordinates\nis specified by a complex $2\\pi P$-periodic function\n$A(\\varphi,t)=Z(\\varphi,t)+i [R(\\varphi,t)-1]$. In the case $|A|\\ll 1$ the\nsystem is described by relatively simple approximate equations for re-scaled\nfunctions $W_n(\\varphi)\\propto A(2\\pi n+\\varphi)$, where $n=0,\\dots,P-1$, and\n$iW_{n,t}=-(W_{n,\\varphi\\varphi}+\\alpha W_n -\\epsilon W_n^*)/2-\\sum_{j\\neq\nn}1/(W_n^*-W_j^*)$. At $\\epsilon=0$, numerical examples of stable solutions as\n$W_n=\\theta_n(\\varphi-\\gamma t)\\exp(-i\\omega t)$ with non-trivial topology have\nbeen found for $P=3$. Besides that, dynamics of various non-stationary knots\nwith $P=3$ was simulated, and in some cases a tendency towards a finite-time\nsingularity has been detected. For $P=2$ at small $\\epsilon\\neq 0$, rotating\naround $z$ axis configurations of the form $(W_0-W_1)\\approx\nB_0\\exp(i\\zeta)+\\epsilon C(B_0,\\alpha)\\exp(-i\\zeta) + \\epsilon\nD(B_0,\\alpha)\\exp(3i\\zeta)$ have been investigated, where $B_0>0$ is an\narbitrary constant, $\\zeta=k_0\\varphi -\\Omega_0 t+\\zeta_0$, $k_0=Q/2$,\n$\\Omega_0=(k_0^2-\\alpha)/2-2/B_0^2$. In the parameter space $(\\alpha, B_0)$,\nwide stability regions for such solutions have been found. In unstable bands, a\nrecurrence of the vortex knot to a weakly excited state has been noted to be\npossible.",
        "positive": "\"Doubly-magic\" conditions in magic-wavelength trapping of ultracold\n  alkalis: In experiments with trapped atoms, atomic energy levels are shifted by the\ntrapping optical and magnetic fields. Regardless of this strong perturbation,\nprecision spectroscopy may be still carried out using specially crafted,\n\"magic\" trapping fields. Finding these conditions for particularly valuable\nmicrowave clock transitions in alkalis has so far remained an open challenge.\nHere I demonstrate that the microwave clock transitions for alkalis may be\nindeed made impervious to both trapping laser intensity and fluctuations of\nmagnetic fields. I consider driving multiphoton transitions between the clock\nlevels and show that these \"doubly-magic\" conditions are realized at special\nvalues of trapping laser wavelengths and fixed values of relatively weak\nmagnetic fields. This finding has implications for precision measurements and\nquantum information processing with qubits stored in hyperfine manifolds."
    },
    {
        "anchor": "Exact results of dynamical structure factor of Lieb-Liniger model: The dynamical structure factor (DSF) represents a measure of dynamical\ndensity-density correlations in a quantum many-body system. Due to the\ncomplexity of many-body correlations and quantum fluctuations in a system of an\ninfinitely large Hilbert space, such kind of dynamical correlations often\nimpose a big theoretical challenge. For one dimensional (1D) quantum many-body\nsystems, qualitative predictions of dynamical response functions are usually\ncarried out by using the Tomonaga-Luttinger liquid (TLL) theory. In this\nscenario, a precise evaluation of the DSF for a 1D quantum system with\narbitrary interaction strength remains a formidable task. In this paper, we use\nthe form factor approach based on algebraic Bethe ansatz theory to calculate\nprecisely the DSF of Lieb-Liniger model with an arbitrary interaction strength\nat a large scale of particle number. We find that the DSF for a system as large\nas 2000 particles enables us to depict precisely its line-shape from which the\npower-law singularity with corresponding exponents in the vicinities of\nspectral thresholds naturally emerge. It should be noted that, the advantage of\nour algorithm promises an access to the threshold behavior of dynamical\ncorrelation functions, further confirming the validity of nonlinear TLL theory\nbesides Kitanine et. al. 2012 J. Stat. Mech. P09001. Finally we discuss a\ncomparison of results with the results from the ABACUS method by J.-S. Caux\n2009 J. Math. Phys. 50 095214 as well as from the strongly coupling expansion\nby Brand and Cherny 2005 Phys. Rev. A 72 033619.",
        "positive": "Stability and phase transition of localized modes in Bose-Einstein\n  condensates with both two- and three-body interactions: We investigate the stability and phase transition of localized modes in\nBose-Einstein Condensates (BECs) in an optical lattice with the discrete\nnonlinear Schr\\\"{o}dinger model by considering both two- and three-body\ninteractions. We find that there are three types of localized modes, bright\ndiscrete breather (DB), discrete kink (DK), and multi-breather (MUB). Moreover,\nboth two- and three-body on-site repulsive interactions can stabilize DB, while\non-site attractive three-body interactions destabilize it. There is a critical\nvalue for the three-body interaction with which both DK and MUB become the most\nstable ones. We give analytically the energy thresholds for the destabilization\nof localized states and find that they are unstable (stable) when the total\nenergy of the system is higher (lower) than the thresholds. The stability and\ndynamics characters of DB and MUB are general for extended lattice systems. Our\nresult is useful for the blocking, filtering, and transfer of the norm in\nnonlinear lattices for BECs with both two- and three-body interactions."
    },
    {
        "anchor": "A generalized phase space approach for solving quantum spin dynamics: Numerical techniques to efficiently model out-of-equilibrium dynamics in\ninteracting quantum many-body systems are key for advancing our capability to\nharness and understand complex quantum matter. Here we propose a new numerical\napproach which we refer to as GDTWA. It is based on a discrete semi-classical\nphase-space sampling and allows to investigate quantum dynamics in lattice spin\nsystems with arbitrary $S\\geq 1/2$. We show that the GDTWA can accurately\nsimulate dynamics of large ensembles in arbitrary dimensions. We apply it for\n$S>1/2$ spin-models with dipolar long-range interactions, a scenario arising in\nrecent experiments with magnetic atoms. We show that the method can capture\nbeyond mean-field effects, not only at short times, but it also correctly\nreproduces long time quantum-thermalization dynamics. We benchmark the method\nwith exact diagonalization in small systems, with perturbation theory for short\ntimes, and with analytical predictions made for closed system which feature\nquantum-thermalization at long times. By computing the Renyi entropy, currently\nan experimentally accessible quantifier of entanglement, we reveal that large\n$S$ systems can feature larger entanglement than corresponding $S=1/2$ systems.\nOur analyses demonstrate that the GDTWA can be a powerful tool for modeling\ncomplex spin dynamics in regimes where other state-of-the art numerical methods\nfail.",
        "positive": "GPU-accelerated solutions of the nonlinear Schr\u00f6dinger equation for\n  simulating 2D spinor BECs: As a first approximation beyond linearity, the nonlinear Schr\\\"odinger\nequation (NLSE) reliably describes a broad class of physical systems. Though\nnumerical solutions of this model are well-established, these methods can be\ncomputationally complex. In this paper, we showcase a code development\napproach, demonstrating how computational time can be significantly reduced\nwith readily available graphics processing unit (GPU) hardware and a\nstraightforward code migration using open-source libraries. This process shows\nhow CPU computations with power-law scaling in computation time with grid size\ncan be made linear using GPUs. As a specific case study, we investigate the\nGross-Pitaevskii equation, a specific version of the nonlinear Schr\\\"odinger\nmodel, as it describes in two dimensions a trapped, interacting, two-component\nBose-Einstein condensate (BEC) subject to a spatially dependent interspin\ncoupling, resulting in an analog to a spin-Hall system. This computational\napproach lets us probe high-resolution spatial features - revealing an\ninteraction-dependent phase transition - all in a reasonable amount of time.\nOur computational approach is particularly relevant for research groups looking\nto easily accelerate straightforward numerical simulation of physical\nphenomena."
    },
    {
        "anchor": "Repulsive Fermions in Optical Lattices: Phase separation versus\n  Coexistence of Antiferromagnetism and d-Superfluidity: We investigate a system of fermions on a two-dimensional optical square\nlattice in the strongly repulsive coupling regime. In this case, the\ninteractions can be controlled by laser intensity as well as by Feshbach\nresonance. We compare the energetics of states with resonating valence bond\nd-wave superfluidity, antiferromagnetic long range order and a homogeneous\nstate with coexistence of superfluidity and antiferromagnetism. We show that\nthe energy density of a hole $e_{hole}(x)$ has a minimum at doping $x=x_c$ that\nsignals phase separation between the antiferromagnetic and d-wave paired\nsuperfluid phases. The energy of the phase-separated ground state is however\nfound to be very close to that of a homogeneous state with coexisting\nantiferromagnetic and superfluid orders. We explore the dependence of the\nenergy on the interaction strength and on the three-site hopping terms and\ncompare with the nearest neighbor hopping {\\it t-J} model.",
        "positive": "The phase-separation mechanism of a binary mixture in a ring trimer: We show that, depending on the ratio between the inter- and the intra-species\ninteractions, a binary mixture trapped in a three-well potential with periodic\nboundary conditions exhibits three macroscopic ground-state configurations\nwhich differ in the degree of mixing. Accordingly, the corresponding quantum\nstates feature either delocalization or a Schr\\\"odinger cat-like structure. The\ntwo-step phase separation occurring in the system, which is smoothed by the\nactivation of tunnelling processes, is confirmed by the analysis of the energy\nspectrum that collapses and rearranges at the two critical points. In such\npoints, we show that also Entanglement Entropy, a quantity borrowed from\nquantum-information theory, features singularities, thus demonstrating its\nability to witness the double mixining-demixing phase transition. The developed\nanalysis, which is of interest to both the experimental and theoretical\ncommunities, opens the door to the study of the demixing mechanism in complex\nlattice geometries."
    },
    {
        "anchor": "Cross-symmetric dipolar-matter-wave solitons in double-well chains: We consider a dipolar Bose-Einstein condensate trapped in an array of\ntwo-well systems with an arbitrary orientations of the dipoles relative to the\nsystem's axis. The system can be built as a chain of local traps sliced into\ntwo parallel lattices by a repelling laser sheet. It is modelled by a pair of\ncoupled discrete Gross-Pitaevskii equations, with dipole-dipole self- and\ncross-interactions. When the dipoles are not polarized perpendicular or\nparallel to the lattice, the cross-interaction is asymmetric, replacing the\nfamiliar symmetric two-component discrete solitons by two new species of\ncross-symmetric ones, on-site- and off-site-centered, which are strongly\naffected by the orientation of the dipoles and separation between the parallel\nlattices. A very narrow region of intermediate asymmetric discrete solitons is\nfound at the boundary between the on- and off-site families. Two different\ntypes of solitons in the $\\mathcal{PT}$%-symmetric version of the system are\nconstructed too, and stability areas are identified for them.",
        "positive": "Strongly Interacting Two-Dimensional Bose Gases: We prepare and study strongly interacting two-dimensional Bose gases in the\nsuperfluid, the classical Berezinskii-Kosterlitz-Thouless (BKT) transition, and\nthe vacuum-to-superfluid quantum critical regimes. A wide range of the two-body\ninteraction strength 0.05 < g < 3 is covered by tuning the scattering length\nand by loading the sample into an optical lattice. Based on the equations of\nstate measurements, we extract the coupling constants as well as critical\nthermodynamic quantities in different regimes. In the superfluid and the BKT\ntransition regimes, the extracted coupling constants show significant\ndown-shifts from the mean-field and perturbation calculations when g approaches\nor exceeds one. In the BKT and the quantum critical regimes, all measured\nthermodynamic quantities show logarithmic dependence on the interaction\nstrength, a tendency confirmed by the extended classical-field and\nrenormalization calculations."
    },
    {
        "anchor": "Dirac Equation For Cold Atoms In Artificial Curved Spacetimes: We argue that the Fermi-Hubbard Hamiltonian describing the physics of\nultracold atoms on optical lattices in the presence of artificial non-Abelian\ngauge fields, is exactly equivalent to the gauge theory Hamiltonian describing\nDirac fermions in the lattice. We show that it is possible to couple the Dirac\nfermions to an \"artificial\" gravitational field, i.e. to consider the Dirac\nphysics in a curved spacetime. We identify the special class of spacetime\nmetrics that admit a simple realization in terms of a Fermi-Hubbard model\nsubjected to an artificial SU(2) field, corresponding to position dependent\nhopping matrices. As an example, we discuss in more detail the physics of the\n2+1D Rindler metric, its possible experimental realization and detection.",
        "positive": "Exact solution of the three-boson problem at vanishing energy: A zero range approach is used to model resonant two-body interactions between\nthree identical bosons. A dimensionless phase parametrizes the three-body\nboundary condition while the scattering length enters the Bethe-Peierls\nboundary condition. The model is solved exactly at zero energy for any value of\nthe scattering length, positive or negative. From this solution, an analytical\nexpression for the rate of three-body recombination to the universal shallow\ndimer is extracted."
    },
    {
        "anchor": "A geometric wave function for few interacting bosons in a harmonic trap: We establish a new geometric wave function that combined with a variational\nprinciple efficiently describes a system of bosons interacting in a\none-dimensional trap. By means of a a combination of the exact wave function\nsolution for contact interactions and the asymptotic behaviour of the harmonic\npotential solution we obtain the ground state energy, probability density and\nprofiles of a few boson system in a harmonic trap. We are able to access all\nregimes, ranging from the strongly attractive to the strongly repulsive one\nwith an original and simple formulation.",
        "positive": "Flux-driven quantum spin liquids in kagome optical lattices: Quantum spin liquids (QSLs) define an exotic class of quantum ground states\nwhere spins are disordered down to zero temperature. We propose routes to QSLs\nin kagome optical lattices using applied flux. An optical flux lattice can be\napplied to induce a uniform flux and chiral three-spin interactions that drive\nthe formation of a gapped chiral spin liquid. A different approach based on\nrecent experiments using laser-assisted tunneling and lattice tilt implements a\nstaggered flux pattern which can drive a gapless spin liquid with symmetry\nprotected nodal lines. Our proposals, therefore, establish kagome optical\nlattices with effective flux as a powerful platform for exploration of QSLs."
    },
    {
        "anchor": "Understanding many-body physics in one dimension from the Lieb-Liniger\n  model: This article presents an elementary introduction on various aspects of the\nprototypical integrable model the Lieb-Liniger Bose gas ranging from the\ncooperative to the collective features of many-body phenomena [1]. In 1963 Lieb\nand Liniger first solved this quantum field theory many-body problem using the\nBethe's hypothesis, i.e. a particular form of wave function introduced by Bethe\nin solving the one-dimensional Heisenberg model in 1931. Despite the\nLieb-Liniger model is arguably the simplest exactly solvable model, it exhibits\nrich quantum many-body physics in terms of the aspects of mathematical\nintegrability and physical universality. Moreover, the Yang-Yang grand\ncanonical ensemble description for the model provides us with a deep\nunderstanding of quantum statistics, thermodynamics and quantum critical\nphenomena at the many-body physics level. Recently, such fundamental physics of\nthis exactly solved model has been attracting growing interest in experiments.\nSince 2004, there have been more than 20 experimental papers that report novel\nobservations of different physical aspects of the Lieb-Liniger model in the\nlab. So far the observed results to date are seen to be in excellent agreement\nwith results obtained using the analysis of this simplest exactly solved model.\nThose experimental observations reveal the unique beauty of integrability.",
        "positive": "Metrology and Many-Body Physics with Ultracold Metastable Helium: Ultracold dilute gases provide ideal settings for measurements of atomic\nstructure. Helium has an internal structure sufficiently simple to permit\nhighly accurate predictions of its resonances and transition rates. Precise\nlaser spectroscopy of helium thus yields empirical constraints on such\ncalculations. These are desirable in the ongoing investigations seeking to\nreconcile the disagreement between independent determinations of nuclear charge\nradius data in both hydrogenic and helium atoms. Either the size of these\nparticles are truly constant and quantum electrodynamics (QED) is flawed, or\nthe theory is correct and some new physics is at play at the atomic scale.\n  Ultracold bose gases also serve as ideal testing ground to better understand\nthe physics of Bose-Einstein condensation, superfluidity, and the effects of\nweak interactions in condensed-matter systems. The large internal energy of\nhelium's metastable excited state enables the measurement of the momentum of\nsingle atoms, providing a new lens through which to examine both\nweakly-interacting and strongly-correlated systems. This feature is employed to\ninvestigate the quantum depletion of a BEC after expansion into the far-field.\nFinally, the appendix reports on early progress towards the realization of an\noptical lattice trap for helium."
    },
    {
        "anchor": "Dipolar condensates with tilted dipoles in a pancake-shaped confinement: The effect of dipolar orientation with respect to the condensate plane on the\nmean-field dynamics of dipolar Bose-Einstein condensates in a pancake-shaped\nconfinement is discussed. The stability of a quasi-two-dimensional condensate,\nwith respect to the tilting angle, is found to be different from a\ntwo-dimensional layer of dipoles, indicating the relevance of the transverse\nextension while characterizing two-dimensional dipolar systems. An anisotropic\nexcitation spectrum exhibiting a highly tunable, rotonlike minimum can arise\nentirely from the dipole-dipole interactions, by tilting the dipoles. At the\nmagic angle and in the absence of contact interactions, the long-wavelength\nexcitations are not phononlike and always unstable. The post-roton-instability\ndynamics, in contrast to phonon instability, in a uniform condensate, is\nfeatured by a transient, defect-free, stripe pattern, which eventually\nundergoes local collapses, and driving the condensate back into the stable\nregime can make them sustained for longer. Hopping between stripes has been\nobserved before it melts into a uniform state in the presence of dissipation.\nFinally, we discuss a class of solutions, in which a quasi-two-dimensional\ncondensate is self-trapped in one direction, as well as a regime of interaction\nparameters, including attractive short-range interactions, at which a\ntwo-dimensional anisotropic soliton can be stabilized, and we show that a\nchromium condensate with a relatively small number of atoms is well suited for\nthis.",
        "positive": "Quantum Quenches in an XXZ Spin Chain from a Spatially Inhomogeneous\n  Initial State: Results are presented for the nonequilibrium dynamics of a quantum $XXZ$-spin\nchain whose spins are initially arranged in a domain wall profile via the\napplication of a magnetic field in the $z$-direction which is spatially varying\nalong the chain. The system is driven out of equilibrium in two ways: a). by\nrapidly turning off the magnetic field, b). by rapidly quenching the\ninteractions at the same time as the magnetic field is turned off. The\ntime-evolution of the domain wall profile as well as various two-point spin\ncorrelation functions is studied by the exact solution of the fermionic problem\nfor the $XX$ chain and via a bosonization approach and a mean-field approach\nfor the $XXZ$ chain. At long times the magnetization is found to equilibrate\n(reach the ground state value), while the two-point correlation functions in\ngeneral do not. In particular, for quenches within the gapless $XX$ phase, the\ntransverse spin correlation functions acquire a spatially inhomogeneous\nstructure at long times whose details depend on the initial domain wall\nprofile. The spatial inhomogeneity is also recovered for the case of classical\nspins initially arranged in a domain wall profile and shows that the\ninhomogeneities arise due to the dephasing of transverse spin components as the\ndomain wall broadens. A generalized Gibbs ensemble approach is found to be\ninadequate in capturing this spatially inhomogeneous state."
    },
    {
        "anchor": "On the role of hyperfine-interactions-mediated Zeeman effect in the\n  condensation temperature shift of trapped atomic Bose-Einstein condensates: We discuss the effect of interatomic interactions on the condensation\ntemperature $T_c$ of a laboratory atomic Bose-Einstein condensate under the\ninfluence of an external trapping magnetic field. We predict that accounting\nfor hyperfine interactions mediated Zeeman term in the mean-field approximation\nproduces, in the case of the $403 \\, G$ Feshbach resonance in the $|F,m_F> =\n|1,1>$ hyperfine state of a $^{39}K$ condensate, with $F$ the total spin of the\natom, an experimentally observed (and not yet explained) shift in the\ncondensation temperature $\\Delta T_{c}/T_{c}^{0}=b^{*}_0+b^{*}_1\n(a/\\lambda_{T}) + b^{*}_2 (a/\\lambda_{T})^2$ with $b^{*}_0 \\simeq 0.0002$,\n$b^{*}_1 \\simeq -3.4$ and $b^{*}_2 \\simeq 47$, where $a$ is the s-wave\nscattering length, and $\\lambda_T$ is the thermal wavelength at $T_{c}^{0}$.\nGeneric expressions for the coefficients $b^*_0$, $b^*_1$ and $b^*_2$ are also\nobtained, which can be used to predict the temperature shift for other Feshbach\nresonances of $^{39}K$ or other atomic condensates.",
        "positive": "Interaction-induced localization of fermionic mobile impurities in a\n  Larkin-Ovchinnikov superfluid: We theoretically investigate the interplay between the fermionic mobile\nimpurity atoms and a Larkin-Ovchinnikov (LO) superfluid in a two dimensional\noptical lattice. We find that the impurity atoms get localized and can form\npairs when the interaction between the impurity atoms and the LO superfluid is\nstrong enough. These features are due to the phenomena of self-localization\nwhose underlying mechanism is revealed by an effective model. The impurity\natoms with finite concentrations can drive the transition from a\ntwo-dimensional-checkerboard-like LO state to a\nquasi-one-dimensional-stripe-like one. Experimental preparations to observe\nthese features are also discussed."
    },
    {
        "anchor": "Quantum Charge Pumps with Topological Phases in Creutz Ladder: Quantum charge pumping phenomenon connects band topology through the dynamics\nof a one-dimensional quantum system. In terms of a microscopic model, the\nSu-Schrieffer-Heeger/Rice-Mele quantum pump continues to serve as a fruitful\nstarting point for many considerations of topological physics. Here we present\na generalized Creutz scheme as a distinct two-band quantum pump model. By\nnoting that it undergoes two kinds of topological band transitions accompanying\nwith a Zak-phase-difference of $\\pi$ and $2\\pi$, respectively, various charge\npumping schemes are studied by applying an elaborate Peierl's phase\nsubstitution. Translating into real space, the transportation of quantized\ncharges is a result of cooperative quantum interference effect. In particular,\nan all-flux quantum pump emerges which operates with time-varying fluxes only\nand transports two charge units. This puts cold atoms with artificial gauge\nfields as an unique system where this kind of phenomena can be realized.",
        "positive": "A repulsive atomic gas in a harmonic trap on the border of itinerant\n  ferromagnetism: Alongside superfluidity, itinerant (Stoner) ferromagnetism remains one of the\nmost well-characterized phases of correlated Fermi systems. A recent experiment\nhas reported the first evidence for novel phase behavior on the repulsive side\nof the Feshbach resonance in a two-component ultracold Fermi gas. By adapting\nrecent theoretical studies to the atomic trap geometry, we show that an\nadiabatic ferromagnetic transition would take place at a weaker interaction\nstrength than is observed in experiment. This discrepancy motivates a simple\nnon-equilibrium theory that takes account of the dynamics of magnetic defects\nand three-body losses. The formalism developed displays good quantitative\nagreement with experiment."
    },
    {
        "anchor": "Stoner ferromagnetism of a strongly interacting Fermi gas in the\n  quasirepulsive regime: Recent advances in rapidly quenched ultracold atomic Fermi gases near a\nFeshbach resonance have brought about a number of interesting problems, in the\ncontext of observing the long-sought Stoner ferromagnetic phase transition. The\npossibility of experimentally obtaining a \"quasirepulsive\" regime in the upper\nbranch of the energy spectrum due to the rapid quench is currently being\ndebated, and the Stoner transition has mainly been investigated theoretically\nby using perturbation theory or at high polarization, due to the limited\ntheoretical approaches in the strongly repulsive regime. In this work, we\npresent a nonperturbative theoretical approach to the quasirepulsive upper\nbranch of a Fermi gas near a broad Feshbach resonance, and we determine the\nfinite-temperature phase diagram for the Stoner instability. Our results agree\nwell with the known quantum Monte-Carlo simulations at zero temperature, and we\nrecover the known virial expansion prediction at high temperature for arbitrary\ninteraction strengths. At resonance, we find that the Stoner transition\ntemperature becomes of the order of the Fermi temperature, around which the\nmolecule formation rate becomes vanishingly small. This suggests a feasible way\nto observe Stoner ferromagnetism in the nondegenerate temperature regime.",
        "positive": "Two-photon photoassociation spectroscopy of an ultracold heteronuclear\n  molecule: We report on two-photon photoassociation (PA) spectroscopy of ultracold\nheteronuclear LiRb molecules. This is used to determine the binding energies of\nthe loosely bound levels of the electronic ground singlet and the lowest\ntriplet states of LiRb. We observe strong two-photon PA lines with power\nbroadened line widths greater than 20 GHz at relatively low laser intensity of\n30 W/cm$^{2}$. The implication of this observation on direct atom to molecule\nconversion using stimulated Raman adiabatic passage (STIRAP) is discussed and\nthe prospect for electronic ground state molecule production is theoretically\nanalyzed."
    },
    {
        "anchor": "Entropy exchange in a mixture of ultracold atoms: We investigate experimentally the entropy transfer between two\ndistinguishable atomic quantum gases at ultralow temperatures. Exploiting a\nspecies-selective trapping potential, we are able to control the entropy of one\ntarget gas in presence of a second auxiliary gas. With this method, we drive\nthe target gas into the degenerate regime in conditions of controlled\ntemperature by transferring entropy to the auxiliary gas. We envision that our\nmethod could be useful both to achieve the low entropies required to realize\nnew quantum phases and to measure the temperature of atoms in deep optical\nlattices. We verified the thermalization of the two species in a 1D lattice.",
        "positive": "Quantum correlations of few dipolar bosons in a double-well trap: We consider $N$ interacting dipolar bosonic atoms at zero temperature in a\ndouble-well potential. This system is described by the two-space-mode extended\nBose-Hubbard (EBH) Hamiltonian which includes (in addition to the familiar BH\nterms) the nearest-neighbor interaction, correlated hopping and bosonic-pair\nhopping. For systems with $N=2$ and $N=3$ particles we calculate analytically\nboth the ground state and the Fisher information, the coherence visibility, and\nthe entanglement entropy that characterize the correlations of the lowest\nenergy state. The structure of the ground state crucially depends on the\ncorrelated hopping $K_c$. On one hand we find that this process makes possible\nthe occurrence of Schr\\\"odinger-cat states even if the onsite interatomic\nattraction is not strong enough to guarantee the formation of such states. On\nthe other hand, in the presence of a strong onsite attraction, sufficiently\nlarge values of $|K_c|$ destroys the cat-like state in favor of a delocalized\natomic coherent state."
    },
    {
        "anchor": "Mesoscopic density grains in the 1d interacting Bose gas from the exact\n  Yang-Yang solution: Number fluctuations in a one-dimensional Bose gas consist of contributions\nfrom many smaller independent localized fluctuations, the density grains. We\nhave derived a set of extended integral equations from the Yang-Yang solution\nfor finite temperature that exactly determine all higher order moments of\nnumber fluctuations. These moments are closely related to the statistics of the\nlocalized (but not zero-range) density grains. We directly calculate the mean\noccupation of these fluctuations, and the variance, skewness, and kurtosis of\ntheir distribution across the whole parameter space of the gas. Findings\ninclude: Large mesoscopic density grains with a fat-tailed distribution in the\nthermal quasicondensate of the dilute gas and in the nonperturbative quantum\nturbulent regime; Regions of negative skewness and below-Gaussian kurtosis in a\npart of the fermionized gas, and an unexplained crossover region along $T\\sim\nT_d/\\gamma$; The existence of a peak in the density-density correlation\nfunction at finite interparticle spacing. We relate these density grain\nstatistics to measurable behavior such as the statistics of coarse imaging\nbins, and finite-size scaling of number fluctuations. We propose how to\nexperimentally test the relationship between thermodynamically independent\ndensity grains and density concentrations visible in single shot images.",
        "positive": "Polaron spectroscopy of interacting Fermi systems: insights from exact\n  diagonalization: Immersing a mobile impurity into a many-body quantum system represents a\ntheoretically intriguing and experimentally effective way of probing its\nproperties.In this work, we study the polaron spectral function in various\nenvironments, within the framework of Fermi-Hubbard models. Inspired by\npossible realizations in cold atoms and semiconductor heterostructures, we\nconsider different configurations for the background Fermi gas, including\ncharge density waves, multiple Fermi seas and pair superfluids. While our\ncalculations are performed using an exact-diagonalization approach, hence\nlimiting our analysis to systems of few interacting Fermi particles, we\nidentify robust spectral features supported by theoretical results. Our work\nprovides a benchmark for computations based on mean-field approaches and reveal\nsurprising features of polaron spectra, inspiring new theoretical\ninvestigations."
    },
    {
        "anchor": "Ground state properties of ultracold trapped bosons with an immersed\n  ionic impurity: We consider a trapped atomic ensemble of interacting bosons in the presence\nof a single trapped ion in a quasi one dimensional geometry. Our study is\ncarried out by means of the newly developed multilayer-multiconfiguration\ntime-dependent Hartree method for bosons, a numerical exact approach to\nsimulate quantum many-body dynamics. In particular, we are interested in the\nscenario by which the ion is so strongly trapped that its motion can be\neffectively neglected. This enables us to focus on the atomic ensemble only.\nWith the development of a model potential for the atom-ion interaction, we are\nable to numerically obtain the exact many-body ground state of the atomic\nensemble in the presence of an ion. We analyse the influence of the atom number\nand the atom-atom interaction on the ground state properties. Interestingly,\nfor weakly interacting atoms, we find that the ion impedes the transition from\nthe ideal gas behaviour to the Thomas-Fermi limit. Furthermore, we show that\nthis effect can be exploited to infer the presence of the ion both in the\nmomentum distribution of the atomic cloud and by observing the interference\nfringes occurring during an expansion of the quantum gas. In the strong\ninteracting regime, the ion modifies the fragmentation process in dependence of\nthe atom number parity which allows a clear identification of the latter in\nexpansion experiments. Hence, we propose in both regimes experimentally viable\nstrategies to assess the impact of the ion on the many-body state of the atomic\ngas. This study serves as the first building block for systematically\ninvestigate many-body physics of such hybrid system.",
        "positive": "Exotic Ising dynamics in a Bose-Hubbard model: We explore the dynamical properties of a one-dimensional Bose-Hubbard model,\nwhere two bosonic species interact via Feshbach resonance. We focus on the\nregion in the phase diagram which is described by an effective, low-energy\nferromagnetic Ising model in both transverse and longitudinal fields. In this\nregime, we numerically calculate the dynamical structure factor of the\nBose-Hubbard model using the time-evolving block decimation method. In the\nferromagnetic phase, we observe both the continuum of excitations and the bound\nstates in the presence of a longitudinal field. Near the Ising critical point,\nwe observe the celebrated E8 mass spectrum in the excited states. We also point\nout possible measurements which could be used to detect these excitations in an\noptical lattice experiment."
    },
    {
        "anchor": "Bose-Einstein condensation in a mixture of interacting Bose and Fermi\n  particles: A self-consistent field model for a mixture of Bose and Fermi particles is\nformulated. There is explored in detail the case of a delta-like interaction,\nfor which the thermodynamic functions are obtained, and Bose-Einstein\ncondensation of interacting particles in the presence of the admixture of\nfermions is studied. It is shown that the admixture of Fermi particles leads to\nreducing of the temperature of Bose-Einstein condensation and smoothing of\nfeatures of thermodynamic quantities at the transition temperature. As in the\ncase of a pure Bose system, in the state of a mixture with condensate the\ndependence of the thermodynamic potential on the interaction constant between\nBose particles has a nonanalytic character, so that it proves impossible to\ndevelop the perturbation theory in the magnitude of interaction of Bose\nparticles.",
        "positive": "Extracting the Quantum Geometric Tensor of an Optical Raman Lattice by\n  Bloch State Tomography: In Hilbert space, the geometry of the quantum state is identified by the\nquantum geometric tensor (QGT), whose imaginary part is the Berry curvature and\nreal part is the quantum metric tensor. Here, we propose and experimentally\nimplement a complete Bloch state tomography to directly measure eigenfunction\nof an optical Raman lattice for ultracold atoms. Through the measured\neigenfunction, the distribution of the complete QGT in the Brillouin zone is\nreconstructed, with which the topological invariants are extracted by the Berry\ncurvature and the distances of quantum states in momentum space are measured by\nthe quantum metric tensor. Further, we experimentally test a predicted\ninequality between the Berry curvature and quantum metric tensor, which reveals\na deep connection between topology and geometry."
    },
    {
        "anchor": "Frustrated orbital Feshbach resonances in a Fermi gas: The orbital Feshbach resonance (OFR) is a novel scheme for magnetically\ntuning the interactions in closed-shell fermionic atoms. Remarkably, unlike the\nFeshbach resonances in alkali atoms, the open and closed channels of the OFR\nare only very weakly detuned in energy. This leads to a unique effect whereby a\nmedium in the closed channel can Pauli block, or frustrate, the two-body\nscattering processes. Here, we theoretically investigate the impact of\nfrustration in the few- and many-body limits of the experimentally accessible\nthree-dimensional $^{173}$Yb system. We find that by adding a closed-channel\natom to the two-body problem, the binding energy of the ground state is\nsignificantly suppressed, and by introducing a closed-channel Fermi sea to the\nmany-body problem, we can drive the system towards weaker fermion pairing.\nThese results are potentially relevant to superconductivity in solid-state\nmultiband materials, as well as to the current and continuing exploration of\nunconventional Fermi-gas superfluids near the OFR.",
        "positive": "Different models of gravitating Dirac fermions in optical lattices: In this paper I construct the naive lattice Dirac Hamiltonian describing the\npropagation of fermions in a generic 2D optical metric for different lattice\nand flux-lattice geometries. First, I apply a top-down constructive approach\nthat we first proposed in [Boada {\\it et al.,New J. Phys.} {\\bf 13} 035002\n(2011)] to the honeycomb and to the brickwall lattices. I carefully discuss how\ngauge transformations that generalize momentum (and Dirac cone) shifts in the\nBrillouin zone in the Minkowski homogeneous case can be used in order to change\nthe phases of the hopping. In particular, I show that lattice Dirac Hamiltonian\nfor Rindler spacetime in the honeycomb and brickwall lattices can be realized\nby considering real and isotropic (but properly position dependent) tunneling\nterms. For completeness, I also discuss a suitable formulation of Rindler Dirac\nHamiltonian in semi-synthetic brickwall and $\\pi$-flux square lattices (where\none of the dimension is implemented by using internal spin states of atoms as\nwe originally proposed in [Boada {\\it et al.,Phys. Rev. Lett. } {\\bf 108}\n133001 (2012)] and [Celi {\\it et al.,Phys. Rev. Lett. } {\\bf 112} 043001\n(2012)])."
    },
    {
        "anchor": "Double-Quantum Spin Vortices in SU(3) Spin-Orbit Coupled Bose Gases: We show that double-quantum spin vortices, which are characterized by doubly\nquantized circulating spin currents and unmagnetized filled cores, can exist in\nthe ground states of SU(3) spin-orbit coupled Bose gases. It is found that the\nSU(3) spin-orbit coupling and spin-exchange interaction play important roles in\ndetermining the ground-state phase diagram. In the case of effective\nferromagnetic spin interaction, the SU(3) spin-orbit coupling induces a\nthree-fold degeneracy to the magnetized ground state, while in the\nantiferromagnetic spin interaction case, the SU(3) spin-orbit coupling breaks\nthe ordinary phase rule of spinor Bose gases, and allows the spontaneous\nemergence of double-quantum spin vortices. This exotic topological defect is in\nstark contrast to the singly quantized spin vortices observed in existing\nexperiments, and can be readily observed by the current magnetization-sensitive\nphase-contrast imaging technique.",
        "positive": "Quantum phase transitions in networks of Lipkin-Meshkov-Glick models: We study the quantum critical behavior of networks consisting of\nLipkin-Meshkov-Glick models with an anisotropic ferromagnetic coupling. We\nfocus on the low-energy properties of the system within a mean-field approach\nand the quantum corrections around the mean-field solution. Our results show\nthat the weak-coupling regime corresponds to the paramagnetic phase when the\nlocal field dominates the dynamics, but the local anisotropy leads to the\nexistence of an exponentially-degenerate ground state. In the strong-coupling\nregime, the ground state is twofold degenerate and possesses long-range\nmagnetic ordering. Analytical results for a network with the ring topology are\nobtained."
    },
    {
        "anchor": "Interplay of Solitons and Radiation in One-Dimensional Bose Gases: We study relaxation dynamics in one-dimensional Bose gases, formulated as an\ninitial value problem for the classical non-linear Schr\\\"{o}dinger equation. We\npropose an analytic technique which takes into account the exact spectrum of\nnon-linear modes, that is both soliton excitations and dispersive continuum of\nradiation modes. Our method relies on the exact large-time asymptotics and uses\nthe so-called dressing transformation to account for the solitons. The obtained\nresults are quantitatively compared with the predictions of the linearized\napproach in the framework of the Bogoliubov--de Gennes theory. In the\nattractive regime, the interplay between solitons and radiation yields a damped\noscillatory motion of the profile which resembles breathing. For the repulsive\ninteraction, the solitons are confined in the sound cone region separated from\nthe supersonic radiation.",
        "positive": "Revivals in the attractive BEC in a double-well potential and their\n  decoherence: We study the dynamics of ultracold attractive atoms in a weakly linked two\npotential wells. We consider an unbalanced initial state and monitor dynamics\nof the population difference between the two wells. The average imbalance\nbetween wells undergoes damped oscillations, like in a classical counterpart,\nbut then it revives almost to the initial value. We explain in details the\nwhole behavior using three different models of the system. Furthermore we\ninvestigate the sensitivity of the revivals on the decoherence caused by one-\nand three-body losses. We include the dissipative processes using appropriate\nmaster equations and solve them using the stochastic wave approximation method."
    },
    {
        "anchor": "Hubbard-Stratonovich Transformation: Successes, Failure, and Cure: We recall the successes of the Hubbard-Stratonovich Transformation (HST) of\nmany-body theory, point out its failure to cope with competing channels of\ncollective phenomena and show how to overcome this by Variational Perturbation\nTheory. That yields exponentially fast converging results, thanks to the help\nof a variety of {\\it collective classical fields}, rather than a fluctuating\n{\\it collective quantum field} as suggested by the HST.",
        "positive": "Viscous Properties of a Degenerate One-Dimensional Fermi Gas: We study the viscous properties of a system of weakly interacting\nspin-$\\frac{1}{2}$ fermions in one dimension. Accounting for the effect of\ninteractions on the quasiparticle energy spectrum, we obtain the bulk viscosity\nof this system at low temperatures. Our result is valid for frequencies that\nare small compared with the rate of fermion backscattering. For frequencies\nlarger than this exponentially small rate, the excitations of the system become\ndecoupled from the center of mass motion, and the fluid is described by\ntwo-fluid hydrodynamics. We calculate the three transport coefficients required\nto describe viscous dissipation in this regime."
    },
    {
        "anchor": "Vortex structure and spectrum of atomic Fermi superfluid in a spherical\n  bubble trap: The structures of multiply quantized vortices (MQVs) of an equal-population\natomic Fermi superfluid in a rotating spherical bubble trap approximated as a\nthin shell are analyzed by solving the Bogoliubov-de Gennes (BdG) equation\nthroughout the BCS-Bose Einstein condensation (BEC) crossover. Consistent with\nthe Poincare-Hopf theorem, a pair of vortices emerge at the poles of the\nrotation axis in the presence of azimuthal symmetry, and the compact geometry\nprovides confinement for the MQVs. While the single-vorticity vortex structure\nis similar to that in a planar geometry, higher-vorticity vortices exhibit\ninteresting phenomena at the vortex center, such as a density peak due to\naccumulation of a normal Fermi gas and reversed circulation of current due to\nin-gap states carrying angular momentum, in the BCS regime but not the BEC\nregime because of the subtle relations between the order parameter and density.\nThe energy spectrum shows the number of the in-gap state branches corresponds\nto the vorticity of a vortex, and an explanation based on a topological\ncorrespondence is provided.",
        "positive": "Quantum Gases in Optical Boxes: Advances in light shaping for optical trapping of neutral particles have led\nto the development of box traps for ultracold atoms and molecules. These traps\nhave allowed the creation of homogeneous quantum gases and opened new\npossibilities for studies of many-body physics. They simplify the\ninterpretation of experimental results, provide more direct connections with\ntheory, and in some cases allow qualitatively new, hitherto impossible\nexperiments. Here we review progress in this emerging field."
    },
    {
        "anchor": "Number-conserving solution for dynamical quantum backreaction in a\n  Bose-Einstein condensate: We provide a number-conserving approach to the backreaction problem of small\nquantum fluctuations onto a classical background for the exactly soluble\ndynamical evolution of a Bose-Einstein condensate, experimentally realizable in\nthe ultracold gas laboratory. A force density exerted on the gas particles\nwhich is of quantum origin is uniquely identified as the deviation from the\nclassical Eulerian force density. The backreaction equations are then explored\nfor the specific example of a finite size uniform density condensate initially\nat rest. By assuming that the condensate starts from a non-interacting regime,\nand in its ground state, we fix a well-defined initial vacuum condition, which\nis driven out-of-equilibrium by instantaneously turning on the interactions.\nThe assumption of this initial vacuum accounts for the ambiguity in choosing a\nvacuum state for interacting condensates, which is due to phase diffusion and\nthe ensuing condensate collapse. As a major finding, we reveal that the time\nevolution of the condensate cloud leads to condensate density corrections that\ncannot in general be disentangled from the quantum depletion in measurements\nprobing the power spectrum of the total density. Furthermore, while the\ncondensate is initially at rest, quantum fluctuations give rise to a nontrivial\ncondensate flux, from which we demonstrate that the quantum force density\nattenuates the classical Eulerian force. Finally, the knowledge of the particle\ndensity as a function of time for a condensate at rest determines, to order\n$N^0$, where $N$ is the total number of particles, the quantum force density,\nthus offering a viable route for obtaining experimentally accessible quantum\nbackreaction effects.",
        "positive": "Cavity-mediated near-critical dissipative dynamics of a driven\n  condensate: We investigate the near-critical dynamics of atomic density fluctuations in\nthe non-equilibrium self-organization transition of an optically driven quantum\ngas coupled to a single mode of a cavity. In this system cavity-mediated\nlong-range interactions between atoms, tunable by the drive strength, lead to\nsoftening of an excitation mode recently observed in experiments. This\nphenomenon has previously been studied within a two-mode approximation for the\ncollective motional degrees of freedom of the atomic condensate which results\nin an effective open-system Dicke model. Here, including the full spectrum of\natomic modes we find a finite lifetime for a roton-like mode in the Bogoliubov\nexcitation spectrum that is strongly pump-dependent. The corresponding decay\nrate and critical exponents for the phase-transition are calculated explaining\nthe non-monotonic pump-dependent atomic damping rate observed in recent\nexperiments. We compute the near-critical behavior of the intra-cavity field\nfluctuations, that has been previously shown to be enhanced with respect to the\nequilibrium Dicke model in a two-mode approximation. We highlight the role of\nthe finite size of the system in the suppression of it below the expectations\nof the open Dicke model."
    },
    {
        "anchor": "Dark Solitons in Waveguide Polariton Fluids Shed Light on Interaction\n  Constants: We study exciton-polariton nonlinear optical fluids in a high momentum regime\nfor the first time. Defects in the fluid develop into dark solitons whose\nhealing length decreases with increasing density. We deduce interaction\nconstants for continuous wave polaritons an order of magnitude larger than with\npicosecond pulses. Time dependent measurements show a 100ps time for the\nbuildup of the interaction strength suggesting a self-generated excitonic\nreservoir as the source of the extra nonlinearity. The experimental results\nagree well with a model of coupled photons, excitons and the reservoir.",
        "positive": "Dynamics of vortex dipoles in anisotropic Bose-Einstein condensates: We study the motion of a vortex dipole in a Bose-Einstein condensate confined\nto an anisotropic trap. We focus on a system of ordinary differential equations\ndescribing the vortices' motion, which is in turn a reduced model of the\nGross-Pitaevskii equation describing the condensate's motion. Using a sequence\nof canonical changes of variables, we reduce the dimension and simplify the\nequations of motion. We uncover two interesting regimes. Near a family of\nperiodic orbits known as guiding centers, we find that the dynamics is\nessentially that of a pendulum coupled to a linear oscillator, leading to\nstochastic reversals in the overall direction of rotation of the dipole. Near\nthe separatrix orbit in the isotropic system, we find other families of\nperiodic, quasi-periodic, and chaotic trajectories. In a neighborhood of the\nguiding center orbits, we derive an explicit iterated map that simplifies the\nproblem further. Numerical calculations are used to illustrate the phenomena\ndiscovered through the analysis. Using the results from the reduced system we\nare able to construct complex periodic orbits in the original, partial\ndifferential equation, mean-field model for Bose-Einstein condensates, which\ncorroborates the phenomenology observed in the reduced dynamical equations."
    },
    {
        "anchor": "Effective theory for the propagation of a wave-packet in a disordered\n  and nonlinear medium: The propagation of a wave-packet in a nonlinear disordered medium exhibits\ninteresting dynamics. Here, we present an analysis based on the nonlinear\nSchr\\\"odinger equation (Gross-Pitaevskii equation). This problem is directly\nconnected to experiments on expanding Bose gases and to studies of transverse\nlocalization in nonlinear optical media. In a nonlinear medium the energy of\nthe wave-packet is stored both in the kinetic and potential parts, and details\nof its propagation are to a large extent determined by the transfer from one\nform of energy to the other. A theory describing the evolution of the\nwave-packet has been formulated in [G. Schwiete and A. Finkelstein, Phys. Rev.\nLett. 104, 103904 (2010)] in terms of a nonlinear kinetic equation. In this\npaper, we present details of the derivation of the kinetic equation and of its\nanalysis. As an important new ingredient we study interparticle-collisions\ninduced by the nonlinearity and derive the corresponding collision integral. We\nrestrict ourselves to the weakly nonlinear limit, for which disorder scattering\nis the dominant scattering mechanism. We find that in the special case of a\nwhite noise impurity potential the mean squared radius in a two-dimensional\nsystem scales linearly with t. This result has previously been obtained in the\ncollisionless limit, but it also holds in the presence of collisions. Finally,\nwe mention different mechanisms through which the nonlinearity may influence\nlocalization of the expanding wave-packet.",
        "positive": "Quantum corrections to a spin-orbit coupled Bose-Einstein Condensate: We study systematically the quantum corrections to a weakly interacting\nBose-Einstein condensate with spin-orbit coupling. We show that quantum\nfluctuations, enhanced by the spin-orbit coupling, modify quantitatively the\nmean-field properties such as the superfluid density, spin polarizability, and\nsound velocity. We find that the phase boundary between the plane wave and zero\nmomentum phases is shifted to a smaller transverse field. We also calculate the\nBeliaev and Landau damping rates and find that the Landau process dominates the\nquasiparticle decay even at low temperature."
    },
    {
        "anchor": "A Tale of Two Distributions: From Few To Many Vortices In\n  Quasi-Two-Dimensional Bose-Einstein Condensates: Motivated by the recent successes of particle models in capturing the\nprecession and interactions of vortex structures in quasi-two-dimensional\nBose-Einstein condensates, we revisit the relevant systems of ordinary\ndifferential equations. We consider the number of vortices $N$ as a parameter\nand explore the prototypical configurations (\"ground states\") that arise in the\ncase of few or many vortices. In the case of few vortices, we modify the\nclassical result of Havelock [Phil. Mag. ${\\bf 11}$, 617 (1931)] illustrating\nthat vortex polygons in the form of a ring are unstable for $N \\geq7$.\nAdditionally, we reconcile this modification with the recent identification of\nsymmetry breaking bifurcations for the cases of $N=2,\\dots,5$. We also briefly\ndiscuss the case of a ring of vortices surrounding a central vortex (so-called\n$N+1$ configuration). We finally examine the opposite limit of large $N$ and\nillustrate how a coarse-graining, continuum approach enables the accurate\nidentification of the radial distribution of vortices in that limit.",
        "positive": "Metastability of quantum droplet clusters: We show that metastable ring-shaped clusters can be constructed from\ntwo-dimensional quantum droplets in systems described by the Gross-Pitaevskii\nequations augmented with Lee-Huang-Yang quantum corrections. The clusters\nexhibit dynamical behaviours ranging from contraction to rotation with\nsimultaneous periodic pulsations, or expansion, depending on the initial radius\nof the necklace pattern and phase shift between adjacent quantum droplets. We\nshow that, using an energy-minimization analysis, one can predict equilibrium\nvalues of the cluster radius that correspond to rotation without radial\npulsations. In such a regime, the clusters evolve as metastable states,\nwithstanding abrupt variations in the underlying scattering lengths and keeping\ntheir azimuthal symmetry in the course of evolution, even in the presence of\nconsiderable perturbations."
    },
    {
        "anchor": "Chiral Modes of Giant Superfluid Vortices: We discuss rapidly rotating states of a superfluid. We concentrate on the\nGiant-Vortex (GV) state, which is a coherent rotating solution with a\nmacroscopic hole at the center. We show that, for any trap, the fluctuations\nobey an approximately chiral dispersion relation, describing arbitrary shape\ndeformations moving with the speed of the ambient superfluid. This dispersion\nrelation is a consequence of a peculiar infinite symmetry group that emerges at\nlarge angular velocity and implies an infinite ground-state degeneracy. The\ndegeneracy is lifted by small corrections which we determine both for smooth\ntraps and the hard trap.",
        "positive": "Cooper pairing and BCS-BEC evolution in mixed-dimensional Fermi gases: Similar to what has recently been achieved with Bose-Bose mixtures [Lamporesi\net al., Phys. Rev. Lett. 104, 153202 (2010)], mixed-dimensional Fermi-Fermi\nmixtures can be created by applying a species-selective one-dimensional optical\nlattice to a two-species Fermi gas ($\\sigma \\equiv \\{\\uparrow, \\downarrow \\}$),\nsuch a way that only one of the species feel the lattice potential and is\nconfined to a quasi-two-dimensional geometry, while having negligible effect on\nthe other, that is leaving it three dimensional. We investigate the ground\nstate phase diagram of superfluidity for such mixtures in the BCS-BEC\nevolution, and find normal, gapped superfluid, gapless superfluid, and phase\nseparated regions. In particular, we find a stable gapless superfluid phase\nwhere the unpaired $\\uparrow$ and $\\downarrow$ fermions coexist with the paired\n(or superfluid) ones in different momentum space regions. This phase is in some\nways similar to the Sarma state found in mixtures with unequal densities, but\nin our case, the gapless superfluid phase is unpolarized and most importantly\nit is stable against phase separation."
    },
    {
        "anchor": "Coexistence of two kinds of superfluidity in Bose-Hubbard model with\n  density-induced tunneling at finite temperatures: With use of the U(1) quantum rotor method in the path integral effective\naction formulation, we have confirmed the mathematical similarity of the phase\nHamiltonian and of the extended Bose-Hubbard model with density-induced\ntunneling (DIT). Moreover, we have shown that the latter model can be mapped to\na pseudospin Hamiltonian that exhibits two coexisting (single-particle and\npair) superfluid phases. Phase separation of the two has also been confirmed,\ndetermining that there exists a range of coefficients in which only pair\ncondensation, and not single-particle superfluidity, is present. The DIT part\nsupports the coherence in the system at high densities and low temperatures,\nbut also has dissipative effects independent of the system's thermal\nproperties.",
        "positive": "Magnetic structure of an imbalanced Fermi gas in an optical lattice: We analyze the repulsive fermionic Hubbard model on square and cubic lattices\nwith spin imbalance and in the presence of a parabolic confinement. We analyze\nthe magnetic structure as a function of the repulsive interaction strength and\npolarization. In the first part of the paper we perform unrestricted\nHartree-Fock calculations for the 2D case and find that above a critical\ninteraction strength $U_c$ the system turns ferromagnetic at the edge of the\ntrap, in agreement with the ferromagnetic Stoner instability of a homogeneous\nsystem away from half-filling. For $U<U_c$ we find a canted antiferromagnetic\nstructure in the Mott region in the center and a partially polarized\ncompressible edge. The antiferromagnetic order in the Mott plateau is\nperpendicular to the direction of the imbalance. In this regime the same\nqualitative behavior is expected for 2D and 3D systems. In the second part of\nthe paper we give a general discussion of magnetic structures above $U_c$. We\nargue that spin conservation leads to nontrivial textures, both in the\nferromagnetic polarization at the edge and for the Neel order in the Mott\nplateau. We discuss differences in magnetic structures for 2D and 3D cases."
    },
    {
        "anchor": "Cooling Quantum Gases with Entropy Localization: We study the dynamics of entropy in a time dependent potential and explore\nhow disorder influences this entropy flow. We show that disorder can trap\nentropy at the edge of the atomic cloud enabling a novel cooling method. We\ndemonstrate the feasibility of our cooling technique by analyzing the evolution\nof entropy in a one-dimensional Fermi lattice gas with a time dependent\nsuperlattice potential.",
        "positive": "Gain/loss effects on spin-orbit coupled ultracold atoms in\n  two-dimensional optical lattices: Due to the fundamental position of spin-orbit coupled ultracold atoms in the\nsimulation of topological insulators, the gain/loss effects on these systems\nshould be evaluated when considering the measurement or the coupling to the\nenvironment. Here, incorporating the mature gain/loss techniques into the\nexperimentally realized spin-orbit coupled ultracold atoms in two-dimensional\noptical lattices, we investigate the corresponding non-Hermitian tight-binding\nmodel and evaluate the gain/loss effects on various properties of the system,\nrevealing the interplay of the non-Hermiticity and the spin-orbit coupling.\nUnder periodic boundary conditions, we analytically obtain the topological\nphase diagram, which undergoes a non-Hermitian gapless interval instead of a\npoint that the Hermitian counterpart encounters for a topological phase\ntransition. We also unveil that the band inversion is just a necessary but not\nsufficient condition for a topological phase in two-level spin-orbit coupled\nnon-Hermitian systems. Because the nodal loops of the upper or lower two\ndressed bands of the Hermitian counterpart can be split into exceptional loops\nin this non-Hermitian model, a gauge-independent Wilson-loop method is\ndeveloped for numerically calculating the Chern number of multiple degenerate\ncomplex bands. Under open boundary conditions, we find that the conventional\nbulk-boundary correspondence does not break down with only on-site gain/loss\ndue to the lack of non-Hermitian skin effect, but the dissipation of chiral\nedge states depends on the boundary selection, which may be used in the control\nof edge-state dynamics. Given the technical accessibility of state-dependent\natom loss, this model could be realized in current cold-atom experiments."
    },
    {
        "anchor": "Vortex entanglement in Bose-Einstein condensates coupled to\n  Laguerre-Gauss beams: We study the establishment of vortex entanglement in remote and weakly\ninteracting Bose Einstein condensates. We consider a two-mode photonic resource\nentangled in its orbital angular momentum (OAM) degree of freedom and, by\nexploiting the process of light-to-BEC OAM transfer, demonstrate that such\nentanglement can be efficiently passed to the matter-like systems. Our proposal\nthus represents a building block for novel low-dissipation and long-memory\ncommunication channels based on OAM. We discuss issues of practical\nrealizability, stressing the feasibility of our scheme and present an operative\ntechnique for the indirect inference of the set vortex entanglement.",
        "positive": "Pseudogap phenomena in ultracold atomic Fermi gases: The pairing and superfluid phenomena in a two-component ultracold atomic\nFermi gas is an analogue of Cooper pairing and superconductivity in an electron\nsystem, in particular, the high $T_c$ superconductors. Owing to the various\ntunable parameters that have been made accessible experimentally in recent\nyears, atomic Fermi gases can be explored as a prototype or quantum simulator\nof superconductors. It is hoped that, utilizing such an analogy, the study of\natomic Fermi gases may shed light to the mysteries of high $T_c$\nsuperconductivity. One obstacle to the ultimate understanding of high $T_c$\nsuperconductivity, from day one of its discovery, is the anomalous yet\nwidespread pseudogap phenomena, for which a consensus is yet to be reached\nwithin the physics community, after over 27 years of intensive research\nefforts. In this article, we shall review the progress in the study of\npseudogap phenomena in atomic Fermi gases in terms of both theoretical\nunderstanding and experimental observations. We show that there is strong,\nunambiguous evidence for the existence of a pseudogap in strongly interacting\nFermi gases. In this context, we shall present a pairing fluctuation theory of\nthe pseudogap physics and show that it is indeed a strong candidate theory for\nhigh $T_c$ superconductivity."
    },
    {
        "anchor": "Dynamical mean-field driven spinor condensate physics beyond the\n  single-mode approximation: $^{23}$Na spin-1 Bose-Einstein condensates are used to experimentally\ndemonstrate that mean-field physics beyond the single-mode approximation can be\nrelevant during the non-equilibrium dynamics. The experimentally observed spin\noscillation dynamics and associated dynamical spatial structure formation\nconfirm theoretical predictions that are derived by solving a set of coupled\nmean-field Gross-Pitaevskii equations [J. Jie et al., Phys. Rev. A 102, 023324\n(2020)]. The experiments rely on microwave dressing of the $f=1$ hyperfine\nstates, where $f$ denotes the total angular momentum of the $^{23}$Na atom. The\nfact that beyond single-mode approximation physics at the mean-field level,\ni.e., spatial mean-field dynamics that distinguishes the spatial density\nprofiles associated with different Zeeman levels, can -- in certain parameter\nregimes -- have a pronounced effect on the dynamics when the spin healing\nlength is comparable to or larger than the size of the Bose-Einstein condensate\nhas implications for using Bose-Einstein condensates as models for quantum\nphase transitions and spin squeezing studies as well as for non-linear SU(1,1)\ninterferometers.",
        "positive": "Diagrammatic Monte Carlo study of quasi-two-dimensional Fermi-polarons: We apply a diagrammatic Monte Carlo method to the problem of an impurity\ninteracting resonantly with a homogeneous Fermi bath for a\nquasi-two-dimensional setup. Notwithstanding the series divergence, we can show\nnumerically that the three particle-hole diagrammatic contributions are not\ncontributing significantly to the final answer, thus demonstrating a nearly\nperfect destructive interference of contributions in subspaces with\nhigher-order particle-hole lines. Consequently, for strong enough confinement\nin the third direction, the transition between the polaron and the molecule\nground state is found to be in good agreement with the pure two-dimensional\ncase and agrees very well with the one found by the wave-function approach in\nthe two-particle-hole subspace."
    },
    {
        "anchor": "Transient supersolid properties in an array of dipolar quantum droplets: We study theoretically and experimentally the emergence of supersolid\nproperties in a dipolar Bose-Einstein condensate. The theory reveals a ground\nstate phase diagram with three distinct regimes - a regular Bose-Einstein\ncondensate, incoherent and coherent arrays of quantum droplets. In the latter\nthe droplets are connected by a finite superfluid density, which leads - in\naddition to the periodic density modulation - to a robust phase coherence\nthroughout the whole system. We further theoretically demonstrate that we are\nable to dynamically approach the ground state in our experiment and that its\nlifetime is only limited by three-body losses. Experimentally we probe and\nconfirm the signatures of the phase diagram by observing the in-situ density\nmodulation as well as the phase coherence using matter wave interference.",
        "positive": "Reply to \"Comment on \"Dispersive Bottleneck Delaying Thermalization of\n  Turbulent Bose-Einstein Condensates\" by E. Kozik\" [arXiv:1102.2943]\": We discuss the comment [ arXiv:1102.2943] by E. Kozik about \"Dispersive\nbottleneck delaying thermalization of turbulent Bose-Einstein Condensates\n[arXiv:1007.4441]\"."
    },
    {
        "anchor": "Pinning of Hidden Vortices in Bose-Einstein Condensate: We study the vortex dynamics and vortex pinning effect in Bose-Einstein\ncondensate in a rotating double-well trap potential and co-rotating optical\nlattice. We show that, in agreement with the experiment, the vortex number do\nnot diverge when the rotational frequency $\\Omega \\rightarrow 1$ if the trap\npotential is of anisotropic double-well type. The critical rotational frequency\nas obtained from numerical simulations agrees very well with the value $\\sqrt\nl/l$ for $l=4$ which supports the conjecture that surface modes with angular\nmomentum $l=4$ are excited when the rotating condensate is trapped in\ndouble-well potential. The vortex lattice structure in a rotating triple-well\ntrap potential and its pinning shows very interesting features. We show the\nexistence and pinning of a new type of hidden vortices whose phase profile is\nsimilar to that of the visible vortices.",
        "positive": "Spontaneous Crystallization of Skyrmions and Fractional Vortices in the\n  Fast-rotating and Rapidly-quenched Spin-1 Bose-Einstein Condensates: We investigate the spontaneous generation of crystallized topological defects\nvia the combining effects of fast rotation and rapid thermal quench on the\nspin-1 Bose-Einstein condensates. By solving the stochastic projected\nGross-Pitaevskii equation, we show that, when the system reaches equilibrium, a\nhexagonal lattice of skyrmions, and a square lattice of half-quantized vortices\ncan be formed in a ferromagnetic and antiferromagnetic spinor BEC, respetively,\nwhich can be imaged by using the polarization-dependent phase-contrast method."
    },
    {
        "anchor": "Multi-orbital and density-induced tunneling of bosons in optical\n  lattices: We show that multi-orbital and density-induced tunneling have a significant\nimpact on the phase diagram of bosonic atoms in optical lattices. Off-site\ninteractions lead to density-induced hopping, the so-called bond-charge\ninteractions, which can be identified with an effective tunneling potential and\ncan reach the same order of magnitude as conventional tunneling. In addition,\ninteraction-induced higher-band processes also give rise to strongly modified\ntunneling, on-site and bond-charge interactions. We derive an extended\noccupation-dependent Hubbard model with multi-orbitally renormalized processes\nand compute the corresponding phase diagram. It substantially deviates from the\nsingle-band Bose-Hubbard model and predicts strong changes of the superfluid to\nMott-insulator transition. In general, the presented beyond-Hubbard physics\nplays an essential role in bosonic lattice systems and has an observable\ninfluence on experiments with tunable interactions.",
        "positive": "A Reduction-Based Strategy for Optimal Control of Bose-Einstein\n  Condensates: Applications of Bose-Einstein Condensates (BEC) often require that the\ncondensate be prepared in a specific complex state. Optimal control is a\nreliable framework to prepare such a state while avoiding undesirable\nexcitations, and, when applied to the time-dependent Gross-Pitaevskii Equation\n(GPE) model of BEC in multiple space dimensions, results in a large\ncomputational problem. We propose a control method based on first reducing the\nproblem, using a Galerkin expansion, from a PDE to a low-dimensional\nHamiltonian ODE system. We then apply a two-stage hybrid control strategy. At\nthe first stage, we approximate the control using a second Galerkin-like method\nknown as CRAB to derive a finite-dimensional nonlinear programming problem,\nwhich we solve with a differential evolution (DE) algorithm. This search method\nthen yields a candidate local minimum which we further refine using a variant\nof gradient descent. This hybrid strategy allows us to greatly reduce\nexcitations both in the reduced model and the full GPE system."
    },
    {
        "anchor": "Quantum Degenerate Mixture of Ytterbium and Lithium Atoms: We have produced a quantum degenerate mixture of fermionic alkali 6Li and\nbosonic spin-singlet 174Yb gases. This was achieved using sympathetic cooling\nof lithium atoms by evaporatively cooled ytterbium atoms in a far-off-resonant\noptical dipole trap. We observe co-existence of Bose condensed (T/T_c~0.8)\n174Yb with 2.3*10^4 atoms and Fermi degenerate (T/T_F~0.3) 6Li with 1.2*10^4\natoms. Quasipure Bose-Einstein condensates of up to 3*10^4 174Yb atoms can be\nproduced in single-species experiments. Our results mark a significant step\ntoward studies of few and many-body physics with mixtures of alkali and\nalkaline-earth-like atoms, and for the production of paramagnetic polar\nmolecules in the quantum regime. Our methods also establish a convenient scheme\nfor producing quantum degenerate ytterbium atoms in a 1064nm optical dipole\ntrap.",
        "positive": "The pinning quantum phase transition in a Tonks Girardeau gas:\n  diagnostics by ground state fidelity and the Loschmidt echo: We study the pinning quantum phase transition in a Tonks-Girardeau gas, both\nin equilibrium and out-of-equilibrium, using the ground state fidelity and the\nLoschmidt echo as diagnostic tools. The ground state fidelity (GSF) will have a\ndramatic decrease when the atomic density approaches the commensurate density\nof one particle per lattice well. This decrease is a signature of the pinning\ntransition from the Tonks to the Mott insulating phase. We study the\napplicability of the fidelity for diagnosing the pinning transition in\nexperimentally realistic scenarios. Our results are in excellent agreement with\nrecent experimental work. In addition, we explore the out of equilibrium\ndynamics of the gas following a sudden quench with a lattice potential. We find\nall properties of the ground state fidelity are reflected in the Loschmidt echo\ndynamics i.e., in the non equilibrium dynamics of the Tonks-Girardeau gas\ninitiated by a sudden quench of the lattice potential."
    },
    {
        "anchor": "Tuning the structural and dynamical properties of a dipolar\n  Bose-Einstein condensate: Ripples and instability islands: It is now well established that the stability of aligned dipolar Bose gases\ncan be tuned by varying the aspect ratio of the external harmonic confinement.\nThis paper extends this idea and demonstrates that a Gaussian barrier along the\nstrong confinement direction can be employed to tune both the structural\nproperties and the dynamical stability of an oblate dipolar Bose gas aligned\nalong the strong confinement direction. In particular, our theoretical\nmean-field analysis predicts the existence of instability islands immersed in\notherwise stable regions of the phase diagram. Dynamical studies indicate that\nthese instability islands, which can be probed experimentally with present-day\ntechnology, are associated with the going soft of a Bogoliubov--de Gennes\nexcitation frequency with radial breathing mode character. Furthermore, we find\ndynamically stable ground state densities with ripple-like oscillations along\nthe radial direction. These structured ground states exist in the vicinity of a\ndynamical radial roton-like instability.",
        "positive": "Thermalization of field driven quantum systems: There is much interest in how quantum systems thermalize after a sudden\nchange, because unitary evolution should preclude thermalization. The\neigenstate thermalization hypothesis resolves this because all observables for\nquantum states in a small energy window have essentially the same value; it is\nviolated for integrable systems due to the infinite number of conserved\nquantities. Here, we show that when a system is driven by a DC electric field\nthere are five generic behaviors: (i) monotonic or (ii) oscillatory approach to\nan infinite-temperature steady state; (iii) monotonic or (iv) oscillatory\napproach to a nonthermal steady state; or (v) evolution to an oscillatory\nstate. Examining the Hubbard model (which thermalizes under a quench) and the\nFalicov-Kimball model (which does not), we find both exhibit scenarios (i-iv),\nwhile only Hubbard shows scenario (v). This shows richer behavior than in\ninteraction quenches and integrability in the absence of a field plays no role."
    },
    {
        "anchor": "Finite-range effects in ultradilute quantum drops: In the first experimental realization of dilute Bose-Bose liquid drops using\ntwo hyperfine states of $^{39}$K some discrepancies between theory and\nexperiment were observed. The standard analysis of the data using the\nLee-Huang-Yang beyond mean-field theory predicted critical numbers which were\nsignificantly off the experimental measurements. Also, the radial size of the\ndrops in the experiment proved to be larger than expected from this theory.\nUsing a new functional, which is based on quantum Monte Carlo results of the\nbulk phase incorporating finite-range effects, we can explain the origin of the\ndiscrepancies in the critical number. This result proves the necessity of\nincluding finite-range corrections to deal with the observed properties in this\nsetup. The controversy on the radial size is reasoned in terms of the departure\nfrom the optimal concentration ratio between the two species of the mixture.",
        "positive": "Simulating twistronics without a twist: Rotational misalignment or twisting of two mono-layers of graphene strongly\ninfluences its electronic properties. Structurally, twisting leads to large\nperiodic supercell structures, which in turn can support intriguing strongly\ncorrelated behaviour. Here, we propose a highly tunable scheme to synthetically\nemulate twisted bilayer systems with ultracold atoms trapped in an optical\nlattice. In our scheme, neither a physical bilayer nor twist is directly\nrealized. Instead, two synthetic layers are produced exploiting\ncoherently-coupled internal atomic states, and a supercell structure is\ngenerated \\emph{via} a spatially-dependent Raman coupling. To illustrate this\nconcept, we focus on a synthetic square bilayer lattice and show that it leads\nto tunable quasi-flatbands and Dirac cone spectra under certain magic supercell\nperiodicities. The appearance of these features are explained using a\nperturbative analysis. Our proposal can be implemented using available\nstate-of-the-art experimental techniques, and opens the route towards the\ncontrolled study of strongly-correlated flat band accompanied by hybridization\nphysics akin to magic angle bilayer graphene in cold atom quantum simulators."
    },
    {
        "anchor": "Many-Body Quantum Geometric Effects on Trapped Ultracold Bosons: Quantum geometric effects in uncorrelated systems are characterized by the\nBerry curvature and quantum metric. Beyond those, we propose three\ngauge-independent tensors describing quantum geometric effects on local\ninteraction between correlated particles. We derive an effective hydrodynamic\ntheory for ultracold bosons in optical lattices. Ground states and collective\nmodes of superfluids in isotropic harmonic traps are solved for highly\nsymmetric lattices. In a dynamic process, the amplitude and phase shift of an\nexcited breathing mode are determined by the geometric properties of Bloch\nwavefunctions. We also give a tight-binding model of a bipartite square lattice\nwith nontrivial quantum geometric effects. Our discovery advances the\nconnections between the modern band theory and quantum many-body physics.",
        "positive": "Pair density waves and vortices in an elongated two-component Fermi gas: We study the vortex structures of a two-component Fermi gas experiencing a\nuniform effective magnetic field in an anisotropic trap that interpolates\nbetween quasi-one dimensional (1D) and quasi-two dimensional (2D). At a fixed\nchemical potential, reducing the anisotropy (or equivalently increasing the\nattractive interactions or increasing the magnetic field) leads to\ninstabilities towards pair density waves, and vortex lattices. Reducing the\nchemical potential stabilizes the system. We calculate the phase diagram, and\nexplore the density and pair density. The structures are similar to those\npredicted for superfluid Bose gases. We further calculate the paired fraction,\nshowing how it depends on chemical potential and anisotropy."
    },
    {
        "anchor": "The condensed fraction of a homogeneous dilute Bose gas within the\n  improved Hartree-Fock approximation: Motivated by the recent experiment [R. Lopes et. al., Phys. Rev. Lett. 119,\n190404 (2017)] with a homogeneous Bose gas, we investigate a homogeneous dilute\nBose gas to calculate the quantum depletion density. By means of the\nCornwall-Jackiw-Tomboulis effective action approach within an improved\nHartree-Fock approximation, the condensed fraction is recovered in a simpler\nmanner and compared with corresponding findings in experimental data.\nAdditionally, higher-order terms are taken into account for several physical\nquantities, in particular for the chemical potential and free energy density.",
        "positive": "Ultracold Bosons on a Regular Spherical Mesh: I study the zero-temperature phase behavior of bosonic particles living on\nthe nodes of a regular spherical mesh (\"Platonic mesh\") and interacting through\nan extended Bose-Hubbard Hamiltonian. Only the hard-core version of the model\nis considered here, for two instances of Platonic mesh. Using the mean-field\ndecoupling approximation, I show that the system may exist in various ground\nstates, which can be regarded as analogs of gas, solid, supersolid, and\nsuperfluid. For one mesh, by comparing the theoretical results with the outcome\nof numerical diagonalization, I manage to uncover the signatures of diagonal\nand off-diagonal spatial orders in a finite quantum system."
    },
    {
        "anchor": "Optimal Gaussian squeezed states for atom-interferometry in the presence\n  of phase diffusion: We optimize the signal-to-noise ratio of a Mach-Zehnder atom interferometer\nwith Gaussian squeezed input states, in the presence interactions. For weak\ninteractions, our results coincide with Phys. Rev. Lett. {\\bf 100}, 250406\n(2008), with optimal initial number-variance $\\sigma_o\\propto N^{1/3}$ and\noptimal signal-to-noise ratio $s_o\\propto N^{2/3}$ for total atom number $N$.\nAs the interaction strength $u$ increases past unity, phase-diffusion becomes\ndominant, leading to a transition in the optimal squeezing from initial\nnumber-squeezing to initial {\\it phase}-squeezing with\n$\\sigma_o\\propto\\sqrt{uN}$ and $s_o\\propto\\sqrt{N/u}$ shot-noise scaling. The\ninitial phase-squeezing translates into hold-time number-squeezing, which is\nless sensitive to interactions than coherent states and improves $s_o$ by a\nfactor of $\\sqrt{u}$.",
        "positive": "Transmission resonances in above-barrier reflection of ultra-cold atoms\n  by the Rosen-Morse potential: Quantum above-barrier reflection of ultra-cold atoms by the Rosen-Morse\npotential is analytically considered within the mean field Gross-Pitaevskii\napproximation. Reformulating the problem of reflectionless transmission as a\nquasi-linear eigenvalue problem for the potential depth, an approximation for\nthe specific height of the potential that supports reflectionless transmission\nof the incoming matter wave is derived via modification of the\nRayleigh-Schroedinger time-independent perturbation theory. The approximation\nprovides highly accurate description of the resonance position for all the\nresonance orders if the nonlinearity parameter is small compared with the\nincoming particles chemical potential. Notably, the result for the first\ntransmission resonance turns out to be exact, i.e., the derived formula for the\nresonant potential height gives the exact value of the first nonlinear\nresonances position for all the allowed variation range of the involved\nparameters, the nonlinearity parameter and chemical potential. This has been\nshown by constructing the exact solution of the problem for the first\nresonance. Furthermore, the presented approximation reveals that, in contrast\nto the linear case, in the nonlinear case reflectionless transmission may occur\nnot only for potential wells but also for potential barriers with positive\npotential height. It also shows that the nonlinear shift of the resonance\nposition from the position of the corresponding linear resonance is\napproximately described as a linear function of the resonance order. Finally, a\ncompact (yet, highly accurate) analytic formula for the n-th order resonance\nposition is constructed via combination of analytical and numerical methods."
    },
    {
        "anchor": "A recipe for topological observables of density matrices: Meaningful topological invariants for mixed quantum states are challenging to\nidentify as there is no unique way to define them, and most choices do not\ndirectly relate to physical observables. Here, we propose a simple pragmatic\napproach to construct topological invariants of mixed states while preserving a\nconnection to physical observables, by continuously deforming known topological\ninvariants for pure (ground) states. Our approach relies on expectation values\nof many-body operators, with no reference to single-particle (e.g., Bloch)\nwavefunctions. To illustrate it, we examine extensions to mixed states of\n$U(1)$ geometric (Berry) phases and their corresponding topological invariant\n(winding or Chern number). We discuss measurement schemes, and provide a\ndetailed construction of invariants for thermal or more general mixed states of\nquantum systems with (at least) $U(1)$ charge-conservation symmetry, such as\nquantum Hall insulators.",
        "positive": "Creation of matter wave Bessel beams: Bessel beams are plane waves with amplitude profiles described by Bessel\nfunctions. They are important because of their property of limited diffraction\nand their capacity to carry orbital angular momentum. Here we report the\ncreation of a Bessel beam of de Broglie matter waves. The Bessel beam is\nproduced by the free evolution of a thin toroidal atomic Bose-Einstein\ncondensate (BEC) which has been set into rotational motion. By attempting to\nstir it at different rotation rates, we show that the toroidal BEC can only be\nmade to rotate at discrete, equally-spaced frequencies, demonstrating that\ncirculation is quantized in atomic BECs. The method used here to generate\nmatter wave Bessel beams with a Painted Potential can be viewed as a form of\nwavefunction engineering which might be extended to implement arbitrary cold\natom matter wave holography."
    },
    {
        "anchor": "Programmable order by disorder effect and underlying phases through\n  dipolar quantum simulators: In this work, we study two different quantum simulators through various\ntheoretical and numerical tools. Our first result provides knowledge upon the\nquantum order by disorder effect of the $S=1/2$ system, which is programmable\nin a quantum simulator composed of circular Rydberg atoms. When the total\nmagnetization is zero, a set of sub-extensive degenerate ground states is\npresent in the classical limit, composed of continuous strings whose\nconfiguration enjoys a large degree of freedom. Among all possible\nconfigurations, we focus on the stripe (up and down spins aligning straightly)\nand kinked (up and down spins forming zigzag spin chains) patterns. Adopting\nthe real space perturbation theory, we estimate the leading order energy\ncorrection when the nearest-neighbor spin exchange coupling, $J$, is\nconsidered, and the overall model becomes an effective XXZ model with a spatial\nanisotropy. Our calculation demonstrates a lifting of the degeneracy, favoring\nthe stripe configuration. When $J$ becomes larger, we adopt the infinite\nprojected entangled-pair state and numerically check the effect of degeneracy\nlifting, showing that even when the spin exchange coupling term is strong the\nstripe pattern is still favored. Next, we study the dipolar bosonic model with\ntilted polar angle which can be realized through a quantum simulator composed\nof cold atomic gas with dipole-dipole interaction in an optical lattice. By\nplacing the atoms in a triangular lattice and tilting the polar angle, the\ndiagonal anisotropy can also be realized in the bosonic system. With our\ncluster mean-field theory calculation, we provide various phase diagrams with\ndifferent tilted angles, showing the abundant underlying phases including the\nsupersolid. Our proposals indicate realizable scenarios through quantum\nsimulators in studying the quantum effect as well as extraordinary phases.",
        "positive": "Collective excitations of an imbalanced fermion gas in a 1D optical\n  lattice: The collective excitations that minimize the Helmholtz free energy of a\npopulation-imbalanced mixture of a $^{6}$Li gas loaded in a quasi\none-dimensional optical lattice are obtained. These excitations reveal a\nrotonic branch after solving the Bethe-Salpeter equation under a generalized\nrandom phase approximation based on a single-band Hubbard Hamiltonian. The\nphase diagram describing stability regions of Fulde-Farrell-Larkin-Ovchinnikov\nand Sarma phases is also analyzed."
    },
    {
        "anchor": "Superfluid excitations in a rotating two-dimensional bubble trap: We studied a rotating BEC confined in a bubble trap, approximated by a\nMexican hat and shifted harmonic oscillator potentials. Using a variational\ntechnique and perturbation theory, we determined the vortex configurations in\nthis system by varying the interparticle interaction and the angular velocity\nof the atomic cloud. We found that the phase diagram of the system has\nmacrovortex structures for small positive values of the interaction parameter,\nand the charge of the central vortex increases with rotation. Strengthening the\natomic interaction makes the macrovortex unstable and decays into multiple\nsingly-charged vortices that arrange themselves in a lattice configuration. We\nalso look for experimentally realizable methods to determine the vortex\nconfiguration without relying upon absorption imaging since the structures are\nnot always visible in the latter. More specifically, we study how the vortex\ndistribution affects the collective modes of the condensate by solving the\nGross-Pitaevskii equation numerically and by analytical predictions using the\nsum-rule approach for the frequencies of the modes. These results reveal\nimportant signatures to characterize the macrovortices and vortex lattice\ntransitions in the experiments.",
        "positive": "Coherently Coupled Mixtures of Bose-Einstein Condensed Gases: This paper summarizes some of the relevant features exhibited by bi-nary\nmixtures of Bose-Einstein condensates in the presence of coherent coupling at\nzero temperature. The coupling, which is experimentally produced by proper\nphoton transitions, can either involve negligible momentum transfer from the\nelectromagnetic radiation (Rabi coupling) or large momentum transfer (Raman\ncoupling) associated with spin-orbit effects.The nature of the quantum phases\nexhibited by coherently coupled mixtures is discussed in detail, including\ntheir paramagnetic, ferromagnetic, and, in the case of spin-orbit coupling,\nsupersolid phases.The behavior of the corresponding elementary excitations is\ndiscussed, with explicit emphasis on the novel features caused by the spin-like\ndegree of freedom. Focus is further given to the topological excitations\n(solitons, vortices) as well as to the superfluid properties. The paper also\npoints out relevant open questions which deserve more systematic theoretical\nand experimental investigations."
    },
    {
        "anchor": "Quantum quench in an atomic one-dimensional Ising chain: We study non-equilibrium dynamics for an ensemble of tilted one-dimensional\natomic Bose-Hubbard chains after a sudden quench to the vicinity of the\ntransition point of the Ising paramagnetic to anti-ferromagnetic quantum phase\ntransition. The quench results in coherent oscillations for the orientation of\neffective Ising spins, detected via oscillations in the number of\ndoubly-occupied lattice sites. We characterize the quench by varying the system\nparameters. We report significant modification of the tunneling rate induced by\ninteractions and show clear evidence for collective effects in the oscillatory\nresponse.",
        "positive": "Hidden-symmetry-protected quantum pseudo-spin Hall effect in optical\n  lattices: We propose a scheme to realize a new Z_2 topological insulator in a square\noptical lattice. Different from the conventional topological insulator\nprotected by the time-reversal symmetry, here, the optical lattice possesses a\nnovel hidden symmetry, which is responsible for the present Z_2 topological\norder. With a properly defined pseudo-spin, such a topological insulator is\ncharacterized by the helical edge states which exhibits pseudo-spin-momentum\nlocking, so that it can be considered as a quantum pseudo-spin Hall insulator.\nThe Z_2 topological invariant is derived and its experimental detection is\ndiscussed as well."
    },
    {
        "anchor": "Quasi-one-dimensional approximation for Bose-Einstein condensates\n  transversely trapped by a funnel potential: Starting from the standard three-dimensional (3D) Gross-Pitaevskii equation\n(GPE) and using a variational approximation, we derive an effective\none-dimensional nonpolynomial Schr\\\"odinger equation (1D-NPSE) governing the\naxial dynamics of atomic Bose-Einstein condensates (BECs) under the action of a\nsingular but physically relevant funnel-shaped transverse trap, i.e., an\nattractive 2D potential $\\sim-1/r$ (where $r$ is the radial coordinate in the\ntransverse plane), in combination with the repulsive self-interaction. Wave\nfunctions of the trapped BEC are regular, in spite of the potential's\nsingularity. The model applies to a condensate of particles (small molecules)\ncarrying a permanent electric dipole moment in the field of a uniformly charged\naxial thread, as well as to a quantum gas of magnetic atoms pulled by an axial\nelectric current. By means of numerical simulations, we verify that the\neffective 1D-NPSE provides accurate static and dynamical results, in comparison\nto the full 3D GPE, for both repulsive and attractive signs of the intrinsic\nnonlinearity.",
        "positive": "Expansion dynamics in the one-dimensional Fermi-Hubbard model: Expansion dynamics of interacting fermions in a lattice are simulated within\nthe one-dimensional (1D) Hubbard model, using the essentially exact\ntime-evolving block decimation (TEBD) method. In particular, the expansion of\nan initial band-insulator state is considered. We analyze the simulation\nresults based on the dynamics of a two-site two-particle system, the so-called\nHubbard dimer. Our findings describe essential features of a recent experiment\non the expansion of a Fermi gas in a two-dimensional lattice. We show that the\nHubbard-dimer dynamics, combined with a two-fluid model for the paired and\nnon-paired components of the gas, gives an efficient description of the full\ndynamics. This should be useful for describing dynamical phenomena of strongly\ninteracting Fermions in a lattice in general."
    },
    {
        "anchor": "Three-dimensional skyrmions in spin-2 Bose-Einstein condensates: We introduce topologically stable three-dimensional skyrmions in the cyclic\nand biaxial nematic phases of a spin-2 Bose-Einstein condensate. These\nskyrmions exhibit exceptionally high mapping degrees resulting from the\nversatile symmetries of the corresponding order parameters. We show how these\nstructures can be created in existing experimental setups and study their\ntemporal evolution and lifetime by numerically solving the three-dimensional\nGross-Pitaevskii equations for realistic parameter values. Although the biaxial\nnematic and cyclic phases are observed to be unstable against transition\ntowards the ferromagnetic phase, their lifetimes are long enough for the\nskyrmions to be imprinted and detected experimentally.",
        "positive": "Modulational Instabity of Spin-Orbit Coupled Bose-Einstein Condensates\n  in Discrete Media: We address the impact of intra-site spin-orbit (SO) coupling and associated\ninter-component Rabi coupling on the modulational instability (MI) of\nplane-wave states in two-component discrete Bose-Einstein condensates (BECs).\nConditions for the onset of the MI and the respective instability are found\nanalytically. SO coupling allows us to produce the MI even for a small initial\nwavenumber (q < {\\pi}/2) for miscible states. In particular, SO coupling\nintroduces MI even in the absence of hopping coefficient, a concept which may\nhave wider ramifications in heavy atomic BECs. Our investigations predict that\nthe impact of Rabi coupling is more pronounced compared to the other system\nparameters. We have also shown how our results of the linear stability analysis\ncan be corroborated numerically. The fact that we have brought out the\nstability criteria in different domains of system parameters means that our\nmodel is tailor made experiments."
    },
    {
        "anchor": "Polaron-molecule transitions in a two-dimensional Fermi gas: We address the problem of a single \"spin-down\" impurity atom interacting\nattractively with a spin-up Fermi gas in two dimensions (2D). We consider the\ncase where the mass of the impurity is greater than or equal to the mass of a\nspin-up fermion. Using a variational approach, we resolve the questions raised\nby previous studies and we show that there is, in fact, a transition between\npolaron and molecule (dimer) ground states in 2D. For the molecule state, we\nuse a variational wave function with a single particle-hole excitation on the\nFermi sea and we find that its energy matches that of the exact solution in the\nlimit of infinite impurity mass. Thus, we expect the variational approach to\nprovide a reliable tool for investigating 2D systems.",
        "positive": "Attractive Solution of Binary Bose Mixtures: Liquid-Vapor Coexistence\n  and Critical Point: We study the thermodynamic behavior of attractive binary Bose mixtures using\nexact path-integral Monte-Carlo methods. Our focus is on the regime of\ninterspecies interactions where the ground state is in a self-bound liquid\nphase, stabilized by beyond mean-field effects. We calculate the isothermal\ncurves in the pressure vs density plane for different values of the attraction\nstrength and establish the extent of the coexistence region between liquid and\nvapor using the Maxwell construction. Notably, within the coexistence region,\nBose-Einstein condensation occurs in a discontinuous way as the density jumps\nfrom the normal gas to the superfluid liquid phase. Furthermore, we determine\nthe critical point where the line of first-order transition ends and\ninvestigate the behavior of the density discontinuity in its vicinity. We also\npoint out that the density discontinuity at the transition could be observed in\nexperiments of mixtures in traps."
    },
    {
        "anchor": "Observation of a superfluid Hall effect: Measurement techniques based upon the Hall effect are invaluable tools in\ncondensed matter physics. When an electric current flows perpendicular to a\nmagnetic field, a Hall voltage develops in the direction transverse to both the\ncurrent and the field. In semiconductors, this behaviour is routinely used to\nmeasure the density and charge of the current carriers (electrons in conduction\nbands or holes in valence bands) -- internal properties of the system that are\nnot accessible from measurements of the conventional resistance. For strongly\ninteracting electron systems, whose behaviour can be very different from the\nfree electron gas, the Hall effect's sensitivity to internal properties makes\nit a powerful tool; indeed, the quantum Hall effects are named after the tool\nby which they are most distinctly measured instead of the physics from which\nthe phenomena originate. Here we report the first observation of a Hall effect\nin an ultracold gas of neutral atoms, revealed by measuring a Bose-Einstein\ncondensate's transport properties perpendicular to a synthetic magnetic field.\nOur observations in this vortex-free superfluid are in good agreement with\nhydrodynamic predictions, demonstrating that the system's global\nirrotationality influences this superfluid Hall signal.",
        "positive": "Superfluids, Fluctuations and Disorder: We present a field-theory description of ultracold bosonic atoms in presence\nof a disordered external potential. By means of functional integration\ntechniques, we aim to investigate and review the interplay between disordered\nenergy landscapes and fluctuations, both thermal and quantum ones. Within the\nbroken-symmetry phase, up to the Gaussian level of approximation, the disorder\ncontribution crucially modifies both the condensate depletion and the\nsuperfluid response. Remarkably, it is found that the ordered (i.e. superfluid)\nphase can be destroyed also in regimes where the random external potential is\nsuitable for a perturbative analysis. We analyze the simplest case of quenched\ndisorder and then we move to present the implementation of the replica trick\nfor ultracold bosonic systems. In both cases, we discuss strengths and\nlimitations of the reviewed approach, paying specific attention to possible\nextensions and the most recent experimental outputs."
    },
    {
        "anchor": "Enstrophy Cascade in Decaying Two-Dimensional Quantum Turbulence: We report evidence for an enstrophy cascade in large-scale point-vortex\nsimulations of decaying two-dimensional quantum turbulence. Devising a method\nto generate quantum vortex configurations with kinetic energy narrowly\nlocalized near a single length scale, the dynamics are found to be\nwell-characterised by a superfluid Reynolds number, $\\mathrm{Re_s}$, that\ndepends only on the number of vortices and the initial kinetic energy scale.\nUnder free evolution the vortices exhibit features of a classical enstrophy\ncascade, including a $k^{-3}$ power-law kinetic energy spectrum, and steady\nenstrophy flux associated with inertial transport to small scales. Clear\nsignatures of the cascade emerge for $N\\gtrsim 500$ vortices. Simulating up to\nvery large Reynolds numbers ($N = 32, 768$ vortices), additional features of\nthe classical theory are observed: the Kraichnan-Batchelor constant is found to\nconverge to $C' \\approx 1.6$, and the width of the $k^{-3}$ range scales as\n$\\mathrm{Re_s}^{1/2}$. The results support a universal phenomenology\nunderpinning classical and quantum fluid turbulence.",
        "positive": "Breathing Mode of a BEC Repulsively Interacting with a Fermionic\n  Reservoir: We investigate the fundamental breathing mode of a small-sized elongated\nBose-Einstein condensate coupled to a large Fermi sea of atoms. Our\nobservations show a dramatic shift of the breathing frequency when the mixture\nundergoes phase separation at strong interspecies repulsion. We find that the\nmaximum frequency shift in the full phase-separation limit depends essentially\non the atom number ratio of the components. We interpret the experimental\nobservations within a model that assumes an adiabatic response of the Fermi\nsea, or within another model that considers single fermion trajectories for a\nfully phase-separated mixture. These two complementary models capture the\nobserved features over the full range of interest."
    },
    {
        "anchor": "Dynamical probing of a topological phase of bosons in one dimension: We study the linear response to time-dependent probes of a symmetry-protected\ntopological phase of bosons in one-dimension, the Haldane insulator (HI). This\nphase is separated from the ordinary Mott insulator (MI) and density-wave (DW)\nphases by continuous transitions, whose field theoretical description is here\nreviewed. Using this technique, we compute the absorption spectrum to two types\nof periodic perturbations and relate the findings to the nature of the critical\nexcitations at the transition between the different phases. The HI-MI phase\ntransition is topological and the critical excitations possess trivial quantum\nnumbers: they correspond to particles and holes at zero momentum. Our findings\nare corroborated by a non-local mean-field approach, which allows us to\ndirectly relate the predicted spectrum to the known microscopic theory.",
        "positive": "Collective dynamics of Fermi-Bose mixtures with an oscillating\n  scattering length: Collective oscillations of superfluid mixtures of ultra cold fermionic and\nbosonic atoms are investigated while varying the fermion-boson scattering\nlength. We study the dynamics with respect to excited center of mass modes and\nbreathing modes in the mixture. Parametric resonances are also analyzed when\nthe scattering length varies periodically in time, by comparing partial\ndifferential equation (PDE) models and ordinary differential equation (ODE)\nmodels for the dynamics. An application to the recent experiment with fermionic\n$^{6}$Li and bosonic $^{7}$Li atoms, which approximately have the same masses,\nis discussed."
    },
    {
        "anchor": "Disorderless quasi-localization of polar gases in one-dimensional\n  lattices: One-dimensional polar gases in deep optical lattices present a severely\nconstrained dynamics due to the interplay between dipolar interactions, energy\nconservation, and finite bandwidth. The appearance of dynamically-bound\nnearest-neighbor dimers enhances the role of the $1/r^3$ dipolar tail,\nresulting, in the absence of external disorder, in quasi-localization via dimer\nclustering for very low densities and moderate dipole strengths. Furthermore,\neven weak dipoles allow for the formation of self-bound superfluid lattice\ndroplets with a finite doping of mobile, but confined, holons. Our results,\nwhich can be extrapolated to other power-law interactions, are directly\nrelevant for current and future lattice experiments with magnetic atoms and\npolar molecules.",
        "positive": "Exploring the many-body localization transition in two dimensions: One fundamental assumption in statistical physics is that generic closed\nquantum many-body systems thermalize under their own dynamics. Recently, the\nemergence of many-body localized systems has questioned this concept,\nchallenging our understanding of the connection between statistical physics and\nquantum mechanics. Here we report on the observation of a many-body\nlocalization transition between thermal and localized phases for bosons in a\ntwo-dimensional disordered optical lattice. With our single site resolved\nmeasurements we track the relaxation dynamics of an initially prepared\nout-of-equilibrium density pattern and find strong evidence for a diverging\nlength scale when approaching the localization transition. Our experiments mark\nthe first demonstration and in-depth characterization of many-body localization\nin a regime not accessible with state-of-the-art simulations on classical\ncomputers."
    },
    {
        "anchor": "The non-condensed fraction of a homogeneous dilute Bose gas within the\n  improved Hartree-Fock approximation at finite temperature: By means of Cornwall-Jackiw-Tomboulis effective action we investigate a\ndilute weakly interacting Bose gas at finite temperature. The shift of critical\ntemperature is obtained in the universal form $\\Delta T_C/T_C^{(0)} =\ncn_0^{1/3}a_s$. The non-condensate fraction is expressed in sum of three terms,\nwhich correspond to the quantum fluctuation, thermal fluctuation and both.",
        "positive": "Dirac and Weyl Rings in Three Dimensional Cold Atom Optical Lattices: Recently three dimensional topological quantum materials with gapless energy\nspectra have attracted considerable interests in many branches of physics.\nBesides the celebrated example, Dirac and Weyl points which possess gapless\npoint structures in the underlying energy dispersion, the topologically\nprotected gapless spectrum can also occur along a ring, named Dirac and Weyl\nnodal rings. Ultra-cold atomic gases provide an ideal platform for exploring\nnew topological materials with designed symmetries. However, whether Dirac and\nWeyl rings can exist in the single-particle spectrum of cold atoms remains\nelusive. Here we propose a realistic model for realizing Dirac and Weyl rings\nin the single-particle band dispersion of a cold atom optical lattice. Our\nscheme is based on previously experimentally already implemented Raman coupling\nsetup for realizing spin-orbit coupling. Without the Zeeman field, the model\npreserves both pseudo-time-reversal and inversion symmetries, allowing Dirac\nrings. The Dirac rings split into Weyl rings with a Zeeman field that breaks\nthe pseudo-time-reversal symmetry. We examine the superfluidity of attractive\nFermi gases in this model and also find Dirac and Weyl rings in the\nquasiparticle spectrum."
    },
    {
        "anchor": "Observation of a continuous time crystal: Time crystals are classified as discrete or continuous depending on whether\nthey spontaneously break discrete or continuous time translation symmetry.\nWhile discrete time crystals have been extensively studied in periodically\ndriven systems since their recent discovery, the experimental realization of a\ncontinuous time crystal is still pending. Here, we report the observation of a\nlimit cycle phase in a continuously pumped dissipative atom-cavity system,\nwhich is characterized by emergent oscillations in the intracavity photon\nnumber. We observe that the phase of this oscillation is random for different\nrealizations, and hence this dynamical many-body state breaks continuous time\ntranslation symmetry spontaneously. The observed robustness of the limit cycles\nagainst temporal perturbations confirms the realization of a continuous time\ncrystal.",
        "positive": "Collapse of triaxial bright solitons in atomic Bose-Einstein condensates: We study triaxial bright solitons made of attractive Bose-condensed atoms\ncharacterized by the absence of confinement in the longitudinal axial direction\nbut trapped by an anisotropic harmonic potential in the transverse plane. By\nnumerically solving the three-dimensional Gross-Pitaevskii equation we\ninvestigate the effect of the transverse trap anisotropy on the critical\ninteraction strength above which there is the collapse of the condensate. The\ncomparison with previous predictions [Phys. Rev. A {\\bf 66}, 043619 (2002)]\nshows significant differences for large anisotropies."
    },
    {
        "anchor": "Propagation of First and Second Sound in a Highly-Elongated Trapped Bose\n  Condensed Gas at Finite temperatures: We study sound propagation in Bose-condensed gases in a highly-elongated\nharmonic trap at finite temperatures. This problem is studied within the\nframework of Zaremba-Nikuni-Griffin (ZNG) formalism, which consistent of a\ngeneralized Gross-Pitaevskii (GP) equation for the condensate and the kinetic\nequation for a thermal cloud. We extend the ZNG formalism to deal with a\nhighly-anisotropic trap potential, and use it to simulate sound propagation\nusing the trap parameters corresponding to the experiment on sound pulse\npropagation at finite temperature. We focus on the high-density two-fluid\nhydrodynamic regime, and explore the possibility of observing first and second\nsound pulse propagation. The results of numerical simulation are compared with\nan analyitical results derived from linearized ZNG hydrodynamic equations. We\nshow that the second sound mode makes a dominant contribution to condensate\nmotion in relatively high temperature, while the first sound mode makes an\nappreciable contribution.",
        "positive": "Atomic physics on a 50 nm scale: Realization of a bilayer system of\n  dipolar atoms: Atomic physics has greatly advanced quantum science, mainly due to the\nability to control the position and internal quantum state of atoms with high\nprecision, often at the quantum limit. The dominant tool for this is laser\nlight, which can structure and localize atoms in space (e.g., in optical\ntweezers, optical lattices, 1D tubes or 2D planes). Due to the diffraction\nlimit of light, the natural length scale for most experiments with atoms is on\nthe order of 500 nm or larger. Here we implement a new super-resolution\ntechnique which localizes and arranges atoms on a sub-50 nm scale, without any\nfundamental limit in resolution. We demonstrate this technique by creating a\nbilayer of dysprosium atoms, mapping out the atomic density distribution with\nsub-10 nm resolution, and observing dipolar interactions between two physically\nseparated layers via interlayer sympathetic cooling and coupled collective\nexcitations. At 50 nm, dipolar interactions are 1,000 times stronger than at\n500 nm. For two atoms in optical tweezers, this should enable purely magnetic\ndipolar gates with kHz speed."
    },
    {
        "anchor": "Counter-diabatic vortex pump in spinor Bose-Einstein condensates: Topological phase imprinting is a well-established technique for\ndeterministic vortex creation in spinor Bose-Einstein condensates of alkali\nmetal atoms. It was recently shown that counter-diabatic quantum control may\naccelerate vortex creation in comparison to the standard adiabatic protocol and\nsuppress the atom loss due to nonadiabatic transitions. Here we apply this\ntechnique, assisted by an optical plug, for vortex pumping to theoretically\nshow that sequential phase imprinting up to 20 cycles generates a vortex with a\nvery large winding number. Our method significantly increases the fidelity of\nthe pump for rapid pumping compared to the case without the counter-diabatic\ncontrol, leading to the highest angular momentum per particle reported to date\nfor the vortex pump. Our studies are based on numerical integration of the\nthree-dimensional multi-component Gross-Pitaevskii equation which conveniently\nyields the density profiles, phase profiles, angular momentum, and other\nphysically important quantities of the spin-1 system. Our results motivate the\nexperimental realization of the vortex pump and studies of the rich physics it\ninvolves.",
        "positive": "Exact Results for the Boundary Energy of One-Dimensional Bosons: We study bosons in a one-dimensional hard-wall box potential. In the case of\ncontact interaction, the system is exactly solvable by the Bethe ansatz, as\nfirst shown by Gaudin in 1971. Although contained in the exact solution, the\nboundary energy in the thermodynamic limit for this problem is only\napproximately calculated by Gaudin, who found the leading order result at weak\nrepulsion. Here we derive an exact integral equation that enables one to\ncalculate the boundary energy in the thermodynamic limit at an arbitrary\ninteraction. We then solve such an equation and find the asymptotic results for\nthe boundary energy at weak and strong interactions. The analytical results\nobtained from the Bethe ansatz are in agreement with the ones found by other\ncomplementary methods, including quantum Monte Carlo simulations. We study the\nuniversality of the boundary energy in the regime of a small gas parameter by\nmaking a comparison with the exact solution for the hard rod gas."
    },
    {
        "anchor": "Reduced density matrix approach to ultracold few-fermion systems in one\n  dimension: The variational determination of the two-fermion reduced density matrix is\ndescribed for harmonically trapped, ultracold few-fermion systems in one\ndimension with equal spin populations. This is accomplished by formulating the\nproblem as a semi-definite program, with the two-fermion reduced density matrix\nbeing subject to well-known $N$-representability conditions. The ground-state\nenergies, as well as the density, pair-correlation function, and lower-order\neigenvalues of the two-fermion reduced density matrix of various fermionic\nsystems are found by utilising an augmented Lagrangian method for semi-definite\nprogramming. The ground-state energies are found to match well to those\ndetermined by full-configuration interaction and coupled-cluster calculations\nand the density, pair-correlation function, and eigenvalue results demonstrate\nthat the salient features of these systems are well-described by this method.\nThese results collectively demonstrate the utility of the reduced density\nmatrix method firstly in describing strong correlation arising from short-range\ninteractions, suggesting that the well-known N-representability conditions are\nsufficient to model ultracold fermionic systems, and secondly in illustrating\nthe prospect of treating larger systems currently out of the reach of\nestablished methods.",
        "positive": "Infrared behavior of interacting bosons at zero temperature: We review the infrared behavior of interacting bosons at zero temperature.\nAfter a brief discussion of the Bogoliubov approximation and the breakdown of\nperturbation theory due to infrared divergences, we present two approaches that\nare free of infrared divergences -- Popov's hydrodynamic theory and the\nnon-perturbative renormalization group -- and allow us to obtain the exact\ninfrared behavior of the correlation functions. We also point out the\nconnection between the infrared behavior in the superfluid phase and the\ncritical behavior at the superfluid--Mott-insulator transition in the\nBose-Hubbard model."
    },
    {
        "anchor": "Anisotropic semi-vortices in dipolar spinor condensates controlled by\n  Zeeman splitting: Spatially anisotropic solitary vortices (AVSs), supported by anisotropic\ndipole-dipole interactions, were recently predicted in spin-orbit-coupled\nbinary Bose-Einstein condensates (BECs), in the form of two-dimensional\nsemi-vortices (complexes built of zero-vorticity and vortical components). We\ndemonstrate that the shape of the AVSs -- horizontal or vertical, with respect\nto the in-plane polarization of the atomic dipole moments in the underlying BEC\n-- may be effectively controlled by strength $\\Omega$ of the Zeeman splitting\n(ZS). A transition from the horizontal to vertical shape with the increase of\n$\\Omega$ is found numerically and explained analytically. At the transition\npoint, the AVS assumes the shape of an elliptical ring. Mobility of horizontal\nAVSs is studied too, with a conclusion that, with the increase of $\\Omega $,\ntheir negative effective mass changes the sign into positive via a point at\nwhich the effective mass diverges. Lastly, we report a new species of\n\\textit{inverted} AVSs, with the zero-vorticity and vortex component placed in\nlower- and higher-energy components, as defined by the ZS. They are excited\nstates, with respect to the ground states provided by the usual AVSs. Quite\nsurprisingly, inverted AVSs are stable in a large parameter region.",
        "positive": "Signatures of unconventional pairing in spin-imbalanced one-dimensional\n  few-fermion systems: A system of a few attractively interacting fermionic $^6$Li atoms in\none-dimensional harmonic confinement is investigated. Non-trivial\ninter-particle correlations induced by interactions in a particle-imbalanced\nsystem are studied in the framework of the noise correlation. In this way, it\nis shown that evident signatures of strongly correlated fermionic pairs in the\nFulde-Ferrell-Larkin-Ovchinnikov state are present in the system and they can\nbe detected by measurements directly accessible within state-of-the-art\ntechniques. The results convincingly show that the exotic pairing mechanism is\na very universal phenomenon and can be captured in systems being essentially\nnon-uniform and far from the many-body limit."
    },
    {
        "anchor": "Landau damping in a collisionless dipolar Bose gas: We present a theory for the Landau damping of low energy quasi-particles in a\ncollisionless, quasi-2D dipolar Bose gas and produce expressions for the\ndamping rate in uniform and non-uniform systems. Using simple energy-momentum\nconservation arguments, we show that in the homogeneous system, the nature of\nthe low energy dispersion in a dipolar Bose gas severely inhibits Landau\ndamping of long wave-length excitations. For a gas with contact and dipolar\ninteractions, the damping rate for phonons tends to decrease with increasing\ndipolar interactions; for strong dipole-dipole interactions, phonons are\nvirtually undamped over a broad range of temperature. The damping rate for\nmaxon-roton excitations is found to be significantly larger than the damping\nrate for phonons.",
        "positive": "Vortex line in the unitary Fermi gas: We report diffusion Monte Carlo results for the ground state of unpolarized\nspin-1/2 fermions in a cylindrical container and properties of the system with\na vortex-line excitation. The density profile of the system with a vortex line\npresents a non-zero density at the core. We calculate the ground-state energy\nper particle, the superfluid pairing gap, and the excitation energy per\nparticle. These simulations can be extended to calculate the properties of\nvortex excitations in other strongly interacting systems, such as superfluid\nneutron matter using realistic nuclear Hamiltonians."
    },
    {
        "anchor": "Coherent back and forward scattering peaks in the quantum kicked rotor: We propose and analyze an experimental scheme using the quantum kicked rotor\nto observe the newly-predicted coherent forward scattering peak together with\nits long-known twin brother, the coherent backscattering peak. Contrary to\ncoherent backscattering, which arises already under weak-localization\nconditions, coherent forward scattering is only triggered by Anderson or strong\nlocalization. So far, coherent forward scattering has not been observed in\nconservative systems with elastic scattering by spatial disorder. We propose to\nturn to the quantum kicked rotor, which has a long and succesful history as an\naccurate experimental platform to observe dynamical localization, i.e.,\nAnderson localization in momentum space. We analyze the coherent forward\nscattering effect for the quantum kicked rotor by extensive numerical\nsimulations, both in the orthogonal and unitary class of disordered quantum\nsystems, and show that an experimental realization involving phase-space\nrotation techniques is within reach of state-of-the-art cold-atom experiments.",
        "positive": "Inverse population transfer of the repulsive Bose-Einstein condensate in\n  a double-well trap: strong interaction-induced support: An inverse population transfer of the repulsive Bose-Einstein condensate\n(BEC) in a weakly bound double-well trap is explored within the 3D\ntime-dependent Gross-Pitaevskii equation. The model avoids numerous common\napproximations (two-mode treatment, time-space factorization, etc) and closely\nfollows the conditions of Heidelberg experiments, thus providing a realistic\ndescription of BEC dynamics. The transfer is driven by a time-dependent shift\nof a barrier separating the left and right wells. It is shown that completeness\nand robustness of the process considerably depend on the amplitude and time\nprofile of the shift velocity. Soft profiles provide the most robust inversion.\nThe repulsive interaction substantially supports the transfer making it\npossible i) in a wide velocity interval and ii) three orders of magnitude\nfaster than in the ideal BEC."
    },
    {
        "anchor": "Dynamics of domain walls in a Bose-Einstein condensate driven by\n  density-dependent gauge field: Dynamical coupling between matter and gauge fields underlies the emergence of\nmany exotic particle-like excitations in condensed matter and high energy\nphysics. An important stepping stone to simulate this physics in atomic quantum\ngases relies on the synthesis of density-dependent gauge fields. Here we\ndemonstrate deterministic formation of domain walls in a stable Bose-Einstein\ncondensate with a synthetic gauge field that depends on the atomic density. The\ngauge field is created by simultaneous modulations of the optical lattice\npotential and interatomic interactions, and results in domains of atoms\ncondensed into two different momenta. Modeling the domain walls as elementary\nexcitations, we find that the domain walls respond to synthetic electric field\nwith a charge-to-mass ratio larger than and opposite to that of the bare atoms.\nOur work offers promising prospects to simulate the dynamics and interactions\nof novel excitations in quantum systems with dynamical gauge fields.",
        "positive": "Identical Spin Rotation Effect and Electron Spin Waves in Quantum Gas of\n  Atomic Hydrogen: We present an experimental study of electron spin waves in atomic hydrogen\ngas compressed to high densities of $\\sim 5 \\times 10^{18}$ cm$^{-3}$ at\ntemperatures ranging from 0.26 to 0.6 K in strong magnetic field of 4.6 T.\nHydrogen gas is in a quantum regime when the thermal de Broglie wavelength is\nmuch larger than the s-wave scattering length. In this regime the identical\nparticle effects play major role in atomic collisions and lead to the Identical\nSpin Rotation effect (ISR). We observed a variety of spin wave modes caused by\nthis effect with strong dependence on the magnetic potential caused by\nvariations of the polarizing magnetic field. We demonstrate confinement of the\nISR modes in the magnetic potential and manipulate their properties by changing\nthe spatial profile of magnetic field. We have found that at a high enough\ndensity of H gas the magnons accumulate in their ground state in the magnetic\ntrap and exhibit long coherence, which has a profound effect on the electron\nspin resonance spectra. Such macroscopic accumulation of the ground state\noccurs at a certain critical density of hydrogen gas, where the chemical\npotential of the magnons becomes equal to the energy of their ground state in\nthe trapping potential."
    },
    {
        "anchor": "AC Stark Effect in Ultracold Polar RbCs Molecules: We investigate the effect of far-off-resonant trapping light on ultracold\nbosonic RbCs molecules. We use kHz-precision microwave spectroscopy to measure\nthe differential AC Stark shifts between the ground and first excited\nrotational levels of the molecule with hyperfine-state resolution. We\ndemonstrate through both experiment and theory that coupling between\nneighboring hyperfine states manifests in rich structure with many avoided\ncrossings. This coupling may be tuned by rotating the polarization of the\nlinearly polarized trapping light. A combination of spectroscopic and\nparametric heating measurements allows complete characterization of the\nmolecular polarizability at a wavelength of 1550~nm in both the ground and\nfirst excited rotational states.",
        "positive": "Composite quasiparticles in strongly-correlated dipolar Fermi liquids: Strong particle-plasmon interaction in electronic systems can lead to\ncomposite \\emph{hole-plasmon} excitations. We investigate the emergence of\nsimilar composite quasiparticles in ultracold dipolar Fermi liquids originating\nfrom the long-range dipole-dipole interaction. We use the $G_0W$ technique with\nan effective interaction obtained from the static structure factor to calculate\nthe quasiparticle properties and single-particle spectral function. We first\ndemonstrate that within this formalism a very good agreement with the quantum\nMonte Carlo results could be achieved over a wide range of coupling strengths\nfor the renormalization constant and effective mass. The composite\n\\textit{quasiparticle-zero sound} excitations which are undamped at long\nwavelengths emerge at intermediate and strong couplings in the spectral\nfunction and should be detectable through the radio frequency spectroscopy of\nnonreactive polar molecules at high densities."
    },
    {
        "anchor": "Spin-orbit Coupling in Optical lattices: In this review, we discuss the physics of spin-orbit coupled quantum gases in\noptical lattices. After reviewing some relevant experimental techniques, we\nintroduce the basic theoretical model and discuss some of its generic features.\nIn particular, we concentrate on the interplay between spin-orbit coupling and\nstrong interactions and show how it leads to various exotic quantum phases in\nboth the Mott insulating and superfluid regimes. Phase transitions between the\nMott and superfluid states are also discussed.",
        "positive": "Strongly repulsive anyons in one dimension: To explore the static properties of the one-dimensional anyon-Hubbard model\nfor a mean density of one particle per site, we apply perturbation theory with\nrespect to the ratio between kinetic energy and interaction energy in the Mott\ninsulating phase. The strong-coupling results for the ground-state energy, the\nsingle-particle excitation energies, and the momentum distribution functions up\nto 6th order in hopping are benchmarked against the numerically exact\n(infinite) density-matrix renormalization group technique. Since these analytic\nexpressions are valid for any fractional phase $\\theta$ of anyons, they will be\nof great value for a sufficiently reliable analysis of future experiments,\navoiding extensive and costly numerical simulations."
    },
    {
        "anchor": "Dissipationless Vector Drag--Superfluid Spin Hall Effect: Dissipationless flows in single-component superfluids have a significant\ndegree of universality. In He4, the dissipationless mass flow occurs with a\nsuperfluid velocity determined by the gradient of the superfluid phase.\nHowever, in interacting superfluid mixtures, principally new effects appear. In\nthis Letter, we demonstrate a new kind of dissipationless phenomenon arising in\nmixtures of interacting bosons in optical lattices. We point out that for a\nparticular class of optical lattices, bosons condense in a state where one of\nthe components' superflow results in dissipationless mass flow of the other\ncomponent, in a direction different from either of the components' superfluid\nvelocities. The free-energy density of these systems contains a vector\nproduct-like interaction of superfluid velocities, producing the\ndissipationless noncollinear entrainment. The effect represents a superfluid\ncounterpart of the Spin Hall effect.",
        "positive": "Half-vortex sheets and domain-wall trains of rotating two-component\n  Bose-Einstein condensates in spin-dependent optical lattices: We investigate half-vortex sheets and domain-wall trains of rotating\ntwo-component Bose-Einstein condensates in spin-dependent optical lattices. The\ntwo-component condensates undergo phase separation in the form of stripes\narranged alternatively. The vortices of one component are aligned in lines in\nthe low-density regions and filled with the other component, which results in a\nstable vortex configuration, straight half-vortex sheets. A train of novel\ndomain walls, with spatially periodic \"eyebrow-like\" spin textures embedded on\nthem, are formed at the interfaces of the two components. We reveal that these\nspatially periodic textures on the domain walls result from the linear gradient\nof the relative phase, which is induced by the alternating arrangement of the\nvortex sheets in the two components. An accurate manipulation of the textures\ncan be realized by adjusting the intercomponent interaction strength, the\nrotating angular frequency and the period of the optical lattices."
    },
    {
        "anchor": "Localization of cold atoms in state-dependent optical lattices via a\n  Rabi pulse: We propose a novel realization of Anderson localization in non-equilibrium\nstates of ultracold atoms trapped in state-dependent optical lattices. The\ndisorder potential leading to localization is generated with a Rabi pulse\ntransfering a fraction of the atoms into a different internal state for which\ntunneling between lattice sites is suppressed. Atoms with zero tunneling create\na quantum superposition of different random potentials, localizing the mobile\natoms. We investigate the dynamics of the mobile atoms after the Rabi pulse for\nnon-interacting and weakly interacting bosons, and we show that the evolved\nwavefunction attains a quasi-stationary profile with exponentially decaying\ntails, characteristic of Anderson localization. The localization length is seen\nto increase with increasing disorder and interaction strength, oppositely to\nwhat is expected for equilibrium localization.",
        "positive": "Poincar\u00e9 index formula and analogy with the Kosterlitz-Thouless\n  transition in a non-rotated cold atom Bose-Einstein condensate: A dilute gas of Bose-Einstein condensed atoms in a non-rotated and axially\nsymmetric harmonic trap is modelled by the time dependent Gross-Pitaevskii\nequation. When the angular momentum carried by the condensate does not vanish,\nthe minimum energy state describes vortices (or antivortices) that propagate\naround the trap center. The number of (anti)vortices increases with the angular\nmomentum, and they repel each other to form Abrikosov lattices. Besides\nvortices and antivortices there are also stagnation points where the superflow\nvanishes; to our knowledge the stagnation points have not been analyzed\npreviously, in the context of the Gross-Pitaevskii equation. The Poincar\\'e\nindex formula states that the difference in the number of vortices and\nstagnation points can never change. When the number of stagnation points is\nsmall, they tend to aggregate into degenerate propagating structures. But when\nthe number becomes sufficiently large, the stagnation points tend to pair up\nwith the vortex cores, to propagate around the trap center in regular lattice\narrangements. There is an analogy with the geometry of the Kosterlitz-Thouless\ntransition, with the angular momentum of the condensate as the external control\nparameter instead of the temperature."
    },
    {
        "anchor": "Dynamical sign reversal of magnetic correlations in dissipative Hubbard\n  models: In quantum magnetism, the virtual exchange of particles mediates an\ninteraction between spins. Here, we show that an inelastic Hubbard interaction\nfundamentally alters the magnetism of the Hubbard model due to dissipation in\nspin-exchange processes, leading to sign reversal of magnetic correlations in\ndissipative quantum dynamics. This mechanism is applicable to both fermionic\nand bosonic Mott insulators, and can naturally be realized with ultracold atoms\nundergoing two-body inelastic collisions. The dynamical reversal of magnetic\ncorrelations can be detected by using a double-well optical lattice or\nquantum-gas microscopy, the latter of which facilitates the detection of the\nmagnetic correlations in one-dimensional systems because of spin-charge\nseparation. Our results open a new avenue toward controlling quantum magnetism\nby dissipation.",
        "positive": "Mott transition for a Lieb-Liniger gas in a shallow quasiperiodic\n  potential: Delocalization induced by disorder: Disorder or quasi-disorder is known to favor the localization in many-body\nBose systems. Here in contrast, we demonstrate an anomalous delocalization\neffect induced by incommensurability in quasiperiodic lattices. Loading\nultracold atoms in two shallow periodic lattices with equal amplitude and\neither equal or incommensurate spatial periods, we show the onset of a Mott\ntransition not only in the periodic case but also in the quasiperiodic case.\nUpon increase of the incommensurate component of the potential we find that the\nMott insulator turns into a delocalized superfluid. Our experimental results\nagree with quantum Monte Carlo calculations, showing anomalous delocalization\ninduced by the interplay between the commensuration and interaction."
    },
    {
        "anchor": "Full distribution of the superfluid fraction and extreme value\n  statistics in a one dimensional disordered Bose gas: The full statistical distribution of the superfluid fraction characterizing\none-dimensional Bose gases in random potentials is discussed. Rare\nconfigurations with extreme fluctuations of the disorder potential can fragment\nthe condensate and reduce the superfluid fraction to zero. The resulting\nbimodal probability distribution for the superfluid fraction is calculated\nnumerically in the quasi-1D mean-field regime of ultracold atoms in laser\nspeckle potentials. Using extreme-value statistics, an analytical scaling of\nthe zero-superfluid probability as function of disorder strength, disorder\ncorrelation length and system size is presented. It is argued that similar\nresults can be expected for point-like impurities, and that these findings are\nin reach for present-day experiments.",
        "positive": "Enhancing the Thermal Stability of Majorana Fermions with Redundancy\n  Using Dipoles in Optical Lattices: Pairing between spinless fermions can generate Majorana fermion excitations\nthat exhibit intriguing properties arising from non-local correlations. But\nsimple models indicate that non-local correlation between Majorana fermions\nbecomes unstable at non-zero temperatures. We address this issue by showing\nthat anisotropic interactions between dipolar fermions in optical lattices can\nbe used to significantly enhance thermal stability. We construct a model of\noriented dipolar fermions in a square optical lattice. We find that domains\nestablished by strong interactions exhibit enhanced correlation between\nMajorana fermions over large distances and long times even at finite\ntemperatures, suitable for stable redundancy encoding of quantum information.\nOur approach can be generalized to a variety of configurations and other\nsystems, such as quantum wire arrays."
    },
    {
        "anchor": "Cooling and entangling ultracold atoms in optical lattices: Scalable, coherent many-body systems can enable the realization of previously\nunexplored quantum phases and have the potential to exponentially speed up\ninformation processing. Thermal fluctuations are negligible and quantum effects\ngovern the behavior of such systems with extremely low temperature. We report\nthe cooling of a quantum simulator with 10,000 atoms and mass production of\nhigh-fidelity entangled pairs. In a two-dimensional plane, we cool Mott\ninsulator samples by immersing them into removable superfluid reservoirs,\nachieving an entropy per particle of $1.9^{+1.7}_{-0.4} \\times 10^{-3}\nk_{\\text{B}}$. The atoms are then rearranged into a two-dimensional lattice\nfree of defects. We further demonstrate a two-qubit gate with a fidelity of\n0.993 $\\pm$ 0.001 for entangling 1250 atom pairs. Our results offer a setting\nfor exploring low-energy many-body phases and may enable the creation of\nlarge-scale entanglement",
        "positive": "Proposal for asymmetric photoemission and tunneling spectroscopies in\n  quantum simulators of the triangular-lattice Fermi-Hubbard model: Recent realization of well-controlled quantum simulators of the\ntriangular-lattice Fermi-Hubbard model, including the triangular optical\nlattices loaded with ultracold Fermions and the heterostructures of the\ntransition-metal dichalcogenides, as well as the more advanced techniques to\nprobe them, pave the way for studying frustrated Fermi-Hubbard physics. Here,\nwe theoretically predict asymmetric photoemission and tunneling spectroscopies\nfor a lightly hole-doped and electron-doped triangular Mott antiferromagnet,\nand reveal two distinct types of magnetic polarons: a \\emph{lightly}\nrenormalized quasiparticle with the same momentum as the spin background and a\n\\emph{heavily} renormalized quasiparticle with a shifted momentum and a nearly\nflat band, using both analytical and unbiased numerical methods. We propose\nthese theoretical findings to be verified in frustrated optical lattices and\nMoir\\'e superlattices by probing various observables including the spectral\nfunction, the density of states, the energy dispersion and the quasiparticle\nweight. Moreover, we reveal the asymmetric response of the spin background\nagainst charge doping, demonstrating that the interplay between the local spin\nand charge degrees of freedom plays a vital role in doped triangular Mott\nantiferromagnets."
    },
    {
        "anchor": "Thermodynamics of the two-component Fermi gas with unequal masses at\n  unitarity: We consider mass-imbalanced two-component Fermi gases for which the\nunequal-mass atoms interact via a zero-range model potential with a diverging\ns-wave scattering length $a_s$, i.e., with $1/a_s=0$. The high temperature\nthermodynamics of the harmonically trapped and homogeneous systems are examined\nusing a virial expansion approach up to third order in the fugacity. We find\nthat the universal part of the third-order virial coefficient associated with\ntwo light atoms and one heavy atom is negative, while that associated with two\nheavy and one light atom changes sign from negative to positive as the mass\nratio $\\kappa$ increases, and diverges when Efimov physics sets in at\n$\\kappa=13.61$. By examining the Helmholtz free energy, we find that the\nequilibrium polarization of the trapped and homogeneous systems is 0 for\n$\\kappa=1$, but finite for $\\kappa \\ne 1$ (with a majority of heavy particles).\nCompared to the equilibrium polarization of the non-interacting system, the\nequilibrium polarization at unitarity is increased for the trapped system and\ndecreased for the homogeneous system. We find that unequal-mass Fermi gases are\nstable for all polarizations.",
        "positive": "Exact Liouvillian Spectrum of a One-Dimensional Dissipative Hubbard\n  Model: A one-dimensional dissipative Hubbard model with two-body loss is shown to be\nexactly solvable. We obtain an exact eigenspectrum of a Liouvillian\nsuperoperator by employing a non-Hermitian extension of the Bethe-ansatz\nmethod. We find steady states, the Liouvillian gap, and an exceptional point\nthat is accompanied by the divergence of the correlation length. A dissipative\nversion of spin-charge separation induced by the quantum Zeno effect is also\ndemonstrated. Our result presents a new class of exactly solvable Liouvillians\nof open quantum many-body systems, which can be tested with ultracold atoms\nsubject to inelastic collisions."
    },
    {
        "anchor": "Physical Realization of von Neumann Lattices in Rotating\n  Dipole-blockaded Bose Gases: A mathematical lattice, called the von Neumann lattice, is a subset of\ncoherent states and exists periodically in the phase space. It is unlike solids\nor Abrikosov lattices that are observable in physical systems. Abrikosov\nlattices are vortices closely packed into a lattice with a flux quantum through\na unit cell. Although Abrikosov lattices appear generally in various physical\nsystems, vortex lattices with multiple-flux quantums through a unit cell are\nmore stable than Abrikosov lattices in some physical regimes of the systems\nwith non-local interactions between particles. No theory is able to describe\nthese vortex lattices today. Here, we develop a theory for these vortex\nlattices by extending von Neumann lattices to the coordinate space with a unit\ncell of area that is proportional to flux quantums through a unit cell. The von\nNeumann lattices not only show the same physical properties as the Abrikosov\nlattice, but also describe vortex lattices with multiple-flux quantums through\na unit cell. From numerical simulations of a rapidly rotating dipole-blockaded\ngas, we confirm that vortex lattices showed in our simulations are the\nrepresentation of von Neumann lattices in the coordinate space. We anticipate\nour theory to be a starting point for developing more sophisticated\nvortex-lattice models. For example, the effect of Landau-level mixing on vortex\nlattice structures, vortices formed inside superfluid droplets and structural\nphase transitions of vortex matter in two-component Bose-Einstein condensates\nwill be relevant for such developments.",
        "positive": "Properties of a Bose Gas in the Presence of Disorder (Laurea thesis): The phenomenon of Bose-Einstein condensation and superfluidity in a Bose gas\nwith disorder is investigated. Diffusion Monte Carlo (DMC) method is used to\ncalculate superfluid and condensate fraction of the system as a function of\ndensity and strength of disorder at zero temperature. The algorithm and\nimplementation of the Diffusion Monte Carlo method is explained in details.\nBogoliubov theory is developed for the analytical description of the problem.\nGround state energy, superfluid fraction and condensate fraction are\ncalculated. It is shown that same results for the superfluid fraction can be\nobtained in a perturbative manner from Gross-Pitaevskii equation. Ground state\nenergy, obtained from DMC calculations, is compared to predictions of\nBogoliubov theory, which are found to be valid in the regime, when the strength\nof disorder is small. It is shown that \"unusual\" situation, when the superfluid\nfraction is smaller than the condensate fraction, can be realized in this\nsystem."
    },
    {
        "anchor": "Hyperfine structure of the hydroxyl free radical (OH) in electric and\n  magnetic fields: We investigate single-particle energy spectra of the hydroxyl free radical\n(OH) in the lowest electronic and rovibrational level under combined static\nelectric and magnetic fields, as an example of heteronuclear polar diatomic\nmolecules. In addition to the fine-structure interactions, the hyperfine\ninteractions and centrifugal distortion effects are taken into account to yield\nthe zero-field spectrum of the lowest ${}^2\\Pi_{3/2}$ manifold to an accuracy\nof less than 2 kHz. We also examine level crossings and repulsions in the\nhyperfine structure induced by applied electric and magnetic fields. Compared\nto previous work, we found more than 10 percent reduction of the magnetic\nfields at level repulsions in the Zeeman spectrum subjected to a perpendicular\nelectric field. It is important to take into account hyperfine structure when\nwe investigate physics of OH molecules at micro-Kelvin temperatures and below.",
        "positive": "Interference of an Array of Independent Bose-Einstein Condensates: Interference of an array of independent Bose-Einstein condensates, whose\nexperiment has been performed recently, is theoretically studied in detail.\nEven if the number of the atoms in each gas is kept finite and the phases of\nthe gases are not well defined, interference fringes are observed on each\nsnapshot. The statistics of the snapshot interference patterns, i.e., the\naverage fringe amplitudes and their fluctuations (covariance), are computed\nanalytically, and concise formulas for their asymptotic values for long time of\nflight are derived. Processes contributing to these quantities are clarified\nand the relationship with the description on the basis of the symmetry-breaking\nscenario is revealed."
    },
    {
        "anchor": "Non-equilibrium aspects of integrable models: Driven by breakthroughs in experimental and theoretical techniques, the study\nof non-equilibrium quantum physics is a rapidly expanding field with many\nexciting new developments. Amongst the manifold ways the topic can be\ninvestigated, one dimensional system provide a particularly fine platform. The\ntrifecta of strongly correlated physics, powerful theoretical techniques and\nexperimental viability have resulted in a flurry of research activity over the\nlast decade or so. In this review we explore the non equilibrium aspects of one\ndimensional systems which are integrable. Through a number of illustrative\nexamples we discuss non equilibrium phenomena which arise in such models, the\nrole played by integrability and the consequences these have for more generic\nsystems.",
        "positive": "Bulk-boundary correspondence in topological systems with the momentum\n  dependent energy shift: Bulk-boundary correspondences (BBCs) remain the central topic in modern\ncondensed matter physics, and are gaining increasing interests with the recent\ndiscovery of non-Hermitian skin effects. However, there still exist profound\nfeatures of BBCs that are beyond the existing framework. Here, we report the\nunexpected behavior of BBC when the Hamiltonian contains term of the form\n$d_0(k) I$, which serves as a momentum dependent energy shift. For Hermitian\ncases, momentum dependent energy shift can force the system to be semimetal,\nwhere topological phase transitions can take place with the upper and the lower\nbands keeping untouched. The proper modified BBC should be reconstructed from\nthe perspective of the direct band gap. In non-Hermitian cases, skin effects\nare found to be capable of coexisting with the preserved BBC, of which the\nprocess can be greatly facilitated by the complex $d_0(k)I$. Remarkably, such\nresults can be led a further step and contrary to the intuitive consideration,\nthe modified BBC in Hermitian systems can be restored to be conventional by\nincluding extra non-Hermiticity. The physical origin for these phenomena lies\nin that $d_0(k)I$ can drastically change the point gap topology. Finally, the\ncorresponding experimental simulations are proposed via the platforms of\nelectric circuits."
    },
    {
        "anchor": "Itinerant ferromagnetism in 1D two-component Fermi gases: We study a one-dimensional two-component atomic Fermi gas with an infinite\nintercomponent contact repulsion. It is found that adding an attractive\nresonant odd-wave interaction breaking the rotational symmetry one can make the\nground state ferromagnetic. A promising system for the observation of this\nitinerant ferromagnetic state is a 1D gas of $^{40}$K atoms, where 3D $s$-wave\nand $p$-wave Feshbach resonances are very close to each other and the 1D\nconfinement significantly reduces the inelastic decay.",
        "positive": "Observation of two-dimensional Anderson localisation of ultracold atoms: Anderson localisation -- the inhibition of wave propagation in disordered\nmedia -- is a surprising interference phenomenon which is particularly\nintriguing in two-dimensional (2D) systems. While an ideal, non-interacting 2D\nsystem of infinite size is always localised, the localisation length-scale may\nbe too large to be unambiguously observed in an experiment. In this sense, 2D\nis a marginal dimension between one-dimension, where all states are strongly\nlocalised, and three-dimensions, where a well-defined phase transition between\nlocalisation and delocalisation exists as the energy is increased. Here we\nreport the results of an experiment measuring the 2D transport of ultracold\natoms between two reservoirs, which are connected by a channel containing\npointlike disorder. The design overcomes many of the technical challenges that\nhave hampered observation of localisation in previous works. We experimentally\nobserve exponential localisation in a 2D ultracold atom system."
    },
    {
        "anchor": "Calculating energy shifts in terms of phase shifts: To clarify the relation of energy shifts to scattering phase shifts in\none-body and many-body problems, we examine their relation in a number of\ndifferent situations. We derive, for a particle in a container of arbitrary\nshape with a short-range scattering center, a general result for the energy\neigenvalues in terms of the s-wave scattering phase shift and the eigenstates\nin the absence of the scatterer. We show that, while the energy shifts for a\nspherical container are proportional to the phase shift over large ranges,\nthose for a cubic container have a more complicated behavior. We connect our\nresult to the description of energy shifts in terms of the scattering T-matrix.\nThe general relation is extended to problems of particles in traps with\nsmoothly varying potentials, including, e.g., the interaction of a small\nneutral atom with a Rydberg atom. We then consider the many-body problem for\nparticles with a two-body interaction and show that the free energy change due\nto the interaction is proportional to an average of a generalized phase shift\nthat includes the effects of the medium. Finally, we discuss why, even though\nindividual energy levels are very sensitive to boundary conditions, the energy\nof a many-body system is not.",
        "positive": "Imprinting persistent currents in tunable fermionic rings: Persistent currents in annular geometries have played an important role in\ndisclosing the quantum phase coherence of superconductors and mesoscopic\nelectronic systems. Ultracold atomic gases in multiply connected traps also\nexhibit long-lived supercurrents, and have attracted much interest both for\nfundamental studies of superfluid dynamics and as prototypes for atomtronic\ncircuits. Here, we report on the realization of supercurrents in homogeneous,\ntunable fermionic rings. We gain exquisite, rapid control over quantized\npersistent currents in all regimes of the BCS-BEC crossover through a universal\nphase-imprinting technique, attaining on-demand circulations $w$ as high as 9.\nHigh-fidelity read-out of the superfluid circulation state is achieved by\nexploiting an interferometric protocol, which also yields local information\nabout the superfluid phase around the ring. In the absence of externally\nintroduced perturbations, we find the induced metastable supercurrents to be as\nlong-lived as the atomic sample. Conversely, we trigger and inspect the\nsupercurrent decay by inserting a single small obstacle within the ring. For\ncirculations higher than a critical value, the quantized current is observed to\ndissipate via the emission of vortices, i.e., quantized phase slips, which we\ndirectly image, in good agreement with numerical simulations. The critical\ncirculation at which the superflow becomes unstable is found to depend starkly\non the interaction strength, taking its maximum value for the unitary Fermi\ngas. Our results demonstrate fast and accurate control of quantized collective\nexcitations in a macroscopic quantum system, and establish strongly interacting\nfermionic superfluids as excellent candidates for atomtronic applications."
    },
    {
        "anchor": "Odd-parity topological superfluidity for fermions in a bond-centered\n  square optical lattice: We propose a physical scheme for the realization of two-dimensional\ntopological odd-parity superfluidity in a spin-independent bond-centered square\noptical lattice based upon interband fermion pairing. The D4 point-group\nsymmetry of the lattice protects a quadratic band crossing, which allows one to\nprepare a Fermi surface of spin-up fermions with odd parity close to the\ndegeneracy point. In the presence of spin-down fermions with even parity\npopulating a different energetically well separated band, odd-parity pairing is\nfavored. Strikingly, as a necessary prerequisite for pairing both Fermi\nsurfaces can be tuned to match well. As a result, topological superfluid phases\nemerge in the presence of merely s-wave interaction. Due to the Z2 symmetry of\nthese odd-parity superfluids, we infer their topological features simply from\nthe symmetry and the Fermi-surface topology as confirmed numerically.",
        "positive": "Spin-orbit coupled spin-1 Bose-Einstein condensate flow past an obstacle\n  in the presence of a Zeeman field: We study the dynamics of a Rashba spin-orbit coupled spin-1 ferromagnetic\nBose-Einstein condensate under a linear Zeeman magnetic field(ZF) disturbed by\na moving obstacle. The Bogoliubov excitation spectrums and corresponding\ncritical excitations in different situations are analyzed. The structure of the\ncoreless vortex or antivortex generated by the moving obstacle has been\ninvestigated. When the ZF is applied along x direction, the vortex cores for\nthe three components of a(an) vortex(antivortex) could be arranged into a\nvertical line, and their order would be reversed as the spin-orbit coupling\nincreases. When the ZF is parallel to z direction, a skyrmion-like vortex\nground state could be induced even by a static obstacle. This topological\nstructure is also found to be dynamically stable if the obstacle is moving at a\nrelatively small velocity."
    },
    {
        "anchor": "Frustration effects in rapidly rotating square and triangular optical\n  lattices: We discuss the ground state of the two-dimensional Bose-Hubbard (BH)\nHamiltonian, relevant for rotating gaseous Bose-Einstein condensates, by\nemploying \\mathrm{U}\\left(1\\right) quantum rotor approach and the topologically\nconstrained path integral that includes a summation over\n\\mathrm{U}\\left(1\\right) topological charge. We derive an effective quantum\naction for the BH model, which enables a non-perturbative treatment of the\nzero-temperature phase transition. We calculate the ground-state phase diagram,\nanalytically deriving maximum repulsive energy for several rational values of\nthe frustration rotation parameter f=0, 1/2, 1/3, 1/4, and 1/6 for the square\nand triangular lattice, which improves upon previous theoretical treatments.\nThe ground state of the rotating Bose-Einstein condensates on a triangular\nlattice appears to be most stable against the effects of rotation. Performed\ncalculations revealed strong dependence of the critical ratio of the kinetic\nenergy to the repulsive on-site energy, that separates the global coherent from\nthe insulating state, on topology of the lattice.",
        "positive": "Exact results on the two-particle Green's function of a Bose-Einstein\n  condensate: Starting from the Dyson-Beliaev and generalized Gross-Pitaevskii equations\nwith an extra nonlocal potential, we derive an exact expression of the\ntwo-particle Green's function K for an interacting Bose-Einstein condensate in\nterms of unambiguously defined self-energies and vertices. The formula can be a\nconvenient basis for approximate calculations of K. It also tells us that poles\nof K are not shared with (i.e. shifted from) those of the single-particle\nGreen's function, contrary to the conclusion of previous studies."
    },
    {
        "anchor": "Transition to a Bose-Einstein condensate of excitons at sub-Kelvin\n  temperatures: Bose-Einstein condensation (BEC) is a quantum mechanical phenomenon directly\nlinked to the quantum statistics of bosons. While cold atomic gases provide a\nnew arena for exploring the nature of BEC, a long-term quest to confirm BEC of\nexcitons, quasi-Bose particles formed as a bound state of an electron-hole\npair, has been underway since its theoretical prediction in the 1960s.\nEnsembles of electrons and holes are complex quantum systems with strong\nCoulomb correlations; thus, it is non-trivial whether nature chooses a form of\nexciton BEC. Various systems have been examined in bulk and two-dimensional\nsemiconductors and also exciton-photon hybrid systems. Among them, the 1s\nparaexciton state in a single crystal of Cu2O has been a prime candidate for\nrealizing three-dimensional BEC. The large binding energy and long lifetime\nenable preparation of cold excitons in thermal equilibrium with the lattice and\ndecoupled from the radiation field. However, collisional loss severely limits\nthe conditions for reaching BEC. Such a system with a large inelastic cross\nsection is excluded in atomic BEC experiments, where a small inelastic\nscattering rate and efficient elastic scattering are necessary for evaporative\ncooling. Here we demonstrate that it is nevertheless possible to achieve BEC by\ncooling paraexcitons to sub-Kelvin temperatures in a cold phonon bath. Emission\nspectra from paraexcitons in a three-dimensional trap show an anomalous\ndistribution in a threshold-like manner at the critical number of BEC expected\nfor ideal bosons. Bosonic stimulated scattering into the condensate and\ncollisional loss compete and limit the condensate to a fraction of about 1%.\nThis observation adds a new class of experimentally accessible BEC for\nexploring a rich variety of matter phases of electron-hole ensembles.",
        "positive": "Dark solitons generation and their instability dynamics in two\n  dimensional condensates: We analyze numerically the formation and the subsequent dynamics of\ntwo-dimensional matter wave dark solitons in a Thomas-Fermi rubidium condensate\nusing various techniques. An initially imprinted sharp phase gradient leads to\nthe dynamical formation of a stationary soliton as well as very shallow grey\nsolitons, whereas a smooth gradient only creates grey solitons. The depth and\nhence, the velocity of the soliton is provided by the spatial width of the\nphase gradient, and it also strongly influences the snake-instability dynamics\nof the two dimensional solitons. The vortex dipoles stemming from the unstable\nsoliton exhibit rich dynamics. Notably, the annihilation of a vortex dipole via\na transient dark lump or a vortexonium state, the exchange of vortices between\neither a pair of vortex dipoles or a vortex dipole and a single vortex, and so\non. For sufficiently large width of the initial phase gradient, the solitons\nmay decay directly into vortexoniums instead of vortex pairs, and also the\ndecay rate is augmented. Later, we discuss alternative techniques to generate\ndark solitons, which involve a Gaussian potential barrier and time-dependent\ninteractions, both linear and periodic. The properties of the solitons can be\ncontrolled by tuning the amplitude or the width of the potential barrier. In\nthe linear case, the number of solitons and their depths are determined by the\nquench time of the interactions. For the periodic modulation, a transient\nsoliton lattice emerges with its periodicity depending on the modulation\nfrequency, through a wave number selection governed by the local Bogoliubov\nspectrum. Interestingly, for sufficiently low barrier potential, both Faraday\npattern and soliton lattice coexist. The snake instability dynamics of the\nsoliton lattice is characteristically modified if the Faraday pattern is\npresent."
    },
    {
        "anchor": "Precession of Vortices in Dilute Bose-Einstein Condensates at Finite\n  Temperature: We demonstrate that the precessional frequencies of vortices in Bose Einstein\ncondensates (BECs) are determined by a conservation law, and not by the lowest\nlying excitation energy mode. We determine the precessional frequency for a\nsingle off-axis vortex and vortex lattices in BECs using the continuity\nequation, and solve this self-consistently with the time-independent\nHartree-Fock-Bogoliubov (HFB) equations in the rotating frame. We find\nagreement with zero temperature calculations (Bogoliubov approximation), and a\nsmooth variation in the precession frequency as the temperature is increased.\nTime-dependent solutions confirm the validity of these predictions.",
        "positive": "Fragmented-condensate solid of dipolar excitons: We discuss a possible link between the recently observed macroscopic ordering\nof ultra cold dipolar excitons (MOES) and the phenomenon of supersolidity. In\nthe dilute limit we predict a stable supersolid state for a\nquasi-one-dimensional system of bosonic dipoles characterized by two- and\nthree-body contact repulsion. We phenomenologically extend our theory to the\nstrongly-correlated regime and find a critical value of the contact interaction\nparameter at which the supersolid exhibits a quantum phase transition to a\nfragmented state. The wavelength of the fragmented-condensate solid is defined\nby the balance between the quantum pressure and the entropy due to fluctuations\nof the relative phases between the fragments. Our model appears to be in good\nagreement with the relevant experimental data, including the very recent\nresults on commensurability effect and wavelength of the MOES."
    },
    {
        "anchor": "Anomalous momentum diffusion in a dissipative many-body system: Decoherence is ubiquitous in quantum physics, from the conceptual foundations\nto quantum information processing or quantum technologies, where it is a threat\nthat must be countered. While decoherence has been extensively studied for\nsimple, well-isolated systems such as single atoms or ions, much less is known\nfor many-body systems where inter-particle correlations and interactions can\ndrastically alter the dissipative dynamics. Here we report an experimental\nstudy of how spontaneous emission destroys the spatial coherence of a gas of\nstrongly interacting bosons in an optical lattice. Instead of the standard\nmomentum diffusion expected for independent atoms, we observe an anomalous\nsub-diffusive expansion, associated with a universal slowing down $\\propto\n1/t^{1/2}$ of the decoherence dynamics. This algebraic decay reflects the\nemergence of slowly-relaxing many-body states, akin to sub-radiant states of\nmany excited emitters. These results, supported by theoretical predictions,\nprovide an important benchmark in the understanding of open many-body systems.",
        "positive": "Disorder-Free Localization as a Purely Classical Effect: Disorder-free localization (DFL) is an ergodicity breaking mechanism that has\nbeen shown to occur in lattice gauge theories in the quench dynamics of initial\nstates spanning an extensive number of gauge superselection sectors. Whether\nDFL is intrinsically a quantum interference effect or can arise classically has\nhitherto remained an open question whose resolution is pertinent to further\nunderstanding the far-from-equilibrium dynamics of gauge theories. In this\nwork, we utilize cellular automaton circuits to model the quench dynamics of\nlarge-scale quantum link model (QLM) formulations of $(1+1)$D quantum\nelectrodynamics, showing excellent agreement with the exact quantum case for\nsmall system sizes. Our results demonstrate that DFL persists in the\nthermodynamic limit as a purely classical effect arising from the finite-size\nregularization of the gauge-field operator in the QLM formulation, and that\nquantum interference, though not a necessary condition, may be employed to\nenhance DFL."
    },
    {
        "anchor": "Contact interaction in an unitary ultracold Fermi gas: An ultracold Fermi atomic gas at unitarity presents universal properties that\nin the diluted limit can be well described by a contact interaction. By\nemploying a guide function with correct boundary conditions and making simple\nmodifications to the sampling procedure we are able to handle for the first\ntime a true contact interaction in a quantum Monte Carlo calculation. The\nresults are obtained with small variances. Our calculations for the Bertsch and\ncontact parameters are in excellent agreement with published experiments. The\npossibility of using a more faithfully description of ultracold atomic gases\ncan help uncover features yet unknown of the ultracold atomic gases. In\naddition, this work paves the way to perform quantum Monte Carlo calculations\nfor systems interacting with contact interactions, where in many cases the\ndescription using potentials with finite effective range might not be accurate.",
        "positive": "Kohn-Sham approximation scheme for an interacting Bose-condensed gas: The grand canonical density functional theory for inhomogeneous systems of\ninteracting bosons is developed in the effective action approach. The Legendre\ntransform of the generating functional for Green's functions is used to define\nthe effective action as a functional of both the particle density and the order\nparameter. Expanding the thermal effective action in powers of the Planck\nconstant we obtain a systematic approximation scheme, which practically\nimplements the Kohn-Sham idea: the problem of interacting bosons is reduced to\na single-particle system in a fictitious external potential. The Kohn-Sham\npotential, the density and the order parameter have to be determined\nself-consistently in a given order approximation."
    },
    {
        "anchor": "Steering matter wave superradiance with an ultra-narrowband optical\n  cavity: A superfluid atomic gas is prepared inside an optical resonator with an\nultra-narrow band width on the order of the single photon recoil energy. When a\nmonochromatic off-resonant laser beam irradiates the atoms, above a critical\nintensity the cavity emits superradiant light pulses with a duration on the\norder of its photon storage time. The atoms are collectively scattered into\ncoherent superpositions of discrete momentum states, which can be precisely\ncontrolled by adjusting the cavity resonance frequency. With appropriate pulse\nsequences the entire atomic sample can be collectively accelerated or\ndecelerated by multiples of two recoil momenta. The instability boundary for\nthe onset of matter wave superradiance is recorded and its main features are\nexplained by a mean field model.",
        "positive": "The long-range interacting Fermi polaron: We construct the simplest density functional for the problem of a single\nimpurity interacting with a Fermi gas via a long--ranged potential using the\nThomas--Fermi approach. We find that the Fermi polaron is fully bosonized in\ntwo dimensions, as the model results in a suitable Landau--Pekar functional\nknown from the Bose polaron problem which describes a self--interacting\nimpurity. In other dimensions, the impurity self--interacts with an infinite\nnumber of its own images, and no bosonization occurs. We discuss applications\nof our theory for the $2d$ exciton--polaron and the ionic polaron problem and\ncompute the effective mass for these cases, finding a self--trapping transition\nwith order depending on the dimensionality."
    },
    {
        "anchor": "Two-body anticorrelation in a harmonically trapped ideal Bose gas: We predict the existence of a dip below unity in the second-order coherence\nfunction of a partially condensed ideal Bose gas in harmonic confinement,\nsignaling the anticorrelation of density fluctuations in the sample. The dip in\nthe second-order coherence function is revealed in a canonical-ensemble\ncalculation, corresponding to a system with fixed total number of particles. In\na grand-canonical ensemble description, this dip is obscured by the\noccupation-number fluctuation catastrophe of the ideal Bose gas. The\nanticorrelation is most pronounced in highly anisotropic trap geometries\ncontaining small particle numbers. We explain the fundamental physical\nmechanism which underlies this phenomenon, and its relevance to experiments on\ninteracting Bose gases.",
        "positive": "Scaling solutions of the two fluid hydrodynamic equations in a\n  harmonically trapped gas at unitarity: We prove that the two fluid Landau hydrodynamic equations, when applied to a\ngas interacting with infinite scattering length (unitary gas) in the presence\nof harmonic trapping, admit exact scaling solutions of mixed compressional and\nsurface nature. These solutions are characterized by a linear dependence of the\nvelocity field on the spatial coordinates and a temperature independent\nfrequency which is calculated in terms of the parameters of the trap. Our\nresults are derived in the regime of small amplitude oscillations and hold both\nbelow and above the superfluid phase transition. They apply to isotropic as\nwell as to deformed configurations, thereby providing a generalization of\nCastin's theorem (Y. Castin, C. R. Phys. \\textbf{5}, 407 (2004)) holding for\nisotropic trapping. Our predictions agree with the experimental findings in\nresonantly interacting atomic Fermi gases. The breathing scaling solution, in\nthe presence of isotropic trapping, is also used to prove the vanishing of two\nbulk viscosity coefficients in the superfluid phase."
    },
    {
        "anchor": "Non-thermal dynamics in a spin-1/2 lattice Schwinger model: Local gauge symmetry is intriguing for the study of quantum thermalization\nbreaking. For example, in the high-spin lattice Schwinger model (LSM), the\nlocal U(1) gauge symmetry underlies the disorder-free many-body localization\n(MBL) dynamics of matter fields. This mechanism, however, would not work in a\nspin-1/2 LSM due to the absence of electric energy in the Hamiltonian. In this\npaper, we show that the spin-1/2 LSM can also exhibit disorder-free MBL\ndynamics, as well as entropy prethermalization, by introducing a four-fermion\ninteraction into the system. The interplay between the fermion interaction and\nU(1) gauge symmetry endows the gauge fields with an effectively disordered\npotential which is responsible for the thermalization breaking. It induces\nanomalous (i.e., non-thermal) behaviors in the long-time evolution of such\nquantities as local observables, entanglement entropy, and correlation\nfunctions. Our work offers a new platform to explore emergent non-thermal\ndynamics in state-of-the-art quantum simulators with gauge symmetries.",
        "positive": "Anderson localization of a Tonks-Girardeau gas in potentials with\n  controlled disorder: We theoretically demonstrate features of Anderson localization in the\nTonks-Girardeau gas confined in one-dimensional (1D) potentials with controlled\ndisorder. That is, we investigate the evolution of the single particle density\nand correlations of a Tonks-Girardeau wave packet in such disordered\npotentials. The wave packet is initially trapped, the trap is suddenly turned\noff, and after some time the system evolves into a localized steady state due\nto Anderson localization. The density tails of the steady state decay\nexponentially, while the coherence in these tails increases. The latter\nphenomenon corresponds to the same effect found in incoherent optical solitons."
    },
    {
        "anchor": "Spontaneous generation of spin-orbit coupling in magnetic dipolar Fermi\n  gases: The stability of an unpolarized two-component dipolar Fermi gas is studied\nwithin mean-field theory. Besides the known instability towards spontaneous\nmagnetization with Fermi sphere deformation, another instability towards\nspontaneous formation of a spin-orbit coupled phase with a Rashba-like spin\ntexture is found. A phase diagram is presented and consequences are briefly\ndiscussed.",
        "positive": "Talbot effect for exciton-polaritons: We demonstrate, experimentally and theoretically, a Talbot effect for hybrid\nlight-matter waves -- exciton-polariton condensate formed in a semiconductor\nmicrocavity with embedded quantum wells. The characteristic 'Talbot carpet' is\nproduced by loading the exciton-polariton condensate into a microstructured one\ndimensional periodic array of mesa traps, which creates an array of sources for\ncoherent polariton flow in the plane of the quantum wells. The spatial\ndistribution of the Talbot fringes outside the mesas mimics the near-field\ndiffraction of a monochromatic wave on a periodic amplitude and phase grating\nwith the grating period comparable to the wavelength. Despite the lossy nature\nof the polariton system, the Talbot pattern persists for distances exceeding\nthe size of the mesas by an order of magnitude."
    },
    {
        "anchor": "Limit cycle phase in driven-dissipative spin systems: We explore the phase diagram of interacting spin-$1/2$ systems in the\npresence of anisotropic interactions, spontaneous decay and driving. We find a\nrich phase diagram featuring a limit cycle phase in which the magnetization\noscillates in time. We analyze the spatio-temporal fluctuations of this limit\ncycle phase at the Gaussian level, and show that spatial fluctuations lead to\nquasi-long-range limit cycle ordering for dimension $d = 2$. This result can be\ninterpreted in terms of a spatio-temporal Goldstone mode corresponding to phase\nfluctuations of the limit cycle. We also demonstrate that the limit-cycle phase\nexhibits an asymmetric power spectrum measurable in fluorescence experiments.",
        "positive": "Spinor Condensates on a Cylindrical Surface in Synthetic Gauge Fields: We point out that by modifying the setup of a recent experiment that\ngenerates a Dirac string, one can create a quasi 2D spinor Bose condensate on a\ncylindrical surface with a synthetic magnetic field pointing radially outward\nfrom the cylindrical surface. The synthetic magnetic field takes the form of\nthe Landau gauge. It is generated by the Berry's phase of a spin texture,\nfrozen by an external quadrupolar magnetic field. Unlike in the planar case,\nthere are two types of vortices (called A and B) with the same vorticity. The\nground state for $5\\le S\\le 9$ consists of a row of alternating AB vortices\nlying at the equatorial circle of the cylinder. For higher values of $S$, the A\nand B vortices split into two rows and are displaced from each other along the\ncylindrical axis $z$. The fact that many properties of a BEC are altered in a\ncylindrical surface implies many rich phenomena will emerge for ground states\nin curved surfaces."
    },
    {
        "anchor": "Unusual Zeeman-field effects in two-dimensional spin-orbit-coupled Fermi\n  superfluids: We investigate the Zeeman field effects on the bulk superfluid properties and\nthe collective modes in two-dimensional (2D) attractive atomic Fermi gases with\nRashba-type spin-orbit coupling. In the presence of a large spin-orbit\ncoupling, the system undergoes a quantum phase transition to a topological\nsuperfluid state at a critical Zeeman field. We show that the nonanalyticities\nof the thermodynamic functions as well as other physical quantities at the\nquantum phase transition originate from the infrared singularities caused by\nthe gapless fermionic spectrum. The same argument applies also to the BCS-BEC\nevolution in 2D fermionic superfluids with $p$- or d-wave pairing. The\nsuperfluid density $n_s$ and the velocity of the Goldstone sound mode $c_s$\nbehave oppositely in the normal and the topological superfluid phases: they are\nsuppressed by the Zeeman field in the normal superfluid phase, but get enhanced\nin the topological superfluid phase. The velocity of the Goldstone sound mode\nalso shows nonanalyticity at the quantum phase transition. For large Zeeman\nfield, we find $n_s\\rightarrow n$ and $c_s\\rightarrow \\upsilon_{\\rm F}$, where\n$n$ is the total fermion density and $\\upsilon_{\\rm F}$ is the Fermi velocity\nof noninteracting system. The unusual behavior of the superfluid density and\nthe collective modes can be understood by the fact that the spin-orbit-coupled\nsuperfluid state at large Zeeman field can be mapped to the $p_x+ip_y$\nsuperfluid state of spinless fermions.",
        "positive": "Generation, propagation and control of quantized vortices and dark\n  solitons in polariton superfluids: Exciton-polaritons are quasi-particles arising from the strong coupling\nregime between excitons and photons. In planar microcavitites, phenomena such\nas superfluidity or Bose-Einstein condensation can be observed. Those systems\nhave demonstrated to be very efficient in the hydrodynamic generation of\ntopological excitations, such as vortex-antivortex pairs or dark solitons.\nHowever, the lifetime and motion of those excitations were limited by the\ndriven dissipative nature of the system. In this thesis, we present a rich\nvariety of results about the generation and control of such topological\nexcitations. Taking advantage of the optical bistability present in our system,\nwe were able to greatly enhanced the propagation length of vortices and\nsolitons generated in the wake of a structural defect, revealing in the mean\ntime an unexpected binding mechanism of the solitons which propagate parallel.\nThis behaviour was recovered in a specifically designed experiment, where we\nartificially imprint dark soliton pairs on demand on a polariton superfluid.\nThe adaptability of our technique allowed for a detailed study of this\nphenomenon, that we directly connected to the driven-dissipative nature of our\nsystem. Finally, confined dark solitons were generated within guided intensity\nchannels on a static polariton fluid. The absence of flow lead to the\ndevelopment of transverse snake instabilities of which we studied the\ninteresting properties."
    },
    {
        "anchor": "Vortex precession and exchange in a Bose-Einstein condensate: Vortices in a Bose-Einstein condensate are modelled as spontaneously symmetry\nbreaking minimum energy solutions of the time dependent Gross-Pitaevskii\nequation, using the method of constrained optimization. In a non-rotating\naxially symmetric trap, the core of a single vortex precesses around the trap\ncenter and, at the same time, the phase of its wave function shifts at a\nconstant rate. The precession velocity, the speed of phase shift, and the\ndistance between the vortex core and the trap center, depend continuously on\nthe value of the conserved angular momentum that is carried by the entire\ncondensate. In the case of a symmetric pair of identical vortices, the\nprecession engages an emergent gauge field in their relative coordinate, with a\nflux that is equal to the ratio between the precession and shift velocities.",
        "positive": "Probing superfluidity of periodically trapped ultracold atoms in a\n  cavity by transmission spectroscopy: We study a system of periodic Bose condensed atoms coupled to cavity photons\nusing the input-output formalism. We show that the cavity will either act as a\nthrough pass Lorentzian filter when the superfluid fraction of the condensate\nis minimum or completely reflect the input field when the superfluid fraction\nis maximum. We show that by monitoring the ratio between the transmitted field\nand the reflected field, one can estimate the superfluid fraction."
    },
    {
        "anchor": "Bose-Einstein condensation of light: General theory: A theory of Bose-Einstein condensation of light in a dye-filled optical\nmicrocavity is presented. The theory is based on the hierarchical maximum\nentropy principle and allows one to investigate the fluctuating behavior of the\nphoton gas in the microcavity for all numbers of photons, dye molecules, and\nexcitations at all temperatures, including the whole critical region. The\nmaster equation describing the interaction between photons and dye molecules in\nthe microcavity is derived and the equivalence between the hierarchical maximum\nentropy principle and the master equation approach is shown. The cases of a\nfixed mean total photon number and a fixed total excitation number are\nconsidered, and a much sharper, nonparabolic onset of a macroscopic\nBose-Einstein condensation of light in the latter case is demonstrated. The\ntheory does not use the grand canonical approximation, takes into account the\nphoton polarization degeneracy, and exactly describes the microscopic,\nmesoscopic, and macroscopic Bose-Einstein condensation of light. Under certain\nconditions, it predicts sub-Poissonian statistics of the photon condensate and\nthe polarized photon condensate, and a universal relation takes place between\nthe degrees of second-order coherence for these condensates. In the macroscopic\ncase, there appear a sharp jump in the degrees of second-order coherence, a\nsharp jump and kink in the reduced standard deviations of the fluctuating\nnumbers of photons in the polarized and whole condensates, and a sharp peak, a\ncusp, of the Mandel parameter for the whole condensate in the critical region.\nThe possibility of nonclassical light generation in the microcavity with the\nphoton Bose-Einstein condensate is predicted.",
        "positive": "Robustness of discrete semifluxons in closed Bose-Hubbard chains: We present the properties of the ground state and low-energy excitations of\nBose-Hubbard chains with a geometry that varies from open to closed and with a\ntunable twisted link. In the vicinity of the symmetric $\\pi-$flux case the\nsystem behaves as an interacting gas of discrete semifluxons for finite chains\nand interactions in the Josephson regime. The energy spectrum of the system is\nstudied by direct diagonalization and by solving the corresponding\nBogoliubov--de Gennes equations. The atom-atom interactions are found to\nenhance the presence of strongly correlated macroscopic superpositions of\nsemifluxons."
    },
    {
        "anchor": "Variation of the spin textures of 2-species spin-1 condensates studied\n  beyond the single spatial mode approximation and the experimental\n  identification of these textures: Based on the numerical solutions of the coupled Gross-Pitaevskii equations,\nthe spin-textures of a Bose-Einstein condensate with two kinds of spin-1 atoms\nhave been studied. Besides, the probability densities of an atom in spin\ncomponent $\\mu$ and of two correlated atoms one in $\\mu$ and one in $\\nu$ have\nbeen calculated. By an analysis of the densities, four types of texture have\nbeen found. (i) Both species are in polar phase. (ii) Both species are in\nferromagnetic (f) phase with all the spins lying along a direction. (iii) Both\nspecies are in f phase but the spins of different species are lying along\nopposite directions. (iv) One species in f phase, one species in quasi-f phase\n(where the spins are divided into two groups lying along opposite directions).\nThis finding simplifies the previous classification. Moreover, we found that\nthe variation and transition of the spin-textures can be sensitively reflected\nby these probability densities. Therefore, the theoretical and experimental\nstudies on these densities provide a way to discriminate the spin-textures\nand/or to determine the parameters (say, the strengths of interaction)\ninvolved.",
        "positive": "Stability of matter-wave solitons in a density-dependent gauge theory: We consider the linear stability of chiral matter-wave solitons described by\na density-dependent gauge theory. By studying the associated Bogoliubov-de\nGennes equations both numerically and analytically, we find that the stability\nproblem effectively reduces to that of the standard Gross-Pitaevskii equation,\nproving that the solitons are stable to linear perturbations. In addition, we\nformulate the stability problem in the framework of the Vakhitov-Kolokolov\ncriterion and provide supplementary numerical simulations which illustrate the\nabsence of instabilities when the soliton is initially perturbed."
    },
    {
        "anchor": "Emergence and destruction of macroscopic wave functions: The concept of the macroscopic wave function is a key for understanding\nmacroscopic quantum phenomena. The existence of this object reflects a certain\norder, as is present in a Bose-Einstein condensate when a single-particle\norbital is occupied by a macroscopic number of bosons. We extend these ideas to\nsituations in which a condensate is acted on by an explicitly time-dependent\nforce. While one might assume that such a force would necessarily degrade any\npre-existing order, we demonstrate that macroscopic wave functions can persist\neven under strong forcing. Our definition of the time-dependent order parameter\nis based on a comparison of the evolution of $N$-particle states on the one\nhand, and of states with $N - 1$ particles on the other. Our simulations\npredict the possibility of an almost instantaneous dynamical destruction of a\nmacroscopic wave function under currently accessible experimental conditions.",
        "positive": "Creation and Characterization of Matter-Wave Breathers: We report the creation of quasi-1D excited matter-wave solitons, \"breathers\",\nby quenching the strength of the interactions in a Bose-Einstein condensate\nwith attractive interactions. We characterize the resulting breathing dynamics\nand quantify the effects of the aspect ratio of the confining potential, the\nstrength of the quench, and the proximity of the 1D-3D crossover for the\n2-soliton breather. We furthermore demonstrate the complex dynamics of a\n3-soliton breather created by a stronger interaction quench. Our experimental\nresults, which compare well with numerical simulations, provide a pathway for\nutilizing matter-wave breathers to explore quantum effects in large many-body\nsystems."
    },
    {
        "anchor": "Quantum hydrodynamic modeling of edge modes in chiral Berry plasmons: A quantum hydrodynamic model is used to study the edge modes of chiral Berry\nplasmons. The transcendental equation of the dispersion relation is solved\nnonlinearly and semi-analytically. We predict a new one-way chiral edge state\nwith the quantum effect compared to that without the quantum effect, at the\nboth side of $q=0$. Indeed, the plasmon frequencies for positive and negative\n$q$, exhibit different limits for $q\\rightarrow 0^{-}$ and $q\\rightarrow\n0^{+}$. As a result, the quantum effect enhances the chirality in the vicinity\nof $q=0$. Both counterpropagating edge modes exhibit greater confinement to the\nedge with the quantum effect. In addition, new localized edge modes are found\nwith increased Berry flux in both cases, i.e., without and with the quantum\neffect.",
        "positive": "Rotating Bose-Einstein condensates: Closing the gap between exact and\n  mean-field solutions: When a Bose-Einstein condensed cloud of atoms is given some angular momentum,\nit forms vortices arranged in structures with a discrete rotational symmetry.\nFor these vortex states, the Hilbert space of the exact solution separates into\na \"primary\" space related to the mean-field Gross-Pitaevskii solution and a\n\"complementary\" space including the corrections beyond mean-field. Considering\na weakly-interacting Bose-Einstein condensate of harmonically-trapped atoms, we\ndemonstrate how this separation can be used to close the conceptual gap between\nexact solutions for systems with only a few atoms and the thermodynamic limit\nfor which the mean-field is the correct leading-order approximation. Although\nwe illustrate this approach for the case of weak interactions, it is expected\nto be more generally valid."
    },
    {
        "anchor": "Supersolid Gap Soliton in a Bose-Einstein Condensate and Optical Ring\n  Cavity coupling system: The system of a transversely pumped Bose-Einstein condensate (BEC) coupled to\na lossy ring cavity can favor a supersolid steady state. Here we find the\nexistence of supersolid gap soliton in such a driven-dissipative system. By\nnumerically solving the mean-field atom-cavity field coupling equations, gap\nsolitons of a few different families have been identified. Their dynamical\nproperties, including stability, propagation and soliton collision, are also\nstudied. Due to the feedback atom-intracavity field interaction, these\nsupersolid gap solitons show numerous new features compared with the usual BEC\ngap solitons in static optical lattices.",
        "positive": "Nonexponential decay of Feshbach molecules: We analyze the temporal behavior of the survival probability of an unstable\n$^6$Li Feshbach molecule close to the BCS-BEC crossover. We find different\ninstances of nonexponential decay as the magnetic field approaches the\nresonance value, at which the molecule becomes stable. We observe a transition\nfrom an exponential decay towards a regime dominated by a stretched-exponential\nlaw."
    },
    {
        "anchor": "Quantum enhanced sensing by echoing spin-nematic squeezing in atomic\n  Bose-Einstein condensate: Quantum entanglement can provide enhanced precision beyond standard quantum\nlimit (SQL), the highest precision achievable with classical means. It remains\nchallenging, however, to observe large enhancement limited by the experimental\nabilities to prepare, maintain, manipulate and detect entanglement. Here, we\npresent nonlinear interferometry protocols based on echoing spin-nematic\nsqueezing to achieve record high enhancement factors in atomic Bose-Einstein\ncondensate. The echo is realized by a state-flip of the spin-nematic squeezed\nvacuum, which serves as the probe state and is refocused back to the vicinity\nof the unsqueezed initial state while carrying out near noiseless amplification\nof a signal encoded. A sensitivity of $21.6\\pm0.5$ decibels (dB) for a\nsmall-angle Rabi rotation beyond the two-mode SQL of 26400 atoms as well as\n$16.6\\pm1.3$ dB for phase sensing in a Ramsey interferometer are observed. The\nabsolute phase sensitivity for the latter extrapolates to\n$103~\\rm{pT/\\sqrt{Hz}}$ at a probe volume of $18~\\mu\\rm{m}^3$ for near-resonant\nmicrowave field sensing. Our work highlights the excellent many-body coherence\nof spin-nematic squeezing and suggests its possible quantum metrological\napplications in atomic magnetometer, atomic optical clock, and fundamental\ntesting of Lorentz symmetry violation, etc.",
        "positive": "Exact analytical solution for density matrix of a non-equilibrium\n  polariton Bose-Einstein condensate: In this letter, we give an analytical quantum description of a\nnon-equilibrium polariton Bose-Einstein condensate (BEC) based on the solution\nof the master equation for the full polariton density matrix in the limit of\nfast thermalization. We find the density matrix of a non-equilibrium BEC, that\ntakes into account quantum correlations between all polariton states. We show\nthat the formation of BEC is accompanied by the build-up of cross-correlations\nbetween the ground state and the excited states reaching their highest values\nat the condensation threshold. Despite the non-equilibrium nature of polariton\nsystems, we show the average population of polariton states exhibits the\nBose-Einstein distribution with an almost zero effective chemical potential\nabove the condensation threshold similar to an equilibrium BEC. We demonstrate\nthat above threshold the effective temperature of polariton condensate drops\nbelow the reservoir temperature."
    },
    {
        "anchor": "Exotic vortex lattices in two-species Bose-Einstein condensates: We numerically investigate vortex lattices in rotating two-component\nBose-Einstein condensates in which the two components have unequal atomic\nmasses and interact attractively with each other. For sufficiently strong\nattraction, the system is found to exhibit exotic ground-state structures in a\nharmonic trap, such as lattices having a square geometry or consisting of\ntwo-quantum vortices. The obtained states satisfy the Feynman relation, and\nthey can be realized with current experimental techniques.",
        "positive": "Finite-size effects in the dynamics of few bosons in a ring potential: We study the temporal evolution of a small number $N$ of ultra-cold bosonic\natoms confined in a ring potential. Assuming that initially the system is in a\nsolitary-wave solution of the corresponding mean-field problem, we identify\nsignificant differences in the time evolution of the density distribution of\nthe atoms when it instead is evaluated with the many-body Schr\\\"odinger\nequation. Three characteristic timescales are derived: the first is the period\nof rotation of the wave around the ring, the second is associated with a\n\"decay\" of the density variation, and the third is associated with periodic\n\"collapses\" and \"revivals\" of the density variations, with a factor of $\\sqrt\nN$ separating each of them. The last two timescales tend to infinity in the\nappropriate limit of large $N$, in agreement with the mean-field approximation.\nThese findings are based on the assumption of the initial state being a\nmean-field state. We confirm this behavior by comparison to the exact solutions\nfor a few-body system stirred by an external potential. We find that the exact\nsolutions of the driven system exhibit similar dynamical features."
    },
    {
        "anchor": "Incompressible polaritons in a flat band: We study the interplay of geometric frustration and interactions in a\nnon-equilibrium photonic lattice system exhibiting a polariton flat band as\ndescribed by a variant of the Jaynes-Cummings-Hubbard model. We show how to\nengineer strong photonic correlations in such a driven, dissipative system by\nquenching the kinetic energy through frustration. This produces an\nincompressible state of photons characterized by short-ranged crystalline order\nwith period doubling. The latter manifests itself in strong spatial\ncorrelations, i.e., on-site and nearest-neighbor anti-bunching combined with\nextended density-wave oscillations at larger distances. We propose a\nstate-of-the-art circuit QED realization of our system, which is tunable in\nsitu.",
        "positive": "Stable spin domains in a non-degenerate ultra-cold gas: We study the stability of two-domain spin structures in an ultra-cold gas of\nmagnetically trapped $^{87}$Rb atoms above quantum degeneracy. Adding a small\neffective magnetic field gradient stabilizes the domains via coherent\ncollective spin rotation effects, despite negligibly perturbing the potential\nenergy relative to the thermal energy. We demonstrate that domain stabilization\nis accomplished through decoupling the dynamics of longitudinal magnetization,\nwhich remains in time-independent domains, from transverse magnetization, which\nundergoes a purely transverse spin wave trapped within the domain wall. We\nexplore the effect of temperature and density on the steady-state domains, and\ncompare our results to a hydrodynamic solution to a quantum Boltzmann equation."
    },
    {
        "anchor": "Two-superfluid Model of Two-component Bose-Einstein Condensates; First\n  Sound and Second Sound: Superfluid $^4$He at a finite temperature is described by the two-fluid model\nwith the normal fluid component and the superfluid component.We formulate the\ntwo-fluid model for two-component BECs, namely two-superfluid model, starting\nfrom the coupled Gross-Pitaevskii equations.The two-superfluid model well\ncorresponds to the two-fluid model in superfluid $^4$He.In a special condition,\nthe two sound modes in the two-superfluid model behave like first and second\nsounds in the two-fluid model of superfluid $^4$He.",
        "positive": "Dynamics of a quantum quench in an ultra-cold atomic BCS superfluid: We study dynamics of an ultra-cold atomic BCS superfluid driven towards the\nBCS superfluid-Fermi liquid quantum critical point by a gradual decrease of the\npairing interaction. We analyze how the BCS superfluid falls out of equilibrium\nand show that the non-equilibrium gap and Cooper pair size reflect critical\nproperties of the transition. We observe three stages of evolution: adiabatic\nwhere the Cooper pair size is inversely proportional to the equilibrium gap,\nweakly non-equilibrium where it is inversely proportional to the\nnon-equilibrium gap, and strongly non-equilibrium where it decouples from both\nequilibrium and non-equilibrium gap. These phenomena should stimulate future\nexperimental characterization of non-equilibrium ultra-cold atomic BCS\nsuperfluids."
    },
    {
        "anchor": "Critical Opalescence across the Doping Driven Mott Transition in Optical\n  Lattices of Ultracold Atoms: Phase transitions and their associated crossovers are imprinted in the\nbehavior of fluctuations. Motivated by recent experiments on ultracold atoms in\noptical lattices, we compute the thermodynamic density fluctuations $\\delta\nN^2$ of the two-dimensional fermionic Hubbard model with plaquette cellular\ndynamical mean-field theory. To understand the length scale of these\nfluctuations, we separate the local from the nonlocal contributions to $\\delta\nN^2$. We determine the effects of particle statistics, interaction strength\n$U$, temperature $T$ and density $n$. At high temperature, our theoretical\nframework reproduces the experimental observations in the doping-driven\ncrossover regime between metal and Mott insulator. At low temperature, there is\nan increase of thermodynamic density fluctuations, analog to critical\nopalescence, accompanied by a surprising reduction of the absolute value of\ntheir nonlocal contributions. This is a precursory sign of an underlying phase\ntransition between a pseudogap phase and a metallic phase in doped Mott\ninsulators, which should play an important role in the cuprate high-temperature\nsuperconductors. Predictions for ultracold atom experiments are made.",
        "positive": "Quantum phases of the biased two-chain-coupled Bose-Hubbard Ladder: We investigate the quantum phases of bosons in a two-chain-coupled ladder.\nThis bosonic ladder is generally in a biased configuration, meaning that the\ntwo chains of the ladder can have dramatically different on-site interactions\nand potential energies. Adopting the numerical density-matrix\nrenormalization-group method, we analyze the phase transitions in various\nparameter spaces. We find signatures of both insulating-to-superfluid and\nsuperfluid-to-insulating quantum phase transitions as the interchain tunnelling\nis increased. Interestingly, tunning the interaction to some intermediate\nvalues, the system can exhibit a reentrant quantum phase transition between\ninsulating and superfluid phases. We show that for infinite interaction bias,\nthe model is amenable to some analytical treatments, whose prediction about the\nphase boundary is in great agreement with the numerical results. We finally\nclarify some critical parameters which separate the system into regimes with\ndistinct phase behaviours, and briefly compare typical properties of the biased\nand unbiased bosonic ladder systems. Our work enriches the Bose-Hubbard\nphysics."
    },
    {
        "anchor": "Tuning linear response dynamics near the Dirac points in the bosonic\n  Mott insulator: Optical lattice systems offer the possibility of creating and tuning Dirac\npoints which are present in the tight-binding lattice dispersions. For example,\nsuch a behavior can be achieved in the staggered flux lattice or honeycomb type\nof lattices. Here we focus on the strongly correlated bosonic dynamics in the\nvicinity of Dirac points. In particular, we investigate bosonic Mott insulator\nphase in which quasiparticle excitations have a simple particle-hole\ninterpretation. We show that linear response dynamics around Dirac points, can\nbe significantly engineered at least in two ways: by the type of external\nperturbation or by changing the lattice properties. The key role is played by\nthe interband transitions. Moreover, we explain that the behavior of these\ntransitions is directly connected to different energy scales of the effective\nhopping amplitudes for particles and holes. Presented in this work theoretical\nstudy about tunability of linear response dynamics near the Dirac points can be\ndirectly simulated in the optical lattice systems.",
        "positive": "Magnetic Richtmyer-Meshkov instability in a two-component Bose-Einstein\n  condensate: The magnetically induced Richtmyer-Meshkov instability in a two-component\nBose-Einstein condensate is investigated. We construct and study analytical\nmodels describing the development of the instability at both the linear and\nnonlinear stages. The models indicate new features of the instability: the\ninfluence of quantum capillary waves and the separation of droplets, which are\nqualitatively different from the classical case. We perform numerical\nsimulations of the instability in a trapped Bose-Einstein condensate using the\nGross-Pitaevskii equation and compare the simulation results to the model\npredictions."
    },
    {
        "anchor": "Attractive Interaction between Vortex and Anti-vortex in Holographic\n  Superfluid: Annihilation process of a pair of vortices in holographic superfluid is\nnumerically simulated. The process is found to consist of two stages which are\namazingly separated by vortex size $2r$. The separation distance $\\delta(t)$\nbetween vortex and anti-vortex as a function of time is well fitted by $\\alpha\n(t_{0}-t)^{n}$, where the scaling exponent $n=1/2$ for $\\delta (t)>2r$, and\n$n=2/5$ for $\\delta(t)<2r$. Then the approaching velocity and acceleration as\nfunctions of time and as functions of separation distance are obtained. Thus\nthe attractive force between vortex and anti-vortex is derived as\n$f(\\delta)\\propto 1/\\delta^{3}$ for the first stage, and $f(\\delta)\\propto\n1/\\delta^{4}$ for the second stage. In the end, we explained why the\nannihilation rate of vortices in turbulent superfluid system obeys the two-body\ndecay law when the vortex density is low.",
        "positive": "Bose Einstein condensation and ferromagnetism of low density Bose gas of\n  particles with arbitrary spin: Properties of the ground state and the spectrum of elementary excitations are\ninvestigated for the low density ultracold spinor 3D Bose gas of particles with\narbitrary nonzero spin. Gross-Pitaevskii equations are derived. Within the\nframework of the considering interaction Hamiltonian it is shown that the\nground state spin structure and spin part of the chemical potential is\ndetermined by the renormalized interaction, being defined by the contribution\nof the virtual large momenta. The ferromagnetic structure of the ground state,\nand the equation of the phase, density, and spin dynamics are obtained from\nGross-Pitaevskii equations."
    },
    {
        "anchor": "Bose-Einstein condensate in a rapidly rotating non-symmetric trap: A rapidly rotating Bose-Einstein condensate in a symmetric two-dimensional\nharmonic trap can be described with the lowest Landau-level set of\nsingle-particle states. The condensate wave function psi(x,y) is a Gaussian\nexp(-r^2/2), multiplied by an analytic function f(z) of the complex variable z=\nx+ i y. The criterion for a quantum phase transition to a non-superfluid\ncorrelated many-body state is usually expressed in terms of the ratio of the\nnumber of particles to the number of vortices. Here, a similar description\napplies to a rapidly rotating non-symmetric two-dimensional trap with arbitrary\nquadratic anisotropy (omega_x^2 < omega_y^2). The corresponding condensate wave\nfunction psi(x,y) is a complex anisotropic Gaussian with a phase proportional\nto xy, multiplied by an analytic function f(z), where z = x + i \\beta_- y is a\nstretched complex variable and 0< \\beta_- <1 is a real parameter that depends\non the trap anisotropy and the rotation frequency. Both in the mean-field\nThomas-Fermi approximation and in the mean-field lowest Landau level\napproximation with many visible vortices, an anisotropic parabolic density\nprofile minimizes the energy. An elongated condensate grows along the soft trap\ndirection yet ultimately shrinks along the tight trap direction. The criterion\nfor the quantum phase transition to a correlated state is generalized (1) in\nterms of N/L_z, which suggests that a non-symmetric trap should make it easier\nto observe this transition or (2) in terms of a \"fragmented\" correlated state,\nwhich suggests that a non-symmetric trap should make it harder to observe this\ntransition. An alternative scenario involves a crossover to a quasi\none-dimensional condensate without visible vortices, as suggested by Aftalion\net al., Phys. Rev. A 79, 011603(R) (2009).",
        "positive": "Criticality and hidden criticality in multi-species Bose-Einstein\n  condensates: A general approach is proposed to solve the coupled Gross-Pitaevskii\nequations (CGP) for K-species Bose-Einstein condensates (BEC). Analytical\nsolutions have been obtained under the Thomas-Fermi approximation. We aim at\nfinding out the common features of the K-species BEC. In particular, two types\nof phase-transitions, full-state-transition and partial-state transition, are\nfound. In the former all species are involved in the transition, while in the\nlatter only a few specified species are essentially involved. This leads to the\ncriticality and the hidden criticality (previously found in multi-band\nsuperconductivity). We further found that the former originates from the\nsingularity of the whole matrix of the CGP, while the latter originates from\nthe singularity of a specified sub-matrix (which is contributed by only a few\nspecified species). It is emphasized that the singularity is not a by-product\nof the TFA, but is inherent in the CGP."
    },
    {
        "anchor": "Spatial correlation of two-dimensional Bosonic multi-mode condensates: We studied the spatial coherence of a Bosonic two-dimensional multi-mode\ncondensate both through measurements and simulations. It is shown that\ncondensates with a constant spatial density must be described as the\nsuperposition of several quantized modes which reduces the overall coherence.\nIn this case, the spatial coherence can appear to decay faster than allowed by\nthe Berezinskii-Kosterlitz-Thouless (BKT) theory. However, we find through\nspectroscopic measurements that the individual modes show a slower decay of the\nspatial coherence than the overall system.",
        "positive": "Proposed Fermi-surface reservoir-engineering and application to\n  realizing unconventional Fermi superfluids: We theoretically propose an idea based on reservoir engineering to process\nthe structure of a Fermi edge to split into multiple Fermi edges, so as to be\nsuitable for the state which we want to realize. When one appropriately tunes\nthe chemical-potential difference between two reservoirs being coupled with the\nsystem, the system is shown to be in the non-equilibrium steady state with the\nmomentum distribution having a two-edge structure. We argue that these edges\nplay similar roles to two Fermi surfaces, which can be designed to realize\nexotic quantum many-body states. To demonstrate this, we consider a model\ndriven-dissipative two-component Fermi gas with an attractive interaction as a\nparadigmatic example and show that it exhibits an unconventional Fermi\nsuperfluid. While the superfluid order parameter of this state has the same\nform as that in the Fulde-Ferrell state discussed in metallic superconductivity\nunder an external magnetic field, the former non-equilibrium pairing state is\nnot accompanied by any spin imbalance. Our proposed reservoir engineering to\nprocess the Fermi momentum distribution would provide further possibilities of\nmany-body quantum phenomena beyond the thermal equilibrium case."
    },
    {
        "anchor": "Energy barriers for vortex nucleation in dipolar condensates: We consider singly-quantized vortex states in a condensate of 52Cr atoms in a\npancake trap. We obtain the vortex solutions by numerically solving the\nGross-Pitaevskii equation in the rotating frame with no further approximations.\nThe behavior of the condensate is studied under three different situations\nconcerning the interactions: only s-wave, s-wave plus dipolar and only dipolar.\nThe energy barrier for the nucleation of a vortex is calculated as a function\nof the vortex displacement from the rotation axis in the three cases. These\nresults are compared to those obtained for contact interaction condensates in\nthe Thomas-Fermi approximation, and to a pseudo-analytical model, showing this\nlatter a very good agreement with the numerical calculation.",
        "positive": "Dynamics of a Pair of Overlapping Polar Bright Solitons in Spin-1\n  Bose-Einstein Condensates: We analyze the dynamics of both population and spin densities, emerging from\nthe spatial overlap between two distinct polar bright solitons in Spin-1 Spinor\nCondensates. The dynamics of overlapping solitons in scalar condensates\nexhibits soliton fusion, atomic switching from one soliton to another and\nrepulsive dynamics depending on the extent of overlap and the relative phase\nbetween the solitons. The scalar case also helps us understand the dynamics of\nthe vector solitons. In the spinor case, non-trivial dynamics emerge in spatial\nand spin degrees of freedom. In the absence of spin changing collisions, we\nobserve Josephson-like oscillations in the population dynamics of each spin\ncomponent. In this case, the population dynamics is independent of the relative\nphase, but the dynamics of the spin-density vector depends on it. The latter\nalso witnesses the appearance of oscillating domain walls. The pair of\noverlapping polar solitons emerge as four ferromagnetic solitons irrespective\nof the initial phase difference for identical spin-dependent and\nspin-independent interaction strengths. But the dynamics of final solitons\ndepends explicitly on the relative phase. Depending on the ratio of\nspin-dependent and spin-independent interaction strengths, a pair of\noscillatons can also emerge as the final state. Then, increasing the extent of\noverlap may lead to the simultaneous formation of both a stationary\nferromagnetic soltion and a pair of oscillatons depending on the relative\nphase."
    },
    {
        "anchor": "Management of the Correlations of Ultracold Bosons in Triple Wells: Ultracold interacting atoms are an excellent tool to study correlation\nfunctions of many-body systems that are generally eluding detection and\nmanipulation. Herein, we investigate the ground state of bosons in a tilted\ntriple-well potential and characterize the many-body state by the eigenvalues\nof its reduced one-body density matrix and Glauber correlation functions. We\nunveil how the interplay between the interaction strength and the tilt can be\nused to control the number of correlated wells as well as the fragmentation,\ni.e. the number of macroscopic eigenvalues of the reduced one-body density\nmatrix.",
        "positive": "Calculation of the even-odd energy difference in superfluid Fermi\n  systems using the pseudopotential theory: The pseudopotential theory is extended to the Bogoliubov-de Gennes equations\nto determine the excess energy when one atom is added to the trapped superfluid\nFermi system with even number of atoms. Particular attention is paid to systems\nbeing at the Feshbach resonance point. The results for relatively small\nparticle numbers are in harmony with the Monte-Carlo calculations, but are also\nrelevant for systems with larger particle numbers. Concerning the additional\none quasiparticle state we define and determine two new universal numbers to\ncharacterize its widths."
    },
    {
        "anchor": "Exact Spectral Function of One-Dimensional Bose Gases: Strong correlation in one-dimensional (1D) quantum systems drastically\nchanges their dynamic and transport properties in the presence of the\ninteraction. In this letter, combining quantum integrable theory with numerics,\nwe exactly compute the spectral function of 1D Lieb-Liniger gas at a many-body\nlevel of large scales. It turns out that a full capture of the power-law\nsingularities in the vicinities of thresholds requires system size as large as\nthousands of particles. Our research essentially confirms the validity of the\nnonlinear Tomonaga-Luttinger liquid and provides a reliable technique for\nstudying critical behaviour emerged only in thermodynamic limit.",
        "positive": "A Bose gas in a single-beam optical dipole trap: We study an ultracold Bose gas in an optical dipole trap consisting of one\nsingle focused laser beam. An analytical expression for the corresponding\ndensity of states beyond the usual harmonic approximation is obtained. We are\nthus able to discuss the existence of a critical temperature for Bose-Einstein\ncondensation and find that the phase transition must be enabled by a cutoff\nnear the threshold. Moreover, we study the dynamics of evaporative cooling and\nobserve significant deviations from the findings for the well-established\nharmonic approximation. Furthermore, we investigate Bose-Einstein condensates\nin such a trap in Thomas-Fermi approximation and determine analytical\nexpressions for chemical potential, internal energy and Thomas-Fermi radii\nbeyond the usual harmonic approximation."
    },
    {
        "anchor": "Statistical properties of the spectrum the extended Bose-Hubbard model: Motivated by the role that spectral properties play for the dynamical\nevolution of a quantum many-body system, we investigate the level spacing\nstatistic of the extended Bose-Hubbard model. In particular, we focus on the\ndistribution of the ratio of adjacent level spacings, useful at large\ninteraction, to distinguish between chaotic and non-chaotic regimes. After\nrevisiting the bare Bose-Hubbard model, we study the effect of two different\nperturbations: next-nearest neighbor hopping and nearest-neighbor interaction.\nThe system size dependence is investigated together with the effect of the\nproximity to integrable points or lines. Lastly, we discuss the consequences of\na cutoff in the number of onsite bosons onto the level statistics.",
        "positive": "From Nodal Ring Topological Superfluids to Spiral Majorana Modes in Cold\n  Atomic Systems: In this work, we consider a 3D cubic optical lattice composed of coupled 1D\nwires with 1D spin-orbit coupling. When the s-wave pairing is induced through\nFeshbach resonance, the system becomes a topological superfluid with ring\nnodes, which are the ring nodal degeneracies in the bulk, and supports a large\nnumber of surface Majorana zero energy modes. The large number of surface\nMajorana modes remain at zero energy even in the presence of disorder due to\nthe protection from a chiral symmetry. When the chiral symmetry is broken, the\nsystem becomes a Weyl topological superfluid with Majorana arcs. With 3D\nspin-orbit coupling, the Weyl superfluid becomes a novel gapless phase with\nspiral Majorana modes on the surface. The spatial resolved radio frequency\nspectroscopy is suggested to detect this novel nodal ring topological\nsuperfluid phase."
    },
    {
        "anchor": "Disorder-controlled relaxation in a 3D Hubbard model quantum simulator: Understanding the collective behavior of strongly correlated electrons in\nmaterials remains a central problem in many-particle quantum physics. A minimal\ndescription of these systems is provided by the disordered Fermi-Hubbard model\n(DFHM), which incorporates the interplay of motion in a disordered lattice with\nlocal inter-particle interactions. Despite its minimal elements, many dynamical\nproperties of the DFHM are not well understood, owing to the complexity of\nsystems combining out-of-equilibrium behavior, interactions, and disorder in\nhigher spatial dimensions. Here, we study the relaxation dynamics of doubly\noccupied lattice sites in the three-dimensional (3D) DFHM using\ninteraction-quench measurements on a quantum simulator composed of fermionic\natoms confined in an optical lattice. In addition to observing the widely\nstudied effect of disorder inhibiting relaxation, we find that the cooperation\nbetween strong interactions and disorder also leads to the emergence of a\ndynamical regime characterized by \\textit{disorder-enhanced} relaxation. To\nsupport these results, we develop an approximate numerical method and a\nphenomenological model that each capture the essential physics of the decay\ndynamics. Our results provide a theoretical framework for a previously\ninaccessible regime of the DFHM and demonstrate the ability of quantum\nsimulators to enable understanding of complex many-body systems through minimal\nmodels.",
        "positive": "Classical verification of a quantum simulator: local relaxation of a 1D\n  Bose gas: In [Nat. Phys. 8, 325-330 (2012)], Trotzky et al. utilize ultracold atoms in\nan optical lattice to simulate the local relaxation dynamics of a strongly\ninteracting Bose gas \"for longer times than present classical algorithms can\nkeep track of\". Here, I classically verify the results of this analog quantum\nsimulator by calculating the evolution of the same quasi-local observables up\nto the time at which they appear \"fully relaxed\". Using a parallel\nimplementation of the time-evolving block decimation (TEBD) algorithm to\nsimulate the system on a supercomputer, I show that local densities and\ncurrents can be calculated in a matter of days rather than weeks. The precision\nof these numerics allows me to observe deviations from the conjectured\npower-law decay and to determine the effects of the harmonic trapping\npotential. As well as providing a robust benchmark for future experimental,\ntheoretical, and numerical methods, this work serves as an example of the\nindependent verification process."
    },
    {
        "anchor": "Non-Fermi liquid fixed point for an imbalanced gas of fermions in\n  $1+\u03b5$ dimensions: We consider a gas of two species of fermions with population imbalance. Using\nthe renormalization group in $d=1+\\epsilon$ dimensions, we show that for\nspinless fermions and $\\epsilon > 0$ a fixed point appears at finite attractive\ncoupling where the quasiparticle residue vanishes, and identify this with the\ntransition to Larkin--Ovchinnikov--Fulde--Ferrell order (inhomogeneous\nsuperconductivity). When the two species of fermions also carry spin degrees of\nfreedom we find a fixed point indicating a transition to spin density wave\norder.",
        "positive": "Spin liquid phases of alkaline-earth-metal atoms at finite temperature: We study spin liquid phases of spin-5/2 alkaline earth atoms on a honeycomb\nlattice at finite temperatures. Our analysis is based on a Gutzwiller\nprojection variational approach recast to a path-integral formalism. In the\nframework of a saddle-point approximation we determine spin liquid phases with\nlowest free energy and study their temperature dependence. We identify a\ncritical temperature, where all the spin liquid phases melt and the system goes\nto the paramagnetic phase. We also study the stability of the saddle-point\nsolutions and show that a time-reversal symmetry breaking state, a so called\nchiral spin liquid phase is realized even at finite temperatures. We also\ndetermine the spin structure factor, which, in principle, is an experimentally\nmeasurable quantity and is the basic tool to map the spectrum of elementary\nexcitations of the system."
    },
    {
        "anchor": "Absence of long-range order in a triangular spin system with dipolar\n  interactions: Antiferromagnetic Heisenberg model on the triangular lattice is perhaps the\nbest known example of frustrated magnets, but it orders at low temperatures.\nRecent density matrix renormalization group (DMRG) calculations find that next\nnearest neighbor interaction $J_2$ enhances the frustration and leads to a spin\nliquid for $J_2/J_1\\in (0.08,0.15)$. In addition, DMRG study of a dipolar\nHeisenberg model with longer range interactions gives evidence for a spin\nliquid at small dipole titling angle $\\theta\\in[0,10^\\circ)$. In both cases,\nthe putative spin liquid region appears to be small. Here, we show that for the\ntriangular lattice dipolar Heisenberg model, a robust quantum paramagnetic\nphase exists in a surprisingly wide region, $\\theta\\in [0,54^\\circ)$, for\ndipoles tilted along the lattice diagonal direction. We obtain the phase\ndiagram of the model by functional renormalization group (RG) which treats all\nmagnetic instabilities on equal footing. The quantum paramagnetic phase is\ncharacterized by a smooth continuous flow of vertex functions and spin\nsusceptibility down to the lowest RG scale, in contrast to the apparent\nbreakdown of RG flow in phases with stripe or spiral order. Our finding points\nto a promising direction to search for quantum spin liquids in ultracold\ndipolar molecules.",
        "positive": "Nematic ferromagnetism on the Lieb lattice: We discuss the properties of possible ferromagnetic orders on the Lieb\nlattice. We show that the presence of a quadratic-flat band crossing point\n(QFBCP) at half filling will dramatically affect the magnetic ordering. In the\npresence of a weak on-site repulsive interaction, we find the ground state is a\nnematic ferromagnetic order with simultaneously broken of time-reversal and\nrotational symmetries. When the interaction strength increases, the rotational\nsymmetry will restore at some critical value, and the system enters a\nconventional ferromagnetic regime. We also point out that the spin gap in both\nthe nematic and conventional ferromagnetic phases is of the order of\ninteraction. This observation suggests that these magnetic orders can be\nrealized and detected in cold atomic systems with present technology."
    },
    {
        "anchor": "Spin-polarized droplets in the unitary Fermi gas: We demonstrate the existence of a new type of spatially localized excitations\nin the unitary Fermi gas: spin polarized droplets with a peculiar internal\nstructure involving the abrupt change of the pairing phase at the surface of\nthe droplet. It resembles the structure of the Josephson-$\\pi$ junction\noccurring when a slice of a ferromagnet is sandwiched between two\nsuperconductors. The stability of the impurity is enhanced by the mutual\ninterplay between the polarization effects and the pairing field, resulting in\nan exceptionally long-lived state. The prospects for its realization in\nexperiment are discussed.",
        "positive": "The superfluid fountain effect in a Bose-Einstein condensate: We consider a simple experimental setup, based on a harmonic confinement,\nwhere a Bose-Einstein condensate and a thermal cloud of weakly interacting\nalkali atoms are trapped in two different vessels connected by a narrow\nchannel. Using the classical field approximation, as described in J. Phys. B\n40, R1 (2007) and optimized in Phys. Rev. A 81, 013629 (2010) for an arbitrary\ntrapping potential, we theoretically investigate the analog of the celebrated\nsuperfluid helium fountain effect. We show that this thermo-mechanical effect\nmight indeed be observed in this system. By analyzing the dynamics of the\nsystem, we are able to identify the superfluid and normal components of the\nflow as well as to distinguish the condensate fraction from the superfluid\ncomponent. We show that the superfluid component can easily flow from the\ncolder vessel to the hotter one while the normal component is practically\nblocked in the latter."
    },
    {
        "anchor": "Enlarging and cooling the N\u00e9el state in an optical lattice: We propose an experimental scheme to favor both the realization and the\ndetection of the N\\'eel state in a two-component gas of ultracold fermions in a\nthree-dimensional simple-cubic optical lattice. By adding three compensating\nGaussian laser beams to the standard three pairs of retroreflected lattice\nbeams, and adjusting the relative waists and intensities of the beams, one can\nsignificantly enhance the size of the N\\'eel state in the trap, thus increasing\nthe signal of optical Bragg scattering. Furthermore, the additional beams\nprovide for adjustment of the local chemical potential and the possibility to\nevaporatively cool the gas while in the lattice. Our proposals are relevant to\nother attempts to realize many-body quantum phases in optical lattices.",
        "positive": "Constrained motions and slow dynamics in one-dimensional bosons with\n  double-well dispersion: We demonstrate slow dynamics and constrained motion of domain walls in\none-dimensional (1D) interacting bosons with double-well dispersion. In the\nsymmetry-broken regime, the domain-wall motion is ``fractonlike'' -- a single\ndomain wall cannot move freely, while two nearby domain walls can move\ncollectively. Consequently, we find an Ohmic-like linear response and a\nvanishing superfluid stiffness, which are atypical for a Bose condensate in a\n1D translation invariant closed quantum system. Near Lifshitz quantum critical\npoint, we obtain superfluid stiffness $\\rho_s\\sim T$ and sound velocity\n$v_s\\sim T^{1/2}$, showing similar unconventional low-temperature slow dynamics\nto the symmetry-broken regime. Particularly, the superfluid stiffness suggests\nan order by disorder effect as $\\rho_s$ increases with temperature. Our results\npave the way for studying fractons in ultracold atom experiments."
    },
    {
        "anchor": "Three-boson spectrum in the presence of 1D spin-orbit coupling: Efimov's\n  generalized radial scaling law: Spin-orbit coupled cold atom systems, governed by Hamiltonians that contain\nquadratic kinetic energy terms typical for a particle's motion in the usual\nSchr\\\"odinger equation and linear kinetic energy terms typical for a particle's\nmotion in the usual Dirac equation, have attracted a great deal of attention\nrecently since they provide an alternative route for realizing fractional\nquantum Hall physics, topological insulators, and spintronics physics. The\npresent work focuses on the three-boson system in the presence of 1D spin-orbit\ncoupling, which is most relevant to ongoing cold atom experiments. In the\nabsence of spin-orbit coupling terms, the three-boson system exibits the Efimov\neffect: the entire energy spectrum is uniquely determined by the $s$-wave\nscattering length and a single three-body parameter, i.e., using one of the\nenergy levels as input, the other energy levels can be obtained via Efimov's\nradial scaling law, which is intimately tied to a discrete scaling symmetry. It\nis demonstrated that the discrete scaling symmetry persists in the presence of\n1D spin-orbit coupling, implying the validity of a generalized radial scaling\nlaw in five-dimensional space. The dependence of the energy levels on the\nscattering length, spin-orbit coupling parameters, and center-of-mass momentum\nis discussed. It is conjectured that three-body systems with other types of\nspin-orbit coupling terms are also governed by generalized radial scaling laws,\nprovided the system exhibits the Efimov effect in the absence of spin-orbit\ncoupling.",
        "positive": "Feynman diagrams versus Fermi-gas Feynman emulator: Precise understanding of strongly interacting fermions, from electrons in\nmodern materials to nuclear matter, presents a major goal in modern physics.\nHowever, the theoretical description of interacting Fermi systems is usually\nplagued by the intricate quantum statistics at play. Here we present a\ncross-validation between a new theoretical approach, Bold Diagrammatic Monte\nCarlo (BDMC), and precision experiments on ultra-cold atoms. Specifically, we\ncompute and measure with unprecedented accuracy the normal-state equation of\nstate of the unitary gas, a prototypical example of a strongly correlated\nfermionic system. Excellent agreement demonstrates that a series of Feynman\ndiagrams can be controllably resummed in a non-perturbative regime using BDMC.\nThis opens the door to the solution of some of the most challenging problems\nacross many areas of physics."
    },
    {
        "anchor": "Sculpting quasi one-dimensional Bose-Einstein condensate to generate\n  calibrated matter-waves: We explore theoretically how to tune the dynamics of a quasi one-dimensional\nharmonically trapped Bose-Einstein condensate (BEC) due to an additional red-\nand blue-detuned Hermite-Gaussian dimple trap (HGdT). To this end we study a\nBEC in a highly non-equilibrium state, which is not possible in a traditional\nharmonically confined trap. Our system is modeled by a time-dependent\nGross-Pitaevskii equation, which is numerically solved by the Crank-Nicolson\nmethod in both imaginary and real time. For equilibrium, we obtain a condensate\nwith two bumps/dips which are induced by the chosen TEM$_{01}$ mode for the\nred/blue-detuned HGdT, respectively. Afterwards, in time-of-flight dynamics, we\nexamine the adherence/decay of the two bumps/dips in the condensate, which are\ninduced by the still present red/blue-detuned HGdT, respectively. On the other\nhand, once the red/blue HGdT potential is switched off, shock-waves or\nbi-trains of gray/dark pair-solitons are created. During this process it is\nfound that the generation of gray/dark pair-solitons bi-trains are generic\nphenomena of collisions of moderately/fully fragmented BEC. Additionally, it\nturns out that the special shape of generated solitons in the harmonically\ntrapped BEC firmly depends upon the geometry of the HGdT.",
        "positive": "Ultracold Atomic Gases: Novel States of Matter: Article to appear in the Encyclopedia of Complexity and Systems Science, Dr.\nR. A. Meyers (Ed.) (Springer Heidelberg, 2009)."
    },
    {
        "anchor": "Boltzmann-type collision operators for Bogoliubov excitations of\n  Bose-Einstein condensates: A unified framework: Starting from the Bogoliubov diagonalization for the Hamiltonian of a weakly\ninteracting Bose gas under the presence of a Bose-Enstein Condensate, we derive\nthe kinetic equation for the Bogoliubov excitations. Without dropping any of\nthe commutators, we find three collisional processes. One of them describes the\n$1\\leftrightarrow2$ interactions between the condensate and the excited atoms.\nThe other two describe the $2\\leftrightarrow2$ and $1\\leftrightarrow3$\ninteractions between the excited atoms themselves.",
        "positive": "Controlling and Detecting Spin Correlations of Ultracold Atoms in\n  Optical lattices: We report on the controlled creation of a valence bond state of delocalized\neffective-spin singlet and triplet dimers by means of a bichromatic optical\nsuperlattice. We demonstrate a coherent coupling between the singlet and\ntriplet states and show how the superlattice can be employed to measure the\nsinglet-fraction employing a spin blockade effect. Our method provides a\nreliable way to detect and control nearest-neighbor spin correlations in\nmany-body systems of ultracold atoms. Being able to measure these correlations\nis an important ingredient to study quantum magnetism in optical lattices. We\nfurthermore employ a SWAP operation between atoms being part of different\ntriplets, thus effectively increasing their bond-length. Such SWAP operation\nprovides an important step towards the massively parallel creation of a\nmulti-particle entangled state in the lattice."
    },
    {
        "anchor": "Coherent zero-field magnetization resonance in a dipolar spin-1\n  Bose-Einstein condensate: With current magnetic field shielding and high precision detection in dipolar\nspinor Bose-Einstein condensates, it is possible to experimentally detect the\nlow or zero field nonsecular dipolar dynamics. Here we analytically investigate\nthe zero-field nonsecular magnetic dipolar interaction effect, with an emphasis\non magnetization dynamics in a spin-1 Bose-Einstein condensate under the single\nspatial mode approximation within the mean field theory. Due to the biaxial\nnature of the dipolar interaction, a novel resonance occurs in the condensate\nmagnetization oscillation, contrast to the previous assumption of a conserved\nmagnetization in strong magnetic fields. Furthermore, we propose a\ndynamical-decoupling detection method for such a resonance, which cancels the\nstray magnetic fields in experiments but restores the magnetization dynamics.\nOur results shed new lights on the dipolar systems and may find potential\napplications beyond cold atoms.",
        "positive": "Quantum Monte Carlo and perturbative study of repulsive two-dimensional\n  Bose-Fermi mixtures: We derive analytically the leading beyond-mean field contributions to the\nzero-temperature equation of state and to the fermionic quasi-particle residue\nand effective mass of a dilute Bose-Fermi mixture in two dimensions. In the\nrepulsive case, we perform quantum Monte Carlo simulations for two\nrepresentative bosonic concentrations and equal masses, extending a method for\ncorrecting finite-size effects in fermionic gases to Bose-Fermi mixtures. We\nfind good agreement between analytic expressions and numerical results for weak\ninteractions, while significant discrepancies appear in the regime close to\nmechanical instability, above which we provide evidence of phase separation of\nthe bosonic component."
    },
    {
        "anchor": "Rapid ramps across the BEC-BCS crossover: a novel route to measuring the\n  superfluid gap: We investigate the response of superfluid Fermi gases to rapid changes of the\nthree-dimensional s-wave scattering length a by solving the time-dependent\nBogoliubov-de Gennes equations. In general the magnitude of the order parameter\n|\\Delta| performs oscillations, which are sometimes called the \"Higgs\" mode,\nwith the angular frequency 2 \\Delta_{gap}/ \\hbar, where \\Delta_{gap} is the gap\nin the spectrum of fermionic excitations. Firstly, we excite the oscillations\nwith a linear ramp of 1/a and study the evolution of |\\Delta|. Secondly, we\ncontinously drive the system with a sinusoidal modulation of 1/a. In the first\ncase, the oscillations in |\\Delta| damp according to a power law. In the second\ncase, the continued driving causes revivals in the oscillations. In both cases,\nthe excitation of the oscillations causes a reduction in the time-averaged\nvalue of |\\Delta|. We propose two experimental protocols, based around the two\napproaches, to measure the frequency and damping of the oscillations, and hence\n\\Delta_{gap}.",
        "positive": "Detecting One-Dimensional Dipolar Bosonic Crystal Orders via Full\n  Distribution Functions: We explore the groundstates of a few dipolar bosons in optical lattices with\nincommensurate filling. The competition of kinetic, potential, and interaction\nenergies leads to the emergence of a variety of crystal state orders with\ncharacteristic one- and two-body densities. We probe the transitions between\nthese orders and construct the emergent state diagram as a function of the\ndipolar interaction strength and the lattice depth. We show that the crystal\nstate orders can be observed using the full distribution functions of the\nparticle number extracted from simulated single-shot images."
    },
    {
        "anchor": "Excited-state quantum phase transitions in spinor Bose-Einstein\n  condensates: Excited-state quantum phase transitions (ESQPTs) extend the notion of quantum\nphase transitions beyond the ground state. They are characterized by closing\nenergy gaps amid the spectrum. Identifying order parameters for ESQPTs poses\nhowever a major challenge. We introduce spinor Bose-Einstein condensates as a\nversatile platform for studies of ESQPTs. Based on the mean-field dynamics, we\ndefine a topological order parameter that distinguishes between excited-state\nphases, and discuss how to interferometrically access the order parameter in\ncurrent experiments. Our work opens the way for the experimental\ncharacterization of excited-state quantum phases in atomic many-body systems.",
        "positive": "A Renormalization-Group Study of Interacting Bose-Einstein Condensates:\n  II. Anomalous Dimension $\u03b7$ for $d\\lesssim 4$ at Finite Temperatures: We study the anomalous dimension $\\eta$ of homogeneous interacting\nsingle-component Bose-Einstein condensates at finite temperatures for\n$d\\lesssim 4$ dimensions. This $\\eta$ is defined in terms of the one-particle\ndensity matrix $\\rho({\\bf r})\\equiv \\langle \\hat\\psi^\\dagger({\\bf\nr}_1)\\hat\\psi({\\bf r}_1+{\\bf r})\\rangle$ through its asymptotic behavior\n$\\rho({\\bf r})\\rightarrow N_{\\bf 0}/V+C r^{-d+2-\\eta}$ for $r\\rightarrow\n\\infty$, where $N_{\\bf 0}/V$ is the condensate density and $C$ is a constant.\nIt is shown that the anomalous dimension is given by $\\eta=0.181\\epsilon^2$ to\nthe leading order in $\\epsilon\\equiv d-4$. The change of the prefactor $0.181$\nfrom the value $0.02$ at the transition point of the ${\\rm O}(2)$ symmetric\n$\\phi^4$ model is attributed to the emergence of three-point vertices and the\nanomalous Green's function when $N_{\\bf 0}$ acquires a finite value."
    },
    {
        "anchor": "A new form of liquid matter: quantum droplets: This brief review summarizes recent theoretical and experimental results\nwhich predict and establish the existence of quantum droplets (QDs), i.e.,\nrobust two- and three-dimensional (2D and 3D) self-trapped states in\nBose-Einstein condensates (BECs), which are stabilized by effective\nselffirepulsion induced by quantum fluctuations around the mean-field (MF)\nstates [alias the Lee-Huang--Yang (LHY) effect]. The basic models are\npresented, taking special care of the dimension crossover, 2D -> 3D. Recently\nreported experimental results, which exhibit stable 3D and quasi-2D QDs in\nbinary BECs, with the inter-component attraction slightly exceeding the MF\nself-repulsion in each component, and in single-component condensates of atoms\ncarrying permanent magnetic moments, are presented in some detail. The summary\nof theoretical results is focused, chiefly, on 3D and quasi-2D QDs with\nembedded vorticity, as the possibility to stabilize such states is a remarkable\nprediction. Stable vortex states are presented both for QDs in free space, and\nfor singular but physically relevant 2D modes pulled to the center by the\ninverse-square potential, with the quantum collapse suppressed by the LHY\neffect.",
        "positive": "Temperature-induced supersolidity in spin-orbit-coupled Bose gases: Close to the superfluid plane-wave (PW) - supersolid stripe (ST) phase\ntransition point of a zero temperature quasi-one-dimensional spin-orbit-coupled\nBose gas, we find that an increase in temperature induces a phase transition to\nthe supersolid phase with a broken translational symmetry from the superfluid\nplane-wave phase. We use the Hartree-Fock-Bogoliubov theory with the Popov\napproximation to investigate the effect of thermal fluctuations on the\ncollective excitation spectrum and investigate the softening of the spin-dipole\nmode corresponding to the shift in the quantum critical point. This is in stark\ncontrast to the PW-ST phase transition in a homogeneous system where non-zero\ntemperatures facilitate the melting of the stripe phase."
    },
    {
        "anchor": "Shear viscosity and spin diffusion in a two-dimensional Fermi gas: We investigate the temperature dependence of the shear viscosity and spin\ndiffusion in a two-dimensional Fermi gas with contact interactions, as realized\nin ultra-cold atomic gases. We describe the transport coefficients in terms of\na Boltzmann equation and present a full numerical solution for the degenerate\ngas. In contrast to previous works we take the medium effects due to finite\ndensity fully into account. This effect reduces the viscosity to entropy ratio,\n$\\eta/s$, by a factor of three, and similarly for spin diffusion. The trap\naveraged viscosity agrees well with recent measurements by Vogt et al. [Phys.\nRev. Lett. 108, 070404 (2012)].",
        "positive": "Area law and its violation: A microscopic inspection into the structure\n  of entanglement and fluctuations: Quantum fluctuations of local quantities can be a direct signature of\nentanglement in an extended quantum many-body system. Hence they may serve as a\ntheoretical (as well as an experimental) tool to detect the spatial properties\nof the entanglement entropy of a subsystem. In the ground state of quantum\nmany-body systems, its scaling is typically linear in the boundary of the\nsubsystem (area law). Here we propose a microscopic insight into the spatial\nstructure of entanglement and fluctuations using the concept of \\emph{contour},\nrecently introduced to decompose the bipartite entanglement entropy of lattice\nfree fermions between two extended regions $A$ and $B$ into contributions from\nsingle sites in $A$. We generalize the notion of contour to the entanglement of\nany quadratic (bosonic or fermionic) lattice Hamiltonian, as well as to\nparticle-number fluctuations. The entanglement and fluctuations contours are\nfound to generally decay when moving away from the boundary between $A$ and\n$B$. We show that in the case of free fermions the decay of the entanglement\ncontour follows closely that of the fluctuation contour. In the case of\nBose-condensed interacting bosons, treated via the Bogoliubov and spin-wave\napproximations, such a link cannot be established -- fluctuation and\nentanglement contours are found to be radically different, as they lead to a\nlogarithmically violated area law for fluctuations, and to a strict area law of\nentanglement. Analyzing in depth the role of the zero-energy Goldstone mode of\nspin-wave theory, and of the corresponding lowest-energy mode in the\nentanglement spectrum, we unveil a subtle interplay between the special contour\nand energy scaling of the latter, and universal additive logarithmic\ncorrections to entanglement area law discussed extensively in the recent\nliterature."
    },
    {
        "anchor": "Retardation effects in induced atomic dipole-dipole interactions: We present mean-field calculations of azimuthally averaged retarded\ndipole-dipole interactions in a Bose-Einstein condensate induced by a laser, at\nboth long and short wavelengths. Our calculations demonstrate that\ndipole-dipole interactions become significantly stronger at shorter\nwavelengths, by as much as 30-fold, due to retardation effects. This\nenhancement, along with inclusion of the dynamic polarizability, indicate a\nmethod of inducing long-range interatomic interactions in neutral atom\ncondensates at significantly lower intensities than previously realized.",
        "positive": "Parametric Excitation of a 1D Gas in Integrable and Nonintegrable Cases: We study the response of a highly excited 1D gas with pointlike interactions\nto a periodic modulation of the coupling constant. We calculate the\ncorresponding dynamic structure factors and show that their low-frequency\nbehavior differs dramatically for integrable and nonintegrable models.\nNonintegrable systems are sensitive to excitations with frequencies as low as\nthe mean level spacing, whereas much higher frequencies are required to excite\nan integrable system. This effect can be used as a probe of integrability for\nmesoscopic 1D systems and can be observed experimentally by measuring the\nheating rate of a parametrically excited gas."
    },
    {
        "anchor": "Quantum Many-Body Scars in Optical Lattices: The concept of quantum many-body scars has recently been put forward as a\nroute to describe weak ergodicity breaking and violation of the Eigenstate\nThermalization Hypothesis. We propose a simple setup to generate quantum\nmany-body scars in a doubly modulated Bose-Hubbard system which can be readily\nimplemented in cold atomic gases. The dynamics are shown to be governed by\nkinetic constraints which appear via density assisted tunneling in a\nhigh-frequency expansion. We find the optimal driving parameters for the\nkinetically constrained hopping which leads to small isolated subspaces of\nscared eigenstates. The experimental signatures and the transition to fully\nthermalizing behavior as a function of driving frequency are analyzed.",
        "positive": "Supervised learning of few dirty bosons with variable particle number: We investigate the supervised machine learning of few interacting bosons in\noptical speckle disorder via artificial neural networks. The learning curve\nshows an approximately universal power-law scaling for different particle\nnumbers and for different interaction strengths. We introduce a network\narchitecture that can be trained and tested on heterogeneous datasets including\ndifferent particle numbers. This network provides accurate predictions for all\nsystem sizes included in the training set and, by design, is suitable to\nattempt extrapolations to (computationally challenging) larger sizes. Notably,\na novel transfer-learning strategy is implemented, whereby the learning of the\nlarger systems is substantially accelerated and made consistently accurate by\nincluding in the training set many small-size instances."
    },
    {
        "anchor": "Perspective on new implementations of atomtronic circuits: In this article, we provide perspectives for atomtronics circuits on quantum\ntechnology platforms beyond simple bosonic or fermionic cold atom matter-wave\ncurrents. Specifically, we consider (i) matter-wave schemes with\nmulti-component quantum fluids; (ii) networks of Rydberg atoms that provide a\nradically new concept of atomtronics circuits in which the flow, rather than in\nterms of matter, occurs through excitations; (iii) hybrid matter-wave circuits\n- cavities systems that can be used to study atomtronic circuits beyond the\nstandard solutions and provide new schemes for integrated matter-wave networks.\nWe also sketch how driving these systems can open new pathways for atomtronics.",
        "positive": "Establishing the Gauge Invariant Linear Response of Fermionic\n  Superfluids with Pair Fluctuations: A Diagrammatic approach: We present a manifestly gauge invariant linear response theory for ultra-cold\nFermi gases undergoing BCS-Bose-Einstein Condensation (BEC) crossover with pair\nfluctuation effect included, especially in the superfluid phase, by introducing\nan effective external electromagnetic (EM) field. For pure BCS-type\nsuperfluids, the gauge invariance of the linear response theory can be\nmaintained by constructing a full external EM vertex by including the\nfluctuation of the order parameters in the same way as the the self-energy\neffect is included in the quasi-particle, therefore the Ward identity (WI) is\nsatisfied. While for the Fermionic superfluids with pairing fluctuation effect\nincluded in the quasi-particle self-energy, the construction of a gauge\ninvariant vertex is non-trivial, since in the broken symmetry phase the effect\nof Nambu-Goldstone modes (collective modes) intertwines with that of the\npairing fluctuation. In this paper, we find that under a suitable diagrammatic\nrepresentation, the construction of such vertex is greatly simplified, which\nallow us to build a WI-maintaining vertex with pseudogap effects included in\nthe superfluid phase. We focus on the $G_0G$ $t$-matrix approach to the pair\nfluctuations, although our formalism should also works equally well for the\n$G_0G_0$ $t$-matrix theory."
    },
    {
        "anchor": "Ultracold-atom collisions in atomic waveguides : A two-channel analysis: Low dimensional behavior of two ultra-cold atoms trapped in two-and\none-dimensional waveguides is investigated in the vicinity of a magnetic\nFeshbach resonance. A quantitative two-channel model for the Feshbach mechanism\nis used allowing an exhaustive analysis of low-dimensional resonant scattering\nbehavior and of the confinement induced bound states. The role of the different\nparameters of the resonance is depicted in this context. Results are compared\nwith the ones of the zero-range approach. The relevance of the effective range\napproximation in low dimensions is studied. Examples of known resonances are\nused to illustrate the bound state properties.",
        "positive": "Behavior of the anomalous correlation function in uniform 2D Bose gas: We investigate the behavior of the anomalous correlation function in two\ndimensional Bose gas. In the local case, we find that this quantity has a\nfinite value in the limit of weak interactions at zero temperature. The effects\nof the anomalous density on some thermodynamic quantities are also considered.\nThese effects can modify in particular the chemical potential, the ground sate\nenergy, the depletion and the superfluid fraction. Our predictions are in good\nagreement with recent analytical and numerical calculations. We show also that\nthe anomalous density presents a significant importance compared to the\nnon-condensed one at zero temperature. The single-particle anomalous\ncorrelation function is expressed in two dimensional homogenous Bose gases by\nusing the density-phase fluctuation. We then confirm that the anomalous average\naccompanies in analogous manner the true condensate at zero temperature while\nit does not exist at finite temperature."
    },
    {
        "anchor": "Chiral spin superfluidity and spontaneous spin Hall effect of\n  interacting bosons: Recent experiments on ultracold atoms in optical lattices have synthesized a\nvariety of tunable bands with degenerate double-well structures in momentum\nspace. Such degeneracies in the single particle spectrum strongly enhance\nquantum fluctuations, and may lead to exotic many-body ground states. Here we\nconsider weakly interacting spinor Bose gases in such bands, and discover a\nuniversal quantum \"order by disorder\" phenomenon which selects a novel chiral\nspin superfluid with remarkable properties such as spontaneous anomalous spin\nHall effect and momentum space antiferromagnetism. For bosons in the excited\nDirac band of a hexagonal lattice, such a state supports staggered spin loop\ncurrents in real space. We show that Bloch oscillations provide a powerful\ndynamical route to quantum state preparation of such a chiral spin superfluid.\nOur predictions can be readily tested in spin resolved time-of-flight\nexperiments.",
        "positive": "A generalized Lieb-Liniger model: In 1963, Lieb and Liniger solved exactly a one dimensional model of bosons\ninteracting by a repulsive \\delta-potential and calculated the ground state in\nthe thermodynamic limit. In the present work, we extend this model to a\npotential of three \\delta-functions, one of them is repulsive and the other two\nare attractive, modeling some aspects of the interaction between atoms, and\npresent an approximate solution for a dilute gas. In this limit, for low energy\nstates, the results are found to be reduced to the ones of an effective Lieb\nLiniger model with an effective \\delta-function of strength $c_{eff}$ and the\nregime of stability is identified. This may shed light on some aspects of\ninteracting bosons."
    },
    {
        "anchor": "Gaussian quantum fluctuations in the superfluid-Mott phase transition: Recent advances in cooling techniques make now possible the experimental\nstudy of quantum phase transitions, which are transitions near absolute zero\ntemperature accessed by varying a control parameter. A paradigmatic example is\nthe superfluid-Mott transition of interacting bosons on a periodic lattice.\nFrom the relativistic Ginzburg-Landau action of this superfluid-Mott transition\nwe derive the elementary excitations of the bosonic system, which contain in\nthe superfluid phase a gapped Higgs mode and a gappless Goldstone mode. We show\nthat this energy spectrum is in good agreement with the available experimental\ndata and we use it to extract, with the help of dimensional regularization,\nmeaningful analytical formulas for the beyond-mean-field equation of state in\ntwo and three spatial dimensions. We find that, while the mean-field equation\nof state always gives a second-order quantum phase transition, the inclusion of\nGaussian quantum fluctuations can induce a first-order quantum phase\ntransition. This prediction is a strong benchmark for next future experiments\non quantum phase transitions.",
        "positive": "Collective P-Wave Orbital Dynamics of Ultracold Fermions: We consider the non-equilibrium orbital dynamics of spin-polarized ultracold\nfermions in the first excited band of an optical lattice. A specific lattice\ndepth and filling configuration is designed to allow the $p_x$ and $p_y$\nexcited orbital degrees of freedom to act as a pseudo-spin. Starting from the\nfull Hamiltonian for p-wave interactions in a periodic potential, we derive an\nextended Hubbard-type model that describes the anisotropic lattice dynamics of\nthe excited orbitals at low energy. We then show how dispersion engineering can\nprovide a viable route to realizing collective behavior driven by p-wave\ninteractions. In particular, Bragg dressing and lattice depth can reduce\nsingle-particle dispersion rates, such that a collective many-body gap is\nopened with only moderate Feshbach enhancement of p-wave interactions. Physical\ninsight into the emergent gap-protected collective dynamics is gained by\nprojecting the Hamiltonian into the Dicke manifold, yielding a one-axis\ntwisting model for the orbital pseudo-spin that can be probed using\nconventional Ramsey-style interferometry. Experimentally realistic protocols to\nprepare and measure the many-body dynamics are discussed, including the effects\nof band relaxation, particle loss, spin-orbit coupling, and doping."
    },
    {
        "anchor": "Detecting the superfluid critical momentum of Bose gases in optical\n  lattices through dipole oscillations: We study stability of superflow of Bose gases in optical lattices by\nanalyzing the Bose-Hubbard model within the Gutzwiller mean-field\napproximation. We calculate the excitation spectra of the homogeneous\nBose-Hubbard model at unit filling to determine the critical momenta for the\nLandau and dynamical instabilities. These two critical momenta are shown to\napproach each other when the on-site interaction increases towards the Mott\ntransition point. In order to make a direct connection with realistic\nexperiments, we next take into account a parabolic trapping potential and\ncompute the real-time dynamics of dipole oscillations induced by suddenly\ndisplacing the trap center. We consider the following two cases: standard\nsoftcore bosons, whose interparticle interactions include the on-site one only,\nand hardcore bosons with long-range dipole-dipole interactions. For both cases,\nwe show that the dipole oscillation is significantly damped when the maximum\nlocal momentum exceeds a certain threshold, which quantitatively agrees with\nthe critical momentum for the dynamical instability in the homogeneous system.\nIn the case of dipolar hardcore bosons, the dynamical instability of dipole\noscillations leads to the formation of checkerboard density waves in the\nsuperfluid phase near the boundary to the supersolid phase.",
        "positive": "Artificial Gauge Fields and Spin-Orbit Couplings in Cold Atom Systems: This article is a report of Projet bibliographique of M1 at \\'Ecole Normale\nSup\\'erieure. In this article we reviewed the historical developments in\nartificial gauge fields and spin-orbit couplings in cold atom systems. We\nresorted to origins of literatures to trace the ideas of the developments. For\npedagogical purposes, we tried to work out examples carefully and clearly, to\nverified the validity of various approximations and arguments in detail, and to\ngive clear physical and mathematical pictures of the problems that we\ndiscussed. The first part of this article introduced the fundamental concepts\nof Berry phase and Jaynes-Cummings model. The second part reviewed two schemes\nto generate artificial gauge fields with N-pod scheme in cold atom systems. The\nfirst one is based on dressed-atom picture which provide a method to generate\nnon-Abelian gauge fields with dark states. The second one is about rotating\nscheme which is achieved earlier historically. Non-Abelian gauge field\ninevitably leads to spin-orbit coupling. We reviewed some developments in\nachieve spin-orbital coupling theoretically and experimentally. The fourth part\nwas devoted to recently developed idea of optical flux lattice that provides a\npossibility to reach the strongly correlated regime in cold atom systems. We\ndeveloped a geometrical interpretation based on Cooper's theory. Some useful\nformulae and their proofs were listed in the Appendix."
    },
    {
        "anchor": "Properties of fermionic systems with the Path-integral ground state\n  method: We investigate strongly correlated many-body systems composed of bosons and\nfermions with a fully quantum treatment using the path-integral ground state\nmethod, PIGS. To account for the Fermi-Dirac statistics, we implement the\nfixed-node approximation into PIGS, which we then call FN-PIGS. In great\ndetail, we discuss the pair density matrices we use to construct the full\ndensity operator in coordinate representation, a vital ingredient of the\nmethod. We consider the harmonic oscillator as a proof-of-concept and, as a\nplatform representing quantum many-body systems, we explore helium atoms. Pure\n$^4$He systems demonstrate most of the features of the method. Complementarily,\nfor pure $^3$He, the fixed-node approximation resolves the ubiquitous sign\nproblem stemming from anti-symmetric wave functions. Finally, we investigate\n$^3$He-$^4$He mixtures, demonstrating the method's robustness. One of the main\nfeatures of FN-PIGS is its ability to estimate any property at temperature\n$T=0$ without any additional bias apart from the FN approximation; biases from\nlong simulations are also excluded. In particular, we calculate the correlation\nfunction of pairs of equal and opposite spins and precise values of the $^3$He\nkinetic energy in the mixture.",
        "positive": "Nonequilibrium phases of ultracold bosons with cavity-induced dynamic\n  gauge fields: Gauge fields are a central concept in fundamental theories of physics, and\nresponsible for mediating long-range interactions between elementary particles.\nRecently, it has been proposed that dynamical gauge fields can be naturally\nengineered by photons in composite, neutral quantum gas--cavity systems using\nsuitable atom-photon interactions. Here we comprehensively investigate\nnonequilibrium dynamical phases appearing in a two-leg bosonic lattice model\nwith leg-dependent, dynamical complex tunnelings mediated by cavity-assisted\ntwo-photon Raman processes. The system constitutes a minimal dynamical\nflux-lattice model. We study fixed points of the equations of motion and their\nstability, the resultant dynamical phase diagram, and the corresponding phase\ntransitions and bifurcations. Notably, the phase diagram features a plethora of\nnonequilibrium dynamical phases including limit-cycle and chaotic phases. In\nthe end, we relate regular periodic dynamics (i.e., limit-cycle phases) of the\nsystem to time crystals."
    },
    {
        "anchor": "Low-Dimensional Stochastic Projected Gross-Pitaevskii Equation: We present reduced-dimensional stochastic projected Gross-Pitaevskii\nequations describing regimes of confinement and temperature where a 1D or 2D\nsuperfluid is immersed in a 3D thermal cloud. The projection formalism provides\nboth a formally rigorous and physically natural way to effect the dimensional\nreduction. The 3D form of the number-damping (growth) terms is unchanged by the\ndimensional reduction. Projection of the energy-damping (scattering) terms\nleads to modified stochastic equations of motion describing energy exchange\nwith the thermal reservoir. The regime of validity of the dimensional reduction\nis investigated via variational analysis. Paying particular attention to 1D, we\nvalidate our variational treatment by comparing numerical simulations of a\ntrapped oblate system in 3D with the 1D theory, and establish a consistent\nchoice of cutoff for the 1D theory. We briefly discuss the scenario involving\ntwo-components with different degeneracy, suggesting that a wider regime of\nvalidity exists for systems in contact with a buffer-gas reservoir.",
        "positive": "Dynamics of a quantum phase transition in the Bose-Hubbard model:\n  Kibble-Zurek mechanism and beyond: In this paper, we study the dynamics of the Bose-Hubbard model by using\ntime-dependent Gutzwiller methods. In particular, we vary the parameters in the\nHamiltonian as a function of time, and investigate the temporal behavior of the\nsystem from the Mott insulator to the superfluid (SF) crossing a second-order\nphase transition. We first solve a time-dependent Schr\\\"odinger equation for\nthe experimental setup recently done by Braun et.al. [Proc. Nat. Acad. Sci.\n112, 3641 (2015)] and show that the numerical and experimental results are in\nfairly good agreement. However, these results disagree with the Kibble-Zurek\nscaling. From our numerical study, we reveal a possible source of the\ndiscrepancy. Next, we calculate the critical exponents of the correlation\nlength and vortex density in addition to the SF order parameter for a\nKibble-Zurek protocol. We show that beside the \"freeze\" time $\\hat{t}$, there\nexists another important time, $t_{\\rm eq}$, at which an oscillating behavior\nof the SF amplitude starts. From calculations of the exponents of the\ncorrelation length and vortex density with respect to a quench time $\\tQ$, we\nobtain a physical picture of a coarsening process. Finally, we study how the\nsystem evolves after the quench. We give a global picture of dynamics of the\nBose-Hubbard model."
    },
    {
        "anchor": "Efficient numerical description of the dynamics of interacting\n  multispecies quantum gases: We present a highly efficient method for the numerical solution of coupled\nGross-Pitaevskii equations describing the evolution dynamics of a multispecies\nmixture of Bose-Einstein condensates in time-dependent potentials. This method,\nbased on a grid-scaling technique, compares favorably to a more standard but\nmuch more computationally expensive solution based on a frozen-resolution grid.\nIt allows an accurate description of the long-time behavior of interacting,\nmulti-species quantum mixtures including the challenging problem of long free\nexpansions relevant for microgravity and space experiments. We demonstrate a\nsuccessful comparison to experimental measurements of a binary Rb-K mixture\nrecently performed with the payload of a sounding rocket experiment.",
        "positive": "Variational Wave Function for Inhomogeneous Bose--Einstein Condensate\n  with 3/2-Body Correlations: We construct a variational wave function for inhomogeneous weakly interacting\nBose--Einstein condensates beyond the mean-field approximation by incorporating\n$3/2$-body correlations. From our numerical results calculated for a system\ntrapped by a one-dimensional harmonic oscillator, the $3/2$-body correlations\ngive a contribution comparable to the mean- field energy toward lowering the\nground-state energy."
    },
    {
        "anchor": "Compacton existence and spin-orbit density dependence in Bose-Einstein\n  condensates: We demonstrate the existence of compactons matter waves in binary mixtures of\nBose-Einstein condensates (BEC) trapped in deep optical lattices (OL) subjected\nto equal contributions of intra-species Rashba and Dresselhaus spin-orbit\ncoupling (SOC) under periodic time modulations of the intra-species scattering\nlength. We show that these modulations lead to the rescaling of the SOC\nparameters that involve the density imbalance of the two components. This gives\nrise to a density-dependent SOC parameters strongly influence the existence and\nstability of compacton matter waves. The stability of SOC-compactons is\ninvestigated both by linear stability analysis and by time integrations of the\ncoupled Gross-Pitaevskii equations. We find that SOC restricts the parameter\nranges for stable stationary SOC-compacton existence but, on the other side, it\ngives a more stringent signature of their occurrence. In particular,\nSOC-compactons should appear when the intra-species interactions and the number\nof atoms in the two components are perfectly balanced (or close to being\nbalanced for metastable cases). The possibility to use SOC-compactons as a tool\nfor indirect measurements of the number of atoms and/or the intra-species\ninteractions, is also suggested.",
        "positive": "Production of quantum degenerate strontium gases: Larger, better,\n  faster, colder: We report on an improved scheme to generate Bose-Einstein condensates (BECs)\nand degenerate Fermi gases of strontium. This scheme allows us to create\nquantum gases with higher atom number, a shorter time of the experimental\ncycle, or deeper quantum degeneracy than before. We create a BEC of 84-Sr\nexceeding 10^7 atoms, which is a 30-fold improvement over previously reported\nexperiments. We increase the atom number of 86-Sr BECs to 2.5x10^4 (a fivefold\nimprovement), and refine the generation of attractively interacting 88-Sr BECs.\nWe present a scheme to generate 84-Sr BECs with a cycle time of 2s, which, to\nthe best of our knowledge, is the shortest cycle time of BEC experiments ever\nreported. We create deeply-degenerate 87-Sr Fermi gases with T/T_F as low as\n0.10(1), where the number of populated nuclear spin states can be set to any\nvalue between one and ten. Furthermore, we report on a total of five different\ndouble-degenerate Bose-Bose and Bose-Fermi mixtures. These studies prepare an\nexcellent starting point for applications of strontium quantum gases\nanticipated in the near future."
    },
    {
        "anchor": "Long-Range Order and Quantum Criticality in a Dissipative Spin Chain: Environmental interaction is a fundamental consideration in any controlled\nquantum system. While interaction with a dissipative bath can lead to\ndecoherence, it can also provide desirable emergent effects including induced\nspin-spin correlations. In this paper we show that under quite general\nconditions, a dissipative bosonic bath can induce a long-range ordered phase,\nwithout the inclusion of any additional direct spin-spin couplings. Through a\nquantum-to-classical mapping and classical Monte Carlo simulation, we\ninvestigate the $T=0$ quantum phase transition of an Ising chain embedded in a\nbosonic bath with Ohmic dissipation. We show that the quantum critical point is\ncontinuous, Lorentz invariant with a dynamical critical exponent $z=1.07(9)$,\nhas correlation length exponent $\\nu=0.80(5)$, and anomalous exponent\n$\\eta=1.02(6)$, thus the universality class distinct from the previously\nstudied limiting cases. The implications of our results on experiments in\nultracold atomic mixtures and qubit chains in dissipative environments are\ndiscussed.",
        "positive": "Pairing in spin chains and spinless fermions with next-nearest neighbour\n  interactions: We investigate the phase diagrams of a one-dimensional lattice model of\nfermions and of a spin chain with interactions extending up to next-nearest\nneighbour range. In particular, we investigate the appearance of regions with\ndominant pairing physics in the presence of nearest-neighbour and\nnext-nearest-neighbour interactions. Our analysis is based on analytical\ncalculations in the classical limit, bosonization techniques and large-scale\ndensity-matrix renormalization group numerical simulations. The phase diagram,\nwhich is investigated in all relevant filling regimes, displays a remarkably\nrich collection of phases, including Luttinger liquids, phase separation,\ncharge-density waves, bond-order phases, and exotic cluster Luttinger liquids\nwith paired particles. In relation with recent studies, we show several\nemergent transition lines with a central charge $c = 3/2$ between the\nLuttinger-liquid and the cluster Luttinger liquid phases. These results could\nbe experimentally investigated using highly-tunable quantum simulators."
    },
    {
        "anchor": "Shortcuts to adiabaticity for trapped ultracold gases: We study, experimentally and theoretically, the controlled transfer of\nharmonically trapped ultracold gases between different quantum states. In\nparticular we experimentally demonstrate a fast decompression and displacement\nof both a non-interacting gas and an interacting Bose-Einstein condensate which\nare initially at equilibrium. The decompression parameters are engineered such\nthat the final state is identical to that obtained after a perfectly adiabatic\ntransformation despite the fact that the fast decompression is performed in the\nstrongly non-adiabatic regime. During the transfer the atomic sample goes\nthrough strongly out-of-equilibrium states while the external confinement is\nmodified until the system reaches the desired stationary state. The scheme is\ntheoretically based on the invariants of motion and scaling equations\ntechniques and can be generalized to decompression trajectories including an\narbitrary deformation of the trap. It is also directly applicable to arbitrary\ninitial non-equilibrium states.",
        "positive": "Nuclear-spin-independent short-range three-body physics in ultracold\n  atoms: We investigate three-body recombination loss across a Feshbach resonance in a\ngas of ultracold 7Li atoms prepared in the absolute ground state and perform a\ncomparison with previously reported results of a different nuclear-spin state\n[N. Gross et.al., Phys. Rev. Lett. 103 163202, (2009)]. We extend the\npreviously reported universality in three-body recombination loss across a\nFeshbach resonance to the absolute ground state. We show that the positions and\nwidths of recombination minima and Efimov resonances are identical for both\nstates which indicates that the short-range physics is nuclear-spin\nindependent."
    },
    {
        "anchor": "Sudden Expansion of a One-Dimensional Bose Gas from Power-Law Traps: We analyze free expansion of a trapped one-dimensional Bose gas after a\nsudden release from the confining trap potential. By using the stationary phase\nand local density approximations, we show that the long-time asymptotic density\nprofile and the momentum distribution of the gas are determined by the initial\ndistribution of Bethe rapidities (quasimomenta) and hence can be obtained from\nthe solutions to the Lieb-Liniger equations in the thermodynamic limit. For\nexpansion from a harmonic trap, and in the limits of very weak and very strong\ninteractions, we recover the self-similar scaling solutions known from the\nhydrodynamic approach. For all other power-law traps and arbitrary interaction\nstrengths, the expansion is not self-similar and shows strong dependence of the\ndensity profile evolution on the trap anharmonicity. We also characterize\ndynamical fermionization of the expanding cloud in terms of correlation\nfunctions describing phase and density fluctuations.",
        "positive": "Polaronic properties of an impurity in a Bose-Einstein condensate in\n  reduced dimensions: The application of optical lattices allows a tuning of the geometry of\nBose-Einstein condensates to effectively reduced dimensions. In the context of\nsolid state physics the consideration of the low-dimensional Fr\\\"ohlich polaron\nresults in an extension of the polaronic strong coupling regime. With this\nmotivation we apply the Jensen-Feynman variational principle to calculate the\nground state properties of the polaron consisting of an impurity in a\nBose-Einstein condensate in reduced dimensions. Also the response of this\nsystem to Bragg scattering is calculated. We show that reducing the dimension\nleads to a larger amplitude of the polaronic features and is expected to\nfacilitate the experimental observation of polaronic properties. In optical\nlattices not only Feshbach resonances but also confinement-induced resonances\ncan be used to tune the polaronic coupling strength. This opens up the\npossibility to experimentally reveal the intermediate and strong polaronic\ncoupling regimes and resolve outstanding theoretical questions regarding\npolaron theory."
    },
    {
        "anchor": "Dynamical properties of a trapped dipolar Fermi gas at finite\n  temperature: We investigate the dynamical properties of a trapped finite-temperature\nnormal Fermi gas with dipole-dipole interaction. For the free expansion\ndynamics, we show that the expanded gas always becomes stretched along the\ndirection of the dipole moment. In addition, we present the temperature and\ninteraction dependences of the asymptotical aspect ratio. We further study the\ncollapse dynamics of the system by suddenly increasing the dipolar interaction\nstrength. We show that, in contrast to the anisotropic collapse of a dipolar\nBose-Einstein condensate, a dipolar Fermi gas always collapses isotropically\nwhen the system becomes globally unstable. We also explore the interaction and\ntemperature dependences for the frequencies of the low-lying collective\nexcitations.",
        "positive": "Instability and Vortex Rings Dynamics in a Three-Dimensional Superfluid\n  Flow Through a Constriction: We study the instability of a superfluid flow through a constriction in three\nspatial dimensions. We consider a Bose-Einstein condensate at zero temperature\nin two different geometries: a straight waveguide and a torus. The constriction\nconsists of a broad, repulsive penetrable barrier. In the hydrodynamic regime,\nwe find that the flow becomes unstable as soon as the velocity at the classical\n(Thomas-Fermi) surface equals the sound speed inside the constriction. At this\ncritical point, vortex rings enter inside the bulk region of the cloud. The\nnucleation and dynamics scenario is strongly affected by the presence of\nasymmetries in the velocity and density of the background condensate flow."
    },
    {
        "anchor": "Quantum states of p-band bosons in optical lattices: We study a gas of repulsively interacting bosons in the first excited band of\nan optical lattice. We explore this p-band physics both within the framework of\na standard mean-field theory as well as with the more accurate generalized\nGutzwiller ansatz. We find the phase diagrams for two- and three-dimensional\nsystems and characterize the first Mott-states in detail. Furthermore, we find\nthat even though the p-band model has strongly anisotropic kinetic energies and\ninter-flavor interaction terms are missing in the lowest band theory, the\nmean-field theory becomes useful quite rapidly once the transition from the\nMott-insulator to the superfluid is crossed.",
        "positive": "Universal range corrections to the Efimov trimer for a class of paths to\n  the unitary limit: Using potential models we analyze range corrections to the universal law\ndictated by the Efimov theory of three bosons. In the case of finite-range\ninteractions we have observed that, at first order, it is necessary to\nsupplement the theory with one finite-range parameter, $\\Gamma_n^3$, for each\nspecific $n$-level [Kievsky and Gattobigio, Phys. Rev. A {\\bf 87}, 052719\n(2013)]. The value of $\\Gamma_n^3$ depends on the way the potentials is changed\nto tune the scattering length toward the unitary limit. In this work we analyze\na particular path in which the length $r_B=a-a_B$, measuring the difference\nbetween the two-body scattering length $a$ and the energy scattering length\n$a_B$, results almost constant. Analyzing systems with very different scales,\nas atomic or nuclear systems, we observe that the finite-range parameter\nremains almost constant along the path with a numerical value of\n$\\Gamma_0^3\\approx 0.87$ for the ground state level. This observation suggests\nthe possibility of constructing a single universal function that incorporate\nfinite-range effects for this class of paths. The result is used to estimate\nthe three-body parameter $\\kappa_*$ in the case of real atomic systems brought\nto the unitary limit thought a broad Feshbach resonances. Furthermore, we show\nthat the finite-range parameter can be put in relation with the two-body\ncontact $C_2$ at the unitary limit."
    },
    {
        "anchor": "Dynamics of rotated spin states and magnetic ordering with two-component\n  bosonic atoms in optical lattices: The microscopic control available over cold atoms in optical lattices has\nopened new opportunities to study the properties of quantum spin models. While\na lot of attention is focussed on experimentally realizing ground or thermal\nstates via adiabatic loading, it would often be more straightforward to prepare\nspecific simple product states and to probe the properties of interacting spins\nby observing their dynamics. We explore this possibility for spin-1/2 and\nspin-1 models that can be realized with bosons in optical lattices, and which\nexhibit \\textit{XY}-ferromagnetic (or counterflow spin superfluid) phases. We\nconsider the dynamics of initial spin-rotated states corresponding to a\nmean-field version of the phases of interest. Using matrix product state\nmethods in one dimension, we compute both non-equilibrium dynamics and\nground/thermal states for these systems. We compare and contrast their\nbehaviour in terms of correlation functions and induced spin currents, which\nshould be directly observable with current experimental techniques. We find\nthat although spin correlations decay substantially at large distances and on\nlong timescales, for induction of spin currents, the rotated states behave\nsimilarly to the ground states on experimentally observable timescales.",
        "positive": "Bogoliubov depletion of the fragmented condensate in the bosonic flux\n  ladder: We theoretically analyze the ground state of weakly interacting bosons in the\nflux ladder -- the system that has been recently realized by means of ultacold\natoms in the specially designed optical lattice [M. Atala, et al., Nat. Phys.\n10, 588 (2014)]. It is argued that, for the system parameters corresponding to\nthe so-called `vortex phase', the ground state is a fragmented condensate. We\nstudy the Bogoliubov depletion of this condensate and discuss the role of\nboundary conditions."
    },
    {
        "anchor": "Bistability and nonequilibrium condensation in a driven-dissipative\n  Josephson array: a c-field model: Developing theoretical models for nonequilibrium quantum systems poses\nsignificant challenges. Here we develop and study a multimode model of a\ndriven-dissipative Josephson junction chain of atomic Bose-Einstein\ncondensates, as realised in the experiment of Labouvie et al. [Phys. Rev. Lett.\n116, 235302 (2016)]. The model is based on c-field theory, a beyond-mean-field\napproach to Bose-Einstein condensates that incorporates fluctuations due to\nfinite temperature and dissipation. We find the c-field model is capable of\ncapturing all key features of the nonequilibrium phase diagram, including\nbistability and a critical slowing down in the lower branch of the bistable\nregion. Our model is closely related to the so-called Lugiato-Lefever equation,\nand thus establishes new connections between nonequilibrium dynamics of\nultracold atoms with nonlinear optics, exciton-polariton superfluids, and\ndriven damped sine-Gordon systems.",
        "positive": "Phase-slippage and self-trapping in a self-induced bosonic Josephson\n  junction: A dipolar condensate confined in a toroidal trap constitutes a self-induced\nJosepshon junction when the dipoles are oriented perpendicularly to the trap\nsymmetry axis and the s-wave scattering length is small enough. The ring-shaped\ndouble-well potential coming from the anisotropic character of the mean-field\ndipolar interaction is robust enough to sustain self-trapping dynamics, which\ntakes place when the initial population imbalance between the two wells is\nlarge. We show that in this system the self-trapping regime is directly related\nto a vortex-induced phase-slip dynamics. A vortex and antivortex are\nspontaneously nucleated in the low density regions, before a minimum of the\npopulation imbalance is reached, and then cross the toroidal section in\nopposite directions through the junctions.This vortex dynamics yields a phase\nslip between the two weakly linked condensates causing an inversion of the\nparticle flux."
    },
    {
        "anchor": "Coupled Dipole Oscillations of a Mass-Imbalanced Bose and Fermi\n  Superfluid Mixture: Recent experimental realizations of superfluid mixtures of Bose and Fermi\nquantum gases provide a unique platform for exploring diverse superfluid\nphenomena. We study dipole oscillations of a double superfluid in a\ncigar-shaped optical dipole trap, consisting of $^{41}$K and $^{6}$Li atoms\nwith a large mass imbalance, where the oscillations of the bosonic and\nfermionic components are coupled via the Bose-Fermi interaction. In our\nhigh-precision measurements, the frequencies of both components are observed to\nbe shifted from the single-species ones, and exhibit unusual features. The\nfrequency shifts of the $^{41}$K component are upward (downward) in the radial\n(axial) direction, whereas the $^{6}$Li component has down-shifted frequencies\nin both directions. Most strikingly, as the interaction strength is varied, the\nfrequency shifts display a resonant-like behavior in both directions, for both\nspecies, and around a similar location at the BCS side of fermionic superfluid.\nThese rich phenomena challenge theoretical understanding of superfluids.",
        "positive": "Degenerate Quantum Gases with Spin-Orbit Coupling: This review focuses on recent developments on studying synthetic spin-orbit\n(SO) coupling in ultracold atomic gases. Two types of SO coupling are\ndiscussed. One is Raman process induced coupling between spin and motion along\none of the spatial directions, and the other is Rashba SO coupling. We\nemphasize their common features in both single-particle and two-body physics\nand their consequences in many-body physics. For instance, single particle\nground state degeneracy leads to novel features of superfluidity and richer\nphase diagram; increased low-energy density-of-state enhances interaction\neffects; the absence of Galilean invariance and spin-momentum locking give rise\nto intriguing behaviors of superfluid critical velocity and novel quantum\ndynamics; and mixing of two-body singlet and triplet states yields novel\nfermion pairing structure and topological superfluids. With these examples, we\nshow that investigating SO coupling in cold atom systems can enrich our\nunderstanding of basic phenomena such as superfluidity, provide a good platform\nfor simulating condensed matter states such as topological superfluids, and\nmore importantly, result in novel quantum systems such as SO coupled unitary\nFermi gas or high spin quantum gases. Finally we also point out major\nchallenges and possible future directions."
    },
    {
        "anchor": "Loss induced collective mode in one-dimensional Bose gases: We show that two-body losses induce a collective excitation in a harmonically\ntrapped one-dimensional Bose gas, even in the absence of a quench in the trap\nor any other external perturbation. Focusing on the dissipatively fermionized\nregime, we perform an exact mode expansion of the rapidity distribution\nfunction and characterize the emergence of the collective motion. We find clear\ncoherent oscillations in both the potential and kinetic energies as well as in\nthe phase space quadrupole mode of the gas. We also discuss how this loss\ninduced collective mode differs from the well known breathing mode studied in\nthe absence of dissipation.",
        "positive": "Turbulent dynamics in two-dimensional paraxial fluid of light: Turbulence in quantum fluids has, surprisingly, a lot in common with its\nclassical counterpart. Recently, cold atomic gases has emerged as a well\ncontrolled experimental platform to study turbulent dynamics. In this work, we\nintroduce a novel system to study quantum turbulence in optics, with the major\nadvantage of having access to a wide range of characterization tools available\nfor light fields. In particular we report the temporal dynamics of density and\nphase and we show the emergence of isotropy in momentum space and the presence\nof different scaling laws in the incompressible kinetic energy spectrum. The\nmicroscopic origin of the algebraic exponents in the energy spectrum is\ndiscussed by studying the internal structure of quantized vortices within the\nhealing length and their clustering at larger length scales. These results are\nobtained using two counter-streaming fluids of light, which allows for a\nprecise preparation of the initial state and the in-situ measurement of the\ncompressible and incompressible fluid velocity."
    },
    {
        "anchor": "Temporal bistability in the dissipative Dicke-Bose-Hubbard system: We consider a driven-dissipative system consisting of an atomic Bose-Einstein\ncondensates loaded into a two-dimensional Hubbard lattice and coupled to a\nsingle mode of an optical cavity. Due to the interplay between strong,\nrepulsive atomic interaction and the atom-cavity coupling, the system exhibits\nseveral phases of atoms and photons including the atomic superfluid (SF) and\nsupersolid (SS). We investigate the dynamical behaviour of the system, where we\ninclude dissipation by means of Lindblad master equation formalism. Due to the\ndiscontinuous nature of the Dicke transition for strong atomic repulsion, we\nfind extended co-existence region of different phases. We investigate the\nresulting switching dynamics, particularly between the coexisting SF and SS\nphases, which eventually becomes damped by the dissipation.",
        "positive": "Topological Density Correlations in a Fermi Gas: A Fermi gas of non-interacting electrons, or ultra-cold fermionic atoms, has\na quantum ground state defined by a region of occupancy in momentum space known\nas the Fermi sea. The Euler characteristic $\\chi_F$ of the Fermi sea serves to\ntopologically classify these gapless fermionic states. The topology of a $D$\ndimensional Fermi sea is physically encoded in the $D+1$ point equal time\ndensity correlation function. In this work, we first present a simple proof of\nthis fact by showing that the evaluation of the correlation function can be\nformulated in terms of a triangulation of the Fermi sea with a collection of\npoints, links and triangles and their higher dimensional analogs. We then make\nuse of the topological $D+1$ point density correlation to reveal universal\nstructures of the more general $M$ point density correlation functions in a $D$\ndimensional Fermi gas. Two experimental methods are proposed for observing\nthese correlations in $D=2$. In cold atomic gases imaged by quantum gas\nmicroscopy, our analysis supports the feasibility of measuring the third order\ndensity correlation, from which $\\chi_F$ can be reliably extracted in systems\nwith as few as around 100 atoms. For solid-state electron gases, we propose\nmeasuring correlations in the speckle pattern of intensity fluctuations in\nnonlinear X-ray scattering experiments."
    },
    {
        "anchor": "Photo-excitation measurement of Tan's contact for a strongly interacting\n  Fermi gas: We derive theoretically an exact relation between Tan's universal contact and\nthe photo-excitation rate of a strongly interacting Fermi gas, in the case of\noptically transferring fermionic pairs to a more tightly bound molecular state.\nOur deviation generalizes the relation between Tan's contact and the\nclosed-channel molecular fraction found earlier by Werner, Tarruell and Castin\nin Eur. Phys. J. B \\textbf{68}, 401 (2009). We use the relation to understand\nthe recent low-temperature photo-excitation measurement in a strongly\ninteracting $^{6}$Li Fermi gas {[}Liu \\textit{et al.}, arXiv:1903.12321{]} and\nshow that there is a reasonable agreement between theory and experiment close\nto the unitary limit. We propose that our relation can be applied to accurately\nmeasure Tan's contact coefficient at finite temperature in future experiments.",
        "positive": "Interferometric Measurement of Local Spin-Fluctuations in a Quantum Gas: The subtle interplay between quantum statistics and interactions is at the\norigin of many intriguing quantum phenomena connected to superfluidity and\nquantum magnetism. The controlled setting of ultracold quantum gases is well\nsuited to study such quantum correlated systems. Current efforts are directed\ntowards the identification of their magnetic properties, as well as the\ncreation and detection of exotic quantum phases. In this context, it has been\nproposed to map the spin-polarization of the atoms to the state of a\nsingle-mode light beam. Here we introduce a quantum-limited interferometer\nrealizing such an atom-light interface with high spatial resolution. We measure\nthe probability distribution of the local spin-polarization in a trapped Fermi\ngas showing a reduction of spin-fluctuations by up to 4.6(3) dB below\nshot-noise in weakly interacting Fermi gases and by 9.4(8) dB for strong\ninteractions. We deduce the magnetic susceptibility as a function of\ntemperature and discuss our measurements in terms of an entanglement witness."
    },
    {
        "anchor": "Proposal for an analog Schwarzschild black hole in condensates of light: By etching a hole in the mirrors or by placing a scatterer in the center of a\ncavity, we can create a sink for light. In a Bose-Einstein condensate of\nphotons this sink results in the creation of a so-called radial vortex, which\nis a two-dimensional analogue of a Schwarzschild black hole. We theoretically\ninvestigate the Hawking radiation and the associated greybody factor of this\nSchwarzschild black hole. In particular, we determine the density-density and\nvelocity-velocity correlation functions of the Hawking radiation, which can be\nmeasured by observing the spatial correlations in the fluctuations in the light\nemitted by the cavity.",
        "positive": "Three-Dimensional Spin-Orbit Coupling in a Trap: We investigate the properties of an atom under the influence of a synthetic\nthree-dimensional spin-orbit coupling (Weyl coupling) in the presence of a\nharmonic trap. The conservation of total angular momentum provides a\nnumerically efficient scheme for finding the spectrum and eigenfunctions of the\nsystem. We show that at large spin-orbit coupling the system undergoes\ndimensional reduction from three to one dimension at low energies, and the\nspectrum is approximately Landau level-like. At high energies, the spectrum is\napproximately given by the three-dimensional isotropic harmonic oscillator. We\nexplore the properties of the ground state in both position and momentum space.\nWe find the ground state has spin textures with oscillations set by the\nspin-orbit length scale."
    },
    {
        "anchor": "Truncated Wigner method for Bose gases: We discuss stochastic phase-space methods within the truncated Wigner\napproximation and show explicitly that they can be used to solve\nnon-equilibrium dynamics of bosonic atoms in one-dimensional traps. We consider\nsystems both with and without an optical lattice, and address different\napproximations in the stochastic synthesization of quantum statistical\ncorrelations of the initial atomic field. We also present a numerically\nefficient projection method for analyzing correlation functions of the\nsimulation results, and demonstrate physical examples of non-equilibrium\nquantum dynamics of solitons and atom number squeezing in optical lattices.",
        "positive": "Observation of Feshbach resonances in an ${}^{167}$Er-${}^6$Li\n  Fermi-Fermi mixture: We present our experimental investigation of the interspecies Feshbach\nspectrum in a mixture of ${}^{167}$Er($F = 19/2, m_F = -19/2$)-${}^6$Li($F =\n1/2, m_F = 1/2$) atoms in the microkelvin temperature regime. These\ntemperatures are achieved by means of sympathetic cooling with ${}^{174}$Yb as\na third species. Interspecies Feshbach resonances are then identified by\ninvestigation of the Er-Li inelastic collisional properties for magnetic fields\nup to 800 G. Numerous narrow resonances as well as six resonances with widths\nabove 1 G could be identified. It is these broader resonances that hold much\npromise for interesting future investigations of, for exmample, novel\nsuperfluid states and Efimov states in large mass-imbalanced, all-fermionic\ntwo-component systems."
    },
    {
        "anchor": "Bose-Einstein condensation of 162Dy and 160Dy: We report Bose-Einstein condensation of two isotopes of the highly magnetic\nelement dysprosium: 162Dy and 160Dy. For 162Dy, condensates with 10^5 atoms\nform below T = 50 nK. We find the evaporation efficiency for the isotope 160Dy\nto be poor; however, by utilizing a low-field Fano-Feshbach resonance to\ncarefully change the scattering properties, it is possible to produce a\nBose-Einstein condensate of 160Dy with 10^3 atoms. The 162Dy BEC reported is an\norder of magnitude larger in atom number than that of the previously reported\n164Dy BEC, and it may be produced within 18 s.",
        "positive": "Complex correlations in high harmonic generation of matter-wave jets\n  revealed by pattern recognition: Correlations in interacting many-body systems are key to the study of quantum\nmaterials and quantum information. More often than not, the complexity of the\ncorrelations grows quickly as the system evolves and thus presents a challenge\nfor experimental characterization and intuitive understanding. In a strongly\ndriven Bose-Einstein condensate, we observe the high harmonic generation of\nmatter-wave jets with complex correlations as a result of bosonic stimulation.\nBased on a pattern recognition scheme, we identify a universal pattern of\ncorrelations which offers essential clues to unveiling the underlying secondary\nscattering processes and high-order correlations. We show that the pattern\nrecognition offers a versatile strategy to visualize and analyze the quantum\ndynamics of a many-body system."
    },
    {
        "anchor": "Density profiles and collective modes of a Bose-Einstein condensate with\n  light-induced spin-orbit coupling: The phases of a Bose-Einstein condensate (BEC) with light-induced spin-orbit\ncoupling (SOC) are studied within the mean-field approximation. The mixed BEC\nphase, in which the system condenses in a superposition of two plane wave\nstates, is found to be stable for sufficiently small light-atom coupling,\nbecoming unstable in a continuous fashion with increasing light-atom coupling.\nThe structure of the phase diagram at fixed chemical potential for bosons with\nSOC is shown to imply an unusual density dependence for a trapped mixed BEC\nphase, with the density of one dressed spin state increasing with increasing\nradius, providing a unique experimental signature of this state. The collective\nBogoliubov sound mode is shown to also provide a signature of the mixed BEC\nstate, vanishing as the boundary to the regime of phase separation is\napproached.",
        "positive": "Quantum Thermalization and the Expansion of Atomic Clouds: The ultimate consequence of quantum many-body physics is that even the air we\nbreathe is governed by strictly unitary time evolution. The reason that we\nperceive it nonetheless as a completely classical high temperature gas is due\nto the incapacity of our measurement machines to keep track of the dense\nmany-body entanglement of the gas molecules. The question thus arises whether\nthere are instances where the quantum time evolution of a macroscopic system is\nqualitatively different from the equivalent classical system? Here we study\nthis question through the expansion of noninteracting atomic clouds. While in\nmany cases the full quantum dynamics is indeed indistinguishable from classical\nballistic motion, we do find a notable exception. The subtle quantum\ncorrelations in a Bose gas approaching the condensation temperature appear to\naffect the expansion of the cloud, as if the system has turned into a diffusive\ncollision-full classical system."
    },
    {
        "anchor": "Experimental Observation of the 2D-1D Dimensional Crossover in Strongly\n  Interacting Ultracold Bosons: Dimensionality plays an essential role in determining the nature and\nproperties of a physical system. For quantum systems the impact of interactions\nand fluctuations is enhanced in lower dimensions, leading to a great diversity\nof genuine quantum effects for reduced dimensionality. In most cases, the\ndimension is fixed to some integer value. Here, we experimentally probe the\ndimensional crossover from two to one dimension using strongly interacting\nultracold bosons in variable lattice potentials and compare the data to\nab-initio theory that takes into account non-homogeneous trapping and non-zero\ntemperature. From a precise measurement of the momentum distribution we analyze\nthe characteristic decay of the one-body correlation function in the two\ndimensionalities and then track how the decay is modified in the crossover. A\nvarying two-slope structure is revealed, reflecting the fact that the particles\nsee their dimensionality as being one or two depending on whether they are\nprobed on short or long distances, respectively. Our observations demonstrate\nhow quantum properties in the strongly-correlated regime evolve in the\ndimensional crossover as a result of the interplay between dimensionality,\ninteractions, and temperature.",
        "positive": "Second Harmonic Generation from Ultracold Bosons in an Optical Cavity: Within a cavity quantum electrodynamics description, we characterize the\nfluorescent spectrum from ultracold bosons atoms, in the second harmonic\ngeneration (SHG) and resonant cases. Two situations are considered: i) bosons\nloaded into an optical lattice and ii) in a trapped two-component dilute\nBose-Einstein Condensate (BEC), in the regime where the Bogoliubov\napproximation is often employed. Atom and photon degrees of freedom are treated\non equal footing within an exact time-dependent configuration interaction\nscheme, and cavity leakage is included by including classical oscillator baths.\nFor optical lattices, we consider few bosons in short chains, described via the\nBose-Hubbard model with two levels per site, and we find that the spectral\nresponse grows on increasing the number of atoms at weak interactions, but\ndiminishes at high interactions (if the number of chain sites does not exceed\nthe number of atoms), and is shifted to lower frequency. In the BEC regime, the\nspectra display at noticeable extent a scaling behavior with the number of\nparticles and a suitable rescaling of the BEC-cavity and inter-particle\ninteractions, whilst the SHG spectrum redshifts at large atom-atom\ncorrelations. Overall, our results provide some general trends for the\nfluorescence from ultracold bosons in optical cavities, which can be of\nreference to experimental studies and further theoretical work."
    },
    {
        "anchor": "Higgs mode in a strongly interacting fermionic superfluid: Higgs and Goldstone modes are possible collective modes of an order parameter\nupon spontaneously breaking a continuous symmetry. Whereas the low-energy\nGoldstone (phase) mode is always stable, additional symmetries are required to\nprevent the Higgs (amplitude) mode from rapidly decaying into low-energy\nexcitations. In high-energy physics, where the Higgs boson has been found after\na decades-long search, the stability is ensured by Lorentz invariance. In the\nrealm of condensed--matter physics, particle--hole symmetry can play this role\nand a Higgs mode has been observed in weakly-interacting superconductors.\nHowever, whether the Higgs mode is also stable for strongly-correlated\nsuperconductors in which particle--hole symmetry is not precisely fulfilled or\nwhether this mode becomes overdamped has been subject of numerous discussions.\nExperimental evidence is still lacking, in particular owing to the difficulty\nto excite the Higgs mode directly. Here, we observe the Higgs mode in a\nstrongly-interacting superfluid Fermi gas. By inducing a periodic modulation of\nthe amplitude of the superconducting order parameter $\\Delta$, we observe an\nexcitation resonance at frequency $2\\Delta/h$. For strong coupling, the peak\nwidth broadens and eventually the mode disappears when the Cooper pairs turn\ninto tightly bound dimers signalling the eventual instability of the Higgs\nmode.",
        "positive": "Observation of the Hanbury Brown and Twiss Effect with Ultracold\n  Molecules: Measuring the statistical correlations of individual quantum objects provides\nan excellent way to study complex quantum systems. Ultracold molecules\nrepresent a powerful platform for quantum science due to their rich and\ncontrollable internal degrees of freedom. However, the detection of\ncorrelations between single molecules in an ultracold gas has yet to be\ndemonstrated. Here we observe the Hanbury Brown and Twiss effect in a gas of\nbosonic $^{23}$Na$^{87}$Rb, enabled by the realization of a quantum gas\nmicroscope for molecules. We detect the characteristic bunching correlations in\nthe density fluctuations of a 2D molecular gas released from and subsequently\nrecaptured in an optical lattice. The quantum gas microscope allows us to\nextract the positions of individual molecules with single-site resolution. As a\nresult, we obtain a high-contrast two-molecule interference pattern with a\nvisibility of $54(13)\\%$. While these measured correlations arise purely from\nthe quantum statistics of the molecules, the demonstrated capabilities pave the\nway toward site-resolved studies of interacting molecular gases in optical\nlattices."
    },
    {
        "anchor": "Effective-range dependence of two-dimensional Fermi gases: The Feshbach resonance provides precise control over the scattering length\nand effective range of interactions between ultracold atoms. We propose the\nultratransferable pseudopotential to model effective interaction ranges $-1.5\n\\leq k_\\mathrm{F}^2 R_\\mathrm{eff}^2 \\leq 0$, here $R_\\mathrm{eff}$ is the\neffective range and $k_\\mathrm{F}$ is the Fermi wave vector, describing narrow\nto broad Feshbach resonances. We develop a mean-field treatment and exploit the\npseudopotential to perform a variational and diffusion Monte Carlo study of the\nground state of the two-dimensional Fermi gas, reporting on the ground-state\nenergy, contact, condensate fraction, momentum distribution, and\npair-correlation functions as a function of the effective interaction range\nacross the BEC-BCS crossover. The limit $k_\\mathrm{F}^2 R_\\mathrm{eff}^2 \\to\n-\\infty$ is a gas of bosons with zero binding energy, whereas $\\ln(k_\\mathrm{F}\na) \\to -\\infty$ corresponds to noninteracting bosons with infinite binding\nenergy.",
        "positive": "Clean Floquet Time Crystals: Models and Realizations in Cold Atoms: Time crystals, a phase showing spontaneous breaking of time-translation\nsymmetry, has been an intriguing subject for systems far away from equilibrium.\nRecent experiments found such a phase both in the presence and absence of\nlocalization, while in theories localization by disorder is usually assumed a\npriori. In this work, we point out that time crystals can generally exist in\nsystems without disorder. A series of clean quasi-one-dimensional models under\nFloquet driving are proposed to demonstrate this unexpected result in\nprinciple. Robust time crystalline orders are found in the strongly interacting\nregime along with the emergent integrals of motion in the dynamical system,\nwhich can be characterized by level statistics and the out-of-time-ordered\ncorrelators. We propose two cold atom experimental schemes to realize the clean\nFloquet time crystals, one by making use of dipolar gases and another by\nsynthetic dimensions."
    },
    {
        "anchor": "Magnetic properties of commensurate Bose-Bose mixtures in\n  one-dimensional optical lattices: We investigate magnetic properties of strongly interacting bosonic mixtures\nconfined in one dimensional geometries, focusing on recently realized Rb-K\ngases with tunable interspecies interactions. By combining analytical\nperturbation theory results with density-matrix-renormalization group\ncalculations, we provide quantitative estimates of the ground state phase\ndiagram as a function of the relevant microscopic quantities, identifying the\nmore favorable experimental regimes in order to access the various magnetic\nphases. Finally, we qualitatively discuss the observability of such phases in\nrealistic setups when finite temperature effects have to be considered.",
        "positive": "Sub-wavelength spin excitations in ultracold gases created by stimulated\n  Raman transitions: Raman transitions are used in quantum simulations with ultracold atoms for\ncooling, spectroscopy and creation of artificial gauge fields. Spatial shaping\nof the Raman fields allows local control of the effective Rabi frequency, which\ncan be mapped to the atomic spin. Evanescent Raman fields are of special\ninterest as they can provide a new degree of control emanating from their\nrapidly decaying profile and for their ability to generate features below the\ndiffraction limit. This opens the door to the formation of sub-wavelength spin\ntextures. In this work, we present a theoretical and numerical study of Raman\nRabi frequency in the presence of evanescent driving fields. We show how spin\ntextures can be created by spatially varying driving fields and demonstrate a\nskyrmionium lattice - a periodic array of topological spin excitations, each of\nwhich is composed of two skyrmions with opposite topological charges. Our\nresults pave the way to quantum simulation of spin excitation dynamics in\nmagnetic materials, especially of itinerant spin models."
    },
    {
        "anchor": "Accelerated Bose-Einstein condensates in a double-well potential: Devices based on ultracold atoms moving in an accelerating optical lattice or\ndouble-well potential are a promising tool for precise measurements of\nfundamental physical constants as well as for the construction of sensors.\nHere, we carefully analyze the model of a couple of BECs separated by a barrier\nin an accelerated field and we show how the observable quantities, mainly the\nperiod of the beating motion or of the phase-shift, are related to the physical\nparameters of the model as well as to the energy of the initial state.",
        "positive": "Calculation of Drag and Superfluid Velocity from the Microscopic\n  Parameters and Excitation Energies of a Two-Component Bose-Einstein\n  Condensate on an Optical Lattice: We investigate a model of a two-component Bose-Einstein condensate residing\non an optical lattice. Within a Bogolioubov-approach at the mean-field level,\nwe derive exact analytical expressions for the excitation spectrum of the\ntwo-component condensate when taking into account hopping and interactions\nbetween arbitrary sites. Our results thus constitute a basis for works that\nseek to clarify the effects of higher-order interactions in the system. We\ninvestigate the excitation spectrum and the two branches of superfluid velocity\nin more detail for two limiting cases of particular relevance. Moreover, we\nrelate the hopping and interaction parameters in the effective Bose-Hubbard\nmodel to microscopic parameters in the system, such as the laserlight\nwavelength and atomic masses of the components in the condensate. These results\nare then used to calculate analytically and numerically the drag coefficient\nbetween the components of the condensate. We find that the drag is most\neffective close to the symmetric case of equal masses between the components,\nregardless of the strength of the intercomponent interaction and the lattice\nwell depth."
    },
    {
        "anchor": "Viscosity spectral functions of the dilute Fermi gas in kinetic theory: We compute the viscosity spectral function of the dilute Fermi gas for\ndifferent values of the s-wave scattering length $a$, including the unitarity\nlimit $a\\to\\infty$. We perform the calculation in kinetic theory by studying\nthe response to a non-trivial background metric. We find the expected structure\nconsisting of a diffusive peak in the transverse shear channel and a sound peak\nin the longitudinal channel. At zero momentum the width of the diffusive peak\nis $\\omega_0\\simeq (2\\epsilon)/(3\\eta)$ where $\\epsilon$ is the energy density\nand $\\eta$ is the shear viscosity. At finite momentum the spectral function\napproaches the collisionless limit and the width is of order $\\omega_0\\sim\nk(T/m)^{1/2}$.",
        "positive": "Detecting entanglement structure in continuous many-body quantum systems: A prerequisite for the comprehensive understanding of many-body quantum\nsystems is a characterization in terms of their entanglement structure. The\nexperimental detection of entanglement in spatially extended many-body systems\ndescribable by quantum fields still presents a major challenge. We develop a\ngeneral scheme for certifying entanglement and demonstrate it by revealing\nentanglement between distinct subsystems of a spinor Bose-Einstein condensate.\nOur scheme builds on the spatially resolved simultaneous detection of the\nquantum field in two conjugate observables which allows the experimental\nconfirmation of quantum correlations between local as well as non-local\npartitions of the system. The detection of squeezing in Bogoliubov modes in a\nmulti-mode setting illustrates its potential to boost the capabilities of\nquantum simulations to study entanglement in spatially extended many-body\nsystems."
    },
    {
        "anchor": "Multi-band spectroscopy of ultracold fermions: Observation of reduced\n  tunneling in attractive Bose-Fermi mixtures: We perform a detailed experimental study of the band excitations and\ntunneling properties of ultracold fermions in optical lattices. Employing a\nnovel multi-band spectroscopy for fermionic atoms we can measure the full band\nstructure and tunneling energy with high accuracy. In an attractive Bose-Fermi\nmixture we observe a significant reduction of the fermionic tunneling energy,\nwhich depends on the relative atom numbers. We attribute this to an\ninteraction-induced increase of the lattice depth due to self-trapping of the\natoms.",
        "positive": "The relevant excitations for the one-body function in the Lieb-Liniger\n  model: We study the ground state one-body correlation function in the Lieb-Liniger\nmodel. In the spectral representation, correlations are built from\ncontributions stemming from different excited states of the model. We aim to\nunderstand which excited states carry significant contributions, specifically\nfocusing on the small energy-momentum part of the dynamic one-body function. We\nconjecture that relevant excitations take form similar to two-spinon states\nknown from XXZ spin chain. We validate this hypothesis by numerical evaluation\nof the correlator with ABACUS algorithm and by analytical computations in the\nstrongly interacting regime."
    },
    {
        "anchor": "Twisted complex superfluids in optical lattices: We show that correlated pair tunneling drives a phase transition to a twisted\nsuperfluid with a complex order parameter. This unconventional superfluid phase\nspontaneously breaks the time-reversal symmetry and is characterized by a\ntwisting of the complex phase angle between adjacent lattice sites. We discuss\nthe entire phase diagram of the extended Bose--Hubbard model for a honeycomb\noptical lattice showing a multitude of quantum phases including twisted\nsuperfluids, pair superfluids, supersolids and twisted supersolids.\nFurthermore, we show that the nearest-neighbor interactions lead to a\nspontaneous breaking of the inversion symmetry of the lattice and give rise to\ndimerized density-wave insulators, where particles are delocalized on dimers.\nFor two components, we find twisted superfluid phases with strong correlations\nbetween the species already for surprisingly small pair-tunneling amplitudes.\nInterestingly, this ground state shows an infinite degeneracy ranging\ncontinuously from a supersolid to a twisted superfluid.",
        "positive": "Manipulating multimer propagation using lattice modulation: We propose a scheme for controlling the movement of dimers, trimers, and\nother multimers in optical lattices by modulating the lattice potential. In\ndeep optical lattices the propagation of deeply bound atomic clusters is slowed\ndown by the high energy cost of virtual intermediate states. Adapting the\nwell-known method of lattice modulation spectroscopy, the movement of the\nclusters can be made resonant by utilizing sequences of bound-bound\ntransitions. Using the scheme, the mobility of each specific cluster can be\nselectively controlled by tuning the modulation frequency. We formulate a\nsimple and intuitive model and confirm the validity of the model by numerical\nsimulations of dimers and trimers in a one-dimensional optical lattice."
    },
    {
        "anchor": "Modulation instability in the nonlinear Schr\u00f6dinger equation with a\n  synthetic magnetic field: gauge matters: We theoretically investigate the phenomenon of modulation instability for\nsystems obeying nonlinear Schr\\\"odinger equation, which are under the influence\nof an external homogeneous synthetic magnetic field. For an initial condition,\nthe instability is detected numerically by comparing dynamics with and without\na small initial perturbation; the perturbations are characterized in a standard\nfashion by wavevectors in momentum space. We demonstrate that the region of\n(in)stability in momentum space, as well as time-evolution in real space, for\nidentical initial conditions, depend on the choice of the gauge (i.e., vector\npotential) used to describe the homogeneous synthetic magnetic field. This\nsuperficially appears as if the gauge invariance is broken, but this is not\ntrue. When the system is evolved from an identical initial condition in two\ndifferent gauges, it is equivalent to suddenly turning on the synthetic\nmagnetic field at $t=0$. This gives rise, via Faraday's law, to an initial\ninstantaneous kick of a synthetic electric field to the wavepacket, which can\ndiffer for gauges yielding an identical uniform magnetic field at $t>0$.",
        "positive": "Fractional Quantum Hall States of Rydberg Polaritons: We propose a scheme for realizing fractional quantum Hall states of light. In\nour scheme, photons of two polarizations are coupled to different atomic\nRydberg states to form two flavors of Rydberg polaritons that behave as an\neffective spin. An array of optical cavity modes overlapping with the atomic\ncloud enables the realization of an effective spin-1/2 lattice. We show that\nthe dipolar interaction between such polaritons, inherited from the Rydberg\nstates, can be exploited to create a flat, topological band for a single\nspin-flip excitation. At half filling, this gives rise to a photonic (or\npolaritonic) fractional Chern insulator -- a lattice-based, fractional quantum\nHall state of light."
    },
    {
        "anchor": "Re-entrance and entanglement in the one-dimensional Bose-Hubbard model: Re-entrance is a novel feature where the phase boundaries of a system exhibit\na succession of transitions between two phases A and B, like A-B-A-B, when just\none parameter is varied monotonically. This type of re-entrance is displayed by\nthe 1D Bose Hubbard model between its Mott insulator (MI) and superfluid phase\nas the hopping amplitude is increased from zero. Here we analyse this\ncounter-intuitive phenomenon directly in the thermodynamic limit by utilizing\nthe infinite time-evolving block decimation algorithm to variationally minimize\nan infinite matrix product state (MPS) parameterized by a matrix size chi.\nExploiting the direct restriction on the half-chain entanglement imposed by\nfixing chi, we determined that re-entrance in the MI lobes only emerges in this\napproximate when chi >= 8. This entanglement threshold is found to be\ncoincident with the ability an infinite MPS to be simultaneously\nparticle-number symmetric and capture the kinetic energy carried by\nparticle-hole excitations above the MI. Focussing on the tip of the MI lobe we\nthen applied, for the first time, a general finite-entanglement scaling\nanalysis of the infinite order Kosterlitz-Thouless critical point located\nthere. By analysing chi's up to a very moderate chi = 70 we obtained an\nestimate of the KT transition as t_KT = 0.30 +/- 0.01, demonstrating the how a\nfinite-entanglement approach can provide not only qualitative insight but also\nquantitatively accurate predictions.",
        "positive": "Generalized Gibbs Ensembles for Quantum Field Theories: We consider the non-equilibrium dynamics in isolated systems, described by\nquantum field theories (QFTs). After being prepared in a density matrix that is\nnot an eigenstate of the Hamiltonian, such systems are expected to relax\nlocally to a stationary state. In a presence of local conservation laws, these\nstationary states are believed to be described by appropriate generalized Gibbs\nensembles. Here we demonstrate that in order to obtain a correct description of\nthe stationary state, it is necessary to take into account conservation laws\nthat are not (ultra-)local in the usual sense of QFT, but fulfil a\nsignificantly weaker form of locality. We discuss implications of our results\nfor integrable QFTs in one spatial dimension."
    },
    {
        "anchor": "Quantized conductance through a spin-selective atomic point contact: We implement a microscopic spin filter for cold fermionic atoms in a quantum\npoint contact (QPC) and create fully spin-polarized currents while retaining\nconductance quantization. Key to our scheme is a near-resonant optical tweezer\ninducing a large effective Zeeman shift inside the QPC while its local\ncharacter limits dissipation. We observe a renormalization of this shift due to\ninteractions of a few atoms in the QPC. Our work represents the analog of an\nactual spintronic device and paves the way to studying the interplay between\nspin-splitting and interactions far from equilibrium.",
        "positive": "Collision Integrals in the Kinetic Equations of dilute Bose-Einstein\n  Condensates: We derive the mean field kinetic equation for the momentum distribution of\nBogoliubov excitations (bogolons) in a spatially uniform Bose-Einstein\ncondensate (BEC), with a focus on the collision integrals. We use the method of\nPeletminksii and Yatsenko rather than the standard non-equilibrium Green's\nfunction formalism. This method produces three collision integrals ${\\cal\nG}^{12}$, ${\\cal G}^{22}$ and ${\\cal G}^{31}$. Only ${\\cal G}^{12}$ and ${\\cal\nG}^{22}$ have been considered by previous authors. The third collision integral\n${\\cal G}^{31}$ contains the effects of processes where one bogolon becomes\nthree and vice versa. These processes are allowed because the total number of\nbogolons is not conserved. Since ${\\cal G}^{31}$ is of the same order in the\ninteraction strength as ${\\cal G}^{22}$, we predict that it will significantly\ninfluence the dynamics of the bogolon gas, especially the relaxation of the\ntotal number of bogolons to its equilibrium value."
    },
    {
        "anchor": "Revealing single-trap condensate fragmentation by measuring\n  density-density correlations after time of flight: We consider ultracold bosonic atoms in a single trap in the Thomas-Fermi\nregime, forming many-body states corresponding to stable macroscopically\nfragmented two-mode condensates. It is demonstrated that upon free expansion of\nthe gas, the spatial dependence of the density-density correlations at late\ntimes provides a unique signature of fragmentation. This hallmark of fragmented\ncondensate many-body states in a single trap is due to the fact that time of\nflight modifies the correlation signal such that two opposite %with respect to\npoints in the expanding cloud become uncorrelated, in distinction to a\nnonfragmented Bose-Einstein condensate, where they remain correlated.",
        "positive": "Evolution of temporal coherence in confined polariton condensates: We study the influence of spatial confinement on the second-order temporal\ncoherence of the emission from a semiconductor microcavity in the strong\ncoupling regime. The confinement, provided by etched micropillars, has a\nfavorable impact on the temporal coherence of solid state quasi-condensates\nthat evolve in our device above threshold. By fitting the experimental data\nwith a microscopic quantum theory based on a quantum jump approach, we\nscrutinize the influence of pump power and confinement and find that\nphonon-mediated transitions are enhanced in the case of a confined structure,\nin which the modes split into a discrete set. By increasing the pump power\nbeyond the condensation threshold, temporal coherence significantly improves in\ndevices with increased spatial confinement, as revealed in the transition from\nthermal to coherent statistics of the emitted light."
    },
    {
        "anchor": "Gravity-induced accelerating expansion of excited-state Bose-Einstein\n  condensate: The Bose-Einstein condensate (BEC) of excited states, provides a different\nplatform to explore the interplay between gravity and quantum physics. In this\nLetter, we study the response of excited-state BECs to an external\ngravitational field and their dynamics under gravity when space is expanding.\nWe reveal the anomalous response of the center-of-mass of the BEC to the\ngravitational field and the exotic gravity-induced accelerating expansion\nphenomena. We demonstrate that these effects result from the interplay among\ngravity, space and quantum effects. We also propose related experiments to\nobserve these anomalies.",
        "positive": "Realizing Fulde-Ferrell Superfluids via a Dark-State Control of Feshbach\n  Resonances: We propose that the long-sought Fulde-Ferrell superfluidity with nonzero\nmomentum pairing can be realized in ultracold two-component Fermi gases of\n$^{40}$K or $^{6}$Li atoms by optically tuning their magnetic Feshbach\nresonances via the creation of a closed-channel dark state with a\nDoppler-shifted Stark effect. In this scheme, two counterpropagating optical\nfields are applied to couple two molecular states in the closed channel to an\nexcited molecular state, leading to a significant violation of Galilean\ninvariance in the dark-state regime and hence to the possibility of\nFulde-Ferrell superfluidity. We develop a field theoretical formulation for\nboth two-body and many-body problems and predict that the Fulde-Ferrell state\nhas remarkable properties, such as anisotropic single-particle dispersion\nrelation, suppressed superfluid density at zero temperature, anisotropic sound\nvelocity and rotonic collective mode. The latter two features can be\nexperimentally probed using Bragg spectroscopy, providing a smoking-gun proof\nof Fulde-Ferrell superfluidity."
    },
    {
        "anchor": "Coherent driving and freezing of bosonic matter wave in an optical Lieb\n  lattice: While kinetic energy of a massive particle generally has quadratic dependence\non its momentum, a flat, dispersionless energy band is realized in crystals\nwith specific lattice structures. Such macroscopic degeneracy causes the\nemergence of localized eigenstates and has been a key concept in the context of\nitinerant ferromagnetism. Here we report the realization of a \"Lieb lattice\"\nconfiguration with an optical lattice, which has a flat energy band as the\nfirst excited state. Our optical lattice potential possesses various degrees of\nfreedom about its manipulation, which enables coherent transfer of a\nBose-Einstein condensate into the flat band. In addition to measuring lifetime\nof the flat band population for different tight-binding parameters, we\ninvestigate the inter-sublattice dynamics of the system by projecting the\nsublattice population onto the band population. This measurement clearly shows\nthe formation of the localized state with the specific sublattice decoupled in\nthe flat band, and even detects the presence of flat-band breaking\nperturbations, resulting in the delocalization. Our results will open up the\npossibilities of exploring physics of flat band with a highly controllable\nquantum system.",
        "positive": "Atomic Quantum Simulation of U(N) and SU(N) Non-Abelian Lattice Gauge\n  Theories: Using ultracold alkaline-earth atoms in optical lattices, we construct a\nquantum simulator for U(N) and SU(N) lattice gauge theories with fermionic\nmatter based on quantum link models. These systems share qualitative features\nwith QCD, including chiral symmetry breaking and restoration at non-zero\ntemperature or baryon density. Unlike classical simulations, a quantum\nsimulator does not suffer from sign problems and can address the corresponding\nchiral dynamics in real time."
    },
    {
        "anchor": "Long-range Order in One-dimensional Spinless Fermi Gas with Attractive\n  Dipole-Dipole Interaction: One-dimensional spinless Fermi gas with attractive dipole-dipole interaction\nis investigated. Results obtained show when the interaction is weak, the\nexcitation spectrum is linear and the superconducting correlation function\ndecays as power law, indicating the validity of the Tomonaga-Luttinger (TL)\nliquid picture. However, when the interaction reaches a critical value, the\nexcitation spectrum is nonlinear and the superconducting correlation function\nkeeps finite for infinity separation, indicating real long-range order\nestablished and the breakdown of the TL liquid picture. We prove that the\nexistence of long-range order is not in contradiction with the Hohenberg\ntheorem and show that this system is related to the Kitaev toy model,\ntherefore, it has potential applications for the future topological quantum\ncomputation.",
        "positive": "Dynamics of defect-induced dark solitons in an exciton-polariton\n  condensate: We study theoretically the emission of dark solitons induced by a moving\ndefect in a nonresonantly pumped exciton-polariton condensate. The number of\ncreated dark solitons per unit of time is found to be strongly dependent on the\npump power. We relate the observed dynamics of this process to the oscillations\nof the drag force experienced by the condensate. We investigate the stability\nof the polariton quantum fluid and present various types of dynamics depending\non the condensate and moving obstacle parameters. Furthermore, we provide\nanalytical expressions for dark soliton dynamics using the variational method\nadapted to the non-equilibrium polariton system. The determined dynamical\nequations are found to be in excellent agreement with the results of numerical\nsimulations."
    },
    {
        "anchor": "Fluctuating hydrodynamics for a discrete Gross-Pitaevskii equation:\n  mapping to Kardar-Parisi-Zhang universality class: We show that several aspects of the low-temperature hydrodynamics of a\ndiscrete Gross-Pitaevskii equation (GPE) can be understood by mapping it to a\nnonlinear version of fluctuating hydrodynamics. This is achieved by first\nwriting the GPE in a hydrodynamic form of a continuity and an Euler equation.\nRespecting conservation laws, dissipation and noise due to the system's chaos\nare added, thus giving us a nonlinear stochastic field theory in general and\nthe Kardar-Parisi-Zhang (KPZ) equation in our particular case. This mapping to\nKPZ is benchmarked against exact Hamiltonian numerics on discrete GPE by\ninvestigating the non-zero temperature dynamical structure factor and its\nscaling form and exponent. Given the ubiquity of the Gross-Pitaevskii equation\n(a.k.a. nonlinear Schrodinger equation), ranging from nonlinear optics to cold\ngases, we expect this remarkable mapping to the KPZ equation to be of paramount\nimportance and far reaching consequences.",
        "positive": "On the role of interactions in trans-sonically flowing atomic\n  condensates: We provide a joint numerical-analytical study of the physics of a flowing\natomic Bose-Einstein condensate in the combined presence of an external trap\nand a step potential which accelerates the atoms out of the condensate creating\na pair of neighbouring black- and white- hole horizons. In particular, we focus\non the rapidly growing density modulation pattern that appears in the\nsupersonic region, an experimentally observed feature that was related to\nblack-hole lasing phenomena. A direct assessment of the role of interactions in\nthis process suggests an interpretation of the experimental data in terms of\nlinear interference of atomic waves rather than collective effects. Our\nconclusions are further supported by an analytical solution of the Schrodinger\nequation in terms of Airy wavefunctions."
    },
    {
        "anchor": "Superfluid vortex dynamics in an elliptical boundary: Recent advances in cold atom platforms, providing experimental accessibility\nto real-time dynamics, have renewed interest in the motion of superfluid\nvortices in two-dimensional domains. Motivated by this development, we study\nthe dynamics of a vortex in a two-dimensional incompressible superfluid inside\nan elliptical boundary. Employing the Joukowsky conformal map from a circle to\nan ellipse, we derive an analytical expression for the complex potential\ndescribing the hydrodynamic flow around the vortex. We integrate the resulting\nequations of motion, finding that the vortex moves along a nearly (but not\nexactly) elliptical trajectory. In addition, we obtain a simple closed\nexpression for the vortex self-energy, which serves as the Hamiltonian of the\nsystem.",
        "positive": "Superfluid rings as quantum pendulums: A feasible experimental proposal to realize a non-dispersive quantum pendulum\nis presented. The proposed setup consists of an ultracold atomic cloud,\nfeaturing attractive interatomic interactions, loaded into a tilted ring\npotential. The classical and quantum domains are switched on by tuned\ninteractions, and the classical dynamical stabilization of unstable states,\ni.e. {\\it a la} Kapitza, is shown to be driven by quantum phase imprinting. The\npotential use of this system as a gravimeter is discussed."
    },
    {
        "anchor": "Pairing, off-diagonal long-range order, and quantum phase transition in\n  strongly attracting ultracold Bose gas mixtures in tight waveguides: A model of two 1D ideal Bose gases A and B with strong AB attractions induced\nby a p-wave AB Feshbach resonance is studied. The model is solved exactly by a\nBose-Bose duality mapping, and it is shown that there is no A-component or\nB-component Bose-Einstein condensation and no AB-pair off-diagonal long-range\norder (ODLRO), but both AA-pair and BB-pair ODLRO. After generalization by\nadding even-wave AA and BB repulsion and reducing the strength of the odd-wave\nAB attraction by Feshbach resonance detuning, a quantum phase transition occurs\nbetween a phase with AB contact nodes and one with no such nodes.",
        "positive": "Tunable source of correlated atom beams: We use a one-dimensional optical lattice to modify the dispersion relation of\natomic matter waves. Four-wave mixing in this situation produces atom pairs in\ntwo well defined beams. We show that these beams present a narrow momentum\ncorrelation, that their momenta are precisely tunable, and that this pair\nsource can be operated both in the regime of low mode occupancy and of high\nmode occupancy."
    },
    {
        "anchor": "Strongly interacting one-dimensional bosons in arbitrary-strength\n  optical lattices: from Bose-Hubbard to sine-Gordon and beyond: We analyze interacting one-dimensional bosons in the continuum, subject to a\nperiodic sinusoidal potential of arbitrary depth. Variation of the lattice\ndepth tunes the system from the Bose-Hubbard limit for deep lattices, through\nthe sine-Gordon regime of weak lattices, to the complete absence of a lattice.\nUsing the Bose-Fermi mapping between strongly interacting bosons and weakly\ninteracting fermions, we derive the phase diagram in the parameter space of\nlattice depth and chemical potential. This extends previous knowledge from\ntight-binding (Bose-Hubbard) studies in a new direction which is important\nbecause the lattice depth is a readily adjustable experimental parameter.\nSeveral other results (equations of state, energy gaps, profiles in harmonic\ntrap) are presented as corollaries to the physics contained in this phase\ndiagram. Generically, both incompressible (gapped) and compressible phases\ncoexist in a trap; this has implications for experimental measurements.",
        "positive": "Dynamics and stability of Bose-Einstein solitons in tilted optical\n  lattices: Bloch oscillations of Bose-Einstein condensates realize sensitive matter-wave\ninterferometers. We investigate the dynamics and stability of bright-soliton\nwave packets in one-dimensional tilted optical lattices with a modulated\nmean-field interaction $g(t)$. By means of a time-reversal argument, we prove\nthe stability of Bloch oscillations of breathing solitons that would be\nquasistatically unstable. Floquet theory shows that these breathing solitons\ncan be more stable against certain experimental perturbations than rigid\nsolitons or even non-interacting wave packets."
    },
    {
        "anchor": "One-dimensional Fermi gas with a single impurity in a harmonic trap:\n  Perturbative description of the upper branch: The transition from \"few to many\" has recently been probed experimentally in\nan ultra cold harmonically confined one-dimensional lithium gas, in which a\nsingle impurity atom interacts with a background gas consisting of one, two, or\nmore identical fermions [A. N. Wenz {\\em{et al.}}, Science {\\bf{342}}, 457\n(2013)]. For repulsive interactions between the background or majority atoms\nand the impurity, the interaction energy for relatively moderate system sizes\nwas analyzed and found to converge toward the corresponding expression for an\ninfinitely large Fermi gas. Motivated by these experimental results, we apply\nperturbative techniques to determine the interaction energy for weak and strong\ncoupling strengths and derive approximate descriptions for the interaction\nenergy for repulsive interactions with varying strength between the impurity\nand the majority atoms and any number of majority atoms.",
        "positive": "Transition states and thermal collapse of dipolar Bose-Einstein\n  condensates: We investigate thermally excited, dipolar Bose-Einstein condensates.\nQuasi-particle excitations of the atomic cloud cause density fluctuations which\ncan induce the collapse of the condensate if the inter-particle interaction is\nattractive. Within a variational approach, we identify the collectively excited\nstationary states of the gas which form transition states on the way to the\nBEC's collapse. We analyze transition states with different $m$-fold rotational\nsymmetry and identify the one which mediates the collapse. The latter's\nsymmetry depends on the trap aspect ratio of the external trapping potential\nwhich determines the shape of the BEC. Moreover, we present the collapse\ndynamics of the BEC and calculate the corresponding decay rate using transition\nstate theory. We observe that the thermally induced collapse mechanism is\nimportant near the critical scattering length, where the lifetime of the\ncondensate can be significantly reduced. Our results are valid for an arbitrary\nstrength of the dipole-dipole interaction. Specific applications are discussed\nfor the elements $^{52}$Cr, $^{164}$Dy and $^{168}$Er with which dipolar BECs\nhave been experimentally realized."
    },
    {
        "anchor": "Measuring Z2 topological invariants in optical lattices using\n  interferometry: We propose an interferometric method to measure Z2 topological invariants of\ntime-reversal invariant topological insulators realized with optical lattices\nin two and three dimensions. We suggest two schemes which both rely on a\ncombination of Bloch oscillations with Ramsey interferometry and can be\nimplemented using standard tools of atomic physics. In contrast to topological\nZak phase and Chern number, defined for individual 1D and 2D Bloch bands, the\nformulation of the Z2 invariant involves at least two Bloch bands related by\ntime- reversal symmetry which one has keep track of in measurements. In one of\nour schemes this can be achieved by the measurement of Wilson loops, which are\nnon-Abelian generalizations of Zak phases. The winding of their eigenvalues is\nrelated to the Z2 invariant. We thereby demonstrate that Wilson loops are not\njust theoretical concepts but can be measured experimentally. For the second\nscheme we introduce a generalization of time-reversal polarization which is\ncontinuous throughout the Brillouin zone. We show that its winding over half\nthe Brillouin zone yields the Z2 invariant. To measure this winding, our\nprotocol only requires Bloch oscillations within a single band, supplemented by\ncoherent transitions to a second band which can be realized by lattice-shaking.",
        "positive": "Collision of rarefaction waves in Bose-Einstein condensates: We consider the problem of expansion of Bose-Einstein condensate released\nform a box. On the contrary to the standard situation of release from a\nharmonic trap, in this case the dynamics is complicated by a process of\ncollision of two rarefaction waves propagating to the center of the initially\nuniform distribution. Complete analytical solution of this problem is obtained\nby Riemann method in hydrodynamic dispersionless approximation and the results\nare compared with the exact numerical solution of the Gross-Pitaevskii\nequation."
    },
    {
        "anchor": "Study to improve the performance of interferometer with ultra-cold atoms: Ultra-cold atoms provide ideal platforms for interferometry. The macroscopic\nmatter-wave property of ultra-cold atoms leads to large coherent length and\nlong coherent time, which enable high accuracy and sensitivity to measurement.\nHere, we review our efforts to improve the performance of the interferometer.\nWe demonstrate a shortcut method for manipulating ultra-cold atoms in an\noptical lattice. Compared with traditional ones, this shortcut method can\nreduce manipulation time by up to three orders of magnitude. We construct a\nmatter-wave Ramsey interferometer for trapped motional quantum states and\nsignificantly increase its coherence time by one order of magnitude with an\necho technique based on this method. Efforts have also been made to enhance the\nresolution by multimode scheme. Application of a noise-resilient\nmulti-component interferometer shows that increasing the number of paths could\nsharpen the peaks in the time-domain interference fringes, which leads to a\nresolution nearly twice compared with that of a conventional double-path\ntwo-mode interferometer. With the shortcut method mentioned above, improvement\nof the momentum resolution could also be fulfilled, which leads to atomic\nmomentum patterns less than 0.6 $\\hbar k_L$. To identify and remove systematic\nnoises, we introduce the methods based on the principal component analysis\n(PCA) that reduce the noise in detection close to the $1/\\sqrt{2}$ of the\nphoton-shot noise and separate and identify or even eliminate noises.\nFurthermore, we give a proposal to measure precisely the local gravity\nacceleration within a few centimeters based on our study of ultracold atoms in\nprecision measurements.",
        "positive": "Linearized regime of the generalized hydrodynamics with diffusion: We consider the generalized hydrodynamics including the recently introduced\ndiffusion term for an initially inhomogeneous state in the Lieb-Liniger model.\nWe construct a general solution to the linearized hydrodynamics equation in\nterms of the eigenstates of the evolution operator and study two prototypical\nclasses of initial states: delocalized and localized spatially. We exhibit some\ngeneral features of the resulting dynamics, among them, we highlight the\ndifference between the ballistic and diffusive evolution. The first one governs\na spatial scrambling, the second, a scrambling of the quasi-particles content.\nWe also go one step beyond the linear regime and discuss the evolution of the\nzero momentum mode that does not evolve in the linear regime."
    },
    {
        "anchor": "Universal Dynamics at the Lowest Temperatures: High-performance graphical processing units (GPU) are used for the repeated\nparallelised propagation of non-linear partial differential equations on large\nspatio-temporal grids. The main challenge results as a combination of the\nrequirement of large grids for exploring scaling over several orders of\nmagnitude, both in space and time, and the need for high statistics in\naveraging over many runs, in computing correlation functions for highly\nfluctuating quantum many-body states. With our simulations, we explore the\ndynamics of complex quantum systems far from equilibrium, with the aim of\nclassifying their universal characteristics such as scaling exponents near\nnon-thermal fixed points. Our results are strongly relevant for the development\nof synthetic quantum systems when exploring the respective physics in the\nlaboratory.",
        "positive": "Time-reversal invariant topological superfluids in Bose-Fermi mixtures: A mixed dimensional system of fermions in two layers immersed in a\nBose-Einstein condensate (BEC) is shown to be a promising setup to realise\ntopological superfluids with time-reversal symmetry (TRS). The induced\ninteraction between the fermions mediated by the BEC gives rise to a\ncompetition between p-wave pairing within each layer and s-wave pairing between\nthe layers. When the layers are far apart, intra-layer pairing dominates and\nthe system forms a topological superfluid either with or without TRS. With\ndecreasing layer separation or increasing BEC coherence length, inter-layer\npairing sets in. We show that this leads either to a second order transition\nbreaking TRS where the edge modes gradually become gapped, or to a first order\ntransition to a topologically trivial s-wave superfluid. Our results provide a\nrealistic roadmap for experimentally realising a topological superfluid with\nTRS in a cold atomic system."
    },
    {
        "anchor": "Optimal lattice depth on lifetime of D-band ultracold atoms in a\n  triangular optical lattice: Ultracold atoms in optical lattices are a flexible and effective platform for\nquantum precision measurement, and the lifetime of high-band atoms is an\nessential parameter for the performance of quantum sensors. In this work, we\ninvestigate the relationship between the lattice depth and the lifetime of\nD-band atoms in a triangular optical lattice and show that there is an optimal\nlattice depth for the maximum lifetime. After loading the Bose Einstein\ncondensate into D-band of optical lattice by shortcut method, we observe the\natomic distribution in quasi-momentum space for the different evolution time,\nand measure the atomic lifetime at D-band with different lattice depths. The\nlifetime is maximized at an optimal lattice depth, where the overlaps between\nthe wave function of D-band and other bands (mainly S-band) are minimized.\nAdditionally, we discuss the influence of atomic temperature on lifetime. These\nexperimental results are in agreement with our numerical simulations. This work\npaves the way to improve coherence properties of optical lattices, and\ncontributes to the implications for the development of quantum precision\nmeasurement, quantum communication, and quantum computing.",
        "positive": "Topological phases of two-component bosons in species-dependent\n  artificial gauge potentials: We study bosonic atoms with two internal states in artificial gauge\npotentials whose strengths are different for the two components. A series of\ntopological phases for such systems is proposed using the composite fermion\ntheory and the parton construction. It is found in exact diagonalization that\nsome of the proposed states may be realized for simple contact interaction\nbetween bosons. The ground states and low-energy excitations of these states\nare modeled using trial wave functions. The effective field theories for these\nstates are also constructed and reveal some interesting properties."
    },
    {
        "anchor": "Symmetry properties of the ground state of the system of interacting\n  spinless bosons: We perform the symmetry analysis of the properties of the ground state of a\nfinite system of interacting spinless bosons for the three most symmetric\nboundary conditions (BCs): zero BCs with spherical and circular symmetries, as\nwell as periodic BCs. The symmetry of the system can lead to interesting\nproperties. For instance, the density of a periodic Bose system is an exact\nconstant: $\\rho(\\textbf{r})=const$. Moreover, under the perfect spherical\nsymmetry of BCs, the crystalline state cannot produce the Bragg peaks. The main\nresult of the article is that symmetry properties and general\nquantum-mechanical theorems admit equally both crystalline and liquid ground\nstate for a Bose system of any density.",
        "positive": "Squeezing the Efimov effect: The quantum mechanical three-body problem is a source of continuing interest\ndue to its complexity and not least due to the presence of fascinating solvable\ncases. The prime example is the Efimov effect where infinitely many bound\nstates of identical bosons can arise at the threshold where the two-body\nproblem has zero binding energy. An important aspect of the Efimov effect is\nthe effect of spatial dimensionality; it has been observed in three dimensional\nsystems, yet it is believed to be impossible in two dimensions. Using modern\nexperimental techniques, it is possible to engineer trap geometry and thus\naddress the intricate nature of quantum few-body physics as function of\ndimensionality. Here we present a framework for studying the three-body problem\nas one (continuously) changes the dimensionality of the system all the way from\nthree, through two, and down to a single dimension. This is done by considering\nthe Efimov favorable case of a mass-imbalanced system and with an external\nconfinement provided by a typical experimental case with a (deformed) harmonic\ntrap."
    },
    {
        "anchor": "Effects of staggered Dzyaloshinskii-Moriya interactions in a\n  quasi-two-dimensional Shastry-Sutherland model: Frustrated quantum spin systems exhibit exotic physics induced by external\nmagnetic field with anisotropic interactions. Here, we study the effect of\nnon-uniform Dzyaloshinskii-Moriya (DM) interactions on a quasi-two-dimensional\nShastry-Sutherland lattice using a matrix product states (MPS) algorithm. We\nfirst recover the magnetization plateau structure present in this geometry and\nthen we show that both interdimer and intradimer DM interactions significantly\nmodify the plateaux. The non-number-conserving intradimer interaction smoothens\nthe shape of the magnetization curve, while the number-conserving interdimer\ninteraction induces different small plateaux, which are signatures of the\nfinite size of the system. Interestingly, the interdimer DM interaction induces\nchirality in the system. We thus characterize these chiral phases with\nparticular emphasis to their robustness against intradimer DM interactions.",
        "positive": "Fluctuations and phase transitions in Larkin-Ovchinnikov liquid crystal\n  states of population-imbalanced resonant Fermi gas: Motivated by a realization of imbalanced Feshbach-resonant atomic Fermi\ngases, we formulate a low-energy theory of the Fulde-Ferrell and the\nLarkin-Ovchinnikov (LO) states and use it to analyze fluctuations, stability,\nand phase transitions in these enigmatic finite momentum-paired superfluids.\nFocusing on the unidirectional LO pair-density wave state, that spontaneously\nbreaks the continuous rotational and translational symmetries, we show that it\nis characterized by two Goldstone modes, corresponding to a superfluid phase\nand a smectic phonon. Because of the liquid-crystalline \"softness\" of the\nlatter, at finite temperature the 3d state is characterized by a vanishing LO\norder parameter, quasi-Bragg peaks in the structure and momentum distribution\nfunctions, and a \"charge\"-4, paired Cooper-pairs, off-diagonal-long-range\norder, with a superfluid-stiffness anisotropy that diverges near a transition\ninto a nonsuperfluid state. In addition to conventional integer vortices and\ndislocations the LO superfluid smectic exhibits composite half-integer\nvortex-dislocation defects. A proliferation of defects leads to a rich variety\nof descendant states, such as the \"charge\"-4 superfluid and Fermi-liquid\nnematics and topologically ordered nonsuperfluid states, that generically\nintervene between the LO state and the conventional superfluid and the\npolarized Fermi-liquid at low and high imbalance, respectively. The fermionic\nsector of the LO gapless superconductor is also quite unique, exhibiting a\nFermi surface of Bogoliubov quasiparticles associated with the Andreev band of\nstates, localized on the array of the LO domain-walls."
    },
    {
        "anchor": "Dipolar Bose Superstripes: We study the superfluid properties of a system of fully polarized dipolar\nbosons moving in the $xy$ plane. We focus on the general case where the\npolarization field forms an arbitrary angle $\\alpha$ with respect to the $z$\naxis, while the system is still stable. We use the diffusion Monte Carlo and\nthe path integral ground state methods to evaluate the one-body density matrix\nand the superfluid fractions in the region of the phase diagram where the\nsystem forms stripes. Despite its oscillatory behavior, the presence of a\nfinite large-distance asymptotic value in the $s$-wave component of the\none-body density matrix indicates the existence of a Bose condensate. The\nsuperfluid fraction along the stripes direction is always close to 1, while in\nthe $y$ direction decreases to a small value that is nevertheless different\nfrom zero. These two facts confirms that the stripe phase of the dipolar Bose\ngas in 2D is superfluid.",
        "positive": "Tamm's surface states and Bose-Einstein condensation: We calculate and discuss the effects on the thermodynamic properties of a 3D\nBose gas caused by a gap $\\Delta$ in the energy of the particles constituting\nthe gas that without the gap behaves like an ideal Bose gas. Explicit formulae\nwith arbitrary $\\Delta$ values are discussed for: the critical temperature\nwhich increases as the gap grows; the condensate fraction; the internal energy;\nand the constant-volume specific heat found to possess a jump-discontinuity for\nany $\\Delta$ different from zero. Three dimensional infinite ideal Bose gas\nresults are recovered when we the energy gap goes to zero."
    },
    {
        "anchor": "The importance of being integrable: out of the paper, into the lab: The scattering matrix (S-matrix), relating the initial and final states of a\nphysical system undergoing a scattering process, is a fundamental object in\nquantum mechanics and quantum field theory. The study of factorised S-matrices,\nin which many-body scattering factorizes into a product of two-body terms to\nyield an integrable model, has long been considered the domain of mathematical\nphysics. Many beautiful results have been obtained over several decades for\nintegrable models of this kind, with far reaching implications in both\nmathematics and theoretical physics. The viewpoint that these were only toy\nmodels changed dramatically with brilliant experimental advances in realizing\nlow-dimensional quantum many-body systems in the lab. These recent experiments\ninvolve both the traditional setting of condensed matter physics and the\ntrapping and cooling of atoms in optical lattices to engineer and study\nquasi-one-dimensional systems. In some cases the quantum physics of\none-dimensional systems is arguably more interesting than their\nthree-dimensional counterparts, because the effect of interactions is more\npronounced when atoms are confined to one dimension. This article provides a\nbrief overview of these ongoing developments, which highlight the fundamental\nimportance of integrability.",
        "positive": "Population-imbalance instability in a Bose-Hubbard ladder in the\n  presence of a magnetic flux: We consider a two-leg Bose-Hubbard ladder in the presence of a magnetic flux.\nWe make use of Gross-Pitaevskii, Bogoliubov, bosonization, and renormalization\ngroup approaches to reveal a structure of ground-state phase diagrams in a\nweak-coupling regime relevant to cold atom experiments. It is found that except\nfor a certain flux $\\phi=\\pi$, the system shows different properties as\nchanging hoppings, which also leads to a quantum phase transition similar to\nthe ferromagnetic XXZ model. This implies that population-imbalance instability\noccurs for certain parameter regimes. On the other hand, for $\\phi=\\pi$, it is\nshown that an umklapp process caused by commensurability of a magnetic flux\nstabilizes a superfluid with chirality and the system does not experience such\na phase transition."
    },
    {
        "anchor": "Solitary-wave solutions in binary mixtures of Bose-Einstein condensates\n  under periodic boundary conditions: We derive solitary-wave solutions within the mean-field approximation in\nquasi-one-dimensional binary mixtures of Bose-Einstein condensates under\nperiodic boundary conditions, for the case of an effective repulsive\ninteratomic interaction. The particular gray-bright solutions that give the\nglobal energy minima are determined. Their characteristics and the associated\ndispersion relation are derived. In the case of weak coupling, we diagonalize\nthe Hamiltonian analytically to obtain the full excitation spectrum of\n\"quantum\" solitary-wave solutions.",
        "positive": "Chiral currents in Bose-Einstein condensates subject to current-density\n  interactions: Persistent currents in quasi-one-dimensional Bose-Einstein condensates become\nchiral in the presence of current-density interactions. This phenomenon is\nexplored in ultracold atoms loaded in a rotating ring geometry, where diverse\ncurrent-carrying stationary states are analytically found to generalize\npreviously known solutions to the mean-field equations of motion. Their\ndynamical stability is tested by numerical simulations that show stable\ncurrents for states with both constant and modulated density profiles, while\ndecaying currents appear only beyond a unidirectional velocity threshold.\nRecent experiments in the field make these states within experimental reach."
    },
    {
        "anchor": "Quantum rotor theory of spinor condensates in tight traps: In this work, we theoretically construct exact mappings of many-particle\nbosonic systems onto quantum rotor models. In particular, we analyze the rotor\nrepresentation of spinor Bose-Einstein condensates. In a previous work it was\nshown that there is an exact mapping of a spin-one condensate of fixed particle\nnumber with quadratic Zeeman interaction onto a quantum rotor model. Since the\nrotor model has an unbounded spectrum from above, it has many more eigenstates\nthan the original bosonic model. Here we show that for each subset of states\nwith fixed spin F_z, the physical rotor eigenstates are always those with\nlowest energy. We classify three distinct physical limits of the rotor model:\nthe Rabi, Josephson, and Fock regimes. The last regime corresponds to a\nfragmented condensate and is thus not captured by the Bogoliubov theory. We\nnext consider the semiclassical limit of the rotor problem and make connections\nwith the quantum wave functions through use of the Husimi distribution\nfunction. Finally, we describe how to extend the analysis to higher-spin\nsystems and derive a rotor model for the spin-two condensate. Theoretical\ndetails of the rotor mapping are also provided here.",
        "positive": "Density engineering via inter-condensate dipole-dipole interactions:\n  axial confinement and supersolids: Exploiting the long-range and anisotropic nature of dipole-dipole\ninteractions, we show that the density of a {\\em target} dipolar Bose-Einstein\ncondensate can be engineered and axially confined using a trapped {\\em control}\ndipolar condensate. Increasing the number of control condensates leads to\nexotic ground state structures, including supersolids and an incoherent array\nof density peaks. Single and double-peaked periodic structures are observed as\na function of spacing between the control condensates. Our ideas may be\ngeneralized to engineer any other dipolar quantum system using another one of a\nsimilar dipole character. For instance, a Rydberg atom with electric dipole\nmoment may be confined and manipulated using a trapped polar molecule and vice\nversa via long-range dipole-dipole interactions."
    },
    {
        "anchor": "Acoustic Analogues of Extremal Rotating Black Holes in Exciton-Polariton\n  Condensates: We theoretically investigate the acoustic analogues of high-angular-momentum\nrotating black holes in exciton-polariton condensates. Performing numerical\nsimulations of a long-lived ring-shaped condensate configuration with an\nacoustic horizon and ergoregion for high angular momentum states, we observed a\nquasi-stable state near critical angular momentum where the acoustic black hole\nhorizon disappears. Our findings offer an insight into the quantum nature of\nthe instability of naked singularity.",
        "positive": "Density oscillations in trapped dipolar condensates: We investigated the ground state wave function and free expansion of a\ntrapped dipolar condensate. We find that dipolar interaction may induce both\nbiconcave and dumbbell density profiles in, respectively, the pancake- and\ncigar-shaped traps. On the parameter plane of the interaction strengths, the\ndensity oscillation occurs only when the interaction parameters fall into\ncertain isolated areas. The relation between the positions of these areas and\nthe trap geometry is explored. By studying the free expansion of the condensate\nwith density oscillation, we show that the density oscillation is detectable\nfrom the time-of-flight image."
    },
    {
        "anchor": "Observation of a Lee-Huang-Yang Fluid: We observe monopole oscillations in a mixture of Bose-Einstein condensates,\nwhere the usually dominant mean-field interactions are canceled. In this case,\nthe system is governed by the next-order Lee-Huang-Yang (LHY) correction to the\nground state energy, which describes the effect of quantum fluctuations.\nExperimentally such a LHY fluid is realized by controlling the atom numbers and\ninteraction strengths in a $^{39}$K spin mixture confined in a spherical trap\npotential. We measure the monopole oscillation frequency as a function of the\nLHY interaction strength as proposed recently by J{\\o}rgensen et al. [Phys.\nRev. Lett. 121, 173403 (2018)] and find excellent agreement with simulations of\nthe complete experiment including the excitation procedure and inelastic\nlosses. This confirms that the system and its collective behavior are initially\ndominated by LHY interactions. Moreover, the monopole oscillation frequency is\nfound to be stable against variations of the involved scattering lengths in a\nbroad region around the ideal values, confirming the stabilizing effect of the\nLHY interaction. These results pave the way for using the non-linearity\nprovided by the LHY term in quantum simulation experiments and for\ninvestigations beyond the LHY regime.",
        "positive": "Anderson localization of pairs in bichromatic optical lattices: We investigate the formation of bound states made of two interacting atoms\nmoving in a one dimensional (1D) quasi-periodic optical lattice. We derive the\nquantum phase diagram for Anderson localization of both attractively and\nrepulsively bound pairs. We calculate the pair binding energy and show\nanalytically that its behavior as a function of the interaction strength\ndepends crucially on the nature -extended, multi-fractal, localized- of the\nsingle-particle atomic states. Experimental implications of our results are\ndiscussed."
    },
    {
        "anchor": "Critical velocity of flowing supersolids of dipolar Bose gases in\n  optical lattices: We study superfluidity of supersolid phases of dipolar Bose gases in\ntwo-dimensional optical lattices. We perform linear stability analyses for the\ncorresponding dipolar Bose-Hubbard model in the hardcore boson limit to show\nthat a supersolid can have stable superflow until the flow velocity reaches a\ncertain critical value. The critical velocity for the supersolid is found to be\nsignificantly smaller than that for a conventional superfluid phase. We propose\nthat the critical velocity can be used as a signature to identify the\nsuperfluidity of the supersolid phase in experiment.",
        "positive": "Generating Steady Topologically Non-Trivial Artificial Spin Texture with\n  Cold Atoms: In this article we proposed a scheme to generating steady topologically\nnon-trivial artificial spin texture in cold atom systems. An example of\ngenerating a texture of charge one skyrmion with Laguerre-Gaussian beam was\ngiven. It provides a scheme for studying skyrmion excitations of quantum Hall\nferromagnetism in cold atom systems."
    },
    {
        "anchor": "Vortex Thermometry for Turbulent Two-Dimensional Fluids: We introduce a new method of statistical analysis to characterise the\ndynamics of turbulent fluids in two dimensions. We establish that, in\nequilibrium, the vortex distributions can be uniquely connected to the\ntemperature of the vortex gas, and apply this vortex thermometry to\ncharacterise simulations of decaying superfluid turbulence. We confirm the\nhypothesis of vortex evaporative heating leading to Onsager vortices proposed\nin Phys. Rev. Lett. 113, 165302 (2014), and find previously unidentified vortex\npower-law distributions that emerge from the dynamics.",
        "positive": "Perfect-fluid behavior of a dilute Fermi gas near unitary: We present an ab initio calculation of the shear viscosity as a function of\ninteraction strength in a two-component unpolarized Fermi gas near the unitary\nlimit, within a finite temperature quantum Monte Carlo (QMC) framework and\nusing the Kubo linear-response formalism. The shear viscosity decreases as we\ntune the interaction strength 1/ak_F from the Bardeen-Cooper-Schrieffer side of\nthe Feshbach resonance towards Bose-Einstein condensation limit and it acquires\nthe smallest value for 1/ak_F approx 0.4, with a minimum value of (eta/s)_min\napprox 0.2 hbar/k_B, which is about twice as small as the value reported for\nexperiments in quark-gluon plasma (eta/s)_QGP lesssim 0.4 hbar/k_B. The Fermi\ngas near unitarity thus emerges as the most \"perfect fluid\" observed so far in\nnature. The clouds of dilute Fermi gas near unitarity exhibit the unusual\nattribute that, for the sizes realized so far in the laboratory or larger (less\nthan 10^9 atoms), can sustain quantum turbulence below the critical\ntemperature, but at the same time the classical turbulence is suppressed in the\nnormal phase."
    },
    {
        "anchor": "Vortex Dynamics of Rotating Bose-Einstein Condensate of Microcavity\n  Polaritons: In this work we perform a numerical study of a rotating, harmonically\ntrapped, Bose-Einstein condensate of microcavity polaritons. An efficient\nnumerical method (toolbox) to solve the complex Gross-Pitaevskii equation is\ndeveloped. Using this method, we investigate how the behavior of the number of\nvortices formed inside the condensate changes as the various system parameters\nare varied. In contrast to the atomic condensates, we show, there exists an\n(experimentally realizable) range of parameter values in which all the vortices\ncan be made to vanish even when there is a high rotation. We further explore\nhow this region can be tuned through other free parameters and also discuss how\nthis study can help to realize the synthetic magnetic field for polaritons and\nhence paving the way for the realization of the quantum Hall physics and many\nother exotic phenomena.",
        "positive": "Bose polaron in spherically symmetric trap potentials: Ground states\n  with zero and lower angular momenta: Single-atomic impurities immersed in a dilute Bose gas in the spherically\nsymmetric harmonic trap potentials are studied at zero temperature. In order to\nfind the ground state of the polarons, we present a conditional variational\nmethod with fixed expectation values of the total angular momentum operators,\n$\\hat{J}^2$ and $\\hat{J}_z$, of the system, using a cranking\ngauge-transformation for bosons to move them in the frame co-rotating with the\nimpurity. In the formulation, the expectation value $\\langle \\hat{J^2}\\rangle$\nis shown to be shared in impurity and bosons, but the value $\\langle\n\\hat{J}_z\\rangle$ is carried by the impurity due to the rotational symmetry. We\nalso analyze the ground-state properties numerically obtained in this\nvariational method for the system of the attractive impurity-boson interaction,\nand find that excited boson distributions around the impurity overlap largely\nwith impurity's wave function in their quantum-number spaces and also in the\nreal space because of the attractive interaction employed."
    },
    {
        "anchor": "Attractive Bose-Einstein Condensates in three dimensions under rotation:\n  Revisiting the problem of stability of the ground state in harmonic traps: We study harmonically trapped ultracold Bose gases with attractive\ninterparticle interactions under external rotation in three spatial dimensions\nand determine the critical value of the attraction strength where the gas\ncollapses as a function of the rotation frequency. To this end we examine the\nstationary state in the corotating frame with a many-body approach as well as\nwithin the Gross-Pitaevskii theory of systems in traps with different\nanisotropies. In contrast to recently reported results [N. A. Jamaludin, N. G.\nParker, and A. M. Martin, Phys. Rev. A \\textbf{77}, 051603(R) (2008)], we find\nthat the collapse is not postponed in the presence of rotation. Unlike\nrepulsive gases, the properties of the attractive system remain practically\nunchanged under rotation in isotropic and slightly anisotropic traps.",
        "positive": "Collisionless drag for a one-dimensional two-component Bose-Hubbard\n  model: We theoretically investigate the elusive Andreev-Bashkin collisionless drag\nfor a two-component onedimensional Bose-Hubbard model on a ring. By means of\ntensor network algorithms, we calculate the superfluid stiffness matrix as a\nfunction of intra- and interspecies interactions and of the lattice filling. We\nthen focus on the most promising region close to the so-called pair-superfluid\nphase, where we observe that the drag can become comparable with the total\nsuperfluid density. We elucidate the importance of the drag in determining the\nlong-range behavior of the correlation functions and the spin speed of sound.\nIn this way, we are able to provide an expression for the spin Luttinger\nparameter $K_S$ in terms of drag and the spin susceptibility. Our results are\npromising in view of implementing the system by using ultracold Bose mixtures\ntrapped in deep optical lattices, where the size of the sample is of the same\norder of the number of particles we simulate. Importantly, the mesoscopicity of\nthe system, far from being detrimental, appears to favor a large drag, avoiding\nthe Berezinskii-Kosterlitz-Thouless jump at the transition to the\npair-superfluid phase which would reduce the region where a large drag can be\nobserved."
    },
    {
        "anchor": "A new Sobolev gradient method for direct minimization of the\n  Gross-Pitaevskii energy with rotation: In this paper we improve traditional steepest descent methods for the direct\nminimization of the Gross-Pitaevskii (GP) energy with rotation at two levels.\nWe first define a new inner product to equip the Sobolev space $H^1$ and derive\nthe corresponding gradient. Secondly, for the treatment of the mass\nconservation constraint, we use a projection method that avoids more\ncomplicated approaches based on modified energy functionals or traditional\nnormalization methods. The descent method with these two new ingredients is\nstudied theoretically in a Hilbert space setting and we give a proof of the\nglobal existence and convergence in the asymptotic limit to a minimizer of the\nGP energy. The new method is implemented in both finite difference and finite\nelement two-dimensional settings and used to compute various complex\nconfigurations with vortices of rotating Bose-Einstein condensates. The new\nSobolev gradient method shows better numerical performances compared to\nclassical $L^2$ or $H^1$ gradient methods, especially when high rotation rates\nare considered.",
        "positive": "Spontaneous symmetry breaking in linearly coupled disk-shaped\n  Bose-Einstein condensates: We study effects of tunnel coupling on a pair of parallel disk-shaped\nBose-Einstein condensates with the self-attractive intrinsic nonlinearity. Each\ncondensate is trapped in a combination of in-plane and transverse\nharmonic-oscillator potentials. It is shown that, depending on the\nself-interaction strength and tunneling coupling, the ground state of the\nsystem exhibits a phase transition which links three configurations: a\nsymmetric one with equal numbers of atoms in the coupled condensates, an\nasymmetric configuration with a population imbalance (a manifestation of the\nmacroscopic quantum self-trapping), and the collapsing state. A modification of\nthe phase diagram of the system in the presence of vortices in the disk-shaped\ncondensates is reported too. The study of dynamics around the stationary\nconfigurations reveals properties which strongly depend on the symmetry of the\nconfiguration."
    },
    {
        "anchor": "Interaction Effects on Number Fluctuations in a Bose-Einstein Condensate\n  of Light: We investigate the effect of interactions on condensate-number fluctuations\nin Bose-Einstein condensates. For a contact interaction we variationally obtain\nthe equilibrium probability distribution for the number of particles in the\ncondensate. To facilitate comparison with experiment, we also calculate the\nzero-time delay autocorrelation function $g^{(2)}(0)$ for different strengths\nof the interaction. Finally, we focus on the case of a condensate of photons\nand discuss possible mechanisms for the interaction.",
        "positive": "Correlational Origin of the Roton Minimum: We present compelling evidence supporting the conjecture that the origin of\nthe roton in Bose-condensed systems arises from strong correlations between the\nconstituent particles. By studying the two dimensional bosonic dipole systems a\nparadigm, we find that classical molecular dynamics (MD) simulations provide a\nfaithful representation of the dispersion relation for a low- temperature\nquantum system. The MD simulations allow one to examine the effect of coupling\nstrength on the formation of the roton minimum and to demonstrate that it is\nalways generated at a sufficiently high enough coupling. Moreover, the\nclassical images of the roton-roton, roton-maxon, etc. states also appear in\nthe MD simulation spectra as a consequence of the strong coupling."
    },
    {
        "anchor": "Hexagonal Plaquette Spin-spin Interactions and Quantum Magnetism in a\n  Two-dimensional Ion Crystal: We propose a trapped ion scheme en route to realize spin Hamiltonians on a\nKagome lattice which, at low energies, are described by emergent Z2 gauge\nfields, and support a topological quantum spin liquid ground state. The\nenabling element in our scheme is the hexagonal plaquette spin-spin\ninteractions in a 2D ion crystal. For this, the phonon-mode spectrum of the\ncrystal is engineered by standing-wave optical potentials or by using Rydberg\nexcited ions, thus generating localized phonon-modes around a hexagon of ions\nselected out of the entire two-dimensional crystal. These tailored modes can\nmediate spin-spin interactions between ion-qubits on a hexagonal plaquette when\nsubject to state-dependent optical dipole forces. We discuss how these\ninteractions can be employed to emulate a generalized Balents-Fisher-Girvin\nmodel in minimal instances of one and two plaquettes. This model is an\narchetypical Hamiltonian in which gauge fields are the emergent degrees of\nfreedom on top of the classical ground state manifold. Under realistic\nsituations, we show the emergence of a discrete Gauss's law as well as the\ndynamics of a deconfined charge excitation on a gauge-invariant background\nusing the two-plaquettes trapped ions spin-system. The proposed scheme in\nprinciple allows further scaling in a future trapped ion quantum simulator, and\nwe conclude that our work will pave the way towards the simulation of emergent\ngauge theories and quantum spin liquids in trapped ion systems.",
        "positive": "Microscopic derivation of multi-channel Hubbard models for ultracold\n  nonreactive molecules in an optical lattice: Recent experimental advances in the cooling and manipulation of bialkali\ndimer molecules have enabled the production of gases of ultracold molecules\nthat are not chemically reactive. It has been presumed in the literature that\nin the absence of an electric field the low-energy scattering of such\nnonreactive molecules (NRMs) will be similar to atoms, in which a single\n$s$-wave scattering length governs the collisional physics. However, in Ref.\n[1], it was argued that the short-range collisional physics of NRMs is much\nmore complex than for atoms, and that this leads to a many-body description in\nterms of a multi-channel Hubbard model. In this work, we show that this\nmulti-channel Hubbard model description of NRMs in an optical lattice is robust\nagainst the approximations employed in Ref. [1] to estimate its parameters. We\ndo so via an exact, albeit formal, derivation of a multi-channel resonance\nmodel for two NRMs from an ab initio description of the molecules in terms of\ntheir constituent atoms. We discuss the regularization of this two-body\nmulti-channel resonance model in the presence of a harmonic trap, and how its\nsolutions form the basis for the many-body model of Ref. [1]. We also\ngeneralize the derivation of the effective lattice model to include multiple\ninternal states (e.g., rotational or hyperfine). We end with an outlook to\nfuture research."
    },
    {
        "anchor": "Quantum Phase Transition with a Simple Variational Ansatz: We study the zero-temperature quantum phase transition between liquid and hcp\nsolid helium-4. We use the variational method with a simple yet\nexchange-symmetric and fully explicit wavefunction. It is found that the\noptimized wavefunction undergoes spontaneous symmetry breaking and describes\nthe quantum solidification of helium at 22 atm. The explicit form of the\nwavefunction allows to consider various contributions to the phase transition.\nWe find that the employed wavefunction is an excellent candidate for describing\nboth a first-order quantum phase transition and the ground state of a Bose\nsolid.",
        "positive": "Stochastic method for calculating the ground state reduced density\n  matrix of trapped Bose particles in one dimension: The reduced density matrix (RDM) is a fundamental contraction of the\nBose-Einstein condensate wave function, encapsulating its one-body properties.\nIt serves as a major analysis tool with which the condensed component of the\ndensity can be identified. Despite its cardinal importance, calculating the\nground-state RDM of trapped interacting bosons is challenging and has been\nfully achieved only for specific models or when the pairwise interaction is\nweak. In this paper we discuss a new approach to compute the RDM based on a\ndouble-walker diffusion Monte Carlo random walk coupled with a stochastic\npermanent calculation. We here describe the new method and study some of its\nstatistical convergence and properties applying it to some model systems."
    },
    {
        "anchor": "Confinement of Half-quantized Vortices in Coherently Coupled\n  Bose-Einstein Condensates: Simulating Quark Confinement in QCD: We demonstrate that the confinement of half-quantized vortices (HQVs) in\ncoherently coupled Bose-Einstein condensates (BECs) simulates certain aspects\nof the confinement in $SU(2)$ quantum chromodynamics (QCD) in 2+1 space-time\ndimensions. By identifying the circulation of superfluid velocity as the baryon\nnumber and the relative phase between two components as a dual gluon, we\nidentify HQVs in a single component as electrically charged particles with a\nhalf baryon number. Further, we show that only singlet states of the relative\nphase of two components can stably exist as bound states of vortices, that is,\na pair of vortices in each component (a baryon) and a pair of a vortex and an\nantivortex in the same component (a meson). We then study the dynamics of a\nbaryon and meson; baryon is static at the equilibrium and rotates once it\ndeviates from the equilibrium, while a meson moves with constant velocity. For\nboth baryon and meson we verify a linear confinement and determine that they\nare broken, thus creating other baryons or mesons in the middle when two\nconstituent vortices are separated by more than some critical distance,\nresembling QCD.",
        "positive": "Superfluid transition of a ferromagnetic Bose gas: The strongly ferromagnetic spin-1 Bose-Einstein condensate (BEC) has recently\nbeen realized with atomic $^{7}$Li. It was predicted that a strong\nferromagnetic interaction can drive the normal gas into a magnetized phase at a\ntemperature above the superfluid transition, and $^{7}$Li likely satisfies the\ncriterion. We re-examine this theoretical proposal employing the\ntwo-particle-irreducible (2PI) effective potential, and conclude that there\nexists no stable normal magnetized phase for a dilute ferromagnetic Bose gas.\nFor $^{7}$Li, we predict that the normal gas undergoes a joint first order\ntransition and jump directly into a state with finite condensate density and\nmagnetization. We estimate the size of the first order jump, and examine how a\npartial spin polarization in the initial sample affects the first order\ntransition. We propose a qualitative phase diagram at fixed temperature for the\ntrapped gas."
    },
    {
        "anchor": "Superfluidity enhanced by spin-flip tunnelling in the presence of a\n  magnetic field: It is well-known that when the magnetic field is stronger than a critical\nvalue, the spin imbalance can break the Cooper pairs of electrons and hence\nhinder the superconductivity in a spin-singlet channel. In a bilayer system of\nultra-cold Fermi gases, however, we demonstrate that the critical value of the\nmagnetic field at zero temperature can be significantly increased by including\na spin-flip tunnelling, which opens a gap in the spin-triplet channel near the\nFermi surface and hence reduces the influence of the effective magnetic field\non the superfluidity. The phase transition also changes from first order to\nsecond order when the tunnelling exceeds a critical value. Considering a\nrealistic experiment, this mechanism can be implemented by applying an\nintralayer Raman coupling between the spin states with a phase difference\nbetween the two layers.",
        "positive": "Dynamics and stability of dark solitons in exciton-polariton condensates: We present a comprehensive analytical theory of localized nonlinear\nexcitations - dark solitons, supported by an incoherently pumped, spatially\nhomogeneous exciton-polariton condensate. We show that, in contrast to dark\nsolitons in conservative systems, these nonlinear excitations \"relax\" by\nblending with the background at a finite time, which critically depends on the\nparameters of the condensate. Our analytical results for trajectory and\nlifetime are in excellent agreement with direct numerical simulations of the\nopen-dissipative mean-field model. In addition, we show that transverse\ninstability of quasi-one-dimensional dark stripes in a two-dimensional\nopen-dissipative condensate demonstrates features that are entirely absent in\nconservative systems, as creation of vortex-antivortex pairs competes with the\nsoliton relaxation process."
    },
    {
        "anchor": "Universal Cooling Scheme for Quantum Simulation: At present, there is a worldwide effort to use cold atoms to simulate\nstrongly correlated quantum many-body systems. It is hoped that these\n\"simulations\" will provide solutions to many unsolved problems. However, the\nrelevant energy scales in most of these experiments are so small that one has\nto go to entropy regimes far below those achievable today. Here, we present a\ngeneral scheme to extract entropy directly from the region of interest. The\nlate stage of this process is equivalent to a continuous \"evaporation\", and is\nable to combat intrinsic heating of the system. For illustration, we show how\nto cool a weak coupling BCS superfluid (with $T_{c}\\sim 10^{-10}$K) to\n$10^{-11}$K with this simple procedure, with entropy per particle as low as\n$5\\times 10^{-4}k_{B}$ in the superfluid region.",
        "positive": "Managing the Flow of Liquid Light: Strongly coupled light-matter systems can carry information over long\ndistances and realize low threshold polariton lasing, condensation and\nsuperfluidity. These systems are highly non-equilibrium in nature, so constant\nnonzero fluxes manifest themselves even at the steady-state and are set by a\ncomplicated interplay between nonlinearity, dispersion, pumping, dissipation\nand interactions between the various constituents of the system. Based on the\nmean-field governing equations of lasers or polariton condensates, we develop a\nmethod for engineering and controlling the velocity profiles by manipulating\nthe system's spatial pumping and dissipation. We present analytically exact\npumping and dissipation profiles that lead to a large variety of spatially\nperiodic density and velocity profiles. Besides these, any physically relevant\nvelocity profiles can be engineered by finding the stationary state of the\nconservative nonlinear Schrodinger equation in an external potential related to\nthe velocity. Our approach opens the way to the controllable implementation of\nlaser or polariton flows for ultra-fast information processing, integrated\ncircuits, and analogue simulators."
    },
    {
        "anchor": "A unified approach to the thermodynamics and quantum scaling functions\n  of one-dimensional strongly attractive $SU(w)$ Fermi Gases: In this letter we present a unified derivation of the pressure equation of\nstates, thermodynamics and scaling functions for the one-dimensional (1D)\nstrongly attractive Fermi gases with $SU(w)$ symmetry. These physical\nquantities provide a rigorous understanding on a universality class of quantum\ncriticality characterised by the critical exponents $z=2$ and correlation\nlength exponent $\\nu=1/2$. Such a universality class of quantum criticality can\noccur when the Fermi sea of one branch of charge bound states starts to fill or\nbecome gapped at zero temperature. The quantum critical cone can be determined\nthrough the double peaks in specific heat which serve to mark two crossover\ntemperatures fanning out from the critical point. Our method opens to further\nstudy on quantum phases and phase transitions in strongly interacting fermions\nwith large $SU(w)$ and non-$SU(w)$ symmetries in one dimension.",
        "positive": "Application of lasers to ultracold atoms and molecules: In this review, we discuss the impact of the development of lasers on\nultracold atoms and molecules and their applications. After a brief historical\nreview of laser cooling and Bose-Einstein condensation, we present important\napplications of ultra cold atoms, including time and frequency metrology, atom\ninterferometry and inertial sensors, atom lasers, simulation of condensed\nmatter systems, production and study of strongly correlated systems, and\nproduction of ultracold molecules."
    },
    {
        "anchor": "Tunneling dynamics of correlated bosons in a double well potential: The quantum dynamics of a few bosons in a double well potential is studied\nusing a Bose Hubbard model. We consider both signs for the on-site\ninterparticle interaction and also investigated the situations where they are\nlarge and small. Interesting distinctive features are noted for the tunneling\noscillations of these bosons corresponding to the above scenarios. Further, the\nsensitivity of the particle dynamics to the initial conditions has been\nstudied. It is found that corresponding to an odd number of particles, such as\nthree (or five), an initial condition of having unequal number of particles in\nthe wells has interesting consequences, which is most discernible when the\npopulation difference between the wells is unity.",
        "positive": "Quenched dynamics and spin-charge separation in an interacting\n  topological lattice: We analyze the static and dynamical properties of a one-dimensional\ntopological lattice, the fermionic Su-Schrieffer-Heeger model, in the presence\nof on-site interactions. Based on a study of charge and spin correlation\nfunctions, we elucidate the nature of the topological edge modes, which\ndepending on the sign of the interactions, either display particles of opposite\nspin on opposite edges, or a pair and a holon. This study of correlation\nfunctions also highlights the strong entanglement that exists between the\nopposite edges of the system. This last feature has remarkable consequences\nupon subjecting the system to a quench, where an instantaneous edge-to-edge\nsignal appears in the correlation functions characterizing the edge modes.\nBesides, other correlation functions are shown to propagate in the bulk\naccording to the light-cone imposed by the Lieb-Robinson bound. Our study\nreveals how one-dimensional lattices exhibiting entangled topological edge\nmodes allow for a non-trivial correlation spreading, while providing an\naccessible platform to detect spin-charge separation using state-of-the-art\nexperimental techniques."
    },
    {
        "anchor": "Renormalization group study of the four-body problem: We perform a renormalization group analysis of the non-relativistic\nfour-boson problem by means of a simple model with pointlike three- and\nfour-body interactions. We investigate in particular the unitarity point where\nthe scattering length is infinite and all energies are at the atom threshold.\nWe find that the four-body problem behaves truly universally, independent of\nany four-body parameter. Our findings confirm the recent conjectures of Platter\net al. and von Stecher et al. that the four-body problem is universal, now also\nfrom a renormalization group perspective. We calculate the corresponding\nrelations between the four- and three-body bound states, as well as the full\nbound state spectrum and comment on the influence of effective range\ncorrections.",
        "positive": "Mean-field approaches to the Bose-Hubbard model with three-body local\n  interaction: The zero temperature properties of the generalized Bose-Hubbard model\nincluding three-body interactions are studied on a mean-field level. We obtain\nanalytical results using the so-called perturbative mean-field method and more\ndetailed numerical results using the Gutzwiller product state variational\nAnsatz. These two approaches yield equivalent results which compare well on a\nqualitative level with recent exact results obtained in the literature."
    },
    {
        "anchor": "Two-Dimensional Homogeneous Fermi Gases: We report on the experimental realization of homogeneous two-dimensional (2D)\nFermi gases trapped in a box potential. In contrast to harmonically trapped\ngases, these homogeneous 2D systems are ideally suited to probe local as well\nas non-local properties of strongly interacting manybody systems. As a first\nmeasurement, we use a local probe to extract the equation of state (EOS) of a\nnon-interacting Fermi gas. We then perform matter wave focusing to extract its\nmomentum distribution and directly observe Pauli blocking in a near unity\noccupation of momentum states. Finally, we measure the momentum distribution of\nstrongly interacting homogeneous 2D gases in the crossover between attractively\ninteracting fermions and deeply-bound bosonic molecules.",
        "positive": "Control of the Bose-Einstein condensate by dissipation. Nonlinear Zeno\n  effect: We show that controlled dissipation can be used as a tool for exploring\nfundamental phenomena and managing mesoscopic systems of cold atoms and\nBose-Einstein condensates. Even the simplest boson-Josephson junction, that is,\na Bose-Einstein condensate in a double-well trap, subjected to removal of atoms\nfrom one of the two potential minima allows one to observe such phenomena as\nthe suppression of losses and the nonlinear Zeno effect. In such a system the\ncontrolled dissipation can be used to create desired macroscopic states and\nimplement controlled switching among different quantum regimes."
    },
    {
        "anchor": "Quantum phase transition of the Bose-Hubbard model on cubic lattice with\n  anisotropic hopping: In quantum many-body system, dimensionality plays a critical role on type of\nthe quantum phase transition. In order to study the quantum system during\ndimensional crossover, we studied the Bose-Hubbard model on cubic lattice with\nanisotropic hopping by using the high order symbolic strong coupling expansion\nmethod. The analytic series expanded boundaries between the Mott-insulator and\nsuperfluid phase up to eighth order are calculated. The critical exponents are\nextracted by Pad\\'{e} re-summation method, which clearly shows the dimensional\ncrossover behavior. Meanwhile, the critical points at commensurate filling can\nalso be obtained, and they match well with the prediction of renormalization\ngroup theory. The scaling of the gap energy and whole phase diagram are given\nat last, and they can be taken as the benchmark for experiment and numerical\nsimulations in the future study.",
        "positive": "Phase separation and pair condensation in a spin-imbalanced 2D Fermi gas: We study a two-component quasi-two-dimensional Fermi gas with imbalanced spin\npopulations. We probe the gas at different interaction strengths and\npolarizations by measuring the density of each spin component in the trap and\nthe pair momentum distribution after time of flight. For a wide range of\nexperimental parameters, we observe in-trap phase separation characterized by\nthe appearance of a spin-balanced condensate surrounded by a polarized gas. Our\nmomentum space measurements indicate pair condensation in the imbalanced gas\neven for large polarizations where phase separation vanishes, pointing to the\npresence of a polarized pair condensate. Our observation of zero momentum pair\ncondensates in 2D spin-imbalanced gases opens the way to explorations of more\nexotic superfluid phases that occupy a large part of the phase diagram in lower\ndimensions."
    },
    {
        "anchor": "Bose-Einstein condensation with spin-orbit coupling: The recent realization of synthetic spin-orbit coupling represents an\noutstanding achievement in the physics of ultracold quantum gases. In this\nreview we explore the properties of a spin-orbit-coupled Bose-Einstein\ncondensate with equal Rashba and Dresselhaus strengths. This system presents a\nrich phase diagram, which exhibits a tricritical point separating a\nzero-momentum phase, a spin-polarized plane-wave phase, and a stripe phase. In\nthe stripe phase translational invariance is spontaneously broken, in analogy\nwith supersolids. Spin-orbit coupling also strongly affects the dynamics of the\nsystem. In particular, the excitation spectrum exhibits intriguing features,\nincluding the suppression of the sound velocity, the emergence of a roton\nminimum in the plane-wave phase, and the appearance of a double gapless band\nstructure in the stripe phase. Finally, we discuss a combined procedure to make\nthe stripes visible and stable, thus allowing for a direct experimental\ndetection.",
        "positive": "Dissipative Effects on Quantum Sticking: Using variational mean-field theory, many-body dissipative effects on the\nthreshold law for quantum sticking and reflection of neutral and charged\nparticles are examined. For the case of an ohmic bosonic bath, we study the\neffects of the infrared divergence on the probability of sticking and obtain a\nnon-perturbative expression for the sticking rate. We find that for weak\ndissipative coupling $\\alpha$, the low energy threshold laws for quantum\nsticking are modified by an infrared singularity in the bath. The sticking\nprobability for a neutral particle with incident energy $E\\to 0$ behaves\nasymptotically as ${\\it s}\\sim E^{(1+\\alpha)/2(1-\\alpha)}$; for a charged\nparticle, we obtain ${\\it s}\\sim E^{\\alpha/2(1-\\alpha)}$. Thus, \"quantum\nmirrors\" --surfaces that become perfectly reflective to particles with incident\nenergies asymptotically approaching zero-- can also exist for charged\nparticles."
    },
    {
        "anchor": "Fragmentation of identical and distinguishable bosons' pairs and natural\n  geminals of a trapped bosonic mixture: In a mixture of two kinds of identical bosons there are two types of pairs,\nidentical bosons' pairs, of either species, and pairs of distinguishable\nbosons. In the present work fragmentation of pairs in a trapped mixture of\nBose-Einstein condensate is investigated using a solvable model, the symmetric\nharmonic-interaction model for mixtures. The natural geminals for pairs made of\nidentical or distinguishable bosons are explicitly contracted by diagonalizing\nthe intra-species and inter-species reduced two-particle density matrices,\nrespectively. Properties of pairs' fragmentation in the mixture are discussed,\nthe role of the mixture's center-of-mass and relative center-of-mass\ncoordinates is elucidated, and a generalization to higher-order reduced density\nmatrices is made. As a complementary result, the exact Schmidt decomposition of\nthe wavefunction of the bosonic mixture is constructed. The entanglement\nbetween the two species is governed by the coupling of their individual\ncenter-of-mass coordinates, and it does not vanish at the limit of an infinite\nnumber of particles where any finite-order intra-species and inter-species\nreduced density matrix per particle is 100\\% condensed. Implications are\nbriefly discussed.",
        "positive": "Critical superfluid velocity in a trapped dipolar gas: We investigate the superfluid properties of a dipolar Bose-Einstein\ncondensate (BEC) in a fully three-dimensional trap. Specifically, we calculate\na superfluid critical velocity for this system by applying the Landau criterion\nto its discrete quasiparticle spectrum. We test this critical velocity by\ndirect numerical simulation of condensate depletion as a blue-detuned laser\nmoves through the condensate. In both cases, the presence of the roton in the\nspectrum serves to lower the critical velocity beyond a critical particle\nnumber. Since the shape of the dispersion, and hence the roton minimum, is\ntunable as a function of particle number, we thereby propose an experiment that\ncan simultaneously measure the Landau critical velocity of a dipolar BEC and\ndemonstrate the presence of the roton in this system."
    },
    {
        "anchor": "Kibble-Zurek universality in a strongly interacting Fermi superfluid: Near a continuous phase transition, systems with different microscopic\norigins display universal dynamics if their underlying symmetries are\ncompatible. In a thermally quenched system, the Kibble-Zurek mechanism for the\ncreation of topological defects unveils this universality through a\ncharacteristic power-law exponent, which captures the dependence of the defect\ndensity on the quench rate. Here, we report the observation of the Kibble-Zurek\nuniversality in a strongly interacting Fermi superfluid. As the system's\nmicroscopic description is tuned from bosonic to fermionic, the quench\nformation of vortices reveals a constant scaling exponent arising from the\n$U(1)$ gauge symmetry of the system. For rapid quenches, destructive vortex\ncollisions lead to the saturation of their densities, whose values can be\nuniversally scaled by the interaction-dependent area of the vortex cores.",
        "positive": "Direct imaging of a digital-micromirror device for configurable\n  microscopic optical potentials: Programable spatial light modulators (SLMs) have significantly advanced the\nconfigurable optical trapping of particles. Typically, these devices are\nutilized in the Fourier plane of an optical system, but direct imaging of an\namplitude pattern can potentially result in increased simplicity and\ncomputational speed. Here we demonstrate high-resolution direct imaging of a\ndigital micromirror device (DMD) at high numerical apertures (NA), which we\napply to the optical trapping of a Bose-Einstein condensate (BEC). We utilise a\n(1200 x 1920) pixel DMD and commercially available 0.45 NA microscope\nobjectives, finding that atoms confined in a hybrid optical/magnetic or\nall-optical potential can be patterned using repulsive blue-detuned (532 nm)\nlight with 630(10) nm full-width at half-maximum (FWHM) resolution, within 5%\nof the diffraction limit. The result is near arbitrary control of the density\nthe BEC without the need for expensive custom optics. We also introduce the\ntechnique of time-averaged DMD potentials, demonstrating the ability to produce\nmultiple grayscale levels with minimal heating of the atomic cloud, by\nutilising the high switching speed (20 kHz maximum) of the DMD. These\ntechniques will enable the realization and control of diverse optical\npotentials for superfluid dynamics and atomtronics applications with quantum\ngases. The performance of this system in a direct imaging configuration has\nwider application for optical trapping at non-trivial NAs."
    },
    {
        "anchor": "Field-induced phase transitions of repulsive spin-1 bosons in optical\n  lattices: We study the phase diagram of repulsively interacting spin-1 bosons in\noptical lattices at unit filling, showing that an externally induced quadratic\nZeeman effect may lead to a rich physics characterized by various phases and\nphase transitions. We find that the main properties of the system may be\ndescribed by an effective field model, which provides the precise location of\nthe phase boundaries for any dimension, being in excellent agreement with our\nnumerical calculations for one-dimensional systems. Our work provides a\nquantitative guide for the experimental analysis of various types of\nfield-induced quantum phase transitions in spin-1 lattice bosons. These\ntransitions, which are precluded in spin-1/2 systems, may be realized using an\nexternally modified quadratic Zeeman coupling, similar to recent experiments\nwith spinor condensates in the continuum.",
        "positive": "Bright soliton quantum superpositions: signatures of high- and\n  low-fidelity states: Scattering quantum bright solitons off barriers has been predicted to lead to\nnonlocal quantum superpositions, in particular the NOON-state. The focus of\nthis paper lies on signatures of both high- and low-fidelity quantum\nsuperposition states. We numerically demonstrate that a one-dimensional\ngeometry with the barrier potential situated in the middle of an additional -\nexperimentally typical - harmonic confinement gives rise to particularly\nwell-observable signatures. In the elastic scattering regime we investigate\nsignatures of NOON-states on the $N$-particle level within an effective\npotential approach. We show that removing the barrier potential and\nsubsequently recombining both parts of the quantum superposition leads to a\nhigh-contrast interference pattern in the center-of-mass coordinate for narrow\nand broad potential barriers. We demonstrate that the presented signatures can\nbe used to clearly distinguish quantum superpositions states from statistical\nmixtures and are sufficiently robust against experimentally relevant\nexcitations of the center-of-mass wave function to higher lying oscillator\nstates. For two-particle solitons we extend these considerations to\nlow-fidelity superposition states: even for strong deviations from the\ntwo-particle NOON-state we find interference patterns with high contrast."
    },
    {
        "anchor": "Relation between the eigenfrequencies of Bogoliubov excitations of\n  Bose-Einstein condensates and the eigenvalues of the Jacobian in a\n  time-dependent variational approach: We study the relation between the eigenfrequencies of the Bogoliubov\nexcitations of Bose-Einstein condensates, and the eigenvalues of the Jacobian\nstability matrix in a variational approach which maps the Gross-Pitaevskii\nequation to a system of equations of motion for the variational parameters. We\ndo this for Bose-Einstein condensates with attractive contact interaction in an\nexternal trap, and for a simple model of a self-trapped Bose-Einstein\ncondensate with attractive 1/r interaction. The stationary solutions of the\nGross-Pitaevskii equation and Bogoliubov excitations are calculated using a\nfinite-difference scheme. The Bogoliubov spectra of the ground and excited\nstate of the self-trapped monopolar condensate exhibits a Rydberg-like\nstructure, which can be explained by means of a quantum defect theory. On the\nvariational side, we treat the problem using an ansatz of time-dependent\ncoupled Gaussians combined with spherical harmonics. We first apply this ansatz\nto a condensate in an external trap without long-range interaction, and\ncalculate the excitation spectrum with the help of the time-dependent\nvariational principle. Comparing with the full-numerical results, we find a\ngood agreement for the eigenfrequencies of the lowest excitation modes with\narbitrary angular momenta. The variational method is then applied to calculate\nthe excitations of the self-trapped monopolar condensates, and the\neigenfrequencies of the excitation modes are compared.",
        "positive": "Rapid non-adiabatic loading in an optical lattice: We present a scheme for non-adiabatically loading a Bose-Einstein condensate\ninto the ground state of a one dimensional optical lattice within a few tens of\nmicroseconds typically, i.e. in less than half the Talbot period. This\ntechnique of coherent control is based on sequences of pulsed perturbations and\nexperimental results demonstrate its feasibility and effectiveness. As the\nloading process is much shorter than the traditional adiabatic loading\ntimescale, this method may find many applications."
    },
    {
        "anchor": "The fate of a gray soliton in a quenched Bose-Einstein condensate: We investigate the destiny of a gray soliton in a repulsive one-dimensional\nBose-Einstein condensate undergoing a sudden quench of the non-linearity\nparameter. The outcome of the quench is found to depend dramatically on the\nratio $\\eta$ of the final and initial values of the speed of sound. For integer\n$\\eta$ the soliton splits into exactly $2\\eta-1$ solitons. For non-integer\n$\\eta$ the soliton decays into multiple solitons and Bogoliubov modes. The case\nof integer $\\eta$ is analyzed in detail. The parameters of solitons in the\nout-state are found explicitly. Our approach exploits the inverse scattering\nmethod and can be easily used for the similar quenches in any classical\nintegrable system.",
        "positive": "Hidden string order in a hole-superconductor with extended correlated\n  hopping: Ultracold fermions in a one-dimensional, spin-dependent, optical lattice are\ndescribed by a non-standard Hubbard model with next-nearest-neighbour\ncorrelated hopping. Periodic driving of the lattice allows wide tuning of the\nsystem parameters. We solve this model exactly for a special value of the\ncorrelated hopping. The solution reveals the general properties of this system\nfor arbitrary filling: exact and asymmetric spin-charge separation, a gapless\nspectrum of lowest energy excitations, a spin-gap, which may be interpreted in\nterms of collective hole pairing and a non-vanishing den Nijs-Rommelse type\nstring correlator. Numerical studies away from the integrable point show the\npersistence of both long range string order and spin-gap."
    },
    {
        "anchor": "An atomtronics transistor for quantum gates: We present a mechanism for quantum gates where the qubits are encoded in the\npopulation distribution of two component ultracold atoms trapped in a\nspecies-selective triple-well potential. The gate operation is a specific\napplication of a new design for an atomtronics transistor where inter-species\ninteraction is used to control transport, and can be realized with either\nindividual atoms or aggregates like Bose-Einstein condensates (BEC). We\ndemonstrate the operational principle with a static external potential, and\nshow feasible implementation with a smooth dynamical potential.",
        "positive": "Anomalous Conductance of a strongly interacting Fermi Gas through a\n  Quantum Point Contact: In this work we study the particle conductance of a strongly interacting\nFermi gas through a quantum point contact. With an atom-molecule two-channel\nmodel, we compute the contribution to particle conductance by both the\nfermionic atoms and the bosonic molecules using the Keldysh formalism. Focusing\non the regime above the Fermi superfluid transition temperature, we find that\nthe fermionic contribution to the conductance is reduced by interaction\ncompared with the quantized value for the non-interacting case; while the\nbosonic contribution to the conductance exhibits a plateau with non-universal\nvalues that is larger than the quantized conductance. This feature is\nparticularly profound at temperature close to the superfluid transition. We\nemphasize that the enhanced conductance arises because of the bosonic nature of\nclosed channel molecules and the low-dimensionality of the quantum point\ncontact."
    },
    {
        "anchor": "Chaotic level mixing in a two-band Bose-Hubbard model: We present a two-band Bose-Hubbard model which is shown to be minimal in the\nnecessary coupling terms at resonant tunneling conditions. The dynamics of the\nmany-body problem is studied by sweeping the system across an avoided level\ncrossing. The linear sweep generalizes Landau-Zener transitions from\nsingle-particle to many-body realizations. The temporal evolution of single-\nand two-body observables along the sweeps is investigated in order to\ncharacterize the non-equilibrium dynamics in our complex quantum system.",
        "positive": "Tan Relations in Dilute Bose Gasses: The exact relations for strongly interacting Fermi gasses, recently derived\nby Tan, are shown to first order in the loop expansion to also apply to dilute\nBose gasses. A simple thermodynamic argument is put forward to support their\nvalidity. As an application, the second-order correction to the depletion of\nthe condensate is determined to logarithmic accuracy."
    },
    {
        "anchor": "Dynamical preparation of stripe states in spin-orbit coupled gases: In spinor Bose-Einstein condensates, spin-changing collisions are a\nremarkable proxy to coherently realize macroscopic many-body quantum states.\nThese processes have been, e.g., exploited to generate entanglement, to study\ndynamical quantum phase transitions, and proposed for realizing nematic phases\nin atomic condensates. In the same systems dressed by Raman beams, the coupling\nbetween spin and momentum induces a spin dependence in the scattering processes\ntaking place in the gas. Here we show that, at weak couplings, such modulation\nof the collisions leads to an effective Hamiltonian which is equivalent to the\none of an artificial spinor gas with spin-changing collisions that are tunable\nwith the Raman intensity. By exploiting this dressed-basis description, we\npropose a robust protocol to coherently drive the spin-orbit coupled condensate\ninto the ferromagnetic stripe phase via crossing a quantum phase transition of\nthe effective low-energy model in an excited-state.",
        "positive": "Multi-particle Wannier states and Thouless pumping of interacting bosons: The study of topological effects in physics is a hot area, and only recently\nresearchers were able to address the important issues of topological properties\nof interacting quantum systems. But it is still a great challenge to describe\nmulti-particle and interaction effects. Here, we introduce multi-particle\nWannier states for interacting systems with co-translational symmetry. We\nreveal how the shift of multi-particle Wannier state relates to the\nmulti-particle Chern number, and study the two-boson Thouless pumping in an\ninteracting Rice-Mele model. In addition to the bound-state Thouless pumping in\nwhich two bosons move unidirectionally as a whole, we find topologically\nresonant tunneling in which two bosons move unidirectionally, one by the other,\nprovided the neighboring-well potential bias matches the interaction energy.\nOur work creates a new paradigm for multi-particle topological effects and lays\na cornerstone for detecting interacting topological states."
    },
    {
        "anchor": "Topological Phases for Fermionic Cold Atoms on the Lieb Lattice: We investigate the properties of the Lieb lattice, i.e a face-centered square\nlattice, subjected to external gauge fields. We show that an Abelian gauge\nfield leads to a peculiar quantum Hall effect, which is a consequence of the\nsingle Dirac cone and the flat band characterizing the energy spectrum. Then we\nexplore the effects of an intrinsic spin-orbit term - a non-Abelian gauge field\n- and demonstrate the occurrence of the quantum spin Hall effect in this model.\nBesides, we obtain the relativistic Hamiltonian describing the Lieb lattice at\nlow energy and derive the Landau levels in the presence of external Abelian and\nnon-Abelian gauge fields. Finally, we describe concrete schemes for realizing\nthese gauge fields with cold fermionic atoms trapped in an optical Lieb\nlattice. In particular, we provide a very efficient method to reproduce the\nintrinsic (Kane-Mele) spin-orbit term with assisted-tunneling schemes.\nConsequently, our model could be implemented in order to produce a variety of\ntopological states with cold-atoms.",
        "positive": "Quantitative test of mean-field description of a trapped two-dimensional\n  Bose gas: We investigate the accuracy of two mean-field theories of the trapped\ntwo-dimensional Bose gas at predicting transition region properties by\ncomparison to non-perturbative classical field calculations. To make these\ncomparisons we examine the density profiles and the predictions for the\nBerezinskii-Kosterlitz-Thouless superfluid transition temperature over a\nparameter range in which the degree of thermal activation in the tightly\ntrapped direction varies considerably. These results present an important test\nof these mean-field theories, and provide a characterization of their typical\naccuracy."
    },
    {
        "anchor": "Evolution of an attractive polarized Fermi gas: From a Fermi liquid of\n  polarons to a non-Fermi liquid at the Fulde-Ferrell-Larkin-Ovchinnikov\n  quantum critical point: The evolution of an attractive polarized two-component Fermi gas at zero\ntemperature is analyzed as its polarization is progressively decreased, from\nfull polarization (corresponding to the polaronic limit) down to a critical\npolarization when superfluidity sets in. This critical polarization and the\nnature of the associated superfluid instability are determined within a fully\nself-consistent $t$-matrix approach implemented exactly at zero temperature. In\nthis way, the polarization-vs-coupling phase diagram at zero temperature is\nconstructed throughout the whole BCS-BEC crossover. Depending on the coupling\nstrength of the inter-particle interaction between the two components, the\nsuperfluid instability can be either toward a Fulde-Ferrel-Larkin-Ovchinnikov\n(FFLO) phase or toward a standard polarized BCS phase. The evolution with\npolarization of the quasi-particle parameters in the normal Fermi gas turns out\nto be notably different in the two cases. When the instability is toward a\npolarized BCS superfluid, quasi-particles in the proximity of the two Fermi\nsurfaces remain well defined for all polarizations. When the instability is\ninstead toward an FFLO superfluid, precursor effects become apparent upon\napproaching the FFLO quantum critical point (QCP), where the quasi-particle\nresidues vanish and the effective masses diverge. This behavior leads to a\ncomplete breakdown of the quasi-particle picture characteristic of a Fermi\nliquid, similarly to what occurs in heavy-fermion materials at an\nantiferromagnetic QCP. At unitarity, the system is further investigated at\nfinite temperature, making it possible to identify a non-Fermi liquid region in\nthe temperature-vs-polarization phase diagram associated with the underlying\nFFLO QCP.",
        "positive": "Tunneling Theory for Tunable Open Quantum Systems of Ultracold Atoms in\n  One-Dimensional Traps: The creation of tunable open quantum systems is becoming feasible in current\nexperiments with ultracold atoms in low-dimensional traps. In particular, the\nhigh degree of experimental control over these systems allows detailed studies\nof tunneling dynamics, e.g., as a function of the trapping geometry and the\ninterparticle interaction strength. In order to address this exciting\nopportunity we present a theoretical framework for two-body tunneling based on\nthe rigged Hilbert space formulation. In this approach, bound, resonant and\nscattering states are included on an equal footing, and we argue that the\ncoupling of all these components is vital for a correct description of the\nrelevant threshold phenomena. In particular, we study the tunneling mechanism\nfor two-body systems in one-dimensional traps and different interaction\nregimes. We find a strong dominance of sequential tunneling of single particles\nfor repulsive and weakly attractive systems, while there is a signature of\ncorrelated pair tunneling in the calculated many-particle flux for strongly\nattractive interparticle interaction."
    },
    {
        "anchor": "Bloch-Zener oscillations across a merging transition of Dirac points: Bloch oscillations are a powerful tool to investigate spectra with Dirac\npoints. By varying band parameters, Dirac points can be manipulated and merged\nat a topological transition towards a gapped phase. Under a constant force, a\nFermi sea initially in the lower band performs Bloch oscillations and may Zener\ntunnel to the upper band mostly at the location of the Dirac points. The\ntunneling probability is computed from the low energy universal Hamiltonian\ndescribing the vicinity of the merging. The agreement with a recent experiment\non cold atoms in an optical lattice is very good.",
        "positive": "Atomtronic circuits: from many-body physics to quantum technologies: Atomtronics is an emerging field that aims to manipulate ultracold atom\nmoving in matter wave circuits for both fundamental studies in quantum science\nand technological applications. In this colloquium, we review recent progress\nin matter-wave circuitry and atomtronics-based quantum technology. After a\nshort introduction to the basic physical principles and the key experimental\ntechniques needed to realize atomtronic systems, we describe the physics of\nmatter-waves in simple circuits such as ring traps and two-terminal systems.\nThe main experimental observations and outstanding questions are discussed. We\nalso present possible applications to a broad range of quantum technologies,\nfrom quantum sensing with atom interferometry to future quantum simulation and\nquantum computation architectures."
    },
    {
        "anchor": "Bosonic impurity in a one-dimensional quantum droplet in the Bose-Bose\n  mixture: We study an impurity immersed in the mixture of Bose ultracold gases in the\nregime where a quantum droplet exists. The quasi-one-dimensional geometry is\nconsidered. We find an effective attractive potential that acts by the quantum\ndroplet onto the impurity. The bound states of the impurity in this potential\nare investigated. These impurity bound states can provide potential probes for\nthe presence of quantum fluctuations effects on the droplet properties. In the\ncase of strong impurity-BEC coupling, we study the properties of the nonlinear\nlocal modes on the impurity induced by the quantum fluctuations.",
        "positive": "Simulations of non-Abelian gauge theories with optical lattices: Many phenomena occurring in strongly correlated quantum systems still await\nconclusive explanations. The absence of isolated free quarks in nature is an\nexample. It is attributed to quark confinement, whose origin is not yet\nunderstood. The phase diagram for nuclear matter at general temperatures and\ndensities, studied in heavy-ion collisions, is not settled. Finally, we have no\ndefinitive theory of high-temperature superconductivity. Though we have\ntheories that could underlie such physics, we lack the tools to determine the\nexperimental consequences of these theories. Quantum simulators may provide\nsuch tools. Here we show how to engineer quantum simulators of non-Abelian\nlattice gauge theories. The systems we consider have several applications: they\ncan be used to mimic quark confinement or to study dimer and valence-bond\nstates (which may be relevant for high-temperature superconductors)."
    },
    {
        "anchor": "Driven Bose-Hubbard Model with a Parametrically Modulated Harmonic Trap: We investigate a one-dimensional Bose-Hubbard model in a parametrically\ndriven global harmonic trap. The delicate interplay of both the local atom\ninteraction and the global driving allows to control the dynamical stability of\nthe trapped quantum many-body state. The mechanism is illustrated for weak\ninteraction by a discretized Gross-Pitaevskii equation within a Gaussian\nvariational ansatz, yielding to a Mathieu equation for the condensate width.\nThe parametric resonance condition can be tuned by the atom interaction\nstrength. For stronger interaction, this mechanism is confirmed by results of\nthe numerically exact time-evolving block decimation scheme. The global\nmodulation also induces an effective time-independent inhomogeneous hopping\nstrength for the atoms.",
        "positive": "Theoretical exploration of competing phases of lattice Bose gases in a\n  cavity: We consider bosonic atoms loaded into optical lattices with cavity-mediated\ninfinite-range interactions. Competing short- and global-range interactions\ncultivates a rich phase diagram. With a systematic field-theoretical\nperspective, we present an $\\emph{analytical}$ construction of global\nground-state phase diagram. We find that the infinite-range interaction\nenhances the fluctuation of the number density. In the strong coupling regime,\nwe find four branches of elementary excitations with two being \"partilce-like\"\nand two being \"hole-like\", and that the excitation gap becomes soft at the\nphase boundary between compressible phases and incompressible phases. We derive\nan effective theory describing compressible superfluid and supersolid states.\nTo complement this perturbative study, we construct a self-consistent\nmean-field theory and find numerical results consistent with our theoretical\nanalysis. We map out the phase diagram and find that a charge density wave may\nundergo a structure phase transition to a different charge density wave before\nit finally enters into the supersolid phase driven by increasing the hopping\namplitude."
    },
    {
        "anchor": "Spontaneous self-ordered states of vortex-antivortex pairs in a\n  Polariton Condensate: Polariton condensates have proved to be model systems to investigate\ntopological defects, as they allow for direct and non-destructive imaging of\nthe condensate complex order parameter. The fundamental topological excitations\nof such systems are quantized vortices. In specific configurations, further\nordering can bring the formation of vortex lattices. In this work we\ndemonstrate the spontaneous formation of ordered vortical states, consisting in\ngeometrically self-arranged vortex-antivortex pairs. A mean-field generalized\nGross-Pitaevskii model reproduces and supports the physics of the observed\nphenomenology.",
        "positive": "Response of the polaron system consisting of an impurity in a\n  Bose-Einstein condensate to Bragg spectroscopy: We expand the existing polaron response theory, expressed within the\nMori-Zwanzig projection operator formalism applicable for the transfer of\narbitrary energy and zero momentum, to the case of finite momentum exchange. A\ngeneral formula is then derived which can be used to calculate the response of\na system to a probe that transfers both momentum and energy to the system. The\nmain extension of the existing polaron response theory is the finite momentum\nexchange which was not needed until now since it is negligible for optical\nabsorption. However, this formalism is needed to calculate the response of the\npolaronic system consisting of an impurity in a Bose-Einstein condensate to\nBragg spectroscopy. We show that the well-known features that appear in the\noptical absorption of the solid state Fr\\\"ohlich polaron are also present in\nthe Bragg response of the BEC-impurity polaron. The f-sum rule is written in a\nform suitable to provide an independent consistency test for our results. The\neffect of lifetime broadening on the BEC-impurity spectrum is examined. The\nresults derived here are discussed in the framework of an experimental\nrealization consisting of a lithium impurity in a sodium condensate."
    },
    {
        "anchor": "Contact and Momentum Distribution of the Unitary Fermi Gas: A key quantity in strongly-interacting resonant Fermi gases is the contact\n$\\mathcal{C}$, which characterizes numerous properties such as the momentum\ndistribution at large momenta or the pair correlation function at short\ndistances. The temperature dependence of $\\mathcal{C}$ was measured at\nunitarity, where existing theoretical predictions differ substantially even at\nthe qualitative level. We report accurate data for the contact and the momentum\ndistribution of the unitary gas in the normal phase, obtained by Bold\nDiagrammatic Monte Carlo and Borel resummation. Our results agree with\nexperimental data within error bars and provide crucial benchmarks for the\ndevelopment of advanced theoretical treatments and precision measurements.",
        "positive": "Quench dynamics of a Tonks-Girardeau gas in one dimensional anharmonic\n  trap: The quench dynamics of a strongly interacting bosons on quartic and sextic\ntrap are studied by solving the time dependent many-boson Schrodinger equation\nnumerically exactly. The dynamics is addressed by the key measures of one-body\ndensity in conjugate space and information entropy. For both cases, rich\nmany-body dynamics is exhibited and loss of Bose-Fermi oscillation in the\nTonks-Girardeau limit is also attributed."
    },
    {
        "anchor": "Visualizing Efimov Correlations in the Bose Polaron: The Bose polaron is a quasi-particle of an impurity dressed by surrounding\nbosons. In few-body physics, it is known that two identical bosons and a third\ndistinguishable particle can form a sequence of Efimov bound states in the\nvicinity of inter-species scattering resonance. On the other hand, in the Bose\npolaron system with an impurity atom embedded in many bosons, no signature of\nEfimov physics has been reported in the existing spectroscopy measurements up\nto date. In this work, we propose that a large mass imbalance between a light\nimpurity and heavy bosons can help produce visible signatures of Efimov physics\nin such a spectroscopy measurement. Using the diagrammatic approach in the\nVirial expansion to include three-body effects from pair-wise interactions, we\ndetermine the impurity self-energy and its spectral function. Taking\n$^{6}$Li-$^{133}$Cs\\ system as a concrete example, we find two visible Efimov\nbranches in the polaron spectrum, as well as their hybridizations with the\nattractive polaron branch. We also discuss the general scenarios for observing\nthe signature of Efimov physics in polaron systems. This work paves the way for\nexperimentally exploring intriguing few-body correlations in a many-body system\nin the near future.",
        "positive": "On the order of BEC transition in weakly interacting gases predicted by\n  mean-field theory: Predictions from Hartree-Fock (HF), Popov (P), Yukalov-Yukalova (YY) and\n$t$-matrix approximations regarding the thermodynamics from the normal to the\nBEC phase in weakly interacting Bose gases are considered. By analyzing the\ndependence of the chemical potential $\\mu$ on temperature $T$ and particle\ndensity $\\rho$ we show that none of them predicts a second-order phase\ntransition as required by symmetry-breaking general considerations. In this\nwork we find that the isothermal compressibility $\\kappa_{T}$ predicted by\nthese theories does not diverge at criticality as expected in a true\nsecond-order phase transition. Moreover the isotherms $\\mu=\\mu(\\rho,T)$\ntypically exhibit a non-singled valued behavior in the vicinity of the BEC\ntransition, a feature forbidden by general thermodynamic principles. This\nbehavior can be avoided if a first order phase transition is appealed. The\nfacts described above show that although these mean field approximations give\ncorrect results near zero temperature they are endowed with thermodynamic\nanomalies in the vicinity of the BEC transition. We address the implications of\nthese results in the interpretation of current experiments with ultracold\ntrapped alkali gases."
    },
    {
        "anchor": "Coherent perfect absorption of nonlinear matter waves: Coherent perfect absorption is the complete extinction of incoming radiation\nby a complex potential in a physical system supporting wave propagation. The\nconcept was proven for linear waves in variety of systems including light\ninteracting with absorbing scatterers, plasmonic metasurfaces and graphene\nfilms, as well as sound waves. We extend the paradigm to coherent perfect\nabsorption of nonlinear waves and experimentally demonstrate it for matter\nwaves in an atomic Bose-Einstein condensate. Coherent absorption of nonlinear\nmatter waves is achieved easier than its linear analogs because the strength of\ntwo-body interactions offers additional freedom for control. Implementation of\nthe coherent perfect absorber of Bose-Einstein condensates paves the way\ntowards broad exploitation of the phenomenon in nonlinear optics,\nexciton-polariton condensates, acoustics, and other areas of nonlinear physics.\nIt also opens perspectives for designing atomic laser.",
        "positive": "Entanglement like properties in Spin-Orbit Coupled Ultra Cold Atom and\n  violation of Bell like Inequality: We show that the general quantum state of synthetically spin-orbit coupled\nultra cold bosonic atom whose condensate was experimentally created recently (\nY. J. Lin {\\it et al.}, Nature, {\\bf 471}, 83, (2011)), shows entanglement\nbetween motional degrees of freedom ( momentum) and internal degrees of freedom\n(hyperfine spin). We demonstrate the violation of Bell-like inequality (CHSH)\nfor such states that provides a unique opportunity to verify fundamental\nprinciple like quantum non-contextuality for commutating observables which are\nnot spatially separated. We analyze in detail the Rabi oscillation executed by\nsuch atom-laser system and how that influneces quantities like entanglement\nentropy, violation of Bell like Inequality etc. We also discuss the implication\nof our result in testing the quantum non-contextuality and Bell's Inequality\nvioaltion by macroscopic quantum object like Bose-Einstein Condensate of ultra\ncold atoms."
    },
    {
        "anchor": "The Quantum Echo in Two-Component Bose-Einstein Condensates: The development of ultracold atom technology has enabled the precise\ninvestigations on quantum dynamics of quantum gases. Recently, inspired by\nexperimental advancement, the $SU(1,1)$ echo, akin to the well-known $SU(2)$\nspin echo, has been proposed for single-component Bose-Einstein condensate\n(BEC). In this paper, we investigate the possibility of quantum echo in the\nmore intricate two-component BEC by fully exploiting its underlying symmetry,\nwhich is the Lie group $Sp(4,R)$. We demonstrate that quantum echo can occur\nfor the two-component BEC by applying a driving protocol consisting of two\nsteps in each period. The first step can be any Bogoliubov Hamiltonian, while\nthe second step is a Hamiltonian with interactions turned off, which plays a\nsimilar role as the $\\pi$-pulse in spin echo. We confirm our theoretical\nresults with numerical calculations for different examples of two-component\nBEC. We further consider the effect of interactions between the excited boson\nmodes on the quantum echo process and discuss the possible experiment\nimplementation of this quantum echo.",
        "positive": "Structure of Spin Correlations in High Temperature SU($N$) Quantum\n  Magnets: Quantum magnets with a large SU($N$) symmetry are a promising playground for\nthe discovery of new forms of exotic quantum matter. Motivated by recent\nexperimental efforts to study SU($N$) quantum magnetism in samples of ultracold\nfermionic alkaline-earth-like atoms in optical lattices, we study here the\ntemperature dependence of spin correlations in the SU($N$) Heisenberg spin\nmodel in a wide range of temperatures. We uncover a sizeable regime in\ntemperature, starting at $T=\\infty$ down to intermediate temperatures and for\nall $N\\ge2$, in which the correlations have a common spatial structure on a\nbroad range of lattices, with the sign of the correlations alternating from one\nManhattan shell to the next, while the amplitude of the correlations is rapidly\ndecreasing with distance. Focussing on the one-dimensional chain and the\ntwo-dimensional square and triangular lattice for certain $N$, we discuss the\nappearance of a disorder and a Lifshitz temperature, separating the\ncommensurate Manhattan high-$T$ regime from a low-$T$ incommensurate regime. We\nobserve that this temperature window is associated to an approximately\n$N$-independent entropy reduction from the $\\ln(N)$ entropy at infinite\ntemperature. Our results are based on high-temperature series arguments and as\nwell as large-scale numerical full diagonalization results of thermodynamic\nquantities for SU($3$) and SU($4$) square lattice samples, corresponding to a\ntotal Hilbert space of up to $4\\times 10^9$ states."
    },
    {
        "anchor": "Simulation of Anderson localization in two-dimensional ultracold gases\n  for point-like disorder: Anderson localization has been observed for a variety of media, including\nultracold atomic gases with speckle disorder in one and three dimensions.\nHowever, observation of Anderson localization in a two-dimensional geometry for\nultracold gases has been elusive. We show that a cause of this difficulty is\nthe relatively high percolation threshold of a speckle potential in two\ndimensions, resulting in strong classical localization. We propose a realistic\npoint-like disorder potential that circumvents this percolation limit with\nlocalization lengths that are experimentally observable. The percolation\nthreshold is evaluated for experimentally realistic parameters, and a regime of\nnegligible classical trapping is identified. Localization lengths are\ndetermined via scaling theory, using both exact scattering cross sections and\nthe Born approximation, and by direct simulation of the time-dependent\nSchr\\\"{o}dinger equation. We show that the Born approximation can underestimate\nthe localization length by four orders of magnitude at low energies, while\nexact cross sections and scaling theory provide an upper bound. Achievable\nexperimental parameters for observing localization in this system are proposed.",
        "positive": "From cold Fermi fluids to the hot QGP: Strongly coupled quantum fluids are found in different forms, including\nultracold Fermi gases or tiny droplets of extremely hot Quark-Gluon Plasma.\nAlthough the systems differ in temperature by many orders of magnitude, they\nexhibit a similar almost inviscid fluid dynamical behavior. In this work, we\nsummarize some of the recent theoretical developments toward better\nunderstanding this property in cold Fermi gases at and near unitarity."
    },
    {
        "anchor": "Toolbox for Abelian lattice gauge theories with synthetic matter: Fundamental forces of Nature are described by field theories, also known as\ngauge theories, based on a local gauge invariance. The simplest of them is\nquantum electrodynamics (QED), which is an example of an Abelian gauge theory.\nSuch theories describe the dynamics of massless photons and their coupling to\nmatter. However, in two spatial dimension (2D) they are known to exhibit gapped\nphases at low temperature. In the realm of quantum spin systems, it remains a\nsubject of considerable debate if their low energy physics can be described by\nemergent gauge degrees of freedom. Here we present a class of simple\ntwo-dimensional models that admit a low energy description in terms of an\nAbelian gauge theory. We find rich phase diagrams for these models comprising\nexotic deconfined phases and gapless phases - a rare example for 2D Abelian\ngauge theories. The counter-intuitive presence of gapless phases in 2D results\nfrom the emergence of additional symmetry in the models. Moreover, we propose\nschemes to realize our model with current experiments using ultracold bosonic\natoms in optical lattices.",
        "positive": "Degenerate approach to the mean field Bose- Hubbard Hamiltonian: A degenerate variant of mean field perturbation theory for the on-site\nBose-Hubbard Hamiltonian is presented. We split the perturbation into two terms\nand perform exact diagonalization in the two-dimensional subspace corresponding\nto the degenerate states. The final relations for the second order ground state\nenergy and first order wave function do not contain singularities at integer\nvalues of the chemical potentials. The resulting equation for the phase\nboundary between superfluid and Mott states coincides with the prediction based\non the conventional mean field perturbation approach."
    },
    {
        "anchor": "From Few to Many: Observing the Formation of a Fermi Sea One Atom at a\n  Time: Knowing when a physical system has reached sufficient size for its\nmacroscopic properties to be well described by many-body theory is difficult.\nWe investigate the crossover from few to many-body physics by studying quasi\none-dimensional systems of ultracold atoms consisting of a single impurity\ninteracting with an increasing number of identical fermions. We measure the\ninteraction energy of such a system as a function of the number of majority\natoms for different strengths of the interparticle interaction. As we increase\nthe number of majority atoms one by one we observe the fast convergence of the\nnormalized interaction energy towards a many-body limit calculated for a single\nimpurity immersed in a Fermi sea of majority particles.",
        "positive": "Low-density expansions for the homogeneous dipolar Bose gas at zero\n  temperature: The low-density expansions for the energy, chemical potential, and condensate\ndepletion of the homogeneous dilute dipolar Bose gas are obtained by\nregularizing the dipole-dipole interaction at long distances. It is shown that\nthe leading term, proportional to the density, allows a simple physical\ninterpretation and consistently describes the thermodynamic stability of the\nsystem. The long-range asymptotics are obtained analytically for the normal and\nanomalous one-particle correlation functions and the pair distribution\nfunction. We discuss the properties of the two-body scattering with zero\nrelative momentum for the dipole-dipole interaction, in particular, we derive\nthe asymptotics of the wave function and a correction to the scattering length\nfor small values of the dipolar range. We show how the density expansions can\nbe derived within the Bogoliubov model of weakly interacting particles without\nany divergence from the assumption of universality of the expansions at low\ndensities."
    },
    {
        "anchor": "Stability and breakdown of Fermi polarons in a strongly interacting\n  Fermi-Bose mixture: We investigate the properties of a strongly interacting imbalanced mixture of\nbosonic $^{41}$K impurities immersed in a Fermi sea of ultracold $^6$Li atoms.\nThis enables us to explore the Fermi polaron scenario for large impurity\nconcentrations including the case where they form a Bose-Einstein condensate.\nThe system is characterized by means of radio-frequency injection spectroscopy\nand interspecies interactions are widely tunable by means of a\nwell-characterized Feshbach resonance. We find that the energy of the Fermi\npolarons formed in the thermal fraction of the impurity cloud remains rather\ninsensitive to the impurity concentration, even as we approach equal densities\nfor both species. The apparent insensitivity to high concentration is\nconsistent with a theoretical prediction, based on Landau's quasiparticle\ntheory, of a weak effective interaction between the polarons. The condensed\nfraction of the bosonic $^{41}$K gas is much denser than its thermal component,\nwhich leads to a break-down of the Fermi polaron description. Instead, we\nobserve a new branch in the radio-frequency spectrum with a small energy shift,\nwhich is consistent with the presence of Bose polarons formed by $^{6}$Li\nfermions inside the $^{41}$K condensate. A closer investigation of the behavior\nof the condensate by means of Rabi oscillation measurements support this\nobservation, indicating that we have realized Fermi and Bose polarons, two\nfundamentally different quasiparticles, in one cloud.",
        "positive": "Artificial Magnetic Fields in Momentum Space in Spin-Orbit Coupled\n  Systems: The Berry curvature is a geometrical property of an energy band which can act\nas a momentum space magnetic field in the effective Hamiltonian of a wide range\nof systems. We apply the effective Hamiltonian to a spin-1/2 particle in two\ndimensions with spin-orbit coupling, a Zeeman field and an additional harmonic\ntrap. Depending on the parameter regime, we show how this system can be\ndescribed in momentum space as either a Fock-Darwin Hamiltonian or a\none-dimensional ring pierced by a magnetic flux. With this perspective, we\ninterpret important single-particle properties, and identify analogue magnetic\nphenomena in momentum space. Finally we discuss the extension of this work to\nhigher spin systems, as well as experimental applications in ultracold atomic\ngases and photonic systems."
    },
    {
        "anchor": "Propagation of phase-imprinted solitons from superfluid core to\n  Mott-insulator shell and superfluid shell: We study phase-imprinted solitons of ultracold bosons in an optical lattice\nwith a harmonic trap, which shows the superfluid (SF) and Mott-insulator (MI)\nshell structures. The earlier study [Konstantin V. Krutitsky, J. Larson, and M.\nLewenstein, Phys. Rev. A 82, 033618 (2010).] reported three types of\nphase-imprinted solitons in the Bose-Hubbard model: in-phase soliton,\nout-of-phase soliton, and wavelet. In this paper, we uncover the dynamical\nphase diagram of these phase-imprinted solitons, and find another type of the\nphase-imprinted soliton namely, the hybrid soliton. In the harmonically trapped\nsystem, the solitonic excitations created at the SF core cannot penetrate into\nthe outer SF shell. This repulsion at the surface of the outer SF shell can be\ncured by inposing a repulsive potential at the center of the trap. These\nresults can be interpreted as a kind of the impedance matching of excitations\nin BECs in terms of the effective chemical potentials or the local particle\nnumbers in the shell, and the analogous results can be observed also in the\nsound wave created by the local single-shot pulse potential.",
        "positive": "Interaction driven exotic quantum phases in spin-orbit coupled spin$-1$\n  bosons: We study the interplay between large-spin, spin-orbit coupling, and\nsuperfluidity for bosons in a two dimensional optical lattice, focusing on the\nspin-1 spin-orbit coupled system recently realized at the Joint Quantum\nInstitute [Campbell et. al., arXiv:1501.05984]. We find a rich quantum phase\ndiagram, where, in addition to the conventional phases ---superfluid and\ninsulator--- contained in the spin-$1$ Bose-Hubbard model, there are new\nlattice symmetry breaking phases. For weak interactions, the interplay between\ntwo length scales, the lattice momentum and the spin-orbit wave-vector induce a\nphase transition from a uniform superfluid to a phase where bosons\nsimultaneously condense at the center and edge of the Brillouin zone at a\nnon-zero spin-orbit strength. This state is characterized by spin density wave\norder, which arises from the spin-$1$ nature of the system. Interactions\nsuppress spin density wave order, and favor a superfluid \\textit{only} at the\nBrillouin zone edge. This state has spatially oscillating mean field order\nparameters, but a homogeneous density. We show that the spin density wave\nsuperfluid phase survives in a two dimensional harmonic trap, and thus\nestablish that our results are directly applicable to experiments on $^{87}$Rb,\n$^7$Li, and $^{41}$K."
    },
    {
        "anchor": "Binary Mixture of quasi one dimensional dipolar Bose Einstein\n  Condensates with tilted dipoles: We consider a $^{168}$Er-$^{164}$Dy dipolar mixture, trapped by a cigar\nshaped harmonic potential. We derive the quasi-1D inter-species effective\npotential exhibiting the tilting angles and show that it is a quite natural\ngeneralization of the situation of a single dipolar gas. By solving the coupled\nGross-Pitaevskii equations, we observe a transition from miscible to immiscible\nmixture as the orientations of the magnetic moments are varied. The atom\nnumbers are also shown to lead to noticeable effects on the mixture.",
        "positive": "Moir\u00e9 super-lattice structures in kicked Bose-Einstein condensates: Vortex lattices in rapidly rotating Bose-Einstein condensates lead to a\nperiodic modulation of the superfluid density with a triangular symmetry. Here\nwe show that this symmetry can be combined with an external perturbation in\norder to create super-lattice structures with two or more periodicities.\nConsidering a condensate which is kicked by an optical lattice potential, we\nfind the appearance of transient moir\\'e lattice structures, which can be\nidentified using the kinetic energy spectrum."
    },
    {
        "anchor": "Topological growing of Laughlin states in synthetic gauge fields: We suggest a scheme for the preparation of highly correlated Laughlin (LN)\nstates in the presence of synthetic gauge fields, realizing an analogue of the\nfractional quantum Hall effect in photonic or atomic systems of interacting\nbosons. It is based on the idea of growing such states by adding weakly\ninteracting composite fermions (CF) along with magnetic flux quanta one-by-one.\nThe topologically protected Thouless pump (\"Laughlin's argument\") is used to\ncreate two localized flux quanta and the resulting hole excitation is\nsubsequently filled by a single boson, which, together with one of the flux\nquanta forms a CF. Using our protocol, filling 1/2 LN states can be grown with\nparticle number N increasing linearly in time and strongly suppressed number\nfluctuations. To demonstrate the feasibility of our scheme, we consider\ntwo-dimensional (2D) lattices subject to effective magnetic fields and strong\non-site interactions. We present numerical simulations of small lattice systems\nand discuss also the influence of losses.",
        "positive": "Collective modes of spin-orbit coupled Fermi gases in the repulsive\n  regime: We investigate the collective modes in the spin-orbit coupled Fermi gas with\nrepulsive s-wave interaction. The interplay between spin-orbit coupling and\natom-atom interactions plays the crucial role in the collective behaviors of\nFermi gas. In contrast with ordinary Fermi liquid, spin-orbit coupled Fermi gas\nhas strongly correlated spin and density excitations. Within the scheme of\nrandom phase approximation, we classify collective modes based on the symmetry\ngroup and determine their properties via the poles of corresponding correlation\nfunctions. Besides, the particle-hole continuum is obtained, where the\nimaginary part of these correlation functions become non-vanishing. We make\ncomparisons with collective excitations in the ordinary Fermi liquid without\nspin-orbit coupling and in a helical liquid, i.e., surface states of a three\ndimensional topological insulator. We also propose an experimental protocol for\ndetecting these collective modes and discuss corresponding experimental\nsignatures in the ultracold Fermi gases experiment."
    },
    {
        "anchor": "Universal thermodynamics of a two-dimensional Bose gas: Using renormalization-group arguments we show that the low-temperature\nthermodynamics of a three- or two-dimensional dilute Bose gas is fully\ndetermined by a universal scaling function $\\calF_d(\\mu/k_BT,\\tilde g(T))$ once\nthe mass $m$ and the s-wave scattering length $a_d$ of the bosons are known\n($d$ is the space dimension). Here $\\mu$ and $T$ denote the chemical potential\nand temperature of the gas, and the temperature-dependent dimensionless\ninteraction constant $\\tilde g(T)$ is a function of $ma_d^2k_BT/\\hbar^2$. We\ncompute the scaling function $\\calF_2$ using a nonperturbative\nrenormalization-group approach and find that both the $\\mu/k_BT$ and $\\tilde\ng(T)$ dependencies are in very good agreement with recent experimental data\nobtained for a quasi-two-dimensional Bose gas with or without optical lattice.\nWe also show that the nonperturbative renormalization-group estimate of the\nBerezinskii-Kosterlitz-Thouless transition temperature compares well with the\nresult obtained from a quantum Monte Carlo simulation of an effective classical\nfield theory.",
        "positive": "One-Dimensional Quantum Systems - From Few to Many Particles: In this thesis, I go through the well-known solutions to the one and\ntwo-particle systems trapped in a quantum harmonic oscillator and then continue\nto the three, four and many-body quantum systems. This is done by developing\nnew analytical models and numerical methods both for the few- and many-body\nsystems. One-dimensional systems are very interesting in a sense that particles\naligned on a line can only change seats by going through each other. This\nproperty can be exploited in the strongly interacting regime, where particles\nare forced to sit in a specific configuration, which can be easily manipulated.\nThe knowledge of how and where the particles are can be exploited in future\nquantum applications. In short, the thesis is about establishing a solid\nknowledge about everything that one needs to know about the one-dimensional\nfew- and many-component interacting quantum systems trapped in harmonic\noscillator potentials."
    },
    {
        "anchor": "Self-energy functional theory with symmetry breaking for disordered\n  lattice bosons: We extend the self-energy functional theory (SFT) to the case of interacting\nlattice bosons in the presence of symmetry breaking and quenched disorder. The\nself-energy functional we derive depends only on the self-energies of the\ndisorder-averaged propagators, allowing for the construction of general\nnon-perturbative approximations. Using a simple single-site reference system\nwith only three variational parameters, we are able to reproduce numerically\nexact quantum Monte Carlo (QMC) results on local observables of the\nBose-Hubbard model with box disorder with high accuracy. At strong\ninteractions, the phase boundaries are reproduced qualitatively but shifted\nwith respect to the ones observed with QMC due to the extremely low condensate\nfraction in the superfluid phase. Deep in the strongly-disordered\nweakly-interacting regime, the simple reference system employed is insufficient\nand no stationary solutions can be found within its restricted variational\nsubspace. By systematically analyzing thermodynamical observables and the\nspectral function, we find that the strongly-interacting Bose glass is\ncharacterized by different regimes, depending on which local occupations are\nactivated as a function of the disorder strength. We find that the particles\ndelocalize into isolated superfluid lakes over a strongly localized background\naround maximally-occupied sites whenever these sites are particularly rare. Our\nresults indicate that the transition from the Bose glass to the superfluid\nphase around unit filling at strong interactions is driven by the percolation\nof superfluid lakes which form around doubly occupied sites.",
        "positive": "Lattice gauge theories simulations in the quantum information era: The many-body problem is ubiquitous in the theoretical description of\nphysical phenomena, ranging from the behavior of elementary particles to the\nphysics of electrons in solids. Most of our understanding of many-body systems\ncomes from analyzing the symmetry properties of Hamiltonian and states: the\nmost striking example are gauge theories such as quantum electrodynamics, where\na local symmetry strongly constrains the microscopic dynamics. The physics of\nsuch gauge theories is relevant for the understanding of a diverse set of\nsystems, including frustrated quantum magnets and the collective dynamics of\nelementary particles within the standard model. In the last few years, several\napproaches have been put forward to tackle the complex dynamics of gauge\ntheories using quantum information concepts. In particular, quantum simulation\nplatforms have been put forward for the realization of synthetic gauge\ntheories, and novel classical simulation algorithms based on quantum\ninformation concepts have been formulated. In this review we present an\nintroduction to these approaches, illustrating the basics concepts and\nhighlighting the connections between apparently very different fields, and\nreport the recent developments in this new thriving field of research."
    },
    {
        "anchor": "Measuring the dynamic structure factor of a quantum gas undergoing a\n  structural phase transition: The dynamic structure factor is a central quantity describing the physics of\nquantum many-body systems, capturing structure and collective excitations of a\nmaterial. In condensed matter, it can be measured via inelastic neutron\nscattering, which is an energy-resolving probe for the density fluctuations. In\nultracold atoms, a similar approach could so far not be applied due to the\ndiluteness of the system. Here, we report on a direct, real-time and\nnon-destructive measurement of the dynamic structure factor of a quantum gas\nexhibiting cavity-mediated long-range interactions. The technique relies on\ninelastic scattering of photons, stimulated by the enhanced vacuum field inside\na high finesse optical cavity. We extract the density fluctuations, their\nenergy and lifetime while the system undergoes a structural phase transition.\nWe observe an occupation of the relevant quasi-particle mode on the level of a\nfew excitations, and provide a theoretical description of this dissipative\nquantum many-body system.",
        "positive": "Two-body relaxation of spin-polarized fermions in reduced\n  dimensionalities near a p-wave Feshbach resonance: We study inelastic two-body relaxation in a spin-polarized ultracold Fermi\ngas in the presence of a p-wave Feshbach resonance. It is shown that in reduced\ndimensionalities, especially in the quasi-one-dimensional case, the enhancement\nof the inelastic rate constant on approach to the resonance is strongly\nsuppressed compared to three dimensions. This may open promising paths for\nobtaining novel many-body states."
    },
    {
        "anchor": "Interaction and filling-induced quantum anomalous Hall effect in\n  ultra-cold neutral Bose-Fermi mixture on hexagonal lattice: We investigate the quantum anomalous Hall effect in a mixture of ultra-cold\nneutral bosons and fermions held on a hexagonal optical lattice. In the strong\natom-atom interaction limit, composite fermions composed of one fermion with\nbosons or bosonic holes in the mixture are formed. Such composite fermions have\nalready been generated successfully in experiment [Nat. Phys. {\\bf 7}, 642\n(2011)]. Here we predict that this kind of composite fermions may provide a\nrealization of the quantum anomalous Hall effect by tuning the atom-atom\ninteraction or the filling of the bosons in the mixture. We also discuss the\ncorresponding experimental signatures of the quantum anomalous Hall effect in\nthe Bose-Fermi mixture on hexagonal optical lattice.",
        "positive": "Projection operator approach to master equations for coarse grained\n  occupation numbers in non-ideal quantum gases: We aim at deriving an equation of motion for specific sums of momentum mode\noccupation numbers from models for electrons in periodic lattices experiencing\nelastic scattering, electron-phonon scattering or electron-electron scattering.\nThese sums correspond to \"grains\" in momentum space. This equation of motion is\nsupposed to involve only a moderate number of dynamical variables and/or\nexhibit a sufficiently simple structure such that neither its construction nor\nits analyzation/solution requires substantial numerical effort. To this we end\ncompute, by means of a projection operator technique, a linear(ized) collision\nterm which determines the dynamics of the above grain-sums. This collision term\nresults as non-singular, finite dimensional rate matrix and may thus be\ninverted regardless of any symmetry of the underlying model. This facilitates\ncalculations of, e.g., transport coefficients, as we demonstrate for a 3-dim.\nAnderson model featuring weak disorder."
    },
    {
        "anchor": "Quantum search with interacting Bose-Einstein condensates: One approach to the development of quantum search algorithms is the quantum\nwalk. A spatial search can be effected by the continuous-time evolution of a\nsingle quantum particle on a graph containing a marked site. In many physical\nimplementations, however, one might expect to have multiple particles. In\ninteracting bosonic systems at zero temperature, the dynamics is well-described\nby a discrete nonlinear Schrodinger equation. We investigate the role of\nnonlinearity in determining the efficiency of the spatial search algorithm\nwithin the quantum walk model, for the complete graph. The analytical\ncalculations reveal that the nonlinear search time scales with size of the\nsearch space N like the square root of N, equivalent to the linear case though\nwith a different overall constant. The results indicate that interacting\nBose-Einstein condensates at zero temperature could be natural systems for the\nimplementation of the quantum search algorithm.",
        "positive": "Many-Body Atomic Speed Sensor in Lattices: We study the properties of transmissivity of a beam of atoms traversing an\noptical lattices loaded with ultracold atoms. The transmission properties as\nfunction of the energy of the incident particles are strongly dependent on the\nquantum phase of the atoms in the lattice. In fact, in contrast to the\nMott-insulator regime, the absence of an energetic gap in the spectrum of the\nsuperfluid phase enables the atoms in the optical lattice to adapt to the\npresence of the beam. This induces a feedback process that has a strong impact\non the transmittivity of the atoms. Based on the corresponding strong\ndependency we propose the implementation of a speed sensor with and estimated\nsensitivity of $10^8 - 10^9$m/s/$\\sqrt{\\rm Hz}$, which we characterize via the\nFisher information. We apply our findings to a bosonic $Li-Rb$ mixture, which\nis relevant for experiments with ultracold atoms. Applications of the presented\nscheme are discussed."
    },
    {
        "anchor": "Dynamics and Bloch oscillations of mobile impurities in one-dimensional\n  quantum liquids: We study dynamics of a mobile impurity moving in a one-dimensional quantum\nliquid. Such an impurity induces a strong non-linear depletion of the liquid\naround it. The dispersion relation of the combined object, called depleton, is\na periodic function of its momentum with the period 2\\pi n, where n is the mean\ndensity of the liquid. In the adiabatic approximation a constant external force\nacting on the impurity leads to the Bloch oscillations of the impurity around a\nfixed position. Dynamically such oscillations are accompanied by the radiation\nof energy in the form of phonons. The ensuing energy loss results in the\nuniform drift of the oscillation center. We derive exact results for the\nradiation-induced mobility as well as the thermal friction force in terms of\nthe equilibrium dispersion relation of the dressed impurity (depleton). These\nresults show that there is a wide range of external forces where the (drifted)\nBloch oscillations exist and may be observed experimentally.",
        "positive": "Entanglement properties and ground-state statistics of free bosons: We calculate analytically the entanglement and R\\'enyi entropies, the\nnegativity and the mutual information together with all the density and\nmany-particle correlation functions for free bosons on a lattice in the ground\nstate, for both homogeneous and inhomogeneous systems. We show that all those\nquantities can be derived from a multinomial form of the reduced density matrix\nin the configuration space whose diagonal elements dictate the statistics of\nthe particle distribution, while the off-diagonal coherence terms control the\nquantum fluctuations. We provide by this analysis a unified approach based on a\nreduced density matrix technique useful to calculate both the entanglement\nproperties and an infinite number of correlation functions."
    },
    {
        "anchor": "$\u03c0$-junction and spontaneous current state in a superfluid Fermi gas: We discuss an idea to realize a spontaneous current in a superfluid Fermi\ngas. When a polarized Fermi superfluid ($N_\\up > N_\\dwn$, where $N_\\sigma$ is\nthe number of atoms in the hyperfine state described by pseudospin\n$\\sigma=\\uparrow, \\downarrow$.) is loaded onto a ring-shaped trap with a weak\npotential barrier, some of excess atoms ($\\Delta N=N_\\uparrow-N_\\downarrow$)\nare localized around the barrier. As shown in our previous paper [T. Kashimura,\nS. Tsuchiya, and Y. Ohashi, Phys. Rev. A \\textbf{82}, 033617 (2010)], this\npolarized potential barrier works as a $\\pi$-junction in the sense that the\nsuperfluid order parameter changes its sign across the barrier. Because of\nthis, the phase of the superfluid order parameter outside the junction is shown\nto be twisted by $\\pi$ along the ring, which naturally leads to a circulating\nsupercurrent. While the ordinary supercurrent state is obtained as a metastable\nstate, this spontaneous current state is shown to be more stable than the case\nwith no current. Our results indicate that localized excess atoms would be\nuseful for the manipulation of the superfluid order parameter in cold Fermi\ngases.",
        "positive": "Dynamics of first-order quantum phase transitions in extended\n  Bose-Hubbard model: From density wave to superfluid and vice-versa: In this paper, we study the nonequilibrium dynamics of the Bose-Hubbard model\nwith the nearest-neighbor repulsion by using time-dependent Gutzwiller (GW)\nmethods. In particular, we vary the hopping parameters in the Hamiltonian as a\nfunction of time, and investigate the dynamics of the system from the density\nwave (DW) to the superfluid (SF) crossing a first-order phase transition and\nvice-versa. From the DW to SF, we find scaling laws for the correlation length\nand vortex density with respect to the quench time. This is a reminiscence of\nthe Kibble-Zurek scaling for continuous phase transitions and contradicts the\ncommon expectation. We give a possible explanation for this observation. On the\nother hand from the SF to DW, the system evolution depends on the initial SF\nstate. When the initial state is the ground-state obtained by the static GW\nmethods, a coexisting state of the SF and DW domains forms after passing\nthrough the critical point. Coherence of the SF order parameter is lost as the\nsystem evolves. This is a phenomenon similar to the glass transition in\nclassical systems. When the state starts from the SF with small local phase\nfluctuations, the system obtains a large-size DW-domain structure with thin\ndomain walls."
    },
    {
        "anchor": "Quantum critical behavior influenced by measurement backaction in\n  ultracold gases: Recent realizations of quantum gas microscope offer the possibility of\ncontinuous monitoring of the dynamics of a quantum many-body system at the\nsingle-particle level. By analyzing effective non-Hermitian Hamiltonians of\ninteracting bosons in an optical lattice and continuum, we demonstrate that the\nbackaction of quantum measurement shifts the quantum critical point and gives\nrise to a unique critical phase beyond the terrain of the standard universality\nclass. We perform mean-field and strong-coupling-expansion analyses and show\nthat non-Hermitian contributions shift the superfluid--to-Mott-insulator\ntransition point. Using a low-energy effective field theory, we discuss\ncritical behavior of the one-dimensional interacting Bose gas subject to the\nmeasurement backaction. We derive an exact ground state of the effective\nnon-Hermitian Hamiltonian and find a unique critical behavior beyond the\nTomonaga-Luttinger liquid universality class. We propose experimental\nimplementations of post-selections using quantum gas microscopes to simulate\nthe non-Hermitian dynamics and argue that our results can be investigated with\ncurrent experimental techniques in ultracold atoms.",
        "positive": "Bose-Einstein condensation of photons in an optical microcavity: Bose-Einstein condensation, the macroscopic ground state accumulation of\nparticles with integer spin (bosons) at low temperature and high density, has\nbeen observed in several physical systems, including cold atomic gases and\nsolid state physics quasiparticles. However, the most omnipresent Bose gas,\nblackbody radiation (radiation in thermal equilibrium with the cavity walls)\ndoes not show this phase transition, because the chemical potential of photons\nvanishes and, when the temperature is reduced, photons disappear in the cavity\nwalls. Theoretical works have considered photon number conserving\nthermalization processes, a prerequisite for Bose-Einstein condensation, using\nCompton scattering with a gas of thermal electrons, or using photon-photon\nscattering in a nonlinear resonator configuration. In a recent experiment, we\nhave observed number conserving thermalization of a two-dimensional photon gas\nin a dye-filled optical microcavity, acting as a 'white-wall' box for photons.\nHere we report on the observation of a Bose-Einstein condensation of photons in\na dye-filled optical microcavity. The cavity mirrors provide both a confining\npotential and a non-vanishing effective photon mass, making the system formally\nequivalent to a two-dimensional gas of trapped, massive bosons. By multiple\nscattering off the dye molecules, the photons thermalize to the temperature of\nthe dye solution (room temperature). Upon increasing the photon density we\nobserve the following signatures for a BEC of photons: Bose-Einstein\ndistributed photon energies with a massively populated ground state mode on top\nof a broad thermal wing, the phase transition occurring both at the expected\nvalue and exhibiting the predicted cavity geometry dependence, and the ground\nstate mode emerging even for a spatially displaced pump spot."
    },
    {
        "anchor": "Persistent Currents in Ferromagnetic Condensates: Persistent currents in Bose condensates with a scalar order parameter are\nstabilized by the topology of the order parameter manifold. In condensates with\nmulticomponent order parameters it is topologically possible for supercurrents\nto `unwind' without leaving the manifold. We study the energetics of this\nprocess in the case of ferromagnetic condensates using a long wavelength energy\nfunctional that includes both the superfluid and spin stiffnesses. Exploiting\nanalogies to an elastic rod and rigid body motion, we show that the current\ncarrying state in a 1D ring geometry transitions between a spin helix in the\nenergy minima and a soliton-like configuration at the maxima. The relevance to\nrecent experiments in ultracold atoms is briefly discussed.",
        "positive": "Square wave oscillation of soliton in double-well potential trapped BEC: We numerically investigate the soliton tunnelling process in double-well\npotential trapped Bose-Einstein condensate. Comparing with the usual low energy\nfew particle tunnelling process, we find that the soliton tunnelling leads to\nmassive particle transport between two wells. The {population imbalance}\nbetween two wells is not evolving sinusoidally with the time as the Josephson\nplasma oscillation, but shows a higher density contrast square-wave pattern due\nto the reflections at the trapping potential boundaries. Such unusual behavior\nclearly demonstrates the topologically stable, localized nature of solitons\nthat propagate in a nonlinear medium without spreading. The square-wave\noscillation of soliton also provides measurable dynamics to define a qubit in\ncold altom system."
    },
    {
        "anchor": "Geometric Resonances in Bose-Einstein Condensates with Two- and\n  Three-Body Interactions: We investigate geometric resonances in Bose-Einstein condensates by solving\nthe underlying time-dependent Gross-Pitaevskii equation for systems with two-\nand three-body interactions in an axially-symmetric harmonic trap. To this end,\nwe use a recently developed analytical method [Phys. Rev. A 84, 013618 (2011)],\nbased on both a perturbative expansion and a Poincar\\'e-Lindstedt analysis of a\nGaussian variational approach, as well as a detailed numerical study of a set\nof ordinary differential equations for variational parameters. By changing the\nanisotropy of the confining potential, we numerically observe and analytically\ndescribe strong nonlinear effects: shifts in the frequencies and mode coupling\nof collective modes, as well as resonances. Furthermore, we discuss in detail\nthe stability of a Bose-Einstein condensate in the presence of an attractive\ntwo-body interaction and a repulsive three-body interaction. In particular, we\nshow that a small repulsive three-body interaction is able to significantly\nextend the stability region of the condensate.",
        "positive": "Cooling phonon modes of a Bose condensate with uniform few body losses: We present a general analysis of the cooling produced by losses on\ncondensates or quasi-condensates. We study how the occupations of the\ncollective phonon modes evolve in time, assuming that the loss process is slow\nenough so that each mode adiabatically follows the decrease of the mean\ndensity. The theory is valid for any loss process whose rate is proportional to\nthe $j$th power of the density, but otherwise spatially uniform. We cover both\nhomogeneous gases and systems confined in a smooth potential. For a\nlow-dimensional gas, we can take into account the modified equation of state\ndue to the broadening of the cloud width along the tightly confined directions,\nwhich occurs for large interactions. We find that at large times, the\ntemperature decreases proportionally to the energy scale $mc^2$, where $m$ is\nthe mass of the particles and $c$ the sound velocity. We compute the asymptotic\nratio of these two quantities for different limiting cases: a homogeneous gas\nin any dimension and a one-dimensional gas in a harmonic trap."
    },
    {
        "anchor": "Dynamics of phase separation in two species Bose-Einstein condensates\n  with vortices: We examine the dynamics associated with the miscibility-immiscibility\ntransition of trapped two-component Bose-Einstein condensates (TBECs) of dilute\natomic gases in presence of vortices. In particular, we consider TBECs of Rb\nhyperfine states, and Rb-Cs mixture. There is an enhancement of the\nphase-separation when the vortex is present in both condensates. In the case of\na singly charged vortex in only one of the condensates, there is enhancement\nwhen the vortex is present in the species which occupy the edges at\nphase-separation. But, suppression occurs when the vortex is in the species\nwhich occupies the core region. To examine the role of the vortex, we quench\nthe inter-species interactions to propel the TBEC from miscible to immiscible\nphase, and use the time dependent Gross-Pitaevskii equation to probe the\nphenomenon of phase-separation. We also examine the effect of higher charged\nvortex.",
        "positive": "Cold atoms in the presence of disorder: The review deals with the physics of cold atomic gases in the presence of\ndisorder. The emphasis is on the theoretical developments, although several\nexperiments are also briefly discussed. The review is intended to be\npedagogical, explaining the basics and, for some of the topics, presenting\nrather detailed calculations."
    },
    {
        "anchor": "Intermode-coupling modulation in the fermion-boson model: heating\n  effects in the BCS regime: Heating induced by an oscillating modulation of the interaction strength in\nan atomic Fermion pair condensate is analyzed. The coupled fermion-boson model,\ngeneralized by incorporating a time-dependent intermode coupling through a\nmagnetic Feshbach resonance, is applied. The dynamics is analytically\ncharacterized in a perturbative scheme. The results account for experimental\nfindings which have uncovered a damped and delayed response of the condensate\nto the modulation. The delay is due to the variation of the quasiparticle\nenergies and the subsequent relaxation of the condensate. The detected damping\nresults from the excitations induced by a nonadiabatic modulation: for driving\nfrequencies larger than twice the pairing gap, quasiparticles are generated,\nand, consequently, heating sets in.",
        "positive": "Floquet prethermalization in a Bose-Hubbard system: Periodic driving has emerged as a powerful tool in the quest to engineer new\nand exotic quantum phases. While driven many-body systems are generically\nexpected to absorb energy indefinitely and reach an infinite-temperature state,\nthe rate of heating can be exponentially suppressed when the drive frequency is\nlarge compared to the local energy scales of the system -- leading to\nlong-lived 'prethermal' regimes. In this work, we experimentally study a\nbosonic cloud of ultracold atoms in a driven optical lattice and identify such\na prethermal regime in the Bose-Hubbard model. By measuring the energy\nabsorption of the cloud as the driving frequency is increased, we observe an\nexponential-in-frequency reduction of the heating rate persisting over more\nthan 2 orders of magnitude. The tunability of the lattice potentials allows us\nto explore one- and two-dimensional systems in a range of different interacting\nregimes. Alongside the exponential decrease, the dependence of the heating rate\non the frequency displays features characteristic of the phase diagram of the\nBose-Hubbard model, whose understanding is additionally supported by numerical\nsimulations in one dimension. Our results show experimental evidence of the\nphenomenon of Floquet prethermalization, and provide insight into the\ncharacterization of heating for driven bosonic systems."
    },
    {
        "anchor": "Dark-bright solitons in spinor polariton condensates under nonresonant\n  pumping: Adopting a mean-field Gross-Pitaevskii description for a spinor polariton\nBose-Einstein condensates under non-resonant pumping, we investigate the static\nand dynamical properties of dark-bright solitons. We derive analytically the\nequation of motion for the center of mass of the dark-bright soliton center,\nusing the Hamiltonian approach. The resulting equation captures how the\ncombination of the open-dissipative character and the spin degrees of freedom\nof a polariton Bose-Einstein condensate affects the properties of a dark-bright\nsoliton, i.e. the dark-bright soliton relaxes by blending with the background\nat a finite time. In this case, we also determine the life time of the DB\nsoliton. Further numerical solutions of the modified dissipative two-component\nGross-Pitaevskii equations are in excellent agreement with the analytical\nresults. In presence of the Langevin noise, we demonstrate that the DB solitons\ncan still propagate for a long time, which is sufficient for their experimental\nobservations within current facilities.",
        "positive": "Asymmetric sequential Landau-Zener dynamics of Bose condensed atoms in a\n  cavity: We explore the asymmetric sequential Landau-Zener (LZ) dynamics in an\nensemble of interacting Bose condensed two-level atoms coupled with a cavity\nfield. Assuming the couplings between all atoms and the cavity field are\nidentical, the interplay between atom-atom interaction and detuning may lead to\na series of LZ transitions. Unlike the conventional sequential LZ transitions,\nwhich are symmetric to the zero detuning, the LZ transitions of Bose condensed\natoms in a cavity field are asymmetric and sensitively depend on the photon\nnumber distribution of the cavity. In LZ processes involving single excitation\nnumbers, both the variance of the relative atom number and the step slope of\nthe sequential population ladder are asymmetric, and the asymmetry become more\nsignificant for smaller excitation numbers. Furthermore, in LZ processes\ninvolving multiple excitation numbers, there may appear asymmetric population\nladders with decreasing step heights. During a dynamical LZ process, due to the\natom-cavity coupling, the cavity field shows dynamical collapse and revivals.\nIn comparison with the symmetric LZ transitions in a classical field, the\nasymmetric LZ transitions in a cavity field originate from the\nphoton-number-dependent Rabi frequency. The asymmetric sequential LZ dynamics\nof Bose condensed atoms in a cavity field may open up a new way to explore the\nfundamental many-body physics in coupled atom-photon systems."
    },
    {
        "anchor": "Coarsening dynamics of an isotropic ferromagnetic superfluid: In zero magnetic field the ground state manifold of a ferromagnetic spin-1\ncondensate is SO(3) and exhibits $\\mathbb{Z}_2$ vortices as topological\ndefects. We investigate the phase ordering dynamics of this system after being\nquenched into this ferromagnetic phase from a zero temperature unmagnetized\nphase. Following the quench, we observe the ordering of both magnetic and gauge\ndomains. We find that these domains grow diffusively, i.e. with domain size\n$L(t)\\sim t^{1/2}$, and exhibit dynamic scale invariance. The coarsening\ndynamics progresses as $\\mathbb{Z}_2$ vortices annihilate, however we find that\nat finite energy a number of these vortices persist in small clumps without\ninfluencing magnetic or gauge order. We consider the influence of a small\nnon-zero magnetic field, which reduces the ground state symmetry, and show that\nthis sets a critical length scale such that when the domains reach this size\nthe system dynamically transitions in order parameter and scaling behaviour\nfrom an isotropic to an anisotropic ferromagnetic superfluid.",
        "positive": "Geometrical quench and dynamical quantum phase transition in the\n  $\u03b1-T_3$ lattice: We investigate quantum quenches and the Loschmidt echo in the two\ndimensional, three band $\\alpha-T_3$ model, a close descendant of the dice\nlattice. By adding a chemical potential to the central site, the integral of\nthe Berry curvature of the bands in different valleys is continously tunable by\nthe ratio of the hopping integrals between the sublattices. By investigating\none and two filled bands, we find that dynamical quantum phase transition\n(DQPT), i.e. nonanalytical temporal behaviour in the rate function of the\nreturn amplitude, occurs for a certain range of parameters, independent of the\nband filling. By focusing on the effective low energy description of the model,\nwe find that DQPTs happen not only in the time derivative of the rate function,\nwhich is a common feature in two dimensional models, but in the rate function\nitself. This feature is not related to the change of topological properties of\nthe system during the quench, but rather follows from population inversion for\nall momenta. This is accompanied by the appearance of dynamical vortices in the\ntime-momentum space of the Pancharatnam geometric phase. The positions of the\nvortices form an infinite vortex ladder, i.e. a macroscopic phase structure,\nwhich allows us to identify the dynamical phases that are separated by the\nDQPT."
    },
    {
        "anchor": "A ship-in-a-bottle quantum gas microscope setup for magnetic mixtures: Quantum gas microscopes are versatile and powerful tools for fundamental\nscience as well as promising candidates for enticing applications such as in\nquantum simulation or quantum computation. Here we present a quantum gas\nmicroscopy setup for experiments with highly magnetic atoms of the lanthanoid\nelements erbium and dysprosium. Our setup features a non-magnetic,\nnon-conducting, large-working-distance, high-numerical-aperture, in-vacuum\nmicroscope objective, mounted inside a glue-free quartz glass cell. The quartz\nglass cell is enclosed by a compact multi-shell ferromagnetic shield that\npassively suppresses external magnetic field noise by a factor of more than a\nthousand. Our setup will enable direct manipulation and probing of the rich\nquantum many-body physics of dipolar atoms in optical lattices, and bears the\npotential to put exciting theory proposals -- including exotic magnetic phases\nand quantum phase transitions -- to an experimental test.",
        "positive": "Trapping of Bose-Einstein condensates in a three-dimensional dark focus\n  generated by conical refraction: We present an efficient three-dimensional dark-focus optical trapping\npotential for neutral atoms and Bose-Einstein condensates. This \"optical\nbottle\" is created by a single blue-detuned light field exploiting the\nphenomenon of conical refraction occurring in biaxial crystals. The conversion\nof a Gaussian input beam to the bottle beam has an efficiency of close to 100 %\nand the optical setup requires the addition of the biaxial crystal and a\ncircular polarizer only. Based on the conical-refraction theory, we derive the\ngeneral form of the potential, the trapping frequencies, and the potential\nbarrier heights. We present experiments on confining a $^{87}$Rb Bose-Einstein\ncondensate in three dimensions. We determine the trap shape, the vibrational\nfrequencies along the weak axis, as well as the lifetime of ultracold atoms in\nthis type of potential."
    },
    {
        "anchor": "Stability of ultracold atomic Bose condensates with Rashba spin-orbit\n  coupling against quantum and thermal fluctuations: We study the stability of Bose condensates with Rashba-Dresselhaus spin-orbit\ncoupling in three dimensions against quantum and thermal fluctuations. The\nground state depletion of the plane-wave condensate due to quantum fluctuations\nis, as we show, finite, and therefore the condensate is stable. We also\ncalculate the corresponding shift of the ground state energy. Although the\nsystem cannot condense in the absence of interparticle interactions, we show by\nestimating the number of excited particles that interactions stabilize the\ncondensate even at non-zero temperature. Unlike in the usual Bose gas, the\nnormal phase is not kinematically forbidden at any temperature; calculating the\nfree energy of the normal phase at finite temperature, and comparing with the\nfree energy of the condensed state, we infer that generally the system is\ncondensed at zero temperature, and undergoes a transition to normal at non-zero\ntemperature.",
        "positive": "Super Bloch oscillations with modulated interaction: We study super Bloch oscillations of ultracold atoms in a shaken lattice\npotential, subjected to a harmonically modulated mean-field interaction.\nUsually, any interaction leads to the decay of the wave packet and its super\nBloch oscillation. Here, we use the phases of interaction and shaking with\nrespect to the free Bloch oscillation as control parameters. We find two types\nof long-living cases: (i) suppression of the immediate broadening of the wave\npacket, and (ii) dynamical stability of all degrees of freedom. The latter\nrelies on the rather robust symmetry argument of cyclic time [Gaul et al.,\nPhys. Rev. A 84, 053627 (2011)]."
    },
    {
        "anchor": "Super-Bloch oscillations with parametric modulation of a parabolic trap: Super-Bloch oscillations are the outcome of a relative phase between Bloch\noscillations and modulations of the periodic lattice. We analyze the dynamics\nfor a model system in which such a relative phase is intrinsically present due\nto the position-dependent force provided by a parabolic trap and therefore an\nexternal detuning is not required. The relative phase is not unique and the\nrealized dynamics depends on the initial phase of the modulated parabolic\npotential. We provide accurate explanations for the different obtained\noscillatory transport and spreading regimes by analyzing the spatio-temporal\ndynamics in real space and by visualizing the relative phase in the k-space\ndynamics. We also compare our numerical results to an approximate semiclassical\nanalytical expression for the group velocity for a modulated constant force\nsystem and find good agreement for coherent oscillations but deviations for\noscillations with spreading dynamics which altogether supports the\ninterpretations of our findings.",
        "positive": "Observing phase jumps of solitons in Bose-Einstein condensates: The phase difference of the macroscopic wave function is a unique structure\nof the soliton in an atomic Bose--Einstein condensate (BEC). However,\nexperiments on ultracold atoms so far have observed the valley of the density\nprofile to study the dynamics of solitons. We propose a method to observe the\nphase difference of a soliton in a BEC by using an interference technique with\nRaman and rf pulses. We introduce a phase jump factor, which is an indicator to\nmeasure the phase difference between two points. It is demonstrated by using\nthe projected Gross--Pitaevskii equation that an interference density ratio,\nthe density ratio of two-component BECs after the Raman and rf pulses,\nreproduces the phase jump factor well. This technique will become an\nalternative method to study the decay and breakdown of a phase imprinted\nsoliton in atomic BECs."
    },
    {
        "anchor": "Thermomagnetic Anomalies by Magnonic Criticality in Ultracold Atomic\n  Transport: We investigate thermomagnetic transport in an ultracold atomic system with\ntwo ferromagnets linked via a magnetic quantum point contact. Using\nnonequilibrium Green's function approach, we show a divergence in spin\nconductance and a slowing down of spin relaxation that manifest in the weak\neffective-Zeeman-field limit. These anomalous spin dynamics result from the\nmagnonic critical point at which magnons become gapless due to spontaneous\nmagnetization. Our findings unveil untapped dynamics in ultracold atomic\nsystems, opening new avenues in thermomagnetism.",
        "positive": "Adiabatically compressing chiral p-wave Bose-Einstein condensates into\n  the lowest landau level: There has been much recent progress in controlling $p$-orbital degrees of\nfreedom in optical lattices, for example with lattice shaking, sublattice\nswapping, and lattice potential programming. Here, we present a protocol of\npreparing lowest Landau level (LLL) states of cold atoms by adiabatically\ncompressing $p$-orbital Bose-Einstein condensates confined in two-dimensional\noptical lattices. The system starts from a chiral $p+ip$ Bose-Einstein\ncondensate (BEC) state, which acquires finite angular momentum by spontaneous\nsymmetry breaking. Such chiral BEC states have been achieved in recent optical\nlattice experiments for cold atoms loaded in the $p$-bands. Through an\nadiabatic adjustment of the lattice potential, we compress the\nthree-dimensional BEC into a two-dimensional system, in which the orbital\ndegrees of freedom continuously morph into LLL states. This process is enforced\nby the discrete rotation symmetry of the lattice potential. The final quantum\nstate inherits large angular momentum from the original chiral $p+ip$ state,\nwith one quantized unit per particle. We investigate the quantum many-body\nground state of interacting bosons in the LLL considering contact repulsion.\nThis leads to an exotic gapped BEC state. Our theory can be readily tested in\nexperiments for the required techniques are all accessible to the current\noptical lattice experiments."
    },
    {
        "anchor": "Theoretical study of stimulated and spontaneous Hawking effects from an\n  acoustic black hole in a hydrodynamically flowing fluid of light: We propose an experiment to detect and characterize the analog Hawking\nradiation in an analog model of gravity consisting of a flowing\nexciton-polariton condensate. Under a suitably designed coherent pump\nconfiguration, the condensate features an acoustic event horizon for sound\nwaves that at the semiclassical level is equivalent to an astrophysical black\nhole horizon. We show that a continuous-wave pump-and-probe spectroscopy\nexperiment allows to measure the analog Hawking temperature from the dependence\nof the stimulated Hawking effect on the pump-probe detuning. We anticipate the\nappearance of an emergent resonant cavity for sound waves between the pump beam\nand the horizon, which results in marked oscillations on top of an overall\nexponential frequency dependence. We finally analyze the spatial correlation\nfunction of density fluctuations and identify the hallmark features of the\ncorrelated pairs of Bogoliubov excitations created by the spontaneous Hawking\nprocess, as well as novel signatures characterizing the emergent cavity.",
        "positive": "Ultrafast control of Rabi oscillations in a polariton condensate: We report the experimental observation and control of space and time-resolved\nlight-matter Rabi oscillations in a microcavity. Our setup precision and the\nsystem coherence are so high that coherent control can be implemented with\namplification or switching off of the oscillations and even erasing of the\npolariton density by optical pulses. The data is reproduced by a fundamental\nquantum optical model with excellent accuracy, providing new insights on the\nkey components that rule the polariton dynamics."
    },
    {
        "anchor": "Feedback Assisted Spin Dynamics in an Inhomogeneous Bias Magnetic Field: We study dynamics of spins in the presence of a feedback magnetic field. The\ninhomogeneity of the bias magnetic field results in that of the Larmor\nfrequencies of the spins. We find that the system exhibits rich nonlinear\ndynamics: beyond limit cycles which have been the focus of previous studies,\nquasi-periodic orbits and chaos emerge in a wide parameter space. The stable\nregions of each phases are determined analytically or numerically. We establish\nthe relation between the synchronization frequency of limit cycles and the\nfield inhomogeneity. Our results have important implications to precision\nmeasurement.",
        "positive": "Low Temperature Transport Properties of Very Dilute Classical Solutions\n  of $^3$He in Superfluid $^4$He: We report microscopic calculations of the thermal conductivity, diffusion\nconstant and thermal diffusion constant for classical solutions of $^3$He in\nsuperfluid $^4$He at temperatures $T \\la 0.6$~K, where phonons are the dominant\nexcitations of the $^4$He. We focus on solutions with $^3$He concentrations\n$\\la \\,10^{-3}$, for which the main scattering mechanisms are phonon-phonon\nscattering via 3-phonon Landau and Beliaev processes, which maintain the\nphonons in a drifting equilibrium distribution, and the slower process of\n$^3$He-phonon scattering, which is crucial for determining the $^3$He\ndistribution function in transport. We use the fact that the relative changes\nin the energy and momentum of a $^3$He atom in a collision with a phonon are\nsmall to derive a Fokker-Planck equation for the $^3$He distribution function,\nwhich we show has an analytical solution in terms of Sonine polynomials. We\nalso calculate the corrections to the Fokker-Planck results for the transport\ncoefficients."
    },
    {
        "anchor": "Thermal-induced Local Imbalance in Repulsive Binary Bose Mixtures: We study repulsive two-component Bose mixtures with equal populations and\nconfined in a finite-size box through path-integral Monte Carlo simulations.\nFor different values of the $s$-wave scattering length of the interspecies\npotential, we calculate the local population imbalance in a region of fixed\nvolume inside the box at different temperatures. We find two different\nbehaviors: for phase-separated states at $T=0$, thermal effects induce a\ndiffusion process which reduces the local imbalance whereas, for miscible\nstates at $T=0$, a maximum in the local population imbalance appears at a\ncertain temperature, below the critical one. We show that this intriguing\nbehavior is strongly related to the bunching effect associated with the\nBose-Einstein statistics of the particles in the mixture and to an unexpected\nbehavior of the cross pair distribution function not reported before.",
        "positive": "Dynamical effects of exchange symmetry breaking in mixtures of\n  interacting bosons: In a double-well potential, a Bose-Einstein condensate exhibits Josephson\noscillations or self-trapping, depending on its initial preparation and on the\nratio of inter-particle interaction to inter-well tunneling. Here, we elucidate\nthe role of the exchange symmetry for the dynamics with a mixture of two\ndistinguishable species with identical physical properties, i.e. which are\ngoverned by an isospecific interaction and external potential. In the\nmean-field limit, the spatial population imbalance of the mixture can be\ndescribed by the dynamics of a single species in an effective potential with\nmodified properties or, equivalently, with an effective total particle number.\nThe oscillation behavior can be tuned by populating the second species while\nmaintaining the spatial population imbalance and all other parameters constant.\nIn the corresponding many-body approach, the single-species description\napproximates the full counting statistics well also outside the realm of\nspin-coherent states. The method is extended to general Bose-Hubbard systems\nand to their classical mean-field limits, which suggests an effective\nsingle-species description of multicomponent Bose gases with weakly\nan-isospecific interactions."
    },
    {
        "anchor": "Direct Geometric Probe of Singularities in Band Structure: The band structure of a crystal may have points where two or more bands are\ndegenerate in energy and where the geometry of the Bloch state manifold is\nsingular, with consequences for material and transport properties. Ultracold\natoms in optical lattices have been used to characterize such points only\nindirectly, e.g., by detection of an Abelian Berry phase, and only at\nsingularities with linear dispersion (Dirac points). Here, we probe\nband-structure singularities through the non-Abelian transformation produced by\ntransport directly through the singular points. We prepare atoms in one Bloch\nband, accelerate them along a quasi-momentum trajectory that enters, turns, and\nthen exits the singularities at linear and quadratic touching points of a\nhoneycomb lattice. Measurements of the band populations after transport\nidentify the winding numbers of these singularities to be 1 and 2,\nrespectively. Our work opens the study of quadratic band touching points in\nultracold-atom quantum simulators, and also provides a novel method for probing\nother band geometry singularities.",
        "positive": "Thermometry of one-dimensional Bose gases with neural networks: We design a neural network to extract and process features from absorption\nimages taken of one-dimensional Bose gases in the quasi-condensate regime.\nSpecifically, the network is trained to predict both the temperature of single\nrealizations of the system and the uncertainty thereof. For multiple\nrealizations, the individual predictions can be combined in an estimate of the\nmean temperature, improving precision. We benchmark our model on both simulated\nand experimentally measured data and compare it to the established method of\ndensity ripples thermometry. We find the predictions of the two methods\ncompatible, although the neural network reaches similar precision needing much\nfewer realizations, thus highlighting the efficiency gain achievable when\nincorporating neural networks into analysis of data from cold gas experiments.\nFurther, we study feature maps to reveal which local features of the condensate\nare extracted by the network and how said features correlate with properties of\nthe system. A similar analysis could be employed to uncover physical relations\nin more complex systems."
    },
    {
        "anchor": "Quantum depletion and superfluid density of a supersolid in Raman\n  spin-orbit coupled Bose gases: We theoretically investigate a three-dimensional weakly interacting Bose gas\nwith one-dimensional Raman-type spin-orbit coupling at zero temperature. By\nemploying an improved ansatz, including high-order harmonics in the stripe\nphase, we show that the critical transition from the stripe to the plane-wave\nphases is shifted to a relatively larger Rabi frequency compared to the\nprediction by previous work [Li $\\textit{et al.}$, Phys. Rev. Lett.\n$\\textbf{108}$, 225301 (2012)] using a first-order stripe ansatz. We also\ndetermine the quantum depletion and superfluid density over a large range of\nRabi frequency in different phases. The depletion exhibits an intriguing\nbehavior with a discontinuous jump at the transition between the stripe and\nplane-wave phases, and a maximum at the transition between the plane-wave and\nzero-momentum phases. The superfluid density is derived through a phase-twist\nmethod. In the plane-wave and zero-momentum phases, it is significantly\nsuppressed along the spin-orbit-coupling direction and vanishes at the\ntransition, consistent with a recent work [Zhang $\\textit{et al.}$, Phys. Rev.\nA $\\textbf{94}$, 033635 (2016)], while in the stripe phase, it smoothly\ndecreases with increasing Rabi frequency. Our predictions would be useful for\nfurther theoretical and experimental studies of the exotic supersolid stripe\nphase.",
        "positive": "Quantum state manipulation and science of ultracold molecules: An increasingly large variety of molecular species are being cooled down to\nlow energies in recent years, and innovative ideas and powerful techniques\ncontinue to emerge to gain ever more precise control of molecular motion. In\nthis brief review we focus our discussions on two widely employed cooling\ntechniques that have brought molecular gases into the quantum regime:\nassociation of ultracold atomic gases into quantum gases of molecules and\ndirect laser cooling of molecules. These advances have brought into reality our\ncapability to prepare and manipulate both internal and external states of\nmolecules quantum mechanically, opening the field of cold molecules to a wide\nrange of scientific explorations."
    },
    {
        "anchor": "Resummation of infrared divergencies in the theory of atomic Bose gases: We present a general strong-coupling approach for the description of an\natomic Bose gas beyond the Bogoliubov approximation, when infrared divergences\nstart to occur that need to be resummed exactly. We consider the determination\nof several important physical properties of the Bose gas, namely the chemical\npotential, the contact, the speed of sound, the condensate density, the\neffective interatomic interaction and the three-body recombination rate. It is\nshown how the approach can be systematically improved with\nrenormalization-group methods and how it reduces to the Bogoliubov theory in\nthe weak-coupling limit.",
        "positive": "Quench dynamics of mass-imbalanced three-body fermionic systems in a\n  spherical trap: We consider a system of two identical fermions of general mass interacting\nwith a third distinguishable particle via a contact interaction within an\nisotropic three-dimensional harmonic trap. We calculate time-dependent\nobservables of the system after it is quenched in s-wave scattering length. To\ndo this we use exact closed form mass-imbalanced hyperspherical solutions to\nthe static three-body problem. These exact solutions enable us to calculate two\ntime-dependent observables, the Ramsey signal and particle separation, after\nthe system undergoes a quench from non-interacting to the unitary regime or\nvice-versa."
    },
    {
        "anchor": "Phase Separation and Dynamics of Two-component Bose-Einstein Condensates: We study the interactions between two atomic species in a binary\nBose-Einstein condensate to revisit the conditions for miscibility, oscillatory\ndynamics between the species, steady state solutions and their stability. By\nemploying a variational approach for a quasi one-dimensional, two-atomic\nspecies, condensate we obtain equations of motion for the parameters of each\nspecies: amplitude, width, position and phase. A further simplification leads\nto a reduction of the dynamics into a simple classical Newtonian system where\ncomponents oscillate in an effective potential with a frequency that depends on\nthe harmonic trap strength and the interspecies coupling parameter. We develop\nexplicit conditions for miscibility that can be interpreted as a phase diagram\nthat depends on the harmonic trap's strength and the interspecies species\ncoupling parameter. We numerically illustrate the bifurcation scenario whereby\nnon-topological, phase-separated states of increasing complexity emerge out of\na symmetric state, as the interspecies coupling is increased. The\nsymmetry-breaking dynamical evolution of some of these states is numerically\nmonitored and the associated asymmetric states are also explored.",
        "positive": "Gap solitons in elongated geometries: the one-dimensional\n  Gross-Pitaevskii equation and beyond: We report results of a systematic analysis of matter-wave gap solitons (GSs)\nin three-dimensional self-repulsive Bose-Einstein condensates (BECs) loaded\ninto a combination of a cigar-shaped trap and axial optical-lattice (OL)\npotential. Basic cases of the strong, intermediate, and weak radial\n(transverse) confinement are considered, as well as settings with shallow and\ndeep OL potentials. Only in the case of the shallow lattice combined with tight\nradial confinement, which actually has little relevance to realistic\nexperimental conditions, does the usual one-dimensional (1D) cubic\nGross-Pitaevskii equation (GPE) furnish a sufficiently accurate description of\nGSs. However, the effective 1D equation with the nonpolynomial nonlinearity,\nderived in Ref. [Phys. Rev. A \\textbf{77}, 013617 (2008)], provides for quite\nan accurate approximation for the GSs in all cases, including the situation\nwith weak transverse confinement, when the soliton's shape includes a\nconsiderable contribution from higher-order transverse modes, in addition to\nthe usual ground-state wave function of the respective harmonic oscillator.\nBoth fundamental GSs and their multipeak bound states are considered. The\nstability is analyzed by means of systematic simulations. It is concluded that\nalmost all the fundamental GSs are stable, while their bound states may be\nstable if the underlying OL potential is deep enough."
    },
    {
        "anchor": "Medium effects and the shear viscosity of the dilute Fermi gas away from\n  the conformal limit: We study the shear viscosity of a dilute Fermi gas as a function of the\nscattering length in the vicinity of the unitarity limit. The calculation is\nbased on kinetic theory, which provides a systematic approach to transport\nproperties in the limit in which the fugacity $z=n\\lambda^3/2$ is small. Here,\n$n$ is the density of the gas and $\\lambda$ is the thermal wave length of the\nfermions. At leading order in the fugacity expansion the shear viscosity is\nindependent of density, and the minimum shear viscosity is achieved at\nunitarity. At the next order medium effects modify the scattering amplitude as\nwell as the quasi-particle energy and velocity. We show that these effects\nshift the minimum of the shear viscosity to the Bose-Einstein condensation\n(BEC) side of the resonance, in agreement with the result of recent\nexperiments.",
        "positive": "Bragg Scattering as a Probe of Atomic Wavefunctions and Quantum Phase\n  Transitions in Optical Lattices: We have observed Bragg scattering of photons from quantum degenerate\n$^{87}$Rb atoms in a three-dimensional optical lattice. Bragg scattered light\ndirectly probes the microscopic crystal structure and atomic wavefunction whose\nposition and momentum width is Heisenberg-limited. The spatial coherence of the\nwavefunction leads to revivals in the Bragg scattered light due to the atomic\nTalbot effect. The decay of revivals across the superfluid to Mott insulator\ntransition indicates the loss of superfluid coherence."
    },
    {
        "anchor": "Exactly solvable tight-binding model on the RAN: fractal energy spectrum\n  and Bose-Einstein condensation: We initially consider a single-particle tight-binding model on the\nRegularized Apollonian Network (RAN). The RAN is defined starting from a\ntetrahedral structure with four nodes all connected (generation 0). At any\nsuccessive generations, new nodes are added and connected with the surrounding\nthree nodes. As a result, a power-law cumulative distribution of connectivity\n$P(k)\\propto {1}/{k^{\\eta}}$ with $\\eta=\\ln(3)/\\ln(2) \\approx 1.585$ is\nobtained.\n  The eigenvalues of the Hamiltonian are exactly computed by a recursive\napproach for any size of the network. In the infinite size limit, the density\nof states and the cumulative distribution of states (integrated density of\nstates) are also exactly determined. The relevant scaling behavior of the\ncumulative distribution close to the band bottom is shown to be power law with\nan exponent depending on the spectral dimension and not on the embedding\ndimension.\n  We then consider a gas made by an infinite number of non-interacting bosons\neach of them described by the tight-binding Hamiltonian on the RAN and we prove\nthat, for sufficiently large bosonic density and sufficiently small\ntemperature, a macroscopic fraction of the particles occupy the lowest\nsingle-particle energy state forming the Bose-Einstein condensate. We determine\nno only the transition temperature as a function of the bosonic density, but\nalso the fraction of condensed particle, the fugacity, the energy and the\nspecific heat for any temperature and bosonic density.",
        "positive": "Photo Reactions with Universal Trimers: Considering one-body and two-body currents, we study the photoassociation and\nphotodissociation of universal bosonic trimers. Analyzing the relative\nimportance of these currents we identify two physical scenarios (i) Normal\nhierarchy, where naive power counting holds and the one-body current dominates,\nand (ii) Strong hierarchy, where the one-body current is suppressed. For both\nscenarios we observe that at the high frequency tail, the response function\nexhibits log periodic oscillations in transition to or from any continuum state\nregardless of the reaction partial wave channel. In contrast, near threshold\nlog periodic oscillations appear only in the leading $s$-wave components. These\noscillations are the fingerprints of universal Efimov physics. We discuss the\nrelevance of this effect to contemporary experiments in ultracold atoms."
    },
    {
        "anchor": "Spatially Resolved Detection of a Spin-Entanglement Wave in a\n  Bose-Hubbard Chain: Entanglement is an essential property of quantum many-body systems. However,\nits local detection is challenging and was so far limited to spin degrees of\nfreedom in ion chains. Here we measure entanglement between the spins of atoms\nlocated on two lattice sites in a one-dimensional Bose-Hubbard chain which\nfeatures both local spin- and particle-number fluctuations. Starting with an\ninitially localized spin impurity, we observe an outwards propagating\nentanglement wave and show quantitatively how entanglement in the spin sector\nrapidly decreases with increasing particle-number fluctuations in the chain.",
        "positive": "Metastable quantum phase transitions in a periodic one-dimensional Bose\n  gas: II. Many-body theory: We show that quantum solitons in the Lieb-Liniger Hamiltonian are precisely\nthe yrast states. We identify such solutions clearly with Lieb's type II\nexcitations from weak to strong interactions, clarifying a long-standing\nquestion of the physical meaning of this excitation branch. We demonstrate that\nthe metastable quantum phase transition previously found in mean field analysis\nof the weakly-interacting Lieb-Liniger Hamiltonian [Phys. Rev. A {\\bf 79},\n063616 (2009)] extends into the medium- to strongly-interacting regime of a\nperiodic one-dimensional Bose gas. Our methods are exact diagonalization,\nfinite-size Bethe ansatz, and the boson-fermion mapping in the Tonks-Girardeau\nlimit."
    },
    {
        "anchor": "Three-body interaction effects on the ground state of one-dimensional\n  anyons: A quantum phase transition driven by the statistics was observed in an\nanyon-Hubbard model with local three-body interactions. Using a fractional\nJordan-Wigner transformation, we arrived at a modified Bose-Hubbard model,\nwhich exhibits Mott insulator and superfluid phases. The absence of a Mott\ninsulator state with one particle per site depends on the anyonic angle, and a\nquantum phase transition from a superfluid to a Mott insulator state is\nobtained for a fixed value of the hopping. The critical points were estimated\nwith the von Neumann block entropy and increase as the hopping grows. The\nstatistics modify the ground state, and three different superfluid regions were\nobserved for larger values of the anyonic angle.",
        "positive": "Measuring the dynamics of a first order structural phase transition\n  between two configurations of a superradiant crystal: We observe a structural phase transition between two configurations of a\nsuperradiant crystal by coupling a Bose-Einstein condensate to an optical\ncavity and applying imbalanced transverse pump fields. We find that this first\norder phase transition is accompanied by transient dynamics of the order\nparameter which we measure in real-time. The phase transition and the\nexcitation spectrum can be derived from a microscopic Hamiltonian in\nquantitative agreement with our experimental data."
    },
    {
        "anchor": "Incoherent charge transport in an organic polariton condensate: We study how polariton condensation modifies charge transport in organic\nmaterials. In typical organic materials, charge transport proceeds via\nincoherent hopping. We therefore provide an approach to determine how the rate\nand final state of this hopping process is affected by strong matter-light\ncoupling and polariton condensation. We show how the hopping process may create\nexcitations when starting from a state with a finite excitation density. That\nis, how hopping can change the state of a lower polariton condensate by\ncreating upper polaritons, optically inactive excitonic dark states, or by\nexciting vibrational sidebands. While the matrix elements for these processes\ncan be large, for typical materials at room temperature, such excitations are\nsuppressed by thermal factors, and ground state processes dominate. We thus\nstudy how the ground state hopping rate depends on condensate density,\nmatter-light coupling, and cavity photon detuning. All these factors change the\nvibrational configuration associated with the optically active molecules, which\ncan enhance or suppress hopping by increasing or decreasing the vibrational\noverlap with the state of a charged molecule. We show that hopping rates can be\nexponentially sensitive to detuning and condensate density, allowing an\nincrease or decrease of hopping rate by two orders of magnitude.",
        "positive": "Numerical calculation of Green's function and momentum distribution for\n  spin-polarized fermions by path integral molecular dynamics: Most recently, path integral molecular dynamics (PIMD) has been successfully\napplied to perform simulations of identical bosons and fermions by B. Hirshberg\net al.. In this work, we demonstrate that PIMD can be developed to calculate\nGreen's function and extract momentum distribution for spin-polarized fermions.\nIn particular, we show that the momentum distribution calculated by PIMD has\npotential application to numerous quantum systems, such as cold atom simulation\nof Mott insulator in Fermi-Hubbard model."
    },
    {
        "anchor": "Quantum Phase Transitions in a Dimerized Bose-Hubbard Model: A DMRG\n  Study: We investigate the phase diagram of a dimerized Bose-Hubbard model, using\ndensity matrix renormalization group technique. We find a new phase, which is\nthe coexistence of superfluid and bond-wave phases, due to the effect of\ndimerization. Experimentally dimerization in optical lattice can be realized by\nusing two counter propagating laser beams of different wavelengths. Apart from\nthe conventional superfluid to Mott insulator transition, we find a new quantum\nphase transition: from superfluid-bond-wave to Mott insulator-bond wave phase.\nOur study suggests a rich phase diagram which can be easily probed.",
        "positive": "Weakly bound states of two- and three-boson systems in the crossover\n  from two to three dimension: The spectrum and properties of quantum bound states is strongly dependent on\nthe dimensionality of space. How this comes about and how one may theoretically\nand experimentally study the interpolation between different dimensions is a\ntopic of great interest in different fields of physics. In this paper we study\nweakly bound states of non-relativistic two and three boson systems when\npassing continuously from a three (3D) to a two-dimensional (2D) regime within\na 'squeezed dimension' model. We use periodic boundary conditions to derive a\nsurprisingly simple form of the three-boson Schr{\\\"o}dinger equation in\nmomentum space that we solve numerically. Our results show a distinct\ndimensional crossover as three-boson states will either disappear into the\ncontinuum or merge with a 2D counterpart, and also a series of sharp\ntransitions in the ratios of three-body and two-body energies from being purely\n2D to purely 3D."
    },
    {
        "anchor": "Conformality Lost in Efimov Physics: A general mechanism for the loss of conformal invariance is the merger and\ndisappearance of an infrared fixed point and an ultraviolet fixed point of a\nrenormalization group flow. We show explicitly how this mechanism works in the\ncase of identical bosons at unitarity as the spatial dimension $d$ is varied.\nFor $d$ between the critical dimensions $d_{\\rm 1}=2.30$ and $d_{\\rm 2}=3.76$,\nthere is loss of conformality as evidenced by the Efimov effect in the\nthree-body sector. The beta function for an appropriate three-body coupling is\na quadratic polynomial in that coupling. For $d<d_{\\rm 1}$ and for $d>d_{\\rm\n2}$, the beta function has two real roots that correspond to infrared and\nultraviolet fixed points. As $d$ approaches $d_{\\rm 1}$ from below and as $d$\napproaches $d_{\\rm 2}$ from above, the fixed points merge and disappear into\nthe complex plane. For $d_{\\rm 1}<d<d_{\\rm 2}$, the beta function has complex\nroots and the renormalization group flow for the three-body coupling is a limit\ncycle.",
        "positive": "Background atoms and decoherence in optical lattices: All experiments with ultracold atoms are performed in the presence of\nbackground residual gas. With the help of a suitable master equation we\ninvestigate a role of these fast atoms on the loss of coherence in optical\nlattices. We present an exact solution of the master equation and give the\nanalytic formulas for all correlation functions in the presence of one body\nlosses. Additionally we discuss existing of a Schr\\\"odinger cat state predicted\nin this system in [1]."
    },
    {
        "anchor": "Visualizing the BEC-BCS crossover in the two-dimensional Fermi gas:\n  pairing gaps and dynamical response functions from ab initio computations: Experiments with ultracold atoms provide a highly controllable laboratory\nsetting with many unique opportunities for precision exploration of quantum\nmany-body phenomena. The nature of such systems, with strong interaction and\nquantum entanglement, makes reliable theoretical calculations challenging.\nEspecially difficult are excitation and dynamical properties, which are often\nthe most directly relevant to experiment. We carry out exact numerical\ncalculations, by Monte Carlo sampling of imaginary-time propagation of Slater\ndeterminants, to compute the pairing gap in the two-dimensional Fermi gas from\nfirst principles. Applying state-of-art analytic continuation techniques, we\nobtain the spectral function, and the density and spin structure factors\nproviding unique tools to visualize the BEC-BCS crossover. These quantities\nwill allow for a direct comparison with experiments.",
        "positive": "Efficient variational approach to the Fermi polaron problem in two\n  dimensions, both in and out of equilibrium: We develop a non-Gaussian variational approach that enables us to study both\nequilibrium and far-from-equilibrium physics of the two-dimensional Fermi\npolaron. This method provides an unbiased analysis of the polaron-to-molecule\nphase transition without relying on truncations in the total number of\nparticle-hole excitations. Our results -- which include the ground state energy\nand quasiparticle residue -- are in qualitative agreement with the known Monte\nCarlo calculations. The main advantage of the non-Gaussian states compared to\nconventional numerical methods is that they enable us to explore long-time\npolaron evolution and, in particular, study various spectral properties\naccessible to both solid-state and ultracold atom experiments. We design two\ntypes of radiofrequency spectroscopies to measure polaronic and molecular\nspectral functions. Depending on the parameter regime, we find that these\nspectral functions and fermionic density profiles near the impurity display\neither long-lived oscillations between the repulsive and attractive polaron\nbranches or exhibit fast relaxational dynamics to the molecular state."
    },
    {
        "anchor": "Spin dynamics of two bosons in an optical lattice site: a role of\n  anharmonicity and anisotropy of the trapping potential: We study a spin dynamics of two magnetic Chromium atoms trapped in a single\nsite of a deep optical lattice in a resonant magnetic field. Dipole-dipole\ninteractions couple spin degrees of freedom of the two particles to their\nmotion in the site. The motion is quantized, therefore a trap geometry combined\nwith two-body contact s-wave interactions influence a spin dynamics through the\nenergy spectrum of the two atom system. Anharmonicity and anisotropy of the\nsite results in a `fine' structure of two body eigenenergies. The structure can\nbe easily resolved by a weak magnetic dipole-dipole interactions. As an example\nwe examine the effect of anharmonicity and anisotropy of the binding potential\non the Einstein-de Haas effect. We show that the weak dipolar interactions\nprovide a perfect tool for a precision spectroscopy of the energy spectrum of\nthe interacting few particle system.",
        "positive": "Universal van der Waals Force Between Heavy Polarons in Superfluids: We investigate the long-range behavior of the induced Casimir interaction\nbetween two spinless heavy impurities, or polarons, in superfluid cold atomic\ngases. With the help of effective field theory (EFT) of a Galilean invariant\nsuperfluid, we show that the induced impurity-impurity potential at long\ndistance universally shows a relativistic van der Waals-like attraction ($\\sim\n1/r^7$) resulting from the exchange of two superfluid phonons. We also clarify\nfinite temperature effects from the same two-phonon exchange process. The\ntemperature $T$ introduces the additional length scale $c_s/T$ with the speed\nof sound $c_s$. Leading corrections at finite temperature scale as $T^6/r$ for\ndistances $r \\ll c_s/T$ smaller than the thermal length. For larger distances\nthe potential shows a nonrelativistic van der Waals behavior ($\\sim T/r^6$)\ninstead of the relativistic one. Our EFT formulation applies not only to weakly\ncoupled Bose or Fermi superfluids but also to that composed of strongly-coupled\nunitary fermions with a weakly coupled impurity. The sound velocity controls\nthe magnitude of the van der Waals potential, which we evaluate for the\nfermionic superfluid in the BCS-BEC crossover."
    },
    {
        "anchor": "Efimov physics from the functional renormalization group: Few-body physics related to the Efimov effect is discussed using the\nfunctional renormalization group method. After a short review of\nrenormalization in its modern formulation we apply this formalism to the\ndescription of scattering and bound states in few-body systems of identical\nbosons and distinguishable fermions with two and three components. The Efimov\neffect leads to a limit cycle in the renormalization group flow. Recently\nmeasured three-body loss rates in an ultracold Fermi gas $^6$Li atoms are\nexplained within this framework. We also discuss briefly the relation to the\nmany-body physics of the BCS-BEC crossover for two-component fermions and the\nformation of a trion phase for the case of three species.",
        "positive": "Monodromy and chaos for condensed bosons in optical lattices: We introduce a theory for the stability of a condensate in an optical\nlattice. We show that the understanding of the stability-to-ergodicity\ntransition involves the fusion of monodromy and chaos theory. Specifically, the\ncondensate can decay if a connected chaotic pathway to depletion is formed,\nwhich requires swap of seperatrices in phase-space."
    },
    {
        "anchor": "Stability change of a multi-charged vortex due to coupling with\n  quadrupole mode: We have studied collective modes of quasi-2D Bose-Einstein condensates with\nmultiply-charged vortices using a variational approach. Two of the four\ncollective modes considered exhibit coupling between the vortex dynamics and\nthe large-scale motion of the cloud. The vortex presence causes a shift in all\nfrequencies of collective modes even for the ones that do not couple\ndynamically with the vortex-core. The coupling between vortex and large-scale\ncollective excitations can induce the multi-charged vortex to decay into\nsingly-charged vortices with the quadrupole mode being one possible channel for\nsuch a decay. Therefore a thorough study was done about the possibility to\nprevent the vortex decay by applying a Gaussian potential with its width\nproportional to the vortex-core radius and varying its height. In such way, we\ncreated a stability diagram of height versus interaction strength which has\nstable regions due the static Gaussian potential. Furthermore, by using a\nsinusoidal time-modulation around the average height of the Gaussian potential,\nwe have obtained a diagram for the parametric resonance which can prevent the\nvortex decay in regions where static potential can not.",
        "positive": "Wannier functions using a discrete variable representation for optical\n  lattices: We propose a numerical method using the discrete variable representation\n(DVR) for constructing real-valued Wannier functions localized in a unit cell\nfor both symmetric and asymmetric periodic potentials. We apply these results\nto finding Wannier functions for ultracold atoms trapped in laser-generated\noptical lattices. Following Kivelson \\cite{kivelson_wannier_1982}, for a\nsymmetric lattice with inversion symmetry, we construct Wannier functions as\neigen states of the position operators $\\hat x$, $\\hat y$ and $\\hat z$\nrestricted to single-particle Bloch functions belonging to one or more bands.\nTo ensure that the Wannier functions are real-valued, we numerically obtain the\nband structure and real-valued eigen states using a uniform Fourier grid DVR.\nWe then show by a comparison of tunneling energies, that the Wannier functions\nare accurate for both inversion symmetric and asymmetric potentials to better\nthan ten significant digits when using double-precision arithmetic. The\ncalculations are performed for an optical lattice with double-wells per unit\ncell with tunable asymmetry along the $x$ axis and a single sinusoidal\npotential along the perpendicular directions. Localized functions at the two\npotential minima within each unit cell are similarly constructed, but using a\nsuperposition of single-particle solutions from the two lowest bands. We\nfinally use these localized basis functions to determine the two-body\ninteraction energies in the Bose-Hubbard (BH) model, and show the dependence of\nthese energies on lattice asymmetry."
    },
    {
        "anchor": "Imaginary time crystal of thermal quantum matter: Spontaneous symmetry breaking is responsible for rich quantum phenomena from\ncrystalline structures to superconductivity. This concept was boldly extended\nto the breaking of time translation, opening an avenue to finding exotic phases\nof quantum matter with collective time modulation and correlation. Here we\nreport that a thermally open quantum ensemble manifests in the dual space of\nimaginary time with crystalline ordering due to a bath-induced retarded\ninteraction. Exact quantum Monte Carlo simulations are performed to show that\nthis imaginary time crystal phase exhibits characteristic ground-state and\nthermal properties absent in conventional quantum manybody systems, especially\nthe striking temperature-oscillating behavior of its physical observables.",
        "positive": "Destabilization effect of exchange dipole-dipole interaction on the\n  spectrum of electric dipolar ultracold Fermi gas: The self-consistent field approach for the electric dipolar ultracold\nspin-1/2 fermions is discussed. Contribution of the exchange part of the\nelectric dipole interaction is found. Hence we obtain a model of dipolar\nfermions beyond the self-consistent field approximation. It is shown that the\nexchange interaction of electric dipolar fermions depends on the\nspin-polarisation of the system. For instance the electric dipole exchange\ninteraction equals to zero for spin-unpolarised systems, namely all low laying\nquantum states occupied by two-particles with opposite spins. In opposite limit\nof the full spin polarisation of the degenerate fermions, then we have one\nparticle in each quantum states, the exchange interaction has maximum value,\nwhich is comparable with the self-consistent field part of the dipole-dipole\ninteraction. The self-consistent part of the electric dipole-dipole interaction\ngives a positive contribution into the spectrum of collective excitations,\nwhile the exchange part of the dipole-dipole interaction leads to a negative\nterm in the spectrum. At angles between the equilibrium polarisation and the\ndirection of wave propagation close to $\\pi/2$ the full dipolar part of the\nspectrum becomes negative. At the electric dipole moment of fermions of order\nof several Debay the dipolar part is large enough to exceed the Fermi pressure,\nthat reveals in an instability."
    },
    {
        "anchor": "Effective two-mode model in Bose-Einstein condensates versus\n  Gross-Pitaevskii simulations: We study the dynamics of three-dimensional Bose-Einstein condensates confined\nby double-well potentials using a two-mode model with an effective on-site\ninteraction energy parameter. The effective on-site interaction energy\nparameter is evaluated for different numbers of particles ranging from a low\nexperimental value to larger ones approaching the Thomas-Fermi limit, yielding\nimportant corrections to the dynamics. We analyze the time periods as functions\nof the initial imbalance and find a closed integral form that includes all\ninteraction-driven parameters. A simple analytical formula for the\nself-trapping period is introduced and shown to accurately reproduce the exact\nvalues provided by the two-mode model. Systematic numerical simulations of the\nproblem in 3D demonstrate the excellent agreement of the two-mode model for\nexperimental parameters.",
        "positive": "Weakly Nonlinear Analysis of Vortex Formation in a Dissipative Variant\n  of the Gross-Pitaevskii Equation: For a dissipative variant of the two-dimensional Gross-Pitaevskii equation\nwith a parabolic trap under rotation, we study a symmetry breaking process that\nleads to the formation of vortices. The first symmetry breaking leads to the\nformation of many small vortices distributed uniformly near the Thomas-Fermi\nradius. The instability occurs as a result of a linear instability of a\nvortex-free steady state as the rotation is increased above a critical\nthreshold. We focus on the second subsequent symmetry breaking, which occurs in\nthe weakly nonlinear regime. At slightly above threshold, we derive a\none-dimensional amplitude equation that describes the slow evolution of the\nenvelope of the initial instability. We show that the mechanism responsible for\ninitiating vortex formation is a modulational instability of the amplitude\nequation. We also illustrate the role of dissipation in the symmetry breaking\nprocess. All analyses are confirmed by detailed numerical computations."
    },
    {
        "anchor": "Correlated quantum dynamics of graphene: Phase-space representations are a family of methods for dynamics of both\nbosonic and fermionic systems, that work by mapping the system's density matrix\nto a quasi-probability density and the Liouville-von Neumann equation of the\nHamiltonian to a corresponding density differential equation for the\nprobability. We investigate here the accuracy and the computational efficiency\nof one approximate phase-space representation, called the fermionic Truncated\nWigner Approximation (fTWA), applied to the Fermi-Hubbard model. On a many-body\n2D system, with hopping strength and Coulomb $U$ tuned to represent the\nelectronic structure of graphene, the method is found to be able to capture the\ntime evolution of first-order (site occupation) and second-order (correlation\nfunctions) moments significantly better than the mean-field, Hartree-Fock\nmethod. The fTWA was also compared to results from the exact diagonalization\nmethod for smaller systems, and in general the agreement was found to be good.\nThe fully parallel computational requirement of fTWA scales in the same order\nas the Hartree-Fock method, and the largest system considered here contained\n198 lattice sites.",
        "positive": "Dynamical Density Fluctuation of Superfluids near Critical Velocities: We propose a stability criterion of superfluids in condensed Bose-Einstein\nsystems, which incorporates the spectral function or the autocorrelation\nfunction of the local density. Within the Gross-Pitaevskii-Bogoliubov theory,\nwe demonstrate the validity of our criterion for the soliton-emission\ninstability, with use of explicit forms of zero modes of the Bogoliubov\nequation and a dynamical scaling near the saddle-node bifurcation. We also show\nthat the criterion is applicable to the Landau phonon instability and the\nLandau roton instability within the single-mode approximation."
    },
    {
        "anchor": "Pumping-assisted multistability of exciton-polariton condensates: We investigate the multistability of exciton-polariton condensates excited by\na nonresonant pump. An increase in pumping power moves the system away from\nnon-Hermitian spectral degeneracy towards spectrum splitting through an\nexceptional point, which induces a transition from monostability to\nmultistability. In the region of multistability, the system contains one steady\nand two metastable states. The analyses of stability show that metastable\nstates maintain a finite lifetime and eventually evolve to steady states. A\nsteady state with multi-peak soliton different from general single-peak soliton\nis discovered for attractive polariton-polariton interaction. Moreover, we\ndepict the diagram of the multistability in full parameter space to accurately\nmanipulate the multistability. Our results open up exciting possibilities for\ncontrolling non-Hermitian quantum multistable states, which may be useful to\ndesigning polariton-based devices exploiting optical multistability.",
        "positive": "Dissipative Quantum Vortices and Superradiant Scattering: Inspired by Analogue Gravity, superradiance has been previously investigated\nin Bose-Einstein condensates (BECs). In this work, we revisit this problem by\nintroducing dissipation to the system. After establishing the possibility of\nquantum vortices in dissipative BECs, we analyze the propagation of elementary\nexcitations and demonstrate the existence of superradiant modes which can be\ninterpreted in terms of the dissipation of ``antiparticles\". Our findings\nsupport the possibility of superradiant scattering around dissipative quantum\nvortices and paves the way for future experimental realization of the\nphenomenon."
    },
    {
        "anchor": "Deconfinement Dynamics of Fractons in Tilted Bose-Hubbard Chains: Fractonic constraints can lead to exotic properties of quantum many-body\nsystems. Here, we investigate the dynamics of fracton excitations on top of the\nground states of a one-dimemnsional, dipole-conserving Bose-Hubbard model. We\nshow that nearby fractons undergo a collective motion mediated by exchanging\nvirtual dipole excitations, which provides a powerful dynamical tool to\ncharacterize the underlying ground state phases. We find that in the gapped\nMott insulating phase, fractons are confined to each other as motion requires\nthe exchange of massive dipoles. When crossing the phase transition into a\ngapless Luttinger liquid of dipoles, fractons deconfine. Their transient\ndeconfinement dynamics scales diffusively and exhibits strong but subleading\ncontributions described by a quantum Lifshitz model. We examine prospects for\nthe experimental realization in tilted Bose-Hubbard chains by numerically\nsimulating the adiabatic state preparation and subsequent time evolution, and\nfind clear signatures of the low-energy fracton dynamics.",
        "positive": "Dilute Fluid Governed by Quantum Fluctuations: Understanding the effects of interactions in complex quantum systems beyond\nthe mean-field paradigm constitutes a fundamental problem in physics. Here, we\nshow how the atom numbers and interactions in a Bose-Bose mixture can be tuned\nto cancel mean-field interactions completely. The resulting system is entirely\ngoverned by quantum fluctuations -- specifically the Lee-Huang-Yang\ncorrelations. We derive an effective one-component Gross-Pitaevskii equation\nfor this system, which is shown to be very accurate by comparison with a full\ntwo-component description. This allows us to show how the Lee-Huang-Yang\ncorrelation energy can be accurately measured using two powerful probes of\natomic gases: collective excitations and radio-frequency spectroscopy.\nImportantly, the behavior of the system is robust against deviations from the\natom number and interaction criteria for canceling the mean-field interactions.\nThis shows that it is feasible to realize a setting where quantum fluctuations\nare not masked by mean-field forces, allowing investigations of the\nLee-Huang-Yang correction at unprecedented precision."
    },
    {
        "anchor": "Thermal friction on quantum vortices in a Bose-Einstein condensate: We investigate the dissipative dynamics of a corotating vortex pair in a\nhighly oblate axisymmetric Bose-Einstein condensate trapped in a harmonic\npotential. The initial vortex state is prepared by creating a doubly charged\nvortex at the center of the condensate and letting it dissociate into two\nsingly charged vortices. The separation of the vortex pair gradually increases\nover time and its increasing rate becomes higher with increasing the sample\ntemperature $T$. The evolution of the vortex state is well described with a\ndissipative point vortex model including longitudinal friction on the vortex\nmotion. For condensates of sodium atoms having a chemical potential of\n$\\mu\\approx k_B\\times 120$ nK, we find that the dimensionless friction\ncoefficient $\\alpha$ increases from 0.01 to 0.03 over the temperature range of\n200 nK $<T<$ 450 nK.",
        "positive": "Ultracold Gases of Ytterbium: Ferromagnetism and Mott States in an SU(6)\n  Fermi System: It is argued that ultracold quantum degenerate gas of ytterbium $^{173}$Yb\natoms having nuclear spin $I = 5/2$ exhibits an enlarged SU$(6)$ symmetry.\nWithin the Landau Fermi liquid theory, stability criteria against Fermi liquid\n(Pomeranchuk) instabilities in the spin channel are considered. Focusing on the\nSU$(n > 2)$ generalizations of ferromagnetism, it is shown within mean-field\ntheory that the transition from the paramagnet to the itinerant ferromagnet is\ngenerically first order. On symmetry grounds, general SU$(n)$ itinerant\nferromagnetic ground states and their topological excitations are also\ndiscussed. These SU$(n > 2)$ ferromagnets can become stable by increasing the\nscattering length using optical methods or in an optical lattice. However, in\nan optical lattice at current experimental temperatures, Mott states with\ndifferent filling are expected to coexist in the same trap, as obtained from a\ncalculation based on the SU$(6)$ Hubbard model."
    },
    {
        "anchor": "Spin Drag in a Bose Gas: It is well known that the charge current in a conductor is proportional to\nthe applied electric field. This famous relation, known as Ohm's law, is the\nresult of relaxation of the current due to charge carriers undergoing\ncollisions, predominantly with impurities and lattice vibrations in the\nmaterial. The field of spintronics, where the spin of the electron is\nmanipulated rather than its charge, has recently also led to interest in spin\ncurrents. Contrary to charge currents, these spin currents can be subject to\nstrong relaxation due to collisions between different spin species, a\nphenomenon known as spin drag. This effect has been observed for electrons in\nsemi-conductors\\cite{Weber} and for cold fermionic atoms, where in both cases\nit is reduced at low temperatures due to the fermionic nature of the particles.\nHere, we perform a transport experiment using ultra-cold bosonic atoms and\nobserve spin drag for bosons for the first time. By lowering the temperature we\nfind that spin drag for bosons is enhanced in the quantum regime due to Bose\nstimulation, which is in agreement with recent theoretical predictions. Our\nwork on bosonic transport shows that this field may be as rich as transport in\nsolid-state physics and may lead to the development of advanced devices in\natomtronics.",
        "positive": "Phase diffusion of a two-component Bose-Einstein condensates: exact and\n  short-time solutions for arbitrary coherent spin state: We investigate phase diffusion of a two-component Bose-Einstein condensates\nprepared initially in arbitrary coherent spin state $|\\theta_0,\\phi_0\\rangle$.\nAnalytical expression of the phase-diffusion time is presented for\n$\\theta_0\\neq\\pi/2$ case. In comparison with the symmetrical case (i.e.,\n$\\theta_0=\\pi/2$), we find that the diffusion process becomes slowly due to the\nreduced atom number variance."
    },
    {
        "anchor": "Finite-momentum Bose-Einstein condensates in shaken 2D square optical\n  lattices: We consider ultracold bosons in a 2D square optical lattice described by the\nBose-Hubbard model. In addition, an external time-dependent sinusoidal force is\napplied to the system, which shakes the lattice along one of the diagonals. The\neffect of the shaking is to renormalize the nearest-neighbor hopping\ncoefficients, which can be arbitrarily reduced, can vanish, or can even change\nsign, depending on the shaking parameter. It is therefore necessary to account\nfor higher-order hopping terms, which are renormalized differently by the\nshaking, and introduce anisotropy into the problem. We show that the\ncompetition between these different hopping terms leads to finite-momentum\ncondensates, with a momentum that may be tuned via the strength of the shaking.\nWe calculate the boundaries between the Mott-insulator and the different\nsuperfluid phases, and present the time-of-flight images expected to be\nobserved experimentally. Our results open up new possibilities for the\nrealization of bosonic analogs of the FFLO phase describing inhomogeneous\nsuperconductivity.",
        "positive": "Level structure of deeply bound levels of the $c^3\u03a3_g^+$ state of\n  $^{87}\\text{Rb}_2$: We spectroscopically investigate the hyperfine, rotational and Zeeman\nstructure of the vibrational levels $\\text{v}'=0$, $7$, $13$ within the\nelectronically excited $c^3\\Sigma_g^+$ state of $^{87}\\text{Rb}_2$ for magnetic\nfields of up to $1000\\,\\text{G}$. As spectroscopic methods we use short-range\nphotoassociation of ultracold Rb atoms as well as photoexcitation of ultracold\nmolecules which have been previously prepared in several well-defined quantum\nstates of the $a^3\\Sigma_u^+$ potential. As a byproduct, we present optical\ntwo-photon transfer of weakly bound Feshbach molecules into $a^3\\Sigma_u^+$,\n$\\text{v}=0$ levels featuring different nuclear spin quantum numbers. A simple\nmodel reproduces well the molecular level structures of the $c^3\\Sigma_g^+$\nvibrational states and provides a consistent assignment of the measured\nresonance lines. Furthermore, the model can be used to predict the relative\ntransition strengths of the lines. From fits to the data we extract for each\nvibrational level the rotational constant, the effective spin-spin interaction\nconstant, as well as the Fermi contact parameter and (for the first time) the\nanisotropic hyperfine constant. In an alternative approach, we perform\ncoupled-channel calculations where we fit the relevant potential energy curves,\nspin-orbit interactions and hyperfine functions. The calculations reproduce the\nmeasured hyperfine level term frequencies with an average uncertainty of\n$\\pm9\\:$MHz, similar as for the simple model. From these fits we obtain a\nsection of the potential energy curve for the $c^3\\Sigma_g^+$ state which can\nbe used for predicting the level structure for the vibrational manifold\n$\\text{v}'=0$ to $13$ of this electronic state."
    },
    {
        "anchor": "Nonlocal pair correlations in a higher-order Bose gas soliton: The truncated Wigner and positive-P phase-space representations are used to\nstudy the dynamics of a one-dimensional Bose gas. This allows calculations of\nthe breathing quantum dynamics of higher-order solitons with 10^{3}-10^{5}\nparticles, as in realistic Bose-Einstein condensation (BEC) experiments.\nAlthough classically stable, these decay quantum mechanically. Our calculations\nshow that there are large nonlocal correlations. These also violate the\nCauchy-Schwarz inequality, showing the presence of nonclassical quantum\nentanglement.",
        "positive": "Visualizing Anderson Localization in 3d using Monte Carlo method: We study the effect of Anderson localization on a Bose-Einstein condesate in\n3d in a disordered potential by Feynman-Kac path integral technique.\nSimulations are performed in continuous space using canonical ensemble. Owing\nto the high degree of control over the system parameters we also study the\ninterplay of disorder and interaction in the system. We numerically compute the\nlocalization length, mobility edge and the density profile of the condensate.\nWe observe that as the interaction strength increases, the wave functions\nbecome more and more delocalized."
    },
    {
        "anchor": "Simulating a quantum commensurate-incommensurate phase transition using\n  two Raman coupled one dimensional condensates: We study a transition between a homogeneous and an inhomogeneous phase in a\nsystem of one-dimensional, Raman tunnel-coupled Bose gases. The homogeneous\nphase shows a flat density and phase profile, whereas the inhomogeneous ground\nstate is characterized by periodic density ripples, and a soliton staircase in\nthe phase difference. We show that under experimentally viable conditions the\ntransition can be tuned by the wavevector difference $Q$ of the Raman beams and\ncan be described by the Pokrovsky-Talapov model for the relative phase between\nthe two condensates. Local imaging available in atom chip experiments allows to\nobserve the soliton lattice directly, while modulation spectroscopy can be used\nto explore collective modes, such as the phonon mode arising from breaking of\ntranslation symmetry by the soliton lattice. In addition, we investigate\nregimes where the cold atom experiment deviates from the Pokrovsky-Talapov\nfield theory. We predict unusual mesoscopic effects arising from the finite\nsize of the system, such as quantized injection of solitons upon increasing\n$Q$, or the system size. For moderate values of $Q$ above criticality, we find\nthat the density modulations in the two gases interplay with the relative phase\nprofile and introduce novel features in the spatial structure of the mode\nwave-functions. Using an inhomogeneous Bogoliubov theory, we show that spatial\nquantum fluctuations are intertwined with the emerging soliton staircase.\nFinally, we comment on the prospects of the ultra-cold atom setup as a tunable\nplatform studying quantum aspects of the Pokrovsky-Talapov theory in and\nout-of-equilibrium.",
        "positive": "Energy level statistics of interacting trapped bosons: It is an well established fact that statistical properties of energy level\nspectra are the most efficient tool to characterize nonintegrable quantum\nsystems. The study of statistical properties and spectral fluctuation in the\ninteracting many boson systems have developed a new interest in this direction.\nSpecially we are interested in the weakly interacting trapped bosons in the\ncontext of Bose-Einstein condensation (BEC) as the energy spectrum shows a\ntransition from the collective to single particle nature with the increase in\nthe number of levels. However this has received less attention as it is\nbelieved that the system may exhibit Poisson like fluctuations due to the\nexistence of external harmonic trap. Here we compute numerically the energy\nlevels of the zero-temperature many-boson systems which are weakly interacting\nthrough the van der Waals potential and are in the 3D confined harmonic\npotential. We study the nearest neighbour spacing distribution and the spectral\nrigidity by unfolding the spectrum. It is found that increase in number of\nenergy levels for repulsive BEC induces a transition from a Wigner like form\ndisplaying level repulsion to Poisson distribution for P(s). It does not follow\nthe GOE prediction. For repulsive interaction, the lower levels are correlated\nand manifest level repulsion. For intermediate levels P (s) shows mixed\nstatistic which clearly signifies the existence of two energy scales: external\ntrap and interatomic interaction. Whereas for very high levels the trapping\npotential dominates, genarating Poisson distribution. Comparison with\nmean-field results for lower levels are also presented. For attractive BEC near\nthe critical point we observe the Shrielman like peak near s=0 which signifies\nthe presence of large number of quasi-degenerate states."
    },
    {
        "anchor": "Attraction from frustration in ladder systems: We analyze the formation of multi-particle bound states in ladders with\nfrustrated kinetic energy in two component bosonic and two component fermionic\nsystems. We focus on the regime of light doping relative to insulating states\nat half-filling, spin polarization close to 100 percent, and strong repulsive\ninteractions. A special feature of these systems is that the binding energy\nscales with single particle tunneling $t$ rather than exchange interactions,\nsince effective attraction arises from alleviating kinetic frustration. For two\ncomponent Fermi systems on a zigzag ladder we find a bound state between a hole\nand a flipped spin (magnon) with a binding energy that can be as large as\n$0.6t$. We demonstrate that magnon-hole attraction leads to formation of\nclusters comprised of several holes and magnons and expound on\nantiferromagentic correlations for the transverse spin components inside the\nclusters. We identify several many-body states that result from\nself-organization of multi-particle bound states, including a Luttinger liquid\nof hole-magnon pairs and a density wave state of two hole - three magnon\ncomposites. We establish a symmetry between the spectra of Bose and Fermi\nsystems and use it to establish the existence of antibound states in two\ncomponent Bose mixtures with SU(2) symmetric repulsion on a zigzag ladder. We\nalso consider Bose and Fermi systems on a square ladder with flux and\ndemonstrate that both systems support bound states. We discuss experimental\nsignatures of multi-particle bound states in both equilibrium and dynamical\nexperiments. We point out intriguing connections between these systems and the\nquark bag model in QCD.",
        "positive": "Non-Equilibrium Mass Transport in the 1D Fermi-Hubbard Model: We experimentally and numerically investigate the sudden expansion of\nfermions in a homogeneous one-dimensional optical lattice. For initial states\nwith an appreciable amount of doublons, we observe a dynamical phase separation\nbetween rapidly expanding singlons and slow doublons remaining in the trap\ncenter, realizing the key aspect of fermionic quantum distillation in the\nstrongly-interacting limit. For initial states without doublons, we find a\nreduced interaction dependence of the asymptotic expansion speed compared to\nbosons, which is explained by the interaction energy produced in the quench."
    },
    {
        "anchor": "Hydrodynamic long-time tails after a quantum quench: After a quantum quench, a sudden change of parameters, generic many particle\nquantum systems are expected to equilibrate. A few collisions of quasiparticles\nare usually sufficient to establish approximately local equilibrium. Reaching\nglobal equilibrium is, however, much more difficult as conserved quantities\nhave to be transported for long distances to build up a pattern of fluctuations\ncharacteristic for equilibrium. Here we investigate the quantum quench of the\none-dimensional bosonic Hubbard model from infinite to finite interaction\nstrength U using semiclassical methods for weak, and exact diagonalization for\nstrong quenches. Equilibrium is approached only slowly, as t^{-1/2} with\nsubleading corrections proportional to t^{-3/4}, consistent with predictions\nfrom hydrodynamics. We show that these long-time tails determine the relaxation\nof a wide range of physical observables.",
        "positive": "Fermion-Mediated Interactions Between Bosonic Atoms: In high energy and condensed matter physics, particle exchange plays an\nessential role in the understanding of long-range interactions. For example,\nthe exchange of massive bosons leads to the Yukawa potential. Phonon exchange\nbetween electrons gives rise to Cooper pairing in superconductors. When a\nBose-Einstein condensate (BEC) of Cs is embedded in a degenerate Fermi gas of\nLi, we show that interspecies interactions can give rise to an effective\ntrapping potential, damping, and attractive boson-boson interactions mediated\nby fermions. The latter, related to the Ruderman-Kittel-Kasuya-Yosida (RKKY)\nmechanism, results from a coherent three-body scattering process. Such mediated\ninteractions are expected to form novel magnetic phases and supersolids. We\nshow that for suitable conditions, the mediated interactions can convert a\nstable BEC into a train of \"Bose-Fermi solitons\"."
    },
    {
        "anchor": "Time-of-flight patterns of ultra-cold bosons in optical lattices in\n  various Abelian artificial magnetic field gauges: We calculate the time-of-flight patterns of strongly interacting bosons\nconfined in two-dimensional square lattice in the presence of an artificial\nmagnetic field using quantum rotor model that is inherently combined with the\nBogolyubov approach. We consider various geometries of the magnetic flux, which\nare expected to be realizable, or have already been implemented in experimental\nsettings. The flexibility of the method let us to study cases of the artificial\nmagnetic field being uniform, staggered or forming a checkerboard\nconfiguration. Effects of additional temporal modulation of the optical\npotential that results from application of Raman lasers driving particle\ntransitions between lattice sites are also included. The presented\ntime-of-flight patterns may serve as a verification of chosen gauge in\nexperiments, but also provide important hints on unconventional, non-zero\nmomentum condensates, or possibility of observing graphene-like physics\nresulting from occurrence of Dirac cones in artificial magnetic fields in\nsystems of ultra-cold bosons in optical lattices. Also, we elucidate on\ndifferences between effects of magnetic field in solids and the artificial\nmagnetic field in optical lattices, which can be controlled on much higher\nlevel leading to effects not possible in condensed matter physics.",
        "positive": "Bright solitons in quasi-one dimensional dipolar condensates with\n  spatially modulated interactions: We introduce a model for the condensate of dipolar atoms or molecules, in\nwhich the dipole-dipole interaction (DDI) is periodically modulated in space,\ndue to a periodic change of the local orientation of the permanent dipoles,\nimposed by the corresponding structure of an external field (the necessary\nfield can be created, in particular, by means of magnetic lattices, which are\navailable to the experiment). The system represents a realization of a nonlocal\nnonlinear lattice, which has a potential to support various spatial modes. By\nmeans of numerical methods and variational approximation (VA), we construct\nbright one-dimensional solitons in this system, and study their stability. In\nmost cases, the VA provides good accuracy, and correctly predicts the stability\nby means of the Vakhitov-Kolokolov (VK)\\ criterion. It is found that the\nperiodic modulation may destroy some solitons, which exist in the usual setting\nwith unmodulated DDI, and can create stable solitons in other cases, not\nverified in the absence of modulations. Unstable solitons typically transform\ninto persistent localized breathers. The solitons are often mobile, with\ninelastic collisions between them leading to oscillating localized modes."
    },
    {
        "anchor": "Localization-delocalization transition of dipolar bosons in a four-well\n  potential: We study interacting dipolar atomic bosons in a four-well potential within a\nring geometry and outline how a four-site Bose-Hubbard (BH) model including\nnext-nearest-neighbor interaction terms can be derived for the above four-well\nsystem. We analyze the ground state of dipolar bosons by varying the strength\nof the interaction between particles in next-nearest-neighbor wells. We perform\nthis analysis both numerically and analytically by reformulating the\ndipolar-boson model within the continuous variable picture applied in [Phys.\nRev. A {\\bf 84}, 061601(R) (2011)]. By using this approach we obtain an\neffective description of the transition mechanism and show that when the\nnext-nearest-neighbor interaction crosses a precise value of the on-site\ninteraction, the ground state exhibits a change from the uniform state\n(delocalization regime) to a macroscopic two-pulse state, with strongly\nlocalized bosons (localization regime). These predictions are confirmed by the\nresults obtained by diagonalizing numerically the four-site BH Hamiltonian.",
        "positive": "Full counting statistics and phase diagram of a dissipative Rydberg gas: Ultra-cold gases excited to strongly interacting Rydberg states are a\npromising system for quantum simulations of many-body systems. For off-resonant\nexcitation of such systems in the dissipative regime, highly correlated\nmany-body states exhibiting, among other characteristics, intermittency and\nmulti-modal counting distributions are expected to be created. So far,\nexperiments with Rydberg atoms have been carried out in the resonant,\nnon-dissipative regime. Here we realize a dissipative gas of rubidium Rydberg\natoms and measure its full counting statistics for both resonant and\noff-resonant excitation. We find strongly bimodal counting distributions in the\noff-resonant regime that are compatible with intermittency due to the\ncoexistence of dynamical phases. Moreover, we measure the phase diagram of the\nsystem and find good agreement with recent theoretical predictions. Our results\npave the way towards detailed studies of many-body effects in Rydberg gases."
    },
    {
        "anchor": "Effective many-body parameters for atoms in non-separable Gaussian\n  optical potentials: We analyze the properties of particles trapped in three-dimensional\npotentials formed from superimposed Gaussian beams, fully taking into account\neffects of potential anharmonicity and non-separability. Although these effects\nare negligible in more conventional optical lattice experiments, they are\nessential for emerging ultracold atom developments. We focus in particular on\ntwo potentials utilized in current ultracold atom experiments: arrays of\ntightly focused optical tweezers and a one-dimensional optical lattice with\ntransverse Gaussian confinement and highly excited transverse modes. Our main\nnumerical tools are discrete variable representations (DVRs), which combine\nmany favorable features of spectral and grid-based methods, such as the\ncomputational advantage of exponential convergence and the convenience of an\nanalytical representation of Hamiltonian matrix elements. Optimizations, such\nas symmetry adaptations and variational methods built on top of DVR methods,\nare presented and their convergence properties discussed. We also present a\nquantitative analysis of the degree of non-separability of eigenstates,\nborrowing ideas from the theory of matrix product states (MPSs), leading to\nboth conceptual and computational gains. Beyond developing numerical\nmethodologies, we present results for construction of optimally localized\nWannier functions and tunneling and interaction matrix elements in optical\nlattices and tweezers relevant for constructing effective models for many-body\nphysics.",
        "positive": "Beyond Gross-Pitaevskii equation for 1D gas: quasiparticles and solitons: Describing properties of a strongly interacting quantum many-body system\nposes a serious challenge both for theory and experiment. In this work, we\nstudy excitations of one-dimensional repulsive Bose gas for arbitrary\ninteraction strength using a hydrodynamic approach. We use linearization to\nstudy particle (type-I) excitations and numerical minimization to study hole\n(type-II) excitations. We observe a good agreement between our approach and\nexact solutions of the Lieb-Liniger model for the particle modes and\ndiscrepancies for the hole modes. Therefore, the hydrodynamical equations find\nto be useful for long-wave structures like phonons and of a limited range of\napplicability for short-wave ones like narrow solitons. We discuss potential\nfurther applications of the method."
    },
    {
        "anchor": "Negative-mass effects in spin-orbit coupled Bose-Einstein condensates: Negative effective masses can be realised by engineering the dispersion\nrelation in a variety of quantum systems. A recent experiment with spin-orbit\ncoupled Bose-Einstein condensates has shown that a negative effective mass can\nhalt the free expansion of the condensate and produce fringes in the density\n[M. Khamehchi et al., Phys. Rev. Lett. 118, 155301 (2017)]. Here, we show that\nthe observed fringes are due to the negativity of only one of the two effective\nmass parameters that characterise the dispersion, which leads to previously\npredicted self-interference of the wave packet. We show how confgurations are\nnevertheless accessible to spin-orbit coupled Bose-Einstein condensates where\nboth mass parameters controlling the propagation and diffusion of the\ncondensate are negative, resulting in the novel phenomenon of\ncounter-propagating self-interfering packets.",
        "positive": "Comment on \"Excitation Spectrum and Superfluid Gap of an Ultracold Fermi\n  Gas\": We present simple arguments suggesting that H. Biss et al [PRL 128, 100401\n(2022)] did not measure with the required accuracy the low-wavenumber curvature\nof the acoustic excitation branch of the ground-state unitary Fermi gas. This\ndifficult-to-calculate quantity is crucial for the relaxation dynamics of the\ngas at low temperature."
    },
    {
        "anchor": "Finite temperature theory of superfluid bosons in optical lattices: A practical finite temperature theory is developed for the superfluid regime\nof a weakly interacting Bose gas in an optical lattice with additional harmonic\nconfinement. We derive an extended Bose-Hubbard model that is valid for shallow\nlattices and when excited bands are occupied. Using the\nHartree-Fock-Bogoliubov-Popov mean-field approach, and applying local density\nand coarse-grained envelope approximations, we arrive at a theory that can be\nnumerically implemented accurately and efficiently. We present results for a\nthree-dimensional system, characterizing the importance of the features of the\nextended Bose-Hubbard model and compare against other theoretical results and\nshow an improved agreement with experimental data.",
        "positive": "Majorana edge-modes in a spinful particle conserving model: We show the presence of Majorana edge modes in an interacting fermionic\nladder with spin in a number conserved setting. The interchain single particle\nhopping is suppressed and only a pair hopping is present between the different\nchains of the ladder. Additionally, the hopping along the chains is spin\nimbalanced and a transverse magnetic field is applied breaking time-reversal\ninvariance. We study the robustness of the topological phase with respect to an\non-site interaction between the spin-up and spin-down fermions and the spin\ndependent imbalance of the hopping. The main result of the present work is that\nthe topological phase survives for a finite region in the parameter space in\nthe presence of interactions. The localized Majorana edge modes seems to be\nmore stable in the case when the on-site interaction is an attraction."
    },
    {
        "anchor": "Gapless topological Fulde-Ferrell superfluidity induced by in-plane\n  Zeeman field: Topological superfluids are recently discovered quantum matters that host\ntopologically protected gapless edge states known as Majorana fermions - exotic\nquantum particles that act as their own anti-particles and obey non-Abelian\nstatistics. Their realizations are believed to lie at the heart of future\ntechnologies such as fault-tolerant quantum computation. To date, the most\nefficient scheme to create topological superfluids and Majorana fermions is\nbased on the Sau-Lutchyn-Tewari-Das Sarma model with a Rashba-type spin-orbit\ncoupling on the }\\textbf{\\textit{x-y}}\\textbf{ plane and a large out-of-plane\n(perpendicular) Zeeman field along the }\\textbf{\\textit{z}}\\textbf{-direction.\nHere we propose an alternative setup, where the topological superfluid phase is\ndriven by applying an in-plane Zeeman field. This scheme offers a number of new\nfeatures, notably Cooper pairings at finite centre-of-mass momentum (i.e.,\nFulde-Ferrell pairing) and gapless excitations in the bulk. As a result, a\nnovel gapless topological quantum matter with inhomogeneous pairing order\nparameter appears. It features unidirected Majorana surface states at\nboundaries, which propagate in the same direction and connect two Weyl nodes in\nthe bulk. We demonstrate the emergence of such an exotic topological matter and\nthe associated Majorana fermions in spin-orbit coupled atomic Fermi gases and\ndetermine its parameter space. The implementation of our scheme in\nsemiconductor/superconductor heterostructures is briefly discussed.",
        "positive": "Atomic momentum patterns with narrower interval: We studied the atomic momentum distribution for a superposition of Bloch\nstates spreading in the lowest band of an optical lattice after the action of\nthe standing wave pulse. By designing the imposing pulse on this superposed\nstate, an atomic momentum pattern appears with narrower interval between the\nadjacent peaks that can be far less than the double recoil momentum. The\npatterns with narrower interval come from the superposition of the action of\nthe designed pulse on many Bloch states with quasi-momenta over the first\nBrillouin zone, where for each quasi-momentum there is an interference among\nseveral lowest bands. Our experimental result of narrow interval peaks is\nconsistent with the theoretical simulation. The patterns of multi modes with\ndifferent quasi-momenta are helpful for precise measurement and atomic\nmanipulation."
    },
    {
        "anchor": "What can we learn from the experiment of electrostatic conveyer for\n  excitons?: Motivated by the experiment of electrostatic conveyer for indirect excitons\n[A. G. Winbow, et al., Phys. Rev. Lett. 106, 196806 (2011)], we studied the\nexciton patterns to understand the exciton dynamics. By analyzing the exciton\ndiffusion, we found that the patterns were from two kinds of excitons\napproximately. The patterns near the laser spot came from the hot excitons\nwhich can be taken as classical particles. However, the patterns far from the\nlaser spot were formed by the cooled excitons or coherent excitons. Considering\nthe Bosonic excitons with the limited lifetime and the interactions, we set up\na time-dependent nonlinear Schr\\\"odinger equation including the non-Hermitian\ndissipation to depict the coherent exciton dynamics. The real-time and\nimaginary-time evolutions were used alternately to solve the Schr\\\"odinger\nequation to study the exciton diffusion accompanied by the exciton cooling in\nthe moving lattices. By calculating the escape probability, we got\ntheoretically the transport distances of the coherent excitons in the conveyer\nwhich is consistent with the experimental data. The exciton cooling speed was\nfound to be the key element to the coherent exciton transport. Moreover, the\nplateau in the average transport distance as a function of the conveyer\namplitude cannot be explained by the dynamical localization-delocalization\ntransition due to the disorder.",
        "positive": "Semiclassics in a system without classical limit: The few-body spectrum\n  of two interacting bosons in one dimension: We present a semiclassical study of the spectrum of a few-body system\nconsisting of two short-range interacting bosonic particles in one dimension, a\nparticular case of a general class of integrable many-body systems where the\nenergy spectrum is given by the solution of algebraic transcendental equations.\nBy an exact mapping between $\\delta$-potentials and boundary conditions on the\nfew-body wave functions, we are able to extend previous semiclassical results\nfor single-particle systems with mixed boundary conditions to the two-body\nproblem. The semiclassical approach allows us to derive explicit analytical\nresults for the smooth part of the two-body density of states that are in\nexcellent agreement with numerical calculations. It further enables us to\ninclude the effect of bound states in the attractive case. Remarkably, for the\nparticular case of two particles in one dimension, the discrete energy levels\nobtained through a requantization condition of the smooth density of states are\nessentially in perfect agreement with the exact ones."
    },
    {
        "anchor": "Intrinsic decoherence and recurrences in a large ferromagnetic $F = 1$\n  spinor Bose-Einstein condensate: Decoherence with recurrences appear in the dynamics of the one-body density\nmatrix of an $F = 1$ spinor Bose-Einstein condensate, initially prepared in\ncoherent states, in the presence of an external uniform magnetic field and\nwithin the single mode approximation. The phenomenon emerges as a many-body\neffect of the interplay of the quadratic Zeeman effect, that breaks the\nrotational symmetry, and the spin-spin interactions. By performing full quantum\ndiagonalizations very accurate time evolution of large condensates are\nanalyzed, leading to heuristic analytic expressions for the time dependence of\nthe one-body density matrix, in the weak and strong interacting regimes, for\ninitial coherent states. We are able to find accurate analytical expressions\nfor both the decoherence and the recurrence times, in terms of the number of\natoms and strength parameters, that show remarkable differences depending on\nthe strength of the spin-spin interactions. The features of the stationary\nstates in both regimes is also investigated. We discuss the nature of these\nlimits in the light of the thermodynamic limit.",
        "positive": "Artificial atoms from cold bosons in one dimension: We investigate the ground-state properties of weakly repulsive\none-dimensional bosons in the presence of an attractive zero-range impurity\npotential. First, we derive mean-field solutions to the problem on a finite\nring for the two asymptotic cases: (i) all bosons are bound to the impurity and\n(ii) all bosons are in a scattering state. Moreover, we derive the critical\nline that separates these regimes in the parameter space. In the thermodynamic\nlimit, this critical line determines the maximum number of bosons that can be\nbound by the impurity potential, forming an artificial atom. Second, we\nvalidate the mean-field results using the flow equation approach and the\nmulti-layer multi-configuration time-dependent Hartree method for atomic\nmixtures. While beyond-mean-field effects destroy long-range order in the Bose\ngas, the critical boson number is unaffected. Our findings are important for\nunderstanding such artificial atoms in low-density Bose gases with static and\nmobile impurities."
    },
    {
        "anchor": "Solvable model of a generic driven mixture of trapped Bose-Einstein\n  condensates and properties of a many-boson Floquet state at the limit of an\n  infinite number of particles: A solvable model of a periodically-driven trapped mixture of Bose-Einstein\ncondensates, consisting of $N_1$ interacting bosons of mass $m_1$ driven by a\nforce of amplitude $f_{L,1}$ and $N_2$ interacting bosons of mass $m_2$ driven\nby a force of amplitude $f_{L,2}$, is presented. The model generalizes the\nharmonic-interaction model for mixtures to the time-dependent domain. The\nresulting many-particle ground Floquet wavefunction and quasienergy, as well as\nthe time-dependent densities and reduced density matrices, are prescribed\nexplicitly and analyzed at the many-body and mean-field levels of theory for\nfinite systems and at the limit of an infinite number of particles. We prove\nthat the time-dependent densities per particle are given at the limit of an\ninfinite number of particles by their respective mean-field quantities, and\nthat the time-dependent reduced one-particle and two-particle density matrices\nper particle of the driven mixture are $100\\%$ condensed. Interestingly, the\nquasienergy per particle {\\it does not} coincide with the mean-field value at\nthis limit, unless the relative center-of-mass coordinate of the two\nBose-Einstein condensates is not activated by the driving forces $f_{L,1}$ and\n$f_{L,2}$. As an application, we investigate the imprinting of angular momentum\nand its fluctuations when steering a Bose-Einstein condensate by an interacting\nbosonic impurity, and the resulting modes of rotations. Whereas the expectation\nvalues per particle of the angular-momentum operator for the many-body and\nmean-field solutions coincide at the limit of an infinite number of particles,\nthe respective fluctuations can differ substantially. The results are analyzed\nin terms of the transformation properties of the angular-momentum operator\nunder translations and boosts and the interactions between the particles.\nImplications are briefly discussed.",
        "positive": "Complex phases in the doped two-species bosonic Hubbard Model: We study a two-dimensional bosonic Hubbard model with two hard-core species\naway from half filling using Quantum Monte Carlo simulations. The model\nincludes a repulsive interspecies interaction and different nearest-neighbor\nhopping terms for the two species. By varying the filling we find a total of\nfive distinct phases, including a normal liquid phase at higher temperature,\nand four different phases at lower temperature. We find an\nanti-ferromagnetically ordered Mott insulator and a region of coexistent\nanti-ferromagnetic and superfluid phases near half filling. Further away from\nhalf filling the phase diagram displays a superfluid phase and a novel phase\ninside the superfluid region at even lower temperatures. In this novel phase\nseparated region, the heavy species has a Mott behavior with integer filling,\nwhile the lighter species shows phase separated Mott and superfluid behaviors."
    },
    {
        "anchor": "Expansion dynamics of a shell-shaped Bose-Einstein condensate: Bose-Einstein condensates (BECs) confined on shell-shaped surfaces have been\nproposed as a platform for exploring many nontrivial quantum phenomena on\ncurved spaces. However, as the shell-shaped trapping potential generated with\nthe conventional radio frequency dressing method is very sensitive to gravity,\nso far experimental studies of shell BECs can only be performed in\nmicro-gravity environments. Here, we overcome this difficulty and create a\nshell BEC in the presence of Earth's gravity with immiscible dual-species BECs\nof sodium and rubidium atoms. After minimizing the displacement between the\ncenters of mass of the two BECs with a magic-wavelength optical dipole trap,\nthe interspecies repulsive interaction ensures the formation of a closed shell\nof sodium atoms with its center filled by rubidium atoms. Releasing the double\nBEC together from the trap, we observe explosion of the filled shell\naccompanied by energy transfer from the inner BEC to the shell BEC. With the\ninner BEC removed, we obtain a hollow shell BEC which shows self-interference\nas a manifestation of implosion. Our results pave an alternative way for\ninvestigating many of the intriguing physics offered by shell BECs.",
        "positive": "The Effective Single-mode model of a Binary Boson Mixture in the Quantum\n  Droplet Region: In a binary quantum droplet, the interspecies attraction dominates over the\nintraspecies repulsions and the mean-field energy is unstable. The mechanical\nstability is restored by the repulsive Lee-Huang-Yang (LHY) energy [1]. In the\nBogoliubov theory of the binary quantum droplet, there are two branches of\ngapless excitations. The lower branch describes the phonon excitation and its\nenergy is imaginary in the long-wavelength limit, implying dynamical\ninstability. Recently it is found that the phonon energy is renormalized by\nhigher-order quantum fluctuations and the dynamical instability is removed [2].\nIn this work, we study a binary quantum droplet in the path integral formalism\nto construct an effective model with the correct phonon energy. By integrating\nout the upper excitation branch, we obtain an effective single-mode model\ndescribing density fluctuations, and derive the extended Gross-Pitaevskii\nequation. In this approach, the LHY energy in the extended-GP equation is\npurely positive without any assumption of neglecting the imaginary part. This\neffective single-mode model can be also used outside and close to the quantum\ndroplet region such as in the LHY gas."
    },
    {
        "anchor": "Angular self-localization of impurities rotating in a bosonic bath: The existence of a self-localization transition in the polaron problem has\nbeen under an active debate ever since Landau suggested it 83 years ago. Here\nwe reveal the self-localization transition for the rotational analogue of the\npolaron -- the angulon quasiparticle. We show that, unlike for the polarons,\nself-localization of angulons occurs at finite impurity-bath coupling already\nat the mean-field level. The transition is accompanied by the\nspherical-symmetry breaking of the angulon ground state and a discontinuity in\nthe first derivative of the ground-state energy. Moreover, the type of the\nsymmetry breaking is dictated by the symmetry of the microscopic impurity-bath\ninteraction, which leads to a number of distinct self-localized states. The\npredicted effects can potentially be addressed in experiments on cold molecules\ntrapped in superfluid helium droplets and ultracold quantum gases, as well as\non electronic excitations in solids and Bose-Einstein condensates.",
        "positive": "Correlation induced localization of lattice trapped bosons coupled to a\n  Bose-Einstein condensate: We investigate the ground state properties of a lattice trapped bosonic\nsystem coupled to a Lieb-Liniger type gas. Our main goal is the description and\nin depth exploration and analysis of the two-species many-body quantum system\nincluding all relevant correlations beyond the standard mean-field approach. To\nachieve this, we use the Multi-Configuration Time-Dependent Hartree method for\nMixtures (ML-MCTDHX). Increasing the lattice depth and the interspecies\ninteraction strength, the wave function undergoes a transition from an\nuncorrelated to a highly correlated state, which manifests itself in the\nlocalization of the lattice atoms in the latter regime. For small interspecies\ncouplings, we identify the process responsible for this cross-over in a\nsingle-particle-like picture. Moreover, we give a full characterization of the\nwave function's structure in both regimes, using Bloch and Wannier states of\nthe lowest band, and we find an order parameter, which can be exploited as a\ncorresponding experimental signature. To deepen the understanding, we use an\neffective Hamiltonian approach, which introduces an induced interaction and is\nvalid for small interspecies interaction. We finally compare the ansatz of the\neffective Hamiltonian with the results of the ML-MCTDHX simulations."
    },
    {
        "anchor": "Entanglement and spin squeezing in non-Hermitian phase transitions: We show that non-Hermitian dynamics generate substantial entanglement in\nmany-body systems. We consider the non-Hermitian Lipkin-Meshkov-Glick model and\nshow that its phase transition occurs with maximum multiparticle entanglement:\nthere is full N-particle entanglement at the transition, in contrast to the\nHermitian case. The non-Hermitian model also exhibits more spin squeezing than\nthe Hermitian model, showing that non-Hermitian dynamics are useful for quantum\nmetrology. Experimental implementations with trapped ions and cavity QED are\ndiscussed.",
        "positive": "A finite element method with mesh adaptivity for computing vortex states\n  in fast-rotating Bose-Einstein condensates: Numerical computations of stationary states of fast-rotating Bose-Einstein\ncondensates require high spatial resolution due to the presence of a large\nnumber of quantized vortices. In this paper we propose a low-order finite\nelement method with mesh adaptivity by metric control, as an alternative\napproach to the commonly used high order (finite difference or spectral)\napproximation methods. The mesh adaptivity is used with two different numerical\nalgorithms to compute stationary vortex states: an imaginary time propagation\nmethod and a Sobolev gradient descent method. We first address the basic issue\nof the choice of the variable used to compute new metrics for the mesh\nadaptivity and show that simultaneously refinement using the real and imaginary\npart of the solution is successful. Mesh refinement using only the modulus of\nthe solution as adaptivity variable fails for complicated test cases. Then we\nsuggest an optimized algorithm for adapting the mesh during the evolution of\nthe solution towards the equilibrium state. Considerable computational time\nsaving is obtained compared to uniform mesh computations. The new method is\napplied to compute difficult cases relevant for physical experiments (large\nnonlinear interaction constant and high rotation rates)."
    },
    {
        "anchor": "Thermalization of a quantum Newton's cradle in a one-dimensional\n  quasicondensate: We study the nonequilibrium dynamics of the quantum Newton's cradle in a\none-dimensional (1D) Bose gas in the weakly-interacting quasicondensate regime.\nThis is the opposite regime to the original quantum Newton's cradle experiment\nof Kinoshita et al. [Nature 440, 900 (2006)], which was realized in the\nstrongly interacting 1D Bose gas. Using finite temperature c-field methods, we\ncalculate the characteristic relaxation rates to the final equilibrium state.\nHence, we identify the different dynamical regimes of the system in the\nparameter space that characterizes the strength of interatomic interactions,\nthe initial temperature, and the magnitude of the Bragg momentum used to\ninitiate the collisional oscillations of the cradle. In all parameter regimes,\nwe find that the system relaxes to a final equilibrium state for which the\nmomentum distribution is consistent with a thermal distribution. For\nsufficiently large initial Bragg momentum, the system can undergo hundreds of\nrepeated collisional oscillations before reaching the final thermal\nequilibrium. The corresponding thermalization timescales can reach tens of\nseconds, which is an order of magnitude smaller than in the strongly\ninteracting regime.",
        "positive": "Coarsening dynamics driven by vortex-antivortex annihilation in\n  ferromagnetic Bose-Einstein condensates: In ferromagnetic Bose-Einstein condensates (BECs), the quadratic Zeeman\neffect controls magnetic anisotropy, which affects on magnetic domain pattern\nformation. While the longitudinal magnetization is dominant (similar to the\nIsing model) for a negative quadratic Zeeman energy, the transverse\nmagnetization is dominant (similar to the XY model) for a positive one. When\nthe quadratic Zeeman energy is positive, the coarsening dynamics is driven by\nvortex-antivortex annihilation in the same way as the XY model. However, due to\nsuperfluid flow of atoms, there exist several combinations of vortex-antivortex\npairs in ferromagnetic BECs, which makes the coarsening dynamics more\ncomplicated than that of the XY model. We propose a revised domain growth law,\nwhich is based on the growth law of the two-dimensional XY model, for a\ntwo-dimensional ferromagnetic BEC with a positive quadratic Zeeman energy."
    },
    {
        "anchor": "Atom-dimer scattering in heteronuclear mixture with finite intra-species\n  scattering length: We study the three-body problem of two ultracold identical bosonic atoms\n(denoted by $B$) and one extra atom (denoted by $X$), where the scattering\nlength $a_{BX}$ between each bosonic atom and atom $X$ is resonantly large and\npositive. We calculate the scattering length $a_{{\\rm ad}}$ between one bosonic\natom and the shallow dimer formed by the other bosonic atom and atom $X$, and\ninvestigate the effect induced by the interaction between the two bosonic\natoms. We find that even if this interaction is weak (i.e., the corresponding\nscattering length $a_{BB}$ is of the same order of the van der Waals length\n$r_{{\\rm vdW}}$ or even smaller), it can still induce a significant effect for\nthe atom--dimer scattering length $a_{{\\rm ad}}$. Explicitly, an atom--dimer\nscattering resonance can always occur when the value of $a_{BB}$ varies in the\nregion with $|a_{BB}|\\lesssim r_{{\\rm vdW}}$. As a result, both the sign and\nthe absolute value of $a_{{\\rm ad}}$, as well as the behavior of the $a_{{\\rm\nad}}$-$a_{BX}$ function, depends sensitively on the exact value of $a_{BB}$.\nOur results show that, for a good quantitative theory, the intra-species\ninteraction is required to be taken into account for this heteronuclear system,\neven if this interaction is weak.",
        "positive": "Three-Body Bound States of Quantum Particles: Higher Stability Through\n  Braiding: Cold atoms embedded in a degenerate Fermi system interact via a fermionic\nanalog of the Casimir force, which is an attraction of a -1/r form at distances\nshorter than the Fermi wavelength. Interestingly, the hydrogenic two-body bound\nstates do not form in this regime because the interaction strength is too weak\nunder realistic conditions, and yet the three-body bound states can have a\nconsiderably higher degree of stability. As a result, the trimer bound states\ncan form even when the dimer states are unstable. A quasiclassical analysis of\nquantum states supported by periodic orbits singles out the \"figure-eight\"\norbits, predicting bound states that are more stable than the ones originating\nfrom circular orbits. The discrete energies of these states form families of\nresonances with a distinct structure, enabling a direct observation of\nsignatures of figure-eightbraiding dynamics."
    },
    {
        "anchor": "Measuring Electromagnetic and Gravitational Responses of Photonic Landau\n  Levels: The topology of an object describes global properties that are insensitive to\nlocal perturbations. Classic examples include string knots and the genus\n(number of handles) of a surface: no manipulation of a closed string short of\ncutting it changes its \"knottedness\"; and no deformation of a closed surface,\nshort of puncturing it, changes how many handles it has. Topology has recently\nbecome an intense focus of condensed matter physics, where it arises in the\ncontext of the quantum Hall effect [1] and topological insulators [2]. In each\ncase, topology is defined through invariants of the material's bulk [3-5], but\nexperimentally measured through chiral/helical properties of the material's\nedges. In this work we measure topological invariants of a quantum Hall\nmaterial through local response of the bulk: treating the material as a\nmany-port circulator enables direct measurement of the Chern number as the\nspatial winding of the circulator phase; excess density accumulation near\nspatial curvature quantifies the curvature-analog of charge known as mean\norbital spin, while the moment of inertia of this excess density reflects the\nchiral central charge. We observe that the topological invariants converge to\ntheir global values when probed over a few magnetic lengths lB, consistent with\nintuition that the bulk/edge distinction exists only for samples larger than a\nfew lB. By performing these experiments in photonic Landau levels of a twisted\nresonator [6], we apply quantum-optics tools to topological matter. Combined\nwith developments in Rydberg-mediated interactions between resonator photons\n[7], this work augurs an era of precision characterization of topological\nmatter in strongly correlated fluids of light.",
        "positive": "Light cone dynamics and reverse Kibble-Zurek mechanism in\n  two-dimensional superfluids following a quantum quench: We study the dynamics of the relative phase of a bilayer of two-dimensional\nsuperfluids after the two superfluids have been decoupled. We find that on\nshort time scales the relative phase shows \"light cone\" like dynamics and\ncreates a metastable superfluid state, which can be supercritical. We also\ndemonstrate similar light cone dynamics for the transverse field Ising model.\nOn longer time scales the supercritical state relaxes to a disordered state due\nto dynamical vortex unbinding. This scenario of dynamically suppressed vortex\nproliferation constitutes a reverse-Kibble-Zurek effect. We study this effect\nboth numerically using truncated Wigner approximation and analytically within a\nnewly suggested time dependent renormalization group approach (RG). In\nparticular, within RG we show that there are two possible fixed points for the\nreal time evolution corresponding to the superfluid and normal steady states.\nSo depending on the initial conditions and the microscopic parameters of the\nHamiltonian the system undergoes a non-equilibrium phase transition of the\nKosterlitz-Thouless type. The time scales for the vortex unbinding near the\ncritical point are exponentially divergent, similar to the equilibrium case."
    },
    {
        "anchor": "Synthetic gauge fields in synthetic dimensions: Interactions and chiral\n  edge modes: Synthetic ladders realized with one-dimensional alkaline-earth(-like)\nfermionic gases and subject to a gauge field represent a promising environment\nfor the investigation of quantum Hall physics with ultracold atoms. Using\ndensity-matrix renormalization group calculations, we study how the quantum\nHall-like chiral edge currents are affected by repulsive atom-atom\ninteractions. We relate the properties of such currents to the asymmetry of the\nspin resolved momentum distribution function, a quantity which is easily\naddressable in state-of-art experiments. We show that repulsive interactions\nsignificantly stabilize the quantum Hall-like helical region and enhance the\nchiral currents. Our numerical simulations are performed for atoms with two and\nthree internal spin states.",
        "positive": "Coupling a mobile hole to an antiferromagnetic spin background:\n  Transient dynamics of a magnetic polaron: Understanding the interplay between charge and spin and its effects on\ntransport is a ubiquitous challenge in quantum many-body systems. In the\nFermi-Hubbard model, this interplay is thought to give rise to magnetic\npolarons, whose dynamics may explain emergent properties of quantum materials\nsuch as high-temperature superconductivity. In this work, we use a cold-atom\nquantum simulator to directly observe the formation dynamics and subsequent\nspreading of individual magnetic polarons. Measuring the density- and\nspin-resolved evolution of a single hole in a 2D Hubbard insulator with\nshort-range antiferromagnetic correlations reveals fast initial delocalization\nand a dressing of the spin background, indicating polaron formation. At long\ntimes, we find that dynamics are slowed down by the spin exchange time, and\nthey are compatible with a polaronic model with strong density and spin\ncoupling. Our work enables the study of out-of-equilibrium emergent phenomena\nin the Fermi-Hubbard model, one dopant at a time."
    },
    {
        "anchor": "Two-colour laser cooling for 40K-87Rb quantum gas mixtures: We present an efficient cooling scheme for fermionic $^{40}{\\text{K}}$ atoms,\nusing laser light red and blue detuned with respect to the $\\mathcal{D}2$ and\n$\\mathcal{D}1$ principle flourescence lines, respectively. The cooling scheme\nis found to significantly increase the saturation level for loading of a\n$^{40}{\\text{K}}$ magneto-optical trap (MOT), resulting in increased atom\nnumbers or decreased cycle times. While the attainable $^{40}{\\text{K}}$ atom\nnumber is approximately doubled if exclusively $^{40}{\\text{K}}$ atoms are\ncooled, the scheme is particularly powerful for dual-species MOTs, for example,\nif $^{40}{\\text{K}}$ and $^{87}{\\text{Rb}}$ atoms are cooled simultaneously in\nthe same MOT configuration. The typical atom losses due to light-assisted\nhetero-nuclear collisions between $^{40}{\\text{K}}$ and $^{87}{\\text{Rb}}$ seem\nto be reduced giving rise to a threefold improvement of the $^{40}{\\text{K}}$\natom number as compared to that in a conventional dual-species MOT, operating\nmerely with $\\mathcal{D}2$ light. Our scheme can be a useful extension to most\ndual-species experiments, aiming to reach simultaneous degeneracy of both\nspecies.",
        "positive": "Deterministic entanglement generation from driving through quantum phase\n  transitions: Many-body entanglement is often created through system evolution, aided by\nnon-linear interactions between the constituting particles. The very dynamics,\nhowever, can also lead to fluctuations and degradation of the entanglement if\nthe interactions cannot be controlled. Here, we demonstrate near-deterministic\ngeneration of an entangled twin-Fock condensate of $\\sim11000$ atoms by driving\na $^{87}$Rb Bose-Einstein condensate undergoing spin mixing through two\nconsecutive quantum phase transitions (QPTs). We directly observe number\nsqueezing of $10.7\\pm0.6$ dB and normalized collective spin length of\n$0.99\\pm0.01$. Together, these observations allow us to infer an\nentanglement-enhanced phase sensitivity of $\\sim6$ dB beyond the standard\nquantum limit and an entanglement breadth of $\\sim910$ atoms. Our work\nhighlights the power of generating large-scale useful entanglement by taking\nadvantage of the different entanglement landscapes separated by QPTs."
    },
    {
        "anchor": "Topological phase transitions on a triangular optical lattice with\n  non-Abelian gauge fields: We study the mean-field BCS-BEC evolution of a uniform Fermi gas on a\nsingle-band triangular lattice, and construct its ground-state phase diagrams,\nshowing a wealth of topological quantum phase transitions between gapped and\ngapless superfluids that are induced by the interplay of an out-of-plane Zeeman\nfield and a generic non-Abelian gauge field.",
        "positive": "Creation and detection of vortices in polariton condensates: We investigate theoretically the creation, persistence and detection of\nquantized vortices in nonequilibrium polariton condensates within a stochastic\nclassical field model. The life time of the quantized vortices is shown to\nincrease with the spatial coherence and to depend on the geometry of the\ncondensate. The relation with superfluidity in conventional superfluids is\ndiscussed. Three different ways to measure the vorticity of the polariton\ncondensate are proposed."
    },
    {
        "anchor": "Dynamical critical scaling of long-range interacting quantum magnets: Slow variations (quenches) of the magnetic field across the\nparamagnetic-ferromagnetic phase transition of spin systems produce heat. In\nsystems with short-range interactions the heat exhibits universal power-law\nscaling as a function of the quench rate, known as Kibble-Zurek scaling. In\nthis work we analyze slow quenches of the magnetic field in the\nLipkin-Meshkov-Glick (LMG) model, which describes fully connected quantum\nspins. We analytically determine the quantum contribution to the residual heat\nas a function of the quench rate $\\delta$ by means of a Holstein-Primakoff\nexpansion about the mean-field value. Unlike in the case of short-range\ninteractions, scaling laws in the LMG model are only found for a ramp ending at\nthe critical point. If instead the ramp is symmetric, as in the typical\nKibble-Zurek scenario, after crossing the critical point the system tends to\nreabsorb the defects formed during the first part of the ramp: the number of\nexcitations exhibits a crossover behavior as a function of $\\delta$ and tends\nto a constant in the thermodynamic limit. Previous, and seemingly\ncontradictory, theoretical studies are identified as specific limits of this\ndynamics. Our results can be tested on several experimental platforms,\nincluding quantum gases and trapped ions.",
        "positive": "Effects of dissipation on the superfluid-Mott-insulator transition of\n  photons: We investigate the superfluid-Mott-insulator transition of a two-dimensional\nphoton gas in a dye-filled optical microcavity and in the presence of a\nperiodic potential. We show that in the random-phase approximation the effects\nof the dye molecules, which generally lead to dissipation in the photonic\nsystem, can be captured by two dimensionless parameters that only depend on\ndye-specific properties. Within the mean-field approximation, we demonstrate\nthat one of these parameters decreases the size of the Mott lobes in the phase\ndiagram. By considering also Gaussian fluctuations, we show that the coupling\nwith the dye molecules results in a finite lifetime of the quasiparticle and\nquasihole excitations in the Mott lobes. Moreover, we show that there are\nnumber fluctuations in the Mott lobes even at zero temperature and therefore\nthat the true Mott-insulating state never exists if the interactions with the\ndye are included."
    },
    {
        "anchor": "On solving quantum many-body problems by experiment: Knowledge of all correlation functions of a system is equivalent to solving\nthe corresponding many-body problem. Already a finite set of correlation\nfunctions can be sufficient to describe a quantum many-body system if\ncorrelations factorise, at least approximately. While being a powerful\ntheoretical concept, an implementation based on experimental data has so far\nremained elusive. Here, this is achieved by applying it to a non-trivial\nquantum many-body problem: A pair of tunnel-coupled one-dimensional atomic\nsuperfluids. From measured interference patterns we extract phase correlation\nfunctions up to tenth order and analyse if, and under which conditions, they\nfactorise. This characterises the essential features of the system, the\nrelevant quasiparticles, their interactions and possible topologically distinct\nvacua. We verify that in thermal equilibrium the physics can be described by\nthe quantum sine-Gordon model, relevant for a wide variety of disciplines from\nparticle to condensed-matter physics. Our experiment establishes a general\nmethod to analyse quantum many-body systems in experiments. It represents a\ncrucial ingredient towards the implementation and verification of quantum\nsimulators.",
        "positive": "Fluctuation Effects on the Transport Properties of Unitary Fermi Gases: In this letter, we investigate the fluctuation effects on the transport\nproperties of unitary Fermi gases in the vicinity of the superfluid transition\ntemperature $T_c$. Based on the time-dependent Ginzburg-Landau formalism of the\nBEC-BCS crossover, we investigate both the residual resistivity below $T_c$\ninduced by phase slips and the paraconductivity above $T_c$ due to pair\nfluctuations. These two effects have been well studied in the weak coupling BCS\nsuperconductor, and here we generalize them to the unitary regime of ultracold\nFermi gases. We find that while the residual resistivity below $T_c$ increases\nas one approaches the unitary limit, consistent with recent experiments, the\nparaconductivity exhibits non-monotonic behavior. Our results can be verified\nwith the recently developed transport apparatus using mesoscopic channels."
    },
    {
        "anchor": "Observation of low-field Fano-Feshbach resonances in ultracold gases of\n  dysprosium: We report the observation of resonance-like loss in the trap population of\nultracold dysprosium as a function of magnetic field, which we attribute to\nanisotropy-induced Fano-Feshbach resonances arising from Dy's large magnetic\ndipole moment and nonzero electronic orbital angular momentum. We recorded\nthese resonances for four different isotopes, three bosonic and one fermionic,\nover a field range of 0-6 G and show that the number of resonances changes\nsignificantly as a function of temperature, even in the nK regime. Most of the\nobserved resonances are of very narrow width. The fermionic isotope, unlike its\nbosonic counterparts, possesses nonzero nuclear spin and exhibits a much higher\ndensity of resonances.",
        "positive": "Landau Levels in Strained Optical Lattices: We propose a hexagonal optical lattice system with spatial variations in the\nhopping matrix elements. Just like in the valley Hall effect in strained\nGraphene, for atoms near the Dirac points the variations in the hopping matrix\nelements can be described by a pseudo-magnetic field and result in the\nformation of Landau levels. We show that the pseudo-magnetic field leads to\nmeasurable experimental signatures in momentum resolved Bragg spectroscopy,\nBloch oscillations, cyclotron motion, and quantization of in-situ densities.\nOur proposal can be realized by a slight modification of existing experiments.\nIn contrast to previous methods, pseudo-magnetic fields are realized in a\ncompletely static system avoiding common heating effects and therefore opening\nthe door to studying interaction effects in Landau levels with cold atoms."
    },
    {
        "anchor": "Comment on \"Kinetic theory for a mobile impurity in a degenerate\n  Tonks-Girardeau gas\": In a recent paper, arxiv:1402.6362, Gamayun, Lychkovskiy, and Cheianov\nstudied the dynamics of a mobile impurity embedded into a one-dimensional\nTonks-Girardeau gas of strongly interacting bosons. Employing the Boltzmann\nequation approach, they arrived at the following main conclusions: (i) a light\nimpurity, being accelerated by a constant force does not exhibit Bloch\noscillations; (ii) a heavy impurity does undergo Bloch oscillations,\naccompanied by a drift with the velocity proportional to the square root of\nforce. In this comment we argue that the result (i) is an artifact of the\nclassical Boltzmann approximation, which misses the formation of the (quasi)\nbound-state between the impurity and a hole. Result (ii), while not valid at\nasymptotically small force, indeed reflects an interesting intermediate-force\nbehavior. Here we clarify its limits of applicability and extend beyond the\nTonks-Girardeau limit.",
        "positive": "Tunable energy-level inversion in spin-orbit-coupled Bose-Einstein\n  condensates: A method to realize controllable inversion of energy levels in a\none-dimensional spin-orbit (SO)-coupled two-component Bose-Einstein condensate\nunder the action of a gradient magnetic field and harmonic-oscillator (HO)\ntrapping potential is proposed. The linear version of the system is solved\nexactly. By adjusting the SO coupling strength and magnetic-field gradient, the\nenergy-level inversion makes it possible to transform any excited state into\nthe ground state. The full nonlinear system is solved numerically, and it is\nfound that the results are consistent with the linear prediction in the case of\nthe repulsive inter-component interaction. On the other hand, the\ninter-component attraction gives rise to states of superposition and edge\ntypes. Similar results are also reported for the system with the HO trap\nreplaced by the box potential. These results suggest a possibility to realize\nany excited state and observe it in the experiment."
    },
    {
        "anchor": "Resonant Five-body Recombination in an Ultracold Gas of Bosonic Atoms: We combine theory and experiment to investigate five-body recombination in an\nultracold gas of atomic cesium at negative scattering length. A refined\ntheoretical model, in combination with extensive laboratory tunability of the\ninteratomic interactions, enables the five-body resonant recombination rate to\nbe calculated and measured. The position of the new observed recombination\nfeature agrees with a recent theoretical prediction and supports the prediction\nof a family of universal cluster states at negative $a$ that are tied to an\nEfimov trimer.",
        "positive": "Staggered quantum phases of dipolar bosons at finite temperatures: The extended Bose-Hubbard model with correlated tunneling exhibits staggered\nsuperfluid and supersolid quantum phases. We study finite-temperature phase\ntransitions of quantum phases of dipolar bosons in a two-dimensional optical\nlattice using Gutzwiller mean-field and quantum Monte Carlo approaches. When\nnearest-neighbor repulsion is comparable to the on-site interaction, we find\nthat the two topologically distinct superfluids are separated by a normal fluid\nphase, while at stronger off-site interactions, density-modulated insulating\nquantum phases appear. We estimate the critical temperature of the staggered\nsuperfluid to normal fluid transition and show that this transition is of the\nKosterlitz-Thouless type. Finally, we elucidate the coexistence of staggered\nquantum phases in the presence of an external trapping potential. Our study\npaves a way to observe novel staggered quantum phases in recent dipolar optical\nlattice experiments."
    },
    {
        "anchor": "Observation of the BKT Transition in a 2D Bose Gas via Matter-Wave\n  Interferometry: We probe local phase fluctuations of trapped two-dimensional (2D) Bose gases\nusing matter-wave interferometry. This enables us to measure the phase\ncorrelation function, which changes from an algebraic to an exponential decay\nwhen the system crosses the Berezinskii-Kosterlitz-Thouless (BKT) transition.\nWe determine the temperature dependence of the BKT exponent $\\eta$ and find the\ncritical value $\\eta_c = 0.17(3)$ for our trapped system. Furthermore, we\nmeasure the local vortex density as a function of the local phase-space\ndensity, which shows a scale-invariant behaviour across the transition. Our\nexperimental investigation is supported by Monte Carlo simulations and provides\na comprehensive understanding of the BKT transition in a trapped system.",
        "positive": "Intra- and interband excitations induced residue decay of the Bose\n  polaron in a one-dimensional double-well: We investigate the polaronic properties of a single impurity immersed in a\nweakly interacting bosonic environment confined within a one-dimensional\ndouble-well potential using an exact diagonalization approach. We find that an\nincrease of the impurity-bath coupling results in a vanishing residue,\nsignifying the occurrence of the polaron orthogonality catastrophe. Asymptotic\nconfigurations of the systems' ground state wave function in the strongly\ninteracting regime are obtained by means of a Schmidt decomposition, which in\nturn accounts for the observed orthogonality catastrophe of the polaron. We\nexemplify that depending on the repulsion of the Bose gas, three distinct\nresidue behaviors appear with respect to the impurity-bath coupling. These\nresidue regimes are characterized by two critical values of the bosonic\nrepulsion and originate from the interplay between the intra- and the interband\nexcitations of the impurity. Moreover, they can be clearly distinguished in the\ncorresponding species reduced density matrices with the latter revealing a\nphase separation on either the one- or the two-body level. The impact of the\ninterspecies mass-imbalance on the impurity's excitation processes is\nappreciated yielding an interaction shift of the residue regions. Our results\nexplicate the interplay of intra- and interband excitation processes for the\npolaron generation in multiwell traps and for designing specific polaron\nentangled states motivating their exposure in current experiments."
    },
    {
        "anchor": "Observation of the Quantum Boomerang Effect: A particle in an Anderson-localized system, if launched in any direction,\nshould on average return to its starting point and stay there. Despite the\ncentral role played by Anderson localization in the modern understanding of\ncondensed matter, this \"quantum boomerang\" effect, an essential feature of the\nlocalized state, was only recently theoretically predicted and has not\npreviously been observed. We report the experimental observation of the quantum\nboomerang effect. Using a degenerate gas and a phase-shifted pair of optical\nlattices, we probe the role of time reversal symmetry breaking, Floquet gauge,\nand initial state symmetry in supporting or disrupting the boomerang effect.\nHighlighting the key role of localization, we observe that as stochastic\nkicking destroys dynamical localization, the quantum boomerang effect also\ndisappears. Measured dynamics are in agreement with analytical and numerical\npredictions. These results showcase a unique experimental probe of the\nunderlying quantum nature of Anderson localized matter.",
        "positive": "Umklapp Superradiance from a Collisionless Quantum Degenerate Fermi Gas: The quantum dynamics of the electromagnetic light mode of an optical cavity\nfilled with a coherently driven Fermi gas of ultracold atoms strongly depends\non geometry of the Fermi surface. Superradiant light generation and\nself-organization of the atoms can be achieved at low pumping threshold due to\nresonant atom-photon Umklapp processes, where the fermions are scattered from\none side of the Fermi surface to the other by exchanging photon momenta. The\ncavity spectrum exhibits sidebands, that, despite strong atom-light coupling\nand cavity decay, retain narrow linewidth, due to absorptionless transparency\nwindows outside the atomic particle-hole continuum and the suppression of\ninhomogeneous broadening and thermal fluctuations in the collisionless Fermi\ngas."
    },
    {
        "anchor": "Spontaneous symmetry breaking and Higgs mode: comparing Gross-Pitaevskii\n  and nonlinear Klein-Gordon equations: We discuss the mechanism of spontaneous symmetry breaking and the elementary\nexcitations for a weakly-interacting Bose gas at finite temperature. We\nconsider both the non-relativistic case, described by the Gross-Pitaevskii\nequation, and the relativistic one, described by the cubic nonlinear\nKlein-Gordon equation. We analyze similarities and differences in the two\nequations and, in particular, in the phase and amplitude modes (i.e. Goldstone\nand Higgs modes) of the bosonic matter field. We show that the coupling between\nphase and amplitude modes gives rise to a single gapless Bogoliubov spectrum in\nthe non-relativistic case. Instead, in the relativistic case the spectrum has\ntwo branches: one is gapless and the other is gapped. In the non-relativistic\nlimit we find that the relativistic spectrum reduces to the Bogoliubov one.\nFinally, as an application of the above analysis, we consider the Bose-Hubbard\nmodel close to the superfluid-Mott quantum phase transition and we investigate\nthe elementary excitations of its effective action, which contains both\nnon-relativistic and relativistic terms.",
        "positive": "Optical signatures of antiferromagnetic ordering of fermionic atoms in\n  an optical lattice: We show how off-resonant light scattering can provide quantitative\ninformation on antiferromagnetic ordering of a two-species fermionic atomic gas\nin a tightly-confined two-dimensional optical lattice. We analyze the emerging\nmagnetic ordering of atoms in the mean-field and in random phase approximations\nand show how the many-body static and dynamic correlations, evaluated in the\nstandard Feynman-Dyson perturbation series, can be detected in the scattered\nlight signal. The staggered magnetization reveals itself in the magnetic Bragg\npeaks of the individual spin components. These magnetic peaks, however, can be\nconsiderably suppressed in the absence of a true long-range antiferromagnetic\norder. The light scattered outside the diffraction orders can be collected by a\nlens a with highly improved signal-to-shot-noise ratio when the diffraction\nmaxima are blocked. The collective and single-particle excitations are\nidentified in the spectrum of the scattered light. We find that the\nspin-conserving and spin-exchanging atomic transitions convey information on\ndensity, longitudinal spin, and transverse spin correlations. The different\ncorrelations and scattering processes exhibit characteristic angular\ndistribution profiles for the scattered light and, e.g., the diagnostic signal\nof transverse spin correlations could be separated from the signal by the\nscattering direction, frequency, or polarization. We also analyze the detection\naccuracy by estimating the number of required measurements, constrained by the\nheating rate that is determined by inelastic light scattering events. The\nimaging technique could be extended to the two-species fermionic states in\nother regions of the phase diagram where the ground state properties are still\nnot fully understood."
    },
    {
        "anchor": "Probing Energy-Dependent Feshbach Resonances by Optical Control: Optical control enables new high resolution probes of narrow collisional\n(Feshbach) resonances, which are strongly dependent on the relative momentum of\ncolliding atom pairs, and important for simulating neutron matter with\nultracold atomic gases. We demonstrate a two-field optical vernier, which\nexpands kHz (mG) magnetic field detunings near a narrow resonance into MHz\noptical field detunings, enabling precise control and characterization of the\nmomentum-dependent scattering amplitude. Two-photon loss spectra are measured\nfor the narrow resonance in $^6$Li, revealing rich structure in very good\nagreement with our theoretical model. However, anomalous frequency shifts\nbetween the measured and predicted two-photon spectra are not yet explained.",
        "positive": "Emergent Symmetry at Superradiance Transition of a Bose Condensate in\n  Two Crossed Beam Cavities: Recently the ETH group has reported an experiment on superradiant transition\nof a Bose condensate in two crossed beam cavities. The surprise is that they\nfind that across the superradiant transition, the cavity light can be emitted\nin any superposition of these two cavity modes. This indicates an additional\n$U(1)$ symmetry that does not exist in the full Hamiltonian. In this letter we\nshow that this symmetry is an emergent symmetry in the vicinity of the phase\ntransition. We identify all the necessary conditions that are required for this\nemergent $U(1)$ symmetry and show that the ETH experiment is a special case\nthat satisfies these conditions. We further show that the superradiant\ntransition in this system can also be driven to a first order one when the\nsystem is tuned away from the point having the emergent symmetry."
    },
    {
        "anchor": "The influence of interaction between quasiparticles on parametric\n  resonance process in Bose-Einstein condensates: We analyze the uniform system of weakly interacting bosonic gas undergoing\nperiodic oscillation of interaction constant. This, within Bogoliubov\napproximation, leads to creation of atom pairs with well defined opposite\nvelocities. We show how interaction between quasiparticles, omitted in the\nBogoliubov approximation, significantly changes the atom pair creation process\nand properties of scattered atoms.",
        "positive": "Berezinskii-Kosterlitz-Thouless transitions in an easy-plane\n  ferromagnetic superfluid: A two-dimensional (2D) spin-1 Bose gas exhibits two\nBerezenskii-Kosterlitz-Thouless (BKT) transitions in the easy-plane\nferromagnetic phase. The higher temperature transition is associated with\nsuperfluidity of the mass current determined predominantly by a single spin\ncomponent. The lower temperature transition is associated with superfluidity of\nthe axial spin current, quasi-long range order of the transverse spin density\nand binding of polar-core spin vortices (PCVs). Above the spin BKT temperature,\nthe component circulations that make up each PCV spatially separate, suggesting\npossible deconfinement analogous to quark deconfinement in high energy physics.\nIntercomponent interactions give rise to superfluid drag between the spin\ncomponents, which we calculate analytically at zero temperature. We present the\nmass/spin superfluid phase diagram as a function of quadratic Zeeman energy\n$q$. At $q=0$ the system is in an isotropic spin phase with $\\mathrm{SO}(3)$\nsymmetry. Here the fluid response exhibits a system size dependence, suggesting\nthe absence of a BKT transition. Despite this, for finite systems the decay of\nspin correlations changes from exponential to algebraic as the temperature is\ndecreased."
    },
    {
        "anchor": "Analytic thermodynamics and thermometry of Gaudin-Yang Fermi gases: We study the thermodynamics of a one-dimensional attractive Fermi gas (the\nGaudin-Yang model) with spin imbalance. The exact solution has been known from\nthe thermodynamic Bethe ansatz for decades, but it involves an infinite number\nof coupled nonlinear integral equations whose physics is difficult to extract.\nHere the solution is analytically reduced to a simple, powerful set of four\nalgebraic equations. The simplified equations become universal and exact in the\nexperimental regime of strong interaction and relatively low temperature. Using\nthe new formulation, we discuss the qualitative features of finite-temperature\ncrossover and make quantitative predictions on the density profiles in traps.\nWe propose a practical two-stage scheme to achieve accurate thermometry for a\ntrapped spin-imbalanced Fermi gas.",
        "positive": "Evidence for Quantum Stripe Ordering in a Triangular Optical Lattice: Understanding strongly correlated quantum materials, such as high\n$T_\\textrm{c}$ superconductors, iron-based superconductors, and twisted bilayer\ngraphene systems, remains to be one of the outstanding challenges in condensed\nmatter physics. Quantum simulation with ultra-cold atoms in particular optical\nlattices, which provide orbital degrees of freedom, is a powerful tool to\ncontribute new insights to this endeavor. Here, we report the experimental\nrealization of an unconventional Bose-Einstein condensate of $^{87}$Rb atoms\npopulating degenerate $p$-orbitals in a triangular optical lattice, exhibiting\nremarkably long coherence times. Using time-of-flight spectroscopy, we observe\nthat this state spontaneously breaks the rotational symmetry and its momentum\nspectrum agrees with the theoretically predicted coexistence of exotic stripe\nand loop current orders. Like certain strongly correlated electronic systems\nwith intertwined orders, as high-$T_\\textrm{c}$ cuprate superconductors,\ntwisted bilayer graphene, and the recently discovered chiral density-wave state\nin kagome superconductors $\\textrm{AV}_3 \\textrm{Sb}_5$ (A=K, Rb, Cs), the\nnewly demonstrated quantum state, in spite of its markedly different energy\nscale and the bosonic quantum statistics, exhibits multiple symmetry breakings\nat ultralow temperatures. These findings hold the potential to enhance our\ncomprehension of the fundamental physics governing these intricate quantum\nmaterials."
    },
    {
        "anchor": "Stationary state after a quench to the Lieb-Liniger from rotating BECs: We study long-time dynamics of a bosonic system after suddenly switching on\nrepulsive delta-like interactions. As initial states, we consider two\nexperimentally relevant configurations: a rotating BEC and two\ncounter-propagating BECs with opposite momentum, both on a ring. In the first\ncase, the rapidity distribution function for the stationary state is derived\nanalytically and it is given by the distribution obtained for the same quench\nstarting from a BEC, shifted by the momentum of each boson. In the second case,\nthe rapidity distribution function is obtained numerically for generic values\nof repulsive interaction and initial momentum. The significant differences for\nthe case of large versus small quenches are discussed.",
        "positive": "Nondestructive imaging of an ultracold lattice gas: We demonstrate the nondestructive imaging of a lattice gas of ultracold\nbosons. Atomic fluorescence is induced in the simultaneous presence of\ndegenerate Raman sideband cooling. The combined influence of these processes\ncontrollably cycles an atom between a dark state and a fluorescing state while\neliminating heating and loss. Through spatially resolved sideband spectroscopy\nfollowing the imaging sequence, we demonstrate the efficacy of this imaging\ntechnique in various regimes of lattice depth and fluorescence acquisition\nrate. Our work provides an important extension of quantum gas imaging to the\nnondestructive detection, control and manipulation of atoms in optical\nlattices. In addition, our technique can also be extended to atomic species\nthat are less amenable to molasses-based lattice imaging."
    },
    {
        "anchor": "Excitation spectrum of Mott shells in optical lattices: We theoretically study the excitation spectrum of confined macroscopic\noptical lattices in the Mott-insulating limit. For large systems, a fast\nnumerical method is proposed to calculate the ground state filling and\nexcitation energies. We introduce many-particle on-site energies capturing\nmulti-band effects and discuss tunnelling on a perturbative level using an\neffectively restricted Hilbert space. Results for small one-dimensional\nlattices obtained by this method are in good agreement with the exact\nmulti-band diagonalization of the Hamiltonian. Spectral properties associated\nwith the formation of regions with constant filling, so-called Mott shells, are\ninvestigated and interfaces between the shells with strong particle\nfluctuations are characterized by gapless local excitations.",
        "positive": "Mott Transition and Spin Structures of Spin-1 Bosons in Two-Dimensional\n  Optical Lattice at Unit Filling: We study the ground state properties of spin-1 bosons in a two-dimensional\noptical lattice, by applying a variational Monte Carlo method to the S=1\nBose-Hubbard model on a square lattice at unit filling. A doublon-holon binding\nfactor introduced in the trial state provides a noticeable improvement in the\nvariational energy over the conventional Gutzwiller wave function and allows us\nto deal effectively with the inter-site correlations of particle densities and\nspins. We systematically show how spin-dependent interactions modify the\nsuperfluid-Mott insulator transitions in the S=1 Bose-Hubbard model due to the\ninterplay between the density and spin fluctuations of bosons. Furthermore,\nregarding the magnetic phases in the Mott region, the calculated spin structure\nfactor elucidates the emergence of nematic and ferromagnetic spin orders for\nantiferromagnetic ($U_2>0$) and ferromagnetic ($U_2<0$) couplings,\nrespectively."
    },
    {
        "anchor": "Equilibrium Phases of Tilted Dipolar Lattice Bosons: The recent advances in creating nearly degenerate quantum dipolar gases in\noptical lattices are opening the doors for the exploration of equilibrium\nphysics of quantum systems with anisotropic and long-range dipolar\ninteractions. In this paper we study the zero- and finite-temperature phase\ndiagrams of a system of hard-core dipolar bosons at half-filling, trapped in a\ntwo-dimensional optical lattice. The dipoles are aligned parallel to one\nanother and tilted out of the optical lattice plane by means of an external\nelectric field. At zero-temperature, the system is a superfluid at all tilt\nangles $\\theta$ provided that the strength of dipolar interaction is below a\ncritical value $V_c(\\theta)$. Upon increasing the interaction strength while\nkeeping $\\theta$ fixed, the superfluid phase is destabilized in favor of a\ncheckerboard or a stripe solid depending on the tilt angle. We explore the\nnature of the phase transition between the two solid phases and find evidence\nof a micro-emulsion phase, following the Spivak-Kivelson scenario, separating\nthese two solid phases. Additionally, we study the stability of these quantum\nphases against thermal fluctuations and find that the stripe solid is the most\nrobust, making it the best candidate for experimental observation.",
        "positive": "Sagnac Interferometry Using Bright Matter-Wave Solitons: We use an effective one-dimensional Gross-Pitaevskii equation to study bright\nmatter-wave solitons held in a tightly confining toroidal trapping potential,\nin a rotating frame of reference, as they are split and recombined on narrow\nbarrier potentials. In particular, we present an analytical and numerical\nanalysis of the phase evolution of the solitons and delimit a velocity regime\nin which soliton Sagnac interferometry is possible, taking account of the\neffect of quantum uncertainty."
    },
    {
        "anchor": "Generalized Hofstadter model on a cubic optical lattice: From nodal\n  bands to the three-dimensional quantum Hall effect: We propose that a tunable generalized three-dimensional Hofstadter\nHamiltonian can be realized by engineering the Raman-assisted hopping of\nultracold atoms in a cubic optical lattice. The Hamiltonian describes a\nperiodic lattice system under artificial magnetic fluxes in three dimensions.\nFor certain hopping configurations, the bulk bands can have Weyl points and\nnodal loops, respectively, allowing the study of both the two nodal semimetal\nstates within this system. Furthermore, we illustrate that with proper rational\nfluxes and hopping parameters, the system can exhibit the three-dimensional\nquantum Hall effect when the Fermi level lies in the band gaps, which is\ntopologically characterized by one or two nonzero Chern numbers. Our proposed\noptical-lattice system provides a promising platform for exploring various\nexotic topological phases in three dimensions.",
        "positive": "Chiral spin liquids in triangular lattice SU(N) fermionic Mott\n  insulators with artificial gauge fields: We show that, in the presence of a $\\pi/2$ artificial gauge field per\nplaquette, Mott insulating phases of ultra-cold fermions with $SU(N)$ symmetry\nand one particle per site generically possess an extended chiral phase with\nintrinsic topological order characterized by a multiplet of $N$ low-lying\nsinglet excitations for periodic boundary conditions, and by chiral edge states\ndescribed by the $SU(N)_1$ Wess-Zumino-Novikov-Witten conformal field theory\nfor open boundary conditions. This has been achieved by extensive exact\ndiagonalizations for $N$ between $3$ and $9$, and by a parton construction\nbased on a set of $N$ Gutzwiller projected fermionic wave-functions with flux\n$\\pi/N$ per triangular plaquette. Experimental implications are briefly\ndiscussed."
    },
    {
        "anchor": "Supersolid phase transitions for hardcore bosons on a triangular lattice: Hard-core bosons on a triangular lattice with nearest neighbor repulsion are\na prototypical example of a system with supersolid behavior on a lattice. We\nshow that in this model the physical origin of the supersolid phase can be\nunderstood quantitatively and analytically by constructing quasiparticle\nexcitations of defects that are moving on an ordered background. The location\nof the solid to supersolid phase transition line is predicted from the\neffective model for both positive and negative (frustrated) hopping parameters.\nFor positive hopping parameters the calculations agree very accurately with\nnumerical Quantum Monte Carlo simulations. The numerical results indicate that\nthe supersolid to superfluid transition is first order.",
        "positive": "Out-of-Time-Ordered Correlation in Anisotropic Dicke Model: Out-of-time-ordered correlation (OTOC) functions have been used as an\nindicator of quantum chaos in a lot of physical systems. In this work, we\ncomputationally demonstrate that zerotemperature OTOC can detect quantum phase\ntransition in anisotropic Dicke model. Phase diagram is given with OTOC.\nFinite-size effect is studied. Finally, temperature effect is discussed."
    },
    {
        "anchor": "Quantum dynamical field theory for non-equilibrium phase transitions in\n  driven open systems: We develop a quantum dynamical field theory for studying phase transitions in\ndriven open systems coupled to Markovian noise, where non-linear noise effects\nand fluctuations beyond semiclassical approximations influence the critical\nbehaviour. We systematically compare the diagrammatics, the properties of the\nrenormalization group flow and the structure of the fixed points, of the novel\nquantum dynamical field theory and of its semi-classical counterpart, which is\nemployed to characterise dynamical criticality in three dimensional\ndriven-dissipative condensates. As an application, we perform the Keldysh\nFunctional Renormalization of a one dimensional driven open Bose gas, where a\ntailored diffusion Markov noise realises an analog of quantum criticality for\ndriven-dissipative condensation. We find that the associated non-equilibrium\nquantum phase transition does not map into the critical behaviour of its three\ndimensional classical driven counterpart.",
        "positive": "Bound-state signatures in quenched Bose-Einstein condensates: We investigate the dynamics of a homogenous Bose-Einstein condensate (BEC)\nfollowing a sudden quench of the scattering length. Our focus is the time\nevolution of short-range correlations via the dynamical contact. We compute the\ndynamics using a combination of two- and many-body models, and we propose an\nintuitive connection between them that unifies their short-time, short-range\npredictions. Our two-body models are exactly solvable and, when properly\ncalibrated, lead to analytic formulae for the contact dynamics. Immediately\nafter the quench, the contact exhibits strong oscillations at the frequency of\nthe two-body bound state. These oscillations are large in amplitude, and their\ntime average is typically much larger than the unregularized Bogoliubov\nprediction. The condensate fraction shows similar oscillations, whose amplitude\nwe are able to estimate. These results demonstrate the importance of including\nthe bound state in descriptions of diabatically-quenched BEC experiments."
    },
    {
        "anchor": "Quantum filaments in dipolar Bose-Einstein condensates: Collapse in dipolar Bose-Einstein condensates may be arrested by quantum\nfluctuations. Due to the anisotropy of the dipole-dipole interactions, the\ndipole-driven collapse induced by soft excitations is compensated by the\nrepulsive Lee-Huang-Yang contribution resulting from quantum fluctuations of\nhard excitations, in a similar mechanism as that recently proposed for\nBose-Bose mixtures. The arrested collapse results in self-bound filament-like\ndroplets, providing an explanation to recent dysprosium experiments. Arrested\ninstability and droplet formation are novel general features directly linked to\nthe nature of the dipole-dipole interactions, and should hence play an\nimportant role in all future experiments with strongly dipolar gases.",
        "positive": "Thermocrystallization of lattice dipolar bosons coupled to a\n  high-finesse cavity: Investigating finite temperature effects on quantum phases is key to their\nexperimental realization. Finite temperature, and the interplay between quantum\nand thermal fluctuations can undermine properties and/or key features of\nquantum systems but they can also bring upon interesting phenomena. In this\npaper, we present a comprehensive investigation of the finite temperature phase\ndiagram of two-dimensional lattice dipolar bosons coupled to a high-finesse\noptical cavity. Interestingly, we observe that checkerboard density-density\ncorrelations are enhanced at finite temperature. Indeed, we found that finite\ntemperature drives a superfluid ground state into a normal state which will\nthen develop checkerboard order at higher temperatures. We show that this\neffect is solely due to the cavity-mediated interactions. We also confirm that\nthe supersolid checkerboard phase survives for a wide range of filling factors\nup to temperature scale of the order of half hopping amplitude, while the\ncheckerboard diagonal order can survive up to temperatures of a few hopping\namplitudes."
    },
    {
        "anchor": "Exploring exchange mechanisms with a cold atom gas: Fermionic atoms trapped in a double well potential are an ideal setting to\nstudy fundamental exchange mechanisms. We use exact diagonalization and\ncomplementary analytic calculations to demonstrate that two trapped fermions\ndeliver a minimal model of the direct exchange mechanism. This is an ideal\nquantum simulator of the Heisenberg antiferromagnet, exposes the competition\nbetween covalent and ionic bonding, and can create, manipulate, and detect\nquantum entanglement. Three trapped atoms form a faithful simulator of the\ndouble exchange mechanism that is the fundamental building block behind many\nHeisenberg ferromagnets.",
        "positive": "Vortex dynamics in spin-orbit coupled Bose-Einstein condensates: I use a time-dependent Lagrangian formalism and a variational trial function\nto study the dynamics of a two-component vortex in a spin-orbit coupled\nBose-Einstein condensate (BEC). For a single-component BEC, various experiments\nhave validated this theoretical approach, for example a thermal quench that\nyields a quantized vortex in roughly 25% of trials. To be definite, I assume\nthe specific spin-orbit form used in recent NIST experiments, which introduces\na spatial asymmetry because of the external Raman laser beams. I here\ngeneralize this formalism to include a two-component order parameter that has\nquantized circulation in each component but not necessarily with the same\ncirculation. For example a singly quantized vortex in just one component yields\na BEC analog of the half-quantum vortex familiar in $^3$He-A and in $p$-wave\nchiral superconductors. This and other unusual two-component vortices have both\nperiodic trajectories and unbounded trajectories that leave the condensate,\ndepending on the initial conditions. The optimized phase of the order parameter\ninduces a term in the particle current that cancels the contribution from the\nvector potential, leaving pure circulating current around the vortex."
    },
    {
        "anchor": "Superlattice quantum solid of dipolar excitons: We study dipolar excitons confined at 330 mK in a square electrostatic\nlattice of a GaAs double quantum well. In the dipolar occupation blockade\nregime, at 3/2 filling, we evidence that excitons form a face-centred\nsuperlattice quantum solid. This phase is realised with high purity across 36\nlattice sites, in a regime where the excitons mean interaction energy exceeds\nthe depth of the lattice confinement. The superlattice solid then closely\nrelates to Wigner crystals.",
        "positive": "Simultaneous dipole and quadrupole moment contribution in the Bogoliubov\n  spectrum: Application of the non-integral Gross-Pitaevskii equation: We present the Gross-Pitaevskii equation for Bose-Einstein condensates (BECs)\npossessing the electric dipole and the electric quadrupole moments in a\nnon-integral form. These equations are coupled with the Maxwell equations. The\nmodel under consideration includes the dipole-dipole, the dipole-quadrupole,\nand the quadrupole-quadrupole interactions in terms of the electric field\ncreated by the dipoles and quadrupoles. We apply this model to obtain the\nBogoliubov spectrum for three dimensional BECs with a repulsive short-range\ninteraction. We obtain an extra term in the Bogoliubov spectrum in compare with\nthe dipolar BECs. We show that the quadrupole-quadrupole interaction gives a\npositive contribution in the Bogoliubov spectrum. Hence this spectrum is\nstable."
    },
    {
        "anchor": "A High Phase-Space Density Gas of NaCs Feshbach Molecules: We report on the creation of ultracold gases of bosonic Feshbach molecules of\nNaCs. The molecules are associated from overlapping gases of Na and Cs using a\nFeshbach resonance at 864.12(5) G. We characterize the Feshbach resonance using\nbound state spectroscopy, in conjunction with a coupled-channel calculation. By\nvarying the temperature and atom numbers of the initial atomic mixtures, we\ndemonstrate the association of NaCs gases over a wide dynamic range of molecule\nnumbers and temperatures, reaching 70 nK for our coldest systems and a\nphase-space density near 0.1. This is an important stepping-stone for the\ncreation of degenerate gases of strongly dipolar NaCs molecules in their\nabsolute ground state.",
        "positive": "Self-consistent Single-band Approximation for Interacting Boson Systems: Traditionally, the single-band approximation for interacting many-body\nsystems is done with pre-determined single-particle Wannier functions, ignoring\nthe dependence of the Wannier function on interaction. We show that the\nsingle-band approximation has to be done self-consistently to properly account\nthe interaction effect on the Wannier functions. This self-consistent\nsingle-band approximation leads to a nonlinear equation for Wannier functions,\nwhich can be recast into a set of nonlinear equations for Bloch functions.\nThese equations are simplified for two special cases, the superfluid regime and\ndeep in the Mott insulator regime. A simple example with double-well potential\nis used to illustrate our results."
    },
    {
        "anchor": "Dynamical stabilization of two-dimensional trapless Bose-Einstein\n  condensates by three-body interaction and quantum fluctuations: Analyzing a Gross-Pitaevskii equation with cubic, quartic, and quintic\nnonlinearities through analytical and numerical methods, we examine the\nstability of two-dimensional (2D) trapless Bose-Einstein condensates (BECs)\nwith two-, three-body interactions and quantum fluctuations. Applying a\nvariational approach, we derive the equation of motion and effective potential\nto discuss in detail the stability of the BECs in 2D free space. We show that\nwith the aid of quantum fluctuations it is possible to stabilize 2D trapless\nBEC without any oscillatory nonlinearities. Also, there is an enhancement of\nthe stability of the system, due to the inclusion of the three-body interaction\nand quantum fluctuations in addition to the two-body interaction. We further\nstudy the stability of 2D trapless BECs with rapid periodic temporal modulation\nof scattering length by using a Feshbach resonance. We discuss all possible\nways of stabilization of trapless BECs in 2D by three-body interaction and\nquantum fluctuations. Finally, we verify our analytical results with numerical\nsimulation using split-step Crank-Nicholson method. These match well with the\nanalytical predictions.",
        "positive": "Superfluid/ferromagnet/superfluid-junction and $\u03c0$-phase in a\n  superfluid Fermi gas at finite temperatures: We investigate the stability of $\\pi$-phase in a polarized superfluid Fermi\ngas ($N_\\uparrow>N_\\downarrow$, where $N_\\sigma$ is the number of atoms in the\nhyperfine state described by pseudospin-$\\sigma$). In our previous paper [T.\nKashimura, S. Tsuchiya, and Y. Ohashi, Phys. Rev. A {\\bf 82}, 033617 (2010)],\nwe showed that excess atoms ($\\Delta N=N_\\uparrow-N_\\downarrow$) localized\naround a potential barrier embedded in the system induces the $\\pi$-phase at\nT=0, where the phase of superfluid order parameter differ by $\\pi$ across the\njunction. In this paper, we extend our previous work to include temperature\neffects within the mean-field theory. We show that the $\\pi$-phase is stable\neven at finite temperatures, although transition from the $\\pi$-phase to\n0-phase eventually occurs at a certain temperature. Our results indicate that\nthe $\\pi$-phase is experimentally accessible in cold Fermi gases."
    },
    {
        "anchor": "Vortex Lattices in the Bose-Fermi Superfluid Mixture: In this letter we show that the vortex lattice structure in the Bose-Fermi\nsuperfluid mixture can undergo a sequence of structure transitions when the\nFermi superfluid is tuned from the BCS regime to the BEC regime. This is due to\ndifferent vortex core structure of the Fermi superfluid in the BCS regime and\nin the BEC regime. In the former the vortex core is nearly filled, while the\ndensity at the vortex core gradually decreases until it empties out at the BEC\nregime. Therefore, with the density-density interaction between the Bose and\nthe Fermi superfluids, the two sets of vortex lattices interact stronger in the\nBEC regime that yields the structure transition of vortex lattices. In view of\nrecent realization of this superfluid mixture and vortices therein, our\ntheoretical predication can be verified experimentally in near future.",
        "positive": "Phase diffusion in a Bose-Einstein condensate of light: We study phase diffusion in a Bose-Einstein condensate of light in a\ndye-filled optical microcavity, i.e., the spreading of the probability\ndistribution for the condensate phase. To observe this phenomenon, we propose\nan interference experiment between the condensed photons and an external laser.\nWe determine the average interference patterns, considering quantum and thermal\nfluctuations as well as dissipative effects due to the dye. Moreover, we show\nthat a representative outcome of individual measurements can be obtained from a\nstochastic equation for the global phase of the condensate."
    },
    {
        "anchor": "Collective excitation and stability of flow-induced gapless Fermi\n  superfluids: We study the collective excitation and stability of superfluid Fermi gases\nflowing with a constant velocity in three-dimensional free space. In\nparticular, we investigate a possible gapless superfluid state induced by the\nsuperflow using the mean-field theory and the generalized random-phase\napproximation (GRPA). For weak attractive interactions, we find that the\nmean-field superfluid order parameter can take a nonzero value even after the\nsuperflow velocity exceeds the threshold for the onset of Bogoliubov\nquasiparticle excitations. Since the Cooper pairs are only partially broken by\nthe quasiparticle excitations, a gapless superfluid state can be formed over a\ncertain range of superflow velocity above the pair-breaking onset. In addition\nto the usual quasiparticle-pair continuum and the Anderson-Bogoliubov\ncollective mode, the GRPA excitation spectrum of the gapless superfluid state\nhas a quasiparticle-quasihole continuum and a second collective mode. We find\nthat the long-wavelength excitations of the second collective mode eventually\ncause dynamical instability of the system when the superflow velocity\nincreases. However, the gapless superfluid state still remains stable in a\nnarrow but finite range of superflow velocity.",
        "positive": "Quantifying hole-motion-induced frustration in doped antiferromagnets by\n  Hamiltonian reconstruction: Unveiling the microscopic origins of quantum phases dominated by the\ninterplay of spin and motional degrees of freedom constitutes one of the\ncentral challenges in strongly correlated many-body physics. When holes move\nthrough an antiferromagnetic spin background, they displace the positions of\nspins, which in turn induces effective frustration in the magnetic environment.\nHowever, a concrete characterization of this effect in a quantum many-body\nsystem is still an unsolved problem. Here we introduce a Hamiltonian\nreconstruction scheme that allows for a precise quantification of\nhole-motion-induced frustration. In particular, we access non-local correlation\nfunctions through projective measurements of the many-body state, from which\neffective spin-Hamiltonians can be recovered after detaching the magnetic\nbackground from dominant charge fluctuations. The scheme is applied to systems\nof mixed dimensionality, where holes are restricted to move in one dimension\n(1D), but $\\mathrm{SU}(2)$ superexchange is two-dimensional (2D). We\ndemonstrate that hole motion drives the spin background into a highly\nfrustrated spin liquid regime, reminiscent of Anderson's resonating valence\nbond paradigm in doped cuprates. We exemplify the direct applicability of the\nreconstruction scheme to ultracold atom experiments by recovering effective\nspin-Hamiltonians of experimentally obtained 1D Fermi-Hubbard snapshots. Our\nmethod can be generalized to fully 2D systems, enabling an unprecedented\nmicroscopic perspective on the doped Hubbard model."
    },
    {
        "anchor": "Quantum dark solitons in the 1D Bose gas and the superfluid velocity: We give explicit connections of quantum one-hole excited states to classical\nsolitons for the one-dimensional Bose gas with repulsive short-range\ninteractions. We call the quantum states connected to classical solitons the\nquantum soliton states. We show that the matrix element of the canonical field\noperator between quantum soliton states with $N-1$ and $N$ particles is given\nby a dark soliton of the Gross-Pitaevskii equation in the weak coupling case.\nWe suggest that the matrix element corresponds to the order parameter of BEC in\nthe quantum soliton state. The result should be useful in the study of\nmany-body effects in Bose-Einstein condensation and superfluids. For instance,\nwe derive the superfluid velocity for a quantum soliton state.",
        "positive": "Bose-Einstein Condensation of Europium: We report the realization of a Bose-Einstein condensate of europium atoms,\nwhich is a strongly dipolar species with unique properties, a highly symmetric\n$[\\mathrm{Xe}]\\ 4f^7 6s^2\\ {}^8\\mathrm{S}_{7/2}$ electronic ground state and a\nhyperfine structure. By means of evaporative cooling in a crossed optical\ndipole trap, we produced a condensate of ${}^{151}$Eu containing up to $5\\times\n10^4$ atoms. The scattering length of ${}^{151}$Eu was estimated to be $a_s =\n110(4)\\, a_\\mathrm{B}$ by comparing the velocities of expansion of condensates\nwith different orientations of the atomic magnetic moments. We observed\ndeformation of the condensate in the vicinity of the Feshbach resonance at\n$1.32\\,\\mathrm{G}$ with a width of $10\\,\\mathrm{mG}$."
    },
    {
        "anchor": "Phonon-polaritons in Bose-Einstein condensates induced by Casimir-Polder\n  interaction with graphene: We consider the mechanical coupling between a two-dimensional Bose-Einstein\ncondensate with a graphene sheet via the vacuum fluctuations of the\nelectromagnetic field which are at the origin of the so-called Casimir-Polder\npotential. By deriving a self-consistent set of equations governing the\ndynamics of the condensate and the flexural (out-of-plane) modes of the\ngraphene, we can show the formation of a new type of purely acoustic\nquasi-particle excitation, a phonon-polariton resulting from the coherent\nsuperposition of quanta of flexural and Bogoliubov modes.",
        "positive": "Non-adiabatic extension of the Zak phase and charge pumping in the\n  Rice--Mele model: In this study, the Landau--Zener (LZ) transition method is applied to\ninvestigate a weak non-adiabatic effect on the Zak phase and the topological\ncharge pumping in the Rice--Mele model. The non-adiabatic effect is formulated\nusing the LZ transfer matrix. The effective lower band wave function picks up\nthe Stokes phase as well as the usual dynamical phase through two avoided\ncrossings appearing in the two band instantaneous energy spectrum. The\ninterference effect from the upper band has a decisive influence on the decay\nbehavior of the lower band population. A non-adiabatic extension of the Zak\nphase can then be formulated, corresponding to the center of mass of the lower\nband Wannier function. Furthermore, we estimate the validity of the LZ\nformalism and verify the breakdown of the quantization of the topological\ncharge pumping by changing the sweeping speed."
    },
    {
        "anchor": "Bose polarons in ultracold atoms in one dimension: beyond the Fr\u00f6hlich\n  paradigm: Mobile impurity atoms immersed in Bose-Einstein condensates provide a new\nplatform for exploring Bose polarons. Recent experimental advances in the field\nof ultracold atoms make it possible to realize such systems with highly tunable\nmicroscopic parameters and to explore equilibrium and dynamical properties of\npolarons using a rich toolbox of atomic physics. In this paper we present a\ndetailed theoretical analysis of Bose polarons in one dimensional systems of\nultracold atoms. By combining a non-perturbative renormalization group approach\nwith numerically exact diffusion Monte Carlo calculations we obtain not only\ndetailed numerical results over a broad range of parameters but also\nqualitative understanding of different regimes of the system. We find that an\naccurate description of Bose polarons requires the inclusion of two-phonon\nscattering terms which go beyond the commonly used Fr\\\"ohlich model.\nFurthermore we show that when the Bose gas is in the strongly interacting\nregime, one needs to include interactions between the phonon modes. We use\nseveral theoretical approaches to calculate the polaron energy and its\neffective mass. The former can be measured using radio-frequency spectroscopy\nand the latter can be studied experimentally using impurity oscillations in a\nharmonic trapping potential. We compare our theoretical results for the\neffective mass to the experiments by Catani et al. [PRA 85, 023623 (2012)]. In\nthe weak-to-intermediate coupling regimes we obtain excellent quantitative\nagreement between theory and experiment, without any free fitting parameter. We\nsupplement our analysis by full dynamical simulations of polaron oscillations\nin a shallow trapping potential. We also use our renormalization group approach\nto analyze the full phase diagram and identify regions that support repulsive\nand attractive polarons, as well as multi-particle bound states.",
        "positive": "Spin drag Hall effect in a rotating Bose mixture: We show that in a rotating two-component Bose mixture, the spin drag between\nthe two different spin species shows a Hall effect. This spin drag Hall effect\ncan be observed experimentally by studying the out-of-phase dipole mode of the\nmixture. We determine the damping of this mode due to spin drag as a function\nof temperature. We find that due to Bose stimulation there is a strong\nenhancement of the damping for temperatures close to the critical temperature\nfor Bose-Einstein condensation."
    },
    {
        "anchor": "A new effective interaction for the trapped fermi gas: the BEC-BCS\n  crossover: We extend a recently introduced separable interaction for the unitary trapped\nFermi gas to all values of the scattering length. We derive closed expressions\nfor the interaction matrix elements and the two-particle eigenvectors and\nanalytically demonstrate the convergence of this interaction to the zero-range\ntwo-body pseudopotential for s-wave scattering. We apply this effective\ninteraction to the three- and four-particle systems along the BEC-BCS\ncrossover, and find that their low-lying energies exhibit convergence in the\nregularization parameter that is much faster than for the conventional\nrenormalized contact interaction. We find similar convergence properties of the\nthree-particle free energy at unitarity.",
        "positive": "Quantized Nonlinear Transport with Ultracold Atoms: In this letter, we propose how to measure the quantized nonlinear transport\nusing two-dimensional ultracold atomic Fermi gases in a harmonic trap. This\nscheme requires successively applying two optical pulses in the left and lower\nhalf-planes and then measuring the number of extra atoms in the first quadrant.\nIn ideal situations, this nonlinear density response to two successive pulses\nis quantized, and the quantization value probes the Euler characteristic of the\nlocal Fermi sea at the trap center. We investigate the practical effects in\nexperiments, including finite pulse duration, finite edge width of pulses, and\nfinite temperature, which can lead to deviation from quantization. We propose a\nmethod to reduce the deviation by averaging measurements performed at the first\nand third quadrants, inspired by symmetry considerations. With this method, the\nquantized nonlinear response can be observed reasonably well with experimental\nconditions readily achieved with ultracold atoms."
    },
    {
        "anchor": "Density and pseudo-spin rotons in a bilayer of soft-core bosons: We study the dynamics of a bilayer system of bosons with repulsive soft-core\nRydberg-dressed interactions within the mean-field Bogoliubov-de Gennes\napproximation. We find roton minima in both symmetric and asymmetric collective\ndensity modes of the symmetric bilayer. Depending on the density of bosons in\neach layer and the spacing between two layers, the homogeneous superfluid phase\nbecomes unstable in either (or both) of these two channels, leading to density\nand pseudo-spin-density wave instabilities in the system. Breaking the symmetry\nbetween two layers, either with a finite counterflow or a density imbalance\nrenormalizes the dispersion of collective modes and makes the system more\nsusceptible to density-wave instability.",
        "positive": "Universality in Efimov associated tetramers in 4He: We calculated, using seven realistic 4He-4He potentials in the literature,\nthe Efimov spectra of the 4He trimer and tetramer and analyzed the universality\nof the systems. The three-(four-)body Schroedinger equations were solved fully\nnonadiabatically with the high-precision calculation method employed in our\nprevious work on the 4He trimer and tetramer [Phys. Rev. A 85, 022502 (2012);\n85, 062505 (2012)]. We found the following universality in the four-boson\nsystem: i) The critical scattering lengths at which the tetramer ground and\nexcited states couple to the four-body threshold are independent of the choice\nof the two-body realistic potentials in spite of the difference in the\nshort-range details and do not contradict the corresponding values observed in\nthe experiments in ultracold alkali atoms when scaled with the van der Waals\nlength r_vdW, and ii) the four-body hyperradial potential has a repulsive\nbarrier at the four-body hyperradius R_4 \\approx 3 r_vdW, which prevents the\nfour particles from getting close together to explore nonuniversal features of\nthe interactions at short distances. This result is an extension of the\nuniversality in Efimov trimers that the appearance of the repulsive barrier at\nthe three-body hyperradius R_3 \\approx 2 r_vdW makes the critical scattering\nlengths independent of the short-range details of the interactions as reported\nin the literature and also in the present work for the 4He trimer with the\nrealistic potentials."
    },
    {
        "anchor": "Collisionally Stable Gas of Bosonic Dipolar Ground State Molecules: Stable ultracold ensembles of dipolar molecules hold great promise for\nmany-body quantum physics, but high inelastic loss rates have been a\nlong-standing challenge. Recently, it was shown that gases of fermionic\nmolecules can be effectively stabilized through external fields. However, many\nquantum applications will benefit from molecular ensembles with bosonic\nstatistics. Here, we stabilize a bosonic gas of strongly dipolar NaCs molecules\nagainst inelastic losses via microwave shielding, decreasing losses by more\nthan a factor of 200 and reaching lifetimes on the scale of 1 second. We also\nmeasure high elastic scattering rates, a result of strong dipolar interactions,\nand observe the anisotropic nature of dipolar collisions. Finally, we\ndemonstrate evaporative cooling of a bosonic molecular gas to a temperature of\n36(5) nK, increasing its phase-space density by a factor of 20. This work is a\ncritical step towards the creation of a Bose-Einstein condensate of dipolar\nmolecules.",
        "positive": "A fermionic impurity in a dipolar quantum droplet: In this article we develop the framework to describe Bose-Fermi mixtures of\nmagnetic atoms, focusing on the interaction of bosonic self-bound dipolar\nquantum droplets with a small number of fermions. We find an attractive\ninteraction potential due to the dipolar interaction with several bound states,\nwhich can be occupied by one fermion each, resulting in a very weak back-action\non the bosons. We conclude, that these impurities might act as unique probes\ngiving access to inherent properties of dipolar quantum droplets."
    },
    {
        "anchor": "Creation and dynamics of two-dimensional skyrmions in antiferromagnetic\n  spin-1 Bose-Einstein condensates: We numerically simulate the creation process of two-dimensional skyrmionic\nexcitations in antiferromagnetic spin-1 Bose--Einstein condensates by solving\nthe full three-dimensional dynamics of the system from the Gross--Pitaevskii\nequation. Our simulations reproduce quantitatively the experimental results of\n[Choi et al., Phys. Rev. Lett. 108, 035301 (2012)] without any fitting\nparameters. Furthermore, we examine the stability of the skyrmion by computing\nthe temporal evolution of the condensate in a harmonic potential. The presence\nof both the quadratic Zeeman effect and dissipation in the simulations is vital\nfor reproducing the experimentally observed decay time.",
        "positive": "Rotating Few-body Atomic Systems in the Fractional Quantum Hall Regime: Topologically-ordered matter is a novel quantum state of matter observed only\nin a small number of physical systems, notably two-dimensional electron systems\nexhibiting fractional quantum Hall effects. It was recently proposed that a\nsimple form of topological matter may be created in interacting systems of\nrotating ultra-cold atoms. We describe ensemble measurements on small, rotating\nclusters of interacting bosonic atoms, demonstrating that they can be induced\ninto quantum ground states closely analogous to topological states of\nelectronic systems. We report measurements of inter-particle correlations and\nmomentum distributions of Bose gases in the fractional quantum Hall limit,\nmaking comparison to a full numerical simulation. The novel experimental\napparatus necessary to produce and measure properties of these deeply entangled\nquantum states is described."
    },
    {
        "anchor": "Pattern formation of quantum Kelvin-Helmholtz instability in binary\n  superfluids: We study theoretically nonlinear dynamics induced by shear-flow instability\nin segregated two-component Bose-Einstein condensates in terms of the Weber\nnumber, defined by extending the past theory on the Kelvin-Helmholtz\ninstability in classical fluids. Numerical simulations of the Gross-Pitaevskii\nequations demonstrate that dynamics of pattern formation is well characterized\nby the Weber number $We$, clarifying the microscopic aspects unique to the\nquantum fluid system. For $We \\lesssim 1$, the Kelvin-Helmholtz instability\ninduces flutter-finger patterns of the interface and quantized vortices are\ngenerated at the tip of the fingers. The associated nonlinear dynamics exhibits\na universal behavior with respect to $We$. When $We \\gtrsim 1$ in which the\ninterface thickness is larger than the wavelength of the interface mode, the\nnonlinear dynamics is effectively initiated by the counter-superflow\ninstability. In a strongly segregated regime and a large relative velocity, the\ninstability causes transient zipper pattern formation instead of generating\nvortices due to the lack of enough circulation to form a quantized vortex per a\nfinger. While, in a weakly segregating regime and a small relative velocity,\nthe instability leads to sealskin pattern in the overlapping region, in which\nthe frictional relaxation of the superflow cannot be explained only by the\nhomogeneous counter-superflow instability. We discuss the details of the linear\nand nonlinear characteristics of this dynamical crossover from small to large\nWeber numbers, where microscopic properties of the interface become important\nfor the large Weber number.",
        "positive": "Entanglement in an expanding toroidal Bose-Einstein condensate: Recent experiments have employed rapidly expanding toroidal Bose-Einstein\ncondensates (BECs) to mimic the inflationary expansion in the early universe.\nOne expected signature of the expansion in such experiments is spontaneous\nparticle creation (of phonons) which is observable in density-density\ncorrelations. We study entanglement of these particles, which are known to\nresult in a two-mode squeezed state. Using techniques for Gaussian states of\ncontinuous variable systems, we quantify the entanglement generated in this\nsystem, including effects such as decoherence and the use of an initially\nsqueezed state, which can suppress and enhance entanglement, respectively. We\nalso describe a protocol to experimentally measure the correlations entering\nthe covariance matrix, allowing an experimental quantification of the\nentanglement properties of the inflationary BEC."
    },
    {
        "anchor": "Measuring and engineering entropy and spin squeezing in weakly linked\n  Bose-Einstein condensates: We propose a method to infer the single-particle entropy of bosonic atoms in\nan optical lattice and to study the local evolution of entropy, spin squeezing,\nand entropic inequalities for entanglement detection in such systems. This\nmethod is based on experimentally feasible measurements of\nnon-nearest-neighbour coherences. We study a specific example of dynamically\ncontrolling atom tunneling between selected sites and show that this could\npotentially also improve the metrologically relevant spin squeezing.",
        "positive": "Diffraction-Unlimited Position Measurement of Ultracold Atoms in an\n  Optical Lattice: We consider a method of high-fidelity, spatially resolved position\nmeasurement of ultracold atoms in an optical lattice. We show that the\natom-number distribution can be nondestructively determined at a spatial\nresolution beyond the diffraction limit by tracking the progressive evolution\nof the many-body wavefunction collapse into a Fock state. We predict that the\nPauli exclusion principle accelerates the rate of wavefunction collapse of\nfermions in comparison with bosons. A possible application of our principle of\nsurpassing the diffraction limit to other imaging systems is discussed."
    },
    {
        "anchor": "Dipolar-Induced Resonance for Ultracold Bosons in a Quasi-1D Optical\n  Lattice: We study the role of the Dipolar-Induced Resonance (DIR) in a\nquasi-one-dimensional system of ultracold bosons. We first describe the effect\nof the DIR on two particles in a harmonic trap. Then, we consider a deep\noptical lattice loaded with ultracold dipolar bosons. In order to describe this\nsystem, we introduce a novel atom-dimer extended Bose-Hubbard model, which is\nthe minimal model correctly accounting for the DIR. We analyze the impact of\nthe DIR on the phase diagram at T=0 by exact diagonalization of a small-sized\nsystem. We show that the DIR strongly affects this phase diagram. In\nparticular, we predict the mass density wave to occur in a narrow domain\ncorresponding to weak nearest-neighbor interactions, and the occurrence of a\ncollapse phase for stronger dipolar interactions.",
        "positive": "Multi-particle bound state formation following a quantum quench to the\n  one-dimensional Bose gas with attractive interactions: We consider quantum quenches from an ideal Bose condensate to the\nLieb-Liniger model with arbitrary attractive interaction strength. We focus on\nthe properties of the non-equilibrium steady state reached at late times after\nthe quench. Using recently developed methods based on integrability, we obtain\nan exact description of the stationary state for a large number of bosons. A\ndistinctive feature of this state is the presence of a hierarchy of\nmulti-particle bound states. We determine the dependence of their densities on\ninteraction strength and obtain an exact expression for the stationary value of\nthe local pair correlation $g_2$. We discuss ramifications of our results for\ncold atom experiments."
    },
    {
        "anchor": "Polaron in the dilute critical Bose condensate: The properties of impurity immersed in the dilute $D$-dimensional Bose gas at\ntemperatures close to the second-order phase transition point are considered.\nParticularly by means of the $1/N$-expansion we calculated the leading-order\npolaron energy and the damping rate in the limit of vanishing boson-boson\ninteraction. It is show that the perturbative effective mass and the\nquasiparticle residue diverge logarithmically in the long-length limit\nsignalling the non-analytic behavior of impurity spectrum and a non-pole\nstructure of a polaron Green's function in the infrared region, respectively.",
        "positive": "Bottleneck accumulation of hybrid magneto-elastic bosons: It is known that an ensemble of magnons, quanta of spin waves, can be\nprepared as a Bose gas of weakly interacting quasiparticles with conservation\nof the particle number. Furthermore, the thermalization of the overpopulated\nmagnon gas can lead to the formation of a Bose-Einstein condensate at the\nbottom of a spin-wave spectrum. However, magnon-phonon scattering processes can\nsignificantly modify this scenario and new quasiparticles are formed -\nmagneto-elastic bosons. Our observations of a parametrically populated magnon\ngas in a single-crystal film of Yttrium Iron Garnet by means of\nwavevector-resolved Brillouin light scattering spectroscopy including\nmagneto-elastic coupling resulted in the discovery of a novel condensation\nphenomenon: A spontaneous accumulation of hybrid magneto-elastic bosonic\nquasiparticles at the intersection of the lowest magnon mode and a transversal\nacoustic wave."
    },
    {
        "anchor": "Larkin-Ovchinnikov superfluidity in a two-dimensional imbalanced atomic\n  Fermi gas: We present an extensive study of two-dimensional Larkin-Ovchinnikov (LO)\nsuperfluidity in a spin-imbalanced two-component atomic Fermi gas. In the\ncontext of Fulde-Ferrell-Larkin- Ovchinnikov (FFLO) phase, we explore a wide\nand generic class of pairing gap functions with ex- plicit spatial dependency.\nThe mean-field theory of such phases is applied through the Bogoliubov-de\nGennes equations in which the pairing gap can be determined self-consistently.\nIn order to systemat- ically explore the configuration space we consider both\nthe canonical and grand canonical ensembles where we control the polarization\nor chemical potentials of the system, respectively. The mean-field calculations\nenable us to understand the nature of the phase transitions in the fully paired\nBardeen- Cooper-Schrieffer (BCS) state, exotic LO phase, and partially\npolarized free Fermi gas. The order of the phase transitions has been examined\nand in particular we find a weak first-order phase transition between the\nexotic inhomogeneous LO phase and the BCS phase. In comparison to the\nthree-dimensional case, where the phase diagram is dominated by a generic\nseparation phase, we predict a broader parameter space for the spatially\ninhomogeneous LO phase. By computing the superfluid density of the LO phase at\ndifferent polarization, we show how the superfluidity of the system is\nsuppressed with increasing spin polarization.",
        "positive": "Dynamics for the Haldane phase in the Bilinear-Biquadratic Model: The BBM is a promising candidate to study spin-one systems and to design\nquantum simulators based on its underlying Hamiltonian. The variety of\ndifferent phases contains amongst other valuable and exotic phases the Haldane\nphase. We study the Kibble-Zurek physics of linear quenches into the Haldane\nphase. We outline ideal quench protocols to minimize defects in the final state\nwhile exploiting different linear quench protocols via the uniaxial or\ninteraction term. Furthermore, we look at the fate of the string order when\nquenching from a topologically non-trivial phase to a trivial phase. Our\nstudies show this depends significantly on the path chosen for quenching; for\nexample, we discover quenches from \\Neel{} to Haldane phase which reach a\nstring order greater than their ground state counterparts for the initial or\nfinal state at intermediate quench times."
    },
    {
        "anchor": "A BCS wavefunction approach to the BEC-BCS crossover of\n  exciton-polariton condensates: The crossover between low and high density regimes of exciton-polariton\ncondensates is examined using a BCS wavefunction approach. Our approach is an\nextension of the BEC-BCS crossover theory for excitons, but includes a cavity\nphoton field. The approach can describe both the low density limit, where the\nsystem can be described as a Bose-Einstein condensate (BEC) of\nexciton-polaritons, and the high density limit, where the system enters a\nphoton dominated regime. In contrast to the exciton BEC-BCS crossover where the\nsystem approaches an electron-hole plasma, the polariton high density limit has\nstrongly correlated electron-hole pairs. At intermediate densities, there is a\nregime with BCS-like properties, with a peak at non-zero momentum of the\nsinglet pair function. We calculate the expected photoluminescence and give\nseveral experimental signatures of the crossover.",
        "positive": "Phonon resonances in atomic currents through Bose-Fermi mixtures in\n  optical lattices: We present an analysis of Bose-Fermi mixtures in optical lattices for the\ncase where the lattice potential of the fermions is tilted and the bosons (in\nthe superfluid phase) are described by Bogoliubov phonons. It is shown that the\nBogoliubov phonons enable hopping transitions between fermionic Wannier-Stark\nstates; these transitions are accompanied by energy dissipation into the\nsuperfluid and result in a net atomic current along the lattice. We derive a\ngeneral expression for the drift velocity of the fermions and find that the\ndependence of the atomic current on the lattice tilt exhibits negative\ndifferential conductance and phonon resonances. Numerical simulations of the\nfull dynamics of the system based on the time-evolving block decimation\nalgorithm reveal that the phonon resonances should be observable under the\nconditions of a realistic measuring procedure."
    },
    {
        "anchor": "Solitons and Josephson-type oscillations in Bose-Einstein condensates\n  with spin-orbit coupling and time-varying Raman frequency: The existence and dynamics of solitons in quasi-one-dimensional Bose-Einstein\ncondensates (BEC) with spin-orbit coupling (SOC) and attractive two-body\ninteractions are described for two coupled atomic pseudo-spin components with\nslowly and rapidly varying time-dependent Raman frequency. By varying the Raman\nfrequency linearly in time, it was shown that ordinary nonlinear\nSchr\\\"odinger-type bright solitons can be converted to striped bright solitons\nand vice versa. The internal Josephson oscillations between atom-number of the\ncoupled soliton components, and the corresponding center-of-mass motion, are\nstudied for different parameter configurations. In this case, a mechanism to\ncontrol the soliton parameters is proposed by considering parametric\nresonances, which can emerge when using time-varying Raman frequencies. Full\nnumerical simulations confirm variational analysis predictions when applied to\nthe region where regular solitons are expected. In the limit of high\nfrequencies, the system is described by a time-averaged Gross-Pitaevskii\nformalism with renormalized nonlinear and SOC parameters and modified\nphase-dependent nonlinearities. By comparing full-numerical simulations with\naveraged results, we have also studied the lower limits for the frequency of\nRaman oscillations in order to obtain stable soliton solutions.",
        "positive": "Artificial gauge fields and topological insulators in Moire\n  superlattices: We propose an innovative quantum emulator based on Moire superlattices\nshowing that, by employing periodical modulation on each lattice site, one can\ncreate tunable, artificial gauge fields with imprinting Peierls phases on the\nhopping parameters and realize an analog of novel Haldane-like phase. As an\napplication, we provide a methodology to directly quantify the topological\ninvariant in such a system from a dynamical quench process. This design shows a\nrobustly integrated platform which opens a new door to investigate topological\nphysics."
    },
    {
        "anchor": "Boltzmann-type approach to transport in weakly interacting\n  one-dimensional fermionic systems: We investigate transport properties of one-dimensional fermionic tight\nbinding models featuring nearest and next-nearest neighbor hopping, where the\nfermions are additionally subject to a weak short range mutual interaction. To\nthis end we employ a pertinent approach which allows for a mapping of the\nunderlying Schr\\\"odinger dynamics onto an adequate linear quantum Boltzmann\nequation. This approach is based on a suitable projection operator method. From\nthis Boltzmann equation we are able to numerically obtain diffusion\ncoefficients in the case of non-vanishing next-nearest neighbor hopping, i.e.,\nthe non-integrable case, whereas the diffusion coefficient diverges without\nnext-nearest neighbor hopping. For the latter case we analytically investigate\nthe decay behavior of the current with the result that arbitrarily small parts\nof the current relax arbitrarily slowly which suggests anomalous diffusive\ntransport behavior within the scope of our approach.",
        "positive": "Atomic topological quantum matter using synthetic dimensions: The realization of topological states of matter in ultracold atomic gases is\ncurrently the subject of intense experimental activity. Using a synthetic\ndimension, encoded in a non-spatial degree of freedom, can greatly simplify the\nsimulation of gauge fields and give access to exotic topological states. We\nreview here recent advances in the field and discuss future perspectives for\ninteracting systems."
    },
    {
        "anchor": "Chern numbers hiding in time-of-flight images: We present a technique for detecting topological invariants -- Chern numbers\n-- from time-of-flight images of ultra-cold atoms. We show that the Chern\nnumbers of integer quantum Hall states of lattice fermions leave their\nfingerprints in the atoms' momentum distribution. We analytically demonstrate\nthat the number of local maxima in the momentum distribution is equal to the\nChern number in two limiting cases, for large hopping anisotropy and in the\ncontinuum limit. In addition, our numerical simulations beyond these two limits\nshow that these local maxima persist for a range of parameters. Thus, an\neveryday observable in cold atom experiments can serve as a useful tool to\ncharacterize and visualize quantum states with non-trivial topology.",
        "positive": "Dissipative dynamics of an impurity with spin-orbit coupling: Brownian motion of a mobile impurity in a bath is affected by spin-orbit\ncoupling (SOC). Here, we discuss a Caldeira-Leggett-type model that can be used\nto propose and interpret quantum simulators of this problem in cold Bose gases.\nFirst, we derive a master equation that describes the model and explore it in a\none-dimensional (1D) setting. To validate the standard assumptions needed for\nour derivation, we analyze available experimental data without SOC; as a\nbyproduct, this analysis suggests that the quench dynamics of the impurity is\nbeyond the 1D Bose-polaron approach at temperatures currently accessible in a\ncold-atom laboratory -- motion of the impurity is mainly driven by dissipation.\nFor systems with SOC, we demonstrate that 1D spin-orbit coupling can be 'gauged\nout' even in the presence of dissipation -- the information about SOC is\nincorporated in the initial conditions. Observables sensitive to this\ninformation (such as spin densities) can be used to study formation of steady\nspin polarization domains during quench dynamics."
    },
    {
        "anchor": "Quantum quench dynamics of tilted dipolar bosons in 2D optical lattices: We investigate the quench dynamics of the dipolar bosons in two dimensional\noptical lattice of square geometry using the time dependent Gutzwiller method.\nThe system exhibits different density orders like the checkerboard and the\nstriped pattern, depending upon the polarization angle of the dipoles. We\nquench the hopping parameter across the striped density wave (SDW) to striped\nsupersolid (SSS) phase transition, and obtain the scaling laws for the\ncorrelation length and topological vortex density, as function of the quench\nrate. The results are reminiscent of the Kibble-Zurek mechanism (KZM). We also\ninvestigate the dynamics from the striped supersolid phase to the checkerboard\nsupersolid phase, obtained by quenching the dipole tilt angle $\\theta$. This is\na first order structural quantum phase transition, and we study the\nnon-equilibrium dynamics from the perspective of the KZM. In particular, we\nfind the number of the domains with checkerboard order follows a power law\nscaling with the quench rate. This indicates the applicability of the KZM to\nthis first order quantum phase transition.",
        "positive": "Excitation spectra and rf-response near the polaron-to-molecule\n  transition from the functional renormalization group: A light impurity in a Fermi sea undergoes a transition from a polaron to a\nmolecule for increasing interaction. We develop a new method to compute the\nspectral functions of the polaron and molecule in a unified framework based on\nthe functional renormalization group with full self-energy feedback. We discuss\nthe energy spectra and decay widths of the attractive and repulsive polaron\nbranches as well as the molecular bound state and confirm the scaling of the\nexcited state decay rate near the transition. The quasi-particle weight of the\npolaron shifts from the attractive to the repulsive branch across the\ntransition, while the molecular bound state has a very small residue\ncharacteristic for a composite particle. We propose an experimental procedure\nto measure the repulsive branch in a Li6 Fermi gas using rf-spectroscopy and\ncalculate the corresponding spectra."
    },
    {
        "anchor": "Correlated dynamics in a synthetic lattice of momentum states: We study the influence of atomic interactions on quantum simulations in\nmomentum-space lattices (MSLs), where driven transitions between discrete\nmomentum states mimic transport between sites of a synthetic lattice. Low\nenergy atomic collisions, which are short ranged in real space, relate to\nnearly infinite-ranged interactions in momentum space. However, the added\nexchange energy between atoms in distinguishable momentum states leads to an\neffectively attractive, finite-ranged interaction in momentum space. In this\nwork, we observe the onset of self-trapping driven by such interactions in a\nmomentum-space double well, paving the way for more complex many-body studies\nin tailored MSLs. We consider the types of phenomena that may result from these\ninteractions, including the formation of chiral solitons in topological zigzag\nlattices.",
        "positive": "Quantum phases of attractive bosons on a Bose-Hubbard ladder with\n  three-body constraint: We obtain the complete quantum phase diagram of bosons on a two-leg ladder in\nthe presence of attractive onsite and repulsive interchain nearest-neighbor\ninteractions by imposing the onsite three-body constraint. We find three\ndistinct phases; namely, the atomic superfluid (ASF), dimer superfluid (DSF),\nand the dimer rung insulator (DRI). In the absence of the interchain\nnearest-neighbor repulsion, the system exhibits a transition from the ASF to\nthe DSF phase with increasing onsite attraction. However, the presence of the\ninterchain nearest-neighbor repulsion stabilizes a gapped DRI phase, which is\nflanked by the DSF phase. We also obtain the phase diagram of the system for\ndifferent values of the interchain nearest-neighbor interaction. By evaluating\ndifferent order parameters, we obtain the complete phase diagram and the\nproperties of the phase transitions using the self-consistent cluster\nmean-field theory."
    },
    {
        "anchor": "Dipolar Bose-Einstein condensate soliton on a two-dimensional optical\n  lattice: Using a three-dimensional mean-field model we study one-dimensional dipolar\nBose-Einstein condensate (BEC) solitons on a weak two-dimensional (2D) square\nand triangular optical lattice (OL) potentials placed perpendicular to the\npolarization direction. The stabilization against collapse and expansion of\nthese solitons for a fixed dipolar interaction and a fixed number of atoms is\npossible for short-range atomic interaction lying between two critical limits.\nThe solitons collapse below the lower limit and escapes to infinity above the\nupper limit. One can also stabilize identical tiny BEC solitons arranged on the\n2D square OL sites forming a stable 2D array of interacting droplets when the\nOL sites are filled with a filling factor of 1/2 or less. Such an array is\nunstable when the filling factor is made more than 1/2 by occupying two\nadjacent sites of OL. These stable 2D arrays of dipolar superfluid BEC solitons\nare quite similar to the recently studied dipolar Mott insulator states on 2D\nlattice in the Bose-Hubbard model by Capogrosso-Sansone et al. [B.\nCapogrosso-Sansone, C. Trefzger, M. Lewenstein, P. Zoller, G. Pupillo, Phys.\nRev. Lett. 104 (2010) 125301].",
        "positive": "High Sensitivity RF Spectroscopy of a Strongly-Interacting Fermi Gas: Rf spectroscopy is one of the most powerful probing techniques in the field\nof ultracold gases. We report on a novel rf spectroscopy scheme with which we\ncan detect very weak signals of only a few atoms. Using this method, we\nextended the experimentally accessible photon-energies range by an order of\nmagnitude compared to previous studies. We verify directly a universal property\nof fermions with short-range interactions which is a power-law scaling of the\nrf spectrum tail all the way up to the interaction scale. We also employ our\ntechnique to precisely measure the binding energy of Feshbach molecules in an\nextended range of magnetic fields. This data is used to extract a new\ncalibration of the Feshbach resonance between the two lowest energy levels of\n40K"
    },
    {
        "anchor": "Berry Phase in Atom-Molecule Conversion Systems and Fractional Monopole: We investigate the geometric phase or Berry phase of adiabatic quantum\nevolution in an atom-molecule conversion system, and find that the Berry phase\nin such system consists of two parts: the usual Berry connection term and a\nnovel term from the nonlinearity brought forth by the atom-molecule conversion.\nThe geometric phase can be viewed as the flux of the magnetic field of a\nmonopole through the surface enclosed by a closed path in parameter space. The\ncharge of the monopole, however, is found to be one third of the elementary\ncharge of the usual quantized monopole.",
        "positive": "The Pairing of Spin-orbit Coupled Fermi Gas in Optical Lattice: We investigate Rashba spin-orbit coupled Fermi gases in square optical\nlattice by using the determinant quantum Monte Carlo (DQMC) simulations which\nis free of the sign-problem. We show that the Berezinskii-Kosterlitz-Thoules\nphase transition temperature is firstly enhanced and then suppressed by\nspin-orbit coupling in the strong attraction region. In the intermediate\nattraction region, spin-orbit coupling always suppresses the transition\ntemperature. We also show that the spin susceptibility becomes anisotropic and\nretains finite values at zero temperature."
    },
    {
        "anchor": "Non-equilibrium Atomic Condensates and Mixtures: Collective Modes,\n  Condensate Growth and Thermalization: The non-equilibrium dynamics of trapped ultracold atomic gases, or mixtures\nthereof, is an extremely rich subject. Despite 20 years of studies, and\nremarkable progress mainly on the experimental front, numerous open question\nremain, related to the growth, relaxation and thermalisation of such systems,\nand there is still no universally-accepted theory for their theoretical\ndescription. In this paper we discuss one of the state-of-the-art kinetic\napproaches, which gives an intuitive picture of the physical processes\nhappening at the microscopic scale, being broadly applicable both below and\nabove the critical region (but not within the critical region itself).\nSpecifically, the Zaremba-Nikuni-Griffin (ZNG) scheme provides a\nself-consistent description of the coupling between the condensate and the\nthermal atoms, including the collisions between these two subsystems. It has\nbeen successfully tested against experiments in various settings, including\ncollective modes (e.g. monopole, dipole and quadrupole modes), topological\nexcitations (solitons and vortices) and surface evaporative cooling. Here, we\nshow that it can capture two important aspects of non- equilibrium dynamics for\nboth single-component and two-component BECs: the Kohn mode (the undamped\ndipole oscillation independent of interactions and temperature) and\n(re)thermalization leading to condensate growth following sudden evaporation.\nOur simulations, performed in a spherically-symmetric trap reveal (i) an\ninteresting two-stage dynamics and the emergence of a prominent monopole mode\nin the evaporative cooling of a single component Bose gas, and (ii) the long\nthermalization time associated with the sympathetic cooling of a realistic\ntwo-component mixture. Related open questions arise about the mechanisms and\nthe nature of thermalization in such systems, where further controlled\nexperiments are needed for benchmarking.",
        "positive": "Spectral intensity distribution of trapped fermions: To calculate static response properties of a many body system, local density\napproximation (LDA) can be safely applied. But applicability of LDA is limited\nfor the case of dynamical response functions since dynamics of the system needs\nto be considered as well. To examine this in the context of cold atoms, we\nconsider a system of non-interacting spin-$1/2$ fermions confined by a harmonic\ntrapping potential. We have calculated a very important response function, the\nspectral intensity distribution function (SIDF), both exactly and using LDA at\nzero temperature and compared with each other for different dimensions, trap\nfrequencies and momenta. The behavior of the SIDF at a particular momentum can\nbe explained by noting the behavior of the density of states (DOS) of the free\nsystem (without trap) in that particular dimension. The agreement between exact\nand LDA SIDFs becomes better with increase in dimensions and number of\nparticles."
    },
    {
        "anchor": "Interference, spectral momentum correlations, entanglement, and Bell\n  inequality for a trapped interacting ultracold atomic dimer: Analogies with\n  biphoton interferometry: Elucidating similarities and differences between quantum-optics biphoton\ninterference phenomena and the quantum physics of quasi-one-dimensional\ndouble-well optically-trapped ultracold neutral bosonic or fermionic atoms, we\nshow that the analog of the optical biphoton joint-coincidence spectral\ncorrelations, studied with massless non-interacting biphotons emanating from\nEPR-Bell-Bohm single-occupancy sources, corresponds to a distinct contribution\nin the total second-order momentum correlations of the massive, interacting,\nand time-evolving ultracold atoms. This single-occupancy contribution can be\nextracted from the total second-order momentum correlation function measured in\ntime-of-flight experiments, which for the trapped atomic system contains, in\ngeneral, a double-occupancy, NOON, component. The dynamics of the two-particle\nsystem are modeled by a Hubbard Hamiltonian. This partial coincidence spectrum\nis a cosine-square quantum beating dependent on the difference of the momenta\nof the two particles, while the corresponding coincidence probability proper,\nfamiliar from its role in describing the Hong-Ou-Mandel coincidence dip of\noverlapping photons, results from an integration over the particle momenta.\nBecause the second-order momentum correlations are mirrored in the\ntime-of-flight spectra in space, our theoretical findings provide impetus for\ntime-of-flight experimental protocols for emulating with (massive) ultracold\natoms venerable optical interferometries that use two space-time separated and\nentangled (massless) photons or double-slit optical sources. The implementation\nof such developments will facilitate testing of fundamental aspects and enable\napplications of quantum physics with trapped massive ultracold atoms, that is,\ninvestigations of nonlocality and violation of Bell inequalities, entanglement,\nand quantum information science.",
        "positive": "Strongly anisotropic vortices in dipolar quantum droplets: We construct strongly anisotropic quantum droplets with embedded vorticity in\nthe 3D space, with mutually perpendicular vortex axis and polarization of the\natomic magnetic moments. Stability of these anisotropic vortex quantum droplets\n(AVQDs) is verified by means of systematic simulations. Their stability area is\nidentified in the parametric plane of the total atom number and scattering\nlength of contact interactions. The application of torque perpendicular to the\nvorticity axis gives rise to robust intrinsic oscillations or rotation of the\nAVQDs. Collisions between slowly and fast moving AVQDs give rise, respectively,\nto the elastic outcome or merger. Finally, we construct stable\nvortex-antivortex-vortex bound states and find their stability regions in the\nparameter space."
    },
    {
        "anchor": "Spectral properties of strongly correlated bosons in two-dimensional\n  optical lattices: Spectral properties of the two-dimensional Bose-Hubbard model, which emulates\nultracold gases of atoms confined in optical lattices, are investigated by\nmeans of the variational cluster approach. The phase boundary of the quantum\nphase transition from Mott phase to superfluid phase is calculated and compared\nto recent work. Moreover the single-particle spectral functions in both the\nfirst and the second Mott lobe are presented and the corresponding densities of\nstates and momentum distributions are evaluated. A qualitatively similar\nintensity distribution of the spectral weight can be observed for spectral\nfunctions in the first and the second Mott lobe.",
        "positive": "Chiral orbital order of interacting bosons without higher bands: Ultracold atoms loaded into higher Bloch bands provide an elegant setting for\nrealizing many-body quantum states that spontaneously break time-reversal\nsymmetry through the formation of chiral orbital order. The applicability of\nthis strategy remains nonetheless limited due to the finite lifetime of atoms\nin high-energy bands. Here we introduce an alternative framework, suitable for\nbosonic gases, which builds on assembling square plaquettes pierced by a\n$\\pi$-flux (half a magnetic-flux quantum). This setting is shown to be formally\nequivalent to an interacting bosonic gas loaded into $p$ orbitals, and we\nexplore the consequences of the resulting chiral orbital order, both for weak\nand strong onsite interactions. We demonstrate the emergence of a chiral\nsuperfluid vortex lattice, exhibiting a long-lived gapped collective mode that\nis characterized by local chiral currents. This chiral superfluid phase is\nshown to undergo a phase transition to a chiral Mott insulator for sufficiently\nstrong interactions. Our work establishes coupled $\\pi$-flux plaquettes as a\npractical route for the emergence of orbital order and chiral phases of matter."
    },
    {
        "anchor": "Thermodynamics of the Hubbard model on stacked honeycomb and square\n  lattices: We present a numerical study of the Hubbard model on simply stacked honeycomb\nand square lattices, motivated by a recent experimental realization of such\nmodels with ultracold atoms in optical lattices. We perform simulations with\ndifferent interlayer coupling and interaction strengths and obtain N\\'eel\ntransition temperatures and entropies. We provide data for the equation of\nstate to enable comparisons of experiments and theory. We find an enhancement\nof the short-range correlations in the anisotropic lattices compared to the\nisotropic cubic lattice, in parameter regimes suitable for the interaction\ndriven adiabatic cooling.",
        "positive": "Collective excitations of a Bose-Einstein condensate of hard-core bosons\n  and their mediated interactions: from two-body bound states to mediated\n  superfluidity: The exchange of collective modes has been demonstrated to be a powerful tool\nfor inducing superconductivity and superfluidity in various condensed matter\nand atomic systems. In this article, we study the mediated interactions of\ncollective excitations in an ultracold gas of hard-core bosons. We show that\nthe induced interaction supports two-body states with energies, symmetries, and\na number of bound states strongly dependent on the properties of the hard-core\nboson gas. The ability to control the nature of the two-body bound states\nmotivates the study of superfluid phases, which we address within the BKT\ntheory. We demonstrate how the superfluid parameters and critical temperatures\ncan be tuned in our system. Our findings may pave the way for future\ntheoretical and experimental studies with ultracold gases and solid-state\nsystems."
    },
    {
        "anchor": "Condensate Fraction and Pair Coherence Lengths of Two-Dimension Fermi\n  Gases with Spin-Orbit Coupling: The effects of Rashba spin-orbit coupling on BCS-BEC crossover, the\ncondensate fraction and pair coherence lengths for a two-component attractive\nFermi gas in two dimension are studied. The results at $T=0K$ indicate that (1)\nwhen the strength of SOC is beyond a critical value, BCS-BEC crossover does not\nhappen in a conventional sense; (2) SOC enhances the condensate fraction, but\nsuppresses pair coherence lengths.",
        "positive": "Observing localisation in a 2D quasicrystalline optical lattice: Quasicrystals are long-range ordered but not periodic, representing an\ninteresting middle ground between order and disorder. We experimentally and\nnumerically study the ground state of non- and weakly-interacting bosons in an\neightfold symmetric quasicrystalline optical lattice. We find extended states\nfor weak lattices but observe a localisation transition at a lattice depth of\n$V_0=1.78(2)\\,E_{\\mathrm{rec}}$ for the non-interacting system. We identify\nthis transition by measuring the timescale required for adiabatic loading into\nthe lattice, which diverges at the critical lattice depth for localisation.\nGross-Pitaevskii simulations show that in interacting systems the transition is\nshifted to deeper lattices, as expected from superfluid order counteracting\nlocalisation. Our experimental results are consistent with such a mean-field\nshift. Quasiperiodic potentials, lacking conventional rare regions, provide the\nideal testing ground to realise many-body localisation in 2D."
    },
    {
        "anchor": "Tuning of dipolar interactions and evaporative cooling in a\n  three-dimensional molecular quantum gas: Ultracold polar molecules possess long-range, anisotropic, and tunable\ndipolar interactions, providing the opportunities to probe quantum phenomena\ninaccessible with existing cold gas platforms. However, experimental progress\nhas been hindered by the dominance of two-body loss over elastic interactions,\nwhich prevents efficient evaporative cooling. Though recent work has\ndemonstrated controlled interactions by confining molecules to a\ntwo-dimensional geometry, a general approach for tuning molecular interactions\nin a three-dimensional (3D), stable system has been lacking. Here, we\ndemonstrate tunable elastic dipolar interactions in a bulk gas of ultracold\n40K87Rb molecules in 3D, facilitated by an electric field-induced shielding\nresonance which suppresses the reactive loss by a factor of thirty. This\nimprovement in the ratio of elastic to inelastic collisions enables direct\nthermalization. The thermalization rate depends on the angle between the\ncollisional axis and the dipole orientation controlled by an external electric\nfield, a direct manifestation of the anisotropic dipolar interaction. We\nachieve evaporative cooling mediated by the dipolar interactions in three\ndimensions. This work demonstrates full control of a long-lived bulk quantum\ngas system with tunable long-range interactions, paving the way for the study\nof collective quantum many-body physics.",
        "positive": "Spectroscopic determination of magnetic-field-dependent interactions in\n  an ultracold Yb(3P2)-Li mixture: We present experimental results on the inelastic and elastic interspecies\ninteractions between ytterbium (Yb) in the metastable ${}^3\\mathrm{P}_2$ state\nloaded into a deep optical lattice and spin polarized lithium (Li) in its\nground state. Focusing on the $m_J = 0$ magnetic sublevel of\nYb(${}^3\\mathrm{P}_2$), bias magnetic fields between 20 G and 800 G are\ninvestigated and significantly enhanced inelastic collision rates with high\nmagnetic fields are found. In addition, by direct spectroscopy of the Yb\nMott-insulator immersed in the Li Fermi gas an upper boundary of the background\nscattering length of the Yb(${}^3\\mathrm{P}_2,\nm_J=0$)-Li(${}^2\\mathrm{S}_{1/2}, F=1/2, m_F=+1/2$) system is estimated,\nrevealing the absence of useful Feshbach resonances. These observations are\nqualitatively consistent with the theoretical calculations."
    },
    {
        "anchor": "Adiabatic entangling gate of Bose-Einstein condensates based on the\n  minimum function: A scheme is presented to perform an entangling gate between two atomic\nensembles or Bose-Einstein condensates in a optical cavity with a common\noptical mode. The method involves using a generalized Stimulated Raman\nAdiabatic Passage (STIRAP) to adiabatically evolve the ground state. We show\nthat dark states exist for any atom number within the cavities, and find that\nthe operation produces an unusual type of evolution where the minimum of the\nnumber of atoms between two levels transitions to another state. This produces\na unconventional type of entangling Hamiltonian which creates a phase depending\non the minimum operation. We analyze its reliability under a variety of\nconditions ranging from the ideal decoherence-free case to that including\nphoton loss and spontaneous emission. Ways of combating decoherence are\nanalyzed and the amount of entanglement that is generated is calculated.",
        "positive": "Temporal shaping and time varying orbital angular momentum of displaced\n  vortices: The fundamental mode of rotation in quantum fluids is given by a vortex,\nwhose quantized value yields the orbital angular momentum (OAM) per particle.\nIf the vortex is displaced (off-centered) from the reference point for\nrotation, the angular momentum is reduced and becomes fractional. Such\ndisplaced vortices can further exhibit a peculiar dynamics in presence of\nconfining potentials or couplings to other fields. We study analytically a\nnumber of 2D systems where displaced vortices exhibit a noteworthy dynamics,\nincluding time-varying self-sustained oscillation of the OAM, complex reshaping\nof their morphology with possible creation of vortex-antivortex pairs and\npeculiar trajectories for the vortex core with sequences of strong\naccelerations and decelerations which can even send the core to infinity and\nbring it back. Interestingly, these do not have to occur conjointly, with\ncomplex time dynamics of the vortex core and/or their wavepacket morphology\npossibly taking place without affecting the total OAM. Our results generalize\nto simple and fundamental systems a phenomenology recently reported with\nRabi-coupled bosonic fields, showing their wider relevance and opening\nprospects for new types of control and structuring of the angular momentum of\nlight and/or quantum fluids."
    },
    {
        "anchor": "Splitting of nonlinear-Schr\u00f6dinger breathers by linear and nonlinear\n  localized potentials: We consider evolution of one-dimensional nonlinear-Schr\\\"odinger (NLS)\ntwo-soliton complexes (breathers) with narrow repulsive or attractive\npotentials (barrier or well, respectively). By means of systematic simulations,\nwe demonstrate that the breather may either split into constituent fundamental\nsolitons (fragments) moving in opposite directions, or bounce as a whole from\nthe barrier. A critical initial position of the breather, which separates these\nscenarios, is predicted by an analytical approximation. The narrow potential\nwell tends to trap the fragment with the larger amplitude, while the other one\nescapes. The interaction of the breather with a nonlinear potential barrier is\nalso considered. The ratio of amplitudes of the emerging free solitons may be\ndifferent from the 3:1 value suggested by the exact NLS solution, especially in\nthe case of the nonlinear potential barrier. Post-splitting velocities of\nescaping solitons may be predicted by an approximation based on the energy\nbalance.",
        "positive": "Controlled Transport between Fermi Superfluids Through a Quantum Point\n  Contact: Recent advances in experimental techniques allow one to create a quantum\npoint contact between two Fermi superfluids in cold atomic gases with a tunable\ntransmission coefficient. In this Letter we propose that three distinct\nbehaviors of charge transports between two Fermi superfluids can be realized in\nthis single setup, which are the multiple Andreev reflection, the self-trapping\nand the Josephson oscillation. We investigate the dynamics of atom number\ndifference between two reservoirs for different initial conditions and\ndifferent transmission coefficients, and present a coherent picture of how the\ncrossover between different regimes takes place. Our results can now be\ndirectly verified in current experimental system."
    },
    {
        "anchor": "Disordered quantum gases under control: When attempting to understand the role of disorder in condensed-matter\nphysics, one faces severe experimental and theoretical difficulties and many\nquestions are still open. Two of the most challenging ones, which have been\ndebated for decades, concern the effect of disorder on superconductivity and\nquantum magnetism. Recent progress in ultracold atomic gases paves the way\ntowards realization of versatile quantum simulators which will be useful to\nsolve these questions. In addition, ultracold gases offer original situations\nand viewpoints, which open new perspectives to the field of disordered systems.",
        "positive": "Anderson localisation in two dimensions: insights from Localisation\n  Landscape Theory, exact diagonalisation, and time-dependent simulations: Motivated by experimental progress in cold atomic systems, we use and advance\nLocalisation Landscape Theory (LLT), to examine two-dimensional systems with\npoint-like random scatterers. We begin by showing that exact eigenstates cannot\nbe efficiently used to extract the localisation length. We then provide a\ncomprehensive review of known LLT, and confirm that the Hamiltonian with the\neffective potential of LLT has very similar low energy eigenstates to that with\nthe physical potential. Next, we use LLT to compute the localisation length for\nvery low-energy, maximally localised eigenstates and test our method against\nexact diagonalisation. Furthermore, we propose a transmission experiment that\noptimally detects Anderson localisation, and demonstrate how one may extract a\nlength scale which is correlated with (and in general smaller than) the\nlocalisation length. In addition, we study the dimensional crossover from one\nto two dimensions, providing a new explanation to the established trends. The\nprediction of a mobility edge coming from LLT is tested by direct Schr\\\"odinger\ntime evolution and is found to be unphysical. Moreover, we investigate\nexpanding wavepackets, to find that these can be useful in detecting and\nquantifying Anderson localisation in a transmission experiment, with the only\ndisadvantage being the inability to resolve the energy dependence of the\nlocalisation length. Then, we utilise LLT to uncover a connection between the\nAnderson model for discrete disordered lattices and continuous two-dimensional\ndisordered systems, which provides powerful new insights. From here, we\ndemonstrate that localisation can be distinguished from other effects by a\ncomparison to dynamics in an ordered potential with all other properties\nunchanged. Finally, we thoroughly investigate the effect of acceleration and\nrepulsive interparticle interactions, as relevant for current experiments."
    },
    {
        "anchor": "Stopping power of electrons in a semiconductor channel for swift point\n  charges: The nonperturbative kinetic framework for the stopping power of a\ncharged-particle system for swift point projectiles is implemented. The\npair-interaction potential energy required in this framework to two-body\nelastic scattering is based on the screened interaction energy between system\nparticles. In such an energetically optimized modeling the swift bare\nprojectile interacts with independent screened constituents of a fixed-density\ninteracting many-body target. The first-order Born momentum-transfer\n(transport) cross section is calculated and thus a comparison with stopping\ndata obtained [Phys. Rev. B {\\bf 26}, 2335 (1982)] by swift ions,\n$Z_1\\in{[9,17]}$ and $(v/v_0)\\simeq{11}$, under channeling condition in Si is\nmade. A quantitative agreement between the elastic scattering-based theoretical\nstopping and the experimentally observed reduced magnitude is found.\nConventionally, such a reduced magnitude for the observable is interpreted,\napplying an equipartition rule, as inelastic energy loss mediated by a\ncollective classical plasma-mode without momentum transfer to the valence-part.\nBeyond the leading, i.e., first-order Born-Bethe term ($Z_1^2$), the Barkas\n($Z_1^3$) and Bloch ($Z_1^4$) terms are discussed, following the arguments of\nLindhard for screened interaction. An extension to the case of stopping of warm\ndense plasma for swift charges is outlined as well.",
        "positive": "Symmetry-Protected Topological Phase for Spin-Tensor-Momentum-Coupled\n  Ultracold Atoms: We propose a realizable experiment scheme to construct a one-dimensional\nsynthetic magnetic flux lattice with spin-tensor-momentum coupled spin-1 atoms\nand explore its exotic topological states. Different from the Altland-Zirnbauer\nclassification, we show that our system hosts a symmetryprotected phase\nprotected by a magnetic group symmetry (M) and characterized by a Z2\ntopological invariant. In single-particle spectra, we show that the topological\nnontrivial phase supports two kinds of edge states, which include two (four)\nzero-energy edge modes in the absence (presence) of two-photon detuning. We\nfurther study the bulk-edge correspondence in a non-Hermitian model by taking\ninto account the particle dissipation. It is shown that the non-Hermitian\nsystem preserves the bulk-edge correspondence under the M symmetry but exhibits\nthe non-Hermitian skin effect with breaking the M symmetry at nonzero magnetic\nflux. This work provides insights in understanding the exotic topological\nquantum states of high-spin systems and facilitating their experimental\nexplorations."
    },
    {
        "anchor": "Phase Separation of Multi-Component Bose-Einstein Condensates of Trapped\n  Atoms and Molecules with a Homonuclear Feshbach Resonance: We investigate phase separation of Bose-Einstein condensates (BECs) of\ntwo-component atoms and one-component molecules with a homonuclear Feshbach\nresonance. We develop a full model for dilute atomic and molecular gases\nincluding correlation of the Feshbach resonance and all kinds of interparticle\ninteractions, and numerically calculate order parameters of the BECs in\nspherical harmonic oscillator traps at zero temperature with the Bogoliubov's\nclassical field approximation. As a result, we find out that the Feshbach\nresonance can induce two types of phase separation. The actual phase structures\nand density profiles of the trapped gases are predicted in the whole parameter\nregion, from the atom dominant regime to the molecule dominant regime. We focus\non the role of the molecules in the phase separation. Especially in the atom\ndominant regime, the role of the molecules is described through effective\ninteractions derived from our model. Furthermore we show that a perturbative\nand semi-classical limit of our model reproduces the conventional atomic BEC\n(single-channel) model.",
        "positive": "Second-order response theory of radio-frequency spectroscopy for cold\n  atoms: We present a theoretical description of the radio-frequency (rf) spectroscopy\nof fermionic atomic gases, based on the second-order response theory at finite\ntemperature. This approach takes into account the energy resolution due to the\nenvelope of the rf pulse. For a noninteracting final state, the momentum- and\nenergy-resolved rf intensity depends on the fermion spectral function and pulse\nenvelope. The contributions due to interactions in the final state can be\nclassified by means of diagrams. Using this formalism, as well as the local\ndensity approximation in two and three dimensions, we study the interplay of\ninhomogeneities and Hartree energy in forming the line shape of the rf signal.\nWe show that the effects of inhomogeneities can be minimized by taking\nadvantage of interactions in the final state, and we discuss the most relevant\nfinal-state effects at low temperature and density, in particular the effect of\na finite lifetime."
    },
    {
        "anchor": "Anderson Localization in Degenerate Spin-Orbit Coupled Fermi Gases with\n  Disorder: Competition between superconductivity and disorder plays an essential role in\nunderstanding the metal-insulator transition. Based on the Bogoliubov-de Gennes\nequation, we studied an s-wave superconductor with both spin-orbit coupling and\ndisorder are presented. With increasing the strength of disorder, the mean\nsuperconducting order parameter will vanish while the energy gap will persist,\nwhich indicates that the system undergoes a transition from a superconducting\nstate to an insulating state. This can be confirmed by calculating the inverse\nparticipation ratio. We also find that, if the strength of disorder is small,\nthe superconducting order parameter and the energy gap will decrease if we\nincrease the strength of spin-orbit coupling and Zeeman field. In the large\ndisorder limits, increasing the strength of spin-orbit coupling will increase\nthe mean superconducting order parameter. This phenomenon shows that the system\nis more insensitive to disorder if the spin-orbit coupling is presented.\nNumerical computing also shows that the whole system breaks up into several\nsuperconducting islands instead of being superconductivity.",
        "positive": "Formation of ultracold weakly bound dimers of bosonic\n  $^{23}\\textrm{Na}^{39}\\textrm{K}$: We create weakly bound bosonic $^{23}\\textrm{Na}^{39}\\textrm{K}$ molecules in\na mixture of ultracold $^{23}\\textrm{Na}$ and $^{39}\\textrm{K}$. The creation\nis done in the vicinity of a so far undetected Feshbach resonance at about\n$196\\,\\text{G}$ which we identify in this work by atom-loss spectroscopy. We\ninvestigate the involved molecular state by performing destructive radio\nfrequency binding energy measurements. For the constructive molecule creation\nwe use radio frequency pulses with which we assemble up to $6000$ molecules. We\nanalyze the molecule creation efficiency as a function of the radio frequency\npulse duration and the atom number ratio between $^{23}\\textrm{Na}$ and\n$^{39}\\textrm{K}$. We find an overall optimal efficiency of $6\\,\\%$ referring\nto the $^{39}\\textrm{K}$ atom number. The measured lifetime of the molecules in\nthe bath of trapped atoms is about $0.3\\,\\textrm{ms}$."
    },
    {
        "anchor": "Polaritonic ultracold reactions: cavity controlled molecular\n  photoassociation: We introduce a prototypical model for cavity polaritonic control of ultracold\nphotochemistry by considering the resonant vibrational strong coupling of a\nrubidium dimer to a terahertz cavity. We demonstrate that at avoided crossings\nbetween a vibrational excitation and the vacuum photon absorption, the\nresulting polaritonic states between the molecule and photons can efficiently\ncontrol the molecular vibrational Franck-Condon (FC) factors. Due to the\nentanglement between light and matter, FC factor is transferred from one\npolaritonic branch to other, leading to a polariton with a substantially\nenhanced FC factor. Utilizing this polariton state for photoassociation results\nin the enhanced formation of ultracold molecules. This work suggests a path to\ncontrolling photoassociation with cavity vacuum fields, and lays the ground for\nthe emerging subfield of polaritonic ultracold chemistry.",
        "positive": "Mass-imbalance induced structures of binary atomic mixtures in box\n  potentials: We consider the ground states of binary atomic boson-boson and\nfermion-fermion mixtures confined in one-dimensional box potentials by\nsimulating the systems using few-body models with delta-function interactions\nand many-body models with density-density interactions. For boson-boson\nmixtures, both models show signatures of phase separation in the strong\nrepulsion regime and sandwiched structures emerge in the presence of mass\nimbalance. The structural difference between equal-mass and mass-imbalanced\nsystems is due to the minimization of the interaction energy and the kinetic\nenergies from the density distortion at the hard walls and at the\nphase-separation interface. The mass imbalance adjusts the kinetic energies and\ncauses the lighter species to avoid the hard walls. For fermion-fermion\nmixtures, few-body simulations show a mass-imbalance induced structural changes\nin the strong repulsion regime, while many-body simulations show two-chunk\nphase separation due to the strong bulk kinetic energy. For equal-mass mixtures\nwith strong inter-species repulsion, the few-body and many-body models predict\ndifferent structures because the mean-field treatment in the many-body model\napproximates the contact interaction and smooths out the wavefunctions."
    },
    {
        "anchor": "Nonequilibrium relaxation transport of ultracold atoms: We analyze the equilibration process between two either fermionic or bosonic\nreservoirs containing ultracold atoms with a fixed total number of particles\nthat are weakly connected via a few-level quantum system. We allow for both the\ntemperatures and particle densities of the reservoirs to evolve in time.\nSubsequently, linearizing the resulting equations enables us to characterize\nthe equilibration process and its time scales in terms of equilibrium reservoir\nproperties and linear-response transport coefficients. Additionally, we\ninvestigate the use of such a device as particle transistor or particle\ncapacitor and analyze its efficiency.",
        "positive": "How is the density of quasi-two-dimensional uniform dipolar quantum Bose\n  gases affected by trap imperfections?: We theoretically investigate the impact of weak perturbations of a flat\npotential on the density of a quasi-two-dimensional dipolar Bose gas. We use a\nmean-field perturbative treatment of the potential defects and derive their\neffects at first order in the mean-field stable regime. We first focus on\ndefects containing a single spatial frequency and study the wavevector\ndependence of the density perturbation. A qualitative modification of the\nwavenumber dependence with the interaction parameters and a sensitivity in the\nexcitation direction reveal the long-range and anisotropic dipolar effects.\nThese effects are found to be most important at intermediate wavenumbers and\ncan give rise to a local maximum in the density perturbation reminiscent of the\nroton mode softening and local instabilities. The dependence on the gas and\ninteraction parameters is studied. The case of a flat potential perturbed with\nwhite noise on a certain momentum range is then examined. Here it is found that\nthe strength perturbation becomes independent of the mean density when\nsufficiently large. Our study touches upon experimentally relevant issues,\ngiving hints on how flat a uniform potential should be to achieve uniform\nquasi-two-dimensional dipolar Bose gases."
    },
    {
        "anchor": "Solvable Model of a Generic Trapped Mixture of Interacting Bosons:\n  Reduced Density Matrices and Proof of Bose-Einstein Condensation: A mixture of two kinds of identical bosons, species $1$ and species $2$, held\nin a harmonic potential and interacting by harmonic intra-species and\ninter-species particle-particle interactions is discussed. To prove\nBose-Einstein condensation of the mixture three steps are needed. First, we\nintegrate the all-particle density matrix, employing a four-parameter matrix\nrecurrence relations, down to the lowest-order intra-species and inter-species\nreduced density matrices of the mixture. Second, the coupled Gross-Pitaevskii\n(mean-field) equations of the mixture are solved analytically. Third, we\nanalyze the mixture's reduced density matrices in the limit of an infinite\nnumber of particles of both species $1$ and $2$ (when the interaction\nparameters, i.e., the products of the number of particles times the\nintra-species and inter-species interaction strengths, are held fixed) and\nprove that: (i) Both species $1$ and $2$ are 100\\% condensed; (ii) The\ninter-species reduced density matrix per particle is separable and given by the\nproduct of the intra-species reduced density matrices per particle; and (iii)\nThe mixture's energy per particle, and reduced density matrices and densities\nper particle all coincide with the Gross-Pitaevskii quantities. Finally, when\nthe infinite-particle limit is taken with respect to, say, species $1$ only\n(with interaction parameters held fixed) we prove that: (iv) Only species $1$\nis 100\\% condensed and its reduced density matrix and density per particle, as\nwell as the mixture's energy per particle, coincide with the Gross-Pitaevskii\nquantities of species $1$ alone; and (v) The inter-species reduced density\nmatrix per particle is nonetheless separable and given by the product of the\nintra-species reduced density matrices per particle.",
        "positive": "Correlations in lowest Landau level vortex states: We show how the configuration-space form of the Bogoliubov ground state wave\nfunction of a bosonic condensate with a single vortex in a harmonic trap can be\ndescribed in terms of bosonic Jastrow correlations. We then generalize this\nresult to study the first effects of such correlations on a mean-field vortex\nlattice state and show that the included correlations lower the energy below\nthat of the mean-field state. Although the reduction is relatively small, it is\na precursor of the more general expected effect of correlations in describing\nthe melting of the vortex lattice at large angular momentum per particle."
    },
    {
        "anchor": "Exploring scale invariance in the expansion of a spherical unitary Fermi\n  gas: A unitary Fermi gas in an isotropic harmonic trap is predicted to show scale\nand conformal symmetry that have important consequences in its thermodynamic\nand dynamical properties. By experimentally realizing an isotropic harmonic\ntrap, we study the expansion of a unitary Fermi gas and demonstrate its\nuniversal expansion dynamics along different directions and at different\ntemperatures. We show that as a consequence of SO(2,1) symmetry, the measured\nrelease energy is equal to that of the trapping energy. In addition, away from\nresonance when scale invariance is broken, we determine the effective exponent\n$\\gamma$ that relates the chemical potential and average density along the\nBEC-BCS crossover, which qualitatively agrees with the mean field predictions.\nThis work opens the possibility of studying non-equilibrium dynamics in a\nconformal invariant system in the future.",
        "positive": "Second order fluid dynamics for the unitary Fermi gas from kinetic\n  theory: We compute second order transport coefficients of the dilute Fermi gas at\nunitarity. The calculation is based on kinetic theory and the Boltzmann\nequation at second order in the Knudsen expansion. The second order transport\ncoefficients describe the shear stress relaxation time, non-linear terms in the\nstrain-stress relation, and non-linear couplings between vorticity and strain.\nAn exact calculation in the dilute limit gives $\\tau_R=\\eta/P$, where $\\tau_R$\nis the shear stress relaxation time, $\\eta$ is the shear viscosity, and $P$ is\npressure. This relation is identical to the result obtained using the\nBhatnagar-Gross-Krook (BGK) approximation to the collision term, but other\ntransport coefficients are sensitive to the exact collision integral."
    },
    {
        "anchor": "Interaction-Assisted Reversal of Thermopower with Ultracold Atoms: We study thermoelectric currents of neutral, fermionic atoms flowing through\na mesoscopic channel connecting a hot and a cold reservoir across the\nsuperfluid transition. The thermoelectric response results from a competition\nbetween density-driven diffusion from the cold to the hot reservoir and the\nchannel favoring transport of energetic particles from hot to cold. We control\nthe relative strength of both contributions to the thermoelectric response\nusing an external optical potential in a nearly non-interacting and a\nstrongly-interacting system. Without interactions, the magnitude of the\nparticle current can be tuned over a broad range but is restricted to flow from\nhot to cold in our parameter regime. Strikingly, strong interparticle\ninteractions additionally reverse the direction of the current. We\nquantitatively model ab initio the non-interacting observations and\nqualitatively explain the interaction-assisted reversal by the reduction of\nentropy transport due to pairing correlations. Our work paves the way to\nstudying the coupling of spin and heat in strongly correlated matter using\nspin-dependent optical techniques with cold atoms.",
        "positive": "Symbiotic solitons in a quasi-one- and quasi-two-dimensional spin-1\n  condensates: We study the formation of spin-1 symbiotic spinor solitons in a quasi-one-\n(quasi-1D) and quasi-two-dimensional (quasi-2D) hyper-fine spin $F=1$\nferromagnetic Bose-Einstein condensate (BEC). The symbiotic solitons\nnecessarily have a repulsive intraspecies interaction and are bound due to an\nattractive interspecies interaction. Due to a collapse instability in higher\ndimensions, an additional spin-orbit coupling is necessary to stabilize a\nquasi-2D symbiotic spinor soliton. Although a quasi-1D symbiotic soliton has a\nsimple Gaussian-type density distribution, novel spatial periodic structure in\ndensity is found in quasi-2D symbiotic SO-coupled spinor solitons. For a weak\nSO coupling, the quasi-2D solitons are of the $(-1, 0, +1)$ or $(+1, 0, -1)$\ntype with intrinsic vorticity and multi-ring structure, for Rashba or\nDresselhaus SO coupling, respectively, where the numbers in the parentheses are\nangular momenta projections in spin components $F_z = +1, 0, -1$, respectively.\nFor a strong SO coupling, stripe and superlattice solitons, respectively, with\na stripe and square-lattice modulation in density, are found in addition to the\nmulti-ring solitons. The stationary states were obtained by imaginary-time\npropagation of a mean-field model; dynamical stability of the solitons was\nestablished by real-time propagation over a long period of time. The\npossibility of the creation of such a soliton by removing the trap of a\nconfined spin-1 BEC in a laboratory is also demonstrated."
    },
    {
        "anchor": "Exactly solvable Gross-Pitaevskii type equations: TWe suggest a method to construct exactly solvable Gross-Pitaevskii type\nequations, especially the variable-coefficient high-order Gross-Pitaevskii type\nequations. We show that there exists a relation between the Gross-Pitaevskii\ntype equations. The Gross-Pitaevskii equations connected by the relation form a\nfamily. In the family one only needs to solve one equation and other equations\nin the family can be solved by a transform. That is, one can construct a series\nof exactly solvable Gross-Pitaevskii type equations from one exactly solvable\nGross-Pitaevskii type equation. As examples, we consider the family of some\nspecial Gross-Pitaevskii type equations: the nonlinear Schr\\\"odinger equation,\nthe quintic Gross-Pitaevskii equation, and cubic-quintic Gross-Pitaevskii\nequation. We also construct the family of a kind of generalized\nGross-Pitaevskii type equation.",
        "positive": "Prethermalization and Persistent Order in the Absence of a Thermal Phase\n  Transition: We numerically study the dynamics after a parameter quench in the\none-dimensional transverse-field Ising model with long-range interactions\n($\\propto 1/r^\\alpha$ with distance $r$), for finite chains and also directly\nin the thermodynamic limit. In nonequilibrium, i.e., before the system settles\ninto a thermal state, we find a long-lived regime that is characterized by a\nprethermal value of the magnetization, which in general differs from its\nthermal value. We find that the ferromagnetic phase is stabilized dynamically:\nas a function of the quench parameter, the prethermal magnetization shows a\ntransition between a symmetry-broken and a symmetric phase, even for those\nvalues of $\\alpha$ for which no finite-temperature transition occurs in\nequilibrium. The dynamical critical point is shifted with respect to the\nequilibrium one, and the shift is found to depend on $\\alpha$ as well as on the\nquench parameters."
    },
    {
        "anchor": "Dark-Antidark Spinor Solitons in Spin-1 Bose Gases: We consider a one-dimensional trapped spin-1 Bose gas and numerically explore\nfamilies of its solitonic solutions, namely antidark-dark-antidark (ADDAD), as\nwell as dark-antidark-dark (DADD) solitary waves. Their existence and stability\nproperties are systematically investigated within the experimentally accessible\neasy-plane ferromagnetic phase by means of a continuation over the atom number\nas well as the quadratic Zeeman energy. It is found that ADDADs are\nsubstantially more dynamically robust than DADDs. The latter are typically\nunstable within the examined parameter range. The dynamical evolution of both\nof these states is explored and the implication of their potential unstable\nevolution is studied. Some of the relevant observed possibilities involve,\ne.g., symmetry-breaking instability manifestations for the ADDAD, as well as\nsplitting of the DADD into a right- and a left-moving dark-antidark pair with\nthe anti-darks residing in a different component as compared to prior to the\nsplitting. In the latter case, the structures are seen to disperse upon\nlong-time propagation.",
        "positive": "Spin transport in a unitary Fermi gas close to the BCS transition: We consider spin transport in a two-component ultracold Fermi gas with\nattractive interspecies interactions close to the BCS pairing transition. In\nparticular, we consider the spin-transport relaxation rate and the\nspin-diffusion constant. Upon approaching the transition, the scattering\namplitude is enhanced by pairing fluctuations. However, as the system\napproaches the transition, the spectral weight for excitations close to the\nFermi level is decreased by the formation of a pseudogap. To study the\nconsequence of these two competing effects, we determine the spin-transport\nrelaxation rate and the spin-diffusion constant using both a Boltzmann approach\nand a diagrammatic approach. The former ignores pseudogap physics and finite\nlifetime effects. In the latter, we incorporate the full pseudogap physics and\nlifetime effects, but we ignore vertex corrections, so that we effectively\ncalculate single-particle relaxation rates instead of transport relaxation\nrates. We find that there is qualitative agreement between these two approaches\nalthough the results for the transport coefficients differ quantitatively."
    },
    {
        "anchor": "St\u00fcckelberg interferometry using spin-orbit-coupled cold atoms in an\n  optical lattice: Time evolution of spin-orbit-coupled cold atoms in an optical lattice is\nstudied, with a two-band energy spectrum having two avoided crossings. A force\nis applied such that the atoms experience two consecutive Landau-Zener\ntunnelings while transversing the avoided crossings. St\\\"uckelberg interference\narises from the phase accumulated during the adiabatic evolution between the\ntwo tunnelings. This phase is gauge field-dependent and thus provides new\nopportunities to measure the synthetic gauge field, which is verified via\ncalculation of spin transition probabilities after a double passage process.\nTime-dependent and time-averaged spin probabilities are derived, in which\nresonances are found. We also demonstrate chiral Bloch oscillation and rich\nspin-momentum locking behavior in this system.",
        "positive": "Coherence and Josephson oscillations between two tunnel-coupled\n  one-dimensional atomic quasicondensates at finite temperature: We revisit the theory of tunnel-coupled atomic quasicondensates in\ndouble-well elongated traps at finite temperatures. Using the\nfunctional-integral approach, we calculate the relative-phase correlation\nfunction beyond the harmonic limit of small fluctuations of the relative phase\nand its conjugate relative-density variable. We show that the thermal\nfluctuations of the relative phase between the two quasicondensates decrease\nthe frequency of Josephson oscillations and even wash out these oscillations\nfor small values of the tunnel coupling."
    },
    {
        "anchor": "Evidence for universal relations describing a gas with $p$-wave\n  interactions: Thermodynamics provides powerful constraints on physical and chemical systems\nin equilibrium. However, non-equilibrium dynamics depends explicitly on\nmicroscopic properties, requiring an understanding beyond thermodynamics.\nRemarkably, in dilute gases, a set of universal relations is known to connect\nthermodynamics directly with microscopic properties. So far, these \"contact\"\nrelations have been established only for interactions with $s$-wave symmetry,\ni.e., without relative angular momentum. We report measurements of two new\nphysical quantities, the \"$p$-wave contacts\", and present evidence that they\nencode the universal aspects of $p$-wave interactions through recently proposed\nrelations. Our experiments use an ultracold Fermi gas of $^{40}$K, in which\n$s$-wave interactions are suppressed by polarising the sample, while $p$-wave\ninteractions are enhanced by working near a scattering resonance. Using\ntime-resolved spectroscopy, we study how correlations in the system develop\nafter \"quenching\" the atoms into an interacting state. Combining\nquasi-steady-state measurements with new contact relations, we infer an\nattractive $p$-wave interaction energy as large as half the Fermi energy. Our\nresults reveal new ways to understand and characterise the properties of a\nresonant $p$-wave quantum gas.",
        "positive": "Spin correlations and doublon production rate for fermionic atoms in\n  modulated optical lattices: We compute the integrated doublon production rate in response to a lattice\nmodulation for two component fermions in an optical lattice. We derive a\ngeneral formula for the integrated intensity, valid in the presence of\ninhomogeneous potentials such as the trap, which gives the integrated intensity\nin terms of equal time correlation functions only. Such a formula is thus well\nsuited for direct numerical calculations. We show that, in the limit of large\nrepulsion for commensurate fillings, or for temperature ranges for which the\nhopping is incoherent, the integrated doublon spectrum is directly related to\nthe nearest neighbor spin-spin correlation function. We compute its temperature\ndependence in this regime using finite temperature quantum Monte Carlo\ncalculation."
    },
    {
        "anchor": "Chiral Spin Condensation in a One-Dimensional Optical Lattice: We study a spinor (two-component) Bose gas confined in a one-dimensional\ndouble-valley optical lattice which has a double-well structure in momentum\nspace. Based on field theory analysis, it is found that spinor bosons in the\ndouble-valley band may form a spin-charge mixed chiral spin quasicondensate\nunder certain conditions. Our numerical calculations in a concrete $\\pi$-flux\ntriangular ladder system confirm the robustness of the chiral spin order\nagainst interactions and quantum fluctuations. This exotic atomic Bose-Einstein\ncondensate exhibits spatially staggered spin loop currents without any charge\ndynamics despite the complete absence of spin-orbit coupling in the system,\ncreating an interesting approach to atom spintronics. The entanglement entropy\nscaling allows us to extract conformal-field-theory central charge and\nestablish the low-energy effective field theory for the chiral spin condensate\nas a two-component Luttinger liquid. Our predictions should be detectable in\natomic experiments through spin-resolved time-of-flight techniques.",
        "positive": "Quantum Phase diagram and time-of-flight absorption pictures of\n  ultracold Bose system in a square optical superlattice: In this letter, by the use of the generalized effective potential theory,\nwith the help of process-chain approach under the framework of Kato formulation\nof perturbation expansion, we calculate out the quantum phase diagram up to\n8-th order for an ultracold Bose system in a square optical superlattice. Base\non these perturbative data, with the help of the linear fit extrapolation\ntechnique, more accurate results are gotten, which are in excellent agreement\nwith recent Monte-Carlo numerical results. Moreover, by employing the\ngeneralized re-summed Green's function method and cumulant expansion, the\nmomentum distribution function of the system is also calculated analytically\nand the time-of-flight absorption pictures of the system are plotted."
    },
    {
        "anchor": "A nonlinear dynamics approach to Bogoliubov excitations of Bose-Einstein\n  condensates: We assume the macroscopic wave function of a Bose-Einstein condensate as a\nsuperposition of Gaussian wave packets, with time-dependent complex width\nparameters, insert it into the mean-field energy functional corresponding to\nthe Gross-Pitaevskii equation (GPE) and apply the time-dependent variational\nprinciple. In this way the GPE is mapped onto a system of coupled equations of\nmotion for the complex width parameters, which can be analyzed using the\nmethods of nonlinear dynamics. We perform a stability analysis of the fixed\npoints of the nonlinear system, and demonstrate that the eigenvalues of the\nJacobian reproduce the low-lying quantum mechanical Bogoliubov excitation\nspectrum of a condensate in an axisymmetric trap.",
        "positive": "Propagation properties and stability of dark solitons in weakly\n  interacting Bose-Bose droplets: We investigate dark solitons in two-component Bose systems with competing\ninteractions in one dimension. Such a system hosts a liquid phase stabilized by\nthe beyond-mean field corrections. Using the generalized Gross-Pitaevskii\nequation, we reveal the presence of two families of solitonic solutions. The\nsolitons in both of them can be engineered to be arbitrarily wide. One family\nof solutions, however, has got an anomalous dispersion relation and our\nanalyses show one of its branches is unstable. We find the presence of a\ncritical velocity demarcating the stable from unstable solutions. Nonetheless,\ngrey anomalous solitons are able to exist inside quantum droplets and can be\ntreated as solitonic excitations thereof."
    },
    {
        "anchor": "Probing the Berry Curvature and Fermi Arcs of a Weyl Circuit: The Weyl particle is the massless fermionic cousin of the photon. While no\nfundamental Weyl particles have been identified, they arise in condensed matter\nand meta-material systems, where their spinor nature imposes topological\nconstraints on low-energy dispersion and surface properties. Here we\ndemonstrate a topological circuit with Weyl dispersion at low-momentum,\nrealizing a 3D lattice that behaves as a half-flux Hofstadter model in all\nprincipal planes. The circuit platform provides access to the complete\ncomplex-valued spin-texture of all bulk- and surface- states, thereby revealing\nnot only the presence of Weyl points and the Fermi arcs that connect their\nsurface-projections, but also, for the first time, the Berry curvature\ndistribution through the Brillouin zone and the associated quantized Chiral\ncharge of the Weyl points. This work opens a path to exploration of interacting\nWeyl physics in superconducting circuits, as well as studies of how manifold\ntopology impacts band topology in three dimensions.",
        "positive": "Hydrodynamic theory of Rotating Ultracold Bose Einstein Condensates in\n  Supersolid Phase: Within mean field Gross-Pitaevskii framework, ultra cold atomic condensates\nwith long range interaction is predicted to have a supersolid like ground state\nbeyond a critical interaction strength. Such mean field supersolid like ground\nstate has periodically modulated superfluid density which implies the\ncoexistence of superfluid and crystalline order. Ultra cold atomic system in\nsuch mean field ground state can be subjected to artificial gauge field created\neither through rotation or by introducing space dependent coupling among\nhyperfine states of the atoms using Raman lasers. Starting from this\nGross-Pitaevskii energy functional that describes such systems at zero\ntemperature, we construct hydrodynamic theory to describe the low energy long\nwavelength excitations of such rotating supersolid of weakly interacting ultra\ncold atoms in two spatial dimensions for generic type of long range\ninteraction. We treat the supersolidity in such system within the framework of\nwell known two fluid approximation. Considering such system in the fast\nrotation limit where a vortex lattice in superfluid coexists with the\nsupersolid lattice, we analytically obtain the dispersion relations of\ncollective excitations around this equilibrium state. The dispersion relation\ngives the modes of the rotating supersolid which can be experimentally measured\nwithin the current technology. We point out that this can clearly identify such\na ultra cold atomic supersolid phase in an unambiguous way."
    },
    {
        "anchor": "Laser Cooling at Resonance: We show experimentally that 3-D laser cooling of lithium atoms is achieved\nwhen the laser light is tuned exactly to resonance with the atomic transition.\nFor a theoretical description of this surprising phenomenon we resolve to a\nfull model which takes into account both the entire atomic structure and the\nlaser light polarization. Here we build such a model for $^7$Li atoms cooled on\nthe $D_{2}$-line in a $\\sigma^+-\\sigma^-$ laser configuration. We take all 24\nZeeman sub-levels into account and obtain good agreement with the experimental\ndata. Moreover, by means of Monte-Carlo simulations we show that coherent\nprocesses play an important role in showing consistency between the theory and\nthe experimental results.",
        "positive": "Effective single-band models for strongly interacting fermions in an\n  optical lattice: To test effective Hamiltonians for strongly interacting fermions in an\noptical lattice, we numerically find the energy spectrum for two fermions\ninteracting across a Feshbach resonance in a double well potential. From the\nspectrum, we determine the range of detunings for which the system can be\ndescribed by an effective lattice model, and how the model parameters are\nrelated to the experimental parameters. We find that for a range of strong\ninteractions the system is well described by an effective $t-J$ model, and the\neffective superexchange term, $J$, can be smoothly tuned through zero on either\nside of unitarity. Right at and around unitarity, an effective one-band general\nHubbard model is appropriate, with a finite and small on-site energy, due to a\nlattice-induced anharmonic coupling between atoms at the scattering threshold\nand a weakly bound Feshbach molecule in an excited center of mass state."
    },
    {
        "anchor": "Emergence of multiple localization transitions in a one-dimensional\n  quasiperiodic lattice: Low dimensional quasiperiodic systems exhibit localization transitions by\nturning all quantum states localized after a critical quasidisorder. While\ncertain systems with modified or constrained quasiperiodic potential undergo\nmultiple localization transitions in one dimension, we predict an emergence of\nmultiple localization transitions without directly imposing any constraints on\nthe quasiperiodic potential. By considering a one-dimensional system described\nby the Aubry-And\\'{r}e (AA) model, we show that an additional staggered onsite\npotential can drive the system through a series of localization transitions as\na function of the staggered potential. Interestingly, we find that the number\nof localization transitions strongly depends on the strength of the\nquasiperiodic potential. Moreover, we obtain the signatures of these\nlocalization transitions in the expansion dynamics and propose an experimental\nscheme for their detection in the quantum gas experiment.",
        "positive": "Prethermalization in quenched spinor condensates: Motivated by recent experiments, we consider the dynamics of spin-one spinor\ncondensates after a quantum quench from the polar to ferromagnetic state from\nvarying the quadratic Zeeman field q. We apply the Truncated Wigner\nApproximation (TWA) to the spinor system, including all spatial and spin\ndegrees of freedom. For short times, we find full agreement with the linearized\nBogoliubov analysis. For longer times, where the Bogoliubov theory fails, we\nfind that the system reaches a quasi-steady prethermalized state. We compute\nthe Bogoliubov spectrum about the ferromagnetic state with general q and show\nthat the resulting finite temperature correlation functions grossly disagree\nwith the full TWA results, thus indicating that the system does not thermalize\neven over very long time scales. Finally we show that the absence of\nthermalization over realistic time scales is consistent with calculations of\nLandau damping rates of excitations in the finite-temperature condensate."
    },
    {
        "anchor": "Spin-orbit coupled fermions in an optical lattice clock: Engineered spin-orbit coupling (SOC) in cold atom systems can aid in the\nstudy of novel synthetic materials and complex condensed matter phenomena.\nDespite great advances, alkali atom SOC systems are hindered by heating from\nspontaneous emission, which limits the observation of many-body effects,\nmotivating research into potential alternatives. Here we demonstrate that SOC\ncan be engineered to occur naturally in a one-dimensional fermionic 87Sr\noptical lattice clock (OLC). In contrast to previous SOC experiments, in this\nwork the SOC is both generated and probed using a direct ultra-narrow optical\nclock transition between two electronic orbital states. We use clock\nspectroscopy to prepare lattice band populations, internal electronic states,\nand quasimomenta, as well as to produce SOC dynamics. The exceptionally long\nlifetime of the excited clock state (160 s) eliminates decoherence and atom\nloss from spontaneous emission at all relevant experimental timescales,\nallowing subsequent momentum- and spin-resolved in situ probing of the SOC band\nstructure and eigenstates. We utilize these capabilities to study Bloch\noscillations, spin-momentum locking, and Van Hove singularities in the\ntransition density of states. Our results lay the groundwork for the use of\nOLCs to probe novel SOC phases of matter.",
        "positive": "Bose-Einstein condensation: Twenty years after: The aim of this introductory article is two-fold. First, we aim to offer a\ngeneral introduction to the theme of Bose-Einstein condensates, and briefly\ndiscuss the evolution of a number of relevant research directions during the\nlast two decades. Second, we introduce and present the articles that appear in\nthis Special Volume of Romanian Reports in Physics celebrating the conclusion\nof the second decade since the experimental creation of Bose-Einstein\ncondensation in ultracold gases of alkali-metal atoms."
    },
    {
        "anchor": "Universal equation of state for wave turbulence in a quantum gas: Boyle's 1662 observation that the volume of a gas is, at constant\ntemperature, inversely proportional to pressure, offered a prototypical example\nof how an equation of state (EoS) can succinctly capture key properties of a\nmany-particle system. Such relations are now cornerstones of equilibrium\nthermodynamics. Extending thermodynamic concepts to far-from-equilibrium\nsystems is of great interest in various contexts including glasses, active\nmatter, and turbulence, but is in general an open problem. Here, using a\nhomogeneous ultracold atomic Bose gas, we experimentally construct an EoS for a\nturbulent cascade of matter waves. Under continuous forcing at a large length\nscale and dissipation at a small one, the gas exhibits a non-thermal, but\nstationary state, which is characterised by a power-law momentum distribution\nsustained by a scale-invariant momentum-space energy flux. We establish the\namplitude of the momentum distribution and the underlying energy flux as\nequilibrium-like state variables, related by an EoS that does not depend on the\ndetails of the energy injection or dissipation, or the history of the system.\nMoreover, we show that the equations of state for a wide range of interaction\nstrengths and gas densities can be empirically scaled onto each other. This\nresults in a universal dimensionless EoS that sets benchmarks for the theory\nand should also be relevant for other turbulent systems.",
        "positive": "Interfaces between Bose-Einstein and Tonks-Girardeau atomic gases: We consider one-dimensional mixtures of an atomic Bose-Einstein condensate\n(BEC) and Tonks- Giradeau (TG) gas. The mixture is modeled by a coupled system\nof the Gross-Pitaevskii equation for the BEC and the quintic nonlinear\nSchroedinger equation for the TG component. An immiscibility condition for the\nbinary system is derived in a general form. Under this condition, three types\nof BEC-TG interfaces are considered: domain walls (DWs) separating the two\ncomponents; bubble-drops (BDs), in the form of a drop of one component immersed\ninto the other (BDs may be considered as bound states of two DWs); and bound\nstates of bright and dark solitons (BDSs). The same model applies to the\ncopropagation of two optical waves in a colloidal medium. The results are\nobtained by means of systematic numerical analysis, in combination with\nanalytical Thomas-Fermi approximations (TFAs). Using both methods, families of\nDW states are produced in a generic form. BD complexes exist solely in the form\nof a TG drop embedded into the BEC background. On the contrary, BDSs exist as\nbound states of TG bright and BEC dark components, and vice versa."
    },
    {
        "anchor": "A variational approach for the ground state profile of a trapped\n  spinor-BEC: A detailed study of phase transition in spin-1 condensate at zero\n  magnetic field: In this article we introduce a multi-modal variational method to analytically\nestimate the full number- and corresponding energy-density profile of a spin-1\nBose-Einstein condensate (BEC) for a number of particles as low as 500 under\nharmonic confinement. To apply this method, we consider a system of spin-1 BEC\nunder three-dimensional isotropic and effective one-dimensional harmonic\nconfinement in the absence (negligible presence) of the magnetic field which\nhas ground state candidates of comparable energy. It should be noted that in\nsuch circumstances kinetic energy contribution to the ground state cannot be\nneglected which puts the applicability of Thomas-Fermi approximation to\nquestion. For anti-ferromagnetic condensates, the T-F approximated energy\ndifference between the competing stationary states (ground state and the first\nexcited state) is approximately 0.3\\%. As T-F approximation is only good for\ncondensates with a large number of particles, T-F approximated predictions can\ncompletely go wrong especially for small condensates. This is where comes the\nrole of a detailed analysis using our variational method, which incorporates\nthe kinetic energy contribution and accurately estimates the number- and\nenergy-density profile even for condensates having a small number of particles.\nResults of our analytical method are supported by numerical simulation. This\nvariational method is general and can be extended to other\nsimilar/higher-dimensional problems to get results beyond the accuracy of the\nThomas-Fermi approximation.",
        "positive": "Exotic few-body bound states in a lattice: Strongly-interacting ultra-cold atoms in tight-binding optical lattice\npotentials provide an ideal platform to realize the fundamental Hubbard model.\nHere, after outlining the elementary single particle solution, we review and\nexpand our recent work on complete characterization of the bound and scattering\nstates of two and three bosonic atoms in a one-dimensional optical lattice. In\nthe case of two atoms, there is a family of interaction-bound \"dimer\" states of\nco-localized particles that exists invariantly for either attractive or\nrepulsive on-site interaction, with the energy below or above the two-particle\nscattering continuum, respectively. Adding then the third particle -- \"monomer\"\n-- we find that, apart from the simple strongly-bound \"trimer\" corresponding to\nall three particles occupying the same lattice site, there are two peculiar\nfamilies of weakly-bound trimers with energies below and above the\nmonomer-dimer scattering continuum, the corresponding binding mechanism being\nan effective particle exchange interaction."
    },
    {
        "anchor": "Roton confinement in trapped dipolar Bose-Einstein condensates: Roton excitations constitute a key feature of dipolar gases, connecting these\ngases with superfluid helium. We show that the density dependence of the roton\nminimum results in a spatial roton confinement, particularly relevant in\npancake dipolar condensates with large aspect ratios. We show that roton\nconfinement plays a crucial role in the dynamics after roton instability, and\nthat arresting the instability may create a trapped roton gas revealed by\nconfined density modulations. We discuss the local susceptibility against\ndensity perturbations, which we illustrate for the case of vortices. Roton\nconfinement is expected to play a key role in experiments.",
        "positive": "Fractional exclusion statistics -- the method to describe interacting\n  particle systems as ideal gases: I show that if the total energy of a system of interacting particles may be\nwritten as a sum of quasiparticle energies, then the system of quasiparticles\ncan be viewed in general as an ideal gas with fractional exclusion statistics\n(FES). The general method for calculating the FES parameters is also provided.\n  The interacting particle system cannot be described as an ideal gas of Bose\nand Fermi quasiparticles except in trivial situations."
    },
    {
        "anchor": "Three-dimensional gap solitons in Bose-Einstein condensates supported by\n  one-dimensional optical lattices: We study fundamental and compound gap solitons (GSs) of matter waves in\none-dimensional (1D) optical lattices (OLs) in a three-dimensional (3D)\nweak-radial-confinement regime, which corresponds to realistic experimental\nconditions in Bose-Einstein condensates (BECs). In this regime GSs exhibit\nnontrivial radial structures. Associated with each 3D linear spectral band\nexists a family of fundamental gap solitons that share a similar transverse\nstructure with the Bloch waves of the corresponding linear band. GSs with\nembedded vorticity $m$ may exist \\emph{inside} bands corresponding to other\nvalues of $m$. Stable GSs, both fundamental and compound ones (including vortex\nsolitons), are those which originate from the bands with lowest axial and\nradial quantum numbers. These findings suggest a scenario for the experimental\ngeneration of robust GSs in 3D settings.",
        "positive": "Universal relations of strongly interacting Fermi gases with multiple\n  scattering channels: Universal relations are important for understanding strongly interacting\nFermi gases, the study of which have been mostly limited to cases with a single\nscattering channel. Here we discover a series universal relations for strongly\ninteracting Fermi gases with multiple scattering channels. Unlike its\ncounterpart across a single channel wide magnetic Feshbach resonance, a new\nkind of contact which we call the cross-channel contact naturally appears in\nthis system, this contact is related to varies thermodynamic quantities as well\nas short range correlation functions."
    },
    {
        "anchor": "Feshbach spectroscopy and dual-species Bose-Einstein condensation of\n  $^{23}\\mathrm{Na}-$$^{39}\\mathrm{K}$ mixtures: We present measurements of interspecies Feshbach resonances and subsequent\ncreation of dual-species Bose-Einstein condensates of $^{23}\\mathrm{Na}$ and\n$^{39}\\mathrm{K}$. We prepare both optically trapped ensembles in the spin\nstate $\\left|f = 1,m_{f}=-1\\right\\rangle$ and perform atom loss spectroscopy in\na magnetic field range from 0 to $700 \\, \\mathrm{G}$. The observed features\ninclude several s-wave poles and a zero crossing of the interspecies scattering\nlength as well as inelastic two-body contributions in the $\\mathcal{M} =\nm_{\\mathrm{Na}}+m_{\\mathrm{K}} = -2$ submanifold. We identify and discuss the\nsuitability of different magnetic field regions for the purposes of sympathetic\ncooling of \\K and achieving dual-species degeneracy. Two condensates are\ncreated simultaneously by evaporation at a magnetic field of about $150 \\,\n\\mathrm{G}$, which provides sizable intra- and interspecies scattering rates\nneeded for fast thermalization. The impact of the differential gravitational\nsag on the miscibility criterion for the mixture is discussed. Our results\nserve as a promising starting point for the magnetoassociation into quantum\ndegenerate $^{23}\\mathrm{Na}^{39}\\mathrm{K}$ Feshbach molecules.",
        "positive": "Superfluid Fraction and Leggett Bound in a Density Modulated Strongly\n  Interacting Fermi Gas at Zero Temperature: We calculate the superfluid fraction of an interacting Fermi gas, in the\npresence of a one-dimensional periodic potential of strength $V_0$ and\nwave-vector $q$. Special focus is given to the unitary Fermi gas, characterized\nby the divergent behavior of the s-wave scattering length. Comparison with the\nLeggett's upper bound $(\\langle n_{1D}\\rangle <1/n_{1D}>)^{-1}$, with $n_{1D}$\nthe 1D column density, explicitly shows that, differently from the case of a\ndilute interacting Bose gas, the bound significantly overestimates the value of\nthe superfluid fraction, except in the phonon regime of small $q$. Sum rule\narguments show that the combined knowledge of the Leggett bound and of the\nactual value of the superfluid fraction allows for the determination of\ncurvature effects providing the deviation of the dispersion of the\nAnderson-Bogoliubov mode from the linear phonon dependence. The comparison with\nthe predictions of the weakly interacting BCS Fermi gas points out the crucial\nrole of two-body interactions. The implications of our predictions on the\nanisotropic behavior of the sound velocity are also discussed."
    },
    {
        "anchor": "Frequency combs with weakly lasing exciton-polariton condensates: We predict the spontaneous modulated emission from a pair of\nexciton-polariton condensates due to coherent (Josephson) and dissipative\ncoupling. We show that strong polariton-polariton inter- action generates\ncomplex dynamics in the weak-lasing domain way beyond Hopf bifurcations. As a\nresult, the exciton-polariton condensates exhibit self-induced oscillations and\nemit an equidistant frequency comb light spectrum. A plethora of possible\nemission spectra with asymmetric peak dis- tributions appears due to\nspontaneously broken time-reversal symmetry. The lasing dynamics is affected by\nthe shot noise arising from the influx of polaritons. That results in a complex\ninhomo- geneous line broadening.",
        "positive": "The Quantum Dynamics of Two-component Bose-Einstein Condensate: an\n  $Sp(4,R)$ Symmetry Approach: The compact groups such as $SU(n)$ and $SO(n)$ groups have been heavily\nstudied and applied in the study of quantum many body systems. However, the\nnon-compact groups such as the real symplectic groups are less touched. In this\npaper, we will reveal that the quantum dynamics of two-component Bose-Einstein\ncondensate can be described by a \\emph{non-compact} real symplectic group\n$Sp(4,R)$. With this group, we can give a explicit form for the wavefunction in\nany time of the evolution, meanwhile, map this whole time evolution to a\ntrajectory in a six-dimensional manifold. By introducing a polar coordinate, we\ncan visualize this six-dimensional manifold in 2d unit disk and reveal the\nrelation between the behavior of the trajectory in this manifold and the\neigen-energies of the Hamiltonian. Furthermore, the time evolution of\nexpectation value of a physical observable such as number operator is proven\nclosely related to the behavior of the trajectory in this manifold."
    },
    {
        "anchor": "Elementary excitations in spinor polariton- electron systems: We consider effective interactions in a 2D hybrid polariton- electron system\nand calculate dispersion of elementary excitations accounting the spin degree\nof freedom of the particles. Due to the crucial role played by the exchange\nterm in polariton- electron interactions the dispersions of this system become\nspin- dependent and show unusual behavior. The coupling of the excitations of\nthe condensate with 2D plasmon can result in appearence of roton minimum in the\ndispersion and destruction of the condensate for close enough situated quantum\nwells with electrons and excitons.",
        "positive": "Spatial separation of rotating binary Bose-Einstein condensate by tuning\n  the dipolar interactions: We are pointing out relevant anisotropic effects, related to spatial\nseparation, miscibility and mass-symmetry, due to dipole-dipole interactions in\nrotating binary dipolar Bose-Einstein condensates, by considering symmetric\n($^{164}$Dy-$^{162}$Dy) and asymmetric ($^{168}$Er-$^{164}$Dy,\n$^{164}$Dy-$^{87}$Rb) dipolar mixtures. The binary mixtures are kept in strong\npancake-shaped trap, modeled by an effective two-dimensional coupled\nGross-Pitaevskii equation. The anisotropy of the dipolar interactions, on\nmiscibility and vortex-lattice structures, is studied by tuning the\npolarization angle of the dipoles $\\varphi$, which can enhance the attractive\npart of the dipole-dipole interaction (DDI) for both inter- and intra-species.\nWithin this procedure of changing to attractive the DDI, a clear spatial\nseparation is verified in the densities at some critical polarization angle.\nThe spatial separations, being angular for symmetric mixtures and radial for\nasymmetric ones, are verified for repulsive contact interactions when the\ninter- to intra-species ratio $\\delta$ is larger than one, implying the system\nis less miscible. The corresponding result for the critical polarization angle\nas a function of $\\delta$ is shown in the particular dipolar symmetric case. A\nstriking outcome of the present study is the observed sensibility of the\nvortex-pattern binary distributions due to the mass-asymmetry. This is\nexemplified by the symmetric dipolar mixture, where the two isotopes are of the\nsame species."
    },
    {
        "anchor": "Phase coherence in quasicondensate experiments: an ab initio analysis\n  via the stochastic Gross-Pitaevskii equation: We perform an ab initio analysis of the temperature dependence of the phase\ncoherence length of finite temperature, quasi-one-dimensional Bose gases\nmeasured in the experiments of Richard et al. (Phys. Rev. Lett. 91, 010405\n(2003)) and Hugbart et al. (Eur. Phys. J. D 35, 155-163 (2005)), finding very\ngood agreement across the entire observed temperature range\n($0.8<T/T_{\\phi}<28$). Our analysis is based on the one-dimensional stochastic\nGross-Pitaevskii equation, modified to self-consistently account for\ntransverse, quasi-one-dimensional effects, thus making it a valid model in the\nregime $\\mu ~ few \\hbar \\omega_\\perp$. We also numerically implement an\nalternative identification of $T_{\\phi}$, based on direct analysis of the\ndistribution of phases in a stochastic treatment.",
        "positive": "Producing and storing spin-squeezed states and\n  Greenberger-Horne-Zeilinger states in a one-dimensional optical lattice: We study the dynamical generation and storage of spin squeezed states, as\nwell as more entangled states up to macroscopic superpositions, in a system\ncomposed of a few ultra-cold atoms trapped in a one-dimensional optical\nlattice. The system, initially in the superfluid phase with each atom in a\nsuperposition of two internal states, is first dynamically entangled by\natom-atom interactions then adiabatically brought to the Mott-insulator phase\nwith one atom per site where the quantum correlations are stored. Exact\nnumerical diagonalization allows us to explore the structure of the stored\nstates by looking at various correlation functions, on site and between\ndifferent sites, both at zero temperature and at finite temperature, as it\ncould be done in an experiment with a quantum-gas microscope."
    },
    {
        "anchor": "Dispersions, weights, and widths of the single-particle spectral\n  function in the normal phase of a Fermi gas: The dispersions, weights, and widths of the peaks of the single-particle\nspectral function in the presence of pair correlations, for a Fermi gas with\neither attractive or repulsive short-range inter-particle interaction, are\ndetermined in the normal phase over a wide range of wave vectors, with a\ntwofold purpose. The first one is to determine how these dispersions identify\nboth an energy scale known as the pseudo-gap near the Fermi wave vector, as\nwell as an additional energy scale related to the contact C at large wave\nvectors. The second one is to differentiate the behaviors of the repulsive gas\nfrom the attractive one in terms of crossing versus avoided crossing of the\ndispersions near the Fermi wave vector. An analogy will also be drawn between\nthe occurrence of the pseudo-gap physics in a Fermi gas subject to pair\nfluctuations and the persistence of local spin waves in the normal phase of\nmagnetic materials.",
        "positive": "Quantum gases in optical lattices: The experimental realization of correlated quantum phases with ultracold\ngases in optical lattices and their theoretical understanding has witnessed\nremarkable progress during the last decade. In this review we introduce basic\nconcepts and tools to describe the many-body physics of quantum gases in\noptical lattices. This includes the derivation of effective lattice\nHamiltonians from first principles and an overview of the emerging quantum\nphases. Additionally, state-of-the-art numerical tools to quantitatively treat\nbosons or fermions on different lattices are introduced."
    },
    {
        "anchor": "Symmetry-breaking vortex-lattice of a binary superfluid in a rotating\n  bucket: We study spontaneous-symmetry-broken phase-separated vortex lattice in a\nweakly interacting uniform rapidly rotating binary Bose superfluid contained in\na quasi-two-dimensional circular or square bucket. For the inter-species\nrepulsion above a critical value, the two superfluid components separate and\nform a demixed phase with practically no overlap in the vortex lattices of the\ntwo components, which will permit an efficient experimental observation of such\nvortices and study their properties. In case of a circular bucket with equal\nintra-species energies of the two components, the two components separate into\ntwo non-overlapping semicircular domains for all frequencies of rotation\n$\\Omega$ generating distinct demixed vortex lattices. In case of a binary Bose\nsuperfluid in both circular and square buckets, (a) the number of vortices\nincreases linearly with $\\Omega$ in agreement with a suggestion by Feynman, and\n(b) the rotational energy in the rotating frame decreases quadratically with\n$\\Omega$ in agreement with a suggestion by Fetter.",
        "positive": "Probing the Hall Voltage in Synthetic Quantum Systems: In the context of experimental advances in the realization of artificial\nmagnetic fields in quantum gases, we discuss feasible schemes to extend\nmeasurements of the Hall polarization to a study of the Hall voltage, allowing\nfor direct comparison with solid state systems. Specifically, for the\nparadigmatic example of interacting flux ladders, we report on characteristic\nzero crossings and a remarkable robustness of the Hall voltage with respect to\ninteraction strengths, particle fillings, and ladder geometries, which is\nunobservable in the Hall polarization. Moreover, we investigate the\nsite-resolved Hall response in spatially inhomogeneous quantum phases."
    },
    {
        "anchor": "Anomalous conductances in an ultracold quantum wire: We analyze the recently measured anomalous transport properties of an\nultracold gas through a ballistic constriction [S. Krinner et al., PNAS\n201601812 (2016)]. The quantized conductance observed at weak interactions\nincreases several-fold as the gas is made strongly interacting, which cannot be\nexplained by the Landauer theory of single-channel transport. We show that this\nphenomenon is due to the multichannel Andreev reflections at the edges of the\nconstriction, where the interaction and confinement result in a superconducting\nstate. Andreev processes convert atoms of otherwise reflecting channels into\nthe condensate propagating through the constriction, leading to a significant\nexcess conductance. Furthermore, we find the spin conductance being suppressed\nby superconductivity; the agreement with experiment provides an additional\nsupport for our model.",
        "positive": "Engineering Non-Hermitian Skin Effect with Band Topology in Ultracold\n  Gases: Non-Hermitian skin effect(NHSE) describes a unique non-Hermitian phenomenon\nthat all eigen-modes are localized near the boundary, and has profound impact\non a wide range of bulk properties. In particular, topological systems with\nNHSE have stimulated extensive research interests recently, given the fresh\ntheoretical and experimental challenges therein. Here we propose a readily\nimplementable scheme for achieving NHSE with band topology in ultracold gases.\nSpecifically, the scheme realizes the one-dimensional optical Raman lattice\nwith two types of spin-orbit coupling (SOC) and an additional laser-induced\ndissipation. By tuning the dissipation and the SOC strengths, NHSE and band\ntopology can be individually controlled such that they can coexist in a\nconsiderable parameter regime. To identify the topological phase in the\npresence of NHSE, we have restored the bulk-boundary correspondence by invoking\nthe non-Bloch band theory, and discussed the dynamic signals for detection. Our\nwork serves as a guideline for engineering topological lattices with NHSE in\nthe highly tunable environment of cold atoms, paving the way for future studies\nof exotic non-Hermitian physics in a genuine quantum many-body setting."
    },
    {
        "anchor": "Quantum phase transition in Bose-Fermi mixtures: We study a quantum Bose-Fermi mixture near a broad Feshbach resonance at zero\ntemperature. Within a quantum field theoretical model a two-step Gaussian\napproximation allows to capture the main features of the quantum phase diagram.\nWe show that a repulsive boson-boson interaction is necessary for thermodynamic\nstability. The quantum phase diagram is mapped in chemical potential and\ndensity space, and both first and second order quantum phase transitions are\nfound. We discuss typical characteristics of the first order transition, such\nas hysteresis or a droplet formation of the condensate which may be searched\nfor experimentally.",
        "positive": "Bose Gases Near Resonance: renormalized interactions in a condensate: We study the interplay between few- and many-body physics in Bose gases near\nresonance. The effect of condensates on the two-body running coupling constant\nis investigated via imposing a boundary condition on a self-consistent\nrenormalization flow equation. Bose gases are found to become nearly\nfermionized when the chemical potential as a function of scattering lengths\nreaches a maximum and the atomic condensates lose meta-stability. The maximum\nand accompanied insta- bility are illustrated as a precursor of the sign change\nof g_2, the renormalized two-body interaction between condensed atoms from\neffectively repulsive to effectively attractive when approaching res- onance\neven though the scattering length is still positive. This occurs when dimers,\nunder the influence of condensates, emerge at zero energy in the atomic gases\nat a finite positive scattering length."
    },
    {
        "anchor": "Measurement of the Homogeneous Contact of a Unitary Fermi gas: By selectively probing the center of a trapped gas, we measure the local, or\nhomogeneous, contact of a unitary Fermi gas as a function of temperature. Tan's\ncontact, C, is proportional to the derivative of the energy with respect to the\ninteraction strength, and is thus an essential thermodynamic quantity for a gas\nwith short-range correlations. Theoretical predictions for the temperature\ndependence of C differ substantially, especially near the superfluid\ntransition, Tc, where C is predicted to either sharply decrease, sharply\nincrease, or change very little. For T/T_F>0.4, our measurements of the\nhomogeneous gas contact show a gradual decrease of C with increasing\ntemperature, as predicted by theory. We observe a sharp decrease in C at\nT/T_F=0.16, which may be due to the superfluid phase transition. While a sharp\ndecrease in C below Tc is predicted by some many-body theories, we find that\nnone of the predictions fully accounts for the data.",
        "positive": "Probing two-particle exchange processes in two-mode Bose-Einstein\n  condensates: We study the fidelity decay and its freeze for an initial coherent state of\ntwo-mode Bose-Einstein condensates in the Fock regime considering a\nBose-Hubbard model that includes two-particle tunneling terms. By using\nlinear-response theory we find scaling properties of the fidelity as a function\nof the particle number that prove the existence of two-particle mode-exchange\nwhen a non-degeneracy condition is fulfilled. Tuning the energy difference of\nthe two modes serves to distinguish the presence of two-particle mode-exchange\nterms through the appearance of certain singularities. Numerical results\nconfirm our findings. Experimental verification of our findings could improve\ncold atom interferometry."
    },
    {
        "anchor": "Bose-Einstein condensation into non-equilibrium states studied by\n  condensate focusing: We report the formation of Bose-Einstein condensates into non-equilibrium\nstates. Our condensates are much longer than equilibrium condensates with the\nsame number of atoms, show strong phase fluctuations, and have a dynamical\nevolution similar to that of quadrupole shape oscillations of regular\ncondensates. The condensates emerge in elongated traps as the result of local\nthermalization when the nucleation time is short compared to the axial\noscillation time. We introduce condensate focusing as a powerful method to\nextract the phase-coherence length of Bose-Einstein condensates.",
        "positive": "Magnetic Phase Transition in the Ground-State Phase Diagram of Binary\n  Bose Gases in Optical Lattices: We investigate the ground-state phase diagram of interacting binary Bose\ngases trapped in two-dimensional optical lattices by means of quantum Monte\nCarlo simulations. Our simulations reveal a magnetic phase transition from a\n$x-y$ ferromagnetic-order to a spin insulator inside the Mott insulating phase\nwith two particles per site for quasi-balanced on-site inter- and\nintra-particle interactions, i.e., $U_{\\uparrow \\downarrow} \\lesssim U$. This\n3D-XY transition is characterized by the establishment of a finite local\nmagnetic moment along the $z$-axis, ferromagnetic correlations in the $x-y$\nplan and by counterflow superfluidity inside the Mott phase. When decreasing\n$U_{\\uparrow \\downarrow}/U$, this transition merges with the Mott-superfluid\ntransition and becomes first-order. The merging of the two transitions is\ninvestigated with respect to $U_{\\uparrow \\downarrow}/U$ parameter."
    },
    {
        "anchor": "Analog Simulation of Weyl Particles with Cold Atoms: We study theoretically, numerically, and experimentally the relaxation of a\ncollisionless gas in a quadrupole trap after a momentum kick. The\nnon-separability of the potential enables a quasi thermalization of the single\nparticle distribution function even in the absence of interactions.\nSuprinsingly, the dynamics features an effective decoupling between the strong\ntrapping axis and the weak trapping plane. The energy delivered during the kick\nis redistributed according to the symmetries of the system and satisfies the\nVirial theorem, allowing for the prediction of the final temperatures. We show\nthat this behaviour is formally equivalent to the relaxation of massless\nrelativistic Weyl fermions after a sudden displacement from the center of a\nharmonic trap.",
        "positive": "Non-Abelian Gauge Fields in Photonic Cavities and Photonic Superfluids: We show that the interplay between the structure anisotropy and the energy\nsplitting between the TE and TM modes of a microcavity leads to the appearance\nof a gauge field for a propagating polariton condensate. This field is analog\nwith a spin-orbit coupling and the field texture can be tuned by rotating the\nsample and ranges continuously from a Rashba to a monopolar field. In the\nlinear regime, the monopolar field leads to a remarkable focusing effect. In\nthe interacting regime, the effective spin-orbit coupling induces a breakdown\nof superfluidity. The spatially homogeneous flows become unstable and\ndynamically evolve into textured ground states such as stripes and domain\nwalls."
    },
    {
        "anchor": "Observation of Quantum Equilibration in Dilute Bose Gases: We investigate experimentally the dynamical relaxation of a non-integrable\nquantum many-body system to its equilibrium state. A Bose-Einstein condensate\nis loaded into the first excited band of an optical lattice and let to evolve\nup to a few hundreds of milliseconds. Signs of quantum equilibration are\nobserved. There is a period of time, roughly 40 ms long, during which both the\naspect ratio of the cloud and its momentum distribution remain constant. In\nparticular, the momentum distribution has a flat top and is not a Gaussian\nthermal distribution. After this period, the cloud becomes classical as its\nmomentum distribution becomes Gaussian.",
        "positive": "The nature of self-localization of Bose-Einstein condensates in deep\n  optical lattices: We analyze the nature of a novel type of self-trapping transition called\nself-localization (SL) of Bose-Einstein condensates in one-dimensional optical\nlattices in the presence of weak local dissipation. SL has recently been\nobserved in several studies based upon the discrete nonlinear Schr\\\"odinger\nequation (DNLS), however, its origin is hitherto an open question. We show that\nSL is based upon a self-trapping crossover in the system. Furthermore, we\nestablish that the origin of the crossover is the Peierls-Nabarro barrier, an\nenergy threshold describing the stability of self-trapped states. Beyond the\nmean-field description the crossover becomes even sharper which is also\nreflected by a sudden change of the coherence of the condensate. While we\nexpect that the crossover can be readily studied in current experiments in deep\noptical lattices, our results allow for the preparation of robust and long-time\ncoherent quantum states."
    },
    {
        "anchor": "A Review of Wave Packet Molecular Dynamics: Warm dense matter systems created in the laboratory are highly dynamical. In\nsuch cases electron dynamics is often needed to accurately simulate the\nevolution and properties of the system. Large systems force one to make simple\napproximations enabling computationally feasibility. Wave packet molecular\ndynamics (WPMD) provides a simple framework for simulating time-dependent\nquantum plasmas. Here, this method is reviewed. The different variants of WPMD\nare shown and compared and their validity is discussed.",
        "positive": "Non-equilibrium dynamics of dipolar polarons: We study the out-of-equilibrium quantum dynamics of dipolar polarons, i.e.,\nimpurities immersed in a dipolar Bose-Einstein condensate, after a quench of\nthe impurity-boson interaction. We show that the dipolar nature of the\ncondensate and of the impurity results in anisotropic relaxation dynamics, in\nparticular, anisotropic dressing of the polaron. More relevantly for cold-atom\nsetups, quench dynamics is strongly affected by the interplay between dipolar\nanisotropy and trap geometry. Our findings pave the way for simulating\nimpurities in anisotropic media utilizing experiments with dipolar mixtures."
    },
    {
        "anchor": "Quantum simulation of a 2D quasicrystal with cold atoms: We describe a way to obtain a two-dimensional quasiperiodic tiling with\neight-fold symmetry using cold atoms. A series of such optical tilings, related\nby scale transformations, is obtained for a series of specific values of the\nchemical potential of the atoms. A theoretical model for the optical system is\ndescribed and compared with that of the well-known cut-and-project method for\nthe Ammann-Beenker tiling. This type of cold atom structure should allow the\nsimulation of several important lattice models for interacting quantum\nparticles and spins in quasicrystals.",
        "positive": "Interaction induced single impurity tunneling in a binary mixture of\n  trapped ultracold bosons: We investigate the tunneling dynamics of an ultracold bosonic impurity\nspecies which interacts repulsively with a second, larger Bose gas. Both\nspecies are held in a finite-sized quasi-one-dimensional box potential. In\naddition, the impurity bosons experience a periodic potential generated by an\noptical lattice. We initially prepare our binary mixture in its ground state,\nsuch that the impurities and Bose gas are phase separated and the impurities\nlocalize pairwise in adjacent sites of the periodic potential, by tuning the\ninteraction strengths and the lattice depth correspondingly. The dynamics is\ninitiated by suddenly lowering the repulsive interspecies interaction strength,\nthereby entering a different regime in the crossover diagram. For specific\npost-quench interspecies interaction strengths we find that a single impurity\ntunnels first to the neighbouring empty site and depending on the quench\nstrength can further tunnel to the next neighbouring site. Interestingly, this\neffect is highly sensitive to the presence of the Bose gas and does not occur\nwhen the Bose gas does not interact with the impurity species throughout the\ndynamics. Moreover, we find that the tunneling process is accompanied by strong\nentanglement between the Bose gas and the impurity species as well as\ncorrelations among the impurities."
    },
    {
        "anchor": "Spectroscopy of dipolar fermions in 2D pancakes and 3D lattices: Motivated by ongoing measurements at JILA, we calculate the recoil-free\nspectra of dipolar interacting fermions, for example ultracold heteronuclear\nmolecules, in a one-dimensional lattice of two-dimensional pancakes,\nspectroscopically probing transitions between different internal (e.g.,\nrotational) states. We additionally incorporate p-wave interactions and losses,\nwhich are important for reactive molecules such as KRb. Moreover, we consider\nother sources of spectral broadening: interaction-induced quasiparticle\nlifetimes and the different polarizabilities of the different rotational states\nused for the spectroscopy. Although our main focus is molecules, some of the\ncalculations are also useful for optical lattice atomic clocks. For example,\nunderstanding the p-wave shifts between identical fermions and small dipolar\ninteractions coming from the excited clock state are necessary to reach future\nprecision goals. Finally, we consider the spectra in a deep 3D lattice and show\nhow they give a great deal of information about static correlation functions,\nincluding \\textit{all} the moments of the density correlations between nearby\nsites. The range of correlations measurable depends on spectroscopic resolution\nand the dipole moment.",
        "positive": "Thermal fading of the $1/k^4$-tail of the momentum distribution induced\n  by the hole anomaly: We study the thermal behavior of correlations in a one-dimensional Bose gas\nwith tunable interaction strength, crossing from weakly-repulsive to\nTonks-Girardeau regime. A reference temperature in this system is that of the\nhole anomaly, observed as a peak in the specific heat and a maximum in the\nchemical potential. We find that at large momenta $k$ and temperature above the\nanomaly threshold, the tail $\\mathcal{C}/k^4$ of the momentum distribution\n(proportional to the Tan contact $\\mathcal{C}$) is screened by the\n$1/|k|^3$-term due to a dramatic thermal increase of the internal energy\nemerging from the thermal occupation of spectral excitation states. The same\nfading is consistently revealed in the behavior at short distances $x$ of the\none-body density matrix (OBDM) where the $|x|^3$-dependence disappears for\ntemperatures above the anomaly. We obtain a new general analytic tail for the\nmomentum distribution and a minimum $k$ fixing its validity range, both\ncalculated with exact Bethe-Ansatz method and valid in all interaction and\nthermal regimes, crossing from the quantum to the classical gas limit. Our\npredictions are confirmed by comparison with ab-initio Path Integral Monte\nCarlo calculations for the momentum distribution and the OBDM exploring a wide\nrange of interaction strength and temperature. Our results unveil a novel\nconnection between excitations and correlations. We expect them to be of\ninterest to any cold atomic, nuclear, solid-state, electronic and spin system\nexhibiting an anomaly or a thermal second-order phase transition."
    },
    {
        "anchor": "Spontaneous symmetry breaking in rotating condensates of ultracold atoms: We describe an equilibrium state of a rotating trapped atomic condensate,\nwhich is characterized by a non-zero internal circulation and spontaneous\nbreaking of the rotational O(2) symmetry with all three major semiaxes of the\ncondensate having different values. The macroscopic rotation of the condensate\nis supported by a mesh of quantized vortices, whose number density is a\nfunction of internal circulation. The oscillation modes of this state are\ncomputed and the Goldstone mode associated with the loss of the symmetry is\nidentified. The possible avenues for experimental identification this state are\ndiscussed.",
        "positive": "Anisotropic pair-superfluidity of trapped two-component Bose gases: We theoretically investigate the pair-superfluid phase of two-component\nultracold gases with negative inter-species interactions in an optical lattice.\nWe establish the phase diagram for filling $n=1$ at zero and finite\ntemperature, by applying Bosonic Dynamical Mean-Field Theory, and confirm the\nstability of pair-superfluidity for asymmetric hopping of the two species.\nWhile the pair superfluid is found to be robust in the presence of a harmonic\ntrap, we observe that it is destroyed already by a small population imbalance\nof the two species."
    },
    {
        "anchor": "Oscillons in coupled Bose-Einstein condensates: Long-lived, spatially localized, and temporally oscillating nonlinear\nexcitations are predicted by numerical simulation of coupled Gross-Pitaevskii\nequations. These oscillons closely resemble the time-periodic breather\nsolutions of the sine-Gordon equation but decay slowly by radiating Bogoliubov\nphonons. Their time-dependent profile is closely matched with solutions of the\nsine-Gordon equation, which emerges as an effective field theory for the\nrelative phase of two linearly coupled Bose fields in the weak-coupling limit.\nFor strong coupling the long-lived oscillons persist and involve both relative\nand total phase fields. The oscillons decay via Bogoliubov phonon radiation\nthat is increasingly suppressed for decreasing oscillon amplitude.\nPossibilities for creating oscillons are addressed in atomic gas experiments by\ncollision of oppositely charged Bose-Josephson vortices and direct phase\nimprinting.",
        "positive": "Topological study of a Bogoliubov-de Gennes system of pseudo spin-$1/2$\n  bosons with conserved magnetization in a honeycomb lattice: We consider a Bogolibov-de Geenes (BdG) Hamiltonian, which is a non-Hermitian\nHamiltonian with pseudo-Hermiticity, for a system of (pseudo) spin-$1/2$ bosons\nin a honeycomb lattice under the condition that the population difference\nbetween the two spin components, i.e., magnetization, is a constant. Such a\nsystem is capable of acting as a topological amplifier, under time-reversal\nsymmetry, with stable bulk bands but unstable edge modes which can be populated\nat an exponentially fast rate. We quantitatively study the topological\nproperties of this model within the framework of the 38-fold way for\nnon-Hermitian systems. We find, through the symmetry analysis of the Bloch\nHamiltonian, that this model is classified either as two copies of symmetry\nclass AIII+$\\eta_-$ or two copies of symmetry class A+$\\eta$ depending on\nwhether the (total) system is time-reversal-symmetric, where $\\eta$ is the\nmatrix representing pseudo-Hermiticity and $\\eta_-$ indicates that\npseudo-Hermiticity and chiral symmetry operators anticommute. We prove, within\nthe context of non-Hermitian physics where eigenstates obey the\nbi-orthonormality relation, that a stable bulk is characterized by a single\ntopological invariant, the Chern number for the Haldane model, independent of\npairing interactions. We construct a convenient analytical description for the\nedge modes of the Haldane model in semi-infinite planes, which is expected to\nbe useful for models built upon copies of the Haldane model across a broad\narray of disciplines. We adapt the theorem in our recent work [Phys. Rev. A\n104, 013305 (2021)] to pseudo-Hermitian Hamiltonians that are less restrictive\nthan BdG Hamiltonians and apply it to highlight that the vanishing of an\nunconventional commutator between number-conserving and number-nonconserving\nparts of the Hamiltonian indicates whether a system can be made to act as a\ntopological amplifier."
    },
    {
        "anchor": "Ramifications of topology and thermal fluctuations in quasi-2D\n  condensates: We explore the topological transformation of quasi-2D Bose-Einstein\ncondensates of dilute atomic gases, and changes in the low-energy\nquasiparticles associated with the geometry of the confining potential. In\nparticular, we show the density profile of the condensate and quantum\nfluctuation follow the transition from a multiply to a simply connected\ngeometry of the confining potential. The thermal fluctuations, in contrast,\nremain multiply connected. The genesis of the key difference lies in the\nstructure of the low-energy quasiparticles. For which we use the\nHartree-Fock-Bogoliubov, and study the evolution of quasiparticles, the dipole\nor the Kohn mode in particular. We, then employ the Hartree-Fock-Bogoliubov\ntheory with the Popov approximation to investigate the density and the momentum\ndistribution of the thermal atoms.",
        "positive": "Dynamic structure function of two interacting atoms in 1D: We consider two atoms trapped in a one-dimensional harmonic oscillator\npotential interacting through a contact interaction. We study the transition\nfrom the non-interacting to the strongly interacting Tonks-Girardeau state, as\nthe interaction is varied from zero to infinitely large repulsive values. The\ndynamic structure function is computed by means of direct diagonalization\ncalculations with a finite number of single particle modes. The response of the\nsystem against a monopolar perturbation is characterized by the moments of the\ndynamic structure function which are explicitly calculated from the dynamic\nstructure function and by means of sum rules."
    },
    {
        "anchor": "Manipulating Cooper pairs with a controllable momentum in periodically\n  driven degenerate Fermi gases: We here present an experimentally feasible proposal for manipulating Cooper\npairs in degenerate Fermi gases trapped by an optical lattice. Upon introducing\nan \\textit{in situ} periodically driven field, the system may be described by\nan effective time-independent Hamiltonian, in which the Cooper pairs, generated\nby the bound molecule state in Feshbach resonance, host a nonzero\ncenter-of-mass momentum. The system thus processes a crossover from a\nBardeen-Cooper-Schrieffer (BCS) superfluid phase to a Fulde-Ferrell (FF) one.\nFurthermore, the magnitude and direction of the Cooper pairs in the synthetic\nFF superfluids are both directly controllable via the periodically driven\nfield. Our proposal offers a reliable and feasible scenario for manipulating\nthe Cooper pairs in cold atoms, serving as a tunable as well as powerful\nplatform for quantum-emulating and exploring the FF superfluid phase.",
        "positive": "Non-Hermitian topological Fermi superfluid near the $p$-wave unitary\n  limit: We theoretically discuss the non-Hermitian superfluid phase transition in\none-dimensional two-component Fermi gases near the $p$-wave Feshbach resonance\naccompanied by the two-body loss associated with the dipolar relaxation. For\nthe first time we point out that this system gives us an opportunity to explore\nthe interplay among various non-trivial properties such as universal\nthermodynamics at divergent $p$-wave scattering length, topological phase\ntransition at vanishing chemical potential, and non-Hermitian\nBardeen-Cooper-Schrieffer(BCS) to Bose-Einstein condensate (BEC) transition, in\na unified manner. In the BCS phase, the loss-induced superfluid-normal\ntransition occurs when the exceptional point appears in the effective\nnon-Hermitian Hamiltonian. In the BEC phase, the diffusive gapless mode can be\nregarded as a precursor of the instability of the superfluid state. Moreover,\nwe show that the superfluid state is fragile against the two-body loss near the\ntopological phase transition point."
    },
    {
        "anchor": "Dynamical crossover between the infinite-volume and empty-lattice limits\n  of ultra-cold fermions in 1D optical lattices: Unlike typical condensed-matter systems, ultra-cold atoms loaded into optical\nlattices allow separate control of both the particle number and system size. As\na consequence, there are two distinct \"thermodynamic\" limits that can be\ndefined for these systems: i) \"infinite-volume limit\" at constant finite\ndensity, and ii) \"empty-lattice limit\" at constant particle number. To probe\nthe difference between these two limits and their crossover, we consider a\npartially occupied lattice and study the transport of non-interacting fermions\nand fermions interacting at the mean-field level into the unoccupied region. In\nthe infinite-volume limit, a finite steady-state current emerges. On the other\nhand, in the empty-lattice limit there is no finite steady-state current. By\nchanging the initial filling, we find a smooth crossover between the two\nlimits. Our predictions may be verified using available experimental tools and\ndemonstrate a fundamental difference between isolated small systems such as\nultra-cold atoms and conventional condensed-matter systems.",
        "positive": "Spontaneous Magnetic Ordering in a Ferromagnetic Spinor Dipolar\n  Bose-Einstein Condensate: We study the spin dynamics in a spin-1 ferromagnetic Bose-Einstein condensate\nwith magnetic dipole-dipole interaction (MDDI) based on the Gross-Pitaevskii\nand Bogoliubov theories. We find that various magnetic structures such as\ncheckerboards and stripes emerge in the course of the dynamics due to the\ncombined effects of spin-exchange interaction, MDDI, quadratic Zeeman and\nfinite-size effects, and non-stationary initial conditions. However, the\nshort-range magnetic order observed by the Berkeley group [Phys. Rev. Lett.\n{\\bf 100}, 170403 (2008)] is not fully reproduced in our calculations; the\nperiodicity of the order differs by a factor of three and the checkerboard\npattern eventually dissolves in our numerical simulations. Possible reasons for\nthe discrepancy are discussed."
    },
    {
        "anchor": "Lifetime of the Bose Gas with Resonant Interactions: We study the lifetime of a Bose gas at and around unitarity using a Feshbach\nresonance in lithium~7. At unitarity, we measure the temperature dependence of\nthe three-body decay coefficient $L_{3}$. Our data follow a $L_3 {=}\n\\lambda_{3} / T^{2}$ law with $\\lambda_{3} = 2.5(3)_{stat}_(6)_{sys} 10^{-20}\n(\\mu K)^2 cm^6 s^{-1}$ and are in good agreement with our analytical result\nbased on the zero-range theory. Varying the scattering length $a$ at fixed\ntemperature, we investigate the crossover between the finite-temperature\nunitary region and the previously studied regime where $|a|$ is smaller than\nthe thermal wavelength. We find that $L_{3}$ is continuous across resonance,\nand over the whole $a {<} 0$ range our data quantitatively agree with our\ncalculation.",
        "positive": "Renormalization of the BCS-BEC crossover by order parameter fluctuations: We use the functional renormalization group approach with partial\nbosonization in the particle-particle channel to study the effect of order\nparameter fluctuations on the BCS-BEC crossover of superfluid fermions in three\ndimensions. Our approach is based on a new truncation of the vertex expansion\nwhere the renormalization group flow of bosonic two-point functions is closed\nby means of Dyson-Schwinger equations and the superfluid order parameter is\nrelated to the single particle gap via a Ward identity. We explicitly calculate\nthe chemical potential, the single-particle gap, and the superfluid order\nparameter at the unitary point and compare our results with experiments and\nprevious calculations."
    },
    {
        "anchor": "S-matrix approach to quantum gases in the unitary limit II: the\n  three-dimensional case: A new analytic treatment of three-dimensional homogeneous Bose and Fermi\ngases in the unitary limit of negative infinite scattering length is presented,\nbased on the S-matrix approach to statistical mechanics we recently developed.\nThe unitary limit occurs at a fixed point of the renormalization group with\ndynamical exponent z=2 where the S-matrix equals -1. For fermions we find T_c\n/T_F is approximately 0.1. For bosons we present evidence that the gas does not\ncollapse, but rather has a critical point that is a strongly interacting form\nof Bose-Einstein condensation. This bosonic critical point occurs at n lambda^3\napproximately 1.3 where n is the density and lambda the thermal wavelength,\nwhich is lower than the ideal gas value of 2.61.",
        "positive": "Autonomous stabilization of photonic Laughlin states through angular\n  momentum potentials: We propose a method to stabilize Laughlin states of a large number of\nstrongly interacting photons by combining a frequency-selective incoherent pump\nwith a step-like potential in the angular momentum basis. Analytical\nexpressions for the preparation efficiency and for the principal error sources\nare obtained. Direct extension of the preparation scheme to states containing\nsingle or multiple quasiholes is discussed."
    },
    {
        "anchor": "Variable Potentials for Thermalized Light and Coupled Condensates: For over a decade, cold atoms in lattice potentials have been an attractive\nplatform to simulate phenomena known from solid state theory, as the\nMott-insulator transition. In contrast, the field of photonics usually deals\nwith non-equilibrium physics. Recent advances towards photonic simulators of\nsolid state equilibrium effects include polariton double-site and lattice\nexperiments, as well as the demonstration of a photon condensate in a\ndye-filled microcavity. Here we demonstrate a technique to create variable\nmicropotentials for light using thermo-optic imprinting within an\nultrahigh-reflectivity mirror microcavity filled with a dye-polymer solution\nthat is compatible with photon gas thermalization. By repeated\nabsorption-emission cycles photons thermalize to the temperature of the dye\nsolution, and in a single microsite we observe a photon Bose-Einstein\nmicrocondensate. Effective interactions between the otherwise nearly\nnon-interacting photons are observed due to thermo-optic effects, and in a\ndouble-well system tunnel coupling between sites is demonstrated, as well as\nthe hybridization of eigenstates. Prospects of the new experimental platform\ninclude photonic structures in which photons thermalize into entangled manybody\nstates.",
        "positive": "Observation of many-body scarring in a Bose--Hubbard quantum simulator: The ongoing quest for understanding nonequilibrium dynamics of complex\nquantum systems underpins the foundation of statistical physics as well as the\ndevelopment of quantum technology. Quantum many-body scarring has recently\nopened a window into novel mechanisms for delaying the onset of thermalization\nby preparing the system in special initial states, such as the $\\mathbb{Z}_2$\nstate in a Rydberg atom system. Here we realize many-body scarring in a\nBose-Hubbard quantum simulator from previously unknown initial conditions such\nas the unit-filling state. We develop a quantum-interference protocol for\nmeasuring the entanglement entropy and demonstrate that scarring traps the\nmany-body system in a low-entropy subspace. Our work makes the resource of\nscarring accessible to a broad class of ultracold-atom experiments, and it\nallows one to explore the relation of scarring to constrained dynamics in\nlattice gauge theories, Hilbert space fragmentation, and disorder-free\nlocalization."
    },
    {
        "anchor": "Numerical calculation of dipolar quantum droplet stationary states: We describe and benchmark a method to accurately calculate the quantum\ndroplet states that can be produced from a dipolar Bose-Einstein condensate.\nOur approach also allows us to consider vortex states, where the atoms\ncirculate around the long-axis of the filament shaped droplet. We apply our\napproach to determine a phase diagram showing where self-bound droplets are\nstable against evaporation, and to quantify the energetics related to the\nfission of a vortex droplet into two non-vortex droplets.",
        "positive": "Quantum beat spectroscopy of repulsive Bose polarons: The physics of impurities in a bosonic quantum environment is a paradigmatic\nand challenging many-body problem that remains to be understood in its full\ncomplexity. Here, this problem is investigated for impurities with strong\nrepulsive interactions based on Ramsey interferometry in a quantum degenerate\ngas of 39K atoms. We observe an oscillatory signal that is consistent with a\nquantum beat between two co-existing coherent quasiparticle states: the\nattractive and repulsive polarons. The interferometric signal allows us to\nextract the polaron energies for a wide range of interaction strengths,\ncomplimenting earlier spectroscopic measurements. We furthermore identify\nseveral dynamical regimes towards the formation of the Bose polaron in good\nagreement with theory. Our results improve the understanding of quantum\nimpurities interacting strongly with a bosonic environment, and demonstrate how\nquasiparticles as well as short-lived non-equilibrium many-body states can be\nprobed using Ramsey interferometry."
    },
    {
        "anchor": "In-medium bound-state formation and inhomogeneous condensation in Fermi\n  gases in a hard-wall box: The formation of bosonic bound states underlies the formation of a superfluid\nground state in the many-body phase diagram of ultracold Fermi gases. We study\nbound-state formation in a spin- and mass-imbalanced ultracold Fermi gas\nconfined in a box with hard-wall boundary conditions. Because of the presence\nof finite Fermi spheres, the center-of-mass momentum of the potentially formed\nbound states can be finite, depending on the parameters controlling mass and\nspin imbalance as well as the coupling strength. We exploit this observation to\nestimate the potential location of inhomogeneous phases in the many-body phase\ndiagram as a function of spin- and mass imbalance as well as the box size. Our\nresults suggest that a hard-wall box does not alter substantially the many-body\nphase diagram calculated in the thermodynamic limit. Therefore, such a box may\nserve as an ideal trap potential to bring experiment and theory closely\ntogether and facilitate the search for exotic inhomogeneous ground states.",
        "positive": "An impurity immersed in a double Fermi Sea: We present a variational calculation of the energy of an impurity immersed a\ndouble Fermi sea of non-interacting Fermions. We show that in the\nstrong-coupling regime, the system undergoes a first order transition between\npolaronic and trimer states. Our result suggests that the smooth crossover\npredicted in previous literature for a superfluid background is the consequence\nof Cooper pairing and is absent in a normal system."
    },
    {
        "anchor": "Quantum phase transition of the two-dimensional Rydberg atom array in an\n  optical cavity: We study the two-dimensional Rydberg atom array in an optical cavity with\nhelp of the meanfield theory and the large-scale quantum Monte Carlo\nsimulations. The strong dipole-dipole interactions between Rydberg atoms can\nmake the system exhibit the crystal structure, and the coupling between\ntwo-level atom and cavity photon mode can result in the formation of the\npolariton. The interplay between them provides a rich quantum phase diagram\nincluding the Mott, solid-1/2, superradiant and superradiant solid phases. As\nthe two-order co-existed phase, the superradiant solid phase breaks both\ntranslational and U(1) symmetries. Based on both numerical and analytic\nresults, we found the region of superradiant solid is much larger than one\ndimensional case, so that it can be more easily observed in the experiment.\nFinally, we discuss how the energy gap of the Rydberg atom can affect the type\nof the quantum phase transition and the number of triple points.",
        "positive": "Microwave-dressed state-selective potentials for atom interferometry: We propose a novel and robust technique to realize a beam splitter for\ntrapped Bose-Einstein condensates (BECs). The scheme relies on the possibility\nof producing different potentials simultaneously for two internal atomic\nstates. The atoms are coherently transferred, via a Rabi coupling between the\ntwo long-lived internal states, from a single well potential to a double-well.\nWe present numerical simulations supporting our proposal and confirming\nexcellent efficiency and fidelity of the transfer process with realistic\nnumbers for a BEC of $^{87}$Rb. We discuss the experimental implementation by\nsuggesting state-selective microwave potentials as an ideal tool to be\nexploited for magnetically trapped atoms. The working principles of this\ntechnique are tested on our atom chip device which features an integrated\ncoplanar micro-wave guide. In particular, the first realization of a\ndouble-well potential by using a microwave dressing field is reported.\nExperimental results are presented together with numerical simulations, showing\ngood agreement. Simultaneous and independent control on the external potentials\nis also demonstrated in the two Rubidium clock states. The transfer between the\ntwo states, featuring respectively a single and a double-well, is characterized\nand it is used to measure the energy spectrum of the atoms in the double-well.\nOur results show that the spatial overlap between the two states is crucial to\nensure the functioning of the beamsplitter. Even though this condition could\nnot be achieve in our current setup, the proposed technique can be realized\nwith current state-of-the-art devices being particularly well suited for atom\nchip experiments. We anticipate applications in quantum enhanced\ninterferometry."
    },
    {
        "anchor": "Stability and dynamics of dark-bright soliton bound states away from the\n  integrable limit: The existence, stability, and dynamics of bound pairs of symbiotic matter\nwaves in the form of dark-bright soliton pairs in two-component mixtures of\natomic Bose-Einstein condensates is investigated. Motivated by the tunability\nof the atomic interactions in recent experiments, we explore in detail the\nimpact that changes in the interaction strengths have on these bound pairs by\nconsidering significant deviations from the Manakov (integrable) limit. It is\nfound that dark-bright soliton pairs exist as stable configurations in a wide\nparametric window spanning both the miscible and the immiscible regime of\ninteractions. Outside this parameter interval two unstable regions are\nidentified and are associated with a supercritical and a subcritical pitchfork\nbifurcation, respectively. Dynamical manifestation of these instabilities gives\nrise to a redistribution of the bright density between the dark solitons, and\nalso to symmetry-broken stationary states that are mass imbalanced (asymmetric)\nwith respect to their bright soliton counterpart. The long-time dynamics of\nboth the stable and the unstable balanced and imbalanced dark-bright soliton\npairs is analyzed.",
        "positive": "Interacting atomic quantum fluids on momentum-space lattices: We study the influence of atomic interactions on quantum simulations in\nmomentum-space lattices (MSLs), where driven atomic transitions between\ndiscrete momentum states mimic transport between sites of a synthetic lattice.\nLow energy atomic collisions, which are short ranged in real space, relate to\nnearly infinite-ranged interactions in momentum space. However, the\ndistinguishability of the discrete momentum states coupled in MSLs gives rise\nto an added exchange energy between condensate atoms in different momentum\norders, relating to an effectively attractive, finite-ranged interaction in\nmomentum space. We explore the types of phenomena that can result from this\ninteraction, including the formation of chiral self-bound states in topological\nMSLs. We also discuss the prospects for creating squeezed states in\nmomentum-space double wells."
    },
    {
        "anchor": "Chaos onset in large rings of Bose-Einstein condensates: We consider large rings of weakly-coupled Bose-Einstein condensates,\nanalyzing their transition to chaotic dynamics and loss of coherence.\nInitially, a ring is considered to be in an eigenstate, i.e. in a commensurate\nconfiguration with equal site fillings and equal phase differences between\nneighboring sites. Such a ring should exhibit a circulating current whose value\nwill depend on the initial, non-zero phase difference. The appearance of such\ncurrents is a signature of an established coherence along the ring. If phase\ndifference falls between $\\pi/2$ and $3\\pi/2$ and interparticle interaction in\ncondensates exceeds a critical interaction value $u_c$, the coherence is\nsupposed to be quickly destroyed because the system enters a chaotic regime due\nto inherent instabilities. This is, however, only a part of the story. It turns\nout that chaotic dynamics and resulting averaging of circular current to zero\nis generally offset by a critical time-scale $t_c$, which is almost two orders\nof magnitude larger than the one expected from the linear stability analysis.\nWe study the critical time-scale in detail in a broad parameter range.",
        "positive": "The Sagnac Effect in Optical Lattices with Laser-Assisted Tunneling: We propose a scheme to realize the rotation sensing using optical lattices\nwith laser-assisted tunneling. We demonstrate that the competition between the\nrotation and the spin-orbit coupling governs the spin-dependent response of the\ncyclotron dynamics of the spin-orbit coupled bosons. The Sagnac-type cumulative\nphase can be read out from the envelop of a beat-frequency particle current in\nthe spin-balanced system and enhanced by the cyclotron motion. We also\ntheoretically show that the sensitivity limit of the spin-orbit-coupled system\nto the rotational motion can reach 7*10^-8 rad s^-1 Hz^1/2."
    },
    {
        "anchor": "Dynamical variational approach to Bose polarons at finite temperatures: We discuss the interaction of a mobile quantum impurity with a Bose-Einstein\ncondensate of atoms at finite temperature. To describe the resulting Bose\npolaron formation we extend the dynamical variational approach of\n[Phys.Rev.Lett. 117, 11302 (2016)] to an initial thermal gas of Bogoliubov\nphonons. We study the polaron formation after switching on the interaction,\ne.g., by a radio-frequency (RF) pulse from a non-interacting to an interacting\nstate. To treat also the strongly-interacting regime, interaction terms beyond\nthe Fr\\\"ohlich model are taken into account. We calculate the real-time\nimpurity Green's function and discuss its temperature dependence. Furthermore,\nwe determine the RF absorption spectrum and find good agreement with recent\nexperimental observations. We predict temperature-induced shifts and a\nsubstantial broadening of spectral lines. The analysis of the real-time Green's\nfunction reveals a crossover to a linear temperature dependence of the thermal\ndecay rate of Bose polarons as unitary interactions are approached.",
        "positive": "Optical cooling and trapping of highly magnetic atoms: The benefits of a\n  spontaneous spin polarization: From the study of long-range-interacting systems to the simulation of gauge\nfields, open-shell Lanthanide atoms with their large magnetic moment and narrow\noptical transitions open novel directions in the field of ultracold quantum\ngases. As for other atomic species, the magneto-optical trap (MOT) is the\nworking horse of experiments but its operation is challenging, due to the large\nelectronic spin of the atoms. Here we present an experimental study of\nnarrow-line Dysprosium MOTs. We show that the combination of radiation pressure\nand gravitational forces leads to a spontaneous polarization of the electronic\nspin. The spin composition is measured using a Stern-Gerlach separation of spin\nlevels, revealing that the gas becomes almost fully spin-polarized for large\nlaser frequency detunings. In this regime, we reach the optimal operation of\nthe MOT, with samples of typically $3\\times 10^8$ atoms at a temperature of\n15\\,$\\mu$K. The spin polarization reduces the complexity of the radiative\ncooling description, which allows for a simple model accounting for our\nmeasurements. We also measure the rate of density-dependent atom losses,\nfinding good agreement with a model based on light-induced Van der Waals\nforces. A minimal two-body loss rate $\\beta\\sim 2\\times10^{-11}\\,$cm$^{3}$/s is\nreached in the spin-polarized regime. Our results constitute a benchmark for\nthe experimental study of ultracold gases of magnetic Lanthanide atoms."
    },
    {
        "anchor": "Exotic Quantum Criticality in One-Dimensional Coupled Dipolar Bosons\n  Tubes: The competition between intertube hopping processes and density-density\ninteractions is investigated in one-dimensional quantum dipolar bosons systems\nof N coupled tubes at zero temperature. Using a phenomenological bosonization\napproach, we show that the resulting competition leads to an exotic quantum\nphase transition described by a U(1) x Z_N conformal field theory with a\nfractional central charge. The emerging Z_N parafermionic critical degrees of\nfreedom are highly nontrivial in terms of the original atoms or polar molecules\nof the model. We further determine the main physical properties of the quantum\ncritical point in a double-tube system which has central charge c=3/2. In\ntriple-tube systems, we show that the competition between the two antagonistic\nprocesses is related to the physics of the two-dimensional Z_3 chiral Potts\nmodel. This work opens the possibility to study the exotic properties of the\nZ_N parafermions in the context of ultracold quantum Bose gases.",
        "positive": "Numerical and variational solutions of the dipolar Gross-Pitaevskii\n  equation in reduced dimensions: We suggest a simple Gaussian Lagrangian variational scheme for the reduced\ntime-dependent quasi-one- and quasi-two-dimensional Gross-Pitaevskii (GP)\nequations of a dipolar Bose-Einstein condensate (BEC) in cigar and disk\nconfigurations, respectively. The variational approximation for stationary\nstates and breathing oscillation dynamics in reduced dimensions agrees well\nwith the numerical solution of the GP equation even for moderately large\nshort-range and dipolar nonlinearities. The Lagrangian variational scheme also\nprovides much physical insight about soliton formation in dipolar BEC."
    },
    {
        "anchor": "Variational approach for impurity dynamics at finite temperature: We present a general variational principle for the dynamics of impurity\nparticles immersed in a quantum-mechanical medium. By working within the\nHeisenberg picture and constructing approximate time-dependent impurity\noperators, we can take the medium to be in any mixed state, such as a thermal\nstate. Our variational method is consistent with all conservation laws and, in\ncertain cases, it is equivalent to a finite-temperature Green's function\napproach. As a demonstration of our method, we consider the dynamics of heavy\nimpurities that have suddenly been introduced into a Fermi gas at finite\ntemperature. Using approximate time-dependent impurity operators involving only\none particle-hole excitation of the Fermi sea, we find that we can successfully\nmodel the results of recent Ramsey interference experiments on $^{40}$K atoms\nin a $^6$Li Fermi gas [M.~Cetina et al., Science \\textbf{354}, 96 (2016)]. We\nalso show that our approximation agrees well with the exact solution for the\nRamsey response of a fixed impurity at finite temperature. Our approach paves\nthe way for the investigation of impurities with dynamical degrees of freedom\nin arbitrary quantum-mechanical mediums.",
        "positive": "Dipole dynamics of an interacting bosonic mixture: We unravel the coupled dipole dynamics of a two-species Bose-Einstein\ncondensate with tunable interspecies interaction. We produce a degenerate\nmixture of $^{41}$K-$^{87}$Rb in an optical trap and we study the dipole\noscillations of both atomic species in the linear response regime. Varying the\ninterspecies interaction from the weakly to the strongly attractive side, we\nmeasure the frequencies and the composition of the two dipole eigenmodes. For\nenough strong interactions, even beyond the mean-field collapse, we find that\nthe frequency of the low-energy eigenmode is determined only by the bare trap\nfrequencies and the species population imbalance. The experimental results are\nwell reproduced by numerical simulations based on two coupled Gross-Pitaevskii\nequations. Our findings provide a detailed picture of the dipole excitations in\nasymmetric bosonic mixtures."
    },
    {
        "anchor": "Dynamical quantum phase transition of a two-component Bose-Einstein\n  condensate in an optical lattice: We study dynamics of a two-component Bose-Einstein condensate where the two\ncomponents are coupled via an optical lattice. In particular, we focus on the\ndynamics as one drives the system through a critical point of a first order\nphase transition characterized by a jump in the internal populations. Solving\nthe time-dependent Gross-Pitaevskii equation, we analyze; breakdown of\nadiabaticity, impact of non-linear atom-atom scattering, and the role of a\nharmonic trapping potential. Our findings demonstrate that the phase transition\nis resilient to both contact interaction between atoms and external trapping\nconfinement.",
        "positive": "Extended Bose-Hubbard Models with Ultracold Magnetic Atoms: The Hubbard model underlies our understanding of strongly correlated\nmaterials. While its standard form only comprises interaction between particles\nat the same lattice site, its extension to encompass long-range interaction,\nwhich activates terms acting between different sites, is predicted to\nprofoundly alter the quantum behavior of the system. We realize the extended\nBose-Hubbard model for an ultracold gas of strongly magnetic erbium atoms in a\nthree-dimensional optical lattice. Controlling the orientation of the atomic\ndipoles, we reveal the anisotropic character of the onsite interaction and\nhopping dynamics, and their influence on the superfluid-to-Mott insulator\nquantum phase transition. Moreover, we observe nearest-neighbor interaction,\nwhich is a genuine consequence of the long-range nature of dipolar\ninteractions. Our results lay the groundwork for future studies of novel exotic\nmany-body quantum phases."
    },
    {
        "anchor": "Exploring quantum criticality based on ultracold atoms in optical\n  lattices: Critical behavior developed near a quantum phase transition, interesting in\nits own right, offers exciting opportunities to explore the universality of\nstrongly-correlated systems near the ground state. Cold atoms in optical\nlattices, in particular, represent a paradigmatic system, for which the quantum\nphase transition between the superfluid and Mott insulator states can be\nexternally induced by tuning the microscopic parameters. In this paper, we\ndescribe our approach to study quantum criticality of cesium atoms in a\ntwo-dimensional lattice based on in situ density measurements. Our research\nagenda involves testing critical scaling of thermodynamic observables and\nextracting transport properties in the quantum critical regime. We present and\ndiscuss experimental progress on both fronts. In particular, the thermodynamic\nmeasurement suggests that the equation of state near the critical point follows\nthe predicted scaling law at low temperatures.",
        "positive": "Entanglement and entropy production in coupled single-mode Bose-Einstein\n  condensates: We investigate the time evolution of the entanglement entropy of coupled\nsingle-mode Bose-Einstein condensates in a double well potential at $T=0$\ntemperature, by combining numerical results with analytical approximations. We\nfind that the coherent oscillations of the condensates result in entropy\noscillations on the top of a linear entropy generation at short time scales.\nDue to dephasing, the entropy eventually saturates to a stationary value, in\nspite of the lack of equilibration. We show that this long time limit of the\nentropy reflects the semiclassical dynamics of the system, revealing the\nself-trapping phase transition of the condensates at large interaction strength\nby a sudden entropy jump. We compare the stationary limit of the entropy to the\nprediction of a classical microcanonical ensemble, and find surprisingly good\nagreement in spite of the non-equilibrium state of the system. Our predictions\nshould be experimentally observable on a Bose-Einstein condensate in a double\nwell potential or on a two-component condensate with inter-state coupling."
    },
    {
        "anchor": "Missing understanding of the phase factor between valence-electron and\n  hole operators: This paper provides the long-missing foundation to connect semiconductor and\natomic notations and to support results incorrectly obtained by doing as if\nsemiconductor electrons possessed an orbital angular momentum. We here show\nthat the phase factor between valence-electron destruction operator and hole\ncreation operator is the same as the one between particle and antiparticle in\nquantum relativity, namely $\\hat{a}_{m}=(-1)^{j-m} \\hat{b}^\\dag_{-m}$ provided\nthat $m=(j,j-1\\cdots,-j)$ labels the degenerate states of the $(2j+1)$-fold\nelectron level at hand. This result is remarkable because $(i)$ the hole is\ndefinitely not a naive antiparticle due to the remaining valence electrons;\n$(ii)$ unlike atomic electrons in a central potential, semiconductor electrons\nin a periodic crystal do not have orbital angular momentum\n$\\textbf{L}=\\textbf{r}\\wedge\\textbf{p}$ nor angular momentum\n$\\textbf{J}=\\textbf{L}+\\textbf{S}$. Consequently, $(j,m)$ for semiconductor\nelectrons merely are convenient notations to label the states of a degenerate\nlevel. To illustrate the physical implications, we discuss the interband\ncouplings between photons and semiconductor, in terms of valence electrons and\nof holes: the phase factor is crucial to establish that bright excitons are in\na spin-singlet state.",
        "positive": "Larkin-Ovchinnikov phases in two-dimensional square lattices: We consider a two-component gas of fermions in optical lattices in the\npresence of a population imbalance within a mean-field theory. We study phase\ntransitions from a normal gas of unpaired fermions to a superfluid phase of\nBose-condensed Cooper pairs. The possibility of Cooper pairs with a nonzero\ncenter-of-mass momentum is included, which corresponds to a so-called\nFulde-Ferrel-Larkin-Ovchinnikov (FFLO) state. We find that for population\nimbalanced systems such states can form the ground state. The FF and LO state\nare compared and it is shown that actually the LO state is energetically more\nfavorable. We complete the mean-field phase diagram for the LO phase and show\nthat it is qualitatively in excellent agreement with recent diagrammatic Monte\nCarlo calculations. Subsequently, we calculate the atomic density modulations\nin the LO phase."
    },
    {
        "anchor": "Collective dynamics of vortices in trapped Bose-Einstein condensates: We have calculated collective mode spectra for three-dimensional, rotating\nBose-Einstein condensates in oblate harmonic traps using the microscopic\nBogoliubov-deGennes field theory. For condensates with $N_v$ vortices, $N_v$\nKelvin-Tkachenko mode branches are obtained. The features of these modes are\ncompared with those predicted by a classical point vortex model. We have\ncreated movies to visualize the motion of the vortices corresponding to the\nKelvin-Tkachenko waves.",
        "positive": "A scripted control system for autonomous hardware timed experiments: We present the labscript suite, an open-source experiment control system for\nautomating shot-based experiments and their analysis. Experiments are composed\nas Python code, which is used to produce low-level hardware instructions. They\nare queued up and executed on the hardware in real time, synchronized by a\npseudoclock. Experiment parameters are manipulated graphically, and analysis\nroutines are run as new data is acquired. With this system, we can easily\nautomate exploration of parameter spaces, including closed-loop optimization."
    },
    {
        "anchor": "Excitation spectrum of the Lieb-Liniger model: We study the integrable model of one-dimensional bosons with contact\nrepulsion. In the limit of weak interaction, we use the microscopic\nhydrodynamic theory to obtain the excitation spectrum. The statistics of\nquasiparticles changes with the increase of momentum. At lowest momenta good\nquasiparticles are fermions, while at higher momenta they are Bogoliubov\nbosons, in accordance with recent studies. In the limit of strong interaction,\nwe analyze the exact solution and find exact results for the spectrum in terms\nof the asymptotic series. Those results undoubtedly suggest that fermionic\nquasiparticle excitations actually exist at all momenta for moderate and strong\ninteraction, and also at lowest momenta for arbitrary interaction. Moreover, at\nstrong interaction we find highly accurate analytical results for several\nrelevant quantities of the Lieb-Liniger model.",
        "positive": "Emergence of coherence and the dynamics of quantum phase transitions: The dynamics of quantum phase transitions poses one of the most challenging\nproblems in modern many-body physics. Here, we study a prototypical example in\na clean and well-controlled ultracold atom setup by observing the emergence of\ncoherence when crossing the Mott insulator to superfluid quantum phase\ntransition. In the one-dimensional Bose-Hubbard model, we find perfect\nagreement between experimental observations and numerical simulations for the\nresulting coherence length. We thereby perform a largely certified analogue\nquantum simulation of this strongly correlated system reaching beyond the\nregime of free quasiparticles. Experimentally, we additionally explore the\nemergence of coherence in higher dimensions where no classical simulations are\navailable, as well as for negative temperatures. For intermediate quench\nvelocities, we observe a power-law behaviour of the coherence length,\nreminiscent of the Kibble-Zurek mechanism. However, we find exponents that\nstrongly depend on the final interaction strength and thus lie outside the\nscope of this mechanism."
    },
    {
        "anchor": "Dimensional crossover of nonrelativistic bosons: We investigate how confining a transverse spatial dimension influences the\nfew- and many-body properties of non-relativistic bosons with pointlike\ninteractions. Our main focus is on the dimensional crossover from three to two\ndimensions, which is of relevance for ultracold atom experiments. Using\nFunctional Renormalization Group equations and T-matrix calculations we study\nhow the phase transition temperature changes as a function of the spatial\nextent of the transverse dimension and relate the 3D and 2D s-wave scattering\nlengths. The analysis reveals how the properties of the lower-dimensional\nsystem are inherited from the higher-dimensional one during the renormalization\ngroup evolution. We limit the discussion to confinements in a potential well\nwith periodic boundary conditions and argue why this qualitatively captures the\nphysics of other compactifications such as transverse harmonic confinement as\nin cold atom experiments.",
        "positive": "Inhomogeneous state of few-fermion superfluids: The few-fermion atomic gas is an ideal setting to explore inhomogeneous\nsuperfluid pairing analogous to the Larkin-Ovchinnikov state. Two up and one\ndown-spin atom is the minimal configuration that displays an inhomogeneous\npairing density whereas imbalanced systems containing more fermions present a\nmore complex pairing topology. With more than eight atoms trapped the system\napproaches the macroscopic superfluid limit. An oblate trap with a central\nbarrier offers a direct experimental probe of pairing inhomogeneity."
    },
    {
        "anchor": "Non-equilibrium dynamics of an unstable quantum pendulum: A pendulum prepared perfectly inverted and motionless is a prototype of\nunstable equilibria and corresponds to an unstable hyperbolic fixed point in\nthe dynamical phase space. Unstable fixed points are central to understanding\nHamiltonian chaos in classical systems. In many-body quantum systems,\nmean-field approximations fail in the vicinity of unstable fixed points and\nlead to dynamics driven by quantum fluctuations. Here, we measure the\nnon-equilibrium dynamics of a many-body quantum pendulum initialized to a\nhyperbolic fixed point of the phase space. The experiment uses a spin-1 Bose\ncondensate, which exhibits Josephson dynamics in the spin populations that\ncorrespond in the mean-field limit to motion of a non-rigid mechanical\npendulum. The condensate is initialized to a minimum uncertainty spin state,\nand quantum fluctuations lead to non-linear spin evolution along a separatrix\nand non-Gaussian probability distributions that are measured to be in good\nagreement with exact quantum calculations up to 0.25 s. At longer times, atomic\nloss due to the finite lifetime of the condensate leads to larger spin\noscillation amplitudes compared to no loss case as orbits depart from the\nseparatrix. This demonstrates how decoherence of a many-body system can result\nin more apparent coherent behaviour. This experiment provides new avenues for\nstudying macroscopic spin systems in the quantum limit and for investigations\nof important topics in non-equilibrium quantum dynamics.",
        "positive": "Particle and spin transports of spin-orbit coupled Fermi gas through a\n  Quantum Point Contact: The particle and spin transport through a quantum point contact between two\nFermi gases with Raman-induced spin-orbit coupling are investigated. We show\nthat the particle and spin conductances both demonstrate the structure of\nplateau due to the mesoscopic scale of the quantum point contact. Compared with\nthe normal Fermi gases the particle conductance can be significantly enhanced\nby the spin-orbit coupling effect. Furthermore, the conversion of the particle\nand spin currents can take place in the spin-orbit coupled system, and we find\nthat it is controlled by the parameter of two-photon detuning. When the\nparameter of two-photon detuning vanishes the particle and spin currents\ndecouple."
    },
    {
        "anchor": "Observation of low-field Feshbach resonances between $^{161}$Dy and\n  $^{40}$K: We report on the observation of Feshbach resonances at low magnetic field\nstrength (below 10 G) in the Fermi-Fermi mixture of $^{161}$Dy and $^{40}$K. We\ncharacterize five resonances by measurements of interspecies thermalization\nrates and molecular binding energies. As a case of particular interest for\napplications, we consider a resonance near 7.29 G, which combines accurate\nmagnetic tunability and access to the universal regime of interactions with\nexperimental simplicity. We show that lifetimes of a few 100 ms can be achieved\nfor the optically trapped, resonantly interacting mixture. We also demonstrate\nthe hydrodynamic expansion of the mixture in the strongly interacting regime\nand the formation of DyK Feshbach molecules. Our work opens up new experimental\npossibilities in view of mass-imbalanced superfluids and related phenomena.",
        "positive": "Optomechanical signature of a frictionless flow of superfluid light: We propose an experimental setup that should make it possible to reveal the\nfrictionless flow of a superfluid of light from the suppression of the drag\nforce that it exerts onto a material obstacle. In the paraxial-propagation\ngeometry considered here, the photon-fluid dynamics is described by a wave\nequation analogous to the Gross-Pitaevskii equation of dilute Bose-Einstein\ncondensates and the obstacle consists in a solid dielectric slab immersed into\na nonlinear optical liquid. By means of an ab initio calculation of the\nelectromagnetic force experienced by the obstacle, we anticipate that\nsuperfluidity is detectable in state-of-the-art experiments from the\ndisappearance of the optomechanical deformation of the obstacle."
    },
    {
        "anchor": "Universal Scaling Laws in the Dynamics of a Homogeneous Unitary Bose Gas: We study the dynamics of an initially degenerate homogeneous Bose gas after\nan interaction quench to the unitary regime at a magnetic Feshbach resonance.\nAs the cloud decays and heats, it exhibits a crossover from degenerate- to\nthermal-gas behaviour, both of which are characterised by universal scaling\nlaws linking the particle-loss rate to the total atom number $N$. In the\ndegenerate and thermal regimes the per-particle loss rate is $\\propto N^{2/3}$\nand $N^{26/9}$, respectively. The crossover occurs at a universal kinetic\nenergy per particle and at a universal time after the quench, in units of\nenergy and time set by the gas density. By slowly sweeping the magnetic field\naway from the resonance and creating a mixture of atoms and molecules, we also\nmap out the dynamics of correlations in the unitary gas, which display a\nuniversal temporal scaling with the gas density, and reach a steady state while\nthe gas is still degenerate.",
        "positive": "Universal trimers emerging from a spin-orbit coupled Fermi sea: We report the existence of a universal trimer state induced by an impurity\ninteracting with a two-component spin-orbit coupled Fermi gas in two\ndimensions. In the zero-density limit with a vanishing Fermi sea, the trimer is\nstabilized by the symmetry of the single-particle spectrum under spin-orbit\ncoupling, and is therefore {\\it universal} against the short-range details of\nthe interaction potential. When the Fermi energy increases, we show that the\ntrimer is further stabilized by particle-hole fluctuations over a considerable\nparameter region. We map out the phase diagram consisting of trimers, dimers,\nand polarons, and discuss the detection of these states using radio-frequency\nspectroscopy. The universal trimer revealed in our work is a direct\nmanifestation of intriguing three-body correlations emerging from a many-body\nenvironment, which, in our case, is cooperatively supported by the\nsingle-particle spectral symmetry and the collective particle-hole excitations."
    },
    {
        "anchor": "Off-diagonal correlations in a one-dimensional gas of dipolar bosons: We present a quantum Monte Carlo study of the one-body density matrix (OBDM)\nand the momentum distribution of one-dimensional dipolar bosons, with dipole\nmoments polarized perpendicular to the direction of confinement. We observe\nthat the long-range nature of the dipole interaction has dramatic effects on\nthe off-diagonal correlations: although the dipoles never crystallize, the\nsystem goes from a quasi-condensate regime at low interactions to a regime in\nwhich quasi-condensation is discarded, in favor of quasi-solidity. For all\nstrengths of the dipolar interaction, the OBDM shows an oscillatory behavior\ncoexisting with an overall algebraic decay; and the momentum distribution shows\nsharp kinks at the wavevectors of the oscillations, $Q = \\pm 2\\pi n$ (where $n$\nis the atom density), beyond which it is strongly suppressed. This\n\\emph{momentum filtering} effect introduces a characteristic scale in the\nmomentum distribution, which can be arbitrarily squeezed by lowering the atom\ndensity. This shows that one-dimensional dipolar Bose gases, realized e.g. by\ntrapped dipolar molecules, show strong signatures of the dipolar interaction in\ntime-of-flight measurements.",
        "positive": "Triplet pair amplitude in a trapped $s$-wave superfluid Fermi gas with\n  broken spin rotation symmetry. II. Three dimensional continuum case: We extend our recent work [Y. Endo et. al., Phys. Rev. 92, 023610 (2015)] for\na parity-mixing effect in a model two-dimensional lattice fermions to a\nrealistic three-dimensional ultracold Fermi gas. Including effects of broken\nlocal spatial inversion symmetry by a trap potential within the framework of\nthe real-space Bogoliubov-de Gennes theory at $T=0$, we point out that an\nodd-parity $p$-wave Cooper-pair amplitude is expected to have already been\nrealized in previous experiments on an (even-parity) $s$-wave superfluid Fermi\ngas with spin imbalance. This indicates that, when one suddenly changes the\n$s$-wave pairing interaction to an appropriate $p$-wave one by using a Feshbach\ntechnique in this case, a non-vanishing $p$-wave superfluid order parameter is\nimmediately obtained, which is given by the product of the $p$-wave interaction\nand the $p$-wave pair amplitude that has already been induced in the\nspin-imbalanced $s$-wave superfluid Fermi gas. Thus, by definition, the system\nis in the $p$-wave superfluid state, at least just after this manipulation.\nSince the achievement of a $p$-wave superfluid state is one of the most\nexciting challenges in cold Fermi gas physics, our results may provide an\nalternative approach to this unconventional pairing state. In addition, since\nthe parity-mixing effect cannot be explained as far as one deals with a trap\npotential in the local density approximation (LDA), it is considered as a\ncrucial example which requires us to go beyond LDA."
    },
    {
        "anchor": "Universal Relations for Range Corrections to Efimov Features: In a three-body system of identical bosons interacting through a large S-wave\nscattering length $a$, there are several sets of Efimov features related by\ndiscrete scale invariance. Effective field theory was recently used to derive\nuniversal relations between these Efimov features that include the first-order\ncorrection due to a nonzero effective range $r_s$. We reveal a simple pattern\nin these range corrections that had not been previously identified. The pattern\nis explained by the renormalization group for the effective field theory, which\nimplies that the Efimov three-body parameter runs logarithmically with the\nmomentum scale at a rate proportional to $r_s/a$. The running Efimov parameter\nalso explains the empirical observation that range corrections can be largely\ntaken into account by shifting the Efimov parameter by an adjustable parameter\ndivided by a. The accuracy of universal relations that include first-order\nrange corrections is verified by comparing with various theoretical\ncalculations using models with nonzero range.",
        "positive": "Electrodynamic duality and vortex unbinding in driven-dissipative\n  condensates: We investigate the superfluid properties of two-dimensional driven Bose\nliquids, such as polariton condensates, using their long-wavelength description\nin terms of a compact Kardar-Parisi-Zhang (KPZ) equation for the phase\ndynamics. We account for topological defects (vortices) in the phase field\nthrough a duality mapping between the compact KPZ equation and a theory of\nnon-linear electrodynamics coupled to charges. Using the dual theory we derive\nrenormalization group equations that describe vortex unbinding in these media.\nWhen the non-equilibirum drive is turned off, the KPZ non-linearity {\\lambda}\nvanishes and the RG flow gives the usual Kosterlitz-Thouless (KT) transition.\nOn the other hand, with non-linearity {\\lambda} > 0 vortices always unbind,\neven if the same system with {\\lambda} = 0 is superfluid. We predict the finite\nsize scaling behavior of the superfluid stiffness in the crossover governed by\nvortex unbinding showing its clear distinction from the scaling associated with\nthe KT transition."
    },
    {
        "anchor": "Nonlinear Zeno dynamics due to atomic interactions in Bose-Einstein\n  condensate: We show that nonlinear interactions induce both the Zeno and anti-Zeno\neffects in the generalised Bose-Josephson model (with the on-site interactions\nand the second-order tunneling) describing Bose-Einstein condensate in\ndouble-well trap subject to particle removal from one of the wells. We find\nthat the on-site interactions induce \\textit{only} the Zeno effect, which\nappears at long evolution times, whereas the second-order tunneling leads to a\nstrong decay of the atomic population at short evolution times, reminiscent of\nthe anti-Zeno effect, and destroys the nonlinear Zeno effect due to the on-site\ninteractions at long times.",
        "positive": "Modulational instability and localized breather modes in the discrete\n  nonlinear Schr\u00f6dinger equation with helicoidal hopping: We study a one-dimensional discrete nonlinear Schr\\\"odinger model with\nhopping to the first and a selected N-th neighbor, motivated by a helicoidal\narrangement of lattice sites. We provide a detailed analysis of the\nmodulational instability properties of this equation, identifying distinctive\nmulti-stage instability cascades due to the helicoidal hopping term.\nBistability is a characteristic feature of the intrinsically localized breather\nmodes, and it is shown that information on the stability properties of weakly\nlocalized solutions can be inferred from the plane-wave modulational\ninstability results. Based on this argument, we derive analytical estimates of\nthe critical parameters at which the fundamental on-site breather branch of\nsolutions turns unstable. In the limit of large N, these estimates predict the\nemergence of an effective threshold behavior, which can be viewed as the result\nof a dimensional crossover to a two-dimensional square lattice."
    },
    {
        "anchor": "Odd-petal states and persistent flows in spin-orbit-coupled\n  Bose-Einstein condensates: We study the phase diagram of a Rashba spin-orbit-coupled Bose-Einstein\ncondensate confined in a two-dimensional toroidal trap. In the immiscible\nregime we find an azimuthally periodic density distribution, with the\nperiodicity highly tuneable as a function of the spin-orbit coupling strength\nand which favours an odd number of petals in each component. This allows for a\nwide range of states that can be created. We further show that in the miscible\nregime, both components possess states with persistent flows with a unit\nwinding number difference between them and with the absolute values of these\nwinding numbers depending on the spin-orbit coupling strength. All features of\nthe odd-petal and the persistent flow states can be explained using a simple\nbut effective model.",
        "positive": "Larkin-Ovchinikov superfluidity in time-reversal symmetric bilayer Fermi\n  gases: Larkin-Ovchinnikov (LO) state which combines the superfluidity and spatial\nperiodicity of pairing order parameter and exhibits the supersolid properties\nhas been attracting intense attention in both condensed matter physics and\nultracold atoms. Conventionally, realization of LO state from an intrinsic\ns-wave interacting system necessitates to break the time-reversal (TR) and\nsometimes spatial-inversion (SI) symmetries. Here we report a novel prediction\nthat the LO state can be realized in a TR and SI symmetric system representing\na bilayer Fermi gas subjected to a laserassisted interlayer tunneling. We show\nthat the intralayer s-wave atomic interaction acts effectively like a p-wave\ninteraction in the pseudospin space. This provides distinctive pairing effects\nin the present system with pseudspin spin-orbit coupling, and leads to a\nspontaneous density-modulation of the pairing order predicted in a very broad\nparameter regime. Unlike the conventional schemes, our results do not rely on\nthe spin imbalance or external Zeeman fields, showing a highly feasible way to\nobserve the long-sought-after LO superfluid phase using the laser-assisted\nbilayer Fermi gases."
    },
    {
        "anchor": "Mott insulating states of the anisotropic SU(4) Dirac fermions: We employ the large-scale quantum Monte-Carlo simulations to investigate the\nMott-insulating states of the half-filled SU(4) Hubbard model on the square\nlattice with a staggered-flux pattern. The noninteracting band structure that\nevolves from a nested Fermi surface at zero flux to isotropic Dirac cones at\n$\\pi$ flux, exhibits anisotropic Dirac cones as the flux varies in between. Our\nsimulations show transitions between the three phases of Dirac semimetal,\nantiferromagnet and valence-bond solid. A direct continuous transition between\nthe antiferromagnetic phase and the valence-bond-solid phase is realized via\nvarying the flux in the Mott regime. Inside the valence-bond-solid phase\ninduced by the flux, the plaquette valence-bond state with vanishing\nsingle-particle gap is identified. At strong coupling, the valence-bond-solid\nphase disappears and the Mott-insulating state is always accompanied by\nantiferromagnetic ordering, regardless of the magnitude of the flux.",
        "positive": "Pairs, trimers and BCS-BEC crossover near a flat band: the sawtooth\n  lattice: We investigate pairing and superconductivity in the attractive Fermi Hubbard\nmodel on the one-dimensional sawtooth lattice, which exhibits a flat band by\nfine-tuning the hopping rates. We first solve the two-body problem, both\nanalytically and numerically, to extract the binding energy and the effective\nmass of the pairs. Based on the DMRG method, we address the ground-state\nproperties of the many-body system, assuming equal spin populations. We compare\nour results with those available for a linear chain, where the model is\nintegrable by Bethe ansatz, and show that the multiband nature of the system\nsubstantially modifies the physics of the BCS-BEC crossover. Near a flat band,\nthe chemical potential remains always close to its zero-density limit predicted\nby the two-body physics. In contrast, the pairing gap exhibits a remarkably\nstrong density dependence and, differently from the pair binding energy, it is\nno longer peaked at the flat-band point. We show that these results can be\ninterpreted in terms of polarization screening effects, due to an anomalous\nattraction between pairs in the medium and single fermions. Importantly, we\nunveil that three-body bound states (trimers) exist in the sawtooth lattice, in\nsharp contrast with the linear chain geometry, and we compute their binding\nenergy. The nature of these states is investigated via a strong coupling\nvariational approach, revealing that they originate from tunneling-induced\nexchange processes."
    },
    {
        "anchor": "Universal description of dissipative Tomonaga-Luttinger liquids with\n  SU($N$) spin symmetry: Exact spectrum and critical exponents: Universal scaling relations for dissipative Tomonaga-Luttinger (TL) liquids\nwith SU($N$) spin symmetry are obtained for both fermions and bosons, by using\nasymptotic Bethe-ansatz solutions and conformal field theory (CFT) in\none-dimensional non-Hermitian quantum many-body systems with SU($N$) symmetry.\nWe uncover that the spectrum of dissipative TL liquids with SU($N$) spin\nsymmetry is described by the sum of one charge mode characterized by a complex\ngeneralization of $c=1$ U(1) Gaussian CFT, and $N-1$ spin modes characterized\nby level-$1$ SU($N$) Kac-Moody algebra with the conformal anomaly $c=N-1$, and\nthereby dissipation only affects the charge mode as a result of spin-charge\nseparation in one-dimensional non-Hermitian quantum systems. The derivation is\nbased on a complex generalization of Haldane's ideal-gas description, which is\nimplemented by the SU($N$) Calogero-Sutherland model with inverse-square\nlong-range interactions.",
        "positive": "Thermodynamics, contact and density profiles of the repulsive\n  Gaudin-Yang model: We address the problem of computing the thermodynamic properties of the\nrepulsive one-dimensional two-component Fermi gas with contact interaction,\nalso known as the Gaudin-Yang model. Using a specific lattice embedding and the\nquantum transfer matrix we derive an exact system of only two nonlinear\nintegral equations for the thermodynamics of the homogeneous model which is\nvalid for all temperatures and values of the chemical potential, magnetic field\nand coupling strength. This system allows for an easy and extremely accurate\ncalculation of thermodynamic properties circumventing the difficulties\nassociated with the truncation of the thermodynamic Bethe ansatz system of\nequations. We present extensive results for the densities, polarization,\nmagnetic susceptibility, specific heat, interaction energy, Tan contact and\nlocal correlation function of opposite spins. Our results show that at low and\nintermediate temperatures the experimentally accessible contact is a\nnon-monotonic function of the coupling strength. As a function of the\ntemperature the contact presents a pronounced local minimum in the\nTonks-Girardeau regime which signals an abrupt change of the momentum\ndistribution in a small interval of temperature. The density profiles of the\nsystem in the presence of a harmonic trapping potential are computed using the\nexact solution of the homogeneous model coupled with the local density\napproximation. We find that at finite temperature the density profile presents\na double shell structure (partially polarized center and fully polarized wings)\nonly when the polarization in the center of the trap is above a critical value\nwhich is monotonically increasing with temperature."
    },
    {
        "anchor": "Mass and chirality inversion of a Dirac cone pair in St\u00fcckelberg\n  interferometry: We show that a St\\\"{u}ckelberg interferometer made of two massive Dirac cones\ncan reveal information on band eigenstates such as the chirality and mass sign\nof the cones. For a given spectrum with two gapped cones, we propose several\nlow-energy Hamiltonians differing by their eigenstates properties. The\ncorresponding inter-band transition probability is affected by such differences\nin its interference fringes being shifted by a new phase of geometrical origin.\nThis phase can be a useful bulk probe for topological band structures realized\nwith artificial crystals.",
        "positive": "Disordered insulator in an optical lattice: Disorder can profoundly affect the transport properties of a wide range of\nquantum materials. Presently, there is significant disagreement regarding the\neffect of disorder on transport in the disordered Bose-Hubbard (DBH) model,\nwhich is the paradigm used to theoretically study disorder in strongly\ncorrelated bosonic systems. We experimentally realize the DBH model by using\noptical speckle to introduce precisely known, controllable, and fine-grained\ndisorder to an optical lattice5. Here, by measuring the dissipation strength\nfor transport, we discover a disorder-induced SF-to-insulator (IN) transition\nin this system, but we find no evidence for an IN-to-SF transition. Emergence\nof the IN at disorder strengths several hundred times the tunnelling energy\nagrees with a predicted SF--Bose glass (BG) transition from recent quantum\nMonte Carlo (QMC) work. Both the SF--IN transition and correlated changes in\nthe atomic quasimomentum distribution--which verify a simple model for the\ninterplay of disorder and interactions in this system--are phenomena new to the\nunit filling regime explored in this work, compared with the high filling limit\nprobed previously. We find that increasing disorder strength generically leads\nto greater dissipation in the regime of mixed SF and Mott-insulator (MI)\nphases, excluding predictions of a disorder-induced, or \"re-entrant,\" SF (RSF).\nWhile the absence of an RSF may be explained by the effect of finite\ntemperature, we strongly constrain theories by measuring bounds on the entropy\nper particle in the disordered lattice."
    },
    {
        "anchor": "Many-body braiding phases in a rotating strongly correlated photon gas: We present a theoretical study of a rotating trapped photon gas where a\nLaguerre-Gauss laser pump with a non-zero orbital angular momentum is used to\ninject rotating photons into a cavity with strong optical nonlinearity. The\nLaughlin-like few-photon eigenstates appear as sharp resonances in the\ntransmission spectra. Using additional localized repulsive potentials,\nquasi-holes can be created in the quantum Hall liquid of photons and then\nbraided around in space: an unambiguous signature of the many-body Berry phase\nunder exchange of two quasi-holes is observed as a spectral shift of the\ncorresponding transmission resonance.",
        "positive": "Two-channel model description of confinement-induced Feshbach molecules: Using a two-channel model, we investigate theoretically the binding energy of\nconfinement-induced Feshbach molecules in two- and one-dimensional ultracold\natomic systems, near a Feshbach resonance. We show that the two-channel\nprediction will evidently deviate from the simple single-channel theory as the\nwidth of Feshbach resonances decreases. For one-dimensional system, we perform\na full two-channel calculation, with the inclusion of bare interatomic\ninteractions in the open channel. Away from the resonance, we find a sizable\ncorrection to the binding energy, if we neglect incorrectly the bare\ninteratomic interactions as in the previous work [Dickerscheid and Stoof, Phys.\nRev. A 72, 053625 (2005)]. We compare our theoretical results with existing\nexperimental data and present predictions for narrow Feshbach resonances that\ncould be tested in future experiments."
    },
    {
        "anchor": "C-Field Methods for Non-Equilibrium Bose Gases: We review c-field methods for simulating the non-equilibrium dynamics of\ndegenerate Bose gases beyond the mean-field Gross-Pitaevskii approximation. We\ndescribe three separate approaches that utilise similar numerical methods, but\nhave distinct regimes of validity. Systems at finite temperature can be treated\nwith either the closed-system projected Gross-Pitaevskii equation (PGPE), or\nthe open-system stochastic projected Gross-Pitaevskii equation (SPGPE). These\nare both applicable in quantum degenerate regimes in which thermal fluctuations\nare significant. At low or zero temperature, the truncated Wigner projected\nGross-Pitaevskii equation (TWPGPE) allows for the simulation of systems in\nwhich spontaneous collision processes seeded by quantum fluctuations are\nimportant. We describe the regimes of validity of each of these methods, and\ndiscuss their relationships to one another, and to other simulation techniques\nfor the dynamics of Bose gases. The utility of the SPGPE formalism in modelling\nnon-equilibrium Bose gases is illustrated by its application to the dynamics of\nspontaneous vortex formation in the growth of a Bose-Einstein condensate.",
        "positive": "Using superlattice potentials to probe long-range magnetic correlations\n  in optical lattices: In Pedersen et al. (2011) we proposed a method to utilize a temporally\ndependent superlattice potential to mediate spin-selective transport, and\nthereby probe long and short range magnetic correlations in optical lattices.\nSpecifically this can be used for detecting antiferromagnetic ordering in\nrepulsive fermionic optical lattice systems, but more generally it can serve as\na means of directly probing correlations among the atoms by measuring the mean\nvalue of an observable, the number of double occupied sites. Here, we provide a\ndetailed investigation of the physical processes which limit the effectiveness\nof this \"conveyer belt method\". Furthermore we propose a simple ways to improve\nthe procedure, resulting in an essentially perfect (error-free) probing of the\nmagnetic correlations. These results shows that suitably constructed\nsuperlattices constitute a promising way of manipulating atoms of different\nspin species as well as probing their interactions."
    },
    {
        "anchor": "Visualization of Dimensional Effects in Collective Excitations of\n  Optically Trapped Quasi-Two-Dimensional Bose Gases: We analyze the macroscopic dynamics of a Bose gas axially confined in an\noptical lattice with a superimposed harmonic trap, taking into account weak\ntunneling effect. Our results show that upon transition to the\nquasi-two-dimensional (2D) regime of the trapped gas, the 3D equation of state\nand equilibrium density profile acquire corrections from 2D many-body effects.\nThe corresponding frequency shift in the transverse breathing mode is\naccessible within current facilities, suggesting a direct observation of\ndimensional effects. Comparisons with other relevant effects are also\npresented.",
        "positive": "Beyond Gaussian pair fluctuation theory for strongly interacting Fermi\n  gases II: The broken-symmetry phase: We theoretically study the thermodynamic properties of a strongly interacting\nFermi gas at the crossover from a Bardeen-Cooper-Schrieffer (BCS) superfluid to\na Bose-Einstein condensate (BEC), by applying a recently outlined\nstrong-coupling theory that includes pair fluctuations beyond the commonly-used\nmany-body $T$-matrix or ladder approximation at the Gaussian level. The beyond\nGaussian pair fluctuation (GPF) theory always respects the exact thermodynamic\nrelations and recovers the Bogoliubov theory of molecules in the BEC limit with\na nearly correct molecule-molecule scattering length. We show that the\nbeyond-GPF theory predicts quantitatively accurate ground-state properties at\nthe BEC-BCS crossover, in good agreement with the recent measurement by\nHorikoshi \\textit{et al.} in Phys. Rev. X \\textbf{7}, 041004 (2017). In the\nunitary limit with infinitely large $s$-wave scattering length, the beyond-GPF\ntheory predicts a reliable universal energy equation of state up to 0.6$T_c$,\nwhere $T_c$ is the superfluid transition temperature at unitarity. The theory\npredicts a Bertsch parameter $\\xi \\simeq 0.365$ at zero temperature, in good\nagreement with the latest quantum Monte Carlo result $\\xi = 0.367(7)$ and the\nlatest experimental measurement $\\xi = 0.367(9)$. We attribute the excellent\nand wide applicability of the beyond-GPF theory in the broken-symmetry phase to\nthe reasonable re-summation of Feynman diagrams following a dimensional\n$\\epsilon$-expansion analysis near four dimensions ($d=4-\\epsilon$), which\ngives rise to accurate predictions at the second order\n$\\mathcal{O}(\\epsilon^2)$. Our work indicates the possibility of further\nimproving the strong-coupling theory of strongly interacting fermions based on\nthe systematic inclusion of large-loop Feynman diagrams at higher orders\n$\\mathcal{O}(\\epsilon^n)$ with $n\\ge 3$."
    },
    {
        "anchor": "Effects of extended correlated hopping in a bose-bose mixture: We study the effects of assisted tunneling or correlated hopping between next\nnearest neighbours in a two species Bose-Hubbard system. The system is the\nbosonic analong of the fermionic system studied in Phys. Rev. Lett. {\\bf 116},\n225303 (2016). Using a combination of cluster mean field theory, exact\ndiagonlization and analytical results, a rich phase diagram is determined\nincluding a pair superfluid phase as well as a superfluid quantum droplet\nphase. The former is the result of the interplay between single particle and\ncorrelated hopping, while the latter is the effect of large correlated hopping.",
        "positive": "Majorana edge state in a number-conserving Fermi gas with tunable p-wave\n  interaction: The remarkable properties and potential applications of Majorana fermions\nhave led to considerable efforts in recent years to realize topological matters\nthat host these excitations. For a number-conserving system, there have been a\nfew proposals, using either coupled-chain models or multi-component system with\nspin-orbit coupling, to create number fluctuation of fermion pairs in achieving\nMajorana fermion. In this work, we show that Majorana edge states can occur in\na spinless Fermi gas in 1D lattices with tunable $p$-wave interaction. This is\nfacilitated by the conversion between a pair of (open-channel) fermions and a\n(close-channel) boson, thereby allowing the number fluctuation of fermion pairs\nin a single chain. This scheme requires neither spin-orbit coupling nor\nmulti-chain setup and can be implemented easily. Using the\ndensity-matrix-renormalization-group method, we have identified the Majorana\nphase in a wide range of parameter regime as well as its associated phase\ntransitions. The topological nature of the Majorana phase manifests itself in a\nstrong edge-edge correlation in an open chain that is robust against disorder,\nas well as in a non-trivial winding number in the bulk generated by using\ntwisted boundary condition. It is also shown that the Majorana phase in this\nsystem can be stable against atom losses due to few-body collisions on the same\nsite, and can be easily identified from the fermion momentum distribution.\nThese results pave the way for probing the intriguing Majorana physics in a\nsimple and stable cold atoms system."
    },
    {
        "anchor": "Out of equilibrium many-body expansion dynamics of strongly interacting\n  bosons: We solve the Schr\\\"odinger equation from first principles to investigate the\nmany-body effects in the expansion dynamics of one-dimensional repulsively\ninteracting bosons released from a harmonic trap. We utilize the\nmulticonfigurational time-dependent Hartree method for bosons (MCTDHB) to solve\nthe many-body Schr\\\"odinger equation at high level of accuracy. The MCTDHB\nbasis sets are explicitly time-dependent and optimised by variational\nprinciple. We probe the expansion dynamics by three key measures; time\nevolution of one-, two- and three-body densities. We observe when the\nmean-field theory results to unimodal expansion, the many-body calculation\nexhibits trimodal expansion dynamics. The many-body features how the initially\nfragmented bosons independently spreads out with time whereas the mean-field\npictures the expansion of the whole cloud. We also present the three different\ntime scale of dynamics of the inner core, outer core and the cloud as a whole.\nWe analyze the key role played by the dynamical fragmentation during expansion.\nA Strong evidence of the many-body effects is presented in the dynamics of two-\nand three-body densities which exhibit correlation hole and pronounced\ndelocalization effect.",
        "positive": "Quantum phases of incommensurate optical lattices due to cavity\n  backaction: Ultracold bosonic atoms are confined by an optical lattice inside an optical\nresonator and interact with a cavity mode, whose wave length is incommensurate\nwith the spatial periodicity of the confining potential. We predict that the\nintracavity photon number can be significantly different from zero when the\natoms are driven by a transverse laser whose intensity exceeds a threshold\nvalue and whose frequency is suitably detuned from the cavity and the atomic\ntransition frequency. In this parameter regime the atoms form clusters in which\nthey emit in phase into the cavity. The clusters are phase locked, thereby\nmaximizing the intracavity photon number. These predictions are based on a\nBose-Hubbard model, whose derivation is here reported in detail. The\nBose-Hubbard Hamiltonian has coefficients which are due to the cavity field and\ndepend on the atomic density at all lattice sites. The corresponding phase\ndiagram is evaluated using Quantum Monte Carlo simulations in one-dimension and\nmean-field calculations in two dimensions. Where the intracavity photon number\nis large, the ground state of the atomic gas lacks superfluidity and possesses\nfinite compressibility, typical of a Bose-glass."
    },
    {
        "anchor": "Universal Dynamics of a Degenerate Bose Gas Quenched to Unitarity: Motivated by an unexpected experimental observation from the Cambridge group,\n[Eigen {\\it et al.,} Nature {\\bf563}, 221 (2018)], we study the evolution of\nthe momentum distribution of a degenerate Bose gas quenched from the weakly\ninteracting to the unitarity regime. For the two-body problem, we establish a\nrelation that connects the momentum distribution at a long time to a\nsub-leading term in the initial wave function. For the many-body problem, we\nemploy the time-dependent Bogoliubov variational wave function and find that,\nin certain momentum regimes, the momentum distribution at long times displays\nthe same exponential behavior found by the experiment. Moreover, we find that\nthis behavior is universal and independent of the short-range details of the\ninteraction potential. Consistent with the relation found in the two-body\nproblem, we also numerically show that this exponential form is hidden in the\nsame sub-leading term of the Bogoliubov wave function in the initial stages.\nOur results establish a consistent picture to understand the universal dynamics\nobserved in the Cambridge experiment.",
        "positive": "Unified theory of the nonlinear Schr\u00f6dinger equation: The nonlinear Schr\\\"odinger equation (NLSE) is a rich and versatile model,\nwhich in one spatial dimension has stationary solutions similar to those of the\nlinear Schr\\\"odinger equation as well as more exotic solutions such as solitary\nwaves and quantum droplets. We present a unified theory of the NLSE, showing\nthat all stationary solutions of the cubic-quintic NLSE can be classified\naccording to a single number called the cross-ratio. Any two solutions with the\nsame cross-ratio can be converted into one another using a conformal\ntransformation, and the same also holds true for traveling wave solutions. In\nthis way we demonstrate a conformal duality between solutions of cubic-quintic\nNLSEs and lower-order NLSEs. The same analysis can be applied to the Newtonian\ndynamics of classical particles with polynomial potentials. Our framework\nprovides a deeper understanding of the connections between the physics of the\nNLSE and the mathematics of algebraic curves and conformal symmetry."
    },
    {
        "anchor": "Creation and detection of skyrmions in a Bose-Einstein condensate: We present the first experimental realization and characterization of\ntwo-dimensional skyrmions and half-skyrmions in a spin-2 Bose-Einstein\ncondensate. The continuous rotation of the local spin of the skyrmion through\nan angle of pi (and half-skyrmion through an angle of pi/2) across the cloud is\nconfirmed by the spatial distribution of the three spin states as parameterized\nby the bending angle of the ell-vector. The winding number, w = (0, 1, 2), of\nthe skyrmions is confirmed through matter-wave interference.",
        "positive": "Stability of dynamical quantum phase transitions in quenched topological\n  insulators: From multiband to disordered systems: Dynamical quantum phase transitions (DQPTs) represent a counterpart in\nnon-equilibrium quantum time evolution of thermal phase transitions at\nequilibrium, where real time becomes analogous to a control parameter such as\ntemperature. In quenched quantum systems, recently the occurrence of DQPTs has\nbeen demonstrated, both with theory and experiment, to be intimately connected\nto changes of topological properties. Here, we contribute to broadening the\nsystematic understanding of this relation between topology and DQPTs to\nmulti-orbital and disordered systems. Specifically, we provide a detailed\nergodicity analysis to derive criteria for DQPTs in all spatial dimensions, and\nconstruct basic counter-examples to the occurrence of DQPTs in multi-band\ntopological insulator models. As a numerical case study illustrating our\nresults, we report on microscopic simulations of the quench dynamics in the\nHarper-Hofstadter model. Furthermore, going gradually from multi-band to\ndisordered systems, we approach random disorder by increasing the (super) unit\ncell within which random perturbations are switched on adiabatically. This\nleads to an intriguing order of limits problem which we address by extensive\nnumerical calculations on quenched one-dimensional topological insulators and\nsuperconductors with disorder."
    },
    {
        "anchor": "Mesoscopic Vortex-Meissner currents in ring ladders: Recent experimental progress have revealed Meissner and Vortex phases in\nlow-dimensional ultracold atoms systems. Atomtronic setups can realize ring\nladders, while explicitly taking the finite size of the system into account.\nThis enables the engineering of quantized chiral currents and phase slips\nin-between them. We find that the mesoscopic scale modifies the current. Full\ncontrol of the lattice configuration reveals a reentrant behavior of Vortex and\nMeissner phases. Our approach allows a feasible diagnostic of the currents'\nconfiguration through time of flight measurements.",
        "positive": "Bose-Einstein condensation of photons in an ideal atomic gas: We study peculiarities of Bose-Einstein condensation of photons that are in\nthermodynamic equilibrium with atoms of noninteracting gases. General equations\nof the thermodynamic equilibrium of the system under study are obtained. We\nexamine solutions of these equations in the case of high temperatures, when the\natomic components of the system can be considered as nondegenerated ideal gases\nof atoms, and the photonic component can form a state with the Bose condensate.\nTranscendental equation for transition temperature and expression for the\ndensity of condensed photons in the considered system are derived. We also\nobtain analytical solutions of the equation for the critical temperature in a\nnumber of particular cases. The existence of two regimes of Bose condensation\nof photons, which differ significantly in nature of transition temperature\ndependence on the total density of photons pumped into the system, is revealed.\nIn one case, this dependence is a traditional fractional-power law, and in\nanother one it is the logarithmic law. Applying numerical methods, we determine\nboundaries of existence and implementation conditions for different regimes of\ncondensation depending on the physical parameters of the system under study. We\nalso show that for a large range of physical systems that are in equilibrium\nwith photons (from ultracold gases of alkali metals to certain types of ideal\nplasma), the condensation of photons should occur according to the logarithmic\nregime."
    },
    {
        "anchor": "Symmetry breaking in self-consistent models: Lessons from an exactly\n  solvable many-fermion model: This work presents a many-fermion Hamiltonian with the following properties:\n1) is exactly solvable, 2) has a second order insulator-metal quantum phase\ntransition, 3) has a well defined mean field approximation and 4) its\nmean-field ground state displays a liquid-solid transition. The phenomenon of\nsymmetry breaking in fermionic self-consistent models is discussed in the light\nof these remarkable properties of the many-body model.",
        "positive": "Enhancing the capture velocity of a Dy magneto-optical trap with\n  two-stage slowing: Magneto-optical traps (MOTs) based on the $626\\;{\\rm nm}$, $136\\;{\\rm\nkHz}$-wide intercombination line of Dy, which has an attractively low Doppler\ntemperature of $3.3\\;\\mu{\\rm K}$, have been implemented in a growing number of\nexperiments over the last several years. A challenge in loading these MOTs\ncomes from their low capture velocities. Slowed atomic beams can spread out\nsignificantly during free-flight from the Zeeman slower to the MOT position,\nreducing the fraction of the beam captured by the MOT. Here we apply, for the\nfirst time in a Dy experiment, a scheme for enhancing the loading rate of the\nMOT wherein atoms are Zeeman-slowed to a final velocity larger than the MOT's\ncapture velocity, and then undergo a final stage of slowing by a pair of\nnear-detuned beams addressing the $421\\;{\\rm nm}$ transition directly in front\nof the MOT. By reducing the free-flight time of the Zeeman-slowed atomic beam,\nwe greatly enhance the slowed flux delivered to the MOT, leading to more than\nan order of magnitude enhancement in the final MOT population."
    },
    {
        "anchor": "Long-range doublon transfer in a dimer chain induced by topology and ac\n  fields: The controlled transfer of particles from one site of a spatial lattice to\nanother is essential for many tasks in quantum information processing and\nquantum communication. Arrays of semiconductor quantum dots and ultracold atoms\nheld in optical lattices, provide two means of studying coherent quantum\ntransport in well-controlled systems. In this work we study how to induce\nlong-range transfer between the two ends of a dimer chain, by coupling states\nthat are localized just on the chain's end-points. This has the appealing\nfeature that the transfer occurs only between the end-points -- the particle\ndoes not pass through the intermediate sites -- making the transfer less\nsusceptible to decoherence. We first show how a repulsively bound-pair of\nfermions, known as a doublon, can be transferred from one end of the chain to\nthe other via topological edge states. We then show how non-topological surface\nstates of the familiar Shockley or Tamm type can be used to produce a similar\nform of transfer under the action of a periodic driving potential. Finally we\nshow that combining these effects can produce transfer by means of more exotic\ntopological effects, in which the driving field can be used to switch the\ntopological character of the edge states, as measured by the Zak phase. Our\nresults demonstrate how to induce long range transfer of strongly correlated\nparticles by tuning both topology and driving.",
        "positive": "Layered Quantum Hall Insulators with Ultracold Atoms: We consider a generalization of the 2-dimensional (2D) quantum-Hall insulator\nto a non-compact, non-Abelian gauge group, the Heisenberg-Weyl group. We show\nthat this kind of insulator is actually a layered 3D insulator with nontrivial\ntopology. We further show that nontrivial combinations of quantized transverse\nconductivities can be engineered with the help of a staggered potential. We\ninvestigate the robustness and topological nature of this conductivity and\nconnect it to the surface modes of the system. We also propose a simple\nexperimental realization with ultracold atoms in 3D confined to a 2D square\nlattice with the third dimension being mapped to a gauge coordinate."
    },
    {
        "anchor": "Spin-orbit coupled bosons interacting in a two-dimensional harmonic trap: A system of bosons in a two-dimensional harmonic trap in the presence of\nRashba-type spin-orbit coupling is investigated. An analytic treatment of the\nground state of a single atom in the weak-coupling regime is presented and used\nas a basis for a perturbation theory in the interacting two-boson system. The\nnumerical diagonalization of both the single-particle and the two-boson\nHamiltonian matrices allows us to go beyond those approximations and obtain not\nonly the ground state, but also the low-energy spectra and the different energy\ncontributions separately. We show that the expectation value of the spin-orbit\nterm is related to the expectation value of $\\hat{\\sigma}_z \\hat{L}_z$ for the\neigenstates of the system, regardless of the trapping potential. The low-energy\nstates of the repulsively interacting two-boson system are characterized. With\nthe presence of a sufficiently strong interaction and spin-orbit coupling\nstrength, there is a direct energy-level crossing in the ground state of the\nsystem between states of different $J_z$, the third component of the total\nangular momentum, that changes its structure. This is reflected in a\ndiscontinuity in the different energy terms and it is signaled in the spatial\ndensity of the system.",
        "positive": "Phase diagrams of 2D and 3D disordered Bose gases in the local density\n  approximation: We study the superfluid transitions in bidimensional (2D) and tridimensional\n(3D) disordered and interacting Bose gases. We work in the limit of long-range\ncorrelated disorder such that it can be treated in the local density\napproximation. We present the superfluid transition curves both in the\ndisorder-temperature plane well as in the disorder-entropy plane in 2D and 3D\nBose gases. Surprisingly, we find that a small amount of disorder is always\nfavorable to the apparition of a superfluid. Our results offer a quantitative\ncomparison with recent experiments in 2D disordered ultra-cold gases, for which\nno exact theory exists."
    },
    {
        "anchor": "On Dunkl-Bose-Einstein Condensation in Harmonic Traps: The use of the Dunkl derivative, which is defined by a combination of the\ndifference-differential and reflection operator, allows the classification of\nthe solutions according to even and odd solutions. Recently, we considered the\nDunkl formalism to investigate the Bose-Einstein condensation of an ideal Bose\ngas confined in a gravitational field. In this work, we address a similar\nproblem and examine an ideal Bose gas trapped by a three-dimensional harmonic\noscillator within the Dunkl formalism. To this end, we derive an analytic\nexpression for the critical temperature of the N particle system, discuss its\nvalue at large-N limit and finally derive and compare the ground state\npopulation with the usual case result. In addition, we explore two thermal\nquantities, namely the Dunkl-internal energy and the Dunkl-heat capacity\nfunctions. The Wigner parameter of the Dunkl formalism can be successfully used\nto obtain a better agreement between experimental and theoretical results.",
        "positive": "Pair fraction in a finite temperature Fermi gas on the BEC side of the\n  BCS-BEC crossover: We investigate pairing in a strongly interacting two-component Fermi gas with\npositive scattering length. In this regime, pairing occurs at temperatures\nabove the superfluid critical temperature; unbound fermions and pairs coexist\nin thermal equilibrium. Measuring the total number of these fermion pairs in\nthe gas we systematically investigate the phases in the sectors of pseudogap\nand preformed-pair. Our measurements quantitatively test predictions from two\ntheoretical models. Interestingly, we find that already a model based on\nclassical atom-molecule equilibrium describes our data quite well."
    },
    {
        "anchor": "Black-hole lasing in coherently coupled two-component atomic condensates: We theoretically study the black-hole lasing phenomenon in a flowing\none-dimensional, coherently coupled two component atomic Bose-Einstein\ncondensate whose constituent atoms interact via a spin-dependent s-wave contact\ninteraction. We show by a numerical analysis the onset of the dynamical\ninstability in the spin branch of the excitations, once a finite supersonic\nregion is created in this branch. We study both a spatially homogeneous\ngeometry and a harmonically trapped condensate. Experimental advantages of the\ntwo-component configuration are pointed out, with an eye towards studies of\nback-reaction phenomena.",
        "positive": "Subradiance-protected excitation spreading in the generation of\n  collimated photon emission from an atomic array: We show how an initial localized radiative excitation in a two-dimensional\narray of cold atoms can be converted into highly-directional coherent emission\nof light by protecting the spreading of the excitation across the array in a\nsubradiant collective eigenmode with a lifetime orders of magnitude longer than\nthat of an isolated atom. We demonstrate how to reach two such strongly\nsubradiant modes, a uniform one where all the dipoles are oscillating in phase\nnormal to the plane and an antiferromagnetic mode where each dipole is $\\pi$\nout of phase with its nearest neighbor. The excitation, which can consist of a\nsingle photon, is then released from the protected subradiant eigenmode by\ncontrolling the Zeeman level shifts of the atoms. Hence, an original localized\nexcitation which emits in all directions is transferred to a delocalized\nsubradiance-protected excitation, with a probabilistic emission of a photon\nonly along the axis perpendicular to the plane of the atoms. This protected\nspreading and directional emission could potentially be used to link stages in\na quantum information or quantum computing architecture."
    },
    {
        "anchor": "Can three-body recombination purify a quantum gas?: Three-body recombination in quantum gases is traditionally associated with\nheating, but it was recently found that it can also cool the gas. We show that\nin a partially condensed three-dimensional homogeneous Bose gas three-body loss\ncould even purify the sample, that is, reduce the entropy per particle and\nincrease the condensed fraction $\\eta$. We predict that the evolution of $\\eta$\nunder continuous three-body loss can, depending on small changes in the initial\nconditions, exhibit two qualitatively different behaviours - if it is initially\nabove a certain critical value, $\\eta$ increases further, whereas clouds with\nlower initial $\\eta$ evolve towards a thermal gas. These dynamical effects\nshould be observable under realistic experimental conditions.",
        "positive": "Tailoring Dynamical Fermionization: Delta kick cooling of a\n  Tonks-Girardeau gas: In one spatial dimension, quantum exchange statistics and interactions are\ninextricably intertwined. As a manifestation, the expansion dynamics of a\nTonks-Girardeau gas is characterized by dynamical fermionization (DF), whereby\nthe momentum distribution approaches that of a spin-polarized Fermi gas. Using\na phase-space analysis and the unitary evolution of the one-body reduced\ndensity matrix, we show that DF can be tailored and reversed, using a\ngeneralization of delta kick cooling (DKC) to interacting systems, establishing\na simple protocol to rescale the initial momentum distribution. The protocol\napplies to both expansions and compressions and can be used for microscopy of\nquantum correlations."
    },
    {
        "anchor": "Enhanced critical temperature, pairing fluctuation effects, and BCS-BEC\n  crossover in a two-band Fermi gas: We study the superfluid critical temperature in a two-band attractive Fermi\nsystem with strong pairing fluctuations associated with both interband and\nintraband couplings. We focus specifically on a configuration where the\nintraband coupling is varied from weak to strong in a shallow band coupled to a\nweakly-interacting deeper band. The whole crossover from the\nBardeen-Cooper-Schrieffer (BCS) condensation of largely overlapping Cooper\npairs to the Bose-Einstein condensation (BEC) of tightly bound molecules is\ncovered by our analysis, which is based on the extension of the\nNozi\\`{e}res-Schmitt-Rink (NSR) approach to a two-band system. In comparison\nwith the single-band case, we find a strong enhancement of the critical\ntemperature, a significant reduction of the preformed pair region where\npseudogap effects are expected, and the entanglement of two kinds of composite\nbosons in the strong-coupling BEC regime.",
        "positive": "The rotor Jackiw-Rebbi model: a cold-atom approach to chiral symmetry\n  restoration and quark confinement: Understanding the nature of confinement, as well as its relation with the\nspontaneous breaking of chiral symmetry, remains one of the long-standing\nquestions in high-energy physics. The difficulty of this task stems from the\nlimitations of current analytical and numerical techniques to address\nnon-perturbative phenomena in non-Abelian gauge theories. In this work, we show\nhow similar phenomena emerge in simpler models, and how these can be further\ninvestigated using state-of-the-art cold-atom quantum simulators. More\nspecifically, we introduce the rotor Jackiw-Rebbi model, a (1+1)-dimensional\nquantum field theory where interactions between Dirac fermions are mediated by\nquantum rotors. Starting from a mixture of ultracold atoms in an optical\nlattice, we show how this quantum field theory emerges in the long-wavelength\nlimit. For a wide and experimentally-relevant parameter regime, the Dirac\nfermions acquire a dynamical mass via the spontaneous breakdown of chiral\nsymmetry. Moreover, we study the effect of both quantum and thermal\nfluctuations, which lead to the phenomenon of chiral symmetry restoration.\nFinally, we uncover a confinement-deconfinement quantum phase transition, where\nmeson-like fermions fractionalise into quark-like quasi-particles bound to\ntopological solitons of the rotor field. The proliferation of these solitons at\nfinite chemical potentials again serves to restore the chiral symmetry,\nyielding a clear analogy with the quark-gluon plasma in quantum chromodynamics,\nwhere this symmetry coexists with the deconfined fractional charges. Our\nresults show how the interplay between these phenomena could be analyse in\nrealistic atomic experiments."
    },
    {
        "anchor": "The fractional Chern insulator with Rydberg-dressed neutral atoms: Topological nontrivial bands can be realized via Rydberg-dressed neutral\natoms. We propose a two-dimensional hard-core boson model with a topological\nground enrgy at band on a honeycomb lattice, where the particle hopping is\nrealized via van der Waals interaction that exchanges the Rydberg states of two\ninteracting atoms, while nonzero phases associated with hopping is created by\ntransferring the optical phase of laser fields to the atomic pair wave\nfunction. Using exactly diagonalization and infinite density matrix\nrenormalization group simulation, we find in the system a fractional Chern\ninsulator phase with a Chern number C = 1/2, which can persist in the presence\nof weak many-body interactions. Our studies indicate that fractional Chern\ninsulators can be studied with neutral-atom arrays.",
        "positive": "Effects of thermal and quantum fluctuations on the phase diagram of a\n  spin-1 87Rb Bose-Einstein condensate: We investigate effects of thermal and quantum fluctuations on the phase\ndiagram of a spin-1 87Rb Bose-Einstein condensate (BEC) under a quadratic\nZeeman effect. Due to the large ratio of spinindependent to spin-dependent\ninteractions of 87Rb atoms, the effect of noncondensed atoms on the condensate\nis much more significant than that in scalar BECs. We find that the condensate\nand spontaneous magnetization emerge at different temperatures when the ground\nstate is in the brokenaxisymmetry phase. In this phase, a magnetized condensate\ninduces spin coherence of noncondensed atoms in different magnetic sublevels,\nresulting in temperature-dependent magnetization of the noncondensate. We also\nexamine the effect of quantum fluctuations on the order parameter at absolute\nzero, and find that the ground-state phase diagram is significantly altered by\nquantum depletion."
    },
    {
        "anchor": "Heating and Cooling in Adiabatic Mixing process: We study the effect of interaction on the temperature change in the process\nof adiabatic mixing two components of fermi gases by the real-space\nBogoliubov-de Gennes (BdG) method. We find that in the process of adiabatic\nmixing, the competition of the adiabatic expansion and the attractive\ninteraction make it possible to cool or heal the system depending on strength\nof interactions and the initial temperature. The change of temperature in a\nbulk system and a trapped system have been investigated respectively.",
        "positive": "Fermi polarons at finite temperature: Spectral function and\n  rf-spectroscopy: We present a systematic study of a mobile impurity immersed in a\nthree-dimensional Fermi sea of fermions at finite temperature, by using the\nstandard non-self-consistent many-body $T$-matrix theory that is equivalent to\na finite-temperature variational approach with the inclusion of\none-particle-hole excitation. The impurity spectral function is determined in\nthe real-frequency domain, avoiding any potential errors due to the numerical\nanalytic continuation in previous $T$-matrix calculations and the small\nspectral broadening parameter used in variational calculations. In the\nweak-coupling limit, we find that the quasiparticle decay rate of both\nattractive and repulsive polarons does not increase significantly with\nincreasing temperature, and therefore Fermi polarons may remain well-defined\nfar above Fermi degeneracy. In contrast, near the unitary limit with strong\ncoupling, the decay rate of Fermi polarons rapidly increase and the\nquasiparticle picture breaks down close to the Fermi temperature. We analyze in\ndetail the recent ejection and injection radio-frequency (rf) spectroscopy\nmeasurements, performed at Massachusetts Institute of Technology (MIT) and at\nEuropean Laboratory for Non-Linear Spectroscopy (LENS), respectively. We show\nthat the momentum average of the spectral function, which is necessary to\naccount for the observed rf-spectroscopy, has a sizable contribution to the\nwidth of the quasiparticle peak in spectroscopy. As a result, the measured\ndecay rate of Fermi polarons could be significantly larger than the calculated\nquasiparticle decay rate at zero momentum. By take this crucial contribution\ninto account, we find that there is a reasonable agreement between theory and\nexperiment for the lifetime of Fermi polarons in the strong-coupling regime, as\nlong as they remain well-defined."
    },
    {
        "anchor": "Spin Josephson effects of spin-orbit-coupled Bose-Einstein condensates\n  in a non-Hermitian double well: In this paper, we investigate the spin and tunneling dynamics of a\nspin-orbit-coupled noninteracting Bose-Einstein condensate in a periodically\ndriven non-Hermitian double-well potential. Under high-frequency driving, we\nobtain the effective time-averaged Hamiltonian by using the standard\ntime-averaging method, and analytically calculate the Floquet quasienergies,\nrevealing that the parity-time (PT)-breaking phase transition appears even for\narbitrarily small non-Hermitian parameters when the spin-orbit coupling\nstrength takes half-integer value, irrespective of the values of other\nparameters used. When the system is PT-symmetric with balanced gain and loss,\nwe find numerically and analytically that in the broken PT-symmetric regions,\nthere will exist the net spin current together with a vanishing atomic current,\nif we drop the contribution of the exponential growth of the norm to the\ncurrent behaviors. When the system is non-PT-symmetric, though the\nquasienergies are partial complex, a stable net spin current can be generated\nby controlling the periodic driving field, which is accompanied by a spatial\nlocalization of the condensate in the well with gain. The results deepen the\nunderstanding of non-Hermitian physics and could be useful for engineering a\nvariety of devices for spintronics.",
        "positive": "Universality of isolated $N$-body resonances at large scattering length: Non Efimovian $N$-body resonances are investigated in the regime of a large\ntwo-body s wave scattering length. In view of a universal description of\nlow-energy bound and quasi-bound states, a contact model is introduced. The\nmodeling requires two parameters in addition to the scattering length. Using a\nmodified scalar product, the contact model provides a normalization of bound\nstates, possibly not square-integrable, that coincides with that of the\ncorresponding finite range model."
    },
    {
        "anchor": "Drag force on a moving impurity in a spin-orbit coupled Bose-Einstein\n  condensate: We investigate the drag force on a moving impurity in a spin-orbit coupled\nBose-Einstein condensate. We prove rigorously that the superfluid critical\nvelocity is zero when the impurity moves in all but one directions, in contrast\nto the case of liquid helium and superconductor where it is finite in all\ndirections. We also find that when the impurity moves in all directions except\ntwo special ones, the drag force has nonzero transverse component at small\nvelocity. When the velocity becomes large and the states of the upper band are\nalso excited, the transverse force becomes very small due to opposite\ncontributions of the two bands. The characteristics of the superfluid critical\nvelocity and the transverse force are results of the order by disorder\nmechanism in spin-orbit coupled boson systems.",
        "positive": "Dynamically decoupled three-body interactions with applications to\n  interaction-based quantum metrology: We propose a stroboscopic method to dynamically decouple the effects of\ntwo-body atom-atom interactions for ultracold atoms, and realize a system\ndominated by elastic three-body interactions. Using this method, we show that\nit is possible to achieve the optimal scaling behavior predicted for\ninteraction-based quantum metrology with three-body interactions. Specifically,\nwe show that for ultracold atoms quenched in an optical lattice, we can measure\nthe three-body interaction strength with a precision proportional to ${\\bar\nn}^{-5/2}$ using homodyne quadrature interferometry, and ${\\bar n}^{-7/4}$\nusing conventional collapse-and-revival techniques, where ${\\bar n}$ is the\nmean number of atoms per lattice site. Both precision scalings surpass the\nnonlinear scaling of ${\\bar n}^{-3/2}$, the best so far achieved or proposed\nwith a physical system. Our method of achieving a decoupled three-body\ninteracting system may also have applications in the creation of exotic\nthree-body states and phases."
    },
    {
        "anchor": "Critical spin transport in Bose gases: We consider spin transport in a two-component atomic Bose gas in three\ndimensions, at temperatures just above the critical temperature for\nBose-Einstein condensation. In these systems the spin conductivity is\ndetermined by spin drag, i.e., frictional drag between the two spin components\ndue to interactions. We find that in the critical region the temperature\ndependence of the spin conductivity deviates qualitatively from the Boltzmann\nresult and is fully determined by the critical exponents of the phase\ntransition. We discuss the size of the critical region where these results may\nbe observed experimentally.",
        "positive": "Particle dynamics and ergodicity-breaking in twisted-bilayer optical\n  lattices: Recent experiments have realized a twisted bilayer-like optical potential for\nultra-cold atoms, which in contrast to solid-state set ups may allow for an\narbitrary ratio between the inter- and intra-layer couplings. For commensurate\nMoir\\'e twistings a large-enough inter-layer coupling results in particle\ntransport dominated by channel formation. For incommensurate twistings, the\ninterlayer coupling acts as an effective disorder strength. Whereas for weak\ncouplings the whole spectrum remains ergodic, at a critical value part of the\neigenspectrum transitions into multifractal states. A similar transition may be\nobserved as well as a function of an energy bias between the two layers. Our\nstudy reveals atoms in optical twisted-bilayer lattices as an interesting new\nplatform for the study of ergodicity breaking and multifractality."
    },
    {
        "anchor": "Tuning universality far from equilibrium: Possible universal dynamics of a many-body system far from thermal\nequilibrium are explored. A focus is set on meta-stable non-thermal states\nexhibiting critical properties such as self-similarity and independence of the\ndetails of how the respective state has been reached. It is proposed that\nuniversal dynamics far from equilibrium can be tuned to exhibit a dynamical\nphase transition where these critical properties change qualitatively. This is\ndemonstrated for the case of a superfluid two-component Bose gas exhibiting\ndifferent types of long-lived but non-thermal critical order. Scaling exponents\ncontrolled by the ratio of experimentally tuneable coupling parameters offer\nthemselves as natural smoking guns. The results shed light on the wealth of\nuniversal phenomena expected to exist in the far-from-equilibrium realm.",
        "positive": "Methods for detecting charge fractionalization and winding numbers in an\n  interacting fermionic ladder: We consider a spin-1/2 fermionic ladder with spin-orbit coupling and a\nperpendicular magnetic field, which shares important similarities with\ntopological superconducting wires. We fully characterize the symmetry-protected\ntopological phase of this ladder through the identification of fractionalized\nedge modes and non-trivial spin winding numbers. We propose an experimental\nscheme to engineer such a ladder system with cold atoms in optical lattices,\nand we present two protocols that can be used to extract the topological\nsignatures from density and momentum-distribution measurements. We then\nconsider the presence of interactions and discuss the effects of a contact\non-site repulsion on the topological phase. We find that such interactions\ncould enhance the extension of the topological phase in certain parameters\nregimes."
    },
    {
        "anchor": "Thermodynamics and static response of anomalous 1D fermions via quantum\n  Monte Carlo in the worldline representation: A system of three-species fermions in one spatial dimension (1D) with a\ncontact three-body interaction is known to display a scale anomaly. This\nanomaly is identical to that of a two-dimensional (2D) system of two-species\nfermions. The exact relation between those two systems, however, is limited to\nthe two-particle sector of the 2D case and the three-particle sector of the 1D\ncase. Here, we implement a non-perturbative Monte Carlo approach, based on the\nworldline representation, to calculate the thermodynamics and static response\nof three-species fermions in 1D, thus tackling the many-body sector of the\nproblem. We determine the energy, density, and pressure equations of state, and\nthe compressibility and magnetic susceptibility for a wide range of\ntemperatures and coupling strengths. We compare our results with the\nthird-order virial expansion.",
        "positive": "Critical Velocity and Dissipation of an ultracold Bose-Fermi Counterflow: We study the dynamics of counterflowing bosonic and fermionic lithium atoms.\nFirst, by tuning the interaction strength we measure the critical velocity vc\nof the system in the BEC-BCS crossover in the low temperature regime and we\ncompare it to the recent prediction of Castin et al., Comptes Rendus Physique,\n16, 241 (2015). Second, raising the temperature of the mixture slightly above\nthe superfluid transitions reveals an unexpected phase-locking of the\noscillations of the clouds. We interpret this observation as resulting from a\nZeno-like effect induced by dissipation."
    },
    {
        "anchor": "Pairing properties of cold fermions in the honeycomb lattice: The pairing properties of ultracold fermions, with an attractive interaction,\nloaded in a honeycomb (graphene-like) optical lattice are studied in a\nmean-field approach. We emphasize, in the presence of a harmonic trap, the\nunambiguous signatures of the linear dispersion relation of the band structure\naround half-filling (i.e. the massless Dirac fermions) in the local order\nparameter, in particular in the situations of either imbalance hoping\nparameters or imbalance populations. It can also be observed in the system\nresponse to external perturbation, for instance by measuring the pair\ndestruction rate when modulating the optical lattice depth. Going beyond the\nmean-field level, we estimate the critical temperature for the \"condensation\"\nof the preformed pairs.",
        "positive": "An analytical approach to atomic multichannel collisions in tight\n  harmonic waveguides: We perform an analytical investigation in the framework of generalized $K$\nmatrix theory of the scattering problem in tight isotropic and harmonic\nwaveguides allowing for several open scattering channels. The scattering\nbehavior is explored for identical bosons and fermions, as well as for\ndistinguishable particles, the main aspect being the confinement-induced\nresonances (CIR) which are attributed to different partial waves. In particular\nwe present the unitarity bounds which emerge when considering a quasi one\ndimensional system. Unitarity bounds are also given for the transition\ncoefficients, which show the limitations for efficient transversal\n(de-)excitations by means of CIRs. We analyze the CIR for $d$-waves and find\nthe intriguing phenomenon of a strong transmission suppression in the presence\nof more than one open channel, which represents an interesting regime to be\napplied in the corresponding many-particle systems. The corresponding channel\nthreshold singularities are studied and it is shown that these are solely\ndetermined by the symmetry class of the partial wave."
    },
    {
        "anchor": "Pathway toward the formation of supermixed states in ultracold boson\n  mixtures loaded in ring lattices: We investigate the mechanism of formation of supermixed soliton-like states\nin bosonic binary mixtures loaded in ring lattices. We evidence the presence of\na common pathway which, irrespective of the number of lattice sites and upon\nvariation of the interspecies attraction, leads the system from a mixed and\ndelocalized phase to a supermixed and localized one, passing through an\nintermediate phase where the supermixed soliton progressively emerges. The\ndegrees of mixing, localization and quantum correlation of the two condensed\nspecies, quantified by means of suitable indicators commonly used in\nStatistical Thermodynamics and Quantum Information Theory, allow one to\nreconstruct a bi-dimensional mixing-supermixing phase diagram featuring two\ncharacteristic critical lines. Our analysis is developed both within a\nsemiclassical approach capable of capturing the essential features of the\ntwo-step mixing-demixing transition and with a fully-quantum approach.",
        "positive": "Splitting and oscillation of Majorana zero modes in the p-wave BCS-BEC\n  evolution with plural vortices: We investigate how the vortex-vortex separation changes Majorana zero modes\nin the vicinity of the BCS-BEC (Bose-Einstein condensation) topological phase\ntransition of p-wave resonant Fermi gases. By analytically and numerically\nsolving the Bogoliubov-de Gennes equation for spinless p-wave superfluids with\nplural vortices, it is demonstrated that the quasiparticle tunneling between\nneighboring vortices gives rise to the quantum oscillation of the low-lying\nspectra on the scale of the Fermi wavelength in addition to the exponential\nsplitting. This rapid oscillation, which appears in the weak coupling regime as\na consequence of quantum oscillations of quasiparticle wave functions,\ndisappears in the vicinity of the BCS-BEC topological phase transition. This is\nunderstandable from that the wave function of the Majorana zero modes is\ndescribed by the modified Bessel function in the strong coupling regime and\nthus it becomes spread over the vortex core region. Due to the exponential\ndivergence of the modified Bessel function, the concrete realization of the\nMajorana zero modes near the topological phase transition requires the\nneighboring vortices to be separated beyond the length scale defined by the\ncoherence length and the dimensionless coupling constant. All these behaviors\nare also confirmed by carrying out the full numerical diagonalization of the\nnon-local Bogoliubov-de Gennes equation in a two dimensional geometry.\nFurthermore, this argument is expanded into the case of three-vortex systems,\nwhere a pair of core-bound and edge-bound Majorana states survive at zero\nenergy state regardless of the vortex separation."
    },
    {
        "anchor": "Tools for designing atom interferometers in a microgravity environment: We present a variational model suitable for rapid preliminary design of atom\ninterferometers in a microgravity environment. The model approximates the\nsolution of the 3D rotating--frame Gross--Pitaevskii equation (GPE) as the sum\nof Nc Gaussian clouds. Each Gaussian cloud is assumed to have time--dependent\ncenter positions, widths, and linear and quadratic phase parameters. We applied\nthe Lagrangian Variational Method (LVM) with this trial wave function to derive\nequations of motion for these parameters that can be adapted to any external\npotential. We also present a 1D version of this variational model. As an\nexample we apply the model to a 1D atom interferometry scheme for measuring\nNewton's gravitational constant, G, in a microgravity environment. We show how\nthe LVM model can (1) constrain the experimental parameter space size, (2) show\nhow the value of G can be obtained from the experimental conditions and\ninterference pattern characteristics, and (3) show how to improve the\nsensitivity of the measurement and construct a preliminary error budget.",
        "positive": "Supersolid-like square- and triangular-lattice crystallization of\n  dipolar droplets in a box trap: Using a beyond-mean-field model including a Lee-Huang-Yang-type interaction,\nwe demonstrate a supersolid-like spatially-periodic square- and\ntriangular-lattice crystallization of droplets in a polarized dipolar\ncondensate confined by an appropriate three-dimensional (3D) box trap. In this\npaper we consider a rectangular box (cuboid) trap, a square box (cuboid with\ntwo equal sides) trap, a cylindrical box trap and a hexagonal box (hexagonal\nprism) trap. The droplet lattice is always formed in the $x$-$y$ plane\nperpendicular to the polarization $z$ direction of dipolar atoms. In contrast\nto a harmonic trap, the box traps allow the formation of a large clean\nsupersolid-like spatially-periodic crystallization in free space without any\ndistortion. Moreover, a droplet lattice can be formed in a 3D box trap with a\nsignificantly reduced number of atoms than in a harmonic trap, which could\nfacilitate the experimental observation of droplet lattice in a box trap. With\npresent know-how such a supersolid-like crystallization of dipolar droplets in\na 3D box trap can be realized in a laboratory thus allowing the study of a\nlarge periodic lattice of dipolar droplets in free space bounded by rigid\nwalls."
    },
    {
        "anchor": "Emergent inflation of the Efimov spectrum under three-body spin-exchange\n  interactions: One of the most fascinating predictions of few-body quantum physics is the\nEfimov effect, a universal accumulation of an infinite geometric series of\nthree-body bound states at a two-body scattering resonance. Ever since the\nfirst experimental observation of such an Efimov state, the precise\ncharacterization of their physical properties has continued to challenge\nfew-body theory. This is demonstrated most strongly by the lithium few-body\npuzzle, a remarkable theoretical discrepancy with the observed Efimov spectrum\nin $^7 \\text{Li}$. Here, we resolve this long-standing puzzle, demonstrating\nthat the discrepancy arises out of the presence of strong non-universal\nthree-body spin-exchange interactions. This conclusion is obtained from a\nthorough numerical solution of the quantum mechanical three-body problem,\nincluding precise interatomic interactions and all spin degrees of freedom for\nthree alkali-metal atoms. Our results show excellent agreement with the\nexperimental data regarding both the Efimov spectrum and the absolute rate\nconstants of three-body recombination, and in addition reveal a general product\npropensity for such triatomic reactions in the Paschen-Back regime, stemming\nfrom Wigner's spin conservation rule.",
        "positive": "A double species $^{23}$Na and $^{87}$Rb Bose-Einstein condensate with\n  tunable miscibility via an interspecies Feshbach resonance: We have realized a dual-species Bose-Einstein condensate (BEC) of $^{23}$Na\nand $^{87}$Rb atoms and observed their immiscibility. Because of the favorable\nbackground intra- and inter-species scattering lengths, stable condensates can\nbe obtained via efficient evaporative cooling and sympathetic cooling without\nthe need for fine tuning of the interactions. Our system thus provides a clean\nplatform for studying inter-species interactions driven effects in superfluid\nmixtures. With a Feshbach resonance, we have successfully created double BECs\nwith largely tunable inter-species interactions and studied the\nmiscible-immiscible phase transition."
    },
    {
        "anchor": "Collective dipole oscillations of a spin-orbit coupled Fermi gas: The collective dipole mode is induced and measured in a spin-orbit (SO)\ncoupled degenerate Fermi gas of $^{173}$Yb atoms. Using a differential optical\nStark shift, we split the degeneracy of three hyperfine states in the ground\nmanifold, and independently couple consecutive spin states with the equal Raman\ntransitions. A relatively long-lived spin-orbit-coupled Fermi gas, readily\nbeing realized with a narrow optical transition, allows to explore a\nsingle-minimum dispersion where three minima of spin-1 system merge into and to\nmonitor collective dipole modes of fermions in the strong coupling regime. The\nmeasured oscillation frequency of the dipole mode is compared with the\nsemi-classical calculation in the single-particle regime. Our work should pave\nthe way towards the characterization of spin-orbit-coupled fermions with large\nspin $s>\\frac{1}{2}$ in the strong coupling regime.",
        "positive": "Quenched Kitaev Chain: Analogous model of Gravitational Collapse: We investigate generalized thermalization in an isolated free Fermionic chain\nevolving from an out of equilibrium initial state through a sudden quench. We\nconsider the quench where a Fermionic chain is broken into two disjoint chains.\nWe focus on the evolution of the local observables namely, occupation number,\nnearest neighbor hopping, information sharing and out-of-time-order\ncorrelations after the quench and study the relaxation of the observable,\nleading to generalized Gibbs ensemble for the system in the thermodynamic limit\nthough it has been argued that non-interacting or free Fermionic models in\ngeneral do not relax to GGE. We obtain the light cone formed by the evolution\nof the observables along the Fermionic lattice chain due to the sudden quench\nwhich abides by the Lieb-Robinson bound in quantum systems. We also\nanalytically study a simpler model which captures the essential features of the\nsystem. Our analysis strongly suggests that the internal interactions within\nthe system do not remain of much importance once the quench is sufficiently\nstrong."
    },
    {
        "anchor": "Steerable optical tweezers for ultracold atom studies: We report on the implementation of an optical tweezer system for controlled\ntransport of ultracold atoms along a narrow, static confinement channel. The\ntweezer system is based on high-efficiency acousto-optical deflectors and\noffers two-dimensional control over beam position. This opens up the\npossibility for tracking the transport channel when shuttling atomic clouds\nalong the guide, forestalling atom spilling. Multiple clouds can be tracked\nindependently by time-shared tweezer beams addressing individual sites in the\nchannel. The deflectors are controlled using a multichannel direct digital\nsynthesizer, which receives instructions on a sub-microsecond time scale from a\nfield-programmable gate array. Using the tweezer system, we demonstrate\nsequential binary splitting of an ultracold $\\rm^{87}Rb$ cloud into $2^5$\nclouds.",
        "positive": "Stroboscopic versus non-stroboscopic dynamics in the Floquet realization\n  of the Harper-Hofstadter Hamiltonian: We study the stroboscopic and non-stroboscopic dynamics in the Floquet\nrealization of the Harper-Hofstadter Hamiltonian. We show that the former\nproduces the evolution expected in the high-frequency limit only for\nobservables which commute with the operator to which the driving protocol\ncouples. On the contrary, non-stroboscopic dynamics is capable of capturing the\nevolution governed by the Floquet Hamiltonian of any observable associated with\nthe effective high-frequency model. We provide exact numerical simulations for\nthe dynamics of the density operator following a quantum cyclotron orbit on a\n$2\\times 2$ plaquette, as well as the chiral current operator flowing along the\nlegs of a $2\\times 20$ ladder. The exact evolution is compared with its\nstroboscopic and non-stroboscopic counterparts, including finite-frequency\ncorrections."
    },
    {
        "anchor": "Effective three-body interactions for bosons in a double-well\n  confinement: When describing the low-energy physics of bosons in a double-well potential\nwith a high barrier between the wells and sufficiently weak atom-atom\ninteractions, one can to a good approximation ignore the high energy states and\nthereby obtain an effective two-mode model. Here, we show that the regime in\nwhich the two-mode model is valid can be extended by adding an on-site\nthree-body interaction term and a three-body interaction-induced tunneling term\nto the two-mode Hamiltonian. These terms effectively account for virtual\ntransitions to the higher energy states. We determine appropriate strengths of\nthe three-body terms by an optimization of the minimal value of the wave\nfunction overlap within a certain time window. Considering different initial\nstates with three or four atoms, we find that the resulting model accurately\ncaptures the dynamics of the system for parameters where the two-mode model\nwithout the three-body terms is poor. We also investigate the dependence of the\nstrengths of the three-body terms on the barrier height and the atom-atom\ninteraction strength. The optimal three-body interaction strengths depend on\nthe initial state of the system.",
        "positive": "Entropy production within a pulsed Bose-Einstein condensate: We suggest to subject anharmonically trapped Bose-Einstein condensates to\nsinusoidal forcing with a smooth, slowly changing envelope, and to measure the\ncoherence of the system after such pulses. In a series of measurements with\nsuccessively increased maximum forcing strength one then expects an adiabatic\nreturn of the condensate to its initial state as long as the pulses remain\nsufficiently weak. In contrast, once the maximum driving amplitude exceeds a\ncertain critical value there should be a drastic loss of coherence, reflecting\nsignificant heating induced by the pulse. This predicted experimental signature\nis traced to the loss of an effective adiabatic invariant, and to the ensuing\nbreakdown of adiabatic motion of the system's Floquet state when the many-body\ndynamics become chaotic. Our scenario is illustrated with the help of a\ntwo-site model of a forced bosonic Josephson junction, but should also hold for\nother, experimentally accessible configurations."
    },
    {
        "anchor": "Structural Superfluid-Mott Insulator Transition for a Bose Gas in\n  Multi-Rods: We report on a novel structural Superfluid-Mott Insulator (SF-MI) quantum\nphase transition for an interacting one-dimensional Bose gas within permeable\nmulti-rod lattices, where the rod lengths are varied from zero to the lattice\nperiod length. We use the ab-initio diffusion Monte Carlo method to calculate\nthe static structure factor, the insulation gap, and the Luttinger parameter,\nwhich we use to determine if the gas is a superfluid or a Mott insulator. For\nthe Bose gas within a square Kronig-Penney (KP) potential, where barrier and\nwell widths are equal, the SF-MI coexistence curve shows the same qualitative\nand quantitative behavior as that of a typical optical lattice with equal\nperiodicity but slightly larger height. When we vary the width of the barriers\nfrom zero to the length of the potential period, keeping the height of the KP\nbarriers, we observe a new way to induce the SF-MI phase transition. Our\nresults are of significant interest, given the recent progress on the\nrealization of optical lattices with a subwavelength structure that would\nfacilitate their experimental observation.",
        "positive": "Momentum distribution of a dilute unitary Bose gas with three-body\n  losses: Using Boltzmann's equation, we study the effect of three-body losses on the\nmomentum distribution of a homogeneous unitary Bose gas in the dilute limit\nwhere quantum correlations are negligible. We calculate the momentum\ndistribution of the gas and show that inelastic collisions are quantitatively\nas important as a second order virial correction."
    },
    {
        "anchor": "Doubly Modulated Optical Lattice Clock Interference and Topology: The quantum system under periodical modulation is the simplest path to\nunderstand the quantum non-equilibrium system, because it can be well described\nby the effective static Floquet Hamiltonian. Under the stroboscopic\nmeasurement, the initial phase is usually irrelevant. However, if two\nuncorrelated parameters are modulated, their relative phase can not be gauged\nout, so that the physics can be dramatically changed. Here, we simultaneously\nmodulate the frequency of the lattice laser and the Rabi frequency in an\noptical lattice clock (OLC) system. Thanks to ultra-high precision and\nultra-stability of OLC, the relative phase could be fine-tuned. As a smoking\ngun, we observed the interference between two Floquet channels. Finally, by\nexperimentally detecting the eigen-energies, we demonstrate the relation\nbetween effective Floquet Hamiltonian and 1-D topological insulator with high\nwinding number. Our experiment not only provides a direction for detecting the\nphase effect, but also paves a way in simulating quantum topological phase in\nOLC platform.",
        "positive": "Bose-Fermi mixtures of self-assembled filaments of fermionic polar\n  molecules: Fermionic polar molecules in deep 1D optical lattices may form self-assembled\nfilaments when the electric dipoles are oriented along the lattice axis. These\ncomposites are bosons or fermions depending on the number of molecules per\nchain, leading to a peculiar and complex Bose-Fermi mixture, which we discuss\nin detail for the simplest case of a three-well potential. We show that the\ninterplay between filament binding energy, transverse filament modes, and\ntrimer Fermi energy leads to a rich variety of possible scenarios ranging from\na degenerate Fermi gas of trimers to a binary mixture of two different types of\nbosonic dimers. We study the intriguing zero temperature and finite temperature\nphysics of these composites for the particular case of an ideal filament gas\nloaded in 1D sites, and discuss possible methods to probe these chain mixtures."
    },
    {
        "anchor": "Phase-separation of vector solitons in spin-orbit coupled spin-1\n  condensates: We study the phase-separation in three-component bright vector solitons in a\nquasi-one-dimensional spin-orbit-coupled hyper-fine spin $F=1$ ferromagnetic\nBose-Einstein condensate upon an increase of the strength of spin-orbit (SO)\ncoupling $p_x \\Sigma_z$ above a critical value, where $p_x$ is the linear\nmomentum and $\\Sigma_z$ is the $z$-component of the spin-1 matrix. The bright\nvector solitons are demonstrated to be mobile and dynamically stable. The\ncollision between two such vector solitons is found to be elastic at all\nvelocities with the conservation of density of each vector soliton. The two\ncolliding vector solitons repel at small separation and at very small colliding\nvelocity, they come close and bounce back with the same velocity without ever\nencountering each other. This repulsion produced by SO coupling is responsible\nfor the phase separation in a vector soliton for large strengths of SO\ncoupling. { The collision dynamics is found to be completely insensitive to the\nrelative phase of the colliding solitons.} However, in the absence of SO\ncoupling, at very small velocity, the two colliding vector solitons attract\neach other and form a vector soliton molecule and the collision dynamics is\nsensitive to the relative phase as in scalar solitons. The present\ninvestigation is carried out through a numerical solution and an analytic\nvariational approximation of the underlying mean-field Gross-Pitaevskii\nequation.",
        "positive": "Ferromagnetic phase in the polarized two-species bosonic Hubbard Model: We recently studied a doped two-dimensional bosonic Hubbard model with two\nhard-core species, with different masses, using quantum Monte Carlo simulations\n[Phys. Rev. B 88, 161101(R) (2013)]. Upon doping away from half-filling, we\nfind several distinct phases, including a phase-separated ferromagnet with Mott\nbehavior for the heavy species and both Mott insulating and superfluid\nbehaviors for the light species. Introducing polarization, an imbalance in the\npopulation between species, we find a fully phase-separated ferromagnet. This\nphase exists for a broad range of temperatures and polarizations. By using\nfinite size scaling of the susceptibility, we find a critical exponent which is\nconsistent with the two-dimensional Ising universality class. Significantly,\nsince the global entropy of this phase is higher than that of the ferromagnetic\nphase with single species, its experimental observation in cold atoms may be\nfeasible."
    },
    {
        "anchor": "Stirring trapped atoms into fractional quantum Hall puddles: We theoretically explore the generation of few-body analogs of fractional\nquantum Hall states. We consider an array of identical few-atom clusters\n(n=2,3,4), each cluster trapped at the node of an optical lattice. By\ntemporally varying the amplitude and phase of the trapping lasers, one can\nintroduce a rotating deformation at each site. We analyze protocols for\ncoherently transferring ground state clusters into highly correlated states,\nproducing theoretical fidelities in excess of 99%.",
        "positive": "Quantum Monte Carlo study of the role of p-wave interactions in\n  ultracold repulsive Fermi gases: Single-component ultracold atomic Fermi gases are usually described using\nnoninteracting many-fermion models. However, recent experiments reached a\nregime where $p$-wave interactions among identical fermionic atoms are\nimportant. In this paper, we employ variational and fixed-node diffusion Monte\nCarlo simulations to investigate the ground-state properties of\nsingle-component Fermi gases with short-range repulsive interactions. We\ndetermine the zero-temperature equation of state, and elucidate the roles\nplayed by the $p$-wave scattering volume and the $p$-wave effective range. A\ncomparison against recently derived second-order perturbative results shows\ngood agreement in a broad range of interaction strength. We also compute the\nquasiparticle effective mass, and we confirm the perturbative prediction of a\nlinear contribution in the $p$-wave scattering volume, while we find\nsignificant deviations from the beyond-mean-field perturbative result, already\nfor moderate interaction strengths. Finally, we determine ground-state energies\nfor two-component unpolarized Fermi gases with both interspecies and\nintraspecies hard-sphere interactions, finding remarkable agreement with a\nrecently derived fourth-order expansion that includes $p$-wave contributions."
    },
    {
        "anchor": "Exploring Vortex Dynamics in the Presence of Dissipation: Analytical and\n  Numerical Results: In this paper, we systematically examine the stability and dynamics of\nvortices under the effect of a phenomenological dissipation used as a\nsimplified model for the inclusion of the effect of finite temperatures in\natomic Bose-Einstein condensates. An advantage of this simplified model is that\nit enables an analytical prediction that can be compared directly (and\nfavorably) to numerical results. We then extend considerations to a case of\nconsiderable recent experimental interest, namely that of a vortex dipole and\nobserve good agreement between theory and numerical computations in both the\nstability properties (eigenvalues of the vortex dipole stationary states) and\nthe dynamical evolution of such configurations.",
        "positive": "Modeling the transport of interacting matter-waves in disorder by a\n  non-linear diffusion equation: We model the expansion of an interacting atomic Bose-Einstein condensate in a\ndisordered lattice with a nonlinear diffusion equation normally used for a\nvariety of classical systems. We find approximate solutions of the diffusion\nequation that well reproduce the experimental observations for both short and\nasymptotic expansion times. Our study establishes a connection between the\npeculiar shape of the expanding density profiles and the microscopic nonlinear\ndiffusion coefficients."
    },
    {
        "anchor": "Particle correlations and evidence for dark state condensation in a cold\n  dipolar exciton fluid: In this paper we show experimental evidence of a few correlation regimes of a\ncold dipolar exciton fluid, created optically in a semiconductor bilayer\nheterostructure. In the higher temperature regime, the average interaction\nenergy between the particles shows a surprising temperature dependence which is\nan evidence for correlations beyond the mean field model. At a lower\ntemperature, there is a sharp increase in the interaction energy of optically\nactive excitons, accompanied by a strong reduction in their apparent\npopulation. This is an evidence for a sharp macroscopic transition to a dark\nstate as was suggested theoretically.",
        "positive": "Hydrodynamic Expansion of a Strongly Interacting Fermi-Fermi Mixture: We report on the expansion of a Fermi-Fermi mixture of Li-6 and K-40 atoms\nunder conditions of strong interactions realized near the center of an\ninterspecies Feshbach resonance. We observe two different phenomena of\nhydrodynamic behavior. The first one is the well-known inversion of the aspect\nratio. The second one is a collective expansion, where both species stick\ntogether and despite of their different masses expand jointly. Our work\nconstitutes a first step to explore the intriguing many-body physics of this\nnovel system."
    },
    {
        "anchor": "Transport in p-wave interacting Fermi gases: The scattering properties of spin-polarized Fermi gases are dominated by\np-wave interactions. Besides their inherent angular dependence, these\ninteractions differ from their s-wave counterparts as they also require the\npresence of a finite effective range in order to understand the low-energy\nproperties of the system. In this article we examine how the shear viscosity\nand thermal conductivity of a three-dimensional spin-polarized Fermi gas in the\nnormal phase depend on the effective range and the scattering volume in both\nthe weakly and strongly interacting limits. We show that although the shear\nviscosity and thermal conductivity both explicitly depend on the effective\nrange near resonance, the Prandtl number which parametrizes the ratio of\nmomentum to thermal diffusivity does not have an explicit interaction\ndependence both at resonance and for weak interactions in the low-energy limit.\nIn contrast to s-wave systems, p-wave scattering exhibits an additional\nresonance at weak attraction from a quasi-bound state at positive energies,\nwhich leads to a pronounced dip in the shear viscosity at specific\ntemperatures.",
        "positive": "Scattering by an oscillating barrier: quantum, classical, and\n  semiclassical comparison: We present a detailed study of scattering by an amplitude-modulated potential\nbarrier using three distinct physical frameworks: quantum, classical, and\nsemiclassical. Classical physics gives bounds on the energy and momentum of the\nscattered particle, while also providing the foundation for semiclassical\ntheory. We use the semiclassical approach to selectively add quantum-mechanical\neffects such as interference and diffraction. We find good agreement between\nthe quantum and semiclassical momentum distributions. Our methods and results\ncan be used to understand quantum and classical aspects of transport mechanisms\ninvolving time-varying potentials, such as quantum pumping."
    },
    {
        "anchor": "Quantum field simulator for dynamics in curved spacetime: The observed large-scale structure in our Universe is seen as a result of\nquantum fluctuations amplified by spacetime evolution. This, and related\nproblems in cosmology, asks for an understanding of the quantum fields of the\nstandard model and dark matter in curved spacetime. Even the reduced problem of\na scalar quantum field in an explicitly time-dependent spacetime metric is a\ntheoretical challenge and thus a quantum field simulator can lead to new\ninsights. Here, we demonstrate such a quantum field simulator in a\ntwo-dimensional Bose-Einstein condensate with a configurable trap and\nadjustable interaction strength to implement this model system. We explicitly\nshow the realisation of spacetimes with positive and negative spatial curvature\nby wave packet propagation and confirm particle pair production in controlled\npower-law expansion of space. We find quantitative agreement with new\nanalytical predictions for different curvatures in time and space. This\nbenchmarks and thereby establishes a quantum field simulator of a new class. In\nthe future, straightforward upgrades offer the possibility to enter new, so far\nunexplored, regimes that give further insight into relativistic quantum field\ndynamics.",
        "positive": "Rapid generation of Mott insulators from arrays of noncondensed atoms: We theoretically analyze a scheme for a fast adiabatic transfer of cold atoms\nfrom the atomic limit of isolated traps to a Mott-insulator close to the\nsuperfluid phase. This gives access to the Bose-Hubbard physics without the\nneed of a prior Bose-Einstein condensate. The initial state can be prepared by\ncombining the deterministic assembly of atomic arrays with resolved Raman\nsideband cooling. In the subsequent transfer the trap depth is reduced\nsignificantly. We derive conditions for the adiabaticity of this process and\ncalculate optimal adiabatic ramp shapes. Using available experimental\nparameters, we estimate the impact of heating due to photon scattering and\ncompute the fidelity of the transfer scheme. Finally, we discuss the particle\nnumber scaling behavior of the method for preparing low-entropy states. Our\nfindings demonstrate the feasibility of the proposed scheme with\nstate-of-the-art technology."
    },
    {
        "anchor": "Single-Particle Momentum Distributions of Efimov States in Mixed-Species\n  Systems: We solve the three-body bound state problem in three dimensions for mass\nimbalanced systems of two identical bosons and a third particle in the\nuniversal limit where the interactions are assumed to be of zero-range. The\nsystem displays the Efimov effect and we use the momentum-space wave equation\nto derive formulas for the scaling factor of the Efimov spectrum for any mass\nratio assuming either that two or three of the two-body subsystems have a bound\nstate at zero energy. We consider the single-particle momentum distribution\nanalytically and numerically and analyse the tail of the momentum distribution\nto obtain the three-body contact parameter. Our finding demonstrate that the\nfunctional form of the three-body contact term depends on the mass ratio and we\nobtain an analytic expression for this behavior. To exemplify our results, we\nconsider mixtures of Lithium with either two Caesium or Rubium atoms which are\nsystems of current experimental interest.",
        "positive": "Experimental observation of magic-wavelength behavior in optical\n  lattice-trapped $^{87}$Rb: We demonstrate the cancellation of the differential ac Stark shift of the\nmicrowave hyperfine clock transition in trapped $^{87}$Rb atoms. Recent\nprogress in metrology exploits so-called \"magic wavelengths,\" whereby an atomic\nensemble can be trapped with laser light whose wavelength is chosen so that\nboth levels of an optical atomic transition experience identical ac Stark\nshifts. Similar magic-wavelength techniques are not possible for the microwave\nhyperfine transitions in the alkalis, due to their simple electronic structure.\nWe show, however, that ac Stark shift cancellation is indeed achievable for\ncertain values of wavelength, polarization, and magnetic field. The\ncancellation comes at the expense of a small magnetic-field sensitivity. The\ntechnique demonstrated here has implications for experiments involving the\nprecise control of optically-trapped neutral atoms."
    },
    {
        "anchor": "Mediated interactions between ions in quantum degenerate gases: We explore the interaction between two trapped ions mediated by a surrounding\nquantum degenerate Bose or Fermi gas. Using perturbation theory valid for weak\natom-ion interaction, we show analytically that the interaction mediated by a\nBose gas has a power-law behaviour for large distances whereas it has a Yukawa\nform for intermediate distances. For a Fermi gas, the mediated interaction is\ngiven by a power-law for large density and by a Ruderman-Kittel-Kasuya-Yosida\nform for low density. For strong atom-ion interactions, we use a diagrammatic\ntheory to demonstrate that the mediated interaction can be a significant\naddition to the bare Coulomb interaction between the ions, when an atom-ion\nbound state is close to threshold. Finally, we show that the induced\ninteraction leads to substantial and observable shifts in the ion phonon\nfrequencies.",
        "positive": "Transport controlled by Poincar\u00e9 orbit topology in a driven\n  inhomogeneous lattice gas: In periodic quantum systems which are both homogeneously tilted and driven,\nthe interplay between drive and Bloch oscillations controls transport dynamics.\nUsing a quantum gas in a modulated optical lattice, we show experimentally that\ninhomogeneity of the applied force leads to a rich new variety of dynamical\nbehaviors controlled by the drive phase, from self-parametrically-modulated\nBloch epicycles to adaptive driving of transport against a force gradient to\nmodulation-enhanced monopole modes. Matching experimental observations to\nfit-parameter-free numerical predictions of time-dependent band theory, we show\nthat these phenomena can be quantitatively understood as manifestations of an\nunderlying inhomogeneity-induced phase space structure, in which topological\nclassification of stroboscopic Poincar\\'e orbits controls the transport\ndynamics."
    },
    {
        "anchor": "Dynamics of noisy quantum systems in the Heisenberg picture: application\n  to the stability of fractional charge: Based on the Heisenberg-picture analog of the master equation, we develop a\nmethod for computing the exact time dependence of noise-averaged observables\nfor general noninteracting fermionic systems with noisy fluctuations. Upon\nnoise averaging, these fluctuations generate effective interactions, limiting\nanalytical approaches. While the short-time dynamics can be studied with\nLangevin-type numerical simulations, the long-time limit is not amenable to\nsuch simulations. Our results provide access to this long-time limit. As a\nsimple example, we examine the fate of the fractional charge in cold-atom\nemulations of polyacetylene after stochastic driving. We find that in a quantum\nquench to a fluctuating hopping Hamiltonian, the fractional charge remains\nrobust for hopping between different sublattices, while it becomes unstable in\nthe presence of noisy hopping on the same sublattice.",
        "positive": "Energy dependent $\\ell$-wave confinement-induced resonances: The universal aspects of two-body collisions in the presence of a harmonic\nconfinement are investigated for both bosons and fermions. The main focus of\nthis study are the confinement-induced resonances (CIR) which are attributed to\ndifferent angular momentum states $\\ell$ and we explicitly show that in\nalkaline collisions only four universal $\\ell$-wave CIRs emerge. Going beyond\nthe single mode regime the energy dependence of $\\ell$-wave CIRs is studied. In\nparticular we show that all the $\\ell$-wave CIRs may emerge even when the\nunderlying two-body potential cannot support any bound state. We observe that\nthe intricate dependence on the energy yields resonant features where the\ncolliding system within the confining potential experiences an effective\nfree-space scattering. Our analysis is done within the framework of the\ngeneralized $K$-matrix theory and the relevant analytical calculations are in\nvery good agreement with the corresponding ab initio numerical scattering\nsimulations."
    },
    {
        "anchor": "Percolation analysis of a disordered spinor Bose gas: We study the effects of an on-site disorder potential in a gas of spinor\n(spin-1) ultracold atoms loaded in an optical lattice corresponding to both\nferromagnetic and antiferromagnetic spin dependent interactions. Starting with\na disordered spinor Bose-Hubbard model (SBHM) on a two dimensional square\nlattice, we observe the appearance of a Bose glass phase using the fraction of\nthe lattice sites having finite superfluid order parameter and non integer\nlocal densities as an indicator. A precise distinction between three different\ntypes of phases namely, superfluid (SF), Mott insulator (MI) and Bose glass\n(BG) is done via a percolation analysis thereby demonstrating that a reliable\nenumeration of phases is possible at particular values of the parameters of the\nSBHM. Finally we present the phase diagram based on the above information for\nboth antiferromagnetic and ferromagnetic interactions.",
        "positive": "From Kinetic Instability to Bose-Einstein Condensation and Magnon\n  Supercurrents: Evolution of an overpopulated gas of magnons to a Bose-Einstein condensate\nand excitation of a magnon supercurrent, propelled by a phase gradient in the\ncondensate wave function, can be observed at room-temperature by means of the\nBrillouin light scattering spectroscopy in an yttrium iron garnet material. We\nstudy these phenomena in a wide range of external magnetic fields in order to\nunderstand their properties when externally pumped magnons are transferred\ntowards the condensed state via two distinct channels: A multistage\nKolmogorov-Zakharov cascade of the weak-wave turbulence or a one-step\nkinetic-instability process. Our main result is that opening the kinetic\ninstability channel leads to the formation of a much denser magnon condensate\nand to a stronger magnon supercurrent compared to the cascade mechanism alone."
    },
    {
        "anchor": "Creation and manipulation of Feshbach resonances with radio-frequency\n  radiation: We present a simple technique for studying collisions of ultracold atoms in\nthe presence of a magnetic field and radio-frequency radiation (rf). Resonant\ncontrol of scattering properties can be achieved by using rf to couple a\ncolliding pair of atoms to a bound state. We show, using the example of 6Li,\nthat in some ranges of rf frequency and magnetic field this can be done without\ngiving rise to losses. We also show that halo molecules of large spatial extent\nrequire much less rf power than deeply bound states. Another way to exert\nresonant control is with a set of rf-coupled bound states, linked to the\ncolliding pair through the molecular interactions that give rise to\nmagnetically tunable Feshbach resonances. This was recently demonstrated for\n87Rb [Kaufman et al., Phys. Rev. A 80:050701(R), 2009]. We examine the\nunderlying atomic and molecular physics which made this possible. Lastly, we\nconsider the control that may be exerted over atomic collisions by placing\natoms in superpositions of Zeeman states, and suggest that it could be useful\nwhere small changes in scattering length are required. We suggest other species\nfor which rf and magnetic field control could together provide a useful tuning\nmechanism.",
        "positive": "Exceptional Bound States and negative Entanglement Entropy: This work introduces a new class of robust states known as Exceptional\nBoundary (EB) states, which are distinct from the well-known topological and\nnon-Hermitian skin boundary states. EB states occur in the presence of\nexceptional points, which are non-Hermitian critical points where eigenstates\ncoalesce and fail to span the Hilbert space. This eigenspace defectiveness not\nonly limits the accessibility of state information, but also interplays with\nlong-range order to give rise to singular propagators only possible in\nnon-Hermitian settings. Their resultant EB eigenstates are characterized by\nrobust anomalously large or negative occupation probabilities, unlike ordinary\nFermi sea states whose probabilities lie between zero and one. EB states remain\nrobust after a variety of quantum quenches and give rise to enigmatic negative\nentanglement entropy contributions. Through suitable perturbations, the\ncoefficient of the logarithmic entanglement entropy scaling can be continuously\ntuned. EB states represent a new avenue for robustness arising from geometric\ndefectiveness, independent of topological protection or non-reciprocal pumping."
    },
    {
        "anchor": "Shell-shaped atomic gases: We review the quantum statistical properties of two-dimensional shell-shaped\ngases, produced by cooling and confining atomic ensembles in thin hollow\nshells. We consider both spherical and ellipsoidal shapes, discussing at zero\nand at finite temperature the phenomena of Bose-Einstein condensation and of\nsuperfluidity, the physics of vortices, and the crossover from the\nBardeen-Cooper-Schrieffer regime to a Bose-Einstein condensate. The novel\naspects associated to the curved geometry are elucidated in comparison with\nflat two-dimensional superfluids. We also describe the hydrodynamic excitations\nand their relation with the Berezinskii-Kosterlitz-Thouless transition for\ntwo-dimensional flat and curved superfluids. In the next years, shell-shaped\natomic gases will be the leading experimental platform for investigations of\nquantum many-body physics in curved spatial domains.",
        "positive": "Controlling phase separation of binary Bose-Einstein condensates via\n  mixed-spin-channel Feshbach resonance: We investigate controlled phase separation of a binary Bose-Einstein\ncondensate (BEC) in the proximity of mixed-spin-channel Feshbach resonance in\nthe |F = 1, mF = +1> and |F = 2,mF = -1> states of 87Rb at a magnetic field of\n9.10 G. Phase separation occurs on the lower magnetic-field side of the\nFeshbach resonance while the two components overlap on the higher\nmagnetic-field side. The Feshbach resonance curve of the scattering length is\nobtained from the shape of the atomic cloud by comparison with the numerical\nanalysis of coupled Gross-Pitaevskii equations."
    },
    {
        "anchor": "Relaxation of Fermionic Excitations in a Strongly Attractive Fermi Gas\n  in an Optical Lattice: We theoretically study the relaxation of high energy single particle\nexcitations into molecules in a system of attractive fermions in an optical\nlattice, both in the superfluid and the normal phase. In a system characterized\nby an interaction scale $U$ and a tunneling rate $t$, we show that the\nrelaxation rate scales as $\\sim Ct\\exp(-\\alpha U^2/t^2)$ in the large $U/t$\nlimit. We obtain explicit expressions for the exponent $\\alpha$, both in the\nlow temperature superfluid phase and the high temperature phase with pairing\nbut no coherence between the molecules. We find that the relaxation rate\ndecreases both with temperature and deviation of the fermion density from\nhalf-filling. We show that quasiparticle and phase degrees of freedom are\neffectively decoupled within experimental timescales allowing for observation\nof ordered states even at high total energy of the system.",
        "positive": "Spontaneous Crystallization And Filamentation Of Solitons In Dipolar\n  Condensates: Inter-site interactions play a crucial role in polar gases in optical\nlattices even in the absence of hopping. We show that due to these long-range\ninteractions a destabilized stack of quasi-one dimensional Bose-Einstein\ncondensates develops a correlated modulational instability in the\nnon-overlapping sites. Interestingly, this density pattern may evolve\nspontaneously into soliton filaments or a crystal of solitons that can be so\ncreated for the first time in ultra-cold gases. These self-assembled structures\nmay be observed under realistic conditions within current experimental\nfeasibilities."
    },
    {
        "anchor": "Molecular spectra in collective Dicke states: We study a model describing competition of interactions between $N$ two-level\nsystems (TLSs) against decoherence. We apply it to analyze dye molecules in an\noptical microcavity, where molecular vibrations provide a local source for\ndecoherence. Most interesting is the case when decoherence strongly affects\neach individual TLS, e.g. via broadening of emission lines as well as\nvibrational satellites, however its influence is strongly suppressed for large\n$N$ due to the interactions between TLSs. In this interaction dominated regime\nwe find unique signatures in the emission spectrum, including strong\n$\\mathcal{O}(\\sqrt{N})$ level shifts, as well as $1/N$ suppression of both the\ndecoherence width and of the vibrational satellites.",
        "positive": "Dynamical generation of dark solitons in spin-orbit-coupled\n  Bose-Einstein condensates: We numerically investigate the ground state, the Raman-driving dynamics and\nthe nonlinear excitations of a realized spin-orbit-coupled Bose-Einstein\ncondensate in a one-dimensional harmonic trap. Depending on the Raman coupling\nand the interatomic interactions, three ground-state phases are identified:\nstripe, plane wave and zero-momentum phases. A narrow parameter regime with\ncoexistence of stripe and zero-momentum or plane wave phases in real space is\nfound. Several sweep progresses across different phases by driving the Raman\ncoupling linearly in time is simulated and the non-equilibrium dynamics of the\nsystem in these sweeps are studied. We find kinds of nonlinear excitations,\nwith the particular dark solitons excited in the sweep from the stripe phase to\nthe plane wave or zero-momentum phase within the trap. Moreover, the number and\nthe stability of the dark solitons can be controlled in the driving, which\nprovide a direct and easy way to generate dark solitons and study their\ndynamics and interaction properties."
    },
    {
        "anchor": "Stabilizing the false vacuum: Mott skyrmions: Topological excitations keep fascinating physicists since many decades. While\nindividual vortices and solitons emerge and have been observed in many areas of\nphysics, their most intriguing higher dimensional topological relatives,\nskyrmions (smooth, topologically stable textures) and magnetic monopoles --\nemerging almost necessarily in any grand unified theory and responsible for\ncharge quantization -- remained mostly elusive. Here we propose that loading a\nthree-component nematic superfluid such as $^{23}$Na into a deep optical\nlattice and thereby creating an insulating core, one can create topologically\nstable skyrmion textures and investigate their properties in detail. We show\nfurthermore that the spectrum of the excitations of the superfluid and their\nquantum numbers change dramatically in the presence of the skyrmion, and they\nreflect the presence of a trapped monopole, as imposed by the skyrmion's\ntopology.",
        "positive": "Energy and condensate dynamics of a Bose-Einstein condensate excited by\n  a moving red laser potential inside a power law trap cutoff by box potential\n  hard walls: We explore the energy dynamics of a two dimensional (2D) trapped\nBose-Einstein condensate (BEC) excited by a moving red-detuned laser potential\n(RDLP). The trap is a combination of a power-law (PL) potential cutoff by a\nhard-wall box potential (HWBP). It is found that by a restricted measurment of\nthe energy within the boundaries of the HWBP, the energy demonstrates\noscillations indicative of solitons. It is then demonstrated, that the geometry\nof the PL potential influences the lifetime of these oscillations, i.e., the\nlifetime of the ensuing solitons inside the HWBP. We argue that the energy\ndynamics in this setup are a good tool for measuring their lifetime. It is also\nfound, that the condensate density dynamics display oscillatory patterns of a\nmagnitude and order controlled by the velocity of the RDLP. A connection to\noscillations in the chemical potential dynamics is also discussed. Essentially,\nwe suggest future experiments for this kind of setup, which would measure the\nphonon energy dynamics to trace the lifetime of solitons."
    },
    {
        "anchor": "Manipulation of p-wave scattering of cold atoms in low dimensions using\n  the magnetic field vector: It is well-known that the magnetic Feshbach resonances of cold atoms are\nsensitive to the magnitude of the external magnetic field. Much less attention\nhas been paid to the direction of such a field. In this work we calculate the\nscattering properties of spin polarized fermionic atoms in reduced dimensions,\nnear a p-wave Feshbach resonance. Because of spatial anisotropy of the p-wave\ninteraction, the scattering has nontrivial dependence on both the magnitude and\nthe direction of the magnetic field. In addition, we identify an inelastic\nscattering process which is impossible in the isotropic-interaction model; the\nrate of this process depends considerably on the direction of the magnetic\nfield. Significantly, an EPR entangled pair of identical fermions may be\nproduced during this inelastic collision. This work opens a new method to\nmanipulate resonant cold atomic interactions.",
        "positive": "The emergence of atomic semifluxons in optical Josephson junctions: We propose to create pairs of semifluxons starting from a flat-phase state in\nlong, optical 0-pi-0 Josephson junctions formed with internal electronic states\nof atomic Bose-Einstein condensates. In this optical system, we can dynamically\ntune the length of the pi-junction, the detuning of the optical transition, or\nthe strength of the laser-coupling, to induce transitions from the flat-phase\nstate to such a semifluxon-pair state. Similarly as in superconducting 0-pi-0\njunctions, there are two, energetically degenerate semifluxon-pair states. A\nlinear mean-field model with two internal electronic states explains this\ndegeneracy and shows the distinct static field configuration in a phase-diagram\nof the junction parameters. This optical system offers the possibility to\ndynamically create a coherent superposition of the distinct semifluxon-pair\nstates and observe macroscopic quantum oscillation."
    },
    {
        "anchor": "Compressing the atomic cloud in a matter-wave stripe soliton: We consider an attractive quasi-one dimensional spin-orbit coupled\nBose-Einstein condensate (SOC BEC) confined in a periodic potential produced by\nthe combination of linear and nonlinear optical lattices, and study the effects\nof squeezing a stripe soliton by varying the inter-atomic interaction in the\nnonlinear lattice. It is observed that the nodes on the soliton arising\nentirely due to the effect of spin-orbit coupling tend to disappear as we\nincrease the squeezing effect to finally get a stable fundamental soliton. This\nleads us to conclude that external pressure can reduce the effect of spin-orbit\ncoupling in the SOC BEC and even convert the system to a traditional BEC\nwithout spin-orbit coupling. We make use of an information theoretic measure to\nvisualize how does the atomic density distribution in the condensate respond to\ncontinual reduction in the spin-orbit coupling effect.",
        "positive": "Inflationary preheating dynamics with ultracold atoms: We discuss the amplification of loop corrections in quantum many-body systems\nthrough dynamical instabilities. As an example, we investigate both\nanalytically and numerically a two-component ultracold atom system in one\nspatial dimension. The model features a tachyonic instability, which\nincorporates characteristic aspects of the mechanisms for particle production\nin early-universe inflaton models. We establish a direct correspondence between\nmeasureable macroscopic growth rates for occupation numbers of the ultracold\nBose gas and the underlying microscopic processes in terms of Feynman loop\ndiagrams. We analyze several existing ultracold atom setups featuring dynamical\ninstabilities and propose optimized protocols for their experimental\nrealization. We demonstrate that relevant dynamical processes can be enhanced\nusing a seeding procedure for unstable modes and clarify the role of initial\nquantum fluctuations and the generation of a non-linear secondary stage for the\namplification of modes."
    },
    {
        "anchor": "Motion of a distinguishable impurity in the Bose gas: Arrested expansion\n  without a lattice and impurity snaking: We consider the real time dynamics of an initially localized distinguishable\nimpurity injected into the ground state of the Lieb-Liniger model. Focusing on\nthe case where integrability is preserved, we numerically compute the time\nevolution of the impurity density operator in regimes far from analytically\ntractable limits. We find that the injected impurity undergoes a stuttering\nmotion as it moves and expands. For an initially stationary impurity, the\ninteraction-driven formation of a quasibound state with a hole in the\nbackground gas leads to arrested expansion -- a period of quasistationary\nbehavior. When the impurity is injected with a finite center of mass momentum,\nthe impurity moves through the background gas in a snaking manner, arising from\na quantum Newton's cradle-like scenario where momentum is exchanged\nback-and-forth between the impurity and the background gas.",
        "positive": "Quantum phases of a two-dimensional polarized degenerate Fermi gas in an\n  optical cavity: In this paper we analytically investigate the ground-state properties of a\ntwo-dimensional polarized degenerate Fermi gas in a high-finesse optical\ncavity, which is governed by a generalized Fermi-Dicke model with tunable\nparameters. By solving the photon-number dependent Bogoliubov-de-Gennes\nequation, we find rich quantum phases and phase diagrams, which depend\ncrucially on the fermion-photon coupling strength, the fermion-fermion\ninteraction strength, and the atomic resonant frequency (effective Zeeman\nfield). In particular, without the fermion-fermion interaction and with a weak\natomic resonant frequency, we find a mixed phase that the normal phase with two\nFermi surfaces and the superradiant phase coexist, and reveal a first-order\nphase transition from this normal phase to the superradiant phase. With the\nintermediate fermion-fermion interaction and fermion-photon coupling strengths,\nwe predict another mixed phase that the superfluid and superradiant phases\ncoexist. Finally, we address briefly how to detect these predicted quantum\nphases and phase diagrams in experiments."
    },
    {
        "anchor": "Bridging quantum many-body scar and quantum integrability in Ising\n  chains with transverse and longitudinal fields: Quantum many-body scar (QMBS) and quantum integrability(QI) have been\nrecognized as two distinct mechanisms for the breakdown of eigenstate\nthermalization hypothesis(ETH) in an isolated system. In this work, we reveal a\nsmooth route to connect these two ETH-breaking mechanisms in the Ising chain\nwith transverse and longitudinal fields. Specifically, starting from an initial\nIsing anti-ferromagnetic state, we find that the dynamical system undergoes a\nsmooth non-thermal crossover from QMBS to QI by changing the Ising\ncoupling($J$) and longitudinal field($h$) simultaneously while keeping their\nratio fixed, which corresponds to the Rydberg Hamiltonian with an arbitrary\nnearest-neighbor repulsion. Deviating from this ratio, we further identify a\ncontinuous thermalization trajectory in ($h,J$) plane that is exactly given by\nthe Ising transition line, signifying an intimate relation between\nthermalization and quantum critical point. Finally, we map out a completely\ndifferent dynamical phase diagram starting from an initial ferromagnetic state,\nwhere the thermalization is shown to be equally facilitated by the resonant\nspin-flip at special ratios of $J$ and $h$. By bridging QMBS and QI in Ising\nchains, our results demonstrate the breakdown of ETH in much broader physical\nsettings, which also suggest an alternative way to characterize quantum phase\ntransition via thermalization in non-equilibrium dynamics.",
        "positive": "Many-body approach to low-lying collective excitations in a BEC\n  approaching collapse: An approximate many-body theory incorporating two-body correlations has been\nemployed to calculate low-lying collective multipole frequencies in a\nBose-Einstein condensate containing $A$ bosons, for different values of the\ninteraction parameter $\\lambda=\\frac{Aa_{s}}{a_{ho}}$. Significant difference\nfrom the variational estimate of the Gross-Pitaevskii equation has been found\nnear the collapse region. This is attributed to two-body correlations and\nfinite range attraction of the realistic interatomic interaction. A large\ndeviation from the hydrodynamic model is also seen for the second monopole\nbreathing mode and the quadrupole mode for large positive $\\lambda$."
    },
    {
        "anchor": "Quantum and thermal effects in dark soliton formation and dynamics in a\n  1D Bose gas: We numerically study the imprinting and dynamics of dark solitons in a\nbosonic atomic gas in a tightly-confined one-dimensional harmonic trap both\nwith and without an optical lattice. Quantum and thermal fluctuations are\nsynthesized within the truncated Wigner approximation in the quasi-condensate\ndescription. We track the soliton coordinates and calculate position and\nvelocity uncertainties. We find that the phase fluctuations {\\em lower} the\nclassically predicted soliton speed and seed instabilities. Individual runs\nshow interactions of solitons with sound waves, splitting and disappearing\nsolitons.",
        "positive": "Tailored particle current in an optical lattice by a weak time-symmetric\n  harmonic potential: Quantum ratchets exhibit asymptotic currents when driven by a time-periodic\npotential of zero mean if the proper spatio-temporal symmetries are broken.\nThere has been recent debate on whether directed currents may arise for\npotentials which do not break these symmetries. We show here that, in the\npresence of degeneracies in the quasienergy spectrum, long-lasting directed\ncurrents can be induced, even if the time reversal symmetry is not broken. Our\nmodel can be realized with ultracold atoms in optical lattices in the\ntight-binding regime, and we show that the time scale of the average current\ncan be controlled by extremely weak fields."
    },
    {
        "anchor": "Interplay between periodicity and nonlinearity of indirect excitons in\n  coupled quantum wells: Inspired by a recent experiment of localization-delocalization transition\n(LDT) of indirect excitons in lateral electrostatic lattices [M. Remeika\n\\textit{et al.}, Phys. Rev. Lett. \\textbf{102}, 186803 (2009)], we investigate\nthe interplay between periodic potential and nonlinear interactions of indirect\nexcitons in coupled quantum wells. It is shown that the model involving both\nattractive two-body and repulsive three-body interactions can lead to a natural\naccount for the LDT of excitons across the lattice when reducing lattice\namplitude or increasing particle density. In addition, the observations that\nthe smooth component of the photoluminescent energy increases with increasing\nexciton density and exciton interaction energy is close to the lattice\namplitude at the transition are also qualitatively explained. Our model\nprovides an alternative way for understanding the underlying physics of the\nexciton dynamics in lattice potential wells.",
        "positive": "Quantum Phase Slips: from condensed matter to ultracold quantum gases: Quantum phase slips are the primary excitations in one-dimensional\nsuperfluids and superconductors at low temperatures. They have been well\ncharacterized in most condensed-matter systems, and signatures of their\nexistence has been recently observed in superfluids based on quantum gases too.\nIn this review we briefly summarize the main results obtained on the\ninvestigation of phase slips from superconductors to quantum gases. In\nparticular we focus our attention on recent experimental results of the\ndissipation in one-dimensional Bose superfluids flowing along a shallow\nperiodic potential, which show signatures of quantum phase slips."
    },
    {
        "anchor": "A topological proof that there is no sign problem in one dimensional\n  Path Integral Monte Carlo simulation of fermions: This work shows that, in one dimension, due to its topology, a closed-loop\nproduct of short-time propagators is always positive, despite the fact that\neach anti-symmetric free fermion propagator can be of either sign.",
        "positive": "Solution of inverse problem for Gross-Pitaevskii equation with\n  artificial neural networks: We propose an Artificial Neural Network (ANN) design to solve the inverse\nproblem for a 1D Gross-Pitaevskii equation (GPE). More precise, the ANN takes\nthe squared modulus of the stationary GPE solution as an input and returns the\nparameters of the potential function and the factor in front of the GPE\nnon-linear term. From the physical point of view the ANN predicts the\nparameters of a trap potential and the interaction constant of 1D Bose-Einstein\nCondensate (BEC) by its density distribution. Using the results of numerical\nsolution of GPE for more than $30 000$ sets of GPE parameters as train and\nvalidation datasets we build the ANN as a fast and accurate inverse GPE solver."
    },
    {
        "anchor": "Superballistic center-of-mass motion in one-dimensional attractive Bose\n  gases: Decoherence-induced Gaussian random walks in velocity space: We show that the spreading of the center-of-mass density of ultracold\nattractively interacting bosons can become superballistic in the presence of\ndecoherence, via single-, two- and/or three-body losses. In the limit of weak\ndecoherence, we analytically solve the numerical model introduced in [Phys.\nRev. A 91, 063616 (2015)]. The analytical predictions allow us to identify\nexperimentally accessible parameter regimes for which we predict superballistic\nspreading of the center-of-mass density. Ultracold attractive Bose gases form\nweakly bound molecules; quantum matter-wave bright solitons. Our\ncomputer-simulations combine ideas from classical field methods (\"truncated\nWigner\") and piecewise deterministic stochastic processes. While the truncated\nWigner approach to use an average over classical paths as a substitute for a\nquantum superposition is often an uncontrolled approximation, here it predicts\nthe exact root-mean-square width when modeling an expanding Gaussian wave\npacket. In the superballistic regime, the leading-order of the spreading of the\ncenter-of-mass density can thus be modeled as a quantum superposition of\nclassical Gaussian random walks in velocity space.",
        "positive": "Superdiffusive nonequilibrium motion of an impurity in a Fermi sea: We treat the nonequilibrium motion of a single impurity atom in a\nlow-temperature single-species Fermi sea, interacting via a contact\ninteraction. In the nonequilibrium regime, the impurity does a superdiffusive\ngeometric random walk where the typical distance traveled grows with time as\n$\\sim t^{d/(d+1)}$ for the $d$-dimensional system with $d\\geq 2$. For nonzero\ntemperature $T$, this crosses over to diffusive motion at long times with\ndiffusivity $D\\sim T^{-(d-1)/2}$. These results apply also to a nonzero\nconcentration of impurity atoms as long as they remain dilute and\nnondegenerate."
    },
    {
        "anchor": "A long-lived Higgs mode in a two-dimensional confined Fermi gas: The Higgs mode corresponds to the collective motion of particles due to the\nvibrations of an invisible field. It plays a fundamental role for our\nunderstanding of both low and high energy physics, giving elementary particles\ntheir mass and leading to collective modes in condensed matter and nuclear\nsystems. The Higgs mode has been observed in a limited number of table-top\nsystems, where it however is characterised by a short lifetime due to decay\ninto a continuum of modes. A major goal which has remained elusive so far, is\ntherefore to realise a long-lived Higgs mode in a controllable system. Here, we\nshow how an undamped Higgs mode can be observed unambiguously in a Fermi gas in\na two-dimensional trap, close to a quantum phase transition between a normal\nand a superfluid phase. We develop a first-principles theory of the pairing and\nthe associated collective modes, which is quantitatively reliable when the\npairing energy is much smaller than the trap level spacing, yet simple enough\nto allow the derivation of analytical results. The theory includes the trapping\npotential exactly, which is demonstrated to stabilize the Higgs mode by making\nits decay channels discrete. Our results show how atoms in micro-traps can\nunravel properties of a long-lived Higgs mode, including the role of\nconfinement and finite size effects.",
        "positive": "Magnetism in the two-dimensional dipolar XY model: Motivated by a recent experiment on a square-lattice Rydberg atom array\nrealizing a long-range dipolar XY model [Chen et al., Nature (2023)], we\nnumerically study the model's equilibrium properties. We obtain the phase\ndiagram, critical properties, entropies, variance of the magnetization, and\nsite-resolved correlation functions. We consider both ferromagnetic and\nantiferromagnetic interactions and apply quantum Monte Carlo and\npseudo-Majorana functional renormalization group techniques, generalizing the\nlatter to a U(1) symmetric setting. Our simulations open the door to directly\nperforming many-body thermometry in dipolar Rydberg atom arrays. Moreover, our\nresults provide new insights into the experimental data, suggesting the\npresence of intriguing quasi-equilibrium features, and motivating future\nstudies on the non-equilibrium dynamics of the system."
    },
    {
        "anchor": "Infinite dipolar droplet -- a simple theory for the macro-droplet regime: In this paper we develop a theory for an infinitely long droplet state of a\nzero temperature dipolar bosonic gas. The infinite droplet theory yields\nsimpler equations to solve for the droplet state and its collective\nexcitations. We explore the behavior of infinite droplets using numerical and\nvariational solutions, and demonstrate that it can provide a quantitative\ndescription of large finite droplets of the type produced in experiments. We\nalso consider the axial speed of sound and the thermodynamic limit of a dipolar\ndroplet.",
        "positive": "Nonequilibrium dynamics of spin-orbit coupled lattice bosons: We study the non-equilibrium dynamics of two component bosonic atoms in a\none-dimensional optical lattice in the presence of spin-orbit coupling. In the\nMott insulating regime, the two-component bosonic system at unity filling can\nbe described by the quantum spin XXZ model. The atoms are initially prepared in\ntheir lower spin states. The system becomes out of equilibrium by suddenly\nintroducing spin-orbit coupling to the atoms. The system shows the relaxation\nand non-stationary dynamics, respectively, in the different interaction\nregimes. We find that the time average of magnetization is useful to\ncharacterize the many-body dynamics. The effects of even and odd numbers of\nsites are discussed. Our result sheds light on non-equilibrium dynamics due to\nthe interplay between spin-orbit coupling and atomic interactions."
    },
    {
        "anchor": "Coherent Microwave Control of Ultracold $^{23}$Na$^{40}$K Molecules: We demonstrate coherent microwave control of rotational and hyperfine states\nof trapped, ultracold, and chemically stable $^{23}$Na$^{40}$K molecules.\nStarting with all molecules in the absolute rovibrational and hyperfine ground\nstate, we study rotational transitions in combined magnetic and electric fields\nand explain the rich hyperfine structure. Following the transfer of the entire\nmolecular ensemble into a single hyperfine level of the first rotationally\nexcited state, $J{=}1$, we observe collisional lifetimes of more than $3\\, \\rm\ns$, comparable to those in the rovibrational ground state, $J{=}0$. Long-lived\nensembles and full quantum state control are prerequisites for the use of\nultracold molecules in quantum simulation, precision measurements and quantum\ninformation processing.",
        "positive": "Domain wall suppression in trapped mixtures of Bose-Einstein condensates: The ground state energy of a binary mixture of Bose-Einstein condensates can\nbe estimated for large atomic samples by making use of suitably regularized\nThomas-Fermi density profiles. By exploiting a variational method on the trial\ndensities the energy can be computed by explicitly taking into account the\nnormalization condition. This yields analytical results and provides the basis\nfor further improvement of the approximation. As a case study, we consider a\nbinary mixture of $^{87}$Rb atoms in two different hyperfine states in a double\nwell potential and discuss the energy crossing between density profiles with\ndifferent numbers of domain walls, as the number of particles and the\ninter-species interaction vary."
    },
    {
        "anchor": "Bose Condensate in the D-Dimensional Case, in Particular, for D=2.\n  Semiclassical transition to the classical thermodynamics: The number-theoretical problem of partition of an integer corresponds to\n$D=2$. This problem obeys the Bose--Eeinstein statistics, where repeated terms\nare admissible in the partition, and to the Fermi--Dirac statistics, where they\nare inadmissible. The Hougen--Watson P,Z-diagram shows that this problem splits\ninto two cases: the positive pressure domain corresponds to the Fermi system,\nand the negative, to the Bose system. This analogy can be applied to the van\nder Waals thermodynamics.\n  The thermodynamic approach is related to four potentials corresponding to the\nenergy, free energy, thermodynamic Gibbs potential, enthalpy. The important\nnotion of de Broglie's wavelength permits passing from particle to wave packet,\nin particular, to Bose and Fermi distributions.\n  Particles of ideal Bose and Fermi gases and the decay of a boson consisting\nof two fermions into separate fermions are studied. The case of finitely many\nparticles $N$ of the order of $10^2$ is considered by heuristic considerations\nlike those Fock used to derive the Hartree--Fock equation. The case of $N\\ll1$\nis studied by Gentile statistics, tropical geometry and nonstandard analysis\n(Leibnitz differential or monad). A relation for the energy of neutron\nseparation from the atomic nucleus is obtained when the atomic nucleus volume\nand de Broglie's wavelength are known. The Appendix is author's paper written\nin 1995.",
        "positive": "s- and p-superfluidity of Fermi atoms in Bose-Fermi mixtures: The p-wave superfluid is characterized by nontrivial topological\ncharacteristics essential for fault-tolerant quantum state manipulation.\nHowever, the practical realization of the p-wave state remains a challenging\nproblem. We study the s- and p-wave superfluidity in mixtures of fermionic and\nspinor bosonic gases and derive a general set of the gap equations for these\nsuperfluid states. Numerically solving the gap equations for the s-wave state,\nwe quantify the physical conditions for the realization of the pure p-wave\nstate in a well-controlled environment of atomic physics in the absence of an\nadmixture of the s-wave state."
    },
    {
        "anchor": "Relaxation of superflow in a network: an application to the dislocation\n  model of supersolidity of helium crystals: We have considered the dislocation network model for the supersolid state in\nHe-4 crystals. In difference with uniform 2D and 3D systems, the temperature of\nsuperfluid transition T_c in the network is much smaller than the degeneracy\ntemperature T_d. It is shown that a crossover into a quasi superfluid state\noccurs in the temperature interval between T_c and T_d. Below the crossover\ntemperature the time of decay of the flow increases exponentially under\ndecrease of the temperature. The crossover has a continuous character and the\ncrossover temperature does not depend on the density of dislocations.",
        "positive": "Probing quasi-integrability of the Gross-Pitaevskii equation in a\n  harmonic-oscillator potential: Previous simulations of the one-dimensional Gross-Pitaevskii equation (GPE)\nwith repulsive nonlinearity and a harmonic-oscillator trapping potential hint\ntowards the emergence of quasi-integrable dynamics -- in the sense of\nquasi-periodic evolution of a moving dark soliton without any signs of\nergodicity -- although this model does not belong to the list of integrable\nequations. To investigate this problem, we replace the full GPE by a suitably\ntruncated expansion over harmonic-oscillator eigenmodes (the Galerkin\napproximation), which accurately reproduces the full dynamics, and then analyze\nthe system's dynamical spectrum. The analysis enables us to interpret the\nobserved quasi-integrability as the fact that the finite-mode dynamics always\nproduces a quasi-discrete power spectrum, with no visible continuous component,\nthe presence of the latter being a necessary manifestation of ergodicity. This\nconclusion remains true when a strong random-field component is added to the\ninitial conditions. On the other hand, the same analysis for the GPE in an\ninfinitely deep potential box leads to a clearly continuous power spectrum,\ntypical for ergodic dynamics."
    },
    {
        "anchor": "Criticality in Trapped Atomic Systems: We discuss generic limits posed by the trap in atomic systems on the accurate\ndetermination of critical parameters for second-order phase transitions, from\nwhich we deduce optimal protocols to extract them. We show that under current\nexperimental conditions the in-situ density profiles are barely suitable for an\naccurate study of critical points in the strongly correlated regime. Contrary\nto recent claims, the proper analysis of time-of-fight images yields critical\nparameters accurately.",
        "positive": "Ring dark solitons in three-dimensional Bose-Einstein condensates: In this work we present a systematic study of the three-dimensional extension\nof the ring dark soliton examining its existence, stability, and dynamics in\nisotropic harmonically trapped Bose-Einstein condensates. Detuning the chemical\npotential from the linear limit, the ring dark soliton becomes unstable\nimmediately, but can be fully stabilized by an external cylindrical potential.\nThe ring has a large number of unstable modes which are analyzed through\nspectral stability analysis. Furthermore, a few typical destabilization\ndynamical scenarios are revealed with a number of interesting vortical\nstructures emerging such as the two or four coaxial parallel vortex rings. In\nthe process of considering the stability of the structure, we also develop a\nmodified version of the degenerate perturbation theory method for\ncharacterizing the spectra of the coherent structure. This semi-analytical\nmethod can be reliably applied to any soliton with a linear limit to explore\nits spectral properties near this limit. The good agreement of the resulting\nspectrum is illustrated via a comparison with the full numerical Bogolyubov-de\nGennes spectrum. The application of the method to the two-component ring\ndark-bright soliton is also discussed."
    },
    {
        "anchor": "Balls and Walls: A Compact Unary Coding for Bosonic States: We introduce a unary coding of bosonic occupation states based on the famous\n\"balls and walls\" counting for the number of configurations of $N$\nindistinguishable particles on $L$ distinguishable sites. Each state is\nrepresented by an integer with a human readable bit string that has a\ncompositional structure allowing for the efficient application of operators\nthat locally modify the number of bosons. By exploiting translational and\ninversion symmetries, we identify a speedup factor of order $L$ over current\nmethods when generating the basis states of bosonic lattice models. The unary\ncoding is applied to a one-dimensional Bose-Hubbard Hamiltonian with up to\n$L=N=20$, and the time needed to generate the ground state block is reduced to\na fraction of the diagonalization time. For the ground state symmetry resolved\nentanglement, we demonstrate that variational approaches restricting the local\nbosonic Hilbert space could result in an error that scales with system size.",
        "positive": "Dynamical Fermionization in One Dimensional Spinor Gases: Dynamical fermionization refers to the phenomenon in Tonks-Girardeau (TG)\ngases where, upon release from harmonic confinement, the gas's momentum density\nprofile evolves asymptotically to that of an ideal Fermi gas in the initial\ntrap. This phenomenon has been demonstrated theoretically in hardcore and\nanyonic TG gases, and recently experimentally observed in a strongly\ninteracting Bose gas. We extend this study to a one dimensional (1D) spinor gas\nof arbitrary spin in the strongly interacting regime, and analytically prove\nthat the total momentum distribution after the harmonic trap is turned off\napproaches that of a spinless ideal Fermi gas, while the asymptotic momentum\ndistribution of each spin component takes the same shape of the initial real\nspace density profile of that spin component. Our work demonstrates the rich\nphysics arising from the interplay between the spin and the charge degrees of\nfreedom in a spinor system."
    },
    {
        "anchor": "Engineering quantum magnetism in one-dimensional trapped Fermi gases\n  with p-wave interactions: The highly controllable ultracold atoms in a one-dimensional (1D) trap\nprovide a new platform for the ultimate simulation of quantum magnetism. In\nthis regard, the Neel-antiferromagnetism and the itinerant ferromagnetism are\nof central importance and great interest. Here we show that these magnetic\norders can be achieved in the strongly interacting spin-1/2 trapped Fermi gases\nwith additional p-wave interactions. In this strong coupling limit, the 1D\ntrapped Fermi gas exhibit an effective Heisenberg spin XXZ chain in the\nanisotropic p-wave scattering channels. For a particular p-wave attraction or\nrepulsion within the same species of fermionic atoms, the system displays\nferromagnetic domains with full spin segregation or the anti-ferromagnetic spin\nconfiguration in the ground state. Such engineered magnetisms are likely to be\nprobed in a quasi-1D trapped Fermi gas of $^{40}$ K atoms with very close\ns-wave and p-wave Feshbach resonances.",
        "positive": "Impurity effects on the quantum coherence of a few-boson system: The impurity effects on the quantum coherence of a few-boson system are\nstudied within the two-site Hubbard model. Periodical collapses and revivals of\ncoherence occur in the presence of either polarized or unpolarized fermionic\nimpurities. The relative strength $U_{BF}/U_{BB}$ of the boson-fermion versus\nthe boson-boson interactions plays a key role in the coherence revivals. As the\naverage filling of the impurity increases, the coherence revivals remain nearly\nunaffected for $U_{BF}/U_{BB}=z$ ($z\\in Z$ is an integer) while the odd revival\npeaks are damped for $U_{BF}/U_{BB}=z+1/2$, in agreement with the experimental\nobservations. For unpolarized fermionic impurities, the coherence revivals are\nirrelevant to the strength of the fermion-fermion interactions."
    },
    {
        "anchor": "Properties of atomic pairs produced in the collision of Bose-Einstein\n  condensates: Collisions of Bose-Einstein condensates can be used as a mean to generate\ncorrelated pairs of atoms. The scattered massive particles, in analogy to\nphoton pairs in quantum optics, might be used in the violation of Bell's\ninequalities, demonstration of Einstein-Podolsky-Rosen correlations, or\nsub-shot noise atomic interferometry. Usually, a theoretical description of the\ncollision relies either on stochastic numerical methods or on analytical\ntreatments involving various approximations. Here, we investigate elastic\nscattering of atoms from colliding elongated Bose-Einstein condensates within\nBogoliubov method, carefully controlling performed approximations at every\nstage of the analysis. We derive expressions for the one and two particle\ncorrelation functions. The obtained formulas, which relate the correlation\nfunctions with condensate wavefunction, are convenient for numerical\ncalculations. We employ variational approach for condensate wavefunctions to\nobtain analytical expressions for the correlation functions, which properties\nwe analyze in details. We also present a useful semiclassical model of the\nprocess, and compare its results with the quantum one. The results are relevant\nfor recent experiments with excited helium atoms, as well as for planned\nexperiments aimed at investigating the nonclassicality of the system.",
        "positive": "Inter-species Tunneling in One-dimensional Bose Mixtures: We study the ground-state properties and quantum dynamics of few-boson\nmixtures with strong inter-species repulsion in one-dimensional traps. If one\nspecies localizes at the center, e.g., due to a very large mass compared to the\nother component, it represents an effective barrier for the latter and the\nsystem can be mapped onto identical bosons in a double well. For weaker\nlocalization, the barrier atoms begin to respond to the light component,\nleading to an induced attraction between the mobile atoms that may even\noutweigh their bare intra-species repulsion. To explain the resulting effects,\nwe derive an effective Hubbard model for the lighter species accounting for the\nbackaction of the barrier in correction terms to the lattice parameters. Also\nthe tunneling is drastically affected: Varying the degree of localization of\nthe \"barrier\" atoms, the dynamics of intrinsically noninteracting bosons can\nchange from Rabi oscillations to effective pair tunneling. For identical\nfermions (or fermionized bosons) this leads to the tunneling of attractively\nbound pairs."
    },
    {
        "anchor": "Finite temperature effective field theory for dark solitons in\n  superfluid Fermi gases: We use a finite temperature effective field theory recently developed for\nsuperfluid Fermi gases to investigate the properties of dark solitons in these\nsuperfluids. Our approach provides an analytic solution for the dip in the\norder parameter and the phase profile accross the soliton, which can be\ncompared with results obtained in the framework of the Bogoliubov - de Gennes\nequations. We present results in the whole range of the BCS-BEC crossover, for\narbitrary temperatures, and taking into account Gaussian fluctuations about the\nsaddle point. The obtained analytic solutions yield an exact energy-momentum\nrelation for a dark soliton showing that the soliton in a Fermi gas behaves\nlike a classical particle even at nonzero temperatures. The spatial profile of\nthe pair field and for the parameters of state for the soliton are analytically\nstudied. In the strong-coupling regime and/or for sufficiently high\ntemperatures, the obtained analytic solutions match well the numeric results\nobtained using the Bogoliubov - de Gennes equations.",
        "positive": "Monte Carlo calculations for Fermi gases in the unitary limit with a\n  zero-range interaction: An ultracold Fermi gas with a zero-range attractive potential in the unitary\nlimit is investigated using variational and diffusion Monte Carlo methods.\nPrevious calculations have used a finite range interactions and extrapolate the\nresults to zero-range. Here we extend the quantum Monte Carlo method to\ndirectly use a zero-range interaction without extrapolation. We employ a trial\nwave function with the correct boundary conditions, and modify the sampling\nprocedures to handle the zero-range interaction. The results are reliable and\nhave low variance."
    },
    {
        "anchor": "Dynamical quantum phase transitions in collapse and revival oscillations\n  of a quenched superfluid: In this work we revisit collapse and revival oscillations in superfluids\nsuddenly quenched by strong local interactions for the case of a\none-dimensional Bose-Hubbard model. As the main result we identify the inherent\nnonequilibrium quantum many-body character of these oscillations by revealing\nthat they are controlled by a sequence of underlying dynamical quantum phase\ntransitions in the real-time evolution after the quench, which manifest as\ntemporal nonanalyticities in return probabilities or Loschmidt echos.\nSpecifically, we find that the time scale of the collapse and revival\noscillations is, firstly, set by the frequency at which dynamical quantum phase\ntransitions appear, and is, secondly, of emergent nonequilibrium nature, since\nit is not only determined by the final Hamiltonian but also depends on the\ninitial condition.",
        "positive": "Magnetic phases of bosons with synthetic spin-orbit coupling in optical\n  lattices: We investigate magnetic properties in the superfluid and Mott-insulating\nstates of two-component bosons with spin-orbit (SO) coupling in 2D square\noptical lattices. The spin-independent hopping integral $t$ and SO coupled one\n$\\lambda $are fitted from band structure calculations in the continuum, which\nexhibit oscillations as increasing SO coupling strength. The magnetic\nsuperexchange model is derived in the Mott-insulating state with one-particle\nper-site, characterized by the Dzyaloshinsky-Moriya (DM) interaction. In the\nlimit of $|\\lambda|\\ll |t|$, we find a spin spiral Mott state whose pitch value\nis the same as that in the incommensurate superfluid state, while in the\nopposite limit $|t| \\ll |\\lambda|$, the ground state can be found by a dual\ntransformation to the $|\\lambda|\\ll|t|$ limit."
    },
    {
        "anchor": "Finite-range bias in fitting three-body loss to the zero-range model: We study the impact of finite-range physics on the zero-range-model analysis\nof three-body recombination in ultracold atoms. We find that temperature\ndependence of the zero-range parameters can vary from one set of measurements\nto another as it may be driven by the distribution of error bars in the\nexperiment, and not by the underlying three-body physics. To study\nfinite-temperature effects in three-body recombination beyond the zero-range\nphysics, we introduce and examine a finite-range model based upon a\nhyperspherical formalism. The systematic error discussed in the paper may\nprovide a significant contribution to the error bars of measured three-body\nparameters.",
        "positive": "Vortex-Bright Soliton Dipoles: Bifurcations, Symmetry Breaking and\n  Soliton Tunneling in a Vortex-Induced Double Well: The emergence of vortex-bright soliton dipoles in two-component Bose-Einstein\ncondensates through bifurcations from suitable eigenstates of the underlying\nlinear system is examined. These dipoles can have their bright solitary\nstructures be in phase (symmetric) or out of phase (anti-symmetric). The\ndynamical robustness of each of these two possibilities is considered and the\nout-of-phase case is found to exhibit an intriguing symmetry-breaking\ninstability that can in turn lead to tunneling of the bright wavefunction\nbetween the two vortex \"wells\". We interpret this phenomenon by virtue of a\nvortex-induced double well system, whose spontaneous symmetry breaking leads to\nasymmetric vortex-bright dipoles, in addition to the symmetric and\nanti-symmetric ones. The theoretical prediction of these states is corroborated\nby detailed numerical computations."
    },
    {
        "anchor": "Superfluid properties of a honeycomb dipolar supersolid: Recent breakthrough experiments on dipolar condensates have reported the\ncreation of supersolids, including two-dimensional arrays of quantum droplets.\nDroplet arrays are, however, not the only possible non-trivial density\narrangement resulting from the interplay of mean-field instability and quantum\nstabilization. Several other possible density patterns may occur in trapped\ncondensates at higher densities, including the so-called honeycomb supersolid,\na phase that exists, as it is also the case of a triangular droplet supersolid,\nin the thermodynamic limit. We show that compared to droplet supersolids,\nhoneycomb supersolids have a much-enhanced superfluid fraction while keeping a\nlarge density contrast, and constitute in this sense a much better dipolar\nsupersolid. However, in contrast to droplet supersolids, quantized vortices\ncannot be created in a honeycomb supersolid without driving a transition into a\nso-called labyrinthic phase. We show that the reduced moment of inertia, and\nwith it the superfluid fraction, can be however reliably probed by studying the\ndynamics following a scissors-like perturbation.",
        "positive": "Intermediate super-exponential localization with Aubry-Andr\u00e9 chains: We demonstrate the existence of an intermediate super-exponential\nlocalization regime for eigenstates of the Aubry-Andr\\'e chain. In this regime,\nthe eigenstates localize factorially similarly to the eigenstates of the\nWannier-Stark ladder. The super-exponential decay emerges on intermediate\nlength scales for large values of the $\\textit{winding length}$ -- the\nquasi-period of the Aubry-Andr\\'e potential. This intermediate localization is\npresent both in the metallic and insulating phases of the system. In the\ninsulating phase, the super-exponential localization is periodically\ninterrupted by weaker decaying tails to form the conventional asymptotic\nexponential decay predicted for the Aubry-Andr\\'e model. In the metallic phase,\nthe super-exponential localization happens for states with energies away from\nthe center of the spectrum and is followed by a super-exponential growth into\nthe next peak of the extended eigenstate. By adjusting the parameters it is\npossible to arbitrarily extend the validity of the super-exponential\nlocalization. A similar intermediate super-exponential localization regime is\ndemonstrated in quasiperiodic discrete-time unitary maps."
    },
    {
        "anchor": "Particle-Number-Conserving Bogoliubov Approximation for Bose-Einstein\n  Condensates Using Extended Catalytic States: We encode the many-body wavefunction of a Bose-Einstein condensate (BEC) in\nthe $N$-particle sector of an extended catalytic state. This catalytic state is\na coherent state for the condensate mode and an arbitrary state for the modes\northogonal to the condensate mode. Going to a time-dependent interaction\npicture where the state of the condensate mode is displaced to the vacuum, we\ncan organize the effective Hamiltonian by powers of ${N}^{-1/2}$. Requiring the\nterms of order ${N}^{1/2}$ to vanish gives the Gross-Pitaevskii equation. Going\nto the next order, $N^0$, we derive equations for the number-conserving\nBogoliubov approximation, first given by Castin and Dum [Phys. Rev. A\n$\\textbf{57}$, 3008 (1998)]. In contrast to other approaches, ours is well\nsuited to calculating the state evolution in the Schr\\\"{o}dinger picture;\nmoreover, it is straightforward to generalize our method to multi-component\nBECs and to higher-order corrections.",
        "positive": "Fractionalization Waves in Two-dimensional Dirac Fermions: Quantum\n  Imprint from One Dimension: Particle fractionalization is believed to orchestrate the physics of many\nstrongly correlated systems, yet its direct experimental detection remains a\nchallenge. We propose a simple measurement for an ultracold matter system, in\nwhich correlations in initially decoupled 1D chains are imprinted via quantum\nquench upon two-dimensional Dirac fermions. Luttinger liquid correlations\nlaunch relativistic \"fractionalization waves\" along the chains, while coupling\nnoninteracting chains induces perpendicular dispersion. These could be easily\ndistinguished in an ultracold gas experiment."
    },
    {
        "anchor": "Anderson transition of cold atoms with synthetic spin-orbit coupling in\n  two-dimensional speckle potentials: We investigate the metal-insulator transition occurring in two-dimensional\n(2D) systems of noninteracting atoms in the presence of artificial spin-orbit\ninteractions and a spatially correlated disorder generated by laser speckles.\nBased on a high order discretization scheme, we calculate the precise position\nof the mobility edge and verify that the transition belongs to the symplectic\nuniversality class. We show that the mobility edge depends strongly on the\nmixing angle between Rashba and Dresselhaus spin-orbit couplings. For equal\ncouplings a non-power-law divergence is found, signaling the crossing to the\northogonal class, where such a 2D transition is forbidden.",
        "positive": "Anomalous scaling at non-thermal fixed points of Burgers' and\n  Gross-Pitaevskii turbulence: Scaling in the dynamical properties of complex many-body systems has been of\nstrong interest since turbulence phenomena became the subject of systematic\nmathematical studies. In this article, dynamical critical phenomena far from\nequilibrium are investigated with functional renormalisation group equations.\nThe focus is set on scaling solutions of the stochastic driven-dissipative\nBurgers equation and their relation to solutions known in the literature for\nBurgers and Kardar-Parisi-Zhang dynamics. We furthermore relate superfluid as\nwell as acoustic turbulence described by the Gross-Pitaevskii model to known\nanalytic and numerical results for scaling solutions. In this way, the\ncanonical Kolmogorov exponent 5/3 for the energy cascade in superfluid\nturbulence is obtained analytically. We also get first results for anomalous\nexponents of acoustic and quantum turbulence. These are consistent with\nexisting experimental data. Our results should be relevant for future\nexperiments with, e.g., exciton-polariton condensates in solid-state systems as\nwell as with ultra-cold atomic gases."
    },
    {
        "anchor": "Design of laser-coupled honeycomb optical lattices supporting Chern\n  insulators: We introduce an explicit scheme to realize Chern insulating phases employing\ncold atoms trapped in a state-dependent optical lattice and laser-induced\ntunneling processes. The scheme uses two internal states, a ground state and a\nlong-lived excited state, respectively trapped in separate triangular and\nhoneycomb optical lattices. A resonant laser coherently coupling the two\ninternal states enables hopping between the two sublattices with a Peierls-like\nphase factor. Although laser-induced hopping by itself does not lead to\ntopological bands with non-zero Chern numbers, we find that such bands emerge\nwhen adding an auxiliary lattice that perturbs the lattice structure,\neffectively turning it at low energies into a realization of the Haldane model:\nA two-dimensional honeycomb lattice breaking time-reversal symmetry. We\ninvestigate the parameters of the resulting tight-binding model using\nfirst-principles band structure calculations to estimate the relevant regimes\nfor experimental implementation.",
        "positive": "Finite temperature phase diagram of a spin-1 Bose gas: We formulate a self-consistent Hartree-Fock theory for a spin-1 Bose gas at\nfinite temperature and apply it to characterizing the phase diagram. We find\nthat spin coherence between thermal atoms in different magnetic sub-levels\ndevelops via coherent collisions with the condensed atoms, and is a crucial\nfactor in determining the phase diagram. We develop analytical expressions to\ncharacterize the interaction and temperature dependent shifts of the phase\nboundaries."
    },
    {
        "anchor": "Quantum Gutzwiller approach for the two-component Bose-Hubbard model: We study the effects of quantum fluctuations in the two-component\nBose-Hubbard model generalizing to mixtures the quantum Gutzwiller approach\nintroduced recently in [Phys. Rev. Research 2, 033276 (2020)]. As a basis for\nour study, we analyze the mean-field ground-state phase diagram and spectrum of\nelementary excitations, with particular emphasis on the quantum phase\ntransitions of the model. Within the quantum critical regimes, we address both\nthe superfluid transport properties and the linear response dynamics to density\nand spin probes of direct experimental relevance. Crucially, we find that\nquantum fluctuations have a dramatic effect on the drag between the superfluid\nspecies of the system, particularly in the vicinity of the paired and\nantipaired phases absent in the usual one-component Bose-Hubbard model.\nAdditionally, we analyse the contributions of quantum corrections to the\none-body coherence and density/spin fluctuations from the perspective of the\ncollective modes of the system, providing results for the few-body correlations\nin all the regimes of the phase diagram.",
        "positive": "Condensation signatures of photogenerated interlayer excitons in a van\n  der Waals heterostack: Atomistic van der Waals heterostacks are ideal systems for high-temperature\nexciton condensation because of large exciton binding energies and long\nlifetimes. Charge transport and electron energy-loss spectroscopy showed first\nevidence of excitonic many-body states in such two-dimensional materials. Pure\noptical studies, the most obvious way to access the phase diagram of\nphotogenerated excitons have been elusive. We observe several criticalities in\nphotogenerated exciton ensembles hosted in MoSe2-WSe2 heterostacks with respect\nto photoluminescence intensity, linewidth, and temporal coherence pointing\ntowards the transition to a coherent quantum state. For this state, the\noccupation is 100 percent and the exciton diffusion length is increased. The\nphenomena survive above 10 kelvin, consistent with the predicted critical\ncondensation temperature. Our study provides a first phase-diagram of many-body\ninterlayer exciton states including Bose Einstein condensation."
    },
    {
        "anchor": "Majorana corner pairs in a two-dimensional $s$-wave cold atomic\n  superfluid: We propose a method to prepare Majorana pairs at the corners of imprinted\ndefects on a two-dimensional cold atom optical lattice with $s$-wave superfluid\npairing. Different from previous proposals that manipulate the effective Dirac\nmasses, our scheme relies on the sign flip of the spin-orbit coupling at the\ncorners, which can be tuned in experiments by adjusting the angle of incident\nRaman lasers. The Majorana corner pairs are found to be located at the\ninterface between two regimes with opposite spin orbit coupling strengths in an\nanticlockwise direction and are robust against certain symmetry-persevered\nperturbations. Our work provides a new way for implementing and manipulating\nMajorana pairs with existing cold-atom techniques.",
        "positive": "Phase diagram of quantum fluids. The role of the chemical potential and\n  the phenomenon of condensation: We discuss the generic phase diagrams of pure systems that remain fluid near\nzero temperature. We call this phase a quantum fluid. We argue that the\nsignature of the transition is the change of sign of the chemical potential,\nbeing negative in the normal phase and becoming positive in the quantum fluid\nphase. We show that this change is characterized by a phenomenon that we call\ncondensation, in which a macroscopic number of particles is in their own\nmany-body ground state, a situation common to Fermi and Bose gases. We show\nthat the ideal Bose-Einstein Condensation fits in this scenario, but that it\nalso permits the occurrence of a situation that we may call \"Fermi-Dirac\nCondensation\". In addition, we argue that this phenomenon is also behind the\ndevelopment of superfluid phases in real interacting fluids. However, only\ninteracting systems may show the change from a thermal fluid to a quantum one\nas a true phase transition. As a corollary, this argument shows the necessity\nof the appearance of a \"supersolid\" phase. We also indicate how these ideas may\nbe useful in the description of of experiments with ultracold alkali gases."
    },
    {
        "anchor": "From Classical Fields to Two-Fluid Model of Superfluidity: Emergent\n  Kinetics and Local Gauge Transformations: The first successful macroscopic theory for the motion of superfluid helium\nwas that of Lev Landau (1941) in which the fluid is modelled phenomenologically\nas an interpenetrating mixture of a superfluid and a normal fluid. It has later\nbeen shown that Landau's two-fluid model can be rigorously derived from a\none-fluid model within the classical fields approximation. Assuming a\nseparation of scales exists between the slowly varying, large-scale, background\n(condensate) field, and the short rapidly evolving excitations, a full\ndescription of the kinetics between the condensate and the thermal cloud can be\nobtained. The kinetics describes three-wave and four-wave interactions that\nresemble the C_{12} and C_{22} terms, respectively, in the collision integral\nof the ZNG theory. The scale separation assumption precludes analysis of the\nhealing layer and thus does not include the dynamics of quantised vortices.\nWhilst the analysis required the use of small parameters arising from the scale\nseparation assumption and the assumption of a weakly depleted condensate, we\nexpect the results to hold true over a wider range of parameters. This belief\nis motivated by the validity of Landau's two-fluid model which can be derived\nfrom a one-fluid model using nothing more than Galilean invariance principles.\nIndeed, we argue that similar arguments can be used to recover a two-fluid\nmodel directly from a classical field simply by invoking a local gauge\ntransformation. This derivation does not require any small parameters to be\nintroduced suggesting that the results that lead to the kinetic equations may\nturn out to be more general.",
        "positive": "Quantum correlations in dipolar droplets: Time-dependent\n  Hartree-Fock-Bogoliubov theory: We investigate the effects of quantum correlations on dipolar quantum\ndroplets. To this end,we derive self-consistent time-dependent\nHartree-Fock-Bogoliubov equations that fairly describe the dynamics of the\norder parameter, the normal, and anomalous quantum correlations of the droplet.\nWe analyze the density profiles, the critical number of particles, the\ncondensate depletion, and the pair correlation function. Our predictions are\ncompared with very recent experimental and Quantum Monte-Carlo simulations\nresults and excellent agreement is found."
    },
    {
        "anchor": "Universal contact and collective excitations of a strongly interacting\n  Fermi gas: We study the relationship between Tan's contact parameter and the macroscopic\ndynamic properties of an ultracold trapped gas, such as the frequencies of the\ncollective oscillations and the propagation of sound in one-dimensional (1D)\nconfigurations. We find that the value of the contact, extracted from the most\nrecent low-temperature measurements of the equation of state near unitarity,\nreproduces with accuracy the experimental values of the collective frequencies\nof the radial breathing mode at the lowest temperatures. The available\nexperiment results for the 1D sound velocities near unitarity are also\ninvestigated.",
        "positive": "Dynamics of the corotating vortices in dipolar Bose-Einstein condensates\n  in the presence of dissipation: We study the dynamics of a single and a corotating vortex pair in a dipolar\nBose-Einstein condensate in the framework of dissipative Gross-Pitaevskii\nequation. This simple model enables us to simulate the effect of finite\ntemperature on the vortex dynamics. We study the effect of dipolar interactions\non the dynamics of a single vortex in the presence of phenomenological\ndissipation. In the case of a corotating vortex pair, an initial asymmetry in\nthe locations of the vortices can lead to different decay rates for the\nconstituent vortices as is the case for the condensates interacting via pure\ncontact interactions. We observe that the anisotropic interaction between the\ncomponent vortices manifests itself as the perceptible difference in the\ntrajectories traversed by the vortices in the condensate at finite\ntemperatures."
    },
    {
        "anchor": "Time reversal symmetry breaking of $p$-orbital bosons in a\n  one-dimensional optical lattice: We study bosons loaded in a one-dimensional optical lattice of two-fold\n$p$-orbital degeneracy at each site. Our numerical simulations find an\nanti-ferro-orbital p$_x$+ip$_y$, a homogeneous p$_x$ Mott insulator phase and\ntwo kinds of superfluid phases distinguished by the orbital order\n(anti-ferro-orbital and para-orbital). The anti-ferro-orbital order breaks time\nreversal symmetry. Experimentally observable evidence is predicted for the\nphase transition between the two different superfluid phases. We also discover\nthat the quantum noise measurement is able to provide a concrete evidence of\ntime reversal symmetry breaking in the first Mott phase.",
        "positive": "Countersuperflow instability in miscible two-component Bose-Einstein\n  condensates: We study theoretically the instability of countersuperflow, i.e., two\ncounterpropagating miscible superflows, in uniform two-component Bose-Einstein\ncondensates. Countersuperflow instability causes mutual friction between the\nsuperfluids, causing a momentum exchange between the two condensates, when the\nrelative velocity of the counterflow exceeds a critical value. The momentum\nexchange leads to nucleation of vortex rings from characteristic density\npatterns due to the nonlinear development of the instability. Expansion of the\nvortex rings drastically accelerates the momentum exchange, leading to a highly\nnonlinear regime caused by intervortex interaction and vortex reconnection\nbetween the rings. For a sufficiently large interaction between the two\ncomponents, rapid expansion of the vortex rings causes isotropic turbulence and\nthe global relative motion of the two condensates relaxes. The maximum vortex\nline density in the turbulence is proportional to the square of the relative\nvelocity."
    },
    {
        "anchor": "Bosonic continuum theory of one-dimensional lattice anyons: Anyons with arbitrary exchange phases exist on 1D lattices in ultracold\ngases. Yet, known continuum theories in 1D do not match. We derive the\ncontinuum limit of 1D lattice anyons via interacting bosons. The theory\nmaintains the exchange phase periodicity fully analogous to 2D anyons. This\nprovides a mapping between experiments, lattice anyons, and continuum theories,\nincluding Kundu anyons with a natural regularization as a special case. We\nnumerically estimate the Luttinger parameter as a function of the exchange\nangle to characterize long-range signatures of the theory and predict different\nvelocities for left- and right-moving collective excitations.",
        "positive": "Sustained propagation and control of topological excitations in\n  polariton superfluid: We present a simple method to compensate for losses in a polariton\nsuperfluid. Based on a weak support field, it allows for an extended\npropagation of a resonantly driven polariton superfluid at a minimal energetic\ncost. Moreover, this setup based on optical bistability, leads to a significant\nrelease of the phase constraint imposed by the resonant driving. This release,\ntogether with the macroscopic polariton propagation, offers a unique\nopportunity to study the hydrodynamics of topological excitations of polariton\nsuperfluids such as quantized vortices and dark solitons. We numerically study\nhow the coherent field supporting the superfluid flow interacts with the\nvortices and how it can be used to control them. Interestingly, we show that\nstandard hydrodynamics does not apply for this driven-dissipative fluid and new\nbehaviours are identified."
    },
    {
        "anchor": "Mean-field regime and Thomas-Fermi approximations of trapped\n  Bose-Einstein condensates with higher order interactions in one and two\n  dimensions: We derive rigorously one- and two-dimensional mean-field equations for cigar-\nand pancake-shaped Bose-Einstein condensates (BEC) with higher order\ninteractions (HOI). We show how the higher order interaction modifies the\ncontact interaction of the strongly confined particles. Surprisingly, we find\nthat the usual Gaussian profile assumption for the strongly confining direction\nis inappropriate for the cigar-shaped BEC case, and a Thomas-Fermi type profile\nshould be adopted instead. Based on the derived mean field equations, the\nThomas-Fermi densities are analyzed in presence of the contact interaction and\nHOI. For both box and harmonic traps in one, two and three dimensions, we\nidentify the analytical Thomas-Fermi densities, which depend on the competition\nbetween the contact interaction and the HOI.",
        "positive": "Dicke quantum spin glass of atoms and photons: Recent studies of strongly interacting atoms and photons in optical cavities\nhave rekindled interest in the Dicke model of atomic qubits coupled to discrete\nphoton cavity modes. We study the multimode Dicke model with variable\natom-photon couplings. We argue that a quantum spin glass phase can appear,\nwith a random linear combination of the cavity modes superradiant. We compute\natomic and photon spectral response functions across this quantum phase\ntransition, both of which should be accessible in experiment."
    },
    {
        "anchor": "Vortex Lattices in Binary Mixtures of Repulsive Superfluids: We present an extension of the framework introduced in [1] to treat\nmulticomponent systems, showing that new degrees of freedom are necessary in\norder to obtain the desired boundary conditions. We then apply this extended\nframework to the coupled Gross-Pitaevskii equations to investigate the ground\nstates of two-component systems with equal masses thereby extending previous\nwork in the lowest Landau limit [2] to arbitrary interactions within\nGross-Pitaevskii theory. We show that away from the lowest-Landau level limit,\nthe predominant vortex lattice consists of two interlaced triangular lattices.\nFinally, we derive a linear relation which accurately describes the phase\nboundaries in the strong interacting regimes.",
        "positive": "Observation of a Strong Atom-Dimer Attraction in a Mass-Imbalanced\n  Fermi-Fermi Mixture: We investigate a mixture of ultracold fermionic $^{40}$K atoms and weakly\nbound $^{6}$Li$^{40}$K dimers on the repulsive side of a heteronuclear atomic\nFeshbach resonance. By radio-frequency spectroscopy we demonstrate that the\nnormally repulsive atom-dimer interaction is turned into a strong attraction.\nThe phenomenon can be understood as a three-body effect in which two heavy\n$^{40}$K fermions exchange the light $^{6}$Li atom, leading to attraction in\nodd partial-wave channels (mainly p-wave). Our observations show that mass\nimbalance in a fermionic system can profoundly change the character of\ninteractions as compared to the well-established mass-balanced case."
    },
    {
        "anchor": "Generation and decoherence of soliton spatial superposition states: Due to their coherence properties, dilute atomic gas Bose-Einstein\ncondensates seem a versatile platform for controlled creation of mesoscopically\nentangled states with a large number of particles and also allow controlled\nstudies of their decoherence. However, the creation of such a state\nintrinsically involves many-body quantum dynamics that cannot be captured by\nmean-field theory, and thus invalidates the most widespread methods for the\ndescription of condensates. We follow up on a proposal, in which a condensate\ncloud as a whole is brought into a superposition of two different spatial\nlocations, by mapping entanglement from a strongly interacting Rydberg atomic\nsystem onto the condensate using off-resonant laser dressing [R. Mukherjee et\nal., Phys. Rev. Lett. 115 040401 (2015)]. A variational many-body Ansatz akin\nto recently developed multi-configurational methods allows us to model this\nentanglement mapping step explicitly, while still preserving the simplicity of\nmean-field physics for the description of each branch of the superposition. In\nthe second part of the article, we model the decoherence process due to atom\nlosses in detail. Altogether we confirm earlier estimates, that tightly\nlocalized clouds of 400 atoms can be brought into a quantum superposition of\ntwo locations about 3 {\\mu}m apart and remain coherent for about 1 ms.",
        "positive": "Quantum Brownian Motion with Inhomogeneous Damping and Diffusion: We analyze the microscopic model of quantum Brownian motion, describing a\nBrownian particle interacting with a bosonic bath through a coupling which is\nlinear in the creation and annihilation operators of the bath, but may be a\nnonlinear function of the position of the particle. Physically, this\ncorresponds to a configuration in which damping and diffusion are spatially\ninhomogeneous. We derive systematically the quantum master equation for the\nBrownian particle in the Born-Markov approximation and we discuss the\nappearance of novel terms, for various polynomials forms of the coupling. We\ndiscuss the cases of linear and quadratic coupling in great detail and we\nderive, using Wigner function techniques, the stationary solutions of the\nmaster equation for a Brownian particle in a harmonic trapping potential. We\npredict quite generally Gaussian stationary states, and we compute the aspect\nratio and the spread of the distributions. In particular, we find that these\nsolutions may be squeezed (super-localized) with respect to the position of the\nBrownian particle. We analyze various restrictions to the validity of our\ntheory posed by non-Markovian effects and by the Heisenberg principle. We\nfurther study the dynamical stability of the system, by applying a Gaussian\napproximation to the time dependent Wigner function, and we compute the\ndecoherence rates of coherent quantum superpositions in position space.\nFinally, we propose a possible experimental realization of the physics\ndiscussed here, by considering an impurity particle embedded in a degenerate\nquantum gas."
    },
    {
        "anchor": "Superfluid stiffness for the attractive Hubbard model on a honeycomb\n  optical lattice: In addition to the conventional contribution that is directly controlled by\nthe single-particle energy spectrum, the superfluid phase stiffness of a\ntwo-component Fermi gas has a geometric contribution that is governed by the\nquantum metric of the honeycomb's band structure. Here, we take both\ncontributions into account, and construct phase diagrams for the critical\nsuperfluid transition temperature as a function of the chemical potential,\nparticle filling, onsite interaction and next-nearest-neighbor hopping. Our\ntheoretical approach is based on a self-consistent solution of the BCS\nmean-field theory for the stationary Cooper pairs and the universal BKT\nrelation for the phase fluctuations.",
        "positive": "Fulde-Ferrell-Larkin-Ovchinnikov Phases in Two-dimensional Spin-Orbit\n  Coupled Degenerate Fermi Gases: The Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase, a superconducting state\nwith non-zero total momentum Cooper pairs in a strong magnetic field, was\npredicted more than 50 years ago and now becomes an important concept in many\nbranches of physics. However, no unambiguous experimental evidences for the\nexistence of FFLO phases have been observed yet. Recently, spin-imbalanced\nultracold degenerate Fermi gases have emerged as a new powerful platform for\nthe observation of FFLO phases due to their high experimental controllability\nand the lack of disorder. However, in three dimensional degenerate Fermi gases\nwhere the FFLO phases can be described within the simple mean field theory, the\nparameter region for the FFLO phases is too small to be observed in\nexperiments. Recently, we showed that the Rashba type spin-orbit coupling and\nin-plane Zeeman field in three dimensional degenerate Fermi gases provide a\nmore efficient way to create the FFLO phase because (1) the parameter region\nfor the FFLO phase is greatly enlarged in the phase diagram and (2) the FFLO\nphase is stabilized due to the enhanced energy difference between FFLO phase\nand conventional Bardeen-Cooper-Schrieffer (BCS) phase. In this work we\ninvestigate the FFLO phase in two dimensional spin-orbit coupled degenerate\nFermi gases using the mean field theory, with special concerns on the physical\norigin of the FFLO state. The basic properties of the FFLO phase are discussed\nand the phase diagram is obtained at zero temperature. The symmetry of\ndifferent quantum phases is examined, which provide important basis for the\nexperimental observation of FFLO phases using the time-of-flight imaging."
    },
    {
        "anchor": "Bright solitons in Bose-Einstein condensates with field-induced dipole\n  moments: We introduce an effectively one-dimensional (1D) model of a bosonic gas of\nparticles carrying collinear dipole moments which are induced by an external\npolarizing field with the strength periodically modulated along the coordinate,\nwhich gives rise to an effective nonlocal nonlinear lattice in the condensate.\nThe existence, shape and stability of bright solitons, appearing in this model,\nare investigated by means of the variational approximation and numerical\nmethods. The mobility of solitons and interactions between them are studied\ntoo.",
        "positive": "Boson thermodynamics in the gravity field: A uniform force like the weight has been shown to forbid Bose-Einstein\ncondensation (BEC), due to the discreteness of the Airy spectrum, resulting\nfrom the weight. We show that BEC is forbidden even if the Airy spectrum is\ntreated as continuous, in what we call the approximate continuous limit (ACL).\nThe absence of BEC is due to the finite difference $\\epsilon_0$ between the\nquantum and the classical ground level. A thorough study is made, showing the\nway the Bose-Einstein condensate grows, at temperatures lower than the fictious\nBEC temperature $T_f$, resulting from the limit $\\epsilon_0\\rightarrow0$. A\ncomparison with some experimental data shows the difference between the\nconfinement in a rigid-wall reservoir and in a harmonic trap."
    },
    {
        "anchor": "Bogoliubov Corner Excitations in Conventional $s$-Wave Superfluids: Higher-order topological superconductors and superfluids have triggered a\ngreat deal of interest in recent years. While Majorana corner or hinge states\nhave been studied intensively, whether superconductors and superfluids, being\ntopological or trivial, host higher-order topological Bogoliubov excitations\nremains elusive. In this work, we propose that Bogoliubov corner excitations\ncan be driven from a trivial conventional $s$-wave superfluid through\nmirror-symmetric local potentials. The topological Bogoliubov excited modes\noriginate from the nontrivial Bogoliubov excitation bands. These modes are\nprotected by mirror symmetry and robust against mirror-symmetric perturbations\nas long as the Bogoliubov energy gap remains open. Our work provides new\ninsight into higher-order topological excitation states in superfluids and\nsuperconductors.",
        "positive": "Controlled Generation of Nonlinear Resonances through Sinusoidal Lattice\n  Modes in Bose-Einstein Condensate: We study Bose-Einstein condensate in the combined presence of time modulated\noptical lattice and harmonic trap in the mean-field approach. Through the\nself-similar method, we show the existence of sinusoidal lattice modes in this\ninhomogeneous system, commensurate with the lattice potential. A significant\nadvantage of this system is wide tunability of the parameters through chirp\nmanagement. The combined effect of the interaction, harmonic trap and lattice\npotential leads to the generation of nonlinear resonances, exactly where the\nmatter wave changes its direction. When the harmonic trap is switched off, the\nBEC undergoes a nonlinear compression for the static optical lattice potential.\nFor better understanding of chirp management and the nature of the sinusoidal\nexcitation, we investigate the energy spectrum of the condensate, which clearly\nreveals the generation of nonlinear resonances in the appropriate regime. We\nhave also identified a classical dynamical phase transition occurring in the\nsystem, where loss of superfluidity takes the superfluid phase to an insulating\nstate."
    },
    {
        "anchor": "Phase Diagram of Solitons in the Polar Phase of a Spin-1 Bose-Einstein\n  Condensate: We theoretically study the structure of a stationary soliton in the polar\nphase of spin-1 Bose--Einstein condensate in the presence of quadratic Zeeman\neffect at zero temperature. The phase diagram of such solitons is mapped out by\nfinding the states of minimal soliton energy in the defining range of polar\nphase. The states are assorted into normal, anti-ferromagnetic,\nbroken-axisymmetry, and ferromagnetic phases according to the number and spin\ndensities in the core. The order of phase transitions between different\nsolitons and the critical behaviour of relevant continuous transitions are\nproved within the mean-field theory.",
        "positive": "Two dimensional momentum state lattices: Building on the development of momentum state lattices (MSLs) over the past\ndecade, we introduce a simple extension of this technique to higher dimensions.\nBased on the selective addressing of unique Bragg resonances in matter-wave\nsystems, MSLs have enabled the realization of tight-binding models with tunable\ndisorder, gauge fields, non-Hermiticity, and other features. Here, we examine\nand outline an experimental approach to building scalable and tunable\ntight-binding models in two dimensions describing the laser-driven dynamics of\natoms in momentum space. Using numerical simulations, we highlight some of the\nsimplest models and types of phenomena this system is well-suited to address,\nincluding flat-band models with kinetic frustration and flux lattices\nsupporting topological boundary states. Finally, we discuss many of the direct\nextensions to this model, including the introduction of disorder and\nnon-Hermiticity, which will enable the exploration of new transport and\nlocalization phenomena in higher dimensions."
    },
    {
        "anchor": "Coherence Properties of the Repulsive Anyon-Hubbard Dimer: One-dimensional anyonic models of the Hubbard type show intriguing\nground-state properties, effectively transmuting between Bose-Einstein and\nFermi-Dirac statistics. The simplest model that one can investigate is an\nanyonic version of the bosonic Josephson junction, the repulsive anyon-Hubbard\ndimer. In the following we find an exact duality relation to the Bethe-solvable\nBose-Hubbard dimer, which is well known from quantum optics and information\ntheory and has interesting connections to spin squeezing and entangled coherent\nstates. Conversely, we show that the anyonic Hubbard dimer has nontrivial\ncoherence properties that emerge from the anyonic statistics. In particular, we\nfind that coherences can be suppressed and amplified and show that these\nfeatures are remarkably robust against additional repulsive on-site\ninteractions highlighting the distinct nature of anyons.",
        "positive": "Dropleton-Soliton Crossover mediated via Trap Modulation: We report a droplet to a soliton crossover by tuning the external confinement\npotential in a dilute Bose-Eienstein condensate by numerically solving the\nmodified Gross-Pitaevskii equation. The testimony of such a crossover is\npresented via studying the fractional density of the condensate which smoothly\nmigrates from being a flat-head curve at weak confinement to a bright soliton\nat strong confinement. Such a transition occurs across a region of the\npotential whose strength varies over an order of magnitude and thus should be\nfit to be termed as a crossover. We supplement our studies via exploring the\nsize of the bound pairs and the ramifications of the particle density therein.\nEventually, all of these aid us in arriving at a phase diagram in a space\ndefined by the trap strength and the particle number that shows the formation\nof two phases consisting of droplets and solitons, along with a regime of\ncoexistence of these two."
    },
    {
        "anchor": "Efficient Creation of Ultracold Ground State\n  $^{6}\\textrm{Li}^{40}\\textrm{K}$ Polar Molecules: We report the creation of ultracold ground state\n$^{6}\\textrm{Li}^{40}\\textrm{K}$ polar molecules with high efficiency. Starting\nfrom weakly-bound molecules state, stimulated Raman adiabatic passage (STIRAP)\nis adopted to coherently transfer the molecules to their singlet ro-vibrational\nground state $|\\textrm{X}^{1}\\Sigma^{+},v=0,J=0>$. By employing a singlet\nSTIRAP pathway and low-phase-noise narrow-linewidth lasers, we observed a\none-way transfer efficiency of 96(4)\\,\\%. Held in an optical dipole trap, the\nlifetime of the ground-state molecules is measured to be 5.0(3)\\,ms. The large\npermanent dipole moment of LiK is confirmed by applying a DC electric field on\nthe molecules and performing Stark shift spectroscopy of the ground state. With\nrecent advances in the quantum control of collisions, our work paves the way\nfor exploring quantum many-body physics with strongly-interacting\n$^{6}\\textrm{Li}^{40}\\textrm{K}$ molecules.",
        "positive": "An SU(N) Mott insulator of an atomic Fermi gas realized by large-spin\n  Pomeranchuk cooling: The Hubbard model, containing only the minimum ingredients of nearest\nneighbor hopping and on-site interaction for correlated electrons, has\nsucceeded in accounting for diverse phenomena observed in solid-state\nmaterials. One of the interesting extensions is to enlarge its spin symmetry to\nSU(N>2), which is closely related to systems with orbital degeneracy. Here we\nreport a successful formation of the SU(6) symmetric Mott insulator state with\nan atomic Fermi gas of ytterbium (173Yb) in a three-dimensional optical\nlattice. Besides the suppression of compressibility and the existence of charge\nexcitation gap which characterize a Mott insulating phase, we reveal an\nimportant difference between the cases of SU(6) and SU(2) in the achievable\ntemperature as the consequence of different entropy carried by an isolated\nspin. This is analogous to Pomeranchuk cooling in solid 3He and will be helpful\nfor investigating exotic quantum phases of SU(N) Hubbard system at extremely\nlow temperatures."
    },
    {
        "anchor": "Interacting Fibonacci anyons in a Rydberg gas: A defining property of particles is their behavior under exchange. In two\ndimensions anyons can exist which, opposed to fermions and bosons, gain\narbitrary relative phase factors or even undergo a change of their type. In the\nlatter case one speaks of non-Abelian anyons - a particularly simple and\naesthetic example of which are Fibonacci anyons. They have been studied in the\ncontext of fractional quantum Hall physics where they occur as quasiparticles\nin the $k=3$ Read-Rezayi state, which is conjectured to describe a fractional\nquantum Hall state at filling fraction $\\nu=12/5$. Here we show that the\nphysics of interacting Fibonacci anyons can be studied with strongly\ninteracting Rydberg atoms in a lattice, when due to the dipole blockade the\nsimultaneous laser excitation of adjacent atoms is forbidden. The Hilbert space\nmaps then directly on the fusion space of Fibonacci anyons and a proper tuning\nof the laser parameters renders the system into an interacting topological\nliquid of non-Abelian anyons. We discuss the low-energy properties of this\nsystem and show how to experimentally measure anyonic observables.",
        "positive": "Density Wave Superradiance of Photonic Fluid in Frustrated Triangle\n  Lattice Cavity Arrays: The spontaneously broken of translational symmetry is usually due to the\ncompetition between local interactions and long-range interactions. However, in\nthis paper, we show how a crystalline order can be generated by the competition\nbetween local interaction and long-range correlation by frustration. Here we\npropose a positive hopping Bose Hubbard model on triangle lattices with a pair\ncreation term which comes from frustrated linked cavity arrays with degenerate\nquantum gases in them. We find by increasing the strength of pair creation term\nagainst local interaction strength, two kinds of density wave ordered\nsuperradiant photonic fluid phase can be realized and a first order transition\nbetween two different density wave ordered states is found. This proposal shows\nus a new way to produce coherent \"solid\" phase without the help of long range\ninteractions."
    },
    {
        "anchor": "Unconventional Fulde-Ferrell-Larkin-Ovchinnikov pairing states in a\n  Fermi gas with spin-orbit coupling: We study the phase diagram in a two-dimensional Fermi gas with the synthetic\nspin-orbit coupling that has recently been realized experimentally. In\nparticular, we characterize in detail the properties and the stability region\nof the unconventional Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states in such a\nsystem, which are induced by spin-orbit coupling and Fermi surface asymmetry.\nWe identify several distinct nodal FFLO states by studying the topology of\ntheir respective gapless contours in momentum space. We then examine the phase\nstructure and the number density distributions in a typical harmonic trapping\npotential under the local density approximation. Our studies provide detailed\ninformation on the FFLO pairing states with spin-orbit coupling and Fermi\nsurface asymmetry, and will facilitate experimental detection of these\ninteresting pairing states in the future.",
        "positive": "Temperature and interaction dependence of the moment of inertia of a\n  rotating condensate boson gas: In this paper, a developed Hartree-Fock semiclassical approximation is used\nto calculate the temperature and interaction dependence of the moment of\ninertia of a rotating condensate Boson gas. A fully classical and quantum\nmechanical treatment for the moment of inertia are given in terms of the\nnormalized temperature. We found that the moment of inertia is considerably\naffected by the interaction. The present analysis, shows that the superfluid\neffects in the moment of inertia of a condensate Boson gas can be observed at\ntemperatures $T > .25 T_0 $ and not dramatically smaller than $T_0$."
    },
    {
        "anchor": "Thermal Phase transitions in attractive extended Bose-Hubbard Model with\n  three-body constraint: By means of quantum Monte Carlo simulations implemented with a two-loop\nupdate scheme, the finite-temperature phase diagram of a three-body constrained\nattractive Bose lattice gas is investigated. The nature of the thermal phase\ntransitions around the dimer superfluid and the atomic superfluid is unveiled.\nWe find that the $Z_2$ symmetry-breaking transitions between these two\nsuperfluid phases are of first order even at nonzero temperatures. More\ninterestingly, the thermal transition from the dimer superfluid to the normal\nfluid is found to be consistent with the Kosterlitz-Thouless type but giving an\nanomalous universal stiffness jump. It demonstrates that this transition is\ndriven by unbinding of pairs of fractional vortices.",
        "positive": "Hydrodynamic collective modes for cold trapped gases: We suggest that collective oscillation frequencies of cold trapped gases can\nbe used to test predictions from quantum many-body physics. Our motivation lies\nboth in rigid experimental tests of theoretical calculations and a possible\nimprovement of measurements of particle number, chemical potential or\ntemperature. We calculate the effects of interaction, dimensionality and\nthermal fluctuations on the collective modes of a dilute Bose gas in the\nhydrodynamic limit. The underlying equation of state is provided by\nnon-perturbative Functional Renormalization Group or by Lee--Yang theory. The\nspectrum of oscillation frequencies could be measured by response techniques.\nOur findings are generalized to bosonic or fermionic quantum gases with an\narbitrary equation of state in the two-fluid hydrodynamic regime. For any given\nequation of state P(\\mu,T) and normal fluid density n_n(\\mu,T) the collective\noscillation frequencies in a $d$-dimensional isotropic potential are found to\nbe the eigenvalues of an ordinary differential operator. We suggest a method of\nnumerical solution and discuss the zero-temperature limit. Exact results are\nprovided for harmonic traps and certain special forms of the equation of state.\nWe also present a phenomenological treatment of dissipation effects and discuss\nthe possibility to excite the different eigenmodes individually."
    },
    {
        "anchor": "Vortices in dipolar Bose-Einstein condensates: Quantized vortices are the hallmark of superfluidity, and are often sought\nout as the first observable feature in new superfluid systems. Following the\nrecent experimental observation of vortices in Bose-Einstein condensates\ncomprised of atoms with inherent long-range dipole-dipole interactions [Nat.\nPhys. 18, 1453-1458 (2022)], we thoroughly investigate vortex properties in the\nthree-dimensional dominantly dipolar regime, where beyond-mean-field effects\nare crucial for stability, and investigate the interplay between trap geometry\nand magnetic field tilt angle.",
        "positive": "A class of compact entities in three component Bose - Einstein\n  condensates: We introduce a new class of soliton-like entities in spinor three component\nBECs. These entities generalize well known solitons. For special values of\ncoupling constants, the system considered is Completely Integrable and supports\n$N$ soliton solutions. The one-soliton solutions can be generalized to systems\nwith different values of coupling constants. However, they no longer interact\nelastically. When two so generalized solitons collide, a spin component\noscillation is observed in both emerging entities. We propose to call these\nnewly found entities oscillatons. They propagate without dispersion and retain\ntheir character after collisions. We derived an exact mathematical model for\noscillatons and showed that the well known one soliton solutions are a\nparticular case."
    },
    {
        "anchor": "Quantum liquid droplets in Bose mixtures with weak disorder: We study the properties of self-bound liquid droplets of three-dimensional\nBose mixtures in a weak random potential with Gaussian correlation function at\nboth zero and finite temperatures. Using the Bogoliubov theory, we derive\nuseful formulas for the ground-state energy, the equilibrium density, the\ndepletion, and the anomalous density of the droplet. The quantum fluctuation\ninduced by the disorder known as the glassy fraction is also systematically\ncomputed. At finite temperature, we calculate the free energy, the thermal\nequilibrium density, and the critical temperature in terms of the disorder\nparameters. We show that when the strength and the correlation length of the\ndisorder potential exceed a certain critical value, the droplet evaporates and\nis eventually entirely destroyed. We calculate the density profiles of this\nexotic state by means of numerical simulations of the corresponding generalized\ndisorder Gross-Pitaevskii equation. Our predictions reveal that as the strength\nof the disorder gets larger, the atomic density varies rapidly in the plateau\nregion. We point out in addition that the peculiar interplay of the disorder\nand the repulsive Lee-Huang-Yang corrections play a pivotal role in the\ncollective modes of the self-bound droplet.",
        "positive": "Maximally localized Wannier functions for ultracold atoms in\n  one-dimensional double-well periodic potentials: We discuss a method for constructing generalized Wannier functions that are\nmaximally localized at the minima of a one-dimensional periodic potential with\na double-well per unit cell. By following the approach of (Marzari M and\nVanderbilt D 1997 Phys. Rev. B 56, 12847), we consider a set of band-mixing\nWannier functions with minimal spread, and design a specific two-step gauge\ntransformation of the Bloch functions for a composite two band system. This\nmethod is suited to efficiently compute the tight-binding coefficients needed\nfor mapping the continuous system to a discrete lattice model. Their behaviour\nis analyzed here as a function of the symmetry properties of the double-well\n(including the possibility of parity-breaking), in a range of feasible\nexperimental parameters."
    },
    {
        "anchor": "Observing topological charges and dynamical bulk-surface correspondence\n  with ultracold atoms: In quenching a topological phase across phase transition, the dynamical\nbulk-surface correspondence emerges that the bulk topology of $d$-dimensional\n($d$D) phase relates to the nontrivial pattern of quench dynamics emerging on\n$(d-1)$D subspace, called band inversion surfaces (BISs) in momentum space.\nHere we report the first experimental observation of the dynamical bulk-surface\ncorrespondence through measuring the topological charges in a 2D quantum\nanomalous Hall model realized in an optical Raman lattice. The system can be\nquenched with respect to every spin axis by suddenly varying the two-photon\ndetuning or phases of the Raman couplings, in which the topological charges and\nBISs are measured dynamically by the time-averaged spin textures. We observe\nthat the total charges in the region enclosed by BISs define a dynamical\ntopological invariant, which equals the Chern index of the post-quench band.\nThe topological charges relate to an emergent dynamical field which exhibits\nnontrivial topology on BIS, rendering the dynamical bulk-surface\ncorrespondence. This study opens a new avenue to explore topological phases\ndynamically.",
        "positive": "Observation of universal Kibble-Zurek scaling in an atomic Fermi\n  superfluid: Half a century ago, T. Kibble proposed a scenario for topological defect\nformation from symmetry breaking during the expansion of the early Universe. W.\nZurek later crystallized the concept to superfluid helium, predicting a\npower-law relation between the number of quantum vortices and the rate at which\nthe system passes through the lambda transition. Here, we report the\nobservation of Kibble-Zurek scaling in a homogeneous, strongly interacting\nFermi gas undergoing a superfluid phase transition. We investigate the\nsuperfluid transition using two distinct control parameters: temperature and\ninteraction strength. The microscopic physics of condensate formation is\nmarkedly different for the two quench parameters, signaled by their two orders\nof magnitude difference in the condensate formation timescale. However,\nregardless of the thermodynamic direction in which the system passes through a\nphase transition, the Kibble-Zurek exponent is identically observed to be about\n0.68 and shows good agreement with theoretical predictions that describe\nsuperfluid phase transitions. This work demonstrates the gedanken experiment\nZurek proposed for liquid helium that shares the same universality class with\nstrongly interacting Fermi gases."
    },
    {
        "anchor": "Effects of quantum fluctuations on the dynamics of dipolar Bose polarons: We study the dynamics of dipolar Bose polarons in the presence of the normal\nand anomalous fluctuations using the time-dependent Hartree-Fock-Bogoliubov\ntheory. The density profiles of the condensate, the anomalous component and the\nimpurity are deeply analyzed. The time evolution of the width and the\ncenter-of-mass oscillation of such quantities is also highlighted. We calculate\ncorrections due to quantum fluctuations and impurity to the chemical potential\nand the radius of the condensate and of the anomalous component in the weak\ncoupling regime using the Thomas-Fermi approximation. Effects of the\ndipole-dipole interaction, impurity-host interaction and the anomalous\nfluctuation on the width and on the breathing frequencies of the impurity are\ndiscussed by variational and numerical means.",
        "positive": "A dual-species magneto-optical trap for lithium and strontium atoms: We present a machine built for experiments with ultracold mixtures of\nstrontium and lithium atoms. The machine includes a science vacuum chamber and\nthe relevant laser systems for cooling and trapping the atoms. With this\nmachine, we realize a D2-line compressed magneto-optical trap (MOT) for\n${^6}$Li and a narrow-linewidth 689-nm MOT for $^{84}$Sr, obtaining ~$10^9$\n${^6}$Li atoms at 700 $\\mu$K and ~$10^7$ $^{84}$Sr atoms at 1.8 $\\mu$K. Such a\ndual-species MOT provides an ideal starting point for realizing double\ndegenerate mixtures of $^6$Li and Sr atoms."
    },
    {
        "anchor": "Momentum distributions and numerical methods for strongly interacting\n  one-dimensional spinor gases: One-dimensional spinor gases with strong delta interaction fermionize and\nform a spin chain. The spatial degrees of freedom of this atom chain can be\ndescribed by a mapping to spinless noninteracting fermions and the spin degrees\nof freedom are described by a spin-chain model with nearest-neighbor\ninteractions. Here, we compute momentum and occupation-number distributions of\nup to 16 strongly interacting spinor fermions and bosons as a function of their\nspin imbalance, the strength of an externally applied magnetic field gradient,\nthe length of their spin, and for different excited states of the multiplet. We\nshow that the ground-state momentum distributions resemble those of the\ncorresponding noninteracting systems, apart from flat background distributions,\nwhich extend to high momenta. Moreover, we show that the spin order of the spin\nchain---in particular antiferromagnetic spin order---may be deduced from the\nmomentum and occupation-number distributions of the system. Finally, we present\nefficient numerical methods for the calculation of the single-particle\ndensities and one-body density matrix elements and of the local exchange\ncoefficients of the spin chain for large systems containing more than 20\nstrongly interacting particles in arbitrary confining potentials.",
        "positive": "Experimental realization of ultracold Yb-$^{7}{\\rm Li}$ mixtures in\n  mixed dimensions: We report on the experimental realization of ultracold $^{174}{\\rm\nYb}$-$^{7}{\\rm Li}$ (Boson-Boson) and $^{173}{\\rm Yb}$-$^{7}{\\rm Li}$\n(Fermion-Boson) mixtures. They are loaded into three dimensional (3D) or one\ndimensional (1D) optical lattices that are species-selectively deep for the\nheavy Ytterbium (Yb) and shallow for the light bosonic Lithium (Li) component,\nrealizing novel mixed dimensional systems. In the 1D optical lattice the band\nstructure of $^{173}{\\rm Yb}$ is reconstructed in the presence of $^{7}{\\rm\nLi}$. Spectroscopic measurements of the $^{174}{\\rm Yb}$-$^{7}{\\rm Li}$ mixture\nin the 3D lattice give access to the $^{174}{\\rm Yb}$ Mott-insulator structure.\nGround state inter-species scattering lengths are determined to be $|a_{\\rm\nbg}(^{174}{\\rm Yb}$-$^{7}{\\rm Li})|=(1.11 \\pm 0.17)~{\\rm nm}$ and $|a_{\\rm\nbg}(^{173}{\\rm Yb}$-$^{7}{\\rm Li})|=(1.16 \\pm 0.18)~{\\rm nm}$. The formation\nand characterization of an ultracold $^{173}{\\rm Yb}$-$^{7}{\\rm Li}$ mixture is\na first step towards a possible realization of a topological $p_x + i\\,p_y$\nsuperfluid in this system."
    },
    {
        "anchor": "Deconfining disordered phase in two-dimensional quantum link models: We explore the ground-state physics of two-dimensional spin-$1/2$ $U(1)$\nquantum link models, one of the simplest non-trivial lattice gauge theories\nwith fermionic matter within experimental reach for quantum simulations.\nWhereas in the large mass limit we observe Ne\\'el-like vortex-antivortex and\nstriped crystalline phases, for small masses there is a transition from the\nstriped phases into a disordered phase whose properties resemble those at the\nRokhsar-Kivelson point of the quantum dimer model. This phase is characterized\non ladders by boundary Haldane-like properties, such as vanishing parity and\nfinite string ordering. Moreover, from studies of the string tension between\ngauge charges, we find that whereas the stripe phases are confined, the novel\ndisordered phase present clear indications of being deconfined. Our results\nopen exciting perspectives of studying highly non-trivial physics in quantum\nsimulators, such as spin-liquid behavior and confinement-deconfinement\ntransitions, without the need of explicitly engineering plaquette terms.",
        "positive": "Universal Vortex Statistics and Stochastic Geometry of Bose-Einstein\n  Condensation: The cooling of a Bose gas in finite time results in the formation of a\nBose-Einstein condensate that is spontaneously proliferated with vortices. We\npropose that the vortex spatial statistics is described by a homogeneous\nPoisson point process (PPP) with a density dictated by the Kibble-Zurek\nmechanism (KZM). We validate this model using numerical simulations of the\ntwo-dimensional stochastic Gross-Pitaevskii equation (SGPE) for both a\nhomogeneous and a hard-wall trapped condensate. The KZM scaling of the average\nvortex number with the cooling rate is established along with the universal\ncharacter of the vortex number distribution. The spatial statistics between\nvortices is characterized by analyzing the two-point defect-defect correlation\nfunction, the corresponding spacing distributions, and the random tessellation\nof the vortex pattern using the Voronoi cell area statistics. Combining the PPP\ndescription with the KZM, we derive universal theoretical predictions for each\nof these quantities and find them in agreement with the SGPE simulations. Our\nresults establish the universal character of the spatial statistics of\npoint-like topological defects generated during a continuous phase transition\nand the associated stochastic geometry."
    },
    {
        "anchor": "Efimov Resonances in Ultracold Quantum Gases: Ultracold atomic gases have developed into prime systems for experimental\nstudies of Efimov three-body physics and related few-body phenomena, which\noccur in the universal regime of resonant interactions. In the last few years,\nmany important breakthroughs have been achieved, confirming basic predictions\nof universal few-body theory and deepening our understanding of such systems.\nWe review the basic ideas along with the fast experimental developments of the\nfield, focussing on ultracold cesium gases as a well-investigated model system.\nTriatomic Efimov resonances, atom-dimer Efimov resonances, and related\nfour-body resonances are discussed as central observables. We also present some\nnew observations of such resonances, supporting and complementing the set of\navailable data.",
        "positive": "A Fermi-Hubbard Optical Tweezer Array: We use lithium-6 atoms in an optical tweezer array to realize an eight-site\nFermi-Hubbard chain near half filling. We achieve single site detection by\ncombining the tweezer array with a quantum gas microscope. By reducing disorder\nin the energy offsets to less than the tunneling energy, we observe Mott\ninsulators with strong antiferromagnetic correlations. The measured spin\ncorrelations allow us to put an upper bound on the entropy of\n0.26(4)$k_\\mathrm{B}$ per atom, comparable to the lowest entropies achieved\nwith optical lattices. Additionally, we establish the flexibility of the\ntweezer platform by initializing atoms on one tweezer and observing tunneling\ndynamics across the array for different 1D geometries."
    },
    {
        "anchor": "Squeezing Bose-Bose liquid drops: We explore ultradilute Bose-Bose liquid droplets squeezed by an external\nharmonic potential in one spatial direction. Our theoretical study is based on\na functional that is built using quantum Monte Carlo results of the bulk phase\nand incorporates finite-range effects. A characteristic feature of these drops\nis the existence of a critical atom number, that is the minimum number of\nparticles to have a many-body bound state. We report results on the critical\natom numbers for different magnetic fields and applying confinement strengths\ntowards a quasi-two-dimensional setup. In the regime where the local density\napproximation is expected to be valid, we find that the critical atom number\ndecreases linearly with the harmonic oscillator length of the confining\npotential. With the largest squeezing explored in our work, we predict stable\ndrops at the level of one thousand atoms. Our functional reduces the critical\nnumbers for any confinement and applied magnetic field with respect to the\nestimations based on the Lee-Huang-Yang model. We observe saturated drops when\nthe number of atoms in the drop is much larger than the critical value, their\ncentral density being higher for the quantum Monte Carlo functional than for\nthe Lee-Huang-Yang one.",
        "positive": "Universal scaling of unequal-time correlation functions in ultracold\n  Bose gases far from equilibrium: We explore the far-from-equilibrium dynamics of Bose gases in a universal\nregime associated to nonthermal fixed points. While previous investigations\nconcentrated on scaling functions and exponents describing equal-time\ncorrelations, we compute the additional scaling functions and dynamic exponent\n$z$ characterizing the frequency dependence or dispersion from unequal-time\ncorrelations. This allows us to compare the characteristic condensation and\ncorrelation times from a finite-size scaling analysis depending on the system's\nvolume."
    },
    {
        "anchor": "Topological atom optics and beyond with knotted quantum wavefunctions: Atom optics demonstrates optical phenomena with coherent matter waves,\nproviding a foundational connection between light and matter. Significant\nadvances in optics have followed the realisation of structured light fields\nhosting complex singularities and topologically non-trivial characteristics.\nHowever, analogous studies are still in their infancy in the field of atom\noptics. Here, we investigate and experimentally create knotted quantum\nwavefunctions in spinor Bose--Einstein condensates which display non-trivial\ntopologies. In our work we construct coordinated orbital and spin rotations of\nthe atomic wavefunction, engineering a variety of discrete symmetries in the\ncombined spin and orbital degrees of freedom. The structured wavefunctions that\nwe create map to the surface of a torus to form torus knots, M\\\"obius strips,\nand a twice-linked Solomon's knot. In this paper we demonstrate striking\nconnections between the symmetries and underlying topologies of multicomponent\natomic systems and of vector optical fields--a realization of topological\natom-optics.",
        "positive": "Searching for the Kardar-Parisi-Zhang phase in microcavity polaritons: Recent approximate analytical work has suggested that, at certain values of\nthe external pump, the optical parametric oscillator (OPO) regime of\nmicrocavity polaritons may provide a long sought realisation of\nKardar-Parisi-Zhang (KPZ) physics in 2D. Here, by solving the full microscopic\nmodel numerically using the truncated Wigner method, we prove that this\npredicted KPZ phase for OPO is robust against the appearance of vortices or\nother effects. For those pump strengths, spatial correlations in the direction\nperpendicular to the pump, and the distribution of phase fluctuations, match\nclosely to the forms characteristic of the KPZ universality. This strongly\nindicates the viability of observing KPZ behaviour in future polariton OPO\nexperiments."
    },
    {
        "anchor": "Antiferromagnetism in a bosonic mixture of rubidium ($^{87}$Rb) and\n  potassium ($^{41}$K): We simulate the experimental possibility of observing the antiferromagnetic\n(AF) order in the bosonic mixtures of rubidium ($^{87}$Rb) and potassium\n($^{41}$K) in a two-dimensional optical lattice in the presence of harmonic\nconfinement. By tuning the interspecies interactions and the lattice heights we\nhave found the ground states, within the mean-field approximation, that\ninterpolate from the phase separation to the AF order. For a moderate lattice\nheight the coexistence of the Mott and AF phase is possible for the Rb atoms\nwhile the K atoms remain in the AF-superfluid phase. This observation may\nprovide an experimental feasibility to hitherto unobserved AF order for\n$^{87}$Rb - $^{41}$K mixture.",
        "positive": "Bosonic Weyl excitations induced by $p$-orbital interactions in a cubic\n  optical lattice: Weyl points exist in a fascinating topological state of matter with linear\nband crossings analogous to magnetic monopoles. Tremendous efforts have been\ndevoted to investigate fermionic topological matters with Weyl points in the\nsingle-particle band dispersion. It remains elusive for realizing\ninteraction-induced Weyl points, especially for bosons. Motivated by recent\nexperimental progress in ultracold atoms, we propose a scheme to create Weyl\npoints for Bogoliubov excitations of a bosonic superfluid in a\nthree-dimensional cubic optical lattice. The unique design of the lattice leads\nto interaction-induced time-reversal symmetry breaking for a $p$-orbital\nsuperfluid, which in turn induces Weyl Bogoliubov excitations. Analogous to\nWeyl semimetals of electronic systems, the superfluid also support\ntopologically protected edge modes due to the bulk-boundary correspondence."
    },
    {
        "anchor": "Observation of coherent oscillations in association of dimers from a\n  thermal gas of ultracold atoms: We report the observation of coherent oscillations in conversion efficiency\nof weakly-bound dimers formed from a thermal gas of ultracold atoms. Finite\nthermal energy of the gas causes loss of coherence when a broad continuum is\nresonantly coupled to a discrete bound state. Restoration of the coherence can\nbe achieved through non-adiabatic transitions of the dressed molecular energy\nlevel that are induced by a strong modulation pulse with fast envelope\ndynamics. Conditions to observe coherent oscillations are verified, and control\nof their properties is demonstrated. The main experimental findings are\nsupported by theoretical modeling and numerical calculations. The observed\nresults may lead to a renewed interest in general studies of a discrete energy\nlevel coupled to a broadband continuum when the properties of both are fully\ncontrolled.",
        "positive": "Exploring quantum phase slips in 1D bosonic systems: Quantum phase slips, i.e the primary excitations in one-dimensional\nsuperfluids at low temperature, have been well characterized in most\ncondensed-matter systems, with the notable exception of ultracold quantum\ngases. Here we present our experimental investigation of the dissipation in\nonedimensional Bose superfluids flowing along a periodic potential, which show\nsignatures of the presence of quantum phase slips. In particular, by\ncontrolling the velocity of the superfluid and the interaction between the\nbosons we are apparently able to drive a crossover from a regime of thermal\nphase slips into a regime of quantum phase slips. Achieving a good control of\nquantum phase slips in ultracold quantum gases requires to keep under control\nother phenomena such as the breaking of superfluidity at the critical velocity\nor the appearance of a Mott insulator in the strongly correlated regime. Here\nwe show our current results in these directions."
    },
    {
        "anchor": "Energy spectrum of harmonically trapped two-component Fermi gases:\n  Three- and Four-Particle Problem: Trapped two-component Fermi gases allow for the investigation of the\nso-called BCS-BEC crossover by tuning the interspecies atom-atom $s$-wave\nscattering length scattering $a^{(aa)}$ from attractive to repulsive, including\nvanishing and infinitely large values. Here, we numerically determine the\nenergy spectrum of the equal-mass spin-balanced four-fermion system---the\nsmallest few-particle system that exhibits BCS-BEC crossover-like behavior---as\na function of $a^{(aa)}$ using the stochastic variational approach. For\ncomparative purposes, we also treat the two- and three-particle systems. States\nwith vanishing and finite total angular momentum as well as with natural and\nunnatural parity are considered. In addition, the energy spectrum of\nweakly-attractive and weakly-repulsive gases is characterized by employing a\nperturbative framework that utilizes hyperspherical coordinates. The\nhyperspherical coordinate approach allows for the straightforward assignment of\nquantum numbers and furthermore provides great insights into the\nstrongly-interacting unitary regime.",
        "positive": "Dynamics of Vortex Dipoles in Confined Bose-Einstein Condensates: We present a systematic theoretical analysis of the motion of a pair of\nstraight counter-rotating vortex lines within a trapped Bose-Einstein\ncondensate. We introduce the dynamical equations of motion, identify the\nassociated conserved quantities, and illustrate the integrability of the\nensuing dynamics. The system possesses a stationary equilibrium as a special\ncase in a class of exact solutions that consist of rotating guiding-center\nequilibria about which the vortex lines execute periodic motion; thus, the\ngeneric two-vortex motion can be classified as quasi-periodic. We conclude with\nan analysis of the linear and nonlinear stability of these stationary and\nrotating equilibria."
    },
    {
        "anchor": "Nonlinear waves in coherently coupled Bose-Einstein condensates: We consider a quasi-one-dimensional two-component Bose-Einstein condensate\nsubject to a coherent coupling between its components, such as realized in\nspin-orbit coupled condensates. We study how nonlinearity modifies the dynamics\nof the elementary excitations. The spectrum has two branches which are affected\nin different ways. The upper branch experiences a modulational instability\nwhich is stabilized by a long wave-short wave resonance with the lower branch.\nThe lower branch is stable. In the limit of weak nonlinearity and small\ndispersion it is described by a Korteweg-de Vries equation or by the Gardner\nequation, depending on the value of the parameters of the system.",
        "positive": "Drag force on an impurity below the superfluid critical velocity in a\n  quasi-one-dimensional Bose-Einstein condensate: The existence of frictionless flow below a critical velocity for obstacles\nmoving in a superfluid is well established in the context of the mean-field\nGross-Pitaevskii theory. We calculate the next order correction due to quantum\nand thermal fluctuations and find a non-zero force acting on a delta-function\nimpurity moving through a quasi-one-dimensional Bose-Einstein condensate at all\nsubcritical velocities and at all temperatures. The force occurs due to an\nimbalance in the Doppler shifts of reflected quantum fluctuations from either\nside of the impurity. Our calculation is based on a consistent extension of\nBogoliubov theory to second order in the interaction strength, and finds new\nanalytical solutions to the Bogoliubov-de Gennes equations for a gray soliton.\nOur results raise questions regarding the quantum dynamics in the formation of\npersistent currents in superfluids."
    },
    {
        "anchor": "Quantum Adiabatic Doping for Atomic Fermi-Hubbard Quantum Simulations: There have been considerable research efforts devoted to quantum simulations\nof Fermi-Hubbard model with ultracold atoms loaded in optical lattices. In such\nexperiments, the antiferromagnetically ordered quantum state has been achieved\nat half filling in recent years. The atomic lattice away from half filling is\nexpected to host d-wave superconductivity, but its low temperature phases have\nnot been reached. In a recent work, we proposed an approach of incommensurate\nquantum adiabatic doping, using quantum adiabatic evolution of an\nincommensurate lattice for preparation of the highly correlated many-body\nground state of the doped Fermi-Hubbard model starting from a unit-filling band\ninsulator. Its feasibility has been demonstrated with numerical simulations of\nthe adiabatic preparation for certain incommensurate particle-doping fractions,\nwhere the major problem to circumvent is the atomic localization in the\nincommensurate lattice. Here we carry out a systematic study of the quantum\nadiabatic doping for a wide range of doping fractions from particle-doping to\nhole-doping, including both commensurate and incommensurate cases. We find that\nthere is still a localization-like slowing-down problem at commensurate\nfillings, and that it becomes less harmful in the hole-doped regime. With\ninteractions, the adiabatic preparation is found to be more efficient for that\ninteraction effect destabilizes localization. For both free and interacting\ncases, we find the adiabatic doping has better performance in the hole-doped\nregime than the particle-doped regime. We also study adiabatic doping starting\nfrom the half-filling Mott insulator, which is found to be more efficient for\ncertain filling fractions.",
        "positive": "Static kinks in chains of interacting atoms: We theoretically analyse the equation of topological solitons in a chain of\nparticles interacting via a repulsive power-law potential and confined by a\nperiodic lattice. Starting from the discrete model, we perform a gradient\nexpansion and obtain the kink equation in the continuum limit for a power law\nexponent $n \\ge 1$. The power-law interaction modifies the sine-Gordon\nequation, giving rise to a rescaling of the coefficient multiplying the second\nderivative (the kink width) and to an additional integral term. We argue that\nthe integral term does not affect the local properties of the kink, but it\ngoverns the behaviour at the asymptotics. The kink behaviour at the center is\ndominated by a sine-Gordon equation and its width tends to increase with the\npower law exponent. When the interaction is the Coulomb repulsion, in\nparticular, the kink width depends logarithmically on the chain size. We define\nan appropriate thermodynamic limit and compare our results with existing\nstudies performed for infinite chains. Our formalism allows one to\nsystematically take into account the finite-size effects and also slowly\nvarying external potentials, such as for instance the curvature in an ion trap."
    },
    {
        "anchor": "Many-body physics in two-component Bose-Einstein condensates in a\n  cavity: fragmented superradiance and polarization: We consider laser-pumped one-dimensional two-component bosons in a parabolic\ntrap embedded in a high-finesse optical cavity. Above a threshold pump power,\nthe photons that populate the cavity modify the effective atom trap and mediate\na coupling between the two components of the Bose-Einstein condensate. We\ncalculate the ground state of the laser-pumped system and find different stages\nof self-organization depending on the power of the laser. The modified\npotential and the laser-mediated coupling between the atomic components give\nrise to rich many-body physics: an increase of the pump power triggers a\nself-organization of the atoms while an even larger pump power causes\ncorrelations between the self-organized atoms -- the BEC becomes fragmented and\nthe reduced density matrix acquires multiple macroscopic eigenvalues. In this\nfragmented superradiant state, the atoms can no longer be described as\ntwo-level systems and the mapping of the system to the Dicke model breaks down.",
        "positive": "Collective excitations of a spherical ultradilute quantum droplet: In three dimensions, exotic new state of matter of self-bound ultradilute\nquantum droplets can be realized in free space, when the mean-field attraction\n(i.e., with mean-field energy $E_{\\textrm{MF}}\\propto-n^{2}$ at the density\n$n$) is balanced by the repulsive beyond-mean-field quantum fluctuations (i.e.,\n$E_{\\textrm{BMF}}\\propto n^{2+\\gamma}$). The parameter $\\gamma>0$ typically\ntakes the value $1/2$ if we consider the Lee-Huang-Yang (LHY) energy\nfunctional, but it can vary when the beyond-LHY-effect becomes important or the\nthree-body interaction becomes dominant. Here, we theoretically investigate how\ncollective excitations of a three-dimensional quantum droplet are affected by\nthe parameter $\\gamma$ and a weak harmonic trapping potential, both of which\ncould be tuned in experiments. We use both the approximate approach based on a\nGaussian variational ansatz and the exact numerical solution of the Bogoliubov\nequations resulting from the linearized time-dependent extended\nGross-Pitaevskii equation. We show that one of the key features of quantum\ndroplets, i.e., the existence of the surface modes with dispersion relation\n$\\omega_{s}\\propto k^{3/2}$ is very robust with respect to the changes either\nin the parameter $\\gamma$ or in the harmonic trapping potential. We predict the\nexcitation spectrum of the droplet realized by binary $^{39}$K mixtures under\nthe typical experimental conditions, which might be readily measured in current\ncold-atom laboratories."
    },
    {
        "anchor": "Composite boson description of a low density gas of excitons: Ground state properties of a fermionic Coulomb gas are calculated using the\nfixed-node diffusion Monte Carlo method. The validity of the composite boson\ndescription is tested for different densities. We extract the exciton-exciton\n$s$-wave scattering length by solving the four-body problem in a harmonic trap\nand mapping the energy to that of two trapped bosons. The equation of state is\nconsistent with the Bogoliubov theory for composite bosons interacting with the\nobtained $s$-wave scattering length. The perturbative expansion at low density\nhas contributions physically coming from (a) exciton binding energy, (b)\nmean-field Gross-Pitaevskii interaction between excitons, (c) quantum depletion\nof the excitonic condensate (Lee-Huang-Yang terms for composite bosons). In\naddition, for low densities we find a good agreement with the Bogoliubov\nbosonic theory for the condensate fraction of excitons. The equation of state\nin the opposite limit of large density is found to be well described by the\nperturbative theory including (a) mixture of two ideal Fermi gases (b) exchange\nenergy. We find that for low densities both energetic and coherent properties\nare correctly described by the picture of composite bosons (excitons).",
        "positive": "General relations for quantum gases in two and three dimensions.\n  Two-component fermions: We derive exact relations for $N$ spin-1/2 fermions with zero-range or\nshort-range interactions, in continuous space or on a lattice, in $2D$ or in\n$3D$, in any external potential. Some of them generalize known relations\nbetween energy, momentum distribution $n(k)$, pair distribution function\n$g^{(2)}(r)$, derivative of the energy with respect to the scattering length\n$a$. Expressions are found for the second order derivative of the energy with\nrespect to $1/a$ (or to $\\ln a$ in $2D$). Also, it is found that the leading\nenergy corrections due to a finite interaction range, are proportional to the\neffective range $r\\_e$ in $3D$ (and to $r\\_e^2$ in $2D$) with exprimable\nmodel-independent coefficients, that give access to the subleading short\ndistance behavior of $g^{(2)}(r)$ and to the subleading $1/k^6$ tail of $n(k)$.\nThis applies to lattice models for some magic dispersion relations, an example\nof which is given. Corrections to exactly solvable two-body and three-body\nproblems are obtained. For the trapped unitary gas, the variation of the\nfinite-$1/a$ and finite $r\\_e$ energy corrections within each $SO(2,1)$ energy\nladder is obtained; it gives the frequency shift and the collapse time of the\nbreathing mode. For the bulk unitary gas, we compare to fixed-node Monte Carlo\ndata, and we estimate the experimental uncertainty on the Bertsch parameter due\nto a finite $r\\_e$."
    },
    {
        "anchor": "Pairing-gap, pseudo-gap, and no-gap phases in the radio-frequency\n  spectra of a trapped unitary 6Li gas: Radio frequency spectra of a trapped unitary 6Li gas are reported and\nanalyzed in terms of a theoretical approach that includes both final-state and\ntrap effects. Final-state effects play a crucial role in evidencing two main\npeaks both above and below the critical temperature Tc as being associated with\ntwo distinct phases that reside in different trap regions. These are the\npairing-gap and pseudo-gap phases below Tc, which evolve into the pseudo-gap\nand no-gap phases above Tc. In this way, a long standing puzzle about the\ninterpretation of rf spectra for 6Li in a trap is solved.",
        "positive": "Directed Transport of Atoms in a Hamiltonian Quantum Ratchet: We demonstrate the operation of a quantum ratchet in the absence of\ndissipative processes within the observation time (Hamiltonian regime). An\natomic rubidium Bose-Einstein condensate is exposed to a sawtooth-like optical\nlattice potential, whose amplitude is periodically modulated in time. The\nratchet transport arises from broken spatiotemporal symmetries of the driven\npotential, resulting in a desymmetrisation of transporting Eigenstates (Floquet\nstates). The measured atomic current oscillates around a non-zero stationary\nvalue at longer observation times, shows resonances at positions determined by\nthe photon recoil and depends on the initial phase of the drive, providing\ndifferent lines of evidence for the full quantum character of the ratchet\ntransport. The results provide a proof of principle demonstration of a quantum\nmotor."
    },
    {
        "anchor": "Two-dimensional expansion of a condensed dense Bose gas: We study the expansion dynamics of a condensate in a strongly interacting\nBose gas in the presence of an obstacle. Our focus is on the generation of\nshock waves after the Bose gas has passed the obstacle. The strongly\ninteracting Bose gas is described in the slave-boson representation. A\nsaddle-point approximation provides a nonlinear equation of motion for the\nmacroscopic wave function, analogous to the Gross-Pitaevskii equation of a\nweakly interacting Bose gas but with different nonlinearity. We compare the\nresults with the Gross-Pitaevskii dynamics of a weakly interacting Bose gas and\nfind a similar behavior with a slower behavior of the strongly interacting\nsystem.",
        "positive": "Disorder-induced Localization in a Strongly Correlated Atomic Hubbard\n  Gas: We observe the emergence of a disorder-induced insulating state in a strongly\ninteracting atomic Fermi gas trapped in an optical lattice. This closed quantum\nsystem free of a thermal reservoir realizes the disordered Fermi-Hubbard model,\nwhich is a minimal model for strongly correlated electronic solids. In\nmeasurements of disorder-induced localization obtained via mass transport, we\ndetect interaction-driven delocalization and localization that persists as the\ntemperature of the gas is raised. These behaviors are consistent with many-body\nlocalization, which is a novel paradigm for understanding localization in\ninteracting quantum systems at non-zero temperature."
    },
    {
        "anchor": "Variational methods with coupled Gaussian functions for Bose-Einstein\n  condensates with long-range interactions. I. General concept: The variational method of coupled Gaussian functions is applied to\nBose-Einstein condensates with long-range interactions. The time-dependence of\nthe condensate is described by dynamical equations for the variational\nparameters. We present the method and analytically derive the dynamical\nequations from the time-dependent Gross-Pitaevskii equation. The stability of\nthe solutions is investigated using methods of nonlinear dynamics. The concept\npresented in this paper will be applied to Bose-Einstein condensates with\nmonopolar 1/r and dipolar 1/r^3 interaction in the subsequent paper [S. Rau et\nal., Phys. Rev. A, submitted], where we will present a wealth of new phenomena\nobtained by using the ansatz with coupled Gaussian functions.",
        "positive": "Quantum Vortex Formation in the \"Rotating Bucket'' Experiment with\n  Polariton Condensates: The appearance of quantised vortices in the classical ``rotating bucket''\nexperiments of liquid helium and ultracold dilute gases provides the means for\nfundamental and comparative studies of different superfluids. Here, we realize\nthe ``rotating bucket'' experiment for optically trapped quantum fluid of light\nbased on exciton-polariton Bose-Einstein condensate in semiconductor\nmicrocavity. We utilise the beating note of two frequency-stabilized\nsingle-mode lasers to generate an asymmetric time-periodic rotating,\nnon-resonant excitation profile that both injects and stirs the condensate\nthrough its interaction with a background exciton reservoir. The pump-induced\nexternal rotation of the condensate results in the appearance of a co-rotating\nquantised vortex. We investigate the rotation-frequency dependence and reveal\nthe range of stirring frequencies (from 1 to 4 GHz) which favors quantised\nvortex formation. We describe the phenomenology using the generalised\nGross-Pitaevskii equation. Our results enable the study of polariton\nsuperfluidity on a par with other superfluids, as well as deterministic,\nall-optical control over structured nonlinear light."
    },
    {
        "anchor": "Thermalization of Atom-Molecule Bose Gases in a Double-Well Potential: We study the non-equiliribium dynamics of atom-molecule Bose gases in a\ndouble-well potential. In this system, the internal atom-molecule tunneling has\nsignificant influence on the dynamics. We investigate the periodicity of\ndynamics by studying the level statistics of the quantum system. We find that\nchaotic energy eigenstates arise from the competition between the interwell and\nthe atom-molecule internal tunnelings. Furthermore, we show that the physical\nquantities relax to the microcanonical averages in the full-quantum dynamics\nwhen the system is chaotic. This thermalization is caused by the verification\nof eigenstate thermalization hypothesis (ETH). We show numerically that the\nonset of ETH occurs simultaneously with that of chaos. In addition, we show\nthat the energy eigenstates become to be exponentially localized states\nsimultaneously with the onset of chaos.",
        "positive": "Equation of State of Ultracold Fermions in the 2D BEC-BCS Crossover\n  Region: We report the experimental measurement of the equation of state of a\ntwo-dimensional Fermi gas with attractive s-wave interactions throughout the\ncrossover from a weakly coupled Fermi gas to a Bose gas of tightly bound dimers\nas the interaction strength is varied. We demonstrate that interactions lead to\na renormalization of the density of the Fermi gas by several orders of\nmagnitude. We compare our data near the ground state and at finite temperature\nto predictions for both fermions and bosons from Quantum Monte Carlo\nsimulations and Luttinger-Ward theory. Our results serve as input for\ninvestigations of close-to-equilibrium dynamics and transport in the\ntwo-dimensional system."
    },
    {
        "anchor": "Drive Induced Delocalization in Aubry-Andr\u00e9 Model: Motivated by the recent experiment by Bordia et al [Nat. Phys. 13, 460\n(2017)], we study single particle delocalization phenomena of Aubry-Andr\\'e\n(AA) model subjected to periodic drives. In two distinct cases we construct an\nequivalent classical description to illustrate that the drive induced\ndelocalization phenomena stems from an instability and onset of chaos in the\nunderlying dynamics. In the first case we analyze the delocalization and the\nthermalization in a time modulated AA potential with respect to driving\nfrequency and demonstrate that there exists a threshold value of the amplitude\nof the drive. In the next example, we show that the periodic modulation of the\nhopping amplitude leads to an unusual effect on delocalization with a\nnon-monotonic dependence on the driving frequency. Within a window of such\ndriving frequency a delocalized Floquet band with mobility edge appears,\nexhibiting multifractality in the spectrum as well as in the Floquet\neigenfunctions. Finally, we explore the effect of interaction and discuss how\nthe results of the present analysis can be tested experimentally.",
        "positive": "Phase diagram of one-dimensional earth-alkaline cold fermionic atoms: The phase diagram of one-dimensional earth-alkaline fermionic atoms and\nytterbium 171 atoms is investigated by means of a low-energy approach and\ndensity-matrix renormalization group calculations. For incommensurate filling,\nfour gapless phases with a spin gap are found and consist of two\nsuperconducting instabilities and two coexisting bond and charge density-waves\ninstabilities. In the half-filled case, seven Mott-insulating phases arise with\nthe emergence of four non-degenerate phases with exotic hidden orderings."
    },
    {
        "anchor": "Quantum and thermal fluctuations in bosonic Josephson junctions: We use the Bose-Hubbard Hamiltonian to study quantum fluctuations in\ncanonical equilibrium ensembles of bosonic Josephson junctions at relatively\nhigh temperatures, comparing the results for finite particle numbers to the\nclassical limit that is attained as $N$ approaches infinity. We consider both\nattractive and repulsive atom-atom interactions, with especial focus on the\nbehavior near the T=0 quantum phase transition that occurs, for large enough\n$N$, when attractive interactions surpass a critical level. Differences between\nBose-Hubbard results for small $N$ and those of the classical limit are quite\nsmall even when $N \\sim 100$, with deviations from the limit diminishing as\n1/N.",
        "positive": "Resonantly enhanced superconductivity mediated by spinor condensates: Achieving strong interactions in fermionic many-body systems is a major theme\nof research in condensed matter physics. It is well-known that interactions\nbetween fermions can be mediated through a bosonic medium, such as a phonon\nbath or Bose-Einstein condensate (BEC). Here, we show that such induced\nattraction can be resonantly enhanced when the bosonic medium is a\ntwo-component spinor BEC. The strongest interaction is achieved by tuning the\nboson-boson scattering to the quantum critical spinodal point of the BEC where\nthe sound velocity vanishes. The fermion pairing gap and the superconducting\ncritical temperature can thus be dramatically enhanced. We propose two\nexperimental realizations of this scenario, with exciton-polariton systems in\ntwo-dimensional semiconductors and ultracold atomic Bose-Fermi mixtures."
    },
    {
        "anchor": "Quantum Bubbles in Microgravity: The recent developments of microgravity experiments with ultracold atoms have\nproduced a relevant boost in the study of shell-shaped ellipsoidal\nBose-Einstein condensates. For realistic bubble-trap parameters, here we\ncalculate the critical temperature of Bose-Einstein condensation, which, if\ncompared to the one of the bare harmonic trap with the same frequencies, shows\na strong reduction. We simulate the zero-temperature density distribution with\nthe Gross-Pitaevskii equation, and we study the free expansion of the hollow\ncondensate. While part of the atoms expands in the outward direction, the\ncondensate self-interferes inside the bubble trap, filling the hole in\nexperimentally observable times. For a mesoscopic number of particles in a\nstrongly interacting regime, for which more refined approaches are needed, we\nemploy quantum Monte Carlo simulations, proving that the nontrivial topology of\na thin shell allows superfluidity. Our work constitutes a reliable benchmark\nfor the forthcoming scientific investigations with bubble traps.",
        "positive": "First-order phase transition and anomalous hysteresis of Bose gases in\n  optical lattices: We study the first-order quantum phase transitions of Bose gases in optical\nlattices. A special emphasis is placed on an anomalous hysteresis behavior, in\nwhich the phase transition occurs in a unidirectional way and a hysteresis loop\ndoes not form. We first revisit the hardcore Bose-Hubbard model with\ndipole-dipole interactions on a triangular lattice to analyze accurately the\nground-state phase diagram and the hysteresis using the cluster mean-field\ntheory combined with cluster-size scaling. Details of the anomalous hysteresis\nare presented. We next consider the two-component and spin-1 Bose-Hubbard\nmodels on a hypercubic lattice and show that the anomalous hysteresis can\nemerge in these systems as well. In particular, for the former model, we\ndiscuss the experimental feasibility of the first-order transitions and the\nassociated hysteresis. We also explain an underlying mechanism of the anomalous\nhysteresis by means of the Ginzburg-Landau theory. From the given cases, we\nconclude that the anomalous hysteresis is a ubiquitous phenomenon of systems\nwith a phase region of lobe shape that is surrounded by the first-order\nboundary."
    },
    {
        "anchor": "Reply to the correspondence of Drummond and Brand [arXiv:1610.07633]: In their correspondence [arXiv:1610.07633] Drummond and Brand criticize our\nwork [Nature Physics 12, 451-454 (2016) http://dx.doi.org/10.1038/nphys3631].\nWe show that their criticism is misleading and unfounded.",
        "positive": "Data-driven discovery of statistically relevant information in quantum\n  simulators: Quantum simulators offer powerful means to investigate strongly correlated\nquantum matter. However, interpreting measurement outcomes in such systems\nposes significant challenges. Here, we present a theoretical framework for\ninformation extraction in synthetic quantum matter, illustrated for the case of\na quantum quench in a spinor Bose-Einstein condensate experiment. Employing\nnon-parametric unsupervised learning tools that provide different measures of\ninformation content, we demonstrate a system-agnostic approach to identify\ndominant degrees of freedom. This enables us to rank operators according to\ntheir relevance, akin to effective field theory. To characterize the\ncorresponding effective description, we then explore the intrinsic dimension of\ndata sets as a measure of the complexity of the dynamics. This reveals a\nsimplification of the data structure, which correlates with the emergence of\ntime-dependent universal behavior in the studied system. Our assumption-free\napproach can be immediately applied in a variety of experimental platforms."
    },
    {
        "anchor": "Improved variational approach to the two-site Bose-Hubbard model: An improved variational ansatz is proposed to capture the most striking\nproperties of the ground state of a slightly biased attractive two-site\nBose-Hubbard Hamiltonian. Our ansatz, albeit its simplicity, is found to\ncapture well the exact properties of the ground state for a wide variety of\nmodel parameters, in particular the fragmentation occurring before the\nformation of cat-like states and also the formation of strongly correlated\ncat-like states.",
        "positive": "Biexciton as a Feshbach resonance and Bose-Einstein condensation of\n  paraexcitons in Cu$_{2}$O: Paraexcitons, the lowest energy exciton states in Cu$_{2}$O, have been\nconsidered a good system for realizing exciton Bose-Einstein condensation\n(BEC). The fact that their BEC has not been attained so far is attributed to a\ncollision-induced loss, whose nature remains unclear. To understand collisional\nproperties of cold paraexcitons governing their BEC, we perform here a\nmicroscopic consideration of the s-wave paraexciton-paraexciton scattering. We\nshow its two-channel character with incoming paraexcitons coupled to a\nbiexciton, which is a Feshbach resonance producing a paraexciton loss and a\ndiminution of their background scattering length. The former elucidates the\nmechanism of the long-observed paraexciton loss, which turns out to be\ninefficient at temperatures near one Kelvin and below, whereas the latter makes\nthe paraexciton scattering length in strain-induced traps negative under stress\nexceeding a critical value. Our rough estimates give this value of order of one\nkilobar, hence already moderate stress creates a serious obstacle to attaining\na stable paraexciton BEC. Thus our results indicate that BEC of trapped\nparaexcitons might be achieved at a subkelvin temperature, but only under low\nstress."
    },
    {
        "anchor": "$n$-body Correlation of Tonks-Girardeau Gas: For the well-known exponential complexity it is a giant challenge to\ncalculate the correlation function for general many-body wave function. We\ninvestigate the ground state $n$th-order correlation functions of the\nTonks-Girardeau (TG) gases. Basing on the wavefunction of free fermions and\nBose-Fermi mapping method we obtain the exact ground state wavefunction of TG\ngases. Utilizing the properties of Vandermonde determinant and Toeplitz matrix,\nthe $n$th-order correlation function is formulated as $(N-n)$-order Toeplitz\ndeterminant, whose element is the integral dependent on 2$(N-n)$ sign functions\nand can be computed analytically. By reducing the integral on domain $[0,2\\pi]$\ninto the summation of the integral on several independent domains, we obtain\nthe explicit form of the Toeplitz matrix element ultimately. As the\napplications we deduce the concise formula of the reduced two-body density\nmatrix and discuss its properties. The corresponding natural orbitals and their\noccupation distribution are plotted. Furthermore, we give a concise formula of\nthe reduced three-body density matrix and discuss its properties. It is shown\nthat in the successive second measurements, atoms appear in the regions where\natoms populate with the maximum probability in the first measurement.",
        "positive": "Yang monopoles and emergent three-dimensional topological defects in\n  interacting bosons: Yang monopole as a zero-dimensional topological defect has been well\nestablished in multiple fields in physics. However, it remains an intriguing\nquestion to understand interaction effects on Yang monopoles. Here, we show\nthat collective motions of many interacting bosons give rise to exotic\ntopological defects that are distinct from Yang monopoles seen by a single\nparticle. Whereas interactions may distribute Yang monopoles in the parameter\nspace or glue them to a single giant one of multiple charges, three-dimensional\ntopological defects also arise from continuous manifolds of degenerate\nmany-body eigenstates. Their projections in lower dimensions lead to knotted\nnodal lines and nodal rings. Our results suggest that ultracold bosonic atoms\ncan be used to create emergent topological defects and directly measure\ntopological invariant that are not easy to access in solids."
    },
    {
        "anchor": "Excitation spectra of fragmented condensates by linear response: General\n  theory and application to a condensate in a double-well potential: Linear response of simple (i.e., condensed) Bose-Einstein condensates is\nknown to lead to the Bogoliubov- de Gennes equations. Here, we derive linear\nresponse for fragmented Bose-Einstein condensates, i.e., for the case where the\nmany-body wave function is not a product of one, but of several single-particle\nstates (orbitals). Our approach is based on the number-conserving variational\ntime-dependent mean field theory [O. E. Alon, A. I. Streltsov, and L. S.\nCederbaum, Phys. Lett. A 362, 453 (2007)], which describes the time evolution\nof best-mean field states. Correspondingly, we call our linear response theory\nfor fragmented states LR-BMF. In the derivation it follows naturally that\nexcitations are orthogonal to the ground-state orbitals. As applications\nexcitation spectra of Bose-Einstein condensates in double-well potentials are\ncalculated. Both symmetric and asymmetric double-wells are studied for several\ninteraction strengths and barrier heights. The cases of condensed and two-fold\nfragmented ground states are compared. Interestingly, even in such situations\nwhere the response frequencies of the two cases are computed to be close to\neach other, which is the situation for the excitations well below the barrier,\nstriking differences in the density response in momentum space are found. For\nexcitations with an energy of the order of the barrier height, both the\nenergies and the density response of condensed and fragmented systems are very\ndifferent. In fragmented systems there is a class of \"swapped\" excitations\nwhere an atom is transfered to the neighboring well. The mechanism of its\norigin is discussed. In asymmetric wells, the response of a fragmented system\nis purely local (i.e., finite in either one or the other well) with different\nfrequencies for the left and right fragments.",
        "positive": "Stochastic Projected Gross-Pitaevskii equation for spinor and\n  multi-component condensates: A stochastic Gross-Pitaevskii equation is derived for partially condensed\nBose gas systems subject to binary contact interactions. The theory we present\nprovides a classical-field theory suitable for describing dissipative dynamics\nand phase transitions of spinor and multi-component Bose gas systems comprised\nof an arbitrary number of distinct interacting Bose fields. A new class of\ndissipative processes involving distinguishable particle interchange between\ncoherent and incoherent regions of phase-space is identified. The formalism and\nits implications are illustrated for two-component mixtures and spin-1\nBose-Einstein condensates. For systems comprised of atoms of equal mass, with\nthermal reservoirs that are close to equilibrium, the dissipation rates of the\ntheory are reduced to analytical expressions that may be readily evaluated. The\nunified treatment of binary contact interactions presented here provides a\ntheory with broad relevance for quasi-equilibrium and far-from-equilibrium\nBose-Einstein condensates."
    },
    {
        "anchor": "Application of the functional renormalization group to Bose gases: from\n  linear to hydrodynamic fluctuations: We study weakly interacting Bose gases using the functional renormalization\ngroup with a hydrodynamic effective action. We use a scale-dependent\nparametrization of the boson fields that interpolates between a Cartesian\nrepresentation at high momenta and an amplitude-phase one for low momenta. We\napply this to Bose gases in two and three dimensions near the superfluid phase\ntransition where they can be described by statistical O(2) models. We are able\nto give consistent physical descriptions of the infrared regime in both two and\nthree dimensions. In particular, and in contrast to previous studies using the\nfunctional renormalization group, we find a stable superfluid phase at finite\ntemperatures in two dimensions. We compare our results for the superfluid and\nboson densities with Monte-Carlo simulations, and we find they are in\nreasonable agreement.",
        "positive": "An Autonomous Stabilizer for Incompressible Photon Fluids and Solids: We suggest a simple approach to populate photonic quantum materials at\nnon-zero chemical potential and near-zero temperature. Taking inspiration from\nforced evaporation in cold-atom experiments, the essential ingredients for our\nlow-entropy thermal reservoir are (a) inter-particle interactions, and (b)\nenergy-dependent loss. The resulting thermal reservoir may then be coupled to a\nbroad class of Hamiltonian systems to produce low-entropy quantum phases. We\npresent an idealized picture of such a reservoir, deriving the scaling of\nreservoir entropy with system parameters, and then propose several practical\nimplementations using only standard circuit quantum electrodynamics tools, and\nextract the fundamental performance limits. Finally, we explore, both\nanalytically and numerically, the coupling of such a thermalizer to the\nparadigmatic Bose-Hubbard chain, where we employ it to stabilize an $n=1$ Mott\nphase. In this case, the performance is limited by the interplay of dynamically\narrested thermalization of the Mott insulator and finite heat capacity of the\nthermalizer, characterized by its repumping rate. This work explores a new\napproach to preparation of quantum phases of strongly interacting photons, and\nprovides a potential route to topologically protected phases that are difficult\nto reach through adiabatic evolution."
    },
    {
        "anchor": "The dressed molecules theory for the quasi-two-dimensional quantum\n  anomaly: In this work, the dressed molecules theory is used to describe the\ntwo-dimensional quantum anomaly of breathing mode in the recent experimental\nsystem\\cite{Holten2018,Peppler2018}. With the aid of a beyond mean-field,\nGaussian pair fluctuation theory, we employ the dressed molecules states to\ncharacterize the axial excited states and the Feshbach molecular states, and\npropose a complete low energy effective theory. We show that, in the whole\ncrossover from a Bardeen-Cooper-Schrieffer (BCS) superfluid to a Bose-Einstein\ncondensate (BEC), our theory can describe the two-dimensional experimental\nsystems precisely in low energe region. We explain the the puzzling\nexperimental observations of the smaller than expected breathing mode frequency\nperfectly. Our establishment of the dressed molecules theory for 2D fermions is\ncrucial to understand the conformal anomaly in the quasi low-dimensional\nquantum systems.",
        "positive": "Creating and manipulating non-Abelian anyons in cold atom systems using\n  auxiliary bosons: The possibility of realizing bosonic fractional quantum Hall effect in\nultra-cold atomic systems suggests a new route to producing and manipulating\nanyons, by introducing auxiliary bosons of a different species that capture\nquasiholes and thus inherit their non-trivial braiding properties. States with\nlocalized quasiholes at any desired locations can be obtained by annihilating\nthe auxiliary bosons at those locations. We explore how this method can be used\nto generate non-Abelian quasiholes of the Moore-Read Pfaffian state for bosons\nat filling factor $\\nu=1$. We show that a Hamiltonian with an appropriate\nthree-body interaction can produce two-quasihole states in two distinct fusion\nchannels of the topological \"qubit.\" Characteristics of these states that are\nrelated to the non-Abelian nature can be probed and verified by a measurement\nof the effective relative angular momentum of the auxiliary bosons, which is\ndirectly related to their pair distribution function. Moore-Read states of more\nthan two quasiholes can also be produced in a similar fashion. We investigate\nsome issues related to the experimental feasibility of this approach, in\nparticular, how large the systems should be for a realization of this physics\nand to what extent this physics carries over to systems with the more standard\ntwo-body contact interaction."
    },
    {
        "anchor": "Quasiexact Kondo Dynamics of Fermionic Alkaline-Earth-Like Atoms at\n  Finite Temperatures: A recent experiment has observed the antiferromagnetic interaction between\nthe ground state $^1S_0$ and the metastable state $^3P_0$ of $^{171}$Yb atoms,\nwhich are fermionic. This observation combined with the use of state-dependent\noptical lattices allows for quantum simulation of the Kondo model. We propose\nthat in this Kondo simulator the anomalous temperature dependence of transport,\nnamely the Kondo effect, can be detected through quench dynamics triggered by\nthe shift of a trap potential. For this purpose, we improve the numerical\nefficiency of the minimally entangled typical thermal states (METTS) algorithm\nby applying additional Trotter gates. Using the improved METTS algorithm, we\ncompute the quench dynamics of the one-dimensional Kondo model at finite\ntemperatures quasi-exactly. We find that the center-of-mass motion exhibits a\nlogarithmic suppression with decreasing the temperature, which is a\ncharacteristic feature of the Kondo effect.",
        "positive": "Reply to arXiv:1002.4366, \"Comment on `Motion of an impurity in an\n  ultracold quasi-one-dimensional gas of hard-core bosons`\", by S. Giraud and\n  R. Combescot: In their Comment [1] Giraud and Combescot point out that the contribution to\nthe impurity-boson distribution function $\\rho_{bi}(x-y)$ of a term we dropped\nis not negligible, rather than being negligible in the thermodynamic limit as\nwe had conjectured. We now agree with them, but nevertheless our results for\n$\\rho_{bi}$ are highly accurate for large impurity-boson mass ratio $m_i/m$ and\nremain qualitatively correct for all values of $m_i/m$ and all values of the\nboson-impurity coupling constant."
    },
    {
        "anchor": "Chaos-induced depletion of a Bose-Einstein condensate: The mean-field limit of a bosonic quantum many-body system is described by\n(mostly) non-linear equations of motion which may exhibit chaos very much in\nthe spirit of classical particle chaos, i.e. by an exponential separation of\ntrajectories in Hilbert space with a rate given by a positive Lyapunov exponent\n$\\lambda$. The question now is whether $\\lambda$ imprints itself onto\nmeasurable observables of the underlying quantum many-body system even at\nfinite particle numbers. Using a Bose-Einstein condensate expanding in a\nshallow potential landscape as a paradigmatic example for a bosonic quantum\nmany-body system, we show, that the number of non-condensed particles is\nsubject to an exponentially fast increase, i.e. depletion. Furthermore, we show\nthat the rate of exponential depletion is given by the Lyapunov exponent\nassociated with the chaotic mean-field dynamics. Finally, we demonstrate that\nthis chaos-induced depletion is accessible experimentally through the\nvisibility of interference fringes in the total density after time of flight,\nthus opening the possibility to measure $\\lambda$, and with it, the interplay\nbetween chaos and non-equilibrium quantum matter, in a real experiment.",
        "positive": "BCS-BEC crossover in three-dimensional Fermi gases with spherical\n  spin-orbit coupling: We present a systematic theoretical study of the BCS-BEC crossover problem in\nthree-dimensional atomic Fermi gases at zero temperature with a spherical\nspin-orbit coupling which can be generated by a synthetic non-Abelian gauge\nfield coupled to neutral fermions. Our investigations are based on the path\nintegral formalism which is a powerful theoretical scheme for the study of the\nproperties of the bound state, the superfluid ground state, and the collective\nexcitations in the BCS-BEC crossover. At large spin-orbit coupling, the system\nenters the BEC state of a novel type of bound state (referred to as rashbon)\nwhich possesses a non-trivial effective mass. Analytical results and\ninteresting universal behaviors for various physical quantities at large\nspin-orbit coupling are obtained. Our theoretical predictions can be tested in\nfuture experiments of cold Fermi gases with three-dimensional spherical\nspin-orbit coupling."
    },
    {
        "anchor": "Exact lowest-Landau-level solutions for vortex precession in\n  Bose-Einstein condensates: The Lowest Landau Level (LLL) equation emerges as an accurate approximation\nfor a class of dynamical regimes of Bose-Einstein Condensates (BEC) in\ntwo-dimensional isotropic harmonic traps in the limit of weak interactions.\nBuilding on recent developments in the field of spatially confined extended\nHamiltonian systems, we find a fully nonlinear solution of this equation\nrepresenting periodically modulated precession of a single vortex. Motions of\nthis type have been previously seen in numerical simulations and experiments at\nmoderately weak coupling. Our work provides the first controlled analytic\nprediction for trajectories of a single vortex, suggests new targets for\nexperiments, and opens up the prospect of finding analytic multi-vortex\nsolutions.",
        "positive": "Exact ground-state correlation functions of an atomic-molecular boson\n  conversion model: We study the ground-state properties of an atomic-molecular boson conversion\nmodel through an exact Bethe Ansatz solution. For a certain range of parameter\nchoices, we prove that the ground-state Bethe roots lie on the positive\nreal-axis. We then use a continuum limit approach to obtain a singular integral\nequation characterising the distribution of these Bethe roots. Solving this\nequation leads to an analytic expression for the ground-state energy. The form\nof the expression is consistent with the existence of a line of quantum phase\ntransitions, which has been identified in earlier studies. This line demarcates\na molecular phase from a mixed phase. Certain correlation functions, which\ncharacterise these phases, are then obtained through the Hellmann-Feynman\ntheorem."
    },
    {
        "anchor": "Quantum Phase Transition in the Sub-Ohmic Spin-Boson Model: Extended\n  Coherent-state Approach: We propose a general extended coherent state approach to the qubit (or\nfermion) and multi-mode boson coupling systems. The application to the\nspin-boson model with the discretization of a bosonic bath with arbitrary\ncontinuous spectral density is described in detail, and very accurate solutions\ncan be obtained. The quantum phase transition in the nontrivial sub-Ohmic case\ncan be located by the fidelity and the order-parameter critical exponents for\nthe bath exponents $s<1/2$ can be correctly given by the fidelity\nsusceptibility, demonstrating the strength of the approach.",
        "positive": "Wilson ratio of Fermi gases in one dimension: We calculate the Wilson ratio of the one-dimensional Fermi gas with spin\nimbalance. The Wilson ratio of attractively interacting fermions is solely\ndetermined by the density stiffness and sound velocity of pairs and of excess\nfermions for the two-component Tomonaga-Luttinger liquid (TLL) phase. The ratio\nexhibits anomalous enhancement at the two critical points due to the sudden\nchange in the density of states. Despite a breakdown of the quasiparticle\ndescription in one dimension, two important features of the Fermi liquid are\nretained, namely the specific heat is linearly proportional to temperature\nwhereas the susceptibility is independent of temperature. In contrast to the\nphenomenological TLL parameter, the Wilson ratio provides a powerful parameter\nfor testing universal quantum liquids of interacting fermions in one, two and\nthree dimensions."
    },
    {
        "anchor": "Five-Body Efimov Effect and Universal Pentamer in Fermionic Mixtures: We show that four heavy fermions interacting resonantly with a lighter atom\n(4+1 system) become Efimovian at mass ratio 13.279(2), which is smaller than\nthe corresponding 2+1 and 3+1 thresholds. We thus predict the five-body Efimov\neffect for this system in the regime where any of its subsystem is non-\nEfimovian. For smaller mass ratios we show the existence and calculate the\nenergy of a universal 4+1 pentamer state, which continues the series of the 2+1\ntrimer predicted by Kartavtsev and Malykh and 3+1 tetramer discovered by Blume.\nWe also show that the effective-range correction for the light-heavy\ninteraction has a strong effect on all these states and larger effective ranges\nincrease their tendency to bind.",
        "positive": "Strong coupling treatment of the polaronic system consisting of an\n  impurity in a condensate: The strong coupling treatment of the Fr\\\"ohlich-type polaronic system, based\non a canonical transformation and a standard Landau-Pekar type variational wave\nfunction, is applied to the polaronic system consisting of an impurity in a\ncondensate. Within this approach the Relaxed Excited States are retrieved as a\ntypical polaronic feature in the energy spectrum. For these states we calculate\nthe corresponding effective mass and the minimal coupling constant required for\nthem to occur. The present approach allows to derive approximate expressions\nfor the transition energies between different Relaxed Excited States in a much\nsimpler way than with the full Mori-Zwanzig approach, and with a good accuracy,\nwhich improves with increasing coupling. The transition energies obtained here\ncan be used as the spectroscopic fingerprint for the experimental observation\nof Relaxed Excited States of impurities in a condensate."
    },
    {
        "anchor": "Feshbach resonances and weakly bound molecular states of boson-boson and\n  boson-fermion NaK pairs: We study theoretically magnetically induced Feshbach resonances and\nnear-threshold bound states in isotopic NaK pairs. Our calculations accurately\nreproduce Feshbach spectroscopy data on Na$^{40}$K and explain the origin of\nthe observed multiplets in the p-wave [Phys. Rev. A 85, 051602(R) (2012)]. We\napply the model to predict scattering and bound state threshold properties of\nthe boson-boson Na$^{39}$K and Na$^{41}$K systems. We find that the Na$^{39}$K\nisotopic pair presents broad magnetic Feshbach resonances and favorable\nground-state features for producing non-reactive polar molecules by two-photon\nassociation. Broad s-wave resonances are also predicted for Na$^{41}$K\ncollisions.",
        "positive": "Magnetic field dependence of Raman coupling in Alkali atoms: We calculate the magnetic field dependence of Rabi rates for two-photon\noptical Raman processes in alkali atoms. Due to a decoupling of the nuclear and\nelectronic spins, these rates fall with increasing field. At the typical\nmagnetic fields of alkali atom Feshbach resonances (B\\sim 200G-1200G), the\nRaman rates have the same order of magnitude as their zero field values,\nsuggesting one can combine Raman-induced gauge fields/spin-orbital coupling\nwith strong Feshbach-induced interactions. The exception is $^6$Li, where there\nis a factor of 7 suppression in the Raman coupling, compared to its already\nsmall zero-field value."
    },
    {
        "anchor": "Expansion of matter waves in static and driven periodic potentials: We study the non-equilibrium dynamics of cold atoms held in an optical\nlattice potential. The expansion of an initially confined atom cloud occurs in\ntwo phases: an initial quadratic expansion followed by a ballistic behaviour at\nlong times. Accounting for this gives a good description of recent experimental\nresults, and provides a robust method to extract the effective intersite\ntunneling from time-of-flight measurements.",
        "positive": "Traces of integrability in scattering of one-dimensional dimers on a\n  barrier: We consider molecules made of two one-dimensional short-range-interacting\nbosonic atoms. We show that in the process of scattering of these molecules off\na narrow barrier, odd incident waves produce \\emph{no unbound atoms, even when\nthe incident energy exceeds the dissociation threshold}. This effect is a\nconsequence of a prohibition on chemical reactions acting in a generally\nunphysical Bethe Ansatz integrable system of a $C_{2}$-type, with which our\nsystem shares the spatially odd eigenstates. We suggest several experimental\nimplementations of the effect. We also propose to use the monomer production as\nan alternative read-out channel in an atom interferometer: unlike in the\nstandard interferometric schemes, no spatial separation of the output channels\nwill be required."
    },
    {
        "anchor": "Heteronuclear Efimov scenario with positive intraspecies scattering\n  length: We investigate theoretically and experimentally the heteronuclear Efimov\nscenario for a three-body system that consists of two bosons and one\ndistinguishable particle with positive intraspecies scattering lengths. The\nthree-body parameter at the three-body scattering threshold and the scaling\nfactor between consecutive Efimov resonances are found to be controlled by the\nscattering length between the two bosons, approximately independent of\nshort-range physics. We observe two excited-state Efimov resonances in the\nthree-body recombination spectra of an ultracold mixture of fermionic $^6 $Li\nand bosonic $^{133} $Cs atoms close to a Li-Cs Feshbach resonance, where the\nCs-Cs interaction is positive. Deviation of the obtained scaling factor of\n4.0(3) from the universal prediction of 4.9 and the absence of the ground state\nEfimov resonance shed new light on the interpretation of the universality and\nthe discrete scaling behavior of heteronuclear Efimov physics.",
        "positive": "Josephson-like oscillations in toroidal spinor Bose-Einstein\n  condensates: a prospective symmetry probe: Josephson junctions are essential ingredients in the superconducting circuits\nused in many existing quantum technologies. Additionally, ultracold atomic\nquantum gases have also become essential platforms to study superfluidity.\nHere, we explore the analogy between superconductivity and superfluidity to\npresent an intriguing effect caused by a thin finite barrier in a\nquasi-one-dimensional toroidal spinor Bose--Einstein condensate (BEC). In this\nsystem, the atomic current density flowing through the edges of the barrier\noscillates, such as the electrical current through a Josephson junction in a\nsuperconductor, but in our case, there is no current circulation through the\nbarrier. We also show how the nontrivial broken-symmetry states of spinor BECs\nchange the structure of this Josephson-like current, creating the possibility\nto probe the spinor symmetry, solely using measurements of this superfluid\ncurrent."
    },
    {
        "anchor": "Quantum fluctuations of the center-of-mass and relative parameters of\n  NLS breathers: We study quantum fluctuations of macroscopic parameters of an NLS breathers,\ni.e., the second-order soliton solution of the nonlinear Schr\\\"odinger\nequation. Uncertainty relations for the parameters are derived and compared to\nsimilar relations for fundamental solitons. We compare two models for the state\nof the quantum field of fluctuations surrounding the classical field of the\nBose-Einstein condensate: a conventionally used, computationally convenient\n\"white noise\", and a correlated noise which assumes that the breather has been\ncreated from a fundamental soliton, by means of the application of the\nfactor-of-four quench of the nonlinearity strength. Theoretical methods used in\nthe work are well suited for a large number of particles, $N$. We thus confirm\nthe possibility of experimental observation of macroscopic quantum\nfluctuations, which is suggested by an extrapolation to large $N$ of recently\nreported low-$N$ Bethe-ansatz results [Phys. Rev. Lett. 119 220401 (2017)].",
        "positive": "Large-$N$ Chern insulators: lattice field theory and quantum simulation\n  approaches to correlation effects in the quantum anomalous Hall effect: Four-Fermi quantum field theories in (2+1) dimensions lie among the simplest\nmodels in high-energy physics, the understanding of which requires a\nnon-perturbative lattice formulation addressing their strongly-coupled fixed\npoints. These lattice models are also relevant in condensed matter, as they\noffer a neat playground to explore strong correlations in the quantum anomalous\nHall (QAH) effect. We give a detailed description of our multidisciplinary\napproach to understand the fate of the QAH phases as the four-Fermi\ninteractions are increased, which combines strong-coupling and\neffective-potential techniques, unveiling a rich phase diagram with large-$N$\nChern insulators and Lorentz-breaking fermion condensates. Moreover, this\ntoolbox can be enlarged with recent advances in quantum information science, as\nwe show that tensor-network algorithms based on projected entangled pairs can\nbe used to improve our understanding of the strong-coupling limit. We also\npresent a detailed scheme that uses ultra-cold atoms in optical lattices with\nsynthetic spin-orbit coupling to build quantum simulators of these four-Fermi\nmodels. This yields a promising alternative to characterise the\nstrongly-coupled fixed points and, moreover, could also explore real-time\ndynamics and finite-fermion densities."
    },
    {
        "anchor": "Systematic investigation of the effects of disorder at the lowest order\n  throughout the BCS-BEC crossover: A systematic investigation of the effects of disorder on the BCS-BEC\ncrossover at the lowest order in the impurity potential is presented for the\nnormal phase above the critical temperature Tc. Starting with the t-matrix\napproach for the clean system, by which pairing correlations between\nopposite-spin fermions evolve from the weak-coupling (BCS) to the\nstrong-coupling (BEC) limits by increasing the strength of the attractive\ninter-particle interaction, all possible diagrammatic processes are considered\nwhere the effects of a disordered potential are retained in the self-energy at\nthe lowest order. An accurate numerical investigation is carried out for all\nthese diagrammatic terms, to determine which of them are mostly important\nthroughout the BCS-BEC crossover. Explicit calculations for the values of Tc,\nthe chemical potential, and the Tan's contact are carried out. In addition, the\neffect of disorder on the single-particle spectral function is analyzed, and a\ncorrelation is found between an increase of Tc and a widening of the pseudo-gap\nenergy at Tc on the BCS side of unitarity in the presence of disorder, while on\nthe BEC side of unitarity the presence of disorder favors the collapse of the\nunderlying Fermi surface. The present investigation is meant to orient future\nstudies when the effects of disorder will be considered at higher orders, with\nthe purpose of limiting the proliferation of diagrammatic terms in which\ninteraction and disorder are considered simultaneously.",
        "positive": "Fractional quantum Hall states of dipolar fermions in a strained optical\n  lattice: We study strongly correlated ground states of dipolar fermions in a honeycomb\noptical lattice with spatial variations in hopping amplitudes. Similar to a\nstrained graphene, such nonuniform hopping amplitudes produce valley-dependent\npseudomagnetic fields for fermions near the two Dirac points, resulting in the\nformation of Landau levels. The dipole moments polarized perpendicular to the\nhoneycomb plane yield a long-range repulsive interaction. By exact\ndiagonalization in the zeroth-Landau-level basis, we show that this repulsive\ninteraction stabilizes a variety of valley-polarized fractional quantum Hall\nstates such as Laughlin and composite-fermion states. The present system thus\noffers an intriguing platform for emulating fractional quantum Hall physics in\na static optical lattice. We calculate the energy gaps above these\nincompressible states, and discuss the temperature scales required for their\nexperimental realization."
    },
    {
        "anchor": "Breakdown of Kohn Theorem Near Feshbach Resonance: We study the collective excitation frequencies of a harmonically trapped 85Rb\nBose-Einstein condensate (BEC) in the vicinity of a Feshbach resonance. To this\nend, we solve the underlying Gross-Pitaevskii (GP) equation by using a Gaussian\nvariational approach and obtain the coupled set of ordinary differential\nequations for the widths and the center of mass of the condensate. A\nlinearization shows that the dipole mode frequency decreases when the bias\nmagnetic field approaches the Feshbach resonance, so the Kohn theorem is\nviolated.",
        "positive": "Textures of Spin-Orbit Coupled F=2 Spinor Bose Einstein Condensates: We study the textures of F=2 spinor Bose-Einstein condensates (BECs) with\nspin-orbit coupling (SOC) induced by a synthetic non-Abelian gauge field. On\nthe basis of the analysis of the SOC energy and the numerical calculation of\nthe Gross-Pitaevskii equation, we demonstrate that the textures originate from\nthe helical modulation of the order parameter (OP) due to the SOC. In\nparticular, the cyclic OP consists of two-dimensional lattice textures, such as\nthe hexagonal lattice and the 1/3-vortex lattice, commonly understandable as\nthe two-dimensional network of the helical modulations."
    },
    {
        "anchor": "Interaction Control of Ultracold Alkaline-Earth Atoms: Ultracold alkaline-earth atoms have now been widely explored for precision\nmeasurements and quantum simulation. Because of its unique atomic structure,\nalkaline earth atoms possess great advantages for quantum simulation and\nstudying quantum many-body matters, such as simulating synthetic gauge field,\nKondo physics and $SU(N)$ physics. To fully explore the potential of ultracold\nalkaline-earth atoms, these systems also need to be equipped with the\ncapability of tuning the inter-atomic interaction to the strongly interacting\nregime. Recently several theoretical proposals and experimental demonstrations\nhave shown that both spin-independent and spin-exchanging interaction can be\ntuned to resonance. In this perspective, we will review these progress and\ndiscuss the new opportunities brought by these interaction control tools for\nfuture quantum simulation studies with ultracold alkaline-earth atoms.",
        "positive": "Far from equilibrium quantum magnetism with ultracold polar molecules: Recent theory has indicated how to emulate tunable models of quantum\nmagnetism with ultracold polar molecules. Here we show that present molecule\noptical lattice experiments can accomplish three crucial goals for quantum\nemulation, despite currently being well below unit filling and not quantum\ndegenerate. The first is to verify and benchmark the models proposed to\ndescribe these systems. The second is to prepare correlated and possibly useful\nstates in well-understood regimes. The third is to explore many-body physics\ninaccessible to existing theoretical techniques. Our proposal relies on a\nnon-equilibrium protocol that can be viewed either as Ramsey spectroscopy or an\ninteraction quench. It uses only routine experimental tools available in any\nultracold molecule experiment."
    },
    {
        "anchor": "Observation of a non-Hermitian phase transition in an optical quantum\n  gas: Quantum gases of light, as photons or polariton condensates in optical\nmicrocavities, are collective quantum systems enabling a tailoring of\ndissipation from e.g. cavity loss. This makes them a tool to study dissipative\nphases, an emerging subject in quantum manybody physics. Here we experimentally\ndemonstrate a non-Hermitian phase transition of a photon Bose-Einstein\ncondensate to a new dissipative phase, characterized by a biexponential decay\nof the condensate's second-order coherence. The phase transition occurs due to\nthe emergence of an exceptional point in the quantum gas. While Bose-Einstein\ncondensation is usually connected to ordinary lasing by a smooth crossover, the\nobserved phase transition separates the novel, biexponential phase from both\nlasing and an intermediate, oscillatory condensate regime. Our findings pave\nthe way for studies of a wide class of dissipative quantum phases, for instance\nin topological or lattice systems.",
        "positive": "Quantum Mechanics with a Momentum-Space Artificial Magnetic Field: The Berry curvature is a geometrical property of an energy band which acts as\na momentum space magnetic field in the effective Hamiltonian describing\nsingle-particle quantum dynamics. We show how this perspective may be exploited\nto study systems directly relevant to ultracold gases and photonics. Given the\nexchanged roles of momentum and position, we demonstrate that the global\ntopology of momentum space is crucially important. We propose an experiment to\nstudy the Harper-Hofstadter Hamiltonian with a harmonic trap that will\nillustrate the advantages of this approach and that will also constitute the\nfirst realization of magnetism on a torus."
    },
    {
        "anchor": "Diffractions of Bose-Einstein Condensate in Quantized Light Fields: We investigate the atomic diffractions of a Bose-Einstein condensate in\nquantized light fields. Situations in which the light fields are in number\nstates or coherent states are studied theoretically. Analytical derivation and\nnumerical calculation are carried out to simulate the dynamics of the atomic\nmotion. In condition that atoms are scattered by light in the number states\nwith imbalanced photon number distribution, the atomic transitions between\ndifferent momentum modes would sensitively depend on the transition order and\nthe photon number distribution. The number-state-nature of the light fields\nmodifies the period of atomic momentum oscillations and makes forward and\nbackward atomic transitions unequal. For light fields in coherent states, no\nmatter the intensities of the light fields are balanced or not, the atomic\ndiffractions are symmetric and independent on the transition order.",
        "positive": "Supersonic and subsonic shock waves in the unitary Fermi gas: We investigate shock waves in the unitary Fermi gas by using the\nzero-temperature equations of superfluid hydrodynamics. We obtain analytical\nsolutions for the dynamics of a localized perturbation of the uniform gas.\nThese supersonic bright and subsonic dark solutions produce, after a transient\ntime, an extremely large (divergent) density gradient: the shock. We calculate\nthe time of formation of the shock and also simulate the space-time behavior of\nthe waves by solving generalized hydrodynamic equations, which include a\nreliable dispersive regularization of the shock. We find that the shock spreads\ninto wave ripples whose properties crucially depend on the chosen initial\nconfiguration."
    },
    {
        "anchor": "Quantum Phase Transition in an Antiferromagnetic Spinor Bose-Einstein\n  Condensate: We have experimentally observed the dynamics of an antiferromagnetic sodium\nBose-Einstein condensate (BEC) quenched through a quantum phase transition.\nUsing an off-resonant microwave field coupling the F = 1 and F = 2 atomic\nhyperfine levels, we rapidly switched the quadratic energy shift q from\npositive to negative values. At q = 0 the system undergoes a transition from a\npolar to antiferromagnetic phase. We measured the dynamical evolution of the\npopulation in the F = 1, m_F = 0 state in the vicinity of this transition point\nand observed a mixed state of all 3 hyperfine components for q < 0. We also\nobserved the coarsening dynamics of the instability for q<0, as it nucleated\nsmall domains that grew to the axial size of the cloud.",
        "positive": "Finite-range effect in the two-dimensional density-induced BCS-BEC\n  crossover: We theoretically investigate the Bardeen-Cooper-Schrieffer (BCS) to\nBose-Einstein condensation (BEC) crossover in a two-dimensional Fermi gas with\nthe finite-range interaction by using the Hartree-Fock-Bogoliubov theory.\nExpanding the scattering phase shift in terms of the scattering length and\neffective range, we discuss the effect of the finite-range interaction on the\npairing and thermodynamic properties. By solving the gap equation and the\nnumber equation self-consistently, we numerically calculate the effective-range\ndependence of the pairing gap, chemical potential, and pair size throughout the\nBCS-BEC crossover. Our results would be useful for further understanding of\nlow-dimensional many-body problems."
    },
    {
        "anchor": "Observation of von K\u00e1rm\u00e1n Vortex Street in an Atomic Superfluid Gas: We report on the experimental observation of vortex cluster shedding from a\nmoving obstacle in an oblate atomic Bose-Einstein condensate. At low obstacle\nvelocities $v$ above a critical value, vortex clusters consisting of two\nlike-sign vortices are generated to form a regular configuration like a von\nK\\'arm\\'an street, and as $v$ is increased, the shedding pattern becomes\nirregular with many different kinds of vortex clusters. In particular, we\nobserve that the Stouhal number associated with the shedding frequency exhibits\nsaturation behavior with increasing $v$. The regular-to-turbulent transition of\nthe vortex cluster shedding reveals remarkable similarities between a\nsuperfluid and a classical viscous fluid. Our work opens a new direction for\nexperimental investigations of the superfluid Reynolds number characterizing\nuniversal superfluid hydrodynamics.",
        "positive": "Criteria for 2D kinematics in an interacting Fermi gas: Ultracold Fermi gases subject to tight transverse confinement offer a highly\ncontrollable setting to study the two-dimensional (2D) BCS to\nBerezinskii-Kosterlitz-Thouless superfluid crossover. Achieving the 2D regime\nrequires confining particles to their transverse ground state which presents\nchallenges in interacting systems. Here, we establish the conditions for an\ninteracting Fermi gas to behave kinematically 2D. Transverse excitations are\ndetected by measuring the transverse expansion rate which displays a sudden\nincrease when the atom number exceeds a critical value $N_{2D}$ signifying a\ndensity driven departure from 2D kinematics. For weak interactions $N_{2D}$ is\nset by the aspect ratio of the trap. Close to a Feshbach resonance, however,\nthe stronger interactions reduce $N_{2D}$ and excitations appear at lower\ndensity."
    },
    {
        "anchor": "Stable higher-order vortex quantum droplets in an annular potential: We address the existence, stability, and evolution of two-dimensional vortex\nquantum droplets (VQDs) in binary Bose-Einstein condensates trapped in a\nring-shaped potential. The interplay of the Lee-Huang-Yang-amended nonlinearity\nand trapping potential supports two VQD branches, controlled by the radius,\nwidth and depth of the potential profile. While the lower-branch VQDs,\nbifurcating from the system's linear modes, are completely unstable, the upper\nbranch is fully stable for all values of the topological charge $m$ and\npotential's parameters. Up to $m=12$ (at least), stable VQDs obey the {\\it\nanti-Vakhitov-Kolokolov} criterion. In the limit of an extremely tight radial\ntrap, the modulational instability of the quasi-1D azimuthal VQDs is studied\nanalytically. We thus put forward an effective way to produce stable VQDs with\nhigher vorticity but a relatively small number of atoms, which is favorable for\nexperimental realization.",
        "positive": "Confined Meson Excitations in Rydberg-Atom Arrays Coupled to a Cavity\n  Field: Confinement is a pivotal phenomenon in numerous models of high-energy and\nstatistical physics. In this study, we investigate the emergence of confined\nmeson excitations within a one-dimensional system, comprising Rydberg-dressed\natoms trapped and coupled to a cavity field. This system can be effectively\nrepresented by an Ising-Dicke Hamiltonian model. The observed ground-state\nphase diagram reveals a first-order transition from a ferromagnetic-subradiant\nphase to a paramagnetic-superradiant phase. Notably, a quench near the\ntransition point within the ferromagnetic-subradiant phase induces meson\noscillations in the spins and leads to the creation of squeezed-vacuum light\nstates. We suggest a method for the photonic characterization of these confined\nexcitations, utilizing homodyne detection and single-site imaging techniques to\nobserve the localized particles. The methodologies and results detailed in this\npaper are feasible for implementation on existing cavity-QED platforms,\nemploying Rydberg-atom arrays in deep optical lattices or optical tweezers."
    },
    {
        "anchor": "Observation of two-orbital spin-exchange interactions with ultracold\n  SU(N)-symmetric fermions: We report on the direct observation of spin-exchanging interactions in a\ntwo-orbital SU(N)-symmetric quantum gas of ytterbium in an optical lattice. The\ntwo orbital states are represented by two different (meta-)stable electronic\nconfigurations of fermionic Yb-173. A strong spin-exchange between particles in\nthe two separate orbitals is mediated by the contact interaction between atoms,\nwhich we characterize by clock shift spectroscopy in a 3D optical lattice. We\nfind the system to be SU(N)-symmetric within our measurement precision and\ncharacterize all relevant scattering channels for atom pairs in combinations of\nthe ground and the excited state. Elastic scattering between the orbitals is\ndominated by the antisymmetric channel, which leads to the strong spin-exchange\ncoupling. The exchange process is directly observed, by characterizing the\ndynamic equilibration of spin imbalances between two large ensembles in the two\norbital states, as well as indirectly in atom pairs via interaction shift\nspectroscopy in a 3D lattice. The realization of a stable SU(N)-symmetric\ntwo-orbital Hubbard Hamiltonian opens the route towards experimental quantum\nsimulation of condensed-matter models based on orbital interactions, such as\nthe Kondo lattice model.",
        "positive": "Universal Energy Functionals for Trapped Fermi Gases in Low Dimensions: We study the system of trapped two-component Fermi gases with zero-range\ninteraction in two dimensions (2D) or one dimension (1D). We calculate the\none-particle density matrices of these systems at small displacements, from\nwhich we show that the $N$-body energies are linear functionals of the\noccupation probabilities of single-particle energy eigenstates. A universal\nenergy functional was first derived in 2011 for trapped zero-range interacting\ntwo-component Fermi gases in three dimensions (3D). We also calculate the\nasymptotic behaviors of the occupation probabilities of single-particle energy\neigenstates at high energies."
    },
    {
        "anchor": "Steady state quantum transport through an anharmonic oscillator strongly\n  coupled to two heat reservoirs: We investigate the transport properties of an anharmonic oscillator, modeled\nby a single-site Bose-Hubbard model, coupled to two different thermal baths\nusing the numerically exact thermofield based chain-mapping matrix product\nstates (TCMPS) approach. We compare the effectiveness of TCMPS to probe the\nnonequilibrium dynamics of strongly interacting system irrespective of the\nsystem-bath coupling against the global master equation approach in\nGorini-Kossakowski-Sudarshan-Lindblad form. We discuss the effect of on-site\ninteractions, temperature bias as well as the system-bath couplings on the\nsteady state transport properties. Last we also show evidence of non-Markovian\ndynamics by studying the non-monotonicity of the time evolution of the trace\ndistance between two different initial states.",
        "positive": "Dynamics of pattern-loaded fermions in bichromatic optical lattices: Motivated by experiments in Munich (M. Schreiber et. al. Science\n\\textbf{349}, 842), we study the dynamics of interacting fermions initially\nprepared in charge density wave states in one-dimensional bichromatic optical\nlattices. The experiment sees a marked lack of thermalization, which has been\ntaken as evidence for an interacting generalization of Anderson localization,\ndubbed \"many-body localization\". We model the experiments using an interacting\nAubry-Andre model and develop a computationally efficient low-density cluster\nexpansion to calculate the even-odd density imbalance as a function of\ninteraction strength and potential strength. Our calculations agree with the\nexperimental results and shed light on the phenomena. We also explore a\ntwo-dimensional generalization. The cluster expansion method we develop should\nhave broad applicability to similar problems in non-equilibrium quantum\nphysics."
    },
    {
        "anchor": "Topological Mott insulators of ultracold atomic mixtures induced by\n  interactions in one-dimensional optical superlattices: We present exactly solvable examples that topological Mott insulators can\nemerge from topologically trivial states due to strong interactions between\natoms for atomic mixtures trapped in one-dimensional optical superlattice\nsystems. The topological Mott insulating state is characterized by nonzero\nChern number and appears in the strongly interacting limit as long as the total\nband filling factor is an integer, which is not sensitive to the filling of\neach component. The topological nature of the Mott phase can be revealed by\nobserving the density profile of the trapped system. Our results can be also\ngeneralized to the multi-component atomic systems.",
        "positive": "Bose polarons at finite temperature and strong coupling: The temperature dependence of a mobile impurity in a dilute Bose gas, the\nBose polaron, is investigated for wide a range of impurity-bath interactions.\nUsing a diagrammatic resummation scheme designed to include scattering\nprocesses important at finite temperature $T$, we show that the phase\ntransition of the environment to a Bose-Einstein condensate at the critical\ntemperature $T_c$ leads to several non-trivial effects. The attractive polaron\npresent at $T=0$ fragments into two quasiparticle states for finite temperature\nwhenever $|a|\\gtrsim a_B$, with $a$ and $a_B$ the impurity-boson and\nboson-boson scattering lengths. While the quasiparticle with higher energy\ndisappears at $T_c$, the ground state quasiparticle remains well-defined across\n$T_c$. Its energy depends non-monotonically on temperature, featuring a minimum\nat $T_c$, after which it increases towards zero, and at $T\\gg T_c$ the polaron\neventually becomes overdamped due to strong scattering with thermally excited\nbosons."
    },
    {
        "anchor": "Exact results for polaron and molecule in one-dimensional spin-1/2 Fermi\n  gas: Using exact Bethe ansatz (BA) solutions, we show that a spin-down fermion\nimmersed into a fully polarized spin-up Fermi sea with a weak attraction is\ndressed by the surrounding spin-up fermions to form the one-dimensional analog\nof a polaron. As the attraction becomes strong, the spin-down fermion binds\nwith one spin-up fermion to form a tightly bound molecule. Throughout the whole\ninteraction regime, a crossover from the polaron to a molecule state is fully\ndemonstrated through exact results of the excitation spectrum, the effective\nmass, binding energy and kinetic energy. Furthermore, a clear distinction\nbetween the polaron and molecule is conceived by the probability distribution,\nsingle particle reduced density matrix and density-density correlations, which\nare calculated directly from the Bethe ansatz wave function. Such a\npolaron-molecule crossover presents a universal nature of an impurity immersed\ninto a fermionic medium with an attraction in one dimension.",
        "positive": "Fragmented Superradiance of a Bose-Einstein Condensate in an Optical\n  Cavity: The Dicke model and the superradiance of two-level systems in a radiation\nfield have many applications. Recently, a Dicke quantum phase transition has\nbeen realized with a Bose-Einstein condensate in a cavity. We numerically solve\nthe many-body Schr\\\"odinger equation and study correlations in the ground state\nof interacting bosons in a cavity as a function of the strength of a driving\nlaser. Beyond a critical strength, the bosons occupy multiple modes\nmacroscopically while remaining superradiant. This fragmented superradiance can\nbe detected by analyzing the variance of single-shot measurements."
    },
    {
        "anchor": "Sign reversal of the boson-boson interaction potential in planar\n  Bose-Fermi mixtures under a synthetic magnetic field: We study the mutually coupled, strongly interacting bosonic and\nnon-interacting fermionic, species of unequal masses in the regime were the\nretardation effects are an important part of the physics. A cloud of neutral\natoms experiences a synthetic magnetic field because of a vector potential that\nimposes a phase shift on the constituents. The magnetic field causes the\noscillations of the magnitude and sign of the effective interaction between\nbosons from repulsive to attractive in contrast to the static case. We show\nthat the dynamics for the gaseous Bose-Fermi mixtures when reaching the\nquantum-Hall regime becomes highly nontrivial.",
        "positive": "Magnetic Solitons in a Binary Bose-Einstein Condensate: We study solitary waves of polarization (magnetic solitons) in a\ntwo-component Bose gas with slightly unequal repulsive intra- and interspin\ninteractions. In experimentally relevant conditions we obtain an analytical\nsolution which reveals that the width and the velocity of magnetic solitons are\nexplicitly related to the spin healing length and the spin sound velocity of\nthe Bose mixture, respectively. We calculate the profiles, the energy and the\neffective mass of the solitons in the absence of external fields and\ninvestigate their oscillation in a harmonic trap where the oscillation period\nis calculated as a function of the oscillation amplitude. The stability of\nmagnetic solitons in two dimensions and the conditions for their experimental\nobservation are also briefly discussed."
    },
    {
        "anchor": "Pinning quantum phase transition for a Luttinger liquid of strongly\n  interacting bosons: One of the most remarkable results of quantum mechanics is the fact that\nmany-body quantum systems may exhibit phase transitions even at zero\ntemperature. Quantum fluctuations, deeply rooted in Heisenberg's uncertainty\nprinciple, and not thermal fluctuations, drive the system from one phase to\nanother. Typically, the relative strength of two competing terms in the\nsystem's Hamiltonian is changed across a finite critical value. A well-known\nexample is the Mott-Hubbard quantum phase transition from a superfluid to an\ninsulating phase, which has been observed for weakly interacting bosonic atomic\ngases. However, for strongly interacting quantum systems confined to\nlower-dimensional geometry a novel type of quantum phase transition may be\ninduced for which an arbitrarily weak perturbation to the Hamiltonian is\nsufficient to drive the transition. Here, for a one-dimensional (1D) quantum\ngas of bosonic caesium atoms with tunable interactions, we observe the\ncommensurate-incommensurate quantum phase transition from a superfluid\nLuttinger liquid to a Mott-insulator. For sufficiently strong interactions, the\ntransition is induced by adding an arbitrarily weak optical lattice\ncommensurate with the atomic granularity, which leads to immediate pinning of\nthe atoms. We map out the phase diagram and find that our measurements in the\nstrongly interacting regime agree well with a quantum field description based\non the exactly solvable sine-Gordon model. We trace the phase boundary all the\nway to the weakly interacting regime where we find good agreement with the\npredictions of the 1D Bose-Hubbard model. Our results open up the experimental\nstudy of quantum phase transitions, criticality, and transport phenomena beyond\nHubbard-type models in the context of ultracold gases.",
        "positive": "Symmetry-breaking magnetization dynamics of spinor dipolar Bose-Einstein\n  condensates: Symmetry-breaking magnetization dynamics of a spin-1 Bose-Einstein condensate\n(BEC) due to the dipole-dipole interaction are investigated using the\nmean-field and Bogoliubov theories. When a magnetic field is applied along the\nsymmetry axis of a pancake-shaped BEC in the m = 0 hyperfine sublevel,\ntransverse magnetization develops breaking the chiral or axial symmetry. A\nvariety of magnetization patterns are formed depending on the strength of the\napplied magnetic field. The proposed phenomena can be observed in 87Rb and 23Na\ncondensates."
    },
    {
        "anchor": "A hexapole-compensated magneto-optical trap on a mesoscopic atom chip: Magneto-optical traps on atom chips are usually restricted to small atomic\nsamples due to a limited capture volume caused primarily by distorted field\nconfigurations. Here we present a magneto-optical trap with minimized\ndistortions based on a mesoscopic wire structure which provides a loading rate\nof 8.4 10^10 atoms/s and a maximum number of 8.7 10^9 captured atoms. The wire\nstructure is placed outside of the vacuum to enable a further adaptation to new\nscientific objectives. Since all magnetic fields are applied locally without\nthe need for external bias fields, the presented setup will facilitate parallel\ngeneration of Bose-Einstein condensates on a conveyor belt with a cycle rate\nabove 1 Hz.",
        "positive": "The role of geometry in the superfluid flow of nonlocal photon fluids: Recent work has unveiled a new class of optical systems that can exhibit the\ncharacteristic features of superfluidity. One such system relies on the\nrepulsive photon-photon interaction that is mediated by a thermal optical\nnonlinearity and is therefore inherently nonlocal due to thermal diffusion.\nHere we investigate how such a nonlocal interaction, which at a first\ninspection would not be expected to lead to superfluid behavior, may be\ntailored by acting upon the geometry of the photon fluid itself. Our models and\nmeasurements show that restricting the laser profile and hence the photon fluid\nto a strongly elliptical geometry modifies thermal diffusion along the major\nbeam axis and reduces the effective nonlocal interaction length by two orders\nof magnitude. This in turn enables the system to display a characteristic trait\nof superfluid flow: the nucleation of quantized vortices in the flow past an\nextended physical obstacle. These results are general and apply to other\nnonlocal fluids, such as dipolar Bose-Einstein condensates, and show that\n\"thermal\" photon superfluids provide an exciting and novel experimental\nenvironment for probing the nature of superfluidity, with applications to the\nstudy of quantum turbulence and analogue gravity."
    },
    {
        "anchor": "One-dimensional mixtures of several ultracold atoms: a review: Recent theoretical and experimental progress on studying one-dimensional\nsystems of bosonic, fermionic, and Bose-Fermi mixtures of a few ultracold atoms\nconfined in traps is reviewed in the broad context of mesoscopic quantum\nphysics. We pay special attention to limiting cases of very strong or very weak\ninteractions and transitions between them. For bosonic mixtures, we describe\nthe developments in systems of three and four atoms as well as different\nextensions to larger numbers of particles. We also briefly review progress in\nthe case of spinor Bose gases of a few atoms. For fermionic mixtures, we\ndiscuss a special role of spin and present a detailed discussion of the two-\nand three-atom cases. We discuss the advantages and disadvantages of different\ncomputation methods applied to systems with intermediate interactions. In the\ncase of very strong repulsion, close to the infinite limit, we discuss\napproaches based on effective spin chain descriptions. We also report on recent\nstudies on higher-spin mixtures and inter-component attractive forces. For both\nstatistics, we pay particular attention to impurity problems and mass imbalance\ncases. Finally, we describe the recent advances on trapped Bose-Fermi mixtures,\nwhich allow for a theoretical combination of previous concepts, well\nillustrating the importance of quantum statistics and inter-particle\ninteractions. Lastly, we report on fundamental questions related to the subject\nwhich we believe will inspire further theoretical developments and experimental\nverification.",
        "positive": "Strain and pseudo-magnetic fields in optical lattices from\n  density-assisted tunneling: Applying time-periodic modulations is routinely used to control and design\nsynthetic matter in quantum-engineered settings. In lattice systems, this\napproach is explored to engineer band structures with non-trivial topological\nproperties, but also to generate exotic interaction processes. A prime example\nis density-assisted tunneling, by which the hopping amplitude of a particle\nbetween neighboring sites explicitly depends on their respective occupations.\nHere, we show how density-assisted tunneling can be tailored in view of\nsimulating the effects of strain in synthetic graphene-type systems.\nSpecifically, we consider a mixture of two atomic species on a honeycomb\noptical lattice: one species forms a Bose-Einstein condensate in an anisotropic\nharmonic trap, whose inhomogeneous density profile induces an effective\nuniaxial strain for the second species through density-assisted tunneling\nprocesses. In direct analogy with strained graphene, the second species\nexperiences a pseudo magnetic field, hence exhibiting relativistic Landau\nlevels and the valley Hall effect. Our proposed scheme introduces a unique\nplatform for the investigation of strain-induced gauge fields and their\npossible interplay with quantum fluctuations and collective excitations."
    },
    {
        "anchor": "Exploring the thermodynamics of spin-1 $^{87}$Rb Bose Gases with\n  synthetic magnetization: In this work, we study the thermodynamic properties of a spin-1 Bose gas\nacross the Bose-Einstein condensation transition. We present the theoretical\ndescription of the thermodynamics of a trapped ideal spin-1 Bose gas and we\ndescribe the phases that can be obtained in this system as a function of the\ntemperature and of the populations in the different spin components. We propose\na simple way to realize a \"synthetic magnetization\" that can be used to probe\nthe entire phase diagram while keeping the real magnetization of the system\nfixed. We experimentally demonstrate the use of such method to explore\ndifferent phases in a sample with zero total magnetization. Our work opens up\nnew perspectives to study isothermal quenching dynamics through different\nmagnetic phases in spinor condensates.",
        "positive": "Many-particle Systems in One Dimension in the Harmonic Approximation: We consider energetics and structural properties of a many particle system in\none dimension with pairwise contact interactions confined in a parabolic\nexternal potential. To render the problem analytically solvable, we use the\nharmonic approximation scheme at the level of the Hamiltonian. We investigate\nthe scaling with particle number of the ground state energies for systems\nconsisting of identical bosons or fermions. We then proceed to focus on bosonic\nsystems and make a detailed comparison to known exact results in the absence of\nthe parabolic external trap for three-body systems. We also consider the\nthermodynamics of the harmonic model which turns out to be similar for bosons\nand fermions due to the lack of degeneracy in one dimension."
    },
    {
        "anchor": "Cooling bosons by dimensional reduction: Cold atomic gases provide a remarkable testbed to study the physics of\ninteracting many-body quantum systems. They have started to play a major role\nas quantum simulators, given the high degree of control that is possible. A\ncrucial element is given by the necessarily non-zero temperature. However\ncooling to the required ultralow temperatures or even simply measuring the\ntemperature directly on the system can prove to be very challenging tasks.\nHere, we implement thermometry on strongly interacting two- and one-dimensional\nBose gases with high sensitivity in the nano-Kelvin temperature range. Our\nmethod is aided by the fact that the decay of the first-order correlation\nfunction is very sensitive to the temperature when interactions are strong. We\nfind that there may be a significant temperature variation when the\nthree-dimensional quantum gas is cut into two-dimensional slices or into\none-dimensional tubes. Strikingly, the temperature for the one-dimensional case\ncan be much lower than the initial temperature. Our findings show that this\ndecrease results from the interplay of dimensional reduction and strong\ninteractions.",
        "positive": "Sisyphus cooling in a continuously loaded trap: We demonstrate continuous Sisyphus cooling combined with a continuous loading\nmechanism used to efficiently slow down and accumulate atoms from a guided\nbeam. While the loading itself is based on a single slowing step, applying a\nradio frequency field forces the atoms to repeat this step many times resulting\nin a so-called Sisyphus cooling. This extension allows efficient loading and\ncooling of atoms from a wide range of initial beam conditions. We study the\ninterplay of the continuous loading and simultaneous Sisyphus cooling in\ndifferent density regimes. In the case of a low density flux we observe a\nrelative gain in phase-space density of nine orders of magnitude. This makes\nthe presented scheme an ideal tool for reaching collisional densities enabling\nevaporative cooling - in spite of unfavourable initial conditions."
    },
    {
        "anchor": "Phonon-mediated Casimir interaction between mobile impurities in\n  one-dimensional quantum liquids: Virtual phonons of a quantum liquid scatter off impurities and mediate a\nlong-range interaction, analogous to the Casimir effect. In one dimension the\neffect is universal and the induced interaction decays as $1/r^3$, much slower\nthan the van der Waals interaction $\\sim1/r^6$, where $r$ is the impurity\nseparation. The sign of the effect is characterized by the product of\nimpurity-phonon scattering amplitudes, which take a universal form and have\nbeen seen to vanish for several integrable impurity models. Thus, if the\nimpurity parameters can be independently tuned to lie on opposite sides of such\nintegrable points, one can observe an attractive interaction turned into a\nrepulsive one.",
        "positive": "Caustics in quantum many-body dynamics: We describe a new class of nonequilibrium quantum many-body phenomena in the\nform of networks of caustics that dominate the many-body wavefunction in the\nsemiclassical regime following a sudden quench. It includes the light cone-like\npropagation of correlations as a particular case. Caustics are singularities\nformed by the birth and death of waves and form a hierarchy of universal\npatterns whose natural mathematical description is via catastrophe theory.\nExamples in classical waves range from rainbows and gravitational lensing in\noptics to tidal bores and rogue waves in hydrodynamics. Quantum many-body\ncaustics are discretized by second-quantization (``quantum catastrophes'') and\nlive in Fock space which can potentially have many dimensions. We illustrate\nthese ideas using the Bose Hubbard dimer and trimer models which are simple\nenough that the caustic structure can be elucidated from first principles and\nyet run the full range from integrable to nonintegrable dynamics. The dimer\ngives rise to discretized versions of fold and cusp catastrophes whereas the\ntrimer allows for higher catastrophes including the codimension-3 hyperbolic\nand elliptic umbilics which are organized by, and projections of, an\n8-dimensional corank-2 catastrophe known as $X_9$. These results describe a\nhitherto unrecognized form of universality in quantum dynamics organized by\nsingularities that manifest as strong fluctuations in mode population\nprobabilities."
    },
    {
        "anchor": "Monte Carlo study of a Fermi gas with infinite scattering length: The Fermi gas at unitarity is a particularly interesting system of cold\natoms, being dilute and strongly interacting at the same time. It can be\nstudied non-perturbatively with Monte Carlo methods, like the recently\ndeveloped worm algorithm. We discuss our implementation and tests of this\nalgorithm and suggest a modification that increases its efficiency by reducing\nautocorrelations. We then show how the worm algorithm can be applied to\ncalculate the critical temperature of an imbalanced Fermi gas (unequal number\nof fermions in the two spin components). We finally present some results\nobtained with the modified algorithm, in the balanced as well as in the\nimbalanced case.",
        "positive": "One- and two-dimensional reductions of the mean-field description of\n  degenerate Fermi gases: We study collective behavior of Fermi gases trapped in various external\npotentials, including optical lattices (OLs), in the framework of the\nmean-field (hydrodynamic) description. Using the variational method, we derive\neffective dynamical equations for the one- and two-dimensional (1D and 2D)\nsettings from the general 3D mean-field equation. The respective confinement is\nprovided by trapping potentials with the cylindrical and planar symmetry,\nrespectively. The resulting equations are nonpolynomial Schr% \\\"{o}dinger\nequations (NPSEs) coupled to equations for the local transverse size of the\ntrapped states. Numerical simulations demonstrate close agreement of results\nproduced by the underlying 3D equation and the effective low-dimensional ones.\nWe consider the ground state in these settings. In particular, analytical\nsolutions are obtained for the effectively 2D non-interacting Fermi gas.\nDifferences between the 1D and 2D configurations are highlighted. Finally, we\nanalyze the dependence of the 1D and 2D density patterns of the trapped gas, in\nthe presence of the OL, on the strengths of the confining and OL potentials,\nand on the scattering length which determines the strength of interactions\nbetween non-identical fermions."
    },
    {
        "anchor": "Semiclassical Hartree-Fock theory of a rotating Bose-Einstein\n  condensation: In this paper, we investigate the thermodynamic behavior of a rotating\nBose-Einstein condensation with non-zero interatomic interactions\ntheoretically. The analysis relies on a semiclassical Hartree-Fock\napproximation where an integral is performed over the phase space and function\nof the grand canonical ensemble is derived. Subsequently, we use this result to\nderive several thermodynamic quantities including the condensate fraction,\ncritical temperature, entropy and heat capacity. Thereby, we investigate the\neffect of the rotation rate and interactions parameter on the thermodynamic\nbehavior. The role of finite size is discussed. Our approach can be extended to\nconsider the rotating condensate in optical potential.",
        "positive": "Experimental observation of a dissipative phase transition in a\n  multi-mode many-body quantum system: We characterize the dissipative phase transition in a driven dissipative\nBose-Einstein condensate of neutral atoms. Our results generalize the work on\ndissipative nonlinear Kerr resonators towards many modes and stronger\ninteractions. We measure the effective Liouvillian gap and analyze the\nmicroscopic system dynamics, where we identify a non-equilibrium condensation\nprocess."
    },
    {
        "anchor": "Dynamical preparation of an atomic condensate in a Hofstadter band: The creation of a Hamiltonian in the quantum regime which has non-trivial\ntopological features is a central goal of the cold-atom community, enabling\nwidespread exploration of novel phases of quantum matter. A general scheme to\nsynthesize such Hamiltonians is based on dynamical modulation of optical\nlattices which thereby generate vector potentials. At the same time the\nmodulation can lead to heating and serious difficulties with equilibration.\nHere we show that these challenges can be overcome by demonstrating how a\nHofstadter Bose-Einstein condensate (BEC) can be dynamically realized, using\nexperimental protocols. From Gross-Pitaevskii simulations our study reveals a\ncomplex, multistage evolution; this includes a chaotic intermediate \"heating\"\nstage followed by a spontaneous reentrance to the BEC. The observed behavior is\nreminiscent of evolution in cosmological models.",
        "positive": "Reservoir-induced Thouless pumping and symmetry protected topological\n  order in open quantum chains: We introduce a classification scheme for symmetry protected topological\nphases applicable to stationary states of open systems based on a\ngeneralization of the many-body polarization. The polarization can be used to\nprobe the topological properties of non-interacting and interacting closed and\nopen systems as well and remains a meaningful quantity even in the presence of\nmoderate particle-number fluctuations. As examples, we discuss two open-system\nversions of a topological Thouless pump in the steady state of one-dimensional\nlattices driven by Markovian reservoirs. In the analogous unitary system, the\nRice-Mele model, symmetries enforce topological properties which lead to a\nnon-trivial winding of the geometric Zak phase upon cyclic variations of model\nparameters. Associated with this is a winding of the many-body polarization,\ncorresponding to a quantized transport in the bulk (Thouless pump). We here\nshow that in the open system, where the Zak phase looses its meaning, the same\nsymmetries enforce a winding of the generalized many- body polarization. This\nwinding is shown to be robust against Hamiltonian perturbations as well as\nhomogeneous dephasing and particle losses.."
    },
    {
        "anchor": "Thermodynamics of inhomogenous imperfect quantum gases in harmonic traps: We discuss thermodynamic properties of harmonically trapped imperfect quantum\ngases. The spatial inhomogeneity of these systems imposes a redefinition of the\nmean-field interparticle potential energy as compared to the homogeneous case.\nIn our approach, it takes the form $\\frac{a}{2} N^2 \\, \\omega^d$, where $N$ is\nthe number of particles, $\\omega$ - the harmonic trap frequency, $d$ - system's\ndimensionality, and $a$ is a parameter characterizing the interparticle\ninteraction. We provide arguments that this model corresponds to the limiting\ncase of a long-ranged interparticle potential of vanishingly small amplitude.\nThis conclusion is drawn from a computation similar to the well-known Kac\nscaling procedure, which is presented here in a form adapted to the case of an\nisotropic harmonic trap. We show that within our model, the imperfect gas of\ntrapped repulsive bosons undergoes the Bose-Einstein condensation provided\n$d>1$. The main result of our analysis is that in $d=1$ the gas of attractive\nimperfect fermions with $a=-a_{F}<0$ is thermodynamically equivalent to the gas\nof repulsive bosons with $a=a_{B}>0$ provided the parameters $a_{F}$ and\n$a_{B}$ fulfill the relation $a_{B}+a_{F}=\\hbar$. This result supplements\nsimilar recent conclusion about thermodynamic equivalence of two-dimensional\nuniform imperfect repulsive Bose and attractive Fermi gases.",
        "positive": "Multiple-camera defocus imaging of ultracold atomic gases: In cold atom experiments, each image of light refracted and absorbed by an\natomic ensemble carries a remarkable amount of information. Numerous imaging\ntechniques including absorption, fluorescence, and phase-contrast are commonly\nused. Other techniques such as off-resonance defocused imaging (ORDI), where an\nin-focus image is deconvolved from a defocused image, have been demonstrated\nbut find only niche applications. The ORDI inversion process introduces\nsystematic artifacts because it relies on regularization to account for missing\ninformation at some spatial frequencies. In the present work, we extend ORDI to\nuse multiple cameras simultaneously at degrees of defocus, eliminating the need\nfor regularization and its attendant artifacts. We demonstrate this technique\nby imaging Bose-Einstein condensates, and show that the statistical\nuncertainties in the measured column density using the multiple-camera\noff-resonance defocused (MORD) imaging method are competitive with absorption\nimaging near resonance and phase contrast imaging far from resonance.\nExperimentally, the MORD method may be incorporated into existing set-ups with\nminimal additional equipment."
    },
    {
        "anchor": "Spin dynamics in a two dimensional quantum gas: We have investigated spin dynamics in a 2D quantum gas. Through spin-changing\ncollisions, two clouds with opposite spin orientations are spontaneously\ncreated in a Bose-Einstein condensate. After ballistic expansion, both clouds\nacquire ring-shaped density distributions with superimposed angular density\nmodulations. The density distributions depend on the applied magnetic field and\nare well explained by a simple Bogoliubov model. We show that the two clouds\nare anti-correlated in momentum space. The observed momentum correlations pave\nthe way towards the creation of an atom source with non-local\nEinstein-Podolsky-Rosen entanglement.",
        "positive": "Dimensional Effects on the Momentum distribution of Bosonic Trimer\n  States: The momentum distribution is a powerful probe of strongly-interacting systems\nthat are expected to display universal behavior. This is contained in the\ncontact parameters which relate few- and many-body properties. Here we consider\na Bose gas in two dimensions and explicitly show that the two-body contact\nparameter is universal and then demonstrate that the momentum distribution at\nnext-to-leading order has a logarithmic dependence on momentum which is vastly\ndifferent from the three-dimensional case. Based on this, we propose a scheme\nfor measuring the effective dimensionality of a quantum many-body system by\nexploiting the functional form of the momentum distribution."
    },
    {
        "anchor": "Magnetic solitons in a spin-1 Bose-Einstein condensate: Vector solitons are a type of solitary, or non-spreading wavepacket occurring\nin a nonlinear medium comprised of multiple components. As such, a variety of\nsynthetic systems can be constructed to explore their properties, from\nnonlinear optics to ultracold atoms, and even in human-scale metamaterials. In\nquantum systems such as photons or Bose-Einstein condensates (BECs), such\nvector nonlinearities offer a window into complex many-body dynamics, and offer\npossibilities for quantum communication and information processing. BECs have a\nrich panoply of internal hyperfine levels, or spin components, which make them\na unique platform for exploring these solitary waves. However, existing\nexperimental work has focused largely on binary systems confined to the Manakov\nlimit of the nonlinear equations governing the soliton behavior, where quantum\nmagnetism plays no role. Here we observe, using a ``magnetic shadowing''\ntechnique, a new type of soliton in a spinor BEC, one that exists only when the\nunderlying interactions are antiferromagnetic, and which is deeply embedded\nwithin a full spin-1 quantum system. Our approach opens up a vista for future\nstudies of ``solitonic matter'' whereby multiple solitons interact with one\nanother at deterministic locations, and eventually to the realization of\nquantum correlated states of solitons, a longstanding and unrealized goal.",
        "positive": "Quench dynamics in integrable systems: These notes cover in some detail lectures I gave at the Les Houches Summer\nSchool 2012. I describe here work done with Deepak Iyer with important\ncontributions from Hujie Guan. I discuss some aspects of the physics revealed\nby quantum quenches and present a formalism for studying the quench dynamics of\nintegrable systems. The formalism presented generalizes an approach by Yudson\nand is applied to Lieb-Liniger model which describes a gas of $N$ interacting\nbosons moving on the continuous infinite line while interacting via a short\nrange potential. We carry out the quench from several initial states and for\nany number of particles and compute the evolution of the density and the noise\ncorrelations. In the long time limit the system dilutes and we find that for\nany value of repulsive coupling independently of the initial state the system\nasymptotes towards astrongly repulsive gas, while for any value of attractive\ncoupling, the system forms a maximal bound state that dominates at longer\ntimes. In either case the system equilibrates but does not thermalize, an\neffect that is consistent with prethermalization. These results can be\nconfronted with experiments. For much more detail see: Phys. Rev. A 87, 053628\n(2013) on which these notes are based. Further applications of the approach to\nthe Heisenberg model and to the Anderson model will be presented elsewhere."
    },
    {
        "anchor": "Classical field records of a quantum system: their internal consistency\n  and accuracy: We determine the regime where the widespread classical field description for\nquantum Bose gases is quantitatively accurate in 1d, 2d, and 3d by a careful\nstudy of the ideal gas limit. Numerical benchmarking in 1d shows that the ideal\ngas results carry over unchanged into the weakly interacting gas. The optimum\nhigh energy cutoff is in general shown to depend strongly on the observable in\nquestion (e.g. energy, density fluctuations, phase coherence length, condensate\nfraction). This explains the wide spread of past results. A consistent\nclassical field representation with less than 10% deviation in all typical\nobservables can be given for systems at temperatures below 0.0064 degeneracy\ntemperature in 1d, and 0.49 critical temperature in 3d. Surprisingly, this is\nnot possible for the 2d ideal gas even at zero temperature because mean\ndensity, density fluctuations and energy cannot be simultaneously matched to\nthe quantum results.",
        "positive": "Landau-Ginzburg Perspective of Finite-Temperature Phase Diagrams of a\n  Two-Component Fermi-Bose Mixture: We consider a mixture of two-component Fermi and (one-component) bose gases\nunder the repulsive Bose-Fermi and attractive Fermi-Fermi interaction. We\nperform a systematic study of the finite-temperature phase diagrams in the\nchemical potential space, identifying, using the Landau-Ginzburg theory, the\nfeatures generic to the phase diagrams within the validity of our model. We\napply the theory to explore the physics of correlated BCS pairing among\nfermions in a tightly confined trap surrounded by a large BEC gas."
    },
    {
        "anchor": "Floquet engineering from long-range to short-range interactions: Quantum simulators based on atoms or molecules often have long-range\ninteractions due to dipolar or Coulomb interactions. We present a method based\non Floquet engineering to turn a long-range interaction into a short-range one.\nBy modulating a magnetic-field gradient with one or a few frequencies, one\nreshapes the interaction profile, such that the system behaves as if it only\nhad nearest-neighbor interactions. Our approach works in both one and two\ndimensions and for both spin-1/2 and spin-1 systems. It does not require\nindividual addressing, and is applicable to all experimental systems with\nlong-range interactions: trapped ions, polar molecules, Rydberg atoms,\nnitrogen-vacancy centers, and cavity QED. Our approach allows one achieve a\nshort-range interaction without relying on Hubbard superexchange.",
        "positive": "Wave chaos as signature for depletion of a Bose-Einstein condensate: We study the expansion of repulsively interacting Bose-Einstein condensates\n(BECs) in shallow one-dimensional potentials. We show for these systems that\nthe onset of wave chaos in the Gross-Pitaevskii equation (GPE), i.e. the onset\nof exponential separation in Hilbert space of two nearby condensate wave\nfunctions, can be used as indication for the onset of depletion of the BEC and\nthe occupation of excited modes within a many-body description. Comparison\nbetween the multiconfigurational time-dependent Hartree for bosons (MCTDHB)\nmethod and the GPE reveals a close correspondence between the many-body effect\nof depletion and the mean-field effect of wave chaos for a wide range of\nsingle-particle external potentials. In the regime of wave chaos the GPE fails\nto account for the fine-scale quantum fluctuations because many-body effects\nbeyond the validity of the GPE are non-negligible. Surprisingly, despite the\nfailure of the GPE to account for the depletion, coarse grained expectation\nvalues of the single-particle density such as the overall width of the atomic\ncloud agree very well with the many-body simulations. The time dependent\ndepletion of the condensate could be investigated experimentally, e.g., via\ndecay of coherence of the expanding atom cloud."
    },
    {
        "anchor": "Atomic spin-orbit coupling synthesized with magnetic-field-gradient\n  pulses: We discuss a general scheme for creating atomic spin-orbit coupling (SOC)\nsuch as the Rashba or Dresselhaus types using magnetic-field-gradient pulses.\nIn contrast to conventional schemes based on adiabatic center-of-mass motion\nwith atomic internal states restricted to a dressed-state subspace, our scheme\nworks for the complete subspace of a hyperfine-spin manifold by utilizing the\ncoupling between the atomic magnetic moment and external magnetic fields. A\nspatially dependent pulsed magnetic field acts as an internal-state-dependent\nimpulse, thereby coupling the atomic internal spin with its orbital\ncenter-of-mass motion, as in the Einstein-de Haas effect. This effective\ncoupling can be dynamically manipulated to synthesize SOC of any type (Rashba,\nDresselhaus, or any linear combination thereof). Our scheme can be realized\nwith most experimental setups of ultracold atoms and is especially suited for\natoms with zero nuclear spins.",
        "positive": "Strongly interacting spin-orbit coupled Bose-Einstein condensates in one\n  dimension: We theoretically study dilute superfluidity of spin-1 bosons with\nantiferromagnetic interactions and synthetic spin-orbit coupling (SOC) in a\none-dimensional lattice. Employing a combination of density matrix\nrenormalization group and quantum field theoretical techniques we demonstrate\nthe appearance of a robust superfluid spin-liquid phase in which the\nspin-sector of this spinor Bose-Einstein condensate remains quantum disordered\neven after introducing quadratic Zeeman and helical magnetic fields. Despite\nremaining disordered, the presence of these symmetry breaking fields lifts the\nperfect spin-charge separation and thus the nematic correlators obey power-law\nbehavior. We demonstrate that, at strong coupling, the SOC induces a charge\ndensity wave state that is not accessible in the presence of linear and\nquadratic Zeeman fields alone. In addition, the SOC induces oscillations in the\nspin and nematic expectation values as well as the bosonic Green's function.\nThese non-trivial effects of a SOC are suppressed under the application of a\nlarge quadratic Zeeman field. We discuss how our results could be observed in\nexperiments on ultracold gases of $^{23}$Na in an optical lattice."
    },
    {
        "anchor": "Mobile impurity probing a two-dimensional superfluid phase transition: The use of atomically sized quantum systems as highly sensitive measuring\ndevices represents an exciting and quickly growing research field. Here, we\nexplore the properties of a quasiparticle formed by a mobile impurity\ninteracting with a two-dimensional fermionic superfluid. The energy of the\nquasiparticle is shown to be lowered by superfluid pairing as this increases\nthe compressibility of the Fermi gas, thereby making it easier for the impurity\nto perturb its surroundings. We demonstrate that the fundamentally\ndiscontinuous nature of the superfluid to normal phase transition of a\ntwo-dimensional system, leads to a rapid increase in the quasiparticle energy\naround the critical temperature. The magnitude of this increase exhibits a\nnonmonotonic behavior as a function of the pairing strength with a sizable\nmaximum in the cross-over region, where the spatial extend of the Cooper pairs\nis comparable to the interparticle spacing.\n  Since the quasiparticle energy is measurable with present experimental\ntechniques, our results illustrate how impurities entangled with their\nenvironment can serve as useful probes for non-trivial thermal and quantum\ncorrelations.",
        "positive": "Instabilities and \"phonons\" of optical lattices in hollow optical fibers: Instabilities are predicted for a sufficiently long hollow photonic optical\nfiber, or \"cavity\", containing a one dimensional Bose-gas in the presence of a\nclassical, far red-detuned, confined weak electromagnetic mode. We examine both\na single beam with Bose gas (a type of Brillouin instability) and the case of a\nstanding wave, or optical lattice. The instabilities of these driven systems\nhave pronounced spatial structure, of combined modulational instabilities in\nthe electromagnetic and Bose density fields. Near the critical wave vectors for\nthe instability the coupled modes of the BEC and light can be interpreted as\n\"phonons\" of the optical lattice. We conjecture these spatially-structured\ninstabilities for the optical lattice, which we predict at weak fields, develop\ninto the source of spatially homogeneous heating predicted for strong fields."
    },
    {
        "anchor": "Tunneling properties of Bogoliubov mode and spin wave modes in\n  supercurrent states of a spin-1 ferromagnetic spinor Bose-Einstein condensate: We investigate tunneling properties of collective excitations in the\nferromagnetic phase of a spin-1 spinor Bose-Einstein condensate (BEC). In\naddition to the Bogoliubov mode, this superfluid phase has two spin\nexcitations, namely, the gapless transverse spin wave and the quadrupolar mode\nwith a finite excitation gap. In the mean-field theory at T=0, we examine how\nthese collective modes tunnel through a barrier potential that couples to the\nlocal density of particles. In the presence of supercurrent with a finite\nmomentum $q$, while the Bogoliubov mode shows the so-called anomalous tunneling\nbehavior (which is characterized by perfect transmission) in the low energy\nlimit, the transverse spin-wave transmits perfectly only when the momentum $k$\nof this mode coincides with $\\pm q$. At $k=\\pm q$, the wave function of this\nspin wave has the same form as the condensate wave function in the current\ncarrying state, so that the mechanism of this perfect transmission is found to\nbe the same as tunneling of supercurrent. Using this fact, the perfect\ntransmission of the spin wave is proved for a generic barrier potential. We\nshow that such perfect transmission does not occur in the quadrupolar mode.\nFurther, we consider the effects of potentials breaking U(1) and spin rotation\nsymmetries on the transmission properties of excitations. Our results would be\nuseful for understanding excitation properties of spinor BECs, as well as the\nanomalous tunneling phenomenon in Bose superfluids.",
        "positive": "Thermography of the superfluid transition in a strongly interacting\n  Fermi gas: Heat transport is a fundamental property of all physical systems and can\nserve as a fingerprint identifying different states of matter. In a normal\nliquid a hot spot diffuses while in a superfluid heat propagates as a wave\ncalled second sound. Despite its importance for understanding quantum\nmaterials, direct imaging of heat transport is challenging, and one usually\nresorts to detecting secondary effects, such as changes in density or pressure.\nHere we establish thermography of a strongly interacting atomic Fermi gas, a\nparadigmatic system whose properties relate to strongly correlated electrons,\nnuclear matter and neutron stars. Just as the color of a glowing metal reveals\nits temperature, the radiofrequency spectrum of the interacting Fermi gas\nprovides spatially resolved thermometry with sub-nanokelvin resolution. The\nsuperfluid phase transition is directly observed as the sudden change from\nthermal diffusion to second sound propagation, and is accompanied by a peak in\nthe second sound diffusivity. The method yields the full heat and density\nresponse of the strongly interacting Fermi gas, and therefore all defining\nproperties of Landau's two-fluid hydrodynamics. Our measurements serve as a\nbenchmark for theories of transport in strongly interacting fermionic matter."
    },
    {
        "anchor": "Three-body constrained bosons in double-well optical lattice: We analyse the ground-state properties of three-body constrained bosons in a\none dimensional optical lattice with staggered hoppings analogous to the double\nwell optical lattice. By considering attractive and repulsive on-site\ninteractions between the bosons, we obtain the phase diagram which exhibits\nvarious quantum phases. Due to the double-well geometry and three-body\nconstraint several gapped phases such as the Mott insulators and\ndimer/bond-order phases emerge at commensurate densities in the repulsive\ninteraction regime. Attractive interaction leads to the pair formation which\nleads to the pair bond order phase at unit filling which resembles the\nvalence-bond solid phase of composite bosonic pairs. At incommensurate\ndensities we see the signatures of the gapless pair superfluid phase.",
        "positive": "One- and two-axis squeezing via laser coupling in an atomic\n  Fermi-Hubbard model: We study a production of spin-squeezed states with ultra-cold atomic fermions\ndescribed by the Fermi-Hubbard model in the Mott insulating phase. We show\nactivation of two twisting mechanisms by a position-dependent laser coupling\nbetween internal degrees of freedom of atoms. A single laser coupling simulates\nthe one-axis twisting model with the orientation of the twisting axis\ndetermined by the coupling phase. Adding a second laser beam with a properly\nchosen phase paves the way to simulate the two-axis counter-twisting model,\nenabling to approach the Heisenberg-limited level of squeezing."
    },
    {
        "anchor": "Topological Fulde-Ferrell Superfluids in Triangular Lattices: Fulde-Ferrell (FF) Larkin-Ovchinnikov (LO) phases were proposed for\nsuperconductors or superfluids in strong magnetic field. With the experimental\nprogresses in ultracold atomic systems, topological FFLO phases has also been\nput forward, since it is a natural consequence of realizable spin-orbital\ncoupling (SOC).In this work, we theoretically investigate a triangular lattice\nmodel with SOC and in-plane field. By constructing the phase diagram, we show\nthat it can produce topological FF states with Chern numbers, $C=\\pm1$ and\n$C=-2$. We get the phase boundaries by the change of the sign of Pfaffian. The\nchiral edge states for different topological FF phases are also elucidated.",
        "positive": "Quantum stochastic description of collisions in a canonical Bose gas: We derive a stochastic process that describes the kinetics of a\none-dimensional Bose gas in a regime where three body collisions are important.\nIn this situation the system becomes non integrable offering the possibility to\ninvestigate dissipative phenomena more simply compared to higher dimensional\ngases. Unlike the quantum Boltzmann equation describing the average momentum\ndistribution, the stochastic approach allows a description of higher-order\ncorrelation functions in a canonical ensemble. As will be shown, this ensemble\ndiffers drastically from the grand canonical one. We illustrate the use of this\nmethod by determining the time evolution of the momentum mode particle number\ndistribution and the static structure factor during the evaporative cooling\nprocess."
    },
    {
        "anchor": "Phase diagrams of bosonic $AB_{n}$ chains: The $AB_{N-1}$ chain is a system that consists of repeating a unit cell with\n$N$ sites, where between the $A$ and $B$ sites there is an energy difference of\n$\\lambda$. We considered bosons in these special lattices and took into account\nthe kinetic energy, the local two-body interaction, and the inhomogenous local\nenergy in the Hamiltonian. We found the charge density wave (CDW) and\nsuperfluid and Mott insulator phases, and constructed the phase diagram for\n$N=2$ and $3$ at the thermodynamic limit. The system exhibited insulator phases\nfor densities $\\rho=\\alpha/N$, with $\\alpha$ being an integer. We obtained that\nsuperfluid regions separate the insulator phases for densities larger than one.\nFor any $N$ value, we found that for integer densities $\\rho$, the system shows\n$\\rho +1$ insulator phases, a Mott insulator phase, and $\\rho$ CDW phases. For\nnon-integer densities larger than one, several CDW phases appear.",
        "positive": "On the number of Bose-selected modes in driven-dissipative ideal Bose\n  gases: In an ideal Bose gas that is driven into a steady state far from thermal\nequilibrium, a generalized form of Bose condensation can occur. Namely, the\nsingle-particle states unambiguously separate into two groups: the group of\nBose-selected states, whose occupations increase linearly with the total\nparticle number, and the group of all other states whose occupations saturate\n[Phys. Rev. Lett. 111, 240405 (2013)]. However, so far very little is known\nabout how the number of Bose-selected states depends on the properties of the\nsystem and its coupling to the environment. The answer to this question is\ncrucial since systems hosting a single, a few, or an extensive number of\nBose-selected states will show rather different behavior. While in the former\ntwo scenarios each selected mode acquires a macroscopic occupation,\ncorresponding to (fragmented) Bose condensation, the latter case rather bears\nresemblance to a high-temperature state of matter. In this paper, we\nsystematically investigate the number of Bose-selected states, considering\ndifferent classes of the rate matrices that characterize the driven-dissipative\nideal Bose gases in the limit of weak system-bath coupling. These include rate\nmatrices with continuum limit, rate matrices of chaotic driven systems, random\nrate matrices, and rate matrices resulting from thermal baths that couple to a\nfew observables only."
    },
    {
        "anchor": "Counterdiabatic control of transport in a synthetic tight-binding\n  lattice: Quantum state transformations that are robust to experimental imperfections\nare important for applications in quantum information science and quantum\nsensing. Counterdiabatic (CD) approaches, which use knowledge of the underlying\nsystem Hamiltonian to actively correct for diabatic effects, are powerful tools\nfor achieving simultaneously fast and stable state transformations. Protocols\nfor CD driving have thus far been limited in their experimental implementation\nto discrete systems with just two or three levels, as well as bulk systems with\nscaling symmetries. Here, we extend the tool of CD control to a discrete\nsynthetic lattice system composed of as many as nine sites. Although this\nsystem has a vanishing gap and thus no adiabatic support in the thermodynamic\nlimit, we show that CD approaches can still give a substantial, several\norder-of-magnitude, improvement in fidelity over naive, fast adiabatic\nprotocols.",
        "positive": "Relaxation towards negative temperatures in bosonic systems: Generalized\n  Gibbs ensembles and beyond integrability: Motivated by the recent experimental observation of negative absolute\ntemperature states in systems of ultracold atomic gases in optical lattices\n[Braun et al., Science 339, 52 (2013)], we investigate theoretically the\nformation of these states. More specifically, we consider the relaxation after\na sudden inversion of the external parabolic confining potential in the\none-dimensional inhomogeneous Bose-Hubbard model. First, we focus on the\nintegrable hard-core boson limit which allows us to treat large systems and\narbitrarily long times, providing convincing numerical evidence for relaxation\nto a generalized Gibbs ensemble at negative temperature T<0, a notion we define\nin this context. Second, going beyond one dimension, we demonstrate that the\nemergence of negative temperature states can be understood in a dual way in\nterms of positive temperatures, which relies on a dynamic symmetry of the\nHubbard model. We complement the study by exact diagonalization simulations at\nfinite values of the on-site interaction."
    },
    {
        "anchor": "Long-time nonlinear dynamical evolution for P-band ultracold atoms in an\n  optical lattice: We report the long-time nonlinear dynamical evolution of ultracold atomic\ngases in the P-band of an optical lattice. A Bose-Einstein condensate (BEC) is\nfast and efficiently loaded into the Pband at zero quasi-momentum with a\nnon-adiabatic shortcut method. For the first one and half milliseconds, these\nmomentum states undergo oscillations due to coherent superposition of different\nbands, which are followed by oscillations up to 60ms of a much longer period.\nOur analysis shows the dephasing from the nonlinear interaction is very\nconducive to the long-period oscillations induced by the variable force due to\nthe harmonic confinement.",
        "positive": "Magnetic Order Driven Topological Transition in the Haldane-Hubbard\n  Model: In this letter we study the Haldane model with on-site repulsive interactions\nat half-filling. We show that the mean-field Hamiltonian with magnetic order\neffectively modifies parameters in the Haldane Hamiltonian, such as sublattice\nenergy difference and phase in next nearest hopping. As interaction increases,\nincreasing of magnetic order corresponds to varying these parameters and\nconsequently, drives topological transitions. At the mean-field level, one\nscenario is that the magnetic order continuously increases, and inevitably, the\nfermion gap closes at the topological transition point with nonzero magnetic\norder. Beyond the mean-field, interaction between fermions mediated by\nspin-wave fluctuations can further open up the gap, rendering a first-order\ntransition. Another scenario is a first-order transition at mean-field level\nacross which a canted magnetic order develops discontinuously, avoiding the\nfermion gap closing. We find that both scenarios exist in the phase diagram of\nthe Haldane-Hubbard model. Our predication is relevant to recent experimental\nrealization of the Haldane model in cold atom system."
    },
    {
        "anchor": "Heisenberg Symmetry and Collective Modes of One Dimensional Unitary\n  Correlated Fermions: The correlated fermionic many-particle system, near infinite scattering\nlength, reveals an underlying Heisenberg symmetry in one dimension, as compared\nto an $SO(2,1)$ symmetry in two dimensions. This facilitates an exact map from\nthe interacting to the non-interacting system, both with and without a harmonic\ntrap, and explains the short-distance scaling behavior of the wave-function.\nTaking advantage of the phenomenological Calogero-Sutherland-type interaction,\nmotivated by the density functional approach, we connect the ground-state\nenergy shift, to many-body correlation effect. For the excited states, modes at\nintegral values of the harmonic frequency $\\omega$, are predicted in one\ndimension, in contrast to the breathing modes with frequency $2\\omega$ in two\ndimensions.",
        "positive": "Quantum Zeno-based Detection and State Engineering of Ultracold Polar\n  Molecules: We present and analyze a toolbox for the controlled manipulation of ultracold\npolar molecules, consisting of detection of molecules, atom-molecule\nentanglement, and engineering of dissipative dynamics. Our setup is based on\nfast chemical reactions between molecules and atoms leading to a quantum\nZeno-based collisional blockade in the system. We demonstrate that the\nexperimental parameters for achieving high fidelities can be found using a\nstraightforward numerical optimization. We exemplify our approach for a system\ncomprised of NaK molecules and Na atoms and we discuss the consequences of\nresidual imperfections such as a finite strength of the quantum Zeno blockade."
    },
    {
        "anchor": "Controlling dark solitons on the healing length scale: While usually the optical diffraction limit is setting a limit for the\nlengthscales on which a typical alkali Bose-Einstein condensate can be\ncontrolled, we show that in certain situations control via matter waves can\nachieve smaller resolutions. For this we consider a small number of impurity\natoms which are trapped inside the density dip of a dark soliton state and show\nthat any grey soliton can be obtained by just driving the impurity atoms. By\ncontrolling the driving force on the impurity, one can therefore fully control\nthe position and velocity of the dark soliton, and also study controlled\ncollisions between these non-linear objects.",
        "positive": "Effective-range signatures in quasi-1D matter waves: sound velocity and\n  solitons: We investigate ultracold and dilute bosonic atoms under strong transverse\nharmonic confinement by using a 1D modified Gross-Pitaevskii equation (1D\nMGPE), which accounts for the energy dependence of the two-body scattering\namplitude within an effective-range expansion. We study sound waves and\nsolitons of the quasi-1D system comparing 1D MGPE results with the 1D GPE ones.\nWe point out that, when the finite-size nature of the interaction is taken into\naccount, the speed of sound and the density profiles of both dark and bright\nsolitons show relevant quantitative changes with respect to what predicted by\nthe standard 1D GPE."
    },
    {
        "anchor": "Optical lattice influenced geometry of quasi-2D binary condensates and\n  quasiparticle spectra: We explore the collective excitations of optical lattices filled with\ntwo-species Bose-Einstein condensates (TBECs). We use a set of coupled discrete\nnonlinear Schr\\\"odinger equations to describe the system, and employ\nHartree-Fock-Bogoliubov (HFB) theory with the Popov approximation to analyze\nthe quasiparticle spectra at zero temperature. The ground state geometry,\nevolution of quasiparticle energies, structure of quasiparticle amplitudes, and\ndispersion relations are examined in detail. The trends observed are in stark\ncontrast to the case of TBECs only with a harmonic confining potential. One key\nobservation is the quasiparticle energies are softened as the system is tuned\ntowards phase separation, but harden after phase separation and mode\ndegeneracies are lifted.",
        "positive": "Entanglement-assisted tunneling dynamics of impurities in a double well\n  immersed in a bath of lattice trapped bosons: We unravel the correlated tunneling dynamics of an impurity trapped in a\ndouble well and interacting repulsively with a majority species of lattice\ntrapped bosons. Upon quenching the tilt of the double well it is found that the\nquench-induced tunneling dynamics depends crucially on the interspecies\ninteraction strength and the presence of entanglement inherent in the system.\nIn particular, for weak couplings the impurity performs a rather irregular\ntunneling process in the double well. Increasing the interspecies coupling it\nis possible to control the response of the impurity which undergoes a delayed\ntunneling while the majority species effectively acts as a material barrier.\nFor very strong interspecies interaction strengths the impurity exhibits a\nself-trapping behaviour. We showcase that a similar tunneling dynamics takes\nplace for two weakly interacting impurities and identify its underlying\ntransport mechanisms in terms of pair and single-particle tunneling processes."
    },
    {
        "anchor": "Topological Polaritons: The interaction between light and matter can give rise to novel topological\nstates. This principle was recently exemplified in Floquet topological\ninsulators, where \\emph{classical} light was used to induce a topological\nelectronic band structure. Here, in contrast, we show that mixing \\emph{single}\nphotons with excitons can result in new topological polaritonic states --- or\n\"topolaritons\". Taken separately, the underlying photons and excitons are\ntopologically trivial. Combined appropriately, however, they give rise to\nnon-trivial polaritonic bands with chiral edge modes allowing for\nunidirectional polariton propagation. The main ingredient in our construction\nis an exciton-photon coupling with a phase that winds in momentum space. We\ndemonstrate how this winding emerges from spin-orbit coupling in the electronic\nsystem and an applied Zeeman field. We discuss the requirements for obtaining a\nsizable topological gap in the polariton spectrum, and propose practical ways\nto realize topolaritons in semiconductor quantum wells and monolayer transition\nmetal dichalcogenides.",
        "positive": "Ground-State Magnetization in Mixtures of a Few Ultra-Cold Fermions in\n  One-Dimensional Traps: Ground-state properties of a few spin-$1/2$ ultra-cold fermions confined in a\none-dimensional trap are studied by the exact diagonalization method. In\ncontrast to previous studies, it is not assumed that the projection of a spin\nof individual particles is fixed. Therefore, the spin is treated as an\nadditional degree of freedom and the global magnetization of the system is\nestablished spontaneously. Depending on the shape of the trap, inter-particle\ninteractions, and an external magnetic field, the phase diagram of the system\nis determined. It is shown that, for particular confinements, some values of\nthe magnetization cannot be reached by the ground-state of the system."
    },
    {
        "anchor": "Effective Mass in Bose-Einstein Condensation in the Bound State and\n  Phonon Propagation in the Unbound States: The dark and bright solitons in different systems are already known in\nKlein-Gordon lattice. Instead of an external driving force, if the intrinsic\nfield is only considered, then the modal dynamics for small oscillations could\nbe characterized by the bound state in a limited range of frequency, revealed\nvia associated Legendre polynomial. Bose Einstein condensation takes place\naround bosonic particles having different wave functions within the bound\nstates in the temperature region T = 0 to Tc having implication for the\neffective mass of the system. The pairing and interplay between the dark and\nbright solitons also occur with their effect on the condensation. This\neffective mass is calculated via statistical mechanics route by two-part\npartition function that also gives an indication for the transition\ntemperature. The disappearance of the bound state after a critical frequency,\nor equivalently, after a critical temperature, gives rise to quasi-particles or\nphonons in the unbound states that propagate through the domains.",
        "positive": "Simulating frustrated magnetism with spinor Bose gases: Although there is a broad consensus on the fact that critical behavior in\nstacked triangular Heisenberg antiferromagnets --an example of frustrated\nmagnets with competing interactions-- is described by a Landau-Ginzburg-Wilson\nHamiltonian with O(3)$\\times$O(2) symmetry, the nature of the phase transition\nin three dimensions is still debated. We show that spin-one Bose gases provide\nus with a simulator of the O(3)$\\times$O(2) model. Using a\nrenormalization-group approach, we argue that the transition is weakly first\norder and shows pseudoscaling behavior, and give estimates of the\npseudocritical exponent $\\nu$ in $^{87}$Rb, $^{41}$K and $^7$Li atom gases\nwhich can be tested experimentally."
    },
    {
        "anchor": "Fulde-Ferrell--Larkin-Ovchinnikov state in the dimensional crossover\n  between one- and three-dimensional lattices: We present a full phase diagram for the one-dimensional (1D) to\nthree-dimensional (3D) crossover of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)\nstate in an attractive Hubbard model of 3D-coupled chains in a har- monic trap.\nWe employ real-space dynamical mean-field theory which describes full local\nquantum fluctuations beyond the usual mean-field and local density\napproximation. We find strong dimensionality effects on the shell structure\nundergoing a crossover between distinctive quasi-1D and quasi-3D regimes. We\npredict an optimal regime for the FFLO state that is considerably extended to\nintermediate interchain couplings and polarizations, directly realizable with\nultracold atomic gases. We find that the 1D-like FFLO feature is vulnerable to\nthermal fluctuations, while the FFLO state of mixed 1D-3D character can be\nstabilized at a higher temperature.",
        "positive": "Resonances in ultracold dipolar atomic and molecular gases: A previously developed approach for the numerical treatment of two particles\nthat are confined in a finite optical-lattice potential and interact via an\narbitrary isotropic interaction potential has been extended to incorporate an\nadditional anisotropic dipole-dipole interaction. The interplay of a model but\nrealistic short-range Born-Oppenheimer potential and the dipole-dipole\ninteraction for two confined particles is investigated. A variation of the\nstrength of the dipole-dipole interaction leads to diverse resonance phenomena.\nIn a harmonic confinement potential some resonances show similarities to\n$s$-wave scattering resonances while in an anharmonic trapping potential like\nthe one of an optical lattice inelastic confinement-induced dipolar resonances\noccur. The latter are due to a coupling of the relative and center-of-mass\nmotion caused by the anharmonicity of the external confinement."
    },
    {
        "anchor": "Probing quantum many-body correlations by universal ramping dynamics: Ramping a physical parameter is one of the most common experimental protocols\nin studying a quantum system, and ramping dynamics has been widely used in\npreparing a quantum state and probing physical properties. Here, we present a\nnovel method of probing quantum many-body correlation by ramping dynamics. We\nramp a Hamiltonian parameter to the same target value from different initial\nvalues and with different velocities, and we show that the first-order\ncorrection on the finite ramping velocity is universal and path-independent,\nrevealing a novel quantum many-body correlation function of the equilibrium\nphases at the target values. We term this method as the non-adiabatic linear\nresponse since this is the leading order correction beyond the adiabatic limit.\nWe demonstrate this method experimentally by studying the Bose-Hubbard model\nwith ultracold atoms in three-dimensional optical lattices. Unlike the\nconventional linear response that reveals whether the quasi-particle dispersion\nof a quantum phase is gapped or gapless, this probe is more sensitive to\nwhether the quasi-particle lifetime is long enough such that the quantum phase\npossesses a well-defined quasi-particle description. In the Bose-Hubbard model,\nthis non-adiabatic linear response is significant in the quantum critical\nregime where well-defined quasi-particles are absent. And in contrast, this\nresponse is vanishingly small in both superfluid and Mott insulators which\npossess well-defined quasi-particles. Because our proposal uses the most common\nexperimental protocol, we envision that our method can find broad applications\nin probing various quantum systems.",
        "positive": "Observation of two-species vortex lattices in a mixture of\n  mass-imbalance Bose and Fermi superfluids: The superfluid mixture of interacting Bose and Fermi species is a remarkable\nmany-body quantum system. Dilute degenerate atomic gases, especially for two\nspecies of distinct masses, are excellent candidates for exploring fundamental\nfeatures of superfluid mixture. However, producing a mass-imbalance Bose-Fermi\nsuperfluid mixture, providing an unambiguous visual proof of two-species\nsuperfluidity and probing inter-species interaction effects remain challenging.\nHere, we report the realization of a two-species superfluid of lithium-6 and\npotassium-41. By rotating the dilute gases, we observe the simultaneous\nexistence of vortex lattices in both species, and thus present a definitive\nvisual evidence for the simultaneous superfluidity of the two species.\nPronounced effects of the inter-species interaction are demonstrated through a\nseries of precision measurements on the formation and decay of two-species\nvortices. Our system provides a new platform for studying novel macroscopic\nquantum phenomena in vortex matter of interacting species."
    },
    {
        "anchor": "Spontaneous PT symmetry breaking of a ferromagnetic superfluid in a\n  gradient field: We consider the interaction of a ferromagnetic spinor Bose-Einstein\ncondensate with a magnetic field gradient. The magnetic field gradient realizes\na spin-position coupling that explicitly breaks time-reversal symmetry T and\nspace parity P, but preserves the combined PT symmetry. We observe using\nnumerical simulations, a first-order phase transition spontaneously breaking\nthis re-maining symmetry. The transition to a low-gradient phase, in which\ngradient effects are frozen out by the ferromagnetic interaction, suggests the\npossibility of high-coherence magnetic sensors unaffected by gradient\ndephasing.",
        "positive": "Non-equilibrium dynamics of bosons with dipole symmetry: Large-$N$\n  Keldysh approach: We study the quench and the ramp dynamics of interacting $N$-component\ncharged bosons with dipole symmetry using Schwinger-Keldysh field theory in the\nlarge $N$ limit. The equilibrium phase diagram of these bosons shows two phases\nin the large $N$ limit. The first is a normal phase where both the global\n$U(N)$ and the dipole symmetries are conserved and the second is a delocalized\ncondensed phase where both the symmetries are broken. In contrast, our explicit\ncomputation of the steady state after an instantaneous quantum quench from the\ncondensed phase shows that an additional, novel, delocalized normal phase,\nwhere the global $U(N)$ symmetry is conserved but the dipole symmetry is\nbroken, can exist for a range of quench parameters. A study of ramp dynamics of\nthe model shows that the above-mentioned steady state exists only above a\ncritical ramp rate which we estimate."
    },
    {
        "anchor": "Charge and statistics of lattice quasiholes from density measurements: a\n  Tree Tensor Network study: We numerically investigate the properties of the quasihole excitations above\nthe bosonic fractional Chern insulator state at filling $\\nu = 1/2$, in the\nspecific case of the Harper-Hofstadter Hamiltonian with hard-core interactions.\nFor this purpose we employ a Tree Tensor Network technique, which allows us to\nstudy systems with up to $N=18$ particles on a $16 \\times 16$ lattice and\nexperiencing an additional harmonic confinement. First, we observe the\nquantization of the quasihole charge at fractional values and its robustness\nagainst the shape and strength of the impurity potentials used to create and\nlocalize such excitations. Then, we numerically characterize quasihole anyonic\nstatistics by applying a discretized version of the relation connecting the\nstatistics of quasiholes in the lowest Landau level to the depletions they\ncreate in the density profile [Macaluso et al., arXiv:1903.03011]. Our results\ngive a direct proof of the anyonic statistics for quasiholes of fractional\nChern insulators, starting from a realistic Hamiltonian. Moreover, they provide\nstrong indications that this property can be experimentally probed through\nlocal density measurements, making our scheme readily applicable in\nstate-of-the-art experiments with ultracold atoms and superconducting qubits.",
        "positive": "Tools for quantum simulation with ultracold atoms in optical lattices: After many years of development of the basic tools, quantum simulation with\nultracold atoms has now reached the level of maturity where it can be used to\ninvestigate complex quantum processes. Planning of new experiments and\nupgrading existing set-ups depends crucially on a broad overview of the\navailable techniques, their specific advantages and limitations. This Technical\nReview aims to provide a comprehensive compendium of the state of the art. We\ndiscuss the basic principles, the available techniques and their current range\nof applications. Focusing on the simulation of varied phenomena in solid-state\nphysics using optical lattice experiments, we review their basics, the\nnecessary techniques and the accessible physical parameters. We outline how to\ncontrol and use interactions with external potentials and between the atoms,\nand how to design new synthetic gauge fields and spin-orbit coupling. We\ndiscuss the latest progress in site-resolved techniques using quantum gas\nmicroscopes, and describe the unique features of quantum simulation experiments\nwith two-electron atomic species."
    },
    {
        "anchor": "Fine-grained domain counting and percolation analysis in 2D lattice\n  systems with linked-lists: We present a fine-grained approach to identify clusters and perform\npercolation analysis in a 2D lattice system. In our approach, we develop an\nalgorithm based on the linked-list data structure whereby the members of a\ncluster are nodes of a path. This path is mapped to a linked-list. This\napproach facilitates unique cluster labeling in a lattice with a single scan.\nWe use the algorithm to determine the critical exponent in the quench dynamics\nfrom the Mott insulator to the superfluid phase of bosons in 2D square optical\nlattices. The results obtained are consistent with the Kibble-Zurek mechanism.\nWe also employ the algorithm to compute the correlation length using\ndefinitions based on percolation theory and use it to identify the quantum\ncritical point of the Bose Glass to superfluid transition in the disordered 2D\nsquare optical lattices. In addition, we compute the critical exponent $\\nu$\nwhich quantify the divergence of the correlation length $\\xi$ across the phase\ntransition and the fractal dimension of the hulls of the superfluid clusters.",
        "positive": "An effective field theory approach to two trapped particles: We discuss the problem of two particles interacting via short-range\ninteractions within a harmonic-oscillator trap. The interactions are organized\naccording to their number of derivatives and defined in truncated model spaces\nmade from a bound-state basis. Leading-order (LO) interactions are iterated to\nall orders, while corrections are treated in perturbation theory. We show\nexplicitly that next-to-LO and next-to-next-to-LO interactions improve\nconvergence as the model space increases. In the large-model-space limit we\nregain results from a pseudopotential. Arbitrary scattering lengths are\nconsidered, as well as a generalization to include the non-vanishing range of\nthe interaction."
    },
    {
        "anchor": "Many-Body Dissipative Flow of a Confined Scalar Bose-Einstein Condensate\n  Driven by a Gaussian Impurity: The many-body dissipative flow induced by a mobile aussian impurity\nharmonically oscillating within a cigar-shaped Bose-Einstein condensate is\ninvestigated. For very {small and large driving frequencies} the superfluid\nphase is preserved. Dissipation is identified, for intermediate driving\nfrequencies, by the non-zero value of the drag force whose abrupt increase\n{signals the spontaneous downstream emission of an array of gray solitons.\nAfter each emission event, typically each of the solitary waves formed decays\nand splits into two daughter gray solitary waves that are found to be robust\npropagating in the bosonic background for large evolution times.} In\nparticular, a smooth transition towards dissipation is observed, with the {\\it\ncritical} velocity for solitary wave formation depending on both the\ncharacteristics of the obstacle, namely its driving frequency and width as well\nas on the interaction strength. The variance of a sample of single-shot\nsimulations indicates the fragmented nature of the system; here it is found to\nincrease during evolution for driving frequencies where the coherent structure\nformation becomes significant. Finally, we demonstrate that for fairly large\nparticle numbers in-situ single-shot images directly capture the gray soliton's\ndecay and splitting.",
        "positive": "Quantum magnetism of ultra-cold fermion systems with the symplectic\n  symmetry: We numerically study quantum magnetism of ultra-cold alkali and\nalkaline-earth fermion systems with large hyperfine spin $F=3/2$, which are\ncharacterized by a generic $Sp(N)$ symmetry with N=4. The methods of exact\ndiagonalization (ED) and density-matrix-renormalization-group are employed for\nthe large size one-dimensional (1D) systems, and ED is applied to a\ntwo-dimensional (2D) square lattice on small sizes. We focus on the magnetic\nexchange models in the Mott-insulating state at quarter-filling. Both 1D and 2D\nsystems exhibit rich phase diagrams depending on the ratio between the spin\nexchanges $J_0$ and $J_2$ in the bond spin singlet and quintet channels,\nrespectively. In 1D, the ground states exhibit a long-range-ordered\ndimerization with a finite spin gap at $J_0/J_2>1$, and a gapless spin liquid\nstate at $J_0/J_2 \\le 1$, respectively. In the former and latter cases, the\ncorrelation functions exhibit the two-site and four-site periodicities,\nrespectively. In 2D, various spin correlation functions are calculated up to\nthe size of $4\\times 4$. The Neel-type spin correlation dominates at large\nvalues of $J_0/J_2$, while a $2\\times 2$ plaquette correlation is prominent at\nsmall values of this ratio. Between them, a columnar spin-Peierls dimerization\ncorrelation peaks. We infer the competitions among the plaquette ordering, the\ndimer ordering, and the Neel ordering in the 2D system."
    },
    {
        "anchor": "Bosonic and fermionic transport phenomena of ultra-cold atoms in 1D\n  optical lattices: Using the micro-canonical picture of transport -- a framework ideally suited\nto describe the dynamics of closed quantum systems such as ultra-cold atom\nexperiments -- we show that the exact dynamics of non-interacting fermions and\nbosons exhibit very different transport properties when the system is set out\nof equilibrium by removing the particles from half of the lattice. We find that\nfermions rapidly develop a finite quasi steady-state current reminiscent of\nelectronic transport in nanoscale systems. This result is robust -- it occurs\nwith or without a harmonic confining potential and at zero or finite\ntemperature. The zero-temperature bosonic current instead exhibits strong\noscillatory behavior that decays into a steady-state of zero current only in\nthe thermodynamic limit. These differences appear most strikingly in the\ndifferent particle number fluctuations on half of the lattice as a consequence\nof the spin statistics. These predictions can be readily verified\nexperimentally.",
        "positive": "Collective spin modes of a trapped quantum ferrofluid: We report on the observation of a collective spin mode in a spinor\nBose-Einstein condensate. Initially, all spins point perpendicular to the\nexternal magnetic field. The lowest energy mode consists in a sinusoidal\noscillation of the local spin around its original axis, with an oscillation\namplitude that linearly depends on the spatial coordinates. The frequency of\nthe oscillation is set by the zero-point kinetic energy of the BEC. The\nobservations are in excellent agreement with hydrodynamic equations. The\nobserved spin mode has a universal character, independent of the atomic spin\nand spin-dependent contact interactions."
    },
    {
        "anchor": "Phase transitions in dipolar spin-1 Bose gases: We study phase transitions in homogeneous spin-1 Bose gases in the presence\nof long-range magnetic dipole-dipole interactions (DDI). We concentrate on\nthree-dimensional geometries and employ momentum shell renormalization group to\nstudy the possible instabilities caused by the dipole-dipole interaction. At\nthe zero-temperature limit where quantum fluctuations prevail, we find the\nphase diagram to be unaffected by the dipole-dipole interaction. When the\nthermal fluctuations dominate, polar and ferromagnetic condensates with DDI\nbecome unstable and we discuss this crossover in detail. On the other hand, the\nspin-singlet condensate remains stable in the presence of dipole-dipole\ninteractions.",
        "positive": "Heavy Solitons in a Fermionic Superfluid: Topological excitations are found throughout nature, in proteins and DNA, as\ndislocations in crystals, as vortices and solitons in superfluids and\nsuperconductors, and generally in the wake of symmetry-breaking phase\ntransitions. In fermionic systems, topological defects may provide bound states\nfor fermions that often play a crucial role for the system's transport\nproperties. Famous examples are Andreev bound states inside vortex cores,\nfractionally charged solitons in relativistic quantum field theory, and the\nspinless charged solitons responsible for the high conductivity of polymers.\nHowever, the free motion of topological defects in electronic systems is\nhindered by pinning at impurities. Here we create long-lived solitons in a\nstrongly interacting fermionic superfluid by imprinting a phase step into the\nsuperfluid wavefunction, and directly observe their oscillatory motion in the\ntrapped superfluid. As the interactions are tuned from the regime of\nBose-Einstein condensation (BEC) of tightly bound molecules towards the\nBardeen-Cooper-Schrieffer (BCS) limit of long-range Cooper pairs, the effective\nmass of the solitons increases dramatically to more than 200 times their bare\nmass. This signals their filling with Andreev states and strong quantum\nfluctuations. For the unitary Fermi gas, the mass enhancement is more than\nfifty times larger than expectations from mean-field Bogoliubov-de Gennes\ntheory. Our work paves the way towards the experimental study and control of\nAndreev bound states in ultracold atomic gases. In the presence of spin\nimbalance, the solitons created here represent one limit of the long\nsought-after Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state of mobile Cooper\npairs."
    },
    {
        "anchor": "Contour-time approach to the Bose-Hubbard model in the strong coupling\n  regime: Studying two-point spatio-temporal correlations at the\n  Hartree-Fock-Bogoliubov level: We develop a formalism that allows the study of correlations in space and\ntime in both the superfluid and Mott insulating phases of the Bose-Hubbard\nModel. Specifically, we obtain a two particle irreducible effective action\nwithin the contour-time formalism that allows for both equilibrium and out of\nequilibrium phenomena. We derive equations of motion for both the superfluid\norder parameter and two-point correlation functions. To assess the accuracy of\nthis formalism, we study the equilibrium solution of the equations of motion\nand compare our results to existing strong coupling methods as well as exact\nmethods where possible. We discuss applications of this formalism to out of\nequilibrium situations.",
        "positive": "Quantum walkers in a disordered lattice with power-law hopping: We study the effects of interparticle interactions and power-law tunneling\ncouplings on quantum walks executed by both a single one and a pair of\nhard-core bosons moving in clean and disordered one-dimensional lattices. For\nthis purpose, we perform exact diagonalization to explicitly evaluate the short\nand long time probabilities of finding the walkers within a surveillance area.\nOur main conclusions, summarized in phase diagrams in the disorder-power-law\nand interaction-disorder spaces, allowed us to discern two different scenarios\nfor the single and two quantum walkers dynamics. While in the single particle\ncase the transition to localized and extended regimes is identified for well\ndefined values of the disorder amplitude and power law hopping, those frontiers\nare replaced by diffuse contours in the interacting two particle case. In fact,\ncounterintuitive transport regimes as diffusion enhanced by disorder, and space\nconstrained dynamics assisted by both interactions and short tunneling range\nare found. Our results are of direct relevance for quantum systems with\nlong-range interactions that are currently realized in the laboratory."
    },
    {
        "anchor": "Floquet engineering of optical solenoids and quantized charge pumping\n  along tailored paths in two-dimensional Chern insulators: The insertion of a local magnetic flux, as the one created by a thin\nsolenoid, plays an important role in gedanken experiments of quantum Hall\nphysics. By combining Floquet engineering of artificial magnetic fields with\nthe ability of single-site addressing in quantum-gas microscopes, we propose a\nscheme for the realization of such local solenoid-type magnetic fields in\noptical lattices. We show that it can be employed to manipulate and probe\nelementary excitations of a topological Chern insulator. This includes\nquantized adiabatic charge pumping along tailored paths inside the bulk, as\nwell as the controlled population of edge modes.",
        "positive": "Gravitational vortex mass in a superfluid: We consider superfluid hydrodynamics of two-dimensional Bose-Einstein\ncondensates. Interpreting the curvature of the macroscopic condensate\nwavefunction as an effective gravity in such a superfluid universe, we argue\nfor a superfluid equivalence principle---that the gravitational mass of a\nquantised vortex should be equal to the inertial vortex mass. In this model,\ngravity and electromagnetism have the same origin and are emergent properties\nof the superfluid universe, which itself emerges from the underlying collective\nstructure of more elementary particles, such as atoms. The Bose-Einstein\ncondensate is identified as the elusive dark matter of the superfluid universe\nwith vortices and phonons, respectively, corresponding to massive charged\nparticles and massless photons. Implications of this cosmological picture of\nsuperfluids to the physics of dense vortex matter are considered."
    },
    {
        "anchor": "Spin-dependent inelastic collisions in spin-2 Bose-Einstein condensates: We studied spin-dependent two-body inelastic collisions in F=2 87Rb\nBose-Einstein condensates both experimentally and theoretically. The 87Rb\ncondensates were confined in an optical trap and selectively prepared in\nvarious spin states in the F=2 manifold at a magnetic field of 3.0 G. Measured\natom loss rates are found to depend on spin states of colliding atoms. We\nmeasured two fundamental loss coefficients for two-body inelastic collisions\nwith the total spin of 0 and 2; the coefficients determine loss rates for all\nthe spin pairs. The experimental results for mixtures of all the spin\ncombinations are in good agreement with numerical solutions of the\nGross-Pitaevskii equations that include the effect of a magnetic field\ngradient.",
        "positive": "Localizing spin dynamics in a spin-1 Bose-Einstein condensate via\n  magnetic pulses: Spin exchange interaction between atoms in a spin-1 Bose-Einstein condensate\ncauses atomic spin evolving periodically under the single spatial mode\napproximation in the mean field theory. By applying fast magnetic pulses\naccording to a two-step or a four-step control protocol, we find analytically\nthat the spin dynamics is significantly suppressed for an arbitrary initial\nstate. Numerical calculations under single mode approximation are carried out\nto confirm the validity and robustness of these protocols. This localization\nmethod can be readily utilized to improve the sensitivity of a magnetometer\nbased on spin-1 Bose-Einstein condensates."
    },
    {
        "anchor": "Two and three particles interacting in a one-dimensional trap: We outline a procedure for using matrix mechanics to compute energy\neigenvalues and eigenstates for two and three interacting particles in a\nconfining trap, in one dimension. Such calculations can bridge a gap in the\nundergraduate physics curriculum between single-particle and many-particle\nquantum systems, and can also provide a pathway from standard quantum mechanics\ncourse material to understanding current research on cold-atom systems. In\nparticular we illustrate the notion of \"fermionization\" and how it occurs not\nonly for the ground state in the presence of strong repulsive interactions, but\nalso for excited states, in both the strongly attractive and strongly repulsive\nregimes.",
        "positive": "Bosonization and entanglement spectrum for one-dimensional polar bosons\n  on disordered lattices: The extended Bose-Hubbard model subjected to a disordered potential is\npredicted to display a rich phase diagram. In the case of uniform random\ndisorder one finds two insulating quantum phases -- the Mott-insulator and the\nHaldane insulator -- in addition to a superfluid and a Bose glass phase. In the\ncase of a quasiperiodic potential further phases are found, eg the\nincommensurate density wave, adiabatically connected to the Haldane insulator.\nFor the case of weak random disorder we determine the phase boundaries using a\nperturbative bosonization approach. We then calculate the entanglement spectrum\nfor both types of disorder, showing that it provides a good indication of the\nvarious phases."
    },
    {
        "anchor": "Quantum diffusion and thermalization at resonant tunneling: Nonequilibrium dynamics and effective thermalization are studied in a\nresonant tunneling scenario via multilevel Landau-Zener crossings. Our\nrealistic many-body system, composed of two energy bands, naturally allows a\nseparation of degrees of freedom. This gives access to an effective temperature\nand single- and two-body observables to characterize the delocalization of\neigenstates and the nonequilibrium dynamics of our paradigmatic complex quantum\nsystem.",
        "positive": "Static structure factors for a spin-1 Bose-Einstein condensate: We consider the total density and spin density fluctuations of a uniform\nspin-1 Bose-Einstein condensate within the Bogoliubov formalism. We present\nresults for the total density and spin density static structure factors for all\nfour magnetic phases. A key result of our work is a set of analytic predictions\nfor the structure factors in the large and small momentum limits. These results\nwill be useful in current experiments aiming to develop a better understanding\nof the excitations and fluctuations of spinor condensates."
    },
    {
        "anchor": "Degeneracies in trapped two-component Fermi gases: We report on previously unobserved inter-system degeneracies in two-component\nequal-mass Fermi gases with interspecies zero-range interactions under\nisotropic harmonic confinement. Over the past 10 years, two-component Fermi\ngases consisting of $n_1$ spin-up and $n_2$ spin-down atoms with interspecies\nzero-range interactions have become a paradigm for modeling condensed matter\nsystems, nuclear matter and neutron matter. We show that the eigen energies of\nthe $(n_1+1,n_2-1)$ system are degenerate with the eigen energies of the\n$(n_1,n_2)$ system for any s-wave scattering length $a_s$, including infinitely\nlarge, positive and negative $a_s$. The existence of the inter-system\ndegeneracies is demonstrated explicitly for few-body systems with $n_1+n_2=4,\n5$ and 6. The degeneracies and associated symmetries are explained within a\ngroup theoretical framework.",
        "positive": "Nonlinear Hall response in the driving dynamics of ultracold atoms in\n  optical lattices: We propose that a nonlinear Hall response can be observed in Bloch\noscillations of ultracold atoms in optical lattices under the condition of\npreserved time-reversal symmetry. In the short-time limit of Bloch oscillations\ndriven by a direct current (dc) field, the nonlinear Hall current dominates,\nbeing a second-order response to the external field strength. The associated\nBerry curvature dipole, which is a second-order nonlinear coefficient of the\ndriving field, can be obtained from the oscillation of atoms. In an alternating\ncurrent (ac) driving field, the nonlinear Hall response has a double frequency\nof the driving force in the case of time-reversal symmetry."
    },
    {
        "anchor": "Ground states of atomic Fermi gases in a two-dimensional optical lattice\n  with and without population imbalance: We study the ground state phase diagram of population balanced and imbalanced\nultracold atomic Fermi gases with a short range attractive interaction\nthroughout the crossover from BCS to Bose-Einstein condensation (BEC), in a\ntwo-dimensional optical lattice (2DOL) comprised of two lattice and one\ncontinuum dimensions. We find that the mixing of lattice and continuum\ndimensions, together with population imbalance, has an extraordinary effect on\npairing and the superfluidity of atomic Fermi gases. In the balanced case, the\nsuperfluid ground state prevails the majority of the phase space. However, for\nrelatively small lattice hopping integral $t$ and large lattice constant $d$, a\npair density wave (PDW) emerges unexpectedly at intermediate coupling strength,\nand the nature of the in-plane and overall pairing changes from particle-like\nto hole-like in the BCS and unitary regimes, associated with an abnormal\nincrease in the Fermi volume with the pairing strength. In the imbalanced case,\nthe stable polarized superfluid phase shrinks to only a small portion of the\nentire phase space spanned by $t$, $d$, imbalance $p$ and interaction strength\n$U$, mainly in the bosonic regime of low $p$, moderately strong pairing, and\nrelatively large $t$ and small $d$. Due to the Pauli exclusion between paired\nand excessive fermions within the confined momentum space, a PDW phase emerges\nand the overall pairing evolves from particle-like into hole-like, as the\npairing strength grows stronger in the BEC regime. In both cases, the ground\nstate property is largely governed by the Fermi surface topology. These\nfindings are very different from the cases of pure 3D continuum, 3D lattice or\n1DOL.",
        "positive": "Probing the critical exponent of superfluid fraction in a strongly\n  interacting Fermi gas: We theoretically investigate the critical behavior of second sound mode in a\nharmonically trapped ultracold atomic Fermi gas with resonant interactions.\nNear the superfluid phase transition with critical temperature $T_{c}$, the\nfrequency or the sound velocity of second sound mode depends crucially on the\ncritical exponent $\\beta$ of superfluid fraction. In an isotropic harmonic\ntrap, we predict that the mode frequency diverges like\n$(1-T/T_{c})^{\\beta-1/2}$ when $\\beta<1/2$. In a highly elongated trap, the\nspeed of second sound reduces by a factor $1/\\sqrt{2\\beta+1}$ from that in a\nhomogeneous three-dimensional superfluid. Our prediction could be readily\ntested by measurements of second sound wave propagation in a setup such as that\nexploited by Sidorenkov \\textit{et al.} {[}Nature \\textbf{498}, 78 (2013){]}\nfor resonantly interacting lithium-6 atoms, once the experimental precision is\nimproved."
    },
    {
        "anchor": "Bose-Einstein condensates in an atom-optomechanical system with\n  effective global non-uniform interaction: We consider a hybrid atom-optomechanical system consisting of a mechanical\nmembrane inside an optical cavity and an atomic Bose-Einstein condensate\noutside the cavity. The condensate is confined in an optical lattice potential\nformed by a traveling laser beam reflected off one cavity mirror. We derive the\ncavity-mediated effective atom-atom interaction potential, and find that it is\nnon-uniform, site-dependent, and does not decay as the interatomic distance\nincreases. We show that the presence of this effective interaction breaks the\nZ$_2$ symmetry of the system and gives rise to new quantum phases and phase\ntransitions. When the long-range interaction dominates, the condensate breaks\nthe translation symmetry and turns into a novel self-organized lattice-like\nstate with increasing particle densities for sites farther away from the\ncavity. We present the phase diagram of the system, and investigate the\nstabilities of different phases by calculating their respective excitation\nspectra. The system can serve as a platform to explore various self-organized\nphenomena induced by the long-range interactions.",
        "positive": "Experimental observation of a topological band gap opening in ultracold\n  Fermi gases with two-dimensional spin-orbit coupling: The recent experimental realization of synthetic spin-orbit coupling (SOC)\nopens a new avenue for exploring novel quantum states with ultracold atoms.\nHowever, in experiments for generating two-dimensional SOC (e.g., Rashba type),\na perpendicular Zeeman field, which opens a band gap at the Dirac point and\ninduces many topological phenomena, is still lacking. Here we theoretically\npropose and experimentally realize a simple scheme for generating two-dimension\nSOC and a perpendicular Zeeman field simultaneously in ultracold Fermi gases by\ntuning the polarization of three Raman lasers that couple three hyperfine\nground states of atoms. The resulting band gap opening at the Dirac point is\nprobed using spin injection radio-frequency spectroscopy. Our observation may\npave the way for exploring topological transport and topological superfluids\nwith exotic Majorana and Weyl fermion excitations in ultracold atoms."
    },
    {
        "anchor": "Quantum Mechanical Stabilization of a Collapsing Bose-Bose Mixture: According to the mean-field theory a condensed Bose-Bose mixture collapses\nwhen the interspecies attraction becomes stronger than the geometrical average\nof the intraspecies repulsions, $g_{12}^2>g_{11} g_{22}$. We show that instead\nof collapsing such a mixture gets into a dilute liquid-like droplet state\nstabilized by quantum fluctuations thus providing a direct manifestation of\nbeyond mean-field effects. We study various properties of the droplet and find,\nin particular, that in a wide range of parameters its excitation spectrum lies\nentirely above the particle emission threshold. The droplet thus automatically\nevaporates itself to zero temperature, the property potentially interesting by\nitself and from the viewpoint of sympathetic cooling of other systems.",
        "positive": "Weakly interacting Bose gas with two-body losses: We study the many-body dynamics of weakly interacting Bose gases with\ntwo-particle losses. We show that both the two-body interactions and losses in\natomic gases may be tuned by controlling the inelastic scattering process\nbetween atoms by an optical Feshbach resonance. Interestingly, the low-energy\nbehavior of the scattering amplitude is governed by a single parameter, i.e.\nthe complex $s$-wave scattering length $a_c$. The many-body dynamics are thus\ndescribed by a Lindblad master equation with complex scattering length. We\nsolve this equation by applying the Bogoliubov approximation in analogy to the\nclosed systems. Various peculiar dynamical properties are discovered, some of\nthem may be regarded as the dissipative counterparts of the celebrated results\nin closed Bose gases. For example, we show that the next-order correction to\nthe mean-field particle decay rate is to the order of $|n a_c^{3}|^{1/2}$,\nwhich is an analogy of the Lee-Huang-Yang correction of Bose gases. It is also\nfound that there exists a dynamical symmetry of the symplectic group\nSp$(4,\\mathbb{C})$ in the quadratic Bogoliubov master equation, which is an\nanalogy of the SU(1,1) dynamical symmetry of the corresponding closed system.\nWe further confirmed the validity of the Bogoliubov approximation by comparing\nits results with a full numerical calculation in a double-well toy model.\nGeneralizations of other alternative approaches such as the dissipative version\nof the Gross-Pitaevskii equation and hydrodynamic theory are also discussed in\nthe last."
    },
    {
        "anchor": "Quantum gas microscopy for single atom and spin detection: A particular strength of ultracold quantum gases are the versatile detection\nmethods available. Since they are based on atom-light interactions, the whole\nquantum optics toolbox can be used to tailor the detection process to the\nspecific scientific question to be explored in the experiment. Common methods\ninclude time-of-flight measurements to access the momentum distribution of the\ngas, the use of cavities to monitor global properties of the quantum gas with\nminimal disturbance and phase-contrast or high-intensity absorption imaging to\nobtain local real space information in high-density settings. Even the ultimate\nlimit of detecting each and every atom locally has been realized in\ntwo-dimensions using so-called quantum gas microscopes. In fact, these\nmicroscopes not only revolutionized the detection, but also the control of\nlattice gases. Here we provide a short overview of this technique, highlighting\nnew observables as well as key experiments that have been enabled by quantum\ngas microscopy.",
        "positive": "Dynamical generation of phase-squeezed states in a two-component\n  Bose-Einstein condensates: As an \"input\" state of a linear (Mach-Zehnder or Ramsey) interferometer, the\nphase-squeezed state proposed by Berry and Wiseman exhibits the best\nsensitivity approaching to the Heisenberg limit [Phys. Rev. Lett. 85, 5098\n(2000)]. In this paper, we find that it can be generated dynamically with\natomic Bose-Einstein condensates confined in a symmetric double well. Similar\nwith the Berry and Wiseman's state, the prepared states show the squeezing\nalong spin operator S_y and the anti-squeezing along S_z, leading to a\nsub-shot-noise of the phase sensitivity."
    },
    {
        "anchor": "Density profiles and correlations of harmonically trapped ultracold\n  fermions via complex Langevin: Standard lattice formulations of non-relativistic Fermi gases with two spin\ncomponents suffer from a sign problem in the cases of repulsive contact\ninteractions and attractive contact interactions with spin imbalance. We\ndiscuss the nature of this sign problem and the applicability of stochastic\nquantisation with complex Langevin evolution in both cases. For repulsive\ninteractions, we find that the results converge, using adaptive step size\nscaling and a Gaussian regulator to modify the lattice action. We present\nresults on density profiles and correlations of a harmonically trapped system\nin one spatial dimension.",
        "positive": "Interaction quenches in Bose gases studied with a time-dependent\n  hypernetted-chain Euler-Lagrange method: We present a new variational method to study the dynamics of a closed bosonic\nmany-body system, the time-dependent hypernetted-chain Euler-Lagrange method,\ntHNC . Based on the Jastrow ansatz, it accounts for quantum fluctuations in a\nnon-perturbative way. tHNC scales well with the number of dimensions, as\ndemonstrated by our results on one, two, and three dimensions. We apply the\ntHNC method to interaction quenches, i.e. sudden changes of the interaction\nstrength, in homogeneous Bose gases. When the quench is strong enough that the\nfinal state has roton excitations (as found and predicted for dipolar and\nRydberg-dressed Bose-Einstein condensates, respectively), the pair distribution\nfunction exhibits stable oscillations. For validation, we compare tHNC results\nwith time-dependent variational Monte Carlo results in one and two dimensions."
    },
    {
        "anchor": "Exact Solution for 1D Spin-Polarized Fermions with Resonant Interactions: Using the asymptotic Bethe Ansatz, we obtain an exact solution of the\nmany-body problem for 1D spin-polarized fermions with resonant p-wave\ninteractions, taking into account the effects of both scattering volume and\neffective range. Under typical experimental conditions, accounting for the\neffective range, the properties of the system are significantly modified due to\nthe existence of \"shape\" resonances. The excitation spectrum of the considered\nmodel has unexpected features, such as the inverted position of the particle-\nand hole-like branches at small momenta, and roton-like minima. We find that\nthe frequency of the \"breathing\" mode in the harmonic trap provides an\nunambiguous signature of the effective range.",
        "positive": "Interaction-induced topological properties of two bosons in flat-band\n  systems: In flat-band systems, destructive interference leads to the localization of\nnon-interacting particles and forbids their motion through the lattice.\nHowever, in the presence of interactions the overlap between neighbouring\nsingle-particle localized eigenstates may enable the propagation of bound pairs\nof particles. In this work, we show how these interaction-induced hoppings can\nbe tuned to obtain a variety of two-body topological states. In particular, we\nconsider two interacting bosons loaded into the orbital angular momentum $l=1$\nstates of a diamond-chain lattice, wherein an effective $\\pi$ flux may yield a\ncompletely flat single-particle energy landscape. In the weakly-interacting\nlimit, we derive effective single-particle models for the two-boson\nquasiparticles which provide an intuitive picture of how the topological states\narise. By means of exact diagonalization calculations, we benchmark these\nstates and we show that they are also present for strong interactions and away\nfrom the strict flat-band limit. Furthermore, we identify a set of doubly\nlocalized two-boson flat-band states that give rise to a special instance of\nAharonov-Bohm cages for arbitrary interactions."
    },
    {
        "anchor": "Floquet engineering of correlated tunneling in the Bose-Hubbard model\n  with ultracold atoms: We report on the experimental implementation of tunable occupation-dependent\ntunneling in a Bose-Hubbard system of ultracold atoms via time-periodic\nmodulation of the on-site interaction energy. The tunneling rate is inferred\nfrom a time-resolved measurement of the lattice site occupation after a quantum\nquench. We demonstrate coherent control of the tunneling dynamics in the\ncorrelated many-body system, including full suppression of tunneling as\npredicted within the framework of Floquet theory. We find that the tunneling\nrate explicitly depends on the atom number difference in neighboring lattice\nsites. Our results may open up ways to realize artificial gauge fields that\nfeature density dependence with ultracold atoms.",
        "positive": "Collective Excitations of Self-Gravitating Bose-Einstein Condensates:\n  Breathing Mode and Appearance of Anisotropy under Self-Gravity: We study the collective mode of self-gravitating Bose-Einstein condensates\n(BECs) described by the Gross-Pitaevskii-Poisson (GPP) equation. The\nself-gravitating BEC recently receives significant attention in cosmology and\nastrophysics as a candidate for dark matter. We investigate the breathing and\nanisotropic collective modes by numerically solving the GPP equation and using\nthe variational method. The breathing mode shows that the period decreases with\nthe total mass due to the density dependence of the self-gravitating BEC, which\nis quantitatively consistent with our analytical results. We also obtain an\nanisotropic collective mode, in which the quadrupole mode is coupled with the\nbreathing mode. The period of the quadrupole mode has the same total mass\ndependence as that of the breathing mode. The characteristics of these periods\nare different from those of ordinary BECs trapped by an external potential.\nHowever, despite the difference in density dependence, their ratio is equal to\nthat of the BEC trapped by an isotropic harmonic potential. Furthermore, a\nvariational method extended to a spheroidal configuration shows that we extract\nonly the quadrupole mode from the anisotropic collective mode."
    },
    {
        "anchor": "Supersolid structure and excitation spectrum of soft-core bosons in 3D: By means of a mean-field method, we have studied the zero temperature\nstructure and excitation spectrum of a three-dimensional soft-core bosonic\nsystem for a value of the interaction strength that favors a crystal structure\nmade of atomic nano-clusters arranged with FCC ordering. In addition to the\nlongitudinal and transverse phonon branches expected for a normal crystal, the\nexcitation spectrum shows a soft mode related to the breaking of gauge\nsymmetry, which signals a partial superfluid character of the solid. Additional\nevidence of supersolidity is provided by the calculation of the superfluid\nfraction, which shows a first-order drop, from 1 to 0.4, at the\nliquid-supersolid transition and a monotonic decrease as the interaction\nstrength parameter is increased. The conditions for the coexistence of the\nsupersolid with the homogeneous superfluid are discussed, and the surface\ntension of a representative solid-liquid interface is calculated.",
        "positive": "Realizing a scalable building block of a U(1) gauge theory with cold\n  atomic mixtures: In the fundamental laws of physics, gauge fields mediate the interaction\nbetween charged particles. An example is quantum electrodynamics -- the theory\nof electrons interacting with the electromagnetic field -- based on U(1) gauge\nsymmetry. Solving such gauge theories is in general a hard problem for\nclassical computational techniques. While quantum computers suggest a way\nforward, it is difficult to build large-scale digital quantum devices required\nfor complex simulations. Here, we propose a fully scalable analog quantum\nsimulator of a U(1) gauge theory in one spatial dimension. To engineer the\nlocal gauge symmetry, we employ inter-species spin-changing collisions in an\natomic mixture. We demonstrate the experimental realization of the elementary\nbuilding block as a key step towards a platform for large-scale quantum\nsimulations of continuous gauge theories."
    },
    {
        "anchor": "Creation of orbital angular momentum states with chiral polaritonic\n  lenses: Controlled transfer of orbital angular momentum to exciton-polariton\nBose-Einstein condensate spontaneously created under incoherent, off-resonant\nexcitation conditions is a long-standing challenge in the field of microcavity\npolaritonics. We demonstrate, experimentally and theoretically, a simple and\nefficient approach to generation of nontrivial orbital angular momentum states\nby using optically-induced potentials -- chiral polaritonic lenses.",
        "positive": "Analytic models for density of a ground-state spinor condensate: We demonstrate that the ground state of a trapped spin-1 and spin-2 spinor\nferromagnetic Bose-Einstein condensate (BEC) can be well approximated by a\nsingle decoupled Gross-Pitaevskii (GP) equation. Useful analytic models for the\nground-state densities of ferromagnetic BECs are obtained from the Thomas-Fermi\napproximation (TFA) to this decoupled equation. Similarly, for the ground\nstates of spin-1 anti-ferromagnetic and spin-2 anti-ferromagnetic and cyclic\nBECs, some of the spin component densities are zero which reduces the coupled\nGP equation to a simple reduced form. Analytic models for ground state\ndensities are also obtained for anti-ferromagnetic and cyclic BECs from the TFA\nto the respective reduced GP equations. The analytic densities are illustrated\nand compared with the full numerical solution of the GP equation with realistic\nexperimental parameters."
    },
    {
        "anchor": "C and Fortran OpenMP programs for rotating Bose-Einstein condensates: We present OpenMP versions of C and Fortran programs for solving the\nGross-Pitaevskii equation for a rotating trapped Bose-Einstein condensate (BEC)\nin two (2D) and three (3D) spatial dimensions. The programs can be used to\ngenerate vortex lattices and study dynamics of rotating BECs. We use the\nsplit-step Crank-Nicolson algorithm for imaginary- and real-time propagation to\ncalculate stationary states and BEC dynamics, respectively. The programs\npropagate the condensate wave function and calculate several relevant physical\nquantities, such as the energy, the chemical potential, and the\nroot-mean-square sizes. The imaginary-time propagation starts with an analytic\nwave function with one vortex at the trap center, modulated by a random phase\nat different space points. Nevertheless, the converged wave function for a\nrapidly rotating BEC with a large number of vortices is most efficiently\ncalculated using the pre-calculated converged wave function of a rotating BEC\ncontaining a smaller number of vortices as the initial state rather than using\nan analytic wave function with one vortex as the initial state. These\npre-calculated initial states exhibit rapid convergence for fast-rotating\ncondensates to states containing multiple vortices with an appropriate phase\nstructure. This is illustrated here by calculating vortex lattices with up to\n61 vortices in 2D and 3D. Outputs of the programs include calculated physical\nquantities, as well as the wave function and different density profiles (full\ndensity, integrated densities in lower dimensions, and density cross-sections).\nThe provided real-time propagation programs can be used to study the dynamics\nof a rotating BEC using the imaginary-time stationary wave function as the\ninitial state. We also study the efficiency of parallelization of the present\nOpenMP C and Fortran programs with different compilers.",
        "positive": "Fermi-Bose Mixtures Near Broad Interspecies Feshbach Resonances: In this Letter we have studied dressed bound states in Fermi-Bose mixtures\nnear broad interspecies resonance, and implications on many-body correlations.\nWe present the evidence for a first order phase transition between a mixture of\nFermi gas and condensate, and a fully paired mixture where extended fermionic\nmolecules occupy a single pairing channel instead of forming a molecular Fermi\nsurface. We have further investigated the effect of Fermi surface dynamics,\npair fluctuations and discussed the validity of our results."
    },
    {
        "anchor": "Impact of density inhomogeneity on the critical velocity for vortex\n  shedding in a harmonically trapped Bose-Einstein condensate: We report on a numerical study of the critical velocity for creation of\nquantized vortices by a moving Gaussian obstacle in a trapped Bose-Einstein\ncondensate, modeled by the Gross-Pitaevskii equation. We pay attention to\nimpact of density inhomogeneity associated with the global inverted-parabolic\nprofile by a trapping potential as well as the local density suppression around\nthe Gaussian obstacle. When the width of the Gaussian potential is large, the\nwake dynamics is significantly influenced by the nonuniformity around the\nobstacle potential. The critical velocity, estimated through the time interval\nbetween the first and second vortex emission, can be explained by the local\nsound velocity by taking into account the above two contributions. We also find\nthat the ratio of the critical velocity to the sound velocity at the center of\nthe system is insensitive to the nonlinear coefficient of the Gross-Pitaevskii\nequation, which supports the universal discussion even in a inhomogeneous\ntrapped condensate under the local density approximation.",
        "positive": "Strongly interacting bosons in multi-chromatic potentials supporting\n  mobility edges: localization, quasi-condensation and expansion dynamics: We provide an account of the static and dynamic properties of hard-core\nbosons in a one-dimensional lattice subject to a multi-chromatic quasiperiodic\npotential for which the single-particle spectrum has mobility edges. We use the\nmapping from strongly interacting bosons to weakly interacting fermions, and\nprovide exact numerical results for hard-core bosons in and out of equilibrium.\nIn equilibrium, we find that the system behaves like a quasi-condensate\n(insulator) depending on whether the Fermi surface of the corresponding\nfermionic system lies in a spectral region where the single-particle states are\ndelocalized (localized). We also study non-equilibrium expansion dynamics of\ninitially trapped bosons, and demonstrate that the extent of partial\nlocalization is determined by the single-particle spectrum."
    },
    {
        "anchor": "Confinement and Mott transitions of dynamical charges in 1D lattice\n  gauge theories: Confinement is an ubiquitous phenomenon when matter couples to gauge fields,\nwhich manifests itself in a linear string potential between two static charges.\nAlthough gauge fields can be integrated out in one dimension, they can mediate\nnon-local interactions which in turn influence the paradigmatic Luttinger\nliquid properties. However, when the charges become dynamical and their\ndensities finite, understanding confinement becomes challenging. Here we show\nthat confinement in 1D $\\mathbb{Z}_2$ lattice gauge theories, with dynamical\nmatter fields and arbitrary densities, is related to translational symmetry\nbreaking in a non-local basis. The exact transformation to this string-length\nbasis leads us to an exact mapping of Luttinger parameters reminiscent of a\nLuther-Emery re-scaling. We include the effects of local, but beyond contact,\ninteractions between the matter particles, and show that confined mesons can\nform a Mott-insulating state when the deconfined charges cannot. While the\ntransition to the Mott state cannot be detected in the Green's function of the\ncharges, we show that the metallic state is characterized by hidden\noff-diagonal quasi-long range order. Our predictions provide new insights to\nthe physics of confinement of dynamical charges, and can be experimentally\naddressed in Rydberg-dressed quantum gases in optical lattices.",
        "positive": "Viscous Flow in a 1D Spin-Polarized Fermi Gas: the Role of Integrability\n  on Viscosity: The transport properties of one-dimensional Fermi gases at low-temperatures\nare often described by the Luttinger liquid (LL) model. However, to study\ndissipation one needs to examine interactions beyond the LL model. In this work\nwe provide a simple model which allows for a direct microscopic calculation of\nthe bulk viscosity, namely the one dimensional spin polarized p-wave Fermi gas.\nWe calculate the bulk viscosity in both the high- and low-temperature limits.\nWe find that the bulk viscosity is finite and consistent with the requirement\nof scale symmetry, in spite of the inherent integrability of the microscopic\nmodel. We argue how integrability does not forbid a finite bulk viscosity, and\ncompare our work to previous kinetic theory calculations."
    },
    {
        "anchor": "Engineering mixing properties of fluids by spatial modulations: We propose a method to change the effective interaction between two fluids by\nmodulation of their local density distributions with external periodic\npotentials, whereby the mixing properties can be controlled. This method is\napplied to a mixture of dilute bosonic gases, and binodal and spinodal curves\nemerge in the phase diagram. Spinodal decomposition into a mixed-bubble state\nbecomes possible, in which one of the coexisting phases has a finite mixing\nratio. A metastable mixture is also realized, which undergoes phase separation\nvia nucleation.",
        "positive": "Orthogonality Catastrophe in Quantum Sticking: The probability that a particle will stick to a surface is fundamental to a\nvariety of processes in surface science, including catalysis, epitaxial growth,\nand corrosion. At ultralow energies, how particles scatter or stick to a\nsurface affects the performance of atomic clocks, matter-wave interferometers,\natom chips and other quantum information processing devices. In this energy\nregime, the sticking probability is influenced by a distinctly quantum\nmechanical effect: quantum reflection, a result of matter wave coherence,\nsuppresses the probability of finding the particle near the surface and reduces\nthe sticking probability. We find that another quantum effect can occur,\nfurther shaping the sticking probability: the orthogonality catastrophe, a\nresult of the change in the quantum ground state of the surface in the presence\nof a particle, can dramatically alter the probability for quantum sticking and\ncreate a superreflective surface at low energies."
    },
    {
        "anchor": "Efimov energy level rebounding off the atom-dimer continuum: The Efimov effect, with its ladder of weakly bound three-atomic molecules,\nposes intriguing questions in the theoretically controversial and\nexperimentally demanding regime of merging of the first excited Efimov energy\nlevel with the atom-dimer continuum. Using an original experimental technique,\nwhere a coherent superposition state of diatomic and triatomic molecules is\nutilized, we investigate this regime and reveal a striking behavior: Instead of\nmerging with the atom-dimer continuum the trimer energy level rebounds from it\nand becomes a deeper bound state again. In addition, instead of a tangential\napproach between the two levels we observe a rather narrow resonance, providing\na new challenge and guide for few-body theories to incorporate realistic\ninteratomic potentials.",
        "positive": "Phonon redshift and Hubble friction in an expanding BEC: We revisit the theoretical analysis of an expanding ring-shaped Bose-Einstein\ncondensate. Starting from the action and integrating over dimensions orthogonal\nto the phonon's direction of travel, we derive an effective one-dimensional\nwave equation for azimuthally-travelling phonons. This wave equation shows that\nexpansion redshifts the phonon frequency at a rate determined by the effective\nazimuthal sound speed, and damps the amplitude of the phonons at a rate given\nby $\\dot{\\cal V}/{\\cal V}$, where $\\cal{V}$ is the volume of the background\ncondensate. This behavior is analogous to the redshifting and \"Hubble friction\"\nfor quantum fields in the expanding universe and, given the scalings with\nradius determined by the shape of the ring potential, is consistent with recent\nexperimental and theoretical results. The action-based dimensional reduction\nmethods used here should be applicable in a variety of settings, and are well\nsuited for systematic perturbation expansions."
    },
    {
        "anchor": "Mesoscopic ensembles of polar bosons in triple-well potentials: Mesoscopic dipolar Bose gases in triple-well potentials offer a minimal\nsystem for the analysis of the long-range character of the dipole-dipole\ninteractions. We show that this long-range character may be clearly revealed by\na variety of possible ground-state phases. In addition, an appropriate control\nof short-range and dipolar interactions may lead to novel scenarios for the\ndynamics of atoms and polar molecules in lattices, including the dynamical\ncreation of mesoscopic Schr\\\"odinger cats, which may be employed as a source of\nhighly-nonclassical states for Heisenberg-limited interferometry.",
        "positive": "Multi-component states for trapped spin-1 Bose-Einstein Condensates in\n  the presence of magnetic field: In presence of a magnetic field, multi-component ground states appear in\ntrapped spin-1 Bose-Einstein condensates for both ferromagnetic and\nanti-ferromagnetic types of spin-spin interaction. We aim to produce an\naccurate analytical description of the multi-component states which is of\nfundamental importance. Despite being in the so-called regime of Thomas-Fermi\napproximation (condensates with large particle number), the scenario of\nmulti-component states is problematic under this approximation due to large\nvariation in densities of the sub-components. We generalize the variational\nmethod that we have introduced in the article [Eur. Phys. J. Plus 137, 547\n(2022)] to overcome the limitations of T-F approximation. We demonstrate that\nthe variational method is crucial in identifying multi-component ground states.\nA comparison of the results of the variational method, which is multi-modal by\nconstruction, with that of single-mode approximation is also presented in this\npaper to demonstrate a marked improvement in accuracy over single-mode\napproximation. We have also looked into the phase transition between the\nphase-matched and polar state in a trapped condensate using the variational\nmethod and have identified substantial change in the phase boundary. The\ncorrespondence of the phase diagram of the trapped case with the homogeneous\none identifies other limitations of T-F approximation as opposed to the more\naccurate variational method."
    },
    {
        "anchor": "Drag force of a exciton-polariton condensate under non-resonant pumping: Exciton-polariton condensate in semiconductor microcavities constitute a\nnovel kind of non-equilibrium superfluid. In a recent experiment [P. Stepanov,\n{\\it et. al.,} Nat. Commun. {\\bf 10}, 1038 (2019)], the dispersion relation of\ncollective excitations in a polariton condensate under the resonant pumping has\nbeen investigated with the emphasis on the role of reservoir of long-lived\nexcitons in determining the superfluidity. Inspired by such an experimental\nadvance, we study the superfluidity of a exciton-polaritonn condensate under\nnon-resonant pumping by calculating the drag force exerted on a classical\nimpurity moving in a polariton condensate. For a non-resonant pumped polariton\ncondensate prepared in the gapped phase, due to the reservoir's modes, the drag\nforce can be large when the velocity of the impurity is small. Besides, as the\nvelocity increases, the drag force can decrease. For not very large velocity,\nthe drag force is enhanced if the condensate is tuned to be more dissipative.\nWhen the condensate is close to the transition point between the gapped phase\nand the gapless one, the drag force is similar to that of the equilibrium\nsuperfluid. Our present work reveals the effects of the reservoir's modes on\nthe superfluidity properties of a polariton condensate with the non-resonant\npumping.",
        "positive": "Excitons and Cavity Polaritons for Optical Lattice Ultracold Atoms: Ultracold atoms uniformly filling an optical lattice can be treated like an\nartificial crystal. An implementation including the atomic occupation of a\nsingle excited atomic state can be represented by a two-component Bose-Hubbard\nmodel. Its phase diagram exhibits a quantum phase transition from a superfluid\nto a Mott insulator phase. The dynamics of electronic excitations governed by\nelectrostatic dipole-dipole interactions in the ordered regime can be well\ndescribed by wave-like collective excitations called excitons. Here we present\nan extensive study of such excitons for a wide range of geometries and\ndimensionality. Their lifetimes can vary over many orders of magnitude from\nmetastable propagation to superradiant decay. Particularly strong effects occur\nin one dimensional atomic chains coupled to tapered optical fibers. For an\noptical lattice within a cavity the excitons are coupled to cavity photons and\nthe resulting collective cavity QED model can be efficiently formulated in\nterms of polaritons. Their properties are explicitly calculated for different\nlattices and they constitute a non-destructive monitoring tool for important\nsystem properties. Even the formation of molecules in optical lattices\nmanifests itself in modified polariton properties as e.g. an anisotropic\noptical spectrum. Partial dissipation of the exciton energy in the lattice\nleads to heating, which can be microscopically understood through a mechanism\ntransferring atoms into higher Bloch bands via a resonant excitation transfer\namong neighboring lattice sites. The presence of lattice defects like vacancies\nin the Mott insulator induces a characteristic scattering of polaritons, which\ncan be optically observed to monitor the lattice integrity. Our models can be\napplied to simulate and understand corresponding collective phenomena in solid\ncrystals, where many effects are often masked by noise and disorder."
    },
    {
        "anchor": "Scale breaking and fluid dynamics in a dilute two-dimensional Fermi gas: We study two observables related to the anomalous breaking of scale\ninvariance in a dilute two dimensional Fermi gas, the frequency shift and\ndamping rate of the monopole mode in a harmonic confinement potential. For this\npurpose we compute the speed of sound and the bulk viscosity of the two\ndimensional gas in the high temperature limit. We show that the anomaly in the\nspeed of sound scales as $(2P-\\rho c_s^2)/P\\sim z/[\\log(T/E_B)]^2$, and that\nthe bulk viscosity $\\zeta$ scales as $\\zeta/\\eta \\sim z^2/[\\log(T/E_B)]^6$.\nHere, $P$ is the pressure, $c_s^2$ is the speed of sound, $\\eta$ is the shear\nviscosity, $z$ is the fugacity, and $E_B$ is the two-body binding energy. We\nshow that our results are consistent with the experimental results of Vogt et\nal. [Phys. Rev. Lett. 108, 070404 (2012)]. Vogt et al. reported a frequency\nshift $\\delta\\omega/\\omega$ of the order of a few percent, and a damping rate\nsmaller than the background rate $\\Gamma/\\omega_0\\sim 5%$.",
        "positive": "Phase space manipulations of many-body wavefunctions: We explore the manipulation in phase space of many-body wavefunctions that\nexhibit self-similar dynamics, under the application of sudden force and/or in\nthe presence of a constant acceleration field. For this purpose, we work out a\ncommon theoretical framework based on the Wigner function. We discuss squeezing\nin position space, phase space rotation and its implications in cooling for\nboth non-interacting and interacting gases, and time reversal operation. We\ndiscuss various optical analogies and calculate the role of spherical-like\naberration in cooling protocols. We also present the equivalent of a spin-echo\ntechnique to improve the robustness of velocity dispersion reduction protocols."
    },
    {
        "anchor": "Polar bosons in one-dimensional disordered optical lattices: We analyze the effects of disorder and quasi-disorder on the ground-state\nproperties of ultra-cold polar bosons in optical lattices. We show that the\ninterplay between disorder and inter-site interactions leads to rich phase\ndiagrams. A uniform disorder leads to a Haldane-insulator phase with finite\nparity order, whereas the density-wave phase becomes a Bose-glass at very weak\ndisorder. For quasi-disorder, the Haldane insulator connects with a gapped\ngeneralized incommesurate density wave without an intermediate critical region.",
        "positive": "Observation of 2D Mott insulator and $\u03c0$-superfluid quantum phase\n  transition in shaking optical lattice: The Mott insulator and superfluid phase transition is one of the most\nprominent phenomena in ultracold atoms. In this work, we report the observation\nof a novel 2D quantum phase transition between Mott insulator and $\\pi$\nsuperfluid in a shaking optical lattice. In the deep optical lattice regime,\nthe lowest $s$-band can be tuned to Mott phase, while the higher $p_{x,y}$\nbands are itinerant for having larger bandwidth. Through a shaking technique\ncoupling the $s$ orbital to $p_{x,y}$ orbital states, we experimentally observe\nthe transition between the states of the $s$ and $p_{x,y}$ bands, leading to a\nquantum phase transition from 2D $s$-orbital Mott phase to the\n$p_{x,y}$-orbital superfluid which condensed at $(\\pi,\\pi)$ momentum."
    },
    {
        "anchor": "Quantum phase slips in one-dimensional superfluids in a periodic\n  potential: We study the decay of superflow of a one-dimensional (1D) superfluid in the\npresence of a periodic potential. In 1D, superflow at zero temperature can\ndecay via quantum nucleation of phase slips even when the flow velocity is much\nsmaller than the critical velocity predicted by mean-field theories. Applying\nthe instanton method to the O(2) quantum rotor model, we calculate the\nnucleation rate of quantum phase slips $\\Gamma$. When the flow momentum $p$ is\nsmall, we find that the nucleation rate per unit length increases algebraically\nwith $p$ as $\\Gamma/L \\propto p^{2K-2}$, where $L$ is the system size and $K$\nis the Tomonaga-Luttinger parameter. Based on the relation between the\nnucleation rate and the quantum superfluid-insulator transition, we present a\nunified explanation on the scaling formulae of the nucleation rate for\nperiodic, disorder, and single-barrier potentials. Using the time-evolving\nblock decimation method, we compute the exact quantum dynamics of the superflow\ndecay in the 1D Bose-Hubbard model at unit filling. From the numerical\nanalyses, we show that the scaling formula is valid for the case of the\nBose-Hubbard model, which can quantitatively describe Bose gases in optical\nlattices.",
        "positive": "Fractional quantum Hall states of a Bose gas with spin-orbit coupling: We study the fractional quantum Hall phases of a pseudospin-1/2 Bose gas in\nan artificial gauge field. In addition to an external magnetic field, the gauge\nfield also mimics an intrinsic spin-orbit coupling of the Rashba type. While\nthe spin degeneracy of the Landau levels is lifted by the spin-orbit coupling,\nthe crossing of two Landau levels at certain coupling strengths gives rise to a\nnew degeneracy. We therefore take into account two Landau levels, and perform\nexact diagonalization of the many-body Hamiltonian. We study and characterize\nthe quantum Hall phases which occur in the vicinity of the degeneracy point.\nNotably, we describe the different states appearing at the Laughlin filling,\n\\nu=1/2. While for this filling incompressible phases disappear at the\ndegeneracy point, denser systems at \\nu=3/2 and \\nu=2 are found to be clearly\ngapped. For filling factors \\nu=2/3 and \\nu=4/3, we discuss the connection of\nthe exact ground state to the non-Abelian spin singlet states, obtained as the\nground state of k+1 body contact interactions."
    },
    {
        "anchor": "Thermodynamics of ideal Bose gas under generic power law potential in\n  $d$-dimension: Thermodynamic properties of ideal Bose gas trapped in an external generic\npower law potential are investigated systematically from the grand\nthermodynamic potential in $d$ dimensional space. The most general conditions\nfor Bose-Einstein condensate and the discontinuous conditions of heat capacity\nat the critical temperature in presence of generic power law potential are\npresented in this manuscript. The dependence of the physical quantities on\nexternal potential, particle characteristics and space dimensionality are\ndiscussed. The more general results obtained in this paper presents an unified\nillustration of Bose-Einstein condensation of ideal Bose systems as they\nreduces to the expressions and conclusions available in the literature with\nappropiate choice of power law exponent.",
        "positive": "Topological charge pumping of bound bosonic pairs: Experiments with bosonic atoms in optical superlattices allow for the\ninteresting possibility to study the adiabatic quantized pumping of bosonic\natoms in the presence of interactions. We investigate this exotic phenomenon\nfor bound bosonic pairs in the paradigmatic Su-Schrieffer-Heeger model where\nthe ground state exhibits topological phase transitions due to dimerized\nhoppings. At unit filling we show that there exist crossovers and phase\ntransitions to bond-order phases of paired bosons known as pair-bond-order\nphase as a function of attractive interactions. The pair bond order phase is\nfound to exhibit effective topological properties such as the presence of\npolarized paired edge states. This is further analyzed by studying the\nemergence and breakdown of the Thouless charge pumping of this bound bosonic\npairs by a parametric extension to the famous Rice-Mele model. Finally we\ndiscuss how the pumping of paired bosons or different regimes of breakdown of\ncharge pumping can be probed by state-of-the art experiments with repulsively\nbound bosons."
    },
    {
        "anchor": "Effects of Spin-Orbit Coupling on Jaynes-Cummings and Tavis-Cummings\n  Models: We consider ultracold atoms inside a ring optical cavity that supports a\nsingle plane-wave mode. The cavity field, together with an external coherent\nlaser field, drives a two-photon Raman transition between two internal\npseudo-spin states of the atom. This gives rise to an effective coupling\nbetween atom's pseudo-spin and external center-of-mass (COM) motion. For the\ncase of a single atom inside the cavity, We show how the spin-orbit coupling\nmodifies the static and dynamic properties of the Jaynes-Cummings (JC) model.\nIn the case of many atoms in thermodynamic limit, we show that the spin-orbit\ncoupling modifies the Dicke superradiance phase transition boundary and the\nnon-superradiant normal phase may become reentrant in some regimes.",
        "positive": "Topological Euler class as a dynamical observable in optical lattices: The last years have witnessed rapid progress in the topological\ncharacterization of out-of-equilibrium systems. We report on robust signatures\nof a new type of topology -- the Euler class -- in such a dynamical setting.\nThe enigmatic invariant $(\\xi)$ falls outside conventional symmetry-eigenvalue\nindicated phases and, in simplest incarnation, is described by triples of bands\nthat comprise a gapless pair, featuring $2\\xi$ stable band nodes, and a gapped\nband. These nodes host non-Abelian charges and can be further undone by\nconverting their charge upon intricate braiding mechanisms, revealing that\nEuler class is a fragile topology. We theoretically demonstrate that quenching\nwith non-trivial Euler Hamiltonian results in stable monopole-antimonopole\npairs, which in turn induce a linking of momentum-time trajectories under the\nfirst Hopf map, making the invariant experimentally observable. Detailing\nexplicit tomography protocols in a variety of cold-atom setups, our results\nprovide a basis for exploring new topologies and their interplay with\ncrystalline symmetries in optical lattices beyond paradigmatic Chern\ninsulators."
    },
    {
        "anchor": "Dynamical fermionization in a one-dimensional Bose-Fermi mixture: After release from the trap the momentum distribution of an impenetrable gas\nasymptotically approaches that of a spinless noninteracting Fermi gas in the\ninitial trap. This phenomenon is called dynamical fermionization and, very\nrecently, has been experimentally confirmed in the case of the Lieb-Liniger\nmodel in the Tonks-Girardeau regime. We prove analytically and confirm\nnumerically that following the removal of axial confinement the strongly\ninteracting Bose-Fermi mixture exhibits dynamical fermionization and the\nasymptotical momentum distribution of each component has the same shape as its\ndensity profile at $t=0$. Under a sudden change of the trap frequency to a new\nnon-zero value the dynamics of both fermionic and bosonic momentum\ndistributions presents characteristics which are similar to the case of single\ncomponent bosons experiencing a similar quench. Our results are derived using a\nproduct representation for the correlation functions which, in addition to\nanalytical considerations, can be implemented numerically very easily with\ncomplexity which scales polynomially in the number of particles.",
        "positive": "Observation of Efimov Universality across a Non-Universal Feshbach\n  Resonance in \\textsuperscript{39}K: We study three-atom inelastic scattering in ultracold \\textsuperscript{39}K\nnear a Feshbach resonance of intermediate coupling strength. The non-universal\ncharacter of such resonance leads to an abnormally large Efimov absolute length\nscale and a relatively small effective range $r_e$, allowing the features of\nthe \\textsuperscript{39}K Efimov spectrum to be better isolated from the\nshort-range physics. Meticulous characterization of and correction for finite\ntemperature effects ensure high accuracy on the measurements of these features\nat large-magnitude scattering lengths. For a single Feshbach resonance, we\nunambiguously locate four distinct features in the Efimov structure. Three of\nthese features form ratios that obey the Efimov universal scaling to within\n10\\%, while the fourth feature, occurring at a value of scattering length\nclosest to $r_e$, instead deviates from the universal value."
    },
    {
        "anchor": "Instabilities of Bosonic Spin Currents in Optical Lattices: We analyze the dynamical and energetic instabilities of spin currents in a\nsystem of two-component bosons in an optical lattice, with a particular focus\non the Neel state. We consider both the weakly interacting superfluid and the\nstrongly interacting Mott insulating limits as well as the regime near the\nsuperfluid-insulator transition and establish the criteria for the onset of\nthese instabilities. We use Bogoliubov theory to treat the weakly interacting\nsuperfluid regime. Near the Mott transition, we calculate the stability phase\ndiagram within a variational Gutzwiller wavefunction approach. In the deep Mott\nlimit we discuss the emergence of the Heisenberg model and calculate the\nstability diagram within this model. Though the Bogoliubov theory and the\nHeisenberg model (appropriate for deep superfluid and deep Mott phase\nrespectively) predict no dynamical instabilities, we find, interestingly,\nbetween these two limiting cases there is a regime of dynamical instability.\nThis result is relevant for the ongoing experimental efforts to realize a\nstable Neel-ordered state in multi-component ultracold bosons.",
        "positive": "Thermal and quantum fluctuations of confined Bose-Einstein condensate\n  beyond the Bogoliubov approximation: The formulation for zero mode of a Bose-Einstein condensate beyond the\nBogoliubov approximation at zero temperature [Y.Nakamura et al., Phys. Rev. A\n89, 013613 (2014)] is extended to finite temperature. Both thermal and quantum\nfluctuations are considered in a manner consistent with a concept of\nspontaneous symmetry breakdown for a finite-size system. Therefore, we need a\nproper treatment of the zero mode operators, which invoke non-trivial\nenhancements in depletion condensate and thermodynamical quantities such as the\nspecific heat. The enhancements are visible in the weak interaction case. Our\napproach reproduces the results of a homogeneous system in the Bogoliubov\napproximation in a large particle number limit."
    },
    {
        "anchor": "Observable signatures of Hall viscosity in lowest Landau level\n  superfluids: Hall viscosity is a non-dissipative viscosity occurring in systems with\nbroken time-reversal symmetry, such as quantum Hall phases and $p+ip$\nsuperfluids. Despite Hall viscosity's expected ubiquity and past observations\nin classical soft matter systems, it has yet to be measured experimentally in\nany quantum phase of matter. Toward this end, we describe the observable\neffects of Hall viscosity in a simple family of rotating Bose-Einstein\ncondensates of electrically neutral bosons, in which all of the bosons condense\ninto a single LLL orbital. Such phases are accessible to current cold atom\nexperiments, and we dub them lowest Landau level (LLL) superfluids. We\ndemonstrate that LLL superfluids possess a non-universal Hall viscosity,\nleading to a range of observable consequences such as rotation of\nvortex-antivortex dipoles and wave-vector dependent corrections to the speed of\nsound. Furthermore, using a coherent state path integral approach, we present a\nmicroscopic derivation of the Landau-Ginzburg equations of a LLL superfluid,\nshowing explicitly how Hall viscosity enters.",
        "positive": "Implementation of an atomtronic SQUID in a strongly confined toroidal\n  condensate: We investigate the dynamics of an atomtronic SQUID created by two mobile\nbarriers, moving at two different, constant velocities in a quasi-1D toroidal\ncondensate. We implement a multi-band truncated Wigner approximation\nnumerically, to demonstrate the functionality of a SQUID reflected in the\noscillatory voltage-flux dependence. The relative velocity of the two barriers\nresults in a chemical potential imbalance analogous to a voltage in an\nelectronic system. The average velocity of the two barriers corresponds to a\nrotation of the condensate, analogous to a magnetic flux. We demonstrate that\nthe voltage equivalent shows characteristic flux-dependent oscillations. We\npoint out the parameter regime of barrier heights and relaxation times for the\nphase slip dynamics, resulting in a realistic protocol for atomtronic SQUID\noperation."
    },
    {
        "anchor": "Towards the simplest model of quantum supremacy: Atomic boson sampling\n  in a box trap: We describe boson sampling of interacting atoms from the noncondensed\nfraction of Bose-Einstein-condensed (BEC) gas confined in a box trap as a new\nplatform for studying computational #P-hardness and quantum supremacy of\nmany-body systems. We calculate the characteristic function and statistics of\natom numbers via newly found hafnian master theorem. Using Bloch-Messiah\nreduction, we find that interatomic interactions give rise to two equally\nimportant entities - eigen-squeeze modes and eigen-energy quasiparticles -\nwhose interplay with sampling atom states determines behavior of the BEC gas.\nWe infer that two necessary ingredients of #P-hardness, squeezing and\ninterference, are self-generated in the gas and, contrary to Gaussian boson\nsampling in linear interferometers, external sources of squeezed bosons are not\nrequired.",
        "positive": "Fermionic suppression of dipolar relaxation: Observation of universal\n  inelastic dipolar scattering: We observe the suppression of inelastic dipolar scattering in ultracold Fermi\ngases of the highly magnetic atom dysprosium: the more energy that is released,\nthe less frequently these exothermic reactions take place, and only quantum\nspin statistics can explain this counterintuitive effect. Inelastic dipolar\nscattering in non-zero magnetic fields leads to heating or to loss of the\ntrapped population, both detrimental to experiments intended to study quantum\nmany-body physics with strongly dipolar gases. Fermi statistics, however, is\npredicted to lead to a kinematic suppression of these harmful reactions.\nIndeed, we observe a 120-fold suppression of dipolar relaxation in fermionic\nversus bosonic Dy, as expected from theory describing universal inelastic\ndipolar scattering, though never before experimentally confirmed. Similarly low\ninelastic cross sections are observed in spin mixtures, also with striking\ncorrespondence to universal dipolar scattering predictions. The suppression of\nrelaxation opens the possibility of employing fermionic dipolar species---atoms\nor molecules---in studies of quantum many-body physics involving, e.g.,\nsynthetic gauge fields and pairing."
    },
    {
        "anchor": "Dipolar Bose-Einstein Condensates in Weak Anisotropic Disorder: Here we study properties of a homogeneous dipolar Bose-Einstein condensate in\na weak anisotropic random potential with Lorentzian correlation at zero\ntemperature. To this end we solve perturbatively the Gross-Pitaevskii equation\nto second order in the random potential strength and obtain analytic results\nfor the disorder ensemble averages of both the condensate and the superfluid\ndepletion, the equation of state, and the sound velocity. For a pure contact\ninteraction and a vanishing correlation length, we reproduce the seminal\nresults of Huang and Meng, which were originally derived within a Bogoliubov\ntheory around a disorder-averaged background field. For dipolar interaction and\nisotropic Lorentzian-correlated disorder, we obtain results which are\nqualitatively similar to the case of an isotropic Gaussian-correlated disorder.\nIn the case of an anisotropic disorder, the physical observables show\ncharacteristic anisotropies which arise from the formation of fragmented\ndipolar condensates in the local minima of the disorder potential.",
        "positive": "Nucleation and kinematics of vortices in stirred Bose Einstein\n  condensates: We apply the Halperin-Mazenco formalism within the Gross-Pitaevskii theory to\ncharacterise the kinematics and nucleation of quantum vortices in a\ntwo-dimensional stirred Bose Einstein condensate. We introduce a smooth defect\ndensity field measuring the superfluid vorticity and is a topologically\nconserved quantity. We use this defect density field and its associated current\ndensity to study the precursory pattern formations that occur inside the\nrepulsive potential of an obstacle and determine the onset of vortex nucleation\nand shedding. We demonstrate that phase slips form inside hard potentials even\nin the absence of vortex nucleation, whereas for soft potentials they occur\nonly above a critical stirring velocity leading to vortex nucleation. The\nHalperin-Mazenco formalism provides an elegant and accurate method of deriving\nthe point vortex dynamic directly from the Gross-Pitaevskii equation."
    },
    {
        "anchor": "Dynamical phase diagram of a one dimensional Bose gas in a box with a\n  tunable weak-link: from Bose-Josephson oscillations to shock waves: We study the dynamics of one-dimensional bosons trapped in a box potential,\nin the presence of a barrier creating a tunable weak-link, thus realizing a one\ndimensional Bose Josephson junction. By varying the initial population\nimbalance and the barrier height we evidence different dynamical regimes. In\nparticular we show that at large barriers a two mode model captures accurately\nthe dynamics, while for low barriers the dynamics involves dispersive shock\nwaves and solitons. We study a quench protocol that can be readily implemented\nin experiments and show that self-trapping resonances can occur. This\nphenomenon can be understood qualitatively within the two-mode model.",
        "positive": "Zitterbewegung with spin-orbit coupled ultracold atoms in a fluctuating\n  optical lattice: Dynamics of non-interacting ultracold atoms with artificial spin-orbit\ncoupling is considered. Spin-orbit coupling is created using two moving optical\nlattices with orthogonal polarizations. Our main goal is to study influence of\nlattice noise on Rabi oscillations. Special attention is paid to the phenomenon\nof the Zitterbewegung being trembling motion caused by Rabi transitions between\nstates with different velocities. Phase and amplitude fluctuations of lattices\nare modelled by means of the two-dimensional stochastic Ornstein-Uhlenbeck\nprocess, also known as harmonic noise. In the the noiseless case the problem is\nsolved analytically in terms of the momentum representation. It is shown that\nlattice noise significantly extends duration of the Zitterbewegung as compared\nto the noiseless case. This effect originates from noise-induced decoherence of\nRabi oscillations."
    },
    {
        "anchor": "BEC-Polaron gas in a boson-fermion mixture : a many-body extension of\n  Lee-Low-Pines theory: We investigate the ground state properties of the gaseous mixture of a single\nspecies of bosons and fermions at zero temperature, where bosons are major in\npopulation over fermions, and form the Bose-Einstein condensate (BEC). The\nboson-boson and boson-fermion interactions are assumed to be weakly repulsive\nand attractive respectively, while the fermion-fermion interaction is absent\ndue to the Pauli exclusion for the low energy $s$-wave scattering. We treat\nfermions as a gas of polarons dressed with Bogoliubov phonons, which is an\nelementary excitation of the BEC, and evaluate the ground state properties with\nthe method developed by Lemmens, Devreese, and Brosens (LDB) originally for the\nelectron polaron gas, and also with a general extension of the Lee-Low-Pines\ntheory for many-body systems (eLLP), which incorporates the phonon drag effects\nas in the original LLP theory. The formulation of eLLP is developed and\ndiscussed in the present paper. The binding (interaction) energy of the polaron\ngas is calculated in these methods, and shown to be finite (negative) for the\ndilute gas of heavy fermions with attractive boson-fermion interactions, though\nthe suppression by the many-body effects exists.",
        "positive": "In situ imaging of atomic quantum gases: One exciting progress in recent cold atom experiments is the development of\nhigh resolution, in situ imaging techniques for atomic quantum gases [1-3].\nThese new powerful tools provide detailed information on the distribution of\natoms in a trap with resolution approaching the level of single atom and even\nsingle lattice site, and complement the well developed time-of-flight method\nthat probes the system in momentum space. In a condensed matter analogy, this\ntechnique is equivalent to locating electrons of a material in a snap shot. In\nsitu imaging has offered a new powerful tool to study atomic gases and inspired\nmany new research directions and ideas. In this chapter, we will describe the\nexperimental setup of in situ absorption imaging, observables that can be\nextracted from the images, and new physics that can be explored with this\ntechnique."
    },
    {
        "anchor": "Measurement of one-dimensional matter-wave quantum breather: Employing the Bethe ansatz approach and numerical simulations of measurements\nof particles' positions we investigate a post-quench many-body dynamics of\nattractively interacting bosons on a ring, which in the mean-field approach\ncorresponds to the so-called breather solution. Despite the fact that the\ninitial many-body ground state is translationally invariant, the measurements\nreveal breather dynamics if quantum fluctuations of the center of mass of the\nsystem are extracted. Moreover, the analysis of the many-body evolution shows\nsignatures of dissociation of the solitons that form the breather.",
        "positive": "Topological pumping in a Floquet-Bloch band: Constructing new topological materials is of vital interest for the\ndevelopment of robust quantum applications. However, engineering such materials\noften causes technological overhead, such as large magnetic fields, specific\nlattice geometries, strong spin-orbit coupling, synthetic dimensions, or\ndynamical superlattice potentials. Simplifying the experimental requirements\nhas been addressed on a conceptual level - by proposing to combine simple\nlattice structures with Floquet engineering - but there has been no\nexperimental implementation. Here, we demonstrate topological pumping in a\nFloquet-Bloch band using a plain sinusoidal lattice potential and two-tone\ndriving with frequencies $\\omega$ and $2\\omega$. We adiabatically prepare a\nnear-insulating Floquet band of ultracold fermions via a frequency chirp, which\navoids gap closings en route from trivial to topological bands. Subsequently,\nwe induce topological pumping by slowly cycling the amplitude and the phase of\nthe $2 \\omega$ drive. Our system is well described by an effective Shockley\nmodel, establishing a novel paradigm to engineer topological matter from simple\nunderlying lattice geometries. This approach could enable the application of\nquantised pumping in metrology, following recent experimental advances on\ntwo-frequency driving in real materials."
    },
    {
        "anchor": "Boson and fermion dynamics in quasi-one-dimensional flat band lattices: The difference between boson and fermion dynamics in quasi-one-dimensional\nlattices is studied with exact simulations of particle motion and by\ncalculating the persistent current in small quantum rings. We consider three\ndifferent lattices which in the tight binding model exhibit flat bands. The\nphysical realization is considered to be an optical lattice with bosonic or\nfermionic atoms. The atoms are assumed to interact with a repulsive short range\ninteraction. The different statistics of bosons and fermions causes different\ndynamics. Spinless fermions are easily trapped in the flat band states due to\nthe Pauli exclusion principle, which prevents them from interacting, while\nboson are able to push each other out from the flat band states.",
        "positive": "Synthetic Random Flux Model in a periodically-driven optical lattice: We propose a realization of a synthetic Random Flux Model in a\ntwo-dimensional optical lattice. Starting from Bose-Hubbard Hamiltonian for two\natom species we show how to use fast-periodic modulation of the system\nparameters to construct random gauge field. We investigate the transport\nproperties of such a system and describe the impact of time-reversal symmetry\nbreaking and correlations in disorder on Anderson localization length."
    },
    {
        "anchor": "Valley-dependent gauge fields for ultracold atoms in square optical\n  superlattices: We propose an experimental scheme to realize the valley-dependent gauge\nfields for ultracold fermionic atoms trapped in a state-dependent square\noptical lattice. Our scheme relies on two sets of Raman laser beams to engineer\nthe hopping between adjacent sites populated by two-component fermionic atoms.\nOne set of Raman beams are used to realize a staggered \\pi-flux lattice, where\nlow energy atoms near two inequivalent Dirac points should be described by the\nDirac equation for spin-1/2 particles. Another set of laser beams with proper\nRabi frequencies are added to further modulate the atomic hopping parameters.\nThe hopping modulation will give rise to effective gauge potentials with\nopposite signs near the two valleys, mimicking the interesting strain-induced\npseudo-gauge fields in graphene. The proposed valley-dependent gauge fields are\ntunable and provide a new route to realize quantum valley Hall effects and\natomic valleytronics.",
        "positive": "Excited state preparation of trapped ultracold atoms via swept\n  potentials: We study the out-of-equilibrium dynamics of non-interacting atoms confined\nwithin a one-dimensional harmonic trap triggered by dragging an external\nlong-range potential through the system. The symmetry-breaking nature of this\nmoving potential couples adjacent eigenstates in the atoms' effective\npotential, leading to an energy landscape reminscent of systems exhibiting\ntrap-induced shape resonances. These couplings may be exploited to selectively\nexcite the atoms into higher vibrational states of the harmonic trap by\ncontrolling the motion of the dragged potential. To this end, we consider two\nprotocols designs: the first protocol strives to maintain adiabaticity at\ncritical points during the atoms' dynamics, whilst the second protocol utilises\nthe fast tunnelling of the atoms within their effective double-well potential.\nThese protocols take place in the few to many millisecond regime and achieve\nhigh-fidelity excitation of the atoms into pure vibrational states and\nsuperpositions thereof. Overall, our study highlights the significance of\ndragged potentials for controlling and manipulating atom dynamics and offers\nintuitive protocols for achieving desired excitations."
    },
    {
        "anchor": "Tensor network simulation of the quantum Kibble-Zurek quench from the\n  Mott to superfluid phase in the two-dimensional Bose-Hubbard model: Quantum simulations of the Bose-Hubbard model (BHM) at commensurate filling\ncan follow spreading of correlations after a sudden quench for times long\nenough to estimate their propagation velocities. In this work we perform tensor\nnetwork simulation of the quantum Kibble-Zurek (KZ) ramp from the Mott towards\nthe superfluid phase in the square lattice BHM and demonstrate that even\nrelatively short ramp/quench times allow one to test the power laws predicted\nby the KZ mechanism (KZM). They can be verified for the correlation length and\nthe excitation energy but the most reliable test is based on the KZM scaling\nhypothesis for the single particle correlation function: the correlation\nfunctions for different quench times evaluated at the same scaled time collapse\nto the same scaling function of the scaled distance. The scaling of the space\nand time variables is done according to the KZ power laws.",
        "positive": "Quench dynamics of a Bose-Einstein condensate under synthetic spin-orbit\n  coupling: We study the quench dynamics of a Bose-Einstein condensate under a\nRaman-assisted synthetic spin-orbit coupling. To model the dynamical process,\nwe adopt a self-consistent Bogoliubov approach, which is equivalent to applying\nthe time-dependent Bogoliubov-de-Gennes equations. We investigate the dynamics\nof the condensate fraction as well as the momentum distribution of the Bose gas\nfollowing a sudden change of system parameters. Typically, the system evolves\ninto a steady state in the long-time limit, which features an oscillating\nmomentum distribution and a stationary condensate fraction which is dependent\non the quench parameters. We investigate how different quench parameters such\nas the inter- and intra-species interactions and the spin-orbit-coupling\nparameters affect the condensate fraction in the steady state. Furthermore, we\nfind that the time average of the oscillatory momentum distribution in the\nlong-time limit can be described by a generalized Gibbs ensemble with two\nbranches of momentum-dependent Gibbs temperatures. Our study is relevant to the\nexperimental investigation of dynamical processes in a spin-orbit coupled\nBose-Einstein condensate."
    },
    {
        "anchor": "Vortex scattering by impurities in a Bose-Einstein condensate: Understanding quantum dynamics in a two-dimensional Bose-Einstein condensate\n(BEC) relies on understanding how vortices interact with each others\nmicroscopically and with local imperfections of the potential which confines\nthe condensate. Within a system consisting of many vortices, the trajectory of\na vortex-antivortex pair is often scattered by a third vortex, an effect\npreviously characterised. However, the natural question remains as to how much\nof this effect is due to the velocity induced by this third vortex and how much\nis due to the density inhomogeneity which it introduces. In this work, we\ndescribe the various qualitative scenarios which occur when a vortex-antivortex\npair interacts with a smooth density impurity whose profile is identical to\nthat of a vortex but lacks the circulation around it.",
        "positive": "Two-step condensation of lattice bosons: We present a theoretical study of Bose-Einstein condensation in highly\nanisotropic harmonic traps. The bosons are considered to be moving in an\noptical lattice in an overall anisotropic harmonic confining potential. We find\nthat two-step condensation occurs for lattice bosons at much reduced harmonic\npotential anisotropy when compared to the case of an ideal bose gas in an\nanisotropic harmonic confinement. We also show that when the bosons are in an\nisotropic harmonic confinement but with highly anisotropic hopping in the\noptical lattice, two-step condensation does not occur. We interpret some of our\nresults using single boson density of energy states corresponding to the\npotentials faced by the bosons."
    },
    {
        "anchor": "Topological phase transition in the quench dynamics of a one-dimensional\n  Fermi gas: We study the quench dynamics of a one-dimensional ultracold Fermi gas in an\noptical lattice potential with synthetic spin-orbit coupling. At equilibrium,\nthe ground state of the system can undergo a topological phase transition and\nbecome a topological superfluid with Majorana edge states. As the interaction\nis quenched near the topological phase boundary, we identify an interesting\ndynamical phase transition of the quenched state in the long-time limit,\ncharacterized by an abrupt change of the pairing gap at a critical quenched\ninteraction strength. We further demonstrate the topological nature of this\ndynamical phase transition from edge-state analysis of the quenched states. Our\nfindings provide interesting clues for the understanding of topological phase\ntransitions in dynamical processes, and can be useful for the dynamical\ndetection of Majorana edge states in corresponding systems.",
        "positive": "Stability Analysis of a Bose-Einstein Condensate Trapped in a Generic\n  Potential: We investigate the dynamical behavior of the Gross-Pitaevskii equation for a\nBose-Einstein condensate trapped in a spherical power law potential restricted\nto the repulsive case, from the dynamical system formalism point of view. A\nfive-dimensional dynamical system is found (due the symmetry of the\nGross-Pitaevskii equation interacting with a potential), where the Thomas-Fermi\napproximation constrains the parameter space of solutions. We show that for\nvalues of the power law exponent equal or smaller than 2 the system seems to be\nstable. However, when the corresponding exponent is bigger than 2, the\ninstability of the system grows when the power law exponent grows, indicating\nthat large values of the aforementioned parameter can be related to a loss in\nthe number of particles from the condensed state. This fact can be used also to\nshow that the stability conditions of the condensate are highly sensitive to\nthe exponent associated with the external potential."
    },
    {
        "anchor": "Dynamic Stark Effect in Strongly Coupled Microcavity Exciton-Polaritons: We present experimental observations of a non-resonant dynamic Stark shift in\nstrongly coupled microcavity quantum well exciton-polaritons - a system which\nprovides a rich variety of solid-state collective phenomena. The Stark effect\nis demonstrated in a GaAs/AlGaAs system at 10K by femtosecond pump-probe\nmeasurements, with the blue shift approaching the meV scale for a pump fluence\nof 2 mJcm^-2 and 50 meV red detuning, in good agreement with theory. The energy\nlevel structure of the strongly coupled polariton Rabi-doublet remains\nunaffected by the blue shift. The demonstrated effect should allow generation\nof ultrafast density-independent potentials and imprinting well-defined phase\nprofiles on polariton condensates, providing a powerful tool for manipulation\nof these condensates, similar to dipole potentials in cold atom systems.",
        "positive": "Sticky collisions of ultracold RbCs molecules: Understanding and controlling collisions is crucial to the burgeoning field\nof ultracold molecules. All experiments so far have observed fast loss of\nmolecules from the trap. However, the dominant mechanism for collisional loss\nis not well understood when there are no allowed 2-body loss processes. Here we\nexperimentally investigate collisional losses of nonreactive ultracold RbCs\nmolecules, and compare our findings with the sticky collision hypothesis that\npairs of molecules form long-lived collision complexes. We demonstrate that\nloss of molecules occupying their rotational and hyperfine ground state is best\ndescribed by second-order rate equations, consistent with the expectation for\ncomplex-mediated collisions, but that the rate is lower than the limit of\nuniversal loss. The loss is insensitive to magnetic field but increases for\nexcited rotational states. We demonstrate that dipolar effects lead to\nsignificantly faster loss for an incoherent mixture of rotational states."
    },
    {
        "anchor": "Logarithmic catastrophes and Stokes's phenomenon in waves at horizons: Waves propagating near an event horizon display interesting features\nincluding logarithmic phase singularities and caustics. We consider an acoustic\nhorizon in a flowing Bose-Einstein condensate where the elementary excitations\nobey the Bogoliubov dispersion relation. In the hamiltonian ray theory the\nsolutions undergo a broken pitchfork bifurcation near the horizon and one might\ntherefore expect the associated wave structure to be given by a Pearcey\nfunction, this being the universal wave function that dresses catastrophes with\ntwo control parameters. However, the wave function is in fact an Airy-type\nfunction supplemented by a logarithmic phase term, a novel type of wave\ncatastrophe. Similar wave functions arise in aeroacoustic flows from jet\nengines and also gravitational horizons if dispersion which violates Lorentz\nsymmetry in the UV is included. The approach we take differs from previous\nauthors in that we analyze the behaviour of the integral representation of the\nwave function using exponential coordinates. This allows for a different\ntreatment of the branches that gives rise to an analysis based purely on\nsaddlepoint expansions, which resolve the multiple real and complex waves that\ninteract at the horizon and its companion caustic. We find that the horizon is\na physical manifestation of a Stokes surface, marking the place where a wave is\nborn, and that the horizon and the caustic do not in general coincide: the\nfinite spatial region between them delineates a broadened horizon.",
        "positive": "Anisotropic Superfluidity in the Two-Species Polar Fermi Gas: We study the superfluid pairing in a two-species gas of heteronuclear\nfermionic molecules with equal density. The interplay of the isotropic s-wave\ninteraction and anisotropic long-range dipolar interaction reveals rich\nphysics. We find that the single-particle momentum distribution has a\ncharacteristic ellipsoidal shape that can be reasonably represented by a\ndeformation parameter $\\alpha$ defined similarly to the normal phase.\nInteresting momentum-dependent features of the order parameter are identified.\nWe calculate the critical temperatures of both the singlet and triplet\nsuperfluid, suggesting a possible pairing symmetry transition by tuning the\ns-wave or dipolar interaction strength."
    },
    {
        "anchor": "Novel phases in rotating Bose-condensed gas: vortices and quantum\n  correlation: We present the exact diagonalization study of rotating Bose-condensed gas\ninteracting via finite-range Gaussian potential confined in a quasi-2D harmonic\ntrap. The system of many-body Hamiltonian matrix is diagonalized in given\nsubspaces of quantized total angular momentum to obtain the lowest-energy\neigenstate employing the beyond lowest-Landau-level approximation. In the\nco-rotating frame, the quantum mechanical stability of angular momentum states\nis discussed for the existence of phase transition between the stable states of\ninteracting system. Thereby analyzing the von Neumann entanglement entropy and\ndegree of condensation provide the information about quantum phase correlation\nin the many-body states. Calculating the conditional probability distribution,\nwe further probe the internal structure of quantum mechanically stable and\nunstable states. Much emphasis is put on finding the spatial correlation of\nbosonic atoms in the rotating system for the formation and entry of singly\nquantized vortices, and then organizing into canonical polygons with and\nwithout a central vortex at the trap center. Results are summarized in the form\nof a movie depicting the vortex patterns having discrete p-fold rotational\nsymmetry with $p = 2,3,4,5,6$.",
        "positive": "Polarons in Ultracold Fermi Superfluids: We study a new type of Fermi polaron induced by an impurity interacting with\nan ultracold Fermi superfluid. Due to the three-component nature of the system,\nthe polaron can become trimer-like with a non-universal energy spectrum. We\nidentify multiple avoided crossings between impurity- and trimer-like solutions\nin both the attractive and the repulsive polaron spectra. In particular, the\nwidths of avoided crossings gradually increase as the Fermi superfluid\nundergoes a crossover from the BCS side towards the BEC side, which suggests\ninstabilities towards three-body losses. Such losses can be reduced for\ninteraction potentials with small effective ranges. We also demonstrate, using\nthe second-order perturbation theory, that the mean-field evaluation of the\nfermion-impurity interaction energy is inadequate even for small\nfermion-impurity scattering lengths, due to the essential effects of Fermi\nsuperfluid and short-range physics in such a system. Our results are\npractically useful for cold atom experiments on mixtures."
    },
    {
        "anchor": "The interaction-sensitive states of a trapped two-component ideal Fermi\n  gas and application to the virial expansion of the unitary Fermi gas: We consider a two-component ideal Fermi gas in an isotropic harmonic\npotential. Some eigenstates have a wavefunction that vanishes when two\ndistinguishable fermions are at the same location, and would be unaffected by\ns-wave contact interactions between the two components. We determine the other,\ninteraction-sensitive eigenstates, using a Faddeev ansatz. This problem is\nnontrivial, due to degeneracies and to the existence of unphysical Faddeev\nsolutions. As an application we present a new conjecture for the fourth-order\ncluster or virial coefficient of the unitary Fermi gas, in good agreement with\nthe numerical results of Blume and coworkers.",
        "positive": "Persistence of a Non-Equilibrium State: Observation of a Boltzmannian\n  Special Case: Well before the atomistic nature of matter was experimentally established,\nLudwig Boltzmann's audacious effort to explain the macroscopic world of human\nexperience in terms of the workings of an unseen microscopic world met with\nvigorous opposition. A contentious point was the problem of irreversibility:\nthe microscopic equations of motion are reversible, yet friction and viscosity\ncause things always to slow down and warm up, never to speed up and cool down.\nWhat was worse, Boltzmann himself discovered that his transport equation\npredicts special cases in which gases never come to thermal equilibrium, a\nparticular example being that the monopole \"breathe\" mode of gas will never\ndamp if it is confined in 3D to a perfectly isotropic harmonic potential. Such\nabsences of damping were not observed in nature. Nondamping of a monopole mode\nin lower dimensional systems has only very recently been observed, using cold\natoms. Kinoshita et al. and Chevy et al. have experimentally observed\nsuppressed relaxation in highly elongated geometries. The difficulty in\ngenerating sufficiently spherical harmonic confinement for ultracold atoms,\nhowever, has meant that Boltzmann's fully 3D, isotropic case has never been\nobserved. With the development of a new magnetic trap capable of producing\nnear-spherical harmonic confinement for ultracold atoms, we have been able to\nmake the first observation of this historically significant oddity. We observe\na monopole mode for which the collisional contribution to damping vanishes, a\nlong-delayed vindication for Boltzmann's microscopic theory."
    },
    {
        "anchor": "Spinor Boson Droplets Stabilized By Spin Fluctuations: Self-trapped droplets stabilized by quantum fluctuations have been\nexperimentally realized in dipolar gases and binary Boson mixtures. We propose\nspinor Bose gases as another candidate for droplet formation in this work. For\nspin-1 gas, we find that spin fluctuations give a dilute but self-trapped state\nfor two different order parameters where the mean-field picture predicts\ncollapse. A polar droplet phase can be stabilized by spin fluctuations for both\nantiferromagnetic and ferromagnetic spin-dependent coupling. An\nantiferromagnetic droplet phase can be stabilized similarly with a negative\nquadratic Zeeman shift. Furthermore, the beyond mean-field energy of the system\ndepends on the quadratic Zeeman coupling, which provides a mechanism to tune\nthe droplet formation and its density. We discuss the parameters necessary for\nthe experimental realization of such spinor droplets.",
        "positive": "Fractional Quantum Hall states in the vicinity of Mott plateaus: We perform variational Monte-Carlo calculations to show that bosons in a\nrotating optical lattice will form analogs of fractional quantum Hall states\nwhen the tunneling is sufficiently weak compared to the interactions and the\ndeviation of density from an integer is commensurate with the effective\nmagnetic field. We compare the energies of superfluid and correlated states to\none-another and to the energies found in full configuration-interaction\ncalculations on small systems. We look at overlaps between our variational\nstates and the exact ground-state, characterizing the ways in which fractional\nquantum Hall effect correlations manifest themselves near the Mott insulating\nstate. We explore the experimental signatures of these states."
    },
    {
        "anchor": "Condensed matter physics in big discrete time crystals: We review the application of discrete time crystals created in a\nBose-Einstein condensate (BEC) of ultracold atoms bouncing resonantly on an\noscillating mirror to the investigation of condensed matter phenomena in the\ntime dimension. Such a bouncing BEC system can exhibit dramatic breaking of\ntime-translation symmetry, allowing the creation of discrete time crystals\nhaving up to about 100 temporal lattice sites and suitable for hosting a broad\nrange of temporal condensed matter phenomena. We first consider single-particle\ncondensed matter phenomena in the time dimension which include Anderson\nlocalization due to temporal disorder, topological time crystals, and\nquasi-crystal structures in time. We then discuss many-body temporal condensed\nmatter phenomena including Mott insulator phases in time, many-body\nlocalization in time, many-body topological time crystals and time crystals\nhaving long-range exotic interactions. We also discuss the construction of two\n(or three) dimensional time lattices, involving the bouncing of a BEC between\ntwo (or three) orthogonal oscillating mirrors and between two oscillating\nmirrors oriented at 45-degrees. The latter configuration supports a versatile\nM\\\"obius strip geometry which can host a variety of two-dimensional time\nlattices including a honeycomb time lattice and a Lieb square time lattice.\nFinally, we discuss the construction of a six-dimensional time-space lattice\nwhich is based on periodically driven BECs trapped in a three-dimensional\noptical lattice.",
        "positive": "Casimir effect in a dilute Bose gas in canonical ensemble within\n  improved Hartree-Fock approximation: The Casimir effect in a dilute Bose gas confined between two planar walls is\ninvestigated in the canonical ensemble at zero temperature by means of\nCornwall-Jackiw-Tomboulis effective action approach within the improved\nHartree-Fock approximation. Our results show that: (i) the Casimir energy and\nthe resulting Casimir force in the canonical ensemble remarkably differ from\nthose in the grand canonical ensemble; (ii) when the distance between two\nplanar walls increases, the Casimir energy and Casimir force decay in\naccordance with a half-integer power law in the canonical ensemble instead of\nan integer power law in the grand canonical ensemble."
    },
    {
        "anchor": "Quantum Monte Carlo study of spin-polarized deuterium: The ground state properties of spin-polarized deuterium (D$\\downarrow$) at\nzero temperature are obtained by means of the diffusion Monte Carlo\ncalculations within the fixed-node approximation. Three D$\\downarrow$ species\nhave been investigated (D$\\downarrow_1$, D$\\downarrow_2$, D$\\downarrow_3$),\ncorresponding respectively to one, two and three equally occupied nuclear spin\nstates. Influence of the backflow correlations on the ground state energy of\nthe systems is explored. The equilibrium densities for D$\\downarrow_2$ and\nD$\\downarrow_3$ liquids are obtained and compared with ones obtained in\nprevious approximate prediction. The density and the pressure at which the\ngas-liquid phase transition occurs at $T$=0 is obtained for D$\\downarrow_1$.",
        "positive": "Thermal equation of state of polarized fermions in one dimension via\n  complex chemical potentials: We present a nonperturbative computation of the equation of state of\npolarized, attractively interacting, nonrelativistic fermions in one spatial\ndimension at finite temperature. We show results for the density, spin\nmagnetization, magnetic susceptibility, and Tan's contact. We compare with the\nsecond-order virial expansion, a next-to-leading-order lattice perturbation\ntheory calculation, and interpret our results in terms of pairing correlations.\nOur lattice Monte Carlo calculations implement an imaginary chemical potential\ndifference to avoid the sign problem. The thermodynamic results on the\nimaginary side are analytically continued to obtain results on the real axis.\nWe focus on an intermediate- to strong-coupling regime, and cover a wide range\nof temperatures and spin imbalances."
    },
    {
        "anchor": "Stable and mobile excited two-dimensional dipolar Bose-Einstein\n  condensate solitons: We demonstrate robust, stable, mobile excited states of quasi-two-dimensional\n(quasi-2D) dipolar Bose-Einstein condensate (BEC) solitons for repulsive\ncontact interaction with a harmonic trap along the $x$ direction perpendicular\nto the polarization direction $z$. Such a soliton can freely move in the y-z\nplane. A rich variety of such excitations is considered: one quanta of\nexcitation for movement along (i) y axis or (ii) z axis or (ii) both. A\nproposal for creating these excited solitonic states in a laboratory by phase\nimprinting is also discussed. We also consider excited states of quasi-2D\ndipolar BEC soliton where the sign of the dipolar interaction is reversed by a\nrotating orienting field. In this sign-changed case the soliton moves freely in\nthe x-y plane under the action of a harmonic trap in the $z$ direction. At\nmedium velocity the head-on collision of two such solitons is found to be quasi\nelastic with practically no deformation. The findings are illustrated using\nnumerical simulation in three and two spatial dimensions employing realistic\ninteraction parameters for a dipolar $^{164}$Dy BEC.",
        "positive": "Spin-incoherent Luttinger liquid of one-dimensional SU($\u03ba$)\n  fermions: We theoretically investigate one-dimensional (1D) SU($\\kappa$) fermions in\nthe regime of spin-incoherent Luttinger liquid. We specifically focus on the\nTonks-Girardeau gas limit where its density is sufficiently low that effective\nrepulsions between atoms become infinite. In such case, spin exchange energy of\n1D SU($\\kappa$) fermions vanishes and all spin configurations are degenerate,\nwhich automatically puts them into spin-incoherent regime. In this limit, we\nare able to express the single-particle density matrices in terms of those of\nanyons. This allows us to numerically simulate the number of particles up to\n$N=32$. We numerically calculate single-particle density matrices in two cases:\n(1) equal populations for each spin components (balanced) and (2) all $S_z$\nmanifolds included. In contrast to noninteracting multi-component fermions, the\nmomentum distributions are broadened due to strong interactions. As $\\kappa$\nincreases, the momentum distributions are less broadened for fixed $N$, while\nthey are more broadened for fixed number of particle per spin component. We\nthen compare numerically calculated high momentum tails with analytical\npredictions which are proportional to $1/p^4$, in good agreement. Thus, our\ntheoretical study provides a comparison with the experiments of repulsive\nmulticomponent alkaline-earth fermions with a tunable SU($\\kappa$)\nspin-symmetry in the spin-incoherent regime."
    },
    {
        "anchor": "Quantum Kibble-Zurek physics in the presence of spatially-correlated\n  dissipation: We study how universal properties of quantum quenches across critical points\nare modified by a weak coupling to thermal dissipation, focusing on the\nparadigmatic case of the transverse field Ising model. Beyond the standard\nquench-induced Kibble-Zurek defect production in the absence of the bath, the\nbath contributes extra thermal defects. We show that spatial correlations in\nthe noise produced by the bath can play a crucial role: one obtains\nquantitatively different scaling regimes depending on whether the correlation\nlength of the noise is smaller or larger than the Kibble-Zurek length\nassociated with the quench speed, and the thermal length set by temperature.\nFor the case of spatially-correlated bath noise, additional thermal defect\ngeneration is restricted to a window that is both quantum critical and excluded\nfrom the non-equilibrium regime surrounding the critical point. We map the\ndissipative quench problem to a set of effectively independent dissipative\nLandau-Zener problems. Using this mapping along with both analytic and\nnumerical calculations allows us to find the scaling of the excess defect\ndensity produced in the quench, and suggests a generic picture for such\ndissipative quenches.",
        "positive": "Excitations and number fluctuations in an elongated dipolar\n  Bose-Einstein condensate: We study the properties of a magnetic dipolar Bose-Einstein condensate (BEC)\nin an elongated (cigar shaped) confining potential in the beyond\nquasi-one-dimensional (quasi-1D) regime. In this system the dipole-dipole\ninteractions (DDIs) develop a momentum-dependence related to the transverse\nconfinement and the polarization direction of the dipoles. This leads to\ndensity fluctuations being enhanced or suppressed at a length scale related to\nthe transverse confinement length, with local atom number measurements being a\npractical method to observe these effects in experiments. We use meanfield\ntheory to describe the ground state, excitations and the local number\nfluctuations. Quantitative predictions are presented based on full numerical\nsolutions and a simplified variational approach that we develop. In addition to\nthe well-known roton excitation, occurring when the dipoles are polarized along\na tightly confined direction, we find an \"anti-roton\" effect for the case of\ndipoles polarized along the long axis: a nearly non-interacting ground state\nthat experiences strongly repulsive interactions with excitations of\nsufficiently short wavelength."
    },
    {
        "anchor": "Spectral functions of the Higgs mode near two-dimensional quantum\n  critical points: We study the Higgs excitation in the Goldstone phase of the relativistic O(N)\nmodel in two spatial dimensions at zero temperature. The response functions of\nthe order parameter, and its magnitude-squared, become universal functions of\nfrequency in the vicinity of the quantum critical point described by the\nWilson-Fisher fixed point, and we compute them to next-to-leading order in 1/N.\nThe Higgs particle has an infrared singular decay to gapless Goldstone\nexcitations, and its response functions are characterized by a pole in the\nlower-half of the complex frequency plane. The pole acquires a non-zero real\npart only at next-to-leading order in 1/N, demonstrating that the Higgs\nexcitation has an oscillatory component even in the scaling limit. Both the\nreal and imaginary parts of the pole position vanish with the correlation\nlength exponent \\nu upon approaching the critical point. We present evidence\nthat the spectral density of the O(N)-invariant amplitude-squared of the order\nparameter has a peak at a non-zero frequency in the scaling limit. We connect\nour results to recent experimental studies of the superfluid-insulator quantum\nphase transition of ultracold bosonic atoms in optical lattices.",
        "positive": "Observation of state-to-state hyperfine-changing collision in a\n  Bose-Fermi mixture of $^6$Li and $^{41}$K atoms: Hyperfine-changing collisions are of fundamental interest for the studying of\nultracold heteronuclear mixtures. Here, we report the state-to-state study of\nthe hyperfine-changing-collision dynamics in a Bose-Fermi mixture of $^6$Li and\n$^{41}$K atoms. The collision products are directly observed and the\nspin-changing dynamics is measured. Based on a two-body collision model, the\nexperimental results are simultaneously fitted from which the spin-changing\nrate coefficient of $ 1.9(2)\\times 10^{-12}~\\rm{cm^3\\cdot s^{-1}}$ is gained,\nbeing consistent with the multi-channel quantum defect theory calculation. We\nfurther show that the contact parameter of $^6$Li-$^{41}$K mixture can be\nextracted from the measured spin-changing dynamics. The obtained results are\nconsistent with the first order perturbation theory in the weakly-interacting\nlimit. Our system offers great promise for studying spin-changing interactions\nin heteronuclear mixtures."
    },
    {
        "anchor": "Quench dynamics of the interacting Bose gas in one dimension: We obtain an exact expression for the time evolution of the interacting Bose\ngas following a quench from a generic initial state using the Yudson\nrepresentation for integrable systems. We study the time evolution of the\ndensity and noise correlation for a small number of bosons and their asymptotic\nbehavior for any number. We show that for any value of the coupling, as long as\nit is repulsive, the system asymptotes towards a strongly repulsive gas, while\nfor any value of an attractive coupling the long time behavior is dominated by\nthe maximal bound state. This occurs independently of the initial state and can\nbe viewed as an emerging \"dynamic universality\".",
        "positive": "Shear viscosity and imperfect fluidity in bosonic and fermionic\n  superfluids: In this paper we address the ratio of the shear viscosity to entropy density\n$\\eta/s$ in bosonic and fermionic superfluids. A small $\\eta/s$ is associated\nwith nearly perfect fluidity, and more general measures of the fluidity\nperfection/imperfection are of wide interest to a number of communities. We use\na Kubo approach to concretely address this ratio via low temperature transport\nassociated with the quasi-particles. Our analysis for bosonic superfluids\nutilizes the framework of the one-loop Bogoliubov approximation, whereas for\nfermionic superfluids we apply BCS theory and its BCS-BEC extension.\nInterestingly, we find that the transport properties of strict BCS and\nBogoliubov superfluids have very similar structures, albeit with different\nquasi-particle dispersion relations. While there is a dramatic contrast between\nthe power law and exponential temperature dependence for $\\eta$ alone, the\nratio $\\eta/s$ for both systems is more similar. Specifically we find the same\nlinear dependence (on the ratio of temperature $T$ to inverse lifetime\n$\\gamma(T)$) with $\\eta/s \\propto T/\\gamma(T)$, corresponding to imperfect\nfluidity. By contrast, near the unitary limit of BCS-BEC superfluids a very\ndifferent behavior results, which is more consistent with near-perfect\nfluidity."
    },
    {
        "anchor": "Dynamical generation of solitons in one-dimensional Fermi superfluids\n  with and without spin-orbit coupling: We theoretically generalize a systematic language to describe the\nphase-imprinting technique to investigate the dynamical generation of solitons\nin a one-dimensional Raman-type spin-orbit-coupled Fermi superfluid. We check\nour method with the simulation of time-dependent Bogoliubov-de Gennes equations\nand find that our method not only can generate stable dark and even gray\nsolitons in a conventional Fermi superfluid by controlling the transferred\nphase jump but also is feasible to create a stable dark soliton in both BCS and\ntopological states of a spin-orbit-coupled Fermi superfluid. We also discuss\nthe physical implication of our method.",
        "positive": "Three-body bound states in a harmonic waveguide with cylindrical\n  symmetry: Highly-elongated quasi-one-dimensional cold atom samples have been studied\nextensively over the past years experimentally and theoretically. This work\ndetermines the energy spectrum of two identical fermions and a third\ndistinguishable particle as functions of the mass ratio $\\kappa$ and the\nfree-space $s$-wave scattering length $a_{3\\text{D}}$ between the identical\nfermions and the distinguishable third particle in a cylindrically symmetric\nwaveguide whose symmetry axis is chosen to be along the $z$-axis. We focus on\nthe regime where the mass of the identical fermions is equal to or larger than\nthat of the third distinguishable particle. Our theoretical framework accounts\nexplicitly for the motion along the transverse confinement direction. In the\nregime where excitations in the transverse direction are absent (i.e., for\nstates with projection quantum number $M_{\\text{rel}}=0$), we determine the\nbinding energies for states with odd parity in $z$. These full\nthree-dimensional energies deviate significantly from those obtained within a\nstrictly one-dimensional framework when the $s$-wave scattering length is of\nthe order of or smaller than the oscillator length in the confinement\ndirection. If transverse excitations are present, we predict the existence of a\nnew class of universal three-body bound states with $|M_{\\text{rel}}|=1$ and\npositive parity in $z$. These bound states arise on the positive $s$-wave\nscattering length side if the mass ratio $\\kappa$ is sufficiently large.\nImplications of our results for ongoing cold atom experiments are discussed."
    },
    {
        "anchor": "Vortex dynamics of rotating dipolar Bose-Einstein condensates: We study the influence of dipole-dipole interaction on the formation of\nvortices in a rotating dipolar Bose-Einstein condensate (BEC) of $^{52}$Cr and\n$^{164}$Dy atoms in quasi two-dimensional geometry. By numerically solving the\ncorresponding time-dependent mean-field Gross-Pitaevskii equation, we show that\nthe dipolar interaction enhances the number of vortices while a repulsive\ncontact interaction increases the stability of the vortices. Further, an\nordered vortex lattice of relatively large number of vortices is found in a\nstrongly dipolar BEC.",
        "positive": "Mesoscopic Bose-Einstein condensates as quantum simulators: Mesoscopic interacting Bose-Einstein condensates confined in a few traps\ndisplay phase transitions that cannot be explained with a mean field theory. By\ndescribing each trap as an effective site of a Bose-Hubbard model and using the\nSchwinger representation of spin operators, these systems can be mapped to spin\nmodels. We show that it is possible to define correlations between bosons in\nsuch a way that critical behavior is associated to the divergence of a\ncorrelation length accompanied by a gapless spectrum in the thermodynamic\nlimit. The latter is now defined as the limit in which the mean field analysis\nbecomes valid. Such description provides critical exponents to the associated\nphase transitions and encompasses the notion of universality demonstrating thus\nthe potential use of mesoscopic Bose-Einstein condensates as quantum simulators\nof condensed matter systems."
    },
    {
        "anchor": "Using an artificial electric field to create the analog of the red spot\n  of Jupiter in light-heavy Fermi-Fermi mixtures of ultracold atoms: Time-of-flight images are a common tool in ultracold atomic experiments,\nemployed to determine the quasimomentum distribution of the interacting\nparticles. If one introduces a constant artificial electric field, then the\nquasimomentum distribution evolves in time as Bloch oscillations are generated\nin the system and then damped showing a complex series of patterns.\nSurprisingly, in different mass Fermi-Fermi mixtures, these patterns can\nsurvive for long times, and resemble the stability of the red spot of Jupiter\nin classical nonlinear hydrodynamics. In this work, we illustrate the rich\nphenomena that can be seen in these driven quantum systems.",
        "positive": "Characterizing dynamical phase transitions in a spinor Bose-Einstein\n  condensate via quantum and semiclassical analyses: Phase transitions in nonequilibrium dynamics of many body quantum systems,the\nso-called dynamical phases transition (DPTs), play an important role for\nunderstanding various dynamical phenomena observed in different branches of\nphysics.In general, there have two types of DPTs, the first one refers to the\nphase transition that is characterized by distinct evolution behaviors of a\nphysical observable, while the second one is marked by the nonanalyticities in\nthe rate function of the initial state survival probability. Here, we focus on\nsuch DPTs from both quantum and semiclassical perspectives in a spinor\nBose-Einstein condensate (BEC), an ideal platform to investigate nonequilibrium\ndynamics.By using the sudden quench process, we demonstrate that the system\nexhibits both types of DPTs as the control parameter quenches through the\ncritical one, referring to as the critical quench. We show analytically how to\ndetermine the critical quenches by means of the semiclassical approach and\ncarry out a detailed examination on both semiclassical and quantum signatures\nof two types of DPTs. Moreover, we further reveal that the occurrence of DPTs\nis closely connected to the separatrix in the underlying classical system. Our\nfindings provide more insights into the properties of DPTs and verify the\nusefulness of semiclassical analysis for understanding DPTs in quantum systems\nwith well-defined semiclassical limit."
    },
    {
        "anchor": "Quench Dynamics and Emergence of Phase Separation in Two-Component\n  Atomic Bose Gases at Zero Temperature and above the BEC Critical Temperature: We study the dynamics of two-component atomic Bose gases initially in a\nmixture encountering a sudden quench of the inter-species interactions. The\ndynamics above the critical temperature $T_c$ is studied using a leading order\nlarge-N approximation that predicted a phase transition from mixing to phase\nseparation as a function of the inter-species coupling. Here we explore the\ndynamics of this phase transition following a quench and compare our results to\nthose found at zero temperature using the time-dependent Gross-Pitaevskii\nequations which ignore quantum and thermal fluctuations. In the regime above\n$T_c$ where no condensate is present, however, the time evolution of the\ndensities following the quench exhibits features similar to that found at zero\ntemperature where only the condensates contribute to the densities. When the\ninter-species interaction jumps above the critical value, we observe dynamical\ntransitions from a homogeneous mixture to a phase-separated structure for both\ncases. Our simulations suggest that at temperatures above $T_c$ where no\ncondensate is present this dynamical transition should still be observable in\nexperiments.",
        "positive": "Monitoring squeezed collective modes of a one-dimensional Bose gas after\n  an interaction quench using density ripples analysis: We investigate the out-of-equilibrium dynamics following a sudden quench of\nthe interaction strength, in a one-dimensional quasi-condensate trapped at the\nsurface of an atom chip. Within a linearized approximation, the system is\ndescribed by independent collective modes and the quench squeezes the phase\nspace distribution of each mode, leading to a subsequent breathing of each\nquadrature. We show that the collective modes are resolved by the power\nspectrum of density ripples which appear after a short time of flight. This\nallows us to experimentally probe the expected breathing phenomenon. Our\nresults are in good agreement with theoretical predictions which take the\nlongitudinal harmonic confinement into account."
    },
    {
        "anchor": "Bistability in Feshbach Resonance: A coupled atom-molecule condensate with an intraspecies Feshbach resonance is\nemployed to explore matter wave bistability both in the presence and in the\nabsence of a unidirectional optical ring cavity. In particular, a set of\nconditions are derived that allow the threshold for bistability, due both to\ntwo-body s-wave scatterings and to cavity-mediated two-body interactions, to be\ndetermined analytically. The latter bistability is found to support, not only\ntransitions between a mixed (atom-molecule) state and a pure molecular state as\nin the former bistability, but also transitions between two distinct mixed\nstates.",
        "positive": "Field-theoretical approach to the Casimir-like interaction in a\n  one-dimensional Bose gas: We study the fluctuation-induced interaction between two impurities in a\nweakly-interacting one-dimensional Bose gas using the field theoretical\napproach. At separations between impurities shorter and of the order of the\nhealing length of the system, the induced interaction has a classical origin\nand behaves exponentially. At separations longer than the healing length, the\ninteraction is of a quantum origin and scales as the third power of the inverse\ndistance. Finite temperature destroys the quasi-long-range order of the Bose\ngas and, accordingly, the induced interaction becomes exponentially suppressed\nbeyond the thermal length. We obtain analytical expressions for the induced\ninteraction at zero and finite temperature that are valid at arbitrary\ndistances. We discuss experimental realizations as well as possible formation\nof bound states of two impurities, known as bipolarons."
    },
    {
        "anchor": "Tan's contact as an indicator of completeness and self-consistency of a\n  theory: It is well known that, Tan's contact could be calculated by using any of\nfollowing three methods: by the asymptotic behavior of momentum distribution;\nby Tan's adiabatic sweep theorem; or by the operator product expansion as an\nexpectation value of the interaction term. We argue that, if a theory\ndescribing Bose (or Fermi) system with the only contact interaction is self\nconsistent, then it should lead to the same result in all three cases. As an\nexample we considered MFT based approaches and established that among existing\napproximations of MFT, the Hartree - Fock - Bogoliubov (HFB) approach is the\nmost self consistent. Actually, HFB is able to describe existing experimental\ndata on Tan's contact for dilute Bose gas, but fails to predict its expected\nbehavior at large gas parameter $(\\gamma > 0.015)$. So, for appropriate\ndescription of properties of a Bose gas even at zero temperature, this\napproximation needs to be expanded by taking into account fluctuations in\nhigher order then the second one.",
        "positive": "Beyond braid statistics: Constructing a lattice model for anyons with\n  exchange statistics intrinsic to one dimension: Anyons obeying fractional exchange statistics arise naturally in two\ndimensions: hard-core two-body constraints make the configuration space of\nparticles not simply-connected. The braid group describes how\ntopologically-inequivalent exchange paths can be associated to non-trivial\ngeometric phases for abelian anyons. Braid-anyon exchange statistics can also\nbe found in one dimension (1D), but this requires broken Galilean invariance to\ndistinguish different ways for two anyons to exchange. However, recently it was\nshown that an alternative form of exchange statistics can occur in 1D because\nhard-core three-body constraints also make the configuration space not\nsimply-connected. Instead of the braid group, the topology of exchange paths\nand their associated non-trivial geometric phases are described by the traid\ngroup. In this article we propose a first concrete model realizing this\nalternative form of anyonic exchange statistics. Starting from a bosonic\nlattice model that implements the desired geometric phases with\nnumber-dependent Peierls phases, we then define anyonic operators so that the\nkinetic energy term in the Hamiltonian becomes local and quadratic with respect\nto them. The ground-state of this traid-anyon-Hubbard model exhibits several\nindications of exchange statistics intermediate between bosons and fermions, as\nwell as signs of emergent approximate Haldane exclusion statistics. The\ncontinuum limit results in a Galilean invariant Hamiltonian with eigenstates\nthat correspond to previously constructed continuum wave functions for traid\nanyons. This provides not only an a-posteriori justification of our lattice\nmodel, but also shows that our construction serves as an intuitive approach to\ntraid anyons, i.e. anyons intrinsic to 1D."
    },
    {
        "anchor": "Signature of reentrant localization in collisional inhomogeneous\n  spin-orbit coupled condensates: We study the localization transition in a spin-orbit (SO) coupled binary\nBose-Einstein condensates (BECs) with collisional inhomogeneous interaction\ntrapped in a one-dimensional quasiperiodic potential. Our numerical analysis\nshows that the competition between the quasiperiodic disorder and inhomogeneous\ninteraction leads to a reentrant localization transition as the interaction\nstrength is tuned from attractive to repulsive in nature. Further, we analyse\nthe combined effect of the SO and Rabi coupling strengths on the localization\ntransition for different interaction strengths and obtain signatures of\nreentrant localization transition as function of SO coupling in the regime of\nweak interactions. We complement our numerical observation with the analytical\nmodel using the variational approach. At the end we show how the reentrant\nlocalization is manifested in the quench dynamics of the condensate. Our study\nprovides an indirect approach to achieve localization transition without tuning\nthe quasiperiodic potential strength, rather by tuning the inhomogeneous\ninteraction.",
        "positive": "Emergence of multi-body interactions in few-atom sites of a fermionic\n  lattice clock: Alkaline-earth (AE) atoms have metastable clock states with minute-long\noptical lifetimes, high-spin nuclei, and SU($N$)-symmetric interactions that\nuniquely position them for advancing atomic clocks, quantum information\nprocessing, and quantum simulation. The interplay of precision measurement and\nquantum many-body physics is beginning to foster an exciting scientific\nfrontier with many opportunities. Few particle systems provide a window to view\nthe emergence of complex many-body phenomena arising from pairwise\ninteractions. Here, we create arrays of isolated few-body systems in a\nfermionic ${}^{87}$Sr three-dimensional (3D) optical lattice clock and use high\nresolution clock spectroscopy to directly observe the onset of both elastic and\ninelastic multi-body interactions. These interactions cannot be broken down\ninto sums over the underlying pairwise interactions. We measure\nparticle-number-dependent frequency shifts of the clock transition for atom\nnumbers $n$ ranging from 1 to 5, and observe nonlinear interaction shifts,\nwhich are characteristic of SU($N$)-symmetric elastic multi-body effects. To\nstudy inelastic multi-body effects, we use these frequency shifts to isolate\n$n$-occupied sites and measure the corresponding lifetimes. This allows us to\naccess the short-range few-body physics free from systematic effects\nencountered in a bulk gas. These measurements, combined with theory, elucidate\nan emergence of multi-body effects in few-body systems of sites populated with\nground-state atoms and those with single electronic excitations. By connecting\nthese few-body systems through tunneling, the favorable energy and timescales\nof the interactions will allow our system to be utilized for studies of\nhigh-spin quantum magnetism and the Kondo effect."
    },
    {
        "anchor": "Microscopic theory of the friction force exerted on a quantum impurity\n  in one-dimensional quantum liquids: We study the motion of a slow quantum impurity in one-dimensional\nenvironments focusing on systems of strongly interacting bosons and weakly\ninteracting fermions. While at zero temperature the impurity motion is\nfrictionless, at low temperatures finite friction appears. The dominant process\nis the scattering of the impurity off two fermionic quasiparticles. We evaluate\nthe friction force and show that, at low temperatures, it scales either as the\nfourth or the sixth power of temperature, depending on the system parameters.\nThis is a result of the scattering of the impurity off two fermionic\nquasiparticles that are situated around different Fermi points. It is the\ndominant process at low temperatures. We also evaluate the contribution to the\nfriction force originating from the scattering of the impurity off two\nfermionic quasiparticles that are situated around different Fermi points. It\nbehaves as the tenth power of temperature.",
        "positive": "Critical exponents for an impurity in a bosonic Josephson junction:\n  Position measurement as a phase transition: We use fidelity susceptibility to calculate quantum critical scaling\nexponents for a system consisting of $N$ identical bosons interacting with a\nsingle impurity atom in a double well potential (bosonic Josephson junction).\nAbove a critical value of the boson-impurity interaction energy there is a\nspontaneous breaking of $\\mathbb{Z}_2$ symmetry corresponding to a second order\nquantum phase transition from a balanced to an imbalanced number of particles\nin either the left or right hand well. We show that the exponents match those\nin the Lipkin-Meshkov-Glick and Dicke models suggesting that the impurity model\nis in the same universality class. The phase transition can be interpreted as a\nmeasurement of the position of the impurity by the bosons."
    },
    {
        "anchor": "Hamiltonian formulation of nonequilibrium quantum dynamics: geometric\n  structure of the BBGKY hierarchy: Time-resolved measurement techniques are opening a window on nonequilibrium\nquantum phenomena that is radically different from the traditional picture in\nthe frequency domain. The simulation and interpretation of nonequilibrium\ndynamics is a conspicuous challenge for theory. This paper presents a novel\napproach to quantum many-body dynamics that is based on a Hamiltonian\nformulation of the Bogoliubov-Born-Green-Kirkwood-Yvon (BBGKY) hierarchy of\nequations of motion for reduced density matrices. These equations have an\nunderlying symplectic structure, and we write them in the form of the classical\nHamilton equations for canonically conjugate variables. Applying canonical\nperturbation theory or the Krylov-Bogoliubov averaging method to the resulting\nequations yields a systematic approximation scheme. The possibility of using\nmemory-dependent functional approximations to close the Hamilton equations at a\nparticular level of the hierarchy is discussed. The geometric structure of the\nequations gives rise to reduced geometric phases that are observable even for\nnoncyclic evolutions of the many-body state. The formalism is applied to a\nfinite Hubbard chain which undergoes a quench in on-site interaction energy U.\nCanonical perturbation theory, carried out to second order, fully captures the\nnontrivial real-time dynamics of the model, including resonance phenomena and\nthe coupling of fast and slow variables.",
        "positive": "Spatiotemporal dynamics of particle collisions in quantum spin chains: Recent developments have highlighted the potential of quantum spin models to\nrealize the phenomenology of confinement leading to the formation of bound\nstates such as mesons. In this work we show that Ising chains also provide a\nplatform to realize and probe particle collisions in pristine form with the key\nadvantage that one can not only monitor the asymptotic particle production, but\nalso the whole spatiotemporal dynamics of the collision event. We study both\nelastic and inelastic collisions between different kinds of mesons and also\nmore complex bound states of mesons, which one can interpret as an analog of\nexotic particles such as the tetraquark in quantum chromodynamics. We argue\nthat our results not only apply to the specific studied spin model, but can be\nreadily extended to lattice gauge theories in a more general context. As the\nconsidered Ising chains admit a natural realization in various quantum\nsimulator platforms, it is a key implication of this work that particle\ncollisions therefore become amenable within current experimental scope.\nConcretely, we discuss a potentially feasible implementation in systems of\nRydberg atoms."
    },
    {
        "anchor": "Dissipative Distillation of Supercritical Quantum Gases: We experimentally realize a method to produce non-equilibrium Bose Einstein\ncondensates with condensed fraction exceeding those of equilibrium samples with\nthe same parameters. To do this, we immerse an ultracold Bose gas of 87Rb in a\ncloud of 39K with substantially higher temperatures, providing a controlled\nsource of dissipation. By combining the action of the dissipative environment\nwith evaporative cooling, we are able to progressively distil the\nnon-equilibrium Bose-Einstein condensate from the thermal cloud. We show that\nby increasing the strength of the dissipation it is even possible to produce\ncondensates above the critical temperature. We finally demonstrate that our\nout-of-equilibrium samples are long-lived and do not reach equilibrium in a\ntime that is accessible for our experiment. Due to its high degree of control,\nour distillation process is a promising tool for the engineering of open\nquantum systems.",
        "positive": "Universal spatiotemporal dynamics of spontaneous superfluidity breakdown\n  in the presence of synthetic gauge fields: According to the famous Kibble-Zurek mechanism (KZM), the universality of\nspontaneous defect generation in continuous phase transitions (CPTs) can be\nunderstood by the critical slowing down. In most CPTs of atomic Bose-Einstein\ncondensates (BECs), the universality of spontaneous defect generations has been\nexplained by the divergent relaxation time associated with the nontrivial\ngapless Bogoliubov excitations. However, for atomic BECs in synthetic gauge\nfields, their spontaneous superfluidity breakdown is resulted from the\ndivergent correlation length associated with the zero Landau critical velocity.\nHere, by considering an atomic BEC ladder subjected to a synthetic magnetic\nfield, we reveal that the spontaneous superfluidity breakdown obeys the KZM.\nThe Kibble-Zurek scalings are derived from the Landau critical velocity which\ndetermines the correlation length. In further, the critical exponents are\nnumerically extracted from the critical spatial-temporal dynamics of the\nbifurcation delay and the spontaneous vortex generation. Our study provides a\ngeneral way to explore and understand the spontaneous superfluidity breakdown\nin CPTs from a single-well dispersion to a double-well one, such as, BECs in\nsynthetic gauge fields, spin-orbit coupled BECs, and BECs in shaken optical\nlattices."
    },
    {
        "anchor": "Modulated pair condensate of p-orbital ultracold fermions: We show that an interesting of pairing occurs for spin-imbalanced Fermi gases\nunder a specific experimental condition---the spin up and spin down Fermi\nlevels lying within the $p_x$ and $s$ orbital bands of an optical lattice,\nrespectively. The pairs condense at a finite momentum equal to the sum of the\ntwo Fermi momenta of spin up and spin down fermions and form a $p$-orbital pair\ncondensate. This $2k_F$ momentum dependence has been seen before in the spin-\nand charge- density waves, but it differs from the usual $p$-wave superfluids\nsuch as $^3$He, where the orbital symmetry refers to the relative motion within\neach pair. Our conclusion is based on the density matrix renormalization group\nanalysis for the one-dimensional (1D) system and mean-field theory for the\nquasi-1D system. The phase diagram of the quasi-1D system is calculated,\nshowing that the $p$-orbital pair condensate occurs in a wide range of\nfillings. In the strongly attractive limit, the system realizes an\nunconventional BEC beyond Feynman's no-node theorem. The possible experimental\nsignatures of this phase in molecule projection experiment are discussed.",
        "positive": "Interactions and dynamics of one-dimensional droplets, bubbles and kinks: We explore the dynamics and interactions of multiple bright droplets and\nbubbles, as well as the interactions of kinks with droplets and with antikinks,\nin the extended one-dimensional Gross-Pitaevskii model including the\nLee-Huang-Yang correction. Existence regions are identified for the\none-dimensional droplets and bubbles in terms of their chemical potential,\nverifying the stability of the droplets and exposing the instability of the\nbubbles. The limiting case of the droplet family is a stable kink. The\ninteractions between droplets demonstrate in-phase (out-of-phase) attraction\n(repulsion), with the so-called Manton's method explicating the observed\ndynamical response, and mixed behavior for intermediate values of the phase\nshift. Droplets bearing different chemical potentials experience mass-exchange\nphenomena. Individual bubbles exhibit core expansion and mutual attraction\nprior to their destabilization. Droplets interacting with kinks are absorbed by\nthem, a process accompanied by the emission of dispersive shock waves and gray\nsolitons. Kink-antikink interactions are repulsive, generating\ncounter-propagating shock waves. Our findings reveal dynamical features of\ndroplets and kinks that can be detected in current experiments."
    },
    {
        "anchor": "Dynamics of Rapidly Rotating Bose-Einstein Quantum Droplets: This work theoretically investigates \\textcolor{black}{the stationary\nproperties} and the dynamics of the rotating quantum liquid droplets confined\nin a two-dimensional symmetric anharmonic trap. Mimicking the quantum Hall\nsystems, the modified Gross-Pitaevskii equation with the inclusion of the\nLee-Huang-Yang nonlinear interaction is analytically solved, and the role of\nthe Landau-level mixing effect is addressed. \\textcolor{black}{Via controlling\nthe nonlinear interaction and the rotation speed, the rotating quantum droplet\nwith multiply quantized vortex can be created, and the preference of the\nenergetically favored quantum states can be distinguished in the phase diagram.\nTo better interpret the underlying physics of the phase singularities, a brief\ncomparison of the rotating quantum droplet and the optical vortex is made. The\ninvestigation of the long-term evolution of the rotating quantum droplets\nconfirms the stability of the quantum states. At certain rotation speeds, the\nmulti-periodic trajectories and breathings provide evidence of the emergence of\nthe collective excitation of the surface mode in the vortex state. For quantum\ndroplets carrying multiply quantized vortex, the microscopic snapshots of the\nrotation field adjusted current density distribution show that the combined\nnonlinear interaction and the anharmonic trapping potential can provide the\nrestoring force to lead the quantum droplet to a regular and stable revolution\nand reach the dynamic equilibrium, revealing the signature of the generation of\nsuperfluids in the new kind of low-dimensional quantum liquids.",
        "positive": "Vortex-peak interaction and lattice shape in rotating two-component\n  Bose-Einstein condensates: When a two-component Bose-Einstein condensate is placed into rotation, a\nlattice of vortices and cores appear. The geometry of this lattice (triangular\nor square) varies according to the rotational value and the intercomponent\ncoupling strengths. In this paper, assuming a Thomas-Fermi regime, we derive a\npoint energy which allows us to determine for which values of the parameters,\nthe lattice goes from triangular to square. It turns out that the separating\ncurve in the phase diagram agrees fully with the complete numerical simulations\nof the Gross-Pitaevskii equations. We also derive a formula for the critical\nvelocity of appearance of the first vortex and prove that the first vortex\nalways appears first in the component with largest support in the case of two\ndisks, and give a criterion in the case of disk and annulus."
    },
    {
        "anchor": "Cluster Luttinger liquids and emergent supersymmetric conformal critical\n  points in the one-dimensional soft-shoulder Hubbard model: We investigate the quantum phases of hard-core bosonic atoms in an extended\nHubbard model where particles interact via soft-shoulder potentials in one\ndimension. Using a combination of field-theoretical methods and strong-coupling\nperturbation theory, we demonstrate that the low-energy phase can be a\nconformal cluster Luttinger liquid (CLL) phase with central charge $c=1$, where\nthe microscopic degrees of freedom correspond to mesoscopic ensembles of\nparticles. Using numerical density-matrix-renormalization-group methods, we\ndemonstrate that the CLL phase, first predicted in [Phys. Rev. Lett. 111,\n165302 (2013)], is separated from a conventional Tomonaga-Luttinger liquid by\nan exotic critical point with central charge $c=3/2$. The latter is expression\nof an emergent conformal supersymmetry, which is not present in the original\nHamiltonian. We discuss the observability of the CLL phase in realistic\nexperimental settings with weakly-dressed Rydberg atoms confined to optical\nlattices. Using quantum Monte-Carlo simulations, we show that the typical\nfeatures of CLLs are stable up to comparatively high temperatures. Using exact\ndiagonalizations and quantum trajectory methods, we provide a protocol for\nadiabatic state preparation as well as quantitative estimates on the effects of\nparticle losses.",
        "positive": "Quantum computation with ultracold atoms in a driven optical lattice: We propose a scheme for quantum computation in optical lattices. The qubits\nare encoded in the spacial wavefunction of the atoms such that spin decoherence\ndoes not influence the computation. Quantum operations are steered by shaking\nthe lattice while qubit addressability can be provided with experimentally\navailable techniques of changing the lattice with single-site resolution.\nNumerical calculations show possible fidelities above 99% with gate times on\nthe order of milliseconds."
    },
    {
        "anchor": "Effective Hamiltonian study of excitations in a boson- fermion mixture\n  with attraction between components: An effective Hamiltonian for the Bose subsystem in the mixture of ultracold\natomic clouds of bosons and fermions with mutual attractive interaction is used\nfor investigating collective excitation spectrum. The ground state and mode\nfrequencies of the $^{87}$Rb and $^{40}$K mixture are analyzed quantitatively\nat zero temperature. We find analytically solutions of the hydrodynamics\nequations in the Thomas- Fermi approximation. We discuss the relation between\nthe onset of collapse and collective modes softening and the dependence of\ncollective oscillations on scattering length and number of boson atoms.",
        "positive": "Experimental generation of phase wraps for subwavelength phase\n  structures in Bose-Einstein condensate with two-dimensional optical lattice: We report an experimental demonstration of engineering phase wraps for\nsub-wavelength structure in a Bose-Einstein condensate (BEC) with\ntwo-dimensional optical lattices. A short lattice pulse is applied on BEC\nworking in the Kapitza-Dirac (or Raman-Nath) regime, which corresponds to phase\nmodulation imprint on matter wave. When the phase modulation on matter wave is\nlarger than $2\\pi$ in a lattice cell, there appears phase wraps with multiple\n$2\\pi$ jumps, generating the sub-wavelength phase structure. The phase wraps\nfor sub-wavelength structure are measured in momentum space via the\ntime-of-flight absorption image, which corresponds to converting phase\ninformation into amplitude. %Two different kinds of two-dimensional optical\nlattice are studied, which show the different subwavelength phase structure.\nMoreover, we identify an additional condition for the validity of Kapitza-Dirac\nregime, which relies crucially on the lattice configurations. This scheme can\nbe used for studying the property of optical lattices and topological defects\nin matter wave."
    },
    {
        "anchor": "Two-dimensional vortex quantum droplets get thick: We study two-dimensional (2D) vortex quantum droplets (QDs) trapped by a\nthicker transverse confinement with a>1um. Under this circumstance, the\nLee-Huang-Yang (LHY) term should be described by its original form in the\nthree-dimensional (3D) configuration. Previous studies have demonstrated that\nstable 2D vortex QDs can be supported by a thin transverse confinement with\na<<1um. In this case, the LHY term is described by a logarithm. Hence, two\nkinds of confinement features result in different mechanisms of the vortex QDs.\nThe stabilities and characteristics of the vortex QDs must be re-identified. In\nthe current system, we find that stable 2D vortex QDs can be supported with\ntopological charge number up to at least 4. We reformulated their density\nprofile, chemical potential and threshold norm for supporting the stable vortex\nQDs according to the new condition. Unlike the QDs under thin confinement, the\nQDs in the current system strongly repel each other because the LHY term\nfeatures a higher-order repulsion than that of the thin confinement system.\nMoreover, elastic and inelastic collisions between two moving vortex QDs are\nstudied throughout the paper. Two kinds of collisions can be characterized by\nexerting different values of related speed. The dynamics of the stable nested\nvortex QD, which is constructed by embedding one vortex QD with a smaller\ntopological number into another vortex QD with a larger number of topological\ncharge, can be supported by the system.",
        "positive": "Quantum entanglement due to modulated Dynamical Casimir Effect: We study the creation and entanglement of quasiparticle pairs due to a\nperiodic variation of the mode frequencies of a homogeneous quantum system.\nDepending on the values of the parameters describing the periodic modulation,\nthe number of created pairs either oscillates or, in a narrow resonant\nfrequency interval, grows exponentially in time. For a system initially in a\nthermal state, we determine in which cases the final state is quantum\nmechanically entangled, i.e., where the bipartite state is nonseparable. We\ninclude some weak dissipation, expected to be found in any experimental setup,\nand study the corresponding reduction of the quantum entanglement. Our findings\nare used to interpret the results of two recent experiments."
    },
    {
        "anchor": "Universal transport in periodically driven systems without long-lived\n  quasiparticles: An intriguing regime of universal charge transport at high entropy density\nhas been proposed for periodically driven interacting one-dimensional systems\nwith Bloch bands separated by a large single-particle band gap. For weak\ninteractions, a simple picture based on well-defined Floquet quasiparticles\nsuggests that the system should host a quasisteady state current that depends\nonly on the populations of the system's Floquet-Bloch bands and their\nassociated quasienergy winding numbers. Here we show that such topological\ntransport persists into the strongly interacting regime where the\nsingle-particle lifetime becomes shorter than the drive period. Analytically,\nwe show that the value of the current is insensitive to interaction-induced\nband renormalizations and lifetime broadening when certain conditions are met\nby the system's non-equilibrium distribution function. We show that these\nconditions correspond to a quasisteady state. We support these predictions\nthrough numerical simulation of a system of strongly interacting fermions in a\nperiodically-modulated chain of Sachdev-Ye-Kitaev dots. Our work establishes\nuniversal transport at high entropy density as a robust far from equilibrium\ntopological phenomenon, which can be readily realized with cold atoms in\noptical lattices.",
        "positive": "Nonlinear Mixing of Collective Modes in Harmonically Trapped\n  Bose-Einstein Condensates: We study nonlinear mixing effects among quadrupole modes and scissors modes\nin a harmonically trapped Bose-Einstein condensate. Using a perturbative\ntechnique in conjunction with a variational approach with a Gaussian trial wave\nfunction for the Gross-Pitaevskii equation, we find that mode mixing\nselectively occurs. Our perturbative approach is useful in gaining qualitative\nunderstanding of the recent experiment [Yamazaki et al., J. Phys. Soc. Japan\n84, 44001 (2015)], exhibiting a beating phenomenon of the scissors mode as well\nas a modulation phenomenon of the low-lying quadrupole mode by the high-lying\nquadrupole mode frequency. Within the second-order treatment of the nonlinear\nmode coupling terms, our approach predicts all the spectral peaks obtained by\nthe numerical simulation of the Gross-Pitaevskii equation."
    },
    {
        "anchor": "Nonequilibrium Phase Diagram of a Driven-Dissipative Many-Body System: We study the nonequilibrium dynamics of a many-body bosonic system on a\nlattice, subject to driving and dissipation. The time-evolution is described by\na master equation, which we treat within a generalized Gutzwiller mean field\napproximation for density matrices. The dissipative processes are engineered\nsuch that the system, in the absence of interaction between the bosons, is\ndriven into a homogeneous steady state with off-diagonal long range order. We\ninvestigate how the coherent interaction affects qualitatively the properties\nof the steady state of the system and derive a nonequilibrium phase diagram\nfeaturing a phase transition into a steady state without long range order. The\nphase diagram exhibits also an extended domain where an instability of the\nhomogeneous steady state gives rise to a persistent density pattern with\nspontaneously broken translational symmetry. In the limit of small particle\ndensity, we provide a precise analytical description of the time-evolution\nduring the instability. Moreover, we investigate the transient following a\nquantum quench of the dissipative processes and we elucidate the prominent role\nplayed by collective topological variables in this regime.",
        "positive": "Identifying a superfluid Reynolds number via dynamical similarity: The Reynolds number provides a characterization of the transition to\nturbulent flow, with wide application in classical fluid dynamics. Identifying\nsuch a parameter in superfluid systems is challenging due to their\nfundamentally inviscid nature. Performing a systematic study of superfluid\ncylinder wakes in two dimensions, we observe dynamical similarity of the\nfrequency of vortex shedding by a cylindrical obstacle. The universality of the\nturbulent wake dynamics is revealed by expressing shedding frequencies in terms\nof an appropriately defined superfluid Reynolds number, ${\\rm Re}_s$, that\naccounts for the breakdown of superfluid flow through quantum vortex shedding.\nFor large obstacles, the dimensionless shedding frequency exhibits a universal\nform that is well-fitted by a classical empirical relation. In this regime the\ntransition to turbulence occurs at ${\\rm Re}_s\\approx 0.7$, irrespective of\nobstacle width."
    },
    {
        "anchor": "Optomechanical Response of a Strongly Interacting Fermi Gas: We study a Fermi gas with strong, tunable interactions dispersively coupled\nto a high-finesse cavity. Upon probing the system along the cavity axis, we\nobserve a strong optomechanical Kerr nonlinearity originating from the density\nresponse of the gas to the intracavity field and measure it as a function of\ninteraction strength. We find that the zero-frequency density response function\nof the Fermi gas increases by a factor of two from the\nBardeen-Cooper-Schrieffer to the Bose-Einstein condensate regime. The results\nare in quantitative agreement with a theory based on operator-product\nexpansion, expressing the density response in terms of universal functions of\nthe interactions, the contact and the internal energy of the gas. This provides\nan example of a driven-dissipative, strongly correlated system with a strong\nnonlinear response, opening up perspectives for the sensing of weak\nperturbations or inducing long-range interactions in Fermi gases.",
        "positive": "Enhancement of super-exchange pairing in the periodically-driven Hubbard\n  model: Recent experiments performed on cuprates and alkali-doped fullerides have\ndemonstated that key signatures of superconductivity can be induced above the\nequilibrium critical temperature by optical modulation. These observations in\ndisparate physical systems may indicate a general underlying mechanism.\nMultiple theories have been proposed, but these either consider specific\nfeatures, such as competing instabilities, or focus on conventional BCS-type\nsuperconductivity. Here we show that periodic driving can enhance electron\npairing in strongly-correlated systems. Focusing on the strongly-repulsive\nlimit of the doped Hubbard model, we investigate in-gap, spatially\ninhomogeneous, on-site modulations. We demonstrate that such modulations\nsubstantially reduce electronic hopping, while simultaneously sustaining\nsuper-exchange interactions and pair hopping via driving-induced virtual charge\nexcitations. We calculate real-time dynamics for the one-dimensional case,\nstarting from zero and finite temperature initial states, and show that\nenhanced singlet--pair correlations emerge quickly and robustly in the\nout-of-equilibrium many-body state. Our results reveal a fundamental pairing\nmechanism that might underpin optically induced superconductivity in some\nstrongly correlated quantum materials."
    },
    {
        "anchor": "Topological classification of vortex-core structures of spin-1\n  Bose-Einstein condensates: We classify vortex-core structures according to the topology of the order\nparameter space. By developing a method to characterize how the order parameter\nchanges inside the vortex core. We apply this method to the spin-1\nBose-Einstein condensates and show that the vortex-core structures are\nclassified by winding numbers that are locally defined in the core region. We\nalso show that a vortex-core structure with a nontrivial winding number can be\nstabilized under a negative quadratic Zeeman effect.",
        "positive": "Observation of heat scaling across a first-order quantum phase\n  transition in a spinor condensate: Heat generated as a result of the breakdown of an adiabatic process is one of\nthe central concepts of thermodynamics. In isolated systems, the heat can be\ndefined as an energy increase due to transitions between distinct energy\nlevels. Across a second-order quantum phase transition (QPT), the heat is\npredicted theoretically to exhibit a power-law scaling, but it is a significant\nchallenge for an experimental observation. In addition, it remains elusive\nwhether a power-law scaling of heat can exist for a first-order QPT. Here we\nexperimentally observe a power-law scaling of heat in a spinor condensate when\na system is linearly driven from a polar phase to an antiferromagnetic phase\nacross a first-order QPT. We experimentally evaluate the heat generated during\ntwo non-equilibrium processes by probing the atom number on a hyperfine energy\nlevel. The experimentally measured scaling exponents agree well with our\nnumerical simulation results. Our work therefore opens a new avenue to\nexperimentally and theoretically exploring the properties of heat in\nnon-equilibrium dynamics."
    },
    {
        "anchor": "Classifying Snapshots of the Doped Hubbard Model with Machine Learning: Quantum gas microscopes for ultracold atoms can provide high-resolution\nreal-space snapshots of complex many-body systems. We implement machine\nlearning to analyze and classify such snapshots of ultracold atoms.\nSpecifically, we compare the data from an experimental realization of the\ntwo-dimensional Fermi-Hubbard model to two theoretical approaches: a doped\nquantum spin liquid state of resonating valence bond type, and the geometric\nstring theory, describing a state with hidden spin order. This approach\nconsiders all available information without a potential bias towards one\nparticular theory by the choice of an observable and can therefore select the\ntheory which is more predictive in general. Up to intermediate doping values,\nour algorithm tends to classify experimental snapshots as\ngeometric-string-like, as compared to the doped spin liquid. Our results\ndemonstrate the potential for machine learning in processing the wealth of data\nobtained through quantum gas microscopy for new physical insights.",
        "positive": "Finite temperature stability and dimensional crossover of exotic\n  superfluidity in lattices: We investigate exotic paired states of spin-imbalanced Fermi gases in\nanisotropic lattices, tuning the dimension between one and three. We calculate\nthe finite temperature phase diagram of the system using real-space dynamical\nmean-field theory in combination with the quantum Monte Carlo method. We find\nthat regardless of the intermediate dimensions examined, the\nFulde-Ferrell-Larkin-Ovchinnikov (FFLO) state survives to reach about one third\nof the BCS critical temperature of the spin-density balanced case. We show how\nthe gapless nature of the state found is reflected in the local spectral\nfunction. While the FFLO state is found at a wide range of polarizations at low\ntemperatures across the dimensional crossover, with increasing temperature we\nfind out strongly dimensionality-dependent melting characteristics of shell\nstructures related to harmonic confinement. Moreover, we show that intermediate\ndimension can help to stabilize an extremely uniform finite temperature FFLO\nstate despite the presence of harmonic confinement."
    },
    {
        "anchor": "Detection of coherent superpositions of phase states by full counting\n  statistics in a Bose Josephson junction: For a Bose Josephson junction realized with a double-well potential we\npropose a strategy to observe the coherent superpositions of phase states\noccurring during the time evolution after a sudden rise of the barrier\nseparating the two wells. We show that their phase content can be obtained by\nthe full-counting statistics of the spin-boson operators characterizing the\njunction, which could be mapped out by repeated measurements of the population\nimbalance after rotation of the state. This measurement can distinguish between\ncoherent superpositions and incoherent mixtures, and can be used for a\ntwo-dimensional, tomographic reconstruction of the phase content of the state.",
        "positive": "Analogues of Josephson junctions and black hole event horizons in atomic\n  Bose-Einstein condensates: We study dynamical processes in coherently coupled atomic Bose-Einstein\ncondensates. Josephson effects in ring-shaped and dumbbell geometries are\ntheoretically investigated. Conditions for observation of the Josephson effect\nare revealed. We found that multicharged persistent current in toroidal\ncondensate can be robust even for supersonic atomic flow. In numerical\nsimulations the acoustic analogues of event horizon in quantized superflow was\nobserved. These theoretical finding open perspectives for investigation of Bose\nJosephson junctions and quantum aspects of acoustic analogue of Hawking\nradiation in existing experimental setups."
    },
    {
        "anchor": "Synthesizing arbitrary dispersion relations in a modulated tilted\n  optical lattice: Dispersion relations are fundamental characteristics of the dynamics of\nquantum and wave systems. In this work we introduce a simple technique to\ngenerate arbitrary dispersion relations in a modulated tilted lattice. The\ntechnique is illustrated by important examples: the Dirac, Bogoliubov and\nLandau dispersion relations (the latter exhibiting the roton and the maxon). We\nshow that adding a slow chirp to the lattice modulation allows one to\nreconstruct the dispersion relation from dynamical quantities. Finally, we\ngeneralize the technique to higher dimensions, and generate graphene-like Dirac\npoints and flat bands in two dimensions.",
        "positive": "Evidence for a Quantum-to-Classical Transition in a Pair of Coupled\n  Quantum Rotors: The understanding of how classical dynamics can emerge in closed quantum\nsystems is a problem of fundamental importance. Remarkably, while classical\nbehavior usually arises from coupling to thermal fluctuations or random\nspectral noise, it may also be an innate property of certain isolated,\nperiodically driven quantum systems. Here, we experimentally realize the\nsimplest such system, consisting of two coupled, kicked quantum rotors, by\nsubjecting a coherent atomic matter wave to two periodically pulsed,\nincommensurate optical lattices. Momentum transport in this system is found to\nbe radically different from that in a single kicked rotor, with a breakdown of\ndynamical localization and the emergence of classical diffusion. Our\nobservation, which confirms a long-standing prediction for many-dimensional\nquantum-chaotic systems, sheds new light on the quantum-classical\ncorrespondence."
    },
    {
        "anchor": "Pairing effects in the normal phase of a two-dimensional Fermi gas: In a recent experiment [M. Feld et al., Nature 480, 75 (2011); B. Froehlich\net al., Phys. Rev. Lett. 109,130403 (2012)], a pairing gap was detected in a\ntwo-dimensional (2D) Fermi gas with attractive interaction at temperatures\nwhere superfluidity does not occur. The question remains open as to whether\nthis gap is a pseudogap phenomenon or is due to a molecular state. In this\npaper, by using a t-matrix approach, we reproduce quite well the experimental\ndata for a 2D Fermi gas, and set the boundary between the pseudogap and\nmolecular regimes. We also show that pseudogap phenomena occurring in 2D and 3D\ncan be related through a variable spanning the BCS-BEC crossover in a universal\nway.",
        "positive": "How does a synthetic non-Abelian gauge field influence the bound states\n  of two spin-$\\half$ fermions?: We study the bound states of two spin-$\\half$ fermions interacting via a\ncontact attraction (characterized by a scattering length) in the singlet\nchannel in 3D space in presence of a uniform non-Abelian gauge field. The\nconfiguration of the gauge field that generates a Rashba type spin-orbit\ninteraction is described by three coupling parameters $(\\lambda_x, \\lambda_y,\n\\lambda_z)$. For a generic gauge field configuration, the critical scattering\nlength required for the formation of a bound state is {\\em negative}, i.e.\nshifts to the \"BCS side\" of the resonance. Interestingly, we find that there\nare special high-symmetry configurations (e.g., $\\lambda_x = \\lambda_y =\n\\lambda_z$) for which there is a two body bound state for {\\em any} scattering\nlength however small and negative. Remarkably, the bound-state wave functions\nobtained for such configurations have nematic spin structure similar to those\nfound in liquid $^3$He. Our results show that the BCS-BEC crossover is\ndrastically affected by the presence of a non-Abelian gauge field. We discuss\npossible experimental signatures of our findings both at high and low\ntemperatures."
    },
    {
        "anchor": "High temperature thermodynamics of strongly interacting s-wave and\n  p-wave Fermi gases in a harmonic trap: We theoretically investigate the high-temperature thermodynamics of a\nstrongly interacting trapped Fermi gas near either s-wave or p-wave Feshbach\nresonances, using a second order quantum virial expansion. The second virial\ncoefficient is calculated based on the energy spectrum of two interacting\nfermions in a harmonic trap. We consider both isotropic and anisotropic\nharmonic potentials. For the two-fermion interaction, either s-wave or p-wave,\nwe use a pseudopotential parametrized by a scattering length and an effective\nrange. This turns out to be the simplest way of encoding the energy dependence\nof the low-energy scattering amplitude or phase shift. This treatment of the\npseudopotential can be easily generalized to higher partial-wave interactions.\nWe discuss how the second virial coefficient and thermodynamics are affected by\nthe existence of these finite-range interaction effects. The virial expansion\nresult for a strongly interacting s -wave Fermi gas has already been proved\nvery useful. In the case of p-wave interactions, our results for the\nhigh-temperature equation of state are applicable to future high-precision\nthermodynamic measurements for a spin-polarized Fermi gas near a p-wave\nFeshbach resonance.",
        "positive": "Dynamics of quantum soliton in Lee-Huang-Yang spin-orbit coupled\n  Bose-Einstein condensates: We present the numerical results of the structure and dynamics of the\nself-bound ground state arising solely because of the presence of beyond mean\nfield quantum fluctuation in spin-orbit coupled binary Bose-Einstein\ncondensates in one dimension. Depending upon spin-obit (SO) and Rabi couplings,\nwe observe that the ground state exhibits either quantum-bright (plane) or\nquantum-stripe soliton nature. We find an analytical soliton solution for\nnon-zero SO coupling that matches quite well with the numerical results.\nFurther, we investigate the dynamical stability of these solitons by adopting\nthree protocols, such as (i) adding initial velocity to each component, (ii)\nquenching the SO and Rabi coupling parameters at initial and finite time, and\n(iii) allowing collision between the two spin-components by giving equal and\nopposite direction velocity to them. Many interesting dynamical features of the\nsolitons, like, multi-fragmented, repelling, and breathing in time and\nspace-time, are observed. For given Rabi coupling frequency, the breathing\nfrequency of the soliton increases upon the increase in SO coupling, attaining\na maximum at the critical SO coupling where the phase transition from the\nbright to stripe soliton occurs. We observe that the maximum breathing\nfrequency exhibits power law dependence on the Rabi coupling frequency with an\nexponent $\\sim 0.16$."
    },
    {
        "anchor": "Super-resolution microscopy of cold atoms in an optical lattice: Super-resolution microscopy has revolutionized the fields of chemistry and\nbiology by resolving features at the molecular level. Such techniques can be\neither \"stochastic,\" gaining resolution through precise localization of point\nsource emitters, or \"deterministic,\" leveraging the nonlinear optical response\nof a sample to improve resolution. In atomic physics, deterministic methods can\nbe applied to reveal the atomic wavefunction and to perform quantum control.\nHere we demonstrate super-resolution imaging based on nonlinear response of\natoms to an optical pumping pulse. With this technique the atomic density\ndistribution can be resolved with a point spread function FWHM of 32(4) nm and\na localization precision below 1 nm. The short optical pumping pulse of 1.4\n$\\mu$s enables us to resolve fast atomic dynamics within a single lattice site.\nA byproduct of our scheme is the emergence of moir\\'{e} patterns on the atomic\ncloud, which we show to be immensely magnified images of the atomic density in\nthe lattice. Our work represents a general approach to accessing the physics of\ncold atoms at the nanometer scale, and can be extended to higher dimensional\nlattices and bulk systems for a variety of atomic and molecular species.",
        "positive": "Quantum Bose-Fermi droplets: We study the stability of a zero temperature mixture of attractively\ninteracting degenerate bosons and spin-polarized fermions in the absence of\nconfinement. We demonstrate that higher order corrections to the standard\nmean-field energy can lead to a formation of Bose-Fermi liquid droplets --\nself-bound systems in three-dimensional space. The stability analysis of the\nhomogeneous case is supported by numerical simulations of finite systems by\nexplicit inclusion of surface effects. We discuss the experimental feasibility\nof formation of quantum droplets and indicate the main obstacle -- inelastic\nthree-body collisions."
    },
    {
        "anchor": "Imbalanced Fermi Gases at Unitarity: We consider imbalanced Fermi gases with strong attractive interactions, for\nwhich Cooper-pair formation plays an important role. The two-component mixtures\nconsist either of identical fermionic atoms in two different hyperfine states,\nor of two different atomic species both occupying only a single hyperfine\nstate. In both cases, the number of atoms for each component is allowed to be\ndifferent, which leads to a spin imbalance, or spin polarization. Two different\natomic species also lead to a mass imbalance. Imbalanced Fermi gases are\nrelevant to condensed-matter physics, nuclear physics and astroparticle\nphysics. They have been studied intensively in recent years, following their\nexperimental realization in ultracold atomic Fermi gases. The experimental\ncontrol in such a system allows for a systematic study of the equation of state\nand the phase diagram as a function of temperature, spin polarization and\ninteraction strength. In this review, we discuss the progress in understanding\nstrongly-interacting imbalanced Fermi gases, where a main goal is to describe\nthe results of the highly controlled experiments. We start by discussing\nFeshbach resonances, after which we treat the imbalanced Fermi gas in\nmean-field theory to give an introduction to the relevant physics. We encounter\nseveral unusual superfluid phases, including phase separation, gapless Sarma\nsuperfluidity, and supersolidity. To obtain a more quantitative description of\nthe experiments, we review also more sophisticated techniques, such as\ndiagrammatic methods and the renormalization-group theory. We end the review by\ndiscussing two theoretical approaches to treat the inhomogeneous imbalanced\nFermi gas, namely the Landau-Ginzburg theory and the Bogoliubov-de Gennes\napproach.",
        "positive": "An impurity in a Fermi sea on a narrow Feshbach resonance: A variational\n  study of the polaronic and dimeronic branches: We study the problem of a single impurity of mass $M$ immersed in a Fermi sea\nof particles of mass $m$. The impurity and the fermions interact through a\ns-wave narrow Feshbach resonance, so that the Feshbach length $R_*$ naturally\nappears in the system. We use simple variational ansatz, limited to at most one\npair of particle-hole excitations of the Fermi sea and we determine for the\npolaronic and dimeronic branches the phase diagram between absolute ground\nstate, local minimum, thermodynamically unstable regions (with negative\neffective mass), and regions of complex energies (with negative imaginary\npart). We also determine the closed channel population which is experimentally\naccessible. Finally we identify a non-trivial weakly attractive limit where\nanalytical results can be obtained, in particular for the crossing point\nbetween the polaronic and dimeronic energy branches."
    },
    {
        "anchor": "Few-boson tunneling in a double well with spatially modulated\n  interaction: We study few-boson tunneling in a one-dimensional double well with a\nspatially modulated interaction. The dynamics changes from Rabi oscillations in\nthe non-interacting case to a highly suppressed tunneling for intermediate\ncoupling strengths followed by a revival near the fermionization limit. With\nextreme interaction inhomogeneity in the regime of strong correlations we\nobserve tunneling between the higher bands. The dynamics is explained on the\nbasis of the few-body spectrum and stationary eigenstates. For higher number of\nparticles, N > 2, it is shown that the inhomogeneity of the interaction can be\ntuned to generate tunneling resonances. Finally, a tilted double-well and its\ninterplay with the interaction asymmetry is discussed.",
        "positive": "Structured Weyl Points in Spin-Orbit Coupled Fermionic Superfluids: We demonstrate that a Weyl point, widely examined in 3D Weyl semimetals and\nsuperfluids, can develop a pair of non-degenerate gapless spheres. Such a\nbouquet of two spheres is characterized by three distinct topological\ninvariants of manifolds with full energy gaps, i.e., the Chern number of a 0D\npoint inside one developed sphere, the winding number of a 1D loop around the\noriginal Weyl point, and the Chern number of a 2D surface enclosing the whole\nbouquet. We show that such structured Weyl points can be realized in the\nsuperfluid quasiparticle spectrum of a 3D degenerate Fermi gas subject to\nspin-orbit couplings and Zeeman fields, which supports Fulde-Ferrell\nsuperfluids as the ground state."
    },
    {
        "anchor": "Observable Vortex Properties in Finite Temperature Bose Gases: We study the dynamics of vortices in finite temperature atomic Bose-Einstein\ncondensates, focussing on decay rates, precession frequencies and core\nbrightness, motivated by a recent experiment (Freilich et al. Science 329, 1182\n(2010)) in which real-time dynamics of a single vortex was observed. Using the\nZNG formalism based on a dissipative Gross-Pitaevskii equation for the\ncondensate coupled to a semi-classical Boltzmann equation for the thermal\ncloud, we find a rapid nonlinear increase of both the decay rate and precession\nfrequency with increasing temperatures. The increase, which is dominated by the\ndynamical condensate-thermal coupling is also dependent on the intrinsic\nthermal cloud collisional dynamics; the precession frequency also varies with\nthe initial radial coordinate. The integrated thermal cloud density in the\nvortex core is for the most part independent of the position of the vortex\n(except when it is near the condensate edge) with its value increasing with\ntemperature. This could potentially be used as a variant to the method of\nCoddington et al. (Phys. Rev. A 70, 063607 (2004)) for experimentally\ndetermining the temperature.",
        "positive": "Two-dimensional quantum droplets in dipolar Bose gases: We calculate analytically the quantum and thermal fluctuations corrections of\na dilute quasi-two-dimensional Bose-condensed dipolar gas. We show that these\nfluctuations may change their character from repulsion to attraction in the\ndensity-temperature plane owing to the striking momentum dependence of the\ndipole-dipole interactions. The dipolar instability is halted by such\nunconventional beyond mean field corrections leading to the formation of a\ndroplet phase. The equilibrium features and coherence properties exhibited by\nsuch droplets are deeply discussed. At finite temperature, we find that the\nequilibrium density crucially depends on the temperature and on the confinement\nstrength and thus, a stable droplet can exist only at ultralow temperature due\nto the strong thermal fluctuations."
    },
    {
        "anchor": "A tractable prescription for large-scale free flight expansion of\n  wavefunctions: A numerical recipe is given for obtaining the density image of an initially\ncompact quantum mechanical wavefunction that has expanded by a large but finite\nfactor under free flight. The recipe given avoids the memory storage problems\nthat plague this type of calculation by reducing the problem to the sum of a\nnumber of fast Fourier transforms carried out on the relatively small initial\nlattice. The final expanded state is given exactly on a coarser magnified grid\nwith the same number of points as the initial state. An important application\nof this technique is the simulation of measured time-of-flight images in\nultracold atom experiments, especially when the initial clouds contain\nsuperfluid defects. It is shown that such a finite-time expansion, rather than\na far-field approximation is essential to correctly predict images of\ndefect-laden clouds, even for long flight times. Examples shown are: an\nexpanding quasicondensate with soliton defects and a matter-wave interferometer\nin 3D.",
        "positive": "Berezinskii-Kosterlitz-Thouless Phase Transition in 2D Spin-Orbit\n  Coupled Fulde-Ferrell Superfluids: The experimental observation of traditional Zeeman-field induced\nFulde-Ferrell-Larkin-Ovchinnikov (FFLO) superfluids has been hindered by\nvarious challenges, in particular, the requirement of low dimensional systems.\nIn 2D, finite temperature phase fluctuations lead to extremely small\nBerezinskii-Kosterlitz-Thouless (BKT) transition temperature for FFLO\nsuperfluids, raising serious concerns regarding their experimental\nobservability. Recently, it was shown that FFLO superfluids can be realized\nusing a Rashba spin-orbit coupled Fermi gas subject to Zeeman fields, which may\nalso support topological excitations such as Majorana fermions in 2D. Here we\naddress the finite temperature BKT transition issue in this system, which may\nexhibit gapped, gapless, topological, and gapless topological FF phases. We\nfind a large BKT transition temperature due to large effective superfluid\ndensities, making it possible to observe 2D FF superfluids at finite\ntemperature. In addition, we show that gapless FF superfluids can be stable due\nto their positive superfluid densities. These findings pave the way for the\nexperimental observation of 2D gapped and gapless FF superfluids and their\nassociated topological excitations at finite temperature."
    },
    {
        "anchor": "Observation of non-Hermitian degeneracies in a chaotic exciton-polariton\n  billiard: Exciton-polaritons are hybrid light-matter quasiparticles formed by strongly\ninteracting photons and excitons (electron-hole pairs) in semiconductor\nmicrocavities. They have emerged as a robust solid-state platform for\nnext-generation optoelectronic applications as well as fundamental studies of\nquantum many-body physics. Importantly, exciton-polaritons are a profoundly\nopen (i.e., non-Hermitian) quantum system: it requires constant pumping of\nenergy and continuously decays releasing coherent radiation. Thus, the\nexciton-polaritons always exist in a balanced potential landscape of gain and\nloss. However, the inherent non-Hermitian nature of this potential has so far\nbeen largely ignored in exciton-polariton physics. Here we demonstrate that\nnon-Hermiticity dramatically modifies the structure of modes and spectral\ndegeneracies in exciton-polariton systems, and, therefore, will affect their\nquantum transport, localisation, and dynamical properties. Using a\nspatially-structured optical pump, we create a chaotic exciton-polariton\nbilliard. Eigenmodes of this billiard exhibit multiple non-Hermitian spectral\ndegeneracies -- exceptional points. These are known to cause remarkable wave\nphenomena, such as unidirectional transport, anomalous lasing/absorption, and\nchiral modes. By varying parameters of the billiard, we observe crossing and\nanti-crossing of energy levels and reveal the nontrivial topological modal\nstructure exclusive to non-Hermitian systems. We also observe the mode\nswitching and topological Berry phase for a parameter loop encircling the\nexceptional point. Our findings pave the way for studies of non-Hermitian\nquantum dynamics of exciton-polaritons, which can lead to novel functionalities\nof polariton-based devices.",
        "positive": "Spin squeezing in a spin-orbit coupled Bose-Einstein condensate: We study the spin squeezing in a spin-1/2 Bose-Einstein condensates (BEC)\nwith Raman induced spin-orbit coupling (SOC). Under the condition of two-photon\nresonance and weak Raman coupling strength, the system possesses two degenerate\nground states, using which we construct an effective two-mode model. The\nHamiltonian of the two-mode model takes the form of the one-axis-twisting\nHamiltonian which is known to generate spin squeezing. More importantly, we\nshow that the SOC provides a convenient control knob to adjust the spin\nnonlinearity responsible for spin squeezing. Specifically, the spin\nnonlinearity strength can be tuned to be comparable to the two-body\ndensity-density interaction, hence is much larger than the intrinsic\nspin-dependent interaction strength in conventional two-component BEC systems\nsuch as $^{87}$Rb and $^{23}$Na in the absence of the SOC. We confirm the spin\nsqueezing by carrying out a fully beyond-mean-field numerical calculation using\nthe truncated Wigner method. Additionally, the experimental implementation is\nalso discussed."
    },
    {
        "anchor": "Analogue Stochastic Gravity in Strongly-Interacting Bose-Einstein\n  Condensates: Collective modes propagating in a moving superfluid are known to satisfy wave\nequations in a curved space time, with a metric determined by the underlying\nsuperflow. We use the Keldysh technique in a curved space-time to develop a\nquantum geometric theory of fluctuations in superfluid hydrodynamics. This\ntheory relies on a 'quantized' generalization of the two-fluid description of\nLandau and Khalatnikov, where the superfluid component is viewed as a\nquasi-classical field coupled to a normal component -- the collective\nmodes/phonons representing a quantum bath. This relates the problem in the\nhydrodynamic limit to the 'quantum friction' problem of Caldeira-Leggett type.\nBy integrating out the phonons, we derive stochastic Langevin equations\ndescribing a coupling between the superfluid component and phonons. These\nequations have the form of Euler equations with additional source terms\nexpressed through a fluctuating stress-energy tensor of phonons. Conceptually,\nthis result is similar to stochastic Einstein equations that arise in the\ntheory of stochastic gravity. We formulate the fluctuation-dissipation theorem\nin this geometric language and discuss possible physical consequences of this\ntheory.",
        "positive": "Bakhtiari, Leskinen and Torma Reply: This is a Reply to: Comment on \"Spectral Signatures of the\nFulde-Ferrell-Larkin-Ovchinnikov Order Parameter in One-Dimensional Optical\nLattices\" R. A. Molina J. Dukelksy, and P. Schmitteckert, Phys. Rev. Lett. 102,\n168901 (2009)"
    },
    {
        "anchor": "Role of conservation laws in the Density Matrix Renormalization Group: We explore matrix product state approximations to wavefunctions which have\nspontaneously broken symmetries or are critical. We are motivated by the fact\nthat symmetries, and their associated conservation laws, lead to block-sparse\nmatrix product states. Numerical calculations which take advantage of these\nsymmetries run faster and require less memory. However, in symmetry-broken and\ncritical phases the block sparse ansatz yields less accurate energies. We\ncharacterize the role of conservation laws in matrix product states and\ndetermine when it is beneficial to make use of them.",
        "positive": "Anderson localization of matter waves in tailored disordered potentials: We show that, in contrast to immediate intuition, Anderson localization of\nnoninteracting particles induced by a disordered potential in free space can\nincrease (i.e., the localization length can decrease) when the particle energy\nincreases, for appropriately tailored disorder correlations. We predict the\neffect in one, two, and three dimensions, and propose a simple method to\nobserve it using ultracold atoms placed in optical disorder. The increase of\nlocalization with the particle energy can serve to discriminate quantum versus\nclassical localization."
    },
    {
        "anchor": "Synthetic spin-orbit coupling mediated by a bosonic environment: We study a mobile quantum impurity, possessing internal rotational degrees of\nfreedom, confined to a ring in the presence of a many-particle bosonic bath. By\nconsidering the recently introduced rotating polaron problem, we define the\nHamiltonian and examine the energy spectrum. The weak-coupling regime is\nstudied by means of a variational ansatz in the truncated Fock space. The\ncorresponding spectrum indicates that there emerges a coupling between the\ninternal and orbital angular momenta of the impurity as a consequence of the\nphonon exchange. We interpret the coupling as a phonon-mediated spin-orbit\ncoupling and quantify it by using a correlation function between the internal\nand orbital angular momentum operators. The strong-coupling regime is\ninvestigated within the Pekar approach and it is shown that the correlation\nfunction of the ground state shows a kink at a critical coupling, that is\nexplained by a sharp transition from the non-interacting state to the states\nthat exhibit strong interaction with the surroundings. The results might find\napplications in such fields as spintronics or topological insulators, where\nspin-orbit coupling is of crucial importance.",
        "positive": "Dissipative Bose-Hubbard system with intrinsic two-body loss: We report an experimental study of dynamics of the metastable $^3P_2$ state\nof bosonic ytterbium atoms in an optical lattice. The dissipative Bose-Hubbard\nsystem with on-site two-body atom loss is realized via its intrinsic strong\ninelastic collision of the metastable $^3P_2$ atoms. We investigate the atom\nloss behavior with the unit-filling Mott insulator as the initial state and\nfind that the atom loss is suppressed by the strong correlation between atoms.\nAlso, as we decrease the potential depth of the lattice, we observe the growth\nof the phase coherence and find its suppression owing to the dissipation."
    },
    {
        "anchor": "Tan contact and universal high momentum behavior of the fermion\n  propagator in the BCS-BEC crossover: We derive the universal high momentum factorization of the fermion\nself-energy in the BCS-BEC crossover of ultracold atoms using nonperturbative\nquantum field theoretical methods. This property is then employed to compute\nthe Tan contact as a function of interaction strength, temperature, chemical\npotential and Fermi momentum. We clarify the mechanism of the factorization\nfrom an analysis of the self-consistent Schwinger-Dyson equation for the\nfermion propagator, and compute the perturbative contact on the BCS and BEC\nsides within this framework. A Functional Renormalization Group approach is\nthen put forward, which allows to determine the contact over the whole\ncrossover and, in particular, for the Unitary Fermi gas. We present numerical\nresults from an implementation of the Renormalization Group equations within a\nbasic truncation scheme.",
        "positive": "Parity solitons in nonresonantly driven-dissipative condensate channels: We study analytically and numerically the condensation of a\ndriven-dissipative exciton-polariton system using symmetric nonresonant pumping\ngeometries. We show that the lowest condensation threshold solution carries a\ndefinite parity as a consequence of the symmetric excitation profile. At higher\npump intensities competition between the two parities can result in critical\nquenching of one and saturation of the other. Using long pump channels, we show\nthat the competition of the condensate parities gives rise to a different type\nof topologically stable defect propagating indefinitely along the condensate.\nThe defects display repulsive interactions and are characterized by a sustained\nwavepacket carrying a pair of opposite parity domain walls in the condensate\nchannel."
    },
    {
        "anchor": "Unitary fermions and Luscher's formula on a crystal: We consider the low-energy particle-particle scattering properties in a\nperiodic simple cubic crystal. In particular, we investigate the relation\nbetween the two-body scattering length and the energy shift experienced by the\nlowest-lying unbound state when this is placed in a periodic finite box. We\nintroduce a continuum model for s-wave contact interactions that respects the\nsymmetry of the Brillouin zone in its regularisation and renormalisation\nprocedures, and corresponds to the na{\\\"i}ve continuum limit of the Hubbard\nmodel. The energy shifts are found to be identical to those obtained in the\nusual spherically symmetric renormalisation scheme upon resolving an important\nsubtlety regarding the cutoff procedure. We then particularize to the Hubbard\nmodel, and find that for large finite lattices the results are identical to\nthose obtained in the continuum limit. The results reported here are valid in\nthe weak, intermediate and unitary limits, and can be used for the extraction\nof scattering information ,via exact diagonalisation or Monte Carlo methods, of\ntwo-body systems in realistic periodic lattices.",
        "positive": "Fractional windings of the spinor condensates on a ring: We study the uniform solutions to the one-dimensional spinor Bose-Einstein\ncondensates on a ring. These states explicitly display the associated motion of\nthe super-current and the spin rotation, which give rise to fractional winding\nnumbers according to the various compositions of the hyperfine states. It\nsimultaneously yields a fractional factor to the global phase due to the\ngauge-spin symmetry. Our method can be applied to explore the fractional\nvortices by identifying the ring as the boundary of two-dimensional spinor\ncondensates."
    },
    {
        "anchor": "Novel soliton in dipolar BEC caused by the quantum fluctuations: Solitons in the extended hydrodynamic model of the dipolar Bose-Einstein\ncondensate with quantum fluctuations are considered. This model includes the\ncontinuity equation for the scalar field of concentration, the Euler equation\nfor the vector field of velocity, the pressure evolution equation for the\nsecond rank tensor of pressure, and the evolution equation for the third rank\ntensor. Large amplitude soliton solution caused by the dipolar part of quantum\nfluctuations is found. It appears as the bright soliton. Hence, it is the area\nof compression of the number of particles. Moreover, it exists for the\nrepulsive short-range interaction.",
        "positive": "Elementary excitations of dipolar Tonks-Girardeau droplets: One-dimensional bosonic gas with strong contact repulsion and attractive\ndipolar interactions may form a quantum droplet with flat-top density profile.\nEmploying effective, hydrodynamic description of the system, we study\nelementary excitations characterizing response of a droplet to small\nperturbation. The excitation spectrum consists of two families: phononic-like\nexcitations inside droplets and the scattering modes. Analysis within the\nlinearized regime is supplemented with the full, nonlinear dynamics of small\nperturbations. Our study focuses mainly on the regime of infinite contact\nrepulsion and tight transversal harmonic confinement, where there are analytic\nformulas for the density profiles. Moreover, we propose a simplified analytic\nansatz suitable to work also outside this regime, provided the gas is in the\ndeep flat-top region of density profiles."
    },
    {
        "anchor": "Strongly interacting Rydberg atoms in synthetic dimensions with a\n  magnetic flux: Synthetic dimensions, wherein dynamics occurs in a set of internal states,\nhave found great success in recent years in exploring topological effects in\ncold atoms and photonics. However, the phenomena thus far explored have largely\nbeen restricted to the non-interacting or weakly interacting regimes. Here, we\nextend the synthetic dimensions playbook to strongly interacting systems of\nRydberg atoms prepared in optical tweezer arrays. We use precise control over\ndriving microwave fields to introduce a tunable $U(1)$ flux in a four-site\nlattice of coupled Rydberg levels. We find highly coherent dynamics, in good\nagreement with theory. Single atoms show oscillatory dynamics controllable by\nthe gauge field. Small arrays of interacting atoms exhibit behavior suggestive\nof the emergence of ergodic and arrested dynamics in the regimes of\nintermediate and strong interactions, respectively. These demonstrations pave\nthe way for future explorations of strongly interacting dynamics and many-body\nphases in Rydberg synthetic lattices.",
        "positive": "Quantum annealing for the number partitioning problem using a tunable\n  spin glass of ions: Exploiting quantum properties to outperform classical ways of\ninformation-processing is an outstanding goal of modern physics. A promising\nroute is quantum simulation, which aims at implementing relevant and\ncomputationally hard problems in controllable quantum systems. Here we\ndemonstrate that in a trapped ion setup, with present day technology, it is\npossible to realize a spin model of the Mattis type that exhibits spin glass\nphases. Remarkably, our method produces the glassy behavior without the need\nfor any disorder potential, just by controlling the detuning of the spin-phonon\ncoupling. Applying a transverse field, the system can be used to benchmark\nquantum annealing strategies which aim at reaching the ground state of the spin\nglass starting from the paramagnetic phase. In the vicinity of a phonon\nresonance, the problem maps onto number partitioning, and instances which are\ndifficult to address classically can be implemented."
    },
    {
        "anchor": "From short-time diffusive to long-time ballistic dynamics: the unusual\n  center-of-mass motion of quantum bright solitons: Brownian motion is ballistic on short time scales and diffusive on long time\nscales. Our theoretical investigations indicate that one can observe the exact\nopposite - an \"anomaleous diffusion process\" where initially diffusive motion\nbecomes ballistic on longer time scales - in an ultracold atom system with a\nsize comparable to macromolecules. This system is a quantum matter-wave bright\nsoliton subject to decoherence via three-particle losses for which we\ninvestigate the center-of-mass motion. Our simulations show that such unusual\ncenter-of-mass dynamics should be observable on experimentally accessible time\nscales.",
        "positive": "Dynamics of a coupled spin vortex pair in dipolar spinor Bose-Einstein\n  condensates: The collisional and magnetic field quench dynamics of a coupled spin-vortex\npair in dipolar spinor Bose-Einstein condensates in a double well potential are\nnumerically investigated in the mean field theory. Upon a sudden release of the\npotential barrier the two layers of condensates collide with each other in the\ntrap center with the chirality of the vortex pair exchanged after each\ncollision, showing the typical signature of in-phase collision for the parallel\nspin vortex phase, and out-of-phase collision for the antiparallel phase. When\nquenching the transverse magnetic field, the vortex center in the\nsingle-layered condensate starts to make a helical motion with oval-shaped\ntrajectories and the displacement of the center position is found to exhibit a\ndamped simple harmonic oscillation with an intrinsic frequency and damping\nrate. The oscillation mode of the spin vortex pair may be tuned by the initial\nmagnetic field and the height of the Gaussian barrier, e.g. the gyrotropic\nmotions for parallel spin vortex pair are out of sync with each other in the\ntwo layers, while those for the antiparallel pair exhibit a\ndouble-helix-structure with the vortex centers moving opposite to each other\nwith the same amplitude."
    },
    {
        "anchor": "Detecting Fractional Chern Insulators in Optical Lattices through\n  Quantized Displacement: The realization of interacting topological states of matter such as\nfractional Chern insulators (FCIs) in cold atom systems has recently come\nwithin experimental reach due to the engineering of optical lattices with\nsynthetic gauge fields providing the required topological band structures.\nHowever, detecting their occurrence might prove difficult since transport\nmeasurements akin to those in solid state systems are challenging to perform in\ncold atom setups and alternatives have to be found. We show that for a $\\nu=\n1/2$ FCI state realized in the lowest band of a Harper-Hofstadter model of\ninteracting bosons confined by a harmonic trapping potential, the fractionally\nquantized Hall conductivity $\\sigma_{xy}$ can be accurately determined by the\ndisplacement of the atomic cloud under the action of a constant force which\nprovides a suitable experimentally measurable signal for detecting the\ntopological nature of the state. Using matrix-product state algorithms, we show\nthat, in both cylinder and square geometries, the movement of the particle\ncloud in time under the application of a constant force field on top of the\nconfining potential is proportional to $\\sigma_{xy}$ for an extended range of\nfield strengths.",
        "positive": "Fit-free determination of scale invariant equations of state:\n  application to the 2D Bose gas across the Berezinksii-Kosterlitz-Thouless\n  transition: We present a general \"fit-free\" method for measuring the equation of state\n(EoS) of a scale-invariant gas. This method, which is inspired from the\nprocedure introduced by Ku et al. [Science 335, 563 (2012)] for the unitary\nthree-dimensional Fermi gas, provides a general formalism which can be readily\napplied to any quantum gas in a known trapping potential, in the frame of the\nlocal density approximation. We implement this method on a weakly-interacting\ntwo-dimensional Bose gas in the vicinity of the Berezinskii-Kosterlitz-Thouless\ntransition, and determine its EoS with unprecedented accuracy in the critical\nregion. Our measurements provide an important experimental benchmark for\nclassical field approaches which are believed to accurately describe quantum\nsystems in the weakly interacting but non-perturbative regime."
    },
    {
        "anchor": "Equilibrium thermodynamic properties of interacting two-component bosons\n  in one dimension: The interplay of quantum statistics, interactions and temperature is studied\nwithin the framework of the bosonic two-component theory with repulsive\ndelta-function interaction in one dimension. We numerically solve the\nthermodynamic Bethe Ansatz and obtain the equation of state as a function of\ntemperature and of the interaction strength, the relative chemical potential\nand either the total chemical potential or a fixed number of particles,\nallowing to quantify the full crossover behaviour of the system between its\nlow-temperature ferromagnetic and high-temperature unpolarized regime, and from\nthe low coupling decoherent regime to the fermionization regime at high\ninteraction.",
        "positive": "Spin-orbit coupled bosons in one dimension: emergent gauge field and\n  Lifshitz transition: In the presence of strong spin-independent interactions and spin-orbit\ncoupling, we show that the spinor Bose liquid confined to one spatial dimension\nundergoes an interaction- or density-tuned quantum phase transition similar to\none theoretically proposed for itinerant magnetic solid-state systems. The\norder parameter describes broken $Z_2$ inversion symmetry, with the ordered\nphase accompanied by non-vanishing momentum which is generated by fluctuations\nof an emergent dynamical gauge field at the phase transition. This quantum\nphase transition has dynamical critical exponent $z \\simeq 2$, typical of a\nLifshitz transition, but is described by a nontrivial interacting fixed point.\nFrom direct numerical simulation of the microscopic model, we extract\npreviously unknown critical exponents for this fixed point. Our model describes\na realistic situation of 1D ultracold atoms with Raman-induced spin-orbit\ncoupling, establishing this system as a platform for studying exotic critical\nbehavior of the Hertz-Millis type."
    },
    {
        "anchor": "Superfluid-insulator transition in weakly interacting disordered Bose\n  gases: a kernel polynomial approach: An iterative scheme based on the kernel polynomial method is devised for the\nefficient computation of the one-body density matrix of weakly interacting Bose\ngases within Bogoliubov theory. This scheme is used to analyze the coherence\nproperties of disordered bosons in one and two dimensions. In the\none-dimensional geometry, we examine the quantum phase transition between\nsuperfluid and Bose glass at weak interactions, and we recover the scaling of\nthe phase boundary that was characterized using a direct spectral approach by\nFontanesi et al. [Phys. Rev. A 81, 053603 (2010)]. The kernel polynomial scheme\nis also used to study the disorder-induced condensate depletion in the\ntwo-dimensional geometry. Our approach paves the way for an analysis of\ncoherence properties of Bose gases across the superfluid-insulator transition\nin two and three dimensions.",
        "positive": "Neutral skyrmion configurations in the low-energy effective theory of\n  spinor condensate ferromagnets: We study the low-energy effective theory of spinor condensate ferromagnets\nfor the superfluid velocity and magnetization degrees of freedom. This\neffective theory describes the competition between spin stiffness and a\nlong-ranged interaction between skyrmions, topological objects familiar from\nthe theory of ordinary ferromagnets. We find exact solutions to the non-linear\nequations of motion describing neutral configurations of skyrmions and\nanti-skyrmions. These analytical solutions provide a simple physical picture\nfor the origin of crystalline magnetic order in spinor condensate ferromagnets\nwith dipolar interactions. We also point out the connections to effective\ntheories for quantum Hall ferromagnets."
    },
    {
        "anchor": "Exact semiclassical dynamics of generic Lipkin-Meshkov-Glick model: Lipkin-Meshkov-Glick model is paradigmatic to study quantum phase transition\nin equilibrium or non-equilibrium systems and entanglement dynamics for a\nvariety of disciplines. In thermodynamics limit, quantum fluctuations are\nnegligible, its semiclassical dynamics in presence of only one nonlinear\ncouplings, as a good benchmark to study quantum fluctuation in finite-size\nsystem, can be well obtained in terms of Jacobi elliptic functions. In this\nwork, we extend this semiclassical analysis into the regime where both\nnonlinear interactions are present, and successfully obtain its exact solutions\nof semiclassical equations by constructing an auxiliary function that is a\nlinear combination of the $y$ and $z$ component of the classical spin in\nthermodynamic limit. Taking implementation of Lipkin-Meshkov-Glick model in a\nBose-Einstein condensate setup as an example, we figure out all classical\ndynamical modes, specially find out mesoscopic self-trapping mode in population\nand phase-difference space even persists in presence of both nonlinear\ncouplings. Our results would be useful to analyze dynamical phase transitions\nand entanglement dynamics of Lipkin-Meshkov-Glick model in presence of both\nnonlinear couplings.",
        "positive": "Disorder in order: Localization without randomness in a cold atom system: We present a mapping between the Edwards model of disorder describing the\nmotion of a single particle subject to randomly-positioned static scatterers\nand the Bose polaron problem of a light quantum impurity interacting with a\nBose-Einstein condensate (BEC) of heavy atoms. The mapping offers an\nexperimental setting to investigate the physics of Anderson localization where,\nby exploiting the quantum nature of the BEC, the time evolution of the quantum\nimpurity emulates the disorder-averaged dynamics of the Edwards model. Valid in\nany space dimension, the mapping can be extended to include interacting\nparticles, arbitrary disorder or confinement, and can be generalized to study\nmany-body localization. Moreover, the corresponding exactly-solvable disorder\nmodel offers means to benchmark variational approaches used to study polaron\nphysics. Here, we illustrate the mapping by focusing on the case of an impurity\ninteracting with a one-dimensional BEC through a contact interaction. While a\nsimple wave function based on the expansion in the number of bath excitations\nmisses the localization physics entirely, a coherent state Ansatz combined with\na canonical transformation captures the physics of disorder and Anderson\nlocalization."
    },
    {
        "anchor": "Revealing the Condensate and Non-Condensate Distributions in the\n  Inhomogeneous Bose-Hubbard Model: We calculate the condensate fraction and the condensate and non-condensate\nspatial and momentum distribution of the Bose-Hubbard model in a trap. From our\nresults, it is evident that using approximate distributions can lead to\nerroneous experimental estimates of the condensate. Strong interactions cause\nthe condensate to develop pedestal-like structures around the central peak that\ncan be mistaken as non-condensate atoms. Near the transition temperature, the\npeak itself can include a significant non-condensate component. Using\ndistributions generated from QMC simulations, experiments can map their\nmeasurements for higher accuracy in identifying phase transitions and\ntemperature.",
        "positive": "Path Integral Monte Carlo study of particles obeying quantum mechanics\n  and classical statistics: Ultracold atomic systems have been of great research interest in the past,\nwith more recent attention being paid to systems of mixed species. In this work\nwe carry out non-perturbative Path Integral Monte Carlo (PIMC) simulations of N\ndistinguishable particles at finite temperature, which can be thought of as an\nultracold atomic system containing N distinct species. We use the PIMC approach\nto calculate thermodynamic properties of particles interacting via hard-sphere\nand hard-cavity potentials. The first problem we study is a two-particle system\ninteracting via a hard-sphere and hard-cavity interaction in order to test the\neffectiveness of two approximations for the thermal density matrix\ncorresponding to these potentials. We then apply the PIMC method to a system of\nmany hard-sphere particles under periodic boundary conditions at varying\ntemperature in order to calculate the energy per particle, pressure, and\nspecific heat of the system. We examine how finite-size effects impact the\nresults of PIMC simulations of hard-sphere particles and when the thermodynamic\nlimit has been reached. Our results provide microscopic benchmarks for a system\ncontaining distinguishable particles, which can be thought of as a limiting\ncase for ultracold atomic systems of mixed species."
    },
    {
        "anchor": "Emergent interlayer nodal superfluidity of a dipolar fermi gas in\n  bilayer optical lattices: Understanding the interplay between magnetism and superconductivity is one of\nthe central issues in condensed matter physics. Such interplay induced nodal\nstructure of superconducting gap is widely believed to be a signature of exotic\npairing mechanism (not phonon mediated) to achieve unconventional\nsuperconductivity, such as in heavy fermion, high $T_c$, and organic\nsuperconductors. Here we report a new mechanism to drive the interplay between\nmagnetism and superfluidity via the spatially anisotropic interaction. This\nscheme frees up the usual requirement of suppressing long-range magnetic order\nto access unconventional superconductivity like through doping or adding\npressure in solids. Surprisingly, even for the half-filling case, such scheme\ncan lead the coexistence of superfluidity and antiferromagnetism and\ninterestingly an unexpected interlayer nodal superfluid emerges, which will be\ndemonstrated through a cold atom system composed of a pseudospin-$1/2$ dipolar\nfermi gas in bilayer optical lattices. Our mechanism should pave an alternative\nway to unveil exotic pairing scheme resulting from the interplay between\nmagnetism and superconductivity or superfluidity.",
        "positive": "Bright-like soliton solution in quasi-one-dimensional BEC in third order\n  on interaction radius: Nonlinear Schr\\\"{o}dinger equations and corresponding quantum hydrodynamic\n(QHD) equations are widely used in studying ultracold boson-fermion mixtures\nand superconductors. In this article, we show that a more exact account of\ninteraction in Bose-Einstein condensate (BEC), in comparison with the\nGross-Pitaevskii (GP) approximation, leads to the existence of a new type of\nsolitons. We use a set of QHD equations in the third order by the interaction\nradius (TOIR), which corresponds to the GP equation in a first order by the\ninteraction radius. The solution for the soliton in a form of expression for\nthe particle concentration is obtained analytically. The conditions of\nexistence of the soliton are studied. It is shown what solution exists if the\ninteraction between the particles is repulsive. Particle concentration of order\nof $10^{12}$-$10^{14}$ $cm^{-3}$ has been achieved experimentally for the BEC,\nthe solution exists if the scattering length is of the order of 1 $\\mu$m, which\ncan be reached using the Feshbach resonance. It is one of the limit case of\nexistence of new solution. The corresponding scattering length decrease with\nthe increasing of concentration of particles. The investigation of effects in\nthe TOIR approximation gives a more detail information on interaction\npotentials between the atoms and can be used for a more detail investigation\ninto the potential structure."
    },
    {
        "anchor": "Few-boson localization in a continuum with speckle disorder: The disorder-induced localization of few bosons interacting via a contact\npotential is investigated through the analysis of the level-spacing statistics\nfamiliar from random matrix theory. The model we consider is defined in a\ncontinuum and describes one-dimensional bosonic atoms exposed to the spatially\ncorrelated disorder due to an optical speckle field. % First, we identify the\nspeckle-field intensity required to observe, in the single-particle case, the\nPoisson level-spacing statistics, which is characteristic of localized quantum\nsystems, in a computationally and experimentally feasible system size. Then, we\nanalyze the two-body and the three-body systems, exploring a broad interaction\nrange, from the noninteracting limit up to moderately strong interactions. Our\nmain result is that the contact potential does not induce a shift towards the\nWigner-Dyson level-spacing statistics, which would indicate the emergence of an\nergodic chaotic state, indicating that localization can occur also in\ninteracting few-body systems in a continuum. We also analyze how the\nground-state energy evolves as a function of the interaction strength",
        "positive": "Static and dynamic phases of a Tonks-Girardeau gas in an optical lattice: We investigate the properties of a Tonks-Girardeau gas in the presence of a\none-dimensional lattice potential. Such a system is known to exhibit a pinning\ntransition when the lattice is commensurate with the particle density, leading\nto the formation of an insulating state even at infinitesimally small lattice\ndepths. Here we examine the properties of the gas at all lattices depths and,\nin addition to the static properties, also consider the non-adiabatic dynamics\ninduced by the sudden motion of the lattice potential with a constant speed.\nOur work provides a continuum counterpart to the work done in discrete lattice\nmodels."
    },
    {
        "anchor": "Analysis of a trapped Bose-Einstein condensate in terms of position,\n  momentum, and angular-momentum variance: We analyze, analytically and numerically, the position, momentum, and in\nparticular the angular-momentum variance of a Bose-Einstein condensate (BEC)\ntrapped in a two-dimensional anisotropic trap for static and dynamic scenarios.\nThe differences between the variances at the mean-field level, which are\nattributed to the shape of the BEC, and the variances at the many-body level,\nwhich incorporate depletion, are used to characterize position, momentum, and\nangular-momentum correlations in the BEC for finite systems and at the limit of\nan infinite number of particles where the bosons are $100\\%$ condensed.\nFinally, we also explore inter-connections between the variances.",
        "positive": "Shallow Trimers of Two Identical Fermions and One Particle in Resonant\n  Regimes: We consider two identical fermions interacting in the p-wave channel. Each\nfermion also interacts with another particle in the vicinity of an s-wave\nresonance. We find that in addition to the Kartavtsev-Malykh universal trimer\nstates resulting from the s-wave particle-fermion interaction, the\nfermion-fermion p-wave interaction induces one or two shallow trimers in a\nlarge domain of the control parameters, including a borromean regime where the\nground-state trimer exists in the absence of dimers at any mass ratio between\nthe fermions and the particle. A generic picture of the trimer spectrum emerges\nfrom this work in terms of the low-energy parameters of the interactions."
    },
    {
        "anchor": "Dynamical vanishing of the order parameter in a confined\n  Bardeen-Cooper-Schrieffer Fermi gas after an interaction quench: We present a numerical study of the Higgs mode in an ultracold confined Fermi\ngas after an interaction quench and find a dynamical vanishing of the\nsuperfluid order parameter. Our calculations are done within a microscopic\ndensity-matrix approach in the Bogoliubov-de Gennes framework which takes the\nthree-dimensional cigar-shaped confinement explicitly into account. In this\nframework, we study the amplitude mode of the order parameter after interaction\nquenches starting on the BCS side of the BEC-BCS crossover close to the\ntransition and ending in the BCS regime. We demonstrate the emergence of a\ndynamically vanishing superfluid order parameter in the spatiotemporal dynamics\nin a three-dimensional trap. Further, we show that the signal averaged over the\nwhole trap mirrors the spatiotemporal behavior and allows us to systematically\nstudy the effects of the system size and aspect ratio on the observed dynamics.\nOur analysis enables us to connect the confinement-induced modifications of the\ndynamics to the pairing properties of the system. Finally, we demonstrate that\nthe signature of the Higgs mode is contained in the dynamical signal of the\ncondensate fraction, which, therefore, might provide a new experimental access\nto the nonadiabatic regime of the Higgs mode.",
        "positive": "Fluctuation based interpretable analysis scheme for quantum many-body\n  snapshots: Microscopically understanding and classifying phases of matter is at the\nheart of strongly-correlated quantum physics. With quantum simulations, genuine\nprojective measurements (snapshots) of the many-body state can be taken, which\ninclude the full information of correlations in the system. The rise of deep\nneural networks has made it possible to routinely solve abstract processing and\nclassification tasks of large datasets, which can act as a guiding hand for\nquantum data analysis. However, though proven to be successful in\ndifferentiating between different phases of matter, conventional neural\nnetworks mostly lack interpretability on a physical footing. Here, we combine\nconfusion learning with correlation convolutional neural networks, which yields\nfully interpretable phase detection in terms of correlation functions. In\nparticular, we study thermodynamic properties of the 2D Heisenberg model,\nwhereby the trained network is shown to pick up qualitative changes in the\nsnapshots above and below a characteristic temperature where magnetic\ncorrelations become significantly long-range. We identify the full counting\nstatistics of nearest neighbor spin correlations as the most important quantity\nfor the decision process of the neural network, which go beyond averages of\nlocal observables. With access to the fluctuations of second-order correlations\n-- which indirectly include contributions from higher order, long-range\ncorrelations -- the network is able to detect changes of the specific heat and\nspin susceptibility, the latter being in analogy to magnetic properties of the\npseudogap phase in high-temperature superconductors. By combining the confusion\nlearning scheme with transformer neural networks, our work opens new directions\nin interpretable quantum image processing being sensible to long-range order."
    },
    {
        "anchor": "Phase diagram of the asymmetric Hubbard model and an entropic\n  chromatographic method for cooling cold fermions in optical lattices: We study the phase diagram of the asymmetric Hubbard model (AHM), which is\ncharacterized by different values of the hopping for the two spin projections\nof a fermion or equivalently, two different orbitals. This model is expected to\nprovide a good description of a mass-imbalanced cold fermionic mixture in a 3D\noptical lattice. We use the dynamical mean field theory to study various\nphysical properties of this system. In particular, we show how\norbital-selective physics, observed in multi-orbital strongly correlated\nelectron systems, can be realized in such a simple model. We find that the\ndensity distribution is a good probe of this orbital selective crossover from a\nFermi liquid to a non-Fermi liquid state.\n  Below an ordering temperature $T_o$, which is a function of both the\ninteraction and hopping asymmetry, the system exhibits staggered long range\norbital order. Apart from the special case of the symmetric limit, i.e.,\nHubbard model, where there is no hopping asymmetry, this orbital order is\naccompanied by a true charge density wave order for all values of the hopping\nasymmetry. We calculate the order parameters and various physical quantities\nincluding the thermodynamics in both the ordered and disordered phases. We find\nthat the formation of the charge density wave is signaled by an abrupt increase\nin the sublattice double occupancies. Finally, we propose a new method,\nentropic chromatography, for cooling fermionic atoms in optical lattices, by\nexploiting the properties of the AHM. To establish this cooling strategy on a\nfirmer basis, we also discuss the variations in temperature induced by the\nadiabatic tuning of interactions and hopping parameters.",
        "positive": "Observability of Quantum Criticality and a Continuous Supersolid in\n  Atomic Gases: We analyze the Bose-Hubbard model with a three-body hardcore constraint by\nmapping the system to a theory of two coupled bosonic degrees of freedom. We\nfind striking features that could be observable in experiments, including a\nquantum Ising critical point on the transition from atomic to dimer\nsuperfluidity at unit filling, and a continuous supersolid phase for strongly\nbound dimers."
    },
    {
        "anchor": "Creating superfluid vortex rings in artificial magnetic fields: Artificial gauge fields are versatile tools that allow to influence the\ndynamics of ultracold atoms in Bose-Einstein condensates. Here we discuss a\nmethod of artificial gauge field generation stemming from the evanescent fields\nof the curved surface of an optical nanofibre. The exponential decay of the\nevanescent fields leads to large gradients in the generalized Rabi frequency\nand therefore to the presence of geometric vector and scalar potentials. By\nsolving the Gross-Pitaevskii equation in the presence of the artificial gauge\nfields originating from the fundamental HE$_{11}$ mode of the fibre, we show\nthat vortex rings can be created in a controlled manner. We also calculate the\nmagnetic fields resulting from the higher order HE$_{21}$, TE$_{01}$, and\nTM$_{01}$ modes and compare them to the fundamental HE$_{11}$ mode.",
        "positive": "Cold atoms at unitarity and semiclassical ground state of a Fermi gas\n  for Haldane-Wu exclusion statistics: We investigate finite particle systems of cold atoms bound in a local\npotential V(r). We derive the ground state energy and the particle density\nusing a recently developed semiclassical theory (2008 Phys. Rev. Lett. 100\n200408), and assuming the particles are described by the Haldane-Wu fractional\nexclusion statistics (FES) at unitarity. This approach is applied to atoms\ntrapped into a three dimensional harmonic oscillator. We show that the\nparameter-free FES semiclassical theory yields results that are consistent with\nnumerical simulations by Chang and Bertsch [2007 Phys. Rev A 76 021603(R)] and\nBulgac (2007 Phys. Rev. A 76 040502)."
    },
    {
        "anchor": "Heating from Continuous Number Density Measurements in Optical Lattices: We explore the effects of continuous number density measurement on atoms in\nan optical lattice. By integrating a master equation for quantum observables,\nwe calculate how single particle correlations decay. We consider weakly- and\nstrongly- interacting bosons and noninteracting fermions. Even in the Mott\nregime, such measurements destroy correlations and increase the average energy,\nas long as some hopping is allowed. We explore the role of spatial resolution,\nand find that the heating rate is proportional to the amount of information\ngained from such measurements.",
        "positive": "Reentrant Localization Transition in a Quasiperiodic Chain: Systems with quasiperiodic disorder are known to exhibit localization\ntransition in low dimension. After a critical strength of disorder all the\nstates of the system become localized, thereby ceasing the particle motion in\nthe system. However, in our analysis we show that in a one dimensional\ndimerized lattice with staggered quasiperiodic disorder, after the localization\ntransition some of the localized eigenstates become extended for a range of\nintermediate disorder strengths. Eventually, the system undergoes a second\nlocalization transition at a higher disorder strength leading to all states\nlocalized. We also show that the two localization transitions are associated\nwith the mobility regions hosting the single particle mobility edges. We\nestablish this re-entrant localization transition by analyzing the\neigenspectra, participation ratios and the density of states of the system."
    },
    {
        "anchor": "A non-relativistic magnetized vector boson gas at any temperature: We study the thermodynamic properties of a neutral vector boson gas in\npresence of a constant magnetic field, by means of a semi-classical approach\nthat allows to introduce the spin in the non-relativistic spectrum of the\nbosons. Bose-Einstein condensation is obtained and it turns out to depend on\nall the parameters involved in the problem: temperature, particle density and\nmagnetic field. An spontaneous magnetization appears at low temperature as a\nconsequence of the condensed state. The axial symmetry imposed in the system by\nthe magnetic field presence, splits the pressure in two components, one along\nand another perpendicular to the magnetic axis. Under certain conditions, the\nperpendicular pressure becomes negative signaling that the system undergoes a\ntransversal magnetic collapse. The spontaneous magnetization might be useful to\nmodel magnetic field production inside compact stars, while the negative\npressures imposes certain limits to the temperatures and densities needed\ninside these objects to support a given magnetic field.",
        "positive": "Collisional Cooling of Ultracold Molecules: Since the original work on Bose-Einstein condensation, quantum degenerate\ngases of atoms have allowed the quantum emulation of important systems from\ncondensed matter and nuclear physics, as well as the study of novel many-body\nstates with no analog in other fields of physics. Ultracold molecules in the\nmicro- and nano-Kelvin regimes promise to bring powerful new capabilities to\nquantum emulation and quantum computing, thanks to their rich internal degrees\nof freedom compared to atoms. They also open new possibilities for precision\nmeasurement and the study of quantum chemistry. Quantum gases of atoms were\nmade possible by collision-based cooling schemes, such as evaporative cooling.\nFor ultracold molecules, thermalization and collisional cooling have not been\nrealized. With other techniques such as supersonic jets and cryogenic buffer\ngases, studies have been limited to temperatures above 10 mK. Here we show\ncooling of NaLi molecules at micro- and nano-Kelvin temperatures through\ncollisions with ultracold Na atoms, both prepared in their stretched hyperfine\nspin states. We find a lower bound on the elastic to inelastic collision ratio\nbetween molecules and atoms greater than 50 -- large enough to support\nsustained collisional cooling. By employing two stages of evaporation, we\nincrease the phase-space density (PSD) of the molecules by a factor of 20,\nachieving temperatures as low as 220 nK. The favorable collisional properties\nof a Na and NaLi mixture show great promise for making deeply quantum\ndegenerate dipolar molecules and suggest the potential for such cooling in\nother systems."
    },
    {
        "anchor": "Designing Arbitrary One-dimensional Potentials on an Atom Chip: We use laser light shaped by a digital micro-mirror device to realize\narbitrary optical dipole potentials for one-dimensional (1D) degenerate Bose\ngases of 87Rb trapped on an atom chip. Superposing optical and magnetic\npotentials combines the high flexibility of optical dipole traps with the\nadvantages of magnetic trapping, such as effective evaporative cooling and the\napplication of radio-frequency dressed state potentials. As applications, we\npresent a 160 ${\\mu}$m long box-like potential with a central tuneable barrier,\na box-like potential with a sinusoidally modulated bottom and a linear\nconfining potential. These potentials provide new tools to investigate the\ndynamics of 1D quantum systems and will allow us to address exciting questions\nin quantum thermodynamics and quantum simulations.",
        "positive": "Expanding ring-shaped Bose-Einstein condensates as analogs of\n  cosmological models: Analytical characterization of the inflationary dynamics: We analytically study the expansion of a Bose-Einstein condensate in a\nring-shaped trap with an increasing central radius. The evolution of the ground\nstate is described using a scaling transform. Additionally, the dynamics of\nexcited azimuthal modes over the varying ground state is analyzed through a\ngeneralization of the Bogoliubov-de Gennes approach. Our results explain some\nof the features observed in recent experiments focused on testing the\napplicability of the system as a parallel of cosmological inflationary models.\nThe radial dynamics, which corresponds to the inflaton field of the\ncosmological counterpart, is analytically characterized: The expansion is found\nto induce the oscillatory displacement of the condensate as well as the coupled\nvariation of the radial and vertical widths. Our findings account also for the\nobserved redshift and emergence of the Hubble friction in the evolution of\ninitially-prepared azimuthal modes. Our description, which traces the role of\nthe different components of the setup in the expansion, enhances the\ncontrollability, and, therefore, the potential of the system as a ground for\nemulating the inflationary dynamics of cosmological models."
    },
    {
        "anchor": "Repulsively interacting fermions in a two-dimensional deformed trap with\n  spin-orbit coupling: We investigate a two-dimensional system of with two values of the internal\n(spin) degree of freedom. It is confined by a deformed harmonic trap and\nsubject to a Zeeman field, Rashba or Dresselhaus one-body spin-orbit couplings\nand two-body short range repulsion. We obtain self-consistent mean-field\n$N$-body solutions as functions of the interaction parameters. Single-particle\nSpectra and total energies are computed and compared to the results without\ninteraction. We perform a statistical analysis for the distributions of nearest\nneighbor energy level spacings and show that quantum signatures of chaos are\nseen in certain parameters regimes. Furthermore, the effects of two-body\nrepulsion on the nearest neighbor distributions are investigated. This\nrepulsion can either promote or destroy the signatures of potential chaotic\nbehavior depending on relative strengths of parameters. Our findings support\nthe suggestion that cold atoms may be used to study quantum chaos both in the\npresence and absence of interactions.",
        "positive": "The Fracton quantum gas: Starting from a simple dipole-conserving Hamiltonian model, after introducing\na proper quantisation framework, we construct the linear-response theory of a\nfracton quantum gas. We show how to consistently construct the density operator\nand we calculate the density-density linear-response function in the limit of\nlarge number of (fracton) flavours. We show how to construct its random-phase\napproximation, from which we calculate the fracton-plasmon dispersion."
    },
    {
        "anchor": "Three-Dimensional Anderson Localization in Variable Scale Disorder: We report on the impact of variable-scale disorder on 3D Anderson\nlocalization of a non-interacting ultracold atomic gas. A spin-polarized gas of\nfermionic atoms is localized by allowing it to expand in an optical speckle\npotential. Using a sudden quench of the localized density distribution, we\nverify that the density profile is representative of the underlying\nsingle-particle localized states. The geometric mean of the disordering\npotential correlation lengths is varied by a factor of four via adjusting the\naperture of the speckle focusing lens. We observe that the root-mean-square\nsize of the localized gas increases approximately linearly with the speckle\ncorrelation length, in qualitative agreement with the scaling predicted by weak\nscattering theory.",
        "positive": "Diversified vortex phase diagram for a rotating trapped two-band Fermi\n  gas in the BCS-BEC crossover: We report the equilibrium vortex phase diagram of a rotating two-band Fermi\ngas confined to a cylindrically symmetric parabolic trapping potential, using\nthe recently developed finite-temperature effective field theory [Phys. Rev. A\n$\\bf{94}$, 023620 (2016)]. A non-monotonic resonant dependence of the free\nenergy as a function of the temperature and the rotation frequency is revealed\nfor a two-band superfluid. We particularly focus on novel features that appear\nas a result of interband interactions and can be experimentally resolved. The\nresonant dependence of the free energy is directly manifested in vortex phase\ndiagrams, where areas of stability for both integer and fractional vortex\nstates are found. The study embraces the BCS-BEC crossover regime and the\nentire temperature range below the critical temperature $T_{c}$. Significantly\ndifferent behavior of vortex matter as a function of the interband coupling is\nrevealed in the BCS and BEC regimes."
    },
    {
        "anchor": "Propagation of a quantum fluid of light in a cavityless nonlinear\n  optical medium: General theory and response to quantum quenches: Making use of a generalized quantum theory of paraxial light propagation\nwhere the radiation-axis and the temporal coordinates play exchanged roles, we\ndiscuss the potential of bulk nonlinear optical media in cavityless\nconfigurations for quantum statistical mechanics studies of the conservative\nmany-body dynamics of a gas of interacting photons. To illustrate the general\nfeatures of this point of view, we investigate the response of the fluid of\nlight to the quantum quenches in the photon-photon interaction constant\nexperienced at the front and the back faces of a finite slab of weakly\nnonlinear material. Extending the standard Bogoliubov theory of dilute\nBose-Einstein condensates, peculiar features are predicted for the statistical\nproperties of the light emerging from the nonlinear medium.",
        "positive": "A compact single-chamber apparatus for Bose-Einstein condensation of\n  $^87$Rb: We describe a simple and compact single-chamber apparatus for robust\nproduction of $^87$Rb Bose-Einstein condensates. The apparatus is built from\noff-the-shelf components and allows production of quasi-pure condensates of >\n$3\\times 10^5$ atoms in < 30 s. This is achieved using a hybrid trap created by\na quadrupole magnetic field and a single red-detuned laser beam [Y.-J. Lin et\nal., Phys. Rev. A 79, 063631 (2009)]. In the same apparatus we also achieve\ncondensation in an optically plugged quadrupole trap [K. B. Davis et al., Phys.\nRev. Lett. 75, 3969 (1995)] and show that as little as 70 mW of plug-laser\npower is sufficient for condensation, making it viable to pursue this approach\nusing inexpensive diode lasers. While very compact, our apparatus features\nsufficient optical access for complex experiments, and we have recently used it\nto demonstrate condensation in a uniform optical-box potential [A. Gaunt et\nal., arXiv:1212.4453 (2012)]."
    },
    {
        "anchor": "Scalable cold-atom quantum simulator for two-dimensional QED: We propose a scalable analog quantum simulator for quantum electrodynamics\n(QED) in two spatial dimensions. The setup for the U(1) lattice gauge field\ntheory employs inter-species spin-changing collisions in an ultra-cold atomic\nmixture trapped in an optical lattice. Building on the previous one-dimensional\nimplementation scheme of Ref. [1] we engineer spatial plaquette terms for\nmagnetic fields, thus solving a major obstacle towards experimental\nrealizations of realistic gauge theories in higher dimensions. We apply our\napproach to pure gauge theory and discuss how the phenomenon of confinement of\nelectric charges can be described by the quantum simulator.",
        "positive": "Bosons condensed in two modes with flavour-changing interaction: A quantum model is considered for $N$ bosons populating two orthogonal\nsingle-particle modes with tunable energy separation in the presence of\nflavour-changing contact interaction. The quantum ground state is well\napproximated as a coherent superposition (for zero temperature) or a mixture\n(at low temperature) of two quasi-classical states. In a mean field\ndescription, the systems realizes one of these states via spontaneous symmetry\nbreaking. Both mean field states, in a certain parameter range, possess finite\nangular momentum and exhibit broken time-reversal symmetry in contrast to the\nquantum ground state. The phase diagram is explored at the mean-field level and\nby direct diagonalisation. The nature of the quantum ground state at zero and\nfinite temperature is analyzed by means of the Penrose Onsager criterion. One\nof three possible phases shows fragmentation on the single-particle level\ntogether with a finite pair order parameter. Thermal and quantum fluctuations\nare characterized with respect to regions of universal scaling behavior. The\nnon-equilibrium dynamics shows a sharp transition between a self-trapping and a\npair-tunneling regime. A recently realized experimental implementation is\ndiscussed with bosonic atoms condensed in the two inequivalent energy minima\n$X_{\\pm}$ of the second band of a bipartite two-dimensional optical lattice."
    },
    {
        "anchor": "Dark solitons near potential and nonlinearity steps: We study dark solitons near potential and nonlinearity steps and combinations\nthereof, forming rectangular barriers. This setting is relevant to the contexts\nof atomic Bose-Einstein condensates (where such steps can be realized by using\nproper external fields) and nonlinear optics (for beam propagation near\ninterfaces separating optical media of different refractive indices). We use\nperturbation theory to develop an equivalent particle theory, describing the\nmatter-wave or optical soliton dynamics as the motion of a particle in an\neffective potential. This Newtonian dynamical problem provides information for\nthe soliton statics and dynamics, including scenarios of reflection,\ntransmission, or quasi-trapping at such steps. The case of multiple such steps\nand its connection to barrier potentials is also touched upon. Our analytical\npredictions are found to be in very good agreement with the corresponding\nnumerical results.",
        "positive": "Creating triple-NOON states with ultracold atoms via chaos-assisted\n  tunneling: Triple-NOON states are superpositions of the form $e^{i \\varphi_1}\n|{N,0,0}\\rangle + e^{i \\varphi_2} |{0,N,0}\\rangle + e^{i \\varphi_3}\n|{0,0,N}\\rangle$ involving $N$ bosonic quanta distributed over three modes. We\ntheoretically show how such highly entangled states can be generated with\ninteracting ultracold bosonic atoms in a symmetric three-site lattice. The\nbasic protocol consists in preparing all atoms on one site of the lattice and\nthen letting the system evolve during a specific time such that collective\ntunneling of the atoms to the other two sites takes place. The key point put\nforward here is that this evolution time can be reduced by several orders of\nmagnitude via the application of a periodic driving of the lattice, thereby\nrendering this protocol feasible in practice. This driving is suitably tuned\nsuch that classical chaos is generated in the entire accessible phase space\nexcept for the Planck cells that host the states participating at the above\ntriple-NOON superposition. Chaos-assisted tunneling can then give rise to a\ndramatic speed-up of this collective tunneling process, without significantly\naffecting the purity of this superposition. A triple-NOON state containing $N =\n5$ particles can thereby be realized with $^{87}$Rb atoms on time scales of the\norder of a few seconds."
    },
    {
        "anchor": "Cavity-Controlled Collective Scattering at the Recoil Limit: We study collective scattering with Bose-Einstein condensates interacting\nwith a high-finesse ring cavity. The condensate scatters the light of a\ntransverse pump beam superradiantly into modes which, in contrast to previous\nexperiments, are not determined by the geometrical shape of the condensate, but\nspecified by a resonant cavity mode. Moreover, since the recoil-shifted\nfrequency of the scattered light depends on the initial momentum of the\nscattered fraction of the condensate, we show that it is possible to employ the\ngood resolution of the cavity as a filter selecting particular quantized\nmomentum states.",
        "positive": "Finite Temperature Matrix Product State Algorithms and Applications: We review the basic theory of matrix product states (MPS) as a numerical\nvariational ansatz for time evolution, and present two methods to simulate\nfinite temperature systems with MPS: the ancilla method and the minimally\nentangled typical thermal state method. A sample calculation with the\nBose-Hubbard model is provided."
    },
    {
        "anchor": "Observation of the supersolid stripe phase in spin-orbit coupled\n  Bose-Einstein condensates: Supersolidity is an intriguing concept. It combines the property of\nsuperfluid flow with the long-range spatial periodicity of solids, two\nproperties which are often mutually exclusive. The original discussion of\nquantum crystals and supersolidity focuses on solid Helium-4 where it was\npredicted that vacancies could form dilute weakly interacting Bose-Einstein\ncondensates. In this system, direct observation of supersolidity has been\nelusive. The concept of supersolidity was then generalized to include other\nsuperfluid systems which break the translational symmetry of space. One of such\nsystems is a Bose-Einstein condensate with spin-orbit coupling which has a\nsupersolid stripe phase. Despite several recent studies of this system, the\nstripe phase has not been observed. Here we report the direct observation of\nthe predicted density modulation of the stripe phase using Bragg reflection.\nOur work establishes a system with unique symmetry breaking properties. Of\nfuture interest is further spatial symmetry breaking through the introduction\nof vortices, solitons, impurities or disorder.",
        "positive": "Rotating a supersolid dipolar gas: Distintictive features of supersolids show up in their rotational properties.\nWe calculate the moment of inertia of a harmonically trapped dipolar\nBose-Einstein condensed gas as a function of the tunable scattering length\nparameter, providing the transition from the (fully) superfluid to the\nsupersolid phase and eventually to an incoherent crystal of self-bound\ndroplets. The transition from the superfluid to the supersolid phase is\ncharacterized by a jump in the moment on inertia, revealing its first order\nnature. In the case of elongated trapping in the plane of rotation we show that\nthe the moment of inertia determines the value of the frequency of the scissors\nmode, which is significantly affected by the reduction of superfluidity in the\nsupersolid phase. The case of isotropic trapping is instead well suited to\nstudy the formation of quantized vortices, which are shown to be characterized,\nin the supersolid phase, by a sizeable deformed core, caused by the presence of\nthe sorrounding density peaks."
    },
    {
        "anchor": "Interferometric approach to measuring band topology in 2D optical\n  lattices: Recently, optical lattices with non-zero Berry's phases of Bloch bands have\nbeen realized. New approaches for measuring Berry's phases and topological\nproperties of bands with experimental tools appropriate for ultracold atoms\nneed to be developed. In this paper, we propose an interferometric method for\nmeasuring Berry's phases of two dimensional Bloch bands. The key idea is to use\na combination of Ramsey interference and Bloch oscillations to measure Zak\nphases, i.e. Berry's phases for closed trajectories corresponding to reciprocal\nlattice vectors. We demonstrate that this technique can be used to measure\nBerry curvature of Bloch bands, the \\pi-Berry's phase of Dirac points, and the\nfirst Chern number of topological bands. We discuss several experimentally\nfeasible realizations of this technique, which make it robust against\nlow-frequency magnetic noise.",
        "positive": "Quantum Phases of Self-Bound Droplets of Bose-Bose Mixtures: We systematically investigate the ground-state properties of self-bound\ndroplets of quasi-two-dimensional binary Bose gases by using the Gaussian state\ntheory. We find that quantum droplets consists two macroscopic squeezed phases\nand a macroscopic coherent phase. We map out the phase diagram and determine\nall phase boundaries via both numerical and nearly analytical methods. In\nparticular, we find three easily accessible signatures for the quantum phases\nand the stablization mechanism of the self-bound droplets by precisely\nmeasuring their radial size. Our studies indicate that binary droplets\nrepresent an ideal platform for in-depth investigations of the quantum nature\nof the droplet state."
    },
    {
        "anchor": "Scrambling and thermalization in a diffusive quantum many-body system: Out-of-time ordered (OTO) correlation functions describe scrambling of\ninformation in correlated quantum matter. They are of particular interest in\nincoherent quantum systems lacking well defined quasi-particles. Thus far, it\nis largely elusive how OTO correlators spread in incoherent systems with\ndiffusive transport governed by a few globally conserved quantities. Here, we\nstudy the dynamical response of such a system using high-performance\nmatrix-product-operator techniques. Specifically, we consider the\nnon-integrable, one-dimensional Bose-Hubbard model in the incoherent\nhigh-temperature regime. Our system exhibits diffusive dynamics in time-ordered\ncorrelators of globally conserved quantities, whereas OTO correlators display a\nballistic, light-cone spreading of quantum information. The slowest process in\nthe global thermalization of the system is thus diffusive, yet information\nspreading is not inhibited by such slow dynamics. We furthermore develop an\nexperimentally feasible protocol to overcome some challenges faced by existing\nproposals and to probe time-ordered and OTO correlation functions. Our study\nopens new avenues for both the theoretical and experimental exploration of\nthermalization and information scrambling dynamics.",
        "positive": "Metastability versus collapse following a quench in attractive\n  Bose-Einstein condensates: We consider a Bose-Einstein condensate (BEC) with attractive two-body\ninteractions in a cigar-shaped trap, initially prepared in its ground state for\na given negative scattering length, which is quenched to a larger absolute\nvalue of the scattering length. Using the mean-field approximation, we compute\nnumerically, for an experimentally relevant range of aspect ratios and initial\nstrengths of the coupling, two critical values of quench: one corresponds to\nthe weakest attraction strength the quench to which causes the system to\ncollapse before completing even a single return from the narrow configuration\n(\"perihelion\") in its breathing cycle. The other is a similar critical point\nfor the occurrence of collapse before completing two returns. In the latter\ncase, we also compute the limiting value, as we keep increasing the strength of\nthe post-quench attraction towards its critical value, of the time interval\nbetween the first two perihelia. We also use a Gaussian variational model to\nestimate the critical quenched attraction strength below which the system is\nstable against the collapse for long times. These time intervals and critical\nattraction strengths---apart from being fundamental properties of nonlinear\ndynamics of self-attractive BECs---may provide clues to the design of upcoming\nexperiments that are trying to create robust BEC breathers."
    },
    {
        "anchor": "Anisotropic merging and splitting of dipolar Bose-Einstein condensates: We study the merging and splitting of quasi-two-dimensional Bose-Einstein\ncondensates with strong dipolar interactions. We observe that if the dipoles\nhave a non-zero component in the plane of the condensate, the dynamics of\nmerging or splitting along two orthogonal directions, parallel and\nperpendicular to the projection of dipoles on the plane of the condensate are\ndifferent. The anisotropic merging and splitting of the condensate is a\nmanifestation of the anisotropy of the roton-like mode in the dipolar system.\nThe difference in dynamics disappears if the dipoles are oriented at right\nangles to the plane of the condensate as in this case the Bogoliubov\ndispersion, despite having roton-like features, is isotropic.",
        "positive": "Demkov-Kunike model in cold molecule formation: We study the dynamics of cold molecule formation via photo- or\nmagneto-association of quantum degenerate atomic gases for the case when the\nfield configuration is defined by the quasi-linear level crossing Demkov-Kunike\nmodel, which is characterized by a bell-shaped pulse and finite variation of\nthe frequency detuning. We generalize the approach developed for the\nLandau-Zener model and propose a cubic polynomial equation for the asymptotic\ntransition probability at infinity applicable in the large detuning regime of\nthe interaction process. The proposed approximation applies to all values of\nthe Rabi frequency; hence, it presents a unified description of previously\nnoticed weak, moderate, and strong interaction limits of the fast sweep regime.\nThis cubic equation for the transition probability provides improvement of\nprevious results by an order of the magnitude."
    },
    {
        "anchor": "Exact correlations in the Lieb-Liniger model and detailed balance\n  out-of-equilibrium: We study the density-density correlation function of the 1D Lieb-Liniger\nmodel and obtain an exact expression for the small momentum limit of the static\ncorrelator in the thermodynamic limit. We achieve this by summing exactly over\nthe relevant form factors of the density operator in the small momentum limit.\nThe result is valid for any eigenstate, including thermal and non-thermal\nstates. We also show that the small momentum limit of the dynamic structure\nfactors obeys a generalized detailed balance relation valid for any equilibrium\nstate.",
        "positive": "Mediated interaction between polarons in a one-dimensional Bose gas: We study a weakly-interacting one-dimensional Bose gas with two impurities\ncoupled locally to the boson density. We derive analytical results for the\ninduced interaction between the impurities at arbitrary coupling and separation\n$r$. At $r\\lesssim \\xi$, where $\\xi$ denotes the healing length of the Bose\ngas, the interaction is well described by the mean-field contribution. Its form\nchanges as the coupling is increased, approaching a linear function of $r$ at\nshort distances in the regime of strong coupling. The mean-field contribution\ndecays exponentially at arbitrary coupling for $r\\gg\\xi$. At such long\ndistances, however, the effect of quantum fluctuations becomes important,\ngiving rise to a long-ranged quantum contribution to the induced interaction.\nAt longest distances it behaves as $1/r^3$, while at strong coupling we find an\nintermediate distance regime with a slower decay, $1/r$. The quantum\ncontribution in the crossover regime is also calculated. The induced\ninteraction between impurities (i.e., polarons) is attractive and leads to the\nformation of their bound state, known as bipolaron. We discuss its binding\nenergy."
    },
    {
        "anchor": "Scattering framework for two particles with isotropic spin-orbit\n  coupling applicable to all energies: Previous work developed a K-matrix formalism applicable to positive energies\nfor the scattering between two $s$-wave interacting particles with two internal\nstates, isotropic spin-orbit coupling and vanishing center-of-mass momentum [H.\nDuan, L. You and B. Gao, Phys. Rev A {\\bf{87}}, 052708 (2013)]. This work\nextends the formalism to the entire energy regime. Explicit solutions are\nobtained for the total angular momentum $J=0$ and $1$ channels. The behavior of\nthe partial cross sections in the negative energy regime is analyzed in detail.\nWe find that the leading contributions to the partial cross sections at the\nnegative energy thresholds are governed by the spin-orbit coupling strength\n$k_{\\text{so}}$ and the mass ratio. The fact that these contributions are\nindependent of the two-body scattering length $a_s$ is a direct consequence of\nthe effective reduction of the dimensionality, and hence of the density of\nstates, near the scattering thresholds due to the single-particle spin-orbit\ncoupling terms. The results are analytically continued to the energy regime\nwhere bound states exist. It is shown that our results are consistent with\nresults obtained by alternative approaches. Our formulation, which can be\nregarded as an extension of the standard textbook partial wave decomposition,\ncan be generalized to two-body systems with other types of spin-orbit coupling,\nincluding cases where the center-of-mass momentum does not vanish.",
        "positive": "Mobility edge of the two dimensional Bose-Hubbard model: We analyze the disorder driven localization of the two dimensional\nBose-Hubbard model by evaluating the full low energy quasiparticle spectrum via\na recently developed fluctuation operator expansion method. For any strength of\nthe local interaction we find a mobility edge that displays an approximately\nexponential decay with increasing disorder strength. We determine the\nfinite-size scaling collapse and exponents at this critical line finding that\nthe localization of excitations is characterized by weak multi-fractality and a\nthermal-like critical gap ratio. A direct comparison to a recent experiment\nyields an excellent match of the predicted finite-size transition point and\nscaling of single particle correlations."
    },
    {
        "anchor": "$F$-wave pairing of cold atoms in optical lattices: The tremendous development of cold atom physics has opened up a whole new\nopportunity to study novel states of matter which are not easily accessible in\nsolid state systems. Here we propose to realize the $f$-wave pairing\nsuperfluidity of spinless fermions in the $p_{x,y}$-orbital bands of the two\ndimensional honeycomb optical lattices. The non-trivial orbital band structure\nrather than strong correlation effects gives rise to the unconventional pairing\nwith the nodal lines of the $f$-wave symmetry. With a confining harmonic trap,\nzero energy Andreev bound states appear around the circular boundary with a\nsix-fold symmetry. The experimental realization and detection of this novel\npairing state are feasible.",
        "positive": "Thermodynamics of ideal Fermi gas under generic power law potential in\n  $d$-dimension: Thermodynamics of ideal Fermi gas trapped in an external generic power law\npotential $U=\\sum_{i=1} ^d c_i |\\frac{x_i}{a_i}|^{n_i}$ are investigated\nsystematically from the grand thermodynamic potential in $d$ dimensional space.\nThese properties are explored deeply in the degenerate limit ($\\mu>> K_BT$),\nwhere the thermodynamic properties are greatly dominated by Pauli exclusion\nprinciple. Pressure and energy along with the isothermal compressibilty is non\nzero at $T=0K$, denoting trapped Fermi system is quite live even at absolute\nzero temperature. The nonzero value of compressibilty denotes zero point\npressure is not just a constant but depends on volume."
    },
    {
        "anchor": "Fermi super-Tonks-Girardeau state for attractive Fermi gases in an\n  optical lattice: We demonstrate that a kind of highly excited state of strongly attractive\nHubbard model, named of Fermi super-Tonks-Girardeau state, can be realized in\nthe spin-1/2 Fermi optical lattice system by a sudden switch of interaction\nfrom the strongly repulsive regime to the strongly attractive regime. In\ncontrast to the ground state of the attractive Hubbard model, such a state is\nthe lowest scattering state with no pairing between attractive fermions. With\nthe aid of Bethe-ansatz method, we calculate energies of both the Fermi\nTonks-Girardeau gas and the Fermi super-Tonks-Girardeau state of spin-1/2\nultracold fermions and show that both energies approach to the same limit as\nthe strength of the interaction goes to infinity. By exactly solving the quench\ndynamics of the Hubbard model, we demonstrate that the Fermi\nsuper-Tonks-Girardeau state can be transferred from the initial repulsive\nground state very efficiently. This allows the experimental study of properties\nof Fermi super-Tonks-Girardeau gas in optical lattices.",
        "positive": "A Hubbard model for ultracold bosonic atoms interacting via\n  zero-point-energy induced three-body interactions: We show that for ultra-cold neutral bosonic atoms held in a three-dimensional\nperiodic potential or optical lattice, a Hubbard model with dominant,\nattractive three-body interactions can be generated. In fact, we derive that\nthe effect of pair-wise interactions can be made small or zero starting from\nthe realization that collisions occur at the zero-point energy of an optical\nlattice site and the strength of the interactions is energy dependent from\neffective-range contributions. We determine the strength of the two- and\nthree-body interactions for scattering from van-der-Waals potentials and near\nFano-Feshbach resonances. For van-der-Waals potentials, which for example\ndescribe scattering of alkaline-earth atoms, we find that the pair-wise\ninteraction can only be turned off for species with a small negative scattering\nlength, leaving the $^{88}$Sr isotope a possible candidate. Interestingly, for\ncollisional magnetic Feshbach resonances this restriction does not apply and\nthere often exist magnetic fields where the two-body interaction is small. We\nillustrate this result for several known narrow resonances between alkali-metal\natoms as well as chromium atoms. Finally, we compare the size of the three-body\ninteraction with hopping rates and describe limits due to three-body\nrecombination."
    },
    {
        "anchor": "Wigner dynamics for quantum gases under inhomogeneous gain and loss\n  processes with dephasing: We present a Wigner function-based approach for the particle density\nevolution in fermionic and bosonic open quantum many-body systems, including\nthe effects of dephasing. In particular, we focus on chains of non-interacting\nparticles coupled to Lindblad baths. The dissipative processes, described by\nlinear and quadratic jump operators, are modulated by inhomogeneous couplings.\nFollowing a semi-classical approach, we find the differential equation\ngoverning the Wigner function evolution, which can be solved in closed form in\nsome particular cases. We check the accuracy of the Wigner approach in\ndifferent scenarios (i.e. Gaussian jump rates), describing the density\nevolution and the transport phenomena in terms of classical quasi-particles.",
        "positive": "Gaussian fluctuations in the two-dimensional BCS-BEC crossover: finite\n  temperature properties: The role of fluctuations is enhanced in lower dimensionality systems: in a\ntwo dimensions off-diagonal long-range order is destroyed by the fluctuations\nat any finite temperature, drastically modifying the critical properties with\nrespect to the three-dimensional counterpart. Recently two-dimensional systems\nof interacting fermions have been the subject of Montecarlo studies and\nexperimental investigations, in particular an ultracold gas of attractive\nfermions with a widely tunable interaction due to a Feshbach resonance has been\nrealized and the Berezinskii-Kosterlitz-Thouless transition has been observed.\n  The present work deals with the theoretical description of an ultracold Fermi\ngas: we discuss the role of Gaussian fluctuations of the order parameter in the\nequation of state, in particular we take into account the first sound velocity,\nshowing that the inclusion of order parameter fluctuations is needed in order\nto get the correct composite-boson limit in the strong-coupling regime. The\ntheory is also compared with experimental data. Finally we focus on the\nsuperfluid density in the weak-coupling, intermediate and strong-coupling\nregimes at finite temperature, through which the\nBerezinskii-Kosterlitz-Thouless critical temperature is obtained."
    },
    {
        "anchor": "Staircase in magnetization and entanglement entropy of spin squeezed\n  condensates: Staircases in response functions are associated with physically observable\nquantities that respond discretely to continuous tuning of a control parameter.\nA well-known example is the quantization of the Hall conductivity in two\ndimensional electron gases at high magnetic fields. Here, we show that such a\nstaircase response also appears in the magnetization of spin-1 atomic ensembles\nevolving under several spin-squeezing Hamiltonians.We discuss three examples,\ntwo mesoscopic and one macroscopic, where the system's magnetization vector\nresponds discretely to continuous tuning of the applied magnetic field or the\natom density, thus producing a magnetization staircase. The examples that we\nconsider are directly related to Hamiltonians that have been implemented\nexperimentally in the context of spin and spin-nematic squeezing. Thus, our\nresults can be readily put to experimental test in spin-1 ferromagnetic\n$^{87}$Rb and anti-ferromagnetic $^{23}$Na condensates.",
        "positive": "Half-skyrmion and meron pair in spinor condensates: We propose a simple experimental scheme to generate spin textures in the\nground state of interacting ultracold bosonic atoms loaded in a two-dimensional\nharmonic trap. Our scheme is based on two co-propagating Laguerre-Gauss laser\nbeams illuminating the atoms and coupling two of their internal ground state\nZeeman sublevels. Using a Gross-Pitaevskii description, we show that the ground\nstate of the atomic system has different topological properties depending on\nthe interaction strength and the laser beam intensity. A half-skyrmion state\ndevelops at low interactions while a meron pair develops at large interactions."
    },
    {
        "anchor": "Quantum dark solitons in the one-dimensional Bose gas: Dark and grey soliton-like states are shown to emerge from numerically\nconstructed superpositions of translationally-invariant eigenstates of the\ninteracting Bose gas in a toroidal trap. The exact quantum many-body dynamics\nreveals a density depression with superdiffusive spreading that is absent in\nthe mean-field treatment of solitons. A simple theory based on finite-size\nbound states of holes with quantum-mechanical center-of-mass motion\nquantitatively explains the time-evolution of the superposition states and\npredicts quantum effects that could be observed in ultra-cold gas experiments.\nThe soliton phase step is shown to be a key ingredient of an accurate finite\nsize approximation, which enables us to compare the theory with numerical\nsimulations. The fundamental soliton width, an invariant property of the\nquantum dark soliton, is shown to deviate from the Gross-Pitaevskii predictions\nin the interacting regime and vanishes in the Tonks-Girardeau limit.",
        "positive": "Double well potentials with a quantum moat barrier or a quantum wall\n  barrier give rise to similar entangled wave functions: The solution to a problem in quantum mechanics is generally a linear\nsuperposition of states. The solutions for double well potentials epitomize\nthis property, and go even further than this: they can often be described by an\neffective model whose low energy features can be described by two states ---\none in which the particle is on one side of the barrier, and a second where the\nparticle is on the other side. Then the ground state remains a linear\nsuperposition of these two macroscopic-like states. In this paper we illustrate\nthat this property is achieved similarly with an attractive potential that\nseparates two regions of space, as opposed to the traditionally repulsive one.\nIn explaining how this comes about we revisit the concept of \"orthogonalized\nplane waves,\" first discussed in 1940 to understand electronic band structure\nin solids, along with the accompanying concept of a pseudopotential. We show\nhow these ideas manifest themselves in a simple double well potential, whose\n\"barrier\" consists of a moat instead of the conventional wall."
    },
    {
        "anchor": "Guiding-center dynamics of vortex dipoles in Bose-Einstein condensates: A quantized vortex dipole is the simplest vortex molecule, comprising two\ncounter-circulating vortex lines in a superfluid. Although vortex dipoles are\nendemic in two-dimensional superfluids, the precise details of their dynamics\nhave remained largely unexplored. We present here several striking observations\nof vortex dipoles in dilute-gas Bose-Einstein condensates, and develop a\nvortex-particle model that generates vortex line trajectories that are in good\nagreement with the experimental data. Interestingly, these diverse trajectories\nexhibit essentially identical quasi-periodic behavior, in which the vortex\nlines undergo stable epicyclic orbits.",
        "positive": "A study on quantum gases: bosons in optical lattices and the\n  one-dimensional interacting Bose gas: Bosonic atoms confined in optical lattices are described by the Bose-Hubbard\nmodel and can exist in two different phases, Mott insulator or superfluid,\ndepending on the strength of the system parameters. In the vicinity of the\nphase boundary, there are degeneracies that occur between every two adjacent\nMott lobes. Because of this, nondegenerate perturbation theory fails to give\nmeaningful results for the condensate density: it predicts a phase transition\nin a point of the phase diagram where no transition occurs. Motivated by this,\nwe develop two different degenerate perturbative methods to solve the\ndegeneracy-related problems. Moreover, we study the one-dimensional repulsively\ninteracting Bose gas under harmonic confinement, with special attention to the\nasymptotic behavior of the momentum distribution, which is a universal $k^{-4}$\ndecay characterized by the Tan's contact. The latter constitutes a direct\nsignature of the short-range correlations in such an interacting system and\nprovides valuable insights about the role of the interparticle interactions. We\ninvestigate the system constituted of $N$ interacting particles in the strongly\ninteracting limit. In such a regime, the strong interparticle interaction makes\nthe bosons behave similarly to the ideal Fermi gas. Because of the difficulty\nin analytically solving the system for $N$ particles at finite interaction, the\nTonks-Girardeau regime provides a favorable scenario to probe the contact.\nTherefore, we are able to provide an analytical formula for the Tan's contact.\nFurthermore, we analyze the scaling properties of the Tan's contact in terms of\n$N$ in the high-temperature regime as well as in the strongly interacting\nregime. Finally, we compare our analytical calculations of the Tan's contact to\nquantum Monte Carlo simulations and discuss some fundamental differences\nbetween the canonical and the grand-canonical ensembles."
    },
    {
        "anchor": "Anomalous pseudogap in population imbalanced Fermi superfluids: In a Fermi superfluid increasing population imbalance leads initially to\nreduction of the transition temperature, then the appearance of modulated\nFulde-Ferrell-Larkin-Ovchinnikov (FFLO) states, and finally the suppression of\npairing itself. For interaction strength such that the `balanced' system has a\nnormal state pseudogap, increasing imbalance reveals anomalous spectral\nbehavior. At a fixed weak imbalance (small polarization) the stable homogeneous\nsuperfluid occurs only above a certain temperature. The density of states has a\nminimum at the Fermi level, then a weak peak {\\it within the gap}, and then the\nlarge, gap edge, coherence features. On heating, this non monotonic energy\ndependence changes to a more conventional fluctuation driven pseudogap, with a\nmonotonic energy dependence. At large imbalance the ground state is FFLO and\n`pseudogapped' due to the modulated order. It changes to a gapless normal state\non heating, and then shows a pseudogap again at a higher temperature. These\nweak imbalance and strong imbalance features both involve effects well beyond\nmean field theory. We establish them by using a Monte Carlo technique on large\nlattices, motivate the results in terms of the pairing field distribution, and\ncompare them to spectroscopic results in the imbalanced unitary Fermi gas.",
        "positive": "Universal Tan relations for quantum gases in one dimension: We investigate universal properties of one-dimensional multi-component\nsystems comprised of fermions, bosons, or an arbitrary mixture, with contact\ninteractions and subjected to an external potential. The masses and the\ncoupling strengths between different types of particles are allowed to be\ndifferent and we also take into account the presence of an arbitrary magnetic\nfield. We show that the momentum distribution of these systems exhibits a\nuniversal $n_\\sigma(k) \\sim C_\\sigma/k^4$ decay with $C_\\sigma$ the contact of\nspecies $\\sigma$ which can be computed from the derivatives of an appropriate\nthermodynamic potential with respect to the scattering lengths. In the case of\nintegrable fermionic systems we argue that at fixed density and repulsive\ninteractions the total contact reaches its maximum in the balanced system and\nmonotonically decreases to zero as we increase the magnetic field. The converse\neffect is present in integrable bosonic systems: the contact is largest in the\nfully polarized state and reaches its minimum when all states are equally\npopulated. We obtain short distance expansions for the Green's function and\npair distribution function and show that the coefficients of these expansions\ncan be expressed in terms of the density, kinetic energy and contact. In\naddition we derive universal thermodynamic identities relating the total energy\nof the system, pressure, trapping energy and contact. Our results are valid at\nzero and finite temperature, for homogeneous or trapped systems and for\nfew-body or many-body states."
    },
    {
        "anchor": "Spin-1 Topological Monopoles in Parameter Space of Ultracold Atoms: Magnetic monopole, a hypothetical elementary particle with isolated magnetic\npole, is crucial for the quantization of electric charge. In recent years,\nanalogues of magnetic monopoles, represented by topological defects in\nparameter spaces, have been studied in a wide range of physical systems. These\nworks mainly focused on Abelian Dirac monopoles in spin-1/2 or non-Abelian Yang\nmonopoles in spin-3/2 systems. Here we propose to realize three types of spin-1\ntopological monopoles and study their geometric properties using the parameter\nspace formed by three hyperfine states of ultracold atoms coupled by\nradio-frequency fields. These spin-1 monopoles, characterized by different\nmonopole charges, possess distinct Berry curvature fields and spin textures,\nwhich are directly measurable in experiments. The topological phase transitions\nbetween different monopoles are accompanied by the emergence of spin \"vortex\",\nand can be intuitively visualized using Majorana's stellar representation. We\nshow how to determine the Berry curvature, hence the geometric phase and\nmonopole charge from dynamical effects. Our scheme provides a simple and highly\ntunable platform for observing and manipulating spin-1 topological monopoles,\npaving the way for exploring new topological quantum matter.",
        "positive": "Adiabatic passage through chaos: We study the process of nonlinear stimulated Raman adiabatic passage within a\nclassical mean-fieldframework. Depending on the sign of interaction, the\nbreakdown of adiabaticity in the interactingnonintegrable system is not related\nto bifurcations in the energy landscape, but rather to the emergence\nofquasistochastic motion that drains the followed quasistationary state.\nConsequently, faster sweep rate,rather than quasistatic variation of\nparameters, is better for adiabaticity"
    },
    {
        "anchor": "Efficient production of polar molecular Bose-Einstein condensates via an\n  all-optical R-type atom-molecule adiabatic passage: We propose a scheme of \"$R$-type\" photoassociative adiabatic passage (PAP) to\ncreate polar molecular condensates from two different species of ultracold\natoms. Due to the presence of a quasi-coherent population trapping state in the\nscheme, it is possible to associate atoms into molecules with a\n\\textit{low-power} photoassociation (PA) laser. One remarkable advantage of our\nscheme is that a tunable atom-molecule coupling strength can be achieved by\nusing a time-dependent PA field, which exhibits larger flexibility than using a\ntunable magnetic field. In addition, our results show that the PA intensity\nrequired in the \"$R$-type\" PAP could be greatly reduced compared to that in a\nconventional \"$\\Lambda $-type\" one.",
        "positive": "Decay of the relative phase domain wall into confined vortex pairs: the\n  case of a coherently coupled bosonic mixture: A domain wall of relative phase in a flattened harmonically-trapped\nBose-Einstein condensed mixture of two atomic hyperfine states, subject to a\nstationary Rabi coupling of intensity $\\Omega$, is predicted to decay through\ntwo different mechanisms. For small values of $\\Omega$ the instability has an\nenergetic nature and is associated with the formation of a vortex-antivortex\npair of the same atomic hyperfine states, whose motion inside the trap causes\nthe emergence of magnetization, the bending of the domain wall and its\nconsequent fragmentation. For large values of $\\Omega$ the domain wall instead\nundergoes a dynamic snake instability, caused by the negative value of its\neffective mass and results in the fast fragmentation of the wall into smaller\ndomain walls confining vortex pairs of different atomic species. Numerical\npredictions are given by solving the time-dependent Gross-Pitaevskii equation\nin experimentally available configurations of mixtures of sodium atomic gases."
    },
    {
        "anchor": "Pseudogap temperature and effects of a harmonic trap in the BCS-BEC\n  crossover regime of an ultracold Fermi gas: We theoretically investigate excitation properties in the pseudogap regime of\na trapped Fermi gas. Using a combined $T$-matrix theory with the local density\napproximation, we calculate strong-coupling corrections to single-particle\nlocal density of states (LDOS), as well as the single-particle local spectral\nweight (LSW). Starting from the superfluid phase transition temperature $T_{\\rm\nc}$, we clarify how the pseudogap structures in these quantities disappear with\nincreasing the temperature. As in the case of a uniform Fermi gas, LDOS and LSW\ngive different pseudogap temperatures $T^*$ and $T^{**}$ at which the pseudogap\nstructures in these quantities completely disappear. Determining $T^*$ and\n$T^{**}$ over the entire BCS (Bardeen-Cooper-Schrieffer)-BEC (Bose-Einstein\ncondensate) crossover region, we identify the pseudogap regime in the phase\ndiagram with respect to the temperature and the interaction strength. We also\nshow that the so-called back-bending peak recently observed in the\nphotoemission spectra by JILA group may be explained as an effect of pseudogap\nphenomenon in the trap center. Since strong pairing fluctuations, spatial\ninhomogeneity, and finite temperatures, are important keys in considering real\ncold Fermi gases, our results would be useful for clarifying normal state\nproperties of this strongly interacting Fermi system.",
        "positive": "Universal dimerized quantum droplets in a one-dimensional lattice: The ground-state properties of two-component bosonic mixtures in a\none-dimensional optical lattice are studied both from few- and many-body\nperspectives. We rely directly on a microscopic Hamiltonian with attractive\ninter-component and repulsive intra-component interactions to demonstrate the\nformation of a quantum liquid. We reveal that its formation and stability can\nbe interpreted in terms of finite-range interactions between dimers. We derive\nan effective model of composite bosons (dimers) which correctly captures both\nthe few- and many-body properties and validate it against exact results\nobtained by DMRG method for the full Hamiltonian. The threshold for the\nformation of the liquid coincides with the appearance of a bound state in the\ndimer-dimer problem and possesses a universality in terms of the two-body\nparameters of the dimer-dimer interaction, namely scattering length and\neffective range. For sufficiently strong effective dimer-dimer repulsion we\nobserve fermionization of the dimers which form an effective Tonks-Girardeau\nstate. Finally, we identify conditions for the formation of a solitonic\nsolution."
    },
    {
        "anchor": "Relaxation of Shannon entropy for trapped interacting bosons with\n  dipolar interactions: We study the dynamics of dipolar bosons in an external harmonic trap. We\nmonitor the time evolution of the occupation in the natural orbitals and\nnormalized first- and second-order Glauber's correlation functions. We focus in\nparticular on the relaxation dynamics of the Shannon entropy. Comparison with\nthe corresponding results for contact interactions is presented. We observe\nsignificant effects coming from the presence of the non-local repulsive part of\nthe interaction. The relaxation process is very fast for dipolar bosons with a\nclear signature of a truly saturated maximum entropy state. We also discuss the\nconnection between the entropy production and the occurrence of correlations\nand loss of coherence in the system. We identify the long-time relaxed state as\na many-body state retaining only diagonal correlations in the first-order\ncorrelation function and building up anti-bunching effect in the second-order\ncorrelation function.",
        "positive": "Dispersion relations and self-localization of quasiparticles in coupled\n  elongated Bose-Einstein condensates: We present a detailed study of the spectrum and dispersion of Bogoliubov\nquasiparticles in two coupled elongated Bose-Einstein condensates. We develop\nan analytically solvable model that approximates two infinite homogeneous\ncondensates and compare its predictions to a numerical simulation of a\nrealistic trapped system. While the comparisons show a reasonable agreement\nbetween the two models, they also manifest the existence of several anomalous\nBogoliubov modes in the spectrum. These modes show degeneracy in both energy\nand momentum together with self-localization in the coordinate space."
    },
    {
        "anchor": "Observation of the Leggett-Rice effect in a unitary Fermi gas: We observe that the diffusive spin current in a strongly interacting\ndegenerate Fermi gas of $^{40}$K precesses about the local magnetization. As\npredicted by Leggett and Rice, precession is observed both in the Ramsey phase\nof a spin-echo sequence, and in the nonlinearity of the magnetization decay. At\nunitarity, we measure a Leggett-Rice parameter $\\gamma = 1.08(9)$ and a bare\ntransverse spin diffusivity $D_0^\\perp = 2.3(4)\\,\\hbar/m$ for a normal-state\ngas initialized with full polarization and at one fifth of the Fermi\ntemperature, where $m$ is the atomic mass. One might expect $\\gamma = 0$ at\nunitarity, where two-body scattering is purely dissipative. We observe $\\gamma\n\\rightarrow 0$ as temperature is increased towards the Fermi temperature,\nconsistent with calculations that show the degenerate Fermi sea restores a\nnon-zero $\\gamma$. Tuning the scattering length $a$, we find that a sign change\nin $\\gamma$ occurs in the range $0 < (k_F a)^{-1} \\lesssim 1.3$, where $k_F$ is\nthe Fermi momentum. We discuss how $\\gamma$ reveals the effective interaction\nstrength of the gas, such that the sign change in $\\gamma$ indicates a\nswitching of branch, between a repulsive and an attractive Fermi gas.",
        "positive": "Dicke transition in open many-body systems determined by fluctuation\n  effects: In recent years, one important experimental achievement was the strong\ncoupling of quantum matter and quantum light. Realizations reach from ultracold\natomic gases in high-finesse optical resonators to electronic systems coupled\nto THz cavities. The dissipative nature of the quantum light field and the\nglobal coupling to the quantum matter leads to many exciting phenomena such as\nthe occurrence of dissipative quantum phase transition to self-organized exotic\nphases. The theoretical treatment of these dissipative hybrid systems of matter\ncoupled to a cavity field is very challenging. Previously, often mean-field\napproaches were applied which characterize the emergence of self-organized\nphases as a zero-temperature transition for the particles, a ground-state Dicke\ntransition. Here we develop a new approach which combines a mean-field approach\nwith a perturbative treatment of fluctuations beyond mean-field, which becomes\nexact in the thermodynamic limit. We argue that these fluctuations are crucial\nin order to determine the mixed state (finite temperature) character of the\ntransition and to unravel universal properties of the self-organized states. We\nvalidate our results by comparing to time-dependent matrix-product-state\ncalculations."
    },
    {
        "anchor": "Multi-ring, stripe, and super-lattice solitons in a spin-orbit coupled\n  spin-1 condensate: We demonstrate exotic stable quasi-two-dimensional solitons in a Rashba or a\nDresselhaus spin-orbit (SO) coupled hyperfine spin-1 ($F=1$) trap-less\nantiferromagnetic Bose-Einstein condensate using the mean-field\nGross-Pitaevskii equation. For weak SO coupling, the solitons are of the\n$(-1,0,+1)$ or $(+1,0,-1)$ type with intrinsic vorticity, for Rashba or\nDresselhaus SO coupling, where the numbers in the parentheses denote angular\nmomentum in spin components $F_z= +1,0,-1$, respectively. For intermediate SO\ncoupling, the solitons have multi-ring structure maintaining the\nabove-mentioned vortices in respective components. For larger SO coupling,\nsuperlattice solitons with a square-lattice structure in total density are\nfound in addition to stripe solitons with stripe pattern in component densities\nwith no periodic modulation in total density.",
        "positive": "Universal relations for hybridized $s$- and $p$-wave interactions from\n  spin-orbital coupling: In this work, we study the universal relations for one-dimensional\nspin-orbital-coupled fermions near both $s$- and $p$-wave resonances using\neffective field theory. Since the spin-orbital coupling mixes different partial\nwaves, a contact matrix is introduced to capture the non-trivial correlation\nbetween dimers. We find the signature of the spin-orbital coupling appears at\nthe leading order for the off-diagonal components of the momentum distribution\nmatrix, which is proportional to $1/q^{3}$ ($q$ is the relative momentum). We\nfurther derive the large frequency behavior of the Raman spectroscopy, which\nserves as an independent measurable quantity for contacts. Finally, we give an\nexplicit example of contacts by considering a two-body problem."
    },
    {
        "anchor": "Spin - orbital-angular-momentum coupling in Bose-Einstein condensates: Spin-orbit coupling (SOC) plays a crucial role in many branches of physics.\nIn this context, the recent experimental realization of the coupling between\nspin and linear momentum of ultracold atoms opens a completely new avenue for\nexploring new spin-related superfluid physics. Here we propose that another\nimportant and fundamental SOC, the coupling between spin and orbital angular\nmomentum (SOAM), can be implemented for ultracold atoms using higher-order\nLaguerre-Gaussian laser beams to induce Raman coupling between two hyperfine\nspin states of atoms. We study the ground-state phase diagrams of SOAM-coupled\nBose-Einstein condensates on a ring trap and explore their applications in\ngravitational force detection. Our results may provide the basis for further\ninvestigation of intriguing superfluid physics induced by SOAM coupling, such\nas collective excitations.",
        "positive": "Hydrodynamics of local excitations after an interaction quench in 1D\n  cold atomic gases: We discuss the hydrodynamic approach to the study of the time evolution\n-induced by a quench- of local excitations in one dimension. We focus on\ninteraction quenches: the considered protocol consists in creating a stable\nlocalized excitation propagating through the system, and then operating a\nsudden change of the interaction between the particles. To highlight the effect\nof the quench, we take the initial excitation to be a soliton. The quench\nsplits the excitation into two packets moving in opposite directions, whose\ncharacteristics can be expressed in a universal way. Our treatment allows to\ndescribe the internal dynamics of these two packets in terms of the different\nvelocities of their components. We confirm our analytical predictions through\nnumerical simulations performed with the Gross-Pitaevskii equation and with the\nCalogero model (as an example of long range interactions and solvable with a\nparabolic confinement). Through the Calogero model we also discuss the effect\nof an external trapping on the protocol. The hydrodynamic approach shows that\nthere is a difference between the bulk velocities of the propagating packets\nand the velocities of their peaks: it is possible to discriminate the two\nquantities, as we show through the comparison between numerical simulations and\nanalytical estimates. In the realizations of the discussed quench protocol in a\ncold atom experiment, these different velocities are accessible through\ndifferent measurement procedures."
    },
    {
        "anchor": "Perturbation-induced defects in trapped superfluids exhibit generic\n  behavior: We investigate equilibration processes shortly after sudden perturbations are\napplied to ultracold trapped superfluids. We show the similarity of phase\nimprinting and localized density depletion perturbations, both of which\ninitially are found to produce \"phase walls\". These planar defects are\nassociated with a sharp gradient in the phase. Importantly they relax following\na quite general sequence. Our studies, based on simulations of the complex\ntime-dependent Ginzburg-Landau equation, address the challenge posed by these\nexperiments: how a superfluid eventually eliminates a spatially extended planar\ndefect. The processes involved are necessarily more complex than equilibration\ninvolving simpler line vortices. An essential mechanism for relaxation involves\nrepeated formation and loss of vortex rings near the trap edge.",
        "positive": "Second-order topological corner states with ultracold atoms carrying\n  orbital angular momentum in optical lattices: We propose a realization of a two-dimensional higher-order topological\ninsulator with ultracold atoms loaded into orbital angular momentum (OAM)\nstates of an optical lattice. The symmetries of the OAM states induce relative\nphases in the tunneling amplitudes that allow to describe the system in terms\nof two decoupled lattice models. Each of these models displays one-dimensional\nedge states and zero-dimensional corner states that are correlated with the\ntopological properties of the bulk. We show that the topologically non-trivial\nregime can be explored in a wide range of experimentally feasible values of the\nparameters of the physical system. Furthermore, we propose an alternative way\nto characterize the second-order topological corner states based on the\ncomputation of the Zak's phases of the bands of first-order edge states."
    },
    {
        "anchor": "Core structure of two-dimensional Fermi gas vortices in the BEC-BCS\n  crossover region: We report $T=0$ diffusion Monte Carlo results for the ground-state and vortex\nexcitation of unpolarized spin-1/2 fermions in a two-dimensional disk. We\ninvestigate how vortex core structure properties behave over the BEC-BCS\ncrossover. We calculate the vortex excitation energy, density profiles, and\nvortex core properties related to the current. We find a density suppression at\nthe vortex core on the BCS side of the crossover, and a depleted core on the\nBEC limit. Size-effect dependencies in the disk geometry were carefully\nstudied.",
        "positive": "Spinor bosons realization of the SU(3) Haldane phase with adjoint\n  representation: The SU(3) Haldane phase with adjoint representation provides the simplest\nnon-trivial symmetry-protected topological phases in the SU($N>2$) spin chains\nfor which a gapped system has been predicted. In this letter, I show how to\nrealize this phase in a two-species spinor Bose gas. The proposed system\nconsists of two intertwined species-dependent zigzag optical lattices with the\ntwo species labeling the quark and antiquark states of SU(3) symmetry. The\nHaldane phase is found connected to a position at which both the string order\nand entanglement spectrum degeneracy are absent, signaling the appearance of a\ncritical point. I show how to understand this absence by a ground-state ansatz."
    },
    {
        "anchor": "Renormalization group analysis of $p$-orbital Bose-Einstein condensates\n  in a square optical lattice: We investigate the quantum fluctuation effects in the vicinity of the\ncritical point of a $p$-orbital bosonic system in a square optical lattice\nusing Wilsonian renormalization group, where the $p$-orbital bosons condense at\nnonzero momenta and display rich phases including both time-reversal symmetry\ninvariant and broken BEC states. The one-loop renormalization group analysis\ngenerates corrections to the mean-field phase boundaries. We also show the\nquantum fluctuations in the $p$-orbital system tend to induce the ordered phase\nbut not destroy it via the the Coleman-Weinberg mechanism, which is qualitative\ndifferent from the ordinary quantum fluctuation corrections to the mean-field\nphase boundaries in $s$-orbital systems. Finally we discuss the observation of\nthese phenomena in the realistic experiment.",
        "positive": "Phonon instability of insulating states in optical lattices: The influence of collective phonon excitations, due to intersite atomic\ninteractions, on the stability of optical lattices is analyzed. These phonon\nexcitations are shown to essentially reduce the ability of atoms to be\nlocalized. The states that seem to be insulating in the absence of the phonon\nexcitations can become delocalized when the latter are present. The\ndelocalization effect exists for both long-range as well as local atomic\ninteractions."
    },
    {
        "anchor": "Experimental Observation of Curved Light-Cones in a Quantum Field\n  Simulator: We investigate signal propagation in a quantum field simulator of the\nKlein-Gordon model realized by two strongly coupled parallel one-dimensional\nquasi-condensates. By measuring local phononic fields after a quench, we\nobserve the propagation of correlations along sharp light-cone fronts. If the\nlocal atomic density is inhomogeneous, these propagation fronts are curved. For\nsharp edges, the propagation fronts are reflected at the system's boundaries.\nBy extracting the space-dependent variation of the front velocity from the\ndata, we find agreement with theoretical predictions based on curved geodesics\nof an inhomogeneous metric. This work extends the range of quantum simulations\nof non-equilibrium field dynamics in general spacetime metrics.",
        "positive": "Non-Equilibrium Bose-Einstein Condensation in a Dissipative Environment: Solid state quantum condensates can differ from other condensates, such as\nHelium, ultracold atomic gases, and superconductors, in that the condensing\nquasiparticles have relatively short lifetimes, and so, as for lasers, external\npumping is required to maintain a steady state. In this chapter we present a\nnon-equilibrium path integral approach to condensation in a dissipative\nenvironment and apply it to microcavity polaritons, driven out of equilibrium\nby coupling to multiple baths, describing pumping and decay. Using this, we\ndiscuss the relation between non-equilibrium polariton condensation, lasing,\nand equilibrium condensation."
    },
    {
        "anchor": "Excitation band topology and edge matter waves in Bose-Einstein\n  condensates in optical lattices: We show that Bose-Einstein condensates in optical lattices with broken\ntime-reversal symmetry can support chiral edge modes originating from\nnontrivial bulk excitation band topology. To be specific, we analyze a\nBose-Hubbard extension of the Haldane model, which can be realized with\nrecently developed techniques of manipulating honeycomb optical lattices. The\ntopological properties of Bloch bands known for the noninteracting case are\nsmoothly carried over to Bogoliubov excitation bands for the interacting case.\nWe show that the parameter ranges that display topological bands enlarge with\nincreasing the Hubbard interaction or the particle density. In the presence of\nsharp boundaries, chiral edge modes appear in the gap between topological\nexcitation bands. We demonstrate that by coherently transferring a portion of a\ncondensate into an edge mode, a density wave is formed along the edge owing to\nan interference with the background condensate. This offers a unique method of\ndetecting an edge mode through a macroscopic quantum phenomenon.",
        "positive": "Bogoliubov Theory and Lee-Huang-Yang Corrections in Spin-1 and Spin-2\n  Bose-Einstein Condensates in the Presence of the Quadratic Zeeman Effect: We develop Bogoliubov theory of spin-1 and spin-2 Bose-Einstein condensates\n(BECs) in the presence of a quadratic Zeeman effect, and derive the\nLee-Huang-Yang (LHY) corrections to the ground-state energy, sound velocity,\nand quantum depletion. We investigate all the phases of spin-1 and spin-2 BECs\nthat can be realized experimentally. We also examine the stability of each\nphase against quantum fluctuations and the quadratic Zeeman effect.\nFurthermore, we discuss a relationship between the number of symmetry\ngenerators that are spontaneously broken and that of Nambu-Goldstone (NG)\nmodes. It is found that in the spin-2 nematic phase there are special\nBogoliubov modes that have gapless linear dispersion relations but do not\nbelong to the NG modes."
    },
    {
        "anchor": "Emergent s-wave interactions between identical fermions in\n  quasi-one-dimensional geometries: Orbital degrees of freedom play an essential role in metals, semiconductors,\nand strongly confined electronic systems. Experiments with ultracold atoms have\nused highly anisotropic confinement to explore low-dimensional physics, but\ntypically eliminate orbital degrees of freedom by preparing motional ground\nstates in strongly confined directions. Here we prepare multi-band systems of\nspin-polarized fermionic potassium ($^{40}$K) in the quasi-one-dimensional\n(q1D) regime and quantify the strength of atom-atom correlations using\nradio-frequency spectroscopy. The activation of orbital degrees of freedom\nleads to a new phenomenon: a low-energy scattering channel that has even\nparticle-exchange parity along the q1D axis, as if the underlying interactions\nwere s-wave. This emergent exchange symmetry is enabled by orbital singlet wave\nfunctions in the strongly confined directions, which also confer high-momentum\ncomponents to low-energy q1D collisions. We measure both the q1D odd-wave and\neven-wave \"contact\" parameters for the first time, and compare them to\ntheoretical predictions of one-dimensional many-body models. The strength and\nspatial symmetry of interactions are tuned by a p-wave Feshbach resonance and\nby transverse confinement strength. Near resonance, the even-wave contact\napproaches its theoretical unitary value, whereas the maximum observed odd-wave\ncontact remains several orders of magnitude below its unitary limit. Low-energy\nscattering channels of multi-orbital systems, such as those found here, may\nprovide new routes for the exploration of universal many-body phenomena.",
        "positive": "Higher Order Quantum Ghost Imaging with Ultra-Cold Atoms: Ghost imaging is a quantum optics technique that uses correlations between\ntwo beams to reconstruct an image in one beam from photons that do not interact\nwith the object being imaged. While pairwise (second order) correlations are\nusually used to create the image, higher order correlations can be utilized to\nimprove the performance of ghost imaging. In this paper, we demonstrate higher\norder atomic ghost imaging, using entangled ultracold metastable helium atoms\nfrom an s-wave collision halo. We construct higher order ghost images up to 5th\norder and show that using higher order correlations can improve the visibility\nof the images without impacting the resolution. This is the first demonstration\nof higher order ghost imaging with massive particles and the first higher order\nghost imaging protocol of any type using a quantum source."
    },
    {
        "anchor": "Finite resolution fluctuation measurements of a trapped Bose-Einstein\n  condensate: We consider the fluctuations in atom number that occur within finite-sized\nmeasurement cells in a trapped Bose-Einstein condensate (BEC). This\napproximates the fluctuation measurements made in current experiments with\nfinite resolution in situ imaging. A numerical scheme is developed to calculate\nthese fluctuations using the quasiparticle modes of a cylindrically symmetric\nthree-dimensionally trapped condensate with either contact or dipole-dipole\ninteractions (DDIs). We use this scheme to study the properties of a pancake\nshaped condensate using cylindrical cells. The extension of the theory to\nwasher shaped cells with azimuthal weighting is made and used to discriminate\nbetween the low energy roton modes in a dipolar condensate according to their\npro- jection of angular momentum. Our results are based on the Bogoliubov\napproach valid for zero and small finite temperatures.",
        "positive": "Diagrammatic Pairing Fluctuations Approach to the BCS-BEC Crossover: This paper gives a survey of a diagrammatic approach for fermionic pairing\nfluctuations, which are relevant to the BCS-BEC crossover realized with\nultracold Fermi gases. Emphasis will be given to the physical intuition about\nthe relevant physical processes that can be associated with this approach.\nSpecific results will be presented for thermodynamic and dynamical quantities,\nwhere a critical comparison with alternative diagrammatic approaches will also\nbe attempted."
    },
    {
        "anchor": "Superfluid transition in quasi-two-dimensional disordered dipolar Fermi\n  gases: We investigate the effect of weak disorder on the superfluid properties of\ntwo-component quasi-two-dimensional dipolar Fermi gases. The dipole-dipole\ninteraction amplitude is momentum dependent, which violates the Anderson\ntheorem claiming that the weak disorder has practically no influence on the\nsuperfluid transition temperature in the weakly interacting regime. We find\nthat for dipolar fermions the transition temperature in this regime can be\nstrongly increased by the disorder like in the purely two-dimensional case.\nHowever, the effect becomes smaller with increasing the intercomponent\nfermion-fermion interaction, and in the strongly interacting regime the\nsuperfluid transition temperature in the weak disorder becomes very close to\nthat in the absence of disorder.",
        "positive": "Landau Quantization for $ \u039b$-Type Neutral Atoms in an Homogeneous\n  Spin-Dependent Gauge Potential: We investigate the quantum dynamics of neutral atoms subject to a uniform\nspin-dependent gauge field. In particular, we analyze a simple experimental\nscheme to generate the Landau quantization in a two dimensional atomic gas with\ninternal three-level $\\Lambda$-type configuration. We show how energy\neigenfunctions and eigenvalues are obtained and discuss the experimental\nconditions for which a variety of physical quantities of the atomic gas can\nexhibit quantum oscillations."
    },
    {
        "anchor": "Quantum phase transition in a multicomponent anyonic Lieb-Liniger model: We study a one-dimensional multicomponent anyon model that reduces to a\nmulticomponent Lieb-Liniger gas of impenetrable bosons (Tonks-Girardeau gas)\nfor vanishing statistics parameter. At fixed component densities, the\ncoordinate Bethe ansatz gives a family of quantum phase transitions at special\nvalues of the statistics parameter. We show that the ground state energy\nchanges extensively between different phases. Special regimes are studied and a\ngeneral classification for the transition points is given. An interpretation in\nterms of statistics of composite particles is proposed.",
        "positive": "Nonlinear Phenomena of Ultracold Atomic Gases in Optical Lattices:\n  Emergence of Novel Features in Extended States: The system of a cold atomic gas in an optical lattice is governed by two\nfactors: nonlinearity originating from the interparticle interaction, and the\nperiodicity of the system set by the lattice. The high level of controllability\nassociated with such an arrangement allows for the study of the competition and\ninterplay between these two, and gives rise to a whole range of interesting and\nrich nonlinear effects. This review covers the basic idea and overview of such\nnonlinear phenomena, especially those corresponding to extended states. This\nincludes \"swallowtail\" loop structures of the energy band, Bloch states with\nmultiple periodicity, and those in \"nonlinear lattices\", i.e., systems with the\nnonlinear interaction term itself being a periodic function in space."
    },
    {
        "anchor": "Many-Body Phases of a Planar Bose-Einstein Condensate with\n  Cavity-Induced Spin-Orbit Coupling: We explore the many-body phases of a two-dimensional Bose-Einstein condensate\nwith cavity-mediated dynamic spin-orbit coupling. By the help of two transverse\nnon-interfering, counterpropagating pump lasers and a single standing-wave\ncavity mode, two degenerate Zeeman sub-levels of the quantum gas are Raman\ncoupled in a double-$\\Lambda$-configuration. Beyond a critical pump strength\nthe cavity mode is populated via coherent superradiant Raman scattering from\nthe two pump lasers, leading to the appearance of a dynamical spin-orbit\ncoupling for the atoms. We identify three quantum phases with distinct atomic\nand photonic properties: the normal ``homogeneous'' phase, the superradiant\n``spin-helix'' phase, and the superradiant ``supersolid spin-density-wave''\nphase. The latter exhibits an emergent periodic atomic density distribution\nwith an orthorhombic centered rectangular-lattice structure due to the\ninterplay between the coherent photon scattering into the resonator and the\ncollision-induced momentum coupling. The transverse lattice spacing of the\nemergent crystal is set by the dynamic spin-orbit coupling.",
        "positive": "Hubbard model for atomic impurities bound by the vortex lattice of a\n  rotating BEC: We investigate cold bosonic impurity atoms trapped in a vortex lattice formed\nby condensed bosons of another species. We describe the dynamics of the\nimpurities by a bosonic Hubbard model containing occupation-dependent\nparameters to capture the effects of strong impurity-impurity interactions.\nThese include both a repulsive direct interaction and an attractive effective\ninteraction mediated by the BEC. The occupation dependence of these two\ncompeting interactions drastically affects the Hubbard model phase diagram,\nincluding causing the disappearance of some Mott lobes"
    },
    {
        "anchor": "Single- to many-body crossover of a quantum carpet: Strongly interacting many-body system of bosons exhibiting the quantum carpet\npattern is investigated exactly by using Gaudin solutions. We show that this\nhighly coherent design usually present in noninteracting, single-body scenarios\ngets destroyed by weak-to-moderate interatomic interactions in an ultracold\nbosonic gas trapped in a box potential. However, it becomes revived in a very\nstrongly interacting regime, when the system undergoes fermionization. We track\nthe whole single- to many-body crossover, providing an analysis of de- and\nrephasing present in the system.",
        "positive": "Prethermalization and wave condensation in a nonlinear disordered\n  Floquet system: Periodically-driven quantum systems make it possible to reach stationary\nstates with new emerging properties. However, this process is notoriously\ndifficult in the presence of interactions because continuous energy exchanges\ngenerally boil the system to an infinite temperature featureless state. Here,\nwe describe how to reach nontrivial states in a periodically-kicked\nGross-Pitaevskii disordered system. One ingredient is crucial: both disorder\nand kick strengths should be weak enough to induce sufficiently narrow and\nwell-separated Floquet bands. In this case, inter-band heating processes are\nstrongly suppressed and the system can reach an exponentially long-lived\nprethermal plateau described by the Rayleigh-Jeans distribution. Saliently, the\nsystem can even undergo a wave condensation process when its initial state has\na sufficiently low total quasi-energy. These predictions could be tested in\nnonlinear optical experiments or with ultracold atoms."
    },
    {
        "anchor": "Localization and spectral structure in two-dimensional quasicrystal\n  potentials: Quasicrystals, a fascinating class of materials with long-range but\nnonperiodic order, have revolutionized our understanding of solid-state physics\ndue to their unique properties at the crossroads of long-range-ordered and\ndisordered systems. Since their discovery, they continue to spark broad\ninterest for their structural and electronic properties. The quantum simulation\nof quasicrystals in synthetic quantum matter systems offers a unique playground\nto investigate these systems with unprecedented control parameters. Here, we\ninvestigate the localization properties and spectral structure of quantum\nparticles in 2D quasicrystalline optical potentials. While states are generally\nlocalized at low energy and extended at high energy, we find alternating\nlocalized and critical states at intermediate energies. Moreover, we identify a\ncomplex succession of gaps in the energy spectrum. We show that the most\nprominent gap arises from strongly localized ring states, with the gap width\ndetermined by the energy splitting between states with different quantized\nwinding numbers. In addition, we find that these gaps are stable for\nquasicrystals with different rotational symmetries and potential depths,\nprovided that other localized states do not enter the gap generated by the ring\nstates. Our findings shed light on the unique properties of quantum\nquasicrystals and have implications for their many-body counterparts.",
        "positive": "Bosonic drops with two- and three-body interactions close to the unitary\n  limit: When the binding energy of a two-body system goes to zero the two-body system\nshows a continuous scaling invariance governed by the large value of the\nscattering length. In the case of three identical bosons, the three-body system\nin the same limit shows the Efimov effect and the scale invariance is broken to\na discrete scale invariance. As the number of bosons increases correlations\nappear between the binding energy of the few- and many-body systems. We discuss\nsome of them as the relation between the saturation properties of the infinite\nsystem and the low-energy properties of the few-boson system."
    },
    {
        "anchor": "Two-state Bogoliubov theory of a molecular Bose gas: We present an analytic Bogoliubov description of a BEC of polar molecules\ntrapped in a quasi-2D geometry and interacting via internal state-dependent\ndipole-dipole interactions. We derive the mean-field ground-state energy\nfunctional, and we derive analytic expressions for the dispersion relations,\nBogoliubov amplitudes, and dynamic structure factors. This method can be\napplied to any homogeneous, two-component system with linear coupling, and\ndirect, momentum-dependent interactions. The properties of the mean-field\nground state, including polarization and stability, are investigated, and we\nidentify three distinct instabilities: a density-wave rotonization that occurs\nwhen the gas is fully polarized, a spin-wave rotonization that occurs near zero\npolarization, and a mixed instability at intermediate fields. These\ninstabilities are clarified by means of the real-space density-density\ncorrelation functions, which characterize the spontaneous fluctuations of the\nground state, and the momentum-space structure factors, which characterize the\nresponse of the system to external perturbations. We find that the gas is\nsusceptible to both density-wave and spin-wave response in the polarized limit\nbut only a spin-wave response in the zero-polarization limit. These results are\nrelevant for experiments with rigid rotor molecules such as RbCs,\n$\\Lambda$-doublet molecules such as ThO that have an anomalously small\nzero-field splitting, and doublet-$\\Sigma$ molecules such as SrF where two\nlow-lying opposite-parity states can be tuned to zero splitting by an external\nmagnetic field.",
        "positive": "Sub-nK thermometry of an interacting $d$-dimensional homogeneous Bose\n  gas: We propose experimentally feasible means for non-destructive thermometry of\nhomogeneous Bose Einstein condensates in different spatial dimensions\n($d\\in\\{1,2,3\\}$). Our impurity based protocol suggests that the fundamental\nerror bound on thermometry at the sub nano Kelvin domain depends highly on the\ndimension, in that the higher the dimension the better the precision.\nFurthermore, sub-optimal thermometry of the condensates by using measurements\nthat are experimentally feasible is explored. We specifically focus on\nmeasuring position and momentum of the impurity that belong to the family of\nGaussian measurements. We show that, generally, experimentally feasible\nmeasurements are far from optimal, except in 1D, where position measurements\nare indeed optimal. This makes realistic experiments perform very well at few\nnano Kelvin temperatures for all dimensions, and at sub nano Kelvin\ntemperatures in the one dimensional scenario. These results take a significant\nstep towards experimental realisation of probe-based quantum thermometry of\nBose Einstein condensates, as it deals with them in one, two and three\ndimensions and uses feasible measurements applicable in current experimental\nsetups."
    },
    {
        "anchor": "Nonlinear transport in the presence of a local dissipation: We characterize the particle transport, particle loss, and nonequilibrium\nsteady states in a dissipative one-dimensional lattice connected to reservoirs\nat both ends. The free-fermion reservoirs are fixed at different chemical\npotentials, giving rise to particle transport. The dissipation is due to a\nlocal particle loss acting on the center site. We compute the conserved current\nand loss current as functions of voltage in the nonlinear regime using a\nKeldysh description. The currents show step-like features which are affected\ndifferently by the local loss: The steps are either smoothened, nearly\nunaffected, or even enhanced, depending on the spatial symmetry of the\nsingle-particle eigenstate giving rise to the step. Additionally, we compute\nthe particle density and momentum distributions in the chain. At a finite\nvoltage, two Fermi momenta can occur, connected to different wavelengths of\nFriedel oscillations on either side of the lossy site. We find that the\nwavelengths are determined by the chemical potentials in the reservoirs rather\nthan the average density in the lattice.",
        "positive": "Supersolid Stripes Enhanced by Correlations in a Raman\n  Spin-Orbit-Coupled System: A Bose gas under the effect of Raman Spin-Orbit Coupling (SOC) is analyzed\nusing the Discrete Spin T-moves Diffusion Monte Carlo method. By computing the\nenergy as well as the static structure factor and the superfluid fraction of\nthe system, the emergence of an energetically favorable supersolid stripe state\nis observed, which is in agreement with recent observations. A significant\nenhancement of the stability of the stripe phase with respect to the mean-field\nprediction is observed when the strength of the inter-atomic correlations is\nincreased. We also quantify and characterize the degree of superfluidity of the\nstripes and show that this quantity is mostly determined by the ratio between\nthe Raman coupling and the square of the momentum difference between the pair\nof SOC inducing laser beams."
    },
    {
        "anchor": "Superradiance of Degenerate Fermi Gases in a Cavity: In this letter we consider spinless Fermi gases placed inside a cavity and\nstudy the critical strength of pumping field for driving a superradiance\ntransition. We emphasize that Fermi surface nesting effect strongly enhances\nthe superradiance tendency. Around certain fillings, when the Fermi surface is\nnearly nested with a relevant nesting momentum, the susceptibility of the\nsystem toward a checkboard density-wave ordered state is strongly enhanced,\nbecause of which a much smaller (sometime even vanishingly small) critical\npumping field strength can lead to superradiance. This leads to interesting\nreentrance behavior and topologically distinct structure in the phase diagram.\nAway from these fillings, the Pauli exclusion principle brings about the\ndominant effect for which the critical pumping strength is lowered in the\nlow-density regime and increased in the high-density regime, in comparison to a\nBose gas with same density. These results open the prospect of studying rich\nphenomena of degenerate Fermi gases in cavity.",
        "positive": "Sub-Doppler laser cooling of 23Na in gray molasses on the D2 line: We report on the efficient gray molasses cooling of sodium atoms using the\n$D_{2}$ optical transition at 589.1 nm. Thanks to the hyperfine split about\n6$\\Gamma$ between the $|F'=2\\rangle$ and $|F'=3\\rangle$ in the excited state\n3$^{2}P_{3/2}$, this atomic transition is effective for the gray molasses\ncooling mechanism. Using this cooling technique, the atomic sample in $F = 2$\nground manifold is cooled from 700 $\\upmu$K to 56 $\\upmu$K in 3.5 ms. We\nobserve that the loading efficiency into magnetic trap is increased due to the\nlower temperature and high phase space density of atomic cloud after gray\nmolasses. This technique offers a promising route for the fast cooling of the\nsodium atoms in the $F=2$ state."
    },
    {
        "anchor": "Omnidirectional spin Hall effect in a Weyl spin-orbit coupled atomic gas: We show that in the presence of a three-dimensional (Weyl) spin-orbit\ncoupling, a transverse spin current is generated in response to either a\nconstant spin-independent force or a time-dependent Zeeman field in an\narbitrary direction. This effect is the non-Abelian counterpart of the\nuniversal intrinsic spin Hall effect characteristic to the two-dimensional\nRashba spin-orbit coupling. We quantify the strength of such an omnidirectional\nspin Hall effect by calculating the corresponding conductivity for fermions and\nnon-condensed bosons. The absence of any kind of disorder in ultracold-atom\nsystems makes the observation of this effect viable.",
        "positive": "Shell-shaped Bose-Einstein condensates realized with dual-species\n  mixtures: Ultracold quantum gases confined in three-dimensional bubble traps are\npromising tools for exploring many-body effects on curved manifolds. As an\nalternative to the conventional technique of radio-frequency dressing, we\npropose to create such shell-shaped Bose-Einstein condensates in microgravity\nbased on dual-species atomic mixtures and we analyze their properties as well\nas the feasibility to realize symmetrically filled shells. Beyond similarities\nwith the radio-frequency dressing method as in the collective-excitation\nspectrum, our approach has several natural advantages like the robustness of\nthe created quantum bubbles and the possibility to magnify shell effects\nthrough an interaction-driven expansion."
    },
    {
        "anchor": "Universal damping behavior of dipole oscillations of one-dimensional\n  ultracold gases induced by quantum phase slips: We study superflow decay via quantum phase slips in trapped one-dimensional\n(1D) quantum gases through dipole oscillations induced by sudden displacement\nof the trapping potential. We find the relation between the damping rate of the\ndipole oscillation $G$ and the phase-slip nucleation rate $\\Gamma$ as $G\\propto\n\\Gamma/v$, where $v$ is the flow velocity. This relation allows us to show that\ndamping of 1D Bose gases in optical lattices, which has been extensively\nstudied in experiment, is due to quantum phase slips. It is also found that the\ndamping rate versus the flow velocity obeys the scaling formula for an impurity\npotential even in the absence of an explicit impurity. We suggest that the\ndamping rate at a finite temperature exhibits a universal crossover behavior\nupon changing the flow velocity.",
        "positive": "Physical Origin of the Universal Three-body Parameter in Atomic Efimov\n  Physics: We address the microscopic origin of the universal three-body parameter that\nfixes the spectrum of three-atom systems in the Efimov regime. We identify it\nwith the van der Waals two-body correlation, which causes the three-atom system\nto deform when the three atoms come within the distance of the van der Waals\nlength, effectively preventing them from coming closer due to the\nkinetic-energy cost associated with this three-body deformation. This\ndeformation mechanism explains the universal ratio of the scattering length at\nthe triatomic resonance to the van der Waals length observed in several\nexperiments and confirmed by numerical calculations."
    },
    {
        "anchor": "Low-lying energy levels of a one-dimensional weakly interacting Bose gas\n  under zero boundary conditions: We diagonalize the second-quantized Hamiltonian of a one-dimensional Bose gas\nwith a nonpoint repulsive interatomic potential and zero boundary conditions.\nAt weak coupling the solutions for the ground-state energy $E_{0}$ and the\ndispersion law $E(k)$ coincide with the Bogoliubov solutions for a periodic\nsystem. In this case, the single-particle density matrix $F_{1}(x,x^{\\prime})$\nat $T=0$ is close to the solution for a periodic system and, at $T>0$, is\nsignificantly different from it. We also obtain that the wave function $\\langle\n\\hat{\\psi}(x,t) \\rangle$ of the effective condensate is close to a constant\n$\\sqrt{N_{0}/L}$ inside the system and vanishes on the boundaries (here,\n$N_{0}$ is the number of atoms in the effective condensate, and $L$ is the size\nof the system). We find the criterion of applicability of the method, according\nto which the method works for a finite system at very low temperature and with\na weak coupling (a weak interaction or a large concentration).",
        "positive": "Spin-Orbit Coupling and Spin Textures in Optical Superlattices: We proposed and demonstrated a new approach for realizing spin orbit coupling\nwith ultracold atoms. We use orbital levels in a double well potential as\npseudospin states. Two-photon Raman transitions between left and right wells\ninduce spin-orbit coupling. This scheme does not require near resonant light,\nfeatures adjustable interactions by shaping the double well potential, and does\nnot depend on special properties of the atoms. A pseudospinor Bose-Einstein\ncondensate spontaneously acquires an antiferromagnetic pseudospin texture which\nbreaks the lattice symmetry similar to a supersolid."
    },
    {
        "anchor": "Berezinskii-Kosterlitz-Thouless Transition in Two-Dimensional Dipolar\n  Stripes: A two-dimensional quantum system of dipoles, with a polarization angle not\nperpendicular to the plane, shows a transition from a gas to a stripe phase. We\nhave studied the thermal properties of these two phases using the path integral\nMonte Carlo (PIMC) method. By simulating the thermal density matrix, PIMC\nprovides exact results for magnitudes of interest such as the superfluid\nfraction and the one-body density matrix. As it is well known, in two\ndimensions the superfluid-to-normal phase transition follows the\nBerezinskii-Kosterlitz-Thouless (BKT) scenario. Our results show that both the\nanisotropic gas and the stripe phases follow the BKT scaling laws. At fixed\ndensity and increasing the tilting angle, the transition temperature decreases\nin going from the gas to the stripe phase. Superfluidity in the perpendicular\ndirection to the stripes is rather small close to the critical temperature but\nit becomes larger at lower temperatures, mainly close to the transition to the\ngas. Our results are in qualitative agreement with the supersolidity observed\nrecently in a quasi-one-dimensional array of dipolar droplets.",
        "positive": "Analyzing Feshbach resonances -- A $^6$Li -$^{133}$Cs case study: We provide a comprehensive comparison of a coupled channels calculation, the\nasymptotic bound state model (ABM), and the multichannel quantum defect theory\n(MQDT). Quantitative results for $^6$Li -$^{133}$Cs are presented and compared\nto previously measured $^6$Li -$^{133}$Cs Feshbach resonances (FRs) [M. Repp et\nal., Phys. Rev. A 87 010701(R) (2013)]. We demonstrate how the accuracy of the\nABM can be stepwise improved by including magnetic dipole-dipole interactions\nand coupling to a non-dominant virtual state. We present a MQDT calculation,\nwhere magnetic dipole-dipole and second order spin-orbit interactions are\nincluded. A frame transformation formalism is introduced, which allows the\nassignment of measured FRs with only three parameters. All three models achieve\na total rms error of < 1G on the observed FRs. We critically compare the\ndifferent models in view of the accuracy for the description of FRs and the\nrequired input parameters for the calculations."
    },
    {
        "anchor": "Quantum hydrodynamic approximations to the finite temperature trapped\n  Bose gases: For the quantum kinetic system modelling the Bose-Einstein Condensate that\naccounts for interactions between condensate and excited atoms, we use the\nChapman-Enskog expansion to derive its hydrodynamic approximations, include\nboth Euler and Navier-Stokes approximations. The hydrodynamic approximations\ndescribe not only the macroscopic behavior of the BEC but also its coupling\nwith the non-condensates, which agrees with Landau's two fluid theory.",
        "positive": "Engineering phase and density of Bose-Einstein condensates in curved\n  waveguides with toroidal topology: We investigate the effects of ellipticity-induced curvature on atomic\nBose-Einstein condensates confined in quasi-one-dimensional closed-loop\nwaveguides. Our theoretical study reveals intriguing phenomena arising from the\ninterplay between curvature and interactions. Density modulations are observed\nin regions of high curvature, but these modulations are suppressed by strong\nrepulsive interactions. Additionally, we observe phase accumulation in regions\nwith the lowest curvature when the waveguide with persistent current is\nsqueezed. Furthermore, waveguides hosting persistent currents exhibit dynamic\ntransformations between states with different angular momenta. These findings\nprovide insights into the behavior of atomic condensates in curved waveguides,\nwith implications for fundamental physics and quantum technologies. The\ninterplay between curvature and interactions offers opportunities for exploring\nnovel quantum phenomena and engineering quantum states in confined geometries."
    },
    {
        "anchor": "Cold atoms in U(3) gauge potentials: We explore the effects of artificial $U(3)$ gauge potentials on ultracold\natoms. We study background gauge fields with both non-constant and constant\nWilson loops around plaquettes, obtaining the energy spectra in each case. The\nscenario of metal-insulator transition for irrational fluxes is also examined.\nFinally, we discuss the effect of such a gauge potential on the\nsuperfluid-insulator transition for bosonic ultracold atoms.",
        "positive": "Application of the Feshbach-resonance management to a tightly confined\n  Bose-Einstein condensate: We study suppression of the collapse and stabilization of matter-wave\nsolitons by means of time-periodic modulation of the effective nonlinearity,\nusing the nonpolynomial Schroedinger equation (NPSE) for BEC trapped in a tight\ncigar-shaped potential. By means of systematic simulations, a stability region\nis identified in the plane of the modulation amplitude and frequency. In the\nlow-frequency regime, solitons feature chaotic evolution, although they remain\nrobust objects."
    },
    {
        "anchor": "Weakly bound solitons and two-soliton molecules in dipolar Bose-Einstein\n  condensates: Analytic expressions have been derived for the interaction potential between\ndipolar bright solitons and the binding energy of a two-soliton molecule. The\nproperties of these localized structures are explored with a focus on their\nbehavior in the weakly bound regime, with a small binding energy. Using the\nvariational approach a coupled system of ordinary differential equations for\nthe parameters of a soliton molecule is obtained for the description of their\nevolution. Predictions of the model are compared with numerical simulations of\nthe governing nonlocal Gross-Pitaevskii equation and good qualitative agreement\nbetween them is demonstrated.",
        "positive": "Dispersion laws of the two-dimensional cavity magnetoexciton-polaritons: The energy spectrum of the 2D cavity magnetoexciton-polaritons has been\ninvestigated previously, using exact solutions for the Landau quantization of\nconduction electrons and heavy holes provided by the Rashba method [1]. Two\nlowest Landau quantization levels for electrons and three lowest Landau levels\nfor heavy-holes, lead to the construction of the six lowest magnetoexciton\nsates. They consist of two dipole-active, two quadrupole-active, and the two\nforbidden quantum transitions from the ground state of the crystal to the\nmagnetoexciton states. The interaction of the four optical-active\nmagnetoexciton states with the cavity mode photons with a given circular\npolarization and with well-defined incidence direction leads to the creation of\nfive magnetoexciton-polariton branches. The fifth order dispersion equation is\nexamined by using numerical calculations and the second order dispersion\nequation is solved analytically, taking into account only one dipole-active\nmagnetoexciton state. The effective polariton mass on the lower polariton\nbranch, the Rabi frequency and the corresponding Hopfield coefficients are\ndetermined in dependence on the magnetic field strength, the Rashba spin-orbit\ncoupling parameters and the electron and hole g-factors."
    },
    {
        "anchor": "A systematic perturbative expansion of the solution of the\n  time-independent Gross-Pitaevskii equation: In this article a perturbative solution of the Gross-Pitaevskii(GP) equation\nin the $D$-dimensional space $R^D$ with a general external potential is\nstudied. The solution describes the condensate wave-function of a gas\ncontaining $N$ Bose particles. A criteria for the validity of the perturbative\nsolution is developed. Furthermore expressions for the particle density, the\nchemical potential, the internal energy and the mean-square radius of the\ncondensate are derived corrected to first order in the coupling constant. The\nscheme is then applied to obtain the solution of the GP equation in $D=1,2,3$\nfor external harmonic potentials. It is shown, in each case, that if $N$\nexceeds a certain value the solution breaks down.",
        "positive": "The virial expansion of attractively interacting Fermi gases in 1D, 2D,\n  and 3D, up to fifth order: The virial expansion characterizes the high-temperature approach to the\nquantum-classical crossover in any quantum many-body system. Here, we calculate\nthe virial coefficients up to the fifth-order of Fermi gases in 1D, 2D, and 3D,\nwith attractive contact interactions, as relevant for a variety of applications\nin atomic and nuclear physics. To that end, we discretize the imaginary-time\ndirection and calculate the relevant canonical partition functions. In coarse\ndiscretizations, we obtain analytic results featuring relationships between the\ninteraction-induced changes $\\Delta b_3$, $\\Delta b_4$, and $\\Delta b_5$ as\nfunctions of $\\Delta b_2$, the latter being exactly known in many cases by\nvirtue of the Beth-Uhlenbeck formula. Using automated-algebra methods, we push\nour calculations to progressively finer discretizations and extrapolate to the\ncontinuous-time limit. We find excellent agreement for $\\Delta b_3$ with\nprevious calculations in all dimensions and we formulate predictions for\n$\\Delta b_4$ and $\\Delta b_5$ in 1D and 2D. We also provide, for a range of\ncouplings,the subspace contributions $\\Delta b_{31}$, $\\Delta b_{22}$, $\\Delta\nb_{41}$, and $\\Delta b_{32}$, which determine the equation of state and static\nresponse of polarized systems at high temperature. As a performance check, we\ncompare the density equation of state and Tan contact with quantum Monte Carlo\ncalculations, diagrammatic approaches, and experimental data where available.\nFinally, we apply Pad\\'e and Pad\\'e-Borel resummation methods to extend the\nusefulness of the virial coefficients to approach and in some cases go beyond\nthe unit-fugacity point."
    },
    {
        "anchor": "Many-body molecule formation at a domain wall in a one-dimensional\n  strongly interacting ultracold Fermi gas: We analyze how the presence of the bound state on top of strong\nintercomponent contact repulsion affects the dynamics of a two-component\nultracold Fermi gas confined in a one-dimensional harmonic trap. By performing\nfull many-body numerical calculations, we retrieve dynamics of an initially\nphase separated state that has been utilized to excite the spin-dipole mode in\nexperimental settings. We observe an appearance of pairing correlations at the\ndomain wall, heralding the onset of a molecular faction at the interlayer\nbetween the components. We find that such a mechanism can be responsible for\nthe stabilization of the phase separation.",
        "positive": "Dynamical Casimir Effect in Superradiant Light Scattering by\n  Bose-Einstein Condensate in an Optomechanical Cavity: We investigate the effects of dynamical Casimir effect in superradiant light\nscattering by Bose-Einstein condensate in an optomechanical cavity. The system\nis studied using both classical and quantized mirror motions. The cavity\nfrequency is harmonically modulated in time for both the cases. The main\nquantity of interest is the number of intracavity scattered photons. The system\nhas been investigated under the weak and strong modulation. It has been\nobserved that the amplitude of the scattered photons is more for the classical\nmirror motion than the quantized mirror motion. Also, initially, the amplitude\nof scattered photons is high for lower modulation amplitude than higher\nmodulation amplitude. We also found that the behaviour of the plots are similar\nunder strong and weak modulation for the quantized mirror motion."
    },
    {
        "anchor": "Skyrmion crystals in the pseudo-spin-1/2 Bose-Einstein condensates: Exact two-dimensional solutions are constructed for the pseudo-spin-1/2\nBose-Einstein condensates which are described by the coupled nonlinear\nGross-Pitaevskii equations where the intraspecies and interspecies coupling\nconstants are assumed to be equal. The equations are decoupled by means of\nre-combinations of the nonlinear terms of the hyperfine states according to the\nspatial dimensions. These stationary solutions form various spin textures which\nare identified as skyrmion crystals. In a special case, the crystal of\nskyrmion-antiskyrmion pairs is formed in the soliton limit.",
        "positive": "BCS and BEC p-wave pairing in Bose-Fermi gases: The pairing of fermionic atoms in a mixture of atomic fermion and boson gases\nat zero temperature is investigated. The attractive interaction between\nfermions, that can be induced by density fluctuations of the bosonic\nbackground, can give rise to a superfluid phase in the Fermi component of the\nmixture. The atoms of both species are assumed to be in only one internal\nstate, so that the pairing of fermions is effective only in odd-l channels. No\nassumption about the value of the ratio between the Fermi velocity and the\nsound velocity in the Bose gas is made in the derivation of the energy gap\nequation. The gap equation is solved without any particular \"ansatz\" for the\npairing field or the effective interaction. The p-wave superfluidity is studied\nin detail. By increasing the strength and/or decreasing the range of the\neffective interaction a transition of the fermion pairing regime, from the\nBardeen-Cooper-Schrieffer state to a system of tightly bound couples can be\nrealized. These composite bosons behave as a weakly-interacting Bose-Einstein\ncondensate."
    },
    {
        "anchor": "Acoustic superradiance from an optical-superradiance-induced vortex in a\n  Bose-Einstein condensate: We consider the simultaneous scattering of an angular momentum carrying\nLaguerre-Gaussian light beam and an acoustic wave from an atomic Bose-Einstein\ncondensate, under condition of optical superradiance induced vortex state. We\nderive the mean field dynamical equations of the light-superfluid system, and\nobtain the equations governing the elementary excitation of the system which\nresult in a massless Klein-Gordon equation with source terms. This equation\ndescribes the propagation of the sound wave in an effective spacetime.\nEmploying a simplifying draining bathtub model for the vortex, we investigate\nthe scattering of the acoustic wave in the vortex phase and obtain a condition\nfor the acoustic superradiance. We conclude that Laguerre-Gaussian beam induced\nsudden transition from homogeneous to vortex state in the superfluid\nsimultaneously leads to the optical and acoustic superradiance.",
        "positive": "Route to supersolidity for the extended Bose-Hubbard model: We use the Gutzwiller ansatz and analyze the phase diagram of the extended\nBose-Hubbard Hamiltonian with on-site (U) and nearest-neighbor (V) repulsions.\nFor $d$-dimensional hypercubic lattices, when 2dV < U, it is well-known that\nthe ground state alternates between the charge-density-wave (CDW) and Mott\ninsulators, and the supersolid (SS) phase occupies small regions around the CDW\ninsulators. However, when 2dV > U, in this paper, we show that the ground state\nhas only CDW insulators, and more importantly, the SS phase occupies a much\nlarger region in the phase diagram, existing up to very large hopping values\nwhich could be orders of magnitude higher than that of the well-known case. In\nparticular, the SS-superfluid phase boundary increases linearly as a function\nof hopping when 2dV \\gtrsim 1.5U, for which the prospects of observing the SS\nphase with dipolar Bose gases loaded into optical lattices is much higher."
    },
    {
        "anchor": "Observation of Spatial Charge and Spin Correlations in the 2D\n  Fermi-Hubbard Model: Strong electron correlations lie at the origin of transformative phenomena\nsuch as colossal magneto-resistance and high-temperature superconductivity.\nAlready near room temperature, doped copper oxide materials display remarkable\nfeatures such as a pseudo-gap and a \"strange metal\" phase with unusual\ntransport properties. The essence of this physics is believed to be captured by\nthe Fermi-Hubbard model of repulsively interacting, itinerant fermions on a\nlattice. Here we report on the site-resolved observation of charge and spin\ncorrelations in the two-dimensional (2D) Fermi-Hubbard model realized with\nultracold atoms. Antiferromagnetic spin correlations are maximal at\nhalf-filling and weaken monotonically upon doping. Correlations between singly\ncharged sites are negative at large doping, revealing the Pauli and correlation\nhole\\textemdash a suppressed probability of finding two fermions near each\nother. However, as the doping is reduced below a critical value, correlations\nbetween such local magnetic moments become positive, signaling strong bunching\nof doublons and holes. Excellent agreement with numerical linked-cluster\nexpansion (NLCE) and determinantal quantum Monte Carlo (DQMC) calculations is\nfound. Positive non-local moment correlations directly imply potential energy\nfluctuations due to doublon-hole pairs, which should play an important role for\ntransport in the Fermi-Hubbard model.",
        "positive": "Orbital phases of fermions in an asymmetric optical ladder: We study a quantum ladder of interacting fermions with coupled s and p\norbitals. Such a model describes dipolar molecules or atoms loaded into a\ndouble-well optical lattice, dipole moments being aligned by an external field.\nThe two orbital components have distinct hoppings. The tunneling between them\nis equivalent to a partial Rashba spin-orbital coupling when the orbital space\n(s, p) is identified as spanned by pseudo-spin 1/2 states. A rich phase\ndiagram, including incommensurate orbital density wave, pair density wave and\nother exotic superconducting phases, is proposed with bosonization analysis. In\nparticular, superconductivity is found in the repulsive regime."
    },
    {
        "anchor": "Dynamics and correlations of a Bose-Einstein condensate of photons: The Tutorial reports recent experimental advances in studies of the dynamics\nas well as the number and phase correlations of a Bose-Einstein condensed\nphoton gas confined in a high-finesse dye-filled microcavity. Repeated\nabsorption-emission-processes of photons on dye molecules here establish a\nthermal coupling of the photonic quantum gas to both a heat bath and a particle\nreservoir comprised of dye molecules. In this way, for the first time\nBose-Einstein condensation under grand-canonical statistical ensemble\nconditions becomes experimentally accessible.",
        "positive": "Finite Temperature Dipolar ultra-cold Bose gas with Exchange\n  Interactions: We develop finite temperature theory for a trapped dipolar Bose gas including\nthermal exchange interactions. Previous treatments neglected these, difficult\nto compute, terms. We present a methodology for numerically evaluating the\nthermal exchange contributions, making use of cylindrical symmetry. We then\ninvestigate properties of the dipolar gas, including calculating the excitation\nspectrum over the full range of trap anisotropy. We evaluate the contributions\ndue to thermal exchange noting that, under some regimes, these effects can be\nat least as significant as the direct interaction. We therefore provide\nguidance as to when these cumbersome terms can be neglected and when care\nshould be exercised regarding their omission."
    },
    {
        "anchor": "Twisted spin vortices in a spinor-dipolar Bose-Einstein condensate with\n  Rashba spin-orbit coupling: We consider a spin-1 Bose-Einstein condensate with Rashba spin-orbit coupling\nand dipole-dipole interaction confined in a cigar-shaped trap. Due to the\ncombined effects of spin-orbit coupling, dipole-dipole interaction, and trap\ngeometry, the system exhibits a rich variety of ground-state spin structures,\nincluding twisted spin vortices. The ground-state phase diagram is determined\nwith respect to the strengths of the spin-orbit coupling and dipole-dipole\ninteraction.",
        "positive": "Compact, robust, and spectrally pure diode-laser system with a filtered\n  output and a tunable copy for absolute referencing: We report on a design of a compact laser system composed of an extended\ncavity diode laser with high passive stability and a pre-filter Fabri-Perot\ncavity. The laser is frequency stabilized relative to the cavity using a\nserrodyne technique with a correction bandwidth of $\\geq 6$ MHz and a dynamic\nrange of $\\geq 700$ MHz. The free running laser system has a power spectral\ndensity (PSD) $\\leq 100$ Hz$^{2}$/Hz centered mainly in the acoustic frequency\nrange. A highly tunable, $0.5-1.3$ GHz copy of the spectrally pure output beam\nis provided, which can be used for further stabilization of the laser system to\nan ultra-stable reference. We demonstrate a simple one-channel lock to such a\nreference that brings down the PSD to the sub-Hz level. The tuning, frequency\nstabilization and sideband imprinting is achieved by a minimum number of key\nelements comprising a fibered EOM (electro-optic modulator), AOM (acousto-optic\nmodulator) and a NLTL (non-linear transmission line). The system is easy to\noperate, scalable, and highly applicable to atomic/molecular experiments\ndemanding high spectral purity, long-term stability, and robustness."
    },
    {
        "anchor": "A simplified approach to the repulsive Bose gas from low to high\n  densities and its numerical accuracy: In 1963, a Simple Approach was developed to study the ground state energy of\nan interacting Bose gas. It consists in the derivation of an Equation, which is\nnot based on perturbation theory, and which gives the exact expansion of the\nenergy at low densities. This Equation is expressed directly in the\nthermodynamic limit, and only involves functions of $3$ variables, rather than\n$3N$. Here, we revisit this approach, and show that the Equation yields\naccurate predictions for various observables for all densities. Specifically,\nin addition to the ground state energy, we have shown that the Simple Approach\ngives predictions for the condensate fraction, two-point correlation function,\nand momentum distribution. We have carried out a variety of tests by comparing\nthe predictions of the Equation with Quantum Monte Carlo calculations, and have\nfound remarkable agreement. We thus show that the Simple Approach provides a\nnew theoretical tool to understand the behavior of the many-body Bose gas, not\nonly in the small and large density ranges, which have been studied before, but\nalso in the range of intermediate density, for which little is known.",
        "positive": "Quantum Simulators at Negative Absolute Temperatures: We propose that negative absolute temperatures in ultracold atomic clouds in\noptical lattices can be used to simulate quantum systems in new regions of\nphase diagrams. First we discuss how the attractive SU(3) Hubbard model in\nthree dimensions can be realized using repulsively interacting 173-Yb atoms,\nthen we consider how an antiferromagnetic S=1 spin chain could be simulated\nusing spinor 87-Rb or 23-Na atoms. The general idea to achieve negative\nabsolute temperatures is to reverse the sign of the external harmonic\npotential. Energy conservation in a deep optical lattice imposes a constraint\non the dynamics of the cloud, which can relax toward a T<0 state. As the\nprocess is strongly non-adiabatic, we estimate the change of the entropy."
    },
    {
        "anchor": "Interaction between an impurity and nonlinear excitations in a polariton\n  condensate: Exploring the dynamics of a mobile impurity immersed in the field excitations\nis challenging, as it requires to account for the entanglement between the\nimpurity and the surrounding excitations. To this end, the impurity's effective\nmass has to be considered as finite, rather than infinite. Here, we\ntheoretically investigate the interaction between a finite-mass impurity and a\ndissipative soliton representing nonlinear excitations in the polariton\nBose-Einstein condensate (BEC). Using the Lagrange variational method and the\nopen-dissipative Gross-Pitaevskii equation, we analytically derive the\ninteraction phase diagram between the impurity and a dissipative bright soliton\nin the polariton BEC. Depending on the impurity mass, we find the dissipative\nsoliton colliding with the impurity can transmit through, get trapped, or be\nreflected. This work opens a new perspective in understanding the impurity\ndynamics immersed in the field excitations, as well as potential applications\nin information processing with polariton solitons.",
        "positive": "Bound states of spin-orbit coupled cold atoms in a Dirac delta-function\n  potential: Dirac delta-function potential is widely studied in quantum mechanics because\nit usually can be exactly solved and at the same time is useful in modeling\nvarious physical systems. Here we study a system of delta-potential trapped\nspinorbit coupled cold atoms. The spin-orbit coupled atomic matter wave has two\nkinds of evanescent modes, one of which has pure imaginary wavevector and is an\nordinary evanescent wave; while the other with a complex number wave vector is\nrecognized as oscillating evanescent wave. We identified the eigenenergy\nspectra and the existence of bound states in this system. The bound states can\nbe constructed analytically using the two kinds of evanescent modes and we\nfound that they exhibit typical features of stripe phase, separated phase or\nzero-momentum phase. In addition to that, the properties of semi-bound states\nare also discussed, which is a localized wave packet on a plane wave\nbackground."
    },
    {
        "anchor": "Quantum gas of rovibronic ground-state molecules in an optical lattice: Control over all internal and external degrees of freedom of molecules at the\nlevel of single quantum states will enable a series of fundamental studies in\nphysics and chemistry. In particular, samples of ground-state molecules at\nultralow temperatures and high number densities will allow novel quantum-gas\nstudies and future applications in quantum information science. However, high\nphase-space densities for molecular samples are not readily attainable as\nefficient cooling techniques such as laser cooling are lacking. Here we produce\nan ultracold and dense sample of molecules in a single hyperfine level of the\nrovibronic ground state with each molecule individually trapped in the motional\nground state of an optical lattice well. Starting from a zero-temperature\natomic Mott-insulator state with optimized double-site occupancy, weakly-bound\ndimer molecules are efficiently associated on a Feshbach resonance and\nsubsequently transferred to the rovibronic ground state by a stimulated\nfour-photon process with >50 % efficiency. The molecules are trapped in the\nlattice and have a lifetime of 8 s. Our results present a crucial step towards\nBose-Einstein condensation of ground-state molecules and, when suitably\ngeneralized to polar heteronuclear molecules, the realization of dipolar\nquantum-gas phases in optical lattices.",
        "positive": "Fulde-Ferrell-Larkin-Ovchinnikov pairing states of a polarized dipolar\n  Fermi gas trapped in a one-dimensional optical lattice: We study the interplay between the long- and short-range interaction of a\none-dimensional optical lattice system of two-component dipolar fermions by\nusing the density matrix renormalization group method. The atomic density\nprofile, pairing-pairing correlation function, and the compressibility are\ncalculated in the ground state, from which we identify the parameter region of\nthe Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) pairing state, half-metal (HM)\nstate, FFLO-HM state, and the normal polarized state, and thus the phase\ndiagram in the coordinates of the long- and short-range interaction strength.\nThe effect of the long-range dipolar interaction on the FFLO state is discussed\nin details. We find that the long-range part of the dipole-dipole interaction\ndoes not sweep away the FFLO superconducting region that is driven by the\nshort-range interaction in the Hubbard model, and thus the FFLO state survives\nin the wide parameter space of the long-range interaction, polarization and the\nfilling."
    },
    {
        "anchor": "Universal Two-Body Spectra of Ultracold Harmonically Trapped Atoms in\n  Two and Three Dimensions: We consider the spectrum of two ultracold harmonically trapped atoms\ninteracting via short-range interactions. The Green's function approach is used\nto unify the two and three dimensional cases. We derive criteria for the\nuniversality of the spectrum, i.e. its independence of the details of the\nshort-range interaction. The results in three dimensions are examplified for\nnarrow s-wave Feshbach resonances and we show how effective range corrections\ncan modify the rearrangement of the level structure. However, this requires\nextremely narrow resonances or very tight traps that are not currently\nexperimentally available. In the two-dimensional case we discuss the p-wave\nchannel in detail and demonstrate how the non-universality of the spectrum\narises within the Green's function approach. We then show that the spectrum is\nnot particularly sensitive to the short-distance details in the case when the\ntwo-body interaction has a bound state.",
        "positive": "Thermodynamics of low-dimensional trapped Fermi gases: The effects of low dimensionality on the thermodynamics of a Fermi gas\ntrapped by isotropic power law potentials are analyzed. Particular attention is\ngiven to different characteristic temperatures that emerge, at low\ndimensionality, in the thermodynamic functions of state and in the\nthermodynamic susceptibilities (isothermal compressibility and specific heat).\nAn energy-entropy argument that physically favors the relevance of one of these\ncharacteristic temperatures, namely, the non vanishing temperature at which the\nchemical potential reaches the Fermi energy value, is presented. Such an\nargument allows to interpret the nonmonotonic dependence of the chemical\npotential on temperature, as an indicator of the appearance of a thermodynamic\nregime, where the equilibrium states of a trapped Fermi gas are characterized\nby larger fluctuations in energy and particle density as is revealed in the\ncorresponding thermodynamics susceptibilities."
    },
    {
        "anchor": "Fragmentation and the Bose-glass phase transition of the disordered 1D\n  Bose gas: We investigate the superfluid-insulator quantum phase transition in a\ndisordered 1D Bose gas in the mean field limit, by studying the probability\ndistribution of the density. The superfluid phase is characterized by a\nvanishing probability to have zero density, whereas a nonzero probability marks\nthe insulator phase. This relation is derived analytically, and confirmed by a\nnumerical study. This fragmentation criterion is particularly suited for\ndetecting the phase transition in experiments. When a harmonic trap is\nincluded, the transition to the insulating phase can be extracted from the\nstatistics of the local density distribution.",
        "positive": "Nonautonomous Bright and Dark Solitons of Bose-Einstein Condensates with\n  Feshbach-Managed Time-Dependent Scattering Length: We present a family of nonautonomous bright and dark soliton solutions of\nBose-Einstein condensates with the time-dependent scattering length in an\nexpulsive parabolic potential. These solutions show that the amplitude, width,\nand velocity of soliton can be manipulated by adjusting the atomic scattering\nlength via Feshbach resonance. For the cases of both attractive and repulsive\ninteraction, the total particles number is a conservation quantity, but the\npeak (dip) density can be controlled by the Feshbach resonance parameter.\nEspecially, we investigate the modulation instability process in uniform\nBose-Einstein condensates with attractive interaction and nonvanishing\nbackground, and clarify that the procedure of pattern formation is in fact the\nsuperposition of the perturbed dark and bright solitary wave. At last, we give\nthe analytical expressions of nonautonomous dark one- and two-soliton solutions\nfor repulsive interaction, and investigate their properties analytically."
    },
    {
        "anchor": "Chiral orbital magnetism of $p$-orbital bosons in optical lattices: Chiral magnetism is a fascinating quantum phenomena that has been found in\nlow-dimensional magnetic materials. It is not only interesting for\nunderstanding the concept of chirality, but also important for potential\napplications in spintronics. Past studies show that chiral magnets require both\nlack of the inversion symmetry and spin-orbit coupling to induce the\nDzyaloshinskii-Moriya (DM) interaction. Here we report that the combination of\ninversion symmetry breaking and quantum degeneracy of orbital degrees of\nfreedom will provide a new paradigm to achieve the chiral orbital magnetism. By\nmeans of the density matrix renormalization group (DMRG) calculation, we\ndemonstrate that the chiral orbital magnetism can be found when considering\nbosonic atoms loaded in the $p$-band of an optical lattice in the Mott regime.\nThe high tunability of our scheme is also illustrated through simply\nmanipulating the inversion symmetry of the system for the cold atom\nexperimental conditions.",
        "positive": "BEC-BCS crossover in a p+ip-wave pairing Hamiltonian coupled to bosonic\n  molecular pairs: We analyse a p+ip-wave pairing BCS Hamiltonian, coupled to a single bosonic\ndegree of freedom representing a molecular condensate, and investigate the\nnature of the BEC-BCS crossover for this system. For a suitable restriction on\nthe coupling parameters, we show that the model is integrable and we derive the\nexact solution by the algebraic Bethe ansatz. In this manner we also obtain\nexplicit formulae for correlation functions and compute these for several\ncases. We find that the crossover between the BEC state and the strong pairing\np+ip phase is smooth for this model, with no intermediate quantum phase\ntransition."
    },
    {
        "anchor": "Particle-number scaling of the quantum work statistics and Loschmidt\n  echo in Fermi gases with time-dependent traps: We investigate the particle-number dependence of some features of the\nout-of-equilibrium dynamics of d-dimensional Fermi gases in the dilute regime.\nWe consider protocols entailing the variation of the external potential which\nconfines the particles within a limited spatial region, in particular sudden\nchanges of the trap size. In order to characterize the dynamic behavior of the\nFermi gas, we consider various global quantities such as the ground-state\nfidelity for different trap sizes, the quantum work statistics associated with\nthe protocol considered, and the Loschmidt echo measuring the overlap of the\nout-of-equilibrium quantum states with the initial ground state. Their\nasymptotic particle-number dependences show power laws for noninteracting Fermi\ngases. We also discuss the effects of short-ranged interactions to the power\nlaws of the average work and its square fluctuations, within the Hubbard model\nand its continuum limit, arguing that they do not generally change the\nparticle-number power laws of the free Fermi gases, in any spatial dimensions.",
        "positive": "Quantal molecular description and universal aspects of the spectra of\n  bosons and fermions in the lowest Landau level: Through the introduction of a class of trial wave functions portraying\ncombined rotations and vibrations of molecules formed through particle\nlocalization in concentric polygonal rings, a correlated basis is constructed\nthat spans the translationally invariant part of the lower-Landau-level (LLL)\nspectra. These trial functions, referred to as rovibrational molecular (RVM)\nfunctions, generalize our previous work which focused exclusively on electronic\ncusp states, describing them as pure vibrationless rotations. From a\ncomputational viewpoint, the RVM correlated basis enables controlled and\nsystematic improvements of the original strongly-correlated variational wave\nfunction. Conceptually, it provides the basis for the development of a quantal\nmolecular description for the full LLL spectra. This quantal molecular\ndescription is universal, being valid for both bosons and fermions, for both\nthe yrast and excited states of the LLL spectra, and for both low and high\nangular momenta. Furthermore, it follows that all other translationally\ninvariant trial functions (e.g., the Jastrow-Laughlin, compact\ncomposite-fermion, or Moore-Read functions) are reducible to a description in\nterms of an excited rotating/vibrating quantal molecule."
    },
    {
        "anchor": "Generation of high winding-number superfluid circulation in\n  Bose-Einstein condensates: We experimentally and numerically demonstrate a method to deterministically\ngenerate multiply-quantized superfluid circulation about an obstacle in highly\noblate Bose-Einstein condensates (BECs). Our method involves spiraling a\nblue-detuned laser beam, which acts as a repulsive optical potential, around\nand towards the center of the BEC. This optical potential serves first as a\nrepulsive stirrer to initiate superflow within the BEC, and then as a pinning\npotential that transports the center of the superfluid circulation to the\ncenter of the condensate. By changing the rate at which the beam moves along\nthe spiral trajectory, we selectively control the net circulation introduced\ninto the BEC. We experimentally achieve pinned superflow with winding numbers\nas high as 11, which persists for at least 4 s. At the end of the spiral\ntrajectory, with the pinning beam on at full power, the BEC has a toroidal\ngeometry with a high winding-number persistent current. Alternatively, the beam\npower can be ramped off, allowing controlled placement of a cluster of\nsingly-quantized vortices of the same circulation. This technique can serve as\na building block in future experimental architectures to create on-demand\nvortex distributions and superfluid circulation in BECs.",
        "positive": "Interspecies singlet pairing in a mixture of two spin-1 Bose condensates: We study the ground state properties of a mixture formed by two spin-1\ncondensates in the absence of an external magnetic field. As the collisional\nsymmetry between interspecies bosonic atoms is broken, the interspecies\ncoupling interaction ($\\beta $) and interspecies singlet pairing interaction\n($\\gamma $) arise. The ground state can be calculated using the angular\nmomentum theory analytically for $\\gamma =0$. The full quantum approach of\nexact diagonalization is adopted numerically to consider the more general case\nas $\\gamma \\neq 0$. We illustrate the competition between the two interspecies\ninteractions and find that as singlet pairing interaction dominates (or the\ntotal spin vanishes), there are still different types of singlet formations\nwhich are well determined by $\\beta $."
    },
    {
        "anchor": "Self-ordered supersolid phase beyond Dicke superradiance in a ring\n  cavity: The supersolid phase characterized by the superfluid and long-range spatial\nperiodicity of crystalline order is central to many branches of science ranging\nfrom condensed matter physics to ultracold atomic physics. Here we study a\nself-ordered checkerboard supersolid phase originating from dynamical\nspin-orbit coupling for a transversely pumped atomic Bose-Einstein condensate\ntrapped in a ring cavity, corresponding to a superradiant anti-Tavis-Cummings\nphase transition. In particular, an undamped gapless Goldstone mode is observed\nin contrast to the experimentally realized lattice supersolid with a gapped\nroton mode for Dicke superradiance. This zero energy mode reveals the rigidity\nof the self-ordered superradiant phase, which spontaneously breaks a continuous\ntranslational symmetry. Our work will highlight the significant opportunities\nfor exploring long-lived supersolid matter by utilizing dynamical spin-orbit\ncoupling in controllable optical cavities.",
        "positive": "Interacting Bose gas across a narrow Feshbach resonance: We use a two-channel model to investigate an interacting Bose gas across a\nnarrow Feshbach resonance within a field path integral approach. The ground\nstate properties show strong deviation from that of a broad Feshbach resonance\nor a single channel interaction. The deviation can be interpreted by the strong\nenergy dependence of two-body scattering length near a narrow Feshbach\nresonance. As the density increases, the chemical potential and energy per\nparticle are found to saturate while the inverse compressibility and phonon\nvelocity undergo a significant reduction. We also take Gaussian fluctuations\ninto account and calculate the ground state energy correction as well as the\nquantum depletion."
    },
    {
        "anchor": "Universal three-body bound states in mixed dimensions beyond the Efimov\n  paradigm: The Efimov effect was first predicted for three particles interacting at an\n$s$-wave resonance in three dimensions. Subsequent study showed that the same\neffect can be realized by considering two-body and three-body interactions in\nmixed dimensions. In this work, we consider the three-body problem of two\nbosonic $A$ atoms interacting with another single $B$ atom in mixed dimensions:\nThe $A$ atoms are confined in a space of dimension $d_A$ and the $B$ atom in a\nspace of dimension $d_B$, and there is an interspecies $s$-wave interaction in\na $d_{\\rm int}$-co-dimensional space accessible to both species. We find that\nwhen the $s$-wave interaction is tuned on resonance, there emerge an infinite\nseries of universal three-body bound states for $\\{d_A,d_B,d_{\\rm\nint}\\}=\\{2,2,0\\}$ and $\\{2,3,1\\}$. Going beyond the Efimov paradigm, the\nbinding energies of these states follow the scaling\n$\\ln|E_n|\\sim-s(n\\pi-\\theta)^2/4$ with the scaling factor $s$ being unity for\nthe former case and $\\sqrt{m_B(2m_A+m_B)}/(m_A+m_B)$ for the latter. We discuss\nhow our mixed dimensional systems can be realized in current cold atom\nexperiment and how the effects of these universal three-body bound states can\nbe detected.",
        "positive": "Universal pair-polaritons in a strongly interacting Fermi gas: Cavity quantum electrodynamics (QED) manipulates the coupling of light with\nmatter, and allows for several emitters to couple coherently with one light\nmode. However, even in a many-body system, the light-matter coupling mechanism\nwas so far restricted to one body processes. Leveraging cavity QED for the\nquantum simulation of complex, many-body systems has thus far relied on\nmulti-photon processes, scaling down the light-matter interaction to the low\nenergy and slow time scales of the many-body problem. Here we report on cavity\nQED experiments using molecular transitions in a strongly interacting Fermi\ngas, directly coupling cavity photons to pairs of atoms. The interplay of\nstrong light-matter and strong inter-particle interactions leads to well\nresolved pair-polaritons, hybrid excitations coherently mixing photons, atom\npairs and molecules. The dependence of the pair-polariton spectrum on\ninteratomic interactions is universal, independent of the transition used,\ndemonstrating a direct mapping between pair correlations in the ground state\nand the optical spectrum. This represents a magnification of many-body effects\nby two orders of magnitude in energy. In the dispersive regime, it enables\nfast, minimally destructive measurements of pair correlations, and opens the\nway towards their measurements at the quantum limit and their coherent\nmanipulation using dynamical, quantized optical fields."
    },
    {
        "anchor": "Crystal, Superfluids, Supersolid and Hetero-Structure in System of\n  Two-Component Strongly-Correlated Bosons in a Cubic Optical Lattice: In the present paper, we study finite-temperature phase structure of\ntwo-component hard-core bosons in a cubic optical lattice. The system that we\nstudy in the present paper is an effective model for the Bose-Hubbard model\nwith strong on-site repulsions and is called bosonic t-J model. This model is a\nbosonic counterpart of the t-J model for the strongly-correlated electron\nsystems like the high-temperature superconducting materials. We study the model\nby means of path-integral methods and Monte-Carlo simulations. We found that\nthis system has a very rich phase structure including checkerboard-type\n\"insulating\" state, superfluid, phase-separated state, inhomogeneous cloudlet\nstate, etc. We are also interested in the possible supersolid phase with both\nthe checkerboard order and superfluidity and found that additional\nnearest-neighbor inter-species attractive force induces the supersolid state.\nIn the supersolid state, paired superfluid appears in addition to the\nsuperfluid of single atom. This result gives important insight into mechanism\nof the high-temperature superconductivity of the cuprate.",
        "positive": "Resonant persistent currents for ultracold bosons on a lattice ring: We consider a one-dimensional bosonic gas on a ring lattice, in the presence\nof a localized barrier, and under the effect of an artificial gauge field. By\nmeans of exact diagonalization we study the persistent currents at varying\ninteractions and barrier strength, for various values of lattice filling. While\ngenerically the persistent currents are strongly suppressed in the Mott\ninsulator phase, they show a resonant behaviour when the barrier strength\nbecomes of the order of the interaction energy. We explain this phenomenon\nusing an effective single-particle model. We show that this effect is robust at\nfinite temperature, up the temperature scale where persistent currents vanish."
    },
    {
        "anchor": "Site-resolved measurement of the spin-correlation function in the\n  Hubbard model: Exotic phases of matter can emerge from strong correlations in quantum\nmany-body systems. Quantum gas microscopy affords the opportunity to study\nthese correlations with unprecedented detail. Here we report site-resolved\nobservations of antiferromagnetic correlations in a two-dimensional,\nHubbard-regime optical lattice and demonstrate the ability to measure the\nspin-correlation function over any distance. We measure the in-situ\ndistributions of the particle density and magnetic correlations, extract\nthermodynamic quantities from comparisons to theory, and observe statistically\nsignificant correlations over three lattice sites. The temperatures that we\nreach approach the limits of available numerical simulations. The direct access\nto many-body physics at the single-particle level demonstrated by our results\nwill further our understanding of how the interplay of motion and magnetism\ngives rise to new states of matter.",
        "positive": "Hysteresis in quantized vortex shedding: It is shown using numerical simulations that flow patterns around an obstacle\npotential moving in a superfluid exhibit hysteresis. In a certain velocity\nregion, there is a bistability between stationary laminar flow and periodic\nvortex shedding. The bistability exists in two and three dimensional systems."
    },
    {
        "anchor": "The dynamics and prethermalization of one dimensional quantum systems\n  probed through the full distributions of quantum noise: Quantum noise correlations have been employed in several areas in physics\nincluding condensed matter, quantum optics and ultracold atom to reveal\nnon-classical states of the systems. So far, such analysis mostly focused on\nsystems in equilibrium. In this paper, we show that quantum noise is also a\nuseful tool to characterize and study the non-equilibrium dynamics of one\ndimensional system. We consider the Ramsey sequence of one dimensional,\ntwo-component bosons, and obtain simple, analytical expressions of time\nevolutions of the full distribution functions for this strongly-correlated,\nmany-body system. The analysis can also be directly applied to the evolution of\ninterference patterns between two one dimensional quasi-condensates created\nfrom a single condensate through splitting. Using the tools developed in this\npaper, we demonstrate that one dimensional dynamics in these systems exhibits\nthe phenomenon known as \"prethermalization\", where the observables of {\\it\nnon-equilibrium}, long-time transient states become indistinguishable from\nthose of thermal {\\it equilibrium} states.",
        "positive": "Light scattering from ultracold gases in disordered optical lattices: We consider a gas of bosons in a bichromatic optical lattice at finite\ntemperatures. As the amplitude of the secondary lattice grows, the\nsingle-particles eigenstates become localized. We calculate the canonical\npartition function using exact methods for the noninteracting and strongly\ninteracting limit and analyze the statistical properties of the superfluid\nphase, localized phase and the strongly interacting gas. We show that those\nphases may be distinguished in experiment using off-resonant light scattering."
    },
    {
        "anchor": "Transition from a polaronic condensate to a degenerate Fermi gas of\n  heteronuclear molecules: The interplay of quantum statistics and interactions in atomic Bose--Fermi\nmixtures leads to a phase diagram markedly different from pure fermionic or\nbosonic systems. However, investigating this phase diagram remains challenging\nwhen bosons condense. Here, we observe evidence for a quantum phase transition\nfrom a polaronic to a molecular phase in a density-matched degenerate\nBose--Fermi mixture. The condensate fraction, representing the order parameter\nof the transition, is depleted by interactions and the build-up of strong\ncorrelations results in the emergence of a molecular Fermi gas. By driving\nthrough the transition, we ultimately produce a quantum-degenerate sample of\nsodium-potassium molecules exhibiting a large molecule-frame dipole moment of\n2.7 Debye. The observed phase transition represents a new phenomenon\ncomplementary to the paradigmatic BEC-BCS crossover observed in Fermi systems.",
        "positive": "Quantum spin dynamics in Fock space following quenches: Caustics and\n  vortices: Caustics occur widely in dynamics and take on shapes classified by\ncatastrophe theory. At finite wavelengths they produce interference patterns\ncontaining networks of vortices (phase singularities). Here we investigate\ncaustics in quantized fields, focusing on the collective dynamics of quantum\nspins. We show that, following a quench, caustics are generated in the Fock\nspace amplitudes specifying the many-body configuration and which are\naccessible in experiments with cold atoms, ions or photons. The granularity of\nquantum fields removes all singularities, including phase singularities,\nconverting point vortices into nonlocal vortices that annihilate in pairs as\nthe quantization scale is increased. Furthermore, the continuous scaling laws\nof wave catastrophes are replaced by discrete versions. Such `quantum\ncatastrophes' are expected to be universal dynamical features of quantized\nfields."
    },
    {
        "anchor": "Perturbative Approach to Superfluidity under Nonuniform Potential: A perturbative way to investigate superfluid properties of various systems\nunder nonuniform potential is presented. We derive the perturbation expansion\nof the superfluid fraction, which indicates how liquid exhibits nonclassical\nrotational inertia, in terms of the strength of nonuniform potential and find\nthat the coefficient of the leading term reflects the density fluctuation of\nthe system. Our formulation does not assume anything about Bose-Einstein\ncondensation and thus is applicable to wide variety of systems. Superfluid\nproperties of some examples including (non-)interacting Bose systems,\nespecially Bose gas in the mean field limit, (non-)interacting Fermi sytems,\nTomonaga-Luttinger liquid and spinless chiral $p$-wave superfluid are\ninvestigated.",
        "positive": "Entangling qubit registers via many-body states of ultracold atoms: Inspired by the experimental measurement of the Renyi entanglement entropy in\na lattice of ultracold atoms by Islam et al., [Nature 528, 77 (2015)] we\npropose a method to entangle two spatially-separated qubits using the quantum\nmany-body state as a resource. Through local operations accessible in an\nexperiment, entanglement is transferred to a qubit register from atoms at the\nends of a one-dimensional chain. We compute the operational entanglement, which\nbounds the entanglement physically transferable from the many-body resource to\nthe register, and discuss a protocol for its experimental measurement. Finally,\nwe explore measures for the amount of entanglement available in the register\nafter transfer, suitable for use in quantum information applications."
    },
    {
        "anchor": "Path-dependent correlations in dynamically tuned Ising models and its\n  short-time behavior: application of Magnus expansion: We study the buildup of antiferromagnetic (AF) correlation in the dynamically\ntuned Ising models which are realized by the Rydberg atomic system. In\nshort-time scale, we apply Magnus expansion (ME) to derive the high-order\nanalytic expression of the connected correlation functions and compare it with\nexactly numerical results for the different lattice geometries, e.g., 1D chain,\n$2 \\times n$ lattice, and $n \\times n$ lattice. It is shown that the high-order\nexpansion is required to describe accurately the buildup of AF correlation in\nthe quench dynamics. Moreover, through a 2D square lattice, we find that the\nmagnitude of AF correlation for the same Manhattan distance is proportional to\nthe number of the shortest paths in a sufficiently long time until long and\ndistinct paths are involved significantly with the buildup of the correlation.\nFinally, we propose an applicable experimental setup to realize our findings.",
        "positive": "Quantum fluctuations inhibit symmetry breaking in the HMF model: It is widely believed that mean-field theory is exact for a wide-range of\nclassical long-range interacting systems. Is this also true once quantum\nfluctuations have been accounted for? As a test case we study the Hamiltonian\nMean Field (HMF) model for a system of indistinguishable bosons which is\npredicted (according to mean-field theory) to undergo a second-order quantum\nphase transition at zero temperature. The ordered phase is characterized by a\nspontaneously broken $O(2)$ symmetry, which, despite occurring in a\none-dimensional model, is not ruled out by the Mermin-Wagner theorem due to the\npresence of long-range interactions. Nevertheless, a spontaneously broken\nsymmetry implies gapless Goldstone modes whose large fluctuations can restore\nbroken symmetries. In this work, we study the influence of quantum fluctuations\nby projecting the Hamiltonian onto the continuous subspace of symmetry breaking\nmean-field states. We find that the energetic cost of gradients in the center\nof mass wavefunction inhibit the breaking of the $O(2)$ symmetry, but that the\nenergetic cost is very small --- scaling as $\\mathcal{O}(1/N^2)$. Nevertheless,\nfor any finite $N$, no matter how large, this implies that the ground state has\na restored $O(2)$ symmetry. Implications for the finite temperature phases, and\nclassical limit, of the HMF model are discussed."
    },
    {
        "anchor": "Z_2 Topological Insulators in Ultracold Atomic Gases: We describe how optical dressing can be used to generate bandstructures for\nultracold atoms with non-trivial Z_2 topological order. Time reversal symmetry\nis preserved by simple conditions on the optical fields. We first show how to\nconstruct optical lattices that give rise to Z_2 topological insulators in two\ndimensions. We then describe a general method for the construction of\nthree-dimensional Z_2 topological insulators. A central feature of our approach\nis a new way to understand Z_2 topological insulators starting from the\nnearly-free electron limit.",
        "positive": "Chern number spectrum of ultra-cold fermions in optical lattices tuned\n  independently via artificial magnetic, Zeeman and spin-orbit fields: We discuss the Chern number spectrum of ultra-cold fermions in square optical\nlattices as a function of artificial magnetic, Zeeman and spin-orbit fields\nthat can be tuned independently. We show the existence of topological quantum\nphase transitions induced by Zeeman and spin-orbit fields, where the total\nnumber and chirality of edge states change for fixed magnetic flux ratio, thus\nleading to topological-insulator phases which are different from those found at\nzero Zeeman and spin-orbit fields. We construct phase diagrams of chemical\npotential versus Zeeman field or spin-orbit coupling and characterize all\ninsulating phases by their topological invariants. Lastly, we obtain a\nstaircase structure in the filling factor versus chemical potential for various\nZeeman and spin-orbit fields, showing the existence of incompressible states at\nrational filling factors derived from a generalized Diophantine equation."
    },
    {
        "anchor": "Finite-Temperature Study of Bose-Fermi Superfluid Mixtures: Ultra-cold atom experiments offer the unique opportunity to study mixing of\ndifferent types of superfluid states. Our interest is in superfluid mixtures\ncomprising particles with different statistics- Bose and Fermi. Such scenarios\noccur naturally, for example, in dense QCD matter. Interestingly, cold atomic\nexperiments are performed in traps with finite spatial extent, thus critically\ndestabilizing the occurrence of various homogeneous phases. Critical to this\nanalysis is the understanding that the trapped system can undergo phase\nseparation, resulting in a unique situation where phase transition in either\nspecies (bosons or fermions) can overlap with the phase separation between\npossible phases. In the present work, we illustrate how this intriguing\ninterplay manifests in an interacting 2-species atomic mixture - one bosonic\nand another fermionic with two spin components - within a realistic trap\nconfiguration. We further show that such interplay of transitions can render\nthe nature of the ground state to be highly sensitive to the experimental\nparameters and the dimensionality of the system.",
        "positive": "Non-equilibrium Floquet steady states of time-periodic driven Luttinger\n  liquids: Time-periodic driving facilitates a wealth of novel quantum states and\nquantum engineering. The interplay of Floquet states and strong interactions is\nparticularly intriguing, which we study using time-periodic fields in a\none-dimensional quantum gas, modeled by a Luttinger liquid with periodically\nchanging interactions. By developing a time-periodic operator algebra, we are\nable to solve and analyze the complete set of non-equilibrium steady states in\nterms of a Floquet-Bogoliubov ansatz and known analytic functions. Complex\nvalued Floquet eigenenergies occur when multiples of driving frequency\napproximately match twice the dispersion energy, which correspond to resonant\nstates. In experimental systems of Lieb-Liniger bosons we predict a change from\npowerlaw correlations to dominant collective density wave excitations at the\ncorresponding wave numbers as the frequency is lowered below a characteristic\ncut-off."
    },
    {
        "anchor": "Topological chiral spin liquids and competing states in triangular\n  lattice SU($N$) Mott insulators: SU($N$) Mott insulators have been proposed and/or realized in solid-state\nmaterials and with ultracold atoms on optical lattices. We study the\ntwo-dimensional SU($N$) antiferromagnets on the triangular lattice. Starting\nfrom an SU($N$) Heisenberg model with the fundamental representation on each\nsite in the large-$N$ limit, we perform a self-consistent calculation and find\na variety of ground states including the valence cluster states, stripe ordered\nstates with a doubled unit-cell and topological chiral spin liquids. The system\nfavors a cluster or ordered ground state when the number of flavors $N$ is less\nthan 6. It is shown that, increasing the number of flavors enhances quantum\nfluctuations and eventually transfer the clusterized ground states into a\ntopological chiral spin liquids. This chiral spin liquid ground state has an\nequivalent for the square lattice SU($N$) magnets. We further identify the\ncorresponding lowest competing states that represent another distinct type of\nchiral spin liquid states. We conclude with a discussion about the relevant\nsystems and the experimental probes.",
        "positive": "A faster scaling in acceleration-sensitive atom interferometers: Atom interferometers have been used to measure acceleration with at best a\n$T^2$ scaling in sensitivity as the interferometer time $T$ is increased. This\nlimits the sensitivity to acceleration which is theoretically achievable by\nthese configurations for a given frequency of acceleration. We predict and\nexperimentally measure the acceleration-sensitive phase shift of a\nlarge-momentum-transfer atom interferometer based upon Bloch oscillations.\nUsing this novel interferometric scheme we demonstrate an improved scaling of\nsensitivity which will scale as $T^3$. This enhanced scaling will allow an\nincrease in achievable sensitivity for any given frequency of an oscillatory\nacceleration signal, which will be of particular use for inertial and\nnavigational sensors, and proposed gravitational wave detectors. A straight\nforward extension should allow a $T^4$ scaling in acceleration sensitivity."
    },
    {
        "anchor": "Two-dimensional anisotropic vortex quantum droplets in dipolar\n  Bose-Einstein condensates: Creation of stable intrinsically anisotropic self-bound states with embedded\nvorticity is a challenging issue. Previously, no such states in Bose-Einstein\ncondensates (BECs) or other physical settings were known. Dipolar BEC suggests\na unique possibility to predict stable anisotropic vortex quantum droplets\n(AVQDs). We demonstrate that they can be created with the vortex' axis oriented\n\\emph{perpendicular} to the polarization of dipoles. The stability area and\ncharacteristics of the AVQDs in the parameter space are revealed by means of\nanalytical and numerical methods. Further, the rotation of the polarizing\nmagnetic field is considered, and the largest angular velocities, up to which\nspinning AVQDs can follow the rotation in clockwise and anti-clockwise\ndirections, are found. Collisions between moving AVQDs are studied too,\ndemonstrating formation of bound states with a vortex-antivortex-vortex\nstructure. A stability domain for such stationary bound states is identified.\nUnstable dipolar states, that can be readily implemented by means of phase\nimprinting, quickly transform into robust AVQDs, which suggests a\nstraightforward possibility for the creation of these states in the experiment.",
        "positive": "How to probe the microscopic onset of irreversibility with ultracold\n  atoms: The microscopic onset of irreversibility is finally becoming an experimental\nsubject. Recent experiments on microscopic open and even isolated systems have\nmeasured statistical properties associated with entropy production, and\nhysteresis-like phenomena have been seen in cold atom systems with dissipation\n(i.e. effectively open systems coupled to macroscopic reservoirs). Here we show\nhow experiments on isolated systems of ultracold atoms can show dramatic\nirreversibility like cooking an egg. In our proposed experiments, a slow\nforward-and-back parameter sweep will sometimes fail to return the system close\nto its initial state. This probabilistic hysteresis is due to the same\nnon-adiabatic spreading and ergodic mixing in phase space that explains\nmacroscopic irreversibility, but realized \\textit{without} dynamical chaos;\nmoreover this fundamental mechanism quantitatively determines the probability\nof return to the initial state as a function of tunable parameters in the\nproposed experiments. Matching the predicted curve of return probability will\nbe a conclusive experimental demonstration of the microscopic onset of\nirreversibility."
    },
    {
        "anchor": "Non-equilibrium fixed points of coupled Ising models: Driven-dissipative systems are expected to give rise to non-equilibrium\nphenomena that are absent in their equilibrium counterparts. However, phase\ntransitions in these systems generically exhibit an effectively classical\nequilibrium behavior in spite of their non-equilibrium origin. In this paper,\nwe show that multicritical points in such systems lead to a rich and genuinely\nnon-equilibrium behavior. Specifically, we investigate a driven-dissipative\nmodel of interacting bosons that possesses two distinct phase transitions: one\nfrom a high- to a low-density phase---reminiscent of a liquid-gas\ntransition---and another to an antiferromagnetic phase. Each phase transition\nis described by the Ising universality class characterized by an (emergent or\nmicroscopic) $\\mathbb{Z}_2$ symmetry. They, however, coalesce at a\nmulticritical point, giving rise to a non-equilibrium model of coupled\nIsing-like order parameters described by a $\\mathbb{Z}_2 \\times \\mathbb{Z}_2$\nsymmetry. Using a dynamical renormalization-group approach, we show that a pair\nof non-equilibrium fixed points (NEFPs) emerge that govern the long-distance\ncritical behavior of the system. We elucidate various exotic features of these\nNEFPs. In particular, we show that a generic continuous scale invariance at\ncriticality is reduced to a discrete scale invariance. This further results in\ncomplex-valued critical exponents and spiraling phase boundaries, and it is\nalso accompanied by a complex Liouvillian gap even close to the phase\ntransition. As direct evidence of the non-equilibrium nature of the NEFPs, we\nshow that the fluctuation-dissipation relation is violated at all scales,\nleading to an effective temperature that becomes \"hotter\" and \"hotter\" at\nlonger and longer wavelengths. Finally, we argue that this non-equilibrium\nbehavior can be observed in cavity arrays with cross-Kerr nonlinearities.",
        "positive": "Mobile vector soliton in a spin-orbit coupled spin-$1$ condensate: We study the formation of bound states and three-component bright vector\nsolitons in a quasi-one-dimensional spin-orbit-coupled hyperfine spin $f=1$\nBose-Einstein condensate using numerical solution and variational approximation\nof a mean-field model. In the antiferromagnetic domain, the solutions are\ntime-reversal symmetric, and the component densities have multi-peak structure.\nIn the ferromagnetic domain, the solutions violate time-reversal symmetry, and\nthe component densities have single-peak structure. The dynamics of the system\nis not Galelian invariant. From an analysis of Galelian invariance, we\nestablish that the single-peak ferromagnetic vector solitons are true solitons\nand can move maintaining constant component densities, whereas the\nantiferromagnetic solitons cannot move with constant component densities."
    },
    {
        "anchor": "Engineering random spin models with atoms in a high-finesse cavity: All-to-all interacting, disordered quantum many-body models have a wide range\nof applications across disciplines, from spin glasses in condensed-matter\nphysics, over holographic duality in high-energy physics, to annealing\nalgorithms in quantum computing. Typically, these models are abstractions that\ndo not find unambiguous physical realisations in nature. Here, we realise an\nall-to-all interacting, disordered spin system by subjecting an atomic cloud in\na cavity to a controllable light shift. Adjusting the detuning between atom\nresonance and cavity mode, we can tune between disordered versions of a\ncentral-mode model and a Lipkin-Meshkov-Glick model. By spectroscopically\nprobing the low-energy excitations of the system, we explore the competition of\ninteractions with disorder across a broad parameter range. We show how disorder\nin the central-mode model breaks the strong collective coupling, making the\ndark state manifold cross over to a random distribution of weakly-mixed\nlight-matter, \"grey\", states. In the Lipkin-Meshkov-Glick model the\nferromagnetic finite-size ground state evolves towards a paramagnet as disorder\nis increased. In that regime, semi-localised eigenstates emerge, as we observe\nby extracting bounds on the participation ratio. These results present\nsignificant steps towards freely programmable cavity-mediated interactions for\nthe design of arbitrary spin Hamiltonians.",
        "positive": "Recent advances in the theory of the BCS-BEC crossover for fermionic\n  superfluidity: The BCS-BEC crossover realized experimentally with ultra-cold Fermi gases may\nbe considered as one of the important scientific achievements occurred during\nthe last several years. The flexibility for operating on these systems on the\nexperimental side and the full control of the relevant system degrees of\nfreedom on the theoretical side make quite stringent at a fundamental level the\ncomparison between the experimental data and the corresponding theoretical\ncalculations. Here, we briefly survey recent theoretical advances resting on a\ndiagrammatic approach at equilibrium that improves in a systematic way on the\nwidely used t-matrix approach, yielding a quite good comparison between theory\nand experiments for several physical quantities of interest. It is proposed\nthat the physical phenomena underlying this theoretical approach may also be\nrelevant to the superconducting phase of condensed-matter materials which\ncannot be described by the standard BCS theory."
    },
    {
        "anchor": "Sub-Doppler laser cooling of fermionic 40K atoms in three-dimensional\n  gray optical molasses: We demonstrate sub-Doppler cooling of 40K on the D_1 atomic transition. Using\na gray molasses scheme, we efficiently cool a compressed cloud of 6.5x10^8\natoms from ~ 4\\mK to 20uK in 8 ms. After transfer in a quadrupole magnetic\ntrap, we measure a phase space density of ~10^-5. This technique offers a\npromising route for fast evaporation of fermionic 40K.",
        "positive": "Magneto--optical matter wave Bragg diffraction: We have performed a principle-proof-experiment of a magneto-optical\ndiffraction (MOD) technique that requires no energy level splitting by\nhomogeneous magnetic field and a circularly polarized optical lattice, avoiding\nsystem errors in an interferometer based on the MOD. The principle for this new\nMOD is that asynchronized switching of quadrupole trap and Ioffe trap in a\nquadrupole-Ioffe-configuration trap can generate a residual magnetic force to\ndrive a Bose-Einstein condensate (BEC) to move. We have observed asymmetric\natomic diffraction resulting from the asymmetric distribution of the Bloch\neigenstates involved in the diffraction process when the condensate is driven\nby such a force, and matter-wave self-imaging due to coherent population\noscillation of the dominantly occupied Bloch eigenstates. We have classified\nthe mechanisms that lead to symmetric or asymmetric diffraction, and found that\nour experiment presents a magnetic alternative to a moving optical lattice,\nwith a great potential to achieve a very large momentum transfer ($>110 \\hbar\nk$) to a BEC using well-developed magnetic trapping techniques."
    },
    {
        "anchor": "Parity violating superfluidity in ultra-cold fermions under the\n  influence of artificial non-Abelian gauge fields: We discuss the creation of parity violating Fermi superfluids in the presence\nof non-Abelian gauge fields involving spin-orbit coupling and crossed Zeeman\nfields. We focus on spin-orbit coupling with equal Rashba and Dresselhaus (ERD)\nstrengths which has been realized experimentally in ultra-cold atoms, but we\nalso discuss the case of arbitrary mixing of Rashba and Dresselhaus (RD) and of\nRashba-only (RO) spin-orbit coupling. To illustrate the emergence of parity\nviolation in the superfluid, we analyze first the excitation spectrum in the\nnormal state and show that the generalized helicity bands do not have inversion\nsymmetry in momentum space when crossed Zeeman fields are present. This is also\nreflected in the superfluid phase, where the order parameter tensor in the\ngeneralized helicity basis violates parity. However, the pairing fields in\nsinglet and triplet channels of the generalized helicity basis are still parity\neven and odd, respectively. Parity violation is further reflected on ground\nstate properties such as the spin-resolved momentum distribution, and in\nexcitation properties such as the spin-dependent spectral function and density\nof states.",
        "positive": "Position swapping and pinching in Bose-Fermi mixtures with two-color\n  optical Feshbach resonances: We examine the density profiles of the quantum degenerate Bose-Fermi mixture\nof $^{174}$Yb-$^{173}$Yb, experimental observed recently, in the mean field\nregime. In this mixture there is a possibility of tuning the Bose-Bose and\nBose-Fermi interactions simultaneously using two well separated optical\nFeshbach resonances, and it is a good candidate to explore phase separation in\nBose-Fermi mixtures. Depending on the Bose-Bose scattering length $a_\\BB$, as\nthe Bose-Fermi interaction is tuned the density of the fermions is pinched or\nswapping with bosons occurs."
    },
    {
        "anchor": "Echo spectroscopy of Anderson localization: We propose a conceptually new framework to study the onset of Anderson\nlocalization in disordered systems. The idea is to expose waves propagating in\na random scattering environment to a sequence of short dephasing pulses. The\nsystem responds through coherence peaks forming at specific echo times, each\necho representing a particular process of quantum interference. We suggest a\nconcrete realization for cold gases, where quantum interferences are observed\nin the momentum distribution of matter waves in a laser speckle potential. This\ndefines a challenging, but arguably realistic framework promising to yield\nunprecedented insight into the mechanisms of Anderson localization.",
        "positive": "Density-Wave Instability and Collective Modes in a Bilayer System of\n  Dipolar Bosons: We consider a bilayer of dipolar bosons in which the polarization of dipoles\nare perpendicular to the planes. Using accurate static structure factor $S(q)$\ndata from hypernetted-chain calculation for single layer dipolar bosons we\nconstruct effective screened interactions for intralayer particles. We adopt\nthe random-phase approximation for interlayer interactions. We study the\ninstability of the homogeneous bilayer system against the formation of density\nwaves by investigating the poles of the density-density response function. The\ndispersion of collective modes of this system also signals the density-wave\ninstability. We also investigate the effect of counterflow on the collective\nmode dispersion and on the density-wave instability and discuss the\ndissipationless superfluid drag effect in the presence of a background\nvelocity."
    },
    {
        "anchor": "Detecting Friedel oscillations in ultracold Fermi gases: Investigating Friedel oscillations in ultracold gases would complement the\nstudies performed on solid state samples with scanning-tunneling microscopes.\nIn atomic quantum gases interactions and external potentials can be tuned\nfreely and the inherently slower dynamics allow to access non-equilibrium\ndynamics following a potential or interaction quench. Here, we examine how\nFriedel oscillations can be observed in current ultracold gas experiments under\nrealistic conditions. To this aim we numerically calculate the amplitude of the\nFriedel oscillations which a potential barrier provokes in a 1D Fermi gas and\ncompare it to the expected atomic and photonic shot noise in a density\nmeasurement. We find that to detect Friedel oscillations the signal from\nseveral thousand one-dimensional systems has to be averaged. However, as up to\n100 parallel one-dimensional systems can be prepared in a single run with\npresent experiments, averaging over about 100 images is sufficient.",
        "positive": "Loop Structure Stability of a Double-Well-Lattice BEC: In this work, we consider excited many-body mean-field states of bosons in a\ndouble-well optical lattice by investigating stationary Bloch solutions to the\nnon-linear equations of motion. We show that, for any positive interaction\nstrength, a loop structure emerges at the edge of the band structure whose\nexistence is entirely due to interactions. This can be contrasted to the case\nof a conventional optical (Bravais) lattice where a loop appears only above a\ncritical repulsive interaction strength. Motivated by the possibility of\nrealizing such non-linear Bloch states experimentally, we analyze the\ncollective excitations about these non-linear stationary states and thereby\nestablish conditions for the system's energetic and dynamical stability. We\nfind that there are regimes that are dynamically stable and thus apt to be\nrealized experimentally."
    },
    {
        "anchor": "Machine-learning enhanced dark soliton detection in Bose-Einstein\n  condensates: Most data in cold-atom experiments comes from images, the analysis of which\nis limited by our preconceptions of the patterns that could be present in the\ndata. We focus on the well-defined case of detecting dark solitons -- appearing\nas local density depletions in a Bose-Einstein condensate (BEC) -- using a\nmethodology that is extensible to the general task of pattern recognition in\nimages of cold atoms. Studying soliton dynamics over a wide range of parameters\nrequires the analysis of large datasets, making the existing\nhuman-inspection-based methodology a significant bottleneck. Here we describe\nan automated classification and positioning system for identifying localized\nexcitations in atomic BECs utilizing deep convolutional neural networks to\neliminate the need for human image examination. Furthermore, we openly publish\nour labeled dataset of dark solitons, the first of its kind, for further\nmachine learning research.",
        "positive": "Renormalization group flows for Wilson-Hubbard matter and the\n  topological Hamiltonian: Understanding the robustness of topological phases of matter in the presence\nof interactions poses a difficult challenge in modern condensed matter, showing\ninteresting connections to high energy physics. In this work, we leverage these\nconnections to present a complete analysis of the continuum long-wavelength\ndescription of a generic class of correlated topological insulators:\nWilson-Hubbard topological matter. We show that a Wilsonian renormalization\ngroup (RG) approach, combined with the so-called topological Hamiltonian,\nprovide a quantitative route to understand interaction-induced topological\nphase transitions that occur in Wilson-Hubbard matter. We benchmark two-loop RG\npredictions for a quasi-1D Wilson-Hubbard model by means of exhaustive\nnumerical simulations based on matrix product states (MPS). The agreement of\nthe RG predictions with MPS simulations motivates the extension of the RG\ncalculations to higher-dimensional topological insulators."
    },
    {
        "anchor": "Single-particle Excitations and Strong Coupling Effects in the BCS-BEC\n  Crossover Regime of a Rare-Earth Fermi Gas with an Orbital Feshbach Resonance: We theoretically investigate normal-state properties of an ultracold Fermi\ngas with an orbital Feshbach resonance (OFR). Recently, OFR has attracted much\nattention as a promising pairing mechanism to realize a superfluid 173Yb Fermi\ngas. Including pairing fluctuations within a T-matrix approximation, and\nremoving effects of an experimentally inaccessible deep bound state, we\nevaluate strong-coupling corrections to single-particle excitations. With\nincreasing the strength of an OFR-induced tunable pairing interaction, the open\nchannel is shown to exhibit the pseudogap phenomenon in the BCS-BEC crossover\nregion, as in the case of a broad magnetic Feshbach resonance (MFR) in 6Li and\n40K Fermi gases. We also show that the strong pairing interaction affects the\nclosed channel, leading to the coexistence of particle and hole branches in the\nsingle-particle spectral weight. Since the latter phenomenon cannot be observed\nin the conventional MFR case, it may be viewed as a characteristic\nstrong-coupling phenomenon peculiar to the OFR case.",
        "positive": "Two- and three-body effective potentials between impurities in ideal BEC: We exactly calculate the full temperature dependence of Casimir-like forces\nappearing between two and three static impurities loaded in the ideal Bose gas\nbelow the Bose-Einstein condensation transition point. Assuming the\nshort-ranged character of the boson-impurity interaction, the calculation\nprocedure presented here can be easily extended on a Bose system with an\narbitrary number of impurities immersed."
    },
    {
        "anchor": "Single-site-resolved measurement of the current statistics in optical\n  lattices: At present, great effort is spent on the experimental realization of gauge\nfields for quantum many-body systems in optical lattices. At the same time, the\nsingle-site-resolved detection of individual atoms has become a new powerful\nexperimental tool. We discuss a protocol for the single-site resolved\nmeasurement of the current statistics of quantum many-body systems, which makes\nuse of a bichromatic optical superlattice and single-site detection. We\nillustrate the protocol by a numerical study of the current statistics for\ninteracting bosons in one and two dimensions and discuss the role of the\non-site interactions for the current pattern and the ground-state symmetry for\nsmall two-dimensional lattices with artificial magnetic fields.",
        "positive": "Maximum Energy Growth Rate in Dilute Quantum Gases: In this letter we study how fast the energy density of a quantum gas can\nincrease in time, when the inter-atomic interaction characterized by the\n$s$-wave scattering length $a_\\text{s}$ is increased from zero with arbitrary\ntime dependence. We show that, at short time, the energy density can at most\nincrease as $\\sqrt{t}$, which can be achieved when the time dependence of\n$a_\\text{s}$ is also proportional to $\\sqrt{t}$, and especially, a universal\nmaximum energy growth rate can be reached when $a_\\text{s}$ varies as\n$2\\sqrt{\\hbar t/(\\pi m)}$. If $a_\\text{s}$ varies faster or slower than\n$\\sqrt{t}$, it is respectively proximate to the quench process and the\nadiabatic process, and both result in a slower energy growth rate. These\nresults are obtained by analyzing the short time dynamics of the short-range\nbehavior of the many-body wave function characterized by the contact, and are\nalso confirmed by numerical solving an example of interacting bosons with\ntime-dependent Bogoliubov theory. These results can also be verified\nexperimentally in ultracold atomic gases."
    },
    {
        "anchor": "Coherent superposition of current flows in an Atomtronic Quantum\n  Interference Device: We consider a correlated Bose gas tightly confined into a ring shaped\nlattice, in the presence of an artificial gauge potential inducing a persistent\ncurrent through it. A weak link painted on the ring acts as a source of\ncoherent back-scattering for the propagating gas, interfering with the forward\nscattered current. This system defines an atomic counterpart of the rf-SQUID:\nthe atomtronics quantum interference device (AQUID). The goal of the present\nstudy is to corroborate the emergence of an effective two-level system in such\na setup and to assess its quality, in terms of its inner resolution and its\nseparation from the rest of the many-body spectrum, across the different\nphysical regimes. In order to achieve this aim, we examine the dependence of\nthe qubit energy gap on the bosonic density, the interaction strength, and the\nbarrier depth, and we show how the superposition between current states appears\nin the momentum distribution (time-of-flight) images. A mesoscopic ring lattice\nwith intermediate-to-strong interactions and weak barrier depth is found to be\na favorable candidate for setting up, manipulating and probing a qubit in the\nnext generation of atomic experiments.",
        "positive": "When are two fermions a simple boson? New Gross-Pitaevskii actions for\n  cold Fermi condensates: The BEC regime of a cold fermi gas is characterised by coupled atoms (dimers)\nwhich, superficially, look like elementary bosons. We examine how\nsimply-bosonic they really are; firstly, in the Bogoliubov approximation and\nfurther, through new actions for the BEC regime in which dimers are represented\nby coupled Gross-Pitaevskii fields. We find identity at the level of the\nBogoliubov approximation in the deep BEC regime, permitting a simple\nGross-Pitaevskii description. This fails rapidly as we move towards the BCS\nregime. However, even in the deep BEC regime there is an intrinsic difference\nif we go beyond the Bogoliubov approximation. To exemplify this we construct\nvortex solutions."
    },
    {
        "anchor": "Topological Properties of Ultracold Bosons in One-Dimensional\n  Quasiperiodic Optical Lattice: We analyze topological properties of the one-dimensional Bose-Hubbard model\nwith a quasiperiodic superlattice potential. This system can be realized in\ninteracting ultracold bosons in optical lattice in the presence of an\nincommensurate superlattice potential. We first analyze the quasiperiodic\nsuperlattice made by the cosine function, which we call Harper-like\nBose-Hubbard model. We compute the Chern number and observe a gap-closing\nbehavior as the interaction strength $U$ is changed. Also, we discuss the\nbulk-edge correspondence in our system. Furthermore, we explore the phase\ndiagram as a function of $U$ and a continuous deformation parameter $\\beta$\nbetween the Harper-like model and another important quasiperiodic lattice, the\nFibonacci model. We numerically confirm that the incommensurate charge density\nwave (ICDW) phase is topologically non-trivial and it is topologically\nequivalent in the whole ICDW region.",
        "positive": "Condensation dynamics in a quantum-quenched Bose gas: By quenching the strength of interactions in a partially condensed Bose gas\nwe create a \"super-saturated\" vapor which has more thermal atoms than it can\ncontain in equilibrium. Subsequently, the number of condensed atoms ($N_0$)\ngrows even though the temperature ($T$) rises and the total atom number decays.\nWe show that the non-equilibrium evolution of the system is isoenergetic and\nfor small initial $N_0$ observe a clear separation between $T$ and $N_0$\ndynamics, thus explicitly demonstrating the theoretically expected \"two-step\"\npicture of condensate growth. For increasing initial $N_0$ values we observe a\ncrossover to classical relaxation dynamics. The size of the observed\nquench-induced effects can be explained using a simple equation of state for an\ninteracting harmonically-trapped atomic gas."
    },
    {
        "anchor": "Condensate formation with three-component ultracold fermions: We investigate the formation of Bose-Einstein condensation and population\nimbalance in a three-component Fermi superfluid by increasing the U(3)\ninvariant attractive interaction. We consider the system at zero temperature in\nthree dimensions and also in two dimensions. Within the mean-field theory, we\nderive explicit formulas for number densities, gap order parameter, condensate\ndensity and condensate fraction of the uniform system, and analyze them in the\ncrossover from the Bardeen-Cooper-Schrieffer (BCS) state of Cooper pairs to the\nBose-Einstein Condensate (BEC) of strongly-bound molecular dimers. In addition,\nwe study this Fermi mixture trapped by a harmonic potential: we calculate the\ndensity profiles of the three components and the condensate density profile of\nCooper pairs in the BCS-BEC crossover.",
        "positive": "Machine learning of XY model on a spherical Fibonacci lattice: We study the XY model on a spherical surface inspired by recently realized\nspherically confined atomic gases. Instead of a traditional latitude-longitude\nlattice, we introduce a much more homogeneous spherical lattice, the Fibonacci\nlattice, and use classical Monte Carlo simulations to determine spin\nconfigurations. The results clearly show that topological defects, in the form\nof vortices, must exist in the stable configuration on a sphere but vanish in a\nplane due to a mathematical theorem. Using these spin configurations as\ntraining samples, we propose a graph-convolutional-network based method to\nrecognize different phases, and successfully predict the phase transition\ntemperature. We also apply the density-based spatial clustering of applications\nwith noise, a powerful machine learning algorithm, to monitor the merging path\nof two vortices with different topological charges on the sphere during Monte\nCarlo simulations. Our results provide reliable predictions for future\nspace-based experiments on ultracold atomic gases confined on spherical lattice\nin the microgravity environment."
    },
    {
        "anchor": "Bloch oscillations in the absence of a lattice: We experimentally investigate the quantum motion of an impurity atom that is\nimmersed in a strongly interacting one-dimensional Bose liquid and is subject\nto an external force. We find that the momentum distribution of the impurity\nexhibits characteristic Bragg reflections at the edge of an emergent Brillouin\nzone. While Bragg reflections are typically associated with lattice structures,\nin our strongly correlated quantum liquid they result from the interplay of\nshort-range crystalline order and kinematic constraints on the many-body\nscattering processes in the one-dimensional system. As a consequence, the\nimpurity exhibits periodic dynamics that we interpret as Bloch oscillations,\nwhich arise even though the quantum liquid is translationally invariant. Our\nobservations are supported by large-scale numerical simulations.",
        "positive": "Vortex formation and dynamics in two-dimensional driven-dissipative\n  condensates: We investigate the real-time evolution of lattice bosons in two spatial\ndimensions whose dynamics is governed by a Markovian quantum master equation.\nWe employ the Wigner-Weyl phase space quantization and derive the functional\nintegral for open quantum many-body systems that governs the time evolution of\nthe Wigner function. Using the truncated Wigner approximation, in which quantum\nfluctuations are only taken into account in the initial state whereas the\ndynamics is governed by classical evolution equations, we study the buildup of\nlong-range correlations due to the action of non-Hermitean quantum jump\noperators that constitute a mechanism for dissipative cooling. Starting from an\ninitially disordered state corresponding to a vortex condensate, the\ndissipative process results in the annihilation of vortex-antivortex pairs and\nthe establishment of quasi long-range order at late times. We observe that a\nfinite vortex density survives the cooling process which disagrees with the\nanalytically constructed vortex-free Bose-Einstein condensate at asymptotic\ntimes. This indicates that quantum fluctuations beyond the truncated Wigner\napproximation need to be included to fully capture the physics of dissipative\nBose-Einstein condensation."
    },
    {
        "anchor": "Proposed Fermi-surface reservoir-engineering and application to\n  realizing unconventional Fermi superfluids in a driven-dissipative\n  non-equilibrium Fermi gas: We develop a theory to describe the dynamics of a driven-dissipative\nmany-body Fermi system, to pursue our proposal to realize exotic quantum states\nbased on reservoir engineering. Our idea is to design the shape of a Fermi\nsurface so as to have multiple Fermi edges, by properly attaching multiple\nreservoirs with different chemical potentials to a fermionic system. These\nemerged edges give rise to additional scattering channels that can destabilize\nthe system into unconventional states, which is exemplified in this work by\nconsidering a driven-dissipative attractively interacting Fermi gas. By\nformulating a quantum kinetic equation using the Nambu-Keldysh Green's function\ntechnique, we explore nonequilibrium steady states in this system and assess\ntheir stability. We find that, in addition to the BCS-type isotropic pairing\nstate, a Fulde-Ferrell-type anisotropic superfluid state being accompanied by\nCooper pairs with non-zero center-of-mass momentum exists as a stable solution,\neven in the absence of a magnetic Zeeman field. Our result implies a great\npotential of realizing quantum matter beyond the equilibrium paradigm, by\nengineering the shape and topology of Fermi surfaces in both electronic and\natomic systems.",
        "positive": "Permutation blocking path integral Monte Carlo: A highly efficient\n  approach to the simulation of strongly degenerate non-ideal fermions: Correlated fermions are of high interest in condensed matter (Fermi liquids,\nWigner molecules), cold atomic gases and dense plasmas. Here we propose a novel\napproach to path integral Monte Carlo (PIMC) simulations of strongly degenerate\nnon-ideal fermions at finite temperature by combining a fourth-order\nfactorization of the density matrix with antisymmetric propagators, i.e.,\ndeterminants, between all imaginary time slices. To efficiently run through the\nmodified configuration space, we introduce a modification of the widely used\ncontinuous space worm algorithm, which allows for an efficient sampling at\narbitrary system parameters. We demonstrate how the application of determinants\nachieves an effective blocking of permutations with opposite signs, leading to\na significant relieve of the fermion sign problem. To benchmark the capability\nof our method regarding the simulation of degenerate fermions, we consider\nmultiple electrons in a quantum dot and compare our results with other ab\ninitio techniques, where they are available. The present permutation blocking\npath integral Monte Carlo approach allows us to obtain accurate results even\nfor $N=20$ electrons at low temperature and arbitrary coupling, where no other\nab initio results have been reported, so far."
    },
    {
        "anchor": "Microscopic Observation of Pauli Blocking in Degenerate Fermionic\n  Lattice Gases: The Pauli exclusion principle is one of the most fundamental manifestations\nof quantum statistics. Here, we report on its local observation in a\nspin-polarized degenerate gas of fermions in an optical lattice. We probe the\ngas with single-site resolution using a new generation quantum gas microscope\navoiding the common problem of light induced losses. In the band insulating\nregime, we measure a strong local suppression of particle number fluctuations\nand a low local entropy per atom. Our work opens a new avenue for studying\nquantum correlations in fermionic quantum matter both in and out of\nequilibrium.",
        "positive": "Analytical results for a spin-orbit coupled atom held in a non-Hermitian\n  double well under synchronous combined modulation: We propose a simple method of synchronous combined modulations to generate\nthe exact analytic solutions for a spin-orbit (SO) coupled ultracold atom held\nin a non-Hermitian double-well potential. Based on the obtained analytical\nsolutions, we mainly study the parity-time ($\\mathcal{PT}$) symmetry of this\nsystem and the system stability for both balanced and unbalanced gain-loss\nbetween two wells. Under balanced gain and loss, the effect of the proportional\nconstants between synchronous combined modulations and the SO-coupling strength\non the $\\mathcal{PT}$-symmetry breaking is revealed analytically. Surprisingly,\nwe find when the Zeeman field is present, the stable spin-flipping tunneling\nbetween two wells can not occur in the non-Hermitian SO-coupled ultracold\natomic system, but the stable spin-conserving tunneling can be performed. Under\nunbalanced gain and loss, the unique set of parameter conditions that can cause\nthe system to stabilize is found. The results may provide a possibility for the\nexact control of $\\mathcal{PT}$-symmetry breaking and quantum spin dynamics in\na non-Hermitian SO-coupled system."
    },
    {
        "anchor": "Vortices on demand in multicomponent Bose-Einstein condensates: We present a simple mechanism to produce vortices at any desired spatial\nlocations in harmonically trapped Bose-Einstein condensates (BEC) with\nmulticomponent spin states coupled to external transverse and axial magnetic\nfields. The vortices appear at the spatial points where the spin-transverse\nfield interaction vanishes and, depending on the multipolar magnetic field\norder, the vortices can acquire different predictable topological charges. We\nexplicitly demonstrate our findings, both numerically and analytically, by\nanalyzing a 2D BEC via the Gross-Pitaevskii equation for atomic systems with\neither two or three internal states. We further show that, by an spontaneous\nsymmetry breaking mechanism, vortices can appear in any spin component, unless\nsymmetry is externally broken at the outset by an axial field. We suggest that\nthis scenario may be tested using an ultracold gas of $^{87}$Rb occupying all\nthree $F = 1$ states in an optical trap.",
        "positive": "Many-body effects in the out-of-equilibrium dynamics of a composite\n  bosonic Josephson junction: The out-of-equilibrium many-body quantum dynamics of an interacting Bose gas\ntrapped in a one-dimensional composite double-well potential is studied by\nsolving the many-body Schr\\\"odinger equation numerically accurately by\nemploying the multiconfigurational time-dependent Hartree for bosons (MCTDHB)\nmethod. The composite double-well is formed by merging two deformed harmonic\nwells having a hump at their centre. We characterised the dynamics by the time\nevolution of survival probability, fragmentation, and many-particle position\nand momentum variances. Our study demonstrates the prominent role played by the\nhigher orbitals in the dynamics and thereby highlighted the necessity of a\nmany-body technique like MCTDHB which can take into account all the relevant\norbitals for the accurate description of complex many-body dynamics. Further,\nwe showed that the universality of fragmentation with respect to the number of\nparticles corresponding to a particular interaction strength is also exhibited\nby the higher-order orbitals. Therefore, it is a robust phenomenon not limited\nto systems that can be described by two orbitals only."
    },
    {
        "anchor": "Nonequilibrium quantum dynamics of partial symmetry breaking for\n  ultracold bosons in an optical lattice ring trap: A vortex in a Bose-Einstein condensate on a ring undergoes quantum dynamics\nin response to a quantum quench in terms of partial symmetry breaking from a\nuniform lattice to a biperiodic one. Neither the current, a macroscopic\nmeasure, nor fidelity, a microscopic measure, exhibit critical behavior.\nInstead, the symmetry memory succeeds in identifying the point at which the\nsystem begins to forget its initial symmetry state. We further identify a\nsymmetry energy difference in the low lying excited states which trends with\nthe symmetry memory.",
        "positive": "Competing interactions in population-imbalanced two-component\n  Bose-Einstein condensates: We consider a two-component Bose-Einstein condensate with and without\nsynthetic \"spin-orbit\" interactions in two dimensions. Density- and\nphase-fluctuations of the condensate are included, allowing us to study the\nimpact of thermal fluctuations and density-density interactions on the physics\noriginating with spin-orbit interactions. In the absence of spin-orbit\ninteractions, we find that inter-component density interactions deplete the\nminority condensate. The thermally driven phase transition is driven by coupled\ndensity and phase-fluctuations, but is nevertheless shown to be a\nphase-transition in the Kosterlitz-Thouless universality class with close to\nuniversal amplitude ratios irrespective of whether both the minority- and\nmajority condensates exist in the ground state, or only one condensate exists.\nIn the presence of spin-orbit interactions we observe three separate phases,\ndepending on the strength of the spin-orbit coupling and inter-component\ndensity-density interactions: a phase-modulated phase with uniform amplitudes\nfor small intercomponent interactions, a completely imbalanced, effectively\nsingle-component, condensate for intermediate spin-orbit coupling strength and\nsuficciently large inter-component interactions, and a phase-modulated\n\\textit{and} amplitude-modulated phase for sufficiently large values of both\nthe spin-orbit coupling and the inter-component density-density interactions.\nThe phase which is modulated by a single $\\bv q$-vector only is observed to\ntransition into an isoptropic liquid through a strong de-pinning transition\nwith periodic boundary conditions, which weakens with open boundaries."
    },
    {
        "anchor": "Natural orbitals and their occupation numbers for free anyons in the\n  magnetic gauge: We investigate the properties of natural orbitals and their occupation\nnumbers of the ground state of two non-interacting anyons characterised by the\nfractional statistics parameter $\\alpha$ and confined in a harmonic trap. We\nwork in the boson magnetic gauge where the anyons are modelled as composite\nbosons with magnetic flux quanta attached to their positions. We derive an\nasymptotic form of the weakly occupied natural orbitals, and show that their\ncorresponding (ordered descendingly) occupation numbers decay according to the\npower law $n^{-(4+2\\alpha)}$, where $n$ is the index of the natural orbital. We\nfind remarkable numerical agreement of the theory with the natural orbitals and\ntheir occupation numbers computed from the spectral decomposition of the\nsystem's wavefunction. We explain that the same results apply to the fermion\nmagnetic gauge.",
        "positive": "Magnetic phases of spin-1 lattice gases with random interactions: A spin-1 atomic gas in an optical lattice, in the unit-filling Mott Insulator\n(MI) phase and in the presence of disordered spin-dependent interaction, is\nconsidered. In this regime, at zero temperature, the system is well described\nby a disordered rotationally-invariant spin-1 bilinear-biquadratic model. We\nstudy, via the density matrix renormalization group algorithm, a bounded\ndisorder model such that the spin interactions can be locally either\nferromagnetic or antiferromagnetic. Random interactions induce the appearance\nof a disordered ferromagnetic phase characterized by a non-vanishing value of\nspin-glass order parameter across the boundary between a ferromagnetic phase\nand a dimer phase exhibiting random singlet order. The study of the\ndistribution of the block entanglement entropy reveals that in this region\nthere is no random singlet order."
    },
    {
        "anchor": "Solitons in Tonks-Girardeau gas with dipolar interactions: The existence of bright solitons in the model of the Tonks-Girardeau (TG) gas\nwith dipole-dipole (DD) interactions is reported. The governing equation is\ntaken as the quintic nonlinear Schr\\\"{o}dinger equation (NLSE) with the\nnonlocal cubic term accounting for the DD attraction. In different regions of\nthe parameter space (the dipole moment and atom number), matter-wave solitons\nfeature flat-top or compacton-like shapes. For the flat-top states, the NLSE\nwith the local cubic-quintic (CQ) nonlinearity is shown to be a good\napproximation. Specific dynamical effects are studied assuming that the\nstrength of the DD interactions is ramped up or drops to zero. Generation of\ndark-soliton pairs in the gas shrinking under the action of the intensifying DD\nattraction is observed. Dark solitons exhibit the particle-like collision\nbehavior. Peculiarities of dipole solitons in the TG gas are highlighted by\ncomparison with the NLSE including the local CQ terms. Collisions between the\nsolitons are studied too. In many cases, the collisions result in merger of the\nsolitons into a breather, due to strong attraction between them.",
        "positive": "Dynamics and Thermodynamics of the Low-Temperature Strongly Interacting\n  Bose Gas: We measure the zero-temperature equation of state of a homogeneous Bose gas\nof $^7$Li atoms by analyzing the \\emph{in-situ} density distributions of\ntrapped samples. For increasing repulsive interactions our data shows a clear\ndeparture from mean-field theory and provides a quantitative test of the\nmany-body corrections first predicted in 1957 by Lee, Huang and Yang. We\nfurther probe the dynamic response of the Bose gas to a varying interaction\nstrength and compare it to simple theoretical models. We deduce a lower bound\nfor the value of the universal constant $\\xi>0.44(8)$ that would characterize\nthe universal Bose gas at the unitary limit."
    },
    {
        "anchor": "Interface properties in three-component Bose-Einstein condensates: Interface properties of a three-component Bose-Einstein condensate, in which\ncomponent 3 is sandwiched by components 1 and 2 at the interface, are\ninvestigated. It is shown that component 3 can serve as a surfactant: the net\ninterfacial tension is reduced by the presence of component 3. We calculate the\ninterfacial tension as a function of the interaction coefficients. The\nstability of the interface is studied by Bogoliubov analysis. When the\ninterfacial tension has a spatial gradient, interfacial flow is induced, which\nresembles the Marangoni flow.",
        "positive": "Fluctuations and quantum self-bound droplets in a dipolar Bose-Bose\n  mixture: We systematically investigate the properties of three-dimensional dipolar\nbinary Bose mixture at low temperatures. A set of coupled self-consistent\nequations of motion are derived for the two condensates. In the homogeneous\ncase, useful analytical formulas for the condensate depletion, the anomalous\ndensity, the ground-state energy, and the equation of state are obtained. The\ntheory is extended to the inhomogeneous case and the importance of the\ninhomogeneity is highlighted. Our results open up a new avenue for studying\ndipolar mixture droplets. Impacts of the dipole-dipole interaction on the\nstability, density profiles, and the size of the self-bound droplet are deeply\ndiscussed. The finite-temperature behavior of such a state is also examined."
    },
    {
        "anchor": "A cavity-induced artificial gauge field in a Bose-Hubbard ladder: We consider theoretically ultracold interacting bosonic atoms confined to\nquasi-one-dimensional ladder structures formed by optical lattices and coupled\nto the field of an optical cavity. The atoms can collect a spatial phase\nimprint during a cavity-assisted tunneling along a rung via Raman transitions\nemploying a cavity mode and a transverse running wave pump beam. By adiabatic\nelimination of the cavity field we obtain an effective Hamiltonian for the\nbosonic atoms, with a self-consistency condition. Using the numerical density\nmatrix renormalization group method, we obtain a rich steady state diagram of\nself-organized steady states. Transitions between superfluid to Mott-insulating\nstates occur, on top of which we can have Meissner, vortex liquid, and vortex\nlattice phases. Also a state that explicitly breaks the symmetry between the\ntwo legs of the ladder, namely the biased-ladder phase is dynamically\nstabilized.",
        "positive": "Low energy dynamics of spinor condensates: We present a derivation of the low energy Lagrangian governing the dynamics\nof the spin degrees of freedom in a spinor Bose condensate, for any phase in\nwhich the average magnetization vanishes. This includes all phases found within\nmean-field treatments except for the ferromagnet, for which the low energy\ndynamics has been discussed previously. The Lagrangian takes the form of a\nsigma model for the rotation matrix describing the local orientation of the\nspin state of the gas."
    },
    {
        "anchor": "Nonuniversal Equation of State of a Quasi-2D Bose Gas in Dimensional\n  Crossover: Equation of state (EOS) for a pure two-dimensional (2D) Bose gas exhibits a\nlogarithmic dependence on the s-wave scattering length [L. Salasnich, Phys.\nRev. Lett. 118, 130402 (2017)]. The pronounced disparity between the EOS of a\n2D Bose gas and its 3D counterpart underscores the significance of exploring\nthe dimensional crossover between these two distinct dimensions. In this work,\nwe are motivated to deduce nonuniversal corrections to EOS for an optically\ntrapped Bose gas along the dimensional crossover from 3D to 2D, incorporating\nthe finite-range effects of the interatomic potential. Employing the framework\nof effective field theory, we derive the analytical expressions for both the\nground state energy and quantum depletion. The introduction of the lattice\ninduces a transition from a 3D to a quasi-2D regime. In particular, we\nsystematically analyze the asymptotic behaviors of both the 2D and 3D aspects\nof the model system, with a specific focus on the nonuniversal effects on the\nEOS arising from finite-range interactions. The nonuniversal effects proposed\nin this study along the dimensional crossover represent a significant stride\ntoward unraveling the intricate interplay between dimensionality and quantum\nfluctuations.",
        "positive": "Emergence of a tunable crystalline order in a Floquet-Bloch system from\n  a parametric instability: Parametric instabilities in interacting systems can lead to the appearance of\nnew structures or patterns. In quantum gases, two-body interactions are\nresponsible for a variety of instabilities that depend on the characteristics\nof both trapping and interactions. We report on the Floquet engineering of such\ninstabilities, on a Bose-Einstein condensate held in a time-modulated optical\nlattice. The modulation triggers a destabilization of the condensate into a\nstate exhibiting a density modulation with a new spatial periodicity. This new\ncrystal-like order directly depends on the modulation parameters: the interplay\nbetween the Floquet spectrum and interactions generates narrow and adjustable\ninstability regions, leading to the growth, from quantum or thermal\nfluctuations, of modes with a density modulation non commensurate with the\nlattice spacing. This study demonstrates the production of metastable exotic\nstates of matter through Floquet engineering, and paves the way for further\nstudies of dissipation in the resulting phase, and of similar phenomena in\nother geometries."
    },
    {
        "anchor": "Phonon decay in 1D atomic Bose quasicondensates via Beliaev-Landau\n  damping: In a 1D Bose gas, there is no non-trivial scattering channel involving three\nBogoliubov quasiparticles that conserves both energy and momentum.\nNevertheless, we show that such 3-wave mixing processes (Beliaev and Landau\ndamping) account for their decay via interactions with thermal fluctuations.\nWithin an appropriate time window where the Fermi Golden Rule is expected to\napply, the occupation number of the initially occupied mode decays\nexponentially and the rate takes a simple analytic form. The result is shown to\ncompare favorably with simulations based on the Truncated Wigner Approximation.\nIt is also shown that the same processes slow down the exponential growth of\nphonons induced by a parametric oscillation.",
        "positive": "Lee-Yang theory of Bose-Einstein condensation: Bose-Einstein condensation happens as a gas of bosons is cooled below its\ntransition temperature, and the ground state becomes macroscopically occupied.\nThe phase transition occurs in the thermodynamic limit of many particles.\nHowever, recent experimental progress has made it possible to assemble quantum\nmany-body systems from the bottom up, for example, by adding single atoms to an\noptical lattice one at a time. Here, we show how one can predict the\ncondensation temperature of a Bose gas from the energy fluctuations of a small\nnumber of bosons. To this end, we make use of recent advances in Lee-Yang\ntheories of phase transitions, which allow us to determine the zeros and the\npoles of the partition function in the complex plane of the inverse temperature\nfrom the high cumulants of the energy fluctuations. By increasing the number of\nbosons in the trapping potential, we can predict the convergence point of the\npartition function zeros in the thermodynamic limit, where they reach the\ninverse critical temperature on the real axis. Using less than 100 bosons, we\ncan estimate the condensation temperature for a Bose gas in a harmonic\npotential in two and three dimensions, and we also find that there is no phase\ntransition in one dimension as one would expect."
    },
    {
        "anchor": "Quantum metrology with ultracold chemical reactions: Chemical chain reactions are known to enable extremely sensitive detection\nschemes in chemical, biological, and medical analysis, and have even been used\nin the search for dark matter. Here we show that coherent, ultracold chemical\nreactions harbor great potential for quantum metrology: In an atom-molecule\nBose-Einstein condensate (BEC), a weak external perturbation can modify the\nreaction dynamics and lead to the coherent creation of molecules in an\natom-dominant regime which can be selectively detected with modern\nspectroscopic techniques. This promises to substantially improve the viability\nof previously proposed BEC-based sensors for acceleration, gravitational waves,\nand other physical quantities, including the detection of dark matter, that so\nfar relied on the detection of the tiny density modulations caused by the\ncreation of single phonons.",
        "positive": "Quantum Register of Fermion Pairs: Fermions are the building blocks of matter, forming atoms and nuclei, complex\nmaterials and neutron stars. Our understanding of many-fermion systems is\nhowever limited, as classical computers are often insufficient to handle the\nintricate interplay of the Pauli principle with strong interactions. Quantum\nsimulators based on ultracold fermionic atoms instead directly realize\nparadigmatic Fermi systems, albeit in \"analog\" fashion, without coherent\ncontrol of individual fermions. Digital qubit-based quantum computation of\nfermion models, on the other hand, faces significant challenges in implementing\nfermionic anti-symmetrization, calling for an architecture that natively\nemploys fermions as the fundamental unit. Here we demonstrate a robust quantum\nregister composed of hundreds of fermionic atom pairs trapped in an optical\nlattice. With each fermion pair forming a spin-singlet, the qubit is realized\nas a set of near-degenerate, symmetry-protected two-particle wavefunctions\ndescribing common and relative motion. Degeneracy is lifted by the atomic\nrecoil energy, only dependent on mass and lattice wavelength, thereby rendering\ntwo-fermion motional qubits insensitive against noise of the confining\npotential. We observe quantum coherence beyond ten seconds. Universal control\nis provided by modulating interactions between the atoms. Via state-dependent,\ncoherent conversion of free atom pairs into tightly bound molecules, we tune\nthe speed of motional entanglement over three orders of magnitude, yielding\n$10^4$ Ramsey oscillations within the coherence time. For site-resolved\nmotional state readout, fermion pairs are coherently split into a double well,\ncreating entangled Bell pairs. The methods presented here open the door towards\nfully programmable quantum simulation and digital quantum computation based on\nfermions."
    },
    {
        "anchor": "Phase diagram of Landau-Zener phenomena in coupled one-dimensional Bose\n  quantum fluids: We study stationary and dynamical properties of the many-body Landau-Zener\ndynamics of a Bose quantum fluid confined in two coupled one-dimensional\nchains, using a many-body generalization recently reported [Y.-A. Chen et al.],\nwithin the decoupling approximation and the one-level band scheme. The energy\nspectrum evidences the structure of the avoided level crossings as a function\nof the on-site inter particle interaction strength. On the dynamical side, a\nphase diagram of the transfer efficiency across ground-state and inverse sweeps\nis presented. A totally different scenario with respect to the original\nsingle-particle Landau-Zener scheme is found for ground-state sweeps, in which\na breakdown of the adiabatic region emerges as the sweep rate decreases. On the\ncontrary, the transfer efficiency across inverse sweeps reveals consistent\nresults with the single-particle Landau-Zener predictions. In the strong\ncoupling regime, we find that there is a critical value of the on-site\ninteraction for which the transfer of particles starts to vanish independently\nof the sweep rate. Our results are in qualitative agreement with those of the\nexperimental counterpart.",
        "positive": "Bogoliubov Theory of Dipolar Bose Gas in Weak Random Potential: We consider a dilute homogeneous Bose gas with both an isotropic short-range\ncontact interaction and an anisotropic long-range dipole-dipole interaction in\na weak random potential at low temperature in three dimensions. Within the\nrealm of Bogoliubov theory we analyze how both condensate and superfluid\ndepletion are depleted due to quantum and thermal fluctuations as well as\ndisorder fluctuations."
    },
    {
        "anchor": "Swallowtail Band Structure of the Superfluid Fermi Gas in an Optical\n  Lattice: We investigate the energy band structure of the superfluid flow of ultracold\ndilute Fermi gases in a one-dimensional optical lattice along the BCS to BEC\ncrossover within a mean-field approach. In each side of the crossover region, a\nloop structure (swallowtail) appears in the Bloch energy band of the superfluid\nabove a critical value of the interaction strength. The width of the\nswallowtail is largest near unitarity. Across the critical value of the\ninteraction strength, the profiles of density and pairing field change more\ndrastically in the BCS side than in the BEC side. It is found that along with\nthe appearance of the swallowtail, there exists a narrow band in the\nquasiparticle energy spectrum close to the chemical potential and the\nincompressibility of the Fermi gas consequently experiences a profound dip in\nthe BCS side, unlike in the BEC side.",
        "positive": "Information geometry and Bose-Einstein condensation: It is a long held conjecture in the connection between information geometry\n(IG) and thermodynamics that the curvature endowed by IG diverges at phase\ntransitions. Recent work on the IG of Bose-Einstein (BE) gases challenged this\nconjecture by saying that in the limit of fugacity approaching unit -- where BE\ncondensation is expected -- curvature does not diverge, rather it converges to\nzero. However, as the discontinuous behavior that identify condensation is only\nobserved at the thermodynamic limit, a study of IG curvature at finite number\nof particles, $N$, is in order from which the thermodynamic behaviour can be\nobserved by taking the thermodynamic limit ($N\\to \\infty$) posteriorly. This\narticle presents such study, which was made possible by the recent advances\npresented in [Phys. Rev. A 104, 043318 (2021)]. We find that for a trapped gas,\nas $N$ increases, the values of curvature decrease proportionally to a power of\n$N$ while the temperature at which the maximum value of curvature occurs\napproaches the usually defined critical temperature. This means that, in the\nthermodynamic limit, curvature has a limited value where a phase transition is\nobserved, contradicting the forementioned conjecture."
    },
    {
        "anchor": "Quantum Spin Ice and dimer models with Rydberg atoms: Quantum spin ice represents a paradigmatic example on how the physics of\nfrustrated magnets is related to gauge theories. In the present work we address\nthe problem of approximately realizing quantum spin ice in two dimensions with\ncold atoms in optical lattices. The relevant interactions are obtained by\nweakly admixing van der Waals interactions between laser admixed Rydberg states\nto the atomic ground state atoms, exploiting the strong angular dependence of\ninteractions between Rydberg p-states together with the possibility of\ndesigning step-like potentials. This allows us to implement Abelian gauge\ntheories in a series of geometries, which could be demonstrated within state of\nthe art atomic Rydberg experiments. We numerically analyze the family of\nresulting microscopic Hamiltonians and find that they exhibit both classical\nand quantum order by disorder, the latter yielding a quantum plaquette valence\nbond solid. We also present strategies to implement Abelian gauge theories\nusing both s- and p-Rydberg states in exotic geometries, e.g. on a 4-8 lattice.",
        "positive": "Linear Response of a Periodically Driven Thermal Dipolar Gas: We study the nonequilibrium dynamics of an ultracold, non-degenerate dipolar\ngas of $^{164}$Dy atoms in a cylindrically symmetric harmonic trap. To do so,\nwe investigate the normal modes and linear response of the gas when driven by\nmeans of periodic modulations to the trap axial-frequency. We find that the\nresonant response of the gas depends strongly on the dipole alignment axis,\nowing to anisotropies in the differential cross section of the atoms. We employ\nthe use of the method of averages as well as numerical Monte Carlo methods for\nour analysis. A striking result is that certain normal modes, termed \"melting\nmodes\", initiated in an anisotropic out-of-equilibrium configuration, relax to\nequilibrium without oscillating."
    },
    {
        "anchor": "Anomalous isothermal compressibility in spin-orbit coupled degenerate\n  Fermi gases: The spin-orbit coupling (SOC) in degenerate Fermi gases can fundamentally\nchange the fate of $s$-wave superfluids with strong Zeeman field and give rise\nto topological superfluids and associated Majorana zero modes. It also\ndramatically changes the thermodynamic properties of the superfluids. Here we\nreport the anomalous isothermal compressibility $\\kappa_T$ in this superfluids\nwith both SOC and Zeeman field. We formulate this quantity from the Gibbs-Duhem\nequation and show that the contribution of $\\kappa_T$ comes from the explicit\ncontribution of chemical potential and implicit contribution of order\nparameter. In the Bardeen-Cooper-Schrieffer (BCS) limit, this compressibility\nis determined by the density of state near the Fermi surface; while in the Bose\nEinstein condensate (BEC) regime it is determined by the scattering length.\nBetween these two limits, we find that the anomalous peaks can only be found in\nthe gapless Weyl phase regime. This anomalous behavior can be regarded as a\nremanent effect of phase separation. The similar physics can also be found in\nthe lattice model away from half filling. These predictions can be measured\nfrom the anomalous response of sound velocity and fluctuation of carrier\ndensity.",
        "positive": "Hydrodynamic Instability and Turbulence in Quantum Fluids: Superfluid turbulence consisting of quantized vortices is called quantum\nturbulence (QT). Quantum turbulence and quantized vortices were discovered in\nsuperfluid $^4$He about 50 years ago, but innovation has occurred recently in\nthis field. One is in the field of superfluid helium. Statistical quantities\nsuch as energy spectra and probability distribution function of the velocity\nfield have been accessible both experimentally and numerically. Visualization\ntechnique has developed and succeeded in the direct visualization of quantized\nvortices. The other innovation is in the field of atomic Bose-Einstein\ncondensation. The modern optical technique has enabled us to control and\nvisualize directly the condensate and quantized vortices. Various kinds of\nhydrodynamic instability have been revealed. Even QT is realized\nexperimentally. This article describes such recent developments as well as the\nmotivation of studying QT."
    },
    {
        "anchor": "Creating fractional quantum Hall states with atomic clusters using\n  light-assisted insertion of angular momentum: We describe a protocol to prepare clusters of ultracold bosonic atoms in\nstrongly-interacting states reminiscent of fractional quantum Hall states. Our\nscheme consists in injecting a controlled amount of angular momentum to an\natomic gas using Raman transitions carrying orbital angular momentum. By\ninjecting one unit of angular momentum per atom, one realizes a single-vortex\nstate, which is well described by mean field theory for large enough particle\nnumbers. We also present schemes to realize fractional quantum Hall states,\nnamely the bosonic Laughlin and Moore-Read states. We investigate the\nrequirements for adiabatic nucleation of a such topological states, in\nparticular comparing linear Landau-Zener ramps and arbitrary ramps obtained\nfrom optimized control methods. We also show that this protocol requires\nexcellent control over the isotropic character of the trapping potential.",
        "positive": "Noise-Free Generation of Bright Matter-Wave Solitons: We show how access to sufficiently flexible trapping potentials could be\nexploited in the generation of three-dimensional atomic bright matter-wave\nsolitons. Our proposal provides a route towards producing bright solitonic\nstates with good fidelity, in contrast to, for example, a non-adiabatic\nsweeping of an applied magnetic field through a Feshbach resonance."
    },
    {
        "anchor": "Stationary states, dynamical stability, and vorticity of Bose-Einstein\n  condensates in tilted rotating harmonic traps: We theoretically investigate a Bose-Einstein condensate confined by a\nrotating harmonic trap whose rotation axis is not aligned with any of its\nprincipal axes. The principal axes of the Thomas-Fermi density profiles of the\nresulting stationary solutions are found to be tilted with respect to those of\nthe rotating trap, representing an extra degree of freedom that is associated\nwith the existence of additional branches of stationary solutions for any given\nrotation axis alignment. By linearizing the time-dependent theory about the\nstationary states, we obtain a semi-analytical prediction of their dynamical\ninstability at high rotation frequencies against collective modes arising from\nenvironmental perturbations. Comparing the stationary states to direct\nsimulations of the Gross-Pitaevskii equation, we predict the nucleation of\nquantum vortices in the dynamically unstable rotational regime. These vortex\nlines are aligned along the rotation axis despite the tilting of the rotating\ntrap although the background density profile is tilted with respect to the\ntrapping and rotation axes.",
        "positive": "Interacting heavy fermions in a disordered optical lattice: We have theoretically studied the effect of disorder on ultracold\nalkaline-earth atoms governed by the Kondo lattice model in an optical lattice\nvia simplified double-well model and hybridization mean-field theory.\nDisorder-induced narrowing and even complete closure of hybridization gap have\nbeen predicted and the compressibility of the system has also been investigated\nfor metallic and Kondo insulator phases in the presence of the disordered\npotential. To make connection to the experimental situation, we have\nnumerically solved the disordered Kondo lattice model with an external harmonic\ntrap and shown both the melting of Kondo insulator plateau and an\ncompressibility anomaly at low-density."
    },
    {
        "anchor": "Quantum scarred eigenstates in a Rydberg atom chain: entanglement,\n  breakdown of thermalization, and stability to perturbations: Recent realization of a kinetically-constrained chain of Rydberg atoms by\nBernien et al. [Nature 551, 579 (2017)] resulted in the observation of unusual\nrevivals in the many-body quantum dynamics. In our previous work\n[arXiv:1711.03528] such dynamics was attributed to the existence of \"quantum\nscarred\" eigenstates in the many-body spectrum of the experimentally realized\nmodel. Here we present a detailed study of the eigenstate properties of the\nsame model. We find that the majority of the eigenstates exhibit anomalous\nthermalization: the observable expectation values converge to their Gibbs\nensemble values, but parametrically slower compared to the predictions of the\neigenstate thermalization hypothesis (ETH). Amidst the thermalizing spectrum,\nwe identify non-ergodic eigenstates that strongly violate the ETH, whose number\ngrows polynomially with system size. Previously, the same eigenstates were\nidentified via large overlaps with certain product states, and were used to\nexplain the revivals observed in experiment. Here we find that these\neigenstates, in addition to highly atypical expectation values of local\nobservables, also exhibit sub-thermal entanglement entropy that scales\nlogarithmically with the system size. Moreover, we identify an additional class\nof quantum scarred eigenstates, and discuss their manifestations in the\ndynamics starting from initial product states. We use forward scattering\napproximation to describe the structure and physical properties of\nquantum-scarred eigenstates. Finally, we discuss the stability of quantum scars\nto various perturbations. We observe that quantum scars remain robust when the\nintroduced perturbation is compatible with the forward scattering\napproximation. In contrast, the perturbations which most efficiently destroy\nquantum scars also lead to the restoration of \"canonical\" thermalization.",
        "positive": "Energy spectra of two interacting fermions with spin-orbit coupling in a\n  harmonic trap: We explore the two-body spectra of spin-$1/2$ fermions in isotropic harmonic\ntraps with external spin-orbit potentials and short range two-body\ninteractions. Using a truncated basis of total angular momentum eigenstates,\nnon-perturbative results are presented for experimentally realistic forms of\nthe spin-orbit coupling: a pure Rashba coupling, Rashba and Dresselhaus\ncouplings in equal parts, and a Weyl-type coupling. The technique is easily\nadapted to bosonic systems and other forms of spin-orbit coupling."
    },
    {
        "anchor": "Dynamic structure factor of one-dimensional Fermi superfluid with\n  spin-orbit coupling: We theoretically calculate the density dynamic structure factor of\none-dimensional Fermi superfluid with Raman-type spin-orbit coupling, and\nanalyze its main dynamical character during phase transition between\nBardeen-Cooper-Schrieffer superfluid and topological superfluid. Our\ntheoretical results display four kinds of single-particle excitations induced\nby the two-branch structure of single-particle spectrum, and the cross\nsingle-particle excitation is much easier to be seen in the spin dynamic\nstructure factor at a small transferred momentum. Also we find a new roton-like\ncollective mode emerges at a fixed transferred momentum $q \\simeq 2k_F$, and it\nonly appears once the system enters the topological superfluid state. The\noccurrence of this roton-like excitation is related to switch of global minimum\nin single-particle spectrum from $k=0$ to $k \\simeq 2k_F$.",
        "positive": "Non-integer Floquet Sidebands Spectroscopy: In the quantum system under periodical modulation, the particle can be\nexcited by absorbing the laser photon with the assistance of integer Floquet\nphotons, so that the Floquet sidebands appear. Here, we experimentally observe\nnon-integer Floquet sidebands (NIFBs) emerging between the integer ones while\nincreasing the strength of the probe laser in the optical lattice clock system.\nThen, we propose the Floquet channel interference hypothesis (FCIH) which\nsurprisingly matches quantitatively well with both experimental and numerical\nresults. With its help, we found both Rabi and Ramsey spectra are very\nsensitive to the initial phase and exhibit additional two symmetries. More\nimportantly, the height of Ramsey NIFBs is comparable to the integer one at\nlarger $g/\\omega_s$ which indicates an exotic phenomenon beyond the\nperturbative description. Our work provides new insight into the spectroscopy\nof the Floquet system and has potential application in quantum technology."
    },
    {
        "anchor": "Quantized Thouless pumps protected by interactions in dimerized Rydberg\n  tweezer arrays: We study Thouless pumps, i.e., adiabatic topological transport, in an\ninteracting spin chain described by the dimerized XXZ Hamiltonian. In the\nnoninteracting case, quantized Thouless pumps can only occur when a topological\nsingularity is encircled adiabatically. In contrast, here we show that, in the\npresence of interactions, such topological transport can even persist for\nexotic paths in which the system gets arbitrarily close to the singularity. We\nillustrate the robustness of these exotic Thouless pumps through the behavior\nof the noninteracting singularity, which for sufficiently strong interactions\nsplits into two singularities separated by a spontaneous antiferromagnetic\ninsulator. We perform a numerical benchmark of these phenomena by means of\ntensor network simulations of ground-state physics and real-time adiabatic\ndynamics. Finally, we propose an experimental protocol with Floquet-driven\nRydberg tweezer arrays.",
        "positive": "Lieb-Liniger model: emergence of dark solitons in the course of\n  measurements of particle positions: Lieb-Liniger model describes bosons with contact interactions in\none-dimensional space. In the limit of weak repulsive particle interactions,\nthere are two types of low lying excitation spectrum. The first is reproduced\nby the Bogoliubov dispersion relation, the other is believed to correspond to\ndark soliton excitations. While there are various evidences that the type II\nspectrum is related to dark solitons, it has not been shown that measurements\nof positions of particles reveal dark soliton density profiles. Here, we employ\nthe Bethe ansatz approach and show that dark solitons emerge in the measurement\nprocess if the system is prepared in an eigenstate corresponding to the type II\nspectrum. We analyze single and double dark solitons as well as weak and strong\ninteraction regime."
    },
    {
        "anchor": "Hysteresis in a quantized, superfluid atomtronic circuit: Atomtronics is an emerging interdisciplinary field that seeks new\nfunctionality by creating devices and circuits where ultra-cold atoms, often\nsuperfluids, play a role analogous to the electrons in electronics. Hysteresis\nis widely used in electronic circuits, e.g., it is routinely observed in\nsuperconducting circuits and is essential in rf-superconducting quantum\ninterference devices [SQUIDs]. Furthermore, hysteresis is as fundamental to\nsuperfluidity (and superconductivity) as quantized persistent currents,\ncritical velocity, and Josephson effects. Nevertheless, in spite of multiple\ntheoretical predictions, hysteresis has not been previously observed in any\nsuperfluid, atomic-gas Bose-Einstein condensate (BEC). Here we demonstrate\nhysteresis in a quantized atomtronic circuit: a ring of superfluid BEC\nobstructed by a rotating weak link. We directly detect hysteresis between\nquantized circulation states, in contrast to superfluid liquid helium\nexperiments that observed hysteresis directly in systems where the quantization\nof flow could not be observed and indirectly in systems that showed quantized\nflow. Our techniques allow us to tune the size of the hysteresis loop and to\nconsider the fundamental excitations that accompany hysteresis. The results\nsuggest that the relevant excitations involved in hysteresis are vortices and\nindicate that dissipation plays an important role in the dynamics. Controlled\nhysteresis in atomtronic circuits may prove to be a crucial feature for the\ndevelopment of practical devices, just as it has in electronic circuits like\nmemory, digital noise filters (e.g., Schmitt triggers), and magnetometers\n(e.g., SQUIDs).",
        "positive": "Landau instability and mobility edges of the interacting one-dimensional\n  Bose gas in weak random potentials: We study the frictional force exerted on the trapped, interacting 1D Bose gas\nunder the influence of a moving random potential. Specifically we consider weak\npotentials generated by optical speckle patterns with finite correlation\nlength. We show that repulsive interactions between bosons lead to a superfluid\nresponse and suppression of frictional force, which can inhibit the onset of\nAnderson localisation. We perform a quantitative analysis of the Landau\ninstability based on the dynamic structure factor of the integrable\nLieb-Liniger model and demonstrate the existence of effective mobility edges."
    },
    {
        "anchor": "Anomalous oscillations of dark solitons in trapped dipolar condensates: Thanks to their immense purity and controllability, dipolar Bose-Einstein\ncondensates are an exemplar for studying fundamental non-local nonlinear\nphysics. Here we show that a family of fundamental nonlinear waves - the dark\nsolitons - are supported in trapped quasi-one-dimensional dipolar condensates\nand within reach of current experiments. Remarkably, the oscillation frequency\nof the soliton is strongly dependent on the atomic interactions, in stark\ncontrast to the non-dipolar case. The failure of a particle analogy, so\nsuccessful for dark solitons in general, to account for this behaviour implies\nthat these structures are inherently extended and non-particle-like. These\nhighly-sensitive waves may act as mesoscopic probes of the underlying quantum\nmatter field.",
        "positive": "Stable vortex loops in two-species BECs: We consider the creation of stable, stationary closed vortex loops, analogue\nto the vortons and superconducting cosmic strings, in cold atom BEC's. We\nexplore the parameter region where these solutions are likely to exist and\ncomment on methods to create them experimentally."
    },
    {
        "anchor": "Second-order topological insulator in periodically driven lattice: The higher-order topological insulator (HOTI) is a new type of topological\nsystem which has special bulkedge correspondence compared with conventional\ntopological insulators. In this work, we propose a scheme to realize Floquet\nHOTI in ultracold atom systems. With the combination of periodically\nspin-dependent driving of the superlattices and a next-next-nearest-neighbor\nd-wave-like anisotropic coupling term between different spin components, a\nFloquet second-order topological insulator with four zero-energy corner states\nemerges, whose Wannier bands are gapless and exhibit interesting bulk topology.\nFurthermore, the anisotropic coupling with nearest-neighbor form will also\ninduce some intriguing topological phenomena, e.g. non-topologically protected\ncorner states and topological semimetal for two different types of lattice\nstructures respectively. Our scheme may give insight into the construction of\ndifferent types of higher-order topological insulators in synthetic systems. It\nalso provides an experimentally feasible platform to research the relations\nbetween different types of topological states and may have a wide range of\napplications in future.",
        "positive": "Quench between a Mott insulator and a Lieb-Liniger liquid: In this work we study a quench between a Mott insulator and a repulsive\nLieb-Liniger liquid. We find explicitly the stationary state when a long time\nhas passed after the quench. It is given by a GGE density matrix which we\ncompletely characterize, calculating the quasiparticle density describing the\nsystem after the quench. In the long time limit we find an explicit form for\nthe local three body density density density correlation function and the\nasymptotic long distance limit of the density density correlation function. The\nlater is shown to have a Gaussian decay at large distances."
    },
    {
        "anchor": "Quantum Bose and Fermi gases with large negative scattering length in\n  the 2-body S-matrix approximation: We study both Bose and Fermi gases at finite temperature and density in an\napproximation that sums an infinite number of many body processes that are\nreducible to 2-body scatterings. This is done for arbitrary negative scattering\nlength, which interpolates between the ideal and unitary gas limits. In the\nunitary limit, we compute the first four virial coefficients within our\napproximation. The second virial coefficient is exact, and we extend the\npreviously known result for fermions to bosons, and also for both bosons and\nfermions for the upper branch on the other side of unitarity (infinitely large\npositive scattering length). Assuming bosons can exist in a meta-stable state\nbefore undergoing mechanical collapse, we map out the critical temperatures for\nstrongly coupled Bose-Einstein condensation as a function of scattering length.",
        "positive": "Ising antiferromagnet with ultracold bosonic mixtures confined in a\n  harmonic trap: We present accurate results based on Quantum Monte Carlo simulations of\ntwo-component bosonic systems on a square lattice and in the presence of an\nexternal harmonic confinement. Starting from hopping parameters and interaction\nstrengths which stabilize the Ising antiferromagnetic phase in the homogeneous\ncase and at half integer filling factor, we study how the presence of the\nharmonic confinement challenge the realization of such phase. We consider\nrealistic trapping frequencies and number of particles, and establish under\nwhich conditions, i.e. total number of particles and population imbalance, the\nantiferromagnetic phase can be observed in the trap."
    },
    {
        "anchor": "Spontaneous symmetry breaking of Bose-Fermi mixtures in double-well\n  potentials: We study the spontaneous symmetry breaking (SSB) of a superfluid Bose-Fermi\n(BF) mixture in a double-well potential (DWP). The mixture is described by the\nGross-Pitaevskii equation (GPE) for the bosons, coupled to an equation for the\norder parameter of the Fermi superfluid, which is derived from the respective\ndensity functional in the unitarity limit (a similar model applies to the BCS\nregime too). Straightforward SSB in the degenerate Fermi gas loaded into a DWP\nis impossible, as it requires an attractive self-interaction, while the\nintrinsic nonlinearity in the Fermi gas is repulsive. Nonetheless, we\ndemonstrate that the symmetry breaking is possible in the mixture with\nattraction between fermions and bosons, like 40K and 87Rb. Numerical results\nare represented by dependencies of asymmetry parameters for both components on\nparticle numbers of the mixture, N_F and N_B, and by phase diagrams in the\n(N_F,N_B) plane, which displays regions of symmetric and asymmetric ground\nstates. The dynamical picture of the SSB, induced by a gradual transformation\nof the single-well potential into the DWP, is reported too. An analytical\napproximation is proposed for the case when GPE for the boson wave function may\nbe treated by means of the Thomas-Fermi (TF) approximation. Under a special\nlinear relation between N_F and N_B, the TF approximation allows us to reduce\nthe model to a single equation for the fermionic function, which includes\ncompeting repulsive and attractive nonlinear terms. The latter one directly\ndisplays the mechanism of the generation of the effective attraction in the\nFermi superfluid, mediated by the bosonic component of the mixture.",
        "positive": "Berry curvature effects in the Bloch oscillations of a quantum particle\n  under a strong (synthetic) magnetic field: We study the magnetic Bloch oscillations performed by a quantum particle\nmoving in a two-dimensional lattice in the presence of a strong (synthetic)\nmagnetic field and a uniform force. An elementary derivation of the Berry\ncurvature effect on the semiclassical trajectory is given as well as an\nexplicit connection to the classical Hall effect in the continuum limit.\nPerspectives to observe these effects in optical systems using synthetic gauge\nfields for photons are discussed."
    },
    {
        "anchor": "Singlet Mott State Simulating the Bosonic Laughlin Wave Function: We study properties of a class of spin singlet Mott states for arbitrary spin\nS bosons on a lattice, with particle number per cite n=S/l+1, where l is a\npositive integer. We show that such a singlet Mott state can be mapped to a\nbosonic Laughlin wave function on the sphere with a finite number of particles\nat filling {\\nu}=1/2l. Spin, particle and hole excitations in the Mott state\nare discussed, among which the hole excitation can be mapped to the quasi-hole\nof the bosonic Laughlin wave function. We show that this singlet Mott state can\nbe realized in a cold atom system on optical lattice, and can be identified\nusing Bragg spectroscopy and Stern-Gerlach techniques. This class of singlet\nMott states may be generalized to simulate bosonic Laughlin states with filling\n{\\nu}=q/2l.",
        "positive": "Eight-dimensional topological systems simulated using time-space\n  crystalline structures: We demonstrate the possibility of using time-space crystalline structures to\nsimulate eight-dimensional systems based on only two physical dimensions. A\nsuitable choice of system parameters allows us to obtain a gapped energy\nspectrum, making topological effects become relevant. The nontrivial topology\nof the system is evinced by considering the adiabatic state pumping along\ntemporal and spatial crystalline directions. Analysis of the system is\nfacilitated by rewriting the system Hamiltonian in a tight-binding form,\nthereby putting space, time, and the additional synthetic dimensions on an\nequal footing."
    },
    {
        "anchor": "Keldysh field theory for nonequilibrium condensation in a parametrically\n  pumped polariton system: We develop a quantum field theory for parametrically pumped polaritons using\nKeldysh Green's function techniques. By considering the mean-field and Gaussian\nfluctuations, we find that the low energy physics of the highly non-equilibrium\nphase transition to the optical parametric oscillator regime is in many ways\nsimilar to equilibrium condensation. In particular, we show that this phase\ntransition can be associated with an effective chemical potential, at which the\nsystem's bosonic distribution function diverges, and an effective temperature.\nAs in equilibrium systems, the transition is achieved by tuning this effective\nchemical potential to the energy of the lowest normal mode. Since the\noccupations of the modes are available, we determine experimentally observable\nproperties, such as the luminescence and absorption spectra.",
        "positive": "Collisions of Majorana Zero Modes: We investigate the collisions of Majorana zero modes, which are presented as\ninter-soliton collisional events in fermionic superfluids with spin-orbit\ncoupling. Our results demonstrate that, the zero energy splitting, induced by\nthe overlapping of inter-soliton Majorana wave-functions upon collision,\ngenerates an effective repulsive force for Majorana states, which in turn\nprotected themselves against into bulk excitation. As a result, the collision\nbetween solitons associated with Majorana zero modes appears to be repulsive\nand elastic, as they do not penetrate each other but instead repel without\nenergy loss. As well, similar repulsive behavior is observed in collisions\nbetween soliton-induced and defect-pinned Majorana zero modes. Our research\noffers new insights into the features of Majorana fermions, and robustness in\nthe collisions of Majorana zero modes bodes well for the prospects of\ntopological quantum computation with a multitude of Majorana qubits."
    },
    {
        "anchor": "Local correlations in the attractive 1D Bose gas: from Bethe ansatz to\n  the Gross-Pitaevskii equation: We consider the ground-state properties of an extended one-dimensional Bose\ngas with pointwise attractive interactions. We take the limit where the\ninteraction strength goes to zero as the system size increases at fixed\nparticle density. In this limit the gas exhibits a quantum phase transition. We\ncompute local correlation functions at zero temperature, both at finite and\ninfinite size. We provide analytic formulas for the experimentally relevant\none-point functions $g_2$, $g_3$ and analyze their finite-size corrections. Our\nresults are compared to the mean-field approach based on the Gross-Pitaevskii\nequation which yields the exact results in the infinite system size limit, but\nnot for finite systems.",
        "positive": "Probing phase-separation in Bose-Fermi mixtures by the critical\n  superfluid velocity: We investigate the effect exerted by spin-polarized fermions on the\ninteraction between superfluid bosons for a Bose-Fermi mixture residing on an\noptical lattice, with particular emphasis on the possibility of an induced\nphase-separation. Using a set of microscopic parameters relevant to a\n$^{40}$K-$^{87}$Rb mixture, we show how the phase-separation criterion may be\ndirectly probed by means of the critical superfluid velocity of the bosonic\ncondensate. We report quantitative results for the magnitude of the superfluid\nvelocity and its dependence on the trap depth, the boson-fermion interaction,\nand the fermionic filling fraction. All of these parameters can be controlled\nexperimentally in a well-defined manner. We propose an experimental setup for\nprobing the critical superfluid velocity."
    },
    {
        "anchor": "Cubic-quintic nonlinearity in superfluid Bose-Bose mixtures in optical\n  lattices: Heavy solitary waves, barrier-induced criticality, and\n  current-phase relations: We study superfluid (SF) states of strongly interacting Bose-Bose mixtures\nwith equal mass and intra-component interaction in optical lattices both in the\npresence and absence of a barrier potential (BP). We show that the SF order\nparameters obey the two-component nonlinear Schroedinger equation (NLSE) with\nnot only cubic but also quintic nonlinearity in the vicinity of the first-order\ntransitions to the Mott insulators with even fillings. In the case of no BP, we\nanalyze solitary-wave (SW) solutions of the cubic-quintic NLSE. When the SF\nstate changes from a ground state to a metastable one, a standard dark SW turns\ninto a bubble-like dark SW, which has a non-vanishing density dip and no pi\nphase kink even in the case of a standing SW. It is shown that the former and\nlatter SW are dynamically unstable against an out-of-phase fluctuation and an\nin-phase fluctuation, respectively, and the dynamical instabilities are\nweakened when one approaches the transition point. We find that the size and\nthe inertial mass of the SW diverge at the first-order transition point. We\nsuggest that the divergence of the inertial mass may be detected through\nmeasurement of the relation between the velocity and the phase jump of the SW.\nIn the presence of BP, we reveal that when the barrier strength exceeds a\ncertain critical value, the SF state that was metastable without the barrier is\ndestabilized towards complete disjunction of the SF. The presence of the\ncritical BP strength indicates that the strong BP qualitatively changes the\ncriticality near the metastability limit of the SF state. We derive critical\nbehaviors of the density, the compressibility, and the critical current near\nthe metastability limit induced by the BP. It is also found that the relation\nbetween the supercurrent and the phase jump across the BP exhibits a peculiar\nbehavior, owing to the non-topological nature of the bubble-like SW.",
        "positive": "Enhanced Superexchange in a Tilted Mott Insulator: In an optical lattice entropy and mass transport by first-order tunneling is\nmuch faster than spin transport via superexchange. Here we show that adding a\nconstant force (tilt) suppresses first-order tunneling, but not spin transport,\nrealizing new features for spin Hamiltonians. Suppression of the superfluid\ntransition can stabilize larger systems with faster spin dynamics. For the\nfirst time in a many-body spin system, we vary superexchange rates by over a\nfactor of 100 and tune spin-spin interactions via the tilt. In a tilted\nlattice, defects are immobile and pure spin dynamics can be studied."
    },
    {
        "anchor": "SuperVortexNet: Reconstructing Superfluid Vortex Filaments Using Deep\n  Learning: We introduce a novel approach to the three-dimensional reconstruction of\nsuperfluid vortex filaments using deep convolutional neural networks.\nSuperfluid vortices, quantum mechanical phenomena of immense scientific\ninterest, are challenging to image due to their small dimensions and intricate\ntopology. Here, we propose a deep-learning methodology that serves as a\nproof-of-principle for fully reconstructing the topology of superfluid vortex\nfilaments. We have trained a convolutional neural network on a large dataset of\nsimulated superfluid density images obtained by solving the Gross--Pitaevskii\nequation at scale, enabling it to learn the complex patterns and features\ninherent to superfluid vortex filaments. The network ingests the integrated\ndensity along the axial, coronal, and sagittal directions and outputs the\nreconstructed superfluid vortex filaments in three dimensions. We demonstrate\nthe success of this approach over a range of vortex densities of simulated\nisotropic quantum turbulence, enabling access to the characteristic scaling law\nof the decaying vortex line length.",
        "positive": "Observation of Stable Jones-Roberts Solitons in Bose-Einstein\n  Condensates: We experimentally generate two-dimensional Jones-Roberts solitons in a\nthree-dimensional atomic Bose-Einstein condensate by imprinting a triangular\nphase pattern. By monitoring their dynamics we observe that this kind of\nsolitary waves are resistant to both dynamic (snaking) and thermodynamic\ninstabilities, that usually are known to strongly limit the lifetime of dark\nplane solitons in dimensions higher than one. We additionally find signatures\nof a possible dipole-like interaction between them. Our results confirm that\nJones-Roberts solitons are stable solutions of the non-linear Schr\\\"odinger\nequation in higher dimensions and promote these excitations for applications\nbeyond matter wave physics, like energy and information transport in noisy and\ninhomogeneous environments."
    },
    {
        "anchor": "Quantitative study of quasi-one-dimensional Bose gas experiments via the\n  stochastic Gross-Pitaevskii equation: The stochastic Gross-Pitaevskii equation is shown to be an excellent model\nfor quasi-one-dimensional Bose gas experiments, accurately reproducing the in\nsitu density profiles recently obtained in the experiments of Trebbia et al.\n[Phys. Rev. Lett. 97, 250403 (2006)] and van Amerongen et al. [Phys. Rev. Lett.\n100, 090402 (2008)], and the density fluctuation data reported by Armijo et al.\n[Phys. Rev. Lett. 105, 230402 (2010)]. To facilitate such agreement, we propose\nand implement a quasi-one-dimensional stochastic equation for the low-energy,\naxial modes, while atoms in excited transverse modes are treated as independent\nideal Bose gases.",
        "positive": "Emergent Bloch oscillations in a kinetically constrained Rydberg spin\n  lattice: We explore the relaxation dynamics of elementary spin clusters of a\nkinetically constrained spin system. Inspired by experiments with Rydberg\nlattice gases, we focus on the situation in which an excited spin leads to a\n\"facilitated\" excitation of a neighboring spin. We show that even weak\ninteractions that extend beyond nearest neighbors can have a dramatic impact on\nthe relaxation behavior: they generate a linear potential, which under certain\nconditions leads to the onset of Bloch oscillations of spin clusters. These\nhinder the expansion of a cluster and more generally the relaxation of\nmany-body states towards equilibrium. This shows that non-ergodic behavior in\nkinetically constrained systems may occur as a consequence of the interplay\nbetween reduced connectivity of many-body states and weak interparticle\ninteractions. We furthermore show that the emergent Bloch oscillations\nidentified here can be detected in experiment through measurements of the\nRydberg atom density, and discuss how spin-orbit coupling between internal and\nexternal degrees of freedom of spin clusters can be used to control their\nrelaxation behavior."
    },
    {
        "anchor": "Efficient numerical methods for computing ground states and dynamics of\n  dipolar Bose-Einstein condensates: New efficient and accurate numerical methods are proposed to compute ground\nstates and dynamics of dipolar Bose-Einstein condensates (BECs) described by a\nthree-dimensional (3D) Gross-Pitaevskii equation (GPE) with a dipolar\ninteraction potential. Due to the high singularity in the dipolar interaction\npotential, it brings significant difficulties in mathematical analysis and\nnumerical simulations of dipolar BECs. In this paper, by decoupling the\ntwo-body dipolar interaction potential into short-range (or local) and\nlong-range interactions (or repulsive and attractive interactions), the GPE for\ndipolar BECs is reformulated as a Gross-Pitaevskii-Poisson type system. Based\non this new mathematical formulation, we prove rigorously existence and\nuniqueness as well as nonexistence of the ground states, and discuss the\nexistence of global weak solution and finite time blowup of the dynamics in\ndifferent parameter regimes of dipolar BECs. In addition, a backward Euler sine\npseudospectral method is presented for computing the ground states and a\ntime-splitting sine pseudospectral method is proposed for computing the\ndynamics of dipolar BECs. Due to the adaption of new mathematical formulation,\nour new numerical methods avoid evaluating integrals with high singularity and\nthus they are more efficient and accurate than those numerical methods\ncurrently used in the literatures for solving the problem.\n  Extensive numerical examples in 3D are reported to demonstrate the efficiency\nand accuracy of our new numerical methods for computing the ground states and\ndynamics of dipolar BECs.",
        "positive": "Formation and structure of vortex lattices in a rotating double-well\n  Bose-Einstein condensate: We investigate the dynamics of vortex formation and the structure of vortex\nlattices in a Bose-Einstein condensate confined within a rotating double-well\n(DW) potential. The dynamical process is a formation process of \"ghost\"\nvortices, \"hidden\" vortices and \"visible\" vortices. The critical rotation\nfrequency for the creation of visible vortex is indicated by a sudden jump in\nthe angular momentum evolution and an inflexion in the energy evolution.\nDifferent visible vortex structures can be formed by ruling the rotation\nfrequency. In particular, structural change of visible vortex patterns can be\nachieved by regulating the anisotropy parameter of the DW potential. This\nfeature allows to flexibly control the distribution of angular momentum in\nmacroscopic quantum systems and study the interplay among rotation,\ninterparticle interaction and external potential in superfluids."
    },
    {
        "anchor": "Solitons under spatially localized cubic-quintic-septimal nonlinearities: We explore stability regions for solitons in the nonlinear Schrodinger\nequation with a spatially confined region carrying a combination of\nself-focusing cubic and septimal terms, with a quintic one of either focusing\nor defocusing sign. This setting can be implemented in optical waveguides based\non colloids of nanoparticles. The solitons stability is identified by solving\nlinearized equations for small perturbations, and is found to fully comply with\nthe Vakhitov-Kolokolov criterion. In the limit case of tight confinement of the\nnonlinearity, results are obtained in an analytical form, approximating the\nconfinement profile by a delta-function. It is found that the confinement\ngreatly increases the largest total power of stable solitons, in the case when\nthe quintic term is defocusing, which suggests a possibility to create tightly\nconfined high-power light beams guided by the spatial modulation of the local\nnonlinearity strength.",
        "positive": "Alkaline earth atoms in optical tweezers: We demonstrate single-shot imaging and narrow-line cooling of individual\nalkaline earth atoms in optical tweezers; specifically, strontium-88 atoms\ntrapped in $515.2~\\text{nm}$ light. We achieve high-fidelity\nsingle-atom-resolved imaging by detecting photons from the broad singlet\ntransition while cooling on the narrow intercombination line, and extend this\ntechnique to highly uniform two-dimensional arrays of $121$ tweezers. Cooling\nduring imaging is based on a previously unobserved narrow-line Sisyphus\nmechanism, which we predict to be applicable in a wide variety of experimental\nsituations. Further, we demonstrate optically resolved sideband cooling of a\nsingle atom close to the motional ground state of a tweezer. Precise\ndetermination of losses during imaging indicate that the branching ratio from\n$^1$P$_1$ to $^1$D$_2$ is more than a factor of two larger than commonly\nquoted, a discrepancy also predicted by our ab initio calculations. We also\nmeasure the differential polarizability of the intercombination line in a\n$515.2~\\text{nm}$ tweezer and achieve a magic-trapping configuration by tuning\nthe tweezer polarization from linear to elliptical. We present calculations, in\nagreement with our results, which predict a magic crossing for linear\npolarization at $520(2)~\\text{nm}$ and a crossing independent of polarization\nat 500.65(50)nm. Our results pave the way for a wide range of novel\nexperimental avenues based on individually controlled alkaline earth atoms in\ntweezers -- from fundamental experiments in atomic physics to quantum\ncomputing, simulation, and metrology implementations."
    },
    {
        "anchor": "Spatial entanglement in interacting Bose-Einstein condensates: The entanglement between spatial regions in an interacting Bose-Einstein\ncondensate is investigated using a quantum field theoretic formalism. Regions\nthat are small compared to the healing length are governed by a\nnon-relativistic quantum field theory in the vacuum limit, and we show that the\nlatter has vanishing entanglement. In the opposite limit of a region that is\nlarge compared to the healing length, the entanglement entropy is like in the\nvacuum of a relativistic theory where the velocity of light is replaced with\nthe velocity of sound and where the inverse healing length provides a natural\nultraviolet regularization scale. Besides the von Neumann entanglement entropy,\nwe also calculate R\\'enyi entanglement entropies for a one-dimensional\nquasi-condensate.",
        "positive": "Dynamical depinning of a Tonks Girardeau gas: We study the dynamical depinning following a sudden turn off of an optical\nlattice for a gas of impenetrable bosons in a tight atomic waveguide. We use a\nBose-Fermi mapping to infer the exact quantum dynamical evolution. At long\ntimes, in the thermodynamic limit, we observe the approach to a non-equilibrium\nsteady state, characterized by the absence of quasi-long-range order and a\nreduced visibility in the momentum distribution. Similar features are found in\na finite-size system at times corresponding to half the revival time, where we\nfind that the system approaches a quasi-steady state with a power-law\nbehaviour."
    },
    {
        "anchor": "Resonant d-wave scattering in harmonic waveguides: We observe and analyze d-wave resonant scattering of bosons in tightly\nconfining harmonic waveguides. It is shown that the d-wave resonance emerges in\nthe quasi-1D regime as an imprint of a 3D d-wave shape resonance. A scaling\nrelation for the position of the d-wave resonance is provided. By changing the\ntrap frequency, ultracold scattering can be continuously tuned from s-wave to\nd-wave resonant behavior. The effect can be utilized for the realization of\nultracold atomic gases interacting via higher partial waves and opens a novel\npossibility for studying strongly correlated atomic systems beyond s-wave\nphysics.",
        "positive": "Complex Langevin approach to interacting Bose gases: Quantitative numerical analyses of interacting dilute Bose-Einstein\ncondensates are most often based on semi-classical approximations. Since the\ncomplex-valued field-theoretic action of the Bose gas does not offer itself to\nthe direct application of standard Monte Carlo techniques, simulations beyond\ntheir scope by now almost exclusively rely on quantum-mechanical techniques.\nHere we explore an alternative approach based on a Langevin-type sampling in an\nextended state space, known as complex Langevin (CL) algorithm. While the use\nof the CL technique has a long-standing history in high-energy physics, in\nparticular in the simulation of QCD at finitebaryon density, applications to\nultracold atoms are still in their infancy. Here we examine the applicability\nof the CL approach for a one- and two-component, three-dimensional\nnon-relativistic Bose gas in thermal equilibrium, below and above the\nBose-Einstein phase transition. By comparison with analytic descriptions at the\nGaussian level, including Bogoliubov and Hartree-Fock theory, we find that the\nmethod allows computing reliably and efficiently observables in the regime of\nexperimentally accessible parameters. Close to the transition, quantum\ncorrections lead to a shift of the critical temperature which we reproduce\nwithin the numerical range known in the literature. With this work, we aim to\nprovide a first test of CL as a potential out-of-the-box tool for the\nsimulation of experimentally realistic situations, including trapping\ngeometries and multicomponent/-species models."
    },
    {
        "anchor": "Bound states and Cooper pairs of molecules in 2D optical lattices\n  bilayer: We investigate the formation of Cooper pairs, bound dimers and the\ndimer-dimer elastic scattering of ultra- cold dipolar Fermi molecules confined\nin a 2D optical lattice bilayer configuration. While the energy and their\nassociated bound states are determined in a variational way, the correlated\ntwo-molecule pair is addressed as in the original Cooper formulation. We\ndemonstrate that the 2D lattice confinement favors the formation of zero center\nmass momentum bound states. Regarding the Cooper pairs binding energy, this\ndepends on the molecule populations in each layer. Maximum binding energies\noccur for non-zero (zero) pair momentum when the Fermi system is polarized\n(unpolarized). We find an analytic expression for the dimer-dimer effective\ninteraction in the deep BEC regime. The present analysis represents a route for\naddressing the BCS-BEC crossover superfluidity in dipolar Fermi gases confined\nin 2D optical lattices within the current experimental panorama.",
        "positive": "Unraveling the Structure of Ultracold Mesoscopic Molecular Ions: We present an in-depth many-body investigation of the so-called mesoscopic\nmolecular ions that can build-up when an ion is immersed into an atomic\nBose-Einstein condensate in one dimension. To this end, we employ the\nMulti-Layer Multi-Configuration Time-Dependent Hartree method for Mixtures of\nultracold bosonic species for solving the underlying many-body Schr\\\"odinger\nequation. This enables us to unravel the actual structure of such massive\ncharged molecules from a microscopic perspective. Laying out their phase\ndiagram with respect to atom number and interatomic interaction strength, we\ndetermine the maximal number of atoms bound to the ion and reveal spatial\ndensities and molecular properties. Interestingly, we observe a strong\ninteraction-induced localization, especially for the ion, that we explain by\nthe generation of a large effective mass, similarly to ions in liquid Helium.\nFinally, we predict the dynamical response of the ion to small perturbations.\nOur results provide clear evidence for the importance of quantum correlations,\nas we demonstrate by benchmarking them with wave function ansatz classes\nemployed in the literature."
    },
    {
        "anchor": "Many-body dynamics of a Bose--Einstein condensate collapsing by quantum\n  tunneling: The dynamics of a Bose-Einstein condensate of atoms having attractive\ninteractions is studied using quantum many-body simulations. The collapse of\nthe condensate by quantum tunneling is numerically demonstrated and the\ntunneling rate is calculated. The correlation properties of the quantum\nmany-body state are investigated.",
        "positive": "Origin of flat-band superfluidity on the Mielke checkerboard lattice: The Mielke checkerboard is known to be one of the simplest two-band lattice\nmodels exhibiting an energetically flat band that is in touch with a\nquadratically dispersive band in the reciprocal space, i.e., its flat band is\nnot isolated. Motivated by the growing interest in understanding the origins of\nflat-band superfluidity in various contexts, here we provide an in-depth\nanalysis showing how the mean-field BCS correlations prevail in this particular\nmodel. Our work reveals the quantum-geometric origin of flat-band superfluidity\nthrough uncovering the leading role by a band-structure invariant, i.e., the\nso-called quantum metric tensor of the single-particle bands, in the inverse\neffective mass tensor of the Cooper pairs."
    },
    {
        "anchor": "Quantum droplets in one-dimensional Bose mixtures: a quantum Monte-Carlo\n  study: We use exact Quantum Monte Carlo techniques to study the properties of\nquantum droplets in two-component bosonic mixtures with contact interactions in\none spatial dimension. We systematically study the surface tension, the density\nprofile and the breathing mode as a function of the number of particles in the\ndroplet and of the ratio of coupling strengths between intra-species repulsion\nand inter-species attraction. We find that deviations from the predictions of\nthe generalized Gross-Pitaevskii equation are small in most cases of interest.",
        "positive": "Repulsive polarons in alkaline-earth(-like) atoms across an orbital\n  Feshbach resonance: We characterize properties of the so-called repulsive polaron across the\nrecently discovered orbital Feshbach resonance in alkaline-earth(-like) atoms.\nBeing a metastable quasiparticle excitation at the positive energy, the\nrepulsive polaron is induced by the interaction between an impurity atom and a\nFermi sea. By analyzing in detail the energy, the polaron residue, the\neffective mass, and the decay rate of the repulsive polaron, we reveal\ninteresting features that are intimately related to the two-channel nature of\nthe orbital Feshbach resonance. In particular, we find that the life time of\nthe repulsive polaron is non-monotonic in the Zeeman-field detuning bewteen the\ntwo channels, and has a maximum on the BEC-side of the resonance. Further, by\nconsidering the stability of a mixture of the impurity and the majority atoms\nagainst phase separation, we show that the itin- erant ferromagnetism may exist\nnear the orbital Feshbach resonance at appropriate densities. Our results can\nbe readily probed experimentally, and have interesting implications for the\nobservation of itinerant ferromagnetism near an orbital Feshbach resonance."
    },
    {
        "anchor": "Observation of Pauli Crystals: The Pauli exclusion principle is a fundamental law underpinning the structure\nof matter. Due to their anti-symmetric wave function, no two fermions can\noccupy the same quantum state. Here, we report on the direct observation of the\nPauli principle in a continuous system of up to six particles in the ground\nstate of a two-dimensional harmonic oscillator. To this end, we sample the full\nmany-body wavefunction by applying a single atom resolved imaging scheme in\nmomentum space. We find so-called Pauli crystals as a manifestation of higher\norder correlations. In contrast to true crystalline phases, these unique\nhigh-order density correlations emerge even without any interactions present.\nOur work lays the foundation for future studies of correlations in strongly\ninteracting systems of many fermions.",
        "positive": "One-particle entanglement for one dimensional spinless fermions after an\n  interaction quantum quench: Particle entanglement provides information on quantum correlations in systems\nof indistinguishable particles. Here, we study the one particle entanglement\nentropy for an integrable model of spinless, interacting fermions both at\nequilibrium and after an interaction quantum quench. Using both large scale\nexact diagonalization and time dependent density matrix renormalization group\ncalculations, we numerically compute the one body reduced density matrix for\nthe J-V model, as well as its post-quench dynamics. We include an analysis of\nthe fermionic momentum distribution, showcasing its time evolution after a\nquantum quench. Our numerical results, extrapolated to the thermodynamic limit,\ncan be compared with field theoretic bosonization in the Tomonaga-Luttinger\nliquid regime. Excellent agreement is obtained using an interaction cutoff that\ncan be determined uniquely in the ground state."
    },
    {
        "anchor": "Dynamics and Density Correlations in Matter Wave Jet Emission of a\n  Driven Condensate: Emission of matter wave jets has been recently observed in a Bose-Einstein\ncondensate confined by a cylindrical box potential, induced by a periodically\nmodulated inter-particle interaction (Nature {\\bf 551}, 356 (2017)). In this\npaper we apply the time-dependent Bogoliubov theory to study the quantum\ndynamics and the correlation effects observed in this highly non-equilibrium\nphenomenon. Without any fitting parameter, our theoretical calculations on the\nnumber of ejected atoms and the angular density correlations are in excellent\nquantitative agreement with the experimental measurements. The exponential\ngrowth in time of the ejected atoms can be understood in terms of a dynamical\ninstability associated with the modulation of the interaction. We interpret the\nangular density correlation of the jets as the Hanbury-Brown-Twiss effect\nbetween the excited quasi-particles with different angular momenta, and our\ntheory explains the puzzling observation of the asymmetric density correlations\nbetween the jets with the same and opposite momenta. Our theory can also\nidentify the main factors that control the height and width of the peaks in the\ndensity correlation function, which can be directly verified in future\nexperiments.",
        "positive": "Induced two-body scattering resonances from a square-well potential with\n  oscillating depth: In systems of ultracold atoms, pairwise interactions can be resonantly\nenhanced by a new mechanism which does not rely upon a magnetic Feshbach\nresonance. In this mechanism, interactions are controlled by tuning the\nfrequency of an oscillating parallel component of the magnetic field close to\nthe Bohr frequency for the transition to a two-atom bound state. The real part\nof the s-wave scattering length $a$ has a resonance as a function of the\noscillation frequency near the Bohr frequency. The resonance parameters can be\ncontrolled by varying the amplitude of the oscillating field. The amplitude\nalso controls the imaginary part of $a$ which arises predominantly because the\noscillating field converts atom pairs into molecules. For the case of a shallow\nbound state in the scattering channel, the dimensionless resonance parameters\nare universal functions of the dimensionless oscillation amplitude."
    },
    {
        "anchor": "Quantum degenerate Fermi gas in an orbital optical lattice: Spin-polarized samples and spin mixtures of quantum degenerate fermionic\natoms are prepared in selected excited Bloch bands of an optical chequerboard\nsquare lattice. For the spin-polarized case, extreme band lifetimes above\n$10\\,$s are observed, reflecting the suppression of collisions by Pauli's\nexclusion principle. For spin mixtures, lifetimes are reduced by an order of\nmagnitude by two-body collisions between different spin components, but still\nremarkably large values of about one second are found. By analyzing momentum\nspectra, we can directly observe the orbital character of the optical lattice.\nThe observations demonstrated here form the basis for exploring the physics of\nFermi gases with two paired spin components in orbital optical lattices,\nincluding the regime of unitarity.",
        "positive": "Nucleation in finite topological systems during continuous metastable\n  quantum phase transitions: Finite topological quantum systems can undergo continuous metastable quantum\nphase transitions to change their topological nature. Here we show how to\nnucleate the transition between ring currents and dark soliton states in a\ntoroidally trapped Bose-Einstein condensate. An adiabatic passage to wind and\nunwind its phase is achieved by explicit global breaking of the rotational\nsymmetry. This could be realized with current experimental technology."
    },
    {
        "anchor": "Superfluidity and Stabilities of a Bose-Einstein condensate with\n  periodically modulated interatomic interaction: We study theoretically the superfluidity and stability of a Bose-Einstein\ncondensate (BEC) whose interatomic scattering length is periodically modulated\nwith optical Feshbach resonance. Our numerical study finds that the properties\nof this periodic BEC are strongly influenced by the modulation strength. When\nthe modulation strength is small, only the Bloch waves close to the Brillouin\nzone edge suffer both Landau and dynamical instabilities. When the modulation\nstrength is strong enough, all Bloch waves become dynamically unstable. In\nother words, the periodic BEC loses its superfluidity completely.",
        "positive": "One-dimensional Fermi polaron in a combined harmonic and periodic\n  potential: We study an impurity in a one-dimensional potential consisting of a harmonic\nand a periodic part using both the time-evolving block decimation (TEBD)\nalgorithm and a variational ansatz. Attractive and repulsive contact\ninteractions with a sea of fermions are considered. We find excellent agreement\nbetween TEBD and variational results and use the variational ansatz to\ninvestigate higher lattice bands. We conclude that the lowest band\napproximation fails at sufficiently strong interactions and develop a new\nmethod for computing the Tan contact parameter."
    },
    {
        "anchor": "Engineering Ising-XY spin models in a triangular lattice via tunable\n  artificial gauge fields: Emulation of gauge fields for ultracold atoms provides access to a class of\nexotic states arising in strong magnetic fields. Here we report on the\nexperimental realisation of tunable staggered gauge fields in a periodically\ndriven triangular lattice. For maximal staggered magnetic fluxes, the doubly\ndegenerate superfluid ground state breaks both a discrete Z2 (Ising) symmetry\nand a continuous U(1) symmetry. By measuring an Ising order parameter, we\nobserve a thermally driven phase transition from an ordered antiferromagnetic\nto an unordered paramagnetic state and textbook-like magnetisation curves. Both\nthe experimental and theoretical analysis of the coherence properties of the\nultracold gas demonstrate the strong influence of the Z2 symmetry onto the\ncondensed phase.",
        "positive": "Optical-lattice-assisted magnetic phase transition in a\n  spin-orbit-coupled Bose-Einstein condensate: We investigate the effect of a periodic potential generated by a\none-dimensional optical lattice on the magnetic properties of an $S=1/2$\nspin-orbit-coupled Bose gas. By increasing the lattice strength one can achieve\na magnetic phase transition between a polarized and an unpolarized Bloch wave\nphase, characterized by a significant enhancement of the contrast of the\ndensity fringes. If the wave vector of the periodic potential is chosen close\nto the roton momentum, the transition could take place at very small lattice\nintensities, revealing the strong enhancement of the response of the system to\na weak density perturbation. By solving the Gross-Pitaevskii equation in the\npresence of a three-dimensional trapping potential, we shed light on the\npossibility of observing the magnetic phase transition in currently available\nexperimental conditions."
    },
    {
        "anchor": "Properties of 2D and Quasi-2D Dipolar Bosons with Non-zero Tilt Angles\n  at T=0: Recent experimental advances in creating stable dipolar bosonic systems,\nincluding polar molecules with large electric dipole moments, have led to\nvigorous theoretical activities. Recent reporting of observation of roton\nfeature in dipolar erbium has provided added impetus to theoretical and\nexperimental work. Here we discuss our mean-field theory work on 2D and\nquasi-2D dipolar bosons with dipoles oriented at an angle to the direction\nperpendicular to the confining 2D plane, i.e. for {\\it non-zero tilt angles}.\nUsing Bogoliubov-de Gennes equations, we present results on a number of T=0\nproperties of both 2D and quasi-2D systems, such as excitation spectra,\nstructure functions, sound velocities, quantum depletion, etc. We explore\ninstabilities at varying tilt angle, density and dipolar coupling. We map out\nphase diagrams as a function of tilt angle, dipole strength and density. We\nfind the development of maxon-roton behavior leading to roton instabilities at\nlarge densities for small tilt angles, and at low densities for large tilt\nangles. The behavior is anisotropic in k-space; accordingly the roton\ninstabilities occur first in the $k_y$ direction, suggestive of inhomogeneity\nand stripe phase, with density mode becoming soft in the $y$-direction. Beyond\na critical tilt angle, at any density, the dipolar system collapses owing to a\nphonon instability. We discuss similarities and differences between the\nproperties of 2D and quasi-2D dipolar systems at non-zero tilt angles.",
        "positive": "Unconventional symmetries of Fermi liquid and Cooper pairing properties\n  with electric and magnetic dipolar fermions: The rapid experimental progress of ultra-cold dipolar fermions opens up a\nwhole new opportunity to investigate novel many-body physics of fermions. In\nthis article, we review theoretical studies of the Fermi liquid theory and\nCooper pairing instabilities of both electric and magnetic dipolar fermionic\nsystems from the perspective of unconventional symmetries. When the electric\ndipole moments are aligned by the external electric field, their interactions\nexhibit the explicit $d_{r^2-3z^2}$ anisotropy. The Fermi liquid properties,\nincluding the single-particle spectra, thermodynamic susceptibilities, and\ncollective excitations, are all affected by this anisotropy. The electric\ndipolar interaction provides a mechanism for the unconventional spin triplet\nCooper pairing, which is different from the usual spin-fluctuation mechanism in\nsolids and the superfluid $^3$He. Furthermore, the competition between pairing\ninstabilities in the singlet and triplet channels gives rise to a novel\ntime-reversal symmetry breaking superfluid state. Unlike electric dipole\nmoments which are induced by electric fields and unquantized, magnetic dipole\nmoments are intrinsic proportional to the hyperfine-spin operators with a Lande\nfactor. Its effects even manifest in unpolarized systems exhibiting an\nisotropic but spin-orbit coupled nature. The resultant spin-orbit coupled Fermi\nliquid theory supports a collective sound mode exhibiting a topologically\nnon-trivial spin distribution over the Fermi surface. It also leads to a novel\n$p$-wave spin triplet Cooper pairing state whose spin and orbital angular\nmomentum are entangled to the total angular momentum $J=1$ dubbed the\n$J$-triplet pairing. This $J$-triplet pairing phase is different from both the\nspin-orbit coupled $^3$He-$B$ phase with $J=0$ and the spin-orbit decoupled\n$^3$He-$A$ phase."
    },
    {
        "anchor": "Bose-Einstein condensation for trapped atomic polaritons in a biconical\n  waveguide cavity: We study the problem of high temperature Bose-Einstein condensation (BEC) of\natom-light polaritons in a waveguide cavity appearing due to interaction of\ntwo-level atoms with (non-resonant) quantized optical radiation, in the strong\ncoupling regime, in the presence of optical collisions (OCs) with buffer gas\nparticles. Specifically, we propose a special biconical waveguide cavity (BWC),\npermitting localization and trapping of low branch (LB) polaritons imposed by\nthe variation of the waveguide radius in longitudinal direction. We have shown\nthat critical temperature of BEC occurring in the system can be high enough --\nfew hundred Kelvins; it is connected with photon-like character of LB\npolaritons and strongly depends on waveguide cavity parameters. In the case of\na linear trapping potential we obtain an Airy-shaped polariton condensate wave\nfunction which, when disturbed out of equilibrium, exhibits small amplitude\noscillations with the characteristic period in the picosecond domain.",
        "positive": "Deterministic creation, pinning, and manipulation of quantized vortices\n  in a Bose-Einstein condensate: We experimentally and numerically demonstrate deterministic creation and\nmanipulation of a pair of oppositely charged singly quantized vortices in a\nhighly oblate Bose-Einstein condensate (BEC). Two identical blue-detuned,\nfocused Gaussian laser beams that pierce the BEC serve as repulsive obstacles\nfor the superfluid atomic gas; by controlling the positions of the beams within\nthe plane of the BEC, superfluid flow is deterministically established around\neach beam such that two vortices of opposite circulation are generated by the\nmotion of the beams, with each vortex pinned to the \\emph{in situ} position of\na laser beam. We study the vortex creation process, and show that the vortices\ncan be moved about within the BEC by translating the positions of the laser\nbeams. This technique can serve as a building block in future experimental\ntechniques to create, on-demand, deterministic arrangements of few or many\nvortices within a BEC for precise studies of vortex dynamics and vortex\ninteractions."
    },
    {
        "anchor": "Trimer quantum spin liquid in a honeycomb array of Rydberg atoms: Quantum spin liquids are elusive but paradigmatic examples of strongly\ncorrelated quantum states that are characterized by long-range quantum\nentanglement. Recently, the direct signatures of a gapped topological\n$\\mathbb{Z}_2$ spin liquid have been observed in a system of Rydberg atoms\narrayed on the ruby lattice. Here, we illustrate the concrete realization of a\nfundamentally different class of spin liquids in a honeycomb array of Rydberg\natoms. Exploring the quantum phase diagram of this system using both\ndensity-matrix renormalization group and exact diagonalization simulations,\nseveral density-wave-ordered phases are characterized and their origins\nexplained. More interestingly, in the regime where third-nearest-neighbor atoms\nlie within the Rydberg blockade radius, we find a novel ground state -- with an\nemergent $\\mathrm{U}(1)\\times \\mathrm{U}(1)$ local symmetry -- formed from\nsuperpositions of classical {\\it trimer} configurations on the dual triangular\nlattice. The fidelity of this trimer spin liquid state can be enhanced via\ndynamical preparation, which we explain by a Rydberg-blockade-based projection\nmechanism associated with the smooth turnoff of the laser drive. Finally, we\ndiscuss the robustness of the trimer spin liquid phase under realistic\nexperimental parameters and demonstrate that our proposal can be readily\nimplemented in current Rydberg atom quantum simulators.",
        "positive": "Superradiant optomechanical phases of cold atomic gases in optical\n  resonators: We theoretically analyze superradiant emission of light from a cold atomic\ngas, when mechanical effects of photon-atom interactions are considered. The\natoms are confined within a standing-wave resonator and an atomic metastable\ndipolar transition couples to a cavity mode. The atomic dipole is incoherently\npumped in the parameter regime that would correspond to stationary\nsuperradiance in absence of inhomogeneous broadening. Starting from the master\nequation for cavity field and atomic degrees of freedom we derive a mean-field\nmodel that allows us to determine a threshold temperature, above which thermal\nfluctuations suppress superradiant emission. We then analyze the dynamics of\nsuperradiant emission when the motion is described by a mean-field model. In\nthe semiclassical regime and below the threshold temperature we observe that\nthe emitted light can be either coherent or chaotic, depending on the\nincoherent pump rate. We then analyze superradiant emission from an ideal Bose\ngas at zero temperature when the superradiant decay rate $\\Lambda$ is of the\norder of the recoil frequency $\\omega_R$. We show that the quantized exchange\nof mechanical energy between the atoms and the field gives rise to a threshold,\n$\\Lambda_c$, below which superradiant emission is damped down to zero. When\n$\\Lambda>\\Lambda_c$ superradiant emission is accompanied by the formation of\nmatter-wave gratings diffracting the emitted photons. The stability of these\ngratings depends on the incoherent pump rate $w$ with respect to a second\nthreshold value $w_c$. For $w>w_c$ the gratings are stable and the system\nachieves stationary superradiance. Below this second threshold the coupled\ndynamics becomes chaotic. We characterize the dynamics across these two\nthresholds and show that the three phases we predict (incoherent, coherent,\nchaotic) can be revealed via the coherence properties of the light at the\ncavity output."
    },
    {
        "anchor": "Three-component Ultracold Fermi Gases with Spin-Orbit Coupling: We investigate the pairing physics in a three-component Fermi-Fermi mixture,\nwhere a few impurities are immersed in a non-interacting spin-$\\frac{1}{2}$\nFermi gas with synthetic spin-orbit coupling (SOC), and interact attractively\nwith one spin species in the Fermi gas. Due to the interplay of SOC and\nspin-selective interaction, the molecular state intrinsically acquires a\nnon-zero center-of-mass momentum, which results in a new type of Fulde-Ferrell\n(FF) pairing in spin-orbit coupled Fermi systems. The existence of the Fermi\nsea can also lead to the competition between FF-like molecular states with\ndifferent center-of-mass momenta, which corresponds to a first-order transition\nbetween FF phases in the thermodynamic limit. As the interaction strength is\ntuned, a polaron-molecule transition occurs in the highly imbalanced system,\nwhere the boundary varies non-monotonically with SOC parameters and gives rise\nto the reentrance of polaron states. The rich physics in this system can be\nprobed using existing experimental techniques.",
        "positive": "Demixing and symmetry breaking in binary dipolar Bose-Einstein\n  condensate solitons: We demonstrate fully demixed (separated) robust and stable bright binary\ndipolar Bose-Einstein condensate soliton in a quasi-one-dimensional setting\nformed due to dipolar interactions for repulsive contact interactions. For\nlarge repulsive interspecies contact interaction the first species may\nspatially separate from the second species thus forming a demixed\nconfiguration, which can be spatially-symmetric or symmetry-broken. In the\nspatially-symmetric case, one of the the species occupies the central region,\nwhereas the other species separates into two equal parts and stay predominantly\nout of this central region. In the symmetry-broken case, the two species stay\nside by side. Stability phase diagrams for the binary solitons are obtained.\nThe results are illustrated with realistic values of parameters in the binary\n164Dy-168Er and 164Dy-162Dy mixtures. The demixed solitons are really soliton\nmolecules formed of two types of atoms. A proposal for creating dipolar\nsolitons in experiments is also presented."
    },
    {
        "anchor": "Temperature-Dependent Contact of Weakly Interacting Single-Component\n  Fermi Gases and Loss Rate of Degenerate Polar Molecules: Motivated by the experimental realization of single-component degenerate\nFermi gases of polar ground state KRb molecules with intrinsic two-body losses\n[L. De Marco, G. Valtolina, K. Matsuda, W. G. Tobias, J. P. Covey, and J. Ye, A\ndegenerate Fermi gas of polar molecules, Science 363, 853 (2019)], this work\nstudies the finite-temperature loss rate of single-component Fermi gases with\nweak interactions. First, we establish a relationship between the two-body loss\nrate and the $p$-wave contact. Second, we evaluate the contact of the\nhomogeneous system in the low-temperature regime using $p$-wave Fermi liquid\ntheory and in the high-temperature regime using the second-order virial\nexpansion. Third, conjecturing that there are no phase transitions between the\ntwo temperature regimes, we smoothly interpolate the results to intermediate\ntemperatures. It is found that the contact is constant at temperatures close to\nzero and increases first quadratically with increasing temperature and finally\n-- in agreement with the Bethe-Wigner threshold law -- linearly at high\ntemperatures. Fourth, applying the local-density approximation, we obtain the\nloss-rate coefficient for the harmonically trapped system, reproducing the\nexperimental KRb loss measurements within a unified theoretical framework over\na wide temperature regime without fitting parameters. Our results for the\ncontact are not only applicable to molecular $p$-wave gases but also to atomic\nsingle-component Fermi gases, such as 40K and 6Li.",
        "positive": "A novel route to Bose-Einstein condensation of two-electron atoms: We present a novel route to Bose-Einstein condensation devised for\ntwo-electron atoms, which do not admit practicable cooling techniques based\nupon narrow intercombination lines. A dipole trap for $^{40}$Ca atoms in the\nsinglet ground state is loaded from a moderately cold source of metastable\ntriplet atoms via spatially and energetically selective optical pumping\npermitting four orders of magnitude increase of the phase space density.\nFurther cooling to quantum degeneracy is achieved by forced evaporation\noptimized to minimize three-body losses. In a combined loading and evaporation\ncycle of less than three seconds we are able to condense 3000 atoms."
    },
    {
        "anchor": "Stability and dispersion relations of three-dimensional solitary waves\n  in trapped Bose-Einstein condensates: We analyse the dynamical properties of three-dimensional solitary waves in\ncylindrically trapped Bose-Einstein condensates. Families of solitary waves\nbifurcate from the planar dark soliton and include the solitonic vortex, the\nvortex ring and more complex structures of intersecting vortex-line known\ncollectively as Chladni solitons. The particle-like dynamics of these guided\nsolitary waves provides potentially profitable features for their\nimplementation in atomtronic circuits, and play a key role in the generation of\nmetastable loop currents. Based on the time-dependent Gross-Pitaevskii equation\nwe calculate the dispersion relations of moving solitary waves and their modes\nof dynamical instability. The dispersion relations reveal a complex crossing\nand bifurcation scenario. For stationary structures we find that for\n$\\mu/\\hbar\\omega_\\perp > 2.65$ the solitonic vortex is the only stable solitary\nwave. More complex Chladni solitons still have weaker instabilities than planar\ndark solitons and may be seen as transient structures in experiments. Fully\ntime-dependent simulations illustrate typical decay scenarios, which may result\nin the generation of multiple separated solitonic vortices.",
        "positive": "Observation of Cavity Rydberg Polaritons: We demonstrate hybridization of optical cavity photons with atomic Rydberg\nexcitations using electromagnetically induced transparency (EIT). The resulting\ndark state Rydberg polaritons exhibit a compressed frequency spectrum and\nenhanced lifetime indicating strong light-matter mixing. We study the coherence\nproperties of cavity Rydberg polaritons and identify the generalized EIT\nlinewidth for optical cavities. Strong collective coupling suppresses polariton\nlosses due to inhomogeneous broadening, which we demonstrate by using different\nRydberg levels with a range of polarizabilities. Our results point the way\ntowards using cavity Rydberg polaritons as a platform for creating photonic\nquantum materials."
    },
    {
        "anchor": "Quantum-geometric perspective on spin-orbit-coupled Bose superfluids: We employ the Bogoliubov approximation to study how the quantum geometry of\nthe helicity states affects the superfluid properties of a spin-orbit-coupled\nBose gas in continuum. In particular we derive the low-energy Bogoliubov\nspectrum for a plane-wave condensate in the lower helicity band and show that\nthe geometric contributions to the sound velocity are distinguished by their\nlinear dependences on the interaction strength, i.e., they are in sharp\ncontrast to the conventional contribution which has a square-root dependence.\nWe also discuss the roton instability of the plane-wave condensate against the\nstripe phase and determine their phase transition boundary. In addition we\nderive the superfluid density tensor by imposing a phase-twist on the\ncondensate order parameter and study the relative importance of its\ncontribution from the interband processes that is related to the quantum\ngeometry.",
        "positive": "Particle-Hole Asymmetry and Brightening of Solitons in A Strongly\n  Repulsive BEC: We study solitary wave propagation in the condensate of a system of hard-core\nbosons with nearest-neighbor interactions. For this strongly repulsive system,\nthe evolution equation for the condensate order parameter of the system,\nobtained using spin coherent state averages is different from the usual\nGross-Pitaevskii equation (GPE). The system is found to support two kinds of\nsolitons when there is a particle-hole imbalance: a dark soliton that dies out\nas the velocity approaches the sound velocity, and a new type of soliton which\nbrightens and persists all the way up to the sound velocity, transforming into\na periodic wave train at supersonic speed. Analogous to the GPE soliton, the\nenergy-momentum dispersion for both solitons is characterized by Lieb II modes."
    },
    {
        "anchor": "Statistical properties of the momentum occupation numbers of the\n  Tonks-Girardeau gas in a harmonic trap: We compute the fluctuations of the number of bosons with a given momentum for\nthe Tonks-Girardeau gas at zero and finite temperature in a harmonic trap. We\nshow that correlations between opposite momentum states $p$, which is an\nimportant fingerprint of long range order in weakly interacting Bose systems\nare suppressed. Non trivial correlations, including negative correlations are\nobserved for momenta smaller or of the order of the inverse radius of the gas.\nThe full distribution of the number of bosons with momentum $p$ exhibits an\ninteresting crossover from a non trivial distribution at zero momentum to an\nexponential distribution. The distribution of the quasi-condensate occupation\nis also studied. Experimental relevance of our findings for recent cold atoms\nexperiments are discussed.",
        "positive": "Fluctuation and interaction induced instability of dark solitons in\n  single and binary condensates: We show that the presence of soliton in a single-species condensate, at zero\ntemperature, enhances the quantum depletion sufficient enough to induce\ndynamical instability of the system. We also predict that for two-species\ncondensates, two Goldstone modes emerge in the excitation spectrum at phase\nseparation. Of these, one is due to the presence of the soliton. We use\nHartree-Fock-Bogoliubov theory with Popov approximation to examine the mode\nevolution, and demonstrate that when the anomalous mode collides with a higher\nenergy mode it renders the solitonic state oscillatory unstable. We also report\nsoliton induced change in the topology of the density profiles of the\ntwo-species condensates at phase-separation."
    },
    {
        "anchor": "Effective mass of $^4$He atom in superfluid and normal phases: The formula for the temperature dependence of the effective mass of a $^{4}%\n$He atom in the superfluid and normal phases is obtained.\\,\\,This expression\nfor the effective mass allows one to eliminate infra-red divergences, being\napplicable at all temperatures, except for a narrow fluctuation region\n0.97~$\\lesssim T/T_{\\rm c}\\leq1$.\\,\\,In the high and low temperature limits, as\nwell as in the interactionless limit, the obtained expression reproduces the\nwell known results.\\,\\,The temperature dependence of the heat capacity and the\nphase transition temperature $T_{\\rm c}\\approx$~2.18~K are calculated, by using\nthe formula obtained for the effective mass.\\,\\,In the framework of the\napproach proposed in this work, the small critical index $\\eta$ is determined\nin the random phase approximation.\\,\\,The obtained value corresponds to the\nwell known result.",
        "positive": "Critical temperature of a Bose gas in an optical lattice: We present theory for the critical temperature of a Bose gas in a combined\nharmonic lattice potential based on a mean-field description of the system. We\ndevelop practical expressions for the ideal-gas critical temperature, and\ncorrections due to interactions, the finite-size effect, and the occupation of\nexcited bands. We compare our expressions to numerical calculations and find\nexcellent agreement over a wide parameter regime."
    },
    {
        "anchor": "Unidirectional transport of wave packets through tilted discrete\n  breathers in nonlinear lattices with asymmetric defects: We consider the transfer of lattice wave packets through a tilted discrete\nbreather (TDB) in opposite directions in the discrete nonlinear Schr\\\"{o}dinger\nmodel with asymmetric defects, which may be realized as a Bose-Einstein\ncondensate trapped in a deep optical lattice, or as optical beams in a\nwaveguide array. A unidirectional transport mode is found, in which the\nincident wave packets, whose energy belongs to a certain interval between full\nreflection and full passage regions, pass the TDB only in one direction, while,\nin the absence of the TDB, the same lattice admits bi-directional propagation.\nThe operation of this mode is accurately explained by an analytical\nconsideration of the respective energy barriers. The results suggest that the\nTDB may emulate the unidirectional propagation of atomic and optical beams in\nvarious settings. In the case of the passage of the incident wave packet, the\nscattering TDB typically shifts by one lattice unit in the direction from which\nthe wave packet arrives, which is an example of the tractor-beam effect,\nprovided by the same system, in addition to the rectification of incident\nwaves.",
        "positive": "Ground state properties of a three-site Bose-Fermi ring with a small\n  number of atoms: We investigate a three-site ring system with a small number of quantum\ndegenerate bosons and fermions. By means of the exact diagonalization of the\nBose-Fermi-Hubbard Hamiltonian, we show that the symmetry of the ground state\nconfiguration is a function of both the boson-boson and the inter-species\ninteraction in the system. The phase diagram of the system, constructed by\ncomputing the exact two-body spatial correlations, reveals nontrivial\ninsulating phases that exist even in the strong bosonic tunneling limit and for\nincommensurate filling of bosons. These insulating phases are due to the\ninter-species interactions in the system and are not necessarily accompanied by\nthe suppression of the particle number fluctuations."
    },
    {
        "anchor": "Superfluid, Supersolid and Checkerboard Solid in Two-Component Bosons in\n  an Optical Lattice: Study by Means of Gross-Pitaevskii Theory and Monte-Carlo\n  Simulations: The bosonic t-J model is a strong-on-site repulsion limit of the\ntwo-component Bose-Hubbard model and is expected to be realized by experiments\nof cold atoms in an optical lattice. In previous papers, we studied the bosonic\nt-J model by both analytical methods and numerical Monte - Carlo (MC)\nsimulations. However, in the case of finite $J_z$, where $J_z$ is the\n$z$-component coupling constant of the pseudospin interaction, the phase\ndiagram of the model was investigated by assuming the checkerboard type of\nboson densities. In this study, we shall continue our previous study of the\nbosonic t-J model using both the Gross-Pitaevskii (GP) theory and MC\nsimulations without assuming any pattern of boson densities. These two methods\ncomplement each other and give reliable results. We show that as $J_z$ is\nincreased, the superfluid state evolves into a supersolid (SS), and furthermore\ninto a genuine solid with the checkerboard symmetry. In the present study, we\npropose a method identifying quantum phase transitions in the GP theory. We\nalso study finite-temperature phase transitions of the superfluidity and the\ndiagonal solid order of the SS by MC simulations.",
        "positive": "Phase diagram of microcavity polariton condensates with a harmonic\n  potential trap: We theoretically explore the phase transition in inhomogeneous\nexciton-polariton condensates with variable pumping conditions. Through\nBogoliubov excitations to the radial-symmetric solutions of complex\nGross-Pitaevskii equation, we determine not only the bifurcation of stable and\nunstable modes by the sign of fluid compressibility but also two distinct\nstable modes which are characterized by the elementary excitations and the\nstability of singly quantized vortex. One state is the quasi-condensate BKT\nphase with Goldstone flat dispersion; the other state is the localized-BEC\nphase which exhibits linear-type dispersion and has an excitation energy gap at\nzero momentum."
    },
    {
        "anchor": "Mean field analysis of quantum phase transitions in a periodic optical\n  superlattice: In this paper we analyze the various phases exhibited by a system of\nultracold bosons in a periodic optical superlattice using the mean field\ndecoupling approximation. We investigate for a wide range of commensurate and\nincommensurate densities. We find the gapless superfluid phase, the gapped Mott\ninsulator phase, and gapped insulator phases with distinct density wave orders.",
        "positive": "Trapped Imbalanced Quantum Droplets: A two-component quantum droplet is an attractive mixture of ultracold bosons\nstabilised against collapse by quantum fluctuations. Commonly, two-component\nquantum droplets are studied within a balanced mixture. However, the mixture\ncan be imbalanced resulting in a lower energy but less stably bound droplet, or\neven a droplet submerged in a gas. This work focuses on the experimentally\nrelevant question: how are imbalanced droplets modified by harmonic trap\npotentials? Droplet ground states and breathing modes are analysed across the\ntwo-dimensional parameter space of imbalance and trap strength. The robustness\nof the droplet imbalance is also studied by releasing the droplet from the\ntrap, demonstrating that this can lead to the creation of free-space,\nimbalanced droplets."
    },
    {
        "anchor": "Parametric resonance of a Bose-Einstein condensate in a ring trap with\n  periodically driven interactions: We study the instability of a ring Bose-Einstein condensate under a periodic\nmodulation of inter-atomic interactions. The condensate exhibits temporal and\nspatial patterns induced by the parametric resonance, which can be\ncharacterized by Bogoliubov quasi-particle excitations in the Floquet basis. As\nthe ring geometry significantly limits the number of excitable Bogoliubov\nmodes, we are able to capture the non-linear dynamics of the condensate using a\nthree-mode model. We further demonstrate the robustness of the temporal and\nspatial patterns against disorder, which are attributed to the mode-locking\nmechanism under the ring geometry. Our results can be observed in cold atomic\nsystems and are also relevant to physical systems described by the non-linear\nSchrodinger's equation.",
        "positive": "Geometry-induced memory effects in isolated quantum systems:\n  Observations and applications: Memory effects can lead to history-dependent behavior of a system, and they\nare ubiquitous in our daily life and have broad applications. Here we explore\npossibilities of generating memory effects in simple isolated quantum systems.\nBy utilizing geometrical effects from a class of lattices supporting flat-bands\nconsisting of localized states, memory effects could be observed in ultracold\natoms in optical lattices. As the optical lattice continuously transforms from\na triangular lattice into a kagome lattice with a flat band, history-dependent\ndensity distributions manifest quantum memory effects even in noninteracting\nsystems, including fermionic as well as bosonic systems in the proper ranges of\ntemperatures. Rapid growth in ultracold technology predicts a bright future for\nquantum memory-effect systems, and here two prototypical applications of\ngeometry-induced quantum memory effects are proposed: An accelerometer\nrecording the mechanical change rate in a coupled system and a rate-controlled\nmemvalve where the rate of ramping the lattice potential acts as a control of\nthe remnant density in the lattice."
    },
    {
        "anchor": "Quantum many-body effects on Rydberg excitons in cuprous oxide: We investigate quantum many-body effects on Rydberg excitons in cuprous oxide\ninduced by the surrounding electron-hole plasma. Line shifts and widths are\ncalculated by full diagonalisation of the plasma Hamiltonian and compared to\nresults in first order perturbation theory, and the oscillator strength of the\nexciton lines is analysed.",
        "positive": "Observation of universal dynamics in a spinor Bose gas far from\n  equilibrium: The dynamics of quantum systems far from equilibrium represents one of the\nmost challenging problems in theoretical many-body physics. While the evolution\nis in general intractable in all its details, relevant observables can become\ninsensitive to microscopic system parameters and initial conditions. This is\nthe basis of the phenomenon of universality. Far from equilibrium, universality\nis identified through the scaling of the spatiotemporal evolution of the\nsystem, captured by universal exponents and functions. Theoretically, this has\nbeen studied in examples as different as the reheating process in inflationary\nuniverse cosmology, the dynamics of nuclear collision experiments described by\nquantum chromodynamics, or the post-quench dynamics in dilute quantum gases in\nnon-relativistic quantum field theory. Here we observe the emergence of\nuniversal dynamics by evaluating spatially resolved spin correlations in a\nquasi one-dimensional spinor Bose-Einstein condensate. For long evolution times\nwe extract the scaling properties from the spatial correlations of the spin\nexcitations. From this we find the dynamics to be governed by transport of an\nemergent conserved quantity towards low momentum scales. Our results establish\nan important class of non-stationary systems whose dynamics is encoded in time\nindependent scaling exponents and functions signaling the existence of\nnon-thermal fixed points. We confirm that the non-thermal scaling phenomenon\ninvolves no fine-tuning, by preparing different initial conditions and\nobserving the same scaling behaviour. Our analog quantum simulation approach\nprovides the basis to reveal the underlying mechanisms and characteristics of\nnon-thermal universality classes. One may use this universality to learn, from\nexperiments with ultra-cold gases, about fundamental aspects of dynamics\nstudied in cosmology and quantum chromodynamics."
    },
    {
        "anchor": "The Molecular Hubbard Hamiltonian: Field Regimes and Molecular Species: The molecular Hubbard Hamiltonian (MHH) naturally arises for ultracold ground\nstate polar alkali dimer molecules in optical lattices. We show that, unlike\nultracold atoms, different molecules display different many-body phases due to\nintrinsic variances in molecular structure even when the molecular symmetry is\nthe same. We also demonstrate a wide variety of experimental controls on\n$^1\\Sigma$ molecules via external fields, including applied static electric and\nmagnetic fields, an AC microwave field, and the polarization and strength of\noptical lattice beams. We provide explicit numerical calculations of the\nparameters of the MHH, including tunneling and direct and exchange\ndipole-dipole interaction energies, for the molecules {$^{6}$Li$^{133}$Cs},\n$^{23}$Na$^{40}$K, $^{87}$Rb$^{133}$Cs, $^{40}$K$^{87}$Rb, and\n{$^{6}$Li$^{23}$Na} in weak and strong applied electric fields. As case studies\nof many-body physics, we use infinite-size matrix product state methods to\nexplore the quantum phase transitions from the superfluid phase to half-filled\nand third-filled crystalline phases in one dimension.",
        "positive": "Magnetic ordering of three-component ultracold fermionic mixtures in\n  optical lattices: We study finite-temperature magnetic phases of three-component mixtures of\nultracold fermions with repulsive interactions in optical lattices with simple\ncubic or square geometry by means of dynamical mean-field theory (DMFT). We\nfocus on the case of one particle per site (1/3 band filling) at moderate\ninteraction strength, where we observe a sequence of thermal phase transitions\ninto two- and three-sublattice ordered states by means of the unrestricted\nreal-space generalization of DMFT. From our quantitative analysis we conclude\nthat long-range ordering in three-component mixtures should be observable at\ncomparable temperatures as in two-component mixtures."
    },
    {
        "anchor": "Spectroscopy and spin dynamics for strongly interacting few spinor\n  bosons in one-dimensional traps: We consider a one-dimensional trapped gas of strongly interacting few spin-1\natoms which can be described by an effective spin chain Hamiltonian. Away from\nthe SU(3) integrable point, where the energy spectrum is highly degenerate, the\nrules of ordering and crossing of the energy levels and the symmetry of the\neigenstates in the regime of large but finite repulsion have been elucidated.\nWe study the spin-mixing dynamics which is shown to be very sensitive to the\nratio between the two channel interactions g0/g2 and the effective spin chain\ntransfers the quantum states more perfectly than the Heisenberg\nbilinear-biquadratic spin chain.",
        "positive": "Mixture of two ultra cold bosonic atoms confined in a ring: stability\n  and persistent currents: In this article we investigate the stability of quantized yrast (QY) states\nin a mixture of two distinguishable equal mass bosonic atoms, $A$ and $B$,\nconfined in a ring. We focus our investigation in the study of the energetic\nstability since the Bloch analysis and the Bogoliubov theory establish that\nonly energetically stable QY states are capable of sustain a persistent\ncurrent. Based on physical considerations the stability is studied in two\ndifferent two-dimensional planes. One is when we are studying the stability of\na single QY state which is realized in the $U_{AB}\\times U$ plane spanned by\nthe inter and intraspecies interaction strengths with fixed values of angular\nmomentum per particle $l$ and population imbalance $f$ equal to the labels of\nthe QY state. We found that the energetic phase boundary is the positive branch\nof a hyperbola and the energetically stable domain the internal region of this\npositive branch. The other is when we are studying the stability at a fixed\ndynamics which is realized in the $l\\times f$ plane spanned by $l$ and $f$ with\nfixed values of the interaction strengths. The QY states are introduced when we\npostulate a correspondence between points in sector of the $l\\times f$ plane of\nphysical significance (SPS), defined by $-\\infty< l<\\infty$ and $-1\\leq f\\leq\n1$, and QY states. The stability diagram in the SPS is determined by the\noverlap of the stability diagram in all $l\\times f$ plane and the SPS. We found\nthat there are critical values of $f$ and $l$. $f_\\mathrm{crit}(l)$ gives the\nsize of the window of energetic stability in the sense that for a given $l$\nonly QY states with $0\\leq f<f_\\mathrm{crit}(l)$ are energetically stable. On\nthe other hand, $l_\\mathrm{crit}$ states that there is none energetically\nstable QY state with $l>l_\\mathrm{crit}$."
    },
    {
        "anchor": "Comparative Study of BCS-BEC Crossover Theories above $T_c$: the Nature\n  of the Pseudogap in Ultra-Cold Atomic Fermi Gases: This paper presents a comparison of two finite-temperature BCS-Bose Einstein\ncondensation (BEC) crossover theories above the transition temperature:\nNozieres Schmitt-Rink (NSR) theory and finite $T$-extended BCS-Leggett theory.\nThe comparison is cast in the form of numerical studies of the behavior of the\nfermionic spectral function both theoretically and as constrained by\n(primarily) radio frequency (RF) experiments. Both theories include pair\nfluctuations and exhibit pseudogap effects, although the nature of this\npseudogap is very different. The pseudogap in finite $T$-extended BCS-Leggett\ntheory is found to follow a BCS-like dispersion which, in turn, is associated\nwith a broadened BCS-like self energy, rather more similar to what is observed\nin high temperature superconductors (albeit, for a d-wave case). The fermionic\nquasi-particle dispersion is different in NSR theory and the damping is\nconsiderably larger. We argue that the two theories are appropriate in\ndifferent temperature regimes with the BCS-Leggett approach more suitable\nnearer to condensation. There should, in effect, be little difference at higher\n$T$ as the pseudogap becomes weaker and where the simplifying approximations\nused in the BCS-Leggett approach break down. On the basis of\nmomentum-integrated radio frequency studies of unpolarized gases, it would be\ndifficult to distinguish which theory is the better. A full comparison for\npolarized gases is not possible since there is claimed to be inconsistencies in\nthe NSR approach (not found in the BCS-Leggett scheme). Future experiments\nalong the lines of momentum resolved experiments look to be very promising in\ndistinguishing the two theories.",
        "positive": "Vortices in the supersolid phase of dipolar Bose-Einstein condensates: Vortices are expected to exist in a supersolid but experimentally their\ndetection can be difficult because the vortex cores are localized at positions\nwhere the local density is very low. We address here this problem by performing\nnumerical simulations of a dipolar Bose-Einstein Condensate (BEC) in a pancake\nconfinement at $T=0$ K and study the effect of quantized vorticity on the\nphases that can be realized depending upon the ratio between dipolar and\nshort-range interaction. By increasing this ratio the system undergoes a\nspontaneous density modulation in the form of an ordered arrangement of\nmulti-atom \"droplets\". This modulated phase can be either a \"supersolid\" (SS)\nor a \"normal solid\" (NS). In the SS state droplets are immersed in a background\nof low-density superfluid and the system has a finite global superfluid\nfraction resulting in non-classical rotational inertia. In the NS state no such\nsuperfluid background is present and the global superfluid fraction vanishes.\nWe propose here a protocol to create vortices in modulated phases of dipolar\nBEC by \"freezing\" into such phases a vortex-hosting superfluid (SF) state. The\nresulting system, depending upon the interactions strengths, can be either a SS\nor a NS To discriminate between these two possible outcome of a \"freezing\"\nexperiment, we show that upon releasing of the radial harmonic confinement, the\nexpanding vortex-hosting SS shows tell-tale quantum interference effects which\ndisplay the symmetry of the vortex lattice of the originating SF, as opposed to\nthe behavior of the NS which shows instead a ballistic radial expansion of the\nindividual droplets. Such markedly different behavior might be used to prove\nthe supersolid character of rotating dipolar condensates."
    },
    {
        "anchor": "Multiple-Channel Scattering Resonance of One-Dimensional Ultracold\n  Spinor Bosons: So far the interaction of ultacold atoms can only be tuned within one\nparticular scattering channel near a resonance, where the spinor structure of\natomic isotopes is destroyed due to the typically large magnetic field. In this\nLetter, we propose a scheme to realize {\\it multiple-channel scattering\nresonance} (MCSR) of ultracold bosons in one-dimension while still keeping\ntheir spinor structure. The MCSR refers to a simultaneous scattering resonance\namong all different scattering channels, including those breaking SU(2) and\nSO(2) spin rotation symmetries. Essential ingredients for MCSR include the 3D\ninteractions, the confinement potential and a spin-flipping field. Near MCSR a\nmany-body spinor system exhibits exotic spin density distributions and pair\ncorrelations, which are significantly different from those near a\nsingle-channel resonance.",
        "positive": "An acoustic probe for quantum vorticity in Bose-Einstein condensates: We investigate the deformation of wavefronts of sound waves in rotating\nBose-Einstein condensates. In irrational fluid flows Berry et al. identified\nthis kind of deformation as the hydrodynamic analogue of the Aharonov-Bohm\neffect. We study this effect in Bose-Einstein condensates and obtain the\nAharonov-Bohm phase shift at all wavelengths. We show that this deformation of\nwave fronts is seen in both phase and density fluctuations. For wavelengths\nlarger than the healing length, the phase fluctuations experience a phase shift\nof the order of $2\\pi$ times the winding number. We also consider lattices of\nvortices. If the angular momentum of the vortices are aligned, the total phase\nshift is $2\\pi$ times the number of vortices in the condensate. Because of this\nbehaviour the hydrodynamic Aharonov-Bohm can be utilized as a probe for quantum\nvorticity, whose experimental realization could offers an alternative route to\ninvestigate quantum turbulence in the laboratory."
    },
    {
        "anchor": "Spin Susceptibility Above the Superfluid Onset in Ultracold Fermi Gases: Ultracold atomic Fermi gases can be tuned to interact strongly, where they\ndisplay spectroscopic signatures above the superfluid transition reminiscent of\nthe pseudogap in cuprates. However, the extent of the analogy can be\nquestioned, since thermodynamic quantities in the low temperature\nspin-imbalanced normal state can be described successfully using Fermi liquid\ntheory. Here we present spin susceptibility measurements across the interaction\nstrength-temperature phase diagram using a novel radiofrequency technique with\nultracold $^6\\textrm{Li}$ gases. For all significant interaction strengths and\nat all temperatures we find the spin susceptibility is reduced compared with\nthe equivalent value for a non-interacting Fermi gas, with the low temperature\nresults consistent with previous studies. However, our measurements extend to\nhigher temperatures, where we find that the reduction persists consistently\nwith a mean-field scenario. At unitarity, we can use the local density\napproximation to extract the spin susceptibility for the uniform gas, which is\nwell described by mean-field models at temperatures from the superfluid\ntransition to the Fermi temperature.",
        "positive": "Scaling dynamics of the ultracold Bose gas: The large-scale expansion dynamics of quantum gases is a central tool for\nultracold gas experiments and poses a significant challenge for theory. In this\nwork we provide an exact reformulation of the Gross-Pitaevskii equation for the\nultracold Bose gas in a coordinate frame that adaptively scales with the system\nsize during evolution, enabling simulations of long evolution times during\nexpansion or similar large-scale manipulation. Our approach makes no\nhydrodynamic approximations, is not restricted to a scaling ansatz, harmonic\npotentials, or energy eigenstates, and can be generalized readily to\nnon-contact interactions via the appropriate stress tensor of the quantum\nfluid. As applications, we simulate the expansion of the ideal gas, a\ncigar-shaped condensate in the Thomas-Fermi regime, and a linear superposition\nof counter propagating Gaussian wavepackets. We recover known scaling for the\nideal gas and Thomas-Fermi regimes, and identify a linear regime of\naspect-ratio preserving free expansion; analysis of the scaling dynamics\nequations shows that an exact, aspect-ratio invariant, free expansion does not\nexist for nonlinear evolution. Our treatment enables exploration of nonlinear\neffects in matter-wave dynamics over large scale-changing evolution."
    },
    {
        "anchor": "Critical velocity of a two-dimensional superflow past a potential\n  barrier of arbitrary penetrability: We theoretically investigate the critical velocity for dissipationless motion\nof a two-dimensional superfluid past a static potential barrier of large width.\nThe circular-shaped barrier provides a comprehensive analytical framework for\nthe critical speed, for which we derive closed-form expressions using the\nhydraulic approximation, the hodograph method, and Janzen-Rayleigh expansions\nof the velocity potential. These analytical estimates are shown to be in good\nagreement with the numerical results of an imaginary-time integration of the\nfull wave equation. In contrast to most of the state of the art, our study is\nnot restricted to an impenetrable potential barrier nor to a quartic\ninteraction Hamiltonian, which enables realistic modeling of recent experiments\nwith atomic Bose-Einstein condensates and paraxial superfluids of light in two\ndimensions.",
        "positive": "High-resolution coherent probe spectroscopy of a polariton quantum fluid: Characterising elementary excitations in quantum fluids is essential to study\ncollective effects within. We present an original angle-resolved coherent probe\nspectroscopy technique to study the dispersion of these excitation modes in a\nfluid of polaritons under resonant pumping. Thanks to the unprecedented\nspectral and spatial resolution, we observe directly the low-energy phononic\nbehaviour and detect the negative-energy modes, i.e. the \\textit{ghost branch},\nof the dispersion relation. In addition, we reveal narrow spectral features\nprecursory of dynamical instabilities due to the intrinsic out-of-equilibrium\nnature of the system. This technique provides the missing tool for the\nquantitative study of quantum hydrodynamics in polariton fluids."
    },
    {
        "anchor": "Coherent Manipulation of Spin Correlations in the Hubbard Model: We coherently manipulate spin correlations in a two-component atomic Fermi\ngas loaded into an optical lattice using spatially and time-resolved Ramsey\nspectroscopy combined with high-resolution \\textit{in situ} imaging. This novel\ntechnique allows us not only to imprint spin patterns but also to probe the\nstatic magnetic structure factor at arbitrary wave vector, in particular the\nstaggered structure factor. From a measurement along the diagonal of the\n$1^\\mathrm{st}$ Brillouin zone of the optical lattice, we determine the\nmagnetic correlation length and the individual spatial spin correlators. At\nhalf filling, the staggered magnetic structure factor serves as a sensitive\nthermometer for the spin temperature, which we employ to study the\nthermalization of spin and density degrees of freedom during a slow quench of\nthe lattice depth.",
        "positive": "Probing eigenstate thermalization in quantum simulators via\n  fluctuation-dissipation relations: The eigenstate thermalization hypothesis (ETH) offers a universal mechanism\nfor the approach to equilibrium of closed quantum many-body systems. So far,\nhowever, experimental studies have focused on the relaxation dynamics of\nobservables as described by the diagonal part of ETH, whose verification\nrequires substantial numerical input. This leaves many of the general\nassumptions of ETH untested. Here, we propose a theory-independent route to\nprobe the full ETH in quantum simulators by observing the emergence of\nfluctuation-dissipation relations, which directly probe the off-diagonal part\nof ETH. We discuss and propose protocols to independently measure fluctuations\nand dissipations as well as higher-order time ordered correlation functions. We\nfirst show how the emergence of fluctuation dissipation relations from a\nnonequilibrium initial state can be observed for the 2D Bose-Hubbard model in\nsuperconducting qubits or quantum gas microscopes. Then we focus on the\nlong-range transverse field Ising model (LTFI), which can be realized with\ntrapped ions. The LTFI exhibits rich thermalization phenomena: For strong\ntransverse fields, we observe prethermalization to an effective\nmagnetization-conserving Hamiltonian in the fluctuation dissipation relations.\nFor weak transverse fields, confined excitations lead to non-thermal features\nresulting in a violation of the fluctuation-dissipation relations up to long\ntimes. Moreover, in an integrable region of the LTFI, thermalization to a\ngeneralized Gibbs ensemble occurs and the fluctuation-dissipation relations\nenable an experimental diagonalization of the Hamiltonian. Our work presents a\ntheory-independent way to characterize thermalization in quantum simulators and\npaves the way to quantum simulate condensed matter pump-probe experiments."
    },
    {
        "anchor": "Pairing Dynamics of Polar States in a Quenched p-wave Superfluid Fermi\n  Gas: We study the pairing dynamics of polar states in a single species p-wave\nsuperfluid Fermi gas following a sudden change of the interaction strength. The\nanisotropy of pair interaction together with the presence of the centrifugal\nbarrier results in profoundly different pairing dynamics compared to the s-wave\ncase. Depending on the direction of quenches, quench to the BCS regime results\nin a large oscillatory depletion of momentum occupation inside the Fermi sea or\na large filling of momentum occupation. We elucidate a crucial role of the\nresonant state supported by the centrifugal barrier in the pairing dynamics.",
        "positive": "Hidden multiparticle excitation in weakly interacting Bose-Einstein\n  Condensate: We investigate multiparticle excitation effect on a collective density\nexcitation as well as a single-particle excitation in a weakly interacting\nBose--Einstein condensate (BEC). We find that although the weakly interacting\nBEC offers weak multiparticle excitation spectrum at low temperatures, this\nmultiparticle excitation effect may not remain hidden, but emerges as\nbimodality in the density response function through the single-particle\nexcitation. Identification of spectra in the BEC between the single-particle\nexcitation and the density excitation is also assessed at nonzero temperatures,\nwhich has been known to be unique nature in the BEC at absolute zero\ntemperature."
    },
    {
        "anchor": "The Stochastic Gross-Pitaevskii Methodology: We review the stochastic Gross-Pitaevskii approach for non-equilibrium finite\ntemperature Bose gases, focussing on the formulation of Stoof; this method\nprovides a unified description of condensed and thermal atoms, and can thus\ndescribe the physics of the critical fluctuation regime. We discuss\nsimplifications of the full theory, which facilitate straightforward numerical\nimplementation, and how the results of such stochastic simulations can be\ninterpreted, including the procedure for extracting phase-coherent\n(`condensate') and density-coherent (`quasi-condensate') fractions. The power\nof this methodology is demonstrated by successful ab initio modelling of\nseveral recent atom chip experiments, with the important information contained\nin each individual realisation highlighted by analysing dark soliton decay\nwithin a phase-fluctuating condensate.",
        "positive": "Phase-slips and vortex dynamics in Josephson oscillations between\n  Bose-Einstein condensates: We study the relation between Josephson dynamics and topological excitations\nin a dilute Bose-Einstein condensate confined in a double-well trap. We show\nthat the phase slips responsible for the self-trapping regime are created by\nvortex rings entering and annihilating inside the weak-link region or created\nat the center of the barrier and expanding outside the system. Large amplitude\noscillations just before the onset of self-trapping are also strictly connected\nwith the dynamics of vortex rings at the edges of the inter-well barrier. Our\nresults extend and analyze the dynamics of the vortex-induced phase slippages\nsuggested a few decades ago in relation to the \"ac\" Josephson effect of\nsuperconducting and superfluid helium systems."
    },
    {
        "anchor": "Exact analytical soliton solutions in dipolar BEC: The bright, dark and grey solitons are well-known soliton solutions of the\nGross-Pitaevskii equation for the attractive and repulsive BEC. We consider\nsolitons in the dipolar BEC of the fully polarized particles, speaking of the\ndipolar BEC we mean both the magnetized BEC and the electrically polarized BEC.\nWe show that these two types of the dipolar BEC reveal different behavior of\nthe collective excitations. This is related to the fact that the electric and\nthe magnetic fields satisfy to the different pairs of the Maxwell equation set.\nThus we consider them independently. We obtain exact analytical solutions for\nthe bright, dark, and grey solitons in the magnetized (electrically polarized)\nBEC when they propagate parallel and perpendicular to an external magnetic\n(electric) field. Comparison of spectrum of the linear collective excitations\nfor the two kinds of the dipolar BEC is presented as well.",
        "positive": "Wigner-localized states in spin-orbit-coupled bosonic ultracold atoms\n  with dipolar interaction: We investigate the occurence of Wigner-localization phenomena in bosonic\ndipolar ultracold few-body systems with Rashba-like spin-orbit coupling. We\nshow that the latter strongly enhances the effects of the dipole-dipole\ninteractions, allowing to reach the Wigner-localized regime for strengths of\nthe dipole moment much smaller than those necessary in the spin-orbit-free\ncase."
    },
    {
        "anchor": "Emergence of a pseudogap in the BCS-BEC crossover: Strongly correlated Fermi systems with pairing interactions become superfluid\nbelow a critical temperature $T_c$. The extent to which such pairing\ncorrelations alter the behavior of the liquid at temperatures $T > T_c$ is a\nsubtle issue that remains an area of debate, in particular regarding the\nappearance of the so-called pseudogap in the BCS-BEC crossover of unpolarized\nspin-$1/2$ nonrelativistic matter. To shed light on this, we extract several\nquantities of crucial importance at and around the unitary limit, namely: the\nodd-even staggering of the total energy, the spin susceptibility, the pairing\ncorrelation function, the condensate fraction, and the critical temperature\n$T_c$, using a non-perturbative, constrained-ensemble quantum Monte Carlo\nalgorithm.",
        "positive": "Towards analogue black hole merger: We study the effects of the wavevector-dependent losses on polariton\ncondensates. We demonstrate that because of these losses, a single vortex\nbecomes a center of a convergent flow, which allows describing it by an\nanalogue Kerr black hole metric with a dynamically evolving origin. For a pair\nof vortices, we find an analogue of the 3rd Kepler's law and estimate the\nemission rate of the gravitational waves. We simulate an analogue of the\ninspiral phase of a black hole merger. Our work therefore suggests that\npolariton condensates with quantum vortices represent a setting with a fully\nself-consistent dynamical metric for broad analogue studies."
    },
    {
        "anchor": "Competing quantum phases of hard-core boson with tilted dipole-dipole\n  interaction: Different quantum phases of hard-core boson induced by dipole-dipole\ninteraction with varying angles of polarization are discussed in this work. We\nconsider the two most influential leading terms with anisotropy due to the\ntilted polarization of the on-site boson in the square lattice. To ensure the\nconcreteness of this truncation, we compare our phase diagrams, obtained\nnumerically from cluster mean-field theory (CMFT) and infinite projected\nentangled-pair state (iPEPS), with that of the long-range interacting model\nfrom quantum Monte Carlo. Next, we focus on the case where the azimuthal angle\nis fixed to $\\phi = \\pi/4$. Using the mean-field analysis where the quantum\nspin operators are replaced by $c$-numbers, we aim to search for the underlying\nphases, especially the supersolid. Our results show a competing scenario mainly\nbetween two ordered phases with different sizes of unit cell, where first-order\ntransition takes place in between them. With the help of CMFT and variational\niPEPS, the phase boundaries predicted by the mean-field theory are determined\nmore precisely. Our discoveries elucidate the possible underlying supersolid\nphases which might be seen in the ultracold experiments with strongly dipolar\natoms. Moreover, our results indicate that an effective triangular optical\nlattice can be realized by fine tuning the polarization of dipoles in a square\nlattice.",
        "positive": "Auxiliary field formalism for dilute fermionic atom gases with tunable\n  interactions: We develop the auxiliary field formalism corresponding to a dilute system of\nspin-1/2 fermions. This theory represents the Fermi counterpart of the BEC\ntheory developed recently by F. Cooper et al. [Phys. Rev. Lett. 105, 240402\n(2010)] to describe a dilute gas of Bose particles. Assuming tunable\ninteractions, this formalism is appropriate for the study of the crossover from\nthe regime of Bardeen-Cooper-Schriffer (BCS) pairing to the regime of\nBose-Einstein condensation (BEC) in ultracold fermionic atom gases. We show\nthat when applied to the Fermi case at zero temperature, the leading-order\nauxiliary field (LOAF) approximation gives the same equations as those obtained\nin the standard BCS variational picture. At finite temperature, LOAF leads to\nthe theory discussed by by Sa de Melo, Randeria, and Engelbrecht [Phys. Rev.\nLett. 71, 3202(1993); Phys. Rev. B 55, 15153(1997)]. As such, LOAF provides a\nunified framework to study the interacting Fermi gas. The mean-field results\ndiscussed here can be systematically improved upon by calculating the\none-particle irreducible (1-PI) action corrections, order by order."
    },
    {
        "anchor": "Quench from Mott Insulator to Superfluid: We study a linear ramp of the nearest-neighbor tunneling rate in the\nBose-Hubbard model driving the system from the Mott insulator state into the\nsuperfluid phase. We employ the truncated Wigner approximation to simulate\nlinear quenches of a uniform system in 1,2, and 3 dimensions, and in a harmonic\ntrap in 3 dimensions. In all these setups the excitation energy decays like one\nover third root of the quench time. The -1/3 scaling arises from an\nimpulse-adiabatic approximation - a variant of the Kibble-Zurek mechanism -\ndescribing a crossover from non-adiabatic to adiabatic evolution when the\nsystem begins to keep pace with the increasing tunneling rate.",
        "positive": "Fast production of Bose-Einstein condensates of metastable Helium: We report on the Bose-Einstein condensation of metastable Helium-4 atoms\nusing a hybrid approach, consisting of a magnetic quadrupole and a crossed\noptical dipole trap. In our setup we cross the phase transition with 2x10^6\natoms, and we obtain pure condensates of 5x10^5 atoms in the optical trap. This\nnovel approach to cooling Helium-4 provides enhanced cycle stability, large\noptical access to the atoms and results in production of a condensate every 6\nseconds - a factor 3 faster than the state-of-the-art. This speed-up will\ndramatically reduce the data acquisition time needed for the measurement of\nmany particle correlations, made possible by the ability of metastable Helium\nto be detected individually."
    },
    {
        "anchor": "Quantum phase diagram of the integrable p_x+ip_y fermionic superfluid: We determine the zero temperature quantum phase diagram of a p_x+ip_y pairing\nmodel based on the exactly solvable hyperbolic Richardson-Gaudin model. We\npresent analytical and large-scale numerical results for this model. In the\ncontinuum limit, the exact solution exhibits a third-order quantum phase\ntransition, separating a strong-pairing from a weak-pairing phase. The mean\nfield solution allows to connect these results to other models with p_x+ip_y\npairing order. We define an experimentally accessible characteristic length\nscale, associated with the size of the Cooper pairs, that diverges at the\ntransition point, indicating that the phase transition is of a\nconfinement-deconfinement type without local order parameter. We show that this\nphase transition is not limited to the p_x+ip_y pairing model, but can be found\nin any representation of the hyperbolic Richardson-Gaudin model and is related\nto a symmetry that is absent in the rational Richardson-Gaudin model.",
        "positive": "Pair condensation in a Finite Trapped Fermi Gas: Superfluidity in the cold atomic two-species Fermi gas system in the unitary\nlimit of infinite scattering length remains incompletely understood. In\nparticular, a pseudogap phase has been proposed to exist above the superfluid\ncritical temperature. Here we apply the auxiliary-field quantum Monte Carlo\nmethod to perform the first ab initio calculations of the temperature\ndependence of three quantities -- the energy-staggering pairing gap, the\ncondensate fraction and the heat capacity -- in a trapped finite-size cold atom\nsystem. As the calculations of the energy-staggering pairing gap require the\nuse of the canonical ensemble, we employ a novel algorithm for the\nstabilization of particle-number projection that is essential for reaching\nconvergence in the size of the model space. We observe clear signatures of the\nsuperfluid phase transition in all three quantities, including a signature of\nthe recently measured lambda peak in the heat capacity, but find no evidence of\na pseudogap effect in the energy-staggering pairing gap."
    },
    {
        "anchor": "Analytical approach to the Bose polaron problem in one dimension: We discuss the ground state properties of a one-dimensional bosonic system\ndoped with an impurity (the so-called Bose polaron problem). We introduce a\nformalism that allows us to calculate analytically the thermodynamic\nzero-temperature properties of this system with weak and moderate boson-boson\ninteraction strengths for any boson-impurity interaction. Our approach is\nvalidated by comparing to exact quantum Monte Carlo calculations. In addition,\nwe test the method in finite size systems using numerical results based upon\nthe similarity renormalization group. We argue that the introduced approach\nprovides a simple analytical tool for studies of strongly interacting impurity\nproblems in one dimension.",
        "positive": "Thermally Condensing Photons into a Coherently Split State of Light: Techniques to control the quantum state of light play a crucial role in a\nwide range of fields, from quantum information science to precision\nmeasurements. While for electrons in solid state materials complex quantum\nstates can be created by mere cooling, in the field of optics manipulation and\ncontrol currently builds on non-thermodynamic methods. Using an optical dye\nmicrocavity, we have split photon wavepackets by thermalization within a\npotential with two minima subject to tunnel coupling. Even at room temperature,\nphotons condense into a quantum-coherent bifurcated ground state. Fringe\nsignals upon recombination show the relative coherence between the two wells,\ndemonstrating a working interferometer with the non-unitary thermodynamic\nbeamsplitter. This energetically driven optical state preparation opens up an\navenue for exploring novel correlated and entangled optical manybody states."
    },
    {
        "anchor": "Photoemission spectrum and effect of inhomogeneous pairing fluctuations\n  in the BCS-BEC crossover regime of an ultracold Fermi gas: We investigate the photoemission-type spectrum in a cold Fermi gas which was\nrecently measured by JILA group [J. T. Stewart {\\it et al}., Nature\n\\textbf{454}, 744 (2008)]. This quantity gives us very useful information about\nsingle-particle properties in the BCS-BEC crossover. In this letter, including\npairing fluctuations within a $T$-matrix theory, as well as effects of a\nharmonic trap within the local density approximation, we show that spatially\ninhomogeneous pairing fluctuations due to the trap potential is an important\nkey to understand the observed spectrum. In the crossover region, while strong\npairing fluctuations lead to the so-called pseudogap phenomenon in the trap\ncenter, such strong-coupling effects are found to be weak around the edge of\nthe gas. Our results including this effect are shown to agree well with the\nrecent photoemission data by JILA group.",
        "positive": "Many-body non-Hermitian skin effect under dynamic gauge coupling: We study an atom-cavity hybrid system where fermionic atoms in a\none-dimensional lattice are subject to a cavity-induced dynamic gauge\npotential. The gauge coupling leads to highly-degenerate steady states in which\nthe fermions accumulate to one edge of the lattice under an open boundary\ncondition. Such a phenomenon originates from the many-body Liouvillian\nsuperoperator of the system, which, being intrinsically non-Hermitian, is\nunstable against boundary perturbations and manifests the non-Hermitian skin\neffect. Contrary to the single-body case, the steady state of a multi-atom\nsystem is approached much slower under the open boundary condition, as the\nlong-time damping of the cavity mode exhibits distinct rates at different\ntimes. This stage-wise slowdown is attributed to the competition between\nlight-assisted hopping and the dynamic gauge coupling, which significantly\nreduces the steady-state degeneracy under the open boundary condition, as\ndistinct hosts of quasi-steady states dominate the dynamics at different time\nscales."
    },
    {
        "anchor": "Mean-field dynamics of two-mode Bose-Einstein condensates in highly\n  anisotropic potentials: Interference, dimensionality, and entanglement: We study the mean-field dynamics and the reduced-dimension character of\ntwo-mode Bose-Einstein condensates (BECs) in highly anisotropic traps. By means\nof perturbative techniques, we show that the tightly confined (transverse)\ndegrees of freedom can be decoupled from the dynamical equations at the expense\nof introducing additional effective three-body, attractive, intra- and\ninter-mode interactions into the dynamics of the loosely confined\n(longitudinal) degrees of freedom. These effective interactions are mediated by\nchanges in the transverse wave function. The perturbation theory is valid as\nlong as the nonlinear scattering energy is small compared to the transverse\nenergy scales. This approach leads to reduced-dimension mean-field equations\nthat optimally describe the evolution of a two-mode condensate in general\nquasi-1D and quasi-2D geometries. We use this model to investigate the relative\nphase and density dynamics of a two-mode, cigar-shaped $^{87}$Rb BEC. We study\nthe relative-phase dynamics in the context of a nonlinear Ramsey interferometry\nscheme, which has recently been proposed as a novel platform for high-precision\ninterferometry. Numerical integration of the coupled, time-dependent,\nthree-dimensional, two-mode Gross-Pitaevskii equations for various atom numbers\nshows that this model gives a considerably more refined analytical account of\nthe mean-field evolution than an idealized quasi-1D description.",
        "positive": "Variational calculations on multilayer stacks of dipolar Bose-Einstein\n  condensates: We investigate a multilayer stack of dipolar Bose-Einstein condensates in\nterms of a simple Gaussian variational ansatz and demonstrate that this\narrangement is characterized by the existence several stationary states. Using\na Hamiltonian picture we show that in an excited stack there is a coupled\nmotion of the individual condensates by which they exchange energy. We find\nthat for high excitations the interaction between the single condensates can\ninduce the collapse of one of them. We furthermore demonstrate that one\ncollapse in the stack can force other collapses, too. We discuss the\npossibility of experimentally observing the coupled motion and the relevance of\nthe variational results found to full numerical investigations."
    },
    {
        "anchor": "Beyond mean-field properties of binary dipolar Bose mixtures at low\n  temperatures: We rigorously analyze the low-temperature properties of homogeneous\nthree-dimensional two-component Bose mixture with dipole-dipole interaction.\nFor such a system the effective hydrodynamic action that governs the behavior\nof low-energy excitations is derived. The infrared structure of the exact\nsingle-particle Green's functions is obtained in terms of macroscopic\nparameters, namely the inverse compressibility and the superfluid density\nmatrices. Within one-loop approximation we calculate the anisotropic superfluid\nand condensate densities and give the beyond mean-field stability condition for\nthe binary dipolar Bose gas. A brief variational derivation of the coupled\nequations that describe macroscopic hydrodynamics of the system in the external\nnon-uniform potential at zero temperature is presented.",
        "positive": "Dynamical universality classes towards an infinite temperature state: Dynamical universality is the observation that the dynamical properties of\ndifferent systems might exhibit universal behavior that are independent of the\nsystem details. In this paper, we study the long-time dynamics of an\none-dimensional noisy quantum magnetic model, and find that even though the\nsystem are inevitably driven to an infinite temperature state, the relaxation\ndynamics towards such featureless state can be highly nontrivial and universal.\nThe effect of various mode-coupling mechanisms (external potential, disorder,\ninteraction, and the interplay between them) as well as the conservation law on\nthe long-time dynamics of the systems have been studied, and their relevance\nwith current ultracold atomic experiments have been discussed."
    },
    {
        "anchor": "Emission of particles from a parametrically driven condensate in a\n  one-dimensional lattice: Motivated by recent experiments, we calculate particle emission from a\nBose-Einstein condensate trapped in a single deep well of a one-dimensional\nlattice when the interaction strength is modulated. In addition to pair\nemission, which has been widely studied, we observe single-particle emission.\nWithin linear response, we are able to write closed-form expressions for the\nsingle-particle emission rates and reduce the pair emission rates to\none-dimensional integrals. The full nonlinear theory of single-particle\nemission is reduced to a single variable integrodifferential equation, which we\nnumerically solve.",
        "positive": "Equilibration of a Tonks-Girardeau gas following a trap release: We study the non-equilibrium dynamics of a Tonks-Girardeau gas released from\na parabolic trap to a circle. We present the exact analytic solution of the\nmany body dynamics and prove that, for large times and in a properly defined\nthermodynamic limit, the reduced density matrix of any finite subsystem\nconverges to a generalized Gibbs ensemble. The equilibration mechanism is\nexpected to be the same for all one-dimensional systems."
    },
    {
        "anchor": "A grand-canonical approach to the disordered Bose gas: We study the problem of disordered interacting bosons within grand-canonical\nthermodynamics and Bogoliubov theory. We compute the fractions of condensed and\nnon-condensed particles and corrections to the compressibility and the speed of\nsound due to interaction and disorder. There are two small parameters, the\ndisorder strength compared to the chemical potential and the dilute-gas\nparameter.",
        "positive": "Analytical study of static beyond-Frohlich Bose polarons in one\n  dimension: Grusdt et al. [New J. Phys. 19, 103035 (2017)] recently made a\nrenormalization group study of a one-dimensional Bose polaron in cold atoms.\nTheir study went beyond the usual Frohlich description, which includes only\nsingle-phonon processes, by including two-phonon processes in which two phonons\nare simultaneously absorbed or emitted during impurity scattering [Shchadilova\net al. Phys. Rev. Lett. 117, 113002 (2016)]. We study this same beyond-Frohlich\nmodel, but in the static impurity limit where the ground state is described by\na multimode squeezed state instead of the multimode coherent state in the\nstatic Frohlich model. We solve the system exactly by applying the generalized\nBogoliubov transformation, an approach that can be straightforwardly adapted to\nhigher dimensions. Using our exact solution, we obtain a polaron energy free of\ninfrared divergences and construct analytically the polaron phase diagram. We\nfind that the repulsive polaron is stable on the positive side of the\nimpurity-boson interaction but is always thermodynamically unstable on the\nnegative side of the impurity-boson interaction, featuring a bound state, whose\nbinding energy we obtain analytically. We find that the attractive polaron is\nalways dynamically unstable, featuring a pair of imaginary energies which we\nobtain analytically. We expect the multimode squeezed state to help with\nstudies that go not only beyond the Frohlich paradigm but also beyond\nBogoliubov theory, just as the multimode coherent state has helped with the\nstudy of Frohlich polarons."
    },
    {
        "anchor": "P-wave superfluidity of atomic lattice fermions: We discuss the emergence of p-wave superfluidity of identical atomic fermions\nin a two-dimensional optical lattice. The optical lattice potential manifests\nitself in an interplay between an increase in the density of states on the\nFermi surface and the modification of the fermion-fermion interaction\n(scattering) amplitude. The density of states is enhanced due to an increase of\nthe effective mass of atoms. In deep lattices the scattering amplitude is\nstrongly reduced compared to free space due to a small overlap of wavefunctions\nof fermion sitting in the neighboring lattice sites, which suppresses the\np-wave superfluidity. However, for moderate lattice depths the enhancement of\nthe density of states can compensate the decrease of the scattering amplitude.\nMoreover, the lattice setup significantly reduces inelastic collisional losses,\nwhich allows one to get closer to a p-wave Feshbach resonance. This opens\npossibilities to obtain the topological $p_x+ip_y$ superfluid phase, especially\nin the recently proposed subwavelength lattices. We demonstrate this for the\ntwo-dimensional version of the Kronig-Penney model allowing a transparent\nphysical analysis.",
        "positive": "Landau-Zener Transitions in Chains: We determine transition probabilities in two exactly solvable multistate\nLandau-Zener (LZ) models and discuss applications of our results to the theory\nof dynamic passage through a phase transition in the dissipationless quantum\nmechanical regime. In particular, we show that statistics of particles in a new\nphase demonstrate scaling behavior. Our results also reveal a symmetry that we\nclaim is a property of a large class of multistate LZ models, whose explicit\nsolutions are not presently known. We support our arguments by direct numerical\nsimulations."
    },
    {
        "anchor": "Landau Effective Interaction between Quasiparticles in a Bose-Einstein\n  Condensate: Landau's description of the excitations in a macroscopic system in terms of\nquasiparticles stands out as one of the highlights in quantum physics. It\nprovides an accurate description of otherwise prohibitively complex many-body\nsystems, and has led to the development of several key technologies. In this\npaper, we investigate theoretically the Landau effective interaction between\nquasiparticles, so-called Bose polarons, formed by impurity particles immersed\nin a Bose-Einstein condensate (BEC). In the limit of weak interactions between\nthe impurities and the BEC, we derive rigorous results for the effective\ninteraction. They show that it can be strong even for weak impurity-boson\ninteraction, if the transferred momentum/energy between the quasiparticles is\nresonant with a sound mode in the BEC. We then develop a diagrammatic scheme to\ncalculate the effective interaction for arbitrary coupling strengths, which\nrecovers the correct weak coupling results. Using this, we show that the Landau\neffective interaction in general is significantly stronger than that between\nquasiparticles in a Fermi gas, mainly because a BEC is more compressible than a\nFermi gas. The interaction is particularly large near the unitarity limit of\nthe impurity-boson scattering, or when the quasiparticle momentum is close to\nthe threshold for momentum relaxation in the BEC. Finally, we show how the\nLandau effective interaction leads to a sizeable shift of the quasiparticle\nenergy with increasing impurity concentration, which should be detectable with\npresent day experimental techniques.",
        "positive": "Loading of bosons in optical lattices into the p band: We present a method for transferring bosonic atoms residing on the lowest\ns-band of an optical lattice to the first excited p-bands. Our idea hinges on\nresonant tunneling between adjacent sites of accelerated lattices. The\nacceleration effectively shifts the quasi-bound energies on each site such that\nthe system can be cast into a Wannier-Stark ladder problem. By adjusting the\nacceleration constant, a situation of resonant tunneling between the s- and\np-bands is achievable. Within a mean-field model, considering 87Rb atoms, we\ndemonstrate population transfer from the s- to the p-bands with around 95 %\nefficiency. Nonlinear effects deriving from atom-atom interactions, as well as\ncoupling of the quasi bound Wannier-Stark states to the continuum, are\nconsidered."
    },
    {
        "anchor": "Spectral flow of trimer states of two heavy impurities and one light\n  condensed boson: The spectral flow of three-body (trimer) states consisting of two heavy\n(impurity) particles sitting in a condensate of light bosons is considered.\nAssuming that the condensate is weakly interaction and that an impurity and a\nboson have a zero-range two-body interaction, we use the Born-Oppenheimer\napproximation to determine the effective three-body potential. We solve the\nresulting Schr\\\"odinger equation numerically and determine the trimer binding\nenergies as a function of the coherence length of the light bosonic condensate\nparticles. The binding energy is found to be suppressed by the presence of the\ncondensate when the energy scale corresponding to the coherence length becomes\nof order the trimer binding energy in the absence of the condensate. We find\nthat the Efimov scaling property is reflected in the critical values of the\ncondensate coherence length at which the trimers are pushed into the continuum.",
        "positive": "Detecting topology through dynamics in interacting fermionic wires: We describe a protocol to read out the topological invariant of interacting\n1D chiral models, based on measuring the mean chiral displacement of\ntime-evolving bulk excitations. We present analytical calculations and\nnumerical Matrix Product State simulations of interacting Su-Schrieffer-Heeger\n(SSH) chains, demonstrating how the mean chiral displacement allows to\ndistinguish between topological insulator, trivial insulator and\nsymmetry-broken phases. Finally, we provide an experimental blueprint for\nrealizing a model displaying these three phases and describe how to detect\nthose."
    },
    {
        "anchor": "Matter-wave recombiners for trapped Bose-Einstein condensates: Interferometry with trapped atomic Bose-Einstein condensates (BECs) requires\nthe development of techniques to recombine the two paths of the interferometer\nand map the accumulated phase difference to a measurable atom number\ndifference. We have implemented and compared two recombining procedures in a\ndouble-well based BEC interferometer. The first procedure utilizes the bosonic\nJosephson effect and controlled tunneling of atoms through the potential\nbarrier, similar to laser light in an optical fibre coupler. The second one\nrelies on the interference of the reflected and transmitted parts of the BEC\nwavefunction when impinging on the potential barrier, analogous to light\nimpinging on a half-silvered mirror. Both schemes were implemented\nsuccessfully, yielding an interferometric contrast of about 20% and 42%\nrespectively. Building efficient matter wave recombiners represents an\nimportant step towards the coherent manipulation of external quantum\nsuperposition states of BECs.",
        "positive": "Vortex Rings in a Trap: We present a simple Hamiltonian description of the dynamics of a quantized\nvortex ring in a trapped superfluid, compare this description with dynamical\nsimulations, and characterize the dependence of the dynamics of the shape of\nthe trap."
    },
    {
        "anchor": "Optical runaway evaporation for multi-BEC production: We report on parallel production of Bose-Einstein condensates (BECs) in\nsteerable, multi-plexed crossed optical dipole traps. Using a conventional\ntrap-weakening evaporation scheme, where the optical trapping power is lowered,\nwe obtain an array of up to four independent BECs. To improve evaporation\nefficiency, we propose to target each crossed trap site with a narrow auxiliary\nlaser beam, creating an escape channel for energetic atoms. We experimentally\ndemonstrate runaway evaporation using this scheme, which is characterized by\nvery modest weakening in atomic confinement such that high densities and\nelastic collision rates can be maintained. Based on discretely time-shared\noptical tweezers, our approach is particularly suited for addressing the\nproblem of simultaneously cooling atoms in multiple traps clouds, providing the\nfreedom to act locally and in a tailored fashion at individual trap sites.",
        "positive": "Yang-Gaudin model: A paradigm of many-body physics: Using Bethe's hypothesis, C N Yang exactly solved the one-dimensional (1D)\ndelta-function interacting spin-1/2 Fermi gas with an arbitrary spin-imbalance\nin 1967. At that time, using a different method, M Gaudin solved the problem of\ninteracting fermions in a spin-balanced case. Later, the 1D delta-function\ninteracting fermion problem was named as the Yang-Gaudin model. It has been in\ngeneral agreed that a key discovery of C N Yang's work was the cubic matrix\nequation for the solvability conditions. % This equation was later\nindependently found by R J Baxter for commuting transfer matrices of 2D exactly\nsolvable vertex models. % The equation has since been referred to Yang-Baxter\nequation, being the master equation to integrability. % The Yang-Baxter\nequation has been used to solve a wide range of 1D many-body problems in\nphysics, such as 1D Hubbard model, $SU(N)$ Fermi gases, Kondo impurity problem\nand strongly correlated electronic systems etc.\n  % In this paper, we will briefly discuss recent developments of the\nYang-Gaudin model on several breakthroughs of many-body phenomena, ranging from\nthe universal thermodynamics to the Luttigner liquid, the spin charge\nseparation, the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)-like pairing state and\nthe quantum criticality.\n  %\n  These developments demonstrate that the Yang-Gaudin model has laid out a\nprofound legacy of the Yang-Baxter equation."
    },
    {
        "anchor": "Impurity-induced multi-body resonances in a Bose gas: We investigate the problem of $N$ identical bosons that are coupled to an\nimpurity particle with infinite mass. For non-interacting bosons, we show that\na dynamical impurity-boson interaction, mediated by a closed-channel dimer, can\ninduce an effective boson-boson repulsion which strongly modifies the bound\nstates consisting of the impurity and $N$ bosons. In particular, we demonstrate\nthe existence of two universal 'multi-body' resonances, where all multi-body\nbound states involving any $N$ emerge and disappear. The first multi-body\nresonance corresponds to infinite impurity-boson scattering length, $a\\to\n+\\infty$, while the second corresponds to the critical scattering length\n$a^*>0$ beyond which the trimer ($N=2$ bound state) ceases to exist. Crucially,\nwe show that the existence of $a^*$ ensures that the ground-state energy in the\nmulti-body bound-state region, $\\infty>a> a^*$, is bounded from below, with a\nbound that is independent of $N$. Thus, even though the impurity can support\nmulti-body bound states, they become increasingly fragile beyond the dimer\nstate. This has implications for the nature of the Bose polaron currently being\nstudied in cold-atom experiments.",
        "positive": "The variational theorem for the scattering length in low dimensions and\n  its applications to universal systems: The variational theorem for the scattering length [Cherny and Shanenko, Phys.\nRev. E 62, 1646 (2000)] is extended to one and two dimensions. It is shown that\nthe arising singularities can be treated in terms of generalized functions. The\nvariational theorem is applied to a universal many-body system of spinless\nbosons. The extended Tan adiabatic sweep theorem is obtained for interacting\npotentials of arbitrary shape with the variation of the one-particle\ndispersion. The pair distribution function is calculated at short distances by\nmeans of the variation of the potential. The suggested scheme is based on\nsimple quantum mechanics; it is physically transparent and free from any\ndivergence."
    },
    {
        "anchor": "Modulation-assisted tunneling in laser-fabricated photonic Wannier-Stark\n  ladders: We observe Wannier-Stark localization in curved photonic lattices, realized\nusing arrays of evanescently coupled optical waveguides. By correctly tuning\nthe strength of inter-site coupling in the lattice, we observe that\nWannier-Stark states become increasingly localized, and eventually fully\nlocalized to one site, as the curvature of the lattice is increased. We then\ndemonstrate that tunneling can be successfully restored in the lattice by\napplying a sinusoidal modulation to the lattice position, an effect that is a\ndirect analogue of photon-assisted tunneling. This precise tuning of the\ntunneling matrix elements, through laser-fabricated on-site modulations, opens\na novel route for the creation of gauge fields in photonic lattices.",
        "positive": "Spontaneous coherence of indirect excitons in a trap: We report on the emergence of spontaneous coherence in a gas of indirect\nexcitons in an electrostatic trap. At low temperatures, the exciton coherence\nlength becomes much larger than the thermal de Broglie wavelength and reaches\nthe size of the exciton cloud in the trap."
    },
    {
        "anchor": "Collective quantum jumps of Rydberg atoms: We study an open quantum system of atoms with long-range Rydberg interaction,\nlaser driving, and spontaneous emission. Over time, the system occasionally\njumps between a state of low Rydberg population and a state of high Rydberg\npopulation. The jumps are inherently collective and in fact exist only for a\nlarge number of atoms. We explain how entanglement and quantum measurement\nenable the jumps, which are otherwise classically forbidden.",
        "positive": "Mesoscopic supersolid of dipoles in a trap: A mesoscopic system of indirect dipolar bosons trapped by a harmonic\npotential is considered. The system has a number of physical realizations\nincluding dipole excitons, atoms with large dipolar moment, polar molecules,\nRydberg atoms in inhomogenious electric field. We carry out a diffusion Monte\nCarlo simulation to define the quantum properties of a two-dimensional system\nof trapped dipoles at zero temperature. In dimensionless units the system is\ndescribed by two control parameters, namely the number of particles and the\nstrength of the interparticle interaction. We have shown that when the\ninterparticle interaction is strong enough a mesoscopic crystal is formed. As\nthe strength of interactions is decreased a multi-stage melting takes place.\nOff-diagonal order in the system is tested using natural orbitals analysis. We\nhave found that the system might be Bose-condensed even in the case of strong\ninterparticle interactions. There is a set of parameters for which a spatially\nordered structure is formed while simultaneously the fraction of Bose condensed\nparticles is non zero. This might be considered as a realization of a\nmesoscopic supersolid."
    },
    {
        "anchor": "Stabilizing Topological Superfluidity of Lattice Fermions: Attractive interaction between spinless fermions in a two-dimensional lattice\ndrives the formation of a topological superfluid. But the topological phase is\ndynamically unstable towards phase separation when the system has a high\ndensity of states and large interaction strength. This limits the critical\ntemperature to an experimentally challenging regime where, for example, even\nultracold atoms and molecules in optical lattices would struggle to realize the\ntopological superfluid. We propose that the introduction of a weaker\nlonger-range repulsion, in addition to the short-range attraction between\nlattice fermions, will suppress the phase separation instability. Taking the\nhoneycomb lattice as an example, we show that our proposal significantly\nenlarges the stable portion of the topological superfluid phase and increases\nthe critical temperature by an order of magnitude. Our work opens a route to\nenhance the stability of topological superfluids by engineering inter-particle\ninteractions.",
        "positive": "Particle-hole symmetric localization in optical lattices using time\n  modulated random on-site potentials: The random hopping models exhibit many fascinating features, such as\ndiverging localization length and density of states as energy approaches the\nbandcenter, due to its particle-hole symmetry. Nevertheless, such models are\nyet to be realized experimentally because the particle-hole symmetry is easily\ndestroyed by diagonal disorder. Here we propose that a pure random hopping\nmodel can be effectively realized in ultracold atoms by modulating a disordered\nonsite potential in particular frequency ranges. This idea is motivated by the\nrecent development of the phenomena called \"dynamical localization\" or\n\"coherent destruction of tunneling\". Investigating the application of this idea\nin one dimension, we find that if the oscillation frequency of the disorder\npotential is gradually increased from zero to infinity, one can tune a\nnon-interacting system from an Anderson insulator to a random hopping model\nwith diverging localization length at the band center, and eventually to a\nuniform-hopping tight-binding model."
    },
    {
        "anchor": "Heralded magnetism in non-Hermitian atomic systems: Quantum phase transitions are usually studied in terms of Hermitian\nHamiltonians. However, cold-atom experiments are intrinsically non-Hermitian\ndue to spontaneous decay. Here, we show that non-Hermitian systems exhibit\nquantum phase transitions that are beyond the paradigm of Hermitian physics. We\nconsider the non-Hermitian XY model, which can be implemented using three-level\natoms with spontaneous decay. We exactly solve the model in one dimension and\nshow that there is a quantum phase transition from short-range order to\nquasi-long-range order despite the absence of a continuous symmetry in the\nHamiltonian. The ordered phase has a frustrated spin pattern. The critical\nexponent $\\nu$ can be 1 or 1/2. Our results can be seen experimentally with\ntrapped ions, cavity QED, and atoms in optical lattices.",
        "positive": "Beyond universality in repulsive SU(N) Fermi gases: Itinerant ferromagnetism in dilute Fermi gases is predicted to emerge at\nvalues of the gas parameter where second-order perturbation theory is not\naccurate enough to properly describe the system. We have revisited perturbation\ntheory for SU(N) fermions and derived its generalization up to third order both\nin terms of the gas parameter and the polarization. Our results agree\nsatisfactorily with quantum Monte Carlo results for hard-sphere and soft-sphere\npotentials for $S = 1/2$. Although the nature of the phase transition depends\non the interaction potential, we find that for a hard-sphere potential a phase\ntransition is guaranteed to occur. While for $S= 1/2$ we observe a\nquasi-continuous transition, for spins $3/2$ and $5/2$, a first-order phase\ntransition is found. For larger spins, a double transition (combination of\ncontinuous and discontinuous) occurs. The critical density reduces drastically\nwhen the spin increases, making the phase transition more accessible to\nexperiments with ultracold dilute Fermi gases. Estimations for Fermi gases of\nYb and Sr with spin $5/2$ and $9/2$, respectively, are reported."
    },
    {
        "anchor": "Topological Insulators with Ultracold Atoms: Ultracold atom research presents many avenues to study problems at the\nforefront of physics. Due to their unprecedented controllability, these systems\nare ideally suited to explore new exotic states of matter, which is one of the\nkey driving elements of the condensed matter research. One such topic of\nconsiderable importance is topological insulators, materials that are\ninsulating in the interior but conduct along the edges. Quantum Hall and its\nclose cousin Quantum Spin Hall states belong to the family of these exotic\nstates and are the subject of this chapter.",
        "positive": "Chiral confinement in quasirelativistic Bose-Einstein condensates: In the presence of a laser-induced spin-orbit coupling an interacting ultra\ncold spinor Bose-Einstein condensate may acquire a quasi-relativistic character\ndescribed by a non-linear Dirac-like equation. We show that as a result of the\nspin-orbit coupling and the non-linearity the condensate may become\nself-trapped, resembling the so-called chiral confinement, previously studied\nin the context of the massive Thirring model. We first consider 1D geometries\nwhere the self-confined condensates present an intriguing sinusoidal dependence\non the inter-particle interactions. We further show that multi-dimensional\nchiral-confinement is also possible under appropriate feasible laser\narrangements, and discuss the properties of 2D and 3D condensates, which differ\nsignificantly from the 1D case."
    },
    {
        "anchor": "Controlling the transverse instability of dark solitons and nucleation\n  of vortices by a potential barrier: We study possibilities to suppress the transverse modulational instability\n(MI) of dark-soliton stripes in two-dimensional (2D) Bose-Einstein condensates\n(BECs) and self-defocusing bulk optical waveguides by means of quasi-1D\nstructures. Adding an external repulsive barrier potential (which can be\ninduced in BEC by a laser sheet, or by an embedded plate in optics), we\ndemonstrate that it is possible to reduce the MI wavenumber band, and even\nrender the dark-soliton stripe completely stable. Using this method, we\ndemonstrate the control of the number of vortex pairs nucleated by each spatial\nperiod of the modulational perturbation. By means of the perturbation theory,\nwe predict the number of the nucleated vortices per unit length. The analytical\nresults are corroborated by the numerical computation of eigenmodes of small\nperturbations, as well as by direct simulations of the underlying\nGross-Pitaevskii/nonlinear Schr\\\"{o}dinger equation.",
        "positive": "Magnetic control of polariton spin transport: We show the full control of the polarization dynamics of a propagating\nexciton-polariton condensate in a planar microcavity by using a magnetic field\napplied in the Voigt geometry. The change of the spin-beat frequency, the\nsuppression of the optical spin Hall effect and the rotation of the\npolarization pattern by the magnetic field are theoretically reproduced by\naccounting for the magneto-induced mixing of exciton-polariton and dark, spin\nforbidden, exciton states."
    },
    {
        "anchor": "Quantum critical behavior of the superfluid-Mott glass transition: We investigate the zero-temperature superfluid to insulator transitions in a\ndiluted two-dimensional quantum rotor model with particle-hole symmetry. We map\nthe Hamiltonian onto a classical $(2+1)$-dimensional XY model with columnar\ndisorder which we analyze by means of large-scale Monte Carlo simulations. For\ndilutions below the lattice percolation threshold, the system undergoes a\ngeneric superfluid-Mott glass transition. In contrast to other quantum phase\ntransitions in disordered systems, its critical behavior is of conventional\npower-law type with universal (dilution-independent) critical exponents\n$z=1.52(3)$, $\\nu=1.16(5)$, $\\beta/\\nu= 0.48(2)$, $\\gamma/\\nu=2.52(4)$, and\n$\\eta=-0.52(4)$. These values agree with and improve upon earlier Monte-Carlo\nresults [Phys. Rev. Lett. 92, 015703 (2004)] while (partially) excluding other\nfindings in the literature. As a further test of universality, we also consider\na soft-spin version of the classical Hamiltonian. In addition, we study the\npercolation quantum phase transition across the lattice percolation threshold;\nits critical behavior is governed by the lattice percolation exponents in\nagreement with recent theoretical predictions. We relate our results to a\ngeneral classification of phase transitions in disordered systems, and we\nbriefly discuss experiments.",
        "positive": "Quantum magnetism and topological ordering via enhanced Rydberg-dressing\n  near F\u007f\u00f6rster-resonances: We devise a cold-atom approach to realizing a broad range of bi-linear\nquantum magnets. Our scheme is based on off-resonant single-photon excitation\nof Rydberg $P$-states (Rydberg-dressing), whose strong interactions are shown\nto yield controllable XYZ-interactions between effective spins, represented by\ndifferent atomic ground states. The distinctive features of F\\\"orster-resonant\nRydberg atom interactions are exploited to enhance the effectiveness of\nRydberg-dressing and, thereby, yield large spin-interactions that greatly\nexceed corresponding decoherence rates. We illustrate the concept on a spin-1\nchain implemented with cold Rubidium atoms, and demonstrate that this permits\nthe dynamical preparation of topological magnetic phases. Generally, the\ndescribed approach provides a viable route to exploring quantum magnetism with\ndynamically tuneable (an)isotropic interactions as well as variable space- and\nspin-dimensions in cold-atom experiments."
    },
    {
        "anchor": "Accessing finite momentum excitations of the one-dimensional\n  Bose-Hubbard model using superlattice modulation spectroscopy: We investigate the response to superlattice modulation of a bosonic quantum\ngas confined to arrays of tubes emulating the one-dimensional Bose-Hubbard\nmodel. We demonstrate, using both time-dependent density matrix renormalization\ngroup and linear response theory, that such a superlattice modulation gives\naccess to the excitation spectrum of the Bose-Hubbard model at finite momenta.\nDeep in the Mott-insulator, the response is characterized by a narrow energy\nabsorption peak at a frequency approximately corresponding to the onsite\ninteraction strength between bosons. This spectroscopic technique thus allows\nfor an accurate measurement of the effective value of the interaction strength.\nOn the superfluid side, we show that the response depends on the lattice\nfilling. The system can either respond at infinitely small values of the\nmodulation frequency or only above a frequency threshold. We discuss our\nnumerical findings in light of analytical results obtained for the Lieb-Liniger\nmodel. In particular, for this continuum model, bosonization predicts power-law\nonsets for both responses.",
        "positive": "Beyond Gaussian pair fluctuation theory for strongly interacting Fermi\n  gases: Interacting Fermi systems in the strongly correlated regime play a\nfundamental role in many areas of physics and are of particular interest to the\ncondensed matter community. Though weakly inter- acting fermions are\nunderstood, strongly correlated fermions are difficult to describe\ntheoretically as there is no small interaction parameter to expand about.\nExisting strong coupling theories rely heavily on the so-called many-body\nT-matrix approximation that sums ladder-type Feynman diagrams. Here, by\nacknowledging the fact that the effective interparticle interaction (i.e., the\nvertex function) becomes smaller above three dimensions, we propose an\nalternative way to reorganize Feynman diagrams and develop a theoretical\nframework for interacting Fermi gases beyond the ladder approximation. As an\napplication, we solve the equation of state for three- and two-dimensional\nstrongly interacting fermions and find excellent agreement with experimental\n[Science 335, 563 (2012)] and other theoretical results above the temperature\n0.5TF ."
    },
    {
        "anchor": "Many-body quantum dynamics of initially trapped systems due to a Stark\n  potential --- thermalization vs. Bloch oscillations: We analyze the dynamics of an initially trapped cloud of interacting quantum\nparticles on a lattice under a linear (Stark) potential. We reveal a dichotomy:\ninitially trapped interacting systems possess features typical of both\nmany-body-localized and self-thermalizing systems. We consider both fermions\n($t$-$V$ model) and bosons (Bose-Hubbard model). For the zero and infinite\ninteraction limits, both systems are integrable: we provide analytic solutions\nin terms of the moments of the initial cloud shape, and clarify how the\nrecurrent dynamics (many-body Bloch oscillations) depends on the initial state.\nAway from the integrable points, we identify and explain the time scale at\nwhich Bloch oscillations decohere.",
        "positive": "Emulation of magneto-optic Faraday effect using ultracold atoms: We propose an arresting scheme for emulating the famous Faraday effect in\nultracold atomic gases. Inspired by the similarities between the light field\nand bosonic atoms, we represent the light propagation in medium by the atomic\ntransport in accompany of the laser-atom interaction. An artificial\nmagneto-optic Faraday effect is readily signaled by the spin imbalance of\natoms, with the setup of laser fields offering a high controllability for\nquantum manipulation. The present scheme is really feasible and can be realized\nwith existing experimental techniques of ultracold atoms. It generalizes the\ncrucial concept of the magneto-optic Faraday effect to ultracold atomic\nphysics, and opens a new way of quantum emulating and exploring the\nmagneto-optic Faraday effect and associated intriguing physics."
    },
    {
        "anchor": "Radiofrequency spectroscopy of a strongly interacting two-dimensional\n  Fermi gas: We realize and study a strongly interacting two-component atomic Fermi gas\nconfined to two dimensions in an optical lattice. Using radio-frequency\nspectroscopy we measure the interaction energy of the strongly interacting gas.\nWe observe the confinement-induced Feshbach resonance and find the existence of\nconfinement-induced molecules in very good agreement with theoretical\npredictions.",
        "positive": "Chaos and quantum scars in Bose-Josephson junction coupled to a bosonic\n  mode: We consider a model describing Bose-Josephson junction (BJJ) coupled to a\nsingle bosonic mode exhibiting quantum phase transition (QPT). Onset of chaos\nabove QPT is observed from semiclassical dynamics as well from spectral\nstatistics. Based on entanglement entropy we analyze the ergodic behavior of\neigenstates with increasing energy density which also reveals the influence of\ndynamical steady state known as $\\pi$-mode on it. We identify the imprint of\nunstable $\\pi$-oscillation as many body quantum scar (MBQS), which leads to the\ndeviation from ergodicity and quantify the degree of scarring. Persistence of\nphase coherence in nonequilibrium dynamics of such initial state corresponding\nto the $\\pi$-mode is an observable signature of MBQS which has relevance in\nexperiments on BJJ."
    },
    {
        "anchor": "Synthetic spin-orbit coupling in an optical lattice clock: We propose the use of optical lattice clocks operated with fermionic\nalkaline-earth-atoms to study spin-orbit coupling (SOC) in interacting\nmany-body systems. The SOC emerges naturally during the clock interrogation\nwhen atoms are allowed to tunnel and accumulate a phase set by the ratio of the\n\"magic\" lattice wavelength to the clock transition wavelength. We demonstrate\nhow standard protocols such as Rabi and Ramsey spectroscopy, that take\nadvantage of the sub-Hertz resolution of state-of-the-art clock lasers, can\nperform momentum-resolved band tomography and determine SOC-induced $s$-wave\ncollisions in nuclear spin polarized fermions. By adding a second\ncounter-propagating clock beam a sliding superlattice can be implemented and\nused for controlled atom transport and as a probe of $p$ and $s$-wave\ninteractions. The proposed spectroscopic probes provide clean and well-resolved\nsignatures at current clock operating temperatures.",
        "positive": "Induced Delocalization by Correlation and Interaction in the\n  one-dimensional Anderson Model: We consider long-range correlated disorder and mutual interacting particles\naccording to a dipole-dipole coupling as modifications to the one-dimensional\nAnderson model. Technically we rely on the (numerical) exact diagonalization of\nthe system's Hamilitonian. From the perspective of different localization\nmeasures we confirm and extend the picture of the emergence of delocalized\nstates with increasing correlations. Beside these studies a definition for\nmulti-particle localization is proposed. In the case of two interacting bosons\nwe observe a sensitivity of localization with respect to the range of the\nparticle-particle interaction and insensitivity to the coupling's sign, which\nshould stimulate new theoretical approaches and experimental investigations\nwith e.g. dipolar cold quantum gases.\n  This revised manuscript is much more explicit compared to the initial version\nof the paper. Major extensions have been applied to Sects. II and III where we\nupdated and added figures and we more extensively compared our results to the\nliterature. Furthermore, Sect. III additionally contains a phenomenological\nline of reasoning that bridges from delocalization by correlation to\ndelocalization by interaction on the basis of the multi-particle Hamilton\nmatrix."
    },
    {
        "anchor": "In Situ Thermometry of Fermionic Cold-Atom Quantum Wires: We study ensembles of fermionic cold-atom quantum wires with tunable\ntransverse mode population and single-wire resolution. From in situ density\nprofiles, we determine the temperature of the atomic wires in the weakly\ninteracting limit and reconstruct the underlying potential landscape. By\nvarying atom number and temperature, we control the occupation of the\ntransverse modes and study the 1D-3D crossover. In the 1D limit, we observe an\nincrease of the reduced temperature $T/T_{F}$ at nearly constant entropy per\nparticle $S/N k_{B}$. The ability to probe individual atomic wires in situ\npaves the way to quantitatively study equilibrium and transport properties of\nstrongly interacting 1D Fermi gases.",
        "positive": "Interferometry using Adiabatic Passage in Dilute Gas Bose-Einstein\n  Condensates: We theoretically examine three-well interferometry in Bose-Einstein\ncondensates using adiabatic passage. Specifically, we demonstrate that a\nfractional coherent transport adiabatic passage protocol enables stable spatial\nsplitting in the presence of nonlinear interactions. A reversal of this\nprotocol produces a coherent recombination of the BEC with a phase-dependent\npopulation of the three wells. The effect of nonlinear interactions on the\ninterferometric measurement is quantified and found to lead to an enhancement\nin sensitivity for moderate interaction strengths."
    },
    {
        "anchor": "Non-local quantum fluctuations and fermionic superfluidity in the\n  imbalanced attractive Hubbard model: We study fermionic superfluidity in strongly anisotropic optical lattices\nwith attractive interactions utilizing the cluster DMFT method, and focusing in\nparticular on the role of non-local quantum fluctuations. We show that\nnon-local quantum fluctuations impact the BCS superfluid transition\ndramatically. Moreover, we show that exotic superfluid states with delicate\norder parameter structure, such as the Fulde-Ferrell-Larkin-Ovchinnikov phase\ndriven by spin population imbalance, can emerge even in the presence of such\nstrong fluctuations.",
        "positive": "Slow relaxation and sensitivity to disorder in trapped lattice fermions\n  after a quench: We consider a system of non-interacting fermions in one dimension subject to\na single-particle potential consisting of (a) a strong optical lattice, (b) a\nharmonic trap, and (c) uncorrelated on-site disorder. After a quench, in which\nthe center of the harmonic trap is displaced, we study the occupation function\nof the fermions and the time-evolution of experimental observables.\nSpecifically, we present numerical and analytical results for the post-quench\noccupation function of the fermions, and analyse the time-evolution of the\nreal-space density profile. Unsurprisingly for a non-interacting (and therefore\nintegrable) system, the infinite-time limit of the density profile is\nnon-thermal. However, due to Bragg-localization of the higher-energy\nsingle-particle states, the approach to even this non-thermal state is\nextremely slow. We quantify this statement, and show that it implies a\nsensitivity to disorder parametrically stronger than that expected from\nAnderson localization."
    },
    {
        "anchor": "Gain-assisted superluminal light propagation through a Bose-Einstein\n  condensate cavity system: The propagation of a probe laser field in a cavity optomechanical system with\na Bose-Einstein condensate is studied. The transmission properties of the\nsystem are investigated and it is shown that the group velocity of the probe\npulse field can be controlled by Rabi frequency of the pump laser field. The\neffect of the decay rate of the cavity photons on the group velocity is studied\nand it is demonstrated that for small values of the decay rates, the slope of\nphase dispersion switches from positive to negative just by changing the Rabi\nfrequency of the pump field. Then, the gain-assisted superluminal light\npropagation due to the cross-Kerr nonlinearity is established in cavity\noptomechanical system with a Bose-Einstein condensate. Such behavior can not\nappear in the pump-probe two-level atomic systems in the normal phase. We also\nfind that the amplification is achieved without inversion in the population of\nthe quantum energy levels.",
        "positive": "Non-equilibrium metastable state in a chain of interacting spinless\n  fermions with localized loss: We investigate a chain of spinless fermions with nearest-neighbour\ninteractions that are subject to a local loss process. We determine the time\nevolution of the system using matrix product state methods. We find that at\nintermediate times a metastable state is formed, which has very different\nproperties than usual equilibrium states. In particular, in a region around the\nloss, the filling is reduced, while Friedel oscillations with a period\ncorresponding to the original filling continue to exist. The associated\nmomentum distribution is emptied at all momenta by the loss process and the\nFermi edge remains approximately at its original value. Even in the presence of\nstrong interactions, where a redistribution by the scattering is naively\nexpected, such a regime can exist over a long time-scale. Additionally, we\npoint out the existence a system."
    },
    {
        "anchor": "Detecting Chiral Edge States in the Hofstadter Optical Lattice: We propose a realistic scheme to detect topological edge states in an optical\nlattice subjected to a synthetic magnetic field, based on a generalization of\nBragg spectroscopy sensitive to angular momentum. We demonstrate that using a\nwell-designed laser probe, the Bragg spectra provide an unambiguous signature\nof the topological edge states that establishes their chiral nature. This\nsignature is present for a variety of boundaries, from a hard wall to a smooth\nharmonic potential added on top of the optical lattice. Experimentally, the\nBragg signal should be very weak. To make it detectable, we introduce a\n\"shelving method\", based on Raman transitions, which transfers angular momentum\nand changes the internal atomic state simultaneously. This scheme allows to\ndetect the weak signal from the selected edge states on a dark background, and\ndrastically improves the detectivity. It also leads to the possibility to\ndirectly visualize the topological edge states, using in situ imaging, offering\na unique and instructive view on topological insulating phases.",
        "positive": "Multiple period states of the superfluid Fermi gas in an optical lattice: We study multiple period states of a two-component unpolarized superfluid\nFermi gas in an optical lattice along the Bardeen-Cooper-Schrieffer (BCS) to\nBose-Einstein condensate (BEC) crossover. The existence of states whose period\nis a multiple of the lattice spacing is a direct consequence of the non-linear\nbehavior of the gas, which is due to the presence of the order parameter\nassociated with superfluidity. By solving Bogoliubov-de Gennes equations for a\nsuperfluid flow with finite quasimomentum, we find that, in the BCS side of the\ncrossover, the multiple period states can be energetically favorable compared\nto the normal Bloch states and their survival time against dynamical\ninstability drastically increases, suggesting that these states can be\naccessible in current experiments, in sharp contrast to the situation in BECs."
    },
    {
        "anchor": "Phases of d-orbital bosons in optical lattices: We explore the properties of bosonic atoms loaded into the d bands of an\nisotropic square optical lattice. Following the recent experimental success\nreported in [Y. Zhai et al., Phys. Rev. A 87, 063638 (2013)], in which\npopulating d bands with a 99% fidelity was demonstrated, we present a\ntheoretical study of the possible phases that can appear in this system. Using\nthe Gutzwiller ansatz for the three d band orbitals we map the boundaries of\nthe Mott insulating phases. For not too large occupation, two of the orbitals\nare predominantly occupied, while the third, of a slightly higher energy,\nremains almost unpopulated. In this regime, in the superfluid phase we find the\nformation of a vortex lattice, where the vortices come in vortex/anti-vortex\npairs with two pairs locked to every site. Due to the orientation of the\nvortices time-reversal symmetry is spontaneously broken. This state also breaks\na discrete Z2-symmetry. We further derive an effective spin-1/2 model that\ndescribe the relevant physics of the lowest Mott-phase with unit filling. We\nargue that the corresponding two dimensional phase diagram should be rich with\nseveral different phases. We also explain how to generate antisymmetric spin\ninteractions that can give rise to novel effects like spin canting.",
        "positive": "Many-body Landau-Zener dynamics in coupled 1D Bose liquids: The Landau-Zener model of a quantum mechanical two-level system driven with a\nlinearly time dependent detuning has served over decades as a textbook paradigm\nof quantum dynamics. In their seminal work [L. D. Landau, Physik. Z. Sowjet. 2,\n46 (1932); C. Zener, Proc. Royal Soc. London 137, 696 (1932)], Landau and Zener\nderived a non-perturbative prediction for the transition probability between\ntwo states, which often serves as a reference point for the analysis of more\ncomplex systems. A particularly intriguing question is whether that framework\ncan be extended to describe many-body quantum dynamics. Here we report an\nexperimental and theoretical study of a system of ultracold atoms, offering a\ndirect many-body generalization of the Landau-Zener problem. In a system of\npairwise tunnel-coupled 1D Bose liquids we show how tuning the correlations of\nthe 1D gases, the tunnel coupling between the tubes and the inter-tube\ninteractions strongly modify the original Landau-Zener picture. The results are\nexplained using a mean-field description of the inter-tube condensate\nwave-function, coupled to the low-energy phonons of the 1D Bose liquid."
    },
    {
        "anchor": "Multiple Transitions of Coupled Atom-Molecule Bosonic Mixtures in Two\n  Dimensions: Motivated by the physics of coherently coupled, ultracold atom-molecule\nmixtures, we investigate a classical model possessing the same symmetry --\nnamely a $U(1)\\times \\mathbb{Z}_2$ symmetry, associated with the mass\nconservation in the mixture ($U(1)$ symmetry), times the $\\mathbb{Z}_2$\nsymmetry in the phase relationship between atoms and molecules. In two spatial\ndimensions the latter symmetry can lead to a finite-temperature Ising\ntransition, associated with (quasi) phase locking between the atoms and the\nmolecules. On the other hand, the $U(1)$ symmetry has an associated\nBerezinskii-Kosterlitz-Thouless (BKT) transition towards quasi-condensation of\natoms or molecules. The existence of the two transitions is found to depend\ncrucially on the population imbalance (or detuning) between atoms and\nmolecules: when the molecules are majority in the system, their BKT\nquasi-condensation transition occurs at a higher temperature than that of the\natoms; the latter has the unconventional nature of an Ising (quasi)\nphase-locking transition, lacking a finite local order parameter below the\ncritical temperature. When the balance is gradually biased towards the atoms,\nthe two transitions merge together to leave out a unique BKT transition, at\nwhich both atoms and molecules acquire quasi-long-range correlations, but only\natoms exhibit conventional BKT criticality, with binding of vortex-antivortex\npairs into short-range dipoles. The molecular vortex-antivortex excitations\nbind as well, but undergo a marked crossover from a high-temperature regime in\nwhich they are weakly bound, to a low-temperature regime of strong binding,\nreminiscent of their transition in the absence of atom-molecule coupling.",
        "positive": "Fast optimal transition between two equilibrium states: We demonstrate a technique based on invariants of motion for a time-dependent\nHamiltonian, allowing a fast transition to a final state identical in theory to\nthat obtained through a perfectly adiabatic transformation. This method is\nexperimentally applied to the fast decompression of an ultracold cloud of\nRubidium 87 atoms held in a harmonic magnetic trap, in the presence of gravity.\nWe are able to decompress the trap by a factor of 15 within 35 ms with a strong\nsuppression of the sloshing and breathing modes induced by the large vertical\ndisplacement and curvature reduction of the trap. When compared to a standard\nlinear decompression, we achieve a gain of a factor of 37 on the transition\ntime."
    },
    {
        "anchor": "Strong correlations in quantum vortex nucleation of ultracold atomic\n  gases: We review some recent developments in the theory of rotating atomic gases.\nThese studies have thrown light on the process of nucleation of vortices in\nregimes where mean-field methods are inadequate. In our review we shall\ndescribe and compare quantum vortex nucleation of a dilute ultracold bosonic\ngas trapped in three different configurations: a one-dimensional ring lattice,\na one-dimensional ring superlattice and a two-dimensional asymmetric harmonic\ntrap. In all of them there is a critical rotation frequency, at which the\nparticles in the ground state exhibit strong quantum correlations. However, the\nentanglement properties vary significantly from case to case. We explain these\ndifferences by characterizing the intermediate states that participate in the\nvortex nucleation process. Finally, we show that noise correlations are\nsensitive to these differences. These new studies have, therefore, shown how\nnovel quantum states may be produced and probed in future experiments with\nrotating neutral atom systems.",
        "positive": "Detecting the phase transition in a strongly-interacting Fermi gas by\n  unsupervised machine learning: We study the critical temperature of the superfluid phase transition of\nstrongly-interacting fermions in the crossover regime between a\nBardeen-Cooper-Schrieffer (BCS) superconductor and a Bose-Einstein condensate\n(BEC) of dimers. To this end, we employ the technique of unsupervised machine\nlearning using an autoencoder neural network which we directly apply to\ntime-of-flight images of the fermions. We extract the critical temperature of\nthe phase transition from trend changes in the data distribution revealed in\nthe latent space of the autoencoder bottleneck."
    },
    {
        "anchor": "Slow heating in a quantum coupled kicked rotors system: We consider a finite-size periodically driven quantum system of coupled\nkicked rotors which exhibits two distinct regimes in parameter space: a\ndynamically-localized one with kinetic-energy saturation in time and a chaotic\none with unbounded energy absorption (dynamical delocalization). We provide\nnumerical evidence that the kinetic energy grows subdiffusively in time in a\nparameter region close to the boundary of the chaotic dynamically-delocalized\nregime. We map the different regimes of the model via a spectral analysis of\nthe Floquet operator and investigate the properties of the Floquet states in\nthe subdiffusive regime. We observe an anomalous scaling of the average inverse\nparticipation ratio (IPR) analogous to the one observed at the critical point\nof the Anderson transition in a disordered system. We interpret the behavior of\nthe IPR and the behavior of the asymptotic-time energy as a mark of the\nbreaking of the eigenstate thermalization in the subdiffusive regime. Then we\nstudy the distribution of the kinetic-energy-operator off-diagonal matrix\nelements. We find that in presence of energy subdiffusion they are not Gaussian\nand we propose an anomalous random matrix model to describe them.",
        "positive": "Strongly localized polaritons in an array of trapped two-level atoms\n  interacting with a light field: We propose a new type of spatially periodic structure, i.e. polaritonic\ncrystal (PolC), to observe a \"slow\"/\"stopped\" light phenomenon due to coupled\natom-field states (polaritons) in a lattice. Under the tightbinding\napproximation, such a system realizes an array of weakly coupled trapped\ntwo-component atomic ensembles interacting with optical field in a\ntunnel-coupled one dimensional cavity array. We have shown that the phase\ntransition to the superfluid Bardeen-Cooper-Schrieffer state, a so-called\n(BCS)-type state of low branch polaritons, occurs under the strong coupling\ncondition. Such a transition results in the appearance of a macroscopic\npolarization of the atomic medium at non-zero frequency. The principal result\nis that the group velocity of polaritons depends essentially on the order\nparameter of the system, i.e. on the average photon number in the cavity array."
    },
    {
        "anchor": "Real time dynamics and proposal for feasible experiments of lattice\n  gauge-Higgs model simulated by cold atoms: Lattice gauge theory has provided a crucial non-perturbative method in\nstudying canonical models in high-energy physics such as quantum\nchromodynamics. Among other models of lattice gauge theory, the lattice\ngauge-Higgs model is a quite important one because it describes wide variety of\nphenomena/models related to the Anderson-Higgs mechanism such as\nsuperconductivity, the standard model of particle physics, and inflation\nprocess of the early universe. In this paper, we first show that atomic\ndescription of the lattice gauge model allows us to explore real time dynamics\nof the gauge variables by using the Gross-Pitaevskii equations. Numerical\nsimulations of the time development of an electric flux reveal some interesting\ncharacteristics of dynamical aspect of the model and determine its phase\ndiagram. Next, to realize a quantum simulator of the U(1) lattice gauge-Higgs\nmodel on an optical lattice filled by cold atoms, we propose two feasible\nmethods: (i) Wannier states in the excited bands and (ii) dipolar atoms in a\nmultilayer optical lattice. We pay attentions to respect the constraint of\nGauss's law and avoid nonlocal gauge interactions.",
        "positive": "Width of the confinement-induced resonance in a quasi-one-dimensional\n  trap with transverse anisotropy: We theoretically study the width of the s-wave confinement-induced resonance\n(CIR) in quasi-one-dimensional atomic gases under tunable transversely\nanisotropic confinement. We find that the width of the CIR can be tuned by\nvarying the transverse anisotropy. The change in the width of the CIR can\nmanifest itself in the position of the discontinuity in the interaction energy\ndensity, which can be probed experimentally."
    },
    {
        "anchor": "Keldysh Field Theory for Driven Open Quantum Systems: Recent experimental developments in diverse areas - ranging from cold atomic\ngases over light-driven semiconductors to microcavity arrays - move systems\ninto the focus, which are located on the interface of quantum optics, many-body\nphysics and statistical mechanics. They share in common that coherent and\ndriven-dissipative quantum dynamics occur on an equal footing, creating genuine\nnon-equilibrium scenarios without immediate counterpart in condensed matter.\nThis concerns both their non-thermal flux equilibrium states, as well as their\nmany-body time evolution. It is a challenge to theory to identify novel\ninstances of universal emergent macroscopic phenomena, which are tied\nunambiguously and in an observable way to the microscopic drive conditions. In\nthis review, we discuss some recent results in this direction. Moreover, we\nprovide a systematic introduction to the open system Keldysh functional\nintegral approach, which is the proper technical tool to accomplish a merger of\nquantum optics and many-body physics, and leverages the power of modern quantum\nfield theory to driven open quantum systems.",
        "positive": "Confinement of matter-wave solitons on top of a pedestal-shaped\n  potential: Reflection of wave packets from downward potential steps and attractive\npotentials, known as a quantum reflection, has been explored for bright\nmatter-wave solitons with the main emphasis on the possibility to trap them on\ntop of a pedestal-shaped potential. In numerical simulations, we observed that\nmoving solitons return from the borders of the potential and remain trapped for\na sufficiently long time. The shuttle motion of the soliton is accompanied by\nshedding some amount of matter at each reflection from the borders of the trap,\nthus reducing its norm. The one- and two- soliton configurations are\nconsidered. A discontinuous jump of trajectories of colliding solitons has been\ndiscussed. The time-shift observed in a step-like decay of the moving soliton's\nnorm in the two-soliton configuration is linked to the trajectory jump\nphenomenon. The obtained results can be of interest for the design of new\nsoliton experiments with Bose-Einstein condensates."
    },
    {
        "anchor": "Quench dynamics of Rydberg-dressed bosons on two-dimensional square\n  lattices: We study the dynamics of bosonic atoms on a two-dimensional square lattice,\nwhere atomic interactions are long-ranged with either a box or soft-core shape.\nThe latter can be realized through laser dressing ground-state atoms to\nelectronically excited Rydberg states. When the range of interactions is equal\nor larger than the lattice constant, the system is governed by an extended\nBose-Hubbard model. We propose a quench process by varying the atomic hopping\nlinearly across phase boundaries of the Mott insulator-supersolid and\nsupersolid-superfluid phases. Starting from a Mott insulating state, the\ndynamical evolution of the superfluid order parameter exhibits a universal\nbehaviour at the early stage, largely independent of interactions. The\ndynamical evolution is significantly altered by strong, long-range interactions\nat later times. Particularly, we demonstrate that density wave excitation is\nimportant when the quench rate is small. Moreover, we show that the quench\ndynamics can be analyzed through time-of-flight images, i.e., measuring the\nmomentum distribution and noise correlations.",
        "positive": "Few-body states of bosons interacting with a heavy quantum impurity: We consider the problem of a fixed impurity coupled to a small number $N$ of\nnon-interacting bosons. We focus on impurity-boson interactions that are\nmediated by a closed-channel molecule, as is the case for tuneable interatomic\ninteractions in cold-atom experiments. We show that this two-channel model can\nbe mapped to a boson model with effective boson-boson repulsion, which enables\nus to solve the three-body ($N=2$) problem analytically and determine the\ntrimer energy for impurity-boson scattering lengths $a>0$. By analysing the\natom-dimer scattering amplitude, we find a critical scattering length $a^*$ at\nwhich the atom-dimer scattering length diverges and the trimer merges into the\ndimer continuum. We furthermore calculate the tetramer energy exactly for $a>0$\nand show that the tetramer also merges with the continuum at $a^*$. Indeed,\nsince the critical point $a^*$ formally resembles the unitary point $1/a = 0$,\nwe find that all higher-body bound states (involving the impurity and $N>1$\nbosons) emerge and disappear at both of these points. We show that the behavior\nat these 'multi-body resonances' is universal, since it occurs for any model\nwith an effective three-body repulsion involving the impurity. Thus, we see\nthat the fixed-impurity problem is strongly affected by a three-body parameter\neven in the absence of the Efimov effect."
    },
    {
        "anchor": "Stabilization of ring dark solitons in Bose-Einstein condensates: Earlier work has shown that ring dark solitons in two-dimensional\nBose-Einstein condensate are generically unstable. In this work, we propose a\nway of stabilizing the ring dark soliton via a radial Gaussian external\npotential. We investigate the existence and stability of the ring dark soliton\nupon variations of the chemical potential and also of the strength of the\nradial potential. Numerical results show that the ring dark soliton can be\nstabilized in a suitable interval of external potential strengths and chemical\npotentials. We also explore different proposed particle pictures considering\nthe ring as a moving particle and find, where appropriate, results in very good\nqualitative and also reasonable quantitative agreement with the numerical\nfindings.",
        "positive": "Virial expansion with Feynman diagrams: We present a field theoretic method for the calculation of the second and\nthird virial coefficients b2 and b3 of 2-species fermions interacting via a\ncontact interaction. The method is mostly analytic. We find a closed expression\nfor b3 in terms of the 2 and 3-body T-matrices. We recover numerically, at\nunitarity, and also in the whole BEC-BCS crossover, previous numerical results\nfor the third virial coefficient b3."
    },
    {
        "anchor": "Tailored generation of quantum states in an entangled spinor\n  interferometer to overcome detection noise: We theoretically investigate how entangled atomic states generated via\nspin-changing collisions in a spinor Bose-Einstein condensate can be designed\nand controllably prepared for atom interferometry that is robust against common\ntechnical issues, such as limited detector resolution. We use analytic and\nnumerical treatments of the spin-changing collision process to demonstrate that\ntriggering the entangling collisions with a small classical seed rather than\nvacuum fluctuations leads to a more robust and superior sensitivity when\ntechnical noise is accounted for, despite the generated atomic state ideally\nfeaturing less metrologically useful entanglement. Our results are relevant for\nunderstanding how entangled atomic states are best designed and generated for\nuse in quantum-enhanced matter-wave interferometry.",
        "positive": "Oscillatory pairing amplitude and magnetic compressible-incompressible\n  transitions in imbalanced fermionic superfluids in optical lattices of\n  elongated tubes: We study two-species fermion gases with attractive interaction in\ntwo-dimensional optical lattices producing an array of elongated tube\nconfinements. Focusing on the interplay of Cooper pairing, spin imbalance (or\nmagnetization) and intertube tunneling, we find the pairing gap can exhibit\noscillatory behavior both along and across the tubes, reminiscent of a\nFulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase. We obtain a Bose-Hubbard-like\nphase diagram that shows that the magnetization of the system undergoes an\nincompressible-compressible transition as a function of magnetic field and\nintertube tunneling strength. We find the parity of tube-filling imbalance in\nincompressible states is protected by that of the oscillatory pairing gap.\nFinally, we discuss signatures of this transition and thus (indirectly) of the\nFFLO pairing in cold atom experiments."
    },
    {
        "anchor": "Bose-Einstein supersolid phase for a novel type of momentum dependent\n  interaction: A novel class of non-local interactions between bosons is found to favor a\ncrystalline Bose-Einstein condensation ground state. By using both low energy\neffective field theory and variational wavefunction method, we compare this\nstate not only with the homogeneous superfluid, as has been done previously,\nbut also with the normal (non-superfluid) crystalline phase and obtain the\nphase diagram. The key characters are: the interaction potential displays a\nnegative minimum at finite momentum which determines the wavevector of this\nsupersolid phase; and the wavelength corresponding to the momentum minimum\nneeds to be greater than the mean inter-boson distance.",
        "positive": "Above threshold scattering about a Feshbach resonance for ultracold\n  atoms in an optical collider: Ultracold atomic gases have realised numerous paradigms of condensed matter\nphysics where control over interactions has crucially been afforded by tunable\nFeshbach resonances. So far, the characterisation of these Feshbach resonances\nhas almost exclusively relied on experiments in the threshold regime near zero\nenergy. Here we use a laser-based collider to probe a narrow magnetic Feshbach\nresonance of rubidium above threshold. By measuring the overall atomic loss\nfrom colliding clouds as a function of magnetic field, we track the\nenergy-dependent resonance position. At higher energy, our collider scheme\nbroadens the loss feature, making the identification of the narrow resonance\nchallenging. However, we observe that the collisions give rise to shifts in the\ncentre-of-mass positions of outgoing clouds. The shifts cross zero at the\nresonance and this allows us to accurately determine its location well above\nthreshold. Our inferred resonance positions are in excellent agreement with\ntheory."
    },
    {
        "anchor": "Losses in interacting quantum gases: ultra-violet divergence and its\n  regularization: We investigate the effect of losses on an interacting quantum gas. We show\nthat, for gases in dimension higher than one, assuming together a vanishing\ncorrelation time of the reservoir where dissipation occurs, and contact\ninteractions leads to a divergence of the energy increase rate. This divergence\nis a combined effect of the contact interactions, which impart arbitrary large\nmomenta to the atoms, and the infinite energy width of the reservoir associated\nto its vanishing correlation time. We show how the divergence is regularized\nwhen taking into account the finite energy width of the reservoir, and, for\nlarge energy width, we give an expression for the energy increase rate that\ninvolves the contact parameter. We then consider the specific case of a weakly\ninteracting Bose Einstein condensate, that we describe using the Bogoliubov\ntheory. Assuming slow losses so that the gas is at any time described by a\nthermal equilibrium, we compute the time evolution of the temperature of the\ngas. Using a Bogoliubov analysis, we also consider the case where the\nregularization of the divergence is due to the finite range of the interaction\nbetween atoms.",
        "positive": "Universality of three-body systems in 2D: parametrization of the bound\n  states energies: Universal properties of mass-imbalanced three-body systems in 2D are studied\nusing zero-range interactions in momentum space. The dependence of the\nthree-particle binding energy on the parameters (masses and two-body energies)\nis highly non-trivial even in the simplest case of two identical particles and\na distinct one. This dependence is parametrized for ground and excited states\nin terms of {\\itshape supercircles} functions in the most general case of three\ndistinguishable particles."
    },
    {
        "anchor": "Gauge Violation Spectroscopy in Synthetic Gauge Theories: Recently synthetic gauge fields have been implemented on quantum simulators.\nUnlike the gauge fields in the real world, in synthetic gauge fields, the gauge\ncharge can fluctuate and gauge invariance can be violated, which leading rich\nphysics unexplored before. In this work, we propose the gauge violation\nspectroscopy as a useful experimentally accessible measurement in the synthetic\ngauge theories. We show that the gauge violation spectroscopy exhibits no\ndispersion. Using three models as examples, two of them can be exactly solved\nby bosonization, and one has been realized in experiment, we further\ndemonstrate the gauge violation spectroscopy can be used to detect the\nconfinement and deconfinement phases. In the confinement phase, it shows a\ndelta function behavior, while in the deconfinement phase, it has a finite\nwidth.",
        "positive": "Effects of anisotropy in simple lattice geometries on many-body\n  properties of ultracold fermions in optical lattices: We study the effects of anisotropic hopping amplitudes on quantum phases of\nultracold fermions in optical lattices described by the repulsive Fermi-Hubbard\nmodel. In particular, using dynamical mean-field theory (DMFT) we investigate\nthe dimensional crossover between the isotropic square and the isotropic cubic\nlattice. We analyze the phase transition from the antiferromagnetic to the\nparamagnetic state and observe a significant change in the critical\ntemperature: Depending on the interaction strength, the anisotropy can lead to\nboth a suppression or increase. We also investigate the localization properties\nof the system, such as the compressibility and double occupancy. Using the\nlocal density approximation in combination with DMFT we conclude that density\nprofiles can be used to detect the mentioned anisotropy-driven transitions."
    },
    {
        "anchor": "Artificial topological models based on a one-dimensional spin-dependent\n  optical lattice: Topological matter is a popular topic in both condensed matter and cold atom\nresearch. In the past decades, a variety of models have been identified with\nfascinating topological features. Some, but not all, of the models can be found\nin materials. As a fully controllable system, cold atoms trapped in optical\nlattices provide an ideal platform to simulate and realize these topological\nmodels. Here we present a proposal for synthesizing topological models in cold\natoms based on a one-dimensional (1D) spin-dependent optical lattice potential.\nIn our system, features such as staggered tunneling, staggered Zeeman field,\nnearest-neighbor interaction, beyond-near-neighbor tunneling, etc. can be\nreadily realized. They underlie the emergence of various topological phases.\nOur proposal can be realized with current technology and hence has potential\napplications in quantum simulation of topological matter.",
        "positive": "Interatomic interaction effects on second-order momentum correlations\n  and Hong-Ou-Mandel interference of double-well-trapped ultracold fermionic\n  atoms: Identification and understanding of the evolution of interference patterns in\ntwo-particle momentum correlations as a function of the strength of interatomic\ninteractions are important in explorations of the nature of quantum states of\ntrapped particles. Together with the analysis of two-particle spatial\ncorrelations, they offer the prospect of uncovering fundamental symmetries and\nstructure of correlated many-body states, as well as opening vistas into\npotential control and utilization of correlated quantum states as quantum\ninformation resources. With the use of the second-order density matrix\nconstructed via exact diagonalization of the microscopic Hamiltonian, and an\nanalytic Hubbard-type model, we explore here the systematic evolution of\ncharacteristic interference patterns in the two-body momentum and spatial\ncorrelation maps of two entangled ultracold fermionic atoms in a double well,\nfor the entire attractive- and repulsive-interaction range. We uncover\nstatistics-governed bunching and antibunching, as well as interaction-dependent\ninterference patterns, in the ground and excited states, and interpret our\nresults in light of the Hong-Ou-Mandel interference physics, widely exploited\nin photon indistinguishability testing and quantum information science."
    },
    {
        "anchor": "Large-N approximation for single- and two-component dilute Bose gases: We discuss the mean-field theories obtained from the leading order in a\nlarge-$N$ approximation for one- and two- component dilute Bose gases. For a\none-component Bose gas this approximation has the following properties: the\nBose-Einstein condensation (BEC) phase transition is second order but the\ncritical temperature $T_c$ is not shifted from the non-interacting gas value\n$T_0$. The spectrum of excitations in the BEC phase resembles the Bogoliubov\ndispersion with the usual coupling constant replaced by the running coupling\nconstant which depends on both temperature and momentum. We then study\ntwo-component Bose gases with both inter- and intra- species interactions and\nfocus on the stability of the mixture state above $T_c$. Our mean-field\napproximation predicts an instability from the mixture state to a\nphase-separated state when the ratio of the inter-species interaction strength\nto the intra-species interaction strength (assuming equal strength for both\nspecies) exceeds a critical value. At high temperature this is a structural\ntransition and the global translational symmetry is broken. Our work\ncomplements previous studies on the instability of the mixture phase in the\npresence of BEC.",
        "positive": "Exciton correlations in coupled quantum wells and their luminescence\n  blue shift: In this paper we present a study of an exciton system where electrons and\nholes are confined in double quantum well structures. The dominating\ninteraction between excitons in such systems is a dipole - dipole repulsion. We\nshow that the tail of this interaction leads to a strong correlation between\nexcitons and substantially affects the behavior of the system. Making use of\nqualitative arguments and estimates we develop a picture of the exciton -\nexciton correlations in the whole region of temperature and concentration where\nexcitons exist. It appears that at low concentration degeneracy of the excitons\nis accompanied with strong multi-particle correlation so that the system cannot\nbe considered as a gas. At high concentration the repulsion suppresses the\nquantum degeneracy down to temperatures that could be much lower than in a Bose\ngas with contact interaction. We calculate the blue shift of the exciton\nluminescence line which is a sensitive tool to observe the exciton - exciton\ncorrelations."
    },
    {
        "anchor": "Quantum Crystals and Laughlin Droplets of Cavity Rydberg Polaritons: Synthetic quantum materials offer an exciting opportunity to explore quantum\nmany-body physics and novel states of matter under controlled conditions. In\nparticular, they provide an avenue to exchange the short length scales and\nlarge energy scales of the solid state for an engineered system with better\ncontrol over the system Hamiltonian, more accurate state preparation, and\nhigher fidelity state readout. Here we propose a unique platform to study\nquantum phases of strongly interacting photons. We introduce ideas for\ncontrolling the dynamics of individual photons by manipulating the geometry of\na multimode optical cavity, and combine them with recently established\ntechniques to mediate strong interactions between photons using Rydberg atoms.\nWe demonstrate that this approach gives rise to crystalline- and fractional\nquantum Hall- states of light, opening the door to studies of strongly\ncorrelated quantum many-body physics in a photonic material.",
        "positive": "Onsager vortex formation in two-component Bose-Einstein condensates: We numerically study the dynamics of quantized vortices in two-dimensional\ntwo-component Bose-Einstein condensates (BECs) trapped by a box potential. For\none-component BECs in a box potential, it is known that quantized vortices form\nOnsager vortices, which are clusters of same-sign vortices. We confirm that the\nvortices of the two components spatially separate from each other-even for\nmiscible two-component BECs-suppressing the formation of Onsager vortices. This\nphenomenon is caused by the repulsive interaction between vortices belonging to\ndifferent components, hence, suggesting a new possibility for vortex phase\nseparation."
    },
    {
        "anchor": "Bose-Einstein Condensates: a model system for particle solvation?: We propose that impurities in Bose-Einstein condensates can serve as a\nminimal laboratory system to explore the effects of quantum and thermal\nfluctuations on solvation. Specifically, we show that the role of quantum\nfluctuations in the formation of solvation shells and the breakdown of linear\nresponse theory can be explored in detail.",
        "positive": "Bound Dimers in Bilayers of Cold Polar Molecules: The exploration of cold polar molecules in different geometries is a rapidly\ndeveloping experimental and theoretical pursuit. Recently, the implementation\nof optical lattices has enabled confinement in stacks of planes, the number of\nwhich is also controllable. Here we consider the bound state structure of two\npolar molecules confined in two adjacent planes as function of the polarization\nangle of the dipole moment of the molecules. We prove analytically and present\nnumerical evidence for the existence of bound states for arbitrary dipole\nmoments and polarization directions in this two-dimensional geometry. The\nspatial structure of the bound states is dominated by two-dimensional s- and\np-waves, where the latter exceeds 40 percent over a large range of polarization\nangles for intermediate or strong dipole strength. Finally, we consider the\ninfluence of the dimer bound states on the potential many-body ground-state of\nthe system."
    },
    {
        "anchor": "Investigation of the momentum distribution of an excited BEC by free\n  expansion: coupling with collective modes: We investigate the evolution of the momentum distribution of a Bose-Einstein\ncondensate subjected to an external small oscillatory perturbation as a\nfunction of the in-trap evolution of the condensate after the external\nperturbation is switched-off. Besides changing its momentum distribution, we\nobserve that the cloud distributes the input energy among its normal collective\nmodes, displaying center-of-mass dipolar mode and quadrupolar mode. While the\ndipolar mode can be easily disregarded, we show that the momentum distribution\nis closely tied to the quadrupolar oscillation mode. This convolution hinders\nthe actual momentum distribution.",
        "positive": "Enhanced repulsively bound atom pairs in topological optical lattice\n  ladders: There is a growing interest in using cold-atom systems to explore the effects\nof strong interactions in topological band structures. Here we investigate\ninteracting bosons in a Cruetz ladder, which is characterised by topological\nflat energy bands where it has been proposed that interactions can lead to the\nformation of bound atomic pairs giving rise to pair superfluidity. By\ninvestigating realistic experimental implementations, we understand how the\nlattice topology enhances the properties of bound pairs giving rise to\nrelatively large effective pair-tunnelling in these systems which can lead to\nrobust pair superfluidity, and we find lattice supersolid phases involving only\npairs. We identify schemes for preparation of these phases via time-dependent\nparameter variation and look at ways to detect and characterise these systems\nin a lattice. This work provides a starting point for investigating the\ninterplay between the effects of topology, interactions and pairing in more\ngeneral systems, with potential future connections to quantum simulation of\ntopological materials."
    },
    {
        "anchor": "Path integral Monte Carlo determination of the fourth-order virial\n  coefficient for unitary two-component Fermi gas with zero-range interactions: The unitary equal-mass Fermi gas with zero-range interactions constitutes a\nparadigmatic model system that is relevant to atomic, condensed matter,\nnuclear, particle, and astro physics. This work determines the fourth-order\nvirial coefficient $b_4$ of such a strongly-interacting Fermi gas using a\ncustomized \\textit{ab initio} path integral Monte Carlo (PIMC) algorithm. In\ncontrast to earlier theoretical results, which disagreed on the sign and\nmagnitude of $b_4$, our $b_4$ agrees within error bars with the experimentally\ndetermined value, thereby resolving an ongoing literature debate. Utilizing a\ntrap regulator, our PIMC approach determines the fourth-order virial\ncoefficient by directly sampling the partition function. An on-the-fly\nanti-symmetrization avoids the Thomas collapse and, combined with the use of\nthe exact two-body zero-range propagator, establishes an efficient general\nmeans to treat small Fermi systems with zero-range interactions.",
        "positive": "Turbulent relaxation to equilibrium in a two-dimensional quantum vortex\n  gas: We experimentally study emergence of microcanonical equilibrium states in the\nturbulent relaxation dynamics of a two-dimensional chiral vortex gas. Same-sign\nvortices are injected into a quasi-two-dimensional disk-shaped atomic\nBose-Einstein condensate using a range of mechanical stirring protocols. The\nresulting long-time vortex distributions are found to be in excellent agreement\nwith the meanfield Poisson-Boltzmann equation for the system describing the\nmicrocanonical ensemble at fixed energy $\\cal{H}$ and angular momentum\n$\\cal{M}$. The equilibrium states are characterized by the corresponding\nthermodynamic variables of inverse temperature $\\hat{\\beta}$ and rotation\nfrequency $\\hat{\\omega}$. We are able to realize equilibria spanning the full\nphase diagram of the vortex gas, including on-axis states near\nzero-temperature, infinite temperature, and negative absolute temperatures. At\nsufficiently high energies the system exhibits a symmetry-breaking transition,\nresulting in an off-axis equilibrium phase at negative absolute temperature\nthat no longer shares the symmetry of the container. We introduce a\npoint-vortex model with phenomenological damping and noise that is able to\nquantitatively reproduce the equilibration dynamics."
    },
    {
        "anchor": "Fermionic superfluidity and spontaneous superflows in optical lattices: We study superfluidity of strongly repulsive fermionic atoms in optical\nlattices. The atoms are paired up through a correlated tunneling mechanism,\nwhich induces superfluidity when repulsive nearest-neighbor interactions are\nincluded in the Hubbard model. This paired superfluid is a metastable state\nwhich persists for a long time as the pair-broken process is severely\nsuppressed. The mean-field phase diagram and low energy excitations are\ninvestigated in a square lattice system. Intriguingly, spontaneous superflows\nmay appear in the ground state of a triangular optical lattice system due to\nantiferromagnetic frustration.",
        "positive": "Scattering of a dark-bright soliton by an impurity: We study the dynamics of a dark-bright soliton interacting with a fixed\nimpurity using a mean-field approach. The system is described by a vector\nnonlinear Schrodinger equation (NLSE) appropriate to multicomponent\nBose-Einstein condensates. We use the variational approximation, based on\nhyperbolic functions, where we have the center of mass of the two components to\ndescribe the propagation of the dark and bright components independently.\nTherefore, it allows the dark-bright soliton to oscillate. The fixed local\nimpurity is modeled by a delta function. Also, we use perturbation methods to\nderive the equations of motion for the center of mass of the two components.\nThe interaction of the dark-bright soliton with a delta function potential\nexcites different modes in the system. The analytical model capture two of\nthese modes: the relative oscillation between the two components and the\noscillation in the widths. The numerical simulations show additional internal\nmodes play an important role in the interaction problem. The excitation of\ninternal modes corresponds to inelastic scattering. In addition, we calculate\nthe maximum velocity for a dark-bright soliton and find it is limited to a\nvalue below the sound speed, depending on the relative number of atoms present\nin the bright soliton component and excavated by the dark soliton component,\nrespectively. Above a critical value of the maximum velocity, the two\ncomponents are no longer described by one center of mass variable and develop\ninternal oscillations, eventually breaking apart when pushed to higher\nvelocities. This effect limits the incident kinetic energy in scattering\nstudies and presents a smoking gun experimental signal."
    },
    {
        "anchor": "Flow equations for cold Bose gases: We derive flow equations for cold atomic gases with one macroscopically\npopulated energy level. The generator is chosen such that the ground state\ndecouples from all other states in the system as the renormalization group flow\nprogresses. We propose a self-consistent truncation scheme for the flow\nequations at the level of three-body operators and show how they can be used to\ncalculate the ground state energy of a general $N$-body system. Moreover, we\nprovide a general method to estimate the truncation error in the calculated\nenergies. Finally, we test our scheme by benchmarking to the exactly solvable\nLieb-Liniger model and find good agreement for weak and moderate interaction\nstrengths.",
        "positive": "Virial coefficients of 1D and 2D Fermi gases by stochastic methods and a\n  semiclassical lattice approximation: We map out the interaction effects on the first six virial coefficients of\none-dimensional Fermi gases with zero-range attractive and repulsive\ninteractions, and the first four virial coefficients of the two-dimensional\nanalog with attractive interactions. To that end, we use two non-perturbative\nstochastic methods: projection by complex stochastic quantization, which allows\nus to determine high-order coefficients at weak coupling and estimate the\nradius of convergence of the virial expansion; and a path-integral\nrepresentation of the virial coefficients. To complement our numerical\ncalculations, we present leading-order results in a semiclassical lattice\napproximation, which we find to be surprisingly close to the expected answers."
    },
    {
        "anchor": "Auxiliary field approach to dilute Bose gases with tunable interactions: We rewrite the Lagrangian for a dilute Bose gas in terms of auxiliary fields\nrelated to the normal and anomalous condensate densities. We derive the loop\nexpansion of the effective action in the composite-field propagators. The\nlowest-order auxiliary field (LOAF) theory is a conserving mean-field\napproximation consistent with the Goldstone theorem without some of the\ndifficulties plaguing approximations such as the Hartree and Popov\napproximations. LOAF predicts a second-order phase transition. We give a set of\nFeynman rules for improving results to any order in the loop expansion in terms\nof composite-field propagators. We compare results of the LOAF approximation\nwith those derived using the Popov approximation. LOAF allows us to explore the\ncritical regime for all values of the coupling constant and we determine\nvarious parameters in the unitarity limit.",
        "positive": "Investigation of Bose condensation in ideal Bose gas trapped under\n  generic power law potential in $d$ dimension: The changes in characteristics of Bose condensation of ideal Bose gas due to\nan external generic power law potential $U=\\sum_{i=1} ^d c_i\n|\\frac{x_i}{a_i}|^{n_i}$ are studied carefully. Detailed calculation of Kim\n$et$ $al.$ (S. H. Kim, C. K. Kim and K. Nahm, J Phys. Condens. Matter 11 10269\n(1999).) yielded the hierarchy of condensation transitions with changing\nfractional dimensionality. In this manuscript, some theorems regarding specific\nheat at constant volume $C_V$ are presented. Careful examination of these\ntheorems reveal the existence of hidden hierarchy of the condensation\ntransition in trapped systems as well."
    },
    {
        "anchor": "2D Superexchange mediated magnetization dynamics in an optical lattice: The competition of magnetic exchange interactions and tunneling underlies\nmany complex quantum phenomena observed in real materials. We study\nnon-equilibrium magnetization dynamics in an extended 2D system by loading\neffective spin-1/2 bosons into a spin-dependent optical lattice, and we use the\nlattice to separately control the resonance conditions for tunneling and\nsuperexchange. After preparing a non-equilibrium anti-ferromagnetically ordered\nstate, we observe relaxation dynamics governed by two well-separated rates,\nwhich scale with the underlying Hamiltonian parameters associated with\nsuperexchange and tunneling. Remarkably, with tunneling off-resonantly\nsuppressed, we are able to observe superexchange dominated dynamics over two\norders of magnitude in magnetic coupling strength, despite the presence of\nvacancies. In this regime, the measured timescales are in agreement with simple\ntheoretical estimates, but the detailed dynamics of this 2D, strongly\ncorrelated, and far-from-equilibrium quantum system remain out of reach of\ncurrent computational techniques.",
        "positive": "Out-of-equilibrium structures in strongly interacting Rydberg gases with\n  dissipation: The non-equilibrium dynamics of a gas of cold atoms in which Rydberg states\nare off-resonantly excited is studied in the presence of noise. The interplay\nbetween interaction and off-resonant excitation leads to an initial dynamics\nwhere aggregates of excited Rydberg atoms slowly nucleate and grow, eventually\nreaching long-lived meta-stable arrangements which then relax further on much\nlonger timescales. This growth dynamics is governed by an effective Master\nequation which permits a transparent and largely analytical understanding of\nthe underlying physics. By means of extensive numerical simulations we study\nthe many-body dynamics and the correlations of the resulting non-equilibrium\nstates in various dimensions. Our results provide insight into the dynamical\nrichness of strongly interacting Rydberg gases in noisy environments, and\nhighlight the usefulness of these kind of systems for the exploration of\nsoft-matter-type collective behaviour."
    },
    {
        "anchor": "A conjugate gradient minimisation approach to generating holographic\n  traps for ultracold atoms: Direct minimisation of a cost function can in principle provide a versatile\nand highly controllable route to computational hologram generation. However, to\ndate iterative Fourier transform algorithms have been predominantly used. Here\nwe show that the careful design of cost functions, combined with numerically\nefficient conjugate gradient minimisation, establishes a practical method for\nthe generation of holograms for a wide range of target light distributions.\nThis results in a guided optimisation process, with a crucial advantage\nillustrated by the ability to circumvent optical vortex formation during\nhologram calculation. We demonstrate the implementation of the conjugate\ngradient method for both discrete and continuous intensity distributions and\ndiscuss its applicability to optical trapping of ultracold atoms.",
        "positive": "Antiferromagnetic Order in a Spin-Orbit Coupled Bose-Einstein Condensate: Spin-orbit coupling related new physics and quantum magnetism are two\nbranches of great interest both in condensed matter physics and in cold atomic\nphysics. With the introduction of a Rashba-like SOC into a Bose-Einstein\ncondensate (BEC) loaded in a two-dimensional bipartite optical square lattice,\nwe find that the ground state of the BEC always favors a coherent condensate\nthan a fragmented condensate and always exhibits very large degeneracy, and\nmost importantly, an antiferromagnetic order of quantum nature emerges when\nparameters satisfy certain condition. This provides an ideal platform to study\nthe interplay of antiferromagnetic phase and superfluid phase."
    },
    {
        "anchor": "Pair correlations in the attractive Hubbard model: The mechanism of fermionic pairing is the key to understanding various\nphenomena such as high-temperature superconductivity and the pseudogap phase in\ncuprate materials. We study the pair correlations in the attractive Hubbard\nmodel using ultracold fermions in a two-dimensional optical lattice. By\ncombining the fluctuation-dissipation theorem and the compressibility equation\nof state, we extract the interacting pair correlation functions and deduce a\ncharacteristic length scale of pairs as a function of interaction and density\nfilling. At sufficiently low filling and weak on-site interaction, we observe\nthat the pair correlations extend over a few lattice sites even at temperatures\nabove the superfluid transition temperature.",
        "positive": "SU(N) Fermi liquid at finite temperature: We consider the thermodynamic potential $\\Omega$ of an N component Fermi gas\nwith a short range interaction obeying SU(N) symmetry. We analyze especially\nthe part of $\\Omega$ that depends on the temperature T non-analytically for\nsmall T . We examine the temperature range where one can observe this $T^4 ln\nT$ contribution and discuss how it can be extracted experimentally."
    },
    {
        "anchor": "On cold gases with anisotropic interactions: A cold gas of particles with anisotropic interactions of general form, due to\na polarizing field, is studied. Special cases are atoms or molecules with\ndipole-dipole or quadrupole-quadrupole interactions. It is shown that the\nangular dependence of an observable on the direction of the polarizing field is\nlargely determined by symmetry. For a gas in a confined quasi two-dimensional\ngeometry, the effective interaction is calculated in general form. Some\nexamples of dipole and quadrupole gases are considered. It is concluded that\nwhen anisotropic forces are studied in a general manner, one can obtain simpler\nresults and better understanding for some problems.",
        "positive": "Spin Transport in a Mott Insulator of Ultracold Fermions: Strongly correlated materials are expected to feature unconventional\ntransport properties, such that charge, spin, and heat conduction are\npotentially independent probes of the dynamics. In contrast to charge\ntransport, the measurement of spin transport in such materials is highly\nchallenging. We observed spin conduction and diffusion in a system of ultracold\nfermionic atoms that realizes the half-filled Fermi-Hubbard model. For strong\ninteractions, spin diffusion is driven by super-exchange and\ndoublon-hole-assisted tunneling, and strongly violates the quantum limit of\ncharge diffusion. The technique developed in this work can be extended to\nfinite doping, which can shed light on the complex interplay between spin and\ncharge in the Hubbard model."
    },
    {
        "anchor": "Classical analogies for the force acting on an impurity in a\n  Bose-Einstein condensate: We study the hydrodynamic forces acting on a small impurity moving in a\ntwo-dimensional Bose-Einstein condensate at non-zero temperature. The\ncondensate is modelled by the damped-Gross Pitaevskii (dGPE) equation and the\nimpurity by a Gaussian repulsive potential coupled to the condensate. For weak\ncoupling, we obtain analytical expressions for the forces acting on the\nimpurity, and compare them with those computed through direct numerical\nsimulations of the dGPE and with the corresponding expressions for classical\nforces. For non-steady flows, there is a time-dependent force dominated by\ninertial effects and which has a correspondence in the Maxey-Riley theory for\nparticles in classical fluids. In the steady-state regime, the force is\ndominated by a self-induced drag. Unlike at zero temperature, where the drag\nforce vanishes below a critical velocity, at low temperatures the impurity\nexperiences a net drag even at small velocities, as a consequence of the energy\ndissipation through interactions of the condensate with the thermal cloud. This\ndissipative force due to thermal drag is similar to the classical Stokes' drag.\nThere is still a critical velocity above which steady-state drag is dominated\nby acoustic excitations and behaves non-monotonically with impurity's speed.",
        "positive": "Analog Hawking radiation from an acoustic black hole in a flowing\n  polariton superfluid: We theoretically study Hawking radiation processes from an analog acoustic\nblack hole in a flowing superfluid of exciton-polaritons in a one-dimensional\nsemiconductor microcavity. Polaritons are coherently injected into the\nmicrocavity by a laser pump with a suitably tailored spot profile. An event\nhorizon with a large analog surface gravity is created by inserting a defect in\nthe polariton flow along the cavity plane. Experimentally observable signatures\nof the analog Hawking radiation are identified in the scattering of phonon\nwavepackets off the horizon, as well as in the spatial correlation pattern of\nquantum fluctuations of the polariton density. The potential of these table-top\noptical systems as analog models of gravitational physics is quantitatively\nconfirmed by numerical calculations using realistic parameters for\nstate-of-the-art devices."
    },
    {
        "anchor": "Tunable space-time crystal in room-temperature magnetodielectrics: We report the experimental realization of a space-time crystal with tunable\nperiodicity in time and space in the magnon Bose-Einstein Condensate (BEC),\nformed in a room-temperature Yttrium Iron Garnet (YIG) film by radio-frequency\nspace-homogeneous magnetic field. The magnon BEC is prepared to have a well\ndefined frequency and non-zero wavevector. We demonstrate how the crystalline\n\"density\" as well as the time and space textures of the resulting crystal may\nbe tuned by varying the experimental parameters: external static magnetic\nfield, temperature, thickness of the YIG film and power of the radio-frequency\nfield. The proposed space-time crystals provide a new dimension for exploring\ndynamical phases of matter and can serve as a model nonlinear Floquet system,\nthat brings in touch the rich fields of classical nonlinear waves, magnonics\nand periodically driven systems.",
        "positive": "Topological inheritance in half-SSH Hubbard models: The interplay between interparticle interactions and topological features may\nresult in unusual phenomena. Interestingly, interactions may induce topological\nfeatures in an originally trivial system, as we illustrate for the case of a\none-dimensional two-component Hubbard model in which one component is subjected\nto Su-Schrieffer-Heeger(SSH) dimerization, whereas the other one is not. We\nshow that due to inter-component interactions the topological properties of one\ncomponent are induced in the originally trivial one. Although for large\ninteractions topological inheritance may be readily explained by on-site\npairing, we show that the threshold for full inheritance occurs at weak\ninteractions, for which the components are not yet paired. We illustrate this\ninheritance by discussing both bulk and edge properties, as well as dynamical\nobservables as mean chiral displacement and charge pumping."
    },
    {
        "anchor": "Wave patterns generated by a flow of two-component Bose-Einstein\n  condensate with spin-orbit interaction past a localized obstacle: It is shown that spin-orbit interaction leads to drastic changes in wave\npatterns generated by a flow of two-component Bose-Einstein condensate (BEC)\npast an obstacle. The combined Rashba and Dresselhaus spin-orbit interaction\naffects in different ways two types of excitations---density and polarization\nwaves---which can propagate in a two-component BEC. We show that the density\nand polarization \"ship wave\" patterns rotate in opposite directions around the\naxis located at the obstacle position and the angle of rotation depends on the\nstrength of spin-orbit interaction. This rotation is accompanied by narrowing\nof the Mach cone. The influence of spin-orbit coupling on density solitons and\npolarization breathers is studied numerically.",
        "positive": "Quantum dynamics of a binary mixture of BECs in a double well potential:\n  an Holstein-Primakoff approach: We study the quantum dynamics of a binary mixture of Bose-Einstein\ncondensates (BEC) in a double-well potential starting from a two-mode\nBose-Hubbard Hamiltonian. Focussing on the regime where the number of atoms is\nvery large, a mapping onto a SU(2) spin problem together with a\nHolstein-Primakoff transformation is performed. The quantum evolution of the\nnumber difference of bosons between the two wells is investigated for different\ninitial conditions, which range from the case of a small imbalance between the\ntwo wells to a coherent spin state. The results show an instability towards a\nphase-separation above a critical positive value of the interspecies\ninteraction while the system evolves towards a coherent tunneling regime for\nnegative interspecies interactions. A comparison with a semiclassical approach\nis discussed together with some implications on the experimental realization of\nphase separation with cold atoms."
    },
    {
        "anchor": "Origin of nonlinear contribution to the shift of the critical\n  temperature in atomic Bose-Einstein condensates: We discuss a possible origin of the experimentally observed nonlinear\ncontribution to the shift $\\Delta T_{c}=T_c-T_{c}^{0}$ of the critical\ntemperature $T_{c}$ in an atomic Bose-Einstein condensate (BEC) with respect to\nthe critical temperature $T_{c}^{0}$ of an ideal gas. We found that accounting\nfor a nonlinear (quadratic) Zeeman effect (with applied magnetic field closely\nmatching a Feshbach resonance field $B_0$) in the mean-field approximation\nresults in a rather significant renormalization of the field-free nonlinear\ncontribution $b_{2}$, namely $\\Delta T_{c}/T_{c}^{0}\\simeq b_{2}^{\\ast\n}(a/\\lambda _{T})^{2}$ (where $a$ is the s-wave scattering length, $\\lambda\n_{T}$ is the thermal wavelength at $T_{c}^{0}$) with $b_{2}^{\\ast }=\\gamma\n^{2}b_{2}$ and $\\gamma =\\gamma (B_0)$. In particular, we predict $b_{2}^{\\ast\n}\\simeq 42.3$ for the $B_{0}\\simeq 403G$ resonance observed in the $\\ ^{39}K$\nBEC.",
        "positive": "Ultracold heteronuclear three-body systems: How diabaticity limits the\n  universality of recombination into shallow dimers: The mass-imbalanced three-body recombination process that forms a shallow\ndimer is shown to possess a rich Efimov-St\\\"uckelberg landscape, with\ncorresponding spectra that differ fundamentally from the homonuclear case. A\nsemi-analytical treatment of the three-body recombination predicts an unusual\nspectra with intertwined resonance peaks and minima, and yields in-depth\ninsight into the behavior of the corresponding Efimov spectra. In particular,\nthe patterns of the Efimov-St\\\"uckelberg landscape are shown to depend\ninherently on the degree of diabaticity of the three-body collisions, which\nstrongly affects the universality of the heteronuclear Efimov states."
    },
    {
        "anchor": "Arbitrary interaction quench phenomena in harmonically trapped two-body\n  systems: We consider the evolution of two contact-interacting harmonically-trapped\nparticles following an arbitrary quench in interaction strength. We calculate\nthe post-quench particle separation as a function of time and the total\npost-quench energy. When quenching from any non-zero interaction strength to\nzero interaction strength we observe that the total energy and particle\nseparation diverge. In particular, the divergent behaviour arises always and\nexclusively when quenching to the non-interacting regime. The source of the\ndivergence is a power-law tail in the probability distribution of particle\nseparation. This validates and builds upon previous work that found divergent\nbehaviour arises when quenching from the strongly interacting limit to the\nnon-interacting limit in both the two and three-body cases.",
        "positive": "Phase separation in optical lattices in a spin-dependent external\n  potential: We investigate the phase separation in one-dimensional Fermi gases on optical\nlattices. The density distributions and the magnetization are calculated by\nmeans of density-matrix renormalization method. The phase separation between\nspin-up and spin-down atoms is induced by the interplay of the spin-dependent\nharmonic confinement and the strong repulsive interaction between\nintercomponent fermions. We find the existence of a critical repulsive\ninteraction strength above which the phase separation evolves. By increasing\nthe trap imbalance, the composite phase of Mott-insulating core is changed into\nthe one of ferromagnetic insulating core, which is incompressible and\noriginates from the Pauli exclusion principle."
    },
    {
        "anchor": "Density and Spin Linear Response of Atomic Fermi Superfluids with\n  Population Imbalance in BCS-BEC Crossover: We present a theoretical study of the density and spin (representing the two\ncomponents) linear response of Fermi superfluids with tunable attractive\ninteractions and population imbalance. In both linear response theories, we\nfind that the fluctuations of the order parameter must be treated on equal\nfooting with the gauge transformations associated with the symmetries of the\nHamiltonian so that important constraints including various sum rules can be\nsatisfied. Both theories can be applied to the whole BCS-Bose-Einstein\ncondensation crossover. The spin linear responses are qualitatively different\nwith and without population imbalance because collective-mode effects from the\nfluctuations of the order parameter survive in the presence of population\nimbalance, even though the associated symmetry is not broken by the order\nparameter. Since a polarized superfluid becomes unstable at low temperatures in\nthe weak and intermediate coupling regimes, we found that the density and spin\nsusceptibilities diverge as the system approaches the unstable regime, but the\nemergence of phase separation preempts the divergence.",
        "positive": "Signatures of the single particle mobility edge in the ground state\n  properties of Tonks-Girardeau and non-interacting Fermi gases in a\n  bichromatic potential: We explore the ground state properties of cold atomic gases, loaded into a\nbichromatic lattice, focusing on the cases of non-interacting fermions and\nhard-core (Tonks-Girardeau) bosons, trapped by the combination of two\npotentials with incommensurate periods. For such systems, two limiting cases\nhave been thoroughly established. In the tight-binding limit, the\nsingle-particle states in the lowest occupied band show a localization\ntransition, as the strength of the second potential is increased above a\ncertain threshold. In the continuous limit, when the tight-binding\napproximation does not hold anymore, a mobility edge is found, whose position\nin energy depends upon the strength of the second potential. Here, we study how\nthe crossover from the discrete to the continuum behavior occurs, and prove\nthat signatures of the localization transition and mobility edge clearly appear\nin the generic many-body properties of the systems. Specifically, we evaluate\nthe momentum distribution, which is a routinely measured quantity in\nexperiments with cold atoms, and demonstrate that, even in the presence of\nstrong boson-boson interactions, the single particle mobility edge can be\nobserved in the ground state properties."
    },
    {
        "anchor": "Dispersive optical detection of magnetic Feshbach resonances in\n  ultracold gases: Magnetically tunable Feshbach resonances in ultracold atomic systems are\nchiefly identified and characterized through time consuming atom loss\nspectroscopy. We describe an off-resonant dispersive optical probing technique\nto rapidly locate Feshbach resonances and demonstrate the method by locating\nfour resonances of $^{87}$Rb, between the $|\\rm{F} = 1, \\rm{m_F}=1 \\rangle$ and\n$|\\rm{F} = 2, \\rm{m_F}=0 \\rangle$ states. Despite the loss features being\n$\\lesssim0.1$ G wide, we require only 21 experimental runs to explore a\nmagnetic field range >18 G, where $1~\\rm{G}=10^{-4}$ T. The resonances consist\nof two known s-wave features in the vicinity of 9 G and 18 G and two previously\nunobserved p-wave features near 5 G and 10 G. We further utilize the dispersive\napproach to directly characterize the two-body loss dynamics for each Feshbach\nresonance.",
        "positive": "Impurity coupled to an artificial magnetic field in a Fermi gas in a\n  ring trap: The dynamics of a single impurity interacting with a many particle background\nis one of the central problems of condensed matter physics. Recent progress in\nultracold atom experiments makes it possible to control this dynamics by\ncoupling an artificial gauge field specifically to the impurity. In this paper,\nwe consider a narrow toroidal trap in which a Fermi gas is interacting with a\nsingle atom. We show that an external magnetic field coupled to the impurity is\na versatile tool to probe the impurity dynamics. Using Bethe Ansatz (BA) we\ncalculate the eigenstates and corresponding energies exactly as a function of\nthe flux through the trap. Adiabatic change of flux connects the ground state\nto excited states due to flux quantization. For repulsive interactions, the\nimpurity disturbs the Fermi sea by dragging the fermions whose momentum matches\nthe flux. This drag transfers momentum from the impurity to the background and\nincreases the effective mass. The effective mass saturates to the total mass of\nthe system for infinitely repulsive interactions. For attractive interactions,\nthe drag again increases the effective mass which quickly saturates to twice\nthe mass of a single particle as a polaron of the impurity and one fermion is\nformed. For excited states with momentum comparable to number of particles,\neffective mass shows a resonant behavior. We argue that standard tools in cold\natom experiments can be used to test these predictions."
    },
    {
        "anchor": "Semiclassical solitons in strongly correlated systems of ultracold\n  bosonic atoms in optical lattices: We investigate theoretically soliton excitations and dynamics of their\nformation in strongly correlated systems of ultracold bosonic atoms in two and\nthree dimensional optical lattices. We derive equations of nonlinear\nhydrodynamics in the regime of strong interactions and incommensurate fillings,\nwhen atoms can be treated as hard core bosons. When parameters change in one\ndirection only we obtain Korteweg-de Vries type equation away from half-filling\nand modified KdV equation at half-filling. We apply this general analysis to a\nproblem of the decay of the density step. We consider stability of one\ndimensional solutions to transverse fluctuations. Our results are also relevant\nfor understanding nonequilibrium dynamics of lattice spin models.",
        "positive": "Topological Thouless Pumping of Ultracold Fermions: A gas of electrons in a one-dimensional periodic potential can be transported\neven in the absence of a voltage bias if the potential is modulated slowly and\nperiodically in time. Remarkably, the transferred charge per cycle is only\nsensitive to the topology of the path in parameter space. Although this\nso-called Thouless charge pump has first been proposed more than thirty years\nago, it has not yet been realized. Here we report the first demonstration of\ntopological Thouless pumping using ultracold atoms in a dynamically controlled\noptical superlattice. We observe a shift of the atomic cloud as a result of\npumping and extract the topological invariance of the pumping process from this\nshift. We demonstrate the topological nature of the Thouless pump by varying\nthe topology of the pumping path and verify that the topological pump indeed\nworks in the quantum region by varying speed and temperature."
    },
    {
        "anchor": "Josephson-type oscillations in spin-orbit coupled Bose-Einstein\n  condensates with nonlinear optical lattices: We consider spin-orbit coupled Bose Einstein Condensate in presence of linear\nand nonlinear optical lattices within the framework of quasi-one-dimensional\nGross-Pitaevskii equation. The population imbalance between the states changes\nperiodically with time and the oscillation amplitude depends sensitively on the\ninitial phase. The optical lattice is found to change phase velocity of the\noscillation of population imbalance. This oscillation can also be arrested\nbeyond critical values of parameters. We find that the optical lattice can\nefficiently be used to control the critical point.",
        "positive": "Bosonic orbital Su-Schrieffer-Heeger model in a lattice of rings: We study the topological properties of interacting and non-interacting bosons\nloaded in the orbital angular momentum states $l=1$ in a lattice of rings with\nalternating distances. At the single-particle level, the two circulation states\nwithin each site lead to two decoupled Su-Schrieffer-Heeger lattices with\ncorrelated topological phases. We characterize the topological configuration of\nthese lattices in terms of the alternating distances, as well as their\nsingle-particle spectrum and topologically protected edge states. Secondly, we\nadd on-site interactions for the two-boson case, which lead to the appearance\nof multiple bound states and edge bound states. We investigate the doublon\nbands in terms of a strong-link model and we analyze the resulting subspaces\nusing perturbation theory in the limit of strong interactions. All analytical\nresults are benchmarked against exact diagonalization simulations."
    },
    {
        "anchor": "A nonlocal kinetic energy functional for an inhomogeneous\n  two-dimensional Fermi gas: The average-density approximation is used to construct a nonlocal kinetic\nenergy functional for an inhomogeneous two-dimensional Fermi gas. This\nfunctional is then used to formulate a Thomas-Fermi von Weizs\\\"acker-like\ntheory for the description of the ground state properties of the system. The\nquality of the kinetic energy functional is tested by performing a fully\nself-consistent calculation for an ideal, harmonically confined,\ntwo-dimensional system. Good agreement with exact results are found, with the\nnumber and kinetic energy densities exhibiting oscillatory structure associated\nwith the nonlocality of the energy functional. Most importantly, this\nfunctional shows a marked improvement over the two-dimensional Thomas-Fermi von\nWeizs\\\"acker theory, particularly in the vicinity of the classically forbidden\nregion.",
        "positive": "Emerging Bosons with Three-Body Interactions from Spin-1 Atoms in\n  Optical Lattices: We study two many-body systems of bosons interacting via an infinite\nthree-body contact repulsion in a lattice: a pairs quasi-condensate induced by\ncorrelated hopping and the discrete version of the Pfaffian wavefunction. We\npropose to experimentally realise systems characterized by such interaction by\nmeans of a proper spin-1 lattice Hamiltonian: spin degrees of freedom are\nlocally mapped into occupation numbers of emerging bosons, in a fashion similar\nto spin-1/2 and hardcore bosons. Such a system can be realized with ultracold\nspin-1 atoms in a Mott Insulator with filling-factor one. The high versatility\nof these setups allows us to engineer spin-hopping operators breaking the SU(2)\nsymmetry, as needed to approximate interesting bosonic Hamiltonians with\nthree-body hardcore constraint. For this purpose we combine bichromatic\nspin-independent superlattices and Raman transitions to induce a different\nhopping rate for each spin orientation. Finally, we illustrate how our setup\ncould be used to experimentally realize the first setup, i.e. the transition to\na pairs quasi-condensed phase of the emerging bosons. We also report on a route\ntowards the realization of a discrete bosonic Pfaffian wavefunction and list\nsome open problems to reach this goal."
    },
    {
        "anchor": "Dynamic Structure Factor of Normal Fermi Gas from Collisionless to\n  Hydrodynamic Regime: The dynamic structure factor of a normal Fermi gas is investigated by using\nthe moment method for the Boltzmann equation. We determine the spectral\nfunction at finite temperatures over the full range of crossover from the\ncollisionless regime to the hydrodynamic regime. We find that the Brillouin\npeak in the dynamic structure factor exhibits a smooth crossover from zero to\nfirst sound as functions of temperature and interaction strength. The dynamic\nstructure factor obtained using the moment method also exhibits a definite\nRayleigh peak ($/omega /sim 0$), which is a characteristic of the hydrodynamic\nregime. We compare the dynamic structure factor obtained by the moment method\nwith that obtained from the hydrodynamic equations.",
        "positive": "Disclination classes, fractional excitations, and the melting of quantum\n  liquid crystals: We consider how fractional excitations bound to a dislocation evolve as the\ndislocation is separated into a pair of disclinations. We show that some\ndislocation-bound excitations (such as Majorana modes and half-quantum\nvortices) are possible only if the elementary dislocation consists of two\ninequivalent disclinations, as is the case for stripes or square lattices but\nnot for triangular lattices. The existence of multiple inequivalent\ndisclination classes governs the two-dimensional melting of quantum liquid\ncrystals (i.e., nematics and hexatics), determining whether superfluidity and\norientational order can simultaneously vanish at a continuous transition."
    },
    {
        "anchor": "Dynamical Control in a Quasi-periodically Modulated Optical Lattice: We investigate quantum tunneling phenomena for an optical lattice subjected\nto a bichromatic ac force. We show that incommensurability of the frequencies\nleads to super Bloch oscillation. We propose directed super Bloch oscillation\nfor the quasi periodically driven optical lattice. We study the dynamical\nlocalization and photon assisted tunneling for a periodical and\nquasi-periodical ac force.",
        "positive": "Interaction dependent heating and atom loss in a periodically driven\n  optical lattice: Periodic driving of optical lattices has enabled the creation of novel\nbandstructures not realizable in static lattice systems, such as topological\nbands for neutral particles. However, especially driven systems of interacting\nbosonic particles often suffer from strong heating. We have systematically\nstudied heating in an interacting Bose-Einstein condensate in a driven\none-dimensional optical lattice. We find interaction-dependent heating rates\nthat depend both on the scattering length and the driving strength and identify\nthe underlying resonant intra- and interband scattering processes. By comparing\nexperimental data and theory, we find that for driving frequencies well above\nthe trap depth, the heating rate is dramatically reduced by the fact that\nresonantly scattered atoms leave the trap before dissipating their energy into\nthe system. This mechanism of Floquet evaporative cooling offers a powerful\nstrategy to minimize heating in Floquet engineered quantum gases."
    },
    {
        "anchor": "Ground-state properties of Dipolar Bose polarons: We consider a quantum impurity immersed in a dipolar Bose Einstein condensate\nand study the properties of the emerging polaron. We calculate the energy,\neffective mass and quasi-particle residue of the dipolar polaron and\ninvestigate their behaviour with respect to the strength of zero-range contact\nand a long-range dipolar interactions among the condensate atoms and with the\nimpurity. While quantum fluctuations in the case of pure contact interactions\ntypically lead to an increase of the polaron energy, dipole-dipole interactions\nare shown to cause a sign reversal. The described signatures of dipolar\ninteractions are shown to be observable with current experimental capabilities\nbased on quantum gases of atoms with large magnetic dipole moments such as\nErbium or Dysprosium condensates.",
        "positive": "Supervised machine learning of ultracold atoms with speckle disorder: We analyze how accurately supervised machine learning techniques can predict\nthe lowest energy levels of one-dimensional noninteracting ultracold atoms\nsubject to the correlated disorder due to an optical speckle field. Deep neural\nnetworks with different numbers of hidden layers and neurons per layer are\ntrained on large sets of instances of the speckle field, whose energy levels\nhave been preventively determined via a high-order finite difference technique.\nThe Fourier components of the speckle field are used as feature vector to\nrepresent the speckle-field instances. A comprehensive analysis of the details\nthat determine the possible success of supervised machine learning tasks,\nnamely the depth and the width of the neural network, the size of the training\nset, and the magnitude of the regularization parameter, is presented. It is\nfound that ground state energies of previously unseen instances can be\npredicted with essentially arbitrary accuracy. First and second excited state\nenergies can be predicted too, albeit with slightly lower accuracy and using\nmore layers of hidden neurons."
    },
    {
        "anchor": "Three-dimensional dynamics of a fermionic Mott wedding-cake in clean and\n  disordered optical lattices: Non-equilibrium quantum phenomena are ubiquitous in nature. Yet, theoretical\npredictions on the real-time dynamics of many-body quantum systems remain\nformidably challenging, especially for high dimensions, strong interactions or\ndisordered samples. Here we consider a notable paradigm of strongly correlated\nFermi systems, the Mott phase of the Hubbard model, in a setup resembling\nultracold-gases experiments. We study the three-dimensional expansion of a\ncloud into an optical lattice after removing the confining potential. We use\ntime-dependent density-functional theory combined with dynamical mean-field\ntheory, considering interactions below and above the Mott threshold, as well as\ndisorder effects. At strong coupling, we observe multiple timescales in the\nmelting of the Mott wedding-cake structure, as the Mott plateau persist orders\nof magnitude longer than the band insulating core. We also show that disorder\ndestabilises the Mott plateau and that, compared to a clean setup, localisation\ncan decrease, creating an interesting dynamic crossover during the expansion.",
        "positive": "Non Classical Rotational Inertia Fraction in a One Dimensional Model of\n  Supersolid: We study the rotational inertia of a model of supersolid in the frame of the\nmean field Gross-Pitaevskii theory in one space dimension. We discuss the\nground state of the model and the existence of a non classical inertia (NCRI)\nunder rotation that models an annular geometry. An explicit formula for the\nNCRI is deduced. It depends on the density profil of the ground state, in full\nagreement with former theories. We compare the NCRI computed through this\ntheory with direct numerical simulations of rotating 1D systems."
    },
    {
        "anchor": "Interacting Hofstadter Interface: Two-dimensional topological insulators possess conducting edge states at\ntheir boundary while being insulating in the bulk. The detection of edge states\nremains an open question in ultracold atom setups. We propose a configuration\nto implement a topological interface within the experimentally realizable\ntime-reversal invariant Hofstadter model which gives rise to a topological\nphase boundary at the center of the system, and investigate the influence of\ntwo-body interactions on the interface in a fermionic system. The interface can\nin principle be probed via the spatially resolved compressibility of the system\nby using a quantum gas microscope. Furthermore, we distinguish the phases\nthrough their Hall response and compute a local spin Chern marker which proves\nthe phase separation of two distinct topological many-body phases. The\nbulk-boundary correspondence for the interacting system is confirmed by\ncomputing the edge state spectra at the interface.",
        "positive": "The thermodynamic origin of the Contact and its relation to the gap in\n  the BEC-BCS crossover: As can be inferred from present experiments in ultracold gases, the\nscattering length is a quantity that determines the thermodynamic state of the\ngas. As such, there exists a conjugate thermodynamic to it. Here, we show that\nthe recently introduced \"contact\" is the conjugate of the inverse of the\nscattering length. We find that this identification allows for a derivation of\nessentially all the known results regarding the contact. Using the mean-field\ntheory for the Bose-Einstein (BEC) to Bardeen-Cooper-Schriefer (BCS) crossover,\nwe also find that the contact is proportional to the square of the gap. We\nanalyze in detail both a homogenous balanced mixture of fermions and its\ninhomogenous counterpart in a harmonic trap."
    },
    {
        "anchor": "Antiferromagnetic long-range order in dissipative Rydberg lattices: We study the dynamics of dissipative spin lattices with power-law\ninteractions, realized via few-level atoms driven by coherent laser-coupling\nand decoherence processes. Using Monte-Carlo simulations, we determine the\nphase diagram in the steady state and analyze the dynamics of its generation.\nAs opposed to mean-field predictions and nearest-neighbour models there is no\nphase transition to long-range ordered phases for realistic interactions and\nresonant driving. However, for finite laser detunings, we demonstrate the\nemergence of crystalline order with a vanishing dissipative gap. Although the\nfound steady states differ considerably from those of an equilibrium Ising\nmagnet, the critical exponent of the revealed dissipative phase transition\nfalls into the 2D Ising universality class. Two complementary schemes for an\nexperimental implementation with cold Rydberg atoms are discussed.",
        "positive": "Structural transitions of nearly second order in classical dipolar gases: Particles with repulsive power-law interactions undergo a transition from a\nsingle to a double chain (zigzag) by decreasing the confinement in the\ntransverse direction. We theoretically characterize this transition when the\nparticles are classical dipoles, polarized perpendicularly to the plane in\nwhich the motion occurs, and argue that this transition is of first order, even\nthough weakly. The nature of the transition is determined by the coupling\nbetween transverse and axial modes of the chain and contrasts with the\nbehaviour found in Coulomb systems, where the linear-zigzag transition is\ncontinuous and belongs to the universality class of the ferromagnetic\ntransition. Our results hold for classical systems with power-law interactions\n$1/r^\\alpha$ when $\\alpha > 2$, and show that structural transitions in dipolar\nsystems and Rydberg atoms can offer the testbed for simulating the critical\nbehaviour of magnets with lattice coupling."
    },
    {
        "anchor": "Strong connection between single-particle and density excitations in\n  Bose-Einstein condensates: Strong connection between the single-particle and collective excitations\nstands out as one of the features of Bose-Einstein condensates (BECs). We\ndiscuss theoretically these excitations of BECs focusing on the exact\nproperties of the one-body and two-body Green's functions developed by Gavoret\nand Nozi\\`eres. We also investigate these excitations by using the many-body\napproximation theory at nonzero temperatures. First, we revisited the earlier\nstudy presented by Gavoret and Nozi\\`eres, involving the subsequent results\ngiven by Nepomnyashchii and Nepomnyashchii, in terms of the matrix formalism\nrepresentation. This formalism is an extension of the Nambu representation for\nthe single-particle Green's function of BECs to discuss the density and current\nresponse functions efficiently. We describe the exact low-energy properties of\nthe correlation functions and the vertex functions, and discuss the\ncorrespondence of the spectra between the single-particle and density\nexcitations in the low-energy and low-momentum limits at $T=0$. After deriving\nthe exact low-energy structures of the one-body and two-body Green's functions,\nwe develop a many-body approximation theory of BECs using the matrix formalism\nfor describing the single-particle Green's function and the density response\nfunction at nonzero temperatures. We show how the peaks of the single-particle\nspectral function and the density response function behave with an increasing\ntemperature. Many-body effect on the single-particle spectral function and the\ndensity response function is included within a random phase approximation,\nwhere satellite structures emerge because of beyond-mean-field effects.\nCriticisms are also made on recent theories casting doubt upon the conventional\nwisdom of the BEC: the equivalence of the dispersion relations between the\nsingle-particle and collective excitations in the low-energy and low-momentum\nregime.",
        "positive": "Strong-coupling expansion for the two-species Bose-Hubbard model: To analyze the ground-state phase diagram of Bose-Bose mixtures loaded into\n$d$-dimensional hypercubic optical lattices, we perform a strong-coupling\npower-series expansion in the kinetic energy term (plus a scaling analysis) for\nthe two-species Bose-Hubbard model with onsite boson-boson interactions. We\nconsider both repulsive and attractive interspecies interaction, and obtain an\nanalytical expression for the phase boundary between the incompressible Mott\ninsulator and the compressible superfluid phase up to third order in the\nhoppings. In particular, we find a re-entrant quantum phase transition from\npaired superfluid (superfluidity of composite bosons, i.e. Bose-Bose pairs) to\nMott insulator and again to a paired superfluid in all one, two and three\ndimensions, when the interspecies interaction is sufficiently large and\nattractive. We hope that some of our results could be tested with ultracold\natomic systems."
    },
    {
        "anchor": "The Raman dressed spin-1 spin-orbit coupled quantum gas: The recently realized spin-orbit coupled quantum gases (Y.-J Lin {\\it et\nal}., Nature 471, 83-86 (2011); P. Wang {\\it et al}., PRL 109, 095301 (2012);\nL. W. Cheuk {\\it et al}., PRL 109, 095302 (2012)) mark a breakthrough in the\ncold atom community. In these experiments, two hyperfine states are selected\nfrom a hyperfine manifold to mimic a pseudospin-1/2 spin-orbit coupled system\nby the method of Raman dressing, which is applicable to both bosonic and\nfermionic gases. In this work, we show that the method used in these\nexperiments can be generalized to create any large pseudospin spin-orbit\ncoupled gas if more hyperfine states are coupled equally by the Raman lasers.\nAs an example, we study in detail a quantum gas with three hyperfine states\ncoupled by the Raman lasers, and show when the state-dependent energy shifts of\nthe three states are comparable, triple-degenerate minima will appear at the\nbottom of the band dispersions, thus realizing a spin-1 spin-orbit coupled\nquantum gas. A novel feature of this three minima regime is that there can be\ntwo different kinds of stripe phases with different wavelengths, which has an\ninteresting connection to the ferromagnetic and polar phases of spin-1 spinor\nBECs without spin-orbit coupling.",
        "positive": "Surmounting the sign problem in non-relativistic calculations: a case\n  study with mass-imbalanced fermions: The calculation of the ground state and thermodynamics of mass-imbalanced\nFermi systems is a challenging many-body problem. Even in one spatial\ndimension, analytic solutions are limited to special configurations and\nnumerical progress with standard Monte Carlo approaches is hindered by the sign\nproblem. The focus of the present work is on the further development of methods\nto study imbalanced systems in a fully non-perturbative fashion. We report our\ncalculations of the ground-state energy of mass-imbalanced fermions using two\ndifferent approaches which are also very popular in the context of the theory\nof the strong interaction (Quantum Chromodynamics, QCD): (a) the hybrid Monte\nCarlo algorithm with imaginary mass imbalance, followed by an analytic\ncontinuation to the real axis; and (b) the Complex Langevin algorithm. We cover\na range of on-site interaction strengths that includes strongly attractive as\nwell as strongly repulsive cases which we verify with non-perturbative\nrenormalization group methods and perturbation theory. Our findings indicate\nthat, for strong repulsive couplings, the energy starts to flatten out,\nimplying interesting consequences for short-range and high-frequency\ncorrelation functions. Overall, our results clearly indicate that the Complex\nLangevin approach is very versatile and works very well for imbalanced Fermi\ngases with both attractive and repulsive interactions."
    },
    {
        "anchor": "Probing pair correlations in Fermi gases with Ramsey-Bragg\n  interferometry: We propose an interferometric method to probe pair correlations in a gas of\nspin-1/2 fermions. The method consists of a Ramsey sequence where both spin\nstates of the Fermi gas are set in a superposition of a state at rest and a\nstate with a large recoil velocity. The two-body density matrix is extracted\nvia the fluctuations of the transferred fraction to the recoiled state. In the\npair-condensed phase, the off-diagonal long-range order is directly reflected\nin the asymptotic behavior of the interferometric signal for long interrogation\ntimes. The method also allows to probe the spatial structure of the condensed\npairs: the interferometric signal is an oscillating function of the\ninterrogation time in the Bardeen-Cooper-Schrieffer regime; it becomes an\noverdamped function in the molecular Bose-Einstein condensate regime.",
        "positive": "Integrable model of a $p$-wave bosonic superfluid: We present an exactly-solvable $p$-wave pairing model for two bosonic\nspecies. The model is solvable in any spatial dimension and shares some\ncommonalities with the $p + ip$ Richardson-Gaudin fermionic model, such as a\nthird order quantum phase transition. However, contrary to the fermionic case,\nin the bosonic model the transition separates a gapless fragmented singlet pair\ncondensate from a pair Bose superfluid, and the exact eigenstate at the quantum\ncritical point is a pair condensate analogous to the fermionic Moore-Read\nstate."
    },
    {
        "anchor": "Spin-Imbalanced Quasi-Two-Dimensional Fermi Gases: We measure the density profiles for a Fermi gas of $^6$Li containing $N_1$\nspin-up atoms and $N_2$ spin-down atoms, confined in a quasi-two-dimensional\ngeometry. The spatial profiles are measured as a function of spin-imbalance\n$N_2/N_1$ and interaction strength, which is controlled by means of a\ncollisional (Feshbach) resonance. The measured cloud radii and central\ndensities are in disagreement with mean-field Bardeen-Cooper-Schrieffer theory\nfor a true two-dimensional system. We find that the data for normal-fluid\nmixtures are reasonably well fit by a simple two-dimensional polaron model of\nthe free energy. Not predicted by the model is a phase transition to a\nspin-balanced central core, which is observed above a critical value of\n$N_2/N_1$. Our observations provide important benchmarks for predictions of the\nphase structure of quasi-two-dimensional Fermi gases.",
        "positive": "Dynamics of localized waves in 1D random potentials: statistical theory\n  of the coherent forward scattering peak: As recently discovered [PRL ${\\bf 109}$ 190601(2012)], Anderson localization\nin a bulk disordered system triggers the emergence of a coherent forward\nscattering (CFS) peak in momentum space, which twins the well-known coherent\nbackscattering (CBS) peak observed in weak localization experiments. Going\nbeyond the perturbative regime, we address here the long-time dynamics of the\nCFS peak in a 1D random system and we relate this novel interference effect to\nthe statistical properties of the eigenfunctions and eigenspectrum of the\ncorresponding random Hamiltonian. Our numerical results show that the dynamics\nof the CFS peak is governed by the logarithmic level repulsion between\nlocalized states, with a time scale that is, with good accuracy, twice the\nHeisenberg time. This is in perfect agreement with recent findings based on the\nnonlinear $\\sigma$-model. In the stationary regime, the width of the CFS peak\nin momentum space is inversely proportional to the localization length,\nreflecting the exponential decay of the eigenfunctions in real space, while its\nheight is exactly twice the background, reflecting the Poisson statistical\nproperties of the eigenfunctions. Our results should be easily extended to\nhigher dimensional systems and other symmetry classes."
    },
    {
        "anchor": "Equation of state and contact of a strongly interacting Bose gas in the\n  normal state: We theoretically investigate the equation of state and Tan's contact of a\nnon-degenerate three dimensional Bose gas near a broad Feshbach resonance,\nwithin the framework of large-$N$ expansion. Our results agree with the\npath-integral Monte Carlo simulations in the weak-coupling limit and recover\nthe second-order virial expansion predictions at strong interactions and high\ntemperatures. At resonance, we find that the chemical potential and energy are\nsignificantly enhanced by the strong repulsion, while the entropy does not\nchange significantly. With increasing temperature, the two-body contact\ninitially increases and then decreases like $T^{-1}$ at large temperature, and\ntherefore exhibits a peak structure at about $4T_{c0}$, where $T_{c0}$ is the\nBose-Einstein condensation temperature of an ideal, non-interacting Bose gas.\nThese results may be experimentally examined with a non-degenerate unitary Bose\ngas, where the three-body recombination rate is substantially reduced. In\nparticular, the non-monotonic temperature dependence of the two-body contact\ncould be inferred from the momentum distribution measurement.",
        "positive": "Quantum-Fluctuation-Driven Dynamics of Droplet Splashing, Recoiling and\n  Deposition in Ultracold Binary Bose Gases: Droplet impact on a surface is practically relevant to a variety of fields in\nnature and industry, while a complete control of its outcomes remains\nchallenging due to various unmanageable factors. In this work, we propose the\nquantum simulation of droplet impact outcomes in the platform of ultracold\natoms. Specifically, we study the quantum-fluctuation-driven dynamics (QFDD) of\ntwo-dimensional Bose-Bose mixtures from an initial Townes soliton towards the\nformation of a quantum droplet. By tuning the fluctuation energy of the initial\nTownes state through its size and number, the subsequent QFDD can produce\nvarious outcomes including splashing, recoiling, and deposition, similar to\nthose in droplet impact dynamics. We have utilized the Weber number to identify\nthe thresholds of splashing and recoiling, and further established a universal\nscaling law between the maximum spreading factor and the Weber number in the\nrecoiling regime. In addition, we show that the residual QFDD in the deposition\nregime can be used to probe the collective breathing modes of a quantum\ndroplet. Our results reveal a mechanism for the droplet impact outcomes, which\ncan be directly tested in cold-atom experiments and can pave the way for\nexploring intriguing droplet dynamics in a clean and fully controlled quantum\nsetting."
    },
    {
        "anchor": "Simulation of the Laughlin state in an optical lattice: We analyze the proposal of achieving a Mott state of Laughlin wave functions\nin an optical lattice [M. Popp {\\it et al.}, Phys. Rev. A 70, 053612 (2004)]\nand study the consequences of considering the anharmonic corrections to each\nsingle site potential expansion that were not taken into account until now. Our\nresult is that, although the anharmonic correction reduces the maximum\nfrequency at which the system can rotate before the atoms escape from each site\n(centrifugal limit), the Laughlin state can still be achieved for a small\nnumber of particles and a realistic value of the laser intensity.",
        "positive": "Statics and dynamics of a binary dipolar Bose-Einstein condensate\n  soliton: We study the statics and dynamics of a binary dipolar Bose-Einstein\ncondensate soliton for repulsive inter- and intraspecies contact interactions\nwith the two components subject to different spatial symmetries $-$ distinct\nquasi-one-dimensional and quasi-two-dimensional shapes - using numerical\nsolution and variational approximation of a three-dimensional mean-field model.\nThe results are illustrated with realistic values of parameters in the binary\n164Dy-168Er mixture. The possibility of forming robust dipolar solitons of very\nlarge number of atoms make them of great experimental interest. The existence\nof the solitons is illustrated in terms of stability phase diagrams. Exotic\nshapes of these solitons are illustrated in isodensity plots. The variational\nresults for statics (size and chemical potential) and dynamics (small\noscillation) of the binary soliton compare well with the numerical results. A\nway of preparing and studying these solitons in laboratory is suggested."
    },
    {
        "anchor": "Laser driving of Superradiant scattering at variable incidence angle: We study superradiant scattering from a Bose-Einstein condensate using a pump\nlaser incident at variable angle and show the presence of asymmetrically\npopulated scattering modes. Experimental data reveal that the direction of the\npump laser plays a significant role in the formation of this asymmetry, result\nwhich is in good agreement with numerical simulations based on coupled\nMaxwell-Schr\\\"{o}dinger equations. Our study complements the gap of previous\nwork in which the pump laser was only applied along the short axis or the long\naxis of a condensate, and extends our knowledge about cooperative scattering\nprocesses.",
        "positive": "Persistent currents, deformation and collectivity in the many-boson\n  yrast problem on the circle: Properties of the yrast states of a system of $N$ bosons confined to a\none-dimensional ring and interacting via contact forces is examined both\nvariationally and by numerical diagonalizations. The latter allow for obtaining\nnumerical correlated many-body wave functions explicitly. The study of\ncorrelation functions involving different yrast states indicates that a quantum\nphase transition previously detected in the properties of the ground state in\nthe case of attractive two-body interactions is an yrast phenomenon involving\nthe onset of `deformation', in the sense given to this term by Bohr and\nMottelson in connection with the description of nuclear spectra, including\nenhanced transition operators and emergence of a shared intrinsic correlation\nstructure. In this case the moment of inertia of the deformed state is\nessentially the rigid moment of inertia, `intrinsic' states being essentially\ndegenerate."
    },
    {
        "anchor": "Second-order hydrodynamics for fermionic cold atoms: Detailed analysis\n  of transport coefficients and relaxation times: We give a detailed derivation of the second-order (local) hydrodynamics for\nBoltzmann equation with an external force by using the renormalization group\nmethod. In this method, we solve the Boltzmann equation faithfully to extract\nthe hydrodynamics without recourse to any ansatz. Our method leads to\nmicroscopic expressions of not only all the transport coefficients that are of\nthe same form as those in Chapman-Enskog method but also those of the viscous\nrelaxation times $\\tau_i$ that admit physically natural interpretations. As an\nexample, we apply our microscopic expressions to calculate the transport\ncoefficients and the relaxation times of the cold fermionic atoms in a\nquantitative way, where the transition probability in the collision term is\ngiven explicitly in terms of the $s$-wave scattering length $a_s$. We thereby\ndiscuss the quantum statistical effects, temperature dependence, and\nscattering-length dependence of the first-order transport coefficients and the\nviscous relaxation times: It is shown that as the temperature is lowered, the\ntransport coefficients and the relaxation times increase rapidly because Pauli\nprinciple acts effectively. On the other hand, as $a_s$ is increased, these\nquantities decrease and become vanishingly small at unitarity because of the\nstrong coupling. The numerical calculation shows that the relation\n$\\tau_\\pi=\\eta/P$, which is derived in the relaxation-time approximation and\nused in most of literature without almost any foundation, turns out to be\nsatisfied quite well, while the similar relation for the relaxation time\n$\\tau_J$ of the heat conductivity is satisfied only approximately with a\nconsiderable error.",
        "positive": "Exciton-polariton X-waves in a microcavity: We investigate the possibility of creating X-waves, or localized wave\npackets, in resonantly excited exciton-polariton superfluids. We demonstrate\nthe existence of X-wave traveling solutions in the coupled exciton-photon\nsystem past the inflection point, where the effective mass of lower polaritons\nis negative in the direction perpendicular to the wavevector of the pumping\nbeam. Contrary to the case of bright solitons, X-waves do not require\nnonlinearity for sustaining their shape. Nevertheless, we show that\nnonlinearity is important for their dynamics, as it allows for their\nspontaneous formation from an initial Gaussian wave packet. Unique properties\nof exciton-polaritons may lead to applications of their X-waves in\nlong-distance signal propagation inside novel integrated optoelectronic\ncircuits based on excitons."
    },
    {
        "anchor": "Interaction-modulated tunneling dynamics in a mixture of Bose-Einstein\n  condensates: We study the interaction-modulated tunneling dynamics of a Bose-Einstein\ncondensate (BEC) in a deep double-well potential, where the tunneling between\nthe two wells is modulated by another BEC trapped in a harmonic potential\nsymmetrically positioned at the center of the double-well potential. The\ninter-species interactions couple the dynamics of the two BECs, which give rise\nto interesting features in the tunneling oscillations. Adopting a two-mode\napproximation for the BEC in the double-well potential and coupling it with the\nGross-Pitaevskii equation of the harmonically trapped BEC, we numerically\ninvestigate the coupled dynamics of the BEC mixture, and map out the phase\ndiagram of the tunneling dynamics. We show that the dynamical back action of\nthe BEC in the harmonic trap leads to strong non-linearity in the oscillations\nof the BEC in the double-well potential, which enriches the system dynamics,\nand enhances macroscopic self trapping. The transition between the Josephson\noscillation and the self-trapping dynamics can be identified by monitoring the\noscillation frequency of the double-well BEC. Our results suggest the\npossibility of tuning the tunneling dynamics of BECs in double-well potentials.",
        "positive": "The Fulde-Ferrell-Larkin-Ovchinnikov state for ultracold fermions in\n  lattice and harmonic potentials: a review: We review the concepts and the present state of theoretical studies of\nspin-imbalanced superfluidity, in particular the elusive\nFulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, in the context of ultracold\nquantum gases. The comprehensive presentation of the theoretical basis for the\nFFLO state that we provide is useful also for research on the interplay between\nmagnetism and superconductivity in other physical systems. We focus on settings\nthat have been predicted to be favourable for the FFLO state, such as optical\nlattices in various dimensions and spin-orbit coupled systems. These are also\nthe most likely systems for near-future experimental observation of the FFLO\nstate. Theoretical bounds, such as Bloch's and Luttinger's theorems, and\nexperimentally important limitations, such as finite-size effects and trapping\npotentials, are considered. In addition, we provide a comprehensive review of\nthe various ideas presented for the observation of the FFLO state. We conclude\nour review with an analysis of the open questions related to the FFLO state,\nsuch as its stability, superfluid density, collective modes and extending the\nFFLO superfluid concept to new types of lattice systems."
    },
    {
        "anchor": "Quantum droplets of bosonic mixtures in a one-dimensional optical\n  lattice: We demonstrate the existence of quantum droplets in two-component\none-dimensional Bose-Hubbard chains. The droplets exist for any strength of\nrepulsive intra-species interactions provided they are balanced by comparable\nattractive inter-species interactions. The ground-state phase diagram is\npresented and the different phases are characterized by examining the density\nprofile and off-diagonal one- and two-body correlation functions. A rich\nvariety of phases is found, including atomic superfluid gases, atomic\nsuperfluid droplets, pair superfluid droplets, pair superfluid gases and a\nMott-insulator phase. A parameter region prone to be experimentally explored is\nidentified, where the average population per site is lower than three atoms,\nthus avoiding three-body losses. Finally, the bipartite entanglement of the\ndroplets is found to have a non-trivial dependence on the number of particles.",
        "positive": "Dark-dark soliton breathing patterns in multi-component Bose-Einstein\n  condensates: In this work, we explore systematically various SO(2)-rotation-induced\nmultiple dark-dark soliton breathing patterns obtained from stationary and\nspectrally stable multiple dark-bright and dark-dark waveforms in trapped\none-dimensional, two-component atomic Bose-Einstein condensates (BECs). The\nstationary states stem from the associated linear limits (as the eigenfunctions\nof the quantum harmonic oscillator problem) and are parametrically continued to\nthe nonlinear regimes by varying the respective chemical potentials, i.e., from\nthe low-density linear limits to the high-density Thomas-Fermi regimes. We\nperform a Bogolyubov-de Gennes (BdG) spectral stability analysis to identify\nstable parametric regimes of these states. Upon SO(2)-rotation, the stable\nsteady-states, one-, two-, three-, four-, and many dark-dark soliton breathing\npatterns are observed in the numerical simulations. Furthermore, analytic\nsolutions up to three dark-bright solitons in the homogeneous setting, and\nthree-component systems are also investigated."
    },
    {
        "anchor": "1D multicomponent Fermions with delta function interaction in strong and\n  weak coupling limits: $\u03ba$-component Fermi gas: We derive the first few terms of the asymptotic expansion of the Fredholm\nequations for one-dimensional $\\kappa$-component fermions with repulsive and\nwith attractive delta-function interaction in strong and weak coupling regimes.\nWe thus obtain a highly accurate result for the ground state energy of a\nmulticomponent Fermi gas with polarization for these regimes. This result\nprovides a unified description of the ground state properties of the Fermi gas\nwith higher spin symmetries. However, in contrast to the two-component Fermi\ngas, there does not exist a mapping that can unify the two sets of Fredholm\nequations as the interacting strength vanishes. Moreover, we find that the\nlocal pair correlation functions shed light on the quantum statistic effects of\nthe $\\kappa$-component interacting fermions. For the balanced spin case with\nrepulsive interaction, the ground state energy obtained confirms Yang and You's\nresult [Chin. Phys. Lett. {\\bf 28}, 020503 (2011)] that the energy per particle\nas $\\kappa \\to \\infty$ is the same as for spinless Bosons.",
        "positive": "Quantum Monte Carlo simulation of BEC-impurity tunneling: Polaron tunneling is a prominent example of a problem characterized by\ndifferent energy scales, for which the standard quantum Monte Carlo methods\nface a slowdown problem. We propose a new quantum-tunneling Monte Carlo (QTMC)\nmethod which is free from this issue and can be used for a wide range of\ntunneling phenomena. We apply it to study an impurity interacting with a\none-dimensional Bose-Einstein condensate and simultaneously trapped in an\nexternal double-well potential. Our scheme works for an arbitrary coupling\nbetween the particle and condensate and, at the same time, allows for an\naccount of tunneling effects. We discover two distinct quasi-particle peaks\nassociated, respectively, with the phonon-assisted tunneling and the\nself-trapping of the impurity, which are in a crossover regime for the system\nmodeled. We observe and analyze changes in the weights and spectral positions\nof the peaks (or, equally, effective masses of the quasi-particles) when the\ncoupling strength is increased. Possible experimental realizations using cold\natoms are discussed."
    },
    {
        "anchor": "Self-localization of magnon Bose-Einstein condensates in the ground\n  state and on excited levels: from harmonic to box-like trapping potential: Long-lived coherent spin precession of 3He-B at low temperatures around 0.2\nTc is a manifestation of Bose-Einstein condensation of spin-wave excitations or\nmagnons in a magnetic trap which is formed by the order-parameter texture and\ncan be manipulated experimentally. When the number of magnons increases, the\norbital texture reorients under the influence of the spin-orbit interaction and\nthe profile of the trap gradually changes from harmonic to a square well, with\nwalls almost impenetrable to magnons. This is the first experimental example of\nBose condensation in a box. By selective rf pumping the trap can be populated\nwith a ground-state condensate or one at any of the excited energy levels. In\nthe latter case the ground state is simultaneously populated by relaxation from\nthe exited level, forming a system of two coexisting condensates.",
        "positive": "Photon-Assisted Tunneling in a Biased Strongly Correlated Bose Gas: We study the impact of coherently generated lattice photons on an atomic Mott\ninsulator subjected to a uniform force. Analogous to an array of tunnel-coupled\nand biased quantum dots, we observe sharp, interaction-shifted photon-assisted\ntunneling resonances corresponding to tunneling one and two lattice sites\neither with or against the force, and resolve multiorbital shifts of these\nresonances. By driving a Landau-Zener sweep across such a resonance, we realize\na quantum phase transition between a paramagnet and an antiferromagnet, and\nobserve quench dynamics when the system is tuned to the critical point. Direct\nextensions will produce gauge fields and site-resolved spin flips, for\ntopological physics and quantum computing."
    },
    {
        "anchor": "Strong-coupling corrections to spin susceptibility in the BCS-BEC\n  crossover regime of a superfluid Fermi gas: We theoretically investigate the uniform spin susceptibility $\\chi$ in the\nsuperfluid phase of an ultracold Fermi gas in the BCS\n(Bardeen-Cooper-Schrieffer)-BEC (Bose-Einstein condensation) crossover region.\nIn our previous paper [H. Tajima, {\\it et. al.}, Phys. Rev. A {\\bf 89}, 033617\n(2014)], including pairing fluctuations within an extended $T$-matrix\napproximation (ETMA), we showed that strong pairing fluctuations cause the\nso-called spin-gap phenomenon, where $\\chi$ is anomalously suppressed even in\nthe normal state near the superfluid phase transition temperature $T_{\\rm c}$.\nIn this paper, we extend this work to the superfluid phase below $T_{\\rm c}$,\nto clarify how this many-body phenomenon is affected by the superfluid order.\nFrom the comparison of the ETMA $\\chi$ with the Yosida function describing the\nspin susceptibility in a weak-coupling BCS superfluid, we identify the region\nwhere pairing fluctuations crucially affect this magnetic quantity below\n$T_{\\rm c}$ in the phase diagram with respect to the strength of a pairing\ninteraction and the temperature. This spin-gap regime is found to be consistent\nwith the previous pseudogap regime determined from the pseudogapped density of\nstates. We also compare our results with a recent experiment on a $^6$Li Fermi\ngas. Since the spin susceptibility is sensitive to the formation of\nspin-singlet preformed pairs, our results would be useful for the study of\npseudogap physics in an ultracold Fermi gas on the viewpoint of the spin\ndegrees of freedom.",
        "positive": "BCS-BEC crossover at finite temperature in spin-orbit coupled Fermi\n  gases: By adopting a $T$-matrix-based method within the $G_0G$ approximation for the\npair susceptibility, we study the effects of the pairing fluctuation on the\nthree-dimensional spin-orbit coupled Fermi gases at finite temperature. The\ncritical temperatures of the superfluid/normal phase transition are determined\nfor three different types of spin-orbit coupling (SOC): (1) the extreme oblate\n(EO) or Rashba SOC, (2) the extreme prolate (EP) or equal Rashba-Dresselhaus\nSOC, and (3) the spherical (S) SOC. For EO- and S-type SOC, the SOC dependence\nof the critical temperature signals a crossover from BCS to BEC state; at\nstrong SOC limit, the critical temperature recover those of ideal BEC of\nrashbons. The pairing fluctuation induces a pseudogap in the fermionic\nexcitation spectrum in both superfluid and normal phases. We find that, for EO-\nand S-type SOC, even at weak coupling, sufficiently strong SOC can induce\nsizable pseudogap. Our research suggests that the spin-orbit coupled Fermi\ngases may open new means to the study of the pseudogap formation in fermionic\nsystems."
    },
    {
        "anchor": "Two rotating particles interacting via two-body Gaussian potential\n  harmonically confined in two spatial dimensions: We study two spinless bosons interacting via two-body Gaussian potential\nsubjected to an externally impressed rotation about an axis confined in a\nharmonic trap in two-spatial dimensions. We obtain a transcendental equation\nfor the relative angular momentum $|m|$ state with various values of the\ntwo-body interaction range $\\sigma$ and the two-body interaction strength\n$g_{2}$ to study the resulting energy spectrum and analyze the role of Hilbert\nspace dimensions $\\widetilde{N}$. We compare results for both attractive and\nrepulsive interaction for $\\delta$-function potential and Gaussian potential\nfor various values of interaction range. We study the effects of interaction\nparameters and relative angular momentum on the ground state energy and its\nvarious components, namely, kinetic energy, trap potential and interaction\npotential. For a given $|m|$ and non-interacting case, we observe that the\nground state energy becomes independent of interaction range. However, for a\ngiven relative angular momentum and interaction strength $g_{2}>0$, there is an\nincrease in ground state energy with an increase in interaction range. Below\nthe interaction strength $g_{2}V(r)\\leq -1$, ground state energy diverges to\nphysically unacceptable negative-infinity for $|m|=0$ state. Further, for\n$|m|=1$, the ground state energy becomes independent of the interaction\nstrength. For a $|m|$, we present a comparative study between the Gaussian\ninteraction potential and the $\\delta$-function potential. Further, we observe\nthat for a given $g_{2}$ and $|m|$, for $\\delta$-function potential {\\it i.e.}\n$\\sigma\\to 0$, to achieve the convergence of ground state energy, we require a\nconsiderably large critical Hilbert space. Whereas, in the case of Gaussian\ninteraction potential with $\\sigma\\to 1$, the ground state energy converges for\na considerably small critical Hilbert space.",
        "positive": "Influence of a static electric field on a one-dimensional Bose-Fermi\n  mixture confined in a double potential welll: In this study, we conducted a detailed investigation into the time evolution\nof the probability density within a 1D double-well potential hosting a\nBose-Fermi mixture. This system comprised spinless bosons and spin one-half\nfermions with weak repulsive contact interactions. Notably, even at very low\neffective coupling constants, periodic probabilities were observed, indicating\ncorrelated tunneling of both bosons and fermions, leading to complete\nmiscibility, which disappears when an external electric field is turned on. The\nelectric field accentuated fermion-fermion interactions due to the Pauli\nexclusion principle, altering both boson density and interactions and leading\nto spatial redistribution of particles. These findings underscore the complex\ninterplay between interactions, external fields, and spatial distributions\nwithin confined quantum systems.\n  Our exploration of higher interaction strengths revealed conditions under\nwhich probability density functions are decoupled. Furthermore, we observed\nthat increased fermion interaction, driven by the electric field, led to higher\ntunneling frequencies for both species because of the repulsive nature of the\nboson-fermion interaction. Conversely, increased boson-boson interaction\nresulted in complete tunneling of both species, especially when boson density\nwas high, leading to effective fermion repulsion. Expanding our analysis to\nscenarios involving four bosons demonstrated that higher interaction values\ncorresponded to increased oscillation frequencies in tunneling probabilities.\nFinally, by manipulating interaction parameters and activating the electric\nfield, we achieved complete tunneling of both species, further increasing\noscillation frequencies and resulting in intervals characterized by overlapping\nprobability functions."
    },
    {
        "anchor": "Bright solitons in a spin-orbit-coupled dipolar Bose-Einstein condensate\n  trapped within a double-lattice: By effectively controlling the dipole-dipole interaction, we investigate the\ncharacteristics of the ground state of bright solitons in a spin-orbit coupled\ndipolar Bose-Einstein condensate. The dipolar atoms are trapped within a\ndouble-lattice which consists of a linear and a nonlinear lattice. We derive\nthe motion equations of the different spin components, taking the controlling\nmechanisms of the diolpe-dipole interaction into account. An analytical\nexpression of dipole-dipole interaction is derived. By adjusting the dipole\npolarization angle, the dipole interaction can be adjusted from attraction to\nrepulsion. On this basis, we study the generation and manipulation of the\nbright solitons using both the analytical variational method and numerical\nimaginary time evolution. The stability of the bright solitons is also analyzed\nand we map out the stability phase diagram. By adjusting the long-range\ndipole-dipole interaction, one can achieve manipulation of bright solitons in\nall aspects, including the existence, width, nodes, and stability. Considering\nthe complexity of our system, our results will have enormous potential\napplications in quantum simulation of complex systems.",
        "positive": "Vortex conveyor belt for matter-wave coherent splitting and\n  interferometry: We numerically study a matter wave interferometer realized by splitting a\ntrapped Bose-Einstein condensate with phase imprinting. We show that a simple\nstep-like imprinting pattern rapidly decays into a string of vortices that can\ngenerate opposite velocities on the two halves of the condensate. We first\nstudy in detail the splitting and launching effect of these vortex structures,\nwhose functioning resembles the one of a conveyor belt, and we show that the\ninitial exit velocity along the vortex conveyor belt can be controlled\ncontinuously by adjusting the vortex distance. We finally characterize the\ncomplete interferometric sequence, demonstrating how the phase of the resulting\ninterference fringe can be used to measure an external acceleration. The\nproposed scheme has the potential to be developed into compact and high\nprecision accelerometers."
    },
    {
        "anchor": "Exact dark state solutions of the coupled atomic-molecular Bose-Einstein\n  condensates in an external potential: We consider a coupled nonlinear Schr\\\"{o}dinger equations describing an\natomic Bose-Einstein condensates coupled to a molecular condensates through the\nstimulated Raman adiabatic passage loaded in an external potential. The\nexistence of dark state are investigated within the full parameter space\naccounts for all the nonlinear collisions, together with the atom-molecule\nconversion coupling and external potential. The results show that there are a\nclass of external potentials such as double-well, periodical and double\nperiodical, and harmonic potentials, where the exact dark solutions can be\nformed. Our results may raise the possibility of relative experiments for dark\nstate in the coupled atomic-molecular Bose-Einstein condensates.",
        "positive": "Finite-temperature phase transitions in quasi-two-dimensional spin-1\n  Bose gases: Recently, the Berezinskii-Kosterlitz-Thouless transition was found to be\nmediated by half-quantum vortices (HQVs) in two-dimensional (2D)\nantiferromagnetic Bose gases [Phys. Rev. Lett. 97, 120406 (2006)]. We study the\nthermal activation of HQVs in the experimentally relevant trapped quasi-2D\nsystems and find that the crossover temperature is shifted upwards if skyrmions\nare allowed. Above the defect binding temperatures we observe transitions\ncorresponding to the onset of a coherent condensate and a quasi-condensate and\ndiscuss the absence of a fragmented condensate."
    },
    {
        "anchor": "Benchmarking the multiconfigurational Hartree method by the exact\n  wavefunction of two harmonically trapped bosons with contact interaction: We consider two bosons in a one-dimensional harmonic trap, interacting by a\ncontact potential, and compare the exact solution of this problem to a\nself-consistent numerical solution by using the multiconfigurational\ntime-dependent Hartree (MCTDH) method. We thereby benchmark the predictions of\nthe MCTDH method with a few-body problem that has an analytical solution for\nthe most commonly experimentally realized interaction potential in ultracold\nquantum gases. It is found that exact ground state energy and first order\ncorrelations are accurately reproduced by MCTDH up to the intermediate\ndimensionless coupling strengths corresponding to typical background scattering\nlengths of magnetically trapped ultracold dilute Bose gases. For larger\ncouplings, established for example by (a combination of) Feshbach resonances\nand optical trapping, the MCTDH approach overestimates the depth of the\ntrap-induced correlation dip of first order correlations in position space, as\nwell as overestimates the fragmentation, defined as the average relative\noccupation of orbitals other than the energetically lowest one. We anticipate\nthat qualitatively similar features in the correlation function may arise for\nlarger particle numbers, paving the way for a quantitative assessment of the\naccuracy of MCTDH by experiments with ultracold atoms.",
        "positive": "Cooling by corralling: a route to ultra-low entropies in optical\n  lattices: A major motivation for cold atom experiments is the search for quantum ground\nstates such as antiferromagnets and d-wave superfluids. The primary obstacle to\nthis task is the difficulty of cooling to sufficiently low temperatures. We\npropose a way to achieve very low temperatures and entropies ($\\sim 0.03k_B$\nper particle) by trapping fermions in a corral formed from another species of\natoms. The Fermi system can then be used as a heat sink, or it can be\nadiabatically evolved into other desired states. In particular, we suggest\nmethods for generating antiferromagnetism using this technique."
    },
    {
        "anchor": "Quantum interferometry at zero and finite temperature with two-mode\n  bosonic Josephson junctions: We analyze phase interferometry realized with a bosonic Josephson junction\nmade of trapped dilute and ultracold atoms. By using a suitable phase\nsensitivity indicator we study the zero temperature junction states useful to\nachieve sub shot-noise precisions. Sub shot-noise phase shift sensitivities can\nbe reached even at finite temperature under a suitable choice of the junction\nstate. We infer a scaling law in terms of the size system (that is, the number\nof particles) for the temperature at which the shot-noise limit is not overcome\nanymore",
        "positive": "Squeezing of nonlinear spin observables by one axis twisting in the\n  presence of decoherence: An analytical study: In an ensemble of two-level atoms that can be described in terms of a\ncollective spin, entangled states can be used to enhance the sensitivity of\ninterferometric precision measurements. While non-Gaussian spin states can\nproduce larger quantum enhancements than spin-squeezed Gaussian states, their\nuse requires the measurement of observables that are nonlinear functions of the\nthree components of the collective spin. In this paper we develop strategies\nthat achieve the optimal quantum enhancements using non-Gaussian states\nproduced by a nonlinear one-axis-twisting Hamiltonian, and show that\nmeasurement-after-interaction techniques, known to amplify the output signals\nin quantum parameter estimation protocols, are effective in measuring nonlinear\nspin observables. Including the presence of the relevant decoherence processes\nfrom atomic experiments, we determine analytically the quantum enhancement of\nnon-Gaussian over-squeezed states as a function of the noise parameters for\narbitrary atom numbers."
    },
    {
        "anchor": "Dissipative quantum systems: from two to many atoms: We study the dynamics of bosonic atoms in a double well potential under the\ninfluence of dissipation. The main effect of dissipation is to destroy quantum\ncoherence and to drive the system towards a unique steady state. We study how\nthe atom-atom interaction affects the decoherence process. We use a systematic\napproach considering different atomic densities. We show that, for two atoms,\nthe interaction already strongly suppresses decoherence: a phenomenon we refer\nto as \"interaction impeded decoherence\". For many atoms, thanks to the\nincreased complexity of the system, the nature of the decoherence process is\ndramatically altered giving rise to an algebraic instead of exponential decay.",
        "positive": "Uniform spin susceptibility and spin-gap phenomenon in the BCS-BEC\n  crossover regime of an ultracold Fermi gas: We investigate the uniform spin susceptibility $\\chi_{\\rm s}$ in the BCS\n(Bardeen-Cooper-Schrieffer)-BEC (Bose-Einstein condensation) crossover regime\nof an ultracold Fermi gas. Including pairing fluctuations within the framework\nof an extended $T$-matrix approximation, we show that $\\chi_{\\rm s}$ exhibits\nnon-monotonic temperature dependence in the normal state. In particular,\n$\\chi_{\\rm s}$ is suppressed near the superfluid phase transition temperature\n$T_{\\rm c}$ due to strong pairing fluctuations. To characterize this anomalous\nbehavior, we introduce the spin-gap temperature $T_{\\rm s}$ as the temperature\nat which $\\chi_{\\rm s}$ takes a maximum value. Determining $T_{\\rm s}$ in the\nwhole BCS-BEC crossover region, we identify the spin-gap regime in the phase\ndiagram of a Fermi gas in terms of the temperature and the strength of a\npairing interaction. We also clarify how the spin-gap phenomenon is related to\nthe pseudogap phenomenon appearing in the single-particle density of states.\nOur results indicate that an ultracold Fermi gas in the BCS-BEC crossover\nregion is a very useful system to examine the pseudogap phenomenon and the\nspin-gap phenomenon in a unified manner."
    },
    {
        "anchor": "Temporal Talbot interferometer of strongly interacting molecular\n  Bose-Einstein condensate: Talbot interferometer, as a periodic reproduction of momentum distribution in\nthe time domain, finds significant applications in multiple research. The\ninter-particle interactions during the diffraction and interference process\nintroduce numerous many-body physics problems, leading to unconventional\ninterference characteristics. This work investigates both experimentally and\ntheoretically the influence of interaction in a Talbot interferometer with a\n$^{6}\\rm Li_2$ molecular Bose-Einstein condensate in a one-dimensional optical\nlattice, with interaction strength directly tunable via magnetic Feshbach\nresonance. A clear dependence of the period and amplitude of signal revivals on\nthe interaction strength can be observed. While interactions increase the decay\nrate of the signal and advance the revivals, we find that over a wide range of\ninteractions, the Talbot interferometer remains highly effective over a certain\nevolutionary timescale, including the case of fractional Talbot interference.\nThis work provides insight into the interplay between interaction and the\ncoherence properties of a temporal Talbot interference in optical lattices,\npaving the way for research into quantum interference in strongly interacting\nsystems.",
        "positive": "Rb-85 tunable-interaction Bose-Einstein condensate machine: We describe our experimental setup for creating stable Bose-Einstein\ncondensates of Rb-85 with tunable interparticle interactions. We use\nsympathetic cooling with Rb-87 in two stages, initially in a tight\nIoffe-Pritchard magnetic trap and subsequently in a weak, large-volume crossed\noptical dipole trap, using the 155 G Feshbach resonance to manipulate the\nelastic and inelastic scattering properties of the Rb-85 atoms. Typical Rb-85\ncondensates contain 4 x 10^4 atoms with a scattering length of a=+200a_0. Our\nminimalist apparatus is well-suited to experiments on dual-species and spinor\nRb condensates, and has several simplifications over the Rb-85 BEC machine at\nJILA (Papp, 2007; Papp and Wieman, 2006), which we discuss at the end of this\narticle."
    },
    {
        "anchor": "Departing from thermality of analogue Hawking radiation in a\n  Bose-Einstein condensate: We study the quantum fluctuations in a one dimensional Bose-Einstein\ncondensate realizing an analogous acoustic black hole. The taking into account\nof evanescent channels and of zero modes makes it possible to accurately\nreproduce recent experimental measurements of the density correlation function.\nWe discuss the determination of Hawking temperature and show that in our model\nthe analogous radiation presents some significant departure from thermality.",
        "positive": "A Coherent Polariton Laser: The semiconductor polariton laser promises a new source of coherent light,\nwhich, compared to conventional semiconductor photon lasers, has input-energy\nthreshold orders of magnitude lower. However, intensity stability, a defining\nfeature of a coherent state, has remained poor. Intensity noise at many times\nof the shot-noise of a coherent state has persisted, which has been attributed\nto multiple mechanisms that are difficult to separate in conventional polariton\nsystems. The large intensity noise in turn limited the phase coherence. These\nlimit the capability of the polariton laser as a source of coherence light.\nHere, we demonstrate a polariton laser with shot-noise limited intensity\nstability, as expected of a fully coherent state. This is achieved by using an\noptical cavity with high mode selectivity to enforce single-mode lasing,\nsuppress condensate depletion, and establish gain saturation. The absence of\nspurious intensity fluctuations moreover enabled measurement of a transition\nfrom exponential to Gaussian decay of the phase coherence of the polariton\nlaser. It suggests large self-interaction energies in the polariton condensate,\nexceeding the laser bandwidth. Such strong interactions are unique to\nmatter-wave laser and important for nonlinear polariton devices. The results\nwill guide future development of polariton lasers and nonlinear polariton\ndevices."
    },
    {
        "anchor": "Improvement of the matching of the exact solution and variational\n  approaches in an interacting two-fermion system: A more reasonable trial ground state wave function is constructed for the\nrelative motion of an interacting two-fermion system in a 1D harmonic\npotential. At the boundaries both the wave function and its first derivative\nare continuous and the quasi-momentum is determined by a more practical\nconstraint condition which associates two variational parameters. The upper\nbound of the ground state energy is obtained by applying the variational\nprinciple to the expectation value of the Hamiltonian of relative motion on the\ntrial wave function. The resulted energy and wave function show better\nagreement with the analytical solution than the original proposal.",
        "positive": "BEC and dimensional crossover in a boson gas within multi-slabs: For an ideal Bose-gas within a multi-slabs periodic structure, we report a\ndimensional crossover and discuss whether a BEC transition at $T_c \\neq 0$\ndisappears or not.\n  The multi-slabs structure is generated via a Kronig-Penney potential\nperpendicular to the slabs of width $a$ and separated by a distance $b$. The\nability of the particles to jump between adjacent slabs is determined by the\nhight $V_0$ and width $b$ of the potential barrier. Contrary to what happens in\nthe boson gas inside a zero-width multilayers case, where the critical\ntemperature diminishes and goes up again as a function of the wall separation,\nhere the $T_c$ decreases continuously as the potential barrier height and the\ncell size $a+b$ increase. We plot the surface $T_c = 10^{-6}$ showing two\nprominent regions in the parameters space, which suggest a phase transition\nBEC-NOBEC at $T \\neq 0$. %The position of the phase transition surface is\nalmost independent of the ratio $r=b/a$ while the cell size $a+b$ is almost\nproportional to the square root of the height of the potential barriers. The\nspecific heat shows a crossover from 3D to 2D when the height of the potential\nor the barrier width increase, in addition to the well known peak related to\nthe Bose-Einstein condensation."
    },
    {
        "anchor": "Quantum systems of ultra-cold bosons with customized inter-particle\n  interactions: Recent progress in cooling and trapping of polarized clouds of chromium\n$^{52}Cr$, dysprosium $^{164}Dy$ and erbium $^{168}Er$ opens a road-map to\nquantum systems where shapes of inter-particle interactions can be customized.\nThe main purpose of this work is to get a deeper insight on a role which the\noverall shape of the inter-particle interaction plays in a context of trapped\nultra-cold bosons. We show that strong inter-particle repulsion inevitably\nleads to multi-hump fragmentation of the ground state. The fragmentation\nphenomenon is universal -- it takes place in traps of different dimensionality\nand topologies and for very broad classes of repulsive inter-particle\npotentials. The physics behind is identified and explained.",
        "positive": "Linear response of a superfluid Fermi gas inside its pair-breaking\n  continuum: We study the signatures of the collective modes of a superfluid Fermi gas in\nits linear response functions for the order-parameter and density fluctuations\nin the Random Phase Approximation (RPA). We show that a resonance associated to\nthe Popov-Andrianov (or sometimes \"Higgs\") mode is visible inside the\npair-breaking continuum at all values of the wavevector $q$, not only in the\n(order-parameter) modulus-modulus response function but also in the\nmodulus-density and density-density responses. At nonzero temperature, the\nresonance survives in the presence of thermally broken pairs even until the\nvicinity of the critical temperature $T_c$, and coexists with both the\nAnderson-Bogoliubov modes at temperatures comparable to the gap $\\Delta$ and\nwith the low-velocity phononic mode predicted by RPA near $T_c$. The existence\nof a Popov-Andrianov-\"Higgs\" resonance is thus a robust, generic feature of the\nhigh-energy phenomenology of pair-condensed Fermi gases, and should be\naccessible to state-of-the-art cold atom experiments."
    },
    {
        "anchor": "Classical fields in the one-dimensional Bose gas: applicability and\n  determination of the optimal cutoff: To finalize information about the accuracy of the classical field approach\nfor the 1d Bose gas, the lowest temperature quasicondensate was studied by\ncomparing the extended Bogoliubov model of Mora and Castin, to its classical\nfield analogue. The parameters for which the physics is well described by\nmatter waves are now presented for all 1d regimes, and concurrently, the\noptimal cutoff that best matches all observables together is also provided.\nThis cutoff rises strongly with density when the chemical potential is higher\nthan the thermal energy to account for kinetic energy. As a consequence, clouds\nthat reach this coldest quantum fluctuating regime are better described using a\ntrap basis than plane waves. This contrasts with higher temperature clouds for\nwhich the basis choice is less important. In passing, estimates for chemical\npotential, density fluctuations, kinetic and interaction energy in the low\ntemperature quasicondensate are obtained up to several leading terms.",
        "positive": "Self-consistent Description of Bose-Bose Droplets: Harmonically Trapped\n  Quasi-2D Droplets: We describe a quantum droplet of a Bose-Bose mixture squeezed by an external\nharmonic forces in one spatial direction. Our approach is based on the\nself-consistent method formulated in [1]. The true spatial droplet profile in\nthe direction of confinement is accounted for, however local density\napproximation is assumed in the free directions. We define a numerical approach\nto find the beyond-mean-field contribution to the chemical potential\n(Lee-Huang-Yang chemical potential) -- the quantity that determines the\ndroplet's profile. In addition to the numerical approach, we find the\nLee-Huang-Yang potential in the analytic form in two limiting cases: a\nperturbative result for a strong confinement and a semiclassical expression\nwhen confinement is very weak."
    },
    {
        "anchor": "Chiral magnetic effect in three-dimensional optical lattices: Although Weyl semimetals have been extensively studied for exploring rich\ntopological physics, the direct observation of the celebrated chiral magnetic\neffect (CME) associated with the so-called dipolar chiral anomaly has long\nintrigued and challenged physicists, still remaining elusive in nature. Here we\npropose a feasible scheme for experimental implementation of ultracold atoms\nthat may enable us to probe the CME with a pure topological current in an\nartificial Weyl semimetal. The paired Weyl points with the dipolar chiral\nanomaly emerge in the presence of the well-designed spin-orbital coupling and\nlaser-assisted tunneling. Both of the two artificial fields are readily\nrealizable and highly tunable via current optical techniques using ultracold\natoms trapped in three-dimensional optical lattices, providing a reliable way\nfor manipulating Weyl points in the momentum-energy space. By applying a weak\nartificial magnetic field, the system processes an auxiliary current originated\nfrom the topology of a paired Weyl points, namely, the pure CME current. This\ntopological current can be extracted from measuring the center-of-mass motion\nof ultracold atoms, which may pave the way to directly and unambiguously\nobserve the CME in experiments.",
        "positive": "Higher-order quantum bright solitons in Bose-Einstein condensates show\n  truly quantum emergent behavior: When an interaction quench by a factor of four is applied to an attractive\nBose-Einstein condensate, a higher-order quantum bright soliton exhibiting\nrobust oscillations is predicted in the semiclassical limit by the\nGross-Pitaevskii equation. Combining matrix-product state simulations of the\nBose-Hubbard Hamiltonian with analytical treatment via the Lieb-Liniger model\nand the eigenstate thermalization hypothesis, we show these oscillations are\nabsent. Instead, one obtains a large stationary soliton core with a small\nthermal cloud, a smoking-gun signal for non-semiclassical behavior on\nmacroscopic scales and therefore a fully quantum emergent phenomenon."
    },
    {
        "anchor": "Instabilities of vortex-ring-bright soliton in trapped binary 3D\n  Bose-Einstein condensates: Instabilities of vortex-ring-bright coherent structures in harmonically\ntrapped two-component three-dimensional Bose-Einstein condensates are studied\nnumerically within the coupled Gross-Pitaevskii equations and interpreted\nanalytically. Interestingly, the filled vortex core with a sufficiently large\namount of the bright component is observed to reduce the parametric interval of\nstability of the vortex ring. We have identified the mechanisms of several\nlinear instabilities and one nonlinear parametric instability in this\nconnection. Two of the linear instabilities are qualitatively different from\nones reported earlier, to our knowledge, and are associated with azimuthal\nmodes of $m=0$ and $m=1$, i.e., deviations of the vortex from the stationary\nring shape. Our nonlinear parametric resonance instability occurs between the\n$m=0$ and $m=2$ modes and signals the exchange of energy between them.",
        "positive": "Finite-frequency normal and superfluid drag effects in two-component\n  atomic Bose-Einstein condensates: Two-component systems consisting of mutually interacting particles can\ndemonstrate both intracomponent transport effects and intercomponent\nentrainment (or drag) effects. In the presence of superfluidity, the\nintracomponent transport is characterized by dissipative conductivity and\nsuperfluid weight in the framework of two-fluid model, and intercomponent\nentrainment gives rise to normal and nondissipative drag effects. We present\nunified treatment of all these effects for spatially homogeneous two-component\natomic Bose-Einstein condensates based on the Bogoliubov theory, focusing\nspecifically on the drag effects. Calculating finite-frequency intra- and\nintercomponent conductivities with taking into account quasiparticle damping,\nwe derive and numerically check analytical Drude-like approximations applicable\nat low frequencies, and Lorentz-like approximations applicable at higher\nfrequencies in vicinity of the resonant energy of spin-to-density Bogoliubov\nquasiparticle conversion. As possible physical realizations of two-component\natomic systems, we consider three-dimensional Bose-Bose mixtures and closely\nspaced two-layered systems of magnetic dipolar atoms."
    },
    {
        "anchor": "Bose-Einstein condensation of heteronuclear bound states formed in a\n  Fermi gas of two atomic species: microscopic approach: We study a many-body system of interacting fermionic atoms of two species\nthat are in thermodynamic equilibrium with their condensed heteronuclear bound\nstates (molecules). In order to describe such an equilibrium state, we use a\nmicroscopic approach that involves the Bogoliubov model for a weakly\ninteracting Bose gas and approximate formulation of the second quantization\nmethod in the presence of bound states of particles elaborated earlier by the\nauthors. This microscopic approach is valid at low temperatures, when the\naverage kinetic energy of all the components in the system is small in\ncomparison with the bound state energy. The coupled equations, which relate the\nchemical potentials of fermionic components and molecular condensate density,\nare obtained within the proposed theory. At zero temperature, these equations\nare analyzed both analytically and numerically, attracting the relevant\nexperimental data. We find the conditions at which a condensate of\nheteronuclear molecules coexists in equilibrium with degenerate components of a\nFermi gas. The ground state energy and single-particle excitation spectrum are\nfound. The boundaries of the applicability of the developed microscopic\napproach are analyzed.",
        "positive": "Topological phonons in arrays of ultracold dipolar particles: The notion of topology in physical systems is associated with the existence\nof a nonlocal ordering that is insensitive to a large class of perturbations.\nThis brings robustness to the behaviour of the system and can serve as a ground\nfor developing new fault-tolerant applications. We discuss how to design and\nstudy a large variety of topology-related phenomena for phonon-like collective\nmodes in arrays of ultracold polarized dipolar particles. These modes are\ncoherently propagating vibrational excitations, corresponding to oscillations\nof particles around their equilibrium positions, which exist in the regime\nwhere long-range interactions dominate over single-particle motion. We\ndemonstrate that such systems offer a distinct and versatile tool to\ninvestigate a wide range of topological effects in a single experimental setup\nwith a chosen underlying crystal structure by simply controlling the anisotropy\nof the interactions via the orientation of the external polarizing field. Our\nresults show that arrays of dipolar particles provide a promising unifying\nplatform to investigate topological phenomena with phononic modes."
    },
    {
        "anchor": "Magnetic phase diagram of a spin-1 condensate in two dimensions with\n  dipole interaction: Several new features arise in the ground-state phase diagram of a spin-1\ncondensate trapped in an optical trap when the magnetic dipole interaction\nbetween the atoms is taken into account along with confinement and spin\nprecession. The boundaries between the regions of ferromagnetic and polar\nphases move as the dipole strength is varied and the ferromagnetic phases can\nbe modulated. The magnetization of the ferromagnetic phase perpendicular to the\nfield becomes modulated as a helix winding around the magnetic field direction,\nwith a wavelength inversely proportional to the dipole strength. This\nmodulation should be observable for current experimental parameters in\n$^{87}$Rb. Hence the much-sought supersolid state, with broken continuous\ntranslation invariance in one direction and broken global U(1) invariance,\noccurs generically as a metastable state in this system as a result of dipole\ninteraction. The ferromagnetic state parallel to the applied magnetic field\nbecomes striped in a finite system at strong dipolar coupling.",
        "positive": "Probing topology by \"heating\": Quantized circular dichroism in ultracold\n  atoms: We reveal an intriguing manifestation of topology, which appears in the\ndepletion rate of topological states of matter in response to an external\ndrive. This phenomenon is presented by analyzing the response of a generic 2D\nChern insulator subjected to a circular time-periodic perturbation: due to the\nsystem's chiral nature, the depletion rate is shown to depend on the\norientation of the circular shake. Most importantly, taking the difference\nbetween the rates obtained from two opposite orientations of the drive, and\nintegrating over a proper drive-frequency range, provides a direct measure of\nthe topological Chern number of the populated band ($\\nu$): this \"differential\nintegrated rate\" is directly related to the strength of the driving field\nthrough the quantized coefficient $\\eta_0\\!=\\!\\nu /\\hbar^2$. Contrary to the\ninteger quantum Hall effect, this quantized response is found to be non-linear\nwith respect to the strength of the driving field and it explicitly involves\ninter-band transitions. We investigate the possibility of probing this\nphenomenon in ultracold gases and highlight the crucial role played by edge\nstates in this effect. We extend our results to 3D lattices, establishing a\nlink between depletion rates and the non-linear photogalvanic effect predicted\nfor Weyl semimetals. The quantized circular dichroism revealed in this work\ndesignates depletion-rate measurements as a universal probe for topological\norder in quantum matter."
    },
    {
        "anchor": "Magnetic and nematic phases in a Weyl type spin-orbit-coupled spin-1\n  Bose gas: We present a variational study of the spin-1 Bose gases in a harmonic trap\nwith three-dimensional spin-orbit coupling of Weyl type. For weak spin-orbit\ncoupling, we treat the single-particle ground states as the form of\nperturbational harmonic oscillator states in the lowest total angular momentum\nmanifold with $j=1, m_j=1,0,-1$. When the two-body interaction is considered,\nwe set the trail order parameter as the superposition of three degenerate\nsingle-particle ground-states and the weight coefficients are determined by\nminimizing the energy functional. Two ground state phases, namely the magnetic\nand the nematic phases, are identified depending on the spin-independent and\nthe spin-dependent interactions. Unlike the non-spin-orbit-coupled spin-1\nBose-Einstein condensate for which the phase boundary between the magnetic and\nthe nematic phase lies exactly at zero spin-dependent interaction, the boundary\nis modified by the spin-orbit-coupling. We find the magnetic phase is featured\nwith phase-separated density distributions, 3D skyrmion-like spin textures and\ncompeting magnetic and biaxial nematic orders, while the nematic phase is\nfeatured with miscible density distributions, zero magnetization and spatially\nmodulated uniaxial nematic order. The emergence of higher spin order creates\nnew opportunities for exploring spin-tensor-related physics in spin-orbit\ncoupled superfluid.",
        "positive": "Ring solids and supersolids in spherical shell-shaped dipolar\n  Bose-Einstein condensates: We study the interplay between the anisotropy of the dipole-dipole\ninteraction and confinement in a curved geometry. We do so through numerical\ncalculations, based on the extended Gross- Pitaevskii equation, to characterize\nthe ground state of a dipolar Bose gas under the effect of a bubble trapping\npotential. As the scattering length and the number of particles are varied, we\nobserve the emergence of a wide variety of dipolar solids, which consist of\narrangements of dipolar droplets along a ring over the equator of the spherical\nshell confinement. By changing the detuning of the trap, we probe different\nring-like supersolid structures with varying number of dipolar clusters, which\nare unobtainable through conventional trapping settings."
    },
    {
        "anchor": "Driven Markovian Quantum Criticality: We identify a new universality class in one-dimensional driven open quantum\nsystems with a dark state. Salient features are the persistence of both the\nmicroscopic non-equilibrium conditions as well as the quantum coherence of\ndynamics close to criticality. This provides a non-equilibrium analogue of\nquantum criticality, and is sharply distinct from more generic driven systems,\nwhere both effective thermalization as well as asymptotic decoherence ensue,\nparalleling classical dynamical criticality. We quantify universality by\ncomputing the full set of independent critical exponents within a functional\nrenormalization group approach.",
        "positive": "Reproducible mesoscopic superpositions of Bose-Einstein condensates and\n  mean-field chaos: In a parameter regime for which the mean-field (Gross-Pitaevskii) dynamics\nbecomes chaotic, mesoscopic quantum superpositions in phase space can occur in\na double-well potential which is shaken periodically. For experimentally\nrealistic initial states like the ground state of some 100 atoms, the emergence\nof mesoscopic quantum superpositions in phase space is investigated\nnumerically. It is shown to be reproducible even if the initial conditions\nslightly change. While the final state is not a perfect superposition of two\ndistinct phase-states, the superposition is reached an order of magnitude\nfaster than in the case of the collapse and revival phenomenon. Furthermore, a\ngenerator of entanglement is identified."
    },
    {
        "anchor": "The evolution from BCS to BEC superfluidity in the presence of disorder: We describe the effects of disorder on the critical temperature of $s$-wave\nsuperfluids from the BCS to the BEC regime, with direct application to\nultracold fermions. We use the functional integral method and the replica\ntechnique to study Gaussian correlated disorder due to impurities, and we\ndiscuss how this system can be generated experimentally. In the absence of\ndisorder, the BCS regime is characterized by pair breaking and phase coherence\ntemperature scales which are essentially the same allowing strong correlations\nbetween the amplitude and phase of the order parameter for superfluidity. As\nnon-pair breaking disorder is introduced the largely overlapping Cooper pairs\nconspire to maintain phase coherence such that the critical temperature remains\nessentially unchanged, and Anderson's theorem is satisfied. However in the BEC\nregime the pair breaking and phase coherence temperature scales are very\ndifferent such that non-pair breaking disorder can affect dramatically phase\ncoherence, and thus the critical temperature, without the requirement of\nbreaking tightly-bound fermion pairs simultaneously. In this case, Anderson's\ntheorem does not apply, and the critical temperature can be more easily reduced\nin comparison to the BCS limit. Lastly, we find that the superfluid is more\nrobust against disorder in the intermediate region near unitarity between the\ntwo regimes.",
        "positive": "Dynamical density wave order in an atom-cavity system: We theoretically and experimentally explore the emergence of a dynamical\ndensity wave order in a driven dissipative atom-cavity system. A Bose-Einstein\ncondensate is placed inside a high finesse optical resonator and pumped\nsideways by an optical standing wave. The pump strength is chosen to induce a\nstationary superradiant checkerboard density wave order of the atoms stabilized\nby a strong intracavity light field. We show theoretically that, when the pump\nis modulated with sufficient strength at a frequency $\\omega_{d}$ close to a\nsystemic resonance frequency $\\omega_{>}$, a dynamical density wave order\nemerges, which oscillates at the two frequencies $\\omega_{>}$ and $\\omega_{<} =\n\\omega_{d} - \\omega_{>}$. This order is associated with a characteristic\nmomentum spectrum, also found in experiments in addition to remnants of the\noscillatory dynamics presumably damped by on-site interaction and heating, not\nincluded in the calculations. The oscillating density grating, associated with\nthis order, suppresses pump-induced light scattering into the cavity. Similar\nmechanisms might be conceivable in light-driven electronic matter."
    },
    {
        "anchor": "Induced interactions in the BCS-BEC crossover of two-dimensional Fermi\n  gases with Rashba spin-orbit coupling: We investigate the Gorkov--Melik-Barkhudarov (GM) correction to superfluid\ntransition temperature in two-dimensional Fermi gases with Rashba spin-orbit\ncoupling (SOC) across the SOC-driven BCS-BEC crossover. In the calculation of\nthe induced interaction, we find that the spin-component mixing due to SOC can\ninduce both of the conventional screening and additional antiscreening\ncontributions that interplay significantly in the strong SOC regime. While the\nGM correction generally lowers the estimate of transition temperature, it turns\nout that at a fixed weak interaction, the correction effect exhibits a\ncrossover behavior where the ratio between the estimates without and with the\ncorrection first decreases with SOC and then becomes insensitive to SOC when it\ngoes into the strong SOC regime. We demonstrate the applicability of the GM\ncorrection by comparing the zero-temperature condensate fraction with the\nrecent quantum Monte Carlo results.",
        "positive": "Superdiffusion of vortices in two-component quantum fluids of light: The quantum diffusion of a vortex in a two-component quantum fluid of light\nis investigated. In these systems, the Kerr nonlinearity promotes interactions\nbetween the photons, displaying features that are analogue of a Bose-Einstein\ncondensates. Quantum fluids of light have the advantage of simulating\nmatter-wave phenomena at room temperatures. While the analogy is true at the\nmean field level, the full quantum dynamics of an impurity in quantum fluids of\nlight of, and therefore the ability of featuring genuine quantum noise, has\nnever been considered. We numerically solve the problem by simulating a\nvortex-like impurity in the presence of noise with the Bogoliubov spectral\ndensity, and show that the vortex undergoes superdiffusion. We support our\nresults with a theory that has been previously developed for the brownian\nmotion of point-like particles."
    },
    {
        "anchor": "Cold bosons in the Landauer setup: We consider one dimensional potential trap that connects two reservoirs\ncontaining cold Bose atoms. The thermal current and single-particle bosonic\nGreen functions are calculated under non-equilibrium conditions. The bosonic\nstatistics leads to Luttinger liquid state with non-linear spectrum of\ncollective modes. This results in suppression of thermal current at low\ntemperatures and affects the single-particle Green functions.",
        "positive": "Detection and manipulation of nuclear spin states in fermionic strontium: Fermionic 87Sr has a nuclear spin of I=9/2, higher than any other element\nwith similar electronic structure. This large nuclear spin has many\napplications in quantum simulation and computation, for which preparation and\ndetection of the spin state are requirements. For an ultracold 87Sr cloud, we\nshow two complementary methods to characterize the spin-state mixture: optical\nStern-Gerlach state separation and state-selective absorption imaging. We use\nthese methods to optimize the preparation of a variety of spin-state mixtures\nby optical pumping and to measure an upper bound of the 87Sr spin relaxation\nrate."
    },
    {
        "anchor": "Coherence and correlation functions of quasi-2D dipolar superfluids at\n  zero temperature: We use the Bogoliubov theory of Bose-Einstein condensation to study the\nproperties of dipolar particles (atoms or molecules) confined in a uniform\ntwo-dimensional geometry at zero temperature. We find equilibrium solutions to\nthe dipolar Gross-Pitaevskii equation and the Bogoliubov-de Gennes equations.\nUsing these solutions we study the effects of quantum fluctuations in the\nsystem, particularly focussing on the instability point, where the roton\nfeature in the excitation spectrum touches zero. Specifically, we look at the\nbehaviour of the noncondensate density, the phase fluctuations, and the density\nfluctuations in the system. Near the instability, the density-density\ncorrelation function shows a particularly intriguing oscillatory behaviour.\nHigher order correlation functions display a distinct hexagonal lattice pattern\nformation, demonstrating how an observation of broken symmetry can emerge from\na translationally symmetric quantum state.",
        "positive": "Rigorous Results for the Ground States of the Spin-2 Bose-Hubbard Model: We present rigorous and universal results for the ground states of the $f=2$\nspinor Bose-Hubbard model. The model includes three two-body on site\ninteraction terms, two of which are spin dependent while the other one is spin\nindependent. We prove that, depending only on the coefficients of the two spin\ndependent terms, the ground state exhibits maximum or minimum total spin or\nSU(5) ferromagnetism. Exact ground-state degeneracies and the forms of\nground-state wave function are also determined in each case. All these results\nare valid regardless of dimension, lattice structure, or particle number. Our\napproach takes advantage of the symmetry of the Hamiltonian and employs\nmathematical tools including the Perron-Frobenius theorem and the Lie algebra\n$\\mathfrak{so}(5)$."
    },
    {
        "anchor": "Quantum and thermal fluctuations in two-component Bose gases: We study the effects of quantum and thermal fluctuations on Bose-Bose\nmixtures at finite temperature employing the time-dependent\nHartree-Fock-Bogoliubov (TDHFB) theory. The theory governs selfconsistently the\nmotion of the condensates, the noncondensates and of the anomalous components\non an equal footing. The finite temperature criterion for the phase separation\nis established. We numerically analyze the temperature dependence of different\ndensities for both miscible and immiscible mixtures. We show that the degree of\nthe overlap between the two condensates and the thermal clouds is lowered and\nthe relative motion of the centers-of-mass of the condensed and thermal\ncomponents is strongly damped due to the presence of the pair anomalous\nfluctuations. Our results are compared with previous theoretical and\nexperimental findings. On the other hand, starting from our TDHFB equations, we\ndevelop a random-phase theory for the elementary excitations in a homogeneous\nmixture. We find that the normal and anomalous fluctuations may lead to enhance\nthe excitations and the thermodynamics of the system.",
        "positive": "Inhomogeneous Pseudogap Phenomenon in the BCS-BEC Crossover Regime of a\n  Trapped Superfluid Fermi Gas: We investigate pseudogap phenomena in the unitarity limit of a trapped\nsuperfluid Fermi gas. Including effect of strong pairing fluctuations within a\n$T$-matrix approximation, as well as effects of a harmonic trap within the\nlocal density approximation (LDA), we calculate the local superfluid density of\nstates below the superfluid phase transition temperature $T_{\\rm c}$. We show\nthat the spatial region where single-particle excitations are dominated by the\npseudogap may still exist even below $T_{\\rm c}$, due to inhomogeneous pairing\nfluctuations caused by the trap potential. From the temperature dependence of\nthe pseudogapped density of states, we identify the pseudogap regime of the\nunitarity Fermi gas with respect to the temperature and spatial position. We\nalso show that the combined $T$-matrix theory with the LDA can quantitatively\nexplain the local pressure which was recently observed in the unitarity limit\nof a $^6$Li Fermi gas."
    },
    {
        "anchor": "Glassy disorder-induced effects in noisy dynamics of Bose-Hubbard and\n  Fermi-Hubbard systems: We address the effects of quenched disorder averaging in the time-evolution\nof systems of ultracold atoms in optical lattices in the presence of noise,\nimposed by of an environment. For bosonic systems governed by the Bose-Hubbard\nHamiltonian, we quantify the response of disorder in Hamiltonian parameters in\nterms of physical observables, including bipartite entanglement in the ground\nstate and report the existence of disorder-induced enhancement in weakly\ninteracting cases. For systems of two-species fermions described by the\nFermi-Hubbard Hamiltonian, we find similar results. In both cases, our\ndynamical calculations show no appreciable change in the effects of disorder\nfrom that of the initial state of the evolution. We explain our findings in\nterms the statistics of the disorder in the parameters and the behaviour of the\nobservables with the parameters.",
        "positive": "Topological phase transitions in four dimensions: We show that four-dimensional systems may exhibit a topological phase\ntransition analogous to the well-known Berezinskii-Kosterlitz-Thouless vortex\nunbinding transition in two-dimensional systems. The realisation of an\nengineered quantum system, where the predicted phase transition shall occur, is\nalso presented. We study a suitable generalization of the sine-Gordon model in\nfour dimensions and the renormalization group flow equation of its couplings,\nshowing that the critical value of the frequency is the square of the\ncorresponding value in $2D$. The value of the anomalous dimension at the\ncritical point is determined ($\\eta=1/32$) and a conjecture for the universal\njump of the superfluid stiffness ($4/\\pi^2$) presented."
    },
    {
        "anchor": "Comment on \"On the relations between large-scale models of superfluid\n  helium-4\" [Phys. Fluids 33, 127124 (2021]\": We comment on the paper by M. S\\'ykora, M. Pavelka, M. La Mantia, D. Jou, and\nM. Grmela \"On the relations between large-scale models of superfluid helium-4,\"\nPhysics of Fluids, 33(12):127124(2021), where the authors have developed a\nformalism for describing a coarse-grained flow of superfluid helium. This\nformalism is greatly based on the Hall-Vinen-Bekarevich-Khalatnikov (HVBK)\nmodel. We strongly disagree with the use of the HVBK equation approach for the\ncase of the three-dimensional quantum turbulence and expose our objections in\nthis comment. We discuss the HVBK method and also criticize the so-called\nvortex bundles model, which serves as a basis for using the HVBK method in a\nthree-dimensional quantum turbulence.",
        "positive": "Statistically induced Phase Transitions and Anyons in 1D Optical\n  Lattices: Anyons - particles carrying fractional statistics that interpolate between\nbosons and fermions - have been conjectured to exist in low dimensional\nsystems. In the context of the fractional quantum Hall effect (FQHE),\nquasi-particles made of electrons take the role of anyons whose statistical\nexchange phase is fixed by the filling factor. Here we propose an experimental\nsetup to create anyons in one-dimensional lattices with fully tuneable exchange\nstatistics. In our setup, anyons are created by bosons with\noccupation-dependent hopping amplitudes, which can be realized by assisted\nRaman tunneling. The statistical angle can thus be controlled in situ by\nmodifying the relative phase of external driving fields. This opens the\nfascinating possibility of smoothly transmuting bosons via anyons into fermions\nand of inducing a phase transition by the mere control of the particle\nstatistics as a free parameter. In particular, we demonstrate how to induce a\nquantum phase transition from a superfluid into an exotic Mott-like state where\nthe particle distribution exhibits plateaus at fractional densities."
    },
    {
        "anchor": "Broad Feshbach resonances in ultracold alkali-metal systems: A comprehensive search for \"broad\" Feshbach resonances (FRs) in all possible\ncombinations of stable alkali-metal atoms is carried out, using a multi-channel\nquantum-defect theory assisted by the analytic wave functions for a long-range\nvan-der-Waals potential. A number of new \"broad\" $s$-, $p$- and $d$-wave FRs in\nthe lowest-energy scattering channels, which are stable against two-body\ndipolar spin-flip loss, are predicted and characterized. Our results also show\nthat \"broad\" FRs of $p$- or $d$-wave type that are free of two-body loss do not\nexist between fermionic alkali-metal atoms for magnetic field up to 1000\\,G.\nThese findings constitute helpful guidance on efforts towards experimental\nstudy of high-partial-wave coupling induced many-body physics.",
        "positive": "Hong-Ou-Mandel atom interferometry in tunnel-coupled optical tweezers: The quantum statistics of atoms is typically observed in the behavior of an\nensemble via macroscopic observables. However, quantum statistics modifies the\nbehavior of even two particles, inducing remarkable consequences that are at\nthe heart of quantum science. Here we demonstrate near-complete control over\nall the internal and external degrees of freedom of two laser-cooled 87Rb atoms\ntrapped in two optical tweezers. This full controllability allows us to\nimplement a massive-particle analog of a Hong-Ou-Mandel interferometer where\natom tunneling plays the role of a photon beamsplitter. We use the\ninterferometer to probe the effect of quantum statistics on the two-atom\ndynamics under tunable initial conditions, chosen to adjust the degree of\natomic indistinguishability. Our work thereby establishes laser-cooled atoms in\noptical tweezers as a new route to bottom-up engineering of scalable,\nlow-entropy quantum systems."
    },
    {
        "anchor": "Generalized Efimov scenario for heavy-light mixtures: Motivated by recent experimental investigations of Cs-Cs-Li Efimov\nresonances, this work theoretically investigates the few-body properties of\n$N-1$ non-interacting identical heavy bosons, which interact with a light\nimpurity through a large $s$-wave scattering length. For Cs-Cs-Cs-Li, we\npredict the existence of universal four-body states with energies $E_4^{(n,1)}$\nand $E_4^{(n,2)}$, which are universally linked to the energy $E_3^{(n)}$ of\nthe $n$th Efimov trimer. For infinitely large $^{133}$Cs-$^6$Li and vanishing\n$^{133}$Cs-$^{133}$Cs scattering lengths, we find\n$(E_4^{(1,1)}/E_3^{(1)})^{1/2} \\approx 1.51$ and $(E_4^{(1,2)}/E_3^{(1)})^{1/2}\n\\approx 1.01$. The $^{133}$Cs-$^6$Li scattering lengths at which these states\nmerge with the four-atom threshold, the dependence of these energy ratios on\nthe mass ratio between the heavy and light atoms, and selected aspects of the\ngeneralized Efimov scenario for $N>4$ are also discussed. Possible implications\nof our results for ongoing cold atom experiments are presented.",
        "positive": "Assessing degrees of entanglement of phonon states in atomic Bose gases\n  through the measurement of commuting observables: We show that measuring commuting observables can be sufficient to assess that\na bipartite state is entangled according to either nonseparability or the\nstronger criterion of 'steerability'. Indeed, the measurement of a single\nobservable might reveal the strength of the interferences between the two\nsubsystems, as if an interferometer were used. For definiteness we focus on the\ntwo-point correlation function of density fluctuations obtained by in situ\nmeasurements in homogeneous one-dimensional cold atomic Bose gases. We then\ncompare this situation to that found in transonic stationary flows mimicking a\nblack hole geometry where correlated phonon pairs are emitted on either side of\nthe sonic horizon by the analogue Hawking effect. We briefly apply our\nconsiderations to two recent experiments."
    },
    {
        "anchor": "Equations of Motion for the Out-of-Equilibrium Dynamics of Isolated\n  Quantum Systems from the Projection Operator Technique: We present a rigorous framework to obtain evolution equations for the\nmomentum distribution and higher order correlation functions in weakly\ninteracting systems based on the Projection Operator Technique. These equations\ncan be numerically solved in an efficient way. We compare the solution of the\nequations with known results for 1D models and find an excellent agreement.",
        "positive": "Finite Temperature Phase Transition in a Cross-Dimensional Triangular\n  Lattice: Atomic many-body phase transitions and quantum criticality have recently\nattracted much attention in non-standard optical lattices. Here we perform an\nexperimental study of finite-temperature superfluid transition of bosonic atoms\nconfined in a three dimensional triangular lattice, whose structure can be\ncontinuously deformed to dimensional crossover regions including quasi-one and\ntwo dimensions. This non-standard lattice system provides a versatile platform\nto investigate many-body correlated phases. For the three dimensional case, we\nfind that the finite temperature superfluid transition agrees quantitatively\nwith the Gutzwiller mean field theory prediction, whereas tuning towards\nreduced dimensional cases, both quantum and thermal fluctuation effects are\nmore dramatic, and the experimental measurement for the critical point becomes\nstrongly deviated from the mean field theory. We characterize the fluctuation\neffects in the whole dimension crossover process. Our experimental results\nimply strong many-body correlations in the system beyond mean field\ndescription, paving a way to study quantum criticality near Mott-superfluid\ntransition in finite temperature dimension-crossover lattices."
    },
    {
        "anchor": "Creation of topological states of a Bose-Einstein condensate in a\n  plaquette: We study a square plaquette of four optical microtraps containing ultracold\n$^{87}$Rb atoms in F=1 hyperfine state. In a presence of external resonant\nmagnetic field the dipolar interactions couple initial $m_F=1$ component to\nother Zeeman sublevels. This process is a generalization of the Einstein-de\nHaas effect to the case when the external potential has only $C_4$\npoint-symmetry. We observe that vortex structures appear in the initially empty\n$m_F=0$ state. Topological properties of this state are determined by\ncompetition between the local axial symmetry of the individual trap and the\ndiscrete symmetry of the plaquette. For deep microtraps vortices are localized\nat individual sites whereas for shallow traps only one discrete vortex appears\nin the plaquette. States created in these two opposite cases have different\ntopological properties related to $C_4$ point-symmetry.",
        "positive": "Feshbach-Stabilized Insulator of Bosons in Optical Lattices: Feshbach resonances - namely resonances between an unbound two-body state\n(atomic state) and a bound (molecular) state, differing in magnetic moment -\nare a unique tool to tune the interaction properties of ultracold atoms. Here\nwe show that the spin-changing interactions, coherently coupling the atomic and\nmolecular state, can act as a novel mechanism to stabilize an insulating phase\n- the Feshbach insulator - for bosons in an optical lattice close to a narrow\nFeshbach resonance. Making use of quantum Monte Carlo simulations and\nmean-field theory, we show that the Feshbach insulator appears around the\nresonance, preventing the system from collapsing when the effective atomic\nscattering length becomes negative. On the atomic side of the resonance, the\ntransition from condensate to Feshbach insulator has a characteristic\nfirst-order nature, due to the simultaneous loss of coherence in the atomic and\nmolecular components. These features appear clearly in the ground-state phase\ndiagram of e.g. $^{87}$Rb around its 414 G resonance, and they are therefore\ndirectly amenable to experimental observation."
    },
    {
        "anchor": "Coherent collective dynamics and entanglement evolution of polar\n  molecules on 1D lattices: We study a LiCs strongly-interacting molecular gas loaded into an\none-dimensional optical lattice at quarter filling. The molecules are in the\nlowest electronic and vibrational state, $X^{1}\\Sigma$ ($\\nu=0$). Due to the\nlarge intermolecular distance and low filling, dipole-dipole interaction in the\nnearest-neighbor approximation governs the dynamics of the rotational\nexcitations. For low DC electric field strengths, the full set of rotational\nlevels $N=0,1$ must be taken into account, nevertheless, our calculations show\nthat very weak fields act as field-selectors disclosing two- and three-level\nsystems out of the original four-level one. The dynamics and the generated von\nNeumann entanglement entropy among the internal rotational states throughout\nthe evolution are presented for low, moderate and strong fields . We observe a\nsharp and monotonous growth of the entanglement as the dynamics take place\nshowing the potential of these molecular systems to be used in quantum\ninformation protocols. The numerical simulations are performed by means of the\nTime-Evolving Block Decimation algorithm based on the Matrix Product State\nformalism and the Susuki-Trotter decomposition.",
        "positive": "Borromean supercounterfluidity: We demonstrate microscopically the existence of a new superfluid state of\nmatter in a three-component Bose mixture trapped in an optical lattice. The\nsuperfluid transport involving coflow of all three components is arrested in\nthat state, while counterflows between any pair of components are\ndissipationless. The presence of three components allows for three different\ntypes of counterflows with only two independent superfluid degrees of freedom."
    },
    {
        "anchor": "Seeing Hofstadter's Butterfly in Atomic Fermi Gases: We propose a novel way to detect the fractal energy spectrum of the\nHofstadter model from the density distributions of ultracold fermions in an\nexternal trap. At low temperature, the local compressibility is proportional to\nthe density of states of the system which reveals the fractal energy spectrum.\nHowever, thermal broadening and noises in the real experimental situation\ninevitably smear out fine features in the density distribution. To overcome\nthis difficulty, we use the maximum entropy method to extract the density of\nstates directly from the noisy thermal density distributions. Simulations show\nthat one is able to restore the core feature of the Hofstadter's butterfly\nspectrum with current experimental techniques. By further reducing the noise or\nthe temperature, one can refine the resolution and observe fine structures of\nthe butterfly spectrum.",
        "positive": "Observation of Quantum Criticality and Luttinger Liquid in\n  One-dimensional Bose Gases: We experimentally investigate the quantum criticality and Tomonaga-Luttinger\nliquid (TLL) behavior within one-dimensional (1D) ultracold atomic gases. Based\non the measured density profiles at different temperatures, the universal\nscaling laws of thermodynamic quantities are observed. The quantum critical\nregime and the relevant crossover temperatures are determined through the\ndouble-peak structure of the specific heat. In the TLL regime, we obtain the\nLuttinger parameter by probing sound propagation. Furthermore, a characteristic\npower-law behavior emerges in the measured momentum distributions of the 1D\nultracold gas, confirming the existence of the TLL."
    },
    {
        "anchor": "Roadmap on Atomtronics: State of the art and perspective: Atomtronics deals with matter-wave circuits of ultra-cold atoms manipulated\nthrough magnetic or laser-generated guides with different shapes and\nintensities. In this way, new types of quantum networks can be constructed, in\nwhich coherent fluids are controlled with the know-how developed in the atomic\nand molecular physics community. In particular, quantum devices with enhanced\nprecision, control and flexibility of their operating conditions can be\naccessed. Concomitantly, new quantum simulators and emulators harnessing on the\ncoherent current flows can also be developed. Here, we survey the landscape of\natomtronics-enabled quantum technology and draw a roadmap for the field in the\nnear future. We review some of the latest progresses achieved in matter-wave\ncircuits design and atom-chips. Atomtronic networks are deployed as promising\nplatforms for probing many-body physics with a new angle and a new twist. The\nlatter can be done both at the level of equilibrium and non-equilibrium\nsituations. Numerous relevant problems in mesoscopic physics, like persistent\ncurrents and quantum transport in circuits of fermionic or bosonic atoms, are\nstudied through a new lens. We summarize some of the atomtronics quantum\ndevices and sensors. Finally, we discuss alkali-earth and Rydberg atoms as\npotential platforms for the realization of atomtronic circuits with special\nfeatures.",
        "positive": "Regular and chaotic dynamics of a matter-wave soliton near the atomic\n  mirror: The dynamics of the soliton in a self-attractive Bose-Einstein condensate\nunder the gravity are investigated. First, we apply the inverse scattering\nmethod, which gives rise to equation of motion for the center-of-mass\ncoordinate of the soliton. We analyze the amplitude-frequency characteristic\nfor nonlinear resonance. Applying the Krylov-Bogoliubov method for the small\nparameters the dynamics of soliton on the phase plane are considered.\nHamiltonian chaos under the action of the gravity on the Poincar\\'e map are\nstudied."
    },
    {
        "anchor": "Effect of optical lattice potentials on the vortices in rotating dipolar\n  Bose-Einstein condensates: We study the interplay of dipole-dipole interaction and optical lattice (OL)\npotential of varying depths on the formation and dynamics of vortices in\nrotating dipolar Bose-Einstein condensates. By numerically solving the\ntime-dependent quasi-two dimensional Gross-Pitaevskii equation, we analyse the\nconsequence of dipole-dipole interaction on vortex nucleation, vortex\nstructure, critical rotation frequency and number of vortices for a range of OL\ndepths. Rapid creation of vortices has been observed due to supplementary\nsymmetry breaking provided by the OL in addition to the dipolar interaction.\nAlso the critical rotation frequency decreases with an increase in the depth of\nthe OL. Further, at lower rotation frequencies the number of vortices increases\non increasing the depth of OL while it decreases at higher rotation\nfrequencies. This variation in the number of vortices has been confirmed by\ncalculating the rms radius, which shrinks in deep optical lattice at higher\nrotation frequencies.",
        "positive": "Self-Induced Decoherence in the Bose-Hubbard model: The conventional conception of decoherence relies on the interaction with an\nexternal set of degrees of freedom - the 'bath' - to which the system loses\nquantum information. But the role of the bath can be played too by any internal\ndegrees of freedom that are not accessible to the observer, and in this sense\nwe can talk about 'Self-Induced Decoherence'. Simulating the exact\ntime-evolution of the few-body Bose-Hubbard Hamiltonian, we provide numerical\nevidence of the decay of quantum purity in the sense of 'temporal typicality'\nreferred in the context of pure state Quantum Statistical Mechanics. We analyse\nthe causes of such purity loss in terms of the structural differences of the\ninteracting many-body Hamiltonian in comparison with its non-interacting\ncounterpart, finding that the predominant role in the long term behaviour is\nplayed by the shifts in the many-body energy spectrum."
    },
    {
        "anchor": "Critical behavior of a chiral superfluid in a bipartite square lattice: We study the critical behavior of Bose-Einstein condensation in the second\nband of a bipartite optical square lattice in a renormalization group framework\nat one-loop order. Within our field theoretical representation of the system,\nwe approximate the system as a two-component Bose gas in three dimensions. We\ndemonstrate that the system is in a different universality class than the\npreviously studied condensation in a frustrated triangular lattice due to an\nadditional Umklapp scattering term, which stabilizes the chiral superfluid\norder at low temperatures. We derive the renormalization group flow of the\nsystem and show that this order persists in the low energy limit. Furthermore,\nthe renormalization flow suggests that the phase transition from the thermal\nphase to the chiral superfluid state is first order.",
        "positive": "Condensing magnons in a degenerate ferromagnetic spinor Bose gas: We observe the condensation of magnon excitations within an $F=1$ $^{87}$Rb\nspinor Bose-Einstein condensed gas. Magnons are pumped into a longitudinally\nspin-polarized gas, allowed to equilibrate to a non-degenerate distribution,\nand then cooled evaporatively at near-constant net longitudinal magnetization\nwhereupon they condense. We find magnon condensation to be described\nquantitatively as the condensation of free particles in an effective potential\nthat is uniform within the ferromagnetic condensate volume, evidenced by the\nnumber and distribution of magnons at the condensation transition. Transverse\nmagnetization images reveal directly the spontaneous, inhomogeneous symmetry\nbreaking by the magnon quasi-condensate, including signatures of Mermin-Ho spin\ntextures that appear as phase singularities in the magnon condensate\nwavefunction."
    },
    {
        "anchor": "Nonequilibrium Transport in a Superfluid Josephson Junction Chain: Is\n  There Negative Differential Conductivity?: We consider the far-from-equilibrium quantum transport dynamics in a 1D\nJosephson junction chain of multi-mode Bose-Einstein condensates. We develop a\ntheoretical model to examine the experiment of R. Labouvie et al. [Phys. Rev.\nLett. 115, 050601 (2015)], wherein the phenomenon of negative differential\nconductivity (NDC) was reported in the refilling dynamics of an initially\ndepleted site within the chain. We demonstrate that a unitary c-field\ndescription can quantitatively reproduce the experimental results over the full\nrange of tunnel couplings, and requires no fitted parameters. With a view\ntowards atomtronic implementations, we further demonstrate that the filling is\nstrongly dependent on spatial phase variations stemming from quantum\nfluctuations. Our findings suggest that the interpretation of the device in\nterms of NDC is invalid outside of the weak coupling regime. Within this\nrestricted regime, the device exhibits a hybrid behaviour of NDC and the AC\nJosephson effect. A simplified circuit model of the device will require an\napproach tailored to atomtronics that incorporates quantum fluctuations.",
        "positive": "Non-linear dynamical response of interacting bosons to synthetic\n  electric field: We theoretically study the non-linear response of interacting neutral bosonic\ngas in a synthetically driven one-dimensional optical lattice. In particular,\nwe examine the bosonic analogue of electronic higher harmonic generation in a\nstrong time-dependent synthetic vector potential manifesting itself as the\nsynthetic electric field. We show that the vector potential can generate\nreasonably high harmonics in the insulating regime, while the superfluid regime\nexhibits only a few harmonics. In the insulating regime, the number of\nharmonics increases with the increase in the strength of the vector potential.\nThis originates primarily due to the field-driven resonant and non-resonant\nexcitations in the neutral Mott state and their recombination with the ground\nstate. If the repulsive interaction between two atoms ($U$) is close to the\nstrength of the gauge potential ($A_0$), the resonant quasiparticle-quasihole\npairs on nearest-neighbor sites, namely dipole states are found to a play a\ndominant role in the generating higher harmonics. However, in the strong-field\nlimit $A_0\\gg U$, the nonresonant states where quasiparticle-quasihole pairs\nare not on nearest-neighbor sites give rise to higher harmonics."
    },
    {
        "anchor": "Bilayer superfluidity of fermionic polar molecules: many body effects: We study the BCS superfluid transition in a single-component fermionic gas of\ndipolar particles loaded in a tight bilayer trap, with the electric dipole\nmoments polarized perpendicular to the layers. Based on the detailed analysis\nof the interlayer scattering, we calculate the critical temperature of the\ninterlayer superfluid pairing transition when the layer separation is both\nsmaller (dilute regime) and of the order or larger (dense regime) than the mean\ninterparticle separation in each layer. Our calculations go beyond the standard\nBCS approach and include the many-body contributions resulting in the mass\nrenormalization, as well as additional contributions to the pairing\ninteraction. We find that the many-body effects have a pronounced effect on the\ncritical temperature, and can either decrease (in the very dilute limit) or\nincrease (in the dense and moderately dilute limits) the transition temperature\nas compared to the BCS approach.",
        "positive": "The Uhlmann Phase Winding in Bose-Einstein Condensates at Finite\n  Temperature: We investigate the Uhlmann phase, a generalization of the celebrated Berry\nphase, for Bose-Einstein condensates (BECs) at finite temperature. The Uhlmann\nphase characterizes topological properties of mixed states, in contrast to the\nBerry phase which is defined for pure states at zero temperature. Using the\n$SU(1,1)$ symmetry of the Bogoliubov Hamiltonian, we derive a general formula\nfor the Uhlmann phase of BECs. Numerical calculations reveal that the Uhlmann\nphase can differ from the Berry phase in the zero-temperature limit, contrary\nto previous studies. As the temperature increases, the Uhlmann phase exhibits a\nwinding behavior, and we relate the total winding degree to the Berry phase.\nThis winding indicates that the Uhlmann phase takes values on a Riemann\nsurface. Furthermore, we propose an experimental scheme to measure the Uhlmann\nphase of BECs by purifying the density matrix using an atomic interferometer."
    },
    {
        "anchor": "Spontaneous Vortex Lattices in Quasi 2D Dipolar Spinor Condensates: Motivated by recent experiments\\cite{BA}\\cite{BB}, we study quasi 2D\nferromagnetic condensates with various aspect ratios. We find that in zero\nmagnetic field, dipolar energy generates a local energy minimum with all the\nspins lie in the 2D plane forming a row of {\\em circular} spin textures with\n{\\em alternating} orientation, corresponding to a packing of vortices of {\\em\nidentical} vorticity in different spin components. In a large magnetic field,\nthe system can fall into a long lived dynamical state consisting of an array of\nelliptic and hyperbolic Mermin-Ho spin textures, while the true equilibrium is\nan uniaxial spin density wave with a single wave-vector along the magnetic\nfield, and a wavelength similar to the characteristic length of the long lived\nvortex array state.",
        "positive": "Topological interface engineering and defect crossing in ultracold\n  atomic gases: We propose an experimentally feasible scheme for topological interface\nengineering and show how it can be used for studies of dynamics of\ntopologically nontrivial interfaces and perforation of defects and textures\nacross such interfaces. The method makes use of the internal spin structure of\nthe atoms together with locally applied control of interaction strengths to\ncreate many-particle states with highly complex topological properties. In\nparticular, we consider a constructed coherent interface between topologically\ndistinct phases of spinor Bose-Einstein condensates."
    },
    {
        "anchor": "Localization and delocalization of ground states of Bose-Einstein\n  condensates under disorder: This paper studies the localization behaviour of Bose-Einstein condensates in\ndisorder potentials, modeled by a Gross-Pitaevskii eigenvalue problem on a\nbounded interval. In the regime of weak particle interaction, we are able to\nquantify exponential localization of the ground state, depending on statistical\nparameters and the strength of the potential. Numerical studies further show\ndelocalization if we leave the identified parameter range, which is in\nagreement with experimental data. These mathematical and numerical findings\nallow the prediction of physically relevant regimes where localization of\nground states may be observed experimentally.",
        "positive": "Universal relations for a spin-polarized Fermi gas in two dimensions: We derive the full set of universal relations for spin-polarized Fermi gases\nwith $p$-wave interaction in two dimensions, simply using the short-range\nasymptotic behavior of fermion-pair wave functions. For $p$-wave interactions,\nan additional contact related to the effective range needs to be introduced,\nbesides the one related to the scattering volume. Since the subleading tail\n($k^{-4}$) of the large-momentum distribution cannot fully be captured by the\ncontacts defined by the adiabatic relations, an extra term resulted from the\ncenter-of-mass motions of the pairs gives rise to an additional divergence in\nthe kinetic energy of the system, besides those related to the contacts\ndefined. We show in Tan's energy theorem that if only two-body correlations are\ntaken into account, all these divergences are reasonably removed, leading to a\nfinite internal energy of the system. In addition, we find that all the other\nuniversal relations, such as the high-frequency behavior of the radio-frequency\nresponse, short-range behavior of the pair correlation function, generalized\nvirial theorem, and pressure relation, remain unaffected by the center-of-mass\nmotions of the pairs, and are fully governed by the contacts defined by the\nadiabatic relations. Our results confirm the feasibility of generalizing the\ncontact theory for higher-partial-wave scatterings, and could readily be\nconfirmed in current experiments with ultracold $^{40}$K and $^{6}$Li atoms."
    },
    {
        "anchor": "Running condensate in moving superfluid: A possibility of the condensation of excitations with non-zero momentum in\nmoving superfluid media is considered in terms of the Ginzburg-Landau model.\nThe results might be applicable to the superfluid $^4$He, ultracold atomic Bose\ngases, various superconducting and neutral systems with pairing, like ultracold\natomic Fermi gases and the neutron component in compact stars. The order\nparameters, the energy gain, and critical velocities are found.",
        "positive": "Quantum transport in ultracold atoms: Ultracold atoms confined by engineered magnetic or optical potentials are\nideal systems for studying phenomena otherwise difficult to realize or probe in\nthe solid state because their atomic interaction strength, number of species,\ndensity, and geometry can be independently controlled. This review focuses on\nquantum transport phenomena in atomic gases that mirror and oftentimes either\nbetter elucidate or show fundamental differences with those observed in\nmesoscopic and nanoscopic systems. We discuss significant progress in\nperforming transport experiments in atomic gases, contrast similarities and\ndifferences between transport in cold atoms and in condensed matter systems,\nand survey inspiring theoretical predictions that are difficult to verify in\nconventional setups. These results further demonstrate the versatility offered\nby atomic systems in the study of nonequilibrium phenomena and their promise\nfor novel applications."
    },
    {
        "anchor": "Quasi-long-range order in trapped two-dimensional Bose gases: We study the fate of algebraic decay of correlations in a harmonically\ntrapped two-dimensional degenerate Bose gas. The analysis is inspired by recent\nexperiments on ultracold atoms where power-law correlations have been observed\ndespite the presence of the external potential. We generalize the spin wave\ndescription of phase fluctuations to the trapped case and obtain an analytical\nexpression for the one-body density matrix within this approximation. We show\nthat algebraic decay of the central correlation function persists to lengths of\nabout 20% of the Thomas--Fermi radius. We establish that the trap-averaged\ncorrelation function decays algebraically with a strictly larger exponent\nweakly changing with trap size and find indications that the recently observed\nenhanced scaling exponents receive significant contributions from the normal\ncomponent of the gas. We discuss radial and angular correlations and propose a\nlocal correlation approximation which captures the correlations very well. Our\nanalysis goes beyond the usual local density approximation and the developed\nsummation techniques constitute a powerful tool to investigate correlations in\ninhomogeneous systems.",
        "positive": "From Planar Solitons to Vortex Rings and Lines: Cascade of Solitonic\n  Excitations in a Superfluid Fermi Gas: We follow the time evolution of a superfluid Fermi gas of resonantly\ninteracting $^6$Li atoms after a phase imprint. Via tomographic imaging, we\nobserve the formation of a planar dark soliton, its subsequent snaking, and its\ndecay into a vortex ring, which in turn breaks to finally leave behind a single\nsolitonic vortex. In intermediate stages we find evidence for an exotic\nstructure resembling the $\\Phi$-soliton, a combination of a vortex ring and a\nvortex line. Direct imaging of the nodal surface reveals its undulation\ndynamics and its decay via the puncture of the initial soliton plane. The\nobserved evolution of the nodal surface represents dynamics beyond superfluid\nhydrodynamics, calling for a microscopic description of unitary fermionic\nsuperfluids out of equilibrium."
    },
    {
        "anchor": "Effective scattering and Efimov physics in the presence of two-body\n  dissipation: Two-body dissipation usually gives rise to a complex interaction. Here, we\nstudy the effect of two-body dissipation on few-body physics, including the\nfundamental two-body effective scattering and the three-body Efimov physics. By\nemploying a two-channel model that incorporates the decay of closed-channel\nmolecules (generating the two-body dissipation), we explicitly relate the real\nand imaginary part of the inverse scattering length (a_s^{-1}) to\nclosed-channel detuning and decay rate. In particular, we show that the\nimaginary part of a_s^{-1} is given by the product of the molecule decay rate\nand the effective range. Such complex scattering length is found to generate an\nadditional imaginary Coulomb potential when three atoms come close to each\nother, thereby suppressing the formation of trimer bound states and modifying\nthe conventional discrete scaling in Efimov physics.",
        "positive": "Analytical pair correlations in ideal quantum gases:\n  Temperature-dependent bunching and antibunching: The fluctuation-dissipation theorem together with the exact density response\nspectrum for ideal quantum gases has been utilized to yield a new expression\nfor the static structure factor, which we use to derive exact analytical\nexpressions for the temperature{dependent pair distribution function g(r) of\nthe ideal gases. The plots of bosonic and fermionic g(r) display \"Bose pile\"\nand \"Fermi hole\" typically akin to bunching and antibunching as observed\nexperimentally for ultracold atomic gases. The behavior of spin-scaled pair\ncorrelation for fermions is almost featureless but bosons show a rich structure\nincluding long-range correlations near T_c. The coherent state at T=0 shows no\ncorrelation at all, just like single-mode lasers. The depicted decreasing trend\nin correlation with decrease in temperature for T < T_c should be observable in\naccurate experiments."
    },
    {
        "anchor": "Thermometry and signatures of strong correlations from Raman\n  spectroscopy of fermionic atoms in optical lattices: We propose a method to directly measure the temperature of a gas of weakly\ninteracting fermionic atoms loaded into an optical lattice. This technique\nrelies on Raman spectroscopy and is applicable to experimentally relevant\ntemperature regimes. Additionally, we show that a similar spectroscopy scheme\ncan be used to obtain information on the quasiparticle properties and Hubbard\nbands of the metallic and Mott-insulating states of interacting fermionic spin\nmixtures. These two methods provide experimentalists with novel probes to\naccurately characterize fermionic quantum gases confined to optical lattices.",
        "positive": "Bose-Einstein condensates and the thin-shell limit in anisotropic bubble\n  traps: Within the many different models that appeared with the use of cold atoms to\ndesign BECs the bubble trap shaped potential has been of great interest. For\nthe anisotropic bubble trap physics in the thin-shell limit the relationship\nbetween the physical parameters and the resulting manifold geometry is yet to\nbe fully understood. In this paper, we work towards this goal showing how the\nparameters of the system must be manipulated in order to allow for a\nnon-collapsing thin-shell limit. In such a limit, a dimensional\ncompactification takes place thus leading to an effective 2D Hamiltonian which\nrelates to up-to-date bubble trap experiments. At last, our Hamiltonian is\npertubatively solved for some particular cases as applications of our theory."
    },
    {
        "anchor": "Spin-1 Bosons in the Presence of Spin-orbit Coupling: In this paper, I'm going to talk about the theoretical and experimental\nprogress in studying spin-orbit coupled spin-1 bosons. Realization of\nspin-orbit coupled quantum gases opens a new avenue in cold atom physics. In\nparticular, the interplay between spin-orbit coupling and inter-atomic\ninteraction leads to many intriguing phenomena. Moreover, the non-zero momentum\nof ground states can be controlled by external fields, which allows for good\nquantum control.",
        "positive": "Sound propagation in a two-dimensional Bose gas across the superfluid\n  transition: Motivated by recent experiments in Phys. Rev. Lett. 121, 145301 (2018), we\nstudy sound propagation in a two-dimensional (2D) Bose gas across the\nsuperfluid-thermal transition using classical field dynamics. Below the\ntransition temperature we find a Bogoliubov and a non-Bogoliubov mode, above it\nwe find the normal sound mode and the diffusive mode, as we determine from the\ndynamical structure factor. Our simulations of the experimental procedure agree\nwith the measured velocities, and show that below the transition temperature\nthe measurements detect the Bogoliubov mode. Above the transition, they either\ndetect the normal sound mode for low densities or weak interactions, or the\ndiffusive mode for high densities or strong interactions. As a key observation,\nwe discuss the weak coupling regime in which the non-Bogoliubov mode has a\nhigher velocity than the Bogoliubov mode, in contrast to a hydrodynamic\nscenario. We propose to detect this regime via step-pulse density perturbation,\nwhich simultaneously detects both sound modes"
    },
    {
        "anchor": "Dipolar fermions in a multilayer geometry: We investigate the behavior of identical dipolar fermions with aligned dipole\nmoments in two-dimensional multilayers at zero temperature. We consider density\ninstabilities that are driven by the attractive part of the dipolar interaction\nand, for the case of bilayers, we elucidate the properties of the stripe phase\nrecently predicted to exist in this interaction regime. When the number of\nlayers is increased, we find that this \"attractive\" stripe phase exists for an\nincreasingly larger range of dipole angles, and if the interlayer distance is\nsufficiently small, the stripe phase eventually spans the full range of angles,\nincluding the situation where the dipole moments are aligned perpendicular to\nthe planes. In the limit of an infinite number of layers, we derive an analytic\nexpression for the interlayer effects in the density-density response function\nand, using this result, we find that the stripe phase is replaced by a collapse\nof the dipolar system.",
        "positive": "Real-time Dynamics in U(1) Lattice Gauge Theories with Tensor Networks: Tensor network algorithms provide a suitable route for tackling real-time\ndependent problems in lattice gauge theories, enabling the investigation of\nout-of-equilibrium dynamics. We analyze a U(1) lattice gauge theory in (1+1)\ndimensions in the presence of dynamical matter for different mass and electric\nfield couplings, a theory akin to quantum-electrodynamics in one-dimension,\nwhich displays string-breaking: the confining string between charges can\nspontaneously break during quench experiments, giving rise to charge-anticharge\npairs according to the Schwinger mechanism. We study the real-time spreading of\nexcitations in the system by means of electric field and particle fluctuations:\nwe determine a dynamical state diagram for string breaking and quantitatively\nevaluate the time-scales for mass production. We also show that the time\nevolution of the quantum correlations can be detected via bipartite von Neumann\nentropies, thus demonstrating that the Schwinger mechanism is tightly linked to\nentanglement spreading. To present the variety of possible applications of this\nsimulation platform, we show how one could follow the real-time scattering\nprocesses between mesons and the creation of entanglement during scattering\nprocesses. Finally, we test the quality of quantum simulations of these\ndynamics, quantifying the role of possible imperfections in cold atoms, trapped\nions, and superconducting circuit systems. Our results demonstrate how\nentanglement properties can be used to deepen our understanding of basic\nphenomena in the real-time dynamics of gauge theories such as string breaking\nand collisions."
    },
    {
        "anchor": "Generation and decay of persistent current in a toroidal Bose-Einstein\n  condensate: Persistent current, or \"flow without friction\", as well as quantum vortices\nare the hallmarks of superfluidity. Recently a very long-lived persistent flow\nof atoms has been experimentally observed in Bose-Einstein condensates trapped\nin a ring-shaped potential. This enables fundamental studies of superfluidity\nand may lead to applications in high-precision metrology and atomtronics. We\noverview our recent theoretical studies of the generation of the persistent\ncurrent in a stirred toroidal atomic Bose-Einstein condensate, and discuss our\nnew investigation of the hysteresis in the atomtronic circuit.",
        "positive": "Coupled exciton-photon Bose condensate in path integral formalism: We study the behavior of exciton polaritons in an optical microcavity with an\nembedded semiconductor quantum well. We use two-component exciton-photon\napproach formulated in terms of path integral formalism. In order to describe\nspatial distributions of the exciton and photon condensate densities, the two\ncoupled equations of the Gross-Pitaevskii type are derived. For a homogeneous\nsystem, we find the noncondensate photon and exciton spectra, calculate the\ncoefficients of transformation from the exciton-photon basis to the lower-upper\npolariton basis, and obtain the exciton and photon occupation numbers of the\nlower and upper polariton branches for nonzero temperatures. For an\ninhomogeneous system, the set of coupled equations of the Bogoliubov-de-Gennes\ntype is derived. The equations govern the spectra and spatial distributions of\nnoncondensate photons and excitons."
    },
    {
        "anchor": "Spatial coherence of spin-orbit-coupled Bose gases: Spin-orbit-coupled Bose-Einstein condensates (SOBECs) exhibit two new phases\nof matter, now known as the stripe and plane-wave phases. When two interacting\nspin components of a SOBEC spatially overlap, density modulations with\nperiodicity given by the spin-orbit coupling strength appear. In equilibrium,\nthese components fully overlap in the miscible stripe phase, and overlap only\nin a domain wall in the immiscible plane-wave phase. Here we probe the density\nmodulation present in any overlapping region with optical Bragg scattering, and\nobserve the sudden drop of Bragg scattering as the overlapping region shrinks.\nUsing an atomic analogue of the Talbot effect, we demonstrate the existence of\nlong-range coherence between the different spin components in the stripe phase\nand surprisingly even in the phase-separated plane-wave phase.",
        "positive": "Local energy density functional for superfluid Fermi gases from\n  effective field theory: Over the past two decades, many studies in the Density Functional Theory\ncontext revealed new aspects and properties of strongly correlated superfluid\nquantum systems in numerous configurations that can be simulated in\nexperiments. This was made possible by the generalization of the Local Density\nApproximation to superfluid systems by Bulgac in [Phys. Rev. C 65, 051305,\n(2002), Phys. Rev. A 76, 040502, (2007)]. In the presented work, we propose an\nextension of the Superfluid Local Density Approximation systematically\nimprovable and applicable to a large range of many-body quantum problems\ngetting rid of the fitting procedures of the functional parameters. It turns\nout that only the knowledge of the density dependence of the quasi-particle\nproperties, namely, the chemical potential, the effective mass, and the pairing\ngap function, are enough to obtain an explicit and accurate local functional of\nthe densities without any adjustment a posteriori. This opens the way toward an\nEffective Field Theory formulation of the Density Functional Theory in the\nsense that we obtain a universal expansion of the functional parameters\nentering in the theory as a series in pairing gap function. Finally, we discuss\npossible applications of the developed approach allowing precise analysis of\nexperimental observations. In that context, we focus our applications on the\nstatic structure properties of superfluid vortices."
    },
    {
        "anchor": "Three-body repulsive forces among identical bosons in one dimension: I consider non-relativistic bosons interacting via pairwise potentials with\ninfinite scattering length and supporting no two-body bound states. To lowest\norder in effective field theory, these conditions lead to non-interacting\nbosons, since the coupling constant of the Lieb-Liniger model vanishes\nidentically in this limit. Since any realistic pairwise interaction is not a\nmere delta function, the non-interacting picture is an idealisation indicating\nthat the effect of interactions is weaker than in the case of off-resonant\npotentials. I show that the leading order correction to the ground state energy\nfor more than two bosons is accurately described by the lowest order three-body\nforce in effective field theory that arises due to the off-shell structure of\nthe two-body interaction. For natural two-body interactions with a\nshort-distance repulsive core and an attractive tail, the emergent three-body\ninteraction is repulsive and, therefore, three bosons do not form any bound\nstates. This situation is analogous to the two-dimensional repulsive Bose gas,\nwhen treated using the lowest-order contact interaction, where the scattering\namplitude exhibits an unphysical Landau pole. The avoidance of this state in\nthe three-boson problem proceeds in a way that parallels the two-dimensional\ncase. These results pave the way for the experimental realisation of\none-dimensional Bose gases with pure three-body interactions using ultracold\natomic gases.",
        "positive": "Spin Hall Effect in a Spinor Dipolar Bose-Einstein Condensate: We theoretically show that the spin Hall effect arises in a Bose-Einstein\ncondensate (BEC) of neutral atoms interacting via the magnetic dipole-dipole\ninteractions (MDDIs). Since the MDDI couples the total spin angular momentum\nand the relative orbital angular momentum of two colliding atoms, it works as a\nspin-orbit coupling. Thus, when we prepare a BEC in a magnetic sublevel $m=0$,\nthermally and quantum-mechanically excited atoms in the $m=1$ and $-1$ states\nfeel the Lorentz-like foces in the opposite directions. This is the origin for\nthe emergence of the the spin Hall effect. We define the mass-current and\nspin-current operators from the equations of continuity and calculate the spin\nHall conductivity from the off-diagonal current-current correlation function\nwithin the Bogoliubov approximation. We find that the correction of the current\noperators due to the MDDI significantly contributes to the spin Hall\nconductivity. Possible experimental situation is also discussed."
    },
    {
        "anchor": "Quantum dynamics of bosons in a two-ring ladder: dynamical algebra,\n  vortex-like excitations and currents: We study the quantum dynamics of the Bose-Hubbard model on a ladder formed by\ntwo rings coupled by tunneling effect. By implementing the Bogoliubov\napproximation scheme, we prove that, despite the presence of the inter-ring\ncoupling term, the Hamiltonian decouples in many independent sub-Hamiltonians\n$\\hat{H}_k$ associated to momentum-mode pairs $\\pm k$. Each sub-Hamiltonian\n$\\hat{H}_k$ is then shown to be part of a specific dynamical algebra. The\nproperties of the latter allow us to perform the diagonalization process, to\nfind energy spectrum, the conserved quantities of the model, and to derive the\ntime evolution of important physical observables. We then apply this solution\nscheme to the simplest possible closed ladder, the double trimer. After\nobserving that the excitations of the system are weakly-populated vortices, we\nexplore the corresponding dynamics by varying the initial conditions and the\nmodel parameters. Finally, we show that the inter-ring tunneling determines a\nspectral collapse when approaching the border of the dynamical-stability\nregion.",
        "positive": "Stripes and honeycomb lattice of quantized vortices in rotating\n  two-component Bose-Einstein condensates: We study numerically the structure of a vortex lattice in two-component\nBose-Einstein condensates with equal atomic masses and equal intra- and\ninter-component coupling strengths. The numerical simulations of the\nGross-Pitaevskii equation show that the quantized vortices form uncertain\nlattice configurations accompanying the vortex stripes, honeycomb lattices, and\ntheir complexes. This is a result of the degeneracy of the system for the SU(2)\nsymmetric operation, which makes a continuous transformation between the above\nstructures. In terms of the pseudospin representation, the complex lattice\nstructures are identified to a hexagonal lattice of doubly-winding\nhalf-skyrmions."
    },
    {
        "anchor": "Induced supersolidity and hypersonic flow of a dipolar Bose-Einstein\n  Condensate in a rotating bubble trap: Motivated by the recent realization of space-borne Bose-Einstein Condensate\n(BEC) under micro-gravity conditions, we extend the understanding of ultracold\ndipolar bosonic gases by exploring their behavior in a novel trapping\nconfiguration known as the ``bubble trap\" topology. Utilizing the\nthree-dimensional numerical simulations within the extended Gross-Pitaevskii\nframework, we unveil diverse ground state phases in such a static curved\ntopology. Subsequently, we investigate the influence of rotation on a dipolar\nBEC confined to the surface of a spherical bubble. Our findings reveal that the\nrotation of a bubble trap with certain rotation frequencies can modify the\neffective local dipole-dipole interaction strength, leading to the induction of\nsupersolidity and the formation of quantum droplets. In addition, we\ndemonstrate that a bubble trap can sustain high circulation and the flow also\npersists for a longer time. Significantly, adjusting the rf detuning parameter\nallows the condensate to achieve hypersonic velocity. Finally, we explore the\nimpact of drastic change in the topological nature of the trap on the rotating\ndipolar BEC, transitioning from a filled shell trap to a bubble trap and vice\nversa.",
        "positive": "Vortex structures of a two-component BEC for large anisotropies: We calculate the vortex structures of an elongated two-component\nBose-Einstein condensate. We study how these structures depend on the\nintra-component and inter-component interaction strengths. We present analytic\nand numeric results respectively at weak and strong interactions; finding\nlattices with different interlocking geometries: triangular, square,\nrectangular and double-core."
    },
    {
        "anchor": "Spin Drag in Ultracold Fermi Mixtures with Repulsive Interactions: We calculate the spin-drag relaxation rate for a two-component ultracold\natomic Fermi gas with positive scattering length between the two spin\ncomponents. In one dimension we find that it vanishes linearly with\ntemperature. In three dimensions the spin-drag relaxation rate vanishes\nquadratically with temperature for sufficiently weak interactions. This\nquadratic temperature dependence is present, up to logarithmic corrections, in\nthe two-dimensional case as well. For stronger interaction the system exhibits\na Stoner ferromagnetic phase transition in two and three dimensions. We show\nthat the spin-drag relaxation rate is enhanced by spin fluctuations as the\ntemperature approaches the critical temperature of this transition from above.",
        "positive": "Two Nambu-Goldstone zero modes for rotating Bose-Einstein condensates: We consider rotating finite size vortex arrays in Bose-Einstein condensates\nthat are confined by cylindrically symmetric external potentials. We show that\nsuch systems possess two exact Nambu-Goldstone zero modes associated with two\nspontaneously broken continuous symmetries of the system. We verify our\nanalytical result via direct numerical diagonalizations of the Bogoliubov-de\nGennes equations. We conclude by comparing rotating vortex lattices in\nsuperfluids to supersolids and discrete time crystals."
    },
    {
        "anchor": "Large-scale characterization of Cu2O monocrystals via Rydberg excitons: Rydberg states of excitons can reach microns in size and require extremely\npure crystals. We introduce an experimental method for the rapid and\nspatially-resolved characterization of Rydberg excitons in copper oxide (Cu2O)\nwith sub-micron resolution over large zones. Our approach involves illuminating\nand imaging the entire sample on a camera to realize a spatially-resolved\nversion of resonant absorption spectroscopy, without any mobile part. This\nyields spatial maps of Rydberg exciton properties, including their energy,\nlinewidth and peak absorption, providing a comprehensive quality assessment of\nthe entire sample in a single shot. Furthermore, by imaging the sample\nphotoluminescence over the same zone, we establish a strong relationship\nbetween the spectral quality map and the photoluminescence map of charged\noxygen vacancies. This results in an independent, luminescence-based quality\nmap that closely matches the results obtained through resonant spectroscopy.\nOur findings reveal that Rydberg excitons in natural Cu2O crystals are\npredominantly influenced by optically-active charged oxygen vacancies, which\ncan be easily mapped. Together, these two complementary methods provide\nvaluable insights into Cu2O crystal properties.",
        "positive": "Unifying treatment of nonequilibrium and unstable dynamics of cold\n  bosonic atom system with time-dependent order parameter in Thermo Filed\n  Dynamics: The coupled equations which describe the temporal evolution of the\nBose-Einstein condensed system are derived in the framework of nonequilibrium\nThermo Field Dynamics. The key element is that they are not the naive\nassemblages of presumable equations, but are the self-consistent ones derived\nby appropriate renormalization conditions. While the order parameter is\ntime-dependent, an explicit quasiparticle picture is constructed by a\ntime-dependent expansion. Our formulation is valid even for the system with a\nunstable condensate, and describes the condensate decay caused by the Landau\ninstability as well as by the dynamical one."
    },
    {
        "anchor": "Landau critical velocity in weakly interacting Bose gases: The flow of a uniform Bose gas at speeds greater than the Landau critical\nvelocity, v_c, does not necessarily destroy superfluidity, but rather need only\nlead to a decrease of the superfluid mass density, {\\rho}_s. Analyzing a weakly\ninteracting Bose gas with a finite range interparticle interaction that leads\nto a Landau critical velocity at non-zero quasiparticle momentum, we explicitly\nconstruct the (non-uniform) condensate for fluid flow faster than v_c and\ncalculate the accompanying decrease in {\\rho}_s. We briefly comment on the\nrelation of the physics to other problems in superfluids, e.g., solitons, and\nvortices in Bose-Einstein condensates, and critical currents in\nsuperconductors.",
        "positive": "Superglass phase of interaction-blockaded gases on a triangular lattice: We investigate the quantum phases of monodispersed bosonic gases confined to\na triangular lattice and interacting via a class of soft-shoulder potentials.\nThe latter correspond to soft-core potentials with an additional hard-core\nonsite interaction. Using exact quantum Monte Carlo simulations, we show that\nthe low temperature phases for weak and strong interactions following a\ntemperature quench are a homogeneous superfluid and a glass, respectively. The\nlatter is an insulating phase characterized by inhomogeneity in the density\ndistribution and structural disorder. Remarkably, we find that for intermediate\ninteraction strengths a {\\it superglass} occurs in an extended region of the\nphase diagram, where glassy behavior coexists with a sizable finite superfluid\nfraction. This glass phase is obtained in the absence of geometrical\nfrustration or external disorder and is a result of the competition of quantum\nfluctuations and cluster formation in the corresponding classical ground state.\nFor high enough temperature, the glass and superglass turn into a floating\nstripe solid and a supersolid, respectively. Given the simplicity and\ngenerality of the model, these phases should be directly relevant for\nstate-of-the-art experiments with Rydberg-dressed atoms in optical lattices."
    },
    {
        "anchor": "Floquet FFLO superfluids and Majorana fermions in a shaken fermionic\n  optical lattice: Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superfluids, Cooper pairings with\nfinite momentum, and Majorana fermions (MFs), quasiparticles with non-Abelian\nexchange statistics, are two topics under intensive investigation in the past\nseveral decades, but unambiguous experimental evidences for them have not been\nfound yet in any physical system. Here we show that the recent experimentally\nrealized cold atom shaken optical lattice provides a new pathway to realize\nFFLO superfluids and MFs. By tuning shaken lattice parameters (shaking\nfrequency and amplitude), various coupling between the s- and p-orbitals of the\nlattice (denoted as the pseudo-spins) can be generated. We show that the\ncombination of the inverted s- and p-band dispersions, the engineered\npseudo-spin coupling, and the attractive on-site atom interaction, naturally\nallows the observation of FFLO superfluids as well as MFs in different\nparameter regions. While without interaction the system is a topological\ninsulator (TI) with edge states, the MFs in the superfluid may be found to be\nin the conduction or valence band, distinguished from previous TI-based schemes\nthat utilize edge states inside the band gap.",
        "positive": "Ghost Imaging with Atoms: Ghost imaging is a technique -- first realized in quantum optics -- in which\nthe image emerges from cross-correlation between particles in two separate\nbeams. One beam passes through the object to a bucket (single-pixel) detector,\nwhile the second beam's spatial profile is measured by a high resolution\n(multi-pixel) detector but never interacts with the object. Neither detector\ncan reconstruct the image independently. However, until now ghost imaging has\nonly been demonstrated with photons.\n  Here we report the first realisation of ghost imaging of an object using\nmassive particles. In our experiment, the two beams are formed by correlated\npairs of ultracold metastable helium atoms, originating from two colliding\nBose-Einstein condensates (BECs) via $s$-wave scattering. We use the\nhigher-order Kapitza-Dirac effect to generate the large number of correlated\natom pairs required, enabling the creation of a ghost image with good\nvisibility and sub-millimetre resolution.\n  Future extensions could include ghost interference as well as tests of EPR\nentantlement and Bell's inequalities."
    },
    {
        "anchor": "Vortices in quantum droplets of heteronuclear Bose mixtures: We have theoretically investigated the structure of spinning self-bound\ndroplets made of $^{41}$K-$^{87}$Rb Bose mixture by solving the\nGross-Pitaevskii equation including beyond-mean-field correction in the\nLee-Huang-Yang form. The structure and energetics of vortex formation in the\nself-bound mixture have been elucidated, showing that the formation of linear\nvortices in the heavier species is energetically favoured over other\nconfigurations. A fake (partially filled) core develops as a consequence in the\nother species, resulting in a hole which might be imaged in experiments. The\ninterplay between vortices and capillary waves, which are the two ways angular\nmomentum can be stored in a swirling superfluid, is studied in detail by\ncomputing the relation between angular momentum and rotational frequency. The\nresults show intriguing similarities with the case of a prototypical\nsuperfluid, i.e. $^4$He droplets when set into rotation. A two-branches curve\nin the stability diagram, qualitatively similar to the one expected for\nclassical (incompressible and viscous) rotating liquid droplets, is obtained\nwhen vortices are present in the droplets, while prolate (i.e. non\naxi-symmetric) shapes are only permitted in vortex-free droplets.",
        "positive": "Quantum droplets in three-dimensional Bose-Einstein condensates: The properties of 3D Bose-Einstein condensate have been studied with\nvariational and numerical methods. In the variational approach, we use the\nsuper-Gaussian trial function, and it is demonstrated that this trial function\ngives a good approach for the descriptions of the quantum droplets. The\nanalytical equations for the variational parameters are obtained. The frequency\nof small oscillations of quantum droplets near the equilibrium position is\nestimated. It is also found that periodic modulation of the coupling constants\nleads to the resonance oscillations of the quantum droplets parameters or\nemission of waves depending on the amplitude of the modulations. The\npredictions are supported by direct numerical simulation of governing equation."
    },
    {
        "anchor": "Entanglement growth in quench dynamics with variable range interactions: Studying entanglement growth in quantum dynamics provides both insight into\nthe underlying microscopic processes and information about the complexity of\nthe quantum states, which is related to the efficiency of simulations on\nclassical computers. Recently, experiments with trapped ions, polar molecules,\nand Rydberg excitations have provided new opportunities to observe dynamics\nwith long-range interactions. We explore nonequilibrium coherent dynamics after\na quantum quench in such systems, identifying qualitatively different behavior\nas the exponent of algebraically decaying spin-spin interactions in a\ntransverse Ising chain is varied. Computing the build-up of bipartite\nentanglement as well as mutual information between distant spins, we identify\nlinear growth of entanglement entropy corresponding to propagation of\nquasiparticles for shorter range interactions, with the maximum rate of growth\noccurring when the Hamiltonian parameters match those for the quantum phase\ntransition. Counter-intuitively, the growth of bipartite entanglement for\nlong-range interactions is only logarithmic for most regimes, i.e.,\nsubstantially slower than for shorter range interactions. Experiments with\ntrapped ions allow for the realization of this system with a tunable\ninteraction range, and we show that the different phenomena are robust for\nfinite system sizes and in the presence of noise. These results can act as a\ndirect guide for the generation of large-scale entanglement in such\nexperiments, towards a regime where the entanglement growth can render existing\nclassical simulations inefficient.",
        "positive": "Zero Dimensional Polariton Laser in a Sub-Wavelength Grating Based\n  Vertical Microcavity: Semiconductor exciton-polaritons in planar microcavities form coherent\ntwo-dimensional condensates in non-equilibrium. However, coupling of multiple\nlower-dimensional polariton quantum systems, critically needed for polaritonic\nquantum device applications and novel cavity-lattice physics, has been limited\ndue to the conventional cavity structures. Here we demonstrate full confinement\nof the polaritons non-destructively using a hybrid cavity made of a\nsingle-layer sub-wavelength grating mirror and a distributed Bragg reflector.\nSingle-mode polariton lasing was observed at a chosen polarization.\nIncorporation of a designable slab mirror into the conventional vertical\ncavity, when operating in the strong-coupling regime, enables confinement,\ncontrol and coupling of polariton gasses in a scalable fashion. It may open a\ndoor to experimental implementation of polariton-based quantum photonic devices\nand coupled cavity quantum electrodynamics systems."
    },
    {
        "anchor": "Ground-State Energy and Condensate Density of a Dilute Bose Gas\n  Revisited: The ground-state energy per particle $E/N$ and condensate density $n_0$ of a\ndilute Bose gas are studied with a self-consistent perturbation expansion\nsatisfying the Hugenholtz-Pines theorem and conservation laws simultaneously. A\nclass of Feynman diagrams for the self-energy, which has escaped consideration\nso far, is shown to add an extra constant $c_{ip}\\sim O(1)$ to the expressions\nreported by Lee, Huang, and Yang [Phys. Rev. 106, 1135 (1957) ] as\n$E/N=(2\\pi\\hbar^2 an/m)[1+(128/15\\sqrt{{\\pi}}+16c_{ip}/5)\\sqrt{{a^3n}}]$ and\n$n_0/n=1-(8/3\\sqrt{{\\pi}}+c_{ip})\\sqrt{{a^3n}}$, where $a$, $n$, and $m$ are\nare the s-wave scattering length, particle density, and particle mass,\nrespectively. We present a couple of estimates for $c_{ip}$; the third-order\nperturbation expansion yields $c_{ip}=0.412$.",
        "positive": "Synthetic topological Kondo insulator in a pumped optical cavity: Motivated by experimental advances on ultracold atoms coupled to a pumped\noptical cavity, we propose a scheme for synthesizing and observing the Kondo\ninsulator in Fermi gases trapped in optical lattices. The synthetic Kondo phase\narises from the screening of localized atoms coupled to mobile ones, which in\nour proposal is generated via the pumping laser as well as the cavity. By\ndesigning the atom-cavity coupling, it can engineer a nearest-neighbor-site\nKondo coupling that plays an essential role for supporting topological Kondo\nphase. Therefore, the cavity-induced Kondo transition is associated with a\nnontrivial topological features, resulting in the coexistence of the\nsuperradiant and topological Kondo state. Our proposal can be realized with\ncurrent technique, and thus has potential applications in quantum simulation of\nthe topological Kondo insulator in ultracold atoms."
    },
    {
        "anchor": "Statistical properties of cold bosons in a ring trap: A study of an interacting system of bosons in a ring trap at a finite\ntemperature is presented. We consider a gas with contact and long-range dipolar\ninteractions within a framework of the classical fields approximation. For a\nrepulsive gas we have obtained coherence length, population of the ground state\nand its fluctuations as a function of temperature. In the case of an attractive\ngas we study local density fluctuations. Additionally, we exactly calculate the\npartition function for the ideal gas in the canonical ensemble and derive\nseveral other macroscopic state functions.",
        "positive": "Incompressible states of a two-component Fermi gas in a double-well\n  optical lattice: We propose a scheme to investigate the effect of frustration on the magnetic\nphase transitions of cold atoms confined in an optical lattice. We also\ndemonstrate how to get two-leg spin ladders with frustrated spin-exchange\ncoupling which display a phase transition from a spin liquid to a fully\nincompressible state. Various experimental quantities are further analyzed for\ndescribing this phase."
    },
    {
        "anchor": "Itinerant ferromagnetism in an interacting Fermi gas with mass imbalance: We study the emergence of itinerant ferromagnetism in an ultra-cold atomic\ngas with a variable mass ratio between the up and down spin species. Mass\nimbalance breaks the SU(2) spin symmetry leading to a modified Stoner\ncriterion. We first elucidate the phase behavior in both the grand canonical\nand canonical ensembles. Secondly, we apply the formalism to a harmonic trap to\ndemonstrate how a mass imbalance delivers unique experimental signatures of\nferromagnetism. These could help future experiments to better identify the\nputative ferromagnetic state. Furthermore, we highlight how a mass imbalance\nsuppresses the three-body loss processes that handicap the formation of a\nferromagnetic state. Finally, we study the time dependent formation of the\nferromagnetic phase following a quench in the interaction strength.",
        "positive": "Encoding a one-dimensional topological gauge theory in a Raman-coupled\n  Bose-Einstein condensate: Topological gauge theories provide powerful effective descriptions of certain\nstrongly correlated systems, a prime example being the Chern-Simons gauge\ntheory of fractional quantum Hall states. Engineering topological gauge\ntheories in controlled quantum systems is of both conceptual and practical\nimportance, as it would provide access to systems with exotic excitations such\nas anyons without the need for strong correlations. Here, we discuss a scheme\nto engineer the chiral BF theory, a minimal model of a topological gauge theory\ncorresponding to a one-dimensional reduction of the Chern-Simons theory, with\nultracold atoms. Using the local conservation laws of the theory, we encode its\nquantum Hamitonian into an ultracold quantum gas with chiral interactions.\nBuilding on a seminal proposal by Edmonds et al. (Phys. Rev. Lett. 110, 085301\n(2013)), we show how to implement it in a Raman-coupled Bose-Einstein\ncondensate with imbalanced scattering lengths, as we have recently realized\nexperimentally (Fr\\\"olian et al., Nature 608, 293 (2022)). We discuss the\nproperties of the chiral condensate from a gauge theory perspective, and assess\nthe validity of the effective quantum description for accessible experimental\nparameters via numerical simulations. Our approach lays the foundation for\nrealizing topological gauge theories in higher dimensions with Bose-Einstein\ncondensates."
    },
    {
        "anchor": "Comparative studies of many-body corrections to an interacting Bose\n  condensate: We compare many-body theories describing fluctuation corrections to the\nmean-field theory in a weakly interacting Bose-condensed gas. Using a\ngeneralized random-phase approximation, we include both density fluctuations\nand fluctuations in the particle-particle scattering channel in a consistent\nmanner. We also separately examine effects of the fluctuations within the\nframework of the random-phase approximation. Effects of fluctuations in the\nparticle-particle scattering channel are also separately examined by using the\nmany-body T-matrix approximation. We assess these approximations with respect\nto the transition temperature, the order of phase transition, as well as the\nso-called Nepomnyashchii-Nepomnyashchii identity, which states the vanishing\noff-diagonal self-energy in the low-energy and low-momentum limit. Since the\nconstruction of a consistent theory for interacting bosons which satisfies\nvarious required conditions is a long standing problem in cold atom physics,\nour results would be useful for this important challenge.",
        "positive": "Crystallized merons and inverted merons in the condensation of spin-1\n  Bose gases with spin-orbit coupling: The non-equilibrium dynamics of a rapidly quenched spin-1 Bose gas with\nspin-orbit coupling is studied. By solving the stochastic projected\nGross-Pitaevskii equation, we show that crystallization of merons can occur in\na spinor condensate of ^{87}Rb. Analytic form and stability of the crystal\nstructure are given. Likewise, inverted merons can be created in a\nspin-polarized spinor condensate of ^{23}Na. Our studies provide a chance to\nexplore the fundamental properties of meron-like matter."
    },
    {
        "anchor": "Sound propagation in a Bose-Fermi mixture: from weak to strong\n  interactions: Particle-like excitations, or quasi-particles, emerging from interacting\nfermionic and bosonic quantum fields underlie many intriguing quantum phenomena\nin high energy and condensed matter systems. Computation of the properties of\nthese excitations is frequently intractable in the strong interaction regime.\nQuantum degenerate Bose-Fermi mixtures offer promising prospects to elucidate\nthe physics of such quasi-particles. In this work, we investigate phonon\npropagation in an atomic Bose-Einstein condensate immersed in a degenerate\nFermi gas with interspecies scattering length $a_\\text{BF}$ tuned by a Feshbach\nresonance. We observe sound mode softening with moderate attractive\ninteractions. For even greater attraction, surprisingly, stable sound\npropagation re-emerges and persists across the resonance. The stability of\nphonons with resonant interactions opens up opportunities to investigate novel\nBose-Fermi liquids and fermionic pairing in the strong interaction regime.",
        "positive": "Superradiant Mott Transition: The combination of strong correlation and emergent lattice can be achieved\nwhen quantum gases are confined in a superradiant Fabry-Perot cavity. In\naddition to the discoveries of exotic phases, such as density wave ordered Mott\ninsulator and superfluid, a surprising kink structure is found in the slope of\nthe cavity strength as a function of the pumping strength. In this Letter, we\nshow that the appearance of such a kink is a manifestation of a liquid-gas like\ntransition between two superfluids with different densities. The slopes in the\nimmediate neighborhood of the kink become divergent at the liquid-gas critical\npoints and display a critical scaling law with a critical exponent 1 in the\nquantum critical region. Our predictions could be tested in current\nexperimental set-up."
    },
    {
        "anchor": "High partial-wave Feshbach resonances in an ultracold $^6$Li-$^{133}$Cs\n  mixture: We measure higher partial wave Feshbach resonances in an ultracold mixture of\nfermionic $^6$Li and bosonic $^{133}$Cs by magnetic field dependent atom-loss\nspectroscopy. For the $p$-wave Feshbach resonances we observe triplet\nstructures corresponding to different projections of the pair rotation angular\nmomentum onto the external magnetic field axis.\n  We attribute the splittings to the spin-spin and spin-rotation couplings by\nmodelling the observation using a full coupled-channel calculation. Comparison\nwith an oversimplified model, estimating the spin-rotation coupling by\ndescribing the weakly bound close-channel molecular state with the perturbative\nmultipole expansion, reveals the significant contribution of the molecular\nwavefunction at short internuclear distances. Our findings highlight the\npotential of Feshbach resonances in providing precise information on short- and\nintermediate-range molecular couplings and wavefunctions. The observed $d$-wave\nFeshbach resonances allow us to refine the LiCs singlet and triplet\nground-state molecular potential curves at large internuclear separations.",
        "positive": "Sudden expansion of Mott insulators in one dimension: We investigate the expansion of bosons and fermions in a homogeneous lattice\nafter a sudden removal of the trapping potential using exact numerical methods.\nAs a main result, we show that in one dimension, both bosonic and fermionic\nMott insulators expand with the same velocity, irrespective of the interaction\nstrength, provided the expansion starts from the ground state of the trapped\ngas. Furthermore, their density profiles become identical during the expansion:\nThe asymptotic density dynamics is identical to that of initially localized,\nnon-interacting particles, and the asymptotic velocity distribution is flat.\nThe expansion velocity for initial correlated Mott insulating states is\ntherefore independent of the interaction strength and particle statistics.\nInterestingly, this non-equilibrium dynamics is sensitive to the interaction\ndriven quantum phase transition in the Bose-Hubbard model: While being constant\nin the Mott phase, the expansion velocity decreases in the superfluid phase and\nvanishes for large systems in the non-interacting limit. These results are\ncompared to the set-up of a recent experiment [PRL 110, 205301 (2013)], where\nthe trap opening was combined with an interaction quench from infinitely strong\ninteractions to finite values. We carry out an analogous analysis for a\ntwo-component Fermi gas, with similar observations. In addition, we study the\neffect of breaking the integrability of hard-core bosons in different ways:\nWhile the fast ballistic expansion from the ground state of Mott insulators in\none dimension remains unchanged for finite interactions, we observe strong\ndeviations from this behavior on a two-leg ladder even in the hard-core case.\nThis change in dynamics bares similarities with the dynamics in the dimensional\ncrossover from one to two dimensions observed in the aformentioned experimental\nstudy."
    },
    {
        "anchor": "Spin squeezing, entanglement and quantum metrology with Bose-Einstein\n  condensates: Squeezed states, a special kind of entangled states, are known as a useful\nresource for quantum metrology. In interferometric sensors they allow to\novercome the \"classical\" projection noise limit stemming from the independent\nnature of the individual photons or atoms within the interferometer. Motivated\nby the potential impact on metrology as wells as by fundamental questions in\nthe context of entanglement, a lot of theoretical and experimental effort has\nbeen made to study squeezed states. The first squeezed states useful for\nquantum enhanced metrology have been proposed and generated in quantum optics,\nwhere the squeezed variables are the coherences of the light field. In this\ntutorial we focus on spin squeezing in atomic systems. We give an introduction\nto its concepts and discuss its generation in Bose-Einstein condensates. We\ndiscuss in detail the experimental requirements necessary for the generation\nand direct detection of coherent spin squeezing. Two exemplary experiments\ndemonstrating adiabatically prepared spin squeezing based on motional degrees\nof freedom and diabatically realized spin squeezing based on internal hyperfine\ndegrees of freedom are discussed.",
        "positive": "Interacting Preformed Cooper Pairs in Resonant Fermi Gases: We consider the normal phase of a strongly interacting Fermi gas, which can\nhave either an equal or an unequal number of atoms in its two accessible spin\nstates. Due to the unitarity-limited attractive interaction between particles\nwith different spin, noncondensed Cooper pairs are formed. The starting point\nin treating preformed pairs is the Nozi\\`{e}res-Schmitt-Rink (NSR) theory,\nwhich approximates the pairs as being noninteracting. Here, we consider the\neffects of the interactions between the Cooper pairs in a Wilsonian\nrenormalization-group scheme. Starting from the exact bosonic action for the\npairs, we calculate the Cooper-pair self-energy by combining the NSR formalism\nwith the Wilsonian approach. We compare our findings with the recent\nexperiments by Harikoshi {\\it et al.} [Science {\\bf 327}, 442 (2010)] and\nNascimb\\`{e}ne {\\it et al.} [Nature {\\bf 463}, 1057 (2010)], and find very good\nagreement. We also make predictions for the population-imbalanced case, that\ncan be tested in experiments."
    },
    {
        "anchor": "Observation of a Degenerate Fermi Gas Trapped by a Bose-Einstein\n  Condensate: We report on the formation of a stable quantum degenerate mixture of\nfermionic $^6$Li and bosonic $^{133}$Cs in an optical trap by sympathetic\ncooling near an interspecies Feshbach resonance. New regimes of the quantum\ndegenerate mixtures are identified. With moderate attractive interspecies\ninteractions, we show that a degenerate Fermi gas of Li can be fully confined\nin the Cs condensate without external potentials. For stronger attraction where\nmean-field collapse is expected, no such instability is observed. In this case,\nwe suggest the stability is a result of dynamic equilibrium, where the\ninterspecies three-body loss prevents the collapse. Our picture is supported by\na rate equation model, and the crossover between the thermalization rate and\nthe observed inelastic loss rate in the regime where the mean-field collapse is\nexpected to occur.",
        "positive": "Contact potential instability in the path-integral description of\n  itinerant ferromagnetism: It has long been predicted that a two-component non-localized Fermi gas will\nexhibit spontaneous polarization for sufficiently strong repulsive\ninteractions, a phenomenon which is called itinerant ferromagnetism. Recent\nexperiments with ultracold atomic gases have reached the interaction strength\nfor which theoretical models have predicted the occurrence of the\nnormal-to-itinerant-ferromagnetic phase transition, but so far this transition\nhas not been observed. The instability of the repulsive branch of the Feshbach\nresonance prevents the formation of the itinerant ferromagnetic state, but it\nis not clear whether this is the only instability impeding its experimental\nrealization. In this article, we use the path-integral formalism with density\nfields in the Hubbard-Stratonovich transformation to study the stability of a\nhomogeneous two-component Fermi gas with contact interactions. Within the\nsaddle-point approximation we show that none of the extrema of the action are\nminima, meaning all extrema are unstable to small density fluctuations. This\nimplies a more general mechanical instability of the polarized (itinerant\nferromagnetic) and normal states of the system in the path-integral formalism.\nWe find that it is important to consider the stability of the system when\nstudying itinerant ferromagnetism. Since (mechanical) stability may be\ninfluenced by the details of the interaction potential, we suggest the use of a\nmore realistic potential than the contact potential in future theoretical\ndescriptions."
    },
    {
        "anchor": "Finite temperature mean-field theory with intrinsic non-hermitian\n  structures for Bose gases in optical lattices: We reveal a divergent issue associated with the mean-field theory for Bose\ngases in optical lattices constructed by the widely used straightforward\nmean-field decoupling of the hopping term, where the corresponding mean-field\nHamiltonian generally assumes no lower energy bound once the spatial dependence\nof the mean-field superfluid order parameter is taken into account. Via a\nsystematic functional integral approach, we solve this issue by establishing a\ngeneral finite temperature mean-field theory that can treat any possible\nspatial dependence of the order parameter without causing the divergent issue.\nInterestingly, we find the theory generally assumes an intrinsic non-hermitian\nstructure that originates from the indefiniteness of the hopping matrix of the\nsystem. Within this theory, we develop an efficient approach for investigating\nthe physics of the system at finite temperature, where properties of the system\ncan be calculated via straightforward investigation on the saddle points of an\neffective potential function for the order parameter. We illustrate our\napproach by investigating the finite temperature superfluid transition of Bose\ngases in optical lattices. Since the underlying finite temperature mean-field\ntheory is quite general, this approach can be straightforwardly applied to\ninvestigate the finite temperature properties of related systems with phases\npossessing complex spatial structures.",
        "positive": "Time-of-flight imaging method to observe signatures of\n  antiferromagnetically ordered states of fermionic atoms in an optical lattice: We propose a simple method to detect the antiferromagnetic (AF) state of\nfermionic atoms in an optical lattice by combining a time-of-flight (TOF)\nimaging method and a Feshbach resonance. In this scheme, the nontrivial\ndynamics of fermionic atoms during the imaging process works as a probe with\nrespect to the breaking of the translational symmetry in the AF state. Precise\nnumerical simulations demonstrate that the characteristic oscillatory dynamics\ninduced by the scattering process that transfers an AF ordering vector appears\nin TOF images, which can be easily observed experimentally."
    },
    {
        "anchor": "Quantized squeezing and even-odd asymmetry of trapped bosons: We investigate the exact nature of the superfluid-to-Mott-insulator crossover\nfor interacting bosons on an optical lattice in a one-dimensional, harmonic\ntrap by high-precision density-matrix renormalization-group calculations. The\nresults reveal an intermediate regime characterized by a cascade of microscopic\nsteps. These arise as a consequence of individual boson \"squeezing\" events and\ndisplay an even-odd alternation dependent on the trap symmetry. We discuss the\nexperimental observation of this behavior, which is generic in an external\ntrapping potential.",
        "positive": "Ultracold atomic spin mixtures in ultrastable magnetic field\n  environments: Ultracold atomic spin mixtures develop rich and intriguing magnetic\nproperties when an external radiation coherently couples different spin states.\nIn particular, the coupled mixture may acquire a critical behavior when the\nspin interactions equal the coupling energy. However, atomic mixtures generally\nfeature a relatively high sensitivity to magnetic fields that can set a\nlimitation to the observable phenomena. In this article, we present an overview\nof experimental studies of magnetism based on superfluid multicomponent gases\nin an ultrastable magnetic field environment, which recently became available."
    },
    {
        "anchor": "Topological excitations in a spin-orbit coupled spin-1 Bose-Einstein\n  condensate under sinusoidally varying magnetic fields: We present a theoretical study of a spin-orbit coupled spin-1 Bose-Einstein\ncondensate under the influence of sinusoidally varying magnetic fields. In the\nground state of the ferromagnetic spin-1 condensate, we investigate topological\nexcitations in the system arising due to the combined effect of Rashba\nspin-orbit coupling and an in-plane sinusoidally varying magnetic field. In\nthis work, we offer a comparative study for various choices of magnetic fields\nin the $x\\rm{-}y$ plane. For a fixed field strength, the spin-orbit coupled\nsystem sustains a rich variety of exotic vortex structures ranging from\nvortex-antivortex lattices to vortex clusters as we increase the coupling\nstrength.",
        "positive": "Unusual behavior of sound velocity of a Bose gas in an optical\n  superlattice at quasi-one-dimension: A Bose gas trapped in a one-dimensional optical superlattice has emerged as a\nnovel superfluid characterized by tunable lattice topologies and tailored band\nstructures. In this work, we focus on the propagation of sound in such a novel\nsystem and have found new features on sound velocity, which arises from the\ninterplay between the two lattices with different periodicity and is not\npresent in the case of a condensate in a monochromatic optical lattice.\nParticularly, this is the first time that the sound velocity is found to first\nincrease and then decrease as the superlattice strength increases even at one\ndimension. Such unusual behavior can be analytically understood in terms of the\ncompetition between the decreasing compressibility and the increasing effective\nmass due to the increasing superlattice strength. This result suggests a new\nroute to engineer the sound velocity by manipulating the superlattice's\nparameters. All the calculations based on the mean-field theory are justified\nby checking the exponent $\\gamma$ of the off-diagonal one-body density matrix\nthat is much smaller than 1. Finally, the conditions for possible experimental\nrealization of our scenario are also discussed."
    },
    {
        "anchor": "Direct Simulation Monte Carlo method for cold atom dynamics: classical\n  Boltzmann equation in the quantum collision regime: In this paper we develop a direct simulation Monte Carlo (DSMC) method for\nsimulating highly nonequilibrium dynamics of nearly degenerate ultra-cold\ngases. We show that our method can simulate the high-energy collision of two\nthermal clouds in the regime observed in experiments [Thomas, et al. Phys. Rev.\nLett. \\textbf{93}, 173201 (2004)], which requires the inclusion of beyond\ns-wave scattering. We also consider the long-time dynamics of this system,\ndemonstrating that this would be a practical experimental scenario for testing\nthe Boltzmann equation and studying rethermalization.",
        "positive": "Heavy-light $N+1$ clusters of two-dimensional fermions: We study binding of $N$ identical heavy fermions by a light atom in two\ndimensions assuming zero-range attractive heavy-light interactions. By using\nthe mean-field theory valid for large $N$ we show that the $N+1$ cluster is\nbound when the mass ratio exceeds $1.074N^2$. The mean-field theory, being\nscale invariant in two dimensions, predicts only the shapes of the clusters\nleaving their sizes and energies undefined. By taking into account\nbeyond-mean-field effects we find closed-form expressions for these quantities.\nWe also discuss differences between the Thomas-Fermi and Hartree-Fock\napproaches for treating the heavy fermions."
    },
    {
        "anchor": "Controllable half-vortex lattices in an incoherently pumped polariton\n  condensate: We show how the transition between synchronized and desynchronized states of\na spinor polariton condensate can be used to drive a transition between\nstationary vortex lattices and half-vortex lattices. This provides a way to\ncontrol polariton spin textures by a combination of pump spot profile and\napplied magnetic fields. To do this, we extend the model of non-equilibrium\nspinor condensates to include relaxation, and study how this affects the\ndesynchronization transition. We discuss how the pattern formation can be\nexplained by behavior of the homogeneous system.",
        "positive": "Theory of the Two-Particle Emission from Superfluid Fermi Gases in the\n  BCS-BEC Crossover: We present a theory of the emission of fermion pairs from a superfluid Fermi\ngas induced by a photon absorption. In the solid state physics, this type of\nprocess is called double photo-emission (DPE). The spectrum of the induced\ntwo-particle current (or DPE current) provides a direct insight into the\npair-correlation of condensate fermion pairs. We develop a general formalism\nfor two-particle current induced by DPE by treating the coupling of two Fermi\ngases with the time-dependent perturbation theory. This formalism is used to\ncalculate energy distributions of DPE current from the superfluid Fermi gas in\nthe BCS-BEC crossover at T=0. We show that the DPE current has distinct\ncontributions of the condensed pair components and uncorrelated pair states. We\nalso calculate the angular dependence of DPE current in the BCS-BEC crossover.\nThe DPE current of the tightly-bound molecules in the BEC regime is found to be\nquite deferent from that of the weakly-bound Cooper pairs."
    },
    {
        "anchor": "Time crystal platform: from quasi-crystal structures in time to systems\n  with exotic interactions: Time crystals are quantum many-body systems which, due to interactions\nbetween particles, are able to spontaneously self-organize their motion in a\nperiodic way in time by analogy with the formation of crystalline structures in\nspace in condensed matter physics. In solid state physics properties of space\ncrystals are often investigated with the help of external potentials that are\nspatially periodic and reflect various crystalline structures. A similar\napproach can be applied for time crystals, as periodically driven systems\nconstitute counterparts of spatially periodic systems, but in the time domain.\nHere we show that condensed matter problems ranging from single particles in\npotentials of quasi-crystal structure to many-body systems with exotic\nlong-range interactions can be realized in the time domain with an appropriate\nperiodic driving. Moreover, it is possible to create molecules where atoms are\nbound together due to destructive interference if the atomic scattering length\nis modulated in time.",
        "positive": "Interferometry of non-Abelian band singularities and Euler class\n  topology: In systems with a real Bloch Hamiltonian band nodes can be characterised by a\nnon-Abelian frame-rotation charge. The ability of these band nodes to\nannihilate pairwise is path dependent, since by braiding nodes in adjacent gaps\nthe sign of their charges can be changed. Here, we theoretically construct and\nnumerically confirm two concrete methods to experimentally probe these\nnon-Abelian braiding processes and charges in ultracold atomic systems. We\nconsider a coherent superposition of two bands that can be created by moving\natoms through the band singularities at some angle in momentum space. Analyzing\nthe dependency on the frame charges, we demonstrate an interferometry scheme\npassing through two band nodes, which reveals the relative frame charges and\nallows for measuring the multi-gap topological invariant. The second method\nrelies on a single wavepacket probing two nodes sequentially, where the frame\ncharges can be determined from the band populations. Our results present a\nfeasible avenue for measuring non-Abelian charges of band nodes and the\nexperimental verification of braiding procedures directly, which can be applied\nin a variety of settings including the recently discovered anomalous\nnon-Abelian phases arising under periodic driving."
    },
    {
        "anchor": "Vibrations of a Columnar Vortex in a Trapped Bose-Einstein Condensate: We derive a governing equation for a Kelvin wave supported on a vortex line\nin a Bose-Einstein condensate, in a rotating cylindrically symmetric parabolic\ntrap. From this solution the Kelvin wave dispersion relation is determined. In\nthe limit of an oblate trap and in the absence of longitudinal trapping our\nresults are consistent with previous work. We show that the derived Kelvin wave\ndispersion in the general case is in quantitative agreement with numerical\ncalculations of the Bogoliubov spectrum and offer a significant improvement\nupon previous analytical work.",
        "positive": "Unconventional states of bosons with synthetic spin-orbit coupling: Spin-orbit coupling with bosons gives rise to novel properties that are\nabsent in usual bosonic systems. Under very general conditions, the\nconventional ground state wavefunctions of bosons are constrained by the\n\"no-node\" theorem to be positive-definite. In contrast, the linear-dependence\nof spin-orbit coupling leads to complex-valued condensate wavefunctions beyond\nthis theorem. In this article, we review the study of this class of\nunconventional Bose-Einstein condensations focusing on their topological\nproperties. Both the 2D Rashba and 3D $\\vec{\\sigma} \\cdot \\vec{p}$-type Weyl\nspin-orbit couplings give rise to Landau-level-like quantization of\nsingle-particle levels in the harmonic trap. The interacting condensates\ndevelop the half-quantum vortex structure spontaneously breaking time-reversal\nsymmetry and exhibit topological spin textures of the skyrmion type. In\nparticular, the 3D Weyl coupling generates topological defects in the\nquaternionic phase space as an SU(2) generalization of the usual U(1) vortices.\nRotating spin-orbit coupled condensates exhibit rich vortex structures due to\nthe interplay between vorticity and spin texture. In the Mott-insulating states\nin optical lattices, quantum magnetism is characterized by the\nDzyaloshinskii-Moriya type exchange interactions."
    },
    {
        "anchor": "Quantum Capillary Waves at the Superfluid--Mott Insulator Interface: We discuss quantum fluctuations of the interface between a superfluid and a\nMott-insulating state of ultracold atoms in a trap. The fluctuations of the\nboundary are due to a new type of surface modes, whose spectrum is similar (but\nnot identical) to classical capillary waves. The corresponding quantum\ncapillary length sets the scale for the penetration of the superfluid into the\nMott-insulating regime by the proximity effect and may be on the order of\nseveral lattice spacings. It determines the typical magnitude of the interface\nwidth due to quantum fluctuations, which may be inferred from single site\nimaging of ultracold atoms in an optical lattice.",
        "positive": "Effective mass and interaction energy of heavy Bose polarons at\n  unitarity: We study the motion of a heavy impurity immersed in a weakly interacting BEC\nusing the Gross-Pitaevskii equation (GPe). We construct a perturbative solution\nto the GPe in powers of impurity velocity in the case when the boson-impurity\npotential is tuned to unitarity and calculate the effective mass of the\npolaron. In addition, we calculate the interaction energy of two unitary\npolarons which are sufficiently far apart. Our formalism also reproduces the\nresults for both the mass and interaction energy obtained at weak\nboson-impurity coupling."
    },
    {
        "anchor": "Bose-Einstein Condensation on Curved Manifolds: Here we describe a weakly interacting Bose gas on a curved manifold, which is\nembedded in the three-dimensional Euclidean space.~To this end we start by\nconsidering a harmonic trap in the normal direction of the manifold, which\nconfines the three-dimensional Bose gas in the vicinity of its\nsurface.~Following the notion of dimensional reduction as outlined in\n[L.~Salasnich et al., Phys.~Rev.~A {\\bf 65}, 043614 (2002)], we assume a large\nenough trap frequency so that the normal degree of freedom of the condensate\nwave function can be approximately integrated out. In this way we obtain an\neffective condensate wave function on the quasi-two-dimensional surface of the\ncurved manifold, where the thickness of the cloud is determined\nself-consistently. For the particular case when the manifold is a sphere, our\nequilibrium results show how the chemical potential and the thickness of the\ncloud increase with the interaction strength.~Furthermore, we determine within\na linear stability analysis the low-lying collective excitations together with\ntheir eigenfrequencies, which turn out to reveal an instability for attractive\ninteractions.",
        "positive": "Experimental study of tune-out wavelengths for spin-dependent optical\n  lattice in $^{87}$Rb Bose-Einstein condensation: We study the periodic potential of one-dimensional optical lattice originated\nfrom scalar shift and vector shift by manipulating the lattice polarizations.\nThe ac Stark shift of optical lattice is measured by Kapitza-Dirac scattering\nof $^{87}$Rb Bose-Einstein condensate and the characteristics of spin-dependent\noptical lattice are presented by scanning the lattice wavelength between the D1\nand D2 lines. At the same time, tune-out wavelengths that ac Stark shift\ncancels can be probed by optical lattice. We give the tune-out wavelengths in\nmore general cases of balancing the contributions of both the scalar and vector\nshift. Our results provide a clear interpretation for spin-dependent optical\nlattice and tune-out wavelengths, and help to design it by choosing the\nappropriate lattice wavelength."
    },
    {
        "anchor": "Local Non-Hermitian Hamiltonian Formalism for Dissipative Fermionic\n  Systems and Loss-Induced Population Increase in Fermi Superfluids: Non-Hermitian Hamiltonian (NHH) is an effective formalism for open quantum\nsystems. In common wisdom, when the system is described by the Lindblad master\nequation, the NHH obtained by neglecting its jump term is believed to be a good\napproximation for a timescale sufficiently shorter than the inverse of the\ndissipation rate. We challenge this common wisdom and develop a scheme to\nobtain an appropriate NHH from the original master equation for dissipative\nfermionic systems. This NHH, called the local NHH, describes the loss process\nin each individual mode locally. As a concrete example, we justify our new\nscheme using fermionic superfluid under one-body loss. Furthermore, we find\nloss-induced population increase in the long time evolution due to the\ndissipation-induced phase locking between the pairing gap and the anomalous\nfield.",
        "positive": "Coherent Flow and Trapping of Polariton Condensates with Long Lifetime: We report new results of Bose-Einstein condensation of polaritons in\nspecially designed microcavities with very high quality factor, on the order of\n$10^6$, giving the polariton lifetimes of the order of 100 ps. When the\npolaritons are created with an incoherent pump, a dissipationless, coherent\nflow of the polaritons occurs over hundreds of microns, which increases as\ndensity increases. At high density, this flow is suddenly stopped, and the gas\nbecomes trapped in a local potential minimum, with strong coherence."
    },
    {
        "anchor": "Non-equilibrium diagrammatic approach to strongly interacting photons: We develop a non-equilibrium field-theoretical approach, based on a\nsystematic diagrammatic expansion, for strongly interacting photons in\noptically dense atomic media. We consider the case where the characteristic\nphoton-propagation range $L_P$ is much larger than the interatomic spacing $a$\nand where the density of atomic excitations is low enough to neglect saturation\neffects. In the highly polarizable medium the photons experience nonlinearities\nthrough the interactions they inherit from the atoms. If the atom-atom\ninteraction range $L_E$ is also large compared to $a$, we show that scattering\nprocesses with momentum transfer between photons are suppressed by a factor\n$a/L_E$. We are then able to perform a self-consistent resummation of a\nspecific (Hartree-like) diagram subclass and obtain quantitative results in the\nhighly non-perturbative regime of large single-atom cooperativity. Here we find\nimportant, conceptually new collective phenomena emerging due to the\ndissipative nature of the interactions, which even give rise to novel phase\ntransitions. The robustness of these is investigated by inclusion of the\nleading corrections in $a/L_E$. We consider specific applications to photons\npropagating under EIT conditions along waveguides near atomic arrays as well as\nwithin Rydberg ensembles.",
        "positive": "Spatial Patterns of Rydberg Excitations from Logarithmic Pair\n  Interactions: The collective excitations in ensembles of dissipative, laser driven\nultracold atoms exhibit crystal-like patterns, a many-body effect of the\nRydberg blockade mechanism. These crystalline structure are revealed in\nexperiment from a post-selection of configurations with fixed numbers of\nexcitations. Here, we show that these sub-ensemble can be well represented by\nensembles of effective particles that interact via logarithmic pair potentials.\nThis allows one to study the emergent patterns with a small number of effective\nparticles to determine the phases of Rydberg crystals and to systematically\nstudy contributions from $N$-body terms."
    },
    {
        "anchor": "Ground-state properties of electron-electron biwire systems: The correlation between electrons in different quantum wires is expected to\naffect the electronic properties of quantum electron-electron biwire systems.\nHere, we use the variational Monte Carlo method to study the ground-state\nproperties of parallel, infinitely thin electron-electron biwires for several\nelectron densities ($r_\\text{s}$) and interwire separations ($d$).\nSpecifically, the ground-state energy, the correlation energy, the interaction\nenergy, the pair-correlation function (PCF), the static structure factor (SSF),\nand the momentum distribution (MD) function are calculated. We find that the\ninteraction energy increases as $\\ln(d)$ for $d\\to 0$ and it decreases as\n$d^{-2}$ when $d\\to \\infty$. The PCF shows oscillatory behavior at all\ndensities considered here. As two parallel wires approach each other, interwire\ncorrelations increase while intrawire correlations decrease as evidenced by the\nbehavior of the PCF, SSF, and MD. The system evolves from two monowires of\ndensity parameter $r_\\text{s}$ to a single monowire of density parameter\n$r_\\text{s}/2$ as $d$ is reduced from infinity to zero. The MD reveals\nTomonaga-Luttinger (TL) liquid behavior with a power-law nature near\n$k_\\text{F}$ even in the presence of an extra interwire interaction between the\nelectrons in biwire systems. It is observed that when $d$ is reduced the MD\ndecreases for $k<k_\\text{F}$ and increases for $k>k_\\text{F}$, similar to its\nbehavior with increasing $r_\\text{s}$. The TL liquid exponent is extracted by\nfitting the MD data near $k_\\text{F}$, from which the TL liquid interaction\nparameter $K_{\\rho}$ is calculated. The value of the TL parameter is found to\nbe in agreement with that of a single wire for large separation between the two\nwires.",
        "positive": "Charge ambiguity and splitting of monopoles: This paper is dedicated to studying various aspects of topological defects,\nappearing in mean-field theory treatments of physical systems such as ultracold\natomic gases and gauge field theories. We start by investigating topological\ncharge ambiguity and addition of topological charges using the mathematical\nformalism of covering spaces, which clarifies many aspects these phenomena.\nSubsequently, we classify topological defect configurations consisting of\nseveral monopoles and unknotted ring defects in terms of homotopy groups and\nfundamental group actions on them, thus generalizing the previous\nclassifications of a single monopole and a single unknotted ring defect.\nFinally, we examine the decay of multiply charged topological monopoles under\nsmall perturbations of the physical system, and analyze the conditions under\nwhich multiply charged monopoles are inclined to split into several singly\ncharged monopoles."
    },
    {
        "anchor": "Supersolid-like states in a two-dimensional trapped spin-orbit-coupled\n  spin-1 condensate: We study supersolid-like states in a quasi-two-dimensional trapped Rashba and\nDresselhaus spin-orbit (SO) coupled spin-1 condensate. For small strengths of\nSO coupling $\\gamma$ ($\\gamma \\lessapprox 0.75$), in the ferromagnetic phase,\ncircularly-symmetric $(0,\\pm 1, \\pm 2)$- and $(\\mp 1, 0,\\pm 1)$-type states are\nformed where the numbers in the parentheses denote the angular momentum of the\nvortex at the center of the components and where the upper (lower) sign\ncorrespond to Rashba (Dresselhaus) coupling; in the antiferromagnetic phase,\nonly $(\\mp 1, 0,\\pm 1)$-type states are formed. For large strengths of SO\ncoupling, supersolid-like superlattice and superstripe states are formed in the\nferromagnetic phase. In the antiferromagnetic phase, for large strengths of SO\ncoupling, supersolid-like superstripe and multi-ring states are formed. For an\nequal mixture of Rashba and Dresselhaus SO couplings, only a superstripe state\nis found. All these states are found to be dynamically stable and hence\naccessible in an experiment and will enhance the fundamental understanding of\ncrystallization onto spatially periodic states in solids.",
        "positive": "Thermalization of interacting quasi-one-dimensional systems: Many experimentally relevant systems are quasi-one-dimensional, consisting of\nnearly decoupled chains. In these systems, there is a natural separation of\nscales between the strong intra-chain interactions and the weak interchain\ncoupling. When the intra-chain interactions are integrable, weak interchain\ncouplings play a crucial part in thermalizing the system. Here, we develop a\nBoltzmann-equation formalism involving a collision integral that is\nasymptotically exact for any interacting integrable system, and apply it to\ndevelop a quantitative theory of relaxation in coupled Bose gases in the\nexperimentally relevant Newton's cradle setup. We find that relaxation involves\na broad spectrum of timescales. We provide evidence that the Markov process\ngoverning relaxation at late times is gapless; thus, the approach to\nequilibrium is generally non-exponential, even for spatially uniform\nperturbations."
    },
    {
        "anchor": "Magnon Bose-Einstein condensates: from time crystals and quantum\n  chromodynamics to vortex sensing and cosmology: Under suitable experimental conditions collective spin-wave excitations,\nmagnons, form a Bose-Einstein condensate (BEC) where the spins precess with a\nglobally coherent phase. Bose-Einstein condensation of magnons has been\nreported in a few systems, including superfluid phases of $^3$He, solid state\nsystems such as Yttrium-iron-garnet (YIG) films, and cold atomic gases. Among\nthese systems, the superfluid phases of $^3$He provide a nearly ideal test\nbench for coherent magnon physics owing to experimentally proven spin\nsuperfluidity, the long lifetime of the magnon condensate, and the versatility\nof the accessible phenomena. We first briefly recap the properties of the\ndifferent magnon BEC systems, with focus on superfluid $^3$He. The main body of\nthis review summarizes recent advances in application of magnon BEC as a\nlaboratory to study basic physical phenomena connecting to diverse areas from\nparticle physics and cosmology to new phases of condensed matter. This line of\nresearch complements the ongoing efforts to utilize magnon BECs as probes and\ncomponents for potentially room-temperature quantum devices. In conclusion, we\nprovide a roadmap for future directions in the field of applications of magnon\nBEC to fundamental research.",
        "positive": "Creation and revival of ring dark solitons in a toroidal Bose-Einstein\n  condensate: We propose a protocol for the simultaneous controlled creation of multiple\nconcentric ring dark solitons in a toroidally trapped Bose-Einstein condensate.\nThe decay of these solitons into a vortex-antivortex necklace shows revivals of\nthe soliton structure, but eventually becomes an example of quantum turbulence."
    },
    {
        "anchor": "Phases of dipolar bosons in a bilayer geometry: We study by first principle computer simulations the low temperature phase\ndiagram of bosonic dipolar gases in a bilayer geometry, as a function of the\ntwo control parameters, i.e., the in-plane density and the interlayer distance.\nWe observe four distinct phases, namely paired and decoupled superfluids, as\nwell as a crystal of dimers and one consisting of two aligned crystalline\nlayers. A direct quantum phase transition from a dimer crystal to two\nindependent superfluids is observed in a relatively wide range of parameters.\nNo supersolid phase is predicted for this system.",
        "positive": "Periodically Driving a Many-Body Localized Quantum System: We experimentally study a periodically driven many-body localized system\nrealized by interacting fermions in a one-dimensional quasi-disordered optical\nlattice. By preparing the system in a far-from-equilibrium state and monitoring\nthe remains of an imprinted density pattern, we identify a localized phase at\nhigh drive frequencies and an ergodic phase at low ones. These two distinct\nphases are separated by a dynamical phase transition which depends on both the\ndrive frequency and the drive strength. Our observations are quantitatively\nsupported by numerical simulations and are directly connected to the change in\nthe statistical properties of the effective Floquet Hamiltonian."
    },
    {
        "anchor": "Crossover from interaction to driven regimes in quantum vortex\n  reconnections: Reconnections of coherent filamentary structures play a key role in the\ndynamics of fluids, redistributing energy and helicity among the length scales,\ntriggering dissipative effects and inducing fine-scale mixing. Unlike ordinary\n(classical) fluids where vorticity is a continuous field, in superfluid helium\nand in atomic Bose-Einstein condensates (BECs) vorticity takes the form of\nisolated quantised vortex lines, which are conceptually easier to study. New\nexperimental techniques now allow visualisation of individual vortex\nreconnections in helium and condensates. It has long being suspected that\nreconnections obey universal laws, particularly a universal scaling with time\nof the minimum distance between vortices $\\delta$. Here we perform a\ncomprehensive analysis of this scaling across a range of scenarios relevant to\nsuperfluid helium and trapped condensates, combining our own numerical\nsimulations with the previous results in the literature. We reveal that the\nscaling exhibit two distinct fundamental regimes: a $\\delta \\sim t^{1/2}$\nscaling arising from the mutual interaction of the reconnecting strands and a\n$\\delta \\sim t$ scaling when extrinsic factors drive the individual vortices.",
        "positive": "Unconventional pairing in one-dimensional systems of a few\n  mass-imbalanced ultracold fermions: We study the ground-state properties of a two-component fermionic mixture\neffectively confined in a one-dimensional harmonic trap. We consider scenarios\nwhen numbers of particles in components are the same but particles have\ndifferent masses. We examine whether it is possible to detect signatures of an\nunconventional pairing between opposite-spin fermions in the presence of\nattractive interactions. For this purpose, we perform the exact diagonalization\nof the many-body Hamiltonian and study the two-particle reduced density matrix.\nIn agreement with expectations, we confirm that the many-body ground state is\ndominated by conventional pairs with a negligible total momentum for a small\nmass imbalance. Furthermore, we show that for sufficiently large mass ratios\nthe domination of fundamentally different pairs is established and the\nFulde-Ferrell-Larkin-Ovchinnikov phase is supported. Finally, we argue that the\ntwo mechanisms can coexist in the regime of moderate mass ratios. Due to the\ncurrent experimental progress in obtaining ultra-cold fermionic systems in a\nfew-body regime, our predictions may have some importance for the upcoming\nexperiments."
    },
    {
        "anchor": "Collective oscillations of a two-component Fermi gas on the repulsive\n  branch: We calculate frequencies of collective oscillations of two-component Fermi\ngas that is kept on the repulsive branch of its energy spectrum. Not only is a\nparamagnetic phase explored, but also a ferromagnetically separated one. Both\nin-, and out-of-phase perturbations are investigated, showing contributions\nfrom various gas excitations. Additionally, we compare results coming from both\ntime-dependent Hartree-Fock and density-functional approaches.",
        "positive": "Superfluid Turbulence: Nonthermal Fixed Point in an Ultracold Bose Gas: Nonthermal fixed points of far-from-equilibrium dynamics of a dilute\ndegenerate Bose gas are analysed in two and three spatial dimensions. For such\nsystems, universal power-law distributions, previously found within a\nnonperturbative quantum-field theoretic approach, are shown to be related to\nvortical dynamics and superfluid turbulence. The results imply an\ninterpretation of the momentum scaling at the nonthermal fixed points in terms\nof independent vortex excitations of the superfluid. Long-wavelength acoustic\nexcitations on the top of these are found to follow a non-thermal power law.\nThe results shed light on fundamental aspects of superfluid turbulence and have\nstrong potential implications for related phenomena studied, e.g., in\nearly-universe inflation or quark-gluon plasma dynamics."
    },
    {
        "anchor": "Elementary excitations of chiral Bose-Einstein condensates: We study the collective modes of a Bose-Einstein condensate subject to an\noptically induced density-dependent gauge potential. The corresponding\ninteracting gauge theory lacks Galilean invariance, yielding an exotic\nsuperfluid state. The nonlinear dynamics in the presence of a current\nnonlinearity and an external harmonic trap are found to give rise to dynamics\nwhich violate Kohn's theorem; where the frequency of the dipole mode strongly\ndepends on the strength of the mass current in the gas. The linearised spectrum\nreveals how the centre of mass and shape oscillations are coupled, whereas in\nthe strongly nonlinear regime the dynamics is irregular.",
        "positive": "Polaron in a $p+ip$ Fermi topological superfluid: We study polaron excitations induced by an impurity interacting with a\ntwo-dimensional $p+ip$ Fermi superfluid. As the Fermi-Fermi pairing interaction\nis tuned, the background Fermi superfluid undergoes a topological phase\ntransition. We show that such a transition is accompanied by a discontinuity in\nthe second derivative of the polaron energy, regardless of the impurity-fermion\ninteraction. We also identify a polaron to trimer crossover when the Fermi\nsuperfluid is in the strongly interacting, thus topologically trivial, regime.\nHowever, the trimer state is metastable against the molecular state where the\nimpurity binds a Bogoliubov quasiparticle from the Fermi superfluid. By\ncomparing the polaron to molecule transition in our system with that of an\nimpurity in a noninteracting Fermi sea, we find that pairing interactions in\nthe background Fermi superfluid effectively facilitate the impurity-fermion\nbinding. Our results suggest the possibility of using the impurity as a probe\nfor detecting topological phase transitions in the background; they also reveal\ninteresting competitions between various many-body states in the system."
    },
    {
        "anchor": "Elastic Scattering Time of Matter-Waves in Disordered Potentials: We report on an extensive study of the elastic scattering time $\\tauS$ of\nmatter-waves in optical disordered potentials. Using direct experimental\nmeasurements, numerical simulations and comparison with first-order Born\napproximation based on the knowledge of the disorder properties, we explore the\nbehavior of $\\tauS$ over more than three orders of magnitude, spanning from the\nweak to the strong scattering regime. We study in detail the location of the\ncrossover and, as a main result, we reveal the strong influence of the disorder\nstatistics, especially on the relevance of the widely used Ioffe-Regel-like\ncriterion $k\\lS\\sim 1$. While it is found to be relevant for\nGaussian-distributed disordered potentials, we observe significant deviations\nfor laser speckle disorders that are commonly used with ultracold atoms. Our\nresults are crucial for connecting experimental investigation of complex\ntransport phenomena, such as Anderson localization, to microscopic theories.",
        "positive": "Quasicontinuous horizontally guided atom laser: coupling spectrum and\n  flux limits: We study in detail the flux properties of a radiofrequency outcoupled\nhorizontally guided atom laser, following the scheme demonstrated in [Guerin W\net al. 2006 Phys. Rev. Lett. 97 200402]. Both the outcoupling spectrum (flux of\nthe atom laser versus rf frequency of the outcoupler) and the flux limitations\nimposed to operate in the quasicontinuous regime are investigated. These\naspects are studied using a quasi-1D model, whose predictions are shown to be\nin fair agreement with the experimental observations. This work allows us to\nidentify the operating range of the guided atom laser and to confirm its good\npromises in view of studying quantum transport phenomena."
    },
    {
        "anchor": "Quantum degenerate dipolar Fermi gas: The interplay between crystallinity and superfluidity is of great fundamental\nand technological interest in condensed matter settings. In particular,\nelectronic quantum liquid crystallinity arises in the non-Fermi liquid,\npseudogap regime neighboring a cuprate's unconventional superconducting phase.\nWhile the techniques of ultracold atomic physics and quantum optics have\nenabled explorations of the strongly correlated, many-body physics inherent in,\ne.g., the Hubbard model, lacking has been the ability to create a quantum\ndegenerate Fermi gas with interparticle interactions---such as the strong\ndipole-dipole interaction---capable of inducing analogs to electronic quantum\nliquid crystals. We report the first quantum degenerate dipolar Fermi gas, the\nrealization of which opens a new frontier for exploring strongly correlated\nphysics and, in particular, the quantum melting of smectics in the pristine\nenvironment provided by the ultracold atomic physics setting. A quantum\ndegenerate Fermi gas of the most magnetic atom 161Dy is produced by laser\ncooling to 10 uK before sympathetically cooling with ultracold, bosonic 162Dy.\nThe temperature of the spin-polarized 161Dy is a factor T/TF=0.2 below the\nFermi temperature TF=300 nK. The co-trapped 162Dy concomitantly cools to\napproximately Tc for Bose-Einstein condensation, thus realizing a novel, nearly\nquantum degenerate dipolar Bose-Fermi gas mixture.",
        "positive": "High-fidelity pseudopotentials for the contact interaction: The contact interaction is often used in modeling ultracold atomic gases,\nalthough it leads to pathological behavior arising from the divergence of the\nmany-body wavefunction when two particles coalesce. This makes it difficult to\nuse this model interaction in quantum Monte Carlo and other popular numerical\nmethods. Researchers therefore model the contact interaction with\npseudopotentials, such as the square well potential, whose scattering\nproperties deviate markedly from those of the contact potential. In this\narticle, we propose a family of pseudopotentials that reproduce the scattering\nphase shifts of the contact interaction up to a hundred times more accurately\nthan the square well potential. Moreover, the pseudopotentials are smooth,\nresulting in significant improvements in efficiency when used in numerical\ncalculations."
    },
    {
        "anchor": "Spin-Current Instability at a Magnetic Domain Wall in a Ferromagnetic\n  Superfluid: a Generation Mechanism of Eccentric Fractional Skyrmions: Spinful superfluids of ultracold atoms are ideal for investigating the\nintrinsic properties of spin current and texture because they are realized in\nan isolated, nondissipative system free from impurities, dislocations, and\nthermal fluctuations. This study theoretically reveals the impact of spin\ncurrent on a magnetic domain wall in spinful superfluids. An exact wall\nsolution is obtained in the ferromagnetic phase of a spin-1 Bose--Einstein\ncondensate with easy-axis anisotropy at zero temperature. The\nbosonic-quasiparticle mechanics analytically show that the spin current along\nthe wall becomes unstable if the velocity exceeds the critical spin-current\nvelocities, leading to complicated situations because of the competition\nbetween transverse magnons and ripplons. Our direct numerical simulation\nreveals that this system has a mechanism to generate an eccentric fractional\nskyrmion, which has a fractional topological charge, but its texture is not\nsimilar to that of a meron. This mechanism is in contrast to the generation of\nconventional skyrmions in easy-axis magnets. The theoretical findings can be\nexamined in the same situation as in a recent experiment on ultracold atoms. In\nterms of the universality of spontaneous symmetry breaking, unexplored similar\nphenomena are expected in different physical systems with the same broken\nsymmetry.",
        "positive": "Can a bright soliton model reveal a genuine time crystal for a finite\n  number of bosons?: We analyze time crystal effects in a finite system of bosons which form a\nbright soliton clump on the Aharonov-Bohm ring. In the large particle number\nlimit, $N\\rightarrow\\infty$, this setup corresponds to the Wilczek model, where\nit is known that the time crystal behavior cannot be observed in the ground\nstate of the system because a spontaneously formed soliton does not move. Here,\nwe show that while the spontaneous formation of a moving soliton in the ground\nstate can occur for $N<\\infty$, the soliton decays before it makes a single\nrevolution along the ring and the time crystal dynamics is impossible."
    },
    {
        "anchor": "Radio frequency spectroscopy of polarons in ultracold Bose gases: Recent experimental advances enabled the realization of mobile impurities\nimmersed in a Bose-Einstein condensate (BEC) of ultracold atoms. Here we\nconsider impurities with two or more internal hyperfine states, and study their\nradio-frequency (RF) absorption spectra, which correspond to transitions\nbetween two different hyperfine states. We calculate RF spectra for the case\nwhen one of the hyperfine states involved interacts with the BEC, while the\nother state is non-interacting, by performing a non-perturbative resummation of\nthe probabilities of exciting different numbers of phonon modes. In the\npresence of interactions the impurity gets dressed by Bogoliubov excitations of\nthe BEC, and forms a polaron. The RF signal contains a delta-function peak\ncentered at the energy of the polaron measured relative to the bare impurity\ntransition frequency with a weight equal to the amount of bare impurity\ncharacter in the polaron state. The RF spectrum also has a broad incoherent\npart arising from the background excitations of the BEC, with a characteristic\npower-law tail that appears as a consequence of the universal physics of\ncontact interactions. We discuss both the direct RF measurement, in which the\nimpurity is initially in an interacting state, and the inverse RF measurement,\nin which the impurity is initially in a non-interacting state. In the latter\ncase, in order to calculate the RF spectrum, we solve the problem of polaron\nformation: a mobile impurity dynamically gets dressed by Bogoliubov phonons.\nOur solution based on a time-dependent variational ansatz of coherent states of\nBogoliubov phonons, becomes exact when the impurity is localized. Moreover we\nshow that such an ansatz compares well with a semiclassical estimate of the\npropagation amplitude of a mobile impurity in the BEC. Our technique can be\nextended to cases when both initial and final impurity states interact with the\nBEC.",
        "positive": "All-order momentum correlations of three ultracold bosonic atoms\n  confined in triple-well traps: Signatures of emergent many-body quantum phase\n  transitions and analogies with three-photon quantum-optics interference: All-order momentum correlation functions associated with the time-of-flight\nspectroscopy of three spinless ultracold bosonic interacting neutral atoms\nconfined in a linear three-well optical trap are presented. The underlying\nHamiltonian employed for the interacting atoms is an augmented three-site\nHubbard model. Our investigations target matter-wave interference of massive\nparticles, aiming at the establishment of experimental protocols for\ncharacterizing the quantum states of trapped attractively or repulsively\ninteracting ultracold particles, with variable interaction strength. The\nmanifested advantages and deep physical insights that can be gained through the\nemployment of the results of our study for a comprehensive understanding of the\nnature of the quantum states of interacting many-particle systems, via analysis\nof the all-order (that is 1st, 2nd and 3rd) momentum correlation functions for\nthree bosonic atoms in a three well confinement, are illustrated and discussed\nin the context of time-of-flight inteferometric interrogations of the\ninteraction-strength-induced emergent quantum phase transition from the Mott\ninsulating phase to the superfluid one. Furthermore, we discuss that our\ninteferometric interrogations establish strong analogies with the\nquantum-optics interference of three photons, including the aspects of genuine\nthree-photon interference, which are focal to explorations targeting the\ndevelopment and implementation of quantum information applications and quantum\ncomputing."
    },
    {
        "anchor": "Probing non-thermal density fluctuations in the one-dimensional Bose gas: Quantum integrable models display a rich variety of non-thermal excited\nstates with unusual properties. The most common way to probe them is by\nperforming a quantum quench, i.e., by letting a many-body initial state\nunitarily evolve with an integrable Hamiltonian. At late times, these systems\nare locally described by a generalized Gibbs ensemble with as many effective\ntemperatures as their local conserved quantities. The experimental measurement\nof this macroscopic number of temperatures remains elusive. Here we show that\nthey can be obtained by probing the dynamical structure factor of the system\nafter the quench and by employing a generalized fluctuation-dissipation theorem\nthat we provide. Our procedure allows us to completely reconstruct the\nstationary state of a quantum integrable system from state-of-the-art\nexperimental observations.",
        "positive": "Confinement-induced collapse of a dipolar Bose-Einstein condensate: We report on the observation of the confinement-induced collapse dynamics of\na dipolar Bose-Einstein condensate (dBEC) in a one-dimensional optical lattice.\nWe show that for a fixed interaction strength the collapse can be initiated\nin-trap by lowering the lattice depth below a critical value. Moreover, a\nstable dBEC in the lattice may become unstable during the time-of-flight\ndynamics upon release, due to the combined effect of the anisotropy of the\ndipolar interactions and inter-site coherence in the lattice."
    },
    {
        "anchor": "The J-triplet Cooper pairing with magnetic dipolar interactions: Recently, cold atomic Fermi gases with the large magnetic dipolar interaction\nhave been laser cooled down to quantum degeneracy. Different from\nelectric-dipoles which are classic vectors, atomic magnetic dipoles are\nquantum-mechanical matrix operators proportional to the hyperfine-spin of\natoms, thus provide rich opportunities to investigate exotic many-body physics.\nFurthermore, unlike anisotropic electric dipolar gases, unpolarized magnetic\ndipolar systems are isotropic under simultaneous spin-orbit rotation. These\nfeatures give rise to a robust mechanism for a novel pairing symmetry: orbital\np-wave (L=1) spin triplet (S=1) pairing with total angular momentum of the\nCooper pair J=1. This pairing is markedly different from both the $^3$He-B\nphase in which J=0 and the $^3$He-$A$ phase in which $J$ is not conserved. It\nis also different from the p-wave pairing in the single-component electric\ndipolar systems in which the spin degree of freedom is frozen.",
        "positive": "Evaluation of the particle numbers via the two root mean square radii in\n  a 2-species Bose-Einstein condensate: The coupled Gross-Pitaevskii equations for two-species BEC have been solved\nanalytically under the Thomas-Fermi approximation (TFA). Based on the\nanalytical solution, two formulae are derived to relate the particle numbers\n$N_A$ and $N_B$ with the root mean square radii of the two kinds of atoms. Only\nthe case that both kinds of atoms have nonzero distribution at the center of an\nisotropic trap is considered. In this case the TFA has been found to work\nnicely. Thus, the two formulae are applicable and are useful for the evaluation\nof $N_A$ and $N_B$."
    },
    {
        "anchor": "Ring Bose-Einstein condensate in a cavity: Chirality Detection and\n  Rotation Sensing: Recently, a method has been proposed to detect the rotation of a ring\nBose-Einstein condensate, in situ, in real-time and with minimal destruction,\nusing a cavity driven with optical fields carrying orbital angular momentum.\nThis method is sensitive to the magnitude of the condensate winding number but\nnot its sign. In the present work, we consider simulations of the rotation of\nthe angular lattice formed by the optical fields and show that the resulting\ncavity transmission spectra are sensitive to the sign of the condensate winding\nnumber. We demonstrate the minimally destructive technique on persistent\ncurrent rotational eigenstates, counter-rotating superpositions, and a soliton\nsingly or in collision with a second soliton. Conversely, we also investigate\nthe sensitivity of the ring condensate, given knowledge of its winding number,\nto the rotation of the optical lattice. This characterizes the effectiveness of\nthe optomechanical configuration as a laboratory rotation sensor. Our results\nare important to studies of rotating ring condensates used in atomtronics,\nsuperfluid hydrodynamics, simulation of topological defects and cosmological\ntheories, interferometry using matter-wave solitons, and optomechanical\nsensing.",
        "positive": "Single-Particle Spectral Density of a Bose Gas in the Two-Fluid\n  Hydrodynamic Regime: In Bose supefluids, the single-particle Green's function can be directly\nrelated to the superfluid velocity-velocity correlation function in the\nhydrodynamic regime. An explicit expression for the single-particle spectral\ndensity was originally written down by Hohenberg and Martin in 1965, starting\nfrom the two-fluid equations for a superfluid. We give a simple derivation of\ntheir results. Using these results, we calculate the relative weights of first\nand second sound modes in the single-particle spectral density as a function of\ntemperature in a uniform Bose gas. We show that the second sound mode makes a\ndominant contribution to the single-particle spectrum in relatively high\ntemperature region. We also discuss the possibility of experimental observation\nof the second sound mode in a Bose gas by photoemission spectroscopy."
    },
    {
        "anchor": "Polarized Superfluidity in the imbalanced attractive Hubbard model: We investigate the attractive Hubbard model in infinite spatial dimensions by\nmeans of dynamical mean-field theory. Using a continuous-time Monte Carlo\nalgorithm in the Nambu formalism as an impurity solver, we directly deal with\nthe superfluid phase in the population imbalanced system. By calculating the\nsuperfluid order parameter, the magnetization, and the density of states, we\ndiscuss how the polarized superfluid state is realized in the attractive\nHubbard model at quarter filling. We find that a drastic change in the density\nof states is induced by spin imbalanced populations in the superfluid state.",
        "positive": "Universal Features of the Excitation Spectrum in Generalized Gibbs\n  Distribution Ensemble: It is shown that excitation spectra of Generalized Gibbs Ensembles (GGE) of\none-dimensional integrable models with isotopic symmetry contain universal\nfeatures insensitive to details of the distribution. Namely, the low energy\nlimit of the subsystem of isotopic (for instance, spin) excitations is\ndescribed by the effective action of a ferromagnet at thermodynamic equilibrium\nwith a single temperature and with the stiffness determined by the initial\nconditions. The condition of universality is that the entropy per excited\nparticle is small."
    },
    {
        "anchor": "Quantum fluctuations and vortex-antivortex unbinding in the 2D BCS-BEC\n  crossover: Very recently quasi two-dimensional (2D) systems made of attractive fermionic\nalkali-metal atoms with a widely tunable interaction due to Fano-Feshbach\nresonances have been realized. In this way it has been achieved the 2D\ncrossover from the Bardeen-Cooper-Schrieffer regime of weakly-interacting\nCooper pairs to the Bose-Einstein condensate regime strongly bound dimers.\nThese experiments pave the way to the investigation of 2D strongly-interacting\nattractive fermions during the Berezinskii-Kosterlitz-Thouless (BKT) transition\nfrom a low-temperature superfluid phase characterized by quasi-condensation to\na high-temperature normal phase, where vortex proliferation driven by quantum\nand thermal fluctuations completely destroys superfluidity. In this paper we\ndiscuss our preliminar theoretical results on the behavior of the BKT critical\ntemperature across the crossover. Our microscopic calculations are based on\nfunctional integration taking into account renormalized Gaussian fluctuations\nand the crucial 2D effect of vortex-antivortex unbinding.",
        "positive": "Topologically protected mid-gap states induced by impurity in\n  one-dimensional superlattices: Based on the discovery of the nontrivial topology of one-dimensional\nsuperlattices, we show that midgap states will emerge in such systems induced\nby a single on-site impurity. Besides the trivial bound state located at the\nimpurity site, these midgap states are localized at the adjacent sides of the\nimpurity, carrying the information of the topology and behaving like the effect\nof the open boundary conditions in the limit of a large attractive or repulsive\nimpurity potential. Using this feature, the impurity can be used to detect the\ntopology of the superlattice system and to realize the adiabatic pumping\nbetween the opposite sides of the impurity in cold-atom experiments or in\nphotonic crystals."
    },
    {
        "anchor": "Lee-Huang-Yang effects in the ultracold mixture of $^{23}$Na and\n  $^{87}$Rb with attractive interspecies interactions: The beyond-mean-field Lee-Huang-Yang (LHY) correction is ubiquitous in dilute\nultracold quantum gases. However, its effects are often elusive due to the\ntypically much larger influence of the mean-field energy. In this work, we\nstudy an ultracold mixture of $^{23}$Na and $^{87}$Rb with tunable attractive\ninterspecies interactions. The LHY effects manifest in the formation of\nself-bound quantum liquid droplets and the expansion dynamics of the gas-phase\nsample. A liquid-to-gas phase diagram is obtained by measuring the critical\natom numbers below which the self-bound behavior disappears. In stark contrast\nto trapped gas-phase condensates, the gas-phase mixture formed following the\nliquid-to-gas phase transition shows an anomalous expansion featuring a larger\nrelease energy for increasing mean-field attractions.",
        "positive": "Spin squeezing of high-spin, spatially extended quantum fields: Investigations of spin squeezing in ensembles of quantum particles have been\nlimited primarily to a subspace of spin fluctuations and a single spatial mode\nin high-spin and spatially extended ensembles. Here, we show that a wider range\nof spin-squeezing is attainable in ensembles of high-spin atoms, characterized\nby sub-quantum-limited fluctuations in several independent planes of\nspin-fluctuation observables. Further, considering the quantum dynamics of an\n$f=1$ ferromagnetic spinor Bose-Einstein condensate, we demonstrate\ntheoretically that a high degree of spin squeezing is attained in multiple\nspatial modes of a spatially extended quantum field, and that such squeezing\ncan be extracted from spatially resolved measurements of magnetization and\nnematicity, i.e.\\ the vector and quadrupole magnetic moments, of the quantum\ngas. Taking into account several experimental limitations, we predict that the\nvariance of the atomic magnetization and nematicity may be reduced as far as 20\ndB below the standard quantum limits."
    },
    {
        "anchor": "Coherent Oscillations in an Exciton-Polariton Josephson Junction: We report on the observation of spontaneous coherent oscillations in a\nmicrocavity polariton bosonic Josephson junction. The condensation of exciton\npolaritons takes place under incoherent excitation in a disordered environment,\nwhere double potential wells tend to appear in the disordered landscape.\nCoherent oscillations set on at an excitation power well above the condensation\nthreshold. The time resolved population and phase dynamics reveal the analogy\nwith the AC Josephson effect. We have introduced a theoretical two-mode model\nto describe the observed effects, which allows us to explain how the different\nrealizations of the pulsed experiment have a similar phase relation.",
        "positive": "Self-interfering dynamics in Bose-Einstein condensates with engineered\n  dispersions: Optical lattice and spin-orbit coupling are typical experimental approaches\nto engineer dispersion. We reveal a self-interfering dynamics in a\nnoninteracting Bose-Einstein condensate with the engineered dispersion by\noptical lattice or spin-orbit coupling. The self-interference results from the\nco-occupation of positive and negative effect mass regimes in the engineered\ndispersion. The physical origination of the self-interference is explained by\nthe Wigner distribution function of the self-interfering wave-packet. We\ncharacterize detail features of the self-interference pattern."
    },
    {
        "anchor": "Thermalization, condensate growth, and defect formation in an\n  out-of-equilibrium Bose gas: We experimentally and numerically investigate thermalization processes of a\ntrapped $^{87}$Rb Bose gas, initially prepared in a non-equilibrium state\nthrough partial Bragg diffraction of a Bose-Einstein condensate (BEC). The\nsystem evolves in a Gaussian potential, where we observe the destruction of the\nBEC due to collisions, and subsequent growth of a new condensed fraction in an\noscillating reference frame. Furthermore, we occasionally observe the presence\nof defects, which we identify as gray solitons. We simulate the evolution of\nour system using the truncated Wigner method and compare the outcomes with our\nexperimental results.",
        "positive": "Fulde-Ferrel-Larkin-Ovchinnikov phase in one dimensional Fermi gas with\n  attractive interactions and transverse spin-orbit coupling: We examine the existence and characteristics of the exotic\nFulde-Ferrel-Larkin-Ovchinnikov (FFLO) phase in a one-dimensional Fermi gas\nwith attractive Hubbard interactions, in the presence of spin-orbit coupling\n(SOC) and Zeeman field. We show that a robust FFLO phase can be created in the\npresence of attractive on-site interactions and Zeeman field, and that the\naddition of SOC suppresses the FFLO order and enhances the pair formation. In\nabsence of SOC, the system shows four phases: Bardeen-Cooper-Schrieffer (BCS),\nFFLO, multi- mode pairing and fully polarized phases by tuning the Zeeman field\nh, and the quantum transition between these phases is discontinuous with\nrespect to h. In the presence of SOC, the transition from the BCS to FFLO phase\nbecomes continuous. We present a complete phase diagram of this model both in\nthe presence and in the absence of SOC at quarter electron filling and also\nexplore the effect of SOC on the FFLO phase."
    },
    {
        "anchor": "Chaoticity without thermalisation in disordered lattices: We study chaoticity and thermalization in Bose-Einstein condensates in\ndisordered lattices, described by the discrete nonlinear Schr\\\"odinger equation\n(DNLS). A symplectic integration method allows us to accurately obtain both the\nfull phase space trajectories and their maximum Lyapunov exponents (mLEs),\nwhich characterize their chaoticity. We find that disorder destroys ergodicity\nby breaking up phase space into subsystems that are effectively disjoint on\nexperimentally relevant timescales, even though energetically, classical\nlocalisation cannot occur. This leads us to conclude that the mLE is a very\npoor ergodicity indicator, since it is not sensitive to the trajectory being\nconfined to a subregion of phase space. The eventual thermalization of a BEC in\na disordered lattice cannot be predicted based only on the chaoticity of its\nphase space trajectory.",
        "positive": "Universal equation of state and pseudogap in the two-dimensional Fermi\n  gas: We determine the thermodynamic properties and the spectral function for a\nhomogeneous two-dimensional Fermi gas in the normal state using the\nLuttinger-Ward, or self-consistent T-matrix, approach. The density equation of\nstate deviates strongly from that of the ideal Fermi gas even for moderate\ninteractions, and our calculations suggest that temperature has a pronounced\neffect on the pressure in the crossover from weak to strong coupling,\nconsistent with recent experiments. We also compute the superfluid transition\ntemperature for a finite system in the crossover region. There is a pronounced\npseudogap regime above the transition temperature: the spectral function shows\na Bogoliubov-like dispersion with back-bending, and the density of states is\nsignificantly suppressed near the chemical potential. The contact density at\nlow temperatures increases with interaction and compares well with both\nexperiment and zero-temperature Monte Carlo results."
    },
    {
        "anchor": "Magnetic polarons in a nonequilibrium polariton condensate: We consider a condensate of exciton-polaritons in a diluted magnetic\nsemiconductor microcavity. Such system may exhibit magnetic self-trapping in\nthe case of sufficiently strong coupling between polaritons and magnetic ions\nembedded in the semiconductor. We investigate the effect of the nonequilibrium\nnature of exciton-polaritons on the physics of the resulting self-trapped\nmagnetic polarons. We find that multiple polarons can exist at the same time,\nand derive a critical condition for self-trapping which is different to the one\npredicted previously in the equilibrium case. Using the Bogoliubov-de Gennes\napproximation, we calculate the excitation spectrum and provide a physical\nexplanation in terms of the effective magnetic attraction between polaritons,\nmediated by the ion subsystem.",
        "positive": "Effective field theory and dispersion law of the phonons of a\n  non-relativistic superfluid: We study the recently proposed effective field theory for the phonon of an\narbitrary non-relativistic superfluid. After computing the one-loop phonon\nself-energy, we obtain the low temperature T contributions to the phonon\ndispersion law at low momentum, and see that the real part of those can be\nparametrized as a thermal correction to the phonon velocity. Because the\nphonons are the quanta of the sound waves, at low momentum their velocity\nshould agree with the speed of sound. We find that our results match at order\nT^4ln(T) with those predicted by Andreev and Khalatnikov for the speed of\nsound, derived from the superfluid hydrodynamical equations and the phonon\nkinetic theory. We get also higher order corrections of order T^4, which are\nnot reproduced pushing naively the kinetic theory computation. Finally, as an\napplication, we consider the cold Fermi gas in the unitarity limit, and find a\nuniversal expression for the low T relative correction to the speed of sound\nfor these systems."
    },
    {
        "anchor": "Quantum tunneling of a vortex between two pinning potentials: A vortex can tunnel between two pinning potentials in an atomic Bose-Einstein\ncondensate on a time scale of the order of 1s under typical experimental\nconditions. This makes it possible to detect the tunneling experimentally. We\ncalculate the tunneling rate by phenomenologically treating vortices as\npoint-like charged particles moving in an inhomogeneous magnetic field. The\nobtained results are in close agreement with numerical simulations based on the\nstochastic c-field theory.",
        "positive": "Cavity Sub- and Superradiance Enhanced Ramsey Spectroscopy: Ramsey spectroscopy in large, dense ensembles of ultra-cold atoms trapped in\noptical lattices suffers from dipole-dipole interaction induced shifts and\ncollective superradiance limiting its precision and accuracy. We propose a\nnovel geometry implementing fast signal readout with minimal heating for large\natom numbers at lower densities via an optical cavity operated in the weak\nsingle atom but strong collective coupling regime. The key idea is controlled\ncollective transverse $\\pi/2$-excitation of the atoms to prepare a macroscopic\ncollective spin protected from cavity superradiance. This requires that the two\nhalves of the atomic ensemble are coupled to the cavity mode with opposite\nphase, which is naturally realized for a homogeneously filled volume covering\nodd and even sites of the cavity mode along the cavity axis. The origin of the\nsuperior precision can be traced back to destructive interference among\nsub-ensembles in the complex nonlinear collective atom field dynamics. In the\nsame configuration we find surprising regular self-pulsing of the cavity output\nfor suitable continuous illumination. Our simulations for large atom numbers\nemploying a cumulant expansion are qualitatively confirmed by a full quantum\ntreatment of smaller ensembles."
    },
    {
        "anchor": "The Bose-Einstein Condensate of G-wave Molecules and Its Intrinsic\n  Angular Momentum: The recent report on the realization of a Bose-Einstein condensate of G-wave\nmolecule made up of bound pairs of Cesium bosons is a surprise. These molecules\nare created at the G-wave resonance at 19.87G, where the severe three-body loss\nusually associated with these resonance are found to be reduced significantly\nwhen the density of the gas is reduced in a quasi 2D setting. The G-wave\nmolecules produced through this resonance have non-zero angular momentum\nprojections, resulting in the first BEC with a macroscopic intrinsic angular\nmomentum. Here, we show that this intrinsic angular momentum will lead to many\nnew quantum effects. They include a splitting of collective modes in the\nabsence of vortices, an orientation dependent energy shift due to the moment of\ninertia of the molecules, and a contribution to angular momentum in non-uniform\nmagnetic fields different from that of the Berry phase current. The intrinsic\nangular momentum also provides a way to probe the half vortices, excitations\nthat are unique to molecular condensates of bosons. The wavefunction giving\nrise to the intrinsic angular momentum can also be mapped out from the noise\ncorrelation.",
        "positive": "Induced interactions in a superfluid Bose-Fermi mixture: We analyse a Bose-Einstein condensate (BEC) mixed with a superfluid\ntwo-component Fermi gas in the whole BCS-BEC cross-over. Using a quasiparticle\nrandom phase approximation combined with Beliaev theory to describe the Fermi\nsuperfluid and the BEC respectively, we show that the single particle and\ncollective excitations of the Fermi gas give rise to an induced interaction\nbetween the bosons, which varies strongly with momentum and frequency. It\ndiverges at the sound mode of the Fermi superfluid, resulting in a sharp\navoided crossing feature and a corresponding sign change of the interaction\nenergy shift in the excitation spectrum of the BEC. In addition, the excitation\nof quasiparticles in the Fermi superfluid leads to damping of the excitations\nin the BEC. Besides studying induced interactions themselves, these prominent\neffects can be used to systematically probe the strongly interacting Fermi gas."
    },
    {
        "anchor": "Momentum distribution and contacts of one-dimensional spinless Fermi\n  gases with an attractive p-wave interaction: We present a rigorous study of momentum distribution and p-wave contacts of\none dimensional (1D) spinless Fermi gases with an attractive p-wave\ninteraction. Using the Bethe wave function, we analytically calculate the\nlarge-momentum tail of momentum distribution of the model. We show that the\nleading ($\\sim 1/p^{2}$) and sub-leading terms ($\\sim 1/p^{4}$) of the\nlarge-momentum tail are determined by two contacts $C_2$ and $C_4$, which we\nshow, by explicit calculation, are related to the short-distance behaviour of\nthe two-body correlation function and its derivatives. We show as one increases\nthe 1D scattering length, the contact $C_2$ increases monotonically from zero\nwhile $C_4$ exhibits a peak for finite scattering length. In addition, we\nobtain analytic expressions for p-wave contacts at finite temperature from the\nthermodynamic Bethe ansatz equations in both weakly and strongly attractive\nregimes.",
        "positive": "Universal nonanalytic behavior of the Hall conductance in a Chern\n  insulator at the topologically driven nonequilibrium phase transition: We study the Hall conductance of a Chern insulator after a global quench of\nthe Hamiltonian. The Hall conductance in the long time limit is obtained by\napplying the linear response theory to the diagonal ensemble. It is expressed\nas the integral of the Berry curvature weighted by the occupation number over\nthe Brillouin zone. We identify a topologically driven nonequilibrium phase\ntransition, which is indicated by the nonanalyticity of the Hall conductance as\na function of the energy gap m_f in the post-quench Hamiltonian H_f. The\ntopological invariant for the quenched state is the winding number of the\nGreen's function W, which equals the Chern number for the ground state of H_f.\nIn the limit that m_f goes to zero, the derivative of the Hall conductance with\nrespect to m_f is proportional to ln(|m_f|), with the constant of\nproportionality being the ratio of the change of W at m_f = 0 to the energy gap\nin the initial state. This nonanalytic behavior is universal in two-band Chern\ninsulators such as the Dirac model, the Haldane model, or the Kitaev honeycomb\nmodel in the fermionic basis."
    },
    {
        "anchor": "Statistical properties of spectra in harmonically trapped spin-orbit\n  coupled systems: We compute single-particle energy spectra for a one-body hamiltonian\nconsisting of a two-dimensional deformed harmonic oscillator potential, the\nRashba spin-orbit coupling and the Zeeman term. To investigate the statistical\nproperties of the obtained spectra as functions of deformation, spin-orbit and\nZeeman strengths we examine the distributions of the nearest neighbor spacings.\nWe find that the shapes of these distributions depend strongly on the three\npotential parameters. We show that the obtained shapes in some cases can be\nwell approximated with the standard Poisson, Brody and Wigner distributions.\nThe Brody and Wigner distributions characterize irregular motion and help\nidentify quantum chaotic systems. We present a special choices of deformation\nand spin-orbit strengths without the Zeeman term which provide a fair\nreproduction of the fourth-power repelling Wigner distribution. By adding the\nZeeman field we can reproduce a Brody distribution, which is known to describe\na transition between the Poisson and linear Wigner distributions.",
        "positive": "Dipole Mode of Trapped Bose--Fermi Mixture Gas: We investigate dipole modes in a trapped Bose--Fermi mixture gas in the\nnormal phase, composed of single-species bosons and single-species fermions\nwith $s$-wave scattering. In the extremely low temperature regime,\nBose--Einstein statistics and Fermi--Dirac statistics may give rise to an\ninteresting temperature dependence of collective modes. Applying the moment\nmethod to the linearized Boltzmann equation, we study the transition of the\ndipole modes between the hydrodynamic regime and the collisionless regime."
    },
    {
        "anchor": "Discrete solitons of spin-orbit coupled Bose-Einstein condensates in\n  optical lattices: We study localized nonlinear excitations of a dilute Bose-Einstein condensate\n(BEC) with spin-orbit coupling in a deep optical lattice (OL). We use Wannier\nfunctions to derive a tight-binding model that includes the spin-orbit coupling\n(SOC) at the discrete level in the form of a generalized discrete nonlinear\nSch\\\"odinger equation. Spectral properties are investigated and the existence\nand stability of discrete solitons and breathers with different symmetry\nproperties with respect to the OL is demonstrated. We show that the symmetry of\nthe modes can be changed from on-site to inter-site and to asymmetric modes\nsimply by changing the interspecies interaction. Asymmetric modes appear to be\nnovel modes intrinsic of the SOC.",
        "positive": "Feshbach resonant scattering of three fermions in one-dimensional wells: We study the weak-tunnelling limit for a system of cold 40K atoms trapped in\na one-dimensional optical lattice close to an s-wave Feshbach resonance. We\ncalculate the local spectrum for three atoms at one site of the lattice within\na two-channel model. Our results indicate that, for this one-dimensional\nsystem, one- and two-channel models will differ close to the Feshbach\nresonance, although the two theories would converge in the limit of strong\nFeshbach coupling. We also find level crossings in the low-energy spectrum of a\nsingle well with three atoms that may lead to quantum phase transition for an\noptical lattice of many wells. We discuss the stability of the system to a\nphase with non-uniform density."
    },
    {
        "anchor": "Parametric Excitation of a Bose-Einstein Condensate: From Faraday Waves\n  to Granulation: We explore, both experimentally and theoretically, the response of an\nelongated Bose-Einstein condensate to modulated interactions. We identify two\ndistinct regimes differing in modulation frequency and modulation strength.\nLongitudinal surface waves are generated either resonantly or parametrically\nfor modulation frequencies near the radial trap frequency or twice the trap\nfrequency, respectively. The dispersion of these waves, the latter being a\nFaraday wave, is well-reproduced by a mean-field theory that accounts for the\n3D nature of the elongated condensate. In contrast, in the regime of lower\nmodulation frequencies we find that no clear resonances occur, but with\nincreased modulation strength, the condensate forms an irregular granulated\ndistribution that is outside the scope of a mean-field approach. We find that\nthe granulated condensate is characterized by large quantum fluctuations and\ncorrelations, which are well-described with single-shot simulations obtained\nfrom wavefunctions computed by a beyond mean-field theory at zero temperature,\nthe multiconfigurational time-dependent Hartree for bosons method.",
        "positive": "The contact in the unitary Fermi gas across the superfluid phase\n  transition: A quantity known as the contact plays a fundamental role in quantum many-body\nsystems with short-range interactions. The determination of the temperature\ndependence of the contact for the unitary Fermi gas of infinite scattering\nlength has been a major challenge, with different calculations yielding\nqualitatively different results. Here we use finite-temperature auxiliary-field\nquantum Monte Carlo (AFMC) methods on the lattice within the canonical ensemble\nto calculate the temperature dependence of the contact for the homogeneous\nspin-balanced unitary Fermi gas. We extrapolate to the continuum limit for 40,\n66, and 114 particles. We observe a dramatic decrease in the contact as the\nsuperfluid critical temperature is approached from below, followed by a gradual\nweak decrease as the temperature increases in the normal phase. Our results are\nin excellent agreement with the most recent precision ultracold atomic gas\nexperiments. We also present results for the energy of the unitary gas as a\nfunction of temperature in the continuum limit."
    },
    {
        "anchor": "Pseudogap Effects of Fermi Gases in the Presence of A Strong Effective\n  Magnetic Field: We address the important question of how to characterize the normal state of\nfermionic superfluids under the influence of a strong effective magnetic field,\nimplemented through rapid rotation or novel artificial field techniques. We\nconsider the effects of crossing from BCS to BEC and the role of non-condensed\npairs, or pseudogap effects. Using a simple extension of Gor'kov theory we\ndemonstrate how these pairs organize above the transition $T_c$ into precursors\nof a vortex configuration, which are associated with distortions of the ideal\nAbrikosov lattice. This non-uniform normal state appears to enable \"Bose\ncondensation\" in a field which is otherwise problematic due to the effective\none-dimensionality of Landau level dispersion.",
        "positive": "Josephson effects in one-dimensional supersolids: We demonstrate that superflow past an obstacle is possible in a solid phase\nin the one-dimensional Gross-Pitaevskii equation with a finite-range two-body\ninteraction. The phenomenon we find is analogous to the DC Josephson effect in\nsuperconductors and we deduce the \"Josephson relation\" between the current and\nphase difference of the condensates separated by the obstacle. We also discuss\npersistent current and nonclassical rotational inertia in annular container\nwith a penetrable potential barrier. The phase diagram in the plane of the\ncurrent and the interaction strength is given. Our result provides a simple\ntheoretical example of supersolidity in the presence of an obstacle."
    },
    {
        "anchor": "Many-body stabilization of a resonant p-wave Fermi gas in one dimension: Using the asymptotic Bethe Ansatz, we study the stabilization problem of the\none-dimensional spin-polarized Fermi gas confined in a hard-wall potential with\ntunable p-wave scattering length and finite effective range. We find that the\ninterplay of two factors, i.e., the finite interaction range and the hard-wall\npotential, will stabilize the system near resonance. The stabilization occurs\neven in the positive scattering length side, where the system undergoes a\nmany-body collapse if any of the factors is absent. At p-wave resonance, the\nfermion system is found to feature the \"quasi-particle condensation\" for any\nvalue of effective range, which is stabilized if the range is above twice the\nmean particle distance. Slightly away from resonance, the correction to the\nstability condition linearly depends on the inverse scattering length. Finally,\na global picture is presented for the energetics and stability properties of\nfermions from weakly attractive to deep bound state regime. Our results raise\nthe possibility for achieving stable p-wave superfluidity in quasi-1D atomic\nsystems, and meanwhile, shed light on the intriguing s- and p-wave physics in\n1D that violate the Bose-Fermi duality.",
        "positive": "Vortex polygons and their stabilities in Bose-Einstein condensates and\n  field theory: We study vortex polygons and their stabilities in miscible two-component\nBose-Einstein condensates, and find that vortex polygons are stable for the\ntotal circulation $Q \\leq 5$, metastable for $Q = 6$, and unstable for $Q \\geq\n7$. As a related model in high-energy physics, we also study the vortex polygon\nof the baby-Skyrme model with an anti-ferromagnetic potential term, and compare\nboth results."
    },
    {
        "anchor": "Macroscopic boundary effects in the one-dimensional extended\n  Bose-Hubbard model: We study the effect of different open boundary conditions on the insulating\nground states of the one-dimensional extended Bose-Hubbard model at and near\nunit filling. To this end, we employ the density matrix renormalization group\nmethod with system sizes up to 250 sites. To characterize the system, various\norder parameters and entanglement entropies are calculated. When opposite edge\npotentials are added to the two ends of the chain, the inversion symmetry is\nexplicitly broken, and the regular bulk phases appear. On the other hand,\nsimple open boundary conditions often exhibit non-degenerate ground states with\na domain wall in the middle of the chain, which induces a sign-flip of an order\nparameter. Such a domain wall can lead to an algebraic behavior of the\noff-diagonals of the single particle density matrix. We show that this\nalgebraic behavior adds only a finite contribution to the entanglement entropy,\nwhich does not diverge as the system size increases. Therefore, it is not an\nindication of a superfluid phase. We confirm this picture by analytical\ncalculations based on an effective Hamiltonian for a domain wall.",
        "positive": "Chiral twodimensional p-wave superfluid from s-wave pairing in the BEC\n  regime: Twodimensional spin-orbit-coupled Fermi gases subject to s-wave pairing can\nbe driven into a topological phase by increasing the Zeeman spin splitting\nbeyond a critical value. In the topological phase, the system exhibits the\nhallmarks of chiral p-wave superfluidity, including exotic Majorana\nexcitations. Previous theoretical studies of this realization of a\ntwodimensional topological Fermi superfluid have focused on the BCS regime\nwhere the s-wave Cooper pairs are only weakly bound and, hence, the induced\nchiral p-wave order parameter has a small magnitude. Motivated by the goal to\nidentify potential new ways for the experimental realization of robust\ntopological superfluids in ultra-cold atom gases, we study the BCS-to-BEC\ncrossover driven by increasing the Cooper-pair binding energy for this system.\nIn particular, we obtain phase diagrams in the parameter space of two-particle\nbound-state energy and Zeeman spin-splitting energy. Ordinary characteristics\nof the BCS-to-BEC crossover, in particular the shrinking and eventual\ndisappearance of the Fermi surface, are observed in the nontopological phase.\nIn contrast, the topological phase retains all features of chiral p-wave\nsuperfluidity, including a well-defined underlying Fermi surface, even for\nlarge s-wave pair-binding energies. Compared to the BCS limit, the topological\nsuperfluid in the BEC regime turns out to be better realizable even for only\nmoderate magnitude of spin-orbit coupling because the chiral p-wave order\nparameter is generally larger and remnants of s-wave pairing are suppressed. We\nidentify optimal parameter ranges that can aid further experimental\ninvestigations and elucidate the underlying physical reason for the persistence\nof the chiral p-wave superfluid."
    },
    {
        "anchor": "Weyl Semimetal Made Ideal with a Crystal of Raman Light and Atoms: Optical lattices are known for their flexibility to emulate condensed matter\nphysics and beyond. Based on an early theoretical proposal [Science Bulletin\n65, 2080 (2020)], a recent experiment published by Wang et al. [Science 372,\n271 (2021)] accomplishes the first experimental realization of topological band\nstructure of the ideal Weyl semimetal in ultracold atomic matter, prompting\nfundamental interest in the context of gapless topological physics. With a neat\ndesign of 3D spin-orbit interaction, the experiment has probed the gapless band\ntopology through spin texture imaging and quantum quench dynamics. This work\nhas far reaching implications to topological effects and quantum anomaly in\ncondensed matter and high energy physics.",
        "positive": "Fractional-charge vortex dipoles in spinor Bose-Einstein condensates: We theoretically and numerically investigate the generation of\nfractional-charge vortex dipoles in spinor condensates with non-zero\nmagnetization. We find that in the antiferromagnetic phase of spin-1 and spin-2\nand the cyclic phase of spin-2 condensate with non-zero magnetization coupling\nof the density (phonon) and a spin-excitation mode results in two critical\nspeeds for vortex-antivortex pair creation in the condensate. As a result, a\nGaussian obstacle potential moving across the antiferromagnetic spin-1 or\nspin-2 and cyclic spin-2 spinor condensates with non-zero magnetization can\nlead to the creation of fractional-charge vortex dipoles. On the other hand,\nfor zero magnetization, the two modes get decoupled, which is illustrated by a\nsingle critical speed for vortex-antivortex pair creation in the condensate due\nto the phonon excitation mode."
    },
    {
        "anchor": "Quantum simulation of expanding space-time with tunnel-coupled\n  condensates: We consider two weakly interacting quasi-1D condensates of cold bosonic\natoms. It turns out that a time-dependent variation of the tunnel-coupling\nbetween those condensates is equivalent with the spatial expansion of a\none-dimensional toy-Universe with regard to the dynamics of the relative phase\nfield. The dynamics of this field is governed by the quantum sine-Gordon\nequation. Thus, this analogy could be used to 'quantum simulate' the dynamics\nof a scalar, interacting quantum field on an expanding background. We discuss,\nhow to observe the freezing out of quantum fluctuations during an accelerating\nexpansion in a possible experiment. We also discuss an experimental protocol to\nstudy the formation of sine-Gordon breathers in the relative phase field out of\nquantum fluctuations.",
        "positive": "Evidences for interaction-induced Haldane fractional exclusion\n  statistics in one and higher dimensions: Haldane fractional exclusion statistics (FES) has a long history of intense\nstudies, but its realization in physical systems is rare. Here we study\nrepulsively interacting Bose gases at and near a quantum critical point, and\nfind evidences that such strongly correlated gases obey simple non-mutual FES\nover a wide range of interaction strengths in both one and two dimensions.\nBased on exact solutions in one dimension, quantum Monte Carlo simulations and\nexperiments in both dimensions, we show that the thermodynamic properties of\nthese interacting gases, including entropy per particle, density and pressure,\nare essentially equivalent to those of non-interacting particles with FES.\nAccordingly, we establish a simple interaction-to-FES mapping that reveals the\nstatistical nature of particle-hole symmetry breaking induced by interaction in\nsuch quantum many-body systems. Whereas strongly interacting Bose gases reach\nfull fermionization in one dimension, they exhibit incomplete fermionization in\ntwo dimensions. Our results open a route to understanding correlated\ninteracting systems via non-interacting particles with FES in arbitrary\ndimensions."
    },
    {
        "anchor": "Gapped spectrum in pair-superfluid bosons: We study the ground state of a bilayer system of dipolar bosons with dipoles\noriented by an external field perpendicularly to the two parallel planes. By\ndecreasing the interlayer distance, for a fixed value of the strength of the\ndipolar interaction, the system undergoes a quantum phase transition from an\natomic to a pair superfluid. We investigate the excitation spectrum across this\ntransition by using microscopic approaches. Quantum Monte Carlo methods are\nemployed to obtain the static structure factors and intermediate scattering\nfunctions in imaginary time. The dynamic response is calculated using both the\ncorrelated basis functions (CBF) method and the approximate inversion of the\nLaplace transform of the quantum Monte Carlo imaginary time data. In the atomic\nphase, both density and spin excitations are gapless. However, in the\npair-superfluid phase a gap opens in the excitation energy of the spin mode.\nFor small separation between layers, the minimal spin excitation energy equals\nthe binding energy of a dimer and is twice the gap value.",
        "positive": "Reflection of a Lieb-Liniger wave packet from the hard-wall potential: Nonequilibrium dynamics of a Lieb-Liniger system in the presence of the\nhard-wall potential is studied. We demonstrate that a time-dependent wave\nfunction, which describes quantum dynamics of a Lieb-Liniger wave packet\ncomprised of N particles, can be found by solving an $N$-dimensional Fourier\ntransform; this follows from the symmetry properties of the many-body\neigenstates in the presence of the hard-wall potential. The presented formalism\nis employed to numerically calculate reflection of a few-body wave packet from\nthe hard wall for various interaction strengths and incident momenta."
    },
    {
        "anchor": "Complex Langevin study for polarons in an attractively interacting\n  one-dimensional two-component Fermi gas: We investigate a polaronic excitation in a one-dimensional spin-1/2 Fermi gas\nwith contact attractive interactions, using the complex Langevin method, which\nis a promising approach to evade a possible sign problem in quantum Monte Carlo\nsimulations. We found that the complex Langevin method works correctly in a\nwide range of temperature, interaction strength, and population imbalance. The\nFermi polaron energy extracted from the two-point imaginary Green's function is\nnot sensitive to the temperature and the impurity concentration in the\nparameter region we considered. Our results show a good agreement with the\nsolution of the thermodynamic Bethe ansatz at zero temperature.",
        "positive": "Quench Dynamics of Thermal Bose Gases Across Wide and Narrow Feshbach: Using high-temperature virial expansion, we study the quench dynamics of the\nthermal Bose gases near a wide, narrow, and intermediate Feshbach resonance.\nOur results show that the shallow bound state near Feshbach resonance leads to\ninteresting phenomena. Near the wide Feshbach resonance, the long-time\n$\\hat{n}_{\\bf k}$ oscillates when the scattering length $a_{s}$ is quenched\nfrom zero to large but with finite positive values. The oscillation frequency\n$\\omega=E_{\\rm b}/\\hbar$ with $E_{\\rm b}$ being the binding energy. When\n$a_{s}$ is quenched to infinity or negative value, the oscillation vanishes.\nNear the narrow Feshbach resonance, the interaction should be characterized by\na two-channel model. When the background scattering length $a_{\\rm\nbg}\\gtrsim\\lambda$, there is an oscillation in the long-time dynamics, and the\nfrequency is determined by the energy of the shallow bound state in the open\nchannel. When $a_{\\rm bg}<0$ or $0<a_{\\rm bg}\\ll\\lambda$, there is no shallow\nbound state in the open channel, hence no long-time oscillation. We check our\nconclusion using some realistic systems, and the results are consistent with\nour conclusion."
    },
    {
        "anchor": "AC Oscillation of a Spin Soliton Driven by a Constant Force: The phenomena of AC oscillation generated by a DC drive, such as the famous\nJosephson AC effect in superconductors and Bloch oscillation in solid physics,\nare of great interest in physics. Here we report another example of such\ncounter-intuitive phenomenon that a spin soliton in a two-component\nBose-Einstein condensate is driven by a constant force: The initially static\nspin soliton first moves in a direction opposite to the force and then changes\ndirection, showing an extraordinary AC oscillation in a long term. In sharp\ncontrast to the Josephson AC effect and Bloch oscillation, we find that the\nnonlinear interactions play important roles and the spin soliton can exhibit a\nperiodic transition between negative and positive inertial mass even in the\nabsence of periodic potentials. We then develop an explicit quasiparticle model\nthat can account for this extraordinary oscillation satisfactorily. Important\nimplications and possible applications of our finding are discussed.",
        "positive": "Individually tunable tunnelling coefficients in optical lattices using\n  local periodic driving: Ultracold atoms in optical lattices have emerged as powerful quantum\nsimulators of translationally invariant systems with many applications in e.g.\nstrongly-correlated and topological systems. However, the ability to locally\ntune all Hamiltonian parameters remains an outstanding goal that would enable\nthe simulation of a wider range of quantum phenomena. Motivated by recent\nadvances in quantum gas microscopes and optical tweezers, we here show\ntheoretically how local control over individual tunnelling links in an optical\nlattice can be achieved by incorporating local time-periodic potentials. We\npropose to periodically modulate the on-site energy of individual lattice sites\nand employ Floquet theory to demonstrate how this can result in full individual\ncontrol over the tunnelling amplitudes in one dimension. We provide various\nexample configurations realising interesting topological models such as\nextended Su-Schrieffer-Heeger models that would be challenging to realize by\nother means. Extending to two dimensions, we present that local periodic\ndriving in a three-site plaquette allows for full simultaneous control over the\nrelative tunnelling amplitudes and the gauge-invariant flux piercing the\nplaquette, providing a clear stepping stone in building a fully programmable 2D\ntight-binding model. This local modulation scheme is applicable to many\ndifferent lattice geometries."
    },
    {
        "anchor": "Superfluid to normal fluid phase transition in the Bose gas trapped in\n  two dimensional optical lattices at finite temperature: We develop the Hartree-Fock-Bogoliubov theory at finite temperature for Bose\ngas trapped in the two dimensional optical lattices. The on-site energy is\nconsidered low enough that the gas presents superfluid properties. We obtain\nthe condensate density as function of the temperature neglecting the anomalous\ndensity in the thermodynamics equations. The condensate fraction provide two\ncritical temperature. Below the temperature $T_{C1}$ there is one condensate\nfraction. Above two possible fractions merger up to the critical temperature\n$T_{C2}$. Then the gas provides an first order transition at temperature above\n$T_{C2}$ where the condensate fraction is null. We resume by a\nfinite-temperature phase diagram where can be identify three domains: the\nnormal fluid, the superfluid and the superfluid with two possible condensate\nfractions.",
        "positive": "Collective many-body interaction in Rydberg dressed atoms: We present a method to control the shape and character of the interaction\npotential between cold atomic gases by weakly dressing the atomic ground state\nwith a Rydberg level. For increasing particle densities, a crossover takes\nplace from a two-particle interaction into a collective many-body interaction,\nwhere the dipole-dipole/van der Waals Blockade phenomenon between the Rydberg\nlevels plays a dominant role. We study the influence of these collective\ninteraction potential on a Bose-Einstein condensate, and present the optimal\nparameters for its experimental detection."
    },
    {
        "anchor": "Quantum control in strongly driven optical lattices: Matter waves can be coherently and adiabatically loaded and controlled in\nstrongly driven optical lattices. This coherent control is used in order to\nmodify the modulus and the sign of the tunneling matrix element in the\ntunneling Hamiltonian. Our findings pave the way for studies of driven quantum\nsystems and new methods for engineering Hamiltonians that are impossible to\nrealize with static techniques.",
        "positive": "Disordered structures in ultracold spin-imbalanced Fermi gas: We investigate properties of spin-imbalanced ultracold Fermi gas in a large\nrange of spin polarizations at low temperatures. We present results of\nmicroscopic calculations based on mean-field and density functional theory\napproaches, with no symmetry constraints. At low polarization values we predict\nthe structure of the system as consisting of several spin-polarized droplets.\nAs the polarization increases, the system self-organizes into a disordered\nstructures similar to liquid crystals, and energetically they can compete with\nordered structures such as grid-like domain walls. At higher polarizations the\nsystem starts to develop regularities that, in principle, can be called\nsupersolid, where periodic density modulation and pairing correlations coexist.\nThe robustness of the results has been checked with respect to temperature\neffects, dimensionality, and the presence of a trapping potential. Dynamical\nstability has also been investigated."
    },
    {
        "anchor": "Topological superradiant state in Fermi gases with cavity induced\n  spin-orbit coupling: Coherently driven atomic gases inside optical cavities hold great promise for\ngenerating rich dynamics and exotic states of matter. It was shown recently\nthat an exotic topological superradiant state exists in a two-component\ndegenerate Fermi gas coupled to a cavity, where local order parameters coexist\nwith global topological invariants. In this work, we characterize in detail\nvarious properties of this exotic state, focusing on the feedback interactions\nbetween the atoms and the cavity field. In particular, we demonstrate that\ncavity-induced interband coupling plays a crucial role in inducing the\ntopological phase transition between the conventional and topological\nsuperradiant states. We analyze the interesting signatures in the cavity field\nleft by the closing and reopening of the atomic bulk gap across the topological\nphase boundary and discuss the robustness of the topological superradiant state\nby investigating the steady-state phase diagram under various conditions.\nFurthermore, we consider the interaction effect and discuss the interplay\nbetween the pairing order in atomic ensembles and the superradiance of the\ncavity mode. Our work provides many valuable insights into the unique\ncavity--atom hybrid system under study and is helpful for future experimental\nexploration of the topological superradiant state.",
        "positive": "Parametric amplification of matter waves in dipolar spinor Bose-Einstein\n  condensates: Spin-changing collisions may lead under proper conditions to the parametric\namplification of matter waves in spinor Bose-Einstein condensates. Magnetic\ndipole-dipole interactions, although typically very weak in alkaline atoms, are\nshown to play a very relevant role in the amplification process. We show that\nthese interactions may lead to a strong dependence of the amplification\ndynamics on the angle between the trap axis and the magnetic-field orientation.\nWe analyze as well the important role played by magnetic-field gradients, which\nmodify also strongly the amplification process. Magnetic-field gradients must\nbe hence carefully controlled in future experiments, in order to observe\nclearly the effects of the dipolar interactions in the amplification dynamics."
    },
    {
        "anchor": "First and second sound in two-dimensional bosonic and fermionic\n  superfluids: We review our theoretical results about the sound propagation in\ntwo-dimensional (2D) systems of ultracold fermionic and bosonic atoms. In the\nsuperfluid phase, characterized by the spontaneous symmetry breaking of the\n$U(1)$ symmetry, there is the coexistence of first and second sound. In the\ncase of weakly-interacting repulsive bosons, we model the recent measurements\nof the sound velocities of 39K atoms in 2D obtained in the weakly-interacting\nregime and around the Berezinskii-Kosterlitz-Thouless (BKT)\nsuperfluid-to-normal transition temperature. In particular, we perform a quite\naccurate computation of the superfluid density and show that it is reasonably\nconsistent with the experiment. For superfluid attractive fermions, we\ncalculate the first and second sound velocities across the whole BCS-BEC\ncrossover. In the low-temperature regime we reproduce the recent measurements\nof first-sound speed with 6Li atoms. We also predict that only in the\nfinite-temperature BEC regime there is mixing between sound modes.",
        "positive": "Quantum Phases and Collective Excitations in Bose-Hubbard Models with\n  Staggered Magnetic Flux: We study the quantum phases of a Bose-Hubbard model with staggered magnetic\nflux in two dimensions, as has been realized recently [Aidelsburger {\\it et\nal.}, PRL, {\\bf 107}, 255301 (2011)]. Within mean field theory, we show how the\nstructure of the condensates evolves from weak to strong coupling limit,\nexhibiting a tricritical point at the Mott-superfluid transition. Non-trivial\ntopological structures (Dirac points) in the quasi-particle (hole) excitations\nin the Mott state are found within random phase approximation and we discuss\nhow interaction modifies their structures. Excitation gap in the Mott state\ncloses at different ${\\bf k}$ points when approaching the superfluid states,\nwhich is consistent with the findings of mean field theory."
    },
    {
        "anchor": "On the low-energy description for tunnel-coupled one-dimensional Bose\n  gases: We consider a model of two tunnel-coupled one-dimensional Bose gases with\nhard-wall boundary conditions. Bosonizing the model and retaining only the most\nrelevant interactions leads to a decoupled theory consisting of a quantum\nsine-Gordon model and a free boson, describing respectively the antisymmetric\nand symmetric combinations of the phase fields. We go beyond this description\nby retaining the perturbation with the next smallest scaling dimension. This\nperturbation carries conformal spin and couples the two sectors. We carry out a\ndetailed investigation of the effects of this coupling on the non-equilibrium\ndynamics of the model. We focus in particular on the role played by spatial\ninhomogeneities in the initial state in a quantum quench setup.",
        "positive": "From multimode to monomode guided atom lasers: an entropic analysis: We have experimentally demonstrated a high level of control of the mode\npopulations of guided atom lasers (GALs) by showing that the entropy per\nparticle of an optically GAL, and the one of the trapped Bose Einstein\ncondensate (BEC) from which it has been produced are the same. The BEC is\nprepared in a crossed beam optical dipole trap. We have achieved isentropic\noutcoupling for both magnetic and optical schemes. We can prepare GAL in a\nnearly pure monomode regime (85 % in the ground state). Furthermore, optical\noutcoupling enables the production of spinor guided atom lasers and opens the\npossibility to tailor their polarization."
    },
    {
        "anchor": "Quantum Monte Carlo simulations of two-dimensional repulsive Fermi gases\n  with population imbalance: The ground-state properties of two-component repulsive Fermi gases in two\ndimensions are investigated by means of fixed-node diffusion Monte Carlo\nsimulations. The energy per particle is determined as a function of the\nintercomponent interaction strength and of the population imbalance. The regime\nof universality in terms of the s-wave scattering length is identified by\ncomparing results for hard-disk and for soft-disk potentials. In the large\nimbalance regime, the equation of state turns out to be well described by a\nLandau-Pomeranchuk functional for two-dimensional polarons. To fully\ncharacterize this expansion, we determine the polarons' effective mass and\ntheir coupling parameter, complementing previous studies on their chemical\npotential. Furthermore, we extract the magnetic susceptibility from\nlow-imbalance data, finding only small deviations from the mean-field\nprediction. While the mean-field theory predicts a direct transition from a\nparamagnetic to a fully ferromagnetic phase, our diffusion Monte Carlo results\nsuggest that the partially ferromagnetic phase is stable in a narrow interval\nof the interaction parameter. This finding calls for further analyses on the\neffects due to the fixed-node constraint.",
        "positive": "Collective Motion of Polarized Dipolar Fermi Gases in the Hydrodynamic\n  Regime: Recently, a seminal STIRAP experiment allowed the creation of 40K-87Rb\nmolecules in the rovibrational ground state [K.-K. Ni et al., Science 322, 231\n(2008)]. In order to describe such a polarized dipolar Fermi gas in the\nhydrodynamic regime, we work out a variational time-dependent Hartree-Fock\napproach. With this we calculate dynamical properties of such a system as, for\ninstance, the frequencies of the low-lying excitations and the time-of-flight\nexpansion. We find that the dipole-dipole interaction induces anisotropic\nbreathing oscillations in momentum space. In addition, after release from the\ntrap, the momentum distribution becomes asymptotically isotropic, while the\nparticle density becomes anisotropic."
    },
    {
        "anchor": "Probing many-body interactions in an optical lattice clock: We present a unifying theoretical framework that describes recently observed\nmany-body effects during the interrogation of an optical lattice clock operated\nwith thousands of fermionic alkaline earth atoms. The framework is based on a\nmany-body master equation that accounts for the interplay between elastic and\ninelastic p-wave and s-wave interactions, finite temperature effects and\nexcitation inhomogeneity during the quantum dynamics of the interrogated atoms.\nSolutions of the master equation in different parameter regimes are presented\nand compared. It is shown that a general solution can be obtained by using the\nso called Truncated Wigner Approximation which is applied in our case in the\ncontext of an open quantum system. We use the developed framework to model the\ndensity shift and decay of the fringes observed during Ramsey spectroscopy in\nthe JILA 87Sr and NIST 171Yb optical lattice clocks. The developed framework\nopens a suitable path for dealing with a variety of strongly-correlated and\ndriven open-quantum spin systems.",
        "positive": "Edge dynamics of an Integer Quantum Hall system: In this master thesis work the linear and non linear edge dynamics of a\nnon-interacting system of fermions in a Integer Quantum Hall state is\ntheoretically and numerically studied."
    },
    {
        "anchor": "The Adiabatic Transport of Bose-Einstein Condensates in a Double-Well\n  Trap: Case a Small Nonlinearity: A complete adiabatic transport of Bose-Einstein condensate in a double-well\ntrap is investigated within the Landau-Zener (LZ) and Gaussian Landau-Zener\n(GLZ) schemes for the case of a small nonlinearity, when the atomic interaction\nis weaker than the coupling. The schemes use the constant (LZ) and\ntime-dependent Gaussian (GLZ) couplings. The mean field calculations show that\nLZ and GLZ suggest essentially different transport dynamics. Significant\ndeviations from the case of a strong coupling are discussed.",
        "positive": "Transverse Demagnetization Dynamics of a Unitary Fermi Gas: Understanding the quantum dynamics of strongly interacting fermions is a\nproblem relevant to diverse forms of matter, including high-temperature\nsuperconductors, neutron stars, and quark-gluon plasma. An appealing benchmark\nis offered by cold atomic gases in the unitary limit of strong interactions.\nHere we study the dynamics of a transversely magnetized unitary Fermi gas in an\ninhomogeneous magnetic field. We observe the demagnetization of the gas, caused\nby diffusive spin transport. At low temperatures, the diffusion constant\nsaturates to the conjectured quantum-mechanical lower bound $\\simeq \\hbar/m$,\nwhere $m$ is the particle mass. The development of pair correlations,\nindicating the transformation of the initially non-interacting gas towards a\nunitary spin mixture, is observed by measuring Tan's contact parameter."
    },
    {
        "anchor": "Coupling Identical 1D Many-Body Localized Systems: We experimentally study the effects of coupling one-dimensional Many-Body\nLocalized (MBL) systems with identical disorder. Using a gas of ultracold\nfermions in an optical lattice, we artifically prepare an initial charge\ndensity wave in an array of 1D tubes with quasi-random onsite disorder and\nmonitor the subsequent dynamics over several thousand tunneling times. We find\na strikingly different behavior between MBL and Anderson Localization. While\nthe non-interacting Anderson case remains localized, in the interacting case\nany coupling between the tubes leads to a delocalization of the entire system.",
        "positive": "Simulating quantum transport with ultracold atoms and interaction\n  effects: Quantum transport can be simulated with ultracold atoms by employing spin\nsuperpositions of fermions interacting with spin-dependent potentials. Here we\nfirst extend this scheme to an arbitrary number of spin components so as to\nallow simulating transport through a multiterminal quantum dot and derive a\ncurrent formula in terms of a spin rotation matrix and potential phase shifts.\nWe then show that a Fano resonance manifests itself in measuring a linear\nconductance at zero temperature in the case of two spin components. We also\nstudy how a weak interparticle interaction in bulk affects quantum transport in\none dimension with the bosonization and renormalization techniques. In\nparticular, we find that the conductance vanishes for an attractive interaction\ndue to a bulk spin gap, while it is enhanced for a repulsive interaction by a\npower law with lowering the temperature or the chemical potential difference."
    },
    {
        "anchor": "Manifestation of relative phase in dynamics of two interacting Bose-Bose\n  droplets: We study coherent dynamics of two interacting Bose-Bose droplets by means of\nthe extended Gross-Pitaevskii equation. The relative motion of the droplets\ncouples to the phases of their components. The dynamics can be understood in\nterms of the evolution of zero-energy modes recovering symmetries spontaneously\nbroken by the mean-field solution. These are translational symmetry and two\nU(1) symmetries, associated with the phases of the droplets' two components. A\nphase-dependent interaction potential and double Josephson-junction equations\nare introduced to explain the observed variety of different scenarios of\ncollision. We show that the evolution of the droplets is a macroscopic\nmanifestation of the hidden dynamics of their phases. The occurrence of\nnondissipative drag between the two supercurrents (Andreev-Bashkin effect) is\nmentioned.",
        "positive": "Probing ultracold Fermi gases with light-induced gauge potentials: We theoretically investigate the response of a two component Fermi gas to\nvector potentials which couple separately to the two spin components. Such\nvector potentials may be implemented in ultracold atomic gases using optically\ndressed states. Our study indicates that light-induced gauge potentials may be\nused to probe the properies of the interacting ultracold Fermi gas, providing.\namongst other things, ways to measure the superfluid density and the strength\nof pairing."
    },
    {
        "anchor": "The Shear Viscosity in an Anisotropic Unitary Fermi Gas: We consider a system consisting of a strongly interacting, ultracold unitary\nFermi gas under harmonic confinement. Our analysis suggests the possibility of\nexperimentally studying, in this system, an anisotropic shear viscosity tensor\ndriven by the anisotropy in the trapping potential. In particular, we suggest\nthat this experimental setup could mimic some features of anisotropic\ngeometries that have recently been studied for strongly coupled field theories\nwhich have a gravitational dual. Results using the AdS/CFT correspondence in\nthese theories show that in systems with a background linear potential, certain\nviscosity components can be made much smaller than the entropy density,\nparametrically violating the bound proposed by Kovtun, Son and Starinets (KSS).\nThis intuition, along with results from a Boltzmann analysis that we perform,\nsuggests that a violation of the KSS bound can perhaps occur in the unitary\nFermi gas system when it is subjected to a suitable anisotropic trapping\npotential which may be approximated to be linear in a suitable range of\nparameters.\n  We give a concrete proposal for an experimental setup where an anisotropic\nshear viscosity tensor may arise. In such situations, it may also be possible\nto observe a reduction in the spin one component of the shear viscosity from\nits lowest value observed so far in ultracold Fermi gases. In extreme\nanisotropic situations, the reduction may be enough to reduce the shear\nviscosity to entropy ratio below the proposed KSS bound, although this regime\nis difficult to analyze in a theoretically controlled manner.",
        "positive": "Bichromatic State-Insensitive Trapping of Cold 133Cs-87Rb Atomic\n  Mixtures: We investigate simultaneous state-insensitive trapping of a mixture of two\ndifferent atomic species, Caesium and Rubidium. The magic wavelengths of the\nCaesium and Rubidium atoms are different, $935.6$ nm and $789.9$ nm\nrespectively, thus single-frequency simultaneous state-insensitive trapping is\nnot possible. We thus identify bichromatic trapping as a viable approach to\ntune the two magic wavelengths to a common value. Correspondingly, we present\nseveral common magic wavelength combinations appropriate for simultaneous\nstate-insensitive trapping of the two atomic species."
    },
    {
        "anchor": "Two component Bose-Hubbard model with higher angular momentum states: We study a Bose-Hubbard Hamiltonian of ultracold two component gas of spinor\nChromium atoms. Dipolar interactions of magnetic moments while tuned resonantly\nby ultralow magnetic field can lead to spin flipping. Due to approximate axial\nsymmetry of individual lattice site, total angular momentum is conserved.\nTherefore, all changes of the spin are accompanied by the appearance of the\nangular orbital momentum. This way excited Wannier states with non vanishing\nangular orbital momentum can be created. Resonant dipolar coupling of the two\ncomponent Bose gas introduces additional degree of control of the system, and\nleads to a variety of different stable phases. The phase diagram for small\nnumber of particles is discussed.",
        "positive": "Effective-mass tensor of the two-body bound states and the\n  quantum-metric tensor of the underlying Bloch states: By considering an onsite attraction between a spin-$\\uparrow$ and a\nspin-$\\downarrow$ fermion in a multiband tight-binding lattice, here we study\nthe two-body spectrum, and derive an exact relation between the inverse of the\neffective-mass tensor of the lowest bound states and the quantum-metric tensor\nof the underlying Bloch states. In addition to the intraband (or the so-called\nconventional) contribution that depends only on the single-particle spectrum\nand the interband (or the so-called geometric) contribution that is controlled\nby the quantum metric, our generalized relation has an additional interband\ncontribution that depends on the so-called band-resolved quantum metric. All of\nour analytical expressions are applicable to those multiband lattices that\nsimultaneously exhibit time-reversal symmetry and fulfill the condition on\nspatially-uniform pairing. As a nontrivial illustration we analyze the two-body\nproblem in a Kagome lattice with nearest-neighbor hoppings, and show that the\nexact relation provides a perfect benchmark."
    },
    {
        "anchor": "Defect-induced supersolidity with soft-core bosons: More than 40 years ago, Andreev, Lifshitz, and Chester suggested the possible\nexistence of a peculiar solid phase of matter, the microscopic constituents of\nwhich can flow superfluidly without resistance due to the formation of\nzero-point defects in the ground state of self-assembled crystals. Yet, a\nphysical system where this mechanism is unambiguously established remains to be\nfound, both experimentally and theoretically. Here we investigate the\nzero-temperature phase diagram of two-dimensional bosons with finite-range\nsoft-core interactions. For low particle densities, the system is show to\nfeature a solid phase in which zero-point vacancies emerge spontaneously and\ngive rice to superfluid flow of particles through the crystal. This provides\nthe first example of defects-induced, continuous-space supersolidity consistent\nwith the Andreev-Lifshitz-Chester scenario.",
        "positive": "Stability of nonstationary states of spin-1 Bose-Einstein condensates: The stability of nonstationary states of homogeneous spin-1 Bose-Einstein\ncondensates is studied by performing Bogoliubov analysis in a frame of\nreference where the state is stationary. In particular, the effect of an\nexternal magnetic field is examined. It is found that a nonzero magnetic field\nintroduces instability in a $^{23}$Na condensate. The wavelengths of this\ninstability can be controlled by tuning the strength of the magnetic field. In\na $^{87}$Rb condensate this instability is present already at zero magnetic\nfield. Furthermore, an analytical bound for the size of a stable condensate is\nfound, and a condition for the validity of the single-mode approximation is\npresented. Realization of the system in a toroidal trap is discussed and the\nfull time development is simulated."
    },
    {
        "anchor": "Glassy behavior in a binary atomic mixture: We experimentally study one-dimensional, lattice-modulated Bose gases in the\npresence of an uncorrelated disorder potential formed by localized impurity\natoms, and compare to the case of correlated quasi-disorder formed by an\nincommensurate lattice. While the effects of the two disorder realizations are\ncomparable deeply in the strongly interacting regime, both showing signatures\nof Bose glass formation, we find a dramatic difference near the\nsuperfluid-to-insulator transition. In this transition region, we observe that\nrandom, uncorrelated disorder leads to a shift of the critical lattice depth\nfor the breakdown of transport as opposed to the case of correlated\nquasi-disorder, where no such shift is seen. Our findings, which are consistent\nwith recent predictions for interacting bosons in one dimension, illustrate the\nimportant role of correlations in disordered atomic systems.",
        "positive": "Phases and dynamics of ultracold bosons in a tilted optical lattice: We present a brief overview of the phases and dynamics of ultracold bosons in\nan optical lattice in the presence of a tilt. We begin with a brief summary of\nthe possible experimental setup for generating the tilt. This is followed by a\ndiscussion of the effective low-energy model for these systems and its\nequilibrium phases. We also chart the relation of this model to the recently\nstudied system of ultracold Rydberg atoms. Next, we discuss the non-equilibrium\ndynamics of this model for quench, ramp and periodic protocols with emphasis on\nthe periodic drive which can be understood in terms of an analytic, albeit\nperturbative, Floquet Hamiltonian derived using Floquet perturbation theory\n(FPT). Finally, taking cue from the Floquet Hamiltonian of the periodically\ndriven tilted boson chain, we discuss a spin model which exhibits Hilbert space\nfragmentation and exact dynamical freezing for wide range of initial states."
    },
    {
        "anchor": "Optical transport and manipulation of an ultracold atomic cloud using\n  focus-tunable lenses: We present an optical setup with focus-tunable lenses to dynamically control\nthe waist and focus position of a laser beam, in which we transport a trapped\nultracold cloud of 87-Rb over a distance of 28 cm. The scheme allows us to\nshift the focus position at constant waist, providing uniform trapping\nconditions over the full transport length. The fraction of atoms that are\ntransported over the entire distance comes near to unity, while the heating of\nthe cloud is in the range of a few microkelvin. We characterize the position\nstability of the focus and show that residual drift rates in focus position can\nbe compensated for by counteracting with the tunable lenses. Beyond being a\ncompact and robust scheme to transport ultracold atoms, the reported control of\nlaser beams makes dynamic tailoring of trapping potentials possible. As an\nexample, we steer the size of the atomic cloud by changing the waist size of\nthe dipole beam.",
        "positive": "Variational ansatz for $p$-wave fermions confined in a one-dimensional\n  harmonic trap: We propose a very accurate and efficient variational scheme for the ground\nstate of the system of $p$-wave attractively interacting fermions confined in a\none-dimensional harmonic trap. By the construction, the method takes the\nnon-analytical part of interactions exactly into account and thus it\napproximates the true ground-state wave function in a whole range of\ninteractions very accurately. Within the method, we determine different\nproperties of the system for a different number of particles and different\ninteractions. In this way, we explore how the system and its features transit\nfrom the ideal non-interacting Fermi gas to the system of infinitely strong\nattractions. Additionally, we demonstrate that the ansatz may also be used on a\nrepulsive branch of interactions where other numerical methods break down. The\npresented method of including zero-range interactions is very universal and may\nbe easily generalized to other one-dimensional confinements."
    },
    {
        "anchor": "Oscillating solitons in a three component BEC: We investigate the properties of three component BEC systems with spin\nexchange interactions. We consider different coupling constants from those\nleading to exact solutions known in the literature. When two solitons collide,\nan oscillation of the emerging entities is observed. This behavior seems to be\ngeneric. A mathematical model is derived for the emerging solitons. It\ndescribes the new oscillatory phenomenon extremely well. Surprisingly, the\nmodel is exact as a solution to the initial equations. This comes as a bonus.",
        "positive": "Roton excitations in a trapped dipolar Bose-Einstein condensate: We consider the quasi-particle excitations of a trapped dipolar Bose-Einstein\ncondensate. By mapping these excitations onto radial and angular momentum we\nshow that the roton modes are clearly revealed as discrete fingers in parameter\nspace, whereas the other modes form a smooth surface. We examine the properties\nof the roton modes and characterize how they change with the dipole interaction\nstrength. We demonstrate how the application of a perturbing potential can be\nused to engineer angular rotons, i.e. allowing us to controllably select modes\nof non-zero angular momentum to become the lowest energy rotons."
    },
    {
        "anchor": "Collective excitations of a trapped Fermi gas at finite temperature: We study collective excitations of a trapped Fermi gas at finite temperature\nusing the Bogoliubov-deGennes mean-field theory in conjunction with the\ngeneralized random phase approximation. The collective excitations are analyzed\nthrough the density response of a monopole excitation. We show the appearance\nof several modes at the normal fluid - superfluid phase transition temperature:\nHiggs mode-like pairing amplitude modulations, analogues of the second sound in\nthe trapped gas, and an edge mode that is also the strongest mode in the\nresponse.",
        "positive": "Implementing quantum electrodynamics with ultracold atomic systems: We discuss the experimental engineering of model systems for the description\nof QED in one spatial dimension via a mixture of bosonic $^{23}$Na and\nfermionic $^6$Li atoms. The local gauge symmetry is realized in an optical\nsuperlattice, using heteronuclear boson-fermion spin-changing interactions\nwhich preserve the total spin in every local collision. We consider a large\nnumber of bosons residing in the coherent state of a Bose-Einstein condensate\non each link between the fermion lattice sites, such that the behavior of\nlattice QED in the continuum limit can be recovered. The discussion about the\nrange of possible experimental parameters builds, in particular, upon\nexperiences with related setups of fermions interacting with coherent samples\nof bosonic atoms. We determine the atomic system's parameters required for the\ndescription of fundamental QED processes, such as Schwinger pair production and\nstring breaking. This is achieved by benchmark calculations of the atomic\nsystem and of QED itself using functional integral techniques. Our results\ndemonstrate that the dynamics of one-dimensional QED may be realized with\nultracold atoms using state-of-the-art experimental resources. The experimental\nsetup proposed may provide a unique access to longstanding open questions for\nwhich classical computational methods are no longer applicable."
    },
    {
        "anchor": "Entanglement Spectroscopy and probing the Li-Haldane Conjecture in\n  Topological Quantum Matter: Topological phases are characterized by their entanglement properties, which\nis manifest in a direct relation between entanglement spectra and edge states\ndiscovered by Li and Haldane. We propose to leverage the power of synthetic\nquantum systems for measuring entanglement via the Entanglement Hamiltonian to\nprobe this relationship experimentally. This is made possible by exploiting the\nquasi-local structure of Entanglement Hamiltonians. The feasibility of this\nproposal is illustrated for two paradigmatic examples realizable with current\ntechnology, an integer quantum Hall state of non-interacting fermions on a 2D\nlattice and a symmetry protected topological state of interacting fermions on a\n1D chain. Our results pave the road towards an experimental identification of\ntopological order in strongly correlated quantum many-body systems.",
        "positive": "Beating dark-dark solitons and Zitterbewegung in spin-orbit coupled\n  Bose-Einstein condensates: We present families of beating dark-dark solitons in spin-orbit (SO) coupled\nBose-Einstein condensates. These families consist of solitons residing\nsimultaneously in the two bands of the energy spectrum. The soliton components\nare characterized by two different spatial and temporal scales, which are\nidentified by a multiscale expansion method. The solitons are \"beating\" ones,\nas they perform density oscillations with a characteristic frequency, relevant\nto Zitterbewegung (ZB). We find that spin oscillations may occur, depending on\nthe parity of each soliton branch, which consequently lead to ZB oscillations\nof the beating dark solitons. Analytical results are corroborated by numerical\nsimulations, illustrating the robustness of the solitons."
    },
    {
        "anchor": "On-demand generation of dark soliton trains in Bose-Einstein condensates: Matter-wave interference mechanisms in one-dimensional Bose-Einstein\ncondensates that allow for the controlled generation of dark soliton trains\nupon choosing suitable box-type initial configurations are described. First,\nthe direct scattering problem for the defocusing nonlinear Schr\\\"odinger\nequation with nonzero boundary conditions and general box-type initial\nconfigurations is discussed, and expressions for the discrete spectrum\ncorresponding to the dark soliton excitations generated by the dynamics are\nobtained. It is found that the size of the initial box directly affects the\nnumber, size and velocity of the solitons, while the initial phase determines\nthe parity of the solutions. The analytical results are compared to those of\nnumerical simulations of the Gross-Pitaevskii equation, both in the absence and\nin the presence of a harmonic trap. The numerical results bear out the\nanalytical results with excellent agreement.",
        "positive": "Dynamical Anderson transition in one-dimensional periodically kicked\n  incommensurate lattices: We study the dynamical localization transition in a one-dimensional\nperiodically kicked incommensurate lattice, which is created by perturbing a\nprimary optical lattice periodically with a pulsed weaker incommensurate\nlattice. The diffusion of wave packets in the pulsed optical lattice exhibits\neither extended or localized behaviors, which can be well characterized by the\nmean square displacement and the spatial correlation function. We show that the\ndynamical localization transition is relevant to both the strength of\nincommensurate potential and the kicked period, and the transition point can be\nrevealed by the information entropy of eigenfunctions of the Floquet\npropagator."
    },
    {
        "anchor": "Repulsive to attractive interaction quenches of 1D Bose gas in a\n  harmonic trap: We consider quantum quenches of harmonically trapped one-dimensional bosons\nfrom repulsive to attractive interactions, and the resulting breathing dynamics\nof the so-called `super-Tonks-Girardeau' (sTG) state. This state is highly\nexcited compared to the ground state of the attractive gas, and is the lowest\neigenstate where the particles are not bound or clustered. We analyze the\ndynamics from a spectral point of view, identifying the relevant eigenstates of\nthe interacting trapped many-body system, and analyzing the nature of these\nquantum eigenstates. To obtain explicit eigenspectra, we use Hamiltonians with\nfinite-dimensional Hilbert spaces to approximate the Lieb-Liniger system. We\nemploy two very different approximate approaches: an expansion in a truncated\nsingle-particle harmonic-trap basis and a lattice (Bose-Hubbard) model. We show\nhow the breathing frequency, identified with the energy difference between the\nsTG state and another particular eigenstate, varies with interaction.",
        "positive": "Berry phase for a Bose gas on a one-dimensional ring: We study a system of strongly interacting one-dimensional (1D) bosons on a\nring pierced by a synthetic magnetic flux tube. By the Fermi-Bose mapping, this\nsystem is related to the system of spin-polarized non-interacting electrons\nconfined on a ring and pierced by a solenoid (magnetic flux tube). On the ring\nthere is an external localized delta-function potential barrier $V(\\phi)=g\n\\delta(\\phi-\\phi_0)$. We study the Berry phase associated to the adiabatic\nmotion of delta-function barrier around the ring as a function of the strength\nof the potential $g$ and the number of particles $N$. The behavior of the Berry\nphase can be explained via quantum mechanical reflection and tunneling through\nthe moving barrier which pushes the particles around the ring. The barrier\nproduces a cusp in the density to which one can associate a missing charge\n$\\Delta q$ (missing density) for the case of electrons (bosons, respectively).\nWe show that the Berry phase (i.e., the Aharonov-Bohm phase) cannot be\nidentified with the quantity $\\Delta q/\\hbar \\oint \\mathbf{A}\\cdot\nd\\mathbf{l}$. This means that the missing charge cannot be identified as a\n(quasi)hole. We point out to the connection of this result and recent studies\nof synthetic anyons in noninteracting systems. In addition, for bosons we study\nthe weakly-interacting regime, which is related to the strongly interacting\nelectrons via Fermi-Bose duality in 1D systems."
    },
    {
        "anchor": "Dynamics of shock waves in a superfluid unitary Fermi gas: We study the formation and dynamics of shock waves initiated by a repulsive\npotential in a superfluid unitary Fermi gas by using the order-parameter\nequation. In the theoretical framework, the regularization process of shock\nwaves mediated by the quantum pressure term is purely dispersive. Our results\nshow good agreement with the experiment of Joseph {\\it et al}. [Phys. Rev.\nLett. {\\bf 106}, 150401 (2011)]. We reveal that the boxlike-shaped density peak\nobserved in the experiment consists of many vortex rings due to the transverse\ninstability of the dispersive shock wave. In addition, we study the transition\nfrom a sound wave to subsonic shock waves by increasing the strength of the\nrepulsive potential and show a strong qualitative change in the propagation\nspeed of the wavefronts. In the relatively small strength regime, the speed\ndecreases below the sound speed with increasing the strength as a scaling\nbehavior, while in the large regime the speed remains almost unchanged, which\nis found to be the same expansion speed of the proliferation of the vortex\nrings.",
        "positive": "Collapse of spin-orbit coupled Bose-Einstein condensates: A finite-size quasi two-dimensional Bose-Einstein condensate collapses if the\nattraction between atoms is sufficiently strong. Here we present a theory of\ncollapse for condensates with the interatomic attraction and spin-orbit\ncoupling. We consider two realizations of spin-orbit coupling: the axial Rashba\ncoupling and balanced, effectively one-dimensional, Rashba-Dresselhaus one. In\nboth cases spin-dependent \"anomalous\" velocity, proportional to the spin-orbit\ncoupling strength, plays a crucial role. For the Rashba coupling, this velocity\nforms a centrifugal component in the density flux opposite to that arising due\nto the attraction between particles and prevents the collapse at a sufficiently\nstrong coupling. For the balanced Rashba-Dresselhaus coupling, the\nspin-dependent velocity can spatially split the initial state in one dimension\nand form spin-projected wavepackets, reducing the total condensate density.\nDepending on the spin-orbit coupling strength, interatomic attraction, and the\ninitial state, this splitting either prevents the collapse or modifies the\ncollapse process. These results show that the collapse can be controlled by a\nspin-orbit coupling, thus, extending the domain of existence of condensates of\nattracting atoms."
    },
    {
        "anchor": "Real-space dynamics of attractive and repulsive polarons in\n  Bose-Einstein condensates: We investigate the formation of a Bose polaron when a single impurity in a\nBose-Einstein condensate is quenched from a non-interacting to an attractively\ninteracting state in the vicinity of a Feshbach resonance. We use a\nbeyond-Fr\\\"ohlich Hamiltonian to describe both sides of the resonance and a\ncoherent-state variational ansatz to compute the time evolution of boson\ndensity profiles in position space. We find that on the repulsive side of the\nFeshbach resonance, the Bose polaron performs long-lived oscillations, which is\nsurprising given that the two-body problem has only one bound state coupled to\na continuum. They arise due to interference between multiply occupied bound\nstates and therefore can be only found with many-body approaches such as the\ncoherent-state ansatz. This is a distinguishing feature of the Bose polaron\ncompared to the Fermi polaron where the bound state can be occupied only once.\nWe derive an implicit equation for the frequency of these oscillations and show\nthat it can be approximated by the energy of the two-body bound state. Finally,\nwe consider an impurity introduced at non-zero velocity and find that, on the\nrepulsive side, it is periodically slowed down or even arrested before speeding\nup again.",
        "positive": "Driven collective instabilities in magneto-optical traps: a\n  fluid-dynamical approach: We present a theoretical model to describe an instability mechanism in\nultra-cold gases, where long-range interactions are taken into account.\nFocusing on the nonlinear coupling between the collective (plasma-like) and the\ncenter-of-mass modes, we show that the resulting dynamics is governed by a\nparametric equation of the generalized Mathieu type and compute the\ncorresponding stability chart. We apply our model to typical ranges of\nmagneto-optical traps (MOT) parameters and find a good agreement with previous\nexperimental observations."
    },
    {
        "anchor": "Localization of an inhomogeneous Bose-Einstein condensate in a moving\n  random potential: We study the dynamics of a harmonically trapped quasi-one-dimensional\nBose-Einstein condensate subjected to a moving disorder potential of finite\nextent. We show that, due to the inhomogeneity of the sample, only a percentage\nof the atoms is localized at supersonic velocities of a random potential. We\nfind that this percentage can be sensitively increased by introducing suitable\ncorrelations in the disorder potential such as those provided by random dimers.",
        "positive": "Correlations in the low-density Fermi gas: Fermi-Liquid state,\n  Dimerization, and BCS Pairing: We present ground state calculations for low-density Fermi gases described by\ntwo model interactions, an attractive square-well potential and a Lennard-Jones\npotential, of varying strength. We use the optimized Fermi-Hypernetted Chain\nintegral equation method which has been proved to provide, in the density\nregimes of interest here, an accuracy better than one percent. We first examine\nthe low-density expansion of the energy and compare with the exact answer by\nHuang and Yang (H. Huang and C. N. Yang, {\\em Phys. Rev.\\/} {\\bf 105}, 767\n(1957)). It is shown that a locally correlated wave function of the\nJastrow-Feenberg type does not recover the quadratic term in the expansion of\nthe energy in powers of $\\a0\\KF$, where $\\a0$ is the vacuum $s$-wave scattering\nlength and $\\KF$ the Fermi wave number. The problem is cured by adding\nsecond-order perturbation corrections in a correlated basis. Going to higher\ndensities and/or more strongly coupled systems, we encounter an instability of\nthe normal state of the system which is characterized by a divergence of the\n{\\em in-medium\\/} scattering length. We interpret this divergence as a\nphonon-exchange driven dimerization of the system, similar to what one has at\nzero density when the vacuum scattering length $\\a0$ diverges. We then study,\nin the stable regime, the superfluid gap and its dependence on the density and\nthe interaction strength. We identify two different corrections to low-density\nexpansions: One is medium corrections to the pairing interaction, and the other\none finite-range corrections. We show that the most important finite-range\ncorrections are a direct manifestation of the many-body nature of the system."
    },
    {
        "anchor": "Scheme to Equilibrate the Quantized Hall Response of Topological Systems\n  from Coherent Dynamics: Two-dimensional topologically distinct insulators are separated by\ntopological gapless points, which exist as Weyl points in three-dimensional\nmomentum space. Slowly varying parameters in the two-dimensional Hamiltonian\nacross two distinct phases therefore necessarily experiences the gap closing\nprocess, which prevents the intrinsic physical observable, the Hall response,\nfrom equilibrating. To equilibrate the Hall response, engineered laser noises\nwere introduced at the price of destroying the quantum coherence. Here we\ndemonstrate a new scheme to equilibrate the quantized Hall response from pure\ncoherent dynamics as the Hamiltonian is slowly tuned from the topologically\ntrivial to nontrivial regimes. We show the elements that affect the process of\nequilibration including the sequence when the electric field is switched on,\nits strength and the band dispersion of the final Hamiltonian. We further apply\nour method to Weyl semimetals in three dimensions and find the equilibrated\nHall response despite the underlying gapless band structure. Our finding not\nonly lays the theoretical foundation for observing the two-dimensional\ntopological phase transition but also for observing and controlling Weyl\nsemimetals in ultracold atomic gases.",
        "positive": "Magnetic domains in 2D moir\u00e9 lattices with square and hexagonal\n  symmetry: We report the persistence of magnetic domains lying in moir\\'e patterns with\nsquare and hexagonal symmetries. Our investigation is based on the dynamical\ndescription of two magnetic domains represented by a two species bosonic\nmixture of $^{87}$Rb ultracold atoms, being each specie initially localized in\nthe left and right halves of a moir\\'e lattice defined by a specific angle\n$\\theta$. To demonstrate the persistence of such initial domains, we follow the\ntime evolution of the superfluid spin texture, and in particular, the\nmagnetization on each halve. The two-component superfluid, confined in the\nmoir\\'e pattern plus a harmonic trap, was described through the time dependent\nGross-Pitaevskii coupled equations for moir\\'e lattices having $90 \\times 90$\nsites. Results showed the existence of rotation-angle-dependent structures for\nwhich the initial magnetic domain is preserved for both, square and hexagonal\nmoir\\'e patterns; above $\\theta >10^\\circ$ the initial magnetic domain is never\ndestroyed. Stationary magnetic states for a single component Bose condensate\nallowed us to identify the lattice parameter associated with moir\\'e crystals\nthat emerge for twisting angles belonging to the intervals $\\theta \\in\n\\left(0^\\circ ,30^\\circ \\right)$ and $\\theta \\in \\left(0^\\circ ,45^\\circ\n\\right)$ for hexagonal and square geometries respectively."
    },
    {
        "anchor": "Dissipation-enhanced collapse singularity of a nonlocal fluid of light\n  in a hot atomic vapor: We study the out-of-equilibrium dynamics of a two-dimensional paraxial fluid\nof light using a near-resonant laser propagating through a hot atomic vapor. We\nobserve a double shock-collapse instability: a shock (gradient catastrophe) for\nthe velocity, as well as an annular (ring-shaped) collapse singularity for the\ndensity. We find experimental evidence that this instability results from the\ncombined effect of the nonlocal photon-photon interaction and the linear photon\nlosses. The theoretical analysis based on the method of characteristics reveals\nthe main counterintuitive result that dissipation (photon losses) is\nresponsible for an unexpected enhancement of the collapse instability. Detailed\nanalytical modeling makes it possible to evaluate the nonlocality range of the\ninteraction. The nonlocality is controlled by adjusting the atomic vapor\ntemperature and is seen to increase dramatically when the atomic density\nbecomes much larger than one atom per cubic wavelength. Interestingly, such a\nlarge range of the nonlocal photon-photon interaction has not been observed in\nan atomic vapor so far and its microscopic origin is currently unknown.",
        "positive": "Chiral Dynamics of Ultracold Atoms under a Tunable SU(2) Synthetic Gauge\n  Field: Surface currents emerge in superconductors exposed to magnetic fields, and\nare a key signature of the Meissner effect. Analogously, chiral dynamics were\nobserved in quantum simulators under synthetic Abelian gauge fields. The\nflexible control of these simulators also facilitates the engineering of\nnon-Abelian gauge fields, but their impact on the chiral dynamics remains\nelusive. Here, by employing the cutting-edge momentum-lattice technique, we\nimplement a synthetic SU(2) gauge field in a spinful 1D ladder and study the\nrich chiral dynamics therein. We confirm the non-Abelian nature of the\nsynthetic potential by observing the non-Abelian Aharonov-Bohm effect on a\nsingle plaquette. More importantly, the chiral current along the two legs of\nthe ladder is observed to be spin-dependent and highly tunable through the\nparameters of the gauge potential. We experimentally map out different dynamic\nregimes of the chiral current, and reveal the underlying competition between\noverlaying flux ladders with distinct spin compositions. Our experiment\ndemonstrates the dramatic impact of non-Abelian gauge fields on the system\ndynamics, paving the way for future studies of exotic synthetic gauge fields on\nthe versatile platform of momentum lattices."
    },
    {
        "anchor": "Making statistics work: a quantum engine in the BEC-BCS crossover: Heat engines convert thermal energy into mechanical work both in the\nclassical and quantum regimes. However, quantum theory offers genuine\nnonclassical forms of energy, different from heat, which so far have not been\nexploited in cyclic engines to produce useful work. We here experimentally\nrealize a novel quantum many-body engine fuelled by the energy difference\nbetween fermionic and bosonic ensembles of ultracold particles that follows\nfrom the Pauli exclusion principle. We employ a harmonically trapped superfluid\ngas of $^6$Li atoms close to a magnetic Feshbach resonance which allows us to\neffectively change the quantum statistics from Bose-Einstein to Fermi-Dirac. We\nreplace the traditional heating and cooling strokes of a quantum Otto cycle by\ntuning the gas between a Bose- Einstein condensate of bosonic molecules and a\nunitary Fermi gas (and back) through a magnetic field. The quantum nature of\nsuch a Pauli engine is revealed by contrasting it to a classical thermal engine\nand to a purely interaction-driven device. We obtain a work output of several\n$10^6$ vibrational quanta per cycle with an efficiency of up to $25\\%$. Our\nfindings establish quantum statistics as a useful thermodynamic resource for\nwork production, shifting the paradigm of energy-conversion devices to a new\nclass of emergent quantum engines.",
        "positive": "Emergence of damped-localized excitations of the Mott state due to\n  disorder: A key aspect of ultracold bosonic quantum gases in deep optical lattice\npotential wells is the realization of the strongly interacting Mott insulating\nphase. Many characteristics of this phase are well understood, however little\nis known about the effects of a random external potential on its gapped\nquasiparticle and quasihole low-energy excitations. In the present study we\ninvestigate the effect of disorder upon the excitations of the Mott insulating\nstate at zero temperature described by the Bose-Hubbard model. Using a\nfield-theoretical approach we obtain a resummed expression for the disorder\nensemble average of the spectral function. Its analysis shows that disorder\nleads to an increase of the effective mass of both quasiparticle and quasihole\nexcitations. Furthermore, it yields the emergence of damped states, which\nexponentially decay during propagation in space and dominate the whole band\nwhen disorder becomes comparable to interactions. We argue that such\ndamped-localized states correspond to single-particle excitations of the\nBose-glass phase."
    },
    {
        "anchor": "Probing surface states with many-body wave packet scattering: The scattering of 1D matter wave bright solitons on attractive potentials\nenables one to populate bound states, a feature impossible with noninteracting\nwave packets. Compared to noninteracting states, the populated states are\nrenormalized by the attractive interactions between atoms and keep the same\ntopology. This renormalization can even transform a virtual state into a bound\nstate. By switching off adiabatically the interactions, the trapped wave\npackets converge towards the true noninteracting bound states. Our numerical\nstudies show how such scattering experiments can reveal and characterize the\nsurface states of a periodic structure whose translational invariance has been\nbroken. We provide evidence that the corresponding 3D regime should be\naccessible with current techniques.",
        "positive": "Trion and Dimer Formation of Three-Color Fermions: We study the problem of three ultracold fermions in different hyperfine\nstates loaded into a lattice with spatial dimension D=1,2. We consider\nSU(3)-symmetric attractive interactions and also eventually include a\nthree-body constraint, which mimics the effect of three-body losses in the\nstrong-loss regime. We combine exact diagonalization with the Lanczos\nalgorithm, and evaluate both the eigenvalues and the eigenstates of the\nproblem. In D=1, we find that the ground state is always a three-body bound\nstate (trion) for arbitrarily small interaction, while in D=2, due to the\nstronger influence of finite-size effects, we are not able to provide\nconclusive evidence of the existence of a finite threshold for trion formation.\nOur data are however compatible with a threshold value which vanishes\nlogarithmically with the size of the system. Moreover we are able to identify\nthe presence of a fine structure inside the spectrum, which is associated with\noff-site trionic states. The characterization of these states shows that only\nthe long-distance behavior of the eigenstate wavefunctions provides clear-cut\nsignatures about the nature of bound states and that onsite observables are not\nenough to discriminate between them. The inclusion of a three-body constraint\ndue to losses promotes these off-site trions to the role of lowest energy\nstates, at least in the strong-coupling regime."
    },
    {
        "anchor": "Dissipative Preparation of Antiferromagnetic Order in the Fermi-Hubbard\n  Model: The Fermi-Hubbard model is one of the key models of condensed matter physics,\nwhich holds a potential for explaining the mystery of high-temperature\nsuperconductivity. Recent progress in ultracold atoms in optical lattices has\npaved the way to studying the model's phase diagram using the tools of quantum\nsimulation, which emerged as a promising alternative to the numerical\ncalculations plagued by the infamous sign problem. However, the temperatures\nachieved using elaborate laser cooling protocols so far have been too high to\nshow the appearance of antiferromagnetic and superconducting quantum phases\ndirectly. In this work, we demonstrate that using the machinery of dissipative\nquantum state engineering, one can efficiently prepare antiferromagnetic order\nin present-day experiments with ultracold fermions. The core of the approach is\nto add incoherent laser scattering in such a way that the antiferromagnetic\nstate emerges as the dark state of the driven-dissipative dynamics. In order to\nelucidate the development of the antiferromagnetic order we employ two\ncomplementary techniques: Monte Carlo wave function simulations for small\nsystems and a recently proposed variational method for open quantum systems,\noperating in the thermodynamic limit. The controlled dissipation channels\ndescribed in this work are straightforward to add to already existing\nexperimental setups.",
        "positive": "Dynamical detection of topological charges: We propose a generic scheme to characterize topological phases via detecting\ntopological charges by quench dynamics. A topological charge is defined as the\nchirality of a monopole at Dirac or Weyl point of spin-orbit field, and\ntopological phases can be classified by total charges in the region enclosed by\nthe so-called band-inversion surfaces (BISs). We show that both the topological\nmonopoles and BISs can be identified by non-equilibrium spin dynamics caused by\na sequence of quenches. From an emergent dynamical field given by time-averaged\nspin textures, the topological charges, as well as the topological invariant,\ncan be readily obtained. An explicit advantage in this scheme is that only a\nsingle spin component needs to be measured to detect all the information of the\ntopological phase. We numerically examine two realistic models, and propose a\nfeasible experimental setup for the measurement. This work opens a new way to\ndynamically classify topological phases."
    },
    {
        "anchor": "Heavy-Light Few Fermion Clusters at Unitarity: We examine the physics of two, three, and four heavy fermions interacting\nwith a single light fermion via short-range interactions. Four-particle bosonic\nEfimov states have proven important experimentally and also been the subject of\nsignificant theoretical effort. Similar fermionic systems are just now being\ninvestigated. We find that with some simple interactions the four- and\nfive-particle states collapse to the interaction range at smaller mass ratios\nthan the three-body state, and also before larger clusters can collapse. These\nstates and their excitations can be studied in cold atom experiments, providing\nunique insights into the role of few-body systems in many-body physics.",
        "positive": "Universal three-body recombination and Efimov resonances in an ultracold\n  Li-Cs mixture: We study Efimov resonances via three-body loss in an ultracold two-component\ngas of fermionic $^6$Li and bosonic $^{133}$Cs atoms close to a Feshbach\nresonance at 843~G, extending results reported previously [Pires \\textit{et\nal.}, Phys. Rev. Lett. 112, 250404 (2014)] to temperatures around 120~nK. The\nexperimental scheme for reaching lower temperatures is based upon compensating\nthe gravity-induced spatial separation of the mass-imbalanced gases with\nbichromatic optical dipole traps. We observe the first and second excited\nLi-Cs-Cs Efimov resonance in the magnetic field dependence of the three-body\nevent rate constant, in good agreement with the universal zero-range theory at\nfinite temperature [Petrov and Werner, Phys. Rev. A 92, 022704 (2015)].\nDeviations are found for the Efimov ground state, and the inelasticity\nparameter $\\eta$ is found to be significantly larger than those for\nsingle-species systems."
    },
    {
        "anchor": "Second Sound in Ultracold Atomic Gases: We provide an overview of the recent theoretical and experimental advances in\nthe study of second sound in ultracold atomic gases. Starting from the Landau\ntwo fluid hydrodynamic equations we develop the theory of first and second\nsound in various configurations characterized by different geometries and\nquantum statistics. These include the weakly interacting 3D Bose gas, the\nstrongly interacting Fermi gas at unitarity in the presence of highly elongated\ntraps and the dilute 2D Bose gas, characterized by the\nBerezinskii-Kosterlitz-Thouless transition. An explicit comparison with the\npropagation of second sound in liquid Helium is carried out to elucidate the\nmain analogies and differences. We also make an explicit comparison with the\navailable experimental data and point out the crucial role played by the\nsuperfluid density in determining the temperature dependence of the second\nsound speed.",
        "positive": "Universal nature and finite-range corrections in elastic atom-dimer\n  scattering below the dimer breakup threshold: We investigate universal behavior in elastic atom-dimer scattering below the\ndimer breakup threshold calculating the atom-dimer effective-range function\n$ak\\cot\\delta$. Using the He-He system as a reference, we solve the\nSchr\\\"odinger equation for a family of potentials having different values of\nthe two-body scattering length $a$ and we compare our results to the universal\nzero-range form deduced by Efimov,\n$ak\\cot\\delta=c_1(ka)+c_2(ka)\\cot[s_0\\ln(\\kappa_*a)+\\phi(ka)]$, for selected\nvalues of the three-body parameter $\\kappa_*$. Using the parametrization of the\nuniversal functions $c_1,c_2,\\phi$ given in the literature, a good agreement\nwith the universal formula is obtained after introducing a particular type of\nfinite-range corrections. Furthermore, we show that the same parametrization\ndescribes a very different system: nucleon-deuteron scattering below the\ndeuteron breakup threshold. Our analysis confirms the universal character of\nthe process, and relates the pole energy in the effective-range function of\nnucleon-deuteron scattering to the three-body parameter $\\kappa_*$."
    },
    {
        "anchor": "Negative differential conductivity in an interacting quantum gas: Negative differential conductivity (NDC) is a widely exploited effect in\nmodern electronic components. Here, a proof-of-principle is given for the\nobservation of NDC in a quantum transport device for neutral atoms employing a\nmulti-mode tunneling junction. The transport of the many-body quantum system is\ngoverned by the interplay between the tunnel coupling, the interaction energy\nand the thermodynamics of intrinsic collisions, which turn the coherent\ncoupling into a hopping process. The resulting current voltage characteristics\nexhibit NDC, for which we identify a new microscopic physical mechanism. Our\nstudy opens new ways for the future implementation and control of complex\nneutral atom quantum circuits.",
        "positive": "Tunable anisotropic magnetism in trapped two-component Bose gases: We theoretically address magnetic ordering at zero and finite temperature in\nboth homogeneous and trapped Bose-Bose mixtures in optical lattices. By using\nBosonic Dynamical Mean-Field Theory, we obtain the phase diagram of the\nhomogeneous two-component Bose-Hubbard model in a three-dimensional (3D) cubic\nlattice, which features competing magnetic order of XY-ferromagnetic and\nanti-ferromagnetic type in addition to the Mott and superfluid states. We show\nthat these magnetic phases persist also in the presence of a harmonic trap."
    },
    {
        "anchor": "Observation of pair condensation in the quasi-2D BEC-BCS crossover: The condensation of fermion pairs lies at the heart of superfluidity.\nHowever, for strongly correlated systems with reduced dimensionality the\nmechanisms of pairing and condensation are still not fully understood. In our\nexperiment we use ultracold atoms as a generic model system to study the phase\ntransition from a normal to a condensed phase in a strongly interacting\nquasi-two-dimensional Fermi gas. Using a novel method, we obtain the in situ\npair momentum distribution of the strongly interacting system and observe the\nemergence of a low-momentum condensate at low temperatures. By tuning\ntemperature and interaction strength we map out the phase diagram of the\nquasi-2D BEC-BCS crossover.",
        "positive": "Reply to the Comment on \"Berezinskii-Kosterlitz-Thouless Transition in\n  Two-Dimensional Dipolar Stripes\": This is a Reply to the Comment from F. Cinti and M. Boninsegni on our recent\nwork on the Berezinskii-Kosterlitz-Thouless (BKT) phase transition in a\ntwo-dimensional dipolar system [R.Bomb\\'in, F. Mazzanti and J. Boronat,\nPhysical Review A 100, 063614 (2019)]. The main criticism about our work,\nexpressed in that Comment, is that we did not explicitly report the two spatial\ncontributions to the total superfluid fraction. Here, we analyze our results\nfor a point of the phase diagram corresponding to the stripe phase, close to\nthe gas to stripe transition line, and for a temperature below the BKT critical\ntemperature. The scaling with the system size of the contribution to the\nsuperfluid fraction, coming from the direction in which spatial order appears,\nshows that it remains finite in the thermodynamic limit, as we already stated\nin our original work. This allow us to state that the stripe phase is\nsuperfluid at low temperatures. Furthermore, we offer some comments that help\nto understand where the differences between the results of Cinti and Boninsegni\nand ours comes from."
    },
    {
        "anchor": "Momentum distribution and ordering in mixtures of ultracold light and\n  heavy fermionic atoms: The momentum distribution is one of the most important quantities which\nprovides information about interactions in many-body systems. At the same time\nit is a quantity that can easily be accessed in experiments on ultracold atoms.\nIn this paper, we consider mixtures of light and heavy fermionic atoms in an\noptical lattice described effectively by the Falicov-Kimball model. Using a\nMonte Carlo method, we study how different ordered density-wave phases can be\ndetected by measurement of the momentum distribution of the light atoms. We\nalso demonstrate that ordered phases can be seen in Bragg scattering\nexperiments. Our results indicate that the main factor that determines the\nmomentum distribution of the light atoms is the trap confinement. On the other\nhand, the pattern formed by the heavy atoms seen in the Bragg scattering\nexperiments is very sensitive to the temperature and possibly can be used in\nlow-temperature thermometry.",
        "positive": "Spin Turbulence in a Trapped Spin-1 Spinor Bose--Einstein Condensate: We numerically study spin turbulence in a two-dimensional trapped spin-1\nspinor Bose--Einstein condensate, focusing on the energy spectrum. The spin\nturbulence in the trapped system is generated by instability of the helical\nstructure of the spin density vector in the initial state. Our numerical\ncalculation finds that in the trapped system the spectrum of the spin-dependent\ninteraction energy in the ferromagnetic case exhibits a -7/3 power law, which\nwas confirmed in a uniform system by our previous study. The relation between\nthe -7/3 power law and the motion of the spin density vector is discussed by\ninvestigating the orbits of dynamical variables in the spin space."
    },
    {
        "anchor": "A Sawtooth Permanent Magnetic Lattice for Ultracold Atoms and BECs: We propose a new permanent magnetic lattice for creating periodic arrays of\nIoffe-Pritchard permanent magnetic microtraps for holding and controlling\nultracold atoms and Bose-Einstein condensates (BECs). Lattice can be designed\non thin layer of magnetic films such as $Tb_6$$Gd_10$$Fe_{80}$$Co_4$. In\ndetails, we investigate single layer and two crossed layers of sawtooth\nmagnetic patterns with thicknesses of 50 and 500nm respectively with a\nperiodicity of 1$\\mu$m. Trap depth and frequencies can be changed via an\napplied bias field to handle tunneling rates between lattice sites. We present\nanalytical expressions and using numerical calculations show that this lattice\nhas non-zero potential minima to avoid majorana spin flips. One advantage of\nthis lattice over previous ones is that it is easier to manufacture.",
        "positive": "Dark soliton collisions in a toroidal Bose-Einstein condensate: We study the dynamics of two gray solitons in a Bose-Einstein condensate\nconfined by a toroidal trap with a tight confinement in the radial direction.\nGross-Pitaevskii simulations show that solitons can be long living objects\npassing through many collisional processes. We have observed quite different\nbehaviors depending on the soliton velocity. Very slow solitons, obtained by\nperturbing the stationary solitonic profile, move with a constant angular\nvelocity until they collide elastically and move in the opposite direction\nwithout showing any sign of lowering their energy. In this case the density\nnotches are always well separated and the fronts are sharp and straight. Faster\nsolitons present vortices around the notches, which play a central role during\nthe collisions. We have found that in these processes the solitons lose energy,\nas the outgoing velocity turns out to be larger than the incoming one. To study\nthe dynamics, we model the gray soliton state with a free parameter that is\nrelated to the soliton velocity. We further analyze the energy, soliton\nvelocity and turning points in terms of such a free parameter, finding that the\nmain features are in accordance with the infinite one-dimensional system."
    },
    {
        "anchor": "Spontaneous quantum Hall effect in an atomic spinor Bose-Fermi mixture: We study a mixture of spin-$1$ bosonic and spin-$1/2$ fermionic cold atoms,\ne.g., $^{87}$Rb and $^{6}$Li, confined in a triangular optical lattice. With\nfermions at $3/4$ filling, Fermi surface nesting leads to spontaneous formation\nof various spin textures of bosons in the ground state, such as collinear,\ncoplanar and even non-coplanar spin orders. The phase diagram is mapped out\nwith varying boson tunneling and Bose-Fermi interactions. Most significantly,\nin one non-coplanar state the mixture is found to exhibit a spontaneous quantum\nHall effect in fermions and crystalline superfluidity in bosons, both driven by\ninteraction.",
        "positive": "Discrete Symmetry Breaking Transitions Between Paired Superfluids: We explore the zero-temperature phase diagram of bosons interacting via\nFeshbach resonant pairing interactions in one dimension. Using DMRG (Density\nMatrix Renormalization Group) and field theory techniques we characterize the\nphases and quantum phase transitions in this low-dimensional setting. We\nprovide a broad range of evidence in support of an Ising quantum phase\ntransition separating distinct paired superfluids, including results for the\nenergy gaps, correlation functions and entanglement entropy. In particular, we\nshow that the Ising correlation length, order parameter and critical properties\nare directly accessible from a ratio of the atomic and molecular two-point\nfunctions. We further demonstrate that both the zero-momentum occupation\nnumbers and the visibility are in accordance with the absence of a purely\natomic superfluid phase. We comment on the connection to recent studies of\nboson pairing in a generalized classical XY model."
    },
    {
        "anchor": "Excited state quantum phase transition and Loschmidt echo spectra in a\n  spinor Bose-Einstein condensate: Identifying dynamical signatures of excited state quantum phase transitions\n(ESQPTs) in experimentally realizable quantum many-body systems is helpful for\nunderstanding the dynamical effects of ESQPTs. In such systems, the highly\ncontrollable spinor Bose-Einstein condensates (BECs) offer an exceptional\nplatform to study ESQPTs. In this work, we investigate the dynamical\ncharacteristics of the ESQPT in spin-$1$ BEC by means of the Loschmidt echo\nspectrum. The Loschmidt echo spectrum is an extension of the well-known\nLoschmidt echo and definded as the overlaps between the evolved state and the\nexcited states of the initial Hamiltonian. We show that both the time evolved\nand long time averaged Loschmidt echo spectrum undergo a remarkable change as\nthe system passes through the critical point of the ESQPT. Moreover, the\nparticular behavior exhibited by the Loschmidt echo spectrum at the critical\npoint stand as a dynamical detector for probing the ESQPT. We further\ndemonstrate how to capture the features of the ESQPT by using the energy\ndistribution associated with the Loschmidt echo spectrum for time evolved and\nlong time averaged cases, respectrively. Our findings contribute to a further\nverification of the usefulness of the Loschmidt echo spectrum for witnessing\nvarious quantum phase transitions in many-body systems and provide a new way to\nexperimentally examine the dynamical consequences of ESQPTs.",
        "positive": "Entangled Superfluids: We study the condensate dynamics of the so-called entangled Bose-Einstein\ncondensation (EBEC), which is the ground state of a mixture of two species of\npseudospin-$\\frac{1}{2}$ atoms with interspecies spin-exchange scattering in\ncertain parameter regimes. EBEC leads to four inter-dependent superfluid\ncomponents, each corresponding to the orbital wave function associated with a\nspin component of a species. The four superflows have various\ncounter-relations, and altogether lead to a conserved total supercurrent and a\nconserved total spin supercurrent. In the homogenous case, we also obtain the\nelementary excitations due to variations of the single-particle orbital wave\nfunctions, by exactly solving the generalized time-dependent Bogoliubov\nequations. There are three gapless Bogoliubov modes and one Klein-Gordon-like\ngapped mode. The origin of these excitations are also discussed from the\nperspective of spontaneous breaking of the symmetries possessed by the system."
    },
    {
        "anchor": "Topological polaritons from photonic Dirac cones coupled to excitons in\n  a magnetic field: We introduce an alternative scheme for creating topological polaritons\n(topolaritons) by exploiting the presence of photonic Dirac cones in photonic\ncrystals with triangular lattice symmetry. As recently proposed, topolariton\nstates can emerge from a coupling between photons and excitons combined with a\nperiodic exciton potential and a magnetic field to open up a topological gap.\nWe show that in photonic crystals the opening of the gap can be substantially\nsimplified close to photonic Dirac points. Coupling to Zeeman-split excitons\nbreaks time reversal symmetry and allows to gap out the Dirac cones in a\nnon-trival way, leading to a topological gap similar to the strength of the\nperiodic exciton potential. Compared to the original topolariton proposal\n[Karzig {\\em et al}, PRX {\\bf 5}, 031001 (2015)], this scheme significantly\nincreases the size of the topological gap over a wide range of parameters.\nMoreover, the gap opening mechanism highlights an interesting connection\nbetween topolaritons and the Haldane and Raghu scheme [Haldane and Raghu, PRL\n{\\bf 100}, 013904 (2008)] to create topological photons in magneto-optically\nactive materials.",
        "positive": "Direct observation of quantum phonon fluctuations in a one dimensional\n  Bose gas: We report the first direct observation of collective quantum fluctuations in\na continuous field. Shot-to-shot atom number fluctuations in small sub-volumes\nof a weakly interacting ultracold atomic 1D cloud are studied using \\textit{in\nsitu} absorption imaging and statistical analysis of the density profiles. In\nthe cloud centers, well in the \\textit{quantum quasicondensate} regime, the\nratio of chemical potential to thermal energy is $\\mu/ k_B T\\simeq4$, and,\nowing to high resolution, up to 20% of the microscopically observed\nfluctuations are quantum phonons. Within a non-local analysis at variable\nobservation length, we observe a clear deviation from a classical field\nprediction, which reveals the emergence of dominant quantum fluctuations at\nshort length scales, as the thermodynamic limit breaks down."
    },
    {
        "anchor": "Excitation spectra of strongly interacting bosons in the flat-band Lieb\n  lattice: The strongly correlated bosons in flat band systems are an excellent platform\nto study a wide range of quantum phenomena. Such systems can be realized in\noptical lattices filled with ultracold atomic gases. In this paper we study the\nBose-Hubbard model in the Lieb lattice by means of the time-dependent\nGutzwiller mean-field approach. We find that in the Mott insulator phase the\nexcitation modes are gapped and display purely particle or purely hole\ncharacter, while in the superfluid phase the excitation spectrum is gapless.\nThe geometry of the Lieb lattice leads to a non-uniform order parameter and\nnon-uniform oscillation energy in the ground state. This results in additional\nanti-crossings between dispersive bands in the excitation spectra, while the\nflat bands remain insensitive to this effect. We analyze the oscillations of\nthe order parameter on the sublattices as well as the particle-hole character\nof the excitations. For certain model parameters we find simultaneous pure\nphase and pure amplitude oscillations within the same mode, separated between\nthe sublattices. Also, we propose a simple method to differentiate between the\nhole- and particle superfluid regions in the Lieb lattice by in-situ\nmeasurement of the atom population on the sublattices.",
        "positive": "Nonlocal quantum superpositions of bright matter-wave solitons and\n  dimers: The scattering of bright quantum solitons at barrier potentials in\none-dimensional geometries is investigated. Such protocols have been predicted\nto lead to the creation of nonlocal quantum superpositions. The centre-of-mass\nmotion of these bright matter-wave solitons generated from attractive\nBose-Einstein condensates can be analysed with the effective potential\napproach. An application to the case of two particles being scattered at a\ndelta potential allows analytical calculations not possible for higher particle\nnumbers as well as a comparison with numerical results. Both for the dimer and\na soliton with particle numbers on the order of N = 100, we investigate the\nsignatures of the coherent superposition states in an interferometric setup and\nargue that experimentally an interference pattern would be particularly well\nobservable in the centre-of-mass density. Quantum superposition states of\nultra-cold atoms are interesting as input states for matter-wave interferometry\nas they could improve signal-to-noise ratios."
    },
    {
        "anchor": "Counter-propagating edge modes and topological phases of a kicked\n  quantum Hall system: A periodically driven quantum Hall system in a fixed magnetic field is found\nto exhibit a series of phases featuring anomalous edge modes with the \"wrong\"\nchirality. This leads to pairs of counter-propagating chiral edge modes at each\nedge, in sharp contrast to stationary quantum Hall systems. We show that the\npair of Floquet edge modes are protected by the chiral (sublattice) symmetry,\nand that they are robust against static disorder. The existence of distinctive\nphases with the same Chern and winding numbers but very different edge state\nspectra points to the important role played by symmetry in classifying\ntopological properties of driven systems. We further explore the evolution of\nthe edge states with driving using a simplified model, and discuss their\nexperimental signatures.",
        "positive": "Cold Atoms in Driven Optical Lattices: The center of mass dynamics of cold atoms and the Bose-Einstein condensate in\none dimensional optical lattice is considered both in the absence and in the\npresence of external forcing. We discuss three situations for matter waves:\nfirst, the cold atoms; second, sufficiently dilute condensate where the\ndynamics are governed by the single particle wave packet dynamics; third,\nstrong interaction regime, where, inter-atomic interaction can no longer be\nignored. The analytical formalism developed for the two regimes, namely, deep\noptical lattice and shallow optical lattice. Parametric dependencies of energy\nspectrum and classical period, revival time and super revival are explained for\nthe two regimes.\n  The dynamics of condensate in driven optical lattice crystal are analyzed by\nstudying dynamical stability of the condensate. The stability is determined by\nthe dispersion behavior of the condensate excited in driven optical lattice.\nThe recurrence behavior of the condensate close to the nonlinear resonances is\nanalyzed as a function of time for delicate recurrences which take place for\ninstance when lattice is weakly perturbed and robust recurrences which may\nmanifest themselves for sufficiently strong external driving force.\n  The analysis is not only valid for dilute condensate but also applicable for\nstrongly interacting homogeneous condensate provided, the external modulation\ncauses no significant change in density profile of the condensate. We explain\nparametric dependence of the dynamical recurrence times which can easily be\nrealized in laboratory experiments. In addition, we find a good agreement\nbetween the obtained analytical results and numerical calculations. The\nstability of condensate is also explored in driven optical lattice numerically."
    },
    {
        "anchor": "Snake instability of dark solitons across the BEC-BCS crossover: an\n  effective field theory perspective: In the present article the snake instability mechanism for dark solitons in\nsuperfluid Fermi gases is studied in the context of a recently developed\neffective field theory [Eur. Phys. J. B 88, 122 (2015)]. This theoretical\ntreatment has proven to be suitable to study stable dark solitons in quasi-1D\nsetups across the BEC-BCS crossover. In this manuscript the nodal plane of the\nstable soliton solution is perturbed by adding a transverse modulation. The\nnumerical solution of the system of coupled nonlinear differential equations\ndescribing the amplitude of the perturbation leads to the instability spectra\nwhich are calculated for a wide range of interaction regimes and compared to\nother theoretical predictions. The maximum transverse size that the atomic\ncloud can have in order to preserve the stability is estimated, and the effects\nof spin-imbalance on this critical length are examined, revealing a\nstabilization of the soliton with increasing imbalance.",
        "positive": "Extracting the Mott gap from energy measurements in trapped atomic gases: We show that the measure of the so-called {\\it release-energy}, which is an\nexperimentally accessible quantity, makes it possible to assess the value of\nthe Mott gap in the presence of the confinement potential that is unavoidable\nin the actual experimental setup. Indeed, the curve of the release-energy as a\nfunction of the total number of particles shows kinks that are directly related\nto the existence of excitation gaps. Calculations are presented within the\nGutzwiller approach, but the final results go beyond this simple approximation\nand represent a genuine feature of the real system. In the case of harmonic\nconfinement, the Mott gaps may be renormalized with respect to the uniform\ncase. On the other hand, in the case of the recently proposed off-diagonal\nconfinement, our results show an almost perfect agreement with the homogeneous\ncase."
    },
    {
        "anchor": "Exploring the grand-canonical phase diagram of interacting bosons in\n  optical lattices by trap squeezing: In this paper we theoretically discuss how quantum simulators based on\ntrapped cold bosons in optical lattices can explore the grand-canonical phase\ndiagram of homogeneous lattice boson models, via control of the trapping\npotential independently of all other experimental parameters (trap squeezing).\nBased on quantum Monte Carlo, we establish the general scaling relation linking\nthe global chemical potential to the Hamiltonian parameters of the Bose-Hubbard\nmodel in a parabolic trap, describing cold bosons in optical lattices; we find\nthat this scaling relation is well captured by a modified Thomas-Fermi scaling\nbehavior - corrected for quantum fluctuations - in the case of high enough\ndensity and/or weak enough interactions, and by a mean-field Gutzwiller Ansatz\nover a much larger parameter range. The above scaling relation allows to\ncontrol experimentally the chemical potential, independently of all other\nHamiltonian parameters, via trap squeezing; given that the global chemical\npotential coincides with the local chemical potential in the trap center,\nmeasurements of the central density as a function of the chemical potential\ngives access to the information on the bulk compressibility of the Bose-Hubbard\nmodel. Supplemented with time-of-flight measurements of the coherence\nproperties, the measurement of compressibility enables one to discern among the\nvarious possible phases realized by bosons in an optical lattice with or\nwithout external (periodic or random) potentials -- e.g. superfluid, Mott\ninsulator, band insulator, and Bose glass. We theoretically demonstrate the\ntrap-squeezing investigation of the above phases in the case of bosons in a\none-dimensional optical lattice, and in a one-dimensional incommensurate\nsuperlattice.",
        "positive": "Vortex Dynamics in an Annular Bose-Einstein Condensate: We theoretically show that the topology of a non-simply-connected annular\natomic Bose-Einstein condensate enforces the inner surface waves to be always\nexcited with outer surface excitations and that the inner surface modes are\nassociated with induced vortex dipoles unlike the surface waves of a\nsimply-connected one with vortex monopoles. Consequently, under stirring to\ndrive an inner surface wave, a peculiar population oscillation between the\ninner and outer surface is generated regardless of annulus thickness. Moreover,\na new vortex nucleation process by stirring is observed that can merge the\ninner vortex dipoles and outer vortex into a single vortex inside the annulus.\nThe energy spectrum for a rotating annular condensate with a vortex at the\ncenter also reveals the distinct connection of the Tkachenko modes of a vortex\nlattice to its inner surface excitations."
    },
    {
        "anchor": "Polarization of a Bose-Einstein Condensate of Photons in a Dye-Filled\n  Microcavity: We measure the polarization of a photon gas in a dye-filled microcavity. The\npolarization is obtained by a single-shot measurement of the Stokes parameters.\nWe find that the polarization of both the thermal cloud and the Bose-Einstein\ncondensate of photons (phBEC) does not differ from shot to shot. In the case of\nthe phBEC, we find that the polarization correlates with the polarization of\nthe pump pulse. The polarization of the thermal cloud is independent of\nparameters varied in the experiment and is governed by a hidden anisotropy in\nthe system.",
        "positive": "The influence of local correlations on the phase states in the model of\n  semi-hard-core bosons on a square lattice: The work considers a model of charged \"semi-hard-core\" bosons on a square\nlattice with a possible filling number at each node, ranging from 0 to 2.\nTemperature phase diagrams of the model are obtained using numerical Monte\nCarlo quantum simulation methods, and the influence of local charge\ncorrelations is examined. Comparison with results from mean-field methods shows\nthat local charge correlations contribute to an increased role of quantum\nfluctuations in the formation of phase states."
    },
    {
        "anchor": "Hybrid synchronization in coupled ultracold atomic gases: We study the time evolution of two coupled many-body quantum systems one of\nwhich is assumed to be Bose condensed. Specifically, we consider two ultracold\natomic clouds populating each two localized single-particle states, i.e. a\ntwo-component Bosonic Josephson junction. The cold atoms cloud can retain its\ncoherence when coupled to the condensate and displays synchronization with the\nlatter, differing from usual entrainment. We term this effect among the\nultracold and the condensed clouds as {\\it hybrid synchronization}. The onset\nof synchronization, which we observe in the evolution of average properties of\nboth gases when increasing their coupling, is found to be related to the\nmany-body properties of the quantum gas, e.g. condensed fraction, quantum\nfluctuations of the particle number differences. We discuss the effects of\ndifferent initial preparations, the influence of unequal particle numbers for\nthe two clouds, and explore the dependence on the initial quantum state, e.g.\ncoherent state, squeezed state and Fock state, finding essentially the same\nphenomenology in all cases.",
        "positive": "Thermodynamic signatures for topological phase transitions to Majorana\n  and Weyl superfluids in ultracold Fermi gases: We discuss the thermodynamic signatures for the topological phase transitions\ninto Majorana and Weyl superfluid phases in ultracold Fermi gases in two and\nthree dimensions in the presence of Rashba spin-orbit coupling and a Zeeman\nfield. We analyze the thermodynamic properties exhibiting the distinct nature\nof the topological phase transitions linked with the Majorana fermions (2D\nFermi gas) and Weyl fermions (3D Fermi gas) which can be observed\nexperimentally, including pressure, chemical potential, isothermal\ncompressibility, entropy, and specific heat, as a function of the interaction\nand the Zeeman field at both zero and finite temperatures. We conclude that\namong the various thermodynamic quantities, the isothermal compressibility and\nthe chemical potential as a function of the artificial Zeeman field have the\nstrongest signatures of the topological transitions in both two and three\ndimensions."
    },
    {
        "anchor": "Realistic Rashba and Dressehaus spin-orbit coupling for neutral atoms: We describe a new class of atom-laser coupling schemes which lead to\nspin-orbit coupled Hamiltonians for ultra-cold neutral atoms. By properly\nsetting the optical phases, a pair of degenerate pseudospin states emerge as\nthe lowest energy states in the spectrum, and are thus immune to collisionally\ninduced decay. These schemes use $N$ cyclically coupled ground or metastable\ninternal states. We specialize to two situations: a three level case giving\nfixed Rashba coupling, and a four-level case that adds a controllable\nDresselhaus contribution. We describe an implementation of the four level\nscheme for $\\Rb87$ and analyze the sensitivity of our approach to realistic\nexperimental limitations and imperfections. Lastly, we argue that no laser\ncoupling scheme can give pure Rashba or Dresselhaus coupling: akin to condensed\nmatter systems, higher order terms spoil the symmetry of these couplings.\nHowever, for sufficiently intense laser fields the continuous rotational\nsymmetry approximately holds, making the Rashba Hamiltonian applicable for cold\natoms.",
        "positive": "Creating, probing, and manipulating fractionally charged excitations of\n  fractional Chern insulators in optical lattices: We propose a set of schemes to create and probe fractionally charged\nexcitations of a fractional Chern insulator state in an optical lattice. This\nincludes the creation of localized quasiparticles and quasiholes using both\nstatic local defects and the dynamical local insertion of synthetic flux\nquanta. Simulations of repulsively interacting bosons on a finite square\nlattice with experimentally relevant open boundary conditions show that already\na four-particle system exhibits signatures of charge fractionalization in the\nquantum-Hall-like state at the filling fraction of $1/2$ particle per flux\nquantum. This result is favorable for the prospects of adiabatic preparation of\nfractional Chern insulators. Our work is inspired by recent experimental\nbreakthroughs in atomic quantum gases: the realization of strong artificial\nmagnetic fields in optical lattices, the ability of single-site addressing in\nquantum gas microscopes, and the preparation of low-entropy insulating states\nby engineering an entropy-absorbing metallic reservoir."
    },
    {
        "anchor": "Quantum dynamics with spatiotemporal control of interactions in a stable\n  Bose-Einstein condensate: Optical control of atomic interactions in a quantum gas is a long-sought goal\nof cold atom research. Previous experiments have been hindered by short\nlifetimes and parasitic deformation of the trap potential. Here, we develop and\nimplement a generic scheme for optical control of Feshbach resonance in quantum\ngases, which yields long condensate lifetimes sufficient to study equilibrium\nand non-equilibrium physics with negligible parasitic dipole force. We show\nthat fast and local control of interactions leads to intriguing quantum\ndynamics in new regimes, highlighted by the formation of van der Waals\nmolecules and partial collapse of a Bose condensate.",
        "positive": "Theoretical analysis of super-Bloch oscillations: Several recent studies have investigated the dynamics of cold atoms in\noptical lattices subject to AC forcing; the theoretically predicted\nrenormalization of the tunneling amplitudes has been verified experimentally.\nRecent observations include global motion of the atom cloud, such as giant\n\"Super-Bloch Oscillations\" (SBOs). We show that, in order to understand\nunexplained features of SBOs, in addition to the renormalization of the\ntunneling, a new and important phase correction must be included. For Fermionic\nsystems with strong attractive interactions, one may engineer different types\nof collisions and recollisions between bound-pairs and unpaired atoms."
    },
    {
        "anchor": "Properties of the density-wave phase of a two-dimensional dipolar Fermi\n  gas: The rapid progress in the production and cooling of molecular gases indicates\nthat experimental studies of quantum gases with a strong dipolar interaction is\nsoon within reach. Dipolar gases are predicted to exhibit very rich physics\nincluding quantum liquid crystal phases such as density-waves as well as\nsuperfluid phases, both of which play an important role for our understanding\nof strongly correlated systems. Here, we investigate the zero temperature\nproperties of the density-wave phase of a two-dimensional (2D) system of\nfermonic dipoles using a conserving Hartree-Fock theory. We calculate the\namplitude of the density waves as a function of the dipole moment and\norientation with respect to the 2D plane. The stripes give rise to a 1D\nBrillouin zone structure, and the corresponding quasiparticle spectrum is shown\nto have gapped as well as gapless regions around the Fermi surface. As a\nresult, the system remains compressible in the density-wave phase, and it\ncollapses for strong attraction. We show that the density-waves has clear\nsignatures in the momentum distribution and in the momentum correlations. Both\ncan be measured in time-of-flight experiments. Finally, we discuss how the\nstriped phase can be realised with experimentally available systems.",
        "positive": "Effect of nonzero temperature to condensed fraction of a homogeneous\n  dilute weakly interacting Bose gas: We investigate the effect of non-zero temperature to the condensate fraction\nof a homogeneous dilute weakly interacting Bose gas in very low-temperature\nregion. Within inproved Hartree-Fock approximation, the\nCornwall-Jackiw-Tomboulis effective action approach shows that the thermal\nfluctuations make the condensate fraction decrease as a second and fourth-order\npower law of temperature. The result is compared with experimental data.\nIndeed, the effect of non-infinite size of the trap is also integrated."
    },
    {
        "anchor": "Correlations in low-dimensional quantum gases: Ultracold gases are a versatile platform to simulate condensed matter\nphysics, as virtually any parameter is experimentally tunable. In particular,\nhighly anisotropic traps allow the realization of low-dimensional systems,\nwhere the role of quantum fluctuations is enhanced. I investigate the\nparadigmatic model of a one-dimensional Bose gas with contact interactions,\na.k.a the Lieb-Liniger model, using powerful analytical tools such as Bethe\nAnsatz, Conformal Field Theory and the Tomonaga-Luttinger liquid formalism, as\nwell as the Bose-Fermi mapping. The effect of an additional harmonic trap in\nthe longitudinal direction is studied within the Local Density Approximation.\nThese methods allow to investigate with high accuracy its ground-state\nthermodynamics of the gas, its excitation spectra and correlation functions,\nfrom the k-body local correlations to the momentum distribution and the\ndynamical structure factor. These quantities characterize the coherence and\nsuperfluidity of the gas. In particular, I study the drag force exerted by a\nweak gaussian barrier stirred into the gas within linear response theory. Then,\nI investigate the appearance of a multimode structure obtained by releasing a\ntransverse trapping, and the dimensional crossover in the limit of an infinite\nnumber of transverse modes.",
        "positive": "Strongly interacting Bose-Fermi mixtures in one dimension: We study one-dimensional strongly interacting Bose-Fermi mixtures by both the\nexact Bethe-ansatz method and variational perturbation theory within the\ndegenerate ground state subspace of the system in the infinitely repulsive\nlimit. Based on the exact solution of the one-dimensional Bose-Fermi gas with\nequal boson-boson and boson-fermion interaction strengths, we demonstrate that\nthe ground state energy is degenerate for different Bose-Fermi configurations\nand the degeneracy is lifted when the interaction deviates the infinitely\ninteracting limit. We then show that the ground properties in the strongly\ninteracting regime can be well characterized by using the variational\nperturbation method within the degenerate ground state subspace, which can be\napplied to deal with more general cases with anisotropic interactions and in\nexternal traps. Our results indicate that the total ground-state density\nprofile in the strongly repulsive regime behaves like the polarized\nnoninteracting fermions, whereas the density distributions of bosons and\nfermions display different properties for different Bose-Fermi configurations\nand are sensitive to the anisotropy of interactions."
    },
    {
        "anchor": "Mobile impurity in a one-dimensional quantum gas: Exact diagonalization\n  in the Bethe Ansatz basis: We consider a mobile impurity particle injected into a one-dimensional\nquantum gas. The time evolution of the system strongly depends on whether the\nmass of the impurity and the masses of the host particles are equal or not. For\nequal masses, the model is Bethe Ansatz solvable, but for unequal masses, the\nmodel is no longer integrable and the Bethe Ansatz technique breaks down. We\nconstruct a controllable numerical method of computing the spectrum of the\nmodel with a finite number of host particles, based on exact diagonalization of\nthe Hamiltonian in the truncated basis of the Bethe Ansatz states. We\nillustrate our approach on a few-body system of 5+1 particles, and trace the\nevolution of the spectrum depending on the mass ratio of the impurity and the\nhost particles.",
        "positive": "Bose-Einstein Condensation and Many-Body Localization of Rotational\n  Excitations of Polar Molecules: We study theoretically the collective dynamics of rotational excitations of\npolar molecules loaded into an optical lattice in two dimensions. These\nexcitations behave as hard-core bosons with a relativistic energy dispersion\narising from the dipolar coupling between molecules. This has interesting\nconsequences for the collective many-body phases. The rotational excitations\ncan form a Bose-Einstein condensate at non-zero temperature, manifesting itself\nas a divergent $T_2$ coherence time of the rotational transition even in the\npresence of inhomogeneous broadening. The dynamical evolution of a dense gas of\nrotational excitations shows regimes of non-ergodicity, characteristic of\nmany-body localization and localization protected quantum order."
    },
    {
        "anchor": "Investigating Dirty Crossover through Fidelity Susceptibility and\n  Density of States: We investigate the BCS-BEC crossover in an ultracold atomic gas in the\npresence of disorder. The disorder is incorporated in the mean-field formalism\nthrough Gaussian fluctuations. We observe evolution to an asymmetric line-shape\nof fidelity susceptibility as a function of interaction coupling with\nincreasing disorder strength which may point to an impending quantum phase\ntransition. The asymmetric line-shape is further analyzed using the statistical\ntools of skewness and kurtosis. We extend our analysis to density of states\n(DOS) for a better understanding of the crossover in the disordered\nenvironment.",
        "positive": "Stationary through-flows in a Bose-Einstein condensate with a\n  PT-symmetric impurity: Superfluid currents in the boson condensate with a source and sink of\nparticles are modelled by the PT-symmetric Gross-Pitaevskii equation with a\ncomplex potential. We demonstrate the existence of through-flows of the\ncondensate --- stationary states with the asymptotically nonvanishing flux. The\nthrough-flows come in two broad varieties determined by the form of their\nnumber density distribution. One variety is described by dip-like solutions\nfeaturing a localised density depression; the other one comprises hump-like\nstructures with a density spike in their core. We exemplify each class by exact\nclosed-form solutions. For a fixed set of parameters of the PT-symmetric\npotential, stationary through-flows form continuous families parametrized by\nthe strength of the background flux. All hump-like and some dip-like members of\nthe family are found to be stable. We show that the through-flows can be\ncontrolled by varying the gain-and-loss amplitude of the complex potential and\nthat these amplitude variations may produce an anomalous response of the flux\nacross the gain-loss interface."
    },
    {
        "anchor": "Topological Edge-State Manifestation of Interacting 2D Condensed\n  Boson-Lattice Systems in a Harmonic Trap: In this Letter, it is shown that interactions can facilitate the emergence of\ntopological edge states of quantum-degenerate bosonic systems in the presence\nof a harmonic potential. This effect is demonstrated with the concrete model of\na hexagonal lattice populated by spin-one bosons under a synthetic gauge field.\nIn fermionic or noninteracting systems, the presence of a harmonic trap can\nobscure the observation of edge states. For our system with weakly interacting\nbosons in the Thomas--Fermi regime, we can clearly see a topological band\nstructure with a band gap traversed by edge states. We also find that the\nnumber of edge states crossing the gap is increased in the presence of a\nharmonic trap, and the edge modes experience an energy shift while traversing\nthe first Brillouin zone which is related to the topological properties of the\nsystem. We find an analytical expression for the edge-state energies and our\ncomparison with numerical computation shows excellent agreement.",
        "positive": "Temperature-dependence of small harmonically trapped atom systems with\n  Bose, Fermi and Boltzmann statistics: While the zero-temperature properties of harmonically trapped cold few-atom\nsystems have been discussed fairly extensively over the past decade, much less\nis known about the finite-temperature properties. Working in the canonical\nensemble, we characterize small harmonically trapped atomic systems as a\nfunction of the temperature using analytical and numerical techniques. We\npresent results for the energetics, structural properties, condensate fraction,\nsuperfluid fraction, and superfluid density. Our calculations for the two-body\nsystem underline that the condensate and superfluid fractions are distinctly\ndifferent quantities. Our work demonstrates that the path integral Monte Carlo\nmethod yields reliable results for bosonic and fermionic systems over a wide\ntemperature range, including the regime where the de Broglie wave length is\nlarge, i.e., where the statistics plays an important role. The regime where the\nFermi sign problem leads to reasonably large signal to noise ratios is mapped\nout for selected parameter combinations. Our calculations for bosons focus on\nthe unitary regime, where the physics is expected to be governed by the\nthree-body parameter. If the three-body parameter is large compared to the\ninverse of the harmonic oscillator length, we find that the bosons form a\ndroplet at low temperature and behave approximately like a non-interacting Bose\nand eventually Boltzmann gas at high temperature. The change of the behavior\noccurs over a fairly narrow temperature range. A simple model that reproduces\nthe key aspects of the phase transition like feature, which can potentially be\nobserved in cold atom Bose gas experiments, is presented."
    },
    {
        "anchor": "Bose-Einstein condensate in Bloch bands with off-diagonal periodic\n  potential: We report the Bose-Einstein condensate (BEC) in the Bloch bands with\noff-diagonal periodic potential (ODPP), which simultaneously plays the role of\nspin-orbit coupling (SOC) and Zeeman field. This model can be realized using\ntwo independent Raman couplings in the same three level system, in which the\ntime-reversal symmetry ensures the energy degeneracy between the two states\nwith opposite momenta. We find that these two Raman couplings can be used to\ntune the spin polarization in momentum space, thus greatly modifies the\neffective scatterings over the Bloch bands. We observe a transition from the\nBloch plane wave phase with condensate at one wave vector to the Bloch stripe\nphase with condensates at the two Bloch states with opposite wave vectors.\nThese two phases will exhibit totally different spin textures and density\nmodulations in real space, which are totally different from that in free space.\nIn momentum space multiple peaks differ by some reciprocal lattice vectors can\nbe observed, reflecting the periodic structure of the ODPP. A three-band\neffective model is proposed to understand these observations. This system can\nprovide a new platform in investigating of various physics, such as collective\nexcitations, polaron and topological superlfuids, over the Bloch bands.",
        "positive": "Boson-mediated quantum spin simulators in transverse fields: XY model\n  and spin-boson entanglement: The coupling of spins to long-wavelength bosonic modes is a prominent means\nto engineer long-range spin-spin interactions, and has been realized in a\nvariety of platforms, such as atoms in optical cavities and trapped ions. To\ndate, much of the experimental focus has been on the realization of long-range\nIsing models, but generalizations to other spin models are highly desirable. In\nthis work, we explore a previously unappreciated connection between the\nrealization of an XY model by off-resonant driving of single sideband of boson\nexcitation (i.e.~a single-beam M{\\o}lmer-S{\\o}rensen scheme) and a\nboson-mediated Ising simulator in the presence of a transverse field. In\nparticular, we show that these two schemes have the same effective Hamiltonian\nin suitably defined rotating frames, and analyze the emergent effective XY spin\nmodel through truncated Magnus series and numerical simulations. In addition to\nXY spin-spin interactions that can be non-perturbatively renormalized from the\nnaive Ising spin-spin coupling constants, we find an effective transverse field\nthat is dependent on the thermal energy of the bosons, as well as other\nspin-boson couplings that cause spin-boson entanglement not to vanish at any\ntime. In the case of a boson-mediated Ising simulator with transverse field, we\ndiscuss the crossover from transverse-field Ising-like to XY-like spin behavior\nas a function of field strength."
    },
    {
        "anchor": "Cluster Luttinger Liquids of Rydberg-dressed Atoms in Optical Lattices: We investigate the zero-temperature phases of bosonic and fermionic gases\nconfined to one dimension and interacting via a class of finite-range\nsoft-shoulder potentials (i.e. soft-core potentials with an additional\nhard-core onsite interaction). Using a combination of analytical and numerical\nmethods, we demonstrate the stabilization of critical quantum liquids with\nqualitatively new features with respect to the Tomonaga-Luttinger liquid\nparadigm. These features result from frustration and cluster formation in the\ncorresponding classical ground-state. Characteristic signatures of these\nliquids are accessible in state-of-the-art experimental setups with\nRydberg-dressed ground-state atoms trapped in optical lattices.",
        "positive": "Metastability of Bose and Fermi gases on the upper branch: We study three dimensional Bose and Fermi gases in the upper branch, a phase\ndefined by the absence of bound states in the repulsive interaction regime,\nwithin an approximation that considers only two-body interactions. Employing a\nformalism based on the S-matrix, we derive useful analytic expressions that\nhold on the upper branch in the weak coupling limit. We determine upper branch\nphase diagrams for both bosons and fermions with techniques valid for arbitrary\npositive scattering length."
    },
    {
        "anchor": "Probing molecular spectral functions and unconventional pairing using\n  Raman spectroscopy: An impurity interacting with an ultracold Fermi gas can form either a polaron\nstate or a dressed molecular state in which the impurity forms a bound state\nwith one gas particle. This molecular state features rich physics, including a\nfirst-order transition to the polaron state and a negative effective mass at\nsmall interactions. However, these features have remained so far experimentally\ninaccessible. In this work we show theoretically how the molecular state can be\ndirectly prepared experimentally even in its excited state using\nstate-of-the-art cold atom Raman spectroscopy techniques. Initializing the\nsystem in the ultra-strong coupling limit, where the binding energy of the\nmolaron is much larger than the Fermi energy, our protocol maps out the\nmomentum-dependent spectral function of the molecule. Using a diagrammatic\napproach we furthermore show that the molecular spectral function serves as a\ndirect precursor of the elusive Fulde-Ferell-Larkin-Ovchinnikov phase, which is\nrealized for a finite density of fermionic impurity particles. Our results pave\nthe way to a systematic understanding of how composite particles form in\nquantum many-body environments and provide a basis to develop new schemes for\nthe observation of exotic phases of quantum many-body systems.",
        "positive": "Analysis of Kapitza-Dirac diffraction patterns beyond the Raman-Nath\n  regime: We study Kapitza-Dirac diffraction of a Bose-Einstein condensate from a\nstanding light wave for a square pulse with variable pulse length but constant\npulse area. We find that for sufficiently weak pulses, the usual analytical\nshort-pulse prediction for the Raman-Nath regime continues to hold for longer\ntimes, albeit with a reduction of the apparent modulation depth of the standing\nwave. We quantitatively relate this effect to the Fourier width of the pulse,\nand draw analogies to the Rabi dynamics of a coupled two-state system. Our\nfindings, combined with numerical modeling for stronger pulses, are of\npractical interest for the calibration of optical lattices in ultracold atomic\nsystems."
    },
    {
        "anchor": "Characterising arbitrary dark solitons in trapped one-dimensional\n  Bose-Einstein condensates: We present a method to detect the presence and depth of dark solitons within\nrepulsive one-dimensional harmonically trapped Bose-Einstein condensates. For a\nsystem with one soliton, we prove that the shift of the density in Fourier\nspace directly maps onto the depth of the soliton. For multi-soliton systems,\ncombining our spectral method with established imaging techniques, the\ncharacter of the solitons present in the condensate can be determined. We\nverify that the detection of solitons by the spectral shift works in the\npresence of waves induced by density engineering methods. Finally we discuss\nimplications for vortex detection in three dimensional Bose-Einstein\ncondensates.",
        "positive": "Critical phenomena in one dimension from a Bethe ansatz perspective: This article briefly reviews recent theoretical developments in quantum\ncritical phenomena in one-dimensional (1D) integrable quantum gases of cold\natoms. We present a discussion on quantum phase transitions, universal\nthermodynamics, scaling functions and correlations for a few prototypical\nexactly solved models, such as the Lieb-Liniger Bose gas, the spin-1 Bose gas\nwith antiferromagnetic spin-spin interaction, the two-component interacting\nFermi gas as well as spin-3/2 Fermi gases. We demonstrate that their\ncorresponding Bethe ansatz solutions provide a precise way to understand\nquantum many-body physics, such as quantum criticality, Luttinger liquids, the\nWilson ratio, Tan's Contact, etc. These theoretical developments give rise to a\nphysical perspective using integrability for uncovering experimentally testable\nphenomena in systems of interacting bosonic and fermonic ultracold atoms\nconfined to 1D."
    },
    {
        "anchor": "Cross Dimensionality and Emergent Nodal Superconductivity with\n  $p$-orbital Atomic Fermions: I study cross dimensionality of $p$-orbital atomic fermions loaded in an\noptical square lattice with repulsive interactions. The cross-dimensionality\nemerges when the transverse tunneling of $p$-orbital fermions is negligible.\nWith renormalization group analysis, the system is found to support two\ndimensional charge, orbital, and spin density wave states with incommensurate\nwavevectors. The transition temperatures of these states are controlled by\nperturbations near a one dimensional Luttinger liquid fixed point. Considering\ntransverse tunneling, the cross-dimensionality breaks down and the density wave\n(DW) orders become unstable, and I find an unconventional superconducting state\nmediated by fluctuation effects. The superconducting gap has an emergent nodal\nstructure determined by the Fermi momentum, which is tunable by controlling\natomic density. Taking an effective description of the superconducting state,\nit is shown that the nodal structure of Cooper pairing can be extracted from\nmomentum-space radio-frequency spectroscopy in atomic experiments. These\nresults imply that $p$-orbital fermions could enrich the possibilities of\nstudying correlated physics in optical lattice quantum emulators beyond the\nsingle-band Fermi Hubbard model.",
        "positive": "Spectral energy transport in two-dimensional quantum vortex dynamics: We explore the possible regimes of decaying two-dimensional quantum\nturbulence, and elucidate the nature of spectral energy transport by\nintroducing a dissipative point-vortex model with phenomenological vortex-sound\ninteractions. The model is valid for a large system with weak dissipation, and\nalso for systems with strong dissipation, and allows us to extract a meaningful\nand unambiguous spectral energy flux associated with quantum vortex motion. For\nweak dissipation and large system size we find a regime of hydrodynamic vortex\nturbulence in which energy is transported to large spatial scales, resembling\nthe phenomenology of the transient inverse cascade observed in decaying\nturbulence in classical incompressible fluids. For strong dissipation the\nvortex dynamics are dominated by dipole recombination and exhibit no\nappreciable spectral transport of energy."
    },
    {
        "anchor": "Evidence for Bosonization in a three-dimensional gas of SU($N$) fermions: Blurring the boundary between bosons and fermions lies at the heart of a wide\nrange of intriguing quantum phenomena in multiple disciplines, ranging from\ncondensed matter physics and atomic, molecular and optical physics to high\nenergy physics. One such example is a multi-component Fermi gas with SU($N$)\nsymmetry that is expected to behave like spinless bosons in the large $N$\nlimit, where the large number of internal states weakens constraints from the\nPauli exclusion principle. However, bosonization in SU($N$) fermions has never\nbeen established in high dimensions where exact solutions are absent. Here, we\nreport direct evidence for bosonization in a SU($N$) fermionic ytterbium gas\nwith tunable $N$ in three dimensions (3D). We measure contacts, the central\nquantity controlling dilute quantum gases, from the momentum distribution, and\nfind that the contact per spin approaches a constant with a 1/$N$ scaling in\nthe low fugacity regime consistent with our theoretical prediction. This\nscaling signifies the vanishing role of the fermionic statistics in\nthermodynamics, and allows us to verify bosonization through measuring a single\nphysical quantity. Our work delivers a highly controllable quantum simulator to\nexchange the bosonic and fermionic statistics through tuning the internal\ndegrees of freedom in any generic dimensions. It also suggests a new route\ntowards exploring multi-component quantum systems and their underlying\nsymmetries with contacts.",
        "positive": "Shortcut to adiabaticity in internal bosonic Josephson junctions: We extend a recent method to shortcut the adiabatic following to internal\nbosonic Josephson junctions in which the control parameter is the linear\ncoupling between the modes. The approach is based on the mapping between the\ntwo-site Bose-Hubbard Hamiltonian and a 1D effective Schr\\\"odinger-like\nequation, valid in the large $N$ (number of particles) limit. Our method can be\nreadily implemented in current internal bosonic Josephson junctions and it\nimproves substantially the production of spin-squeezing with respect to usually\nemployed linear rampings."
    },
    {
        "anchor": "Repulsive Fermi and Bose Polarons in Quantum Gases: Polaron quasiparticles are formed when a mobile impurity is coupled to the\nelementary excitations of a many-particle background. In the field of ultracold\natoms, the study of the associated impurity problem has attracted a growing\ninterest over the last fifteen years. Polaron quasiparticle properties are\nessential to our understanding of a variety of paradigmatic quantum many-body\nsystems realized in ultracold atomic gases and in the solid state, from\nimbalanced Bose-Fermi and Fermi-Fermi mixtures to fermionic Hubbard models. In\nthis topical review, we focus on the so-called repulsive polaron branch, which\nemerges as an excited many-body state in systems with underlying attractive\ninteractions such as ultracold atomic mixtures, and is characterized by an\neffective repulsion between the impurity and the surrounding medium. We give a\nbrief account of the current theoretical and experimental understanding of\nrepulsive polaron properties, for impurities embedded in both fermionic and\nbosonic media, and we highlight open issues deserving future investigations.",
        "positive": "Topological flat bands in optical checkerboard-like lattices: We present comparatively simple two-dimensional and three-dimensional\ncheckerboard-like optical lattices possessing nontrivial topological\nproperties. By simple tuning of the parameters these lattices can have a\ntopological insulating phase, a topological semi-metallic phase, or a trivial\ninsulating phase. This allows study of different topological phase transitions\nwithin a single cold atom system. In the topologically nontrivial phases flat\nbands appear at the surfaces of the system. These surface states possess short\nlocalization lengths such that they are observable even in systems with small\nlattice dimensions. Our proposed lattices neither need spin-orbit coupling nor\nnon-Abelian gauge fields to reach topologically nontrivial states."
    },
    {
        "anchor": "Path-Integral Ground-State and Superfluid Hydrodynamics of a Bosonic Gas\n  of Hard Spheres: We study a bosonic gas of hard spheres by using of the exact zero-temperature\nPath-Integral Ground-State (PIGS) Monte Carlo method and the equations of\nsuperfluid hydrodynamics. The PIGS method is implemented to calculate for the\nbulk system the energy per particle and the condensate fraction through a large\nrange of the gas parameter $na^3$ (with $n$ the number density and $a$ the\ns--wave scattering length), going from the dilute gas into the solid phase. The\nMaxwell construction is then adopted to determine the freezing at\n$na^3=0.278\\pm 0.001$ and the melting at $na^3=0.286\\pm 0.001$. In the liquid\nphase, where the condensate fraction is finite, the equations of superfluid\nhydrodynamics, based on the PIGS equation of state, are used to find other\nrelevant quantities as a function of the gas parameter: the chemical potential,\nthe pressure and the sound velocity. In addition, within the Feynman's\napproximation, from the PIGS static structure factor we determine the full\nexcitation spectrum, which displays a maxon-roton behavior when the gas\nparameter is close to the freezing value. Finally, the equations of superfluid\nhydrodynamics with the PIGS equation of state are solved for bosonic system\nunder axially--symmetric harmonic confinement obtaining its collective\nbreathing modes.",
        "positive": "Quantum Monte Carlo study of superfluid density in quasi-one-dimensional\n  hard-core bosons: Effect of suppression of phase slippage: We study the superfluid density of hard-core bosons on quasi-one-dimensional\nlattices using the quantum Monte Carlo method. Because of phase slippage, the\nsuperfluid density drops quickly to zero at finite temperatures with increasing\nthe system length $\\ell$ and the superfluid transition temperature is zero in\none spatial dimension and also in quasi-one dimension in the limit of\n$\\ell\\rightarrow\\infty$. We calculate the superfluid density of a model where\nno phase slippage is allowed and show that the superfluid density remains\nfinite at finite temperatures even in the one-dimensional limit. We also\ndiscuss how finite superfluid density can be observed in a\nquasi-one-dimensional system using a torsional oscillator."
    },
    {
        "anchor": "Strongly correlated Bose gases: The strongly interacting Bose gas is one of the most fundamental paradigms of\nquantum many-body physics and the subject of many experimental and theoretical\ninvestigations. We review recent progress on strongly correlated Bose gases,\nstarting with a description of beyond mean-field corrections. We show that the\nEfimov effect leads to non universal phenomena and to a metastability of the\nlow temperature Bose gas through three-body recombination to deeply bound\nmolecular states. We outline differences and similarities with ultracold Fermi\ngases, discuss recent experiments on the unitary Bose gas, and finally present\na few perspectives for future research.",
        "positive": "Frustrated magnets without geometrical frustration in bosonic flux\n  ladders: We propose a scheme to realize a frustrated Bose-Hubbard model with ultracold\natoms in an optical lattice that comprises the frustrated spin-1/2 quantum XX\nmodel. Our approach is based on a square ladder of magnetic flux close to $\\pi$\nwith one real and one synthetic spin dimension. Although this system does not\nhave geometrical frustration, we show that at low energies it maps into an\neffective triangular ladder with staggered fluxes for specific values of the\nsynthetic tunneling. We numerically investigate its rich phase diagram and show\nthat it contains bond-ordered-wave and chiral superfluid phases. Our scheme\ngives access to minimal instances of frustrated magnets without the need for\nreal geometrical frustration, in a setup of minimal experimental complexity."
    },
    {
        "anchor": "Mean-field dynamics to negative absolute temperatures in the\n  Bose-Hubbard model: We apply time-dependent Gutzwiller mean-field theory to provide a qualitative\nunderstanding for bosons in optical lattices that approach states corresponding\nto negative absolute temperatures. We perform the dynamical simulations to\nrelate to the recent experiments by Braun et al. [ S. Braun, J. P. Ronzheimer,\nM. Schreiber, S. S. Hodgman, T. Rom, I. Bloch and U. Schneider, Science 339 52\n(2013)]. Time-of-flight images calculated from the two-dimensional numerical\nsimulations reproduce characteristics of the experimental observations, in\nparticular, the emergence of the four peaks at the corners of the Brillouin\nzone.",
        "positive": "Comment on \"Motion of an impurity particle in an ultracold\n  quasi-one-dimensional gas of hard-core bosons [Phys. Rev. A 79, 033610\n  (2009)]\": Very recently Girardeau and Minguzzi [arXiv:0807.3366v2, Phys. Rev. A 79,\n033610 (2009)] have studied an impurity in a one-dimensional gas of hard-core\nbosons. In particular they deal with the general case where the mass of the\nimpurity is different from the mass of the bosons and the impurity-boson\ninteraction is not necessarily infinitely repulsive. We show that one of their\ninitial step is erroneous, contradicting both physical intuition and known\nexact results. Their results in the general case apply only actually when the\nmass of the impurity is infinite."
    },
    {
        "anchor": "Quantum impurities: from mobile Josephson junctions to depletons: We overview the main features of mobile impurities moving in one-dimensional\nsuperfluid backgrounds by modeling it as a mobile Josephson junction, which\nleads naturally to the periodic dispersion of the impurity. The dissipation\nprocesses, such as radiative friction and quantum viscosity, are shown to\nresult from the interaction of the collective phase difference with the\nbackground phonons. We develop a more realistic depleton model of an\nimpurity-hole bound state that provides a number of exact results interpolating\nbetween the semiclassical weakly-interacting picture and the strongly\ninteracting Tonks-Girardeau regime. We also discuss the physics of a trapped\nimpurity, relevant to current experiments with ultra cold atoms.",
        "positive": "Exact out-of-time-ordered correlation functions for an interacting\n  lattice fermion model: Exact solutions for local equilibrium and nonequilibrium out-of-time-ordered\ncorrelation (OTOC) functions are obtained for a lattice fermion model with\non-site interactions, namely the Falicov-Kimball (FK) model, in the large\ndimensional and thermodynamic limit. Our approach is based on the\nnonequilibrium dynamical mean-field theory generalized to an extended\nKadanoff-Baym contour. We find that the density-density OTOC is most enhanced\nat intermediate coupling around the metal-insulator phase transition. In the\nhigh-temperature limit, the OTOC remains nontrivially finite and\ninteraction-dependent, even though dynamical charge correlations probed by an\nordinary response function are completely suppressed. We propose an experiment\nto measure OTOCs of fermionic lattice systems including the FK and Hubbard\nmodels in ultracold atomic systems."
    },
    {
        "anchor": "Several fermions strongly interacting with a heavy mobile impurity in a\n  one-dimensional harmonic trap: We propose a numerically exact method for a mixture with a single impurity\nimmersed in several majority fermions, confined in a harmonic potential. We\nseparate one of the degrees of freedom through an appropriately tailored\ncanonical transformation and perform exact diagonalization on the simplified\nHamiltonian. This method is especially effective for a heavy impurity, where it\noutmatches the typical exact diagonalization approach. We used our method to\ncalculate energy and density profiles of the first few eigenstates for the\nmixture with up to ten majority fermions.",
        "positive": "Quantitative comparison between theoretical predictions and experimental\n  results for Bragg spectroscopy of a strongly interacting Fermi superfluid: Theoretical predictions for the dynamic structure factor of a harmonically\ntrapped Fermi superfluid near the BEC-BCS crossover are compared with recent\nBragg spectroscopy measurements at large transferred momenta. The calculations\nare based on a random-phase (or time-dependent Hartree-Fock-Gorkov)\napproximation generalized to the strongly interacting regime. Excellent\nagreement with experimental spectra at low temperatures is obtained, with no\nfree parameters. Theoretical predictions for zero-temperature static structure\nfactor are also found to agree well with the experimental results and\nindependent theoretical calculations based on the exact Tan relations. The\ntemperature dependence of the structure factors at unitarity is predicted."
    },
    {
        "anchor": "Homogeneous Floquet time crystal protected by gauge invariance: We show that homogeneous lattice gauge theories can realize nonequilibrium\nquantum phases with long-range spatiotemporal order protected by gauge\ninvariance instead of disorder. We study a kicked $\\mathbb{Z}_2$-Higgs gauge\ntheory and find that it breaks the discrete temporal symmetry by a period\ndoubling. In a limit solvable by Jordan-Wigner analysis we extensively study\nthe time-crystal properties for large systems and further find that the\nspatiotemporal order is robust under the addition of a solvability-breaking\nperturbation preserving the $\\mathbb{Z}_2$ gauge symmetry. The protecting\nmechanism for the nonequilibrium order relies on the Hilbert space structure of\nlattice gauge theories, so that our results can be directly extended to other\nmodels with discrete gauge symmetries.",
        "positive": "The attractive Bose gas in two dimensions: an analytical study of its\n  fragmentation and collapse: An attractive Bose-Einstein condensate in two spatial dimensions is expected\nto collapse for supercritical values of the interaction strength. Moreover, it\nis known that for nonzero quanta of angular momentum and infinitesimal\nattraction the gas prefers to fragment and distribute its angular momentum over\ndifferent orbitals. In this work we examine the two-dimensional Bose gas for\nfinite values of attraction and describe the ground state in connection to its\nangular momentum by theoretical methods that go beyond the standard\nGross-Pitaevskii theory. By applying the best mean field approach, we derive\nanalytical relations for the energy, the fragmentation of the ground states and\nthe critical (for collapse) value of the attraction strength as a function of\nthe total angular momentum $L$."
    },
    {
        "anchor": "Canonical ensemble of an interacting Bose gas: stochastic matter fields\n  and their coherence: We present a novel quantum stochastic evolution equation for a matter field\ndescribing the canonical state of a weakly interacting ultracold Bose gas. In\nthe ideal gas limit our approach is exact. This numerically very stable\nequation suppresses high-energy fluctuations exponentially, which enables us to\ndescribe condensed and thermal atoms within the same formalism. We present\napplications to ground state occupation and fluctuations, density profile of\nground state and thermal cloud, and ground state number statistics. Our main\naim are spatial coherence properties which we investigate through the\ndetermination of interference contrast and spatial density correlations.\nParameters are taken from actual experiments [1].\n  [1] S. Hofferberth et al., Nature Physics 4, 489 (2008).",
        "positive": "Nonequilibrium Steady States and Resonant Tunneling in Time-Periodically\n  Driven Systems with Interactions: Time-periodically driven systems are a versatile toolbox for realizing\ninteresting effective Hamiltonians. Heating, caused by excitations to\nhigh-energy states, is a challenge for experiments. While most setups address\nthe relatively weakly-interacting regime so far, it is of general interest to\nstudy heating in strongly correlated systems. Using Floquet dynamical\nmean-field theory, we study non-equilibrium steady states (NESS) in the\nFalicov-Kimball model, with time-periodically driven kinetic energy or\ninteraction. We systematically investigate the nonequilibrium properties of the\nNESS. For a driven kinetic energy, we show that resonant tunneling, where the\ninteraction is an integer multiple of the driving frequency, plays an important\nrole in the heating. In the strongly correlated regime, we show that this can\nbe well understood using Fermi\\textquoteright s golden rule and the\nSchrieffer-Wolff transformation for a time-periodically driven system. We\nfurthermore demonstrate that resonant tunneling can be used to control the\npopulation of Floquet states to achieve \"photo-doping\". For driven interactions\nintroduced by an oscillating magnetic field near a Feshbach resonance widely\nadopted, we find that the double occupancy is strongly modulated. Our\ncalculations apply to shaken ultracold atom systems, and to solid state systems\nin a spatially uniform but time-dependent electric field. They are also closely\nrelated to lattice modulation spectroscopy. Our calculations are helpful to\nunderstand the latest experiments on strongly correlated Floquet systems."
    },
    {
        "anchor": "Emergent classicality in continuous quantum measurements: We develop a classical theoretical description for nonlinear many-body\ndynamics that incorporates the back-action of a continuous measurement process.\nThe classical approach is compared with the exact quantum solution in an\nexample with an atomic Bose-Einstein condensate in a double-well potential\nwhere the atom numbers in both potential wells are monitored by light\nscattering. In the classical description the back-action of the measurements\nappears as diffusion of the relative phase of the condensates on each side of\nthe trap. When the measurements are frequent enough to resolve the system\ndynamics, the system behaves classically. This happens even deep in the quantum\nregime, and demonstrates how classical physics emerges from quantum mechanics\nas a result of measurement back-action.",
        "positive": "The Talbot effect in the presence of interactions: We study both experimentally and theoretically, considering bosonic atoms in\na periodic potential, the influence of interactions in a Talbot interferometer.\nWhile interactions decrease the contrast of the revivals, we find that over a\nwide range of interactions the Talbot signal is still proportional to the phase\ncoherence of the matter wave field. Our results confirm that Talbot\ninterferometry can be a useful tool to study finite range phase correlations in\nan optical lattice even in the presence of interactions. The relative\nrobustness of the Talbot signal is supported by the first demonstration of the\nthree-dimensional Talbot effect."
    },
    {
        "anchor": "Breakdown of the superfluidity of a matter wave in a random environment: We consider a guided Bose-Einstein matter wave flowing through a disordered\npotential. We determine the critical velocity at which superfluidity is broken\nand compute its statistical properties. They are shown to be connected to\nextreme values of the random potential. Experimental implementations of this\nphysics are discussed.",
        "positive": "Nonequilibrium dynamics of spin-boson models from phase space methods: An accurate description of the nonequilibrium dynamics of systems with\ncoupled spin and bosonic degrees of freedom remains theoretically challenging,\nespecially for large system sizes and in higher than one dimension. Phase space\nmethods such as the Truncated Wigner Approximation (TWA) have the advantage of\nbeing easily scalable and applicable to arbitrary dimensions. In this work we\nadapt the TWA to generic spin-boson models by making use of recently developed\nalgorithms for discrete phase spaces [Schachenmayer, PRX 5, 011022 (2015)].\nFurthermore we go beyond the standard TWA approximation by applying a scheme\nbased on the Bogoliubov-Born-Green-Kirkwood-Yvon (BBGKY) hierarchy of equations\n[Pucci, PRB 93, 174302 (2016)] to our coupled spin-boson model. This allows in\nprinciple to study how systematically adding higher order corrections improves\nthe convergence of the method. To test various levels of approximation we study\nan exactly solvable spin-boson model which is particularly relevant for\ntrapped-ion arrays. Using TWA and its BBGKY extension we accurately reproduce\nthe time evolution of a number of one- and two-point correlation functions in\nseveral dimensions and for arbitrary number of bosonic modes."
    },
    {
        "anchor": "Renormalization group approach to the Fr\u00f6hlich polaron model:\n  application to impurity-BEC problem: We develop a renormalization group approach for analyzing Fr\\\"ohlich polarons\nand apply it to a problem of impurity atoms immersed in a Bose-Einstein\ncondensate of ultra cold atoms. Polaron energies obtained by our method are in\nexcellent agreement with recent diagrammatic Monte Carlo calculations for a\nwide range of interaction strengths. We calculate the effective mass of\npolarons and find a smooth crossover from weak to strong coupling regimes.\nPossible experimental tests of our results in current experiments with ultra\ncold atoms are discussed.",
        "positive": "Nonequilibrium dynamics of one-dimensional hard-core anyons following a\n  quench: Complete relaxation of one-body observables: We demonstrate the role of interactions in driving the relaxation of an\nisolated integrable quantum system following a sudden quench. We consider a\nfamily of integrable hard-core lattice anyon models that continuously\ninterpolates between noninteracting spinless fermions and strongly interacting\nhard-core bosons. A generalized Jordan-Wigner transformation maps the entire\nfamily to noninteracting fermions. We find that, aside from the singular\nfree-fermion limit, the entire single-particle density matrix and therefore all\none-body observables relax to the predictions of the generalized Gibbs ensemble\n(GGE). This demonstrates that, in the presence of interactions, correlations\nbetween particles in the many-body wave function provide the effective\ndissipation required to drive relaxation of all one-body observables to the\nGGE. This relaxation does not depend on translational invariance, or the\ntracing out of any spatial domain of the system."
    },
    {
        "anchor": "Quantum Monte Carlo-based density functional for one-dimensional\n  Bose-Bose mixtures: We propose and benchmark a Gross-Pitaevskii-like equation for two-component\nBose mixtures with competing interactions in 1D. Our approach follows the\ndensity-functional theory with the energy functional based on the exact Quantum\nMonte Carlo (QMC) simulations. Our model covers, but goes beyond, the popular\napproach with the Lee-Huang-Yang corrections. We first benchmark our approach\nagainst available QMC data in all interaction regimes and then study dynamical\nproperties, inaccessible by ab initio many-body simulations. Our analysis\nincludes a study of monopole modes and reveals the presence of anomalous dark\nsolitons.",
        "positive": "Quantum fluctuations of a resonantly interacting $p$-wave Fermi\n  superfluid in two dimensions: Using the Gaussian pair fluctuation theory, we investigate quantum\nfluctuations of a strongly interacting two-dimensional chiral \\textit{p}-wave\nFermi superfluid at the transition from a Bose-Einstein condensate (BEC) to a\ntopologically non-trivial Bardeen-Cooper-Schrieffer (BCS) superfluid. Near the\ntopological phase transition at zero chemical potential, $\\mu=0$, we observe\nthat quantum fluctuations strongly renormalize the zero-temperature equations\nof state, sound velocity, pair-breaking velocity, and\nBerezinskii-Kosterlitz-Thouless (BKT) critical temperature of the Fermi\nsuperfluid, all of which can be non-analytic functions of the interaction\nstrength. The indication of non-analyticity is particularly evident in the BKT\ncritical temperature, which also exhibits a pronounced peak near the\ntopological phase transition. Across the transition and towards the BEC limit\nwe find that the system quickly becomes a trivial interacting Bose liquid,\nwhose properties are less dependent on the interparticle interaction. The\nqualitative behavior of composite bosons in the BEC limit remains to be\nunderstood."
    },
    {
        "anchor": "Triangular and Honeycomb Lattices of Cold Atoms in Optical Cavities: We consider a two-dimensional homogeneous ensemble of cold bosonic atoms\nloaded inside two optical cavities and pumped by a far-detuned external laser\nfield. We examine the conditions for these atoms to self-organize into\ntriangular and honeycomb lattices as a result of superradiance. By collectively\nscattering the pump photons, the atoms feed the initially empty cavity modes.\nAs a result, the superposition of the pump and cavity fields creates a\nspace-periodic light-shift external potential and atoms self-organize into the\npotential wells of this optical lattice. Depending on the phase of the cavity\nfields with respect to the pump laser, these minima can either form a\ntriangular or a hexagonal lattice. By numerically solving the dynamical\nequations of the coupled atom-cavity system, we have shown that the two stable\natomic structures at long times are the triangular lattice and the honeycomb\nlattice with equally-populated sites. We have also studied how to drive atoms\nfrom one lattice structure to another by dynamically changing the phase of the\ncavity fields with respect to the pump laser.",
        "positive": "Dzyaloshinskii-Moriya Interaction and Spiral Order in Spin-orbit Coupled\n  Optical Lattices: We show that the recent experimental realization of spin-orbit coupling in\nultracold atomic gases can be used to study different types of spin spiral\norder and resulting multiferroic effects. Spin-orbit coupling in optical\nlattices can give rise to the Dzyaloshinskii-Moriya (DM) spin interaction which\nis essential for spin spiral order. By taking into account spin-orbit coupling\nand an external Zeeman field, we derive an effective spin model in the Mott\ninsulator regime at half filling and demonstrate that the DM interaction in\noptical lattices can be made extremely strong with realistic experimental\nparameters. The rich finite temperature phase diagrams of the effective spin\nmodels for fermions and bosons are obtained via classical Monte Carlo\nsimulations."
    },
    {
        "anchor": "Fermi Gases in the Two-Dimensional to Quasi-Two-Dimensional Crossover: We tune the dimensionality of pancake-shaped strongly-interacting $^6$Li\nFermi gas clouds from two-dimensional (2D) to quasi-2D, by controlling the\nratio of the radial Fermi energy $E_F$ to the harmonic oscillator energy\n$h\\nu_z$ in the tightly confined direction. In the 2D regime, where\n$E_F<<h\\nu_z$, the measured radio frequency resonance spectra are in agreement\nwith 2D-BCS theory. In the quasi-2D regime, where $E_F\\simeq h\\nu_z$, the\nmeasured spectra deviate significantly from 2D-BCS theory. For both regimes,\nthe measured cloud radii disagree with 2D-BCS mean field theory, but agree\napproximately with predictions using a free energy derived from the\nBethe-Goldstone equation.",
        "positive": "Quantum emulation of topological magneto-optical effects using ultracold\n  atoms: Magneto-optical effect is a fundamental but broad concept in magnetic\nmediums. Here we propose a scheme for its quantum emulation using ultracold\natoms. By representing the light-medium interaction in the quantum-emulation\nmanner, the artificial magneto-optical effect emerges under an entirely\ndifferent mechanism from the conventional picture. The underlying polarization\nstate extracted in the synthetic dimension displays a different response to\nvarious experimental setups. Notably, the magneto-optical rotation is related\nto the bulk topology in synthetic dimensions, and thus provides an unambiguous\nevidence for the desired topological magneto-optical effect, which has not been\ndeveloped hitherto in ultracold atoms. This scheme is simple and feasible, and\ncan be realized by current experimental techniques. The implementation of the\nscheme is able to offer an intriguing platform for exploring topological\nmagneto-optical effects and associated physics."
    },
    {
        "anchor": "Proposed method to realize the $p$-wave superfluid state using a\n  $s$-wave superfluid Fermi gas with a synthetic spin-orbit interaction: We theoretically propose an idea to reach the $p$-wave superfluid phase in an\nultracold Fermi gas. The key of our idea is that the pairing symmetry of a\nFermi superfluid is fully dominated by the symmetry of the superfluid order\nparameter, which is essentially given by the product of a pair amplitude and a\npairing interaction. Noting this, in our proposal, we first prepare a $p$-wave\npair amplitude by, not using a $p$-wave interaction, but using the phenomenon\nthat a $p$-wave pair amplitude is induced in an $s$-wave superfluid Fermi gas\nwith antisymmetric spin-orbit interaction. In this case, although the system is\nstill in the $s$-wave superfluid state with the $s$-wave superfluid order\nparameter, when one suddenly replaces the $s$-wave interaction by an\nappropriate $p$-wave one (which is possible in cold Fermi gases by using a\nFeshbach resonance technique), the product of the $p$-wave interaction and the\n$p$-wave pair amplitude that has already been prepared in the spin-orbit\ncoupled $s$-wave superfluid state immediately gives a finite $p$-wave\nsuperfluid order parameter. Thus, at least just after this manipulation, the\nsystem is in the $p$-wave superfluid state, being characterized by the\nartificially produced $p$-wave superfluid parameter. In this paper, to assess\nour idea, we evaluate the $p$-wave pair amplitude in a spin-orbit coupled\n$s$-wave superfluid Fermi gas at $T=0$. We determine the region where a large\n$p$-wave pair amplitude is obtained in the phase diagram with respect to the\nstrengths of the $s$-wave pairing interaction and the spin-orbit coupling. We\nalso discuss the accessibility of this optimal region on the viewpoint of the\nsuperfluid phase transition temperature. Since the achievement of a $p$-wave\nsuperfluid Fermi gas is one of the most crucial issues in cold atom physics,\nour proposal would be useful for this exciting challenge.",
        "positive": "Quasiparticle decay in a one-dimensional Bose-Fermi mixture: In a one-dimensional weakly interacting Bose-Fermi mixture one branch of\nelementary excitations is well described by the Bogoliubov spectrum. Here we\nuse the microscopic theory to study the decay of such quasiparticle\nexcitations. The main scattering process which leads to their decay is the\nbackscattering of a Bogoliubov quasiparticle off the Fermi sea, where a\nparticle-hole pair is excited. For a low-momentum quasiparticle (phonon) of\nmomentum $q$, we find that the decay rate scales as $q^3$ provided $q$ is\nsmaller than the Fermi momentum $k_F$, while in the opposite case the decay\nbehaves as $q^2$. If the ratio of the masses of fermions and bosons equals to\nthe ratio of the boson-fermion and the boson-boson interaction strengths, the\ndecay rate changes dramatically. It scales as $q^7$ for $q<k_F$ while we find\n$q^6$ scaling at $q>k_F$. For a high momentum Bogoliubov quasiparticle, we find\na constant decay rate for $q<k_F$, while it scales as $1/q$ for $q>k_F$. We\nalso find an analytic expression for the decay rate in the crossover region\nbetween low and high momenta. The decay rate is a continuous, but nonanalytic\nfunction of the momentum at $q=k_F$. In the special case when the parameters of\nour system correspond to the integrable model, we observe that the decay rate\nvanishes."
    },
    {
        "anchor": "Dynamical Instability Induced by Zero Mode Under Symmetry Breaking\n  External Perturbation: A complex eigenvalue in the Bogoliubov-de Gennes equations for a stationary\nBose-Einstein condensate in ultracold atomic system indicates the dynamical\ninstability of the system. We also have the modes with zero eigenvalues for the\ncondensate, called the zero modes, which originate from the spontaneous\nbreakdown of symmetries. Although the zero modes are suppressed in many\ntheoretical analyses, we take account of them in this paper and argue that a\nzero mode can change into one with a pure imaginary eigenvalue by applying a\nsymmetry breaking external perturbation potential. This emergence of a pure\nimaginary mode adds a new type of scenario of dynamical instability to that\ncharacterized by complex eigenvalue of the usual excitation modes. For\nillustration, we deal with two one-dimensional homogeneous Bose-Einstein\ncondensate systems with a single dark soliton under a respective perturbation\npotential, breaking the invariance under translation, to derive pure imaginary\nmodes.",
        "positive": "Bose-Einstein condensation in large time-averaged optical ring\n  potentials: Interferometric measurements with matter waves are established techniques for\nsensitive gravimetry, rotation sensing, and measurement of surface\ninteractions, but compact interferometers will require techniques based on\ntrapped geometries. In a step towards the realization of matter wave\ninterferometers in toroidal geometries, we produce a large, smooth ring trap\nfor Bose-Einstein condensates using rapidly scanned time-averaged dipole\npotentials. The trap potential is smoothed by using the atom distribution as\ninput to an optical intensity correction algorithm. Smooth rings with a\ndiameter up to 300 $\\mu$m are demonstrated. We experimentally observe and\nsimulate the dispersion of condensed atoms in the resulting potential, with\ngood agreement serving as an indication of trap smoothness. Under time of\nflight expansion we observe low energy excitations in the ring, which serves to\nconstrain the lower frequency limit of the scanned potential technique. The\nresulting ring potential will have applications as a waveguide for atom\ninterferometry and studies of superfluidity."
    },
    {
        "anchor": "Droplet formation in a one-dimensional system of attractive spinless\n  fermions: A translation invariant one-dimensional system of spinless fermions with a\nfinite-range attraction experiences a quantum phase transition to a\nphase-separated state. While being a conventional Luttinger liquid for a small\ninteraction strength, spinless fermions form a droplet with the size smaller\nthan the available one-dimensional volume when the interaction strength exceeds\nsome critical value. A particularly remarkable signature of the droplet\nformation is the change in the lower edge of the many-body excitation spectrum.\nIn the homogeneous phase, it has a Luttinger-liquid shape of periodic arcs on\ntop of the shallow parabolic dispersion of the center-of-mass. When the\ninteraction strength is increased, the arcs disappear completely as soon as the\ndroplet is formed. We perform an exact diagonalization study of this system\nwith the focus on the signatures of the quantum phase transition and the\ndroplet properties. The one-particle and density-density correlation functions,\nthe pressure, the sound velocity, and the droplet density are examined. The\nvalue of the critical interaction strength obtained from numerical data\nreasonably agrees with a simple mean-field analytical estimate. Due to the\nboson-fermion correspondence valid in one dimension, our results also hold for\nhard-core bosons with a finite-range attraction.",
        "positive": "Momentum-resolved Raman spectroscopy of bound molecules in ultracold\n  Fermi gas: The binding energy of Feshbach molecules from a two component Fermi gas of\n$^{40}$K atoms has been experimentally measured with the momentum-resolved\nRaman spectroscopy. Comparing with the radio-frequency spectroscopy, in the\npresent experiment the signal of unpaired (free atoms) and the bound molecules\ncan be directly observed and the binding energy can be simultaneously\ndetermined in a single running experiment. The energy-momentum dispersion\nspectra of the strongly interacting ultracold Fermi gas in BEC side are also\nmeasured and reconstructed. The present experimental technology of the\nmomentum-resolved Raman spectroscopy can be easily extended to perform\nspatially momentum-resolved Raman spectroscopy and to obtain the response\nspectra of a homogeneous system in the local density approximation."
    },
    {
        "anchor": "Rotating mixed $^3$He-$^4$He nanodroplets: Mixed $^3$He-$^4$He droplets created by hydrodynamic instability of a\ncryogenic fluid-jet may acquire angular momentum during their passage through\nthe nozzle of the experimental apparatus. These free-standing droplets cool\ndown to very low temperatures undergoing isotopic segregation, developing a\nnearly pure $^3$He crust surrounding a very $^4$He-rich superfluid core. Here,\nthe stability and appearance of rotating mixed helium droplets are investigated\nusing Density Functional Theory for an isotopic composition that highlights,\nwith some marked exceptions related to the existence of the superfluid inner\ncore, the analogies with viscous rotating droplets.",
        "positive": "Onset of a Pseudogap Regime in Ultracold Fermi Gases: We show, using an ab initio approach based on Quantum Monte Carlo technique,\nthat the pseudogap regime emerges in ultracold Fermi gases close to the unitary\npoint. We locate the onset of this regime at a value of the interaction\nstrength corresponding to (k_{F}a)^{-1}\\approx -0.05 (a - scattering length).\nWe determine the evolution of the gap as a function of temperature and\ninteraction strength in the Fermi gas around the unitary limit and show that\nour results exhibit a remarkable agreement with the recent wave-vector resolved\nradio frequency spectroscopy data. Our results indicate that a finite\ntemperature structure of the Fermi gas around unitarity is more complicated and\ninvolves the presence of the phase with preformed Cooper pairs, which however\ndo not contribute to the long range order."
    },
    {
        "anchor": "Exotic many-body physics with large-spin Fermi gases: The experimental realization of quantum degenerate cold Fermi gases with\nlarge hyperfine spins opens up a new opportunity for exotic many-body physics.",
        "positive": "Formation of local and global currents in a toroidal Bose--Einstein\n  condensate via an inhomogeneous artificial gauge field: We study the effects of a position-dependent artificial gauge field on an\natomic Bose--Einstein condensate in quasi-one-dimensional and two-dimensional\nring settings. The inhomogeneous artificial gauge field can induce global and\nlocal currents in the Bose--Einstein condensate via phase gradients along the\nring and vortices, respectively. We observe two different regimes in the system\ndepending on the radial size of the ring and strength of the gauge field. For\nweak artificial gauge fields, the angular momentum increases, as expected, in a\nquantized manner; however, for stronger values of the fields, the angular\nmomentum exhibits a linear (non-quantized) behavior. We also characterize the\nangular momentum for non-cylindrically symmetric traps."
    },
    {
        "anchor": "Superfluid Density of a Spin-orbit Coupled Bose Gas: We discuss the superfluid properties of a Bose-Einstein condensed gas with\nspin-orbit coupling, recently realized in experiments. We find a finite normal\nfluid density $\\rho_n$ at zero temperature which turns out to be a function of\nthe Raman coupling. In particular, the entire fluid becomes normal at the\ntransition point from the zero momentum to the plane wave phase, even though\nthe condensate fraction remains finite. We emphasize the crucial role played by\nthe gapped branch of the elementary excitations and discuss its contributions\nto various sum rules. Finally, we prove that an independent definition of\nsuperfluid density $\\rho_s$, using the phase twist method, satisfies the\nequality $\\rho_n+\\rho_s=\\rho$, the total density, despite the breaking of\nGalilean invariance.",
        "positive": "Topological Mott Insulator with Bosonic Edge Modes in 1D Fermionic\n  Superlattices: We investigate topological phase transitions driven by interaction and\nidentify a novel topological Mott insulator state in one-dimensional fermionic\noptical superlattices through numerical density matrix renormalization group\n(DMRG) method. Remarkably, the low-energy edge excitations change from spin-1/2\nfermionic single-particle modes to spin-1 bosonic collective modes across the\nphase transition. Due to spin-charge separation, the low-energy theory is\ngoverned by an effective spin superexchange model, whereas the charge degree of\nfreedom is fully gapped out. Such topological Mott state can be characterized\nby a spin Chern number and gapless magnon modes protected by a finite spin gap.\nThe proposed experimental setup is simple and may pave the way for the\nexperimental observation of exotic topological Mott states."
    },
    {
        "anchor": "Improving the efficiency of ultracold dipolar molecule formation by\n  first loading onto an optical lattice: Ultracold ground state dipolar 40K-87Rb molecules have recently been produced\nin a loose harmonic trap by employing a magnetic field sweep across a Feshbach\nresonance followed by stimulated Raman adiabatic passage [K.-K. Ni et al.,\nScience 322, 231 (2008)]. The overall experimental efficiency for molecule\nformation was around 20%. We show that the efficiency can be increased to\nnearly 100% if one first loads the atomic gases into an optical lattice of the\nappropriate depth and tunes the interspecies attraction to have exactly one\natom of each species at an occupied lattice site. Our proposed scheme provides\na large enhancement to the dipolar molecule density even at relatively high\ntemperatures, and avoids three-body recombination loss by preventing lattice\nsites from being triply occupied.",
        "positive": "Hugenholtz -- Pines relations and the critical temperature of a Rabi\n  coupled binary Bose system: Using a theoretical field Gaussian approximation we have studied Rabi coupled\nbinary Bose system at low temperatures. We have derived extended Hugenholtz -\nPines relations taking into account one body interaction (e.g. Rabi coupling)\nand studied the critical temperature $T_c$ of Bose-Einstein condensate\ntransition. We have shown that, the shift of $T_c$ due to this interaction can\nnot exceed $\\sim 60 \\%$ and goes to a plateau with increasing the parameter\n$\\Omega_R/T_{c}^{0}$, where $\\Omega_R$ is the intensity of the coupling and\n$T_{c}^{0}$ is the critical temperature of the system with $\\Omega_R=0$.\nMoreover, the shift is always positive and does not depend on the sign of the\none body interaction."
    },
    {
        "anchor": "Signatures of correlated magnetic phases in the local two-particle\n  density matrix: Experiments with quantum gas microscopes have started to explore the\nantiferromagnetic phase of the two-dimensional Fermi-Hubbard model and effects\nof doping with holes away from half filling. In this work we show how direct\nmeasurements of the system averaged two-spin density matrix and its full\ncounting statistics can be used to identify different correlated magnetic\nphases with or without long-range order. We discuss examples of phases which\nare potentially realized in the Hubbard model close to half filling, including\nantiferrromagnetically ordered insulators and metals, as well as insulating\nspin-liquids and metals with topological order. For these candidate states we\npredict the doping- and temperature dependence of local correlators, which can\nbe directly measured in current experiments.",
        "positive": "Ultrafast Many-Body Dynamics in an Ultracold Rydberg-Excited Atomic Mott\n  Insulator: We report the observation and control of ultrafast non-equilibrium many-body\nelectron dynamics in Rydberg-excited spatially-ordered ultracold atoms created\nfrom a three-dimensional unity-filling atomic Mott insulator. By implementing\ntime-domain Ramsey interferometry with attosecond precision in our Rydberg\natomic system, we observe picosecond-scale ultrafast many-body dynamics that is\nessentially governed by the emergence and evolution of many-body correlations\nbetween long-range interacting atoms in an optical lattice. We analyze our\nobservations with different theoretical approaches and find that quantum\nfluctuations have to be included beyond semi-classical descriptions to describe\nthe observed dynamics. Our Rydberg lattice platform combined with an ultrafast\napproach, which is robust against environmental noises, opens the door for\nsimulating strongly-correlated electron dynamics by long-range van der Waals\ninteraction and resonant dipole-dipole interaction to the charge-overlapping\nregime in synthetic ultracold atomic crystals."
    },
    {
        "anchor": "Quantum criticality in disordered bosonic optical lattices: Using the exact Bose-Fermi mapping, we study universal properties of\nground-state density distributions and finite-temperature quantum critical\nbehavior of one-dimensional hard-core bosons in trapped incommensurate optical\nlattices. Through the analysis of universal scaling relations in the quantum\ncritical regime, we demonstrate that the superfluid to Bose glass transition\nand the general phase diagram of disordered hard-core bosons can be uniquely\ndetermined from finite-temperature density distributions of the trapped\ndisordered system.",
        "positive": "Robust stripes in the mixed-dimensional $t-J$ model: Microscopically understanding competing orders in strongly correlated systems\nis a key challenge in modern quantum many-body physics. For example, the origin\nof stripe order and its relation to pairing in the Fermi-Hubbard model remains\none of the central questions, and may help to understand the origin of\nhigh-temperature superconductivity in cuprates. Here, we analyze stripe\nformation in the doped mixed-dimensional (mixD) variant of the $t-J$ model,\nwhere charge carriers are restricted to move only in one direction, whereas\nmagnetic $\\mathrm{SU}(2)$ interactions are two-dimensional. Using the density\nmatrix renormalization group at finite temperature, we find a stable vertical\nstripe phase in the absence of pairing, featuring incommensurate magnetic order\nand long-range charge density wave profiles over a wide range of dopings. We\nfind high critical temperatures on the order of the magnetic coupling $J$,\nhence being within reach of current quantum simulators. Snapshots of the\nmany-body state, accessible to quantum simulators, reveal hidden spin\ncorrelations in the mixD setting, whereby antiferromagnetic correlations are\nenhanced when considering purely the magnetic background. The proposed model\ncan be viewed as realizing a parent Hamiltonian of the stripe phase, whose\nhidden spin correlations lead to the predicted resilience against quantum and\nthermal fluctuations."
    },
    {
        "anchor": "Anomalous thermoelectric transport in two-dimensional Bose gas: In condensed matter physics, transport measurements are essential not only\nfor the characterization of materials, but also to discern between quantum\nphases and identify new ones. The extension of these measurements into atomic\nquantum gases is emerging and will expand the scope of quantum simulation and\natomtronics. To push this frontier, we demonstrate an innovative approach to\nextract transport properties from the time-resolved redistribution of the\nparticles and energy of a trapped atomic gas. Based on the two-dimensional (2D)\nBose gas subject to weak three-body recombination we find clear evidence of\nboth conductive and thermoelectric currents. We then identify the contributions\nto the currents from thermoelectric forces and determine the Seebeck\ncoefficient (a.k.a. thermopower) and Lorenz number, both showing anomalous\nbehavior in the fluctuation and superfluid regimes. Our results call for\nfurther exploration of the transport properties, particularly thermoelectric\nproperties, of atomic quantum gases.",
        "positive": "Quasi-compactons and bistability in exciton-polariton condensates: We address stationary patterns in exciton-polariton condensates supported by\na narrow external pump beam, and we discover that even in the absence of\ntrapping potentials, such condensates may support stable localized stationary\ndissipative solutions (quasi-compactons), whose field decays faster than\nexponentially or even vanishes everywhere outside the pump spot. More general\nconditions lead to dissipative solitons which may display bistability. The\nbistability in exciton-polariton condensates, which manifests itself in\nsimultaneous existence of two stable and one unstable localized solitons with\ndifferent amplitudes, widths, and exciton-photon fractions under the same\nphysical conditions, strongly depends on the width of pump beam and is found to\ndisappear for sufficiently narrow pump beams."
    },
    {
        "anchor": "Opposite effect of spin-orbit coupling on condensation and superfluidity: We investigated effects of a Rashba-type spin-orbit coupling (SOC) on the\ncondensed density and superfluid density tensor of a two-component Fermi gas in\nthe BCS-BEC crossover at zero temperature. In anisotropic three dimensions\n(3D), we found that SOC has an opposite effect on condensation (enhanced) and\nsuperfluidity (suppressed in the SOC direction) and this effect becomes most\npronounced for very weak interactions and the SOC strength being larger than a\ncharacteristic value. Furthermore, as functions of SOC strength, the condensed\ndensity changes monotonously for all interaction parameters while the\nsuperfluid density has a minimum when the interaction parameter is below a\ncritical value. We also discussed the isotropic two dimensional (2D) case where\nanalytical expressions for the gap and number equations were obtained and the\nsame phenomena was found as that of the 3D case.",
        "positive": "Tunneling-Induced Restoration of the Degeneracy and the Time-Reversal\n  Symmetry Breaking in Optical Lattices: We study the ground-state properties of bosons loaded into the $p$-band of a\none dimensional optical lattice. We show that the phase diagram of the system\nis substantially affected by the anharmonicity of the lattice potential. In\nparticular, for a certain range of tunneling strength, the full many-body\nground state of the system becomes degenerate. In this region, an additional\nsymmetry of the system, namely the parity of the occupation number of the\nchosen orbital, is spontaneously broken. The state with nonvanishing staggered\nangular momentum, which breaks the time-reversal symmetry, becomes the true\nground state of the system."
    },
    {
        "anchor": "A damped point-vortex model for polar-core spin vortices in a\n  ferromagnetic spin-1 Bose-Einstein condensate: Ferromagnetic spin-1 Bose-Einstein condensates in the broken-axisymmetric\nphase support polar-core spin vortices (PCVs), which are intimately linked to\nthe nonequilibrium dynamics of the system. For a purely transversely magnetized\nsystem, the Turner point-vortex model predicts that PCVs behave like massive\ncharged particles interacting via a two-dimensional Coulomb potential. We test\nthe accuracy of the Turner model for two oppositely charged PCVs, via\ncomparisons with numerical simulations. While the bare Turner model shows\ndiscrepancies with our numerical results, we find that a simple rescaling of\nthe PCV mass gives much better agreement. This can be explained via a\nphenomenological damping arising from coupling to modes extrinsic to the\npoint-vortex phase space. We also identify the excitations produced following\nPCV annihilation, which help elucidate recent phase ordering results. We extend\nthe Turner model to cases where the system is magnetized both transversally and\naxially, identifying a crossover to scalar vortex dynamics for increasing\nexternal Zeeman field.",
        "positive": "Global and local condensate and superfluid fraction of a few hard core\n  bosons in a cubic optical lattice plus external harmonic confinement: We explore the global and local condensate and superfluid (SF) fractions in a\nsystem of a few hard core (HC) bosons (N=8 and N=40) trapped inside a combined\nharmonic optical cubic lattice (CHOCL) at T=0 K. The condensate fraction (CF)\nis computed for individual lattice wells by separating the one-body density\nmatrix (OBDM) of the whole system into components at the various lattice sites.\nThen each \"lattice-site\" component is diagonalized to find its eigenvalues. The\neigenvalues are obtained by a method presented earlier [Dubois and Glyde, Phys.\nRev. A {\\bf 63}, 023602 (2001)]. The effects of interference between the\ncondensates in the lattice wells on the CF in one well is also investigated.\nThe SF fraction (SFF) is calculated for N=40 by using the diffusion formula of\nPollock and Ceperley [Pollock and Ceperley, Phys. Rev. B {\\bf 36}, 8343\n(1987)]. Our chief result is an opposing behavior of the global CF and SFF with\nincreasing lattice wave vector $k$. In addition, the CF in a lattice well is\nenhanced by the interference with its neighbor wells beyond the result when the\ninterference is neglected. The global SF is depleted with a rise of the\nrepulsion between the bosons, yet at very strong interaction superfluidity is\nstill present. The global CF remains almost constant with increasing HC\nrepulsion. A reduction in the lattice dimension, i.e. an increase in the\nlattice wave vector, increases the local CF in each lattice well, but reduces\nthe corresponding local SFF. At large HC repulsion, a coexisting SF-(vacuum)MI\nphase is established."
    },
    {
        "anchor": "Finite-size effects on the cluster expansions for quantum gases in\n  restricted geometries: We have analytically obtained 1-particle density matrices for ideal Bose and\nFermi gases in both the 3-D box geometries and the harmonically trapped\ngeometries for the entire range of temperature. We have obtained quantum\ncluster expansions of the grand free energies in closed forms for the same\nsystems in the restricted geometries. We have proposed a theorem (with a proof)\nabout the generic form of the quantum cluster integral. We also have considered\nshort ranged interactions in our analyses for the quasi 1-D cases of Bose and\nFermi gases in the box geometries. Our theoretical results are exact, and are\ndirectly useful for understanding finite-size effects on quantum cluster\nexpansion of Bose and Fermi gases in the restricted geometries. Our results\nwould be relevant in the context of experimental study of spatial correlations\nin ultra-cold systems of dilute Bose and Fermi gases of alkali atoms (i) in 3-D\nmagneto-optical box traps with quasi-uniform potential around the center [1],\nand (ii) in 3-D harmonic traps [2, 3].",
        "positive": "Laser cooling to quantum degeneracy: We report on Bose-Einstein condensation (BEC) in a gas of strontium atoms,\nusing laser cooling as the only cooling mechanism. The condensate is formed\nwithin a sample that is continuously Doppler cooled to below 1\\muK on a\nnarrow-linewidth transition. The critical phase-space density for BEC is\nreached in a central region of the sample, in which atoms are rendered\ntransparent for laser cooling photons. The density in this region is enhanced\nby an additional dipole trap potential. Thermal equilibrium between the gas in\nthis central region and the surrounding laser cooled part of the cloud is\nestablished by elastic collisions. Condensates of up to 10^5 atoms can be\nrepeatedly formed on a timescale of 100ms, with prospects for the generation of\na continuous atom laser."
    },
    {
        "anchor": "Quasiparticle disintegration in fermionic superfluids: We study the fermionic quasiparticle spectrum in a zero-temperature\nsuperfluid Fermi gas, and in particular how it is modified by different\ndisintegration processes. On top of the disintegration by emission of a\ncollective boson ($1\\to2$, subject of a previous study, PRL 124, 073404), we\nconsider here disintegration events where three quasiparticles are emitted\n($1\\to3$). We show that both disintegration processes are described by a\n$t$-matrix self-energy (as well as some highly off-resonant vacuum processes),\nand we characterize the associated disintegration continua. At strong coupling,\nwe show that the quasiparticle spectrum is heavily distorted near the $1\\to3$\ndisintegration threshold. Near the dispersion minimum, where the quasiparticles\nremain well-defined, the main effect of the off-shell disintegration processes\nis to shift the location of the minimum by a value that corresponds to the\nHartree shift in the BCS limit. With our approximation of the self-energy, the\ncorrection to the energy gap with respect to the mean-field result however\nremains small, in contrast with experimental measurements.",
        "positive": "Quantum simulation of exotic PT-invariant topological nodal loop bands\n  with ultracold atoms in an optical lattice: Since the well-known PT symmetry has its fundamental significance and\nimplication in physics, where PT denotes the combined operation of\nspace-inversion P and time-reversal T, it is extremely important and intriguing\nto completely classify exotic PT-invariant topological metals and to physically\nrealize them. Here we, for the first time, establish a rigorous classification\nof topological metals that are protected by the PT symmetry using KO-theory. As\na physically realistic example, a PT-invariant nodal loop (NL) model in a 3D\nBrillouin zone is constructed, whose topological stability is revealed through\nits PT-symmetry-protected nontrivial Z2 topological charge. Based on these\nexact results, we propose an experimental scheme to realize and to detect\ntunable PT-invariant topological NL states with ultracold atoms in an optical\nlattice, in which atoms with two hyperfine spin states are loaded in a\nspin-dependent 3D OL and two pairs of Raman lasers are used to create\nout-of-plane spin-flip hopping with site-dependent phase. Such a realistic\ncold-atom setup can yield topological NL states, having a tunable ring-shaped\nband-touching line with the two-fold degeneracy in the bulk spectrum and\nnon-trivial surface states. The states are actually protected by the combined\nPT symmetry even in the absence of both P and T symmetries, and are\ncharacterized by a Z2-type invariant (a quantized Berry phase). Remarkably, we\ndemonstrate with numerical simulations that (i) the characteristic NL can be\ndetected by measuring the atomic transfer fractions in a Bloch-Zener\noscillation; (ii) the topological invariant may be measured based on the\ntime-of-flight imaging; and (iii) the surface states may be probed through\nBragg spectroscopy. The present proposal for realizing topological NL states in\ncold atom systems may provide a unique experimental platform for exploring\nexotic PT-invariant topological physics."
    },
    {
        "anchor": "Fermi accelerating an Anderson-localized Fermi gas to superdiffusion: Disorder can have dramatic impact on the transport properties of quantum\nsystems. On the one hand, Anderson localization, arising from destructive\nquantum interference of multiple-scattering paths, can halt transport entirely.\nOn the other hand, processes involving time-dependent random forces such as\nFermi acceleration, proposed as a mechanism for high-energy cosmic particles,\ncan expedite particle transport significantly. The competition of these two\neffects in time-dependent inhomogeneous or disordered potentials can give rise\nto interesting dynamics but experimental observations are scarce. Here, we\nexperimentally study the dynamics of an ultracold, non-interacting Fermi gas\nexpanding inside a disorder potential with finite spatial and temporal\ncorrelations. Depending on the disorder's strength and rate of change, we\nobserve several distinct regimes of tunable anomalous diffusion, ranging from\nweak localization and subdiffusion to superdiffusion. Especially for strong\ndisorder, where the expansion shows effects of localization, an intermediate\nregime is present in which quantum interference appears to counteract\nacceleration. Our system connects the phenomena of Anderson localization with\nsecond-order Fermi acceleration and paves the way to experimentally\ninvestigating Fermi acceleration when entering the regime of quantum transport.",
        "positive": "Observation of spin-space quantum transport induced by an atomic quantum\n  point contact: Quantum transport is ubiquitous in physics. So far, quantum transport between\nterminals has been extensively studied in solid state systems from the\nfundamental point of views such as the quantized conductance to the\napplications to quantum devices. Recent works have demonstrated a cold-atom\nanalog of a mesoscopic conductor by engineering a narrow conducting channel\nwith optical potentials, which opens the door for a wealth of research of\natomtronics emulating mesoscopic electronic devices and beyond. Here we realize\nan alternative scheme of the quantum transport experiment with ytterbium atoms\nin a two-orbital optical lattice system. Our system consists of a\nmulti-component Fermi gas and a localized impurity, where the current can be\ncreated in the spin space by introducing the spin-dependent interaction with\nthe impurity. We demonstrate a rich variety of localized-impurity-induced\nquantum transports, which paves the way for atomtronics exploiting spin degrees\nof freedom."
    },
    {
        "anchor": "Stochastic Wave-Function Simulation of Irreversible Emission Processes\n  for Open Quantum Systems in a Non-Markovian Environment: When conducting the numerical simulation of quantum transport, the main\nobstacle is a rapid growth of the dimension of entangled Hilbert subspace. The\nQuantum Monte Carlo simulation techniques, while being capable of treating the\nproblems of high dimension, are hindered by the so-called \"sign problem\". In\nthe quantum transport, we have fundamental asymmetry between the processes of\nemission and absorption of environment excitations: the emitted excitations are\nrapidly and irreversibly scattered away. Whereas only a small part of these\nexcitations is absorbed back by the open subsystem, thus exercising the\nnon-Markovian self-action of the subsystem onto itself. We were able to devise\na method for the exact simulation of the dominant quantum emission processes,\nwhile taking into account the small backaction effects in an approximate\nself-consistent way. Such an approach allows us to efficiently conduct\nsimulations of real-time dynamics of small quantum subsystems immersed in\nnon-Markovian bath for large times, reaching the quasistationary regime. As an\nexample we calculate the spatial quench dynamics of Kondo cloud for a bozonized\nKodno impurity model.",
        "positive": "Interference of Two-Dimensional Bose-Einstein Condensates in\n  Micro-Gravity: We investigate the interference of two-dimensional Bose-Einstein condensates\nin micro-gravity, which influenced by the interaction strength, initial\nmomentum, gravitational potential and phase difference. We demonstrate that the\ngravitational potential from the Earth can change the density distribution and\nphase distribution of the condensate's wave function. As time evolves, a\nportion of the gravitational potential energy of the microscopic particles can\nbe converted into kinetic energy, which changes the motion of the microscopic\nparticles, and leads to the varying of the density and phase distribution of\nthe wave function. Nevertheless, the influences of the Earth's gravity on the\nwave function can be eliminated by the micro-gravity environment, which\nconfirmed by many micro-gravity cold atom experiments. Our results present the\ninfluences of gravity and other parameters on interference of Bose-Einstein\ncondensates, which help us to reveal the intrinsic natures of the related\ntheoretical predictions and experimental phenomena. Furthermore, our work\nbuilds a bridge between the related physical phenomena and our physical\nintuition about the Bose-Einstein condensates in micro-gravity environment."
    },
    {
        "anchor": "Vortex pump for Bose-Einstein condensates utilizing a time-averaged\n  orbiting potential trap: We show that topological vortex pumping can be implemented for a dilute\nBose-Einstein condensate confined in a magnetic time-averaged orbiting\npotential trap with axial optical confinement. Contrary to earlier proposals\nfor the vortex pump, we do not employ an additional optical potential to trap\nthe condensate in the radial direction, but instead, the radial confinement is\nprovided by the magnetic field throughout the pumping cycle. By performing\nnumerical simulations based on the spin-1 Gross-Pitaevskii equation, we find\nthat several pumping cycles can be carried out to produce a highly charged\nvortex before a majority of the particles escape from the trap or before the\nvortex splits into singly charged vortices. On the other hand, we observe that\nan additional, relatively weak optical plug potential is efficient in\npreventing splitting and reducing particle loss. With these results, we hope to\nbring the vortex pump closer to experimental realization.",
        "positive": "Emergent force in a bilayer superfluid Bose-Fermi mixture: We investigate a system of two-atomic species in mixed dimensions, in which\none species is spread in a three-dimensional space and the other species is\nconfined in two parallel layers. The presence of atoms in 3-dimensions creates\nan induced potential for the ones confined in layers. Depending on the\neffective scattering length and the layer separation, the formation of p-wave\npairing within the same layer or s-wave pairing between different layers has\nbeen suggested. It is shown that these pairs cannot coexist when time-reversal\nsymmetry (TRS) is on, and there appears a transition from p-wave to s-wave as\nthe ratio of the layer separation and the effective scattering length\ndecreases. With the formation of the inter-layer pairing, we find an emergent\nforce to be present at the critical point and show that it can be derived from\nthe thermodynamic potential. This result offers a tool for experimentally\nrealizing such transitions, and can find notable potential in the field of\nquantum-thermodynamics."
    },
    {
        "anchor": "Quantum turbulence in atomic Bose-Einstein condensates: Weakly interacting, dilute atomic Bose-Einstein condensates (BECs) have\nproved to be an attractive context for the study of nonlinear dynamics and\nquantum effects at the macroscopic scale. Recently, atomic BECs have been used\nto investigate quantum turbulence both experimentally and theoretically,\nstimulated largely by the high degree of control which is available within\nthese quantum gases. In this article we motivate the use of atomic BECs for the\nstudy of turbulence, discuss the characteristic regimes of turbulence which are\naccessible, and briefly review some selected investigations of quantum\nturbulence and recent results. We focus on three stages of turbulence - the\ngeneration of turbulence, its steady state and its decay - and highlight some\nfundamental questions regarding our understanding in each of these regimes.",
        "positive": "Revealing the origin of super-Efimov states in the hyperspherical\n  formalism: Super-Efimov states are a new kind of universal three-body bound states\npredicted for three identical fermions with $p$-wave resonant interactions in\ntwo dimensions by a recent field-theoretic calculation\n[Phys.~Rev.~Lett.~\\textbf{110}, 235301 (2013)]. The binding energies of these\nstates obey a dramatic double exponential scaling $E_n=E_*\\exp(-2 e^{\\pi\nn/s_0+\\theta})$ with universal scaling $s_0=4/3$ and three-body parameters\n$E_*$ and $\\theta$. We use the hyperspherical formalism and show that the\nsuper-Efimov states originate from an emergent effective potential\n$-1/4\\rho^2-(s_0^2+1/4)/\\rho^2\\ln^2\\left(\\rho\\right)$ at large hyperradius\n$\\rho$. Moreover, for pairwise interparticle potentials with van der Waals\ntails, our numerical calculation indicates that the three-body parameters $E_*$\nand $\\theta$ are also universal and the ground super-Efimov state shall cross\nthe threshold when the $2$D $p$-wave scattering area is about $-42.0\\,\nl_\\text{vdW}^2$ with $l_\\text{vdW}$ the van der Waals length."
    },
    {
        "anchor": "Quantum dynamics of cavity assisted photoassociation of Bose-Einstein\n  condensed atoms: We explore the quantum dynamics of photoassociation of Bose-Einstein\ncondensed atoms into molecules using an optical cavity field. Inside of an\noptical resonator, photoassociation of quantum degenerate atoms involves the\ninteraction of three coupled quantum fields for the atoms, molecules, and the\nphotons. The feedback created by a high-Q optical cavity causes the cavity\nfield to become a dynamical quantity whose behavior is linked in a nonlinear\nmanner to the atoms inside and where vacuum fluctuations have a more important\nrole than in free space. We develop and compare several methods for calculating\nthe dynamics of the atom-molecule conversion process with a coherently driven\ncavity field. We first introduce an alternate operator representation for the\nHamiltonian from which we derive an improved form of mean field theory and an\napproximate solution of the Heisenberg-Langevin (HL) equations that properly\naccounts for quantum noise in the cavity field. It is shown that our improved\nmean field theory corrects several deficiencies in traditional mean field\ntheory based on expectation values of annihilation/creation operators. Also, we\nshow by direct comparison to numerical solutions of the density matrix\nequations that our approximate quantum solution of HL equations gives an\naccurate description of weakly or undriven cavities where mean field theories\nbreak down.",
        "positive": "Competition between the Fulde-Ferrell-Larkin-Ovchinnikov phase and the\n  BCS phase in the presence of an optical potential: In three dimensional Fermi gases with spin imbalance, a competition exists\nbetween Cooper pairing with zero and with finite momentum. The latter gives\nrise to the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superfluid phase, which\nonly exists in a restricted area of the phase diagram as a function of chemical\npotential imbalance and interaction strength. Applying an optical potential\nalong one direction enhances the FFLO region in this phase diagram. In this\npaper, we construct the phase diagram as a function of polarization and\ninteraction strength in order to study the competition between the FFLO phase\nand the spin balanced BCS phase. This allows to take into account the region of\nphase separation, and provides a more direct connection with experiment.\nSubsequently, we investigate the effects of the wavelength and the depth of the\noptical potential, which is applied along one direction, on the FFLO state. It\nis shown that the FFLO state can exist up to a higher level of spin imbalance\nif the wavelength of the optical potential becomes smaller. Our results give\nrise to an interesting effect: the maximal polarization at which the FFLO state\ncan exist, decreases when the interaction strength exceeds a certain critical\nvalue. This counterintuitive phenomenon is discussed and the connection to the\noptical potential is explained."
    },
    {
        "anchor": "A dark incompressible dipolar liquid of excitons: The possible phases and the nano-scale particle correlations of\ntwo-dimensional interacting dipolar particles is a long-sought problem in\nmany-body physics. Here we observe a spontaneous condensation of trapped\ntwo-dimensional dipolar excitons with internal spin degrees of freedom from an\ninteracting gas into a high density, closely packed liquid state made mostly of\ndark dipoles. Another phase transition, into a bright, highly repulsive plasma\nis observed at even higher excitation powers. The dark liquid state is formed\nbelow a critical temperature $T_c \\approx 4.8K$, and it is manifested by a\nclear spontaneous spatial condensation to a smaller and denser cloud,\nsuggesting an attractive part to the interaction which goes beyond the purely\nrepulsive dipole-dipole forces. Contributions from quantum mechanical\nfluctuations are expected to be significant in this strongly correlated, long\nliving dark liquid. This is a new example of a two-dimensional atomic-like\ninteracting dipolar quantum liquid, but where the coupling of light to its\ninternal spin degrees of freedom plays a crucial role in the dynamical\nformation and the nature of resulting ground state.",
        "positive": "Quantum walks accompanied by spin flipping in one-dimensional optical\n  lattices: We investigate continuous-time quantum walks of two fermionic atoms loaded in\none-dimensional optical lattices with on-site interaction and subjected to a\nZeeman field. The quantum walks are accompanied by spin-flipping processes. We\ncalculate the time-dependent density distributions of the two fermions with\nopposite spins which are initially positioned on the center site by means of\nexact numerical method. Besides the usual fast linear expansion behavior, we\nfind an interesting spin-flipping induced localization in the time-evolution of\ndensity distributions. We show that the fast linear expansion behavior could be\nrestored by simply ramping on the Zeeman field or further increasing the\nspin-flipping strength. The intrinsic origin of this exotic phenomenon is\nattributed to the emergence of a flat band in the single particle spectrum of\nthe system. Furthermore, we investigate the effect of on-site interaction on\nthe dynamics of the quantum walkers. The two-particle correlations are\ncalculated and signal of localization is also shown therein. A simple potential\nexperimental application of this interesting phenomenon is proposed."
    },
    {
        "anchor": "Spin transport in a tunable Heisenberg model realized with ultracold\n  atoms: Simple models of interacting spins play an important role in physics. They\ncapture the properties of many magnetic materials, but also extend to other\nsystems, such as bosons and fermions in a lattice, systems with gauge fields,\nhigh-Tc superconductors, and systems with exotic particles such as anyons and\nMajorana fermions. In order to study and compare these models, a versatile\nplatform is needed. Realizing such a system has been a long-standing goal in\nthe field of ultracold atoms. So far, spin transport has only been studied in\nthe isotropic Heisenberg model. Here we implement the Heisenberg XXZ model with\nadjustable anisotropy and use this system to study spin transport far from\nequilibrium after quantum quenches from imprinted spin helix patterns. In the\nnon-interacting XX model, we find ballistic behavior of spin dynamics, while in\nthe isotropic XXX model, we find diffusive behavior. For positive anisotropies,\nthe dynamics ranges from anomalous super-diffusion to sub-diffusion depending\non anisotropy, whereas for negative anisotropies, we observe a crossover in the\ntime domain from ballistic to diffusive transport. This behavior contrasts with\nexpectations for the linear response regime and raises new questions in\nunderstanding quantum many-body dynamics far away from equilibrium.",
        "positive": "Collective modes of a one-dimensional trapped Bose gas in the presence\n  of the anomalous density: We study the collective modes of a one-dimensional harmonically trapped\nBose-Einstein condensate in the presence of the anomalous density using the\ntime-dependent Hartree-Fock-Bogoliubov theory. Within the hydrodynamic\nequations, we derive analytical expressions for the mode frequencies and the\ndensity fluctuations of the anomalous density which constitutes the minority\ncomponent at very low temperature and feels an effective external potential\nexerted by the majority component, i.e., the condensate. On the other hand, we\nnumerically examine the temperature dependence of the breathing mode\noscillations of the condensate at finite temperature in the weak-coupling\nregime. At zero temperature, we compare our predictions with available\nexperimental data, theoretical treatments, and Monte carlo simulations in all\ninteraction regimes and the remaining hindrances are emphasized. We show that\nthe anomalous correlations have a non-negligible role on the collective modes\nat both zero and finite temperatures."
    },
    {
        "anchor": "Dilute Fermi and Bose Gases: I give a unified perspective on the properties of a variety of quantum\nliquids using the theory of quantum phase transitions. A central role is played\nby a zero density quantum critical point which is argued to control the\nproperties of the dilute gas. An exact renormalization group analysis of such\nquantum critical points leads to a computation of the universal properties of\nthe dilute Bose gas and the spinful Fermi gas near a Feshbach resonance.",
        "positive": "Spontaneously axisymmetry breaking phase in a binary mixture of spinor\n  Bose-Einstein condensates: We study the ground state phases for a mixture of two atomic spin-1\nBose-Einstein condensates (BECs) in the presence of a weak magnetic (B-) field.\nThe ground state is found to contain a broken-axisymmetry (BA) phase due to\ncompetitions among intra- and inter-species spin exchange interactions and the\nlinear Zeeman shifts. This is in contrast to the case of a single species spin-\n1 condensate, where the axisymmetry breaking results from competitions among\nthe linear and quadratic Zeeman shifts and the intra-species ferromagnetic\ninteraction. All other remaining ground state phases for the mixture are found\nto preserve axisymmetry. We further elaborate on the ground state phase diagram\nand calculate their Bogoliubov excitation spectra. For the BA phase, there\nexist three Goldstone modes attempting to restore the broken U(1) and SO(2)\nsymmetries."
    },
    {
        "anchor": "Quantum phases of dipolar bosons in multilayer optical lattice: We consider a minimal model to investigate the quantum phases of hardcore,\npolarized dipolar atoms confined in multilayer optical lattices. The model is a\nvariant of the extended Bose-Hubbard model, which incorporates intralayer\nrepulsion and interlayer attraction between the atoms in nearest-neighbour\nsites. We study the phases of this model emerging from the competition between\nthe attractive interlayer interaction and the interlayer hopping. Our results\nfrom the analytical and cluster-Gutzwiller mean-field theories reveal that\nmultimer formation occurs in the regime of weak intra and interlayer hopping\ndue to the attractive interaction. In addition, intralayer isotropic repulsive\ninteraction results in the checkerboard ordering of the multimers. This leads\nto an incompressible checkerboard multimer phase at half-filling. At higher\ninterlayer hopping, the multimers are destabilized to form resonating\nvalence-bond like states. Furthermore, we discuss the effects of thermal\nfluctuations on the quantum phases of the system.",
        "positive": "Hamiltonian Tomography of Photonic Lattices: In this letter we introduce a novel approach to Hamiltonian tomography of\nnon-interacting tight-binding photonic lattices. To begin with, we prove that\nthe matrix element of the low-energy effective Hamiltonian between sites $i$\nand $j$ may be obtained directly from $S_{ij}(\\omega)$, the (suitably\nnormalized) two-port measurement between sites $i$ and $j$ at frequency\n$\\omega$. This general result enables complete characterization of both on-site\nenergies and tunneling matrix elements in arbitrary lattice networks by\nspectroscopy, and suggests that coupling between lattice sites is actually a\ntopological property of the two-port spectrum. We further provide extensions of\nthis technique for measurement of band-projectors in finite, disordered systems\nwith good flatness ratios, and apply the tool to direct real-space measurement\nof the Chern number. Our approach demonstrates the extraordinary potential of\nmicrowave quantum circuits for exploration of exotic synthetic materials,\nproviding a clear path to characterization and control of single-particle\nproperties of Jaynes-Cummings-Hubbard lattices. More broadly, we provide a\nrobust, unified method of spectroscopic characterization of linear networks\nfrom photonic crystals to microwave lattices and everything in-between."
    },
    {
        "anchor": "Production and manipulation of wave packets from ultracold atoms in an\n  optical lattice: Within the combined potential of an optical lattice and a harmonic magnetic\ntrap, it is possible to form matter wave packets by intensity modulation of the\nlattice. An analysis of the production and motion of these wave packets\nprovides a detailed understanding of the dynamical evolution of the system. The\nmodulation technique also allows for a controllable transfer (de-excitation) of\natoms from such wave packets to a state bound by the lattice. Thus, it acts as\na beam splitter for matter waves that can selectively address different bands,\nenabling the preparation of atoms in selected localized states. The combination\nof wave packet creation and de-excitation closely resembles the well-known\nmethod of pump-probe spectroscopy. Here, we use the de-excitation for precision\nspectroscopy of the anharmonicity of the magnetic trap. Finally, we demonstrate\nthat lattice modulation can be used to excite matter wave packets to even\nhigher momenta, producing fast wave packets with potential applications in\nprecision measurements.",
        "positive": "Effective control of chemical potentials by Rabi coupling with rf-fields\n  in ultracold mixtures: We show that a linear term coupling the atoms of an ultracold binary mixture\nprovides a simple method to induce an effective and tunable population\nimbalance between them. This term is easily realized by a Rabi coupling between\ndifferent hyperfine levels of the same atomic species. The resulting effective\nimbalance holds for one-particle states dressed by the Rabi coupling and\nobtained diagonalizing the mixing matrix of the Rabi term. This way of\ncontrolling the chemical potentials applies for both bosonic and fermionic\natoms and it allows also for spatially and temporally dependent imbalances. As\na first application, we show that, in the case of two attractive fermionic\nhyperfine levels with equal chemical potentials and coupled by the Rabi pulse,\nthe same superfluid properties of an imbalanced binary mixture are recovered.\nWe finally discuss the properties of m-species mixtures in the presence of\nSU(m)-invariant interactions."
    },
    {
        "anchor": "Exotic superfluidity and pairing phenomena in atomic Fermi gases in\n  mixed dimensions: Atomic Fermi gases have been an ideal platform for simulating conventional\nand engineering exotic physical systems owing to their multiple tunable control\nparameters. Here we investigate the effects of mixed dimensionality on the\nsuperfluid and pairing phenomena of a two-component ultracold atomic Fermi gas\nwith a short-range pairing interaction, while one component is confined on a\none-dimensional (1D) optical lattice whereas the other is in a homogeneous 3D\ncontinuum. We study the phase diagram and the pseudogap phenomena throughout\nthe entire BCS-BEC crossover, using a pairing fluctuation theory. We find that\nthe effective dimensionality of the non-interacting lattice component can\nevolve from quasi-3D to quasi-1D, leading to strong Fermi surface mismatch.\nUpon pairing, the system becomes effectively quasi-two dimensional in the BEC\nregime. The behavior of $T_c$ bears similarity to that of a regular 3D\npopulation imbalanced Fermi gas, but with a more drastic departure from the\nregular 3D balanced case, featuring both intermediate temperature superfluidity\nand possible pair density wave ground state. Unlike a simple 1D optical lattice\ncase, $T_c$ in the mixed dimensions has a constant BEC asymptote.",
        "positive": "Possible condensation of Cooper triples: We theoretically discuss the possible condensation of Cooper triples, which\ncorrespond to a three-body version of Cooper pairs, in three-component Fermi\nsystems with three-body attractive interactions. A macroscopic number of Cooper\ntriples can occupy a zero center-of-mass momentum state in the presence of a\nFermi surface of constituent particles, even though the three-body operator\nexhibits anti-commutation relation associated with the Fermi-Dirac statistics.\nSuch a condensation with internal degrees of freedom is similar to bosonization\nin a system of infinite-component fermions. We propose a variational wave\nfunction for condensed Cooper triples and show that in the ground state, the\ncondensed state is energetically favored compared to the normal state. Also, we\ndiscuss effects of the Fermi-surface distortion in a lattice system described\nby a three-component Hubbard model."
    },
    {
        "anchor": "Beyond mean-field study of a binary bosonic mixture in a state-dependent\n  honeycomb lattice: We investigate a binary mixture of bosonic atoms loaded into a\nstate-dependent honeycomb lattice. For this system, the emergence of a\nso-called twisted-superfluid ground state was experimentally observed in\n[Soltan-Panahi et al., Nat. Phys. 8, 71 (2012)]. Theoretically, the origin of\nthis effect is not understood. We perform numerical simulations of an extended\nBose-Hubbard model adapted to the experimental parameters employing the\nMulti-Layer Multi-Configuration Time-Dependent Hartree method for Bosons. Our\nresults confirm the overall applicability of mean-field theory within the\nrelevant parameter range. Beyond this, we provide a detailed analysis of\ncorrelation effects correcting the mean-field result. These have the potential\nto induce asymmetries in single shot time-of-flight measurements, but we find\nno indication of the patterns characteristic of the twisted superfluid. We\ncomment on the restrictions of our model and possible extensions.",
        "positive": "Short-Time Operator Product Expansion for rf Spectroscopy of a\n  Strongly-interacting Fermi Gas: Universal relations that hold for any state provide powerful constraints on\nsystems consisting of fermions with two spin states interacting with a large\nscattering length. In radio-frequency (rf) spectroscopy, the mean shift in the\nrf frequency and the large frequency tail of the rf transition rate are\nproportional to the contact, which measures the density of pairs with small\nseparations. We show that these universal relations can be derived and extended\nby using the short-time operator product expansion of quantum field theory.\nThis is a general method for identifying aspects of many-body physics that are\ncontrolled by few-body physics."
    },
    {
        "anchor": "Symmetry-protected topological phases in lattice gauge theories:\n  topological QED$_2$: The interplay of symmetry, topology, and many-body effects in the\nclassification of possible phases of matter poses a formidable challenge that\nis attracting great attention in condensed-matter physics. Such many-body\neffects are typically induced by inter-particle interactions involving an\naction at a distance, such as the Coulomb interaction between electrons in a\nsymmetry-protected topological (SPT) phase. In this work, we show that similar\nphenomena also appear in high-energy physics, where inter-particle interactions\nare mediated by gauge bosons, and constrained by a local gauge symmetry. We\nintroduce a variant of the so-called Schwinger model, which describes quantum\nelectrodynamics in (1+1) dimensions (QED$_2$), and show that it can host SPT\nphases with a topological contribution to the vacuum {\\theta} angle, which\nleads to a new type of topological QED$_2.$ We use bosonization and\ndensity-matrix renormalization group techniques to study its rich phase diagram\nin great detail, and present a scheme for its realization in experiments of\nultra-cold atoms in optical lattices.",
        "positive": "Impurity in a three-dimensional unitary Bose gas: By using simple and efficient method we discuss properties of a single\nimpurity immersed in three-dimensional Bose gas with the interaction between\nparticles tuned to unitary limit. Particularly, adopting the mean-field-like\napproximation we present the first estimations for the low-momentum parameters\nof the impurity spectrum, namely, the binding energy, the effective mass and\nthe quasiparticle residue both for repulsive and attractive Bose polarons in\nthe unitary gas."
    },
    {
        "anchor": "Detecting D-Wave Pairing and Collective Modes in Fermionic Condensates\n  with Bragg Scattering: We show how the appearance of d-wave pairing in fermionic condensates\nmanifests itself in inelastic light scattering. Specifically, we calculate the\nBragg scattering intensity from the dynamic structure factor and the spin\nsusceptibility, which can be inferred from spin flip Raman transitions. This\ninformation provides a precise tool with which we can identify nontrivial\ncorrelations in the state of the system beyond the information contained in the\ndensity profile imaging alone. Due to the lack of Coulomb effects in neutral\nsuperfluids, this is also an opportunity to observe the Anderson-Bogoliubov\ncollective mode.",
        "positive": "Quantum glass of interacting bosons with off-diagonal disorder: We study disordered interacting bosons described by the Bose-Hubbard model\nwith Gaussian-distributed random tunneling amplitudes. It is shown that the\noff-diagonal disorder induces a spin-glass-like ground state, characterized by\nrandomly frozen quantum-mechanical U(1) phases of bosons. To access\ncriticality, we employ the \"$n$-replica trick\", as in the spin-glass theory,\nand the Trotter-Suzuki method for decomposition of the statistical density\noperator, along with numerical calculations. The interplay between disorder,\nquantum and thermal fluctuations leads to phase diagrams exhibiting a glassy\nstate of bosons, which are studied as a function of model parameters. The\nconsidered system may be relevant for quantum simulators of optical-lattice\nbosons, where the randomness can be introduced in a controlled way. The latter\nis supported by a proposition of experimental realization of the system in\nquestion."
    },
    {
        "anchor": "Self-consistent derivation of the modified Gross-Pitaevskii equation\n  with Lee-Huang-Yang correction: We consider a dilute and ultracold bosonic gas of weakly-interacting atoms.\nWithin the framework of quantum field theory we derive a zero-temperature\nmodified Gross-Pitaevskii equation with beyond-mean-field corrections due to\nquantum depletion and anomalous density. This result is obtained from the\nstationary equation of the Bose-Einstein order parameter coupled to the\nBogoliubov-de Gennes equations of the out-of-condensate field operator. We show\nthat, in the presence of a generic external trapping potential, the key steps\nto get the modified Gross-Pitaevskii equation are the semiclassical\napproximation for the Bogoliubov-de Gennes equations, a slowly-varying order\nparameter, and a small quantum depletion. In the uniform case, from the\nmodified Gross-Pitaevskii equation we get the familiar equation of state with\nLee-Huang-Yang correction.",
        "positive": "An eccentrically perturbed Tonks-Girardeau gas: We investigate the static and dynamic properties of a Tonks-Girardeau gas in\na harmonic trap with an eccentric $\\delta$-perturbation of variable strength.\nFor this we first find the analytic eigensolution of the single particle\nproblem and use this solution to calculate the spatial density and energy\nprofiles of the many particle gas as a function of the strength and position of\nthe perturbation. We find that the crystal nature of the Tonks state is\nreflected in both the lowest occupation number and momentum distribution of the\ngas. As a novel application of our model, we study the time evolution of the\nthe spatial density after a sudden removal of the perturbation. The dynamics\nexhibits collapses and revivals of the original density distribution which\noccur in units of the trap frequency. This is reminiscent of the Talbot effect\nfrom classical optics."
    },
    {
        "anchor": "Spin-polarized fermions with $p$-wave interactions: We study quantum degenerate Fermi gases of ${^6}$Li atoms at high densities\n($10^{15}$ cm$^{-3}$) and observe elastic and inelastic $p$-wave collisions far\naway from any Feshbach resonance. $P$-wave evaporation reaches temperatures of\n$T/T_F=0.42$ partially limited by the slow transfer of energy from high to low\nvelocities through $p$-wave collisions. Via cross-dimensional thermalization,\nthe $p$-wave background scattering volume is determined to be $\\lvert V_p\n\\rvert =(39^{+1.3}_{-1.6}a_0)^3$. $P$-wave dipolar relaxation creates a\nmetastable mixture of the lowest and highest hyperfine states.",
        "positive": "Out-of-equilibrium dynamics of multiple second-order quantum phase\n  transitions in extended Bose-Hubbard model: Superfluid, supersolid and\n  density wave: In this paper, we study the dynamics of the Bose-Hubbard model with the\nnearest-neighbor repulsion by using time-dependent Gutzwiller methods. Near the\nunit filling, the phase diagram of the model contains density wave (DW),\nsupersolid (SS) and superfluid (SF). The three phases are separated by two\nsecond-order phase transitions. We study \"slow-quench\" dynamics by varying the\nhopping parameter in the Hamiltonian as a function of time. In the phase\ntransitions from the DW to SS and from the DW to SF, we focus on how the SF\norder forms and study scaling laws of the SF correlation length, vortex\ndensity, etc. The results are compared with the Kibble-Zurek scaling. On the\nother hand from the SF to DW, we study how the DW order evolves with generation\nof the domain walls and vortices. Measurement of first-order SF coherence\nreveals interesting behavior in the DW regime."
    },
    {
        "anchor": "Effects of atom losses on a one-dimensional lattice gas of hardcore\n  bosons: Atom losses occur naturally during cold atoms experiments. Since this\nphenomenon is unavoidable, it is important to understand its effect on the\nremaining atoms. Here we study a gas of hard-core bosons on a lattice subject\nto $K$-body losses (where $K=1,2,3,\\dots$ is the number of atoms lost in each\nloss event), and in particular we investigate the effect of losses on the\nrapidity distribution $\\rho(k)$ of the atoms. Under the assumption that losses\nare weak enough so that the system relaxes between two loss events, we are able\nto determine the loss functional $F[\\rho](k)$ encoding the loss process for\n$K$-body losses. We derive closed expressions for the cases of one- and\ntwo-body losses, and show their effects on the evolution of the total number of\nparticles. Then we add a harmonic trapping potential and study the evolution of\nthe position-dependent rapidity distribution of this system by solving\nnumerically the evolution equation for one-, two- and three-body losses.",
        "positive": "Bose-Hubbard model in a ring-shaped optical lattice with high filling\n  factors: The high-barrier quantum tunneling regime of a Bose-Einstein condensate\nconfined in a ring-shaped optical lattice is investigated. By means of a change\nof basis transformation, connecting the set of `vortex' Bloch states and a\nWannier-like set of localized wave functions, we derive a generalized\nBose-Hubbard Hamiltonian. In addition to the usual hopping rate terms, such a\nHamiltonian takes into account interaction-driven tunneling processes, which\nare shown to play a principal role at high filling factors, when the standard\nhopping rate parameter turns out to be negative. By calculating the energy and\natomic current of a Bloch state, we show that such a hopping rate must be\nreplaced by an effective hopping rate parameter containing the additional\ncontribution an interaction-driven hopping rate. Such a contribution turns out\nto be crucial at high filling factors, since it preserves the positivity of the\neffective hopping rate parameter. Level crossings between the energies per\nparticle of a Wannier-like state and the superfluid ground state are\ninterpreted as a signature of the transition to configurations with\nmacroscopically occupied states at each lattice site."
    },
    {
        "anchor": "Vortices and antivortices in two-dimensional ultracold Fermi gases: Vortices are commonly observed in the context of classical hydrodynamics:\nfrom whirlpools after stirring the coffee in a cup to a violent atmospheric\nphenomenon such as a tornado, all classical vortices are characterized by an\narbitrary circulation value of the local velocity field. On the other hand the\nappearance of vortices with quantized circulation represents one of the\nfundamental signatures of macroscopic quantum phenomena. In two-dimensional\nsuperfluids quantized vortices play a key role in determining\nfinite-temperature properties, as the superfluid phase and the normal state are\nseparated by a vortex unbinding transition, the Berezinskii-Kosterlitz-Thouless\ntransition. Very recent experiments with two-dimensional superfluid fermions\nmotivate the present work: we present theoretical results based on the\nrenormalization group showing that the universal jump of the superfluid density\nand the critical temperature crucially depend on the interaction strength,\nproviding a strong benchmark for forthcoming investigations.",
        "positive": "N\u00e9el temperature and thermodynamics of the half-filled 3D Hubbard\n  model by Diagrammatic Determinant Monte Carlo: We study thermodynamics of the 3D Hubbard model at half filling on approach\nto the N\\'eel transition by means of large-scale unbiased Diagrammatic\nDeterminant Monte Carlo simulations. We obtain the transition temperature in\nthe strongly correlated regime, as well as temperature dependence of energy,\nentropy, double occupancy, and the nearest-neighbor spin correlation function.\nOur results improve the accuracy of previous unbiased studies and present\naccurate benchmarks in the ongoing effort to realize the antiferromagnetic\nstate of matter with ultracold atoms in optical lattices."
    },
    {
        "anchor": "Quantum and Thermal Phase Transitions in a Bosonic Atom-Molecule Mixture\n  in a Two-dimensional Optical Lattice: We study the ground state and the thermal phase diagram of a two-species\nBose-Hubbard model, with $U(1)\\times \\mathbb{Z}_2$ symmetry, describing atoms\nand molecules on a 2D optical lattice interacting via a Feshbach resonance.\nUsing quantum Monte Carlo simulations and mean field theory, we show that the\nconversion between the two-species, coherently coupling the atomic and\nmolecular states, has a crucial impact on the Mott-Superfluid transition and\nstabilizes an insulating phase with a gap controlled by the conversion term --\n\\textit{the Feshbach insulator} -- instead of a standard Mott insulating phase.\nDepending on the detuning between atoms and molecules, this model exhibits\nthree phases: the Feshbach insulator, a molecular condensate coexisting with\nnon condensed atoms and a mixed atomic-molecular condensate. Employing a\nfinite-size scaling method, we observe 3D XY (3D Ising) transition when $U(1)$\n($ \\mathbb{Z}_2$) is broken whereas the transition is first-order when both\n$U(1)$ and $ \\mathbb{Z}_2$ symmetries are spontaneously broken. The finite\ntemperature phase diagram is also discussed. The thermal disappearance of the\nmolecular superfluid leads to a Berezinskii-Kosterlitz-Thouless transition with\nunusual universal jump in the superfluid density. The loss of the\nquasi-long-range coherence of the mixed atomic and molecular superfluid is more\nsubtle since only atoms exhibit conventional Berezinskii-Kosterlitz-Thouless\ncriticality. We also observe a classical first-order transition between the\nmixed superfluid and the normal Bose liquid at low temperature.",
        "positive": "Atom-dimer and dimer-dimer scattering in fermionic mixtures near a\n  narrow Feshbach resonance: We develop a diagrammatic approach for solving few-body problems in\nheteronuclear fermionic mixtures near a narrow interspecies Feshbach resonance.\nWe calculate s-, p-, and d-wave phaseshifts for the scattering of an atom by a\nweakly-bound dimer. The fermionic statistics of atoms and the composite nature\nof the dimer lead to a strong angular momentum dependence of the atom-dimer\ninteraction, which manifests itself in a peculiar interference of the scattered\ns- and p-waves. This effect strengthens with the mass ratio and is remarkably\npronounced in 40K-(40K-6Li) atom-dimer collisions. We calculate the scattering\nlength for two dimers formed near a narrow interspecies resonance. Finally, we\ndiscuss the collisional relaxation of the dimers to deeply bound states and\nevaluate the corresponding rate constant as a function of the detuning and\ncollision energy."
    },
    {
        "anchor": "Feshbach resonances in 3He*-4He* mixtures: We discuss the stability of homonuclear and heteronuclear mixtures of 3He and\n4He atoms in the metastable 2^3S_1 state (He*) and predict positions and widths\nof Feshbach resonances by using the Asymptotic Bound-state Model (ABM). All\ncalculations are performed without fit parameters, using \\emph{ab-initio}\ncalculations of molecular potentials. One promising very broad Feshbach\nresonance (\\Delta B=72.9^{+18.3}_{-19.3} mT) is found that allows for tuning of\nthe inter-isotope scattering length.",
        "positive": "Polariton condensation with saturable molecules dressed by vibrational\n  modes: Polaritons, mixed light-matter quasiparticles, undergo a transition to a\ncondensed, macroscopically coherent state at low temperatures or high\ndensities. Recent experiments show that coupling light to organic molecules\ninside a microcavity allows condensation at room temperature. The molecules act\nas saturable absorbers with transitions dressed by molecular vibrational modes.\nMotivated by this we calculate the phase diagram and spectrum of a modified\nTavis-Cummings model, describing vibrationally dressed two-level systems,\ncoupled to a cavity mode. Coupling to vibrational modes can induce re-entrance,\ni.e. a normal-condensed-normal sequence with decreasing temperature and can\ndrive the transition first order."
    },
    {
        "anchor": "Heavy fermions in an optical lattice: We employ a mean-field theory to study ground-state properties and transport\nof a two-dimensional gas of ultracold alklaline-earth metal atoms governed by\nthe Kondo Lattice Hamiltonian plus a parabolic confining potential. In a\nhomogenous system this mean-field theory is believed to give a qualitatively\ncorrect description of heavy fermion metals and Kondo insulators: it reproduces\nthe Kondo-like scaling of the quasiparticle mass in the former, and the same\nscaling of the excitation gap in the latter. In order to understand\nground-state properties in a trap we extend this mean-field theory via\nlocal-density approximation. We find that the Kondo insulator gap manifests as\na shell structure in the trapped density profile. In addition, a strong\nsignature of the large Fermi surface expected for heavy fermion systems\nsurvives the confinement, and could be probed in time-of-flight experiments.\nFrom a full self-consistent diagonalization of the mean-field theory we are\nable to study dynamics in the trap. We find that the mass enhancement of\nquasiparticle excitations in the heavy Fermi liquid phase manifests as slowing\nof the dipole oscillations that result from a sudden displacement of the trap\ncenter.",
        "positive": "Bose-Einstein condensation of photons and grand-canonical condensate\n  fluctuations: We review recent experiments on the Bose-Einstein condensation of photons in\na dye-filled optical microresonator. The most well-known example of a photon\ngas, photons in blackbody radiation, does not show Bose-Einstein condensation.\nInstead of massively populating the cavity ground mode, photons vanish in the\ncavity walls when they are cooled down. The situation is different in an\nultrashort optical cavity imprinting a low-frequency cutoff on the photon\nenergy spectrum that is well above the thermal energy. The latter allows for a\nthermalization process in which both temperature and photon number can be tuned\nindependently of each other or, correspondingly, for a non-vanishing photon\nchemical potential. We here describe experiments demonstrating the\nfluorescence-induced thermalization and Bose-Einstein condensation of a\ntwo-dimensional photon gas in the dye microcavity. Moreover, recent\nmeasurements on the photon statistics of the condensate, showing Bose-Einstein\ncondensation in the grandcanonical ensemble limit, will be reviewed."
    },
    {
        "anchor": "Fractional quantum Hall physics and higher-order momentum correlations\n  in a few spinful fermionic contact-interacting ultracold atoms in rotating\n  traps: The fractional quantum Hall effect (FQHE) is theoretically investigated, with\nnumerical and algebraic approaches, in assemblies of a few spinful ultracold\nneutral fermionic atoms, interacting via repulsive contact potentials and\nconfined in a single rapidly rotating two-dimensional harmonic trap. Going\nbeyond the commonly used second-order correlations in the real configuration\nspace, the methodology in this paper will assist the analysis of experimental\nobservations by providing benchmark results for $N$-body spin-unresolved, as\nwell as spin-resolved, momentum correlations measurable in time-of-flight\nexperiments with individual particle detection. Our analysis shows that the\nfew-body lowest-Landau-level (LLL) states with good magic angular momenta\nexhibit inherent ordered quantum structures in the $N$-body correlations,\nsimilar to those associated with rotating Wigner molecules (WMs), familiar from\nthe field of semiconductor quantum dots under high magnetic fields. The\napplication of a small perturbing stirring potential induces, at the ensuing\navoided crossings, formation of symmetry broken states exhibiting ordered\npolygonal-ring structures, explicitly manifest in the single-particle density\nprofile of the trapped particles. Away from the crossings, an LLL state\nobtained from exact diagonalization of the microscopic Hamiltonian, found to be\nwell-described by a (1,1,1) Halperin two-component variational wavefunction,\nrepresents also a spinful rotating WM. Analysis of the calculated LLL\nwavefunction enables a two-dimensional generalization of the Girardeau\none-dimensional 'fermionization' scheme, originally invoked for mapping of\nbosonic-type wave functions to those of spinless fermions.",
        "positive": "Fate of a Bose-Einstein Condensate in the Presence of Spin-Orbit\n  Coupling: Intensive theoretical studies have recently predicted that a Bose-Einstein\ncondensate will exhibit a variety of novel properties if spin-orbit coupling is\npresent. However, an unambiguous fact has also been pointed out: Rashba\ncoupling destroys a condensate of noninteracting bosons even in high\ndimensions. Therefore, a conceptually important question arises as to whether\nor not a condensate exists in the presence of interaction and a general type of\nspin-orbit coupling. Here we show that interaction qualitatively changes the\nground state of bosons under Rashba spin-orbit coupling. Any infinitesimal\nrepulsion forces bosons either to condense at one or two momentum states or to\nform a superfragmented state that is a superposition of infinite numbers of\nfragmented condensates. The superfragmented state is unstable against the\nanisotropy of spin-orbit coupling in systems with large numbers of particles,\nleading to the revival of a condensate in current experiments."
    },
    {
        "anchor": "Response functions for the two-dimensional ultracold Fermi gas:\n  dynamical BCS theory and beyond: Response functions are central objects in physics. They provide crucial\ninformation about the behavior of physical systems, and they can be directly\ncompared with scattering experiments involving particles like neutrons, or\nphotons. Calculations of such functions starting from the many-body Hamiltonian\nof a physical system are challenging, and extremely valuable. In this paper we\nfocus on the two-dimensional (2D) ultracold Fermi atomic gas which has been\nrealized experimentally. We present an application of the dynamical BCS theory\nto obtain response functions for different regimes of interaction strengths in\nthe 2D gas with zero-range attractive interaction. We also discuss\nauxiliary-field quantum Monte Carlo (AFQMC) methods for the calculation of\nimaginary-time correlations in these dilute Fermi gas systems. Illustrative\nresults are given and comparisons are made between AFQMC and dynamical BCS\ntheory results to assess the accuracy of the latter.",
        "positive": "Speed of sound in disordered Bose-Einstein condensates: Disorder modifies the sound-wave excitation spectrum of Bose-Einstein\ncondensates. We consider the classical hydrodynamic limit, where the disorder\ncorrelation length is much longer than the condensate healing length. By\nperturbation theory, we compute the phonon lifetime and correction to the speed\nof sound. This correction is found to be negative in all dimensions, with\nuniversal asymptotics for smooth correlations. Considering in detail optical\nspeckle potentials, we find a quite rich intermediate structure. This has\nconsequences for the average density of states, particularly in one dimension,\nwhere we find a \"boson dip\" next to a sharp \"boson peak\" as function of\nfrequency. In one dimension, our prediction is verified in detail by a\nnumerical integration of the Gross-Pitaevskii equation."
    },
    {
        "anchor": "Quantum damping of Fermi-Pasta-Ulam revivals in ultracold Bose gases: We propose an experimental scheme for studying the Fermi-Pasta-Ulam (FPU)\nphenomenon in a quantum mechanical regime using ultracold atoms. Specifically,\nwe suggest and analyze a setup of one-dimensional Bose gases confined into an\noptical lattice. The strength of quantum fluctuations is controlled by tuning\nthe number of atoms per lattice sites (filling factor). By simulating the\nreal-time dynamics of the Bose-Hubbard model by means of the exact numerical\nmethod of time-evolving block decimation, we investigate the effects of quantum\nfluctuations on the FPU recurrence and show that strong quantum fluctuations\ncause significant damping of the FPU oscillation.",
        "positive": "Probing three-body correlations in a quantum gas using the measurement\n  of the third moment of density fluctuations: We perform measurements of the third moment of atom number fluctuations in\nsmall slices of a very elongated weakly interacting degenerate Bose gas. We\nfind a positive skewness of the atom number distribution in the ideal gas\nregime and a reduced skewness compatible with zero in the quasi-condensate\nregime. For our parameters, the third moment is a thermodynamic quantity whose\nmeasurement constitutes a sensitive test of the equation of state and our\nresults are in agreement with a modified Yang-Yang thermodynamic prediction.\nMoreover, we show that the measured skewness reveals the presence of true three\nbody correlations in the system."
    },
    {
        "anchor": "Phase transitions of the coherently coupled two-component Bose gas in a\n  square optical lattice: We investigate properties of an ultracold, two-component bosonic gas in a\nsquare optical lattice at unit filling. In addition to density-density\ninteractions, the atoms are subject to coherent light-matter interactions that\ncouple different internal states. We examine the influence of this coherent\ncoupling on the system and its quantum phases by using Gutzwiller mean field\ntheory as well as bosonic dynamical mean field theory. We find that the\ninterplay of strong inter-species repulsion and coherent coupling affects the\nMott insulator to superfluid transition and shifts the tip of the Mott lobe\ntoward higher values of the tunneling amplitude. In the strongly interacting\nMott regime, the resulting Bose-Hubbard model can be mapped onto an effective\nspin Hamiltonian that offers additional insights into the observed phenomena.",
        "positive": "Grey solitons in a strongly interacting superfluid Fermi Gas: The Bardeen-Cooper-Schrieffer to Bose-Einstein condensate (BCS to BEC)\ncrossover problem is solved for stationary grey solitons via the Boguliubov-de\nGennes equations at zero temperature. These \\emph{crossover solitons} exhibit a\nlocalized notch in the gap and a characteristic phase difference across the\nnotch for all interaction strengths, from BEC to BCS regimes. However, they do\nnot follow the well-known Josephson-like sinusoidal relationship between\nvelocity and phase difference except in the far BEC limit: at unitary the\nvelocity has a nearly linear dependence on phase difference over an extended\nrange. For fixed phase difference the soliton is of nearly constant depth from\nthe BEC limit to unitarity and then grows progressively shallower into the BCS\nlimit, and on the BCS side Friedel oscillations are apparent in both gap\namplitude and phase. The crossover soliton appears fundamentally in the gap; we\nshow, however, that the density closely follows the gap, and the soliton is\ntherefore observable. We develop an approximate power law relationship to\nexpress this fact: the density of grey crossover solitons varies as the square\nof the gap amplitude in the BEC limit and a power of about 1.5 at unitarity."
    },
    {
        "anchor": "Unconventional Spin Density Waves in Dipolar Fermi Gases: The conventional spin density wave (SDW) phase (Overhauser, 1962), as found\nin antiferromagnetic metal for example (Fawcett 1988), can be described as a\ncondensate of particle-hole pairs with zero angular momentum, $\\ell=0$,\nanalogous to a condensate of particle-particle pairs in conventional\nsuperconductors. While many unconventional superconductors with Cooper pairs of\nfinite $\\ell$ have been discovered, their counterparts, density waves with\nnon-zero angular momenta, have only been hypothesized in two-dimensional\nelectron systems (Nayak, 2000). Using an unbiased functional renormalization\ngroup analysis, we here show that spin-triplet particle-hole condensates with\n$\\ell=1$ emerge generically in dipolar Fermi gases of atoms (Lu, Burdick, and\nLev, 2012) or molecules (Ospelkaus et al., 2008; Wu et al.) on optical lattice.\nThe order parameter of these exotic SDWs is a vector quantity in spin space,\nand, moreover, is defined on lattice bonds rather than on lattice sites. We\ndetermine the rich quantum phase diagram of dipolar fermions at half-filling as\na function of the dipolar orientation, and discuss how these SDWs arise amidst\ncompetition with superfluid and charge density wave phases.",
        "positive": "Superfluid-Mott glass quantum multicritical point on a percolating\n  lattice: We employ large-scale Monte Carlo simulations to study a particle-hole\nsymmetric site-diluted quantum rotor model in two dimensions. The ground state\nphase diagram of this system features two distinct quantum phase transitions\nbetween the superfluid and the insulating (Mott glass) phases. They are\nseparated by a multicritical point. The generic transition for dilutions below\nthe lattice percolation threshold is driven by quantum fluctuations while the\ntransition across the percolation threshold is due to the geometric\nfluctuations of the lattice. We determine the location of the multicritical\npoint between these two transitions and find its critical behavior. The\nmulticritical exponents read $z=1.72(2)$, $\\beta/\\nu=0.41(2)$, and\n$\\gamma/\\nu=2.90(5)$ . We compare our results to other quantum phase\ntransitions in disordered systems, and we discuss experiments."
    },
    {
        "anchor": "Smooth, holographically generated ring trap for the investigation of\n  superfluidity in ultracold atoms: We discuss the suitability of holographically generated optical potentials\nfor the investigation of superfluidity in ultracold atoms. By using a spatial\nlight modulator and a feedback enabled algorithm we generate a smooth ring with\nvariable bright regions that can be dynamically rotated to stir ultracold atoms\nand induce superflow. We also comment on its future integration into a cold\natoms experiment.",
        "positive": "Estimated values of the kinetic energy for liquid $^3$He: The kinetic energy is estimated for the ground-state of liquid $^3$He at\nequilibrium density. The obtained value for this quantity, $10.16\\pm0.05$\nK/atom at density $0.0163~\\mbox{\\AA}$, is in agreement with most of the\nexperimental data found in the literature. This result resolves a long-standing\ncontroversy between experimental and theoretical values of this quantity. The\nvariational path integral method, an \"exact\" quantum Monte Carlo method\nextended for fermionic systems, is applied in the calculations. The results\nobtained are subjected only to the restrictions imposed by a chosen nodal\nstructure without any further approximation, even for quantities that do not\ncommute with the Hamiltonian. The required fixed-node approximation entails an\nimplementation that allows a more effective estimation of the quantities of\ninterest. Total and potential energies together with the radial distribution\nfunction are also computed."
    },
    {
        "anchor": "Fluctuations and correlations in rotating Bose-Einstein condensates: We investigate the effects of correlations on the properties of the ground\nstate of the rotating harmonically-trapped Bose gas by adding Bogoliubov\nfluctuations to the mean-field ground state of an $N$-particle single-vortex\nsystem. We demonstrate that the fluctuation-induced correlations lower the\nenergy compared to that of the mean-field ground state, that the vortex core is\npushed slightly away from the center of the trap, and that an unstable mode\nwith negative energy (for rotations slower than a critical frequency) emerges\nin the energy spectrum, thus, pointing to a better state for slow rotation. We\nconstruct mean-field ground states of 0-, 1-, and 2-vortex states as a function\nof rotation rate and determine the critical frequencies for transitions between\nthese states, as well as the critical frequency for appearance of a metastable\nstate with an off-center vortex and its image vortex in the evanescent tail of\nthe cloud.",
        "positive": "The role of inter-well tunneling strength on coherence dynamics of\n  two-species Bose-Einstein condensates: Coherence dynamics of two-species Bose-Einstein condensates in double wells\nis investigated in mean field approximation. We show that the system can\nexhibit decoherence phenomena even without the condensate-environment coupling\nand the variation tendency of the degree of coherence depends on not only the\nparameters of the system but also the initial states. We also investigate the\ntime evolution of the degree of coherence for a Rosen-Zener form of tunneling\nstrength, and propose a method to get a condensate system with certain degree\nof coherence through a time-dependent tunneling strength."
    },
    {
        "anchor": "Finite-temperature properties of one-dimensional hard-core bosons in a\n  quasiperiodic optical lattice: We investigate the properties of impenetrable bosons confined in a\none-dimensional lattice at finite temperature in the presence of an additional\nincommensurate periodic potential. Relying on the exact Fermi-Bose mapping, we\nstudy the effects of temperature on the one-particle density matrix and related\nquantities such as the momentum distribution function and the natural orbitals.\nWe found evidence of a finite-temperature crossover related to the\nzero-temperature superfluid-to-Bose-glass transition that induces a\ndelocalization of the lowest natural orbitals.",
        "positive": "Topologically non-trivial superfluid phases and Majorana fermions from\n  Kohn-Luttinger effect: Spin-triplet p-wave superfluids of single-species (or spin-polarized)\nfermionic atoms is a topological superfluid. In 2D such a superfluid supports\nzero-energy topological Majorana fermion excitations in order parameter defects\nsuch as vortices and sample edges. In 3D these superfluids support\ntopologically protected Dirac points in the bulk spectrum and flat surface\nMajorana arcs. Despite the promise, creating a spin-triplet p-wave\nsingle-species fermionic superfluid either from direct p-wave Feshbach\nresonance or indirectly from the recently proposed artificial spin-orbit and\nZeeman couplings can be technologically challenging. Here we show that such\ntopological superfluids can be far more simply created by using the\nKohn-Luttinger effect applied to two species of spin-polarized fermions with a\ndensity imbalance. We discuss how the topological Majorana excitations of the\nresulting superfluids can be identified using recently-developed experimental\ntechniques."
    },
    {
        "anchor": "Peaks and widths of radio-frequency spectra: An analysis of the phase\n  diagram of ultra-cold Fermi gases: We provide a comprehensive theoretical study of the radio-frequency (rf)\nspectra of a two-component Fermi gas with balanced populations in the normal\nregion of the temperature-vs-coupling phase diagram. In particular, rf spectra\nare analyzed in terms of two characteristic peaks, which can be either distinct\nor overlapping. On the BEC side of the crossover, these two contributions are\nassociated with a fermionic quasi-particle peak and a bosonic-like contribution\ndue to pairing. On the BCS side of the crossover, the two peaks are instead\nassociated with interactions between particles occurring, respectively, at high\nor low relative momenta. Through this two-peak analysis, we show how and to\nwhat extent the correlation between the widths of the rf spectra and the pair\nsize, previously identified in the superfluid phase at low temperature, can be\nextended to the normal phase, as well as how the temperature-vs-coupling phase\ndiagram of the BCS-BEC crossover can be partitioned in a number of distinct\nphysical sectors. Several analytic results for the shape and widths of the rf\nspectra are also derived in appropriate temperature and coupling limits.",
        "positive": "Effective field theory for two-species bosons in an optical lattice:\n  Multiple order, the Nambu-Goldstone bosons, the Higgs mode and vortex lattice: In the previous papers, we studied the bosonic t-J mode and derived an\neffective field theory, which is a kind of quantum XY model. The bosonic t-J\nmodel is expected to be realized by experiments of two-component cold atoms in\nan optical lattice. In this paper, we consider a similar XY model that\ndescribes phase diagram of the t-J model with a mass difference. Phase diagram\nand critical behavior of the quantum XY model are clarified by means of the\nMonte-Carlo simulations. Effective field theory that describes the phase\nstructure and low-energy excitations of the quantum XY model is derived.\nNambu-Goldstone bosons and the Higgs mode are studied by using the effective\nfield theory and interesting findings are obtained for the system with multiple\norder, i.e., Bose-Einstein condensations and pseudo-spin symmetry. We also\ninvestigate physical properties of the quantum XY model in an effective\nmagnetic field that is realized by rotating the optical lattice, etc. We show\nthat low-energy states of the system strongly depend on the strength of the\n\"magnetic field\". For some specific strength of the magnetic field, vortex\nlattice forms and the correlation function of the bosons exhibits solid like\nbehavior, which is a kind of Bose-Einstein condensation."
    },
    {
        "anchor": "Magnetic impurity in a one-dimensional few-fermion system: We present a numerical analysis of spin-$\\frac{1}{2}$ fermions in a\none-dimensional harmonic potential in the presence of a magnetic point-like\nimpurity at the center of the trap. The model represents a few-body analogue of\na magnetic impurity in the vicinity of an $s$-wave superconductor. Already for\na few particles we find a ground-state level crossing between sectors with\ndifferent fermion parities. We interpret this crossing as a few-body precursor\nof a quantum phase transition, which occurs when the impurity `breaks' a Cooper\npair. This picture is further corroborated by analyzing density-density\ncorrelations in momentum space. Finally, we discuss how the system may be\nrealized with existing cold-atoms platforms.",
        "positive": "Condensation of Cooper Triples: The condensation of Cooper pairs, originating from the Fermi-surface\ninstability due to a weakly attractive interaction between two fermions, opened\na new frontier for exploring many-body physics in interdisciplinary contexts.\nIn this work, we discuss the possible condensation of Cooper triples, which are\nthree-body counterparts of Cooper pairs for three-component fermions with a\nthree-body attraction. Although each composite trimer-like state obeys the\nFermi-Dirac statistics, its aggregate can form a condensate at zero\ncenter-of-mass momentum in the presence of the internal degrees of freedom\nassociated with the relative momenta of constituent particles of momenta close\nto the Fermi surface. Such condensation can be regarded as bosonization in\ninfinite-component fermions. We propose a variational wave function for the\ncondensate of Cooper triples in analogy with the Bardeen-Cooper-Schrieffer\nground state and obtain the ground-state energy."
    },
    {
        "anchor": "Tracking evaporative cooling of a mesoscopic atomic quantum gas in real\n  time: The fluctuations in thermodynamic and transport properties in many-body\nsystems gain importance as the number of constituent particles is reduced.\nUltracold atomic gases provide a clean setting for the study of mesoscopic\nsystems; however, the detection of temporal fluctuations is hindered by the\ntypically destructive detection, precluding repeated precise measurements on\nthe same sample. Here, we overcome this hindrance by utilizing the enhanced\nlight--matter coupling in an optical cavity to perform a minimally invasive\ncontinuous measurement and track the time evolution of the atom number in a\nquasi two-dimensional atomic gas during evaporation from a tilted trapping\npotential. We demonstrate sufficient measurement precision to detect atom\nnumber fluctuations well below the level set by Poissonian statistics.\nFurthermore, we characterize the non-linearity of the evaporation process and\nthe inherent fluctuations of the transport of atoms out of the trapping volume\nthrough two-time correlations of the atom number. Our results establish coupled\natom--cavity systems as a novel testbed for observing thermodynamics and\ntransport phenomena in mesosopic cold atomic gases and, generally, pave the way\nfor measuring multi-time correlation functions of ultracold quantum gases.",
        "positive": "Metastable ferromagnetic clusters in dissipative many-body systems of\n  polar molecules: We investigate the effect of two-body loss due to chemical reactions on\nquantum magnetism of fermionic polar molecules in an optical lattice. We show\nthat an interplay between dissipation and strong long-range interactions leads\nto formation of metastable ferromagnetic clusters. The spin states of clusters\nare controlled by interaction parameters and reflect the symmetry of\ninteractions. The size of clusters strongly depends on the initial\nconfiguration of molecules due to Hilbert-space fragmentation during\ndissipative many-body dynamics. We construct an effective model to show the\nemergence of metastable states as quasi-dark states. Application to quantum\nsimulation of the spin-$S$ Heisenberg model is discussed."
    },
    {
        "anchor": "Traveling Majorana solitons in a one-dimensional spin-orbit coupled\n  Fermi superfluid: We investigate traveling solitons of a one-dimensional spin-orbit coupled\nFermi superfluid in both topologically trivial and non-trivial regimes by\nsolving the static and time-dependent Bogoliubov-de Gennes equations. We find a\ncritical velocity $v_{h}$ for traveling solitons that is much smaller than the\nvalue predicted using the Landau criterion due to the presence of spin-orbit\ncoupling, which strongly upshifts the energy level of the soliton-induced\nAndreev bound states towards the quasi-particle scattering continuum. Above\n$v_{h}$, our time-dependent simulations in harmonic traps indicate that\ntraveling solitons decay by radiating sound waves. In the topological phase, we\npredict the existence of peculiar Majorana solitons, which host two Majorana\nfermions and feature a phase jump of $\\pi$ across the soliton, irrespective of\nthe velocity of travel. These unusual properties of Majorana solitons may open\nan alternative way to manipulate Majorana fermions for fault-tolerant\ntopological quantum computations.",
        "positive": "Shortcuts to adiabaticity in a time-dependent box: A method is proposed to drive an ultrafast non-adiabatic dynamics of an\nultracold gas trapped in a box potential. The resulting state is free from\nspurious excitations associated with the breakdown of adiabaticity, and\npreserves the quantum correlations of the initial state up to a scaling factor.\nThe process relies on the existence of an adiabatic invariant and the inversion\nof the dynamical self-similar scaling law dictated by it. Its physical\nimplementation generally requires the use of an auxiliary expulsive potential\nanalogous to those used in soliton control. The method is extended to a broad\nfamily of many-body systems. As illustrative examples we consider the ultrafast\nexpansion of a Tonks-Girardeau gas and of Bose-Einstein condensates in\ndifferent dimensions, where the method exhibits an excellent robustness against\ndifferent regimes of interactions and the features of an experimentally\nrealizable box potential."
    },
    {
        "anchor": "Density-functional theory for 1D harmonically trapped Bose-Fermi mixture: We present a density-functional theory for the one dimensional harmonically\ntrapped Bose-Fermi mixture with repulsive contact interactions. The ground\nstate density distribution of each component is obtained by solving the\nKohn-Sham equations numerically based on the Local Density Approximation and\nthe exact solution for the homogeneous system given by Bethe ansatz method. It\nis shown that for strong enough interaction, a considerable amount of fermions\nare repelled out of the central region of the trap, exhibiting partial phase\nseparation of Bose and Fermi components. Oscillations emerge in the Bose\ndensity curves reflecting the strong correlation with Fermions. For infinite\nstrong interaction, the ground state energy of the mixture and the total\ndensity are consistent with the scenario that all atoms in the mixture are\nfully fermionized.",
        "positive": "Seeing bulk topological properties of band insulators in small photonic\n  lattices: We present a general scheme for measuring the bulk properties of\nnon-interacting tight-binding models realized in arrays of coupled photonic\ncavities. Specifically, we propose to implement a single unit cell of the\ntargeted model with tunable twisted boundary conditions in order to simulate\nlarge systems and, most importantly, to access bulk topological properties\nexperimentally. We illustrate our method by demonstrating how to measure\ntopological invariants in a two-dimensional quantum Hall-like model."
    },
    {
        "anchor": "Hydrodynamics and two-dimensional dark lump solitons for polariton\n  superfluids: We study a two-dimensional incoherently pumped exciton-polariton condensate\ndescribed by an open-dissipative Gross-Pitaevskii equation for the polariton\ndynamics coupled to a rate equation for the exciton density. Adopting a\nhydrodynamic approach, we use multiscale expansion methods to derive several\nmodels appearing in the context of shallow water waves with viscosity. In\nparticular, we derive a Boussinesq/Benney-Luke type equation and its far-field\nexpansion in terms of Kadomtsev-Petviashvili-I (KP-I) equations for right- and\nleft-going waves. From the KP-I model, we predict the existence of\nvorticity-free, weakly (algebraically) localized two-dimensional dark-lump\nsolitons. We find that, in the presence of dissipation, dark lumps exhibit a\nlifetime three times larger than that of planar dark solitons. Direct numerical\nsimulations show that dark lumps do exist, and their dissipative dynamics is\nwell captured by our analytical approximation. It is also shown that lump-like\nand vortex-like structures can spontaneously be formed as a result of the\ntransverse \"snaking\" instability of dark soliton stripes.",
        "positive": "Probing Slow Relaxation and Many-Body Localization in Two-Dimensional\n  Quasi-Periodic Systems: In a many-body localized (MBL) quantum system, the ergodic hypothesis breaks\ndown completely, giving rise to a fundamentally new many-body phase. Whether\nand under which conditions MBL can occur in higher dimensions remains an\noutstanding challenge both for experiments and theory. Here, we experimentally\nexplore the relaxation dynamics of an interacting gas of fermionic potassium\natoms loaded in a two-dimensional optical lattice with different quasi-periodic\npotentials along the two directions. We observe a dramatic slowing down of the\nrelaxation for intermediate disorder strengths and attribute this partially to\nconfigurational rare-region effects. Beyond a critical disorder strength, we\nsee negligible relaxation on experimentally accessible timescales, indicating a\npossible transition into a two-dimensional MBL phase. Our experiments reveal a\ndistinct interplay of interactions, disorder, and dimensionality and provide\ninsights into regimes where controlled theoretical approaches are scarce."
    },
    {
        "anchor": "Gauge fields for ultracold atoms in optical superlattices: We present a scheme that produces a strong U(1)-like gauge field on cold\natoms confined in a two-dimensional square optical lattice. Our proposal relies\non two essential features, a long-lived metastable excited state that exists\nfor alkaline-earth or Ytterbium atoms, and an optical superlattice. As in the\nproposal by Jaksch and Zoller [New Journal of Physics 5, 56 (2003)],\nlaser-assisted tunneling between adjacent sites creates an effective magnetic\nfield. In the tight-binding approximation, the atomic motion is described by\nthe Harper Hamiltonian, with a flux across each lattice plaquette that can\nrealistically take any value between 0 and $\\pi$. We show how to take advantage\nof the superlattice to ensure that each plaquette acquires the same phase, thus\nsimulating a uniform magnetic field. We discuss the observable consequences of\nthe artificial gauge field on non-interacting bosonic and fermionic gases. We\nalso outline how the scheme can be generalized to non-Abelian gauge fields.",
        "positive": "Molecular Bose-Einstein condensation in a Bose gas with a wide Feshbach\n  resonance at finite temperatures: Bose-Einstein condensation (BEC) of Feshbach molecules in a homogeneous Bose\ngas is studied at finite temperatures in a single-channel mean-field approach\nwhere the Hartree-Fock energy and pairing gap are determined self-consistently.\nIn the molecular-BEC state, the atomic excitation is gapped and the molecular\nexcitation is gapless. The binding energy of Feshbach molecules is shifted from\nthe vacuum value due to many-body effect. When the scattering length $a_s$ of\natoms is negative, the system is subject to mechanical collapse due to negative\ncompressibility. The system is stable in most regions with positive scattering\nlengths. However at low temperatures near the resonance, the molecular-BEC\nstate vanishes, and the coherent mixture of atomic and molecular BEC is subject\nto mechanical collapse."
    },
    {
        "anchor": "Phase diagram of imbalanced fermions in optical lattices: The zero-temperature phase diagrams of imbalanced fermions in 3D optical\nlattices are investigated to evaluate the validity of the Fermi-Hubbard model.\nIt is found that depending on the filling factor, s-wave scattering strength\nand lattice potential, the system may fall into the normal($N$) phase,\nmagnetized superfluid(SF$_M$) or phase separation of $N$ and BCS state. By\ntuning these parameters, the superfluidity could be favorable by enhanced\neffective couplings or suppressed by the increased band gap. The phase profiles\nin the presence of a harmonic trap are also investigated under LDA, which show\nsome exotic shell structures compared to those without the optical lattice.",
        "positive": "Competing many-body instabilities in two-dimensional dipolar Fermi gases: Experiments on quantum degenerate Fermi gases of magnetic atoms and dipolar\nmolecules begin to probe their broken symmetry phases dominated by the\nlong-range, anisotropic dipole-dipole interaction. Several candidate phases\nincluding the p-wave superfluid, the stripe density wave, and a supersolid have\nbeen proposed theoretically for two-dimensional spinless dipolar Fermi gases.\nYet the phase boundaries predicted by different approximations vary greatly,\nand a definitive phase diagram is still lacking. Here we present a theory that\ntreats all competing many-body instabilities in the particle-particle and\nparticle-hole channel on equal footing. We obtain the low temperature phase\ndiagram by numerically solving the functional renormalization-group flow\nequations and find a nontrivial density wave phase at small dipolar tilting\nangles and strong interactions, but no evidence of the supersolid phase. We\nalso estimate the critical temperatures of the ordered phases."
    },
    {
        "anchor": "Controlled Generation of Dark-Bright Soliton Complexes in Two-Component\n  and Spinor Bose-Einstein Condensates: We report on the controlled creation of multiple soliton complexes of the\ndark-bright type in one-dimensional two-component, three-component and spinor\nBose-Einstein condensates. The formation of these states is based on the\nso-called matter wave interference of separated condensate fragments. In all\nthree cases a systematic numerical study is carried out upon considering\ndifferent variations of each systems' parameters both in the absence and in the\npresence of a harmonic trap. It is found that the judicious selection of the\ninitial separation or the chemical potential of the participating components\ncan be utilized to tailor the number of nucleated states. The latter increases\nas the former parameters are increased. Similarities and differences of the\ndistinct models considered herein are showcased while the robustness of the\nemerging states is illustrated via the numerical experiments demonstrating\ntheir long time propagation. Importantly, for the spinorial system, we unravel\nthe existence of beating dark soliton arrays that are formed due to the\nspin-mixing dynamics. These states persist in the presence of a parabolic trap,\noften relevant for associated experimental realizations.",
        "positive": "Observation of Two Sound Modes in a Binary Superfluid Gas: We study the propagation of sound waves in a binary superfluid gas with two\nsymmetric components. The binary superfluid is constituted using a\nBose-Einstein condensate of $^{23}$Na in an equal mixture of two hyperfine\nground states. Sound waves are excited in the condensate by applying a local\nspin-dependent perturbation with a focused laser beam. We identify two distinct\nsound modes, referred to as density sound and spin sound, where the densities\nof the two spin components oscillate in phase and out of phase, respectively.\nThe observed sound propagation is explained well by the two-fluid hydrodynamics\nof the binary superfluid. The ratio of the two sound velocities is precisely\nmeasured with no need for absolute density calibration, and we find it in\nquantitatively good agreement with known interaction properties of the binary\nsystem."
    },
    {
        "anchor": "A phonon laser in ultra-cold matter: We show the possible excitation of a phonon laser instability in an\nultra-cold atomic gas confined in a magneto-optical trap. Such an effect\nresults from a negative Landau damping of the collective density perturbations\nin the gas, leading to the coherent emission of phonons. This laser instability\ncan be driven by a blue-detuned laser superimposed to the usual red-detuning\nlaser beams which usually provide the cooling mechanism. Threshold conditions,\ninstability growth rates and saturation levels are derived. This work\ngeneralizes, on theoretical grounds, the recent results obtained with single\nion phonon laser, to an ultra-cold atomic gas, where real phonons can be\nexcited. Future phonon lasers could thus adequately be called phasers.",
        "positive": "Ab initio simulation of the universal properties of unitary Fermi gas in\n  a harmonic trap: Chang and Bertsch [Phys. Rev. A 76, 021603(R) (2007)] proposed a simple\nformula for the ground state energy of a unitary Fermi gas in a harmonic trap,\nbased on their Green's function Monte Carlo simulations of up to 22 fermions,\ncombined with general assumptions about the universal thermodynamic behavior of\nthe unitary Fermi gas. In this work, we perform the ab initio simulations of\nthe ground state energy of up to one hundred fermions using the fictitious\nidentical particle method to overcome the Fermion sign problem, and we find\nthat the formula proposed by Chang and Bertsch remains highly accurate. Since\nthe number of fermions we simulate is much larger than that simulated by Chang\nand Bertsch when they proposed the formula, our work provides strong evidence\nfor the universal validity of the formula. Our work demonstrates that\nfictitious identical particles provide a valuable tool for the ab initio\nsimulations of ultracold Fermi gases."
    },
    {
        "anchor": "Detection of roton and phonon excitations in a spin-orbit coupled\n  Bose-Einstein condensate with a moving barrier: We propose to detect phonon and roton excitations in a two-dimensional\nBose-Einstein condensate with Raman-induced spin-orbit coupling by perturbing\nthe atomic cloud with a weak barrier. The two excitation modes can be observed\nby moving the barrier along different directions in appropriate parameter\nregimes. Phonon excitations are identified by the appearance of solitary waves,\nwhile roton excitations lead to distinctive spatial density modulations. We\nshow that this method can also be used to determine the anisotropic critical\nvelocities of superfluid.",
        "positive": "Coherent magnon optics in a ferromagnetic spinor Bose-Einstein\n  condensate: We measure the mass, gap, and magnetic moment of a magnon in the\nferromagnetic $F=1$ spinor Bose-Einstein condensate of $^{87}$Rb. We find an\nunusually heavy magnon mass of $1.038(2)_\\mathrm{stat}(8)_\\mathrm{sys}$ times\nthe atomic mass, as determined by interfering standing and running coherent\nmagnon waves within the dense and trapped condensed gas. This measurement is\nshifted significantly from theoretical estimates. The magnon energy gap of\n$h\\times 2.5(1)_\\mathrm{stat}(2)_\\mathrm{sys}\\;\\mathrm{Hz}$ and the effective\nmagnetic moment of $-1.04(2)_\\mathrm{stat}(8)\\,\\mu_\\textrm{bare}$ times the\natomic magnetic moment are consistent with mean-field predictions. The nonzero\nenergy gap arises from magnetic dipole-dipole interactions."
    },
    {
        "anchor": "Fractional-charge vortex in a spinor Bose-Einstein condensate: We classify all possible fractional charge vortices of charge less than unity\nin spin-1 and spin-2 polar and cyclic Bose-Einstein condensates (BECs) with\nzero magnetization. Statics and dynamics of these vortices in\nquasi-two-dimensional spinor BECs are studied employing accurate numerical\nsolution and a Lagrange variational approximation. The results for density and\ncollective-mode oscillation are illustrated using fractional-charge BEC vortex\nof $^{23}$Na and $^{87}$Rb atoms with realistic interaction and trapping\npotential parameters.",
        "positive": "Vortex structures and zero energy states in the BCS-to-BEC evolution of\n  p-wave resonant Fermi gases: Multiply quantized vortices in the BCS-to-BEC evolution of p-wave resonant\nFermi gases are investigated theoretically. The vortex structure and the\nlow-energy quasiparticle states are discussed, based on the self-consistent\ncalculations of the Bogoliubov-de Gennes and gap equations. We reveal the\ndirect relation between the macroscopic structure of vortices, such as particle\ndensities, and the low-lying quasiparticle state. In addition, the net angular\nmomentum for multiply quantized vortices with a vorticity $\\kappa$ is found to\nbe expressed by a simple equation, which reflects the chirality of the Cooper\npairing. Hence, the observation of the particle density depletion and the\nmeasurement of the angular momentum will provide the information on the\ncore-bound state and $p$-wave superfluidity. Moreover, the details on the zero\nenergy Majorana state are discussed in the vicinity of the BCS-to-BEC\nevolution. It is demonstrated numerically that the zero energy Majorana state\nappears in the weak coupling BCS limit only when the vortex winding number is\nodd. There exist the $\\kappa$ branches of the core bound states for a vortex\nstate with vorticity $\\kappa$, whereas only one of them can be the zero energy.\nThis zero energy state vanishes at the BCS-BEC topological phase transition,\nbecause of interference between the core-bound and edge-bound states."
    },
    {
        "anchor": "Mapping as a probe for heating suppression in periodically driven\n  quantum many-body systems: Experiments on periodically driven quantum systems have effectively realized\nquasi-Hamiltonians, in the sense of Floquet theory, that are otherwise\ninaccessible in static condensed matter systems. Although the Floquet\nquasi-Hamiltonians are time-independent, however, these continuously driven\nsystems can still suffer from heating due to a secular growth in the\nexpectation value of the time-dependent physical Hamiltonian. Here we use an\nexact space-time mapping to construct a class of many-body systems with rapid\nperiodic driving which we nonetheless prove to be completely free of heating,\nby mapping them exactly onto time-independent systems. The absence of heating\ndespite the periodic driving occurs in these cases of harmonically trapped\ndilute Bose gas because the driving is a certain periodic but anharmonic\nmodulation of the gas's two-body contact interaction, at a particular\nfrequency. Although we prove that the absence of heating is exact within full\nquantum many-body theory, we then use mean-field theory to simulate 'Floquet\nheating spectroscopy' and compute the heating rate when the driving frequency\nis varied away from the critical value for zero heating. In both weakly and\nstrongly non-linear regimes, the heating rate as a function of driving\nfrequency appears to show a number of Fano resonances, suggesting that the\nexactly proven absence of heating at the critical frequency may be explained in\nterms of destructive interferences between excitation modes.",
        "positive": "Ground-state properties of dilute spinless fermions in fractional\n  dimensions: We analyze zero-temperature universal properties of the simplest\nGalilean-invariant model of spinless low-dimensional fermions with short-range\ntwo-body interactions. In particular, it is shown that after proper\nrenormalization of the coupling constant, even the dilute system possesses rich\nphase diagram that includes the superfluid state and the metastable `upper\nbranch' behavior."
    },
    {
        "anchor": "2D spin-orbit coupling for ultracold atoms in optical lattices: Spin-orbit coupling (SOC) is at the heart of many exotic band-structures and\ncan give rise to many-body states with topological order. Here we present a\ngeneral scheme based on a combination of microwave driving and lattice shaking\nfor the realization of time-reversal invariant 2D SOC with ultracold atoms in\nsystems with inversion symmetry. We show that the strengths of Rashba and\nDresselhaus SOC can be independently tuned in a spin-dependent square lattice.\nMore generally, our method can be used to open gaps between different spin\nstates without breaking time-reversal symmetry. We demonstrate that this allows\nfor the realization of topological insulators in the presence of SOC, which is\nclosely related to the Kane-Mele model.",
        "positive": "Second Josephson oscillations: As a model for mesoscopic quantum systems in thermal contact, we consider a\nfour-mode Bose-Hubbard model with two greatly differing tunneling rates. By a\nseries of Holstein-Primakoff transformations we show that the low-frequency\ndynamics of this system consists in general of two slow Josephson oscillations,\nrather than the single slow mode predicted by linear Bogoliubov theory. We\nidentify the second slow Josephson oscillation as a heat exchange mode\nanalogous to second sound."
    },
    {
        "anchor": "Relaxation and hysteresis near Shapiro resonances in a driven spinor\n  condensate: We study the coherent and dissipative aspects of a driven spin-1\nBose-Einstein condensate (BEC) when the Zeeman energy is modulated around a\nstatic bias value. Resonances appear when the bias energy matches an integer\nnumber of modulation quanta. They constitute the atomic counterpart of Shapiro\nresonances observed in microwave-driven superconducting Josephson junctions.\nThe population dynamics near each resonance corresponds to slow and non-linear\nsecular oscillations on top of a rapid `micromotion'. At long times and in a\nnarrow window of modulation frequencies around each resonance, we observe a\nrelaxation to asymptotic states that are unstable without drive. These\nstationary states correspond to phase-locked solutions of the Josephson\nequations generalized to include dissipation, and are analogous to the\nstationary states of driven superconducting junctions. We find that dissipation\nis essential to understand this long-time behavior, and we propose a\nphenomenological model to explain quantitatively the experimental results.\nFinally, we demonstrate hysteresis in the asymptotic state of the driven spinor\nBEC when sweeping the modulation frequency across a Shapiro resonance.",
        "positive": "The impact of spatial correlation on the tunneling dynamics of few-boson\n  mixtures in a combined triple well and harmonic trap: We investigate the tunneling properties of a two-species few-boson mixture in\na one-dimensional triple well and harmonic trap. The mixture is prepared in an\ninitial state with a strong spatial correlation for one species and a complete\nlocalization for the other species. We observe a correlation-induced tunneling\nprocess in the weak interspecies interaction regime. The onset of the\ninterspecies interaction disturbes the spatial correlation of one species and\ninduces tunneling among the correlated wells. The corresponding tunneling\nproperties can be controlled by the spatial correlations with an underlying\nmechanism which is inherently different from the well known resonant tunneling\nprocess. We also observe the correlated tunneling of both species in the\nintermediate interspecies interaction regime and the tunneling via higher band\nstates for strong interactions."
    },
    {
        "anchor": "Polariton chimeras: Bose-Einstein condensates with intrinsic chaoticity\n  and spontaneous long-range ordering: The system of cavity polaritons driven by a plane electromagnetic wave is\nfound to undergo the spontaneous breaking of spatial symmetry, which results in\na lifted phase locking with respect to the driving field and, consequently, in\nthe possibility of internal ordering. In particular, periodic spin and\nintensity patterns arise in polariton wires; they exhibit strong long-range\norder and can serve as media for signal transmission. Such patterns have the\nproperties of dynamical chimeras: they are formed spontaneously in perfectly\nhomogeneous media and can be partially chaotic. The reported new mechanism of\nchimera formation requires neither time-delayed feedback loops nor non-local\ninteractions.",
        "positive": "Dispersion relation and excitation character of a two-component\n  Bose-Einstein condensate: We present a study for the dispersion relation and character of the\nexcitations of a single and two component Bose Einstein Condensate (BEC). We\nstudy the single component dispersion for a finite BEC system and look at\nexamples of quasiparticles to understand and characterize the dispersion\nrelation. Next we present the dispersion relation for a two component BEC in\nboth the miscible and immiscible parameter regimes. Then we present examples of\nthe quasiparticles for both regimes."
    },
    {
        "anchor": "Finite temperature effects in two-mode bosonic Josephson junctions: We analyze the effects of the temperature on a bosonic Josephson junction\nrealized with ultracold and dilute atoms in a double-well potential. Starting\nfrom the eigenstates of the two-site Bose-Hubbard Hamiltonian, we calculate the\ncoherence visibility and the fluctuation of the on-site occupation number and\nstudy them as functions of the temperature. We show that, contrary to naive\nexpectations, when the boson-boson interaction is suitably chosen thermal\neffects can increase the coherence visibility and reduce the on-site number\nfluctuation.",
        "positive": "Vortex Formation in Two-Dimensional Bose Gas: We discuss the stability of a homogeneous two-dimensional Bose gas at finite\ntemperature against formation of isolated vortices. We consider a patch of\nseveral healing lengths in size and compute its free energy using the Euclidean\nformalism. Since we deal with an open system, which is able to exchange\nparticles and angular momentum with the rest of the condensate, we use the\nsymmetry-breaking (as opposed to the particle number conserving) formalism, and\ninclude configurations with all values of angular momenta in the partition\nfunction. At finite temperature, there appear sphaleron configurations\nassociated to isolated vortices. The contribution from these configurations to\nthe free energy is computed in the dilute gas approximation. We show that the\nEuclidean action of linearized perturbations of a vortex is not positive\ndefinite. As a consequence the free energy of the 2D Bose gas acquires an\nimaginary part. This signals the instability of the gas. This instability may\nbe identified with the Berezinskii, Kosterlitz and Thouless (BKT) transition."
    },
    {
        "anchor": "Out-of-equilibrium quantum dynamics of fermionic gases in the presence\n  of localized particle loss: We address the effects of dissipative defects giving rise to a localized\nparticle loss, in one-dimensional non-interacting lattice fermionic gases\nconfined within a region of size $\\ell$. We consider homogeneous systems within\nhard walls and inhomogeneous systems where the particles are trapped by\nspace-dependent external potentials, such as harmonic traps. We model the\ndissipative particle-decay mechanism by Lindblad master equations governing the\ntime evolution of the density matrix. The resulting quantum dynamics is\nanalyzed in protocols starting from the ground state of the Hamiltonian for\n$N_0$ particles, then evolving under the effect of one dissipative\nparticle-loss defect, for example at the center of the system. We study the\ninterplay between time, size $\\ell$ and the number $N_0$ of initial particles,\nconsidering two different situations: (i) fixed number $N_0$ of initial\nparticles; (ii) fixed ratio $N_0/\\ell$, corresponding to the thermodynamic\nlimit of the initial equilibrium state. We show that the quantum evolutions of\nthe particle number and density develop various asymptotic and intermediate\ndynamic regimes, and nontrivial large-time states when the dissipative\nmechanism acts at the center of the system.",
        "positive": "Probing superfluidity of a mesoscopic Tonks-Girardeau gas: We study the dynamical response of a Tonks-Girardeau gas on a ring induced by\na moving delta-barrier potential. An exact solution based on the time-dependent\nBose-Fermi mapping allows to obtain the particle current, its fluctuations and\nthe drag force acting on the barrier. The exact solution is analyzed\nnumerically as well as analytically in the perturbative regime of weak barrier\nstrength. In the weak barrier limit the stirring drives the system into a state\nwith net zero current for velocities $v$ smaller than $v_c=\\pi\\hbar /mL$, with\n$m$ the atomic mass and $L$ the ring circumference. At $v$ approaching $v_c$\nangular momentum can be transferred to the fluid and a nonzero drag force\narises. The existence of a velocity threshold for current generation indicates\nsuperfluid-like behavior of the mesoscopic Tonks-Girardeau gas, different from\nthe non-superfluid behavior predicted for Tonks-Girardeau gas in an infinite\ntube."
    },
    {
        "anchor": "Mesoscopics of half-quantum vortex pair deconfinement in a trapped\n  spin-one condensate: Motivated by a recent experiment in an antiferromagnetic spin-1 Bose-Einstein\ncondensate of ${}^{23} \\textrm{Na}$ atoms, we study the energetical stability\nof a singly quantum vortex injected into the center of a quasi-two-dimensional\ngas with zero total spin against dissocation into a pair of half-quantum\nvortices. We find that the critical dissociation point of this\nconfinement-deconfinement type phase transition can be expressed in terms of\nthe ratio of density-density ($c_0$) and spin-spin ($c_2$) coupling constants.\nThe transition of bound to unbound vortices, in particular, sensitively depends\non (1) the ratio of system size ($R$) to density healing length ($\\xi_d$), and\n(2) the trap potential. Specifically, the critical ratio $(c_2 /\nc_0)_{\\textrm{cr}}$ increases when $R / \\xi_d$ decreases, and is relatively\nlarger in a harmonic trap than in a box trap. Dissociation is energetically\ngenerally favored for $c_2 / c_0 < (c_2 / c_0)_{\\textrm{cr}}$, which as a\ncorollary implies that vortex dissociation is observed as well for negative\n$c_2 < 0$, e.g., in a rubidium spin-1 BEC, whereas in a sodium spin-1 BEC\n($c_2>0$) it is energetically blocked above the critical ratio $(c_2 /\nc_0)_{\\textrm{cr}}$. Tuning the coupling ratio $c_2/c_0$ by using microwave\ncontrol techniques, the dependence of the deconfinement phase transition on\ncoupling parameters, density, and system size we predict, can be verified in\nexperiments with ultracold spinor gases.",
        "positive": "BEC array in a Malleable Optical Trap formed in a Traveling Wave Cavity: Although quantum degenerate gases of neutral atoms have shown remarkable\nprogress in the study of many body quantum physics, condensed matter physics,\nprecision measurements, and quantum information processing, experimental\nprogress is needed in order to reach their full potential in these fields. More\ncomplex spatial geometries as well as novel methods for engineering interesting\ninteractions are needed. Here we demonstrate a novel experimental platform for\nthe realization of quantum degenerate gases with a wide range of tune-ability\nin the spatial geometries experienced by the atoms and with the possibility of\nnon-trivial long-range interactions both within and between multiple 87Rb\nBose-Einstein condensates (BECs). We explore the use of a large mode-volume\nbow-tie ring cavity resonant at two wavelengths, $\\lambda$ =1560 and 780 nm,\nfor the creation of multiple BECs within a Malleable optical trap which also\npossesses the ability of photon-mediated long-range interactions. By exciting\ndiverse transverse modes at 1560 nm, we can realize many optical trapping\ngeometries which can open the door to spatial quantum state engineering with\ncavity-coupled BECs. As representative examples we realize a BEC in the\nfundamental TEM00 and a double BEC in the TEM01 mode of the cavity. By\ncontrolling the power between the fundamental and the higher transverse cavity\nmode, splitting and merging of cold thermal atomic ensemble is shown as well as\nthe potential of creating more complex trapping geometries such as uniform\npotentials. Due to the double resonance of the cavity, we can envision a\nquantum network of BECs coupled via cavity-mediated interactions in non-trivial\ngeometries."
    },
    {
        "anchor": "Long Josephson junctions with exciton-polariton condensates: We demonstrate the possibility to build stable Josephson $\\pi$-junction\nstripes with exciton-polariton condensates. The stability of the $\\pi$-junction\nbetween arbitrary long polariton stripes is achieved at low pumping by\nbalancing the snaking instability with counter-propagating flows towards the\njunction. Not dissimilar from a dark soliton, the instability becomes relevant\nat high pumping leading to formation of vortex dipoles. The resulting\nstructures can be stabilised to produce static lattices of Josephson vortices\nin straight and ring geometries. Our results build towards realization of\nquantum technological applications based on the Josephson effect at room\ntemperature.",
        "positive": "On the kinetic energy of unitary Fermi gas in a harmonic trap: We have considered the orbital-free approximation of the kinetic energy\nfunctional to investigate the zero temperature properties of dilute\nharmonically trapped two component Fermi gas at unitarity. It is shown that our\napproach provides a realible and inexpensive method to study superfluid\nstrongly interacting dilute Fermi gases."
    },
    {
        "anchor": "Ultracold atoms in U(2) non-Abelian gauge potentials preserving the\n  Landau levels: We study ultracold atoms subjected to U(2) non-Abelian potentials: we\nconsider gauge potentials having, in the Abelian limit, degenerate Landau\nlevels and we then investigate the effect of general homogeneous non-Abelian\nterms. The conditions under which the structure of degenerate Landau levels is\npreserved are classified and discussed. The typical gauge potentials preserving\nthe Landau levels are characterized by a fictitious magnetic field and by an\neffective spin-orbit interaction, e.g. obtained through the rotation of\ntwo-dimensional atomic gases coupled with a tripod scheme. The single-particle\nenergy spectrum can be exactly determined for a class of gauge potentials,\nwhose physical implementation is explicitly discussed. The corresponding Landau\nlevels are deformed by the non-Abelian contribution of the potential and their\nspin degeneracy is split. The related deformed quantum Hall states for fermions\nand bosons (in the presence of strong intra-species interaction) are determined\nfar from and at the degeneracy points of the Landau levels. A discussion of the\neffect of the angular momentum is presented, as well as results for U(3) gauge\npotentials.",
        "positive": "Direct measurement of topological invariants in optical lattices: We propose an experimental technique for classifying the topology of band\nstructures realized in optical lattices, based on a generalization of\ntopological charge pumping in quantum Hall systems to cold atom in optical\nlattices. Time-of-flight measurement along one spatial direction combined with\nin situ detection along the transverse direction provide a direct measure of\nthe system's Chern number, as we illustrate by calculations for the Hofstadter\nlattice. Based on an analogy with Wannier functions techniques of topological\nband theory, the method is very general and also allows the measurement of\nother topological invariants, such as the $Z_2$ topological invariant of\ntime-reversal symmetric insulators."
    },
    {
        "anchor": "Spin-orbit coupled fermions in ladder-like optical lattices at\n  half-filling: We study the ground-state phase diagram of two-component fermions loaded in a\nladder-like lattice at half filling in the presence of spin-orbit coupling. For\nrepulsive fermions with unidirectional spin-orbit coupling along the legs we\nidentify a N\\'{e}el state which is separated from rung-singlet and\nferromagnetic states by Ising phase transition lines. These lines cross for\nmaximal spin-orbit coupling and a direct Gaussian phase transition between\nrung-singlet and ferro phases is realized. For the case of Rashba-like\nspin-orbit coupling, besides the rung singlet phases two distinct striped\nferromagnetic phases are formed. In case of attractive fermions with spin-orbit\ncoupling at half-filling for decoupled chains we identify a dimerized state\nthat separates a singlet superconductor and a ferromagnetic states.",
        "positive": "Hybrid Boltzmann Gross-Pitaevskii Theory of Bose-Einstein Condensation\n  and Superfluidity in Open Driven-Dissipative Systems: We derive a theoretical model which describes Bose-Einstein condensation in\nan open driven-dissipative system. It includes external pumping of a thermal\nreservoir, finite life time of the condensed particles and energy relaxation.\nThe coupling between the reservoir and the condensate is described with\nsemi-classical Boltzmann rates. This results in a dissipative term in the\nGross-Pitaevskii equation for the condensate, which is proportional to the\nenergy of the elementary excitations of the system. We analyse the main\nproperties of a condensate described by this hybrid Boltzmann Gross-Pitaevskii\nmodel, namely, dispersion of the elementary excitations, bogolon distribution\nfunction, first order coherence, dynamic and energetic stability, drag force\ncreated by a disorder potential. We find that the dispersion of the elementary\nexcitations of a condensed state fulfils the Landau criterion of superfluidity.\nThe condensate is dynamically and energetically stable as longs it moves at a\nvelocity smaller than the speed of excitations. First order spatial coherence\nof the condensate is found to decay exponentially in 1D and with a power law in\n2D, similarly with the case of conservative systems. The coherence lengths are\nfound to be longer due to the finite life time of the condensate excitations.\nWe compare these properties with the ones of a condensate described by the\npopular \"diffusive\" models in which the dissipative term is proportional to the\nlocal condensate density. In the latter, the dispersion of excitations is\ndiffusive which as soon as the condensate is put into motion implies finite\nmechanical friction and can lead to an energetic instability."
    },
    {
        "anchor": "Transport regimes of cold gases in a two-dimensional anisotropic\n  disorder: We numerically study the dynamics of cold atoms in a two-dimensional\ndisordered potential. We consider an anisotropic speckle potential and focus on\nthe classical regime, which is relevant to some recent experiments. First, we\nstudy the behavior of particles with a fixed energy and identify different\ntransport regimes. For low energy, the particles are classically localized due\nto the absence of a percolating cluster. For high energy, the particles undergo\nnormal diffusion and we show that the diffusion constants scale algebraically\nwith the particle energy, with an anisotropy factor which significantly differs\nfrom that of the disordered potential. For intermediate energy, we find a\ntransient sub-diffusive regime, which is relevant to the time scale of typical\nexperiments. Second, we study the behavior of a cold-atomic gas with an\narbitrary energy distribution, using the above results as a groundwork. We show\nthat the density profile of the atomic cloud in the diffusion regime is\nstrongly peaked and, in particular, that it is not Gaussian. Its behavior at\nlarge distances allows us to extract the energy-dependent diffusion constants\nfrom experimental density distributions. For a thermal cloud released into the\ndisordered potential, we show that our numerical predictions are in agreement\nwith experimental findings. Not only does this work give insights to recent\nexperimental results, but it may also serve interpretation of future\nexperiments searching for deviation from classical diffusion and traces of\nAnderson localization.",
        "positive": "Non-equilibrium criticality in quench dynamics of infinite-range spin\n  models: Long-range interacting spin systems are ubiquitous in physics and exhibit a\nvariety of ground state disorder-to-order phase transitions. We consider a\nprototype of infinite-range interacting models known as the\nLipkin-Meshkov-Glick (LMG) model describing the collective interaction of $N$\nspins, and investigate the dynamical properties of fluctuations and\ncorrelations after a sudden quench of the Hamiltonian. Specifically, we focus\non critical quenches, where the initial state and/or the quench Hamiltonian are\ncritical. Depending on the type of quench, we identify three distinct behaviors\nwhere both the short-time dynamics and the stationary state at long times are\neffectively thermal, quantum, and genuinely non-equilibrium, characterized by\ndistinct universality classes and static and dynamical critical exponents.\nThese behaviors can be identified by an infrared effective temperature that is\nfinite, zero, and infinite (the latter scaling with the system size as\n$N^{1/3}$), respectively. The quench dynamics is studied through a combination\nof exact numerics and analytical calculations utilizing the non-equilibrium\nKeldysh field theory. Our results are amenable to realization in experiments\nwith trapped-ion experiments where long-range interactions naturally arise."
    },
    {
        "anchor": "An ultra-bright atom laser: We present a novel, ultra-bright atom-laser and ultra-cold thermal atom beam.\nUsing rf-radiation we strongly couple the magnetic hyperfine levels of 87Rb\natoms in a magnetically trapped Bose-Einstein condensate. At low rf-frequencies\ngravity opens a small hole in the trapping potenital and a well collimated,\nextremely bright atom laser emerges from just below the condensate. As opposed\nto traditional atom lasers based on weak coupling, this technique allows us to\noutcouple atoms at an arbitrarily large rate. We demonstrate an increase in\nflux per atom in the BEC by a factor of sixteen compared to the brightest\nquasi-continuous atom laser. Furthermore, we produce by two orders of magnitude\nthe coldest thermal atom beam to date (200 nK).",
        "positive": "Global phase diagram of two-component Bose gases in antiparallel\n  magnetic fields: We study the ground-state phase diagram of two-dimensional two-component (or\npseudospin-1/2) Bose gases in mutually antiparallel synthetic magnetic fields\nin the space of the total filling factor and the ratio of the intercomponent\ncoupling $g_{\\uparrow\\downarrow}$ to the intracomponent one g>0. This\ntime-reversal-invariant setting represents a bosonic analogue of spin Hall\nsystems. Using exact diagonalization, we find that (fractional) quantum spin\nHall states composed of a pair of nearly independent quantum Hall states are\nremarkably robust and persist for $g_{\\uparrow\\downarrow}$ up to as large as g.\nFor $g_{\\uparrow\\downarrow}=-g$, we find the exact many-body ground state in\nwhich particles in different spin states form pairs. This gives the exact\ncritical line beyond which the system collapses."
    },
    {
        "anchor": "Topological influence and back-action between topological excitations: Topological objects can influence each other if the underlying homotopy\ngroups are non-Abelian. Under such circumstances, the topological charge of\neach individual object is no longer a conserved quantity and can be transformed\nto each other. Yet, we can identify the conservation law by considering the\nback-action of topological influence. We develop a general theory of\ntopological influence and back-action based on the commutators of the\nunderlying homotopy groups. We illustrate the case of the topological influence\nof a half-quantum vortex on the sign change of a point defect and point out\nthat the topological back-action from the point defect is such twisting of the\nvortex that the total twist of the vortex line carries the change in the\npoint-defect charge to conserve the total charge. We use this theory to\nclassify charge transfers in condensed matter systems and show that a\nnon-Abelian charge transfer can be realized in a spin-2 Bose-Einstein\ncondensate.",
        "positive": "Pairing in two-dimensional Fermi gases with a coordinate-space potential: In this work we theoretically study pairing in two-dimensional Fermi gases, a\nsystem which is experimentally accessible using cold atoms. We start by\nderiving the mean-field pairing gap equation for a coordinate-space potential\nwith a finite interaction range, and proceed to solve this numerically. We find\nthat for sufficiently short effective ranges the answer is identical to the\nzero-range one. We then use Diffusion Monte Carlo to evaluate the total energy\nfor many distinct particle numbers; we employ several variational parameters to\nproduce a good ground-state energy and then use these results to extract the\npairing gap across a number of interaction strengths in the strongly\ninteracting two-dimensional crossover. Extracting the gap via the odd-even\nenergy staggering, our microscopic results can be used as benchmarks for other\ntheoretical approaches."
    },
    {
        "anchor": "Asymptotically exact trial wave functions for yrast states of rotating\n  Bose gases: We revisit the composite fermion (CF) construction of the lowest angular\nmomentum yrast states of rotating Bose gases with weak short range interaction.\nFor angular momenta at and below the single vortex, $L \\leq N$, the overlaps\nbetween these trial wave functions and the corresponding exact solutions {\\it\nincrease} with increasing system size and appear to approach unity in the\nthermodynamic limit. In the special case $L=N$, this remarkable behaviour was\npreviously observed numerically. Here we present methods to address this point\nanalytically, and find strongly suggestive evidence in favour of similar\nbehaviour for all $L \\leq N$. While not constituting a fully conclusive proof\nof the converging overlaps, our results do demonstrate a striking similarity\nbetween the analytic structure of the exact ground state wave functions at $L\n\\leq N$, and that of their CF counterparts. Results are given for two different\nprojection methods commonly used in the CF approach.",
        "positive": "Andreev-reflection and Aharonov-Bohm dynamics in atomtronic circuits: We study the quantum transport through two specific atomtronic circuits: a\nY-junction and a ring-shaped condensate pierced by an effective magnetic flux.\nWe demonstrate that for bosons, the two circuits display Andreev-like\nreflections. For the Y-junction, the transport depends on the coupling strength\nof the Y-junction. For the ring-shaped condensate, the transport crucially\ndepends on the particle statistics. For interacting bosons we find that the\nAharonov-Bohm interference effect is absent. By breaking the translational\ninvariance of the ring, the flux dependence can be restored. A complementary\nview of the problem is obtained through a specific non-equilibrium quench\nprotocol. We find that the steady-state is independent of the flux, however the\nactual time-dynamics depends on the flux. The dynamics of the full closed\nsystem can be fitted with an approximated open system approach. For all the\nprotocols we studied, we find striking differences in the dynamics of the\nBose-Hubbard model and the Gross-Pitaevskii equation."
    },
    {
        "anchor": "Consequences of integrability breaking in quench dynamics of pairing\n  Hamiltonians: We study the collisionless dynamics of two classes of nonintegrable pairing\nmodels. One is a BCS model with separable energy-dependent interactions, the\nother - a 2D topological superconductor with spin-orbit coupling and a\nband-splitting external field. The long-time quantum quench dynamics at\nintegrable points of these models are well understood. Namely, the squared\nmagnitude of the time-dependent order parameter $\\Delta(t)$ can either vanish\n(Phase I), reach a nonzero constant (Phase II), or periodically oscillate as an\nelliptic function (Phase III). We demonstrate that nonintegrable models too\nexhibit some or all of these nonequilibrium phases. Remarkably, elliptic\nperiodic oscillations persist, even though both their amplitude and functional\nform change drastically with integrability breaking. Striking new phenomena\naccompany loss of integrability. First, an extremely long time scale emerges in\nthe relaxation to Phase III, such that short-time numerical simulations risk\nerroneously classifying the asymptotic state. This time scale diverges near\nintegrable points. Second, an entirely new Phase IV of quasiperiodic\noscillations of $|\\Delta|$ emerges in the quantum quench phase diagrams of\nnonintegrable pairing models. As integrability techniques do not apply for the\nmodels we study, we develop the concept of asymptotic self-consistency and a\nlinear stability analysis of the asymptotic phases. With the help of these new\ntools, we determine the phase boundaries, characterize the asymptotic state,\nand clarify the physical meaning of the quantum quench phase diagrams of BCS\nsuperconductors. We also propose an explanation of these diagrams in terms of\nbifurcation theory.",
        "positive": "Realization of density-dependent Peierls phases to engineer quantized\n  gauge fields coupled to ultracold matter: Gauge fields that appear in models of high-energy and condensed matter\nphysics are dynamical quantum degrees of freedom due to their coupling to\nmatter fields. Since the dynamics of these strongly correlated systems is hard\nto compute, it was proposed to implement this basic coupling mechanism in\nquantum simulation platforms with the ultimate goal to emulate lattice gauge\ntheories. Here, we realize the fundamental ingredient for a density-dependent\ngauge field acting on ultracold fermions in an optical lattice by engineering\nnon-trivial Peierls phases that depend on the site occupations. We propose and\nimplement a Floquet scheme that relies on breaking time-reversal symmetry (TRS)\nby driving the lattice simultaneously at two frequencies which are resonant\nwith the onsite interactions. This induces density-assisted tunnelling\nprocesses that are controllable in amplitude and phase. We demonstrate\ntechniques in a Hubbard dimer to quantify the amplitude and to directly measure\nthe Peierls phase with respect to the single-particle hopping. The tunnel\ncoupling features two distinct regimes as a function of the modulation\namplitudes, which can be characterised by a $\\mathbb{Z}_2$-invariant. Moreover,\nwe provide a full tomography of the winding structure of the Peierls phase\naround a Dirac point that appears in the driving parameter space."
    },
    {
        "anchor": "Universal thermodynamics of a strongly interacting Fermi gas: theory\n  versus experiment: Strongly interacting, dilute Fermi gases exhibit a scale-invariant, universal\nthermodynamic behaviour. This is notoriously difficult to understand\ntheoretically because of the absence of a small interaction parameter. Here we\npresent a systematic comparison of theoretical predictions from different\nquantum many-body theories with recent experimental data of Nascimbene et. al.\n(arXiv:0911.0747v1). Our comparisons have no adjustable parameters, either\ntheoretically or experimentally. A simple Gaussian pair fluctuation theory is\nshown to give the best quantitative agreement in the superfluid state below\nthreshold. In the normal state, we also calculate the equation of state by\nusing a quantum cluster expansion theory and explore in detail its\napplicability to low temperatures. Using the accurate experimental result for\nthe thermodynamic function $S(T)$, we determine the temperature $T$ of a\ntrapped Fermi gas at unitarity as a function of a non-interacting temperature\n$T_{i}$ which can be obtained by an adiabatic sweep to the free gas limit. By\nanalyzing the recent experimental data, we find a normal-superfluid transition\ntemperature $(T/T_{F})_{c}=0.19\\pm0.02$ or $(T_{i}/T_{F})_{c}=0.16\\pm0.02$ in a\nharmonic trap, where $T_{F}$ is the Fermi temperature for a trapped ideal,\nnon-interacting Fermi gas.",
        "positive": "Virial coefficients for Bose and Fermi trapped gases beyond the unitary\n  limit: an S-Matrix approach: We study the virial expansion for three-dimensional Bose and Fermi gases at\nfinite temperature using an approximation that only considers two-body\nprocesses and is valid for high temperatures and low densities. The first\nvirial coefficients are computed and the second is exact. The results are\nobtained for the full range of values of the scattering length and the unitary\nlimit is recovered as a particular case. A weak coupling expansion is performed\nand the free case is also obtained as a proper limit. The influence of an\nanisotropic harmonic trap is considered using the Local Density Approximation -\nLDA, analytical results are obtained and the special case of the isotropic trap\nis discussed in detail."
    },
    {
        "anchor": "Energy Cascade in Quantum Gases: Energy cascade is ubiquitous in systems far from equilibrium. Facilitated by\nparticle interactions and external forces, it can lead to highly complex\nphenomena like fully developed turbulence, characterized by power law velocity\ncorrelation functions. Yet despite decades of research, how these power laws\nemerge from first principle remains unclear. Recently, experiments show that\nwhen a Bose condensate is subjected to periodic shaking, its momentum\ndistribution exhibits a power law behavior. The flexibility of cold atom\nexperiments has provided new opportunities to explore the emergence of these\npower laws, and to disentangle different sources of energy cascade. Here, we\npoint out that recent experiments in cold atoms imply that classical turbulence\nis part of a larger family of scale invariant phenomena that include ideal\ngases. Moreover, the property of the entire family is contained in the\nstructure of its Floquet states. For ideal gases, we show analytically that its\nmomentum distribution acquires a $1/q^2$ tail in each dimension when it is\nshaken periodically.",
        "positive": "Nonequilibrium scenarios in cluster-forming quantum lattice models: We investigate the out-of-equilibrium physics of monodisperse bosonic\nensembles on a square lattice. The effective Hamiltonian description of these\nsystems is given in terms of an extended Hubbard model with cluster-forming\ninteractions relevant to experimental realizations with cold Rydberg-dressed\natoms. The ground state of the model, recently investigated in Phys. Rev. Lett.\n123, 045301 (2019), features, aside from a superfluid and a stripe crystalline\nphase occurring at small and large interaction strength $V$, respectively, a\nrare first-order transition between an isotropic and an anisotropic stripe\nsupersolid at intermediate $V$. By means of quantum Monte Carlo calculations we\nshow that the equilibrium crystal may be turned into a glass by simulated\ntemperature quenches and that out-of-equilibrium isotropic (super)solid states\nmay emerge also when their equilibrium counterparts are anisotropic. These\nout-of-equilibrium states are of experimental interest, their excess energy\nwith respect to the ground state being within the energy window typically\naccessed in cold atom experiments. We find, after quenching, no evidence of\ncoexistence between superfluid and glassy behavior. Such an absence of\nsuperglassiness is qualitatively explained."
    },
    {
        "anchor": "Anomalous tunneling of collective excitations and effects of superflow\n  in the polar phase of a spin-1 spinor Bose-Einstein condensate: We investigate tunneling properties of collective modes in the polar phase of\na spin-1 spinor Bose-Einstein condensate. This spinor BEC state has two kinds\nof gapless modes, i.e., Bogoliubov mode and spin-wave. Within the framework of\nthe mean-field theory at T=0, we show that these Goldstone modes exhibit the\nperfect transmission in the low-energy limit. Their anomalous tunneling\nbehaviors still hold in the presence of superflow, except in the critical\ncurrent state. In the critical current state, while the tunneling of Bogoliubov\nmode is accompanied by finite reflection, the spin-wave still exhibit the\nperfect transmission, unless the strengths of a spin-dependent and\nspin-independent interactions take the same value.",
        "positive": "Searching for Non-Abelian Phases in the Bose-Einstein Condensate of\n  Dysprosium: The recently realized Bose-Einstein condensate of Dysprosium will become a\nspin-8 spinor condensate at ultralow magnetic fields. In such a high spin\ncondensate, many phases with different symmetries can exist. Among them the\nmost interesting ones are those with non-abelian point group symmetry. In this\nletter we discuss the variety of symmetry phases in a spin-8 condensate\nresulting from numerical solutions of the Hamiltonian. We show that these\nsymmetries can be determined uniquely from the measurements of density\npopulation on each spin component in an ultralow magnetic field, together with\nthe measurements of the collective modes in the zero-field limit. This method\ncan also be applied to Bose-Einstein condensate of other magnetic atoms, such\nas Cr and Er."
    },
    {
        "anchor": "Understanding superradiant phenomena with synthetic vector potentials in\n  atomic Bose-Einstein condensates: We theoretically investigate superradiance effects in quantum field theories\nin curved space-times by proposing an analogue model based on Bose--Einstein\ncondensates subject to a synthetic vector potential. The breaking of the\nirrotationality constraint of superfluids allows to study superradiance in\nsimple planar geometries and obtain intuitive insight in the amplified\nscattering processes at ergosurfaces. When boundary conditions are modified\nallowing for reflections, dynamical instabilities are found, similar to the\nones of ergoregions in rotating space-times. Their stabilization by horizons in\nblack hole geometries is discussed. All these phenomena are reinterpreted\nthrough an exact mapping with the physics of one-dimensional relativistic\ncharged scalar fields in electrostatic potentials. Our study provides a deeper\nunderstanding on the basic mechanisms of superradiance: by disentangling the\ndifferent ingredients at play, it shines light on some misconceptions on the\nrole of dissipation and horizons and on the competition between superradiant\nscattering and instabilities.",
        "positive": "Effective range from tetramer dissociation data for cesium atoms: The shifts in the four-body recombination peaks, due to an effective range\ncorrection to the zero-range model close to the unitary limit, are obtained and\nused to extract the corresponding effective range of a given atomic system. The\napproach is applied to an ultracold gas of cesium atoms close to broad Feshbach\nresonances, where deviations of experimental values from universal model\npredictions are associated to effective range corrections. The effective range\ncorrection is extracted, with a weighted average given by 3.9$\\pm 0.8 R_{vdW}$,\nwhere $R_{vdW}$ is the van der Waals length scale; which is consistent with the\nvan der Waals potential tail for the $Cs_2$ system. The method can be generally\napplied to other cold atom experimental setups to determine the contribution of\nthe effective range to the tetramer dissociation position."
    },
    {
        "anchor": "Study of implosion in an attractive Bose-Einstein condensate: By solving the Gross-Pitaevskii equation analytically and numerically, we\nreexamine the implosion phenomena that occur beyond the critical value of the\nnumber of atoms of an attractive Bose-Einstein condensate (BEC) with\ncigar-shape trapping geometry. We theoretically calculate the critical number\nof atoms in the condensate by using Ritz's variational optimization technique\nand investigate the stability and collapse dynamics of the attractive BEC by\nnumerically solving the time dependent Gross-Pitavskii equation.",
        "positive": "Tunable itinerant spin dynamics with polar molecules: Strongly interacting spins underlie many intriguing phenomena and\napplications ranging from magnetism to quantum information processing.\nInteracting spins combined with motion display exotic spin transport phenomena,\nsuch as superfluidity arising from pairing of spins induced by spin attraction.\nTo understand these complex phenomena, an interacting spin system with high\ncontrollability is desired. Quantum spin dynamics have been studied on\ndifferent platforms with varying capabilities. Here we demonstrate tunable\nitinerant spin dynamics enabled by dipolar interactions using a gas of\npotassium-rubidium molecules confined to two-dimensional planes, where a\nspin-1/2 system is encoded into the molecular rotational levels. The dipolar\ninteraction gives rise to a shift of the rotational transition frequency and a\ncollision-limited Ramsey contrast decay that emerges from the coupled spin and\nmotion. Both the Ising and spin exchange interactions are precisely tuned by\nvarying the strength and orientation of an electric field, as well as the\ninternal molecular state. This full tunability enables both static and\ndynamical control of the spin Hamiltonian, allowing reversal of the coherent\nspin dynamics. Our work establishes an interacting spin platform that allows\nfor exploration of many-body spin dynamics and spin-motion physics utilizing\nthe strong, tunable dipolar interaction."
    },
    {
        "anchor": "Dissipative time evolution of a chiral state after a quantum quench: We investigate the dynamics of fermionic atoms in a high-finesse optical\nresonator after a sudden switch on of the coupling between the atoms and the\ncavity. The atoms are additionally confined by optical lattices to a ladder\ngeometry. The tunneling mechanism on a rung of a ladder is induced by a cavity\nassisted Raman process. At long times after the quantum quench the arising\nsteady state can carry a chiral current. In this work we employ exact\ndiagonalization techniques on small system sizes to study the dissipative\nattractor dynamics after the quench towards the steady state and deviations of\nthe properties of the steady state from predictions obtained by adiabatically\neliminating the cavity mode.",
        "positive": "Destruction of Long-range Order by Quenching the Hopping Range in One\n  Dimension: We study the dynamics in a one dimensional hard-core Bose gas with power-law\nhopping after an abrupt reduction of the hopping range using the time-dependent\ndensity-matrix renormalization group (t-DMRG) and bosonization techniques. In\nparticular, we focus on the destruction of the Bose-Einstein condensate (BEC),\nwhich is present in the initial state in the thermodynamic limit. We argue that\nthis type of quench is akin to a sudden reduction in the effective\ndimensionality $d$ of the system (from $d > 1$ to $d = 1$). We identify two\nregimes in the evolution of the BEC fraction. For short times the decay of the\nBEC fraction is Gaussian while for intermediate to long times, it is well\ndescribed by a stretched exponential with an exponent that depends on the\ninitial effective dimensionality of the system. These results are potentially\nrelevant for cold trapped-ion experiments which can simulate an equivalent of\nhard-core bosons, i.e. spins, with tunable long-range interactions."
    },
    {
        "anchor": "Renormalization group analysis of dipolar Heisenberg model on square\n  lattice: We present a detailed functional renormalization group analysis of spin-1/2\ndipolar Heisenberg model on square lattice. This model is similar to the well\nknown $J_1$-$J_2$ model and describes the pseudospin degrees of freedom of\npolar molecules confined in deep optical lattice with long-range anisotropic\ndipole-dipole interactions. Previous study of this model based on tensor\nnetwork ansatz indicates a paramagnetic ground state for certain dipole tilting\nangles which can be tuned in experiments to control the exchange couplings. The\ntensor ansatz formulated on a small cluster unit cell is inadequate to describe\nthe spiral order, and therefore the phase diagram at high azimuthal tilting\nangles remains undetermined. Here we obtain the full phase diagram of the model\nfrom numerical pseudofermion functional renormalization group calculations. We\nshow that an extended quantum paramagnetic phase is realized between the\nN\\'{e}el and stripe/spiral phase. In this region, the spin susceptibility flows\nsmoothly down to the lowest numerical renormalization group scales with no sign\nof divergence or breakdown of the flow, in sharp contrast to the flow towards\nthe long-range ordered phases. Our results provide further evidence that the\ndipolar Heisenberg model is a fertile ground for quantum spin liquids.",
        "positive": "Van der Waals universality in homonuclear atom-dimer elastic collisions: The universal aspects of atom-dimer elastic collisions are investigated\nwithin the framework of Faddeev equations. The two-body interactions between\nthe neutral atoms are approximated by the separable potential approach. Our\nanalysis considers a pure van der Waals potential tail as well as soft-core van\nder Waals interactions permitting us in this manner to address the universally\ngeneral features of atom-dimer resonant spectra. In particular, we show that\nthe atom-dimer resonances are solely associated with the {\\it excited} Efimov\nstates. Furthermore, the positions of the corresponding resonances for a\nsoft-core potentials with more than 5 bound states are in good agreement with\nthe corresponding results from an infinitely deep pure van der Waals tail\npotential."
    },
    {
        "anchor": "Superfluid phases induced by the dipolar interactions: We determine the quantum ground state of dipolar bosons in a\nquasi-one-dimensional optical lattice and interacting via $s$-wave scattering.\nThe Hamiltonian is an extended Bose-Hubbard model which includes hopping terms\ndue to the interactions. We identify the parameter regime for which the\ncoefficients of the interaction-induced hopping terms become negative. For\nthese parameters we numerically determine the phase diagram for a canonical\nensemble and by means of density matrix renormalization group. We show that at\nsufficiently large values of the dipolar strength there is a quantum\ninterference between the tunneling due to single-particle effects and the one\ndue to the interactions. Because of this phenomenon, incompressible phases\nappear at relatively large values of the single-particle tunneling rates. This\nquantum interference cuts the phase diagram into two different, disconnected\nsuperfluid phases. In particular, at vanishing kinetic energy, the phase is\nalways superfluid with a staggered superfluid order parameter. These dynamics\nemerge from quantum interference phenomena between quantum fluctuations and\ninteractions and shed light into their role in determining the thermodynamic\nproperties of quantum matter.",
        "positive": "Theory of Bosons in two-leg ladders with large magnetic fields: We calculate the ground state of a Bose gas trapped on a two-leg ladder where\nRaman-induced hopping mimics the effect of a large magnetic field. In the\nmean-field limit, where there are large numbers of particles per site, this\nmaps onto a uniformly frustrated two-leg ladder classical spin model. The net\nparticle current always vanishes in the ground state, but generically there is\na finite \"chiral current\", corresponding to equal and opposite flow on the two\nlegs. We vary the strength of the hopping across the rungs of the ladder and\nthe interaction between the bosons. We find three phases: (1) A \"saturated\nchiral current phase\" (SCCP), where the density is uniform and the chiral\ncurrent is simply related to the strength of the magnetic field. In this state\nthe only broken symmetry is the $U(1)$ condensate phase. (2) A \"biased ladder\nphase\" (BLP), where the density is higher on one leg than the other. The fluid\nvelocity is higher on the lower density leg, so the net current is zero. In\naddition to the $U(1)$ condensate phase, this has a broken $Z_2$ reflection\nsymmetry. (3) A \"modulated density phase\" (MDP), where the atomic density is\nmodulated along the ladder. In addition to the $U(1)$ condensate phase, this\nhas a second broken $U(1)$ symmetry corresponding to translations of the\ndensity wave. We further study the fluctuations of the condensate in the BLP,\nfinding a roton-maxon like excitation spectrum. Decreasing the hopping along\nthe rungs softens the spectrum. As the energy of the \"roton\" reaches to zero,\nthe BLP becomes unstable. We describe the experimental signatures of these\nphases, including the response to changing the frequency of the Raman\ntransition."
    },
    {
        "anchor": "Pattern formation and exotic order in driven-dissipative Bose-Hubbard\n  systems: Modern experimental platforms such as supercoducting-circuit arrays call for\nthe exploration of bosonic tight-binding models in unconventional situations\nwith no counterpart in real materials. Here we investigate one of such\nsituations, in which excitations are driven and damped by pairs, leading to\npattern formation and exotic bosonic states emerged from a non-equilibrium\nquantum many-body system. Focusing on a two-dimensional driven-dissipative\nBose-Hubbard model, we find that its steady states are characterized by the\ncondensation of bosons around momenta lying on a \"Bose surface\", a bosonic\nanalogue of the Fermi surface in solid-state systems. The interplay between\ninstabilities generated by the driving, the nonlinear dissipative\nmode-coupling, and the underlaying lattice effect, allows the system to\nequilibrate into an exotic superfluid state of bosons condensed on a closed\nring in momentum space instead of discrete points. Such an unconventional state\nwith a spatially uniform density distribution goes beyond the traditional scope\nof pattern formation, and thus has no counterpart in the classical literature.\nIn addition, it is a state connected to several open problems in modern\ncondensed-matter physics, and here we provide the means to stabilize it,\nopening the way to its experimental study. Moreover, we also provide a concrete\nexperimental implementation of our model in currently-available\nsuperconducting-circuit arrays. We also investigate the relaxation spectrum\naround the condensate, which shows a characteristic purely diffusive behavior.",
        "positive": "Bose-Einstein condensation in a one-dimensional system of interacting\n  bosons: Using the Vakarchuk formulae for the density matrix, we calculate the number\nN_k of atoms with momentum \\hbar k for the ground state of a uniform\none-dimensional periodic system of interacting bosons. We obtain for\nimpenetrable point bosons N_0 = 2\\sqrt{N} and N_{k=2\\pi j/L} =\n0.31N_{0}/\\sqrt{|j|}. That is, there is no condensate or quasicondensate on low\nlevels at large N. For almost point bosons with weak coupling\n(\\beta=\\frac{\\nu_{0}m}{\\pi^{2}\\hbar^{2}n} \\ll 1), we obtain N_{0}/N =\n(\\frac{2}{N\\sqrt{\\beta}})^{\\sqrt{\\beta}/2} and N_{k=2\\pi j/L} =\n\\frac{N_0\\sqrt{\\beta}}{4|j|^{1-\\sqrt{\\beta}/2}}. In this case, the\nquasicondensate exists on the level with k=0 and on low levels with k\\neq 0, if\nN is large and $\\beta$ is small (e.g., for N = 10^{10}, \\beta = 0.01). A method\nof measurement of such fragmented quasicondensate is proposed."
    },
    {
        "anchor": "Rayleigh surface wave interaction with 2D exciton Bose-Einstein\n  condensate: We describe the interaction of the Rayleigh surface acoustic wave (SAW)\ntraveling on the semiconductor substrate and interacting with excitonic gas in\na double quantum well located on the substrate surface. We study the SAW\nattenuation and its velocity renormalization due to coupling with excitons.\nBoth the deformation potential and piezoelectric mechanisms of the SAW-exciton\ninteraction are considered. We focus our attention on the frequency and\nexcitonic density dependencies of the SAW absorption coefficient and velocity\nrenormalization at temperatures both above and well below the critical\ntemperature of Bose-Einstein condensation of excitonic gas. We demonstrate that\nthe SAW attenuation and velocity renormalization are strongly different below\nand above the critical temperature.",
        "positive": "Bernoulli's formula and Poisson's equations for a confined quantum gas:\n  Effects due to a moving piston: We study a nonequilibrium equation of states of an ideal quantum gas confined\nin the cavity under a moving piston with a small but finite velocity in the\ncase that the cavity wall suddenly begins to move at time origin. Confining to\nthe thermally-isolated process, quantum non-adiabatic (QNA) contribution to\nPoisson's adiabatic equations and to Bernoulli's formula which bridges the\npressure and internal energy is elucidated. We carry out a statistical mean of\nthe non-adiabatic (time-reversal-symmetric) force operator found in our\npreceding paper (K. Nakamura et al, Phys. Rev. E Vol.83, 041133, (2011)) in\nboth the low-temperature quantum-mechanical and high temperature\nquasi-classical regimes. The QNA contribution, which is proportional to square\nof the piston's velocity and to inverse of the longitudinal size of the cavity,\nhas a coefficient dependent on temperature, gas density and dimensionality of\nthe cavity. The investigation is done for a unidirectionally-expanding 3-d\nrectangular parallelepiped cavity as well as its 1-d version. Its relevance in\na realistic nano-scale heat engine is discussed."
    },
    {
        "anchor": "Superfluid gap formation in a fermionic optical lattice with spin\n  imbalanced populations: We investigate the attractive Hubbard model in infinite spatial dimensions at\nquarter filling. By combining dynamical mean-field theory with continuous-time\nquantum Monte Carlo simulations in the Nambu formalism, we directly deal with\nthe superfluid phase in the population imbalanced system. We discuss the low\nenergy properties in the polarized superfluid state and the pseudogap behavior\nin the vicinity of the critical temperature.",
        "positive": "Periodically-driven cold atoms: the role of the phase: Numerous theoretical and experimental studies have investigated the dynamics\nof cold atoms subjected to time periodic fields. Novel effects dependent on the\namplitude and frequency of the driving field, such as Coherent Destruction of\nTunneling have been identified and observed. However, in the last year or so,\nthree distinct types of experiments have demonstrated for the first time,\ninteresting behaviour associated with the driving phase: i.e. for systems\nexperiencing a driving field of general form $V(x)\\sin (\\omega t + \\phi)$,\ndifferent types of large scale oscillations and directed motion were observed.\nWe investigate and explain the phenomenon of Super-Bloch Oscillations (SBOs) in\nrelation to the other experiments and address the role of initial phase in\ngeneral. We analyse and compare the role of $\\phi$ in systems with homogeneous\nforces ($V'(x)= const$), such as cold atoms in shaken or amplitude-modulated\noptical lattices, as well as non-homogeneous forces ($V'(x)\\neq const$), such\nas the sloshing of atoms in driven traps, and clarify the physical origin of\nthe different $\\phi$-dependent effects."
    },
    {
        "anchor": "Shock waves in strongly interacting Fermi gas from time-dependent\n  density functional calculations: Motivated by a recent experiment [Phys. Rev. Lett. 106, 150401 (2011)] we\nsimulate the collision between two clouds of cold Fermi gas at unitarity\nconditions by using an extended Thomas-Fermi density functional. At variance\nwith the current interpretation of the experiments, where the role of viscosity\nis emphasized, we find that a quantitative agreement with the experimental\nobservation of the dynamics of the cloud collisions is obtained within our\nsuperfluid effective hydrodynamics approach, where density variations during\nthe collision are controlled by a purely dispersive quantum gradient term. We\nalso suggest different initial conditions where dispersive density ripples can\nbe detected with the available experimental spatial resolution.",
        "positive": "Thermodynamics of a deeply degenerate SU($N$)-symmetric Fermi gas: Many-body quantum systems can exhibit a striking degree of symmetry\nunparalleled by their classical counterparts. While in real materials SU($N$)\nsymmetry is an idealization, this symmetry is pristinely realized in fully\ncontrollable ultracold alkaline-earth atomic gases. Here, we study an\nSU($N$)-symmetric Fermi liquid of $^{87}$Sr atoms, where $N$ can be tuned to be\nas large as 10. In the deeply degenerate regime, we show through precise\nmeasurements of density fluctuations and expansion dynamics that the large $N$\nof spin states under SU($N$) symmetry leads to pronounced interaction effects\nin a system with a nominally negligible interaction parameter. Accounting for\nthese effects we demonstrate thermometry accurate to one-hundredth of the Fermi\nenergy. We also demonstrate record speed for preparing degenerate Fermi seas,\nreaching $T/T_F = 0.12$ in under 3 s, enabled by the SU($N$) symmetric\ninteractions. This, along with the introduction of a new spin polarizing\nmethod, enables operation of a 3D optical lattice clock in the band\ninsulating-regime."
    },
    {
        "anchor": "Few-body bound states of two-dimensional bosons: We study clusters of the type A$_N$B$_M$ with $N\\leq M\\leq 3$ in a\ntwo-dimensional mixture of A and B bosons, with attractive AB and equally\nrepulsive AA and BB interactions. In order to check universal aspects of the\nproblem, we choose two very different models: dipolar bosons in a bilayer\ngeometry and particles interacting via separable Gaussian potentials. We find\nthat all the considered clusters are bound and that their energies are\nuniversal functions of the scattering lengths $a_{AB}$ and $a_{AA}=a_{BB}$, for\nsufficiently large attraction-to-repulsion ratios $a_{AB}/a_{BB}$. When\n$a_{AB}/a_{BB}$ decreases below $\\approx 10$, the dimer-dimer interaction\nchanges from attractive to repulsive and the population-balanced AABB and\nAAABBB clusters break into AB dimers. Calculating the AAABBB hexamer energy\njust below this threshold, we find an effective three-dimer repulsion which may\nhave important implications for the many-body problem, particularly for\nobserving liquid and supersolid states of dipolar dimers in the bilayer\ngeometry. The population-imbalanced ABB trimer, ABBB tetramer, and AABBB\npentamer remain bound beyond the dimer-dimer threshold. In the dipolar model,\nthey break up at $a_{AB}\\approx 2 a_{BB}$ where the atom-dimer interaction\nswitches to repulsion.",
        "positive": "Critical Dynamics of a Two-dimensional Superfluid near a Non-Thermal\n  Fixed Point: Critical dynamics of an ultracold Bose gas far from equilibrium is studied in\ntwo spatial dimensions. Superfluid turbulence is created by quenching the\nequilibrium state close to zero temperature. Instead of immediately\nre-thermalizing, the system approaches a meta-stable transient state,\ncharacterized as a non-thermal fixed point. A focus is set on the vortex\ndensity and vortex-antivortex correlations which characterize the evolution\ntowards the non-thermal fixed point and the departure to final\n(quasi-)condensation. Two distinct power-law regimes in the vortex-density\ndecay are found and discussed in terms of a vortex binding-unbinding transition\nand a kinetic description of vortex scattering. A possible relation to decaying\nturbulence in classical fluids is pointed out. By comparing the results to\nequilibrium studies of a two-dimensional Bose gas, an intuitive understanding\nof the location of the non-thermal fixed point in a reduced phase space is\ndeveloped."
    },
    {
        "anchor": "Topological spin-orbit-coupled fermions beyond rotating wave\n  approximation: The realization of spin-orbit-coupled ultracold gases has driven a wide range\nof researches and is typically based on the rotating wave approximation (RWA).\nBy neglecting the counter-rotating terms, RWA characterizes a single\nnear-resonant spin-orbit (SO) coupling in a two-level system. Here, we propose\nand experimentally realize a new scheme for achieving a pair of two-dimensional\n(2D) SO couplings for ultracold fermions beyond RWA. This work not only\nrealizes the first anomalous Floquet topological Fermi gas beyond RWA, but also\nsignificantly improves the lifetime of the 2D-SO-coupled Fermi gas. Based on\npump-probe quench measurements, we observe a deterministic phase relation\nbetween two sets of SO couplings, which is characteristic for our beyond-RWA\nscheme and enables the two SO couplings to be simultaneously tuned to the\noptimum 2D configurations. We observe intriguing band topology by measuring\ntwo-ring band-inversion surfaces, quantitatively consistent with a Floquet\ntopological Fermi gas in the regime of high Chern numbers. Our study can open\nan avenue to explore exotic SO physics and anomalous topological states based\non long-lived SO-coupled ultracold fermions.",
        "positive": "Reponse to Comment on \"Direct mapping of the finite temperature phase\n  diagram of strongly correlated quantum models\": Pollet et al have questioned our claim staked in Phys. Rev. Lett. 103, 085701\n(2009) that from the location of sharp features in the compressibility in the\ntrap, it is possible to map out the phase boundary between two phases within\nreasonable accuracy. We stand by it and use this reply to sharpen the\nconditions under which \"sharp\" features in compressibility reflect the effects\nof critical fluctuations."
    },
    {
        "anchor": "Topology of Quantum Grey Soliton in Multi-Component Inhomogeneous\n  Bose-Einstein Condensates: We study the dispersion mechanism of Lieb mode excitations of both single and\nmulti component ultra-cold atomic Bose gas, subject to a harmonic confinement\nthrough chirp management. It is shown that in some parameter domain, the\nhole-like excitations lead to the soliton's negative mass regime, arising due\nto the coupling between chirp momentum and Kohn mode. In low momenta region the\ntrap considerably affects the dispersion of the grey soliton, which opens a new\nwindow to observe Lieb-mode excitations. Further, we extend our analysis to\nbinary condensate, which yields usual shape compatible grey-bright soliton\npairs. The inter-species interaction induces a shift in the Lieb-mode\nexcitations, where the pair can form a bound state. We emphasize that the\npresent model provides an opportunity to study such excitations in the low\nmomenta regime, as well as the formation of bound state in binary condensate.",
        "positive": "Multi-site mean-field theory for cold bosonic atoms in optical lattices: We present a detailed derivation of a multi-site mean-field theory (MSMFT)\nused to describe the Mott-insulator to superfluid transition of bosonic atoms\nin optical lattices. The approach is based on partitioning the lattice into\nsmall clusters which are decoupled by means of a mean field approximation. This\napproximation invokes local superfluid order parameters defined for each of the\nboundary sites of the cluster. The resulting MSMFT grand potential has a\nnon-trivial topology as a function of the various order parameters. An\nunderstanding of this topology provides two different criteria for the\ndetermination of the Mott insulator superfluid phase boundaries. We apply this\nformalism to $d$-dimensional hypercubic lattices in one, two and three\ndimensions, and demonstrate the improvement in the estimation of the phase\nboundaries when MSMFT is utilized for increasingly larger clusters, with the\nbest quantitative agreement found for $d=3$. The MSMFT is then used to examine\na linear dimer chain in which the on-site energies within the dimer have an\nenergy separation of $\\Delta$. This system has a complicated phase diagram\nwithin the parameter space of the model, with many distinct Mott phases\nseparated by superfluid regions."
    },
    {
        "anchor": "Dynamic Super Efimov Effect: Super Efimov effect is a recently proposed three-body effect characterized by\na double-exponential scaling, which has not been observed experimentally yet.\nHere, we present the general dynamic equations determining the cloud size of a\nscale invariant quantum gas in a time dependent harmonic trap. We show that a\ndouble-log periodicity as the hallmark of the super Efimov effect emerges when\nthe trap frequency is decreased with a specially designed time-dependence. We\nalso demonstrate that this dynamic super Efimov effect can be realized with\nrealistic choices of parameters in current experiments.",
        "positive": "Unconventional pairing in few-fermion systems tuned by external\n  confinement: We study the ground-state properties of a two-component one-dimensional\nsystem of a few ultra-cold fermions with attractive interactions. We show that,\nby ramping up an external potential barrier felt by one of the components, it\nis possible to induce regions of exotic superfluid phases, characterized by a\ntunable finite net momentum of the Cooper pair, without changing the overall\nspin populations. We show that these phases, which are the few-body analogs of\nthe celebrated Fulde-Ferrell-Larkin-Ovchinnikov state, can be distinguished by\nanalyzing a specific two-particle correlation encoded in the noise correlation\nfunction. Our theoretical results can be addressed in current experiments with\ncold atoms confined in spin-selective optical traps."
    },
    {
        "anchor": "Dynamics of Hubbard Hamiltonians with the multiconfigurational\n  time-dependent Hartree method for indistinguishable particles: We apply the multiconfigurational time-dependent Hartree method for\nindistinguishable particles (MCTDH-X) to systems of bosons or fermions in\nlattices described by Hubbard type Hamiltonians with long-range or short-range\ninterparticle interactions. The wavefunction is expanded in a variationally\noptimized time-dependent many-body basis generated by a set of effective\ncreation operators that are related to the original particle creation operators\nby a time-dependent unitary transform. We use the time-dependent variational\nprinciple for the coefficients of this transform as well as the expansion\ncoefficients of the wavefunction in the time-dependent many-body basis as\nvariational parameters to derive equations of motion. The convergence of\nMCTDH-X is shown by comparing its results to the exact diagonalization of one-,\ntwo-, and three-dimensional lattices filled with bosons with contact\ninteractions. We use MCTDH-X to study the buildup of correlations in the\nlong-time splitting dynamics of a Bose-Einstein condensate loaded into a large\ntwo-dimensional lattice subject to a barrier that is ramped up in the center.\nWe find that the system is split into two parts with emergent time-dependent\ncorrelations that depend on the ramping time -- for most barrier-raising-times\nthe system becomes two-fold fragmented, but for some of the very fast ramps,\nthe system shows revivals of coherence.",
        "positive": "Out-of-Time-Order Correlation at a Quantum Phase Transition: In this paper we numerically calculate the out-of-time-order correlation\nfunctions in the one-dimensional Bose-Hubbard model. Our study is motivated by\nthe conjecture that a system with Lyapunov exponent saturating the upper bound\n$2\\pi/\\beta$ will have a holographic dual to a black hole at finite\ntemperature. We further conjecture that for a many-body quantum system with a\nquantum phase transition, the Lyapunov exponent will have a peak in the quantum\ncritical region where there exists an emergent conformal symmetry and is absent\nof well-defined quasi-particles. With the help of a relation between the\nR\\'enyi entropy and the out-of-time-order correlation function, we argue that\nthe out-of-time-order correlation function of the Bose-Hubbard model will also\nexhibit an exponential behavior at the scrambling time. By fitting the\nnumerical results with an exponential function, we extract the Lyapunov\nexponents in the one-dimensional Bose-Hubbard model across the quantum critical\nregime at finite temperature. Our results on the Bose-Hubbard model support the\nconjecture. We also compute the butterfly velocity and propose how the echo\ntype measurement of this correlator in the cold atom realizations of the\nBose-Hubbard model without inverting the Hamiltonian."
    },
    {
        "anchor": "Quantum vortex dynamics in two-dimensional neutral superfluids: We derive an effective action for the vortex position degree-of-freedom in a\nsuperfluid by integrating out condensate phase and density fluctuation\nenvironmental modes. When the quantum dynamics of environmental fluctuations is\nneglected, we confirm the occurrence of the vortex Magnus force and obtain an\nexpression for the vortex mass. We find that this adiabatic approximation is\nvalid only when the superfluid droplet radius $R$, or the typical distance\nbetween vortices, is very much larger than the coherence length $\\xi$. We go\nbeyond the adiabatic approximation numerically, accounting for the quantum\ndynamics of environmental modes and capturing their dissipative coupling to\ncondensate dynamics. For the case of an optical-lattice superfluid we\ndemonstrate that vortex motion damping can be adjusted by tuning the ratio\nbetween the tunneling energy $J$ and the on-site interaction energy $U$. We\ncomment on the possibility of realizing vortex Landau level physics.",
        "positive": "Hydrodynamic equation of a spinor dipolar Bose-Einstein condensate: We introduce equations of motion for spin dynamics in a ferromagnetic\nBose-Einstein condensate with magnetic dipole-dipole interaction, written using\na vector expressing the superfluid velocity and a complex scalar describing the\nmagnetization. This simple hydrodynamical description extracts the dynamics of\nspin wave and affords a straightforward approach by which to investigate the\nspin dynamics of the condensate. To demonstrate the advantages of the\ndescription, we illustrate dynamical instability and magnetic fluctuation\npreference, which are expressed in analytical forms."
    },
    {
        "anchor": "Polarons in a ferromagnetic spinor Bose-Einstein condensates: We investigate the polarons formed by immersing a spinor impurity in a\nferromagnetic state of $F=1$ spinor Bose-Einstein condensate. The ground state\nenergies and effective masses of the polarons are calculated in both\nweak-coupling regime and strong-coupling regime. In the weakly interacting\nregime the second order perturbation theory is performed. In the strong\ncoupling regime we use a simple variational treatment. The analytical\napproximations to the energy and effective mass of the polarons are\nconstructed. Especially, a transition from the mobile state to the\nself-trapping state of the polaron in the strong coupling regime is discussed.\nWe also estimate the signatures of polaron effects in spinor BEC for the future\nexperiments.",
        "positive": "Pairing in few-fermion systems with attractive interactions: We have studied quasi one-dimensional few-particle systems consisting of one\nto six ultracold fermionic atoms in two different spin states with attractive\ninteractions. We probe the system by deforming the trapping potential and by\nobserving the tunneling of particles out of the trap. For even particle numbers\nwe observe a tunneling behavior which deviates from uncorrelated\nsingle-particle tunneling indicating the existence of pair correlations in the\nsystem. From the tunneling timescales we infer the differences in interaction\nenergies of systems with different number of particles which show a strong\nodd-even effect, similar to the one observed for neutron separation experiments\nin nuclei."
    },
    {
        "anchor": "Internal structure and stability of vortices in a dipolar spinor\n  Bose-Einstein condensate: We demonstrate how dipolar interactions can have pronounced effects on the\nstructure of vortices in atomic spinor Bose-Einstein condensates and illustrate\ngeneric physical principles that apply across dipolar spinor systems. We then\nfind and analyze the cores of singular vortices with non-Abelian charges in the\npoint-group symmetry of a spin-3 $^{52}$Cr condensate. Using a simpler model\nsystem, we analyze the underlying dipolar physics and show how a characteristic\nlength scale arising from the magnetic dipolar coupling interacts with the\nhierarchy of healing lengths of the s-wave scattering, and leads to simple\ncriteria for the core structure: When the interactions both energetically favor\nthe ground-state spin condition, such as in the spin-1 ferromagnetic phase, the\nsize of singular vortices is restricted to the shorter spin-dependent healing\nlength. Conversely, when the interactions compete (e.g., in the spin-1 polar\nphase), we find that the core of a singular vortex is enlarged by increasing\ndipolar coupling. We further demonstrate how the spin-alignment arising from\nthe interaction anisotropy is manifest in the appearance of a ground-state\nspin-vortex line that is oriented perpendicularly to the condensate axis of\nrotation, as well as in potentially observable internal core spin textures. We\nalso explain how it leads to interaction-dependent angular momentum in\nnonsingular vortices as a result of competition with rotation-induced spin\nordering. When the anisotropy is modified by a strong magnetic field, we show\nhow it gives rise to a symmetry-breaking deformation of a vortex core into a\nspin-domain wall.",
        "positive": "Wannier-Stark flatbands in Bravais lattices: We systematically construct flatbands (FB) for tight-binding models on simple\nBravais lattices in space dimension $d \\geq 2$ in the presence of a static\nuniform DC field. Commensurate DC field directions yield irreducible\nWannier-Stark (WS) bands in perpendicular dimension $d - 1$ with\n$d$-dimensional eigenfunctions. The irreducible bands turn into dispersionless\nflatbands in the absence of nearest neighbor hoppings between lattice sites in\nany direction perpendicular to the DC field. The number of commensurate\ndirections which yield flatbands is of measure one. We arrive at a complete\nhalt of transport, with the DC field prohibiting transport along the field\ndirection, and the flatbands prohibiting transport in all perpendicular\ndirections as well. The anisotropic flatband eigenstates are localizing at\nleast factorially (faster than exponential)."
    },
    {
        "anchor": "Tunable symmetry-protected higher-order topological states with\n  fermionic atoms in bilayer optical lattices: Higher-order topological states that possess gapped bulk energy bands and\nexotic topologically protected boundary states with at least two dimension\nlower than the bulk have significantly opened a new perspective for\nunderstanding of topological quantum matters. Here, we propose to generate\ntwo-dimensional topological boundary states for implementing synthetic magnetic\nflux of ultracold atoms trapped in bilayer optical lattices, which includes\nChern insulator, Dirac semimetals, and second-order topological phase (SOTP) by\nthe interplay of the two-photon detuning and effective Zeeman shift. These\nobserved topological phases can be well characterized by the energy gap of\nbulk, Wilson loop spectra, and the spin textures at the higher symmetric points\nof system. We show that the SOTP exhibits a pair of $0$D boundary states. While\nthe phases of Dirac semimetals and Chern insulator support the conventional\n$1$D boundary states due to the principle of bulk-boundary correspondence.\nStrikingly, the emerged boundary states for Dirac semimetals and SOTP are\ntopologically protected by $\\cal P T$-symmetry and chiral-mirror symmetry\n($\\mathcal{\\widetilde{M}}_{\\alpha}$), respectively. In particular, the location\nof $0$D corner states for SOTP which are associated with existing\n$\\mathcal{\\widetilde{M}}_{\\alpha}$-symmetry can be highly manipulated by tuning\nmagnetic flux. Our scheme herein provides a platform for emerging exotic\ntopological boundary states, which may facilitate the study of higher-order\ntopological phases in ultracold atomic gases.",
        "positive": "Dynamical Resonances and Stepped Current in an Attractive Quantum Pump: We report on the transport properties of a single mode quantum pump that\noperates by the simultaneous translation and oscillation of a potential well.\nWe examine the dynamics comparatively using quantum, classical and\nsemiclassical simulations. The use of an attractive or well potential is found\nto present several striking features absent if a barrier potential is used\ninstead, as usually favored. The trapping of particles by the well for variable\ndurations and subsequent release leads to a fractal-like structure in the\ndistribution of the classical scattering trajectories. Interference among them\nleads to a rich dynamical structure in the quantum current, conspicuously\nmissing in the classical current. Specifically, we observe sharp steps, spikes\nand dips in the current as a function of the incident energy of the carriers,\nand determine that a dynamical version of Fano resonance has a role that\ndepends on the direction of incidence and on multiple scattering by the\npotential."
    },
    {
        "anchor": "Particle Correlations in Bose-Einstein Condensates: The impact of interparticle correlations on the behavior of Bose-Einstein\nCondensates (BECs) is discussed using two approaches. In the first approach,\nthe wavefunction of a BEC is encoded in the $N$-particle sector of an extended\n\"catalytic state\". Going to a time-dependent interaction picture, we can\norganize the effective Hamiltonian by powers of ${N}^{-1/2}$. Requiring the\nterms of order ${N}^{1/2}$ to vanish, we get the Gross-Pitaevskii Equation.\nGoing to the next order, $N^0$, we obtain the number-conserving Bogoliubov\napproximation. Our approach allows one to stay in the Schr\\\"{o}dinger picture\nand to apply many techniques from quantum optics. Moreover, it is easier to\ntrack different orders in the Hamiltonian and to generalize to the\nmulti-component case. In the second approach, I consider a state of $N =l\\times\nn$ bosons that is derived by symmetrizing the $n$-fold tensor product of an\narbitrary $l$-boson state. Particularly, we are interested in the pure state\ncase for $l=2$, which we call the Pair-Correlated State (PCS). I show that PCS\nreproduces the number-conserving Bogoliubov approximation; moreover, it also\nworks in the strong interaction regime where the Bogoliubov approximation\nfails. For the two-site Bose-Hubbard model, I find numerically that the error\n(measured by the trace distance of the two-particle reduced density matrices)\nof PCS is less than two percent over the entire parameter space, thus making\nPCS a bridge between the superfluid and Mott insulating phases. Amazingly, the\nerror of PCS does not increase, in the time-dependent case, as the system\nevolves for longer times. I derive both time-dependent and -independent\nequations for the ground state and the time evolution of the PCS ansatz. The\ntime complexity of simulating PCS does not depend on $N$ and is linear in the\nnumber of orbitals in use.",
        "positive": "Repulsive Fermi polarons with negative effective mass: Recent LENS experiment on a 3D Fermi gas has reported a negative effective\nmass ($m^*<0$) of Fermi polarons in the strongly repulsive regime. There\nnaturally arise a question whether the negative $m^*$ is a precursor of the\ninstability towards phase separation (or itinerant ferromagnetism). In this\nwork, we make use of the exact solutions to study the ground state and\nexcitation properties of repulsive Fermi polarons in 1D, which can also exhibit\na negative $m^*$ in the super Tonks-Girardeau regime. By analyzing the total\nspin, quasi-momentum distribution and pair correlations, we conclude that the\nnegative $m^*$ is irrelevant to the instability towards ferromagnetism or phase\nseparation, but rather an intrinsic feature of collective excitations for\nfermions in the strongly repulsive regime. Surprisingly, for large and negative\n$m^*$, such excitation is accompanied with a spin density modulation when the\nmajority fermions move closer to the impurity rather than being repelled far\naway, contrary to the picture of phase separation. These results suggest an\nalternative interpretation of negative $m^*$ as observed in recent LENS\nexperiment."
    },
    {
        "anchor": "Driven-Dissipative Supersolid in a Ring Cavity: Supersolids are characterized by the counter-intuitive coexistence of\nsuperfluid and crystalline order. Here we study a supersolid phase emerging in\nthe steady state of a driven-dissipative system. We consider a transversely\npumped Bose-Einstein condensate trapped along the axis of a ring cavity and\ncoherently coupled to a pair of degenerate counter-propagating cavity modes.\nAbove a threshold pump strength the interference of photons scattered into the\ntwo cavity modes results in an emergent superradiant lattice, which\nspontaneously breaks the continuous translational symmetry towards a periodic\natomic pattern. The crystalline steady state inherits the superfluidity of the\nBose-Einstein condensate, thus exhibiting genuine properties of a supersolid. A\ngapless collective Goldstone mode correspondingly appears in the superradiant\nphase, which can be non-destructively monitored via the relative phase of the\ntwo cavity modes on the cavity output. Despite cavity-photon losses the\nGoldstone mode remains undamped, indicating the robustness of the supersolid\nphase.",
        "positive": "Simulating the Berezinskii-Kosterlitz-Thouless Transition with Complex\n  Langevin: Numerical simulations of the full quantum properties of interacting many-body\nsystems by means of field-theoretic Monte-Carlo techniques are often limited\ndue to a sign problem. Here we simulate properties of a dilute two-dimensional\nBose gas in the vicinity of the Berezinskii-Kosterlitz-Thouless (BKT)\ntransition by means of the Complex Langevin (CL) algorithm, thereby extending\nour previous CL study of the three-dimensional Bose gas to the\nlower-dimensional case. The purpose of the paper is twofold. On the one hand,\nit adds to benchmarking of the CL method and thus contributes to further\nexploring the range of applicability of the method. With the respective\nresults, the universality of the equation of state is recovered, as well as the\nlong-wave-length power-law dependence of the single-particle momentum spectrum\nbelow the BKT transition. Analysis of the rotational part of the current\ndensity corroborates vortex unbinding in crossing the transition. Beyond these\nmeasures of consistency we compute quantum corrections to the critical density\nand chemical potential in the weakly coupled regime. Our results show a shift\nof these quantities to lower values as compared to those obtained from\nclassical field theory. It points in the opposite direction as compared to the\nshift of the critical density found by means of the path-integral Monte-Carlo\nmethod at larger values of the coupling. Our simulations widen the perspective\nfor precision comparisons with experiment."
    },
    {
        "anchor": "Magnetic field dependence and the possibility of filtering ultraslow\n  light pulses in atomic gases with Bose-Einstein condensates: This paper studies theoretically the ultraslow light phenomenon in\nBose-Einstein condensates of alkali-metal atoms. The description is based on\nthe linear approach that is developed in the framework of the Green function\nformalism. It is pointed out that the group velocity of light pulses that are\ntuned up close to resonant lines of the alkali atoms' spectrum may strongly\ndepend on the intensity of the external static magnetic field. The possibility\nof filtering optical pulses using the ultraslow light phenomenon in Bose\ncondensates is discussed.",
        "positive": "Second sound and the superfluid fraction in a resonantly interacting\n  Fermi gas: Superfluidity is a macroscopic quantum phenomenon, which shows up below a\ncritical temperature and leads to a peculiar behavior of matter, with\nfrictionless flow, the formation of quantized vortices, and the quenching of\nthe moment of inertia being intriguing examples. A remarkable explanation for\nmany phenomena exhibited by a superfluid at finite temperature can be given in\nterms of a two-fluid mixture comprised of a normal component that behaves like\na usual fluid and a superfluid component with zero viscosity and zero entropy.\nImportant examples of superfluid systems are liquid helium and neutron stars.\nMore recently, ultracold atomic gases have emerged as new superfluid systems\nwith unprecedented possibilities to control interactions and external\nconfinement. Here we report the first observation of `second sound' in an\nultracold Fermi gas with resonant interactions. Second sound is a striking\nmanifestation of the two-component nature of a superfluid and corresponds to an\nentropy wave, where the superfluid and the non-superfluid components oscillate\nin opposite phase, different from ordinary sound (`first sound'), where they\noscillate in phase. The speed of second sound depends explicitly on the value\nof the superfluid fraction, a quantity sensitive to the spectrum of elementary\nexcitations. Our measurements allow us to extract the temperature dependence of\nthe superfluid fraction, which in strongly interacting quantum gases has been\nan inaccessible quantity so far."
    },
    {
        "anchor": "Seeing topological order in time-of-flight measurements: In this work we provide a general methodology to directly measure topological\norder in cold atom systems. As an application we propose the realisation of a\ncharacteristic topological model, introduced by Haldane, using optical lattices\nloaded with fermionic atoms in two internal states. We demonstrate that\ntime-of-flight measurements directly reveal the topological order of the system\nin the form of momentum space skyrmions.",
        "positive": "Spin Entanglement and Magnetic Competition via Long-range Interactions\n  in Spinor Quantum Optical Lattices: Quantum matter at ultra-low temperatures offers a testbed for analyzing and\ncontrolling desired properties in strongly correlated systems. Under typical\nconditions the nature of the atoms fixes the magnetic character of the system.\nBeyond classical light potentials leading to optical lattices and short range\ninteractions, high-Q cavities introduce novel dynamics into the system via the\nquantumness of light. Here we propose a theoretical model and we analyze it\nusing exact diagonalization and density matrix renormalization group\nsimulations. We explore the effects of cavity mediated long range magnetic\ninteractions and optical lattices in ultracold matter. We find that global\ninteractions modify the underlying magnetic character of the system while\nintroducing competition scenarios. Antiferromagnetic correlated bosonic matter\nemerges in conditions beyond to what nature typically provides. These allow new\nalternatives toward the design of robust mechanisms for quantum information\npurposes, exploiting the properties of magnetic phases of strongly correlated\nquantum matter."
    },
    {
        "anchor": "Stability of spherically trapped three-dimensional Bose-Einstein\n  condensates against macroscopic fragmentation: We consider spherically trapped Bose gases in three dimensions with contact\ninteractions, and investigate whether the Bose-Einstein condensate at zero\ntemperature is stable against macroscopic fragmentation into a small number of\nmutually incoherent pieces. Our results are expressed in terms of a\ndimensionless interaction measure proportional to the Thomas-Fermi parameter.\nIt is shown that while three-dimensional condensates are inherently much more\nstable against macroscopic fragmentation than their quasi-one- and\nquasi-two-dimensional counterparts, they fragment at a sufficiently large value\nof the dimensionless interaction measure, which we determine both fully\nnumerically and semianalytically from a continuum limit of large particle\nnumbers.",
        "positive": "The properties of Tonk-Girardeau Gas at Finite Temperature and\n  Comparison with Polarized Free Fermions: In the present paper we investigate the Tonks-Girardeau gas confined in a\nharmonic trap at finite temperature with thermal Bose-Fermi mapping method. The\npair distribution, density distribution, reduced one-body density matrix, the\noccupations number of natural orbitals, and momentum distribution are\nevaluated. In the whole temperature regime the pair distribution and density\ndistribution exhibit the same properties as those of polarized free Fermions\nbecause both of them depend on the modulus of wavefunction rather than\nwavefunction. While the reduced one-body density matrix, the natural orbital\noccupation, momentum distribution, which depend on wavefunction, of Tonks gas\ndisplays Bose properties different from polarized free Fermions at low\ntemperature. At high temperature we can not distinguish Tonks gas from the\npolarized free Fermi gas by all properties qualitatively."
    },
    {
        "anchor": "Dipolar Bose gas with three-body interactions at finite temperature: We investigate effects of three-body contact interactions on a trapped\ndipolar Bose gas at finite temperature using the Hartree-Fock-Bogoliubov\napproximation. We analyze numerically the behavior of the transition\ntemperature and the condensed fraction. Effects of the three-body interactions,\nanomalous pair correlations and temperature on the collective modes are\ndiscussed.",
        "positive": "Generalized Josephson relation for conserved charges in multi-component\n  bosons: The Josephson relation is generalized for conserved charges in\nmulti-component bosons. With linear response theory, a formula for derivation\nof generalized superfluid density is given. When there are several conserved\ncharges, the superfluid density is generally a second order tensor in internal\nspin space. When the rank of Green's function matrix is one, Josephson relation\nis given explicitly with phase operator method. For two-component bosons, with\nquantum field theory, we show a generalized Hugenholtz-Pines relation hold and\nexistence of two gapless phonons. When the interactions are $U(2)$ invariant,\nwe show there is a gapless quadratic dispersion excitation no matter how strong\nthe interactions are. The corresponding generalized Josephson relation is\nexpressed with Green's function matrix elements."
    },
    {
        "anchor": "On the hydrodynamics of Bose-condensed fluids subject to\n  density-dependent gauge potentials: When the energy functional of a Bose-condensed state of matter features an\neffective gauge potential which depends on the density $\\rho$ of the\ncondensate, the kinetic energy density of the matter field becomes nonlinear in\n$\\rho$ and additional flow-dependent terms enter the wave equation for the\nphase of the condensate wavefunction. To begin with, we consider a certain\nclass of density-dependent `single-component' gauge potentials, and later\nextend this class to encompass more general `multi-component' potentials. The\nnonlinear flow terms are cast into the general form of an inner-product between\nthe velocity field of the fluid and the gauge potential. This is achieved by\nintroducing a coupling matrix of dimensionless functions $\\gamma_{ij}\\left(\n\\rho \\right)$, which characterises the particular functional form of the gauge\npotential and regulates the strengths of the nonlinear terms accordingly. In\nthe momentum-transport equation of the fluid, two non-trivial terms emerge due\nto the density-dependent vector potential. A body-force of dilation appears as\na product of the gauge potential and the dilation rate of the fluid, while the\nfluid stress tensor features a flow-dependent pressure contribution given by\nthe inner-product of the gauge potential and the current density of the fluid.\nThis explicit dependence of the fluid pressure on the flow highlights the lack\nof Galilean invariance of the nonlinear fluid.",
        "positive": "Realization of ideal Weyl semimetal band in ultracold quantum gas with\n  3D Spin-Orbit coupling: The Weyl semimetals [1-6] are three-dimensional (3D) gapless topological\nphases with Weyl cones in the bulk band, and host massless quasiparticles known\nas Weyl fermions which were theorized by Hermann Weyl in the last twenties [7].\nThe lattice theory constrains that Weyl cones must come in pairs, with the\nminimal number of cones being two. The semimetal with only two Weyl cones is an\nideal Weyl semimetal (IWSM) which is the optimal platform to explore broad Weyl\nphysics but hard to engineer in solids. Here, we report the experimental\nrealization of the IWSM band by synthesising for the first time a 3D spin-orbit\n(SO) coupling for ultracold atoms. Engineering a 3D configuration-tunable\noptical Raman lattice [8], we realize the Weyl type SO coupling for ultracold\nquantum gas, with which the IWSM band is achieved with controllability. The\ntopological Weyl points are clearly measured via the virtual slicing imaging\ntechnique [8, 9] in equilibrium, and further resolved in the quench dynamics,\nrevealing the key information of the realized IWSM bands. The realization of\nthe IWSM band opens an avenue to investigate various exotic phenomena based on\nthe optimal Weyl semimetal platforms."
    },
    {
        "anchor": "Critical exponents and fluctuations at BEC in a 2D harmonically trapped\n  ideal gas: The critical properties displayed by an ideal 2D Bose gas trapped in a\nharmonic potential are determined and characterized in an exact numerical\nfashion. Beyond thermodynamics, addressed in terms of the global pressure and\nvolume which are the appropriate variables of a fluid confined in a non-uniform\nharmonic potential, the density-density correlation function is also calculated\nand the corresponding correlation length is found. Evaluation of all these\nquantities as Bose-Einstein condensation (BEC) is approached manifest its\ncritical continuous phase transition character. The divergence of the\ncorrelation length as the critical temperature is reached, unveils the expected\nspatial scale invariance proper of a critical transition. The logarithmic\nsingularities of this transition are traced back to the non-analytic behavior\nof the thermodynamic variables at vanishing chemical potential, which is the\nonset of BEC. The critical exponents associated with the ideal BEC transition\nin the 2D inhomogeneous fluid reveals its own universality class.",
        "positive": "Rotating superfluids in anharmonic traps: From vortex lattices to giant\n  vortices: We study a superfluid in a rotating anharmonic trap and explicate a rigorous\nproof of a transition from a vortex lattice to a giant vortex state as the\nrotation is increased beyond a limiting speed determined by the interaction\nstrength. The transition is characterized by the disappearance of the vortices\nfrom the annulus where the bulk of the superfluid is concentrated due to\ncentrifugal forces while a macroscopic phase circulation remains. The analysis\nis carried out within two-dimensional Gross-Pitaevskii theory at large coupling\nconstant and reveals significant differences between 'soft' anharmonic traps\n(like a quartic plus quadratic trapping potential) and traps with a fixed\nboundary: In the latter case the transition takes place in a parameter regime\nwhere the size of vortices is very small relative to the width of the annulus\nwhereas in 'soft' traps the vortex lattice persists until the width of the\nannulus becomes comparable to the vortex cores. Moreover, the density profile\nin the annulus where the bulk is concentrated is, in the 'soft' case,\napproximately gaussian with long tails and not of the Thomas-Fermi type like in\na trap with a fixed boundary."
    },
    {
        "anchor": "Multipolar condensates and multipolar Josephson effects: When single-particle dynamics are suppressed in certain strongly correlated\nsystems, dipoles arise as elementary carriers of quantum kinetics. These\ndipoles can further condense, providing physicists with a rich realm to study\nfracton phases of matter. Whereas recent theoretical discoveries have shown\nthat an unconventional lattice model may host a dipole condensate as the ground\nstate, fundamental questions arise as to whether dipole condensation is a\ngeneric phenomenon rather than a specific one unique to a particular model and\nwhat new quantum macroscopic phenomena a dipole condensate may bring us with.\nHere, we show that dipole condensates prevail in bosonic systems. Because of a\nself-proximity effect, where single-particle kinetics inevitably induces a\nfinite order parameter of dipoles, dipole condensation readily occurs in\nconventional normal phases of bosons. Our findings allow experimentalists to\nmanipulate the phase of a dipole condensate and deliver dipolar Josephson\neffects, where supercurrents of dipoles arise in the absence of particle flows.\nThe self-proximity effects can also be utilized to produce a generic multipolar\ncondensate. The kinetics of the $n$-th order multipoles unavoidably creates a\ncondensate of the $(n+1)$-th order multipoles, forming a hierarchy of\nmultipolar condensates that will offer physicists a whole new class of\nmacroscopic quantum phenomena.",
        "positive": "Phase Diagram of Mixed-Dimensional Anisotropic t-J-Models: We study the phase diagram of two different mixed-dimensional\n$t-J_z-J_{\\perp}$-models on the square lattice, in which the hopping amplitude\n$t$ is only nonzero along the $x$-direction. In the first, bosonic, model, the\nspin exchange amplitude $J_{\\perp}$ is negative and isotropic along the $x$ and\n$y$ directions of the lattice, and $J_z$ is isotropic and positive. The\nlow-energy physics is characterized by spin-charge separation: the holes hop as\nfree fermions in an easy-plane ferromagnetic background. In the second model,\n$J_{\\perp}$ is restricted to the $x$-axis while $J_z$ remains isotropic and\npositive. The model is agnostic to particle statistics, and shows stripe\npatterns with anti-ferromagnetic N{\\'e}el order at low temperature and high\nhole concentrations, in resemblance of the mixed-dimensional $t-J_z$ and $t-J$\nmodels. At lower hole concentration, a very strong first order transition and\nhysteresis loop is seen extending to a remarkably high 14(1)% hole doping."
    },
    {
        "anchor": "Ground State Energy of Hydrogen-Like Ions in Quantum Plasmas: Using the asymptotic iteration method (AIM) we investigate the variation in\nthe 1s energy levels of hydrogen and helium-like static ions in fully\ndegenerate electron gas. The semiclassical Thomas-Fermi (TF), Shukla-Eliasson\n(SE) and corrected Shukla-Eliasson (cSE) models are compared. It is remarked\nthat these models merge into the vacuum level for hydrogen and helium-like ions\nin the dilute classical electron gas regime. While in the TF model hydrogen\nground state level lifts monotonically towards the continuum limit with\nincrease in the electron concentration, in the SE and cSE models universal\nbound stabilization valley through the energy minimization occurs at a\nparticular electron concentration range for the hydrogen-like ion which for cSE\nmodel closely matches the electron concentrations in typical metals. The later\nstabilizing mechanism appears to be due to the interaction between plasmon\nexcitations and the Fermi lengthscales in metallic density regime. In the case\nof helium-like ions, however, no such stability mechanism is found. The\napplication of cSE model with electron exchange and correlation effects reveals\nthat cSE model qualitatively accounts for the number-density and lattice\nparameters of elemental metals within the framework of free electron\nassumption. According to the cSE model of static charge screening a simple\nmetal-insulator transition criterion is defined. Current investigation may\nfurther elucidate the underlying physical mechanisms in the formation and\ndielectric properties of metallic compounds.",
        "positive": "Imbalanced thee-component Fermi gas with attractive interactions:\n  Multiple FFLO-pairing, Bose-Fermi and Fermi-Fermi mixtures versus collapse\n  and phase separation: We present a detailed study of the population imbalanced three-component\nHubbard chain with attractive interactions. Such a system can be realized\nexperimentally with three different hyperfine states of ultra cold $^6$Li atoms\nin an optical lattice. We find that there are different phases that compete\nwith each other in this system: A molecular superfluid phase in which the three\nfermion species pair up to form molecules (trions), a usual pairing phase\ninvolving two species with exactly opposite momenta, and a more exotic\ngeneralized Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase consisting of three\ncompeting pairing tendencies with different non-zero center-of-mass momenta. At\nlarge attractive interactions the system exhibits strong tendencies towards\ncollapse and phase separation. Employing the\ndensity-matrix-renormalization-group-method (DMRG) to determine the decay\nexponents of the various correlators we establish the phase diagram of this\nmodel for different fillings and interactions. We also discuss the\nexperimentally relevant situation in a trap and report the existence of an\nadditional region where two species are dynamically balanced."
    },
    {
        "anchor": "Quadrupole oscillation in a dipolar Fermi gas: hydrodynamic vs\n  collisionless regime: The surface quadrupole mode of an harmonically trapped dipolar Fermi gas is\nstudied in both the hydrodynamic and collisionless regimes. The anisotropy and\nlong range effects of the dipolar force as well as the role of the trapping\ngeometry are explicitly investigated. In the hydrodynamic regime the frequency\nis always slightly smaller than the $\\sqrt{2}\\omega_\\perp$ value holding for\ngases interacting with contact interactions. In the collisionless regime the\nfrequency can be either pretty smaller or larger than the non-interacting value\n$2\\omega_\\perp$, depending on the cloud aspect ratio. Our results suggest that\nthe frequency of the surface quadrupole oscillation can provide a useful test\nfor studying, at very low temperatures, the transition between the normal and\nthe superfluid phase and, in the normal phase at higher temperatures, the\ncrossover between the collisional and collisionless regimes. The consequences\nof the anisotropy of the dipolar force on the virial theorem are also\ndiscussed.",
        "positive": "Collapse and revival of the monopole mode of a degenerate Bose gas in an\n  isotropic harmonic trap: We study the monopole (breathing) mode of a finite temperature Bose-Einstein\ncondensate in an isotropic harmonic trap recently developed by Lobser et al.\n[Nat.~Phys., \\textbf{11}, 1009 (2015)]. We observe a nonexponential collapse of\nthe amplitude of the condensate oscillation followed by a partial revival. This\nbehavior is identified as being due to beating between two eigenmodes of the\nsystem, corresponding to in-phase and out-of-phase oscillations of the\ncondensed and noncondensed fractions of the gas. We perform finite temperature\nsimulations of the system dynamics using the Zaremba-Nikuni-Griffin methodology\n[J.~Low Temp.~Phys., \\textbf{116}, 277 (1999)], and find good agreement with\nthe data, thus confirming the two mode description."
    },
    {
        "anchor": "Dispersive detection of atomic ensembles in the presence of strong\n  lensing: We experimentally and theoretically investigate in-medium propagation effects\nof off-resonant light in dense, spatially homogeneous ultacold atomic gases.\nFocussing on frequency modulation spectroscopy as the dispersive detection tool\nof atoms, we observe that the refractive gradient-index lenses presented by\nlocalised atomic ensembles can significantly modify the interpretation of the\ndispersive signal even for large probe detuning, owing to the collective\ndispersive response of the atoms. We identify criteria for distinguishing\nbetween thin and thick atomic lenses, leading to either diffraction-dominated\nand lensing dominated regimes for the outgoing probe beams. Our findings are\nconsistent with experimental data and solutions of paraxial wave equation for\nlight propagation. Our study provides important practical insights for\ndispersive, minimally intrusive optical detection and imaging schemes of\nultracold atoms and will be valuable for choosing optimal parameter regimes in\nnumerous applications.",
        "positive": "Observation of scale invariance in two-dimensional matter-wave Townes\n  solitons: We report near-deterministic generation of two-dimensional (2D) matter-wave\nTownes solitons, and a precision test on scale invariance in attractive 2D\nBoses gases. We induce a shape-controlled modulational instability in an\nelongated 2D matter-wave to create an array of isolated solitary waves of\nvarious sizes and peak densities. We confirm scale invariance by observing the\ncollapse of solitary-wave density profiles onto a single curve in a\ndimensionless coordinate rescaled according to their peak densities, and\nobserve that the scale-invariant profiles measured at different coupling\nconstants $g$ can further collapse onto the universal profile of Townes\nsolitons. The reported scaling behavior is tested with a nearly 60-fold\ndifference in soliton interaction energies, and allows us to discuss the impact\nof a non-negligible magnetic dipole-dipole interaction (MDDI) on 2D scale\ninvariance. We confirm that the effect of MDDI in our alkali cesium quasi-2D\nsamples effectively conforms to the same scaling law governed by a contact\ninteraction to well within our experiment uncertainty."
    },
    {
        "anchor": "Analytical theory of the dressed bound state in highly polarized Fermi\n  gases: We present an analytical treatment of a single \\down atom within a Fermi sea\nof \\up atoms, when the interaction is strong enough to produce a bound state,\ndressed by the Fermi sea. Our method makes use of a diagrammatic analysis, with\nthe involved diagrams taking only into account at most two particle-hole pairs\nexcitations. The agreement with existing Monte-Carlo results is excellent. In\nthe BEC limit our equation reduces exactly to the Skorniakov and\nTer-Martirosian equation. We present results when \\up and \\down atoms have\ndifferent masses, which is of interest for experiments in progress.",
        "positive": "Illustration of universal relations for trapped four-fermion system with\n  arbitrary s-wave scattering length: A two-component four-fermion system with equal masses, interspecies s-wave\nscattering length a and vanishing intraspecies interactions under external\nspherically symmetric harmonic confinement is considered. Using a correlated\nGaussian basis set expansion approach, we determine the energies and various\nstructural properties of the energetically lowest-lying gas-like state\nthroughout the crossover for various ranges of the underlying two-body\npotential. Extrapolating to the zero-range limit, our numerical results show\nexplicitly that the total energy, the trap energy as well as certain aspects of\nthe pair distribution function and of the momentum distribution are related\nthrough the so-called integrated contact intensity I(a). Furthermore, it is\nshown explicitly that the total energy and the trap energy are related through\na generalized virial theorem that accounts for a non-zero range."
    },
    {
        "anchor": "Dynamics of dipolar Atom-Molecular BEC in a double well potential:\n  Effect of atom-molecular coherent coupling: In the present work we have studied the dynamics of dipolar atom-molecular\nBose Einstein Condensates coupled via Feshbach Resonance in a double well\npotential. We have numerically solved four coupled GP like equations, two for\nleft well and two for right well for this atom molecular coupled system. Our\nnumerical results show that both the long-range dipole-dipole interaction\n(chosen to be positive) and the coherent coupling interaction (which is\npositive for bosons) facilitate the transmission of atoms and molecules from\nleft well to the right well when the population in the right well dominates\nover that in the left well and is trapped for a period of time. Whereas in\nabsence of any one of these interactions probability of transient transmission\ndecreases. However in absence of both the interactions (dipole-dipole and\ncoherent coupling) i.e. when only the repulsive contact interaction is present,\nit leads to self trapping in the left well for a period of time. It is also\nshown that the signature of coherent coupling between atoms and molecules on\nthe density distribution of atoms in the double well potential is present both\nin absence and presence of dipole-dipole interaction.",
        "positive": "Efimov Physics in 6Li Atoms: A new narrow 3-atom loss resonance associated with an Efimov trimer crossing\nthe 3-atom threshold has recently been discovered in a many-body system of\nultracold 6Li atoms in the three lowest hyperfine spin states at a magnetic\nfield near 895 G. O'Hara and coworkers have used measurements of the 3-body\nrecombination rate in this region to determine the complex 3-body parameter\nassociated with Efimov physics. Using this parameter as the input, we calculate\nthe universal predictions for the spectrum of Efimov states and for the 3-body\nrecombination rate in the universal region above 600 G where all three\nscattering lengths are large. We predict an atom-dimer loss resonance at (672\n+/- 2) G associated with an Efimov trimer disappearing through an atom-dimer\nthreshold. We also predict an interference minimum in the 3-body recombination\nrate at (759 +/- 1) G where the 3-spin mixture may be sufficiently stable to\nallow experimental study of the many-body system."
    },
    {
        "anchor": "Optical probing in a bilayer dark-bright condensate system: We consider a bilayer system of two-dimensional Bose-Einstein-condensed\ndipolar dark excitons (upper layer) and bright ones (bottom layer). We\ndemonstrate that the interlayer interaction leads to a mixing between\nexcitations from different layers. This mixing leads to the appearance of a\nsecond spectral branch in the spectrum of bright condensate. The excitation\nspectrum of the condensate of dark dipolar excitons then becomes optically\naccessible during luminescence spectra measurements of the bright condensate,\nwhich allows one to probe its kinetic properties. This approach is relevant for\nexperimental setups, where detection via conventional techniques remains\nchallenging; in particular, the suggested method is useful for studying dark\ndipolar excitons in transition metal dichalcogenide monolayers.",
        "positive": "Spontaneous population imbalance in two-component Bose and Fermi gases: We study two-component (or pseudo-spin-1/2) Bose or Fermi gases in one\ndimension, in which particles are convertible between the components. Through\nbosonization and numerical analyses of a simple lattice model, we demonstrate\nthat, in such gases, a strong intercomponent repulsion induces spontaneous\npopulation imbalance between the components, namely, the ferromagnetism of the\npseudo spins. The imbalanced phase contains gapless charge excitations\ncharacterized as a Tomonaga-Luttinger liquid and gapped spin excitations. We\nuncover a crucial effect of the intercomponent particle hopping on the\ntransition to the imbalanced phase. In the absence of this hopping, the\ntransition is of first order. At the transition point, the energy spectrum\nreveals certain degeneracy indicative of an emergent SU(2) symmetry. With an\ninfinitesimal intercomponent hopping, the transition becomes of Ising type. We\ndetermine the phase diagram of the model accurately and test the reliability of\nthe weak-coupling bosonization formalism."
    },
    {
        "anchor": "Twisted unwinding of multi-charged quantum vortex and generation of\n  turbulence in atomic Bose-Einstein condensates: We report the observation of the twisted decay of quadruply charged vortices\nin an atomic Bose-Einstein condensate. Supporting numerical simulations show\nthat the singly-charged vortices, which result from the decay of a\nmulti-charged vortex, twist around intertwined in the shape of helical Kelvin\nwaves. Finally, we propose to apply this effect to generate an almost isotropic\nstate of turbulence which we characterize in terms of the velocity statistics.",
        "positive": "Density-Matrix Renormalization Group for Continuous Quantum Systems: We introduce a versatile and practical framework for applying matrix product\nstate techniques to continuous quantum systems. We divide space into multiple\nsegments and generate continuous basis functions for the many-body state in\neach segment. By combining this mapping with existing numerical Density-Matrix\nRenormalization Group routines, we show how one can accurately obtain the\nground-state wave function, spatial correlations, and spatial entanglement\nentropy directly in the continuum. For a prototypical mesoscopic system of\nstrongly-interacting bosons we demonstrate faster convergence than standard\ngrid-based discretization. We illustrate the power of our approach by studying\na superfluid-insulator transition in an external potential. We outline how one\ncan directly apply or generalize this technique to a wide variety of\nexperimentally relevant problems across condensed matter physics and quantum\nfield theory."
    },
    {
        "anchor": "Log-Periodic Oscillations in the Photo Response of Efimov Trimers: The photoassociation of Efimov trimer, composed of three identical bosons, is\nstudied utilizing the multipole expansion. For identical particles the leading\ncontribution comes from the r^2 s-mode operator and from the quadrupole d-mode\noperator. Log-periodic oscillations are found in the photoassociation response\nfunction, both near the energy threshold for the leading s-wave reaction, and\nin the high frequency tail for all partial waves.",
        "positive": "Mini droplet, mega droplet and stripe formation in a dipolar condensate: We demonstrate mini droplet, mega droplet and stripe formation in a dipolar\n164Dy condensate, using an improved mean-field model including a\nLee-Huang-Yang-type interaction, employing a quasi-two-dimensional (quasi-2D)\ntrap in a way distinct from that in the pioneering experiment, M. A. Norcia et.\nal., Nature 596, 357 (2021), where the polarization z direction was taken to be\nperpendicular to the quasi-2D x-y plane. In the present study we take the\npolarization z direction in the quasi-2D x-z plane. Employing the same trapping\nfrequencies as in the experiment, and interchanging the frequencies along the y\nand z directions, we find the formation of mini droplets for number of atoms N\nas small as N = 1000. With the increase of number of atoms, a\nspatially-periodic supersolid-like one-dimensional array of mega droplets\ncontaining 50000 to 200000 atoms are formed along the x direction in the x-y\nplane. These mega droplets are elongated along the polarization z direction,\nconsequently, the spatially periodic arrangement of droplets appears as a\nstripe pattern in the x-z plane. To establish the supersolidity of the droplets\nwe demonstrate continued dipole-mode and scissors-mode oscillations of the\ndroplet-lattice pattern. The main findings of the present study can be tested\nexperimentally with the present know-how."
    },
    {
        "anchor": "Two distinguishable impurities in BEC: squeezing and entanglement of two\n  Bose polarons: We study entanglement and squeezing of two uncoupled impurities immersed in a\nBose-Einstein condensate. We treat them as two quantum Brownian particles\ninteracting with a bath composed of the Bogoliubov modes of the condensate. The\nLangevin-like quantum stochastic equations derived exhibit memory effects. We\nstudy two scenarios: (i) In the absence of an external potential, we observe\nsudden death of entanglement; (ii) In the presence of an external harmonic\npotential, entanglement survives even at the asymptotic time limit. Our study\nconsiders experimentally tunable parameters.",
        "positive": "Superfluidity breakdown of Rabi-coupled two-component Bose-Einstein\n  condensates in optical lattices: We demarcate the unstable regimes of superfluids in a Rabi-coupled\ntwo-component Bose-Einstein condensate in the presence of optical lattices. We\nfind that the Rabi coupling can stabilize superfluids. A significant separation\nbetween Landau and dynamical instabilities is presented in a Rabi-coupled\nZeeman lattice."
    },
    {
        "anchor": "Mott Transitions of Three-Component Fermionic Atoms with Repulsive\n  Interaction in Optical Lattices: We investigate the Mott transitions of three-component (colors) repulsive\nfermionic atoms in optical lattices using the dynamical mean field theory. We\nfind that for SU(3) symmetry breaking interactions the Mott transition occurs\nat incommensurate half filling. As a result, a characteristic Mott insulating\nstate appears, where paired atoms with two different colors and atoms with the\nthird color are localized at different sites. We also find another Mott state\nwhere atoms with two different colors are localized at different sites and\natoms with the third color remain itinerant. We demonstrate that these exotic\nMott phases can be detected by experimental double occupancy observations.",
        "positive": "Stability of a Floquet Bose-Einstein condensate in a one-dimensional\n  optical lattice: Motivated by recent experimental observations (C.V. Parker {\\it et al.},\nNature Physics, {\\bf 9}, 769 (2013)), we analyze the stability of a\nBose-Einstein condensate (BEC) in a one-dimensional lattice subjected to\nperiodic shaking. In such a system there is no thermodynamic ground state, but\nthere may be a long-lived steady-state, described as an eigenstate of a\n\"Floquet Hamiltonian\". We calculate how scattering processes lead to a decay of\nthe Floquet state. We map out the phase diagram of the system and find regions\nwhere the BEC is stable and regions where the BEC is unstable against atomic\ncollisions. We show that Parker et al. perform their experiment in the stable\nregion, which accounts for the long life-time of the condensate ($\\sim$ 1\nsecond). We also estimate the scattering rate of the bosons in the region where\nthe BEC is unstable."
    },
    {
        "anchor": "Expansion dynamics of interacting bosons in homogeneous lattices in one\n  and two dimensions: We experimentally and numerically investigate the expansion of initially\nlocalized ultracold bosons in homogeneous one- and two-dimensional optical\nlattices. We find that both dimensionality and interaction strength crucially\ninfluence these non-equilibrium dynamics. While the atoms expand ballistically\nin all integrable limits, deviations from these limits dramatically suppress\nthe expansion and lead to the appearance of almost bimodal cloud shapes,\nindicating diffusive dynamics in the center surrounded by ballistic wings. For\nstrongly interacting bosons, we observe a dimensional crossover of the dynamics\nfrom ballistic in the one-dimensional hard-core case to diffusive in two\ndimensions, as well as a similar crossover when higher occupancies are\nintroduced into the system.",
        "positive": "Dual trapped-ion quantum simulators: an alternative route towards exotic\n  quantum magnets: We present a route towards the quantum simulation of exotic quantum magnetism\nin ion traps by exploiting dual relations between different spin models. Our\nstrategy allows one to start from Hamiltonians that can be realized with\ncurrent technology, while properties of an exotic dual model are inferred from\nmeasurements of non-local, string-order-like, operators. The latter can be\nachieved from fluorescence, or from certain spectroscopic measurements, both of\nwhich can be combined with finite-size scaling by controlling the number of\nions in the dual quantum simulator. We apply this concept to propose quantum\nsimulators of frustrated quantum magnets, and Ising models with multi-spin\ninteractions. We test the validity of the idea by showing numerically that the\npredictions of an ideal dual quantum simulator are not qualitatively modified\nby relevant perturbations that occur naturally in the trapped-ion scenario."
    },
    {
        "anchor": "Stability of Logarithmic Bose-Einstein Condensate in Harmonic Trap: In this paper we investigate the stability of a recently introduced\nBose-Einstein condensate (BEC) which involves logarithmic interaction between\natoms. The Gaussian variational approach is employed to derive equations of\nmotion for condensate widths in the presence of a harmonic trap. Then we derive\nthe analytical solutions for these equations and find them to be in good\nagrement with numerical data. By analyzing deeply the frequencies of collective\noscillations, and the mean-square radius, we find that the system is always\nstable for both negative and positive week logarithmic coupling. However, for\nstrong interaction the situation is quite different: our condensate collapses\nfor positive coupling and oscillates with fixed frequency for negative one.\nThese special results remain the most characteristic features of the\nlogarithmic BEC compared to that involving two-body and three-body\ninteractions.",
        "positive": "Position-dependent spin-orbit coupling for ultracold atoms: We theoretically explore atomic Bose-Einstein condensates (BECs) subject to\nposition-dependent spin-orbit coupling (SOC). This SOC can be produced by\ncyclically laser coupling four internal atomic ground (or metastable) states in\nan environment where the detuning from resonance depends on position. The\nresulting spin-orbit coupled BEC phase-separates into domains, each of which\ncontain density modulations - stripes - aligned either along the x or y\ndirection. In each domain, the stripe orientation is determined by the sign of\nthe local detuning. When these stripes have mismatched spatial periods along\ndomain boundaries, non-trivial topological spin textures form at the interface,\nincluding skyrmions-like spin vortices and anti-vortices. In contrast to\nvortices present in conventional rotating BECs, these spin-vortices are stable\ntopological defects that are not present in the corresponding homogenous\nstripe-phase spin-orbit coupled BECs."
    },
    {
        "anchor": "Even-Odd effect of an Spin-S impurity coupled to a quantum critical\n  system: We discuss an even-odd effect for an impurity with an $N$-fold degenerate\ninternal states immersed in a two-dimensional superfluid--Mott-insulator\nquantum critical bath, which is described by an spin-$S$ XY Bose-Kondo impurity\nmodel with $N=2S+1$. Using a dimensional- and momentum-cut off regularized\nrenormalization group and unbiased large-scale Monte Carlo numerical\nsimulations, we establish the phase diagram for the $S=1$ impurity with all the\nrelevant terms included. We show that the $S=1$ impurity with 3-fold degeneracy\nis fully screened by the critical bath, in qualitative contrast to the spin-1/2\ncase where the impurity is only partially screened. We then argue that all\nimpurities with odd 2$S$ share the same universal physics as the spin-1/2 case,\nand all impurities with even 2$S$ are as the spin-1 case. We validate our\nconjecture with unbiased Monte Carlo simulations up to $S=2$. A physical\nconsequence of this even-odd effect is that two $N=2$ degenerate impurities in\nthe critical bath form a bound state at a sufficiently low temperature, which\ncan be realized using ultracold atoms in an optical lattice.",
        "positive": "Strong-coupling corrections to ground-state properties of a superfluid\n  Fermi gas: We theoretically present an economical and convenient way to study\nground-state properties of a strongly interacting superfluid Fermi gas. Our\nstrategy is that complicated strong-coupling calculations are used only to\nevaluate quantum fluctuation corrections to the chemical potential $\\mu$. Then,\nwithout any further strong-coupling calculations, we calculate the\ncompressibility, sound velocity, internal energy, pressure, and Tan's contact,\nfrom the calculated $\\mu$ without loss of accuracy, by using exact\nthermodynamic identities. Using a recent precise measurement of $\\mu$ in a\nsuperfluid $^6$Li Fermi gas, we show that an extended $T$-matrix approximation\n(ETMA) is suitable for our purpose, especially in the BCS-unitary regime, where\nour results indicate that many-body corrections are dominated by superfluid\nfluctuations. Since precise determinations of physical quantities are not\nalways easy in cold Fermi gas physics, our approach would greatly reduce\nexperimental and theoretical efforts toward the understanding of ground-state\nproperties of this strongly interacting Fermi system."
    },
    {
        "anchor": "Creating solitons with controllable and near zero velocity in\n  Bose-Einstein condensates: Established techniques for deterministically creating dark solitons in\nrepulsively interacting atomic Bose-Einstein condensates (BECs) can only access\na narrow range of soliton velocities. Because velocity affects the stability of\nindividual solitons and the properties of soliton-soliton interactions, this\ntechnical limitation has hindered experimental progress. Here we create dark\nsolitons in highly anisotropic cigar-shaped BECs with arbitrary position and\nvelocity by simultaneously engineering the amplitude and phase of the\ncondensate wavefunction, improving upon previous techniques which only\nexplicitly manipulated the condensate phase. The single dark soliton solution\npresent in true 1D systems corresponds to the kink soliton in anisotropic 3D\nsystems and is joined by a host of additional dark solitons including vortex\nring and solitonic vortex solutions. We readily create dark solitons with\nspeeds from zero to half the sound speed. The observed soliton oscillation\nfrequency suggests that we imprinted solitonic vortices, which for our\ncigar-shaped system are the only stable solitons expected for these velocities.\nOur numerical simulations of 1D BECs show this technique to be equally\neffective for creating kink solitons when they are stable. We demonstrate the\nutility of this technique by deterministically colliding dark solitons with\ndomain walls in two-component spinor BECs.",
        "positive": "Strongly nonequilibrium Bose-condensed atomic systems: A trapped Bose-Einstein condensate, being strongly perturbed, exhibits\nseveral spatial structures. First, there appear quantum vortices. Increasing\nthe amount of the injected energy leads to the formation of vortex tangles\nrepresenting quantum vortex turbulence. Continuing energy injection makes the\nsystem so strongly perturbed that vortices become destroyed and there develops\nanother kind of spatial structures with essentially heterogeneous spatial\ndensity. These structures consist of high-density droplets, or grains,\nsurrounded by the regions of low density. The droplets are randomly distributed\nin space, where they can move; however they live sufficiently long time to be\ntreated as a type of metastable creatures. Such structures have been observed\nin nonequilibrium trapped Bose gases of $^{87}$Rb subject to the action of an\noscillatory perturbation modulating the trapping potential. Perturbing the\nsystem even stronger transforms the droplet structure into wave turbulence,\nwhere Bose condensate is destroyed. Numerical simulations are in good agreement\nwith experimental observations."
    },
    {
        "anchor": "Universal relations for the two-dimensional spin-1/2 Fermi gas with\n  contact interactions: We present universal relations for a two-dimensional Fermi gas with pairwise\ncontact interactions. The derivation of these relations is made possible by\nobtaining the explicit form of a generalized function -- selector -- in the\nmomentum representation. The selector implements the short-distance boundary\ncondition between two fermions in a straightforward manner, and leads to simple\nderivations of the universal relations, in the spirit of Tan's original method\nfor the three-dimensional gas.",
        "positive": "Spiral spin textures of bosonic Mott insulator with SU(3) spin-orbit\n  coupling: We study the Mott phase of three-component bosons, with one particle per\nsite, in an optical lattice by mapping it onto an SU(3) spin model. In the\nsimplest case of full SU(3) symmetry, one obtains a ferromagnetic Heisenberg\nmodel. Introducing an SU(3) analog of spin-orbit coupling, additional spin-spin\ninteractions are generated. We first consider the scenario of spin-dependent\nhopping phases, leading to Dzyaloshinskii-Moriya-type interactions. They result\nin the formation of spiral spin textures, which in one dimension can be\nunderstood by a local unitary transformation. Applying classical Monte Carlo\nsimulations, we extend our study to two-dimensional systems, and systems with\n\"true\" spin-orbit coupling, involving spin-changing hoppings."
    },
    {
        "anchor": "Topological phases in spin-orbit coupled dipolar lattice bosons: We study the topological phases in spin-orbit coupled dipolar bosons in a\none-dimensional optical lattice. The magnetic dipolar interactions between\natoms give rise to the inter-site interactions. In the Mott-insulating regime,\nthis system can be described by the quantum XYZ spin model with the\nDzyaloshinskii-Moriya interactions in a transverse field. We focus on\ninvestigating the effect of dipolar interactions on the topological phase. The\ntopological phase can be shown when spin-orbit coupling incorporates with the\nrepulsive dipolar interaction. We find that the dipolar interaction can broaden\nthe range of parameters of spin-orbit coupling and transverse field for\nexhibiting the topological phase. The sum of spin correlations between the two\nnearest neighbouring atoms can be used to indicate the topological phase. This\nmay be useful for detecting topological phases in experiments.",
        "positive": "Phase-imprint induced domain formations and spin dynamics in spinor\n  condensates: We demonstrate that certain domain structures can be created both in ferro-\nand antiferro-magnetic spinor condensates if the initial phase is spatially\nmodulated. Meanwhile, spin dynamics of the condensate with modulated phases\nexhibits exotic features in comparison with those of a condensate with a\nuniform phase. We expect that these phenomena could be observed experimentally\nusing a phase-imprinting method."
    },
    {
        "anchor": "Efimov-like physics in fraction-dimensional Bose systems with three-body\n  interaction: A few-body properties of spinless Bose particles interacting via the contact\nthree-body potential in geometries with fractional dimensions $1<d<2$ are\nconsidered. In the four-body sector at three-body resonance we predict the\nexistence of infinite tower of the Efimov bound states, and a similar behavior\nis found in the five-body problem. It is shown that a ratio of the high-energy\nlevels in these two sectors is a universal constant. The consequences of\nemergence of the Efimov physics on the many-body behavior are briefly\ndiscussed.",
        "positive": "Confined Quasiparticle Dynamics in Long-Range Interacting Quantum Spin\n  Chains: We study the quasiparticle excitation and quench dynamics of the\none-dimensional transverse-field Ising model with power-law ($1/r^{\\alpha}$)\ninteractions. We find that long-range interactions give rise to a confining\npotential, which couples pairs of domain walls (kinks) into bound\nquasiparticles, analogous to mesonic bound states in high-energy physics. We\nshow that these quasiparticles have signatures in the dynamics of order\nparameters following a global quench and the Fourier spectrum of these order\nparameters can be expolited as a direct probe of the masses of the confined\nquasiparticles. We introduce a two-kink model to qualitatively explain the\nphenomenon of long-range-interaction induced confinement, and to quantitatively\npredict the masses of the bound quasiparticles. Furthermore, we illustrate that\nthese quasiparticle states can lead to slow thermalization of one-point\nobservables for certain initial states. Our work is readily applicable to\ncurrent trapped-ion experiments."
    },
    {
        "anchor": "Hanbury-Brown and Twiss bunching of phonons and of the quantum depletion\n  in a strongly-interacting Bose gas: We report the realisation of a Hanbury-Brown and Twiss (HBT)-like experiment\nwith a gas of strongly interacting bosons at low temperatures. The regime of\nlarge interactions and low temperatures is reached in a three-dimensional\noptical lattice and atom-atom correlations are extracted from the detection of\nindividual metastable Helium atoms after a long free-fall. We observe a HBT\nbunching in the non-condensed fraction of the gas whose properties strongly\ndeviate from the HBT signals expected for non-interacting bosons. In addition,\nwe show that the measured correlations reflect the peculiar quantum statistics\nof atoms belonging to the quantum depletion and of the Bogoliubov phonons,\ni.e., of collective excitations of the many-body quantum state. Our results\ndemonstrate that atom-atom correlations provide information about the quantum\nstate of strongly-interacting particles, extending the interest of HBT-like\nexperiments beyond the case of non-interacting particles.",
        "positive": "Conical intersections in laboratory coordinates with ultracold molecules: For two states of opposite parity that cross as a function of an external\nmagnetic field, the addition of an electric field will break the symmetry and\ninduce an avoided crossing. A suitable arrangement of fields may be used to\ncreate a conical intersection as a function of external spatial coordinates. We\nconsider the effect of the resulting geometric phase for ultracold polar\nmolecules. For a Bose-Einstein condensate in the mean-field approximation, the\ngeometric phase effect induces stable states of persistent superfluid flow that\nare characterized by half-integer quantized angular momentum."
    },
    {
        "anchor": "Non-Markovian stochastic Gross-Pitaevskii equation for the\n  exciton-polariton Bose-Einstein condensate: In this paper, a non-Markovian Gross-Pitaevskii equation is proposed to\ndescribe the formation of a condensate in an exciton-polariton system under\nincoherent pumping. By introducing spatially delta-correlated noise terms, we\nobserve a transition from a spatially ordered phase to a disordered one as the\ntemperature increases. In course of this process, the population of the\ncondensate is significantly reduced. Irregularly located separate dense spots\nof condensate above the transition temperature are revealed. Using the Gabor\ntransform, it is shown that, with increasing temperature, the condensate\ndecoheres, that is accompanied by the transition from narrowband to broadband\nspectral density.",
        "positive": "New perspectives on superfluidity in resonantly--driven polariton fluids: In this paper we discuss, within the Gross--Pitaevskii framework,\nsuperfluidity, soliton nucleation, and instabilities in a non-equilibrium\npolariton fluid injected by a spatially localized and continuous-wave coherent\npump and flowing against a defect located outside the pump spot. In contrast to\nequilibrium condensates, the steady-state solutions of the driven-dissipative\nequations in this specific geometry hardly show a clean superfluid flow around\nthe defect and rather feature a crossover from shallow to deep soliton-like\nperturbation. This is explained in terms of the properties of one-dimensional\nflows, in particular their weak dependence on the pump parameters and their\nrapid transition to a super-sonic regime under the effect of the quantum\npressure; such a highly nonlinear behaviour calls for quantitative experimental\ntests of the underlying Gross--Pitaevskii equation. The role of disorder and of\na incoherent reservoir in inducing non-stationary behaviours with moving\nvortices is also highlighted."
    },
    {
        "anchor": "Mean-field predictions for a dipolar Bose-Einstein condensate with\n  $^{164}$Dy: We study dipolar Bose-Einstein condensates for a realistic set of parameters\nclose to actual experimental setups with dysprosium. Our analysis is based on\nthe extended Gross-Pitaevskii equation, which we solve numerically exact on a\nthree-dimensional grid. We present stability and phase diagrams, and study the\nexpansion dynamics of dipolar condensates. Our calculations show signatures of\nthe dipole-dipole interaction in terms of structured states and a deviation of\nthe well-known inversion of the aspect ratio of the cloud during a time of\nflight.",
        "positive": "Hybrid OpenMP/MPI programs for solving the time-dependent\n  Gross-Pitaevskii equation in a fully anisotropic trap: We present hybrid OpenMP/MPI (Open Multi-Processing/Message Passing\nInterface) parallelized versions of earlier published C programs (D. Vudragovic\net al., Comput. Phys. Commun. 183, 2021 (2012)) for calculating both stationary\nand non-stationary solutions of the time-dependent Gross-Pitaevskii (GP)\nequation in three spatial dimensions. The GP equation describes the properties\nof dilute Bose-Einstein condensates at ultra-cold temperatures. Hybrid versions\nof programs use the same algorithms as the C ones, involving real- and\nimaginary-time propagation based on a split-step Crank-Nicolson method, but\nconsider only a fully-anisotropic three-dimensional GP equation, where\nalgorithmic complexity for large grid sizes necessitates parallelization in\norder to reduce execution time and/or memory requirements per node. Since\ndistributed memory approach is required to address the latter, we combine MPI\nprograming paradigm with existing OpenMP codes, thus creating fully flexible\nparallelism within a combined distributed/shared memory model, suitable for\ndifferent modern computer architectures. The two presented C/OpenMP/MPI\nprograms for real- and imaginary-time propagation are optimized and accompanied\nby a customizable makefile. We present typical scalability results for the\nprovided OpenMP/MPI codes and demonstrate almost linear speedup until\ninter-process communication time starts to dominate over calculation time per\niteration. Such a scalability study is necessary for large grid sizes in order\nto determine optimal number of MPI nodes and OpenMP threads per node."
    },
    {
        "anchor": "Chaos and ergodicity across the energy spectrum of interacting bosons: We identify the chaotic phase of the Bose-Hubbard Hamiltonian by the\nenergy-resolved correlation between spectral features and structural changes of\nthe associated eigenstates as exposed by their generalized fractal dimensions.\nThe eigenvectors are shown to become ergodic in the thermodynamic limit, in the\nconfiguration space Fock basis, in which random matrix theory offers a\nremarkable description of their typical structure. The distributions of the\ngeneralized fractal dimensions, however, are ever more distinguishable from\nrandom matrix theory as the Hilbert space dimension grows.",
        "positive": "Dynamics of long-range order in an exciton-polariton condensate: We report on time resolved measurements of the first order spatial coherence\nin an exciton polariton Bose-Einstein condensate. Long range spatial coherence\nis found to set in right at the onset of stimulated scattering, on a picosecond\ntime scale. The coherence reaches its maximum value after the population and\ndecays slower, staying up to a few hundreds of picoseconds. This behavior can\nbe qualitatively reproduced, using a stochastic classical field model\ndescribing interaction between the polariton condensate and the exciton\nreservoir within a disordered potential."
    },
    {
        "anchor": "A universal pairing gap measurement proposal by dynamical excitations in\n  2D doped attractive Fermi-Hubbard model with spin-orbit coupling: By calculating dynamical structure factor of two-dimensional doped attractive\nFermi-Hubbard model with Rashba spin-orbit coupling, we not only investigate\ncollective modes and single-particle excitations of the system during the phase\ntransition between Bardeen-Cooper-Schrieffer superfluid and topological\nsuperfluid, but also propose a universal method to measure pairing gap\nmeasurement in an optical lattice system. Our numerical results show that the\narea of the molecular excitation peak at the transferred momentum ${\\bf\nq}=\\left[\\pi,\\pi\\right]$ is proportional to the square of the pairing gap in\nthe system with Rashba SOC. In particular, this method is very sensitive to the\npairing gap. This goes on verifying that this method is universal to measure\nthe pairing gap in a doped optical lattice with Rashba SOC. These theoretical\nresults are important for experimentally measuring the pairing gap and studying\nthe topological superfluid in an optical lattice.",
        "positive": "Robust platform for engineering pure-quantum-state transitions in\n  polariton condensates: We report on pure-quantum-state polariton condensates in optical annular\ntraps. The study of the underlying mechanism reveals that the polariton\nwavefunction always coalesces in a single pure-quantum-state that,\ncounter-intuitively, is always the uppermost confined state with the highest\noverlap to the exciton reservoir. The tunability of such states combined with\nthe short polariton lifetime allows for ultrafast transitions between coherent\nmesoscopic wavefunctions of distinctly different symmetries rendering optically\nconfined polariton condensates a promising platform for applications such as\nmany-body quantum circuitry and continuous-variable quantum processing."
    },
    {
        "anchor": "Spectrum and entanglement of phonons in quantum fluids of light: We study the quantum state of phonons propagating on top of a fluid of light\ncoherently generated in a planar microcavity device by a quasi-resonant\nincident laser beam. In the steady-state under a monochromatic pump, because of\nthe finite radiative lifetime of photons, a sizable incoherent population of\nlow frequency phonons is predicted to appear. Their mean occupation number\ndiffers from a Planck distribution and is independent on the photon lifetime.\nWhen the photon fluid is subjected to a sudden change of its parameters,\nadditional phonon pairs are created in the fluid with remarkable two-mode\nsqueezing and entanglement properties. Schemes to assess non-separability of\nthe phonon state from measurements of the correlation functions of the emitted\nlight are discussed.",
        "positive": "Discrete Breather and Soliton-Mode Collective Excitations in\n  Bose-Einstein Condensates in a Deep Optical Lattice with Tunable Three-body\n  Interactions: We have studied the dynamic evolution of the collective excitations in\nBose-Einstein condensates in a deep optical lattice with tunable three-body\ninteractions. Their dynamics is governed by a high order discrete nonlinear\nSchrodinger equation (DNLSE). The dynamical phase diagram of the system is\nobtained using the variational method. The dynamical evolution shows very\ninteresting features. The discrete breather phase totally disappears in the\nregime where the three-body interaction completely dominates over the two-body\ninteraction. The soliton phase in this particular regime exists only when the\nsoliton line approaches the critical line in the phase diagram. When weak\ntwo-body interactions are reintroduced into this regime, the discrete breather\nsolutions reappear, but occupies a very small domain in the phase space.\nLikewise, in this regime, the soliton as well as the discrete breather phases\ncompletely disappear if the signs of the two-and three-body interactions are\nopposite. We have analysed the causes of this unusual dynamical evolution of\nthe collective excitations of the Bose-Einstein condensate with tunable\ninteractions. We have also performed direct numerical simulations of the\ngoverning DNLS equation to show the existence of the discrete soliton solution\nas predicted by the variational calculations, and also to check the long term\nstability of the soliton solution."
    },
    {
        "anchor": "Topological degeneracy and pairing in a one-dimensional gas of spinless\n  Fermions: We revisit the low energy physics of one dimensional spinless fermion\nliquids, showing that with sufficiently strong interactions the conventional\nLuttinger liquid can give way to a strong pairing phase. While the density\nfluctuations in both phases are described by a gapless Luttinger liquid, single\nfermion excitations are gapped only in the strong pairing phase. Smooth spatial\nInterfaces between the two phases lead to topological degeneracies in the\nground state and low energy phonon spectrum. Using a concrete microscopic\nmodel, with both single particle and pair hopping, we show that the strong\npairing state is established through emergence of a new low energy fermionic\nmode. We characterize the two phases with numerical calculations using the\ndensity matrix renormalization group. In particular we find enhancement of the\ncentral charge from $c=1$ in the two Luttinger liquid phases to $c=3/2$ at the\ncritical point, which gives direct evidence for an emergent critical Majorana\nmode. Finally, we confirm the existence of topological degeneracies in the low\nenergy phonon spectrum, associated with spatial interfaces between the two\nphases.",
        "positive": "Two-dimensional vortex quantum droplets: It was recently found that the Lee-Huang-Yang (LHY) correction to the\nmean-field Hamiltonian suppresses the collapse and creates stable localized\nmodes (two-component \"quantum droplets\", QDs) in two and three dimensions. We\nconstruct two-dimensional\\ self-trapped modes in the form of QDs with vorticity\n$S$ embedded into each component. The QDs feature a flat-top shape, which\nexpands with the increase of $S$ and norm $N$. An essential finding, produced\nby a systematic numerical analysis and analytical estimates, is that the\nvortical QDs are \\emph{stable} (which is a critical issue for vortex solitons\nin nonlinear models) up to $S=5$, for $N$ exceeding a certain threshold value.\nIn the condensate of $^{39}$K atoms, in which QDs with $S=0$ and a quasi-2D\nshape were created recently, the vortical droplets may have radial size\n$\\lesssim 30$ $\\mathrm{\\mu}$m, with the number of atoms in the range of\n$10^{4}-10^{5}$. It is worthy to note that \\textit{hidden-vorticity} states in\nQDs with topological charges $% S_{+}=-S_{-}=1$ in its components, which are\nprone to strong instability in other settings, have their stability region too,\nalthough it may be located beyond applicability limits of the underlying model.\nDynamics of elliptically deformed QDs, which form rotating elongated patterns\nor ones with strong oscillations of the eccentricity, as well as collisions of\nQDs, are also addressed."
    },
    {
        "anchor": "Theory of the vortex-clustering transition in a confined two-dimensional\n  quantum fluid: Clustering of like-sign vortices in a planar bounded domain is known to occur\nat negative temperature, a phenomenon that Onsager demonstrated to be a\nconsequence of bounded phase space. In a confined superfluid, quantized\nvortices can support such an ordered phase, provided they evolve as an almost\nisolated subsystem containing sufficient energy. A detailed theoretical\nunderstanding of the statistical mechanics of such states thus requires a\nmicrocanonical approach. Here we develop an analytical theory of the vortex\nclustering transition in a neutral system of quantum vortices confined to a\ntwo-dimensional disk geometry, within the microcanonical ensemble. As the\nsystem energy increases above a critical value, the system develops global\norder via the emergence of a macroscopic dipole structure from the homogeneous\nphase of vortices, spontaneously breaking the Z2 symmetry associated with\ninvariance under vortex circulation exchange, and the rotational SO(2) symmetry\ndue to the disk geometry. The dipole structure emerges characterized by the\ncontinuous growth of the macroscopic dipole moment which serves as a global\norder parameter, resembling a continuous phase transition. The critical\ntemperature of the transition, and the critical exponent associated with the\ndipole moment, are obtained exactly within mean-field theory. The clustering\ntransition is shown to be distinct from the final state reached at high energy,\nknown as supercondensation. The dipole moment develops via two macroscopic\nvortex clusters and the cluster locations are found analytically, both near the\nclustering transition and in the supercondensation limit. The microcanonical\ntheory shows excellent agreement with Monte Carlo simulations, and signatures\nof the transition are apparent even for a modest system of 100 vortices,\naccessible in current Bose-Einstein condensate experiments.",
        "positive": "Mott made easy: The realization of a Mott insulating state in a system of ultracold fermions\ncomprising far more internal components than the electron, provides an avenue\nfor probing many-body physics that is difficult to access in solids."
    },
    {
        "anchor": "Observation of Slow Dynamics near the Many-Body Localization Transition\n  in One-Dimensional Quasiperiodic Systems: In the presence of sufficiently strong disorder or quasiperiodic fields, an\ninteracting many-body system can fail to thermalize and become many-body\nlocalized. The associated transition is of particular interest, since it occurs\nnot only in the ground state but over an extended range of energy densities. So\nfar, theoretical studies of the transition have focused mainly on the case of\ntrue-random disorder. In this work, we experimentally and numerically\ninvestigate the regime close to the many-body localization transition in\nquasiperiodic systems. We find slow relaxation of the density imbalance close\nto the transition, strikingly similar to the behavior near the transition in\ntrue-random systems. This dynamics is found to continuously slow down upon\napproaching the transition and allows for an estimate of the transition point.\nWe discuss possible microscopic origins of these slow dynamics.",
        "positive": "Topological defects of spin-orbit coupled Bose-Einstein condensates in a\n  rotating anharmonic trap: We investigate the topological defects and spin structures of binary\nBose-Einstein condensates (BECs) with Dresselhaus spin-orbit coupling (D-SOC)\nin a rotating anharmonic trap. Our results show that for initially mixed BECs\nwithout SOC the increasing rotation frequency can lead to the structural phase\ntransition of the system. In the presence of isotropic D-SOC, the system\nsustains vortex pair,Anderson--Toulouse coreless vortices, circular vortex\nsheets, and combined vortex structures. In particular, when the rotation\nfrequency is fixed above the radial trapping frequency the strong D-SOC results\nin a peculiar topological structure which is comprised of multi-layer visible\nvortex necklaces, hidden vortex necklaces and a hidden giant vortex. In\naddition, the system exhibits rich spin textures including basic skyrmion,\nmeron cluster, skyrmion string and various skyrmion lattices. The skyrmions\nwill be destroyed in the limit of large D-SOC or rotation frequency.\nFurthermore, the effects of anisotropic D-SOC and Rashba-Dresselhaus SOC on the\ntopological structures of the system are discussed."
    },
    {
        "anchor": "Interferometric Measurements of Many-body Topological Invariants using\n  Mobile Impurities: Topological quantum phases cannot be characterized by Ginzburg-Landau type\norder parameters, and are instead described by non-local topological\ninvariants. Experimental platforms capable of realizing such exotic states now\ninclude \"synthetic\" many-body systems such as ultracold atoms or photons.\nUnique tools available in these systems enable a new characterization of\nstrongly correlated many-body states. Here we propose a general scheme for\ndetecting topological order using interferometric measurements of elementary\nexcitations. The key ingredient is the use of mobile impurities which bind to\nquasiparticles of a host many-body system. Specifically we show how fractional\ncharges can be probed in the bulk of fractional quantum Hall systems. We\ndemonstrate that combining Ramsey interference with Bloch oscillations can be\nused to measure Chern numbers of individual quasiparticles, which gives a\ndirect probe of their fractional charges. We discuss possible extensions of our\nmethod to other topological many-body systems, such as spin liquids.",
        "positive": "Spectral moment sum rules for the retarded Green's function and\n  self-energy of the inhomogeneous Bose-Hubbard model in equilibrium and\n  nonequilibrium: We derive expressions for the zeroth and the first three spectral moment sum\nrules for the retarded Green's function and for the zeroth and the first\nspectral moment sum rules for the retarded self-energy of the inhomogeneous\nBose-Hubbard model in nonequilibrium, when the local on-site repulsion and the\nchemical potential are time-dependent, and in the presence of an external\ntime-dependent electromagnetic field. We also evaluate these moments for\nequilibrium, where all time dependence and external fields vanish. Unlike\nsimilar sum rules for the Fermi-Hubbard model, in the Bose-Hubbard model case,\nthe sum rules often depend on expectation values that cannot be determined\nsimply from parameters in the Hamiltonian like the interaction strength and\nchemical potential, but require knowledge of equal time many-body expectation\nvalues from some other source. We show how one can approximately evaluate these\nexpectation values for the Mott-insulating phase in a systematic\nstrong-coupling expansion in powers of the hopping divided by the interaction.\nWe compare the exact moments to moments of spectral functions calculated from a\nvariety of different approximations and use them to benchmark their accuracy."
    },
    {
        "anchor": "Diffusive density profiles in a cold-atom expansion experiment: In a recent experiment [McGehee et al., Phys. Rev. Lett. 111, 145303 (2013)],\nthe expansion of non-interacting ultracold fermions was studied in a random\nspeckle potential, and the observed density profiles were interpreted based on\n3D Anderson localization. The purpose of this note is to demonstrate that slow\ndiffusion of particles with a broad energy distribution and an energy-dependent\ndiffusion coefficient leads to density profiles that agree with the measured\ndata, but not with the behavior expected for 3D Anderson localization.",
        "positive": "Many-body dynamical localization in the kicked Bose-Hubbard chain: We provide evidence that a clean kicked Bose-Hubbard model exhibits a\nmany-body dynamically localized phase. This phase shows ergodicity breaking up\nto the largest sizes we were able to consider. We argue that this property\npersists in the limit of large size. The Floquet states violate eigenstate\nthermalization and then the asymptotic value of local observables depends on\nthe initial state and is not thermal. This implies that the system does not\ngenerically heat up to infinite temperature, for almost all the initial states.\nDifferently from many-body localization here the entanglement entropy linearly\nincreases in time. This increase corresponds to space-delocalized Floquet\nstates which are nevertheless localized across specific subsectors of the\nHilbert space: In this way the system is prevented from randomly exploring all\nthe Hilbert space and does not thermalize."
    },
    {
        "anchor": "Laser cooling of a magnetically guided ultra cold atom beam: We report on the transverse laser cooling of a magnetically guided beam of\nultra cold chromium atoms. Radial compression by a tapering of the guide is\nemployed to adiabatically heat the beam. Inside the tapered section heat is\nextracted from the atom beam by a two-dimensional optical molasses\nperpendicular to it, resulting in a significant increase of atomic phase space\ndensity. A magnetic offset field is applied to prevent optical pumping to\nuntrapped states. Our results demonstrate that by a suitable choice of the\nmagnetic offset field, the cooling beam intensity and detuning, atom losses and\nlongitudinal heating can be avoided. Final temperatures below 65 microkelvin\nhave been achieved, corresponding to an increase of phase space density in the\nguided beam by more than a factor of 30.",
        "positive": "Fulde-Ferrell-Larkin-Ovchinnikov pairing states between $s$- and\n  $p$-orbital fermions: We study pairing states in an largely imbalanced two-component Fermi gas\nloaded in an anisotropic two-dimensional optical lattice, where the spin up and\nspin down fermions filled to the $s$- and $p_x$-orbital bands, respectively. We\nshow that due to the relative inversion of band structures of the $s$ and $p_x$\norbitals, the system favors pairing between two fermions on the same side of\nthe Brillouin zone, leading to a large stable regime for states with finite\ncenter-of-mass momentum, i.e., the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)\nstate. In particular, when the two Fermi surfaces are close in momentum space,\na nesting effect stabilizes a special kind of $\\pi$-FFLO phase with spatial\nmodulation of $\\pi$ along the easily tunneled $x$-direction. We map out the\nzero temperature phase diagrams within mean-field approach for various aspect\nratio within the two-dimensional plane, and calculate the\nBerezinskii-Kosterlitz-Thouless (BKT) transition temperatures $T_{\\rm BKT}$ for\ndifferent phases."
    },
    {
        "anchor": "Superconductivity and charge order of confined Fermi systems: The low-temperature properties of the two-dimensional attractive Hubbard\nmodel are strongly influenced by the fermion density. Away from half-filling,\nthere is a finite-temperature transition to a phase with s-wave pairing order.\nHowever, the critical temperature is suppressed to zero at half-filling, where\nlong-range charge-density-wave order also appears, degenerate with\nsuperconductivity. This paper presents Determinant Quantum Monte Carlo\nsimulations of the attractive Hubbard model in the presence of a confining\npotential V which makes the fermion density \\rho{} inhomogeneous across the\nlattice. Pair correlations are shown to be large at low temperatures in regions\nof the trapped system with incommensurate filling, and to exhibit a minimum as\nthe local density \\rho(i) passes through one fermion per site. In this ring of\n\\rho=1, charge order is enhanced. A comparison is made between treating V\nwithin the local-density approximation (LDA) and in an ab initio manner. It is\nargued that certain sharp features of the LDA result at integer filling do not\nsurvive the proximity of doped sites. The critical temperature of confined\nsystems of fixed characteristic density is estimated.",
        "positive": "Mesoscopic disorder in double-well optical lattices: Double-well optical lattices are considered, each cite of which is formed by\na double-well potential. The lattice is assumed to be in an insulating state\nand order and disorder are defined with respect to the displacement of atoms\ninside the double-well potential. It is shown that in such lattices, in\naddition to purely ordered and disordered states, there can exist an\nintermediate mixed state, where, inside a generally ordered lattice, there\nappear disordered regions of mesoscopic size."
    },
    {
        "anchor": "Theoretical Prediction of Non-Hermitian Skin Effect in Ultracold Atom\n  Systems: Non-Hermitian skin effect, which refers to the phenomenon that an extensive\nnumber of eigenstates are localized at the boundary, has been widely studied in\nlattice models and experimentally observed in several classical systems. In\nthis work, we predict that the existence of the non-Hermitian skin effect in\nthe dissipative ultracold fermions with spin-orbit coupling, a continuous model\nthat has been implemented by the Hong-Kong group in a recent experiment. This\nskin effect is robust against the variation of external parameters and trapping\npotentials. We further reveal a dynamic sticky effect in our system, which has\na common physical origin with the non-Hermitian skin effect. Our work paves the\nway for studying novel physical responses of non-Hermitian skin effect in\nquantum systems.",
        "positive": "A connection between non-local one-body and local three-body\n  correlations of the Lieb-Liniger model: We derive a connection between the fourth coefficient of the short-distance\nTaylor expansion of the one-body correlation function, and the local three-body\ncorrelation function of the Lieb-Liniger model of $\\delta$-interacting spinless\nbosons in one dimension. This connection, valid at arbitrary interaction\nstrength, involves the fourth moment of the density of quasi-momenta.\nGeneralizing recent conjectures, we propose approximate analytical expressions\nfor the fourth coefficient covering the whole range of repulsive interactions,\nvalidated by comparison with accurate numerics. In particular, we find that the\nfourth coefficient changes sign at interaction strength $\\gamma_c\\simeq 3.816$,\nwhile the first three coefficients of the Taylor expansion of the one-body\ncorrelation function retain the same sign throughout the whole range of\ninteraction strengths."
    },
    {
        "anchor": "Evolution of Goldstone mode in binary condensate mixtures: We show that the third Goldstone mode in the two-species condensate mixtures,\nwhich emerges at phase-separation, gets hardened when the confining potentials\nhave separated trap centers. The {\\em sandwich} type condensate density\nprofiles, in this case, acquire a {\\em side-by-side} density profile\nconfiguration. We use Hartree-Fock-Bogoliubov theory with Popov approximation\nto examine the mode evolution and density profiles for these phase transitions\nat $T=0$.",
        "positive": "Synthetic dimensions in the strong-coupling limit: supersolids and\n  pair-superfluids: We study the many-body phases of bosonic atoms with $N$ internal states\nconfined to a 1D optical lattice under the influence of a synthetic magnetic\nfield and strong repulsive interactions. The $N$ internal states of the atoms\nare coupled via Raman transitions creating the synthetic magnetic field in the\nspace of internal spin states corresponding to recent experimental\nrealisations. We focus on the case of strong $\\mbox{SU}(N)$ invariant local\ndensity-density interactions in which each site of the 1D lattice is at most\nsingly occupied, and strong Raman coupling, in distinction to previous work\nwhich has focused on the weak Raman coupling case. This allows us to keep only\na single state per site and derive a low energy effective spin $1/2$ model. The\neffective model contains first-order nearest neighbour tunnelling terms, and\nsecond-order nearest neighbour interactions and correlated next-nearest\nneighbour tunnelling terms. By adjusting the flux $\\phi$ one can tune the\nrelative importance of first-order and second-order terms in the effective\nHamiltonian. In particular, first-order terms can be set to zero, realising a\nnovel model with dominant second-order terms. We show that the resulting\ncompetition between density-dependent tunnelling and repulsive density-density\ninteraction leads to an interesting phase diagram including a phase with\nlong-ranged pair-superfluid correlations. The method can be straightforwardly\nextended to higher dimensions and lattices of arbitrary geometry including\ngeometrically frustrated lattices where the interplay of frustration,\ninteractions and kinetic terms is expected to lead to even richer physics."
    },
    {
        "anchor": "Dynamic structure function of a cold Fermi gas at unitarity: We present a theoretical study of the dynamic structure function of a\nresonantly interacting two-component Fermi gas at zero temperature. Our\napproach is based on dynamic many-body theory able to describe excitations in\nstrongly correlated Fermi systems. The fixed-node diffusion Monte Carlo method\nis used to produce the ground-state correlation functions which are used as an\ninput for the excitation theory. Our approach reproduces recent Bragg\nscattering data in both the density and the spin channel. In the BCS regime,\nthe response is close to that of the ideal Fermi gas. On the BEC side, the Bose\npeak associated with the formation of dimers dominates the density channel of\nthe dynamic response. When the fraction of dimers is large our theory departs\nfrom the experimental data, mainly in the spin channel.",
        "positive": "Optical spin transport theory of spin-1/2 topological Fermi superfluids: We theoretically investigate optical (frequency-dependent) bulk spin\ntransport properties in a spin-1/2 topological Fermi superfluid. We\nspecifically consider a one-dimensional system with an interspin {\\it p}-wave\ninteraction, which can be realized in ultracold atom experiments. Developing\nthe BCS-Leggett theory to describe the Bardeen-Cooper-Schrieffer (BCS) to\nBose-Einstein condensate (BEC) evolution and the $\\mathbb{Z}_2$ topological\nphase transition in this system, we show how the spin transport reflects these\nmany-body aspects. We find that the optical spin conductivity, which is a small\nAC response of a spin current, shows the spin gapped spectrum in the wide\nparameter region and the gap closes at $\\mathbb{Z}_2$ topological phase\ntransition point. Moreover, the validity of the low-energy effective model of\nthe Majorana zero mode is discussed along the BCS-BEC evolution in connection\nwith the scale invariance at {\\it p}-wave unitarity."
    },
    {
        "anchor": "Polaron residue and spatial structure in a Fermi gas: We study the problem of a mobile impurity of mass $M$ interacting {\\sl via} a\ns-wave broad or narrow Feshbach resonance with a Fermi sea of particles of mass\n$m$. Truncating the Hilbert space to at most one pair of particle-hole\nexcitations of the Fermi sea, we determine ground state properties of the\npolaronic branch other than its energy, namely the polaron quasiparticle\nresidue $Z$, and the impurity-to-fermion pair correlation function $G(x)$. We\nshow that $G(x)$ deviates from unity at large distances as $-(A\\_4+B\\_4 \\cos 2\nk\\_F x)/(k\\_F x)^4$, where $k\\_F$ is the Fermi momentum; since $A\\_4>0$ and\n$B\\_4>0$, the polaron has a diverging rms radius and exhibits Friedel-like\noscillations. In the weakly attractive limit, we obtain analytical results,\nthat in particular detect the failure of the Hilbert space truncation for a\ndiverging mass impurity, as expected from Anderson orthogonality catastrophe;\nat distances between $\\sim 1/k\\_F$ and the asymptotic distance where the\n$1/x^4$ law applies, they reveal that $G(x)$ exhibits an intriguing multiscale\nstructure.",
        "positive": "Multi-Component Quantum Gases in Spin-Dependent Hexagonal Lattices: Periodicity is one of the most fundamental structural characteristics of\nsystems occurring in nature. The properties of these systems depend strongly on\nthe symmetry of the underlying periodic structure. In solid state materials -\nfor example - the static and transport properties as well as the magnetic and\nelectronic characteristics are crucially influenced by the crystal symmetry. In\nthis context, hexagonal structures play an extremely important role and lead to\nnovel physics like that of carbon nanotubes or graphene. Here we report on the\nfirst realization of ultracold atoms in a spin-dependent optical lattice with\nhexagonal symmetry. We show how combined effects of the lattice and\ninteractions between atoms lead to a forced antiferromagnetic N\\'eel order when\ntwo spin-components localize at different lattice sites. We also demonstrate\nthat the coexistence of two components - one Mott-insulating and the other one\nsuperfluid - leads to the formation of a forced supersolid. Our observations\nare consistent with theoretical predictions using Gutzwiller mean-field theory."
    },
    {
        "anchor": "Random spin textures in turbulent spinor Bose-Einstein condensates: We numerically investigate the stationary turbulent states of spin-1\nBose-Einstein condensates under continuous spin driving. We analyze the\nentanglement entropy and magnetization correlation function to demonstrate the\nisotropic nature of the intricate spin texture that is generated in the\nnonequilibrium steady state. We observe a $-7/3$ power-law behavior in the\nspin-dependent interaction energy spectrum. To gain further insight into the\nstatistical properties of the spin texture, we introduce a spin state ensemble\nobtained through position projection, revealing its close resemblance to the\nHaar random ensemble for spin-1 systems. We also present the probability\ndistribution of the spin vector magnitude in the turbulent condensate, which\ncan be tested in experiments. Our numerical study highlights the\ncharacteristics of stationary turbulence in the spinor BEC system and confirms\nprevious experimental findings by Hong et al. [Phys. Rev. A 108, 013318\n(2023)].",
        "positive": "Anomalous supersolidity in a weakly interacting dipolar Bose mixture on\n  a square lattice: We calculate the mean-field phase diagram of a zero-temperature, binary Bose\nmixture on a square optical lattice, where one species possesses a\nnon-negligible dipole moment. Remarkably, this system exhibits supersolidity\nfor anomalously weak dipolar interaction strengths, which are readily\naccessible with current experimental capabilities. The supersolid phases are\nrobust, in that they occupy large regions in the parameter space. Further, we\nidentify a first-order quantum phase transition between supersolid and\nsuperfluid phases. Our results demonstrate the rich features of the dipolar\nBose mixture, and suggest that this system is well-suited for exploring\nsupersolidity in the experimental setting."
    },
    {
        "anchor": "Stochastic-field approach to the quench dynamics of the one-dimensional\n  Bose polaron: We consider the dynamics of a quantum impurity after a sudden interaction\nquench into a one-dimensional degenerate Bose gas. We use the Keldysh path\nintegral formalism to derive a truncated Wigner like approach that takes the\nback action of the impurity onto the condensate into account already on the\nmean-field level and further incorporates thermal and quantum effects up to\none-loop accuracy. This framework enables us not only to calculate the real\nspace trajectory of the impurity but also the absorption spectrum. We find that\nquantum corrections and thermal effects play a crucial role for the impurity\nmomentum at weak to intermediate impurity-bath couplings.Furthermore, we see\nthe broadening of the absorption spectrum with increasing temperature.",
        "positive": "Localization by bichromatic potentials versus Anderson localization: The one-dimensional propagation of waves in a bichromatic potential may be\nmodeled by the Aubry-Andr\\'e Hamiltonian. The latter presents a\ndelocalization-localization transition, which has been observed in recent\nexperiments using ultracold atoms or light. It is shown here that, in contrast\nto Anderson localization, this transition has a classical origin, namely the\nlocalization mechanism is not due to a quantum suppression of a classically\nallowed transport process. Explicit comparisons with the Anderson model, as\nwell as with experiments, are done."
    },
    {
        "anchor": "Observation of self-oscillating supersonic flow across an acoustic\n  horizon in two dimensions: Understanding the dynamics and stability of transonic flows in quantum\nfluids, especially for those beyond one spatial dimension, is an outstanding\nchallenge, with applications ranging from nonlinear optics and condensed matter\nto analogue gravity. One intriguing possibility is that a system with a\nspatially bounded supersonic flow may evolve into a self-oscillating state that\nperiodically emits solitons, in a process originating from the well-known\nLandau instability. Here, we report observation of self-oscillating supersonic\nflows in a two-dimensional atomic superfluid. By imposing a local particle sink\nwith strong loss, we induce a convergent radial flow forming an acoustic\nanalogue of a black-hole horizon and an inner horizon around the sink. The\nobserved superflow appears to be modulated by quasi-periodic bursts of\nsuperluminal signals. We measure their frequencies and find agreement with\nnumerical simulations of soliton oscillation frequencies within the black-hole\nhorizon. The presented experiment demonstrates a new method for creating\nsupersonic flows in atomic superfluids, which may find applications in quantum\nsimulations of curved spacetime, supersonic turbulence, and self-oscillating\ndynamics in dissipative many-body systems.",
        "positive": "Simulating Cosmological Evolution by Quantum Quench of an Atomic BEC: In cosmological evolution, it is the homogeneous scalar field (inflaton) that\ndrives the universe to expand isotropically and to generate standard model\nparticles. However, to simulate cosmology, atomic gas research has focused on\nthe dynamics of Bose-Einstein condensates (BEC) with continuously applied\nforces. In this paper we argue a complementary approach needs also to be\npursued; we, thus, consider the analogue BEC experiments in a non-driven,\nclosed atomic system. We implement this using a BEC in an optical lattice\nwhich, after a quench, freely transitions from an unstable to a stable state.\nThis dynamical evolution displays the counterpart \"preheating\", \"reheating\" and\n\"thermalization\" phases of cosmology. Importantly, our studies of these\nanalogue processes yield tractable analytic models. Of great utility to the\ncold atom community, such understanding elucidates the dynamics of\nnon-adiabatic condensate preparation."
    },
    {
        "anchor": "Superfluid vortex dynamics on a spherical film: Motivated by ongoing experimental efforts to make closed Bose-Einstein\ncondensate (BEC) shells in microgravity environments, this work studies the\nenergy and dynamics of singly quantized vortices on a thin spherical superfluid\nshell, where the overall vortex charge must vanish (as on any compact surface).\nFor each vortex, stereographic projection yields the corresponding complex\npotential on the tangent plane. The resulting stream function then provides\nboth the total energy and the dynamics of a system of overall neutral vortices\non a spherical film. Although a single vortex dipole follows a simple dynamical\norbit, four vortices can present a variety of situations. We study a few\nsymmetric initial configurations and then focus on the special case of two\nsmall vortex dipoles.",
        "positive": "Exciton-Polariton Condensates: A Fourier Neural Operator Approach: Advancements in semiconductor fabrication over the past decade have catalyzed\nextensive research into all-optical devices driven by exciton-polariton\ncondensates. Preliminary validations of such devices, including transistors,\nhave shown encouraging results even under ambient conditions. A significant\nchallenge still remains for large scale application however: the lack of a\nrobust solver that can be used to simulate complex nonlinear systems which\nrequire an extended period of time to stabilize. Addressing this need, we\npropose the application of a machine-learning-based Fourier Neural Operator\napproach to find the solution to the Gross-Pitaevskii equations coupled with\nextra exciton rate equations. This work marks the first direct application of\nNeural Operators to an exciton-polariton condensate system. Our findings show\nthat the proposed method can predict final-state solutions to a high degree of\naccuracy almost 1000 times faster than CUDA-based GPU solvers. Moreover, this\npaves the way for potential all-optical chip design workflows by integrating\nexperimental data."
    },
    {
        "anchor": "Artificial gauge fields with ultracold atoms: Gauge fields are ubiquitous in nature. In the context of quantum\nelectrodynamics, you may be most familiar with the photon, which represents the\ngauge field mediating electromagnetic forces. But there are also gluons, which\nmediate strong forces, and the W and Z particles, which mediate the weak\nforces. According to the standard model, those few gauge bosons, in fact,\nmediate all elementary interactions.",
        "positive": "Quantized conductance through the quantum evaporation of bosonic atoms: We analyze theoretically the quantization of conductance occurring with cold\nbosonic atoms trapped in two reservoirs connected by a constriction with an\nattractive gate potential. We focus on temperatures slightly above the\ncondensation threshold in the reservoirs. We show that a conductance step\noccurs, coinciding with the appearance of a condensate in the constriction.\nConductance relies on a collective process involving the quantum condensation\nof an atom into an elementary excitation and the subsequent quantum evaporation\nof an atom, in contrast with ballistic fermion transport. The value of the\nbosonic conductance plateau is strongly enhanced compared to fermions and\nexplicitly depends on temperature. We highlight the role of weak repulsive\ninteractions between the bosons in preventing them from collapsing into the\nconstriction."
    },
    {
        "anchor": "Tunable nanomagnetism in moderately cold fermions on optical lattices: Localized defects, unavoidable in real solids, may be simulated in\n(generically defect-free) cold-atom systems, e.g., via modifications of the\noptical lattice. We study the Hubbard model on a square lattice with single\nimpurities, pairs of nearby impurities, or lines of impurities using\nnumerically exact determinantal quantum Monte Carlo simulations. In all cases,\ncorrelations on the \"impurity\" sites are enhanced either by larger on-site\ninteractions or by a reduced coupling to the environment.\n  We find highly nontrivial magnetic correlations, which persist at elevated\ntemperatures and should be accessible in cold-atom systems with current\nexperimental techniques. With improved cooling techniques, these features could\nbe followed towards generic quantum antiferromagnetism in the homogeneous\nlimit. More generally, tunable crossing points between different correlation\nfunctions could be used, in a quantum steelyard balance setup, as robust\nthermometers.",
        "positive": "Floquet analysis of a quantum system with modulated periodic driving: We consider a quantum system periodically driven with a strength which varies\nslowly on the scale of the driving period. The analysis is based on a general\nformulation of the Floquet theory relying on the extended Hilbert space. It is\nshown that the dynamics of the system can be described in terms of a slowly\nvarying effective Floquet Hamiltonian that captures the long-term evolution, as\nwell as rapidly oscillating micromotion operators. We obtain a systematic\nhigh-frequency expansion of all these operators. Generalizing the previous\nstudies, the expanded effective Hamiltonian is now time-dependent and contains\nextra terms appearing due to changes in the periodic driving. The same applies\nto the micromotion operators which exhibit a slow temporal dependence in\naddition to the rapid oscillations. As an illustration, we consider a\nquantum-mechanical spin in an oscillating magnetic field with a slowly changing\ndirection. The effective evolution of the spin is then associated with\nnon-Abelian geometric phases reflecting the geometry of the extended Floquet\nspace. The developed formalism is general and also applies to other\nperiodically driven systems, such as shaken optical lattices with a\ntime-dependent shaking strength, a situation relevant to the cold atom\nexperiments."
    },
    {
        "anchor": "Reliability of the Ginzburg-Landau Theory in the BCS-BEC Crossover by\n  Including Gaussian Fluctuations for 3D Attractive Fermions: We calculate the parameters of the Ginzburg-Landau (GL) equation of a\nthree-dimensional attractive Fermi gas around the superfluid critical\ntemperature. We compare different levels of approximation throughout the\nBardeen-Cooper-Schrieffer (BCS) to the Bose-Einstein Condensate (BEC) regime.\nWe show that the inclusion of Gaussian fluctuations strongly modifies the\nvalues of the Ginzburg-Landau parameters approaching the BEC regime of the\ncrossover. We investigate the reliability of the Ginzburg-Landau theory, with\nfluctuations, studying the behavior of the coherence length and of the critical\nrotational frequencies throughout the BCS-BEC crossover. The effect of the\nGaussian fluctuations gives qualitative correct trends of the considered\nphysical quantities from the BCS regime up to the unitary limit of the BCS-BEC\ncrossover. Approaching the BEC regime, the Ginzburg-Landau equation with the\ninclusion of Gaussian fluctuations turns out to be unreliable.",
        "positive": "Interacting non-Hermitian ultracold atoms in a harmonic trap: Two-body\n  exact solution and high-order exceptional point: We study interacting ultracold atoms in a three-dimensional (3D) harmonic\ntrap with spin-selective dissipations, which can be effectively described by\nnon-Hermitian parity-time ($\\mathcal{PT}$) symmetric Hamiltonians. By solving\nthe non-Hermitian two-body problem of spin-1/2 (spin-1) bosons in a 3D harmonic\ntrap exactly, we find that the system can exhibit third-order (fifth-order)\nexceptional point (EP) with ultra-sensitive cube-root (fifth-root) spectral\nresponse due to interaction anisotropies in spin channels. We also present the\ngeneral principle for the creation of high-order EPs and their spectral\nsensitivities with arbitrary particle number $N$ and arbitrary spin $s$.\nGenerally, with spin-independent interactions, the EP order of bosons can be as\nhigh as $2Ns+1$, and the spectral response around EP can be as sensitive as\n$\\sim \\epsilon^{1/(2ks+1)}$ under a $k$-body interaction anisotropy. Moreover,\nwe propose to detect the ultra-sensitive spectral response through the\nprobability dynamics of certain state. These results suggest a convenient route\ntowards more powerful sensor devices in spinor cold atomic systems."
    },
    {
        "anchor": "Measurable signatures of bosonic fractional Chern insulator states and\n  their fractional excitations in a quantum-gas microscope: The recent progress in engineering topological band structures in\noptical-lattice systems makes it promising to study fractional Chern insulator\nstates in these systems. Here we consider a realistic finite system of a few\nrepulsively interacting bosons on a square lattice with magnetic flux and sharp\nedges, as it can be realized in quantum-gas microscopes. We investigate under\nwhich conditions a fractional Chern insulator state corresponding to the\nLaughlin-like state at filling $\\nu=1/2$ can be stabilized and its fractional\nexcitations probed. Using numerical simulations, we find an incompressible bulk\ndensity at the expected filling for systems, whose linear extent is as small as\n6-8 sites. This is a promising result, since such small systems are favorable\nwith respect to the required adiabatic state preparation. Moreover, we also see\nvery clear signatures of excitations with fractional charge in response both to\nstatic pinning potentials and dynamical flux insertion. Since the compressible\nedges, which are found to feature chiral currents, can serve as a reservoir,\nthese observations are robust against changes in the total particle number. Our\nresults suggest that signatures of both a fractional Chern insulator state and\nits fractional excitations can be found under realistic experimental\nconditions.",
        "positive": "Nonlinear dressed states at the miscibility-immiscibility threshold: The dynamical evolution of spatial patterns in a complex system can reveal\nthe underlying structure and stability of stationary states. As a model system\nwe employ a two-component rubidium Bose-Einstein condensate at the transition\nfrom miscible to immiscible with the additional control of linear\ninterconversion. Excellent agreement is found between the detailed experimental\ntime evolution and the corresponding numerical mean-field computations.\nAnalyzing the dynamics of the system, we find clear indications of stationary\nstates that we term nonlinear dressed states. A steady state bifurcation\nanalysis reveals a smooth connection of these states with dark-bright soliton\nsolutions of the integrable two-component Manakov model."
    },
    {
        "anchor": "Extracting the field theory description of a quantum many-body system\n  from experimental data: Quantum field theory is a powerful tool to describe the relevant physics\ngoverning complex quantum many-body systems. Here we develop a general pathway\nto extract the irreducible building blocks of quantum field theoretical\ndescriptions and its parameters purely from experimental data. This is\naccomplished by extracting the one-particle irreducible (1PI) vertices from\nwhich one can construct all observables. To match the capabilities of\nexperimental techniques used in quantum simulation experiments, our approach\nemploys a formulation of quantum field theory based on equal-time correlation\nfunctions only. We illustrate our procedure by applying it to the quantum\nsine-Gordon model in thermal equilibrium. The theoretical foundations are\nillustrated by estimating the irreducible vertices at equal times both\nanalytically and using numerical simulations. We then demonstrate explicitly\nhow to extract these quantities from an experiment where we quantum simulate\nthe sine-Gordon model by two tunnel-coupled superfluids. We extract the full\ntwo-point function and the interaction vertex (four-point function) and their\nvariation with momentum, encoding the `running' of the couplings. The measured\n1PI vertices are compared to the theoretical estimates, verifying our\nprocedure. Our work opens new ways of addressing fundamental questions in\nquantum field theory, which are relevant in high-energy and condensed matter\nphysics, and in taking quantum phenomena from fundamental science to practical\ntechnology.",
        "positive": "Counting rule of Nambu-Goldstone modes for internal and spacetime\n  symmetries: Bogoliubov theory approach: When continuous symmetry is spontaneously broken, there appear\nNambu-Goldstone modes (NGMs) with linear and quadratic dispersion relations,\nwhich are called type-I and type-II, respectively. We propose a framework to\ncount these modes including the coefficients of the dispersion relations with\napplying the standard Gross-Pitaevskii-Bogoliubov theory. Our method is mainly\nbased on (i) zero-mode solutions of the Bogoliubov equation originated from\nspontaneous symmetry breaking and (ii) their generalized orthogonal relations,\nwhich naturally arises from well-known Bogoliubov transformations and is\nreferred to as \"$\\sigma$-orthogonality\" in this paper. Unlike previous works,\nour framework is applicable without any modification to the cases where there\nare additional zero modes, which do not have a symmetry origin, such as\nquasi-NGMs, and/or where spacetime symmetry is spontaneously broken in the\npresence of a topological soliton or a vortex. As a by-product of the\nformulation, we also give a compact summary for mathematics of bosonic\nBogoliubov equations and Bogoliubov transformations, which becomes a foundation\nfor any problem of Bogoliubov quasiparticles. The general results are\nillustrated by various examples in spinor Bose-Einstein condensates (BECs). In\nparticular, the result on the spin-3 BECs includes new findings such as a\ntype-I-type-II transition and an increase of the type-II dispersion coefficient\ncaused by a linearly-independent pair of zero modes."
    },
    {
        "anchor": "High signal to noise absorption imaging of alkali atoms at moderate\n  magnetic fields: We present an improved scheme for absorption imaging of alkali atoms at\nmoderate magnetic fields, where the excited state is well in the Paschen-Back\nregime but the ground state hyperfine manifold is not. It utilizes four atomic\nlevels to obtain an approximately closed optical cycle. With the resulting\nabsorption of the corresponding two laser frequencies we extract the atomic\ncolumn density of a $^{39}$K Bose-Einstein condensate. The scheme can be\nreadily applied to all other alkali-like species.",
        "positive": "Dynamics of Two-Component Bose-Einstein Condensates Coupled with\n  Environment: We investigate the dynamics of an open Bose-Einstein condensate system\nconsisting of two hyperfine states of the same atomic species which are coupled\nby tunable Raman laser. It is already suggested that the detuning between the\nlaser frequency and transition frequency affect significantly on the dynamics\nof the pure condensate. Here we show that the detuning effect is suppressed by\nnoise and dissipation caused by the environment. The increase of coherence and\npurity are also displayed for specific parameters. As a verification to the\nlowest-order approximation we derive the hierarchy of motion equations in the\nsecond-order approximation. It turns out that the former one can describe the\ndynamical evolution qualitatively for weak noise and dissipation and\nquantitatively for strong noise and dissipation."
    },
    {
        "anchor": "Dynamical formation of quantum droplets in a $^{39}$K mixture: We report on the dynamical formation of self-bound quantum droplets in\nattractive mixtures of $^{39}$K atoms. Considering the experimental\nobservations of Semeghini et al., Phys. Rev. Lett. 120, 235301 (2018), we\nperform numerical simulations to understand the relevant processes involved in\nthe formation of a metastable droplet from an out-of-equilibrium mixture. We\nfirst analyze the so-called self-evaporation mechanism, where the droplet\ndissipates energy by releasing atoms, and then we consider the effects of\nlosses due to three-body recombinations and to the balancing of populations in\nthe mixture. We discuss the importance of these three mechanisms in the\nobserved droplet dynamics and their implications for future experiments.",
        "positive": "Cosine Edge Mode in a Periodically Driven Quantum System: Time-periodic (Floquet) topological phases of matter exhibit bulk-edge\nrelationships that are more complex than static topological insulators and\nsuperconductors. Finding the edge modes unique to driven systems usually\nrequires numerics. Here we present a minimal two-band model of Floquet\ntopological insulators and semimetals in two dimensions where all the bulk and\nedge properties can be obtained analytically. It is based on the extended\nHarper model of quantum Hall effect at flux one half. We show that periodical\ndriving gives rise to a series of phases characterized by a pair of integers.\nThe model has a most striking feature: the spectrum of the edge modes is always\ngiven by a single cosine function, $\\omega(k_y)\\propto \\cos k_y$ where $k_y$ is\nthe wave number along the edge, as if it is freely dispersing and completely\ndecoupled from the bulk. The cosine mode is robust against the change in\ndriving parameters and persists even to semi-metallic phases with Dirac points.\nThe localization length of the cosine mode is found to contain an integer and\nin this sense quantized."
    },
    {
        "anchor": "Lasing, quantum geometry and coherence in non-Hermitian flat bands: We show that lasing in flat band lattices can be stabilized by means of the\ngeometrical properties of the Bloch states, in settings where the\nsingle-particle dispersion is flat in both its real and imaginary parts. We\nillustrate a general projection method and compute the collective excitations,\nwhich are shown to display a diffusive behavior ruled by quantum geometry\nthrough a peculiar coefficient involving gain, losses and interactions. Then,\nwe analytically show that the phase dynamics display a surprising cancellation\nof the Kardar-Parisi-Zhang nonlinearity at the leading order. Because of the\nrelevance of Kardar-Parisi-Zhang universality in one-dimensional geometries, we\nfocus our study on the diamond chain and provide confirmation of these results\nthrough full numerical simulations.",
        "positive": "$p$-wave chiral superfluidity from an $s$-wave interacting atomic Fermi\n  gas: Chiral $p$-wave superfluids are fascinating topological quantum states of\nmatter that have been found in the liquid $^3$He-A phase and arguably in the\nelectronic Sr$_2$RuO$_4$ superconductor. They are shown fundamentally related\nto the fractional $5/2$ quantum Hall state which supports fractional exotic\nexcitations. A common understanding is that such states require spin-triplet\npairing of fermions due to $p$-wave interaction. Here we report by controlled\ntheoretical approximation that a center-of-mass Wannier $p$-wave chiral\nsuperfluid state can arise from spin-singlet pairing for an $s$-wave\ninteracting atomic Fermi gas in an optical lattice. Despite a conceptually\ndifferent origin, it shows topological properties similar to the conventional\nchiral $p$-wave state. These include a non-zero Chern number and the appearance\nof chiral fermionic zero modes bounded to domain walls. Several signature\nquantities are calculated for the cold atom experimental condition."
    },
    {
        "anchor": "Vortex reconnections and rebounds in trapped atomic Bose--Einstein\n  condensates: Reconnections and interactions of filamentary coherent structures play a\nfundamental role in the dynamics of fluids, plasmas and nematic liquid\ncrystals. In fluids, vortex reconnections redistribute energy and helicity\namong the length scales and induce fine-scale turbulent mixing. Unlike ordinary\nfluids where vorticity is a continuous field, in quantum fluids vorticity is\nconcentrated into discrete (quantized) vortex lines turning vortex\nreconnections into isolated events, making it conceptually easier to study.\nHere we report experimental and numerical observations of three-dimensional\nquantum vortex interactions in a cigar-shaped atomic Bose-Einstein Condensate\n(BEC). In addition to standard reconnections, already numerically and\nexperimentally observed in homogeneous systems away from boundaries, we show\nthat double reconnections, rebounds and ejections can also occur as a\nconsequence of the non-homogeneous, confined nature of the system.",
        "positive": "Dual-species Bose-Einstein condensates of $^{7}$Li and $^{133}$Cs: We report the creation of dual-species Bose-Einstein condensates (BECs) of\n$^{7}$Li and $^{133}$Cs. These BECs are formed in a bichromatic optical dipole\ntrap created with 1550-nm and 780-nm laser beams. During the production\nprocess, an external magnetic field of 886~G is applied to adjust the\nscattering lengths to $a_{\\rm{Cs}} = 123a_0$, $a_{\\rm{Li}} = 484a_0$, and\n$a_{\\rm{LiCs}} = 248a_0$. These scattering lengths allow for efficient\nevaporation and sympathetic cooling. The dual-species BECs are typically\nproduced with $1.5\\times 10^4$ Cs atoms and $6.0\\times 10^3$ Li atoms. This\nquantum degenerate mixture of Li and Cs provides an ideal platform for\nexploring phenomena such as polarons and Efimov trimers, as well as for\ncreating ground-state LiCs molecules."
    },
    {
        "anchor": "Multipolar Fermi-surface deformation in a Rydberg-dressed Fermi gas with\n  long-range anisotropic interactions: We study theoretically the deformation of the Fermi surface (FS) of a\nthree-dimensional gas of Rydberg-dressed $^6$Li atoms. The laser dressing to\nhigh-lying Rydberg $D$ states results in angle-dependent soft-core-shaped\ninteractions whose anisotropy is described by multiple spherical harmonics. We\nshow that this can drastically modify the shape of the FS and that its\ndeformation depends on the interplay between the Fermi momentum $k_F$ and the\nreciprocal momentum $\\bar{k}$ corresponding to the characteristic soft-core\nradius of the dressing-induced potential. When $k_F< \\bar{k}$, the dressed\ninteraction stretches a spherical FS into an ellipsoid. When $k_F\\gtrsim\n\\bar{k}$, complex deformations are encountered which exhibit multipolar\ncharacteristics. We analyze the formation of Cooper pairs around the deformed\nFS and show that they occupy large orbital angular momentum states ($p$, $f$,\nand $h$ wave) coherently. Our study demonstrates that Rydberg dressing to high\nangular momentum states may pave a route toward the investigation of\nunconventional Fermi gases and multiwave superconductivity.",
        "positive": "Probing the roton excitation spectrum of a stable dipolar Bose gas: We measure the excitation spectrum of a stable dipolar Bose--Einstein\ncondensate over a wide momentum-range via Bragg spectroscopy. We precisely\ncontrol the relative strength, $\\epsilon_{\\rm dd}$, of the dipolar to the\ncontact interactions and observe that the spectrum increasingly deviates from\nthe linear phononic behavior for increasing $\\epsilon_{\\rm dd}$. Reaching the\ndipolar dominated regime $\\epsilon_{\\rm dd}>1$, we observe the emergence of a\nroton minimum in the spectrum and its softening towards instability. We\ncharacterize how the excitation energy and the strength of the density-density\ncorrelations at the roton momentum vary with $\\epsilon_{\\rm dd}$. Our findings\nare in excellent agreement with numerical calculations based on mean-field\nBogoliubov theory. When including beyond-mean-field corrections, in the form of\na Lee-Huang-Yang potential, we observe a quantitative deviation from the\nexperiment, questioning the validity of such a description in the roton regime."
    },
    {
        "anchor": "Dynamics of cold bosons in optical lattices: Effects of higher Bloch\n  bands: The extended effective multiorbital Bose-Hubbard-type Hamiltonian which takes\ninto account higher Bloch bands, is discussed for boson systems in optical\nlattices, with emphasis on dynamical properties, in relation with current\nexperiments. It is shown that the renormalization of Hamiltonian parameters\ndepends on the dimension of the problem studied. Therefore, mean field phase\ndiagrams do not scale with the coordination number of the lattice. The effect\nof Hamiltonian parameters renormalization on the dynamics in reduced\none-dimensional optical lattice potential is analyzed. We study both the\nquasi-adiabatic quench through the superfluid-Mott insulator transition and the\nabsorption spectroscopy, that is energy absorption rate when the lattice depth\nis periodically modulated.",
        "positive": "Quasiparticle nature of the Bose polaron at finite temperature: The Bose polaron has attracted theoretical and experimental interest because\nthe mobile impurity is surrounded by a bath that undergoes a\nsuperfluid-to-normal phase transition. Although many theoretical works have\nstudied this system in its ground state, only few analyze its behavior at\nfinite temperature. We have studied the effect of temperature on a Bose polaron\nsystem performing ab-initio Path Integral Monte Carlo simulations. This method\nis able to approach the critical temperature without losing accuracy, in\ncontrast with perturbative approximations. We have calculated the polaron\nenergy for the repulsive and attractive branches and we have observed an\nasymmetric behavior between the two branches. When the potential is repulsive,\nthe polaron energy decreases when the temperature increases, and contrariwise\nfor the attractive branch. Our results for the effective mass and the dynamical\nstructure factor of the polaron show unambiguously that its quasiparticle\nnature disappears close to the critical temperature, in agreement with recent\nexperimental findings. Finally, we have also estimated the fraction of bosons\nin the condensate as well as the superfluid fraction, and we have concluded\nthat the impurity hinders the condensation of the rest of bosons."
    },
    {
        "anchor": "Two Cold Atoms in a Time-Dependent Harmonic Trap in One Dimension: We analyze the dynamics of two atoms with a short-ranged pair interaction in\na one-dimensional harmonic trap with time-dependent frequency. Our analysis is\nfocused on two representative cases: (i) a sudden change of the trapping\nfrequency from one value to another, and (ii) a periodic trapping frequency. In\ncase (i), the dynamics of the interacting and the corresponding non-interacting\nsystems turn out to be similar. In the second case, however, the interacting\nsystem can behave quite differently, especially close to parametric resonance.\nFor instance, in the regions where such resonance occurs we find that the\ninteraction can significantly reduce the rate of energy increase. The\nimplications for applications of our findings to cool or heat the system are\nalso dicussed.",
        "positive": "The Gross-Pitaevskii Equation and Bose-Einstein condensates: The Gross-Pitaevskii equation is discussed at the level of an advanced course\non statistical physics. In the standard literature the Gross-Pitaevskii\nequation is usually obtained in the framework of the second quantisation\nformalism, which in many cases goes beyond the material covered in many\nadvanced undergraduate courses. In this paper, we motivate the derivation of\nthe Gross-Pitaevskii equation (GPE) in relationship to concepts from\nstatistical physics, highlighting a number of applications from dynamics of a\nBose-Einstein condensate to the excitations of the gas cloud. This paper may be\nhelpful not only in encouraging the discussion of modern developments in a\nstatistical mechanics course, but also can be of use in other contexts such as\nmathematical physics and modelling. The paper is suitable for undergraduate and\ngraduate students, as well as general physicists."
    },
    {
        "anchor": "Large phonon time-of-flight fluctuations in expanding flat condensates\n  of cold fermi gases: We reexamine how quantum density fluctuations in condensates of ultra-cold\nfermi gases lead to fluctuations in phonon times-of-flight, an effect that\nincreases as density is reduced. We suggest that these effects should be\nmeasurable in pancake-like (two-dimensional) condensates on their release from\ntheir confining optical traps, providing their initial (width/thickness) aspect\nratio is suitably large.",
        "positive": "Long range interaction induced density modulated state in a\n  Bose-Einstein condensate: We consider a Gross-Pitaevskii model of BEC with non-local s-wave scattering\nto study the density modulated state in 1D. We resort to a perturbative Taylor\nseries expansion for the order parameter. By perturbative calculations, we show\nthat under long range s-wave scattering a density modulated state is\nenergetically favourable as compared to the uniform density state. We obtain\ndensity modulated state as a solution to the perturbative non-local GP\nequation, rather than the conventional approach of introducing amplitude\nmodulations on top of the uniform density state and lowering the roton minimum."
    },
    {
        "anchor": "Vortex arrays in neutral trapped Fermi gases throughout the BCS-BEC\n  crossover: Vortex arrays in type-II superconductors admit the translational symmetry of\nan infinite system. There are cases, however, like ultra-cold trapped Fermi\ngases and the crust of neutron stars, where finite-size effects make it quite\nmore complex to account for the geometrical arrangement of vortices. Here, we\nself-consistently generate these arrays of vortices at zero and finite\ntemperature through a microscopic description of the non-homogeneous superfluid\nbased on a differential equation for the local order parameter, obtained by\ncoarse graining the Bogoliubov-de Gennes (BdG) equations. In this way, the\nstrength of the inter-particle interaction is varied along the BCS-BEC\ncrossover, from largely overlapping Cooper pairs in the BCS limit to dilute\ncomposite bosons in the BEC limit. Detailed comparison with two landmark\nexperiments on ultra-cold Fermi gases, aimed at revealing the presence of the\nsuperfluid phase, brings out several features that makes them relevant for\nother systems in nature as well.",
        "positive": "Higgs amplitude mode in the vicinity of a $(2+1)$-dimensional quantum\n  critical point: a nonperturbative renormalization-group approach: We study the \"Higgs\" amplitude mode in the relativistic quantum O($N$) model\nin two space dimensions. Using the nonperturbative renormalization group and\nthe Blaizot--M\\'endez-Galain--Wschebor approximation (which we generalize to\ncompute 4-point correlation functions), we compute the O($N$) invariant scalar\nsusceptibility at zero temperature in the vicinity of the quantum critical\npoint. In the ordered phase, we find a well-defined Higgs resonance for $N=2$\nand $N=3$ and determine its universal properties. No resonance is found for\n$N\\geq 4$. In the disordered phase, the spectral function exhibits a threshold\nbehavior with no Higgs-like peak. We also show that for $N=2$ the Higgs mode\nmanifests itself as a very broad peak in the longitudinal susceptibility in\nspite of the infrared divergence of the latter. We compare our findings with\nresults from quantum Monte Carlo simulations and $\\epsilon=4-(d+1)$ expansion\nnear $d=3$."
    },
    {
        "anchor": "Anomalous breaking of scale invariance in a two-dimensional Fermi gas: The frequency of the breathing mode of a classical two dimensional Fermi gas\nin a harmonic confinement is fixed by the scale invariance of the Hamiltonian.\nScale invariance is broken on the quantum mechanical level by introducing the\ntwo dimensional scattering length as a regulator. This is an example of a\nquantum anomaly in the field of ultracold atoms and leads to a shift of the\nfrequency of the collective breathing mode of the cloud. In this work, we study\nthis anomalous frequency shift for a two component Fermi gas in the strongly\ninteracting regime. We measure significant shifts away from the scale invariant\nresult that depend strongly on both interactions and temperature. We find\nqualitative agreement with theoretical calculations at zero temperature.",
        "positive": "Manipulating atom-number distributions and detecting spatial\n  distributions in lattice-confined spinor gases: We present an experimental study demonstrating the manipulation of\natom-number distributions of spinor gases after nonequilibrium quantum quenches\nacross superfluid to Mott-insulator phase transitions in cubic optical\nlattices. Our data indicate that atom distributions in individual Mott lobes\ncan be tuned by properly designing quantum quench sequences, which suggests\nmethods of maximizing the fraction of atoms in Mott lobes of even occupation\nnumbers and has applications in attaining different quantum magnetic phases\nincluding massively entangled states. Spatial distributions of gases in\nthree-dimensional lattices are derived from the observed number distributions,\nwhich reveal complex spatial dynamics during the quantum quenches. Qualitative\nagreements are also found between our experimental data and numerical\nsimulations based on time-dependent Gutzwiller approximations in\ntwo-dimensional systems."
    },
    {
        "anchor": "Pair interactions of heavy vortices in quantum fluids: The dynamics of quantum vortex pairs carrying heavy doping matter trapped\ninside their cores is studied. The nonlinear classical matter field formalism\nis used to build a universal mathematical model of a heavy vortex applicable to\ndifferent types of quantum mixtures. It is shown how the usual vortex dynamics\ntypical for undoped pairs qualitatively changes when heavy dopants are used:\nheavy vortices with opposite topological charges (chiralities) attract each\nother, while vortices with the same charge are repelled. The force responsible\nfor such behavior appears as a result of superposition of vortices velocity\nfields in the presence of doping substance and can be considered as a special\nrealization of the Magnus effect. The force is evaluated quantitatively and its\ninverse proportionality to the distance is demonstrated. The mechanism\ndescribed in this paper gives an example of how a light nonlinear classical\nfield may realize repulsive and attractive interactions between embedded heavy\nimpurities.",
        "positive": "Lattice approaches to dilute Fermi gases: Legacy of broken Galilean\n  invariance: In the dilute limit, the properties of fermionic lattice models with\nshort-range attractive interactions converge to those of a dilute Fermi gas in\ncontinuum space. We investigate this connection using mean-field and we show\nthat the existence of a finite lattice spacing has consequences down to very\nsmall densities. In particular we show that the reduced translational\ninvariance associated to the lattice periodicity has a pivotal role in the\nfinite-density corrections to the universal zero-density limit.\n  For a parabolic dispersion with a sharp cut-off, we provide an analytical\nexpression for the leading-order corrections in the whole BCS-BEC crossover.\nThese corrections, which stem only from the unavoidable cut-off, contribute to\nthe leading-order corrections to the relevant observables. In a generic lattice\nwe find a universal power-law behavior $n^{1/3}$ which leads to significant\ncorrections already for small densities. Our results pose strong constraints on\nlattice extrapolations of dilute Fermi gas properties."
    },
    {
        "anchor": "Microscopic derivation of the extended Gross-Pitaevskii equation for\n  quantum droplets in binary Bose mixtures: An ultradilute quantum droplet is a self-bound liquid-like state recently\nobserved in ultracold Bose-Einstein condensates. In all previous theoretical\nstudies, it is described by a phenomenological low-energy effective theory,\ntermed as the extended Gross\\textendash Pitaevskii equation. Here, we\nmicroscopically derive the Gross\\textendash Pitaevskii equation for the\ncondensate and also for a pairing field in an inhomogeneous quantum droplet\nrealized by Bose-Bose mixtures with attractive inter-species interaction. We\nshow that the inclusion of the pairing field is essential, in order to have a\nconsistent description of the droplet state. We clarify that, the extended\nGross\\textendash Pitaevskii equation used earlier should be understood as the\nequation of motion for the pairing field, rather than the condensate. The\nfluctuations of the pairing field give rise to low-energy collective\nexcitations of the droplet. We also present the Bogoliubov equations for\ngapless phonon modes and gapped modes due to pairing in real space, which\ncharacterizes single-particle-like excitations of the droplet. The equations of\nmotion derived in this work for the condensate and the pairing field serve an\nideal starting point to understand the structure and collective excitations of\nnon-uniform ultradilute quantum droplets in on-going cold-atom experiments.",
        "positive": "Adiabatic formation of bound states in the 1d Bose gas: We consider the 1d interacting Bose gas in the presence of time-dependent and\nspatially inhomogeneous contact interactions. Within its attractive phase, the\ngas allows for bound states of an arbitrary number of particles, which are\neventually populated if the system is dynamically driven from the repulsive to\nthe attractive regime. Building on the framework of Generalized Hydrodynamics,\nwe analytically determine the formation of bound states in the limit of\nadiabatic changes in the interactions. Our results are valid for arbitrary\ninitial thermal states and, more generally, Generalized Gibbs Ensembles."
    },
    {
        "anchor": "Density correlations and dynamical Casimir emission of Bogoliubov\n  phonons in modulated atomic Bose-Einstein condensates: We present a theory of the density correlations that appear in an atomic\nBose-Einstein condensate as a consequence of the dynamical Casimir emission of\npairs of Bogoliubov phonons when the atom-atom scattering length is modulated\nin time. Different regimes as a function of the temporal shape of the\nmodulation are identified and a simple physical picture of the phenomenon is\ndiscussed. Analytical expressions for the density correlation function are\nprovided for the most significant limiting cases. This theory is able to\nexplain some unexpected features recently observed in numerical calculations of\nHawking radiation from analog black holes.",
        "positive": "Pi-phases in balanced fermionic superfluids on spin-dependent optical\n  lattices: We study a balanced two-component system of ultracold fermions in one\ndimension with attractive interactions and subject to a spin-dependent optical\nlattice potential of opposite sign for the two components. We find states with\ndifferent types of modulated pairing order parameters which are conceptually\nsimilar to pi-phases discussed for superconductor-ferromagnet heterostructures.\nIncreasing the lattice depth induces sharp transitions between states of\ndifferent parity. While the origin of the order parameter oscillations is\nsimilar to the FFLO phase for paired states with spin imbalance, the current\nsystem is intrinsically stable to phase separation. We discuss experimental\nrequirements for creating and probing these novel phases."
    },
    {
        "anchor": "One-dimensional many-body entangled open quantum systems with tensor\n  network methods: We present a collection of methods to simulate entangled dynamics of open\nquantum systems governed by the Lindblad equation with tensor network methods.\nTensor network methods using matrix product states have been proven very useful\nto simulate many-body quantum systems and have driven many innovations in\nresearch. Since the matrix product state design is tailored for closed\none-dimensional systems governed by the Schr\\\"odinger equation, the next step\nfor many-body quantum dynamics is the simulation of open quantum systems. We\nreview the three dominant approaches to the simulation of open quantum systems\nvia the Lindblad master equation: quantum trajectories, matrix product density\noperators, and locally purified tensor networks. Selected examples guide\npossible applications of the methods and serve moreover as a benchmark between\nthe techniques. These examples include the finite temperature states of the\ntransverse quantum Ising model, the dynamics of an exciton traveling under the\ninfluence of spontaneous emission and dephasing, and a double-well potential\nsimulated with the Bose-Hubbard model including dephasing. We analyze which\napproach is favorable leading to the conclusion that a complete set of all\nthree methods is most beneficial, push- ing the limits of different scenarios.\nThe convergence studies using analytical results for macroscopic variables and\nexact diagonalization methods as comparison, show, for example, that matrix\nproduct density operators are favorable for the exciton problem in our study.\nAll three methods access the same library, i.e., the software package Open\nSource Matrix Product States, allowing us to have a meaningful comparison\nbetween the approaches based on the selected examples. For example, tensor\noperations are accessed from the same subroutines and with the same\noptimization eliminating one possible bias in a comparison of such numerical\nmethods.",
        "positive": "Scattering lengths of calcium and barium isotopes: We have calculated the s-wave scattering length of all the even isotopes of\ncalcium (Ca) and barium (Ba), in order to investigate the prospect of\nBose-Einstein condensation (BEC). For Ca we have used an accurate molecular\npotential based on detailed spectroscopic data. Our calculations show that Ca\ndoes not provide other isotopes alternative to the recently Bose condensed 40Ca\nthat suffers strong losses because of a very large scattering length. For Ba we\nshow by using a model potential that the even isotopes cover a broad range of\nscattering lengths, opening the possibility of BEC for at least one of the\nisotopes."
    },
    {
        "anchor": "Bose-Einstein condensation of 86Sr: We report on the attainment of Bose-Einstein condensation of 86Sr. This\nisotope has a scattering length of about +800 a0 and thus suffers from fast\nthree-body losses. To avoid detrimental atom loss, evaporative cooling is\nperformed at low densities around 3x10^12 cm^-3 in a large volume optical\ndipole trap. We obtain almost pure condensates of 5x10^3 atoms.",
        "positive": "Computation of local exchange coefficients in strongly interacting\n  one-dimensional few-body systems: local density approximation and exact\n  results: One-dimensional multi-component Fermi or Bose systems with strong zero-range\ninteractions can be described in terms of local exchange coefficients and\nmapping the problem into a spin model is thus possible. For arbitrary external\nconfining potentials the local exchanges are given by highly non-trivial\ngeometric factors that depend solely on the geometry of the confinement through\nthe single-particle eigenstates of the external potential. To obtain accurate\neffective Hamiltonians to describe such systems one needs to be able to compute\nthese geometric factors with high precision which is difficult due to the\ncomputational complexity of the high-dimensional integrals involved. An\napproach using the local density approximation would therefore be a most\nwelcome approximation due to its simplicity. Here we assess the accuracy of the\nlocal density approximation by going beyond the simple harmonic oscillator that\nhas been the focus of previous studies and consider some double-wells of\ncurrent experimental interest. We find that the local density approximation\nworks quite well as long as the potentials resemble harmonic wells but break\ndown for larger barriers. In order to explore the consequences of applying the\nlocal density approximation in a concrete setup we consider quantum state\ntransfer in the effective spin models that one obtains. Here we find that even\nminute deviations in the local exchange coefficients between the exact and the\nlocal density approximation can induce large deviations in the fidelity of\nstate transfer for four, five, and six particles."
    },
    {
        "anchor": "Two-dimensional Fermi gas in antiparallel magnetic fields: We study a two-dimensional Fermi gas with an attractive interaction subjected\nto synthetic magnetic fields assumed to be mutually antiparallel for two\ndifferent spin components. By employing the mean-field approximation, we find\nthat its phase diagram at zero temperature consists of pair superfluid and\nquantum spin Hall insulator phases and closely resembles that of the\nBose-Hubbard model. The resulting two phases are separated by a second-order\nquantum phase transition classified into the universality class of either the\ndilute Bose gas or the XY model. We also show that the pairing gap can be\nenhanced significantly by the antiparallel magnetic fields as a consequence of\nmagnetic catalysis, which may facilitate the realization of the pair superfluid\nin two dimensions by ultracold atom experiments.",
        "positive": "An escape of vector matter-wave soliton from a parabolic trap: We show that a vector matter-wave soliton in Bose-Einstein condensate loaded\ninto an optical lattice can escape from a trap formed by a parabolic potential,\nresembling a Hawking emission. The particle-antiparticle pair is emulated by a\nlow-amplitude bright-bright soliton in two-component Bose-Einstein condensate\nwith effective masses of opposite signs. It is shown that the parabolic\npotential leads to a spatial separation of BEC components. One component with\nchemical potential in a semi-infinite gap exerts periodical oscillations, while\nthe other BEC component, with negative effective mass, escapes from the trap.\nThe mechanism of atoms transfer from one BEC component to another by spatially\nperiodic linear coupling term is discussed."
    },
    {
        "anchor": "Hyperspherical Treatment of Strongly-Interacting Few-Fermion Systems in\n  One Dimension: We examine a one-dimensional two-component fermionic system in a trap,\nassuming that all particles have the same mass and interact through a strong\nrepulsive zero-range force. First we show how a simple system of three strongly\ninteracting particles in a harmonic trap can be treated using the\nhyperspherical formalism. Next we discuss the behavior of the energy for the\nN-body system.",
        "positive": "Dynamic virial theorem at nonequilibrium and applications: We show that a variety of nonequilibrium dynamics of interacting many-body\nsystems are universally characterized by an elegant relation, which we call the\ndynamic virial theorem. The out-of-equilibrium dynamics of quantum correlations\nis entirely governed by Tan\\textquoteright s contact. It gives rise to a series\nof observable consequences and is closely related to experiments with ultracold\natoms. Especially, we show that the dynamic virial theorem provides an\nexperimentally accessible verification of maximum energy growth theorem [Qi et\nal., Phys. Rev. Lett. 126, 240401 (2021)], which is encoded in the evolution of\nthe atomic cloud size during expansion. In addition, the dynamic virial theorem\nleads to a simple thermodynamic relation of strongly interacting quantum gases\nin the framework of two-fluid hydrodynamic theory, which holds in a wide range\nof temperature. This thermodynamic relation is a kind of the out-of-equilibrium\nanalog of Tan's pressure relation at equilibrium. Our results provide\nfundamental understanding of generic behaviors of interacting many-body systems\nat nonequilibrium, and are readily examined in experiments with ultracold\natoms."
    },
    {
        "anchor": "Quantum Joule Expansion of One-Dimensional Systems: We investigate the Joule expansion of nonintegrable quantum systems that\ncontain bosons or spinless fermions in one-dimensional lattices. A barrier\ninitially confines the particles to be in half of the system in a thermal state\ndescribed by the canonical ensemble and is removed at time $t = 0$. We\ninvestigate the properties of the time-evolved density matrix, the diagonal\nensemble density matrix and the corresponding canonical ensemble density matrix\nwith an effective temperature determined by the total energy conservation using\nexact diagonalization. The weights for the diagonal ensemble and the canonical\nensemble match well for high initial temperatures that correspond to negative\neffective final temperatures after the expansion. At long times after the\nbarrier is removed, the time-evolved R\\'enyi entropy of subsystems bigger than\nhalf can equilibrate to the thermal entropy with exponentially small\nfluctuations. The time-evolved reduced density matrix at long times can be\napproximated by a thermal density matrix for small subsystems. Few-body\nobservables, like the momentum distribution function, can be approximated by a\nthermal expectation of the canonical ensemble with strongly suppressed\nfluctuations. The negative effective temperatures for finite systems go to\nnonnegative temperatures in the thermodynamic limit for bosons, but is a true\nthermodynamic effect for fermions, which is confirmed by finite temperature\ndensity matrix renormalization group calculations. We propose the Joule\nexpansion as a way to dynamically create negative temperature states for\nfermion systems with repulsive interactions.",
        "positive": "Two component quantum walk in one-dimensional lattice with hopping\n  imbalance: We investigate the two-component quantum walk in one-dimensional lattice. We\nshow that the inter-component interaction strength together with the hopping\nimbalance between the components exhibit distinct features in the quantum walk\nfor different initial states. When the walkers are initially on the same site,\nboth the slow and fast particles perform independent particle quantum walks\nwhen the interaction between them is weak. However, stronger inter-particle\ninteractions result in quantum walks by the repulsively bound pair formed\nbetween the two particles. For different initial states when the walkers are on\ndifferent sites initially, the quantum walk performed by the slow particle is\nalmost independent of that of the fast particle, which exhibits reflected and\ntransmitted components across the particle with large hopping strength for weak\ninteractions. Beyond a critical value of the interaction strength, the wave\nfunction of the fast particle ceases to penetrate through the slow particle\nsignalling a spatial phase separation. However, when the two particles are\ninitially at the two opposite edges of the lattice, then the interaction\nfacilitates the complete reflection of both of them from each other. We analyze\nthe above mentioned features by examining various physical quantities such as\nthe on-site density evolution, two-particle correlation functions and\ntransmission coefficients."
    },
    {
        "anchor": "Correlation versus commensurability effects for finite bosonic systems\n  in one-dimensional lattices: We investigate few-boson systems in finite one-dimensional multi-well traps\ncovering the full interaction crossover from uncorrelated to fermionized\nparticles. Our treatment of the ground state properties is based on the\nnumerically exact Multi-Configurational Time-Dependent Hartree method. For\ncommensurate filling we trace the fingerprints of localisation, as the\ninteraction strength increases, in several observables like reduced density\nmatrices, fluctuations and momentum distribution. For filling factor larger\nthan one we observe on-site repulsion effects in the densities and\nfragmentation of particles beyond the validity of the Bose-Hubbard model upon\napproaching the Tonks-Girardeau limit. The presence of an incommensurate\nfraction of particles induces incomplete localisation and spatial modulations\nof the density profiles, taking into account the finite size of the system.",
        "positive": "Exact quasiparticle properties of a heavy polaron in BCS Fermi\n  superfluids: We present the Ramsey response and radio-frequency spectroscopy of a heavy\nimpurity immersed in an interacting Fermi superfluid, using exact functional\ndeterminant approach. We describe the Fermi superfluid through the conventional\nBardeen-Cooper-Schrieffer theory and investigate the role of the pairing gap on\nquasiparticle properties revealed by the two spectroscopies. The energy cost\nfor pair breaking prevents Anderson\\textquoteright s orthogonality catastrophe\nthat occurs in a non-interacting Fermi gas and allows the existence of polaron\nquasiparticles in the exactly solvable heavy impurity limit. Hence, we\nrigorously confirm the remarkable features such as dark continuum,\nmolecule-hole continuum and repulsive polaron. For a magnetic impurity\nscattering at finite temperature, we predict additional resonances related to\nthe sub-gap Yu-Shiba-Rusinov bound state, whose positions can be used to\nmeasure the superfluid pairing gap. For a non-magnetic scattering at zero\ntemperature, we surprisingly find undamped repulsive polarons. These exact\nresults might be readily observed in quantum gas experiments with Bose-Fermi\nmixtures that have a large-mass ratio."
    },
    {
        "anchor": "Characteristics of Two-Dimensional Quantum Turbulence in a Compressible\n  Superfluid: Under suitable forcing a fluid exhibits turbulence, with characteristics\nstrongly affected by the fluid's confining geometry. Here we study\ntwo-dimensional quantum turbulence in a highly oblate Bose-Einstein condensate\nin an annular trap. As a compressible quantum fluid, this system affords a rich\nphenomenology, allowing coupling between vortex and acoustic energy.\nSmall-scale stirring generates an experimentally observed disordered vortex\ndistribution that evolves into large-scale flow in the form of a persistent\ncurrent. Numerical simulation of the experiment reveals additional\ncharacteristics of two-dimensional quantum turbulence: spontaneous clustering\nof same-circulation vortices, and an incompressible energy spectrum with\n$k^{-5/3}$ dependence for low wavenumbers $k$ and $k^{-3}$ dependence for high\n$k$.",
        "positive": "Magnetic phases of mass- and population-imbalanced ultracold fermionic\n  mixtures in optical lattices: We study magnetic phases of two-component mixtures of ultracold fermions with\nrepulsive interactions in optical lattices in the presence of both hopping and\npopulation imbalance by means of dynamical mean-field theory (DMFT). It is\nshown that these mixtures can have easy-axis antiferromagnetic, ferrimagnetic,\ncharge-density wave, and canted-antiferromagnetic order or be unordered\ndepending on parameters of the system. We study the resulting phase diagram in\ndetail and investigate the stability of the different phases with respect to\nthermal fluctuations. We also perform a quantitative analysis for a gas\nconfined in a harmonic trap, both within the local density approximation and\nusing a full real-space generalization of DMFT."
    },
    {
        "anchor": "Collisionless Dynamics in Two-Dimensional Bosonic Gases: We study the dynamics of dilute and ultracold bosonic gases in a quasi\ntwo-dimensional (2D) configuration and in the collisionless regime. We adopt\nthe 2D Landau-Vlasov equation to describe a three-dimensional gas under very\nstrong harmonic confinement along one direction. We use this effective equation\nto investigate the speed of sound in quasi 2D bosonic gases, i.e. the sound\npropagation around a Bose-Einstein distribution in collisionless 2D gases. We\nderive coupled algebraic equations for the real and imaginary parts of the\nsound velocity, which are then solved taking also into account the equation of\nstate of the 2D bosonic system. Above the Berezinskii-Kosterlitz-Thouless\ncritical temperature we find that there is rapid growth of the imaginary\ncomponent of the sound velocity which implies a strong Landau damping. Quite\nremarkably, our theoretical results are in good agreement with very recent\nexperimental data obtained with a uniform 2D Bose gas of $^{87}$Rb atoms.",
        "positive": "Precise photoexcitation measurement of Tan's contact in the entire\n  BCS-BEC crossover: We study two-body correlations in a spin-balanced ultracold harmonically\ntrapped Fermi gas of $^6$Li atoms in the crossover from the\nBardeen-Cooper-Schrieffer (BCS) to the Bose-Einstein-Condensate (BEC) regime.\nFor this, we precisely measure Tan's contact using a novel method based on\nphotoexcitation of atomic pairs, which was recently proposed by Wang et al.\n[Phys. Rev. A 104 063309 (2021)]. We map out the contact in the entire phase\ndiagram of the BCS-BEC crossover for various temperatures and interaction\nstrengths, probing regions in phase-space that have not been investigated yet.\nOur measurements reach an uncertainty of $\\approx 2 \\%$ and thus represent a\nprecise quantitative benchmark. We compare our data to theoretical predictions\nand interpolations and localize the regions in phase space where the latter\ngive valid results. In regions where the contact is already well known we find\nexcellent agreement with our measurements. Thus, our results demonstrate that\nphotoinduced loss is a precise probe to measure quantum correlations in a\nstrongly interacting Fermi gas."
    },
    {
        "anchor": "Optimizing a spin-flip Zeeman slower: We present a design of a spin-flip Zeeman slower controlled by a fast\nfeedback circuit for a sodium Bose-Einstein condensate apparatus. We also\ndemonstrate how the efficiency of the slower strongly depends on its intrinsic\nparameters, and compare these observations with a few theoretical models. Our\nfindings lead to a simple three-step procedure of designing an optimal Zeeman\nslower for neutral atoms, especially for those atomic species with high initial\nvelocities, such as sodium and lithium atoms.",
        "positive": "Zonal estimators for quasiperiodic bosonic many-body phases: In this work, we explore the relevant methodology for the investigation of\ninteracting systems with contact interactions, and we introduce a class of\nzonal estimators for path-integral Monte Carlo methods, designed to provide\nphysical information about limited regions of inhomogeneous systems.We\ndemonstrate the usefulness of zonal estimators by their application to a system\nof trapped bosons in a quasiperiodic potential in two dimensions, focusing on\nfinite temperature properties across a wide range of values of the potential.\nFinally, we comment on the generalization of such estimators to local\nfluctuations of the particle numbers and to magnetic ordering in\nmulti-component systems, spin systems, and systems with nonlocal interactions."
    },
    {
        "anchor": "Superfluid density and critical velocity near the fermionic\n  Berezinskii-Kosterlitz-Thouless transition: We theoretically investigate superfluidity in a strongly interacting Fermi\ngas confined to two dimensions at finite temperature. Using a Gaussian pair\nfluctuation theory in the superfluid phase, we calculate the superfluid density\nand determine the critical temperature and chemical potential at the\nBerezinskii-Kosterlitz-Thouless transition. We propose that the transition can\nbe unambiguously demonstrated in cold-atom experiments by stirring the\nsuperfluid Fermi gas using a red detuned laser beam, to identify the\ncharacteristic jump in the local Landau critical velocity at the\nsuperfluid-normal interface, as the laser beam moves across the cloud.",
        "positive": "Exploring kinetically induced bound states in triangular lattices with\n  ultracold atoms: spectroscopic approach: Quantum simulations with ultracold fermions in triangular optical lattices\nhave recently emerged as a new platform for studying magnetism in frustrated\nsystems. Experimental realizations of the Fermi Hubbard model revealed striking\ncontrast between magnetism in bipartite and triangular lattices. In bipartite\nlattices magnetism peaks at half filling, and doped charge carriers tend to\nsuppress magnetic correlations. In triangular lattices for large $U/t$,\nmagnetism is enhanced by doping away from $n=1$ because kinetic energy of\ndopants can be lowered through developing magnetic correlations. This\ncorresponds to formation of magnetic polarons, with hole and doublon doping\nresulting in antiferro- and ferromagnetic polarons respectively. Snapshots\nobtained with quantum gas microscopes revealed formation of magnetic polarons\naround dopants at temperatures exceeding the superexchange energy scale. In\nthis work we discuss theoretically that additional insight into properties of\nmagnetic polarons can be achieved using spectroscopic experiments with\nultracold atoms. We consider starting from a spin polarized state with small\nhole doping and applying a two-photon Raman photoexcitation, which transfers\natoms into a different spin state. We show that such magnon injection spectra\nexhibit a separate peak corresponding to formation of a bound state between a\nhole and a magnon. This polaron peak is separated from the simple magnon\nspectrum by energy proportional to single particle tunneling and can be easily\nresolved with currently available experimental techniques. For some momentum\ntransfer there is an additional peak corresponding to photoexciting a bound\nstate between two holes and a magnon. We point out that in two component Bose\nmixtures in triangular lattices one can also create dynamical magnetic\npolarons, with one hole and one magnon forming a repulsive bound state."
    },
    {
        "anchor": "Rydberg dressing of a one-dimensional Bose-Einstein condensate: We study the influence of Rydberg dressed interactions in a one-dimensional\n(1D) Bose-Einstein Condensate (BEC). We show that a 1D geometry offers several\nadvantages over 3D for observing BEC Rydberg dressing. The effects of dressing\nare studied by investigating collective BEC dynamics after a rapid switch-off\nof the Rydberg dressing interaction. The results can be interpreted as an\neffective modification of the s-wave scattering length. We include this\nmodification in an analytical model for the 1D BEC, and compare it to numerical\ncalculations of Rydberg dressing under realistic experimental conditions.",
        "positive": "Materia cu\u00e1ntica en cavidades de alta reflectancia (Many-body CQED): This article gives details of the course on \"Quantum Matter in optical\nlattices and high-Q cavities\" given at the School of Physics XXVIII at UNAM in\n2021. The notes describe useful concepts for analog quantum simulation and\ndetails of models in optical lattices and high-Q cavities. The notes are in\nSpanish.\n  En este art\\'iculo se discuten algunos detalles del curso sobre \"Materia\ncu\\'antica en redes \\'opticas y cavidades de alta reflectancia (Many-body\nCQED)\" de la escuela de verano de F\\'isica XVIII (2021) en la UNAM. Se\ndescriben conceptos \\'utiles para la simulaci\\'on cu\\'antica an\\'aloga, as\\'i\ncomo se introducen detalles de modelos de materia cu\\'antica en redes \\'opticas\ny en cavidades de alta reflectancia."
    },
    {
        "anchor": "Investigation of the role of the Roentgen interaction in angular\n  momentum transfer within an electric Bose Einstein Condensate: The exact action of the Roentgen effect at an atomic level is investigated\nwithin the context of vortex formation using two Laguerre Gaussian beams.\nStarting from a modified Gross-Pitaevskii equation in the dipole approximation\nthat takes into account the coupling of the atomic system to the\nelectromagnetic fields the Roentgen interaction term is introduced and viewed\nwithin the context of such a Raman transition. A rigorous investigation of the\ncorresponding Rabi frequency reveals that the Roentgen term acts at different\nlevels compared to the (-d.E) term and thus would not cause any changes in a\nfully quantum mechanical treatment.",
        "positive": "Matter wave propagation above a step potential within the\n  cubic-nonlinear Schr\u00f6dinger equation: We analyze the matter wave transmission above a step potential within the\nframework of the cubic-nonlinear Schr\\\"odinger equation. We present a\ncomprehensive analysis of the corresponding stationary problem based on an\nexact second-order nonlinear differential equation for the probability density.\nThe exact solution of the problem in terms of the Jacobi elliptic sn-function\nis presented and analyzed. Qualitatively distinct types of wave propagation\npicture are classified depending on the input parameters of the system.\nAnalyzing the 2D space of involved dimensionless parameters, the nonlinearity\nand the reflecting potential's height/depth given in the units of the chemical\npotential, we show that the region of the parameters that does not sustain\nrestricted solutions is given by a closed curve consisting of a segment of an\nelliptic curve and two line intervals. We show that there exists a specific\nsingular point, belonging to the elliptic curve, which causes a jump from one\nevolution scenario to another one. The position of this point is determined and\nthe peculiarities of the evolution scenarios (oscillatory, non-oscillatory and\ndiverging) for all the allowed regions of involved parameters are described and\nanalyzed in detail."
    },
    {
        "anchor": "Two- and one-dimensional gap solitons in spin-orbit-coupled systems with\n  Zeeman splitting: We elaborate a mechanism for the formation of stable solitons of the\nsemi-vortex type (with vorticities 0 and 1 in their two components), populating\na finite bandgap in the spectrum of the spin-orbit-coupled binary Bose-Einstein\ncondensate with the Zeeman splitting, in the two-dimensional free space, under\nconditions which make the kinetic-energy terms in the respective coupled\nGross-Pitaevskii equations negligible. Unlike a recent work which used\nlong-range dipole-dipole interactions to construct stable gap solitons in a\nsimilar setting, we here demonstrate that stable solitons are supported by\ngeneric local interactions of both attractive and repulsive signs, provided\nthat the relative strength of the cross/self interaction in the two-component\nsystem does not exceed a critical value ~ 0.77. A boundary between stable and\nunstable fundamental 2D gap solitons is precisely predicted by the\nVakhitov-Kolokolov criterion, while all excited states of the 2D solitons, with\nvorticities (m, 1 + m) in the two components, m = 1, 2, ..., are unstable. The\nanalysis of the one-dimensional (1D) reduction of the system produces an exact\nanalytical solution for the family of gap solitons which populate the entire\nbandgap, the family being fully stable. Motion of the 1D solitons in the\ntrapping potential is considered too, showing that their effective mass is\npositive or negative if the cubic nonlinearity is attractive or repulsive,\nrespectively.",
        "positive": "Topological phase transitions in tilted optical lattices: We analyze the energy spectrum and eigenstates of cold atoms in a tilted\nbrick-wall optical lattice. When the tilt is applied, the system exhibits a\nsequence of topological phase transitions reflected in an abrupt change of the\neigenstates. It is demonstrated that these topological phase transitions can be\neasily detected in a laboratory experiment by observing Bloch oscillations of\ncold atoms."
    },
    {
        "anchor": "Determination of Chern numbers with a phase retrieval algorithm: Ultracold atoms in optical lattices form a clean quantum simulator platform\nwhich can be utilized to examine topological phenomena and test exotic\ntopological materials. Here we propose an experimental scheme to measure the\nChern numbers of two-dimensional multiband topological insulators with bosonic\natoms. We show how to extract the topological invariants out of a sequence of\ntime-of-flight images by applying a phase retrieval algorithm to matter waves.\nWe illustrate advantages of using bosonic atoms as well as efficiency and\nrobustness of the method with two prominent examples: the Harper-Hofstadter\nmodel with an arbitrary commensurate magnetic flux and the Haldane model on a\nbrick-wall lattice.",
        "positive": "Vertically-coupled dipolar exciton molecules: While the interaction potential between two dipoles residing in a single\nplane is repulsive, in a system of two vertically adjacent layers of dipoles it\nchanges from repulsive interaction in the long range to attractive interaction\nin the short range. Here we show that for dipolar excitons in semiconductor\nheterostructures, such a potential may give rise to bound states if two such\nexcitons are excited in two separate layers, leading to the formation of\nvertically coupled dipolar exciton molecules. Our calculations prove the\nexistence of such bound states and predict their binding energy as a function\nof the layers separation as well as their thermal distributions. We show that\nthese molecules should be observed in realistic systems such as semiconductor\ncoupled quantum well structures and the more recent van-der-Waals bound\nheterostructures. Formation of such molecules can lead to new effects such as a\ncollective dipolar drag between layers and new forms of multi-particle\ncorrelations, as well as to the study of dipolar molecular dynamics in a\ncontrolled system."
    },
    {
        "anchor": "Complex wave fields in the interacting one-dimensional Bose gas: We study the temperature regimes of the 1d interacting gas to determine when\nthe matter wave (c-field) theory is, in fact, correct and usable. The judgment\nis made by investigating the level of discrepancy in many observables at once\nin comparison to the exact Yang-Yang theory. We also determine what cutoff\nmaximizes the accuracy of such an approach. Results are given in terms of a\nbound on accuracy, as well as an optimal cutoff prescription. For a wide range\nof temperatures the optimal cutoff is independent of density or interaction\nstrength and so its temperature dependent form is suitable for many cloud\nshapes and, possibly, basis choices. However, this best global choice is higher\nin energy than most prior determinations. The high value is needed to obtain\nthe correct kinetic energy, but does not detrimentally affect other\nobservables.",
        "positive": "Spin squeezing: transforming one-axis-twisting into two-axis-twisting: Squeezed spin states possess unique quantum correlation or entanglement that\nare of significant promises for advancing quantum information processing and\nquantum metrology. In recent back to back publications [C. Gross \\textit{et al,\nNature} \\textbf{464}, 1165 (2010) and Max F. Riedel \\textit{et al, Nature}\n\\textbf{464}, 1170 (2010)], reduced spin fluctuations are observed leading to\nspin squeezing at -8.2dB and -2.5dB respectively in two-component atomic\ncondensates exhibiting one-axis-twisting interactions (OAT). The noise\nreduction limit for the OAT interaction scales as $\\propto 1/{N^{2/3}}$, which\nfor a condensate with $N\\sim 10^3$ atoms, is about 100 times below standard\nquantum limit. We present a scheme using repeated Rabi pulses capable of\ntransforming the OAT spin squeezing into the two-axis-twisting type, leading to\nHeisenberg limited noise reduction $\\propto 1/N$, or an extra 10-fold\nimprovement for $N\\sim 10^3$."
    },
    {
        "anchor": "Topological superfluid in one-dimensional spin-orbit coupled atomic\n  Fermi gases: ARC Centre of Excellence for Quantum-Atom Optics, Centre for Atom Optics and\nUltrafast Spectroscopy, Swinburne University of Technology, Melbourne 3122,\nAustralia",
        "positive": "Vortex Solutions in a Binary Immiscible Bose-Einstein Condensate: We consider the mean-field vortex solutions and their stability within a\ntwo-component Bose Einstein condensate in the immiscible limit. A variational\napproach is employed to study a system consisting of a majority component which\ncontains a single quantised vortex and a minority component which fills the\nvortex core. We show that a super-Gaussian function is a good approximation to\nthe two-component vortex solution for a range of atom numbers of the in-filling\ncomponent, by comparing the variational solutions to the full numerical\nsolutions of the coupled Gross-Pitaevskii equations. We subsequently examine\nthe stability of the vortex solutions by perturbing the in-filling component\naway from the centre of the vortex core, thereby demonstrating their stability\nto small perturbations."
    },
    {
        "anchor": "Observation of Half Quantum Vortices in an Exciton-Polariton Condensate: Singly quantized vortices have been already observed in many systems\nincluding the superfluid helium, Bose Einstein condensates of dilute atomic\ngases, and condensates of exciton polaritons in the solid state. Two\ndimensional superfluids carrying spin are expected to demonstrate a different\ntype of elementary excitations referred to as half quantum vortices\ncharacterized by a pi rotation of the phase and a pi rotation of the\npolarization vector when circumventing the vortex core. We detect half quantum\nvortices in an exciton-polariton condensate by means of polarization resolved\ninterferometry, real space spectroscopy and phase imaging. Half quantum\nvortices coexist with single quantum vortices in our sample.",
        "positive": "Dynamic hysteresis from bistability in an antiferromagnetic spinor\n  condensate: We study the emergence of hysteresis during the process of quantum phase\ntransition from an antiferromagnetic to a phase-separated state in a spin-1\nBose Einstein condensate of ultracold atoms. We explicitly demonstrate the\nappearance of a hysteresis loop with various quench times showing that it is\nrate-independent for large magnetizations only. In other cases scaling of the\nhysteresis loop area is observed, which we explain by using the Kibble-Zurek\ntheory in the limit of small magnetization. The effect of an external harmonic\ntrapping potential is also discussed."
    },
    {
        "anchor": "Attenuating Dynamics of Strongly Interacting Fermionic Superfluids in\n  SYK Solvable Models: Quench dynamics of fermionic superfluids are an active topic both\nexperimentally and theoretically. Using the BCS theory, such non-equilibrium\nproblems can be reduced to nearly independent spin dynamics, only with a\ntime-dependent mean-field pairing term. This results in persisting oscillations\nof the pairing strength in certain parameter regimes. However, experiments have\nobserved that the oscillations decay rapidly when the interaction becomes\nstrong, such as in the unitary Fermi gas. Theoretical analysis on this matter\nis still absent. In this work, we construct an SYK-like model to analyze the\neffect of strong interactions in a one-dimensional BCS system. We employ the\nlarge-$N$ approximation and a Green's function-based technique to solve the\nequilibrium problem and quench dynamics. Our findings reveal that a strong SYK\ninteraction suppresses the pairing order. Additionally, we verify that the\nsystem quickly thermalizes with SYK interactions, whether it involves intrinsic\npairing order or proximity effect, resulting in a rapid decay of the\noscillation strength. The decay rates exhibit different scaling laws against\nSYK interaction, which can be understood in terms of the Boltzmann equation.\nThis work represents a first step towards understanding the attenuating\ndynamics of strongly interacting fermionic superfluids.",
        "positive": "Topology in the space-time scaling limit of quantum dynamics: We investigate the role of topology in the space-time scaling limit of\nquantum quench dynamics, where both time and system size tend to infinity at a\nconstant ratio. There, while the standard topological characterization relying\non local unitary transformations becomes ill defined, we show how a different\ndynamical notion of topology naturally arises through a dynamical winding\nnumber encoding the linear response of the Berry phase to a magnetic flux.\nSpecifically, we find that the presence of a locally invisible constant\nmagnetic flux is revealed by a dynamical staircase behavior of the Berry phase,\nwhose topologically quantized plateaus characterize the space-time scaling\nlimit of a quenched Rice-Mele model. These jumps in the Berry phase are also\nshown to be related to the interband elements of the DC current operator. We\noutline possible experimental platforms for observing the predicted phenomena\nin finite systems."
    },
    {
        "anchor": "Introduction to quantum turbulence: The term quantum turbulence denotes the turbulent motion of quantum fluids,\nsystems such as superfluid helium and atomic Bose-Einstein condensates which\nare characterized by quantized vorticity, uperfluidity and, at finite\ntemperatures, two-fluid behavior. This article introduces their basic\nproperties, describes types and regimes of turbulence which have been observed,\nand highlights similarities and differences between quantum turbulence and\nclassical turbulence in ordinary fluids. Our aim is also to link together the\narticles of this special issue, and to provide a perspective of the future\ndevelopment of a subject which contains aspects of fluid mechanics, atomic\nphysics, condensed matter and low temperature physics.",
        "positive": "State selective cooling of $\\mathrm{SU}(N)$ Fermi-gases: We investigate a species selective cooling process of a trapped\n$\\mathrm{SU}(N)$ Fermi gas using entropy redistribution during adiabatic\nloading of an optical lattice. Using high-temperature expansion of the Hubbard\nmodel, we show that when a subset $N_A < N$ of the single-atom levels\nexperiences a stronger trapping potential in a certain region of space, the\ndimple, it leads to improvement in cooling as compared to a $\\mathrm{SU}(N_A)$\nFermi gas only. We show that optimal performance is achieved when all atomic\nlevels experience the same potential outside the dimple and we quantify the\ncooling for various $N_A$ by evaluating the dependence of the final entropy\ndensities and temperatures as functions of the initial entropy. Furthermore,\nconsidering ${}^{87}{\\rm Sr}$ and ${}^{173}{\\rm Yb}$ for specificity, we\nprovide a quantitative discussion of how the state selective trapping can be\nachieved with readily available experimental techniques."
    },
    {
        "anchor": "Fermi-Hubbard physics with atoms in an optical lattice: The Fermi-Hubbard model is a key concept in condensed matter physics and\nprovides crucial insights into electronic and magnetic properties of materials.\nYet, the intricate nature of Fermi systems poses a barrier to answer important\nquestions concerning d-wave superconductivity and quantum magnetism. Recently,\nit has become possible to experimentally realize the Fermi-Hubbard model using\na fermionic quantum gas loaded into an optical lattice. In this atomic approach\nto the Fermi-Hubbard model the Hamiltonian is a direct result of the optical\nlattice potential created by interfering laser fields and short-ranged\nultracold collisions. It provides a route to simulate the physics of the\nHamiltonian and to address open questions and novel challenges of the\nunderlying many-body system. This review gives an overview of the current\nefforts in understanding and realizing experiments with fermionic atoms in\noptical lattices and discusses key experiments in the metallic,\nband-insulating, superfluid and Mott-insulating regimes.",
        "positive": "Vortex rings and vortex ring solitons in shaken Bose-Einstein condensate: In a shaken Bose-Einstein condensate, confined in a vibrating trap, there can\nappear different nonlinear coherent modes. Here we concentrate on two types of\nsuch coherent modes, vortex ring solitons and vortex rings. In a cylindrical\ntrap, vortex ring solitons can be characterized as nonlinear Hermite-Laguerre\nmodes, whose description can be done by means of optimized perturbation theory.\nThe energy, required for creating vortex ring solitons, is larger than that\nneeded for forming vortex rings. This is why, at a moderate excitation energy,\nvortex rings appear before vortex ring solitons. The generation of vortex rings\nis illustrated by numerical simulations for trapped $^{87}$Rb atoms."
    },
    {
        "anchor": "Elementary excitations of antiferromagnetic spin-1 bosons in an optical\n  lattice: We study elementary excitations of spin-1 bosons with antiferromagnetic\ninteraction in an optical lattice by applying the Gutzwiller approximation to\nthe spin-1 Bose-Hubbard model. There appear various excitations associated with\nspin degrees of freedom in the Mott-insulator (MI) phase as well as in the\nsuperfluid (SF) phase. In this system, the ground state in the MI phase is\nknown to exhibit a remarkable effect of even-odd parity of particle filling, in\nwhich even fillings stabilize the MI state due to formation of spin-singlet\npairs. We find that excitation spectra in the MI phase exhibit characteristic\nfeatures that reflect the even-odd parity effect of the ground state. We\nclarify evolution of elementary excitations across the quantum critical point\nof the SF-MI transition.",
        "positive": "Path-integral Monte Carlo worm algorithm for Bose systems with periodic\n  boundary conditions: We provide a detailed description of the path-integral Monte Carlo worm\nalgorithm used to exactly calculate the thermodynamics of Bose systems in the\ncanonical ensemble. The algorithm is fully consistent with periodic boundary\nconditions, that are applied to simulate homogeneous phases of bulk systems,\nand it does not require any limitation in the length of the Monte Carlo moves\nrealizing the sampling of the probability distribution function in the space of\npath configurations. The result is achieved adopting a representation of the\npath coordinates where only the initial point of each path is inside the\nsimulation box, the remaining ones being free to span the entire space.\nDetailed balance can thereby be ensured for any update of the path\nconfigurations without the ambiguity of the selection of the periodic image of\nthe particles involved. We benchmark the algorithm using the non-interacting\nBose gas model for which exact results for the partition function at finite\nnumber of particles can be derived. Convergence issues and the approach to the\nthermodynamic limit are also addressed for interacting systems of hard spheres\nin the regime of high density."
    },
    {
        "anchor": "Controlled excitation and resonant acceleration of ultracold few-boson\n  systems by driven interactions in a harmonic trap: We investigate the excitation properties of finite utracold bosonic systems\nin a one-dimensional harmonic trap with a time-dependent interaction strength.\nThe driving of the interatomic coupling induces excitations of the relative\nmotion exclusively with specific and controllable contributions of momentarily\nexcited many-body states. Mechanisms for selective excitation to few-body\nanalogues of collective modes and acceleration occur in the vicinity of\nresonances. We study via the few-body spectrum and a Floquet analysis the\nexcitation mechanisms, and the corresponding impact of the driving frequency\nand strength as well as the initial correlation of the bosonic state. The\nfundamental case of two atoms is analyzed in detail and forms a key ingredient\nfor the bottom-up understanding of cases with higher atom numbers, thereby\nexamining finite-size corrections to macroscopic collective modes of\noscillation.",
        "positive": "Opto-mechanical effects in superradiant light scattering by\n  Bose-Einstein condensate in a cavity: We investigate the effects of a movable mirror (cantilever) of an optical\ncavity on the superradiant light scattering from a Bose-Einstein condensate\n(BEC) in an optical lattice. We show that the mirror motion has a dynamic\ndispersive effect on the cavity-pump detuning. Varying the intensity of the\npump beam, one can switch between the pure superradiant regime and the Bragg\nscattering regime. The mechanical frequency of the mirror strongly influences\nthe time interval between two Bragg peaks. We found that when the system is in\nthe resolved side band regime for mirror cooling, the superradiant scattering\nis enhanced due to coherent energy transfer from the mechanical mirror mode to\nthe cavity field mode."
    },
    {
        "anchor": "Causality and quantum criticality in long-range lattice models: Long-range quantum lattice systems often exhibit drastically different\nbehavior than their short-range counterparts. In particular, because they do\nnot satisfy the conditions for the Lieb-Robinson theorem, they need not have an\nemergent relativistic structure in the form of a light cone. Adopting a\nfield-theoretic approach, we study the one-dimensional transverse-field Ising\nmodel with long-range interactions, and a fermionic model with long-range\nhopping and pairing terms, explore their critical and near-critical behavior,\nand characterize their response to local perturbations. We deduce the dynamic\ncritical exponent, up to the two-loop order within the renormalization group\ntheory, which we then use to characterize the emergent causal behavior. We show\nthat beyond a critical value of the power-law exponent of the long-range\ncouplings, the dynamics effectively becomes relativistic. Various other\ncritical exponents describing correlations in the ground state, as well as\ndeviations from a linear causal cone, are deduced for a wide range of the\npower-law exponent.",
        "positive": "The Aubry-Andr\u00e9 model as the hobbyhorse for understanding localization\n  phenomenon: We present a thorough pedagogical analysis of the single particle\nlocalization phenomenon in a quasiperiodic lattice in one dimension.\nDescription of disorder in the lattice is represented by the Aubry-Andr\\'e\nmodel. Characterization of localization is performed through the analysis of\nboth, stationary and dynamical properties. The stationary properties\ninvestigated are the inverse participation ratio (IPR), the normalized\nparticipation ratio (NPR) and the energy spectrum as a function of the disorder\nstrength. As expected, the distinctive Hofstadter pattern is found. Two\ndynamical quantities allow discerning the localization phenomenon, being the\nspreading of an initially localized state and the evolution of population\nimbalance in even and odd sites across the lattice."
    },
    {
        "anchor": "Controlled collisions of two ultracold atoms in separate harmonic traps: We consider controlled collisions between two ultracold atoms guided by\nexternal harmonic potentials. We derive analytical solutions of the\nSchroedinger equation for this system, and investigate the properties of\neigenergies and eigenstates for different trap geometries as a function of a\ntrap separation and of the scattering length. When varying the trap separation\nthe energy spectrum exhibits avoided crossings, corresponding to trap-induced\nshape resonances. Introducing an energy-dependent scattering length we\ninvestigate the behavior of the system in the vicinity of a magnetic Feshbach\nresonance. Finally, we illustrate our analytical results with two examples: the\nquantum phase gate controlled by the external magnetic field, and a scheme for\na coherent transport of atoms in optical lattices into higher Bloch bands.",
        "positive": "First and second sound of a unitary Fermi gas in highly elongated\n  harmonic traps: Using a variational approach, we present the full solutions of the simplified\none-dimensional two-fluid hydrodynamic equations for a unitary Fermi gas\ntrapped in a highly elongated harmonic potential, which is recently derived by\nStringari and co-workers {[}Phys. Rev. Lett. \\textbf{105}, 150402 (2010){]}. We\ncalculate the discretized mode frequencies of first and second sound along the\nweak axial trapping potential, as a function of temperature and the form of\nsuperfluid density. We show that the density fluctuations in second sound\nmodes, due to their coupling to first sound modes, are large enough to be\nmeasured in current experimental setups such as that exploited by Tey\n\\textit{et al}. at the University of Innsbruck {[}Phys. Rev. Lett.\n\\textbf{110}, 055303 (2013){]}. Owing to the sensitivity of second sounds on\nthe form of superfluid density, the high precision of the measured second sound\nfrequencies may provide us a promising way to accurately determine the\nsuperfluid density of a unitary Fermi gas, which so far remains elusive."
    },
    {
        "anchor": "Landauer, Kubo, and microcanonical approaches to quantum transport and\n  noise: A comparison and implications for cold-atom dynamics: We compare the Landauer, Kubo, and microcanonical [J. Phys. Cond. Matter {\\bf\n16}, 8025 (2004)] approaches to quantum transport for the average current, the\nentanglement entropy and the semiclassical full-counting statistics (FCS). Our\nfocus is on the applicability of these approaches to isolated quantum systems\nsuch as ultra-cold atoms in engineered optical potentials. For two lattices\nconnected by a junction, we find that the current and particle number\nfluctuations from the microcanonical approach compare well with the values\npredicted by the Landauer formalism and FCS assuming a binomial distribution.\nHowever, we demonstrate that well-defined reservoirs (i.e., particles in\nFermi-Dirac distributions) are not present for a substantial duration of the\nquasi-steady state. Thus, the Landauer assumption of reservoirs and/or\ninelastic effects is not necessary for establishing a quasi-steady state.\nMaintaining such a state indefinitely requires an infinite system, and in this\nlimit well-defined Fermi-Dirac distributions can occur. A Kubo approach -- in\nthe spirit of the microcanonical picture -- bridges the gap between the two\nformalisms, giving explicit analytical expressions for the formation of the\nsteady state. The microcanonical formalism is designed for closed, finite-size\nquantum systems and is thus more suitable for studying particle dynamics in\nultra-cold atoms. Our results highlight both the connection and differences\nwith more traditional approaches to calculating transport properties in\ncondensed matter systems, and will help guide the way to their simulations in\ncold-atom systems.",
        "positive": "Dispersion relation of the collective excitations in a resonantly driven\n  polariton fluid: Exciton-polaritons in semiconductor microcavities constitute the archetypal\nrealization of a quantum fluid of light. Under coherent optical drive,\nremarkable effects such as superfluidity, dark solitons or the nucleation of\nhydrodynamic vortices have been observed. These phenomena can be all understood\nas a specific manifestation of collective excitations forming on top of the\npolariton condensate. In this work, we performed a Brillouin scattering\nexperiment to measure their dispersion relation $\\omega(\\mathbf{k})$ directly.\nThe result, such as a speed of sound which is apparently twice too low, cannot\nbe explained upon considering the polariton condensate alone. In a combined\ntheoretical and experimental analysis, we demonstrate that the presence of a\nreservoir of long-lived excitons interacting with polaritons has a dramatic\ninfluence on the nature and characteristic of the quantum fluid, and that it\nexplains our measurement quantitatively. This work clarifies the role of such a\nreservoir in the different polariton hydrodynamics phenomena occurring under\nresonant optical drive. It also provides an unambiguous tool to determine the\ncondensate-to-reservoir fraction in the quantum fluid, and sets an accurate\nframework to approach novel ideas for polariton-based quantum-optical\napplications."
    },
    {
        "anchor": "Dispersion relation of a polaron in the Yang-Gaudin Bose gas: We study a one-dimensional Bose gas with two internal states described by the\nYang-Gaudin model and calculate analytically the dispersion relation of a\npolaron quasiparticle, which is the lowest excitation branch. We study the\ndispersion in the thermodynamic limit in the regimes of weak and strong\ninteraction without limitations on the momentum. At weak interaction the\npolaron dispersion is in the vicinity of the dark soliton one; we calculate the\nleading deviation in the parametric form. At strong interaction we find an\nansatz for the explicit form of the polaron dispersion. It has the form of a\npower series of the sine function of the momentum with interaction-dependent\ncoefficients. By increasing the power of the series, the corresponding\ncoefficients show faster decay and thus one practically needs only a few of\nthem; we give the results for the first three. The coefficients of the series\nare connected to the Maclaurin series of the polaron dispersion and thus it is\nsufficient to calculate latter quantity to automatically find the power series\nresult for the dispersion at all momenta. The derived results for the\ndispersion can be used to obtain explicit expressions for the exponents of the\npower-law singularities in the response functions at the spectral edge.",
        "positive": "Association of Atoms into Universal Dimers using an Oscillating Magnetic\n  Field: In a system of ultracold atoms near a Feshbach resonance, pairs of atoms can\nbe associated into universal dimers by an oscillating magnetic field with\nfrequency near that determined by the dimer binding energy. We present a simple\nexpression for the transition rate that takes into account many-body effects\nthrough a transition matrix element of the contact. In a thermal gas, the width\nof the peak in the transition rate as a function of the frequency is determined\nby the temperature. In a dilute Bose-Einstein condensate of atoms, the width is\ndetermined by the inelastic scattering rates of a dimer with zero-energy atoms.\nNear an atom-dimer resonance, there is a dramatic increase in the width from\ninelastic atom-dimer scattering and from atom-atom-dimer recombination. The\nrecombination contribution provides a signature for universal tetramers that\nare Efimov states consisting of two atoms and a dimer."
    },
    {
        "anchor": "Skyrmion-antiSkyrmion pairs in Ultracold Atomic Gases: We study theoretically the dynamics of two-component Bose-Einstein\ncondensates in two dimensions, which admit topological excitations related to\nthe Skyrmions of nuclear physics. We show that there exists a branch of\nuniformly propagating solitary waves characterised by a conserved momentum.\nThese excitations exhibit a cross-over from spatially extended spin-wave states\nat low momentum to a localised \"spin-wave droplet\" at intermediate momentum; at\nstill higher momentum, the configuration evolves continuously into a\nSkyrmion-antiSkyrmion pair. We discuss how these solitary waves can be\ngenerated and studied in experiment.",
        "positive": "Dynamics of Dark-Bright Solitons in Cigar-Shaped Bose-Einstein\n  Condensates: We explore the stability and dynamics of dark-bright solitons in\ntwo-component elongated Bose-Einstein condensates by developing effective 1D\nvector equations as well as solving the corresponding 3D Gross-Pitaevskii\nequations. A strong dependence of the oscillation frequency and of the\nstability of the dark-bright (DB) soliton on the atom number of its components\nis found. Spontaneous symmetry breaking leads to oscillatory dynamics in the\ntransverse degrees of freedom for a large occupation of the component\nsupporting the dark soliton. Moreover, the interactions of two DB solitons are\ninvestigated with special emphasis on the importance of their relative phases.\nExperimental results showcasing dark-bright soliton dynamics and collisions in\na BEC consisting of two hyperfine states of $^{87}$Rb confined in an elongated\noptical dipole trap are presented."
    },
    {
        "anchor": "Stabilizing lattice gauge theories through simplified local pseudo\n  generators: The postulate of gauge invariance in nature does not lend itself directly to\nimplementations of lattice gauge theories in modern setups of quantum synthetic\nmatter. Unavoidable gauge-breaking errors in such devices require gauge\ninvariance to be enforced for faithful quantum simulation of gauge-theory\nphysics. This poses major experimental challenges, in large part due to the\ncomplexity of the gauge-symmetry generators. Here, we show that gauge\ninvariance can be reliably stabilized by employing simplified \\textit{local\npseudogenerators} designed such that within the physical sector they act\nidentically to the actual local generator. Dynamically, they give rise to\nemergent exact gauge theories up to timescales polynomial and even exponential\nin the protection strength. This obviates the need for implementing often\ncomplex multi-body full gauge symmetries, thereby further reducing experimental\noverhead in physical realizations. We showcase our method in the $\\mathbb{Z}_2$\nlattice gauge theory, and discuss experimental considerations for its\nrealization in modern ultracold-atom setups.",
        "positive": "Orbital magnetism of ultracold fermionic gases in a lattice: dynamical\n  mean-field approach: We study finite-temperature properties of ultracold four-component mixtures\nof alkaline-earth-like atoms in optical lattices that can be effectively\ndescribed by the two-band spin-$1/2$ Hubbard model including the Hund's\nexchange coupling term. Our main goal is to investigate the effect of exchange\ninteractions on finite-temperature magnetic phases for a wide range of lattice\nfillings. We use the dynamical mean-field theory approach and its real-space\ngeneralization to obtain finite-temperature phase diagrams including\ntransitions to magnetically-ordered phases. It allows to determine optimal\nexperimental regimes for approaching long-range ferromagnetic ordering in\nultracold gases. We also calculate the entropy in the vicinity of\nmagnetically-ordered phases, which provides quantitative predictions for\non-going and future experiments aiming at approaching and studying long-range\nordered states in optical lattices."
    },
    {
        "anchor": "Comment on \"Observation of two-dimensional Anderson localisation of\n  ultracold atoms\": Here I provide additional experimental information and criticise the\nanalysis, modelling, interpretation and claims presented in the recent paper\n[Nature Communications 11, 4942 (2020)]. I argue that the authors have no clear\nexperimental evidence of Anderson localisation (as they claim) and their\nnumerical simulations are very far indeed from reproducing the experiment, as\nstated in their article. Furthermore, some effects that are ascribed to real\nphysical mechanisms are revealed to be simply artefacts.",
        "positive": "Bright solitons in a spin-tensor-momentum-coupled Bose-Einstein\n  condensate: Synthetic spin-tensor-momentum coupling has recently been proposed to realize\nin atomic Bose-Einstein condensates. Here we study bright solitons in\nBose-Einstein condensates with spin-tensor-momentum coupling and spin-orbit\ncoupling. The properties and dynamics of spin-tensor-momentum-coupled and\nspin-orbit-coupled bright solitons are identified to be different. We\ncontribute the difference to the different symmetries."
    },
    {
        "anchor": "Ground state of the two-dimensional attractive Fermi gas: essential\n  properties from few- to many-body: We calculate the ground-state properties of unpolarized two-dimensional\nattractive fermions in the range from few to many particles. Using\nfirst-principles lattice Monte Carlo methods, we determine the ground-state\nenergy, Tan's contact, momentum distribution, and single-particle correlation\nfunction. We investigate those properties for systems of $N=4,8,...,40$\nparticles and for a wide range of attractive couplings. As the attractive\ncoupling is increased, the thermodynamic limit is reached at progressively\nlower $N$ due to the dominance of the two-body sector. At large momenta $k$,\nthe momentum distribution displays the expected $k^{-4}$ behavior, but its\nonset shifts from $k \\simeq 1.8 k^{}_F$ at weak coupling towards higher $k$ at\nstrong coupling.",
        "positive": "Impurity in a Bose-Einstein condensate: study of the attractive and\n  repulsive branch using quantum Monte-Carlo methods: We investigate the properties of an impurity immersed in a dilute Bose gas at\nzero temperature using quantum Monte-Carlo methods. The interactions between\nbosons are modeled by a hard sphere potential with scattering length $a$,\nwhereas the interactions between the impurity and the bosons are modeled by a\nshort-range, square-well potential where both the sign and the strength of the\nscattering length $b$ can be varied by adjusting the well depth. We\ncharacterize the attractive and the repulsive polaron branch by calculating the\nbinding energy and the effective mass of the impurity. Furthermore, we\ninvestigate structural properties of the bath, such as the impurity-boson\ncontact parameter and the change of the density profile around the impurity. At\nthe unitary limit of the impurity-boson interaction, we find that the effective\nmass of the impurity remains smaller than twice its bare mass, while the\nbinding energy scales with $\\hbar^2n^{2/3}/m$, where $n$ is the density of the\nbath and $m$ is the common mass of the impurity and the bosons in the bath. The\nimplications for the phase diagram of binary Bose-Bose mixtures at small\nconcentrations are also discussed."
    },
    {
        "anchor": "Two infinite families of resonant solutions for the Gross-Pitaevskii\n  equation: We consider the two-dimensional Gross-Pitaevskii equation describing a\nBose-Einstein condensate in an isotropic harmonic trap. In the small coupling\nregime, this equation is accurately approximated over long times by the\ncorresponding nonlinear resonant system whose structure is determined by the\nfully resonant spectrum of the linearized problem. We focus on two types of\nconsistent truncations of this resonant system: first, to sets of modes of\nfixed angular momentum, and second, to excited Landau levels. Each of these\ntruncations admits a set of explicit analytic solutions with initial conditions\nparametrized by three complex numbers. Viewed in position space, the fixed\nangular momentum solutions describe modulated oscillations of dark rings, while\nthe excited Landau level solutions describe modulated precession of small\narrays of vortices and antivortices. We place our findings in the context of\nsimilar results for other spatially confined nonlinear Hamiltonian systems in\nrecent literature.",
        "positive": "Direct excitation of Kelvin waves on quantized vortices: Helices and spirals, prevalent across various systems, play a crucial role in\ncharacterizing symmetry, describing dynamics, and imparting unique\nfunctionalities, attributed to their inherent simplicity and chiral nature. A\nhelical excitation on a quantized vortex, an example of a one-dimensional\ntopological defect, emerges as a Nambu-Goldstone mode following spontaneous\nsymmetry breaking, known as a Kelvin wave. Kelvin waves play a vital role in\nenergy dissipation within inviscid quantum fluids. However, deliberately\nexciting Kelvin waves has proven to be challenging. Here, we introduce a\ncontrolled method for exciting Kelvin waves on a quantized vortex in superfluid\nhelium-4. We used a charged nanoparticle, oscillated by a time-varying electric\nfield, to stimulate Kelvin waves on the vortex. A major breakthrough in our\nresearch is the confirmation of the helical nature of Kelvin waves through\nthree-dimensional image reconstruction, providing visual evidence of their\ncomplex dynamics. Additionally, we determined the dispersion relation and the\nphase velocity of the Kelvin wave and identified the vorticity direction,\nenhancing our understanding of quantum fluid behavior. This work elucidates the\ndynamics of Kelvin waves and pioneers a novel approach for manipulating and\nobserving quantized vortices in three dimensions, thereby opening new avenues\nfor exploring quantum fluidic systems."
    },
    {
        "anchor": "Relaxation rates and collision integrals for Bose-Einstein condensates: Near equilibrium, the rate of relaxation to equilibrium and the transport\nproperties of excitations (bogolons) in a dilute Bose-Einstein condensate (BEC)\nare determined by three collision integrals, $\\mathcal{G}^{12}$,\n$\\mathcal{G}^{22}$, and $\\mathcal{G}^{31}$. All three collision integrals\nconserve momentum and energy during bogolon collisions, but only $\n\\mathcal{G}^{22}$ conserves bogolon number. Previous works have considered the\ncontribution of only two collision integrals, $ \\mathcal{G}^{22}$ and $\n\\mathcal{G}^{12}$. In this work, we show that the third collision integral $\n\\mathcal{G}^{31}$ makes a significant contribution to the bogolon number\nrelaxation rate and needs to be retained when computing relaxation properties\nof the BEC. We provide values of relaxation rates in a form that can be applied\nto a variety of dilute Bose-Einstein condensates.",
        "positive": "An eight-fold optical quasicrystal with cold atoms: We propose a means to realize two-dimensional quasiperiodic structures by\ntrapping atoms in an optical potential. The structures have eight-fold symmetry\nand are closely related to the well-known quasiperiodic octagonal\n(Ammann-Beenker) tiling. We describe the geometrical properties of the\nstructures obtained by tuning parameters of the system. We discuss some\nfeatures of the corresponding tight-binding models, and experiments to probe\nquantum properties of this optical quasicrystal."
    },
    {
        "anchor": "Fermionic bound states on a one-dimensional lattice: We study bound states of two fermions with opposite spins in an extended\nHubbard chain. The particles interact when located both on a site or on\nadjacent sites. We find three different types of bound states. Type U is\npredominantly formed of basis states with both fermions on the same site, while\ntwo states of type V originate from both fermions occupying neighbouring sites.\nType U, and one of the states from type V, are symmetric with respect to spin\nflips. The remaining one from type V is antisymmetric. V-states are\ncharacterized by a diverging localization length below some critical wave\nnumber. All bound states become compact for wave numbers at the edge of the\nBrilloin zone.",
        "positive": "Cooperative phase transitions in the system of photons and dye molecules: Bose condensed light can form new phases [1] in a dye filled cavity due to\nthe presence of the orientational disorder created by dye molecules which are\nessentially frozen on the time scale of the photonic thermalization (few ps).\nAt longer times (few ns) molecular degrees of freedom -- orientations and\npositions -- become important. Including them on equal footing with photons can\nchange the nature of the photonic condensation -- it can proceed as Ist order\nphase transition which can also result in the mutual phase separation effect --\nfor photons and dye. The analysis is conducted within the mean field approach\nin the thermodynamic limit. Recommendations for the experimental detection of\nthe transition nature are formulated."
    },
    {
        "anchor": "Genuine many-body quantum scars along unstable modes in Bose-Hubbard\n  systems: The notion of many-body quantum scars is associated with special eigenstates,\nusually concentrated in certain parts of Hilbert space, that give rise to\nrobust persistent oscillations in a regime that globally exhibits\nthermalization. Here we extend these studies to many-body systems possessing a\ntrue classical limit characterized by a high-dimensional chaotic phase space,\nwhich are not subject to any particular dynamical constraint. We demonstrate\ngenuine quantum scarring of wave functions concentrated in the vicinity of\nunstable classical periodic mean-field modes in the paradigmatic Bose-Hubbard\nmodel. These peculiar quantum many-body states exhibit distinct phase-space\nlocalization about those classical modes. Their existence is consistent with\nHeller's scar criterion and appears to persist in the thermodynamic\nlong-lattice limit. Launching quantum wave packets along such scars leads to\nobservable long-lasting oscillations, featuring periods that scale\nasymptotically with classical Lyapunov exponents, and displaying intrinsic\nirregularities that reflect the underlying chaotic dynamics, as opposed to\nregular tunnel oscillations.",
        "positive": "The exact solution of a generalized Bose-Hubbard model: I present the exact solution of a family of fragmented Bose-Hubbard models\nand represent the models as graphs in one-dimension, two-dimensions and\nthree-dimensions with the condensates in the vertices. The models are solved by\nthe algebraic Bethe ansatz method."
    },
    {
        "anchor": "Quantum Treatment for Bose-Einstein Condensation in Non-Equilibrium\n  Systems: We develop an approach based on stochastic quantum trajectories for an\nincoherently pumped system of interacting bosons relaxing their energy in a\nthermal reservoir. Our approach enables the study of the versatile coherence\nproperties of the system. We apply the model to exciton polaritons in a\nsemiconductor microcavity. Our results demonstrate the onset of macroscopic\noccupation in the lowest-energy mode accompanied by the establishment of both\ntemporal and spatial coherence. We show that temporal coherence exhibits a\ntransition from a thermal to coherent statistics and the spatial coherence\nreveals off-diagonal long-range order.",
        "positive": "Evidence of spin liquid with hard-core bosons in a square lattice: We show that laser assisted hopping of hard core bosons in a square optical\nlattice can be described by an antiferromagnetic $J_{1}$-$J_{2}$ XY model with\ntunable ratio of $J_{2}/J_{1}$. We numerically investigate the phase diagram of\nthe $J_{1}$-$J_{2}$ XY model using both the tensor network algorithm for\ninfinite systems and the exact diagonalization for small clusters and find\nstrong evidence that in the intermediate region around $% J_{2}/J_{1}\\sim 0.5$,\nthere is a spin liquid phase with vanishing magnetization and valence bond\norders, which interconnects the Neel state on the $J_{2}\\ll J_{1}$ side and the\nstripe antiferromagnetic phase on the $% J_{2}\\gg J_{1}$ side. This finding\nopens up the possibility of studying the exotic spin liquid phase in a\nrealistic experimental system using ultracold atoms in an optical lattice."
    },
    {
        "anchor": "Observation of the Second Triatomic Resonance in Efimov's Scenario: We report the observation of a three-body recombination resonance in an\nultracold gas of cesium atoms at a very large negative value of the $s$-wave\nscattering length. The resonance is identified as the second triatomic Efimov\nresonance, which corresponds to the situation where the first excited Efimov\nstate appears at the threshold of three free atoms. This observation, together\nwith a finite-temperature analysis and the known first resonance, allows the\nmost accurate demonstration to date of the discrete scaling behavior at the\nheart of Efimov physics. For the system of three identical bosons, we obtain a\nscaling factor of $21.0(1.3)$, close to the ideal value of $22.7$.",
        "positive": "Monte Carlo study of quantum phase transitions at zero temperature: In this Ph.D. thesis quantum Monte Carlo methods are applied to investigate\nthe properties of a number of ultracold quantum systems. In Chapter 1 we\ndiscuss the analytical approaches and approximations used in the subsequent\nChapters; also we describe the general concepts of the two-particle scattering\nproblem as a tool to construct Jastrow terms in trial wave functions. Chapter 2\nexplains in details the Quantum Monte Carlo methods employed in our\ncalculations from the theoretical and practical points of view. In Chapter 3 we\nexplain the Ewald summation technique, applied to a power-law 1/|r|k\ninteraction potential, and a generic approach to obtain the Ewald terms. The\nobtained expressions of this analytic work are implemented into simulations of\ndifferent physically relevant systems (Rydberg atoms and Yukawa particles).\nChapter 5 is devoted to the modelling of a system, governed by the model\npotential between Rydberg atoms $1/r^6$. The phase diagram of the system is\nobtained for a relevant range of densities and temperatures, combining quantum\nsimulations at low temperature and classical treatment at higher temperature. A\nspecial attention is paid to the classical description of this system, composed\nof Rydberg atoms, and its comparison to the quantum system. In Chapter 4 we\npresent the simulation of a system with the Yukawa interaction potential. The\nfollowing Chapter 6 presents the results of the Quantum Monte Carlo simulations\nof molecular para-hydrogen at zero and finite temperatures, performed in our\nGroup. Conclusions are drawn in Chapter 7."
    },
    {
        "anchor": "Functional RG for imbalanced many-fermion systems: The Functional Renormalisation Group approach is applied the imbalanced\nmany-fermion systems. The system is found to exhibit the first order phase\ntransition from the superfluid to normal phase when the density (chemical\npotential) mismatch becomes larger then some critical values. The perspectives\nof using fermionic cold atoms to study nuclear/quark matter is briefly\ndiscussed.",
        "positive": "Micromagnetic modeling of magnon coherent states in a nonuniform\n  magnetic field: The study of the dynamics of magnetically ordered states in strong excitation\nthrough micromagnetic modeling has become relevant due to the observation of\nmagnon Bose condensation. In particular, the question has arisen about the\npossibility of describing the coherent quantum state by the quasi-classical\nLandau-Lifshitz-Gilbert equations. We performed micromagnetic simulations of\nmagnetization precession with a high angle of deviation in an out-of-plane\nnonuniform dc field. Our results confirm the formation of coherent magnon state\nunder conditions of high excitation. This coherent state extends over long\ndistances and described by a spatially inhomogeneous amplitude and a\nhomogeneous precession phase."
    },
    {
        "anchor": "Bipolarons bound by repulsive phonon-mediated interactions: When dressed particles (polarons) exchange quantum phonons, the resulting\ninteractions are generally attractive. If the particles have hard-core\nstatistics and the coupling to phonons is through the kinetic energy terms,\nphonon-mediated interactions are repulsive. Here, we show that such repulsive\nphonon-mediated interactions bind dressed particles into bipolarons with unique\nproperties. These bipolaron states appear in the gap between phonon\nexcitations, above the two-polaron continuum. While thermodynamically unstable,\nthe bipolaron is protected by energy and momentum conservation and represents a\nnovel quasiparticle with a large dispersion and a negative effective mass near\nzero momentum. We discuss possible experimental implementation of the\nconditions for the formation of such repulsively bound bipolarons.",
        "positive": "Simulating Chiral Magnetic and Separation Effects with Spin-Orbit\n  Coupled Atomic Gases: The chiral magnetic and chiral separation effects---quantum-anomaly-induced\nelectric current and chiral current along an external magnetic field in\nparity-odd quark-gluon plasma---have received intense studies in the community\nof heavy-ion collision physics. We show that analogous effects occur in\nrotating trapped Fermi gases with Weyl-Zeeman spin-orbit coupling where the\nrotation plays the role of an external magnetic field. These effects can induce\na mass quadrupole in the atomic cloud along the rotation axis which may be\ntested in future experiments. Our results suggest that the spin-orbit coupled\natomic gases are potential simulators of the chiral magnetic and separation\neffects."
    },
    {
        "anchor": "From GPE to KPZ: finite temperature dynamical structure factor of the 1D\n  Bose gas: We study the finite temperature dynamical structure factor $S(k,\\omega)$ of a\n1D Bose gas using numerical simulations of the Gross--Pitaevskii equation\nappropriate to a weakly interacting system. The lineshape of the phonon peaks\nin $S(k,\\omega)$ has a width $\\propto |k|^{3/2}$ at low wavevectors. This\nanomalous width arises from resonant three-phonon interactions, and reveals a\nremarkable connection to the Kardar--Parisi--Zhang universality class of\ndynamical critical phenomena.",
        "positive": "Phase diagram of the Bose Kondo-Hubbard model: We study a bosonic version of the Kondo lattice model with an on-site\nrepulsion in the conduction band, implemented with alkali atoms in two bands of\nan optical lattice. Using both weak and strong-coupling perturbation theory, we\nfind that at unit filling of the conduction bosons the superfluid to Mott\ninsulator transition should be accompanied by a magnetic transition from a\nferromagnet (in the superfluid) to a paramagnet (in the Mott insulator).\nFurthermore, an analytic treatment of Gutzwiller mean-field theory reveals that\nquantum spin fluctuations induced by the Kondo exchange cause the otherwise\ncontinuous superfluid to Mott-insulator phase transition to be first order. We\nshow that lattice separability imposes a serious constraint on proposals to\nexploit excited bands for quantum simulations, and discuss a way to overcome\nthis constraint in the context of our model by using an experimentally realized\nnon-separable lattice. A method to probe the first-order nature of the\ntransition based on collapses and revivals of the matter-wave field is also\ndiscussed."
    },
    {
        "anchor": "Implications of hydrodynamic fluctuations on the minimum shear viscosity\n  of the dilute Fermi gas at unitarity: We confirm and expand on work by Chafin and Schaefer on hydrodynamic\nfluctuations in the unitary Fermi gas. Using the result for the equation of\nstate from a recent MIT experiment, we derive lower bounds for \\eta/n and\n\\eta/s as a function of temperature. Re-analyzing recent quantum Monte Carlo\ndata for the shear-viscosity spectral function we point out a possible\nresolution for the tension between the viscosity bound \\eta/n> 0.3 from Chafin\nand Schaefer and the quantum Monte Carlo results \\eta/n<0.2$ from Wlazlowski et\nal. near the critical temperature",
        "positive": "Mapping out spin and particle conductances in a quantum point contact: We study particle and spin transport in a single mode quantum point contact\nusing a charge neutral, quantum degenerate Fermi gas with tunable, attractive\ninteractions. This yields the spin and particle conductance of the point\ncontact as a function of chemical potential or confinement. The measurements\ncover a regime from weak attraction, where quantized conductance is observed,\nto the resonantly interacting superfluid. Spin conductance exhibits a broad\nmaximum when varying the chemical potential at moderate interactions, which\nsignals the emergence of Cooper pairing. In contrast, the particle conductance\nis unexpectedly enhanced even before the gas is expected to turn into a\nsuperfluid, continuously rising from the plateau at 1/h for weak interactions\nto plateaux-like features at non-universal values as high as 4/h for\nintermediate interactions. For strong interactions, the particle conductance\nplateaux disappear and the spin conductance gets suppressed, confirming the\nspin-insulating character of a superfluid. Our observations document the\nbreakdown of universal conductance quantization as many-body correlations\nappear. The observed anomalous quantization challenges a Fermi liquid\ndescription of the normal phase, shedding new light on the nature of the\nstrongly attractive Fermi gases."
    },
    {
        "anchor": "The influence of the interaction between quasiparticles on parametric\n  resonance in Bose-Einstein quasicondensates: We perform a simulation of the experiment [1] where the temporal modification\nof the effective one dimensional interaction constant was used to create pairs\nof atoms with opposite velocities. The simulations clearly demonstrate huge\nimpact of interaction between quasiparticles due to finite temperature on the\npair production process, explaining relatively small atom pair production and\nthe absence of the number squeezing in the experiment.",
        "positive": "Binding of heavy fermions by a single light atom in one dimension: We consider the problem of $N$ identical fermions interacting via a\nzero-range attractive potential with a lighter atom in one dimension. Using the\nfew-body approach based on the Skorniakov and Ter-Martirosian equation, we\ndetermine the energies and the critical mass ratios for the emergence of the\ntetramer, pentamer, and hexamer. For large $N$, we solve the problem\nanalytically by using the mean-field theory based on the Thomas-Fermi\napproximation. The system becomes bound when the heavy-to-light mass ratio\nexceeds a critical value which grows as $N^3$ at large $N$. We also employ a\nmore sophisticated Hartree-Fock approach, which turns out to be equivalent to\nthe Thomas-Fermi approximation for determining the energies, but provides a\nbetter description of the microscopic structure of the clusters."
    },
    {
        "anchor": "Superfluidity, Sound Velocity and Quasi Condensation in the 2D BCS-BEC\n  Crossover: We study finite-temperature properties of a two-dimensional superfluid made\nof ultracold alkali-metal atoms in the BCS-BEC crossover. We investigate the\nregion below the critical temperature $T_{BKT}$ of the\nBerezinskii-Kosterlitz-Thouless phase transition, where there is\nquasi-condensation, by analyzing the effects of phase and amplitude\nfluctuations of the order parameter. In particular, we calculate the superfluid\nfraction, the sound velocity and the quasi-condensate fraction as a function of\nthe temperature and of the binding energy of fermionic pairs.",
        "positive": "Observation of $1/k^4$-tails after expansion of Bose-Einstein\n  Condensates with impurities: We measure the momentum density in a Bose-Einstein condensate (BEC) with\ndilute spin impurities after an expansion in the presence of interactions. We\nobserve tails decaying as $1/k^4$ at large momentum $k$ in the condensate and\nin the impurity cloud. These algebraic tails originate from the impurity-BEC\ninteraction, but their amplitudes greatly exceed those expected from two-body\ncontact interactions at equilibrium in the trap. Furthermore, in the absence of\nimpurities, such algebraic tails are not found in the BEC density measured\nafter the interaction-driven expansion. These results highlight the key role\nplayed by impurities when present, a possibility that had not been considered\nin our previous work [Phys. Rev. Lett. 117, 235303 (2016)]. Our measurements\nsuggest that these unexpected algebraic tails originate from the non-trivial\ndynamics of the expansion in the presence of impurity-bath interactions."
    },
    {
        "anchor": "Itinerant Ferromagnetism in a polarized two-component Fermi gas: We analyze when a repulsively interacting two-component Fermi gas becomes\nthermodynamically unstable against phase separation. We focus on the strongly\npolarised limit where the free energy of the homogeneous mixture can be\ncalculated accurately in terms of well-defined quasiparticles, the repulsive\npolarons. Phase diagrams as a function of polarisation, temperature, mass\nimbalance, and repulsive polaron energy, as well as scattering length and range\nparameter are provided. We show that the lifetime of the repulsive polaron\nincreases significantly with the interaction range and the mass of the minority\natoms, raising the prospects of detecting the transition to the elusive\nitinerant ferromagnetic state with ultracold atoms.",
        "positive": "Two types of dark solitons in a spin-orbit-coupled Fermi gas: Dark solitons in quantum fluids are well known nonlinear excitations that are\nusually characterized by a single length scale associated with the underlying\nbackground fluid. We show that in the presence of spin-orbit coupling and a\nlinear Zeeman field, superfluid Fermi gases support two different types of\nnonlinear excitations featured by corresponding length scales related to the\nexistence of two Fermi surfaces. Only one of these types, which occurs for\nfinite spin-orbit coupling and a Zeeman field, survives to the topological\nphase transition, and is therefore capable to sustain Majorana zero modes. At\nthe point of the emergence of this soliton for varying the Zeeman field, the\nassociated Andreev bound states present a minigap that vanishes for practical\npurposes, in spite of lacking the reality condition of Majorana modes."
    },
    {
        "anchor": "The role of interaction-induced tunneling in the dynamics of polar\n  lattice bosons: Inter-site dipolar interactions induce, even in absence of disorder, an\nintriguing non-ergodic dynamics for dipolar bosons in an optical lattice. We\nshow that the inherent dipole-induced density-dependent tunneling, typically\nneglected, plays a crucial role in this dynamics. For shallow-enough lattices,\nthe delocalization stemming from the interaction-induced hopping overcomes the\nlocalization induced by inter-site interactions. As a result, in stark contrast\nto the more studied case of hard-core bosons, delocalization is\ncounter-intuitively strengthen when the dipolar strength increases.\nFurthermore, the quasi-cancellation between bare and interaction-induced\ntunneling may lead, near a lattice-depth-dependent value of the dipole\nstrength, to an exact decoupling of the Hilbert space between ergodic hard-core\nstates and strongly non-ergodic soft-core ones. Our results show that\ninteraction-induced hopping should play a crucial role in future experiments on\nthe dynamics of polar lattice gases.",
        "positive": "Effect of spin-orbit coupling on tunnelling escape of Bose-Einstein\n  condensate: We theoretically investigate quantum tunnelling escape of a spin-orbit (SO)\ncoupled Bose-Einstein condensate (BEC) from a trapping well. The condensate is\ninitially prepared in a quasi-one-dimensional harmonic trap. Depending on the\nsystem parameters, the ground state can fall in different phases --- single\nminimum, separated or stripe. Then, suddenly the trapping well is opened at one\nside. The subsequent dynamics of the condensate is studied by solving nonlinear\nSchr\\\"{o}dinger equations. We found that the diverse phases will greatly change\nthe tunneling escape behavior of SO coupled BECs. In single minimum and\nseparated phases, the condensate escapes the trapping well continuously, while\nin stripe phase it escapes the well as an array of pulses. We also found that\nSO coupling has a suppressing effect on the tunnelling escape of atoms.\nEspecially, for BECs without inter-atom interaction, the tunnelling escape can\nbe almost completely eliminated when the system is tuned near the transition\npoint between single minimum and stripe phase. Our work thus suggests that SO\ncoupling may be a useful tool to control the tunnelling dynamic of BECs, and\npotentially be applied in realization of atom lasers and matter wave switches."
    },
    {
        "anchor": "Two classes of organization principle: quantum/topological phase\n  transitions meet complete/in-complete devil staircases and their experimental\n  realizations: There exists many quantum or topological phases in Nature. One well known\norganization principle is through various quantum or topological phases\ntransitions between or among these phases. Another is through either complete\nor in-complete devil staircases in their quantized forms. Here, we show that\nboth classes of organization principle appear in an experimentally accessible\nsystem: strongly interacting spinor bosons subject to any of the linear\ncombinations of the Rashba and Dresselhaus spin-orbit coupling (SOC) in the\nspace of the two SOC parameters $ ( \\alpha, \\beta) $ in a square lattice. In\nthe strong coupling limit, it leads to a new quantum spin model called Rotated\nFerromagnetic Heisenberg model (RFHM). The RFHM leads to rich and\nunconventional magnetic phases even in a bipartite lattice. For the first\nclass, by identifying a suitable low energy mode, we investigate a new quantum\nLifshitz transition from the Y-x to the IC-SkX-y phase. For the second class,\nwe introduce the topological rational and irrational winding numbers $ W $ to\ncharacterize the incomplete or complete devil staircases and also perform their\nquantizations. The IC-YZ-x/LQx phases form a Cantor set with a fractal\ndimension along the complete devil staircase. They also take most of measures\nin the incomplete devil staircases when $ \\beta \\ll \\alpha $. Quantum chaos and\nquantum information scramblings along the diagonal line $ \\alpha=\\beta $ are\ndiscussed. Implications on un-conventional magnetic ordered phases detected in\nthe 4d- or 5d-orbital strongly correlated materials with SOC and in the current\nor near future cold atom systems are presented.",
        "positive": "Synthetic Dimensions with Magnetic Fields and Local Interactions in\n  Photonic Lattices: We discuss how one can realize a photonic device that combines synthetic\ndimensions and synthetic magnetic fields with spatially local interactions.\nUsing an array of ring cavities, the angular coordinate around each cavity\nspans the synthetic dimension. The synthetic magnetic field arises as the\nintercavity photon hopping is associated with a change of angular momentum.\nPhoton-photon interactions are local in the periodic angular coordinate around\neach cavity. Experimentally observable consequences of the synthetic magnetic\nfield and of the local interactions are pointed out."
    },
    {
        "anchor": "Many-body adiabatic passage: Quantum detours around chaos: We study the many-body dynamics of stimulated Raman adiabatic passage in the\npresence of on-site interactions. In the classical mean-field limit, explored\nin Phys. Rev. Lett. {\\bf 121}, 250405 (2018), interaction-induced chaos leads\nto the breakdown of adiabaticity under the quasi-static variation of the\nparameters, thus producing {\\em low} sweep rate boundaries on efficient\npopulation transfer. We show that for the corresponding many-body system,\nalternative quantum pathways from the initial to the target state, open up at\neven slower sweep rates. These quantum detours avoid the chaotic classical path\nand hence allow a robust and efficient population transfer.",
        "positive": "Onsager vortex formation in Bose-Einstein condensates in two-dimensional\n  power-law traps: We study computationally dynamics of quantised vortices in two-dimensional\nsuperfluid Bose-Einstein condensates confined in highly oblate power-law traps.\nWe have found that the formation of large scale Onsager vortex clusters\nprevalent in steep-walled traps is suppressed in condensates confined by\nharmonic potentials. However, the shape of the trapping potential does not\nappear to adversely affect the evaporative heating efficiency of the vortex\ngas. Instead, the suppression of Onsager vortex formation in harmonic traps can\nbe understood in terms of the energy of the vortex configurations. Furthermore,\nwe find that the vortex-antivortex pair annihilation that underpins the vortex\nevaporative heating mechanism requires the interaction of at least three\nvortices. We conclude that experimental observation of Onsager vortices should\nbe the most apparent in flat or inverted-bottom traps."
    },
    {
        "anchor": "Electronic properties and polaronic dynamics of semi-Dirac system within\n  ladder approximation: We investigate the electronic properties of the semi-Dirac system and its\npolaronic dynamics when coupled with a fermi bath with quadratic dispersion.\nThe electronic anisotropic transport properties and the semiclassical dynamics\nof the semi-Dirac system are studied, including the density-of-states,\nconductivity, transport relaxation rate, specific heat, electrical current\ndenity, and free energy. The attractive polaron formed as the semi-Dirac\nimpurity dressed with the particle-hole excitations in a two-dimensional system\nare studied both analytically and numerically. The pair propagator,\nself-energy, spectral function are being detailly calculated and discussed.",
        "positive": "Bilayer fractional quantum Hall states with ultracold dysprosium: We show how dipolar interactions between dysprosium atoms in an optical\nlattice can be used to obtain fractional quantum Hall states. In our approach,\ndysprosium atoms are trapped one atom per site in a deep optical lattice with\nnegligible tunneling. Microwave and spatially dependent optical dressing fields\nare used to define an effective spin-1/2 or spin-1 degree of freedom in each\natom. Thinking of spin-1/2 particles as hardcore bosons, dipole-dipole\ninteractions give rise to boson hopping, topological flat bands with Chern\nnumber 1, and the \\nu = 1/2 Laughlin state. Thinking of spin-1 particles as\ntwo-component hardcore bosons, dipole-dipole interactions again give rise to\nboson hopping, topological flat bands with Chern number 2, and the bilayer\nHalperin (2,2,1) state. By adjusting the optical fields, we find a phase\ndiagram, in which the (2,2,1) state competes with superfluidity.\nGeneralizations to solid-state magnetic dipoles are discussed."
    },
    {
        "anchor": "Topological Varma superfluid in optical lattices: Topological states of matter are peculiar quantum phases showing different\nedge and bulk transport properties connected by the bulk-boundary\ncorrespondence. While non-interacting fermionic topological insulators are well\nestablished by now and have been classified according to a ten-fold scheme, the\npossible realisation of topological states for bosons has not been much\nexplored yet. Furthermore, the role of interactions is far from being\nunderstood. Here, we show that a topological state of matter exclusively driven\nby interactions may occur in the p-band of a Lieb optical lattice filled with\nultracold bosons. The single-particle spectrum of the system displays a\nremarkable parabolic band-touching point, with both bands exhibiting\nnon-negative curvature. Although the system is neither topological at the\nsingle-particle level, nor for the interacting ground state, on-site\ninteractions induce an anomalous Hall effect for the excitations, carrying a\nnon-zero Chern number. Our work introduces an experimentally realistic strategy\nfor the formation of interaction-driven topological states of bosons.",
        "positive": "Scattering amplitudes for dark and bright excitons: Using the composite boson many-body formalism that takes single-exciton\nstates rather than free carrier states as a basis, we derive the integral\nequation fulfilled by the exciton-exciton effective scattering from which the\nrole of fermion exchanges can be unraveled. For excitons made of\n$(\\pm1/2)$-spin electrons and $(\\pm3/2)$-spin holes, as in GaAs\nheterostructures, one major result is that most spin configurations lead to\nbrightness-conserving scatterings with equal amplitude $\\Delta$, in spite of\nthe fact that they involve different carrier exchanges. A brightness-changing\nchannel also exists when two opposite-spin excitons scatter: dark excitons\n$(2,-2)$ can end either in the same dark states with an amplitude $\\Delta_e$,\nor in opposite-spin bright states $(1,-1)$, with a different amplitude\n$\\Delta_o$, the number of carrier exchanges being even or odd respectively.\nAnother major result is that these amplitudes are linked by a striking\nrelation, $\\Delta_e+\\Delta_o=\\Delta$, which has decisive consequence for\nexciton Bose-Einstein condensation. Indeed, this relation leads to the\nconclusion that the exciton condensate can be optically observed through a\nbright part only when excitons have a large dipole, that is, when the electrons\nand holes are well separated in two adjacent layers."
    },
    {
        "anchor": "Fracton-elasticity duality of two-dimensional superfluid vortex\n  crystals: defect interactions and quantum melting: Employing the fracton-elastic duality, we develop a low-energy effective\ntheory of a zero-temperature vortex crystal in a two-dimensional bosonic\nsuperfluid which naturally incorporates crystalline topological defects. We\nextract static interactions between these defects and investigate several\ncontinuous quantum transitions triggered by the Higgs condensation of vortex\nvacancies/interstitials and dislocations. We propose that the quantum melting\nof the vortex crystal towards the hexatic or smectic phase may occur via a pair\nof continuous transitions separated by an intermediate vortex supersolid phase.",
        "positive": "Dimensional crossover in the superfluid-supersolid quantum phase\n  transition: We assess experimentally and theoretically the character of the\nsuperfluid-supersolid quantum phase transition recently discovered in trapped\ndipolar quantum gases. We find that one-row supersolids can have already two\ntypes of phase transitions, discontinuous and continuous, that are reminiscent\nof the first- and second-order transitions predicted in the thermodynamic limit\nin 2D and 1D, respectively. The smooth crossover between the two regimes is\npeculiar to supersolids and can be controlled via the transverse confinement\nand the atom number. We justify our observations on the general ground of the\nLandau theory of phase transitions. The quasi-adiabatic crossing of a\ncontinuous phase transition opens new directions of investigation for\nsupersolids."
    },
    {
        "anchor": "Topological orbital ladders: We unveil a topological phase of interacting fermions on a two-leg ladder of\nunequal parity orbitals, derived from the experimentally realized double-well\nlattices by dimension reduction. $Z_2$ topological invariant originates simply\nfrom the staggered phases of $sp$-orbital quantum tunneling, requiring none of\nthe previously known mechanisms such as spin-orbit coupling or artificial gauge\nfield. Another unique feature is that upon crossing over to two dimensions with\ncoupled ladders, the edge modes from each ladder form a parity-protected flat\nband at zero energy, opening the route to strongly correlated states controlled\nby interactions. Experimental signatures are found in density correlations and\nphase transitions to trivial band and Mott insulators.",
        "positive": "Novel Fermi Liquid of 2D Polar Molecules: We study Fermi liquid properties of a weakly interacting 2D gas of\nsingle-component fermionic polar molecules with dipole moments $d$ oriented\nperpendicularly to the plane of their translational motion. This geometry\nallows the minimization of inelastic losses due to chemical reactions for\nreactive molecules and, at the same time, provides a possibility of a clear\ndescription of many-body (beyond mean field) effects. The long-range character\nof the dipole-dipole repulsive interaction between the molecules, which scales\nas $1/r^3$ at large distances $r$, makes the problem drastically different from\nthe well-known problem of the two-species Fermi gas with repulsive contact\ninterspecies interaction. We solve the low-energy scattering problem and\ndevelop a many-body perturbation theory beyond the mean field. The theory\nrelies on the presence of a small parameter $k_Fr_*$, where $k_F$ is the Fermi\nmomentum, and $r_*=md^2/\\hbar^2$ is the dipole-dipole length, with $m$ being\nthe molecule mass. We obtain thermodynamic quantities as a series of expansion\nup to the second order in $k_Fr_*$ and argue that many-body corrections to the\nground-state energy can be identified in experiments with ultracold molecules,\nlike it has been recently done for ultracold fermionic atoms. Moreover, we show\nthat only many-body effects provide the existence of zero sound and calculate\nthe sound velocity."
    },
    {
        "anchor": "Absence of thermalisation in a Fermi liquid: We study a weak interaction quench in a three-dimensional Fermi gas. We first\nshow that, under some general assumptions on time-dependent perturbation\ntheory, the perturbative expansion of the long-wavelength structure factor\n$S(\\bq)$ is not compatible with the hypothesis that steady-state averages\ncorrespond to thermal ones. In particular, $S(\\bq)$ does develop an analytical\ncomponent $\\sim const. + O(q^2)$ at $\\bq\\to\\bnot$, as implied by\nthermalization, but, in contrast, it maintains a non-analytic part $\\sim |\\bq|$\ncharacteristic of a Fermi-liquid at zero-temperature. In real space, this\nnon-analyticity corresponds to persisting power-law decaying density-density\ncorrelations, whereas thermalization would predict only an exponential decay.\nWe next consider the case of a dilute gas, where one can obtain\nnon-perturbative results in the interaction strength but at lowest order in the\ndensity. We find that in the steady-state the momentum distribution jump at the\nFermi surface remains finite, though smaller than in equilibrium, up to second\norder in $k_F f_0$, where $f_0$ is the scattering length of two particles in\nthe vacuum. Both results question the emergence of a finite length scale in the\nquench-dynamics as expected by thermalization.",
        "positive": "Condensation and thermalization of an easy-plane ferromagnet in a spinor\n  Bose gas: The extensive control of spin makes spintronics a promising candidate for\nfuture scalable quantum devices. For the generation of spin-superfluid systems,\na detailed understanding of the build-up of coherence and relaxation is\nnecessary. However, to determine the relevant parameters for robust coherence\nproperties and faithfully witnessing thermalization, the direct access to\nspace- and time-resolved spin observables is needed. Here, we study the\nthermalization of an easy-plane ferromagnet employing a homogeneous\none-dimensional spinor Bose gas. Building on the pristine control of\npreparation and readout we demonstrate the dynamic emergence of long-range\ncoherence for the spin field and verify spin-superfluidity by experimentally\ntesting Landau's criterion. We reveal the structure of the emergent\nquasi-particles: one 'massive'(Higgs) mode, and two 'massless' (Goldstone)\nmodes - a consequence of explicit and spontaneous symmetry breaking,\nrespectively. Our experiments allow for the first time to observe the\nthermalization of an easy-plane ferromagnetic Bose gas; we find agreement for\nthe relevant momentum-resolved observables with a thermal prediction obtained\nfrom an underlying microscopic model within the Bogoliubov approximation. Our\nmethods and results pave the way towards a quantitative understanding of\ncondensation dynamics in large magnetic spin systems and the study of the role\nof entanglement and topological excitations for its thermalization."
    },
    {
        "anchor": "Quantum Fluctuation Driven First-order Phase Transitions in Optical\n  Lattices: We study quantum fluctuation driven first-order phase transitions of a\ntwo-species bosonic system in a three-dimensional optical lattice. Using\neffective potential method we find that the superfluid-Mott insulator phase\ntransition of one type of bosons can be changed from second-order to\nfirst-order by the quantum fluctuations of the other type of bosons. The study\nof the scaling behaviors near the quantum critical point shows that the\nfirst-order phase transition has a different universality from the second-order\none. We also discuss the observation of this exotic phenomenon in the realistic\ncold-atom experiments.",
        "positive": "Nonlinear multi-state tunneling dynamics in a spinor Bose-Einstein\n  condensate: We present an experimental realization of dynamic self-trapping and\nnon-exponential tunneling in a multi-state system consisting of ultracold\nsodium spinor gases confined in moving optical lattices. Taking advantage of\nthe fact that the tunneling process in the sodium spinor system is resolvable\nover a broader dynamic energy scale than previously observed in rubidium scalar\ngases, we demonstrate that the tunneling dynamics in the multi-state system\nstrongly depends on an interaction induced nonlinearity and is influenced by\nthe spin degree of freedom under certain conditions. We develop a rigorous\nmulti-state tunneling model to describe the observed dynamics. Combined with\nour recent observation of spatially-manipulated spin dynamics, these results\nopen up prospects for alternative multi-state ramps and state transfer\nprotocols."
    },
    {
        "anchor": "Stable Fractional Vortices in the Cyclic States of Bose-Einstein\n  Condensates: We propose methods to create fractional vortices in the cyclic state of an F\n= 2 spinor Bose-Einstein condensate by manipulating its internal spin structure\nusing pulsed microwave and laser fields. The stability of such vortices is\nstudied as a function of the rotation frequency of the confining harmonic trap\nboth in pancake and cigar shaped condensates. We find a range of parameters for\nwhich the so-called 1/3-vortex state is energetically favorable. Such\nfractional vortices could be created in condensates of 87Rb atoms using current\nexperimental techniques facilitating probing of topological defects with\nnon-Abelian statistics.",
        "positive": "Quantum Monte Carlo simulation of thermodynamic properties of SU(2N)\n  ultracold fermions in optical lattices: We have systematically studied the thermodynamic properties of a\ntwo-dimensional half-filled SU(2N) Hubbard model on a square lattice by using\nthe determinant quantum Monte Carlo method. The entropy-temperature relation,\nthe isoentropy curve, and the probability distribution of the onsite occupation\nnumber are calculated in both SU(4) and SU(6) cases, which exhibit prominent\nfeatures of the Pomeranchuk effect. We analyze these thermodynamic behaviors\nbased on charge and spin energy scales. In the charge channel, the interaction\nstrength that marks the crossover from the weak to strong interaction regimes\nincreases with the number of fermion components. In the spin channel,\nincreasing the number of fermion components enhances quantum spin fluctuations,\nwhich is shown in the simulations of uniform spin susceptibilities and\nantiferromagnetic structure factors."
    },
    {
        "anchor": "Physics of Low-Dimensional Ultracold Bose Gases: In this work we investigate the unique properties of ultracold Bose gases in\none and two dimensions. In two dimensions, we present simulations of the\nBerezinskii-Kosterlitz-Thouless (BKT) phase transition using the projected\nGross-Pitaevskii equation formalism. We confirm the presence of the BKT phase\nby observing algebraic decay in the first-order correlation function, unbinding\nof vortex pairs, and behaviour of the superfluid fraction. In one dimension we\nuse a transverse Gaussian ansatz and the Lagrangian approach to derive an\neffective equation of motion for the one dimensional Bose gas at zero\ntemperature.",
        "positive": "Size and dynamics of vortex dipoles in dilute Bose-Einstein condensates: Recently, Freilich et al. [Science 329, 1182 (2010)] experimentally\ndiscovered stationary states of vortex dipoles, pairs of vortices of opposite\ncirculation, in dilute Bose-Einstein condensates. To explain their\nobservations, we perform simulations based on the Gross-Pitaevskii equation and\nobtain excellent quantitative agreement on the size of the stationary dipole.\nWe also investigate how their imaging method, in which atoms are repeatedly\nextracted from a single condensate, affects the vortex dynamics. We find that\nit mainly induces isotropic size oscillations of the condensate without\notherwise disturbing the vortex trajectories. Thus, the imaging technique\nappears to be a promising tool for studying real-time superfluid dynamics."
    },
    {
        "anchor": "Resolving the puzzle of sound propagation in a dilute Bose-Einstein\n  condensate: A unified model of a dilute Bose-Einstein condensate is proposed, combining\nof the logarithmic and Gross-Pitaevskii nonlinear terms in a wave equation,\nwhere the Gross-Pitaevskii term describes two-body interactions, as suggested\nby standard perturbation theory; while the logarithmic term is essentially\nnon-perturbative, and takes into account quantum vacuum effects. The model is\nshown to have excellent agreement with sound propagation data in the condensate\nof cold sodium atoms known since the now classic works by Andrews and\ncollaborators. The data also allowed us to place constraints on two of the\nunified model's parameters, which describe the strengths of the logarithmic and\nGross-Pitaevskii terms. Additionally, we suggest an experiment constraining the\nvalue of the third parameter (the characteristic density scale of the\nlogarithmic part of the model), using the conjectured attraction-repulsion\ntransition of many-body interaction inside the condensate.",
        "positive": "Controlling phase separation of a two-component Bose-Einstein condensate\n  by confinement: We point out that the widely accepted condition g11g22<g122 for phase\nseparation of a two-component Bose-Einstein condensate is insufficient if\nkinetic energy is taken into account, which competes against the intercomponent\ninteraction and favors phase mixing. Here g11, g22, and g12 are the intra- and\nintercomponent interaction strengths, respectively. Taking a d-dimensional\ninfinitely deep square well potential of width L as an example, a simple\nscaling analysis shows that if d=1 (d=3), phase separation will be suppressed\nas L\\rightarrow0 (L\\rightarrow\\infty) whether the condition g11g22<g122 is\nsatisfied or not. In the intermediate case of d=2, the width L is irrelevant\nbut again phase separation can be partially or even completely suppressed even\nif g11g22<g122. Moreover, the miscibility-immiscibility transition is turned\nfrom a first-order one into a second-order one by the kinetic energy. All these\nresults carry over to d-dimensional harmonic potentials, where the harmonic\noscillator length {\\xi}ho plays the role of L. Our finding provides a scenario\nof controlling the miscibility-immiscibility transition of a two-component\ncondensate by changing the confinement, instead of the conventional approach of\nchanging the values of the g's."
    },
    {
        "anchor": "Resistive flow in a weakly interacting Bose-Einstein condensate: We report the direct observation of resistive flow through a weak link in a\nweakly interacting atomic Bose-Einstein condensate. Two weak links separate our\nring-shaped superfluid atomtronic circuit into two distinct regions, a source\nand a drain. Motion of these weak links allows for creation of controlled flow\nbetween the source and the drain. At a critical value of the weak link\nvelocity, we observe a transition from superfluid flow to superfluid plus\nresistive flow. Working in the hydrodynamic limit, we observe a conductivity\nthat is 4 orders of magnitude larger than previously reported conductivities\nfor a Bose-Einstein condensate with a tunnel junction. Good agreement with\nzero-temperature Gross-Pitaevskii simulations and a phenomenological model\nbased on phase slips indicate that the creation of excitations plays an\nimportant role in the resulting conductivity. Our measurements of resistive\nflow elucidate the microscopic origin of the dissipation and pave the way for\nmore complex atomtronic devices.",
        "positive": "Superfluid-insulator transition of two-dimensional disordered Bose gases: We study the two-dimensional weakly repulsive Bose gas at zero temperature in\nthe presence of correlated disorder. Using large-scale simulations, we show\nthat the low-energy Bogoliubov cumulative density of states remains quadratic\nup to a critical disorder strength, beyond which a power law with\ndisorder-dependent exponent $\\beta<2$ sets in. We associate this threshold\nbehavior with the transition from superfluid to Bose glass, and compare the\nresulting mean-field phase diagram with scaling laws and the Thomas-Fermi\npercolation threshold of the mean-field density profile."
    },
    {
        "anchor": "Phonon damping in a 2D superfluid: insufficiency of Fermi's golden rule\n  at low temperature: It is generally accepted that the phonon gas of a superfluid always enters a\nweak coupling regime at sufficiently low temperatures, whatever the strength of\nthe interactions between the underlying particles (constitutive of the\nsuperfluid). Thus, in this limit, we should always be able to calculate the\ndamping rate of thermal phonons by applying Fermi's golden rule to the $H\\_3$\nHamiltonian of cubic phonon-phonon coupling taken from quantum hydrodynamics,\nat least in the case of a convex acoustic branch and in the collisionless\nregime (where the eigenfrequency of the considered phonons remains much greater\nthan the gas thermalization rate). Using the many-body Green's function method,\nwe predict that, unexpectedly, this is not true in two dimensions, contrary to\nthe three-dimensional case. We confirm this prediction with classical\nphonon-field simulations and a non-perturbative theory in $H\\_3$, where the\nfourth order is regularized by hand, giving a complex energy to the virtual\nphonons of the four-phonon collisional processes. For a weakly interacting\nfluid and a phonon mode in the long-wavelength limit, we predict a damping rate\nabout three times lower than that of the golden rule.",
        "positive": "Topological invariant and cotranslational symmetry in strongly\n  interacting multi-magnon systems: It is still an outstanding challenge to characterize and understand the\ntopological features of strongly interacting states such as bound-states in\ninteracting quantum systems. Here, by introducing a cotranslational symmetry in\nan interacting multi-particle quantum system, we systematically develop a\nmethod to define a Chern invariant, which is a generalization of the well-known\nThouless-Kohmoto-Nightingale-den Nijs invariant, for identifying strongly\ninteracting topological states. As an example, we study the topological\nmulti-magnon states in a generalized Heisenberg XXZ model, which can be\nrealized by the currently available experiment techniques of cold atoms [Phys.\nRev. Lett. \\textbf{111}, 185301 (2013); Phys. Rev. Lett. \\textbf{111}, 185302\n(2013)]. Through calculating the two-magnon excitation spectrum and the defined\nChern number, we explore the emergence of topological edge bound-states and\ngive their topological phase diagram. We also analytically derive an effective\nsingle-particle Hofstadter superlattice model for a better understanding of the\ntopological bound-states. Our results not only provide a new approach to\ndefining a topological invariant for interacting multi-particle systems, but\nalso give insights into the characterization and understanding of strongly\ninteracting topological states."
    },
    {
        "anchor": "Quantitative analysis of $p$-wave three-body losses via cascade process: We describe the three-body loss coefficient of identical fermions with\n$p$-wave interactions using a set of rate equations in which three-body\nrecombination happens via an indirect process. Our theoretical treatment\nexplains experimental results just above the universal scaling law regime of\nweak interactions. Furthermore, we theoretically extend and experimentally\nverify the rate equation model for the case of atoms trapped in two dimensions.\nMoreover, we find that the three-body loss coefficient in a two-dimensional\ntrap is proportional to $A_{p}^{3}$ in the weakly interacting regime, where\n$A_{p}$ is the scattering area. Our results are useful in understanding\nthree-body physics with $p$-wave interactions.",
        "positive": "Anomalous pairing of bosons: Effect of multi body interactions in\n  optical lattice: An interesting first order type phase transition between Mott lobes has been\nreported in Phys. Rev. Lett. 109, 135302 (2012) for a two-dimensional\nBose-Hubbard model in the presence of attractive three-body interaction. We\nre-visit the scenario in a system of ultracold bosons in a one-dimensional\noptical lattice using the density matrix renormalization group method and show\nthat an unconventional pairing of particles occurs due to the competing\ntwo-body repulsive and three-body attractive interactions. This leads to a pair\nsuperfluid phase sandwiched between the Mott insulator lobes corresponding to\ndensities $\\rho=1$ and $\\rho=3$ in the strongly interacting regime. We further\nextend our analysis to a two dimensional Bose-Hubbard model using the self\nconsistent cluster-mean-field theory approach and confirm that the\nunconventional pair superfluid phase stabilizes in the region between the Mott\nlobes in contrast to the direct first order jump as predicted before. In the\nend we establish connection to the most general Bose-Hubbard model and analyse\nthe fate of the pair superfluid phase in presence of an external trapping\npotential."
    },
    {
        "anchor": "Induced interactions in dilute atomic gases and liquid helium mixtures: In dilute mixtures of two atomic gases, interactions between two minority\natoms acquire a contribution due to interaction with the majority component.\nUsing thermodynamic arguments, we derive expressions for this induced\ninteraction for both fermions and bosons for arbitrary strength of the\ninteraction between the two components. Implications of the work for the theory\nof dilute solutions of $^3$He in liquid $^4$He are discussed.",
        "positive": "Outcoupling from a Bose-Einstein condensate in the strong-field limit: Atoms can be extracted from a trapped Bose-Einstein condensate (BEC) by\ndriving spin-flips to untrapped states. The coherence properties of the BEC are\ntransfered to the released atoms, creating a coherent beam of matter refered to\nas an atom laser. In this work, the extraction of atoms from a BEC is\ninvestigated numerically by solving a coupled set of Gross-Pitaevskii equations\nin up to three dimensions. The result is compared to experimental data and a\nsemiclassical rate model. In the weak-coupling regime, quantitative agreement\nis reached between theory and experiment and a semiclassical rate model. In the\nstrong-coupling regime, the atom laser enters a trapped state that manifests\nitself in a saturation of the rate of out-coupled atoms observed in new\nexperimental data. The semiclassical rate model fails, but the numerical\ndescriptions yield qualitative agreement with experimental data at the onset of\nsaturation."
    },
    {
        "anchor": "Momentum-resolved observation of thermal and quantum depletion in an\n  interacting Bose gas: We report on the single-atom-resolved measurement of the distribution of\nmomenta $\\hbar k$ in a weakly interacting Bose gas after a 330 ms\ntime-of-flight. We investigate it for various temperatures and clearly separate\ntwo contributions to the depletion of the condensate by their $k$-dependence.\nThe first one is the thermal depletion. The second contribution falls of as\n$k^{-4}$, and its magnitude increases with the in-trap condensate density as\npredicted by the Bogoliubov theory at zero temperature. These observations\nsuggest associating it with the quantum depletion. How this contribution can\nsurvive the expansion of the released interacting condensate is an intriguing\nopen question.",
        "positive": "Experimental Demonstration of a Synthetic Lorentz Force by Using\n  Radiation Pressure: Synthetic magnetism in cold atomic gases opened the doors to many exciting\nnovel physical systems and phenomena. Ubiquitous are the methods used for the\ncreation of synthetic magnetic fields. They include rapidly rotating\nBose-Einstein condensates employing the analogy between the Coriolis and the\nLorentz force, and laser-atom interactions employing the analogy between the\nBerry phase and the Aharonov-Bohm phase. Interestingly, radiation pressure -\nbeing one of the most common forces induced by light - has not yet been used\nfor synthetic magnetism. We experimentally demonstrate a synthetic Lorentz\nforce, based on the radiation pressure and the Doppler effect, by observing the\ncentre-of-mass motion of a cold atomic cloud. The force is perpendicular to the\nvelocity of the cold atomic cloud, and zero for the cloud at rest. Our novel\nconcept is straightforward to implement in a large volume, for a broad range of\nvelocities, and can be extended to different geometries."
    },
    {
        "anchor": "Condensate fraction in metallic superconductors and ultracold atomic\n  vapors: We investigate the condensate density and the condensate fraction of\nconduction electrons in weak-coupling superconductors by using the BCS theory\nand the concept of off-diagonal-long-range-order. We discuss the analytical\nformula of the zero-temperature condensate density of Cooper pairs as a\nfunction of Debye frequency and energy gap, and calculate the condensate\nfraction for some metals. We study the density of Cooper pairs also at finite\ntemperature showing its connection with the gap order parameter and the effects\nof the electron-phonon coupling. Finally, we analyze similarities and\ndifferences between superconductors and ultracold Fermi atoms in the\ndetermination of their condensate density by using the BCS theory.",
        "positive": "Thermal phase transitions for Dicke-type models in the ultra-strong\n  coupling limit: We consider the Dicke model in the ultra-strong coupling limit to investigate\nthermal phase transitions and their precursors at finite particle numbers $N$\nfor bosonic and fermionic systems. We derive partition functions with\ndegeneracy factors that account for the number of configurations and derive\nexplicit expressions for the Landau free energy. This allows us to discuss the\ndifference between the original Dicke (fermionic) and the bosonic case. We find\na crossover between these two cases that shows up, e.g., in the specific heat."
    },
    {
        "anchor": "Exploring Symmetry Breaking at the Dicke Quantum Phase Transition: We study symmetry breaking at the Dicke quantum phase transition by coupling\na motional degree of freedom of a Bose-Einstein condensate to the field of an\noptical cavity. Using an optical heterodyne detection scheme we observe\nsymmetry breaking in real-time and distinguish the two superradiant phases. We\nexplore the process of symmetry breaking in the presence of a small\nsymmetry-breaking field, and study its dependence on the rate at which the\ncritical point is crossed. Coherent switching between the two ordered phases is\ndemonstrated.",
        "positive": "Observing dipolar confinement-induced resonances in waveguides: We develop a theoretical framework for the quasi-low-dimensional\nconfinement-induced resonances (CIRs) of particles with the arbitrary\nthree-dimensional two-body interactions, based on the Huang-Yang\npseudopotential and the treatment of Feshbach resonances. Using this new\napproach, we analytically obtain some universal properties of dipolar CIRs in\nquasi-one-dimensional (1D) waveguides. We also show that the dipolar CIRs can\nbe induced by tuning the angle between the dipole moments and the waveguide,\nwhich is experimentally observable in quasi-1D Cr and Dy atomic gases. We\nexpect that these tilting angle induced CIRs will open up a new simpler way to\ncontrol the resonant scatterings in quasi-low-dimensional systems."
    },
    {
        "anchor": "Emergent Kinetics and Fractionalized Charge in 1D Spin-Orbit Coupled\n  Flatband Optical Lattices: Recent ultracold atomic gas experiments implementing synthetic spin-orbit\ncoupling allow access to flatbands that emphasize interactions. We model\nspin-orbit coupled fermions in a one-dimensional flatband optical lattice. We\nintroduce an effective Luttinger-liquid theory to show that interactions\ngenerate collective excitations with emergent kinetics and fractionalized\ncharge, analogous to properties found in the two-dimensional fractional quantum\nHall regime. Observation of these excitations would provide an important\nplatform for exploring exotic quantum states derived solely from interactions.",
        "positive": "Spontaneous generation, enhanced propagation and optical imprinting of\n  quantized vortices and dark solitons in a polariton superfluid: towards the\n  control of quantum turbulence: In resonantly pumped polariton superfluids we recently explored a new regime\nbased on the bistability of the polariton system to enhance the propagation of\npolariton fluids up to macroscopic distances. This technique together with an\nall-optical imprinting method allowed the generation and control of various\ntopological excitations such as quantized vortices and dark solitons. The\nflexibility and scalability of the new experimental scheme opens the way to the\nsystematic study of quantum turbulence in driven dissipative quantum fluids of\nlight. In this article we review the basic working principles of the\nbistability enhanced propagation and of the imprinting technique and we discuss\nthe main achieved results as well as the most promising future research\ndirections."
    },
    {
        "anchor": "Rotating three-dimensional solitons in Bose Einstein condensates with\n  gravity-like attractive nonlocal interaction: We study formation of rotating three-dimensional high-order solitons\n(azimuthons) in Bose Einstein condensate with attractive nonlocal nonlinear\ninteraction. In particular, we demonstrate formation of toroidal rotating\nsolitons and investigate their stability. We show that variational methods\nallow a very good approximation of such solutions and predict accurately the\nsoliton rotation frequency. We also find that these rotating localized\nstructures are very robust and persist even if the initial condensate\nconditions are rather far from the exact soliton solutions. Furthermore, the\npresence of repulsive contact interaction does not prevent the existence of\nthose solutions, but allows to control their rotation. We conjecture that\nself-trapped azimuthons are generic for condensates with attractive nonlocal\ninteraction.",
        "positive": "A Three-Dimensional Optical Lattice of Ytterbium and Lithium Atomic\n  Mixture: We develop an optical lattice system for an ultracold atomic gas mixture of\nytterbium (174Yb) and lithium (6Li), which is an ideal system to study disorder\nand impurity problems. We load a Bose-Einstein condensate of 174Yb into a\nthree-dimensional optical lattice and observe the interference patterns in\ntime-of-flight (TOF) images. Furthermore, we perform a laser spectroscopy of\n174Yb in an optical lattice using the ultra-narrow optical transition 1S0-3P2\nin both cases with and without 6Li. Due to the weak interspecies interaction,\nwe do not observe the clear influences of 6Li in the obtained interference\npatterns and the excitation spectra. However, this is an important first step\nof optical control of atomic impurity in ultracold fermions. We also measure\nthe polarizabilities of the 3P2 state of 174Yb atoms in an optical trap with a\nwavelength of 1070 nm. We reveal that the polarizability can be tuned to\npositive, zero, or the same as the ground state, which are useful for certain\napplications."
    },
    {
        "anchor": "Trapped $^{173}$Yb Fermi gas across an orbital Feshbach resonance: Starting with the two-band description of an orbital Feshbach resonance, we\nstudy superfluid properties of a trapped $^{173}$Yb Fermi gas under the\nassumptions of a local-density approximation for the trapping potential and a\nmean-field approximation for the intra-band Cooper pairings. In particular, we\ninvestigate the competition and interplay between the pair-breaking effect that\nis caused by the inter-band detuning energy, and the pair-breaking and\nthermal-broadening effects that are simultaneously caused by the temperature.\nWe predict several experimental signatures that are directly caused by this\ninterplay including a spatial separation of superfluid and normal phases within\nthe trap, and could play decisive roles in probing two-band superfluidity in\nthese systems.",
        "positive": "Out-of-equilibrium dynamics of repulsive Fermi gases in quasi-periodic\n  potentials: a Density Functional Theory study: The dynamics of a one-dimensional two-component Fermi gas in the presence of\na quasi-periodic optical lattice (OL) is investigated by means of a Density\nFunctional Theory approach. Inspired by the protocol implemented in recent\ncold-atom experiments, designed to identify the many-body localization\ntransition, we analyze the relaxation of an initially prepared imbalance\nbetween the occupation number of odd and of even sites. For quasi-disorder\nstrength beyond the Anderson localization transition, the imbalance survives\nfor long times, indicating the inability of the system to reach local\nequilibrium. The late time value diminishes for increasing interaction\nstrength. Close to the critical quasi-disorder strength corresponding to the\nnoninteracting (Anderson) transition, the interacting system displays an\nextremely slow relaxation dynamics, consistent with sub-diffusive behavior. The\namplitude of the imbalance fluctuations around its running average is found to\ndecrease with time, and such damping is more effective with increasing\ninteraction strengths. While our study addresses the setup with two equally\nintense OLs, very similar effects due to interactions have been observed also\nin recent cold-atom experiments performed in the tight-binding regime, i.e.\nwhere one of the two OLs is very deep and the other is much weaker."
    },
    {
        "anchor": "Dipolar and spinor bosonic systems: The main properties and methods of describing dipolar and spinor atomic\nsystems, composed of bosonic atoms or molecules, are reviewed. The general\napproach for the correct treatment of Bose-condensed atomic systems with\nnonlocal interaction potentials is explained. The approach is applied to\nBose-condensed systems with dipolar interaction potentials. The properties of\nsystems with spinor interaction potentials are described. Trapped atoms and\natoms in optical lattices are considered. Effective spin Hamiltonians for atoms\nin optical lattices are derived. The possibility of spintronics with cold atom\nis emphasized. The present review differs from the previous review articles by\nconcentrating on a thorough presentation of basic theoretical points, helping\nthe reader to better follow mathematical details and to make clearer physical\nconclusions.",
        "positive": "Josephson tunneling of dark solitons in a double-well potential: We study the dynamics of matter waves in an effectively one-dimensional\nBose-Einstein condensate in a double well potential. We consider in particular\nthe case when one of the double wells confines excited states. Similarly to the\nknown ground state oscillations, the states can tunnel between the wells\nexperiencing the physics known for electrons in a Josephson junction, or be\nself-trapped. As the existence of dark solitons in a harmonic trap are\ncontinuations of such non-ground state excitations, one can view the\nJosephson-like oscillations as tunnelings of dark solitons. Numerical existence\nand stability analysis based on the full equation is performed, where it is\nshown that such tunneling can be stable. Through a numerical path following\nmethod, unstable tunneling is also obtained in different parameter regions. A\ncoupled-mode system is derived and compared to the numerical observations.\nRegions of (in)stability of Josephson tunneling are discussed and highlighted.\nFinally, we outline an experimental scheme designed to explore such dark\nsoliton dynamics in the laboratory."
    },
    {
        "anchor": "Light cone dynamics in excitonic states of two-component Bose and Fermi\n  gases: We consider the non-equilibrium dynamics of two-component one dimensional\nquantum gases in the limit of extreme population imbalance where the minority\nspecies has but a single particle. We consider the situation where the gas is\nprepared in a state with a single spatially localized exciton: the single\nparticle of the minority species is spatially localized while the density of\nthe majority species in the vicinity of the minority particle sees a\ndepression. Remarkably, we are able to consider cases where the gas contains on\nthe order of $N=100$ particles, comparable to that studied in experiments on\ncold atomic gases. We are able to do by exploiting the integrability of the gas\ntogether with the observation that the excitonic state can be constructed\nthrough a simple superposition of exact eigenstates of the gas. The number of\nstates in this superposition, rather than being exponentially large in the\nnumber of particles, scales linearly with $N$.\n  We study the evolution of such spatially localized states in both strongly\ninteracting Bose and Fermi gases. The behavior of the light cones when the\ninteraction strength and density of the gas is varied can be understood from\nexact results for the spin excitation spectrum in these systems. We argue that\nthe light cone in both cases exhibits scaling collapse. However unique to the\nBose gas, we show that the presence of gapped finite-momentum roton-like\nexcitations provide the Bose gas dynamics with secondary light cones.",
        "positive": "Local condensate depletion at trap center under strong interactions: Cold trapped Bose-condensed atoms, interacting via hard-sphere repulsive\npotentials are considered. Simple mean-field approximations show that the\ncondensate distribution inside a harmonic trap always has the shape of a hump\nwith the maximum condensate density occurring at the trap center. However Monte\nCarlo simulations at high density and strong interactions display the\ncondensate depletion at the trap center. The explanation of this effect of\nlocal condensate depletion at trap center is suggested in the frame of\nself-consistent theory of Bose-condensed systems. The depletion is shown to be\ndue to the existence of the anomalous average that takes into account pair\ncorrelations and appears in systems with broken gauge symmetry."
    },
    {
        "anchor": "Atom Loss Resonances in a Bose-Einstein Condensate: Atom loss resonances in ultracold trapped atoms have been observed at\nscattering lengths near atom-dimer resonances, at which Efimov trimers cross\nthe atom-dimer threshold, and near two-dimer resonances, at which universal\ntetramers cross the dimer-dimer threshold. We propose a new mechanism for these\nloss resonances in a Bose-Einstein condensate of atoms. As the scattering\nlength is ramped to the large final value at which the atom loss rate is\nmeasured, the time-dependent scattering length generates a small condensate of\nshallow dimers coherently from the atom condensate. The coexisting atom and\ndimer condensates can be described by a low-energy effective field theory with\nuniversal coefficients that are determined by matching exact results from\nfew-body physics. The classical field equations for the atom and dimer\ncondensates predict narrow enhancements in the atom loss rate near atom-dimer\nresonances and near two-dimer resonances due to inelastic dimer collisions.",
        "positive": "Supercurrent and dynamical instability of spin-orbit-coupled ultracold\n  Bose gases: We investigate the stability of supercurrents in a Bose-Einstein condensate\nwith one-dimensional spin-orbit and Raman couplings. The consequence of the\nlack of Galilean invariance is explicitly discussed. We show that in the\nplane-wave phase, characterized by a uniform density, the supercurrent state\ncan become dynamically unstable, the instability being associated with the\noccurrence of a complex sound velocity, in a region where the effective mass is\nnegative. We also discuss the emergence of energetic instability in these\nsupercurrent states. We argue that both the dynamical and the energetic\ninstabilities in these systems can be generated experimentally through\nexcitation of the collective dipole oscillation."
    },
    {
        "anchor": "Observation of a Geometric Hall Effect in a Spinor Bose-Einstein\n  Condensate with a Skyrmion Spin Texture: For a spin-carrying particle moving in a spatially varying magnetic field,\neffective electromagnetic forces can arise due to the geometric phase\nassociated with adiabatic spin rotation of the particle. We report the\nobservation of a geometric Hall effect in a spinor Bose-Einstein condensate\nwith a skyrmion spin texture. Under translational oscillations of the spin\ntexture, the condensate resonantly develops a circular motion in a harmonic\ntrap, demonstrating the existence of an effective Lorentz force. When the\ncondensate circulates, quantized vortices are nucleated in the boundary region\nof the condensate and the vortex number increases over 100 without significant\nheating. We attribute the vortex nucleation to the shearing effect of the\neffective Lorentz force from the inhomogeneous effective magnetic field.",
        "positive": "Shear viscosity and damping of collective modes in a two-dimensional\n  Fermi gas: We compute the shear viscosity of a two dimensional Fermi gas interacting via\na short range potential with scattering length $a_{2d}$ in kinetic theory. We\nfind that kinetic theory predicts that the shear viscosity to entropy density\nratio of a strongly interacting two dimensional gas is comparable to that of\nthe three dimensional unitary gas. We use our results to compute the damping of\ncollective modes in a trapped Fermi gas, and compare to experimental data\nrecently obtained in E. Vogt et al., arXiv:1111.1173."
    },
    {
        "anchor": "Dimensionality-enhanced quantum state transfer in long-range interacting\n  spin systems: In this work we study the single-qubit quantum state transfer in uniform\nlong-range spin XXZ systems in high-dimensional geometries. We consider\nprototypical long-range spin exchanges that are relevant for experiments in\ncold atomic platforms: Coulomb, dipolar and van der Waals-like interactions. We\nfind that in all these cases the fidelity increases with the dimensionality of\nthe lattice. This can be related to the emergence of a pair of bilocalized\nstates on the sender and receiver site due to the onset of an effective\nweak-coupling Hamiltonian. The enhancement of the quantum state transfer\nfidelity is more pronounced both with the increase of the couplings interaction\nrange and in going from a 1D to a 2D lattice. Finally, we test our predictions\nin the presence of temperature-induced disorder introducing a model for the\nthermal displacement of the lattice sites, considered as a set of local\nadiabatic oscillators.",
        "positive": "Sieve of Eratosthenes for Bose-Einstein Condensates in Optical Moir\u00e9\n  Lattices: We catalog known optical moir\\'e lattices and uncover exotic lattice\nconfigurations following a geometric analog of the ancient sieve of\nEratosthenes algorithm for finding prime numbers. Rich dynamics of\nBose-Einstein condensates loaded into these optical lattices is revealed from\nnumerical simulations of time-of-flight interference patterns. What sets this\nmethod apart is the ability to tune the periodicity of the optical lattices\nwithout changing the wavelength of the laser, yet maintaining the local\npotential at the individual lattices sites. In addition, we discuss the ability\nto spatially translate the optical lattice through applying a structured phase\nonly."
    },
    {
        "anchor": "Higgs amplitude mode in the vicinity of a $(2+1)$-dimensional quantum\n  critical point: We study the \"Higgs\" amplitude mode in the relativistic quantum O($N$) model\nin two space dimensions. Using the nonperturbative renormalization group we\ncompute the O($N$)-invariant scalar susceptibility in the vicinity of the\nzero-temperature quantum critical point. In the zero-temperature ordered phase,\nwe find a well defined Higgs resonance for $N=2$ with universal properties in\nagreement with quantum Monte Carlo simulations. The resonance persists at\nfinite temperature below the Berezinskii-Kosterlitz-Thouless transition\ntemperature. In the zero-temperature disordered phase, we find a maximum in the\nspectral function which is however not related to a putative Higgs resonance.\nFurthermore we show that the resonance is strongly suppressed for $N\\geq 3$.",
        "positive": "Interference dynamics of matter-waves of SU($N$) fermions: We analyze the two main physical observables related to the momenta of\nstrongly correlated SU($N$) fermions in ring-shaped lattices pierced by an\neffective magnetic flux: homodyne (momentum distribution) and self-heterodyne\ninterference patterns. We demonstrate how their analysis allows us to monitor\nthe persistent current pattern. We find that both homodyne and self-heterodyne\ninterference display a specific dependence on the structure of the Fermi\ndistribution and particles' correlations. For homodyne protocols, the momentum\ndistribution is affected by the particle statistics in two distinctive ways.\nThe first effect is a purely statistical one: at zero interactions, the\ncharacteristic hole in the momentum distribution around the momentum\n$\\mathbf{k}=0$ opens up once half of the SU($N$) Fermi sphere is displaced. The\nsecond effect originates from interaction: the fractionalization in the\ninteracting system manifests itself by an additional `delay' in the flux for\nthe occurrence of the hole, that now becomes a depression at $\\mathbf{k}=0$. In\nthe case of self-heterodyne interference patterns, we are not only able to\nmonitor, but also observe the fractionalization. Indeed, the fractionalized\nangular momenta, due to level crossings in the system, are reflected in\ndislocations present in interferograms. Our analysis demonstrate how the study\nof the interference fringes grants us access to both number of particles and\nnumber of components of SU($N$) fermions."
    },
    {
        "anchor": "Fermionic Functional Renormalization Group Approach to Bose-Einstein\n  Condensation of Dimers: Fermionic functional renormalization group (f-FRG) is applied to describe\nBose-Einstein condensation (BEC) of dimers for a two-component fermionic system\nwith attractive contact interaction. In order to describe the system of dimers\nwithout introducing auxiliary bosonic fields (bosonization), we propose a new\nexact evolution-equation of the effective action in f-FRG with an infrared\nregulator for the fermion vertex. Then we analyze its basic properties in\ndetails. We show explicitly that the critical temperature of the free Bose gas\nis obtained naturally by this method without bosonization. Methods to make\nsystematic improvement from the deep BEC limit are briefly discussed.",
        "positive": "Absence of breakdown of ferrodark solitons exhibiting snake instability: We investigate the dynamical stability and real time dynamics of the\ntwo-types of ferrodark solitons (FDSs) which occur as topological magnetic\ndomain walls in the easy-plane phase of a quasi-two-dimensional (2D)\nferromagnetic spin-1 Bose-Einstein condensate. The type-I FDS has positive\ninertial mass and exhibits a single dynamical instability that generates in\nplane spin winding, causing polar-core spin vortex dipoles. The positive\ninertial mass leads to the elastic oscillations of the soliton under transverse\nperturbations. The type-II FDS has negative inertial mass and exhibits a snake\ninstability and a spin-twist instability, with the latter involving the\ngeneration of out of plane spin winding. Distinct from the normal dynamics of\nnegative mass solitons under long wave length transverse perturbations, the\nsnake instability does not lead to the type-II FDS breaking down. Instead,\nsegments of the type-II FDS convert to type-I and mass vortex dipoles are\nproduced. The resulting hybridized-chain of the two soliton types and vortices\nexhibits complex 2D soliton dynamics at long times while the vortices remain\nconfined and the topological structure of a magnetic domain wall is preserved."
    },
    {
        "anchor": "Breaking of Goldstone modes in two component Bose-Einstein condensate: We study the decay rate $\\Gamma(k)$ of density excitations of two-component\nBose-Einstein condensates at zero temperature. Those excitations, where the two\ncomponents oscillate in phase, include the Goldstone mode resulting from\ncondensation. While within Bogoliubov approximation the density sector and the\nspin (out-of-phase) sector are independent, they couple at the three-phonon\nlevel. For a Bose-Bose mixture we find that the Belyaev decay is slightly\nmodified due to the coupling with the gapless spin mode. At the phase\nseparation point the decay rate changes instead from the standard $k^5$ to a\n$k^{5/2}$ behaviour due to the parabolic nature of the spin mode. In presence\nof coherent coupling between the two components the spin sector is gapped and,\naway from the ferromagnetic-like phase transition point, the decay of density\nmode is not affected. On the other hand at the transition point, when the spin\nfluctuations become critical, the Goldstone mode is not well defined anymore\nsince $\\Gamma(k)\\propto k$. As a consequence, we show that the friction induced\nby a moving impurity is enahnced -- a feature which could be experimentally\ntested. Our results apply to every non-linear 2-component quantum hydrodynamic\nHamiltonian which is time-reversal invariant, and possesses an $U(1)\\times\n{\\mathbf Z}_2$ symmetry.",
        "positive": "Trapping Ultracold Atoms in a Time-Averaged Adiabatic Potential: We report the first experimental realization of ultracold atoms confined in a\ntime-averaged, adiabatic potential (TAAP). This novel trapping technique\ninvolves using a slowly oscillating ($\\sim$ kHz) bias field to time-average the\ninstantaneous potential given by dressing a bare magnetic potential with a high\nfrequency ($\\sim$ MHz) magnetic field. The resultant potentials provide a\nconvenient route to a variety of trapping geometries with tunable parameters.\nWe demonstrate the TAAP trap in a standard time-averaged orbiting potential\ntrap with additional Helmholtz coils for the introduction of the radio\nfrequency dressing field. We have evaporatively cooled 5 $\\times 10^4$ atoms of\n$^{87}$Rb to quantum degeneracy and observed condensate lifetimes of over\n\\unit[3]{s}.-"
    },
    {
        "anchor": "Observation of subdiffusive dynamic scaling in a driven and disordered\n  Bose gas: We explore the dynamics of a tuneable box-trapped Bose gas under strong\nperiodic forcing in the presence of weak disorder. In absence of interparticle\ninteractions, the interplay of the drive and disorder results in an isotropic\nnonthermal momentum distribution that shows subdiffusive dynamic scaling, with\nsublinear energy growth and the universal scaling function captured well by a\ncompressed exponential. We explain that this subdiffusion in momentum space can\nnaturally be understood as a random walk in energy space. We also\nexperimentally show that for increasing interaction strength, the gas behavior\nsmoothly crosses over to wave turbulence characterized by a power-law momentum\ndistribution, which opens new possibilities for systematic studies of the\ninterplay of disorder and interactions in driven quantum systems.",
        "positive": "Topological edge states in the one-dimensional super-lattice\n  Bose-Hubbard model: We analyze interacting ultra-cold bosonic atoms in a one-dimensional (1D)\nsuper-lattice potential with alternating tunneling rates t_1 and t_2 and\ninversion symmetry, which is the bosonic analogue of the Su-Schrieffer-Heeger\n(SSH) model. A Z2 topological order parameter is introduced which is quantized\nfor the Mott insulating (MI) phases. Depending on the ratio t_1/t_2 the n=1/2\nMI phase is topologically non-trivial, which results in many-body edge states\nat open boundaries. In contrast to the SSH model the bosonic counterpart lacks\nchiral symmetry and the edge states are no longer mid-gap. This leads to a\ngeneralization of the bulk-edge correspondence, which we discuss in detail. The\nedge states can be observed in cold atom experiments by creating a step in the\neffective confining potential, e.g. by a second heavy atom species, which leads\nto an interface between two MI regions with filling n=1 and n=1/2. Shape and\nenergy of the edge states as well as conditions for their occupation are\ndetermined analytically in the strong coupling limit and in general by\ndensity-matrix renormalization group (DMRG) simulations."
    },
    {
        "anchor": "Interaction Effects on Wannier Functions for Bosons in Optical Lattice: We have numerically calculated the single band Wannier functions for\ninteracting Bose gases in optical lattices with a self-consistent approach. We\nfind that the Wannier function is broadened by repulsive atom interaction. The\ntunneling parameter J and on-site interaction U computed with the broadened\nWannier functions are found to change significantly for different atomic number\nper site. Our theory can explain the nonuniform atomic clock shift observed in\n[Campbell et al., Science 313, 649 (2006)].",
        "positive": "A fresh view on Frenkel excitons: Electron-hole pair exchange and\n  many-body formalism: We here present a fresh approach to Frenkel excitons in cubic semiconductor\ncrystals, with a special focus on the spin and spatial degeneracies of the\nelectronic states. This approach uses a second quantization formulation of the\nproblem in terms of creation operators for electronic states on all lattice\nsites -- their creation operators being true fermion operators in the\ntight-binding limit valid for semiconductors hosting Frenkel excitons. This\noperator formalism avoids using cumbersome ($6N_s$ x $6N_s$) Slater\ndeterminants -- 2 for spin, 3 for spatial degeneracy and $N_s$ for the number\nof lattice sites -- to represent state wave functions out of which the Frenkel\nexciton eigenstates are derived. A deep understanding of the tricky Coulomb\nphysics that takes place in the Frenkel exciton problem, is a prerequisite for\npossibly diagonalizing this very large matrix analytically. This is done in\nthree steps: (i) the first diagonalization, with respect to lattice sites,\nfollows from transforming excitations on the $N_s$ lattice sites\n$\\mathbf{R}_\\ell$ into $N_s$ exciton waves $\\mathbf{K}_n$, by using appropriate\nphase prefactors; (ii) the second diagonalization, with respect to spin,\nfollows from the introduction of spin-singlet and spin-triplet electron-hole\npair states, through the commonly missed sign change when transforming\nelectron-absence operators into hole operators; (iii) the third\ndiagonalization, with respect to threefold spatial degeneracy, leads to the\nsplitting of the exciton level into one longitudinal and two transverse modes,\nthat result from the singular interlevel Coulomb scattering in the small\n$\\mathbf{K}_n$ limit."
    },
    {
        "anchor": "Measuring molecular electric dipoles using trapped atomic ions and\n  ultrafast laser pulses: We study a hybrid quantum system composed of an ion and an electric dipole.\nWe show how a trapped ion can be used to measure the small electric field\ngenerated by a classical dipole. We discuss the application of this scheme to\nmeasure the electric dipole moment of cold polar molecules, whose internal\nstate can be controlled with ultrafast laser pulses, by trapping them in the\nvicinity of a trapped ion.",
        "positive": "Origin and evolution of the multiply-quantised vortex instability: We show that the dynamical instability of quantum vortices with more than a\nsingle quantum of angular momentum results from a superradiant bound state\ninside the vortex core. Our conclusion is supported by an analytic WKB\ncalculation and numerical simulations of both linearised and fully non-linear\nequations of motion for a doubly-quantised vortex at the centre of a circular\nbucket trap. In the late stage of the instability, we reveal a striking novel\nbehaviour of the system in the non-linear regime. Contrary to expectation, in\nthe absence of dissipation the system never enters the regime of two\nwell-separated phase defects described by Hamiltonian vortex dynamics. Instead,\nthe separation between the two defects undergoes modulations which never exceed\na few healing lengths, in which compressible kinetic energy and incompressible\nkinetic energy are exchanged. This suggests that, under the right conditions,\npairs of vortices may be able to form meta-stable bound states."
    },
    {
        "anchor": "Vortex graphs as N-omers and CP(N-1) Skyrmions in N-component\n  Bose-Einstein condensates: Stable vortex N-omers are constructed in coherently coupled N-component\nBose-Einstein condensates. We classify all possible N-omers in terms of the\nmathematical graph theory and numerically construct all graphs for N=2,3,4. We\nalso find that N-omers are well described as CP(N-1) skyrmions when\ninter-component and intra-component couplings are U(N) symmetric, and we\nevaluate their size dependence on the Rabi coupling.",
        "positive": "Ultracold Atoms in a Tunable Optical Kagome Lattice: Geometrically frustrated systems with a large degeneracy of low energy states\nare of central interest in condensed-matter physics. The kagome net - a pattern\nof corner-sharing triangular plaquettes - presents a particularly high degree\nof frustration, reflected in the non-dispersive orbital bands. The ground state\nof the kagome quantum antiferromagnet, proposed to be a quantum spin liquid or\nvalence bond solid, remains uncertain despite decades of work. Solid-state\nkagome magnets suffer from significant magnetic disorder or anisotropy that\ncomplicates the interpretation of experimental results. Here, we realize the\nkagome geometry in a two-dimensional optical superlattice for ultracold\n$^{87}$Rb atoms. We employ atom optics to characterize the lattice as it is\ntuned between various geometries, including kagome, one-dimensional stripe, and\ndecorated triangular lattices, allowing for a sensitive control of frustration.\nThe lattices implemented in this work offer a near-ideal realization of a\nparadigmatic model of many-body quantum physics."
    },
    {
        "anchor": "Stable two-dimensional soliton complexes in Bose-Einstein condensates\n  with helicoidal spin-orbit coupling: We show that attractive two-dimensional spinor Bose-Einstein condensates with\nhelicoidal spatially periodic spin-orbit coupling (SOC) support a rich variety\nof stable fundamental solitons and bound soliton complexes. Such states exist\nwith chemical potentials belonging to the semi-infinite gap in the band\nspectrum created by the periodically modulated SOC. All these states exist\nabove a certain threshold value of the norm. The chemical potential of\nfundamental solitons attains the bottom of the lowest band, whose locus is a\nring in the space of Bloch momenta, and the radius of the ring is a\nnon-monotonous function of the SOC strength. The chemical potential of soliton\ncomplexes does not attain the band edge. The complexes are bound states of\nseveral out-of-phase fundamental solitons whose centers are placed at local\nmaxima of the SOC-modulation phase. In this sense, the impact of the helicoidal\nSOC landscape on the solitons is similar to that of a periodic two-dimensional\npotential. In particular, it can compensate repulsive forces between\nout-of-phase solitons, making their bound states stable. Extended stability\ndomains are found for complexes built of two and four solitons (dipoles and\nquadrupoles, respectively). They are typically stable below a critical value of\nthe chemical potential.",
        "positive": "Nontrivial Haldane phase of an atomic two-component Fermi gas trapped in\n  a 1d optical lattice: We propose how to create a non-trivial Haldane phase in atomic two-component\nFermi-gas loaded on one-dimensional (1-D) optical lattice with trap potential.\nThe Haldane phase is naturally formed on $p$-band Mott core in a wide range of\nthe strong on-site repulsive interaction. The present proposal is composed of\ntwo steps, one of which is theoretical derivation of an effective 1-D S=1\ninteracting-chain model from the original tight-binding Hamiltonian handling\nthe two $p$-orbitals, and the other of which is numerical demonstration\nemploying the density-matrix renormalization-group for the formation of the\nHaldane phase on $p$-band Mott core and its associated features in the original\ntight-binding model with the harmonic trap potential."
    },
    {
        "anchor": "Suppressing defect production during passage through a quantum critical\n  point: We show that a closed quantum system driven through a quantum critical point\nwith two rates $\\omega_1$ (which controls its proximity to the quantum critical\npoint) and $\\omega_2$ (which controls the dispersion of the low-energy\nquasiparticles at the critical point) exhibits novel scaling laws for defect\ndensity $n$ and residual energy $Q$. We demonstrate suppression of both $n$ and\n$Q$ with increasing $\\omega_2$ leading to an alternate route to achieving\nnear-adiabaticity in a finite time for a quantum system during its passage\nthrough a critical point. We provide an exact solution for such dynamics with\nlinear drive protocols applied to a class of integrable models, supplement this\nsolution with scaling arguments applicable to generic many-body Hamiltonians,\nand discuss specific models and experimental systems where our theory may be\ntested.",
        "positive": "Bond Order via Light-Induced Synthetic Many-body Interactions of\n  Ultracold Atoms in Optical Lattices: We show how bond order emerges due to light mediated synthetic interactions\nin ultracold atoms in optical lattices in an optical cavity. This is a\nconsequence of the competition between both short- and long-range interactions\ndesigned by choosing the optical geometry. Light induces effective many-body\ninteractions that modify the landscape of quantum phases supported by the\ntypical Bose-Hubbard model. Using exact diagonalization of small system sizes\nin one dimension, we present the many-body quantum phases the system can\nsupport via the interplay between the density and bond (or matter-wave\ncoherence) interactions. We find numerical evidence to support that dimer\nphases due to bond order are analogous to valence bond states. Different\npossibilities of light-induced atomic interactions are considered that go\nbeyond the typical atomic system with dipolar and other intrinsic interactions.\nThis will broaden the Hamiltonian toolbox available for quantum simulation of\ncondensed matter physics via atomic systems."
    },
    {
        "anchor": "Spin mixing and protection of ferromagnetism in a spinor dipolar\n  condensate: We study spin mixing dynamics in a chromium dipolar Bose-Einstein Condensate,\nafter tilting the atomic spins by an angle $\\theta$ with respect to the\nmagnetic field. Spin mixing is triggered by dipolar coupling, but, once\ndynamics has started, it is mostly driven by contact interactions. For the\nparticular case $\\theta=\\pi/2$, an external spin-orbit coupling term induced by\na magnetic gradient is required to enable the dynamics. Then the initial\nferromagnetic character of the gas is locally preserved, an unexpected feature\nthat we attribute to large spin-dependent contact interactions.",
        "positive": "A Dielectric Superfluid of Polar Molecules: We show that, under achievable experimental conditions, a Bose-Einstein\ncondensate (BEC) of polar molecules can exhibit dielectric character. In\nparticular, we derive a set of self-consistent mean-field equations that couple\nthe condensate density to its electric dipole field, leading to the emergence\nof polarization modes that are coupled to the rich quasiparticle spectrum of\nthe condensate. While the usual roton instability is suppressed in this system,\nthe coupling can give rise to a phonon-like instability that is characteristic\nof a dielectric material with a negative static dielectric function."
    },
    {
        "anchor": "Quantum dynamics of few dipolar bosons in a double-well potential: We study the few-body dynamics of dipolar bosons in one-dimensional\ndouble-wells. Increasing the interaction strength, by investigating one-body\nobservables, we study in the considered few-body systems tunneling\noscillations, self-trapping and the regime exhibting an equilibrating\nbehaviour. The corresponding two-body correlation dynamics exhibits a strong\ninterplay between the interatomic correlation due to non-local nature of the\nrepulsion and the inter-well coherence. We also study the link between the\ncorrelation dynamics and the occupation of natural orbitals of the one-body\ndensity matrix.",
        "positive": "Excitation spectrum of a supersolid: Conclusive experimental evidence of a supersolid phase in any known condensed\nmatter system is presently lacking. On the other hand, a supersolid phase has\nbeen recently predicted for a system of spinless bosons in continuous space,\ninteracting via a broad class of soft-core, repulsive potentials. Such an\ninteraction can be engineered in assemblies of ultracold atoms, providing a\nwell-defined pathway to the unambiguous observation of this fascinating phase\nof matter. In this article, we study by first principle computer simulations\nthe elementary excitation spectrum of the supersolid, and show that it features\ntwo distinct modes, namely a solid-like phonon and a softer collective\nexcitation, related to broken translation and gauge symmetry respectively."
    },
    {
        "anchor": "Realizing Exactly Solvable SU(N) Magnets with Thermal Atoms: We show that $n$ thermal fermionic alkaline-earth atoms in a flat-bottom trap\nallow one to robustly implement a spin model displaying two symmetries: the\n$S_n$ symmetry that permutes atoms occupying different vibrational levels of\nthe trap and the SU($N$) symmetry associated with $N$ nuclear spin states. The\nhigh symmetry makes the model exactly solvable, which, in turn, enables the\nanalytic study of dynamical processes such as spin diffusion in this SU($N$)\nsystem. We also show how to use this system to generate entangled states that\nallow for Heisenberg-limited metrology. This highly symmetric spin model should\nbe experimentally realizable even when the vibrational levels are occupied\naccording to a high-temperature thermal or an arbitrary non-thermal\ndistribution.",
        "positive": "Spin-orbit coupled repulsive Fermi atoms in a one-dimensional optical\n  lattice: Motivated by recent experimental development, we investigate spin-orbit\ncoupled repulsive Fermi atoms in a one-dimensional optical lattice. Using the\ndensity-matrix renormalization group method, we calculate momentum distribution\nfunction, gap, and spin-correlation function to reveal rich ground-state\nproperties. We find that spin-orbit coupling (SOC) can generate unconventional\nmomentum distribution, which depends crucially on the filling. We call the\ncorresponding phase with zero gap the SOC-induced metallic phase. We also show\nthat SOC can drive the system from the antiferromagnetic to ferromagnetic Mott\ninsulators with spin rotating. As a result, a second-order quantum phase\ntransition between the spin-rotating ferromagnetic Mott insulator and the\nSOC-induced metallic phase is predicted at the strong SOC. Here the spin\nrotating means that the spin orientations of the nearest-neighbor sites are not\nparallel or antiparallel, i.e., they have an intersection angle $\\theta \\in\n(0,\\pi )$. Finally, we show that the momentum $k_{\\mathrm{peak}}$, at which\npeak of the spin-structure factor appears, can also be affected dramatically by\nSOC. The analytical expression of this momentum with respect to the SOC\nstrength is also derived. It suggests that the predicted spin-rotating\nferromagnetic ($k_{\\mathrm{peak}% }<\\pi /2$) and antiferromagnetic ($\\pi\n/2<k_{\\mathrm{peak}}<\\pi $) correlations can be detected experimentally by\nmeasuring the SOC-dependent spin-structure factor via the time-of-flight\nimaging."
    },
    {
        "anchor": "Appropriate probe condition for absorption imaging of ultracold $^6$Li\n  atoms: One of the readily accessible observables in trapped cold-atom experiments is\nthe column density, which is determined from optical depth (OD) obtained from\nabsorption imaging and the absorption cross-section ($\\sigma_{\\rm abs}$). Here\nwe report on simple and accurate determination of OD for dense gases of light\natoms such as lithium-6. We investigate theoretically and experimentally an\nappropriate condition for the probe intensity and duration to achieve good\nsignal-to-noise ratio by considering the influences of photon recoils and\nphoton shot noises. As a result, we have succeeded in measuring OD which\nreached 2.5 with a signal-to-noise ratio of 10 under spatial resolution of 1.7\n$\\mu$m.",
        "positive": "Three fluid hydrodynamics of spin-1 Bose-Einstein condensates: We study excitations of the spin-1 Bose gas at finite temperatures and in the\npresence of a not so strong magnetic field, or equivalently, when the gas\nsample is partially polarized. Motivated by the success of two-fluid\nhydrodynamics of scalar superfluids we develop a three-fluid hydrodynamic\ndescription to treat the low frequency and long wavelength excitations of the\nspin-1 Bose gas. We derive the coupled linear hydrodynamic equations of the\nthree sounds and evaluate them numerically in a self-consistent mean field\napproximation valid for the dilute gas at the intermediate and critical\ntemperature regions. In this latter region we identify the critical mode."
    },
    {
        "anchor": "Quantum phases in tunable state-dependent hexagonal optical lattices: We study the ground-state properties of ultracold bosonic atoms in a\nstate-dependent graphene-like honeycomb optical lattice, where the degeneracy\nbetween the two triangular sublattices A and B can be lifted. We discuss the\nvarious geometries accessible with this lattice setup and present a novel\nscheme to control the energy offset with external magnetic fields. The\ncompetition of the on-site interaction with the offset energy leads to Mott\nphases characterized by population imbalances between the sublattices. For the\ndefinition of an optimal Hubbard model, we demonstrate a scheme that allows for\nthe efficient computation of Wannier functions. Using a cluster mean-field\nmethod, we compute the phase diagrams and provide a universal representation\nfor arbitrary energy offsets. We find good agreement with the experimental data\nfor the superfluid to Mott insulator transition.",
        "positive": "Ultrafast many-body interferometry of impurities coupled to a Fermi sea: The fastest possible collective response of a quantum many-body system is\nrelated to its excitations at the highest possible energy. In condensed-matter\nsystems, the corresponding timescale is typically set by the Fermi energy.\nTaking advantage of fast and precise control of interactions between ultracold\natoms, we report on the observation of ultrafast dynamics of impurities coupled\nto an atomic Fermi sea. Our interferometric measurements track the\nnon-perturbative quantum evolution of a fermionic many-body system, revealing\nin real time the formation dynamics of quasiparticles and the quantum\ninterference between attractive and repulsive states throughout the full depth\nof the Fermi sea. Ultrafast time-domain methods to manipulate and investigate\nstrongly interacting quantum gases open up new windows on the dynamics of\nquantum matter under extreme non-equilibrium conditions."
    },
    {
        "anchor": "Momentum-space Harper-Hofstadter model: We show how the weakly trapped Harper-Hofstadter model can be mapped onto a\nHarper-Hofstadter model in momentum space. In this momentum-space model, the\nband dispersion plays the role of the periodic potential, the Berry curvature\nplays the role of an effective magnetic field, the real-space harmonic trap\nprovides the momentum-space kinetic energy responsible for the hopping, and the\ntrap position sets the boundary conditions around the magnetic Brillouin zone.\nSpatially local interactions translate into nonlocal interactions in momentum\nspace: within a mean-field approximation, we show that increasing interparticle\ninteractions leads to a structural change of the ground state, from a single\nrotationally symmetric ground state to degenerate ground states that\nspontaneously break rotational symmetry.",
        "positive": "Generation, manipulation and detection of snake state trajectories of a\n  neutral atom in a ring-cavity: We propose a set-up which can be used to create and detect the atomic\ncounterpart of snake state trajectories observed in electronic systems where\neither sign of the charge-carrier changes or the magnetic field changes\ndirection. In this work, we use a laser-induced synthetic gauge field that\ndepends on the cavity photon numbers to generate such trajectories. We analyse\nthe motion of a single atom in the presence of such a gauge field while\nincluding the back-action of the cavity fields. We demonstrate that the output\ncavity field provides a non-destructive way of observing the real-time atomic\ndynamics inside the ring cavity. We also show that we can tune the system\nparameters to modify the properties of the snake state and even amplify the\neffect of cavity feedback to destroy the snake-like trajectories."
    },
    {
        "anchor": "A simple and efficient all-optical production of spinor condensates: We present a simple and optimal experimental scheme for an all-optical\nproduction of a sodium spinor Bose-Einstein condensate (BEC). With this scheme,\nwe demonstrate that the number of atoms in a pure BEC can be greatly boosted by\na factor of 5 in a simple setup that includes a single-beam optical trap or a\ncrossed optical trap. This optimal scheme avoids technical challenges\nassociated with some all-optical BEC methods, and can be applied to other\noptically trappable atomic species. In addition, we find a good agreement\nbetween our theoretical model and data. The upper limit for the efficiency of\nevaporative cooling in all-optical BEC approaches is also discussed.",
        "positive": "$\u03bc$-Symmetry breaking: an algebraic approach to finding mean fields of\n  quantum many-body systems: One of the most fundamental problems in quantum many-body systems is the\nidentification of a mean field in spontaneous symmetry breaking which is\nusually made in a heuristic manner. We propose a systematic method of finding a\nmean field based on the Lie algebra and the dynamical symmetry by introducing a\nclass of symmetry broken phases which we call $\\mu$-symmetry breaking. We show\nthat for $\\mu$-symmetry breaking the quadratic part of an effective Lagrangian\nof Nambu-Goldstone modes can be block-diagonalized and that homotopy groups of\ntopological excitations can be calculated systematically."
    },
    {
        "anchor": "Restoring quasi-reversibility with a single topological charge: We numerically study a rotating Bose-Einstein condensate placed transiently\nover the critical rotation frequency i.e. in a regime where the rotation\nfrequency is larger than the radial frequency of the confinement. We study the\nreversibility of this process depending on the strength of the interactions and\nthe presence of vortices. We find that the reversibility is broken by the\ninteractions in the absence of vortices but systematically quasi-restored in\nthe presence of a single vortex.",
        "positive": "Tomography of band insulators from quench dynamics: We propose a simple scheme for tomography of band-insulating states in one-\nand two-dimensional optical lattices with two sublattice states. In particular,\nthe scheme maps out the Berry curvature in the entire Brillouin zone and\nextracts topological invariants such as the Chern number. The measurement\nrelies on observing---via time-of-flight imaging---the time evolution of the\nmomentum distribution following a sudden quench in the band structure. We\nconsider two examples of experimental relevance: the Harper model with\n$\\pi$-flux and the Haldane model on a honeycomb lattice. Moreover, we\nillustrate the performance of the scheme in the presence of a parabolic trap,\nnoise, and finite measurement resolution."
    },
    {
        "anchor": "Crystallization of an exciton superfluid: Indirect excitons -- pairs of electrons and holes spatially separated in\nsemiconductor bilayers or quantum wells -- are known to undergo Bose-Einstein\ncondensation and to form a quantum fluid. Here we show that this superfluid may\ncrystallize upon compression. However, further compression results in quantum\nmelting back to a superfluid. This unusual behavior is explained by the\neffective interaction potential between indirect excitons which strongly\ndeviates from a dipole potential at small distances due to many-particle and\nquantum effects. Based on first principle path integral Monte Carlo\nsimulations, we compute the complete phase diagram of this system and predict\nthe relevant parameters necessary to experimentally observe exciton\ncrystallization in semiconductor quantum wells.",
        "positive": "Rabi-Josephson oscillations and self-trapped dynamics in atomic\n  junctions with two bosonic species: We investigate the dynamics of two-component Bose-Einstein condensates\n(BECs), composed of atoms in two distinct hyperfine states, which are linearly\ncoupled by two-photon Raman transitions. The condensate is loaded into a\ndouble-well potential (DWP). A variety of dynamical behaviors, ranging from\nregular Josephson oscillations, to mixed Rabi-Josephson oscillations and to\nregimes featuring an increasing complexity, are described in terms of a reduced\nHamiltonian system with four degrees of freedoms, which are the numbers of\natoms in each component in the left and right potential wells, whose\ncanonically conjugate variables are phases of the corresponding wave functions.\nUsing the system with the four degrees of freedom, we study the dynamics of\nfractional imbalances of the two bosonic components, and compare the results to\ndirect simulations of the Gross-Pitaevskii equations (GPEs) describing the\nbosonic mixture. We perform this analysis when the fractional imbalance\noscillates around a zero-time averaged value and in the self-trapping regime as\nwell."
    },
    {
        "anchor": "Topological phase transitions in finite-size periodically driven\n  translationally invariant systems: It is known that, in the thermodynamic limit, the Chern number of a\ntranslationally invariant system cannot change under unitary time evolutions\nthat are smooth in momentum space. Yet a real-space counterpart of the Chern\nnumber, the Bott index, has been shown to change in periodically driven systems\nwith open boundary conditions. Here we prove that the Bott index and the Chern\nnumber are identical in translationally invariant systems in the thermodynamic\nlimit. Using the Bott index, we show that, in finite-size translationally\ninvariant systems, a Fermi sea under a periodic drive that is turned on slowly\ncan acquire a different topology from that of the initial state. This can\nhappen provided that the gap-closing points in the thermodynamic limit are\nabsent in the discrete Brillouin zone of the finite system. Hence, in such\nsystems, a periodic drive can be used to dynamically prepare topologically\nnontrivial states starting from topologically trivial ones.",
        "positive": "Quantum particle in a parabolic lattice in the presence of a gauge field: We analyze the eigenstates of a two-dimensional lattice with additional\nharmonic confinement in the presence of an artificial magnetic field. While the\nsoftness of the confinement makes a distinction between bulk and edge states\ndifficult, the interplay of harmonic potential and lattice leads to a different\nclassification of states in three energy regions: In the low-energy regime,\nwhere lattice effects are small, all states are transporting topologically\nnon-trivial states. For large energies above a certain critical value, the\nperiodic lattice causes localization of all states through a mechanism similar\nto Wannier-Stark localization. In the intermediate energy regime transporting,\ntopologically non- trivial states coexist with topologically trivial\ncounter-transporting chaotic states. The character of the eigenstates, in\nparticular their transport properties are studied numerically and are explained\nusing a semiclassical analysis."
    },
    {
        "anchor": "Controlling Correlated Tunneling and Superexchange Interactions with\n  AC-Driven Optical Lattices: The dynamical control of tunneling processes of single particles plays a\nmajor role in science ranging from Shapiro steps in Josephson junctions to the\ncontrol of chemical reactions via light in molecules. Here we show how such\ncontrol can be extended to the regime of strongly interacting particles.\nThrough a weak modulation of a biased tunnel contact, we have been able to\ncoherently control single particle and correlated two-particle hopping\nprocesses. We have furthermore been able to extend this control to\nsuperexchange spin interactions in the presence of a magnetic-field gradient.\nWe show how such photon assisted superexchange processes constitute a novel\napproach to realize arbitrary XXZ spin models in ultracold quantum gases, where\ntransverse and Ising type spin couplings can be fully controlled in magnitude\nand sign.",
        "positive": "Polarized Rabi-Coupled and Spinor Boson Droplets: Self-bound quantum droplets form when the mean-field tendency of the gas to\ncollapse is stabilized by the effectively repulsive beyond mean-field\nfluctuations. The beyond mean-field effects depend on Rabi-frequency $\\omega_R$\nand quadratic Zeeman effect $q$ for the Rabi-coupled Bose mixtures and the\nspinor gases, respectively. The effects of varying $\\omega_R$ and $q$ on the\nquantum droplet have recently been examined for unpolarized Rabi-coupled Bose\nmixture with zero detuning $\\delta = 0$ and unpolarized spinor gas with\n$\\langle F_z \\rangle=0$. In this paper, we theoretically explore the stability\nof the droplet phase for polarized $\\delta \\neq 0$ Rabi-coupled Bose mixture\nand $\\langle F_z \\rangle \\neq 0$ spinor gas. We calculate the Lee-Huang-Yang\ncorrections for both gases with polarized order parameters and obtain the phase\ndiagram of the droplets on the parameter space of $\\omega_R$-$\\delta$ and\n$q$-$p$ for Rabi-coupled mixture and spinor gas, respectively. Finally, we\nhighlight the similarities and differences between the two systems and discuss\ntheir experimental feasibility."
    },
    {
        "anchor": "Constrained extrapolation problem and order-dependent mappings: We consider the problem of extrapolating the perturbation series for the\ndilute Fermi gas in three dimensions to the unitary limit of infinite\nscattering length and into the BEC region, using the available strong-coupling\ninformation to constrain the extrapolation problem. In this constrained\nextrapolation problem (CEP) the goal is to find classes of approximants that\ngive well converged results already for low perturbative truncation orders.\nFirst, we show that standard Pad\\'{e} and Borel methods are too restrictive to\ngive satisfactory results for this CEP. A generalization of Borel extrapolation\nis given by the so-called Maximum Entropy extrapolation method (MaxEnt).\nHowever, we show that MaxEnt requires extensive elaborations to be applicable\nto the dilute Fermi gas and is thus not practical for the CEP in this case.\nInstead, we propose order-dependent-mapping extrapolation (ODME) as a simple,\npractical, and general method for the CEP. We find that the ODME approximants\nfor the ground-state energy of the dilute Fermi gas are robust with respect to\nchanges of the mapping choice and agree with results from quantum Monte Carlo\nsimulations within uncertainties.",
        "positive": "Linear limit continuation: Theory and an application to two-dimensional\n  Bose-Einstein condensates: We present a coherent and effective theoretical framework to systematically\nconstruct numerically exact nonlinear solitary waves from their respective\nlinear limits. First, all possible linear degenerate sets are classified for a\nharmonic potential using lattice planes. For a generic linear degenerate set,\ndistinct wave patterns are identified in the near-linear regime using a random\nsearching algorithm by suitably mixing the linear degenerate states, followed\nby a numerical continuation in the chemical potential extending the waves into\nthe Thomas-Fermi regime. The method is applied to the two-dimensional,\none-component Bose-Einstein condensates, yielding a spectacular set of\nwaveforms. Our method opens a remarkably large program, and many more solitary\nwaves are expected. Finally, the method can be readily generalized to three\ndimensions, and also multi-component condensates, providing a highly powerful\ntechnique for investigating solitary waves in future works."
    },
    {
        "anchor": "Particles and Fields in Superfluids: Insights from the Two-dimensional\n  Gross-Pitaevskii Equation: We carry out extensive direct numerical simulations (DNSs) to investigate the\ninteraction of active particles and fields in the two-dimensional (2D)\nGross-Pitaevskii (GP) superfluid, in both simple and turbulent flows. The\nparticles are active in the sense that they affect the superfluid even as they\nare affected by it. We tune the mass of the particles, which is an important\ncontrol parameter. At the one-particle level, we show how light, neutral, and\nheavy particles move in the superfluid, when a constant external force acts on\nthem; in particular, beyond a critical velocity, at which a vortex-antivortex\npair is emitted, particle motion can be periodic or chaotic. We demonstrate\nthat the interaction of a particle with vortices leads to dynamics that depends\nsensitively on the particle characteristics. We also demonstrate that\nassemblies of particles and vortices can have rich, and often turbulent\nspatiotemporal evolution. In particular, we consider the dynamics of the\nfollowing illustrative initial configurations: (a) one particle placed in front\nof a translating vortex-antivortex pair; (b) two particles placed in front of a\ntranslating vortex-antivortex pair; (c) a single particle moving in the\npresence of counter-rotating vortex clusters; and (d) four particles in the\npresence of counter-rotating vortex clusters. We compare our work with earlier\nstudies and examine its implications for recent experimental studies in\nsuperfluid Helium and Bose-Einstein condensates.",
        "positive": "Dynamic optical lattices of sub-wavelength spacing for ultracold atoms: We propose a scheme to realize lattice potentials of sub-wavelength spacing\nfor ultracold atoms. It is based on spin-dependent optical lattices with a\ntime-periodic modulation. We show that the atomic motion is well described by\nthe combined action of an effective, time-independent, lattice of small\nspacing, together with a micro-motion associated with the time-modulation. A\nnumerical simulation shows that an atomic gas can be adiabatically loaded into\nthe effective lattice ground state, for timescales comparable to the ones\nrequired for adiabatic loading of standard optical lattices. We generalize our\nscheme to a two-dimensional geometry, leading to Bloch bands with non-zero\nChern numbers. The realization of lattices of sub-wavelength spacing allows for\nthe enhancement of energy scales, which could facilitate the achievment of\nstrongly-correlated (topological) states."
    },
    {
        "anchor": "Comment on \"Fermi-Bose Mixtures near Broad Interspecies Feshbach\n  Resonances\": In a recent Letter (Phys. Rev. lett. 105, 195301 (2010)), Song et al.\nintroduced a new variational approach to treat strong attractive boson-fermion\n(BF) correlations in BF atomic mixtures. The proposed theory predicts a first\norder phase transition to a condensate of composite BF pairs with center of\nmass momentum Q=0 as opposed to a composite fermionic molecular Fermi gas. We\nshow in this comment that their approach is incorrect and moreover, by\nresorting to an exactly solvable model we demonstrate that there cannot be more\nthan one correlated Q=0 BF pair in complete contradiction with their\nconclusions.",
        "positive": "Density Fluctuations in Uniform Quantum Gases: Analytical expressions are given for the static structure factor S(k) and the\npair correlation function g(r) for uniform ideal Bose-Einstein and Fermi-Dirac\ngases for all temperatures. In the vicinity of Bose Einstein condensation (BEC)\ntemperature, g(r) becomes long ranged and remains so in the condensed phase. In\nthe dilute gas limit, g(r) of bosons & fermions do not coincide with\nMaxwell-Boltzmann gas but exhibit bunching & anti-bunching effect respectively.\nThe width of these functions depends on the temperature and is scaled as \\surd\n(inverse atomic mass). Our numerical results provide the precise quantitative\nvalues of suppression/increase (antibunching and bunching) of the density\nfluctuations at small distances in ideal quantum gases in qualitative agreement\nwith the experimental observation for almost non-trapped dilute gases."
    },
    {
        "anchor": "Quantum Monte-Carlo study of the Bose polaron problem in a\n  one-dimensional gas with contact interactions: We present a theoretical study based upon quantum Monte Carlo methods of the\nBose polaron in one-dimensional systems with contact interactions. In this\ninstance of the problem of a single impurity immersed in a quantum bath, the\nmedium is a Lieb-Liniger gas of bosons ranging from the weakly interacting to\nthe Tonks-Girardeau regime, whereas the impurity is coupled to the bath via a\ndifferent contact potential producing both repulsive and attractive\ninteractions. Both the case of a mobile impurity, having the same mass as the\nparticles in the medium, and of a static impurity with infinite mass are\nconsidered. We make use of exact numerical techniques that allow us to\ncalculate the ground-state energy of the impurity, its effective mass as well\nas the contact parameter between the impurity and the bath. These quantities\nare investigated as a function of the strength of interactions between the\nimpurity and the bath and within the bath. In particular, we find that the\neffective mass rapidly increases to very large values when the impurity gets\nstrongly coupled to an otherwise weakly repulsive bath. This heavy impurity\nhardly moves within the medium, thereby realizing the \"self-localization\"\nregime of the Landau-Pekar polaron. Furthermore, we compare our results with\npredictions of perturbation theory valid for weak interactions and with exact\nsolutions available when the bosons in the medium behave as impenetrable\nparticles.",
        "positive": "Dynamics of highly unbalanced Bose-Bose mixtures: miscible vs immiscible\n  gases: We study the collective modes of the minority component of a highly\nunbalanced Bose-Bose mixtures. In the miscible case the minority component\nfeels an effective external potential and we derive an analytical expression\nfor the mode frequencies. The latter is independent of the minority component\ninteraction strength. In the immiscible case we find that the ground state can\nbe a two-domain walls soliton. Although the mode frequencies are continuous at\nthe transition, their behaviour is very different with respect to the miscible\ncase. The dynamical behaviour of the solitonic structure and the frequency\ndependence on the inter- and intra-species interaction is numerically studied\nusing coupled Gross-Pitaevskii equations."
    },
    {
        "anchor": "Applying machine learning optimization methods to the production of a\n  quantum gas: We apply three machine learning strategies to optimize the atomic cooling\nprocesses utilized in the production of a Bose-Einstein condensate (BEC). For\nthe first time, we optimize both laser cooling and evaporative cooling\nmechanisms simultaneously. We present the results of an evolutionary\noptimization method (Differential Evolution), a method based on non-parametric\ninference (Gaussian Process regression) and a gradient-based function\napproximator (Artificial Neural Network). Online optimization is performed\nusing no prior knowledge of the apparatus, and the learner succeeds in creating\na BEC from completely randomized initial parameters. Optimizing these cooling\nprocesses results in a factor of four increase in BEC atom number compared to\nour manually-optimized parameters. This automated approach can maintain\nclose-to-optimal performance in long-term operation. Furthermore, we show that\nmachine learning techniques can be used to identify the main sources of\ninstability within the apparatus.",
        "positive": "Exact one-particle density matrix for SU($N$) fermionic matter-waves in\n  the strong repulsive limit: We consider a gas of repulsive $N$-component fermions confined in a\nring-shaped potential, subject to an effective magnetic field. For large\nrepulsion strengths, we work out a Bethe ansatz scheme to compute the two-point\ncorrelation matrix and then the one-particle density matrix. Our results holds\nin the mesoscopic regime of finite but sufficiently large number of particles\nand system size that are not accessible by numerics. We access the momentum\ndistribution of the system and analyse its specific dependence of interaction,\nmagnetic field and number of components $N$. In the context of cold atoms, the\nexact computation of the correlation matrix to determine the interference\npatterns that are produced by releasing cold atoms from ring traps is carried\nout."
    },
    {
        "anchor": "Emergent topology and symmetry-breaking order in correlated quench\n  dynamics: Quenching a quantum system involves three basic ingredients: the initial\nphase, the post-quench target phase, and the non-equilibrium dynamics which\ncarries the information of the former two. Here we propose a dynamical theory\nto characterize both the topology and symmetry-breaking order in correlated\nquantum system, through quenching the Haldane-Hubbard model from an initial\nmagnetic phase to topologically nontrivial regime. The equation of motion for\nthe complex pseudospin dynamics is obtained with the flow equation method, with\nthe pseudospin evolution shown to obey a microscopic\nLandau-Lifshitz-Gilbert-Bloch equation. We find that the correlated quench\ndynamics exhibit robust universal behaviors on the so-called band-inversion\nsurfaces (BISs), from which the nontrivial topology and magnetic order can be\nextracted. In particular, the topology of the post-quench regime can be\ncharacterized by an emergent dynamical topological pattern of quench dynamics\non BISs, which is robust against dephasing and heating induced by interactions;\nthe pre-quench symmetry-breaking orders is read out from a universal scaling\nbehavior of the quench dynamics emerging on the BIS, which is valid beyond the\nmean-field regime. This work opens a way to characterize both the topology and\nsymmetry-breaking orders by correlated quench dynamics.",
        "positive": "Geometric squeezing of rotating quantum gases into the lowest Landau\n  level: The simulation of quantum Hall physics with rotating quantum gases is\nwitnessing a revival due to recent experimental advances that enabled the\nobservation of a Bose-Einstein condensate entirely contained in its lowest\nkinetic energy state, i.e. the lowest Landau level. We theoretically describe\nthis experimental result, and show that it can be interpreted as a squeezing of\nthe geometric degree of freedom of the problem, the guiding center metric. This\n\"geometric squeezing\" offers an unprecedented experimental control over the\nquantum geometry in Landau-level analogues, and at the same time opens a\nrealistic path towards achieving correlated quantum phases akin to quantum Hall\nstates with neutral atoms."
    },
    {
        "anchor": "Precursor of Laughlin state of hard core bosons on a two leg ladder: We study hard core bosons on a two leg ladder lattice under the orbital\neffect of a uniform magnetic field. At densities which are incommensurate with\nflux, the ground state is a Meissner state, or a vortex state, depending on the\nstrength of the flux. When the density is commensurate with the flux,\nanalytical arguments predict the existence of a ground state of central charge\n$c = 1$, which displays signatures compatible with the expected Laughlin state\nat $\\nu=1/2$. This differs from the coupled wire construction of the Laughlin\nstate in that there exists a nonzero backscattering term in the edge\nHamiltonian. We construct a phase diagram versus density and flux in order to\ndelimit the region where this precursor to the Laughlin state is the ground\nstate, by using a combination of bosonization and numerics based on the density\nmatrix renormalization group (DMRG) and exact diagonalization. We obtain the\nphase diagram from local observables and central charge. We use bipartite\ncharge fluctuations to deduce the Luttinger parameter for the edge Luttinger\nliquid corresponding to the Laughlin state. The properties studied with local\nobservables are confirmed by the long distance behavior of correlation\nfunctions. Our findings are consistent with a calculation of the many body\nground state transverse conductivity in a thin torus geometry for parameters\ncorresponding to the Laughlin state. The model considered is simple enough such\nthat the precursor to the Laughlin state could be realized in current ultracold\natom, Josephson junction array, and quantum circuit experiments.",
        "positive": "Thermometry of bosonic mixtures in Optical Lattices via Demixing: Motivated by recent experiments and theoretical investigations on binary\nmixtures, we investigate the miscible-immiscible transition at finite\ntemperature by means of Quantum Monte Carlo. Based on the observation that the\nsegregated phase is strongly affected by temperature, we propose to use the\ndegree of demixing for thermometry of a binary bosonic mixture trapped in an\noptical lattice. We show that the proposed method is especially sensitive at\nlow temperatures, of the order of the tunnelling amplitude, and therefore is\nparticularly suitable in the regime where quantum magnetism is expected."
    },
    {
        "anchor": "Exotic pairing states in a Fermi gas with three-dimensional spin-orbit\n  coupling: We investigate properties of exotic pairing states in a three-dimensional\nFermi gas with three-dimensional spin-orbit coupling and an effective Zeeman\nfield. The interplay of spin-orbit coupling, effective Zeeman field and pairing\ncan lead to first-order phase transitions between different phases, and to\ninteresting nodal superfluid states with gapless surfaces in the momentum\nspace. We then demonstrate that pairing states with zero center-of-mass\nmomentum are unstable against finite center-of-mass momentum\nFulde-Ferrell-Larkin-Ovchinnikov (FFLO) states, with the center-of-mass\nmomentum of the pairs opposite to the direction of the effective Zeeman field.\nUnlike conventional FFLO states, these FFLO states are induced by the\ncoexistence of spin-orbit coupling and Fermi surface deformation, and have\nintriguing features like first-order transitions between different FFLO states,\nnodal FFLO states with gapless surfaces in momentum space, and exotic fully\ngapped FFLO states. With the recent theoretical proposals for realizing\nthree-dimensional spin-orbit coupling in ultracold atom gases, our work is\nhelpful for the future experimental studies, and provides valuable information\nfor the general understanding of pairing physics in spin-orbit coupled\nfermionic systems.",
        "positive": "Quantum Monte Carlo study of ultracold gases (PhD thesis): This Dissertation presents results of a thorough study of ultracold bosonic\nand fermionic gases in three-dimensional and quasi-one-dimensional systems.\nAlthough the analyses are carried out within various theoretical frameworks\n(Gross-Pitaevskii, Bethe ansatz, local density approximation, etc.) the main\ntool of the study is the Quantum Monte Carlo method in different modifications\n(variational Monte Carlo, diffusion Monte Carlo, fixed-node Monte Carlo\nmethods). We benchmark our Monte Carlo calculations by recovering known\nanalytical results (perturbative theories in dilute limits, exactly solvable\nmodels, etc.) and extend calculations to regimes, where the results are so far\nunknown. In particular we calculate the equation of state and correlation\nfunctions for gases in various geometries and with various interatomic\ninteractions."
    },
    {
        "anchor": "Fermi Gases with Synthetic Spin-Orbit Coupling: We briefly review recent progress on ultracold atomic Fermi gases with\ndifferent types of synthetic spin-orbit coupling, including the one-dimensional\n(1D) equal weight Rashba-Dresselhaus and two-dimensional (2D) Rasbha spin-orbit\ncouplings. Theoretically, we show how the single-body, two-body and many-body\nproperties of Fermi gases are dramatically changed by spin-orbit coupling. In\nparticular, the interplay between spin-orbit coupling and interatomic\ninteraction may lead to several long-sought exotic superfluid phases at low\ntemperatures, such as anisotropic superfluid, topological superfluid and\ninhomogeneous superfluid. Experimentally, only the first type - equal weight\ncombination of Rasbha and Dresselhaus spin-orbit couplings - has been realized\nvery recently using a two-photon Raman process. We show how to characterize a\nnormal spin-orbit coupled atomic Fermi gas in both non-interacting and\nstrongly-interacting limits, using particularly momentum-resolved\nradio-frequency spectroscopy. The experimental demonstration of a\nstrongly-interacting spin-orbit coupled Fermi gas opens a promising way to\nobserve various exotic superfluid phases in the near future.",
        "positive": "Experimental verification of the very strong coupling regime in a GaAs\n  quantum well microcavity: When the coupling between light and matter becomes comparable to the energy\ngap between different excited states they hybridize, leading to the appearance\nof a rich and complex phenomenology which attracted remarkable interest in\nrecent years. While the mixing between states with different number of\nexcitations, so-called ultrastrong coupling regime, has been observed in\nvarious implementations, the effect of the hybridization between different\nsingle excitation states, referred to as very strong coupling regime, has\nremained elusive. In semiconductor quantum wells such a regime is predicted to\nmanifest as a photon-mediated electron-hole coupling leading to different\nexcitonic wavefunctions for the two polaritonic branches when the ratio of the\ncoupling strength to exciton binding energy approaches unity. Here, we verify\nexperimentally the existence of this regime in magneto-optical measurements on\na microcavity with 28 GaAs quantum wells, showing that the average\nelectron-hole separation of the upper polariton is significantly increased\ncompared to the bare quantum well exciton Bohr radius. This manifests in a\ndiamagnetic shift around zero detuning that exceeds the shift of the lower\npolariton by one order of magnitude and the bare quantum well exciton\ndiamagnetic shift by a factor of two. The lower polariton exhibits a\ndiamagnetic shift smaller than expected from the coupling of a rigid exciton to\nthe cavity mode which suggests more tightly bound electron-hole pairs than in\nthe bare quantum well."
    },
    {
        "anchor": "Two-field optical methods to control magnetic Feshbach resonances: Using an optically-trapped mixture of the two lowest hyperfine states of a\n$^6$Li Fermi gas, we observe two-field optical tuning of the narrow Feshbach\nresonance by up to 3 G and an increase in spontaneous lifetime near the broad\nresonance from $0.5$ ms to $0.4$ s. We present a new model of light-induced\nloss spectra, employing continuum-dressed basis states, that agrees in shape\nand magnitude with measurements for both broad and narrow resonances.",
        "positive": "Decay and fragmentation in an open Bose-Hubbard chain: We analyze the decay of ultracold atoms from an optical lattice with loss\nform a single lattice site. If the initial state is dynamically stable a\nsuitable amount of dissipation can stabilize a Bose-Einstein condensate, such\nthat it remains coherent even in the presence of strong interactions. A\ntransition between two different dynamical phases is observed if the initial\nstate is dynamically unstable. This transition is analyzed here in detail. For\nstrong interactions, the system relaxes to an entangled quantum state with\nremarkable statistical properties: The atoms bunch in a few \"breathers\" forming\nat random positions. Breathers at different positions are coherent, such that\nthey can be used in precision quantum interferometry and other applications."
    },
    {
        "anchor": "Topological Gapless Matters in Three-dimensional Ultracold Atomic Gases: Three-dimensional topological gapless matters with gapless degeneracies\nprotected by a topological invariant defined over a closed manifold in momentum\nspace have attracted considerable interest in various fields ranging from\ncondensed matter materials to ultracold atomic gases. As a highly controllable\nand disorder free system, ultracold atomic gases provide a versatile platform\nto simulate topological gapless matters. Here, the current progress in studies\nof topological gapless phenomena in three-dimensional cold atom systems is\nsummarized in the review. It is mainly focused on Weyl points, structured\n(type-II) Weyl points, Dirac points, nodal rings and Weyl exceptional rings in\ncold atoms. Since interactions in cold atoms can be controlled via Feshbach\nresonances, the progress in both superfluids for attractive interactions and\nnon-interacting cold atom gases is reviewed.",
        "positive": "Thermalization in a quasi-1D ultracold bosonic gas: We study the collisional processes that can lead to thermalization in\none-dimensional systems. For two body collisions excitations of transverse\nmodes are the prerequisite for energy exchange and thermalzation. At very low\ntemperatures excitations of transverse modes are exponentially suppressed,\nthermalization by two body collisions stops and the system should become\nintegrable. In quantum mechanics virtual excitations of higher radial modes are\npossible. These virtually excited radial modes give rise to effective\nthree-body velocity-changing collisions which lead to thermalization. We show\nthat these three-body elastic interactions are suppressed by pairwise quantum\ncorrelations when approaching the strongly correlated regime. If the relative\nmomentum $k$ is small compared to the two-body coupling constant $c$ the\nthree-particle scattering state is suppressed by a factor of $(k/c)^{12}$,\nwhich is proportional to $\\gamma ^{12}$, that is to the square of the\nthree-body correlation function at zero distance in the limit of the\nLieb-Liniger parameter $\\gamma \\gg 1$. This demonstrates that in one\ndimensional quantum systems it is not the freeze-out of two body collisions but\nthe strong quantum correlations which ensures absence of thermalization on\nexperimentally relevant time scales."
    },
    {
        "anchor": "Single-Particle Momentum Distribution of an Efimov trimer: Experimental progress in the study of strongly interacting ultracold atoms\nhas recently allowed the observation of Efimov trimers. We study theoretically\na non-conventional observable for these trimer states, that may be accessed\nexperimentally, the momentum distribution n(k) of the constitutive bosonic\nparticles. The large momentum part of the distribution is particularly\nintriguing: In addition to the expected 1/k^4 tail associated to contact\ninteractions, it exhibits a subleading tail 1/k^5 which is a hall-mark of\nEfimov physics and leads to a breakdown of a previously proposed expression of\nthe energy as a functional of the momentum distribution.",
        "positive": "Quasiparticles of widely tuneable inertial mass: The dispersion relation\n  of atomic Josephson vortices and related solitary waves: Superconducting Josephson vortices have direct analogues in ultracold-atom\nphysics as solitary-wave excitations of two-component superfluid Bose gases\nwith linear coupling. Here we numerically extend the zero-velocity Josephson\nvortex solutions of the coupled Gross-Pitaevskii equations to non-zero\nvelocities, thus obtaining the full dispersion relation. The inertial mass of\nthe Josephson vortex obtained from the dispersion relation depends on the\nstrength of linear coupling and has a simple pole divergence at a critical\nvalue where it changes sign while assuming large absolute values. Additional\nlow-velocity quasiparticles with negative inertial mass emerge at finite\nmomentum that are reminiscent of a dark soliton in one component with\ncounter-flow in the other. In the limit of small linear coupling we compare the\nJosephson vortex solutions to sine-Gordon solitons and show that the\ncorrespondence between them is asymptotic, but significant differences appear\nat finite values of the coupling constant. Finally, for unequal and non-zero\nself- and cross-component nonlinearities, we find a new solitary-wave\nexcitation branch. In its presence, both dark solitons and Josephson vortices\nare dynamically stable while the new excitations are unstable."
    },
    {
        "anchor": "Quantum Bose liquids with logarithmic nonlinearity: Self-sustainability\n  and emergence of spatial extent: The Gross-Pitaevskii (GP) equation is a long-wavelength approach widely used\nto describe the dilute Bose-Einstein condensates (BEC). However, in many\nphysical situations, such as higher densities, this approximation unlikely\nsuffices hence one might need models which would account for long-range\ncorrelations and multi-body interactions. We show that the Bose liquid\ndescribed by the logarithmic wave equation has a number of drastic differences\nfrom the GP one. It possesses the self-sustainability property: while the free\nGP condensate tends to spill all over the available volume the logarithmic one\ntends to form a Gaussian-type droplet - even in the absence of an external\ntrapping potential. The quasi-particle modes of the logarithmic BEC are shown\nto acquire a finite size despite the bare particles being assumed point-like,\ni.e., the spatial extent emerges here as a result of quantum many-body\ncorrelations. Finally, we study the elementary excitations and demonstrate that\nthe background density changes the topological structure of their momentum\nspace which, in turn, affects their dispersion relations. Depending on the\ndensity the latter can be of the massive relativistic, massless relativistic,\ntachyonic and quaternionic type.",
        "positive": "Mathematical theory and numerical methods for Bose-Einstein condensation: In this paper, we mainly review recent results on mathematical theory and\nnumerical methods for Bose-Einstein condensation (BEC), based on the\nGross-Pitaevskii equation (GPE). Starting from the simplest case with\none-component BEC of the weakly interacting bosons, we study the reduction of\nGPE to lower dimensions, the ground states of BEC including the existence and\nuniqueness as well as nonexistence results, and the dynamics of GPE including\ndynamical laws, well-posedness of the Cauchy problem as well as the finite time\nblow-up. To compute the ground state, the gradient flow with discrete\nnormalization (or imaginary time) method is reviewed and various full\ndiscretization methods are presented and compared. To simulate the dynamics,\nboth finite difference methods and time splitting spectral methods are\nreviewed, and their error estimates are briefly outlined. When the GPE has\nsymmetric properties, we show how to simplify the numerical methods. Then we\ncompare two widely used scalings, i.e. physical scaling (commonly used) and\nsemiclassical scaling, for BEC in strong repulsive interaction regime\n(Thomas-Fermi regime), and discuss semiclassical limits of the GPE. Extensions\nof these results for one-component BEC are then carried out for rotating BEC by\nGPE with an angular momentum rotation, dipolar BEC by GPE with long range\ndipole-dipole interaction, and two-component BEC by coupled GPEs. Finally, as a\nperspective, we show briefly the mathematical models for spin-1 BEC, Bogoliubov\nexcitation and BEC at finite temperature."
    },
    {
        "anchor": "Dynamical structure factor and a new method to measure the pairing gap\n  in two-dimensional attractive Fermi-Hubbard model: By calculating the dynamical structure factor along the high symmetry\ndirections in the Brillouin zone, the dynamical excitations in two-dimensional\nattractive Fermi-Hubbard model are studied based on the random-phase\napproximation. At the small transfer momentum, the sound speed can be obtained\nand is suppressed by the interaction strength. In particular, at the transfer\nmomentum ${\\bf q}=\\left[\\pi,\\pi\\right]$, the dynamical structure factor\nconsists of a sharp bosonic molecular excitation peak in the low-energy region\nand a broad atomic excitation band in the higher energy region. Furthermore, as\nthe hopping strength increases (the interaction strength decreases), the weight\nof the molecular excitation peak decreases monotonically while the weight of\nthe atomic excitations increases quickly. The area of the molecular excitation\npeak scales with the square of the pairing gap, which also applies to the\nspin-orbit coupling case. These theoretical results show that the pairing gap\nin optical lattice can be obtained experimentally by measuring the dynamical\nstructure factor at ${\\bf q}=\\left[\\pi,\\pi\\right]$.",
        "positive": "Absorption imaging of a quasi 2D gas: a multiple scattering analysis: Absorption imaging with quasi-resonant laser light is a commonly used\ntechnique to probe ultra-cold atomic gases in various geometries. Here we\ninvestigate some non-trivial aspects of this method when it is applied to in\nsitu diagnosis of a quasi two-dimensional gas. Using Monte Carlo simulations we\nstudy the modification of the absorption cross-section of a photon when it\nundergoes multiple scattering in the gas. We determine the variations of the\noptical density with various parameters, such as the detuning of the light from\nthe atomic resonance and the thickness of the gas. We compare our results to\nthe known three-dimensional result (Beer-Lambert law) and outline the specific\nfeatures of the two-dimensional case."
    },
    {
        "anchor": "Dissipative nonlinear waves in a gravitating quantum fluid: Nonlinear wave propagation is studied analytically in a dissipative,\nself-gravitating Bose Einstein condensate, in the framework of Gross-Pitaevskii\nmodel. The linear dispersion relation shows that the effect of dissipation is\nto suppress dynamical instabilities that destabilize the system. The small\namplitude analysis using reductive perturbation technique is found to yield a\nmodified form of KdV equation. The soliton energy, amplitude and velocity are\nfound to decay with time, whereas the soliton width increases, such that the\nsoliton exists for a finite time only",
        "positive": "Probing quantum transport by engineering correlations in a speckle\n  potential: We develop a procedure to modify the correlations of a speckle potential.\nThis procedure, that is suitable for spatial light modulator devices, allows\none to increase the localization efficiency of the speckle in a narrow energy\nregion whose position can be easily tuned. This peculiar energy-dependent\nlocalization behavior is explored by pulling the potential through a\ncigar-shaped Bose-Einstein condensate. We show that the percentage of dragged\natoms as a function of the pulling velocity depends on the potential\ncorrelations below a threshold of the disorder strength. Above this threshold,\ninterference effects are no longer clearly observable during the condensate\ndrag."
    },
    {
        "anchor": "Superradiant phase transition with cavity assisted dynamical spin-orbit\n  coupling: Superradiant phase transition represents an important quantum phenomenon that\nshows the collective excitations based on the coupling between atoms and cavity\nmodes. The spin-orbit coupling is another quantum effect which induced from the\ninteraction of the atom internal degrees of freedom and momentum of\ncenter-of-mass. In this work, we consider the cavity assisted dynamical\nspin-orbit coupling which comes from the combination of these two effects. It\ncan induce a series of interesting quantum phenomena, such as the flat spectrum\nand the singularity of the excitation energy spectrum around the critical point\nof quantum phase transition. We further discuss the influence of atom decay and\nnonlinear coupling to the phase diagram. The atom decay suppresses the\nsingularity of the phase diagram and the nonlinear coupling can break the\nsymmetric properties of the phase transition. Our work provide the theoretical\nmethods to research the rich quantum phenomena in this dynamic many-body\nsystems.",
        "positive": "Reply to Comment on \"Quantum quasicrystals of spin-orbit coupled dipolar\n  bosons'': In a recent Letter [Phys. Rev. Lett. 111, 185304 (2013)], we proposed a\nscheme for realizing quantum quasicrystals using spin-orbit coupled dipolar\nbosons. We remarked that these quantum quasicrystals have additional\n``phason''-like modes compared with their classical counterparts. A recent\ncomment by Lifshitz [arXiv:1312.1388] contests this claim. We argue here that\nour enumeration of gapless modes is indeed the physically relevant one; whether\nthe additional modes are ``phasons'' is, however, a matter of definition."
    },
    {
        "anchor": "Exact diagonalization of the truncated Bogoliubov Hamiltonian: The present short note is simply intended to communicate that I have\nanalytically diagonalized the Bogoliubov truncated Hamiltonian\n$H_c$~\\cite{Bogo1,Bogo2}, in an interacting bosonic gas. This is the natural\nprosecution of my work~\\cite{MS}, now denoted as (I), where the diagonalization\nwas performed only in the subspace corresponding to zero momentum collective\nexcitations (CE).",
        "positive": "Time crystals: analysis of experimental conditions: Time crystals are quantum many-body systems which are able to self-organize\ntheir motion in a periodic way in time. Discrete time crystals have been\nexperimentally demonstrated in spin systems. However, the first idea of\nspontaneous breaking of discrete time translation symmetry, in ultra-cold atoms\nbouncing on an oscillating mirror, still awaits experimental demonstration.\nHere, we perform a detailed analysis of the experimental conditions needed for\nthe realization of such a discrete time crystal. Importantly, the considered\nsystem allows for the realization of dramatic breaking of discrete time\ntranslation symmetry where a symmetry broken state evolves with a period tens\nof times longer than the driving period. Moreover, atoms bouncing on an\noscillating mirror constitute a suitable system for the realization of\ndynamical quantum phase transitions in discrete time crystals and for the\ndemonstration of various non-trivial condensed matter phenomena in the time\ndomain. We show that Anderson localization effects, which are typically\nassociated with spatial disorder and exponential localization of eigenstates of\na particle in configuration space, can be observed in the time domain when\nultra-cold atoms are bouncing on a randomly moving mirror."
    },
    {
        "anchor": "Quantum Caging in Interacting Many-Body All-Bands-Flat Lattices: We consider translationally invariant tight-binding all-bands-flat networks\nwhich lack dispersion. In a recent work [arXiv:2004.11871] we derived the\nsubset of these networks which preserves nonlinear caging, i.e. keeps compact\nexcitations compact in the presence of Kerr-like local nonlinearities. Here we\nreplace nonlinear terms by Bose-Hubbard interactions and study quantum caging.\nWe prove the existence of degenerate energy renormalized compact states for two\nand three particles, and use an inductive conjecture to generalize to any\nfinite number M of participating particles in one dimension. Our results\nexplain and generalize previous observations for two particles on a diamond\nchain [Vidal et.al. Phys. Rev. Lett. 85, 3906 (2000)]. We further prove that\nquantum caging conditions guarantee the existence of extensive sets of\nconserved quantities in any lattice dimension, as first revealed in [Tovmasyan\net al Phys. Rev. B 98, 134513 (2018)] for a set of specific networks.\nConsequently transport is realized through moving pairs of interacting\nparticles which break the single particle caging.",
        "positive": "Kilohertz-driven Bose-Einstein condensates in optical lattices: We analyze time-of-flight absorption images obtained with dilute\nBose-Einstein con-densates released from shaken optical lattices, both\ntheoretically and experimentally. We argue that weakly interacting, ultracold\nquantum gases in kilohertz-driven optical potentials constitute equilibrium\nsystems characterized by a steady-state distri-bution of Floquet-state\noccupation numbers. Our experimental results consistently indicate that a\ndriven ultracold Bose gas tends to occupy a single Floquet state, just as it\noccupies a single energy eigenstate when there is no forcing. When the driving\namplitude is sufficiently high, the Floquet state possessing the lowest mean\nenergy does not necessarily coincide with the Floquet state connected to the\nground state of the undriven system. We observe strongly driven Bose gases to\ncondense into the former state under such conditions, thus providing nontrivial\nexamples of dressed matter waves."
    },
    {
        "anchor": "Resonantly interacting $p$-wave Fermi superfluid in two dimensions:\n  Tan's contact and breathing mode: Inspired by the renewed experimental activities on $p$-wave resonantly\ninteracting atomic Fermi gases, we theoretically investigate some experimental\nobservables of such systems at zero temperature in two dimensions, using both\nmean-field theory and Gaussian pair fluctuation theory. These observables\ninclude the two $p$-wave contact parameters and the breathing mode frequency,\nwhich can be readily measured in current cold-atom setups with $^{40}$K and\n$^{6}$Li atoms. We find that the many-body component of the two contact\nparameters exhibits a pronounced peak slightly above the resonance and\nconsequently leads to a dip in the breathing mode frequency. In the resonance\nlimit, we discuss the dependence of the equation of state and the breathing\nmode frequency on the dimensionless effective range of the interaction,\n$k_{F}R_{p}\\ll1$, where $k_{F}$ is the Fermi wavevector and $R_{p}$ is the\neffective range. The breathing mode frequency $\\omega_{B}$ deviates from the\nscale-invariant prediction of $\\omega_{c}=2\\omega_{0}$, where $\\omega_{0}$ is\nthe trapping frequency of the harmonic potential. This frequency shift is\ncaused by the necessary existence of the effective range. In the small range\nlimit, we predict that the mode frequency deviation at the leading order is\ngiven by, $\\delta\\omega_{B}\\simeq-(\\omega_{0}/4)\\ln^{-1}(k_{F}R_{p})$.",
        "positive": "A synthetic electric force acting on neutral atoms: Electromagnetism is a simple example of a gauge theory where the underlying\npotentials -- the vector and scalar potentials -- are defined only up to a\ngauge choice. The vector potential generates magnetic fields through its\nspatial variation and electric fields through its time-dependence. We\nexperimentally produce a synthetic gauge field that emerges only at low energy\nin a rubidium Bose-Einstein condensate: the neutral atoms behave as charged\nparticles do in the presence of a homogeneous effective vector potential. We\nhave generated a synthetic electric field through the time dependence of an\neffective vector potential, a physical consequence even though the vector\npotential is spatially uniform."
    },
    {
        "anchor": "Ultracold few fermionic atoms in needle-shaped double wells: spin chains\n  and resonating spin clusters from microscopic Hamiltonians emulated via\n  antiferromagnetic Heisenberg and t-J models: Advances with trapped ultracold atoms intensified interest in simulating\ncomplex physical phenomena, including quantum magnetism and transitions from\nitinerant to non-itinerant behavior. Here we show formation of\nantiferromagnetic ground states of few ultracold fermionic atoms in single and\ndouble well (DW) traps, through microscopic Hamiltonian exact diagonalization\nfor two DW arrangements: (i) two linearly oriented one-dimensional, 1D, wells,\nand (ii) two coupled parallel wells, forming a trap of two-dimensional, 2D,\nnature. The spectra and spin-resolved conditional probabilities reveal for both\ncases, under strong repulsion, atomic spatial localization at extemporaneously\ncreated sites, forming quantum molecular magnetic structures with non-itinerant\ncharacter. These findings usher future theoretical and experimental\nexplorations into the highly-correlated behavior of ultracold\nstrongly-repelling fermionic atoms in higher dimensions, beyond the\nfermionization physics that is strictly applicable only in the 1D case. The\nresults for four atoms are well described with finite Heisenberg spin-chain and\ncluster models. The numerical simulations of three fermionic atoms in symmetric\ndouble wells reveal the emergent appearance of coupled resonating 2D Heisenberg\nclusters, whose emulation requires the use of a t-J-like model, akin to that\nused in investigations of high T$_c$ superconductivity. The highly entangled\nstates discovered in the microscopic and model calculations of controllably\ndetuned, asymmetric, double wells suggest three-cold-atom DW quantum computing\nqubits.",
        "positive": "Engineering tunable local loss in a synthetic lattice of momentum states: Dissipation can serve as a powerful resource for controlling the behavior of\nopen quantum systems.Recently there has been a surge of interest in the\ninfluence of dissipative coupling on large quantum systems and, more\nspecifically, how these processes can influence band topology and phenomena\nlike many-body localization. Here, we explore the engineering of local, tunable\ndissipation in so-called synthetic lattices, arrays of quantum states that are\nparametrically coupled in a fashion analogous to quantum tunneling. Considering\nthe specific case of momentum-state lattices, we investigate two distinct\nmechanisms for engineering controlled loss: one relying on an explicit form of\ndissipation by spontaneous emission, and another relying on reversible coupling\nto a large reservoir of unoccupied states. We experimentally implement the\nlatter and demonstrate the ability to tune the local loss rate over a large\nrange. The introduction of controlled loss to the synthetic lattice toolbox\npromises to pave the way for studying the interplay of dissipation with\ntopology, disorder, and interactions."
    },
    {
        "anchor": "Topological phases in odd-legs frustrated synthetic ladders: The realization of the Hofstadter model in a strongly anisotropic ladder\ngeometry has now become possible in one-dimensional optical lattices with a\nsynthetic dimension. In this work, we show how the Hofstadter Hamiltonian in\nsuch ladder configurations hosts a topological phase of matter which is\nradically different from its two-dimensional counterpart. This topological\nphase stems directly from the hybrid nature of the ladder geometry, and is\nprotected by a properly defined inversion symmetry. We start our analysis\nconsidering the paradigmatic case of a three-leg ladder which supports a\ntopological phase exhibiting the typical features of topological states in one\ndimension: robust fermionic edge modes, a degenerate entanglement spectrum and\na non-zero Zak phase; then, we generalize our findings - addressable in the\nstate-of-the-art cold atom experiments - to ladders with an higher number of\nlegs.",
        "positive": "Stochastic Growth Dynamics and Composite Defects in Quenched Immiscible\n  Binary Condensates: We study the sensitivity of coupled condensate formation dynamics on the\nhistory of initial stochastic domain formation in the context of\ninstantaneously quenched elongated harmonically-trapped immiscible\ntwo-component atomic Bose gases. The spontaneous generation of defects in the\nfastest condensing component, and subsequent coarse-graining dynamics, can lead\nto a deep oscillating microtrap into which the other component condenses,\nthereby establishing a long-lived composite defect in the form of a dark-bright\nsolitary wave. We numerically map out diverse key aspects of these competing\ngrowth dynamics, focussing on the role of shot-to-shot fluctuations and global\nparameter changes (initial state choices, quench parameters and condensate\ngrowth rates). We conclude that phase-separated structures observable on\nexperimental timescales are likely to be metastable states whose form is\ninfluenced by the stability and dynamics of the spontaneously-emerging\ndark-bright solitary wave."
    },
    {
        "anchor": "Universal Feature in Optical Control of a p-wave Feshbach Resonance: In this Letter we report the experimental results on optical control of a\np-wave Feshbach resonance, by utilizing a laser driven bound-to-bound\ntransition to shift the energy of closed channel molecule. The magnetic field\nlocation for p-wave resonance as a function of laser detuning can be captured\nby a simple formula with essentially one parameter, which describes how\nsensitive the resonance depends on the laser detuning. The key result of this\nwork is to demonstrate, both experimentally and theoretically, that the ratio\nbetween this parameter for $m=0$ resonance and that for $m=\\pm 1$ resonance, to\nlarge extent, is universal. We also show that this optical control can create\nintriguing situations where interesting few- and many-body physics can occurs,\nsuch as a p-wave resonance overlapping with an s-wave resonance or three p-wave\nresonances being degenerate.",
        "positive": "Engineering of a Low-Entropy Quantum Simulator for Strongly Correlated\n  Electrons Using SU($\\mathcal{N}$)-Symmetric Cold Atom Mixtures: An advanced cooling scheme, incorporating entropy engineering, is vital for\nisolated artificial quantum systems designed to emulate the low-temperature\nphysics of strongly correlated electron systems (SCESs). This study\ntheoretically demonstrates a cooling method employing multi-component Fermi\ngases with SU($\\mathcal{N}$)-symmetric interactions, focusing on the case of\n$^{173}$Yb atoms in a two-dimensional optical lattice. Adiabatically\nintroducing a nonuniform state-selective laser gives rise to two distinct\nsubsystems: a central low-temperature region, exclusively composed of two\nspecific spin components, acts as a quantum simulator for SCESs, while the\nsurrounding $\\mathcal{N}$-component mixture retains a significant portion of\nthe entropy of the system. The SU($\\mathcal{N}$)-symmetric interactions ensure\nthat the total particle numbers for each component become good quantum numbers,\ncreating a sharp boundary for the two-component region. The cooling efficiency\nis assessed through extensive finite-temperature Lanczos calculations. The\nresults lay the foundation for quantum simulations of two-dimensional systems\nof Hubbard or Heisenberg type, offering crucial insights into intriguing\nlow-temperature phenomena in condensed-matter physics."
    },
    {
        "anchor": "Local and spatially extended sub-Poisson atom number fluctuations in\n  optical lattices: We demonstrate that ultracold interacting bosonic atoms in an optical lattice\nshow sub-Poissonian on-site and inter-site atom number fluctuations. The\nexperimental observations agree with numerical predictions of the truncated\nWigner approximation. The correlations persist in the presence of multi-mode\natom dynamics and even over large spatially extended samples involving several\nsites and large populations.",
        "positive": "SU(2) Ginzburg-Landau theory for degenerate Fermi gases with synthetic\n  non-Abelian gauge fields: The non-Abelian gauge fields play a key role in achieving novel quantum\nphenomena in condensed-matter and high-energy physics. Recently, the synthetic\nnon-Abelian gauge fields have been created in the neutral degenerate Fermi\ngases, and moreover, generate many exotic effects. All the previous predictions\ncan be well understood by the microscopic Bardeen-Cooper-Schrieffer theory. In\nthis work, we establish an SU(2) Ginzburg-Landau theory for degenerate Fermi\ngases with the synthetic non-Abelian gauge fields. We firstly address a\nfundamental problem how the non-Abelian gauge fields, imposing originally on\nthe Fermi atoms, affect the pairing field with no extra electric charge by a\nlocal gauge-field theory,and then obtain the first and second SU(2)\nGinzburg-Landau equations. Based on these obtained SU(2) Ginzburg-Landau\nequations, we find that the superfluid critical temperature of the intra-\n(inter-) band pairing increases (decreases) linearly, when increasing the\nstrength of the synthetic non-Abelian gauge fields. More importantly, we\npredict a novel SU(2) non-Abelian Josephson effect, which can be used to design\na new atomic superconducting quantum interference device."
    },
    {
        "anchor": "Observation of the phononic Lamb shift with a synthetic vacuum: The quantum vacuum fundamentally alters the properties of embedded particles.\nIn contrast to classical empty space, it allows for creation and annihilation\nof excitations. For trapped particles this leads to a change in the energy\nspectrum, known as Lamb shift. Here, we engineer a synthetic vacuum building on\nthe unique properties of ultracold atomic gas mixtures. This system makes it\npossible to combine high-precision spectroscopy with the ability of switching\nbetween empty space and quantum vacuum. We observe the phononic Lamb shift, an\nintruiguing many-body effect orginally conjectured in the context of solid\nstate physics. Our study therefore opens up new avenues for high-precision\nbenchmarking of non-trivial theoretical predictions in the realm of the quantum\nvacuum.",
        "positive": "Feshbach spectroscopy and scattering properties of ultracold Li+Na\n  mixtures: We have observed 26 interspecies Feshbach resonances at fields up to 2050 G\nin ultracold $^6$Li+$^{23}$Na mixtures for different spin-state combinations.\nApplying the asymptotic bound-state model to assign the resonances, we have\nfound that most resonances have d-wave character. This analysis serves as\nguidance for a coupled-channel calculation, which uses modified interaction\npotentials to describe the positions of the Feshbach resonances well within the\nexperimental uncertainty and to calculate their widths. The scattering length\nderived from the improved interaction potentials is experimentally confirmed\nand deviates from previously reported values in sign and magnitude. We give\nprospects for $^7$Li+$^{23}$Na and predict broad Feshbach resonances suitable\nfor tuning."
    },
    {
        "anchor": "Trapped one-dimensional ideal Fermi gas with a single impurity: Properties of a single impurity in a one-dimensional Fermi gas are\ninvestigated in homogeneous and trapped geometries. In a homogeneous system we\nuse McGuire's expression [J. B. McGuire, J. Math. Phys. 6, 432 (1965)] to\nobtain interaction and kinetic energies, as well as the local pair correlation\nfunction. The energy of a trapped system is obtained (i) by generalizing\nMcGuire expression (ii) within local density approximation (iii) using\nperturbative approach in the case of a weakly interacting impurity and (iv)\ndiffusion Monte Carlo method. We demonstrate that a closed formula based on the\nexact solution of the homogeneous case provides a precise estimation for the\nenergy of a trapped system for arbitrary coupling constant of the impurity even\nfor a small number of fermions. We analyze energy contributions from kinetic,\ninteraction and potential components, as well as spatial properties such as the\nsystem size. Finally, we calculate the frequency of the breathing mode. Our\nanalysis is directly connected and applicable to the recent experiments in\nmicrotraps.",
        "positive": "Ultracold plasmas from strongly anti-correlated Rydberg gases in the\n  Kinetic Field Theory formalism: The dynamics of correlated systems is relevant in many fields ranging from\ncosmology to plasma physics. However, they are challenging to predict and\nunderstand even for classical systems due to the typically large numbers of\nparticles involved. Here, we study the evolution of an ultracold, correlated\nmany-body system with repulsive interactions and initial correlations set by\nthe Rydberg blockade using the analytical framework of Kinetic Field Theory\n(KFT). The KFT formalism is based on the path-integral formulation for\nclassical mechanics and was first developed and successfully used in cosmology\nto describe structure formation in Dark Matter. The theoretical framework\noffers a high flexibility regarding the initial configuration and interactions\nbetween particles and, in addition, is computationally cheap. More importantly,\nthe analytic approach allows us to gain better insight into the processes which\ndominate the dynamics. In this work we show that KFT can be applied in a much\nmore general context and study the evolution of a correlated ion plasma. We\nfind good agreement between the analytical KFT results for the evolution of the\ncorrelation function and results obtained from numerical simulations. We use\nthe correlation functions obtained with KFT to compute the temperature increase\nin the ionic system due to disorder-induced heating. For certain choices of\nparameters we observe that the effect can be reversed, leading to correlation\ncooling. Due to its numerical efficiency as compared to numerical simulations,\na detailed study using KFT can help to constrain parameter spaces where\ndisorder-induced heating is minimal in order to reach the regime of strong\ncoupling."
    },
    {
        "anchor": "Analytical and numerical studies of Bose-Fermi mixtures in a\n  one-dimensional harmonic trap: In this paper we study a mixed system of bosons and fermions with up to six\nparticles in total. All particles are assumed to have the same mass. The\ntwo-body interactions are repulsive and are assumed to have equal strength in\nboth the Bose-Bose and the Fermi-Boson channels. The particles are confined\nexternally by a harmonic oscillator one-body potential. For the case of four\nparticles, two identical fermions and two identical bosons, we focus on the\nstrongly interacting regime and analyze the system using both an analytical\napproach and DMRG calculations using a discrete version of the underlying\ncontinuum Hamiltonian. This provides us with insight into both the ground state\nand the manifold of excited states that are almost degenerate for large\ninteraction strength. Our results show great variation in the density profiles\nfor bosons and fermions in different states for strongly interacting mixtures.\nBy moving to slightly larger systems, we find that the ground state of balanced\nmixtures of four to six particles tends to separate bosons and fermions for\nstrong (repulsive) interactions. On the other hand, in imbalanced Bose-Fermi\nmixtures we find pronounced odd-even effects in systems of five particles.\nThese few-body results suggest that question of phase separation in\none-dimensional confined mixtures are very sensitive to system composition,\nboth for the ground state and the excited states.",
        "positive": "Many-site coherence revivals in the extended Bose-Hubbard model and the\n  Gutzwiller approximation: We investigate the collapse and revival of first-order coherence in deep\noptical lattices when long-range interactions are turned on, and find that the\nfirst few revival peaks are strongly attenuated already for moderate values of\nthe nearest-neighbor interaction coupling. It is shown that the conventionally\nemployed Gutzwiller wavefunction, with only onsite-number dependence of the\nvariational amplitudes, leads to incorrect predictions for the collapse and\nrevival oscillations. We provide a modified variant of the Gutzwiller ansatz,\nreproducing the analytically calculated time dependence of first-order\ncoherence in the limit of zero tunneling."
    },
    {
        "anchor": "Optimal control for unitary preparation of many-body states: application\n  to Luttinger liquids: Many-body ground states can be prepared via unitary evolution in cold atomic\nsystems. Given the initial state and a fixed time for the evolution, how close\ncan we get to a desired ground state if we can tune the Hamiltonian in time?\nHere we study this optimal control problem focusing on Luttinger liquids with\ntunable interactions. We show that the optimal protocol can be obtained by\nsimulated annealing. We find that the optimal interaction strength of the\nLuttinger liquid can have a nonmonotonic time dependence. Moreover, the system\nexhibits a marked transition when the ratio $\\tau/L$ of the preparation time to\nthe system size exceeds a critical value. In this regime, the optimal protocols\ncan prepare the states with almost perfect accuracy. The optimal protocols are\nrobust against dynamical noise.",
        "positive": "Parametric instability of oscillations of a vortex ring in a\n  $z$-periodic Bose-Einstein condensate and the recurrence to starting state: The dynamics of deformations of a quantum vortex ring in a Bose-Einstein\ncondensate with periodic equilibrium density $\\rho(z)= 1-\\epsilon\\cos z$ has\nbeen considered within the local induction approximation. Parametric\ninstabilities of the normal modes with azimuthal numbers $\\pm m$ have been\nrevealed at the energy integral $E$ near values $E_m^{(p)}=2m\\sqrt{m^2-1}/p$,\nwhere $p$ is the resonance order. Numerical simulations have shown that already\nat $\\epsilon\\sim 0.03$ a rapid growth of unstable modes with $m=2$, $p=1$ to\nmagnitudes of order of unity is typical, which is then followed, after a few\nlarge oscillations, by fast return to a weakly excited state. Such behavior\ncorresponds to an integrable Hamiltonian of the form $H\\propto\n\\sigma(E_2^{(1)}-E)(|b_+|^2 + |b_-|^2) -\\epsilon(b_+ b_- + b_+^* b_-^*)\n+u(|b_+|^4 +|b_-|^4) + w |b_+|^2|b_-|^2$ for two complex envelopes $b_\\pm(t)$.\nThe results have been compared to parametric instabilities of vortex ring in\ncondensate with density $\\rho(z,r)=1-r^2-\\alpha z^2$, which take place at\n$\\alpha\\approx 8/5$ and at $\\alpha\\approx 16/7$."
    },
    {
        "anchor": "Dynamics of entanglement entropy of interacting fermions in a 1D driven\n  harmonic trap: Following up on a recent analysis of two cold atoms in a time-dependent\nharmonic trap in one dimension, we explore the entanglement entropy of two and\nthree fermions in the same situation when driven through a parametric\nresonance. We find that the presence of such a resonance in the two-particle\nsystem leaves a clear imprint on the entanglement entropy. We show how the\nsignal is modified by attractive and repulsive contact interactions, and how it\nremains present for the three-particle system. Additionaly, we extend the work\nof recent experiments to demonstrate how restricting observation to a limited\nsubsystem gives rise to locally thermal behavior.",
        "positive": "Quantum Many-Body Scar States in Two-Dimensional Rydberg Atom Arrays: We find exponentially many exact quantum many-body scar states in a\ntwo-dimensional PXP model -- an effective model for a two-dimensional Rydberg\natom array in the nearest-neighbor blockade regime. Such scar states are\nremarkably simple valence bond solids despite being at effectively infinite\ntemperature, and thus strongly violate the eigenstate thermalization\nhypothesis. Given a particular boundary condition, such eigenstates have\ninteger-valued energies. Moreover, certain charge-density-wave initial states\ngive rise to strong oscillations in the Rydberg excitation density after a\nquantum quench and tower-like structures in their overlaps with eigenstates."
    },
    {
        "anchor": "Transverse spin diffusion in strongly interacting Fermi gases: We compute spin diffusion in a dilute Fermi gas at arbitrary temperature,\npolarization and strong interaction in the normal phase using kinetic theory.\nWhile the longitudinal spin diffusivity depends weakly on polarization and\ndiverges for small temperatures, the transverse spin diffusivity D_\\perp has a\nstrong polarization dependence and approaches a finite value for T->0 in the\nFermi liquid phase. For a 3D unitary Fermi gas at infinite scattering length\nthe diffusivities reach a minimum near the quantum limit of diffusion \\hbar/m\nin the quantum degenerate regime and are strongly suppressed by medium\nscattering, and we discuss the importance of the spin-rotation effect. In two\ndimensions, D_\\perp attains a minimum at strong coupling -1 < ln(kFa2D) < 1 and\nreaches D_\\perp~0.2...0.3\\hbar/m at large polarization. These values are\nconsistent with recent measurements of two-dimensional ultracold atomic gases\nin the strong coupling regime.",
        "positive": "Manipulating Majorana fermions in one-dimensional spin-orbit coupled\n  atomic Fermi gases: Majorana fermions are promising candidates for storing and processing\ninformation in topological quantum computation. The ability to control such\nindividual information carriers in trapped ultracold atomic Fermi gases is a\nnovel theme in quantum information science. However, fermionic atoms are\nneutral and thus are difficult to manipulate. Here, we theoretically\ninvestigate the control of emergent Majorana fermions in one-dimensional\nspin-orbit coupled atomic Fermi gases. We discuss (i) how to move Majorana\nfermions by increasing or decreasing an effective Zeeman field, which acts like\na solid state control voltage gate; and (ii) how to create a pair of Majorana\nfermions by adding a magnetic impurity potential. We discuss the experimental\nrealization of our control scheme in an ultracold Fermi gas of $^{40}$K atoms."
    },
    {
        "anchor": "Active learning phase boundaries of a quantum many-body system: We describe how to use techniques from the field of Machine Learning to\ndirect a variational energy minimization scheme to search for phase boundaries\nof a quantum many-body system. The modeled physical system presents states of\nfinite momentum condensate, also known as FFLO states, as well as a uniform\nsuperfluid phase-all of which is interesting in its own right; however, a full\ndescription of the multitude of phase boundaries is expensive from a\ncomputational standpoint. In this work, we treat the output of the energy\nminimization as a labeled sythetic data set to train a support vector\nclassifier to separate states of finite momentum condensate from superfluid and\nnormal states. We can then use the trained support vector classifier to refocus\nthe minimizer to intensify its calculations near the boundary separating each\nof the three regions. Doing so will preclude using the minimizer to perform\nexpensive calculations deep within the normal or superfluid regions, resulting\nin more efficient use of compute time. The application of the procedure we\ndescribe is straightforward and should be applicable in any computational\nsearch of phase boundaries.",
        "positive": "Random-Phase-Approximation Excitation Spectra for Bose-Hubbard Models: We obtain the excitation spectra of the following three generalized\nBose-Hubbard (BH) models: (1) a two-species generalization of the spinless BH\nmodel, (2) a single-species, spin-1 BH model, and (3) the extended Bose-Hubbard\nmodel (EBH) for spinless interacting bosons of one species. In all the phases\nof these models we provide a unified treatment of random-phase-approximation\n(RPA) excitation spectra. These spectra have gaps in all the MI phases and gaps\nin the DW phases in the EBH model; they are gapless in all the SF phases in\nthese models and in the SS phases in the EBH model. We obtain the dependence of\n(a) gaps $\\Delta$ and (b) the sound velocity $u_s$ on the parameters of these\nmodels and examine $\\Delta$ and $u_s$ as these systems go through phase\ntransitions. At the SF-MI transitions in the spin-1 BH model, $u_s$ goes to\nzero continuously (discontinuously) for MI phases with an odd (even) number of\nbosons per site; this is consistent with the natures of these transition in\nmean-field theory. In the SF phases of these models, our excitation spectra\nagree qualitatively, at weak couplings, with those that can be obtained from\nGross-Pitaevskii-type models. We compare the results of our work with earlier\nstudies of related models and discuss implications for experiments."
    },
    {
        "anchor": "Universality of Brunnian ($N$-body Borromean) four and five-body systems: We compute binding energies and root mean square radii for weakly bound\nsystems of $N=4$ and $5$ identical bosons. Ground and first excited states of\nan $N$-body system appear below the threshold for binding the system with $N-1$\nparticles. Their root mean square radii approach constants in the limit of weak\nbinding. Their probability distributions are on average located in\nnon-classical regions of space which result in universal structures. Radii\ndecrease with increasing particle number. The ground states for more than five\nparticles are probably non-universal whereas excited states may be universal.",
        "positive": "Spin-orbital exchange of strongly interacting fermions on the $p$-band\n  of a two-dimensional optical lattice: Mott insulators with both spin and orbital degeneracy are pertinent to a\nlarge number of transition metal oxides. The intertwined spin and orbital\nfluctuations can lead to rather exotic phases such as quantum spin-orbital\nliquids. Here we consider two-component (spin 1/2) fermionic atoms with strong\nrepulsive interactions on the $p$-band of the optical square lattice. We derive\nthe spin-orbital exchange for quarter filling of the $p$-band when the density\nfluctuations are suppressed, and show it frustrates the development of long\nrange spin order. Exact diagonalization indicates a spin-disordered ground\nstate with ferro-orbital order. The system dynamically decouples into\nindividual Heisenberg spin chains, each realizing a Luttinger liquid accessible\nat higher temperatures compared to atoms confined to the $s$-band."
    },
    {
        "anchor": "Real-space probe for lattice quasiholes: We propose a real-space probe that is based on density measurements to\nextract distinct signatures of quasihole-like states of bosons experiencing a\nsynthetic magnetic field in a two-dimensional lattice. We numerically show that\ncertain ratios of the mean square radii of the particle cloud, obtainable\nthrough the density profile, approach the continuum values expected from\nLaughlin's ansatz wave functions quickly as the magnetic flux quanta per unit\ncell of the lattice decrease, even in a small lattice with few particles. This\nmethod could equally be used in both ultra-cold atomic and photonic systems.",
        "positive": "Fractional quantization of the topological charge pumping in a\n  one-dimensional superlattice: A one-dimensional quantum charge pump transfers a quantized charge in each\npumping cycle. This quantization is topologically robust being analogous to the\nquantum Hall effect. The charge transferred in a fraction of the pumping period\nis instead generally unquantized. We show, however, that with specific\nsymmetries in parameter space the charge transferred at well-defined fractions\nof the pumping period is quantized as integer fractions of the Chern number. We\nillustrate this in a one-dimensional Harper-Hofstadter model and show that the\nfractional quantization of the topological charge pumping is independent of the\nspecific boundary conditions taken into account. We further discuss the\nrelevance of this phenomenon for cold atomic gases in optical superlattices."
    },
    {
        "anchor": "Many-body localization and thermalization in disordered Hubbard chains: We study the many-body localization transition in one-dimensional Hubbard\nchains using exact diagonalization and quantum chaos indicators. We also study\ndynamics in the delocalized (ergodic) and localized phases and discuss\nthermalization and eigenstate thermalization, or the lack thereof, in such\nsystems. Consistently within the indicators and observables studied, we find\nthat ergodicity is very robust against disorder, namely, even in the presence\nof weak Hubbard interactions the disorder strength needed for the system to\nlocalize is large. We show that this robustness might be hidden by finite size\neffects in experiments with ultracold fermions.",
        "positive": "Kinked linear response from non-Hermitian pumping: Non-Hermiticity is known to give rise to modified topological bulk-boundary\ncorrespondences, which predict the presence of topological boundary modes\nthrough appropriately modified topological invariants. Yet, little is currently\nknown about how non-Hermiticity affects the precise linear response of\nwavepackets beyond their overall spectral flow. In this work, we discover that\ngenerically, non-Hermiticity gives rise to abrupt and prominent kinks in the\nsemi-classical wavepacket trajectories of quantum gases, despite the absence of\nsudden physical impulses. This physically stems from a hitherto\nunder-appreciated intrinsic non-locality from non-Hermitian pumping, even if\nall physical couplings are local, thereby resulting in enigmatic singularities\nin the band structure that lead to discontinuous band geometry and Berry\ncurvature. For concrete experimental demonstration, we propose an ultracold\natomic setup in a two-dimensional optical lattice with laser-induced loss, such\nthat response kinks can be observed without fine-tuning in the physical atomic\ncloud dynamics. Our results showcases unique non-monotonic behavior from\nnon-Hermitian pumping beyond the non-Hermitian skin effect, and suggests new\navenues for investigating non-Hermitian dynamics in ultracold atomic platforms."
    },
    {
        "anchor": "Persistence of equilibrium states in an oscillating double-well\n  potential: We investigate numerically parametrically driven coupled nonlinear\nSchrodinger equations modelling the dynamics of coupled wavefields in a\nperiodically oscillating double-well potential. The equations describe among\nother things two coupled periodically-curved optical waveguides with Kerr\nnonlinearity or horizontally shaken Bose-Einstein condensates in a double-well\nmagnetic trap. In particular, we study the persistence of equilibrium states of\nthe undriven system due to the presence of the parametric drive. Using\nnumerical continuations of periodic orbits and calculating the corresponding\nFloquet multipliers, we find that the drive can (de)stabilize a continuation of\nan equilibrium state indicated by the change of the (in)stability of the orbit.\nHence, we show that parametric drives can provide a powerful control to\nnonlinear (optical or matter wave) field tunneling. Analytical approximations\nbased on an averaging method are presented. Using perturbation theory the\ninfluence of the drive on the symmetry breaking bifurcation point is discussed.",
        "positive": "Two-Element Mixture of Bose and Fermi Superfluids: We report on the production of a stable mixture of bosonic and fermionic\nsuperfluids composed of the elements $^{174}$Yb and $^6$Li which feature a\nstrong mismatch in mass and distinct electronic properties. We demonstrate\nelastic coupling between the superfluids by observing the shift in dipole\noscillation frequency of the bosonic component due to the presence of the\nfermions. The measured magnitude of the shift is consistent with a mean-field\nmodel and its direction determines the previously unknown sign of the\ninterspecies scattering length to be positive. We also observe the exchange of\nangular momentum between the superfluids from the excitation of a scissors mode\nin the bosonic component through interspecies interactions. We explain this\nobservation using an analytical model based on superfluid hydrodynamics."
    },
    {
        "anchor": "Photon-mediated Peierls Transition of a 1D Gas in a Multimode Optical\n  Cavity: The Peierls instability toward a charge density wave is a canonical example\nof phonon-driven strongly correlated physics and is intimately related to\ntopological quantum matter and exotic superconductivity. We propose a method to\nrealize an analogous photon-mediated Peierls transition, using a system of\none-dimensional tubes of interacting Bose or Fermi atoms trapped inside a\nmultimode confocal cavity. Pumping the cavity transversely engineers a\ncavity-mediated metal--to--insulator transition in the atomic system. For\nstrongly interacting bosons in the Tonks-Girardeau limit, this transition can\nbe understood (through fermionization) as being the Peierls instability. We\nextend the calculation to finite values of the interaction strength and derive\nanalytic expressions for both the cavity field and mass gap. They display\nnontrivial power law dependence on the dimensionless matter-light coupling.",
        "positive": "Two-dimensional exciton-polariton interactions beyond the Born\n  approximation: We provide a many-body theory for the interactions of two-dimensional\nexcitons and polaritons beyond the Born approximation. Taking into account\nGaussian quantum fluctuations via the Bogoliubov theory, we find that the\ntwo-body interaction strength in two-dimensions has an inverse logarithmic\ndependence on the scattering length and ground state energy. This leads to a\nvanishing exciton interaction strength in the zero-momentum limit but a finite\npolariton interaction strength due to strong light-matter coupling. We also\nderive the exact Tan relations for exciton-polaritons and calculate Tan's\ncontact coefficient. We show the polariton interaction strength and Tan's\ncontact both exhibit an anomalous enhancement at red photon-exciton detuning\nwhen the scattering length is large. Our predictions may provide a\nqualitatively correct guide for studies of exciton and polariton\nnonlinearities, and suggest a route to achieving strongly nonlinear polariton\ngases."
    },
    {
        "anchor": "Observation of antiferromagnetic correlations in the Hubbard model with\n  ultracold atoms: Ultracold atoms in optical lattices have great potential to contribute to a\nbetter understanding of some of the most important issues in many-body physics,\nsuch as high-$T_c$ superconductivity. The Hubbard model describes many of the\nfeatures shared by the copper oxides, including an interaction-driven Mott\ninsulating state and an antiferromagnetic (AFM) state. Optical lattices filled\nwith a two-spin-component Fermi gas of ultracold atoms can faithfully realise\nthe Hubbard model with readily tunable parameters, and thus provide a platform\nfor the systematic exploration of its phase diagram. Realisation of strongly\ncorrelated phases, however, has been hindered by the need to cool the atoms to\ntemperatures as low as the magnetic exchange energy, and also by the lack of\nreliable thermometry. Here we demonstrate spin-sensitive Bragg scattering of\nlight to measure AFM spin correlations in a realisation of the 3D Hubbard model\nat temperatures down to 1.4 times that of the AFM phase transition. This\ntemperature regime is beyond the range of validity of a simple high-temperature\nseries expansion, which brings our experiment close to the limit of the\ncapabilities of current numerical techniques. We reach these low temperatures\nusing a unique compensated optical lattice technique, in which the confinement\nof each lattice beam is compensated by a blue-detuned laser beam. The\ntemperature of the atoms in the lattice is deduced by comparing the light\nscattering to determinantal quantum Monte Carlo and numerical linked-cluster\nexpansion calculations. Further refinement of the compensated lattice may\nproduce even lower temperatures which, along with light scattering thermometry,\nwould open avenues for achieving and characterising other novel quantum states\nof matter, such as the pseudogap regime of the 2D Hubbard model.",
        "positive": "Linking invariant for the quench dynamics of a two-dimensional two-band\n  Chern insulator: We discuss the topological invariant in the (2+1)-dimensional quench dynamics\nof a two-dimensional two-band Chern insulator starting from a topological\ninitial state (i.e., with a nonzero Chern number $c_i$), evolved by a\npost-quench Hamiltonian (with Chern number $c_f$). In contrast to the process\nwith $c_i=0$ studied in previous works, this process cannot be characterized by\nthe Hopf invariant that is described by the sphere homotopy group\n$\\pi_3(S^2)=\\mathbb{Z}$. It is possible, however, to calculate a variant of the\nChern-Simons integral with a complementary part to cancel the Chern number of\nthe initial spin configuration, which at the same time does not affect the\n(2+1)-dimensional topology. We show that the modified Chern-Simons integral\ngives rise to a topological invariant of this quench process, i.e., the linking\ninvariant in the $\\mathbb{Z}_{2c_i}$ class: $\\nu = (c_f - c_i) \\mod (2c_i)$. We\ngive concrete examples to illustrate this result and also show the detailed\ndeduction to get this linking invariant."
    },
    {
        "anchor": "Laser assisted tunneling in a Tonks-Girardeau gas: We investigate the applicability of laser assisted tunneling in a strongly\ninteracting one-dimensional Bose gas (the Tonks-Girardeau gas) in optical\nlattices. We find that the stroboscopic dynamics of the Tonks-Girardeau gas in\na continuous Wannier-Stark-ladder potential, supplemented with laser assisted\ntunneling, effectively realizes the ground state of one-dimensional hard-core\nbosons in a discrete lattice with nontrivial hopping phases. We compare\nobservables that are affected by the interactions, such as the momentum\ndistribution, natural orbitals and their occupancies, in the time-dependent\ncontinuous system, to those of the ground state of the discrete system.\nStroboscopically, we find an excellent agreement, indicating that laser\nassisted tunneling is a viable technique for realizing novel ground states and\nphases with hard-core one-dimensional Bose gases.",
        "positive": "Confinement-induced Resonances in Quasi-one-dimensional Traps with\n  Transverse Anisotropy: We study atom-atom scattering in quasi-one-dimensional geometries with\ntransverse anisotropy. By assuming an s-wave pseudo-potential of contact\ninteraction, we show that the system would exhibit a single confinement-induced\nresonance, where the scattering process degenerates to a total reflection as a\none-dimensional gas of impenetrable bosons. For a general form of interaction,\nwe present a formal calculation based on the two-channel model and conclude the\nexistence of only one confinement-induced resonance. Our findings are\ninconsistent with a recent experiment by Haller et al. [Phys. Rev. Lett. 104,\n153203 (2010)], where a splitting of confinement-induced resonances has been\nobserved in an anisotropic quasi-one-dimensional quantum gas of Cs atoms."
    },
    {
        "anchor": "Parametric tuning of dynamical phase transitions in ultracold reactions: Advances in ultracold chemistry have led to the possibility of a coherent\ntransformation between ultracold atoms and molecules including between\ncompletely bosonic condensates. Such transformations are enabled by the\nmagneto-association of atoms at a Feshbach resonance which results in a passage\nthrough a quantum critical point. In this study, we show that the presence of\ngeneric interaction between the formed molecules can fundamentally alter the\nnature of the critical point, change the yield of the reaction and the order of\nthe consequent phase transition. We find that the correlations introduced by\nthis rather general interaction induce nontrivial many-body physics such as\ncoherent oscillations between atoms and molecules, and a selective formation of\nsqueezed molecular quantum states and quantum cat states. We provide analytical\nand numerical descriptions of these many-body effects, along with scaling laws\nfor the reaction yield in both the adiabatic and non-adiabatic regimes, and\nhighlight the potential experimental relevance in quantum sensing.",
        "positive": "Microcavity Polaritons for Quantum simulation: Quantum simulations are one of the pillars of quantum technologies. These\nsimulations provide insight in fields as varied as high energy physics,\nmany-body physics, or cosmology to name only a few. Several platforms, ranging\nfrom ultracold-atoms to superconducting circuits through trapped ions have been\nproposed as quantum simulators. This article reviews recent developments in\nanother well established platform for quantum simulations: polaritons in\nsemiconductor microcavities. These quasiparticles obey a nonlinear\nSchr\\\"odigner equation (NLSE), and their propagation in the medium can be\nunderstood in terms of quantum hydrodynamics. As such, they are considered as\n\"fluids of light\". The challenge of quantum simulations is the engineering of\nconfigurations in which the potential energy and the nonlinear interactions in\nthe NLSE can be controlled. Here, we revisit some landmark experiments with\npolaritons in microcavities, discuss how the various properties of these\nsystems may be used in quantum simulations, and highlight the richness of\npolariton systems to explore non-equilibrium physics"
    },
    {
        "anchor": "Exact quantum field mappings between different experiments on quantum\n  gases: Experiments on trapped quantum gases can probe challenging regimes of quantum\nmany-body dynamics, where strong interactions or non-equilibrium states prevent\nexact solutions. Here we present an exact result which holds even when no exact\nsolutions can be found: a class of spacetime mappings of different experiments\nonto each other, as long as the gas particles interact via two-body potentials\nwhich possess a scaling property that most real interactions do possess. Since\nour result is an identity relating second-quantized field operators in the\nHeisenberg picture of quantum mechanics, it is otherwise general; it applies to\narbitrary measurements on any mixtures of Bose or Fermi gases, in arbitrary\ninitial states. Practical applications of this mapping include perfect\nsimulation of non-trivial experiments with other experiments which may be\neasier to perform.",
        "positive": "Superfluid-quasicrystal in a Bose-Einstein condensate: Quasicrystal is a class of ordered structures defying conventional\nclassification of solid crystals and may carry classically forbidden (e.g.,\n5-fold) rotational symmetries. In view of long-sought supersolids, a natural\nquestion is whether a superfluid can spontaneously form quasicrystalline order\nthat is not possessed by the underlying Hamiltonian, forming\n\"superfluid-quasicrystals\". Here we show that a superfluid-quasicrystal stripe\nstate with the minimal 5-fold rotational symmetry can be realized as the ground\nstate of a Bose-Einstein condensate within a practical experimental scheme.\nThere exists a rich phase diagram consisting of various\nsuperfluid-quasicrystal, supersolid, and plane-wave phases. Our scheme can be\ngeneralized for generating other higher-order (e.g., 7-fold) quasicrystal\nstates, and provides a platform for investigating such new exotic quantum\nmatter."
    },
    {
        "anchor": "Stable Skyrmions in SU(2) Gauged Bose-Einstein Condensates: We demonstrate that the three-dimensional Skyrmion, which has remained\nelusive so far, spontaneously appears as the ground state of $SU$(2) symmetric\nBose-Einstein condensates coupled with a non-Abelian gauge field. The gauge\nfield is a three-dimensional analogue of the Rashba spin-orbit coupling. Upon\nsquashing the SO(3) symmetric gauge field to one- or two-dimensional shapes, we\nfind that the ground state continuously undergoes a change from a\nthree-dimensional to a one- or two-dimensional Skyrmion, which is identified by\nestimating winding numbers and helicity. All of the emerged Skyrmions are\nphysically understandable with the concept of the helical modulation in a\nunified way. These topological objects might potentially be realizable in\ntwo-component BECs experimentally.",
        "positive": "Functional-renormalization-group approach to strongly coupled Bose-Fermi\n  mixtures in two dimensions: We study theoretically the phase diagram of strongly coupled two-dimensional\nBose-Fermi mixtures interacting with attractive short-range potentials as a\nfunction of the particle densities. We focus on the limit where the size of the\nbound state between a boson and a fermion is small compared to the average\ninterboson separation and develop a functional-renormalization-group approach\nthat accounts for the bound-state physics arising from the extended\nFr\\\"{o}hlich Hamiltonian. By including three-body correlations we are able to\nreproduce the polaron-to-molecule transition in two-dimensional Fermi gases in\nthe extreme limit of vanishing boson density. We predict frequency- and\nmomentum-resolved spectral functions and study the impact of three-body\ncorrelations on quasiparticle properties. At finite boson density, we find that\nwhen the bound-state energy exceeds the Fermi energy by a critical value, the\nfermions and bosons can form a fermionic composite with a well-defined Fermi\nsurface. These composites constitute a Fermi sea of dressed Feshbach molecules\nin the case of ultracold atoms while in the case of atomically thin\nsemiconductors a trion liquid emerges. As the boson density is increased\nfurther, the effective energy gap of the composites decreases, leading to a\ntransition into a strongly correlated phase where polarons are hybridized with\nmolecular degrees of freedom. We highlight the universal connection between\ntwo-dimensional semiconductors and ultracold atoms and we discuss perspectives\nfor further exploring the rich structure of strongly coupled Bose-Fermi\nmixtures in these complementary systems."
    },
    {
        "anchor": "Few-body perspective of a quantum anomaly in two-dimensional Fermi gases: Quantum anomaly manifests itself in the deviation of breathing mode frequency\nfrom the scale invariant value of $2\\omega$ in two-dimensional harmonically\ntrapped Fermi gases, where $\\omega$ is the trapping frequency. Its recent\nexperimental observation with cold-atoms reveals an unexpected role played by\nthe effective range of interactions, which requires quantitative theoretical\nunderstanding. Here we provide accurate, benchmark results on quantum anomaly\nfrom a few-body perspective. We consider the breathing mode of a few trapped\ninteracting fermions in two dimensions up to six particles and present the mode\nfrequency as a function of scattering length for a wide range of effective\nrange. We show that the maximum quantum anomaly gradually reduces as effective\nrange increases while the maximum position shifts towards the weak-coupling\nlimit. We extrapolate our few-body results to the many-body limit and find a\ngood agreement with the experimental measurements. Our results may also be\ndirectly applicable to a few-fermion system prepared in microtraps and optical\ntweezers.",
        "positive": "Critical Velocity for Vortex Shedding in a Bose-Einstein Condensate: We present measurements of the critical velocity for vortex shedding in a\nhighly oblate Bose-Einstein condensate with a moving repulsive Gaussian laser\nbeam. As a function of the barrier height $V_0$, the critical velocity $v_c$\nshows a dip structure having a minimum at $V_0 \\approx \\mu $, where $\\mu$ is\nthe chemical potential of the condensate. At fixed $V_0\\approx 7\\mu$, we\nobserve that the ratio of $v_c$ to the speed of sound $c_s$ monotonically\nincreases for decreasing $\\sigma/\\xi$, where $\\sigma$ is the beam width and\n$\\xi$ is the condensate healing length. The measured upper bound for $v_c/c_s$\nis about 0.4, which is in good agreement with theoretical predictions for a\ntwo-dimensional superflow past a circular cylinder. We explain our results with\nthe density reduction effect of the soft boundary of the Gaussian obstacle,\nbased on the local Landau criterion for superfluidity."
    },
    {
        "anchor": "Frustration in a dipolar Bose-Einstein condensate introduced by an\n  optical lattice: We study the application of a square perturbing lattice to the naturally\nforming hexagonal arrays of dipolar droplets in a dipolar Bose-Einstein\ncondensate. We find that the application of the lattice causes spontaneous\npattern formation and leads to frustration in some regimes. For certain\nparameters, the ground state has neither the symmetry of the intrinsic\nhexagonal supersolid nor the symmetry of the square lattice. These results may\ngive another axis on which to explore dipolar Bose-Einstein condensates and to\nprobe the nature of supersolidity.",
        "positive": "Angular collapse of dipolar Bose-Einstein condensates: We explore the structure and dynamics of dipolar Bose-Einstein condensates\n(DBECs) near their threshold for instability. Near this threshold a DBEC may\nexhibit nontrivial, biconcave density distributions, which are associated with\ninstability against collapse into \"angular roton\" modes. Here we discuss\nexperimental signatures of these novel features. In the first, we infer local\ncollapse of the DBEC from the experimental stability diagram. In the second, we\nexplore the dynamics of collapse and find that a nontrivial angular\ndistribution is a signature of the DBEC possessing a biconcave structure."
    },
    {
        "anchor": "Hysteresis and metastability of Bose-Einstein condensed clouds of atoms\n  confined in ring potentials: We consider a Bose-Einstein condensed cloud of atoms which rotate in a\ntoroidal/annular potential. Assuming one-dimensional motion, we evaluate the\ncritical frequencies associated with the effect of hysteresis and the critical\ncoupling for stability of the persistent currents. We perform these\ncalculations using both the mean-field approximation and the method of\nnumerical diagonalization of the many-body Hamiltonian which includes\ncorrections due to the finiteness of the atom number.",
        "positive": "Parametric cooling of a degenerate Fermi gas in an optical trap: We demonstrate a novel technique for cooling a degenerate Fermi gas in a\ncrossed-beam optical dipole trap, where high-energy atoms can be selectively\nremoved from the trap by modulating the stiffness of the trapping potential\nwith anharmonic trapping frequencies. We measure the dependence of the cooling\neffect on the frequency and amplitude of the parametric modulations. It is\nfound that the large anharmonicity along the axial trapping potential allows to\ngenerate a degenerate Fermi gas with anisotropic energy distribution, in which\nthe cloud energy in the axial direction can be reduced to the ground state\nvalue."
    },
    {
        "anchor": "Spin-incoherent one-dimensional spin-1 Bose Luttinger liquid: We investigate spin-incoherent Luttinger liquid of a one-dimensional spin-1\nBose gas in a harmonic trap. In this regime highly degenerate spin\nconfigurations emerge since the spin exchange energy is much less than the\nthermal energy of the system, while the temperature is low enough that the\nlowest energetic orbitals are occupied. As an example we numerically study the\nmomentum distribution of a one-dimensional spin-1 Bose gas in Tonks- Girardeau\ngas limit and in the sector of zero magnetization.We find that the momentum\ndistributions broaden as the number of atoms increase due to the averaging of\nspin function overlaps. Large momentum ($p$) asymptotic is analytically\nderived, showing the universal $1/p^4$ dependence. We demonstrate that the\nspin-incoherent Luttinger liquid has a momentum distribution also distinct from\nspinless bosons at finite temperature.",
        "positive": "Condensates induced by interband coupling in a double-well lattice: We predict novel inter-band physics for bosons in a double-well lattice. An\nintrinsic coupling between the s and px band due to interaction gives rise to\nlarger Mott regions on the phase diagram at even fillings than the ones at odd\nfillings. On the other hand, the ground state can form various types of\ncondensates, including a mixture of single-particle condensates of both bands,\na mixture of a single-particle condensate of one band and a pair-condensate of\nthe other band, and a pair-condensate composed of one particle from one band\nand one hole from the other band. The predicted phenomena should be observable\nin current experiments on double-well optical lattices."
    },
    {
        "anchor": "Finite Temperature Phase Diagram of Quasi-Two-Dimensional Imbalanced\n  Fermi Gases Beyond Mean-Field: We investigate the superfluid transition temperature of quasi-two-dimensional\nimbalanced Fermi gases beyond the mean-field approximation, through the\nsecond-order (or induced) interaction effects. For a balanced Fermi system the\ntransition temperature is suppressed by a factor $\\approx 2.72$. For imbalanced\nFermi systems, the polarization and transition temperature of the tricritical\npoint are significantly reduced as the two-body binding energy $|\\epsilon_B|$\nincreases.",
        "positive": "Finite-temperature Hatree-Fock-Bogoliubov theory for exciton-polaritons: Microcavity exciton-polaritons, known to exhibit non-equilibrium Bose\ncondensation at high critical temperatures, can be also brought in thermal\nequilibrium with the surrounding medium and form a quantum degenerate\nBose-Einstein distribution. It happens when their thermalization time in the\nregime of positive detunings -- or, alternatively, for high-finesse\nmicrocavities -- becomes shorter than their lifetime. Here we present the\nself-consistent finite-temperature Hartree-Fock-Bogoliubov description for such\na system of polaritons, universally addressing the excitation spectrum,\nmomentum-dependent interactions, condensate depletion, and the background\npopulation of dark excitons that contribute to the system's chemical potential.\nEmploying the derived expressions, we discuss the implications for the\nBogoliubov sound velocity, confirmed by existing experiments, and define the\ncritical temperatures of (quasi-)condensation and the integral particle\nlifetime dependencies on the detuning. Large positive detunings are shown to\nprovide conditions for the total lifetime reaching nanosecond timescales. This\nallows realization of thermodynamically-equilibrium polariton systems with\nBose-Einstein condensate forming at temperatures as high as tens of Kelvin."
    },
    {
        "anchor": "Spin relaxation in ultracold spin-orbit coupled $^{40}$K gas: We report the anomalous Dyakonov-Perel' spin relaxation in ultracold\nspin-orbit coupled $^{40}$K gas when the coupling between $|9/2,9/2\\ >$ and\n$|9/2,7/2\\ >$ states (atcing as the effective Zeeman magnetic field) is much\nstronger than the spin-orbit coupled field. Both the transverse and\nlongitudinal spin relaxations are investigated with small and large spin\npolarizations. It is found that with small spin polarization, the transverse\n(longitudinal) spin relaxation is divided into four (two) regimes: the normal\nweak scattering regime, the anomalous Dyakonov-Perel'-like regime, the\nanomalous Elliott-Yafet-like regime and the normal strong scattering regime\n(the anomalous Elliott-Yafet-like regime and the normal strong scattering\nregime), with only the normal weak scattering regime being in the weak\nscattering limit. This is very different from the conventional situation under\nthe weak magnetic field, which is divided into the weak and strong scattering\nregimes according to the weak/strong scattering limit. With large spin\npolarization, we find that the Hartree-Fock self-energy, which acts as an\neffective magnetic field, can markedly suppress the transverse spin relaxation\nin both weak and strong scattering limits. Moreover, by noting that as both the\nmomentum relaxation time and the Hartree-Fock effective magnetic field vary\nwith the scattering length in cold atoms, the anomalous Dyakonov-Perel'-like\nregime is suppressed and the transverse spin relaxation is hence divided into\nthree regimes in the scattering length dependence: the normal weak scattering\nregime, the anomalous Elliott-Yafet-like regime and the strong scattering\nregime. On the other hand, the longitudinal spin relaxation is again divided\ninto the anomalous EY-like and normal strong scattering regimes. ...",
        "positive": "Local Topological Markers in Odd Dimensions: Local topological markers have proven to be a valuable tool for investigating\nsystems with topologically non-trivial bands. Due to their local nature, such\nmarkers can treat translationally invariant systems and spatially inhomogeneous\nsystems on an equal footing. Among the most prevalent of these is the so-called\nChern marker, which is available for systems in two spatial dimensions. In this\npaper, we describe how to generalize this marker to 1d and 3d systems, by\nshowing that the relevant expressions accurately describe the phenomenon of\ntopological pumping given by the first and second Chern numbers in 1d and 3d\nrespectively. In addition to providing general derivations, we verify the\nmarkers by numerically considering model Hamiltonians. These results will open\nthe door for future studies including the influence of disorder on topological\npumping and topological phase transitions in odd-dimensional systems."
    },
    {
        "anchor": "Dissipation-induced squeezing: We present a method for phase and number squeezing in two-mode Bose systems\nusing dissipation. The effectiveness of this method is demonstrated by\nconsidering cold Bose gases trapped in a double-well potential. The extension\nof our formalism to an optical lattice gives control of the phase boundaries of\nthe steady-state phase diagram, and we discover a new phase characterized by a\nnon-zero condensate fraction and thermal-like particle-number statistics. We\nalso show how to perform amplitude squeezing in a single-mode system using\ndissipation.",
        "positive": "Diffusion of cold atomic gases in the presence of an optical speckle\n  potential: We consider diffusion of a cold Fermi gas in the presence of a random optical\nspeckle potential. The evolution of the initial atomic cloud in space and time\nis discussed. Analytical and numerical results are presented in various\nregimes. Diffusion of a Bose-Einstein condensate is also briefly discussed and\nsimilarity with the Fermi gas case is pointed out."
    },
    {
        "anchor": "Sub-micron period lattice structures of magnetic microtraps for\n  ultracold atoms on an atom chip: We report on the design, fabrication and characterization of magnetic\nnanostructures to create a lattice of magnetic traps with sub--micron period\nfor trapping ultracold atoms. These magnetic nanostructures were fabricated by\npatterning a Co/Pd multilayered magnetic film grown on a silicon substrate\nusing high precision e-beam lithography and reactive ion etching. The Co/Pd\nfilm was chosen for its small grain size and high remanent magnetization and\ncoercivity. The fabricated structures are designed to magnetically trap\n$^{87}$Rb atoms above the surface of the magnetic film with 1D and 2D\n(triangular and square) lattice geometries and sub-micron period. Such magnetic\nlattices can be used for quantum tunneling and quantum simulation experiments,\nincluding using geometries and periods that may be inaccessible with optical\nlattice.",
        "positive": "Criteria of off-diagonal long-range order in Bose and Fermi systems\n  based on the Lee-Yang cluster expansion method: The quantum-statistical cluster expansion method of Lee and Yang is extended\nto investigate off-diagonal long-range order (ODLRO) in one- and\nmulti-component mixtures of bosons or fermions. Our formulation is applicable\nto both a uniform system and a trapped system without local-density\napproximation and allows systematic expansions of one- and multi-particle\nreduced density matrices in terms of cluster functions which are defined for\nthe same system with Boltzmann statistics. Each term in this expansion can be\nassociated with a Lee-Yang graph. We elucidate a physical meaning of each\nLee-Yang graph; in particular, for a mixture of ultracold atoms and bound\ndimers, an infinite sum of the ladder-type Lee-Yang 0-graphs is shown to lead\nto Bose-Einstein condensation of dimers below the critical temperature. In the\ncase of Bose statistics, an infinite series of Lee-Yang 1-graphs is shown to\nconverge and gives the criteria of ODLRO at the one-particle level.\nApplications to a dilute Bose system of hard spheres are also made. In the case\nof Fermi statistics, an infinite series of Lee-Yang 2-graphs is shown to\nconverge and gives the criteria of ODLRO at the two-particle level.\nApplications to a two-component Fermi gas in the tightly bound limit are also\nmade."
    },
    {
        "anchor": "Controlling superfluid flows using dissipative impurities: We propose and analyze a protocol to create and control the superfluid flow\nin a one dimensional, weakly interacting Bose gas by noisy point contacts\ncoupled to the density of the bosons. Considering first a single contact in a\nstatic or moving condensate, we identify three different dynamical phases: I. a\nlinear response regime, where the noise induces a coherent flow in proportion\nto the strength of the noise accompanied by a counterflow of the normal\ncomponent of the gas, II. a Zeno regime with suppressed currents and negative\ndifferential current to noise characteristics, and III. for a non-vanishing\nrelative velocity, a regime of continuous soliton emission. The velocity of the\ncondensate at the dissipative impurity determines the threshold for Zeno\nsuppression of the current through the point contact, and the onset of the\nnon-stationary regime of soliton \"shooting\" from the defect. Generalizing to\ntwo point contacts in a condensate at rest we show that noise tuning can be\nemployed to control, stabilize or eventually shunt the superfluid transport of\nparticles along the segment which connects them, with perspectives for an\natomtronic analogue of a superfluid-current source for studying quantum\ntransport phenomena.",
        "positive": "Quantum simulation of frustrated magnetism in triangular optical\n  lattices: Magnetism plays a key role in modern technology as essential building block\nof many devices used in daily life. Rich future prospects connected to\nspintronics, next generation storage devices or superconductivity make it a\nhighly dynamical field of research. Despite those ongoing efforts, the\nmany-body dynamics of complex magnetism is far from being well understood on a\nfundamental level. Especially the study of geometrically frustrated\nconfigurations is challenging both theoretically and experimentally. Here we\npresent the first realization of a large scale quantum simulator for magnetism\nincluding frustration. We use the motional degrees of freedom of atoms to\ncomprehensively simulate a magnetic system in a triangular lattice. Via a\nspecific modulation of the optical lattice, we can tune the couplings in\ndifferent directions independently, even from ferromagnetic to\nantiferromagnetic. A major advantage of our approach is that standard\nBose-Einstein-condensate temperatures are sufficient to observe magnetic\nphenomena like N\\'eel order and spin frustration. We are able to study a very\nrich phase diagram and even to observe spontaneous symmetry breaking caused by\nfrustration. In addition, the quantum states realized in our spin simulator are\nyet unobserved superfluid phases with non-trivial long-range order and\nstaggered circulating plaquette currents, which break time reversal symmetry.\nThese findings open the route towards highly debated phases like spin-liquids\nand the study of the dynamics of quantum phase transitions."
    },
    {
        "anchor": "Density Wave -Supersolid and Mott Insulator-Superfluid transition in\n  presence of an artificial gauge field : a strong coupling perturbation\n  approach: We study the effect of an artificial gauge field on the zero temperature\nphase diagram of extended Bose Hubbard model, that describes ultra cold atoms\nin optical lattices with long range interaction using strong coupling\nperturbation theory . We determine analytically the effect of the artificial\ngauge field on the density wave - supersolid (DW-SS) and the the Mott\ninsulator-superfluid (MI -SF) transition boundary . The momentum distribution\nat these two transition boundaries is also calculated in this approach. It is\nshown that such momentum distribution which can be observed in time of flight\nmeasurement, reveals the symmetry of the gauge potential through the formation\nof magnetic Brillouin zone and clearly distinguishes between the DW-SS and\nMI-SF boundary. We also point out that in symmetric gauge the momentum\ndistribution structure at these transition boundaries bears distinctive\nsignatures of vortices in supersolid and superfluid phases.",
        "positive": "Dimensional crossover of Bose-Einstein condensation phenomena in quantum\n  gases confined within slab geometries: We investigate systems of interacting bosonic particles confined within\nslab-like boxes of size L^2 x Z with Z<<L, at their three-dimensional (3D) BEC\ntransition temperature T_c, and below T_c where they experience a quasi-2D\nBerezinskii-Kosterlitz-Thouless transition (at T_BKT < T_c depending on the\nthickness Z). The low-temperature phase below T_BKT shows quasi-long-range\norder: the planar correlations decay algebraically as predicted by the 2D\nspin-wave theory. This dimensional crossover, from a 3D behavior for T > T_c to\na quasi-2D critical behavior for T < T_BKT, can be described by a transverse\nfinite-size scaling limit in slab geometries. We also extend the discussion to\nthe off-equilibrium behavior arising from slow time variations of the\ntemperature across the BEC transition. Numerical evidence of the 3D->2D\ndimensional crossover is presented for the Bose-Hubbard model defined in\nanisotropic L^2 x Z lattices with Z<<L."
    },
    {
        "anchor": "Impurity states in the one-dimensional Bose gas: The detailed study of the low-energy spectrum for a mobile impurity in the\none-dimensional bosonic enviroment is performed. Particularly we have\nconsidered only two analytically accessible limits, namely, the case of an\nimpurity immersed in a dilute Bose gas, where one can use many-body\nperturbation techniques for low-dimensional bosonic systemsm and the case of\nthe Tonks-Girardeau gas, for which the usual fermionic diagrammatic expansion\nup to the second order is applied.",
        "positive": "Magnetic field dependent interactions in an ultracold Li-Yb($^3$P$_2$)\n  mixture: Magnetic Feshbach resonances have allowed great success in the production of\nultracold diatomic molecules from bi-alkali mixtures, but have so far eluded\nobservation in mixtures of alkali and alkaline-earth-like atoms. Inelastic\ncollisional properties of ultracold atomic systems exhibit resonant behavior in\nthe vicinity of such resonances, providing a detection signature. We study\nmagnetic field dependent inelastic effects via atom loss spectroscopy in an\nultracold heteronuclear mixture of alkali $^6$Li in the ground state and\nalkaline-earth-like $^{174}$Yb in an excited electronic metastable state\n($^3$P$_2$, m$_J$ = -1). We observe a variation of the interspecies inelastic\ntwo-body rate coefficient by nearly one order of magnitude over a 100-520G\nmagnetic field range. By comparing to ab-initio calculations we link our\nobservations to interspecies Feshbach resonances arising from anisotropic\ninteractions in this novel collisional system."
    },
    {
        "anchor": "Self-Assembled Chains and Solids of Dipolar Atoms in a Multilayer: We predict that ultracold bosonic dipolar gases, confined within a multilayer\ngeometry, may undergo self-assembling processes, leading to the formation of\nchain gases and solids. These dipolar chains, with dipoles aligned across\ndifferent layers, emerge at low densities and resemble phases observed in\nliquid crystals, such as nematic and smectic phases. We calculate the phase\ndiagram using quantum Monte Carlo methods, introducing a newly devised trial\nwave function designed for describing the chain gas, where dipoles from\ndifferent layers form chains without in-plane long-range order. We find gas,\nsolid, and chain phases, along with quantum phase transitions between these\nstates. Specifically, we predict a quantum phase transition from a gaseous to a\nself-ordered phase, which occurs at a critical interlayer distance. Remarkably,\nin the self-organized phases, the mean interparticle distance can significantly\nexceed the characteristic length of the interaction potential, yielding solids\nand chain gases with densities several orders of magnitude lower than those of\nconventional quantum solids.",
        "positive": "Measuring correlations from the collective spin fluctuations of a large\n  ensemble of lattice-trapped dipolar spin-3 atoms: We perform collective spin measurements to study the buildup of two-body\ncorrelations between $\\approx10^4$ spin $s=3$ chromium atoms pinned in a 3D\noptical lattice. The spins interact via long range and anisotropic dipolar\ninteractions. From the fluctuations of total magnetization, measured at the\nstandard quantum limit, we estimate the dynamical growth of the connected\npairwise correlations associated with magnetization. The quantum nature of the\ncorrelations is assessed by comparisons with short and long time expansions,\nand numerical simulations. Our work shows that measuring fluctuations of spin\npopulations provides new ways to characterize correlations in quantum many-body\nsystems, for $s>1/2$ spins"
    },
    {
        "anchor": "Engineering long-range interactions between ultracold atoms with light: Ultracold temperatures in dilute quantum gases opened the way to an exquisite\ncontrol of matter at the quantum level. Here we focus on the control of\nultracold atomic collisions using a laser to engineer their interactions at\nlarge interatomic distances. We show that the entrance channel of two colliding\nultracold atoms can be coupled to a repulsive collisional channel by the laser\nlight so that the overall interaction between the two atoms becomes repulsive:\nthis prevents them to come close together and to undergo inelastic processes,\nthus protecting the atomic gases from unwanted losses. We illustrate such an\noptical shielding mechanism with potassium and cesium atoms colliding at\nultracold temperature (\\textless 1 microkelvin). The process is described in\nthe framework of the dressed-state picture and we then solve the resulting\nstaionary coupled Schr\\\"{o}dinger equations. The role of spontaneous emission\nand photoinduced inelastic scattering is also investigated as possible\nlimitations of the shielding efficiency. We predict an almost complete\nsuppression of inelastic collisions using a laser-induced coupling\ncharacterized by a Rabi frequency of $\\omega = 200$~MHz and a frequency detuned\nfrom the potassium D2 transition by $\\Delta = 200$~MHz. We found the\npolarization of the laser has no influence on this efficiency. This proposal\ncould easily be formulated for other bi-alkali-metal pairs as their long-range\ninteraction are all very similar to each other.",
        "positive": "Supersolid-like square- and honeycomb-lattice crystallization of\n  droplets in a dipolar condensate: We demonstrate a supersolid-like spatially-periodic square- and\nhoneycomb-lattice crystallization of droplets, in addition to the\ncommonly-studied triangular-lattice crystallization, in a\ncylindrically-symmetric quasi-two-dimensional trapped dipolar condensate, using\na beyond-mean-field model including a quantum-fluctuation Lee-Huang-Yang-type\ninteraction. These three types of crystallization of droplets may appear for\nthe same atomic interactions and the same trap frequencies. The energy $E$ of\nall three crystallization as a function of number $N$ of atoms satisfy the\nuniversal scaling relation $E\\sim N^{0.4}$ indicating that all three\narrangements of the droplets should be energetically probable processes of\nphenomenological interest. The state of square-lattice crystallization may have\nthe central site occupied or unoccupied, corresponding to a parity-symmetric or\nparity-antisymmetric state, respectively. The state of square-lattice\ncrystallization with the occupied central site and the state of\ntriangular-lattice crystallization, for a fixed $N$, constitute two\nquasi-degenerate ground states while the other states are low-lying excited\nstates. This makes the square-lattice crystallization with the occupied central\nsite an ideal candidate for future experimental observation."
    },
    {
        "anchor": "Probing polaron clouds by Rydberg atom spectroscopy: In recent years, Rydberg excitations in atomic quantum gases have become a\nsuccessful platform to explore quantum impurity problems. A single impurity\nimmersed in a Fermi gas leads to the formation of a polaron, a quasiparticle\nconsisting of the impurity being dressed by the surrounding medium. With a\nradius of about the Fermi wavelength, the density profile of a polaron cannot\nbe explored using in-situ optical imaging techniques. In this work, we propose\na new experimental measurement technique that enables the in-situ imaging of\nthe polaron cloud in ultracold quantum gases. The impurity atom is first\nexcited to an interacting state which induces the formation of a polaron cloud.\nThis is followed by the excitation of the impurity atom to a Rydberg state. Due\nto the mesoscopic interaction range of Rydberg excitations, which can be tuned\nby the principal numbers of the Rydberg state, atoms extracted from the polaron\ncloud form dimers with the impurity. By performing first principle calculations\nof the absorption spectrum based on a functional determinant approach, we show\nhow the occupation of the dimer state can be directly observed in spectroscopy\nexperiments and can be mapped onto the density profile of the gas particles,\nhence providing a direct, real-time, and in-situ measure of the polaron cloud.",
        "positive": "Dynamics of Rydberg excitations and quantum correlations in an atomic\n  array coupled to a photonic crystal waveguide: We study the dynamics of up to two Rydberg excitations and the correlation\ngrowth in a chain of atoms coupled to a photonic crystal waveguide. In this\nsetup, an excitation can hop from one atom to another via exponentially\ndecaying exchange interactions mediated by the waveguide. An initially\nlocalized excitation undergoes a continuous-time quantum walk for short-range\nhopping, and for long-range, it experiences quasi-localization. Besides that,\nthe inverse participation ratio reveals a super-ballistic diffusion of the\nexcitation in short times, whereas, at a long time, it becomes ballistic. For\ntwo initially localized excitations, intriguing, and complex dynamical\nscenarios emerge for different initial separations due to the competition\nbetween the Rydberg-Rydberg and exchange interactions. In particular, the\ntwo-point correlation reveals a light-cone behavior even for sufficiently\nlong-range exchange interactions. Additionally, we characterize the growth of\nbipartite entanglement entropy, which exhibits a global bound if only one\nexcitation is present in the dynamics. Finally, we analyze the effect of\nimperfections due to spontaneous emission from the Rydberg state into photons\noutside the waveguide and show that all physical phenomena we predict are well\nwithin experimental reach."
    },
    {
        "anchor": "Non-equilibrium dynamics of coupled Luttinger liquids: In this work we consider the dynamics of two tunnel coupled chains after a\nquench in the tunneling strength is performed and the two systems are let\nevolve independently. We describe the form of the initial state comparing with\nprevious results concerning the dynamics after the splitting of a\none-dimensional gas of bosons into two phase coherent systems. We compute\ndifferent correlation functions, among which those that are relevant for\ninterference measurements, and discuss the emergence of effective temperatures\nalso in connection with previous works.",
        "positive": "Interplay between shell structure and trap deformation in dipolar fermi\n  gases: Finite fermion systems are known to exhibit shell structure in the\nweakly-interacting regime, as well known from atoms, nuclei, metallic clusters\nor even quantum dots in two dimensions. All these systems have in common that\nthe particle interactions between electrons or nucleons are spatially\nisotropic. Dipolar quantum systems as they have been realized with ultra-cold\ngases, however, are governed by an intrinsic anisotropy of the two-body\ninteraction that depends on the orientation of the dipoles relative to each\nother. Here we investigate how this interaction anisotropy modifies the shell\nstructure in a weakly interacting two-dimensional anisotropic harmonic trap.\nGoing beyond Hartree-Fock by applying the so-called \"importance-truncated\"\nconfiguration interaction (CI) method as well as quadratic CI with single- and\ndouble-substitutions, we show how the magnetostriction in the system may be\ncounteracted upon by a deformation of the isotropic confinement, restoring the\nsymmetry."
    },
    {
        "anchor": "Quantum phase transitions and Berezinskii-Kosterlitz-Thouless\n  temperature in a two-dimensional spin-orbit-coupled Fermi gas: We study the effect of spin-orbit coupling on both the zero-temperature and\nnon-zero temperature behavior of a two-dimensional (2D) Fermi gas. We include a\ngeneric combination of Rashba and Dresselhaus terms into the system\nHamiltonian, which allows us to study both the experimentally relevant\nequal-Rashba-Dresselhaus (ERD) limit and the Rashba-only (RO) limit. At zero\ntemperature, we derive the phase diagram as a function of the two-body binding\nenergy and Zeeman field. In the ERD case, this phase diagram reveals several\ntopologically distinct uniform superfluid phases, classified according to the\nnodal structure of the quasiparticle excitation energies. Furthermore, we use a\nmomentum dependent SU(2)-rotation to transform the system into a generalized\nhelicity basis, revealing that spin-orbit coupling induces a triplet pairing\ncomponent of the order parameter. At non-zero temperature, we study the\nBerezinskii-Kosterlitz-Thouless (BKT) phase transition by including phase\nfluctuations of the order parameter up to second order. We show that the\nsuperfluid density becomes anisotropic due to the presence of spin-orbit\ncoupling (except in the RO case). This leads both to elliptic vortices and\nantivortices, and to anisotropic sound velocities. The latter prove to be\nsensitive to quantum phase transitions between topologically distinct phases.\nWe show further that at a fixed non-zero Zeeman field, the BKT critical\ntemperature is increased by the presence of ERD spin-orbit coupling.\nSubsequently, we demonstrate that the Clogston limit becomes infinite:\n$T_{\\rm{BKT}}$ remains non-zero at all finite values of the Zeeman field. We\nconclude by extending the quantum phase transition lines to non-zero\ntemperature, using the nodal structure of the quasiparticle spectrum, thus\nconnecting the BKT critical temperature with the zero-temperature results.",
        "positive": "Induced p-wave superfluidity in strongly interacting imbalanced Fermi\n  gases: The induced interaction among the majority spin species, due to the presence\nof the minority species, is computed for the case of a population-imbalanced\nresonantly-interacting Fermi gas. It is shown that this interaction leads to an\ninstability, at low temperatures, of the recently observed polaron Fermi liquid\nphase of strongly imbalanced Fermi gases to a p-wave superfluid state. We find\nthat the associated transition temperature, while quite small in the weakly\ninteracting BCS regime, is experimentally accessible in the strongly\ninteracting unitary regime."
    },
    {
        "anchor": "Detecting paired and counterflow superfluidity via dipole oscillations: We suggest an experimentally feasible procedure to observe paired and\ncounterflow superfluidity in ultra-cold atom systems. We study the time\nevolution of one-dimensional mixtures of bosonic atoms in an optical lattice\nfollowing an abrupt displacement of an additional weak confining potential. We\nfind that the dynamic responses of the paired superfluid phase for attractive\ninter-species interactions and the counterflow superfluid phase for repulsive\ninteractions are qualitatively distinct and reflect the quasi long-range order\nthat characterizes these states. These findings suggest a clear experimental\nprocedure to detect these phases, and give an intuitive insight into their\ndynamics.",
        "positive": "Super Hamiltonian in superspace for incommensurate superlattices and\n  quasicrystals: Infinite quasiperiodic arrangements in space, such as quasicrystals, are\ntypically described as projections of higher-dimensional periodic lattices onto\nthe physical dimension. The concept of a reference higher-dimensional space,\ncalled a superspace, has proved useful in relation to quasiperiodic systems.\nAlthough some quantum-mechanical systems in quasiperiodic media have been shown\nto admit quasiperiodic states, any sort of general Hamiltonian formalism in\nsuperspace is lacking to this date. Here, we show how to extend generic\nquantum-mechanical Hamiltonians to higher dimensions in such a way that\neigenstates of the original Hamiltonian are obtained as projections of the\nHamiltonian in superspace, which we call the super Hamiltonian. We apply the\nsuper Hamiltonian formalism to a simple, yet realistic one-dimensional quantum\nparticle in a quasiperiodic potential without the tight-binding approximation,\nand obtain continuously labelled eigenstates of the system corresponding to a\ncontinuous spectrum. All states corresponding to the continuum are\nquasiperiodic. We also obtain the Green's functions for continuum states in\nclosed form and, from them, the density of states and local density of states,\nand scattering states off defects and impurities. The closed form of this\none-dimensional Green's function is equally valid for any continuum state in\nany one-dimensional single-particle quantum system admitting continuous\nspectrum. With the basis set we use, which is periodic in superspace, and\ntherefore quasiperiodic in physical space, we find that Anderson-localised\nstates are also quasiperiodic if distributional solutions are admitted, but\ncircumvent this difficulty by generalising the superspace method to open\nboundary conditions (cont'd)."
    },
    {
        "anchor": "Rydberg crystallization detection by statistical means: We investigate an ensemble of atoms which can be excited into a Rydberg\nstate. Using a disordered quantum Ising model, we perform a numerical\nsimulation of the experimental procedure and calculate the probability\ndistribution function $P(M)$ to create a certain number of Rydberg atoms $M$,\nas well as their pair correlation function. Using the latter, we identify the\ncritical interaction strength above which the system undergoes a phase\ntransition to a Rydberg crystal. We then show that this phase transition can be\ndetected using $P(M)$ alone.",
        "positive": "Weakly bound molecules trapped with discrete scaling symmetries: When the scattering length is proportional to the distance from the center of\nthe system, two particles are shown to be trapped about the center.\nFurthermore, their spectrum exhibits discrete scale invariance, whose scale\nfactor is controlled by the slope of the scattering length. While this\nresembles the Efimov effect, our system has a number of advantages when\nrealized with ultracold atoms. We also elucidate how the emergent discrete\nscaling symmetry is violated for more than two bosons, which may shed new light\non Efimov physics. Our system thus serves as a tunable model system to\ninvestigate universal physics involving scale invariance, quantum anomaly, and\nrenormalization group limit cycle, which are important in a broad range of\nquantum physics."
    },
    {
        "anchor": "Universality of Fragmentation in the Schr\u00f6dinger Dynamics of Bosonic\n  Josephson Junctions: The many-body Schr\\\"odinger dynamics of a one-dimensional bosonic Josephson\njunction is investigated for up to ten thousand bosons and long times. The\ninitial states are fully condensed and the interaction strength is weak. We\nreport on a universal fragmentation dynamics on the many-body level: systems\nconsisting of different numbers of particles fragment to the same value at\nconstant mean-field interaction strength. The phenomenon manifests itself in\nobservables such as the correlation functions of the system. We explain this\nuniversal fragmentation dynamics analytically based on the Bose-Hubbard model.\nWe thereby show that the extent to which many-body effects become important at\nlater times depends crucially on the initial state. Even for arbitrarily large\nparticle numbers and arbitrarily weak interaction strength the dynamics is\nmany-body in nature and the fragmentation universal. There is no weakly\ninteracting limit where the Gross-Piatevskii mean-field is valid for long\ntimes.",
        "positive": "Magnetic soliton: from two to three components with SO(3) symmetry: Recent theoretical and experimental research has explored magnetic solitons\nin binary Bose-Einstein condensates (BECs). Here we demonstrate that such\nsolitons are part of an SO(3) soliton family when embedded within a full\nthree-component spin-1 manifold with spin-rotational symmetry. To showcase\nthis, we have experimentally created a new type of domain wall magnetic soliton\n(DWMS) obtained by 90 degree rotations, which consist of a boundary between\neasy-axis and easy-plane polar phases. Collisions between SO(3) solitons are\ninvestigated by numerically solving the Gross-Pitaevskii equations, which\nexhibit novel properties including rotation and dissipation of soliton spin\npolarization."
    },
    {
        "anchor": "Solution of the Bogoliubov-de Gennes equations at zero temperature\n  throughout the BCS-BEC crossover: Josephson and related effects: We investigate the evolution of the Josephson and related effects throughout\nthe BCS-BEC crossover, by performing a systematic numerical solution of the\n(time-independent) Bogoliubov-de Gennes equations at zero temperature in a\nfully self-consistent fashion. The numerical strategies and algorithms we have\nadopted are described in detail, with the aim of easing further independent\nstudies. Several results are obtained by the present calculation. The profiles\nof the magnitude and phase of the gap parameter across the Josephson barrier\nare determined under a variety of conditions. We find that the Josephson\ncurrent is considerably enhanced at about unitarity for all barriers we have\nconsidered. A related enhancement is also found in the contribution to the\ntotal current from the Andreev bound states, which stem from the depression of\nthe gap profile about the barrier.For vanishing barrier height, we find that\nthe critical Josephson current approaches the limiting value predicted by the\nLandau criterion, which is determined by either pair-breaking or sound-mode\nexcitations depending on the coupling value. In the BCS limit, we reveal the\npresence of Friedel oscillations in the oscillatory modulations of the gap and\ndensity profiles. In this limit, we also emphasize the special role played by\nthe Andreev bound state in determining the critical Josephson current in the\npresence of a barrier. Finally, the stability of the two branches, out of which\nthe Josephson characteristics are composed, is analyzed by calculating the\nenergy required to produce a given spatial profile of the gap parameter.",
        "positive": "Bogoliubov excitations of a polariton condensate in dynamical\n  equilibrium with an incoherent reservoir: The classic Bogoliubov theory of weakly interacting Bose gases rests upon the\nassumption that nearly all the bosons condense into the lowest quantum state at\nsufficiently low temperatures. Here we develop a generalized version of\nBogoliubov theory for the case of a driven-dissipative exciton-polariton\ncondensate with a large incoherent uncondensed component, or excitonic\nreservoir. We argue that such a reservoir can consist of both excitonic\nhigh-momentum polaritons and optically dark superpositions of excitons across\ndifferent optically active layers, such as multiple quantum wells in a\nmicrocavity. In particular, we predict interconversion between the dark and\nbright (light-coupled) excitonic states that can lead to a dynamical\nequilibrium between the condensate and reservoir populations. We show that the\npresence of the reservoir fundamentally modifies both the energy and the\namplitudes of the Bogoliubov quasiparticle excitations due to the\nnon-Galilean-invariant nature of polaritons. Our theoretical findings are\nsupported by our experiment, where we directly detect the Bogoliubov excitation\nbranches of an optically trapped polariton condensate in the high-density\nregime. By analyzing the measured occupations of the excitation branches, we\nextract the Bogoliubov amplitudes across a range of momenta and show that they\nagree with our generalized theory."
    },
    {
        "anchor": "Crossover from exciton-polariton to photon Bose-Einstein condensation: BEC of exciton-polaritons and related effects such as superfluidity1,2,\nspontaneous symmetry breaking3,4 and quantised vortices5,6 open way to creation\nof novel light sources7 and optical logic elements8. Remarkable observations of\nexciton-polariton BEC in microcavities9-12 have been reported in the recent ten\nyears. Very recently, thermalisation and subsequent condensation of cavity\nphotons in a dye-filled microcavity have been observed13. Here we show that BEC\nof both exciton-polaritons and photons can be created in the same system under\ndifferent optical excitation conditions. A dynamic phase transition between a\nphoton and a polariton BEC takes place after a single high-power excitation\npulse and we find both condensed states in thermal equilibrium with the excited\nstates. At the crossover, photons and polaritons coexist, which results in a\ndecrease in the long-range spatial coherence. Build-up and successive depinning\nof polarisation is observed at the threshold of both polariton and photon\ncondensation.",
        "positive": "Universal duality transformations in interacting one-dimensional quantum\n  systems: One-dimensional quantum systems admit duality relations that put hard core\nspinless bosons and fermions in one-to-one correspondence via Girardeau's\nmapping theorem. The simplest models of soft bosons interacting via zero-range\npotentials can also be mapped onto dual interacting fermions. However, a\nsystematic approach to one-dimensional statistical transmutation for arbitrary\nlow-energy interactions in the spinless and spinful or multicomponent cases has\nremained elusive. I develop a general theory of local unitary transformations\nbetween one-dimensional quantum systems of bosons and fermions with arbitrary\nspin or internal structure, single-particle dispersion -- including\nnon-relativistic, relativistic or otherwise -- and low-energy interactions in\nthe universal regime. These transformations generate families of new duality\nrelations and models that relate the strong and weak coupling limits of the\nrespective dual theories."
    },
    {
        "anchor": "Density wave patterns for fermionic dipolar molecules on a square\n  optical lattice: Mean-field-theory analysis: We model a system of ultracold fermionic dipolar molecules on a\ntwo-dimensional square lattice. Assuming that the molecules are in their\nnondegenerate hyperfine ground state, and that the dipole moment is polarized\nperpendicular to the plane (as in the recent experiments on 40K-87Rb\nmolecules), we approximate these molecules as spinless fermions with long range\nrepulsive dipolar interactions. We use mean field theory to obtain the\nrestricted phase diagram as a function of the filling, the strength of\ninteraction and the temperature. We find a number of ordered density wave\nphases in the system, as well as phase separation between these phases. A Monte\nCarlo analysis shows that the higher-period phases are usually suppressed in\nthe exact solution.",
        "positive": "Phase Transitions in Three-Dimensional Bosonic Systems in Optical\n  Lattices: We formulate the Collective Quantum Field Theory for three-dimensional\nbosonic optical lattices and evaluate its consequences in a mean-field\napproximation to two collective fields, proposed by Fred Cooper et al. and in a\nlowest-order Variational Perturbation Theory (VPT). It is shown that present\nmean-field approximation predicts some essential features of the experimentally\nobserved dependence of the critical temperature on the coupling strength and a\nsecond - order quantum phase transition.In contrast to a recent prediction for\natomic gases by Fred Cooper et. al., we find no superfluid state with zero\ncondensate fraction."
    },
    {
        "anchor": "Spinor self-ordering of a quantum gas in a cavity: We observe the joint spin-spatial (spinor) self-organization of a\ntwo-component BEC strongly coupled to an optical cavity. This unusual\nnonequilibrium Hepp-Lieb-Dicke phase transition is driven by an off-resonant\ntwo-photon Raman transition formed from a classical pump field and the emergent\nquantum dynamical cavity field. This mediates a spinor-spinor interaction that,\nabove a critical strength, simultaneously organizes opposite spinor states of\nthe BEC on opposite checkerboard configurations of an emergent 2D lattice. The\nresulting spinor density-wave polariton condensate is observed by directly\ndetecting the atomic spin and momentum state and by holographically\nreconstructing the phase of the emitted cavity field. The latter provides a\ndirect measure of the spin state, and a spin-spatial domain wall is observed.\nThe photon-mediated spin interactions demonstrated here may be engineered to\ncreate dynamical gauge fields and quantum spin glasses.",
        "positive": "Superfluid behavior of a Bose-Einstein condensate in a random potential: We investigate the relation between Bose-Einstein condensation (BEC) and\nsuperfluidity in the ground state of a one-dimensional model of interacting\nBosons in a strong random potential. We prove rigorously that in a certain\nparameter regime the superfluid fraction can be arbitrarily small while\ncomplete BEC prevails. In another regime there is both complete BEC and\ncomplete superfluidity, despite the strong disorder."
    },
    {
        "anchor": "Superfluid density of states and pseudogap phenomenon in the BCS-BEC\n  crossover regime of a superfluid Fermi gas: We investigate single-particle excitations and strong-coupling effects in the\nBCS-BEC crossover regime of a superfluid Fermi gas. Including phase and\namplitude fluctuations of the superfluid order parameter within a $T$-matrix\ntheory, we calculate the superfluid density of states (DOS), as well as\nsingle-particle spectral weight, over the entire BCS-BEC crossover region below\nthe superfluid transition temperature $T_{\\rm c}$. We clarify how the pseudogap\nin the normal state evolves into the superfluid gap, as one passes through\n$T_{\\rm c}$. While the pseudogap in DOS continuously evolves into the\nsuperfluid gap in the weak-coupling BCS regime, the superfluid gap in the\ncrossover region is shown to appear in DOS after the pseudogap disappears below\n$T_{\\rm c}$. In the phase diagram with respect to the temperature and\ninteraction strength, we determine the region where strong pairing fluctuations\ndominate over single-particle properties of the system. Our results would be\nuseful for the study of strong-coupling phenomena in the BCS-BEC crossover\nregime of a superfluid Fermi gas.",
        "positive": "Manipulating polariton condensates by Rashba-Dresselhaus coupling at\n  room temperature: The spin-orbit coupling plays an important role in the spin Hall effect and\nthe topological insulators. In addition, the spin-orbit coupled Bose-Einstein\ncondensates show remarkable quantum many-body phase transition. In this work we\ntune the exciton polariton condensate by virtue of the Rashba-Dresselhaus (RD)\nspin-orbit coupling in a liquid-crystal filled microcavity where perovskite\nCsPbBr3 microplates act as the gain material at room temperature. We realize an\nartificial gauge field on the CsPbBr3 exciton polariton condensate, which\nsplits the condensates with opposite spins in both momentum and real spaces.\nOur work paves the way to manipulate the exciton polariton condensate with a\nsynthetic gauge field based on the RD spin-orbit coupling at room temperature."
    },
    {
        "anchor": "Toroidal Dipolar Supersolid with a Rotating Weak Link: Ring-shaped superfluids with weak links provide a perfect environment for\nstudying persistent currents and dynamic stirring protocols. Here, we\ninvestigate the effects of a weak-link system on dipolar supersolids. By\ncalculating the ground state energy at fixed angular momenta, we find that\nmetastable persistent currents may exist in the supersolid phase near the\nsuperfluid transition point. When stirring the weak link rapidly enough, we\nshow that vortices can enter the supersolid. These vortex entries cause phase\nslips, emitting solitonic excitations that interfere with the crystalline\nstructure of the supersolid, leading to a continuous melting and\nrecrystallization of the droplets. Finally, we examine the release of\nvortex-carrying supersolids from the trap, observing that the released density\nexhibits a discrete structure associated with the density modulation and a\ncentral hole resulting from the vortex core.",
        "positive": "Superconducting Vortex Lattices for Ultracold Atoms: We propose and analyze a nanoengineered vortex array in a thin-film type-II\nsuperconductor as a magnetic lattice for ultracold atoms. This proposal\naddresses several of the key questions in the development of atomic quantum\nsimulators. By trapping atoms close to the surface, tools of nanofabrication\nand structuring of lattices on the scale of few tens of nanometers become\navailable with a corresponding benefit in energy scales and temperature\nrequirements. This can be combined with the possibility of magnetic single site\naddressing and manipulation together with a favorable scaling of\nsuperconducting surface-induced decoherence."
    },
    {
        "anchor": "Life Cycle of Superfluid Vortices and Quantum Turbulence in the Unitary\n  Fermi Gas: The unitary Fermi gas (UFG) offers an unique opportunity to study quantum\nturbulence both experimentally and theoretically in a strongly interacting\nfermionic superfluid. It yields to accurate and controlled experiments, and\nadmits the only dynamical microscopic description via time-dependent density\nfunctional theory (DFT) - apart from dilute bosonic gases - of the crossing and\nreconnection of superfluid vortex lines conjectured by Feynman in 1955 to be at\nthe origin of quantum turbulence in superfluids at zero temperature. We\ndemonstrate how various vortex configurations can be generated by using well\nestablished experimental techniques: laser stirring and phase imprinting. New\nimagining techniques demonstrated by the MIT group [Ku et al. arXiv:1402.7052]\nshould be able to directly visualize these crossings and reconnections in\ngreater detail than performed so far in liquid helium. We demonstrate the\ncritical role played by the geometry of the trap in the formation and dynamics\nof a vortex in the UFG and how laser stirring and phase imprint can be used to\ncreate vortex tangles with clear signatures of the onset of quantum turbulence.",
        "positive": "Large-momentun tail of one-dimensional Fermi gases with spin-orbit\n  coupling: We study the contacts, large-momentum tail, radio-frequency spectroscopy, and\nsome other universal relations for an ultracold one-dimensional (1D)\ntwo-component Fermi gas with spin-orbit coupling (SOC). Different from previous\nstudies, we find that the $q^{-8}$ tail in the spin-mixing (off-diagonal) terms\nof the momentum distribution matrix is dependent on the two SOC parameters in\nthe laboratory frame for 1D systems, where $q$ is the relative momentum. This\ntail can be observed through time-of-flight measurement as a direct\nmanifestation of the SOC effects on the many-body level. Besides the\ntraditional 1D even-wave scattering length, we find that two new physical\nquantities must be introduced due to the SOC. Consequently, two new adiabatic\nenergy relations with respect to the two SOC parameters are obtained.\nFurthermore, we derive the pressure relation and virial theorem at short\ndistances for this system. To find how the SOC modifies the large-momentum\nbehavior, we take the SOC parameters as perturbations since the strength of the\nSOC should be much smaller than the corresponding strength scale of the\ninteratomic interactions. In addition, by using the operator product expansion\nmethod, we derive the asymptotic behavior of the large-momentum distribution\nmatrix up to the $q^{-8}$ order and find that the diagonal terms of the\ndistribution matrix include the contact of traditional 1D even-wave scattering\nlength as the leading term and the SOC modified terms beyond the leading term,\nthe off-diagonal term is beyond the subleading term and is corrected by the SOC\nparameters. We also find that the momentum distribution matrix shows\nspin-dependent and anisotropic features. Furthermore, we calculate the momentum\ndistribution matrix in the laboratory frame for the experimental implication."
    },
    {
        "anchor": "Cold atoms at unitarity and inverse square interaction: Consider two identical atoms in a spherical harmonic oscillator interacting\nwith a zero-range interaction which is tuned to produce an s-wave zero-energy\nbound state. The quantum spectrum of the system is known to be exactly\nsolvable. We note that the same partial wave quantum spectrum is obtained by\nthe one-dimensional scale-invariant inverse square potential. Long known as the\nCalogero-Sutherland-Moser (CSM) model, it leads to Fractional Exclusion\nStatistics (FES) of Haldane and Wu. The statistical parameter is deduced from\nthe analytically calculated second virial coefficient. When FES is applied to a\nFermi gas at unitarity, it gives good agreement with experimental data without\nthe use of any free parameter.",
        "positive": "Zero-temperature phase diagram of Yukawa bosons: We study the zero-temperature phase diagram of bosons interacting via\nscreened Coulomb (Yukawa) potential by means of the diffusion Monte Carlo\nmethod. The Yukawa potential is used as a model interaction in the neutron\nmatter, dusty plasmas and charged colloids. As shown by D. S. Petrov et al.\n[Phys. Rev. Lett. 99, 130407 (2007)], interactions between weakly bound\nmolecules of heavy and light fermionic atoms are described by an effective\nYukawa potential with a strength related to the heavy-light mass ratio M/m\nwhich might lead to crystallization in a two-dimensional geometry if the mass\nratio of heavy-light fermions exceeds a certain critical value. In the present\nwork we do a thorough study of the quantum three-dimensional Yukawa system. For\nstrong interactions (equivalently, large mass ratios) the system experiences\nseveral phase transitions as the density is increased, passing from gas to\nsolid and to gas phase again. Weakly interacting Yukawa particles do not\ncrystallize at any density. We find the minimal interaction strength at which\nthe crystallization happens. In terms of the two-component fermionic system,\nthis strength corresponds to a heavy-light mass ratio of M/m ~ 180, so that it\nis impossible to realize the gas-crystal transition in a conventional bulk\nsystem. For the Yukawa model of fermionic mixtures we also analyze the\npossibility of building molecular systems with very large effective mass ratios\nby confining the heavy component to a sufficiently deep optical lattice. We\nshow how the effective mass of the heavy component can be made arbitrarily\nlarge by increasing the lattice depth, thus leading to a tunable effective mass\nratio that can be used to realize a molecular superlattice."
    },
    {
        "anchor": "First-order Bose-Einstein condensation with three-body interacting\n  bosons: Bose-Einstein condensation, observed in either strongly interacting liquid\nhelium or weakly interacting atomic Bose gases, is widely known to be a\nsecond-order phase transition. Here, we predict a first-order Bose-Einstein\ncondensation in a cloud of harmonically trapped bosons interacting with both\nattractive two-body interaction and repulsive three-body interaction,\ncharacterized respectively by an $s$-wave scattering length $a<0$ and a\nthree-body scattering hypervolume $D>0$. It happens when the harmonic trapping\npotential is weak, so with increasing temperature the system changes from a\nlow-temperature liquid-like quantum droplet to a normal gas, and therefore\nexperiences a first-order liquid-to-gas transition. At large trapping\npotential, however, the quantum droplet can first turn into a superfluid gas,\nrendering the condensation transition occurred later from a superfluid gas to a\nnormal gas smooth. We determine a rich phase diagram and show the existence of\na tri-critical point, where the three phases - quantum droplet, superfluid gas\nand normal gas - meet together. We argue that an ensemble of spin-polarized\ntritium atoms could be a promising candidate to observe the predicted\nfirst-order Bose-Einstein condensation, across which the condensate fraction or\ncentral condensate density jumps to zero and the surface-mode frequencies\ndiverge.",
        "positive": "Polar Phase of 1D Bosons with Large Spin: Spinor ultracold gases in one dimension represent an interesting example of\nstrongly correlated quantum fluids. They have a rich phase diagram and exhibit\na variety of quantum phase transitions. We consider a one-dimensional spinor\ngas of bosons with a large spin $S$. A particular example is the gas of\nchromium atoms (S=3), where the dipolar collisions efficiently change the\nmagnetization and make the system sensitive to the linear Zeeman effect. We\nargue that in one dimension the most interesting effects come from the pairing\ninteraction. If this interaction is negative, it gives rise to a\n(quasi)condensate of singlet bosonic pairs with an algebraic order at zero\ntemperature, and for $(2S+1)\\gg 1$ the saddle point approximation leads to\nphysically transparent results. Since in one dimension one needs a finite\nenergy to destroy a pair, the spectrum of spin excitations has a gap. Hence, in\nthe absence of magnetic field there is only one gapless mode corresponding to\nphase fluctuations of the pair quasicondensate. Once the magnetic field exceeds\nthe gap another condensate emerges, namely the quasicondensate of unpaired\nbosons with spins aligned along the magnetic field. The spectrum then contains\ntwo gapless modes corresponding to the singlet-paired and spin-aligned unpaired\nbose-condensed particles, respectively. At T=0 the corresponding phase\ntransition is of the commensurate-incommensurate type."
    },
    {
        "anchor": "Dynamic structure factor of two-dimensional Fermi superfluid with Rashba\n  spin-orbit coupling: We theoretically calculate the dynamic structure factor of two-dimensional\nRashba-type spinorbit coupled (SOC) Fermi superfluid with random phase\napproximation, and analyse the main characters of dynamical excitation sh own\nby both density and spin dynamic structure factor during a continuous phase\ntransition between Bardeen-Cooper-Schrieffer superfluid and topological\nsuperfluid. Generally we find three different excitations, including collective\nphonon excitation, two-atom molecular and atomic excitations, and pair-breaking\nexcitations due to two-branch structure of quasi-particle spectrum. It should\nbe emphasized that collective phonon excitation is overlapped with a gapless DD\ntype pair-breaking excitation at the critical Zeeman field hc, and is imparted\na finite width to phonon peak when transferred momentum q is around Fermi\nvector kF. At a much larger transferred momentum (q = 4kF ), the pair-breaking\nexcitation happens earlier than two-atom molecular excitation, which is\ndifferent from the conventional Fermi superfluid without SOC effect.",
        "positive": "Inert-states of spin-5 and spin-6 Bose-Einstein condensates: In this paper we consider spinor Bose-Einstein condensates with spin f=5 and\nf=6 in the presence and absence of external magnetic field at the mean field\nlevel. We calculate all of so-called inert-states of these systems.\nInert-states are very unique class of stationary states because they remain\nstationary while Hamiltonian parameters change. Their existence comes from\nMichel's theorem. For illustration of symmetry properties of the inert-states\nwe use method that allows classification of the systems as a polyhedron with 2f\nvertices proposed by R. Barnett et al., Phys. Rev. Lett. 97, 180412 (2006)."
    },
    {
        "anchor": "Amplifying single impurities immersed in a gas of ultra cold atoms: We present a method for amplifying a single or scattered impurities immersed\nin a background gas of ultra cold atoms so that they can be optically imaged\nand spatially resolved. Our approach relies on a Raman transfer between two\nstable atomic hyperfine states that is conditioned on the presence of an\nimpurity atom. The amplification is based on the strong interaction among atoms\nexcited to Rydberg states. We perform a detailed analytical study of the\nperformance of the proposed scheme with particular emphasis on the influence of\nmany-body effects.",
        "positive": "Integrability breaking in the one dimensional Bose gas: Atomic losses\n  and energy loss: The one dimensional $\\delta$-function interacting Bose gas (the Lieb-Liniger\nmodel) is an integrable system, which can model experiments with ultra cold\natoms in one dimensional traps. Even though the model is integrable,\nintegrability breaking effects are always present in the real world\nexperiments. In this work we consider the integrability breaking due to atomic\nloss, which is the most relevant effect in the experiments. We set up a\nframework for the exact computation of the losses of the canonical charges of\nthe model, and compute an exact result for the energy loss due to the local\n$K$-body processes, valid for arbitrary $K$. Our result takes the form of\nmultiple integrals, which are explicitly factorized in the experimentally\nrelevant cases of $K=1,2,3$."
    },
    {
        "anchor": "Topological superfluidity of lattice fermions inside a Bose-Einstein\n  condensate: We calculate the phase diagram of identical fermions in a 2-dimensional (2D)\nlattice immersed in a 3D Bose-Einstein condensate (BEC). The fermions exchange\ndensity fluctuations in the BEC, which gives rise to an attractive induced\ninteraction. The resulting zero temperature phase diagram exhibits topological\n$p_x+ip_y$ superfluid phases as well as a phase separation region. We show how\nto use the flexibility of the Bose-Fermi mixture to tune the induced\ninteraction, so that it maximises the pairing between nearest neighbour sites,\nwhereas phase separation originating from long range interactions is\nsuppressed. Finally, we calculate the Berezinskii-Kosterlitz-Thouless (BKT)\ncritical temperature of the topological superfluid in the lattice and discuss\nexperimental realisations.",
        "positive": "Metastability and Coherence of Repulsive Polarons in a Strongly\n  Interacting Fermi Mixture: Ultracold Fermi gases with tuneable interactions represent a unique test bed\nto explore the many-body physics of strongly interacting quantum systems. In\nthe past decade, experiments have investigated a wealth of intriguing\nphenomena, and precise measurements of ground-state properties have provided\nexquisite benchmarks for the development of elaborate theoretical descriptions.\nMetastable states in Fermi gases with strong repulsive interactions represent\nan exciting new frontier in the field. The realization of such systems\nconstitutes a major challenge since a strong repulsive interaction in an atomic\nquantum gas implies the existence of a weakly bound molecular state, which\nmakes the system intrinsically unstable against decay. Here, we exploit\nradio-frequency spectroscopy to measure the complete excitation spectrum of\nfermionic 40K impurities resonantly interacting with a Fermi sea of 6Li atoms.\nIn particular, we show that a well-defined quasiparticle exists for strongly\nrepulsive interactions. For this \"repulsive polaron\" we measure its energy and\nits lifetime against decay. We also probe its coherence properties by measuring\nthe quasiparticle residue. The results are well described by a theoretical\napproach that takes into account the finite effective range of the interaction\nin our system. We find that a non-zero range of the order of the interparticle\nspacing results in a substantial lifetime increase. This major benefit for the\nstability of the repulsive branch opens up new perspectives for investigating\nnovel phenomena in metastable, repulsively interacting fermion systems."
    },
    {
        "anchor": "Optical control of Feshbach resonances in Fermi gases using molecular\n  dark states: We propose a general method for optical control of magnetic Feshbach\nresonances in ultracold atomic gases with more than one molecular state in an\nenergetically closed channel. Using two optical frequencies to couple two\nstates in the closed channel, inelastic loss arising from spontaneous emission\nis greatly suppressed by destructive quantum interference at the two-photon\nresonance, i.e., dark-state formation, while the scattering length is widely\ntunable by varying the frequencies and/or intensities of the optical fields.\nThis technique is of particular interest for a two-component atomic Fermi gas,\nwhich is stable near a Feshbach resonance.",
        "positive": "Quantum Back-action Limits in Dispersively Measured Bose-Einstein\n  Condensates: A fundamental tenet of quantum mechanics is that measurements change a\nsystem's wavefunction to that most consistent with the measurement outcome,\neven if no observer is present. Weak measurements produce only limited\ninformation about the system, and as a result only minimally change the\nsystem's state. Here, we theoretically and experimentally characterize quantum\nback-action in atomic Bose-Einstein condensates interacting with a far-from\nresonant laser beam. We theoretically describe this process using a quantum\ntrajectories approach where the environment measures the scattered light and\npresent a measurement model based on an ideal photodetection mechanism. We\nexperimentally quantify the resulting wavefunction change in terms of the\ncontrast of a Ramsey interferometer and control parasitic effects associated\nwith the measurement process. The observed back-action is in good agreement\nwith our measurement model; this result is a necessary precursor for achieving\ntrue quantum back-action limited measurements of quantum gases."
    },
    {
        "anchor": "Controlled wave-packet manipulation with driven optical lattices: Motivated by recent experimental progress achieved with ultracold atoms in\nkilohertz-driven optical lattices, we provide a theoretical discussion of\nmechanisms governing the response of a particle in a cosine lattice potential\nto strong forcing pulses with smooth envelope. Such pulses effectuate adiabatic\nmotion of a wave packet's momentum distribution on quasienergy surfaces created\nby spatiotemporal Bloch waves. Deviations from adiabaticity can then\ndeliberately be exploited for exerting coherent control and for reaching target\nstates which may not be accessible by other means. As one particular example,\nwe consider an analog of the \\pi-pulses known from optical resonance. We also\nsuggest adapting further techniques previously developed for controlling atomic\nand molecular dynamics by laser pulses to the coherent control of matter waves\nin shaken optical lattices.",
        "positive": "Gap solitons in Rabi lattices: We introduce a two-component one-dimensional system, which is based on two\nnonlinear Schr\\\"{o}dinger/Gross-Pitaevskii equations (GPEs) with spatially\nperiodic modulation of linear coupling (\"Rabi lattice\") and self-repulsive\nnonlinearity. The system may be realized in a binary Bose-Einstein condensate,\nwhose components are resonantly coupled by a standing optical wave, as well as\nin terms of the bimodal light propagation in periodically twisted fibers. The\nsystem supports various types of gap solitons (GSs), which are constructed, and\ntheir stability is investigated, in the first two finite bandgaps of the\nunderlying spectrum. These include on- and off-site-centered solitons (the GSs\nof the off-site type are additionally categorized as spatially even and odd\nones), which may be symmetric or antisymmetric, with respect to the coupled\ncomponents. The GSs are chiefly stable in the first finite bandgap, and\nunstable in the second one. In addition to that, there are narrow regions near\nthe right edge of the first bandgap, and in the second one, which feature\nintricate alternation of stability and instability. Unstable solitons evolve\ninto robust breathers or spatially confined turbulent modes. On-site-centered\nGSs are also considered in a version of the system which is made asymmetric by\nthe Zeeman effect, or by birefringence of the optical fiber. A region of\nalternate stability is found in the latter case too. In the limit of strong\nasymmetry, GSs are obtained in a semi-analytical approximation, which reduces\ntwo coupled GPEs to a single one with an effective lattice potential."
    },
    {
        "anchor": "Pattern Formation and Evidence of Quantum Turbulence in Binary\n  Bose-Einstein Condensates Interacting with a Pair of Laguerre-Gaussian Laser\n  Beams: We theoretically investigate the out-of-equilibrium dynamics in a binary\nBose-Einstein condensate confined within two-dimensional box potentials. One\nspecies of the condensate interacts with a pair of oppositely wound, but\notherwise identical Laguerre-Gaussian laser pulses, while the other species is\ninfluenced only via the interspecies interaction. Starting from the\nHamiltonian, we derive the equations of motion that accurately delineate the\nbehavior of the condensates during and after the light-matter interaction.\nDepending on the number the helical windings (or the magnitude of topological\ncharge), the species directly participating in the interaction with lasers is\ndynamically segmented into distinct parts which collide together as the pulses\ngradually diminish. This collision event generates nonlinear structures in the\nrelated species, coupled with the complementary structures produced in the\nother species, due to the interspecies interaction. The long-time dynamics of\nthe optically perturbed species is found to develop the Kolmogorov-Saffman\nscaling law in the incompressible kinetic energy spectrum, a characteristic\nfeature of the quantum turbulent state. However, the same scaling law is not\ndefinitively exhibited in the other species. This study warrants the usage of\nLaguerre-Gaussian beams for future experiments on quantum turbulence in\nBose-Einstein condensates.",
        "positive": "Mapping atomic trapping in an optical superlattice onto the libration of\n  a planar rotor in electric fields: We show that two seemingly unrelated problems - the trapping of an atom in an\noptical superlattice (OSL) and the libration of a planar rigid rotor in\ncombined electric and optical fields - have isomorphic Hamiltonians. Formed by\nthe interference of optical lattices whose spatial periods differ by a factor\nof two, OSL gives rise to a periodic potential that acts on atomic translation\nvia the AC Stark effect. The latter system, also known as the generalized\nplanar pendulum (GPP), is realized by subjecting a planar rigid rotor to\ncombined orienting and aligning interactions due to the coupling of the rotor's\npermanent and induced electric dipole moments with the combined fields. The\nmapping makes it possible to establish correspondence between concepts\ndeveloped for the two eigenproblems individually, such as localization on the\none hand and orientation/alignment on the other. Moreover, since the GPP\nproblem is conditionally quasi-exactly solvable (C-QES), so is atomic trapping\nin an OSL. We make use of both the correspondence and the quasi-exact\nsolvability to treat ultracold atoms in an optical superlattice as a\nsemifinite-gap system. The band structure of this system follows from the\neigenenergies and their genuine and avoided crossings obtained previously for\nthe GPP as analytic solutions of the Whittaker-Hill equation. These solutions\ncharacterize both the squeezing and the tunneling of atoms trapped in an\noptical superlattice and pave the way to unraveling their dynamics in analytic\nform."
    },
    {
        "anchor": "Mobile Impurity in a Two-Leg Bosonic Ladder: We study the dynamics of a mobile impurity in a two-leg bosonic ladder. The\nimpurity moves both along and across the legs and interacts with a bath of\ninteracting bosonic particles present in the ladder. We use both analytical\n(Tomonaga-Luttinger liquid - TLL) and numerical (Density Matrix Renormalization\nGroup - DMRG) methods to compute the Green's function of the impurity. We find\nthat for a small impurity-bath interaction, the bonding mode of the impurity\neffectively couples only to the gapless mode of the bath while the anti-bonding\nmode of the impurity couples to both gapped and gapless mode of the bath. We\ncompute the time dependence of the Green's function of the impurity, for\nimpurity created either in the anti-bonding or bonding mode with a given\nmomentum. The later case leads to a decay as a power-law below a critical\nmomentum and exponential above, while the former case always decays\nexponentially. We compare the DMRG results with analytical results using the\nlinked cluster expansion and find a good agreement. In addition we use DMRG to\nextract the lifetime of the quasi-particle, when the Green's function decays\nexponentially. We also treat the case of an infinite bath-impurity coupling for\nwhich both the bonding and antibonding modes are systematically affected. For\nthis case the impurity Green's function in the bonding mode decays as a\npower-law at zero momentum.The corresponding exponent increases with increasing\ntransverse-tunneling of the impurity. We compare our results with the other\nimpurity problems for which the motion of either the impurity or the bath is\nlimited to a single chain. Finally we comments on the consequences of our\nfindings for experiments with the ultracold gasses.",
        "positive": "Chiral Mott Insulators, Meissner Effect, and Laughlin States in Quantum\n  Ladders: We introduce generic bosonic models exemplifying that chiral Meissner\ncurrents can persist in insulating phases of matter. We first consider\ninteracting bosons on a two-leg ladder. The total density sector can be gapped\nin a bosonic Mott insulator at odd-integer filling, while the relative density\nsector remains superfluid due to interchain hopping. Coupling the relative\ndensity to gauge fields yields a pseudospin Meissner effect. We show that the\nsame phase arises if the bosons are replaced by spinful fermions confined in\nCooper pairs, and find a dual fermionic Mott insulator with spinon currents. We\nprove that by tuning the mean density the Mott insulator with Meissner currents\nturns into a low-dimensional bosonic $\\nu = \\frac{1}{2}$ Laughlin state for\nstrong enough repulsive interactions across the ladder rungs. We finally\ndiscuss extensions to multileg ladders and bilayers in which spinon superfluids\nwith Meissner currents become possible. We propose two experimental\nrealizations, one with ultracold atoms in the setup of Atala et al., Nat. Phys.\n\\textbf{8}, 588 (2014) and another with Josephson junction arrays. We also\naddress a Bose-Fermi mixture subject to a magnetic field in connection with the\npseudo-gap phase of high-Tc cuprates."
    },
    {
        "anchor": "Bose-Einstein Condensation of Long-Lifetime Polaritons in Thermal\n  Equilibrium: Exciton-polaritons in semiconductor microcavities have been used to\ndemonstrate quantum effects such as Bose-Einstein condensation, superfluity,\nand quantized vortices. However, in these experiments, the polaritons have not\nreached thermal equilibrium when they undergo the transition to a coherent\nstate. This has prevented the verification of one of the canonical predictions\nfor condensation, namely the phase diagram. In this work, we have created a\npolariton gas in a semiconductor microcavity in which the quasiparticles have a\nlifetime much longer than their thermalization time. This allows them to reach\nthermal equilibrium in a laser-generated confining trap. Their energy\ndistributions are well fit by equilibrium Bose-Einstein distributions over a\nbroad range of densities and temperatures from very low densities all the way\nup to the threshold for Bose-Einstein condensation. The good fits of the\nBose-Einstein distribution over a broad range of density and temperature imply\nthat the particles obey the predicted power law for the phase boundary of\nBose-Einstein condensation.",
        "positive": "Slow quench dynamics of periodically driven quantum gases: We study the evolution of bosons in a periodically driven optical lattice\nduring a slow change of the driving amplitude. Both the regime of high\nfrequency and low frequency driving are investigated. In the low frequency\nregime, resonant absorption of energy is observed. In the high frequency\nregime, the dynamics is compared to a system with an effective Hamiltonian in\nwhich the atoms are `dressed' by the driving field. This `dressing' can\ndramatically change the amplitude and sign of the effective tunneling. A\nparticular focus of this study is the investigation of the time-scales\nnecessary for the evolving quantum state to follow almost adiabatically to the\nground-state of the effective many body system."
    },
    {
        "anchor": "Quantum phase diagrams of fermionic dipolar gases for an arbitrary\n  orientation of dipole moment in a planar array of 1D tubes: We systematically study ground state properties of fermionic dipolar gases in\na planar array of one-dimensional potential tubes for an arbitrary orientation\nof dipole moments. Using the Luttinger liquid theory with the generalized\nBogoliubov transformation, we calculate the elementary excitations and the\nLuttinger scaling exponents for various relevant quantum orders. The complete\nquantum phase diagrams for arbitrary polar angle of the dipole moment is\nobtained, including charge density wave, p-wave superfluid, inter-tube\ngauge-phase density wave, and inter-tube s-wave superfluid, where the last two\nbreaks the U(1) gauge symmetry of the system (conservation of particle number\nin each tube) and occurs only when the inter-tube interaction is larger than\nthe intra-tube interaction. We then discuss the physical properties of these\nmany-body phases and their relationship with some solid state systems.",
        "positive": "Kinetics of Bose-Einstein condensation in a dimple potential: We model the dynamics of condensation in a bimodal trap, consisting of a\nlarge reservoir region, and a tight \"dimple\" whose depth can be controlled.\nExperimental investigations have found that such dimple traps provide an\nefficient means of achieving condensation. In our kinetic equations, we include\ntwo- and three-body processes. The two-body processes populate the dimple, and\nlead to loss when one of the colliding atoms is ejected from the trap. The\nthree-body processes produce heating and loss. We explain the principal trends,\ngive a detailed description of the dynamics, and provide quantitative\npredictions for timescales and condensate yields. From these simulations, we\nextract optimal parameters for future experiments."
    },
    {
        "anchor": "Metastable spin-phase diagrams in antiferromagnetic Bose-Einstein\n  condensates: Spinor Bose-Einstein condensates under external magnetic fields exhibit\nwell-characterized spin domains of its ground state due to spin-dependent\ninteractions. At low temperatures, collision-induced spin-mixing instabilities\nmay promote the condensate to dwell into metastable states occurring near the\nphase boundaries. In this work, we study theoretically the metastable\nspin-phase diagram of a spin-1 antiferromagnetic Bose-Einstein condensate at\nzero and finite temperatures. The approach makes use of Hartree-Fock theory and\nexploits the symmetry of the Hamiltonian and of the order parameters yielding a\nclosed system of transcendental equations for the free energy, fully avoiding\nthe use of selfconsistency. Our results are consistent with recent experiments\nand allow us to explain qualitatively the different types of observed quench\ndynamics. In addition, we found that similar phenomena should occur in\nantiferromagnetic spinor condensates with a sudden change in the temperature.\nIt is shown also that the increase of temperature induces a traceable shift of\nthe Ferromagnetic-Polar transition boundary, behavior previously not noticed by\nselfconsistent mean-field calculations.",
        "positive": "Thermodynamics of Bose gases from functional renormalization with a\n  hydrodynamic low-energy effective action: The functional renormalization group for the effective action is used to\nconstruct an effective hydrodynamic description of weakly interacting Bose\ngases. We employ a scale-dependent parametrization of the boson fields\ndeveloped previously to start the renormalization evolution in a Cartesian\nrepresentation at high momenta and interpolate to an amplitude-phase one in the\nlow-momentum regime. This technique is applied to Bose gases in one, two and\nthree dimensions, where we study thermodynamic quantities such as the pressure\nand energy per particle. The interpolation leads to a very natural description\nof the Goldstone modes in the physical limit, and compares well to analytic and\nMonte-Carlo simulations at zero temperature. The results show that our method\nimproves aspects of the description of low-dimensional systems, with stable\nresults for the superfluid phase in two dimensions and even in one dimension."
    },
    {
        "anchor": "Excitation Spectrum and Superfluid Gap of an Ultracold Fermi Gas: Ultracold atomic gases are a powerful tool to experimentally study strongly\ncorrelated quantum many-body systems. In particular, ultracold Fermi gases with\ntunable interactions have allowed to realize the famous BEC-BCS crossover from\na Bose-Einstein condensate (BEC) of molecules to a Bardeen-Cooper-Schrieffer\n(BCS) superfluid of weakly bound Cooper pairs. However, large parts of the\nexcitation spectrum of fermionic superfluids in the BEC-BCS crossover are still\nunexplored. In this work, we use Bragg spectroscopy to measure the full\nmomentum-resolved low-energy excitation spectrum of strongly interacting\nultracold Fermi gases. This enables us to directly observe the smooth\ntransformation from a bosonic to a fermionic superfluid that takes place in the\nBEC-BCS crossover. We also use our spectra to determine the evolution of the\nsuperfluid gap and find excellent agreement with previous experiments and\nself-consistent T-matrix calculations both in the BEC and crossover regime.\nHowever, towards the BCS regime a calculation that includes the effects of\nparticle-hole correlations shows better agreement with our data.",
        "positive": "Angular Fulde-Ferrell-Larkin-Ovchinnikov superfluid due to\n  self-one-dimensionalization in imbalanced cold fermion gases: We study the angular Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, in which\nthe rotation symmetry is spontaneously broken, in population imbalanced fermion\ngases. The superfluid gases at near T=0 are investigated on the basis of the\nBogoliubov-de Gennes (BdG) equation. We find that the angular FFLO state is\nstabilized in the gases confined in the toroidal trap, but not in the harmonic\ntrap. We discuss the mechanism of the angular FFLO state based on the\nself-one-dimensionalization of the superfluid gas."
    },
    {
        "anchor": "Competing order in two-band Bose-Hubbard chains with extended-range\n  interactions: Motivated by the recent progress in realizing and controlling extended\nBose-Hubbard systems using excitonic or atomic devices, the present Letter\ntheoretically investigates the case of a two-band Bose-Hubbard chain with\nnearest-neighbor interactions. Specifically, this study concentrates on the\nscenario where, due to the interactions, one band supports a density wave\nphase, i.e. a correlated insulating phase with spontaneous breaking of\ntranslational symmetry in the lattice, while the other band supports superfluid\nbehavior. Using the density matrix renormalization group method, we show that\nsupersolid order can emerge from such a combination, that is, an elusive\nquantum state that combines crystalline order with long-range phase coherence.\nDepending on the filling of the bands and the interband interaction strength,\nthe supersolid phase competes with phase-separation, superfluid order, or Mott\ninsulating density-wave order. As a possible setup to observe supersolidity, we\npropose the combination of a lower band supporting density-wave order and a\nthermally excited band that supports superfluidity due to weaker lattice\nconfinement.",
        "positive": "Fragility of the Laughlin state in an anharmonically-trapped\n  Bose-Einstein condensate: When a Bose-Einstein condensate rotates in a purely harmonic potential with\nan angular frequency which is close to the trap frequency, its many-body state\nbecomes highly correlated, with the most well-known being the bosonic Laughlin\nstate. To take into account that in a real experiment no trapping potential is\never exactly harmonic, we introduce an additional weak, quartic potential and\ndemonstrate that the Laughlin state is highly sensitive to this extra\npotential. Our results imply that achieving these states experimentally is\nessentially impossible, at least for a macroscopic atom number."
    },
    {
        "anchor": "Clusterization of weakly-interacting bosons in one dimension: an\n  analytic study at zero temperature: We study a system of penetrable bosons on a line, focusing on the\nhigh-density/weak-interaction regime, where the ground state is, to a good\napproximation, a condensate. Under compression, the system clusterizes at zero\ntemperature, i.e., particles gather together in separate, equally populated\nbunches. We compare predictions from the Gross-Pitaevskii (GP) equation with\nthose of two distinct variational approximations of the single-particle state,\nwritten as either a sum of Gaussians or the square root of it. Not only the\nwave functions in the three theories are similar, but also the phase-transition\ndensity is the same for all. In particular, clusterization occurs together with\nthe softening of roton excitations in GP theory. Compared to the latter theory,\nGaussian variational theory has the advantage that the mean-field energy\nfunctional is written in (almost) closed form, which enables us to extract the\nphase-transition and high-density behaviors in fully analytic terms. We also\ncompute the superfluid fraction of the clustered system, uncovering its exact\nbehavior close, as well as very far away from, the transition.",
        "positive": "Possible quantum phase-manipulation of a two-leg ladder in\n  mixed-dimensional fermionic cold atoms: The recent realization of mixed-dimensional systems of cold atoms has\nattracted much attention from both experimentalists and theorists. Different\neffective interactions and novel correlated quantum many-body phases may be\nengineered in these systems, with the different phases being tunable via\nexternal parameters. In this article we investigate a two-species Fermi atom\nmixture: one species of atom exists in two hyperfine states and is confined to\nmove in a two-leg ladder, interacting with an on-site interaction, and the\nother moves freely in a two dimensional square lattice that contains the\ntwo-leg ladder. The two species of atoms interact via an on-site interaction on\nthe ladder. In the limit of weak inter-species interactions, the\ntwo-dimensional gas can be integrated out, leading to an effective long-range\nmediated interaction in the ladder, generated by to the on-site inter-species\ninteraction. We show that the form of the mediated interaction can be\ncontrolled by the density of the two-dimensional gas and that it enhances the\ncharge density wave instability in the two-leg ladder after the renormalization\ngroup transformation. Parameterizing the phase diagram with various\nexperimentally controllable quantities, we discuss the possible tuning of the\nmacroscopic quantum many-body phases of the two-leg ladder in this\nmixed-dimensional fermionic cold atom system."
    },
    {
        "anchor": "Sine-Gordon model coupled with a free scalar field emergent in the\n  low-energy phase dynamics of a mixture of pseudospin-1/2 Bose gases with\n  interspecies spin exchange: Using the approach of low-energy effective field theory, the phase diagram is\nstudied for a mixture of two species of pseudospin-$\\1/2$ Bose atoms with\ninterspecies spin-exchange. There are four mean-field regimes on the parameter\nplane of $g_e$ and $g_z$, where $g_e$ is the interspecies spin-exchange\ninteraction strength, while $g_z$ is the difference between the interaction\nstrength of interspecies scattering without spin-exchange of equal spins and\nthat of unequal spins. Two regimes, with $|g_z| > |g_e|$, correspond to ground\nstates with the total spins of the two species parallel or antiparallel along\n$z$ direction, and the low energy excitations are equivalent to those of\ntwo-component spinless Bosons. The other two regimes, with $|g_e| > |g_z|$,\ncorrespond to ground states with the total spins of the two species parallel or\nantiparallel on $xy$ plane, and the low energy excitations are described by a\nsine-Gordon model coupled with a free scalar field, where the effective fields\nare combinations of the phases of the original four Boson fields. In\n(1+1)-dimension, they are described by Kosterlitz-Thouless renormalization\ngroup (RG) equations, and there are three sectors in the phase plane of a\nscaling dimension and a dimensionless parameter proportional to the strength of\nthe cosine interaction, both depending on the densities. The gaps of these\nelementary excitations are experimental probes of the underlying many-body\nground states.",
        "positive": "Quantum quench dynamics: Quench dynamics is an active area of study encompassing condensed matter\nphysics and quantum information, with applications to cold-atomic gases and\npump-probe spectroscopy of materials. Recent theoretical progress in studying\nquantum quenches is reviewed. Quenches in interacting one dimensional systems\nas well as systems in higher spatial dimensions are covered. The appearance of\nnon-trivial steady states following a quench in exactly solvable models is\ndiscussed, and the stability of these states to perturbations is described.\nProper conserving approximations needed to capture the onset of thermalization\nat long times are outlined. The appearance of universal scaling for quenches\nnear critical points, and the role of the renormalization group in capturing\nthe transient regime, are reviewed. Finally the effect of quenches near\ncritical points on the dynamics of entanglement entropy and entanglement\nstatistics is discussed. The extraction of critical exponents from the\nentanglement statistics is outlined."
    },
    {
        "anchor": "Unitary boson-boson and boson-fermion mixtures: third virial coefficient\n  and three-body parameter on a narrow Feshbach resonance: We give exact integral expressions of the third cluster or virial\ncoefficients of binary mixtures of ideal Bose or Fermi gases, with interspecies\ninteractions of zero range and infinite s-wave scattering length. In general\nthe result depends on three-body parameters Rt appearing in three-body contact\nconditions, because an Efimov effect is present or because the mixture is in a\npreefimovian regime with a mass ratio close to an Efimov effect threshold. We\ngive a new, exact integral expression of Rt for the microscopic narrow Feshbach\nresonance model. A divergence of Rt in the preefimovian regime at a scaling\nexponent s = 1/2 is predicted and physically discussed. The analytical results\nare applied to typical species used in cold atom experiments.",
        "positive": "Detection of Fermi Pairing via Electromagnetically Induced Transparency: An optical spectroscopic method based on the principle of\nelectromagnetically-induced transparency (EIT) is proposed as quite a generic\nprobing tool that provides valuable insights into the nature of Fermi paring in\nultracold Fermi gases of two hyperfine states. This technique has the\ncapability of allowing spectroscopic response to be determined in a nearly\nnon-destructive manner and the whole spectrum may be obtained by scanning the\nprobe laser frequency faster than the lifetime of the sample without\nre-preparing the atomic sample repeatedly. A quasiparticle picture is\nconstructed to facilitate a simple physical explanation of the pairing\nsignature in the EIT spectra."
    },
    {
        "anchor": "Ab initio methods for finite temperature two-dimensional Bose gases: The stochastic Gross-Pitaevskii equation and modified Popov theory are shown\nto provide an ab initio description of finite temperature, weakly-interacting\ntwo-dimensional Bose gas experiments. Using modified Popov theory, a systematic\napproach is developed in which the momentum cut-off inherent to classical field\nmethods is removed as a free parameter. This is shown to yield excellent\nagreement with the recent experiment of Hung et al. [Nature, 470, 236 (2011)],\nverifying that the stochastic Gross-Pitaevskii equation captures the observed\nuniversality and scale-invariance.",
        "positive": "Unveiling hidden structure of many-body wavefunctions of integrable\n  systems via sudden expansion experiments: In the theory of Bethe-ansatz integrable quantum systems, rapidities play an\nimportant role as they are used to specify many-body states, apart from phases.\nThe physical interpretation of rapidities going back to Sutherland is that they\nare the asymptotic momenta after letting a quantum gas expand into a larger\nvolume making it dilute and noninteracting. We exploit this picture to make a\ndirect connection to quantities that are accessible in sudden-expansion\nexperiments with ultracold quantum gases. By a direct comparison of\nBethe-ansatz and time-dependent density matrix renormalization group results,\nwe demonstrate that the expansion velocity of a one-dimensional Fermi-Hubbard\nmodel can be predicted from knowing the distribution of occupied rapidities\ndefined by the initial state. Curiously, an approximate Bethe-ansatz solution\nworks well also for the Bose-Hubbard model."
    },
    {
        "anchor": "Oblique Half-Solitons and their Generation in Exciton-Polariton\n  Condensates: We describe oblique half-solitons, a new type of topological defects in a two\ndimensional spinor Bose Einstein condensate. A realistic protocol based on the\noptical spin Hall effect is proposed toward their generation within an\nexciton-polariton system.",
        "positive": "Analytical and numerical study of trapped strongly correlated bosons in\n  two- and three-dimensional lattices: We study the ground-state properties of trapped inhomogeneous systems of\nhardcore bosons in two- and three-dimensional lattices. We obtain our results\nboth numerically, using quantum Monte Carlo techniques, and via several\nanalytical approximation schemes, such as the Gutzwiller-mean-field approach, a\ncluster-mean-field method and a spin-wave analysis which takes quantum\nfluctuations into account. We first study the homogeneous case, for which\nsimple analytical expressions are obtained for all observables of interest, and\ncompare the results with the numerical ones. We obtain the equation of state of\nthe system along with other thermodynamic properties such as the free energy,\nkinetic energy, superfluid density, condensate fraction and compressibility. In\nthe presence of a trap, superfluid and insulating domains coexist in the\nsystem. We show that the spin-wave-based method reproduces the quantum\nMonte-Carlo results for global as well as for local quantities with a high\ndegree of accuracy. We also discuss the validity of the local density\napproximation in those systems. Our analysis can be used to describe bosons in\noptical lattices where the onsite interaction U is much larger than the hopping\namplitude t."
    },
    {
        "anchor": "Polaron bubble stabilised by medium-induced three-body interactions: Mixing two kinds of particles that repel each other usually results in either\na homogeneous mixture when the repulsion is weak, or a complete phase\nseparation of the two kinds when their repulsion is too strong. It is shown\nhowever that there is an intermediate regime where the two kinds can coexist in\ntheir ground state as a bubble immersed in a gas of one kind. Such a situation\nis obtained by adding heavy repulsive impurities into a Bose-Einstein\ncondensate. Above a certain strength of the mutual repulsion, a stable bubble\nof impurities and bosons can be formed, resulting from the equilibrium between\nthe interactions induced by the bosons inside the bubble and the outside\npressure from the surrounding bosons. At some particular strength, the\neffective interactions between the impurities consist of only three-body\ninteractions. Finally, above a critical strength, the bosons are ejected from\nthe bubble and the impurities collapse into a pure bubble of impurities. This\nphenomenon could be observed with an imbalanced mixture of ultra-cold atoms of\ndifferent masses. Moreover, it appears possible to reach a regime where the\nimpurities form a dense bubble of strongly-interacting particles.",
        "positive": "Quantum Monte Carlo study of strongly interacting bosonic\n  one-dimensional systems in periodic potentials: We present diffusion Monte Carlo (DMC) and path-integral Monte Carlo (PIMC)\ncalculations of a one-dimensional Bose system with realistic interparticle\ninteractions in a periodic external potential. Our main aim is to test the\npredictions of the Luttinger liquid (LL) theory, in particular with respect to\nthe superfluid-Mott insulator transition at both zero and finite temperatures,\nin the predicted robust and fragile superfluid regimes. For that purpose, we\npresent our results of the superfluid fraction $\\rho_s/\\rho_0$, the one-body\ndensity matrix, the two-body correlation functions, and the static structure\nfactor. The DMC and PIMC results in the limit of very low temperature for\n$\\rho_s/\\rho_0$ agree, but the LL model for scaling $\\rho_s/\\rho_0$ does not\nfit the data well. The critical depth of the periodic potential is close to the\nvalues obtained for ultracold gases with different models of interaction, but\nwith the same value of the bare LL parameter, demonstrating the universality of\nLL description. Algebraic decay of correlation functions is observed in the\nsuperfluid regime and exponential decay in the Mott-insulator one, as well as\nin all regimes at finite temperature for distances larger than a characteristic\nlength."
    },
    {
        "anchor": "Pair correlation of atoms scattered from colliding Bose-Einstein\n  quasicondensates: A collision of Bose-Einstein condensates is a useful source of single\nnonclassically correlated pairs of atoms. Here, we consider elastic scattering\nof atoms from elongated clouds taking into account an effective, finite\nduration of the collision due to the expansion of the condensates. Also, we\ninclude the quasicondensate nature of the degenerate quantum gases, due to a\nfinite temperature of the system. We evaluate the pair correlation function\nmeasured experimentally in K. V. Kheruntsyan, et. al. Phys. Rev. Lett. 108,\n260401 (2012). We show that the finite duration of the collision is an\nimportant factor determining the properties of the correlations. Our analytic\ncalculations are in agreement with the measurements. The analytical model we\nprovide, useful for identifying physical processes that influence the\ncorrelations, is relevant for experiments with nonclassical pairs of atoms.",
        "positive": "Proximity effects in cold atom artificial graphene: Cold atoms in an optical lattice with brick-wall geometry have been used to\nmimic graphene, a two-dimensional material with characteristic Dirac\nexcitations. Here we propose to bring such artificial graphene into the\nproximity of a second atomic layer with a square lattice geometry. For\nnon-interacting fermions, we find that such bilayer system undergoes a phase\ntransition from a graphene-like semi-metal phase, characterized by a band\nstructure with Dirac points, to a gapped band insulator phase. In the presence\nof attractive interactions between fermions with pseudospin-1/2 degree of\nfreedom, a competition between semi-metal and superfluid behavior is found at\nthe mean-field level. Using the quantum Monte Carlo method, we also investigate\nthe case of strong repulsive interactions. In the Mott phase, each layer\nexhibits a different amount of long-range magnetic order. Upon coupling both\nlayers, a valence-bond crystal is formed at a critical coupling strength.\nFinally, we discuss how these bilayer systems could be realized in existing\ncold atom experiments."
    },
    {
        "anchor": "Non-equilibrium fluctuations and metastability arising from non-additive\n  interactions in dissipative multi-component Rydberg gases: We study the out-of-equilibrium dynamics of dissipative gases of atoms\nexcited to two or more high-lying Rydberg states. This situation bears\ninteresting similarities to classical binary (in general $p$-ary) mixtures of\nparticles. The effective forces between the components are determined by the\ninter-level and intra-level interactions of Rydberg atoms. These systems permit\nto explore new parameter regimes which are physically inaccessible in a\nclassical setting, for example one in which the mixtures exhibit non-additive\ninteractions. In this situation the out-of-equilibrium evolution is\ncharacterized by the formation of metastable domains that reach partial\nequilibration long before the attainment of stationarity. In experimental\nsettings with mesoscopic sizes, this collective behavior may in fact take the\nappearance of dynamic symmetry breaking.",
        "positive": "Phases and collective modes of bosons in a triangular lattice at finite\n  temperature: A cluster mean field study: Motivated by the realization of Bose-Einstein condensates (BEC) in non-cubic\nlattices, in this work we study the phases and collective excitation of bosons\nwith nearest neighbor interaction in a triangular lattice at finite\ntemperature, using mean field (MF) and cluster mean field (CMF) theory. We\ncompute the finite temperature phase diagram both for hardcore and softcore\nbosons, as well analyze the effect of correlation arising due to lattice\nfrustration and interaction systematically using CMF method. A semi-analytic\nestimate of the transition temperatures between different phases are derived\nwithin the framework of MF Landau theory, particularly for hardcore bosons.\nApart from the usual phases such as density waves (DW) and superfluid (SF), we\nalso characterize different supersolids (SS). These phases and their\ntransitions at finite temperature are identified from the collective modes. The\nlow lying excitations, particularly Goldstone and Higgs modes of the supersolid\ncan be detected in the ongoing cold atom experiments."
    },
    {
        "anchor": "Vortex patterns in the almost-bosonic anyon gas: We study theoretically and numerically the ground state of a gas of 2D\nabelian anyons in an external trapping potential. We treat anyon statistics in\nthe magnetic gauge picture, perturbatively around the bosonic end. This leads\nto a mean-field energy functional, whose ground state displays vortex lattices\nsimilar to those found in rotating Bose-Einstein condensates. A crucial\ndifference is however that the vortex density is proportional to the underlying\nmatter density of the gas.",
        "positive": "A note on a relation between ac Josephson effect and double-well BEC\n  oscillations: In this brief note we comment on the relation between the ac Josephson effect\nand the coherent oscillations of a Bose-Einstein condensate confined to a\ndouble-well potential. The goal is to elucidate the extent to which the latter\nis a realization of the former. We detail the correspondence that emerges in\nthe high occupation limit of the double-well potential, and particularly note\nthe relation between the two oscillation frequencies."
    },
    {
        "anchor": "Low-Lying Excitation Modes of Trapped Dipolar Fermi Gases: From\n  Collisionless to Hydrodynamic Regime: By means of the Boltzmann-Vlasov kinetic equation we investigate dynamical\nproperties of a trapped, one-component Fermi gas at zero temperature, featuring\nthe anisotropic and long-range dipole-dipole interaction. To this end, we\ndetermine an approximate solution by rescaling both space and momentum\nvariables of the equilibrium distribution, thereby obtaining coupled ordinary\ndifferential equations for the corresponding scaling parameters. Based on\nprevious results on how the Fermi sphere is deformed in the hydrodynamic regime\nof a dipolar Fermi gas, we are able to implement the relaxation-time\napproximation for the collision integral. Then, we proceed by linearizing the\nequations of motion around the equilibrium in order to study both the\nfrequencies and the damping of the low-lying excitation modes all the way from\nthe collisionless to the hydrodynamic regime. Our theoretical results are\nexpected to be relevant for understanding current experiments with trapped\ndipolar Fermi gases.",
        "positive": "Many-body correlations in one-dimensional optical lattices with\n  alkaline-earth(-like) atoms: We explore the rich nature of correlations in the ground state of ultracold\natoms trapped in state-dependent optical lattices. In particular, we consider\ninteracting fermionic ytterbium or strontium atoms, realizing a two-orbital\nHubbard model with two spin components. We analyze the model in one-dimensional\nsetting with the experimentally relevant hierarchy of tunneling and interaction\namplitudes by means of exact diagonalization and matrix product states\napproaches, and study the correlation functions in density, spin, and orbital\nsectors as functions of variable densities of atoms in the ground and\nmetastable excited states. We show that in certain ranges of densities these\natomic systems demonstrate strong density-wave, ferro- and antiferromagnetic,\nas well as antiferroorbital correlations."
    },
    {
        "anchor": "Thermally activated local collapse of a flattened dipolar condensate: We consider the metastable dynamics of a flattened dipolar condensate. We\ndevelop an analytic model that quantifies the energy barrier to the system\nundergoing local collapse to form a density spike. We also develop a stochastic\nGross-Pitaevskii equation (SGPE) theory for a flatted dipolar condensate, which\nwe use to perform finite temperature simulations verifying the local collapse\nscenario. We predict that local collapses play a significant role in the regime\nwhere rotons are predicted to exist, and will be an important consideration for\nexperiments looking to detect these excitations.",
        "positive": "Twin matter waves for interferometry beyond the classical limit: Interferometers with atomic ensembles constitute an integral part of modern\nprecision metrology. However, these interferometers are fundamentally\nrestricted by the shot noise limit, which can only be overcome by creating\nquantum entanglement among the atoms. We used spin dynamics in Bose-Einstein\ncondensates to create large ensembles of up to $10^4$ pair-correlated atoms\nwith an interferometric sensitivity $-1.61^{+0.98}_{-1.1}$ dB beyond the shot\nnoise limit. Our proof-of-principle results point the way toward a new\ngeneration of atom interferometers."
    },
    {
        "anchor": "Dipolar Molecules in Optical Lattices: We study the extended Bose--Hubbard model describing an ultracold gas of\ndipolar molecules in an optical lattice, taking into account all on-site and\nnearest-neighbor interactions, including occupation-dependent tunneling and\npair tunneling terms. Using exact diagonalization and the multiscale\nentanglement renormalization ansatz, we show that these terms can destroy\ninsulating phases and lead to novel quantum phases. These considerable changes\nof the phase diagram have to be taken into account in upcoming experiments with\ndipolar molecules.",
        "positive": "Heavily Enhanced Dynamic Stark Shift in a System of Bose Einstein\n  Condensation of Photons: The dynamic Stark shift of a high-lying atom in a system of Bose Einstein\ncondensation (BEC) of photons is discussed within the framework of\nnonrelativistic quantum electrodynamics (QED) theory. It is found that the\nStark shift of an atom in BEC of photons is modified by a temperature dependent\nfactor, compared to that in a normal two-dimensional photonic fluid. In\nphotonic BEC, the value of Stark shift is always greater than that in\ntwo-dimensional free space. Physical origin of the phenomenon is presented and\npotential application is also discussed."
    },
    {
        "anchor": "An exact formalism for the quench dynamics of integrable models: We describe a formulation for studying the quench dynamics of integrable\nsystems generalizing an approach by Yudson. We study the evolution of the\nLieb-Liniger model, a gas of interacting bosons moving on the continuous\ninfinite line and interacting via a short range potential. The formalism allows\nus to quench the system from any initial state. We find that for any value of\nrepulsive coupling independently of the initial state the system asymptotes\ntowards a strongly repulsive gas, while for any value of attractive coupling,\nthe system forms a maximal bound state that dominates at longer times. In\neither case the system equilibrates but does not thermalize. We compare this to\nquenches in a Bose-Hubbard lattice and show that there, initial states\ndetermine long-time dynamics independent of the sign of the coupling.",
        "positive": "Torus quantum vortex knots in the Gross-Pitaevskii model for\n  Bose-Einstein condensates: We examine on the static and dynamical properties of quantum knots in a\nBose-Einstein condensate. In particular, we consider the Gross-Pitaevskii model\nand revise a technique to construct ab initio the condensate wave-function of a\ngeneric torus knot. After analysing its excitation energy, we study its\ndynamics relating the topological parameter to its translational velocity and\ncharacteristic size. We also investigate the breaking mechanisms of non\nshape-preserving torus knots confirming an evidence of universal decaying\nbehaviour previously observed."
    },
    {
        "anchor": "Quantum Pumping with Ultracold Atoms on Microchips: Fermions versus\n  Bosons: We present a design for simulating quantum pumping of electrons in a\nmesoscopic circuit with ultra-cold atoms in a micro-magnetic chip trap. We\ncalculate theoretical results for quantum pumping of both bosons and fermions,\nidentifying differences and common features, including geometric behavior and\nresonance transmission. We analyze the feasibility of experiments with bosonic\n$^{87}$Rb and fermionic $^{40}$K atoms with an emphasis on reliable atomic\ncurrent measurements.",
        "positive": "Detecting Entrainment in Fermi-Bose Mixtures: We propose an experimental protocol to directly detect the Andreev-Bashkin\neffect (entrainment) in the bulk mixture of a bosonic and fermionic superfluid\nusing a ring geometry. Our protocol involves the interferometric detection of\nthe entrainment-induced phase gradient across a superfluid due to the flow of\nanother in which it is immersed. The choice of ring geometry eliminates\nvariations in the stronger mean-field interaction which can thwart the\ndetection of entrainment in other geometries. A significant enhancement of the\nentrainment phase shift signal is possible, if the dimer-boson scattering\nlength turns out to be large, which can be measured by tuning the interaction\nto the limit of miscibility of the two superfluids. With suggested improvements\nand careful design implementation, one may achieve $\\approx 67$% shift in the\ninterferometer fringes."
    },
    {
        "anchor": "Weyl Exceptional Rings in a Three-Dimensional Dissipative Cold Atomic\n  Gas: Three-dimensional topological Weyl semimetals can generally support a\nzero-dimensional Weyl point characterized by a quantized Chern number or a\none-dimensional Weyl nodal ring (or line) characterized by a quantized Berry\nphase in the momentum space. Here, in a dissipative system with particle gain\nand loss, we discover a new type of topological ring, dubbed Weyl exceptional\nring consisting of exceptional points at which two eigenstates coalesce. Such a\nWeyl exceptional ring is characterized by both a quantized Chern number and a\nquantized Berry phase, which are defined via the Riemann surface. We propose an\nexperimental scheme to realize and measure the Weyl exceptional ring in a\ndissipative cold atomic gas trapped in an optical lattice.",
        "positive": "Exact surface-wave spectrum of a dilute quantum liquid: We consider a dilute gas of bosons with repulsive contact interactions,\ndescribed on the mean-field level by the Gross-Pitaevskii equation, and bounded\nby an impenetrable \"hard\" wall (either rigid or flexible). We solve the\nBogoliubov-de Gennes equations for excitations on top of the Bose-Einstein\ncondensate analytically, by using matrix-valued hypergeometric functions. This\nleads to the exact spectrum of gapless Bogoliubov excitations localized near\nthe boundary. The dispersion relation for the surface excitations represents\nfor small wavenumbers $k$ a ripplon mode with fractional power law dispersion\nfor a flexible wall, and a phonon mode (linear dispersion) for a rigid wall.\nFor both types of excitation we provide, for the first time, the exact\ndispersion relations of the dilute quantum liquid for all $k$ along the\nsurface, extending to $k \\rightarrow \\infty$. The small wavelength excitations\nare shown to be bound to the surface with a maximal binding energy $\\Delta=\n\\frac18 (\\sqrt{17}-3)^2 mc^2 \\simeq 0.158\\, mc^2$, which both types of\nexcitation asymptotically approach, where $m$ is mass of bosons and $c$ bulk\nspeed of sound. We demonstrate that this binding energy is close to the\nexperimental value obtained for surface excitations of helium II confined in\nnanopores, reported in Phys. Rev. B 88, 014521 (2013)."
    },
    {
        "anchor": "Localization and topological transitions in generalized non-Hermitian\n  SSH models: We study the localization and topological transitions of the generalized\nnon-Hermitian SSH models, where the non-Hermiticities are introduced by the\ncomplex quasiperiodic hopping and the nonreciprocal hopping. We elucidate the\nuniversality of the models and how many models can be mapped to them. Under the\nopen boundary condition, two delocalization transitions are found due to the\ncompetition between the Anderson localization and the boundary localization\nfrom the nontrivial edge states and the non-Hermitian skin effect. Under the\nperiodic boundary condition, only one delocalization transition is found due to\nthe disappearance of the non-Hermitian skin effect. The winding numbers of\nenergy and the Lyapunov exponents in analytical form are obtained to exactly\ncharacterize the two deloaclizateon transitions. It finds that the\ndelocalization transitions don't accompany the topological transition.\nFurthermore, the large on-site non-Hermiticity and the large nonreciprocal\nhopping are all detrimental to the topological transitions. However, the large\nnonreciprocal hopping enhances the Anderson localizations. The above analyses\nare verified by calculating the energy gap and the inverse of the participation\nratio numerically.",
        "positive": "Many-body localization in a quantum gas with long-range interactions and\n  linear external potential: We study theoretically transitions between the localized and chaotic\nmany-body regimes in one-dimensional quantum lattice systems with long-range\ncouplings between particles and linear external potential. In terms of\nestablished criteria characterizing localization, we construct effective phase\ndiagrams for several types of lattice systems with variable amplitude of the\nexternal linear tilt and interaction strength. By means of exact\ndiagonalization and time-dependent variational principle numerical approaches\nwe analyze system dynamics after quenches. Our results reveal that the Stark\nlocalization without any artificial source of disorder remains stable upon\ninclusion of long-range interactions."
    },
    {
        "anchor": "Cloud shape of a molecular Bose-Einstein condensate in a disordered\n  trap: a case study of the dirty boson problem: We investigate, both experimentally and theoretically, the static geometric\nproperties of a harmonically trapped Bose-Einstein condensate of ${}^6$Li$_2$\nmolecules in laser speckle potentials. Experimentally, we measure the in-situ\ncolumn density profiles and the corresponding transverse cloud widths over many\nlaser speckle realizations. We compare the measured widths with a theory that\nis non-perturbative with respect to the disorder and includes quantum\nfluctuations. Importantly, for small disorder strengths we find quantitative\nagreement with the perturbative approach of Huang and Meng, which is based on\nBogoliubov theory. For strong disorder our theory perfectly reproduces the\ngeometric mean of the measured transverse widths. However, we also observe a\nsystematic deviation of the individual measured widths from the theoretically\npredicted ones. In fact, the measured cloud aspect ratio monotonously decreases\nwith increasing disorder strength, while the theory yields a constant ratio. We\nattribute this discrepancy to the utilized local density approximation, whose\npossible failure for strong disorder suggests a potential future improvement.",
        "positive": "Stable multiple vortices in collisionally inhomogeneous attractive\n  Bose-Einstein condensates: We study stability of solitary vortices in the two-dimensional trapped\nBose-Einstein condensate (BEC) with a spatially localized region of\nself-attraction. Solving the respective Bogoliubov-de Gennes equations and\nrunning direct simulations of the underlying Gross-Pitaevskii equation reveals\nthat vortices with topological charge up to S = 6 (at least) are stable above a\ncritical value of the chemical potential (i.e., below a critical number of\natoms, which sharply increases with S). The largest nonlinearity-localization\nradius admitting the stabilization of the higher-order vortices is estimated\nanalytically and accurately identified in a numerical form. To the best of our\nknowledge, this is the first example of a setting which gives rise to stable\nhigher-order vortices, S > 1, in a trapped self-attractive BEC. The same\nsetting may be realized in nonlinear optics too."
    },
    {
        "anchor": "Stabilization and pumping of giant vortices in dilute Bose-Einstein\n  condensates: Recently, it was shown that giant vortices with arbitrarily large quantum\nnumbers can possibly be created in dilute Bose-Einstein condensates by\ncyclically pumping vorticity into the condensate. However, multiply quantized\nvortices are typically dynamically unstable in harmonically trapped nonrotated\ncondensates, which poses a serious challenge to the vortex pump procedure. In\nthis theoretical study, we investigate how the giant vortices can be stabilized\nby the application of a Gaussian potential peak along the vortex core. We find\nthat achieving dynamical stability is feasible up to high quantum numbers. To\ndemonstrate the efficiency of the stabilization method, we simulate the\nadiabatic creation of an unsplit 20-quantum vortex with the vortex pump.",
        "positive": "Role of the confinement-induced effective range on the thermodynamics of\n  a strongly correlated Fermi gas in two dimensions: We theoretically investigate the thermodynamic properties of a strongly\ncorrelated two-dimensional Fermi gas with a confinement-induced negative\neffective range of interactions, which is described by a two-channel model\nHamiltonian. By extending the many-body T-matrix approach by Nozi\\`eres and\nSchmitt-Rink to the two-channel model, we calculate the equation of state in\nthe normal phase and present several thermodynamic quantities as functions of\ntemperature, interaction strength, and effective range. We find that there is a\nnon-trivial dependence of thermodynamics on the effective range. In experiment,\nwhere the effective range is set by the tight axial confinement, the\ncontribution of the effective range becomes non-negligible as the temperature\ndecreases down to the degenerate temperature. We compare our finite-range\nresults with recent measurements on the density equation of state, and show\nthat the effective range has to be taken into account for the purpose of a\nquantitative understanding of the experimental data."
    },
    {
        "anchor": "Quantum quench dynamics of the sine-Gordon model in some solvable limits: In connection with the the thermalization problem in isolated quantum\nsystems, we investigate the dynamics following a quantum quench of the\nsine-Gordon model in the Luther-Emery and the semiclassical limits. We consider\nthe quench from the gapped to the gapless phase as well as reversed one. By\nobtaining analytic expressions for the one and two-point correlation functions\nof the order parameter operator at zero-temperature, the manifestations of\nintegrability in the absence of thermalization in the sine-Gordon model are\nstudied. It is thus shown that correlations in the long time regime after the\nquench are well described by a generalized Gibbs ensemble. We also consider the\ncase where the system is initially in contact with a reservoir at finite\ntemperature. The possible relevance of our results to current and future\nexperiments with ultracold atomic systems is also critically considered.",
        "positive": "Metastable order protected by destructive many-body interference: The phenomenon of metastability can shape dynamical processes on all temporal\nand spatial scales. Here, we induce metastable dynamics by pumping ultracold\nbosonic atoms from the lowest band of an optical lattice to an excitation band,\nvia a sudden quench of the unit cell. The subsequent relaxation process to the\nlowest band displays a sequence of stages, which include a metastable stage,\nduring which the atom loss from the excitation band is strongly suppressed.\nUsing classical-field simulations and analytical arguments, we provide an\nexplanation for this experimental observation, in which we show that the\ntransient condensed state of the atoms in the excitation band is a dark state\nwith regard to collisional decay and tunneling to a low-energy orbital.\nTherefore the metastable state is stabilized by destructive interference due to\nthe chiral phase pattern of the condensed state. Our experimental and\ntheoretical study provides a detailed understanding of the different stages of\na paradigmatic example of many-body relaxation dynamics."
    },
    {
        "anchor": "Spontaneous quantum superradiant emission in atomic Bose-Einstein\n  condensates subject to a synthetic vector potential: We theoretically investigate the spontaneous quantum emission of phonon pairs\nby superradiant processes in an atomic Bose-Einstein condensate subject to a\nsynthetic vector potential. Within the analog gravity perspective, this effect\ncorresponds to the spontaneous emission of radiation from the ergosurface of\nrotating black holes. A general input-output formalism is built and used to\ncharacterize the spectral and correlation properties of the emission.\nExperimentally accessible signatures of the emission are pointed out in the\ncorrelation functions of the atomic gas.",
        "positive": "A strontium quantum-gas microscope: The development of quantum-gas microscopes has brought novel ways of probing\nquantum degenerate many-body systems at the single-atom level. Until now, most\nof these setups have focused on alkali atoms. Expanding quantum-gas microscopy\nto alkaline-earth elements will provide new tools, such as SU(N)-symmetric\nfermionic isotopes or ultranarrow optical transitions, to the field of quantum\nsimulation. Here, we demonstrate the site-resolved imaging of a $^{84}$Sr\nbosonic quantum gas in a Hubbard-regime optical lattice. The quantum gas is\nconfined by a two-dimensional in-plane lattice and a light-sheet potential,\nwhich operate at the strontium clock-magic wavelength of 813.4 nm. We realize\nfluorescence imaging using the broad 461 nm transition, which provides high\nspatial resolution. Simultaneously, we perform attractive Sisyphus cooling with\nthe narrow 689 nm intercombination line. We reconstruct the atomic occupation\nfrom the fluorescence images, obtaining imaging fidelities above 94%. Finally,\nwe realize a $^{84}$Sr superfluid in the Bose-Hubbard regime. We observe its\ninterference pattern upon expansion, a probe of phase coherence, with\nsingle-atom resolution. Our strontium quantum-gas microscope provides a new\nplatform to study dissipative Hubbard models, quantum optics in atomic arrays,\nand SU(N) fermions at the microscopic level."
    },
    {
        "anchor": "Energy spectrum of a harmonically trapped two-atom system with\n  spin-orbit coupling: Ultracold atomic gases provide a novel platform with which to study\nspin-orbit coupling, a mechanism that plays a central role in the nuclear shell\nmodel, atomic fine structure and two-dimensional electron gases. This paper\nintroduces a theoretical framework that allows for the efficient determination\nof the eigenenergies and eigenstates of a harmonically trapped two-atom system\nwith short-range interaction subject to an equal mixture of Rashba and\nDresselhaus spin-orbit coupling created through Raman coupling of atomic\nhyperfine states. Energy spectra for experimentally relevant parameter\ncombinations are presented and future extensions of the approach are discussed.",
        "positive": "Universal behavior of the BEC critical temperature for a multislab ideal\n  Bose gas: For an ideal Bose-gas within a multi-slab periodic structure, we discuss the\neffect of the spatial distribution of the gas on its Bose-Einstein condensation\ncritical temperature $T_c$, as well as on the origin of its dimensional\ncrossover observed in the specific heat. The multi-slabs structure is generated\nby applying a Kronig-Penney potential to the gas in the perpendicular direction\nto the slabs of width $b$ and separated by a distance $a$, and allowing the\nparticles to move freely in the other two directions. We found that $T_c$\ndecreases continuously as the potential barrier height increases, becoming\ninversely proportional to the square root of the barrier height when it is\nlarge enough. This behavior is {\\it universal} as it is independent of the\nwidth and spacing of the barriers. The specific heat at constant volume shows a\ncrossover from 3D to 2D when the height of the potential or the barrier width\nincrease, in addition to the well known peak related to the Bose-Einstein\ncondensation. These features are due to the trapping of the bosons by the\npotential barriers, and can be characterized by the energy difference between\nthe energy bands below the potential height."
    },
    {
        "anchor": "Chaotic Synchronization between Atomic Clocks: We predict synchronization of the chaotic dynamics of two atomic ensembles\ncoupled to a heavily damped optical cavity mode. The atoms are dissipated\ncollectively through this mode and pumped incoherently to achieve a macroscopic\npopulation of the cavity photons. Even though the dynamics of each ensemble are\nchaotic, their motions repeat one another. In our system, chaos first emerges\nvia quasiperiodicity and then synchronizes. We identify the signatures of\nsynchronized chaos, chaos, and quasiperiodicity in the experimentally\nobservable power spectra of the light emitted by the cavity.",
        "positive": "The Compressibility in Strongly Correlated Superconductors and\n  Superfluids: From BCS to BEC: We present a theoretical study of the compressibility, $\\kappa$, in a Fermi\ngas with attractive contact interactions, providing predictions for the\nstrongly-attractive regime and the superfluid phase. Our work emphasizes the\ncompressibility sum rule and gauge invariance as constraints on $\\kappa$ and we\nshow how within a particular $t$-matrix approach, these can be satisfied in the\nnormal phase when no approximations are made. For tractability, approximations\nmust be introduced, and it is believed that thermodynamical approaches to\n$\\kappa$ are more reliable, than correlation function based schemes.\nContrasting with other studies in the literature, we present thermodynamic\ncalculations of $\\kappa$; these yield semi-quantitative agreement with\nexperiment and provide physical insight into similar results obtained via\nquantum Monte Carlo simulations."
    },
    {
        "anchor": "Dark-bright Solitons and their Lattices in Atomic Bose-Einstein\n  Condensates: In the present contribution, we explore a host of different stationary\nstates, namely dark-bright solitons and their lattices, that arise in the\ncontext of multi-component atomic Bose-Einstein condensates. The latter, are\nmodeled by systems of coupled Gross-Pitaevskii equations with general\ninteraction (nonlinearity) coefficients $g_{ij}$. It is found that in some\nparticular parameter ranges such solutions can be obtained in analytical form,\nhowever, numerically they are computed as existing in a far wider parametric\nrange. Many features of the solutions under study, such as their analytical\nform without the trap or the stability/dynamical properties of one dark-bright\nsoliton even in the presence of the trap are obtained analytically and\ncorroborated numerically. Additional features, such as the stability of soliton\nlattice homogeneous states or their existence/stability in the presence of the\ntrap, are examined numerically.",
        "positive": "Critical temperature in the BCS-BEC crossover with spin-orbit coupling: We review the study of the superfluid phase transition in a system of\nfermions whose interaction can be tuned continuously along the crossover from\nBardeen-Cooper-Schrieffer (BCS) superconducting phase to a Bose-Einstein\ncondensate (BEC), also in the presence of a spin-orbit coupling. Below a\ncritical temperature the system is characterized by an order parameter.\nGenerally a mean field approximation cannot reproduce the correct behavior of\nthe critical temperature $T_c$ over the whole crossover. We analyze the crucial\nrole of quantum fluctuations beyond the mean-field approach useful to find\n$T_c$ along the crossover in the presence of a spin-orbit coupling, within a\npath integral approach. A formal and detailed derivation for the set of\nequations useful to derive $T_c$ is performed in the presence of Rashba,\nDresselhaus and Zeeman couplings. In particular in the case of only Rashba\ncoupling, for which the spin-orbit effects are more relevant, the two-body\nbound state exists for any value of the interaction, namely in the full\ncrossover. As a result the effective masses of the emerging bosonic excitations\nare finite also in the BCS regime."
    },
    {
        "anchor": "Observation of Four-body Ring-exchange Interactions and Anyonic\n  Fractional Statistics: Ring exchange is an elementary interaction for modeling unconventional\ntopological matters which hold promise for efficient quantum information\nprocessing. We report the observation of four-body ring-exchange interactions\nand the topological properties of anyonic excitations within an ultracold atom\nsystem. A minimum toric code Hamiltonian in which the ring exchange is the\ndominant term, was implemented by engineering a Hubbard Hamiltonian that\ndescribes atomic spins in disconnected plaquette arrays formed by two\northogonal superlattices. The ring-exchange interactions were resolved from the\ndynamical evolutions in the spin orders, matching well with the predicted\nenergy gaps between two anyonic excitations of the spin system. A braiding\noperation was applied to the spins in the plaquettes and an induced phase\n$1.00(3)\\pi$ in the four-spin state was observed, confirming\n$\\frac{1}{2}$-anynoic statistics. This work represents an essential step\ntowards studying topological matters with many-body systems and the\napplications in quantum computation and simulation.",
        "positive": "Evidence of a Four-Body Force in an Interaction-Tunable Trapped\n  Cold-Atom System: A two-body interaction or force between quantum particles is ubiquitous in\nnature, and the microscopic description in terms of the bare two-body\ninteraction is the basis for quantitatively describing interacting few- and\nmany-body systems. Alternatively, the effective description in terms of an\neffective two-body interaction successfully captures the essence of the\nsystems. However, for several important observations, the explanation in terms\nof an effective two-body interaction is not satisfactory, and the effective\nthree-body interaction has played an essential role in understanding the\nsystems. In this study, we investigate a few-body system comprising of\nultracold bosons tightly confined in a deep optical lattice site, which is\neffectively described as zero-dimensional bosons. By combining an\noccupancy-resolving high-resolution laser spectroscopy with an inter-orbital\nFeshbach resonance controlling the bare two-body interaction over a wide range,\nwe obtain a clear evidence of an effective four-body force, which has never\nbeen observed in any few-body quantum system so far. This will open the door\nfor the study of multi-body forces in various few-body systems."
    },
    {
        "anchor": "Turbulent superfluid as continuous vortex mixture: A statistical model is advanced for describing quantum turbulence in a\nsuperfluid system with Bose-Einstein condensate. Such a turbulent superfluid\ncan be realized for trapped Bose atoms subject to either an alternating\ntrapping potential or to an alternating magnetic field modulating the atomic\nscattering length by means of Feshbach resonance. The turbulent system is\nrepresented as a continuous mixture of states each of which is characterized by\nits own vorticity corresponding to a particular vortex.",
        "positive": "Anomalous quantum-reflection of Bose-Einstein condensates as a\n  self-screening effect: We discuss the effect of anomalous quantum-reflection of Bose-Einstein\ncondensates as a screening effect, that is created by the condensate itself. We\nderive an effective, time-independent single-mode approach, that allows us to\ndefine different paths of reflection. We compare our theory with experimental\nresults."
    },
    {
        "anchor": "Critical velocity for superfluidity in the one-dimensional mean-field\n  regime: From matter to light quantum fluids: We determine in a nonperturbative way the critical velocity for superfluidity\nof a generic quantum fluid flowing past a localized obstacle in the\none-dimensional mean-field regime. We get exact expressions in the narrow- and\nwide-obstacle limits and interpolate them numerically using an original\nrelaxation algorithm for the stationary problem. The existence of a\nJosephson-type critical current across a very high and slowly varying obstacle\nis discussed. Particle losses, if present, are treated within an adiabatic\napproach of the dynamics giving results in excellent agreement with full\nnumerics. Relevant for experiments with quantum fluids of matter, of mixed\nmatter-light, and of light, our study paves the way for further nonperturbative\ninvestigations in higher dimensions and beyond mean-field theory.",
        "positive": "Quantum Monte Carlo study of the indirect Pauli exclusion effect in\n  Bose-Fermi mixtures: We study the momentum distributions of a three-dimensional resonant\nBose-Fermi mixture in the molecular limit at zero temperature. For\nconcentration of the bosons with respect to the fermions less or equal to one,\neach boson is bound to a fermion and the system is composed of fermionic\nmolecules plus excess fermions. Not only the bosonic condensate fraction goes\nto zero, signaling a quantum phase transition towards a normal phase, but a\nfinite region of low momenta is depleted, depending on the concentration. This\nphenomenon is named indirect Pauli exclusion effect and is demonstrated via\nFixed-Node Diffusion Monte Carlo simulations and T-matrix calculations."
    },
    {
        "anchor": "Spin relaxation and band excitation of a dipolar BEC in 2D optical\n  lattices: We observe interband transitions mediated by the dipole-dipole interaction\nfor an array of 1D quantum gases of chromium atoms, trapped in a 2D optical\nlattice. Interband transitions occur when dipolar relaxation releases an energy\nwhich matches or overcomes the lattice band gap. We analyze the role of\ntunneling in higher lattice bands on this process. We compare the experimental\ndipolar relaxation rate with a calculation based on a multiple Fermi Golden\nRule approach, when the lattice sites are symmetric, and the magnetic field is\nparallel to the lattice axis. We also show that an almost complete suppression\nof dipolar relaxation is obtained below a magnetic field threshold set by the\ndepth of the lattice: 1D quantum gases in an excited Zeeman state then become\nmetastable.",
        "positive": "Thermodynamic stability, compressibility matrix, and effects of mediated\n  interactions in a strongly-interacting Bose-Fermi mixture: We theoretically investigate the thermodynamic stability of a normal-state\nBose-Fermi mixture, with a tunable Bose-Fermi pairing interaction $-U_{\\rm\nBF}<0$ associated with a hetero-nuclear Feshbach resonance, as well as a weak\nrepulsive Bose-Bose interaction $U_{\\rm BB}\\ge 0$. Including strong\nhetero-pairing fluctuations associated with the former interaction within the\nself-consistent $T$-matrix approximation, as well as the latter within the\nmean-field level, we calculate the compressibility matrix, to assess the\nstability of this system against density fluctuations. In the weak- and the\nintermediate-coupling regime with respect $-U_{\\rm BF}$, we show that an\neffective attractive interaction between bosons mediated by density\nfluctuations in the Fermi component makes the system unstable below a certain\ntemperature $T_{\\rm clp}$ (leading to density collapse). When $U_{\\rm BB}=0$,\n$T_{\\rm clp}$ is always higher than the Bose-Einstein condensation (BEC)\ntemperature $T_{\\rm c}$. When $U_{\\rm BB}>0$, the density collapse is\nsuppressed, and the BEC transition becomes possible. It is also suppressed by\nthe formation of tightly bound Bose-Fermi molecules when the hetero-pairing\ninteraction $-U_{\\rm BF}$ is strong; however, since the system may be viewed as\na molecular Fermi gas in this case, the BEC transition does not also occur.\nSince quantum gases involving Bose atoms are known to be sensitive to\ninter-particle correlations, our results would be useful for the study of\nmany-body properties of a Bose-Fermi mixture in a stable manner, without facing\nthe unwanted density collapse."
    },
    {
        "anchor": "Resonantly Interacting Fermions In a Box: We use two fundamental theoretical frameworks to study the finite-size\n(shell) properties of the unitary gas in a periodic box: 1) an ab initio\nQuantum Monte Carlo (QMC) calculation for boxes containing 4 to 130 particles\nprovides a precise and complete characterization of the finite-size behavior,\nand 2) a new Density Functional Theory (DFT) fully encapsulates these effects.\nThe DFT predicts vanishing shell structure for systems comprising more than 50\nparticles, and allows us to extrapolate the QMC results to the thermodynamic\nlimit, providing the tightest bound to date on the ground-state energy of the\nunitary gas: \\xi_S <= 0.383(1). We also apply the new functional to\nfew-particle harmonically trapped systems, comparing with previous\ncalculations.",
        "positive": "Emergence of continuous rotational symmetries in ultracold atoms coupled\n  to optical cavities: We investigate the physics of a gas of ultracold atoms coupled to three\nsingle-mode optical cavities and transversely pumped with a laser. Recent work\nhas demonstrated that, for two cavities, the $\\mathbb{Z}_{2}$ symmetries of\neach cavity can be combined into a global $U(1)$ symmetry. Here, we show that\nwhen adding an extra cavity mode, the low-energy description of this system can\nadditionally exhibit an $SO(3)$ rotational symmetry which can be spontaneously\nbroken. This leads to a superradiant phase transition in all the cavities\nsimultaneously, and the appearance of Goldstone and amplitude modes in the\nexcitation spectrum. We determine the phase diagram of the system, which shows\nthe emergence and breaking of the continuous symmetries and displays first- and\nsecond-order phase transitions. We also obtain the excitation spectrum for each\nphase and discuss the atomic self-organized structures that emerge in the\ndifferent superradiant phases. We argue that coupling the atoms equally to $n$\ndifferent modes will in general generate a global $SO(n)$ symmetry if the mode\nfrequencies can be tuned to the same value."
    },
    {
        "anchor": "Magnetism and pairing of two-dimensional trapped fermions: The emergence of local phases in a trapped two-component Fermi gas in an\noptical lattice is studied using quantum Monte Carlo simulations. We treat\ntemperatures that are comparable or lower than those presently achievable in\nexperiments and large enough systems that both magnetic and paired phases can\nbe detected by inspection of the behavior of suitable short-range correlations.\nWe use the latter to suggest the interaction strength and temperature range at\nwhich experimental observation of incipient magnetism and d-wave pairing are\nmore likely and evaluate the relation between entropy and temperature in\ntwo-dimensional confined fermionic systems.",
        "positive": "Robust Weyl points in a 1D superlattice with transverse spin-orbit\n  coupling: Weyl points, synthetic magnetic monopoles in the 3D momentum space, are the\nkey features of topological Weyl semimetals. The observation of Weyl points in\nultracold atomic gases usually relies on the realization of high-dimensional\nspin-orbit coupling (SOC) for two pseudospin states (% \\textit{i.e.,}\nspin-1/2), which requires complex laser configurations and precise control of\nlaser parameters, thus has not been realized in experiment. Here we propose\nthat robust Wely points can be realized using 1D triple-well superlattices\n(spin-1/three-band systems) with 2D transverse SOC achieved by Raman-assisted\ntunnelings. The presence of the third band is responsible to the robustness of\nthe Weyl points against system parameters (e.g., Raman laser polarization,\nphase, incident angle, etc.). Different from a spin-1/2 system, the non-trivial\ntopology of Weyl points in such spin-1 system is characterized by both the spin\nvector and tensor textures, which can be probed using momentum-resolved Rabi\nspectroscopy. Our proposal provides a simple yet powerful platform for\nexploring Weyl physics and related high-dimensional topological phenomena using\nhigh pseudospin ultracold atoms."
    },
    {
        "anchor": "Impurity probe of topological superfluid in one-dimensional spin-orbit\n  coupled atomic Fermi gases: We investigate theoretically non-magnetic impurity scattering in a\none-dimensional atomic topological superfluid in harmonic traps, by solving\nself-consistently the microscopic Bogoliubov-de Gennes equation. In sharp\ncontrast to topologically trivial Bardeen-Cooper-Schrieffer \\textit{s}-wave\nsuperfluid, topological superfluid can host a mid-gap state that is bound to\nlocalized non-magnetic impurity. For strong impurity scattering, the bound\nstate becomes universal, with nearly zero energy and a wave-function that\nclosely follows the symmetry of that of Majorana fermions. We propose that the\nobservation of such a universal bound state could be a useful evidence for\ncharacterizing the topolgoical nature of topological superfluids. Our\nprediction is applicable to an ultracold resonantly-interacting Fermi gas of\n$^{40}$K atoms with spin-orbit coupling confined in a two-dimensional optical\nlattice.",
        "positive": "Preserving coherent spin and squeezed spin states of a spin-1\n  Bose-Einstein condensate with rotary echoes: A challenge in precision measurement with squeezed spin state arises from the\nspin dephasing due to stray magnetic fields. To suppress such environmental\nnoises, we employ a continuous driving protocol, rotary echo, to enhance the\nspin coherence of a spin-1 Bose-Einstein condensate in stray magnetic fields.\nOur analytical and numerical results show that the coherent and the squeezed\nspin states are preserved for a significantly long time, compared to the free\ninduction decay time, if the condition $h\\tau = m\\pi$ is met with $h$ the pulse\namplitude and $\\tau$ pulse width. In particular, both the spin average and the\nspin squeezing, including the direction and the amplitude, are simultaneously\nfixed for a squeezed spin state. Our results point out a practical way to\nimplement quantum measurements based on a spin-1 condensate beyond the standard\nquantum limit."
    },
    {
        "anchor": "Coherence oscillations between weakly coupled Bose-Hubbard dimers: We study theoretically the dynamics of two weakly-coupled Bose-Josephson\njunctions, prepared with the same particle number $N$ and Josephson excitation\nnumber $\\nu$ but with different reduced one-particle purity $\\gamma$. A novel\nentropy oscillation mode is predicted, in which one-particle coherence is\ntransferred between the Bose-Hubbard dimers with no particle or energy\ntransfer. We explain this purity oscillation using a semiclassical picture.",
        "positive": "Theory of vibronic assistance in the nonequilibrium condensation of\n  exciton polaritons in optically--pumped organic single crystal microcavities: We present a reaction/diffusion model for the formation of a lower polariton\ncondensate in a micro cavity containing an organic semiconducting molecular\ncrystalline film. Our model--based upon an anthracene film sandwiched between\ntwo reflecting dielectric mirrors--consists of three coupled fields\ncorresponding to a gas of excitons created by an external driving pulse, a\nreservoir of vibron states formed by the coupling between a ground-state\nvibrational model and a cavity photon, and a lower polariton condensate. We\nshow that at finite temperature, the presence of the vibron reservoir can\naugment the exciton population such that a lower critical pumping threshold is\nrequired to achieve condensation."
    },
    {
        "anchor": "Ultra-cold fermions in real or fictitious magnetic fields: The BCS-BEC\n  evolution and the type-I--type-II transition: We study ultra-cold neutral fermion superfluids in the presence of fictitious\nmagnetic fields, as well as charged fermion superfluids in the presence of real\nmagnetic fields. Charged fermion superfluids undergo a phase transition from\ntype-I to type-II superfluidity, where the magnetic properties of the\nsuperfluid change from being a perfect diamagnet without vortices to a partial\ndiamagnet with the emergence of the Abrikosov vortex lattice. The transition\nfrom type-I to type-II superfluidity is tunned by changing the scattering\nparameter (interaction) for fixed density. We also find that neutral fermion\nsuperfluids such as $^6$Li and $^{40}$K are extreme type-II superfluids, and\nthat they are more robust to the penetration of a fictitious magnetic field in\nthe BCS-BEC crossover region near unitarity, where the critical fictitious\nmagnetic field reaches a maximum as a function of the scattering parameter\n(interaction).",
        "positive": "Transverse collisional instabilities of a Bose-Einstein condensate in a\n  driven one-dimensional lattice: Motivated by recent experiments, we analyse the stability of a\nthree-dimensional Bose-Einstein condensate (BEC) loaded in a periodically\ndriven one-dimensional optical lattice. Such periodically driven systems do not\nhave a thermodynamic ground state, but may have a long-lived steady state which\nis an eigenstate of a \"Floquet Hamiltonian\". We explore collisional\ninstabilities of the Floquet ground state which transfer energy into the\ntransverse modes. We calculate decay rates, finding that the lifetime scales as\nthe inverse square of the scattering length and inverse of the peak three-\ndimensional density. These rates can be controlled by adding additional\ntransverse potentials."
    },
    {
        "anchor": "Flavour-selective localization in interacting lattice fermions via SU(N)\n  symmetry breaking: A large repulsion between particles in a quantum system can lead to their\nlocalization, as it happens for the electrons in Mott insulating materials.\nThis paradigm has recently branched out into a new quantum state, the\norbital-selective Mott insulator, where electrons in some orbitals are\npredicted to localize, while others remain itinerant. We provide a direct\nexperimental realization of this phenomenon, that we extend to a more general\nflavour-selective localization. By using an atom-based quantum simulator, we\nengineer SU(3) Fermi-Hubbard models breaking their symmetry via a tunable\ncoupling between flavours, observing an enhancement of localization and the\nemergence of flavour-dependent correlations. Our realization of\nflavour-selective Mott physics opens the path to the quantum simulation of\nmulticomponent materials, from superconductors to topological insulators.",
        "positive": "Charged polarons and molecules in a Bose-Einstein Condensate: We investigate the properties a mobile ion immersed in a Bose-Einstein\ncondensate (BEC) using different theoretical approaches. A coherent state\nvariational ansatz predicts that the ion spectral function exhibits several\nbranches in addition to polaronic quasiparticle states, and we employ a\ndiagrammatic analysis of the ion-atom scattering in the BEC to identify them as\narising from the binding of an increasing number of bosons to the ion. We\ndevelop a simplified model describing the formation of these molecular ions\nshowing that their spectral weight scales with the number of bound atoms. The\nnumber of atoms in the dressing cloud around the ion are calculated from\nthermodynamic arguments, and we finally show that the dynamics ensuing the\ninjection of an ion into the BEC exhibits various regimes governed by coherent\nquasiparticle propagation and decay."
    },
    {
        "anchor": "Dissipative Dynamics of Quantum Vortices in Fermionic Superfluid: In a recent article, Kwon et al. [Nature (London) {\\bf 600}, 64 (2021)]\nrevealed nonuniversal dissipative dynamics of quantum vortices in a fermionic\nsuperfluid. The enhancement of the dissipative process is pronounced for the\nBardeen-Cooper-Schrieffer interaction regime, and it was suggested that the\neffect is due to the presence of quasiparticles localized inside the vortex\ncore. We test this hypothesis through numerical simulations with time-dependent\ndensity-functional theory: a fully microscopic framework with fermionic degrees\nof freedom. The results of fully microscopic calculations expose the impact of\nthe vortex-bound states on dissipative dynamics in a fermionic superfluid.\nTheir contribution is too weak to explain the experimental measurements, and we\nidentify that thermal effects, giving rise to mutual friction between\nsuperfluid and the normal component, dominate the observed dynamics.",
        "positive": "Ultra-cold fermions in the flatland: evolution from BCS to Bose\n  superfluidity in two-dimensions with spin-orbit and Zeeman fields: We discuss the evolution from BCS to Bose superfluidity for ultracold\nfermions in two-dimensions and in the presence of simultaneous spin-orbit and\nZeeman fields. We analyze several thermodynamic properties to characterize\ndifferent superfluid phases including pressure, compressibility, induced\npolarization, and spin susceptibility. Furthermore, we compute the momentum\ndistribution and construct topological invariants for each of the superfluid\nphases."
    },
    {
        "anchor": "Collision of one dimensional (1D) spin polarized Fermi gases in an\n  optical lattice: In this work we analyze the dynamical behavior of the collision between two\nclouds of fermionic atoms with opposite spin polarization. By means of the\ntime-evolving block decimation (TEBD) numerical method, we simulate the\ncollision of two one-dimensional clouds in a lattice. There is a symmetry in\nthe collision behaviour between the attractive and repulsive interactions. We\nanalyze the pair formation dynamics in the collision region, providing a\nquantitative analysis of the pair formation mechanism in terms of a simple\ntwo-site model.",
        "positive": "Density and spin modes in imbalanced normal Fermi gases from\n  collisionless to hydrodynamic regime: We study mass and population imbalance effect on density (in-phase) and spin\n(out-of-phase) collective modes in a two-component normal Fermi gas. By\ncalculating eigenmodes of the linearized Boltzmann equation as well as the\ndensity/spin dynamic structure factor, we show that mass and population\nimbalance effects offer a variety of collective mode crossover behaviors from\ncollisionless to hydrodynamic regimes. The mass imbalance effect shifts the\ncrossover regime to the higher-temperature, and a significant peak of the spin\ndynamic structure factor emerges only in the collisionless regime. This is in\ncontrast to the case of mass and population balanced normal Fermi gases, where\nthe spin dynamic response is always absent. Although the population imbalance\neffect does not shift the crossover regime, the spin dynamic structure factor\nsurvives both in the collisionless and hydrodynamic regimes."
    },
    {
        "anchor": "Metallic state in bosonic systems with continuously degenerate minima: In systems above one dimension a continuously degenerate minimum of the\nsingle particle dispersion is realized due to one or a combination of\nsystem-parameters such as lattice structure, isotropic spin-orbit coupling, and\ninteractions. A unit codimension of the dispersion-minima leads to a divergent\ndensity of states which enhances the effects of interactions, and may lead to\nnovel states of matter as exemplified by Luttinger liquids in one dimensional\nbosonic systems. Here we show that in dilute, homogeneous bosonic systems above\none dimension, weak, spin-independent, inter-particle interactions stabilize a\nmetallic state at zero temperature in the presence of a curved manifold of\ndispersion minima. In this metallic phase the system possesses a quasi\nlong-range order with non-universal scaling exponents. At a fixed positive\ncurvature of the manifold, increasing either the dilution or the interaction\nstrength destabilizes the metallic state towards charge density wave states\nthat break one or more symmetries. The magnitude of the wave vector of the\ndominant charge density wave state is controlled by the product of the mean\ndensity of bosons and the curvature of the manifold. We obtain the zero\ntemperature phase diagram, and identify the phase boundary.",
        "positive": "Impurity coupled to a lattice with disorder: We study the time-dependent occupation of an impurity state hybridized with a\ncontinuum of extended or localized states. Of particular interest is the return\nprobability, which gives the long-time limit of the average impurity\noccupation. In the extended case, the return probability is zero unless there\nare bound states of the impurity and continuum. We present exact expressions\nfor the return probability of an impurity state coupled to a lattice, and show\nthat the existence of bound states depends on the dimension of the lattice. In\na disordered lattice with localized eigenstates, the finite extent of the\neigenstates results in a non-zero return probability. We investigate different\nparameter regimes numerically by exact diagonalization, and show that the\nreturn probability can serve as a measure of the localization length in the\nregime of weak hybridization and disorder. Possible experimental realizations\nwith ultracold atoms are discussed."
    },
    {
        "anchor": "Topological Floquet engineering using two frequencies in two dimensions: Using two-frequency driving in two dimensions opens up new possibilites for\nFloquet engineering, which range from controlling specific symmetries to tuning\nthe properties of resonant gaps. In this work, we study two-band lattice models\nsubject to two-tone Floquet driving and analyse the resulting effective Floquet\nbandstructures both numerically and analytically. On the one hand, we extend\nthe methodology of Sandholzer et al. [10.1103/PhysRevResearch.4.013056] from\none to two dimensions and find competing topological phases in a simple Bravais\nlattice when the two resonant drives at $1\\omega$ and $2\\omega$ interfere. On\nthe other hand, we explore driving-induced symmetry breaking in the hexagonal\nlattice, in which the breaking of either inversion or time-reversal symmetry\ncan be tuned independently via the Floquet modulation. Possible applications of\nour work include a simpler generation of topological bands for ultracold atoms,\nand the realisation of non-linear Hall effects as well as Haldane's parity\nanomaly in inversion-symmetric parent lattices.",
        "positive": "Emergent topological ordered phase for the Ising-XY Model revealed by\n  cluster-updating Monte-Carlo method: The two-component cold atom systems with anisotropic hopping amplitudes can\nbe phenomenologically described by a two-dimensional Ising-XY coupled model\nwith spatial anisotropy. At low temperatures, theoretical predictions [Phys.\nRev. A 72, 053604 (2005)] and [arXiv:0706.1609] indicate the existence of a\ntopological ordered phase characterized by Ising and XY disorder but with 2XY\nordering. However, due to ergodic difficulties faced by Monte Carlo methods at\nlow temperatures, this topological phase has not been numerically explored. We\npropose a linear cluster updating Monte Carlo method, which flips spins without\nrejection in the anisotropy limit but does not change the energy. Using this\nscheme and conventional Monte Carlo methods, we succeed in revealing the nature\nof topological phases with half-vortices and domain walls. In the constructed\nglobal phase diagram, Ising and XY type transitions are very close to each\nother and differ significantly from the schematic phase diagram reported\nearlier. We also propose and explore a wide range of quantities, including\nmagnetism, superfluidity, specific heat, susceptibility, and even percolation\nsusceptibility, and obtain consistent results. Furthermore, we observe\nfirst-order transitions characterized by common intersection points in\nmagnetizations for different system sizes, as opposed to the conventional phase\ntransition where Binder cumulants of various sizes share common intersections.\nThe results are useful to help cold atom experiments explore the half-vortex\ntopological phase."
    },
    {
        "anchor": "Superfluid Fermi atomic gas as a quantum simulator for the study of\n  neutron-star equation of state: We theoretically propose an idea to use an ultracold Fermi gas as a quantum\nsimulator for the study of the neutron-star equation of state (EoS) in the\nlow-density region. Our idea is different from the standard quantum simulator\nthat heads for {\\it perfect} replication of another system, such as a Hubbard\nmodel discussed in high-$T_{\\rm c}$ cuprates. Instead, we use the {\\it\nsimilarity} between two systems, and theoretically make up for the difference\nbetween them. That is, (1) we first show that the strong-coupling theory\ndeveloped by Nozi\\`eres-Schmitt Rink (NSR) can quantitatively explain the\nrecent EoS experiment on a $^6$Li superfluid Fermi gas in the BCS\n(Bardeen-Cooper-Schrieffer)-unitary limit far below the superfluid phase\ntransition temperature $T_{\\rm c}$. This region is considered to be very\nsimilar to the low density region (crust regime) of a neutron star (where a\nnearly unitary $s$-wave neutron superfluid is expected). (2) We then\ntheoretically compensate the difference that, while the effective range $r_{\\rm\neff}$ is negligibly small in a superfluid $^6$Li Fermi gas, it cannot be\nignored ($r_{\\rm eff}=2.7$ fm) in a neutron star, by extending the NSR theory\nto include effects of $r_{\\rm eff}$. The calculated EoS when $r_{\\rm eff}=2.7$\nfm is shown to agree well with the previous neutron-star EoS in the low density\nregion predicted in nuclear physics. Our idea indicates that an ultracold\natomic gas may more flexibly be used as a quantum simulator for the study of\nother complicated quantum many-body systems, when we use, not only the\nexperimental high tunability, but also the recent theoretical development in\nthis field. Since it is difficult to directly observe a neutron-star interior,\nour idea would provide a useful approach to the exploration for this mysterious\nastronomical object.",
        "positive": "Long-lived periodic revivals of coherence in an interacting\n  Bose-Einstein condensate: We observe the coherence of an interacting two-component Bose-Einstein\ncondensate (BEC) surviving for seconds in a trapped Ramsey interferometer.\nMean-field driven collective oscillations of two components lead to periodic\ndephasing and rephasing of condensate wave functions with a slow decay of the\ninterference fringe visibility. We apply spin echo synchronous with the\nself-rephasing of the condensate to reduce the influence of state-dependent\natom losses, significantly enhancing the visibility up to 0.75 at the evolution\ntime of 1.5s. Mean-field theory consistently predicts higher visibility than\nexperimentally observed values. We quantify the effects of classical and\nquantum noise and infer a coherence time of 2.8 s for a trapped condensate of\n5.5e4 interacting atoms."
    },
    {
        "anchor": "Feshbach resonances in an ultracold $^{7}$Li-$^{133}$Cs Bose-Bose\n  mixture: We present a study of interspecies Feshbach resonances in ultracold\n$^{7}$Li-$^{133}$Cs Bose-Bose mixtures. We locate ten interspecies resonances\nin three different spin-state combinations. By comparing to coupled-channel\ncalculations, we assign six of the resonances to $s$-wave channels and the rest\nto $p$-wave channels. We use the $s$-wave resonances to refine the ground-state\npotentials of LiCs in the coupled-channel calculations and then obtain an\naccurate characterization of the scattering and bound-state properties of the\nmixtures. Our results will be useful for future experiments with ultracold\n$^{7}$Li-$^{133}$Cs mixtures.",
        "positive": "Exotic superfluidity in cold atoms: We derived the low energy effective action for the collective modes in\nasymmetric fermionic systems with attractive interaction. We obtained the phase\ndiagram in terms of the chemical potentials. It features a stable gapless\nsuperfluidity with one Fermi surface on the BEC side of the resonance. Also we\npredict a sharp increase in outer core of a vortex, i.e. vortex size, upon\nentering into the gapless phase. This may serve as a signature of a gapless\nphase."
    },
    {
        "anchor": "Dynamic spin response of a strongly interacting Fermi gas: We present an experimental investigation of the dynamic spin response of a\nstrongly interacting Fermi gas using Bragg spectroscopy. By varying the\ndetuning of the Bragg lasers, we show that it is possible to measure the\nresponse in the spin and density channels separately. At low Bragg energies,\nthe spin response is suppressed due to pairing, whereas the density response is\nenhanced. These experiments provide the first independent measurements of the\nspin-parallel and spin-antiparallel dynamic and static structure factors and\nopen the way to a complete study of the structure factors at any momentum. At\nhigh momentum the spin-antiparallel dynamic structure factor displays a\nuniversal high frequency tail, proportional to $\\omega^{-5/2}$, where $\\hbar\n\\omega$ is the probe energy.",
        "positive": "Few-body bound states in dipolar gases and their detection: We consider dipolar interactions between heteronuclear molecules in a\nlow-dimensional setup consisting of two one-dimensional tubes. We demonstrate\nthat attraction between molecules in different tubes can overcome intratube\nrepulsion and complexes with several molecules in the same tube are stable. In\nsitu detection schemes of the few-body complexes are proposed. We discuss\nextensions to the case of many tubes and layers, and outline the implications\nof our results on many-body physics."
    },
    {
        "anchor": "Spatial correlations of one dimensional driven-dissipative systems of\n  Rydberg atoms: We consider a one-dimensional lattice of atoms with laser excitation to a\nRydberg state and spontaneous emission. The atoms are coupled due to the\ndipole-dipole interaction of the Rydberg states. This driven-dissipative system\nhas a broad range of non-equilibrium phases, such as antiferromagnetic ordering\nand bistability. Using the quantum trajectory method, we calculate the spatial\ncorrelation function throughout the parameter space for up to 20 lattice sites.\nWe show that bistability significantly strengthens the spatial correlations and\nentanglement.",
        "positive": "Topological charge pumping with subwavelength Raman lattices: Recent experiments demonstrated deeply subwavelength lattices using atoms\nwith $N$ internal states Raman-coupled with lasers of wavelength $\\lambda$. The\nresulting unit cell was $\\lambda/2N$ in extent, an $N$-fold reduction compared\nto the usual $\\lambda/2$ periodicity of an optical lattice. For resonant Raman\ncoupling, this lattice consists of $N$ independent sinusoidal potentials (with\nperiod $\\lambda/2$) displaced by $\\lambda/2N$ from each other. We show that\ndetuning from Raman resonance induces tunneling between these potentials.\nPeriodically modulating the detuning couples the $s$- and $p$-bands of the\npotentials, creating a pair of coupled subwavelength Rice--Mele chains. This\noperates as a novel topological charge pump that counter-intuitively can give\nhalf the displacement per pump cycle of each individual Rice--Mele chain\nseparately. We analytically describe this behavior in terms of infinite-system\nChern numbers, and numerically identify the associated finite-system edge\nstates."
    },
    {
        "anchor": "Dressing the Orbital Feshbach Resonance using single-manifold Raman\n  scheme: The recently discovered Orbital Feshbach Resonance (OFR) offers the\npossibility of tuning the interaction between alkaline earth(-like) metal atoms\nwith magnetic field. Here, we introduce a single-manifold Raman scheme to dress\nthe OFR, which allows us to tune the interaction with the optical field and it\nis readily realizable in experiment. We demonstrate the scattering resonance\ncould be shifted by the dressing Raman laser using few-body and many-body\nmean-field calculation, which give rise to an optical dependent two-body bound\nstate and Raman coupling induced BCS-BEC crossover in the BCS-type mean field\ntheory. Besides, we also discuss the application of single-manifold Raman\nscheme in Kondo research by writing down a Kondo lattice model.",
        "positive": "Solvable Model of a Generic Trapped Mixture of Interacting Bosons:\n  Many-Body and Mean-Field Properties at the Infinite-Particle Limit: A solvable model of a generic trapped bosonic mixture, $N_1$ bosons of mass\n$m_1$ and $N_2$ bosons of mass $m_2$ trapped in an harmonic potential of\nfrequency $\\omega$ and interacting by harmonic inter-particle interactions of\nstrengths $\\lambda_1$, $\\lambda_2$, and $\\lambda_{12}$, is discussed. It has\nrecently been shown for the ground state [J. Phys. A {\\bf 50}, 295002 (2017)]\nthat in the infinite-particle limit, when the interaction parameters\n$\\lambda_1(N_1-1)$, $\\lambda_2(N_2-1)$, $\\lambda_{12}N_1$, $\\lambda_{12}N_2$\nare held fixed, each of the species is $100\\%$ condensed and its density per\nparticle as well as the total energy per particle are given by the solution of\nthe coupled Gross-Pitaevskii equations of the mixture. In the present work we\ninvestigate properties of the trapped generic mixture at the infinite-particle\nlimit, and find differences between the many-body and mean-field descriptions\nof the mixture, despite each species being $100\\%$. We compute analytically and\nanalyze, both for the mixture and for each species, the center-of-mass position\nand momentum variances, their uncertainty product, the angular-momentum\nvariance, as well as the overlap of the exact and Gross-Pitaevskii\nwavefunctions of the mixture. The results obtained in this work can be\nconsidered as a step forward in characterizing how important are many-body\neffects in a fully condensed trapped bosonic mixture at the infinite-particle\nlimit."
    },
    {
        "anchor": "Slow Thermalization of Exact Quantum Many-Body Scar States Under\n  Perturbations: Quantum many-body scar states are exceptional finite energy density\neigenstates in an otherwise thermalizing system that do not satisfy the\neigenstate thermalization hypothesis. We investigate the fate of exact\nmany-body scar states under perturbations. At small system sizes, deformed scar\nstates described by perturbation theory survive. However, we argue for their\neventual thermalization in the thermodynamic limit from the finite-size scaling\nof the off-diagonal matrix elements. Nevertheless, we show numerically and\nanalytically that the nonthermal properties of the scars survive for a\nparametrically long time in quench experiments. We present a rigorous argument\nthat lower-bounds the thermalization time for any scar state as $t^{*} \\sim\nO(\\lambda^{-1/(1+d)})$, where $d$ is the spatial dimension of the system and\n$\\lambda$ is the perturbation strength.",
        "positive": "Ground state phase diagram of spin-1/2 bosons in a two-dimensional\n  optical lattice: We study a two-species bosonic Hubbard model on a two-dimensional square\nlattice by means of quantum Monte Carlo simulations. In addition to the usual\ncontact repulsive interactions between the particles, the Hamiltonian has an\ninterconversion term which allows the transformation of two particles from one\nspecies to the other. The phases are characterized by their solid or superfluid\nproperties and by their polarization, i.e. the difference in the populations.\nWhen inter-species interactions are smaller than the intra-species ones, the\nsystem is unpolarized, whereas in the opposite case the system is unpolarized\nin even Mott insulator lobes and polarized in odd Mott lobes and also in the\nsuperfluid phase. We show that in the latter case the transition between the\nMott insulator of total density two and the superfluid can be either of second\nor first order depending on the relative values of the interactions, whereas\nthe transitions are continuous in all other cases."
    },
    {
        "anchor": "Quantum State Transfer through Coherent Atom-Molecule Conversion in\n  Bose-Einstein Condensate: We demonstrate complete quantum state transfer of an atomic Bose-Einstein\ncondensate to molecular condensate, mediated by solitonic excitations in a\ncigar shaped mean-field geometry. Starting with a localized solitonic atomic\ncondensate, we show compatible gray solitonic configuration in the molecular\ncondensate, which results in complete atom-molecule conversion. The effect of\ninter and intra-species interactions on the formation of molecular condensate\nis explicated in the presence of Raman Photoassociation. It is found that\nphotoassociation plays a crucial role in the coherent atom-molecule conversion\nas well as in the soliton dynamics. The gray soliton dispersion reveals\nbistable behaviour, showing a re-entrant phase in a physically accessible\nparametric domain.",
        "positive": "Quantum limited sound attenuation in a dilute atomic Fermi gas: A new experiment (P. B. Patel et al., Science 370 (2020) 6521, 1222)\ninvolving resonantly interacting atoms confined by laser beams sheds light on\nmomentum and energy diffusion in quantum fluids."
    },
    {
        "anchor": "The impact of the injection protocol on an impurity's stationary state: We examine stationary state properties of an impurity particle injected into\na one-dimensional quantum gas. We show that the value of the impurity's end\nvelocity lies between zero and the speed of sound in the gas, and is determined\nby the injection protocol. This way, the impurity's constant motion is a\ndynamically emergent phenomenon whose description goes beyond accounting for\nthe kinematic constraints of Landau approach to superfluidity. We provide exact\nanalytic results in the thermodynamic limit, and perform finite-size numerical\nsimulations to demonstrate that the predicted phenomena are within the reach of\nthe existing ultracold gases experiments.",
        "positive": "Coherent spin mixing via spin-orbit coupling in Bose gases: We study beyond-mean-field properties of interacting spin-1 Bose gases with\nsynthetic Rashba-Dresselhaus spin-orbit coupling at low energies. We derive a\nmany-body Hamiltonian following a tight-binding approximation in quasi-momentum\nspace, where the effective spin dependence of the collisions that emerges from\nspin-orbit coupling leads to dominant correlated tunneling processes that\ncouple the different bound states. We discuss the properties of the spectrum of\nthe derived Hamiltonian and its experimental signatures. In a certain region of\nthe parameter space, the system becomes integrable, and its dynamics becomes\nanalogous to that of a spin-1 condensate with spin-dependent collisions.\nRemarkably, we find that such dynamics can be observed in existing experimental\nsetups through quench experiments that are robust against magnetic\nfluctuations."
    },
    {
        "anchor": "Polaron formation in the vicinity of a narrow Feshbach resonance in\n  atomic and exciton-polariton condensates: The polaronic system consisting of an impurity in a dilute Bose-Einstein\ncondensate is considered in the presence of a narrow Feshbach resonance. For\nthis purpose a coupled-channel model is used, which at the mean field level\npredicts the formation of quasiparticles that are a superposition of the\nimpurity and the molecular states. The impurity-boson interactions and the\ncoupling between the open and closed channels are then considered weak and a\nperturbative calculation of the corrections to the mean field results is\npresented. This allows to examine the properties of the quasiparticles, such as\nthe lifetime and the effective mass. The model is applied to two physical\nsystems: an impurity atom in a Bose-condensed atomic gas in 3D and a spin down\nlower polariton in a Bose-Einstein condensate of spin up lower polaritons in\n2D. The model parameters are linked to the physical parameters by identifying\nthe low energy T-matrix and applying a proper renormalization scheme.",
        "positive": "Failure of the GGE hypothesis for integrable models with bound states: In this work we study the applicability of the GGE to integrable one\ndimensional systems with bound states. We find that the GGE fails to describe\nthe long time dynamics for most initial states including eigenstates. We\npresent our calculations studying the attractive Lieb-Liniger gas and the XXZ\nmagnet, though similar results may be obtained for other models."
    },
    {
        "anchor": "Superfluidity in the absence of kinetics in spin-orbit-coupled optical\n  lattices: At low temperatures bosons typically condense to minimize their\nsingle-particle kinetic energy while interactions stabilize superfluidity.\nOptical lattices with artificial spin-orbit coupling challenge this paradigm\nbecause here kinetic energy can be quenched in an extreme regime where the\nsingle-particle band flattens. To probe the fate of superfluidity in the\nabsence of kinetics we construct and numerically solve interaction-only\ntight-binding models in flat bands. We find that novel superfluid states arise\nentirely from interactions operating in quenched kinetic energy bands, thus\nrevealing a distinct and unexpected condensation mechanism. Our results have\nimportant implications for the identification of quantum condensed phases of\nultracold bosons beyond conventional paradigms.",
        "positive": "Three-body scattering hypervolumes of particles with short-range\n  interactions: The low-energy scattering of three bosons or distinguishable particles with\nshort-range interactions is characterized by a fundamental parameter, the\nthree-body scattering hypervolume. Its imaginary part is directly related to\nthe three-body recombination rate in a quantum gas consisting of such\nparticles. We derive an analytical formula of it for weak interactions, and\nperform its first numerical calculations for bosons with a variable\nnonzero-range potential. For attractive interactions, we identify several\nthree-body resonances at which the three-body scattering hypervolume becomes\ndivergent or anomalously large."
    },
    {
        "anchor": "Collective strong coupling in a lossy optical cavity: We observe vacuum Rabi splitting in a lossy nearly confocal cavity indicating\nthe strong coupling regime, despite a weak single-atom single-mode coupling.\nStrong collective interaction manifests itself in the typical\n$\\sqrt{N}$-dependence of the normal mode splitting on the number of atoms $N$.\nThe $TEM_{00}$-mode coupling parameters are\n$(g,\\kappa,\\gamma)=2\\pi\\times(0.12,0.8,2.6)$ MHz and up to $(1.33\\pm\n0.08)\\times10^5$ cesium atoms were loaded into the mode volume.",
        "positive": "Harmonically trapped attractive and repulsive spin-orbit and Rabi\n  coupled Bose-Einstein condensates: Numerically we investigate the ground state of effective one-dimensional\nspin-orbit (SO) and Rabi coupled two pseudo-spinor Bose-Einstein condensates\n(BECs) under the effect of harmonic traps. For both signs of the interaction,\ndensity profiles of SO and Rabi coupled BECs in harmonic potentials, which\nsimulate a real experimental situation are obtained. The harmonic trap causes a\nstrong reduction of the multi-peak nature of the condensate and it increases\nits density. For repulsive interactions, the increase of SO coupling results in\nan uncompressed less dense condensate and with increased multi-peak nature of\nthe density. The increase of Rabi coupling leads to a density increase with an\nalmost constant number of multi-peaks. For both signs of the interaction and\nnegative values of Rabi coupling, the condensate develops a notch in the\ncentral point and it seems to a dark-in-bright soliton. In the case of the\nattractive nonlinearity, an interesting result is the increase of the collapse\nthreshold under the action of the SO and Rabi couplings."
    },
    {
        "anchor": "Stationary states of a nonlinear Schr\u00f6dinger lattice with a harmonic\n  trap: We study a discrete nonlinear Schr\\\"odinger lattice with a parabolic trapping\npotential. The model, describing, e.g., an array of repulsive Bose-Einstein\ncondensate droplets confined in the wells of an optical lattice, is\nanalytically and numerically investigated. Starting from the linear limit of\nthe problem, we use global bifurcation theory to rigorously prove that - in the\ndiscrete regime - all linear states lead to nonlinear generalizations thereof,\nwhich assume the form of a chain of discrete dark solitons (as the density\nincreases). The stability of the ensuing nonlinear states is studied and it is\nfound that the ground state is stable, while the excited states feature a chain\nof stability/instability bands. We illustrate the mechanisms under which\ndiscreteness destabilizes the dark-soliton configurations, which become stable\nonly inside the continuum regime. Continuation from the anti-continuum limit is\nalso considered, and a rich bifurcation structure is revealed.",
        "positive": "Mobile Impurities and Orthogonality Catastrophe in two-dimensional\n  Vortex Lattices: We investigate the properties of a neutral impurity atom coupled with the\nTkachenko modes of a two-dimensional vortex lattice Bose-Einstein condensate.\nIn contrast with polarons in homogeneous condensates, the marginal\nimpurity-boson interaction in the vortex lattice leads to infrared\nsingularities in perturbation theory and to the breakdown of the quasiparticle\npicture in the low energy limit. These infrared singularities are interpreted\nin terms of a renormalization of the coupling constant, quasiparticle weight\nand effective impurity mass. The divergence of the effective mass in the low\nenergy limit gives rise to an orthogonality catastrophe which is manifested as\na power law singularity in the impurity spectral function."
    },
    {
        "anchor": "Probing non-Abelian statistics of Majorana fermions in ultracold atomic\n  superfluid: We propose an experiment to directly probe the non-Abelian statistics of\nMajorana fermions by braiding them in an s-wave superfluid of ultracold atoms.\nWe show different orders of braiding operations give orthogonal output states\nthat can be distinguished through Raman spectroscopy. Realization of Majorana\nbound states in an s-wave superfluid requires strong spin-orbital coupling and\na controllable Zeeman field in the perpendicular direction. We present a simple\nlaser configuration to generate the artificial spin-orbital coupling and the\nrequired Zeeman field in the dark state subspace.",
        "positive": "Strongly Interacting Quantum Gases in One-Dimensional Traps: Under the second-order degenerate perturbation theory, we show that the\nphysics of $N$ particles with arbitrary spin confined in a one dimensional trap\nin the strongly interacting regime can be described by super-exchange\ninteraction. An effective spin-chain Hamiltonian (non-translational-invariant\nSutherland model) can be constructed from this procedure. For spin-1/2\nparticles, this model reduces to the non-translational-invariant Heisenberg\nmodel, where a transition between Heisenberg anti-ferromagnetic (AFM) and\nferromagnetic (FM) states is expected to occur when the interaction strength is\ntuned from the strongly repulsive to the strongly attractive limit. We show\nthat the FM and the AFM states can be distinguished in two different methods:\nthe first is based on their distinct response to a spin-dependent magnetic\ngradient, and the second is based on their distinct momentum distribution. We\nconfirm the validity of the spin-chain model by comparison with results\nobtained from several unbiased techniques"
    },
    {
        "anchor": "Scale and conformal invariance in rotating few-fermion systems: We show that rotating two-dimensional Fermi gases possess a nonrelativistic\nscale and conformal invariance at weak interactions, where the scale invariance\nof universal short-range interactions is not broken by quantum effects. We\ndemonstrate the symmetry in the excitation spectrum of few-fermion ensembles in\na harmonic trap obtained by exact diagonalization, which are constrained by the\noperator-state correspondence. The excitation spectrum is shown to split in a\nset of primary states, the energies of which correspond to scaling dimensions\nof conformal operators, and derived excited states that consist of breathing\nmodes as well as two different center-of-mass excitations, which describe\ncyclotron and guiding-center excitations of the total particle cloud.\nFurthermore, the conformal symmetry is manifest in the many-body wave function,\nwhere it dictates the form of the hyperradial component, which we demonstrate\nusing Monte Carlo sampling of few-body wave functions.",
        "positive": "Bound States and Universality in Layers of Cold Polar Molecules: The recent experimental realization of cold polar molecules in the rotational\nand vibrational ground state opens the door to the study of a wealth of\nphenomena involving long-range interactions. By applying an optical lattice to\na gas of cold polar molecules one can create a layered system of planar traps.\nDue to the long-range dipole-dipole interaction one expects a rich structure of\nbound complexes in this geometry. We study the bilayer case and determine the\ntwo-body bound state properties as a function of the interaction strength. The\nresults clearly show that a least one bound state will always be present in the\nsystem. In addition, bound states at zero energy show universal behavior and\nextend to very large radii. These results suggest that non-trivial bound\ncomplexes of more than two particles are likely in the bilayer and in more\ncomplicated chain structures in multi-layer systems."
    },
    {
        "anchor": "Finite temperature contact for SU(2) fermions trapped in a 1D harmonic\n  confinement: We calculate the finite-temperature Tan's contact for N SU(2) fermions,\ncharacterized by repulsive contact interaction, trapped in a 1D harmonic\nconfinement within a local density approximation on top of a thermodynamic\nBethe Ansatz. The Tan's contact for such a system, as in the homogeneous case,\ndisplays a minimum at a very low temperature. By means of an exact canonical\nensemble calculation for two fermions, we provide an explicit formula for the\ncontact at very low temperatures that reveals that the minimum is due to the\nmixing of states with different exchange symmetries. In the unitary regime,\nthis symmetry blending corresponds to a maximal entanglement entropy.",
        "positive": "Density excitations of a harmonically trapped ideal gas: The dynamic structure factor of a harmonically trapped Bose gas has been\ncalculated well above the Bose-Einstein condensation temperature by treating\nthe gas cloud as a canonical ensemble of noninteracting classical particles.\nThe static structure factor is found to vanish as wavenumber squared in the\nlong-wavelength limit. We also incorporate a relaxation mechanism\nphenomenologically by including a stochastic friction force to study the\ndynamic structure factor. A significant temperature dependence of the\ndensity-fluctuation spectra is found. The Debye-Waller factor has been\ncalculated for the trapped thermal cloud as function of wavenumber and of\nparticle number. A substantial difference is found between clouds of small and\nlarge particle number."
    },
    {
        "anchor": "0D-2D Heterostructure for making very Large Quantum Registers using\n  itinerant Bose-Einstein Condensate of Excitons: Presence of coherent resonant tunneling in quantum dot (zero-dimensional) -\nquantum well (two-dimensional) heterostructure is necessary to explain the\ncollective oscillations of average electrical polarization of excitonic dipoles\nover a macroscopically large area. This was measured using photo excited\ncapacitance as a function of applied voltage bias. Resonant tunneling in this\nheterostructure definitely requires momentum space narrowing of charge carriers\ninside the quantum well and that of associated indirect excitons, which\nindicates bias dependent itinerant Bose-Einstein condensation of excitons.\nObservation of periodic variations in negative quantum capacitance points to\nin-plane coulomb correlations mediated by long range spatial ordering of\nindirect, dipolar excitons. Enhanced contrast of quantum interference beats of\nexcitonic polarization waves even under white light and observed Rabi\noscillations over a macroscopically large area also support the presence of\ndensity driven excitonic condensation having long range order. Periodic\npresence (absence) of splitting of excitonic peaks in photocapacitance spectra\neven demonstrate collective coupling (decoupling) between energy levels of the\nquantum well and quantum dots with applied biases, which can potentially be\nused for quantum gate operations. All these observations point to experimental\ncontrol of macroscopically large, quantum state of a two-component\nBose-Einstein condensate of excitons in this quantum dot - quantum well\nheterostructure. Therefore, in principle, millions of two-level excitonic\nqubits can be intertwined to fabricate large quantum registers using such\nhybrid heterostructure by controlling the local electric fields and also by\nvarying photoexcitation intensities of overlapping light spots.",
        "positive": "Supefluidity of flat band Bose-Einstein condensates revisited: We consider the superfluid weight, speed of sound and excitation fraction of\na flat band Bose-Einstein condensate (BEC) within multiband Bogoliubov theory.\nThe superfluid weight is calculated by introducing a phase winding and\nminimizing the free energy with respect to it. We find that the superfluid\nweight has a contribution arising from the change of the condensate density and\nchemical potential upon the phase twist that has been neglected in the previous\nliterature. We also point out that the speed of sound and the excitation\nfraction are proportional to orbital-position-independent generalizations of\nthe quantum metric and the quantum distance, and reduce to the usual quantum\nmetric (Fubini-Study metric) and the Hilbert-Schmidt quantum distance only in\nspecial cases. We derive a second order perturbation correction to the\ndependence of the speed of sound on the generalized quantum metric, and show\nthat it compares well with numerical calculations. Our results provide a\nconsistent connection between flat band BEC and quantum geometry, with physical\nobservables being independent of the orbital positions as they should, and\ncomplete formulas for the evaluation of the superfluid weight within the\nBogoliubov theory. We discuss the limitations of the Bogoliubov theory in\nevaluating the superfluid weight."
    },
    {
        "anchor": "Time-periodic quantum states of weakly interacting bosons in a harmonic\n  trap: We consider identical quantum bosons with weak contact interactions in a\ntwo-dimensional isotropic harmonic trap, and focus on states at the Lowest\nLandau Level (LLL). At linear order in the coupling parameter $g$, we exploit\nthe rich algebraic structure of the problem to give an explicit construction of\na large family of quantum states with energies of the form $E_0+gE_1/4+O(g^2)$,\nwhere $E_0$ and $E_1$ are integers. As a result, any superposition of these\nstates evolves periodically with a period of at most $8\\pi/g$ until, at much\nlonger time scales of order $1/g^2$, corrections to the energies of order $g^2$\nbecome important and may upset this perfectly periodic behavior. We further\nconstruct coherent-like combinations of these states that naturally connect to\nclassical dynamics in an appropriate regime, and explain how our findings\nrelate to the known time-periodic features of the corresponding weakly\nnonlinear classical theory. We briefly comment on possible generalizations of\nour analysis to other numbers of spatial dimensions and other analogous\nphysical systems.",
        "positive": "Tetramer Bound States in Heteronuclear Systems: We calculate the universal spectrum of trimer and tetramer states in\nheteronuclear mixtures of ultracold atoms with different masses in the vicinity\nof the heavy-light dimer threshold. To extract the energies, we solve the\nthree- and four-body problem for simple two- and three-body potentials tuned to\nthe universal region using the Gaussian expansion method. We focus on the case\nof one light particle of mass $m$ and two or three heavy bosons of mass $M$\nwith resonant heavy-light interactions. We find that trimer and tetramer cross\ninto the heavy-light dimer threshold at almost the same point and that as the\nmass ratio $M/m$ decreases, the distance between the thresholds for trimer and\ntetramer states becomes smaller. We also comment on the possibility of\nobserving exotic three-body states consisting of a dimer and two atoms in this\nregion and compare with previous work."
    },
    {
        "anchor": "Dynamical phase transitions in quantum spin models with\n  antiferromagnetic long-range interactions: In recent years, dynamical phase transitions and out-of-equilibrium\ncriticality have been at the forefront of ultracold gases and condensed matter\nresearch. Whereas universality and scaling are established topics in\nequilibrium quantum many-body physics, out-of-equilibrium extensions of such\nconcepts still leave much to be desired. Using exact diagonalization and the\ntime-dependent variational principle in uniform martrix product states, we\ncalculate the time evolution of the local order parameter and Loschmidt return\nrate in transverse-field Ising chains with antiferromagnetic power law-decaying\ninteractions, and map out the corresponding rich dynamical phase diagram.\n\\textit{Anomalous} cusps in the return rate, which are ubiquitous at small\nquenches within the ordered phase in the case of ferromagnetic long-range\ninteractions, are absent within the accessible timescales of our simulations in\nthe antiferromagnetic case, showing that long-range interactions are not a\nsufficient condition for their appearance. We attribute this to much weaker\ndomain-wall binding in the antiferromagnetic case. For quenches across the\nquantum critical point, \\textit{regular} cusps appear in the return rate and\nconnect to the local order parameter changing sign, indicating the concurrence\nof two major concepts of dynamical phase transitions. Our results consolidate\nconclusions of previous works that a necessary condition for the appearance of\nanomalous cusps in the return rate after quenches within the ordered phase is\nfor topologically trivial local spin flips to be the energetically dominant\nexcitations in the spectrum of the quench Hamiltonian. Our findings are readily\naccessible in modern trapped-ion setups, and we outline the associated\nexperimental considerations.",
        "positive": "Composite localized modes in discretized spin-orbit-coupled\n  Bose-Einstein condensates: We introduce a discrete model for binary spin-orbit-coupled (SOC)\nBose-Einstein condensates (BEC) trapped in a deep one-dimensional optical\nlattice. Two different types of the couplings are considered, with spatial\nderivatives acting inside each species, or between the species. The discrete\nsystem with inter-site couplings dominated by the SOC, while the usual hopping\nis negligible, \\textit{emulates} condensates composed of extremely heavy atoms,\nas well as those with opposite signs of the effective atomic masses in the two\ncomponents.\\ Stable localized composite states of miscible and immiscible types\nare constructed. The effect of the SOC on the immiscibility-miscibility\ntransition in the localized complexes, which emulates the phase transition\nbetween insulating and conducting states in semiconductors, is studied."
    },
    {
        "anchor": "Theory of Electromagnetically Induced Transparency in Strongly\n  Correlated Quantum Gases: We develop a general theory to study the electromagnetically induced\ntransparency (EIT) in ultracold quantum gases, applicable for both Bose and\nFermi gases with arbitrary inter-particle interaction strength. We show that,\nin the weak probe field limit, the EIT spectrum is solely determined by the\nsingle particle Green's function of the ground state atoms, and reflects\ninteresting quantum many-body effects when atoms are virtually coupled to the\nlow-lying Rydberg states. As an example, we apply our theory to 1D Luttinger\nliquid, Bose-Mott insulator state, and the superfluid state of two-component\nFermi gases, and show how the many-body features can be observed\nnon-destructively in the unconventional EIT spectrum.",
        "positive": "Pushing Photons with Electrons: Observation of the Polariton Drag Effect: We show the direct effect of free electrons colliding with polaritons,\nchanging their momentum. The result of this interaction of the electrons with\nthe polaritons is a change in the angle of emission of the photons from our\ncavity structure. Because the experiment is a photon-in, photon-out system,\nthis is equivalent to optical beam steering of photons using a direct\nelectrical current. The effect is asymmetric, significantly slowing down the\npolaritons when they move oppositely to the electrons, while the polaritons are\nonly slightly accelerated by electrons moving in the same direction. We present\na theoretical model which describes this effect as well as energy dissipation\nin a polariton condensate."
    },
    {
        "anchor": "Noise correlations in the expansion of an interacting 1D Bose gas from a\n  regular array: We consider the one dimensional expansion of a system of interacting bosons,\nstarting from a regular array. Without interactions the familiar Hanbury Brown\nand Twiss effect for bosons gives rise to a series of peaks in the\ndensity-density correlations of the expanded system. Infinitely repulsive\nparticles likewise give a series of dips, a signature of the underlying\ndescription in terms of free fermions. In the intermediate case of finite\ninteraction the noise correlations consist of a set of Fano resonance\nlineshapes, with an asymmetry parameter determined by the scattering phase\nshift of a pair of particles, and a width depending on the initial momentum\nspread of the particles.",
        "positive": "Collisional dynamics of polaronic clouds immersed in a Fermi sea: We propose a new protocol to examine many-polaron properties in a cold atom\nexperiment. Initially, polaronic clouds are prepared around the opposite edges\nof a majority gas cloud. After time evolution, the collision of two clouds\nexhibits various polaronic effects. To see how {\\it collective} properties of\nmany polarons with mediated interactions appear in the case in which the\nimpurity and majority gases are composed of mass-balanced fermions with\ndifferent spin components, we perform a nonlinear hydrodynamic simulation for\ncollisional dynamics of two Fermi polaronic clouds. We found that the dynamics\nis governed by the impurity Fermi pressure, polaron energy, and multi-polaron\ncorrelations. In particular, shock waves occur in such a way as to reflect the\nmany-body properties of polarons through the first sound of minority clouds.\nOur idea is applicable to other systems such as Bose polarons as well as\nmass-imbalanced mixtures."
    },
    {
        "anchor": "Thermally induced coherence in a Mott insulator of bosonic atoms: Conventional wisdom is that increasing temperature causes quantum coherence\nto decrease. Using finite temperature perturbation theory and exact\ncalculations for the strongly correlated bosonic Mott insulating state we show\na practical counter-example that can be explored in optical lattice\nexperiments: the short-range coherence of the Mott insulating phase can\nincrease substantially with increasing temperature. We demonstrate that this\nphenomenon originates from thermally produced defects that can tunnel with\nease. Since the near zero temperature coherence properties have been measured\nwith high precision we expect these results to be verifiable in current\nexperiments.",
        "positive": "A dipolar droplet bound in a trapped Bose-Einstein condensate: We study the statics and dynamics of a dipolar Bose-Einstein condensate (BEC)\ndroplet bound by inter-species contact interaction in a trapped non-dipolar\nBEC. Our findings are demonstrated in terms of stability plots of a dipolar\n164Dy droplet bound in a trapped non-dipolar 87Rb BEC with a variable number of\n164Dy atoms and the inter-species scattering length. A trapped non-dipolar BEC\nof a fixed number of atoms can only bind a dipolar droplet containing atoms\nless than a critical number for the inter-species scattering length between two\ncritical values. The shape and size (statics) as well as the small breathing\noscillation (dynamics) of the dipolar BEC droplet are studied using the\nnumerical and variational solutions of a mean-field model. We also suggest an\nexperimental procedure for achieving such a 164Dy droplet by relaxing the trap\non the 164Dy BEC in a trapped binary 87Rb-164Dy mixture."
    },
    {
        "anchor": "Feshbach resonances in the 6Li-40K Fermi-Fermi mixture: Elastic versus\n  inelastic interactions: We present a detailed theoretical and experimental study of Feshbach\nresonances in the 6Li-40K mixture. Particular attention is given to the\ninelastic scattering properties, which have not been considered before. As an\nimportant example, we thoroughly investigate both elastic and inelastic\nscattering properties of a resonance that occurs near 155 G. Our theoretical\npredictions based on a coupled channels calculation are found in excellent\nagreement with the experimental results. We also present theoretical results on\nthe molecular state that underlies the 155G resonance, in particular concerning\nits lifetime against spontaneous dissociation. We then present a survey of\nresonances in the system, fully characterizing the corresponding elastic and\ninelastic scattering properties. This provides the essential information to\nidentify optimum resonances for applications relying on interaction control in\nthis Fermi-Fermi mixture.",
        "positive": "Decoherence of an impurity in a one-dimensional fermionic bath with mass\n  imbalance: We study the transport, decoherence and dissipation of an impurity\ninteracting with a bath of free fermions in a one-dimensional lattice.\nNumerical simulations are made with the time-evolving block decimation method.\nWe introduce a mass imbalance between the impurity and bath particles and find\nthat the fastest decoherence occurs for a light impurity in a bath of heavy\nparticles. By contrast, the fastest dissipation of energy occurs when the\nmasses are equal. We present a simple model for decoherence in the heavy bath\nlimit, and a linear density response description of the interaction which\npredicts maximum dissipation for equal masses."
    },
    {
        "anchor": "Symmetry-protected topological states for interacting fermions in\n  alkaline-earth-like atoms: We discuss the quantum simulation of symmetry-protected topological (SPT)\nstates for interacting fermions in quasi-one-dimensional gases of\nalkaline-earth-like atoms such as $^{173}$Yb. Taking advantage of the\nseparation of orbital and nuclear-spin degrees of freedom in these atoms, we\nconsider Raman-assisted spin-orbit couplings in the clock states, which,\ntogether with the spin-exchange interactions in the clock-state manifolds, give\nrise to SPT states for interacting fermions. We numerically investigate the\nphase diagram of the system, and study the phase transitions between the SPT\nphase and the symmetry-breaking phases. The interaction-driven topological\nphase transition can be probed by measuring local density distribution of the\ntopological edge modes.",
        "positive": "Prototyping method for Bragg-type atom interferometers: We present a method for rapid prototyping of new Bragg ultra-cold atom\ninterferometer (AI) designs useful for assessing the performance of such\ninterferometers. The method simulates the overall effect on the condensate wave\nfunction in a given AI design using two separate elements. These are (1)\nmodeling the effect of a Bragg pulse on the wave function and (2) approximating\nthe evolution of the wave function during the intervals between the pulses. The\nactual sequence of these pulses and intervals is then followed to determine the\napproximate final wave function from which the interference pattern can be\ncalculated. The exact evolution between pulses is assumed to be governed by the\nGross-Pitaevskii (GP) equation whose solution is approximated using a\nLagrangian Variational Method to facilitate rapid prototyping. The method\npresented here is an extension of an earlier one that was used to analyze the\nresults of an experiment [J.E. Simsarian, et al., Phys. Rev. Lett. 83, 2040\n(2000)], where the phase of a Bose-Einstein condensate was measured using a\nMach- Zehnder-type Bragg AI. We have developed both 1D and 3D versions of this\nmethod and we have determined their validity by comparing their predicted\ninterference patterns with those obtained by numerical integration of the 1D GP\nequation and with the results of the above experiment. We find excellent\nagreement between the 1D interference patterns predicted by this method and\nthose found by the GP equation. We show that we can reproduce all of the\nresults of that experiment without recourse to an ad hoc velocity-kick\ncorrection needed by the earlier method, including some experimental results\nthat the earlier model did not predict. We also found that this method provides\nestimates of 1D interference patterns at least four orders-of-magnitude faster\nthan direct numerical solution of the 1D GP equation."
    },
    {
        "anchor": "Simulating generic spin-boson models with matrix product states: The global coupling of few-level quantum systems (\"spins\") to a discrete set\nof bosonic modes is a key ingredient for many applications in quantum science,\nincluding large-scale entanglement generation, quantum simulation of the\ndynamics of long-range interacting spin models, and hybrid platforms for force\nand spin sensing. We present a general numerical framework for treating the\nout-of-equilibrium dynamics of such models based on matrix product states. Our\napproach applies for generic spin-boson systems: it treats any spatial and\noperator dependence of the two-body spin-boson coupling and places no\nrestrictions on relative energy scales. We show that the full counting\nstatistics of collective spin measurements and infidelity of quantum simulation\ndue to spin-boson entanglement, both of which are difficult to obtain by other\ntechniques, are readily calculable in our approach. We benchmark our method\nusing a recently developed exact solution for a particular spin-boson coupling\nrelevant to trapped ion quantum simulators. Finally, we show how decoherence\ncan be incorporated within our framework using the method of quantum\ntrajectories, and study the dynamics of an open-system spin-boson model with\nspatially non-uniform spin-boson coupling relevant for trapped atomic ion\ncrystals in the presence of molecular ion impurities.",
        "positive": "Neutral Impurities in a Bose-Einstein Condensate for Simulation of the\n  Fr\u00f6hlich-Polaron: We present an experimental system to study the Bose polaron by immersion of\nsingle, well-controllable neutral Cs impurities into a Rb Bose-Einstein\ncondensate (BEC). We show that, by proper optical traps, independent control\nover impurity and BEC allows for precision relative positioning of the two\nsub-systems as well as for independent read-out. We furthermore estimate that\nmeasuring the polaron binding energy of Fr\\\"ohlich-type Bose polarons in the\nlow and intermediate coupling regime is feasible with our experimental\nconstraints and limitations discussed."
    },
    {
        "anchor": "Dynamics of Bose-Einstein condensates in a one-dimensional optical\n  lattice with double-well potential: We study dynamical behaviors of the weakly interacting Bose-Einstein\ncondensate in the one-dimensional optical lattice with an overall double-well\npotential by solving the time-dependent Gross-Pitaevskii equation. It is\nobserved that the double-well potential dominates the dynamics of such a system\neven if the lattice depth is several times larger than the height of the\ndouble-well potential. This result suggests that the condensate flows without\nresistance in the periodic lattice just like the case of a single particle\nmoving in periodic potentials. Nevertheless, the effective mass of atoms is\nincreased, which can be experimentally verified since it is connected to the\nJosephson oscillation frequency. Moreover, the periodic lattice enhances the\nnonlinearity of the double-well condensate, making the condensate more\n\"self-trapped\" in the $\\pi$-mode self-trapping regime.",
        "positive": "Comment on \"Bose-Einstein condensation with a finite number of particles\n  in a power-law trap\": In Jaouadi et al. [Phys. Rev. A 83, 023616 (2011)] the authors derive an\nanalytical finite-size expansion for the Bose-Einstein condensation critical\ntemperature of an ideal Bose gas in a generic power-law trap. In the case of a\nharmonic trap, this expansion adds higher order terms to the well- known first\norder correction. We point out a delicate point in connection to these results,\nshowing that the claims of Jaouadi et al. should be treated with caution. In\nparticular, for a harmonic trap, the given expansion yields results that,\ndepending on what is considered to be the critical temperature of the finite\nsystem, do not generally improve on the established first order correction. For\nsome non-harmonic traps, the results differ at first order from other results\nin the literature."
    },
    {
        "anchor": "Non-equilibrium dynamics of ultracold lattice bosons inside a cavity: We study the non-equilibrium quench dynamics crossing a continuous phase\ntransition between the charge density wave (CDW) and supersolid (SS) phases of\na bosonic lattice gas with cavity-mediated interactions. When changing the\nhopping amplitude in the Hamiltonian as a function of time, we investigate the\nscaling behavior of the correlation length and vortex density with respect to\nthe quench time and find that there is a threshold of the quench rate\nseparating two distinct scaling regimes. When slowly varying the system below\nthat threshold, we find a power-law scaling as predicted by the Kibble-Zurek\nmechanism (KZM). While considering fast quench above that threshold, a\ndeviation from the KZM prediction occurs, manifested by a saturation of the\ndefect density. We further show that such distinct scaling behaviors during\ndifferent dynamic procedures can be understood through comparing the relaxation\ntime and the quench rate.",
        "positive": "Floquet engineering to exotic topological phases in systems of cold\n  atoms: Topological phases with a widely tunable number of edge modes have been\nextensively studied as a typical class of exotic states of matter with\npotentially important applications. Although several models have been shown to\nsupport such phases, they are not easy to realize in solid-state systems due to\nthe complexity of various intervening factors. Inspired by the realization of\nsynthetic spin-orbit coupling in a cold-atom system [Z. Wu {\\it et al.},\nScience \\textbf{354}, 83 (2016)], we propose a periodic quenching scheme to\nrealize large-topological-number phases with multiple edge modes in optical\nlattices. Via introducing the periodic quenching to the Raman lattice, it is\nfound that a large number of edge modes can be induced in a controllable manner\nfrom the static topologically trivial system. Our result provides an\nexperimentally accessible method to artificially synthesize and manipulate\nexotic topological phases with large topological numbers and multiple edge\nmodes."
    },
    {
        "anchor": "Sharp crossover from composite fermionization to phase separation in\n  mesoscopic mixtures of ultracold bosons: We show that a two-component mixture of a few repulsively interacting\nultracold atoms in a one-dimensional trap possesses very different quantum\nregimes and that the crossover between them can be induced by tuning the\ninteractions in one of the species. In the composite fermionization regime,\nwhere the interactions between both components are large, none of the species\nshow large occupation of any natural orbital. Our results show that by\nincreasing the interaction in one of the species, one can reach the\nphase-separated regime. In this regime, the weakly interacting component stays\nat the center of the trap and becomes almost fully phase coherent, while the\nstrongly interacting component is displaced to the edges of the trap. The\ncrossover is sharp, as observed in the in the energy and the in the largest\noccupation of a natural orbital of the weakly interacting species. Such a\ntransition is a purely mesoscopic effect which disappears for large atom\nnumbers.",
        "positive": "Quantum anomalous Hall phase in synthetic bilayers via twistless\n  twistronics: We recently proposed quantum simulators of \"twistronic-like\" physics based on\nultracold atoms and syntheticdimensions [Phys. Rev. Lett. 125, 030504 (2020)].\nConceptually, the scheme is based on the idea that aphysical monolayer optical\nlattice of desired geometry is upgraded to a synthetic bilayer system by\nidentifyingthe internal states of the trapped atoms with synthetic spatial\ndimensions. The couplings between the internalstates, i.e. between sites on the\ntwo layers, can be exquisitely controlled by laser induced Raman transitions.By\nspatially modulating the interlayer coupling, Moir\\'e-like patterns can be\ndirectly imprinted on the latticewithout the need of a physical twist of the\nlayers. This scheme leads practically to a uniform pattern across thelattice\nwith the added advantage of widely tunable interlayer coupling strengths. The\nlatter feature facilitates theengineering of flat bands at larger \"magic\"\nangles, or more directly, for smaller unit cells than in conventionaltwisted\nmaterials. In this paper we extend these ideas and demonstrate that our system\nexhibits topologicalband structures under appropriate conditions. To achieve\nnon-trivial band topology we consider imanaginarynext-to-nearest neighbor\ntunnelings that drive the system into a quantum anomalous Hall phase. In\nparticular,we focus on three groups of bands, whose their Chern numbers triplet\ncan be associated to a trivial insulator(0,0,0), a standard non-trivial\n(-1,0,1) and a non-standard non-trivial (-1,1,0). We identify regimes of\nparameterswhere these three situations occur. We show the presence of an\nanomalous Hall phase and the appearance oftopological edge states. Our works\nopen the path for experiments on topological effects in twistronics without\natwist"
    },
    {
        "anchor": "Topological Superfluid in one-dimensional Ultracold Atomic System with\n  Spin-Orbit Coupling: We propose a one-dimensional Hamiltonian $H_{1D}$ which supports Majorana\nfermions when $d_{x^{2}-y^{2}}$-wave superfluid appears in the ultracold atomic\nsystem and obtain the phase-separation diagrams both for the\ntime-reversal-invariant case and time-reversal-symmetry-breaking case. From the\nphase-separation diagrams, we find that the single Majorana fermions exist in\nthe topological superfluid region, and we can reach this region by tuning the\nchemical potential $\\mu$ and spin-orbit coupling $\\alpha_{R}$. Importantly, the\nspin-orbit coupling has realized in ultracold atoms by the recent experimental\nachievement of synthetic gauge field, therefore, our one-dimensional ultra-cold\natomic system described by $H_{1D}$ is a promising platform to find the\nmysterious Majorana fermions.",
        "positive": "Chiral switching of many-body steady states in a dissipative Rydberg gas: Dissipative Rydberg gases are an outstanding platform for the investigation\nof many-body quantum open systems. Despite the wealth of existing studies, the\nnon-equilibrium dynamics of dissipative Rydberg gases are rarely examined or\nharnessed from the perspective of non-Hermitian physics, which is but intrinsic\nto open systems. Here we report the experimental observation of a chiral\nswitching between many-body steady states in a dissipative thermal Rydberg\nvapor, where the interplay of many-body effects and non-Hermiticity plays a key\nrole. Specifically, as the parameters are adiabatically varied around a closed\ncontour, depending on the chirality of the parameter modulation, the Rydberg\nvapor can change between two collective steady states with distinct Rydberg\nexcitations and optical transmissions. Adopting a mean-field description, we\nreveal that both the existence of the bistable steady states and chiral\ndynamics derive from an exceptional structure in the parameter space, where\nmultiple steady states of the many-body Liouvillian superoperator coalesce. We\ndemonstrate that both the exceptional structure and the resulting\nstate-switching dynamics are tunable through microwave dressing and temperature\nvariations, confirming their reliance on the many-body dissipative nature of\nthe Rydberg vapor."
    },
    {
        "anchor": "Local emergence of thermal correlations in an isolated quantum many-body\n  system: We experimentally demonstrate how thermal properties in an non-equilibrium\nquantum many- body system emerge locally, spread in space and time, and finally\nlead to the globally relaxed state. In our experiment, we quench a\none-dimensional (1D) Bose gas by coherently splitting it into two parts. By\nmonitoring the phase coherence between the two parts we observe that the\nthermal correlations of a prethermalized state emerge locally in their final\nform and propagate through the system in a light-cone-like evolution. Our\nresults underline the close link between the propagation of correlations and\nrelaxation processes in quantum many-body systems.",
        "positive": "Effective-range dependence of resonant Fermi gases: A Fermi gas of cold atoms allows precise control over the dimensionless\neffective range, $k_\\mathrm{F} R_\\mathrm{eff}$, of the Feshbach resonance. Our\npseudopotential formalism allows us to create smooth potentials with effective\nrange, $-2 \\leq k_\\mathrm{F} R_\\mathrm{eff} \\leq 2$, which we use for a\nvariational and diffusion Monte Carlo study of the ground state of a unitary\nFermi gas. We report values for the universal constants of $\\xi = 0.388(1)$ and\n$\\zeta = 0.087(1)$, and compute the condensate fraction, momentum distribution,\nand pair correlations functions. Finally, we show that a gas with $k_\\mathrm{F}\nR_\\mathrm{eff} \\gtrsim 1.9$ is thermodynamically unstable."
    },
    {
        "anchor": "Controlling excitation avalanches in driven Rydberg gases: Recent experiments with strongly interacting, driven Rydberg ensembles have\nintroduced a promising setup for the study of self-organized criticality (SOC)\nin cold atom systems. Based on this setup, we theoretically propose a control\nmechanism for the paradigmatic avalanche dynamics of SOC in terms of a\ntime-dependent drive amplitude. This gives access to a variety of avalanche\ndominated, self-organization scenarios, prominently including self-organized\ncriticality, as well as sub- and supercritical dynamics. We analyze the\ndependence of the dynamics on external scales and spatial dimensionality. It\ndemonstrates the potential of driven Rydberg systems as a playground for the\nexploration of an extended SOC phenomenology and their relation to other common\nscenarios of SOC, such as e.g. in neural networks and on graphs.",
        "positive": "Two-dimensional symbiotic solitons and quantum droplets in a\n  quasi-one-dimensional optical lattice: Symbiotic solitons (SS) and quantum droplets (QD) are self-trapped localized\nmodes emerging in binary Bose-gas mixtures with intra-component repulsion and\ninter-component attraction. We have shown that two-dimensional SS can be\nstabilized against collapse or decay by means of a quasi-one-dimensional\noptical lattice (OL). Mobility of SSs along the free direction of the potential\nallows us to explore interactions and collisions of SSs moving in the same\nchannel and neighboring channels of the quasi-1D OL. For the case of equal atom\nnumbers in both components of the binary Bose-Einstein condensate (BEC) we have\ndeveloped a variational approach that showed the stability of SS. For parameter\nsettings when the SS stays on the verge of collapse instability, we take into\naccount the Lee-Huang-Yang quantum fluctuations (QF) term in the coupled\nGross-Pitaevskii equations. Repulsive QF prevents the mean-field collapse and\ngives rise to the formation of 2D QDs with peculiar properties such as\nincompressibility and surface tension, which are inherent to liquids. The\nproposed model of binary BEC loaded in a quasi-1D OL allows us to demonstrate\nthe manifestations of the incompressibility and surface tension of 2D QDs. The\nformation of QD in imbalanced binary BEC with different numbers of atoms of the\ncomponents in the presence of a quasi-1D OL has been investigated. The possible\napplication of the proposed model to studies of anisotropic superfluidity is\ndiscussed."
    },
    {
        "anchor": "Separation of quadrupole, spin, and charge across the magnetic phases of\n  a one-dimensional interacting spin-1 gas: We study the low-energy collective properties of a 1D spin-1 Bose gas using\nbosonization. After giving an overview of the technique, emphasizing the\nphysical aspects, we apply it to the $S=1$ Bose-Hubbard Hamiltonian and find a\nnovel separation of the quadrupole-spin-charge sectors, confirmed by time-MPS\nnumerical simulations. Additionally, through the single particle spectrum, we\nshow the existence of the superfluid-Mott insulator transition and the point at\nwhich the physics are described by a Heisenberg-like Hamiltonian. The magnetic\nphase diagrams are found for both the superfluid and insulating regimes; the\nlatter is determined by decomposing the complete Heisenberg\nbilinear-biquadratic Hamiltonian, which describes the Mott insulator, into\nsimpler, effective Hamiltonians. This allows us to keep our methods flexible\nand transferable to other interesting interacting condensed matter systems.",
        "positive": "Two-Stage Melting in Systems of Strongly Interacting Rydberg Atoms: We analyze the ground state properties of a one-dimensional cold atomic\nsystem in a lattice, where Rydberg excitations are created by an external laser\ndrive. In the classical limit, the ground state is characterized by a complete\ndevil's staircase for the commensurate solid structures of Rydberg excitations.\nUsing perturbation theory and a mapping onto an effective low energy\nHamiltonian, we find a transition of these commensurate solids into a floating\nsolid with algebraic correlations. For stronger quantum fluctuations the\nfloating solid eventually melts within a second quantum phase transition and\nthe ground state becomes paramagnetic."
    },
    {
        "anchor": "Accessing the topological Mott insulator in cold atom quantum simulators\n  with realistic Rydberg dressing: The interplay between many-body interactions and the kinetic energy gives\nrise to rich phase diagrams hosting, among others, interaction-induced\ntopological phases. These phases are characterized by both a local order\nparameter and a global topological invariant, and can exhibit exotic ground\nstates such as self-trapped polarons and interaction-induced edge states. In\nthis work, we investigate a realistic scenario for the quantum simulation of\nsuch systems using cold Rydberg-dressed atoms in optical lattices. We consider\nspinless fermions on a checkerboard lattice, interacting via the tunable-range\neffective potential induced by the Rydberg dressing. We perform a detailed\nanalysis of the phase diagram at half- and incommensurate fillings, in the\nmean-field approximation. We furthermore study the stability of the phases with\nrespect to temperature within the mean-field approximation and with respect to\nquantum fluctuations using the density matrix renormalization group method.\nFinally, we propose an implementation protocol, and in particular identify\nattainable regimes of experimental parameters in which the topological\nproperties of the model become accessible. Our work, thereby, opens a realistic\npathway to the outstanding experimental observation of this predicted phase in\nstate-of-the-art cold atom quantum simulators.",
        "positive": "Statistical Interparticle Potential of an Ideal Gas of Non-Abelian\n  Anyons: We determine and study the statistical interparticle potential of an ideal\nsystem of non-Abelian Chern-Simons (NACS) particles, comparing our results with\nthe corresponding results of an ideal gas of Abelian anyons. In the Abelian\ncase, the statistical potential depends on the statistical parameter and it has\na \"quasi-bosonic\" behaviour for statistical parameter in the range (0,1/2)\n(non-monotonic with a minimum) and a \"quasi-fermionic\" behaviour for\nstatistical parameter in the range (1/2,1) (monotonically decreasing without a\nminimum). In the non-Abelian case the behavior of the statistical potential\ndepends on the Chern- Simons coupling and the isospin quantum number: as a\nfunction of these two parameters, a phase diagram with quasi-bosonic,\nquasi-fermionic and bosonic-like regions is obtained and investigated. Finally,\nusing the obtained expression for the statistical potential, we compute the\nsecond virial coefficient of the NACS gas, which correctly reproduces the\nresults available in literature."
    },
    {
        "anchor": "Kinetics of the disordered Bose gas with collisions: We discuss the kinetics of the disordered interacting Bose gas using the\nBoltzmann transport equation. The theory may serve as a unifying framework for\nstudying questions of dynamics of the expanding Bose gas at different stages of\nthe expansion. We show that the transport theory allows us to straightforwardly\nreproduce and generalize a number of results previously obtained from\nmicroscopic models in different formalisms. Based on estimates for the\ninterparticle scattering rates, we discuss the relevance of interaction effects\nfor the localization problem in the interacting disordered Bose gas. We argue\nthat, if the number of particles is large enough, the size of the expanding\ncloud may exceed the localization length. We describe the spreading of the wave\npacket in this regime as collision-induced diffusion and compare the obtained\nrate of expansion to known results on subdiffusive spreading in nonlinear\ndisordered lattices.",
        "positive": "Probing the BCS-BEC crossover with persistent currents: We study the persistent currents of an attractive Fermi gas confined in a\ntightly-confining ring trap and subjected to an artificial gauge field all\nthrough the BCS-BEC crossover. At weak attractions, on the BCS side, fermions\ndisplay a parity effect in the persistent currents, ie their response to the\ngauge field is paramagnetic or diamagnetic depending on the number of pairs on\nthe ring. At resonance and on the BEC side of the crossover we find a doubling\nof the periodicity of the ground-state energy as a function of the artificial\ngauge field and disappearance of the parity effect, indicating that persistent\ncurrents can be used to infer the formation of tightly-bound bosonic pairs. Our\npredictions can be accessed in ultracold atoms experiments through noise\ninterferograms."
    },
    {
        "anchor": "Superfluid transition in the attractive Hofstadter-Hubbard model: We consider a Fermi gas that is loaded onto a square optical lattice and\nsubjected to a perpendicular artificial magnetic field, and determine its\nsuperfluid transition boundary by adopting a BCS-like mean-field approach in\nmomentum space. The multi-band structure of the single-particle Hofstadter\nspectrum is taken explicitly into account while deriving a generalized pairing\nequation. We present the numerical solutions as functions of the artificial\nmagnetic flux, interaction strength, Zeeman field, chemical potential, and\ntemperature, with a special emphasis on the roles played by the density of\nsingle-particle states and center-of-mass momentum of Cooper pairs.",
        "positive": "Universal Scaling of the Dynamic BKT Transition in Quenched 2D Bose\n  Gases: While renormalization group theory is a fully established method to capture\nequilibrium phase transitions, the applicability of RG theory to universal\nnon-equilibrium behavior remains elusive. Here we address this question by\nmeasuring the non-equilibrium dynamics triggered by a quench from superfluid to\nthermal phase across the Berezinskii-Kosterlitz-Thouless transition in a 2D\nBose gas. We quench the system by splitting the 2D gas in two and probe the\nrelaxation dynamics by measuring the phase correlation function and vortex\ndensity via matter-wave interferometry. The dynamics occur via a two-step\nprocess of rapid phonon thermalization followed by slow dynamic vortex\nunbinding. We demonstrate universal scaling laws for the algebraic exponents\nand vortex density, supported by classical-field simulations, and show their\nagreement with the real-time RG theory."
    },
    {
        "anchor": "Half-quantum vortex generation in a two-component Bose-Einstein\n  condensate by an oscillatory magnetic obstacle: We numerically investigate the dynamics of vortex generation in a\ntwo-dimensional, twocomponent Bose-Einstein condensate subjected to an\noscillatory magnetic obstacle. The obstacle creates both repulsive and\nattractive Gaussian potentials for the two symmetric spin-$\\uparrow$ and\n$\\downarrow$ components, respectively. We demonstrate that, as the oscillating\nfrequency f increases, two distinct critical dynamics arise in the generation\nof half-quantum vortices (HQVs) with different spin circulations.\nSpin-$\\uparrow$ vortices are nucleated directly from the moving obstacle at low\nf, while spin-$\\downarrow$ vortices are created at high f by breaking a spin\nwave pulse in front of the obstacle. We find that vortex generation is\nsuppressed for sufficiently weak obstacles, in agreement with recent\nexperimental results by Kim et al. [Phys. Rev. Lett. 127, 095302 (2021)]. This\nsuppression is caused by the finite sweeping distance of the oscillating\nobstacle and the reduction in friction in a supersonic regime. Finally, we show\nthat the characteristic length scale of the HQV generation dynamics is\ndetermined by the spin healing length of the system.",
        "positive": "Impossibility of the Efimov effect for p-wave interactions: Whether the Efimov effect is possible, in principle, for p-wave or higher\npartial-wave interactions is a fundamental question. Recently, there has been a\nclaim that three nonrelativistic particles with resonant p-wave interactions\nexhibit the Efimov effect. We point out that the assumed p-wave scattering\namplitude inevitably causes a negative probability. This indicates that the\nEfimov states found there cannot be realized in physical situations. We also\nrestate our previous argument that the Efimov effect, defined as an infinite\ntower of universal bound states characterized by discrete scale invariance, is\nimpossible for p-wave or higher partial-wave interactions."
    },
    {
        "anchor": "Efimov trimers under strong confinement: The dimensionality of a system can fundamentally impact the behaviour of\ninteracting quantum particles. Classic examples range from the fractional\nquantum Hall effect to high temperature superconductivity. As a general rule,\none expects confinement to favour the binding of particles. However,\nattractively interacting bosons apparently defy this expectation: while three\nidentical bosons in three dimensions can support an infinite tower of Efimov\ntrimers, only two universal trimers exist in the two dimensional case. We\nreveal how these two limits are connected by investigating the problem of three\nidentical bosons confined by a harmonic potential along one direction. We show\nthat the confinement breaks the discrete Efimov scaling symmetry and destroys\nthe weakest bound trimers. However, the deepest bound Efimov trimer persists\nunder strong confinement and hybridizes with the quasi-two-dimensional trimers,\nyielding a superposition of trimer configurations that effectively involves\ntunnelling through a short-range repulsive barrier. Our results suggest a way\nto use strong confinement to engineer more stable Efimov-like trimers, which\nhave so far proved elusive.",
        "positive": "The two-atom energy spectrum in a harmonic trap near a Feshbach\n  resonance at higher partial waves: Two atoms in an optical lattice may be made to interact strongly at higher\npartial waves near a Feshbach resonance. These atoms, under appropriate\nconstraints, could be bosonic or fermionic. The universal $l=2$ energy spectrum\nfor such a system, with a caveat, is presented in this paper, and checked with\nthe spectrum obtained by direct numerical integration of the Schr\\\"odinger\nequation. The results reported here extend those of Yip for p-wave resonance\n(Phys. Rev. A {\\bf 78}, 013612 (2008)), while exploring the limitations of a\nuniversal expression for the spectrum for the higher partial waves."
    },
    {
        "anchor": "Decay of phase-imprinted dark soliton in Bose-Einstein condensate at\n  non-zero temperature: We study relaxation dynamics of dark soliton, created by a phase-imprinted\nmethod, in a two-dimensional trapped Bose-Einstein condensate at non-zero\ntemperatures by using the projected Gross-Pitaevskii equation. At absolute zero\ntemperature, a dark soliton is known to decay with a snake instability. At\nnon-zero temperature, as we expected, we find that this snake instability\ncannot be clearly seen as in the absolute zero temperature case because of the\npresence of thermal fluctuations. However, we find that the decay rate, the\nhalf width of the overlap integral with respect to the phase-imprinted initial\nstate, shows a power low decay as a function of the energy and finally remains\na non-zero value.",
        "positive": "Localization of weakly interacting bosons in two dimensions: disorder vs\n  lattice geometry effects: We investigate the effects of disorder and lattice geometry against\nlocalisation phenomena in a weakly interacting ultracold bosonic gas confined\nin a 2D optical lattice. The behaviour of the quantum fluid is studied at the\nmean-field level performing computational experiments, as a function of\ndisorder strength for lattices of sizes similar to current experiments.\nQuantification of localisation, away from the Bose glass phase, was obtained\ndirectly from the stationary density profiles through a robust statistical\nanalysis of the condensate component, as a function of the disorder amplitude.\nOur results show a smooth transition, or crossover, to localisation induced by\ndisorder in square and triangular lattices. In contrast, associated to its\nlarger tunneling amplitude, honeycomb lattices show absence of localisation for\nthe same range of disorder strengths and same lattice amplitude, while also\nexhibiting partial localisation for large disorder amplitudes. We also conclude\nthat the coordination number z have a partial influence on how fast this smooth\ntransition occurs as the system size increases. Signatures of disorder are also\nfound in the ground state energy spectrum, where a continuous distribution\nemerges instead of a distribution of sharp peaks proper to the system in the\nabsence of disorder."
    },
    {
        "anchor": "Controlling the interactions in a cold atom quantum impurity system: We implement an experimental architecture in which a single atom of K is\ntrapped in an optical tweezer, and is immersed in a bath of Rb atoms at\nultralow temperatures. In this regime, the motion of the single trapped atom is\nconfined to the lowest quantum vibrational levels. This realizes an elementary\nand fully controllable quantum impurity system. For the trapping of the K atom,\nwe use a species-selective dipole potential, that allows us to independently\nmanipulate the quantum impurity and the bath. We concentrate on the\ncharacterization and control of the interactions between the two subsystems. To\nthis end, we perform Feshbach spectroscopy, detecting several inter-dimensional\nconfinement-induced Feshbach resonances for the KRb interspecies scattering\nlength, that parametrizes the strength of the interactions. We compare our data\nto a theory for inter-dimensional scattering, finding good agreement. Notably,\nwe also detect a series of p-wave resonances stemming from the underlying\nfree-space s-wave interactions. We further determine how the resonances behave\nas the temperature of the bath and the dimensionality of the interactions\nchange. Additionally, we are able to screen the quantum impurity from the bath\nby finely tuning the wavelength of the light that produces the optical tweezer,\nproviding us with a new effective tool to control and minimize the\ninteractions. Our results open a range of new possibilities in quantum\nsimulations of quantum impurity models, quantum information, and quantum\nthermodynamics, where the interactions between a quantized system and the bath\nis a powerful yet largely underutilized resource.",
        "positive": "Probing the quantum state of a 1D Bose gas using off-resonant light\n  scattering: We present a theoretical treatment of coherent light scattering from an\ninteracting 1D Bose gas at finite temperatures. We show how this can provide a\nnondestructive measurement of the atomic system states. The equilibrium states\nare determined by the temperature and interaction strength, and are\ncharacterized by the spatial density-density correlation function. We show how\nthis correlation function is encoded in the angular distribution of the\nfluctuations of the scattered light intensity, thus providing a sensitive,\nquantitative probe of the density-density correlation function and therefore\nthe quantum state of the gas."
    },
    {
        "anchor": "Universal contact for a Tonks-Girardeau gas at finite temperature: We determine the finite-temperature momentum distribution of a strongly\ninteracting 1D Bose gas in the Tonks-Girardeau (impenetrable-boson) limit under\nharmonic confinement, and explore its universal properties associated to the\nscale invariance of the model. We show that, at difference from the unitary\nFermi gas in three dimensions, the weight of its large-momentum tails -- given\nby the Tan's contact -- increase with temperature, and calculate the\nhigh-temperature universal second contact coefficient using a virial expansion.",
        "positive": "Quantum noise reduction using a cavity with a Bose Einstein condensate: We study an optomechanical system in which the collective density excitations\n(Bogoliubov modes) of a Bose Einstein condensate (BEC) is coupled to a cavity\nfield. We show that the optical force changes the frequency and the damping\nconstant of the collective density excitations of the BEC. We further analyze\nthe occurrence of normal mode splitting (NMS) due to mixing of the fluctuations\nof the cavity field and the fluctuations of the condensate with finite atomic\ntwo-body interaction. The NMS is found to vanish for small values of the\ntwo-body interaction. We further show that the density excitations of the\ncondensate can be used to squeeze the output quantum fluctuations of the light\nbeam. This system may serve as an optomechanical control of quantum\nfluctuations using a Bose Einstein condensate."
    },
    {
        "anchor": "Observation of gauge invariance in a 71-site Bose-Hubbard quantum\n  simulator: The modern description of elementary particles, as formulated in the Standard\nModel of particle physics, is built on gauge theories. Gauge theories implement\nfundamental laws of physics by local symmetry constraints. For example, in\nquantum electrodynamics, Gauss's law introduces an intrinsic local relation\nbetween charged matter and electromagnetic fields, which protects many salient\nphysical properties including massless photons and a long-ranged Coulomb law.\nSolving gauge theories by classical computers is an extremely arduous task,\nwhich has stimulated a vigorous effort to simulate gauge-theory dynamics in\nmicroscopically engineered quantum devices. Previous achievements implemented\ndensity-dependent Peierls phases without defining a local symmetry, realized\nmappings onto effective models to integrate out either matter or electric\nfields, or were limited to very small systems. The essential gauge symmetry has\nnot been observed experimentally. Here, we report the quantum simulation of an\nextended U(1) lattice gauge theory, and experimentally quantify the gauge\ninvariance in a many-body system comprising matter and gauge fields. These are\nrealized in defect-free arrays of bosonic atoms in an optical superlattice of\n71 sites. We demonstrate full tunability of the model parameters and benchmark\nthe matter--gauge interactions by sweeping across a quantum phase transition.\nEnabled by high-fidelity manipulation techniques, we measure the degree to\nwhich Gauss's law is violated by extracting probabilities of locally\ngauge-invariant states from correlated atom occupations. Our work provides a\nway to explore gauge symmetry in the interplay of fundamental particles using\ncontrollable large-scale quantum simulators.",
        "positive": "Two-mode dipolar bosonic junctions: We consider a two-mode atomic Josephson junction realized with dilute dipolar\nbosons confined by a double-well. We employ the two-site extended Bose-Hubbard\nHamiltonian and characterize the ground-state of this system by the Fisher\ninformation, coherence visibility, and entanglement entropy. These quantities\nare studied as functions of the interaction between bosons in different wells.\nThe emergence of Schroedinger-cat like state with a loss of coherence is also\ncommented."
    },
    {
        "anchor": "Slow-light probe of Fermi pairing through an atom-molecule dark state: We consider the two-color photooassociation of a quantum degenerate atomic\ngas into ground-state diatomic molecules via a molecular dark state. This\nprocess can be described in terms of a lambda level scheme that is formally\nanalogous to the situation in electromagnetically-induced transparency (EIT) in\natomic systems, and therefore can result in slow light propagation. We show\nthat the group velocity of the light field depends explicitly on whether the\natoms are bosons or fermions, as well as on the existence or absence of a\npairing gap in the case of fermions, so that the measurement of the group\nvelocity realizes a non-destructive diagnosis of the atomic state and the\npairing gap.",
        "positive": "Exotic Vortex Lattices in Binary Repulsive Superfluids: We investigate a mixture of two repulsively interacting superfluids with\ndifferent constituent particle masses: $m_1\\ne m_2$. Solutions to the\nGross-Pitaevskii equation for homogeneous infinite vortex lattices predict the\nexistence of rich vortex lattice configurations, a number of which correspond\nto Platonic and Archimedean planar tilings. Some notable geometries include the\nsnub-square, honeycomb, kagome, and herringbone lattice configurations. We\npresent a full phase diagram for the case $m_2/m_1 = 2$ and list a number of\ngeometries that are found for higher integer mass ratios."
    },
    {
        "anchor": "Fulde-Ferrell-Larkin-Ovchinnikov state in bilayer dipolar systems: We study the phase diagram of fermionic polar molecules in a bilayer system,\nwith an imbalance of molecular densities of the layers. For the imbalance\nexceeding a critical value the system undergoes a transition from the uniform\ninterlayer superfluid to the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state with\na stripe structure, and at sufficiently large imbalance a transition from the\nFFLO to normal phase. Compared to the case of contact interactions, the FFLO\nregime is enhanced by the long-range character of the interlayer dipolar\ninteraction, which can combine the s-wave and p-wave pairing in the order\nparameter.",
        "positive": "Annihilation Process of Quantum Vortices in Dissipative Gross-Pitaevskii\n  Equation Model: In two dimensional superfluid, annihilation processes of vortices are\ninvestigated by numerical simulation within the dissipative Gross-Pitaevskii\nequation (GPE) model. First, quantum vortex solution is obtained and its\nfitting function is found. Second, the simulation show that positive and\nnegative vortices accelerate in both x,y directions, until they annihilate into\na soliton and then a crescent-shaped shock wave. The processes are found to be\ncontrolled by the dissipative parameter and the general Magnus force. For the\nbehavior of separation distance between vortices d(t), an universal scaling\nexponent 1/2 is found which is same with the three dimensional cases. Third,\nsystem's energy is surprisingly found to be determined by system's\nconfiguration and their relation are obtained. Then we derive the general\nMagnus force which decreases with the increases of d(t) for large d(t) and\nincreases with the increases of d(t) for small d(t)."
    },
    {
        "anchor": "On Berezinskii-Kosterlitz-Thouless Phase Transition in Quasi-One\n  Dimensional Bose-Einstein Condensate: We show that quasi-one dimensional Bose-Einstein condensate under suitable\nconditions can exhibit a Berezinskii-Kosterlitz-Thouless phase transition. The\nrole played by quantized vortices in two dimensional case, is played in this\ncase by dark solitons. We find that the critical temperature for this\ntransition lies in nano Kelvin range and below, for a wide range of\nexperimentally accessible parameters. It is seen that the high temperature\n(disordered) phase differs from low temperature (ordered) phase in terms of\nphase coherence, which can be used as an experimental signature for observing\nthis transition.",
        "positive": "Thermodynamics of rotating quantum matter in the virial expansion: We characterize the high-temperature thermodynamics of rotating bosons and\nfermions in two- (2D) and three-dimensional (3D) isotropic harmonic trapping\npotentials. We begin by calculating analytically the conventional virial\ncoefficients $b_n$ for all $n$ in the noninteracting case, as functions of the\ntrapping and rotational frequencies. We also report on the virial coefficients\nfor the angular momentum and associated moment of inertia. Using the bn\ncoefficients, we analyze the deconfined limit (in which the angular frequency\nmatches the trapping frequency) and derive explicitly the limiting form of the\npartition function, showing from the thermodynamic standpoint how both the 2D\nand 3D cases become effectively homogeneous 2D systems. To tackle the virial\ncoefficients in the presence of weak interactions, we implement a coarse\ntemporal lattice approximation and obtain virial coefficients up to third\norder."
    },
    {
        "anchor": "Entanglement properties of the critical quench of O(N) bosons: The entanglement properties of quenched quantum systems have been studied for\na decade, however results in dimensions other than $d=1$ are generally lacking.\nWe remedy this by investigating the entanglement properties of bosonic critical\nsystems in $d=3$, both numerically and analytically, comparing the free and the\ninteracting critical quench of an $O(N)$ model. We find that the evolution of\nthe entanglement entropy for these two systems is nearly identical, as expected\nfrom the \"quasi-particle\" picture. However, the low-lying entanglement spectrum\nis controlled by the different critical exponent of the two systems, and\ntherefore these exponents may be extracted by purely entanglement-theoretic\ncalculations. We verify this scaling numerically.",
        "positive": "Fano resonance through Higgs bound states in tunneling of\n  Nambu-Goldstone modes: We study collective modes of superfluid Bose gases in optical lattices\ncombined with potential barriers. We assume that the system is in the vicinity\nof the quantum phase transition to a Mott insulator at a commensurate filling,\nwhere emergent particle-hole symmetry gives rise to two types of collective\nmode, namely a gapless Nambu-Goldstone (NG) phase mode and a gapful Higgs\namplitude mode. We consider two kinds of potential barrier: One does not break\nthe particle-hole symmetry while the other does. In the presence of the former\nbarrier, we find Higgs bound states that have binding energies lower than the\nbulk Higgs gap and are localized around the barrier. We analyze tunneling\nproperties of the NG mode incident to both barriers to show that the latter\nbarrier couples the Higgs bound states with the NG mode, leading to Fano\nresonance mediated by the bound states. Thanks to the universality of the\nunderlying field theory, it is expected that Higgs bound states may be present\nalso in other condensed matter systems with a particle-hole symmetry and\nspontaneous breaking of a continuous symmetry, such as quantum dimer\nantiferromagnets, superconductors, and charge-density-wave materials."
    },
    {
        "anchor": "Spin-Induced Orbital Frustration in a Hexagonal Optical Lattice: Complex lattices provide a versatile ground for fascinating quantum many-body\nphysics. Here, we propose an exotic mechanics for generating orbital\nfrustration in hexagonal lattices. We study two-component (pseudospin-$1/2$)\nBose gases in $p$-orbital bands of two-dimensional hexagonal lattices, and find\nthat the system exhibits previously untouched orbital frustration as a result\nof the interplay of spin and orbital degrees of freedom, in contrast to normal\nIsing-type orbital ordering of spinless $p$-orbital band bosons in\ntwo-dimensional hexagonal lattices. Based on the classification by symmetry\nanalysis, we find the interplay of orbital frustration and strong interaction\nleads to exotic Mott and superfluid phases with spin-orbital intertwined\norders, in spite of the complete absence of spin-orbital interaction in the\nHamiltonian. Our study implies many-body correlations in a multi-orbital\nsetting could induce rich spin-orbital intertwined physics in complex lattice\nstructures.",
        "positive": "Self-induced Bose glass phase in quantum cluster quasicrystals: We study the emergence of Bose glass phases in self sustained bosonic\nquasicrystals induced by a pair interaction between particles of\nLifshitz-Petrich type. By using a mean field variational method designed in\nmomentum space as well as Gross-Pitaevskii simulations we determine the phase\ndiagram of the model. The study of the local and global superfluid fraction\nallows the identification of supersolid, super quasicrystal, Bose glass and\ninsulating phases. The Bose glass phase emerges as a quasicrystal phase in\nwhich the global superfluidity is essentially zero, while the local\nsuperfluidity remains finite in certain ring structures of the quasicrystalline\npattern. Furthermore, we perform continuous space Path Integral Monte Carlo\nsimulations for a case in which the interaction between particles stabilizes a\nquasicrystal phase. Our results show that as the strength of the interaction\nbetween particles is increased the system undergoes a sequence of states\nconsistent with the super quasicrystal, Bose glass, and quasicrystal insulator\nthermodynamic phases."
    },
    {
        "anchor": "Quantum walks of interacting Mott insulator defects with three-body\n  interactions: Quantum walks of interacting particles may display non-trivial features due\nto the interplay between the statistical nature and the many-body interactions\nassociated to them. We analyze the quantum walk of interacting defects on top\nof an uniform bosonic Mott insulator at unit filling in an one dimensional\ngraph. While the quantum walk of single particle defect shows trivial features,\nthe case of two particles exhibits interesting phenomenon of quantum walk\nreversal as a function of additional onsite three-body attractive interactions.\nIn the absence of the three-body interaction a quantum walk of pairs of\nparticles is obtained and as the strength of the three-body interaction becomes\nmore and more attractive, the independent particle behavior in quantum walk\nappears. Interestingly, further increase in the three-body interaction leads to\nthe re-appearance of the quantum walk associated to a pair of particles. This\nquantum-walk reversal phenomenon is studied using the real-space density\nevolution, Bloch oscillation as well as two-particle correlation functions.",
        "positive": "Floquet Engineering Ultracold Polar Molecules to Simulate Topological\n  Insulators: We present a quantitative, near-term experimental blueprint for the quantum\nsimulation of topological insulators using lattice-trapped ultracold polar\nmolecules. In particular, we focus on the so-called Hopf insulator, which\nrepresents a three-dimensional topological state of matter existing outside the\nconventional tenfold way and crystalline-symmetry-based classifications of\ntopological insulators. Its topology is protected by a \\emph{linking number}\ninvariant, which necessitates long-range spin-orbit coupled hoppings for its\nrealization. While these ingredients have so far precluded its realization in\nsolid state systems and other quantum simulation architectures, in a companion\nmanuscript [1901.08597] we predict that Hopf insulators can in fact arise\nnaturally in dipolar interacting systems. Here, we investigate a specific such\narchitecture in lattices of polar molecules, where the effective `spin' is\nformed from sublattice degrees of freedom. We introduce two techniques that\nallow one to optimize dipolar Hopf insulators with large band gaps, and which\nshould also be readily applicable to the simulation of other exotic\nbandstructures. First, we describe the use of Floquet engineering to control\nthe range and functional form of dipolar hoppings and second, we demonstrate\nthat molecular AC polarizabilities (under circularly polarized light) can be\nused to precisely tune the resonance condition between different rotational\nstates. To verify that this latter technique is amenable to current generation\nexperiments, we calculate from first principles the AC polarizability for\n$\\sigma^+$ light for ${}^{40}$K$^{87}$Rb. Finally, we show that experiments are\ncapable of detecting the unconventional topology of the Hopf insulator by\nvarying the termination of the lattice at its edges, which gives rise to three\ndistinct classes of edge mode spectra."
    },
    {
        "anchor": "Adiabatic invariant analysis of dark and dark-bright soliton stripes in\n  two-dimensional Bose-Einstein condensates: In the present work, we develop an adiabatic invariant approach for the\nevolution of quasi-one-dimensional (stripe) solitons embedded in a\ntwo-dimensional Bose-Einstein condensate. The results of the theory are\nobtained both for the one-component case of dark soliton stripes, as well as\nfor the considerably more involved case of the two-component dark-bright (alias\n\"filled dark\") soliton stripes. In both cases, analytical predictions regarding\nthe stability and dynamics of these structures are obtained. One of our main\nfindings is the determination of the instability modes of the waves as a\nfunction of the parameters of the system (such as the trap strength and the\nchemical potential). Our analytical predictions are favorably compared with\nresults of direct numerical simulations.",
        "positive": "Interface dynamics of a two-component Bose-Einstein condensate driven by\n  an external force: The dynamics of an interface in a two-component Bose-Einstein condensate\ndriven by a spatially uniform time-dependent force is studied. Starting from\nthe Gross-Pitaevskii Lagrangian, the dispersion relation for linear waves and\ninstabilities at the interface is derived by means of a variational approach. A\nnumber of diverse dynamical effects for different types of the driving force is\ndemonstrated, which includes the Rayleigh-Taylor instability for a constant\nforce, the Richtmyer-Meshkov instability for a pulse force, dynamic\nstabilization of the Rayleigh-Taylor instability and onset of the parametric\ninstability for an oscillating force. Gaussian Markovian and non-Markovian\nstochastic forces are also considered. It is found that the Markovian\nstochastic force does not produce any average effect on the dynamics of the\ninterface, while the non-Markovian force leads to exponential perturbation\ngrowth."
    },
    {
        "anchor": "Signatures of bath-induced quantum avalanches in a many-body--localized\n  system: Strongly correlated systems can exhibit surprising phenomena when brought in\na state far from equilibrium. A spectacular example are quantum avalanches,\nthat have been predicted to run through a many-body--localized system and\ndelocalize it. Quantum avalanches occur when the system is locally coupled to a\nsmall thermal inclusion that acts as a bath. Here we realize an interface\nbetween a many-body--localized system and a thermal inclusion of variable size,\nand study its dynamics. We find evidence for accelerated transport into the\nlocalized region, signature of a quantum avalanche. By measuring the\nsite-resolved entropy we monitor how the avalanche travels through the\nlocalized system and thermalizes it site by site. Furthermore, we isolate the\nbath-induced dynamics by evaluating multipoint correlations between the bath\nand the system. Our results have fundamental implications on the robustness of\nmany-body--localized systems and their critical behavior.",
        "positive": "Simulation and detection of Weyl fermions in ultracold Fermi gases with\n  Raman-assisted spin-orbit coupling: Weyl fermion, also referred to as pseudo-magnetic monopole in momentum space,\nis an undiscovered massless elementary particle with half-integer spin\npredicted according to relativistic quantum field theory. Motivated by the\nrecent experimental observation of Weyl semimetal band in ultracold Bose gases\nwith Raman-assisted 3D spin-orbit coupling, we investigate the properties and\npossible observation of Weyl fermions in the low-energy quasi-particle\nexcitations of ultracold Fermi gases. Following a previous suggestion that the\nexisting Raman lattice scheme can be readily generalized to fermionic systems,\nhere we discuss the movement of the Weyl points in the Brillouin Zone, as well\nas the creation and annihilation of Weyl fermions by adjusting the effective\nZeeman field. The relevant topological properties are also demonstrated by\ncalculating the Chern number. Furthermore, we propose how to experimentally\nverify the existence of the Weyl fermions and the associated quantum phase\ntransition via density profile measurements."
    },
    {
        "anchor": "Nonholonomy of order parameters and su(3) vortices in spin-1\n  Bose-Einstein condensates: A generalized Mermin-Ho relation for a spin-1 BEC is derived, which is\napplicable to vortices regardless of the symmetry and spin polarization of the\norder parameter. The obtained relation implies an su(3) mass-current\ncirculation and two classes of vortices corresponding to two different su(2)\nsubalgebras.",
        "positive": "Nonlinear caging in All-Bands-Flat Lattices: We study the impact of classical short-range nonlinear interactions on\ntransport in lattices with no dispersion. The single particle band structure of\nthese lattices contains flat bands only, and cages non-interacting particles\ninto compact localized eigenstates. We demonstrate that there always exist\nlocal unitary transformations that detangle such lattices into decoupled sites\nin dimension one. Starting from a detangled representation, inverting the\ndetangling into entangling unitary transformations and extending to higher\nlattice dimensions, we arrive at an All-Bands-Flat generator for single\nparticle states in any lattice dimension. The entangling unitary\ntransformations are parametrized by sets of angles. For a given member of the\nset of all-bands-flat, additional short-range nonlinear interactions destroy\ncaging in general, and induce transport. However, fine-tuned subsets of the\nunitary transformations allow to completely restore caging. We derive the\nnecessary and sufficient fine-tuning conditions for nonlinear caging, and\nprovide computational evidence of our conclusions for one-dimensional systems."
    },
    {
        "anchor": "Adiabatic transport of Bose-Einstein condensate in double-well trap: A complete irreversible adiabatic transport of Bose-Einstein condensate (BEC)\nin a double-well trap is investigated within the mean field approximation. The\ntransfer is driven by time-dependent (Gaussian) coupling between the wells and\ntheir relative detuning. The protocol successfully works in a wide range of\nboth repulsive and attractive BEC interaction. The nonlinear effects caused by\nthe interaction can be turned from detrimental into favorable for the\ntransport. The results are compared with familiar Landau-Zener scenarios using\nthe constant coupling. It is shown that the pulsed Gaussian coupling provides a\nnew transport regime where coupling edges are decisive and convenient switch of\nthe transport is possible.",
        "positive": "Creation of ultracold Sr2 molecules in the electronic ground state: We report on the creation of ultracold 84Sr2 molecules in the electronic\nground state. The molecules are formed from atom pairs on sites of an optical\nlattice using stimulated Raman adiabatic passage (STIRAP). We achieve a\ntransfer efficiency of 30% and obtain 4x10^4 molecules with full control over\nthe external and internal quantum state. STIRAP is performed near the narrow\n1S0-3P1 intercombination transition, using a vibrational level of the 0u\npotential as intermediate state. In preparation of our molecule association\nscheme, we have determined the binding energies of the last vibrational levels\nof the 0u, 1u excited-state, and the 1\\Sigma_g^+ ground-state potentials. Our\nwork overcomes the previous limitation of STIRAP schemes to systems with\nFeshbach resonances, thereby establishing a route that is applicable to many\nsystems beyond bi-alkalis."
    },
    {
        "anchor": "Persistent oscillations of the order parameter and interaction quench\n  phase diagram for a confined Bardeen-Cooper-Schrieffer Fermi gas: We present a numerical study of the interaction quench dynamics in a\nsuperfluid ultracold Fermi gas confined in a three-dimensional cigar-shaped\nharmonic trap. In the present paper we investigate the amplitude mode of the\nsuperfluid order parameter after interaction quenches which start deep in the\nBCS phase and end in the BCS-BEC crossover regime. To this end, we exploit the\nBogoliubov-de Gennes formalism which takes the confinement potential explicitly\ninto account and provides a microscopic fully coherent description of the\nsystem. We find an anharmonic nonlinear oscillation of the modulus of the\nsuperfluid order parameter, i.e., of the Higgs mode. This oscillation persists\nfor large times with only a small amplitude modulation being visible. We\nconnect the frequency and the mean value of this oscillation with the breaking\nof Cooper pairs in the superfluid phase. Additionally, we demonstrate that the\noccurrence of this persistent oscillation is connected to the onset of chaotic\ndynamics in our model. Finally, we calculate an interaction quench phase\ndiagram of the Higgs mode for quenches on the BCS side of the BCS-BEC crossover\nand discuss its properties as a function of the aspect ratio of the\ncigar-shaped trap.",
        "positive": "Vortices in Fermi gases with spin-dependent rotation potentials: The rotation of two-component Fermi gases and the subsequent appearance of\nvortices have been the subject of numerous experimental and theoretical\nstudies. Recent experimental advances in hyperfine state-dependent potentials\nand highly degenerate heteronuclear Fermi gases suggest that it would be\nfeasible to create component-dependent rotation potentials in future\nexperiments. In this study we use an effective field theory for Fermi gases to\nconsider the effects of rotating only one component of the Fermi gas. We find\nthat the superfluid band gap in bulk exists up to higher rotation frequencies\nbecause the superfluid at rest, far away from the vortex, has to resist only\nhalf of the rotational effects. The vortex remains the energetically favorable\nstate above a critical frequency but exhibits a larger core size."
    },
    {
        "anchor": "Simulating two-dimensional dynamics within a large-size atomic spin: Encoding a dimension in the internal degree of freedom of an atom provides an\ninteresting tool for quantum simulation, facilitating the realization of\nartificial gauge fields. We propose an extension of the synthetic dimension\ntoolbox, making it possible to encode two dimensions within a large atomic\nspin. The protocol combines first- and second-order spin couplings, such that\nthe spin projection $m$ and the remainder $r=m$ (mod 3) of its Euclidian\ndivision by 3 act as orthogonal coordinates on a synthetic cylinder. It is\nsuited for an implementation with lanthanide atoms, which feature a large\nelectronic spin and narrow optical transitions for applying the required spin\ncouplings. This method is useful for simulating geometries with periodic\nboundary conditions, and engineering various types of topological systems\nevolving in high dimensions.",
        "positive": "Splitting dynamics of giant vortices in dilute Bose-Einstein condensates: We study the splitting of multiply quantized vortices with large quantum\nnumbers in dilute nonrotated Bose-Einstein condensates in the zero-temperature\nlimit. The splitting is observed to result in vortex-free condensate fragments\nwhich are separated by vortex sheets. The number of these fragments is found to\nbe equal to the angular-momentum quantum number of the Bogoliubov excitation\nmode responsible for the splitting, although the formulation of the fragments\ncannot be described by small-amplitude excitations. Thus, the realization of an\nisolated giant vortex and the observation of its splitting would provide a\nmeans to directly relate the experimental data to discrete theoretical\nquantities."
    },
    {
        "anchor": "Optical Lattice Hamiltonians for Relativistic Quantum Electrodynamics: We show how interpenetrating optical lattices containing Bose-Fermi mixtures\ncan be constructed to emulate the thermodynamics of quantum electrodynamics\n(QED). We present models of neutral atoms on lattices in 1+1, 2+1 and 3+1\ndimensions whose low energy effective action reduces to that of photons coupled\nto Dirac fermions of the corresponding dimensionality. We give special\nattention to 2+1 dimensional electrodynamics (QED3) and discuss how two of its\nmost interesting features, chiral symmetry breaking and Chern-Simons physics,\ncould be observed experimentally.",
        "positive": "Internal Josephson Effects in Spinor Dipolar Bose--Einstein Condensates: We theoretically study the internal Josephson effect, which is driven by spin\nexchange interactions and magnetic dipole-dipole interactions, in a three-level\nsystem for spin-1 Bose--Einstein condensates, obtaining novel spin dynamics. We\nintroduce single spatial mode approximations into the Gross--Pitaevskii\nequations and derive the Josephson type equations, which are analogous to\ntunneling currents through three junctions between three superconductors. From\nan analogy with two interacting nonrigid pendulums, we identify unique varied\noscillational modes, called the 0--$\\pi$, 0--$running$, $running$--$running$,\n$2n\\pi & running$--$2\\pi$, $single nonrigid pendulum$, and $two rigid\npendulums$ phase modes. These Josephson modes in the three states are expected\nto be found in real atomic Bose gas systems."
    },
    {
        "anchor": "Oblique solitons in the flow of polariton condensate past an obstacle: Formation of oblique solitons by a flow of polariton condensate past an\nobstacle is considered. The flow is non-uniform due to a finite life-time of\npolaritons what changes drastically the conditions of formation of oblique\nsolitons compared with the atomic condensate case. The theory shows that the\npolariton solitons can be generated by a subsonic flow in agreement with the\nrecent experiment [A. Amo {\\it et al.}, Science, {\\bf 332,} 1167 (2011)].\nGeometric form of oblique solitons and other their parameters are calculated\nanalytically and analytical results are confirmed by numerical simulations.",
        "positive": "Formation of Bose-Einstein condensates: The problem of understanding how a coherent, macroscopic Bose-Einstein\ncondensate (BEC) emerges from the cooling of a thermal Bose gas has attracted\nsignificant theoretical and experimental interest over several decades. The\npioneering achievement of BEC in weakly-interacting dilute atomic gases in 1995\nwas followed by a number of experimental studies examining the growth of the\nBEC number, as well as the development of its coherence. More recently there\nhas been interest in connecting such experiments to universal aspects of\nnonequilibrium phase transitions, in terms of both static and dynamical\ncritical exponents. Here, the spontaneous formation of topological structures\nsuch as vortices and solitons in quenched cold-atom experiments has enabled the\nverification of the Kibble-Zurek mechanism predicting the density of\ntopological defects in continuous phase transitions, first proposed in the\ncontext of the evolution of the early universe. This chapter reviews progress\nin the understanding of BEC formation, and discusses open questions and future\nresearch directions in the dynamics of phase transitions in quantum gases."
    },
    {
        "anchor": "Coherent multiple scattering of out-of-equilibrium interacting Bose\n  gases: We review recent theoretical and experimental progresses in the coherent\nmultiple scattering of weakly interacting disordered Bose gases. These systems\nhave allowed, in the recent years, a characterization of weak and strong\nlocalization phenomena in disorder at an unprecedented level of control. In\nthis paper, we first discuss the main physical concepts and recent experimental\nachievements associated with a few emblematic \"mesoscopic\" effects in disorder\nlike coherent back scattering, coherent forward scattering or mesoscopic echos,\nfocusing on the context of out-of-equilibrium cold-atom setups. We then address\nthe role of weak particle interactions and explain how, depending on their\nrelative strength with respect to the disorder and on the time scales probed,\nthey can give rise to a dephasing mechanism for weak localization, thermalize a\nnon-equilibrium Bose gas or make it become a superfluid.",
        "positive": "Bipolarons and multi-polarons consisting of impurity atoms in a\n  Bose-Einstein condensate: The variational Feynman formalism for the polaron, extended to an\nall-coupling treatment of bipolarons, is applied for two impurity atoms in a\nBose-Einstein condensate. This shows that if the polaronic coupling strength is\nlarge enough the impurities will form a bound state (the bipolaron). As a\nfunction of the mutual repulsion between the impurities two types of bipolaron\nare distinguished: a tightly bound bipolaron at weak repulsion and a dumbbell\nbipolaron at strong repulsion. Apart from the binding energy, also the\nevolution of the bipolaron radius and its effective mass are examined as a\nfunction of the strength of the repulsive interaction between the impurities\nand of the polaronic cupling strength. We then apply the strong-coupling\nformalism to multiple impuritiy atoms in a condensate which leads to the\nprediction of multi-polaron formation in the strong coupling regime. The\nresults of the two formalisms are compared for two impurities in a condensate\nwhich results in a general qualitative agreement and a quantitative agreement\nat strong coupling. Typically the system of impurity atoms in a Bose-Einstein\ncondensate is expected to exhibit the polaronic weak coupling regime. However,\nthe polaronic coupling strength is in principle tunable with a Feshbach\nresonance."
    },
    {
        "anchor": "Drude weight and the many-body quantum metric in one-dimensional Bose\n  systems: We study the effect of quantum geometry on the many-body ground state of\none-dimensional interacting bosonic systems. We find that the Drude weight is\ngiven by the sum of the kinetic energy and a term proportional to the many-body\nquantum metric of the ground state. Notably, the many-body quantum metric\ndetermines the upper bound of the Drude weight. We validate our results on the\nCreutz ladder, a flat band model, using exact diagonalization at half and unit\ndensities. Our work sheds light on the importance of the many-body quantum\ngeometry in one-dimensional interacting bosonic systems.",
        "positive": "Tunable Fr\u00f6hlich Polarons of slow-light polaritons in a\n  two-dimensional Bose-Einstein condensate: When an impurity interacts with a bath of phonons it forms a polaron. For\nincreasing interaction strengths the mass of the polaron increases and it can\nbecome self-trapped. For impurity atoms inside an atomic Bose-Einstein\ncondensate (BEC) the nature of this transition is subject of debate. While\nFeynman's variational approach predicts a sharp transition for light\nimpurities, renormalization group studies always predict an extended\nintermediate-coupling region characterized by large phonon correlations. To\ninvestigate this intricate regime we suggest a versatile experimental setup\nthat allows to tune both the mass of the impurity and its interactions with the\nBEC. The impurity is realized as a dark-state polariton (DSP) inside a quasi\ntwo-dimensional BEC. We show that its interactions with the Bogoliubov phonons\nlead to photonic polarons, described by the Bogoliubov-Fr\\\"ohlich Hamiltonian,\nand make theoretical predictions using an extension of a recently introduced\nrenormalization group approach to Fr\\\"ohlich polarons."
    },
    {
        "anchor": "Multi-frequency optical lattice for dynamic lattice-geometry control: Ultracold atoms in optical lattices are pristine model systems with a\ntunability and flexibility that goes beyond solid-state analogies, e.g.,\ndynamical lattice-geometry changes allow tuning a graphene lattice into a\nboron-nitride lattice. However, a fast modulation of the lattice geometry\nremains intrinsically difficult. Here we introduce a multi-frequency lattice\nfor fast and flexible lattice-geometry control and demonstrate it for a\nthree-beam lattice, realizing the full dynamical tunability between honeycomb\nlattice, boron-nitride lattice and triangular lattice. At the same time, the\nscheme ensures intrinsically high stability of the lattice geometry. We\nintroduce the concept of a geometry phase as the parameter that fully controls\nthe geometry and observe its signature as a staggered flux in a momentum space\nlattice. Tuning the geometry phase allows to dynamically control the sublattice\noffset in the boron-nitride lattice. We use a fast sweep of the offset to\ntransfer atoms into higher Bloch bands, and perform a new type of Bloch band\nspectroscopy by modulating the sublattice offset. Finally, we generalize the\ngeometry phase concept and the multi-frequency lattice to three-dimensional\noptical lattices and quasi-periodic potentials. This scheme will allow further\napplications such as novel Floquet and quench protocols to create and probe,\ne.g., topological properties.",
        "positive": "Mobile impurities in integrable models: We use a mobile impurity or depleton model to study elementary excitations in\none-dimensional integrable systems. For Lieb-Liniger and bosonic Yang-Gaudin\nmodels we express two phenomenological parameters characterising renormalised\ninter- actions of mobile impurities with superfluid background: the number of\ndepleted particles, $N$ and the superfluid phase drop $\\pi J$ in terms of the\ncorresponding Bethe Ansatz solution and demonstrate, in the leading order, the\nabsence of two-phonon scattering resulting in vanishing rates of inelastic\nprocesses such as viscosity experienced by the mobile impurities"
    },
    {
        "anchor": "Phonon spectrum and correlations in a transonic flow of an atomic Bose\n  gas: Motivated by a recent experiment of J.~Steinhauer, we reconsider the spectrum\nand the correlations of the phonons spontaneously emitted in stationary\ntransonic flows. The latter are described by \"waterfall\" configurations which\nform a one-parameter family of stable flows. For parameters close to their\nexperimental values, in spite of high gradients near the sonic horizon, the\nspectrum is accurately planckian in the relevant frequency domain, where the\ntemperature differs from the relativistic prediction by less than $10 \\%$. We\nthen study the density correlations across the horizon and the non-separable\ncharacter of the final state. We show that the relativistic expressions provide\naccurate approximations when the initial temperature is not too high. We also\nshow that the phases of the scattering coefficients introduce a finite shift of\nthe location of the correlations which was so far overlooked. This shift is due\nto the asymmetry of the flow across the horizon, and persists in the\ndispersion-less regime. Finally we show how the formation of the sonic horizon\nmodifies both local and non-local density correlations.",
        "positive": "Threshold for creating excitations in a stirred superfluid ring: We have measured the threshold for creating long-lived excitations when a\ntoroidal Bose-Einstein condensate is stirred by a rotating (optical) barrier of\nvariable height. When the barrier height is on the order of or greater than\nhalf of the chemical potential, the critical barrier velocity at which we\nobserve a change in the circulation state is much less than the speed for sound\nto propagate around the ring. In this regime we primarily observe discrete\njumps (phase slips) from the non-circulating initial state to a simple,\nwell-defined, persistent current state. For lower barrier heights, the critical\nbarrier velocity at which we observe a change in the circulation state is\nhigher, and approaches the effective sound speed for vanishing barrier height.\nThe response of the condensate in this small-barrier regime is more complex,\nwith vortex cores appearing in the bulk of the condensate. We find that the\nvariation of the excitation threshold with barrier height is in qualitative\nagreement with the predictions of an effective 1D hydrodynamic model."
    },
    {
        "anchor": "Fermi-to-Bose crossover in a trapped quasi-2D gas of fermionic atoms: Physics of many-body systems where particles are restricted to move in two\nspatial dimensions is challenging and even controversial: On one hand, neither\nlong-range order nor Bose condensation may appear in infinite uniform 2D\nsystems at finite temperature, on the other hand this does not prohibit\nsuperfluidity or superconductivity. Moreover, 2D superconductors, such as\ncuprates, are among the systems with highest critical temperatures. Ultracold\natoms are a platform for studying 2D physics. Uniquely to other physical\nsystems, quantum statistics may be completely changed in an ultracold gas: an\natomic Fermi gas may be smoothly crossed over into a gas of Bose molecules (or\ndimers) by tuning interatomic interactions. We review recent experiments where\nsuch crossover has been demonstrated as well as critical phenomena in the\nFermi-to-Bose crossover. We also present simple theoretical models describing\nthe gas at different points of the crossover and compare the data to these and\nmore advanced models.",
        "positive": "Variational methods with coupled Gaussian functions for Bose-Einstein\n  condensates with long-range interactions. II. Applications: Bose-Einstein condensates with an attractive 1/r interaction and with\ndipole-dipole interaction are investigated in the framework of the Gaussian\nvariational ansatz introduced by S. Rau, J. Main, and G. Wunner [Phys. Rev. A,\nsubmitted]. We demonstrate that the method of coupled Gaussian wave packets is\na full-fledged alternative to direct numerical solutions of the\nGross-Pitaevskii equation, or even superior in that coupled Gaussians are\ncapable of producing both, stable and unstable states of the Gross-Pitaevskii\nequation, and thus of giving access to yet unexplored regions of the space of\nsolutions of the Gross-Pitaevskii equation. As an alternative to numerical\nsolutions of the Bogoliubov-de Gennes equations, the stability of the\nstationary condensate wave functions is investigated by analyzing the stability\nproperties of the dynamical equations of motion for the Gaussian variational\nparameters in the local vicinity of the stationary fixed points. For\nblood-cell-shaped dipolar condensates it is shown that on the route to collapse\nthe condensate passes through a pitchfork bifurcation, where the ground state\nitself turns unstable, before it finally vanishes in a tangent bifurcation."
    },
    {
        "anchor": "Spontaneous symmetry breaking of fundamental states, vortices, and\n  dipoles in two- and one-dimensional linearly coupled traps with cubic\n  self-attraction: We introduce two- and one-dimensional (2D and 1D) systems of two\nlinearly-coupled Gross-Pitaevskii equations (GPEs) with the cubic\nself-attraction and harmonic-oscillator (HO) trapping potential in each GPE.\nThe system models a Bose-Einstein condensate with a negative scattering length,\nloaded in a double-pancake trap, combined with the in-plane HO potential. In\naddition to that, the 1D version applies to the light transmission in a\ndual-core waveguide with the Kerr nonlinearity and in-core confinement\nrepresented by the HO potential. The subject of the analysis is spontaneous\nsymmetry breaking in 2D and 1D ground-state (GS, alias fundamental) modes, as\nwell as in 2D vortices and 1D dipole modes (the latter ones do not exist\nwithout the HO potential). By means of the variational approximation and\nnumerical analysis, it is found that both the 2D and 1D systems give rise to a\nsymmetry-breaking bifurcation (SBB) of the supercrtical type. Stability of\nsymmetric states and asymmetric ones, produced by the SBB, is analyzed through\nthe computation of eigenvalues for perturbation modes, and verified by direct\nsimulations. The asymmetric GSs are always stable, while the stability region\nfor vortices shrinks and eventually disappears with the increase of the\nlinear-coupling constant, $ \\kappa $. The SBB in the 2D system does not occur\nif $\\kappa $ is too large (at $\\kappa >\\kappa_{\\max }$); in that case, the\ntwo-component system behaves, essentially, as its single-component counterpart.\nIn the 1D system, both asymmetric and symmetric dipole modes feature an\nadditional oscillatory instability, unrelated to the symmetry breaking. This\ninstability occurs in several regions, which expand with the increase of\n$\\kappa $.",
        "positive": "Order from chaos: Observation of large-scale flow from turbulence in a\n  two-dimensional superfluid: Interacting systems driven far from equilibrium tend to evolve to steady\nstates exhibiting large-scale structure and order. In two-dimensional turbulent\nflow the seemingly random swirling motion of a fluid can evolve towards\npersistent large-scale vortices. Lars Onsager proposed a model based on\nstatistical mechanics of quantized vortices to explain such behavior. Here we\nreport the first experimental confirmation of Onsager's model of turbulence. We\ndrag a grid barrier through an oblate superfluid Bose--Einstein condensate to\ngenerate non-equilibrium distributions of vortices. We observe an inverse\nenergy cascade driven by the evaporative heating of vortices, leading to\nsteady-state configurations characterized by negative temperatures. Our results\nopen a pathway for quantitative studies of emergent structures in interacting\nquantum systems driven far from equilibrium."
    },
    {
        "anchor": "Reaching Fractional Quantum Hall States with Optical Flux Lattices: We present a robust scheme by which fractional quantum Hall states of bosons\ncan be achieved for ultracold atomic gases. We describe a new form of optical\nflux lattice, suitable for commonly used atomic species with groundstate\nangular momentum $J_g = 1$, for which the lowest energy band is topological and\nnearly dispersionless. Through exact diagonalization studies, we show that,\neven for moderate interactions, the many-body groundstates consist of bosonic\nfractional quantum Hall states, including the Laughlin state and the Moore-Read\n(Pfaffian) state. Under realistic conditions, these phases are shown to have\nenergy gaps that are larger than temperature scales achievable in ultracold\ngases.",
        "positive": "One-dimensional Bose-Hubbard model with local three-body interactions: We employ the (dynamical) density matrix renormalization group technique to\ninvestigate the ground-state properties of the Bose-Hubbard model with\nnearest-neighbor transfer amplitudes t and local two-body and three-body\nrepulsion of strength U and W, respectively. We determine the phase boundaries\nbetween the Mott-insulating and superfluid phases for the lowest two Mott lobes\nfrom the chemical potentials. We calculate the tips of the Mott lobes from the\nTomonaga-Luttinger liquid parameter and confirm the positions of the\nKosterlitz-Thouless points from the von Neumann entanglement entropy. We find\nthat physical quantities in the second Mott lobe such as the gap and the\ndynamical structure factor scale almost perfectly in t/(U+W), even close to the\nMott transition. Strong-coupling perturbation theory shows that there is no\ntrue scaling but deviations from it are quantitatively small in the\nstrong-coupling limit. This observation should remain true in higher dimensions\nand for not too large attractive three-body interactions."
    },
    {
        "anchor": "Spinor bosons in optical superlattices: a numerical study: The ground state of spin-1 ultracold bosons trapped in a periodic\none-dimensional optical superlattice is studied. The two sites of the unit cell\nhave an energy shift between them, whose competition with the spin-dependent\nstrength is the main focus of this paper. Charge density wave (CDW) phases\nappear for semi-integer and integer densities, leading to rich phase diagrams\nwith Mott insulator, superfluid and CDW phases. The spin-dependent interaction\nfavors insulator phases for integer densities and disfavors CDW phases for\nsemi-integer densities, which tend to disappear. Also, quantum phase\ntransitions at finite values of the spin-dependent strength were observed. For\ninteger densities, Mott insulator-superfluid-CDW insulator transitions appear\nfor an energy shift lower (higher) than the local repulsion for the global\ndensity $\\rho=1$ ($\\rho=2$).",
        "positive": "Exact solution for the degenerate ground-state manifold of a strongly\n  interacting one-dimensional Bose-Fermi mixture: We present the exact solution for the many-body wavefunction of a\none-dimensional mixture of bosons and spin-polarized fermions with equal masses\nand infinitely strong repulsive interactions under external confinement. Such a\nmodel displays a large degeneracy of the ground state. Using a generalized\nBose-Fermi mapping we find the solution for the whole set of ground-state\nwavefunctions of the degenerate manifold and we characterize them according to\ngroup-symmetry considerations. We find that the density profile and the\nmomentum distribution depends on the symmetry of the solution. By combining the\nwavefunctions of the degenerate manifold with suitable symmetry and guided by\nthe strong-coupling form of the Bethe-Ansatz solution for the homogeneous\nsystem we propose an analytic expression for the many-body wavefunction of the\ninhomogeneous system which well describes the ground state at finite, large and\nequal interactions strengths, as validated by numerical simulations."
    },
    {
        "anchor": "Resonant Pairing of Excitons in Semiconductor Heterostructures: We suggest indirect excitons in 2D semiconductor heterostructures as a\nplatform for realization of a bosonic analog of the Bardeen-Cooper-Schrieffer\nsuperconductor. The quantum phase transition to a biexcitonic gapped state can\nbe controlled in situ by tuning the electric field applied to the structure in\nthe growth direction. The proposed playground should allow one to go to\nstrongly correlated and high-temperature regimes, unattainable with Feshbach\nresonant atomic gases.",
        "positive": "Self-adapted Floquet Dynamics of Ultracold Bosons in a Cavity: Floquet dynamics of a quantum system subject to periodic modulations of\nsystem parameters provide a powerful tool for engineering new quantum matter\nwith exotic properties. While system dynamics are significantly altered, the\nperiodic modulation itself is usually induced externally and independent of\nFloquet dynamics. Here we propose a new type of Floquet physics for a\nBose-Einstein condensate (BEC) subject to a shaken lattice generated inside a\ncavity, where the shaken lattice and atomic Floquet bands are mutually\ndependent, resulting in self-adapted Floquet dynamics. In particular, the\nshaken lattice induces Floquet quasi-energy bands for the BEC, whose back\naction leads to a self-adapted dynamical normal-superradiant phase transition\nfor the shaken lattice. Such self-adapted Floquet dynamics show two surprising\nand unique features: \\textit{i}) the normal-superradiant phase transition\npossesses a hysteresis even without atom interactions; \\textit{ii}) the\ndynamical atom-cavity steady state could exist at free energy maxima. The atom\ninteractions strongly affect the phase transition of the BEC from zero to\nfinite momenta. Our results provide a powerful platform for exploring\nself-adapted Floquet dynamics, which may open an avenue for engineering novel\nquantum materials."
    },
    {
        "anchor": "Decoherence of Impurities in a Fermi Sea of Ultracold Atoms: We investigate the decoherence of $^{40}$K impurities interacting with a\nthree-dimensional Fermi sea of $^{6}$Li across an interspecies Feshbach\nresonance. The decoherence is measured as a function of the interaction\nstrength and temperature using a spin-echo atom interferometry method. For weak\nto moderate interaction strengths, we interpret our measurements in terms of\nscattering of K quasiparticles by the Fermi sea and find very good agreement\nwith a Fermi liquid calculation. For strong interactions, we observe\nsignificant enhancement of the decoherence rate, which is largely independent\nof temperature, pointing to behavior that is beyond the Fermi liquid picture.",
        "positive": "Quantum relaxation and metastability of lattice bosons with\n  cavity-induced long-range interactions: The coupling of cold atoms to the radiation field within a high-finesse\noptical resonator, an optical cavity, induces long-range interactions which can\ncompete with an underlying optical lattice. The interplay between short- and\nlong-range interactions gives rise to new phases of matter including\nsupersolidity (SS) and density waves (DW), and interesting quantum dynamics.\nHere it is shown that for hard-core bosons in one dimension the ground state\nphase diagram and the quantum relaxation after sudden quenches can be\ncalculated exactly in the thermodynamic limit. Remanent DW order is observed\nfor quenches from a DW ground state into the superfluid (SF) phase below a\ndynamical transition line. After sufficiently strong SF to DW quenches beyond a\nstatic metastability line DW order emerges on top of remanent SF order, giving\nrise to a dynamically generated supersolid state."
    },
    {
        "anchor": "Localized-Interaction-Induced Quantum Reflection and Filtering of\n  Bosonic Matter in a One-Dimensional Lattice Guide: We study the dynamics of quantum bosonic waves confined in a one-dimensional\ntilted optical lattice. The bosons are under the action of an effective\nspatially localized nonlinear two-body potential barrier set in the central\npart of the lattice. This version of the Bose-Hubbard model can be realized in\natomic Bose-Einstein condensates, by means of localized Feshbach resonance, and\nin quantum optics, using an arrayed waveguide with selectively doped guiding\ncores. Our numerical analysis demonstrates that the central barrier induces\nanomalous quantum reflection of incident wave packets acting solely on bosonic\ncomponents with multiple onsite occupancies. From the other side\nsingle-occupancy components can pass the barrier thus allowing one to distill\nthem in the central interacting zone. As a consequence, in this region one\nfinds a state in which the multiple occupancy is forbidden, i.e., a\nTonks-Girardeau gas. Our results demonstrate that this regime can be obtained\ndynamically, using relatively weak interactions, irrespective of their sign.",
        "positive": "Many-body dynamical localization and thermalization: We show that a quantum dynamical localization effect can be observed in a\ngeneric thermalization process of two weakly-coupled chaotic subsystems.\nSpecifically, our model consists of the minimal experimentally relevant\nsubsystems that exhibit chaos, which are 3-site Bose-Hubbard units. Due to the\nhigh dimensionality of the composite 6-site system, the quantum localization\neffect is weak and can not be resolved merely by the breakdown of\nquantum-to-classical correspondence. Instead, we adopt an intrinsic definition\nof localization as the memory of initial conditions, that is not related to the\nunderlying classical dynamics. We discuss the dynamics in the chaotic sea, and\nin the vicinity of the mobility edge, beyond which ergodization is suppressed."
    },
    {
        "anchor": "Spin-dependent Bragg spectroscopy of a spinor Bose gas: We develop a general theory of spin-dependent Bragg spectroscopy for spinor\nBose-Einstein condensates. This spectroscopy involves using a density and\nspin-coupled optical probe to excite the system. We show that within the linear\nresponse regime the momentum or energy transferred by the probe is determined\nby a set of density and spin-density dynamic structure factors. We derive a set\nof $f$-sum rules that provide rigorous constraints for the first energy moments\nof these structure factors. As an application we compute the dynamic structure\nfactors for cases within all four distinct phases of a spin-1 condensate using\nBogoliubov theory. Our results demonstrate that spin-dependent Bragg\nspectroscopy can be used to selectively investigate the various phonon and\nmagnon excitation branches and will be a useful tool for advancing our\nunderstanding of spinor condensates.",
        "positive": "Two-component Bose gas trapped by harmonic and annular potentials:\n  Supercurrent, vortex flow and instability of superfluidity by Rabi coupling: In this paper, we study a system of two-component Bose gas in an artificial\nmagnetic field trapped by concentric harmonic and annular potentials,\nrespectively. The system is realized by gases with two-internal states like the\nhyperfine states of $^{87}$Rb. We are interested in effects of a Rabi\noscillation between them. Two-component Bose Hubbard model is introduced to\ndescribe the system, and Gross-Pitaevskii equations are used to study the\nsystem. We first study the Bose gas system in the annular trap by varying the\nwidth of the annulus and strength of the magnetic field, in particular, we\nfocus on the phase slip and superflow. Then we consider the coupled Bose gas\nsystem in a magnetic field. In a strong magnetic field, vortices form a\nAbrikosov triangular lattice in both Bose-Einstein condensates (BECs), and\nlocations of vortices in the BECs correlate with each other by the Rabi\ncoupling. However, as the strength of the Rabi coupling is increased, vortices\nstart to vibrate around their equilibrium locations. As the strength is\nincreased further, vortices in the harmonic trap start to move along the\nboundaries of the annulus. Finally for a large Rabi coupling, the BECs are\ndestroyed. Based on our findings about the BEC in the annular trap, we discuss\nthe origin of above mentioned phenomena."
    },
    {
        "anchor": "Dynamical quantum phase transition in a bosonic system with long-range\n  interactions: In this paper, we investigate the dynamical quantum phase transitions\nappearing in the Loschmidt echo and the time-dependent order parameter of a\nquantum system of harmonically coupled degenerate bosons as a function of the\npower-law decay $\\sigma$ of long-range interactions. Following a sudden quench,\nthe nonequilibrium dynamics of this system are governed by a set of nonlinear\ncoupled Ermakov equations. To solve them, we develop an analytical\napproximation valid at late times. Based on this approximation, we show that\nthe emergence of a dynamical quantum phase transition hinges on the generation\nof a finite mass gap following the quench, starting from a massless initial\nstate. In general, we can define two distinct dynamical phases characterized by\nthe finiteness of the post-quench mass gap. The Loschmidt echo exhibits\nperiodical nonanalytic cusps whenever the initial state has a vanishing mass\ngap and the final state has a finite mass gap. These cusps are shown to\ncoincide with the maxima of the time-dependent long-range correlations.",
        "positive": "Relationship between the transverse-field Ising model and the XY model\n  via the rotating-wave approximation: In a large transverse field, there is an energy cost associated with flipping\nspins along the axis of the field. This penalty can be employed to relate the\ntransverse-field Ising model in a large field to the XY model in no field (when\nmeasurements are performed at the right stroboscopic times). We describe the\ndetails for how this relationship works and, in particular, we also show under\nwhat circumstances it fails. We examine wavefunction overlap between the two\nmodels and observables, such as spin-spin Green's functions. In general, the\nmapping is quite robust at short times, but will ultimately fail if the run\ntime becomes too long. There is also a trade-off between the length of time one\ncan run a simulation out to and the time jitter of the stroboscopic\nmeasurements that must be balanced when planning to employ this mapping."
    },
    {
        "anchor": "Controllable splitting dynamics of a doubly quantized vortex in a\n  rotating ring-shaped condensate: We study the dynamics of a doubly quantized vortex (DQV), created by\nreleasing a ring-shaped Bose-Einstein condensate with quantized circulation\ninto harmonic potential traps. It is shown that a DQV can be generated and\nexists stably in the middle of the ring-shaped condensate with the initial\ncirculation $s = 2$ after released into the rotationally symmetric trap\npotential. For an asymmetric trap with a small degree of anisotropy the DQV\ninitially splits into two singly quantized vortices and revives again but\neventually evolves into two unit vortices due to the dynamic instability. For\nthe degree of anisotropy above a critical value, the DQV is extremely unstably\nand decays rapidly into two singlet vortices. The geometry-dependent lifetime\nof the DQV and vortex-induced excitations are also discussed intensively.",
        "positive": "Few-body bound state stability of dipolar molecules in two dimensions: Bound structures among dipolar molecules in multilayers are a topic of great\ninterest in the light of recent experiments that have demonstrated the\nfeasibility of the setup. While it is known that two molecules in two adjacent\nlayers will always bind, larger complexes have only been scarcely addressed\nthus far. Here we prove rigorously that three- and four-body states will never\nbe bound when the dipoles are oriented perpendicular to the layers. The\ntechnique employed is general and can be used for more molecules/layers and\nother geometries. Our analytical findings are supported by numerical\ncalculations for both fermionic and bosonic molecules. Furthermore, we\ncalculate the reduction in intralayer repulsion necessary to bind large\ncomplexes and estimate the influence of bound complexes in systems with many\nlayers."
    },
    {
        "anchor": "Bose Einstein condensation and superfluidity in an open system: theory: We propose a new theoretical formalism which describes the Bose Einstein\ncondensation of weakly interacting bosons with finite life time interacting\nwith a thermal bath. We show that if a quasi-thermal distribution function of\nparticles is achieved, the elementary excitations of the condensate show a\nlinear spectrum characteristic of a superfluid, with a renormalized sound\nvelocity with respect to the equilibrium case.",
        "positive": "Strongly Spinor Ferromagnetic Bose Gases: By studying the zero-temperature and nonzero-temperature phase diagrams of\nthe ferromagnetic spin-1 Bose-Hubbard model under an external magnetic field,\nwe find that the competition between ferromagnetism and the quadratic Zeeman\nenergy yields two superfluid phases, which feature discontinuous first-order\nphase transitions between them for a strongly spinor Bose gas such as ${}^7$Li,\ncontrary to the corresponding continuum system."
    },
    {
        "anchor": "Unconventional pairing in few-fermion systems at finite temperature: Attractively interacting two-component mixtures of fermionic particles\nconfined in a one-dimensional harmonic trap are investigated. Properties of\nbalanced and imbalanced systems are systematically explored with the exact\ndiagonalization approach, focusing on the finite-temperature effects. Using\nsingle- and two-particle density distributions, specific non-classical pairing\ncorrelations are analyzed in terms of the noise correlations -- quantity\ndirectly accessible in state-of-the-art experiments with ultra-cold atoms. It\nis shown that along with increasing temperature, any imbalanced system hosting\nFulde-Ferrel-Larkin-Ovchinnikov pairs crossovers to a standard\nBardeen-Cooper-Schrieffer one characterized by zero net momentum of resulting\npairs. By performing calculations for systems with different imbalances, the\napproximate boundary between the two phases on a phase diagram is determined.",
        "positive": "Emergence of Classical Rotation in Superfluid Bose-Einstein Condensates: Phase transitions can modify quantum behaviour on mesoscopic scales and give\naccess to new and unusual quantum dynamics. Here we investigate the superfluid\nproperties of a rotating two-component Bose--Einstein condensate as a function\nof changes in the interaction energy and in particular through the phase\ntransition from miscibility to immiscibility. We show that the breaking of one\nof the hallmarks of superfluid flow, namely the quantisation condition on\ncirculation, is continuous throughout an azimuthal phase separation process and\ndisplays intriguing density dynamics. We find that the resulting currents are\nstable for long times and possess a phase boundary that exhibits classical\nsolid body rotation, despite the quantum nature of superfluid flow. To support\nthis co-existence of classical and quantum behaviour the system develops a\nunique velocity flow profile, which includes unusual radial flow in regions\nnear the phase boundary."
    },
    {
        "anchor": "Zero-energy states in rotating trapped Bose-Einstein condensates: We have calculated low-lying quasiparticle excitation spectra of rotating\nthree-dimensional Bose-Einstein condensates. As opposed to the prediction of\nhydrodynamic continuum theories, we find a minimum in the Tkachenko mode\nspectrum at intermediate rotation frequencies of the harmonic trap. Such a\nminimum can harbour a Tkachenko quasiparticle with zero excitation energy. We\ndiscuss the experimental signatures of such a zero mode.",
        "positive": "Spatial order in a two-dimensional spin-orbit-coupled spin-1/2\n  condensate: superlattice, multi-ring and stripe formation: We demonstrate the formation of stable spatially-ordered states in a {\\it\nuniform} and also {\\it trapped} quasi-two-dimensional (quasi-2D) Rashba or\nDresselhaus spin-orbit (SO) coupled pseudo spin-1/2 Bose-Einstein condensate\nusing the mean-field Gross-Pitaevskii equation. For weak SO coupling, one can\nhave a circularly-symmetric $(0,+1)$- or $(0,-1)$-type multi-ring state with\nintrinsic vorticity, for Rashba or Dresselhaus SO coupling, respectively, where\nthe numbers in the parentheses denote the net angular momentum projection in\nthe two components, in addition to a circularly-asymmetric degenerate state\nwith zero net angular momentum projection. For intermediate SO couplings, in\naddition to the above two types, one can also have states with stripe pattern\nin component densities with no periodic modulation in total density. The stripe\nstate continues to exist for large SO coupling. In addition, a new\nspatially-periodic state appears in the uniform system: a superlattice state,\npossessing some properties of a supersolid, with a square-lattice pattern in\ncomponent densities and also in total density. In a trapped system the\nsuperlattice state is slightly different with multi-ring pattern in component\ndensity and a square-lattice pattern in total density. For an equal mixture of\nRashba and Dresselhaus SO couplings, in both uniform and trapped systems, only\nstripe states are found for all strengths of SO couplings. In a uniform system\nall these states are quasi-2D solitonic states."
    },
    {
        "anchor": "Supersolid behavior in one-dimensional self-trapped Bose-Einstein\n  condensate: Supersolid is an exotic state of matter, showing crystalline order with a\nsuperfluid background, observed recently in dipolar Bose-Einstein condensate\n(BEC) in a trap. Here, we present exact solutions of the desired Bloch form in\nthe self-trapped free-floating quantum fluid. Our general solutions of the\namended nonlinear Schr{\\\"o}dinger equation, governing the mean-field and beyond\nmean-field dynamics, are obtained through a M{\\\"o}bius transform, connecting a\nwide class of supersolid solutions to the ubiquitous cnoidal waves. The\nsolutions yield the constant condensate, supersolid behavior and the\nself-trapped droplet in different parameter domains. The lowest residual\ncondensate is found to be exactly one-third of the constant background.",
        "positive": "Phase diagram of two-component dipolar fermions in one-dimensional\n  optical lattices: We theoretically map out the ground state phase diagram of interacting\ndipolar fermions in one-dimensional lattice. Using a bosonization theory in the\nweak coupling limit at half filing, we show that one can construct a rich phase\ndiagram by changing the angle between the lattice orientation and the\npolarization direction of the dipoles. In the strong coupling limit, at a\ngeneral filing factor, we employ a variational approach and find that the\nemergence of a Wigner crystal phases. The structure factor provides clear\nsignatures of the particle ordering in the Wigner crystal phases."
    },
    {
        "anchor": "Superfluid drag in the two-component Bose-Hubbard model: In multicomponent superfluids and superconductors, co- and counter-flows of\ncomponents have in general different properties. It was discussed in 1975 by\nAndreev and Bashkin, in the context of He$^3$/He$^4$ superfluid mixtures, that\ninter-particle interactions produce a dissipationless drag. The drag can be\nunderstood as a superflow of one component induced by phase gradients of the\nother component. Importantly the drag can be both positive (entrainment) and\nnegative (counter-flow). The effect is known to be of crucial importance for\nmany properties of diverse physical systems ranging from the dynamics of\nneutron stars, rotational responses of Bose mixtures of ultra-cold atoms to\nmagnetic responses of multicomponent superconductors. Although there exists a\nsubstantial literature that includes the drag interaction phenomenologically,\nmuch fewer regimes are covered by quantitative studies of the microscopic\norigin of the drag and its dependence on microscopic parameters. Here we study\nthe microscopic origin and strength of the drag interaction in a quantum system\nof two-component bosons on a lattice with short-range interaction. By\nperforming quantum Monte-Carlo simulations of a two-component Bose-Hubbard\nmodel we obtain dependencies of the drag strength on the boson-boson\ninteractions and properties of the optical lattice. Of particular interest are\nthe strongly-correlated regimes where the ratio of co-flow and counter-flow\nsuperfluid stiffnesses can diverge, corresponding to the case of saturated\ndrag.",
        "positive": "Disconnecting a Traversable Wormhole: Universal Quench Dynamics in\n  Random Spin Models: Understanding strongly interacting quantum matter and quantum gravity are\nboth important open issues in theoretical physics, and the holographic duality\nbetween quantum field theory and gravity theory nicely brings these two topics\ntogether. Nevertheless, direct connections between gravity physics and\nexperimental observations in quantum matter are still rare. Here we utilize the\ngravity physics picture to understand quench dynamics experimentally observed\nin a class of random spin models realized in several different quantum systems,\nwhere the dynamics of magnetization are measured after the external\npolarization field is suddenly turned off. Two universal features of the\nmagnetization dynamics, namely, a slow decay described by a stretched\nexponential function and an oscillatory behavior, are respectively found in\ndifferent parameter regimes across different systems. This work addresses the\nissues of generic conditions under which these two universal features can\noccur, and we find that a natural answer to this question emerges in the\ngravity picture. By the holographic duality bridged by a model proposed by\nMaldacena and Qi, the quench dynamics after suddenly turning off the external\npolarization field is mapped to disconnecting an eternal traversable wormhole.\nOur studies show that insight from gravity physics can help unifying different\nexperiments in quantum systems."
    },
    {
        "anchor": "Hydrodynamic model of skyrmions and vorticities in the spin-1\n  Bose-Einstein condensate in ferromagnetic phase at finite temperatures: Quantum hydrodynamic of skyrmions in spinor ultracold bosons at the finite\ntemperature is described. The limit regime of BEC appearing at the zero\ntemperature is discussed either. The skyrmions are found as the solution of the\nspin evolution equation for the ferromagnetic phase of spin-1 ultracold bosons.\nIt is demonstrated that the quantum part of the spin current gives major\ncontribution in the formation of the skyrmions. The interplay between the\nquantum (spin) vorticity and the classic vorticity is considered for the finite\ntemperatures. Bosons are presented as two fluids associated with the\nBose-Einstein condensate and the normal fluid. All effects are considered for\nthe ferromagnetic phase.",
        "positive": "Observation of the diffusive Nambu-Goldstone mode of a non-equilibrium\n  phase transition: Second-order phase transitions are governed by spontaneous symmetry breaking,\nwhich yield collective excitations with a gapless spectrum called\nNambu-Goldstone (NG) modes. While NG modes in conservative systems are\npropagating excitations, non-equilibrium phase transitions have been predicted\nto feature a diffusive NG mode. We present the first experimental evidence of a\ndiffusive NG mode in a non-equilibrium Bose-Einstein condensate of microcavity\npolaritons. The NG mode is observed as a spectral narrowing in the\nspectroscopic response of the condensate. Additionally, explicitly breaking the\nsymmetry causes the opening of a gap in the spectrum and the disappearance of\nthe NG mode. Our observations confirm the diffusive dynamics of the NG mode of\nnon-equilibrium phase transitions and establish a promising framework to\ninvestigate fundamental questions in statistical mechanics."
    },
    {
        "anchor": "Quantum phases in $p$-orbital degenerated attractive 1D fermionic\n  optical lattices: We examine quantum phases emerged by double degeneracy of $p$-orbital bands\nin attractive atomic Fermi gases loaded on a 1D optical lattice. Our numerical\nsimulations by the density-matrix renormalization group predict the emergence\nof a state with a charge excitation gap, the Haldane insulator phase. A mapping\nonto an effective spin-$1$ model reveals its physical origin. Moreover, we show\nthat population imbalance leads to richer diversity of the quantum phases,\nincluding a phase-separated polarized state. Finally, we study the effects of\nharmonic trap potential in this 1D chain.",
        "positive": "Topological Floquet-Thouless energy pump: We explore adiabatic pumping in the presence of periodic drive, finding a new\nphase in which the topologically quantized pumped quantity is energy rather\nthan charge. The topological invariant is given by the winding number of the\nmicromotion with respect to time within each cycle, momentum, and adiabatic\ntuning parameter. We show numerically that this pump is highly robust against\nboth disorder and interactions, breaking down at large values of either in a\nmanner identical to the Thouless charge pump. Finally, we suggest experimental\nprotocols for measuring this phenomenon."
    },
    {
        "anchor": "A driven-dissipative spin chain model based on exciton-polariton\n  condensates: An infinite chain of driven-dissipative condensate spins with uniform\nnearest-neighbor coherent coupling is solved analytically and investigated\nnumerically. Above a critical occupation threshold the condensates undergo\nspontaneous spin bifurcation (becoming magnetized) forming a binary chain of\nspin-up or spin-down states. Minimization of the bifurcation threshold\ndetermines the magnetic order as a function of the coupling strength. This\nallows control of multiple magnetic orders via adiabatic (slow ramping of)\npumping. In addition to ferromagnetic and anti-ferromagnetic ordered states we\nshow the formation of a paired-spin ordered state $\\left|\\dots \\uparrow\n\\uparrow \\downarrow \\downarrow \\dots \\right. \\rangle$ as a consequence of the\nphase degree of freedom between condensates.",
        "positive": "Particle-wave duality in quantum tunneling of a bright soliton: One of the most fundamental difference between classical and quantum\nmechanics is observed in the particle tunneling through a localized potential:\nthe former predicts a discontinuous transmission coefficient ($T$) as a\nfunction in incident velocity between one (complete penetration) and zero\n(complete reflection), while the later always changes smoothly as a wave\nnature. Here we report a systematic study of the quantum tunneling property for\na bright soliton in ultracold atoms, which behaves as a classical particle\n(matter wave) in the limit of small (large) incident velocity. In the\nintermediate regime, the classical and quantum properties are combined via a\nfinite (but not full) discontinuity in the tunneling transmission coefficient.\nWe demonstrate that the formation of a localized bound state is essential to\ndescribe such inelastic collisions, showing a nontrivial nonlinear effect on\nthe quantum transportation of a bright soliton."
    },
    {
        "anchor": "Correlation-enhanced interaction of a Bose-Einstein condensate with\n  parametric magnon pairs and virtual magnons: Nonlinear interactions are crucial in science and engineering. Here, we\ninvestigate wave interactions in a highly nonlinear magnetic system driven by\nparametric pumping leading to Bose--Einstein condensation of spin-wave quanta\n-- magnons. Using Brillouin light scattering spectroscopy in yttrium-iron\ngarnet films, we found and identified a set of nonlinear processes resulting in\noff-resonant spin-wave excitations -- virtual magnons. In particular, we\ndiscovered a dynamically-strong, correlation-enhanced four-wave interaction\nprocess of the magnon condensate with pairs of parametric magnons having\nopposite wavevectors and fully correlated phases.",
        "positive": "Quantum phases of a spin-1 ultracold Bose gas with three body\n  interactions: We study the effects of both a repulsive and an attractive three body\ninteraction potential on a spin-1 ultracold Bose gas using mean field approach\n(MFA). For an antiferromagnetic (AF) inter- action, we have found the existence\nof the odd-even asymmetry in the Mott insulating (MI) lobes in presence of both\nthe repulsive two and three body interactions. In case of a purely three body\nrepulsive interaction, the higher order MI lobes stabilize against the\nsuperfluid phase. However, the spin nematic (singlet) formation is restricted\nupto the first (second) MI lobes for the former one, while there is neither any\nasymmetry nor spin nematic (singlet) formation is observed for the later case.\nThe results are confirmed after carefully scrutinizing the spin eigen value and\nspin nematic order parameter for both the cases. On the other hand, for an\nattractive three body interaction, the third MI lobe is predominantly affected,\nwhere it completely engulfs the second and the fourth MI lobes at large values\nof the interaction strength. Albeit no significant change is observed beyond\nthe fourth MI lobe. In the ferromagnetic case, the phase diagram shows similar\nfeatures as that of a scalar Bose gas. We have compared our results on the MFA\nphase diagrams for both types of the interaction potential via a perturbation\nexpansion in both the cases."
    },
    {
        "anchor": "Different lattice geometries with synthetic dimension: The possibility of creating different geometries with the help of an extra\nsynthetic dimension in optical lattices is studied. Additional linear potential\nand Raman assisted tunnelings are used to engineer well controlled tunnelings\nbetween available states. The great flexibility of the system allows us to\nobtain different geometries of synthetic lattices with possibility of adding\nsynthetic gauge fields.",
        "positive": "Understanding chemical reactions in a quantum degenerate gas of polar\n  molecules via complex formation: A recent experiment reported for the first time the preparation of a Fermi\ndegenerate gas of polar molecules and observed a suppression of their chemical\nreaction rate compared to the one expected from a purely classical treatment.\nWhile it was hypothesized that the suppression in the ultracold regime had its\nroots in the Fermi statistics of the molecules, this argument is inconsistent\nwith the fact that the Fermi pressure should set a lower bound for the chemical\nreaction rate. Therefore it can not be explained from standard two-body\n$p$-wave inelastic collisions. Here we develop a simple model of chemical\nreactions that occur via the formation and decay of molecular complexes. We\nindeed find that pure two-body molecule losses are unable to explain the\nobserved suppression. Instead we extend our description beyond two-body physics\nby including effective complex-molecule interactions possible emerging from\nmany-body and effective medium effects at finite densities and in the presence\nof trapping light. %Under this framework we observe that additional\ncomplex-molecule collisions, which manifest as a net three-body molecular\ninteraction could give rise to the additional suppression. Although our\neffective model is able to quantitatively reproduce recent experimental\nobservations, a detailed understanding of the actual physical mechanism\nresponsible for these higher-order interaction processes is still pending."
    },
    {
        "anchor": "Many-body physics with ultracold plasmas: Quenched randomness and\n  localization: The exploration of large-scale many-body phenomena in quantum materials has\nproduced many important experimental discoveries, including novel states of\nentanglement, topology and quantum order as found for example in quantum spin\nices, topological insulators and semimetals, complex magnets, and high-$T_c$\nsuperconductors. Yet, the sheer scale of solid-state systems and the difficulty\nof exercising exacting control of their quantum mechanical degrees of freedom\nlimit the pace of rational progress in advancing the properties of these and\nother materials. With extraordinary effort to counteract natural processes of\ndissipation, precisely engineered ultracold quantum simulators could point the\nway to exotic new materials. Here, we look instead to the quantum mechanical\ncharacter of the arrested state formed by a quenched ultracold molecular\nplasma. This novel class of system arises spontaneously, without a deliberate\nengineering of interactions, and evolves naturally from state-specified initial\nconditions, to a long-lived final state of canonical density, in a process that\nconflicts with classical notions of plasma dissipation and neutral\ndissociation. We take information from experimental observations to develop a\nconceptual argument that attempts to explain this state of arrested relaxation\nin terms of a minimal phenomenological model of randomly interacting dipoles of\nrandom energies. This model of the plasma forms a starting point to describe\nits observed absence of relaxation in terms of many-body localization (MBL).\nThe large number of accessible Rydberg and excitonic states gives rise to an\nunconventional web of many-body interactions that vastly exceeds the complexity\nof MBL in a conventional few-level scheme. This experimental platform thus\nopens an avenue for the coupling of dipoles in disordered environments that\nwill demand the development of new theoretical tools.",
        "positive": "Creation and manipulation of quantized vortices in Bose-Einstein\n  condensates using reinforcement learning: We apply the technique of reinforcement learning to the control of nonlinear\nmatter waves. In this method, an agent controls the position, strength, and\nshape of an external Gaussian potential to create and manipulate quantized\nvortices in a Bose-Einstein condensate (BEC) trapped in a harmonic potential.\nThe density and velocity distributions of the BEC at each moment obtained by\nthe Gross-Pitaevskii evolution are directly input into a convolutional neural\nnetwork to determine the next action of the agent. We demonstrate that a\nstationary single-vortex state can be produced in a two-dimensional system, and\na stationary vortex-ring state can be produced in a three-dimensional system."
    },
    {
        "anchor": "Reinforcement Learning in Ultracold Atom Experiments: Cold atom traps are at the heart of many quantum applications in science and\ntechnology. The preparation and control of atomic clouds involves complex\noptimization processes, that could be supported and accelerated by machine\nlearning. In this work, we introduce reinforcement learning to cold atom\nexperiments and demonstrate a flexible and adaptive approach to control a\nmagneto-optical trap. Instead of following a set of predetermined rules to\naccomplish a specific task, the objectives are defined by a reward function.\nThis approach not only optimizes the cooling of atoms just as an\nexperimentalist would do, but also enables new operational modes such as the\npreparation of pre-defined numbers of atoms in a cloud. The machine control is\ntrained to be robust against external perturbations and able to react to\nsituations not seen during the training. Finally, we show that the time\nconsuming training can be performed in-silico using a generic simulation and\ndemonstrate successful transfer to the real world experiment.",
        "positive": "Frustrated Bose-Einstein condensates with non-collinear orbital ordering: We investigate the unconventional Bose-Einstein condensations (BEC) with the\norbital degree of freedom in the 3D cubic optical lattice, which give rise to\nvarious exotic features absent in conventional scalar and spinor BECs. Orbital\nangular momentum moments are formed on lattice sites breaking time-reversal\nsymmetry spontaneously. Furthermore, they exhibit orbital frustrations and\ndevelop a chiral ordering selected by the \"order-from-disorder\" mechanism."
    },
    {
        "anchor": "Two-flavor mixture of a few fermions of different mass in a\n  one-dimensional harmonic trap: A system of two species of fermions of different mass confined in a\none-dimensional harmonic trap is studied with an exact diagonalization\napproach. It is shown independently on the number of particles that a mass\ndifference between fermionic species induces a separation in the lighter flavor\nsystem. The mechanism of emerging of separated phases is explained\nphenomenologically and confirmed with the help of a direct inspection of the\nground-state of the system. Finally, it is shown that the separation driven by\na mass difference, in contrast to the separation induced by a difference of\npopulations, is robust to the interactions with thermal environment.",
        "positive": "Bipolarons in a Bose-Einstein Condensate: Mobile impurities in a Bose-Einstein condensate form quasiparticles called\npolarons. Here, we show that two such polarons can bind to form a bound\nbipolaron state. Its emergence is caused by an induced nonlocal interaction\nmediated by density oscillations in the condensate, and we derive using field\ntheory an effective Schr\\\"odinger equation describing this for arbitrarily\nstrong impurity-boson interaction. We furthermore compare with Quantum Monte\nCarlo simulations finding remarkable agreement, which underlines the predictive\npower of the developed theory. It is found that bipolaron formation typically\nrequires strong impurity interactions beyond the validity of more commonly used\nweak-coupling approaches that lead to local Yukawa-type interactions. We\npredict that the bipolarons are observable in present experiments and describe\na procedure to probe their properties."
    },
    {
        "anchor": "A laser based accelerator for ultracold atoms: We present first results on our implementation of a laser based accelerator\nfor ultracold atoms. Atoms cooled to a temperature of 420 nK are confined and\naccelerated by means of laser tweezer beams and the atomic scattering is\ndirectly observed in laser absorption imaging. The optical collider has been\ncharacterized using Rb87 atoms in the |F=2,mF=2> state, but the scheme is not\nrestricted to atoms in any particular magnetic substates and can readily be\nextended to other atomic species as well.",
        "positive": "Calorimetry of a Bose-Einstein condensed photon gas: Phase transitions, as the condensation of a gas to a liquid, are often\nrevealed by a discontinuous behavior of thermodynamic quantities. For liquid\nHelium, for example, a divergence of the specific heat signals the transition\nfrom the normal fluid to the superfluid state. Apart from liquid helium,\ndetermining the specific heat of a Bose gas has proven to be a challenging\ntask, for example for ultracold atomic Bose gases. Here we examine the\nthermodynamic behavior of a trapped two-dimensional photon gas, a system that\nallows us to spectroscopically determine the specific heat and the entropy of a\nnearly ideal Bose gas from the classical high temperature to the Bose-condensed\nquantum regime. The critical behavior at the phase transition is clearly\nrevealed by a cusp singularity of the specific heat. Regarded as a test of\nquantum statistical mechanics, our results demonstrate a quantitative agreement\nwith its predictions at the microscopic level."
    },
    {
        "anchor": "Many-particle Quantum Hydrodynamics of Spin-1 Bose-Einstein Condensates: We develop a novel model of the magnetized spin-1 Bose-Einstein condensate\n(BEC) of neutral atoms, using the method of many-particle quantum hydrodynamic\n(QHD) and propose an original derivation of the system of continual equations.\nWe consider bosons with a spin-spin interaction and a short range interaction\nin the first order in the interaction radius, on the of basis of the\nself-consistent field approximation of the QHD equations. We demonstrate that\nthe dynamics of the fluid velocity and magnetization is determined by a\nnontrivial modification of the Euler and Landau-Lifshitz equation, and show\nthat a nontrivial modification of the spin density evolution equation contains\nthe spin torque effect that arises from the self-interactions between spins of\nthe bosons. The properties of the dispersion spectrum of collective excitations\nare described. We obtain the new contribution of the self-interaction of spins\nin the spin wave spectrum together with the influence of an external magnetic\nfield and spin-spin interactions between polarized particles. The anisotropic\nspin wave instability is predicted.",
        "positive": "Synthetic topology and Floquet dynamic quantum phase transition in a\n  periodically driven Raman lattice: Stimulated by the recent progress in engineering topological band structures\nin cold atomic gases, we study the dynamic topological phenomena for atoms\nloaded in a periodically driven optical lattice. When the frequency of the\nperiodic modulation is low, the time-dependent Hamiltonian can be mapped to a\ntwo-dimensional topological insulator, with the discretized frequency\ncomponents playing the role of an additional, synthetic dimension. In the\nhigh-frequency limit, we derive the effective Floquet Hamiltonian of the\nsystem, and reveal the occurrence of Floquet dynamic quantum phase transitions\n-- an emergent topological phenomenon in the micromotion of the Floquet\ndynamics. Addressing the relation between the topology of the effective Floquet\nHamiltonian and the presence of dynamic topological phenomena, we demonstrate\nthat the topologically non-trivial nature of the Floquet Hamiltonian is a\nsufficient but not necessary condition for the onset of the Floquet dynamic\nquantum phase transition. We further discuss the relation of the topology of\nthe Floquet Hamiltonian with the existence of dynamic skyrmion structures in\nthe emergent momentum-time manifold of the micromotion, as well as the fate of\nthese dynamic topological phenomena when the modulation frequency decreases\naway from the high-frequency limit. Finally, making use of the rich level\nstructures of $^{171}$Yb atoms, we show that the system under study can be\nimplemented in a one-dimensional Raman lattice where states in the $^1S_0$\nground-state manifold are coupled by Raman beams with periodically modulated\namplitudes."
    },
    {
        "anchor": "The Unitary Fermi Gas: From Monte Carlo to Density Functionals: In this chapter, we describe three related studies of the universal physics\nof two-component unitary Fermi gases with resonant short-ranged interactions.\nFirst we discuss an ab initio auxiliary field quantum Monte Carlo technique for\ncalculating thermodynamic properties of the unitary gas from first principles.\nWe then describe in detail a Density Functional Theory (DFT) fit to these\nthermodynamic properties: the Superfluid Local Density Approximation (SLDA) and\nits Asymmetric (ASLDA) generalization. We present several applications,\nincluding vortex structure, trapped systems, and a supersolid\nLarkin-Ovchinnikov (FFLO/LOFF) state. Finally, we discuss the time-dependent\nextension to the density functional (TDDFT) which can describe quantum dynamics\nin these systems, including non-adiabatic evolution, superfluid to normal\ntransitions and other modes not accessible in traditional frameworks such as a\nLandau-Ginzburg, Gross-Pitaevskii, or quantum hydrodynamics.",
        "positive": "Spectral analysis for compressible quantum fluids: Turbulent fluid dynamics typically involves excitations on many different\nlength scales. Classical incompressible fluids can be cleanly represented in\nFourier space enabling spectral analysis of energy cascades and other\nturbulence phenomena. In quantum fluids, additional phase information and\nsingular behaviour near vortex cores thwarts the direct extension of standard\nspectral techniques. We develop a formal and numerical spectral analysis for\n$U(1)$ symmetry-breaking quantum fluids suitable for analyzing turbulent flows,\nwith specific application to the Gross-Pitaevskii fluid. Our analysis builds\nnaturally on the canonical approach to spectral analysis of velocity fields in\ncompressible quantum fluids, and establishes a clear correspondence between\nenergy spectral densities, power spectral densities, and autocorrelation\nfunctions, applicable to energy residing in velocity, quantum pressure,\ninteraction, and potential energy of the fluid. Our formulation includes all\nquantum phase information and also enables arbitrary resolution spectral\nanalysis, a valuable feature for numerical analysis. A central vortex in a\ntrapped planar Bose-Einstein condensate provides an analytically tractable\nexample with spectral features of interest in both the infrared and ultraviolet\nregimes. Sampled distributions modelling the dipole gas, plasma, and clustered\nregimes exhibit velocity correlation length increasing with vortex energy,\nconsistent with known qualitative behaviour across the vortex clustering\ntransition. The spectral analysis of compressible quantum fluids presented here\noffers a rigorous tool for analysing quantum features of superfluid turbulence\nin atomic or polariton condensates."
    },
    {
        "anchor": "Models of spin-orbit coupled oligomers: We address the stability and dynamics of eigenmodes in linearly-shaped\nstrings (dimers, trimers, tetramers, and pentamers) built of droplets of a\nbinary Bose-Einstein condensate (BEC). The binary BEC is composed of atoms in\ntwo pseudo-spin states with attractive interactions, dressed by properly\narranged laser fields, which induce the (pseudo-) spin-orbit (SO) coupling. We\ndemonstrate that the SO-coupling terms help to create eigenmodes of particular\ntypes in the strings. Dimer, trimer, and pentamer eigenmodes of the linear\nsystem, which correspond to the zero eigenvalue (EV, alias chemical potential)\nextend into the nonlinear ones, keeping an exact analytical form, while\ntetramers do not admit such a continuation, because the respective spectrum\ndoes not contain a zero EV. Stability areas of these modes shrink with the\nincreasing nonlinearity. Besides these modes, other types of nonlinear states,\nwhich are produced by the continuation of their linear counterparts\ncorresponding to some nonzero EVs, are found in a numerical form (including\nones for the tetramer system). They are stable in nearly entire existence\nregions in trimer and pentamer systems, but only in a very small area for the\ntetramers. Similar results are also obtained, but not displayed in detail, for\nhexa- and septamers.",
        "positive": "Two-dimensional Bose and Fermi gases beyond weak coupling: Using a formalism based on the two-body S-matrix we study two-dimensional\nBose and Fermi gases with both attractive and repulsive interactions.\nApproximate analytic expressions, valid at weak coupling and beyond, are\ndeveloped and applied to the Berezinskii-Kosterlitz-Thouless (BKT) transition.\nWe successfully recover the correct logarithmic functional form of the critical\nchemical potential and density for the Bose gas. For fermions, the BKT critical\ntemperature is calculated in BCS and BEC regimes through consideration of Tan's\ncontact."
    },
    {
        "anchor": "Upper bound of one-magnon excitation and lower bound of effective mass\n  for ferromagnetic spinor Bose and Fermi gases: Using a variational method, we derive an exact upper bound for one-magnon\nexcitation energy in ferromagnetic spinor gases, which limits the quantum\ncorrections to the effective mass of a magnon to be positive. We also derive an\nupper bound for one-magnon excitation energy in lattice systems. The results\nhold for both Bose and Fermi systems in $d$ dimensions as long as the\ninteraction is local and invariant under spin rotation.",
        "positive": "Dynamical phase interferometry of cold atoms in optical lattices: We study the propagation of cold-atom wave packets in an interferometer with\na Mach-Zehnder topology based on the dynamical phase of Bloch oscillation in a\nweakly forced optical lattice with a narrow potential barrier that functions as\na cold-atom wave packet splitter. We calculate analytically the atomic wave\nfunction, and show that the expected number of atoms in the two outputs of the\ninterferometer oscillates rapidly as a function of the angle between the\npotential barrier and the forcing direction with period proportional to the\nexternal potential difference across a lattice spacing divided by the lattice\nband energy scale. The interferometer can be used as a high precision force\nprobe whose principle of operation is different from current interferometers\nbased on the overall position of Bloch oscillating wave packets."
    },
    {
        "anchor": "Performance evaluation of the discrete truncated Wigner approximation\n  for quench dynamics of quantum spin systems with long-range interactions: The discrete truncated Wigner approximation (DTWA) is a powerful tool for\nanalyzing dynamics of quantum spin systems. Since the DTWA includes the\nleading-order quantum corrections to a mean-field approximation, it is\nnaturally expected that the DTWA becomes more accurate when the range of\ninteractions of the system increases. However, quantitative corroboration of\nthis expectation is still lacking mainly because it is generally difficult in a\nlarge system to evaluate a timescale on which the DTWA is quantitatively valid.\nIn order to investigate how the validity timescale depends on the interaction\nrange, we analyze dynamics of quantum spin models with a step function type\ninteraction subjected to a sudden quench of a magnetic field by means of both\nDTWA and its extension including the second-order correction, which is derived\nfrom the Bogoliubov-Born-Green-Kirkwood-Yvon equation. We also develop a\nformulation for calculating the second-order R\\'enyi entropy within the\nframework of the DTWA. By comparing the time evolution of the R\\'enyi entropy\ncomputed by the DTWA with that by the extension including the correction, we\nfind that both in the one- and two-dimensional systems the validity timescale\nincreases algebraically with the range of the step function type interaction.",
        "positive": "Collinear Four-Wave Mixing of Two-Component Matter Waves: We demonstrate atomic four-wave mixing of two-component matter waves in a\ncollinear geometry. Starting from a single-species Bose-Einstein condensate,\nseed and pump modes are prepared through microwave state transfer and\nstate-selective Kapitza-Dirac diffraction. Four-wave mixing then populates the\ninitially empty output modes. Simulations based on a coupled-mode expansion of\nthe Gross-Pitaevskii equation are in very good agreement with the experimental\ndata. We show that four-wave mixing can play an important role in studies of\nbosonic mixtures in optical lattices. Moreover our system should be of interest\nin the context of quantum atom optics."
    },
    {
        "anchor": "Bright solitons in a quasi-one-dimensional reduced model of a dipolar\n  Bose-Einstein condensate with repulsive short-range interactions: We study the formation and dynamics of bright solitons in a\nquasi-one-dimensional reduced mean-field Gross-Pitaevskii equation of a dipolar\nBose-Einstein condensate with repulsive short-range interactions. The study is\ncarried out using a variational approximation and a numerical solution. Plots\nof chemical potential and root mean square (rms) size of solitons are obtained\nfor the quasi-one-dimensional model of three different dipolar condensates of\n52Cr, 168Er and 164Dy atoms. The results achieved are in good agreement with\nthose produced by the full three-dimensional mean-field model of the\ncondensate. We also study the dynamics of the collision of a train of two\nsolitons in the quasi-one-dimensional model of every condensate above. At small\nvelocities (zero or close to zero) the dynamics is attractive for a phase\ndifference {\\delta} = 0, the solitons coalesce and these oscillate forming a\nbound soliton molecule. For a phase difference {\\delta} = {\\pi} the effect is\nrepulsive. At large velocities the collision is independent of the initial\nphase difference {\\delta}. This is quasi-elastic and the result is two\nquasi-solitons.",
        "positive": "Four-body Efimov effect: We study three same spin state fermions of mass M interacting with a\ndistinguishable particle of mass m in the unitary limit where the interaction\nhas a zero range and an infinite s-wave scattering length. We predict an\ninterval of mass ratio 13.384 < M/m < 13.607 where there exists a purely\nfour-body Efimov effect, leading to the occurrence of weakly bound tetramers\nwithout Efimov trimers."
    },
    {
        "anchor": "Switching waves in multi-level incoherently driven polariton condensates: We show theoretically that an open-dissipative polariton condensate confined\nwithin a trapping potential and driven by an incoherent pumping scheme gives\nrise to bistability between odd and even modes of the potential. Switching from\none state to the other can be controlled via incoherent pulsing which becomes\nan important step towards construction of low-powered opto-electronic devices.\nThe origin of the effect comes from modulational instability between odd and\neven states of the trapping potential governed by the nonlinear\npolariton-polariton interactions.",
        "positive": "Generalized Effective Potential Landau Theory for Bosonic Quadratic\n  Superlattices: We study the properties of the Bose-Hubbard model for a quadratic optical\nsuperlattice. To this end we generalize a recently established effective\npotential Landau theory for a single component to the case of multi components\nand find not only the characteristic incompressible solid phases with\nfractional filling, but also obtain the underlying quantum phase diagram in the\nwhole parameter region at zero temperature. Comparing our analytic results with\ncorresponding ones from quantum Monte Carlo simulations demonstrates the high\naccuracy of the generalized effective potential Landau theory (GEPLT). Finally,\nwe comment on the advantages and disadvantages of the GEPLT in view of a direct\ncomparison with a corresponding decoupled mean-field theory."
    },
    {
        "anchor": "Floquet Topological Superfluid and Majorana Zero Modes in\n  Two-Dimensional Periodically Driven Fermi Systems: We propose a simple approach to realize two-dimensional Floquet topological\nsuperfluid by periodically tuning the depth of square optical lattice\npotentials. We show that the periodic driving can induce topological phase\ntransitions between trivial superfluid and Floquet topological superfluid. For\nthis systems we verify the anomalous bulk-boundary correspondence, namely that\nthe robust chiral Floquet edge states can appear even when the winding number\nof all the bulk Floquet bands is zero. We establish the existence of two\nFloquet Majorana zero modes separated in the quasienergy space, with\n$\\varepsilon_{0,\\pi}=0,\\pi/T$ at the topological defects.",
        "positive": "A Quantum Theory of Cold Bosonic Atoms in Optical Lattices: Ultracold atoms in optical lattices undergo a quantum phase transition from a\nsuperfluid to a Mott insulator as the lattice potential depth is increased. We\ndescribe an approximate theory of interacting bosons in optical lattices which\nprovides a qualitative description of both superfluid and insulator states. The\ntheory is based on a change of variables in which the boson coherent state\namplitude is replaced by an effective potential which promotes phase coherence\nbetween different number states on each lattice site. It is illustrated here by\napplying it to uniform and fully frustrated lattice cases, but is simple enough\nthat it can easily be applied to spatially inhomogeneous lattice systems."
    },
    {
        "anchor": "Double resonance of Raman transitions in a degenerate Fermi gas: We measure momentum-resolved Raman spectra of a spin-polarized degenerate\nFermi gas of $^{173}$Yb atoms for a wide range of magnetic fields, where the\natoms are irradiated by a pair of counterpropagating Raman laser beams as in\nthe conventional spin-orbit coupling scheme. Double resonance of first- and\nsecond-order Raman transitions occurs at a certain magnetic field and the\nspectrum exhibits a doublet splitting for high laser intensities. The measured\nspectral splitting is quantitatively accounted for by the Autler-Townes effect.\nWe show that our measurement results are consistent with the spinful band\nstructure of a Fermi gas in the spatially oscillating effective magnetic field\ngenerated by the Raman laser fields.",
        "positive": "Interaction-induced instability and chaos in the photoassociative\n  stimulated Raman adiabatic passage from atomic to molecular Bose-Einstein\n  condensates: We study the effect of interactions on the conversion of atomic -to molecular\nBose-Einstein condensates via stimulated Raman adiabatic passage. Both\nenergetic instability during avoided crossings and dynamical instability during\nchaotic intervals limit adiabaticity and impose {\\em low} sweep-rate boundaries\non the efficiency of the process. For the diabatic traverse of avoided\ncrossings, we find a reciprocal power-law dependence of the final unconverted\npopulation on sweep rate. For the traverse of chaos, we find a sharp low-rate\nboundary determined by the dynamical instability parameters. The interplay of\nthese two mechanisms determines which instability controls the failure of\nmolecular production. A judicious choice of sweep parameters is hence required\nto restore the process efficiency."
    },
    {
        "anchor": "Self-bound crystals of antiparallel dipolar mixtures: Recent experiments have created supersolids of dipolar quantum droplets. The\nresulting crystals lack, however, a genuine cohesive energy and are maintained\nby the presence of an external confinement, bearing a resemblance to the case\nof ion Coulomb crystals. We show that a mixture of two antiparallel dipolar\ncondensates allows for the creation of potentially large, self-bound crystals\nwhich, resembling ionic crystals in solid-state physics, are maintained by the\nmutual dipolar attraction between the components, with no need of transversal\nconfinement. This opens intriguing novel possibilities, including\nthree-dimensionally self-bound droplet-ring structures, stripe/labyrinthic\npatterns, and self-bound crystals of droplets surrounded by an interstitial\nsuperfluid, resembling the case of superfluid Helium in porous media.",
        "positive": "Probing the topology of density matrices: The mixedness of a quantum state is usually seen as an adversary to\ntopological quantization of observables. For example, exact quantization of the\ncharge transported in a so-called Thouless adiabatic pump is lifted at any\nfinite temperature in symmetry-protected topological insulators. Here, we show\nthat certain directly observable many-body correlators preserve the integrity\nof topological invariants for mixed Gaussian quantum states in one dimension.\nOur approach relies on the expectation value of the many-body\nmomentum-translation operator, and leads to a physical observable --- the\n\"ensemble geometric phase\" (EGP) --- which represents a bona fide geometric\nphase for mixed quantum states, in the thermodynamic limit. In cyclic\nprotocols, the EGP provides a topologically quantized observable which detects\nencircled spectral singularities (\"purity-gap\" closing points) of density\nmatrices. While we identify the many-body nature of the EGP as a key\ningredient, we propose a conceptually simple, interferometric setup to directly\nmeasure the latter in experiments with mesoscopic ensembles of ultracold atoms."
    },
    {
        "anchor": "Synthetic magnetic fields for cold erbium atoms: The implementation of the fractional quantum Hall effect in ultracold atomic\nquantum gases remains, despite substantial advances in the field, a major\nchallenge. Since atoms are electrically neutral, a key ingredient is the\ngeneration of sufficiently strong artificial gauge fields. Here we\ntheoretically investigate the synthetization of such fields for bosonic erbium\natoms by phase imprinting with two counterpropagating optical Raman beams.\nGiven the nonvanishing orbital angular momentum of the rare-earth atomic\nspecies erbium in the electronic ground state and the availability of\nnarrow-line transitions, heating from photon scattering is expected to be lower\nthan in atomic alkali-metal species. We give a parameter regime for which\nstrong synthetic magnetic fields with good spatial homogeneity are predicted.\nWe also estimate the size of the Laughlin gap expected from the s-wave\ncontribution of the interactions for typical experimental parameters of a\ntwo-dimensional atomic erbium microcloud. Our analysis shows that cold\nrare-earth atomic ensembles are highly attractive candidate systems for\nexperimental explorations of the fractional quantum Hall regime.",
        "positive": "Thermalization in closed quantum systems: semiclassical approach: Thermalization in closed quantum systems can be explained either by means of\nthe eigenstate thermalization hypothesis or the concept of canonical\ntypicality. Both concepts are based on quantum mechanical formalism such as\nspectral properties of the eigenstates or entanglement between subsystems\nrespectively. Here we study the onset of thermalization of Bose particles in a\ntwo-band double well potential using the truncated Wigner approximation. This\nallows us to use the familiar classical formalism to explain quantum\nthermalization in this system. In particular, we demonstrate that sampling of\nan initial quantum state plays the role of a statistical mechanical ensemble,\nwhile subsequent chaotic classical evolution turns the initial quantum state\ninto the thermal state."
    },
    {
        "anchor": "Excitations and correlations in the driven-dissipative Bose-Hubbard\n  model: Using a field-theoretic approach within the Schwinger-Keldysh formalism, we\nstudy a Bose-Hubbard model in the presence of a driving field and dissipation\ndue to one-body losses. We recover the bistability diagram from the\nGross-Pitaevski equation and analyze the different phases with respect to their\nelementary excitations and correlations. We find the low-density solution to be\nsubdivided into a dynamically instable, a gapped, and a gapless regime. The\ncorrelations decay exponentially, but a substantial increase of correlation\nlength marks the regime of gapless excitations.",
        "positive": "Driven impurity in an ultracold 1D Bose gas with intermediate\n  interaction strength: We study a single impurity driven by a constant force through a 1D Bose gas\nusing a Lieb-Liniger based approach. Our calculaton is exact in the interaction\namongst the particles in the Bose gas, and is perturbative in the interaction\nbetween the gas and the impurity. In contrast to previous studies of this\nproblem, we are able to handle arbitrary interaction strength for the Bose gas.\nWe find very good agreement with recent experiments [Phys. Rev. Lett. 103,\n150601 (2009)]."
    },
    {
        "anchor": "Phase diagram for strong-coupling Bose polarons: Important properties of complex quantum many-body systems and their phase\ndiagrams can often already be inferred from the impurity limit. The Bose\npolaron problem describing an impurity atom immersed in a Bose-Einstein\ncondensate is a paradigmatic example. One of the most interesting features of\nthis model is the competition between the emergent impurity-mediated attraction\nbetween the bosons and their intrinsic repulsion. The arising higher-order\ncorrelations make the physics rich and interesting, but also complex to\ndescribe theoretically. To tackle this challenge, we develop a quantum\nchemistry-inspired computational technique and compare two state-of-the-art\nvariational methods that fully include both the boson-impurity and boson-boson\ninteractions on a non-perturbative level. For a sweep of the boson-impurity\ninteraction strength, we find two regimes of qualitatively different behaviour.\nIf the impurity-mediated interactions overcome the repulsion between the\nbosons, the polaron becomes unstable due to the formation of large bound\nclusters. If instead the interboson interactions dominate, the impurity will\nexperience a crossover from a polaron into a small molecule. We achieve a\nunified understanding incorporating both of these regimes and the transition\nbetween them. We show that both the instability and crossover regime can be\nstudied in realistic cold-atom experiments. Moreover, we develop a simple\nanalytical model that allows us to interpret these phenomena in the typical\nLandau framework of first-order phase transitions that turn second-order at a\ncritical endpoint, revealing a deep connection of the Bose polaron model to\nboth few- and many-body physics.",
        "positive": "Stability and The Existence of Coherent Structure in Demixed State of\n  Binary BEC: From a linear stability analysis of the Gross Pitaevskii equation for binary\nBose Einstein condensates, it is found that the uniform state becomes unstable\nto a periodic perturbation of wave number k if k exceeds a critical value kc.\nHowever we find that a stationary spatially periodic state does not exist. We\nshow the existence of pulse type solutions, when the pulse structure for one\ncondensate is strongly influenced by the presence of the other condensate."
    },
    {
        "anchor": "Experimental realization of a fermionic spin-momentum lattice: We experimentally realize a spin-momentum lattice with a homogeneously\ntrapped Fermi gas. The lattice is created via cyclically-rotated atom-laser\ncouplings between three bare atomic spin states, and are such that they form a\ntriangular lattice in a synthetic spin-momentum space. We demonstrate the\nlattice and explore its dynamics with spin- and momentum-resolved absorption\nimaging. This platform will provide new opportunities for synthetic spin\nsystems and the engineering of topological bands. In particular, the use of\nthree spin states in two spatial dimensions would allow the simulation of\nsynthetic magnetic fields of high spatial uniformity, which would lead to\nultra-narrow Chern bands that support robust fractional quantum Hall states.",
        "positive": "Versatile electric fields for the manipulation of ultracold NaK\n  molecules: In this paper, we present an electrode geometry for the manipulation of\nultracold rovibrational ground state NaK molecules. The electrode system allows\nto induce a dipole moment in trapped diatomic NaK molecules with a magnitude up\nto $68 \\%$ of their internal dipole moment along any direction in a given\ntwo-dimensional plane. The strength, the sign and the direction of the induced\ndipole moment is therefore fully tunable. Furthermore, the possibility to\ncreate strong electric field gradients provides the opportunity to address\nmolecules in single layers of an optical lattice. The maximal relative\nvariation of the electric field over the trapping volume is below $10^{-6}$. At\nthe desired electric field value of 10 kV/cm this corresponds to a deviation of\n0.01 V/cm. The electrode structure is made of transparent indium tin oxide and\ncombines large optical access for sophisticated optical dipole traps and\noptical lattice configurations with the possibility to create versatile\nelectric field configurations."
    },
    {
        "anchor": "Controlled excitation of rotons in superfluid helium with an optical\n  centrifuge: We experimentally demonstrate a controlled transfer of angular momentum to\nroton pairs in superfluid helium. The control is executed with an optical\ncentrifuge and detected with coherent time- and frequency-resolved Raman\nscattering. We show that the sign of the Raman shift, and hence the orientation\nof the angular momentum transferred from the laser field to the rotons, is\ndictated by the centrifuge. The magnitude of the shift reflects the two-roton\nenergy and indicates that the centrifuge-induced hot roton pairs are far from\nthe equilibrium with the colder quantum bath. The observed decay of the\ncoherent Raman signal suggests that the decoherence is governed by the\nscattering on thermal rotons and phonons. The demonstrated method offers ways\nof examining microscopic origins of superfluidity by controlling collective\nexcitations in superfluids.",
        "positive": "Magnonic spin current shot noise in an itinerant Fermi gas: Spin transport phenomena at strongly-correlated interfaces play central roles\nin fundamental physics as well as spintronic applications. To anatomize\nspin-transport carriers, we propose the detection of the spin current noise in\ninteracting itinerant fermions. The Fano factor given by the ratio between the\nspin current and its noise reflects elementary carriers of spin transport at\nthe interface of spin-polarized Fermi gases realized in ultracold atoms. The\nchange of the Fano factor microscopically evinces a crossover from the\nquasiparticle transport to magnon transport in itinerant fermionic systems."
    },
    {
        "anchor": "Resonance States and Quantum Tunneling of Bose Einstein condensates in a\n  3D shallow trap: A correlated quantum many-body method is applied to describe resonance states\nof atomic Bose-Einstein condensates (BEC) in a realistic shallow trap (as\nopposed to infinite traps commonly used). The realistic van der Waals\ninteraction is adopted as the interatomic interaction. We calculate\nexperimentally measurable decay rates of the lowest quasi-bound state in the\nshallow trap. The most striking result is the observation of a new metastable\nbranch besides the usual one for attractive BEC in a pure harmonic trap. As the\nparticle number increases the new metastable branch appears, then gradually\ndisappears and finally usual metastable branch (associated with the attractive\nBEC in a harmonic trap) appears, eventually leading to the collapse of the\ncondensate.",
        "positive": "Flat bands and dynamical localization of spin-orbit coupled\n  Bose-Einstein condensates: Flat bands and dynamical localization of binary mixtures of Bose-Einstein\ncondensates, with spin-orbit coupling subjected to a deep optical lattice which\nis shaking in time and to a periodic time modulation of the Zeeman field, are\ninvestigated. In contrast with usual dynamical localization in the absence of\nspin-orbit coupling, we find that to fully suppress the tunneling in the system\nthe optical lattice shaking is not enough, and a proper tuning of the\nspin-orbit term, achievable via the Zeeman field modulation, is also required.\nThis leads to a sequence of Zeeman parameter values where energy bands become\nflat, the tunneling in the system is suppressed, and the dynamical localization\nphenomenon occurs. Exact wave functions at the dynamical localization points\nshow that the binary mixture localizes on a dimer with the two components\noccupying different sites. This type of localization occurs in exact form also\nfor the ground state of the system at the dynamical localization points in the\npresence of nonlinearity and remains valid, although in approximate form, for a\nwide range of the Zeeman parameter around these points. The possibility of\nobserving the above phenomena in real experiments is also briefly discussed."
    },
    {
        "anchor": "Comment on \"Quantum Time Crystals and Interacting Gauge Theories in\n  Atomic Bose-Einstein Condensates\": In a recent letter [Phys. Rev. Lett. 123, 250402], \\\"Ohberg and Wright\ndescribe a Bose-Einstein condensate trapped on a ring in the presence of the\ndensity-dependent gauge potential. It is claimed that the ground state of the\nsystem corresponds to a rotating chiral bright soliton and consequently it\nforms a genuine time crystal which minimizes its energy by performing periodic\nmotion. We show that the energy of the chiral soliton in the laboratory frame\nis not correctly calculated in the letter. The correct energy becomes minimal\nif the soliton does not move.",
        "positive": "Ferroelectric nano-traps for polar molecules: We propose and analyze an electrostatic-optical nano-scale trap for cold\ndiatomic polar molecules. The main ingredient of our proposal is an\nsquare-array of ferroelectric nano-rods {with alternating polarization}. We\nshow that, in contrast to electrostatic traps using the linear Stark effect, a\nquadratic Stark potential supports long-lived trapped states. The molecules are\nkept at a fixed height from the nano-rods by a standing-wave optical dipole\ntrap. For the molecules and materials considered, we find that nano-traps with\ntrap frequency up to 1MHz, ground-state width $\\sim20$nm with lattice\nperiodicity of $\\sim 200$nm. Analyzing the loss mechanisms due to\nnon-adiabaticity, surface-induced radiative transitions, and laser-induced\ntransitions, we show the existence of trapped states with life-time $\\sim 1$s,\ncompetitive with current traps created via optical mechanisms. As an\napplication we extend our discussion to an 1D array of nano-traps to simulate\nof a long-range spin Hamiltonian in our structure."
    },
    {
        "anchor": "$1/N$-expansion for the critical temperature of the Bose gas: We revised the large-$N$ expansion for a three-dimensional Bose system with\nshort-range repulsion in normal phase. Particularly, for the model potential\nthat is characterised only by the $s$-wave scattering length $a$ the full\nnumerical calculations of the critical temperature in the $1/N$-approximation\nas a function of the gas parameter $an^{1/3}$ are performed. Additionally to\nthe well-known result in the dilute limit we estimated analytically the\nleading-order strong-coupling behavior of the Bose-Einstein condensation\ntransition temperature. It is shown that the critical temperature shift of the\nnon-ideal Bose gas grows at small $an^{1/3}$, reaches some maximal value and\nthen falls down becoming negative.",
        "positive": "Creating atom-number states around tapered optical fibres by loading\n  from an optical lattice: We describe theoretically a setup in which a tapered optical nanofibre is\nintroduced into an optical lattice potential for cold atoms. Firstly, we\nconsider the disturbance to the geometry of the lattice potential due to\nscattering of the lattice lasers from the dielectric fibre surface and show\nthat the resulting distortion to the lattice can be minimized by placing the\nfibre at an appropriate position in the lattice. We then calculate the\nmodifications of the local potentials that are achievable by transmitting\noff-resonant light through the fibre. The availability of such a technique\nholds the potential to deterministically create and address small well-defined\nsamples of atoms in the evanescent field of the tapered nanofibre."
    },
    {
        "anchor": "Quantum simulation of conductivity plateaux and fractional quantum Hall\n  effect using ultracold atoms: We analyze the role of impurities in the fractional quantum Hall effect using\na highly controllable system of ultracold atoms. We investigate the mechanism\nresponsible for the formation of plateaux in the resistivity/conductivity as a\nfunction of the applied magnetic field in the lowest Landau level regime. To\nthis aim, we consider an impurity immersed in a small cloud of an ultracold\nquantum Bose gas subjected to an artificial magnetic field. We consider\nscenarios corresponding to experimentally realistic systems with gauge fields\ninduced either by rotation or by appropriately designed laser fields. Systems\nof this kind are adequate to simulate quantum Hall effects in ultracold atom\nsetups. We use exact diagonalization for few atoms and, to emulate transport\nequations, we analyze the time evolution of the system under a periodic\nperturbation. We provide a theoretical proposal to detect the up-to-now elusive\npresence of strongly correlated states related to fractional filling factors in\nthe context of ultracold atoms. We analyze the conditions under which these\nstrongly correlated states are associated with the presence of the\nresistivity/conductivity plateaux. Our main result is the presence of a plateau\nin a region, where the transfer between localized and non-localized particles\ntakes place, as a necessary condition to maintain a constant value of the\nresistivity/conductivity as the magnetic field increases.",
        "positive": "Thermodynamics of rotating Bose gases in a trap: Novel ground state properties of rotating Bose gases have been intensively\nstudied in the context of neutral cold atoms. We investigate the rotating Bose\ngas in a trap from a thermodynamic perspective, taking the charged ideal Bose\ngas in magnetic field (which is equivalent to a neutral gas in a synthetic\nmagnetic field) as an example. It is indicated that the Bose-Einstein\ncondensation temperature is irrelevant to the magnetic field, conflicting with\nestablished intuition that the critical temperature decreases with the field\nincreasing. The specific heat and Landau diamagnetization also exhibit\nintriguing behaviors. In contrast, we demonstrate that the condensation\ntemperature for neutral Bose gases in a rotating frame drops to zero in the\nfast rotation limit, signaling a non-condensed quantum phase in the ground\nstate."
    },
    {
        "anchor": "Discrete nature of thermodynamics in confined ideal Fermi gases: Intrinsic discrete nature in thermodynamic properties of Fermi gases appears\nunder strongly confined and degenerate conditions. For a rectangular\nconfinement domain, thermodynamic properties of an ideal Fermi gas are\nexpressed in their exact summation forms. For 1D, 2D and 3D nano domains,\nvariations of both number of particles and internal energy per particle with\nchemical potential are examined. It is shown that their relation with chemical\npotential exhibits a discrete nature which allows them to take only some\ndefinite values. Furthermore, quasi-irregular oscillatory-like sharp peaks are\nobserved in heat capacity. New nano devices can be developed based on these\nbehaviors.",
        "positive": "Coexistence of spin-1/2 and spin-1 Dirac-Weyl fermions in the\n  edge-centered honeycomb lattice: We investigate the properties of an edge-centered honeycomb lattice, and show\nthat this lattice features both spin-1/2 and spin-1 Dirac-Weyl fermions at\ndifferent filling fractions f (f=1/5,4/5 for spin-1/2 and f=1/2 for spin-1).\nThis five-band system is the simplest lattice that can support simultaneously\nthe two different paradigmatic Dirac-Weyl fermions with half-integer spin and\ninteger spin. We demonstrate that these pseudo-relativistic structures,\nincluding a flat band at half-filling, can be deduced from the underlying\nKagome sublattice. We further show that the signatures of the two kinds of\nrelativistic fermions can be clearly revealed by several perturbations, such as\na uniform magnetic field, a Haldane-type spin-orbit term, and charge density\nwaves. We comment on the possibility to probe the similarities and differences\nbetween the two kinds of relativistic fermions, or even to isolate them\nindividually. We present a realistic scheme to realize such a system using cold\natoms."
    },
    {
        "anchor": "Lattice Unruh effect and world-line entanglement for the XXZ chain: For the XXZ chain, we discuss the relation between a lattice version of Unruh\neffect and the ground-state entanglement on the basis of the corner\nHamiltonian. We find that the lattice Unruh temperature is interpreted as\n$\\beta_\\lambda = 2\\pi/a$ with an effective acceleration $a=\\pi/\\lambda$, where\n$\\lambda$ denotes the anisotropy parameter of the XXZ chain. Using quantum\nMonte Carlo simulation for the corner Hamiltonian at $\\beta_\\lambda$, we\ndemonstrate that world lines of spins surrounding the entangle point provides\nan intuitive understanding the quantum entanglement. We also propose an\nXXZ-chain analogue of the detector for the thermalized entanglement spectrum\nwith use of the angular time evolution defined by the corner Hamiltonian.",
        "positive": "Realizing limit cycles in dissipative bosonic systems: We propose a general mechanism for generating limit cycle (LC) oscillations\nby coupling a linear bosonic mode to a dissipative nonlinear bosonic mode. By\nanalyzing the stability matrix, we show that LCs arise due to a supercritical\nHopf bifurcation. We find that the existence of LCs is independent of the sign\nof the effective nonlinear interaction. The LC phase can be classified as a\ncontinuous time crystal (CTC), if it emerges in a many-body system. The bosonic\nmodel can be realised in three-level systems interacting with a quantised light\nmode as realised in atom-cavity systems. Using such a platform, we\nexperimentally observe LCs for the first time in an atom-cavity system with\nattractive optical pump lattice, thereby confirming our theoretical\npredictions."
    },
    {
        "anchor": "Robust Vortex Lines, Vortex Rings and Hopfions in 3D Bose-Einstein\n  Condensates: Performing a systematic Bogoliubov-de Gennes spectral analysis, we illustrate\nthat stationary vortex lines, vortex rings and more exotic states, such as\nhopfions, are robust in three-dimensional atomic Bose-Einstein condensates, for\nlarge parameter intervals. Importantly, we find that the hopfion can be\nstabilized in a simple parabolic trap, without the need for trap rotation or\ninhomogeneous interactions. We supplement our spectral analysis by studying the\ndynamics of such stationary states; we find them to be robust against\nsignificant perturbations of the initial state. In the unstable regimes, we not\nonly identify the unstable mode, such as a quadrupolar or hexapolar mode, but\nwe also observe the corresponding instability dynamics. Furthermore, deep in\nthe Thomas-Fermi regime, we investigate the particle-like behavior of vortex\nrings and hopfions.",
        "positive": "Collective oscillations of a Bose-Einstein condensate induced by a\n  vortex ring: We study the collective oscillations of three-dimensional Bose-Einstein\ncondensates (BECs) excited by a vortex ring. We identify independent,\nintegrated, and stationary modes of the center-of-mass oscillation of the\ncondensate with respect to the vortex ring movement. We show that the\noscillation amplitude {of the center-of-mass of the condensate} depends\nstrongly on the initial radius of the vortex ring, the inter-atomic\ninteraction, and the aspect ration of the trap, while the oscillation frequency\nis fixed and equal to the frequency of the harmonic trap in the direction of\nthe ring movement. However, when applying Kelvin wave perturbations on the\nvortex ring, the center-of-mass oscillation of the BEC is changed nontrivially\nwith respect to the perturbation modes, the long-scale perturbation strength as\nwell as the wave number of the perturbations. The parity of the wave number of\nthe Kelvin perturbations plays important role on the mode of the center-of-mass\noscillation of the condensate."
    },
    {
        "anchor": "Non-equilibrium dynamics in Bose-Hubbard ladders: Motivated by a recent experiment on the non-equilibrium dynamics of\ninteracting bosons in ladder-shaped optical lattices, we report exact\ncalculations on the sweep dynamics of Bose-Hubbard systems in finite two-leg\nladders. The sweep changes the energy bias between the legs linearly over a\nfinite time. As in the experiment, we study the cases of [a] the bosons\ninitially all in the lower-energy leg (ground state sweep) and [b] the bosons\ninitially all in the higher-energy leg (inverse sweep). The approach to\nadiabaticity in the inverse sweep is intricate, as the transfer of bosons is\nnon-monotonic as a function of both sweep time and intra-leg tunnel coupling.\nOur exact study provides explanations for these non-monotonicities based on\nfeatures of the full spectrum, without appealing to concepts (e.g., gapless\nexcitation spectrum) that are more appropriate for the thermodynamic limit. We\nalso demonstrate and study Stueckelberg oscillations in the finite-size\nladders.",
        "positive": "Quantum Monte Carlo study of the dynamic structure factor in the gas and\n  crystal phase of hard-sphere bosons: We investigate the dynamic structure factor of a system of Bose particles at\nzero temperature using quantum Monte Carlo methods. Interactions are modeled\nusing a hard-sphere potential of size $a$ and simulations are performed for\nvalues of the gas parameter $na^3$ ranging from the dilute regime up to\ndensities $n$ where the thermodynamically stable phase is a solid. With\nincreasing density we observe a crossover of the dispersion of elementary\nexcitations from a Bogoliubov-like spectrum to a phonon--maxon--roton curve and\nthe emergence of a broad multiphonon contribution accompanying the\nsingle-quasiparticle peak. In particular, for $na^3=0.2138$, which corresponds\nto superfluid $^4$He at equilibrium density, the extracted spectrum turns out\nto be in good agreement with the experimental energy--momentum dispersion\nrelation in the roton region and for higher momenta. The behavior of the\nspectral function at the same density in the stable solid and metastable gas\nphase above the freezing point is also discussed."
    },
    {
        "anchor": "Thermal and quantum noncondensate particles near the superfluid to Mott\n  insulator transition: We investigate the finite temperature momentum distribution of bosonic\nnoncondensate particles inside a 3D optical lattice near the superfluid to Mott\ninsulator transition point, treating the quantum fluctuation and thermal\nfluctuation effects on equal footing. We explicitly address the different\nmomentum ($q$) dependence of quasi-particles excitations resulted from thermal\nand quantum origin: the former scales as $|\\bfq|^{-2}$ and hence is dominant in\nthe small momentum region, while the later scales as $|\\bfq|^{-1}$ and hence\ndominant in the large momentum limit. Analytic and semi-analytic results are\nderived, providing a unique method to determine the temperature, condensate\ndensity, coherent length and/or single particle gap etc. inside the optical\nlattice. Our results also agree with the scaling theory of a quantum $XY$ model\nnear the transition point. Experimental implication of the TOF measurement is\nalso discussed.",
        "positive": "Infrared behavior of dipolar Bose systems at low temperatures: We rigorously discuss the infrared behavior of the uniform three dimensional\ndipolar Bose systems. In particular, it is shown that low-temperature physics\nof the system is controlled by two parameters, namely isothermal\ncompressibility and intensity of the dipole-dipole interaction. By using\nhydrodynamic approach we calculate the spectrum and damping of low-lying\nexcitations and analyze infrared behavior of the one-particle Green's function.\nThe low-temperature corrections to the anisotropic superfluid density as well\nas condensate depletion are found. Additionally we derive equations of the\ntwo-fluid hydrodynamics for dipolar Bose systems and calculate velocities of\nfirst and second sound."
    },
    {
        "anchor": "Quench Dynamics of Three-Dimensional Disordered Bose Gases:\n  Condensation, Superfluidity and Fingerprint of Dynamical Bose Glass: In an equilibrium three-dimensional (3D) disordered condensate, it's well\nestablished that disorder can generate an amount of normal fluid equaling to\n$\\frac{4}{3}$ of the condensate depletion. The concept that the superfluid is\nmore volatile to the existence of disorder than the condensate is crucial to\nthe understanding of Bose glass phase. In this Letter, we show that, by\nbringing a weakly disordered 3D condensate to nonequilibrium regime via a\nquantum quench in the interaction, disorder can destroy superfluid\nsignificantly more, leading to a steady state in which the normal fluid density\nfar exceeds $\\frac{4}{3}$ of the condensate depletion. This suggests a\npossibility of engineering Bose Glass in the dynamic regime. As both the\ncondensate density and superfluid density are measurable quantities, our\nresults allow an experimental demonstration of the dramatized interplay between\nthe disorder and interaction in the nonequilibrium scenario.",
        "positive": "Inflationary quasiparticle creation and thermalization dynamics in\n  coupled Bose-Einstein condensates: A Bose gas in a double-well potential, exhibiting a true Bose-Einstein\ncondensate (BEC) amplitude and initially performing Josephson oscillations, is\na prototype of an isolated, non-equilibrium many-body system. We investigate\nthe quasiparticle (QP) creation and thermalization dynamics of this system by\nsolving the time-dependent Keldysh-Bogoliubov equations. We find avalanche-like\nQP creation due to a parametric resonance between BEC and QP oscillations,\nfollowed by slow, exponential relaxation to a thermal state at an elevated\ntemperature, controlled by the initial excitation energy of the oscillating BEC\nabove its ground state. The crossover between the two regimes occurs because of\nan effective decoupling of the QP and BEC oscillations. This dynamics is\nanalogous to elementary particle creation in models of the early universe. The\nthermalization in our set-up occurs because the BEC acts as a grand canonical\nreservoir for the quasiparticle system."
    },
    {
        "anchor": "Adiabatic loading of one-dimensional SU(N) alkaline earth fermions in\n  optical lattices: Ultracold fermionic alkaline earth atoms confined in optical lattices realize\nHubbard models with internal SU(N) symmetries, where N can be as large as ten.\nSuch systems are expected to harbor exotic magnetic physics at temperatures\nbelow the superexchange energy scale. Employing quantum Monte Carlo simulations\nto access the low-temperature regime, we show that after adiabatically loading\na weakly interacting gas into the strongly interacting regime of an optical\nlattice, the final temperature decreases with increasing N. Furthermore, we\nestimate the temperature scale required to probe correlations associated with\nlow-temperature SU(N) magnetism. Our findings are encouraging for the\nexploration of exotic large-N magnetic states in ongoing experiments.",
        "positive": "Induced interactions for ultracold Fermi gases in optical lattices: We investigate the effect of optical lattices on the BCS superfluidity by\nusing the Gorkov--Melik-Barkhudarov (GMB) correction for a two-component Fermi\ngas. We find that the suppression of the order parameter is strongly enhanced\nby the lattice effects. The predictions made by the GMB corrections are in\nqualitative and, for the cases studied, quantitative agreement with previous\nquantum Monte Carlo results. We discuss how the GMB correction extends the\nvalidity of the mean-field theory to a wider range of tunable optical lattice\nsystems in different dimensions."
    },
    {
        "anchor": "Optical control of the density and spin spatial profiles of a planar\n  Bose gas: We demonstrate the arbitrary control of the density profile of a\ntwo-dimensional Bose gas by shaping the optical potential applied to the atoms.\nWe use a digital micromirror device (DMD) directly imaged onto the atomic cloud\nthrough a high resolution imaging system. Our approach relies on averaging the\nresponse of many pixels of the DMD over the diffraction spot of the imaging\nsystem, which allows us to create an optical potential with arbitrary grey\nlevels and with micron-scale resolution. The obtained density distribution is\noptimized with a feedback loop based on the measured absorption images of the\ncloud. Using the same device, we also engineer arbitrary spin distributions\nthanks to a two-photon Raman transfer between internal ground states.",
        "positive": "Many-body Dynamics with Time-dependent Interaction: Recent advances in optical Feshbach resonance technique have enabled the\nexperimental investigation of atomic gases with time-dependent interaction. In\nthis work, we study the many-body dynamics of weakly interacting bosons subject\nwith an arbitrary time varying scattering length. By employing a variational\nansatz, we derive an effective Hamiltonian that governs the dynamics of thermal\nparticles. Crucially, we show that there exists a hidden symmetry in this\nHamiltonian that can map the many-body dynamics to the precession of an SU(1,1)\n\"spin\". As a demonstration, we calculate the situation where the scattering\nlength is sinusoidally modulated. We show that the non-compactness of the\nSU(1,1) group naturally leads to solutions with exponentially growth of\nBogoliubov modes and causes instabilities."
    },
    {
        "anchor": "Dynamics of a quenched spin-1 antiferromagnetic condensate in a harmonic\n  trap: In this paper we consider a recent experiment [Kang et al. PRA 95 053638\n(2017)] in which an antiferromagnetic spin-1 condensate of 23Na atoms was\nquenched from the easy-axis polar phase into the easy-plane polar phase. We\nsimulate the phase transition dynamics using a classical field method with\nnoisy initial conditions and find good agreement to the experimental\nobservations. We analyse the late-time dynamics in terms of phase ordering\nusing the nematic order parameter that we have developed in earlier work [Symes\net al. PRA 96, 013602 (2017)]. We show that these experiments are able to\nexplore the early stages of universal phase ordering where the domains grow\ndiffusively.",
        "positive": "Decay mechanisms of superflow of Bose-Einstein condensates in ring traps: We study the supercurrent decay of a Bose-Einstein condensate in a ring trap\ncombined with a repulsive barrier potential. In recent experiments, Kumar {\\it\net al.} [Phys. Rev. A {\\bf 95}, 021602(R) (2017)] have measured the dependence\nof the decay rate on the temperature and the barrier strength. However, the\norigin of the decay observed in the experiment remains unclear. We calculate\nthe rate of supercurrent decay due to thermally activated phase slips (TAPS) by\nusing the Kramers formula based on the Gross-Pitaevskii mean-field theory. The\nresulting decay rate is astronomically small compared to that measured in the\nexperiment, thus excluding the possibility of TAPS as the decay mechanism.\nAlternatively, we argue that three-body losses can be relevant to the observed\ndecay and predict that one can observe supercurrent decay via TAPS by\ndecreasing the number of atoms."
    },
    {
        "anchor": "Closed system approach to open systems: Tunneling decay of interacting\n  cold bosons in an optical lattice: A Bose-Hubbard Hamiltonian, modeling cold bosons in an optical lattice, is\nused to simulate the dynamics of interacting open quantum systems as subsystems\na larger closed system, avoiding complications like the introduction of baths,\ncomplex absorbing potentials or absorbing boundaries. The numerically exact\nunitary dynamics is compared with effective descriptions of the subsystems\nbased on non-Hermitian Hamiltonians or Lindblad master equations. The validity\nof popular models with constant decay rates is explicitly analyzed for decaying\nsingle and double wells. In addition we present a discrete lattice version of\nthe Siegert approximation method for calculating decay rates.",
        "positive": "Origin of the Three-body Parameter Universality in Efimov Physics: In recent years extensive theoretical and experimental studies of universal\nfew-body physics have led to advances in our understanding of universal Efimov\nphysics [1]. The Efimov effect, once considered a mysterious and esoteric\neffect, is today a reality that many experiments in ultracold quantum gases\nhave successfully observed and continued to explore [2-14]. Whereas theory was\nthe driving force behind our understanding of Efimov physics for decades,\nrecent experiments have contributed an unexpected discovery. Specifically,\nmeasurements have found that the so-called three-body parameter determining\nseveral properties of the system is universal, even though fundamental\nassumptions in the theory of the Efimov effect suggest that it should be a\nvariable property that depends on the precise details of the short-range two-\nand three-body interactions. The present Letter resolves this apparent\ncontradiction by elucidating unanticipated implications of the two-body\ninteractions. Our study shows that the three-body parameter universality\nemerges because a universal effective barrier in the three-body potentials\nprevents the three particles from simultaneously getting close to each other.\nOur results also show limitations on this universality, as it is more likely to\noccur for neutral atoms and less likely to extend to light nuclei."
    },
    {
        "anchor": "Determination of dynamical quantum phase transition for boson systems\n  using the Loschmidt cumulants method: We study the dynamical quantum phase transition(DQPT) of the Bose-Hubbard\nmodel utilizing recently developed Loschmidt cumulants method. We determine the\ncomplex Loschmidt zeros of the Loschmidt amplitude analogous to the Lee-Yang\nzeros of the thermal partition function. We obtain the DQPT critical points\nthrough identifying the crossing points with the imaginary axis. The critical\npoints show high accuracy when compared to those obtained using the matrix\nproduct states method. In addition, we show that how the critical points of\nDQPT can be determined by analyzing the energy fluctuation of the initial\nstate, making it a valuable tool for future studies in this area. Finally, DQPT\nin the extended Bose-Hubbaed model is also investigated.",
        "positive": "Multiple scattering dynamics of fermions at an isolated p-wave resonance: The wavefunction for indistinguishable fermions is anti-symmetric under\nparticle exchange, which directly leads to the Pauli exclusion principle, and\nhence underlies the structure of atoms and the properties of almost all\nmaterials. In the dynamics of collisions between two indistinguishable fermions\nthis requirement strictly prohibits scattering into 90 degree angles. Here we\nexperimentally investigate the collisions of ultracold clouds fermionic\n$\\rm^{40}K$ atoms by directly measuring scattering distributions. With\nincreasing collision energy we identify the Wigner threshold for p-wave\nscattering with its tell-tale dumb-bell shape and no $90^\\circ$ yield. Above\nthis threshold effects of multiple scattering become manifest as deviations\nfrom the underlying binary p-wave shape, adding particles either isotropically\nor axially. A shape resonance for $\\rm^{40}K$ facilitates the separate\nobservation of these two processes. The isotropically enhanced multiple\nscattering mode is a generic p-wave threshold phenomenon, while the axially\nenhanced mode should occur in any colliding particle system with an elastic\nscattering resonance."
    },
    {
        "anchor": "Frustrated Bose condensates in optical lattices: We study the Bose-condensed ground states of bosons in a two-dimensional\noptical lattice in the presence of frustration due to an effective vector\npotential, for example, due to lattice rotation. We use a mapping to a large-S\nfrustrated magnet to study quantum fluctuations in the condensed state. Quantum\neffects are introduced by considering a 1/S expansion around the classical\nground state. The large-S regime should be relevant to systems with many\nparticles per site. As the system approaches the Mott insulating state, the\nhole density becomes small. Our large-S results show that, even when the system\nis very dilute, the holes remain a (partially) condensed system. Moreover, the\nsuperfluid density is comparable to the condensate density. In other words, the\nlarge-S regime does not display an instability to noncondensed phases. However,\nfor cases with fewer than 1/3 flux quantum per lattice plaquette, we find that\nthe fractional condensate depletion increases as the system approaches the Mott\nphase, giving rise to the possibility of a noncondensed state before the Mott\nphase is reached for systems with smaller S.",
        "positive": "Ground States of a Bose-Hubbard Ladder in an Artificial Magnetic Field:\n  Field-Theoretical Approach: We consider a Bose-Hubbard ladder subject to an artificial magnetic flux and\ndiscuss its different ground states, their physical properties, and the quantum\nphase transitions between them. A low-energy effective field theory is derived,\nin the two distinct regimes of a small and large magnetic flux, using a\nbosonization technique starting from the weak-coupling limit. Based on this\neffective field theory, the ground-state phase diagram at a filling of one\nparticle per site is investigated for a small flux and for a flux equal to\n$\\pi$ per plaquette. For $\\pi$-flux, this analysis reveals a tricritical point\nwhich has been overlooked in previous studies. In addition, the Mott insulating\nstate at a small magnetic flux is found to display Meissner currents."
    },
    {
        "anchor": "On the effective Dirac equation for ultracold atoms in optical lattices:\n  role of the localization properties of the Wannier functions: We review the derivation of the effective Dirac equation for ultracold atoms\nin one-dimensional bichromatic optical lattices, following the proposal by\nWitthaut et al. Phys. Rev. A 84, 033601 (2011). We discuss how such a\nderivation - based on a suitable rotation of the Bloch basis and on a coarse\ngraining approximation - is affected by the choice of the Wannier functions\nentering the coarsening procedure. We show that in general the Wannier\nfunctions obtained by rotating the maximally localized Wannier functions for\nthe original Bloch bands can be sufficiently localized for justifying the\ncoarse graining approximation. We also comment on the relation between the\nrotation needed to achieve the Dirac form and the standard Foldy-Wouthuysen\ntransformation. Our results provide a solid ground for the interpretation of\nthe experimental results by Salger et al. Phys. Rev. Lett. 107, 240401 (2011)\nin terms of an effective Dirac dynamics.",
        "positive": "Quantum phases of Bose-Einstein condensates with synthetic spin -\n  orbital-angular-momentum coupling: The experimental realization of emergent spin-orbit coupling through\nlaser-induced Raman transitions in ultracold atoms paves the way for exploring\nnovel superfluid physics and simulating exotic many-body phenomena. A recent\nproposal with the use of Laguerre-Gaussian lasers enables another fundamental\ntype of coupling between spin and orbital angular momentum (SOAM) in ultracold\natoms. We hereby study quantum phases of a realistic Bose-Einstein condensate\n(BEC) with this synthetic SOAM coupling in a disk-shaped geometry, respecting\nradial inhomogeneity of the Raman coupling. We find that the experimental\nsystem naturally resides in a strongly interacting regime in which the phase\ndiagram significantly deviates from the single-particle picture. The interplay\nbetween SOAM coupling and interaction leads to rich structures in spin-resolved\nposition and momentum distributions, including a stripe phase and various types\nof immiscible states. Our results would provide a guide for an experimental\ninvestigation of SOAM-coupled BECs."
    },
    {
        "anchor": "Route to turbulence in a trapped Bose-Einstein condensate: We have studied a Bose-Einstein condensate of $^{87}Rb$ atoms under an\noscillatory excitation. For a fixed frequency of excitation, we have explored\nhow the values of amplitude and time of excitation must be combined in order to\nproduce quantum turbulence in the condensate. Depending on the combination of\nthese parameters different behaviors are observed in the sample. For the lowest\nvalues of time and amplitude of excitation, we observe a bending of the main\naxis of the cloud. Increasing the amplitude of excitation we observe an\nincreasing number of vortices. The vortex state can evolve into the turbulent\nregime if the parameters of excitation are driven up to a certain set of\ncombinations. If the value of the parameters of these combinations is exceeded,\nall vorticity disappears and the condensate enters into a different regime\nwhich we have identified as the granular phase. Our results are summarized in a\ndiagram of amplitude versus time of excitation in which the different\nstructures can be identified. We also present numerical simulations of the\nGross-Pitaevskii equation which support our observations.",
        "positive": "Dynamics of quantum quenching for BCS-BEC systems in the shallow BEC\n  regime: The problem of coupled Fermi-Bose mixtures of an ultracold gas near a narrow\nFeshbach resonance is approached through the time-dependent and complex\nGinzburg-Landau (TDGL) theory. The dynamical system is constructed using\nGinzburg-Landau-Abrikosov-Gor'kov (GLAG) path integral methods with the single\nmode approximation for the composite Bosons, and the equilibrium states are\nobtained in the BEC regime for adiabatic variations of the Feshbach detuning\nalong the stationary solutions of the dynamical system. Investigations into the\nrich superfluid dynamics of this system in the shallow BEC regime yields the\nonset of multiple interference patterns in the dynamics as the system is\nquenched from the deep-BEC regime. This results in a partial collapse and\nrevival of the coherent matter wave field of the BEC, whose temporal profile is\nreported."
    },
    {
        "anchor": "The Higgs mode in a two-dimensional superfluid: We present solid evidence for the existence of a well-defined Higgs amplitude\nmode in two-dimensional relativistic field theories based on analytically\ncontinued results from quantum Monte Carlo simulations of the Bose-Hubbard\nmodel in the vicinity of the superfluid-Mott insulator quantum critical point,\nfeaturing emergent particle-hole symmetry and Lorentz-invariance. The Higgs\nboson, seen as a well-defined low-frequency resonance in the spectral density,\nis quickly pushed to high energies in the superfluid phase and disappears by\nmerging with the broad secondary peak at the characteristic interaction scale.\nSimulations of a trapped system of ultra-cold $^{87}$Rb atoms demonstrate that\nthe low-frequency resonance feature is lost for typical experimental\nparameters, while the characteristic frequency for the onset of strong response\nis preserved.",
        "positive": "Universality class of quantum criticality for strongly repulsive spin-1\n  bosons with antiferromagnetic spin-exchange interaction: Using the thermodynamic Bethe ansatz equations we study the quantum phase\ndiagram, thermodynamics and criticality of one-dimensional spin-1 bosons with\nstrongly repulsive density-density and antiferromagnetic spin-exchange\ninteractions. We analytically derive a high precision equation of state from\nwhich the Tomonaga-Luttinger liquid physics and quantum critical behavior of\nthe system are computed. We obtain explicit forms for the scaling functions\nnear the critical points yielding the dynamical exponent $z=2$ and correlation\nlength exponent $\\nu=1/2$ for the quantum phase transitions driven by either\nthe chemical potential or the magnetic field. Consequently, we further\ndemonstrate that quantum criticality of the system can be mapped out from the\nfinite temperature density and magnetization profiles of the 1D trapped gas.\nOur results provide the physical origin of quantum criticality in a 1D\nmany-body system beyond the Tomonaga-Luttinger liquid description."
    },
    {
        "anchor": "Dynamical excitation of maxon and roton modes in a Rydberg-Dressed\n  Bose-Einstein Condensate: We investigate the dynamics of a three-dimensional Bose-Einstein condensate\nof ultracold atomic gases with a soft-core shape long-range interaction, which\nis induced by laser dressing the atoms to a highly excited Rydberg state. For a\nhomogeneous condensate, the long-range interaction drastically alters the\ndispersion relation of the excitation, supporting both roton and maxon modes.\nRotons are typically responsible for the creation of supersolids, while maxons\nare normally dynamically unstable in BECs with dipolar interactions. We show\nthat maxon modes in the Rydberg-dressed condensate, on the contrary, are\ndynamically stable. We find that the maxon modes can be excited through an\ninteraction quench, i.e. turning on the soft-core interaction instantaneously.\nThe emergence of the maxon modes is accompanied by oscillations at high\nfrequencies in the quantum depletion, while rotons lead to much slower\noscillations. The dynamically stable excitation of the roton and maxon modes\nleads to persistent oscillations in the quantum depletion. Through a\nself-consistent Bogoliubov approach, we identify the dependence of the maxon\nmode on the soft-core interaction. Our study shows that maxon and roton modes\ncan be excited dynamically and simultaneously by quenching Rydberg-dressed\nlong-range interactions. This is relevant to current studies in creating and\nprobing exotic states of matter with ultracold atomic gases.",
        "positive": "Thermalization in a one-dimensional integrable system: We present numerical results demonstrating the possibility of thermalization\nof single-particle observables in a one-dimensional integrable system (a\nquasicondensate of ultra-cold, weakly-interacting bosonic atoms being studied\nas a definite example). These results may seem counterintuitive because the\nphysical system is integrable in both the quantum and classical (mean-field)\ndescriptions. However, we find a class of initial conditions that admits the\nrelaxation of distributions of single-particle observables to the equilibrium\nstate very close to the Bose-Einstein thermal distribution of Bogoliubov\nquasiparticles. Our numerical results allow us to explain experimentally\nobserved thermalization in one-dimensional ultracold atomic gases on a short\n(~1 ms) time scale."
    },
    {
        "anchor": "Leading- and next-to-leading order semiclassical approximation to the\n  first seven virial coefficients of spin-1/2 fermions across spatial\n  dimensions: Following up on recent calculations, we investigate the leading- and\nnext-to-leading order semiclassical approximation to the virial coefficients of\na two-species fermion system with a contact interaction. Using the analytic\nresult for the second-order virial coefficient as a renormalization condition,\nwe derive expressions for up to the seventh-order virial coefficient $\\Delta\nb_7$. Our results at leading order, though approximate, furnish simple analytic\nformulas that relate $\\Delta b_n$ to $\\Delta b_2$ for arbitrary dimension,\nproviding a glimpse into the behavior of the virial expansion across dimensions\nand coupling strengths. As an application, we calculate the pressure and Tan's\ncontact of the 2D attractive Fermi gas and examine the radius of convergence of\nthe virial expansion as a function of the coupling strength.",
        "positive": "Post-adiabatic Hamiltonian for low-energy excitations in a slowly\n  time-dependent BCS-BEC crossover: We develop a Hamiltonian that describes the time-dependent formation of a\nmolecular Bose-Einstein condensate (BEC) from a Bardeen-Cooper-Schrieffer (BCS)\nstate of fermionic atoms as a result of slowly sweeping through a Feshbach\nresonance. In contrast to many other calculations in the field (see e.g.\n[1-4]), our Hamiltonian includes the leading post-adiabatic effects that arise\nbecause the crossover proceeds at a non-zero sweep rate. We apply a path\nintegral approach and a stationary phase approximation for the molecular zero\nmomentum background, which is a good approximation for narrow resonances (see\ne.g. [5, 6]). We use two-body adiabatic approximations to solve the atomic\nevolution within this background. The dynamics of the non-zero momentum\nmolecular modes is solved within a dilute gas approximation and by mapping it\nonto a purely bosonic Hamiltonian. Our main result is a post-adiabatic\neffective Hamiltonian in terms of the instantaneous bosonic\n(Anderson-)Bogoliubov modes, which holds throughout the whole resonance, as\nlong as the Feshbach sweep is slow enough to avoid breaking Cooper pairs."
    },
    {
        "anchor": "Superfluid drag of two-species Bose-Einstein condensates in optical\n  lattices: We study two-species Bose-Einstein condensates in quasi two-dimensional\noptical lattices of varying geometry and potential depth. Based on the\nnumerically exact Bloch and Wannier functions obtained using the plane-wave\nexpansion method, we quantify the drag (entrainment coupling) between the\ncondensate components. This drag originates from the (short range)\ninter-species interaction and increases with the kinetic energy. As a result of\nthe interplay between interaction and kinetic energy effects, the\nsuperfluid-drag coefficient shows a non-monotonic dependence on the lattice\ndepth. To make contact with future experiments, we quantitatively investigate\nthe drag for mass ratios corresponding to relevant atomic species.",
        "positive": "Bose-Einstein condensation and density collapse in a weakly coupled\n  boson-fermion mixture: We investigate the mechanical instability toward density collapse and the\ntransition temperature of Bose-Einstein condensation in the weakly coupled\nboson-fermion many-body mixture of single-component boson and fermion gases, in\nthe case of the repulsive boson-boson and attractive boson-fermion\ninteractions; no fermion-fermion interaction is assumed due to the Pauli\nexclusion because of the diluteness of the mixture. The mechanical instability\noccurs in the part of bosonic gas in the case where the induced boson-boson\nattraction mediated by the fermion polarization overcomes the boson-boson\nrepulsive interaction at low temperatures. We calculate the onset temperature\nof the mechanical instability and the BEC transition temperature for the\ninteraction strength and the boson-fermion number ratio. We also discuss the\nrelation between the mechanical instability and the BEC transition using a\ndiagrammatic method."
    },
    {
        "anchor": "Quantum Many-Body Scars and Quantum Criticality: In this letter, we study the PXP Hamiltonian with an external magnetic field\nthat exhibits both quantum scar states and quantum criticality. It is known\nthat this model hosts a series of quantum many-body scar states violating\nquantum thermalization at zero magnetic field, and it also exhibits an Ising\nquantum phase transition driven by finite magnetic field. Although the former\ninvolves the properties of generic excited states and the latter concerns the\nlow-energy physics, we discover two surprising connections between them,\ninspired by the observation that both states possess log-volume law\nentanglement entropies. First, we show that the quantum many-body scar states\ncan be tracked to a set of quantum critical states, whose nature can be\nunderstood as pair-wisely occupied Fermi sea states. Second, we show that the\npartial violation of quantum thermalization diminishes in the quantum critical\nregime. We envision that these connections can be extended to general\nsituations and readily verified in existing cold atom experimental platforms.",
        "positive": "All-optical transport and compression of ytterbium atoms into the\n  surface of a solid immersion lens: We present an all-optical method to load 174Yb atoms into a single layer of\nan optical trap near the surface of a solid immersion lens which improves the\nnumerical aperture of a microscope system. Atoms are transported to a region 20\num below the surface using a system comprised by three optical dipole traps.\nThe \"optical accordion\" technique is used to create a condensate and compress\nthe atoms to a width of 120 nm and a distance of 1.8 um away from the surface.\nMoreover, we are able to verify that after compression the condensate behaves\nas a two-dimensional quantum gas."
    },
    {
        "anchor": "Topological superfluidity with repulsive alkaline-earth atoms in optical\n  lattices: Topological superfluids are of technological relevance since they are\nbelieved to host Majorana bound states, a powerful resource for quantum\ncomputation and memory. Here we propose to realize topological superfluidity\nwith fermionic atoms in an optical lattice. We consider a situation where atoms\nin two internal states experience different lattice potentials: one species is\nlocalized and the other itinerant, and show how quantum fluctuations of the\nlocalized fermions give rise to an attraction and strong spin-orbit coupling in\nthe itinerant band. At low temperature, these effects stabilize a topological\nsuperfluid of mobile atoms even if their bare interactions are repulsive. This\nemergent state can be engineered with ${}^{87}$Sr atoms in a superlattice with\na dimerized unit cell. To probe its unique properties we describe protocols\nthat use high spectral resolution and controllability of the Sr clock\ntransition, such as momentum-resolved spectroscopy and supercurrent response to\na synthetic (laser-induced) magnetic field.",
        "positive": "Ultracold Fermionic Feshbach Molecules of $^{23}$Na$^{40}$K: We report on the formation of ultracold fermionic Feshbach molecules of\n$^{23}$Na$^{40}$K, the first fermionic molecule that is chemically stable in\nits ground state. The lifetime of the nearly degenerate molecular gas exceeds\n100 ms in the vicinity of the Feshbach resonance. The measured dependence of\nthe molecular binding energy on the magnetic field demonstrates the\nopen-channel character of the molecules over a wide field range and implies\nsignificant singlet admixture. This will enable efficient transfer into the\nsinglet vibrational ground state, resulting in a stable molecular Fermi gas\nwith strong dipolar interactions."
    },
    {
        "anchor": "Fermions in 2D Optical Lattices: Temperature and Entropy Scales for\n  Observing Antiferromagnetism and Superfluidity: One of the major challenges in realizing antiferromagnetic and superfluid\nphases in optical lattices is the ability to cool fermions. We determine\nconstraints on the entropy for observing these phases in two-dimensional\nHubbard models. We investigate antiferromagnetic correlations in the repulsive\nmodel at half filling and superfluidity of s-wave pairs in the attractive case\naway from half filling using determinantal quantum Monte Carlo simulations that\nare free of the fermion sign problem. We find that an entropy per particle\n~log(2) is sufficient to observe the charge gap in the repulsive Hubbard model\nor the pairing pseudogap in the attractive case. Observing antiferromagnetic\ncorrelations or superfluidity in 2D systems requires a further reduction in\nentropy by a factor of three or more. In contrast to higher dimensions, we find\nthat adiabatic cooling is not useful to achieve the required low temperatures.\nWe also show that double occupancy measurements are useful for thermometry for\ntemperatures greater than the nearest-neighbor hopping.",
        "positive": "Oscillatory-like Expansion of a Fermionic Superfluid: We study the expansion behaviours of a Fermionic superfluid in a cigar-shaped\noptical dipole trap for the whole BEC-BCS crossover and various temperatures.\nAt low temperature ($0.06(1) T_F$), the atom cloud undergoes an anisotropic\nhydrodynamic expansion over 30~ms, which behaves like oscillation in the\nhorizontal plane. By analyzing the expansion dynamics according to the\nsuperfluid hydrodynamic equation, the effective polytropic index $\\bar{\\gamma}$\nof Equation-of-State of Fermionic superfluid is extracted. The $\\bar{\\gamma}$\nvalues show a non-monotonic behavior over the BEC-BCS crossover, and have a\ngood agreement with the theoretical results in the unitarity and BEC side. The\nnormalized quasi-frequencies of the oscillatory expansion are measured, which\ndrop significantly from the BEC side to the BCS side and reach a minimum value\nof 1.73 around $1/k_Fa=-0.25$. Our work improves the understanding of the\ndynamic properties of strongly interacting Fermi gas."
    },
    {
        "anchor": "Outcoupling vector solitons from a Bose-Einstein condensate with\n  time-dependent interatomic forces: We discuss the possibility of emitting vector solitons from a two-component\nelongated BEC by manipulating in time the inter- or intra-species scattering\nlengths with Feshbach resonance tuning. We present different situations which\ndo not have an analogue in the single species case. In particular, we show\nvector soliton out-coupling by tuning the interspecies forces, how the\nevolution in one species is controlled by tuning the dynamics of the other, and\nhow one can implement the so-called supersolitons. The analysis is performed by\nnumerical simulations of the one-dimensional Gross-Pitaevskii equation. Simple\nanalytic arguments are also presented in order to give a qualitative insight.",
        "positive": "Spin-orbit-coupled spin-1 Bose-Einstein condensates in a toroidal trap:\n  even-petal-number necklacelike state and persistent flow: Spin-orbit coupling has novel spin-flip symmetries, a spin-1 spinor\nBose-Einstein condensate owns meaningful interactions, and a toroidal trap is\ntopologically nontrivial. We incorporate the three together and study the\nground-state phase diagram in a Rashba spin-orbit-coupled spin-1 Bose-Einstein\ncondensate with a toroidal trap. The spin-flip symmetries give rise to two\ndifferent interesting phases: persistent flows with a unit phase winding\ndifference between three components, and necklace states with even\npetal-number. The existing parameter regimes and properties of these phases are\ncharacterized by two-dimension numerical calculations and an azimuthal\nanalytical one-dimension model."
    },
    {
        "anchor": "Exact Diagonalisation of Photon Bose-Einstein Condensates with\n  Thermo-Optic Interaction: Although photon Bose-Einstein condensates have already been used for studying\nmany interesting effects, the precise role of the photon-photon interaction is\nnot fully clarified up to now. In view of this, it is advantageous that these\nsystems allow measuring both the intensity of the light leaking out of the\ncavity and its spectrum at the same time. Therefore, the photon-photon\ninteraction strength can be determined once via analysing the condensate\nbroadening and once via examining the interaction-induced modifications of the\ncavity modes. As the former method depends crucially on the concrete shape of\nthe trapping potential and the spatial resolution of the used camera,\ninterferometric methods promise more precise measurements. To this end, the\npresent paper works out the impact of the photon-photon interaction upon the\ncavity modes. A quantum mechanical description of the photon-photon\ninteraction, including the thermal cloud, builds the theoretical backbone of\nthe method. An exact diagonalisation approach introduced here exposes how the\neffective photon-photon interaction modifies both the spectrum and the width of\nthe photon gas. A comparison with a variational approach based on the\nGross-Pitaevskii equation quantifies the contribution of the thermal cloud in\nthe respective applications.",
        "positive": "Master-slave synchronization of Bose-Einstein condensate in 1D tilted\n  bichromatical optical lattice: This paper investigates the synchronization of chaotic behavior in a model of\nBose-Einstein condensate (BEC) held in a 1D tilted bichromatical optical\nlattice potential by using the active control technique. The synchronization is\npresented in the master-slave configuration which implies that the master\nsystem evolves freely and drives the dynamics of the slave system. Also the\nnumerical simulations are given to indicate the practicability and the\neffectiveness of the used controllers."
    },
    {
        "anchor": "Kibble-Zurek Mechanism in a Spin-1 Bose-Einstein Condensate: We observe power-law scaling of the temporal onset of excitations with quench\nspeed in the neighborhood of the quantum phase transition between the polar and\nbroken-axisymmetry phases in a small spin-1 ferromagnetic Bose-Einstein\ncondensate. As the system is driven through the quantum critical point by\ntuning the Hamiltonian, the vanishing energy gap between the ground state and\nfirst excited state causes the reaction time scale of the system to diverge,\npreventing it from adiabatically following the ground state. We measure the\ntemporal evolution of the spin populations for different quench speeds and\ndetermine the exponents characterizing the scaling of the onset of excitations,\nwhich are in good agreement with the predictions of the Kibble-Zurek mechanism.",
        "positive": "Conductivity spectrum of ultracold atoms in an optical lattice: We measure the conductivity of neutral fermions in a cubic optical lattice.\nUsing in-situ fluorescence microscopy, we observe the alternating current\nresultant from a single-frequency uniform force applied by displacement of a\nweak harmonic trapping potential. In the linear response regime, a\nneutral-particle analogue of Ohm's law gives the conductivity as the ratio of\ntotal current to force. For various lattice depths, temperatures, interaction\nstrengths, and fillings, we measure both real and imaginary conductivity, up to\na frequency sufficient to capture the transport dynamics within the lowest\nband. The spectral width of the real conductivity reveals the current\ndissipation rate in the lattice, and the integrated spectral weight is related\nto thermodynamic properties of the system through a sum rule. The global\nconductivity decreases with increased band-averaged effective mass, which at\nhigh temperatures approaches a T-linear regime. Relaxation of current is\nobserved to require a finite lattice depth, which breaks Galilean invariance\nand enables damping through collisions between fermions."
    },
    {
        "anchor": "Modulational instability and quantum droplets in a two-dimensional\n  Bose-Einstein condensate: Modulational instability of a uniform two-dimensional binary Bose-Einstein\ncondensate (BEC) in the presence of quantum fluctuations is studied. The\nanalysis is based on the coupled Gross-Pitaevskii equations. It is shown that\nquantum fluctuations can induce instability when the BEC density is below a\nthreshold. The dependence of the growth rate of modulations on the BEC\nparameters is found. It is observed that an asymmetry of the interaction\nparameters and/or initial densities of the components typically decreases the\ngrowth rate. Further development of the instability results in a break-up of\nthe BEC into a set of quantum droplets. These droplets merge dynamically with\neach other so that the total number of droplets decreases rapidly. The rate of\nthis decrease is evaluated numerically for different initial parameters.",
        "positive": "Effects of fermion exchanges on the polarization of exciton condensates: Exchange processes are responsible for the stability of elementary boson\ncondensates with respect to their possible fragmentation. This remains true for\ncomposite bosons when single fermion exchanges are included but spin degrees of\nfreedom are ignored. We here show that their inclusion can produce a\n\"spin-fragmentation\" of a condensate of dark excitons, i.e., an unpolarized\ncondensate with equal amount of dark excitons with spins (+2) and (-2). Quite\nsurprisingly, for spatially indirect excitons of semiconductor bilayers, we\npredict that the condensate polarization can switch from unpolarized to fully\npolarized, depending on the distance between the layers confining electrons and\nholes. Remarkably, the threshold distance associated to this switching lies in\nthe regime where experiments are nowadays carried out."
    },
    {
        "anchor": "Parity Symmetry Breaking and Topological Phases in a Superfluid Ring: We study analytically the superfluid flow of a Bose-Einstein condensate in a\nring geometry in presence of a rotating barrier. We show that a phase\ntransition breaking a parity symmetry among two topological phases occurs at a\ncritical value of the height of the barrier. Furthermore, a discontinuous\n(accompanied by hysteresis) phase transition is observed in the ordered phase\nwhen changing the angular velocity of the barrier. At the critical point where\nthe hysteresis area vanishes, chemical potential of the ground state develops a\ncusp (a discontinuity in the first derivative). Along this path, the jump\nbetween the two corresponding states having a different winding number shows\nstrict analogies with a topological phase transition. We finally study the\ncurrent-phase relation of the system and compare some of our calculations with\npublished experimental results.",
        "positive": "Variational theory for the ground state and collective excitations of an\n  elongated dipolar condensate: We develop a variational theory for a dipolar condensate in an elongated\n(cigar shaped) confinement potential. Our formulation provides an effective\none-dimensional extended meanfield theory for the ground state and its\ncollective excitations. We apply our theory to investigate the properties of\nrotons in the system comparing the variational treatment to a full numerical\nsolution. We consider the effect of quantum fluctuations on the scattering\nlength at which the roton excitation softens to zero energy."
    },
    {
        "anchor": "Simulating dense QCD matter with ultracold atomic boson-fermion mixtures: We delineate, as an analog of two-flavor dense quark matter, the phase\nstructure of a many-body mixture of atomic bosons and fermions in two internal\nstates with a tunable boson-fermion attraction. The bosons b correspond to\ndiquarks, and the fermions f to unpaired quarks. For weak b-f attraction, the\nsystem is a mixture of a Bose-Einstein condensate and degenerate fermions,\nwhile for strong attraction composite b-f fermions N, analogs of the nucleon,\nare formed, which are superfluid due to the N-N attraction in the spin-singlet\nchannel. We determine the symmetry breaking patterns at finite temperature as a\nfunction of the b-f coupling strength, and relate the phase diagram to that of\ndense QCD.",
        "positive": "Theory of condensation of indirect excitons in a trap: We present theoretical studies of condensation of indirect excitons in a\ntrap. Our model quantifies the effect of screening of the trap potential by\nindirect excitons on exciton condensation. The theoretical studies are applied\nto a system of indirect excitons in a GaAs/AlGaAs coupled quantum well\nstructure in a diamond-shaped electrostatic trap where exciton condensation was\nstudied in earlier experiments. The estimated condensation temperature of the\nindirect excitons in the trap reaches hundreds of milliKelvin."
    },
    {
        "anchor": "Observation of the Efimovian Expansion in Scale Invariant Fermi Gases: Scale invariance emerges and plays an important role in strongly correlated\nmany-body systems such as critical regimes nearby phase transitions and the\nunitary Fermi gases. Discrete scaling symmetry also manifests itself in quantum\nfew-body systems such as the Efimov effect. Here we report both theoretical\npredication and experimental observation of a novel type expansion dynamics for\nscale invariant quantum gases. When the frequency of the harmonic trap holding\nthe gas decreases continuously as the inverse of time $t$, surprisingly, the\nexpansion of cloud size exhibits a sequence of plateaus. Remarkably, the\nlocations of these plateaus obey a discrete geometric scaling law with a\ncontrollable scale factor and the entire expansion dynamics is governed by a\nlog-periodic function. This striking expansion of quantum Fermi gases shares\nsimilar scaling laws and same mathematical description as the Efimov effect.\nOur work demonstrates the first expansion dynamics of a quantum many-body\nsystem with the temporal discrete scaling symmetry, which reveals the\nunderlying spatial continuous scaling symmetry of the many-body system.",
        "positive": "Coherence and decoherence in the Harper-Hofstadter model: We quantum-simulated the 2D Harper-Hofstadter (HH) lattice model in a highly\nelongated tube geometry -- three sites in circumference -- using an atomic\nBose-Einstein condensate. In addition to the usual transverse (out-of-plane)\nmagnetic flux, piercing the surface of the tube, we threaded a longitudinal\nflux $\\Phi_{\\rm L}$ down the axis of the tube This geometry evokes an\nAharonov-Bohm interferometer, where noise in $\\Phi_{\\rm L}$ would readily\ndecohere the interference present in trajectories encircling the tube. We\nobserve this behavior only when transverse flux is a rational fraction of the\nflux-quantum, and remarkably find that for irrational fractions the decoherence\nis absent. Furthermore, at rational values of transverse flux, we show that the\ntime evolution averaged over the noisy longitudinal flux matches the time\nevolution at nearby irrational fluxes. Thus, the appealing intuitive picture of\nan Aharonov-Bohm interferometer is insufficient. Instead, we quantitatively\nexplain our observations by transforming the HH model into a collection of\nmomentum-space Aubry-Andr\\'{e} models."
    },
    {
        "anchor": "Linear dependencies between Composite Fermion states: It has been observed that the composite fermion (CF) approach tends to\novercount the number of linearly independent candidate states for fixed sets of\nquantum numbers [number of particles, total angular momentum, and (pseudo)spin\nif applicable]. That is, CF Slater determinants that are orthogonal before\nprojection, may lead to wave functions that are identical, or possess linear\ndependencies, after projection. This has been pointed out both in the context\nof rotating bosons in the lowest Landau level, and for excited bands of the\n(fermionic) fractional quantum Hall effect. We present a systematic approach\nthat enables us to reveal all linear dependencies between bosonic compact\nstates in the lowest CF \"cyclotron energy\" sub-band, and almost all\ndependencies in higher sub-bands, at the level of the CF Slater determinants,\ni.e. before projection, which implies a major computational simplification. Our\napproach is introduced for so-called simple states of two-species rotating\nbosons, and then generalised to generic compact bosonic states, both one- and\ntwo-species. Some perspectives also apply to fermionic systems. The identities\nand linear dependencies we find, are analytically exact for \"brute force\"\nprojection in the disk geometry.",
        "positive": "Observation of Correlated Particle-Hole Pairs and String Order in\n  Low-Dimensional Mott Insulators: Quantum phases of matter are characterized by the underlying correlations of\nthe many-body system. Although this is typically captured by a local order\nparameter, it has been shown that a broad class of many-body systems possesses\na hidden non-local order. In the case of bosonic Mott insulators, the ground\nstate properties are governed by quantum fluctuations in the form of correlated\nparticle-hole pairs that lead to the emergence of a non-local string order in\none dimension. Using high-resolution imaging of low-dimensional quantum gases\nin an optical lattice, we directly detect these pairs with single-site and\nsingle-particle sensitivity and observe string order in the one-dimensional\ncase."
    },
    {
        "anchor": "Full and fractional defects across the Berezinskii-Kosterlitz-Thouless\n  transition in a driven-dissipative spinor quantum fluid: We investigate the properties of a two-dimensional \\emph{spinor} microcavity\npolariton system driven by a linearly polarised continuous pump. In particular,\nwe establish the role of the elementary excitations, namely the so-called\nhalf-vortices and full-vortices; these objects carry a quantum rotation only in\none of the two, or both, spin components respectively. Our numerical analysis\nof the steady-state shows that it is only the half-vortices that are present in\nthe vortex-antivortex pairing/dissociation responsible for the\nBerezinskii-Kosterlitz-Thouless transition. These are the relevant elementary\nexcitations close to the critical point. However, by exploring the\nphase-ordering dynamics following a sudden quench across the transition we\nprove that full-vortices become the relevant excitations away from the critical\npoint in a deep quasi-ordered state at late times. The time-scales for\nhalf-vortices binding into full vortices are much faster than the\nvortex-antivortex annihilations.",
        "positive": "Clock shifts in a Fermi gas interacting with a minority component: a\n  soluble model: We consider the absorption spectrum of a Fermi gas mixed with a minority\nspecies when majority fermions are transferred to another internal state by an\nexternal probe. In the limit when the minority species is much more massive\nthan the majority one, we show that the minority species may be treated as\nstatic impurities and the problem can be solved in closed form. The analytical\nresults bring out the importance of vertex corrections, which change\nqualitatively the nature of the absorption spectrum. It is demonstrated that\nlarge line shifts are not associated with resonant interactions in general. We\nalso show that the commonly used ladder approximation fails when the majority\ncomponent is degenerate for large mass ratios between the minority and majority\nspecies and that bubble diagrams, which correspond to the creation of many\nparticle--hole pairs, must be taken into account. We carry out detailed\nnumerical calculations, which confirm the analytical insights and we point out\nthe connection to shadowing phenomena in nuclear physics."
    },
    {
        "anchor": "Bose-Hubbard model on polyhedral graphs: Ever since the first observation of Bose-Einstein condensation in the\nnineties, ultracold quantum gases have been the subject of intense research,\nproviding a unique tool to understand the behavior of matter governed by the\nlaws of quantum mechanics. Ultracold bosonic atoms loaded in an optical lattice\nare usually described by the Bose-Hubbard model or a variant of it. In addition\nto the common insulating and superfluid phases, other phases (like density\nwaves and supersolids) may show up in the presence of a short-range\ninterparticle repulsion and also depending on the geometry of the lattice. We\nherein explore this possibility, using the graph of a convex polyhedron as\n\"lattice\" and playing with the coordination of nodes to promote the wanted\nfinite-size ordering. To accomplish the job we employ the method of decoupling\napproximation, whose efficacy is tested in one case against exact\ndiagonalization. We report zero-temperature results for two Catalan solids, the\ntetrakis hexahedron and the pentakis dodecahedron, for which a thorough\nground-state analysis reveals the existence of insulating \"phases\" with\npolyhedral order and a widely extended supersolid region. The key to this\noutcome is the unbalance in coordination between inequivalent nodes of the\ngraph. The predicted phases can be probed in systems of ultracold atoms using\nprogrammable holographic optical tweezers.",
        "positive": "Generalized ABCD propagation for interacting atomic clouds: We present a treatment of the nonlinear matter wave propagation inspired from\noptical methods, which includes interaction effects within the atom optics\nequivalent of the aberrationless approximation. The atom-optical ABCD matrix\nformalism, considered so far for non-interacting clouds, is extended\nperturbatively beyond the linear regime of propagation. This approach, applied\nto discuss the stability of a matter-wave resonator involving a free-falling\nsample, agrees very well with the predictions of the full nonlinear paraxial\nwave equation. An alternative optical treatment of interaction effects, based\non the aberrationless approximation and suitable for cylindrical paraxial beams\nof uniform linear density, is also adapted for matter waves."
    },
    {
        "anchor": "Magnetic lattices for ultracold atoms: This article reviews the development in our laboratory of magnetic lattices\ncomprising periodic arrays of magnetic microtraps created by patterned magnetic\nfilms to trap periodic arrays of ultracold atoms. Recent achievements include\nthe realisation of multiple Bose-Einstein condensates in a 10 micron-period\none-dimensional magnetic lattice; the fabrication of sub-micron-period square\nand triangular magnetic lattice structures suitable for quantum tunnelling\nexperiments; the trapping of ultracold atoms in a sub-micron-period triangular\nmagnetic lattice; and a proposal to use long-range interacting Rydberg atoms to\nachieve spin-spin interactions between sites in a large-spacing magnetic\nlattice.",
        "positive": "Spin-Orbit Coupled One-Dimensional Fermi Gases with Infinite Repulsion: The current efforts of studying many-body effects with spin-orbit coupling\n(SOC) using alkali-metal atoms are impeded by the heating effects due to\nspontaneous emission. Here, we show that even for SOCs too weak to cause any\nheating, dramatic many-body effects can emerge in a one-dimensional(1D) spin\n1/2 Fermi gas provided the interaction is sufficiently repulsive. For weak\nrepulsion, the effect of a weak SOC (with strength $\\Omega$) is perturbative.\ninducing a weak spin spiral (with magnitude proportional to $\\Omega$). However,\nas the repulsion $g$ increases beyond a critical value ($g_c\\sim 1/\\Omega$),\nthe magnitude of the spin spiral rises rapidly to a value of order 1\n(independent of $\\Omega$). Moreover, near $g=+\\infty$, the spins of neighboring\nfermions can interfere destructively due to quantum fluctuations of particle\nmotion, strongly distorting the spin spiral and pulling the spins substantially\naway from the direction of the local field at various locations. These effects\nare consequences of the spin-charge separation in the strongly repulsive limit.\nThey will also occur in other 1D quantum gases with higher spins."
    },
    {
        "anchor": "Stepwise Bose-Einstein condensation in a spinor gas: We observe multi-step condensation of sodium atoms with spin $F=1$, where the\ndifferent Zeeman components $m_F=0,\\pm 1$ condense sequentially as the\ntemperature decreases. The precise sequence changes drastically depending on\nthe magnetization $m_z$ and on the quadratic Zeeman energy $q$ (QZE) in an\napplied magnetic field. For large QZE, the overall structure of the phase\ndiagram is the same as for an ideal spin 1 gas, although the precise locations\nof the phase boundaries are significantly shifted by interactions. For small\nQZE, antiferromagnetic interactions qualitatively change the phase diagram with\nrespect to the ideal case, leading for instance to condensation in $m_F=\\pm 1$,\na phenomenon that cannot occur for an ideal gas with $q>0$.",
        "positive": "Numerical method for evolving the dipolar projected Gross-Pitaevskii\n  equation: We describe a method for evolving the projected Gross-Pitaevskii equation\n(PGPE) for an interacting Bose gas in a harmonic oscillator potential, with the\ninclusion of a long-range dipolar interaction. The central difficulty in\nsolving this equation is the requirement that the field is restricted to a\nsmall set of prescribed modes that constitute the low energy c-field region of\nthe system. We present a scheme, using a Hermite-polynomial based spectral\nrepresentation, that precisely implements this mode restriction and allows an\nefficient and accurate solution of the dipolar PGPE. We introduce a set of\nauxiliary oscillator states to perform a Fourier transform necessary to\nevaluate the dipolar interaction in reciprocal space. We extensively\ncharacterize the accuracy of our approach, and derive Ehrenfest equations for\nthe evolution of the angular momentum."
    },
    {
        "anchor": "Stability and spatial coherence of nonresonantly pumped\n  exciton-polariton condensates: We investigate the stability and coherence properties of one-dimensional\nexciton-polariton condensates under nonresonant pumping. We model the\ncondensate dynamics using the open-dissipative Gross-Pitaevskii equation. In\nthe case of spatially homogeneous pumping, we find that the instability of the\nsteady state leads to significant eduction of the coherence length. We consider\ntwo effects that can lead to the stabilization of the steady state, i.e. the\npolariton energy relaxation and the influence of an inhomogeneous pumping\nprofile. We find that, while the former has little effect on the stability, the\nlatter is very effective in stabilizing the condensate which results in a large\ncoherence length.",
        "positive": "Elementary excitations in a spin-orbit-coupled spin-1 Bose-Einstein\n  condensate: While a spin-orbit-coupled spin-1 Bose-Einstein condensate has been\nexperimentally observed, its elementary excitations remain unclear in the\nstripe phase. Here, we systematically study the elementary excitations in three\ndistinct phases of a spin-orbit-coupled spin-1 Bose-Einstein condensate. We\nfind that the excitation spectrum as well as the corresponding static response\nfunction and structure factor depend strongly on spin-orbit coupling parameters\nsuch as the quadratic Zeeman field and the Rabi frequency. In the stripe phase,\nbesides two gapless Goldstone modes, we show the existence of roton\nexcitations. Finally, we demonstrate that quantum phase transitions between\nthese different phases including the zero-momentum, plane wave and stripe\nphases are characterized by the sound velocities and the quantum depletion."
    },
    {
        "anchor": "Connecting dissipation and phase slips in a Josephson junction between\n  fermionic superfluids: We study the emergence of dissipation in an atomic Josephson junction between\nweakly-coupled superfluid Fermi gases. We find that vortex-induced phase\nslippage is the dominant microscopic source of dissipation across the BEC-BCS\ncrossover. We explore different dynamical regimes by tuning the bias chemical\npotential between the two superfluid reservoirs. For small excitations, we\nobserve dissipation and phase coherence to coexist, with a resistive current\nfollowed by well-defined Josephson oscillations. We link the junction transport\nproperties to the phase-slippage mechanism, finding that vortex nucleation is\nprimarily responsible for the observed trends of conductance and critical\ncurrent. For large excitations, we observe the irreversible loss of coherence\nbetween the two superfluids, and transport cannot be described only within an\nuncorrelated phase-slip picture. Our findings open new directions for\ninvestigating the interplay between dissipative and superfluid transport in\nstrongly correlated Fermi systems, and general concepts in out-of-equlibrium\nquantum systems.",
        "positive": "Role of the relative phase in the merging of two independent\n  Bose-Einstein condensates: We study the merging of two independent Bose-Einstein condensates with\narbitrary initial phase difference, in the framework of a one-dimensional\ntime-dependent Gross-Pitaevskii model. The role of the initial phase difference\nin the process is discussed, and various types of phase-sensitive excitations\nare identified."
    },
    {
        "anchor": "Sum rules for spin-$1/2$ quantum gases in states with well-defined\n  spins: spin-independent interactions and spin-dependent external fields: Analytical expressions are derived for sums of matrix elements and their\nsquared moduli over many-body states with given total spin --- the states built\nfrom spin and spatial wavefunctions belonging to multidimensional irreducible\nrepresentations of the symmetric group, unless the total spin has the maximal\nallowed value. For spin-dependent one-body interactions with external fields\nand spin-independent two-body ones between the particles, the sum dependence on\nthe many-body states is given by universal factors, which are independent of\nthe interaction details and Hamiltonians of non-interacting particles. The sum\nrules are applied to perturbative analysis of energy spectra.",
        "positive": "Ultra-cold Polarized Fermi Gases: Recent experiments with ultra-cold atoms have demonstrated the possibility of\nrealizing experimentally fermionic superfluids with imbalanced spin\npopulations. We discuss how these developments have shed a new light on a half-\ncentury old open problem in condensed matter physics, and raised new\ninterrogations of their own."
    },
    {
        "anchor": "Immiscible and miscible states in binary condensates in the ring\n  geometry: We report detailed investigation of the existence and stability of mixed and\ndemixed modes in binary atomic Bose-Einstein condensates with repulsive\ninteractions in a ring-trap geometry. The stability of such states is examined\nthrough eigenvalue spectra for small perturbations, produced by the\nBogoliubov-de Gennes equations, and directly verified by simulations based on\nthe coupled Gross-Pitaevskii equations, varying inter- and intra-species\nscattering lengths so as to probe the entire range of miscibility-immiscibility\ntransitions. In the limit of the one-dimensional (1D) ring, i.e., a very narrow\none, stability of mixed states is studied analytically, including\nhidden-vorticity (HV) modes, i.e., those with opposite vorticities of the two\ncomponents and zero total angular momentum. The consideration of demixed 1D\nstates reveals, in addition to stable composite single-peak structures, double-\nand triple-peak ones, above a certain particle-number threshold. In the 2D\nannular geometry, stable demixed states exist both in radial and azimuthal\nconfigurations. We find that stable radially-demixed states can carry arbitrary\nvorticity and, counter-intuitively, the increase of the vorticity enhances\nstability of such states, while unstable ones evolve into randomly oscillating\nangular demixed modes. The consideration of HV states in the 2D geometry\nexpands the stability range of radially-demixed states.",
        "positive": "Parametric Resonance in Bose-Einstein Condensates: We demonstrate parametric resonance in Bose-Einstein condensates (BECs) with\nattractive two-body interaction in a harmonic trap under parametric excitation\nby periodic modulation of the s-wave scattering length. We obtain nonlinear\nequations of motion for the widths of the condensate using a Gaussian\nvariational ansatz for the Gross-Pitaevskii condensate wave function. We\nconduct both linear and nonlinear stability analyses for the equations of\nmotion and find qualitative agreement, thus concluding that the stability of\ntwo equilibrium widths of a BEC might be inverted by parametric excitation."
    },
    {
        "anchor": "Two-band description of resonant superfluidity in atomic Fermi gases: Fermionic superfluidity in atomic Fermi gases across a Feshbach resonance is\nnormally described by the atom-molecule theory, which treats the closed channel\nas a noninteracting point boson. In this work we present a theoretical\ndescription of the resonant superfluidity in analogy to the two-band\nsuperconductors. We employ the underlying two-channel scattering model of\nFeshbach resonance where the closed channel is treated as a composite boson\nwith binding energy $\\varepsilon_0$ and the resonance is triggered by the\nmicroscopic interchannel coupling $U_{12}$. The binding energy $\\varepsilon_0$\nnaturally serves as an energy scale of the system, which has been sent to\ninfinity in the atom-molecule theory. We show that the atom-molecule theory can\nbe viewed as a leading-order low-energy effective theory of the underlying\nfermionic theory in the limit $\\varepsilon_0\\rightarrow\\infty$ and\n$U_{12}\\rightarrow0$, while keeping the phenomenological atom-molecule coupling\nfinite. The resulting two-band description of the superfluid state is in\nanalogy to the BCS theory of two-band superconductors. In the dilute limit\n$\\varepsilon_0\\rightarrow\\infty$, the two-band description recovers precisely\nthe atom-molecule theory. The two-band theory provides a natural approach to\nstudy the corrections because of a finite binding energy $\\varepsilon_0$ in\nrealistic experimental systems. For broad and moderate resonances, the\ncorrection is not important for current experimental densities. However, for\nextremely narrow resonance, we find that the correction becomes significant.\nThe finite binding energy correction could be important for the stability of\nhomogeneous polarized superfluid against phase separation in imbalanced Fermi\ngases across a narrow Feshbach resonance.",
        "positive": "Suppression of inter-band heating for random driving: Heating to high-lying states strongly limits the experimental observation of\ndriving induced non-equilibrium phenomena, particularly when the drive has a\nbroad spectrum. Here we show that, for entire families of structured random\ndrives known as random multipolar drives, particle excitation to higher bands\ncan be well controlled even away from a high-frequency driving regime. This\nopens a window for observing drive-induced phenomena in a long-lived prethermal\nregime in the lowest band."
    },
    {
        "anchor": "Persistent bright solitons in sign-indefinite coupled nonlinear\n  Schrodinger equations with a time-dependent harmonic trap: We introduce a model based on a system of coupled nonlinear Schrodinger (NLS)\nequations with opposite signs infront of the kinetic and gradient terms in the\ntwo equations. It also includes time-dependent nonlinearity coefficients and a\nparabolic expulsive potential. By means of a gauge transformation, we\ndemonstrate that, with a special choice of the time dependence of the trap, the\nsystem gives rise to persistent solitons. Exact single and two-soliton\nanalytical solutions and their stability are corroborated by numerical\nsimulations. In particular, the exact solutions exhibit inelastic collisions\nbetween solitons.",
        "positive": "Quantum probe spectroscopy for cold atomic systems: We study a two-level impurity coupled locally to a quantum gas on an optical\nlattice. For state-dependent interactions between the impurity and the gas, we\nshow that its evolution encodes information on the local excitation spectrum of\ngas at the coupling site. Based on this, we design a nondestructive method to\nprobe the system's excitations in a broad range of energies by measuring the\nstate of the probe using standard atom optics methods. We illustrate our\nfindings with numerical simulations for quantum lattice systems, including\nrealistic dephasing noise on the quantum probe, and discuss practical limits on\nthe probe dephasing rate to fully resolve both regular and chaotic spectra."
    },
    {
        "anchor": "Topological charge pumping in spin-dependent superlattices with glide\n  symmetry: Topological charge pumping represents an important quantum phenomenon that\nshows the fundamental connection to the topological properties of dynamical\nsystems. Here, we introduce a pumping process in a spin-dependent double-well\noptical lattice with glide symmetry. In the dynamic process, the glide symmetry\nprotects the band touching points and topological properties of the system are\ncharacterised by the non-Abelian Berry curvature. By engineering suitable form\nof interaction between different spin components, the model not only\ndemonstrates topological phase transition, but also shows hybridisation between\nthe spatial and temporal domain with novel topological features captured by the\nWilson line along the synthetic directions. Our work provides a new model based\non ultracold atoms towards the implementation of versatile topological matters\nand topological phenomena.",
        "positive": "Vortex Phases of Rotating Superfluids: We report on the first mathematically rigorous proofs of a transition to a\ngiant vortex state of a superfluid in rotating anharmonic traps. The analysis\nis carried out within two-dimensional Gross-Pitaevskii theory at large coupling\nconstant and large rotational velocity and is based on precise asymptotic\nestimates on the ground state energy. An interesting aspect is a significant\ndifference between 'soft' anharmonic traps (like a quartic plus quadratic\ntrapping potential) and traps with a fixed boundary. In the former case\nvortices persist in the bulk until the width of the annulus becomes comparable\nto the size of the vortex cores. In the second case the transition already\ntakes place in a parameter regime where the size of vortices is very small\nrelative to the width of the annulus. Moreover, the density profiles in the\nannulus are different in the two cases. In both cases rotational symmetry of\nthe density in a true ground state is broken, even though a symmetric\nvariational ansatz gives an excellent approximation to the energy."
    },
    {
        "anchor": "Nonequilibrium States of a Quenched Bose Gas: Yin and Radzihovsky [1] recently developed a self-consistent extension of a\nBogoliubov theory, in which the condensate number density $n_c$ is treated as a\nmean field that changes with time, in order to analyze a JILA experiment by\nMakotyn et al. [2] on a $^{85}$Rb Bose gas following a deep quench to a large\nscattering length. We apply this theory to construct a closed set of equations\nthat highlight the role of $\\dot{n}_c$, which is to induce an effective\ninteraction between quasiparticles. We show analytically that such a system\nsupports a steady state characterized by a constant condensate density and a\nsteady but periodically changing momentum distribution, whose time average is\ndescribed exactly by the generalized Gibbs ensemble. We discuss how the\n$\\dot{n}_{c}$-induced effective interaction, which cannot be ignored on the\ngrounds of the adiabatic approximation for modes near the gapless Goldstone\nmode, can significantly affect condensate populations and Tan's contact for a\nBose gas that has undergone a deep quench.",
        "positive": "Vortex formation of a Bose-Einstein condensate in a rotating deep\n  optical lattice: We study the dynamics of vortex nucleation and lattice formation in a\nBose--Einstein condensate in a rotating square optical lattice by numerical\nsimulations of the Gross--Pitaevskii equation. Different dynamical regimes of\nvortex nucleation are found, depending on the depth and period of the optical\nlattice. We make an extensive comparison with the experiments by Williams {\\it\net al.} [Phys. Rev. Lett. {\\bf 104}, 050404 (2010)], especially focusing on the\nissues of the critical rotation frequency for the first vortex nucleation and\nthe vortex number as a function of rotation frequency."
    },
    {
        "anchor": "Ultracold fermions in a cavity-induced artificial magnetic field: We show how a fermionic quantum gas in an optical lattice and coupled to the\nfield of an optical cavity can self-organize into a state in which the\nspontaneously emerging cavity field amplitude induces an artificial magnetic\nfield. The fermions form either a chiral insulator or a chiral liquid carrying\nedge currents. The feedback mechanism via the cavity field enables robust and\nfast switching of the edge currents and the cavity output can be employed for\nnon-destructive measurements of the atomic dynamics.",
        "positive": "Exact $\\mathcal{N}$-point function mapping between pairs of experiments\n  with Markovian open quantum systems: We formulate an exact spacetime mapping between the $\\mathcal{N}$-point\ncorrelation functions of two different experiments with open quantum gases. Our\nformalism extends a quantum-field mapping result for closed systems [Phys. Rev.\nA \\textbf{94}, 043628 (2016)] to the general case of open quantum systems with\nMarkovian property. For this, we consider an open many-body system consisting\nof a $D$-dimensional quantum gas of bosons or fermions that interacts with a\nbath under Born-Markov approximation and evolves according to a Lindblad master\nequation in a regime of loss or gain. Invoking the independence of expectation\nvalues on pictures of quantum mechanics and using the quantum fields that\ndescribe the gas dynamics, we derive the Heisenberg evolution of any arbitrary\n$\\mathcal{N}$-point function of the system in the regime when the Lindblad\ngenerators feature a loss or a gain. Our quantum field mapping for closed\nquantum systems is rewritten in the Schr\\\"odinger picture and then extended to\nopen quantum systems by relating onto each other two different evolutions of\nthe $\\mathcal{N}$-point functions of the open quantum system. As a concrete\nexample of the mapping, we consider the mean-field dynamics of a simple\ndissipative quantum system that consists of a one-dimensional Bose-Einstein\ncondensate being locally bombarded by a dissipating beam of electrons in both\ncases when the beam amplitude or the waist is steady and modulated."
    },
    {
        "anchor": "Devil's staircase of topological Peierls insulators and Peierls\n  supersolids: We consider a mixture of ultracold bosonic atoms on a one-dimensional lattice\ndescribed by the XXZ-Bose-Hubbard model, where the tunneling of one species\ndepends on the spin state of a second deeply trapped species. We show how the\ninclusion of antiferromagnetic interactions among the spin degrees of freedom\ngenerates a Devil's staircase of symmetry-protected topological phases for a\nwide parameter regime via a bosonic analog of the Peierls mechanism in\nelectron-phonon systems. These topological Peierls insulators are examples of\nsymmetry-breaking topological phases, where long-range order due to spontaneous\nsymmetry breaking coexists with topological properties such as fractionalized\nedge states. Moreover, we identify a region of supersolid phases that do not\nrequire long-range interactions. They appear instead due to a Peierls\nincommensurability mechanism, where competing orders modify the underlying\ncrystalline structure of Peierls insulators, becoming superfluid. Our work show\nthe possibilities that ultracold atomic systems offer to investigate\nstrongly-correlated topological phenomena beyond those found in natural\nmaterials.",
        "positive": "Collective modes in the anisotropic unitary Fermi gas and the inclusion\n  of a backflow term: We study the collective modes of the confined unitary Fermi gas under\nanisotropic harmonic confinement as a function of the number of atoms. We use\nthe equations of extended superfluid hydrodynamics, which take into account a\ndispersive von Weizsacker-like term in the equaton of state. We also discuss\nthe inclusion of a backflow term in the extended superfluid Lagrangian and the\neffects of this anomalous term on sound waves and Beliaev damping of phonons."
    },
    {
        "anchor": "Simulation and measurement of the fractional particle number in\n  one-dimensional optical lattices: We propose a scheme to mimic and directly measure the fractional particle\nnumber in a generalized Su-Schrieffer-Heeger model with ultracold fermions in\none-dimensional optical lattices. We show that the fractional particle number\nin this model can be simulated in the momentum-time parameter space in terms of\nBerry curvature without a spatial domain wall. In this simulation, a hopping\nmodulation is adiabatically tuned to form a kink-type configuration and the\ninduced current plays the role of an analogous soliton distributing in the time\ndomain, such that the mimicked fractional particle number is expressed by the\nparticle transport. Two feasible experimental setups of optical lattices for\nrealizing the required Su-Schrieffer-Heeger Hamiltonian with tunable parameters\nand time-varying hopping modulation are presented. We also show practical\nmethods for measuring the particle transport in the proposed cold atom systems\nby numerically calculating the shift of the Wannier center and the center of\nmass of an atomic cloud.",
        "positive": "Verification of universal relations in a strongly interacting Fermi gas: Many-body fermion systems are important in many branches of physics,\nincluding condensed matter, nuclear, and now cold atom physics. In many cases,\nthe interactions between fermions can be approximated by a contact interaction.\nA recent theoretical advance in the study of these systems is the derivation of\na number of exact universal relations that are predicted to be valid for all\ninteraction strengths, temperatures, and spin compositions. These equations,\nreferred to as the Tan relations, relate a microscopic quantity, namely, the\namplitude of the high-momentum tail of the fermion momentum distribution, to\nthe thermodynamics of the many-body system. In this work, we provide\nexperimental verification of the Tan relations in a strongly interacting gas of\nfermionic atoms. Specifically, we measure the fermion momentum distribution\nusing two different techniques, as well as the rf excitation spectrum and\ndetermine the effect of interactions on these microscopic probes. We then\nmeasure the potential energy and release energy of the trapped gas and test the\npredicted universal relations."
    },
    {
        "anchor": "Self-bound Bose-Fermi liquids in lower dimensions: We study weakly interacting mixtures of ultracold atoms composed of bosonic\nand fermionic species in 2D and 1D. When interactions between particles are\nappropriately tuned, self-bound quantum liquids can be formed. We show that\nwhile formation of these droplets in 2D is due to the higher order correction\nterms contributing to the total energy and originating in quantum fluctuations,\nin 1D geometry the quantum fluctuations have a negligible role on formation of\nthe self-bound systems. The leading mean-field interactions are then sufficient\nfor droplet formation in 1D. We analyse stability conditions for 2D and 1D\nsystems and predict values of equilibrium densities of droplets.",
        "positive": "Matter-wave propagation in optical lattices: geometrical and flat-band\n  effects: The geometry of optical lattices can be engineered allowing the study of\natomic transport along paths arranged in patterns that are otherwise difficult\nto probe in the solid state. A question readily accessible to atomic systems is\nrelated to the speed of propagation of matter-waves as a function of the\nlattice geometry. To address this issue, we have investigated theoretically the\nquantum transport of non-interacting and weakly-interacting ultracold fermionic\natoms in several 2D optical lattice geometries. We find that the triangular\nlattice has a higher propagation velocity compared to the square lattice,\ndespite supporting longer paths. The body-centered square lattice has even\nlonger paths, nonetheless the propagation velocity is yet faster. This apparent\nparadox arises from the mixing of the momentum states which leads to different\ngroup velocities in quantum systems. Standard band theory provides an\nexplanation and allows for a systematic way to search and design systems with\ncontrollable matter-wave propagation. Moreover, the presence of a flat band\nsuch as in a two-leg ladder geometry leads to a dynamical density\ndiscontinuity, which contrasts the behavior of mobile and localized atoms in\nquantum transport. Our predictions are realizable with present experimental\ncapability."
    },
    {
        "anchor": "Environment mediated multipartite and multidimensional entanglement: Quantum entanglement is usually considered a fragile quantity and decoherence\nthrough coupling to an external environment, such as a thermal reservoir, can\nquickly destroy the entanglement resource. This doesn't have to be the case and\nthe environment can be engineered to assist in the formation of entanglement.\nWe investigate a system of qubits and higher dimensional spins interacting only\nthrough their mutual coupling to a reservoir. We explore the entanglement of\nmultipartite and multidimensional system as mediated by the bath and show that\nat low temperatures and intermediate coupling strengths multipartite\nentanglement may form between qubits and between higher spins, i.e., qudits. We\ncharacterise the multipartite entanglement using an entanglement witness based\nupon the structure factor and demonstrate its validity versus the directly\ncalculated entanglement of formation, suggesting possible experiments for its\nmeasure.",
        "positive": "Impurity in a Bose-Einstein condensate and the Efimov effect: We investigate the zero-temperature properties of an impurity particle\ninteracting with a Bose-Einstein condensate (BEC), using a variational\nwavefunction that includes up to two Bogoliubov excitations of the BEC. This\nallows one to capture three-body Efimov physics, as well as to recover the\nfirst non-trivial terms in the weak-coupling expansion. We show that the energy\nand quasiparticle residue of the dressed impurity (polaron) are significantly\nlowered by three-body correlations, even for weak interactions where there is\nno Efimov trimer state in a vacuum. For increasing attraction between the\nimpurity and the BEC, we observe a smooth crossover from atom to Efimov trimer,\nwith a superposition of states near the Efimov resonance. We furthermore\ndemonstrate that three-body loss does not prohibit the experimental observation\nof these effects. Our results thus suggest a route to realizing Efimov physics\nin a stable quantum many-body system for the first time."
    },
    {
        "anchor": "Breathing dynamics of the Bose polaron in a species-selective harmonic\n  trap: We perform an extensive numerical study on the breathing dynamics of a\nfew-body Bose polaron setup in a one-dimensional species-selective harmonic\ntrap. The dynamics is triggered by a quench of the impurity trap. The\nexcitation of the background majority atoms is mediated via the\nmajority-impurity interaction. The breathing spectrum is obtained for different\nnumbers of majority particles, several values of the majority-component\ninteraction strengths and trap ratios. It is further compared to the breathing\nspectrum of a particle-balanced few-body Bose-Bose mixture. In particular, for\nequal post-quench traps the employed protocol allows to couple states of\ndifferent center-of-mass parity in contrast to species-symmetric trap quenches.\nAmong the participating eigenstates we identify one having odd center-of-mass\nparity and even global parity. The breathing frequency induced by this state is\na monotonically decreasing function of the coupling parameter. Importantly, in\norder to be observable it requires the entanglement between the species to be\ntaken into account. We demonstrate this by comparing the numerically exact\nresults obtained by means of the Multi-Layer Multi-Configuration Time-Dependent\nHartree Method for Mixtures to the ones of a species mean-field ansatz. The\nentanglement-sensitive breathing frequency persists also for unequal\npost-quench traps where the center-of-mass cannot be decoupled. Finally, we\nanalyze the impact of parity symmetry on the breathing dynamics by initializing\na state of odd global parity. We evidence a striking resemblance to the ground\nstate breathing dynamics.",
        "positive": "Cyclotron dynamics of interacting bosons in artificial magnetic fields: We study theoretically quantum dynamics of interacting bosons in artificial\nmagnetic fields as engineered in recent ultracold atomic experiments, where\nquantum cyclotron orbital motion has been observed. With exact numerical\nsimulations and perturbative analyses, we find that interactions induce damping\nin the cyclotron motion. The damping time is found to be dependent on\ninteraction and tunneling strengths monotonically, while its dependence on\nmagnetic flux is non-monotonic. Sufficiently strong interactions would render\nbosons dynamically localized inhibiting the cyclotron motion. The damping\npredicted by us can be construed as an interaction-induced quantum decoherence\nof the cyclotron motion."
    },
    {
        "anchor": "Ground-state stability and excitation spectrum of a one-dimensional\n  dipolar supersolid: We study the behavior of the excitation spectrum across the quantum phase\ntransition from a superfluid to a supersolid phase of a dipolar Bose gas\nconfined to a one-dimensional geometry. Including the leading beyond-mean-field\neffects within an effective Hamiltonian, the analysis is based on Bogoliubov\ntheory with several order parameters accounting for the superfluid as well as\nsolid structure. We find fast convergence of the ground-state energy in the\nsupersolid with the number of order parameters and demonstrate a stable\nexcitation spectrum with two Goldstone modes and an amplitude mode in the\nlow-energy regime. Our results suggest that there exists an experimentally\nachievable parameter regime for dysprosium atoms, where the supersolid phase\nexhibits a stable excitation spectrum in the thermodynamic limit and the\ntransition into the supersolid phase is of second order driven by the roton\ninstability.",
        "positive": "Rashbons: Properties and their significance: In presence of a synthetic non-Abelian gauge field that induces a Rashba like\nspin-orbit interaction, a collection of weakly interacting fermions undergoes a\ncrossover from a BCS ground state to a BEC ground state when the strength of\nthe gauge field is increased [Phys. Rev. B {\\bf 84}, 014512 (2011)]. The BEC\nthat is obtained at large gauge coupling strengths is a condensate of tightly\nbound bosonic fermion-pairs whose properties are solely determined by the\nRashba gauge field -- hence called rashbons. In this paper, we conduct a\nsystematic study of the properties of rashbons and their dispersion. This study\nreveals a new qualitative aspect of the problem of interacting fermions in\nnon-Abelian gauge fields, i.e., that the rashbon state induced by the gauge\nfield for small centre of mass momenta of the fermions ceases to exist when\nthis momentum exceeds a critical value which is of the order of the gauge\ncoupling strength. The study allows us to estimate the transition temperature\nof the rashbon BEC, and suggests a route to enhance the exponentially small\ntransition temperature of the system with a fixed weak attraction to the order\nof the Fermi temperature by tuning the strength of the non-Abelian gauge field.\nThe nature of the rashbon dispersion, and in particular the absence of the\nrashbon states at large momenta, suggests a regime of parameter space where the\nnormal state of the system will be a dynamical mixture of uncondensed rashbons\nand unpaired helical fermions. Such a state should show many novel features\nincluding pseudogap physics."
    },
    {
        "anchor": "s-Wave Scattering Resonances Induced by Dipolar Interactions of Polar\n  Molecules: We show that s-wave scattering resonances induced by dipolar interactions in\na polar molecular gas have a universal large and positive effective range,\nwhich is very different from Feshbach resonances realized in cold atoms before,\nwhere the effective range is either negligible or negative. Such a difference\nhas important consequence in many-body physics. At high temperature regime, a\npositive effective range gives rise to stronger repulsive interaction energy\nfor positive scattering length, and weaker attractive interaction energy for\nnegative scattering length. While at low-temperatures, we study polaron problem\nformed by single impurity molecule, and we find that the polaron binding energy\nincreases at the BEC side and decreases at the BCS side. All these effects are\nin opposite to narrow Feshbach resonances where the effective range is\nnegative.",
        "positive": "Quantum critical behavior of ultracold atoms in two-dimensional optical\n  lattices: As the temperature of a many-body system approaches absolute zero, thermal\nfluctuations of observables cease and quantum fluctuations dominate.\nCompetition between different energies, such as kinetic energy, interactions or\nthermodynamic potentials, can induce a quantum phase transition between\ndistinct ground states. Near a continuous quantum phase transition, the\nmany-body system is quantum critical, exhibiting scale invariant and universal\ncollective behavior \\cite{Coleman05Nat, Sachdev99QPT}. Quantum criticality has\nbeen actively pursued in the study of a broad range of novel materials\n\\cite{vdMarel03Nat, Lohneysen07rmp, G08NatPhys, Sachdev08NatPhys}, and can\ninvoke new insights beyond the Landau-Ginzburg-Wilson paradigm of critical\nphenomena \\cite{Senthil04prb}. It remains a challenging task, however, to\ndirectly and quantitatively verify predictions of quantum criticality in a\nclean and controlled system. Here we report the observation of quantum critical\nbehavior in a two-dimensional Bose gas in optical lattices near the\nvacuum-to-superfluid quantum phase transition. Based on \\textit{in situ}\ndensity measurements, we observe universal scaling of the equation of state at\nsufficiently low temperatures, locate the quantum critical point, and determine\nthe critical exponents. The universal scaling laws also allow determination of\nthermodynamic observables. In particular, we observe a finite entropy per\nparticle in the critical regime, which only weakly depends on the atomic\ninteraction. Our experiment provides a prototypical method to study quantum\ncriticality with ultracold atoms, and prepares the essential tools for further\nstudy on quantum critical dynamics."
    },
    {
        "anchor": "Tuning Feshbach resonance in cold atomic gases with inter-channel\n  coupling: We show that the essential properties of a Feshbach resonance in cold atomic\ngases can be tuned by dressing the atomic states in different scattering\nchannels through inter-channel couplings. Such a scheme can be readily\nimplemented in the orbital Feshbach resonance of alkaline-earth-like atoms by\ncoupling hyperfine states in the clock-state manifolds. Using $^{173}$Yb atoms\nas an example, we find that both the resonance position and the two-body\nbound-state energy depend sensitively on the inter-channel coupling strength,\nwhich offers control parameters in tuning the inter-atomic interactions. We\nalso demonstrate the dramatic impact of the dressed Feshbach resonance on\nmany-body processes such as the polaron to molecule transition and the BCS-BEC\ncrossover.",
        "positive": "T-matrix approach to the phonon-mediated Casimir interaction: We develop a theory of the phonon mediated Casimir interaction between two\npoint-like impurities, which is based on the single impurity scattering\nT-matrix approach. Within this, we show that the Casimir interaction at $T = 0$\nfalls off as a power law with the distance between the impurities. We find that\nthe power in the weak and in the unitary phonon-impurity scattering limits\ndiffers, and we relate the power law to the low-energy properties of the single\nimpurity scattering T-matrix. In addition, we consider the Casimir interaction\nat finite temperature and show that at finite temperatures the Casimir\ninteraction becomes exponential at large distances."
    },
    {
        "anchor": "Universality in modelling non-equilibrium pattern formation in polariton\n  condensates: The key to understanding the universal behaviour of systems driven away from\nequilibrium lies in the common description obtained when particular microscopic\nmodels are reduced to order parameter equations. Universal order parameter\nequations written for complex matter fields are widely used to describe systems\nas different as Bose-Einstein condensates of ultra cold atomic gases, thermal\nconvection, nematic liquid crystals, lasers and other nonlinear systems.\nExciton-polariton condensates recently realised in semiconductor microcavities\nare pattern forming systems that lie somewhere between equilibrium\nBose-Einstein condensates and lasers. Because of the imperfect confinement of\nthe photon component, exciton-polaritons have a finite lifetime, and have to be\ncontinuously re-populated. As photon confinement improves, the system more\nclosely approximates an equilibrium system. In this chapter we review a number\nof universal equations which describe various regimes of the dynamics of\nexciton-polariton condensates: the Gross-Pitaevskii equation, which models\nweakly interacting equilibrium condensates, the complex Ginsburg-Landau\nequation---the universal equation that describes the behaviour of systems in\nthe vicinity of a symmetry--breaking instability, and the complex\nSwift-Hohenberg equation that in comparison with the complex Ginsburg-Landau\nequation contains additional nonlocal terms responsible for spacial mode\nselection. All these equations can be derived asymptotically from a generic\nlaser model given by Maxwell-Bloch equations. Such an universal framework\nallows the unified treatment of various systems and continuously cross from one\nsystem to another. We discuss the relevance of these equations, and their\nconsequences for pattern formation.",
        "positive": "Dynamics of solitary waves in ultracold gases in terms of observable\n  quantities: A variety of solitary waves, such as solitons, vortex rings, solitonic\nvortices, and more complex entities, have recently been predicted to exist.\nThey can move in superfluid ultracold gases along elongated traps. The\ntheoretical description of this motion requires knowledge of the inertial\nsoliton mass and the effective number of particles in it as functions of the\nsoliton energy. While these functions can be calculated by a microscopic\ntheory, it is also possible to express them directly in terms of observable\nquantities, such as the order parameter phase jump and the particle number\ndepletion in the soliton. In this article, the corresponding equations are\nderived in a simple and physically clear way and applied to the recently\npredicted `magnetic soliton' in mixtures of Bose gases in various spin states."
    },
    {
        "anchor": "Noise correlations of a strongly attractive spin-1/2 Fermi gas in an\n  optical lattice: We calculate density-density correlations of an expanding gas of strongly\nattractive ultra-cold spin-1/2 fermions in an optical lattice. The phase\ndiagram of the tightly bound fermion pairs exhibits a Bose-Einstein condensed\nstate and a Mott insulating state with a single molecule per lattice site. We\nstudy the effects of quantum fluctuations on the correlations in both phases\nand show that they are especially important in the Bose-Einstein condensate\nstate, leading to the appearance of singular peaks. In the Mott insulating\nstate the correlations are characterized by sharp dips. This can be utilized in\nexperiments to distinguish between these two phases.",
        "positive": "Long-lived and transient supersolid behaviors in dipolar quantum gases: By combining theory and experiments, we demonstrate that dipolar quantum\ngases of both $^{166}$Er and $^{164}$Dy support a state with supersolid\nproperties, where a spontaneous density modulation and a global phase coherence\ncoexist. This paradoxical state occurs in a well defined parameter range,\nseparating the phases of a regular Bose-Einstein condensate and of an\ninsulating droplet array, and is rooted in the roton mode softening, on the one\nside, and in the stabilization driven by quantum fluctuations, on the other\nside. Here, we identify the parameter regime for each of the three phases. In\nthe experiment, we rely on a detailed analysis of the interference patterns\nresulting from the free expansion of the gas, quantifying both its density\nmodulation and its global phase coherence. Reaching the phases via a slow\ninteraction tuning, starting from a stable condensate, we observe that\n$^{166}$Er and $^{164}$Dy exhibit a striking difference in the lifetime of the\nsupersolid properties, due to the different atom loss rates in the two systems.\nIndeed, while in $^{166}$Er the supersolid behavior only survives a few tens of\nmilliseconds, we observe coherent density modulations for more than $150\\,$ms\nin $^{164}$Dy. Building on this long lifetime, we demonstrate an alternative\npath to reach the supersolid regime, relying solely on evaporative cooling\nstarting from a thermal gas."
    },
    {
        "anchor": "Griffiths Phase in a Facilitated Rydberg Gas at Low Temperature: The spread of excitations by Rydberg facilitation bears many similarities to\nepidemics. Such systems can be modeled with Monte-Carlo simulations of\nclassical rate equations to great accuracy as a result of high dephasing. In\nthis paper, we analyze the dynamics of a Rydberg many-body system in the\nfacilitation regime in the limits of high and low temperatures. While in the\nhigh-temperature limit a homogeneous mean-field behaviour is recovered,\ncharacteristic effects of heterogeneity can be seen in a frozen gas. At large\ntemperatures the system displays an absorbing-state phase transition and, in\nthe presence of an additional loss channel, self-organized criticality. In a\nfrozen or low-temperature gas, excitations are constrained to a network\nresembling an Erd\\\"os-Renyi graph. We show that the absorbing-state phase\ntransition is replaced with an extended Griffiths phase, which we accurately\ndescribe by a susceptible-infected-susceptible model on the Erd\\\"os-Renyi\nnetwork taking into account Rydberg blockade. Furthermore, we expand upon an\nexisting macroscopic Langevin equation to more accurately describe the density\nof Rydberg atoms in the frozen and finite temperature regimes.",
        "positive": "Self-bound dipolar droplet: a localized matter-wave in free space: We demonstrate that a dipolar condensate can be prepared into a\nthree-dimensional wavepacket that remains localized when released in\nfree-space. Such self-bound states arise from the interplay of the two-body\ninteractions and quantum fluctuations. We develop a phase diagram for the\nparameter regimes where these self-bound states are stable, examine their\nproperties, and demonstrate how they can be produced in current experiments."
    },
    {
        "anchor": "Normal density and moment of inertia of a moving superfluid: In this work, the normal density $\\rho_n$ and moment of inertia of a moving\nsuperfluid are investigated. We find that, even at zero temperature, there\nexists a finite normal density for the moving superfluid. When the velocity of\nsuperfluid reaches sound velocity, the normal density becomes total mass\ndensity $\\rho$, which indicates that the system losses superfluidity. At the\nsame time, the Landau's critical velocity also becomes zero. The existence of\nthe non-zero normal density is attributed to the coupling between the motion of\nsuperflow and density fluctuation in transverse directions. With Josephson\nrelation, the superfluid density $\\rho_s$ is also calculated and the identity\n$\\rho_s+\\rho_n=\\rho$ holds. Further more, we find that the finite normal\ndensity also results in a quantized moment of inertia in a moving superfluid\ntrapped by a ring. The normal density and moment of inertia at zero temperature\ncould be verified experimentally by measuring the angular momentum of a moving\nsuperfluid in a ring trap.",
        "positive": "Fluctuating and dissipative dynamics of dark solitons in\n  quasi-condensates: The fluctuating and dissipative dynamics of matter-wave dark solitons within\nharmonically trapped, partially condensed Bose gases is studied both\nnumerically and analytically. A study of the stochastic Gross-Pitaevskii\nequation, which correctly accounts for density and phase fluctuations at finite\ntemperatures, reveals dark soliton decay times to be lognormally distributed at\neach temperature, thereby characterizing the previously predicted long lived\nsoliton trajectories within each ensemble of numerical realizations (S.P.\nCockburn {\\it et al.}, Phys. Rev. Lett. 104, 174101 (2010)). Expectation values\nfor the average soliton lifetimes extracted from these distributions are found\nto agree well with both numerical and analytic predictions based upon the\ndissipative Gross-Pitaevskii model (with the same {\\it ab initio} damping).\nProbing the regime for which $0.8 k_{B}T < \\mu < 1.6 k_{B}T$, we find average\nsoliton lifetimes to scale with temperature as $\\tau\\sim T^{-4}$, in agreement\nwith predictions previously made for the low-temperature regime $k_{B}T\\ll\\mu$.\nThe model is also shown to capture the experimentally-relevant decrease in the\nvisibility of an oscillating soliton due to the presence of background\nfluctuations."
    },
    {
        "anchor": "Semi-vortex solitons and their excited states in spin-orbit-coupled\n  binary bosonic condensates: It is known that two-dimensional two-component fundamental solitons of the\nsemi-vortex (SV) type, with vorticities $(s_{+},s_{-})=(0,1)$ in their\ncomponents, are stable ground states (GSs) in the spin-orbit-coupled (SOC)\nbinary Bose-Einstein condensate with the contact self-attraction acting in both\ncomponents, in spite of the possibility of the critical collapse in the system.\nHowever, excited states(ESs) of the SV solitons, with the vorticity set\n$(s_{+},s_{-})=( S_{+},S_{+}+1)$ and $S_{+}=1,2,3,...$, are unstable in the\nsame system. We construct ESs of SV solitons in the SOC system with opposite\nsigns of the self-interaction in the two components. The main finding is\nstability of the ES-SV solitons, with the extra vorticity (at least) up to\n$S_{+}=6$. The threshold value of the norm for the onset of the critical\ncollapse, $N_{\\mathrm{thr}}$, in these excited states is higher than the\ncommonly known critical value, $N_{c}\\approx 5.85$,associated with the\nsingle-component Townes solitons, $N_{\\mathrm{thr}}$ increasing with the growth\nof $S_{+}$. A velocity interval for stable motion of the GS-SV solitons is\nfound too. The results suggest a solution for the challenging problem of the\ncreation of stable vortex solitons with high topological charges.",
        "positive": "Particle-hole bound states of dipolar molecules in optical lattice: We investigate the particle-hole pair excitations of dipolar molecules in\noptical lattice, which can be described with an extended Bose-Hubbard model.\nFor strong enough dipole-dipole interaction, the particle-hole pair excitations\ncan form bound states in one and two dimensions. With decreasing dipole-dipole\ninteraction, the energies of the bound states increase and merge into the\nparticle-hole continuous spectrum gradually. The existence regions, the energy\nspectra and the wave functions of the bound states are carefully studied and\nthe symmetries of the bound states are analyzed with group theory. For a given\ndipole-dipole interaction, the number of bound states varies in momentum space\nand a number distribution of the bound states is illustrated. We also discuss\nhow to observe these bound states in future experiments."
    },
    {
        "anchor": "An effective-field-theory analysis of Efimov physics in heteronuclear\n  mixtures of ultracold atomic gases: We use an effective-field-theory framework to analyze the Efimov effect in\nheteronuclear three-body systems consisting of two species of atoms with a\nlarge interspecies scattering length. In the leading-order description of this\ntheory, various three-body observables in heteronuclear mixtures can be\nuniversally parameterized by one three-body parameter. We present the\nnext-to-leading corrections, which include the effects of the finite\ninterspecies effective range and the finite intraspecies scattering length, to\nvarious three-body observables. We show that only one additional three-body\nparameter is required to render the theory predictive at this order. By\nincluding the effective range and intraspecies scattering length corrections,\nwe derive a set of universal relations that connect the different Efimov\nfeatures near the interspecies Feshbach resonance. Furthermore, we show that\nthese relations can be interpreted in terms of the running of the three-body\ncounterterms that naturally emerge from proper renormalization. Finally, we\nmake predictions for recombination observables of a number of atomic systems\nthat are of experimental interest.",
        "positive": "Fragmented Many-Body states of definite angular momentum and stability\n  of attractive 3D Condensates: A three dimensional attractive Bose-Einstein Condensate (BEC) is expected to\ncollapse, when the number of the particles $N$ in the ground state or the\ninteraction strength $\\lambda_0$ exceeds a critical value. We study systems of\ndifferent particle numbers and interaction strength and find that even if the\noverall ground state is collapsed there is a plethora of fragmented excited\nstates that are still in the metastable region. Utilizing the\n\\emph{configuration interaction} expansion we determine the spectrum of the\nground (`yrast') and excited many-body states with definite total angular\nmomentum quantum numbers $0\\leqslant L\\leqslant N$ and $-L\\leqslant\nM_L\\leqslant L$, and we find and examine states that survive the collapse. This\nopens up the possibility of realizing a metastable system with overcritical\nnumbers of bosons in a ground state with angular momentum $L\\neq0$. The\nmulti-orbital mean-field theory predictions about the existence of fragmented\nmetastable states with overcritical numbers of bosons are verified and\nelucidated at the many-body level. The descriptions of the total angular\nmomentum within the mean-field and the many-body approaches are compared."
    },
    {
        "anchor": "Observation of Massless and Massive Collective Excitations with Faraday\n  Patterns in a Two-Component Superfluid: We report on the experimental measurement of the dispersion relation of the\ndensity and spin collective excitation modes in an elongated two-component\nsuperfluid of ultracold bosonic atoms. Our parametric spectroscopic technique\nis based on the external modulation of the transverse confinement frequency,\nleading to the formation of density and spin Faraday waves. We show that the\napplication of a coherent coupling between the two components reduces the phase\nsymmetry and gives a finite mass to the spin modes.",
        "positive": "The fourth- and fifth-order virial coefficients from weak-coupling to\n  unitarity: In the current era of precision quantum many-body physics, one of the most\nscrutinized systems is the unitary limit of the nonrelativistic spin-$1/2$\nFermi gas, due to its simplicity and relevance for atomic, condensed matter,\nand nuclear physics. The thermodynamics of this strongly correlated system is\ndetermined by universal functions which, at high temperature, are governed by\nuniversal virial coefficients $b_n$ that capture the effects of the $n$-body\nsystem on the many-body dynamics. Currently, $b_2$ and $b_3$ are well\nunderstood, but the situation is less clear for $b_4$, and no predictions have\nbeen made for $b_5$. To answer these open questions, we implement a\nnonperturbative analytic approach based on the Trotter-Suzuki factorization of\nthe imaginary-time evolution operator, using progressively finer temporal\nlattice spacings. Implementing these factorizations and automated algebra\ncodes, we obtain the interaction-induced change $\\Delta b_n$ from weak coupling\nto unitarity. At unitarity, we find: $\\Delta b_3 = -0.356(4)$, in agreement\nwith previous results; $\\Delta b_4 = 0.062(2)$, in agreement with all previous\ntheoretical estimates but at odds with experimental determinations; and $\\Delta\nb_5 = 0.078(6)$, which is a prediction. We show the impact of those answers on\nthe density equation of state and Tan contact, and track their origin back to\ntheir polarized and unpolarized components."
    },
    {
        "anchor": "Orbital superfluidity in the $P$-band of a bipartite optical square\n  lattice: The successful emulation of the Hubbard model in optical lattices has\nstimulated world wide efforts to extend their scope to also capture more\ncomplex, incompletely understood scenarios of many-body physics. Unfortunately,\nfor bosons, Feynmans fundamental \"no-node\" theorem under very general\ncircumstances predicts a positive definite ground state wave function with\nlimited relevance for many-body systems of interest. A promising way around\nFeynmans statement is to consider higher bands in optical lattices with more\nthan one dimension, where the orbital degree of freedom with its intrinsic\nanisotropy due to multiple orbital orientations gives rise to a structural\ndiversity, highly relevant, for example, in the area of strongly correlated\nelectronic matter. In homogeneous two-dimensional optical lattices, lifetimes\nof excited bands on the order of a hundred milliseconds are possible but the\ntunneling dynamics appears not to support cross-dimensional coherence. Here we\nreport the first observation of a superfluid in the $P$-band of a bipartite\noptical square lattice with $S$-orbits and $P$-orbits arranged in a\nchequerboard pattern. This permits us to establish full cross-dimensional\ncoherence with a life-time of several ten milliseconds. Depending on a small\nadjustable anisotropy of the lattice, we can realize real-valued striped\nsuperfluid order parameters with different orientations $P_x \\pm P_y$ or a\ncomplex-valued $P_x \\pm i P_y$ order parameter, which breaks time reversal\nsymmetry and resembles the $\\pi$-flux model proposed in the context of high\ntemperature superconductors. Our experiment opens up the realms of orbital\nsuperfluids to investigations with optical lattice models.",
        "positive": "Topological excitations in rotating Bose-Einstein condensates with\n  Rashba-Dresselhaus spin-orbit coupling in a two-dimensional optical lattice: We study the ground-state configurations and spin textures of rotating\ntwo-component Bose-Einstein condensates (BECs) with Rashba-Dresselhaus\nspin-orbit coupling (RD-SOC), which are confined in a two-dimensional (2D)\noptical lattice plus a 2D harmonic trap. In the absence of rotation, a\nrelatively small isotropic 2D RD-SOC leads to the generation of ghost vortices\nfor initially miscible BECs, while it gives rise to the creation of rectangular\nvortex-antivortex lattices for initially immiscible BECs. As the strength of\nthe 2D RD-SOC enhances, the visible vortices or the 2D vortex-antivortex chains\nare created for the former case, whereas the rectangular vortex-antivortex\nlattices are transformed into vortex-antivortex rings for the later case. For\nthe initially immiscible BECs with fixed 2D RD-SOC strength, the increase of\nrotation frequency can result in the structural phase transition from square\nvortex lattice to irregular triangular vortex lattice and the system transition\nfrom initial phase separation to phase mixing. In addition, we analyze the\ncombined effects of 1D RD-SOC and rotation on the vortex configurations of the\nground states for the case of initial phase separation. The increase of 1D SOC\nstrength, rotation frequency or both of them may result in the formation of\nvortex chain and phase mixing. Furthermore, the typical spin textures for both\nthe cases of 2D RD-SOC and 1D RD-SOC are discussed. It is shown that the system\nfavors novel spin textures and skyrmion configurations including an exotic\nskyrmion-half-skyrmion lattice (skyrmion-meron lattice), a complicated meron\nlattice, a skyrmion chain, and a Bloch domain wall."
    },
    {
        "anchor": "Superfluidity vs prethermalisation in a nonlinear Floquet system: We show that superfluidity can be used to prevent thermalisation in a\nnonlinear Floquet system. Generically, periodic driving boils an interacting\nsystem to a featureless infinite temperature state. Fast driving is a known\nstrategy to postpone Floquet heating with a large but always finite boiling\ntime. In contrast, using a nonlinear periodically-driven system on a lattice,\nwe show the existence of a continuous class of initial states which do not\nthermalise at all. This absence of thermalisation is associated to the\nexistence and persistence of a stable superflow motion.",
        "positive": "Modeling spontaneous breaking of time-translation symmetry: We show that an ultra-cold atomic cloud bouncing on an oscillating mirror can\nreveal spontaneous breaking of a discrete time translation symmetry. In\nmany-body simulations we illustrate the process of the symmetry breaking that\ncan be induced by atomic losses or by a measurement of particle positions. The\nresults pave the way for understanding and realization of the time crystal idea\nwhere crystalline structures form in the time domain due to spontaneous\nbreaking of continuous time translation symmetry."
    },
    {
        "anchor": "Controllable Production of Degenerate Fermi Gases of $^6$Li Atoms in the\n  2D-3D Crossover: The many-body physics in the dimensional crossover regime attracts much\nattention in cold atom experiments, but yet to explore systematically. One of\nthe technical difficulties existed in the experiments is the lack of the\nexperimental technique to quantitatively tune the atom occupation ratio of the\ndifferent lattice bands. In this letter, we report such techniques in a process\nof transferring a 3D Fermi gas into a 1D optical lattice, where the capability\nof tuning the occupation of the energy band is realized by varying the trapping\npotentials of the optical dipole trap (ODT) and the lattice, respectively. We\ncould tune a Fermi gas with the occupation in the lowest band from unity to\n50$\\%$ quantitatively. This provides a route to experimentally study the\ndependence of many-body interaction on the dimensionality in a Fermi gas.",
        "positive": "Induced p-wave Superfluidity in Imbalanced Fermi Gases in a Synthetic\n  Gauge Field: We study pairing formation and the appearance of induced spin-triplet p-wave\nsuperfluidity in dilute three-dimensional imbalanced Fermi gases in the\npresence of a uniform non-Abelian gauge field. This gauge field generates a\nsynthetic Rashba-type spin-orbit interaction which has remarkable consequences\nin the induced p-wave pairing gaps. Without the synthetic gauge field, the\np-wave pairing occurs in one of the components due to the induced\n(second-order) interaction via an exchange of density fluctuations in the other\ncomponent. We show that this p-wave superfluid gap induced by density\nfluctuations is greatly enhanced due to the Rashba-type spin-orbit coupling."
    },
    {
        "anchor": "Resonance triplet dynamics in the quenched unitary Bose gas: The quenched unitary Bose gas is a paradigmatic example of a strongly\ninteracting out-of-equilibrium quantum system, whose dynamics become difficult\nto describe theoretically due to the growth of non-Gaussian quantum\ncorrelations. We develop a conserving many-body theory capable of capturing\nthese effects, allowing us to model the post-quench dynamics in previously\ninaccessible time regimes. By comparing our results directly to experiment, we\nanswer long-standing fundamental questions regarding the heating and population\ndynamics in the gas, specifically highlighting the dominance of strong lossless\ncorrelations rather than incoherent atomic losses. Our general framework, which\nreframes the dynamics of unitary quantum systems in terms of explicit\nconnections to microscopic physics, can be broadly applied to any quantum\nsystem containing strong few-body correlations.",
        "positive": "Symmetry-protected transport through a lattice with a local particle\n  loss: We study particle transport through a chain of coupled sites connected to\nfree-fermion reservoirs at both ends, subjected to a local particle loss. The\ntransport is characterized by calculating the conductance and particle density\nin the steady state using the Keldysh formalism for open quantum systems.\nBesides a reduction of conductance, we find that transport can remain (almost)\nunaffected by the loss for certain values of the chemical potential in the\nlattice. We show that this \"protected\" transport results from the spatial\nsymmetry of single-particle eigenstates. At a finite voltage, the density\nprofile develops a drop at the lossy site, connected to the onset of\nnon-ballistic transport."
    },
    {
        "anchor": "Collective excitations in Bose-Fermi mixtures: We investigate collective excitations of density fluctuations and a dynamic\ndensity structure factor in a mixture of Bose and Fermi gases in a normal\nphase. With decreasing temperature, we find that the frequency of the\ncollective excitation deviates from that of the hydrodynamic sound mode. Even\nat temperature much lower than the Fermi temperature, the collective mode\nfrequency does not reach the collisionless limit analogous to zero sound in a\nFermi gas, because of collisions between bosons and fermions.",
        "positive": "Observation of vortex dipoles in an oblate Bose-Einstein condensate: We report experimental observations and numerical simulations of the\nformation, dynamics, and lifetimes of single and multiply charged quantized\nvortex dipoles in highly oblate dilute-gas Bose-Einstein condensates (BECs). We\nnucleate pairs of vortices of opposite charge (vortex dipoles) by forcing\nsuperfluid flow around a repulsive gaussian obstacle within the BEC. By\ncontrolling the flow velocity we determine the critical velocity for the\nnucleation of a single vortex dipole, with excellent agreement between\nexperimental and numerical results. We present measurements of vortex dipole\ndynamics, finding that the vortex cores of opposite charge can exist for many\nseconds and that annihilation is inhibited in our highly oblate trap geometry.\nFor sufficiently rapid flow velocities we find that clusters of like-charge\nvortices aggregate into long-lived dipolar flow structures."
    },
    {
        "anchor": "Breached pair superfluidity: a brief review: Interior gap superfluidity was introduced together with Frank Wilczek. Later\non together with our collaborators, we generalized this new possibility of\nsuperfluidity to a broader concept, breach pair superfluidity. In the occasion\nto celebrate Professor Frank Wilczek's seventieth birthday and his productive\ncareer in several major areas in physics, I dedicate this note to recall the\nexciting times of developing this idea, the main aspects of the proposed phase,\nand the discussion on its stability condition.",
        "positive": "Thermometry of cold atoms in optical lattices via artificial gauge\n  fields: Artificial gauge fields are a unique way of manipulating the motional state\nof cold atoms. Here we propose the use of artificial gauge fields -- obtained\ne.g. via lattice shaking -- to perform primary noise thermometry of cold atoms\nin optical lattices - not requiring any form of prior calibration. The proposed\nthermometric scheme relies on fundamental fluctuation-dissipation relations,\nconnecting the global response to the variation of the applied gauge field and\nthe fluctuation of quantities related to the momentum distribution (such as the\naverage kinetic energy or the average current). We demonstrate gauge-field\nthermometry for several physical situations, including free fermions and\nstrongly interacting bosons. The proposed approach is extremely robust to\nquantum fluctuations - even in the vicinity of a quantum phase transition -\nwhen it relies on the thermal fluctuations of an emerging classical field,\nassociated with the onset of Bose condensation or chiral order."
    },
    {
        "anchor": "Phase separations induced by a trapping potential in one-dimensional\n  fermionic systems as a source of core-shell structures: Ultracold fermionic gases in optical lattices give a great opportunity for\ncreating different types of novel states. One of them is phase separation\ninduced by a trapping potential between different types of superfluid phases.\nThe core-shell structures, occurring in systems with a trapping potential, are\na good example of such separations. The types and the sequences of phases which\nemerge in such structures can depend on spin-imbalance, shape of the trap and\non-site interaction strength. In this work, we investigate the properties of\nsuch structures within an attractive Fermi gas loaded in the optical lattice,\nin the presence of the trapping potential and their relations to the phase\ndiagram of the homogeneous system. Moreover, we show how external and internal\nparameters of the system and parameters of the trap influence their properties.\nIn particular, we show a possible occurrence of the core-shell structure in a\nsystem with a harmonic trap, containing the BCS and FFLO states. Additionally,\nwe find a spatial separation of two superfuild states in the system, one in the\nBCS limit as well as the other one in the tightly bound local pairs (BEC)\nregime.",
        "positive": "Two Rydberg-dressed atoms escaping from an open well: A comprehensive analysis of the dynamics of two Rydberg-dressed particles\n(bosons or fermions) tunneling from a potential well into open space is\nprovided. We show that the dominant decay mechanism switches from sequential\ntunneling to pair tunneling when the interaction strength is tuned below a\ncertain critical value. These critical values can be modified by tuning the\neffective range of the interaction potential. By comparing the dynamics for\nbosons and fermions, we show that there are significant differences between the\ntwo cases. In particular, increasing the interaction range modifies the\ntunneling rate in opposite ways for fermions and bosons. Furthermore, for the\nfermionic system much stronger attractive interactions are needed to achieve\npair tunneling. The results provide insight into the dynamics of tunneling\nsystems and, in light of recent realizations of tunneling few-body systems and\nRydberg dressing of atoms, they offer promise for future experiments."
    },
    {
        "anchor": "Roton Excitations in an Oblate Dipolar Quantum Gas: We observe signatures of radial and angular roton excitations around a\ndroplet crystallization transition in dipolar Bose-Einstein condensates. In\nsitu measurements are used to characterize the density fluctuations near this\ntransition. The static structure factor is extracted and used to identify the\nradial and angular roton excitations by their characteristic symmetries. These\nfluctuations peak as a function of interaction strength indicating the\ncrystallization transition of the system. We compare our observations to a\ntheoretically calculated excitation spectrum allowing us to connect the\ncrystallization mechanism with the softening of the angular roton modes.",
        "positive": "Efimov-like states and quantum funneling effects on synthetic hyperbolic\n  surfaces: Engineering lattice models with tailored inter-site tunnelings and onsite\nenergies could synthesize essentially arbitrary Riemannian surfaces with highly\ntunable local curvatures. Here, we point out that discrete synthetic Poincar\\'e\nhalf-planes and Poincar\\'e disks, which are created by lattices in flat planes,\nsupport infinitely degenerate eigenstates for any nonzero eigenenergies. Such\nEfimov-like states exhibit a discrete scaling symmetry and imply an\nunprecedented apparatus for studying quantum anomaly using hyperbolic surfaces.\nFurthermore, all eigenstates are exponentially localized in the hyperbolic\ncoordinates, signifying the first example of quantum funneling effects in\nHermitian systems. As such, any initial wave packet travels towards the edge of\nthe Poincar\\'e half-plane or its equivalent on the Poincar\\'e disk, delivering\nan efficient scheme to harvest light and atoms in two dimensions. Our findings\nunfold the intriguing properties of hyperbolic spaces and suggest that Efimov\nstates may be regarded as a projection from a curved space with an extra\ndimension."
    },
    {
        "anchor": "Van der Waals five-body size-energy universality: A universal relationship between scaled size and scaled energy is explored in\nfive-body self-bound quantum systems. The ground-state binding energy and\nstructure properties are obtained by means of the diffusion Monte Carlo method.\nWe use pure estimators to eliminate any residual bias in the estimation of the\ncluster size. Strengthening the inter-particle interaction, we extend the\nexploration from the halo region to classical systems. Universal scaled\nsize-scaled energy line, which does not depend on the short-range potential\ndetails and binding strength, is found for homogeneous pentamers with\ninteraction potentials decaying at long range predominantly as $r^{-6}$. For\nmixed pentamers, we discuss under which conditions the universal line can\napproximately describe the size-energy ratio. Our data is compatible with\ngeneralized Tjon lines, which assume a linear dependence between the binding\nenergy of the pentamers and the one of tetramers, when both are divided by the\ntrimer energies.",
        "positive": "Density-dependent synthetic magnetism for ultracold atoms in optical\n  lattices: Raman-assisted hopping can allow for the creation of density-dependent\nsynthetic magnetism for cold neutral gases in optical lattices. We show that\nthe density-dependent fields lead to a non-trivial interplay between density\nmodulations and chirality. This interplay results in a rich physics for atoms\nin two-leg ladders, characterized by a density-driven Meissner- to\nvortex-superfluid transition, and a non-trivial dependence of the density\nimbalance between the legs. Density-dependent fields also lead to intriguing\nphysics in square lattices. In particular, it leads to a density-driven\ntransition between a non-chiral and a chiral superfluid, both characterized by\nnon-trivial charge density-wave amplitude. We finally show how the physics due\nto the density-dependent fields may be easily probed in experiments by\nmonitoring the expansion of doublons and holes in a Mott insulator, which\npresents a remarkable dependence on quantum fluctuations."
    },
    {
        "anchor": "Spin and topological order in a periodically driven spin chain: The periodically driven quantum Ising chain has recently attracted a large\nattention in the context of Floquet engineering. In addition to the common\nparamagnet and ferromagnet, this driven model can give rise to new topological\nphases. In this work we systematically explore its quantum phase diagram, by\nexamining the properties of its Floquet ground state. We specifically focus on\ndriving protocols with time-reversal invariant points, and demonstrate the\nexistence of an infinite number of distinct phases. These phases are separated\nby second-order quantum phase transitions, accompanied by continuous changes of\nlocal and string order parameters, as well as sudden changes of a topological\nwinding number and of the number of protected edge states. When one of these\nphase transitions is adiabatically crossed, the correlator associated to the\norder parameter is nonvanishing over a length scale which shows a Kibble-Zurek\nscaling. In some phases, the Floquet ground state spontaneously breaks the\ndiscrete time-translation symmetry of the Hamiltonian. Our findings provide a\nbetter understanding of topological phases in periodically driven clean\nintegrable models.",
        "positive": "The double-well Bose Hubbard model with nearest-neighbor and\n  cavity-mediated long-range interactions: We consider a one-dimensional Bose-Hubbard model (BHM) with on-site\ndouble-well potentials and study the effect of nearest-neighbor repulsion and\ncavity-mediated long-range interactions by calculating the ground-state phase\ndiagrams with quantum Monte-Carlo simulations. We show that when the intra-well\nrepulsion is as strong as the on-site repulsion a dimerized Mott insulator\nphase appears at the tip of the dimerized Density Wave phase for a density of\none particle per double well. Furthermore, we find a dimerized Haldane\ninsulator phase in the double-well BHM with nearest-neighbor interaction, which\nis identical to a dimerized BHM with repulsive interactions up to the third\nneighbor."
    },
    {
        "anchor": "Vortex structures in rotating Bose-Einstein condensates: We present an analytical solution for the vortex lattice in a rapidly\nrotating trapped Bose-Einstein condensate (BEC) in the lowest Landau level and\ndiscuss deviations from the Thomas-Fermi density profile. This solution is\nexact in the limit of a large number of vortices and is obtained for the cases\nof circularly symmetric and narrow channel geometries. The latter is realized\nwhen the trapping frequencies in the plane perpendicular to the rotation axis\nare different from each other and the rotation frequency is equal to the\nsmallest of them. This leads to the cancelation of the trapping potential in\nthe direction of the weaker confinement and makes the system infinitely\nelongated in this direction. For this case we calculate the phase diagram as a\nfunction of the interaction strength and rotation frequency and identify the\norder of quantum phase transitions between the states with a different number\nof vortex rows.",
        "positive": "Vortex Lattice Formation in Dipolar Bose-Einstein Condensates via\n  Rotation of the Polarization: The behaviour of a harmonically trapped dipolar Bose-Einstein condensate with\nits dipole moments rotating at angular frequencies lower than the transverse\nharmonic trapping frequency is explored in the co-rotating frame. We obtain\nsemi-analytical solutions for the stationary states in the Thomas-Fermi limit\nof the corresponding dipolar Gross-Pitaevskii equation and utilise linear\nstability analysis to elucidate a phase diagram for the dynamical stability of\nthese stationary solutions with respect to collective modes. These results are\nverified via direct numerical simulations of the dipolar Gross-Pitaevskii\nequation, which demonstrate that dynamical instabilities of the co-rotating\nstationary solutions lead to the seeding of vortices that eventually relax into\na triangular lattice configuration. Our results illustrate that rotation of the\ndipole polarization represents a new route to vortex formation in dipolar\nBose-Einstein condensates."
    },
    {
        "anchor": "Coherent ratchets in driven Bose-Einstein condensates: We study the response of a Bose-Einstein condensate to an unbiased periodic\ndriving potential. By controlling the space and time symmetries of the driving\nwe show how a directed current can be induced, producing a coherent quantum\nratchet. Weak driving induces a regular behavior that is strongly governed by\nthe interparticle interaction. Breaking both space and time symmetries is\nrequired to produce current flow. For strong driving the behavior becomes\nchaotic. The resulting effective irreversibility renders the space asymmetry\nsufficient to produce the ratchet effect, although the system is completely\ncoherent.",
        "positive": "Lattice bosons with infinite range checkerboard interactions: Motivated by experiments performed by Landig et al. [Nature 532, 476-479], we\nconsider a two dimensional Bose gas in an optical lattice, trapped inside a\nsingle mode superradiant Fabry Perot cavity. The cavity mediates infinite range\ncheckerboard interactions between the atoms, which produces competition between\nMott insulator, charge density wave, superfluid and supersolid phases. We\ncalculate the phase diagram of this Bose gas in a homogeneous system and in the\npresence of a harmonic trap."
    },
    {
        "anchor": "All-optical cooling of Fermi gases via Pauli inhibition of spontaneous\n  emission: A technique is proposed to cool Fermi gases to the regime of quantum\ndegeneracy based on the expected inhibition of spontaneous emission due to the\nPauli principle. The reduction of the linewidth for spontaneous emission\noriginates a corresponding reduction of the Doppler temperature, which under\nspecific conditions may give rise to a runaway process through which fermions\nare progressively cooled. The approach requires a combination of a\nmagneto-optical trap as a cooling system and an optical dipole trap to enhance\nquantum degeneracy. This results in expected Fermi degeneracy factors $T/T_F$\ncomparable to the lowest values recently achieved, with potential for a direct\nimplementation in optical lattices. The experimental demonstration of this\ntechnique should also indirectly provide a macroscopic manifestation of the\nPauli exclusion principle at the atomic physics level.",
        "positive": "Dipolar Bose-Hubbard Model in finite-size real-space cylindrical\n  lattices: Recent experimental progress in magnetic atoms and polar molecules has\ncreated the prospect of simulating dipolar Hubbard models with off-site\ninteractions. When applied to real-space cylindrical optical lattices, these\nanisotropic dipole-dipole interactions acquire a tunable spatially-dependent\ncomponent while they remain translationally-invariant in the axial direction,\ncreating a sublattice structure in the azimuthal direction. We numerically\nstudy how the coexistence of these classes of interactions affects the ground\nstate of hardcore dipolar bosons at half-filling in a finite-size cylindrical\noptical lattice with octagonal rings. When these two interaction classes\ncooperate, we find a solid state where the density order is determined by the\nazimuthal sublattice structure and builds smoothly as the interaction strength\nincreases. For dipole polarisations where the axial interactions are\nsufficiently repulsive, the repulsion competes with the sublattice structure,\nsignificantly increasing entanglement and creating two distinct ordered density\npatterns. The spatially-varying interactions cause the emergence of these\nordered states in small lattices as a function of interaction strength to be\nstaggered according to the azimuthal sublattices."
    },
    {
        "anchor": "Periodic Array of Bose-Einstein condensates in a Magnetic Lattice: We report the realization of a periodic array of Bose-Einstein condensates of\n87Rb |F = 1; mF = -1> atoms trapped in a one-dimensional magnetic lattice close\n(8 micrometres) to the surface of an atom chip. A clear signature for the onset\nof BEC in the magnetic lattice is provided by in-situ site-resolved\nradiofrequency (RF) spectra, which exhibit a pronounced bimodal distribution\nconsisting of a narrow component characteristic of a BEC together with a broad\nthermal cloud component. Similar bimodal distributions are found for various\nsites across the magnetic lattice. The realization of a periodic array of\nmultiple BECs in a magnetic lattice represents a major advance towards the\nimplementation of magnetic lattices to simulate many-body condensed matter\nphenomena in lattices of complex geometry and arbitrary period.",
        "positive": "Vortex unbinding transition in nonequilibrium photon condensates: We present a theoretical study of a Berezinskii-Kosterlitz-Thouless like\nphase transition in lattices of nonequilibrium photon condensates. Starting\nfrom linearized fluctuation theory and the properties of vortices, we propose\nan analytical formula for the critical point containing four fitting\nparameters, that captures well all our numerical simulations. We find that the\nordered phase becomes more stable when driving and dissipation is increased."
    },
    {
        "anchor": "Engineering interactions and anyon statistics by multicolor\n  lattice-depth modulations: We show that a multicolor modulation of the depth of an optical lattice\nallows for a flexible independent control of correlated hopping,\noccupation-dependent gauge fields, effective on-site interactions without\nFeshbach resonances, and nearest-neighbor interactions. As a result, the\nlattice-depth modulation opens the possibility of engineering with minimal\nexperimental complexity a broad class of lattice models in current experiments\nwith ultra-cold atoms, including Hubbard models with correlated hopping,\npeculiar extended models, and two-component anyon-Hubbard models.",
        "positive": "Realization of a Cold Mixture of Fermionic Chromium and Lithium Atoms: We report on the production of a novel cold mixture of fermionic $^{53}$Cr\nand $^{6}$Li atoms delivered by two Zeeman-slowed atomic beams and collected\nwithin a magneto-optical trap (MOT). For lithium, we obtain clouds of up to $4\n\\,10^8$ atoms at temperatures of about $500\\,\\mu$K. A gray optical molasses\nstage allows us to decrease the gas temperature down to $45(5)\\,\\mu$K. For\nchromium, we obtain MOTs comprising up to $1.5\\, 10^6$ atoms. The availability\nof magnetically trappable metastable $D$-states, from which $P$-state atoms can\nradiatively decay onto, enables to accumulate into the MOT quadrupole samples\nof up to $10^7$ $^{53}$Cr atoms. After repumping $D$-state atoms back into the\ncooling cycle, a final cooling stage decreases the chromium temperature down to\n$145(5)\\,\\mu$K. While the presence of a lithium MOT decreases the lifetime of\nmagnetically trapped $^{53}$Cr atoms, we obtain, within a 5 seconds duty cycle,\nsamples of about $4\\, 10^6$ chromium and $1.5\\,10^8$ lithium atoms. Our work\nprovides a crucial step towards the production of degenerate Cr-Li Fermi\nmixtures."
    },
    {
        "anchor": "Equilibrium vortex lattices of a binary rotating atomic Bose-Einstein\n  condensate with unequal atomic masses: We perform a detailed numerical study of the equilibrium ground-state\nstructures of a binary rotating Bose-Einstein condensate with unequal atomic\nmasses. Our results show that the ground-state distribution and its related\nvortex configurations are complex events that differ markedly depending\nstrongly on the strength of rotation frequency, as well as on the ratio of\natomic masses. We also discuss the structure and radius of the clouds, the\nnumber and the size of the core region of the vortices, as a function of the\nrotation frequency, and of the ratio of atomic masses, and the analytical\nresults agree well with our numerical simulations. This work may open an\nalternate way in the quantum control of the binary rotating quantum gases with\nunequal atomic masses.",
        "positive": "Quantum Phases of Bose-Hubbard Model in Optical Superlattices: In this paper, we analyze the quantum phases of multiple component\nBose-Hubbard model in optical superlattices, using a mean-field method, the\ndecoupling approximation. We find that the phase diagrams exhibit complected\npatterns and regions with various Charge Density Wave (CDW) for both one- and\ntwo- component cases. We also analyze the effective spin dynamics for the\ntwo-component case in strong-coupling region at unit filling, and show the\npossible existence of a Spin Density Wave (SDW) order."
    },
    {
        "anchor": "Ground-State Wave Function with Interactions between Different Species\n  in $M$-Component Miscible Bose-Einstein Condensates: We construct a variational ground-state wave function of weakly interacting\nM-component Bose-Einstein condensates beyond the mean-field theory by\nincorporating the dynamical 3/2-body processes, where one of the two colliding\nparticles drops into the condensate and vice versa. Our numerical results with\nvarious masses and particle numbers show that the 3/2-body processes between\ndifferent particles make finite contributions to lowering the ground-state\nenergy, implying that many-body correlation effects between different particles\nare essential even in the weak-coupling regime of the Bose--Einstein\ncondensates. We also consider the stability condition for $2$-component\nmiscible states using the new ground-state wave function. Through this\ncalculation, we obtain the relation $U^{2}_{AB}/U_{AA}U_{BB}<1+\\alpha$, where\n$U_{ij}$ is the effective contact potential between particles $i$ and $j$ and\n$\\alpha$ is the correction, which originates from the $3/2$-body and $2$-body\nprocesses.",
        "positive": "Simulating a two component Bose-Hubbard model with imbalanced hopping in\n  a Rydberg tweezer array: Optical tweezer arrays of neutral atoms provide a versatile platform for\nquantum simulation due to the range of interactions and Hamiltonians that can\nbe realized and explored. We propose to simulate a two-component Bose-Hubbard\nmodel with power-law hopping using arrays of multilevel Rydberg atoms featuring\nresonant dipolar interactions. The diversity of states that can be used to\nencode the local Hilbert space of the Bose-Hubbard model enables control of the\nrelative hopping rate of each component and even the realization of spin-flip\nhopping. We use numerical simulations to show how multilevel Rydberg atoms\nprovide an opportunity to explore the diverse non-equilibrium quench dynamics\nof the model. For example, we demonstrate a separation of the relaxation\ntimescales of effective spin and charge degrees of freedom, and observe regimes\nof slow relaxation when the effective hopping rates of the two components are\nvastly different due to dynamical constraints arising from hardcore boson\ninteractions. We discuss the technical details of realizing our proposal in\nstate-of-the-art Rydberg tweezer arrays."
    },
    {
        "anchor": "Three-component Fulde-Ferrell superfluids in a two-dimensional Fermi gas\n  with spin-orbit coupling: We investigate the pairing physics of a three-component spin-orbit coupled\nFermi gas in two spatial dimensions. The three atomic hyperfine states of the\nsystem are coupled by the recently realized synthetic spin-orbit coupling\n(SOC), which mixes different hyperfine states into helicity branches in a\nmomentum-dependent manner. As a consequence, the interplay of spin-orbit\ncoupling and the hyperfine-state dependent interactions leads to the emergence\nof Fulde-Ferrell (FF) pairing states with finite center-of-mass momenta even in\nthe absence of the Fermi-surface asymmetry that is usually mandatory to\nstabilize an SOC-induced FF state. We show that, for different combinations of\nspin-dependent interactions, the ground state of the system can either be the\nconventional Bardeen-Cooper-Schrieffer pairing state with zero center-of-mass\nmomentum or be the FF pairing states. Of particular interest here is the\nexistence of a three-component FF pairing state in which every two out of the\nthree components form FF pairing. We map out the phase diagram of the system\nand characterize the properties of the three-component FF state, such as the\norder parameters, the gapless contours and the momentum distributions. Based on\nthese results, we discuss possible experimental detection schemes for the\ninteresting pairing states in the system.",
        "positive": "Capillary waves at the interface of two Bose-Einstein condensates. Long\n  wavelengths asymptotic by trial function approach: The dispersion relation for capillary waves at the boundary of two different\nBose condensates is investigated using a trial wave-function approach applied\nto the Gross-Pitaevskii (GP) equations. The surface tension is expressed by the\nparameters of the GP equations. In the long wave-length limit the usual\ndispersion relation is re-derived while for wavelengths comparable to the\nhealing length we predict significant deviations from the $\\omega\\propto\nk^{3/2}$ law which can be experimentally observed. We approximate the wave\nvariables by a frozen order parameter, i.e. the wave function is frozen in the\nsuperfluid analogous to the magnetic field in highly conductive space plasmas."
    },
    {
        "anchor": "Peltier cooling of fermionic quantum gases: We propose a cooling scheme for fermionic quantum gases, based on the\nprinciples of the Peltier thermoelectric effect and energy filtering. The\nsystem to be cooled is connected to another harmonically trapped gas acting as\na reservoir. The cooling is achieved by two simultaneous processes: (i) the\nsystem is evaporatively cooled and (ii) cold fermions from deep below the Fermi\nsurface of the reservoir are injected below the Fermi level of the system, in\norder to fill the 'holes' in the energy distribution. This is achieved by a\nsuitable energy dependence of the transmission coefficient connecting the\nsystem to the reservoir. The two processes can be viewed as simultaneous\nevaporative cooling of particles and holes. We show that both a significantly\nlower entropy per particle and faster cooling rate can be achieved than by\nusing only evaporative cooling.",
        "positive": "Negative Refraction of Excitations in the Bose-Hubbard Model: Ultracold atoms in optical lattices provide a unique opportunity to study\nBose- Hubbard physics. In this work we show that by considering a spatially\nvarying onsite interaction it is possible to manipulate the motion of\nexcitations above the Mott phase in a Bose-Hubbard system. Specifically, we\nshow that it is possible to \"engineer\" regimes where excitations will\nnegatively refract, facilitating the construction of a flat lens."
    },
    {
        "anchor": "Birth, life, and death of a dipolar supersolid: In the short time since the first observation of supersolid states of\nultracold dipolar atoms, substantial progress has been made in understanding\nthe zero-temperature phase diagram and low-energy excitations of these systems.\nLess is known, however, about their finite-temperature properties, particularly\nrelevant for supersolids formed by cooling through direct evaporation. Here, we\nexplore this realm by characterizing the evaporative formation and subsequent\ndecay of a dipolar supersolid by combining high-resolution in-trap imaging with\ntime-of-flight observables. As our atomic system cools towards quantum\ndegeneracy, it first undergoes a transition from thermal gas to a crystalline\nstate with the appearance of periodic density modulation. This is followed by a\ntransition to a supersolid state with the emergence of long-range phase\ncoherence. Further, we explore the role of temperature in the development of\nthe modulated state.",
        "positive": "Analytic Treatment of Kapitza-Dirac Effect: Connecting Raman-Nath and\n  Bragg Approximations: We develop an analytical approach for probability amplitudes of Kapitza-Dirac\neffect that merge together the Raman-Nath and Bragg regimes of interaction."
    },
    {
        "anchor": "Single-atom imaging of fermions in a quantum-gas microscope: Single-atom-resolved detection in optical lattices using quantum-gas\nmicroscopes has enabled a new generation of experiments in the field of quantum\nsimulation. Fluorescence imaging of individual atoms has so far been achieved\nfor bosonic species with optical molasses cooling, whereas detection of\nfermionic alkaline atoms in optical lattices by this method has proven more\nchallenging. Here we demonstrate single-site- and single-atom-resolved\nfluorescence imaging of fermionic potassium-40 atoms in a quantum-gas\nmicroscope setup using electromagnetically-induced-transparency cooling. We\ndetected on average 1000 fluorescence photons from a single atom within 1.5s,\nwhile keeping it close to the vibrational ground state of the optical lattice.\nOur results will enable the study of strongly correlated fermionic quantum\nsystems in optical lattices with resolution at the single-atom level, and give\naccess to observables such as the local entropy distribution and individual\ndefects in fermionic Mott insulators or anti-ferromagnetically ordered phases.",
        "positive": "Emergence of order from turbulence in an isolated planar superfluid: We study the relaxation dynamics of an isolated zero temperature\nquasi-two-dimensional superfluid Bose-Einstein condensate (BEC) that is\nimprinted with a spatially random distribution of quantum vortices. Following a\nperiod of vortex annihilation, we find that the remaining vortices\nself-organise into two macroscopic coherent `Onsager vortex' clusters that are\nstable indefinitely. We demonstrate that this occurs due to a novel physical\nmechanism --- the evaporative heating of the vortices --- that results in a\nnegative temperature phase transition in the vortex degrees of freedom. At the\nend of our simulations the system is trapped in a non-thermal state. Our\ncomputational results provide a pathway to observing Onsager vortex states in a\nsuperfluid Bose gas."
    },
    {
        "anchor": "Finite temperature stability of a trapped dipolar Bose gas: We calculate the stability diagram for a trapped normal Bose gas with\ndipole-dipole interactions. Our study characterizes the roles of trap geometry,\ntemperature, and short-ranged interactions on the stability. We predict a\nrobust double instability feature in oblate trapping geometries arising from\nthe interplay of thermal gas saturation and the anisotropy of the interaction.\nOur results are relevant to current experiments with polar molecules and will\nbe useful in developing strategies to obtain a polar molecule Bose-Einstein\ncondensate.",
        "positive": "Emergent structure in a dipolar Bose gas in a one-dimensional lattice: We consider an ultracold dipolar Bose gas in a one-dimensional lattice. For a\nsufficiently large lattice recoil energy, such a system becomes a series of\nnon-overlapping Bose-Einstein condensates that interact via the long-range\ndipole-dipole interaction (ddi). We model this system via a coupled set of\nnon-local Gross-Pitaevskii equations (GPEs) for lattices of both infinite and\nfinite extent. We find significantly modified stability properties in the\nlattice due to the softening of a discrete roton-like mode, as well as\n\"islands\" in parameter space where biconcave densities are predicted to exist\nthat only exist in the presence of the other condensates on the lattice. We\nsolve for the elementary excitations of the system to check the dynamical\nstability of these solutions and to uncover the nature of their collapse. By\nsolving a coupled set of GPEs exactly on a full numeric grid, we show that this\nemergent biconcave structure can be realized in a finite lattice with atomic\n$^{52}$Cr."
    },
    {
        "anchor": "Faraday patterns in coupled one-dimensional dipolar condensates: We study Faraday patterns in quasi-one-dimensional dipolar Bose-Einstein\ncondensates with parametrically driven dipolar interactions. We show that in\nthe presence of a roton minimum in the excitation spectrum, the emergent\nFaraday waves differ substantially in two- and one-dimensional geometries,\nproviding a clear example of the key role of confinement dimensionality in\ndipolar gases. Moreover, Faraday patterns constitute an excellent tool to study\nnon-local effects in polar gases, as we illustrate for two parallel\nquasi-one-dimensional dipolar condensates. Non-local interactions between the\ncondensates give rise to an excitation spectrum characterized by symmetric and\nanti-symmetric modes, even in the absence of hopping. We show that this\nfeature, absent in non-dipolar gases, results in a critical driving frequency\nat which a marked transition occurs between correlated and anti-correlated\nFaraday patterns in the two condensates. Interestingly, at this critical\nfrequency, the emergent Faraday pattern stems from a spontaneous symmetry\nbreaking mechanism.",
        "positive": "Two-dimensional dipolar Bose gas with the roton-maxon excitation\n  spectrum: We discuss fluctuations in a dilute two-dimensional Bose-condensed dipolar\ngas, which has a roton-maxon character of the excitation spectrum. We calculate\nthe density-density correlation function, fluctuation corrections to the\nchemical potential, compressibility, and the normal (superfluid) fraction. It\nis shown that the presence of the roton strongly enhances fluctuations of the\ndensity, and we establish the validity criterion of the Bogoliubov approach. At\nT=0 the condensate depletion becomes significant if the roton minimum is\nsufficiently close to zero. At finite temperatures exceeding the roton energy,\nthe effect of thermal fluctuations is stronger and it may lead to a large\nnormal fraction of the gas and compressibility."
    },
    {
        "anchor": "Optimized Observable Readout from Single-shot Images of Ultracold Atoms\n  via Machine Learning: Single-shot images are the standard readout of experiments with ultracold\natoms -- the tarnished looking glass into their many-body physics. The\nefficient extraction of observables from single-shot images is thus crucial.\nHere, we demonstrate how artificial neural networks can optimize this\nextraction. In contrast to standard averaging approaches, machine learning\nallows both one- and two-particle densities to be accurately obtained from a\ndrastically reduced number of single-shot images. Quantum fluctuations and\ncorrelations are directly harnessed to obtain physical observables for bosons\nin a tilted double-well potential at an unprecedented accuracy. Strikingly,\nmachine learning also enables a reliable extraction of momentum-space\nobservables from real-space single-shot images and vice versa. This obviates\nthe need for a reconfiguration of the experimental setup between in-situ and\ntime-of-flight imaging, thus potentially granting an outstanding reduction in\nresources.",
        "positive": "Dispersive effects in the unitary Fermi gas: We investigate within density functional theory various physical properties\nof the zero-temperature unitary Fermi gas which critically depend on the\npresence of a dispersive gradient term in the equation of state. First, we\nconsider the unitary Fermi superfluid gas confined to a semi-infinite domain\nand calculate analytically its density profile and surface tension. Then we\nstudy the quadrupole modes of the superfluid system under harmonic confinement\nfinding a reliable analytical formula for the oscillation frequency, which\nreduces to the familiar Thomas-Fermi one in the limit of a large number of\natoms. Finally, we discuss the formation and propagation of dispersive shock\nwaves in the collision between two resonant fermionic clouds, and compare our\nfindings with recent experimental results."
    },
    {
        "anchor": "Floquet superradiance lattices in thermal atoms: Floquet modulation has been widely used in optical lattices for coherent\ncontrol of quantum gases, in particular for synthesizing artificial gauge\nfields and simulating topological matters. However, such modulation induces\nheating which can overwhelm the signal of quantum dynamics in ultracold atoms.\nHere we report that the thermal motion, instead of being a noise source,\nprovides a new control knob in Floquet-modulated superradiance lattices, which\nare momentum-space tight-binding lattices of collectively excited states of\natoms. The Doppler shifts combined with Floquet modulation provide effective\nforces along arbitrary directions in a lattice in frequency and momentum\ndimensions. Dynamic localization, dynamic delocalization and chiral edge\ncurrents can be simultaneously observed from a single transport spectrum of\nsuperradiance lattices in thermal atoms. Our work paves a way for simulating\nFloquet topological matters in room-temperature atoms and facilitates their\napplications in photonic devices.",
        "positive": "Bose-Fermi solid and its quantum melting in an one-dimensional optical\n  lattice: We investigate the quantum phase diagram of Bose-Fermi mixtures of ultracold\ndipolar particles trapped in one-dimensional optical lattices in the\nthermodynamic limit. With the presence of nearest-neighbor (N.N.) interactions,\na long-ranged ordered crystalline phase (Bose-Fermi solid) is found stabilized\nbetween a Mott insulator of bosons and a band-insulator of fermions in the\nlimit of weak inter-site tunneling ($J$). When $J$ is increased, such a\nBose-Fermi solid can be quantum melted into a Bose-Fermi liquid through either\na two-stage or a three-stage transition, depending on whether the crystalline\norder is dominated by the N.N. interaction between fermions or bosons. These\nproperties can be understood as quantum competition between a pseudo-spin\nfrustration and a pseudo-spin-charge separation, qualitatively different from\nthe classical picture of solid-liquid phase transition."
    },
    {
        "anchor": "Synthetic gauge fields in synthetic dimensions: We describe a simple technique for generating a cold-atom lattice pierced by\na uniform magnetic field. Our method is to extend a one-dimensional optical\nlattice into the \"dimension\" provided by the internal atomic degrees of\nfreedom, yielding a synthetic 2D lattice. Suitable laser-coupling between these\ninternal states leads to a uniform magnetic flux within the 2D lattice. We show\nthat this setup reproduces the main features of magnetic lattice systems, such\nas the fractal Hofstadter butterfly spectrum and the chiral edge states of the\nassociated Chern insulating phases.",
        "positive": "Plasmon dispersion and Landau damping in the nonlinear quantum regime: We study the dispersion properties of electron plasma waves, or plasmons,\nwhich can be excited in quantum plasmas in the nonlinear regime. In order to\ndescribe nonlinear electron response to finite amplitude plasmons, we apply the\nVolkov approach to non-relativistic electrons. For that purpose, we use the\nSchr\\\"odinger equation and describe the electron population of a quantum plasma\nas a mixture of quantum states. Within the kinetic framework that we are able\nto derive from the Volkov solutions, we discuss the role of the wave amplitude\non the nonlinear plasma response. Finally, we focus on the quantum properties\nof nonlinear Landau damping and study the contributions of multi-plasmon\nabsorption and emission processes."
    },
    {
        "anchor": "The Miscible-Immiscible Quantum Phase Transition in Coupled\n  Two-Component Bose-Einstein Condensates in 1D Optical Lattices: Using numerical techniques, we study the miscible-immiscible quantum phase\ntransition in a linearly coupled binary Bose-Hubbard model Hamiltonian that can\ndescribe low-energy properties of a two-component Bose-Einstein condensate in\noptical lattices. With the quantum many-body ground state obtained from density\nmatrix renormalization group algorithm, we calculate the characteristic\nphysical quantities of the phase transition controlled by the linear coupling\nbetween two components. Furthermore we calculate the Binder cumulant to\ndetermine the critical point and draw the phase diagram. The strong-coupling\nexpansion shows that in the Mott insulator regime the model Hamiltonian can be\nmapped to a spin 1/2 XXZ model with a transverse magnetic field.",
        "positive": "Strong-coupling ansatz for the one-dimensional Fermi gas in a harmonic\n  potential: A major challenge in modern physics is to accurately describe strongly\ninteracting quantum many-body systems. One-dimensional systems provide\nfundamental insights since they are often amenable to exact methods. However,\nno exact solution is known for the experimentally relevant case of external\nconfinement. Here, we propose a powerful ansatz for the one-dimensional Fermi\ngas in a harmonic potential near the limit of infinite short-range repulsion.\nFor the case of a single impurity in a Fermi sea, we show that our ansatz is\nindistinguishable from numerically exact results in both the few- and many-body\nlimits. We furthermore derive an effective Heisenberg spin-chain model\ncorresponding to our ansatz, valid for any spin-mixture, within which we obtain\nthe impurity eigenstates analytically. In particular, the classical Pascal's\ntriangle emerges in the expression for the ground-state wavefunction. As well\nas providing an important benchmark for strongly correlated physics, our\nresults are relevant for emerging quantum technologies, where a precise\nknowledge of one-dimensional quantum states is paramount."
    },
    {
        "anchor": "One- and Two-Particle Problem with Correlated Disorder Potential: Motivated by the recent experimental and theoretical progresses in the\nexploration of the effect of disorder in interacting system, we examine the\neffect of two types of correlated disorder, the quasi-periodic potential and\nspeckle disorder potential, on one- and two-particle problem with exact\ndiagonalization (ED) method. We give the phase diagram for single particle in\nthe presence of quasi-periodic potential and also analyse the effect of strong\ninteraction on the phase diagram for ground state in two dimensions. For the\nspeckle disorder potential case, we examine both the effect of correlation\nlength and disorder strength on single particle ground state energy and\ntwo-particle binding energy. The transport property for different interaction\nstrength under speckle disorder potential is also calculated and discussed at\nlast.",
        "positive": "Thermodynamics, density profiles and correlation functions of the\n  inhomogeneous one-dimensional spinor Bose gas: We investigate the finite temperature properties of the one-dimensional\ntwo-component Bose gas (2CBG) with repulsive contact interaction in a harmonic\ntrap. Making use of a new lattice embedding for the 2CBG and the quantum\ntransfer matrix we derive a system of two nonlinear integral equations\ncharacterizing the thermodynamics of the uniform system for all values of the\nrelevant parameters: temperature, strength of the interaction, chemical\npotential and magnetic field. This system allows for an easy numerical\nimplementation in stark contrast with the infinite number of equations obtained\nby employing the thermodynamic Bethe ansatz. We use this exact solution coupled\nwith the local density approximation to compute the density profiles and local\ndensity correlation function of the inhomogeneous gas for a wide range of\ncoupling strengths and temperatures. Our results show that the polarization in\nthe center of the trap influences heavily the local correlator especially in\nthe experimentally accessible Tonks-Girardeau regime."
    },
    {
        "anchor": "Direct Probe of Topological Order for Cold Atoms: Cold-atom experiments in optical lattices offer a versatile platform to\nrealize various topological quantum phases. A key challenge in those\nexperiments is to unambiguously probe the topological order. We propose a\nmethod to directly measure the characteristic topological invariants (order)\nbased on the time-of-flight imaging of cold atoms. The method is generally\napplicable to detection of topological band insulators in one, two, or three\ndimensions characterized by integer topological invariants. Using detection of\nthe Chern number for the 2D anomalous quantum Hall states and the Chern-Simons\nterm for the 3D chiral topological insulators as examples, we show that the\nproposed detection method is practical, robust to typical experimental\nimperfections such as limited imaging resolution, inhomogeneous trapping\npotential, and disorder in the system.",
        "positive": "Many-body effects on second-order phase transitions in spinor\n  Bose-Einstein condensates and breathing dynamics: We unravel the correlation effects of the second-order quantum phase\ntransitions emerging on the ground state of a harmonically trapped spin-1 Bose\ngas, upon varying the involved Zeeman terms, as well as its breathing dynamics\ntriggered by quenching the trapping frequency. It is found that the boundaries\nof the associated magnetic phases are altered in the presence of interparticle\ncorrelations for both ferromagnetic and anti-ferromagnetic spin-spin\ninteractions, an effect which becomes more prominent in the few-body scenario.\nMost importantly, we unveil a correlation-induced shrinking of the\nanti-ferromagnetic and broken-axisymmetry phases implying that ground states\nwith bosons polarized in a single spin-component are favored. Turning to the\ndynamical response of the spinor gas it is shown that its breathing frequency\nis independent of the system parameters while correlations lead to the\nformation of filamentary patterns in the one-body density of the participating\ncomponents. The number of filaments is larger for increasing spin-independent\ninteraction strengths or for smaller particle numbers. Each filament maintains\nits coherence and exhibits an anti-correlated behavior while distinct filaments\nshow significant losses of coherence and are two-body correlated.\nInterestingly, we demonstrate that for an initial broken-axisymmetry phase an\nenhanced spin-flip dynamics takes place which can be tuned either via the\nlinear Zeeman term or the quench amplitude."
    },
    {
        "anchor": "Thermodynamics of one-dimensional SU(4) and SU(6) fermions with\n  attractive interactions: Motivated by advances in the manipulation and detection of ultracold atoms\nwith multiple internal degrees of freedom, we present a finite-temperature\nlattice Monte Carlo calculation of the density and pressure equations of state,\nas well as Tan's contact, of attractively interacting SU(4)- and\nSU(6)-symmetric fermion systems in one spatial dimension. We also furnish a\nnonperturbative proof of a universal relation whereby quantities computable in\nthe SU(2) case completely determine the virial coefficients of the SU($N_f$)\ncase. These one-dimensional systems are appealing because they can be\nexperimentally realized in highly constrained traps and because of the dominant\nrole played by correlations. The latter are typically nonperturbative and are\ncrucial for understanding ground states and quantum phase transitions. While\nquantum fluctuations are typically overpowered by thermal ones in one and two\ndimensions at any finite temperature, we find that quantum effects do leave\ntheir imprint in thermodynamic quantities. Our calculations show that the\nadditional degrees of freedom, relative to the SU(2) case, provide a dramatic\nenhancement of the density and pressure (in units of their noninteracting\ncounterparts) in a wide region around vanishing $\\beta\\mu$, where $\\beta$ is\nthe inverse temperature and $\\mu$ the chemical potential. As shown recently in\nexperiments, the thermodynamics we explore here can be measured in a controlled\nand precise fashion in highly constrained traps and optical lattices. Our\nresults are a prediction for such experiments in one dimension with atoms of\nhigh nuclear spin.",
        "positive": "Ferromagnetism of a Repulsive Atomic Fermi Gas in an Optical Lattice: a\n  Quantum Monte Carlo Study: Using continuous-space quantum Monte Carlo methods we investigate the\nzero-temperature ferromagnetic behavior of a two-component repulsive Fermi gas\nunder the influence of periodic potentials that describe the effect of a\nsimple-cubic optical lattice. Simulations are performed with balanced and with\nimbalanced components, including the case of a single impurity immersed in a\npolarized Fermi sea (repulsive polaron). For an intermediate density below half\nfilling, we locate the transitions between the paramagnetic, and the partially\nand the fully ferromagnetic phases. As the intensity of the optical lattice\nincreases, the ferromagnetic instability takes place at weaker interactions,\nindicating a possible route to observe ferromagnetism in experiments performed\nwith ultracold atoms. We compare our findings with previous predictions based\non the standard computational method used in material science, namely density\nfunctional theory, and with results based on tight-binding models."
    },
    {
        "anchor": "Phase diagram of dipolar bosons in 2D with tilted polarization: We analyze the ground state of a system of dipolar bosons moving in the $XY$\nplane and such that their dipolar moments are all aligned in a fixed direction\nin space. We focus on the general case where the polarization field forms a\ngeneric angle $\\alpha$ with respect to the $Z$ axis. We use the Path Integral\nGround State method to analyze the static properties of the system as both\n$\\alpha$ and the density $n$ vary over a wide range were the system is stable.\nWe use the maximum of the static structure function as an order parameter to\ncharacterize the different phases and the transition lines among them. We find\nthat aside of a superfluid gas and a solid phase, the system reaches a stripe\nphase at large tilting angles that is entirely induced by the anisotropic\ncharacter of the interaction. We also show that the quantum phase transition\nfrom the gas to the stripe phase is of second order, and report approximate\nvalues for the critical exponents.",
        "positive": "Collective Excitation Interferometry with a Toroidal Bose-Einstein\n  Condensate: The precision of compact inertial sensing schemes using trapped- and\nguided-atom interferometers has been limited by uncontrolled phase errors\ncaused by trapping potentials and interactions. Here, we propose an acoustic\ninterferometer that uses sound waves in a toroidal Bose-Einstein condensate to\nmeasure rotation, and we demonstrate experimentally several key aspects of this\ntype of interferometer. We use spatially patterned light beams to excite\ncounter-propagating sound waves within the condensate and use \\emph{in situ}\nabsorption imaging to characterize their evolution. We present an analysis\ntechnique by which we extract separately the oscillation frequencies of the\nstanding-wave acoustic modes, the frequency splitting caused by static\nimperfections in the trapping potential, and the characteristic precession of\nthe standing-wave pattern due to rotation. Supported by analytic and numerical\ncalculations, we interpret the noise in our measurements, which is dominated by\natom shot noise, in terms of rotation noise. While the noise of our acoustic\ninterferometric sensor, at the level of $\\sim \\mbox{rad}\\,\n\\mbox{s}^{-1}/\\sqrt{\\mbox{Hz}}$, is high owing to rapid acoustic damping and\nthe small radius of the trap, the proof-of-concept device does operate at $10^4\n- 10^6$ times higher density and in a volume $10^9$ times smaller than\nfree-falling atom interferometers."
    },
    {
        "anchor": "Self-trapping of excitations: Two-dimensional quasiparticle solitons in\n  an extended Bose-Hubbard dimer array: Considering a two-dimensional Bose-Hubbard spinor lattice with weak nearest\nneighbour interactions and no particle transfer between sites, we theoretically\nstudy the transport of energy from one initially excited dimer, to the rest of\nthe lattice. Beyond a critical interaction strength, low energy on-site\nexcitations are quickly dispersed throughout the array, while stronger\nexcitations are self trapped, resulting in localized energy breathers and\nsolitons. These structures are quasiparticle analogues to the discrete 2D\nsolitons in photonic lattices. Full many-body simulations additionally\ndemonstrate the localization of one-particle entropy.",
        "positive": "Cavity-induced generation of non-trivial topological states in a\n  two-dimensional Fermi gas: We propose how topologically non-trivial states can dynamically organize in a\nfermionic quantum gas which is confined to a two-dimensional optical lattice\npotential and coupled to the field of an optical cavity. The spontaneously\nemerging cavity field induces together with coherent pump laser fields a\ndynamical gauge field for the atoms. Upon adiabatic elimination of the cavity\ndegree of freedom, the system is described by an effective Hofstadter model\nwith a self-consistency condition which determines the tunneling amplitude\nalong the cavity direction. The fermions are found to self-organize into\ntopologically non-trivial states which carry an extended edge state for a\nfinite system size. Due to the dissipative nature of the cavity field, the\ntopological steady states are protected from external perturbations."
    },
    {
        "anchor": "Universal bound states of one-dimensional bosons with two- and\n  three-body attractions: When quantum particles are confined into lower dimensions, an effective\nthree-body interaction inevitably arises and may cause significant\nconsequences. Here we study bosons in one dimension with weak two-body and\nthree-body interactions, predict the existence of two three-body bound states\nwhen both interactions are attractive, and determine their binding energies as\nuniversal functions of the two-body and three-body scattering lengths. We also\nshow that an infinitesimal three-body attraction induces an excited bound state\nonly for 3, 39, or more bosons. Our findings herein have direct relevance to a\nbroad range of quasi-one-dimensional systems realized with ultracold atoms.",
        "positive": "Nonlocal field theory of quasiparticle scattering in dipolar\n  Bose-Einstein condensates: We consider the propagation of quasiparticle excitations in a dipolar\nBose-Einstein condensate, and derive a nonlocal field theory of quasiparticle\nscattering at a stepwise inhomogeneity of the sound speed, obtained by tuning\nthe contact coupling part of the interaction on one side of the barrier. To\nsolve this problem $ab$ $initio$, i.e., without prior assumptions on the form\nof the solutions, we reformulate the dipolar Bogoliubov-de Gennes equation as a\nsingular integral equation. The latter is of a $novel$ $hypersingular$ type, in\nhaving a kernel which is hypersingular at only two isolated points. Deriving\nits solution, we show that the integral equation reveals a continuum of\nevanescent channels at the sound barrier which is absent for a purely\ncontact-interaction condensate. We furthermore demonstrate that by performing a\ndiscrete approximation for the kernel, one achieves an excellent solution\naccuracy for already a moderate number of discretization steps. Finally, we\nshow that the non-monotonic nature of the system dispersion, corresponding to\nthe emergence of a roton minimum in the excitation spectrum, results in\npeculiar features of the transmission and reflection at the sound barrier which\nare nonexistent for contact interactions."
    },
    {
        "anchor": "Variational study of polarons in Bose-Einstein condensates: We use a class of variational wave functions to study the properties of an\nimpurity in a Bose-Einstein condensate, i.e. the \"Bose polaron\". The impurity\ninteracts with the condensate through a contact interaction, which can be tuned\nby a Feshbach resonance. We find a stable attractive polaron branch that\nevolves continuously across the resonance to a tight-binding diatomic molecule\ndeep in the positive scattering length side. A repulsive polaron branch with\nfinite lifetime is also observed and it becomes unstable as the interaction\nstrength increases. The effective mass of the attractive polaron also changes\nsmoothly across the resonance connecting the two well-understood limits deep on\nboth sides.",
        "positive": "Excitation properties and effects of mass imbalance in the BCS-BEC\n  crossover regime of an ultracold Fermi gas: We investigate single-particle properties of a mass-imbalanced Fermi gas in\nthe BCS (Bardeen-Cooper-Schrieffer)-BEC (Bose-Einstein condensation) crossover\nregion. In the presence of mass imbalance, we point out that the ordinary\n$T$-matrix approximation, which has been extensively used to clarify various\nBCS-BEC crossover physics in the mass-balanced case, unphysically gives a\ndouble-valued solution in terms of the superfluid phase transition temperature\n$T_{\\rm c}$ in the crossover region. To overcome this serious problem, we\ninclude higher order strong-coupling corrections beyond the $T$-matrix level.\nUsing this extended $T$-matrix theory, we calculate single-particle excitations\nin the normal state above $T_{\\rm c}$. The so-called pseudogap phenomena\noriginating from pairing fluctuations are shown to be different between the\nlight mass component and heavy mass component, which becomes more remarkable at\nhigher temperatures. Since Fermi condensates with hetero-Cooper pairs have\nrecently been discussed in various fields, such as exciton (polariton)\ncondensates, as well as color superconductivity, our results would be useful\nfor the further development of Fermi superfluid physics, beyond the\nconventional superfluid state with homo-Cooper pairs."
    },
    {
        "anchor": "Engineering interband transport by time-dependent disorder: We show how the evolution of atoms in a tilted lattice can be changed and\ncontrolled by phase noise on the lattice. Dependent on the characteristic\nparameters of the noise, the interband transport can either be suppressed or\nenhanced, which is of interest for high precision control in experimental\nrealization with Bose-Einstein condensates. The effect of the noise on the\nsurvival probability in the ground band is summarized in a scaling plot\nstressing the universality of our results.",
        "positive": "Quantum anomaly, universal relations, and breathing mode of a\n  two-dimensional Fermi gas: In this Letter, we show that the classical SO(2,1) symmetry of a harmonically\ntrapped Fermi gas in two dimensions is broken by quantum effects. The anomalous\ncorrection to the symmetry algebra is given by a two-body operator that is well\nknown as the contact. Taking into account this modification, we are able to\nderive the virial theorem for the system and a universal relation for the\npressure of a homogeneous gas. The existence of an undamped breathing mode is\nassociated with the classical symmetry. We provide an estimate for the\nanomalous frequency shift of this oscillation at zero temperature and compare\nthe result with a recent experiment by [E. Vogt et al., Phys. Rev. Lett. 108,\n070404 (2012)]. Discrepancies are attributed to finite temperature effects."
    },
    {
        "anchor": "Uncover Topology by Quantum Quench Dynamics: Topological quantum states are characterized by nonlocal invariants, and\ntheir detection is intrinsically challenging. Various strategies have been\ndeveloped to study topological Hamiltonians through their equilibrium states.\nWe present a fundamentally new, high-precision dynamical approach, revealing\ntopology through the unitary evolution after a quench from a topological\ntrivial initial state with a two-dimensional Chern band realized in an\nultracold $^{87}$Rb atom gas. The emerging ring structure in the spin dynamics\nuniquely determines the Chern number for the post-quench band and enables\nprobing the full phase diagram of the band topology with high precision.\nBesides, we also measure the topological band gap and the domain wall structure\ndynamically formed in the momentum space during the long-term evolution. Our\ndynamical approach provides a way towards observing a universal bulk-ring\ncorrespondence, and has broad applications in exploring topological quantum\nmatter.",
        "positive": "Signatures of Fractional Exclusion Statistics in the Spectroscopy of\n  Quantum Hall Droplets: We show how spectroscopic experiments on a small Laughlin droplet of rotating\nbosons can directly demonstrate Haldane fractional exclusion statistics of\nquasihole excitations. The characteristic signatures appear in the\nsingle-particle excitation spectrum. We show that the transitions are governed\nby a \"many-body selection rule\" which allows one to relate the number of\nallowed transitions to the number of quasihole states on a finite geometry. We\nillustrate the theory with numerically exact simulations of small numbers of\nparticles."
    },
    {
        "anchor": "Following Floquet states in high-dimensional Hilbert spaces: An iterative algorithm is established which enables one to compute individual\nFloquet states even for many-body systems with high-dimensional Hilbert spaces\nthat are not accessible to commonly employed conventional methods. A strategy\nis proposed for following a Floquet state in response to small changes of a\ngiven system's Hamiltonian. The scheme is applied to a periodically driven\nBose-Hubbard chain, verifying the possibility of pseudoadiabatic Floquet state\nfollowing. In particular, it is demonstrated that a driving-induced Mott\ninsulatorlike target Floquet state can be populated with high efficiency if the\ndriving amplitude is turned on smoothly but not too slowly. We conclude that\nthe algorithm constitutes a powerful tool for the future investigation of\nmany-body Floquet systems.",
        "positive": "Verification of exceptional points in the collapse dynamics of\n  Bose-Einstein condensates: In Bose-Einstein condensates with an attractive contact interaction the\nstable ground state and an unstable excited state emerge in a tangent\nbifurcation at a critical value of the scattering length. At the bifurcation\npoint both the energies and the wave functions of the two states coalesce,\nwhich is the characteristic of an exceptional point. In numerical simulations\nsignatures of the exceptional point can be observed by encircling the\nbifurcation point in the complex extended space of the scattering length,\nhowever, this method cannot be applied in an experiment. Here we show in which\nway the exceptional point effects the collapse dynamics of the Bose-Einstein\ncondensate. The harmonic inversion analysis of the time signal given as the\nspatial extension of the collapsing condensate wave function can provide clear\nevidence for the existence of an exceptional point. This method can be used for\nan experimental verification of exceptional points in Bose-Einstein\ncondensates."
    },
    {
        "anchor": "Strongly interacting fermions in an optical lattice: We analyze a system of two-component fermions which interact via a Feshbach\nresonance in the presence of a three-dimensional lattice potential. By\nexpressing a two-channel model of the resonance in the basis of Bloch states\nappropriate for the lattice, we derive an eigenvalue equation for the\ntwo-particle bound states which is nonlinear in the energy eigenvalue. Compact\nexpressions for the interchannel matrix elements, numerical methods for the\nsolution of the nonlinear eigenvalue problem, and a renormalization procedure\nto remove ultraviolet divergences are presented. From the structure of the\ntwo-body solutions we identify the relevant degrees of freedom which describe\nthe resonance behavior in the lowest Bloch band. These degrees of freedom,\nwhich we call dressed molecules, form an effective closed channel in a\nmany-body model of the resonance, the Fermi resonance Hamiltonian (FRH). It is\nshown how the properties of the FRH can be determined numerically by solving a\nprojected lattice two-channel model at the two-particle level. As opposed to\nsingle-channel lattice models such as the Hubbard model, the FRH is valid for\ngeneral s-wave scattering length and resonance width. Hence, the FRH provides\nan accurate description of the BEC-BCS crossover for ultracold fermions on an\noptical lattice.",
        "positive": "Topological Polaritons and Excitons in Garden Variety Systems: Topological polaritons (aka topolaritons) present a new frontier for\ntopological behavior in solid-state systems. They combine light and matter,\nwhich allows to probe and manipulate them in a variety of ways. They can also\nbe made strongly interacting, due to their excitonic component. So far,\nhowever, their realization was deemed rather challenging. Here we present a\nscheme which allows to realize topolaritons in garden variety zinc-blende\nquantum wells. Our proposal requires a moderate magnetic field and a potential\nlandscape which can be implemented, e.g., via surface acoustic waves or\npatterning. We identify indirect excitons in double quantum wells as a\nparticularly appealing alternative for topological states in exciton-based\nsystems. Indirect excitons are robust and long lived (with lifetimes up to\nmilliseconds), and, therefore, provide a flexible platform for the realization,\nprobing, and utilization of topological coupled light-matter states."
    },
    {
        "anchor": "A Universal Energy Functional for Trapped Fermi Gases with Large\n  Scattering Length: Yoram Alhassid conjectured that the total energy of a harmonically trapped\ntwo-component Fermi gas with large scattering length is a linear functional of\nthe occupation probabilities of single-particle energy eigenstates. We confirm\nhis conjecture and derive the functional explicitly. We show that the\nfunctional applies to ALL smooth potentials having a minimum, not just harmonic\ntraps. We also calculate the occupation probabilities of high energy states.",
        "positive": "Thermodynamics of spin-orbit-coupled Bose-Einstein condensates: In this paper we develop a quantum field approach to reveal the thermodynamic\nproperties of the trapped BEC with the equal Rashba and Dresselhaus spin-orbit\ncouplings. In the experimentally-feasible regime, the phase transition from the\nseparate phase to the single minimum phase can be well driven by the tunable\ntemperature. Moreover, the critical temperature, which is independent of the\ntrapped potential, can be derived exactly. At the critical point, the specific\nheat has a large jump and can be thus regarded as a promising candidate to\ndetect this temperature-driven phase transition. In addition, we obtain the\nanalytical expressions for the specific heat and the entropy in the different\nphases. In the single minimum phase, the specific heat as well as the entropy\nare governed only by the Rabi frequency. However, in the separate phase with\nlower temperature, we find that they are determined only by the strength of\nspin-orbit coupling. Finally, the effect of the effective atom interaction is\nalso addressed. In the separate phase, this effective atom interaction affects\ndramatically on the critical temperature and the corresponding thermodynamic\nproperties."
    },
    {
        "anchor": "Existence of a critical point in the phase diagram of the ideal\n  relativistic neutral Bose gas: We explore the phase transitions of the ideal relativistic neutral Bose gas\nconfined in a cubic box, without assuming the thermodynamic limit nor\ncontinuous approximation. While the corresponding non-relativistic canonical\npartition function is essentially a one-variable function depending on a\nparticular combination of temperature and volume, the relativistic canonical\npartition function is genuinely a two-variable function of them. Based on an\nexact expression of the canonical partition function, we performed numerical\ncomputations for up to hundred thousand particles. We report that if the number\nof particles is equal to or greater than a critical value, which amounts to\n7616, the ideal relativistic neutral Bose gas features a spinodal curve with a\ncritical point. This enables us to depict the phase diagram of the ideal Bose\ngas. The consequent phase transition is first-order below the critical pressure\nor second-order at the critical pressure. The exponents corresponding to the\nsingularities are 1/2 and 2/3 respectively. We also verify the recently\nobserved `Widom line' in the supercritical region.",
        "positive": "Dynamical thermalization of Bose-Einstein condensate in Bunimovich\n  stadium: We study numerically the wavefunction evolution of a Bose-Einstein condensate\nin a Bunimovich stadium billiard being governed by the Gross-Pitaevskii\nequation. We show that for a moderate nonlinearity, above a certain threshold,\nthere is emergence of dynamical thermalization which leads to the Bose-Einstein\nprobability distribution over the linear eigenmodes of the stadium. This\ndistribution is drastically different from the energy equipartition over\noscillator degrees of freedom which would lead to the ultra-violet catastrophe.\nWe argue that this interesting phenomenon can be studied in cold atom\nexperiments."
    },
    {
        "anchor": "Abelian and non-Abelian quantum spin liquids in a three-component Bose\n  gas on optical Kagome lattices: Realization of non-Abelian anyons in topological phases is a crucial step\ntoward topological quantum computation. We propose a scheme to realize a\nnon-Abelian quantum spin liquid (QSL) phase in a three-component Bose gas with\ncontact interaction on optical Kagome lattices. In the strong coupling regime,\nthe system is described by an effective spin-1 model with two- and three-body\ninteractions between neighboring spins. By mapping out the phase diagram via\nvariational Monte Carlo method, we find a non-Abelian chiral spin liquid phase\nin which the Ising-type anyons obey non-Abelian braiding statistics. The\ngapless chiral edge states can be detected by measuring the spin-spin\ncorrelation from atomic population. Furthermore, an interesting Z2 QSL phase is\nobserved exhibiting both topological order and lattice symmetry breaking order.\nOur scheme can be implemented in cold quantum gases of bosonic atoms.",
        "positive": "Topological pump and bulk-edge-correspondence in an extended\n  Bose-Hubbard model: An extended Bose-Hubbard model (EBHM) with three- and four-body constraints\ncan be feasible in cold atoms in an optical lattice. A rich phase structure\nincluding various symmetry-protected topological (SPT) phases is obtained\nnumerically with suitable parameter settings and particle filling. The SPT\nphase is characterized by the Berry phase as a local topological order\nparameter and the structure of the entanglement spectrum (ES). Based on the\npresence of various topological phases, separated by gapless phase boundaries,\nthe EBHM exhibits various bosonic topological pumps, which are constructed by\nconnecting the different SPT phases without gap closing. The bulk topological\npumps exhibit the plateau transitions characterized by many-body Chern numbers.\nFor the system with boundary, the center of mass (CoM) under grand canonical\nensemble elucidates the contributions of multiple edge states and reveals the\ntopology of the system. We demonstrate that the interacting bosonic pumps obey\nthe bulk-edge-correspondence."
    },
    {
        "anchor": "Wave functions of the super Tonks-Girardeau gas and the trapped 1D hard\n  sphere Bose gas: Recent theoretical and experimental results demonstrate a close connection\nbetween the super Tonks-Girardeau (sTG) gas and a 1D hard sphere Bose (HSB) gas\nwith hard sphere diameter nearly equal to the 1D scattering length $a_{1D}$ of\nthe sTG gas, a highly excited gas-like state with nodes only at interparticle\nseparations $|x_{j\\ell}|=x_{node}\\approx a_{1D}$. It is shown herein that when\nthe coupling constant $g_B$ in the Lieb-Liniger interaction\n$g_B\\delta(x_{j\\ell})$ is negative and $|x_{12}|\\ge x_{node}$, the sTG and HSB\nwave functions for $N=2$ particles are not merely similar, but identical; the\nonly difference between the sTG and HSB wave functions is that the sTG wave\nfunction allows a small penetration into the region $|x_{12}|<x_{node}$,\nwhereas for a HSB gas with hard sphere diameter $a_{h.s.}=x_{node}$, the HSB\nwave function vanishes when all $|x_{12}|<a_{h.s.}$. Arguments are given\nsuggesting that the same theorem holds also for $N>2$. The sTG and HSB wave\nfunctions for N=2 are given exactly in terms of a parabolic cylinder function,\nand for $N\\ge 2$, $x_{node}$ is given accurately by a simple parabola. The\nmetastability of the sTG phase generated by a sudden change of the coupling\nconstant from large positive to large negative values is explained in terms of\nthe very small overlap between the ground state of the Tonks-Girardeau gas and\ncollapsed cluster states.",
        "positive": "Boltzmann equation simulation for a trapped Fermi gas of atoms: The dynamics of an interacting Fermi gas of atoms at sufficiently high\ntemperatures can be efficiently studied via a numerical simulation of the\nBoltzmann equation. In this work we describe in detail the setup we used\nrecently to study the oscillations of two spin-polarised fermionic clouds in a\ntrap. We focus here on the evaluation of interparticle interactions. We compare\ndifferent ways of choosing the phase space coordinates of a pair of atoms after\na successful collision and demonstrate that the exact microscopic setup has no\ninfluence on the macroscopic outcome."
    },
    {
        "anchor": "Patterns, spin-spin correlations and competing instabilities in driven\n  quasi-two-dimensional spin-1 Bose-Einstein condensates: We analyze the formation of transient patterns and spin-spin correlations in\nquasi-two-dimensional spin-1 homogeneous Bose-Einstein condensates subjected to\nparametric driving of $s$-wave scattering lengths. The dynamics for an initial\nferromagnetic phase is identical to that of a scalar condensate. In contrast,\nintriguing dynamics emerges for an initial polar state. For instance, we show\nthat competition exists between density patterns and spin-mixing dynamics.\nDominant spin-mixing dynamics lead to a gas of polar core vortices and\nanti-vortices of different spin textures. The density modes of the Bogoliubov\nspectrum govern the wavenumber selection of Faraday patterns. The spin modes\ndetermine the vortex density and the spatial dependence of spin-spin\ncorrelation functions. When the density patterns outgrow the spin-mixing\ndynamics, the spin-spin correlations decay exponentially with a correlation\nlength of the order a spin healing length; otherwise, they exhibit a Bessel\nfunction dependence. Strikingly, competing instabilities within density and\nspin modes emerge when both scattering lengths are modulated at different\nfrequencies and appropriate modulation amplitudes. The competing instability\nleads to a superposition of density patterns or correlation functions of two\ndistinct wavelengths. Our studies reveal that fine control over the driven\ndynamics can be attained by tuning interaction strengths, quadratic Zeeman\nfield, driving frequencies, and amplitudes.",
        "positive": "Single-domain Bose condensate magnetometer achieves energy resolution\n  per bandwidth below $\\hbar$: We present a magnetic sensor with energy resolution per bandwidth $E_R <\n\\hbar$. We show how a $^{87}\\mathrm{Rb}$ single domain spinor Bose-Einstein\ncondensate, detected by non-destructive Faraday-rotation probing, achieves\nsingle shot dc magnetic sensitivity of $72(8)~\\mathrm{fT}$ measuring a volume\n$V= 1091(30)~\\mu\\mathrm{m}^3$ for $3.5~\\mathrm{s}$, and thus $E_R =\n0.075(16)~\\hbar$. We measure experimentally the condensate volume, spin\ncoherence time, and readout noise, and use phase-space methods, backed by 3+1D\nmean-field simulations, to compute the spin noise. Contributions to the spin\nnoise include one-body and three-body losses and shearing of the projection\nnoise distribution, due to competition of ferromagnetic contact interactions\nand quadratic Zeeman shifts. Nonetheless, the fully-coherent nature of the\nsingle-domain, ultracold two-body interactions allows the system to escape the\ncoherence vs.~density trade-off that imposes an energy resolution limit on\ntraditional spin-precession sensors. We predict that other Bose-condensed\nalkalis, especially the antiferromagnetic $^{23}\\mathrm{Na}$, can further\nimprove the energy resolution of this method."
    },
    {
        "anchor": "Matter-Wave Imaging of Quantum Density Fluctuations in Ultracold Bosons\n  in an Optical Lattice: We study the influence of quantum density fluctuations in ultracold atoms in\nan optical lattice on the scattering of matter waves. Such fluctuations are\ncharacteristic of the superfluid phase and vanish due to increased interactions\nin the Mott insulating phase. We employ an analytical treatment of the\nscattering and demonstrate that the fluctuations lead to incoherent processes,\nwhich we propose to observe via decoherence of the fringes in a Mach-Zender\ninterferometer. In this way we extract the purely coherent part of the\nscattering. Further, we show that the quantum density fluctuations can also be\nobserved directly in the differential angular scattering cross section for an\natomic beam scattered from the atoms in a lattice. Here we find an explicit\ndependence of the scale of the inelastic scattering on the quantum density\nfluctuations.",
        "positive": "Superfluid Drag in Multicomponent Bose-Einstein Condensates on a Square\n  Optical Lattice: The superfluid drag-coefficient of a weakly interacting three-component\nBose-Einstein condensate is computed deep into the superfluid phase, starting\nfrom a Bose-Hubbard model with component-conserving, on-site interactions and\nnearest-neighbor hopping. Rayleigh-Schr\\\"odinger perturbation theory is\nemployed to provide an analytic expression for the drag density. In addition,\nthe Hamiltonian is diagonalized numerically to compute the drag within\nmean-field theory at both zero and finite temperatures to all orders in\ninter-component interactions. Moreover, path integral Monte Carlo simulations\nhave been performed to support the mean-field results. In the two-component\ncase the drag increases monotonically with the magnitude of the inter-component\ninteraction $\\gamma_{AB}$ between the two components A and B. This no longer\nholds when an additional third component C is included. Instead of increasing\nmonotonically, the drag can either be strengthened or weakened depending on the\ndetails of the interaction strengths, for weak and moderately strong\ninteractions. The general picture is that the drag-coefficient between\ncomponent A and B is a non-monotonic function of the inter-component\ninteraction strength $\\gamma_{AC}$ between A and a third component C. For weak\n$\\gamma_{AC}$ compared to the direct interaction $\\gamma_{AB}$ between A and B,\nthe drag-coefficient between A and B can {\\it decrease}, contrary to what one\nnaively would expect. When $\\gamma_{AC}$ is strong compared to $\\gamma_{AB}$,\nthe drag between A and B increases with increasing $\\gamma_{AC}$, as one would\nnaively expect. We attribute the subtle reduction of $\\rho_{d,AB}$ with\nincreasing $\\gamma_{AC}$, which has no counterpart in the two-component case,\nto a renormalization of the inter-component scattering vertex $\\gamma_{AB}$ via\nintermediate excited states of the third condensate $C$."
    },
    {
        "anchor": "Effective thermalization of a many-body dynamically localized Bose gas: Dynamical localization is the analog of Anderson localization in momentum\nspace, where the system's energy saturates and the single-particle\nwave-functions are exponentially localized in momentum space. In the presence\nof interactions, in the context of a periodically kicked Bose gas, it has been\nargued that dynamical localization persists. Focusing on the Tonks (strongly\ninteracting) regime, we show that the many-body dynamically localized phase is\neffectively thermal, a clear deviation from the breaking of ergodicity observed\nin standard many-body localized systems. We relate the effective temperature to\nthe driving parameters, and thus quantitatively describe the loss of coherence\nat large distances in this phase. Contrary to the non-interacting case, the\nmomentum distribution decays as a power-law at large momenta, characterized by\nan effectively thermal Tan's contact. This is a rare example where driving and\nmany-body (dynamical) localization lead to an effectively ergodic state.",
        "positive": "Collective modes across the soliton-droplet crossover in binary Bose\n  mixtures: We study the collective modes of a binary Bose mixture across the soliton to\ndroplet crossover in a quasi one dimensional waveguide with a beyond-mean-field\nequation of state and a variational Gaussian ansatz for the scalar bosonic\nfield of the corresponding effective action. We observe a sharp difference in\nthe collective modes in the two regimes. Within the soliton regime modes vary\nsmoothly upon the variation of particle number or interaction strength. On the\ndroplet side collective modes are inhibited by the emission of particles. This\nmechanism turns out to be dominant for a wide range of particle numbers and\ninteractions. In a small window of particle number range and for intermediate\ninteractions we find that monopole frequency is likely to be observed. In the\nlast part we focus on the spin-dipole modes for the case of equal intraspecies\ninteractions and equal equilibrium particle numbers in the presence of a weak\nlongitudinal confinement. We found that such modes might be unobservable in the\nreal-time dynamics close to the equilibrium as their frequency is higher than\nthe particle emission spectrum by at least one order of magnitude in the\ndroplet phase. Our results are relevant for experiments with two-component BECs\nfor which we provide realistic parameters."
    },
    {
        "anchor": "Comprehensive classification for Bose-Fermi mixtures: We present analytical studies of a boson-fermion mixture at zero temperature\nwith spin-polarized fermions. Using the Thomas-Fermi approximation for bosons\nand the local-density approximation for fermions, we find a large variety of\ndifferent density shapes. In the case of continuous density, we obtain analytic\nconditions for each configuration for attractive as well as repulsive\nboson-fermion interaction. Furthermore, we analytically show that all the\nscenarios we describe are minima of the grand-canonical energy functional.\nFinally, we provide a full classification of all possible ground states in the\ninterpenetrative regime. Our results also apply to binary mixtures of bosons.",
        "positive": "Ground state properties and excitation spectrum of a two dimensional gas\n  of bosonic dipoles: We present a quantum Monte Carlo study of two-dimensional dipolar Bose gases\nin the limit of zero temperature. The analysis is mainly focused on the\nanisotropy effects induced in the homogeneous gas when the polarization angle\nwith respect to the plane is changed. We restrict our study to the regime where\nthe dipolar interaction is strictly repulsive, although the strength of the\npair repulsion depends on the vector interparticle distance. Our results show\nthat the effect of the anisotropy in the energy per particle scales with the\ngas parameter at low densities as expected, and that this scaling is preserved\nfor all polarization angles even at the largest densities considered here. We\nalso evaluate the excitation spectrum of the dipolar Bose gas in the context of\nthe Feynman approximation and compare the results obtained with the Bogoliubov\nones. As expected, we find that these two approximations agree at very low\ndensities, while they start to deviate from each other as the density\nincreases. For the largest densities studied, we observe a significant\ninfluence of the anisotropy of the dipole-dipole interaction in the excitation\nspectrum."
    },
    {
        "anchor": "Superfluid to Bose-glass transition in a 1D weakly interacting Bose gas: We study the one-dimensional Bose gas in spatially correlated disorder at\nzero temperature, using an extended density-phase Bogoliubov method. We analyze\nin particular the decay of the one-body density matrix and the behaviour of the\nBogoliubov excitations across the phase boundary. We observe that the\ntransition to the Bose glass phase is marked by a power-law divergence of the\ndensity of states at low energy. A measure of the localization length displays\na power-law energy dependence in both regions, with the exponent equal to -1 at\nthe boundary. We draw the phase diagram of the superfluid-insulator transition\nin the limit of small interaction strength.",
        "positive": "Mean-field Dynamics of Spin-Orbit Coupled Bose-Einstein Condensates: Spin-orbit coupling (SOC), the interaction between the spin and momentum of a\nquantum particle, is crucial for many important condensed matter phenomena. The\nrecent experimental realization of SOC in neutral bosonic cold atoms provides a\nnew and ideal platform for investigating spin-orbit coupled quantum many-body\nphysics. In this Letter, we derive a generic Gross-Pitaevskii equation as the\nstarting point for the study of many-body dynamics in spin-orbit coupled\nBose-Einstein condensates. We show that different laser setups for realizing\nthe same SOC may lead to different mean field dynamics. Various ground state\nphases (stripe, phase separation, etc.) of the condensate are found in\ndifferent parameter regions. A new oscillation period induced by the SOC,\nsimilar to the Zitterbewegung oscillation, is found in the center of mass\nmotion of the condensate."
    },
    {
        "anchor": "Two-dimensional composite solitons in a spin-orbit-coupled Fermi gas in\n  free space: We address a possibility of creating soliton states in oblate\nbinary-fermionic clouds in the framework of the density-functional theory,\nwhich includes the spin-orbit coupling (SOC) and nonlinear attraction between\nspin-up and down-polarized components of the spinor wave function. In the limit\nwhen the inter-component attraction is much stronger than the effective\nintra-component Pauli repulsion, the resulting model also represents a system\nof Gross-Pitaevskii equations for a binary Bose-Einstein condensate including\nthe SOC effect. We show that the model gives rise to two-dimensional quiescent\ncomposite solitons in free space. A stability region is identified for solitons\nof the mixed-mode type (which feature mixtures of zero-vorticity and vortical\nterms in both components), while solitons of the other type, semi-vortices\n(with the vorticity carried by one component) are unstable. Due to breaking of\nthe Galilean invariance by SOC, the system supports moving solitons with\nvelocities up to a specific critical value. Collisions between moving solitons\nare briefly considered too. The collisions lead, in particular, to a\nquasi-elastic rebound, or an inelastic outcome, which features partial merger\nof the solitons.",
        "positive": "Faraday waves in BEC with engineering three-body interactions: We consider Bose-Einstein condensates with two- and three-body interactions\nperiodically varying in time. Two models of time-dependent three-body\ninteractions, with quadratic and quartic dependence on the two-body atomic\nscattering length $a_s$, are studied. It is shown that parametric instabilities\nin the condensate leads to the generation of Faraday waves (FW), with\nwavelengths depending on the background scattering length, as well as on the\nfrequency and amplitude of the modulations of $a_s$. In an experimental\nperspective, this opens a new possibility to tune the period of Faraday\npatterns by varying not only the frequency of modulations and background\nscattering length, but also through the amplitude of the modulations. The\nlatter effect can be used to estimate the parameters of three-body interactions\nfrom the FW experimental results. Theoretical predictions are confirmed by\nnumerical simulations of the corresponding extended Gross-Pitaevskii equation."
    },
    {
        "anchor": "Ultra-quantum turbulence in a quenched homogeneous Bose gas: Using the classical field method, we study numerically the characteristics\nand decay of the turbulent tangle of superfluid vortices which is created in\nthe evolution of a Bose gas from highly nonequilibrium initial conditions. By\nanalysing the vortex line density, the energy spectrum and the velocity\ncorrelation function, we determine that the turbulence resulting from this\neffective thermal quench lacks the coherent structures and the Kolmogorov\nscaling; these properties are typical of both ordinary classical fluids and of\nsuperfluid helium when driven by grids or propellers. Instead, thermal quench\nturbulence has properties akin to a random flow, more similar to another\nturbulent regime called ultra-quantum turbulence which has been observed in\nsuperfluid helium.",
        "positive": "NOON state of Bose atoms in the double-well potential via an excited\n  state quantum phase transition: We suggest a simple scheme for creating a NOON state of repulsively\ninteracting Bose atoms in the double-well potential. The protocol consists of\ntwo steps. First, by setting atom-atom interactions to zero, the system is\ndriven to the upper excited state. Second, the interactions is slowly increased\nand, simultaneously, the inter-well tunneling is decreased to zero. We analyze\nfidelity of the final state to the NOON state depending on the number of atoms,\nramp rate, and fluctuations of the system parameters. It is shown that for a\ngiven fidelity the ramp rate scales algebraically with the number of atoms."
    },
    {
        "anchor": "Stoner-Wohlfarth switching of the condensate magnetization in a dipolar\n  spinor gas and the metrology of excitation damping: We consider quasi-one-dimensional dipolar spinor Bose-Einstein condensates in\nthe homogeneous-local-spin-orientation approximation, that is with\nunidirectional local magnetization. By analytically calculating the exact\neffective dipole-dipole interaction, we derive a Landau-Lifshitz-Gilbert\nequation for the dissipative condensate magnetization dynamics, and show how it\nleads to the Stoner-Wohlfarth model of a uni-axial ferro-magnetic particle,\nwhere the latter model determines the stable magnetization patterns and\nhysteresis curves for switching between them. For an external magnetic field\npointing along the axial, long direction, we analytically solve the\nLandau-Lifshitz-Gilbert equation. The solution explicitly demonstrates that the\nmagnetic dipole-dipole interaction {\\it accelerates} the dissipative dynamics\nof the magnetic moment distribution and the associated dephasing of the\nmagnetic moment direction. Under suitable conditions, dephasing of the\nmagnetization direction due to dipole-dipole interactions occurs within time\nscales up to two orders of magnitude smaller than the lifetime of currently\nexperimentally realized dipolar spinor condensates, e.g., produced with the\nlarge magnetic-dipole-moment atoms ${}^{166} \\textrm{Er}$. This enables\nexperimental access to the dissipation parameter $\\Gamma$ in the\nGross-Pitaevski\\v\\i~mean-field equation, for a system currently lacking a\ncomplete quantum kinetic treatment of dissipative processes and, in particular,\nan experimental check of the commonly used assumption that $\\Gamma$ is a single\nscalar independent of spin indices.",
        "positive": "Nonuniversal beyond mean field properties of quasi-two-dimensional\n  dipolar Bose gases: We study a quasi-two dimensional gas of bosonic dipoles, calculating the\nbeyond mean field corrections to the ground state energy and chemical potential\nneglecting the transverse mode structure. We show that the corrections are\nsensitive to the high momentum part of the interaction and cannot be expressed\nsolely in terms of the scattering length and the dipole strength. While\nnonuniversal, the correction is found to be negative, which provides an\nadditional attractive term in the extended Gross-Pitaevskii equation, enhancing\nthe roton instability."
    },
    {
        "anchor": "On the long-term stability of space-time crystals: We investigate a space-time crystal in a superfluid Bose gas. Using a\nwell-controlled periodic drive we excite only one crystalline mode in the\nsystem, which can be accurately modeled in the rotating frame of the drive.\nUsing holographic imaging we observe the stability of the crystal over an\nextended period of time and show the robustness of its structure in both space\nand time. By introducing a fourth-order term in the Hamiltonian we show that\nthe crystal stabilizes at a fixed number of quanta. The results of the model\nare compared to the experimental data and show good agreement, with a small\nnumber of free parameters. The results yield insights in the long-term\nstability of the crystal, which can only be obtained by the combination of the\nextended control in the experiment and the nearly ab-initio character of the\nmodel. From the model we derive a phase diagram of the system, which can be\nexploited in the future to study the phase transitions for this new state of\nmatter in even more detail.",
        "positive": "Dynamics of Bose-Einstein condensates under anharmonic trap: The dynamics of weakly interacting three-dimensional Bose-Einstein\ncondensates (BECs), trapped in external axially symmetric plus anharmonic\ndistortion potential are studied. Within a variational approach and\ntime-dependent Gross-Pitaevskii equation, the coupled condensate width\nequations are derived. By modulating anharmonic distortion of the trapping\npotential, nonlinear features are studied numerically and illustrated\nanalytically, such as mode coupling of oscillation modes, and resonances.\nFurthermore, the stability of attractive interaction BEC in both repulsive and\nattractive anharmonic distortion is examined. We demonstrate that a small\nrepulsive and attractive anharmonic distortion is effective in reducing\n(extending) the condensate stability region since it decreases (increases) the\ncritical number of atoms in the trapping potential."
    },
    {
        "anchor": "Onset of a modulational instability in trapped dipolar Bose-Einstein\n  condensates: We explore the phase diagram of a finite-sized dysprosium dipolar\nBose-Einstein condensate in a cylindrical harmonic trap. We monitor the final\nstate after the scattering length is lowered from the repulsive BEC regime to\nthe quantum droplet regime. Either an adiabatic transformation between a BEC\nand a quantum droplet is obtained or, above a critical trap aspect ratio\n$\\lambda_{\\rm c}=1.87(14)$, a modulational instability results in the formation\nof multiple droplets. This is in full agreement with the predicted structure of\nthe phase diagram with a crossover region below $\\lambda_{\\rm c}$ and a\nmultistable region above. Our results provide the missing piece connecting the\npreviously explored regimes resulting in a single or multiple dipolar quantum\ndroplets.",
        "positive": "Quantum liquids and droplets with low-energy interactions in one\n  dimension: We consider interacting one-dimensional bosons in the universal low-energy\nregime. The interactions consist of a combination of attractive and repulsive\nparts that can stabilize quantum gases, droplets and liquids. In particular, we\nstudy the role of effective three-body repulsion, in systems with weak\nattractive pairwise interactions. Its low-energy description is often argued to\nbe equivalent to a model including only two-body interactions with non-zero\nrange. Here, we show that, at zero temperature, the equations of state in both\ntheories agree quantitatively at low densities for overall repulsion, in the\ngas phase, as can be inferred from the $S$-matrix formulation of statistical\nmechanics. However, this agreement is absent in the attractive regime, where\nuniversality only occurs in the long-distance properties of quantum droplets.\nWe develop analytical tools to investigate the properties of the theory, and\nobtain astounding agreement with exact numerical calculations using the\ndensity-matrix renormalization group."
    },
    {
        "anchor": "Cooling a Fermi gas with three-body recombination near a narrow Feshbach\n  resonance: Three-body recombination is a phenomenon common in atomic and molecular\ncollisions, producing heating in the system. However, we find the cooling\neffect of the three-body recombination of a 6Li Fermi gas near its s-wave\nnarrow Feshbach resonance. Such counter-intuitive behavior is explained as\nfollows, the threshold energy of the quasi-bounded Feshbach molecule acts as\nthe knife of cooling, expelling the scattering atoms with selected kinetic\nenergy from the trap. When the threshold energy happens to be larger than\n3/2kBT, each lost atom in the three-body recombination process has more than\n3kBT energy which results in cooling. The best cooling is found with the\nthreshold energy set at about 3kBT, consistent with a theoretical model. The\nthree-body recombination induced cooling raises potential applications for\ncooling complex atomic systems.",
        "positive": "Dynamics for partially coherent Bose-Einstein condensates in double\n  wells: The dynamical properties of partially coherent Bose-Einstein condensates in\ndouble wells are investigated in three typical regimes. In the extreme Fock\nregime, the time evolution of the degree of coherence is shown to decay\nrapidly. In the Rabi regime, a relation between the amplitude of Rabi\noscillation and the degree of coherence is obtained, which is expected to\ndetermine the degree of coherence by measuring the amplitude of Rabi\noscillation. The study on the self-trapping phenomena in the Josephson regime\nexhibits that both the degree of coherence and the initial relative phase can\naffect the final particle distribution."
    },
    {
        "anchor": "Two-point phase correlations of a one-dimensional bosonic Josephson\n  junction: We realize a one-dimensional Josephson junction using quantum degenerate Bose\ngases in a tunable double well potential on an atom chip. Matter wave\ninterferometry gives direct access to the relative phase field, which reflects\nthe interplay of thermally driven fluctuations and phase locking due to\ntunneling. The thermal equilibrium state is characterized by probing the full\nstatistical distribution function of the two-point phase correlation.\nComparison to a stochastic model allows to measure the coupling strength and\ntemperature and hence a full characterization of the system.",
        "positive": "Resonant atom-dimer collisions in cesium: Testing universality at\n  positive scattering lengths: We study the collisional properties of an ultracold mixture of cesium atoms\nand dimers close to a Feshbach resonance near 550G in the regime of positive\n$s$-wave scattering lengths. We observe an atom-dimer loss resonance that is\nrelated to Efimov's scenario of trimer states. The resonance is found at a\nvalue of the scattering length that is different from a previous observation at\nlow magnetic fields. This indicates non-universal behavior of the Efimov\nspectrum for positive scattering lengths. We compare our observations with\npredictions from effective field theory and with a recent model based on the\nvan der Waals interaction. We present additional measurements on pure atomic\nsamples in order to check for the presence of a resonant loss feature related\nto an avalanche effect as suggested by observations in other atomic species. We\ncould not confirm the presence of such a feature."
    },
    {
        "anchor": "Spin-dependent Optical Superlattice: We propose and implement a lattice scheme for coherently manipulating atomic\nspins. Using the vector light shift and a superlattice structure, we\ndemonstrate experimentally the capability on parallel spin addressing in\ndouble-wells and square plaquettes with subwavelength resolution. Quantum\ncoherence of spin manipulations is verified through measuring atom tunneling\nand spin exchange dynamics. Our experiment presents a building block for\nengineering many-body quantum states in optical lattices for realizing quantum\nsimulation and computation tasks.",
        "positive": "Bose-Fermi mixture in one-dimensional optical lattices with hard-core\n  interactions: We study a mixture of $N_{b}$ bosons with point hard-core boson-boson\ninteractions and $N_{f}$ noninteracting spinless fermions with point hard-core\nboson-fermion interactions in 1D optical lattice with external harmonic confine\npotential. Using an extended Jordan-Winger transformation (JWT) which maps the\nhard-core Bose-Fermi mixture into two component noninteracting spinless\nfermions with hard-core interactions between them, we get the ground states of\nthe system. Then we determine in details the one particle density matrix,\ndensity profile, momentum distribution, the natural orbitals and their\noccupations based on the constructed ground state wavefunctions. We also\ndiscuss the ground state properties of the system with large but finite\ninteractions which lead to the lift of ground degeneracy. Our results show\nthat, although the total density profile is almost not affected, the\ndistributions for bosons and fermions strongly depend on the relative\nstrengthes of boson-boson interactions and boson-fermion interactions."
    },
    {
        "anchor": "Emergence of Anyons on the Two-Sphere in Molecular Impurities: Recently it was shown that anyons on the two-sphere naturally arise from a\nsystem of molecular impurities exchanging angular momentum with a many-particle\nbath (Phys. Rev. Lett. 126, 015301 (2021)). Here we further advance this\napproach and rigorously demonstrate that in the experimentally realized regime\nthe lowest spectrum of two linear molecules immersed in superfluid helium\ncorresponds to the spectrum of two anyons on the sphere. We develop the\nformalism within the framework of the recently experimentally observed angulon\nquasiparticle.",
        "positive": "Cavity-mediated unconventional pairing in ultracold fermionic atoms: We investigate long-range pairing interactions between ultracold fermionic\natoms confined in an optical lattice which are mediated by the coupling to a\ncavity. In the absence of other perturbations, we find three degenerate pairing\nsymmetries for a two-dimensional square lattice. By tuning a weak local atomic\ninteraction via a Feshbach resonance or by tuning a weak magnetic field, the\nsuperfluid system can be driven from a topologically trivial s-wave to\ntopologically ordered, chiral superfluids containing Majorana edge states. Our\nwork points out a novel path towards the creation of exotic superfluid states\nby exploiting the competition between long-range and short-range interactions."
    },
    {
        "anchor": "Controlled interference of association paths in the conversion of\n  ultracold atoms into molecules: We present a proposal for controlling the conversion of ultracold atoms into\nmolecules by fixing the phase difference between two oscillating magnetic\nfields. The scheme is based on the use of a magnetic Feshbach resonance with a\nfield modulation that incorporates terms oscillating with frequencies\ncorresponding to the main resonance and one of the subharmonics. The\ninterference between the two association processes activated by the oscillating\nterms is controlled via the phase difference. As a result, significant increase\nor decrease of the effective interaction strength can be achieved. The\nrealization of the proposal is feasible under standard technical conditions. In\nparticular, the method is found to be robust against the effect of the sources\nof decoherence present in the practical setup. The applicability of the\napproach to deal with quadratic terms in the field modulation is discussed.",
        "positive": "Nonequilibrium Phase Transition of Interacting Bosons in an Intra-Cavity\n  Optical Lattice: We investigate the nonlinear light-matter interaction of a Bose-Einstein\ncondensate trapped in an external periodic potential inside an optical cavity\nwhich is weakly coupled to vacuum radiation modes and driven by a transverse\npump field. Based on a generalized Bose-Hubbard model which incorporates a\nsingle cavity mode, we include the collective backaction of the atoms on the\ncavity light field and determine the nonequilibrium quantum phases within the\nnonperturbative bosonic dynamical mean-field theory.With the system parameters\nadapted to recent experiments, we find a quantum phase transition from a normal\nphase to a self-organized superfluid phase, which is related to the\nHepp-Lieb-Dicke superradiance phase transition. For even stronger pumping, a\nself-organized Mott insulator phase arises."
    },
    {
        "anchor": "Negative refraction and rotons in the relativistic Bose gas: We investigate the dispersion of a classical electromagnetic field in a\nrelativistic ideal gas of charged bosons using scalar quantum electrodynamics\nat finite temperature and charge density. We derive the effective\nelectromagnetic responses and the electromagnetic propagation modes that\ncharacterize the gas as a left-handed material with negative effective index of\nrefraction $n_{\\rm eff}=-1$ below the transverse plasmon frequency. In the\ncondensed phase, we show that the longitudinal plasmon dispersion relation\nexhibits a roton-type local minimum that disappears at the transition\ntemperature.",
        "positive": "First and second sound in cylindrically trapped gases: We investigate the propagation of density and temperature waves in a\ncylindrically trapped gas with radial harmonic confinement. Starting from\ntwo-fluid hydrodynamic theory we derive effective 1D equations for the chemical\npotential and the temperature which explicitly account for the effects of\nviscosity and thermal conductivity. Differently from quantum fluids confined by\nrigid walls, the harmonic confinement allows for the propagation of both first\nand second sound in the long wave length limit. We provide quantitative\npredictions for the two sound velocities of a superfluid Fermi gas at\nunitarity. For shorter wave-lengths we discover a new surprising class of\nexcitations continuously spread over a finite interval of frequencies. This\nresults in a non-dissipative damping in the response function which is\nanalytically calculated in the limiting case of a classical ideal gas."
    },
    {
        "anchor": "Minimizing nonadiabaticities in optical-lattice loading: In the quest to reach lower temperatures of ultra-cold gases in optical\nlattice experiments, non-adiabaticites during lattice loading are one of the\nlimiting factors that prevent the same low temperatures to be reached as in\nexperiments without lattice. Simulating the loading of a bosonic quantum gas\ninto a one-dimensional optical lattice with and without a trap, we find that\nthe redistribution of atomic density inside a global confining potential is by\nfar the dominant source of heating. Based on these results we propose to adjust\nthe trapping potential during loading to minimize changes to the density\ndistribution. Our simulations confirm that a very simple linear interpolation\nof the trapping potential during loading already significantly decreases the\nheating of a quantum gas and we discuss how loading protocols minimizing\ndensity redistributions can be designed.",
        "positive": "Critical fluctuations in a confined driven-dissipative quantum\n  condensate: Phase fluctuations determine the low-energy properties of quantum\ncondensates. However, at the condensation threshold, both density and phase\nfluctuations are relevant. While strong emphasis has been given to the\ninvestigation of phase fluctuations, which dominate the physics of the quantum\nsystem away from the critical point -- number fluctuations have been much less\nexplored, even in thermal equilibrium. In this work, we report experimental\nobservation and theoretical description of fluctuations in a\ncircularly-confined non-equilibrium Bose-Einstein condensate of polaritons near\nthe condensation threshold. We observe critical fluctuations, which combine the\nnumber fluctuations of a single-mode condensate state and competition between\ndifferent states. The latter are analogous to mode hopping in photon lasers.\nOur theoretical analysis indicates that this phenomenon is of a quantum\ncharacter, while classical noise of the pump is not sufficient to explain the\nexperiments. The manifestation of a critical quantum state competition unlocks\nnew possibilities for the study of condensate formation while linking to\npractical realizations in photonic lasers."
    },
    {
        "anchor": "Recent developments in Quantum Monte-Carlo simulations with applications\n  for cold gases: This is a review of recent developments in Monte Carlo methods in the field\nof ultra cold gases. For bosonic atoms in an optical lattice we discuss path\nintegral Monte Carlo simulations with worm updates and show the excellent\nagreement with cold atom experiments. We also review recent progress in\nsimulating bosonic systems with long-range interactions, disordered bosons,\nmixtures of bosons, and spinful bosonic systems. For repulsive fermionic\nsystems determinantal methods at half filling are sign free, but in general no\nsign-free method exists. We review the developments in diagrammatic Monte Carlo\nfor the Fermi polaron problem and the Hubbard model, and show the connection\nwith dynamical mean-field theory. We end the review with diffusion Monte Carlo\nfor the Stoner problem in cold gases.",
        "positive": "Cross-dimensional phase transition from an array of 1D Luttinger liquids\n  to a 3D Bose-Einstein condensate: We study the thermodynamic properties of a 2D array of coupled\none-dimensional Bose gases. The system is realized with ultracold bosonic atoms\nloaded in the potential tubes of a two-dimensional optical lattice. For\nnegligible coupling strength, each tube is an independent weakly interacting 1D\nBose gas featuring Tomonaga Luttinger liquid behavior. By decreasing the\nlattice depth, we increase the coupling strength between the 1D gases and allow\nfor the phase transition into a 3D condensate. We extract the phase diagram for\nsuch a system and compare our results with theoretical predictions. Due to the\nhigh effective mass across the periodic potential and the increased 1D\ninteraction strength, the phase transition is shifted to large positive values\nof the chemical potential. Our results are prototypical to a variety of\nlow-dimensional systems, where the coupling between the subsystems is realized\nin a higher spatial dimension such as coupled spin chains in magnetic\ninsulators."
    },
    {
        "anchor": "Spin-orbit coupling induced Fulde-Ferrell-Larkin-Ovchinnikov-like Cooper\n  pairing and skyrmion-like polarization textures in trapped optical lattices: We study the interplay between the Zeeman field and spin-orbit coupling (SOC)\nin harmonically trapped Fermi gases loaded into a two-dimensional single-band\ntight-binding optical lattice. Using the Bogoliubov-de Gennes theory, we find\nthat the Zeeman field combined with a Rashba SOC gives rise to $(i)$\nFulde-Ferrell-like superfluidity and $(ii)$ skyrmion-like polarization textures\nnear the edges of the system. We also discussed the effects of interaction,\ntemperature, SOC anisotropy and Zeeman field anisotropy on the superfluid\nground state and polarization textures.",
        "positive": "Thermodynamical properties of a trapped interacting Bose gas: The thermodynamical properties of interacting Bose atoms in a harmonic\npotential are studied within the mean-field approximation. For weak\ninteractions, the quantum statistics is equivalent to an ideal gas in an\neffective mean-field potential. The eigenvalue of the Gross-Pitaevskii equation\nis identified as the chemical potential of the ideal gas. The condensation\ntemperature and density profile of atoms are calculated. It is found that the\ncritical temperature $T_c$ decreases as the interactions increase. Below the\ncritical point, the condensation fraction exhibits a universal relation of\n$N_0/N=1-(T/T_c)^{\\gamma}$, with the index $\\gamma\\approx 2.3$ independent of\nthe interaction strength, the chemical potential, as well as the frequency of\nthe confining potential."
    },
    {
        "anchor": "Spatial two-particle NOON-states in periodically shaken three-well\n  potentials: Few-particle dynamics in a three-well potential are investigated numerically.\nIt is shown that periodically shaking the potential can considerably increase\nthe fidelity of emerging spatial quantum superpositions. Such NOON-states are\nimportant for quantum interferometry. If the two particles initially sit in the\nmiddle well, the probability to return to this state can distinguish pure\nquantum dynamics from statistical mixtures. The numeric implementation of\ndecoherence via particle losses shows clear differences from the pure quantum\nbehaviour. A three-well lattice could be an ideal system for experimental\nrealisations.",
        "positive": "Perspective on Quantum Bubbles in Microgravity: Progress in understanding quantum systems has been driven by the exploration\nof the geometry, topology, and dimensionality of ultracold atomic systems. The\nNASA Cold Atom Laboratory (CAL) aboard the International Space Station has\nenabled the study of ultracold atomic bubbles, a terrestrially-inaccessible\ntopology. Proof-of-principle bubble experiments have been performed on CAL with\nan rf-dressing technique; an alternate technique (dual-species\ninteraction-driven bubbles) has also been proposed. Both techniques can drive\ndiscovery in the next decade of fundamental physics research in microgravity."
    },
    {
        "anchor": "Energy lower bound for the unitary N+1 fermionic model: We consider the stability problem for a unitary N+1 fermionic model, i.e., a\nsystem of $N$ identical fermions interacting via zero-range interactions with a\ndifferent particle, in the case of infinite two-body scattering length. We\npresent a slightly more direct and simplified proof of a recent result obtained\nin \\cite{CDFMT}, where a sufficient stability condition is proved under a\nsuitable assumption on the mass ratio.",
        "positive": "Pair-correlation ansatz for the ground state of interacting bosons in an\n  arbitrary one-dimensional potential: We derive and describe a very accurate variational scheme for the ground\nstate of the system of a few ultra-cold bosons confined in one-dimensional\ntraps of arbitrary shapes. It is based on assumption that all inter-particle\ncorrelations have two-body nature. By construction, the proposed ansatz is\nexact in the noninteracting limit, exactly encodes boundary conditions forced\nby contact interactions, and gives full control on accuracy in the limit of\ninfinite repulsions. We show its efficiency in a whole range of intermediate\ninteractions for different external potentials. Our results manifest that for\ngeneric non-parabolic potentials mutual correlations forced by interactions\ncannot be captured by distance-dependent functions."
    },
    {
        "anchor": "Diffusion Monte Carlo methods for Spin-Orbit-Coupled ultracold Bose\n  gases: We present two Diffusion Monte Carlo (DMC) algorithms for systems of\nultracold quantum gases featuring synthetic spin-orbit interactions. The first\none is a discrete spin generalization of the T- moves spin-orbit DMC, which\nprovides an upper bound to the fixed-phase energy. The second is a\nspin-integrated DMC method which recovers the fixed-phase property by avoiding\nthe definition of the effective Hamiltonian involved in the T-moves approach.\nThe latter is a more accurate method but it is restricted to spin-independent\ntwo-body interactions. We report a comparison between both algorithms for\ndifferent systems. As a check of the efficiency of both methods, we compare the\nDMC energies with results obtained with other numerical methods, finding\nagreement between both estimation",
        "positive": "Spontaneous rotating vortex rings in a parametrically driven polariton\n  fluid: We present the theoretical prediction of spontaneous rotating vortex rings in\na parametrically driven quantum fluid of polaritons -- coherent superpositions\nof coupled quantum well excitons and microcavity photons. These rings arise not\nonly in the absence of any rotating drive, but also in the absence of a\ntrapping potential, in a model known to map quantitatively to experiments. We\nbegin by proposing a novel parametric pumping scheme for polaritons, with\ncircular symmetry and radial currents, and characterize the resulting\nnonequilibrium condensate. We show that the system is unstable to spontaneous\nbreaking of circular symmetry via a modulational instability, following which a\nvortex ring with large net angular momentum emerges, rotating in one of two\ntopologically distinct states. Such rings are robust and carry distinctive\nexperimental signatures, and so they could find applications in the new\ngeneration of polaritonic devices."
    },
    {
        "anchor": "Velocity-dependent quantum phase slips in 1D atomic superfluids: Quantum phase slips are the primary excitations in one-dimensional\nsuperfluids and superconductors at low temperatures but their existence in\nultracold quantum gases has not been demonstrated yet. We now study\nexperimentally the nucleation rate of phase slips in one-dimensional\nsuperfluids realized with ultracold quantum gases, owing along a periodic\npotential. We observe a crossover between a regime of temperature-dependent\ndissipation at small velocity and interaction and a second regime of\nvelocity-dependent dissipation at larger velocity and interaction. This\nbehavior is consistent with the predicted crossover from thermally-assisted\nquantum phase slips to purely quantum phase slips.",
        "positive": "Itinerant chiral ferromagnetism in a trapped Rashba spin-orbit coupled\n  Fermi gas: How ferromagnetic phases emerge in itinerant systems is an outstanding\nproblem in quantum magnetism. Here we consider a repulsive two-component Fermi\ngas confined in a two dimensional isotropic harmonic potential and subject to a\nlarge Rashba spin-orbit (SO) coupling, whose single-particle dispersion can be\ntailored by adjusting the SO coupling strength. We show that the interplay\namong SO coupling, correlation effects and mean-field repulsion leads to a\ncompetition between ferromagnetic and non-magnetic phases. At intermediate\ninteraction strengths, ferromagnetic phase emerges which can be well described\nby the mean-field Hartree-Fock theory; whereas at strong interaction strengths,\na strongly correlated non-magnetic phase is favored due to the\nbeyond-mean-field quantum correlation effects. Furthermore, the ferromagnetic\nphase of this system possesses a chiral current density induced by the Rashba\nspin-orbit coupling, whose experimental signature is investigated."
    },
    {
        "anchor": "Experimental Determination of Bose-Hubbard Energies: We present the first experimental measurement of the ensemble averages of\nboth the kinetic and interaction energies of the three-dimensional\nBose--Hubbard model at finite temperature and various optical lattice depths\nacross weakly to strongly interacting regimes, for an almost unit filling\nfactor. The kinetic energy is obtained through Fourier transformation of a\ntime-of-flight signal, and the interaction energy is measured using a newly\ndeveloped atom-number-projection spectroscopy technique, by exploiting an\nultra-narrow optical transition of two-electron atoms. The obtained\nexperimental results can be used as benchmarks for state-of-the-art numerical\nmethods of quantum many-body theory. As an illustrative example, we compare the\nmeasured energies with numerical calculations involving the Gutzwiller and\ncluster-Gutzwiller approximations, assuming realistic trap potentials and\nparticle numbers at nonzero entropy (finite temperature); we obtain good\nagreement without fitting parameters. We also discuss the possible application\nof this method to temperature estimations for atoms in optical lattices using\nthe thermodynamic relation. This study offers a unique advantage of cold atom\nsystem for `quantum simulators', because, to the best of our knowledge, it is\nthe first experimental determination of both the kinetic and interaction\nenergies of quantum many-body system.",
        "positive": "Dynamical Quantum Phase Transitions in Spin Chains with Long-Range\n  Interactions: Merging different concepts of non-equilibrium criticality: We theoretically study the dynamics of a transverse-field Ising chain with\npower-law decaying interactions characterized by an exponent $\\alpha$, which\ncan be experimentally realized in ion traps. We focus on two classes of\nemergent dynamical critical phenomena following a quantum quench from a\nferromagnetic initial state: The first one manifests in the time averaged order\nparameter, which vanishes at a critical transverse field. We argue that such a\ntransition occurs only for long-range interactions $\\alpha \\leq 2$ . The second\nclass corresponds to the emergence of time-periodic singularities in the return\nprobability to the ground state manifold (a.k.a. Loschmidt echo) which is\nobtained for all values of $\\alpha$ and agrees with the order parameter\ntransition for $\\alpha\\leq 2$. We characterize how the two classes of\nnonequilibrium criticality correspond to each other and give a physical\ninterpretation based on the symmetry of the time-evolved quantum states."
    },
    {
        "anchor": "Ground states of 2D tilted dipolar bosons with density-induced hopping: Motivated by recent experiments with ultracold magnetic atoms trapped in\noptical lattices where the orientation of atomic dipoles can be fully\ncontrolled by external fields, we study the ground state properties of dipolar\nbosons trapped in a two-dimensional lattice with density-induced hopping and\nwhere the dipoles are tilted along the $xz$ plane. We present ground state\nphase diagrams of the above system at different tilt angles. We find that, as\nthe dipolar interaction increases, the superfluid phase at half filling factor\nis destroyed in favor of either a checkerboard or stripe solid phase for tilt\nangle $\\theta \\lesssim 35.3^{\\circ}$ or $\\theta \\gtrsim 35.3^{\\circ}$\nrespectively. More interesting physics happens at tilt angles $\\theta \\gtrsim\n58^{\\circ}$, where we find that, as the dipolar interaction strength increases,\nsolid phases first appear at filling factor lower than $0.5$. Moreover, unlike\nwhat observed at lower tilt angles, we find that, at half filling, a stripe\nsupersolid intervenes between the superfluid and stripe solid phase.",
        "positive": "Engineering spin waves in a high-spin ultracold Fermi gas: We report on the detailed study of multi-component spin-waves in an s=3/2\nFermi gas where the high spin leads to novel tensorial degrees of freedom\ncompared to s = 1/2 systems. The excitations of a spin-nematic state are\ninvestigated from the linear to the nonlinear regime, where the tensorial\ncharacter is particularly pronounced. By tuning the initial state we engineer\nthe tensorial spin-wave character, such that the magnitude and sign of the\ncounterflow spin-currents are effectively controlled. A comparison of our data\nwith numerical and analytical results shows excellent agreement."
    },
    {
        "anchor": "Lattice modulation spectroscopy of one-dimensional quantum\n  gases:Universal scaling of the absorbed energy: Lattice modulation spectroscopy is a powerful tool for probing low-energy\nexcitations of interacting many-body systems. By means of bosonization we\nanalyze the absorbed power in a one dimensional interacting quantum gas of\nbosons or fermions, subjected to a periodic drive of the optical lattice. For\nthese Tomonaga Luttinger liquids we find a universal $\\omega^3$ scaling of the\nabsorbed power, that at very low-frequency turns into an $\\omega^2$ scaling\nwhen scattering processes at the boundary of the system are taken into account.\nWe confirm this behavior numerically by simulations based on time-dependent\nmatrix product states. Furthermore, in the presence of impurities, the theory\npredicts an $\\omega^2$ bulk scaling. While typical response functions of\nTomonaga Luttinger liquids are characterized by exponents that depend on the\ninteraction strength, modulation spectroscopy of cold atoms leads to a\nuniversal power-law exponent of the absorbed power. Our findings can be readily\ndemonstrated in ultracold atoms in optical lattices with current experimental\ntechnology.",
        "positive": "Spin dynamics in lattices of spinor atoms with quadratic Zeeman effect: A lattice system of spinor atoms or molecules experiencing quadratic Zeeman\neffect is considered. This can be an optical lattice with sufficiently deep\nwells at lattice sites, so that the system is in an isolating state, where\natoms are well localized. But their effective spins can move in the presence of\nexternal magnetic fields. The dynamics of spins, starting from an initial\nnonequilibrium state, is investigated. The system is immersed into a magnetic\ncoil of an electric circuit, creating a magnetic feedback field. Two types of\nquadratic Zeeman effect are treated, a nonresonant, so-called static-current\nquadratic Zeeman effect and a quasi-resonant alternating-current quadratic\nZeeman effect. Spin dynamics in these conditions is highly nonlinear. Different\nregimes of spin dynamics, starting from a strongly nonequilibrium state, are\nstudied. Conditions for realizing fast spin reversal are found, which can be\nused in quantum information processing and spintronics."
    },
    {
        "anchor": "Caustics in the sine-Gordon model from quenches in coupled 1D Bose gases: Caustics are singularities that occur naturally in optical, hydrodynamic and\nquantum waves, giving rise to high amplitude patterns that can be described\nusing catastrophe theory. In this paper we study caustics in a statistical\nfield theory setting in the form of the sine-Gordon model that describes a\nvariety of physical systems including coupled 1D superfluids. Specifically, we\nuse classical field simulations to study the dynamics of two ultracold 1D Bose\ngases (quasi-condensates) that are suddenly coupled to each other and find that\nthe resulting non-equilibrium dynamics are dominated by caustics. Thermal noise\nis included by sampling the initial states from a Boltzmann distribution for\nphononic excitations. We find that caustics pile up over time in both the\nnumber and phase difference observables leading to a characteristic non-thermal\n`circus tent' shaped probability distribution at long times.",
        "positive": "Chiral Ladders and the Edges of Chern Insulators: The realization and detection of topological phases with ultracold atomic\ngases is at the frontier of current theoretical and experimental research.\nHere, we identify cold atoms in optical ladders subjected to synthetic magnetic\nfields as readily realizable bridges between one-dimensional spin-orbit (time\nreversal) topological insulators and two-dimensional Chern insulators. We\nreveal three instances of their promising potential: i) they realize spin-orbit\ncoupling, with the left-right leg degree of freedom playing the role of an\neffective spin, ii) their energy bands and eigenstates exactly reproduce the\ntopological chiral edge modes of two-dimensional Chern insulators, and iii)\nthey can be tailored to realize a topological phase transition from a trivial\nto a topological insulating phase. We propose realistic schemes to observe the\nchiral and topological properties of ladder systems with current optical\nlattice-based experiments. Our findings open a door to the exploration of the\nphysics of the edges of Chern insulators and to the realization of spin-orbit\ncoupling and topological superfluid phases with ultracold atomic gases."
    },
    {
        "anchor": "On the different Floquet Hamiltonians in a periodic-driven\n  Bose-Josephson junction: The bosonic Josephson junction, one of the maximally simple models for\nperiodic-driven many-body systems, has been intensively studied in the past two\ndecades. Here, we revisit this problem with five different methods, all of\nwhich have solid theoretical reasoning. We find that to the order of\n$\\omega^{-2}$ ($\\omega$ is the modulating frequency), these approaches will\nyield slightly different Floquet Hamiltonians. In particular, the parameters in\nthe Floquet Hamiltonians may be unchanged, increased, or decreased, depending\non the approximations used. Especially, some of the methods generate new\ninteractions, which still preserve the total number of particles; and the\nothers do not. The validity of these five effective models is verified using\ndynamics of population imbalance and self-trapping phase transition. In all\nresults, we find the method by first performing a unitary rotation to the\nHamiltonian will have the highest accuracy. The difference between them will\nbecome significate when the modulating frequency is comparable with the driving\namplitude. The results presented in this work indicate that the analysis of the\nFloquet Hamiltonian has some kind of subjectivity, which will become an\nimportant issue in future experiments with the increasing of precision. We\ndemonstrate this physics using a Bose-Josephson junction, and it is to be hoped\nthat the validity of these methods and their tiny differences put forward in\nthis work can be verified in realistic experiments in future using quantum\nsimulating platforms, including but not limited to ultracold atoms.",
        "positive": "Statistical transmutation in Floquet driven optical lattices: We show that interacting bosons in a periodically-driven two dimensional (2D)\noptical lattice may effectively exhibit fermionic statistics. The phenomenon is\nsimilar to the celebrated Tonks-Girardeau regime in 1D. The Floquet band of a\ndriven lattice develops the moat shape, i.e. a minimum along a closed contour\nin the Brillouin zone. Such degeneracy of the kinetic energy favors fermionic\nquasiparticles. The statistical transmutation is achieved by the Chern-Simons\nflux attachment similar to the fractional quantum Hall case. We show that the\nvelocity distribution of the released bosons is a sensitive probe of the\nfermionic nature of their stationary Floquet state."
    },
    {
        "anchor": "Negative Compressability of Non-Equilibrium Non-Ideal Bose--Einstein\n  Condensate: An ideal equilibrium Bose--Einstein condensate (BEC) is usually considered in\nthe grand canonical ($\\mu V T$) ensemble, which implies the presence of the\nchemical equilibrium with the environment. However, in most experimental\nscenarios, the total amount of particles in BEC is determined either by the\ninitial conditions or by the balance between dissipation and pumping. As a\nresult, BEC may possess the thermal equilibrium but almost never the chemical\nequilibrium. In addition, many experimentally achievable BECs are non-ideal due\nto interaction between particles. In the recent work\n[10.1103/PhysRevLett.128.065301], it has been shown that invariant subspaces in\nthe system Hilbert space appear in non-equilibrium BEC in the fast\nthermalization limit. In each of these subspaces, Gibbs distribution is\nestablished with a certain number of particles that makes it possible to\ninvestigate properties of non-ideal non-equilibrium BEC independently in each\ninvariant subspace. In this work, we analyze the BEC stability due to change in\ndispersion curve caused by non-ideal interactions in BEC. Generally, non-ideal\ninteractions lead to the redshift or blueshift of the dispertion curve and to\nthe change in the effective mass of the particles. We show that the redshift of\nthe dispersion curve can lead to the negative compressibility of BEC, whereas\nthe change in the effective mass always makes BEC more stable. We find the\nexplicit condition for the particle density in BEC, at which the negative\ncompressibility appears.",
        "positive": "Softening of Roton and Phonon Modes in a Bose-Einstein Condensate with\n  Spin-Orbit Coupling: Roton-type excitations usually emerge from strong correlations or long-range\ninteractions, as in superfluid helium or dipolar ultracold atoms. However, in\nweakly short-range interacting quantum gas, the recently synthesized spin-orbit\n(SO) coupling can lead to various unconventional phases of superfluidity, and\ngive rise to an excitation spectrum of roton-maxon character. Using Bragg\nspectroscopy we study a SO coupled Bose-Einstein condensate of $^{87}$Rb atoms,\nand show that the excitation spectrum in a \"magnetized\" phase clearly possesses\na two-branch and roton-maxon structure. As Raman coupling strength $\\Omega$ is\ndecreased, a roton-mode softening is observed, as a precursor of the phase\ntransition to a stripe phase that spontaneously breaks spatially translational\nsymmetry. The measured roton gaps agree well with theoretical calculations.\nFurther, we determine sound velocities both in the magnetized and the\nnon-magnetized phase, and a phonon-mode softening is observed around the phase\ntransition in between. The validity of the $f$-sum rule is examined."
    },
    {
        "anchor": "Adiabatic cooling of bosons in lattices to magnetic ordering: We suggest and analyze a new scheme to adiabatically cool bosonic atoms to\npicokelvin temperatures which should allow the observation of magnetic ordering\nvia superexchange in optical lattices. The starting point is a gapped phase\ncalled the spin Mott phase where each site is occupied by one spin-up and one\nspin-down atom. An adiabatic ramp leads to an xy-ferromagnetic phase. We show\nthat the combination of time-dependent density matrix renormalization group\nmethods with quantum trajectories can be used to fully address possible\nexperimental limitations due to decoherence, and demonstrate that the magnetic\ncorrelations are robust for experimentally realizable ramp speeds. Using a\nmicroscopic master equation treatment of light scattering in the many-particle\nsystem, we test the robustness of adiabatic state preparation against\ndecoherence. Due to different ground-state symmetries, we also find a\nmetastable state with xy-ferromagnetic order if the ramp crosses to regimes\nwhere the ground state is a z-ferromagnet. The bosonic spin Mott phase as the\ninitial gapped state for adiabatic cooling has many features in common with a\nfermionic band insulator, but the use of bosons should enable experiments with\nsubstantially lower initial entropies.",
        "positive": "Optimization of collisional Feshbach cooling of an ultracold\n  nondegenerate gas: We optimize a collision-induced cooling process for ultracold atoms in the\nnondegenerate regime. It makes use of a Feshbach resonance, instead of rf\nradiation in evaporative cooling, to selectively expel hot atoms from a trap.\nUsing functional minimization we analytically show that for the optimal cooling\nprocess the resonance energy must be tuned such that it linearly follows the\ntemperature. Here, optimal cooling is defined as maximizing the phase-space\ndensity after a fixed cooling duration. The analytical results are confirmed by\nnumerical Monte-Carlo simulations. In order to simulate more realistic\nexperimental conditions, we show that background losses do not change our\nconclusions, while additional non-resonant two-body losses make a lower initial\nresonance energy with non-linear dependence on temperature preferable."
    },
    {
        "anchor": "Observation of a non-Abelian Yang Monopole: From New Chern Numbers to a\n  Topological Transition: Because global topological properties are robust against local perturbations,\nunderstanding and manipulating the topological properties of physical systems\nis essential in advancing quantum science and technology. For quantum\ncomputation, topologically protected qubit operations can increase\ncomputational robustness, and for metrology the quantized Hall effect directly\ndefines the von Klitzing constant. Fundamentally, topological order is\ngenerated by singularities called topological defects in extended spaces, and\nis quantified in terms of Chern numbers, each of which measures different sorts\nof fields traversing surfaces enclosing these topological singularities. Here,\ninspired by high energy theories, we describe our synthesis and\ncharacterization of a singularity present in non-Abelian gauge theories - a\nYang monopole - using atomic Bose-Einstein condensates in a five-dimensional\nspace, and quantify the monopole in terms of Chern numbers measured on\nenclosing manifolds. While the well-known 1st Chern number vanished, the 2nd\nChern number, measured for the first time in any physical settings, did not. By\ndisplacing the manifold, we then observed a phase transition from \"topological\"\nto \"trivial\" as the monopole left the manifold.",
        "positive": "Natural and unnatural parity states of small trapped equal-mass\n  two-component Fermi gases at unitarity and fourth-order virial coefficient: Equal-mass two-component Fermi gases under spherically symmetric external\nharmonic confinement with large s-wave scattering length are considered. Using\nthe stochastic variational approach, we determine the lowest 286 and 164\nrelative eigenenergies of the (2,2) and (3,1) systems at unitarity as a\nfunction of the range $r_0$ of the underlying two-body potential and\nextrapolate to the $r_0 \\rightarrow 0$ limit. Our calculations include all\nstates with vanishing and finite angular momentum $L$ (and natural and\nunnatural parity $\\Pi$) with relative energy up to $10.5 \\hbar \\Omega$, where\n$\\Omega$ denotes the angular trapping frequency of the external confinement.\nOur extrapolated zero-range energies are estimated to have uncertainties of\n0.1% or smaller. The (2,2) and (3,1) energies are used to determine the\nfourth-order virial coefficient of the trapped unitary two-component Fermi gas\nin the low-temperature regime. Our results are compared with recent predictions\nfor the fourth-order virial coefficient of the homogeneous system. We also\ncalculate small portions of the energy spectra of the (3,2) and (4,1) systems\nat unitarity."
    },
    {
        "anchor": "In situ observation of strongly interacting ferromagnetic domains in a\n  shaken optical lattice: Solid state systems derive their richness from the interplay between\ninterparticle interactions and novel band structures that deviate from those of\nfree particles. Strongly interacting systems, where both of these phenomena are\nof equal importance, exhibit a variety of theoretically interesting and\npractically useful phases. Systems of ultracold atoms are rapidly emerging as\nprecise and controllable simulators, and it is precisely in this strongly\ninteracting regime where simulation is the most useful. Here we demonstrate how\nto hybridize Bloch bands in optical lattices to introduce long-range\nferromagnetic order in an itinerant atomic system. We find spontaneously broken\nsymmetry for bosons with a double-well dispersion condensing into one of two\ndistinct minima, which we identify with spin-up and spin-down. The density\ndynamics following a rapid quench to the ferromagnetic state confirm quantum\ninterference between the two states as the mechanism for symmetry breaking.\nUnlike spinor condensates, where interaction is driven by small spin-dependent\ndifferences in scattering length, our interactions scale with the scattering\nlength itself, leading to domains which equilibrate rapidly and develop sharp\nboundaries characteristic of a strongly interacting ferromagnet.",
        "positive": "Exactly solvable models for multiatomic molecular Bose-Einstein\n  condensates: I introduce two family of exactly solvable models for multiatomic\nhetero-nuclear and homo-nuclear molecular Bose-Einstein condensates through the\nalgebraic Bethe ansatz method. The conserved quantities of the respective\nmodels are also showed."
    },
    {
        "anchor": "Condensate wave function and elementary excitations of bosonic polar\n  molecules: beyond the first Born approximation: We investigate the condensate wave function and elementary excitations of\nstrongly interacting bosonic polar molecules in a harmonic trap, treating the\nscattering amplitude beyond the standard first Born approximation (FBA). By\nusing an appropriate trial wave function in the variational method, effects of\nthe leading order correction beyond the FBA have been investigated and shown to\nbe significantly enhanced when the system is close to the phase boundary of\ncollapse. How such leading order effect of going beyond the FBA can be observed\nin a realistic experiment is also discussed.",
        "positive": "Solitary waves in mixtures of Bose gases confined in annular traps: A two-component Bose-Einstein condensate that is confined in a\none-dimensional ring potential supports solitary-wave solutions, which we\nevaluate analytically. The derived solutions are shown to be unique. The\ncorresponding dispersion relation that generalizes the case of a\nsingle-component system shows interesting features."
    },
    {
        "anchor": "Difference in Bose-Einstein condensation of conserved and unconserved\n  particles: The peculiarities in the Bose-Einstein condensation of particles and\nquasiparticles are discussed. The difference between the condensation of\nconserved and unconserved particles is analyzed. A classification of\nquasiparticles is given. The emphasis is made on the ability of particles and\nquasiparticles to condense. Illustrations include: general Bose-condensed\natomic systems, such as ensembles of trapped atoms, Bose gases with conserved\nand unconserved number of atoms, vibrating atoms in double-well lattices,\nHolstein-Primakoff magnons, Schwinger bosons, slave bosons, and the\ncondensation of singletons and triplons. The basic difference is that the\nsystem of particles, whose total number is conserved, can form equilibrium as\nwell as nonequilibrium condensates, while unconserved particles can condense\nonly in a nonequilibrium system subject to external pumping supporting the\ndensity of these particles sufficient for their condensation. The examples of\nsuch a nonequilibrium condensation of unconserved particles are the\nBose-Einstein condensation of excitons, polaritons, and photons. Elementary\ncollective excitations, such as bogolons and phonons, being self-consistently\ndefined, do not condense. Magnons cannot condense in equilibrium systems.\nControversies, existing in literature with regard to the Bose-Einstein\ncondensation of some quasiparticles, are explained. Pushing a system out of\nequilibrium may favor the condensation of unconserved quasiparticles, but\nsuppresses the condensate fraction of conserved particles.",
        "positive": "Multiple-scale approach for the expansion scaling of superfluid quantum\n  gases: We present a general method, based on a multiple-scale approach, for deriving\nthe perturbative solutions of the scaling equations governing the expansion of\nsuperfluid ultracold quantum gases released from elongated harmonic traps. We\ndiscuss how to treat the secular terms appearing in the usual naive expansion\nin the trap asymmetry parameter epsilon, and calculate the next-to-leading\ncorrection for the asymptotic aspect ratio, with significant improvement over\nthe previous proposals."
    },
    {
        "anchor": "The Anyon Hubbard Model in One-Dimensional Optical Lattices: Raman-assisted hopping may be used to realize the anyon Hubbard model in\none-dimensional optical lattices. We propose a feasible scenario that\nsignificantly improves the proposal of [T. Keilmann et al., Nature Commun. 2,\n361 (2011)], allowing as well for an exact realization of the two-body\nhard-core constraint, and for controllable effective interactions without the\nneed of Feshbach resonances. We show that the combination of anyonic statistics\nand two-body hard-core constraint leads to a rich ground state physics,\nincluding Mott insulators with attractive interactions, pair superfluids, dimer\nphases, and multicritical points. Moreover, the anyonic statistics results in a\nnovel two-component superfluid of holon and doublon dimers, characterized by a\nlarge but finite compressibility and a multipeaked momentum distribution, which\nmay be easily revealed experimentally.",
        "positive": "Superfluid transition of disordered dipolar Fermi gases in a 2D lattice: We consider a superfluid transition in two-component dipolar Fermi gases in a\ntwo-dimensional lattice with a weak on-site disorder. The momentum dependent\ndipole-dipole interaction amplitude violates the Anderson theorem and in the\nweakly interacting regime this leads to an increase of the superfluid\ntransition temperature. We find that in a sufficiently deep lattice\n(tight-binding regime) and in the low momentum limit superfluid properties can\nbe considered in the same way as in free space replacing the mass of atoms by\nan effective mass in the lattice. The disorder-induced increase of the critical\ntemperature can be significantly more pronounced than in free space."
    },
    {
        "anchor": "Polarons in the radio-frequency spectrum of a quasi-two-dimensional\n  Fermi gas: We measure radio-frequency spectra for a two-component mixture of a $^6$Li\natomic Fermi gas in the quasi-two-dimensional regime. Near the Feshbach\nresonance, where the transverse Fermi energy is large compared to the\nconfinement-induced dimer binding energies for the initial and final states, we\nfind that the observed resonances do not correspond to transitions between\nconfinement-induced dimers. The spectrum appears to be well-described by\ntransitions between noninteracting polaron states in two dimensions.",
        "positive": "Composite Spin Approach to the Blockade Effect in Rydberg Atom Arrays: The Rydberg blockade induces strongly correlated many-body effects in Rydberg\natom arrays, including rich ground-state phases and many-body scar states in\nthe excitation spectrum. In this letter, we propose a composite spin\nrepresentation that can provide a unified description for major features in\nthis system. The composite spin combines Rydberg excitation and the auxiliary\nfermions, which are introduced to implement the Rydberg blockade constraint\nautomatically. First, we focus on the PXP model describing one-dimensional\narrays with the Rydberg blocking radius being a lattice spacing. Using\ncomposite spins, the ground state is simply a ferromagnetic product state of\ncomposite spins, and the magnon excitations of these composite spins can\naccurately describe the many-body scar states and signal the quantum phase\ntransition driven by detuning. Then, we show that Rydberg atom arrays with\ndifferent blocking radii can share a universal description of the composite\nspin representation, and the difference between different blockade radii can be\nabsorbed in the formation of composite spins."
    },
    {
        "anchor": "Competing superfluid orders in spin-orbit coupled fermionic cold atom\n  optical lattices: The Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase, a superconducting state\nwith non-zero total momentum Cooper pairs in a large magnetic field, was first\npredicted about 50 years ago, and since then became an important concept in\nmany branches of physics. Despite intensive search in various materials,\nunambiguous experimental evidence for the FFLO phase is still lacking in\nexperiments. In this paper, we show that both FF (uniform order parameter with\nplane-wave phase) and LO phase (spatially varying order parameter amplitude)\ncan be observed using fermionic cold atoms in spin-orbit coupled optical\nlattices. The increasing spin-orbit coupling enhances the FF phase over the LO\nphase. The coexistence of superfluid and magnetic orders is also found in the\nnormal BCS phase. The pairing mechanism for different phases is understood by\nvisualizing superfluid pairing densities in different spin-orbit bands. The\npossibility of observing similar physics using spin-orbit coupled\nsuperconducting ultra-thin films is also discussed.",
        "positive": "Enhancing laser sideband cooling in one-dimensional optical lattices via\n  the dipole interaction: We study resolved sideband laser cooling of a one-dimensional optical lattice\nwith one atom per site, and in particular the effect of the dipole interaction\nbetween radiating atoms. For simplicity, we consider the case where only a\nsingle cooling laser is applied. We derive a master equation, and solve it in\nthe limit of a deep lattice and weak laser driving. We find that the dipole\ninteraction significantly changes the final temperature of the particles,\nincreasing it for some phonon wavevectors and decreasing it for others. The\ntotal phonon energy over all modes is typically higher than in the\nnon-interacting case, but can be made lower by the right choice of parameters."
    },
    {
        "anchor": "Suppression of relative flow by multiple domains in two-component\n  Bose-Einstein condensates: We investigate flow properties of immiscible Bose-Einstein condensates\ncomposed of two different Zeeman spin states of 87Rb. Spatially overlapping two\ncondensates in the optical trap are prepared by application of a resonant radio\nfrequency pulse, and then the magnetic field gradient is applied in order to\nproduce the atomic flow. We find that the spontaneous multiple domain formation\narising from the immiscible nature drastically changes the fluidity. The\nhomogeneously overlapping condensates readily separate under the magnetic field\ngradient, and they form stable configuration composed of the two layers. In\ncontrast, the relative flow between two condensates are largely suppressed in\nthe case where the magnetic field gradient is applied after spontaneous domain\nformation.",
        "positive": "Observation of Bose-enhanced photoassociation products: We produce ${^{84}\\mathrm{Sr}_2}$ molecules using Bose-enhanced Raman\nphotoassociation. We apply the stimulated Raman adiabatic passage (STIRAP)\ntechnique on a Bose-Einstein condensate (BEC) to produce more than $8 \\times\n10^3$ ultracold molecules. This chemical reaction is only made possible because\nof the Bose enhancement of the optical transition dipole moment between the\ninitial atomic state and an intermediate molecular state. We study the effect\nof Bose enhancement by measuring the transition Rabi frequency in a BEC and by\ncomparing it with measurements for two atoms in sites of a Mott insulator. By\nbreaking the dimers' bond and directly observing the separated atoms, we\nmeasure the molecular inelastic collision rate parameters. We discuss the\npossibility of applying Bose-enhanced STIRAP to convert a BEC of atoms into a\nBEC of molecules, and argue that the required efficiency for STIRAP is within\nexperimental reach."
    },
    {
        "anchor": "Tuning the Tricritical Point with Spin-orbit Coupling in Polarized\n  Fermionic Condensates: We investigate a two-component atomic Fermi gas with population imbalance in\nthe presence of Rashba-type spin-orbit coupling (SOC). As a competition between\nSOC and population imbalance, the finite-temperature phase diagram reveals a\nlarge varieties of new features, including the expanding of the superfluid\nstate regime and the shrinking of both the phase separation and the normal\nregimes. For sufficiently strong SOC, the phase separation region disappears,\ngiving way to the superfluid state. We find that the tricritical point moves\ntoward regime of low temperature, high magnetic field, and high polarization as\nthe SOC increases.",
        "positive": "Fermi liquid theory and ferromagnetism: There is demonstrated that an isotropic ferromagnetic Fermi liquid reveals\ninstability of the ferromagnetic state in respect to the transversal\ninhomogeneous deviations of magnetization from equilibrium. The result was\nobtained by derivation of the spin waves spectrum by means of kinetic equation."
    },
    {
        "anchor": "Sine-Gordon dynamics in spin transport: We study spin transport in a one-dimensional finite-length wire connected to\nfermionic leads. The interacting wire is described by the sine-Gordon model\nwhile the leads are either noninteracting or interacting Luttinger liquids. We\ncalculate the spin current driven by a spin bias by solving numerically the\nclassical equation of motion, and find that the cosine term in the sine-Gordon\nmodel gives rise to an oscillating spin current when the spin bias exceeds its\ncritical value. We discuss the results in connection with transport experiments\nwith ultracold atoms.",
        "positive": "Decay rates and energies of free magnons and bound states in dissipative\n  XXZ chains: Chains of coupled two-level atoms behave as 1D quantum spin systems,\nexhibiting free magnons and magnon bound states. While these excitations are\nwell studied for closed systems, little consideration has been given to how\nthey are altered by the presence of an environment. This will be especially\nimportant in systems that exhibit nonlocal dissipation, e.g. systems in which\nthe magnons decay due to optical emission. In this work, we consider free\nmagnon excitations and two-magnon bound states in an XXZ chain with nonlocal\ndissipation. We prove that whilst the energy of the bound state can lie outside\nthe two-magnon continuum of energies, the decay rate of the bound state has to\nalways lie within the two-magnon continuum of decay rates. We then derive\nanalytically the bound state solutions for a system with nearest-neighbour and\nnext-nearest-neighbour XY interaction and nonlocal dissipation, finding that\nthe inclusion of nonlocal dissipation allows more freedom in engineering the\nenergy and decay rate dispersions for the bound states. Finally, we numerically\nstudy a model of an experimental set-up that should allow the realisation of\ndissipative bound states by using Rydberg-dressed atoms coupled to a photonic\ncrystal waveguide (PCW). We demonstrate that this model can exhibit many key\nfeatures of our simpler models."
    },
    {
        "anchor": "Probing chiral edge dynamics and bulk topology of a synthetic Hall\n  system: Quantum Hall systems are characterized by the quantization of the Hall\nconductance -- a bulk property rooted in the topological structure of the\nunderlying quantum states. In condensed matter devices, material imperfections\nhinder a direct connection to simple topological models. Artificial systems,\nsuch as photonic platforms or cold atomic gases, open novel possibilities by\nenabling specific probes of topology or flexible manipulation e.g. using\nsynthetic dimensions. However, the relevance of topological properties requires\nthe notion of a bulk, which was missing in previous works using synthetic\ndimensions of limited sizes. Here, we realize a quantum Hall system using\nultracold dysprosium atoms, in a two-dimensional geometry formed by one spatial\ndimension and one synthetic dimension encoded in the atomic spin $J=8$. We\ndemonstrate that the large number of magnetic sublevels leads to distinct bulk\nand edge behaviors. Furthermore, we measure the Hall drift and reconstruct the\nlocal Chern marker, an observable that has remained, so far, experimentally\ninaccessible. In the center of the synthetic dimension -- a bulk of 11 states\nout of 17 -- the Chern marker reaches 98(5)\\% of the quantized value expected\nfor a topological system. Our findings pave the way towards the realization of\ntopological many-body phases.",
        "positive": "mm-wave Rydberg-Rydberg resonances as a witness of intermolecular\n  coupling in the arrested relaxation of a molecular ultracold plasma: Out-of-equilibrium, strong correlation in a many-body system triggers\nemergent properties that can act in important ways to constrain the natural\ndissipation of energy and matter. Networks of atoms, intricately engineered to\narrange positions and tune interaction energies, exhibit striking dynamics.\nBut, strong correlation itself can also act to restrict available phase space.\nRelaxation confined by strong correlation gives rise to scale invariance and\ndensity distributions characteristic of self-organized criticality. For some\ntime, we have observed signs of self-organization in the avalanche, bifurcation\nand quench of a state-selected Rydberg gas of nitric oxide to form an\nultracold, strongly correlated ultracold plasma. The robust arrested relaxation\nof this system forms a disordered state with quantum-mechanical properties that\nappear to support a coherent destruction of transport. Work reported here\nfocuses on initial stages of avalanche and quench, using the mm-wave\nspectroscopy of an embedded quantum probe to characterize the intermolecular\ninteraction dynamics associated with the evolution to plasma. Double-resonance\nexcitation prepares a Rydberg gas of nitric oxide composed of a single selected\nstate, $n_0f(2)$. Penning ionization, followed by an avalanche of\nelectron-Rydberg collisions, forms a plasma of NO$^+$ ions and weakly bound\nelectrons, in which a residual population of $n_0$ Rydberg molecules evolves to\nhigh-$\\ell$. At long times, $n_0\\ell(2) \\rightarrow (n_0 \\pm 1)d(2)$ depletion\nresonances signal collision-free energy redistribution in the basis of\ncentral-field Rydberg states. The widths and asymmetries of Fano lineshapes\nwitness the degree to which coupling to the arrested bath broadens the bright\nstate as well as how bright-state predissociation mixes the network of levels\nin the localized ensemble."
    },
    {
        "anchor": "Fermionization of two-component few-fermion systems in a one-dimensional\n  harmonic trap: The nature of strongly interacting Fermi gases and magnetism is one of the\nmost important and studied topics in condensed-matter physics. Still, there are\nmany open questions. A central issue is under what circumstances strong\nshort-range repulsive interactions are enough to drive magnetic correlations.\nRecent progress in the field of cold atomic gases allows to address this\nquestion in very clean systems where both particle numbers, interactions and\ndimensionality can be tuned. Here we study fermionic few-body systems in a one\ndimensional harmonic trap using a new rapidly converging effective-interaction\ntechnique, plus a novel analytical approach. This allows us to calculate the\nproperties of a single spin-down atom interacting with a number of spin-up\nparticles, a case of much recent experimental interest. Our findings indicate\nthat, in the strongly interacting limit, spin-up and spin-down particles want\nto separate in the trap, which we interpret as a microscopic precursor of\none-dimensional ferromagnetism in imbalanced systems. Our predictions are\ndirectly addressable in current experiments on ultracold atomic few-body\nsystems.",
        "positive": "$SU(3)$ Topological Insulators in the Honeycomb Lattice: We investigate realizations of topological insulators with spin-1 bosons\nloaded in a honeycomb optical lattice and subjected to a $SU(3)$ spin-orbit\ncoupling - a situation which can be realized experimentally using cold atomic\ngases. In this paper, we focus on the topological properties of the\nsingle-particle band structure, namely Chern numbers (lattice with periodic\nboundary conditions) and edge states (lattice with strip geometry). While\n$SU(2)$ spin-orbit couplings always lead to time-reversal symmetric Hubbard\nmodels, and thereby to topologically trivial band structures, suitable $SU(3)$\nspin-orbit couplings can break time reversal symmetry and lead to topologically\nnon-trivial bulk band structures and to edge states in the strip geometry. In\naddition, we show that one can trigger a series of topological transitions\n(i.e. integer changes of the Chern numbers) that are specific to the geometry\nof the honeycomb lattice by varying a single parameter in the Hamiltonian."
    },
    {
        "anchor": "Quantum Fluctuations of Vortex Lattices in Ultracold Gases: We discuss the effects of quantum fluctuations on the properties of vortex\nlattices in rapidly rotating ultracold atomic gases. We develop a variational\nmethod that goes beyond the Bogoliubov theory by including the effects of\ninteractions between the quasiparticle excitations. These interactions are\nfound to have significant quantitative effects on physical properties even at\nrelatively large filling factors. We use our theory to predict the expected\nexperimental signatures of quantum fluctuations of vortices, and to assess the\ncompetition of the triangular vortex lattice phase with other phases in\nfinite-sized systems.",
        "positive": "Supersolid formation time shortcut and excitation reduction by\n  manipulating the dynamical instability: Supersolids are a phase of matter exhibiting both superfluidity and a\nperiodic density modulation typical of crystals. When formed via quantum phase\ntransition from a superfluid, they require a formation time before their\ndensity pattern develops. Along this paper some protocols/schemes are proposed\nfor experimental applications, building on earlier descriptions of the role\nroton instability plays in the supersolid formation process and the associated\nformation time. In particular, the Parachutejump scheme sought to lessen the\nexcitation produced when crossing the phase transition, and the Bang-Bang\nmethod sought to shorten the formation time. As a case study of the impact that\nmechanical fluctuations (noise) can have on the phase transition when\nconducting an experiment, the impact of a mechanical kick before the transition\nis also investigated. The proposed schemes are able to fulfill their objectives\nsuccessfully as both the shortening of the formation process and the reduction\nof excitation are achieved within the framework of extended Gross Pitaevskii\ntheory."
    },
    {
        "anchor": "One-dimensional three-boson problem with two- and three-body\n  interactions: We solve the three-boson problem with contact two- and three-body\ninteractions in one dimension and analytically calculate the ground and excited\ntrimer-state energies. Then, by using the diffusion Monte Carlo technique we\ncalculate the binding energy of three dimers formed in a one-dimensional\nBose-Bose or Fermi-Bose mixture with attractive interspecies and repulsive\nintraspecies interactions. Combining these results with our three-body\nanalytics we extract the three-dimer scattering length close to the dimer-dimer\nzero crossing. In both considered cases the three-dimer interaction turns out\nto be repulsive. Our results constitute a concrete proposal for obtaining a\none-dimensional gas with a pure three-body repulsion.",
        "positive": "Exotic superfluidity in spin-orbit coupled Bose-Einstein condensates: We study the superfluidity of a spin-orbit coupled Bose-Einstein condensate\n(BEC) by computing its Bogoliubov excitations, which are found to consist of\ntwo branches: one is gapless and phonon-like at long wavelength; the other is\ntypically gapped. These excitations imply a superfluidity that has two new\nfeatures: ({\\it i}) due to the absence of the Galilean invariance, one can no\nlonger define the critical velocity of superfluidity independent of the\nreference frame; ({\\it ii}) the superfluidity depends not only on whether the\nspeed of the BEC exceeds a critical value, but also on {\\it cross helicity}\nthat is defined as the direction of the cross product of the spin and the\nkinetic momentum of the BEC."
    },
    {
        "anchor": "Rabi Spectroscopy and Sensitivity of a Floquet Engineered Optical\n  Lattice Clock: We periodically modulate the lattice trapping potential of a $^{87}$Sr\noptical clock to Floquet engineer the clock transition. In the context of\natomic gases in lattices, Floquet engineering has been used to shape the\ndispersion and topology of Bloch quasi-energy bands. Differently from these\nprevious works manipulating the external (spatial) quasi-energies, we target\nthe internal atomic degrees of freedom. We shape Floquet spin quasi-energies\nand measure their resonance profiles with Rabi spectroscopy. We provide the\nspectroscopic sensitivity of each band by measuring the Fisher information and\nshow that this is not depleted by the Floquet dynamical modulation. The\ndemonstration that the internal degrees of freedom can be selectively\nengineered by manipulating the external degrees of freedom inaugurates a novel\ndevice with potential applications in metrology, sensing and quantum\nsimulations.",
        "positive": "Hydrodynamics of nonlinear gauge-coupled quantum fluids: By constructing a hydrodynamic canonical formalism, we show that the\noccurrence of an arbitrary density-dependent gauge potential in the meanfield\nHamiltonian of a Bose-condensed fluid invariably leads to nonlinear\nflow-dependent terms in the wave equation for the phase, where such terms arise\ndue to the explicit dependence of the mechanical flow on the fluid density. In\naddition, we derive a canonical momentum transport equation for this class of\nnonlinear fluid and obtain an expression for the stress tensor. Further, we\nstudy the hydrodynamic equations in a particular nonlinear fluid, where the\neffective gauge potential results from the introduction of weak contact\ninteractions in an ultracold dilute Bose gas of optically-addressed two-level\natoms. In the Cauchy equation of mechanical momentum transport of the\nsuperfluid, two non-trivial terms emerge due to the density-dependent vector\npotential. A body-force of dilation appears as a product of the gauge potential\nand the dilation rate of the fluid, while the stress tensor features a\ncanonical flow pressure term given by the inner-product of the gauge potential\nand the canonical current density. By numerical simulation, we illustrate an\ninteresting effect of the nonlinear gauge potential on the groundstate\nwavefunction of a superfluid in the presence of a foreign impurity. We find\nthat the groundstate adopts a non-trivial local phase, which is antisymmetric\nunder reversal of the gauge potential. The phase profile leads to a\ncanonical-flow or phase-flow dipole about the impurity, resulting in a skirting\nmechanical flow. As a result, the pressure becomes asymmetric about the object\nand the condensate undergoes a deformation."
    },
    {
        "anchor": "Band gap structures for matter waves: Spatial gaps correspond to the projection in position space of the gaps of a\nperiodic structure whose envelope varies spatially. They can be easily\ngenerated in cold atomic physics using finite-size optical lattice, and provide\na new kind of tunnel barriers which can be used as a versatile tool for quantum\ndevices. We present in detail different theoretical methods to quantitatively\ndescribe these systems, and show how they can be used to realize in one\ndimension matter wave Fabry-Perot cavities. We also provide experimental and\nnumerical results that demonstrate the interest of spatial gaps structures for\nphase space engineering. We then generalize the concept of spatial gaps in two\ndimensions and show that this enables to design multiply connected cavities\nwhich generate a quantum dot structure for atoms or allow to construct curved\nwave guides for matter waves. At last, we demonstrate that modulating in time\nthe amplitude of the periodic structure offers a wide variety of possible atom\nmanipulations including the control of the scattering of an incoming wave\npacket, the loading of cavities delimited by spatial gaps, their coupling by\nmultiphonon processes or the realization of a tunable source of atoms. This\nlarge range of possibilities offered by space and time engineering of optical\nlattices demonstrates the flexibility of such band gap structures for matter\nwave control, quantum simulators and atomtronics.",
        "positive": "Topological Superfluidity of Spin-Orbit Coupled Bilayer Fermi Gases: Topological superfluid, new quantum matter that possesses gapless exotic\nexcitations known as Majorana fermions, has attracted extensive attention\nrecently. These excitations, which can encode topological qubits, could be\ncrucial ingredients for fault-tolerant quantum computation. However, creating\nand manipulating multiple Majorana fermions remain an ongoing challenge.\nLoading a topologically protected system in multi-layer structures would be a\nnatural and simple way to achieve this goal. Here we investigate the system of\nbilayer Fermi gases with spin-orbit coupling and show that the topological\ncondition is significantly influenced by the inter-layer tunneling, yielding\ntwo novel topological phases, which support more Majorana Fermions. We\ndemonstrate the existence of such novel topological phases and associated\nmultiple Majorana fermions using bilayer Fermi gases trapped inside a harmonic\npotential. This research pave a new way for generating multiple Majorana\nfermions and would be a significant step towards topological quantum\ncomputation."
    },
    {
        "anchor": "Phase transition to Bose-Einstein condensation for a Bosonic gas\n  confined in a combined trap: We present a study of phase transition to macroscopic superfluidity for an\nultracold bosonic gas confined in a combined trap formed by a one-dimensional\noptical lattice and a harmonic potential, focusing on the critical temperature\nof this system and the interference patterns of the Bose gas released from the\ncombined trap. Based on a semiclassical energy spectrum, we develop an analytic\napproximation for the critical temperature $T_{c}$, and compare the analytic\nresults with that obtained by numerical computations. For finite temperatures\nbelow $T_{c}$, we calculate the interference patterns for both the normal gas\nand the superfluid gas. The total interference pattern shows a feature of\n``peak-on-a-peak\". As a comparison, we also present the experimentally observed\ninterference patterns of $^{87}$Rb atoms released from a one-dimensional\noptical lattice system in accord with our theoretical model. Our observations\nare consistent with the theoretical results.",
        "positive": "Fourier transform spectroscopy of a spin-orbit coupled Bose gas: We describe a Fourier transform spectroscopy technique for directly measuring\nband structures, and apply it to a spin-1 spin-orbit coupled Bose-Einstein\ncondensate. In our technique, we suddenly change the Hamiltonian of the system\nby adding a spin-orbit coupling interaction and measure populations in\ndifferent spin states during the subsequent unitary evolution. We then\nreconstruct the spin and momentum resolved spectrum from the peak frequencies\nof the Fourier transformed populations. In addition, by periodically modulating\nthe Hamiltonian, we tune the spin-orbit coupling strength and use our\nspectroscopy technique to probe the resulting dispersion relation. The\nfrequency resolution of our method is limited only by the coherent evolution\ntimescale of the Hamiltonian and can otherwise be applied to any system, for\nexample, to measure the band structure of atoms in optical lattice potentials."
    },
    {
        "anchor": "Quantum many-body scars in the Bose-Hubbard model with a three-body\n  constraint: We uncover the exact athermal eigenstates in the Bose-Hubbard (BH) model with\na three-body constraint, motivated by the exact construction of quantum\nmany-body scar (QMBS) states in the $S=1$ $XY$ model. These states are\ngenerated by applying an $\\rm SU(2)$ ladder operator consisting of a linear\ncombination of two-particle annihilation operators to the fully occupied state.\nBy using the improved Holstein-Primakoff expansion, we clarify that the QMBS\nstates in the $S=1$ $XY$ model are equivalent to those in the constrained BH\nmodel with additional correlated hopping terms. We also find that, in the\nstrong-coupling limit of the constrained BH model, the QMBS state exists as the\nlowest-energy eigenstate of the effective model in the highest-energy sector.\nThis fact enables us to prepare the QMBS states in a certain adiabatic process\nand opens up the possibility of observing them in ultracold-atom experiments.",
        "positive": "Spectral properties and observables in ultracold Fermi gases: We calculate non-perturbative self-consistent fermionic and bosonic spectral\nfunctions of ultra-cold Fermi gases with the spectral functional approach. This\napproach allows for a direct real-time computation of non-perturbative\ncorrelation functions, and in the present work we use spectral Dyson-Schwinger\nequations. We focus on the normal phase of the spin-balanced Fermi gas and\nprovide numerical results for the full fermionic and bosonic spectral\nfunctions. The spectral functions are then used for the determination of the\nequation of state, the Tan contact and ejection rf spectra at unitarity. These\nresults are compared to experimental data, the self-consistent T-matrix\napproach and lattice results. Our approach offers a wide range of applications,\nincluding the ab initio calculation of transport and spectral properties of the\nsuperfluid phase in the BCS-BEC crossover."
    },
    {
        "anchor": "Multifaceted phase ordering kinetics of an antiferromagnetic spin-1\n  condensate: We study phase domain coarsening in the long time limit after a quench of\nmagnetic field in a quasi one-dimensional spin-1 antiferromagnetic condensate.\nWe observe that the growth of correlation length obeys scaling laws predicted\nby the two different models of phase ordering kinetics, namely the binary\nmixture and vector field. We derive regimes of clear realization for both of\nthem. We demonstrate appearance of atypical scaling laws, which emerge in\nintermediate regions.",
        "positive": "Non-equilibrium quantum magnetism in a dipolar lattice gas: Research on quantum magnetism with ultra-cold gases in optical lattices is\nexpected to open fascinating perspectives for the understanding of fundamental\nproblems in condensed-matter physics. Here we report on the first realization\nof quantum magnetism using a degenerate dipolar gas in an optical lattice. In\ncontrast to their non-dipolar counterparts, dipolar lattice gases allow for\ninter-site spin-spin interactions without relying on super-exchange energies,\nwhich constitutes a great advantage for the study of spin lattice models. In\nthis paper we show that a chromium gas in a 3D lattice realizes a lattice model\nresembling the celebrated t-J model, which is characterized by a\nnon-equilibrium spinor dynamics resulting from inter-site Heisenberg-like\nspin-spin interactions provided by non-local dipole-dipole interactions.\nMoreover, due to its large spin, chromium lattice gases constitute an excellent\nenvironment for the study of quantum magnetism of high-spin systems, as\nillustrated by the complex spin dynamics observed for doubly-occupied sites."
    },
    {
        "anchor": "Quantum Many-Body Dynamics of Dark Solitons in Optical Lattices: We present a fully quantum many-body treatment of dark solitons formed by\nultracold bosonic atoms in one-dimensional optical lattices. Using\ntime-evolving block decimation to simulate the single-band Bose-Hubbard\nHamiltonian, we consider the quantum dynamics of density and phase engineered\ndark solitons as well as the quantum evolution of mean-field dark solitons\ninjected into the quantum model. The former approach directly models how one\nmay create quantum entangled dark solitons in experiment. While we have already\npresented results regarding the latter approach elsewhere [Phys. Rev. Lett.\n{\\bf 103}, 140403 (2009)], we expand upon those results in this work. In both\ncases, quantum fluctuations cause the dark soliton to fill in and may induce an\ninelasticity in soliton-soliton collisions. Comparisons are made to the\nBogoliubov theory which predicts depletion into an anomalous mode that fills in\nthe soliton. Our many-body treatment allows us to go beyond the Bogoliubov\napproximation and calculate explicitly the dynamics of the system's natural\norbitals.",
        "positive": "Error estimates and specification parameters for functional\n  renormalization: We present a strategy for estimating the error of truncated functional flow\nequations. While the basic functional renormalization group equation is exact,\napproximated solutions by means of truncations do not only depend on the choice\nof the retained information, but also on the precise definition of the\ntruncation. Therefore, results depend on specification parameters that can be\nused to quantify the error of a given truncation. We demonstrate this for the\nBCS-BEC crossover in ultracold atoms. Within a simple truncation the precise\ndefinition of the frequency dependence of the truncated propagator affects the\nresults, indicating a shortcoming of the choice of a frequency independent\ncutoff function."
    },
    {
        "anchor": "Spinor Bose-Einstein Condensate Interferometer within the Undepleted\n  Pump Approximation: Role of the Initial State: Most interferometers operate with photons or dilute, non-condensed cold atom\nclouds in which collisions are strongly suppressed. Spinor Bose-Einstein\ncondensates (BECs) provide an alternative route toward realizing three-mode\ninterferometers; in this realization, spin-changing collisions provide a\nresource that generates mode entanglement. Working in the regime where the pump\nmode, i.e., the m=0 hyperfine state, has a much larger population than the side\nor probe modes (m=+1 and m=-1 hyperfine states), f=1 spinor BECs approximate\nSU(1,1) interferometers. We derive analytical expressions within the undepleted\npump approximation for the phase sensitivity of such an SU(1,1) interferometer\nfor two classes of initial states: pure Fock states and coherent spin states.\nThe interferometer performance is analyzed for initial states without seeding,\nwith single-sided seeding, and with double-sided seeding. The validity regime\nof the undepleted pump approximation is assessed by performing quantum\ncalculations for the full spin Hamiltonian. Our analytical results and the\nassociated dynamics are expected to guide experiments as well as numerical\nstudies that explore regimes where the undepleted pump approximation makes\nquantitatively or qualitatively incorrect predictions.",
        "positive": "Dipolar Bose gas in highly anharmonic traps: By means of mean-field theory, we have studied the structure and excitation\nspectrum of a purely dipolar Bose gas in pancake-shaped trap where the\nconfinement in the x-y plane is provided by a highly anharmonic potential\nresulting in an almost uniform confinement in the plane. We show that the\nstable condensates is characterized by marked radially structured density\nprofiles. The stability diagram is calculated by independently varying the\nstrength of the interaction and the trap geometry. By computing the Bogoliubov\nexcitation spectrum near the instability line we show that soft \"angular\"\nrotons are responsible for the collapse of the system. The free expansion of\nthe cloud after the trap is released is also studied by means of time-dependent\ncalculations, showing that a prolate, cigar-shaped condensate is dynamically\nstabilized during the expansion, which would otherwise collapse. Dipolar\ncondensates rotating with sufficiently high angular velocity show the formation\nof multiply-quantized giant vortices, while the condensates acquire a\nring-shaped form."
    },
    {
        "anchor": "Spin-orbit-coupling-assisted roton softening and superstripes in a\n  Rydberg-dressed Bose-Einstein Condensate: Rotons can exist in ultracold atomic gases either with long-range\ninteractions or with spin-orbitcoupled dispersions. We find that two different\nkinds of rotons coexist in a joint system combining long-range interactions and\nspin-orbit coupling. One roton originates from spin-orbit coupling and two\nothers come from long-range interactions. Their softening can be controlled\nseparately. The interesting new phenomenon which we find is that\nspin-orbit-coupled roton can push down the energy of one long-range-interaction\nroton. The spin-orbit coupling accelerates the softening of this roton. The\npost phase of spin-orbit-coupling-assisted roton softening and instability is\nidentified as a superstripe.",
        "positive": "Emergence of caustics in dynamics of the Kitaev model: We study quasiparticle dynamics in two-dimensional (2D) integrable Kitaev\nhoneycomb model both without and in the presence of an external periodic drive.\nWe identify light-cones in wavefunction propagation as a signature of quantum\ncaustic, i.e. bright structures formed during quantum dynamics analogous to\nthat of imperfect focusing in geometrical optics. We show that this dynamics\nfollows an angle in spatial direction and it is anisotropic with respect to\nmodel parameters. Using coalescence of critical points, we provide an exact\nsolution to the envelope of caustic, which corresponds to the Lieb-Robinson\nbound in 2D. Further, consedering the system to be periodically driven, we\npoint out that the caustic structure completely changes in presence of external\ntime dependent drive."
    },
    {
        "anchor": "Quantum criticality of spin-1 bosons in a 1D harmonic trap: We investigate universal thermodynamics and quantum criticality of spin-1\nbosons with strongly repulsive density-density and antiferromagnetic\nspin-exchange interactions in a one-dimensional harmonic trap. From the\nequation of state, we find that a partially-polarized core is surrounded by two\nwings composed of either spin-singlet pairs or a fully spin-aligned\nTonks-Girardeau gas depending on the polarization. We describe how the scaling\nbehaviour of density profiles can reveal the universal nature of quantum\ncriticality and map out the quantum phase diagram. We further show that at\nquantum criticality the dynamical critical exponent $z = 2$ and correlation\nlength exponent $\\nu=1/2$. This reveals a subtle resemblance to the physics of\nthe spin-1/2 attractive Fermi gas.",
        "positive": "Spin-orbit coupling and spin Hall effect for neutral atoms without\n  spin-flips: We propose a scheme which realizes spin-orbit coupling and the spin Hall\neffect for neutral atoms in optical lattices without relying on near resonant\nlaser light to couple different spin states. The spin-orbit coupling is created\nby modifying the motion of atoms in a spin-dependent way by laser recoil. The\nspin selectivity is provided by Zeeman shifts created with a magnetic field\ngradient. Alternatively, a quantum spin Hamiltonian can be created by\nall-optical means using a period- tripling, spin-dependent superlattice."
    },
    {
        "anchor": "Phase tunable Josephson junction and spontaneous mass current in a\n  spin-orbit coupled Fermi superfluid: Atomtronics has the potential for engineering new types of functional\ndevices, such as Josephson junctions (JJs). Previous studies have mainly\nfocused on JJs whose ground states have 0 or $\\pi $ superconducting phase\ndifference across the junctions, while arbitrarily tunable phase JJs may have\nimportant applications in superconducting electronics and quantum computation.\nHere we show that a phase tunable JJ can be implemented in a spin-orbit coupled\ncold atomic gas with the magnetic tunneling barrier generated by a\nspin-dependent focused laser beam. We consider the JJ confined in either a\nlinear harmonic trap or a circular ring trap. In the ring trap, the magnetic\nbarrier induces a spontaneous mass current for the ground state of the JJ,\ndemonstrating the magnetoelectric effects of cold atoms.",
        "positive": "Gauge-potential-induced rotation of spin-orbit-coupled Bose-Einstein\n  condensates: We demonstrate that a spin-orbit-coupled Bose-Einstein condensate can be\neffectively rotated by adding a real magnetic field to inputting gauge angular\nmomentum, which is distinctly different from the traditional ways of rotation\nby stirring or Raman laser dressing to inputting canonical angular momentum.\nThe gauge angular momentum is accompanied by the spontaneous generation of\nequal and opposite canonical angular momentum in the ground states, and it\nleads to the nucleation of quantized vortices. We explain this by indicating\nthat the effective rotation with the vortex nucleation results from the\neffective magnetic flux induced by the gauge potential, which is essentially\ndifferent from the previous scheme of creating vortices by synthetic magnetic\nfields. In the weakly interacting regime, symmetrically placed domains\nseparated by vortex lines as well as half-integer giant vortices are\ndiscovered. With relatively strong interatomic interaction, we predict a\nstructure of coaxially arranged annular vortex arrays, which is in stark\ncontrast to the familiar Abrikosov vortex lattice. The developed way of\nrotation may be extended to a more general gauge system."
    },
    {
        "anchor": "Many-body collisional dynamics of impurities injected into a double-well\n  trapped Bose-Einstein condensate: We unravel the many-body dynamics of a harmonically trapped impurity\ncolliding with a bosonic medium confined in a double-well upon quenching the\ninitially displaced harmonic trap to the center of the double-well. We reveal\nthat the emerging correlation dynamics crucially depends on the impurity-medium\ninteraction strength allowing for a classification into different dynamical\nresponse regimes. For strong attractive impurity-medium couplings the impurity\nis bound to the bosonic bath, while for intermediate attractions it undergoes\nan effective tunneling. In the case of weak attractive or repulsive couplings\nthe impurity penetrates the bosonic bath and performs a dissipative oscillatory\nmotion. Further increasing the impurity-bath repulsion results in the pinning\nof the impurity between the density peaks of the bosonic medium, a phenomenon\nthat is associated with a strong impurity-medium entanglement. For strong\nrepulsions the impurity is totally reflected by the bosonic medium. To unravel\nthe underlying microscopic excitation processes accompanying the dynamics we\nemploy an effective potential picture. We extend our results to the case of two\nbosonic impurities and demonstrate the existence of a qualitatively similar\nimpurity dynamics.",
        "positive": "Strongly interacting bosons in a 1D optical lattice at incommensurate\n  densities: We investigate quantum phase transitions occurring in a system of strongly\ninteracting ultracold bosons in a 1D optical lattice. After discussing the\ncommensurate-incommensurate transition, we focus on the phases appearing at\nincommensurate filling. We find a rich phase diagram, with superfluid,\nsupersolid and solid (kink-lattice) phases. Supersolids generally appear in\ntheoretical studies of systems with long-range interactions; our results break\nthis paradigm and show that they may also emerge in models including only\nshort-range (contact) interactions, provided that quantum fluctuations are\nproperly taken into account."
    },
    {
        "anchor": "Dynamic and Energetic Stabilization of Persistent Currents in\n  Bose-Einstein Condensates: We study conditions under which vortices in a highly oblate harmonically\ntrapped Bose-Einstein condensate (BEC) can be stabilized due to pinning by a\nblue-detuned Gaussian laser beam, with particular emphasis on the potentially\ndestabilizing effects of laser beam positioning within the BEC. Our approach\ninvolves theoretical and numerical exploration of dynamically and energetically\nstable pinning of vortices with winding number up to $S=6$, in correspondence\nwith experimental observations. Stable pinning is quantified theoretically via\nBogoliubov-de Gennes excitation spectrum computations and confirmed via direct\nnumerical simulations for a range of conditions similar to those of\nexperimental observations. The theoretical and numerical results indicate that\nthe pinned winding number, or equivalently the winding number of the superfluid\ncurrent about the laser beam, decays as a laser beam of fixed intensity moves\naway from the BEC center. Our theoretical analysis helps explain previous\nexperimental observations, and helps define limits of stable vortex pinning for\nfuture experiments involving vortex manipulation by laser beams.",
        "positive": "Insulator phases of Bose-Fermi mixtures induced by next-neighbor\n  interactions between fermions: We study a one-dimensional mixture of two-color fermions and scalar bosons at\nthe hard-core limit, focusing on the effect that the next-neighbor interaction\nbetween fermions has on the zero-temperature ground state of the system for\ndifferent fillings of each carrier. Exploring the parameters of the problem, we\nobserved that the non-local interaction modifies the well-known mixed and\nspin-selective Mott insulators, and we also found the emergence of three\nunusual insulating states with peculiar charge density wave orderings, a fully\nout-of-phase density of carriers for bosonic half-filling, an insulator with\nthe same bosonic and fermionic fillings, and a different spin-selective\ninsulator where the bosonic filling matches the density of one kind of fermion.\nModern cold-atom setups correspond to the ideal experimental setting where\nthese incommensurable insulators can be observed."
    },
    {
        "anchor": "1D Quantum Liquids with Power-Law Interactions: a Luttinger Staircase\n  with Polar Molecules: We study one dimensional fermionic and bosonic gases with repulsive power-law\ninteractions $1/|x|^{\\beta}$, with $\\beta>1$, in the framework of\nTomonaga-Luttinger liquid (LL) theory. We obtain an accurate analytical\nexpression linking the LL parameter to the microscopic Hamiltonian, for\narbitrary $\\beta$ and strength of the interactions. In the presence of a small\nperiodic potential, power-law interactions make the LL unstable towards the\nformation of a cascade of lattice solids with fractional filling, thus forming\na \"Luttinger staircase\". Several of these quantum phases and phase transitions\nare realized with groundstate polar molecules and weakly-bound magnetic\nFeshbach molecules.",
        "positive": "Collision of two self-trapped atomic matter wave packets in an optical\n  ring cavity: The interaction between atomic Bose-Einstein condensate (BEC) and light field\nin an optical ring cavity gives rise to many interesting phenomena such as\nsupersolid and movable self-trapped matter wave packets. Here we examined the\ncollision of two self-trapped atomic matter wave packets in an optical ring\ncavity, and abundant colliding phenomena have been found in the system.\nDepending on the magnitude of colliding velocity, the collision dynamics\nexhibit very different features compared with the cavity-free case. When the\ninitial colliding velocities of the two wave packets are small, they\ncorrelatedly oscillate around their initial equilibrium positions with a small\namplitude. Increasing the collision velocity leads to severe scattering of the\nBEC atoms; after the collision, the two self-trapped wave packets usually break\ninto small pieces. Interestingly, we found that such a medium velocity\ncollision is of great phase sensitivity, which may make the system useful in\nprecision matter wave interferometry. When the colliding velocity is further\nincreased, in the bad cavity limit, the two wave packets collide phenomenally\nsimilar to two classical particles -- they firstly approach each other, then\nseparate with their shape virtually maintained. However, beyond the bad cavity\nlimit, they experience severe spatial spreading."
    },
    {
        "anchor": "Experimental realization of an ideal Floquet disordered system: The atomic Quantum Kicked Rotor is an outstanding \"quantum simulator\" for the\nexploration of transport in disordered quantum systems. Here we study\nexperimentally the phase-shifted quantum kicked rotor, which we show to display\nproperties close to an ideal disordered quantum system, opening new windows\ninto the study of Anderson physics.",
        "positive": "Simulating sympathetic cooling of atomic mixtures in nonlinear traps: We discuss the dynamics of sympathetic cooling of atomic mixtures in\nrealistic, nonlinear trapping potentials using a microscopic effective model\ndeveloped earlier for harmonic traps. We contrast the effectiveness of\ndifferent atomic traps, such as Ioffe-Pritchard magnetic traps and optical\ndipole traps, and the role their intrinsic nonlinearity plays in speeding up or\nslowing down thermalization between the two atomic species. This discussion\nincludes cases of configurations with lower effective dimensionality. From a\nmore theoretical standpoint, our results provide the first exploration of a\ngeneralized Caldeira-Leggett model with nonlinearities both in the trapping\npotential as well as in the interspecies interactions, and no limitations on\ntheir coupling strength."
    },
    {
        "anchor": "Dissipation-induced dynamical phase transition in postselected quantum\n  trajectories: It is known that effects of dissipation or measurement backreaction in\npostselected quantum trajectories are described by non-Hermitian Hamiltonian,\nbut their consequences in real-time dynamics of many-body systems are yet to be\nelucidated. Through a study of a non-Hermitian Hubbard model, we reveal a novel\ndissipation-induced dynamical phase transition in postselected quantum\ntrajectories, where time controls the strength of postselection and becomes the\nintrinsic parameter inducing the phase transition. Our findings are testable in\nultracold atom experiments and may open a new avenue in the dissipative\nengineering of quantum systems.",
        "positive": "Phase Separation and Dynamics of two-component Bose-Einstein condensates: The miscibility of two interacting quantum systems is an important testing\nground for the understanding of complex quantum systems. Two-component\nBose-Einstein condensates enable the investigation of this scenario in a\nparticularly well controlled setting. In a homogeneous system, the transition\nbetween mixed and separated phases is fully characterised by a `miscibility\nparameter', based on the ratio of intra- to inter-species interaction\nstrengths. Here we show, however, that this parameter is no longer the optimal\none for trapped gases, for which the location of the phase boundary depends\ncritically on atom numbers. We demonstrate how monitoring of damping rates and\nfrequencies of dipole oscillations enables the experimental mapping of the\nphase diagram by numerical implementation of a fully self-consistent\nfinite-temperature kinetic theory for binary condensates. The change in damping\nrate is explained in terms of surface oscillation in the immiscible regime, and\ncounterflow instability in the miscible regime, with collisions becoming only\nimportant in the long time evolution."
    },
    {
        "anchor": "Correlation properties of a three-body bosonic mixture in a harmonic\n  trap: We make use of a simple pair correlated wave function approach to obtain\nresults for the ground-state densities and momentum distribution of a\none-dimensional three-body bosonic system with different interactions in a\nharmonic trap. For equal interactions this approach is able to reproduce the\nknown analytical cases of zero and infinite repulsion. We show that our results\nfor the correlations agree with the exact diagonalization in all interaction\nregimes and with analytical results for the strongly repulsive impurity. This\nmethod also enables us to access the more complicated cases of mixed\ninteractions, and the probability densities of these systems are analyzed.",
        "positive": "Green's function formalism for a condensed Bose gas consistent with\n  infrared-divergent longitudinal susceptibility and\n  Nepomnyashchii-Nepomnyashchii identity: We present a Green's function formalism for an interacting Bose-Einstein\ncondensate (BEC) satisfying the two required conditions: (i) the\ninfrared-divergent longitudinal susceptibility with respect to the BEC order\nparameter, and (ii) the Nepomnyashchii-Nepomnyashchii identity stating the\nvanishing off-diagonal self-energy in the low-energy and low-momentum limit.\nThese conditions cannot be described by the ordinary mean-field Bogoliubov\ntheory, the many-body $T$-matrix theory, as well as the random-phase\napproximation with the vertex correction. In this paper, we show that these\nrequired conditions can be satisfied, when we divide many-body corrections into\nsingular and non-singular parts, and separately treat them as different\nself-energy corrections. The resulting Green's function may be viewed as an\nextension of the Popov's hydrodynamic theory to the region at finite\ntemperatures. Our results would be useful in constructing a consistent theory\nof BECs satisfying various required conditions, beyond the mean-field level."
    },
    {
        "anchor": "Non-local correlation and entanglement of ultracold bosons in the\n  two-dimensional Bose-Hubbard lattice at finite temperature: We investigate the temperature-dependent behavior emerging in the vicinity of\nthe superfluid (SF) to Mott-insulator (MI) transition of interacting bosons in\na two-dimensional optical lattice, described by the Bose-Hubbard model. The\nequilibrium phase diagram at finite temperature is computed using the cluster\nmean-field (CMF) theory including a finite cluster-size scaling. The SF, MI,\nand normal fluid (NF) phases are characterized as well as the transition or\ncrossover temperatures between them are estimated by computing physical\nquantities such as the superfluid fraction, compressibility and sound velocity\nusing the CMF method. We find that the non-local correlations included in a\nfinite cluster, when extrapolated to infinite size, leads to quantitative\nagreement of the phase boundaries with quantum Monte Carlo (QMC) results as\nwell as with experiments. Moreover, we show that the von Neumann entanglement\nentropy within a cluster corresponds to the system's entropy density and that\nit is enhanced near the SF-MI quantum critical point (QCP) and at the SF- NF\nboundary. The behavior of the transition lines near this QCP, at and away from\nthe particle-hole (p-h) symmetric point located at the Mott-tip, is also\ndiscussed. Our results obtained by using the CMF theory can be tested\nexperimentally using the quantum gas microscopy method.",
        "positive": "Dynamic Stimulation of Quantum Coherence in Lattice Bosons: Thermal fluctuations tend to destroy long-range phase correlations.\nConsequently, bosons in a lattice will undergo a transition from a\nphase-coherent superfluid as the temperature rises. Contrary to common\nintuition, however, we show that non-equilibrium driving can be used to reverse\nthis thermal decoherence. This is possible because the energy distribution at\nequilibrium is rarely optimal for the manifestation of a given quantum\nproperty. We demonstrate this in the Bose-Hubbard model by calculating the\nnon-equilibrium spatial correlation function with periodic driving. We show\nthat the non-equilibrium phase boundary between coherent and incoherent states\nat finite bath temperatures can be made qualitatively identical to the familiar\nzero-temperature phase diagram, and we discuss the experimental manifestation\nof this phenomenon in cold atoms."
    },
    {
        "anchor": "Photoassociation of Universal Efimov Trimers: In view of recent experiments in ultracold atomic systems, the\nphotoassociation of Efimov trimers, composed of three identical bosons, is\nstudied utilizing the multipole expansion. We study both the normal hierarchy\ncase, where one-body current is dominant, and the strong hierarchy case,\nrelevant for photoassociation in ultracold atoms, where two-body current is\ndominant. For identical particles in the normal hierarchy case, the leading\ncontribution comes from the r^2 s-mode operator and from the quadrupole d-mode\noperator. The s-mode reaction is found to be dominant at low temperature, while\nas the temperature increases the d-mode becomes as significant. For the strong\nhierarchy case, the leading contribution comes from a 2-body s-wave {\\delta}\noperator. In both cases log periodic oscillations are found in the cross\nsection. For large but finite scattering length the amplitude of the\noscillations becomes larger in comparison to infinite scattering length case.\nWe apply our theory to photoassociation of 7Li ultracold atoms and show a good\nfit to the available experimental results.",
        "positive": "Nonadiabatic Dynamics of Ultracold Fermions in Optical Superlattices: We study the time-dependent dynamical properties of two-component ultracold\nfermions in a one-dimensional optical superlattice by applying the adaptive\ntime-dependent density matrix renormalization group to a repulsive Hubbard\nmodel with an alternating superlattice potential. We clarify how the time\nevolution of local quantities occurs when the superlattice potential is\nsuddenly changed to a normal one. For a Mott-type insulating state at quarter\nfilling, the time evolution exhibits a profile similar to that expected for\nbosonic atoms, where correlation effects are less important. On the other hand,\nfor a band-type insulating state at half filling, the strong repulsive\ninteraction induces an unusual pairing of fermions, resulting in some striking\nproperties in time evolution, such as a paired fermion co-tunneling process and\nthe suppression of local spin moments. We further address the effect of a\nconfining potential, which causes spatial confinement of the paired fermions."
    },
    {
        "anchor": "Energy-resolved spin correlation measurements: Decoding transverse spin\n  dynamics in weakly interacting Fermi gases: We study transverse spin dynamics on a microscopic level by measuring\nenergy-resolved spin correlations in weakly interacting Fermi gases (WIFGs).\nThe trapped cloud behaves as a many-body spin-lattice in energy space with\neffective long-range interactions, simulating a collective Heisenberg model. We\nobserve the flow of correlations in energy space in this quasi-continuous\nsystem, revealing the connection between the evolution of the magnetization and\nthe localization or spread of correlations. This work highlights energy-space\ncorrelation as a new observable in quantum phase transition studies of WIFGs,\ndecoding system features that are hidden in macroscopic measurements.",
        "positive": "Dynamic Density Response of Trapped Interacting Quantum Gases: An expression for the dynamic density response function has been obtained for\nan interacting quantum gas in Random Phase Approximation (RPA) including first\norder self and exchange contribution. It involves the single particle wave\nfunctions and eigen values. The expression simplifies when diagonal elements\nare considered. The diagonal elements of the imaginary part of Fourier\ntransformed response function is relevant in the measurement of Bragg\nscattering cross-section and in several other applications."
    },
    {
        "anchor": "Transport and interaction blockade of cold bosonic atoms in a\n  triple-well potential: We theoretically investigate the transport properties of cold bosonic atoms\nin a quasi one-dimensional triple-well potential that consists of two large\nouter wells, which act as microscopic source and drain reservoirs, and a small\ninner well, which represents a quantum-dot-like scattering region. Bias and\ngate \"voltages\" introduce a time-dependent tilt of the triple-well\nconfiguration, and are used to shift the energetic level of the inner well with\nrespect to the outer ones. By means of exact diagonalization considering a\ntotal number of six atoms in the triple-well potential, we find diamond-like\nstructures for the occurrence of single-atom transport in the parameter space\nspanned by the bias and gate voltages. We discuss the analogy with Coulomb\nblockade in electronic quantum dots, and point out how one can infer the\ninteraction energy in the central well from the distance between the diamonds.",
        "positive": "Lieb-Liniger gas in a constant force potential: We use Gaudin's Fermi-Bose mapping operator to calculate exact solutions for\nthe Lieb-Liniger model in a linear (constant force) potential (the constructed\nexact stationary solutions are referred to as the Lieb-Liniger-Airy wave\nfunctions). The ground state properties of the gas in the wedge-like trapping\npotential are calculated in the strongly interacting regime by using\nGirardeau's Fermi-Bose mapping and the pseudopotential approach in the\n$1/c$-approximation ($c$ denotes the strength of the interaction). We point out\nthat quantum dynamics of Lieb-Liniger wave packets in the linear potential can\nbe calculated by employing an $N$-dimensional Fourier transform as in the case\nof free expansion."
    },
    {
        "anchor": "Solitons in a hard-core bosonic system: Gross-Pitaevskii type and beyond: A unified formulation that obtains solitary waves for various background\ndensities in the Bose-Einstein condensate of a system of hard-core bosons with\nnearest neighbor attractive interactions is presented.\n  In general, two species of solitons appear: A nonpersistent (NP) type that\nfully delocalizes at its maximum speed, and a persistent (P) type that survives\neven at its maximum speed, and transforms into a periodic train of solitons\nabove this speed. When the background condensate density is nonzero, both\nspecies coexist, the soliton is associated with a constant intrinsic frequency,\nand its maximum speed is the speed of sound. In contrast, when the background\ncondensate density is zero, the system has neither a fixed frequency, nor a\nspeed of sound. Here, the maximum soliton speed depends on the frequency, which\ncan be tuned to lead to a cross-over between the NP-type and the P-type at a\ncertain critical frequency, determined by the energy parameters of the system.\nWe provide a single functional form for the soliton profile, from which diverse\ncharacteristics for various background densities can be obtained. Using the\nmapping to spin systems enables us to characterize the corresponding class of\nmagnetic solitons in\n  Heisenberg spin chains with different types of anisotropy, in a unified\nfashion.",
        "positive": "Observation of Dirac Monopoles in a Synthetic Magnetic Field: Magnetic monopoles --- particles that behave as isolated north or south\nmagnetic poles --- have been the subject of speculation since the first\ndetailed observations of magnetism several hundred years ago. Numerous\ntheoretical investigations and hitherto unsuccessful experimental searches have\nfollowed Dirac's 1931 development of a theory of monopoles consistent with both\nquantum mechanics and the gauge invariance of the electromagnetic field. The\nexistence of even a single Dirac magnetic monopole would have far-reaching\nphysical consequences, most famously explaining the quantization of electric\ncharge. Although analogues of magnetic monopoles have been found in exotic\nspin-ices and other systems, there has been no direct experimental observation\nof Dirac monopoles within a medium described by a quantum field, such as\nsuperfluid helium-3. Here we demonstrate the controlled creation of Dirac\nmonopoles in the synthetic magnetic field produced by a spinor Bose-Einstein\ncondensate. Monopoles are identified, in both experiments and matching\nnumerical simulations, at the termini of vortex lines within the condensate. By\ndirectly imaging such a vortex line, the presence of a monopole may be\ndiscerned from the experimental data alone. These real-space images provide\nconclusive and long-awaited experimental evidence of the existence of Dirac\nmonopoles. Our result provides an unprecedented opportunity to observe and\nmanipulate these quantum-mechanical entities in a controlled environment."
    },
    {
        "anchor": "Spinor Bose-Einstein condensates: An overview on the physics of spinor and dipolar Bose-Einstein condensates\n(BECs) is given. Mean-field ground states, Bogoliubov spectra, and many-body\nground and excited states of spinor BECs are discussed. Properties of\nspin-polarized dipolar BECs and those of spinor-dipolar BECs are reviewed. Some\nof the unique features of the vortices in spinor BECs such as fractional\nvortices and non-Abelian vortices are delineated. The symmetry of the order\nparameter is classified using group theory, and various topological excitations\nare investigated based on homotopy theory. Some of the more recent developments\nin a spinor BEC are discussed.",
        "positive": "Analyzing a Bose polaron across resonant interactions: Recently, two independent experiments reported the observation of long-lived\npolarons in a Bose-Einstein condensate, providing an excellent setting to study\nthe generic scenario of a mobile impurity interacting with a quantum reservoir.\nHere, we expand the experimental analysis by disentangling the effects of trap\ninhomogeneities and the many-body continuum in one of these experiments. This\nmakes it possible to extract the energy of the polaron at a well-defined\ndensity as a function of the interaction strength. Comparisons with quantum\nMonte-Carlo as well as diagrammatic calculations show good agreement, and\nprovide a more detailed picture of the polaron properties at stronger\ninteractions than previously possible. Moreover, we develop a semi-classical\ntheory for the motional dynamics and three-body loss of the polarons, which\npartly explains a previously unresolved discrepancy between theory and\nexperimental observations for repulsive interactions. Finally, we utilize\nquantum Monte-Carlo calculations to demonstrate that the findings reported in\nthe two experiments are consistent with each other."
    },
    {
        "anchor": "Self-induced entanglement resonance in a disordered Bose-Fermi mixture: Different regimes of entanglement growth under measurement have been\ndemonstrated for quantum many-body systems, with an entangling phase for low\nmeasurement rates and a disentangling phase for high rates (quantum Zeno\neffect). Here we study entanglement growth on a disordered Bose-Fermi mixture\nwith the bosons playing the role of the effective self-induced measurement for\nthe fermions. Due to the interplay between the disorder and a non-Abelian\nsymmetry, the model features an entanglement growth resonance when the\nboson-fermion interaction strength is varied. With the addition of a magnetic\nfield, the model acquires a dynamical symmetry leading to experimentally\nmeasurable long-time local oscillations. At the entanglement growth resonance,\nwe demonstrate the emergence of the cleanest oscillations. Furthermore, we show\nthat this resonance is distinct from both noise enhanced transport and a\nstandard stochastic resonance. Our work paves the way for experimental\nrealizations of self-induced correlated phases in multi-species systems.",
        "positive": "Strong correlations in lossy one-dimensional quantum gases: from the\n  quantum Zeno effect to the generalized Gibbs ensemble: We consider strong two-body losses in bosonic gases trapped in\none-dimensional optical lattices. We exploit the separation of time scales\ntypical of a system in the many-body quantum Zeno regime to establish a\nconnection with the theory of the time-dependent generalized Gibbs ensemble.\nOur main result is a simple set of rate equations that capture the simultaneous\naction of coherent evolution and two-body losses. This treatment gives an\naccurate description of the dynamics of a gas prepared in a Mott insulating\nstate and shows that its long-time behaviour deviates significantly from\nmean-field analyses. The possibility of observing our predictions in an\nexperiment with $^{174}$Yb in a metastable state is also discussed."
    },
    {
        "anchor": "Two Ultracold Atoms in a Quasi-Two-Dimensional Box Confinement: We investigate the scattering and two-body bound states of two ultracold\natoms in a quasi-two-dimensional (quasi-2D) confinement, with the confinement\npotential being an infinite square well (box potential) in the transverse\n($z$-) direction, and the motion of the atoms in the $x$-$y$ plane being free.\nSpecifically, we calculate the effective 2D scattering length and 2D effective\nrange of the low-energy scattering, as well as the energy and the\ntransverse-excited-mode probability of the bound states. Comparing these\nresults with those obtained under a harmonic transverse confinement potential,\nwe find that in most of the cases the 2D effective range for the box\nconfinement is approximately 0.28 of the one for the harmonic confinement.\nMoreover, the transverse-excited-mode probability of the bound states for the\nbox confinement is also much lower than the one for the harmonic confinement.\nThese results suggest that the transverse excitation in the box confinement is\nnotably weaker than the one in a harmonic confinement. Therefore, achieving\nquasi-2D ultracold gases well-described by pure-2D effective models,\nparticularly those with 2D contact interaction, is more feasible through box\nconfinement. Our results are helpful for the quantum simulation of 2D many-body\nphysics with ultracold atoms, e.g., the suppression of 2D effective range may\nlead to an enhancement of quantum anomaly in two-dimensional Fermi Gases.\nAdditionally, our calculation method is applicable to the two-body problems of\nultracold atoms in other types of quasi-2D confinements.",
        "positive": "Large Chern Number Topological Superfluids in Coupled Layer System: We investigate the topological phase transition with large Chern number in a\ncoupled layer system. The topological transitions between different topological\nsuperfluids can be realized by controlling the binding energy, interlay\ntunneling and layer asymmetry {\\it etc}. These topological phase transitions\ncan be characterized by energy gap closing and reopening at the critical points\nat zero momentum, where the Pfaffian and Chern number undergo a discontinuous\nchange. The bulk-edge correspondence ensures that the number of edge modes\nexactly equals the Chern number. However all these edge modes localized at the\nsame edge have the same chirality and propagate along the same direction. These\ntopological phases can be detected by spin texture at or near zero momentum,\nwhich changes discontinuously across the phase transition point due to band\ninversion. This model can be easily generalized to multilayer system in which\nthe Chern number equals any positive integer --- similar to that in integer\nquantum Hall effect --- can be realized. This work paves a new way in the\nrealization of topological superfluids with large Chern number."
    },
    {
        "anchor": "Finite temperature spin dynamics of a two-dimensional Bose-Bose atomic\n  mixture: We examine the role of thermal fluctuations in uniform two-dimensional binary\nBose mixtures of dilute ultracold atomic gases. We use a mean-field\nHartree-Fock theory to derive analytical predictions for the\nmiscible-immiscible transition. A nontrivial result of this theory is that a\nfully miscible phase at $T=0$ may become unstable at $T\\neq0$, as a consequence\nof a divergent behaviour in the spin susceptibility. We test this prediction by\nperforming numerical simulations with the Stochastic (Projected)\nGross-Pitaevskii equation, which includes beyond mean-field effects. We\ncalculate the equilibrium configurations at different temperatures and\ninteraction strengths and we simulate spin oscillations produced by a weak\nexternal perturbation. Despite some qualitative agreement, the comparison\nbetween the two theories shows that the mean-field approximation is not able to\nproperly describe the behavior of the two-dimensional mixture near the\nmiscible-immiscible transition, as thermal fluctuations smoothen all sharp\nfeatures both in the phase diagram and in spin dynamics, except for temperature\nwell below the critical temperature for superfluidity.",
        "positive": "Current algebra for a generalized two-site Bose-Hubbard model: We present a current algebra for a generalized two-site Bose-Hubbard model\nand use it to get the quantum dynamics of the currents. For different choices\nof the Hamiltonian parameters we get different currents dynamics. We generalize\nthe Heisenberg equation of motion to write the n-th time derivative of any\noperator."
    },
    {
        "anchor": "Collective excitations of a dipolar Bose-Einstein condensate: We have measured the effect of dipole-dipole interactions on the frequency of\na collective mode of a Bose-Einstein condensate. At relatively large numbers of\natoms, the experimental measurements are in good agreement with zero\ntemperature theoretical predictions based on the Thomas Fermi approach.\nExperimental results obtained for the dipolar shift of a collective mode show a\nlarger dependency to both the trap geometry and the atom number than the ones\nobtained when measuring the modification of the condensate aspect ratio due to\ndipolar forces. These findings are in good agreement with simulations based on\na gaussian ansatz.",
        "positive": "Quantum many-body scars from unstable periodic orbits: Unstable periodic orbits (UPOs) play a key role in the theory of chaos,\nconstituting the \"skeleton\" of classical chaotic systems and \"scarring\" the\neigenstates of the corresponding quantum system. Recently, nonthermal many-body\neigenstates embedded in an otherwise thermal spectrum have been identified as a\nmany-body generalization of quantum scars. The latter, however, are not clearly\nassociated to a chaotic phase space, and the connection between the single- and\nmany-body notions of quantum scars remains therefore incomplete. Here, we find\nthe first quantum many-body scars originating from UPOs of a chaotic phase\nspace. Remarkably, these states verify the eigenstate thermalization\nhypothesis, and we thus refer to them as thermal quantum many-body scars. While\nthey do not preclude thermalization, their spectral structure featuring\napproximately equispaced towers of states yields an anomalous oscillatory\ndynamics preceding thermalization for wavepackets initialized on an UPO.\nRemarkably, our model hosts both types of scars, thermal and nonthermal, and\nallows to study the crossover between the two. Our work illustrates the\nfundamental principle of classical-quantum correspondence in a many-body\nsystem, and its limitations."
    },
    {
        "anchor": "How to realise a homogeneous dipolar Bose gas in the roton regime: Homogeneous quantum gases open up new possibilities for studying many-body\nphenomena and have now been realised for a variety of systems. For gases with\nshort-range interactions the way to make the cloud homogeneous is, predictably,\nto trap it in an ideal (homogeneous) box potential. We show that creating a\nclose to homogeneous dipolar gas in the roton regime, when long-range\ninteractions are important, actually requires trapping particles in soft-walled\n(inhomogeneous) box-like potentials. In particular, we numerically explore a\ndipolar gas confined in a pancake trap which is harmonic along the polarisation\naxis and a cylindrically symmetric power-law potential $r^p$ radially. We find\nthat intermediate $p$'s maximise the proportion of the sample that can be\nbrought close to the critical density required to reach the roton regime,\nwhereas higher $p$'s trigger density oscillations near the wall even when the\nbulk of the system is not in the roton regime. We characterise how the optimum\ndensity distribution depends on the shape of the trapping potential and find it\nis controlled by the trap wall steepness.",
        "positive": "Correlated Chern insulators in two-dimensional Raman lattices: a\n  cold-atom regularization of strongly-coupled four-Fermi field theories: We show that ultra-cold atoms with synthetic spin-orbit coupling in Raman\nlattices can be used as versatile quantum simulators to explore the connections\nbetween correlated Chern insulators and strongly-coupled four-Fermi field\ntheories related to the Gross-Neveu model in (2+1) dimensions. Exploiting this\nmultidisciplinary perspective, we identify a large-$N$ quantum anomalous Hall\n(QAH) effect in absence of any external magnetic field, and use it to delimit\nregions in parameter space where these correlated topological phases appear,\nthe boundaries of which are controlled by strongly-coupled fixed points of the\nfour-Fermi relativistic field theory. We further show how, for strong\ninteractions, the QAH effect gives way to magnetic phases described by a\ntwo-dimensional quantum compass model in a transverse field. We present a\ndetailed description of the phase diagram using the large-$N$ effective\npotential, and variational techniques such as projected entangled pairs."
    },
    {
        "anchor": "Bogoliubov approach to superfluid-Bose glass phase transition of a\n  disordered Bose-Hubbard Model in weakly interacting regime: We investigate the disorder effect on coherent fraction and the quantum phase\ntransition of ultracold dilute Bose gases trapped in disordered optical\nlattices. Within the framework of Bogoliubov theory, an analytical expression\nfor the particle density is derived and the dependence of coherent fraction on\ndisorder strength as well as on lattice depth is discussed. In weak disorder\nregime, we find a decreased sensitivity of coherent fraction to disorder with\nthe increase of on-site interaction strength. For strong disorder, the quantum\nphase boundary between superfluid phase and Bose glass phase in the disordered\nBose-Hubbard system in weak interaction regime is discussed qualitatively. The\nobtained phase diagram is in agreement with the empirical square-root law. The\ndependence of the corresponding critical value of the disorder strength on\noptical lattice depth is presented as well, and may serve as a reference object\nfor possible experimental investigation.",
        "positive": "Quench dynamics of 1D Bose gas in an optical lattice: does the system\n  relax?: Understanding the relaxation process is the most important unsolved problem\nin non-equilibrium quantum physics. Current understanding primarily concerns on\nif and how an isolated quantum many-body system thermalize. However, there is\nno clear understanding of what conditions and on which time-scale do\nthermalization occurs. In this article, we simulate the quench dynamics of\none-dimensional Bose gas in an optical lattice from an{\\it {ab initio}}\nperspective by solving the time-dependent many-boson Schr\\\"odinger equation\nusing the multi-configurational time-dependent Hartree method for bosons\n(MCTDHB). We direct a superfluid (SF) to Mott-insulator (MI) transition by\nperforming two independent quenches: an interaction quench when the interaction\nstrength is changed instantaneously, and a lattice depth quench where the depth\nof the lattice is altered suddenly. We show that although the Bose-Hubbard\nmodel predicts identical physics, the general many-body treatment shows\nsignificant differences between the two cases. We observe that lattice depth\nquench exhibits a large time-scale to reach the MI state and shows an\noscillatory phase collapse-revival dynamics and a complete absence of\nthermalization that reveals through the analysis of the time-evolution of the\nreduced one-body density matrix, two-body density, and entropy production. In\ncontrast, the interaction quench shows a swift transition to the MI state and\nshows a clear signature of thermalization for strong quench values. We provide\na physical explanation for these differences and prescribe an analytical\nfitting formula for the time required for thermalization."
    },
    {
        "anchor": "Dynamical characterization of $Z_{2}$ Floquet topological phases via\n  quantum quenches: The complete characterization of a generic $d$-dimensional Floquet\ntopological phase is usually hard for the requirement of information about the\nmicromotion throughout the entire driving period. In a recent work [L. Zhang et\nal., Phys. Rev. Lett. 125, 183001 (2020)], an experimentally feasible dynamical\ndetection scheme was proposed to characterize the integer Floquet topological\nphases using quantum quenches. However, this theory is still far away from\ncompletion, especially for free-fermion Floquet topological phases, where the\nstates can also be characterized by $Z_{2}$ invariants. Here we develop the\nfirst full and unified dynamical characterization theory for the $Z_{2}$\nFloquet topological phases of different dimensionality and tenfold-way symmetry\nclasses by quenching the system from a trivial and static initial state to the\nFloquet topological regime through suddenly changing the parameters and turning\non the periodic driving. By measuring the minimal information of Floquet bands\nvia the stroboscopic time-averaged spin polarizations, we show that the\ntopological spin texture patterns emerging on certain discrete momenta of\nBrillouin zone called the $0$ or $\\pi$ gap highest-order band-inversion\nsurfaces provide a measurable dynamical $Z_{2}$ Floquet invariant, which\nuniquely determines the Floquet boundary modes in the corresponding quasienergy\ngap and characterizes the $Z_{2}$ Floquet topology. The applications of our\ntheory are illustrated via one- and two-dimensional models that are accessible\nin current quantum simulation experiments. Our work provides a highly feasible\nway to detect the $Z_{2}$ Floquet topology and completes the dynamical\ncharacterization for the full tenfold classes of Floquet topological phases,\nwhich shall advance the research in theory and experiments.",
        "positive": "Collective modes as a probe of imbalanced Fermi gases: We theoretically investigate the collective modes of imbalanced two component\none-dimensional Fermi gases with attractive interactions. This is done for\ntrapped and untrapped systems both at zero and non-zero temperature, using\nself-consistent mean-field theory and the random phase approximation. We\ndiscuss how the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state can be detected\nand the periodicity of the associated density modulations determined from its\ncollective mode spectrum. We also investigate the accuracy of the single mode\napproximation for low-lying collective excitations in a trap by comparing\nfrequencies obtained via sum rules with frequencies obtained from direct\ncollective mode calculations. It is found that, for collective excitations\nwhere the atomic clouds of the two spin species oscillate largely in phase, the\nsingle mode approximation holds well for a large parameter regime. Finally we\ninvestigate the collective mode spectrum obtained by parametric modulation of\nthe coupling constant."
    },
    {
        "anchor": "Polarons in Alkaline-earth-like Atoms with Multi Background Fermi\n  Surfaces: We study the impurity problem in a Fermi gas of $^{173}$Yb atoms near an\norbital Feshbach resonance, where a single moving particle in the $^3P_0$ state\ninteracting with two background Fermi seas of particles in different nuclear\nstates of the ground $^1S_0$ manifold. By employing wave function ansatzs for\nmolecule and polaron states, we investigate various properties of the molecule,\nthe attractive polaron, and the repulsive polaron states. We find that in\ncomparison to the case of only one Fermi sea is populated, the presence of an\nadditional Fermi sea acts as an energy shift between the two channels of the\norbital Feshbach resonance. Besides, the fluctuation around the Fermi level\nwould also bring sizable effects to the attractive and repulsive polaron\nstates.",
        "positive": "Universal behaviour of four-boson systems from a functional\n  renormalisation group: We apply a functional renormalisation group to systems of four bosonic atoms\nclose to the unitary limit. We work with a local effective action that includes\na dynamical trimer field and we use this field to eliminate structures that do\nnot correspond to the Faddeev-Yakubovsky equations. In the physical limit, we\nfind three four-body bound states below the shallowest three-body state. The\nvalues of the scattering lengths at which two of these states become bound are\nin good agreement with exact solutions of the four-body equations and\nexperimental observations. The third state is extremely shallow. During the\nevolution we find an infinite number of four-body states based on each\nthree-body state which follow a double-exponential pattern in the running\nscale. None of the four-body states shows any evidence of dependence on a\nfour-body parameter."
    },
    {
        "anchor": "Competing ground states of strongly correlated bosons in the\n  Harper-Hofstadter-Mott model: Using an efficient cluster approach, we study the physics of two-dimensional\nlattice bosons in a strong magnetic field in the regime where the tunneling is\nmuch weaker than the on-site interaction strength. We study both dilute, hard\ncore bosons at filling factors much smaller than unity occupation per site, and\nthe physics in the vicinity of the superfluid-Mott lobes as the density is\ntuned away from unity. For hardcore bosons, we carry out extensive numerics for\na fixed flux per plaquette $\\phi=1/5$ and $\\phi = 1/3$. At large flux, the\nlowest energy state is a strongly correlated superfluid, analogous to He-$4$,\nin which the order parameter is dramatically suppressed, but non-zero. At\nfilling factors $\\nu=1/2,1$, we find competing incompressible states which are\nmetastable. These appear to be commensurate density wave states. For small\nflux, the situation is reversed, and the ground state at $\\nu = 1/2$ is an\nincompressible density-wave solid. Here, we find a metastable lattice\nsupersolid phase, where superfluidity and density-wave order coexist. We then\nperform careful numerical studies of the physics near the vicinity of the Mott\nlobes for $\\phi = 1/2$ and $\\phi = 1/4$. At $\\phi = 1/2$, the superfluid ground\nstate has commensurate density-wave order. At $\\phi = 1/4$, incompressible\nphases appear outside the Mott lobes at densities $n = 1.125$ and $n = 1.25$,\ncorresponding to filling fractions $\\nu = 1/2$ and $1$ respectively. These\nphases, which are absent in single-site mean-field theory are metastable, and\nhave slightly higher energy than the superfluid, but the energy difference\nbetween them shrinks rapidly with increasing cluster size, suggestive of an\nincompressible ground state. We thus explore the interplay between Mott\nphysics, magnetic Landau levels, and superfluidity, finding a rich phase\ndiagram of competing compressible and incompressible states.",
        "positive": "Dipolar polaritons squeezed at unitarity: Interaction of dipolar polaritons can be efficiently tuned by means of a\nshape resonance in their excitonic component. Provided the resonance width is\nlarge, a squeezed population of strongly interacting polaritons may persist on\nthe repulsive side of the resonance. We derive an analytical expression for the\npolariton coupling constant and show that it may have very large values in\ntypical experimental conditions. Our arguments provide a new direction for the\nquest of interactions in quantum photonics."
    },
    {
        "anchor": "Distinguishing phases using the dynamical response of driven-dissipative\n  light-matter systems: We present a peculiar transition triggered by infinitesimal dissipation in\nthe interpolating Dicke-Tavis-Cummings model. The model describes a ubiquitous\nlight-matter setting using a collection of two-level systems interacting with\nquantum light trapped in an optical cavity. In a previous work [Phys. Rev.\nLett. 120, 183603 (2018)], dissipation was shown to extend a normal phase (dark\nstate) into new regions of the model's parameter space. Harnessing Keldysh's\naction formalism to compute the response function of the light, we show that\nthe normal phase does not merely spread but encompasses a transition between\nthe old and the dissipation-stabilized regimes of the normal phase. This\ntransition, however, solely manifests in the dynamical fluctuations atop the\nempty cavity, through stabilization of an excited state of the closed system.\nConsequently, we reveal that the fluctuations flip from being particlelike to\nholelike across this transition. This inversion is also accompanied by the\nbehavior of the Liouvillian eigenvalues akin to exceptional points. Our work\nforges the way to discovering transitions in a wide variety of\ndriven-dissipative systems and is highly pertinent for current experiments.",
        "positive": "Infinitely-long-range nonlocal potentials and the Bose-Einstein\n  supersolid phase: It is shown, with the aid of the Bogoliubov inequality, that a Bose-Einstein\ncondensate has the Bloch form and represents a self-organized supersolid\nprovided the interaction between the condensate atoms is nonlocal and of\ninfinitely long-range."
    },
    {
        "anchor": "Bose-Einstein Condensation of $^{88}$Sr Through Sympathetic Cooling with\n  $^{87}$Sr: We report Bose-Einstein condensation of $^{88}$Sr, which has a small,\nnegative s-wave scattering length ($a_{88}=-2$\\,$a_0$). We overcome the poor\nevaporative cooling characteristics of this isotope by sympathetic cooling with\n$^{87}$Sr atoms. $^{87}$Sr is effective in this role in spite of the fact that\nit is a fermion because of the large ground state degeneracy arising from a\nnuclear spin of $I=9/2$, which reduces the impact of Pauli blocking of\ncollisions. We observe a limited number of atoms in the condensate\n($N_{max}\\approx 10^4$) that is consistent with the value of $a_{88}$ and the\noptical dipole trap parameters.",
        "positive": "Dynamical structure factor of one-dimensional Bose gases: experimental\n  signatures of beyond-Luttinger liquid physics: Interactions are known to have dramatic effects on bosonic gases in one\ndimension (1D). Not only does the ground state transform from a condensate-like\nstate to an effective Fermi sea, but new fundamental excitations, which do not\nhave any higher-dimensional equivalents, are predicted to appear. In this work,\nwe trace these elusive excitations via their effects on the dynamical structure\nfactor of 1D strongly-interacting Bose gases at low temperature. An array of 1D\nBose gases is obtained by loading a $^{87}$Rb condensate in a 2D lattice\npotential. The dynamical structure factor of the system is probed by energy\ndeposition through low-momentum Bragg excitations. The experimental signals are\ncompared to recent theoretical predictions for the dynamical structure factor\nof the Lieb-Liniger model at $T > 0$. Our results demonstrate that the main\ncontribution to the spectral widths stems from the dynamics of the\ninteraction-induced excitations in the gas, which cannot be described by the\nLuttinger liquid theory."
    },
    {
        "anchor": "Creating two-dimensional bright solitons in dipolar Bose-Einstein\n  condensates: We propose a realistic experimental setup for creating quasi-two-dimensional\n(2D) bright solitons in dipolar Bose-Einstein condensates (BECs), the existence\nof which was proposed in Phys. Rev. Lett. 100, 090406 (2008). A challenging\nfeature of the expected solitons is their strong inherent anisotropy, due to\nthe necessary in-plane orientation of the local moments in the dipolar gas.\nThis may be the first chance of making multidimensional matter-wave solitons,\nas well as solitons featuring the anistropy due to their intrinsic dynamics.\nOur analysis is based on the extended Gross-Pitaevskii equation, which includes\nthree-body losses and noise in the scattering length, induced by fluctuations\nof currents inducing the necessary magnetic fields, which are factors crucial\nto the adequate description of experimental conditions. By means of systematic\n3D simulations, we find a ramping scenario for the change of the scattering\nlength and trap frequencies which results in the creation of robust solitons,\nthat readily withstand the concomitant excitation of the condensate.",
        "positive": "Trap and population imbalanced two-component Fermi gas in the BEC limit: We study equal mass population imbalanced two-component atomic Fermi gas with\nunequal trap frequencies $(\\omega_{\\uparrow} \\neq \\omega_{\\downarrow})$ at zero\ntemperature using the local density approximation (LDA). We consider the\nstrongly attracting Bose-Einstein condensation (BEC) limit where polarized\n(gapless) superfluid is stable. The system exhibits shell structure:\nunpolarized SF$\\to$polarized SF$\\to$normal N. Compared to trap symmetric case,\nwhen the majority component is tightly confined the gapless superfluid shell\ngrows in size leading to reduced threshold polarization to form polarized\n(gapless) superfluid core. In contrast, when the minority component is tightly\nconfined, we find that the superfluid phase is dominated by unpolarized\nsuperfluid phase with gapless phase forming a narrow shell. The shell radii for\nvarious phases as a function of polarization at different values of trap\nasymmetry are presented and the features are explained using the phase diagram."
    },
    {
        "anchor": "Confinement induced impurity states in spin chains: Quantum simulators hold the promise of probing central questions of\nhigh-energy physics in tunable condensed matter platforms, for instance the\nphysics of confinement. Local defects can be an obstacle in these setups\nharming their simulation capabilities. However, defects in the form of\nimpurities can also be useful as probes of many-body correlations and may lead\nto fascinating new phenomena themselves. Here, we investigate the interplay\nbetween impurity and confinement physics in a basic spin chain setup, showing\nthe emergence of new exotic excitations as impurity-meson bound states with a\nlong lifetime. For weak confinement, semiclassical approximations can describe\nthe capture process in a meson-impurity scattering event. In the\nstrong-confining regime, intrinsic quantum effects are visible through the\nquantization of the emergent bound state energies which can be readily probed\nin quantum simulators.",
        "positive": "Flux enhanced localization and reentrant delocalization in the quantum\n  walk of interacting bosons on two-leg ladder: We study the quantum walk of two bosons possessing onsite repulsive\ninteraction on a two-leg ladder and show that the presence of uniform flux\npiercing through the plaquettes of the ladder favors the localization of the\nbound states in the dynamics. We find that when the two bosons are\nsymmetrically initialized on the edge rung of the ladder, they tend to\nedge-localize in their quantum walk - a phenomenon which is not possible in the\nabsence of flux. On the other hand, when the bosons are initialized on the bulk\nrung they never localize and exhibit linear spreading in their quantum walk.\nInterestingly, however, we find that in the later case a finite flux favours\nlocalization of the bulk bound states in the presence of sufficiently weak\nquasiperiodic disorder which is otherwise insufficient to localize the\nparticles in the absence of flux. In both the cases, we obtain that the\nlocalization in the dynamics strongly depends on the combined effect of the\nflux and interaction strengths, as a result which we obtain a signature of\nre-entrant delocalization as a function of flux (interaction) for fixed\ninteraction (flux) strengths."
    },
    {
        "anchor": "Simulation of the many-body dynamical quantum Hall effect in an optical\n  lattice: We propose an experimental scheme to simulate the many-body dynamical quantum\nHall effect with ultra-cold bosonic atoms in a one-dimensional optical lattice.\nWe first show that the required model Hamiltonian of a spin-1/2 Heisenberg\nchain with an effective magnetic field and tunable parameters can be realized\nin this system. For dynamical response to ramping the external fields, the\nquantized plateaus emerge in the Berry curvature of the interacting atomic spin\nchain as a function of the effective spin-exchange interaction. The\nquantization of this response in the parameter space with the\ninteraction-induced topological transition characterizes the many-body\ndynamical quantum Hall effect. Furthermore, we demonstrate that this phenomenon\ncan be observed in practical cold-atom experiments with numerical simulations.",
        "positive": "Non-universal bound states of two identical heavy fermions and one light\n  particle: We study the behavior of the bound state energy of a system consisting of two\nidentical heavy fermions of mass M and a light particle of mass m. The heavy\nfermions interact with the light particle through a short-range two-body\npotential with positive s-wave scattering length a_s. We impose a short-range\nboundary condition on the logarithmic derivative of the hyperradial\nwavefunction and show that, in the regime where Efimov states are absent, a\nnon-universal three-body state \"cuts through\" the universal three-body states\npreviously described by Kartavtsev and Malykh [O. I. Kartavtsev and A. V.\nMalykh, J. Phys. B 40, 1429 (2007)]. The presence of the non-universal state\nalters the behavior of the universal states in certain regions of the parameter\nspace. We show that the existence of the non-universal state is predicted\naccurately by a simple quantum defect theory model that utilizes hyperspherical\ncoordinates. An empirical two-state model is employed to quantify the coupling\nof the non-universal state to the universal states."
    },
    {
        "anchor": "Observation of spin-exchange dynamics between itinerant and localized\n  $^{171}\\mathrm{Yb}$ atoms: We report on the observation of the spin-exchange dynamics of\n$^{171}\\mathrm{Yb}$ atoms in the ground state $^1\\mathrm{S}_0$ and in the\nmetastable state $^3\\mathrm{P}_0$. We implement the mixed-dimensional\ntwo-orbital system using a near-resonant and magic-wavelength optical lattices,\nwhere the $^1\\mathrm{S}_0$ and $^3\\mathrm{P}_0$ atoms are itinerant in a\none-dimensional tube and localized in three dimensions, respectively. By\nexploiting an optical Stern-Gerlach method, we observe the spin depolarization\nof the $^1\\mathrm{S}_0$ atoms induced by the spin-exchange interaction with the\n$^3\\mathrm{P}_0$ atom. Our work could open the way to the quantum simulation of\nthe Kondo effect.",
        "positive": "A path integral Monte Carlo method for R\u00e9nyi entanglement entropies: We introduce a quantum Monte Carlo algorithm to measure the R\\'enyi\nentanglement entropies in systems of interacting bosons in the continuum. This\napproach is based on a path integral ground state method that can be applied to\ninteracting itinerant bosons in any spatial dimension with direct relevance to\nexperimental systems of quantum fluids. We demonstrate how it may be used to\ncompute spatial mode entanglement, particle partitioned entanglement, and the\nentanglement of particles, providing insights into quantum correlations\ngenerated by fluctuations, indistinguishability and interactions. We present\nproof-of-principle calculations, and benchmark against an exactly soluble model\nof interacting bosons in one spatial dimension. As this algorithm retains the\nfundamental polynomial scaling of quantum Monte Carlo when applied to\nsign-problem-free models, future applications should allow for the study of\nentanglement entropy in large scale many-body systems of interacting bosons."
    },
    {
        "anchor": "Contact and Structure Factor for Bosonic and Fermionic Mixtures: We study measurable quantities of bosonic and fermionic mixtures on a\none-dimensional ring. These few-body ensembles consist of majority atoms\nobeying certain statistics (Fermi or Bose) and an impurity atom in a different\nhyperfine state. The repulsive interactions between majority-impurity and\nmajority-majority are varied from weak to strong. We show that the\nmajority-impurity repulsion is mainly responsible for the loss of coherence in\nthe strongly interacting regime. The momentum distribution follows the\n$\\mathcal{C}/p^4$ universal behaviour for the high momentum tail, but the\ncontact $\\mathcal{C}$ is strongly dependent on the strength of the\nmajority-impurity and in a different way on the majority-majority interactions.\nThe static structure factor of the majority atoms exposes a low-momentum peak\nfor strong majority-impurity repulsion, which is attributed to an effective\nattraction not expected for purely repulsive forces.",
        "positive": "Pairing instabilities in quasi-two-dimensional Fermi gases: We study non-equilibrium dynamics of ultracold two-component Fermi gases in\nlow-dimensional geometries after the interactions are quenched from weakly\ninteracting to strongly interacting regime. We develop a T-matrix formalism\nthat takes into account the interplay between Pauli blocking and tight\nconfinement in low-dimensional geometries. We employ our formalism to study the\nformation of molecules in quasi-two-dimensional Fermi gases near Feshbach\nresonance and show that the rate at which molecules form depends strongly on\nthe transverse confinement. Furthermore, Pauli blocking gives rise to a sizable\ncorrection to the binding energy of molecules."
    },
    {
        "anchor": "Realizing bright matter-wave soliton collisions with controlled relative\n  phase: We propose a method to split the ground state of an attractively interacting\natomic Bose-Einstein condensate into two bright solitary waves with controlled\nrelative phase and velocity. We analyze the stability of these waves against\ntheir subsequent re-collisions at the center of a cylindrically symmetric,\nprolate harmonic trap as a function of relative phase, velocity, and trap\nanisotropy. We show that the collisional stability is strongly dependent on\nrelative phase at low velocity, and we identify previously unobserved\noscillations in the collisional stability as a function of the trap anisotropy.\nAn experimental implementation of our method would determine the validity of\nthe mean field description of bright solitary waves, and could prove an\nimportant step towards atom interferometry experiments involving bright\nsolitary waves.",
        "positive": "Trajectory Characters of Rogue Waves: We present a simple representation for arbitrary-order rogue wave solution\nand study on the trajectories of them explicitly. We find that the global\ntrajectories on temporal-spatial distribution all look like \"X\" shape for rogue\nwaves. Short-time prediction on rogue wave can be done through measuring the\ninformation contained in the initial perturbation twice."
    },
    {
        "anchor": "Unconventional pairings of spin-orbit coupled attractive degenerate\n  Fermi gas in a one dimensional optical lattice: Understanding novel pairings in attractive degenerate Fermi gases is crucial\nfor exploring rich superfluid physics. In this report, we reveal unconventional\npairings induced by spin-orbit coupling (SOC) in a one-dimensional optical\nlattice, using a state-of-the-art density-matrix renormalization group method.\nWhen both bands are partially occupied, we find a strong competition between\nthe interband Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) and intraband\nBardeen-Cooper-Schrieffer (BCS) pairings. In particular, for the weak and\nmoderate SOC strengths, these two pairings can coexist, giving rise to a new\nphase called the FFLO-BCS phase, which exhibits a unique three-peak structure\nin pairing momentum distribution. For the strong SOC strength, the intraband\nBCS pairing always dominates in the whole parameter regime, including the half\nfilling. We figure out the whole phase diagrams as functions of filling factor,\nSOC strength, and Zeeman field. Our results are qualitatively different from\nrecent mean-field predictions. Finally, we address that our predictions could\nbe observed in a weaker trapped potential.",
        "positive": "Bose-Einstein Condensation and Symmetry Breaking of a Complex Charged\n  Scalar Field: In this work the Klein-Gordon (KG) equation for a complex scalar field with\nU(1) symmetry endowed in a mexican-hat scalar field potential with thermal and\nelectromagnetic contributions is written as a Gross-Pitaevskii (GP)-like\nequation. This equation is interpreted as a charged generalization of the GP\nequation at finite temperatures found in previous works. Its hydrodynamical\nrepresentation is obtained and the corresponding thermodynamical properties are\nderived and related to measurable quantities. The condensation temperature in\nthe non-relativistic regime associated with the aforementioned system within\nthe semiclassical approximation is calculated. Also, a generalized equation for\nthe conservation of energy for a charged bosonic gas is found when\nelectromagnetic fields are introduced, and it is studied how under certain\ncircumstances its breaking of symmetry can give some insight on the phase\ntransition of the system not just into the condensed phase but also on other\nrelated systems."
    },
    {
        "anchor": "Josephson relation for disordered superfluids: The Josephson sum rule relates the superfluid density to the condensate order\nparameter, via the infrared residue of the single-particle Green's function. We\nestablish an effective Josephson relation for disordered condensates valid upon\nensemble averaging. This relation has the merit to show explicitly how\nsuperfluidity links to the coherent density, i.e., the density of particles\nwith zero momentum. Detailed agreement is reached with perturbation theory for\nweak disorder.",
        "positive": "Macroscopic coherence between quantum condensates formed at different\n  times: We demonstrate macroscopic coherence between quantum condensates generated at\ndifferent times, separated by more than the particle dephasing time. This is\npossible due to the dressed light-matter nature of exciton-polaritons, which\ncan be injected resonantly by optical excitation at well-defined momenta. We\nshow that the build-up of coherence between condensates depends on the\ninteraction between the particles, particle density, as well as temperature\ndespite the non-equilibrium nature of the condensate, whereas the mass of the\nparticles plays no role in the condensation of resonantly injected polaritons.\nThis experiment also makes it possible for us to measure directly the large\nnonlinear phase shift resulting from the polariton-polariton interaction\nenergy. Our results provide direct evidence for coherence between different\ncondensates and demonstrate a new approach for probing their ultrafast\ndynamics, opening new directions in the study of matter coherence as well as in\npractical applications such as quantum information and ultrafast logic."
    },
    {
        "anchor": "Controlled generation of momentum states in a high-finesse ring cavity: A Bose-Einstein condensate in a high-finesse ring cavity scatters the photons\nof a pump beam into counterpropagating cavity modes, populating a\nbi-dimensional momentum lattice. A high-finesse ring cavity with a sub-recoil\nlinewidth allows to control the quantized atomic motion, selecting particular\ndiscrete momentum states and generating atom-photon entanglement. The\nsemiclassical and quantum model for the 2D collective atomic recoil lasing\n(CARL) are derived and the superradiant and good-cavity regimes discussed. For\npump incidence perpendicular to the cavity axis, the momentum lattice is\nsymmetrically populated. Conversely, for oblique pump incidence the motion\nalong the two recoil directions is unbalanced and different momentum states can\nbe populated on demand by tuning the pump frequency.",
        "positive": "Atom Pairing in Optical Superlattices: We study the pairing of fermions in a one-dimensional lattice of tunable\ndouble-well potentials using radio-frequency spectroscopy. The spectra reveal\nthe coexistence of two types of atom pairs with different symmetries. Our\nmeasurements are in excellent quantitative agreement with a theoretical model,\nobtained by extending the Green's function method of Orso et al., [Phys. Rev.\nLett. 95, 060402 (2005)], to a bichromatic 1D lattice with finite harmonic\nradial confinement. The predicted spectra comprise hundreds of discrete\ntransitions, with symmetry-dependent initial state populations and transition\nstrengths. Our work provides an understanding of the elementary pairing states\nin a superlattice, paving the way for new studies of strongly interacting\nmany-body systems."
    },
    {
        "anchor": "Fractional photon-assisted tunneling for Bose-Einstein condensates in a\n  double well: Half-integer photon-resonances in a periodically shaken double well are\ninvestigated on the level of the N-particle quantum dynamics. Contrary to\nnon-linear mean-field equations, the linear N-particle Schrodinger equation\ndoes not contain any non-linearity which could be the origin of such\nresonances. Nevertheless, analytic calculations on the N-particle level explain\nwhy such resonances can be observed even for particle numbers as low as N = 2.\nThese calculations also demonstrate why fractional photon resonances are not\nrestricted to half-integer values.",
        "positive": "The Gross-Pitaevskii Soliton: Relating Weakly and Strongly Repulsive\n  Bosonic condensates and the magnetic soliton: We show that the dark soliton of the Gross-Pitaevskii equation (GPE) that\ndescribes the Bose-Einstein condensate (BEC) density of a system of weakly\nrepulsive bosons, also describes that of a system of strongly repulsive hard\ncore bosons at half filling. This connection establishes a relationship between\nthe GPE soliton and the magnetic soliton of an easy-plane ferromagnet, where\nthe BEC density relates to the square of the in-plane magnetization of the\nsystem. This mapping between well known solitons in two distinct physical\nsystems provides an intuitive understanding of various characteristics of the\nsolitons."
    },
    {
        "anchor": "SU(3) truncated Wigner approximation for strongly interacting Bose gases: We develop and utilize the SU(3) truncated Wigner approximation (TWA) in\norder to analyze far-from-equilibrium quantum dynamics of strongly interacting\nBose gases in an optical lattice. Specifically, we explicitly represent the\ncorresponding Bose--Hubbard model at an arbitrary filling factor with\nrestricted local Hilbert spaces in terms of SU(3) matrices. Moreover, we\nintroduce a discrete Wigner sampling technique for the SU(3) TWA and examine\nits performance as well as that of the SU(3) TWA with the Gaussian\napproximation for the continuous Wigner function. We directly compare outputs\nof these two approaches with exact computations regarding dynamics of the\nBose--Hubbard model at unit filling with a small size and that of a\nfully-connected spin-1 model with a large size. We show that both approaches\ncan quantitatively capture quantum dynamics on a timescale of $\\hbar/(Jz)$,\nwhere $J$ and $z$ denote the hopping energy and the coordination number. We\napply the two kinds of SU(3) TWA to dynamical spreading of a two-point\ncorrelation function of the Bose--Hubbard model on a square lattice with a\nlarge system size, which has been measured in recent experiments. Noticeable\ndeviations between the theories and experiments indicate that proper inclusion\nof effects of the spatial inhomogeneity, which is not straightforward in our\nformulation of the SU(3) TWA, may be necessary.",
        "positive": "Anharmonicity Induced Resonances for Ultracold Atoms and their Detection: When two atoms interact in the presence of an anharmonic potential, such as\nan optical lattice, the center of mass motion cannot be separated from the\nrelative motion. In addition to generating a confinement-induced resonance (or\nshifting the position of an existing Feshbach resonance), the external\npotential changes the resonance picture qualitatively by introducing new\nresonances where molecular excited center of mass states cross the scattering\nthreshold. We demonstrate the existence of these resonances, give their\nquantitative characterization in an optical superlattice, and propose an\nexperimental scheme to detect them through controlled sweeping of the magnetic\nfield."
    },
    {
        "anchor": "Exotic phases of interacting p-band bosons: We study a model of interacting bosons that occupy the first excited p-band\nstates of a two-dimensional optical lattice. In contrast to the much studied\nsingle band Bose-Hubbard Hamiltonian, this more complex model allows for\nnon-trivial superfluid phases associated with condensation at non-zero momentum\nand staggered order of the orbital angular momentum in addition to the\nsuperfluid-Mott insulator transition. More specifically, we observe staggered\norbital angular momentum order in the Mott phase at commensurate filling and\nsuperfluidity at all densities. We also observe a transition between the\nstaggered angular momentum superfluid phase and a striped superfluid, with an\nalternation of the phase of the superfluid along one direction. The transition\nbetween these two phases was observed in a recent experiment, which is then\nqualitatively well described by our model.",
        "positive": "Characterization of nonequilibrium states of trapped Bose-Einstein\n  condensates: Generation of different nonequilibrium states in trapped Bose-Einstein\ncondensates is studied by numerically solving nonlinear Schrodinger equation.\nInducing nonequilibrium states by shaking the trap, the following states are\ncreated: weak nonequilibrium, the state of vortex germs, the state of vortex\nrings, the state of straight vortex lines, the state of deformed vortices,\nvortex turbulence, grain turbulence, and wave turbulence. A characterization of\nnonequilibrium states is advanced by introducing effective temperature, Fresnel\nnumber, and Mach number."
    },
    {
        "anchor": "Trapped two-component Fermi gases with up to six particles: Energetics,\n  structural properties, and molecular condensate fraction: We investigate small equal-mass two-component Fermi gases under external\nspherically symmetric confinement in which atoms with opposite spins interact\nthrough a short-range two-body model potential. We employ a non-perturbative\nmicroscopic framework, the stochastic variational approach, and determine the\nsystem properties as functions of the interspecies s-wave scattering length a,\nthe orbital angular momentum L of the system, and the numbers N1 and N2 of\nspin-up and spin-down atoms (with N1-N2 =0 or 1 and N < 7, where N=N1+N2). At\nunitarity, we determine the energies of the five- and six-particle systems for\nvarious ranges r0 of the underlying two-body model potential and extrapolate to\nthe zero-range limit. These energies serve as benchmark results that can be\nused to validate and assess other numerical approaches. We also present\nstructural properties such as the pair distribution function and the radial\ndensity. Furthermore, we analyze the one-body and two-body density matrices. A\nmeasure for the molecular condensate fraction is proposed and applied. Our\ncalculations show explicitly that the natural orbitals and the momentum\ndistributions of atomic Fermi gases approach those characteristic for a\nmolecular Bose gas if the s-wave scattering length a, a>0, is sufficiently\nsmall.",
        "positive": "Kohn-Sham approach to Fermi gas superfluidity: the bilayer of fermionic\n  polar molecules: By using a well established 'ab initio' theoretical approach developed in the\npast to quantitatively study the superconductivity of condensed matter systems,\nwhich is based on the Kohn-Sham Density Functional theory, I study the\nsuperfluid properties and the BCS-BEC crossover of two parallel bi-dimensional\nlayers of fermionic dipolar molecules, where the pairing mechanism leading to\nsuperfluidity is provided by the inter-layer coupling between dipoles. The\nfinite temperature superfluid properties of both the homogeneous system and one\nwere the fermions in each layer are confined by a square optical lattice are\nstudied at half filling conditions, and for different values of the strength of\nthe confining optical potential. The T=0 results for the homogeneous system are\nfound to be in excellent agreement with Diffusion Monte Carlo results. The\nsuperfluid transition temperature in the BCS region is found to increase, for a\ngiven inter-layer coupling, with the strength of the confining optical\npotential. A transition occurs at sufficiently small interlayer distances,\nwhere the fermions becomes localized within the optical lattice sites in a\nsquare geometry with an increased effective lattice constant, forming a system\nof localized composite bosons. This transition should be signalled by a sudden\ndrop in the superfluid fraction of the system."
    },
    {
        "anchor": "Topological Bands for Ultracold Atoms: There have been significant recent advances in realizing bandstructures with\ngeometrical and topological features in experiments on cold atomic gases. We\nprovide an overview of these developments, beginning with a summary of the key\nconcepts of geometry and topology for Bloch bands. We describe the different\nmethods that have been used to generate these novel bandstructures for cold\natoms, as well as the physical observables that have allowed their\ncharacterization. We focus on the physical principles that underlie the\ndifferent experimental approaches, providing a conceptual framework within\nwhich to view these developments. However, we also describe how specific\nexperimental implementations can influence physical properties. Moving beyond\nsingle-particle effects, we describe the forms of inter-particle interactions\nthat emerge when atoms are subjected to these energy bands, and some of the\nmany-body phases that may be sought in future experiments.",
        "positive": "Coherently driven microcavity-polaritons and the question of\n  superfluidity: Due to their driven-dissipative nature, photonic quantum fluids present new\nchallenges in understanding superfluidity. Some associated effects have been\nobserved, and notably the report of nearly dissipationless flow for coherently\ndriven microcavity-polaritons was taken as a smoking gun for superflow. Here we\nshow that the superfluid response --- the difference between responses to\nlongitudinal and transverse forces --- is zero for coherently driven\npolaritons. This is a consequence of the gapped excitation spectrum caused by\nexternal phase locking. Furthermore, while a normal component exists at finite\npump momentum, the remainder forms a rigid state that is unresponsive to either\nlongitudinal or transverse perturbations. Interestingly, the total response\nalmost vanishes when the real part of the excitation spectrum has a linear\ndispersion, which was the regime investigated experimentally. This suggests\nthat the observed suppression of scattering should be interpreted as a sign of\nthis new rigid state and not a superfluid."
    },
    {
        "anchor": "Anisotropy in s-wave Bose-Einstein condensate collisions and its\n  relationship to superradiance: We report the experimental realization of a single-species atomic four-wave\nmixing process with BEC collisions for which the angular distribution of\nscattered atom pairs is not isotropic, despite the collisions being in the\n$s$-wave regime. Theoretical analysis indicates that this anomalous behavior\ncan be explained by the anisotropic nature of the gain in the medium. There are\ntwo competing anisotropic processes: classical trajectory deflections due to\nthe mean-field potential, and Bose enhanced scattering which bears similarity\nto super-radiance. We analyse the relative importance of these processes in the\ndynamical buildup of the anisotropic density distribution of scattered atoms,\nand compare to optically pumped super-radiance.",
        "positive": "Quantum Liquid: From the perspective of Surface Tension: We analyze the surface tension in ultra-cold atomic gases in quasi one\ndimensional and one dimensional geometry. In recent years, experimental\nobservations have confirmed the ``clustering of atoms\" to form droplets in\nultra-cold atomic gases and the emergence of this new phase is attributed to\nthe beyond mean-field interaction. However, two decades earlier, liquid\nformation was predicted due to the competition of two-body and three-body\ninteractions. Here, we review both the propositions and comment on the role of\nbeyond mean-field and three-body interaction in liquid formation by calculating\nthe surface tension."
    },
    {
        "anchor": "Split and overlapped binary solitons in optical lattices: We analyze the energetic and dynamical properties of bright-bright (BB)\nsoliton pairs in a binary mixture of Bose-Einstein condensates subjected to the\naction of a combined optical lattice, acting as an external potential for the\nfirst species, while modulating the intraspecies coupling constant of the\nsecond. In particular, we use a variational approach and direct numerical\nintegrations to investigate the existence and stability of BB solitons in which\nthe two species are either spatially separated (split soliton) or located at\nthe same optical lattice site (overlapped soliton). The dependence of these\nsolitons on the interspecies interaction parameter is explicitly investigated.\nFor repulsive interspecies interaction we show the existence of a series of\ncritical values at which transitions from an initially overlapped soliton to\nsplit solitons occur. For attractive interspecies interaction only single\ndirect transitions from split to overlapped BB solitons are found. The\npossibility to use split solitons for indirect measurements of scattering\nlengths is also suggested.",
        "positive": "Dirac Point Structure in a Bose-Einstein Condensate in a Honeycomb\n  Optical Lattice: We study the Bose-Einstein condensate in a honeycomb optical lattice within\nBogoliubov theory and find that for a ${\\bf k} = 0$ condensate, the Dirac\npoints appear in the Bogoliubov excitation spectrum when $0 < \\beta < 2$, which\nillustrates that the bose-bose interaction does not change the Dirac point\nstructure but only give a modification of the velocity of the Dirac cone. When\nthe bosons are driven to condense at ${\\bf k} = {\\bf K}$, however, we find that\nthe topology of the Dirac points will be altered by arbitrary weak interaction.\nFurthermore, we find that the next-nearest-neighbor hopping in an isotropic and\nan anisotropic lattice has different effects to the dynamics of the condensate\nand it should be taken into account when the lattice is not sufficiently deep."
    },
    {
        "anchor": "Three identical bosons: Properties in non-integer dimensions and in\n  external fields: Three-body systems that are continuously squeezed from a three-dimensional\n(3D) space into a two-dimensional (2D) space are investigated. Such a squeezing\ncan be obtained by means of an external confining potential acting along a\nsingle axis. However, this procedure can be numerically demanding, or even\nundoable, especially for large squeezed scenarios. An alternative is provided\nby use of the dimension $d$ as a parameter that changes continuously within the\nrange $2\\leq d \\leq 3$. The simplicity of the $d$-calculations is exploited to\ninvestigate the evolution of three-body states after progressive confinement.\nThe case of three identical spinless bosons with relative $s$-waves in 3D, and\na harmonic oscillator squeezing potential is considered. We compare results\nfrom the two methods and provide a translation between them, relating\ndimension, squeezing length, and wave functions from both methods. All\ncalculations are then possible entirely within the simpler $d$-method, but\nsimultaneously providing the equivalent geometry with the external potential.",
        "positive": "Solitons in One Dimensional Systems at BCS-BEC Crossover: We developed a comprehensive semiclassical theory of solitons in one\ndimensional systems at BCS-BEC crossover to provide a semiclassical explanation\nof their excitation spectra. Our semiclassical results agree well with the\nexact solutions on both the deep BCS and deep BEC side and explain\nqualitatively the smooth crossover between them. Especially, we showed that the\nminimum energy of the $S=1/2$ excitation is achieved exactly at the Fermi\nmomentum $k_F=\\pi n/2$, where $nm_F$ ($m_F$ is the mass of the fermionic atom)\nis the total mass density of the system. This momentum remains unchanged along\nthe whole crossover, whether the mass is contained in the bosonic molecules as\non the deep BEC side or in the fermionic atoms as on the deep BCS side. This\nphenomenon comes about as a result of a special feature of one dimensional\nsystems that the conventional quasiparticle is not stable with respect to\nsoliton formation. It is valid not only in exactly solvable models but also on\nthe level of semiclassical theory. Besides, we also resolved the inconsistency\nof existing semiclassical theory with the exact solution of soliton-like $S=0$\nexcitations on the deep BCS side by a new proposal of soliton configuration."
    },
    {
        "anchor": "Miscibility-Immiscibility transition of strongly interacting bosonic\n  mixtures in optical lattices: Interaction plays key role in the mixing properties of a multi-component\nsystem. The miscibility-immiscibility transition (MIT) in a weakly interacting\nmixture of Bose gases is predominantly determined by the strengths of the intra\nand inter-component two-body contact interactions. On the other hand, in the\nstrongly interacting regime interaction induced processes become relevant.\nDespite previous studies on bosonic mixtures in optical lattices, the effects\nof the interaction induced processes on the MIT remains unexplored. In this\nwork, we investigate the MIT in the strongly interacting phases of\ntwo-component bosonic mixture trapped in a homogeneous two-dimensional square\noptical lattice. Particularly we examine the transition when both the\ncomponents are in superfluid (SF), one-body staggered superfluid (OSSF) or\nsupersolid (SS) phases. Our study prevails that, similar to the contact\ninteractions, the MIT can be influenced by competing intra and inter-component\ndensity induced tunnelings and off-site interactions. To probe the MIT in the\nstrongly interacting regime, we study the extended version of the Bose-Hubbard\nmodel with the density induced tunneling and nearest-neighbouring interaction\nterms, and focus in the regime where the hopping processes are considerably\nweaker than the on-site interaction. We solve this model through\nsite-decoupling mean-field theory with Gutzwiller ansatz and characterize the\nmiscibility through the site-wise co-existence of the two-component across the\nlattice. Our study contributes to the better understanding of miscibility\nproperties of multi-component systems in the strongly interacting regime.",
        "positive": "Universality and tails of long range interactions in one dimension: Long-range interactions and, in particular, two-body potentials with\npower-law long-distance tails are ubiquitous in nature. For two bosons or\nfermions in one spatial dimension, the latter case being formally equivalent to\nthree-dimensional $s$-wave scattering, we show how generic asymptotic\ninteraction tails can be accounted for in the long-distance limit of scattering\nwave functions. This is made possible by introducing a generalisation of the\ncollisional phase shifts to include space dependence. We show that this\ndistance dependence is universal, in that it does not depend on short-distance\ndetails of the interaction. The energy dependence is also universal, and is\nfully determined by the asymptotic tails of the two-body potential. As an\nimportant application of our findings, we describe how to eliminate finite-size\neffects with long-range potentials in the calculation of scattering phase\nshifts from exact diagonalisation. We show that even with moderately small\nsystem sizes it is possible to accurately extract phase shifts that would\notherwise be plagued with finite-size errors. We also consider multi-channel\nscattering, focusing on the estimation of open channel asymptotic interaction\nstrengths via finite-size analysis."
    },
    {
        "anchor": "An ideal Josephson junction in an ultracold two-dimensional Fermi gas: The role of reduced dimensionality in high temperature superconductors is\nstill under debate. Recently, ultracold atoms have emerged as an ideal model\nsystem to study such strongly correlated 2D systems. Here, we report on the\nrealisation of a Josephson junction in an ultracold 2D Fermi gas. We measure\nthe frequency of Josephson oscillations as a function of the phase difference\nacross the junction and find excellent agreement with the sinusoidal current\nphase relation of an ideal Josephson junction. Furthermore, we determine the\ncritical current of our junction in the crossover from tightly bound molecules\nto weakly bound Cooper pairs. Our measurements clearly demonstrate phase\ncoherence and provide strong evidence for superfluidity in a strongly\ninteracting 2D Fermi gas.",
        "positive": "Interacting bosons in two-dimensional flat band systems: The Hubbard model of bosons on two dimensional lattices with a lowest flat\nband is discussed. In these systems there is a critical density, where the\nground state is known exactly and can be represented as a charge density wave.\nAbove this critical filling, depending on the lattice structure and the\ninteraction strength, the additional particles are either delocalised and\ncondensate in the ground state, or they form pairs. Pairs occur at strong\ninteractions, e.g., on the chequerboard lattice. The general mechanism behind\nthis phenomenon is discussed."
    },
    {
        "anchor": "Quantum fluctuation induced time of flight correlations of an\n  interacting trapped Bose gas: We investigate numerically the momentum correlations in a two dimensional,\nharmonically trapped interacting Bose system at $T=0$ temperature, by using a\nparticle number preserving Bogoliubov approximation. Interaction induced\nquantum fluctuations of the quasi-condensate lead to a large anti-correlation\ndip between particles of wave numbers $\\mathbf{k}$ and $-\\mathbf{k}$ for\n$|\\mathbf{k}|\\sim 1/R_c$, with $R_c$ typical size of the condensate. The\nanti-correlation dip found is a clear fingerprint of coherent quantum\nfluctuations of the condensate. In contrast, for larger wave numbers,\n$|\\mathbf{k}| >> 1/R_c$, a weak positive correlation is found between particles\nof wave numbers $\\mathbf{k}$ and $-\\mathbf{k}$, in accordance with the\nBogoliubov result for homogeneous interacting systems.",
        "positive": "Analog vacuum decay from vacuum initial conditions: Ultracold atomic gases can undergo phase transitions that mimic relativistic\nvacuum decay, allowing us to empirically test early-Universe physics in\ntabletop experiments. We investigate the physics of these analog systems, going\nbeyond previous analyses of the classical equations of motion to study quantum\nfluctuations in the cold-atom false vacuum. We show that the fluctuation\nspectrum of this vacuum state agrees with the usual relativistic result in the\nregime where the classical analogy holds, providing further evidence for the\nsuitability of these systems for studying vacuum decay. Using a suite of\nsemiclassical lattice simulations, we simulate bubble nucleation from this\nanalog vacuum state in a 1D homonuclear potassium-41 mixture, finding\nqualitative agreement with instanton predictions. We identify realistic\nparameters for this system that will allow us to study vacuum decay with\ncurrent experimental capabilities, including a prescription for efficiently\nscanning over decay rates, and show that this setup will probe the quantum\n(rather than thermal) decay regime at temperatures $T\\lesssim10\\,\\mathrm{nK}$.\nOur results help lay the groundwork for using upcoming cold-atom experiments as\na new probe of nonperturbative early-Universe physics."
    },
    {
        "anchor": "Bogoliubov-de Gennes theory of the \"snake\" instability of gray solitons\n  in higher dimensions: Gray solitons are a one-parameter family of solutions to the one-dimensional\nnon-linear Schr\\\"odinger equation (NLSE) with positive cubic nonlinearity, as\nfound in repulsively interacting dilute Bose-Einstein condensates or\nelectromagnetic waves in the visible spectrum in waveguides described by\nGross-Pitaevskii mean field theory. In two dimensions these solutions to the\nNLSE appear as a line or plane of depressed condensate density or light\nintensity, but numerical solutions show that this line is dynamically unstable\nto `snaking': the initially straight line of density or intensity minimum\nundulates with exponentially growing amplitude. To assist future studies of\nquantum mechanical instability beyond mean field theory, we here pursue an\napproximate analytical description of the snake instability within\nBogoliubov-de Gennes perturbation theory. Within this linear approximation the\ntwo-dimensional result applies trivially to three dimensions as well,\ndescribing buckling modes of the low-density plane. We extend the analytical\nresults of Kuznetsov and Turitsyn [Sov. Phys. JETP \\textbf{67}, 1583 (1988)] to\nshorter wavelengths of the `snake' modulation and show to what extent the snake\nmode can be described accurately as a parametric instability, in which the\nposition and grayness parameter of the initial soliton simply become dependent\non the transverse dimension(s). We find that the parametric picture remains\naccurate up to second order in the snaking wave number, if the snaking soliton\nis also dressed by an outward-propagating sound wave, but that beyond second\norder in the snaking wave number the parametric description breaks down.",
        "positive": "Fixed-node diffusion Monte Carlo study of the BCS-BEC crossover in a\n  bilayer system of fermionic dipoles: We investigate the BCS-BEC crossover in a bilayer system of fermionic dipoles\nat zero temperature using the fixed-node diffusion Monte Carlo technique. The\ndipoles are confined on two parallel planes separated by a distance $\\lambda$\nand are aligned perpendicular to the planes by an external field. The\ninterlayer pairing, which is responsible for the superfluid behavior of the\nsystem, crosses from a weak to a strong-coupling regime by reducing the\nseparation distance $\\lambda$. For a fixed in-plane density, equal in the two\nlayers, we calculate the ground-state energy, the chemical potential, the\npairing gap and the quasiparticle dispersion as a function of the interlayer\nseparation. At large $\\lambda$ one recovers the ground-state energy of a single\nlayer of fermions and at small $\\lambda$ the one of a single layer of composite\nbosons with twice the particle mass and the dipole moment. The superfluid gap\nvaries instead from the exponentially small BCS result to half of the large\ntwo-body binding energy in the BEC regime of strong interlayer pairing. Results\nare compared with the predictions of the simplest mean-field theory valid in\nthe low-density limit and deviations are observed both in the BCS regime, where\nin-plane repulsions are important, and in the BEC regime where the mean-field\napproach fails to describe the physics of composite dipolar bosons."
    },
    {
        "anchor": "Macroscopic excitations in confined Bose-Einstein condensates, searching\n  for quantum turbulence: We present a survey of macroscopic excitations of harmonically confined\nBose-Einstein condensates (BEC), described by Gross-Pitaevskii (GP) equation,\nin search of routes to develop quantum turbulence. These excitations can all be\ncreated by phase imprinting techniques on an otherwise equilibrium\nBose-Einstein condensate. We analyze two crossed vortices, two parallel\nanti-vortices, a vortex ring, a vortex with topological charge Q = 2, and a\ntangle of 4 vortices. Since GP equation is time-reversal invariant, we are\ncareful to distinguish time intervals in which this symmetry is preserved and\nthose in which rounding errors play a role. We find that the system tends to\nreach stationary states that may be widely classified as having either an array\nof vortices with collective excitations at different length scales or an\nagitated state composed mainly of Bogoliubov phonons.",
        "positive": "Probing the Dynamics of Spontaneous Quantum Vortices in Polariton\n  Superfluids: The experimental investigation of spontaneously created vortices is of utmost\nimportance for the understanding of quantum phase transitions towards a\nsuperfluid phase, especially for two dimensional systems that are expected to\nbe governed by the Berezinski-Kosterlitz-Thouless physics. By means of time\nresolved near-field interferometry we track the path of such vortices, created\nat random locations in an exciton-polariton condensate under pulsed\nnon-resonant excitation, to their final pinning positions imposed by the\nstationary disorder. We formulate a theoretical model that successfully\nreproduces the experimental observations."
    },
    {
        "anchor": "A comparative study of deconvolution techniques for quantum-gas\n  microscope images: Quantum-gas microscopes are used to study ultracold atoms in optical lattices\nat the single particle level. In these system atoms are localised on lattice\nsites with separations close to or below the diffraction limit. To determine\nthe lattice occupation with high fidelity, a deconvolution of the images is\noften required. We compare three different techniques, a local iterative\ndeconvolution algorithm, Wiener deconvolution and the Lucy-Richardson\nalgorithm, using simulated microscope images. We investigate how the\nreconstruction fidelity scales with varying signal-to-noise ratio, lattice\nfilling fraction, varying fluorescence levels per atom, and imaging resolution.\nThe results of this study identify the limits of singe-atom detection and\nprovide quantitative fidelities which are applicable for different atomic\nspecies and quantum-gas microscope setups.",
        "positive": "Dynamical instability of a non-equilibrium exciton-polariton condensate: By imaging single-shot realizations of an organic polariton quantum fluid, we\nobserve the long-sought dynamical instability of non-equilibrium condensates.\nWithout any free parameters, we find an excellent agreement between the\nexperimental data and a numerical simulation of the open-dissipative\nGross-Pitaevskii equation, which allows us to draw several important\nconclusions about the physics of the system. We find that the reservoir\ndynamics are in the strongly nonadiabatic regime, which renders the complex\nGinzburg-Landau description invalid. The observed transition from stable to\nunstable fluid can only be explained by taking into account the specific form\nof reservoir-mediated instability as well as particle currents induced by the\nfinite extent of the pump spot."
    },
    {
        "anchor": "Giant spin oscillations in an ultracold Fermi sea: Collective behavior in many-body systems is the origin of many fascinating\nphenomena in nature ranging from swarms of birds and modeling of human behavior\nto fundamental magnetic properties of solids. We report on the first\nobservation of collective spin dynamics in an ultracold Fermi sea with large\nspin: We observe long-lived and large-amplitude coherent spin oscillations,\ndriven by local spin interactions. At ultralow temperatures, Pauli blocking\nstabilizes the collective behavior and the Fermi sea behaves as a single entity\nin spin space. With increasing temperature, we observe a stronger damping\nassociated with particle-hole excitations. As a striking feature, we find a\nhigh-density regime where excited spin configurations are collisionally\nstabilized.",
        "positive": "Effects Beyond Center-of-Mass Separability in a Trapped Bosonic Mixture:\n  Exact Results: An exactly solvable model mimicking demixing of two Bose-Einstein condensates\nat the many-body level of theory is devised. Various properties are expressed\nin closed form along the demixing pathway and investigated. The connection\nbetween the center-of-mass coordinate and in particular the relative\ncenter-of-mass coordinate and demixing is explained. The model is also exactly\nsolvable at the mean-field level of theory, allowing thereby comparison between\nmany-body and mean-field properties. Applications are briefly discussed."
    },
    {
        "anchor": "Dynamics of binary Bose-Einstein condensate via Ehrenfest like\n  equations: Appearance of almost shape invariant states: We derive Ehrenfest like equations for the coupled Gross Pitaevskii equations\n(CGPE) which describe the dynamics of the binary Bose-Einstein condensate\n(BBEC) both in the free particle regime and in the regime where condensate is\nwell trapped. Instead of traditional variational technique, we propose a new\nEhrenfest based approach to explore so far unrevealed dynamics for CGPE and\nillustrate the possibility of almost shape invariant states in both the\nregimes. In absence of trapping potential, when all the interactions present in\nthe system are attractive, it is possible for an initially mixed Gaussian state\nto propagate with almost no change in width if the proper initial condition is\nsatisfied. Even for repulsive intra-atomic and attractive inter-atomic\ninteraction ($g_{\\alpha\\beta}$) one can tune $|g_{\\alpha\\beta}|$ such that the\nwidth of the propagating wave packet remains bounded within almost about\n$10\\%$. We also discuss the dynamics of the initially phase separated\ncondensate and have shown the breakdown of Gaussian nature of the wave packets\ndue to collisions. However, when BEC is trapped in simple harmonic\noscillator(SHO) potential, for $g_{\\alpha\\beta}>0$, it is possible for an\ninitially overlapping state to retain its initial shape if $g_{\\alpha\\beta}$ is\nless than a critical value ($g_{\\alpha\\beta}^c$). If $g_{\\alpha\\beta}$ exceeds\n$g_{\\alpha\\beta}^c$, an overlapping state can become phase separated while\nkeeping its shape unchanged.",
        "positive": "Fermionic formalism for driven-dissipative multi-level systems: We present a fermionic description of non-equilibrium multi-level systems.\nOur approach uses the Keldysh path integral formalism and allows us to take\ninto account periodic drives, as well as dissipative channels. The technique is\nbased on the Majorana fermion representation of spin-1/2 models which follows\nearlier applications in the context of spin and Kondo systems. We apply this\nformalism to problems of increasing complexity: a dissipative two-level system,\na driven-dissipative multi-level atom, and a generalized Dicke model describing\nmany multi-level atoms coupled to a single cavity. We compare our theoretical\npredictions with recent QED experiments and point out the features of a\ncounter-lasing transition. Our technique provides a convenient and powerful\nframework for analyzing driven-dissipative quantum systems, complementary to\nother approaches based on the solution of Lindblad master equations."
    },
    {
        "anchor": "Half-quantum vortex state in a spin-orbit coupled Bose-Einstein\n  condensate: We investigate theoretically the condensate state and collective excitations\nof a two-component Bose gas in two-dimensional harmonic traps subject to\nisotropic Rashba spin-orbit coupling. In the weakly interacting regime when the\ninter-species interaction is larger than the intra-species interaction\n($g_{\\uparrow\\downarrow}>g$), we find that the condensate ground state has a\nhalf-quantum-angular-momentum vortex configuration with spatial rotational\nsymmetry and skyrmion-type spin texture. Upon increasing the interatomic\ninteraction beyond a threshold $g_{c}$, the ground state starts to involve\nhigher-order angular momentum components and thus breaks the rotational\nsymmetry. In the case of $g_{\\uparrow\\downarrow}<g$, the condensate becomes\nunstable towards the superposition of two degenerate half-quantum vortex\nstates. Both instabilities (at $g>g_{c}$ and $g_{\\uparrow\\downarrow}<g$) can be\ndetermined by solving the Bogoliubov equations for collective density\noscillations of the half-quantum vortex state, and by analyzing the softening\nof mode frequencies. We present the phase diagram as functions of the\ninteratomic interactions and the spin-orbit coupling. In addition, we directly\nsimulate the time-dependent Gross-Pitaevskii equation to examine the dynamical\nproperties of the system. Finally, we investigate the stability of the\nhalf-quantum vortex state against both the trap anisotropy and anisotropy in\nthe spin-orbit coupling term.",
        "positive": "Observation of local temporal correlations in trapped quantum gases: We measure the temporal pair correlation function $g^{(2)}(\\tau)$ of a\ntrapped gas of bosons above and below the critical temperature for\nBose-Einstein condensation. The measurement is performed {\\it in situ} using a\nlocal, time-resolved single-atom sensitive probing technique. Third and fourth\norder correlation functions are also extracted. We develop a theoretical model\nand compare it with our experimental data, finding good quantitative agreement\nand highlighting the role of interactions. Our results promote temporal\ncorrelations as new observables to study the dynamics of ultracold quantum\ngases."
    },
    {
        "anchor": "An analogous Wu-Yang monopole in superfluid: By identifying the Schr\\\"{o}dinger equation with the hydrodynamic equations\nin superfluid ${^3}$He, the effective potential is introduced in the\nSchr\\\"{o}dinger equation to solve the quantum pressure in steady state. The\npure gauge velocity solutions of hydrodynamic equations provide an analogous\nWu-Yang monopole potential. The two cases of velocity in superfluid are\nequivalent to the two regions of Wu-Yang monopole potential. Due to the\ncompressibility of superfluid, the physical models are limited, such as hard\ncore and harmonic oscillator. It is important that the constraint condition of\n$\\nabla\\rho\\cdot \\textbf{v}=0$ plays a key role, which determines that the\nintegral quantum numbers are selected in monopole harmonics and shows the\nspecial analogous Wu-Yang monopole. The results provide a new possibility for\nthe simulation of Wu-Yang monopole.",
        "positive": "Bose-Einstein condensation in systems with flux equilibrium: We consider flux equilibrium in dissipative nonlinear wave systems subject to\nexternal energy pumping. In such systems, the elementary excitations, or\nquasiparticles, can create a Bose-Einstein condensate. We develop a theory on\nthe Bose-Einstein condensation of quasiparticles for various regimes of\nexternal excitation, ranging from weak and stationary to ultra-strong pumping,\nenabling us to determine the number of quasiparticles near the bottom of the\nenergy spectrum and their distribution along wave vectors. We identify physical\nphenomena leading to condensation in each of the regimes. For weak stationary\npumping, where the distribution of quasiparticles deviates only slightly from\nthermodynamic equilibrium, we define a range of pumping parameters where the\ncondensation occurs and estimate the density of the condensate and the fraction\nof the condensed quasiparticles. As the pumping amplitude increases, a powerful\ninflux of injected quasiparticles is created by the Kolmogorov-Zakharov\nscattering cascade, leading to their Bose-Einstein condensation. With even\nstronger pumping, kinetic instability may occur, resulting in a direct transfer\nof injected quasiparticles to the bottom of the spectrum. For the case of\nultra-strong parametric pumping, we have developed a stationary nonlinear\ntheory of kinetic instability. The theory agrees qualitatively with\nexperimental data obtained using Brillouin light scattering spectroscopy during\nparametric pumping of magnons in room-temperature films of yttrium-iron garnet."
    },
    {
        "anchor": "Gaussian trajectory description of fragmentation in an isolated spinor\n  condensate: Spin-1 Bose gases quenched to spin degeneracy exhibit fragmentation: the\nappearance of a condensate in more than one single-particle state. Due to its\nhighly entangled nature, the dynamics leading to this collective state are\nbeyond the scope of a Gaussian variational approximation of the many-body wave\nfunction. Here, we improve the performance of the Gaussian variational Ansatz\nby considering dissipation into a fictitious environment, effectively\nsuppressing entanglement within individual quantum trajectories at the expense\nof introducing a classical mixture of states. We find that this quantum\ntrajectory approach captures the dynamical formation of a fragmented\ncondensate, and analyze how much dissipation should be added to the experiment\nin order to keep a single realization in a non-fragmented state.",
        "positive": "Vortices in spin-orbit-coupled Bose-Einstein condensates: Realistic methods to create vortices in spin-orbit-coupled Bose-Einstein\ncondensates are discussed. It is shown that, contrary to common intuition,\nrotation of the trap containing a spin-orbit condensate does not lead to an\nequilibrium state with static vortex structures, but gives rise instead to\nnon-equilibrium behavior described by an intrinsically time-dependent\nHamiltonian. We propose here the following alternative methods to induce\nthermodynamically stable static vortex configurations: (1) to rotate both the\nlasers and the anisotropic trap; and (2) to impose a synthetic Abelian field on\ntop of synthetic spin-orbit interactions. Effective Hamiltonians for spin-orbit\ncondensates under such perturbations are derived for most currently known\nrealistic laser schemes that induce synthetic spin-orbit couplings. The\nGross-Pitaevskii equation is solved for several experimentally relevant\nregimes. The new interesting effects include spatial separation of left- and\nright-moving spin-orbit condensates, the appearance of unusual vortex\narrangements, and parity effects in vortex nucleation where the topological\nexcitations are predicted to appear in pairs. All these phenomena are shown to\nbe highly non-universal and depend strongly on a specific laser scheme and\nsystem parameters."
    },
    {
        "anchor": "Atomic Bose-Einstein condensate in a twisted-bilayer optical lattice: Observation of strong correlations and superconductivity in\ntwisted-bilayer-graphene have stimulated tremendous interest in fundamental and\napplied physics. In this system, the superposition of two twisted honeycomb\nlattices, generating a Moir$\\acute{\\mathrm{e}}$ pattern, is the key to the\nobserved flat electronic bands, slow electron velocity and large density of\nstates. Despite these observations, a full understanding of the emerging\nsuperconductivity from the coupled insulating layers and the appearance of a\nsmall magic angle remain a hot topic of research. Here, we demonstrate a\nquantum simulation platform to study superfluids in twisted bilayer lattices\nbased on Bose-Einstein condensates loaded into spin-dependent optical lattices.\nThe lattices are made of two sets of laser beams that independently address\natoms in different spin states, which form the synthetic dimension of the two\nlayers. The twisted angle of the two lattices is controlled by the relative\nangle of the laser beams. We show that atoms in each spin state only feel one\nset of the lattice and the interlayer coupling can be controlled by microwave\ncoupling between the spin states. Our system allows for flexible control of\nboth the inter- and intralayer couplings. Furthermore we directly observe the\nspatial Moir$\\acute{\\mathrm{e}}$ pattern and the momentum diffraction, which\nconfirm the presence of atomic superfluid in the bilayer lattices. Our system\nconstitutes a powerful platform to investigate the physics underlying the\nsuperconductivity in twisted-bilayer-graphene and to explore other novel\nquantum phenomena difficult to realize in materials.",
        "positive": "Stability of the singular vortex and associated Majorana zero modes in\n  trapped p-wave resonant superfluids of neutral cold atoms: The stability conditions for the singular vortex which accompanies Majorana\nzero modes at the core are investigated for p-wave resonant superfluids of\natomic Fermi gases. Within the Ginzburg-Landau framework we determine the\nstable conditions in the parameter space for the external rotation frequency\nand the harmonic trap frequency. There exists the narrow stable region in this\nparameter space for quasi-two-dimensional condensates. We also describe the\ndetailed characterizations of the spatial structure of the order parameter in\nthe chiral p-wave superfluids under rotation."
    },
    {
        "anchor": "Light-cone and diffusive propagation of correlations in a many-body\n  dissipative system: We analyze the propagation of correlations after a sudden interaction change\nin a strongly interacting quantum system in contact with an environment. In\nparticular, we consider an interaction quench in the Bose-Hubbard model, deep\nwithin the Mott-insulating phase, under the effect of dephasing. We observe\nthat dissipation effectively speeds up the propagation of single-particle\ncorrelations while reducing their coherence. In contrast, for two-point density\ncorrelations, the initial ballistic propagation regime gives way to diffusion\nat intermediate times. Numerical simulations, based on a time-dependent matrix\nproduct state algorithm, are supplemented by a quantitatively accurate\nfermionic quasi-particle approach providing an intuitive description of the\ninitial dynamics in terms of holon and doublon excitations.",
        "positive": "On quantum time crystals and interacting gauge theories in atomic\n  Bose-Einstein condensates: We study the dynamics of a Bose-Einstein condensate trapped circumferentially\non a ring, and which is governed by an interacting gauge theory. We show that\nthe associated density-dependent gauge potential and concomitant current\nnonlinearity permits a ground state in the form of a rotating chiral bright\nsoliton. This chiral soliton is constrained to move in one direction by virtue\nof the current nonlinearity, and represents a time crystal in the same vein as\nWilczek's original proposal."
    },
    {
        "anchor": "Spin-imbalance-induced transverse magnetization in the\n  Hofstadter-Hubbard model: The fermionic, time-reversal invariant Hofstadter-Hubbard model with a\npopulation difference between the two spin states is investigated. In the\nstrongly interacting regime, where the system can be described by an effective\nspin model, we find an exotic spin structure by means of classical Monte-Carlo\ncalculations. Remarkably, this spin structure exhibits a transverse net\nmagnetization perpendicular to the magnetization induced by the population\nimbalance. It is thus inherently different from canted antiferromagnetism. We\nfurther investigate effects of quantum fluctuations within the dynamical\nmean-field approximation and obtain a rich phase diagram including\nferromagnetic, anti-ferromagnetic, ferrimagnetic, and transverse magnetization\nphases.",
        "positive": "Properties of spin-polarized impurities -- ferrons, in the unitary Fermi\n  gas: A new excitation mode has been predicted to exist in the unitary Fermi gas.\nIt has a form of a spin-polarized impurity, which was dubbed as ferron. It is\ncharacterized by a closed nodal surface of the pairing field surrounding a\npartially spin-polarized superfluid region, where the phase differs by $\\pi$.\nIn this paper, we discuss the effect of temperature on the generation of the\nferron and the adiabaticity of the spin-polarizing potential together with\nferron's ground state properties."
    },
    {
        "anchor": "Driving Quantum Correlated Atom-Pairs from a Bose-Einstein Condensate: The ability to cool quantum gases into the quantum degenerate realm has\nopened up possibilities for an extreme level of quantum-state control. In this\npaper, we investigate one such control protocol that demonstrates the resonant\namplification of quasimomentum pairs from a Bose-Einstein condensate by the\nperiodic modulation of the two-body s-wave scattering length. This shows a\ncapability to selectively amplify quantum fluctuations with a predetermined\nmomentum, where the momentum value can be spectroscopically tuned. A classical\nexternal field that excites pairs of particles with the same energy but\nopposite momenta is reminiscent of the coherently-driven nonlinearity in a\nparametric amplifier crystal in nonlinear optics. For this reason, it may be\nanticipated that the evolution will generate a squeezed matter-wave state in\nthe quasiparticle mode on resonance with the modulation frequency. Our model\nand analysis is motivated by a recent experiment by Clark et al. that observed\na time-of-flight pattern similar to an exploding firework. Since the drive is a\nhighly coherent process, we interpret the observed firework patterns as arising\nfrom a monotonic growth in the two-body correlation amplitude, so that the jets\nshould contain correlated atom pairs with nearly equal and opposite momenta. We\npropose a potential future experiment based on applying Ramsey interferometry\nto experimentally probe these pair correlations.",
        "positive": "OpenMP solver for rotating spin-one spin-orbit- and Rabi-coupled\n  Bose-Einstein condensates: We present OpenMP version of a Fortran program for solving the\nGross-Pitaevskii equation for a harmonically trapped three-component rotating\nspin-1 spinor Bose-Einstein condensate (BEC) in two spatial dimensions with or\nwithout spin-orbit (SO) and Rabi couplings. The program uses either Rashba or\nDresselhaus SO coupling. We use the split-step Crank-Nicolson discretization\nscheme for imaginary- and real-time propagation to calculate stationary states\nand BEC dynamics, respectively."
    },
    {
        "anchor": "Observation of pairs of atoms at opposite momenta in an equilibrium\n  interacting Bose gas: Quantum fluctuations play a central role in the properties of quantum matter.\nIn non-interacting ensembles, they manifest as fluctuations of non-commuting\nobservables, quantified by Heisenberg inequalities. In the presence of\ninteractions, additional quantum fluctuations appear, from which many-body\ncorrelations and entanglement arise. In the context of many-body physics, the\nBogoliubov theory provides us with an illuminating microscopic picture of how\nthis occurs for weakly-interacting bosons, with the appearance of the quantum\ndepletion formed by pairs of bosons with opposite momenta. Here, we report the\nobservation of these atom pairs in the depletion of an equilibrium interacting\nBose gas. A quantitative study of atom-atom correlations, both at opposite and\nclose-by momenta, allows us to fully characterise the equilibrium many-body\nstate. We show that the atom pairs share the properties of two-mode squeezed\nstates, including relative number squeezing. Our results illustrate how\ninteracting systems acquire non-trivial quantum correlations as a result of the\ninterplay between quantum fluctuations and interactions",
        "positive": "Quantum criticality of a Bose gas in an optical lattice near the Mott\n  transition: We derive the equation of state of bosons in an optical lattice in the\nframework of the Bose-Hubbard model. Near the density-driven Mott transition,\nthe expression of the pressure P({\\mu},T) versus chemical potential and\ntemperature is similar to that of a dilute Bose gas but with renormalized mass\nm^* and scattering length a^*. m^* is the mass of the elementary excitations at\nthe quantum critical point governing the transition from the superfluid phase\nto the Mott insulating phase, while a^* is related to their effective\ninteraction at low energy. We use a nonperturbative renormalization-group\napproach to compute these parameters as a function of the ratio t/U between\nhopping amplitude and on-site repulsion."
    },
    {
        "anchor": "Hopping modulation in a one-dimensional Fermi-Hubbard Hamiltonian: We consider a strongly repulsive two-component Fermi gas in a one-dimensional\n(1D) optical lattice described in terms of a Hubbard Hamiltonian. We analyze\nthe response of the system to a periodic modulation of the hopping amplitude in\npresence of large two body interaction. By (essentially) exact simulations of\nthe time evolution, we find a non-trivial double occupancy frequency\ndependence. We show how the dependence relates to the spectral features of the\nsystem given by the Bethe ansatz. The discrete nature of the spectrum is\nclearly reflected in the double occupancy after long enough modulation time. We\nalso discuss the implications of the 1D results to experiments in higher\ndimensional systems.",
        "positive": "Effects of Interactions on Bose-Einstein Condensation: Bose-Einstein condensation is a unique phase transition in that it is not\ndriven by inter-particle interactions, but can theoretically occur in an ideal\ngas, purely as a consequence of quantum statistics. This chapter addresses the\nquestion \\emph{`How is this ideal Bose gas condensation modified in the\npresence of interactions between the particles?' } This seemingly simple\nquestion turns out to be surprisingly difficult to answer. Here we outline the\ntheoretical background to this question and discuss some recent measurements on\nultracold atomic Bose gases that have sought to provide some answers."
    },
    {
        "anchor": "Universal dynamical phase diagram of lattice spin models and strongly\n  correlated ultracold atoms in optical lattices: We study semiclassical dynamics of anisotropic Heisenberg models in two and\nthree dimensions. Such models describe lattice spin systems and hard core\nbosons in optical lattices. We solve numerically Landau-Lifshitz type equations\non a lattice and show that in the phase diagram of magnetization and\ninteraction anisotropy, one can identify several distinct regimes of dynamics.\nThese regions can be distinguished based on the character of one dimensional\nsolitonic excitations, and stability of such solitons to transverse modulation.\nSmall amplitude and long wavelength perturbations can be analyzed analytically\nusing mapping of non-linear hydrodynamic equations to KdV type equations.\nNumerically we find that properties of solitons and dynamics in general remain\nsimilar to our analytical results even for large amplitude and short distance\ninhomogeneities, which allows us to obtain a universal dynamical phase diagram.\nAs a concrete example we study dynamical evolution of the system starting from\na state with magnetization step and show that formation of oscillatory regions\nand their stability to transverse modulation can be understood from the\nproperties of solitons. In regimes unstable to transverse modulation we observe\nformation of lump type solutions with modulation in all directions. We discuss\nimplications of our results for experiments with ultracold atoms.",
        "positive": "Third-order momentum correlation interferometry maps for entangled\n  quantal states of three singly trapped massive ultracold fermions: Analytic higher-order momentum correlation functions associated with the\ntime-of-flight spectroscopy of three ultracold fermionic atoms singly-confined\nin a linear three-well optical trap are presented, corresponding to the W- and\nGreenberger-Horne-Zeilinger-type (GHZ) states that belong to characteristic\nclasses of tripartite entanglement and represent the strong-interaction regime\ncaptured by a three-site Heisenberg Hamiltonian. The methodology introduced\nhere contrasts with and goes beyond that based on the standard Wick's\nfactorization scheme; it enables determination of both third-order and\nsecond-order spin-resolved and spin-unresolved momentum correlations, aiming at\nmatter-wave interference investigations with trapped massive particles in\nanalogy with, and having the potential for expanding the scope of, recent\nthree-photon quantum-optics interferometry."
    },
    {
        "anchor": "Higgs-like Excitations of Cold Atom System with Spin-orbit Coupling: The Higgs-like excitations, which distinguish from the Higgs amplitude mode\nin many-body system, are single-particle excitations in system with non-Abelian\ngauge potential. We investigate the Higgs-like excitations of cold atom system\nin artificial non-Abelian gauge potential. We demonstrate that when a\nnon-Abelian gauge potential is reduced to Abelian potential, its Abelian part\nconstructs spin-orbit coupling, and its non-Abelian part emerges Higgs-like\nexcitations. The Higgs-like excitations induce a mass of the non-Abelian gauge\nfield, which offsets the defect of massless of the gauge theories. We show that\nthe mass of gauge field can affect the spin Hall currents which are produced by\nthe spin-orbit coupling. We also discuss the observation of these phenomena in\nreal experiment.",
        "positive": "Dynamical Casimir Effect in dissipative media: When is the final state\n  non-separable ?: We study the consequences of dissipation in homogeneous media when the system\nis subject to a sudden change, thereby producing pairs of correlated\nquasi-particles with opposite momenta. We compute both the modifications of the\nspectrum, and those of the correlations. In particular, we compute the final\ncoherence level, and identify the regimes where the state is non-separable. To\nisolate the role of dissipation, we first consider dispersive media and study\nthe competition between the intensity of the jump which induces some coherence,\nand the temperature which reduces it. The contributions of stimulated and\nspontaneous emission are clearly identified. We then study how dissipation\nmodifies this competition."
    },
    {
        "anchor": "Topological pumping of a single magnon in a one-dimensional\n  spin-dependent optical superlattice: Topological pumping of ultracold atomic gases has recently been demonstrated\nin two experiments (Nat. Phys. 12, 296; 12, 350 (2016)). Here we study the\ntopological pumping of a single magnon in a dynamically controlled\nspin-dependent optical superlattice. When the interaction between atoms is\nstrong, this system supports a dynamical version of topological magnon\ninsulator phase. By initially putting a single magnon in the superlattice and\nslowly varying the dynamical controlled parameter over one period, the shift of\nthe magnon density center is quantized and equal to the topological Chern\nnumber. Moreover, we also find that the direction of this quantized shift is\nentanglement-dependent. Our result provides a route for realizing topological\npumping of quasiparticles in strongly correlated ultracold atomic system and\nfor studying the interplay between topological pumping and quantum\nentanglement.",
        "positive": "Anderson Localization in Low-Dimensional Optical Lattices: Topic of the thesis is a theoretical description of the ultracold atomic\ngases in one- and two-dimensional optical lattices in the presence of the\ndisorder leading to the Anderson localization. The disorder is created by\ninteraction of the main fraction of atoms with the second immobilized fraction\ndistributed randomly over the lattice.\n  In low-dimensional systems there is no transition from the Anderson localized\nto the conducting phase, although in the presence of correlations a discrete\nset of extended states can exist. The first part of the thesis is devoted to\nproperties of such states. In the finite size lattices, the presence of those\nstates results in the appearance of `windows of transport' -- energy ranges, in\nwhich the localization length is longer than the system size.The analytical\nmethod of determining the extended states energies for correlations of\ngeneralized $N$-mers type is presented, along with a proof that indeed those\nstates are extended in the infinite system. Subsequently, the way of\nexperimental creation of this type of correlations is proposed, as well as the\ntechnique of generation of the disorder in the tunneling amplitudes, which\nsignificantly enhances tunability of the proposed energy filters.\n  The second part of the thesis describes the method which allows to simulate a\nspecific type of the disorder: random magnetic field. Systems of such a class,\ncreated in a two dimensional lattice using simultaneous fast periodic\nmodulation of the lattice height and interactions with immobilized species, may\nallow in future to investigate the range of topics from the condensed matter\nphysics, for example fractional quantum Hall effect at half-filling. In the\nthesis, the most interesting features observed upon investigation of such\nsystems are presented. Especially, the anomalously low localization length for\ncorrelated disorder is explained."
    },
    {
        "anchor": "Unitarity-limited behavior of three-body collisions in a p-wave\n  interacting Fermi gas: We experimentally investigate the unitarity-limited behavior of the\nthree-body loss near a p-wave Feshbach resonance in a single-component Fermi\ngas of $^6$Li atoms. At the unitarity limit, the three-body loss coefficient\n$L_{3}$ exhibits universality in the sense that it is independent of the\ninteraction strength and follows the predicted temperature scaling law of $L_3\n\\propto T^{-2}$. When decreasing the interaction strength from the unitarity\nregime, the three-body loss coefficient as a function of the interaction\nstrength and temperature can be described by the theory based on the\nassociation of an excited resonant quasibound state and its relaxation into a\ndeep stable dimer by collision with a third atom in the framework of the\nstandard Breit-Wigner theoretical approach. The results reported here are\nimportant to understand the properties of a resonant p-wave Fermi gas in the\nprospect of quantum few- and many-body physics.",
        "positive": "Quadrature interferometry for nonequilibrium ultracold bosons in optical\n  lattices: We develop an interferometric technique for making time-resolved measurements\nof field-quadrature operators for nonequilibrium ultracold bosons in optical\nlattices. The technique exploits the internal state structure of magnetic atoms\nto create two subsystems of atoms in different spin states and lattice sites. A\nFeshbach resonance turns off atom-atom interactions in one spin subsystem,\nmaking it a well-characterized reference state, while atoms in the other\nsubsystem undergo nonequilibrium dynamics for a variable hold time. Interfering\nthe subsystems via a second beam-splitting operation, time-resolved quadrature\nmeasurements on the interacting atoms are obtained by detecting relative spin\npopulations. The technique can provide quadrature measurements for a variety of\nHamiltonians and lattice geometries (e.g., cubic, honeycomb, superlattices),\nincluding systems with tunneling, spin-orbit couplings using artificial gauge\nfields, and higher-band effects. Analyzing the special case of a deep lattice\nwith negligible tunneling, we obtain the time evolution of both quadrature\nobservables and their fluctuations. As a second application, we show that the\ninterferometer can be used to measure atom-atom interaction strengths with\nsuper-Heisenberg scaling n^(-3/2) in the mean number of atoms per lattice site\nn, and standard quantum limit scaling M^(-1/2) in the number of lattice sites\nM. In our analysis, we require M >> 1 and for realistic systems n is small, and\ntherefore the scaling in total atom number N = nM is below the Heisenberg\nlimit; nevertheless, measurements testing the scaling behaviors for\ninteraction-based quantum metrologies should be possible in this system."
    },
    {
        "anchor": "Rydberg-dressed Fermi liquid: correlations and signatures of droplet\n  crystallization: We investigate the effects of many-body correlations on the ground-state\nproperties of a single component ultra-cold Rydberg-dressed Fermi liquid with\npurely repulsive inter-particle interactions, in both three and two spatial\ndimensions. We have employed the Fermi-hypernetted-chain Euler-Lagrange\napproximation and observed that the contribution of the correlation energy on\nthe ground-state energy becomes significant at intermediate values of the\nsoft-core radius and large coupling strengths. For small and large soft-core\nradii, the correlation energy is negligible and the ground-state energy\napproaches the Hartree-Fock value. The positions of the main peaks in static\nstructure factor and pair distribution function in the homogeneous fluid phase\nsignal the formation of quantum droplet crystals with several particles\nconfined inside each droplet.",
        "positive": "Supersonic flow of a Bose-Einstein condensate past an oscillating\n  attractive-repulsive obstacle: We investigate by numerical simulations the pattern formation after an\noscillating attractive-repulsive obstacle inserted into the flow of a\nBose-Einstein condensate. For slow oscillations we observe a complex emission\nof vortex dipoles. For moderate oscillations organized lined up vortex dipoles\nare emitted. For high frequencies no dipoles are observed but only lined up\ndark fragments. The results shows that the drag force turns negative for\nsufficiently high frequency. We also successfully model the {\\it ship waves} in\nfront of the obstacle. In the limit of very fast oscillations all the\nexcitations of the system tend to vanish."
    },
    {
        "anchor": "Splitting instability of a doubly quantized vortex in superfluid Fermi\n  gases: The splitting instability of a doubly-quantized vortex in the BEC-BCS\ncrossover of a superfluid Fermi gas is investigated by means of a low-energy\neffective field theory. Our linear stability analysis and non-equilibrium\nnumerical simulations reveal that the character of the instability drastically\nchanges across the crossover. In the BEC-limit, the splitting of the vortex\ninto two singly-quantized vortices occurs through the emission of phonons,\nwhile such an emission is completely absent in the BCS-limit. In the\ncrossover-regime, the instability and phonon emission are enhanced, and the\nlifetime of a doubly-quantized vortex becomes minimal. The emitted phonon can\nbe observed as a spiraling pattern amplified due to the rotational\nsuperradiance, known as a mechanism to carry away energy and angular momentum\nfrom a spinning black hole. We also investigate the influence of temperature,\npopulation imbalance, and three-dimensional effects.",
        "positive": "Mean-field approach to Rydberg facilitation in a gas of atoms at high\n  and low temperatures: The excitation spread caused by Rydberg facilitation in a gas of laser driven\natoms is an interesting model system for studying epidemic dynamics. We derive\na mean-field approach to describe this facilitation process in the limits of\nhigh and low temperatures, which takes into account Rydberg blockade and the\nnetwork character of excitation spreading in a low-temperature gas. As opposed\nto previous mean-field models, our approach accurately predicts all stages of\nthe facilitation dynamics from the initial fast epidemic growth, an extended\nsaturation period, to the final relaxation phase."
    },
    {
        "anchor": "Measurement of the Canonical Equation of State of a Weakly Interacting\n  3D Bose Gas: Using a multiple-image reconstruction method applied to a harmonically\ntrapped Bose gas, we determine the equation of state of uniform matter across\nthe critical transition point, within the local density approximation. Our\nexperimental results provide the canonical description of pressure as a\nfunction of the specific volume, emphasizing the dramatic deviations from the\nideal Bose gas behavior caused by interactions. They also provide clear\nevidence for the non-monotonic behavior with temperature of the chemical\npotential, which is a consequence of superfluidity. The measured thermodynamic\nquantities are compared to mean-field predictions available for the interacting\nBose gas. The limits of applicability of the local density approximation near\nthe critical point are also discussed, focusing on the behavior of the\nisothermal compressibility.",
        "positive": "The few-atom problem: These lectures contain a theoretical introduction to the few-body problem\nwith short-range resonant binary interactions. In the first part we discuss the\neffective range expansion for the two-body scattering amplitude emphasizing the\nrole of the resonance width. In the second part we review the Efimov effect for\nthree atoms, describe the difference in between the Efimovian and non-Efimovian\nregimes, and discuss the dependence of three-body observables on quantum\nsymmetry, mass imbalance, and resonance width. In the third part we derive the\nSkorniakov and Ter-Martirosian equation and give several illustrative examples\nof its solution."
    },
    {
        "anchor": "Measurement of the order parameter and its spatial fluctuations across\n  Bose-Einstein condensation: We investigate the strong out-of-equilibrium dynamics occurring when a\nharmonically trapped ultracold bosonic gas is evaporatively cooled across the\nBose--Einstein condensation transition. By imaging the cloud after free\nexpansion, we study how the cooling rate affects the timescales for the growth\nof the condensate order parameter and the relaxation dynamics of its spatial\nfluctuations. We find evidence of a delay on the condensate formation related\nto the collisional properties and a universal condensate growth following the\ncooling rate. Finally, we measure an exponential relaxation of the spatial\nfluctuations of the order parameter that also shows a universal scaling.\nNotably, the scaling for the condensate growth and for the relaxation of its\nfluctuations follow different power laws.",
        "positive": "Beyond-mean-field effects in mixtures: few-body and many-body aspects: The discovery of ultracold dilute liquids has significantly elevated our\ninterest in various phenomena which go under the name of beyond-mean-field\n(BMF) physics. In these lecture notes we give an elementary introduction to the\nquantum stabilization and liquefaction of a collapsing weakly interacting\nBose-Bose mixture. A detailed derivation of the leading BMF correction, also\nknown as the Lee-Huang-Yang (LHY) term, in this system is presented in a manner\nsuitable for further generalizations and extensions. Although the LHY term is a\nnonanalytic function of the density $n$, under certain conditions the leading\nBMF correction becomes analytic and can be expanded in integer powers of $n$,\neffectively introducing three-body and higher-order interactions. We discuss\nwhy and how well the Bogoliubov approach can predict these few-body\nobservables."
    },
    {
        "anchor": "Hartree-Fock Mean-Field Theory for Trapped Dirty Bosons: Here we work out in detail a non-perturbative approach to the dirty boson\nproblem, which relies on the Hartree-Fock theory and the replica method. For a\nweakly interacting Bose gas within a trapped confinement and a delta-correlated\ndisorder potential at finite temperature, we determine the underlying free\nenergy. From it we determine via extremization self-consistency equations for\nthe three components of the particle density, namely the condensate density,\nthe thermal density, and the density of fragmented local Bose-Einstein\ncondensates within the respective minima of the random potential landscape.\nSolving these self-consistency equations in one and three dimensions in two\nother publications has revealed how these three densities change for increasing\ndisorder strength.",
        "positive": "Metastable states and macroscopic quantum tunneling in a cold atom\n  Josephson ring: We study macroscopic properties of a system of weakly interacting neutral\nbosons confined in a ring-shaped potential with a Josephson junction. We derive\nan effective low energy action for this system and evaluate its properties. In\nparticular we find that the system possesses a set of metastable\ncurrent-carrying states and evaluate the rates of transitions between these\nstates due to macroscopic quantum tunneling. Finally we discuss signatures of\ndifferent metastable states in the time-of-flight images and argue that the\neffect is observable within currently available experimental technique."
    },
    {
        "anchor": "Ground states of one-dimensional dipolar lattice bosons at unit filling: Recent experiments on ultracold dipoles in optical lattices open exciting\npossibilities for the quantum simulation of extended Hubbard models. When\nconsidered in one dimension, these models present at unit filling a\nparticularly interesting ground-state physics, including a symmetry-protected\ntopological phase known as Haldane insulator. We show that the tail of the\ndipolar interaction beyond nearest-neighbors, which may be tailored by means of\nthe transversal confinement, does not only modify quantitatively the Haldane\ninsulator regime and lead to density waves of larger periods, but results as\nwell in unexpected insulating phases. These insulating phases may be\ntopological or topologically trivial, and are characterized by peculiar\ncorrelations of the site occupations. These phases may be realized and observed\nin state-of-the-art experiments.",
        "positive": "Loschmidt Echo for quantum metrology: We propose a versatile Loschmidt echo protocol to detect and quantify\nmultiparticle entanglement. It allows us to extract the quantum Fisher\ninformation for arbitrary pure states, and finds direct application in quantum\nmetrology. In particular, the protocol applies to states that are generally\ndifficult to characterize, as non-Gaussian states, and states that are not\nsymmetric under particle exchange. We focus on atomic systems, including\ntrapped ions, polar molecules, and Rydberg atoms, where entanglement is\ngenerated dynamically via long-range interaction, and show that the protocol is\nstable against experimental detection errors."
    },
    {
        "anchor": "Efficiently Extracting Multi-Point Correlations of a Floquet Thermalized\n  System: Nonequilibrium dynamics of many-body systems is challenging for classical\ncomputing, providing opportunities for demonstrating practical quantum\ncomputational advantage with analogue quantum simulators. It is proposed to be\nclassically intractable to sample driven thermalized many-body states of\nBose-Hubbard systems, and further extract multi-point correlations for\ncharacterizing quantum phases. Here, leveraging dedicated precise manipulations\nand number-resolved detection through a quantum gas microscope, we implement\nand sample a 32-site driven Hubbard chain in the thermalized phase. Multi-point\ncorrelations of up to 14th-order extracted from experimental samples offer\nclear distinctions between the thermalized and many-body-localized phases. In\nterms of estimated computational powers, the quantum simulator is comparable to\nthe fastest supercomputer with currently known best algorithms. Our work paves\nthe way towards practical quantum advantage in simulating Floquet dynamics of\nmany-body systems.",
        "positive": "Spin diffusion in ultracold spin-orbit coupled $^{40}$K gas: We investigate the steady-state spin diffusion for ultracold spin-orbit\ncoupled $^{40}$K gas by the kinetic spin Bloch equation approach both\nanalytically and numerically. Four configurations, i.e., the spin diffusions\nalong two specific directions with the spin polarization perpendicular\n(transverse configuration) and parallel (longitudinal configuration) to the\neffective Zeeman field are studied. It is found that the behaviors of the\nsteady-state spin diffusion for the four configurations are very different,\nwhich are determined by three characteristic lengths: the mean free path\n$l_{\\tau}$, the Zeeman oscillation length $l_{\\Omega}$ and the spin-orbit\ncoupling oscillation length $l_{\\alpha}$. It is analytically revealed and\nnumerically confirmed that by tuning the scattering strength, the system can be\ndivided into {\\it five} regimes: I, weak scattering regime ($l_{\\tau}\\gtrsim\nl_{\\Omega}, l_{\\alpha}$); II, Zeeman field-dominated moderate scattering regime\n($l_{\\Omega}\\ll l_{\\tau}\\ll l_{\\alpha}$); III, spin-orbit coupling-dominated\nmoderate scattering regime ($l_{\\alpha}\\ll l_{\\tau}\\ll l_{\\Omega}$); IV,\nrelatively strong scattering regime ($l_{\\tau}^c\\ll l_{\\tau}\\ll l_{\\Omega},\nl_{\\alpha}$); V, strong scattering regime ($l_{\\tau}\\ll l_{\\Omega},\nl_{\\alpha},l_{\\tau}^c$), with $l_{\\tau}^c$ representing the crossover length\nbetween the relatively strong and strong scattering regimes. In different\nregimes, the behaviors of the spacial evolution of the steady-state spin\npolarization are very rich, showing different dependencies on the scattering\nstrength, Zeeman field and spin-orbit coupling strength. The rich behaviors of\nthe spin diffusions in different regimes are hard to be understood in the\nframework of the simple drift-diffusion model or the direct inhomogeneous\nbroadening picture in the literature. ..."
    },
    {
        "anchor": "Spin-Orbit Coupling Induced Coherent Production of Feshbach Molecules in\n  a Degenerate Fermi Gas: In this work we demonstrate a dynamic process in which SO coupling can\ncoherently produce s-wave Feshbach molecules from a fully polarized Fermi gas,\nand can induce a coherent oscillation between Feshbach molecules and spin\npolarized gas. For comparison, we also show that such phenomena are absent if\nthe inter-component coupling is momentum-independent. This demonstrates\nexperimentally that SO coupling does provide finite matrix element between a\nsinglet state and a triplet state, and therefore, implies the bound pairs of a\nsystem with SO coupling have triplet p-wave component, which can become\ntopological superfluid by further cooling these pairs to condensation and\nconfining them to lower dimension.",
        "positive": "Band Gap Closing in a Synthetic Hall Tube of Neutral Fermions: We report the experimental realization of a synthetic three-leg Hall tube\nwith ultracold fermionic atoms in a one-dimensional optical lattice. The legs\nof the synthetic tube are composed of three hyperfine spin states of the atoms,\nand the cyclic inter-leg links are generated by two-photon Raman transitions\nbetween the spin states, resulting in a uniform gauge flux $\\phi$ penetrating\neach side plaquette of the tube. Using quench dynamics, we investigate the band\nstructure of the Hall tube system for a commensurate flux $\\phi=2\\pi/3$.\nMomentum-resolved analysis of the quench dynamics reveals that a critical point\nof band gap closing as one of the inter-leg coupling strengths is varied, which\nis consistent with a topological phase transition predicted for the Hall tube\nsystem."
    },
    {
        "anchor": "su(N) Mermin-Ho relation: The Mermin-Ho relation expresses the vorticity of a coreless su(2) vortex in\nterms of the spin-1 or l vector which characterizes fully polarized superfluid\ntextures. We generalize it to an su(N) vortex which is applicable to\narbitrarily polarized superfluid textures with higher spin or angular momentum.\nThe obtained relation is expressed in terms of the mean-field generators and\ntheir structure factors.",
        "positive": "Symmetry-protected Bose-Einstein condensation of interacting hardcore\n  Bosons: We introduce a mechanism stabilizing a one-dimensional quantum many-body\nphase, characterized by a certain wave vector $k_0$, from a $k_0$-modulated\ncoupling to a center site, via the protection of an emergent $\\mathbb Z_2$\nsymmetry. We illustrate this mechanism by constructing the solution of the full\nquantum many-body problem of hardcore bosons on a wheel geometry, which are\nknown to form a Bose-Einstein condensate. The robustness of the condensate is\nshown numerically by adding nearest-neighbor interactions to the wheel\nHamiltonian. We identify the energy scale that controls the protection of the\nemergent $\\mathbb Z_2$ symmetry. We discuss further applications such as\ngeometrically inducing finite-momentum condensates. Since our solution strategy\nis based on a generic mapping from a wheel geometry to a projected ladder, our\nanalysis can be applied to various related problems with extensively scaling\ncoordination numbers."
    },
    {
        "anchor": "Adiabatic Preparation of a Heisenberg Antiferromagnet Using an Optical\n  Superlattice: We analyze the possibility to prepare a Heisenberg antiferromagnet with cold\nfermions in optical lattices, starting from a band insulator and adiabatically\nchanging the lattice potential. The numerical simulation of the dynamics in 1D\nallows us to identify the conditions for success, and to study the influence\nthat the presence of holes in the initial state may have on the protocol. We\nalso extend our results to two-dimensional systems.",
        "positive": "Large-$N$ expansion for condensation and stability of Bose-Bose mixtures\n  at finite temperatures: The two-component mixture of Bose particles with short-range pairwise\ninteraction at finite temperatures in three dimensions is considered.\nParticularly we examine, by means of the large-$N$ expansion technique, the\nstability of mixed state below the Bose-Einstein transition point and the\ntemperature dependence of the condensate density for symmetric mixture of Bose\ngases. The presented analysis reveals the importance of finite-temperature\nexcitations of the non-condensed particles in formation of the phase diagram of\ntwo-component Bose systems."
    },
    {
        "anchor": "Exact solutions to the spin-2 Gross-Pitaevskii equations: We present several exact solutions to the coupled nonlinear Gross-Pitaevskii\nequations which describe the motion of the one-dimensional spin-2 Bose-Einstein\ncondensates. The nonlinear density-density interactions are decoupled by making\nuse of the properties of Jacobian elliptical functions. The distinct time\nfactors in each hyperfine state implies a \"Lamor\" procession in these\nsolutions. Furthermore, exact time-evolving solutions to the time-dependent\nGross-Pitaevskii equations are constructed through the spin-rotational symmetry\nof the Hamiltonian. The spin-polarizations and density distributions in the\nspin-space are analyzed.",
        "positive": "1D quasicrystals and topological markers: Local topological markers are effective tools for determining the topological\nproperties of both homogeneous and inhomogeneous systems. The Chern marker is\nan established topological marker that has previously been shown to effectively\nreveal the topological properties of 2D systems. In an earlier work, the\npresent authors have developed a marker that can be applied to 1D\ntime-dependent systems which can be used to explore their topological\nproperties, like charge pumping under the presence of disorder. In this paper,\nwe show how to alter the 1D marker so that it can be applied to quasiperiodic\nand aperiodic systems. We then verify its effectiveness against different\nquasicrystal Hamiltonians, some which have been addressed in previous studies\nusing existing methods, and others which possess topological structures that\nhave been largely unexplored. We also demonstrate that the altered 1D marker\ncan be productively applied to systems that are fully aperiodic."
    },
    {
        "anchor": "Resonant Manipulation of d-wave Interaction of Cold Atoms with Two\n  Lasers and a Magnetic Field: We present a theory for manipulation of d-wave interaction of cold atoms with\ntwo lasers strongly driving two photoassociative transitions. The theory\npredicts the occurrence of a coherence between two excited ro-vibrational bound\nstates due to the photoassociative dipole-couplings of ground-state d-wave\nscattering state to the bound states. We show that this excited-state coherence\nsignificantly influences atom-atom interaction. In particular, this leads to\nthe enhancement of d-wave elastic scattering and to the suppression of\ninelastic scattering. In the presence of an s-wave magnetic Feshbach resonance,\nthe two lasers can couple the s-wave resonance with the d-wave scattering state\nleading to the further enhancement in d-wave scattering at relatively low\nenergy. Our numerical calculations based on realistic parameters show that\nd-wave manipulation would be most effective in case of atoms having excited\ndiatomic states with narrow natural linewidth. We estimate that at 100 $\\mu$K\nthe inelastic scattering rate in Yb can be reduced to 20 s$^{-1}$ while the\nelastic scattering rate can be two orders of magnitude larger.",
        "positive": "Revealing Hidden Antiferromagnetic Correlations in Doped Hubbard Chains\n  via String Correlators: Topological phases, like the celebrated Haldane phase in spin-1 chains, defy\ncharacterization through local order parameters. Instead, non-local string\norder parameters can be employed to reveal their hidden order. Similar diluted\nmagnetic correlations appear in doped one-dimensional lattice systems due to\nthe phenomenon of spin-charge separation. Here we report on the direct\nobservation of such hidden magnetic correlations via quantum gas microscopy of\nhole-doped ultracold Fermi-Hubbard chains. The measurement of non-local\nspin-density correlation functions reveals a hidden finite-range\nantiferromagnetic order, a direct consequence of spin-charge separation. Our\ntechnique demonstrates how topological order can directly be measured in\nexperiments and it can be extended to higher dimensions to study the complex\ninterplay between magnetic order and density fluctuations."
    },
    {
        "anchor": "Energy bands and Landau levels of ultracold fermions in the bilayer\n  honeycomb optical lattice: We investigate the spectrum and eigenstates of ultracold fermionic atoms in\nthe bilayer honeycomb optical lattice. In the low energy approximation, the\ndispersion relation has parabolic form and the quasiparticles are chiral. In\nthe presence of the effective magnetic field, which is created for the system\nwith optical means, the energy spectrum shows an unconventional Landau level\nstructure. Furthermore, the experimental detection of the spectrum is proposed\nwith the Bragg scattering techniques.",
        "positive": "Magnetism of one-dimensional strongly repulsive spin-1 bosons with\n  antiferromagnetic spin exchange interaction: We investigate magnetism and quantum phase transitions in a one-dimensional\nsystem of integrable spin-1 bosons with strongly repulsive density-density\ninteraction and antiferromagnetic spin exchange interaction via the\nthermodynamic Bethe ansatz method. At zero temperature, the system exhibits\nthree quantum phases: (i) a singlet phase of boson pairs when the external\nmagnetic field $H$ is less than the lower critical field $H_{c1}$; (ii) a\nferromagnetic phase of atoms in the hyperfine state $|F=1, m_{F}=1>$ when the\nexternal magnetic field exceeds the upper critical field $H_{c2}$; and (iii) a\nmixed phase of singlet pairs and unpaired atoms in the intermediate region\n$H_{c1}<H<H_{c2}$. At finite temperatures, the spin fluctuations affect the\nthermodynamics of the model through coupling the spin bound states to the\ndressed energy for the unpaired $m_{F}=1$ bosons. However, such spin dynamics\nis suppressed by a sufficiently strong external field at low temperatures. Thus\nthe singlet pairs and unpaired bosons may form a two-component Luttinger liquid\nin the strong coupling regime."
    },
    {
        "anchor": "Non-stationary vortex ring in a Bose-Einstein condensate with Gaussian\n  density: The local induction equation, approximately describing dynamics of a\nquantized vortex filament in a trapped Bose-Einstein condensate in the\nThomas-Fermi regime on a spatially nonuniform density background $\\rho({\\bf\nr})$ and taking dimensionless form ${\\mathbf R}_t=\\varkappa {\\mathbf\nb}+[\\nabla\\ln\\rho({\\mathbf R})\\times {\\boldsymbol \\tau}]$ (where $\\varkappa$ is\na local curvature of the filament, ${\\mathbf b}$ is the unit binormal vector,\nand ${\\boldsymbol \\tau}$ is the unit tangent vector), is shown to admit a\nfinite-dimensional reduction if the density profile is an isotropic Gaussian,\n$\\rho\\propto\\exp(-|{\\bf r}|^2/2)$. The reduction corresponds to a geometrically\nperfect vortex ring centered at position ${\\bf A}(t)$, with orientation and\nsize both determined by a vector ${\\bf B}(t)$. Parameters ${\\bf A}$ and ${\\bf\nB}$ exhibit the same dynamics as velocity and position of a Newtonian particle\ndo in 3D: $\\dot {\\bf A}={\\bf B}/|{\\bf B}|^2-{\\bf B}$, and $\\dot {\\bf B}={\\bf\nA}$.",
        "positive": "Ground-state energy and excitation spectrum of the Lieb-Liniger model :\n  accurate analytical results and conjectures about the exact solution: We study the ground-state properties and excitation spectrum of the\nLieb-Liniger model, i.e. the one-dimensional Bose gas with repulsive contact\ninteractions. We solve the Bethe-Ansatz equations in the thermodynamic limit by\nusing an analytic method based on a series expansion on orthogonal polynomials\ndeveloped in \\cite{Ristivojevic} and push the expansion to an unprecedented\norder. By a careful analysis of the mathematical structure of the series\nexpansion, we make a conjecture for the analytic exact result at zero\ntemperature and show that the partially resummed expressions thereby obtained\ncompete with accurate numerical calculations. This allows us to evaluate the\ndensity of quasi-momenta, the ground-state energy, the local two-body\ncorrelation function and Tan's contact. Then, we study the two branches of the\nexcitation spectrum. Using a general analysis of their properties and\nsymmetries, we obtain novel analytical expressions at arbitrary interaction\nstrength which are found to be extremely accurate in a wide range of\nintermediate to strong interactions."
    },
    {
        "anchor": "Many-body interferometry of magnetic polaron dynamics: The physics of quantum impurities coupled to a many-body environment is among\nthe most important paradigms of condensed matter physics. In particular, the\nformation of polarons, quasiparticles dressed by the polarization cloud, is key\nto the understanding of transport, optical response, and induced interactions\nin a variety of materials. Despite recent remarkable developments in ultracold\natoms and solid-state materials, the direct measurement of their ultimate\nbuilding block, the polaron cloud, has remained a fundamental challenge. We\npropose and anlalyze a unique platform to probe time-resolved dynamics of\npolaron-cloud formation with an interferometric protocol. We consider an\nimpurity atom immersed in a two-component Bose-Einstein condensate, where the\nimpurity generates spin-wave excitations that can be directly measured by the\nRamsey interference of surrounding atoms. The dressing by spin waves leads to\nthe formation of magnetic polarons and reveals a unique interplay between few-\nand many-body physics that is signified by single- and multi-frequency\noscillatory dynamics corresponding to the formation of many-body bound states.\nFinally, we discuss concrete experimental implementations in ultracold atoms.",
        "positive": "Dissipative fluid dynamics for the dilute Fermi gas at unitarity: Free\n  expansion and rotation: We investigate the expansion dynamics of a dilute Fermi gas at unitarity in\nthe context of dissipative fluid dynamics. Our aim is to quantify the effects\nof shear viscosity on the time evolution of the system. We compare exact\nnumerical solutions of the equations of viscous hydrodynamics to various\napproximations that have been proposed in the literature. Our main findings\nare: i) Shear viscosity leads to characteristic features in the expansion\ndynamics; ii) a quantitative description of these effects has to include\nreheating; iii) dissipative effects are not sensitive to the equation of state\nP(n,T) as long as the universal relation P=(2/3)E is satisfied; iv) the\nexpansion dynamics mainly constrains the cloud average of the shear viscosity."
    },
    {
        "anchor": "Deep inelastic collision of two-dimensional anisotropic dipolar\n  condensate solitons: The possibility of generating stable anisotropic solitons in dipolar\nBose-Einstein condensates (BECs) leads to a different scenario not possible in\na nondipolar BEC with contact interaction. We study the statics and dynamics of\nanisotropic bright solitons in quasi-two-dimensional BECs consisting of\npolarized dipolar atoms.We study the collision dynamics of two such solitons at\ndifferent velocities for different angles between the polarization and\ncollision directions. The collision is found to be quasi elastic at large\nvelocities. At small velocities the collision is inelastic leading to the\nformation of a coalesced soliton in an excited scissors mode, monopole mode or\nquadrupole mode. Also, at small velocities, after collision, a large change of\ndirection of motion of the solitons is possible. The investigation is performed\nthrough a numerical solution of the underlying mean-field Gross-Pitaevskii\nequation.",
        "positive": "The physics of dipolar bosonic quantum gases: This article reviews the recent theoretical and experimental advances in the\nstudy of ultracold gases made of bosonic particles interacting via the\nlong-range, anisotropic dipole-dipole interaction, in addition to the\nshort-range and isotropic contact interaction usually at work in ultracold\ngases. The specific properties emerging from the dipolar interaction are\nemphasized, from the mean-field regime valid for dilute Bose-Einstein\ncondensates, to the strongly correlated regimes reached for dipolar bosons in\noptical lattices."
    },
    {
        "anchor": "Recovering quantum correlations in optical lattices from interaction\n  quenches: Quantum simulations with ultra-cold atoms in optical lattices open up an\nexciting path towards understanding strongly interacting quantum systems. Atom\ngas microscopes are crucial for this as they offer single-site density\nresolution, unparalleled in other quantum many-body systems. However, currently\na direct measurement of local coherent currents is out of reach. In this work,\nwe show how to achieve that by measuring densities that are altered in response\nto quenches to non-interacting dynamics, e.g., after tilting the optical\nlattice. For this, we establish a data analysis method solving the closed set\nof equations relating tunnelling currents and atom number dynamics, allowing to\nreliably recover the full covariance matrix, including off-diagonal terms\nrepresenting coherent currents. The signal processing builds upon semi-definite\noptimization, providing bona fide covariance matrices optimally matching the\nobserved data. We demonstrate how the obtained information about non-commuting\nobservables allows to lower bound entanglement at finite temperature which\nopens up the possibility to study quantum correlations in quantum simulations\ngoing beyond classical capabilities.",
        "positive": "Two dipolar atoms in a harmonic trap: Two identical dipolar atoms moving in a harmonic trap without an external\nmagnetic field are investigated. Using the algebra of angular momentum a semi -\nanalytical solutions are found. We show that the internal spin - spin\ninteractions between the atoms couple to the orbital angular momentum causing\nan analogue of Einstein - de Haas effect. We show a possibility of\nadiabatically pumping our system from the s-wave to the d-wave relative motion.\nThe effective spin-orbit coupling occurs at anti-crossings of the energy\nlevels."
    },
    {
        "anchor": "Temperature induced decay of persistent currents in a superfluid\n  ultracold gas: We study how temperature affects the lifetime of a quantized, persistent\ncurrent state in a toroidal Bose-Einstein condensate (BEC). When the\ntemperature is increased, we find a decrease in the persistent current\nlifetime. Comparing our measured decay rates to simple models of thermal\nactivation and quantum tunneling, we do not find agreement. We also measured\nthe size of hysteresis loops size in our superfluid ring as a function of\ntemperature, enabling us to extract the critical velocity. The measured\ncritical velocity is found to depend strongly on temperature, approaching the\nzero temperature mean-field solution as the temperature is decreased. This\nindicates that an appropriate definition of critical velocity must incorporate\nthe role of thermal fluctuations, something not explicitly contained in\ntraditional theories.",
        "positive": "Towards a kinetic theory of a dark soliton gas in one-dimensional\n  superfluids: Soliton hydrodynamics is an appealing tool to describe strong turbulence in\nlow-dimensional systems. Strong turbulence in quasi-one dimensional\nspuerfluids, such as Bose-Einstein condensates, involves the dynamics of dark\nsolitons and, therefore, the description of a statistical ensemble of\ndark-solitons, i.e. soliton gases, is necessary. In this work, we propose a\nphase-space (kinetic) description of dark-soliton gases, introducing a kinetic\nequation that is formally similar to the Vlasov equation in plasma physics. We\nshow that the proposed kinetic theory can capture the dynamical features of\nsoliton gases and show that it sustains an acoustic mode, a fact that we\ncorroborate with the help of direct numerical simulations. Our findings\nmotivate the investigation of the microscopic structure of out-of-equilibrium\nand turbulent regimes in low-dimensional superfluids."
    },
    {
        "anchor": "Regularization of fluctuations near the sonic horizon due to the quantum\n  potential and its influence on the Hawking radiation: We consider dynamics of fluctuations in transonically accelerating\nBose-Einstein condensates and luminous liquids (coherent light propagating in a\nKerr nonlinear medium) using the hydrodynamic approach. It is known that\nneglecting the quantum potential (QP) leads to a singular behavior of quantum\nand classical fluctuations in the vicinity of the Mach (sonic) horizon, which\nin turn gives rise to the Hawking radiation. The neglect of QP is well founded\nat not too small distances $|x| \\gg l_h$ from the horizon, where $l_h$ is the\nhealing length. Taking the QP into account we show that a second characteristic\nlength $l_r > l_h$ exists, such that the linear fluctuation modes become\nregularized for $|x| \\ll l_r$. At $|x| \\gg l_r$ the modes keep their singular\nbehavior, which however is influenced by the QP. As a result we find a\ndeviation of the high frequency tail of the spectrum of Hawking radiation from\nPlanck's black body radiation distribution. Similar results hold for the wave\npropagation in Kerr nonlinear media where the length $l_h$ and $l_r$ exist due\nto the nonlinearity.",
        "positive": "Self-Accelerating Matter Waves: The free particle Schrodinger equation admits a non-trivial self-accelerating\nAiry wave packet solution. Recently, the Airy beams that freely accelerate in\nspace was experimentally realized in photonics community. Here we present\nself-accelerating waves for the Bose-Einstein condensate in a time dependent\nharmonic oscillator potential. We show that parity and time reversal symmetries\nfor self accelerating waves are spontaneously broken."
    },
    {
        "anchor": "Effect of boson on-site repulsion on the superfluidity in the\n  boson-fermion-Hubbard model: We analyze the finite-temperature phase diagram of the boson-fermion-Hubbard\nmodel with Feshbach converting interaction, using the coherent-state\npath-integral method. We show that depending on the position of the bosonic\nband, this type of interaction, even if weak, can drive the system into the\nresonant superfluid phase in the strong bosonic interaction limit. It turns out\nthat this phase can exist for an arbitrary number of fermions (i.e., fermionic\nconcentration between 0 and 2) but with the bosonic particle number very close\nto an integer value. We point out that the standard time-of-flight method in\noptical lattice experiments can be an adequate technique to confirm the\nexistence of this resonant phase. Moreover, in the non-resonant regime, the\nenhancement of the critical temperature of the superfluid phase due to Feshbach\ninteraction is also observed. We account for this interesting phenomena for a\nhole- or particlelike pairing mechanism depending on the system density and\nmutual location of the fermionic and bosonic bands.",
        "positive": "A classification of the ground states and topological defects in a\n  rotating two-component Bose-Einstein condensate: We classify the ground states and topological defects of a rotating\ntwo-component condensate when varying several parameters: the intracomponent\ncoupling strengths, the intercomponent coupling strength and the particle\nnumbers.No restriction is placed on the masses or trapping frequencies of the\nindividual components. We present numerical phase diagrams which show the\nboundaries between the regions of coexistence, spatial separation and symmetry\nbreaking. Defects such as triangular coreless vortex lattices, square coreless\nvortex lattices and giant skyrmions are classified. Various aspects of the\nphase diagrams are analytically justified thanks to a non-linear $\\sigma$ model\nthat describes the condensate in terms of the total density and a pseudo-spin\nrepresentation."
    },
    {
        "anchor": "Antiferrosmectic ground state of two-component dipolar Fermi gases -- an\n  analog of meson condensation in nuclear matter: We show that an antiferrosmectic-C phase has lower energy at high densities\nthan the non-magnetized Fermi gas and ferronematic phases in an ultracold gas\nof fermionic atoms, or molecules, with large magnetic dipole moments. This\nphase, which is analogous to meson condensation in dense nuclear matter, is a\none-dimensional periodic structure in which the fermions localize in layers\nwith their pseudospin direction aligned parallel to the layers, and staggered\nlayer by layer.",
        "positive": "Experimental verification of a reversed Clausius inequality in an\n  isolated system: The second law of thermodynamics is a fundamental law of Nature. It is almost\nuniversally associated with the Clausius inequality that lower bounds a change\nin entropy by the ratio of supplied heat and temperature. However, this result\npresupposes that a system is in contact with a heat bath that drives it to a\nthermal state. For isolated systems that are moved from an initial equilibrium\nstate by a dissipative heat exchange, the Clausius inequality has been\npredicted to be reversed. We here experimentally investigate the nonequilibrium\nthermodynamics of an isolated dilute gas of ultracold Cesium atoms that can be\neither thermalized or pushed out of equilibrium by means of laser cooling\ntechniques. We determine in both cases the phase-space dynamics by tracing the\nevolution of the gas with position-resolved fluorescence imaging, from which we\nevaluate all relevant thermodynamic quantities. Our results confirm the\nvalidity of the usual Clausius inequality for the first process and of the\nreversed Clausius inequality for the second transformation."
    },
    {
        "anchor": "$n$-body anti-bunching in a degenerate Fermi gas of $^3$He* atoms: A key observable in investigations into quantum systems are the $n$-body\ncorrelation functions, which provide a powerful tool for experimentally\ndetermining coherence and directly probing the many-body wavefunction. While\nthe (bosonic) correlations of photonic systems are well explored, the\ncorrelations present in matter-wave systems, particularly for fermionic atoms,\nare still an emerging field. In this work, we use the unique single-atom\ndetection properties of $^3$He* atoms to perform simultaneous measurements of\nthe $n$-body quantum correlations, up to the fifth-order, of a degenerate Fermi\ngas. In a direct demonstration of the Pauli exclusion principle, we observe\nclear anti-bunching at all orders and find good agreement with predicted\ncorrelation volumes. Our results pave the way for using correlation functions\nto probe some of the rich physics associated with fermionic systems, such as\nd-wave pairing in superconductors.",
        "positive": "No hair theorems for analogue black holes: We show that transonic one dimensional flows which are analogous to black\nholes obey no-hair theorems both at the level of linear perturbations and in\nnon-linear regimes. Considering solutions of the Gross-Pitaevskii (or\nKorteweg-de Vries) equation, we show that stationary flows which are\nasymptotically uniform on both sides of the horizon are stable and act as\nattractors. Using Whitham's modulation theory, we analytically characterize the\nemitted waves when starting from uniform perturbations. Numerical simulations\nconfirm the validity of this approximation and extend the results to more\ngeneral perturbations and to the (non-integrable) cubic-quintic\nGross-Pitaevskii equation. When considering time reversed flows that correspond\nto white holes, the asymptotically uniform flows are unstable to sufficiently\nlarge perturbations and emit either a macroscopic undulation in the supersonic\nside, or a non-linear superposition of soliton trains."
    },
    {
        "anchor": "SU(4)-symmetric Hubbard model at quarter filling: Insights from the\n  dynamical mean-field approach: We apply the dynamical mean-field approach to the four-component\nSU(4)-symmetric Fermi-Hubbard model to study transitions between different\nmagnetically ordered phases as well as the hysteresis behavior in the unordered\nregime. At quarter filling (one particle per site) on the square lattice we\nidentify both the two-sublattice and plaquette-ordered antiferromagnetic phases\nwith the corresponding entropy-driven hierarchy for critical temperatures. We\nalso analyze the behavior of thermodynamic characteristics: the local double\noccupancy, compressibility, and entropy per particle, which are relevant for\nexperiments with ultracold alkaline-earth(-like) atoms in optical lattices.",
        "positive": "Expansion dynamics of Bose-Einstein condensates in a synthetic magnetic\n  field: We investigate the expansion dynamics of spin-orbit-coupled Bose-Einstein\ncondensates subjected to a synthetic magnetic field, after their release from\nan external harmonic trap. Our findings reveal that the condensate experiences\na spin-dependent rotation and separation due to the rigid-like rotational\nvelocity field, which leads to a spin density deflection. The deflection angle\nreaches a peak at a time that is inversely related to the frequency of the\nharmonic trap. When the detuning gradient is below a critical value for vortex\nnucleation, our analytical results derived from a spinor hydrodynamic theory\nalign closely with numerical results using the coupled Gross-Pitaevskii\nequations. Beyond this critical value, we also numerically simulated the\nexpansion dynamics of the condensates containing vortices with negative\ncirculation. Our findings highlight the pivotal role of the rigid-like\nrotational velocity field on the dynamics of the condensate and may stimulate\nfurther experimental investigations into the rich superfluid dynamics induced\nby synthetic magnetic fields."
    },
    {
        "anchor": "Stability of a flattened dipolar binary condensate: emergence of the\n  spin roton: We develop theory for a two-component miscible dipolar condensate in a planar\ntrap. Using numerical solutions and a variational theory we solve for the\nexcitation spectrum and identify regimes where density- and spin-roton\nexcitations are favored. We characterize the various instabilities that can\nemerge in this system over a wide parameter regime and present results for the\nstability phase diagram. Importantly this allows us to identify the parameter\nregimes where a novel roton-immiscibility transition can occur, driven by the\nsoftening of the spin roton excitation.",
        "positive": "Electronic pair alignment and roton feature in the warm dense electron\n  gas: The study of matter under extreme densities and temperatures as they occur\ne.g. in astrophysical objects and nuclear fusion applications has emerged as\none of the most active frontiers in physics, material science, and related\ndisciplines. In this context, a key quantity is given by the dynamic structure\nfactor $S(\\mathbf{q},\\omega)$, which is probed in scattering experiments -- the\nmost widely used method of diagnostics at these extreme conditions. In addition\nto its crucial importance for the study of warm dense matter, the modelling of\nsuch dynamic properties of correlated quantum many-body systems constitutes one\nof the most fundamental theoretical challenges of our time. Here we report a\nhitherto unexplained \\emph{roton feature} in $S(\\mathbf{q},\\omega)$ of the warm\ndense electron gas, and introduce a microscopic explanation in terms of a new\n\\emph{electronic pair alignment} model. This new paradigm will be highly\nimportant for the understanding of warm dense matter, and has a direct impact\non the interpretation of scattering experiments. Moreover, we expect our\nresults to give unprecedented insights into the dynamics of a number of\ncorrelated quantum many-body systems such as ultracold helium, dipolar\nsupersolids, and bilayer heterostructures."
    },
    {
        "anchor": "Winding real and order-parameter spaces via lump solitons of spinor BEC\n  on sphere: The three condensate wavefunctions of a spinor BEC on a spherical shell can\nmap the real space to the order-parameter space that also has a spherical\ngeometry, giving rise to topological excitations called lump solitons. The\nhomotopy of the mapping endows the lump solitons with quantized winding numbers\ncounting the wrapping between the two spaces. We present several lump-soliton\nsolutions to the nonlinear coupled equations minimizing the energy functional.\nThe energies of the lump solitons with different winding numbers indicate\ncoexistence of lumps with different winding numbers and a lack of advantage to\nbreak a higher-winding lump soliton into multiple lower-winding ones. Possible\nimplications are discussed since the predictions are testable in cold-atom\nexperiments.",
        "positive": "Continuous-wave solutions and modulational instability in spinor\n  condensates of positronium: We obtain general continuous-wave (CW)\\ solutions in the model of a spinor\npositronium condensate in the absence of magnetic field. The CW solutions with\nboth in-phase ($n=0$) and out-of-phase ($n=1$) spin components exist, with\ntheir ranges limited by the total particle density, $\\rho $. In the limit of\nnegligible population exchange between the spin components, the CW solutions\nare found to be stable or unstable, depending on the particle density of the\npara positronium. Ortho positronium, in the $F=1$ spinor state, forms a\nferromagnetic condensate with stable in-phase CW solutions only. Subsequent\nexamination of the modulational instability (MI) is carried out both in the\nlimit case of identical wavenumbers in the spin components, $% \\Delta k\\equiv\nk_{1}-k_{-1}=0$, and in the more general case of $\\Delta k\\neq 0$ too. The CW\nsolutions with $n=0$ and $1$ solutions, which are stable in the case of $\\Delta\nk=0$, are unstable for $\\Delta k\\neq 0$, for the natural repulsive sign of the\nnonlinearities. The total particle density, $\\rho $, in the limit of $\\Delta\nk=0$ is found to have a significant role for the stability of the condensate,\nwhich is determined by the sign of the self-interaction nonlinearity."
    },
    {
        "anchor": "Precursor phenomena of nucleations of quantized vortices in the presence\n  of a uniformly moving obstacle in Bose-Einstein condensates: We investigate excitations and fluctuations of Bose-Einstein condensates in a\ntwo-dimensional torus with a uniformly moving Gaussian potential by solving the\nGross-Pitaevskii equation and the Bogoliubov equation. The energy gap $\\Delta$\nbetween the current-flowing metastable state (that reduces to the ground state\nfor sufficiently slowly-moving potential) and the first excited state vanishes\nwhen the moving velocity $v$ of the potential approaches a critical velocity\nv_c(>0). We find a scaling law $\\Delta \\propto (1-|v|/v_c)^{1/4}$, which\nimplies that a characteristic time scale diverges toward the critical velocity.\nNear the critical velocity, we show that low-energy local density fluctuations\nare enhanced. These behaviors can be regarded as precursor phenomena of the\nvortex nucleation.",
        "positive": "Universal description of three two-component fermions: A quantum mechanical three-body problem for two identical fermions of mass\n$m$ and a distinct particle of mass $m_1$ in the universal limit of zero-range\ntwo-body interaction is studied. For the unambiguous formulation of the problem\nin the interval $\\mu_r < m/m_1 \\le \\mu_c$ ($\\mu_r \\approx 8.619$ and $\\mu_c\n\\approx 13.607$) an additional parameter $b$ determining the wave function near\nthe triple-collision point is introduced; thus, a one-parameter family of\nself-adjoint Hamiltonians is defined. The dependence of the bound-state\nenergies on $m/m_1$ and $b$ in the sector of angular momentum and parity $L^P =\n1^-$ is calculated and analysed with the aid of a simple model."
    },
    {
        "anchor": "Tuning the Chern number and Berry curvature with spin-orbit coupling and\n  magnetic textures: We obtain the band structure of a particle moving in a magnetic spin texture,\nclassified by its chirality and structure factor, in the presence of spin-orbit\ncoupling. This rich interplay leads to a variety of novel topological phases\ncharacterized by the Berry curvature and their associated Chern numbers. We\nsuggest methods of experimentally exploring these topological phases by Hall\ndrift measurements of the Chern number and Berry phase interferometry to map\nthe Berry curvature.",
        "positive": "Pseudogap phenomenon and effects of population imbalance in the normal\n  state of a unitary Fermi gas: We investigate strong-coupling corrections to single-particle excitations in\nthe normal state of a spin-polarized unitary Fermi gas. Within the framework of\nan extended T-matrix approximation, we calculate the single-particle density of\nstates, as well as the single-particle spectral weight, to show that the\nso-called pseudogap phenomenon gradually disappears with increasing the\nmagnitude of an effective magnetic field. In the highly spin-polarized regime,\nthe calculated spin-polarization rate as a function of the effective magnetic\nfield agrees well with the recent experiment on a 6Li Fermi gas. Although this\nexperiment has been considered to be incompatible with the existence of the\npseudogap in an unpolarized Fermi gas, our result clarifies that the observed\nspin-polarization rate in the highly spin-polarized regime and the pseudogap in\nthe unpolarized limit can be explained in a consistent manner, when one\ncorrectly includes effects of population imbalance on single-particle\nexcitations. Since it is a crucial issue to clarify whether the pseudogap\nexists or not in the BCS (Bardeen-Cooper-Schrieffer)-BEC (Bose-Einstein\ncondensation) crossover regime of an ultracold Fermi gas, our results would be\nuseful for the understanding of this strongly interacting fermion system."
    },
    {
        "anchor": "On the observability of Pauli crystals: The best known manifestation of the Fermi-Dirac statistics is the Pauli\nexclusion principle: no two identical fermions can occupy the same one-particle\nstate. This principle enforces high order correlations in systems of many\nidentical fermions and is responsible for a particular geometric arrangement of\ntrapped particles even when all mutual interactions are absent [1]. These\ngeometric structures, called Pauli crystals, are predicted for a system of $N$\nidentical atoms trapped in a harmonic potential. They emerge as the most\nfrequent configurations in a collection of single-shot pictures of the system.\nHere we study how fragile Pauli crystals are when realistic experimental\nlimitations are taken into account. The influence of the number of single-shots\npictures available to analysis, thermal fluctuations and finite efficiency of\ndetection are considered. The role of these sources of noise on the possibility\nof experimental observation of Pauli crystals is shown and conditions necessary\nfor the detection of the geometrical arrangements of particles are identified.",
        "positive": "One-dimensional matter waves as a multi-state bit: We design a technique to control the position of a localized matter wave. Our\nsystem is composed by a two counter-phased periodic potentials and a third\noptical lattice which can be chosen to be either periodic or disordered. The\nonly control needed on the system is a three-state switch that allows the\ninstantaneous selection of the desired potential. We show that this framework\nis robust and the multi-state bit behavior can be observed under generic\nhypothesis."
    },
    {
        "anchor": "Low-Dimensional Fluctuations and Pseudogap in Gaudin-Yang Fermi Gases: Pseudogap is a ubiquitous phenomenon in strongly correlated systems such as\nhigh-$T_{\\rm c}$ superconductors, ultracold atoms and nuclear physics. While\npairing fluctuations inducing the pseudogap are known to be enhanced in\nlow-dimensional systems, such effects have not been explored well in one of the\nmost fundamental 1D models, that is, Gaudin-Yang model. In this work, we show\nthat the pseudogap effect can be visible in the single-particle excitation in\nthis system using a diagrammatic approach. Fermionic single-particle spectra\nexhibit a unique crossover from the double-particle dispersion to pseudogap\nstate with increasing the attractive interaction and the number density at\nfinite temperature. Surprisingly, our results of thermodynamic quantities in\nunpolarized and polarized gases show an excellent agreement with the recent\nquantum Monte Carlo and complex Langevin results, even in the region where the\npseudogap appears.",
        "positive": "Momentum-Resolved Bragg Spectroscopy in Optical Lattices: Strongly correlated many-body systems show various exciting phenomena in\ncondensed matter physics such as high-temperature superconductivity and\ncolossal magnetoresistance. Recently, strongly correlated phases could also be\nstudied in ultracold quantum gases possessing analogies to solid-state physics,\nbut moreover exhibiting new systems such as Fermi-Bose mixtures and magnetic\nquantum phases with high spin values. Particularly interesting systems here are\nquantum gases in optical lattices with fully tunable lattice and atomic\ninteraction parameters. While in this context several concepts and ideas have\nalready been studied theoretically and experimentally, there is still great\ndemand for new detection techniques to explore these complex phases in detail.\n  Here we report on measurements of a fully momentum-resolved excitation\nspectrum of a quantum gas in an optical lattice by means of Bragg spectroscopy.\nThe bandstructure is measured with high resolution at several lattice depths.\nInteraction effects are identified and systematically studied varying density\nand excitation fraction."
    },
    {
        "anchor": "Classical fields and quantum measurement for Bose-Einstein condensate: We analyze a process of splitting of the Bose-Einstein condensate and the\nmutual coherence of two separated atomic clouds. Within the classical fields\napproximation we show that coherence between clouds is degraded if atoms\ninteract and if we account for the sufficiently long observation time. We also\nshow, that upon recombination, the coherence across the sample is restored. The\ncoherence is not fully degraded if the splitting potential remains sufficiently\npenetrable. We calculate the variance of atom number difference for this\ntime-averaging measurement and show that for low temperatures it can be well\nbelow Poissonian limit like it was observed in the experiments.",
        "positive": "Roton spectroscopy in a harmonically trapped dipolar Bose-Einstein\n  condensate: We study a harmonically trapped Bose-Einstein condensate with dipole-dipole\ninteractions in a regime where a roton spectrum emerges. We show that the roton\nspectrum is clearly revealed in the static and dynamic structure factors which\ncan be measured using Bragg spectroscopy. We develop and validate a theory\nbased on the local density approximation for the dynamic structure factor."
    },
    {
        "anchor": "Phases, many-body entropy measures and coherence of interacting bosons\n  in optical lattices: Already a few bosons with contact interparticle interactions in small optical\nlattices feature a variety of quantum phases: superfluid, Mott-insulator and\nfermionized Tonks gases can be probed in such systems. To detect these phases\n-- pivotal for both experiment and theory -- as well as their many-body\nproperties we analyze several distinct measures for the one-body and many-body\nShannon information entropies. We exemplify the connection of these entropies\nwith spatial correlations in the many-body state by contrasting them to the\nGlauber normalized correlation functions. To obtain the ground-state for\nlattices with commensurate filling (i.e. an integer number of particles per\nsite) for the full range of repulsive interparticle interactions we utilize the\nmulticonfigurational time-dependent Hartree method for bosons (MCTDHB) in order\nto solve the many-boson Schr\\\"odinger equation. We demonstrate that all\nemergent phases -- the superfluid, the Mott insulator, and the fermionized gas\ncan be characterized equivalently by our many-body entropy measures and by\nGlauber's normalized correlation functions. In contrast to our many-body\nentropy measures, single-particle entropy cannot capture these transitions.",
        "positive": "Bose-Einstein condensates in multiple well potentials from a variational\n  path integral: We apply a path integral variational approach to obtain analytical\nexpressions for condensate wave functions of an ultracold, interacting trapped\nBose gases. As in many recent experiments, the particles are confined in a 1D\nor 3D harmonic oscillator trap which is superimposed by a periodic potential in\none direction. Based on the first order cumulant expansion with respect to a\nharmonic trial action, and emplyoing a mean-field approximation, optimal\nvariational parameters are obtained by minimizing an analytical expression for\nthe ground state energy. Our largely analytical results for energy and\ncondensate wave function are in good agreement with fully numerical\ncalculations based on the Gross-Pitaevskii equation."
    },
    {
        "anchor": "Mesoscopic superpositions of Tonks-Girardeau states and the Bose-Fermi\n  mapping: We study a one dimensional gas of repulsively interacting ultracold bosons\ntrapped in a double-well potential as the atom-atom interactions are tuned from\nzero to infinity. We concentrate on the properties of the excited states which\nevolve from the so-called NOON states to the NOON Tonks-Girardeau states. The\nrelation between the latter and the Bose-Fermi mapping limit is explored. We\nstate under which conditions NOON Tonks-Girardeau states, which are not\npredicted by the Bose-Fermi mapping, will appear in the spectrum.",
        "positive": "Vortices and vortex states in Rashba spin-orbit-coupled condensates: The Rashba spin-orbit coupling is equivalent to the finite Yang-Mills flux of\na static SU(2) gauge field. It gives rise to the protected edge states in\ntwo-dimensional topological band-insulators, much like magnetic field yields\nthe integer quantum Hall effect. An outstanding question is which collective\ntopological behaviors of interacting particles are made possible by the Rashba\nspin-orbit coupling. Here we addresses one aspect of this question by exploring\nthe Rashba SU(2) analogues of vortices in superconductors. Using the\nLandau-Ginzburg approach and conservation laws, we classify the prominent\ntwo-dimensional condensates of two- and three-component spin-orbit-coupled\nbosons, and characterize their vortex excitations. There are two prominent\ntypes of condensates that take advantage of the Rashba spin-orbit coupling.\nTheir vortices exist in multiple flavors whose number is determined by the spin\nrepresentation, and interact among themselves through logarithmic or linear\npotentials as a function of distance. The vortices that interact linearly\nexhibit confinement and asymptotic freedom similar to quarks in quantum\nchromodynamics. One of the two condensate types supports small metastable\nneutral quadruplets of vortices, and their tiles as metastable vortex lattices.\nQuantum melting of such vortex lattices could give rise to non-Abelian\nfractional topological insulators, SU(2) analogues of fractional quantum Hall\nstates. The physical systems in which these states could exist are trapped two-\nand three-component bosonic ultra-cold atoms subjected to artificial gauge\nfields, as well as solid-state quantum wells made either from Kondo insulators\nsuch as SmB$_6$ or conventional topological insulators interfaced with\nconventional superconductors."
    },
    {
        "anchor": "Strong-coupling expansion for the spin-1 Bose-Hubbard model: In this study, we perform a strong-coupling expansion up to third order of\nthe hopping parameter $t$ for the spin-1 Bose--Hubbard model with\nantiferromagnetic interaction. As expected from previous studies, the Mott\ninsulator phase is considerably more stable against the superfluid phase when\nfilling with an even number of bosons than when filling with an odd number of\nbosons. The phase-boundary curves are consistent with the perturbative\nmean-field theory in the limit of infinite dimensions. The critical value of\nthe hopping parameter $t_{\\rm C}$ at the peak of the Mott lobe depends on the\nantiferromagnetic interaction. This result indicates the reliability of the\nstrong coupling expansion when $U_2$ possesses large (intermediate) values for\nMott lobe with an even (odd) number of bosons. Moreover, in order to improve\nour results, we apply a few extrapolation methods up to infinite order in $t$.\nThe fitting results of the phase-boundary curves agree better with those of the\nperturbative mean-field approximation. In addition, the linear fit error of\n$t_{\\rm C}$ is very small for the strong antiferromagnetic interaction.",
        "positive": "Trimer superfluid and supersolid on two-dimensional optical lattices: By the photoassociation method, the trimer superfluid phase disappears in the\none dimensional state-dependent optical lattice if the ratio of the three-body\ninteraction $W$ to the trimer tunneling $J$is kept at $W/J=12$ [Phys Rev A.\n{\\bf 90}, 033622(2014)]. To search for a trimer superfluid and trimer\nsupersolid, we load the cold atom into two-dimensional lattices, whose\ncoordinate number $z$ and kinetic energy $-zJ$ are respectively larger and\nlower than those of a one dimensional lattice. Herein, we study the\nBose-Hubbard model, which has an additional trimer tunneling term, a three-body\ninteraction and a next-nearest repulsion. The on-site trimer and trimer\nsuperfluid exist if the on-site two-body repulsion and three-body repulsion are\nsmaller than some thresholds. With atom-tunneling terms, the phase transitions\nfrom trimer superfluid phase to both atom superfluid and atom supersolid phases\nare first order. With $W/J=12$, in a one dimensional lattice, the trimer\nsuperfluid phase does not exist at all. In contrast, the trimer superfluid\nphase, exists in the lower density regions $0 \\textless \\rho \\textless2$ on the\nsquare lattice if $J$ is not very large. The trimer superfluid phase emerges in\na wider range $0 \\textless \\rho \\textless3$ in the triangular lattice, or in\nthe cubic lattice ($z=6$). When the three-body interaction is turned on, a\ntrimer supersolid phase emerges due to the classical degeneracy between the\nquasi trimer solid and the trimer solid being broken by the quantum\nfluctuation. The phase transitions from the trimer supersolid phase to quasi\ntrimer solid are first order and the phase transition from the trimer\nsupersolid phase to trimer solid is continuous. Our results, obtained by\nmean-field and quantum Monte Carlo methods, will be helpful in realizing the\ntrimer superfluid and supersolid by cold atom experiments."
    },
    {
        "anchor": "Quasi-static Lineshape Theory for Rydberg Excitations: This work presents a theoretical approach for lineshapes of Rydberg\nexcitations. In particular, we introduce the quasi-static lineshape theory,\nleading to a methodic and general approach, and its validity is studied. Next,\nusing $^{84}$Sr as a prototypical scenario, we discuss the role of the thermal\natoms and core-perturber interactions, generally disregarded in Rydberg\nphysics. Finally, we present a characterization of the role of Ryderg-core\nperturber interactions based on the density and principal quantum number that,\nbeyond affecting the lineshape, could potentially apply to chemi-ionization\nreactions responsible for the decay or Rydberg atoms in high density media.",
        "positive": "Are smooth pseudopotentials a good choice for representing short-range\n  interactions?: When seeking a numerical representation of a quantum-mechanical multiparticle\nproblem it is tempting to replace a singular short-range interaction by a\nsmooth finite-range pseudopotential. Finite basis set expansions, e.g.~in Fock\nspace, are then guaranteed to converge exponentially. The need to faithfully\nrepresent the artificial length scale of the pseudopotential, however, places a\ncostly burden on the basis set. Here we discuss scaling relations for the\nrequired size of the basis set and demonstrate the basis set convergence on the\nexample of a two-dimensional system of few fermions with short-range $s$-wave\ninteractions in a harmonic trapping potential. In particular we show that the\nnumber of harmonic-oscillator basis functions needed to reach a regime of\nexponential convergence for a Gaussian pseudopotential scales with the fourth\npower of the pseudopotential length scale, which can be improved to quadratic\nscaling when the basis functions are re-scaled appropriately. Numerical\nexamples for three fermions with up to a few hundred single-particle basis\nfunctions are presented and implications for the feasibility of accurate\nnumerical multi-particle simulations of interacting ultra-cold atom systems are\ndiscussed."
    },
    {
        "anchor": "Quadratic scaling path integral molecular dynamics for fictitious\n  identical particles and its application to fermion systems: Recently, fictitious identical particles have provided a promising way to\novercome the fermion sign problem and have been used in path integral Monte\nCarlo (PIMC) to accurately simulate warm dense matter with up to 1000 electrons\n(T. Dornheim et al., arXiv:2311.08098 (2023)). The inclusion of fictitious\nidentical particles in path integral molecular dynamics (PIMD) can provide\nanother way to simulate fermion systems. In a recent paper (J. Chem. Phys. 159,\n154107 (2023)), Feldman and Hirshberg improved the recursive formula for PIMD\nof N identical bosons, significantly reducing the computational complexity from\n$O(PN^3)$ to $O(N^2+PN)$. In this paper, we extend this latest recursive\nformula for bosons to PIMD of fictitious identical particles to improve the\nefficiency of simulating fermion systems. We also provide the virial estimator\nfor calculating energy by using the recursive technique. As an example, we use\nthe quadratic scaling PIMD for fictitious identical particles to study the\nsimulation of hundreds of fermions in a two-dimensional periodic potential, in\nthe hope of providing a simulation tool for two-dimensional Fermi-Hubbard model\nand other strongly correlated fermion systems, such as the simulation of\nultracold fermionic gases in optical lattices.",
        "positive": "Continuous matrix product states for non-relativistic quantum fields: a\n  lattice algorithm for inhomogeneous systems: By combining the continuous matrix product state (cMPS) representation for\nquantum fields in the continuum with standard optimization techniques for\nmatrix product states (MPS) on the lattice, we obtain an approximation\n$|\\Psi\\rangle$, directly in the continuum, of the ground state of\nnon-relativistic quantum field theories. This construction works both for\ntranslation invariant systems and in the more challenging context of\ninhomogeneous systems, as we demonstrate for an interacting bosonic field in a\nperiodic potential. Given the continuum Hamiltonian $H$, we consider a sequence\nof discretized Hamiltonians $\\{H(\\epsilon_{\\alpha})\\}_{\\alpha=1,2,\\cdots,p}$ on\nincreasingly finer lattices with lattice spacing $\\epsilon_1 > \\epsilon_2 >\n\\cdots > \\epsilon_p$. We first use energy minimization to optimize an MPS\napproximation $|\\Psi(\\epsilon_1)\\rangle$ for the ground state of\n$H(\\epsilon_1)$. Given the MPS $|\\Psi(\\epsilon_{\\alpha})\\rangle$ optimized for\nthe ground state of $H(\\epsilon_{\\alpha})$, we use it to initialize the energy\nminimization for Hamiltonian $H(\\epsilon_{\\alpha+1})$, resulting in the\noptimized MPS $|\\Psi(\\epsilon_{\\alpha+1})\\rangle$. By iteration we produce an\noptimized MPS $|\\Psi(\\epsilon_{p})\\rangle$ for the ground state of\n$H(\\epsilon_p)$, from which we finally extract the cMPS approximation\n$|\\Psi\\rangle$ for the ground state of $H$. Two key ingredients of our proposal\nare: (i) a procedure to discretize $H$ into a lattice model where each site\ncontains a two-dimensional vector space (spanned by vacuum $|0\\rangle$ and one\nboson $|1\\rangle$ states), and (ii) a procedure to map MPS representations from\na coarser lattice to a finer lattice."
    },
    {
        "anchor": "Measuring topology in a laser-coupled honeycomb lattice: From Chern\n  insulators to topological semi-metals: Ultracold fermions trapped in a honeycomb optical lattice constitute a\nversatile setup to experimentally realize the Haldane model [Phys. Rev. Lett.\n61, 2015 (1988)]. In this system, a non-uniform synthetic magnetic flux can be\nengineered through laser-induced methods, explicitly breaking time-reversal\nsymmetry. This potentially opens a bulk gap in the energy spectrum, which is\nassociated with a non-trivial topological order, i.e., a non-zero Chern number.\nIn this work, we consider the possibility of producing and identifying such a\nrobust Chern insulator in the laser-coupled honeycomb lattice. We explore a\nlarge parameter space spanned by experimentally controllable parameters and\nobtain a variety of phase diagrams, clearly identifying the accessible\ntopologically non-trivial regimes. We discuss the signatures of Chern\ninsulators in cold-atom systems, considering available detection methods. We\nalso highlight the existence of topological semi-metals in this system, which\nare gapless phases characterized by non-zero winding numbers, not present in\nHaldane's original model.",
        "positive": "Abelian gauge potentials on cubic lattices: The study of the properties of quantum particles in a periodic potential\nsubject to a magnetic field is an active area of research both in physics and\nmathematics; it has been and it is still deeply investigated. In this review we\ndiscuss how to implement and describe tunable Abelian magnetic fields in a\nsystem of ultracold atoms in optical lattices. After discussing two of the main\nexperimental schemes for the physical realization of synthetic gauge potentials\nin ultracold set-ups, we study cubic lattice tight-binding models with\ncommensurate flux. We finally examine applications of gauge potentials in\none-dimensional rings."
    },
    {
        "anchor": "Optical Abelian Lattice Gauge Theories: We discuss a general framework for the realization of a family of abelian\nlattice gauge theories, i.e., link models or gauge magnets, in optical\nlattices. We analyze the properties of these models that make them suitable to\nquantum simulations. Within this class, we study in detail the phases of a\nU(1)-invariant lattice gauge theory in 2+1 dimensions originally proposed by\nOrland. By using exact diagonalization, we extract the low-energy states for\nsmall lattices, up to 4x4. We confirm that the model has two phases, with the\nconfined entangled one characterized by strings wrapping around the whole\nlattice. We explain how to study larger lattices by using either tensor network\ntechniques or digital quantum simulations with Rydberg atoms loaded in optical\nlattices where we discuss in detail a protocol for the preparation of the\nground state. We also comment on the relation between standard compact U(1) LGT\nand the model considered.",
        "positive": "Confinement-Induced Resonance with Weak Background Interaction: We studied the scattering problem of two distinguishable atoms with unequal\nmass, where one atom (atom $\\alpha$) is trapped in a quasi-one-dimensional\n(quasi-1D) tube and the other one (atom $\\beta$) is localized by a 3D harmonic\ntrap. We show that in such a system if atom $\\alpha$ is much heavier than\n$\\beta$, confinement-induced resonance (CIR) can appear when the 3D $s$-wave\nscattering length $a_s$ of these two atoms is much smaller than the\ncharacteristic lengths (CLs) of the confinements, for either $a_s>0$ or\n$a_s<0$. This is quite different from the usual CIRs which occurs only when\n$a_s$ is comparable with the CL of confinement. Moreover, the CIRs we find are\nbroad enough that can serve as a tool for the control of effective inter-atomic\ninteraction. We further show the mechanism of these CIRs via the\nBorn-Oppenheimer approximation. Our results can be used for the realization of\nstrongly-interacting systems with ultracold atoms with weak 3D background\ninteraction (i.e., small $a_s$), e.g., the realization of ultracold gases with\nstrong spin-dependent interaction at zero magnetic fields."
    },
    {
        "anchor": "Superfluidity breakdown of periodic matter waves in quasi\n  one-dimensional annular traps via resonant scattering with moving defects: We investigate, both analytically and numerically, the quasi-superfluidity\nproperties of periodic Bose-Einstein condensates (BECs) in a\nquasi-one-dimensional (1D) ring with optical lattices (OL) of different kinds\n(linear and nonlinear) and with a moving defect of an infinite mass inside. To\nstudy the dynamics of the condensate we used a mean-field approximation\ndescribing the condensate by use of the Gross-Pitaevskii equation for the order\nparameter. We show that the resonant scattering of sound Bloch waves with the\ndefect profoundly affect BEC superfluidity. In particular, a moving defect\nalways leads to the breakdown of superfluidity independently of the value of\nits velocity. For weak periodic potentials the superfluidity breakdown may\noccur on a very long time scale (quasisuperfluidity) but the breakdown process\ncan be accelerated by increasing the strength of the OL. Quite remarkably, we\nfind that when the length of the ring is small enough to imply the discreteness\nof the reciprocal space, it becomes possible to avoid the resonant scattering\nand to restore quasi-superfluidity.",
        "positive": "Non-Abelian dynamical gauge field and topological superfluids in optical\n  Raman lattice: We propose an experimental scheme to realize non-Abelian dynamical gauge\nfield for ultracold fermions, which induces a novel pairing mechanism of\ntopological superfluidity. The dynamical gauge fields arise from nontrivial\ninterplay effect between the strong Zeeman splitting and Hubbard interaction in\na two-dimensional (2D) optical Raman lattice. The spin-flip transitions are\nforbidden by the large Zeeman detuning, but are restored when the Zeeman\nsplitting is compensated by Hubbard interaction. This scheme allows to generate\na dynamical non-Abelian gauge field that leads to a Dirac type correlated 2D\nspin-orbit interaction depending on local state configurations. The topological\nsuperfluid from a novel pairing driven by 2D dynamical gauge fields is reached,\nwith analytic and numerical results being obtained. Our work may open up a door\nto emulate non-Abelian dynamical gauge fields and correlated topological phases\nwith experimental feasibility."
    },
    {
        "anchor": "Driven-Dissipative Bose-Einstein Condensation and the Upper Critical\n  Dimension: Driving and dissipation can stabilize Bose-Einstein condensates. Using\nKeldysh field theory, we analyze this phenomenon for Markovian systems that can\ncomprise on-site two-particle driving, on-site single-particle and two-particle\nloss, as well as edge-correlated pumping. Above the upper critical dimension,\nmean-field theory shows that pumping and two-particle driving induce\ncondensation right at the boundary between the stable and unstable regions of\nthe non-interacting theory. With nonzero two-particle driving, the condensate\nis gapped. This picture is consistent with the recent observation that, without\nsymmetry constraints beyond invariance under single-particle basis\ntransformations, all gapped quadratic bosonic Liouvillians belong to the same\nphase. For systems below the upper critical dimension, the edge-correlated\npumping penalizes high-momentum fluctuations, rendering the theory\nrenormalizable. We perform the one-loop renormalization group analysis, finding\na condensation transition inside the unstable region of the non-interacting\ntheory. Interestingly, its critical behavior is determined by a\nWilson-Fisher-like fixed point with universal correlation-length exponent\n$\\nu=0.6$ in three dimensions.",
        "positive": "Programmable Quantum Annealing Architectures with Ising Quantum Wires: Quantum annealing aims at solving optimization problems efficiently by\npreparing the ground state of an Ising spin-Hamiltonian quantum mechanically. A\nprerequisite of building a quantum annealer is the implementation of\nprogrammable long-range two-, three- or multi-spin Ising interactions. We\ndiscuss an architecture, where the required spin interactions are implemented\nvia two-port, or in general multi-port quantum Ising wires connecting the spins\nof interest. This quantum annealing architecture of spins connected by Ising\nquantum wires can be realized by exploiting the three dimensional (3D)\ncharacter of atomic platforms, including atoms in optical lattices and Rydberg\ntweezer arrays. The realization only requires engineering on-site terms and\ntwo-body interactions between nearest neighboring qubits. The locally coupled\nspin model on a 3D cubic lattice is sufficient to effectively produce arbitrary\nall-to-all coupled Ising Hamiltonians. We illustrate the approach for few spin\ndevices solving Max-Cut and prime factorization problems, and discuss the\npotential scaling to large atom based systems."
    },
    {
        "anchor": "Stable Solitons in Three Dimensional Free Space: Self-Trapped\n  Bose-Einstein Condensates with Spin-Orbit Coupling: By means of variational methods and systematic numerical analysis, we\ndemonstrate the existence of stable solitons in three-dimensional (3D) free\nspace, in the context of binary atomic condensates combining contact\nself-attraction and spin-orbit coupling, which can be engineered by available\nexperimental techniques. Depending on the relative strength of the intra- and\ninter-component attraction, the stable solitons feature a semi-vortex or\nmixed-mode structure. In spite of the fact that the local cubic self-attraction\ngives rise to the supercritical collapse in 3D, the solitons are stable against\nrandom perturbations, motion, and collisions.",
        "positive": "Fractional corner charges in a 2D super-lattice Bose-Hubbard model: We study a two dimensional super-lattice Bose-Hubbard model with alternating\nhoppings in the limit of strong on-site interactions. We evaluate the phase\ndiagram of the model around half-filling using the density matrix\nrenormalization group method and find two gapped phases separated by a gapless\nsuperfluid region. We demonstrate that the gapped states realize two distinct\nhigher order symmetry protected topological phases, which are protected by a\ncombination of charge conservation and $C_4$ lattice symmetry. The phases are\ndistinguished in terms of a quantized fractional corner charge and a many-body\ntopological invariant that is robust against arbitrary, symmetry preserving\nedge manipulations. We support our claims by numerically studying the full\ncounting statistics of the corner charge, finding a sharp distribution peaked\naround the quantized values. These results are experimentally observable in\nultracold atomic settings using state of the art quantum gas microscopy."
    },
    {
        "anchor": "Quantum Field Theory for the Three-Body Constrained Lattice Bose Gas --\n  Part II: Application to the Many-Body Problem: We analyze the ground state phase diagram of attractive lattice bosons, which\nare stabilized by a three-body onsite hardcore constraint. A salient feature of\nthis model is an Ising type transition from a conventional atomic superfluid to\na dimer superfluid with vanishing atomic condensate. The study builds on an\nexact mapping of the constrained model to a theory of coupled bosons with\npolynomial interactions, proposed in a related paper [11]. In this framework,\nwe focus by analytical means on aspects of the phase diagram which are\nintimately connected to interactions, and are thus not accessible in a mean\nfield plus spin wave approach. First, we determine shifts in the mean field\nphase border, which are most pronounced in the low density regime. Second, the\ninvestigation of the strong coupling limit reveals the existence of a new\ncollective mode, which emerges as a consequence of enhanced symmetries in this\nregime. Third, we show that the Ising type phase transition, driven first order\nvia the competition of long wavelength modes at generic fillings, terminates\ninto a true Ising quantum critical point in the vicinity of half filling.",
        "positive": "Synthetic dimensions and spin-orbit coupling with an optical clock\n  transition: We demonstrate a novel way of synthesizing spin-orbit interactions in\nultracold quantum gases, based on a single-photon optical clock transition\ncoupling two long-lived electronic states of two-electron $^{173}$Yb atoms. By\nmapping the electronic states onto effective sites along a synthetic\n\"electronic\" dimension, we have engineered synthetic fermionic ladders with\ntunable magnetic fluxes. We have detected the spin-orbit coupling with\nfiber-link-enhanced clock spectroscopy and directly measured the emergence of\nchiral edge currents, probing them as a function of the magnetic field flux.\nThese results open new directions for the investigation of topological states\nof matter with ultracold atomic gases."
    },
    {
        "anchor": "Disordered one-dimensional Bose-Fermi mixtures: The Bose-Fermi glass: We analyze an interacting Bose-Fermi mixture in a 1D disordered potential\nusing a combination of renormalization group and variational methods. We obtain\nthe complete phase diagram in the incommensurate case as a function of bosonic\nand inter-species interaction strengths, in the weak disorder limit. We find\nthat the system is characterized by several phase transitions between\nsuperfluid and various glassy insulating states, including a new Bose-Fermi\nglass phase, where both species are coupled and localized. We show that the\ndynamical structure factor, as measured through Bragg scattering experiments,\ncan distinguish between the various localized phases and probe their dynamics.",
        "positive": "Early-time dynamics of Bose gases quenched into the strongly interacting\n  regime: We study the early-time dynamics of a degenerate Bose gas after a sudden\nquench of the interaction strength, starting from a weakly interacting gas. By\nmaking use of a time-dependent generalization of the Nozi\\`eres-Saint-James\nvariational formalism, we describe the crossover of the early-time dynamics\nfrom shallow to deep interaction quenches. We analyze the coherent oscillations\nthat characterize both the density of excited states and the Tan's contact as a\nfunction of the final scattering length. For shallow quenches, the oscillatory\nbehaviour is negligible and the dynamics is universally governed by the healing\nlength and the mean-field interaction energy. By increasing the final\nscattering length to intermediate values, we reveal a universal regime where\nthe period of the coherent atom-molecule oscillations is set by the molecule\nbinding energy. For the largest scattering lengths we can numerically simulate\nin the unitary regime, we find a universal scaling behaviour of the typical\ngrowth time of the momentum distribution in agreement with recent experimental\nobservations [C. Eigen et al., Nature 563, 221 (2018)]."
    },
    {
        "anchor": "Phase Separation in Mixtures of Repulsive Fermi Gases Driven by Mass\n  Difference: We show that phase separation must occur in a mixture of fermions with\nrepulsive interaction if their mass difference is sufficiently large. This\nphenomenon is highly dimension-dependent. Consequently, the density profiles of\nphase separated 3d mixtures are very different from those in 1d. Noting that\nthe ferromagnetic transition of a spin-1/2 repulsive Fermi gas is the equal\nmass limit of the phase separation in mixtures, we show from the Bethe Ansatz\nsolution that a ferromagnetic transition will take place in the scattering\nstates when the repulsive interaction passes through resonance and becomes\nattractive.",
        "positive": "Superfluidity in the 1D Bose-Hubbard Model: We study superfluidity in the 1D Bose-Hubbard model using a variational\nmatrix product state technique. We determine the superfluid density as a\nfunction of the Hubbard parameters by calculating the energy cost of phase\ntwists in the thermodynamic limit. As the system is critical, correlation\nfunctions decay as power laws and the entanglement entropy grows with the bond\ndimension of our variational state. We relate the resulting scaling laws to the\nsuperfluid density. We compare two different algorithms for optimizing the\ninfinite matrix product state and develop a physical explanation why one of\nthem (VUMPS) is more efficient than the other (iDMRG). Finally, we comment on\nfinite-temperature superfluidity in one dimension and how our results can be\nrealized in cold atom experiments."
    },
    {
        "anchor": "On the Ground State Quantum Droplet for Large Chemical Potentials: In the present work we revisit the problem of the quantum droplet in atomic\nBose-Einstein condensates with an eye towards describing its ground state in\nthe large density, so-called Thomas-Fermi limit. We consider the problem as\nbeing separable into 3 distinct regions: an inner one, where the Thomas-Fermi\napproximation is valid, a sharp transition region where the density abruptly\ndrops towards the (vanishing) background value and an outer region which\nasymptotes to the background value. We analyze the spatial extent of each of\nthese regions, and develop a systematic effective description of the rapid\nintermediate transition region. Accordingly, we derive a uniformly valid\ndescription of the ground state that is found to very accurately match our\nnumerical computations. As an additional application of our considerations, we\nshow that this formulation allows for an analytical approximation of excited\nstates such as the (trapped) dark soliton in the large density limit.",
        "positive": "Symmetry-enriched Bose-Einstein condensates in spin-orbit coupled\n  bilayer system: We consider the fate of Bose-Einstein condensation (BEC) with time-reversal\nsymmetry and inversion symmetry in a spin-orbit coupled bilayer system. When\nthese two symmetry operators commute, all the single particle bands are exactly\ntwo-fold degenerate in the momentum space. The scattering in the two-fold\ndegenerate rings can relax the spin-momentum locking effect resulting from\nspin-orbit coupling, thus we can realize the spin polarized plane wave phase\neven when the inter-particle interaction dominates. When these two operators\nanti-commute, the lowest two bands may have the same minimal energy, which have\ntotally different spin structures. As a result, the competition between\ndifferent condensates in these two energetically degenerate rings can give rise\nto interesting stripe phases with atoms condensed at two or four colinear\nmomenta. We find that the crossover between these two cases is accompanied by\nthe excited band condensation when the interference energy can overcome the\nincreased single particle energy in the excited band. This effect is not based\non strong interaction, thus can be realized even with moderate interaction\nstrength."
    },
    {
        "anchor": "Level statistics of the one-dimensional dimerized Hubbard model: The statistical properties of level spacings provide valuable insights into\nthe dynamical properties of a many-body quantum systems. We investigate the\nlevel statistics of the Fermi-Hubbard model with dimerized hopping amplitude\nand find that after taking into account translation, reflection, spin and\n{\\eta} pairing symmetries to isolate irreducible blocks of the Hamiltonian, the\nlevel spacings in the limit of large system sizes follow the distribution\nexpected for hermitian random matrices from the Gaussian orthogonal ensemble.\nWe show this by analyzing the distribution of the ratios of consecutive level\nspacings in this system, its cumulative distribution and quantify the\ndeviations of the distributions using their mean, standard deviation and\nskewness.",
        "positive": "Binary matter-wave compactons induced by inter-species scattering length\n  modulations: Binary mixtures of quasi one-dimensional Bose-Einstein condensates (BEC)\ntrapped in deep optical lattices (OL) in the presence of periodic time\nmodulations of the inter-species scattering length, are investigated. We adopt\na mean field description and use the tight binding approximation and the\naveraging method to derive averaged model equations in the form of two coupled\ndiscrete nonlinear Schr\\\"odinger equations (DNLSE) with tunneling constants\nthat nonlinearly depend on the inter-species coupling. We show that for strong\nand rapid modulations of the inter-species scattering length, the averaged\nsystem admits exact compacton solutions, e.g. solutions that have no tails and\nare fully localized on a compact which are achieved when the densities at the\ncompact edges are in correspondence with zeros of the Bessel function (zero\ntunneling condition). Deviations from exact conditions give rise to the\nformation of quasi-compactons, e.g. non exact excitations which look as\ncompactons for any practical purpose, for which the zero tunneling condition is\nachieved dynamically thanks to an effective nonlinear dispersive coupling\ninduced by the scattering length modulation. Stability properties of compactons\nand quasi-compactons are investigated by linear analysis and by numerical\nintegrations of the averaged system, respectively, and results compared with\nthose from the original (unaveraged) system. In particular, the occurrence od\ndelocalizing transitions with existence of thresholds in the mean inter-species\nscattering length is explicitly demonstrated. Under proper management\nconditions, stationary compactons and quasi-compactons are quite stable and\nrobust excitations that can survive on very long time scale. A parameter design\nand a possible experimental setting for observation of these excitations are\nbriefly discussed."
    },
    {
        "anchor": "Phase transitions in one-dimensional correlated Fermi gases with\n  cavity-induced umklapp scattering: The phase transitions of one dimensional correlated Fermi gases in a\ntransversely driven optical cavity, under the umklapp condition that the cavity\nwavenumber equals two times of Fermi wavenumber, are studied with the\nbosonization and renormalization group (RG) techniques. The bosonization of\nFermi fields gives rise to an all-to-all sine-Gordon (SG) model due to the\ncavity-assisted non-local interactions, where the Bose fields at any two\nspatial points are coupled. The superradiant phase transition is then linked to\nthe Kosterlitz-Thouless (KT) phase transition of the all-to-all SG model. The\nnesting effect, in which the superradiant phase transition can be triggered by\ninfinitely small atom-cavity coupling strength, is preserved for any\nnon-attractive local interactions. The phase transition occurs at finite\ncritical coupling strength for attractive local interactions. Nevertheless, the\ncritical dimension of the KT phase transition is also 2 like that in an\nordinary local SG model. Our work provides an analytical framework for\nunderstanding the phase transitions in correlated intra-cavity Fermi gases.",
        "positive": "Quantum charge glasses of itinerant fermions with cavity-mediated\n  long-range interactions: We study models of itinerant spinless fermions with random long-range\ninteractions. We motivate such models from descriptions of fermionic atoms in\nmulti-mode optical cavities. The solution of an infinite-range model yields a\nmetallic phase which has glassy charge dynamics, and a localized glass phase\nwith suppressed density of states at low energies. We compare these phases to\nthe conventional disordered Fermi liquid, and the insulating electron glass of\nsemiconductors. Prospects for the realization of such glassy phases in cold\natom systems are discussed."
    },
    {
        "anchor": "Optimizing persistent currents in a ring-shaped Bose-Einstein condensate\n  using machine learning: We demonstrate a method for generating persistent currents in Bose-Einstein\ncondensates by using a Gaussian process learner to experimentally control the\nstirring of the superfluid. The learner optimizes four different outcomes of\nthe stirring process: (O.I) targeting and (O.II) maximization of the persistent\ncurrent winding number; and (O.III) targeting and (O.IV) maximization with time\nconstraints. The learner optimizations are determined based on the achieved\nwinding number and the number of spurious vortices introduced by stirring. We\nfind that the learner is successful in optimizing the stirring protocols,\nalthough the optimal stirring profiles vary significantly depending strongly on\nthe choice of cost function and scenario. These results suggest that stirring\nis robust and persistent currents can be reliably generated through a variety\nof stirring approaches.",
        "positive": "Information compression at the turbulent-phase transition in cold atom\n  gases: The statistical properties of physical systems in thermal equilibrium are\nblatantly different from their far-from-equilibrium counterparts. In the\nlatter, fluctuations often dominate the dynamics and might cluster in ordered\npatterns in the form of dissipative coherent structures. Here, we study the\ntransition of a cold atomic cloud, driven close to a sharp electronic\nresonance, from a stable to a turbulent phase. From the atomic density\ndistribution -- measured using a spatially-resolved pump-probe technique -- we\nhave computed the Shannon entropy on two different basis sets. Information\ncompression, corresponding to a minimum in the Shannon entropy, has been\nobserved at criticality, where the system fluctuations organize into high-order\n(low-entropy) patterns. Being independent of the representation used, this\nfeature is a property shared by a vast class of physical systems undergoing\nphase transitions."
    },
    {
        "anchor": "Fractional quantum Hall effect in the interacting Hofstadter model via\n  tensor networks: We show via tensor network methods that the Harper-Hofstadter Hamiltonian for\nhard-core bosons on a square geometry supports a topological phase realizing\nthe $\\nu=1/2$ fractional quantum Hall effect on the lattice. We address the\nrobustness of the ground state degeneracy and of the energy gap, measure the\nmany-body Chern number, and characterize the system using Green functions,\nshowing that they decay algebraically at the edges of open geometries,\nindicating the presence of gapless edge modes. Moreover, we estimate the\ntopological entanglement entropy by taking a combination of lattice\nbipartitions that reproduces the topological structure of the original\nproposals by Kitaev and Preskill, and Levin and Wen. The numerical results show\nthat the topological contribution is compatible with the expected value $\\gamma\n= 1/2$. Our results provide extensive evidence that FQH states are within reach\nof state-of-the-art cold atom experiments.",
        "positive": "Population imbalance and pairing in the BCS-BEC crossover of\n  three-component ultracold fermions: We investigate the phase diagram and the BCS-BEC crossover of a homogeneous\nthree-component ultracold Fermi gas with a U(3) invariant attractive\ninteraction. We show that the system at sufficiently low temperatures exhibits\npopulation imbalance, as well as fermionic pairing. We describe the crossover\nin this system, connecting the weakly interacting BCS regime of the partially\npopulation-imbalanced fermion pairing state and the BEC limit with three weakly\ninteracting species of molecules, including pairing fluctuations within a\nt-matrix calculation of the particle self-energies."
    },
    {
        "anchor": "Rotation-driven transition into coexistent Josephson modes in an\n  atomtronic dc-SQUID: By means of a two-mode model, we show that transitions to different arrays of\ncoexistent regimes in the phase space can be attained by rotating a double-well\nsystem, which consists of a toroidal condensate with two diametrically placed\nbarriers. Such a configuration corresponds to the atomtronic counterpart of the\nwell-known direct-current superconducting quantum interference device. Due to\nthe phase gradient experimented by the on-site localized functions when the\nsystem is subject to rotation, a phase difference appears on each junction in\norder to satisfy the quantization of the velocity field around the torus. We\ndemonstrate that such a phase can produce a significant change on the relative\nvalues of different types of hopping parameters. In particular, we show that\nwithin a determined rotation frequency interval, a hopping parameter, usually\ndisregarded in nonrotating systems, turns out to rule the dynamics. At the\nlimits of such a frequency interval, bifurcations of the stationary points\noccur, which substantially change the phase space portrait that describes the\norbits of the macroscopic canonical conjugate variables. We analyze the\nemerging dynamics that combines the $0$ and $\\pi$ Josephson modes, and evaluate\nthe small-oscillation time-periods of such orbits at the frequency range where\neach mode survives. All the findings predicted by the model are confirmed by\nGross-Pitaevskii simulations.",
        "positive": "Brillouin propagation modes of cold atoms in dissipative optical\n  lattices: An exact series expansion of the average velocity of cold atoms in\ndissipative optical lattices under probe driving, based on the amplitudes of\nthe excited atomic density waves, is derived from the semiclassical equations\nfor the phase space densities of the Zeeman ground-state sublevels. This\nexpansion permits the identification of the precise contribution to the current\nof a propagating atomic wave for the specific driving, as well as providing the\ngeneral threshold for the transition into the regime of infinite density."
    },
    {
        "anchor": "Chandrasekhar-Clogston limit and critical polarization in a Fermi-Bose\n  superfluid mixture: We study mixtures of a population-imbalanced strongly-interacting Fermi gas\nand of a Bose-Einstein condensed gas at zero temperature. In the homogeneous\ncase, we find that the Chandrasekhar-Clogston critical polarization for the\nonset of instability of Fermi superfluidity is enhanced due to the interaction\nwith the bosons. Predictions for the critical polarization are also given in\nthe trapped case, with a special focus to the situation of equal Fermi-Bose and\nBose-Bose coupling constants, where the density of fermions becomes flat in the\ncenter of the trap. This regime can be realized experimentally using Feshbach\nresonances and is well suited to investigate the emergence of exotic\nconfigurations, such as the occurrence of spin domains or the FFLO phase.",
        "positive": "Nonlinear Floquet dynamics of spinor condensates in an optical cavity:\n  Cavity-amplified parametric resonance: We investigate Floquet dynamics of a cavity-spinor Bose-Einstein condensate\ncoupling system via periodic modulation of the cavity pump laser. Parametric\nresonances are predicted and we show that due to cavity feedback-induced\nnonlinearity the spin oscillation can be amplified to all orders of resonance,\nthus facilitating its detection. Real-time observation on Floquet dynamics via\ncavity output is also discussed."
    },
    {
        "anchor": "Dynamical resistivity of a few interacting fermions to the\n  time-dependent potential barrier: We study the dynamical response of a harmonically trapped two-component\nfew-fermion mixture to the external gaussian potential barrier moving across\nthe system. The simultaneous role played by inter-particle interactions,\nrapidity of the barrier, and the fermionic statistics is explored for systems\ncontaining up to four particles. The response is quantified in terms of the\ntemporal fidelity of the time-evolved state and the amount of quantum\ncorrelations between components being dynamically generated. Results are also\nsupported by analysis of the single-particle densities and temporal number of\noccupied many-body eigenstates. In this way, we show that the dynamical\nproperties of the system crucially depend on non-trivial mutual relations\nbetween temporal many-body eigenstates, and in consequence, they lead to\nvolatility of the dynamics. Counterintuitively, imbalanced systems manifest\nmuch higher resistivity and stability than their balanced counterparts.",
        "positive": "Bosonic Dynamical Mean-Field Theory: We derive the Bosonic Dynamical Mean-Field equations for bosonic atoms in\noptical lattices with arbitrary lattice geometry. The equations are presented\nas a systematic expansion in 1/z, z being the number of lattice neighbors.\nHence the theory is applicable in sufficiently high dimensional lattices. We\napply the method to a two-component mixture, for which a rich phase diagram\nwith spin-order is revealed."
    },
    {
        "anchor": "Formation of nonlinear X-waves in condensed matter systems: X-waves are an example of a localized wave packet solution of the homogeneous\nwave equation, and can potentially arise in any area of physics relating to\nwave phenomena, such as acoustics, electromagnetism, or quantum mechanics. They\nhave been predicted in condensed matter systems such as atomic Bose-Einstein\ncondensates in optical lattices, and were recently observed in\nexciton-polariton condensates. Here we show that polariton X-waves result from\nan interference between two separating wave packets that arise from the\ncombination of a locally hyperbolic dispersion relation and nonlinear\ninteractions. We show that similar X-wave structures could also be observed in\nexpanding spin-orbit coupled Bose-Einstein condensates.",
        "positive": "Wave function network description and Kolmogorov complexity of quantum\n  many-body systems: Programmable quantum devices are now able to probe wave functions at\nunprecedented levels. This is based on the ability to project the many-body\nstate of atom and qubit arrays onto a measurement basis which produces\nsnapshots of the system wave function. Extracting and processing information\nfrom such observations remains, however, an open quest. One often resorts to\nanalyzing low-order correlation functions - i.e., discarding most of the\navailable information content. Here, we introduce wave function networks - a\nmathematical framework to describe wave function snapshots based on network\ntheory. For many-body systems, these networks can become scale free - a\nmathematical structure that has found tremendous success in a broad set of\nfields, ranging from biology to epidemics to internet science. We demonstrate\nthe potential of applying these techniques to quantum science by introducing\nprotocols to extract the Kolmogorov complexity corresponding to the output of a\nquantum simulator, and implementing tools for fully scalable cross-platform\ncertification based on similarity tests between networks. We demonstrate the\nemergence of scale-free networks analyzing data from Rydberg quantum simulators\nmanipulating up to 100 atoms. We illustrate how, upon crossing a phase\ntransition, the system complexity decreases while correlation length increases\n- a direct signature of build up of universal behavior in data space. Comparing\nexperiments with numerical simulations, we achieve cross-certification at the\nwave-function level up to timescales of 4 $\\mu$ s with a confidence level of\n90%, and determine experimental calibration intervals with unprecedented\naccuracy. Our framework is generically applicable to the output of quantum\ncomputers and simulators with in situ access to the system wave function, and\nrequires probing accuracy and repetition rates accessible to most currently\navailable platforms."
    },
    {
        "anchor": "Efimov-driven phase transitions of the unitary Bose gas: In quantum physics, Efimov trimers are bound states of three particles that\nfall apart like Borromean rings when one of them is removed. Initially\npredicted in nuclear physics, these striking bosonic states are hard to\nobserve, but the \"unitary\" interactions at which they form is commonly realized\nin current cold atoms experiments. There, they set the stage for a new class of\nuniversal physics: Two-body interactions are all but invisible, but three-body\neffects allow the emergence of a largely uncharted new world of many-particle\nbound states. Three-particle systems were characterized theoretically, and the\nground-state properties of small unitary clusters computed numerically, but the\nmacroscopic many-body behaviour has remained unknown. Here we show, using a\nPath-Integral Monte Carlo algorithm backed up by theoretical arguments, that\nthe unitary Bose gas presents a first-order phase transition from a normal gas\nto a superfluid Efimov liquid. The normal gas is very well described by the\navailable virial coefficients. At unitarity, the phase diagram of the bosonic\nsystem is universal in rescaled pressure and temperature. A triple point\nseparates the normal gas, the superfluid Efimov liquid, and a third phase, the\nconventional superfluid gas. These two superfluid phases are separated by a\ncritical line that ends in a critical point at high temperature. This rich\nphase diagram should allow for a number of experimental protocols that would\nprobe these universal transitions between the normal gas, the superfluid gas,\nand the superfluid Efimov liquid.",
        "positive": "Equation of state and phase transition in spin-orbit-coupled Bose gases\n  at finite temperature: A perturbation approach: We study two-component Bose gases with Raman induced spin-orbit coupling via\na perturbation approach at finite temperature. For weak coupling, free energy\nis expanded in terms of Raman coupling strength up to the second order, where\nthe coefficient (referred to as Raman susceptibility) is determined according\nto linear response theory. The equation of state for the stripe phase and the\nplane-wave phase are obtained in Popov approximation, and the first order\ntransition between these two phases is investigated. As temperature increases,\nwe find the phase boundary bends toward the stripe phase side in most\ntemperature regions, which implies the ferromagnetic order is more robust than\nthe crystalline order in presence of thermal fluctuations. Our results\nqualitatively agree with the recent experimental observation in rubidium atomic\ngases. A method to measure the Raman susceptibility through the two-photon\nBragg scattering experiment is also discussed."
    },
    {
        "anchor": "Vortex lattices for ultracold bosonic atoms in a non-Abelian gauge\n  potential: The use of coherent optical dressing of atomic levels allows the coupling of\nultracold atoms to effective gauge fields. These can be used to generate\neffective magnetic fields, and have the potential to generate non-Abelian gauge\nfields. We consider a model of a gas of bosonic atoms coupled to a gauge field\nwith U(2) symmetry, and with constant effective magnetic field. We include the\neffects of weak contact interactions by applying Gross-Pitaevskii mean-field\ntheory. We study the effects of a U(2) non-Abelian gauge field on the vortex\nlattice phase induced by a uniform effective magnetic field, generated by an\nAbelian gauge field or, equivalently, by rotation of the gas. We show that,\nwith increasing non-Abelian gauge field, the nature of the groundstate changes\ndramatically, with structural changes of the vortex lattice. We show that the\neffect of the non-Abelian gauge field is equivalent to the introduction of\neffective interactions with non-zero range. We also comment on the consequences\nof the non-Abelian gauge field for strongly correlated fractional quantum Hall\nstates.",
        "positive": "Probing superfluidity in a quasi two-dimensional Bose gas through its\n  local dynamics: We report direct evidence of superfluidity in a quasi two-dimensional Bose\ngas by observing its dynamical response to a collective excitation. Relying on\na novel local correlation analysis, we are able to probe inhomogeneous clouds\nand reveal their local dynamics. We identify in this way the superfluid and\nthermal phases inside the gas and locate the boundary at which the\nBerezinskii--Kosterlitz--Thouless crossover occurs. This new analysis also\nallows to evidence the coupling of the two fluids which induces at finite\ntemperatures damping rates larger than the usual Landau damping."
    },
    {
        "anchor": "Time-Reversal-Invariant Hofstadter-Hubbard Model with Ultracold Fermions: We consider the time-reversal-invariant Hofstadter-Hubbard model which can be\nrealized in cold atom experiments. In these experiments, an additional\nstaggered potential and an artificial Rashba--type spin-orbit coupling are\navailable. Without interactions, the system exhibits various phases such as\ntopological and normal insulator, metal as well as semi--metal phases with two\nor even more Dirac cones. Using a combination of real-space dynamical\nmean-field theory and analytical techniques, we discuss the effect of on-site\ninteractions and determine the corresponding phase diagram. In particular, we\ninvestigate the semi--metal to antiferromagnetic insulator transition and the\nstability of different topological insulator phases in the presence of strong\ninteractions. We compute spectral functions which allow us to study the edge\nstates of the strongly correlated topological phases.",
        "positive": "Long range mediated interactions in a mixed dimensional system: We present a mixed-dimensional atomic gas system to unambiguously detect and\nsystematically probe mediated interactions. In our scheme, fermionic atoms are\nconfined in two parallel planes and interact via exchange of elementary\nexcitations in a three-dimensional background gas. This interaction gives rise\nto a frequency shift of the out-of-phase dipole oscillations of the two clouds,\nwhich we calculate using a strong coupling theory taking the two-body\nmixed-dimensional scattering into account exactly. The shift is shown to be\neasily measurable for strong interactions and can be used as a probe for\nmediated interactions."
    },
    {
        "anchor": "Rotating a Bose-Einstein condensate by shaking an anharmonic\n  axisymmetric magnetic potential: We present an experimental method for rotating a Bose-Einstein condensate\ntrapped in an axisymmetric magnetic potential. This method is based on the\nanharmonicity of the trapping potential, which couples the center-of-mass\nmotion of the condensate to its internal motion. By circularly shaking the\ntrapping potential, we generate a circular center-of-mass motion of the\ncondensate around the trap center. The circulating condensate undergoes\nrotating shape deformation and eventually relaxes into a rotating condensate\nwith a vortex lattice. We discuss the vortex nucleation mechanism and in\nparticular, the role of the thermal cloud in the relaxation process. Finally,\nwe investigate the dependence of the vortex nucleation on the elliptical\npolarization of the trap shaking. The response of the condensate is asymmetric\nwith respect to the sign of the shaking polarization, demonstrating the gauge\nfield effect due to the spin texture of the condensate in the magnetic\npotential.",
        "positive": "Spin-orbit-coupled spinor gap solitons in Bose-Einstein condensates: Spin-1 spin-orbit-coupled spinor Bose-Einstein condensates have been realized\nin experiment. We study spin-orbit-coupled spinor gap solitons in this\nexperimentally realizable system with an optical lattice. The spin-dependent\nparity symmetry of the spin-orbit coupling plays an important role in\nproperties of gap solitons. Two families of solitons with opposite\nspin-dependent parity are found. Using an approximating model by replacing the\noptical lattice with a Harmonic trap, we demonstrate the physical origination\nof these two families. For a large negative quadratic Zeeman shift, we also\nfind a type of gap solitons that spontaneously breaks the spin-dependent parity\nsymmetry due to the ferromagnetic spinor interactions."
    },
    {
        "anchor": "Exactly solvable model for a solitonic vortex in a compressible\n  superfluid: Vortex motion is a complex problem due to the interplay between the\nshort-range physics at the vortex core level and the long-range hydrodynamical\neffects. Here we show that the hydrodynamic equations of vortex motion in a\ncompressible superfluid can be solved exactly in a model \"slab\" geometry.\nStarting from an exact solution for an incompressible fluid, the hydrodynamic\nequations are solved with a series expansion in a small tunable parameter\nprovided by the ratio of the healing length, characterizing the vortex cores,\nto the slab width. The key dynamical properties of the vortex, the inertial and\nphysical masses, are well defined and renormalizable. They are calculated at\nleading order beyond the logarithmic accuracy that has limited previous\napproaches. Our results provide a solid framework for further detailed study of\nthe vortex mass and vortex forces in strongly-correlated and exotic\nsuperfluids. The proposed geometry can be realised in quantum-gas experiments\nwhere high-precision measurements of vortex mass parameters are feasible.",
        "positive": "Scattering of matter-waves in spatially inhomogeneous environments: We study scattering of quasi one-dimensional matter-waves at an interface of\ntwo spatial domains, one with repulsive and one with attractive interatomic\ninteractions. It is shown that the incidence of a Gaussian wavepacket from the\nrepulsive to the attractive region gives rise to generation of a soliton train.\nMore specifically, the number of emergent solitons can be controlled e.g. by\nthe variation of the amplitude or the width of the incoming wavepacket.\nFurthermore, we study the reflectivity of a soliton incident from the\nattractive region to the repulsive one. We find the reflection coefficient\nnumerically and employ analytical methods, that treat the soliton as a particle\n(for moderate and large amplitudes) or a quasi-linear wavepacket (for small\namplitudes), to determine the critical soliton momentum - as function of the\nsoliton amplitude - for which total reflection is observed."
    },
    {
        "anchor": "Precision Test of the Limits to Universality in Few-Body Physics: We perform precise studies of two- and three-body interactions near an\nintermediate-strength Feshbach resonance in $^{39}\\mathrm{K}$ at\n$33.5820(14)\\thinspace$G. Precise measurement of dimer binding energies,\nspanning three orders of magnitude, enables the construction of a complete\ntwo-body coupled-channel model for determination of the scattering lengths with\nan unprecedented low uncertainty. Utilizing an accurate scattering length map,\nwe measure the precise location of the Efimov ground state to test van der\nWaals universality. Precise control of the sample's temperature and density\nensures that systematic effects on the Efimov trimer state are well understood.\nWe measure the ground Efimov resonance location to be at $-14.05(17)$ times the\nvan der Waals length $r_{\\mathrm{vdW}}$, significantly deviating from the value\nof $-9.7 \\thinspace r_{\\mathrm{vdW}}$ predicted by van der Waals universality.\nWe find that a refined multichannel three-body model, built on our measurement\nof two-body physics, can account for this difference and even successfully\npredict the Efimov inelasticity parameter $\\eta$.",
        "positive": "Spectral analysis of two-dimensional Bose-Hubbard models: One-dimensional Bose-Hubbard models are well known to obey a transition from\nregular to quantum-chaotic spectral statistics. We are extending this concept\nto relatively simple two-dimensional many-body models. Also in two dimensions a\ntransition from regular to chaotic spectral statistics is found and discussed.\nIn particular, we analyze the dependence of the spectral properties on the bond\nnumber of the two-dimensional lattices and the applied boundary conditions. For\nmaximal connectivity, the systems behave most regularly in agreement with the\napplicability of mean-field approaches in the limit of many nearest-neighbor\ncouplings at each site."
    },
    {
        "anchor": "Collisions of anisotropic two-dimensional bright solitons in dipolar\n  Bose-Einstein condensates: We investigate the coherent collision of anisotropic quasi-two-dimensional\nbright solitons in dipolar Bose-Einstein condensates. Our analysis is based on\nthe extended Gross-Pitaevskii equation, and we use the split-operator method\nfor the grid calculations and the time-dependent variational principle with an\nansatz of coupled Gaussian functions to calculate the time evolution of the\nground state. We compare the results of both approaches for collisions where\ninitially the solitons are in the repelling side-by-side configuration and move\ntowards each other with a specific momentum. We change the relative phases of\nthe condensates, and introduce a total angular momentum by shifting the\nsolitons in opposite direction along the polarization axis. Our calculations\nshow that collisions result in breathing-mode-like excitations of the solitons.",
        "positive": "Interactions of solitons with a Gaussian barrier: Splitting and\n  recombination in quasi-1D and 3D: The interaction of matter-wave solitons with a potential barrier is a\nfundamentally important problem, and the splitting and subsequent recombination\nof the soliton by the barrier is the essence of soliton matter-wave\ninterferometry. We demonstrate the three-dimensional (3D) character of the\ninteractions in the case relevant to ongoing experiments, where the number of\natoms in the soliton is sufficiently large that the soliton is close to\ncollapse. The mean-field description is quite accurate, but the proximity to\nthe collapse threshold makes the use of the 1D Gross-Pitaevskii equation (GPE)\nirrelevant. We examine the soliton dynamics in the framework of the effectively\n1D nonpolynomial Schr{\\\"{o}}dinger equation (NPSE), which admits the collapse\nin a modified form, and in parallel we use the full 3D GPE. Both approaches\nproduce results which are very different from those produced in recent work\nwhich used the 1D cubic GPE. The features observed in both the NPSE and the 3D\nGPE include (a) an increase in the first reflection coefficient for increasing\nbarrier height and decreasing atom number; (b) strong modulation in the\nsecondary reflection/recombination probability vs. barrier height; (c) a\npronounced asymmetry in the oscillation amplitudes of the transmitted and\nreflected fragments; (d) an enhancement of the transverse excitations as the\nnumber of atoms is increased. We also explore effects produced by variations of\nthe barrier width and outcomes of the secondary collision upon phase imprinting\non the fragment in one arm of the interferometer."
    },
    {
        "anchor": "Efimov physics beyond three particles: Efimov physics originally refers to a system of three particles. Here we\nreview recent theoretical progress seeking for manifestations of Efimov physics\nin systems composed of more than three particles. Clusters of more than three\nbosons are tied to each Efimov trimer, but no independent Efimov physics exists\nthere beyond three bosons. The case of a few heavy fermions interacting with a\nlighter atom is also considered, where the mass ratio of the constituent\nparticles plays a significant role. Following Efimov's study of the (2+1)\nsystem, the (3+1) system was shown to have its own critical mass ratio to\nbecome Efimovian. We show that the (4+1) system becomes Efimovian at a mass\nratio which is smaller than its sub-systems thresholds, giving a pure five-body\nEfimov effect. The (5+1) and (6+1) systems are also discussed, and we show the\nabsence of 6- and 7-body Efimov physics there.",
        "positive": "Localization landscape for interacting Bose gases in one-dimensional\n  speckle potentials: While the properties and the shape of the ground state of a gas of ultracold\nbosons are well understood in harmonic potentials, they remain for a large part\nunknown in the case of random potentials. Here, we use the\nlocalization-landscape (LL) theory to study the properties of the solutions to\nthe Gross-Pitaevskii equation (GPE) in one-dimensional (1D) speckle potentials.\nIn the cases of attractive interactions, we find that the LL allows one to\npredict the position of the localization center of the ground state (GS) of the\nGPE. For weakly repulsive interactions, we point out that the GS of the\nquasi-1D GPE can be understood as a superposition of a finite number of\nsingle-particle states, which can be computed by exploiting the LL. For\nintermediate repulsive interactions, we introduce a Thomas-Fermi-like approach\nfor the GS which holds in the smoothing regime, well beyond the usual\napproximation involving the original potential. Moreover, we show that, in the\nLifshitz glass regime, the particle density and the chemical potential can be\nwell estimated by the LL. Our approach can be applied to any positive-valued\nrandom potential endowed with finite-range correlations and can be generalized\nto higher-dimensional systems."
    },
    {
        "anchor": "Hubbard model: Pinning of occupation numbers and role of symmetries: Fermionic natural occupation numbers do not only obey Pauli's exclusion\nprinciple, but are even further restricted by so-called generalized Pauli\nconstraints. Such restrictions are particularly relevant whenever they are\nsaturated by given natural occupation numbers $\\vec{\\lambda}=(\\lambda_i)$. For\nfew-site Hubbard models we explore the occurrence of this pinning effect. By\nvarying the on-site interaction $U$ for the fermions we find sharp transitions\nfrom pinning of $\\vec{\\lambda}$ to the boundary of the allowed region to\nnonpinning. We analyze the origin of this phenomenon which turns out be either\na crossing of natural occupation numbers $\\lambda_{i}(U), \\lambda_{i+1}(U)$ or\na crossing of $N$-particle energies. Furthermore, we emphasize the relevance of\nsymmetries for the occurrence of pinning. Based on recent progress in the field\nof ultracold atoms our findings suggest an experimental set-up for the\nrealization of the pinning effect.",
        "positive": "Evaporative cooling and self-thermalization in an open system of\n  interacting fermions: We study depletion dynamics of an open system of weakly interacting fermions\nwith two-body random interactions. In this model fermions are escaping from the\nhigh-energy one-particle orbitals, that mimics the evaporation process used in\nlaboratory experiments with neutral atoms to cool them to ultra-low\ntemperatures. It is shown that due to dynamical thermalization the system\ninstantaneously adjusts to the new chemical potential and temperature, so that\noccupation numbers of the one-particle orbitals always obey the Fermi-Dirac\ndistribution. In this way we are able to describe the evaporation process which\nleads to a significant cooling of particles remaining inside the system. We\nalso briefly discuss the evaporation process in the SYK black hole model that\ncorresponds to strongly interacting fermions."
    },
    {
        "anchor": "Critical velocity of a mobile impurity in one-dimensional quantum\n  liquids: We study the notion of superfluid critical velocity in one spatial dimension.\nIt is shown that for heavy impurities with mass $M$ exceeding a critical mass\n$M_\\mathrm{c}$, the dispersion develops periodic metastable branches resulting\nin dramatic changes of dynamics in the presence of an external driving force.\nIn contrast to smooth Bloch Oscillations for $M<M_\\mathrm{c}$, a heavy impurity\nclimbs metastable branches until it reaches a branch termination point or\nundergoes a random tunneling event, both leading to an abrupt change in\nvelocity and an energy loss. This is predicted to lead to a non-analytic\ndependence of the impurity drift velocity on small forces.",
        "positive": "Superradiant Transition to a Fermionic Quasicrystal in a Cavity: Recently, the steady state superradiance in degenerate Fermi gases has been\nrealized in a cavity, following the previous discovery of the Dicke transition\nin Bose gases. The most prominent signature of fermionic Dicke transition is\nits density dependence, which is manifested as the Fermi surface nesting effect\nand the Pauli blocking effect. We study the superradiant transition in\none-dimensional Fermi gases in a cavity with the presence of an incommensurate\ndipolar lattice. We find a first-order Dicke transition induced by indirect\nresonance effect, which is a resonance between two atomic levels by the level\nrepulsion from a third level, and causes extra gap opening. By formulating a\nphenomenological theory, we find that the critical pumping strength for this\nfirst-order Dicke transition shows a linear V-shape kink near a particular\nindirect resonance modified filling $\\nu_{\\rm IRM}$. The presence and the\nunique density dependence of this transition manifest the fermionic nature and\nverify the mechanism of the quasicrystal superradiant transition."
    },
    {
        "anchor": "Phonon instability and self-organized structures in multi-layer stacks\n  of confined dipolar Bose-Einstein condensates in optical lattices: In calculations to date [1,2] of multi-layer stacks of dipolar condensates,\ncreated in one-dimensional optical lattices, the condensates have been assumed\nto be two-dimensional. In a real experiment, however, the condensates do not\nextend to infinity in the oblate direction, but have to be confined by a trap\npotential, too. By three-dimensional numerical simulations of this realistic\nexperimental situation we find a crucial dependence of the phonon instability\nboundary on the number of layers. Moreover, near the boundary of the phonon\ninstability, a variety of structured ground-state wave functions emerges, which\nmay indicate the onset of a roton instability [3,4].",
        "positive": "Chiral $p\\pm ip$ superfluid on a sphere: We consider a spinless fermionic $p\\pm ip$ superfluid living on a\ntwo-dimensional sphere. Using superfluid hydrodynamics we show that the ground\nstate necessarily exhibits topological defects: either a pair of elementary\nvortices or a domain wall between $p\\pm ip$ phases. In the topologically\nnontrivial BCS phase we identify the chiral fermion modes localized on the\ntopological defects and compute their low-energy spectrum."
    },
    {
        "anchor": "Effective potential and quantum criticality for imbalanced Fermi\n  mixtures: We study the analytical structure of the effective action for spin- and\nmass-imbalanced Fermi mixtures at the onset of the superfluid state. Of our\nparticular focus is the possibility of suppressing the tricritical temperature\nto zero, so that the transition remains continuous down to $T=0$ and the phase\ndiagram hosts a quantum critical point. At mean-field level we analytically\nidentify such a possibility in a regime of parameters in dimensionality $d=3$.\nIn contrast, in $d=2$ we demonstrate that the occurrence of a quantum critical\npoint is (at the mean-field level) excluded. We show that the Landau expansion\nof the effective potential remains well-defined in the limit $T\\to 0^+$ except\nfor a subset of model parameters which includes the standard BCS limit. We\ncalculate the mean-field asymptotic shape of the transition line. Employing the\nfunctional renormalization group framework we go beyond the mean field theory\nand demonstrate the stability of the quantum critical point in $d=3$ with\nrespect to fluctuations.",
        "positive": "Artificial gauge fields for the Bose-Hubbard model on a checkerboard\n  superlattice and extended Bose-Hubbard model: We study the effects of an artificial gauge field on the ground-state phases\nof the Bose-Hubbard model on a checkerboard superlattice in two dimensions,\nincluding the superfluid phase and the Mott and alternating Mott insulators.\nFirst, we discuss the single-particle Hofstadter problem, and show that the\npresence of a checkerboard superlattice gives rise to a magnetic\nflux-independent energy gap in the excitation spectrum. Then, we consider the\nmany-particle problem, and derive an analytical mean-field expression for the\nsuperfluid-Mott and superfluid--alternating-Mott insulator phase transition\nboundaries. Finally, since the phase diagram of the Bose-Hubbard model on a\ncheckerboard superlattice is in many ways similar to that of the extended\nBose-Hubbard model, we comment on the effects of magnetic field on the latter\nmodel, and derive an analytical mean-field expression for the\nsuperfluid-insulator phase transition boundaries as well."
    },
    {
        "anchor": "Floquet topological phases with large winding number: Recently, anomalous Floquet topological phases without static counterparts\nhave been observed in different systems, where periodically driven models are\nrealized to support a winding number of 1 and a pair of edge modes in each\nquasienergy gap. Here, we focus on cold atomic gases in optical lattices and\npropose a novel driving scheme that breaks rotation symmetry but maintains\ninversion symmetry of the instantaneous Hamiltonian, and discover a novel type\nof anomalous Floquet topological phase with winding number larger than 1. By\nanalyzing the condition of band touching under symmetry constraint, we map out\nthe phase diagram exactly by varying the driving parameters and discuss the\nquasienergy spectra of typical topological phases, which can present multiple\npairs of edge modes within a single gap. Finally, we suggest to characterize\nthe topology of such phases by detecting the band inversion surfaces via quench\ndynamics.",
        "positive": "Topological phases of spinless $p$-orbital fermions in zigzag optical\n  lattices: Motivated by the experiment [St-Jean {\\it et al}., Nature Photon. {\\bf 11},\n651 (2017)] on topological phases with collective photon modes in a zigzag\nchain of polariton micropillars, we study spinless $p$-orbital fermions with\nlocal interorbital hoppings and repulsive interactions between $p_x$ and $p_y$\nbands in zigzag optical lattices. We show that spinless $p$-band fermions in\nzigzag optical lattices can mimic the interacting Su-Schrieffer-Heeger model\nand the effective transverse field Ising model in the presence of local\nhoppings. We analytically and numerically discuss the ground-state phases and\nquantum phase transitions of the model. This work provides a simple scheme to\nsimulate topological phases and the quench dynamics of many-body systems in\noptical lattices."
    },
    {
        "anchor": "Dipole oscillation of a trapped Bose--Fermi-mixture gas in collisionless\n  and hydrodynamic regimes: Dipole oscillation is studied in a normal phase of a trapped\nBose--Fermi-mixture gas composed of single-species bosons and single-species\nfermions. Applying the moment method to the linearized Boltzmann equation, we\nderive a closed set of equations of motion for the center-of-mass position and\nmomentum of both components. By solving the coupled equations, we reveal the\nbehavior of dipole modes in the transition between the collisionless regime and\nthe hydrodynamic regime. We find that two oscillating modes in the\ncollisionless regime have distinct fates in the hydrodynamic regime: one\ncollisionless mode shows a crossover to a hydrodynamic in-phase mode, and the\nother collisionless mode shows a transition to two purely damped modes. The\ntemperature dependence of these dipole modes are also discussed.",
        "positive": "Characterizing Topological Excitations of a Long-Range Heisenberg Model\n  with Trapped Ions: Realizing and characterizing interacting topological phases in synthetic\nquantum systems is a formidable challenge. Here, we propose a Floquet protocol\nto realize the antiferromagnetic Heisenberg model with power-law decaying\ninteractions. Based on analytical and numerical arguments, we show that this\nmodel features a quantum phase transition from a liquid to a valence bond solid\nthat spontaneously breaks lattice translational symmetry and is reminiscent of\nthe Majumdar-Ghosh state. The different phases can be probed dynamically by\nmeasuring the evolution of a fully dimerized state. We moreover introduce an\ninterferometric protocol to characterize the topological excitations and the\nbulk topological invariants of the interacting many-body system."
    },
    {
        "anchor": "Strongly bound fermion pairs on a ring: a composite-boson approach: Particles made of two fermions can in many cases be treated as elementary\nbosons, but the conditions for this treatment to be valid are nontrivial. The\nso-called \"coboson formalism\" is a powerful tool to tackle compositeness\neffects relevant for instance for exciton physics and ultracold atomic dimers.\nA key element of this theory is an ansatz for the ground state of N pairs,\nbuilt from the single-pair ground state combined with the exclusion principle.\nWe show that this ansatz can fail in one-dimensional systems which fulfill the\nconditions expected to make the ansatz valid. Nevertheless, we also explain how\ncoboson theory can recover the correct ground state. Thus, our work highlights\nlimitations and strengths of the formalism and leads to a better treatment of\ncomposite bosons.",
        "positive": "Dynamics of gap solitons in a dipolar Bose-Einstein condensate on a\n  three-dimensional optical lattice: We suggest and study the stable disk- and cigar-shaped gap solitons of a\ndipolar Bose-Einstein condensate of $^{52}$Cr atoms localized in the lowest\nband gap by three optical-lattice (OL) potentials along orthogonal directions.\nThe one-dimensional version of these solitons of experimental interest confined\nby an OL along the dipole moment direction and harmonic traps in transverse\ndirections is also considered. Important dynamics of (i) breathing oscillation\nof a gap soliton upon perturbation and (ii) dragging of a gap soliton by a\nmoving lattice along axial $z$ direction demonstrates the stability of gap\nsolitons. A movie clip of dragging of three-dimensional gap soliton is\nincluded."
    },
    {
        "anchor": "Ground-state properties and elementary excitations of quantum droplets\n  in dipolar Bose-Einstein condensates: Recent experiments have revealed the formation of stable droplets in dipolar\nBose-Einstein condensates. This surprising result has been explained by the\nstabilization given by quantum fluctuations. We study in detail the properties\nof a BEC in the presence of quantum stabilization. The ground-state phase\ndiagram presents three main regimes: mean-field regime, in which the quantum\ncorrection is perturbative, droplet regime, in which quantum stabilization is\ncrucial, and a multi-stable regime. In the absence of a multi-stable region,\nthe condensate undergoes a crossover from the mean-field to the droplet\nsolution marked by a characteristic growth of the peak density that may be\nemployed to clearly distinguish quantum stabilization from other stabilization\nmechanisms. Interestingly quantum stabilization allows for three-dimensionally\nself-bound condensates. We characterized these self-bound solutions, and\ndiscuss their realization in experiments. We conclude with a discussion of the\nlowest-lying excitations both for trapped condensates, and for self-bound\nsolutions.",
        "positive": "Vortex lattice in a uniform Bose-Einstein condensate in a box trap: We study numerically the vortex-lattice formation in a rapidly rotating\nuniform quasi-two-dimensional Bose-Einstein condensate (BEC) in a box trap. We\nconsider two types of boxes: square and circle. In a square-shaped 2D box trap,\nwhen the number of generated vortices is the square of an integer, the vortices\nare found to be arranged in a perfect square lattice, although deviations near\nthe center are found when the number of generated vortices is arbitrary. In\ncase of a circular box trap, the generated vortices in the rapidly rotating BEC\nlie on concentric closed orbits. Near the center, these orbits have the shape\nof polygons, whereas near the periphery the orbits are circles. The circular\nbox trap is equivalent to the rotating cylindrical bucket used in early\nexperiment(s) with liquid He II. The number of generated vortices in both cases\nis in qualitative agreement with Feynman's universal estimate. The numerical\nsimulation for this study is performed by a solution of the underlying\nmean-field Gross-Pitaevskii (GP) equation in the rotating frame, where the wave\nfunction for the generated vortex lattice is a stationary state. Consequently,\nthe imaginary-time propagation method can be used for a solution of the GP\nequation, known to lead to an accurate numerical solution. We also demonstrated\nthe dynamical stability of the vortex lattices in real-time propagation upon a\nsmall change of the angular frequency of rotation, using the converged\nimaginary-time wave function as the initial state."
    },
    {
        "anchor": "Strongly Interacting One-Dimensional Systems with Small Mass Imbalance: We study a strongly interacting system of N identical bosons and one impurity\nin a one-dimensional trap. First, we assume that the particles have identical\nmasses and analyze the corresponding set-up. After that, we study the influence\nof a small mass asymmetry on our analysis. In particular, we discuss how the\nstructure of the wave function and the degeneracy in the impenetrable regime\ndepend on the mass ratio and the shape of the trapping potential. To illustrate\nour findings, we consider a four-body system in a box and in an oscillator. We\nshow that in the former case the system has the smallest energy when a heavy\n(light) impurity is close to the edge (center) of the trap. And we demonstrate\nthat the opposite is true in the latter case.",
        "positive": "Bright solitary matter waves: formation, stability and interactions: In recent years, bright soliton-like structures composed of gaseous\nBose-Einstein condensates have been generated at ultracold temperature. The\nexperimental capacity to precisely engineer the nonlinearity and potential\nlandscape experienced by these solitary waves offers an attractive platform for\nfundamental study of solitonic structures. The presence of three spatial\ndimensions and trapping implies that these are strictly distinct objects to the\ntrue soliton solutions. Working within the zero-temperature mean-field\ndescription, we explore the solutions and stability of bright solitary waves,\nas well as their interactions. Emphasis is placed on elucidating their\nsimilarities and differences to the true bright soliton. The rich behaviour\nintroduced in the bright solitary waves includes the collapse instability and\nsymmetry-breaking collisions. We review the experimental formation and\nobservation of bright solitary matter waves to date, and compare to theoretical\npredictions. Finally we discuss the current state-of-the-art of this area,\nincluding beyond-mean-field descriptions, exotic bright solitary waves, and\nproposals to exploit bright solitary waves in interferometry and as surface\nprobes."
    },
    {
        "anchor": "Dark-Bright Solitons in a Superfluid Bose-Fermi Mixture: The recent experimental realization of Bose-Fermi superfluid mixtures of\ndilute ultracold atomic gases has opened new perspectives in the study of\nquantum many-body systems. Depending on the values of the scattering lengths\nand the amount of bosons and fermions, a uniform Bose-Fermi mixture is\npredicted to exhibit a fully mixed phase, a fully separated phase or, in\naddition, a purely fermionic phase coexisting with a mixed phase. The\noccurrence of this intermediate configuration has interesting consequences when\nthe system is nonuniform. In this work we theoretically investigate the case of\nsolitonic solutions of coupled Bogoliubov-de Gennes and Gross-Pitaevskii\nequations for the fermionic and bosonic components, respectively. We show that,\nin the partially separated phase, a dark soliton in Fermi superfluid is\naccompanied by a broad bosonic component in the soliton, forming a dark-bright\nsoliton which keeps full spatial coherence.",
        "positive": "Josephson plasma oscillations and the Gross-Pitaevskii equation:\n  Bogoliubov approach vs two-mode model: We show that the Josephson plasma frequency for a condensate in a double-well\npotential, whose dynamics is described by the Gross-Pitaevskii (GP) equation,\ncan be obtained with great precision by means of the usual Bogoliubov approach,\nwhereas the two-mode model - commonly constructed by means of a linear\ncombinations of the low-lying states of the GP equation - generally provides\naccurate results only for weak interactions. A proper two-mode model in terms\nof the Bogoliubov functions is also discussed, revealing that in general a\ntwo-mode approach is formally justified only for not too large interactions,\neven in the limit of very small amplitude oscillations. Here we consider\nspecifically the case of a one-dimensional system, but the results are expected\nto be valid in arbitrary dimensions."
    },
    {
        "anchor": "Reaction kinetics of ultracold molecule-molecule collisions: Studying chemical reactions on a state-to-state level tests and improves our\nfundamental understanding of chemical processes. For such investigations it is\nconvenient to make use of ultracold atomic and molecular reactants as they can\nbe prepared in well defined internal and external quantum states$^{1-4}$. In\ngeneral, even cold reactions have many possible final product states$^{5-15}$\nand reaction channels are therefore hard to track individually$^{16}$. In\nspecial cases, however, only a single reaction channel is essentially\nparticipating, as observed e.g. in the recombination of two atoms forming a\nFeshbach molecule$^{17-19}$ or in atom-Feshbach molecule exchange\nreactions$^{20,21}$. Here, we investigate a single-channel reaction of two\nLi$_2$-Feshbach molecules where one of the molecules dissociates into two atoms\n$2\\mathrm{AB}\\Rightarrow \\mathrm{AB}+\\mathrm{A}+\\mathrm{B}$. The process is a\nprototype for a class of four-body collisions where two reactants produce three\nproduct particles. We measure the collisional dissociation rate constant of\nthis process as a function of collision energy/ temperature and scattering\nlength. We confirm an Arrhenius-law dependence on the collision energy, an\n$a^4$ power-law dependence on the scattering length $a$ and determine a\nuniversal four body reaction constant.",
        "positive": "Dissipation Mechanisms in Fermionic Josephson Junction: We characterize numerically the dominant dynamical regimes in a superfluid\nultracold fermionic Josephson junction. Beyond the coherent Josephson plasma\nregime, we discuss the onset and physical mechanism of dissipation due to the\nsuperflow exceeding a characteristic speed, and provide clear evidence\ndistinguishing its physical mechanism across the weakly- and\nstrongly-interacting limits, despite qualitative dynamics of global\ncharacteristics being only weakly sensitive to the operating dissipative\nmechanism. Specifically, dissipation in the strongly interacting regime occurs\nthrough the phase-slippage process, caused by the emission and propagation of\nquantum vortices, and sound waves -- similar to the Bose-Einstein condensation\nlimit. Instead, in the weak interaction limit, the main dissipative channel\narises through the pair-breaking mechanism."
    },
    {
        "anchor": "Quantum effective action for the bosonic Josephson junction: We investigate a bosonic Josephson junction by using the path-integral\nformalism with relative phase and population imbalance as dynamical variables.\nWe derive an effective only-phase action performing functional integration over\nthe population imbalance. We then analyze the quantum effective only-phase\naction, which formally contains all the quantum corrections. To the second\norder in the derivative expansion and to the lowest order in $\\hbar$, we obtain\nthe quantum correction to the Josephson frequency of oscillation. Finally, the\nsame quantum correction is found by adopting an alternative approach. Our\npredictions are a useful theoretical tool for experiments with atomic or\nsuperconducting Josephson junctions.",
        "positive": "Properties of a dipolar condensate with three-body interactions: We obtain the phase diagram for a harmonically trapped dilute dipolar\ncondensate with a short ranged conservative three-body interaction. We show\nthat this system supports two distinct fluid states: a usual condensate state\nand a self-cohering droplet state. We develop a simple model to quantify the\nenergetics of these states, which we verify with full numerical calculations.\nBased on our simple model we develop a phase diagram showing that there is a\nfirst order phase transition between the states. Using dynamical simulations we\nexplore the phase transition dynamics, revealing that the droplet crystal\nobserved in previous work is an excited state that arises from heating as the\nsystem crosses the phase transition. Utilising our phase diagram we show it is\nfeasible to produce a single droplet by dynamically adjusting the confining\npotential."
    },
    {
        "anchor": "Universal Quantum Viscosity in a Unitary Fermi Gas: A Fermi gas of atoms with resonant interactions is predicted to obey\nuniversal hydrodynamics, where the shear viscosity and other transport\ncoefficients are universal functions of the density and temperature. At low\ntemperatures, the viscosity has a universal quantum scale $\\hbar n$ where $n$\nis the density, while at high temperatures the natural scale is $p_T^3/\\hbar^2$\nwhere $p_T$ is the thermal momentum. We employ breathing mode damping to\nmeasure the shear viscosity at low temperature. At high temperature $T$, we\nemploy anisotropic expansion of the cloud to find the viscosity, which exhibits\nprecise $T^{3/2}$ scaling. In both experiments, universal hydrodynamic\nequations including friction and heating are used to extract the viscosity. We\nestimate the ratio of the shear viscosity to the entropy density and compare to\nthat of a perfect fluid.",
        "positive": "Chiral Supersolid in Spin-Orbit-Coupled Bose Gases with Soft-Core\n  Long-Range Interactions: Chirality represents a kind of symmetry breaking characterized by the\nnoncoincidence of an object with its mirror image and has been attracting\nintense attention in a broad range of scientific areas. The recent realization\nof spin-orbit coupling in ultracold atomic gases provides a new perspective to\nstudy quantum states with chirality. In this Letter, we demonstrate that the\ncombined effects of spin-orbit coupling and interatomic soft-core long-range\ninteraction can induce an exotic supersolid phase in which the chiral symmetry\nis broken with spontaneous emergence of circulating particle current. This\nimplies that a finite angular momentum can be generated with neither rotation\nnor effective magnetic field. The direction of the angular momentum can be\naltered by adjusting the strength of spin-orbit coupling or interatomic\ninteraction. The predicted chiral supersolid phase can be experimentally\nobserved in Rydberg-dressed Bose-Einstein condensates with spin-orbit coupling."
    },
    {
        "anchor": "Fidelity plateaus from correlated noise in isolated few-level quantum\n  systems: We show that, in an isolated two-level quantum system described by a\ntime-dependent Hamiltonian, correlated noise in the Hamiltonian's parameters\ncan lead to an arbitrarily long plateau in the state-preparation fidelity as a\nfunction of elapsed time. We explain the formation of this plateau using the\nBloch-sphere representation, deriving analytical expressions for its start and\nend times and its height. We also briefly discuss the extent to which this\nphenomenon is expected to be visible in more general quantum systems with $N>2$\nlevels.",
        "positive": "Semiclassical spectral function for matter waves in random potentials: An $\\hbar$-expansion is presented for the ensemble-averaged spectral function\nof noninteracting matter waves in random potentials. We obtain the leading\nquantum corrections to the deep classical limit at high energies by the\nWigner-Weyl formalism. The analytical results are checked with success against\nnumerical data for Gaussian and laser speckle potentials with Gaussian spatial\ncorrelation in two dimensions."
    },
    {
        "anchor": "Dynamical phase transition in the open Dicke model: The Dicke model with a weak dissipation channel is realized by coupling a\nBose-Einstein condensate to an optical cavity with ultra-narrow bandwidth. We\nexplore the dynamical critical properties of the Hepp-Lieb-Dicke phase\ntransition by performing quenches across the phase boundary. We observe\nhysteresis in the transition between a homogeneous phase and a self-organized\ncollective phase with an enclosed loop area showing power law scaling with\nrespect to the quench time, which suggests an interpretation within a general\nframework introduced by Kibble and Zurek. The observed hysteretic dynamics is\nwell reproduced by numerically solving the mean field equation derived from a\ngeneralized Dicke Hamiltonian. Our work promotes the understanding of\nnonequilibrium physics in open many-body systems with infinite range\ninteractions.",
        "positive": "Solitonic Vortices in Bose-Einstein Condensates: We analyse, theoretically and experimentally, the nature of solitonic\nvortices (SV) in an elongated Bose-Einstein condensate. In the experiment, such\ndefects are created via the Kibble-Zurek mechanism, when the temperature of a\ngas of sodium atoms is quenched across the BEC transition, and are imaged after\na free expansion of the condensate. By using the Gross-Pitaevskii equation, we\ncalculate the in-trap density and phase distributions characterizing a SV in\nthe crossover from an elongate quasi-1D to a bulk 3D regime. The simulations\nshow that the free expansion strongly amplifies the key features of a SV and\nproduces a remarkable twist of the solitonic plane due to the quantized\nvorticity associated with the defect. Good agreement is found between\nsimulations and experiments."
    },
    {
        "anchor": "Dynamics in asymmetric double-well condensates: The dynamics of Bose-Einstein condensates in asymmetric double-wells is\nstudied. We construct a two-mode model and analyze the properties of the\ncorresponding phase-space diagram, showing in particular that the minimum of\nthe phase-space portrait becomes shifted from the origin as a consequence of\nthe nonvanishing overlap between the ground and excited states from which the\nlocalized states are derived. We further incorporate effective interaction\ncorrections in the set of two-mode model parameters. Such a formalism is\napplied to a recent experimentally explored system, which is confined by a\ntoroidal trap with radial barriers forming an arbitrary angle between them. We\nconfront the model results with Gross-Pitaevskii simulations for various angle\nvalues finding a very good agreement. We also analyze the accuracy of a\npreviously employed simple model for moving barriers, exploring a possible\nimprovement that could cover a wider range of trap asymmetries.",
        "positive": "Observation of bosonic condensation in a hybrid monolayer MoSe2-GaAs\n  microcavity: Condensation of bosons into a macroscopic quantum state belongs to the most\nintriguing phenomena in nature. It was first realized in quantum gases of\nultra-cold atoms, but more recently became accessible in open-dissipative,\nexciton-based solid-state systems at elevated temperatures. Semiconducting\nmonolayer crystals have emerged as a new platform for studies of strongly bound\nexcitons in ultimately thin materials. Here, we demonstrate the formation of a\nbosonic condensate driven by excitons hosted in an atomically thin layer of\nMoSe2, strongly coupled to light in a solid-state resonator. The structure is\noperated in the regime of collective strong coupling, giving rise to hybrid\nexciton-polariton modes composed of a Tamm-plasmon resonance, GaAs quantum well\nexcitons and two-dimensional excitons confined in a monolayer of MoSe2.\nPolariton condensation in a monolayer crystal manifests by a superlinear\nincrease of emission intensity from the hybrid polariton mode at injection\npowers as low as 4.8 pJ/pulse, as well as its density-dependent blueshift and a\ndramatic collapse of the emission linewidth as a hallmark of temporal\ncoherence. Importantly, we observe a significant spin-polarization in the\ninjected polariton condensate, a fingerprint of the core property of monolayer\nexcitons subject to spin-valley locking. The observed effects clearly underpin\nthe perspective of building novel highly non-linear valleytronic devices based\non light-matter fluids, coherent bosonic light sources based on atomically thin\nmaterials, and paves the way towards studying materials with unconventional\ntopological properties in the framework of bosonic condensation."
    },
    {
        "anchor": "Giant Enhancement of the Thermo-Particle Transport Figure of Merit and\n  Breakdown of the Wiedemann-Franz Law in Unitary Fermi Gases: We theoretically investigate the thermo-particle transport properties of an\nunitary Fermi gas be- tween two reservoirs connected by a quantum point\ncontact. We find several distinguished properties that are qualitatively\ndifferent from those of weak or non-interacting gas systems. The particle\ntrans- port figure of merit is drastically enhanced in the unitary regime and\nit increases as the transmission coefficient increases, exactly opposite to the\nbehavior in the weak or non-interacting gas systems. The Lorentz number\nviolates the Wiedemann-Franz law, demonstrating the breakdown of Fermi liquid.\nThese transport properties are the hallmarks of the unitary Fermi gas and are\nattributed to the existence of preformed Cooper pairs.",
        "positive": "Particle Fluctuations in Mesoscopic Bose Systems: Particle fluctuations in mesoscopic Bose systems of arbitrary spatial\ndimensionality are considered. Both ideal Bose gases and interacting Bose\nsystems are studied in the regions above the Bose-Einstein condensation\ntemperature $T_c$ as well as below this temperature. The strength of particle\nfluctuations defines whether the system is stable or not. Stability conditions\ndepend on the spatial dimensionality $d$ and on the confining dimension $D$ of\nthe system. The consideration shows that mesoscopic systems, experiencing\nBose-Einstein condensation, are stable when: (i) ideal Bose gas is confined in\na rectangular box of spatial dimension $d>2$ above $T_c$ and in a box of $d>4$\nbelow $T_c$; (ii) ideal Bose gas is confined in a power-law trap of a confining\ndimension $D>2$ above $T_c$ and of a confining dimension $D>4$ below $T_c$;\n(iii) interacting Bose system is confined in a rectangular box of dimension\n$d>2$ above $T_c$, while below $T_c$ particle interactions stabilize the\nBose-condensed system making it stable for $d=3$; (iv) nonlocal interactions\ndiminish the condensation temperature, as compared with the fluctuations in a\nsystem with contact interactions."
    },
    {
        "anchor": "Exact Solutions to Two-Component Many-Body Systems in One Dimension: We introduce a new type of models for two-component systems in one dimension\nsubject to exact solutions by Bethe ansatz, where the interspecies interactions\nare tunable via Feshbach resonant interactions. The applicability of Bethe\nansatz is obtained by fine-tuning the resonant energies, and the resulting\nsystems can be described by introducing intraspecies repulsive and interspecies\nattractive couplings $c_1$ and $c_2$. This kind of systems admits two types of\ninteresting solutions: In the regime with $c_1>c_2$, the ground state is a\nFermi sea of two-strings, where the Fermi momentum $Q$ is constrained to be\nsmaller than a certain value $Q^*$, and it provides an ideal scenario to\nrealize BCS-BEC crossover (from weakly attractive atoms to weakly repulsive\nmolecules) in one dimension; In the opposite regime with $c_1<c_2$, the ground\nstate is a single bright soliton even for fermionic atoms, which reveals itself\nas an embedded string solution.",
        "positive": "Cold chemistry: a few-body perspective on impurity physics of a single\n  ion in an ultracold bath: Impurity physics is a traditional topic in condensed matter physics that\nnowadays is being explored in the field of ultracold gases. Among the different\nclasses of impurities, we focus on charged impurities in an ultracold bath.\nWhen a single ion is brought in contact with an ultracold gas it is subjected\nto different reactive processes that can be understood from a cold chemistry\napproach. In this work, we present an outlook of approaches for the dynamics of\na single ion in a bath of ultracold atoms or molecules, complementing the usual\nmany-body approaches characteristic of impurity physics within condensed matter\nphysics. In particular, we focus on the evolution of a charged impurity in\ndifferent baths, including external time-dependent trapping potentials and we\nexplore the effect of the external laser sources present in ion-neutral hybrid\ntraps into the lifetime of an impurity."
    },
    {
        "anchor": "Creating artificial magnetic fields for cold atoms by photon-assisted\n  tunneling: This paper proposes a simple setup for introducing an artificial magnetic\nfield for neutral atoms in 2D optical lattices. This setup is based on the\nphenomenon of photon-assisted tunneling and involves a low-frequency periodic\ndriving of the optical lattice. This low-frequency driving does not affect the\nelectronic structure of the atom and can be easily realized by the same means\nwhich employed to create the lattice. We also address the problem of detecting\nthis effective magnetic field. In particular, we study the center of mass\nwave-packet dynamics, which is shown to exhibit certain features of cyclotron\ndynamics of a classical charged particle.",
        "positive": "Tuning the relaxation dynamics of ultracold atoms with an optical cavity: We investigate the out-of-equilibrium dynamics of ultracold atoms trapped in\nan optical lattice and loaded into an optical resonator that is driven\ntransversely. We derive an effective quantum master equation for weak\natom-light coupling that can be brought into Lindblad form both in the bad and\ngood cavity limits. In the so-called bad cavity regime, we find that the steady\nstate is always that of infinite temperature, but that the relaxation dynamics\ncan be highly non-trivial. For small hopping, the interplay between dissipation\nand strong interactions generally leads to anomalous diffusion in the space of\natomic configurations. However, for a fine-tuned ratio of cavity-mediated and\non-site interactions, we discover a limit featuring normal diffusion. In\ncontrast, for large hopping and vanishing on-site interactions, the system can\nbe described by a linear rate equation leading to an exponential approach of\nthe infinite-temperature steady state. Finally, in the good cavity regime, we\nshow that for vanishing on-site interactions, the system allows for optical\npumping between momentum mode pairs enabling cavity cooling."
    },
    {
        "anchor": "Catastrophes in non-equilibrium many-particle wave functions:\n  universality and critical scaling: As part of the quest to uncover universal features of quantum dynamics, we\nstudy catastrophes that form in simple many-body wave functions after a quench,\nfocusing on two-mode systems that include the two-site Bose Hubbard model, and\nunder some circumstances optomechanical systems and the Dicke model. When the\nwave function is plotted in Fock space plus time certain characteristic\nstructures generically appear that we identify as cusp caustics. In the\nvicinity of such a catastrophe the wave function takes on a universal form\ndescribed by the Pearcey function and obeys scaling relations which depend on\nthe total number of particles $N$. In the thermodynamic limit ($N \\rightarrow\n\\infty$) the cusp becomes singular, but at finite $N$ it is decorated by an\ninterference pattern. This pattern contains an intricate network of\nvortex-antivortex pairs, initiating a theory of topological structures in Fock\nspace. In the case where the quench takes the form of a $\\delta$-kick we show\nhow to analytically map the wave function onto the Pearcey function and hence\nobtain the scaling exponents for the size and position of the cusp, as well as\nthose for the amplitude and characteristic length scales of its interference\npattern.",
        "positive": "Controlling Many-Body Quantum Chaos: Bose-Hubbard systems: This work develops a quantum control application of many-body quantum chaos\nfor ultracold bosonic gases trapped in optical lattices. It is long known how\nto harness exponential sensitivity to changes in initial conditions for control\npurposes in classically chaotic systems. In the technique known as targeting,\ninstead of a hindrance to control, the instability becomes a resource.\nRecently, this classical targeting has been generalized to quantum systems\neither by periodically countering the inevitable quantum state spreading or by\nintroducing a control Hamiltonian, where both enable localized states to be\nguided along special chaotic trajectories toward any of a broad variety of\ndesired target states. Only strictly unitary dynamics are involved; i.e., it\ngives a coherent quantum targeting. In this paper, the introduction of a\ncontrol Hamiltonian is applied to Bose-Hubbard systems in chaotic dynamical\nregimes. Properly selected unstable mean field solutions can be followed quite\nrapidly to states possessing precise phase relationships and occupancies. In\nessence, the method generates a quantum simulation technique that can access\nrather special states. The protocol reduces to a time-dependent control of the\nchemical potentials, opening up the possibility for application in optical\nlattice experiments. Explicit applications to custom state preparation and\nstabilization of quantum many-body scars are presented in one- and\ntwo-dimensional lattices (three-dimensional applications are similarly\npossible)."
    },
    {
        "anchor": "Interface potential and line tension for Bose-Einstein condensate\n  mixtures near a hard wall: Within Gross-Pitaevskii (GP) theory we derive the interface potential V (l)\nwhich describes the interaction between the interface separating two demixed\nBose-condensed gases and an optical hard wall at a distance l. Previous work\nrevealed that this interaction gives rise to extraordinary wetting and\nprewetting phenomena. Calculations that explore non-equilibrium properties by\nusing l as a constraint provide a thorough explanation for this behavior. We\nfind that at bulk two-phase coexistence, V (l) for both complete wetting and\npartial wetting is monotonic with exponential decay. Remarkably, at the\nfirst-order wetting phase transition, V(l) is independent of l. This anomaly\nexplains the infinite continuous degeneracy of the grand potential reported\nearlier. As a physical application, using V(l) we study the three-phase contact\nline where the interface meets the wall under a contact angle theta. Employing\nan interface displacement model we calculate the structure of this\ninhomogeneity and its line tension tau. Contrary to what happens at a usual\nfirst-order wetting transition in systems with short-range forces, tau does not\napproach a nonzero positive constant for theta going to zero, but instead\napproaches zero (from below) as would be expected for a critical wetting\ntransition. This hybrid character of tau is a consequence of the absence of a\nbarrier in V(l) at wetting. For a typical V(l) we provide a conjecture for the\nexact line tension within GP theory.",
        "positive": "Superfluid flow above the critical velocity: Superfluidity and superconductivity have been studied widely since the last\ncentury in many different contexts ranging from nuclear matter to atomic\nquantum gases. The rigidity of these systems with respect to external\nperturbations results in frictionless motion for superfluids and\nresistance-free electric current in superconductors. This peculiar behaviour is\nlost when external perturbations overcome a critical threshold, i.e. above a\ncritical magnetic field or a critical current for superconductors. In\nsuperfluids, such as liquid helium or ultracold gases, the corresponding\nquantities are critical rotation rate and critical velocity, respectively.\nEnhancing the critical values is of great fundamental and practical value. Here\nwe demonstrate that superfluidity can be achieved for flow above the critical\nvelocity through quantum interference induced resonances. This has far reaching\nconsequences for the fundamental understanding of superfluidity and\nsuperconductivity and opens up new application possibilities in quantum\nmetrology, e.g. in rotation sensing."
    },
    {
        "anchor": "Preparation of the spin-Mott state: a spinful Mott insulator of\n  repulsively bound pairs: We observe and study a special ground state of bosons with two spin states in\nan optical lattice: the spin-Mott insulator, a state that consists of\nrepulsively bound pairs which is insulating for both spin and charge transport.\nBecause of the pairing gap created by the interaction anisotropy, it can be\nprepared with low entropy and can serve as a starting point for adiabatic state\npreparation. We find that the stability of the spin-Mott state depends on the\npairing energy, and observe two qualitatively different decay regimes, one of\nwhich exhibits protection by the gap.",
        "positive": "Fermi distribution of semicalssical non-eqilibrium Fermi states: When a classical device suddenly perturbs a degenerate Fermi gas a\nsemiclassical non-equilibrium Fermi state arises. Semiclassical Fermi states\nare characterized by a Fermi energy or Fermi momentum that slowly depends on\nspace or/and time. We show that the Fermi distribution of a semiclassical Fermi\nstate has a universal nature. It is described by Airy functions regardless of\nthe details of the perturbation. In this letter we also give a general\ndiscussion of coherent Fermi states."
    },
    {
        "anchor": "Generalized formula for the Landau-Zener transition in interacting\n  Bose-Einstein condensates: We present a rigorous analysis of the generalized Landau-Zener problem for\nthe two-level interacting Bose-Einstein condensates. We show that the dynamics\nof the system is accurately, in detail, described by a two-term variational\nansatz that is valid for the whole time domain and is applicable for any set of\ninvolved parameters. Applying an exact third order nonlinear differential\nequation we construct an advanced fifth order polynomial equation for the final\ntransition probability serving as a highly accurate generalized Landau-Zener\nformula.",
        "positive": "Interaction-Shaped Vortex-Antivortex Lattices in Polariton Fluids: Topological defects such as quantized vortices are one of the most striking\nmanifestations of the superfluid nature of Bose-Einstein condensates and\ntypical examples of quantum mechanical phenomena on a macroscopic scale. Here\nwe demonstrate the formation of a lattice of vortex-antivortex pairs and study,\nfor the first time, its properties in the non-linear regime at high\npolarion-density where polariton-polariton interactions dominate the behaviour\nof the system. In this work first we demonstrate that the array of\nvortex-antivortex pairs can be generated in a controllable way in terms of size\nof the array and in terms of size and shape of it fundamental unit cell. Then\nwe demonstrate that polariton-polariton repulsion can strongly deform the\nlattice unit cell and determine the pattern distribution of the\nvortex-antivortex pairs, reaching a completely new behaviour with respect to\ngeometrically generated vortex lattices whose shape is determined only by the\ngeometry of the system."
    },
    {
        "anchor": "Interaction induced dynamical $\\mathcal{PT}$ symmetry breaking in\n  dissipative Fermi-Hubbard models: We investigate the dynamical properties of one-dimensional dissipative\nFermi-Hubbard models, which are described by the Lindblad master equations with\nsite-dependent jump operators. The corresponding non-Hermitian effective\nHamiltonians with pure loss terms possess parity-time ($\\mathcal{PT}$) symmetry\nif we compensate the system additionally an overall gain term. By solving the\ntwo-site Lindblad equation with fixed dissipation exactly, we find that the\ndynamics of rescaled density matrix shows an instability as the interaction\nincreases over a threshold, which can be equivalently described in the scheme\nof non-Hermitian effective Hamiltonians. This instability is also observed in\nmulti-site systems and closely related to the $\\mathcal{PT}$ symmetry breaking\naccompanied by appearance of complex eigenvalues of the effective Hamiltonian.\nMoreover, we unveil that the dynamical instability of the anti-ferromagnetic\nMott phase comes from the $\\mathcal{PT}$ symmetry breaking in highly excited\nbands, although the low-energy effective model of the non-Hermitian Hubbard\nmodel in the strongly interacting regime is always Hermitian. We also provide a\nquantitative estimation of the time for the observation of dynamical\n$\\mathcal{PT}$ symmetry breaking which could be probed in experiments.",
        "positive": "Ultracold Gas of Dipolar NaCs Ground State Molecules: We report on the creation of bosonic NaCs molecules in their absolute\nrovibrational ground state via stimulated Raman adiabatic passage. We create\nultracold gases with up to 22,000 dipolar NaCs molecules at a temperature of\n300(50) nK and a peak density of $1.0(4) \\times 10^{12}$ cm$^{-3}$. We\ndemonstrate comprehensive quantum state control by preparing the molecules in a\nspecific electronic, vibrational, rotational, and hyperfine state. Employing\nthe tunability and strength of the permanent electric dipole moment of NaCs, we\ninduce dipole moments of up to 2.6 D. Dipolar systems of NaCs molecules are\nuniquely suited to explore strongly interacting phases in dipolar quantum\nmatter."
    },
    {
        "anchor": "Non-equilibrium dynamics of fluctuations in an ultra-cold atomic mixture: We investigate an ultra-cold mixture of Bose gases interacting via\nspin-changing collisions by studying the dynamics of spin fluctuations. The\nexperimental implementation employs $^{23}$Na and $^{7}$Li atoms, which are\nprepared out of equilibrium across a wide range of initial conditions. We\nidentify three regimes in the dynamics of the system for different initial\nstates: a long-lived metastable regime, an instability range with strong growth\nof fluctuations, and a fast relaxing regime approaching thermal equilibrium.\nTheoretical modelling of the data allows us to reconstruct effective potentials\nwhich characterize the different dynamical regimes of the system.",
        "positive": "Ferroelectric quantum phase transition with cold polar molecules: We analyze a system of polar molecules in a one-dimensional optical lattice.\nBy controlling the internal structure of the polar molecules with static\nelectric and microwave fields, we demonstrate the appearance of a quantum phase\ntransition into a ferroelectric phase via spontaneous breaking of a $U(1)$\nsymmetry. The phase diagram is first analyzed within mean-field theory, while\nin a second step the results are verified by a mapping onto the Bose-Hubbard\nmodel for hard-core bosons. The latter is studied within the well-established\nbosonization procedure. We find that the ferroelectric phase is characterized\nby (quasi) long-range order for the electric dipole moments."
    },
    {
        "anchor": "Microscopic picture of superfluid $^4$He: We elucidate the microscopic quantum mechanism of superfluid $^4$He by\nuncovering a novel characteristic of its many-body energy levels. At\ntemperature below the transition point, the system's low-lying levels exhibit a\nfundamental grouping behavior, wherein each level belongs exclusively to a\nsingle group. In a superflow state, the system establishes thermal equilibrium\nwith its surroundings on a group-specific basis. Specifically, the levels of a\nselected group, initially occupied, become thermally populated, while the\nremaining groups of levels stay vacant due to absence of transitions between\ngroups. The macroscopic properties of the system, such as its superflow\nvelocity and thermal energy density, are statistically determined by the\nthermal distribution of the occupied group. Additionally, we infer that the\nthermal energy of a superflow has an unusual relationship with flow velocity,\nsuch that the larger the flow velocity, the smaller the thermal energy. This\nrelationship is responsible for a range of intriguing phenomena, including the\nmechano-caloric effect and the fountain effect, which highlight a fundamental\ncoupling between the thermal motion and hydrodynamic motion of the\nsystem.Furthermore, we present experimental evidence of a counterintuitive\nself-heating effect in $^4$He superflows, confirming that a $^4$He superflow\ncarries significant thermal energy related to its velocity.",
        "positive": "Superfluid Motion of Light: Superfluidity, the ability of a fluid to move without dissipation, is one of\nthe most spectacular manifestations of the quantum nature of matter. We explore\nhere the possibility of superfluid motion of light. Controlling the speed of a\nlight packet with respect to a defect, we demonstrate the presence of\nsuperfluidity and, above a critical velocity, its breakdown through the onset\nof a dissipative phase. We describe a possible experimental realization based\non the transverse motion through an array of waveguides. These results open new\nperspectives in transport optimization."
    },
    {
        "anchor": "Phonon Stability of Quantum Droplets in a dipolar Bose gases: Stabilized by quantum fluctuations, dipolar Bose-Einstein condensates can\nform self-bound liquidlike droplets in the mean-field unstable regime. However\nin the Bogoliubov theory, some phonon energies are imaginary in the\nlong-wavelength limit, implying dynamical instability of this system. A similar\ninstability appears in the Bogoliubov theory of a binary quantum droplet, and\nis removed due to higher-order quantum fluctuations as shown recently [1]. In\nthis work, we study the phonon energy of a dipolar quantum droplet in the\nBeliaev formalism, and find that quantum fluctuations can enhance the phonon\nstability. We obtain the anisotropic sound velocity which can be tested in\nexperiment.",
        "positive": "Excited states of two-dimensional solitons supported by the spin-orbit\n  coupling and field-induced dipole-dipole repulsion: It was recently found that excited states of semi-vortex and mixed-mode\nsolitons are unstable in spin-orbit-coupled Bose-Einstein condensates (BECs)\nwith contact interactions. We demonstrate a possibility to stabilize such\nexcited states in a setting based on repulsive dipole-dipole interactions\ninduced by a polarizing field, oriented perpendicular to the plane in which the\ndipolar BEC is trapped. The strength of the field is assumed to grow in the\nradial direction $\\sim $ $r^{4}$. Excited states of semi-vortex solitons have\nvorticities $S$ and $S+1$ in their two components, each being an eigenstate of\nthe angular momentum. They are fully stable up to $S=5$. Excited state of\nmixed-mode solitons feature interweaving necklace structures with opposite\nfractional values of the angular momentum in the two components. They are\nstable if they are built of dominant angular harmonics $\\pm S$, with $S\\leq 4$.\nCharacteristics and stability of these two types of previously unknown\nhigher-order solitons are systematically analyzed. Their characteristic size is\n$\\sim 10$ $\\mathrm{\\mu }$m, with the number of atoms $\\lesssim 10^{5}$"
    },
    {
        "anchor": "Remote multi-user control of the production of Bose-Einstein condensates\n  for research and education: Remote control of experimental systems allows for improved collaboration\nbetween research groups as well as unique remote educational opportunities\naccessible by students and citizen scientists. Here, we describe an experiment\nfor the production and investigation of ultracold quantum gases capable of\nasynchronous remote control by multiple remote users. This is enabled by a\nqueuing system coupled to an interface that can be modified to suit the user,\ne.g. a gamified interface for use by the general public or a scripted interface\nfor an expert. To demonstrate this, the laboratory was opened to remote experts\nand the general public. During the available time, remote users were given the\ntask of optimising the production of a Bose-Einstein condensate (BEC). This\nwork thus provides a stepping stone towards the exploration and realisation of\nmore advanced physical models by remote experts, students and citizen\nscientists alike.",
        "positive": "Few-particle systems: An analysis of some strongly correlated states: The analysis of the quantum Hall response of a small system of ultracold\nbosonic atoms through the variation of its Hall resistivity against the applied\ngauge magnetic field, provides a powerful method to unmask its strongly\ncorrelated states in a quite eshaustive way. Within a fixed range of values of\nthe magnetic field in the lowest Landau-level regime, where the resistivity\ndisplays two successive plateaux, we identify the implied states as the\nPfaffian and the state with filling factor \\nu=2/3 in the thermodynamic limit.\nWe fix the conditions to have good observability."
    },
    {
        "anchor": "Realization of uniform synthetic magnetic fields by periodically shaking\n  an optical square lattice: Shaking a lattice system, by modulating the location of its sites\nperiodically in time, is a powerful method to create effective magnetic fields\nin engineered quantum systems, such as cold gases trapped in optical lattices.\nHowever, such schemes are typically associated with space-dependent effective\nmasses (tunneling amplitudes) and non-uniform flux patterns. In this work we\ninvestigate this phenomenon theoretically, by computing the effective\nHamiltonians and quasienergy spectra associated with several kinds of\nlattice-shaking protocols. A detailed comparison with a method based on moving\nlattices, which are added on top of a main static optical lattice, is provided.\nThis study allows the identification of novel shaking schemes, which\nsimultaneously provide uniform effective mass and magnetic flux, with direct\nimplications for cold-atom experiments and photonics.",
        "positive": "Symmetry-broken states in a system of interacting bosons on a two-leg\n  ladder with a uniform Abelian gauge field: We study the quantum phases of bosons with repulsive contact interactions on\na two-leg ladder in the presence of a uniform Abelian gauge field. The model\nrealizes many interesting states, including Meissner phases, vortex-fluids,\nvortex-lattices, charge-density-waves and the biased-ladder phase. Our work\nfocuses on the subset of these states that break a discrete symmetry. We use\ndensity matrix renormalization group simulations to demonstrate the existence\nof three vortex-lattice states at different vortex densities and we\ncharacterize the phase transitions from these phases into neighboring states.\nFurthermore, we provide an intuitive explanation of the chiral-current reversal\neffect that is tied to some of these vortex lattices. We also study a\ncharge-density-wave state that exists at 1/4 particle filling at large\ninteraction strengths and flux values close to half a flux quantum. By changing\nthe system parameters, this state can transition into a completely gapped\nvortex-lattice Mott-insulating state. We elucidate the stability of these\nphases against nearest-neighbor interactions on the rungs of the ladder\nrelevant for experimental realizations with a synthetic lattice dimension. A\ncharge-density-wave state at 1/3 particle filling can be stabilized for flux\nvalues close to half a flux-quantum and for very strong on-site interactions in\nthe presence of strong repulsion on the rungs. Finally, we analytically\ndescribe the emergence of these phases in the low-density regime, and, in\nparticular, we obtain the boundaries of the biased-ladder phase, i.e., the\nphase that features a density imbalance between the legs. We make contact to\nrecent quantum-gas experiments that realized related models and discuss\nsignatures of these quantum states in experimentally accessible observables."
    },
    {
        "anchor": "A proposed signature of Anderson localization and correlation-induced\n  delocalization in an N-leg optical lattice: We propose a realization of the one-dimensional random dimer model and\ncertain N-leg generalizations using cold atoms in an optical lattice. We show\nthat these models exhibit multiple delocalization energies that depend strongly\non the symmetry properties of the corresponding Hamiltonian and we provide\nanalytical and numerical results for the localization length as a function of\nenergy. We demonstrate that the N-leg systems possess similarities with their\n1D ancestors but are demonstrably distinct. The existence of critical\ndelocalization energies leads to dips in the momentum distribution which serve\nas a clear signal of the localization-delocalization transition. These momentum\ndistributions are different for models with different group symmetries and are\nidentical for those with the same symmetry.",
        "positive": "Controlling the scattering length of ultracold dipolar molecules: By applying a circularly polarized and slightly blue-detuned microwave field\nwith respect to the first excited rotational state of a dipolar molecule, one\ncan engineer a long-range, shallow potential well in the entrance channel of\nthe two colliding partners. As the applied microwave ac-field is increased, the\nlong-range well becomes deeper and can support a certain numbers of bound\nstates, which in turn bring the value of the molecule-molecule scattering\nlength from a large negative value to a large positive one. We adopt an\nadimensional approach where the molecules are described by a rescaled\nrotational constant $\\tilde{B} = B/s_{E_3} $ where $s_{E_3}$ is a\ncharacteristic dipolar energy. We found that molecules with $\\tilde{B} > 10^8$\nare immune to any quenching losses when a sufficient ac-field is applied, the\nratio elastic to quenching processes can reach values above $10^3$, and that\nthe value and sign of the scattering length can be tuned. The ability to\ncontrol the molecular scattering length opens the door for a rich, strongly\ncorrelated, many-body physics for ultracold molecules, similar than that for\nultracold atoms."
    },
    {
        "anchor": "Dynamical symmetry and pair tunneling in a one-dimensional Bose gas\n  colliding with a mobile impurity: Using the time-dependent density matrix renormalization group (TDMRG) we\ntheoretically study the collision of a one-dimensional gas of interacting\nbosons with an impurity trapped in a shallow box potential. We study the\ndynamic response of both the impurity and the bosonic gas and find an\napproximate independence of the sign of the interaction (attractive or\nrepulsive) between the impurity and the bosons. This sign-independence breaks\ndown when the interaction energy is of the same order as the box potential\ndepth, leading to resonant pair tunneling. Our predictions can be tested using\ncontemporary techniques with ultracold atoms.",
        "positive": "Abnormal Superfluid Fraction of Harmonically Trapped Few-Fermion Systems: Superfluidity is a fascinating phenomenon that, at the macroscopic scale,\nleads to dissipationless flow and the emergence of vortices. While these\nmacroscopic manifestations of superfluidity are well described by theories that\nhave their origin in Landau's two-fluid model, our microscopic understanding of\nsuperfluidity is far from complete. Using analytical and numerical \\textit{ab\ninitio} approaches, this paper determines the superfluid fraction and local\nsuperfluid density of small harmonically trapped two-component Fermi gases as a\nfunction of the interaction strength and temperature. At low temperature, we\nfind that the superfluid fraction is, in certain regions of the parameter\nspace, negative. This counterintuitive finding is traced back to the symmetry\nof the system's ground state wave function, which gives rise to a diverging\nquantum moment of inertia $I_{\\text{q}}$. Analogous abnormal behavior of\n$I_{\\text{q}}$ has been observed in even-odd nuclei at low temperature. Our\npredictions can be tested in modern cold atom experiments."
    },
    {
        "anchor": "Dynamical Buildup of a Quantized Hall Response from Non-Topological\n  States: We consider a two-dimensional system initialized in a topologically trivial\nstate before its Hamiltonian is ramped through a phase transition into a Chern\ninsulator regime. This scenario is motivated by current experiments with\nultracold atomic gases aimed at realizing time-dependent dynamics in\ntopological insulators. Our main findings are twofold. First, considering\ncoherent dynamics, the non-equilibrium Hall response is found to approach a\ntopologically quantized time averaged value in the limit of slow but\nnon-adiabatic parameter ramps, even though the Chern number of the state\nremains trivial. Second, adding dephasing, the destruction of quantum coherence\nis found to stabilize this Hall response, while the Chern number generically\nbecomes undefined. We provide a geometric picture of this phenomenology in\nterms of the time-dependent Berry curvature.",
        "positive": "Simulation of nodal-line semimetal in amplitude-shaken optical lattices: With topologcial semimetal developing, semimetal with nodal-line ring comes\ninto people's vision as a powerful candidate for practical application of\ntopological devices. We propose a method using ultracold atoms in\ntwo-dimensional amplitude-shaken bipartite hexagonal optical lattice to\nsimulate nodal-line semimetal, which can be achieved in experiment by attaching\none triangular optical lattice to a hexangonal optical lattice and periodically\nmodulating the intensity and position of the triangular lattice. By amplitude\nshaking, a time-reversal-symmetry-unstable mode is introduced into the\nbipartite optical lattice, and then the nodal-line semimetal is gotten by\nadjusting the proportion of such mode and the trivial mode of hexagonal\nlattice. Through calculating the energy spectrum of effective Hamiltonian, the\ntransformation from Dirac semimetal to nodal-line semimetal in pace with\nchanging shaking parameters is observed. We also study the change of Berry\ncurvature and Berry phase in the transformation, which provides guidance on\nmeasuring the transformation in experiment. By analyzing the symmetry of the\nsystem, the emergence of the time-reversal-symmetry-unstable mode is\nresearched. This proposal provides a way to research the pure nodal-line\nsemimetal without the influence of other bands, which may contribute to the\nstudy of those unique features of surface states and bulk states of nodal-line\nsemimetal."
    },
    {
        "anchor": "Bose Hubbard Model in a Strong Effective Magnetic Field: Emergence of a\n  Chiral Mott Insulator Ground State: Motivated by experiments on Josephson junction arrays, and cold atoms in an\noptical lattice in a synthetic magnetic field, we study the \"fully frustrated\"\nBose-Hubbard (FFBH) model with half a magnetic flux quantum per plaquette. We\nobtain the phase diagram of this model on a two-leg ladder at integer filling\nvia the density matrix renormalization group approach, complemented by Monte\nCarlo simulations on an effective classical XY model. The ground state at\nintermediate correlations is consistently shown to be a chiral Mott insulator\n(CMI) with a gap to all excitations and staggered loop currents which\nspontaneously break time reversal symmetry. We characterize the CMI state as a\nvortex supersolid or an indirect exciton condensate, and discuss various\nexperimental implications.",
        "positive": "Interferometry of Efimov states in thermal gases by modulated magnetic\n  fields: We demonstrate that an interferometer based on modulated magnetic field\npulses enables precise characterization of the energies and lifetimes of Efimov\ntrimers irrespective of the magnitude and sign of the interactions in 85Rb\nthermal gases. Despite thermal effects, interference fringes develop when the\ndark time between the pulses is varied. This enables the selective excitation\nof coherent superpositions of trimer, dimer and free atom states. The\ninterference patterns possess two distinct damping timescales at short and long\ndark times that are either equal to or twice as long as the lifetime of Efimov\ntrimers, respectively. Specifically, this behavior at long dark times provides\nan interpretation of the unusually large damping timescales reported in a\nrecent experiment with 7Li thermal gases [Phys. Rev. Lett. 122, 200402 (2019)].\nApart from that, our results constitute a stepping stone towards a high\nprecision few-body state interferometry for dense quantum gases."
    },
    {
        "anchor": "Density and spin response of a strongly-interacting Fermi gas in the\n  attractive and quasi-repulsive regime: Recent experimental advances in ultra-cold Fermi gases allow for exploring\nresponse functions under different dynamical conditions. In particular, the\nissue of obtaining a \"quasi-repulsive\" regime starting from a Fermi gas with an\nattractive inter-particle interaction while avoiding the formation of the\ntwo-body bound state is currently debated. Here, we provide a calculation of\nthe density and spin response for a wide range of temperature and coupling both\nin the attractive and quasi-repulsive regime, whereby the system is assumed to\nevolve non-adiabatically toward the \"upper branch\" of the Fermi gas. A\ncomparison is made with the available experimental data for these two\nquantities.",
        "positive": "An extension of Bogoliubov theory for a many-body system with a time\n  scale hierarchy: the quantum mechanics of second Josephson oscillations: Adiabatic approximations are a powerful tool for simplifying nonlinear\nquantum dynamics, and are applicable whenever a system exhibits a hierarchy of\ntime scales. Current interest in small nonlinear quantum systems, such as\nfew-mode Bose-Hubbard models, warrants further development of adiabatic methods\nin the particular context of these models. Here we extend our recent work on a\nsimple four-mode Bose-Hubbard model with two distinct dynamical time scales, in\nwhich we showed that among the perturbations around excited stationary states\nof the system is a slow collective excitation that is not present in the\nBogoliubov spectrum. We characterized this mode as a resonant energy exchange\nwith its frequency shifted by nonlinear effects, and referred to it as a second\nJosephson oscillation, in analogy with the second sound mode of liquid helium\nII. We now generalize our previous theory beyond the mean field regime, and\nconstruct a general Bogoliubov free quasiparticle theory that explicitly\nrespects the system's adiabatic invariant as well the exact conservation of\nparticles. We compare this theory to the numerically exact quantum energy\nspectrum with up to forty particles, and find good agreement over a significant\nrange of parameter space."
    },
    {
        "anchor": "Dissipative dynamics of a driven quantum spin coupled to a bath of\n  ultracold fermions: We explore the dynamics and the steady state of a driven quantum spin coupled\nto a bath of fermions, which can be realized with a strongly imbalanced mixture\nof ultracold atoms using currently available experimental tools.\nRadio-frequency driving can be used to induce tunneling between the spin\nstates. The Rabi oscillations are modified due to the coupling of the quantum\nspin to the environment, which causes frequency renormalization and damping.\nThe spin-bath coupling can be widely tuned by adjusting the scattering length\nthrough a Feshbach resonance. When the scattering potential creates a bound\nstate, by tuning the driving frequency it is possible to populate either the\nground state, in which the bound state is filled, or a metastable state in\nwhich the bound state is empty. In the latter case, we predict an emergent\ninversion of the steady-state magnetization. Our work shows that different\nregimes of dissipative dynamics can be explored with a quantum spin coupled to\na bath of ultracold fermions.",
        "positive": "On the direct diagonalization method for a few particles trapped in\n  harmonic potentials: We describe a procedure to systematically improve direct diagonalization\nresults for few-particle systems trapped in one-dimensional harmonic potentials\ninteracting by contact interactions. We start from the two-body problem to\ndefine a renormalization method for the interparticle interactions. The\nprocedure is benchmarked with state-of-the-art numerical results for three and\nfour symmetric fermions."
    },
    {
        "anchor": "Sorting Fermionization from Crystallization in Many-Boson Wavefunctions: Fermionization is what happens to the state of strongly interacting repulsive\nbosons interacting with contact interactions in one spatial dimension.\nCrystallization is what happens for sufficiently strongly interacting repulsive\nbosons with dipolar interactions in one spatial dimension. Crystallization and\nfermionization resemble each other: in both cases -- due to their repulsion --\nthe bosons try to minimize their spatial overlap. We trace these two hallmark\nphases of strongly correlated one-dimensional bosonic systems by exploring\ntheir ground state properties using the one- and two-body density matrix. We\nsolve the $N$-body Schr\\\"odinger equation accurately and from first principles\nusing the multiconfigurational time-dependent Hartree for bosons (MCTDHB) and\nfor fermions (MCTDHF) methods. Using the one- and two-body density,\nfermionization can be distinguished from crystallization in position space. For\n$N$ interacting bosons, a splitting into an $N$-fold pattern in the one-body\nand two-body density is a unique feature of both, fermionization and\ncrystallization. We demonstrate that the splitting is incomplete for\nfermionized bosons and restricted by the confinement potential. This incomplete\nsplitting is a consequence of the convergence of the energy in the limit of\ninfinite repulsion and is in agreement with complementary results that we\nobtain for fermions using MCTDHF. For crystalline bosons, in contrast, the\nsplitting is complete: the interaction energy is capable of overcoming the\nconfinement potential. Our results suggest that the spreading of the density as\na function of the dipolar interaction strength diverges as a power law. We\ndescribe how to distinguish fermionization from crystallization experimentally\nfrom measurements of the one- and two-body density.",
        "positive": "Atom chips with free-standing two-dimensional electron gases: advantages\n  and challenges: In this work we consider the advantages and challenges of using free-standing\ntwo-dimensional electron gases (2DEG) as active components in atom chips for\nmanipulating ultracold ensembles of alkali atoms. We calculate trapping\nparameters achievable with typical high-mobility 2DEGs in an atom chip\nconfiguration, and identify advantages of this system for trapping atoms at\nsub-micron distances from the atom chip. We show how the sensitivity of atomic\ngases to magnetic field inhomogeneity can be exploited for controlling the\natoms with quantum electronic devices and, conversely, using the atoms to probe\nthe structural and transport properties of semiconductor devices."
    },
    {
        "anchor": "Many Fermi polarons at nonzero temperature: An extremely polarized mixture of an ultracold Fermi gas is expected to\nreduce to a Fermi polaron system, which consists of a single impurity immersed\nin the Fermi sea of majority atoms. By developing a many-body T -matrix theory,\nwe investigate spectral properties of the polarized mixture in experimentally\nrelevant regimes in which the system of finite impurity concentration at\nnonzero temperature is concerned. We explicitly demonstrate presence of polaron\nphysics in the polarized limit and discuss effects of many polarons in an\nintermediate regime in a self-consistent manner. By analyzing the spectral\nfunction at finite impurity concentration, we extract the attractive and\nrepulsive polaron energies. We find that a renormalization of majority atoms\nvia an interaction with minority atoms and a thermal depletion of the impurity\nchemical potential are of significance to depict the many-polaron regime.",
        "positive": "Quantum effects on one-dimensional collision dynamics of fermion\n  clusters: Recently, many experiments with cold atomic gases have been conducted from\ninterest in the non-equilibrium dynamics of correlated quantum systems. Of\nthese experiments, the mixing dynamics of fermion clusters motivates us to\nresearch cluster-cluster collision dynamics in one-dimensional Fermi systems.\nWe adopt the one-dimensional Fermi-Hubbard model and apply the time-dependent\ndensity matrix renormalization group method. We simulate collisions between two\nfermion clusters of spin-up and spin-down, and calculate reflectance of the\nclusters R changing the particle number in each cluster and the interaction\nstrength between two fermions with up and down spins. We also evaluate the\nquasi-classical (independent collision) reflectance R^{qc} to compare it with\nR. The quasi-classical picture is quantitatively valid in the limit of weak\ninteraction, but it is not valid when interaction is strong."
    },
    {
        "anchor": "Exotic magnetic orders for high spin ultracold fermions: We study Hubbard models for ultracold bosonic or fermionic atoms loaded into\nan optical lattice. The atoms carry a high spin $F>1/2$, and interact on site\nvia strong repulsive Van der Waals forces. Making convenient rearrangements of\nthe interaction terms, and exploiting their symmetry properties, we derive low\nenergy effective models with nearest-neighbor interactions, and their\nproperties. We apply our method to $F=3/2$, and 5/2 fermions on two-dimensional\nsquare lattice at quarter, and 1/6 fillings, respectively, and investigate\nmean-field equations for repulsive couplings. We find for $F=3/2$ fermions that\nthe plaquette state appearing in the highly symmetric SU(4) case does not\nrequire fine tuning, and is stable in an extended region of the phase diagram.\nThis phase competes with an SU(2) flux state, that is always suppressed for\nrepulsive interactions in absence of external magnetic field. The SU(2) flux\nstate has, however, lower energy than the plaquette phase, and stabilizes in\nthe presence of weak applied magnetic field. For $F=5/2$ fermions a similar\nSU(2) plaquette phase is found to be the ground state without external magnetic\nfield.",
        "positive": "Grey solitons in the ultracold fermions at the full spin polarization: A minimal coupling quantum hydrodynamic model of spin-1/2 fermions at the\nfull spin polarization corresponding to a nonlinear Schrodinger equation is\nconsidered. The nonlinearity is primarily caused by the Fermi pressure. It\nprovides an effective repulsion between fermions. However, there is the\nadditional contribution of the short-range interaction appearing in the third\norder by the interaction radius. It leads to the modification of the pressure\ncontribution. Solitons are considered for the infinite medium with no\nrestriction on the amplitude of the wave. The Fermi pressure leads to the\nsoliton in form of the area of decreased concentration. However, the center of\nsolution corresponding to the area of minimal concentration has nonzero value\nof concentration. Therefore, the grey soliton is found. Soliton exist if the\nspeed of its propagation is below the Fermi velocity."
    },
    {
        "anchor": "Quench induced vortex-bright-soliton formation in binary Bose-Einstein\n  condensates: We unravel the spontaneous generation of vortex-bright-soliton structures in\nbinary Bose-Einstein condensates with a small mass imbalance between the\nspecies confined in a two-dimensional harmonic trap where one of the two\nspecies has been segmented into two parts by a potential barrier. To trigger\nthe dynamics the potential barrier is suddenly removed and subsequently the\nsegments perform a counterflow dynamics. We consider a relative phase\ndifference of $\\pi$ between the segments, while a singly quantized vortex may\nbe imprinted at the center of the other species. The number of vortex\nstructures developed within the segmented species following the merging of its\nsegments is found to depend on the presence of an initial vortex on the other\nspecies. In particular, a $\\pi$ phase difference in the segmented species and a\nvortex in the other species result in a single vortex-bright-soliton structure.\nHowever, when the non-segmented species does not contain a vortex the\ncounterflow dynamics of the segmented species gives rise to a vortex dipole in\nit accompanied by two bright solitary waves arising in the non-segmented\nspecies. Turning to strongly mass imbalanced mixtures, with a heavier segmented\nspecies, we find that the same overall dynamics takes place, while the\nquench-induced nonlinear excitations become more robust. Inspecting the\ndynamics of the angular momentum we show that it can be transferred from one\nspecies to the other, and its transfer rate can be tuned by the strength of the\ninterspecies interactions and the mass of the atomic species.",
        "positive": "Bosonic binary mixtures with Josephson-type interactions: Motivated by experiments in bosonic mixtures composed of a single element in\ntwo different hyperfine states, we study bosonic binary mixtures in the\npresence of Josephson interactions between species. We focus on a particular\nmodel with $O(2)$ isospin symmetry, lifted by an imbalanced population\nparametrized by a Rabi frequency, $\\Omega _{R}$, and a detuning, $\\nu $, which\ncouples the phases of both species. We have studied the model at mean-field\napproximation plus Gaussian fluctuations. We have found that both species\nsimultaneously condensate below a critical temperature $T_{c}$ and the relative\nphases are locked by the applied laser phase, $\\alpha$. Moreover, the\ncondensate fractions are strongly dependent on the ratio $\\Omega _{R}/|\\nu |$\nthat is not affected by thermal fluctuations."
    },
    {
        "anchor": "Hyper-entangling mesoscopic bound states: We predict hyper-entanglement generation during binary scattering of\nmesoscopic bound states, solitary waves in Bose-Einstein condensates containing\nthousands of identical Bosons. The underlying many-body Hamiltonian must not be\nintegrable, and the pre-collision quantum state of the solitons fragmented.\nUnder these conditions, we show with pure state quantum field simulations that\nthe post-collision state will be hyper-entangled in spatial degrees of freedom\nand atom number within solitons, for realistic parameters. The effect links\naspects of non-linear systems and quantum-coherence and the entangled\npost-collision state challenges present entanglement criteria for identical\nparticles. Our results are based on simulations of colliding quantum solitons\nin a quintic interaction model beyond the mean-field, using the truncated\nWigner approximation.",
        "positive": "Two-species boson mixture on a ring: A group theoretic approach to the\n  quantum dynamics of low-energy excitations: We investigate the weak excitations of a system made up of two condensates\ntrapped in a Bose-Hubbard ring and coupled by an interspecies repulsive\ninteraction. Our approach, based on the Bogoliubov approximation scheme, shows\nthat one can reduce the problem Hamiltonian to the sum of sub-Hamiltonians\n$\\hat{H}_k$, each one associated to momentum modes $\\pm k$. Each $\\hat{H}_k$ is\nthen recognized to be an element of a dynamical algebra. This uncommon and\nremarkable property allows us to present a straightforward diagonalization\nscheme, to find constants of motion, to highlight the significant microscopic\nprocesses, and to compute their time evolution. The proposed solution scheme is\napplied to a simple but still very interesting closed circuit, the trimer. The\ndynamics of low-energy excitations, corresponding to weakly-populated vortices,\nis investigated considering different choices of the initial conditions, and\nthe angular-momentum transfer between the two condensates is evidenced.\nFinally, the condition for which the spectral collapse and dynamical\ninstability are observed is derived analytically."
    },
    {
        "anchor": "Efficient demagnetization cooling of atoms and its limits: Demagnetization cooling relies on spin-orbit coupling that brings motional\nand spin degrees of freedom into thermal equilibrium. In the case of a gas, one\nhas the advantage that the spin degree of freedom can be cooled very\nefficiently using optical pumping. We investigate demagnetization cooling of a\nchromium gas in a deep optical dipole trap over a large temperature range and\nreach high densities up to $5\\times 10^{19} m^{-3}$. We study the loss\nmechanism under such extreme conditions and identify excited-state collisions\nas the main limiting process. We discuss that in some systems demagnetization\ncooling has a realistic potential of reaching degeneracy by optical cooling\nonly.",
        "positive": "Exact Tkachenko modes and their damping in the vortex lattice regime of\n  rapidly rotating bosons: We have found an exact analytical solution of the Bogoliubov-de Gennes\nequations for the Tkachenko modes of the vortex lattice in the lowest Landau\nlevel (LLL) in the thermodynamic limit at any momenta and calculated their\ndamping rates. At finite temperatures both Beliaev and Landau damping leads to\nmomentum independent damping rates in the low-energy limit, which shows that at\nsufficiently low energies Tkachenko modes become strongly damped. We then found\nthat the mean square fluctuations of the density grow logarithmically at large\ndistances, which indicates that the state is ordered in the vortex lattice only\non a finite (although exponentially large) distance scale and introduces a\nlow-momentum cut-off. Using this circumstance we showed that at finite\ntemperatures the one-body density matrix undergoes an exponential decay at\nlarge distances."
    },
    {
        "anchor": "Long-lived fermionic Feshbach molecules with tunable $p$-wave\n  interactions: Ultracold fermionic Feshbach molecules are promising candidates for exploring\nquantum matter with strong $p$-wave interactions, however, their lifetimes were\nmeasured to be short. Here, we characterize the $p$-wave collisions of\nultracold fermionic $^{23}\\mathrm{Na}^{40}\\mathrm{K}$ Feshbach molecules for\ndifferent scattering lengths and temperatures. By increasing the binding energy\nof the molecules, the two-body loss coefficient reduces by three orders of\nmagnitude leading to a second-long lifetime, 20 times longer than that of\nground-state molecules. We exploit the scaling of elastic and inelastic\ncollisions with the scattering length and temperature to identify a regime\nwhere the elastic collisions dominate over the inelastic ones allowing the\nmolecular sample to thermalize. Our work provides a benchmark for four-body\ncalculations of molecular collisions and is essential for producing a\ndegenerate Fermi gas of Feshbach molecules.",
        "positive": "Tunable Superfluidity and Quantum Magnetism with Ultracold Polar\n  Molecules: By selecting two dressed rotational states of ultracold polar molecules in an\noptical lattice, we obtain a highly tunable generalization of the t-J model,\nwhich we refer to as the t-J-V-W model. In addition to XXZ spin exchange, the\nmodel features density-density interactions and novel density-spin\ninteractions; all interactions are dipolar. We show that full control of all\ninteraction parameters in both magnitude and sign can be achieved independently\nof each other and of the tunneling. As a first step towards demonstrating the\npotential of the system, we apply the density matrix renormalization group\nmethod (DMRG) to obtain the 1D phase diagram of the simplest experimentally\nrealizable case. Specifically, we show that the tunability and the long-range\nnature of the interactions in the t-J-V-W model enable enhanced superfluidity.\nFinally, we show that Bloch oscillations in a tilted lattice can be used to\nprobe the phase diagram experimentally."
    },
    {
        "anchor": "Pairing imbalance in BCS-BEC crossover of inhomogeneous three-component\n  Fermi-gas in two dimensions: We in this paper investigate the phase diagram associated with the BCS-BEC\ncrossover of a three-component ultracold superfluid-Fermi-gas of different\nchemical-potentials and equal masses in two dimensions. The gap order parameter\nand number densities are found analytically by using the functional\npath-integral method. The balance of paring will be broken in the free space\ndue to the unequal chemical-potentials. We obtain the same particle\nnumber-density and condensed fraction in the BCS superfluid phase as that in a\nrecent paper (Phys. Rev. A 83, 033630), while the Sarma phase of coexistence of\nnormal and superfluid Fermi gases is the characteristics of inhomogeneous\nsystem. The minimum ratio of BCS superfluid phase becomes 1/3 in the BCS limit\ncorresponding to the zero-ratio in the two-component system in which the\ncritical point of phase separation is {\\epsilon}B/{\\epsilon}F = 2 but becomes 3\nin the three-component case.",
        "positive": "Long-time expansion of a Bose-Einstein condensate: Can Anderson\n  localization be observed?: We numerically explore the long-time expansion of a one-dimensional\nBose-Einstein condensate in a disorder potential employing the Gross-Pitaevskii\nequation. The goal is to search for unique signatures of Anderson localization\nin the presence of particle-particle interactions. Using typical experimental\nparameters we show that the time scale for which the non-equilibrium dynamics\nof the interacting system begins to diverge from the non-interacting system\nexceeds the observation times up to now accessible in the experiment. We find\nevidence that the long-time evolution of the wavepacket is characterized by\n(sub)diffusive spreading and a growing effective localization length suggesting\nthat interactions destroy Anderson localization."
    },
    {
        "anchor": "Dynamical control of the conductivity of an atomic Josephson junction: We propose to dynamically control the conductivity of a Josephson junction\ncomposed of two weakly coupled one dimensional condensates of ultracold atoms.\nA current is induced by a periodically modulated potential difference between\nthe condensates, giving access to the conductivity of the junction. By using\nparametric driving of the tunneling energy, we demonstrate that the\nlow-frequency conductivity of the junction can be enhanced or suppressed,\ndepending on the choice of the driving frequency. The experimental realization\nof this proposal provides a quantum simulation of optically enhanced\nsuperconductivity in pump-probe experiments of high temperature\nsuperconductors.",
        "positive": "Scattering and bound states in two-dimensional anisotropic potentials: We propose a framework for calculating scattering and bound state properties\nin anisotropic two-dimensional potentials. Using our method, we derive\nsystematic approximations of partial wave phase shifts and binding energies.\nMoreover, the method is suitable for efficient numerical computations. We\ncalculate the s-wave phase shift and binding energy of polar molecules in two\nlayers polarized by an external field along an arbitrary direction. We find\nthat scattering depends strongly on their polarization direction and that\nabsolute interlayer binding energies are larger than thermal energies at\ntypical ultracold temperatures."
    },
    {
        "anchor": "Dissociation of one-dimensional matter-wave breathers due to quantum\n  many-body effects: We use the ab initio Bethe Ansatz dynamics to predict the dissociation of\none-dimensional cold-atom breathers that are created by a quench from a\nfundamental soliton. We find that the dissociation is a robust quantum\nmany-body effect, while in the mean-field (MF) limit the dissociation is\nforbidden by the integrability of the underlying nonlinear Schr\\\"{o}dinger\nequation. The analysis demonstrates the possibility to observe quantum\nmany-body effects without leaving the MF range of experimental parameters. We\nfind that the dissociation time is of the order of a few seconds for a typical\natomic-soliton setting.",
        "positive": "Quantum Kelvin-Helmholtz instability in phase-separated two-component\n  Bose-Einstein condensates: We theoretically study the Kelvin-Helmholtz instability in phase-separated\ntwo-component Bose-Einstein condensates using the Gross-Pitaevskii and\nBogoliubov-de Gennes models. A flat interface between the two condensates is\nshown to deform into sawtooth or Stokes-like waves, leading to the formation of\nsingly quantized vortices on the peaks and troughs of the waves. This scenario\nof interface instability in quantum fluids is quite different from that in\nclassical fluids."
    },
    {
        "anchor": "Physics of ultracold Fermi gases revealed by spectroscopies: This article provides a brief review of how various spectroscopies have been\nused to investitage many-body quantum phenomena in the context of ultracold\nFermi gases. In particular, work done with RF spectroscopy, Bragg spectroscopy\nand lattice modulation spectroscopy is considered. The theoretical basis of\nthese spectroscopies, namely linear response theory in the many-body quantum\nphysics context is briefly presented. Experiments related to the BCS-BEC\ncrossover, imbalanced Fermi gases, polarons, possible pseudogap and Fermi\nliquid behaviour and measuring the contact are discussed. Remaining open\nproblems and goals in the field are sketched from the perspective how\nspectroscopies could contribute.",
        "positive": "Effect of an oscillating Gaussian obstacle in a Dipolar Bose-Einstein\n  condensate: We study the dynamics of vortex dipoles in erbium ($^{168}$Er) and dysprosium\n($^{164}$Dy) dipolar Bose-Einstein condensates (BECs) by applying an\noscillating blue-detuned laser (Gaussian obstacle). For observing vortex\ndipoles, we solve a nonlocal Gross-Pitaevskii (GP) equation in quasi\ntwo-dimensions in real-time. We calculate the critical velocity for the\nnucleation of vortex dipoles in dipolar BECs with respect to dipolar\ninteraction strengths. We also show the dynamics of the group of vortex dipoles\nand rarefaction pulses in dipolar BECs. In the dipolar BECs with Gaussian\nobstacle, we observe rarefaction pulses due to the interaction of dynamically\nmigrating vortex dipoles."
    },
    {
        "anchor": "Two-body correlations and natural orbital tomography in ultracold\n  bosonic systems of definite parity: The relationship between natural orbitals, one-body coherences and two-body\ncorrelations is explored for bosonic many-body systems of definite parity with\ntwo occupied single-particle states. We show that the strength of local\ntwo-body correlations at the parity-symmetry center characterizes the number\nstate distribution and controls the structure of non-local two-body\ncorrelations. A recipe for the experimental reconstruction of the natural\norbital densities and quantum depletion is derived. These insights into the\nstructure of the many-body wave-function are applied to the predicted\nquantum-fluctuations induced decay of dark solitons.",
        "positive": "Three body on-site interactions in ultracold bosonic atoms in optical\n  lattices and superlattices: The Mott insulator-superfluid transition for ultracold bosonic atoms in an\noptical lattice has been extensively studied in the framework of the\nBose-Hubbard model with two-body on-site interactions. In this paper, we\nanalyze the additional effect of the three-body on-site interactions on this\nphase transition in optical lattice and the transitions between the various\nphases that arise in an optical superlattice. Using the mean-field theory and\nthe density matrix renormalization group method, we find the phase diagrams\ndepicting the relationships between various physical quantities in an optical\nlattice and superlattice. We also suggest possible experimental signatures to\nobserve the three-body interactions."
    },
    {
        "anchor": "Quantum Degenerate Mixtures of Cs and Yb: We report the production of quantum degenerate Bose-Bose mixtures of Cs and\nYb with both attractive (Cs + $^{174}$Yb) and repulsive (Cs + $^{170}$Yb)\ninterspecies interactions. Dual-species evaporation is performed in a\nbichromatic optical dipole trap that combines light at 1070 nm and 532 nm to\nenable control of the relative trap depths for Cs and Yb. Maintaining a trap\nwhich is shallower for Yb throughout the evaporation leads to highly efficient\nsympathetic cooling of Cs for both isotopic combinations at magnetic fields\nclose to the Efimov minimum in the Cs three-body recombination rate at around\n22 G. For Cs + $^{174}$Yb, we produce quantum mixtures with typical atom\nnumbers of $N_\\mathrm{Yb} \\sim 5 \\times 10^4$ and $N_\\mathrm{Cs} \\sim 5 \\times\n10^3$. We find that the attractive interspecies interaction (characterised by\nthe scattering length $a_\\mathrm{CsYb} = -75\\,a_0$) is stabilised by the\nrepulsive intraspecies interactions. For Cs + $^{170}$Yb, we produce quantum\nmixtures with typical atom numbers of $N_\\mathrm{Yb} \\sim 4 \\times 10^4$, and\n$N_\\mathrm{Cs} \\sim 1 \\times 10^4$. Here, the repulsive interspecies\ninteraction ($a_\\mathrm{CsYb} = 96\\,a_0$) can overwhelm the intraspecies\ninteractions, such that the mixture sits in a region of partial miscibility.",
        "positive": "Variational analysis of driven-dissipative Rydberg gases: We study the non-equilibrium steady state arising from the interplay between\ncoherent and dissipative dynamics in strongly interacting Rydberg gases using a\nrecently introduced variational method [H. Weimer, Phys. Rev. Lett. 114, 040402\n(2015)]. We give a detailed discussion of the properties of this novel\napproach, and we provide a comparison with methods related to the\nBogoliubov-Born-Green-Kirkwood-Yvon hierarchy. We find that the variational\napproach offers some intrinsic advantages, and we also show that it is able to\nexplain the experimental results obtained in an ultracold Rydberg gas on an\nunprecedented quantitative level."
    },
    {
        "anchor": "Matter rogue wave in Bose-Einstein condensates with attractive atomic\n  interaction: We investigate the matter rogue wave in Bose-Einstein Condensates with\nattractive interatomic interaction analytically and numerically. Our results\nshow that the formation of rogue wave is mainly due to the accumulation of\nenergy and atoms toward to its central part; Rogue wave is unstable and the\ndecay rate of the atomic number can be effectively controlled by modulating the\ntrapping frequency of external potential. The numerical simulation demonstrate\nthat even a small periodic perturbation with small modulation frequency can\ninduce the generation of a near-ideal matter rogue wave. We also give an\nexperimental protocol to observe this phenomenon in Bose-Einstein Condensates.",
        "positive": "Hydrodynamic relaxation of spin helices: Motivated by recent cold atom experiments, we study the relaxation of spin\nhelices in quantum XXZ spin chains. The experimentally observed relaxation of\nspin helices follows scaling laws that are qualitatively different from\nlinear-response transport. We construct a theory of the relaxation of helices,\ncombining generalized hydrodynamics (GHD) with diffusive corrections and the\nlocal density approximation. Although helices are far from local equilibrium\n(so GHD need not apply a priori), our theory reproduces the experimentally\nobserved relaxational dynamics of helices. In particular, our theory explains\nthe existence of temporal regimes with apparent anomalous diffusion, as well as\nthe asymmetry between positive and negative anisotropy regimes."
    },
    {
        "anchor": "Strong photon interactions from weakly interacting particles: The hybridization of light and matter excitations in the form of polaritons\nhas enabled major advances in understanding and controlling optical\nnonlinearities. Entering the quantum regime of strong interactions between\nindividual photons has however remained challenging since the strength of\nachievable polariton interactions is typically limited by the available\ninteractions in the material. Here, we investigate collisions between\ndark-state polaritons in three-level systems and discover a resonant process\nthat yields effective interactions, which are much larger than the underlying\ninteraction between their matter constituents. We systematically investigate\nthe underlying mechanism and demonstrate a substantial enhancement of polariton\ninteractions by several orders of magnitude. This suggests a promising approach\nto quantum nonlinear optics in a range of physical settings, from atomic gases\nto excitons in semiconductors and two-dimensional bilayer materials.",
        "positive": "Spin squeezing in mixed-dimensional anisotropic lattice models: We describe a theoretical scheme for generating scalable spin squeezing with\nnearest-neighbour interactions between spin-1/2 particles in a 3D lattice,\nwhich are naturally present in state-of-the-art 3D optical lattice clocks. We\npropose to use strong isotropic Heisenberg interactions within individual\nplanes of the lattice, forcing the constituent spin-1/2s to behave as large\ncollective spins. These large spins are then coupled with XXZ anisotropic\ninteractions along a third direction of the lattice. This system can be\nrealized via superexchange interactions in a 3D optical lattice subject to an\nexternal linear potential, such as gravity, and in the presence of spin-orbit\ncoupling (SOC) to generate spin anisotropic interactions. We show there is a\nwide range of parameters in this setting where the spin squeezing improves with\nincreasing system size even in the presence of holes."
    },
    {
        "anchor": "Growing Extended Laughlin States in a Quantum Gas Microscope: A\n  Patchwork Construction: The study of fractional Chern insulators and their exotic anyonic excitations\nposes a major challenge in current experimental and theoretical research.\nQuantum simulators, in particular ultracold atoms in optical lattices, provide\na promising platform to realize, manipulate, and understand such systems with a\nhigh degree of controllability. Recently, an atomic $\\nu=1/2$ Laughlin state\nhas been realized experimentally for a small system of two particles on 4 by 4\nsites. The next challenge concerns the preparation of Laughlin states in\nextended systems, ultimately giving access to anyonic braiding statistics or\ngapless chiral edge-states in systems with open boundaries. Here, we propose\nand analyze an experimentally feasible scheme to grow larger Laughlin states by\nconnecting multiple copies of the already existing 4-by-4-system. First, we\npresent a minimal setting obtained by coupling two of such patches, producing\nan extended 8-by-4-system with four particles. Then, we analyze different\npreparation schemes, setting the focus on two shapes for the extended system,\nand discuss their respective advantages: While growing strip-like lattices\ncould give experimental access to the central charge, square-like geometries\nare advantageous for creating quasi-hole excitations in view of braiding\nprotocols. We highlight the robust quantization of the fractional quasi-hole\ncharge upon using our preparation protocol. We benchmark the performance of our\npatchwork preparation scheme by comparing it to a protocol based on coupling\none-dimensional chains. We find that the patchwork approach consistently gives\nhigher target-state fidelities, especially for elongated systems. The results\npresented here pave the way towards near-term implementations of extended\nLaughlin states in quantum gas microscopes and the subsequent exploration of\nexotic properties of topologically ordered systems in experiments.",
        "positive": "Emergence of Reflectionless Scattering from Linearizations of Integrable\n  PDEs around Solitons: We present four examples of integrable partial differential equations (PDEs)\nof mathematical physics that---when linearized around a stationary\nsoliton---exhibit scattering without reflection at {\\it all} energies. Starting\nfrom the most well-known and the most empirically relevant phenomenon of the\ntransparency of one-dimensional bright bosonic solitons to Bogoliubov\nexcitations, we proceed to the sine-Gordon, Korteweg-de Vries, and Liouville's\nequation whose stationary solitons also support our assertion. The proposed\nconnection between integrability and reflectionless scattering seems to span at\nleast two distinct paradigms of integrability: S-integrability in the first\nthree cases, and C-integrability in the last one. We argue that the\ntransparency of linearized integrable PDEs is necessary to ensure that they can\nsupport the transparency of stationary solitons in the original integrable\nPDEs. As contrasting cases, the analysis is further extended to cover two\nnon-integrable systems: a sawtooth-Gordon and a $\\phi^4$ model."
    },
    {
        "anchor": "Drude weight increase by orbital and repulsive interactions in fermionic\n  ladders: In strictly one-dimensional systems, repulsive interactions tend to reduce\nparticle mobility on a lattice. Therefore, the Drude weight, controlling the\ndivergence at zero-frequency of optical conductivities in perfect conductors,\nis lower than in non-interacting cases. We show that this is not the case when\nextending to quasi one-dimensional ladder systems. Relying on bosonization,\nperturbative and matrix product states (MPS) calculations, we show that\nnearest-neighbor interactions and magnetic fluxes provide a bias between back-\nand forward-scattering processes, leading to linear corrections to the Drude\nweight in the interaction strength. As a consequence, Drude weights\ncounter-intuitively increase (decrease) with repulsive (attractive)\ninteractions. Our findings are relevant for the efficient tuning of Drude\nweights in the framework of ultracold atoms trapped in optical lattices and\nequally affect topological edge states in condensed matter systems.",
        "positive": "Synthetic Hall ladder with tunable magnetic flux: We describe a synthetic three-leg Hall ladder system with a tunable magnetic\nflux for neutral $^{173}$Yb atoms in a one-dimensional optical lattice. The\nladder legs are formed by three hyperfine ground spin states of the atoms, and\nthe complex interleg links are generated through Raman couplings between the\nspin states using multiple laser beams. The effective magnetic flux through a\nladder plaquette, $\\phi$, is controlled by the angles of the Raman laser beams\nwith the lattice axis. We investigate the quench dynamics of the Hall ladder\nsystem for $\\phi\\approx\\frac{\\pi}{3}, \\frac{\\pi}{2},$ and $\\frac{2\\pi}{3}$\nafter a sudden application of the Raman coupling in various interleg link\nconfigurations. The semi-classical trajectory of the atoms in the plane of the\nspin composition and lattice position exhibits the characteristic motion for\nthe effective magnetic field. In a tube configuration with the three legs\ncyclically linked, the quench evolution was observed to be substantially\ndamped, which is attributed to the random flux threading the Hall tube."
    },
    {
        "anchor": "Quasi-two-dimensional Fermi gases at finite temperature: We consider a Fermi gas with short-range attractive interactions that is\nconfined along one direction by a tight harmonic potential. For this\nquasi-two-dimensional (quasi-2D) Fermi gas, we compute the pressure equation of\nstate, radio frequency spectrum, and the superfluid critical temperature $T_c$\nusing a mean-field theory that accounts for all the energy levels of the\nharmonic confinement. Our calculation for $T_c$ provides a natural\ngeneralization of the Thouless criterion to the quasi-2D geometry, and it\ncorrectly reduces to the 3D expression derived from the local density\napproximation in the limit where the confinement frequency $\\omega_z \\to 0$.\nFurthermore, our results suggest that $T_c$ can be enhanced by relaxing the\nconfinement and perturbing away from the 2D limit.",
        "positive": "Fast transport of Bose-Einstein condensates in anharmonic traps: We present a method to transport Bose-Einstein condensates (BECs) in\nanharmonic traps and in the presence of atom-atom interactions in short times\nwithout residual excitation. Using a combination of a variational approach and\ninverse engineering methods, we derive a set of Ermakov-like equations that\ntake into account the coupling between the center of mass motion and the\nbreathing mode. By an appropriate inverse engineering strategy of those\nequations, we then design the trap trajectory to achieve the desired boundary\nconditions. Numerical examples for cubic or quartic anharmonicities are\nprovided for fast and high-fidelity transport of BECs. Potential applications\nare atom interferometry and quantum information processing."
    },
    {
        "anchor": "Mapping the Berry Curvature from Semiclassical Dynamics in Optical\n  Lattices: We propose a general method by which experiments on ultracold gases can be\nused to determine the topological properties of the energy bands of optical\nlattices, as represented by the map of the Berry curvature across the Brillouin\nzone. The Berry curvature modifies the semiclassical dynamics and hence the\ntrajectory of a wave packet undergoing Bloch oscillations. However, in two\ndimensions these trajectories may be complicated Lissajous-like figures, making\nit difficult to extract the effects of Berry curvature in general. We propose\nhow this can be done using a \"time-reversal\" protocol. This compares the\nvelocity of a wave packet under positive and negative external force, and\nallows a clean measurement of the Berry curvature over the Brillouin zone. We\ndiscuss how this protocol may be implemented and explore the semiclassical\ndynamics for three specific systems: the asymmetric hexagonal lattice, and two\n\"optical flux\" lattices in which the Chern number is nonzero. Finally, we\ndiscuss general experimental considerations for observing Berry curvature\neffects in ultracold gases.",
        "positive": "The imbalanced antiferromagnet in an optical lattice: We study the rich properties of the imbalanced antiferromagnet in an optical\nlattice. We present its phase diagram, discuss spin waves and explore the\nemergence of topological excitations in two dimensions, known as merons, which\nare responsible for a Kosterlitz-Thouless transition that has never\nunambiguously been observed."
    },
    {
        "anchor": "Topological phase transitions generated by the order from quantum\n  disorder: The order from quantum disorder (OFQD) phenomenon was first discovered in\nquantum spin systems in geometric frustrated lattice. Similar phenomenon was\nalso discovered in interacting bosonic systems or quantum spin systems with\nspin-orbit coupling in a bipartite lattice. Here we show that the OFQD also\nleads to a topological phase transition. We demonstrate this new connection in\nthe experimentally realized weakly interacting Quantum Anomalous Hall system of\nspinor bosons in an optical lattice. There are two classes of topological\nphenomena: the first class is a perturbative one smoothly connected to the\nnon-interacting limit. The second one is a non-perturbative one which has no\nanalog in the non-interacting limit. Their experimental detections are also\ndiscussed.",
        "positive": "Ab initio interaction potentials and scattering lengths for ultracold\n  mixtures of metastable helium and alkali-metal atoms: We have obtained accurate ab initio quartet potentials for the diatomic\nmetastable triplet helium + alkali-metal (Li, Na, K, Rb) systems, using\nall-electron restricted open-shell coupled cluster singles and doubles with\nnoniterative triples corrections [CCSD(T)] calculations and accurate\ncalculations of the long-range $C_6$ coefficients. These potentials provide\naccurate ab initio quartet scattering lengths, which for these many-electron\nsystems is possible, because of the small reduced masses and shallow potentials\nthat results in a small amount of bound states. Our results are relevant for\nultracold metastable triplet helium + alkali-metal mixture experiments."
    },
    {
        "anchor": "Symmetric and asymmetric solitons trapped in H-shaped potentials: We report results of numerical and analytical studies of the spontaneous\nsymmetry breaking in solitons, both two- and one-dimensional, which are trapped\nin H-shaped potential profiles, built of two parallel potential troughs linked\nby a narrow rung in the transverse direction. This system can be implemented in\nself-attractive Bose-Einstein condensates (BECs), as well as in a nonlinear\nbulk optical waveguide.We demonstrate that the introduction of the transverse\nlink changes the character of the symmetry-breaking bifurcation (SBB) in the\nsystem from subcritical to supercritical (in terms of the corresponding phase\ntransition, it is a change between the first and second kinds). A noteworthy\nfeature of the SBB in this setting is a non-monotonous dependence of the\nsoliton's norm at the bifurcation point on the strength of the transverse link.\nIn the full 2D system, the results are obtained in a numerical form. An exact\nanalytical solution is found for the bifurcation in the 1D version of the\nmodel, with the transverse rung modeled by the local linear coupling between\nthe parallel troughs with the Delta-functional longitudinal profile. Replacing\nthe Delta-function by its finite-width Gaussian counterpart, similar results\nare obtained by means of the variational approximation (VA). The VA is also\napplied to the 1D system with a mixed linear and nonlinear transverse localized\ncoupling. Comparison of the results produced by the different varieties of the\nsystem clearly reveals basic features of the symmetry-breaking transition in\nit.",
        "positive": "Mott transition in the $\u03c0$-flux SU($4$) Hubbard model on a square\n  lattice: We employ the projector quantum Monte Carlo simulations to study the\nground-state properties of the square-lattice SU(4) Hubbard model with a $\\pi$\nflux per plaquette. In the weak coupling regime, its ground state is in the\ngapless Dirac semi-metal phase. With increasing repulsive interaction, we show\nthat, a Mott transition occurs from the semimetal to the valence bond solid,\naccompanied by the $Z_4$ discrete symmetry breaking. Our simulations\ndemonstrate the existence of a second-order phase transition, which confirms\nthe Ginzburg-Landau analysis. The phase transition point and the critical\nexponent $\\eta$ are also estimated. To account for the effect of a $\\pi$ flux\non the ordering in the strong coupling regime, we analytically derive by the\nperturbation theory the ring-exchange term which describes the leading-order\ndifference between the $\\pi$-flux and zero-flux SU(4) Hubbard models."
    },
    {
        "anchor": "New kind of condensation of Bose particles through stimulated processes: We show that stimulated scattering of an isolated system of N Bose particles\nwith initially broad energy distribution can yield condensation of particles\ninto excited collective state in which most of the bosons occupy one or several\nmodes. During condensation, the total particle number and energy are conserved,\nwhile entropy of the system grows. Onset of condensation occurs at a critical\nparticle occupation number when spectrum narrowing due to stimulated processes\novercomes spectrum broadening due to diffusion. This differs from Bose-Einstein\ncondensation in which particles undergo condensation into the equilibrium state\ndue to thermalization processes.",
        "positive": "Dark solitons near the Mott-insulator--superfluid phase transition: Dark solitons of ultracold bosons in the vicinity of the\nMott-insulator--superfluid phase transition are studied. Making use of the\nGutzwiller ansatz we have found antisymmetric eigenstates corresponding to\nstanding solitons, as well as propagating solitons created by phase imprinting.\nNear the phase boundary, superfluidity has either a particle or a hole\ncharacter depending on the system parameters, which greatly affects the\ncharacteristics of both types of solitons. Within the insulating Mott regions,\nsoliton solutions are prohibited by lack of phase coherence between the lattice\nsites. Linear and modulational stability show that the soliton solutions are\nsensitive to small perturbations and, therefore, unstable. In general, their\nlifetimes differ for on-site and off-site modes. For the on-site modes, there\nare small areas between the Mott-insulator regions where the lifetime is very\nlarge, and in particular much larger than that for the off-site modes."
    },
    {
        "anchor": "Induced interaction in a spin-polarized Fermi gas: We study the effect of the induced interaction on the superfluidtransition\ntemperature of a spin-polarized Fermi gas. In the BCS limit, the polarization\nis very small in the superfluid state, and the effect of the induced\ninteraction is almost the same as in the spin-balanced case. The temperature Tt\nand the polarization Pt of the tricritical point are both reduced from\nmean-field results by a factor about 2.22. This reduction is also significant\nbeyond the BCS limit. In the unitary limit, we find (Pt,Tt/TF)=(0.42,0.16), in\ncomparison with mean-field and experimental results.",
        "positive": "Spin-orbit Coupled Bose-Einstein Condensates in Spin-dependent Optical\n  Lattices: We investigate the ground-state properties of spin-orbit coupled\nBose-Einstein condensates in spin-dependent optical lattices. The competition\nbetween the spin-orbit coupling strength and the depth of the optical lattice\nleads to a rich phase diagram. Without spin-orbit coupling, the spin-dependent\noptical lattices separate the condensates into alternating spin domains with\nopposite magnetization directions. With relatively weak spin-orbit coupling,\nthe spin domain wall is dramatically changed from N\\'{e}el wall to Bloch wall.\nFor sufficiently strong spin-orbit coupling, vortex chains and antivortex\nchains are excited in the spin-up and spin-down domains respectively,\ncorresponding to the formation of a lattice composed of meron-pairs and\nantimeron-pairs in the pseudospin representation. We also discuss how to\nobserve these phenomena in real experiments."
    },
    {
        "anchor": "First and second sound in a highly elongated Fermi gas at unitarity: We consider a Fermi gas at unitarity trapped by a highly elongated harmonic\npotential and solve the equations of two fluid hydrodynamics at finite\ntemperature. The propagation of sound waves as well as the discretized\nsolutions in the presence of weak axial trapping are considered. The relevant\nthermodynamic functions entering the hydrodynamic equations are discussed in\nthe superfluid and normal regimes in terms of universal scaling functions. Both\nfirst sound and second sound solutions are calculated as a function of\ntemperature and the role of the superfluid density is explicitly pointed out.\nThe density fluctuations in the second sound wave are found to be large enough\nto be measured as a consequence of the finite thermal expansion coefficient of\nthe gas. Emphasis is given to the comparison with recent experimental data.",
        "positive": "Floquet Edge States with Ultracold Atoms: We describe an experimental setup for imaging topologically protected Floquet\nedge states using ultracold bosons in an optical lattice. Our setup involves a\ndeep two dimensional optical lattice with a time dependent superlattice that\nmodulates the hopping between neighboring sites. The finite waist of the\nsuperlattice beam yields regions with different topological numbers. One can\nobserve chiral edge states by imaging the real-space density of a bosonic\npacket launched from the boundary between two topologically distinct regions."
    },
    {
        "anchor": "Dynamics of Bose-Einstein Recondensation in Higher Bands: Motivated by recent experiments, we explore the kinetics of Bose-Einstein\ncondensation in the upper band of a double well optical lattice. These\nexperiments engineer a non-equilibrium situation in which the highest energy\nstate in the band is macroscopically occupied. The system subsequently relaxes\nand the condensate moves to the lowest energy state. We model this process,\nfinding that the kinetics occurs in three phases: The condensate first\nevaporates, forming a highly non-equilibrium gas with no phase coherence.\nEnergy is then redistributed among the noncondensed atoms. Finally the atoms\nrecondense. We calculate the time-scales for each of these phases, and explain\nhow this scenario can be verified through future experiments.",
        "positive": "Quantum mechanical limitations to spin diffusion in the unitary Fermi\n  gas: We compute spin transport in the unitary Fermi gas using the strong-coupling\nLuttinger-Ward theory. In the quantum degenerate regime the spin diffusivity\nattains a minimum value of $D_s \\simeq 1.3 \\hbar/m$ approaching the quantum\nlimit of diffusion for a particle of mass $m$. Conversely, the spin drag rate\nreaches a maximum value of $\\Gamma_\\sd \\simeq 1.2 k_B T_F/\\hbar$ in terms of\nthe Fermi temperature $T_F$. The frequency-dependent spin conductivity\n$\\sigma_s(\\omega)$ exhibits a broad Drude peak, with spectral weight\ntransferred to a universal high-frequency tail $\\sigma_s(\\omega \\to\\infty) =\n\\hbar^{1/2}C/3\\pi(m\\omega)^{3/2}$ proportional to the Tan contact density $C$.\nFor the spin susceptibility $\\chi_s(T)$ we find no downturn in the normal\nphase."
    },
    {
        "anchor": "Information processing with topologically protected vortex memories in\n  exciton-polariton condensates: We show that in a non-equilibrium system of an exciton-polariton condensate,\nwhere polaritons are generated from incoherent pumping, a ring-shaped pump\nallows for stationary vortex memory elements of topological charge $m = 1$ or\n$m = -1$. Using simple potential guides we can choose whether to copy the same\ncharge or invert it onto another spatially separate ring pump. Such\nmanipulation of binary information opens the possibility of a new type\nprocessing using vortices as topologically protected memory components.",
        "positive": "Analytic results for a quantum quench from free to hard-core one\n  dimensional bosons: It is widely believed that the stationary properties after a quantum quench\nin integrable systems can be described by a generalized Gibbs ensemble (GGE),\neven if all the analytical evidence is based on free theories in which the pre-\nand post-quench modes are linearly related. In contrast, we consider the\nexperimentally relevant quench of the one-dimensional Bose gas from zero to\ninfinite interaction, in which the relation between modes is nonlinear, and\nconsequently Wick's theorem does not hold. We provide exact analytical results\nfor the time evolution of the dynamical density-density correlation function at\nany time after the quench and we prove that its stationary value is described\nby a GGE in which Wick's theorem is restored."
    },
    {
        "anchor": "Measuring the equation of state of trapped ultracold bosonic systems in\n  an optical lattice with in-situ density imaging: We analyze quantitatively how imaging techniques with single-site resolution\nallow to measure thermodynamical properties that cannot be inferred from\ntime-of-light images for the trapped Bose-Hubbard model. If the normal state\nextends over a sufficiently large range, the chemical potential and the\ntemperature can be extracted from a single shot, provided the sample is in\nthermodynamic equilibrium. When the normal state is too narrow, temperature is\nlow but can still be extracted using the fluctuation-dissipation theorem over\nthe entire trap range as long as the local density approximation remains valid,\nas was recently suggested by Qi Zhou and Tin-Lun Ho [arXiv:0908.3015]. However,\nfor typical present-day experiments, the number of samples needed is of the\norder of 1000 in order to get the temperature at least $10 \\%$ accurate, but it\nis possible to reduce the variance by 2 orders of magnitude if the\ndensity-density correlation length is short, which is the case for the\nBose-Hubbard model. Our results provide further evidence that cold gases in an\noptical lattices can be viewed as quantum analog computers.",
        "positive": "A Hydrodynamical Description of Bose Liquid with Fractional Exclusion\n  Statistics: Hydrodynamical systems are usually taken as chaotic systems with fast\nrelaxations. It is counter intuitive for \"ideal\" gas to have a hydrodynamical\ndescription. We find that a hydrodynamical model of one-dimensional $|\\Phi|^6$\ntheory shares the same ground state density profile, density-wave excitation,\nas well as the similar dynamical and statistical properties with the\nCalogero-Sutherland model in thermodynamic limit when their interaction\nstrengths matches each other. The interaction strength g0 in the\n$|\\Phi|^6$theory is then the index of fractional statistics. Although the model\nis interacting in Bose liquid sense, but it shows integrability with periodical\ncoherent evolution. We also discussed the fractional statistics emerges from\nthe $|\\Phi|^6$ theory."
    },
    {
        "anchor": "Beating Effects of Vector Solitons in Bose-Einstein Condensate: We study the beating effects of solitons in multi-component coupled\nBose-Einstein condensate systems. Our analysis indicate that the period of\nbeating behavior is determined by the energy eigenvalue difference in the\neffective quantum well induced by solitons, and the beating pattern is\ndetermined by the eigen-states of quantum well which are involved in the\nbeating behavior. We show that the beating solitons correspond to linear\nsuperpositions of eigen-states in some quantum wells, and the correspondence\nrelations are identical for solitons in both attractive interaction and\nrepulsive interaction condensate. This provides a possible way to understand\nthe beating effects of solitons for attractive and repulsive interaction cases\nin a unified way, based on the knowledge of quantum eigen-states. Moreover, our\nresults demonstrate many different beating patterns for solitons in\nthree-component coupled condensate, in sharp contrast to the beating dark\nsoliton reported before. The beating behavior can be used to test the\neigenvalue differences of some certain quantum wells, and more abundant beating\npatterns are expected to exist in more components coupled systems.",
        "positive": "Aspects of Superfluid Cold Atomic Gases in Optical Lattices: We review our studies on Bose and Fermi superfluids of cold atomic gases in\noptical lattices at zero temperature. Especially, we focus on superfluid Fermi\ngases along the crossover between the Bardeen-Cooper-Schrieffer (BCS) and the\nBose-Einstein condensate (BEC) states, which enable us to study the Bose and\nthe Fermi superfluids in a unified point of view. We discuss basic static and\nlong-wavelength properties (such as the equation of state, incompressibility,\nand effective mass), energetic stability, and energy band structures of the\nsuperfluid Fermi gases in an optical lattice periodic along one spatial\ndirection. The periodic potential causes pairs of atoms to be strongly bound,\nand this can affect the static and long-wavelength properties and the stability\nof the superflow. Regarding the band structure, a peculiar loop structure\ncalled \"swallowtail\" can appear in superfluid Fermi gases and in the Bose case,\nbut the mechanism of emergence in the Fermi case is very different from that in\nbosonic case. Other quantum phases that the cold atomic gases in optical\nlattices can show are also briefly discussed based on their roles as quantum\nsimulators of Hubbard models."
    },
    {
        "anchor": "Realization of a fractional period adiabatic superlattice: We propose and realize a deeply sub-wavelength optical lattice for ultracold\nneutral atoms using $N$ resonantly Raman-coupled internal degrees of freedom.\nAlthough counter-propagating lasers with wavelength $\\lambda$ provided\ntwo-photon Raman coupling, the resultant lattice-period was $\\lambda/2N$, an\n$N$-fold reduction as compared to the conventional $\\lambda/2$ lattice period.\nWe experimentally demonstrated this lattice built from the three $F=1$ Zeeman\nstates of a $^{87}{\\rm Rb}$ Bose-Einstein condensate, and generated a lattice\nwith a $\\lambda/6= 132\\ {\\rm nm}$ period from $\\lambda=790 \\ {\\rm nm}$ lasers.\nLastly, we show that adding an additional RF coupling field converts this\nlattice into a superlattice with $N$ wells uniformly spaced within the original\n$\\lambda/2$ unit cell.",
        "positive": "Coupled Atomic Wires in a Synthetic Magnetic Field: We propose and study systems of coupled atomic wires in a perpendicular\nsynthetic magnetic field as a platform to realize exotic phases of quantum\nmatter. This includes (fractional) quantum Hall states in arrays of many wires\ninspired by the pioneering work [Kane et al. PRL {\\bf{88}}, 036401 (2002)], as\nwell as Meissner phases and Vortex phases in double-wires. With one continuous\nand one discrete spatial dimension, the proposed setup naturally complements\nrecently realized discrete counterparts, i.e. the Harper-Hofstadter model and\nthe two leg flux ladder, respectively. We present both an in-depth theoretical\nstudy and a detailed experimental proposal to make the unique properties of the\nsemi-continuous Harper-Hofstadter model accessible with cold atom experiments.\nFor the minimal setup of a double-wire, we explore how a sub-wavelength spacing\nof the wires can be implemented. This construction increases the relevant\nenergy scales by at least an order of magnitude compared to ordinary optical\nlattices, thus rendering subtle many-body phenomena such as Lifshitz\ntransitions in Fermi gases observable in an experimentally realistic parameter\nregime. For arrays of many wires, we discuss the emergence of Chern bands with\nreadily tunable flatness of the dispersion and show how fractional quantum Hall\nstates can be stabilized in such systems. Using for the creation of optical\npotentials Laguerre-Gauss beams that carry orbital angular momentum, we detail\nhow the coupled atomic wire setups can be realized in non-planar geometries\nsuch as cylinders, discs, and tori."
    },
    {
        "anchor": "Quantum Simulation of Competing Orders with Fermions in Quantum Optical\n  Lattices: Ultracold Fermi atoms confined in optical lattices coupled to quantized modes\nof an optical cavity are an ideal scenario to engineer quantum simulators in\nthe strongly interacting regime. The system has both short range and cavity\ninduced long range interactions. We propose such a scheme to investigate the\ncoexistence of superfluid pairing, density order and quantum domains having an-\ntiferromagnetic or density order in the Hubbard model in a high finesse optical\ncavity at T = 0. We demonstrate that those phases can be accessed by properly\ntuning the linear polarizer of an external pump beam via the cavity back-action\neffect, while modulating the system doping. This allows emulate the typical\nscenarios of analog strongly correlated electronic systems.",
        "positive": "Time-of-Flight Measurements as a Possible Method to Observe Anyonic\n  Statistics: We propose a standard time-of-flight experiment as a method for observing the\nanyonic statistics of quasiholes in a fractional quantum Hall state of\nultracold atoms. The quasihole states can be stably prepared by pinning the\nquasiholes with localized potentials and a measurement of the mean square\nradius of the freely expanding cloud, which is related to the average total\nangular momentum of the initial state, offers direct signatures of the\nstatistical phase. Our proposed method is validated by Monte Carlo calculations\nfor $\\nu=1/2$ and $1/3$ fractional quantum Hall liquids containing a realistic\nnumber of particles. Extensions to quantum Hall liquids of light and to\nnon-Abelian anyons are briefly discussed."
    },
    {
        "anchor": "Glassy Dynamics from Quark Confinement: Atomic Quantum Simulation of\n  Gauge-Higgs Model on Lattice: In the previous works, we proposed atomic quantum simulations of the U(1)\ngauge-Higgs model by ultra-cold Bose gases. By studying extended Bose-Hubbard\nmodels (EBHMs) including long-range repulsions, we clarified the locations of\nthe confinement, Coulomb and Higgs phases. In this paper, we study the EBHM\nwith nearest-neighbor repulsions in one and two dimensions at large fillings by\nthe Gutzwiller variational method. We obtain phase diagrams and investigate\ndynamical behavior of electric flux from the gauge-theoretical point of view.\nWe also study if the system exhibits glassy quantum dynamics in the absence and\npresence of quenched disorder. We explain that the obtained results have a\nnatural interpretation in the gauge theory framework. Our results suggest\nimportant perspective on many-body localization in strongly-correlated systems.\nThey are also closely related to anomalously slow dynamics observed by recent\nexperiments performed on Rydberg atom chain, and our study indicates existence\nof similar phenomenon in two-dimensional space.",
        "positive": "How Infrared Singularities Affect Nambu-Goldstone Bosons at Finite\n  Temperatures: Ordered phases realized through broken continuous symmetries embrace\nlong-range order-parameter fluctuations as manifest in the power-law decays of\nboth the transverse and longitudinal correlations, which are similar to those\nat the second-order transition point. We calculate the transverse one-loop\ncorrection to the dispersion relation of nonrelativistic Nambu-Goldstone (NG)\nbosons at finite temperatures, assuming that they have well-defined dispersion\nrelations with some integer exponents. It is found that the transverse\ncorrelations make the lifetime of the NG bosons vanish right on the assumed\ndispersion curve below three dimensions at finite temperatures. Combined with\nthe vanishing of the longitudinal \"mass\", the result indicates that the\ncorrelations generally bring both an intrinsic lifetime to the excitations and\na qualitative change in the dispersion relation at long wavelengths below three\ndimensions at finite temperatures, unless it is protected by some conservation\nlaw. A more detailed calculation performed specifically on a single-component\nBose-Einstein condensate reveals that the gapless Bogoliubov mode predicted by\nthe perturbative treatment is modified substantially after incorporating the\ncorrelations to have (i) an intrinsic lifetime and (ii) a peak shift at long\nwavelengths from the linear dispersion relation. Thus, the NG bosons may be\nfluctuating intrinsically into and out of the ordered \"vacuum\" to maintain the\norder temporally."
    },
    {
        "anchor": "Self-trapping of Fermi and Bose gases under spatially modulated\n  repulsive nonlinearity and transverse confinement: We show that self-localized ground states can be created in the spin-balanced\ngas of fermions with repulsion between the spin components, whose strength\ngrows from the center to periphery, in combination with the harmonic-oscillator\n(HO) trapping potential acting in one or two transverse directions. We also\nconsider the ground state in the non-interacting Fermi gas under the action of\nthe spatially growing tightness of the one- or two-dimensional (1D or 2D) HO\nconfinement. These settings are considered in the framework of the\nThomas-Fermi-von Weizsacker (TF-vW) density functional. It is found that the vW\ncorrection to the simple TF approximation (the gradient term) is nearly\nnegligible in all situations. The properties of the ground state under the\naction of the 2D and 1D HO confinement with the tightness growing in the\ntransverse directions is investigated too for the Bose-Einstein condensate\n(BEC) with the self-repulsive nonlinearity.",
        "positive": "Reservoir interactions during Bose-Einstein condensation: modified\n  critical scaling in the Kibble-Zurek mechanism of defect formation: As a test of the Kibble-Zurek mechanism (KZM) of defect formation, we\nsimulate the Bose-Einstein condensation transition in a toroidally confined\nBose gas using the stochastic projected Gross-Pitaevskii equation (SPGPE), with\nand without the energy-damping reservoir interaction. Energy-damping alters the\nscaling of the winding number distribution with the quench time - a departure\nfrom the universal KZM theory that relies on equilibrium critical exponents.\nNumerical values are obtained for the correlation-length critical exponent\n$\\nu$ and the dynamical critical exponent $z$ for each variant of reservoir\ninteraction theory. The energy-damping reservoir interactions cause significant\nmodification of the dynamical critical exponent of the phase transition, whilst\npreserving the essential KZM critical scaling behavior. Comparison of numerical\nand analytical two-point correlation functions further illustrates the effect\nof energy damping on the correlation length during freeze out."
    },
    {
        "anchor": "Spinor Bose gases: Explorations of symmetries, magnetism and quantum\n  dynamics: Spinor Bose gases form a family of quantum fluids manifesting both magnetic\norder and superfluidity. This article reviews experimental and theoretical\nprogress in understanding the static and dynamic properties of these fluids.\nThe connection between system properties and the rotational symmetry properties\nof the atomic states and their interactions are investigated. Following a\nreview of the experimental techniques used for characterizing spinor gases,\ntheir mean-field and many-body ground states, both in isolation and under the\napplication of symmetry-breaking external fields, are discussed. These states\nserve as the starting point for understanding low-energy dynamics, spin\ntextures and topological defects, effects of magnetic dipole interactions, and\nvarious non-equilibrium collective spin-mixing phenomena. The paper aims to\nform connections and establish coherence among the vast range of works on\nspinor Bose gases, so as to point to open questions and future research\nopportunities.",
        "positive": "Quantum distillation and confinement of vacancies in a doublon sea: Ultracold atomic gases have revolutionized the study of non-equilibrium\ndynamics in quantum many-body systems. Many counterintuitive non-equilibrium\neffects have been observed, such as suppressed thermalization in a\none-dimensional (1D) gas, the formation of repulsive self-bound dimers, and\nidentical behaviors for attractive and repulsive interactions. Here, we observe\nthe expansion of a bundle of ultracold 1D Bose gases in a flat-bottomed optical\nlattice potential. By combining in situ measurements with photoassociation, we\nfollow the spatial dynamics of singly, doubly, and triply occupied lattice\nsites. The system sheds interaction energy by dissolving some doublons and\ntriplons. Some singlons quantum distill out of the doublon center, while others\nremain confined. Our Gutzwiller mean-field model captures these experimental\nfeatures in a physically clear way. These experiments might be used to study\nthermalization in systems with particle losses or the evolution of quantum\nentanglement, or if applied to fermions, to prepare very low entropy states."
    },
    {
        "anchor": "Supersolid stripe crystal from finite-range interactions on a lattice: Strong, long-range interactions present a unique challenge for the\ntheoretical investigation of quantum many-body lattice models, due to the\ngeneration of large numbers of competing states at low energy. Here, we\ninvestigate a class of extended bosonic Hubbard models with off-site terms\ninterpolating between short and infinite range, thus allowing for an exact\nnumerical solution for all interaction strengths. We predict a novel type of\nstripe crystal at strong coupling. Most interestingly, for intermediate\ninteraction strengths we demonstrate that the stripes can turn superfluid, thus\nleading to a self-assembled array of quasi-one-dimensional superfluids. These\nbosonic superstripes turn into an isotropic supersolid with decreasing the\ninteraction strength. The mechanism for stripe formation is based on cluster\nself-assembling in the corresponding classical ground state, reminiscent of\nclassical soft-matter models of polymers, different from recently proposed\nmechanisms for cold gases of alkali or dipolar magnetic atoms.",
        "positive": "Observation of density-dependent gauge fields in a Bose-Einstein\n  condensate based on micromotion control in a shaken two-dimensional lattice: We demonstrate a density-dependent gauge field, induced by atomic\ninteractions, for quantum gases. The gauge field results from the synchronous\ncoupling between the interactions and micromotion of the atoms in a modulated\ntwo-dimensional optical lattice. As a first step, we show that a coherent\nshaking of the lattice in two directions can couple the momentum and\ninteractions of atoms and break the four-fold symmetry of the lattice. We then\ncreate a full interaction-induced gauge field by modulating the interaction\nstrength in synchrony with the lattice shaking. When a condensate is loaded\ninto this shaken lattice, the gauge field acts to preferentially prepare the\nsystem in different quasimomentum ground states depending on the modulation\nphase. We envision that these interaction-induced fields, created by fine\ncontrol of micromotion, will provide a stepping stone to model new quantum\nphenomena within and beyond condensed matter physics."
    },
    {
        "anchor": "Simulation of gauge transformations on systems of ultracold atoms: We show that gauge transformations can be simulated on systems of ultracold\natoms. We discuss observables that are invariant under these gauge\ntransformations and compute them using a tensor network ansatz that escapes the\nphase problem. We determine that the Mott-insulator-to-superfluid critical\npoint is monotonically shifted as the induced magnetic flux increases. This\nresult is stable against the inclusion of a small amount of entanglement in the\nvariational ansatz.",
        "positive": "Dynamical Instability of 3d Stationary and Traveling Planar Dark\n  Solitons: Here we revisit the topic of stationary and propagating solitonic excitations\nin self-repulsive three-dimensional Bose-Einstein condensates by quantitatively\ncomparing theoretical analysis and associated numerical computations with our\nexperimental results. Using fully 3d numerical simulations, we explore the\nexistence, stability, and evolution dynamics of planar dark solitons, as well\nas their instability-induced decay products including solitonic vortices and\nvortex rings. In the trapped case and with no adjustable parameters, our\nnumerical findings are in correspondence with experimentally observed coherent\nstructures. Without a longitudinal trap, we identify numerically exact\ntraveling solutions and quantify how their transverse destabilization threshold\nchanges as a function of the solitary wave speed."
    },
    {
        "anchor": "A note on the spectrum of a two-particle Rashba Hamiltonian: In a series of recent papers it was shown that, when the attractive s-wave\ninteraction is dominant, the spin-orbit coupled fermions form a bound state.\nAttributed to a convenient momentum representation, it became a common\ncondition of agreement to express the bound state as a function of the\ncenter-of-mass momentum Q. In this letter we prove that the bound state of\nRashba fermions does not depend on the chosen representation. That is, all the\nstates characterized by nonzero Q fail to obey the translation symmetry.",
        "positive": "The uncertainty product of an out-of-equilibrium many-particle system: In the present work we show, analytically and numerically, that the variance\nof many-particle operators and their uncertainty product for an\nout-of-equilibrium Bose-Einstein condensate (BEC) can deviate from the outcome\nof the time-dependent Gross-Pitaevskii dynamics, even in the limit of infinite\nnumber of particles and at constant interaction parameter when the system\nbecomes 100% condensed. We demonstrate our finding on the dynamics of the\ncenter-of-mass position--momentum uncertainty product of a freely expanding as\nwell as of a trapped BEC. This time-dependent many-body phenomenon is explained\nby the existence of time-dependent correlations which manifest themselves in\nthe system's reduced two-body density matrix used to evaluate the uncertainty\nproduct. Our work demonstrates that one has to use a many-body propagation\ntheory to describe an out-of-equilibrium BEC, even in the infinite particle\nlimit."
    },
    {
        "anchor": "Berezinskii-Kosterlitz-Thouless transition of spin-1 spinor Bose gases\n  in the presence of the quadratic Zeeman effect: We numerically study the Berezinskii-Kosterlitz-Thouless (BKT) transition of\na spin-1 spinor Bose gas under the quadratic Zeeman effect. A calculation of\nthe mass and spin superfluid densities shows that (i) the BKT transition occurs\nonly when vortices are classified by the integer group $\\mathbb{Z}$, and\n$\\mathbb{Z}_2$ vortices do not contribute to the BKT transition, (ii) the two\nBKT transition temperatures for mass and spin superfluid densities are\ndifferent for a positive quadratic Zeeman effect and equal for a negative\nquadratic Zeeman effect, and (iii) the universal relation of the superfluid\ndensities at the BKT transition temperature is changed when multiple kinds of\nvortices contribute to the transition. We have further found that (iv)\nspin-singlet pairs in non-magnetic states show the\nquasi-off-diagonal-long-range order at the different temperature lower than the\nBKT transition temperature, giving the new universal relation of the superfluid\ndensity.",
        "positive": "Artificial magnetism for a harmonically trapped Fermi gas in a synthetic\n  magnetic field: We have analytically explored the artificial magnetism for a 3-D\nspin-polarized harmonically trapped ideal Fermi gas of electrically neutral\nparticles exposed to a uniform synthetic magnetic field. Though polarization of\nthe spin is necessary for trapping electrically neutral atoms in a\nmagneto-optical trap, Pauli paramagnetism can not be studied for the\nspin-polarized Fermi system. However, it is possible to study Landau\ndiamagnetism and de Haas-van Alphen effect for such a system. We have unified\nthe artificial Landau diamagnetism and the artificial de Haas-van Alphen effect\nin a single framework for all temperatures as well as for all possible\nmagnitudes of the synthetic magnetic field in the thermodynamic limit. Our\nprediction is testable in the present-day experimental setup for ultracold\nfermionic atoms in magneto-optical trap."
    },
    {
        "anchor": "Spin effects in Bose-Glass phases: We study the mechanism of formation of Bose glass (BG) phases in the spin-1\nBose Hubbard model when diagonal disorder is introduced. To this aim, we\nanalyze first the phase diagram in the zero-hopping limit, there disorder\ninduces superposition between Mott insulator (MI) phases with different filling\nnumbers. Then BG appears as a compressible but still insulating phase. The\nphase diagram for finite hopping is also calculated with the Gutzwiller\napproximation. The bosons' spin degree of freedom introduces another scattering\nchannel in the two-body interaction modifying the stability of MI regions with\nrespect to the action of disorder. This leads to some peculiar phenomena such\nas the creation of BG of singlets, for very strong spin correlation, or the\ndisappearance of BG phase in some particular cases where fluctuations are not\nable to mix different MI regions.",
        "positive": "Dynamical Quasicondensation of Hard-Core Bosons at Finite Momenta: Long-range order in quantum many-body systems is usually associated with\nequilibrium situations. Here, we experimentally investigate the\nquasicondensation of strongly-interacting bosons at finite momenta in a\nfar-from-equilibrium case. We prepare an inhomogeneous initial state consisting\nof one-dimensional Mott insulators in the center of otherwise empty\none-dimensional chains in an optical lattice with a lattice constant $d$. After\nsuddenly quenching the trapping potential to zero, we observe the onset of\ncoherence in spontaneously forming quasicondensates in the lattice. Remarkably,\nthe emerging phase order differs from the ground-state order and is\ncharacterized by peaks at finite momenta $\\pm (\\pi/2) (\\hbar / d)$ in the\nmomentum distribution function."
    },
    {
        "anchor": "Mapping onto Electrodynamics of a Two-dimensional Bose-Einstein\n  Condensate: A thorough mapping between the hydrodynamics of a two-dimensional\nBose-Einstein condensate and the nonrelativistic classical electrodynamics of a\ncharged material medium is proposed. This is shown to provide a very useful\nframe to discuss several features of vortex dynamics. Two important local\nconservation theorems of energy and angular momentum are derived and further\napplications are summarized.",
        "positive": "Delayed response of a fermion-pair condensate to a modulation of the\n  interaction strength: The effect of a sinusoidal modulation of the interaction strength on a\nfermion-pair condensate is analytically studied. The system is described by a\ngeneralization of the coupled fermion-boson model that incorporates a\ntime-dependent intermode coupling induced via a magnetic Feshbach resonance.\nNontrivial effects are shown to emerge depending on the relative magnitude of\nthe modulation period and the relaxation time of the condensate. Specifically,\na nonadiabatic modulation drives the system out of thermal equilibrium: the\nexternal field induces a variation of the quasiparticle energies, and, in turn,\na disequilibrium of the associated populations. The subsequent relaxation\nprocess is studied and an analytical description of the gap dynamics is\nobtained. Recent experimental findings are explained: the delay observed in the\nresponse to the applied field is understood as a temperature effect linked to\nthe condensate relaxation time."
    },
    {
        "anchor": "Tunable non-reciprocal quantum transport through a dissipative\n  Aharonov-Bohm ring in ultracold atoms: We report the experimental observation of tunable, non-reciprocal quantum\ntransport of a Bose-Einstein condensate in a momentum lattice. By implementing\na dissipative Aharonov-Bohm (AB) ring in momentum space and sending atoms\nthrough it, we demonstrate a directional atom flow by measuring the momentum\ndistribution of the condensate at different times. While the dissipative AB\nring is characterized by the synthetic magnetic flux through the ring and the\nlaser-induced loss on it, both the propagation direction and transport rate of\nthe atom flow sensitively depend on these highly tunable parameters. We\ndemonstrate that the non-reciprocity originates from the interplay of the\nsynthetic magnetic flux and the laser-induced loss, which simultaneously breaks\nthe inversion and the time-reversal symmetries. Our results open up the avenue\nfor investigating non-reciprocal dynamics in cold atoms, and highlight the\ndissipative AB ring as a flexible building element for applications in quantum\nsimulation and quantum information.",
        "positive": "Controlling spontaneous-emission noise in measurement-based feedback\n  cooling of a Bose-Einstein Condensate: Off-resonant optical imaging is the most popular method for continuous\nmonitoring of a Bose-Einstein condensate (BEC). However, the disturbance caused\nby scattered photons places a serious limitation on the lifetime of such\ncontinuously-monitored condensates. In this paper, we demonstrate that a new\nchoice of feedback control can overcome the heating effects of the measurement\nbackaction. In particular, we show that the measurement backaction caused by\noff-resonant optical imaging is a multimode quantum-field effect, as the entire\nheating process is not seen in single-particle or mean-field models of the\nsystem. Correctly simulating such continuously-monitored systems is only\npossible using the number-phase Wigner (NPW) particle filter, which is a hybrid\nbetween the leading techniques for simulating non-equilibrium dynamics in\ncondensates and particle filters for simulating high-dimensional non-Gaussian\nfilters in the field of engineering. The new control scheme will enable\nlong-term continuous measurement and feedback on one of the leading platforms\nfor precision measurement and the simulation of quantum fields, allowing for\nthe possibility of single-shot experiments, adaptive measurements and robust\nstate-preparation and manipulation."
    },
    {
        "anchor": "Quasiparticle energy in a strongly interacting homogeneous Bose-Einstein\n  condensate: Using two-photon Bragg spectroscopy, we study the energy of particle-like\nexcitations in a strongly interacting homogeneous Bose-Einstein condensate, and\nobserve dramatic deviations from Bogoliubov theory. In particular, at large\nscattering length $a$ the shift of the excitation resonance from the\nfree-particle energy changes sign from positive to negative. For an excitation\nwith wavenumber $q$, this sign change occurs at $a \\approx 4/(\\pi q)$, in\nagreement with the Feynman energy relation and the static structure factor\nexpressed in terms of the two-body contact. For $a \\gtrsim 3/q$ we also see a\nbreakdown of this theory, and better agreement with calculations based on the\nWilson operator product expansion. Neither theory explains our observations\nacross all interaction regimes, inviting further theoretical efforts.",
        "positive": "Anisotropic Ginzburg-Landau and Lawrence-Doniach Models for Layered\n  Ultracold Fermi Gases: We study the anisotropic Ginzburg-Landau and Lawrence-Doniach models\ndescribing a layered superfluid ultracold Fermi gas in optical lattices. We\nderive the coefficients of the anisotropic Ginzburg-Landau and the mass tensor\nas a function of anisotropy, filling and interaction, showing that near the\nunitary limit the effective anisotropy of the masses is significantly reduced.\nThe anisotropy parameter is shown to vary in realistic setups in a wide range\nof values. We also derive the Lawrence-Doniach model - often used to describe\nthe 2D-3D dimensional crossover in layered superconductors - for a layered\nultracold Fermi gas, obtaining a relation between the interlayer Josephson\ncouplings and the Ginzburg-Landau masses. Comparing to the Ginzburg-Landau\ndescription, we find that the region of validity of the Lawrence-Doniach model\nis near the unitary limit."
    },
    {
        "anchor": "Supersolid in a one-dimensional optical lattice in the presence of a\n  harmonic trap: We study a system of ultra-cold atoms possessing long range interaction (e.g.\ndipole-dipole interaction) in a one dimensional optical lattice in the presence\nof a confining harmonic trap. We have shown that for large enough on-site and\nnearest neighbor interaction a supersolid phase can be stabilized, consistent\nwith the previous Quantum Monte Carlo and DMRG results for the homogeneous\nsystem. Due to the external harmonic trap potential the supersolid phase\ncoexists with other phases. We emphasize on the experimental signatures of the\nvarious ground state phases in the presence of a trap.",
        "positive": "Rotating atomic quantum gases with light-induced azimuthal gauge\n  potentials and the observation of Hess-Fairbank effect: We demonstrate synthetic azimuthal gauge potentials for Bose-Einstein\ncondensates from engineering atom-light couplings. The gauge potential is\ncreated by adiabatically loading the condensate into the lowest energy\nRaman-dressed state, achieving a coreless vortex state. The azimuthal gauge\npotentials act as effective rotations and are tunable by the Raman coupling and\ndetuning. We characterize the spin textures of the dressed states, in\nagreements with the theory. The lowest energy dressed state is stable with a\n4.5-s half-atom-number-fraction lifetime. In addition, we exploit the azimuthal\ngauge potential to demonstrate the Hess-Fairbank effect, the analogue of\nMeissner effect in superconductors. The atoms in the absolute ground state has\na zero quasi-angular momentum and transits into a polar-core vortex when the\nsynthetic magnetic flux is tuned to exceed a critical value. Our demonstration\nserves as a paradigm to create topological excitations by tailoring atom-light\ninteractions where both types of SO(3) vortices in the $|\\langle\n\\vec{F}\\rangle|=1$ manifold, coreless vortices and polar-core vortices, are\ncreated in our experiment. The gauge field in the stationary Hamiltonian opens\na path to investigating rotation properties of atomic superfluids under thermal\nequilibrium."
    },
    {
        "anchor": "Adiabatic approximation and fluctuations in exciton-polariton\n  condensates: We study the relation between the models commonly used to describe the\ndynamics of nonresonantly pumped exciton-polariton condensates, namely the ones\ndescribed by the complex Ginzburg-Landau equation, and by the open-dissipative\nGross-Pitaevskii equation including a separate equation for the reservoir\ndensity. In particular, we focus on the validity of the adiabatic approximation\nthat allows to reduce the coupled condensate-reservoir dynamics to a single\npartial differential equation. We find that the adiabatic approximation\nconsists of three independent analytical conditions that have to be fulfilled\nsimultaneously. By investigating stochastic versions of the two corresponding\nmodels, we verify that the breakdown of the adiabatic approximation can lead to\ndiscrepancies in correlation lengths and distributions of fluctuations.\nAdditionally, we consider the phase diffusion and number fluctuations of a\ncondensate in a box, and show that self-consistent description requires\ntreatment beyond the typical Bogoliubov approximation.",
        "positive": "Measurement of the excitation spectrum of a dipolar gas in the\n  macrodroplet regime: The excitation spectrum of a cigar-shaped strongly dipolar quantum gas at the\ncrossover from a Bose-Einstein condensate to a trapped macrodroplet is\npredicted to exhibit peculiar features - a strong upward shift of low momentum\nexcitation energies together with a strong multi-band response for high\nmomenta. By performing Bragg spectroscopy over a wide range of momenta, we\nobserve both key elements and also confirm the predicted stiffening of\nexcitation modes when approaching the macrodroplet regime. Our measurements are\nin good agreement with numerical calculations taking into account finite size\neffects."
    },
    {
        "anchor": "Hydrodynamic spectrum of a superfluid in an elongated trap: --In this article we study the hydrodynamic spectrum of a superfluid confined\nin a cylindrical trap. We show that the dispersion relation $\\omega$(q) of the\nphonon branch scales like $\\sqrt$ q at large q, leading to a vanishingly small\nsuperfluid critical velocity. In practice the critical velocity is set by the\nbreakdown of the hydrodynamic approximation. For a broad class of superfluids,\nthis entails a reduction of the critical velocity by a factor ($\\omega$ $\\perp$\n/\\\"i1/2c) 1/3 with respect to the free-space prediction (here $\\omega$ $\\perp$\nis the trapping frequency and \\\"i1/2c the chemical potential of the cloud).",
        "positive": "How does an interacting many-body system tunnel through a potential\n  barrier to open space?: The tunneling process in a many-body system is a phenomenon which lies at the\nvery heart of quantum mechanics. It appears in nature in the form of\nalpha-decay, fusion and fission in nuclear physics, photoassociation and\nphotodissociation in biology and chemistry. A detailed theoretical description\nof the decay process in these systems is a very cumbersome problem, either\nbecause of very complicated or even unknown interparticle interactions or due\nto a large number of constitutent particles. In this work, we theoretically\nstudy the phenomenon of quantum many-body tunneling in a more transparent and\ncontrollable physical system, in an ultracold atomic gas. We analyze a full,\nnumerically exact many-body solution of the Schr\\\"odinger equation of a\none-dimensional system with repulsive interactions tunneling to open space. We\nshow how the emitted particles dissociate or fragment from the trapped and\ncoherent source of bosons: the overall many-particle decay process is a quantum\ninterference of single-particle tunneling processes emerging from sources with\ndifferent particle numbers taking place simultaneously. The close relation to\natom lasers and ionization processes allows us to unveil the great relevance of\nmany-body correlations between the emitted and trapped fractions of the\nwavefunction in the respective processes."
    },
    {
        "anchor": "Emergence of chaotic scattering in ultracold Er and Dy: We show that for ultracold magnetic lanthanide atoms chaotic scattering\nemerges due to a combination of anisotropic interaction potentials and Zeeman\ncoupling under an external magnetic field. This scattering is studied in a\ncollaborative experimental and theoretical effort for both dysprosium and\nerbium. We present extensive atom-loss measurements of their dense magnetic\nFeshbach resonance spectra, analyze their statistical properties, and compare\nto predictions from a random-matrix-theory inspired model. Furthermore,\ntheoretical coupled-channels simulations of the anisotropic molecular\nHamiltonian at zero magnetic field show that weakly-bound, near threshold\ndiatomic levels form overlapping, uncoupled chaotic series that when combined\nare randomly distributed. The Zeeman interaction shifts and couples these\nlevels, leading to a Feshbach spectrum of zero-energy bound states with\nnearest-neighbor spacings that changes from randomly to chaotically distributed\nfor increasing magnetic field. Finally, we show that the extreme temperature\nsensitivity of a small, but sizeable fraction of the resonances in the Dy and\nEr atom-loss spectra is due to resonant non-zero partial-wave collisions. Our\nthreshold analysis for these resonances indicates a large collision-energy\ndependence of the three-body recombination rate.",
        "positive": "Nonlinear dynamics of Aharonov-Bohm cages: The interplay of $\\pi$-flux and lattice geometry can yield full localization\nof quantum dynamics in lattice systems, a striking interference phenomenon\nknown as Aharonov-Bohm caging. At the level of the single-particle energy\nspectrum, this full-localization effect is attributed to the collapse of Bloch\nbands into a set of perfectly flat (dispersionless) bands. In such lattice\nmodels, the effects of inter-particle interactions generally lead to a breaking\nof the cages, and hence, to the spreading of the wavefunction over the lattice.\nMotivated by recent experimental realizations of analog Aharonov-Bohm cages for\nlight, using coupled-waveguide arrays, we hereby demonstrate that caging always\noccurs in the presence of local nonlinearities. As a central result, we focus\non special caged solutions, which are accompanied by a breathing motion of the\nfield intensity, that we describe in terms of an effective two-mode model\nreminiscent of a bosonic Josephson junction. Moreover, we explore the quantum\nregime using small particle ensembles, and we observe quasi-caged\ncollapse-revival dynamics with negligible leakage. The results stemming from\nthis work open an interesting route towards the characterization of nonlinear\ndynamics in interacting flat band systems."
    },
    {
        "anchor": "Radio-frequency spectroscopy of weakly bound molecules in spin-orbit\n  coupled atomic Fermi gases: We investigate theoretically radio-frequency spectroscopy of weakly bound\nmolecules in an ultracold spin-orbit-coupled atomic Fermi gas. We consider two\ncases with either equal Rashba and Dresselhaus coupling or pure Rashba\ncoupling. The former system has been realized very recently at Shanxi\nUniversity [Wang et al., arXiv:1204.1887] and MIT [Cheuk et al.,\narXiv:1205.3483]. We predict realistic radio-frequency signals for revealing\nthe unique properties of anisotropic molecules formed by spin-orbit coupling.",
        "positive": "The true mechanism of spontaneous order from turbulence in\n  two-dimensional superfluid manifolds: In a two-dimensional (2D) turbulent fluid containing point-like vortices,\nLars Onsager predicted that adding energy to the fluid can lead to the\nformation of persistent clusters of like-signed vortices, i.e., Onsager vortex\n(OV) clusters. In the evolution of 2D superfluid turbulence in a uniform\ndisk-shaped Bose-Einstein condensate (BEC), it was discovered that a pair of OV\nclusters with opposite signs can form without any energy input. This striking\nspontaneous order was explained as due to a vortex evaporative-heating\nmechanism, i.e., annihilations of vortex-antivortex pairs which remove the\nlowest-energy vortices and thereby boost the mean energy per vortex. However,\nin our search for exotic OV states in a boundaryless 2D spherical BEC, we found\nthat OV clusters never form despite the annihilations of vortex pairs. Our\nanalysis reveals that contrary to the general belief, vortex-pair annihilation\nemits intense sound waves, which damp the motion of all vortices and hence\nsuppress the formation of OV clusters. We also present unequivocal evidences\nshowing that the true mechanism underlying the observed spontaneous OV state is\nthe escaping of vortices from the BEC boundary. Uncovering this mechanism paves\nthe way for a comprehensive understanding of emergent vortex orders in 2D\nmanifolds of superfluids driven far from equilibrium."
    },
    {
        "anchor": "Synthetic Gauge Field with Highly Magnetic Lanthanide Atoms: We present a scheme for generating a synthetic magnetic field and spin-orbit\ncoupling via Raman coupling in highly magnetic lanthanide atoms such as\ndysprosium. Employing these atoms offer several advantages for realizing\nstrongly correlated states and exotic spinor phases. The large spin and narrow\noptical transitions of these atoms allow the generation of synthetic magnetic\nfields an order of magnitude larger than those in the alkalis, but with\nconsiderable reduction of the heating rate for equal Raman coupling. The\neffective hamiltonian of these systems differs from that of the alkalis' by an\nadditional nematic coupling term, which leads to a phase transition in the\ndressed states as detuning varies. For \\text{high-spin} condensates, spin-orbit\ncoupling leads to a spatially periodic structure, which is described in\nMajorana representation by a set of points moving periodically on a unit\nsphere. We name this a \"Majorana spinor helix\" in analogy to the persistent\nspin-1/2 helix observed in electronic systems.",
        "positive": "Splitting bright matter-wave solitons on narrow potential barriers:\n  quantum to classical transition and applications to interferometry: We study bright solitons in the Gross-Pitaevskii equation as they are split\nand recombined in a low energy system. We present new analytic results\ndetermining the general region in which a soliton may not be split on a\npotential barrier, and confirm these results numerically. Furthermore, we\nanalyse the energetic regimes where quantum fluctuations in the initial center\nof mass position and momentum become influential on the outcome of soliton\nsplitting and recombination events. We then use the results of this analysis to\ndetermine a parameter regime where soliton interferometry is practicable."
    },
    {
        "anchor": "Lifetime of Excitations in Atomic and Molecular Bose-Einstein\n  Condensates: Recent experimental progress has produced Molecular Superfluids (MSF) in\nthermal equilibrium; this opens the door to a new class of experiments\ninvestigating the associated thermodynamic and dynamical responses. We review\nthe theoretical picture of the phase diagram and quasiparticle spectrum in the\nAtomic Superfluid (ASF) and MSF phases. We further compute the parametric\ndependence of the quasiparticle lifetimes at one-loop order. In the MSF phase,\nthe $U(1)$ particle number symmetry breaks to $\\mathbb{Z}_2$ and the spectrum\nexhibits a gapless Goldstone mode in addition to a gapped\n$\\mathbb{Z}_2$-protected atom-like mode. In the ASF phase, the $U(1)$ symmetry\nbreaks completely, leaving behind a Goldstone mode and an unprotected gapped\nmode. In both phases, the Goldstone mode decays with a rate given by the\ncelebrated Belyaev result, as in a single component condensate. In the MSF\nphase, the gapped mode is sharp up to a critical Cherenkov momentum beyond\nwhich it emits phonons. In the ASF phase, the gapped mode decays with a\nconstant rate even at small momenta. These decay rates govern the spectral\nresponse in microtrap tunneling experiments and lead to sharp features in the\ntransmission spectrum of atoms fired through molecular clouds.",
        "positive": "Interaction beween polarons and analogous effects in polarized Fermi\n  gases: We consider an imbalanced mixture of two different ultracold Fermi gases,\nwhich are strongly interacting. Calling spin-down the minority component and\nspin-up the majority component, the limit of small relative density $x=n\\ds\n/n\\us$ is usually considered as a gas of non interacting polarons. This allows\nto calculate, in the expansion of the total energy of the system in powers of\n$x$, the terms proportional to $x$ (corresponding to the binding energy of the\npolaron) and to $x^{5/3}$ (corresponding to the kinetic energy of the polaron\nFermi sea). We investigate in this paper terms physically due to an interaction\nbetween polarons and which are proportional to $x^2$ and $x^{7/3}$. We find\nthree such terms. A first one corresponds to the overlap between the clouds\ndressing two polarons. The two other ones are due to the modification of the\nsingle polaron binding energy caused by the non-zero density of polarons. The\nsecond term is due to the restriction of the polaron momentum by the Fermi sea\nformed by the other polarons. The last one results from the modification of the\nspin-up Fermi sea brought by the other polarons. The calculation of all these\nterms is made at the simplest level of a single particle-hole excitation. It is\nperformed for all the possible interaction strengths within the stability range\nof the polaron. At unitarity the last two terms give a fairly weak contribution\nwhile the first one is strong and leads to a marked disagreement with\nMonte-Carlo results. The possible origins of this discrepancy are discussed."
    },
    {
        "anchor": "Bottom-up configuration-interaction emulations of ultracold fermions in\n  entangled optical plaquettes: building blocks of unconventional\n  superconductivity: A microscopic configuration-interaction (CI) methodology is introduced to\nenable bottom-up Schroedinger-equation emulation of unconventional\nsuperconductivity in ultracold optical traps. We illustrate the method by\nexploring the properties of Lithium-6 atoms in a single square plaquette in the\nhole-pairing regime, and by analyzing the entanglement (symmetry-preserving)\nand disentanglement physics (via symmetry-breaking, associated with the\nseparation of charge and spin density waves) of two coupled plaquettes in the\nsame regime. The single-occupancy RVB states contribute only partially to the\nexact many-body solutions, and the CI results map onto a Hubbard Hamiltonian,\nbut not onto the double-occupancy-excluding t-J one. For the double-plaquette\ncase, effects brought about by breaking the symmetry between two\nweakly-interacting plaquettes, either by distorting, or by tilting and\ndetuning, one of the plaquettes with respect to the other, as well as spectral\nchanges caused by increased coupling between the two plaquettes, are explored.",
        "positive": "Super Tonks-Girardeau state in an attractive one-dimensional dipolar gas: The ground state of a one-dimensional (1D) quantum gas of dipoles oriented\nperpendicular to the longitudinal axis, with a strong 1/x^3 repulsive\npotential, is studied at low 1D densities $n$. Near contact the dependence of\nthe many-body wave function on the separation x_{jl} of two particles reduces\nto a two-body wave function \\Psi_{rel}(x_{jl}). Immediately after a sudden\nrotation of the dipoles so that they are parallel to the longitudinal axis,\nthis wave function will still be that of the repulsive potential, but since the\npotential is now that of the attractive potential, it will not be stationary.\nIt is shown that as nd^2 -> 0 the rate of change of this wave function\napproaches zero. It follows that for small values of nd^2, this state is\nmetastable and is an analog of the super Tonks-Girardeau state of bosons with a\nstrong zero-range attraction. The dipolar system is equivalent to a spinor\nFermi gas with spin $z$ components \\sigma_{\\uparrow}=\\perp (perpendicular to\nthe longitudinal axis) and \\sigma_{\\downarrow}=|| (parallel to the longitudinal\naxis). A Fermi-Fermi mapping from spinor to spinless Fermi gas followed by the\nstandard 1960 Fermi-Bose mapping reduces the Fermi system to a Bose gas.\nPotential experiments realizing the sudden spin rotation with ultracold dipolar\ngases are discussed, and a few salient properties of these states are\naccurately evaluated by a Monte Carlo method."
    },
    {
        "anchor": "The variational reduction for low-dimensional Fermi gases and Bose -\n  Fermi mixtures: A brief review: We present a summary of some recent theoretical results for matter-wave\npatterns in Fermi and Bose-Fermi degenerate gases, obtained in the framework of\nthe quasi-mean-field approximation. We perform a dimensional reduction from the\nthree-dimensional (3D) equations of motion to 2D and 1D effective equations. In\nboth cases, comparison of the low-dimensional reductions to the full model is\nperformed, showing very good agreement for ground-state solutions. Some complex\ndynamical regimes are reported too for the corresponding 1D systems.",
        "positive": "Real-space imaging of a topological protected edge state with ultracold\n  atoms in an amplitude-chirped optical lattice: Topological states of matter, as quantum Hall systems or topological\ninsulators, cannot be distinguished from ordinary matter by local measurements\nin the bulk of the material. Instead, global measurements are required,\nrevealing topological invariants as the Chern number. At the heart of\ntopological materials are topologically protected edge states that occur at the\nintersection between regions of different topological order. Ultracold atomic\ngases in optical lattices are promising new platforms for topological states of\nmatter, though the observation of edge states has so far been restricted in\nthese systems to the state space imposed by the internal atomic structure. Here\nwe report on the observation of an edge state between two topological distinct\nphases of an atomic physics system in real space using optical microscopy. An\ninterface between two spatial regions of different topological order is\nrealized in a one-dimensional optical lattice of spatially chirped amplitude.\nTo reach this, a magnetic field gradient causes a spatial variation of the\nRaman detuning in an atomic rubidium three- level system and a corresponding\nspatial variation of the coupling between momentum eigenstates. This novel\nexperimental technique realizes a cold atom system described by a Dirac\nequation with an inhomogeneous mass term closely related to the SSH-model. The\nobserved edge state is characterized by measuring the overlap to various\ninitial states, revealing that this topological state has singlet nature in\ncontrast to the other system eigenstates, which occur pairwise. We also\ndetermine the size of the energy gap to the adjacent eigenstate doublet. Our\nfindings hold prospects for the spectroscopy of surface states in topological\nmatter and for the quantum simulation of interacting Dirac systems."
    },
    {
        "anchor": "Fate of topological states in incommensurate generalized Aubry-Andr\u00e9\n  models: We study one-dimensional optical lattices described by generalized\nAubry-Andr\\'e models that include both commensurate and incommensurate\nmodulations of the hopping amplitude. This brings together two interesting\nfeatures of this class of systems: Anderson localization and the existence of\ntopological edge states. We follow changes of the single-particle energy\nspectrum induced by variations of the system parameters, with focus on the\nsurvival of topological states in the localized regime.",
        "positive": "Topologically driven nonequilibrium phase transitions in diagonal\n  ensembles: We identify a new class of topologically driven phase transitions when\ncalculating the Hall conductance of two-band Chern insulators in the long-time\nlimit after a global quench of the Hamiltonian. The Hall conductance is\nexpressed as the integral of the Berry curvature in the diagonal ensemble. Even\nif the topological invariant of the wave function is conserved under unitary\nevolution, the Hall conductance as a function of the energy gap in the\npost-quench Hamiltonian displays a continuous but nonanalytic behavior, that is\nit has a logarithmically divergent derivative as the gap closes. The\ncoefficient of this logarithmic function is the ratio of the change of Chern\nnumber in the ground state of the post-quench Hamiltonian to the energy gap in\nthe initial state. This nonanalytic behavior is universal in two-band Chern\ninsulators."
    },
    {
        "anchor": "Damping of the Anderson-Bogolyubov mode by spin and mass imbalance in\n  Fermi mixtures: We study the temporally nonlocal contributions to the gradient expansion of\nthe pair fluctuation propagator for spin- and mass-imbalanced Fermi mixtures.\nThese terms are related to damping processes of sound-like\n(Anderson-Bogolyubov) collective modes and are relevant for the structure of\nthe complex pole of the pair fluctuation propagator. We derive conditions under\nwhich damping occurs even at zero temperature for large enough mismatch of the\nFermi surfaces. We compare our analytical results with numerically computed\ndamping rates of the Anderson-Bogolyubov mode.",
        "positive": "Probing anisotropic superfluidity of rashbons in atomic Fermi gases: Motivated by the prospect of realizing a Fermi gas of $^{40}$K atoms with a\nsynthetic non-Abelian gauge field, we investigate theoretically a strongly\ninteracting Fermi gas in the presence of a Rashba spin-orbit coupling. As the\ntwo-fold spin degeneracy is lifted by spin-orbit interaction, bound pairs with\nmixed singlet and triplet pairings (referred to as rashbons) emerge, leading to\nan anisotropic superfluid. We show that this anisotropic superfluidity can be\nprobed via measuring the momentum distribution and single-particle spectral\nfunction in a trapped atomic $^{40}$K cloud near a Feshbach resonance."
    },
    {
        "anchor": "Comment on Influence of induced interactions on superfluid properties of\n  quasi-two-dimensional dilute Fermi gases with spin-orbit coupling: In an article in 2013, Caldas et al. [Phys. Rev. A 88, 023615 (2013)] derived\nanalytical expressions of the induced interaction within the scheme of Gorkov\nand Melik-Barkhudrov in quasi-two-dimensional Fermi gases with Rashba\nspin-orbit coupling (SOC). They claimed that the induced interaction is exactly\nthe same as the one for the case without SOC when the SOC is weak, and in the\nregion of strong SOC, it starts from a reduced value and then recovers the\nvalue for the zero SOC in the limit of large SOC. We point out that their\ncalculations contain the critical errors and inconsistencies that significantly\naffect the basis of these claims.",
        "positive": "Density form factors of the 1D Bose gas for finite entropy states: We consider the Lieb-Liniger model for a gas of bosonic $\\delta-$interacting\nparticles. Using Algebraic Bethe Ansatz results we compute the thermodynamic\nlimit of the form factors of the density operator between finite entropy\neigenstates such as finite temperature states or generic non-equilibrium highly\nexcited states. These form factors are crucial building blocks to obtain the\nthermodynamic exact dynamic correlation functions of such physically relevant\nstates. As a proof of principle we compute an approximated dynamic structure\nfactor by including only the simplest types of particle-hole excitations and\nshow the agreement with known results."
    },
    {
        "anchor": "Route towards classical frustration and band flattening via optical\n  lattice distortion: We propose and experimentally explore a method for realizing frustrated\nlattice models using a Bose-Einstein condensate held in an optical square\nlattice. A small lattice distortion opens up an energy gap such the lowest band\nsplits into two. Along the edge of the first Brillouin zone for both bands a\nnearly flat energy-momentum dispersion is realized. For the excited band a\nhighly degenerate energy minimum arises. By loading ultracold atoms into the\nexcited band, a classically frustrated $XY$ model is formed, describing rotors\non a square lattice with competing nearest and next nearest tunnelling\ncouplings. Our experimental optical lattice provides a regime, where a fully\ncoherent Bose-Einstein condensate is observed, and a regime where frustration\nis expected. If we adiabatically tune from the condensate regime to the regime\nof frustration, the momentum spectra shows a complete loss of coherence. Upon\nslowly tuning back to the condensate regime, coherence is largely restored.\nGood agreement with model calculations is obtained.",
        "positive": "Time-dependent currents of 1D bosons in an optical lattice: We analyse the time-dependence of currents in a 1D Bose gas in an optical\nlattice. For a 1D system, the stability of currents induced by accelerating the\nlattice exhibits a broad crossover as a function of the magnitude of the\nacceleration, and the strength of the inter-particle interactions. This differs\nmarkedly from mean-field results in higher dimensions. Using the infinite Time\nEvolving Block Decimation algorithm, we characterise this crossover by making\nquantitative predictions for the time-dependent behaviour of the currents and\ntheir decay rate. We also compute the time-dependence of quasi-condensate\nfractions which can be measured directly in experiments. We compare our results\nto calculations based on phase-slip methods, finding agreement with the scaling\nas the particle density increases, but with significant deviations near unit\nfilling."
    },
    {
        "anchor": "Detection of Weak Force using a Bose-Einstein Condensate: We investigate the possibility of detecting a weak coherent force by means of\na hybrid optomechanical quantum device formed by a Bose Einstein Condensate\n(BEC) confined in a high quality factor optical cavity with an oscillatory end\nmirror. We show using the stochastic cooling technique that the atomic two-body\ninteraction can be utilized to cool the mirror and achieve position squeezing\nessential for making sensitive measurements of weak forces. We further show\nthat the atomic two-body interaction can also increase the signal to noise\nratio (SNR) and decrease the noise of the off-resonant stationary spectral\nmeasurements.",
        "positive": "Orbital Josephson effect and interactions in driven atom condensates on\n  a ring: In a system of ac-driven condensed bosons we study a new type of Josephson\neffect occurring between states sharing the same region of space and the same\ninternal atom structure. We first develop a technique to calculate the long\ntime dynamics of a driven interacting many-body system. For resonant\nfrequencies, this dynamics can be shown to derive from an effective\ntime-independent Hamiltonian which is expressed in terms of standard creation\nand annihilation operators. Within the subspace of resonant states, and if the\nundriven states are plane waves, a locally repulsive interaction between bosons\ntranslates into an effective attraction. We apply the method to study the\neffect of interactions on the coherent ratchet current of an asymmetrically\ndriven boson system. We find a wealth of dynamical regimes which includes Rabi\noscillations, self-trapping, and chaotic behavior. In the latter case, a full\nmany-body calculation deviates from the mean-field results by predicting large\nquantum fluctuations of the relative particle number."
    },
    {
        "anchor": "Quasiparticle dynamics in a Bose insulator probed by inter-band Bragg\n  spectroscopy: We investigate experimentally and theoretically the dynamical properties of a\nMott insulator in decoupled one-dimensional chains. Using a theoretical\nanalysis of the Bragg excitation scheme we show that the spectrum of inter-band\ntransitions holds information on the single-particle Green's function of the\ninsulator. In particular the existence of particle-hole coherence due to\nquantum fluctuations in the Mott state is clearly seen in the Bragg spectra and\nquantified. Finally we propose a scheme to directly measure the full, momentum\nresolved spectral function as obtained in angle-resolved photoemission\nspectroscopy of solids.",
        "positive": "Finite Temperature Phase Transitions in the SU$(N)$ Hubbard model: We investigate the SU($N$) Hubbard model for the multi-component fermionic\noptical lattice system, combining dynamical mean-field theory with the\ncontinuous-time quantum Monte Carlo method. We obtain the finite temperature\nphase diagrams with $N\\le 6$ and find that low temperature properties depends\non the parity of the components. The magnetically ordered state competes with\nthe correlated metallic state in the system with the even number of components\n$(N\\ge 4)$, yielding the first-order phase transition. It is also clarified\nthat, in the odd-component system, the ordered state is realized at relatively\nlower temperatures and the critical temperature is constant in the strong\ncoupling limit."
    },
    {
        "anchor": "Particle entanglement in continuum many-body systems via quantum Monte\n  Carlo: Entanglement of spatial bipartitions, used to explore lattice models in\ncondensed matter physics, may be insufficient to fully describe itinerant\nquantum many-body systems in the continuum. We introduce a procedure to measure\nthe R\\'enyi entanglement entropies on a particle bipartition, with general\napplicability to continuum Hamiltonians via path integral Monte Carlo methods.\nVia direct simulations of interacting bosons in one spatial dimension, we\nconfirm a logarithmic scaling of the single-particle entanglement entropy with\nthe number of particles in the system. The coefficient of this logarithmic\nscaling increases with interaction strength, saturating to unity in the\nstrongly interacting limit. Additionally, we show that the single-particle\nentanglement entropy is bounded by the condensate fraction, suggesting a\npractical route towards its measurement in future experiments.",
        "positive": "Dynamical vortex production and quantum turbulence in perturbed\n  Bose-Einstein condensates: Dynamical vortex production and quantum turbulence emerging in periodic\nperturbed quasi-two-dimensional (q2D) Bose-Einstein condensates are reported by\nconsidering two distinct time-dependent approaches. In both cases, dynamical\nsimulations were performed by solving the corresponding 2D mean-field\nGross-Pitaevskii formalism. (i) In the first model, a binary mass-imbalanced\nsystem is slightly perturbed by a stirring time-dependent elliptic external\npotential. (ii) In the second model, for single dipolar species confined in q2D\ngeometry, a circularly moving external Gaussian-shaped obstacle is applied in\nthe condensate, at a fixed radial position and constant rotational speed,\nenough for the production of vortex-antivortex pairs. Within the first case,\nvortex patterns are crystalized after enough longer period, whereas in the\nsecond case, the vortex pairs remains interacting dynamically inside the fluid.\nIn both cases, the characteristic Kolmogorov spectral scaling law for\nturbulence can be observed at some short time interval."
    },
    {
        "anchor": "Degenerate Bose Gas: A New Tool for Accurate Frequency Measurement: We propose a new way of detecting frequencies using superradiant Rayleigh\nscattering from degenerate Bose gases. A measurement of the time evolution of\npopulation at the initial momentum state could determine an unknown frequency\nwith respect to a known one at which the pump laser's frequency modulates. A\nrange of frequencies from kHz to MHz could be determined with a fractional\nuncertainty of 10^{-6}.",
        "positive": "Resonant scattering of matter wave gap-solitons by optical lattice\n  defects: The physical mechanism underlying scattering properties of matter wave\ngap-solitons by linear optical lattice defects is investigated. The occurrence\nof repeated reflection, transmission and trapping regions for increasing\nstrengths of an optical lattice defect are shown to be due to impurity modes\ninside the defect potential with chemical potentials and numbers of atoms\nmatching corresponding quantities of an incoming gap-soliton. For gap-solitons\nwith chemical potentials very close to band edges, the number of resonances\nobserved in the scattering coincides with the number of bound states which can\nexist in the defect potential for the given defect strength. The dependence of\nthe positions and widths of the transmission resonant on the incoming\ngap-soliton velocities are investigated by means of a defect mode analysis and\neffective mass theory. The comparisons with direct integrations of the\nGross-Pitaevskii equation provide a very good agreement confirming the\ncorrectness of our interpretation. The possibility of multiple resonant\ntransmission through arrays of optical lattice defects is also demonstrated. In\nparticular, we show that it is possible to design the strength of the defects\nso to balance the velocity detunings and to allow the resonant transmission\nthrough a larger number of defects. The possibility of using these results for\nvery precise gap-soliton dynamical filters is suggested."
    },
    {
        "anchor": "Effects of interaction on the diffusion of atomic matter waves in\n  one-dimensional quasi-periodic potentials: We study the behaviour of an ultracold atomic gas of bosons in a bichromatic\nlattice, where the weaker lattice is used as a source of disorder. We\nnumerically solve a discretized mean-field equation, which generalizes the\none-dimensional Aubry-Andr\\`e model for particles in a quasi-periodic potential\nby including the interaction between atoms. We compare the results for\ncommensurate and incommensurate lattices. We investigate the role of the\ninitial shape of the wavepacket as well as the interplay between two competing\neffects of the interaction, namely self-trapping and delocalization. Our\ncalculations show that, if the condensate initially occupies a single lattice\nsite, the dynamics of the interacting gas is dominated by self-trapping in a\nwide range of parameters, even for weak interaction. Conversely, if the\ndiffusion starts from a Gaussian wavepacket, self-trapping is significantly\nsuppressed and the destruction of localization by interaction is more easily\nobservable.",
        "positive": "Inducing spin-dependent tunneling to probe magnetic correlations in\n  optical lattices: We suggest a simple experimental method for probing antiferromagnetic spin\ncorrelations of two-component Fermi gases in optical lattices. The method\nrelies on a spin selective Raman transition to excite atoms of one spin species\nto their first excited vibrational mode where the tunneling is large. The\nresulting difference in the tunneling dynamics of the two spin species can then\nbe exploited, to reveal the spin correlations by measuring the number of doubly\noccupied lattice sites at a later time. We perform quantum Monte Carlo\nsimulations of the spin system and solve the optical lattice dynamics\nnumerically to show how the timed probe can be used to identify\nantiferromagnetic spin correlations in optical lattices."
    },
    {
        "anchor": "Solution of the BEC to BCS Quench in One Dimension: A gas of interacting fermions confined in a quasi one-dimensional geometry\nshows a BEC to BCS crossover upon slowly driving its coupling constant through\na confinement-induced resonance. On one side of the crossover the fermions form\ntightly-bound bosonic molecules behaving as a repulsive Bose gas, while on the\nother they form Cooper pairs, whose size is much larger than the average\ninter-particle distance. Here we consider the situation arising when the\ncoupling constant is varied suddenly from the BEC to the BCS value. Namely, we\nstudy a BEC-to-BCS quench. By exploiting a suitable continuum limit of recently\ndiscovered solvable quenches in the Hubbard model, we show that the local\nstationary state reached at large times after the quench can be determined\nexactly by means of the Quench Action approach. We provide an\nexperimentally-accessible characterisation of the stationary state by computing\nlocal pair correlation function as well as the quasi-particle distribution\nfunctions. We find that the steady state is increasingly dominated by two\nparticle spin singlet bound states for stronger interaction strength but that\nbound state formation is inhibited at larger BEC density. The bound state\nrapidity distribution displays quartic power law decay suggesting a violation\nof Tan's contact relations.",
        "positive": "Black-Hole evaporation and Quantum-depletion in Bose-Einstein\n  condensates: We study the analogy between the Hawking radiation in Black-Holes and the\nQuantum depletion process of a Bose-Einstein condensate by using the Bogoliubov\ntransformations method. We find that the relation between the Bogoliubov\ncoefficients is similar in both cases (in the appropriate regimes). We then\nconnect the condensate variables with those associated to the Black-Hole,\ndemonstrating then that the zero temperature regime of the condensate is\nequivalent to the existence of an event horizon in gravity."
    },
    {
        "anchor": "Anomalous localization and multifractality in a kicked quasicrystal: Multifractal states offer a \"third way\" for quantum matter, neither fully\nlocalized nor ergodic, exhibiting singular continuous spectra, self-similar\nwavefunctions, and transport and entanglement scaling exponents intermediate\nbetween extended and localized states. While multifractality in equilibrium\nsystems generally requires fine-tuning to a critical point, externally driven\nquantum matter can exhibit multifractal states with no equilibrium counterpart.\nWe report the experimental observation of multifractal matter and anomalous\nlocalization in a kicked Aubry-Andr\\'e-Harper quasicrystal. Our cold-atom\nrealization of this previously-unexplored model is enabled by apodized Floquet\nengineering techniques which expand the accessible phase diagram by five orders\nof magnitude. This kicked quantum quasicrystal exhibits a rich phase diagram\nincluding not only fully localized and fully delocalized phases but also an\nextended region comprising an intricate nested pattern of localized,\ndelocalized, and multifractal states. Mapping transport properties throughout\nthe phase diagram, we observe disorder-driven re-entrant delocalization and\nsub-ballistic transport, and present a theoretical explanation of these\nphenomena based on eigenstate multifractality. These results open up the\nexploration of new states of matter characterized by an intricate interplay of\nfractal structure and quantum dynamics.",
        "positive": "The Floquet-Boltzmann equation: Periodically driven quantum systems can be used to realize quantum pumps,\nratchets, artificial gauge fields and novel topological states of matter.\nStarting from the Keldysh approach, we develop a formalism, the\nFloquet-Boltzmann equation, to describe the dynamics and the scattering of\nquasiparticles in such systems. The theory builds on a separation of\ntime-scales. Rapid, periodic oscillations occurring on a time scale $T_0=2\n\\pi/\\Omega$, are treated using the Floquet formalism and quasiparticles are\ndefined as eigenstates of a non-interacting Floquet Hamiltonian. The dynamics\non much longer time scales, however, is modelled by a Boltzmann equation which\ndescribes the semiclassical dynamics of the Floquet-quasiparticles and their\nscattering processes. As the energy is conserved only modulo $\\hbar \\Omega$,\nthe interacting system heats up in the long-time limit. As a first application\nof this approach, we compute the heating rate for a cold-atom system, where a\nperiodical shaking of the lattice was used to realize the Haldane model."
    },
    {
        "anchor": "Excited-state quantum phase transitions in spin-orbit coupled Bose gases: Excited-state quantum phase transitions depend on and reveal the structure of\nthe whole spectrum of many-body systems. While they are theoretically well\nunderstood, finding suitable signatures and detect them in actual experiments\nremains challenging. For instance, in spinor gases, excited-state phases have\nbeen identified and characterized through a topological order parameter that is\nchallenging to measure in experiments. Here, we propose the Raman-dressed\nspin-orbit coupled gas as a novel platform to explore excited-state quantum\nphase transitions. In a weakly-coupled regime, the dressed system is equivalent\nto a spinor gas with tunable spin-spin interactions. Through this equivalence\nwe are able to define a new excited-state phase of the dressed gas. The phase\nis characterize by the the behavior of the spatial density modulations, or\nstripes, induced by spin-orbit coupling, and can in principle be measured in\ncurrent state-of-the-art experiments with ultracold atoms. Conversely, we show\nthat the properties of the excited phase can be exploited to prepare stripe\nstates with large and stable density modulations.",
        "positive": "The pseudogap regime in the unitary Fermi gas: We discuss the pseudogap regime in the cold atomic unitary Fermi gas, with a\nparticular emphasis on the auxiliary-field quantum Monte Carlo (AFMC) approach.\nWe discuss possible signatures of the pseudogap, review experimental results,\nand survey analytic and quantum Monte Carlo techniques before focusing on AFMC\ncalculations in the canonical ensemble. For the latter method, we discuss\nresults for the heat capacity, energy-staggering pairing gap, spin\nsusceptibility, and compare to experiment and other theoretical methods."
    },
    {
        "anchor": "Energy-level inversion for vortex states in spin-orbit coupled\n  Bose-Einstein condensates: We investigate vortex states in Bose-Einstein condensates under the combined\naction of the spin-orbit coupling (SOC), gradient magnetic field, and\nharmonic-oscillator trapping potential. The linear version of the system is\nsolved exactly. Through the linear-spectrum analysis, we find that, varying the\nSOC strength and magnetic-field gradient, one can perform energy-level\ninversion. With suitable parameters, initial higher-order vortex states can be\nmade the ground state (GS). The nonlinear system is solved numerically,\nrevealing that the results are consistent with the linear predictions in the\ncase of repulsive inter-component interactions. On the other hand,\ninter-component attraction creates the GS in the form of mixed-mode states in a\nvicinity of the GS phase-transition points. The spin texture of both vortex-\nand mixed-mode GSs reveals that they feature the structure of 2D (baby)\nskyrmions.",
        "positive": "Condensed phase of Bose-Fermi mixtures with a pairing interaction: We study the condensed phase of a Bose-Fermi mixture with a tunable pairing\ninteraction between bosons and fermions with many-body diagrammatic methods and\nfixed-node diffusion Quantum Monte Carlo simulations. A universal behavior of\nthe condensate fraction and bosonic momentum distribution with respect to the\nboson concentration is found to hold in an extended range of boson-fermion\ncouplings and concentrations. For vanishing boson density, we prove that the\nbosonic condensate fraction reduces to the quasiparticle weight Z of the Fermi\npolaron studied in the context of polarized Fermi gases, unifying in this way\ntwo apparently unrelated quantities."
    },
    {
        "anchor": "BEC-BCS crossover and the mobility edge: superfluid-insulator\n  transitions and reentrant superfluidity in disordered Fermi gases: A superfluid-insulator transition is known to occur in strongly disordered\nFermi gases, in both the BCS and BEC regimes; here, we address the properties\nof this transition across the BEC-BCS crossover. We argue that the critical\ndisorder strength at which superfluidity is lost changes non-monotonically with\ndetuning from Feshbach resonance, and that a reentrant superfluid phase arises\nfor detunings near the fermionic mobility edge. Our analysis of the\nintermediate regime is quantitatively valid for narrow resonances and near four\ndimensions, and provides a simple physical picture of this regime, in terms of\ntwo distinct but coexisting insulators.",
        "positive": "Coexistence of density wave and superfluid order in a dipolar Fermi gas: We analyse the coexistence of superfluid and density wave (stripe) order in a\nquasi-two-dimensional gas of dipolar fermions aligned by an external field.\nRemarkably, the anisotropic nature of the dipolar interaction allows for such a\ncoexistence in a large region of the zero temperature phase diagram. In this\nregion, the repulsive part of the interaction drives the stripe formation and\nthe attractive part induces the pairing, resulting in a supersolid with\n$p$-wave Cooper pairs aligned along the stripes. From a momentum space\nperspective, the stability of the supersolid phase is due to the fact that the\nstripe order renders the Fermi surface only partially gapped, leaving gapless\nregions that are most important for $p$-wave pairing. We finally demonstrate\nhow this supersolid phase can be detected in time-of-flight experiments."
    },
    {
        "anchor": "Renormalization of the superfluid density in the two-dimensional BCS-BEC\n  crossover: We analyze the theoretical derivation of the beyond-mean-field equation of\nstate for a two-dimensional gas of dilute, ultracold alkali-metal atoms in the\nBardeen-Cooper-Schrieffer (BCS) to Bose-Einstein condensate (BEC) crossover. We\nshow that at zero temperature our theory -- considering Gaussian fluctuations\non top of the mean-field equation of state -- is in very good agreement with\nexperimental data. Subsequently, we investigate the superfluid density at\nfinite temperature and its renormalization due to the proliferation of\nvortex-antivortex pairs. By doing so, we determine the\nBerezinskii-Kosterlitz-Thouless (BKT) critical temperature -- at which the\nrenormalized superfluid density jumps to zero -- as a function of the\ninter-atomic potential strength. We find that the Nelson-Kosterlitz criterion\noverestimates the BKT temperature with respect to the renormalization group\nequations, this effect being particularly relevant in the intermediate regime\nof the crossover.",
        "positive": "Bound-State Band Reconstruction and Resonance in Spin-1/2 Bose Gas with\n  1D Spin-Orbit Coupling: In this work, we study two-body bound states in two-component Bose gas with a\none-dimensional (1D) spin-orbit coupling (SOC) induced by Raman lasers. The\nfinite Raman coupling strength generates coupling among three spin channels,\nresulting in the reconstruction of three bound-state bands. In addition,\nmultiple resonances can be induced at finite scattering lengths. By tuning the\ninteraction in one intra-species channel, one bound-state band can be lifted\nand three resonances can be achieved at different center-of-mass momenta, which\ncan be observable under current experimental conditions in ${}^{87}$Rb atoms."
    },
    {
        "anchor": "Topological defects in rotating spin-orbit-coupled dipolar spin-1\n  Bose-Einstein condensates: We consider the topological defects and spin structures of spin-1\nBose-Einstein condensates (BECs) with spin-orbit coupling (SOC) and\ndipole-dipole interaction (DDI) in a rotating harmonic plus quartic trap. The\ncombined effects of SOC, DDI and rotation on the ground-state phases of the\nsystem are analyzed. Our results show that for fixed rotation frequency\nstructural phase transitions can be achieved by adjusting the magnitudes of the\nSOC and DDI. A ground-state phase diagram is given as a function of the SOC and\nDDI strengths. It is shown that the system exhibits rich quantum phases\nincluding vortex string phase with isolated density peaks (DPs), triangular\n(square) vortex lattice phase with DPs, checkerboard phase, and stripe phase\nwith hidden vortices and antivortices. For given SOC and DDI strengths, the\nsystem can display pentagonal vortex lattice with DPs, vortex necklace with\nDPs, and exotic topological structure composed of multi-layer visible vortex\nnecklaces, a hidden giant vortex and hidden vortex necklaces, depending on the\nrotation frequency. In addition, the system sustains fascinating novel spin\ntextures and skyrmion excitations, such as an antiskyrmion pair,\nantiskyrmion-half-antiskyrmion (antiskyrmion-antimeron) cluster,\nskyrmion-antiskyrmion lattice, skyrmion-antiskyrmion cluster,\nskyrmion-antiskyrmion-meron-antimeron lattice, double-layer half-antiskyrmion\nnecklaces, and composite giant-antiskyrmion-antimeron necklaces.",
        "positive": "Multi-Particle Tunneling Transport at Strongly-Correlated Interfaces: We elucidate the multi-particle transport of pair- and spin-tunnelings in\nstrongly correlated interfaces. Not only usual single-particle tunneling but\nalso interaction-induced multi-particle tunneling processes naturally arise\nfrom a conventional microscopic model without any empirical parameters, through\nthe overlap of the many-body wave functions around the interface. We\ndemonstrate how anomalous tunneling currents occur in a strongly interacting\nsystem due to the pair-tunneling process which we derived microscopically. Our\nformulation is useful for junction systems in various disciplines, including\natomtronics, spintronics, and nuclear reactions."
    },
    {
        "anchor": "Control of tunneling in an atomtronic switching device: The precise control of quantum systems will play a major role in the\nrealization of atomtronic devices. As in the case of electronic systems, a\ndesirable property is the ability to implement switching. Here we show how to\nimplement switching in a model of dipolar bosons confined to three coupled\nwells. The model describes interactions between bosons, tunneling of bosons\nbetween adjacent wells, and the effect of an external field. We conduct a study\nof the quantum dynamics of the system to probe the conditions under which\nswitching behavior can occur. The analysis considers both integrable and\nnon-integrable regimes within the model. Through variation of the external\nfield, we demonstrate how the system can be controlled between various\nswitched-on and switched-off configurations.",
        "positive": "Many-body dynamical phase transition in quasi-periodic potential: Much has been learned regarding dynamical quantum phase transition (DQPT) due\nto sudden quenches across quantum critical points in traditional quantum\nsystems. However, not much has been explored when a system undergoes a\nlocalization-delocalization transition. Here, we study one dimensional\nfermionic systems in presence of a quasi-periodic potential, which induces\ndelocalization-localization transition even in 1D. We show signatures of DQPT\nin the many-body dynamics, when quenching is performed between phases belonging\nto different universality classes. We investigate how the non-analyticity in\nthe dynamical free energy gets affected with filling fractions in the bare\nsystem and, further, study the fate of DQPT under interaction. Strikingly,\nwhenever quenching is performed from the low-entangled localized phase to the\nhigh-entangled delocalized phase, our studies suggest an intimate relationship\nbetween DQPT and the rate of the entanglement growth -- Faster growths of\nentanglement entropy ensures quicker manifestation of the non-analiticties in\nthe many-body dynamical free energy."
    },
    {
        "anchor": "Optical shielding of destructive chemical reactions between ultracold\n  ground-state NaRb molecules: We propose a method to suppress the chemical reactions between ultracold\nbosonic ground-state $^{23}$Na$^{87}$Rb molecules based on optical shielding.\nBy applying a laser with a frequency blue-detuned from the transition between\nthe lowest rovibrational level of the electronic ground state $X^1\\Sigma^+\n(v_X=0, j_X=0)$, and the long-lived excited level $b^3\\Pi_0 (v_b=0, j_b=1)$,\nthe long-range dipole-dipole interaction between the colliding molecules can be\nengineered, leading to a dramatic suppression of reactive and photoinduced\ninelastic collisions, for both linear and circular laser polarizations. We\ndemonstrate that the spontaneous emission from $b^3\\Pi_0 (v_b=0, j_b=1)$ does\nnot deteriorate the shielding process. This opens the possibility for a strong\nincrease of the lifetime of cold molecule traps, and for an efficient\nevaporative cooling. We also anticipate that the proposed mechanism is valid\nfor alkali-metal diatomics with sufficiently large dipole-dipole interactions.",
        "positive": "Critical transport and vortex dynamics in a thin atomic Josephson\n  junction: We study the onset of dissipation in an atomic Josephson junction between\nFermi superfluids in the molecular Bose-Einstein condensation limit of strong\nattraction. Our simulations identify the critical population imbalance and the\nmaximum Josephson current delimiting dissipationless and dissipative transport,\nin quantitative agreement with recent experiments. We unambiguously link\ndissipation to vortex ring nucleation and dynamics, demonstrating that quantum\nphase slips are responsible for the observed resistive current. Our work\ndirectly connects microscopic features with macroscopic dissipative transport,\nproviding a comprehensive description of vortex ring dynamics in\nthree-dimensional inhomogeneous constricted superfluids at zero and finite\ntemperatures."
    },
    {
        "anchor": "High-temperature expansion for interacting fermions: We present a general method for the high-temperature expansion of the\nself-energy of interacting particles. Though the method is valid for fermions\nand bosons, we illustrate it for spin one half fermions interacting via a zero\nrange potential, in the Bose Einstein Condensate - Bardeen Cooper Schrieffer\n(BEC-BCS) crossover. The small parameter of the expansion is the fugacity z.\nOur results include terms of order z and z^2, which take into account\nrespectively two and three body correlations. We give results for the high\ntemperature expansion of Tan's contact at order z^3 in the whole BEC-BCS\ncrossover. We apply our method to calculate the spectral function at the\nunitary limit. We find new structures which were overlooked by previous\napproaches, which included only two body correlations. This shows that\nincluding three-body correlations can play an important role in the structures\nof the spectral function.",
        "positive": "Experimental realization of a two-dimensional synthetic spin-orbit\n  coupling in ultracold Fermi gases: Spin-orbit coupling (SOC) is central to many physical phenomena, including\nfine structures of atomic spectra and quantum topological matters. Whereas SOC\nis in general fixed in a physical system, atom-laser interaction provides\nphysicists a unique means to create and control synthetic SOC for ultracold\natoms \\cite{Dalibard}. Though significant experimental progresses have been\nmade, a bottleneck in current studies is the lack of a two-dimensional (2D)\nsynthetic SOC, which is crucial for realizing high-dimensional topological\nmatters. Here, we report the experimental realization of 2D SOC in ultracold\n$^{40}$K Fermi gases using three lasers, each of which dresses one atomic\nhyperfine spin state. Through spin injection radio-frequency (rf) spectroscopy,\nwe probe the spin-resolved energy dispersions of dressed atoms, and observe a\nhighly controllable Dirac point created by the 2D SOC. Our work paves the way\nfor exploring high-dimensional topological matters in ultracold atoms using\nRaman schemes."
    },
    {
        "anchor": "Universal quantum dynamics of Bose polarons: Predicting the emergent properties of impurities immersed in a quantum bath\nis a fundamental challenge that can defy quasiparticle treatments. Here, we\nmeasure the spectral properties and real-time dynamics of mobile impurities\ninjected into a homogeneous Bose--Einstein condensate, using two Feshbach\nresonances to tune both the impurity-bath and intrabath interactions. We map\nout both attractive and repulsive branches of polaron quasiparticles, resolving\nthe repulsive polaron and the molecular state associated with the Feshbach\nresonance in the strongly interacting regime, and show that the latter also has\na many-body character. Our measurements reveal remarkably universal behavior,\ncontrolled by the bath density and a single dimensionless interaction\nparameter; for near-resonant interactions the polarons are no longer well\ndefined, but the universality still holds.",
        "positive": "Exciton-polariton condensates: Recently a new type of system exhibiting spontaneous coherence has emerged --\nthe exciton-polariton condensate. Exciton-polaritons (or polaritons for short)\nare bosonic quasiparticles that exist inside semiconductor microcavities,\nconsisting of a superposition of an exciton and a cavity photon. Above a\nthreshold density the polaritons macroscopically occupy the same quantum state,\nforming a condensate. The lifetime of the polaritons are typically comparable\nto or shorter than thermalization times, making them possess an inherently\nnon-equilibrium nature. Nevertheless, they display many of the features that\nwould be expected of equilibrium Bose-Einstein condensates (BECs). The\nnon-equilibrium nature of the system raises fundamental questions of what it\nmeans for a system to be a BEC, and introduces new physics beyond that seen in\nother macroscopically coherent systems. In this review we focus upon several\nphysical phenomena exhibited by exciton-polariton condensates. In particular we\nexamine topics such as the difference between a polariton BEC, a polariton\nlaser, and a photon laser, as well as physical phenomena such as superfluidity,\nvortex formation, BKT (Berezinskii-Kosterlitz-Thouless) and BCS\n(Bardeen-Cooper-Schrieffer) physics. We also discuss the physics and\napplications of engineered polariton structures."
    },
    {
        "anchor": "Isotropic contact forces in arbitrary representation: heterogeneous\n  few-body problems and low dimensions: The Bethe-Peierls asymptotic approach which models pairwise short-range\nforces by contact conditions is introduced in arbitrary representation for\nspatial dimensions less than or equal to 3. The formalism is applied in various\nsituations and emphasis is put on the momentum representation. In the presence\nof a transverse harmonic confinement, dimensional reduction toward\ntwo-dimensional (2D) or one-dimensional (1D) physics is derived within this\nformalism. The energy theorem relating the mean energy of an interacting system\nto the asymptotic behavior of the one-particle density matrix illustrates the\nmethod in its second quantized form. Integral equations that encapsulate the\nBethe-Peierls contact condition for few-body systems are derived. In three\ndimensions, for three-body systems supporting Efimov states, a nodal condition\nis introduced in order to obtain universal results from the Skorniakov\nTer-Martirosian equation and the Thomas collapse is avoided. Four-body bound\nstate eigenequations are derived and the 2D '3+1' bosonic ground state is\ncomputed as a function of the mass ratio.",
        "positive": "One-dimensional Repulsive Fermi Gas in a Tunable Periodic Potential: By using unbiased continuos-space quantum Monte Carlo simulations, we\ninvestigate the ground state properties of a one-dimensional repulsive Fermi\ngas subjected to a commensurate periodic optical lattice (OL) of arbitrary\nintensity. The equation of state and the magnetic structure factor are\ndetermined as a function of the interaction strength and of the OL intensity.\nIn the weak OL limit, Yang's theory for the energy of a homogeneous Fermi gas\nis recovered. In the opposite limit (deep OL), we analyze the convergence to\nthe Lieb-Wu theory for the Hubbard model, comparing two approaches to map the\ncontinuous-space to the discrete-lattice model: the first is based on\n(noninteracting) Wannier functions, the second effectively takes into account\nstrong-interaction effects within a parabolic approximation of the OL wells. We\nfind that strong antiferromagnetic correlations emerge in deep OLs, and also in\nvery shallow OLs if the interaction strength approaches the Tonks-Girardeau\nlimit. In deep OLs we find quantitative agreement with density matrix\nrenormalization group calculations for the Hubbard model. The spatial decay of\nthe antiferromagnetic correlations is consistent with quasi long-range order\neven in shallow OLs, in agreement with previous theories for the half-filled\nHubbard model."
    },
    {
        "anchor": "Ground state properties of hard-core anyons in a harmonic potential: Using anyon-fermion mapping method, we investigate the ground state\nproperties of hard-core anyons confined in a one-dimensional harmonic trap. The\nconcise analytical formula of the reduced one-body density matrix are obtained.\nBasing on the formula, we evaluated the momentum distribution, the natural\norbitals and their occupation distributions for different statistical\nparameters. The occupation and occupation fraction of the lowest natural\norbital versus anyon number are also displayed. It is shown that the ground\nstate properties of anyons interplay between Bosons and Fermions continuously.\nWe can expect that the hard-core anyons of larger statistical parameter exhibit\nthe similar properties to the hard-core Bosons although anyon system satisfy\nspecific fractional statistics.",
        "positive": "Bose-Einstein Condensates in Spin-Orbit Coupled Optical Lattices: Flat\n  Bands and Superfluidity: Recently spin-orbit (SO) coupled superfluids in free space or harmonic traps\nhave been extensively studied, motivated by the recent experimental realization\nof SO coupling for Bose-Einstein condensates (BEC). However, the rich physics\nof SO coupled BEC in optical lattices has been largely unexplored. In this\npaper, we show that in suitable parameter region the lowest Bloch state forms\nan isolated flat band in a one dimensional (1D) SO coupled optical lattice,\nwhich thus provides an experimentally feasible platform for exploring the\nrecently celebrated topological flat band physics in lattice systems. We show\nthat the flat band is preserved even with the mean field interaction in BEC. We\ninvestigate the superfluidity of the BEC in SO coupled lattices through\ndynamical and Landau stability analysis, and show that the BEC is stable on the\nwhole flat band."
    },
    {
        "anchor": "Quantum Phases from Competing Van der Waals and Dipole-Dipole\n  Interactions of Rydberg Atoms: Competing short- and long-range interactions represent distinguished\ningredients for the formation of complex quantum many-body phases. Their study\nis hard to realize with conventional quantum simulators. In this regard,\nRydberg atoms provide an exception as their excited manifold of states have\nboth density-density and exchange interactions whose strength and range can\nvary considerably. Focusing on one-dimensional systems, we leverage the van der\nWaals and dipole-dipole interactions of the Rydberg atoms to obtain the\nzero-temperature phase diagram for a uniform chain and a dimer model. For the\nuniform chain, we can influence the boundaries between ordered phases and a\nLuttinger liquid phase. For the dimerized case, a new type of\nbond-order-density-wave phase is identified. This demonstrates the versatility\nof the Rydberg platform in studying physics involving short- and long-ranged\ninteractions simultaneously.",
        "positive": "Exotic domain walls in Bose-Einstein condensates with double-well\n  dispersion: We study the domain walls which form when Bose condensates acquire a\ndouble-well dispersion. Experiments have observed such domain walls in\ncondensates driven across a $\\mathbb{Z}_2$ symmetry-breaking phase transition\nin a shaken optical lattice. We derive a generic model to describe the\ndispersion and to compute the wavefunctions and energies of the domain walls.\nWe find two distinct regimes which demand different physical pictures. In the\nweak coupling regime, where interactions are weak compared to the kinetic\nenergy barrier, \"density wave domain walls\" form that support an extended\ndensity wave and a series of phase steps. These features can be understood as\nthe quantum interference between domains with distinct momenta. In the strong\ncoupling regime where interaction dominates, the system forms \"phase domain\nwalls\" which have the minimum width allowed by the uncertainty principle and\nsuppressed density modulation. Analytic results for the domain wall\nwavefunctions are obtained in the two regimes. The energy of domain walls\nbehaves similarly to that of topological defects in paradigmatic field\ntheories."
    },
    {
        "anchor": "Fractional Quantum Hall States of Dipolar Gases in Chern Bands: We study fermions and hardcore bosons with long range dipolar interactions at\nfractional fillings in a topological checkerboard lattice with short-range\nhoppings up to next-next-nearest neighbors \\cite{Neupert2011}. We consider the\ncase that the dipoles are aligned in the perpendicular direction by an external\nfield without the complication of anisotropic interaction. Using exact\ndiagonalization, we find clear signatures of fractional quantum Hall (FQH)\nstates at filling factors 1/3 and 1/5 for fermions (1/2 and 1/4 for bosons) in\nthe lowest Chern band with a robust spectrum gap at moderate dipolar\ninteraction strength. The robustness of these FQH states against long-range\ninteraction tail and band flatness is investigated. When the dipolar\ninteraction decreases, the fermionic FQH states turn into normal states, and\nthe bosonic 1/4-FQH state turns into a superfluid state. The bosonic 1/2-FQH\nstate survives even in the absence of the dipolar interaction, but vanishes\nwhen the hard core becomes a soft core with a critical onsite repulsion. In the\nthin torus limit, the static density structure factors indicates that the FQH\nstate turns into a commensurate charge density wave (CDW) state.",
        "positive": "Single-particle and many-body analyses of a quasiperiodic integrable\n  system after a quench: In general, isolated integrable quantum systems have been found to relax to\nan apparent equilibrium state in which the expectation values of few-body\nobservables are described by the generalized Gibbs ensemble. However, recent\nwork has shown that relaxation to such a generalized statistical ensemble can\nbe precluded by localization in a quasiperiodic lattice system. Here we\nundertake complementary single-particle and many-body analyses of\nnoninteracting spinless fermions and hard-core bosons within the Aubry-Andre\nmodel to gain insight into this phenomenon. Our investigations span both the\nlocalized and delocalized regimes of the quasiperiodic system, as well as the\ncritical point separating the two. Considering first the case of spinless\nfermions, we study the dynamics of the momentum distribution function and\ncharacterize the effects of real-space and momentum-space localization on the\nrelevant single-particle wave functions and correlation functions. We show that\nalthough some observables do not relax in the delocalized and localized\nregimes, the observables that do relax in these regimes do so in a manner\nconsistent with a recently proposed Gaussian equilibration scenario, whereas\nrelaxation at the critical point has a more exotic character. We also construct\nvarious statistical ensembles from the many-body eigenstates of the fermionic\nand bosonic Hamiltonians and study the effect of localization on their\nproperties."
    },
    {
        "anchor": "Counterflow in a doubly superfluid mixture of Bosons and Fermions: In this article, we calculate the friction between two counter-flowing\nbosonic and fermionic super-fluids. In the limit where the boson-boson and\nboson-fermion interactions can be treated within the mean-field approximation,\nwe show that the force can be related to the dynamical structure factor of the\nfermionic component. Finally, we provide asymptotic expressions for weakly and\nstrongly attractive fermions and show that the damping rate obeys simple\nscaling laws close to the critical velocity.",
        "positive": "Phases and phase transitions of Bose condensed light: Bose-Einstein condensation of light in 2D is characterized by two classical\nfields corresponding to two polarizations of light as well as by the\ndistribution of dye molecules inducing light thermalization through dipolar\ntransition. In the case when this transition is triple-degenerate the resulting\nfield theory for the condensate of light is O(4) symmetric, which precludes\nalgebraic long range order in 2D at any finite temperature $T$. If the dipolar\ndegeneracy is removed, then, equilibrium phases with lower symmetries --\nO(2)$\\times$Z$_2$ and O(2) can emerge. Accordingly, algebraic off diagonal\norder of light condensate becomes possible. An orientationsl disorder\nintroduced by local dipolar anisotropy can destroy algebraic order in\none-photon density matrix while preserving it in the two-photon one. This\nrepresents formation of the condensate of photon pairs."
    },
    {
        "anchor": "Density dependent tunneling in the extended Bose-Hubbard model: Recently, it has become apparent that, when the interactions between polar\nmolecules in optical lattices becomes strong, the conventional description\nusing the extended Hubbard model has to be modified by additional terms, in\nparticular a density-dependent tunneling term. We investigate here the\ninfluence of this term on the ground-state phase diagrams of the two\ndimensional extended Bose-Hubbard model. Using Quantum Monte Carlo simulations,\nwe investigate the changes of the superfluid, supersolid, and phase-separated\nparameter regions in the phase diagram of the system. By studying the interplay\nof the density-dependent hopping with the usual on-site interaction U and\nnearest-neighbor repulsion V, we show that the ground-state phase diagrams\ndiffer significantly from the ones that are expected from the standard extended\nBose-Hubbard model. However we find no indication of pair-superfluid behavior\nin this two dimensional square lattice study in contrast to the one-dimensional\ncase.",
        "positive": "Virial Expansion for a Three-Component Fermi Gas in One Dimension: The\n  Quantum Anomaly Correspondence: In this paper we explore the transport properties of three-component Fermi\ngases confined to one spatial dimension, interacting via a three-body\ninteraction, in the high temperature limit. At the classical level, the\nthree-body interaction is scale invariant in one dimension. However, upon\nquantization, an anomaly appears which breaks the scale invariance. This is\nvery similar to the physics of two-component fermions in two spatial\ndimensions, where the two-body interaction is also anomalous. Previous studies\nhave already hinted that the physics of these two systems are intimately\nrelated. Here we expand upon those studies by examining the thermodynamic\nproperties of this anomalous one dimensional system in the high temperature\nlimit. We show there is an exact mapping between the traditional two-body\nanomalous interaction in two dimensions, to that of three-body interaction in\none dimension. This result is valid in the high temperature limit, where the\nthermodynamics can be understood in terms of few-body correlations."
    },
    {
        "anchor": "Numerical Computation of Dynamically Important Excited States of\n  Many-Body Systems: We present an extension of the time-dependent Density Matrix Renormalization\nGroup (t-DMRG), also known as Time Evolving Block Decimation algorithm (TEBD),\nallowing for the computation of dynamically important excited states of\none-dimensional many-body systems. We show its practical use for analyzing the\ndynamical properties and excitations of the Bose-Hubbard model describing\nultracold atoms loaded in an optical lattice from a Bose-Einstein condensate.\nThis allows for a deeper understanding of nonadiabaticity in experimental\nrealizations of insulating phases.",
        "positive": "Out-of-Equilibrium Dynamics in the Two-Component Bose-Hubbard Model: We study the out-of-equilibrium dynamics of the Bose-Hubbard model for\ntwo-component bosons using a strong-coupling approach within the\nclosed-time-path formalism and develop an effective theory for the action of\nthis problem. We obtain equations of motion for the superfluid order parameters\nof both boson species for both the superfluid and Mott-insulating phases and\nstudy these in the low-frequency, long-wavelength limit during a quantum quench\nfor various initial conditions. We find that an additional degree of freedom\nfor bosons leads to a richer phase diagram and out-of-equilibrium dynamics than\nthe single-component situation."
    },
    {
        "anchor": "Composite boson signature in the interference pattern of atomic dimer\n  condensates: We predict the existence of high frequency modes in the interference pattern\nof two condensates made of fermionic-atom dimers. These modes, which result\nfrom fermion exchanges between condensates, constitute a striking signature of\nthe dimer composite nature. From the 2-coboson spatial correlation function,\nthat we derive analytically, and the Shiva diagrams that visualize many-body\neffects specific to composite bosons, we identify the physical origin of these\nhigh frequency modes and determine the conditions to see them experimentally by\nusing bound fermionic-atom pairs trapped on optical lattice sites. The dimer\ngranularity which appears in these modes comes from Pauli blocking that\nprevents two dimers to be located at the same lattice site.",
        "positive": "Induced interaction and crystallization of self-localized impurity\n  fields in a Bose-Einstein condensate: We model the behavior of N classical impurity fields immersed in a larger\nBose-Einstein condensate by N+1 coupled nonlinear Schrodinger equations in 1,\n2, and 3 space dimensions. We discuss the stability of the uniform miscible\nsystem and show the importance of surface tension for self localization of the\nimpurity fields. We derive analytically the attractive tail of\nimpurity-impurity interaction due to mediation by the underlying condensate.\nAssuming all impurity fields interact with the same strength, we explore the\nresulting phase diagram, which contains four phases: {\\it I}) all fields are\nmiscible; {\\it II}) the impurity fields are miscible with each other but phase\nseparate from the condensate as a single bubble; {\\it III}) the localized\nimpurity fields stay miscible with the condensate, but not with each other; and\n{\\it IV}) the impurity fields phase separate from the condensate and each\nother, forming a crystalline structure within a bubble. Thus, we show that a\ncrystal can be constructed solely from superfluid components. Finally, we argue\nthat the crystalline phases maintain their superfluid behavior, i.e. they\npossess a nonclassical rotational inertia, which, combined with lattice order,\nis a characteristic of supersolidity."
    },
    {
        "anchor": "Bose-Einstein condensation of alkaline earth atoms: $^{40}${Ca}: We have achieved Bose-Einstein condensation of $^{40}$Ca, the first for an\nalkaline earth element. The influence of elastic and inelastic collisions\nassociated with the large ground state s-wave scattering length of $^{40}$Ca\nwas measured. From these findings, an optimized loading and cooling scheme was\ndeveloped that allowed us to condense about $2 \\cdot 10^4$ atoms after laser\ncooling in a two-stage magneto-optical trap and subsequent forced evaporation\nin a crossed dipole trap within less than 3 s. The condensation of an alkaline\nearth element opens novel opportunities for precision measurements on the\nnarrow intercombination lines as well as investigations of molecular states at\nthe $^1$S--$^3$P asymptotes.",
        "positive": "Vortex-lattice structures in rotating Bose-Fermi superfluid mixtures: The system of Bose-Fermi superfluid mixture offers a playground to explore\nrich macroscopic quantum phenomena. In a recent experiment of Yao {\\it et al.}\n[Phys. Rev. Lett. {\\bf 117}, 145301 (2016)], $^{41}$K-$^{6}$Li superfluid\nmixture is implemented. Coupled quantized vortices are generated via rotating\nthe superfluid mixture, and a few unconventional behaviors on the formations of\nvortex numbers are observed, which can be traced to boson-fermion interactions.\nHere we provide a theoretical insight into the unconventional behaviors\nobserved in the experiment. To this end, the orbital-free density functional\ntheory is hired, and its utility is validated by making comparison of the\nnumerical results and a microscopic theory for vortex lattices in strongly\ninteracting Fermi superfluids alone. We also predict interesting phenomena\nwhich can be readily explored experimentally, including the novel structures of\nbosonic-fermionic vortices, and attractive interactions between the bosonic and\nfermionic vortices."
    },
    {
        "anchor": "Information theoretic measures on quantum droplets in ultracold atomic\n  systems: We consider Shannon entropy, Fisher information, R\\'enyi entropy, and Tsallis\nentropy to study the transition from localized phase to droplet phase in\nBose-Einstein condensates. Based on an effective Gross-Pitaevskii equation with\nLee-Huang-Yang correction, we calculate density distributions both in localized\nand the droplet phases and show that the entropy measures can efficiently\ndetect the transition from localized to droplet phase. We find that the Shannon\nentropies in coordinate space increase both in localized and droplet phases.\nThe increase of entropy in droplet phase is abrupt while it is gradual in\nlocalized phase. We observe an opposite trend in the case of Fisher\ninformation. These results are found to be consistent with the R\\'enyi and\nTsallis entropic measures.",
        "positive": "Minimal scattering entanglement in one-dimensional trapped gases: The prospect of controlling entanglement in interacting quantum systems\noffers a myriad of technological and scientific promises, given the progress in\nexperimental studies in systems such as ultracold trapped gases. This control\nis often challenging because of decoherence, the process by which environmental\ninteractions create spurious entanglements that can destroy the desired\nentanglement. Considering the collisional decoherence that is relevant for\nquantum measurements utilizing scattering in one-dimensional trapped gases,\nhere we derive a relationship between particle masses and wave packet widths\nthat minimizes the entanglement created during scattering. We assess the\nrelevance of our results by directly observing this relationship in the\nemergent scales of a master equation for a particle undergoing nonthermal\nscattering. Our relationship is independent of the details of the particle\ninteractions and sheds light on how to design scattering processes that\nminimize decoherence."
    },
    {
        "anchor": "Increasing Quantum Degeneracy by Heating a Superfluid: We consider a uniform superfluid confined in two compartments connected by a\nsuperleak and initially held at equal temperatures. If one of the two\ncompartments is heated, a fraction of the superfluid will flow through the\nsuperleak. We show that, under certain thermodynamic conditions, the atoms flow\nfrom the hotter to the colder compartment, contrary to what happens in the\nfountain effect observed in superfluid Helium. This flow causes quantum\ndegeneracy to increase in the colder compartment. In superfluid Helium, this\nnovel thermomechanical effect takes place in the phonon regime of very low\ntemperatures. In dilute quantum gases, it occurs at all temperatures below Tc .\nThe increase in quantum degeneracy reachable through the adiabatic displacement\nof the wall separating the two compartments is also discussed.",
        "positive": "Topological chiral currents in the Gross-Neveu model extension: We unveil an interesting connection of Lorentz-violating quantum field\ntheories, studied in the context of the standard model extension, and\nHubbard-type models of topological crystalline phases. These models can be\ninterpreted as a regularisation of the former and, as hereby discussed,\nexplored with current quantum simulators based on ultra-cold atoms in optical\nRaman lattices. In particular, we present a complete analysis of the\nCreutz-Hubbard ladder under a generic magnetic flux, which regularises a\nGross-Neveu model extension, and presents a characteristic circulating chiral\ncurrent whose non-zero value arises from a specific violation of Lorentz\ninvariance. We present a complete phase diagram with trivial insulators,\nferromagnetic and anti-ferromagnetic phases, and current-carrying topological\ncrystalline phases. These predictions are benchmarked using tools from\ncondensed matter and quantum-information science, showing that self-consistent\nHartree-Fock and strong-coupling Dzyaloshinskii-Moriya methods capture the\nessence of the phase diagram in different regimes, which is further explored\nusing extensive numerical simulations based on matrix-product states."
    },
    {
        "anchor": "Nonequilibrium thermodynamics and optimal cooling of a dilute atomic gas: Characterizing and optimizing thermodynamic processes far from equilibrium is\na challenge. This is especially true for nanoscopic systems made of few\nparticles. We here theoretically and experimentally investigate the\nnonequilibrium dynamics of a gas of few noninteracting Cesium atoms confined in\na nonharmonic optical dipole trap and exposed to degenerate Raman sideband\ncooling pulses. We determine the axial phase-space distribution of the atoms\nafter each Raman cooling pulse by tracing the evolution of the gas with\nposition-resolved fluorescence imaging. We evaluate from it the entropy\nproduction and the statistical length between each cooling steps. A single\nRaman pulse leads to a nonequilibrium state that does not thermalize on its\nown, due to the absence of interparticle collisions. Thermalization may be\nachieved by combining free phase-space evolution and trains of cooling pulses.\nWe minimize the entropy production to a target thermal state to specify the\noptimal spacing between a sequence of equally spaced pulses and achieve in this\nway optimal thermalization. We finally use the statistical length to verify a\nrefined version of the second law of thermodynamics. Altogether, these findings\nprovide a general, theoretical and experimental, framework to analyze and\noptimize far-from-equilibrium processes of few-particle systems.",
        "positive": "Decay of symmetry-protected quantum states: We study the decay of bosonic many-body states in the three well Bose-Hubbard\nchain where bosons in the central well can escape into a reservoir. For\nvanishing inter-particle interaction this system supports a non-decaying\nmany-body state which is the antisymmetric Bose-Einstein condensate with\nparticles occupying only the edge wells. In the classical approach this quantum\nstate corresponds to a symmetry protected non-decaying state which is stable\neven at finite interaction below a certain intensity threshold. Here we\ndemonstrate that despite the classical counterpart is stable the antisymmetric\nBose-Einstein condensate is always metastable at finite interatomic\ninteractions due to quantum fluctuations."
    },
    {
        "anchor": "Topological Floquet engineering of a 1D optical lattice via resonantly\n  shaking with two harmonic frequencies: We investigate the topological properties of a resonantly shaken\none-dimensional optical lattice system, where the lattice position is\nperiodically driven with two harmonic frequencies to generate one- and\ntwo-photon couplings between the two lowest orbitals. In a two-band\napproximation, we numerically show that degenerate edge states appear under a\ncertain driving condition and that the corresponding topological phase is\nprotected by the chiral symmetry of the periodically driven system. The\nsystem's micromotion is characterized with oscillating Zak phases and we find\nthat the Zak phases are quantized only at the time when the chiral symmetry\ncondition is explicitly satisfied. Finally, we describe the topological charge\npumping effect which arises when the driving parameters are slowly modulated\naround a critical point, and investigate its adiabaticity for increasing the\nmodulation frequency.",
        "positive": "The A-Cycle Problem for Transverse Ising Ring: Traditionally, the transverse Ising model is mapped to the fermionic c-cycle\nproblem, which neglects the boundary effect due to thermodynamic limit. If\npersisting on a perfect periodic boundary condition, we can get a so-called\na-cycle problem that has not been treated seriously so far (Lieb et al., 1961\n\\textit{Ann. of Phys.} \\textbf{16} 407). In this work, we show a little\nsurprising but exact result in this respect. We find the odevity of the number\nof lattice sites, $N$, in the a-cycle problem plays an unexpected role even in\nthe thermodynamic limit, $N\\rightarrow\\infty$, due to the boundary constraint.\nWe pay a special attention to the system with $N(\\in Odd)\\rightarrow\\infty$,\nwhich is in contrast to the one with $N(\\in Even)\\rightarrow\\infty$, because\nthe former suffers a ring frustration. As a new effect, we find the ring\nfrustration induces a low-energy gapless spectrum above the ground state. By\nproving a theorem for a new type of Toeplitz determinant, we demonstrate that\nthe ground state in the gapless region exhibits a peculiar longitudinal\nspin-spin correlation. The entangled nature of the ground state is also\ndisclosed by the evaluation of its entanglement entropy. At low temperatures,\nnew behavior of specific heat is predicted. We also propose an experimental\nprotocol for observing the new phenomenon due to the ring frustration."
    },
    {
        "anchor": "Vortices in quantum droplets: Analogies between boson and fermion\n  systems: The main theme of this review is the many-body physics of vortices in quantum\ndroplets of bosons or fermions, in the limit of small particle numbers. Systems\nof interest include cold atoms in traps as well as electrons confined in\nquantum dots. When set to rotate, these in principle very different quantum\nsystems show remarkable analogies. The topics reviewed include the structure of\nthe finite rotating many-body state, universality of vortex formation and\nlocalization of vortices in both bosonic and fermionic systems, and the\nemergence of particle-vortex composites in the quantum Hall regime. An overview\nof the computational many-body techniques sets focus on the configuration\ninteraction and density-functional methods. Studies of quantum droplets with\none or several particle components, where vortices as well as coreless vortices\nmay occur, are reviewed, and theoretical as well as experimental challenges are\ndiscussed.",
        "positive": "Quantum localization and bound state formation in Bose-Einstein\n  condensates: We discuss the possibility of exponential quantum localization in systems of\nultracold bosonic atoms with repulsive interactions in open optical lattices\nwithout disorder. We show that exponential localization occurs in the maximally\nexcited state of the lowest energy band. We establish the conditions under\nwhich the presence of the upper energy bands can be neglected, determine the\nsuccessive stages and the quantum phase boundaries at which localization\noccurs, and discuss schemes to detect it experimentally by visibility\nmeasurements. The discussed mechanism is a particular type of quantum\nlocalization that is intuitively understood in terms of the interplay between\nnonlinearity and a bounded energy spectrum."
    },
    {
        "anchor": "Parametric instabilities of interacting bosons in periodically-driven 1D\n  optical lattices: Periodically-driven quantum systems are currently explored in view of\nrealizing novel many-body phases of matter. This approach is particularly\npromising in gases of ultracold atoms, where sophisticated shaking protocols\ncan be realized and inter-particle interactions are well controlled. The\ncombination of interactions and time-periodic driving, however, often leads to\nuncontrollable heating and instabilities, potentially preventing practical\napplications of Floquet-engineering in large many-body quantum systems. In this\nwork, we experimentally identify the existence of parametric instabilities in\nweakly-interacting Bose-Einstein condensates in strongly-driven optical\nlattices through momentum-resolved measurements. Parametric instabilities can\ntrigger the destruction of weakly-interacting Bose-Einstein condensates through\nthe rapid growth of collective excitations, in particular in systems with weak\nharmonic confinement transverse to the lattice axis.",
        "positive": "Angle-resolved photoemission spectroscopy with quantum gas microscopes: Quantum gas microscopes are a promising tool to study interacting quantum\nmany-body systems and bridge the gap between theoretical models and real\nmaterials. So far they were limited to measurements of instantaneous\ncorrelation functions of the form $\\langle \\hat{O}(t) \\rangle$, even though\nextensions to frequency-resolved response functions $\\langle \\hat{O}(t)\n\\hat{O}(0) \\rangle$ would provide important information about the elementary\nexcitations in a many-body system. For example, single particle spectral\nfunctions, which are usually measured using photoemission experiments in\nelectron systems, contain direct information about fractionalization and the\nquasiparticle excitation spectrum. Here, we propose a measurement scheme to\nexperimentally access the momentum and energy resolved spectral function in a\nquantum gas microscope with currently available techniques. As an example for\npossible applications, we numerically calculate the spectrum of a single hole\nexcitation in one-dimensional $t-J$ models with isotropic and anisotropic\nantiferromagnetic couplings. A sharp asymmetry in the distribution of spectral\nweight appears when a hole is created in an isotropic Heisenberg spin chain.\nThis effect slowly vanishes for anisotropic spin interactions and disappears\ncompletely in the case of pure Ising interactions. The asymmetry strongly\ndepends on the total magnetization of the spin chain, which can be tuned in\nexperiments with quantum gas microscopes. An intuitive picture for the observed\nbehavior is provided by a slave-fermion mean field theory. The key properties\nof the spectra are visible at currently accessible temperatures."
    },
    {
        "anchor": "Reference data for phase diagrams of triangular and hexagonal bosonic\n  lattices: We investigate systems of bosonic particles at zero temperature in triangular\nand hexagonal optical lattice potentials in the framework of the Bose-Hubbard\nmodel. Employing the process-chain approach, we obtain accurate values for the\nboundaries between the Mott insulating phase and the superfluid phase. These\nresults can serve as reference data for both other approximation schemes and\nupcoming experiments. Since arbitrary integer filling factors g are amenable to\nour technique, we are able to monitor the behavior of the critical hopping\nparameters with increasing filling. We also demonstrate that the g-dependence\nof these exact parameters is described almost perfectly by a scaling relation\ninferred from the mean-field approximation.",
        "positive": "Ramsey imaging of optical traps: Mapping the potential landscape with high spatial resolution is crucial for\nquantum technologies based on ultracold atoms. Yet, imaging optical dipole\ntraps is challenging because purely optical methods, commonly used to profile\nlaser beams in free space, are not applicable in vacuum. In this work, we\ndemonstrate precise in-situ imaging of optical dipole traps by probing a\nhyperfine transition with Ramsey interferometry. Thereby, we obtain an absolute\nmap of the potential landscape with micrometer resolution and\nshot-noise-limited spectral precision. The idea of the technique is to control\nthe polarization ellipticity of the trap laser beam to induce a differential\nlight shift proportional to the trap potential. By studying the response to\npolarization ellipticity, we uncover a small but significant nonlinearity in\naddition to a dominant linear behavior, which is explained by the geometric\ndistribution of the atomic ensemble. Our technique for imaging of optical traps\ncan find wide application in quantum technologies based on ultracold atoms, as\nit applies to multiple atomic species and is not limited to a particular\nwavelength or trap geometry."
    },
    {
        "anchor": "Mixture of Tonks-Girardeau gas and Fermi gas in one-dimensional optical\n  lattices: We study the Bose-Fermi mixture with infinitely boson-boson repulsion and\nfinite boson-Fermion repulsion. By using a generalized Jordan-Wigner\ntransformation, we show that the system can be mapped to a repulsive Hubbard\nmodel and thus can be solved exactly for the case with equal boson and fermion\nmasses. By using the Bethe-ansatz solutions, we investigate the ground state\nproperties of the mixture system. Our results indicate that the system with\ncommensurate filling $n=1$ is a charge insulator but still a superfluid with\nnon-vanishing superfluid density. We also briefly discuss the case with unequal\nmasses for bosons and fermions.",
        "positive": "Quantum unbinding near a zero temperature liquid-gas transition: We discuss the quantum phase transition from a liquid to a gaseous ground\nstate in a Bose fluid with increasing strength of the zero point motion. It is\nshown that in the zero pressure limit, the two different ground states are\nseparated by a quantum tricritical point whose position is determined by a\nvanishing two-body scattering length. In the presence of a finite three-body\nscattering amplitude, the superfluid gas at this point exhibits sound modes\nwhose velocity scales linearly with density while the compressibility diverges\n$\\sim p^{-1/3}$ in the limit of vanishing pressure $p$. In the liquid regime of\nnegative scattering lengths, it is shown that $N$-body bound states exist up to\narbitrary $N$, consistent with a theorem by Seiringer. The asymptotic scaling\n$a_{-}(N)\\sim N^{-1/2}$ of the scattering lengths where they appear from the\ncontinuum is determined from a finite size scaling analysis in the vicinity of\nthe quantum tricritical point. This also provides a qualitative understanding\nof numerical results for the quantum unbinding of small clusters."
    },
    {
        "anchor": "Thermodynamics and coherence of a trapped dipolar Fermi gas: We develop a meanfield treatment of a polarized trapped Fermi gas with\ndipole-dipole interactions. Our approach is based on self-consistent\nsemiclassical Hartree-Fock theory that accounts for direct and exchange\ninteractions. We discuss our procedure for numerically implementing the\ncalculation. We study the thermodynamic and the first and second order\ncorrelation properties of the system. We find that the system entropy depends\non the trap geometry, allowing the system to be cooled as the trap aspect ratio\nis increased, and that exchange interactions cause the correlation functions to\nbe anisotropic in the low temperature regime. We also find that many uniform\ngas thermodynamic predictions, for which direct interaction effects vanish, are\nqualitatively unreliable for trapped systems, most notably for oblate traps. We\ndevelop a simplified Hartree formalism that is applicable to anisotropic\nharmonic traps.",
        "positive": "Analogue Hawking radiation in an exactly solvable model of BEC: Hawking radiation, the spontaneous emission of thermal photons from an event\nhorizon, is one of the most intriguing and elusive predictions of field theory\nin curved spacetimes. A formally analogue phenomenon occurs at the supersonic\ntransition of a fluid: in this respect, ultracold gases stand out among the\nmost promising systems but the theoretical modelling of this effect has always\nbeen carried out in semiclassical approximation, borrowing part of the analysis\nfrom the gravitational analogy. Here we discuss the exact solution of a\none-dimensional Bose gas flowing against an obstacle, showing that spontaneous\nphonon emission (the analogue of Hawking radiation) is predicted without\nreference to the gravitational analogy. Long after the creation of the\nobstacle, the fluid settles into a stationary state displaying the emission of\nsound waves (phonons) in the upstream direction. A careful analysis shows that\na precise correspondence between this phenomenon and the spontaneous emission\nof radiation from an event horizon requires additional conditions to be met in\nfuture experiments aimed at identifying the occurrence of the Hawking-like\nmechanism in Bose-Einstein condensates."
    },
    {
        "anchor": "Experimental observation of Josephson oscillations in a room-temperature\n  Bose-Einstein magnon condensate: The alternating current (ac) Josephson effect in a time-independent\nspatially-inhomogeneous setting is manifested by the occurrence of Josephson\noscillations - periodic macroscopic phase-induced collective motions of the\nquantum condensate. So far, this phenomenon was observed at cryogenic\ntemperatures in superconductors, in superfluid helium, and in Bose-Einstein\ncondensates (BECs) of trapped atoms. Here, we report on the discovery of the ac\nJosephson effect in a magnon BEC carried by a room-temperature ferrimagnetic\nfilm. The BEC is formed in a parametrically populated magnon gas in the spatial\nvicinity of a magnetic trench created by a dc electric current. The appearance\nof the Josephson effect is manifested by oscillations of the magnon BEC density\nin the trench, caused by a coherent phase shift between this BEC and the BEC in\nthe nearby regions. Our findings advance the physics of room-temperature\nmacroscopic quantum phenomena and will allow for their application for data\nprocessing in magnon spintronics devices.",
        "positive": "Non-classical Rotational Inertia in a Two-dimensional Bosonic Solid\n  Containing Grain Boundaries: We study the occurrence of non-classical rotational inertia (NCRI) arising\nfrom superfluidity along grain boundaries in a two-dimensional bosonic system.\nWe make use of a standard mapping between the zero-temperature properties of\nthis system and the statistical mechanics of interacting vortex lines in the\nmixed phase of a type-II superconductor. In the mapping, the liquid phase of\nthe vortex system corresponds to the superfluid bosonic phase. We consider\nnumerically obtained polycrystalline configurations of the vortex lines in\nwhich the microcrystals are separated by liquid-like grain boundary regions\nwhich widen as the vortex system temperature increases. The NCRI of the\ncorresponding zero-temperature bosonic systems can then be numerically\nevaluated by solving the equations of superfluid hydrodynamics in the channels\nnear the grain boundaries. We find that the NCRI increases very abruptly as the\nliquid regions in the vortex system (equivalently, superfluid regions in the\nbosonic system) form a connected, system-spannig structure with one or more\nclosed loops. The implications of these results for experimentally observed\nsupersolid phenomena are discussed."
    },
    {
        "anchor": "Hubbard parameters for programmable tweezer arrays: The experimental realization of Fermi-Hubbard tweezer arrays opens a new\nstage for engineering fermionic matter, where programmable lattice geometries\nand Hubbard model parameters are combined with single-site imaging. In order to\nuse these versatile experimental Fermi-Hubbard models as quantum simulators, it\nis crucial to know the Hubbard parameters describing them. Here we develop\nmethods to calculate the Hubbard model parameters of arbitrary two-dimensional\nlattice geometries: the tunneling $t$, on-site potential $V$, and interaction\n$U$, for multiple bands and for both fermions and bosons. We show several\nexamples. One notable finding is that a finite array of equally strong and\nseparated individual tweezer potentials actually sums to give a non-periodic\ntotal potential and thus spatially non-uniform Hubbard parameters. We\ndemonstrate procedures to find trap configurations that equalize these\nparameters. More generally, these procedures solve the inverse problem of\ncalculating Hubbard parameters: given desired Hubbard parameters, find trap\nconfigurations to realize them. These methods will be critical tools for using\ntunnel-coupled tweezer arrays.",
        "positive": "Damping in two component Bose gas: We investigate the Landau and Baliaev damping of the collective modes in a\ntwo-component Bose gas using the mean-field approximation. We show that due to\nthe two body atom-atom interaction, oscillations of each component is coupled\nto the thermal excitations of the other component which gives rise to creation\nor destruction of the elementary excitations that can take place in the two\nseparate components.In addition we find that the damping is also enhanced due\nto inter-component coupling."
    },
    {
        "anchor": "Itinerant ferromagnetism entrenched by the anisotropy of spin-orbit\n  coupling in a dipolar Fermi gas: We investigate the the itinerant ferromagnetism in a dipolar Fermi atomic\nsystem with the anisotropic spin-orbit coupling (SOC),which is traditionally\nexplored with isotropic contact interaction.We first study the ferromagnetism\ntransition boundaries and the properties of the ground states through the\ndensity and spin-flip distribution in momentum space, and we find that both the\nanisotropy and the magnitude of the SOC play an important role in this process.\nWe propose a helpful scheme and a quantum control method which can be applied\nto conquering the difficulties of previous experimental observation of\nitinerant ferromagnetism. Our further study reveals that exotic Fermi surfaces\nand an abnormal phase region can exist in this system by controlling the\nanisotropy of SOC, which can provide constructive suggestions for the research\nand the application of a dipolar Fermi gas. Furthermore, we also calculate the\nferromagnetism transition temperature and novel distributions in momentum space\nat finite temperature beyond the ground states from the perspective of\nexperiment.",
        "positive": "Variance as a sensitive probe of correlations enduring the infinite\n  particle limit: Bose-Einstein condensates made of ultracold trapped bosonic atoms have become\na central venue in which interacting many-body quantum systems are studied. The\nground state of a trapped Bose-Einstein condensate has been proven to be 100%\ncondensed in the limit of infinite particle number and constant interaction\nparameter [Lieb and Seiringer, Phys. Rev. Lett. {\\bf 88}, 170409 (2002)]. The\nmeaning of this result is that properties of the condensate, noticeably its\nenergy and density, converge to those obtained by minimizing the\nGross-Pitaevskii energy functional. This naturally raises the question whether\ncorrelations are of any importance in this limit. Here, we demonstrate both\nanalytically and numerically that even in the infinite particle limit many-body\ncorrelations can lead to a substantial modification of the \\textit{variance} of\nany operator compared to that expected from the Gross-Pitaevskii result. The\nstrong deviation of the variance stems from its explicit dependence on terms of\nthe reduced two-body density matrix which otherwise do not contribute to the\nenergy and density in this limit. This makes the variance a sensitive probe of\nmany-body correlations even when the energy and density of the system have\nalready converged to the Gross-Pitaevskii result. We use the center-of-mass\nposition operator to exemplify this persistence of correlations. Implications\nof this many-body effect are discussed."
    },
    {
        "anchor": "Superfluid phases of ultracold Fermi gases on a checkerboard\n  superlattice: We analyze the ground-state phase diagram of two-component Fermi gases loaded\ninto a two-dimensional checkerboard superlattice, i.e. a double-well optical\nlattice, potential within the BCS mean-field theory. We show that, by coupling\nthe two s-wave sublattice superfluid order parameters, a checkerboard potential\ngives rise to a Hamiltonian that has the form of a two-band superfluidity with\nthree (two intraband and an interband) nonlocal order parameters. We study the\nevolution of these order parameters as a function of particle filling,\ninteraction strength and checkerboard potential, and find that the system\nalways prefers the 0-phase solutions, i.e. the phase difference between\nsublattice order parameters is 0, but never the $\\pi$-phase one. In addition,\nwe find that the ground-state of the system undergo a superfluid-normal quantum\nphase transition at half fillings beyond a critical checkerboard potential $C$,\nthe threshold of which is precisely determined by the magnitude of the order\nparameter at $C = 0$, and that the normal state rapidly turns into a\ncheckerboard insulator as $C$ increases.",
        "positive": "Mean-field phase diagram of the Bose-Fermi Hubbard model: We analyze the ground state properties of Bose-Fermi mixtures using a\nmean-field treatment of the boson-fermion interaction on a simple cubic\nlattice. In the deep superfluid limit of the bosonic sector and the BCS regime\nof the fermion sector, we derive BCS-type equations to determine the phase\ndiagram of the system. We find a competition between a charge density wave and\na superconducting phase. In the opposite limit, we study the Mott insulator to\nsuperfluid transition of the bosonic sector in the presence of a staggered\ndensity-induced alternating potential provided by the fermions, and determine\nthe mean-field transition line. In the two-superfluid phase of the mixture we\nrestrict to nearest-neighbor induced interactions between the fermions and\nconsider the extended Hubbard model. We perform a mean-field analysis of the\ncritical temperature for the formation of boson-assisted $s$-, extended $s^-$-,\n$d$-, and $p$-wave pairs at fermionic half filling. We compare our results with\na recent dynamical mean-field study [Anders \\emph{et al.} Phys. Rev. Lett. {\\bf\n109}, 206401]."
    },
    {
        "anchor": "Revisiting the Vashishta-Singwi dielectric scheme for the warm dense\n  uniform electron fluid: The finite temperature version of the Vashishta-Singwi (VS) dielectric scheme\nfor the paramagnetic warm dense uniform electron fluid is revisited correcting\nfor an earlier thermodynamic derivative error. The VS scheme handles quantum\nmechanical effects at the level of the random phase approximation and treats\ncorrelations via the density expansion of a generalized\nSingwi-Tosi-Land-Sj\\\"olander (STLS) closure that inserts a parameter determined\nby enforcing the compressibility sum rule. Systematic comparison with\nquasi-exact results, based on quantum Monte Carlo simulations, reveals a\nstructural superiority of the VS scheme towards strong coupling and a\nthermodynamic superiority of the STLS scheme courtesy of a favorable\ncancellation of errors. Guidelines are provided for the construction of\ndielectric schemes that are expected to be more accurate but computationally\ncostly.",
        "positive": "Dynamical Generation of Topological Magnetic Lattices for Ultracold\n  Atoms: We propose a scheme to dynamically synthesize a space-periodic effective\nmagnetic field for neutral atoms by time-periodic magnetic field pulses. When\natomic spin adiabatically follows the direction of the effective magnetic\nfield, an adiabatic scalar potential together with a geometric vector potential\nemerges for the atomic center-of-mass motion, due to the Berry phase effect.\nWhile atoms hop between honeycomb lattice sites formed by the minima of the\nadiabatic potential, complex Peierls phase factors in the hopping coefficients\nare induced by the vector potential, which facilitate a topological Chern\ninsulator. With further tuning of external parameters, both a topological phase\ntransition and topological flat bands can be achieved, highlighting realistic\nprospects for studying strongly correlated phenomena in this system. Our Letter\npresents an alternative pathway towards creating and manipulating topological\nstates of ultracold atoms by magnetic fields."
    },
    {
        "anchor": "Viscosity Sum Rules at Large Scattering Lengths: We use the operator product expansion (OPE) and dispersion relations to\nobtain new model-independent \"Borel-resummed\" sum rules for both shear and bulk\nviscosity of many-body systems of spin-1/2 fermions with predominantly short\nrange S-wave interactions. These sum rules relate Gaussian weights of the\nfrequency-dependent viscosities to the Tan contact parameter C(a). Our results\nare valid for arbitrary values of the scattering length a, but receive small\ncorrections from operators of dimension larger than 5 in the OPE, and can be\nused to study transport properties in the vicinity of the infinite scattering\nlength fixed point. In particular, we find that the exact dependence of the\nshear viscosity sum rule on scattering length is controlled by the function\nC(a). The sum rules that we obtain depend on a frequency scale w that can be\noptimized to maximize their overlap with low-energy data.",
        "positive": "Bogoliubov theory of interacting bosons on a lattice in a synthetic\n  magnetic field: We consider theoretically the problem of an artificial gauge potential\napplied to a cold atomic system of interacting neutral bosons in a\ntight-binding optical lattice. Using the Bose-Hubbard model, we show that an\neffective magnetic field leads to superfluid phases with simultaneous spatial\norder, which we analyze using Bogoliubov theory. This gives a consistent\nexpansion in terms of quantum and thermal fluctuations, in which the lowest\norder gives a Gross-Pitaevskii equation determining the condensate\nconfiguration. We apply an analysis based on the magnetic symmetry group to\nshow how the spatial structure of this configuration depends on commensuration\nbetween the magnetic field and the lattice. Higher orders describe the\nquasiparticle excitations, whose spectrum combines the intricacy the Hofstadter\nbutterfly with the characteristic features of the superfluid phase. We use the\ndepletion of the condensate to determine the range of validity of our\napproximations and also to find an estimate for the onset of the Mott insulator\nphase. Our theory provides concrete experimental predictions, for both\ntime-of-flight imagery and Bragg spectroscopy."
    },
    {
        "anchor": "Generalized effective-potential Landau theory for a tunable\n  state-dependent hexagonal optical lattice: We analytically study the ground-state phase diagrams of ultracold bosons\nwith various values of the effective magnetic quantum number $m$ in a\nstate-dependent hexagonal optical lattice by using the generalized\neffective-potential Landau theory, where the site-offset energy between the two\ntriangular sublattice A and B is tunable. Our analytical calculations of\nthird-order corrections are in reasonably good agreement with the previous\ncluster Gutzwiller calculations. Furthermore, we reveal the reason why the\nregions of the Mott lobes $(n,n)$ in phase diagrams for $m=0.02$ are\nunexpectedly expanded with increasing $J/U$ in deep lattice.",
        "positive": "Nonequilibrium Model of Photon Condensation: We develop a nonequilibrium model of condensation and lasing of photons in a\ndye filled microcavity. We examine in detail the nature of the thermalization\nprocess induced by absorption and emission of photons by the dye molecules, and\ninvestigate when the photons are able to reach a thermal equilibrium\nBose-Einstein distribution. At low temperatures, or large cavity losses, the\nabsorption and emission rates are too small to allow the photons to reach\nthermal equilibrium and the behavior becomes more like that of a conventional\nlaser."
    },
    {
        "anchor": "Quantum Dynamics of Disordered Bosons in an Optical Lattice: We study the equilibrium and non-equilibrium properties of strongly\ninteracting bosons on a lattice in presence of a random bounded disorder\npotential. Using a Gutzwiller projected variational technique, we study the\nequilibrium phase diagram of the disordered Bose Hubbard model and obtain the\nMott insulator, Bose glass and superfluid phases. We also study the non\nequilibrium response of the system under a periodic temporal drive where,\nstarting from the superfluid phase, the hopping parameter is ramped down\nlinearly in time, and back to its initial value. We study the density of\nexcitations created, the change in the superfluid order parameter and the\nenergy pumped into the system in this process as a function of the inverse ramp\nrate $\\tau$. For the clean case the density of excitations goes to a constant,\nwhile the order parameter and energy relaxes as $1/\\tau$ and $1/\\tau^2$\nrespectively. With disorder, the excitation density decays exponentially with\n$\\tau$, with the decay rate increasing with the disorder, to an asymptotic\nvalue independent of the disorder. The energy and change in order parameter\nalso decrease as $\\tau$ is increased.",
        "positive": "Domain wall dynamics in a two-component Bose-Mott insulator: We model the dynamics of two species of bosonic atoms trapped in an optical\nlattice within the Mott regime by mapping the system onto a spin model. A field\ngradient breaks the cloud into two domains. We study how the domain wall\nevolves under adiabatic and diabatic changes of this gradient. We determine the\ntimescales for adiabaticity, and study how temperature evolves for slow ramps.\nWe show that after large, sudden changes of the field gradient, the system does\nnot equilibrate on typical experimental timescales. We find interesting spin\ndynamics even when the initial temperature is large compared to the\nsuper-exchange energy. We discuss the implication of our results for\nexperiments wishing to use such a two-component system for thermometry, or as\npart of a cooling scheme."
    },
    {
        "anchor": "Detecting d-wave superfluid and d-density wave states of ultracold\n  Fermions on optical lattices: We propose a pump probe experiment for detecting the d-wave superfluid and\nd-density wave phases of ultracold Fermions on an optical lattice. The pump\nconsists of periodic modulations of the optical lattice intensity which creates\nquasiparticle pairs in these systems. The changes in the momentum distribution\nunder the drive can be used to measure quasiparticle dispersion and gap\nanisotropy. Further, we show that the pattern of peaks and dips in the spin\nselective density-density correlation function provides a phase sensitive probe\nof the symmetry of the order parameter in these systems.",
        "positive": "Optical lattice platform for the SYK model: The tractability of the Sachdev-Ye-Kitaev (SYK) model at large $N$ limit\nmakes it ideal to theoretically study its chaotic non-Fermi liquid behavior and\nholographic duality properties. We show that the complex SYK Hamiltonian\nemerges from a system of spinless itinerant fermions in an optical Kagome\nlattice with a strong disorder. We discuss the regimes supporting flat band\nspectra in a Kagome lattice, where the system can be non-dispersive. Random\ninteraction between non-dispersive fermions is induced due to randomly\ndistributed immobile impurities in the optical lattice, that exclude the\npresence of itinerant fermions at their locations. We show that the proposed\nsetup is a reliable experimental platform to realize the SYK model and study\nits exotic behavior. We show that the velocity distribution of the released\nfermions is a sensitive probe of the many-body Wigner-Dyson spectral density of\nstates while the averaged many-body Loschmidt echo scheme can measure two-point\nout-of-time-ordered correlation functions of the SYK system."
    },
    {
        "anchor": "Two-dimensional coherent spectroscopy of trion-polaritons and\n  exciton-polaritons in atomically thin transition metal dichalcogenides: We present a microscopic many-body calculation of the nonlinear\ntwo-dimensional coherent spectroscopy (2DCS) of trion-polaritons and\nexciton-polaritons in charge-tunable transition-metal-dichalcogenides\nmonolayers placed in an optical microcavity. The charge tunability leads to an\nelectron gas with nonzero density that brings brightness to the trion - a\npolaron quasiparticle formed by an exciton with a nonzero residue bounded to\nthe electron gas. As a result, a trion-polariton is created under strong\nlight-matter coupling, as observed in the recent experiment by Sidler\n\\textit{et al.} {[}Nat. Phys. \\textbf{13}, 255 (2017){]}. We analyze in detail\nthe structure of trion-polaritons, by solving an extended Chevy ansatz for the\ntrion quasiparticle wave-function. We confirm that the effective light-matter\ncoupling for trion-polaritons is determined by the residue of the trion\nquasiparticle. The solution of the full many-body polaron states within Chevy\nansatz enables us to microscopically calculate the nonlinear 2DCS spectrum of\nboth trion-polaritons and exciton-polaritons. We predict the existence of three\nkinds of off-diagonal cross-peaks in the 2DCS spectrum, as an indication of the\ncoherence among the different branches of trion-polaritons and\nexciton-polaritons. Due to the sensitivity of 2DCS spectrum to quasiparticle\ninteractions, our work provides a good starting point to explore the strong\nnonlinearity exhibited by trion-polaritons in some recent exciton-polariton\nexperiments.",
        "positive": "Revealing the Superfluid Lambda Transition in the Universal\n  Thermodynamics of a Unitary Fermi Gas: We have observed the superfluid phase transition in a strongly interacting\nFermi gas via high-precision measurements of the local compressibility, density\nand pressure down to near-zero entropy. Our data completely determine the\nuniversal thermodynamics of strongly interacting fermions without any fit or\nexternal thermometer. The onset of superfluidity is observed in the\ncompressibility, the chemical potential, the entropy, and the heat capacity. In\nparticular, the heat capacity displays a characteristic lambda-like feature at\nthe critical temperature of $T_c/T_F = 0.167(13)$. This is the first clear\nthermodynamic signature of the superfluid transition in a spin-balanced atomic\nFermi gas. Our measurements provide a benchmark for many-body theories on\nstrongly interacting fermions, relevant for problems ranging from\nhigh-temperature superconductivity to the equation of state of neutron stars."
    },
    {
        "anchor": "Supersolid phase in atomic gases with magnetic dipole interaction: A major obstacle for the experimental realization of a supersolid phase with\ncold atomic gases in an optical lattice is the weakness of the nearest-neighbor\ninteractions achievable via magnetic dipole-dipole interactions. In this\nletter, we show that using a large filling of atoms within each well the\ncharacteristic energy scales are strongly enhanced. Within this regime, the\nsystem is well described by the rotor model, and the qualitative behavior of\nthe phase diagram derives from mean-field theory. We find a stable supersolid\nphase for realistic parameters with chromium atoms.",
        "positive": "Thermally isolated Luttinger liquids with noisy Hamiltonians: We study the dynamics of a quantum-coherent thermally isolated Luttinger\nliquid with noisy Luttinger parameter. To characterize the fluctuations of the\nabsorbed energy in generic noise-driven systems, we first identify two types of\nenergy moments, which can help tease apart the effects of classical\n(sample-to-sample) and quantum sources of fluctuations. One type of moment\ncaptures the total fluctuations due to both sources, while the other one\ncaptures the effect of the classical source only. We then demonstrate that in\nthe Luttinger liquid case, the two types of moments agree in the thermodynamic\nlimit, indicating that the classical source dominates. In contrast to\nequilibrium thermodynamics, in this driven system the relative fluctuations of\nenergy do not decay with the system size. Additionally, we study the deviations\nof equal-time correlation functions from their ground-state value, and find a\nsimple scaling behavior."
    },
    {
        "anchor": "Universal scaling of three-dimensional bosonic gases in a trapping\n  potential: We investigate the critical properties of cold bosonic gases in three\ndimensions, confined by an external quadratic potential coupled to the particle\ndensity, and realistically described by the Bose-Hubbard (BH) model. The\ntrapping potential is often included in experiments with cold atoms and\nmodifies the critical finite-size scaling of the homogeneous system in a non\ntrivial way. The trap-size scaling (TSS) theory accounts for this effect\nthrough the exponent $\\theta$.\n  We perform extensive simulations of the BH model at the critical temperature,\nin the presence of harmonic traps. We find that the TSS predictions are\nuniversal once we account for the effective way in which the trap locally\nmodifies the chemical potential $\\mu$ of the system. The trap exponent for the\nBH model at $\\mu=0$ is the one corresponding to an effective quartic potential.\nAt positive $\\mu$, evidence suggests that TSS breaks down sufficiently far from\nthe centre of the trap, as the system encounters an effective phase boundary.",
        "positive": "Measuring the Superfluid Fraction of an Ultracold Atomic Gas: We propose a method to measure the superfluid fraction of an atomic gas. The\nmethod involves the use of a vector potential generated by optical beams with\nnon-zero angular momentum to simulate uniform rotation. The induced change in\nangular momentum of the atomic gas can be measured spectroscopically. This\nallows a direct determination of the superfluid fraction."
    },
    {
        "anchor": "Finite phase coherence time of a quantum field created by an ideal Bose\n  gas: A quantitative quantum field approach for a very weakly interacting, dilute\nBose gas is presented. Within the presented model, which assumes the constraint\nof particle number conservation at constant average energy in the canonical\nensemble, both coherent oscillations, as well as decay times of quantum\ncoherence for a quantum field created by the atomic cloud of a Bose-Einstein\ncondensate, are modeled simultaneously by a unique complex time variable and\ntwo different characteristic frequencies for the oscillation and decoherence of\nthe field. Within the present theory, it is illustrated that the occurrence of\ncoherence and a macroscopic ground state population has its origin in finite\ncoherence times of the ensemble of quantum particles in the Bose gas, which -\nin contrast to the incoherent interactions between the different particles -\nleads to the preparation of a thermodynamically stable many-body quantum state\nwith coherent superpositions of discrete and quantized condensate and\nnon-condensate atom number states at constant total atom number.",
        "positive": "Fractional topological states of dipolar fermions in one-dimensional\n  optical superlattices: We study the properties of dipolar fermions trapped in one-dimensional\nbichromatic optical lattices and show the existence of fractional topological\nstates in the presence of strong dipole-dipole interactions. We find some\ninteresting connections between fractional topological states in\none-dimensional superlattices and the fractional quantum Hall states: (i) the\none-dimensional fractional topological states for systems at filling factor\n\\nu=1/p have p-fold degeneracy, (ii) the quasihole excitations fulfill the same\ncounting rule as that of fractional quantum Hall states, and (iii) the total\nChern number of p-fold degenerate states is a nonzero integer. The existence of\ncrystalline order in our system is also consistent with the thin-torus limit of\nthe fractional quantum Hall state on a torus. The possible experimental\nrealization in cold atomic systems offers a new platform for the study of\nfractional topological phases in one-dimensional superlattice systems."
    },
    {
        "anchor": "A quantum Monte Carlo based density functional for Dysprosium dipolar\n  system: We present a quantum Monte Carlo based density functional to describe droplet\nformation and supersolidity in dipolar systems. The usual Lee-Huang-Yang term,\naccounting for quantum correlations in the conventional extended\nGross-Pitaievskii equation (eGPE), has been substituted by the correlation\nenergy evaluated with Quantum Monte Carlo. We demonstrate the ability of the\nnew functional to reproduce existing experimental data for the minimum critical\nnumber of atoms $N_\\mathrm{c}$ required for droplet formation. $N_\\mathrm{c}$\nis a challenging quantity for theoretical predictions, and the eGPE provides\nonly a qualitative description of it, mainly when it is applied to Dysprosium.\nWe also use the new approach to characterize the BEC-supersolid transition. The\nquantum Monte Carlo based functional can be easily implemented in any existing\neGPE code, improving the description of dipolar systems without increasing the\ncomputational cost.",
        "positive": "The Unitary Fermi Gas in a Harmonic Trap and its Static Response: We use harmonically trapped systems to find the leading gradient corrections\nof the supefluid local density approximation (SLDA) - a density functional\ntheory (DFT) describing the unitary Fermi gas (UFG). We find the leading order\ncorrection to be negative, and predict the q^2 coefficient of the long-range\nstatic response c = 1.5(3) - a factor of two smaller than predicted by\nmean-field theory - thereby establishing a new and experimentally measurably\nuniversal constant."
    },
    {
        "anchor": "Theory of degenerate Bose gas without anomalous averages: Theory of a weakly non-ideal Bose gas in the canonical ensemble is developed\nwithout assumption of the C-number representation of the creation and\nannihilation operators with zero momentum. It is shown that the pole of the\n\"density-density\" Green function exactly coincides with the Bogolybov's\nphonon-roton spectrum of excitations. At the same time in the one-particle\nexcitation spectrum a gap exists. The value of this gap is connected with the\ndensity of particles in the \"condensate\".",
        "positive": "Quench dynamics of a weakly interacting disordered Bose gas in momentum\n  space: We theoretically study the out-of-equilibrium dynamics in momentum space of a\nweakly interacting disordered Bose gas launched with a finite velocity. In the\nabsence of interactions, coherent multiple scattering gives rise to a\nbackground of diffusive particles, on top of which a coherent backscattering\ninterference emerges. We revisit this scenario in the presence of interactions,\nusing a diagrammatic quantum transport theory. We find that the dynamics is\ngoverned by coupled kinetic equations describing the thermalization of the\ndiffusive and coherent components of the gas. This phenomenon leads to a\ndestruction of coherent backscattering, well described by an exponential\nrelaxation whose rate is controlled by the particle collision time. These\npredictions are confirmed by numerical simulations."
    },
    {
        "anchor": "Oblique breathers generated by a flow of two-component Bose-Einstein\n  condensate past a polarized obstacle: We predict that oblique breathers can be generated by a flow of two-component\nBose-Einstein condensate past a polarized obstacle which attracts one component\nof the condensate and repels the other one. The breather exists if\nintra-species interaction constants differ from the inter-species interaction\nconstant and it corresponds to the nonlinear excitation of the so-called\npolarization mode with domination of the relative motion of the components.\nApproximate analytical theory is developed for the case of small-amplitude\nbreathers that is in reasonable agreement with the exact numerical results.",
        "positive": "Observation and quantification of pseudogap in unitary Fermi gases: The nature of pseudogap lies at the heart of strongly-interacting\nsuperconductivity and superfluidity. With known pairing interactions, unitary\nFermi gases provide an ideal testbed to verify whether a pseudogap can arise\nfrom many-body pairing. Here we report the observation of the long-sought\npair-fluctuation-driven pseudogap in homogeneous unitary Fermi gases of\nlithium-6 atoms, by precisely measuring the spectral function through\nmomentum-resolved microwave spectroscopy without the serious effects of\nfinal-state effect. We find a large pseudogap above the superfluid transition.\nThe inverse pair lifetime exhibits a thermally-activated exponential behavior,\nuncovering the microscopic virtual pair breaking and recombination mechanism.\nThe obtained large, T-independent single-particle scattering rate is comparable\nwith that set by the Planckian limit. Our findings quantitatively characterize\nthe pseudogap in strongly-interacting Fermi gases, highlighting the role of\npreformed pairing as a precursor to superfluidity."
    },
    {
        "anchor": "Dipole condensates in tilted Bose-Hubbard chains: We study the quantum phase diagram of a Bose-Hubbard chain whose dynamics\nconserves both boson number and boson dipole moment, a situation which can\narise in strongly tilted optical lattices. The conservation of dipole moment\nhas a dramatic effect on the phase diagram, which we analyze by combining a\nfield theory analysis with DMRG simulations. Unlike the conventional\nBose-Hubbard model, the phase diagram contains no compressible phases, and is\ninstead dominated by various types of exotic dipolar condensates. We suggest\nways by which these condensates can be identified in near-term cold atom\nexperiments.",
        "positive": "Dynamics of a Polariton Condensate in an Organic Semiconducting\n  Microcavity: Recent experiments on thin-film microcavities give evidence of Bose\ncondensation of exciton-polariton states. Inspired by these observations, we\nconsider the possibility that such exotic \"half-light/half matter\" states could\nbe observed in thin-film organic semiconductors where the oscillator strength\nis generally stronger than in inorganic systems. Here we present a theoretical\nmodel and simulations of macroscopic exciton-polartiton condensates in thracene\nthin films sandwiched within a micro-meter scale resonant cavity and establish\ncriteria for the conditions under which BEC could be achieved in these systems.\nWe consider the effect of lattice disorder on the threshold intensities\nnecessary to create polartion superfluid states and conclude that even allowing\nfor up to 5% angular disorder of the molecules within the crystal lattice, the\nsuperfluid transition remains sharp."
    },
    {
        "anchor": "Oscillating Quantum Droplets from the free expansion of Logarithmic\n  One-Dimensional Bose Gases: We analyze some issues related to the stability and free expansion of a\none-dimensional logarithmic Bose-Einstein condensate, particularly its eventual\nrelation to the formation of quantum droplet-type configurations. We prove that\nthe corresponding properties, such as the energy of the associated N-body\nground state, differ substantially with respect to its three-dimensional\ncounterpart. Consequently, the free velocity expansion also shows differences\nwith respect to the three-dimensional system when logarithmic interactions are\ntaken into account. The one-dimensional logarithmic condensate tends to form\nquantum droplet-type configurations when the external trapping potential is\nturned off, i.e., the self-sustainability or self-confinement appears as in\nthree-dimensions. However, we obtain that for some specific values of the\nself-interaction parameters and the number of particles under consideration,\nthe cloud oscillates during the free expansion around to a specific equilibrium\nsize. These results show that we can get scenarios in which the one-dimensional\ncloud reaches stable configurations, i.e., oscillating quantum droplets.",
        "positive": "Quasi-localized excitations induced by long-range interactions in\n  translationally-invariant quantum spin chains: We show that long-range ferromagnetic interactions in quantum spin chains can\ninduce spatial quasi-localization of topological magnetic defects, i.e.,\ndomain-walls, even in the absence of quenched disorder. By means of\nmatrix-product-states numerical techniques, we study the non-equilibrium\nevolution of initial states with one or more domain-walls under the effect of a\ntransverse field in variable-range quantum Ising chains. Upon increasing the\nrange of these interactions, we demonstrate the occurrence of a sharp\ntransition characterized by the suppression of spatial diffusion of the\nmagnetic defects during the accessible time scale: the excess energy density\nremains localized around the initial domain-wall positions, hindering\nthermalization. This quasi-localization is accurately reproduced by an\neffective semiclassical model, which elucidates the crucial role that\nlong-range interactions play in this phenomenon. These predictions can be\ntested in current experiments with trapped ions."
    },
    {
        "anchor": "Quantized Topological Response in Trapped Quantum Gases: In this letter, we propose a quantized topological response in trapped 1D\nquantum gases. The experimental protocol for the response requires the\napplication of an instant optical pulse to a half-infinite region in an\nasymptotically harmonic trap and measuring the density distribution. We show\nthat the corresponding linear response is described by a universal quantized\nformula in the thermal dynamical limit, which is invariant under local\ncontinuous deformations of the trapping potential $V$, atom distribution\n$f_\\Lambda$, the spatial envelope of the optical pulse $\\Theta_p$, and the\nmeasurement region $\\Theta_m$. We test the statement by various numerical\nanalysis, the result of which is consistent with the analytical prediction to\nhigh accuracy. We further show that a short but finite optical pulse duration\nonly results in a violation of the quantization near the transition time, which\nsuggests that quantized response could be observed in realistic experiments. We\nalso generalize our results to non-linear quantized topological responses for\natoms in higher dimensional harmonic traps.",
        "positive": "Imaginary Potential Induced Quantum Coherence for Bose-Einstein\n  Condensates: The role of complex potentials in single-body Schr\\H{o}dinger equation has\nbeen studied intensively. We study the quantum coherence for degenerate Bose\ngases in complex potentials, when the exchange symmetry of identical bosons is\nconsidered. For initially independent Bose-Einstein condensates, it is shown\nthat even very weak imaginary potential can induce perfect quantum coherence\nbetween different condensates. The scheme to observe imaginary potential\ninduced quantum coherence is discussed."
    },
    {
        "anchor": "Observation of the Fermionic Joule-Thomson Effect: We report the observation of the quantum Joule-Thomson (JT) effect in ideal\nand unitary Fermi gases. We study the temperature dynamics of these systems\nwhile they undergo an energy-per-particle conserving rarefaction. For\nscale-invariant systems, whose equations of state satisfy the relation\n$U\\propto PV$, this rarefaction conserves the specific enthalpy, which makes it\nthermodynamically equivalent to a JT throttling process. We observe JT heating\nin an ideal Fermi gas, stronger at higher quantum degeneracy, a result of the\nrepulsive quantum-statistical `force' arising from Pauli blocking. In a unitary\nFermi gas, we observe that the JT heating is marginal in the temperature range\n$0.2 \\lesssim T/T_{\\mathrm{F}} \\lesssim 0.8 $ as the repulsive\nquantum-statistical effect is lessened by the attractive interparticle\ninteraction.",
        "positive": "Modification of roton instability due to the presence of a second\n  dipolar Bose-Einstein condensate: We study the behavior of two coupled purely dipolar Bose-Einstein\ncondensates, each located in a cylindrically symmetric pancake-shaped external\nconfining potential, as the separation b between the traps along the tight\nconfining direction is varied. The solutions of the coupled Gross-Pitaevskii\nand Bogoliubov-de Gennes equations, which account for the full dynamics, show\nthat the system behavior is modified by the presence of the second dipolar BEC.\nFor sufficiently small b, the presence of the second dipolar BEC destabilizes\nthe system dramatically. In this regime, the coupled system collapses through a\nmode that is notably different from the radial roton mode that induces the\ncollapse of the uncoupled system. Finally, we comment on the shortcomings of an\napproach that neglects the dynamics in the z-direction, which is assumed to be\na good approximation for highly pancake-shaped dipolar BECs in the literature."
    },
    {
        "anchor": "Atomic Bloch-Zener Oscillations and St\u00fcckelberg Interferometry in\n  Optical Lattices: We report on experiments investigating quantum transport and band\ninterferometry of an atomic Bose-Einstein condensate in an optical lattice with\na two-band miniband structure, realized with a Fourier-synthesized optical\nlattice potential. Bloch-Zener oscillations, the coherent superposition of\nBloch oscillations and Landau-Zener tunneling between the two bands are\nobserved. When the relative phase between paths in different bands is varied,\nan interference signal is observed, demonstrating the coherence of the dynamics\nin the miniband system. Measured fringe patterns of this St\\\"uckelberg\ninterferometer allow to interferometrically map out the band structure of the\noptical lattice over the full Brillouin zone.",
        "positive": "Interacting bosons on a Su-Schrieffer-Heeger ladder: Topological phases\n  and Thouless pumping: We study the topological properties of hardcore bosons on a two-leg ladder\nconsisting of two Su-Schrieffer-Heeger (SSH) chains that are coupled via\nhopping and interaction. We chart out the phase diagram for the system and show\nthat based on the relative hopping dimerization pattern along the legs,\ndistinctly different topological phases and phase transitions can occur. When\nthe dimerization along the legs are uniform, we find that the topological\nnature vanishes for even the slightest rung hopping. For staggered\ndimerization, the system exhibits a well defined topological character and a\ntopological phase transition as a function of rung hopping. While the\ntopological phase shows bond order character, the trivial phase shows the\nbehavior of a rung-Mott insulator. For this case, the topological nature is\nfound to survive even in the presence of finite inter-leg interactions.\nMoreover, we find that the critical point of the topological phase transition\nshifts to a higher or a lower rung hopping strength depending on the attractive\nor repulsive nature of the interaction. To highlight the marked effects of\ninteractions, we propose a scheme involving a Thouless charge pump that\nprovides insights for the topological phases characterized by a quantised\nparticle transport through a periodic modulation of appropriate system\nparameters. In our studies, we show an interaction induced charge pumping\nfollowing specific pumping protocols in the case of staggered dimerization."
    },
    {
        "anchor": "Linear response of heat conductivity of normal-superfluid interface of a\n  polarized Fermi gas to orbital magnetic field: Using perturbed Bogoliubov equations, we study the linear response to a weak\norbital magnetic field of the heat conductivity of the normal-superfluid\ninterface of a polarized Fermi gas at sufficiently low temperature. We consider\nthe various scattering regions of the BCS regime and analytically obtain the\ntransmission coefficients and the heat conductivity across the interface in an\narbitrary weak orbital field. For a definite choice of the field, we consider\nvarious values of the scattering length in the BCS range and numerically obtain\nthe allowed values of the average and species-imbalance chemical potentials.\nThus, taking Andreev reflection into account, we describe how the heat\nconductivity is affected by the field and the species imbalance. In particular,\nwe show that the additional heat conductivity due to the orbital field\nincreases with the species imbalance, which is more noticeable at higher\ntemperatures. Our results indicate how the heat conductivity may be controlled,\nwhich is relevant to sensitive magnetic field sensors/regulators at the\ninterface.",
        "positive": "Observation of dense collisional soliton complexes in a two-component\n  Bose-Einstein condensate: We present an experimental and theoretical study of hydrodynamic phenomena in\na two-component atomic Bose-Einstein condensate emerging from the imprinting of\na periodic spin pattern. By employing a microwave pulse-based winding\ntechnique, we prepare a tunable initial state which evolves into an array of\nsolitary waves. We observe the ensuing dynamics, including shape deformations,\nthe emergence of dark-antidark solitons, apparent spatial frequency tripling,\nand decay and revival of contrast related to soliton collisions. For the\ndensest arrays, we obtain soliton complexes where solitons undergo continued\ncollisions for long evolution times providing an avenue towards the\ninvestigation of soliton gases in atomic condensates."
    },
    {
        "anchor": "Persistent Hall response in a quantum quench: Out-of-equilibrium systems can host phenomena that transcend the usual\nrestrictions of equilibrium systems. Here we unveil how out-of-equilibrium\nstates, prepared via a quantum quench, can exhibit a non-zero Hall-type\nresponse that persists at long times, and even when the instantaneous\nHamiltonian is time reversal symmetric; both these features starkly contrast\nwith equilibrium Hall currents. Interestingly, the persistent Hall effect\narises from processes beyond those captured by linear response, and is a\nsignature of the novel dynamics in out-of-equilibrium systems. We propose\nquenches in two-band Dirac systems as natural venues to realize persistent Hall\ncurrents, which exist when either mirror or time-reversal symmetry are broken\n(before or after the quench). Its long time persistence, as well as sensitivity\nto symmetry breaking, allow it to be used as a sensitive diagnostic of the\ncomplex out-equilibrium dynamics readily controlled and probed in cold-atomic\noptical lattice experiments.",
        "positive": "Linear response study of collisionless spin drag: In this work we are concerned with the understanding of the collisionless\ndrag or entrainment between two superfluids, also called Andreev-Bashkin\neffect, in terms of current response functions. The drag density is shown to be\nproportional to the cross transverse current-current response function, playing\nthe role of a normal component for the single species superfluid density. We\ncan in this way link the existence of finite entrainment with the exhaustion of\nthe energy-weighted sum rule in the spin channel. The formalism is then used to\nreproduce some known results for a weakly interacting Bose-Bose mixture.\nFinally we include the drag effect to determine the beyond mean-field\ncorrection on the speed of sound and on the spin dipole excitations for a\nhomogeneous and trapped gas, respectively."
    },
    {
        "anchor": "Controlled polarization of two-dimensional quantum turbulence in atomic\n  Bose-Einstein condensates: We propose a scheme for generating two-dimensional turbulence in harmonically\ntrapped atomic condensates with the novelty of controlling the polarization\n(net rotation) of the turbulence. Our scheme is based on an initial giant\n(multicharged) vortex which induces a large-scale circular flow. Two thin\nobstacles, created by blue-detuned laser beams, speed up the decay of the giant\nvortex into many singly-quantized vortices of the same circulation; at the same\ntime, vortex-antivortex pairs are created by the decaying circular flow past\nthe obstacles. Rotation of the obstacles against the circular flow controls the\nrelative proportion of positive and negative vortices, from the limit of\nstrongly anisotropic turbulence (almost all vortices having the same sign) to\nthat of isotropic turbulence (equal number of vortices and antivortices). Using\nthe new scheme, we numerically study quantum turbulence and report on its decay\nas a function of the polarization.",
        "positive": "Kubo-Martin-Schwinger relation for an interacting mobile impurity: In this work we study the Kubo-Martin-Schwinger (KMS) relation in the\nYang-Gaudin model of an interacting mobile impurity. We use the integrability\nof the model to compute the dynamic injection and ejection Green's functions at\nfinite temperatures. We show that due to separability of the Hilbert space with\nan impurity, the ejection Green's in a canonical ensemble cannot be reduced to\na single expectation value as per microcanonical picture. Instead, it involves\na thermal average over contributions from different subspaces of the Hilbert\nspace which, due to the integrability, are resolved using the so-called spin\nrapidity. It is then natural to consider the injection and ejection Green's\nfunctions within each subspace. By means of reformulating the original KMS\ncondition as a Riemann-Hilbert problem, we analytically demonstrate that such\nGreen's functions obey a refined analogous relation, which is finally\ncorroborated by numerical evaluation."
    },
    {
        "anchor": "Phase diagram of strongly attractive $p$-orbital fermions on optical\n  lattices: We examine a system of doubly degenerate $p$-orbital polarized fermions on a\ntwo-dimensional square lattice with a strong on-site interaction. We consider\nthe system density at the half filling limit and tackle the strong attractive\ninteraction using a perturbation theory. We treat the four-site square\nplaquette interaction term generated from the directional tunneling dependence\nof $p$-orbitals using the fourth order in perturbation theory. We map the\nstrong coupling particle Hamiltonian into an effective spin-Hamiltonian and\nthen use a variational mean field approach and a linear spin-wave theory to\nstudy the phase diagram. Further, we discuss the experimental signatures of\nthese phases within the context of current cold-atom experimental techniques.",
        "positive": "Loading Ultracold Gases in Topological Floquet Bands: Current and\n  Center-of-Mass Responses: Topological band structures can be designed by subjecting lattice systems to\ntime-periodic modulations, as was recently demonstrated in cold atoms and\nphotonic crystals. However, changing the topological nature of Floquet Bloch\nbands from trivial to non-trivial, by progressively launching the\ntime-modulation, is necessarily accompanied with gap-closing processes: this\nhas important consequences for the loading of particles into a target Floquet\nband with non-trivial topology, and hence, on the subsequent measurements. In\nthis work, we analyse how such loading sequences can be optimized in view of\nprobing the topology of Floquet bands through transport measurements. In\nparticular, we demonstrate the robustness of center-of-mass responses, as\ncompared to current responses, which present important irregularities due to an\ninterplay between the micro-motion of the drive and inter-band interference\neffects. The results presented in this work illustrate how probing the\ncenter-of-mass displacement of atomic clouds offers a reliable method to detect\nthe topology of Floquet bands, after realistic loading sequences."
    },
    {
        "anchor": "Topological Superfluids with Finite Momentum Pairing and Majorana\n  Fermions: Majorana fermions, quantum particles that are their own anti-particles, are\nnot only of fundamental importance in elementary particle physics and dark\nmatter, but also building blocks for fault-tolerant quantum computation.\nRecently Majorana fermions have been intensively studied in solid state and\ncold atomic systems. These studies are generally based on superconducting\npairing between two Fermions with opposite momenta (\\textit{% i.e.}, zero total\nmomentum). On the other hand, finite total momentum Cooper pairings, known as\nFulde-Ferrell-Larkin-Ovchinnikov (FFLO) states, were predicted 50 years ago and\nthen widely studied in many branches of physics. However, whether FFLO\nsuperconductors can also support Majorana fermions has not been explored. Here\nwe show that Majorana fermions can exist in certain types of gapped FFLO\nstates, yielding a new topological quantum matter: topological FFLO\nsuperfluids/superconductors. We demonstrate the existence of such topological\nFFLO superfluids and the associated Majorana fermions using spin-orbit coupled\ndegenerate Fermi gases and derive their physical parameter regions. The\npotential implementation of topological FFLO superconductors in\nsemiconductor/superconductor heterostructures are also discussed.",
        "positive": "Breathing oscillations of a trapped impurity in a Bose gas: Motivated by a recent experiment [J. Catani et al., arXiv:1106.0828v1\npreprint, 2011], we study breathing oscillations in the width of a harmonically\ntrapped impurity interacting with a separately trapped Bose gas. We provide an\nintuitive physical picture of such dynamics at zero temperature, using a\ntime-dependent variational approach. In the Gross-Pitaevskii regime we obtain\nbreathing oscillations whose amplitudes are suppressed by self trapping, due to\ninteractions with the Bose gas. Introducing phonons in the Bose gas leads to\nthe damping of breathing oscillations and non-Markovian dynamics of the width\nof the impurity, the degree of which can be engineered through controllable\nparameters. Our results reproduce the main features of the impurity dynamics\nobserved by Catani et al. despite experimental thermal effects, and are\nsupported by simulations of the system in the Gross-Pitaevskii regime.\nMoreover, we predict novel effects at lower temperatures due to self-trapping\nand the inhomogeneity of the trapped Bose gas."
    },
    {
        "anchor": "Observation of Nonlinear Response and Onsager Regression in a Photon\n  Bose-Einstein Condensate: The quantum regression theorem states that the correlations of a system at\ntwo different times are governed by the same equations of motion as the\ntemporal response of the average values. Such a relation provides a powerful\nframework for the investigation of physical systems by establishing a formal\nconnection between intrinsic microscopic behaviour and a macroscopic 'effect'\ndue to an external 'cause'. Measuring the response to a controlled perturbation\nin this way allows to determine, for example, structure factors in condensed\nmatter systems as well as other correlation functions of material systems. Here\nwe experimentally demonstrate that the two-time particle number correlations in\na photon Bose-Einstein condensate inside a dye-filled microcavity exhibit the\nsame dynamics as the response of the condensate to a sudden perturbation of the\ndye molecule bath. This confirms the regression theorem for a quantum gas and,\nmoreover, establishes a test of this relation in an unconventional form where\nthe perturbation acts on the bath and only the condensate response is\nmonitored. For strong perturbations, we observe nonlinear relaxation dynamics\nwhich our microscopic theory relates to the equilibrium fluctuations, thereby\nextending the regression theorem beyond the regime of linear response. The\ndemonstrated nonlinearity of the condensate-bath system paves the way for\nstudies of novel elementary excitations in lattices of driven-dissipative\nphoton condensates.",
        "positive": "Anisotropic relaxation dynamics in a dipolar Fermi gas driven out of\n  equilibrium: We report on the observation of a large anisotropy in the rethermalization\ndynamics of an ultracold dipolar Fermi gas driven out of equilibrium. Our\nsystem consists of an ultracold sample of strongly magnetic $^{167}$Er\nfermions, spin-polarized in the lowest Zeeman sublevel. In this system, elastic\ncollisions arise purely from universal dipolar scattering. Based on\ncross-dimensional rethermalization experiments, we observe a strong anisotropy\nof the scattering, which manifests itself in a large angular dependence of the\nthermal relaxation dynamics. Our result is in very good agreement with recent\ntheoretical predictions. Furthermore, we measure the rethermalization rate as a\nfunction of temperature for different angles and find that the suppression of\ncollisions by Pauli blocking is not influenced by the dipole orientation."
    },
    {
        "anchor": "Construction of Fractal Order and Phase Transition with Rydberg Atoms: We propose the construction of a many-body phase of matter with fractal\nstructure using arrays of Rydberg atoms. The degenerate low energy excited\nstates of this phase form a self-similar fractal structure. This phase is\nanalogous to the so-called \"type-II fracton topological states\". The main\nchallenge in realizing fracton-like models in standard condensed matter\nplatforms is the creation of multi-spin interactions, since realistic systems\nare typically dominated by two-body interactions. In this work, we demonstrate\nthat the Van der Waals interaction and experimental tunability of Rydberg-based\nplatforms enable the simulation of exotic phases of matter with fractal\nstructures, and the study of a quantum phase transition involving a fractal\nordered phase.",
        "positive": "Fermionic Functional Renormalization Group Approach to Superfluid Phase\n  Transition: Fermionic functional renormalization group (FRG) is applied to describe the\nsuperfluid phase transition of the two-component fermionic system with\nattractive contact interaction. Connection between the fermionic FRG approach\nand the conventional Bardeen-Cooper-Schrieffer (BCS) theory with Gorkov and\nMelik-Barkhudarov (GMB) correction are clarified in details in the weak\ncoupling region by using the renormalization group flow of the fermionic\nfour-point vertex with particle-particle and particle-hole scattering\ncontributions. To go beyond the BCS+GMB theory, coupled FRG flow equations of\nthe fermion self-energy and the four-point vertex are studied under an Ansatz\nconcerning their frequency/momentum dependence. We found that the fermion\nself-energy turns out to be substantial even in the weak couping region, and\nthe frequency dependence of the four-point vertex is essential to obtain the\ncorrect asymptotic-ultraviolet behavior of the flow for the self-energy. The\nsuperfluid transition temperature and the associated chemical potential are\ncalculated in the region of negative scattering lengths."
    },
    {
        "anchor": "Breathing Modes in Rotating Bose-Condensed Gas: An Exact Diagonalization\n  Study: We present an exact diagonalization study of the breathing mode collective\nexcitations for a rotating Bose-Einstein condensate of $N=10$ spinless bosons\ninteracting via repulsive finite-range Gaussian potential and harmonically\nconfined in quasi-two-dimension. The yrast state and the low-lying excited\nstates are variationally obtained in given subspaces of the quantized total\nangular momentum $L$ employing the beyond lowest Landau level approximation in\nslowly rotating regime with $0 \\le L < 2N$. For a given $L$, the low-energy\neigenspectra (bands) are obtained in weakly to moderately interacting regime.\nFurther, for a given interaction, the split in low-lying eigenenergies with\nincreasing $L$ is the precursor to spontaneous symmetry breaking of the\naxisymmetry associated with the entry of the first vortex. With increase in\nrepulsive interaction, the value of the first breathing mode increases for\nstable total angular momentum states $L=0~\\mbox{and}~N$, but decreases for\nintermediate $0<L<N$ metastable states. The position of the observed first\nbreathing modes in the eigenspectrum remains unchanged as the interaction is\nvaried over several orders of magnitude.",
        "positive": "Eightfold way to dark states in SU(3) cold gases with two-body losses: We study the quantum dynamics of a one-dimensional SU(3)-symmetric system of\ncold atoms in the presence of two-body losses. We exploit the representation\ntheory of SU(3), the so-called eightfold way, as a scheme to organize the dark\nstates of the dissipative dynamics in terms of generalized Dicke states and\nshow how they are dynamically approached, both in the weakly- and and\nstrongly-interacting and dissipative regimes. Our results are relevant for a\nwide class of alkaline-earth(-like) gases experiments, paving the way to the\ndissipative preparation and exploitation of generalized Dicke states."
    },
    {
        "anchor": "Impact of local integrals of motion to metastable non-equilibrium states: We analyse the stationary behaviour of correlations in a strongly correlated\nBose gas out of equilibrium. The dynamics are triggered by a quench of the\ninteraction starting from the strongly interacting limit where the system is in\na perfect Mott state. Despite the complete integrability of our theoretical\ndescription, we find seemingly thermal behaviour for the experimentally\nmeasurable correlations at large interactions. Quite opposed, away from the\nstrongly interacting regime these correlation functions show highly non-thermal\nstationary values. This behaviour is explained by overlaps of the integrals of\nmotion with the observable and the initial state in an effective thermal\nensemble. These results suggest that non-equilibrium Mazur equalities are an\nefficient way to calculate short range correlations for arbitrary integrable\nmodels.",
        "positive": "Influence of Induced Interactions on Superfluid Properties of Quasi-Two\n  Dimensional Dilute Fermi Gases With Spin-Orbit Coupling: We study the effects of induced interactions on the pairing gap, transition\ntemperature and chemical potential of a quasi-two dimensional Fermi gas of\natoms with spin-orbit coupling. We find that these mean-field parameters are\nsignificantly modified when induced interactions are taken into account. We\nalso investigate the implications of induced interactions corrections for the\nBCS-BEC crossover driven by spin-orbit coupling, that happens even for small\n(compared to the Fermi energy) values of the binding energy."
    },
    {
        "anchor": "Two-Dimensional Supersolid Formation in Dipolar Condensates: Dipolar condensates have recently been coaxed to form the long-sought\nsupersolid phase. While one-dimensional supersolids may be prepared by\ntriggering a roton instability, we find that such a procedure in two dimensions\n(2D) leads to a loss of both global phase coherence and crystalline order.\nUnlike in 1D, the 2D roton modes have little in common with the supersolid\nconfiguration. We develop a finite-temperature stochastic Gross-Pitaevskii\ntheory that includes beyond-mean-field effects to explore the formation process\nin 2D and find that evaporative cooling directly into the supersolid\nphase--hence bypassing the first-order roton instability--can produce a robust\nsupersolid in a circular trap. Importantly, the resulting supersolid is stable\nat the final nonzero temperature. We then experimentally produce a 2D\nsupersolid in a near-circular trap through such an evaporative procedure. Our\nwork provides insight into the process of supersolid formation in 2D and\ndefines a realistic path to the formation of large two-dimensional supersolid\narrays.",
        "positive": "Coarsening and thermalisation properties of a quenched ferromagnetic\n  spin-1 condensate: We examine the dynamics of a quasi-two-dimensional spin-1 condensate in which\nthe quadratic Zeeman energy q is suddenly quenched to a value where the system\nhas a ferromagnetic ground state. There are two distinct types of ferromagnetic\nphases, i.e. a range of q values where the magnetization prefers to be in the\ndirection of the external field (easy-axis), and a range of q values where it\nprefers to be transverse to the field (easy-plane). We study the quench\ndynamics for a variety of q values and show that there is a single dynamical\ncritical exponent to characterize the scale invariant domain growth for each\nferromagnetic phase. For both quenches we give simple analytic models that\ncapture the essential scale invariant dynamics, and correctly predict the\nexponents. Because the order parameter for each phase is different, the natures\nof the domains and the relevant topological defects in each type of coarsening\nis also different. To explore these differences we characterize the fractal\ndimension of the domain walls, and the relationship of polar-core spin vortices\nto the domains in the easy-plane phase. Finally, we consider how the energy\nliberated from the quench thermalizes in the easy-axis quench. We show that\nlocal equilibrium is established in the spin waves on moderate time scales, but\ncontinues to evolve as the domains anneal."
    },
    {
        "anchor": "Efimov scenario for overlapping narrow Feshbach resonances: While Efimov physics in ultracold atoms is usually modeled with an isolated\nFeshbach resonance many real world resonances appear in close vicinity to each\nother and are therefore overlapping. Here we derive a realistic model based on\nthe mutual coupling of an open channel and two closed molecular channels while\nneglecting short-range physics as permitted by the narrow character of the\nconsidered resonances. The model is applied to three distinct scenarios with\nexperimental relevance. We show that the effect of overlapping resonances is\nmanifested most strikingly at a narrow resonance in whose vicinity there is a\nslightly narrower one. In this system the Efimov ground state extends not only\nover the scattering length zero crossing between the two resonances but also\nover the pole of the second resonance to finally meet the dissociation\nthreshold below it. In the opposite scenario, when a narrow resonance is\nconsidered in the vicinity of a slightly broader one, we observe that the\nEfimov features are pushed to lower binding energies and smaller scattering\nlengths by a significant factor facilitating their experimental investigation.\nBoth scenarios are referenced to the case of two narrow resonances which are\nfar enough away from each other to be effectively decoupled. In this case the\ntwo-channel model results are recovered. Finally, we analyze the rich\nexcitation spectrum of the system and construct and explain its nodal pattern.",
        "positive": "Mean-field vs RPA calculation of the energy of an impurity immersed in a\n  spin 1/2 superfluid: In this article we calculate the energy of an impurity weakly coupled to a\nspin 1/2 fermionic superfluid. We show that the divergences resulting from\nthree-body physics can only be cured using a proper description of the\nexcitations of the many-body background. We highlight the crucial role played\nby interactions between quasiparticles which are overlooked within BCS\n(Bardeen-Cooper-Schrieffer) mean-field theory of fermionic superfluidity. By\ncontrast, we prove that their addition using the Random Phase Approximation\n(RPA) allows us to regularize the energy of the impurity. Finally, we show that\nthese beyond mean-field corrections should be observable by the analysis of the\nfrequency shift of the impurity center of mass oscillations in an external\nconfining potential."
    },
    {
        "anchor": "Liquid quantum droplets of ultracold magnetic atoms: The simultaneous presence of two competing inter-particle interactions can\nlead to the emergence of new phenomena in a many-body system. Among others,\nsuch effects are expected in dipolar Bose-Einstein condensates, subject to\ndipole-dipole interaction and short-range repulsion. Magnetic quantum gases and\nin particular Dysprosium gases, offering a comparable short-range contact and a\nlong-range dipolar interaction energy, remarkably exhibit such emergent\nphenomena. In addition an effective cancellation of mean-field effects of the\ntwo interactions results in a pronounced importance of quantum-mechanical\nbeyond mean-field effects. For a weakly-dominant dipolar interaction the\nstriking consequence is the existence of a new state of matter equilibrated by\nthe balance between weak mean-field attraction and beyond mean-field repulsion.\nThough exemplified here in the case of dipolar Bose gases, this state of matter\nshould appear also with other microscopic interactions types, provided a\ncompetition results in an effective cancellation of the total mean-field. The\nmacroscopic state takes the form of so-called quantum droplets. We present the\neffects of a long-range dipolar interaction between these droplets.",
        "positive": "Quantum phase crossover and chaos in generalized Jahn-Teller lattice\n  model: The generalized multispin Jahn-Teller model on a finite lattice or formally\nequivalent Dicke model extended to two long-wavelength coherent bosons of\ndifferent frequencies is shown to exhibit a crossover between the\npolaron-modified \"quasi-normal\" and the squeezed \"radiation\" domains. We\ninvestigate effects of two kinds of interfering fluctuations on the phase\ncrossover and on statistical characteristics of boson complex spectra: (i)\nFluctuations in the electron subsystem- finite-size quantum fluctuations- are\nresponsible for the dephasing of the coherence in the radiation domain and for\nthe moderate occupation of the excited states in the normal domain. In the\nquasiclassical limit, radiation phase implies existence of a coherent acoustic\nsuper-radiant phase. (ii) Level-spacing fluctuations in excited boson level\nsubsystem with strong level repulsions. Related probability distributions are\nshown to be non-universally spread between the limiting universal Wigner-Dyson\nand Poisson distributions. We proved that the difference in boson frequencies\nis responsible for reaching the most stochastic limit of the Wigner-Dyson\ndistribution. Instanton lattice as a sequence of tunneling events in the most\nchaotic radiation domain exhibits maximal number of level-avoidings\n(repulsions). The non-universality of the distributions is caused by boson\ncorrelations which compete the level repulsions."
    },
    {
        "anchor": "Doubly dressed bosons - exciton-polaritons in a strong terahertz field: We demonstrate the existence of a novel quasiparticle: an exciton in a\nsemiconductor doubly dressed with two photons of different wavelengths: near\ninfrared cavity photon and terahertz (THz) photon, with the THz coupling\nstrength approaching the ultra-strong coupling regime. This quasiparticle is\ncomposed of three different bosons, being a mixture of a matter-light\nquasiparticle. Our observations are confirmed by a detailed theoretical\nanalysis, treating quantum mechanically all three bosonic fields. The doubly\ndressed quasiparticles retain the bosonic nature of their constituents, but\ntheir internal quantum structure strongly depends on the intensity of the\napplied terahertz field.",
        "positive": "Quantum states of a binary mixture of spinor Bose-Einstein condensates: We study the structure of quantum states for a binary mixture of spin-1\natomic Bose-Einstein condensates. In contrast to collision between identical\nbosons, the s-wave scattering channel between inter-species does not conform to\na fixed symmetry. The spin-dependent Hamiltonian thus contains non-commuting\nterms, making the exact eigenstates more challenging to obtain because they now\ndepend more generally on both the intra- and inter-species interactions. We\ndiscuss two limiting cases, where the spin-dependent Hamiltonian reduces\nrespectively to sums of commuting operators. All eigenstates can then be\ndirectly constructed, and they are independent of the detailed interaction\nparameters."
    },
    {
        "anchor": "Unitary Fermi gas, epsilon expansion, and nonrelativistic conformal\n  field theories: We review theoretical aspects of unitary Fermi gas (UFG), which has been\nrealized in ultracold atom experiments. We first introduce the epsilon\nexpansion technique based on a systematic expansion in terms of the\ndimensionality of space. We apply this technique to compute the thermodynamic\nquantities, the quasiparticle spectrum, and the critical temperature of UFG. We\nthen discuss consequences of the scale and conformal invariance of UFG. We\nprove a correspondence between primary operators in nonrelativistic conformal\nfield theories and energy eigenstates in a harmonic potential. We use this\ncorrespondence to compute energies of fermions at unitarity in a harmonic\npotential. The scale and conformal invariance together with the general\ncoordinate invariance constrains the properties of UFG. We show the vanishing\nbulk viscosities of UFG and derive the low-energy effective Lagrangian for the\nsuperfluid UFG. Finally we propose other systems exhibiting the nonrelativistic\nscaling and conformal symmetries that can be in principle realized in ultracold\natom experiments.",
        "positive": "Quantum Quench of the \"Speed of Light\": Quantum Dynamical Universality\n  Classes and Short-time Universal Behavior: A long-lived prethermal state may emerge upon a sudden quench of a quantum\nsystem. In this paper, we study a quantum quench of an initial {\\it critical}\nstate, and show that the resulting prethermal state exhibits a genuinely\nquantum and dynamical universal behavior. Specifically, we consider a scenario\nwhere the \"speed of light\" characterizing the propagation of local\nperturbations is suddenly quenched at criticality. We also find that the system\napproaches the prethermal state in a universal way described by a new exponent\nthat characterizes a kind of quantum aging."
    },
    {
        "anchor": "Adiabatic spin-dependent momentum transfer in an SU(N) degenerate Fermi\n  gas: We introduce a spin-orbit coupling scheme, where a retro-reflected laser beam\nselectively diffracts two spin components in opposite directions. Spin\nsensitivity is provided by sweeping through a magnetic-field sensitive\ntransition while dark states ensure that spontaneous emission remains low. The\nscheme is adiabatic and thus inherently robust. This tailored spin-orbit\ncoupling allows simultaneous measurements of the spin and momentum\ndistributions of a strontium degenerate Fermi gas, and thus opens the path to\nmomentum-resolved spin correlation measurements on SU(N) quantum magnets.",
        "positive": "Selection Rule for Topological Amplifiers in Bogoliubov de Gennes\n  Systems: Dynamical instability is an inherent feature of bosonic systems described by\nthe Bogoliubov de Geenes (BdG) Hamiltonian. Since it causes the BdG system to\ncollapse, it is generally thought that it should be avoided. Recently, there\nhas been much effort to harness this instability for the benefit of creating a\ntopological amplifier with stable bulk bands but unstable edge modes which can\nbe populated at an exponentially fast rate. We present a theorem for\ndetermining the stability of states with energies sufficiently away from zero,\nin terms of an unconventional commutator between the number conserving part and\nnumber nonconserving part of the BdG Hamiltonian. We apply the theorem to a\ngeneralization of a model from Galilo et al. [Phys. Rev. Lett, 115,\n245302(2015)] for creating a topological amplifier in an interacting spin-1\natom system in a honeycomb lattice through a quench process. We use this model\nto illustrate how the vanishing of the unconventional commutator selects the\nsymmetries for a system so that its bulk states are stable against (weak)\npairing interactions. We find that as long as time reversal symmetry is\npreserved, our system can act like a topological amplifier, even in the\npresence of an onsite staggered potential which breaks the inversion symmetry."
    },
    {
        "anchor": "Extraction and identification of noise patterns for ultracold atoms in\n  an optical lattice: To extract useful information about quantum effects in cold atom experiments,\none central task is to identify the intrinsic quantum fluctuation from\nextrinsic system noises of various kinds. As a data processing method,\nprincipal component analysis can decompose fluctuations in experimental data\ninto eigen modes, and give a chance to separate noises originated from\ndifferent physical sources. In this paper, we demonstrate for Bose-Einstein\ncondensates in one-dimensional optical lattices that the principal component\nanalysis can be applied to time-of-flight images to successfully separate and\nidentify noises from different origins of leading contribution, and can help to\nreduce or even eliminate noises via corresponding data processing procedures.\nThe attribution of noise modes to their physical origins is also confirmed by\nnumerical analysis within a mean-field theory.",
        "positive": "Anisotropic and long-range vortex interactions in two-dimensional\n  dipolar Bose gases: We perform a theoretical study into how dipole-dipole interactions modify the\nproperties of superfluid vortices within the context of a two-dimensional\natomic Bose gas of co-oriented dipoles. The reduced density at a vortex acts\nlike a giant anti-dipole, changing the density profile and generating an\neffective dipolar potential centred at the vortex core whose most slowly\ndecaying terms go as $1/\\rho^2$ and $\\ln(\\rho)/\\rho^3$. These effects modify\nthe vortex-vortex interaction which, in particular, becomes anisotropic for\ndipoles polarized in the plane. Striking modifications to vortex-vortex\ndynamics are demonstrated, i.e. anisotropic co-rotation dynamics and the\nsuppression of vortex annihilation."
    },
    {
        "anchor": "Dynamics of a Space-Time Crystal in an Atomic Bose-Einstein Condensate: A space-time crystal has recently been observed in a superfluid Bose gas.\nHere we construct a variational model that allows us to describe from first\nprinciples the coupling between the radial breathing mode and the higher-order\naxial modes that underlies the observation of the space-time crystal. By\ncomparing with numerical simulations we verify the validity of our variational\nAnsatz. From the model we determine the requirements for the observation of the\nspace-time crystal and the Ising-like nature of the symmetry breaking involved.\nAlso, we find the onset and growth rate of the space-time crystal, which can be\ncompared to experiments.",
        "positive": "Emergence of anyonic correlations from spin and charge dynamics in one\n  dimension: We propose a transformation for spin and charge degrees of freedom in\none-dimensional lattice systems, constrained to have no doubly occupied sites,\nthat allows direct access to the dynamical correlations of the system. The\ntransformation delivers particle creation and annihilation operators in a form\nof a spinless particle and a non-local operator acting on the space of states\nof a spin-$1/2$ chain. This permits a decomposition of dynamical correlation\nfunctions as a convolution of those for impenetrable anyons together with those\nof a spin chain. Further analysis can be done by methods tailored for each part\nof the convolution, greatly increasing the impact and flexibility of the\napproach."
    },
    {
        "anchor": "Metastability in spin polarised Fermi gases and quasiparticle decays: We investigate the metastability associated with the first order transition\nfrom normal to superfluid phases in the phase diagram of two-component\npolarised Fermi gases.We begin by detailing the dominant decay processes of\nsingle quasiparticles.Having determined the momentum thresholds of each process\nand calculated their rates, we apply this understanding to a Fermi sea of\npolarons by linking its metastability to the stability of individual polarons,\nand predicting a region of metastability for the normal partially polarised\nphase. In the limit of a single impurity, this region extends from the\ninteraction strength at which a polarised phase of molecules becomes the\ngroundstate, to the one at which the single quasiparticle groundstate changes\ncharacter from polaronic to molecular. Our argument in terms of a Fermi sea of\npolarons naturally suggests their use as an experimental probe. We propose\nexperiments to observe the threshold of the predicted region of metastability,\nthe interaction strength at which the quasiparticle groundstate changes\ncharacter, and the decay rate of polarons.",
        "positive": "Spontaneous Vortex Production in Driven Condensates with Narrow Feshbach\n  Resonances: We explore the possibility that, at zero temperature, vortices can be created\nspontaneously in a condensate of cold Fermi atoms, whose scattering is\ncontrolled by a narrow Feshbach resonance, by rapid magnetic tuning from the\nBEC to BCS regime. This could be achievable with current experimental\ntechniques."
    },
    {
        "anchor": "Quantum Hysteresis in Coupled Light-Matter Systems: We investigate the non-equilibrium quantum dynamics of a canonical\nlight-matter system, namely the Dicke model, when the light-matter interaction\nis ramped up and down through a cycle across the quantum phase transition. Our\ncalculations reveal a rich set of dynamical behaviors determined by the cycle\ntimes, ranging from the slow, near adiabatic regime through to the fast, sudden\nquench regime. As the cycle time decreases, we uncover a crossover from an\noscillatory exchange of quantum information between light and matter that\napproaches a reversible adiabatic process, to a dispersive regime that\ngenerates large values of light-matter entanglement. The phenomena uncovered in\nthis work have implications in quantum control, quantum interferometry, as well\nas in quantum information theory.",
        "positive": "Prethermalization Revealed by the Relaxation Dynamics of Full\n  Distribution Functions: We detail the experimental observation of the non-equilibrium many-body\nphenomenon prethermalization. We study the dynamics of a rapidly and coherently\nsplit one-dimensional Bose gas. An analysis based on the use of full quantum\nmechanical probability distributions of matter wave interference contrast\nreveals that the system evolves towards a quasi-steady state. This state, which\ncan be characterized by an effective temperature, is not the final thermal\nequilibrium state. We compare the evolution of the system to an integrable\nTomonaga-Luttinger liquid model and show that the system dephases to a\nprethermalized state rather than undergoing thermalization towards a final\nthermal equilibrium state."
    },
    {
        "anchor": "Spontaneous formation and non-equilibrium dynamics of a soliton-shaped\n  Bose-Einstein condensate in a trap: The Bose-stimulated self-organization of a quasi-two dimensional\nnon-equilibrium Bose-Einstein condensate in an in-plane potential is proposed.\nWe obtained the solution of the nonlinear, driven-dissipative Gross-Pitaevskii\nequation for a Bose-Einstein condensate trapped in an external asymmetric\nparabolic potential within the method of the spectral expansion. We found that,\nin sharp contrast to previous observations, the condensate can spontaneously\nacquire a soliton-like shape for spatially homogenous pumping. This condensate\nsoliton performs oscillatory motion in a parabolic trap and, also, can\nspontaneously rotate. Stability of the condensate soliton in the spatially\nasymmetric trap is analyzed. In addition to the nonlinear dynamics of\nnon-equilibrium Bose-Einstein condensates of ultra-cold atoms, our findings can\nbe applied to the condensates of quantum well excitons and cavity polaritons in\nsemiconductor heterostructure, and to the condensates of photons.",
        "positive": "Multi-speed prethermalization in spin models with power-law decaying\n  interactions: The relaxation of uniform quantum systems with finite-range interactions\nafter a quench is generically driven by the ballistic propagation of long-lived\nquasi-particle excitations triggered by a sufficiently small quench. Here we\ninvestigate the case of long-range ($1/r^{\\alpha}$) interactions for\n$d$-dimensional lattice spin models with uniaxial symmetry, and show that, in\nthe regime $d < \\alpha < d+2$, the entanglement and correlation buildup is\nradically altered by the existence of a non-linear dispersion relation of\nquasi-particles, $\\omega\\sim k^{z<1}$, at small wave vectors, leading to a\ndivergence of the quasiparticle group velocity and super-ballistic propagation.\nThis translates in a super-linear growth of correlation fronts with time, and\nsub-linear growth of relaxation times of subsystem observables with size, when\nfocusing on $k=0$ fluctuations. Yet the large dispersion in group velocities\nleads to an extreme wavelength dependence of relaxation times of finite-$k$\nfluctuations, with entanglement being susceptible to the longest of them. Our\npredictions are directly relevant to current experiments probing the\nnonequilibrium dynamics of trapped ions, or ultracold magnetic and Rydberg\natoms in optical lattices."
    },
    {
        "anchor": "Probing Entanglement in Adiabatic Quantum Optimization with Trapped Ions: Adiabatic quantum optimization has been proposed as a route to solve\nNP-complete problems, with a possible quantum speedup compared to classical\nalgorithms. However, the precise role of quantum effects, such as entanglement,\nin these optimization protocols is still unclear. We propose a setup of cold\ntrapped ions that allows one to quantitatively characterize, in a controlled\nexperiment, the interplay of entanglement, decoherence, and non-adiabaticity in\nadiabatic quantum optimization. We show that, in this way, a broad class of\nNP-complete problems becomes accessible for quantum simulations, including the\nknapsack problem, number partitioning, and instances of the max-cut problem.\nMoreover, a general theoretical study reveals correlations of the success\nprobability with entanglement at the end of the protocol. From exact numerical\nsimulations for small systems and linear ramps, however, we find no substantial\ncorrelations with the entanglement during the optimization. For the final\nstate, we derive analytically a universal upper bound for the success\nprobability as a function of entanglement, which can be measured in experiment.\nThe proposed trapped-ion setups and the presented study of entanglement address\npertinent questions of adiabatic quantum optimization, which may be of general\ninterest across experimental platforms.",
        "positive": "Pairing in population imbalanced Fermion systems: We use Quantum Monte Carlo (QMC) simulations to study the pairing mechanism\nin a one-dimensional fermionic system governed by the Hubbard model with\nattractive contact interaction and with imbalance between the two spin\npopulations. This is done for the uniform system and also for the system\nconfined in a harmonic trap to compare with experiments on confined ultra-cold\natoms. In the uniform case we determine the phase diagram in the\npolarization-temperature plane and find that the\n\"Fulde-Ferrell-Larkin-Ovchinnikov\" (FFLO) phase is robust and persists to\nhigher temperature for higher polarization. In the confined case, we also find\nthat the FFLO phase is stabilized by higher polarization and that it is within\nthe range of detection of experiments currently underway."
    },
    {
        "anchor": "Efimov spectrum in bosonic systems with increasing number of particles: It is well-known that three-boson systems show the Efimov effect when the\ntwo-body scattering length $a$ is large with respect to the range of the\ntwo-body interaction. This effect is a manifestation of a discrete scaling\ninvariance (DSI). In this work we study DSI in the $N$-body system by analysing\nthe spectrum of $N$ identical bosons obtained with a pairwise gaussian\ninteraction close to the unitary limit. We consider different universal ratios\nsuch as $E_N^0/E_3^0$ and $E_N^1/E_N^0$, with $E_N^i$ being the energy of the\nground ($i=0$) and first-excited ($i=1$) state of the system, for $N\\le16$. We\ndiscuss the extension of the Efimov radial law, derived by Efimov for $N=3$, to\ngeneral $N$.",
        "positive": "Tunneling Time of Bose-Einstein Condensates on Real Time Stochastic\n  Approach: We study tunneling processes of Bose-Einstein condensate (BEC) on the real\ntime stochastic approach and reveal some properties of their tunneling time. An\nimportant result is that the tunneling time decreases as the repulsive\ninteratomic interaction becomes stronger. Furthermore, the tunneling time in a\nstrong interaction region is not much affected by the potential height and is\nrepresented by an almost constant function. We also obtain the other related\ntimes such as the hesitating and interaction ones and investigate their\ndependence on the interaction strength. Finally, we calculate the mean arrival\ntime of BEC wave packet and show the large displacement of its peak position."
    },
    {
        "anchor": "Spin dynamics and Andreev-Bashkin effect in mixtures of one-dimensional\n  Bose gases: We investigate the propagation of spin waves in two-component mixtures of\none-dimensional Bose gases interacting through repulsive contact potentials. By\nusing quantum Monte Carlo methods we calculate static ground-state properties,\nsuch as the spin susceptibility and the spin structure factor, as a function of\nboth the intra-species and inter-species coupling strength and we determine the\ncritical parameters for phase separation. In homogeneous mixtures, results of\nthe velocity of spin waves and of its softening close to the critical point of\nphase separation are obtained by means of a sum-rule approach. We quantify the\nnon-dissipative drag effect, resulting from the Andreev-Bashkin current-current\ninteraction between the two components of the gas, and we show that in the\nregime of strong coupling it causes a significant suppression of the spin-wave\nvelocity.",
        "positive": "Mass-driven vortex collisions in flat superfluids: Quantum vortices are often endowed with an effective inertial mass, due, for\nexample, to massive particles in their cores. Such \"massive vortices\" display\nnew phenomena beyond the standard picture of superfluid vortex dynamics, where\nthe mass is neglected. In this work, we demonstrate that massive vortices are\nallowed to collide, as opposed to their massless counterparts. We propose a\nscheme to generate controllable, repeatable, deterministic collisional events\nin pairs of quantum vortices. We demonstrate two mass-driven fundamental\nprocesses: (i) the annihilation of two counter-rotating vortices and (ii) the\nmerging of two co-rotating vortices, thus pointing out new mechanisms\nsupporting incompressible-to-compressible kinetic energy conversion, as well as\ndoubly-quantized vortices stabilization in flat superfluids."
    },
    {
        "anchor": "Short note on the excitonic Mott phase: An exciton gas on a lattice is analyzed in terms of a convergent hopping\nexpansion. For a given chemical potential our calculation provides a sufficient\ncondition for the hopping rate to obtain an exponential decay of the exciton\ncorrelation function. This result indicates the existence of a Mott phase in\nwhich strong fluctuations destroy the long range correlations in the exciton\ngas at any temperature, either by thermal or by quantum fluctuations.",
        "positive": "Chiral Rashba spin textures in ultra-cold Fermi gases: Spin-orbit coupling is an important ingredient in many recently discovered\nphenomena such as the spin-Hall effect and topological insulators. Of\nparticular interest is topological superconductivity, with its potential\napplication in topological quantum computation. The absence of disorder in\nultra-cold atomic systems makes them ideal for quantum computation\napplications, however, the spin-orbit (SO) coupling schemes proposed thus far\nare experimentally impractical owing to large spontaneous emission rates in the\nalkali fermions. In this paper, we develop a scheme to generate Rashba SO\ncoupling with a low spontaneous emission extension to a recent experiment. We\nshow that this scheme generates a Fermi surface spin texture for $^{40}\\rm{K}$\natoms, which is observable in time-of-flight measurements. The chiral spin\ntexture, together with conventional $s$-wave interactions leads to topological\nsuperconductivity and non-Abelian Majorana quasiparticles."
    },
    {
        "anchor": "Response to comment on \"Lack of a genuine time crystal in a chiral\n  soliton model\" by \u00d6hberg and Wright: In the paper [Phys. Rev. Research 2, 032038] we have analyzed a chiral\nsoliton model and shown that despite the claim of \\\"Ohberg and Wright [Phys.\nRev. Lett. 124, 178902], there is no indication that a genuine quantum time\ncrystal can be observed in the system. Here, we response to the recent comment\non our paper written by \\\"Ohberg and Wright.",
        "positive": "Enhanced magnetic sensitivity with non-gaussian quantum fluctuations: The precision of a quantum sensor can overcome its classical counterpart when\nits constituents are entangled. In gaussian squeezed states, quantum\ncorrelations lead to a reduction of the quantum projection noise below the shot\nnoise limit. However, the most sensitive states involve complex non-gaussian\nquantum fluctuations, making the required measurement protocol challenging.\nHere we measure the sensitivity of non-classical states of the electronic spin\n$J = 8$ of dysprosium atoms, created using light-induced non-linear spin\ncoupling. Magnetic sublevel resolution enables us to reach the optimal\nsensitivity of non-gaussian (oversqueezed) states, well above the capability of\nsqueezed states and about half the Heisenberg limit."
    },
    {
        "anchor": "Superfluidity in density imbalanced bilayers of dipolar fermions: We study the zero temperature phase diagram of an imbalanced bilayer of\ndipolar fermions. We consider perpendicularly aligned identical dipoles in two\nlayers and investigate the effect of population imbalance on the ground state\nphase at different layer spacings and average densities. The attractive part of\nthe interlayer interaction could lead to the BEC-BCS crossover and the Fermi\nsurface mismatch between two layers results in interesting uniform and\nnonuniform superfluid phases, which we have investigated here using the BCS\nmean-field theory together with the superfluid-mass density criterion. The\ndensity imbalance reduces the pairing gap. At low densities, where the system\nis on the BEC side of the crossover, this reduction is quite smooth while a\ndense system rapidly becomes normal at intermediate density polarizations.\nStable homogeneous superfluidity is predicted to appear on the phase diagram\nwhen the dipolar length exceeds both the layer spacing and the average\nintralayer distance between dipoles, a regime which should be readily\naccessible experimentally. This homogeneous superfluid phase becomes unstable\nat intermediate densities and layer spacings. We have also examined that these\nuniform and inhomogeneous superfluid phases survive when the effects of\nintralayer screenings are also incorporated in the formalism.",
        "positive": "Cavity optomechanics with synthetic Landau levels of ultra cold Fermi\n  gas: Ultra cold fermionic atoms placed in a synthetic magnetic field arrange\nthemselves in Landau levels. We theoretically study the optomechanical\ninteraction between the light field and collective excitations of such\nfermionic atoms in synthetic magnetic field by placing them in side a Fabry\nPerot cavity. We derive the effective hamiltonian for particle hole excitations\nfrom a filled Landau level using a bosonization technique and obtain an\nexpression for the cavity transmission spectrum. Using this we show that the\ncavity transmission spectrum demonstrates cold atom analogue of Subnikov de\nHass oscillation in electronic condensed matter systems. We discuss the\nexperimental consequences for this oscillation for such system and the related\noptical bistability."
    },
    {
        "anchor": "Vortex and half-vortex dynamics in a spinor quantum fluid of interacting\n  polaritons: Spinorial or multi-component Bose-Einstein condensates may sustain fractional\nquanta of circulation, vorticant topological excitations with half integer\nwindings of phase and polarization. Matter-light quantum fluids, such as\nmicrocavity polaritons, represent a unique test bed for realising strongly\ninteracting and out-of-equilibrium condensates. The direct access to the phase\nof their wavefunction enables us to pursue the quest of whether half vortices\n---rather than full integer vortices--- are the fundamental topological\nexcitations of a spinor polariton fluid. Here, we are able to directly generate\nby resonant pulsed excitations, a polariton fluid carrying either the half or\nfull vortex states as initial condition, and to follow their coherent evolution\nusing ultrafast holography. Surprisingly we observe a rich phenomenology that\nshows a stable evolution of a phase singularity in a single component as well\nas in the full vortex state, spiraling, splitting and branching of the initial\ncores under different regimes and the proliferation of many vortex anti-vortex\npairs in self generated circular ripples. This allows us to devise the\ninterplay of nonlinearity and sample disorder in shaping the fluid and driving\nthe phase singularities dynamics",
        "positive": "Matter-wave localization in a random potential: By numerical and variational solution of the Gross-Pitaevskii equation, we\nstudied the localization of a noninteracting and weakly-interacting\nBose-Einstein condensate (BEC) in a disordered cold atom lattice and a speckle\npotential. In the case of a single BEC fragment, the variational analysis\nproduced good results. For a weakly disordered potential, the localized BECs\nare found to have an exponential tail as in weak Anderson localization. We also\ninvestigated the expansion of a noninteracting BEC in these potential. We find\nthat the BEC will be locked in an appropriate localized state after an initial\nexpansion and will execute breathing oscillation around a mean shape when a BEC\nat equilibrium in a harmonic trap is suddenly released into a disorder\npotential."
    },
    {
        "anchor": "Collectively induced many-vortices topology via rotatory Dicke quantum\n  phase transition: We examine the superradiance of a Bose-Einstein condensate pumped with a\nLaguerre-Gaussian laser of high winding number, e.g., $\\ell = 7$. The laser\nbeam transfers its orbital angular momentum (OAM) to the condensate at once due\nto the collectivity of the superradiance. An $\\ell$-fold rotational symmetric\nstructure emerges with the take place of rotatory superradiance. $\\ell$ number\nof single-charge vortices appear at the arms of this structure. Even though the\npump and the condensate profiles initially have cylindrical symmetry, we\nobserve that it is broken to $\\ell$-fold rotational symmetry during the\nsuperradiance. Breaking of the cylindrical symmetry into the $\\ell$-fold\nsymmetry and OAM transfer to the BEC become possible after the same critical\npump strength. Reorganization of the condensate resembles the ordering in the\nexperiment by Esslinger and colleagues [Nature, {\\bf 264}, 1301 (2010)]. We\nshow that the critical point for the onset of the reorganization follows the\nform of the Dicke quantum phase transition.",
        "positive": "Three-component topological superfluid in one-dimensional Fermi gases\n  with spin-orbit coupling: We theoretically investigate one-dimensional three-component\nspin-orbit-coupled Fermi gases in the presence of Zeeman field. By solving the\nBogoliubov-de-Gennes equations, we obtain the phase diagram at given chemical\npotential and order parameter. We show that the system undergoes a phase\ntransition from Bardeen-Cooper-Schrieffer superfluid to topological superfluid\nas increasing the intensity of Zeeman field. By comparing to the two-component\nsystem, we find, besides the topological phase transition from the trivial\nsuperfluid to nontrivial topological superfluid, the system can always be in a\nnontrivial topological superfluid, and there are two Majorana zero energy\nregions while increasing the magnetic field. We find the three-component\nspin-orbit-coupled Fermi gases in certain parameter range is more optimizing\nfor experimental realization due to the smaller magnetic field needed. We\ntherefore propose a promising candidate for realizing topological superfluid."
    },
    {
        "anchor": "Shear viscosity in a superfluid cold Fermi gas at unitarity: We analyze the contributions of Nambu-Goldstone modes to the shear viscosity\nof a superfluid atomic Fermi gas close to unitarity. We show that the low\ntemperature experimental values of the shear viscosity to entropy ratio,\n$\\eta/s$, are reproduced considering an effective shear viscosity which takes\ninto account the collisions among Nambu-Goldstone bosons and the finite size of\nthe optical trap. We predict that, for $T \\lesssim 0.1 T_F$, $\\eta/s$ should\ncorrelate with the size of the trap and linearly decrease with decreasing\ntemperature. For $T \\gtrsim 0.1 T_F$, we find agreement with the experimental\ndata assuming that the Nambu-Goldstone modes have an anomalous dispersion law.",
        "positive": "Observation of Floquet band topology change in driven ultracold Fermi\n  gases: Periodic driving of a quantum system can significantly alter its energy bands\nand even change the band topology, opening a completely new avenue for\nengineering novel quantum matter. Although important progress has been made\nrecently in measuring topological properties of Floquet bands in different\nsystems, direct experimental measurement of Floquet band dispersions and their\ntopology change is still demanding. Here we directly measure Floquet band\ndispersions in a periodically driven spin-orbit coupled ultracold Fermi gas.\nUsing spin injection radio-frequency spectroscopy, we observe that the Dirac\npoint originating from two dimensional spin-orbit coupling can be manipulated\nto emerge at the lowest or highest two dressed bands by fast modulating Raman\nlaser frequencies, demonstrating topological change of Floquet bands. Our work\nwill provide a powerful tool for understanding fundamental Floquet physics as\nwell as engineering exotic topological quantum matter."
    },
    {
        "anchor": "Nearest-Neighbor Tunneling Ansatz in the Bose-Hubbard Mode: A recently introduced recurrence-relation ansatz applied to the\nJaynes-Cummings-Hubbard model is here applied to the Bose-Hubbard model that\nreduced the model to an easily soluble model. The results obtained for the\ntwo-point density correlations resemble somewhat those obtained recently also\nbut in a much more complicated fashion. Our ansatz may be of value for the\nsolution of many-body quantum mechanical problems.",
        "positive": "On the finite-size effects in two segregated Bose-Einstein condensates\n  restricted by a hard wall: The finite-size effects in two segregated Bose-Einstein condensates (BECs)\nrestricted by a hard wall is studied by means of the Gross-Pitaevskii equations\nin the double-parabola approximation (DPA). Starting from the consistency\nbetween the boundary conditions (BCs) imposed on condensates in confined\ngeometry and in the full space, we find all possible BCs together with the\ncorresponding condensate profiles and interface tensions. We discover two\nfinite-size effects: a) The ground state derived from the Neumann BC is stable\nwhereas the ground states derived from the Robin and Dirichlet BCs are\nunstable. b) Thereby, there equally manifest two possible wetting phase\ntransitions originating from two unstable states. However, the one associated\nwith the Robin BC is more favourable because it corresponds to a smaller\ninterface tension."
    },
    {
        "anchor": "Critical Vortex Shedding in a Strongly Interacting Fermionic Superfluid: We study the critical vortex shedding in a strongly interacting fermionic\nsuperfluid of $^{6}$Li across the BEC-BCS crossover. By moving an optical\nobstacle in the sample and directly imaging the vortices after time of flight,\nthe critical velocity $v_{{\\rm c}}$ for vortex shedding is measured as a\nfunction of the obstacle travel distance $L$. The observed $v_{\\rm c}$\nincreases with decreasing $L$, where the rate of increase is the highest in the\nunitary regime. In the deep BEC regime, an empirical dissipation model well\ncaptures the dependence of $v_{{\\rm c}}$ on $L$, characterized by a constant\nvalue of $\\eta = -\\frac{{\\rm d}(1/v_{{\\rm c}})}{{\\rm d}(1/L)}$. However, as the\nsystem is tuned across the resonance, a step increase of $\\eta$ develops about\na characteristic distance $L_{\\rm c}$ as $L$ is increased, where $L_{\\rm c}$ is\ncomparable to the obstacle size. This bimodal behavior is strengthened as the\nsystem is tuned towards the BCS regime. We attribute this evolution of $v_{{\\rm\nc}}$ to the participation of pair breaking in the vortex shedding dynamics of a\nfermionic superfluid.",
        "positive": "Transversal effects on the ground-state of hard-core dipolar bosons in\n  one-dimensional optical lattices: Polar lattice gases are usually assumed to have an inter-site interaction\nthat decays with the inter-particle distance $r$ as $1/r^3$. However, a\nloose-enough transversal confinement may strongly modify the dipolar decay in\none-dimensional lattices. We show that this modification alters significantly\nthe ground-state properties of hard-core dipolar bosons. For repulsive\ninter-site interactions, the corrected decay alters the conditions for devil's\nstaircase insulators, affecting significantly the particle distribution in the\npresence of an overall harmonic confinement. For attractive interactions, it\nresults in a reduction of the critical dipole interaction for the formation of\nself-bound clusters, and for a marked enhancement of the region of liquefied\nlattice droplets."
    },
    {
        "anchor": "Dimensional reduction and localization of a Bose-Einstein condensate in\n  a quasi-1D bichromatic optical lattice: We analyze the localization of a Bose-Einstein condensate (BEC) in a\none-dimensional bichromatic quasi-periodic optical-lattice potential by\nnumerically solving the 1D Gross-Pitaevskii equation (1D GPE). We first derive\nthe 1D GPE from the dimensional reduction of the 3D quantum field theory of\ninteracting bosons obtaining two coupled differential equations (for axial\nwavefuction and space-time dependent transverse width) which reduce to the 1D\nGPE under strict conditions. Then, by using the 1D GPE we report the\nsuppression of localization in the interacting BEC when the repulsive\nscattering length between bosonic atoms is sufficiently large.",
        "positive": "Quantum correlations and spatial localization in one-dimensional\n  ultracold bosonic mixtures: We present the complete phase diagram for one-dimensional binary mixtures of\nbosonic ultracold atomic gases in a harmonic trap. We obtain exact results with\ndirect numerical diagonalization for small number of atoms, which permits us to\nquantify quantum many-body correlations. The quantum Monte Carlo method is used\nto calculate energies and density profiles for larger system sizes. We study\nthe system properties for a wide range of interaction parameters. For the\nextreme values of these parameters, different correlation limits can be\nidentified, where the correlations are either weak or strong. We investigate in\ndetail how the correlation evolve between the limits. For balanced mixtures in\nthe number of atoms in each species, the transition between the different\nlimits involves sophisticated changes in the one- and two-body correlations.\nParticularly, we quantify the entanglement between the two components by means\nof the von Neumann entropy. We show that the limits equally exist when the\nnumber of atoms is increased, for balanced mixtures. Also, the changes in the\ncorrelations along the transitions among these limits are qualitatively\nsimilar. We also show that, for imbalanced mixtures, the same limits with\nsimilar transitions exist. Finally, for strongly imbalanced systems, only two\nlimits survive, i.e., a miscible limit and a phase-separated one, resembling\nthose expected with a mean-field approach."
    },
    {
        "anchor": "Influence of thermal effects on atomic Bloch oscillation: Advancements in the experimental toolbox of cold atoms have enabled the\nmeticulous control of atomic Bloch oscillation within optical lattices, thereby\nenhancing the capabilities of gravity interferometers. This work delves into\nthe impact of thermal effects on Bloch oscillation in 1D accelerated optical\nlattices aligned with gravity by varying the system's initial temperature.\nThrough the application of Raman cooling, we effectively reduce the\nlongitudinal thermal effect, stabilizing the longitudinal coherence length over\nthe timescale of its lifetime. The atomic losses over multiple Bloch\noscillation is measured, which are primarily attributed to transverse\nexcitation. Furthermore, we identify two distinct inverse scaling behaviors in\nthe oscillation lifetime scaled by the corresponding density with respect to\ntemperatures, implying diverse equilibrium processes within or outside the\nBose-Einstein condensate regime. The competition between the system's coherence\nand atomic density leads to a relatively smooth variation in the actual\nlifetime versus temperature. Our findings provide valuable insights into the\ninteraction between thermal effects and Bloch oscillation, offering avenues for\nthe refinement of quantum measurement technologies.",
        "positive": "Bloch Oscillations in Optical and Zeeman Lattices in the Presence of\n  Spin-Orbit Coupling: We address Bloch oscillations of a spin-orbit coupled atom in periodic\npotentials of two types: Optical and Zeeman lattices. We show that in optical\nlattices the spin-orbit coupling allows controlling the direction of atomic\nmotion and may lead to complete suppression of the oscillations at specific\nvalues of the coupling strength. In Zeeman lattices the energy bands are found\nto cross each other at the boundaries of the Brillouin zone, resulting in\nperiod-doubling of the oscillations. In all cases, the oscillations are\naccompanied by rotation of the pseudo-spin, with a dynamics that is determined\nby the strength of the spin-orbit coupling. The predicted effects are discussed\nalso in terms of a Wannier-Stark ladder, which in optical lattices consist of\ntwo mutually-shifted equidistant sub-ladders."
    },
    {
        "anchor": "Dipole Interaction Mediated Laser Cooling of Polar Molecules to\n  Ultra-cold Temperatures: We present a method to design a finite decay rate for excited rotational\nstates in polar molecules. The setup is based on a hybrid system of polar\nmolecules with atoms driven into a Rydberg state. The atoms and molecules are\ncoupled via the strong dipolar exchange interaction between two rotation levels\nof the polar molecule and two Rydberg states. Such a controllable decay rate\nopens the way to optically pump the hyperfine levels of polar molecules and it\nenables the application of conventional laser cooling techniques for cooling\npolar molecules into quantum degeneracy.",
        "positive": "Mesoscopic quantum switching of a Bose-Einstein condensate in an optical\n  lattice governed by the parity of the number of atoms: It is shown that for a $N$-boson system the parity of $N$ can be responsible\nfor a qualitative difference in the system response to variation of a\nparameter. The nonlinear boson model is considered, which describes tunneling\nof boson pairs between two distinct modes $X_{1,2}$ of the same energy and\napplies to a Bose-Einstein condensate in an optical lattice. By varying the\nlattice depth one induces the parity-dependent quantum switching, i.e. $X_1\\to\nX_2$ for even $N$ and $X_1\\to X_1$ for odd $N$, for arbitrarily large $N$. A\nsimple scheme is proposed for observation of the parity effect on the\n\\textit{mesoscopic scale} by using the bounce switching regime, which is\ninsensitive to the initial state preparation (as long as only one of the two\n$X_l$ modes is significantly populated), stable under small perturbations and\nrequires an experimentally accessible coherence time."
    },
    {
        "anchor": "Crystalline Phases of Laser-Driven Dipolar Bose-Einstein Condensates: Although crystallization is a ubiquitous phenomenon in nature, crystal\nformation and melting still remain fascinating processes with several open\nquestions yet to be addressed. In this work, we study the emergent\ncrystallization of a laser-driven dipolar Bose-Einstein condensate due to the\ninterplay between long-range magnetic and effectively infinite-range\nlight-induced interactions. The competition between these two interactions\nresults in a collective excitation spectrum with two roton minima that\nintroduce two different length scales at which crystalline order can emerge. In\naddition to the formation of regular crystals with simple periodic patterns due\nto the softening of one of the rotons, we find that both rotons can also soften\nsimultaneously, resulting in the formation of exotic, complex periodic or\naperiodic density patterns. We also demonstrate dynamic state-preparation\nschemes for achieving all the found crystalline ground states for\nexperimentally relevant and feasible parameter regimes",
        "positive": "Relaxation dynamics of an isolated large-spin Fermi gas far from\n  equilibrium: A fundamental question in many-body physics is how closed quantum systems\nreach equilibrium. We address this question experimentally and theoretically in\nan ultracold large-spin Fermi gas where we find a complex interplay between\ninternal and motional degrees of freedom. The fermions are initially prepared\nfar from equilibrium with only a few spin states occupied. The subsequent\ndynamics leading to redistribution among all spin states is observed\nexperimentally and simulated theoretically using a kinetic Boltzmann equation\nwith full spin coherence. The latter is derived microscopically and provides\ngood agreement with experimental data without any free parameters. We identify\nseveral collisional processes, which occur on different time scales. By varying\ndensity and magnetic field, we control the relaxation dynamics and are able to\ncontinuously tune the character of a subset of spin states from an open to a\nclosed system."
    },
    {
        "anchor": "Quantitative estimation of effective viscosity in quantum turbulence: We study freely decaying quantum turbulence by performing high resolution\nnumerical simulations of the Gross-Pitaevskii equation (GPE) in the\nTaylor-Green geometry. We use resolutions ranging from $1024^3$ to $4096^3$\ngrid points. The energy spectrum confirms the presence of both a Kolmogorov\nscaling range for scales larger than the intervortex scale $\\ell$, and a second\ninertial range for scales smaller than $\\ell$. Vortex line visualizations show\nthe existence of substructures formed by a myriad of small-scale knotted\nvortices. Next, we study finite temperature effects in the decay of quantum\nturbulence by using the stochastic Ginzburg-Landau equation to generate thermal\nstates, and then by evolving a combination of these thermal states with the\nTaylor-Green initial conditions using the GPE. We extract the mean free path\nout of these simulations by measuring the spectral broadening in the Bogoliubov\ndispersion relation obtained from spatio-temporal spectra, and use it to\nquantify the effective viscosity as a function of the temperature. Finally, in\norder to compare the decay of high temperature quantum and that of classical\nflows, and to further calibrate the estimations of viscosity from the mean free\npath in the GPE simulations, we perform low Reynolds number simulations of the\nNavier-Stokes equations.",
        "positive": "SU(1,1) echoes for breathers in quantum gases: Though the celebrated spin echoes have been widely used to reverse quantum\ndynamics, they are not applicable to systems whose constituents are beyond the\ncontrol of the su(2) algebra. Here, we design echoes to reverse quantum\ndynamics of breathers in three-dimensional unitary fermions and two-dimensional\nbosons and fermions with contact interactions, which are governed by an\nunderlying su(1,1) algebra. Geometrically, SU(1,1) echoes produce closed\ntrajectories on a single or multiple Poincare disks and thus could recover any\ninitial states without changing the sign of the Hamiltonian. In particular, the\ninitial shape of a breather determines the superposition of trajectories on\nmultiple Poincare disks and whether the revival time has period multiplication.\nOur work provides physicists with a recipe to tailor collective excitations of\ninteracting many-body systems."
    },
    {
        "anchor": "Pump-probe coupling of matter wave packets to remote lattice states: The coherent manipulation of wave packets is an important tool in many areas\nof physics. We demonstrate the experimental realization of quasi-free wave\npackets of ultra-cold atoms bound by an external harmonic trap. The wave\npackets are produced by modulating the intensity of an optical lattice\ncontaining a Bose-Einstein condensate. The evolution of these wave packets is\nmonitored in-situ and their reflection on a band gap is observed. In direct\nanalogy with pump-probe spectroscopy, a probe pulse allows for the resonant\nde-excitation of the wave packet into localized lattice states at a long,\ncontrollable distance of more than 100 lattice sites from the main component.\nThis coherent control mechanism for ultra-cold atoms thus enables controlled\nquantum state preparation, opening exciting perspectives for quantum metrology\nand simulation.",
        "positive": "Nonlinear Inverse Spin Galvanic Effect in Anisotropic Disorder-free\n  Systems: Spin transport phenomena in solid materials suffer limitations from spin\nrelaxation associated to disorder or lack of translational invariance.\nUltracold atoms, free of that disorder, can provide a platform to observe\nphenomena beyond the usual two-dimensional electron gas. By generalizing the\napproach used for isotropic two-dimensional electron gases, we theoretically\ninvestigate the inverse spin galvanic effect in the two-level atomic system in\nthe presence of anisotropic Rashba-Dresselhaus spin-orbit couplings (SOC) and\nexternal magnetic field. We show that the combination of the SOC results in an\nasymmetric case: the total spin polarization considered for a small momentum\nhas a longer spin state than in a two-dimensional electron gas when the SOC\nfield prevails over the external electric field. Our results can be relevant\nfor advancing experimental and theoretical investigations in spin dynamics as a\nbasic approach for studying spin state control."
    },
    {
        "anchor": "Theoretical and numerical evidence for the potential realization of the\n  Peregrine soliton in repulsive two-component Bose-Einstein condensates: The present work is motivated by the recent experimental realization of the\nTownes soliton in an effective two-component Bose-Einstein condensate by B.\nBakkali-Hassan et al. [Phys. Rev. Lett. 127, 023603 (2021)]. Here, we use a\nsimilar multicomponent platform to exemplify theoretically and numerically,\nwithin the mean-field Gross-Pitaevskii framework, the potential toward the\nexperimental realization of a different fundamental wave structure, namely the\nPeregrine soliton. Leveraging the effective attractive interaction produced\nwithin the mixture's minority species in the immiscible regime, we illustrate\nhow initialization of the condensate with a suitable power-law decaying spatial\ndensity pattern yields the robust emergence of the Peregrine wave in the\nabsence and in the presence of a parabolic trap. We then showcase the\nspontaneous emergence of the Peregrine soliton via a suitably crafted wide\nGaussian initialization, again both in the homogeneous case and in the trap\nscenario. It is also found that narrower wave packets may result in periodic\nrevivals of the Peregrine soliton, while broader ones give rise to a cascade of\nPeregrine solitons arranged in a so-called Christmas-tree structure.\nStrikingly, the persistence of these rogue-wave structures is demonstrated in\ncertain temperature regimes as well as in the presence of transversal\nexcitations through three-dimensional computations in a quasi-one-dimensional\nregime. This proof-of-principle illustration is expected to represent a\npractically feasible way to generate and observe this rogue wave in realistic\ncurrent ultracold atom experimental settings.",
        "positive": "Recurrence time in the quantum dynamics of the 1D Bose gas: Recurrence time is evaluated for some initial quantum states in the\none-dimensional Bose gas with repulsive short-range interactions. In the\nrelatively strong and weak coupling cases some different types of initial\nstates show almost complete recurrence and the estimates of recurrence time are\nproportional to some powers of the system size at least in some range of the\nsystem size. They are much longer than in the case of free particles such as\n100 times. In the free-bosonic and free-fermionic regimes we evaluate the\nrecurrence time rigorously, which is proportional to the square of the system\nsize. The estimate of recurrence time is given by the order of ten milliseconds\nin the corresponding experimental systems of cold atoms trapped in one\ndimension of ten micrometers in length. It is much shorter than the estimate in\na generic quantum many-body system, which may be as long as the age of the\nuniverse."
    },
    {
        "anchor": "Metamorphoses of the flow past an obstacle of a resonantly-driven\n  bistable polariton fluid: Motivated by recent experiments, we theoretically analyze the flow past an\nobstacle of a one-dimensional \"quantum fluid of light\" which is resonantly\ndriven, and exhibits bistability. The flow is found to abruptly change several\ntimes when the fluid velocity or the obstacle potential strength are increased.\nIn contrast to the cases of usual fluids and superfluids, the transitions take\nplace between stationary states. They involve the fluid bistability in an\nessential way. Remarkably, at the transitions points, the fluid in the obstacle\nwake lies in the unstable intermediate density state.",
        "positive": "OpenMP Fortran programs for solving the time-dependent dipolar\n  Gross-Pitaevskii equation: In this paper we present Open Multi-Processing (OpenMP) Fortran 90/95\nversions of previously published numerical programs for solving the dipolar\nGross-Pitaevskii (GP) equation including the contact interaction in one, two\nand three spatial dimensions. The atoms are considered to be polarized along\nthe z axis and we consider different cases, e.g., stationary and non-stationary\nsolutions of the GP equation for a dipolar Bose-Einstein condensate (BEC) in\none dimension (along x and z axes), two dimensions (in x-y and x-z planes), and\nthree dimensions. The algorithm used is the split-step semi-implicit\nCrank-Nicolson scheme for imaginary- and real-time propagation to obtain\nstationary states and BEC dynamics, respectively, as in the previous version\n[R. Kishor Kumar et al., Comput. Phys. Commun. 195, 117 (2015)]. These OpenMP\nversions have significantly reduced execution time in multicore processors."
    },
    {
        "anchor": "Rotating quantum turbulence in the unitary Fermi gas: Quantized vortices carry the angular momentum in rotating superfluids, and\nare key to the phenomenon of quantum turbulence. Advances in ultra-cold atom\ntechnology enable quantum turbulence to be studied in regimes with both\nexperimental and theoretical control, unlike the original contexts of\nsuperfluid helium experiments. While much work has been performed with bosonic\nsystems, detailed studies of fermionic quantum turbulence are nascent, despite\nwide applicability to other contexts such as rotating neutron stars. In this\npaper, we present the first large-scale study of quantum turbulence in rotating\nfermionic superfluids using an accurate orbital based time-dependent density\nfunctional theory (DFT) called the superfluid local density approximation\n(SLDA). We identify two different modes of turbulent decay in the dynamical\nequilibration of a rotating fermionic superfluid, and contrast these results\nwith a computationally simpler orbital-free DFT, which we find can\nqualitatively reproduce these decay mechanisms if dissipation is explicitly\nincluded. These results demonstrate that one-body dissipation mechanisms\nintrinsic to fermionic superfluids play a key role differentiating fermionic\nfrom bosonic turbulence, but also suggest that simpler orbital-free theories\nmay be corrected so that these more efficient techniques can be used to model\nextended physical systems such as neutron superfluids in neutron stars.",
        "positive": "Asymmetric many-body loss in a bosonic double well: A Bose gas in a double well is investigated in the presence of\nsingle-particle, two-body and three-body asymmetric loss. The loss induces an\ninteresting decay behavior of the total population as well as a possibility to\ncontrol the dynamics of the system. In the noninteracting limit with asymmetric\nsingle-body dissipation, the dynamics of the populations can be obtained\nanalytically. The general many-body problem requires, however, an adequate\napproximation. We use a mean-field approximation and the Bogoliubov\nback-reaction beyond mean-field truncation, which we extend up to three-body\nloss. Both methods are compared with exact many-body Monte-Carlo simulations."
    },
    {
        "anchor": "Mott insulating phases and magnetism of fermions in a double-well\n  optical lattice: We theoretically investigate, using non-perturbative strong correlation\ntechniques, Mott insulating phases and magnetic ordering of two-component\nfermions in a two-dimensional double-well optical lattice. At filling of two\nfermions per site, there are two types of Mott insulators, one of which is\ncharacterized by spin-1 antiferromagnetism below the Neel temperature. The\nsuper-exchange interaction in this system is induced by the interplay between\nthe inter-band interaction and the spin degree of freedom. A great advantage of\nthe double-well optical lattice is that the magnetic quantum phase diagram and\nthe Neel temperature can be easily controlled by tuning the orbital energy\nsplitting of the two-level system. Particularly, the Neel temperature can be\none order of magnitude larger than that in standard optical lattices,\nfacilitating the experimental search for magnetic ordering in optical lattice\nsystems.",
        "positive": "Frustration and time reversal symmetry breaking for Fermi and Bose-Fermi\n  systems: The modulation of an optical lattice potential that breaks time-reversal\nsymmetry enables the realization of complex tunneling amplitudes in the\ncorresponding tight-binding model. For a superfluid Fermi gas in a triangular\nlattice potential with complex tunnelings the pairing function acquires a\ncomplex phase, so the frustrated magnetism of fermions can be\nrealized.Bose-Fermi mixture of bosonic molecules and unbound fermions in the\nlattice shows also an interesting behavior. Due to boson-fermion coupling, the\nfermions become slaved by the bosons and the corresponding pairing function\ntakes the complex phase determined by bosons. In the presence of bosons the\nFermi system can reveal both gap and gapless superfluidity."
    },
    {
        "anchor": "Complex Langevin simulation of quantum vortices in a Bose-Einstein\n  condensate: The ab-initio simulation of quantum vortices in a Bose-Einstein condensate is\nperformed by adopting the complex Langevin techniques. We simulate the\nnonrelativistic boson field theory at finite chemical potential under rotation.\nIn the superfluid phase, vortices are generated above a critical angular\nvelocity and the circulation is clearly quantized even in the presence of\nquantum fluctuations.",
        "positive": "Investigation of Feshbach Resonances in ultra-cold 40 K spin mixtures: Magnetically-tunable Feshbach resonances are an indispensable tool for\nexperiments with atomic quantum gases. We report on twenty thus far unpublished\nFeshbach resonances and twenty one further probable Feshbach resonances in spin\nmixtures of ultracold fermionic 40 K with temperatures well below 100 nK. In\nparticular, we locate a broad resonance at B=389.6 G with a magnetic width of\n26.4 G. Here 1 G=10^-4 T. Furthermore, by exciting low-energy spin waves, we\ndemonstrate a novel means to precisely determine the zero crossing of the\nscattering length for this broad Feshbach resonance. Our findings allow for\nfurther tunability in experiments with ultracold 40 K quantum gases."
    },
    {
        "anchor": "Probing the Flat Band of Optically-Trapped Spin-Orbital Coupled Bose\n  Gases Using Bragg Spectroscopy: Motivated by the recent efforts in creating the flat band in ultracold atomic\nsystems, we investigate how to probe the flat band in an optically-trapped\nspin-orbital coupled Bose-Einstein condensate using Bragg spectroscopy. We have\nfound that the excitation spectrum and the dynamic structure factor of the\ncondensate alter dramatically, when the band structure exhibits various level\nof flatness. In particular, when the band exhibits perfect flatness around the\nband minima corresponding to a near infinite effective mass, a quadratic\ndispersion emerges in the low-energy excitation spectrum; in sharp contrast,\nfor the opposite case when an ordinary band is present, the familiar linear\ndispersion arises. Such linear-to-quadratic crossover in the energy spectrum\npresents a striking manifestation of the transition of an ordinary band into a\nflat band, thereby allows the direct probe of the flat band by using Bragg\nspectroscopy.",
        "positive": "Polarized Fermi gases at finite temperature in the BCS-BEC crossover: We consider a polarized Fermi gas in the BCS-BEC crossover region above the\ncritical temperature within a T matrix formalism. By treating the mean-field\nlike shift of the quasiparticle energies in a self-consistent manner, we avoid\nthe known pathological behavior of the standard Nozieres-Schmitt-Rink approach\nin the polarized case, i.e., the polarization has the right sign and the spin\npolarizability is positive. The momentum distributions of the correlated system\nare computed and it is shown that, in the zero-temperature limit, they satisfy\nthe Luttinger theorem. Results for the phase diagram, the spin susceptibility,\nand the compressibility are discussed."
    },
    {
        "anchor": "Universal phase structure of dilute Bose gases with Rashba spin-orbit\n  coupling: A Bose gas subject to a light-induced Rashba spin-orbit coupling possesses a\ndispersion minimum on a circle in momentum space; we show that kinematic\nconstraints due to this dispersion cause interactions to renormalize to\nuniversal, angle-dependent values that govern the phase structure in the\ndilute-gas limit. We find that, regardless of microscopic interactions, (a) the\nground state involves condensation at two opposite momenta, and is, in finite\nsystems, a fragmented condensate; and (b) there is a nonzero-temperature\ninstability toward the condensation of pairs of bosons. We discuss how our\nresults can be reconciled with the qualitatively different mean-field phase\ndiagram, which is appropriate for dense gases.",
        "positive": "Dicke Quantum Spin and Photon Glass in Optical Cavities: Non-equilibrium\n  theory and experimental signatures: In the context of ultracold atoms in multimode optical cavities, the\nappearance of a quantum-critical glass phase of atomic spins has been predicted\nrecently. Due to the long-range nature of the cavity-mediated interactions, but\nalso the presence of a driving laser and dissipative processes such as cavity\nphoton loss, the quantum optical realization of glassy physics has no analog in\ncondensed matter, and could evolve into a \"cavity glass microscope\" for\nfrustrated quantum systems out-of-equilibrium. Here we develop the\nnon-equilibrium theory of the multimode Dicke model with quenched disorder and\nMarkovian dissipation. Using a unified Keldysh path integral approach, we show\nthat the defining features of a low temperature glass, representing a critical\nphase of matter with algebraically decaying temporal correlation functions, are\nseen to be robust against the presence of dissipation due to cavity loss. The\nuniversality class however is modified due to the Markovian bath. The presence\nof strong disorder leads to an enhanced equilibration of atomic and photonic\ndegrees of freedom, including the emergence of a common low-frequency effective\ntemperature. The imprint of the atomic spin glass physics onto a \"photon glass\"\nmakes it possible to detect the glass state by standard experimental techniques\nof quantum optics. We provide an unambiguous characterization of the\nsuperradiant and glassy phases in terms of fluorescence spectroscopy, homodyne\ndetection, and the temporal photon correlation function $g^{(2)}(\\tau)$."
    },
    {
        "anchor": "Zero-energy modes of two-component Bose-Bose droplets: Bose-Bose droplets are self-bound objects emerging from a mixture of two\ninteracting Bose-Einstein condensates when their interactions are appropriately\ntuned. During droplet formation three continuous symmetries of the system's\nHamiltonian are broken: translational symmetry and two U1 symmetries, allowing\nfor arbitrary choice of phases of the mean-field wavefunctions describing the\ntwo components. Breaking of these symmetries must be accompanied by appearance\nof zero-energy excitations in the energy spectrum of the system recovering the\nbroken symmetries. Normal modes corresponding to these excitations are the\nzero-energy modes. Here we find analytic expressions for these modes and\nintroduce Hamitonians generating their time evolution -- dynamics of the\ndroplet's centers of mass as well as dynamics of the phases of the two\ndroplet's wavefunctions. When internal types of excitations (quasiparticles)\nare neglected then the very complex system of a quantum droplet is described\nusing only few \"global\" degrees of freedom - the position of the center of mass\nof the droplet and two phases of two wave-functions, all these being quantum\noperators. This gives the possibility of describing in a relatively easy way\nprocesses of interaction of these quantum droplets, such as collisions.",
        "positive": "Dispersive probing of driven pseudo-spin dynamics in a gradient field: We have studied the coherent evolution of ultracold atomic rubidium clouds\nsubjected to a microwave field driving Rabi oscillations between the stretched\nstates of the F=1 and F=2 hyperfine levels. A phase winding of the two-level\nsystem pseudo-spin vector is encountered for elongated samples of atoms exposed\nto an axial magnetic field gradient and can be observed directly in\nstate-selective absorption imaging. When dispersively recording the\nsample-integrated spin population during the Rabi drive, we observe a damped\noscillation directly related to the magnetic field gradient, which we quantify\nusing a simple dephasing model. By analyzing such dispersively acquired data\nfrom millimeter sized atomic samples, we demonstrate that field gradients can\nbe determined with an accuracy of $\\sim25$ nT/mm. The dispersive probing of\ninhomogeneously broadened Rabi oscillations in prolate samples opens up a path\nto gradiometry with bandwidths in the kilohertz domain."
    },
    {
        "anchor": "The universe on a table top: engineering quantum decay of a relativistic\n  scalar field from a metastable vacuum: The quantum decay of a relativistic scalar field from a metastable state\n(\"false vacuum decay\") is a fundamental idea in quantum field theory and\ncosmology. This occurs via local formation of bubbles of true vacuum with their\nsubsequent rapid expansion. It can be considered as a relativistic analog of a\nfirst-order phase transition in condensed matter. Here we expand upon our\nrecent proposal [EPL 110, 56001 (2015)] for an experimental test of false\nvacuum decay using an ultra-cold spinor Bose gas. A false vacuum for the\nrelative phase of two spin components, serving as the unstable scalar field, is\ngenerated by means of a modulated linear coupling of the spin components. We\nanalyze the system theoretically using the functional integral approach and\nshow that various microscopic degrees of freedom in the system, albeit leading\nto dissipation in the relative phase sector, will not hamper the observation of\nthe false vacuum decay in the laboratory. This is well supported by numerical\nsimulations demonstrating the spontaneous formation of true vacuum bubbles on\nmillisecond time-scales in two-component $^{7}$Li or $^{41}$K bosonic\ncondensates in one-dimensional traps of $\\sim100\\,\\mu \\mathrm{m}$ size.",
        "positive": "Scanning electron microscopy of Rydberg-excited Bose-Einstein\n  condensates: We report on the realization of high resolution electron microscopy of\nRydberg-excited ultracold atomic samples. The implementation of an ultraviolet\nlaser system allows us to excite the atom, with a single-photon transition, to\nRydberg states. By using the electron microscopy technique during the Rydberg\nexcitation of the atoms, we observe a giant enhancement in the production of\nions. This is due to $l$-changing collisions, which broaden the Rydberg level\nand therefore increase the excitation rate of Rydberg atoms. Our results pave\nthe way for the high resolution spatial detection of Rydberg atoms in an atomic\nsample."
    },
    {
        "anchor": "Spatially varying interactions induced in atomic gases by optical\n  Feshbach resonance: Optical Feshbach resonance is capable of inducing spatially varying\ninteractions in ultra-cold atoms. Its applications to pancake-shaped clouds of\nbosons and fermions enable one to study several fresh phenomena. We examine\npossibilities of inducing counter-intuitive structures such as creating a\nsuperfluid enclave inside a Mott insulator for bosons and a normal-gas core\nenclosed by a superfluid shell for fermions. We discuss feasible experimental\nsetups and signatures of those interesting structures, which can be very\ndifferent from common structures observed in experiments so far. While a\nsuperfluid enclave in a Mott insulator can be useful for constructing atomic\ndevices for atomtronics, superconducting islands observed in scanning-tunneling\nmicroscopy of heavily underdoped high-temperature superconductors may be\nstudied with cold Fermi gases with spatially varying attractions.",
        "positive": "Symmetry protected bosonic topological phase transitions: Quantum\n  Anomalous Hall system of weakly interacting spinor bosons in a square lattice: We study possible many body phenomena in the Quantum Anomalous Hall system of\nweakly interacting spinor bosons in a square lattice. There are various novel\nspin-bond correlated superfluids (SF) and quantum or topological phase\ntransitions among these SF phases. One transition is a first order one driven\nby roton droppings ( but with non-zero gaps $ \\Delta_R $ ) tuned by the Zeeman\nfield $ h $. Another is a second order bosonic Lifshitz transition with the\ndynamic exponents $ z_x=z_y=2 $ and an accompanying $ [C_4 \\times C_4]_D $\nsymmetry breaking. It is driven by the softening of the superfluid Goldstone\nmode tuned by the ratio of spin-orbit coupled (SOC) strength over the hopping\nstrength. The two phase boundaries meet at a topological tri-critical (TT)\npoint which separates the $ h=0 $ line into two SF phases with $ N=2 $ and $\nN=4 $ condensation momenta respectively. At the $ h=0 $ line where the system\nhas an anti-unitary $ Z_2 $ Reflection symmetry, there are infinite number of\nclassically degenerate family of states on both sides. We perform a systematic\norder from quantum disorder analysis to find the quantum ground states, also\ncalculate the roton gaps $ \\Delta_R $ generated by the order from disorder\nmechanism on both sides of the TT point. The $ N=2 $ and $ N=4 $ SF phases have\nthe same spin-orbital XY-AFM spin structure, respect the anti-unitary symmetry\nand break the $ [C_4 \\times C_4]_D $ symmetry, so they be distinguished only by\nthe different topology of the BEC condensation momenta instead of by any\ndifferences in the symmetry breaking patterns. All these novel quantum or\ntopological phenomena can be probed in the recent experimentally realized\nweakly interacting Quantum Anomalous Hall (QAH) model of $ ^87 Rb $ by Wu, {\\sl\net.al}, Science 354, 83-88 (2016)."
    },
    {
        "anchor": "C programs for solving the time-dependent Gross-Pitaevskii equation in a\n  fully anisotropic trap: We present C programming language versions of earlier published Fortran\nprograms (Muruganandam and Adhikari, Comput. Phys. Commun. 180 (2009) 1888) for\ncalculating both stationary and non-stationary solutions of the time-dependent\nGross-Pitaevskii (GP) equation. The GP equation describes the properties of\ndilute Bose-Einstein condensates at ultra-cold temperatures. C versions of\nprograms use the same algorithms as the Fortran ones, involving real- and\nimaginary-time propagation based on a split-step Crank-Nicolson method. In a\none-space-variable form of the GP equation, we consider the one-dimensional,\ntwo-dimensional, circularly-symmetric, and the three-dimensional\nspherically-symmetric harmonic-oscillator traps. In the two-space-variable\nform, we consider the GP equation in two-dimensional anisotropic and\nthree-dimensional axially-symmetric traps. The fully-anisotropic\nthree-dimensional GP equation is also considered. In addition to these twelve\nprograms, for six algorithms that involve two and three space variables, we\nhave also developed threaded (OpenMP parallelized) programs, which allow\nnumerical simulations to use all available CPU cores on a computer. All 18\nprograms are optimized and accompanied by makefiles for several popular C\ncompilers. We present typical results for scalability of threaded codes and\ndemonstrate almost linear speedup obtained with the new programs, allowing a\ndecrease in execution times by an order of magnitude on modern multi-core\ncomputers.",
        "positive": "Effect of disorder on topological charge pumping in the Rice-Mele model: Recent experiments with ultracold quantum gases have successfully realized\ninteger-quantized topological charge pumping in optical lattices. Motivated by\nthis progress, we study the effects of static disorder on topological Thouless\ncharge pumping. We focus on the half-filled Rice-Mele model of free spinless\nfermions and consider random diagonal disorder. In the instantaneous basis, we\ncompute the polarization, the entanglement spectrum, and the local Chern\nmarker. As a first main result, we conclude that the space-integrated local\nChern marker is best suited for a quantitative determination of topological\ntransitions in a disordered system. In the time-dependent simulations, we use\nthe time-integrated current to obtain the pumped charge in slowly periodically\ndriven systems. As a second main result, we observe and characterize a\ndisorder-driven breakdown of the quantized charge pump. There is an excellent\nagreement between the static and the time-dependent ways of computing the\npumped charge. The topological transition occurs well in the regime where all\nstates are localized on the given system sizes and is therefore not tied to a\ndelocalization-localization transition of Hamiltonian eigenstates. For\nindividual disorder realizations, the breakdown of the quantized pumping occurs\nfor parameters where the spectral bulk gap inherited from the band gap of the\nclean system closes, leading to a globally gapless spectrum. As a third main\nresult and with respect to the analysis of finite-size systems, we show that\nthe disorder average of the bulk gap severely overestimates the stability of\nquantized pumping. A much better estimate is the typical value of the\ndistribution of energy gaps, also called mode of the distribution."
    },
    {
        "anchor": "Composite-Field Goldstone States and Higgs Mechanism in Dilute Bose\n  Gases: We show that a composite-field (diatom) Goldstone state is expected in a\ndilute Bose gas for temperatures between the Bose gas critical temperature\nwhere the atom Bose-Einstein condensate appears and the temperature where\nsuperfluidity sets in. The presence of superfluidity is tied to the existence\nof a U(1) charge-two diatom condensate in the system. By promoting the global\nU(1) symmetry of the theory to a gauge symmetry, we find that the mass of the\ngauge particle generated through the Anderson-Higgs mechanism is related to the\nsuperfluid density via the Meissner effect and the superfluid density is\nrelated to the square of the anomalous density in the Bose system.",
        "positive": "Forming complex neurons by four-wave mixing in a Bose-Einstein\n  condensate: A physical artificial complex-valued neuron is formed by four-wave mixing in\na homogeneous three-dimensional Bose-Einstein condensate. Bragg beamsplitter\npulses prepare superpositions of three plane-waves states as an input- and the\nfourth wave as an output signal. The nonlinear dynamics of the non-degenerate\nfour-wave mixing process leads to Josephson-like oscillations within the closed\nfour-dimensional subspace and defines the activation function of a neuron. Due\nto the high number of symmetries, closed form solutions can be found by\nquadrature and agree with numerical simulation. The ideal behaviour of an\nisolated four-wave mixing setup is compared to a situation with additional\npopulation of rogue states. We observe a robust persistence of the main\noscillation. As an application for neural learning of this physical system, we\ntrain it on the XOR problem. After $100$ training epochs, the neuron responds\nto input data correctly at the $10^{-5}$ error level."
    },
    {
        "anchor": "Anyon optics with time-of-flight two-particle interference of\n  double-well-trapped interacting ultracold atoms: The subject of bianyon interference with ultracold atoms is introduced\nthrough theoretical investigations pertaining to the second-order momentum\ncorrelation maps of two anyons (built upon spinless and spin-1/2 bosonic, as\nwell as spin-1/2 fermionic ultracold atoms) trapped in a double-well optical\ntrap. The two-particle system is modeled according to the recently proposed\nprotocols for emulating an anyonic Hubbard Hamiltonian in ultracold-atom\none-dimensional lattices. Because the second-order momentum correlations are\nmirrored in the time-of-flight second-order interference patterns in space, our\nfindings provide impetus for time-of-flight experimental protocols for\ndetecting anyonic statistics via interferometry measurements of massive\nparticles that broaden the scope of the biphoton interferometry of quantum\noptics.",
        "positive": "Phase ordering kinetics of a nonequilibrium exciton-polariton condensate: We investigate the process of coarsening via annihilation of\nvortex-antivortex pairs, following the quench to the condensate phase in a\nnonresonantly pumped polariton system. We find that the late-time dynamics is\nan example of universal phase ordering kinetics, characterized by scaling of\ncorrelation functions in time. Depending on the parameters of the system, the\nevolution of the characteristic length scale L(t) can be the same as for the\ntwo-dimensional XY model, described by a power law with the dynamical exponent\nz \\aprox 2 and a logarithmic correction, or z \\aprox 1 which agrees with\nprevious studies of conservative superfluids."
    },
    {
        "anchor": "Mott insulator phases of non-locally coupled bosons in bilayer optical\n  superlattices: We investigate the ground state properties of a non-locally coupled bosonic\nsystem in a bilayer optical superlattice by considering bosons in one layer to\nbe of softcore in nature and separately allowing two and three body hardcore\nconstraints on the other layer. We find that the presence of different\nconstraints on bosons in one layer influences the overall phase diagram\nexhibiting various Mott insulator phases at incommensurate densities due to the\npresence of the superlattice potential apart from the usual Mott insulators at\ncommensurate densities. Moreover, the presence of two or three-body constraints\nsignificantly modifies the Mott insulator-Superfluid phase transition points as\na function of the superlattice potential. Due to the various competing\ninteractions, constraints and superlattice potential the phase diagrams exhibit\nsignificantly different features. We obtain the complete phase diagrams by\nusing the cluster-mean-field theory approach. We further extend this work to a\ncoupled two-leg ladder superlattice where we obtain similar physics using the\ndensity matrix renormalization group method .",
        "positive": "An adjustable-length cavity and Bose-Einstein condensate apparatus for\n  multimode cavity QED: We present a novel cavity QED system in which a Bose-Einstein condensate\n(BEC) is trapped within a high-finesse optical cavity whose length may be\nadjusted to access both single-mode and multimode configurations. We\ndemonstrate the coupling of an atomic ensemble to the cavity in both\nconfigurations. The atoms are confined either within an intracavity\nfar-off-resonance optical dipole trap (FORT) or a crossed optical dipole trap\nvia transversely oriented lasers. Multimode cavity QED provides fully emergent\nand dynamical optical lattices for intracavity BECs. Such systems will enable\nexplorations of quantum soft matter, including superfluid smectics, superfluid\nglasses, and spin glasses as well as neuromorphic associative memory."
    },
    {
        "anchor": "Schrieffer-Wolff Transformations for Experiments: Dynamically\n  Suppressing Virtual Doublon-Hole Excitations in a Fermi-Hubbard Simulator: In strongly interacting systems with a separation of energy scales,\nlow-energy effective Hamiltonians help provide insights into the relevant\nphysics at low temperatures. The emergent interactions in the effective model\nare mediated by virtual excitations of high-energy states: For example, virtual\ndoublon-hole excitations in the Fermi-Hubbard model mediate antiferromagnetic\nspin-exchange interactions in the derived effective model, known as the\n$t-J-3s$ model. Formally this procedure is described by performing a unitary\nSchrieffer-Wolff basis transformation. In the context of quantum simulation, it\ncan be advantageous to consider the effective model to interpret experimental\nresults. However, virtual excitations such as doublon-hole pairs can obfuscate\nthe measurement of physical observables. Here we show that quantum simulators\nallow one to access the effective model even more directly by performing\nmeasurements in a rotated basis. We propose a protocol to perform a\nSchrieffer-Wolff transformation on Fermi-Hubbard low-energy eigenstates (or\nthermal states) to dynamically prepare approximate $t-J-3s$ model states using\nfermionic atoms in an optical lattice. Our protocol involves performing a\nlinear ramp of the optical lattice depth, which is slow enough to eliminate the\nvirtual doublon-hole fluctuations but fast enough to freeze out the dynamics in\nthe effective model. We perform a numerical study using exact diagonalization\nand find an optimal ramp speed for which the state after the lattice ramp has\nmaximal overlap with the $t-J-3s$ model state. We compare our numerics to\nexperimental data from our Lithium-6 fermionic quantum gas microscope and show\na proof-of-principle demonstration of this protocol. More generally, this\nprotocol can be beneficial to studies of effective models by enabling the\nsuppression of virtual excitations in a wide range of quantum simulation\nexperiments.",
        "positive": "Floquet Topological States in Shaking Optical Lattices: In this letter we propose realistic schemes to realize topologically\nnontrivial Floquet states by shaking optical lattices, using both one-dimension\nlattice and two-dimensional honeycomb lattice as examples. The topological\nphase in the two-dimensional model exhibits quantum anomalous Hall effect. The\ntransition between topological trivial and nontrivial states can be easily\ncontrolled by shaking frequency and amplitude. Our schemes have two major\nadvantages. First, both the static Hamiltonian and the shaking scheme are\nsufficiently simple to implement. Secondly, it requires relatively small\nshaking amplitude and therefore heating can be minimized. These two advantages\nmake our scheme much more practical."
    },
    {
        "anchor": "Dynamics of imbalanced quasi-one-dimensional binary Bose-Einstein\n  condensate in external potentials: In the framework of coupled 1D Gross-Pitaevskii equations, we explore the\ndynamics of a binary Bose-Einstein condensate where the intra-component\ninteraction is repulsive, while the inter-component one is attractive. The\nexistence regimes of stable self-trapped localized states in the form of\nsymbiotic solitons have been analyzed. Imbalanced mixtures, where the number of\natoms in one component exceeds the number of atoms in the other component, are\nconsidered in parabolic potential and box-like trap. When all the intra-species\nand inter-species interactions are repulsive, we numerically find a new type of\nsymbiotic solitons resembling dark-bright solitons. A variational approach has\nbeen developed which allows us to find the stationary state of the system and\nfrequency of small amplitude dynamics near the equilibrium. It is shown that\nthe strength of inter-component coupling can be retrieved from the frequency of\nthe localized state's vibrations.",
        "positive": "Two-Particle Interference with Double Twin-Atom Beams: We demonstrate a source for correlated pairs of atoms characterized by two\nopposite momenta and two spatial modes forming a Bell state only involving\nexternal degrees of freedom. We characterize the state of the emitted atom\nbeams by observing strong number squeezing up to -10 dB in the correlated\ntwo-particle modes of emission. We furthermore demonstrate genuine two-particle\ninterference in the normalized second-order correlation function $g^{(2)}$\nrelative to the emitted atoms."
    },
    {
        "anchor": "Laser cooling of a potassium-argon gas mixture using collisional\n  redistribution of radiation: We study laser cooling of atomic gases by collisional redistribution, a\ntechnique applicable to ultradense atomic ensembles at a pressure of a few\nhundred bar. Frequent collisions of an optically active atom with a buffer gas\nshift atoms into resonance with a far red detuned laser beam, while spontaneous\ndecay occurs close to the unperturbed resonance frequency. In such an\nexcitation cycle, a kinetic energy of the order of the thermal energy kT is\nextracted from the sample. Here we report of recent experiments investigating\nthe cooling of a potassium-argon gas mixture, which compared to an\nrubidium-argon mixture investigated in earlier experiments has a smaller fine\nstructure of the optically active alkali atom. We observe a relative cooling of\nthe potassium-argon gas mixture by 120 K.",
        "positive": "Convergence of a renormalization group approach to dimer-dimer\n  scattering: We study the convergence of a functional renormalisation group technique by\nlooking at the ratio between the fermion-fermion scattering length and the\ndimer-dimer scattering length for a system of nonrelativistic fermions. We find\nthat in a systematic expansion in powers of the fields there is a rapid\nconvergence of the result that agrees with know exact results."
    },
    {
        "anchor": "A long-lived spin-orbit-coupled degenerate dipolar Fermi gas: We describe the creation of a long-lived spin-orbit-coupled gas of quantum\ndegenerate atoms using the most magnetic fermionic element, dysprosium.\nSpin-orbit-coupling arises from a synthetic gauge field created by the\nadiabatic following of degenerate dressed states comprised of optically coupled\ncomponents of an atomic spin. Because of dysprosium's large electronic orbital\nangular momentum and large magnetic moment, the lifetime of the gas is limited\nnot by spontaneous emission from the light-matter coupling, as for gases of\nalkali-metal atoms, but by dipolar relaxation of the spin. This relaxation is\nsuppressed at large magnetic fields due to Fermi statistics. We observe\nlifetimes up to 400 ms, which exceeds that of spin-orbit-coupled fermionic\nalkali atoms by a factor of 10-100, and is close to the value obtained from a\ntheoretical model. Elastic dipolar interactions are also observed to influence\nthe Rabi evolution of the spin, revealing an interacting fermionic system. The\nlong lifetime of this weakly interacting spin-orbit-coupled degenerate Fermi\ngas will facilitate the study of quantum many-body phenomena manifest at longer\ntimescales, with exciting implications for the exploration of exotic\ntopological quantum liquids.",
        "positive": "Damping transition in an open generalized Aubry-Andr\u00e9-Harper model: We study the damping dynamics of the single-particle correlation for an open\nsystem under periodic and aperiodic order, which is dominated by the Lindblad\nmaster equation. In the absence of the aperiodic order, the Liouvillian\nsuperoperator exhibits the non-Hermitian skin effect, which leads to\nunidirectional damping dynamics, dubbed as \"chiral damping\". Due to the\nnon-Hermitian skin effect, the damping dynamics is boundary sensitive: The\nlong-time damping of such open systems is algebraic under periodic boundary\nconditions but exponential under open boundary conditions. We reveal the phase\ntransition with the inclusion of the hopping amplitude modulation. By using the\nspectral topology and a finite-size scaling analysis in the commensurate case,\nwe show there exists a phase transition of the skin effect with non-Bloch\nanti-parity-time symmetry breaking. For the incommensurate case, we find richer\nphases with the coexistence of the non-Hermitian skin effect and the Anderson\nlocalization, which are separated by a generalized mobility edge. We reveal the\ntransition of the damping dynamics as a consequence of the phase transition.\nFurthermore, we propose a possible scheme with ultracold atoms in a dissipative\nmomentum lattice to realize and detect the damping dynamics."
    },
    {
        "anchor": "On the ground-state energy of a mixture of two different oppositely\n  polarized fermionic gases: We report the results of the computation of the order $(k_{\\rm F}a_0)^2$\ncorrection, where $k_{\\rm F}=3\\pi^2\\rho$ is the Fermi wave vector and $a_0$ the\n$s$-wave scattering length of the repulsive interaction, to the ground-state\nenergy of a mixture of oppositely polarized $N_a$ spin $1/2$ fermions $a$ of\nmasses $m_a$ and $N_b$ spin $1/2$ fermions $b$ of masses $m_b$ ($\\rho=N/V$,\n$N=N_a+N_b$). It is shown that the results of the paper \\cite{FraPil} in which\nthe same correction has been computed entirely numerically, using a more\ntraditional approach, can be easily and semianalytically reproduced using the\neffective field theory technique.",
        "positive": "Few-body solutions under spin-exchange interaction: magnetic bound state\n  and the Kondo screening effect: Motivated by recent progresses on ultracold alkaline-earth atoms towards the\ngoal of simulating Kondo physics, in this work we exactly solve the few-body\nproblem of one and two trapped fermions in one dimension interacting with a\nlocalized impurity under tunable spin-exchange interaction. It is found that\ndepending on the sign of the spin-exchange coupling, ferromagnetic(FM) or\nanti-ferromagnetic(AFM), the attractive and repulsive branches can hold\ndifferent magnetic structures. For the two fermions case, we demonstrate the\nKondo screening effect for the attractive branch with AFM coupling, and show\nthat such screening is absent for the ground state with FM coupling. Moreover,\nwe find a sequence of FM upper branches in the AFM coupling side. These FM\nstates are orthogonal to all other attractive branches and their wave functions\nfeature a full spin-charge separation. The effect of an additional contact\ninteraction and the extension of our results to many particles are also\ndiscussed. This work reveals the intriguing physics uniquely associated with\nthe spin-exchange interaction in the few-body point of view, which are\npromisingly to be explored in the experiment of ultracold alkaline-earth atoms."
    },
    {
        "anchor": "Identities and Many-Body Approaches in Bose-Einstein Condensates: This paper discusses exact relations in Bose--Einstein condensates (BECs),\nstarting from basic properties of an ideal Bose gas. In particular, focused on\nare the Hugenholtz--Pines relation, Nepomnyashchii--Nepomnyashchii identity,\nand identities for the density response function. After introducing these exact\nrelations, a few approaches of many-body approximations are discussed, which\nsatisfy the exact relations in BECs. This paper will serve as a bridge between\ntheories on exact relations and those on approximations in BECs.",
        "positive": "Competing Orders in a Dipolar Bose-Fermi Mixture on a Square Optical\n  Lattice: Mean-Field Perspective: We consider a mixture of a two-component Fermi gas and a single-component\ndipolar Bose gas in a square optical lattice and reduce it into an effective\nFermi system where the Fermi-Fermi interaction includes the attractive\ninteraction induced by the phonons of a uniform dipolar Bose-Einstein\ncondensate. Focusing on this effective Fermi system in the parameter regime\nthat preserves the symmetry of $D_4$, the point group of a square, we explore,\nwithin the Hartree-Fock-Bogoliubov mean-field theory, the phase competition\namong density wave orderings and superfluid pairings. We construct the matrix\nrepresentation of the linearized gap equation in the irreducible\nrepresentations of $D_4$. We show that in the weak coupling regime, each matrix\nelement, which is a four-dimensional (4D) integral in momentum space, can be\nput in a separable form involving a 1D integral, which is only a function of\ntemperature and the chemical potential, and a pairing-specific \"effective\"\ninteraction, which is an analytical function of the parameters that\ncharacterize the Fermi-Fermi interactions in our system. We analyze the\ncritical temperatures of various competing orders as functions of different\nsystem parameters in both the absence and presence of the dipolar interaction.\nWe find that close to half filling, the d_{x^{2}-y^{2}}-wave pairing with a\ncritical temperature in the order of a fraction of Fermi energy (at half\nfilling) may dominate all other phases, and at a higher filling factor, the\np-wave pairing with a critical temperature in the order of a hundredth of Fermi\nenergy may emerge as a winner. We find that tuning a dipolar interaction can\ndramatically enhance the pairings with $d_{xy}$- and g-wave symmetries but not\nenough for them to dominate other competing phases."
    },
    {
        "anchor": "Supersolid phases of ultracold bosons trapped in optical lattices\n  dressed with Rydberg $p$-states: Engineering quantum phases with spontaneously broken symmetries is a major\ngoal of research in different fields. Trapped ultracold Rydberg-excited atoms\nin optical lattices are a promising platform for realizing quantum phases with\nbroken lattice translational symmetry since they are interacting over distances\nlarger than the lattice constant. Although numerous theoretical works on\ntrapped Rydberg-excited gases have predicted such phases, in particular density\nwave or supersolid phases, their experimental observation proves to be\ndifficult due to challenges such as scattering processes and the limited\nexperimentally achievable coupling strength. Most of these previous studies\nhave focused on isotropically interacting gases dressed with Rydberg\n$s$-states, while the effect of anisotropic interactions due to Rydberg-excited\n$p$-states in trapped quantum gases remains much less investigated.\nAdditionally, it was shown that the excitation scheme used to excite Rydberg\n$p$-states possesses advantages regarding achievable coupling strengths and\nlimitation of scattering processes compared to its $s$-state counterpart, which\nmakes the investigation of Rydberg $p$-state dressed quantum gases even more\ninteresting. In the present work, we study the extended, two-component\nBose-Hubbard model, realized with a bosonic quantum gas with Rydberg-excited\n$p$-states trapped in an optical lattice, within Gutzwiller mean-field theory.\nWe compute the ground state phase diagram and investigate its different\nregimes. By comparison to the phase diagram of the isotropic case, we find the\nanisotropic interaction to be more advantageous for the observation of\nsupersolid phases.",
        "positive": "Thermodynamic properties of ultracold Bose gas: transition exponents and\n  universality: We report exact numerical calculation of chemical potential, condensate\nfraction and specific heat of $N$ non-interacting bosons confined in an\nisotropic harmonic oscillator trap in one, two and three dimensions, as also\nfor interacting bosons in a 3D trap. Quasi phase transitions are observed in\nall these cases, including one-dimension, as shown by a rapid change of all the\nthermodynamic quantities at the transition point. The change becomes more rapid\nas $N$ increases in 2D and 3D cases. However with increase in $N$, the sudden\nchange in the nature of specific heat, gets gradually wiped out in 1D, while it\nbecomes more drastic in 2D and 3D. The sudden change in the nature of\ncondensate fraction and chemical potential as $N$ increases becomes more\ndrastic even in 1D. Defining transition exponents, which characterize the\nnature of a thermodynamic quantity at the transition point of a quasi phase\ntransition, we evaluate them by careful numerical calculation very near the\ntransition temperature. These exponents are found to be independent of the size\nof the system and whether the bosons are interacting or not, demonstrating\ntheir universality property."
    },
    {
        "anchor": "Clock spectroscopy of interacting bosons in deep optical lattices: We report on high-resolution optical spectroscopy of interacting bosonic\n$^{174}$Yb atoms in deep optical lattices with negligible tunneling. We prepare\nMott insulator phases with singly- and doubly-occupied isolated sites and probe\nthe atoms using an ultra-narrow \"clock\" transition. Atoms in singly-occupied\nsites undergo long-lived Rabi oscillations. Atoms in doubly-occupied sites are\nstrongly affected by interatomic interactions, and we measure their inelastic\ndecay rates and energy shifts. We deduce from these measurements all relevant\ncollisional parameters involving both clock states, in particular the intra-\nand inter-state scattering lengths.",
        "positive": "A Multi-Purpose Platform for Analog Quantum Simulation: Atom-based quantum simulators have had tremendous success in tackling\nchallenging quantum many-body problems, owing to the precise and dynamical\ncontrol that they provide over the systems' parameters. They are, however,\noften optimized to address a specific type of problems. Here, we present the\ndesign and implementation of a $^6$Li-based quantum gas platform that provides\nwide-ranging capabilities and is able to address a variety of quantum many-body\nproblems. Our two-chamber architecture relies on a robust and easy-to-implement\ncombination of gray molasses and optical transport from a laser-cooling chamber\nto a glass cell with excellent optical access. There, we first create unitary\nFermi superfluids in a three-dimensional axially symmetric harmonic trap and\ncharacterize them using in situ thermometry, reaching temperatures below 20 nK.\nThis allows us to enter the deep superfluid regime with samples of extreme\ndiluteness, where the interparticle spacing is sufficiently large for direct\nsingle-atom imaging. Secondly, we generate optical lattice potentials with\ntriangular and honeycomb geometry in which we study diffraction of molecular\nBose-Einstein condensates, and show how going beyond the Kapitza-Dirac regime\nallows us to unambiguously distinguish between the two geometries. With the\nability to probe quantum many-body physics in both discrete and continuous\nspace, and its suitability for bulk and single-atom imaging, our setup\nrepresents an important step towards achieving a wide-scope quantum simulator."
    },
    {
        "anchor": "Ultra cold atoms and Bose-Einstein condensation for quantum metrology: This paper is a short introduction to cold atom physics and Bose-Einstein\ncondensation. Light forces on atoms are presented, together with laser cooling,\nand a few atom traps: the magneto-optical trap, dipole traps and magnetic\ntraps. A brief description of Bose-Einstein condensation is given together with\nsome important links with condensed matter physics. The reader is referred to\ncomprehensive reviews and to other lecture notes for further details on atom\ncooling, trapping and Bose-Einstein condensation.",
        "positive": "A self-consistent Hartree-Fock approach for interacting bosons in\n  optical lattices: A theoretical study of interacting bosons in a periodic optical lattice is\npresented. Instead of the commonly used tight-binding approach (applicable near\nthe Mott insulating regime of the phase diagram), the present work starts from\nthe exact single-particle states of bosons in a cubic optical lattice,\nsatisfying the Mathieu equation, an approach that can be particularly useful at\nlarge boson fillings. The effects of short-range interactions are incorporated\nusing a self-consistent Hartree-Fock approximation, and predictions for\nexperimental observables such as the superfluid transition temperature,\ncondensate fraction, and boson momentum distribution are presented."
    },
    {
        "anchor": "Magnetic field induced dynamical instabilities in an anti-ferromagnetic\n  spin-1 Bose-Einstein condensate: We theoretically investigate four types of dynamical instability, in\nparticular the periodic and oscillatory type $I_O$, in an anti-ferromagnetic\nspin-1 Bose-Einstein condensate in a nonzero magnetic field, by employing the\ncoupled-mode theory and numerical method. This is in sharp contrast to the\ndynamical stability of the same system in zero field. Remarkably, a pattern\ntransition from a periodic dynamical instability $I_O$ to a uniform one $III_O$\noccurs at a critical magnetic field. All the four types of dynamical\ninstability and the pattern transition are ready to be detected in $^{23}$Na\ncondensates within the availability of the current experimental techniques.",
        "positive": "Density Functional of a Two-Dimensional Gas of Dipolar Atoms:\n  Thomas-Fermi-Dirac Treatment: We derive the density functional for the ground-state energy of a\ntwo-dimensional, spin-polarized gas of neutral fermionic atoms with\nmagnetic-dipole interaction, in the Thomas-Fermi-Dirac approximation. For many\natoms in a harmonic trap, we give analytical solutions for the single-particle\nspatial density and the ground-state energy, in dependence on the interaction\nstrength, and we discuss the weak-interaction limit that is relevant for\nexperiments. We then lift the restriction of full spin polarization and account\nfor a time-independent inhomogeneous external magnetic field. The field\nstrength necessary to ensure full spin polarization is derived."
    },
    {
        "anchor": "Optical Flux Lattices for Two-Photon Dressed States: We describe a simple scheme by which \"optical flux lattices\" can be\nimplemented in ultracold atomic gases using two-photon dressed states. This\nscheme can be applied, for example, to the ground state hyperfine levels of\ncommonly used atomic species. The resulting flux lattices simulate a magnetic\nfield with high mean flux density, and have low energy bands analogous to the\nlowest Landau level. We show that in practical cases the atomic motion\nsignificantly deviates from the adiabatic following of one dressed state, and\nthat this can lead to significant interactions even for fermions occupying a\nsingle band. Our scheme allows experiments on cold atomic gases to explore\nstrong correlation phenomena related to the fractional quantum Hall effect,\nboth for fermions and bosons.",
        "positive": "Exact few-body results for strongly correlated quantum gases in two\n  dimensions: The study of strongly correlated quantum gases in two dimensions has\nimportant ramifications for understanding many intriguing pheomena in solid\nmaterials, such as high-$T_{c}$ superconductivity and the fractional quantum\nHall effect. However, theoretical methods are plagued by the existence of\nsignificant quantum fluctuations. Here, we present two- and three-body exact\nsolutions for both fermions and bosons trapped in a two-dimensional harmonic\npotential, with an arbitrary $s$-wave scattering length. These few-particle\nsolutions link in a natural way to the high-temperature properties of\nmany-particle systems via a quantum virial expansion. As a concrete example,\nusing the energy spectrum of few fermions, we calculate the second and third\nvirial coefficients of a strongly interacting Fermi gas in two dimensions, and\nconsequently investigate its high-temperature thermodynamics. Our thermodynamic\nresults may be useful for ongoing experiments on two-dimensional Fermi gases.\nThese exact results also provide an unbiased benchmark for quantum Monte Carlo\nsimulations of two-dimensional Fermi gases at high temperatures."
    },
    {
        "anchor": "Dimension Crossing Turbulent Cascade in an Excited Lattice Bose Gas: Turbulence is an intriguing non-equilibrium state, which originates from\nfluid mechanics and has far-reaching consequences in the description of climate\nphysics, the characterization of quantum hydrodynamics, and the understanding\nof cosmic evolution. The concept of turbulent cascade describing the energy\nredistribution across different length scales offers one profound route to\nreconcile fundamental conservative forces with observational energy\nnon-conservation of accelerating expansion of the universe bypassing the\ncosmological constant. Here, we observe a dimension crossing turbulent energy\ncascade in an atomic Bose-Einstein condensate confined in a two-dimensional\n(2d) optical lattice forming a 2d array of tubes, which exhibits universal\nbehaviors in the dynamical energy-redistribution across different dimensions.\nBy exciting atoms into the optical-lattice high bands, the excessive energy of\nthis quantum many-body system is found to cascade from the transverse\ntwo-dimensional lattice directions to the continuous dimension, giving rise to\na one-dimensional turbulent energy cascade, which is in general challenging to\nreach due to integrability. We expect this observed novel phenomenon of\ndimension-crossing energy cascade may inspire microscopic theories for modeling\npositive cosmological constant of our inflationary universe.",
        "positive": "Spin-gapped magnets with weak anisotropies I: Constraints on the phase\n  of the condensate wave function: We study the thermodynamic properties of dimerized spin-gapped quantum\nmagnets with and without exchange anisotropy (EA) and Dzyaloshinsky and Moriya\n(DM) anisotropies within the mean-field approximation (MFA). For this purpose\nwe obtain the thermodynamic potential $\\Omega$ of a triplon gas taking into\naccount the strength of DM interaction up to second order. The minimization of\n$\\Omega$ with respect to self-energies $\\Sigma_n$ and $\\Sigma_{an}$ yields the\nequation for $X_{1,2}=\\Sigma_n\\pm\\Sigma_{an}-\\mu$, which define the dispersion\nof quasiparticles $E_k=\\sqrt{\\epsilon_k+X_1}\\sqrt{\\epsilon_k+X_2}$ where\n$\\epsilon_k$ is the bare dispersion of triplons. The minimization of $\\Omega$\nwith respect to the magnitude $\\rho_0$ and the phase $\\Theta$ of triplon\ncondensate leads to coupled equations for $\\rho_0$ and $\\Theta$. We discuss the\nrestrictions on $\\rho_0$ and $\\Theta$ imposed by these equations for systems\nwith and without anisotropy. The requirement of dynamical stability conditions\n$(X_1>0, X_2>0)$ in equilibrium, as well as the Hugenholtz-Pines theorem,\nparticularly for isotropic Bose condensate, impose certain conditions to the\nphysical solutions of these equations. It is shown that the phase angle of a\npurely homogenous Bose-Einstein condensate (BEC) without any anisotropy may\nonly take values $\\Theta=\\pi n $ (n=0,$\\pm 1,\\pm 2$...) while that of BEC with\neven a tiny DM interaction results in $\\Theta=\\pi/2+2\\pi n$. In contrast to the\nwidely used Hartree-Fock-Popov approximation, which allows arbitrary phase\nangle, our approach predicts that the phase angle may have only discrete\nvalues, while the phase of the wave function of the whole system remains\narbitrary as expected. The consequences of this phase locking for interference\nof two Bose condensates and to their possible Josephson junction is studied."
    },
    {
        "anchor": "Connection between rotation and miscibility in a two-component\n  Bose-Einstein condensate: A two-component Bose-Einstein condensate rotating in a toroidal trap is\ninvestigated. The topological constraint depends on the density distribution of\neach component along the circumference of the torus, and therefore the\nquantization condition on the circulation can be controlled by changing the\nmiscibility using the Feshbach resonance. We find that the system exhibits a\nvariety of dynamics depending on the initial angular momentum when the\nmiscibility is changed.",
        "positive": "Mobile impurities interacting with a few one-dimensional lattice bosons: We report a comprehensive study of the ground-state properties of one and two\nbosonic impurities immersed in small one-dimensional optical lattices loaded\nwith a few interacting bosons. We model the system with a two-component\nBose-Hubbard model and solve the problem numerically by means of the exact\ndiagonalization (ED) method. We report binding energies of one and two\nimpurities across the superfluid (SF) to Mott-insulator (MI) transition and\nconfirm the formation of two-body bound states of impurities induced by\nrepulsive interactions. In particular, we found that an insulator bath induces\ntightly bound di-impurity dimers, whereas a superfluid bath induces shallower\nbound states."
    },
    {
        "anchor": "Coupled spin-vortex pair in dipolar spinor Bose-Einstein condensates: We investigate the ground-state and magnetic properties of a dipolar spin-1\nBose-Einstein condensate trapped in a symmetric double-well potential. In\nparticular, we focus on the spin-vortex states by assuming that each potential\nwell is highly pancake shaped. We show that the presence of the double-well\npotential gives rise to two different spin configurations for the spin-vortex\npair states. We also study the response of the coupled spin-vortex pair to\nstatic transverse magnetic fields.",
        "positive": "Few-Boson Processes in the Presence of an Attractive Impurity under\n  One-Dimensional Confinement: We consider a few-boson system confined to one dimension with a single\ndistinguishable particle of lesser mass. All particle interactions are modeled\nwith $\\delta$-functions, but due to the mass imbalance the problem is\nnonintegrable. Universal few-body binding energies, atom-dimer and atom-trimer\nscattering lengths are all calculated in terms of two parameters, namely the\nmass ratio: $m_{\\text{L}}/m_{\\text{H}}$, and ratio\n$g_{\\text{HH}}/g_{\\text{HL}}$ of the $\\delta$-function couplings. We\nspecifically identify the values of these ratios for which the atom-dimer or\natom-trimer scattering lengths vanish or diverge. We identify regions in this\nparameter space in which various few-body inelastic process become\nenergetically allowed. In the Tonks-Girardeau limit ($g_{\\text{HH}}\\rightarrow\n\\infty$), our results are relevant to experiments involving trapped fermions\nwith an impurity atom."
    },
    {
        "anchor": "On some rigorous aspects of fragmented condensation: In this paper we discuss some aspects of fragmented condensation from a\nmathematical perspective. We first propose a simple way of characterizing\nfinite fragmentation. Then, inspired by recent results of semiclassical\nanalysis applied to bosonic systems with infinitely many degrees of freedom, we\naddress the problem of persistence of fragmented condensation. We show that the\nlatter occurs in interacting systems, in the mean-field regime, and in the\nlimit of large gap of the one-body Hamiltonian.",
        "positive": "Quantum N-Boson States and Quantized Motion of Solitonic Droplets:\n  Universal Scaling Properties in Low Dimensions: In this article, we illustrate the scaling properties of a family of\nsolutions for N attractive bosonic atoms in the limit of large $N$. These\nsolutions represent the quantized dynamics of solitonic degrees of freedom in\natomic droplets. In dimensions lower than two, or $d=2-\\epsilon$, we\ndemonstrate that the number of isotropic droplet states scales as\n$N^{3/2}/\\epsilon^{1/2}$, and for $\\epsilon=0$, or $d=2$, scales as ${N^2}$.\nThe ground state energies scale as $N^{2 / \\epsilon + 1}$ in $d=2-\\epsilon$,\nand when $d=2$, scale as an exponential function of N. We obtain the universal\nenergy spectra and the generalized Tjon relation; their scaling properties are\nuniquely determined by the asymptotic freedom of quantum bosonic fields at\nshort distances, a distinct feature in low dimensions. We also investigate the\neffect of quantum loop corrections that arise from various virtual processes\nand show that the resultant lifetime for a wide range of excited states scales\nas $N^{\\epsilon/2}E^{1-\\epsilon/2}$."
    },
    {
        "anchor": "Quantum Generalized Hydrodynamics: Physical systems made of many interacting quantum particles can often be\ndescribed by Euler hydrodynamic equations in the limit of long wavelengths and\nlow frequencies. Recently such a classical hydrodynamic framework, now dubbed\nGeneralized Hydrodynamics (GHD), was found for quantum integrable models in one\nspatial dimension. Despite its great predictive power, GHD, like any Euler\nhydrodynamic equation, misses important quantum effects, such as quantum\nfluctuations leading to non-zero equal-time correlations between fluid cells at\ndifferent positions. Focusing on the one-dimensional gas of bosons with delta\nrepulsion, and on states of zero entropy, for which quantum fluctuations are\nlarger, we reconstruct such quantum effects by quantizing GHD. The resulting\ntheory of quantum GHD can be viewed as a multi-component Luttinger liquid\ntheory, with a small set of effective parameters that are fixed by the\nThermodynamic Bethe Ansatz. It describes quantum fluctuations of truly\nnonequilibrium systems where conventional Luttinger liquid theory fails.",
        "positive": "Noisy quantum phase transitions: an intuitive approach: Equilibrium thermal noise is known to destroy any quantum phase transition.\nWhat are the effects of non-equilibrium noise? In two recent papers we have\nconsidered the specific case of a resistively-shunted Josephson junction driven\nby $1/f$ charge noise. At equilibrium, this system undergoes a sharp quantum\nphase transition at a critical value of the shunt resistance. By applying a\nreal-time renormalization group (RG) approach, we found that the noise has\nthree main effects: It shifts the phase transition, renormalizes the\nresistance, and generates an effective temperature. In this paper we explain\nhow to understand these effects using simpler arguments, based on Kirchhoff\nlaws and time-dependent perturbation theory. We also show how these effects\nmodify physical observables and especially the current-voltage characteristic\nof the junction. In the appendix we describe two possible realizations of the\nmodel with ultracold atoms confined to one dimension."
    },
    {
        "anchor": "Quantum Lifshitz points and fluctuation-induced first-order phase\n  transitions in imbalanced Fermi mixtures: We perform a detailed analysis of the phase transition between the uniform\nsuperfluid and normal phases in spin- and mass-imbalanced Fermi mixtures. At\nmean-field level we demonstrate that at temperature $T\\to 0$ the gradient term\nin the effective action can be tuned to zero for experimentally relevant sets\nof parameters, thus providing an avenue to realize a quantum Lifshitz point. We\nsubsequently analyze damping processes affecting the order-parameter field\nacross the phase transition. We show that, in the low energy limit, Landau\ndamping occurs only in the symmetry-broken phase and affects exclusively the\nlongitudinal component of the order-parameter field. It is however unavoidably\npresent in the immediate vicinity of the phase transition at temperature $T=0$.\nWe subsequently perform a renormalization-group analysis of the system in a\nsituation, where, at mean-field level, the quantum phase transition is second\norder (and not multicritical). We find that, at $T$ sufficiently low, including\nthe Landau damping term in a form derived from the microscopic action\ndestabilizes the renormalization group flow towards the Wilson-Fisher fixed\npoint. This signals a possible tendency to drive the transition weakly\nfirst-order by the coupling between the order-parameter fluctuations and\nfermionic excitations effectively captured by the Landau damping contribution\nto the order-parameter action.",
        "positive": "DMFT vs Second Order Perturbation Theory for the Trapped 2D\n  Hubbard-Antiferromagnet: In recent literature on trapped ultracold atomic gases, calculations for\n2D-systems are often done within the Dynamical Mean Field Theory (DMFT)\napproximation. In this paper, we compare DMFT to a fully two-dimensional,\nself-consistent second order perturbation theory for weak interactions in a\nrepulsive Fermi-Hubbard model. We investigate the role of quantum and of\nspatial fluctuations when the system is in the antiferromagnetic phase, and\nfind that, while quantum fluctuations decrease the order parameter and critical\ntemperatures drastically, spatial fluctuations only play a noticeable role when\nthe system undergoes a phase transition, or at phase boundaries in the trap. We\nconclude from this that DMFT is a good approximation for the antiferromagnetic\nFermi-Hubbard model for experimentally relevant system sizes."
    },
    {
        "anchor": "Controlling the dynamics of an open many-body quantum system with\n  localized dissipation: We experimentally investigate the action of a localized dissipative potential\non a macroscopic matter wave, which we implement by shining an electron beam on\nan atomic Bose-Einstein condensate (BEC). We measure the losses induced by the\ndissipative potential as a function of the dissipation strength observing a\nparadoxical behavior when the strength of the dissipation exceeds a critical\nlimit: for an increase of the dissipation rate the number of atoms lost from\nthe BEC becomes lower. We repeat the experiment for different parameters of the\nelectron beam and we compare our results with a simple theoretical model,\nfinding excellent agreement. By monitoring the dynamics induced by the\ndissipative defect we identify the mechanisms which are responsible for the\nobserved paradoxical behavior. We finally demonstrate the link between our\ndissipative dynamics and the measurement of the density distribution of the BEC\nallowing for a generalized definition of the Zeno effect. Due to the high\ndegree of control on every parameter, our system is a promising candidate for\nthe engineering of fully governable open quantum systems.",
        "positive": "Localization-Delocalization Transition in the Random Dimer Model: The random-dimer model is probably the most popular model for a\none-dimensional disordered system where correlations are responsible for\ndelocalization of the wave functions. This is the primary model used to justify\nthe insulator-metal transition in conducting polymers and in DNA. However, for\nsuch systems, the localization-delocalization regimes have only been observed\nby deeply modifying the system itself, including the correlation function of\nthe disordered potential. In this article, we propose to use an ultracold\natomic mixture to cross the transition simply by externally tuning the\ninterspecies interactions, and without modifying the impurity correlations."
    },
    {
        "anchor": "Quasi-1D atomic gases across wide and narrow\n  confinement-induced-resonances: We study quasi-one-dimensional atomic gases across wide and narrow\nconfinement-induced-resonances (CIR). We show from Virial expansion that by\ntuning the magnetic field, the repulsive scattering branch initially prepared\nat low fields can continuously go across CIR without decay; instead, the decay\noccurs when approaching the non-interacting limit. The interaction properties\nessentially rely on the resonance width of CIR. Universal thermodynamics holds\nfor scattering branch right at wide CIR, but is smeared out in narrow CIR due\nto strong energy-dependence of coupling strength. In wide and narrow CIR, the\ninteraction energy of scattering branch shows different types of strong\nasymmetry when approaching the decay from opposite sides of magnetic field.\nFinally we discuss the stability of repulsive branch for a repulsively\ninteracting Fermi gas in different trapped geometries at low temperatures.",
        "positive": "Parametric Excitation and Squeezing in a Many-Body Spin System: We demonstrate a new method to coherently excite and control the quantum spin\nstates of an atomic Bose gas using parametric excitation of the collective spin\nby time varying the relative strength of the Zeeman and spin-dependent\ncollisional interaction energies at multiples of the natural frequency of the\nsystem. Compared to the usual single-particle quantum control techniques used\nto excite atomic spins (e.g. Rabi oscillations using rf or microwave fields),\nthe method demonstrated here is intrinsically many-body, requiring\ninter-particle interactions. While parametric excitation of a classical system\nis ineffective from the ground state, we show that in our quantum system,\nparametric excitation from the quantum ground state leads to the generation of\nquantum squeezed states."
    },
    {
        "anchor": "Artificial Magnetic Field Quenches in Synthetic Dimensions: Recent cold atom experiments have realized models where each hyperfine state\nat an optical lattice site can be regarded as a separate site in a synthetic\ndimension. In such synthetic ribbon configurations, manipulation of the\ntransitions between the hyperfine levels provide direct control of the hopping\nin the synthetic dimension. This effect was used to simulate a magnetic field\nthrough the ribbon. Precise control over the hopping matrix elements in the\nsynthetic dimension makes it possible to change this artificial magnetic field\nmuch faster than the time scales associated with atomic motion in the lattice.\nIn this paper, we consider such a magnetic flux quench scenario in synthetic\ndimensions. Sudden changes have not been considered for real magnetic fields as\nsuch changes in a conducting system would result in large induced currents.\nHence, we first study the difference between a time varying real magnetic field\nand an artificial magnetic field using a minimal six site model. This minimal\nmodel clearly shows the connection between gauge dependence and the lack of on\nsite induced scalar potential terms. We then investigate the dynamics of a\nwavepacket in an infinite two or three leg ladder following a flux quench and\nfind that the gauge choice has a dramatic effect on the packet dynamics.\nSpecifically, a wavepacket splits into a number of smaller packets. Both the\nweights and the number of packets depend on the implemented gauge. If an\ninitial packet, prepared under zero flux in a n--leg ladder, is quenched to\nHamiltonian with a vector potential parallel to the ladder; it splits into at\nmost $n$ smaller wavepackets. The same initial packet splits up to $n^2$\npackets if the vector potential is implemented to be along the rungs. Finally,\nwe show that edge states in a thick ribbon are robust under the quench only\nwhen the same gap supports an edge state for the final Hamiltonian.",
        "positive": "Quantum reflection of ultracold atoms from thin films, graphene, and\n  semiconductor heterostructures: We show that thin dielectric films can be used to enhance the performance of\npassive atomic mirrors by enabling quantum reflection probabilities of over 90%\nfor atoms incident at velocities ~1 mm/s, achieved in recent experiments. This\nenhancement is brought about by weakening the Casimir-Polder attraction between\nthe atom and the surface, which induces the quantum reflection. We show that\nsuspended graphene membranes also produce higher quantum reflection\nprobabilities than bulk matter. Temporal changes in the electrical resistance\nof such membranes, produced as atoms stick to the surface, can be used to\nmonitor the reflection process, non-invasively and in real time. The resistance\nchange allows the reflection probability to be determined purely from\nelectrical measurements without needing to image the reflected atom cloud\noptically. Finally, we show how perfect atom mirrors may be manufactured from\nsemiconductor heterostructures, which employ an embedded two-dimensional\nelectron gas to tailor the atom-surface interaction and so enhance the\nreflection by classical means."
    },
    {
        "anchor": "Anyonic statistics of quantum impurities in two dimensions: We demonstrate that identical impurities immersed in a two-dimensional\nmany-particle bath can be viewed as flux-tube-charged-particle composites\ndescribed by fractional statistics. In particular, we find that the bath\nmanifests itself as an external magnetic flux tube with respect to the\nimpurities, and hence the time-reversal symmetry is broken for the effective\nHamiltonian describing the impurities. The emerging flux tube acts as a\nstatistical gauge field after a certain critical coupling. This critical\ncoupling corresponds to the intersection point between the quasiparticle state\nand the phonon wing, where the angular momentum is transferred from the\nimpurity to the bath. This amounts to a novel configuration with emerging\nanyons. The proposed setup paves the way to realizing anyons using electrons\ninteracting with superfluid helium or lattice phonons, as well as using atomic\nimpurities in ultracold gases.",
        "positive": "Collective mode evidence of high-spin bosonization in a trapped\n  one-dimensional atomic Fermi gas with tunable spin: We calculate the frequency of collective modes of a one-dimensional\nrepulsively interacting Fermi gas with high-spin symmetry confined in harmonic\ntraps at zero temperature. This is a system realizable with fermionic\nalkaline-earth-metal atoms such as $^{173}$Yb, which displays an exact\nSU($\\kappa$) spin symmetry with $\\kappa\\geqslant2$ and behaves like a spinless\ninteracting Bose gas in the limit of infinite spin components\n$\\kappa\\rightarrow\\infty$, namely high-spin bosonization. We solve the\nhomogeneous equation of state of the high-spin Fermi system by using Bethe\nansatz technique and obtain the density distribution in harmonic traps based on\nlocal density approximation. The frequency of collective modes is calculated by\nexactly solving the zero-temperature hydrodynamic equation. In the limit of\nlarge number of spin-components, we show that the mode frequency of the system\napproaches to that of a one-dimensional spinless interacting Bose gas, as a\nresult of high-spin bosonization. Our prediction of collective modes is in\nexcellent agreement with a very recent measurement for a Fermi gas of\n$^{173}$Yb atoms with tunable spin confined in a two-dimensional tight optical\nlattice."
    },
    {
        "anchor": "Low-density molecular gas of tightly-bound Rashba-Dresselhaus fermions: We study interacting Rashba-Dresselhaus fermions in two spatial dimensions.\nFirst, we present a new exact solution to the two-particle pairing problem of\nspin-orbit-coupled fermions for arbitrary Rashba and Dresselhaus spin-orbit\ninteractions. An exact molecular wave function and the Green function are\nexplicitly derived along with the binding energy and the spectrum of the\nmolecular state. In the second part, we consider a thermal Boltzmann gas of\nfermionic molecules and compute the time-of-flight velocity and spin\ndistributions for a single fermion in the gas. We show that the pairing\nsignatures can be observed already in the first-moment expectation values, such\nas time-of-flight density and spin profiles.",
        "positive": "Nonlinear dependence observed in quadrupolar collective excitation of a\n  trapped BEC: We report the experimental observation of the collective excitations induced\nin a magnetically trapped 87Rb Bose-Einstein condensate. Low-lying mode\nexcitations were studied by tracking the condensate's center-of-mass\ndisplacement, and its aspect ratio as a function of the hold time in the trap.\nWe were able to partially control the modes onset by modulating the amplitude\nof the additional field gradient used to excite the BEC. The measured\nexcitation frequencies were found to be in good agreement with the literature.\nWe have also found that the modulation amplitude was able to change the phase\nof the center-of-mass oscillation. Finally, an interesting, non-linear\ndependence was observed on the condensate aspect ratio as a function of the\nperturbing amplitude which induces the quadrupolar mode."
    },
    {
        "anchor": "The Local Spin Structure of Large Spin Fermions: We show that large spin fermions have very rich spin structures. The local\nspin order of a spin-$f$ Fermi gas is a linear combination of $2f$\n(particle-hole) angular momentum states, $L=1,..,2f$. $L=1, 2$ represent\nferromagnetic and nematic spin order, while $L\\geq 3$ are higher spin orders\nthat has no analog in spin-1/2 systems. Each $L$ spin sector is characterized\nas $L$ pairs of antipodal points on a sphere. Model calculations show that some\nof these spin-orders have the symmetry of Platonic solid, and many of them have\nnon-abelian line defects.",
        "positive": "Ground-State Phase Diagram of the Two-Dimensional Extended Bose-Hubbard\n  Model: We investigate the ground-state phase diagram of the soft-core Bose-Hubbard\nmodel with the nearest-neighbor repulsion on a square lattice by using an\nunbiased quantum Monte Carlo method. In contrast to the previous study[P.\nSengupta {\\it et. al.}, Phys. Rev. Lett. {\\bf 94}, 207202 (2005)], we present\nthe ground-state phase diagrams up to large hopping parameters. As a result, in\naddition to the known supersolid above half-filling, we find supersolid even\nbelow and at half-filling for large hopping parameters. Furthermore, for the\nstrong nearest-neighbor repulsion, we show that the supersolid phase occupies a\nremarkably broad region in the phase diagram. The results are in qualitative\nagreement with that obtained by the Gutzwiller mean-field approximation[M.\nIskin, Phys. Rev. A {\\bf 83}, 051606(R) (2011) and T. Kimura, Phys. Rev. A {\\bf\n84}, 063630 (2011)]."
    },
    {
        "anchor": "Inducing spin-order with an impurity: phase diagram of the magnetic Bose\n  polaron: We investigate the formation of magnetic Bose polaron, an impurity atom\ndressed by spin-wave excitations, in a one-dimensional spinor Bose gas. In\nterms of an effective potential model the impurity is strongly confined by the\nhost excitations which can even overcome the impurity-medium repulsion leading\nto a self-localized quasi-particle state. The phase diagram of the attractive\nand self-bound repulsive magnetic polaron, repulsive non-magnetic (Fr{\\\"\no}hlich-type) polaron and impurity-medium phase-separation regimes is explored\nwith respect to the Rabi-coupling between the spin components, spin-spin\ninteractions and impurity-medium coupling. The residue of such magnetic\npolarons decreases substantially in both strong attractive and repulsive\nbranches with strong impurity-spin interactions, illustrating significant\ndressing of the impurity. The impurity can be used to probe and maneuver the\nspin polarization of the magnetic medium while suppressing ferromagnetic\nspin-spin correlations. It is shown that mean-field theory fails as the spinor\ngas approaches immiscibility since the generated spin-wave excitations are\nprominent. Our findings illustrate that impurities can be utilized to generate\ncontrollable spin-spin correlations and magnetic polaron states which can be\nrealized with current cold atom setups.",
        "positive": "Effective time-independent description of optical lattices with periodic\n  driving: For a periodically driven quantum system an effective time-independent\nHamiltonian is derived with an eigen-energy spectrum, which in the regime of\nlarge driving frequencies approximates the quasi-energies of the corresponding\nFloquet Hamiltonian. The effective Hamiltonian is evaluated for the case of\noptical lattice models in the tight-binding regime subjected to strong periodic\ndriving. Three scenarios are considered: a periodically shifted one-dimensional\n(1D) lattice, a two-dimensional (2D) square lattice with inversely phased\ntemporal modulation of the well depths of adjacent lattice sites, and a 2D\nlattice subjected to an array of microscopic rotors commensurate with its\nplaquette structure. In case of the 1D scenario the rescaling of the tunneling\nenergy, previously considered by Eckardt et al. in Phys. Rev. Lett. 95, 260404\n(2005), is reproduced. The 2D lattice with well depth modulation turns out as a\ngeneralization of the 1D case. In the 2D case with staggered rotation, the\nexpression previously found in the case of weak driving by Lim et al. in Phys.\nRev. Lett. 100, 130402 (2008) is generalized, such that its interpretation in\nterms of an artificial staggered magnetic field can be extended into the regime\nof strong driving."
    },
    {
        "anchor": "Spin-Orbit Coupled Quantum Gases: In this review we will discuss the experimental and theoretical progresses in\nstudying spin-orbit coupled degenerate atomic gases during the last two years.\nWe shall first review a series of pioneering experiments in generating\nsynthetic gauge potentials and spin-orbit coupling in atomic gases by\nengineering atom-light interaction. Realization of spin-orbit coupled quantum\ngases opens a new avenue in cold atom physics, and also brings out a lot of new\nphysical problems. In particular, the interplay between spin-orbit coupling and\ninter-atomic interaction leads to many intriguing phenomena. Here, by reviewing\nrecent theoretical studies of both interacting bosons and fermions with\nisotropic Rashba spin-orbit coupling, the key message delivered here is that\nspin-orbit coupling can enhance the interaction effects, and make the\ninteraction effects much more dramatic even in the weakly interacting regime.",
        "positive": "Finite-size scaling analysis of localization transitions in the\n  disordered two-dimensional Bose-Hubbard model within the fluctuation operator\n  expansion method: The disordered Bose-Hubbard model in two dimensions at non-integer filling\nadmits a superfluid to Bose-glass transition at weak disorder. Less understood\nare the properties of this system at strong disorder and energy densities\ncorresponding to excited states. In this work we study the Bose-glass\ntransition of the ground state and the related finite energy localization\ntransition, the mobility edge of the quasiparticle spectrum, a critical energy\nseparating extended from localized quasiparticle excitations. To study these\nthe fluctuation operator expansion is used. The level spacing statistics of the\nquasiparticle excitations, the fractal dimension and decay of the corresponding\nwave functions are consistent with a many-body mobility edge. The finite-size\nscaling of the lowest gaps yields a correction to the mean-field prediction of\nthe superfluid to Bose-glass transition. In its vicinity we discuss spectral\nproperties of the ground state in terms of the dynamic structure factor and the\nspectral function which also shows distinct behavior above and below the\nmobility edge."
    },
    {
        "anchor": "Quantum many-body thermal machines enabled by atom-atom correlations: Particle-particle correlations, characterized by the second-order Glauber\ncorrelation function, play an important role in the understanding of various\nphenomena in radio and optical astronomy, quantum and atom optics, particle\nphysics, condensed matter physics, and quantum many-body theory. However, the\nrelevance of such correlations to quantum thermodynamics has so far remained\nillusive. Here, we propose and investigate a class of quantum many-body thermal\nmachines whose operation is directly enabled by second-order atom-atom\ncorrelations in an ultracold atomic gas. More specifically, we study quantum\nthermal machines that operate in a sudden interaction-quench Otto cycle and\nutilize a one-dimensional Lieb-Liniger gas of repulsively interacting bosons as\nthe working fluid. The atom-atom correlations in such a gas are different to\nthose of a classical ideal gas, and are a result of the interplay between\ninterparticle interactions, quantum statistics, and thermal fluctuations. We\nshow that operating these thermal machines in the intended regimes, such as a\nheat engine, refrigerator, thermal accelerator, or heater, would be impossible\nwithout such atom-atom correlations. Our results constitute a step forward in\nthe design of conceptually new quantum thermodynamic devices which take\nadvantage of uniquely quantum resources such as quantum coherence,\ncorrelations, and entanglement.",
        "positive": "Spin-momentum coupled Bose-Einstein condensates with lattice band\n  pseudospins: The quantum emulation of spin-momentum coupling (SMC), a crucial ingredient\nfor the emergence of topological phases, is currently drawing considerable\ninterest. In previous quantum gas experiments, typically two atomic hyperfine\nstates were chosen as pseudospins. Here, we report the observation of a new\nkind of SMC achieved by loading a Bose-Einstein condensate (BEC) into\nperiodically driven optical lattices. The s- and p-bands of a static lattice,\nwhich act as pseudospins, are coupled through an additional moving lattice\nwhich induces a momentum dependent coupling between the two pseudospins,\nresulting in s-p hybrid Floquet-Bloch bands. We investigate the band structures\nby measuring the quasimomentum of the BEC for different velocities and\nstrengths of the moving lattice and compare our measurements to theoretical\npredictions. The realization of SMC with lattice bands as pseudospins paves the\nway for engineering novel quantum matter using hybrid orbital bands."
    },
    {
        "anchor": "Versatile transporter apparatus for experiments with optically trapped\n  Bose-Einstein condensates: We describe a versatile and simple scheme for producing magnetically and\noptically-trapped Rb-87 Bose-Einstein condensates, based on a moving-coil\ntransporter apparatus. The apparatus features a TOP trap that incorporates the\nmovable quadrupole coils used for magneto-optical trapping and long-distance\nmagnetic transport of atomic clouds. As a stand-alone device, this trap allows\nfor the stable production of condensates containing up to one million atoms. In\ncombination with an optical dipole trap, the TOP trap acts as a funnel for\nefficient loading, after which the quadrupole coils can be retracted, thereby\nmaximizing optical access. The robustness of this scheme is illustrated by\nrealizing the superfluid-to-Mott insulator transition in a three-dimensional\noptical lattice.",
        "positive": "Propagation of first and second sound in a two-dimensional Fermi\n  superfluid: Sound propagation is a macroscopic manifestation of the interplay between the\nequilibrium thermodynamics and the dynamical transport properties of fluids.\nHere, for a two-dimensional system of ultracold fermions, we calculate the\nfirst and second sound velocities across the whole BCS-BEC crossover and we\nanalyze the system response to an external perturbation. In the low-temperature\nregime we reproduce the recent measurements [Phys Rev. Lett. {\\bf 124}, 240403\n(2020)] of the first sound velocity, which, due to the decoupling of density\nand entropy fluctuations, is the sole mode excited by a density probe.\nConversely, a heat perturbation excites only the second sound, which, being\nsensitive to the superfluid depletion, vanishes in the deep BCS regime, and\njumps discontinuously to zero at the Berezinskii-Kosterlitz-Thouless superfluid\ntransition. A mixing between the modes occurs only in the finite-temperature\nBEC regime, where our theory converges to the purely bosonic results."
    },
    {
        "anchor": "Quantum simulators by design - many-body physics in reconfigurable\n  arrays of tunnel-coupled traps: We present a novel platform for the bottom-up construction of itinerant\nmany-body systems: ultracold atoms transferred from a Bose-Einstein condensate\ninto freely configurable arrays of micro-lens generated focused-beam dipole\ntraps. This complements traditional optical lattices and gives a new quality to\nthe field of two-dimensional quantum simulators. The ultimate control of\ntopology, well depth, atom number, and interaction strength is matched by\nsufficient tunneling. We characterize the required light fields, derive the\nBose-Hubbard parameters for several alkali species, investigate the loading\nprocedures and heating mechanisms. To demonstrate the potential of this\napproach, we analyze coupled annular Josephson contacts exhibiting many-body\nresonances.",
        "positive": "String order via Floquet interactions in atomic systems: We study the transverse-field Ising model with interactions that are\nmodulated in time. In a rotating frame, the system is described by a\ntime-independent Hamiltonian with many-body interactions, similar to the\ncluster Hamiltonians of measurement-based quantum computing. In one dimension,\nthere is a three-body interaction, which leads to string order instead of\nconventional magnetic order. We show that the string order is robust to\npower-law interactions that decay with the cube of distance. In two and three\ndimensions, there are five- and seven-body interactions. We discuss adiabatic\npreparation of the ground state as well as experimental implementation with\ntrapped ions, Rydberg atoms, and polar molecules."
    },
    {
        "anchor": "Binary mixture of pseudospin-1/2 Bose gases with interspecies spin\n  exchange: from classical fixed points and ground states to quantum ground\n  states: We consider the effective spin Hamiltonian describing a mixture of two\nspecies of pseudo-spin-1/2 Bose gases with interspecies spin exchange. First we\nanalyze the stability of the fixed points of the corresponding classical\ndynamics, of which the signature is found in quantum dynamics with a\ndisentangled initial state. Focusing on the case without an external potential,\nwe find all the ground states by taking into account quantum fluctuations\naround the classical ground state in each parameter regime. The nature of\nentanglement and its relation with classical bifurcation is investigated. When\nthe total spins of the two species are unequal, the maximal entanglement at the\nparameter point of classical bifurcation is possessed by the excited state\ncorresponding to the classical fixed point which bifurcates, rather than by the\nground state.",
        "positive": "Supercurrent-carrying supersolid in spin-orbit-coupled Bose-Einstein\n  condensates: One of brilliant achievements in spin-orbit-coupled Bose-Einstein condensates\nis the discovery and observation of the supersolid stripe states. So far, all\nstudied supersolid stripe states do not carry supercurrent. In this work, we\nreveal the existence of novel supercurrent-carrying supersolids in\nspin-orbit-coupled Bose-Einstein condensates. The supersolid family has a\nparabolic-like dispersion relation and carries supercurrent which is\nproportional to the quasimomentum. Energetic and dynamical instabilities can\nbreak supercurrent-carrying ability of this supersolid family. An insightful\ninterpretation of the dynamical instability of supercurrent-carrying\nsupersolids from the pure plane-wave phase is provided."
    },
    {
        "anchor": "Spin-charge correlations in finite one-dimensional multi-band Fermi\n  systems: We investigate spin-charge separation of a spin-1/2 Fermi system confined in\na triple well where multiple bands are occupied. We assume that our finite\nfermionic system is close to fully spin polarized while being doped by a hole\nand an impurity fermion with opposite spin. Our setup involves ferromagnetic\ncouplings among the particles in different bands, leading to the development of\nstrong spin-transport correlations in an intermediate interaction regime.\nInteractions are then strong enough to lift the degeneracy among singlet and\ntriplet spin configurations in the well of the spin impurity but not strong\nenough to prohibit hole-induced magnetic excitations to the singlet state.\nDespite the strong spin-hole correlations, the system exhibits spin-charge\ndeconfinement allowing for long-range entanglement of the spatial and spin\ndegrees of freedom.",
        "positive": "Quantum kinetics of quenched two-dimensional Bose superfluids: We study theoretically the non-equilibrium dynamics of a two-dimensional (2D)\nuniform Bose superfluid following a quantum quench, from its short-time\n(prethermal) coherent dynamics to its long-time thermalization. Using a quantum\nhydrodynamic description combined with a Keldysh field formalism, we derive\nquantum kinetic equations for the low-energy phononic excitations of the system\nand characterize both their normal and anomalous momentum distributions. We\napply this formalism to the interaction quench of a 2D Bose gas and study the\nensuing dynamics of its quantum structure factor and coherence function, both\nrecently measured experimentally. Our results indicate that in two dimensions,\na description in terms of independent quasi-particles becomes quickly\ninaccurate and should be systematically questioned when dealing with\nnon-equilibrium scenarios."
    },
    {
        "anchor": "Berry-electrodynamics - Anomalous drift and pumping from time-dependent\n  Berry connection: The Berry curvature of a Bloch band can be interpreted as a local magnetic\nfield in reciprocal space. This analogy can be extended by defining an electric\nfield analog in reciprocal space which arises from the time-dependent Berry\nconnection. We explore the term in the semi-classical equation of motion that\ngives rise to this phenomenon, and show that it can lead to anomalous drift in\nwave packet motion. A similar effect arises from changes in the band population\ndue to periodic driving, where the resulting drift depends on the nature of the\ndrive and can be expressed in terms of a shift vector. Finally, these effects\ncan be combined to build a pump with a net anomalous drift during a cyclic\nevolution in momentum space.",
        "positive": "Conditions for order and chaos in the dynamics of a trapped\n  Bose-Einstein condensate in coordinate and energy space: We investigate numerically conditions for order and chaos in the dynamics of\nan interacting Bose- Einstein condensate (BEC) confined by an external trap cut\noff by a hard-wall box potential. The BEC is stirred by a laser to induce\nexcitations manifesting as irregular spatial and energy oscillations of the\ntrapped cloud. Adding laser stirring to the external trap results in an\neffective time-varying trapping frequency in connection with the dynamically\nchanging combined external+laser potential trap. The resulting dynamics are\nanalyzed by plotting their trajectories in coordinate phase space and in energy\nspace. The Lyapunov exponents are computed to confirm the existence of chaos in\nthe latter space. Quantum effects and trap anharmonicity are demonstrated to\ngenerate chaos in energy space, thus confirming its presence and implicating\neither quantum effects or trap anharmonicity as its generator. The presence of\nchaos in energy space does not necessarily translate into chaos in coordinate\nspace. In general, a dynamic trapping frequency is found to promote chaos in a\ntrapped BEC. An apparent means to suppress chaos in a trapped BEC is achieved\nby increasing the characteristic scale of the external trap with respect to the\ncondensate size."
    },
    {
        "anchor": "Ferro-Nematic ground state of the dilute dipolar Fermi gas: It is shown that a homogeneous two-component Fermi gas with (long range)\ndipolar and short-range isotropic interactions has a {\\em ferro-nematic} phase\nfor suitable values of the dipolar and short-range coupling constants. The\nferro-nematic phase is characterized by having a non-zero magnetization and\nlong range orientational uniaxial order. The Fermi surface of spin up (down)\ncomponent is elongated (compressed) along the direction of the magnetization.",
        "positive": "Geometry of system-bath coupling and gauge fields in bosonic ladders:\n  manipulating currents and driving phase transitions: Quantum systems in contact with an environment display a rich physics\nemerging from the interplay between dissipative and Hamiltonian terms. Here we\nfocus on the role of the geometry of the coupling between the system and the\nbaths. In the specific we consider a dissipative boundary driven ladder in\npresence of a gauge field which can be implemented with ion microtraps arrays.\nWe show that, depending on the geometry, the currents imposed by the baths can\nbe strongly affected by the gauge field resulting in non-equilibrium phase\ntransitions. In different phases both the magnitude of the current and its\nspatial distribution are significantly different. These findings allow for\nnovel strategies to manipulate and control transport properties in quantum\nsystems."
    },
    {
        "anchor": "Many-body interferometry of a Rydberg-dressed spin lattice: Ultracold atoms are an ideal platform to study strongly correlated phases of\nmatter in and out of equilibrium. Much of the experimental progress in this\nfield crucially relies on the control of the contact interaction between two\natoms. Control of strong long-range interactions between distant ground state\natoms has remained a long standing goal, opening the path towards the study of\nfundamentally new quantum many-body systems including frustrated or topological\nmagnets and supersolids. Optical dressing of ground state atoms by\nnear-resonant laser coupling to Rydberg states has been proposed as a versatile\nmethod to engineer such interactions. However, up to now the great potential of\nthis approach for interaction control in a many-body setting has eluded\nexperimental confirmation. Here we report the realisation of coherent\nRydberg-dressing in an ultracold atomic lattice gas and directly probe the\ninduced interaction potential using an interferometric technique with single\natom sensitivity. We use this approach to implement a two-dimensional synthetic\nspin lattice and demonstrate its versatility by tuning the range and anisotropy\nof the effective spin interactions. Our measurements are in remarkable\nagreement with exact solutions of the many-body dynamics, providing further\nevidence for the high degree of accurate interaction control in these systems.\nFinally, we identify a collective many-body decay process, and discuss possible\nroutes to overcome this current limitation of coherence times. Our work marks\nthe first step towards the use of laser-controlled Rydberg interactions for the\nstudy of exotic quantum magnets in optical lattices.",
        "positive": "Selective photoexcitation of exciton-polariton vortices: We resonantly excite exciton-polariton states confined in cylindrical traps.\nUsing a homodyne detection setup, we are able to image the phase and amplitude\nof the confined polariton states. We evidence the excitation of vortex states,\ncarrying an integer angular orbital momentum m, analogous to the transverse\nTEM01* \"donut\" mode of cylindrically symmetric optical resonators. Tuning the\nexcitation conditions allows us to select the charge of the vortex. In this\nway, the injection of singly charged (m = 1 & m = -1) and doubly charged (m =\n2) polariton vortices is shown. This work demonstrates the potential of\nin-plane confinement coupled with selective excitation for the topological\ntailoring of polariton wavefunctions."
    },
    {
        "anchor": "Interacting spin-orbit-coupled spin-1 Bose-Einstein condensates: The recent experimental realization of spin-orbit (SO) coupling for spin-1\nultracold atoms opens an interesting avenue for exploring SO-coupling-related\nphysics in large-spin systems, which is generally unattainable in electronic\nmaterials. In this paper, we study the effects of interactions between atoms on\nthe ground states and collective excitations of SO-coupled spin-1 Bose-Einstein\ncondensates (BECs) in the presence of a spin-tensor potential. We find that\nferromagnetic interaction between atoms can induce a stripe phase exhibiting\nin-phase or out-of-phase modulating patterns between spin-tensor and\nzero-spin-component density waves. We characterize the phase transitions\nbetween different phases using the spin-tensor density as well as the\ncollective dipole motion of the BEC. We show that there exists a double\nmaxon-roton structure in the Bogoliubov-excitation spectrum, attributed to the\nthree band minima of the SO-coupled spin-1 BEC.",
        "positive": "Universal relations for ultracold reactive molecules: The realization of ultracold polar molecules in laboratories has pushed both\nphysics and chemistry to new realms. In particular, these polar molecules offer\nscientists unprecedented opportunities to explore chemical reactions in the\nultracold regime where quantum effects become profound. However, a key question\nabout how two-body losses depend on quantum correlations in an interacting\nmany-body system remains open so far. Here, we present a number of universal\nrelations that directly connect two-body losses to other physical observables,\nincluding the momentum distribution and density correlation functions. These\nrelations, which are valid for arbitrary microscopic parameters, such as the\nparticle number, the temperature, and the interaction strength, unfold the\ncritical role of contacts, a fundamental quantity of dilute quantum systems in\ndetermining the reaction rate of quantum reactive molecules in a many-body\nenvironment. Our work opens the door to an unexplored area intertwining quantum\nchemistry, atomic, molecular and optical physics, and condensed matter physics."
    },
    {
        "anchor": "Multi-particle composites in density-imbalanced quantum fluids: We consider two-component one-dimensional quantum gases with density\nimbalance. While generically such fluids are two-component Luttinger liquids,\nwe show that if the ratio of the densities is a rational number, p/q, and mass\nasymmetry between components is sufficiently strong, one of the two eigenmodes\nacquires a gap. The gapped phase corresponds to (algebraic) ordering of\n(p+q)-particle composites. In particular, for attractive mixtures, this implies\nthat the superconducting correlations are destroyed. We illustrate our\npredictions by numerical simulations of the fermionic Hubbard model with\nhopping asymmetry.",
        "positive": "Nonperturbative renormalization-group approach to strongly-correlated\n  lattice bosons: We present a nonperturbative renormalization-group approach to the\nBose-Hubbard model. By taking as initial condition of the renormalization-group\nflow the (local) limit of decoupled sites, we take into account both local and\nlong-distance fluctuations in a nontrivial way. This approach yields a phase\ndiagram in very good quantitative agreement with quantum Monte Carlo\nsimulations, and reproduces the two universality classes of the\nsuperfluid--Mott-insulator transition. The critical behavior near the\nmulticritical points, where the transition takes place at constant density,\nagrees with the original predictions of Fisher {\\it et al.} [Phys. Rev. B {\\bf\n40}, 546 (1989)] based on simple scaling arguments. At a generic transition\npoint, the critical behavior is mean-field like with logarithmic corrections in\ntwo dimensions. In the weakly-correlated superfluid phase (far away from the\nMott insulating phase), the renormalization-group flow is controlled by the\nBogoliubov fixed point down to a characteristic (Ginzburg) momentum scale $k_G$\nwhich is much smaller than the inverse healing length $k_h$. In the vicinity of\nthe multicritical points, when the density is commensurate, we identify a sharp\ncrossover from a weakly- to a strongly-correlated superfluid phase where the\ncondensate density and the superfluid stiffness are strongly suppressed and\nboth $k_G$ and $k_h$ are of the order of the inverse lattice spacing."
    },
    {
        "anchor": "Feshbach Resonance in a Synthetic Non-Abelian Gauge Field: We study the Feshbach resonance of spin-1/2 particles in the presence of a\nuniform synthetic non-Abelian gauge field that produces spin orbit coupling\nalong with constant spin potentials. We develop a renormalizable quantum field\ntheory that includes the closed channel boson which engenders the Feshbach\nresonance, in the presence of the gauge field. By a study of the scattering of\ntwo particles in the presence of the gauge field, we show that the Feshbach\nmagnetic field, where the apparent low energy scattering length diverges,\ndepends on the conserved centre of mass momentum of the two particles. For high\nsymmetry gauge fields, such as the one which produces an isotropic Rashba spin\norbit coupling, we show that the system supports two bound states over a regime\nof magnetic fields for a negative background scattering length and resonance\nwidth comparable to the energy scale of the spin orbit coupling. We discuss the\nconsequences of these findings for the many body setting, and point out that a\nbroad resonance (width larger than spin orbit coupling energy scale) is most\nfavourable for the realization of the rashbon condensate.",
        "positive": "Spin transport between polarized Fermi gases near the ferromagnetic\n  phase transition: We theoretically study the spin current between two polarized Fermi gases\nwith repulsive interactions near the itinerant ferromagnetic phase transition.\nWe consider a two-terminal model where the left reservoir is fixed to be fully\npolarized while the polarization of the right reservoir is tuned through a\nfictitious magnetic field defined by the chemical-potential difference between\ndifferent atomic hyperfine states. We calculate the spectra of the spin-flip\nsusceptibility function, which displays a magnon dispersion emerging from the\nStoner continuum at low momentum in the ferromagnetic phase. Based on the\nspin-flip susceptibility and using Keldysh Green's function formalism, we\ninvestigate the spin current induced by quasiparticle and spin-flip tunneling\nprocesses, respectively, and show their dependence on the polarization bias\nbetween two reservoirs. The one-body (quasiparticle) tunneling demonstrates a\nlinear dependence with respect to the polarization bias. In contrast, the\nspin-flip process manifests a predominantly cubic dependence on the bias. While\nindicating an enhanced magnon tunneling in the strong-coupling regime, our\nresults also demonstrate a characteristic behavior around the critical\nrepulsive strength for ferromagnetic phase transition at low temperatures."
    },
    {
        "anchor": "Ultracold mixtures of metastable He and Rb: scattering lengths from ab\n  initio calculations and thermalization measurements: We have investigated the ultracold interspecies scattering properties of\nmetastable triplet He and Rb. We performed state-of-the-art ab initio\ncalculations of the relevant interaction potential, and measured the\ninterspecies elastic cross section for an ultracold mixture of metastable\ntriplet $^4$He and $^{87}$Rb in a quadrupole magnetic trap at a temperature of\n0.5 mK. Our combined theoretical and experimental study gives an interspecies\nscattering length $a_{4+87}=+17^{+1}_{-4}$ $a_0$, which prior to this work was\nunknown. More general, our work shows the possibility of obtaining accurate\nscattering lengths using ab initio calculations for a system containing a\nheavy, many-electron atom, such as Rb.",
        "positive": "Stability against three-body clustering in one-dimensional spinless\n  p-wave fermions: We theoretically investigate in-medium two- and three-body correlations in\none-dimensional spinless fermions with attractive two-body p-wave interaction.\nBy investigating the variational problem of two- and three-body states above\nthe Fermi sea, we elucidate the fate of the in-medium two- and three-body\ncluster states. The one-dimensional system with the strong p-wave interaction\nis found to be stable against the formation of three-body clusters even in the\npresence of the Fermi sea, in contrast to higher-dimensional systems that\nsuffer the strong three-body loss associated with the trimer formation."
    },
    {
        "anchor": "Particle partition entanglement of one dimensional spinless fermions: We investigate the scaling of the R\\'{e}nyi entanglement entropies for a\nparticle bipartition of interacting spinless fermions in one spatial dimension.\nIn the Tomonaga-Luttinger liquid regime, we calculate the second R\\'{e}nyi\nentanglement entropy and show that the leading order finite-size scaling is\nequal to a universal logarithm of the system size plus a non-universal\nconstant. Higher-order corrections decay as power-laws in the system size with\nexponents that depend only on the Luttinger parameter. We confirm the\nuniversality of our results by investigating the one dimensional $t-V$ model of\ninteracting spinless fermions via exact-diagonalization techniques. The\nresulting sensitivity of the particle partition entanglement to boundary\nconditions and statistics supports its utility as a probe of quantum liquids.",
        "positive": "Negative differential conductivity and quantum statistical effects in a\n  three-site Bose-Hubbard model: The use of an electron beam to remove ultracold atoms from selected sites in\nan optical lattice has opened up new opportunities to study transport in\nquantum systems [R. Labouvie {\\it et al.\\ }, Phys.\\ Rev.\\ Lett.\\ {\\bf 115},\n050601 (2015)]. Inspired by this experimental result, we examine the effects of\nnumber difference, dephasing, and initial quantum statistics on the filling of\nan initially depleted middle well in the three-well inline Bose-Hubbard model.\nWe find that the well-known phenomenon of macroscopic self-trapping is the main\ncontributor to oscillatory negative differential conductivity in our model,\nwith phase diffusion being a secondary effect. However, we find that phase\ndiffusion is required for the production of direct atomic current, with the\ncoherent process showing damped oscillatory currents. We also find that our\nresults are highly dependent on the initial quantum states of the atoms in the\nsystem."
    },
    {
        "anchor": "Two supersolid phases in hard-core extended Bose-Hubbard model: The effect of the next-nearest-neighbor (nnn) tunneling on the hard-core\nextended Bose-Hubbard model on square lattices is investigated. By means of the\ncluster mean-field theory, the ground-state phase diagrams are determined. When\na modest nnn tunneling is introduced, depending on its sign, two distinct\nsupersolid states with checkerboard crystal structures are found away from\nhalf-filing. The characters of various phase transitions out of these two\nsupersolid states are discussed. In particular, for the case with kinetic\nfrustration, the existence of a half supersolid phase possessing both solid and\nunconventional superfluid orders is established. Our work hence sheds light on\nthe search of this interesting supersolid phase in real ultracold lattice gases\nwith frustrated tunnelings.",
        "positive": "Universal relations for dilute systems with two-body decays in reduced\n  dimensions: Physical systems in reduced dimensions exhibit intriguing properties. For\ninstance, the dependences of two-body and many-body physics on scattering\nlengths are distinct from their counterparts in three dimensions. Whereas many\nstudies of ultracold atoms and molecules in reduced dimensions have been\nfocusing on closed systems, two-body losses may occur in such systems. Here, we\nshow that the two-body inelastic loss rate in reduced dimensions can be\nexpressed in universal relations that are governed by contacts. These universal\nrelations correlate the two-body decay rate with other physical observables at\narbitrary temperatures and interaction strengths. Our results will provide\nexperimentalists with a new protocol to study inelastic scatterings in both\nfew- and many-body systems in reduced dimensions."
    },
    {
        "anchor": "Exciton-Polariton Trapping and Potential Landscape Engineering: Exciton-polaritons in semiconductor microcavities have advanced to become a\nmodel system for studying dynamical Bose-Einstein condensation, macroscopic\ncoherence, many-body effects, nonclassical states of light and matter, and\npossibly quantum phase transitions in a solid state. Being low mass bosons,\nthese light-matter quasiparticles can condense at comparably high temperatures\nup to 300K, while preserving fundamental properties such as coherence in space\nand time domain even when they are out of equilibrium with the environment.\nAlthough the presence of an in-plane polariton confinement potential is not\nstrictly necessary in order to observe condensation of polaritons, engineering\nthe polariton confinement is a key to controlling, shaping and directing the\nflow of polaritons. Prototype polariton-based optoelectronic devices rely on\nultrafast photon-like velocities and strong nonlinearities, as well as on\ntailored confinement. Nanotechnology provides several pathways to achieving\nsuch a confinement, and the specific features and advantages of the different\ntechniques are discussed in this paper. As hybrid exciton-photon\nquasiparticles, polaritons can be trapped via their excitonic as well as their\nphotonic component, which leads to a wide choice of highly complementary\ntechniques. Here we highlight the almost free choice of trapping geometries and\ndepths of confinement that provides a powerful tool for control and\nmanipulation of polariton systems both in semi-classical and quantum domain.\nFurthermore, the possibility to observe effects of polariton blockade, Mott\ninsulator physics, and population of higher-order bands in sophisticated\nlattice potentials is discussed. The observation of such effects will signify\nthe opportunity for the realization of novel polaritonic non-classical light\nsources and quantum simulators.",
        "positive": "Driven dissipative preparation of few-body Laughlin states of Rydberg\n  polaritons in twisted cavities: We present a driven dissipative protocol for creating an optical analog of\nthe Laughlin state in a system of Rydberg polaritons in a twisted optical\ncavity. We envision resonantly driving the system into a 4-polariton state by\ninjecting photons in carefully selected modes. The dissipative nature of the\npolariton-polariton interactions leads to a decay into a two-polariton analog\nof the Laughlin state. Generalizations of this technique could be used to\nexplore fractional statistics and anyon based quantum information processing.\nWe also model recent experiments that attempt to coherently drive into this\nsame state."
    },
    {
        "anchor": "Twisted behavior of dipolar BECs: Dipole-dipole interaction beyond the\n  self-consistent field approximation and exchange electric dipole interaction: Dipole-dipole interaction is a long-range interaction, hence we could expect\nthat the self-consistent field approximation might be applied. In most cases it\nis correct, but dipolar BECs reveal a surprise. Structure of the\nself-consistent field term requires that interacting particles are in different\nquantum states, while in BECs all particles in a single quantum state. This\nfact requires to consider the two-particle polarisation, which describes\ndipole-dipole interaction, in more details. We present this consideration and\nshow an astonishing result that the two-particle quantum correlation in dipolar\nBECs reveals in the same form as the self-consistent field term.",
        "positive": "Effective theory of chiral two-dimensional superfluids: We construct, to leading orders in the momentum expansion, an effective\ntheory of a chiral $p_x + ip_y$ two-dimensional fermionic superfluid at zero\ntemperature that is consistent with nonrelativistic general coordinate\ninvariance. This theory naturally incorporates the parity and time reversal\nviolating effects such as the Hall viscosity and the edge current. The particle\nnumber current and stress tensor are computed and their linear response to\nelectromagnetic and gravitational sources is calculated. We also consider an\nisolated vortex in a chiral superfluid and identify the leading chirality\neffect in the density depletion profile."
    },
    {
        "anchor": "Neural-network quantum states for ultra-cold Fermi gases: Ultra-cold Fermi gases display diverse quantum mechanical properties,\nincluding the transition from a fermionic superfluid BCS state to a bosonic\nsuperfluid BEC state, which can be probed experimentally with high precision.\nHowever, the theoretical description of these properties is challenging due to\nthe onset of strong pairing correlations and the non-perturbative nature of the\ninteraction among the constituent particles. This work introduces a novel\nPfaffian-Jastrow neural-network quantum state that includes backflow\ntransformation based on message-passing architecture to efficiently encode\npairing, and other quantum mechanical correlations. Our approach offers\nsubstantial improvements over comparable ans\\\"atze constructed within the\nSlater-Jastrow framework and outperforms state-of-the-art diffusion Monte Carlo\nmethods, as indicated by our lower ground-state energies. We observe the\nemergence of strong pairing correlations through the opposite-spin pair\ndistribution functions. Moreover, we demonstrate that transfer learning\nstabilizes and accelerates the training of the neural-network wave function,\nenabling the exploration of the BCS-BEC crossover region near unitarity. Our\nfindings suggest that neural-network quantum states provide a promising\nstrategy for studying ultra-cold Fermi gases.",
        "positive": "Bosonic fractional quantum Hall conductance in shaken honeycomb optical\n  lattices without flat bands: We propose a scheme to realize bosonic fractional quantum Hall conductance in\nshaken honeycomb optical lattices. This scheme does not require a very flat\nband, and the necessary long-range interaction relies on s-wave scattering,\nwhich is common in many ultracold-atom experiments. By filling the lattice at\n1/4 with identical bosons under Feshbach resonance, two degenerate many-body\nground states share one Chern number of 1 and correspond exactly to the\nfractional quantum Hall conductance of 1/2. Meanwhile, we prove that the\nfractional quantum Hall state can be prepared by adiabatically turning on the\nlattice shaking, and the fractional conductance is robust in the shaken\nlattice. This provides an easy way to initialize and prepare the fractional\nquantum Hall states in ultracold-atom platforms, and it paves the way to\ninvestigate and simulate strongly correlated quantum matters with degenerate\nquantum gas."
    },
    {
        "anchor": "Anderson localisation in steady states of microcavity polaritons: We present an experimental signature of the Anderson localisation of\nmicrocavity polaritons, and provide a systematic study of the dependence on\ndisorder strength. We reveal a controllable degree of localisation, as\ncharacterised by the inverse-participation ratio, by tuning the positional\ndisorder of arrays of interacting mesas. This constitutes the realisation of\ndisorder-induced localisation in a driven-dissipative system. In addition to\nbeing an ideal candidate for investigating localisation in this regime,\nmicrocavity polaritons hold promise for low-power, ultra-small devices and\ntheir localisation could be used as a resource in quantum memory and quantum\ninformation processing.",
        "positive": "Simulating artificial one-dimensional physics with ultra-cold fermionic\n  atoms: three exemplary themes: For over twenty years, ultra-cold atomic systems have formed an almost\nperfect arena for simulating different quantum many-body phenomena and exposing\ntheir non-obvious and very often counterintuitive features. Thanks to extremely\nprecise controllability of different parameters they are able to capture\ndifferent quantum properties which were previously recognized only as\ntheoretical curiosities. Here, we go over the current experimental progress in\nexploring the curious one-dimensional quantum world of fermions from the\nperspective of three subjectively selected trends being currently under\nvigorous experimental validation: (i) unconventional pairing in attractively\ninteracting fermionic mixtures, (ii) fermionic systems subjected to the\nartificial spin-orbit coupling, (iii) fermionic gases of atoms with high SU(N)\nsymmetry of internal states."
    },
    {
        "anchor": "Semisuper Efimov effect of two-dimensional bosons at a three-body\n  resonance: Wave-particle duality in quantum mechanics allows for a halo bound state\nwhose spatial extension far exceeds a range of the interaction potential. What\nis even more striking is that such quantum halos can be arbitrarily large on\nspecial occasions. The two examples known so far are the Efimov effect and the\nsuper Efimov effect, which predict that spatial extensions of higher excited\nstates grow exponentially and double exponentially, respectively. Here, we\nestablish yet another new class of arbitrarily large quantum halos formed by\nspinless bosons with short-range interactions in two dimensions. When the\ntwo-body interaction is absent but the three-body interaction is resonant, four\nbosons exhibit an infinite tower of bound states whose spatial extensions scale\nas $R_n\\sim e^{(\\pi n)^2/27}$ for a large $n$. The emergent scaling law is\nuniversal and is termed a semisuper Efimov effect, which together with the\nEfimov and super Efimov effects constitutes a trio of few-body universality\nclasses allowing for arbitrarily large quantum halos.",
        "positive": "Derivation of non-Markoffian transport equations for trapped cold atoms\n  in nonequilibrium thermal field theory: The non-Markoffian transport equations for the systems of cold Bose atoms\nconfined by a external potential both without and with a Bose-Einstein\ncondensate are derived in the framework of nonequilibrium thermal filed theory\n(Thermo Field Dynamics). Our key elements are an explicit particle\nrepresentation and a self-consistent renormalization condition which are\nessential in thermal field theory. The non-Markoffian transport equation for\nthe non-condensed system, derived at the two-loop level, is reduced in the\nMarkoffian limit to the ordinary quantum Boltzmann equation derived in the\nother methods. For the condensed system, we derive a new transport equation\nwith an additional collision term which becomes important in the Landau\ninstability."
    },
    {
        "anchor": "Topological Condensate in an Interaction Induced Gauge Potential: We systematically investigate the ground state and elementary excitations of\na Bose-Einstein Condensate with a synthetic vector potential, which is induced\nby the many-body effects and atom-light coupling. For a sufficiently strong\ninter-atom interaction, we find the condensate undergoes a Stoner-type\nferromagnetic transition through the self-consistent coupling with the vector\npotential. For a weak interaction, the critical velocity of a supercurrent is\nfound anisotropic due to the density fluctuations affecting the gauge field. We\nfurther analytically demonstrate the topological ground state with a coreless\nvortex ring in a 3D harmonic trap and a coreless vortex-antivortex pair in a 2D\ntrap. The circulating persistent current is measurable in the time-of-flight\nexperiment or in the dipolar oscillation through the violation of Kohn theorem.",
        "positive": "Path-integral approach to the thermodynamics of bosons with memory:\n  Partition function and specific heat: For a system of bosons that interact through a class of general memory\nkernels, a recurrence relation for the partition function is derived within the\npath-integral formalism. This approach provides a generalization to previously\nknown treatments in the literature of harmonically coupled systems of identical\nparticles. As an example the result is applied to the specific heat of a\nsimplified model of an open quantum system of bosons, harmonically coupled to a\nreservoir of distinguishable fictitious masses."
    },
    {
        "anchor": "Orbital ordering of ultracold alkaline-earth atoms in optical lattices: We report on a dynamical mean-field theoretical analysis of emerging\nlow-temperature phases in multicomponent gases of fermionic\nalkaline-earth(-like) atoms in state-dependent optical lattices. Using the\nexample of $^{173}$Yb atoms, we show that a two-orbital mixture with two\nnuclear spin components is a promising candidate for studies of not only\nmagnetic but also staggered orbital ordering peculiar to certain solid-state\nmaterials. We calculate and study the phase diagram of the full Hamiltonian\nwith parameters similar to existing experiments and reveal an antiferroorbital\nphase. This long-range-ordered phase is inherently stable, and we analyze the\nchange of local and global observables across the corresponding transition\nlines, paving the way for experimental observations. Furthermore, we suggest a\nrealistic extension of the system to include and probe a Jahn-Teller source\nfield playing one of the key roles in real crystals.",
        "positive": "Vortex macroscopic superpositions in ultracold bosons in a double-well\n  potential: We study macroscopic superpositions in the orbital rather than the spatial\ndegrees of freedom, in a three-dimensional double-well system. We show that the\nensuing dynamics of $N$ interacting excited ultracold bosons, which in general\nrequires at least eight single-particle modes and ${N+7 \\choose N}$ Fock\nvectors, is described by a surprisingly small set of many-body states. An\ninitial state with half the atoms in each well, and purposely excited in one of\nthem, gives rise to the tunneling of axisymmetric and transverse vortex\nstructures. We show that transverse vortices tunnel orders of magnitude faster\nthan axisymmetric ones and are therefore more experimentally accessible. The\ntunneling process generates macroscopic superpositions only distinguishable by\ntheir orbital properties and within experimentally realistic times."
    },
    {
        "anchor": "Disorder-Driven Loss of Phase Coherence in a Quasi-2D Cold Atom System: We study the order parameter of a quasi-2D gas of ultracold atoms trapped in\nan optical potential in the presence of controllable disorder. Our results show\nthat disorder drives phase fluctuations without significantly affecting the\namplitude of the quasi-condensate order parameter. This is evidence that\ndisorder can drive phase fluctuations in 2D systems, relevant to the\nphase-fluctuation mechanism for the superconductor-to-insulator phase\ntransition (SIT) in disordered 2D superconductors.",
        "positive": "WKB approach and quantum corrections to classical dynamics in the\n  Josephson problem: We apply a many-body Wentzel-Kramers-Brillouin (WKB) approach to determine\nthe leading quantum corrections to the semiclassical dynamics of the Josephson\nmodel, describing interacting bosons able to tunnel between two localized\nstates. The semiclassical dynamics is known to divide between regular\noscillations and self-trapped oscillations where the sign of the imbalance\nremains fixed. In both cases, the WKB wave functions are matched to Airy\nfunctions, yielding a modified Bohr-Sommerfeld quantization condition. At the\ncritical energy dividing normal and self-trapped oscillations, the WKB wave\nfunctions should instead be matched to parabolic cylinder functions, leading to\na quantization formula that is not just the Bohr-Sommerfeld formula, and\nrecovering the known logarithmic quantum break times at this energy. This work\nthus provides another illustration of the usefulness of the WKB approach in\ncertain many-body problems."
    },
    {
        "anchor": "Stoner ferromagnetism in a thermal pseudospin-1/2 Bose gas: We compute the finite-temperature phase diagram of a pseudospin-$1/2$ Bose\ngas with contact interactions, using two complementary methods: the random\nphase approximation (RPA) and self-consistent Hartree-Fock theory. We show that\nthe inter-spin interactions, which break the (pseudo) spin-rotational symmetry\nof the Hamiltonian, generally lead to the appearance of a magnetically ordered\nphase at temperatures above the superfluid transition. In three dimensions, we\npredict a normal easy-axis/easy-plane ferromagnet for sufficiently strong\nrepulsive/attractive inter-species interactions respectively. The normal\neasy-axis ferromagnet is the bosonic analog of Stoner ferromagnetism known in\nelectronic systems. For the case of inter-spin attraction, we also discuss the\npossibility of a \\textit{bosonic} analog of the Cooper paired phase. This state\nis shown to significantly lose in energy to the transverse ferromagnet in three\ndimensions, but is more energetically competitive in lower dimensions.\nExtending our calculations to a spin-orbit-coupled Bose gas with equal Rashba\nand Dresselhaus-type couplings (as recently realized in experiment), we\ninvestigate the possibility of stripe ordering in the normal phase. Within our\napproximations however, we do not find an instability towards stripe formation,\nsuggesting that the stripe order melts below the condensation temperature,\nwhich is consistent with the experimental observations of Ji \\textit{et al.}\n[Ji \\textit{et al.}, Nature Physics \\textbf{10}, 314 (2014)].",
        "positive": "Snake instability of dark solitons in fermionic superfluids: We present numerical calculations of the snake instability in a Fermi\nsuperfluid within the Bogoliubov-de Gennes theory of the BEC to BCS crossover\nusing the random phase approximation complemented by time-dependent\nsimulations. We examine the snaking behaviour across the crossover and quantify\nthe timescale and lengthscale of the instability. While the dynamic shows\nextensive snaking before eventually producing vortices and sound on the BEC\nside of the crossover, the snaking dynamics is preempted by decay into sound\ndue to pair breaking in the deep BCS regime. At the unitarity limit,\nhydrodynamic arguments allow us to link the rate of snaking to the\nexperimentally observable ratio of inertial to physical mass of the soliton. In\nthis limit we witness an unresolved discrepancy between our numerical estimates\nfor the critical wavenumber of suppression of the snake instability and recent\nexperimental observations with an ultra-cold Fermi gas."
    },
    {
        "anchor": "Dipolar bright solitons and solitary vortices in a radial lattice: Stabilizing vortex solitons with high values of the topological charge, S, is\na challenging issue in optics, studies of Bose-Einstein condensates (BECs) and\nother fields. To develop a new approach to the solution of this problem, we\nconsider a two-dimensional dipolar BEC under the action of an axisymmetric\nradially periodic lattice potential, $V(r)\\sim \\cos (2r+\\delta )$, with dipole\nmoments polarized perpendicular to the system's plane, which gives rise to\nisotropic repulsive dipole-dipole interactions (DDIs). Two radial lattices are\nconsidered, with $\\delta =0$ and $\\pi $, i.e., a potential maximum or minimum\nat $r=0$, respectively. Families of vortex gapsoliton (GSs) with $S=1$ and\n$S\\geq 2$, the latter ones often being unstable in other settings, are\ncompletely stable in the present system (at least, up to $S=11$), being trapped\nin different annular troughs of the radial potential. The vortex solitons with\ndifferent $S$ may stably coexist in sufficiently far separated troughs.\nFundamental GSs, with $S=0$, are found too. In the case of $\\delta =0$, the\nfundamental solitons are ring-shaped modes, with a local minimum at $r=0.$At\n$\\delta =\\pi $, they place a density peak at the center.",
        "positive": "Virial relations for ultracold trapped Fermi gases with finite range\n  interactions through the BCS-BEC crossover: We study the virial relations for ultracold trapped two component Fermi gases\nin the case of short finite range interactions. Numerical verifications for\nsuch relations are reported through the BCS-BEC crossover. As an intermediate\nstep, it is necessary to evaluate the partial derivatives of the many body\nenergy with respect to the inverse of the scattering length and with respect to\nthe interaction range. They are found to have extreme values at the unitary\nlimit. The virial results are used to check the quality of the variational wave\nfunction involved in the calculations."
    },
    {
        "anchor": "Light-induced coherence in an atom-cavity system: We demonstrate light-induced formation of coherence in a cold atomic gas\nsystem that utilizes the suppression of a competing density wave (DW) order.\nThe condensed atoms are placed in an optical cavity and pumped by an external\noptical standing wave, which induces a long-range interaction mediated by\nphoton scattering and a resulting DW order above a critical pump strength. We\nshow that light-induced temporal modulation of the pump wave can suppress this\nDW order and restore coherence. This establishes a foundational principle of\ndynamical control of competing orders analogous to a hypothesized mechanism for\nlight-induced superconductivity in high-$T_c$ cuprates.",
        "positive": "Interaction Quench Induced Multimode Dynamics of Finite Atomic Ensembles: The correlated non-equilibrium dynamics of few-boson systems in\none-dimensional finite lattices is investigated. Starting from weak\ninteractions we perform a sudden interaction quench and employ the numerically\nexact Multi-Layer Multi-Configuration time-dependent Hartree method for bosons\nto obtain the resulting quantum dynamics. Focusing on the low-lying modes of\nthe finite lattice we observe the emergence of density-wave tunneling,\nbreathing and cradle-like processes. In particular, the tunneling induced by\nthe quench leads to a \"global\" density-wave oscillation. The resulting\nbreathing and cradle modes are inherent to the local intrawell dynamics and\nconnected to excited-band states. Moreover, the interaction quenches couple the\ndensity-wave and the cradle modes allowing for resonance phenomena. These are\nassociated with an avoided-crossing in the respective frequency spectrum and\nlead to a beating dynamics for the cradle. Finally, complementing the numerical\nstudies, an effective Hamiltonian in terms of the relevant Fock states is\nderived for the description of the spectral properties and the related resonant\ndynamics."
    },
    {
        "anchor": "Density wave instability in a 2D dipolar Fermi gas: We consider a uniform dipolar Fermi gas in two-dimensions (2D) where the\ndipole moments of fermions are aligned by an orientable external field. We\nobtain the ground state of the gas in Hartree-Fock approximation and\ninvestigate RPA stability against density fluctuations of finite momentum. It\nis shown that the density wave instability takes place in a broad region where\nthe system is stable against collapse. We also find that the critical\ntemperature can be a significant fraction of Fermi temperature for a realistic\nsystem of polar molecules.",
        "positive": "The inverse problem for the Gross - Pitaevskii equation: Two different methods are proposed for the generation of wide classes of\nexact solutions to the stationary Gross - Pitaevskii equation (GPE). The first\nmethod, suggested by the work by Kondrat'ev and Miller (1966), applies to\none-dimensional (1D) GPE. It is based on the similarity between the GPE and the\nintegrable Gardner equation, all solutions of the latter equation (both\nstationary and nonstationary ones) generating exact solutions to the GPE, with\nthe potential function proportional to the corresponding solutions. The second\nmethod is based on the \"inverse problem\" for the GPE, i.e. construction of a\npotential function which provides a desirable solution to the equation.\nSystematic results are presented for 1D and 2D cases. Both methods are\nillustrated by a variety of localized solutions, including solitary vortices,\nfor both attractive and repulsive nonlinearity in the GPE. The stability of the\n1D solutions is tested by direct simulations of the time-dependent GPE."
    },
    {
        "anchor": "Laser Manipulation of Spin-Exchange Interaction Between Alkaline-Earth\n  Atoms in $^1$S$_0$ and $^3$P$_2$ States: Ultracold gases of fermionic alkaline-earth (like) atoms are hopeful\ncandidates for the quantum simulation of many-body physics induced by magnetic\nimpurities (e.g., the Kondo physics), because there are spin-exchange\ninteractions (SEIs) between two atoms in the electronic ground ($^1$S$_0$) and\nmetastable ($^3$P) state, respectively. Nevertheless, this SEI cannot be tuned\nvia magnetic Feshbach resonance. In this work we propose three methods to\ncontrol the SEI between one atom in the $^1$S$_0$ state and another atom in the\n$^3$P$_2$ states or $^3$P$_2$-$^3$P$_0$ dressed states, with one or two laser\nbeams.These methods are based on the spin-dependent AC-Stark shifts of the\n$^3$P$_2$ states, or the $^3$P$_2$-$^3$P$_0$ Raman coupling. We show that due\nto the structure of alkaline-earth (like) atoms, the heating effects induced by\nthe laser beams of our methods are very weak. For instance, for ultracold Yb\natoms, AC-Stark-shift difference of variant spin states of the $^3$P$_2(F=3/2)$\nlevel, or the strength of the $^3$P$_2$-$^3$P$_0$ Raman coupling, could be of\nthe order of $(2\\pi)$MHz, while the heating rate (photon scattering rate) is\nonly of the order of Hz. As a result, the Feshbach resonances, with which one\ncan efficiently control the SEI by changing the laser intensity, may be induced\nby the laser beams with low-enough heating rate, even if the scattering lengths\nof the bare inter-atomic interaction are so small that being comparable with\nthe length scale associated with the van der Waals interaction.",
        "positive": "Dark solitons in cigar-shaped Bose-Einstein condensates in double-well\n  potentials: We study the statics and dynamics of dark solitons in a cigar-shaped\nBose-Einstein condensate confined in a double-well potential. Using a\nmean-field model with a non-cubic nonlinearity, appropriate to describe the\ndimensionality crossover regime from one to three dimensional, we obtain\nbranches of solutions in the form of single- and multiple-dark soliton states,\nand study their bifurcations and stability. It is demonstrated that there exist\ndark soliton states which do not have a linear counterpart and we highlight the\nrole of anomalous modes in the excitation spectra. Particularly, we show that\nanomalous mode eigenfrequencies are closely connected to the characteristic\nsoliton frequencies as found from the solitons' equations of motion, and how\nanomalous modes are related to the emergence of instabilities. We also analyze\nin detail the role of the height of the barrier in the double well setting,\nwhich may lead to instabilities or decouple multiple dark soliton states."
    },
    {
        "anchor": "Quantum state of the fermionic carriers in a transport channel\n  connecting particle reservoirs: We analyze quantum state of fermionic carriers in a transport channel\nattached to a particle reservoir. The analysis is done from the first\nprinciples by considering microscopic models of the reservoir and transport\nchannel. In the case of infinite effective temperature of the reservoir we\ndemonstrate a full agreement between the results of straightforward numerical\nsimulations of the system dynamics and solution of the specified master\nequation on the single-particle density matrix of the carriers in the channel.\nThis allows us to predict the quantum state of carriers in the case where\ntransport channel connects two reservoirs with different chemical potentials.",
        "positive": "Eigenfunction structure and scaling of two interacting particles in the\n  one-dimensional Anderson model: The localization properties of eigenfunctions for two interacting particles\nin the one-dimensional Anderson model are studied for system sizes up to\n$N=5000$ sites corresponding to a Hilbert space of dimension $\\approx 10^7$\nusing the Green function Arnoldi method. The eigenfunction structure is\nillustrated in position, momentum and energy representation, the latter\ncorresponding to an expansion in non-interacting product eigenfunctions.\nDifferent types of localization lengths are computed for parameter ranges in\nsystem size, disorder and interaction strengths inaccessible until now. We\nconfirm that one-parameter scaling theory can be successfully applied provided\nthat the condition of $N$ being significantly larger than the one-particle\nlocalization length $L_1$ is verified. The enhancement effect of the\ntwo-particle localization length $L_2$ behaving as $L_2\\sim L_1^2$ is clearly\nconfirmed for a certain quite large interval of optimal interactions strengths.\nFurther new results for the interaction dependence in a very large interval, an\nenergy value outside the band center, and different interaction ranges are\nobtained."
    },
    {
        "anchor": "Hydrodynamic VS collisionless dynamics of a 1D harmonically trapped Bose\n  gas: By using a sum rule approach we investigate the transition between the\nhydrodynamic and the collisionless regime of the collective modes in a 1D\nharmonically trapped Bose gas. Both the weakly interacting gas and the\nTonks-Girardeau limits are considered. We predict that the excitation of the\ndipole compression mode is characterized, in the high temperature collisionless\nregime, by a beating signal of two different frequencies ($\\omega_z$ and\n$3\\omega_z$) while, in the high temperature collisional regime, the excitation\nconsists of a single frequency ($\\sqrt{7}\\omega_z$). This behaviour differs\nfrom the case of the lowest breathing mode whose excitation consists of a\nsingle frequency ($2\\omega_z$) in both regimes. Our predictions for the dipole\ncompression mode open promising perspectives for the experimental investigation\nof collisional effects in 1D configurations.",
        "positive": "Symmetry-broken momentum distributions induced by matter-wave\n  diffraction during time-of-flight expansion of ultracold atoms: We study several effects which lead to symmetry-broken momentum distributions\nof quantum gases released from optical lattices. In particular, we demonstrate\nthat interaction within the first milliseconds of the time-of-flight expansion\ncan strongly alter the measurement of the initial atomic momentum distribution.\nFor bosonic mixtures in state-dependent lattices, inter-species scattering\nprocesses lead to a symmetry breaking in momentum space. The underlying\nmechanism is identified to be diffraction of the matter wave from the total\ndensity lattice, which gives rise to a time-dependent interaction potential.\nOur findings are of fundamental relevance for the interpretation of\ntime-of-flight measurements and for the study of exotic quantum phases such as\nthe twisted superfluid. Beyond that, the observed matter-wave diffraction can\nalso be used as an interferometric probe. In addition, we report on diffraction\nfrom the state-dependent standing light field, which leads to the same\nsymmetry-broken momentum distributions, even for single component condensates."
    },
    {
        "anchor": "Combining machine learning with physics: A framework for tracking and\n  sorting multiple dark solitons: In ultracold-atom experiments, data often comes in the form of images which\nsuffer information loss inherent in the techniques used to prepare and measure\nthe system. This is particularly problematic when the processes of interest are\ncomplicated, such as interactions among excitations in Bose-Einstein\ncondensates (BECs). In this paper, we describe a framework combining machine\nlearning (ML) models with physics-based traditional analyses to identify and\ntrack multiple solitonic excitations in images of BECs. We use an ML-based\nobject detector to locate the solitonic excitations and develop a\nphysics-informed classifier to sort solitonic excitations into physically\nmotivated subcategories. Lastly, we introduce a quality metric quantifying the\nlikelihood that a specific feature is a longitudinal soliton. Our trained\nimplementation of this framework, SolDet, is publicly available as an\nopen-source python package. SolDet is broadly applicable to feature\nidentification in cold-atom images when trained on a suitable user-provided\ndataset.",
        "positive": "Controlling higher-orbital quantum phases of ultracold atoms via\n  coupling to optical cavities: Orbital degree of freedom plays an important role in understanding exotic\nphenomena of strongly correlated materials. We study strongly correlated\nultracold bosonic gases coupled to a high-finesse cavity, pumped by a\nblue-detuned laser in the transverse direction. Based on an extended\nBose-Hubbard model with parameters adapted to recent experiments, we find that\nby tuning the reflection of pump laser, atoms can be selectively transferred to\nthe odd-parity $p$-orbital, or to even-parity $d$-orbital band of a\ntwo-dimensional square lattice, accompanied with cavity-photon excitations. By\ninteracting with cavity field, atoms self-organize to form stable\nhigher-orbital superfluid and Mott-insulating phases with orbital-density\nwaves, as a result of cavity induced orbital-flip processes. Our study opens\nthe route to manipulate orbital degrees of freedom in strongly correlated\nquantum gases via coupling to optical cavities."
    },
    {
        "anchor": "Matter-wave dark solitons and their excitation spectra in spin-orbit\n  coupled Bose-Einstein condensates: We present three types of dark solitons in quasi-one-dimensional spin-orbit\ncoupled repulsive Bose-Einstein condensates. Among these families, two are\nalways stable, while the third one is only stable sufficiently close to the\nlinear regime. The solitons' excitation spectra reveal the potential existence\nof a second anomalous mode. While the first such mode describes the soliton\noscillatory motion in a parabolic trap, the second, when present, reflects the\ndouble well structure of the underlying single-particle spectrum. This novel\nmode results in moving density stripes in the vicinity of the soliton core, or\nin an out-of-phase oscillation of the constituent components, with little\neffect on the nearly stationary striped total density of the composite soliton.",
        "positive": "Scaling approach to quantum non-equilibrium dynamics of many-body\n  systems: Understanding non-equilibrium quantum dynamics of many-body systems is one of\nthe most challenging problems in modern theoretical physics. While numerous\napproximate and exact solutions exist for systems in equilibrium, examples of\nnon-equilibrium dynamics of many-body systems, which allow reliable theoretical\nanalysis, are few and far between. In this paper we discuss a broad class of\ntime-dependent interacting systems subject to external linear and parabolic\npotentials, for which the many-body Schr\\\"{o}dinger equation can be solved\nusing a scaling transformation. We demonstrate that scaling solutions exist for\nboth local and nonlocal interactions and derive appropriate self-consistency\nequations. We apply this approach to several specific experimentally relevant\nexamples of interacting bosons in one and two dimensions. As an intriguing\nresult we find that weakly and strongly interacting Bose-gases expanding from a\nparabolic trap can exhibit very similar dynamics."
    },
    {
        "anchor": "Dynamics of weakly interacting bosons in optical lattices with flux: Realization of strong synthetic magnetic fields in driven optical lattices\nhas enabled implementation of topological bands in cold-atom setups. A\nmilestone has been reached by a recent measurement of a finite Chern number\nbased on the dynamics of incoherent bosonic atoms. The measurements of the\nquantum Hall effect in semiconductors are related to the Chern-number\nmeasurement in a cold-atom setup, however, the design and complexity of the two\ntypes of measurements are quite different. Motivated by these recent\ndevelopments, we investigate the dynamics of weakly interacting incoherent\nbosons in a two-dimensional driven optical lattice exposed to an external\nforce, which provides a direct probe of the Chern number. We consider a\nrealistic driving protocol in the regime of high driving frequency and focus on\nthe role of weak repulsive interactions. We find that interactions lead to the\nredistribution of atoms over topological bands both through the conversion of\ninteraction energy into kinetic energy during the expansion of the atomic cloud\nand due to an additional heating. Remarkably, we observe that the moderate\natomic repulsion facilitates the measurement by flattening the distribution of\natoms in the quasi-momentum space. Our results also show that weak interactions\ncan suppress the contribution of some higher-order non-topological terms in\nfavor of the topological part of the effective model.",
        "positive": "Dynamical Unbinding Transition in a Periodically Driven Mott Insulator: We study the double occupancy in a fermionic Mott insulator at half-filling\ngenerated via a dynamical periodic modulation of the hopping amplitude. Tuning\nthe modulation amplitude, we describe a crossover in the nature of\ndoublon-holon excitations from a Fermi Golden Rule regime to damped Rabi\noscillations. The decay time of excited states diverges at a critical\nmodulation strength, signaling the transition to a dynamically bound\nnon-equilibrium state of doublon-holon pairs. A setup using a fermionic quantum\ngas should allow to study the critical exponents."
    },
    {
        "anchor": "The influence of sublattice bias on superfluid to Mott insulator\n  transitions: We model the superfluid to Mott insulator transition for a Bose gas on a\nlattice with two inequivalent sublattices. Using the Gutzwiller ansatz, we\nproduce phase diagrams and provide an understanding of the interplay between\nsuperfluidity on each sublattice. We explore how the Mott lobes split, and\ndescribe the experimental signatures.",
        "positive": "Quantum quench in a p + i p superfluid: Winding numbers and topological\n  states far from equilibrium: We study the non-adiabatic dynamics of a 2D p+ip superfluid following a\nquantum quench of the BCS coupling constant. The model describes a topological\nsuperconductor with a non-trivial BCS (trivial BEC) phase appearing at weak\n(strong) coupling strengths. We extract the exact long-time asymptotics of the\norder parameter \\Delta(t) by exploiting the integrability of the classical\np-wave Hamiltonian, which we establish via a Lax construction. Three different\ntypes of behavior can occur depending upon the strength and direction of the\nquench. In phase I, the order parameter asymptotes to zero. In phase II,\n\\Delta(t) goes to a non-zero constant. Phase III is characterized by persistent\noscillations of \\Delta(t). For quenches within I and II, we determine the\ntopological character of the asymptotic states. We show that two different\nformulations of the bulk topological winding number, although equivalent in the\nground state, must be regarded as independent out of equilibrium. The first\nnumber Q characterizes the Anderson pseudospin texture of the initial state; we\nshow that it is conserved. For non-zero Q, this leads to the prediction of a\n\"gapless topological\" state when \\Delta(t) goes to zero. The presence or\nabsence of Majorana edge modes in a sample with a boundary is encoded in the\nsecond winding number W, formulated in terms of the retarded Green's function.\nWe show that W can change following a quench across the quantum critical point.\nWe discuss the implications for the (dis)appearance of Majorana edge modes.\nFinally, we show that the parity of zeros in the bulk out-of-equilibrium Cooper\npair distribution function constitutes a Z2-valued quantum number, which is\nnon-zero whenever W differs from Q. The pair distribution can in principle be\nmeasured using RF spectroscopy in an ultracold atom realization, allowing\ndirect experimental detection of the bulk Z2 number."
    },
    {
        "anchor": "Critical velocity of antiferromagnetic spin-1 Bose-Einstein condensates\n  at finite temperature: We study the instability of a moving spinor Bose-Einstein condensate when the\nspeed of flow reaches the critical velocity. This we identify on the basis of\nLandau's criterion, i.e. the velocity above which some elementary excitation\nenergy becomes negative. We show that the first-to-become unstable excitations\nare spin-carrying quasiparticles. We also discuss the temperature dependence of\nthe critical velocity in a more advanced mean-field approximation.",
        "positive": "Role of temperature effects in the phenomenon of ultraslow\n  electromagnetic pulses in Bose-Einstein condensates of alkali-metal atoms: We study the temperature dependence of optical properties of dilute gases of\nalkali-metal atoms in the state with Bose-Einstein condensates. The description\nis constructed in the framework of the microscopic approach that is based on\nthe Green-functions formalism. We find the expressions for the scalar Green\nfunctions describing a linear response of a condensed gas to a weak external\nelectromagnetic field (laser). It is shown that these functions depend on the\ntemperature, other physical properties of a system, and on the frequency\ndetuning of a laser. We compare the relative contributions of the condensate\nand non-condensate particles in the system response. The influence of the\ntemperature effects is studied by the example of two- and three-level systems.\nWe show that in these cases, which are most commonly realized in the present\nexperiments, the group velocity and the absorption rate of pulses practically\ndo not depend on the gas temperature in the region from the absolute zero to\nthe critical temperature. We discuss also the cases when the temperature\neffects can play a significant role in the phenomenon of slowing of\nelectromagnetic pulses in a gas of alkali-metal atoms with Bose-Einstein\ncondensates."
    },
    {
        "anchor": "Quench dynamics of a Tonks-Girardeau gas released from a harmonic trap: We consider the non-equilibrium dynamics of a gas of impenetrable bosons\nreleased from a harmonic trapping potential to a circle. The many body dynamics\nis solved analytically and the time dependence of all the physically relevant\ncorrelations is described. We prove that, for large times and in the\nthermodynamic limit, the reduced density matrix of any subsystem converges to a\ngeneralized Gibbs ensemble as a consequence of the integrability of the model.\nWe discuss the approach to the stationary behavior at late times. We also\ndescribe the time-dependence of the entanglement entropy which attains a very\nsimple form in the stationary state.",
        "positive": "Bose-Einstein condensation of atoms in a uniform potential: We have observed Bose-Einstein condensation of an atomic gas in the\n(quasi-)uniform three-dimensional potential of an optical box trap.\nCondensation is seen in the bimodal momentum distribution and the anisotropic\ntime-of-flight expansion of the condensate. The critical temperature agrees\nwith the theoretical prediction for a uniform Bose gas. The momentum\ndistribution of our non-condensed quantum-degenerate gas is also clearly\ndistinct from the conventional case of a harmonically trapped sample and close\nto the expected distribution in a uniform system. We confirm the coherence of\nour condensate in a matter-wave interference experiment. Our experiments open\nmany new possibilities for fundamental studies of many-body physics."
    },
    {
        "anchor": "Polaritonic linear dynamic in Keldysh formalism: We study the dynamic of polaritons in the Keldysh functional formalism.\nDissipation is considered through the coupling of the exciton and photon fields\nto two independent photonic and excitonic baths. As such, this theory allows to\ndescribe more intricate decay mechanisms that depend dynamically on the state\nof the system, such as a direct upper-polariton lifetime, that is motivated\nfrom experiments. We show that the dynamical equations in the Keldysh framework\notherwise follow the same Josephson--like equations of motions than the\nstandard master equation approach, that is however limited to simple decay\nchannels. We also discuss the stability of the dynamic and reconsider the\ncriterion of strong coupling in the presence of upper polariton decay.",
        "positive": "Angular-momentum modes in a bosonic condensate trapped in the\n  inverse-square potential: In the mean-field approximation, the well-known effect of the critical\nquantum collapse in a 3D gas of particles pulled to the center by potential\nU(r) = -U_0/r^2 is suppressed by repulsive interparticle interactions, which\ncreate the otherwise non-existing s-wave ground state. Here, we address excited\nbound states carrying angular momentum, with the orbital and magnetic quantum\nnumbers, l and m. They exist above a threshold value of the potential's\nstrength, U_0 > l(l+1). The sectoral, tesseral, and zonal modes, which\ncorrespond to m = l, 0 < m < l, and m = 0, respectively, are found in an\napproximate analytical form for relatively small values of U_0 - l(l+1).\nExplicit results are produced for the p- and d-wave states, with l = 1 and 2,\nrespectively. In the general form, the bound states are obtained numerically,\nconfirming the accuracy of the analytical approximation."
    },
    {
        "anchor": "Cluster Mean Field plus Density Matrix Renormalization theory for the\n  Bose Hubbard Model: We develop a novel approach to understand the phases of one-dimensional\nBose-Hubbard models. We integrate the simplicity of the mean-field theory and\nthe numerical power of the density matrix renormalization group method to build\nan effective numerical technique with moderate computational resources to\ndetermine superfluid order parameters and correlation functions of large\none-dimensional systems. We demonstrate the applicability of this method to\ndirectly identify superfluid, Mott insulator, and density wave phases in\nBose-Hubbard models.",
        "positive": "Effect of non-local interactions on the vortex solution in Bose-Einstein\n  Condensates: We consider the Gross-Pitaevskii (GP) model of a Bose-Einstein Condensate\n(BEC) to study a single vortex line in the presence of non-local repulsive\ns-wave scattering. We show that in addition to the vortex solution with core\nwidth of the order of the healing length, there exists a vortex solution whose\nwidth is a microscopic length scale of the order of s-wave scattering length\nand is independent of the healing length. We compare the two classes of vortex\nsolution and show the region where one can possibly observe the vortex whose\nwidth is of the order of scattering length."
    },
    {
        "anchor": "Phase Diagram Detection via Gaussian Fitting of Number Probability\n  Distribution: We investigate the number probability density function that characterizes\nsub-portions of a quantum many-body system with globally conserved number of\nparticles. We put forward a linear fitting protocol capable of mapping out the\nground-state phase diagram of the rich one-dimensional extended Bose-Hubbard\nmodel: The results are quantitatively comparable with more sophisticated\ntraditional and machine learning techniques. We argue that the studied quantity\nshould be considered among the most informative bipartite properties, being\nmoreover readily accessible in atomic gases experiments.",
        "positive": "Integrable model for density-modulated quantum condensates: solitons\n  passing through a soliton lattice: An integrable model possessing inhomogeneous ground states is proposed as an\neffective model of non-uniform quantum condensates such as supersolids and\nFulde--Ferrell--Larkin--Ovchinnikov superfluids. The model is a higher-order\nanalog of the nonlinear Schr\\\"odinger equation. We derive an $n$-soliton\nsolution via the inverse scattering theory with elliptic-functional background,\nand reveal various kinds of soliton dynamics such as dark soliton billiards,\ndislocations, gray solitons, and envelope solitons. We also provide the exact\nbosonic and fermionic quasiparticle eigenstates and clarify their tunneling\nphenomena. The solutions are expressed by a determinant of theta functions."
    },
    {
        "anchor": "Onsager-Kraichnan Condensation in Decaying Two-Dimensional Quantum\n  Turbulence: Despite the prominence of Onsager's point-vortex model as a statistical\ndescription of 2D classical turbulence, a first-principles development of the\nmodel for a realistic superfluid has remained an open problem. Here we develop\na mapping of a system of quantum vortices described by the homogeneous 2D\nGross-Pitaevskii equation (GPE) to the point-vortex model, enabling Monte-Carlo\nsampling of the vortex microcanonical ensemble. We use this approach to survey\nthe full range of vortex states in a 2D superfluid, from the vortex-dipole gas\nat positive temperature to negative-temperature states exhibiting both\nmacroscopic vortex clustering and kinetic energy condensation, which we term an\nOnsager-Kraichnan condensate (OKC). Damped GPE simulations reveal that such OKC\nstates can emerge dynamically, via aggregation of small-scale clusters into\ngiant OKC-clusters, as the end states of decaying 2D quantum turbulence in a\ncompressible, finite-temperature superfluid. These statistical equilibrium\nstates should be accessible in atomic Bose-Einstein condensate experiments.",
        "positive": "Quantum quench dynamics of the attractive one-dimensional Bose gas via\n  the coordinate Bethe ansatz: We use the coordinate Bethe ansatz to study the Lieb-Liniger model of a\none-dimensional gas of bosons on a finite-sized ring interacting via an\nattractive delta-function potential. We calculate zero-temperature correlation\nfunctions for seven particles in the vicinity of the crossover to a localized\nsolitonic state and study the dynamics of a system of four particles quenched\nto attractive interactions from the ideal-gas ground state. We determine the\ntime evolution of correlation functions, as well as their temporal averages,\nand discuss the role of bound states in shaping the postquench correlations and\nrelaxation dynamics."
    },
    {
        "anchor": "Superflow decay in a toroidal Bose gas: The effect of quantum and\n  thermal fluctuations: We theoretically investigate the stochastic decay of persistent currents in a\ntoroidal ultracold atomic superfluid caused by a perturbing barrier.\nSpecifically, we perform detailed three-dimensional simulations to model the\nexperiment of Kumar et al. in [Phys. Rev. A 95 021602 (2017)], which observed a\nstrong temperature dependence in the timescale of superflow decay in an\nultracold Bose gas. Our ab initio numerical approach exploits a classical-field\nframework that includes thermal fluctuations due to interactions between the\nsuperfluid and a thermal cloud, as well as the intrinsic quantum fluctuations\nof the Bose gas. In the low-temperature regime our simulations provide a\nquantitative description of the experimental decay timescales, improving on\nprevious numerical and analytical approaches. At higher temperatures, our\nsimulations give decay timescales that range over the same orders of magnitude\nobserved in the experiment, however, there are some quantitative discrepancies\nthat are not captured by any of the mechanisms we explore. Our results suggest\na need for further experimental and theoretical studies into superflow\nstability.",
        "positive": "Mesoscopic spin transport between strongly interacting Fermi gases: We investigate a mesoscopic spin current for strongly interacting Fermi gases\nthrough a quantum point contact. Under the situation where spin polarizations\nin left and right reservoirs are same in magnitude but opposite in sign, we\ncalculate the contribution of quasiparticles to the current by means of the\nlinear response theory and many-body $T$-matrix approximation. For a small\nspin-bias regime, the current in the vicinity of the superfluid transition\ntemperature is strongly suppressed due to the formation of pseudogaps. For a\nlarge spin-bias regime where the gases become highly polarized, on the other\nhand, the current is affected by the enhancement of a minority density of\nstates due to Fermi polarons. We also discuss the broadening of a quasiparticle\npeak associated with an attractive polaron at a large momentum, which is\nrelevant to the enhancement."
    },
    {
        "anchor": "Discrete bright solitons in Bose-Einstein condensates and dimensional\n  reduction in quantum field theory: We first review the derivation of an effective one-dimensional (1D) discrete\nnonpolynomial Schr\\\"odinger equation from the continuous 3D Gross-Pitaevskii\nequation with transverse harmonic confinement and axial periodic potential.\nThen we study the bright solitons obtained from this discrete nonpolynomial\nequation showing that they give rise to the collapse of the condensate above a\ncritical attractive strength. We also investigate the dimensional reduction of\na bosonic quantum field theory, deriving an effective 1D nonpolynomial\nHeisenberg equation from the 3D Heisenberg equation of the continuous bosonic\nfield operator under the action of transverse harmonic confinement. Moreover,\nby taking into account the presence of an axial periodic potential we find a\ngeneralized Bose-Hubbard model which reduces to the familiar 1D Bose-Hubbard\nHamiltonian only if a strong inequality is satisfied. Remarkably, in the\nabsence of axial periodic potential our 1D nonpolynomial Heisenberg equation\ngives the generalized Lieb-Liniger theory we obtained some years ago.",
        "positive": "Dimerized Mott insulators in hexagonal optical lattices: We study bosonic atoms in optical honeycomb lattices with anisotropic\ntunneling and find dimerized Mott insulator phases with fractional filling.\nThese incompressible insulating phases are characterized by an\ninteraction-driven localization of particles in respect to the individual\ndimers and large local particle-number fluctuations within the dimers. We\ncalculate the ground-state phase diagrams and the excitation spectra using an\naccurate cluster mean-field method. The cluster treatment enables us to probe\nthe fundamental excitations of the dimerized Mott insulator where the\nexcitation gap is dominated by the intra-dimer tunneling amplitude. This allows\nthe distinction from normal Mott insulating phases gapped by the on-site\ninteraction. In addition, we present analytical results for the phase diagram\nderived by a higher-order strong-coupling perturbative expansion approach. By\ncomputing finite lattices with large diameters the influence of a harmonic\nconfinement is discussed in detail. It is shown that a large fraction of atoms\nforms the dimerized Mott insulator under experimental conditions. The necessary\nanisotropic tunneling can be realized either by periodic driving of the optical\nlattice or by engineering directly a dimerized lattice potential. The dimers\ncan be mapped to to their antisymmetric states creating a lattice with coupled\np-orbitals."
    },
    {
        "anchor": "Casimir force of a dilute Bose gas confined by a parallel plate geometry\n  in improved Hatree-Fock approximation: Within framework of quantum field theory, in improved Hatree-Fock (IHF)\napproximation, we have considered a dilute single Bose-Einstein condensate\n(BEC) confined between two parallel plates. We found that the effective mass\nand order parameter of BEC strongly depend on distance separating two plates.\nOur results shows that the effective mass, order parameter and the Casimir\nforce in IHF approximation equal to their values in one-loop approximation\nadded a corrected term due to contribution of two-loop diagrams. We also show\nthat the one-loop approximation is enough for calculating Casimir effect in an\nideal Bose gas.",
        "positive": "Enhancement effect of mass imbalance on Fulde-Ferrell-Larkin-Ovchinnikov\n  type of pairing in Fermi-Fermi mixtures of ultracold quantum gases: Ultracold two-component Fermi gases with a tunable population imbalance have\nprovided an excellent opportunity for studying the exotic\nFulde-Ferrell-Larkin-Ovchinnikov (FFLO) states, which have been of great\ninterest in condensed matter physics. However, the FFLO states have not been\nobserved experimentally in Fermi gases in three dimensions (3D), possibly due\nto their small phase space volume and extremely low temperature required for an\nequal-mass Fermi gas. Here we explore possible effects of mass imbalance,\nmainly in a $^6$Li--$^{40}$K mixture, on the one-plane-wave FFLO phases for a\n3D homogeneous case at the mean-field level. We present various phase diagrams\nrelated to the FFLO states at both zero and finite temperatures, throughout the\nBCS-BEC crossover, and show that a large mass ratio may enhance substantially\nFFLO type of pairing."
    },
    {
        "anchor": "Cluster stability driven by quantum fluctuations: By means of an accurate path-integral Monte Carlo we investigate a\ntwo-dimensional ensemble of particles interacting via a\nLifshitz-Petrich-Gaussian potential. In particular, analysing structures\ndescribed by a commensurate ratio between the two wave numbers that mark the\npattern, the Lifshitz-Petrich-Gaussian boson model may display a stable and\nwell-defined stripe phase lacking any global phase coherence but featuring a\nsuperfluid signal along the stripe direction only. Upon increasing quantum\nfluctuations and quantum-mechanical exchange of bosons, the double-degeneration\nof the negative minima in the Fourier transform of the potential is removed at\nthe expense of a density modulation peculiar to a cluster triangular crystal.\nWe also show that this last structure possess all features adhering to the\ndefinition of a supersolid phase.",
        "positive": "Extreme Spin Squeezing from Deep Reinforcement Learning: Spin squeezing (SS) is a recognized resource for realizing measurement\nprecision beyond the standard quantum limit $\\propto 1/\\sqrt{N}$. The\nrudimentary one-axis twisting (OAT) interaction can facilitate SS and has been\nrealized in diverse experiments, but it cannot achieve extreme SS for precision\nat Heisenberg limit $\\propto 1/{N}$. Aided by deep reinforcement learning\n(DRL), we discover size-independent universal rules for realizing nearly\nextreme SS with OAT interaction using merely a handful of rotation pulses. More\nspecifically, only 6 pairs of pulses are required for up to $10^4$ particles,\nwhile the time taken to reach extreme SS remains on the same order of the\noptimal OAT squeezing time, which makes our scheme viable for experiments that\nreported OAT squeezing. This study highlights the potential of DRL for\ncontrolled quantum dynamics."
    },
    {
        "anchor": "Two-Dimensional Thouless Pumping of Ultracold Fermions in Obliquely\n  Introduced Optical Superlattice: We propose a two-dimensional (2D) version of Thouless pumping that can be\nrealized by using ultracold atoms in optical lattices. To be specific, we\nconsider a 2D square lattice tight-binding model with an obliquely introduced\nsuperlattice. It is demonstrated that quantized particle transport occurs in\nthis system, and that the transport is expressed as a solution of a Diophantine\nequation. This topological nature can be understood by mapping the Hamiltonian\nto a three-dimensional (3D) cubic lattice model with a homogeneous magnetic\nfield. We also propose a continuum model with obliquely introduced superlattice\nand obtain the amount of pumping by calculating the Berry curvature. For this\nmodel, the same Diophantine equation can be derived from the plane-wave\napproximation. Furthermore, we investigate the effect of a harmonic trap by\nsolving the time-dependent Schr\\\"odinger equation. Under a harmonic trap\npotential, as often used in cold atom experiments, we show, by numerical\nsimulations, that nearly quantized pumping occurs when the phase of the\nsuperlattice potential is driven at a moderate speed. Also, we find that two\nregions appear, the Hofstadter region and the rectifying region, depending on\nthe modulation amplitude of the superlattice potential. In the rectifying\nregion with larger modulation amplitudes, we uncover that the pumping direction\nis restricted to exactly the $x$-axis or the $y$-axis direction. This\ndifference in these two regions causes a crossover behavior, characterizing the\neffect of the harmonic trap.",
        "positive": "Persistent currents in coherently coupled Bose-Einstein condensates in a\n  ring trap: We study the stability of persistent currents in a coherently coupled\nquasi-2D Bose-Einstein condensate confined in a ring trap at T=0. By\nnumerically solving Gross-Pitaevskii equations and by analyzing the excitation\nspectrum obtained from diagonalization of the Bogoliubov-de Gennes matrix, we\ndescribe the mechanisms responsible for the decay of the persistent currents\ndepending on the values of the interaction coupling constants and the Rabi\nfrequency. When the unpolarized system decays due to an energetic instability\nin the density channel, the spectrum may develop a roton-like minimum, which\ngives rise to the finite wavelength excitation necessary for vortex nucleation\nat the inner surface. When decay in the unpolarized system is driven by\nspin-density excitations, the finite wavelength naturally arises from the\nexistence of a gap in the excitation spectrum. In the polarized phase of the\ncoherently coupled condensate, there is an hybridization of the excitation\nmodes that leads to complex decay dynamics. In particular, close to the phase\ntransition, a state of broken rotational symmetry is found to be stationary and\nstable."
    },
    {
        "anchor": "Bose-Einstein condensation in a magnetic double-well potential: We present the first experimental realisation of Bose-Einstein condensation\nin a purely magnetic double-well potential. This has been realised by combining\na static Ioffe-Pritchard trap with a time orbiting potential (TOP). The double\ntrap can be rapidly switched to a single harmonic trap of identical oscillation\nfrequencies thus accelerating the two condensates towards each other.\nFurthermore, we show that time averaged potentials can be used as a means to\ncontrol the radial confinement of the atoms. Manipulation of the radial\nconfinement allows vortices and radial quadrupole oscillations to be excited.",
        "positive": "Vortex excitation in a stirred toroidal Bose-Einstein condensate: Motivated by the recent experiment [Wright et al., Phys. Rev. A 88, 063633\n(2013)], we investigate formation of vortices in an annular BEC stirred by a\nnarrow blue-detuned optical beam. In the framework of a two-dimensional mean\nfield model, we study the dissipative dynamics of the condensate with\nparameters matched to the experimental conditions. Vortex-antivortex pairs\nappear near the center of the stirrer in the bulk of the condensate for slow\nmotion of the stirring beam. When the barrier angular velocity is above some\ncritical value, an outer edge surface mode develops and breaks into the\nvortices entering the condensate annulus. We determine the conditions for\ncreation of the vortex excitations in the stirred toroidal condensate and\ncompare our results with the experimental observations."
    },
    {
        "anchor": "Rapid generation of metastable helium Bose-Einstein condensates: We report the realisation of Bose-Einstein condensation (BEC) of metastable\nhelium atoms using an in-vacuum coil magnetic trap and a crossed beam optical\ndipole trap. A novel quadrupole-Ioffe configuration (QUIC) magnetic trap made\nfrom in-vacuum hollow copper tubes provides fast switching times while\ngenerating traps with a 10G bias, without compromising optical access. The bias\nenables in-trap 1D doppler cooling to be used, which is the only cooling stage\nbetween the magneto-optic trap (MOT) and the optical dipole trap. This allows\ndirect transfer to the dipole trap without the need for any additional\nevaporative cooling in the magnetic trap. The entire experimental sequence\ntakes 3.3 seconds, with essentially pure BECs observed with $\\sim 10^6$ atoms\nafter evaporative cooling in the dipole trap.",
        "positive": "Single shot simulations of dynamic quantum many-body systems: The single-particle density is the most basic quantity that can be calculated\nfrom a given many-body wave function. It provides the probability to find a\nparticle at a given position when the average over many realizations of an\nexperiment is taken. However, the outcome of single experimental shots of\nultracold atom experiments is determined by the $N$-particle probability\ndensity. This difference can lead to surprising results. For example,\nindependent Bose-Einstein condensates (BECs) with definite particle numbers\nform interference fringes even though no fringes would be expected based on the\nsingle-particle density [1-4]. By drawing random deviates from the $N$-particle\nprobability density single experimental shots can be simulated from first\nprinciples [1, 3, 5]. However, obtaining expressions for the $N$-particle\nprobability density of realistic time-dependent many-body systems has so far\nbeen elusive. Here, we show how single experimental shots of general ultracold\nbosonic systems can be simulated based on numerical solutions of the many-body\nSchr\\\"odinger equation. We show how full counting distributions of observables\ninvolving any number of particles can be obtained and how correlation functions\nof any order can be evaluated. As examples we show the appearance of\ninterference fringes in interacting independent BECs, fluctuations in the\ncollisions of strongly attractive BECs, the appearance of randomly fluctuating\nvortices in rotating systems and the center of mass fluctuations of attractive\nBECs in a harmonic trap. The method described is broadly applicable to bosonic\nmany-body systems whose phenomenology is driven by information beyond what is\ntypically available in low-order correlation functions."
    },
    {
        "anchor": "Momentum-resolved radio-frequency spectroscopy of ultracold atomic Fermi\n  gases in a spin-orbit coupled lattice: We investigate theoretically momentum-resolved radio-frequency (rf)\nspectroscopy of a noninteracting atomic Fermi gas in a spin-orbit coupled\nlattice. This lattice configuration has been recently created at MIT [Cheuk et\nal., arXiv:1205.3483] for 6Li atoms, by coupling the two hyperfine spin-states\nwith a pair of Raman laser beams and additional rf coupling. Here, we show that\nmomentum-resolved rf spectroscopy can measure single-particle energies and\neigenstates and therefore resolve the band structure of the spin-orbit coupled\nlattice. In our calculations, we take into account the effects of temperatures\nand harmonic traps. Our predictions are to be confronted with future\nexperiments on spin-orbit coupled Fermi gases of 40K atoms in a lattice\npotential.",
        "positive": "Fermi polaron in atom-ion hybrid systems: Charged quasiparticles dressed by the low excitations of an electron gas,\nconstitute one of the fundamental pillars for understanding quantum many-body\neffects in some materials. Quantum simulation of quasiparticles arising from\natom-ion hybrid systems may shed light on solid-state uncharted regimes. Here\nwe investigate the ionic Fermi polaron consisting of a charged impurity\ninteracting with a polarized Fermi bath. Employing state-of-the-art quantum\nMonte Carlo techniques tailored for strongly correlated systems, we\ncharacterize the charged quasiparticle by computing the energy spectrum,\nquasiparticle residue, and effective mass, as well as the structural properties\nof the system. Our findings in the weak coupling regime agree with field-theory\npredictions within the ladder approximation. However, stark deviations emerge\nin the strongly interacting regime attributed to the vastly large density\ninhomogeneity around the ion, resulting in strong correlations for distances on\nthe order of the atom-ion potential range. Moreover, we find a smooth\npolaron-molecule transition for strong coupling, in contrast with the neutral\ncase, where the transition smoothens only for finite temperature and finite\nimpurity density. This study may provide valuable insights into alternative\nsolid-state systems such as Fermi excitons polarons in atomically thin\nsemiconductors beyond the short-range limit."
    },
    {
        "anchor": "Condensate fraction and critical temperature of interacting Bose gas in\n  anharmonic trap: By using a correlated many body method and using the realistic van der Waals\npotential we study several statistical measures like the specific heat,\ntransition temperature and the condensate fraction of the interacting Bose gas\ntrapped in an anharmonic potential. As the quadratic plus a quartic confinement\nmakes the trap more tight, the transition temperature increases which makes\nmore favourable condition to achieve Bose-Einstein condensation (BEC)\nexperimentally. BEC in 3D isotropic harmonic potential is also critically\nstudied, the correction to the critical temperature due to finite number of\natoms and also the correction due to inter-atomic interaction are calculated by\nthe correlated many-body method. Comparison and discussion with the mean-field\nresults are presented.",
        "positive": "Synthetic Unruh effect in cold atoms: We propose to simulate a Dirac field near an event horizon using ultracold\natoms in an optical lattice. Such a quantum simulator allows for the\nobservation of the celebrated Unruh effect. Our proposal involves three stages:\n(1) preparation of the ground state of a massless 2D Dirac field in Minkowski\nspacetime; (2) quench of the optical lattice setup to simulate how an\naccelerated observer would view that state; (3) measurement of the local\nquantum fluctuation spectra by one-particle excitation spectroscopy in order to\nsimulate a De Witt detector. According to Unruh's prediction, fluctuations\nmeasured in such a way must be thermal. Moreover, following Takagi's inversion\ntheorem, they will obey the Bose-Einstein distribution, which will smoothly\ntransform into the Fermi-Dirac as one of the dimensions of the lattice is\nreduced."
    },
    {
        "anchor": "Bose-Bose Mixtures with Synthetic Spin-Orbit Coupling in Optical\n  Lattices: We investigate the ground state properties of Bose-Bose mixtures with\nRashba-type spin-orbit (SO) coupling in a square lattice. The system displays\nrich physics from the deep Mott-insulator (MI) all the way to the superfluid\n(SF) regime. In the deep MI regime, novel spin-ordered phases arise due to the\neffective Dzyaloshinskii-Moriya type super-exchange interactions. By employing\nthe non-perturbative Bosonic Dynamical Mean-Field-Theory (BDMFT), we\nnumerically study and establish the stability of these magnetic phases against\nincreasing hopping amplitude. We show that as hopping is increased across the\nMI to SF transition, exotic superfluid phases with magnetic textures emerge. In\nparticular, we identify a new spin-spiral magnetic texture with spatial period\n3 in the superfluid close to the MI-SF transition.",
        "positive": "Quench Dynamics in Bose condensates in the Presence of a Bath: Theory\n  and Experiment: In this paper we study the transient dynamics of a Bose superfluid subsequent\nto an interaction quench. Essential for equilibration is a source of\ndissipation which we include following the approach of Caldeira and Leggett.\nHere we solve the equations of motion exactly by integrating out an\nenvironmental bath. We thereby derive precisely the time dependent density\ncorrelation functions with the appropriate analytic and asymptotic properties.\nThe resulting structure factor exhibits the expected damping and thereby\ndiffers from that of strict Bogoliubov theory. These damped sound modes, which\nreflect the physics beyond mean field approaches, are characterized and the\nstructure factors are found to compare favorably with experiment."
    },
    {
        "anchor": "Numerical study of the unitary Fermi gas across the superfluid\n  transition: We present results from Monte Carlo calculations investigating the properties\nof the homogeneous, spin-balanced unitary Fermi gas in three dimensions. The\ntemperature is varied across the superfluid transition allowing us to determine\nthe temperature dependence of the chemical potential, the energy per particle\nand the contact density. Numerical artifacts due to finite volume and\ndiscretization are systematically studied, estimated, and reduced.",
        "positive": "Probing many-body systems near spectral degeneracies: The diagonal elements of the time correlation matrix are used to probe closed\nquantum systems that are measured at random times. This enables us to extract\ntwo distinct parts of the quantum evolution, a recurrent part and an\nexponentially decaying part. This separation is strongly affected when spectral\ndegeneracies occur, for instance, in the presence of spontaneous symmetry\nbreaking. Moreover, the slowest decay rate is determined by the smallest energy\nlevel spacing, and this decay rate diverges at the spectral degeneracies.\nProbing the quantum evolution with the diagonal elements of the time\ncorrelation matrix is discussed as a general concept and tested in the case of\na bosonic Josephson junction. It reveals for the latter characteristic\nproperties at the transition to Hilbert-space localization."
    },
    {
        "anchor": "Goldstone modes and bifurcations in phase-separated binary condensates\n  at finite temperature: We show that the third Goldstone mode, which emerges in binary condensates at\nphase-separation, persists to higher inter-species interaction for density\nprofiles where one component is surrounded on both sides by the other\ncomponent. This is not the case with symmetry-broken density profiles where one\nspecies is to entirely to the left and the other is entirely to the right. We,\nthen, use Hartree-Fock-Bogoliubov theory with Popov approximation to examine\nthe mode evolution at $T\\neq0$ and demonstrate the existence of mode\nbifurcation near the critical temperature. The Kohn mode, however, exhibits\ndeviation from the natural frequency at finite temperatures after the phase\nseparation. This is due to the exclusion of the non-condensate atoms in the\ndynamics.",
        "positive": "Non-equilibrium Bose-Einstein Condensation: We investigate formation of Bose-Einstein condensates under non-equilibrium\nconditions using numerical simulations of the three-dimensional\nGross-Pitaevskii equation. For this, we set initial random weakly nonlinear\nexcitations and the forcing at high wave numbers, and study propagation of the\nturbulent spectrum toward the low wave numbers. Our primary goal is to compare\nthe results for the evolving spectrum with the previous results obtained for\nthe kinetic equation of weak wave turbulence. We demonstrate existence of a\nregime for which good agreement with the wave turbulence results is found in\nterms of the main features of the previously discussed self-similar solution.\nIn particular, we find a reasonable agreement with the low-frequency and the\nhigh-frequency power-law asymptotics of the evolving solution, including the\nanomalous power-law exponent $x^* \\approx 1.24$ for the three-dimensional\nwaveaction spectrum. We also study the regimes of very weak turbulence, when\nthe evolution is affected by the discreteness of the Fourier space, and the\nstrong turbulence regime when emerging condensate modifies the wave dynamics\nand leads to formation of strongly nonlinear filamentary vortices."
    },
    {
        "anchor": "Bose-Hubbard triangular ladder in an artificial gauge field: We consider interacting bosonic particles on a two-leg triangular ladder in\nthe presence of an artificial gauge field. We employ density matrix\nrenormalization group numerical simulations and analytical bosonization\ncalculations to study the rich phase diagram of this system. We show that the\ninterplay between the frustration induced by the triangular lattice geometry\nand the interactions gives rise to multiple chiral quantum phases. Phase\ntransition between superfluid to Mott-insulating states occur, which can have\nMeissner or vortex character. Furthermore, a state that explicitly breaks the\nsymmetry between the two legs of the ladder, the biased chiral superfluid, is\nfound for values of the flux close to $\\pi$. In the regime of hardcore bosons,\nwe show that the extension of the bond order insulator beyond the case of the\nfully frustrated ladder exhibits Meissner-type chiral currents. We discuss the\nconsequences of our findings for experiments in cold atomic systems.",
        "positive": "Effects of dipole-dipole interaction between cigar-shaped BECs of cold\n  alkali atoms: Towards inverse-squared interactions: We show that the dipole-dipole coupling between Wannier modes in cigar-shaped\nBose-Einstein condensates (BECs) is significantly enhanced while the\nshort-range coupling strongly suppressed. As a result, the dipole-dipole\ninteraction can become the dominant interaction between ultracold alkali Bose\natoms. In the long length limit of a cigar-shaped BEC, the resulting effective\none-dimensional models possess an effective inverse squared interacting\npotential, the Calogero-Sutherland potential, which plays a fundamental role in\nmany fields of contemporary physics; but its direct experimental realization\nhas been a challenge for a long time. We propose to realize the\nCalogero-Sutherland model in ultracold alkali Bose atoms and study the effects\nof the dipole-dipole interaction."
    },
    {
        "anchor": "Quantum phase transition in a shallow one-dimensional optical lattice: In this article the extended Bose-Hubbard model describing ultra-cold atoms\nconfined in a shallow, one-dimensional optical lattice is introduced and\nstudied by the exact diagonalization approach. All parameters of the model are\nrelated to the only relevant parameter controlled experimentally -- the depth\nof the optical potential. Changes in a shape of the insulating lobe in the\nphase diagram of the system are explored and the value of the critical\ntunneling for which the system undergoes the phase transition (from the\ninsulating to the superfluid phase) is predicted. It is shown that the value of\ncritical tunneling is substantially affected by the presence of the tunnelings\nto distant sites of the optical lattice. The results may have some importance\nin upcoming experiments on quantum quench through phase transition points.",
        "positive": "Conformal symmetry of trapped Bose-Einstein condensates and massive\n  Nambu-Goldstone modes: The Gross-Pitaevskii (GP) or nonlinear Schr\\\"odinger equation relevant to\nultracold atomic gaseous Bose-Einstein condensates possess a modified\nSchr\\\"odinger symmetry in two spatial dimensions, in the presence of a harmonic\ntrapping potential, an (artificial) constant magnetic field (or rotation) and\nan electric field of a quadratic electrostatic potential. We find that a\nvariance and a center of a trapped gas with or without a vorticity can be\nregarded as massive Nambu-Goldstone (NG) modes associated with spontaneous\nbreaking of the modified Schr\\\"odinger symmetry. We show that the Noether\ntheorem for the modified Schr\\\"odinger symmetry gives universal equations of\nmotion which describe exact time-evolutions of the trapped gases such as a\nharmonic oscillation, a cyclotron motion and a breathing oscillation with\nfrequencies determined by the symmetry independently of the details of the\nsystem. We further construct an exact effective action for all the NG modes."
    },
    {
        "anchor": "In Situ Momentum Distribution Measurement of a Quantum Degenerate Fermi\n  Gas using Raman Spectroscopy: The ability to directly measure the momentum distribution of quantum gases is\nboth unique to these systems and pivotal in extracting many other important\nobservables. Here we use Raman transitions to measure the momentum distribution\nof a weakly-interacting Fermi gas in a harmonic trap. For narrow atomic\ndispersions, momentum and energy conservation imply a linear relation between\nthe two-photon detuning and the atomic momentum. We detect the number of atoms\ntransferred by the Raman beams using sensitive fluorescence detection in a\nmagneto-optical trap. We employ this technique to a degenerate\nweakly-interacting Fermi gas at different temperatures. The measured momentum\ndistributions match theoretical curves over two decades, and the extracted\ntemperatures are in very good agreement with the ones obtained from a\nconventional time-of-flight technique. The main advantages of our measurement\nscheme are that it can be spatially selective and applied to a trapped gas, it\ncan be completed in a relatively short time, and due to its high sensitivity,\nit can be used with very small clouds.",
        "positive": "Stabilization of the p-wave superfluid state in an optical lattice: It is hard to stabilize the p-wave superfluid state of cold atomic gas in\nfree space due to inelastic collisional losses. We consider the p-wave Feshbach\nresonance in an optical lattice, and show that it is possible to have a stable\np-wave superfluid state where the multi-atom collisional loss is suppressed\nthrough the quantum Zeno effect. We derive the effective Hamiltonian for this\nsystem, and calculate its phase diagram in a one-dimensional optical lattice.\nThe results show rich phase transitions between the p-wave superfluid state and\ndifferent types of insulator states induced either by interaction or by\ndissipation."
    },
    {
        "anchor": "Surface waves and bulk Ruderman mode of a bosonic superfluid vortex\n  crystal in the lowest Landau level: We determine and analyze collective normal modes of a finite disk-shaped\ntwo-dimensional vortex crystal formed in a compressible bosonic superfluid in\nan artificial magnetic field. Using the microscopic Gross-Pitaevskii theory in\nthe lowest Landau level approximation, we generate vortex crystal ground states\nand solve the Bogoliubov-de Gennes equations for small amplitude collective\noscillations. We find chiral surface waves that propagate at frequencies larger\nthan those of the bulk Tkachenko modes. Furthermore, we study low frequency\nbulk excitations and identify a torsional Ruderman mode, which we find is\nwell-described by a previously developed low-energy effective field theory.",
        "positive": "Long-range Ordering of Topological Excitations in a Two-Dimensional\n  Superfluid Far From Equilibrium: We study the relaxation of a 2D ultracold Bose-gas from a nonequilibrium\ninitial state containing vortex excitations in experimentally realizable square\nand rectangular traps. We show that the subsystem of vortex gas excitations\nresults in the spontaneous emergence of a coherent superfluid flow with a\nnon-zero coarse-grained vorticity field. The streamfunction of this emergent\nquasi-classical 2D flow is governed by a Boltzmann-Poisson equation. This\nequation reveals that maximum entropy states of a neutral vortex gas that\ndescribe the spectral condensation of energy can be classified into types of\nflow depending on whether or not the flow spontaneously acquires angular\nmomentum. Numerical simulations of a neutral point vortex model and a Bose gas\ngoverned by the 2D Gross-Pitaevskii equation in a square reveal that a large\nscale monopole flow field with net angular momentum emerges that is consistent\nwith predictions of the Boltzmann-Poisson equation. The results allow us to\ncharacterise the spectral energy condensate in a 2D quantum fluid that bears\nstriking similarity with similar flows observed in experiments of 2D classical\nturbulence. By deforming the square into a rectangular region, the resulting\nmaximum entropy state switches to a dipolar flow field with zero net angular\nmomentum."
    },
    {
        "anchor": "Unitary Fermi superfluid near the critical temperature: thermodynamics\n  and sound modes from elementary excitations: We compare recent experimental results [Science 375, 528 (2022)] of the\nsuperfluid unitary Fermi gas near the critical temperature with a thermodynamic\nmodel based on elementary excitations of the system. We find very good\nagreement between experimental data and our theory for several quantities such\nas first sound, second sound, and superfluid fraction. We also show that mode\nmixing between first and second sound occurs. Finally, we characterize the\nresponse amplitude to a density perturbation: close to the critical temperature\nboth first and second sound can be excited through a density perturbation,\nwhereas at lower temperatures only the first sound mode exhibits a significant\nresponse.",
        "positive": "Singularity in the matrix of the coupled Gross-Pitaevskii equations and\n  the related state-transitions in three-species condensates: An approach is proposed to solve the coupled Gross-Pitaevskii equations (CGP)\nof the 3-species BEC in an analytical way under the Thomas-Fermi approximation\n(TFA). It was found that, when the strength of a kind of interaction increases\nand crosses over a critical value, a specific type of state-transition will\noccur and will cause a jump in the total energy. Due to the jump, the energy of\nthe lowest symmetric state becomes considerably higher. This leaves a\nparticular opportunity for the lowest asymmetric state to replace the symmetric\nstates as the ground state. It was further found that the critical values are\nrelated to the singularity of either the matrix or a sub-matrix of the CGP.\nThese critical values are not arising from the TFA but inherent in the CGP, and\nthey can be analytically expressed. Furthermore, a model (in which two kinds of\natoms separated from each other asymmetrically) has been proposed for the\nevaluation of the energy of the lowest asymmetric state. With this model the\nemergence of the asymmetric ground state is numerically confirmed under the\nTFA. The theoretical formalism of this paper is quite general and can be\ngeneralized for BEC with more than three species."
    },
    {
        "anchor": "Exactly solvable models and ultracold Fermi gases: Exactly solvable models of ultracold Fermi gases are reviewed via their\nthermodynamic Bethe Ansatz solution. Analytical and numerical results are\nobtained for the thermodynamics and ground state properties of two- and\nthree-component one-dimensional attractive fermions with population imbalance.\nNew results for the universal finite temperature corrections are given for the\ntwo-component model. For the three-component model, numerical solution of the\ndressed energy equations confirm that the analytical expressions for the\ncritical fields and the resulting phase diagrams at zero temperature are highly\naccurate in the strong coupling regime. The results provide a precise\ndescription of the quantum phases and universal thermodynamics which are\napplicable to experiments with cold fermionic atoms confined to one-dimensional\ntubes.",
        "positive": "Birefringent break up of Dirac fermions in a square optical lattice: We generalize a proposal by Sorensen et al. [Phys. Rev. Lett. 94, 086803\n(2005)] for creating an artificial magnetic field in a cold atom system on a\nsquare optical lattice. This leads us to an effective lattice model with\ntunable spatially periodic modulation of the artificial magnetic field and the\nhopping amplitude. When there is an average flux of half a flux quantum per\nplaquette the spectrum of low-energy excitations can be described by massless\nDirac fermions in which the usually doubly degenerate Dirac cones split into\ncones with different \"speeds of light\" which can be tuned to give a single\nDirac cone and a flat band. These gapless birefringent Dirac fermions arise\nbecause of broken chiral symmetry in the kinetic energy term of the effective\nlow energy Hamiltonian. We characterize the effects of various perturbations to\nthe low-energy spectrum, including staggered potentials, interactions, and\ndomain wall topological defects."
    },
    {
        "anchor": "Breathing Mode of a Bose-Einstein Condensate Immersed in a Fermi Sea: By analyzing breathing mode of a Bose-Einstein condensate repulsively\ninteracting with a polarized fermionic cloud, we further the understanding of a\nBose-Fermi mixture recently realized by Lous et al. [\\textit{Phys. Rev. Lett.}\n\\textbf{120}, 243403]. We show that a hydrodynamic description of a domain wall\nbetween bosonic and fermionic atoms reproduces experimental data of Huang et\nal. [\\textit{Phys. Rev. A} \\textbf{99}, 041602(R)]. Two different types of\ninteraction renormalization are explored, based on lowest order constrained\nvariational and perturbation techniques. In order to replicate nonmonotonic\nbehavior of the oscillation frequency observed in the experiment, temperature\neffects have to be included. We find that the frequency down-shift is caused by\nthe fermion-induced compression and rethermalization of the bosonic species as\nthe system is quenched into the strongly interacting regime.",
        "positive": "Phase space theory of Bose-Einstein condensates and time-dependent modes: A phase space theory approach for treating dynamical behaviour of\nBose-Einstein condensates applicable to situations such as interferometry with\nBEC in time-dependent double well potentials is presented. Time-dependent mode\nfunctions are used, chosen so that one, two,.. highly occupied modes describe\nwell the physics of interacting condensate bosons in time dependent potentials\nat well below the transition temperature. Time dependent mode annihilation,\ncreation operators are represented by time dependent phase variables, but time\nindependent total field annihilation, creation operators are represented by\ntime independent field functions. Two situations are treated, one (mode theory)\nis where specific mode annihilation, creation operators and their related phase\nvariables and distribution functions are dealt with, the other (field theory)\nis where only field creation, annihilation operators and their related field\nfunctions and distribution functionals are involved. The paper focuses on the\nhybrid approach, where the modes are divided up between condensate (highly\noccupied) modes and non-condensate (sparsely occupied) modes. It is found that\nthere are extra terms in the Ito stochastic equations both for the stochastic\nphases and stochastic fields, involving coupling coefficients defined via\noverlap integrals between mode functions and their time derivatives. For the\nhybrid approach both the Fokker-Planck and functional Fokker-Planck equations\ndiffer from those derived via the correspondence rules, the drift vectors are\nunchanged but the diffusion matrices contain additional terms involving the\ncoupling coefficients. Results are also presented for the combined approach\nwhere all the modes are treated as one set."
    },
    {
        "anchor": "Construction of analytical many body wave functions for correlated\n  bosons in a harmonic trap: We develop an analytical many-body wave function to accurately describe the\ncrossover of a one-dimensional bosonic system from weak to strong interactions\nin a harmonic trap. The explicit wave function, which is based on the exact\ntwo-body states, consists of symmetric multiple products of the corresponding\nparabolic cylinder functions, and respects the analytically known limits of\nzero and infinite repulsion for arbitrary number of particles. For intermediate\ninteraction strengths we demonstrate, that the energies, as well as the reduced\ndensities of first and second order, are in excellent agreement with large\nscale numerical calculations.",
        "positive": "Resonantly Enhanced Tunneling and Transport of Ultracold Atoms on Tilted\n  Optical Lattices: We investigate the resonantly enhanced tunneling dynamics of ultracold bosons\nloaded on a tilted 1-D optical lattice, which can be used to simulate a chain\nof Ising spins and associated quantum phase transitions. The center of mass\nmotion after a sudden tilt both at commensurate and incommensurate fillings is\nobtained via analytic, time-dependent exact diagonalization and density matrix\nrenormalization group methods (adaptive t-DMRG). We identify a maximum in the\namplitude of the center of mass oscillations at the quantum critical point of\nthe effective spin system. For the dynamics of incommensurate systems, which\ncannot be mapped to a spin model, we develop an analytical approach in which\nthe time evolution is obtained by projecting onto resonant families of small\nclusters. We compare the results of this approach at low fillings to the exact\ntime evolution and find good agreement even at filling factors as large as 2/3.\nUsing this projection onto small clusters, we propose a controllable transport\nscheme applicable in the context of Atomtronic devices on optical lattices\n(`slinky scheme')."
    },
    {
        "anchor": "The self-energy of an impurity in an ideal Fermi gas to second order in\n  the interaction strength: We study in three dimensions the problem of a spatially homogeneous\nzero-temperature ideal Fermi gas of spin-polarized particles of mass $m$\nperturbed by the presence of a single distinguishable impurity of mass $M$. The\ninteraction between the impurity and the fermions involves only the partial\n$s$-wave through the scattering length $a$, and has negligible range $b$\ncompared to the inverse Fermi wave number $1/\\kf$ of the gas. Through the\ninteractions with the Fermi gas the impurity gives birth to a quasi-particle,\nwhich will be here a Fermi polaron (or more precisely a {\\sl monomeron}). We\nconsider the general case of an impurity moving with wave vector $\\KK\\neq\\OO$:\nThen the quasi-particle acquires a finite lifetime in its initial momentum\nchannel because it can radiate particle-hole pairs in the Fermi sea. A\ndescription of the system using a variational approach, based on a finite\nnumber of particle-hole excitations of the Fermi sea, then becomes\ninappropriate around $\\KK=\\mathbf{0}$. We rely thus upon perturbation theory,\nwhere the small and negative parameter $\\kf a\\to0^-$ excludes any branches\nother than the monomeronic one in the ground state (as e.g.\\ the dimeronic\none), and allows us a systematic study of the system. We calculate the impurity\nself-energy $\\Sigma^{(2)}(\\KK,\\omega)$ up to second order included in $a$.\nRemarkably, we obtain an analytical explicit expression for\n$\\Sigma^{(2)}(\\KK,\\omega)$ allowing us to study its derivatives in the plane\n$(K,\\omega)$. These present interesting singularities, which in general appear\nin the third order derivatives $\\partial^3 \\Sigma^{(2)}(\\KK,\\omega)$. In the\nspecial case of equal masses, $M=m$, singularities appear already in the\nphysically more accessible second order derivatives $\\partial^2\n\\Sigma^{(2)}(\\KK,\\omega)$; using a self-consistent heuristic approach based on\n$\\Sigma^{(2)}$ we then regularise the divergence of the second order derivative\n$\\partial\\_K^2 \\Delta E(\\KK)$ of the complex energy of the quasi-particle found\nin reference [C. Trefzger, Y. Castin, Europhys. Lett. {\\bf 104}, 50005 (2013)]\nat $K=\\kf$, and we predict an interesting scaling law in the neighborhood of\n$K=\\kf$. As a by product of our theory we have access to all moments of the\nmomentum of the particle-hole pair emitted by the impurity while damping its\nmotion in the Fermi sea, at the level of Fermi's golden rule.",
        "positive": "The Inhomogeneous Extended Bose-Hubbard Model: A Mean-Field Theory: We develop an inhomogeneous mean-field theory for the extended Bose-Hubbard\nmodel with a quadratic, confining potential. In the absence of this potential,\nour mean-field theory yields the phase diagram of the homogeneous extended\nBose-Hubbard model. This phase diagram shows a superfluid (SF) phase and lobes\nof Mott-insulator (MI), density-wave (DW), and supersolid (SS) phases in the\nplane of the chemical potential (\\mu) and on-site repulsion (U); we present\nphase diagrams for representative values of V, the repulsive energy for bosons\non nearest-neighbor sites. We demonstrate that, when the confining potential is\npresent, superfluid and density-wave order parameters are nonuniform; in\nparticular, we obtain, for a few representative values of parameters, spherical\nshells of SF, MI, DW, and SS phases. We explore the implications of our study\nfor experiments on cold-atom dipolar condensates in optical lattices in a\nconfining potential"
    },
    {
        "anchor": "Super-Tonks-Girardeau Quench in the Extended Bose-Hubbard Model: We investigate the effect of a quench from a one-dimensional gas with strong\nand repulsive local interactions to a strongly attractive one, known as the\nsuper-Tonks-Girardeau effect. By incorporating both an optical lattice and\nnon-local interactions (specifically nearest-neighbor), we discover a\npreviously unexplored phenomenon: the disruption of the state during the\nquench, but within a specific range of interactions. Our study employs the\nextended Bose-Hubbard model across various system sizes, starting with\nanalytical results for two atoms and progressing to few-body systems using\nexact diagonalization, DMRG and TDVP methods. Finally, we use a numerical\nimplementation of the local density approximation for a macroscopic number of\natoms. Consistently, our findings unveil a region where the initially\nself-bound structure expands due to the super-Tonks-Girardeau quench. The fast\nevaporation provides a tool to characterize the phase diagram in state-of-art\nexperiments exploring the physics of the extended Bose-Hubbard model.",
        "positive": "OpenMP, OpenMP/MPI, and CUDA/MPI C programs for solving the\n  time-dependent dipolar Gross-Pitaevskii equation: We present new versions of the previously published C and CUDA programs for\nsolving the dipolar Gross-Pitaevskii equation in one, two, and three spatial\ndimensions, which calculate stationary and non-stationary solutions by\npropagation in imaginary or real time. Presented programs are improved and\nparallelized versions of previous programs, divided into three packages\naccording to the type of parallelization. First package contains improved and\nthreaded version of sequential C programs using OpenMP. Second package\nadditionally parallelizes three-dimensional variants of the OpenMP programs\nusing MPI, allowing them to be run on distributed-memory systems. Finally,\nprevious three-dimensional CUDA-parallelized programs are further parallelized\nusing MPI, similarly as the OpenMP programs. We also present speedup test\nresults obtained using new versions of programs in comparison with the previous\nsequential C and parallel CUDA programs. The improvements to the sequential\nversion yield a speedup of 1.1 to 1.9, depending on the program. OpenMP\nparallelization yields further speedup of 2 to 12 on a 16-core workstation,\nwhile OpenMP/MPI version demonstrates a speedup of 11.5 to 16.5 on a computer\ncluster with 32 nodes used. CUDA/MPI version shows a speedup of 9 to 10 on a\ncomputer cluster with 32 nodes."
    },
    {
        "anchor": "Effective interactions in a quantum Bose-Bose mixture: We generalize the Beliaev diagrammatic theory of an interacting spinless\nBose-Einstein condensate to the case of a binary mixture. We derive a set of\ncoupled Dyson equations and find analytically the Green's functions of the\nsystem. The elementary excitation spectrum consists of two branches, one of\nwhich takes the characteristic parabolic form in the limit of a\nspin-independent interaction. We observe renormalization of the magnon mass and\nthe spin-wave velocity due to the Andreev-Bashkin entrainment effect. For a 3D\nweakly-interacting gas the spectrum can be obtained by applying the Bogoliubov\ntransformation to the second-quantized Hamiltonian in which the microscopic\ntwo-body potentials in each channel are replaced by the corresponding off-shell\nscattering amplitudes. The superfluid drag density can be calculated by\nconsidering a mixture of phonons and magnons interacting via the effective\npotentials. We show that this problem is identical to the second-order\nperturbative treatment of a Bose polaron. In 2D the drag contributes to the\nmagnon dispersion already in the first approximation. Our consideration\nprovides a basis for systematic study of emergent phases in quantum degenerate\nBose-Bose mixtures.",
        "positive": "Potential insights into non-equilibrium behavior from atomic physics: This chapter seeks to outline a few basic problems in quantum statistical\nphysics where recent experimental advances from the atomic physics community\noffer the hope of dramatic progress. The focus is on nonequilibrium situations\nwhere the powerful concepts and methods of equilibrium statistical physics and\n\"linear response\" theory (for small deviations from equilibrium) are not\napplicable. The problems discussed here are chosen in part because they have a\nhigh degree of \"universality\" or generality across different microscopic\nsituations, as the major challenge in nonequilibrium statistical physics, both\nquantum and classical, has been to find principles as general as the basic\nprinciples of equilibrium statistical physics or linear response."
    },
    {
        "anchor": "Realization of a fractional quantum Hall state with ultracold atoms: Strongly interacting topological matter exhibits fundamentally new phenomena\nwith potential applications in quantum information technology. Emblematic\ninstances are fractional quantum Hall states, where the interplay of magnetic\nfields and strong interactions gives rise to fractionally charged\nquasi-particles, long-ranged entanglement, and anyonic exchange statistics.\nProgress in engineering synthetic magnetic fields has raised the hope to create\nthese exotic states in controlled quantum systems. However, except for a recent\nLaughlin state of light, preparing fractional quantum Hall states in engineered\nsystems remains elusive. Here, we realize a fractional quantum Hall (FQH) state\nwith ultracold atoms in an optical lattice. The state is a lattice version of a\nbosonic $\\nu=1/2$ Laughlin state with two particles on sixteen sites. This\nminimal system already captures many hallmark features of Laughlin-type FQH\nstates: we observe a suppression of two-body interactions, we find a\ndistinctive vortex structure in the density correlations, and we measure a\nfractional Hall conductivity of $\\sigma_\\text{H}/\\sigma_0= 0.6(2)$ via the bulk\nresponse to a magnetic perturbation. Furthermore, by tuning the magnetic field\nwe map out the transition point between the normal and the FQH regime through a\nspectroscopic probe of the many-body gap. Our work provides a starting point\nfor exploring highly entangled topological matter with ultracold atoms.",
        "positive": "Effect of an Impurity on Grey Soliton Dynamics in Cigar-Shaped\n  Bose-Einstein Condensate: In a cigar shaped Bose-Einstein condensate, explicit solutions of the coupled\nmean-field equations, describing defect-grey soliton dynamics are obtained,\ndemonstrating the coexistence of grey soliton and a localized defect. Unlike\nthe case of dark soliton, where the defect trapping center has vanishing\nsuperfluid density, the moving grey soliton necessarily possesses a finite\nsuperfluid component at the defect location. The wave vector of the impurity is\ncontrolled by the velocity of the grey soliton, which has an upper bound. It is\nfound that the presence of the impurity lowers the speed of the grey soliton,\nas compared to the defect free case, where it can reach the sound velocity. The\ngrey soliton's energy gets substantially modified through its interaction with\nthe defect, opening up the possibility of its control through defect dynamics."
    },
    {
        "anchor": "Dilaton in a cold Fermi gas: These are the notes for a lecture which I presented at the International\nConference on New Frontiers in Physics in Kolymbari, Crete in July, 2018. They\nreview an idea which posits a phase of a two-dimensional system of cold\nN-component Fermions which exhibits spontaneously broken approximate scale\nsymmetry when studied in the large N expansion. Near criticality, the phase\nexhibits anomalously small pressure and large compressibility. Some of the\nconsequences of the approximate scale symmetry, such as the existence of a\ndilaton and its properties are discussed.",
        "positive": "Entanglement and violation of classical inequalities in the Hawking\n  radiation of flowing atom condensates: We consider a sonic black-hole scenario where an atom condensate flows\nthrough a subsonic-supersonic interface. We discuss several criteria that\nreveal the existence of nonclassical correlations resulting from the quantum\ncharacter of the spontaneous Hawking radiation. We unify previous general work\nas applied to Hawking radiation analogs. We investigate the measurability of\nthe various indicators and conclude that, within a class of detection schemes,\nonly the violation of quadratic Cauchy-Schwarz inequalities can be discerned.\nWe show numerical results that further support the viability of measuring deep\nquantum correlations in concrete scenarios."
    },
    {
        "anchor": "Two-dimensional miscible-immiscible supersolid and droplet crystal state\n  in a homonuclear dipolar bosonic mixture: The recent realization of binary dipolar BEC [Phys. Rev. Lett. 121, 213601\n(2018)] opens new exciting aspects for studying quantum droplets and\nsupersolids in a binary mixture. Motivated by this experiment, we study\ngroundstate phases and dynamics of a Dy-Dy mixture. Dipolar bosonic mixture\nexhibits qualitatively novel and rich physics. Relying on the three-dimensional\nnumerical simulations in the extended Gross-Pitaevskii framework, we unravel\nthe groundstate phase diagrams and characterize different groundstate phases.\nThe emergent phases include both miscible and immiscible single droplet (SD),\nmultiple droplets (MD), supersolid (SS), and superfluid (SF) states. More\nintriguing mixed groundstates may occur for an imbalanced binary mixture,\nincluding a combination of SS-SF, SS-MD, and SS-SS phases. We observed the\ndynamical transition from a miscible MD state to an immiscible MD state with\nmultiple domains formed along the axial direction by tuning the inter-species\nscattering length. Also by linear quenches of intra-species scattering lengths\nacross the aforementioned phases, we monitor the dynamical formation of\nsupersolid clusters and droplet lattices. Although we have demonstrated the\nresults for a Dy-Dy mixture and for a specific parameter range of intra-species\nand inter-species scattering lengths, our results are generally valid for other\ndipolar mixtures and may become an important benchmark for future experimental\nscenarios.",
        "positive": "Entropy of the BEC Ground State: Correlation vs Ground State Entropy: Calculation of the entropy of an ideal Bose Einstein Condensate (BEC) in a\nthree dimensional trap reveals unusual, previously unrecognized, features of\nthe Canonical Ensemble. It is found that, for any temperature, the entropy of\nthe Bose gas is equal to the entropy of the excited particles although the\nentropy of the particles in the ground state is nonzero. We explain this by\nconsidering the correlations between the ground state particles and particles\nin the excited states. These correlations lead to a correlation entropy which\nis exactly equal to the contribution from the ground state. The correlations\nthemselves arise from the fact that we have a fixed number of particles obeying\nquantum statistics. We present results for correlation functions between the\nground and excited states in Bose gas, so to clarify the role of fluctuations\nin the system. We also report the sub-Poissonian nature of the ground state\nfluctuations."
    },
    {
        "anchor": "Adiabatic preparation of Floquet condensates: We argue that a Bose-Einstein condensate can be transformed into a Floquet\ncondensate, that is, into a periodically time-dependent many-particle state\npossessing the coherence properties of a mesoscopically occupied\nsingle-particle Floquet state. Our reasoning is based on the observation that\nthe denseness of the many-body system's quasienergy spectrum does not\nnecessarily obstruct effectively adiabatic transport. Employing the idealized\nmodel of a driven bosonic Josephson junction, we demonstrate that only a small\namount of Floquet entropy is generated when a driving force with judiciously\nchosen frequency and maximum amplitude is turned on smoothly.",
        "positive": "Achieving the quantum field theory limit in far-from-equilibrium quantum\n  link models: Realizations of gauge theories in setups of quantum synthetic matter open up\nthe possibility of probing salient exotic phenomena in condensed matter and\nhigh-energy physics, along with potential applications in quantum information\nand science technologies. In light of the impressive ongoing efforts to achieve\nsuch realizations, a fundamental question regarding quantum link model\nregularizations of lattice gauge theories is how faithfully they capture the\nquantum field theory limit of gauge theories. Recent work [Zache, Van Damme,\nHalimeh, Hauke, and Banerjee, at\nhttps://journals.aps.org/prd/abstract/10.1103/PhysRevD.106.L091502 has shown\nthrough analytic derivations, exact diagonalization, and infinite matrix\nproduct state calculations that the low-energy physics of $1+1$D\n$\\mathrm{U}(1)$ quantum link models approaches the quantum field theory limit\nalready at small link spin length $S$. Here, we show that the approach to this\nlimit also lends itself to the far-from-equilibrium quench dynamics of lattice\ngauge theories, as demonstrated by our numerical simulations of the Loschmidt\nreturn rate and the chiral condensate in infinite matrix product states, which\nwork directly in the thermodynamic limit. Similar to our findings in\nequilibrium that show a distinct behavior between half-integer and integer link\nspin lengths, we find that criticality emerging in the Loschmidt return rate is\nfundamentally different between half-integer and integer spin quantum link\nmodels in the regime of strong electric-field coupling. Our results further\naffirm that state-of-the-art finite-size ultracold-atom and NISQ-device\nimplementations of quantum link lattice gauge theories have the real potential\nto simulate their quantum field theory limit even in the far-from-equilibrium\nregime."
    },
    {
        "anchor": "Twist-and-store entanglement in bimodal and spin-1 Bose-Einstein\n  condensates: A scheme for dynamical stabilization of entanglement quantified by the\nquantum Fisher information is analyzed numerically and analytically for bimodal\nand spin-1 Bose-Einstein condensates in the context of atomic interferometry.\nThe scheme consists of twisting dynamics followed by a single rotation of a\nstate which limits further evolution around stable center fixed points in the\nmean-field phase space. The resulting level of entanglement is of the order or\nlarger than at the moment of rotation. It is demonstrated that the readout\nmeasurement of parity quantifies the level of entanglement during entire\nevolution.",
        "positive": "Bloch oscillations and accelerated Bose-Einstein condensates in an\n  optical lattice: We discuss the method for the measurement of the gravity acceleration g by\nmeans of Bloch oscillations of an accelerated BEC in an optical lattice. This\nmethod has a theoretical critical point due to the fact that the period of the\nBloch oscillations depends, in principle, on the initial shape of the BEC\nwavepacket. Here, by making use of the nearest-neighbor model for the numerical\nanalysis of the BEC wavefunction, we show that in real experiments the period\nof the Bloch oscillations does not really depend on the shape of the initial\nwavepacket and that the relative uncertainty, due to the fact that the initial\nshape of the wavepacket may be asymmetrical, is smaller than the one due to\nexperimental errors. Furthermore, we also show that the relation between the\noscillation period and the scattering length of the BEC's atoms is linear; this\nfact suggest us a new experimental procedure for the measurement of the\nscattering length of atoms."
    },
    {
        "anchor": "Experimental Methods for Generating Two-Dimensional Quantum Turbulence\n  in Bose-Einstein Condensates: Bose-Einstein condensates of dilute gases are well-suited for investigations\nof vortex dynamics and turbulence in quantum fluids, yet there has been little\nexperimental research into the approaches that may be most promising for\ngenerating states of two-dimensional turbulence in these systems. Here we give\nan overview of techniques for generating the large and disordered vortex\ndistributions associated with two-dimensional quantum turbulence. We focus on\ndescribing methods explored in our Bose-Einstein condensation laboratory, and\ndiscuss the suitability of these methods for studying various aspects of\ntwo-dimensional quantum turbulence. We also summarize some of the open\nquestions regarding our own understanding of these mechanisms of\ntwo-dimensional quantum turbulence generation in condensates. We find that\nwhile these disordered distributions of vortices can be generated by a variety\nof techniques, further investigation is needed to identify methods for\nobtaining quasi-steady-state quantum turbulence in condensates.",
        "positive": "Critical behaviours of contact near phase transitions: A central quantity of importance for ultracold atoms is contact, which\nmeasures two-body correlations at short distances in dilute systems. It appears\nin universal relations among thermodynamic quantities, such as large momentum\ntails, energy, and dynamic structure factors, through the renowned Tan\nrelations. However, a conceptual question remains open as to whether or not\ncontact can signify phase transitions that are insensitive to short-range\nphysics. Here we show that, near a continuous classical or quantum phase\ntransition, contact exhibits a variety of critical behaviors, including scaling\nlaws and critical exponents that are uniquely determined by the universality\nclass of the phase transition and a constant contact per particle. We also use\na prototypical exactly solvable model to demonstrate these critical behaviors\nin one-dimensional strongly interacting fermions. Our work establishes an\nintrinsic connection between the universality of dilute many-body systems and\nuniversal critical phenomena near a phase transition."
    },
    {
        "anchor": "Bosonic Functional Determinant Approach and its Application to Polaron\n  Spectra: The functional determinant approach (FDA) is a simple method to compute\nexactly certain observables for ideal quantum systems and has been successfully\napplied to the Fermi polaron problem to obtain the dynamical overlap and\nspectral function. Unfortunately, its application to Bosonic ultracold gases is\nprohibited by the failure of the grand canonical ensemble for these systems. In\nthis paper, we show how to circumvent this problem and develop a Bosonic FDA.\nThis yields exact injection and ejection spectra for ideal Bose polarons at\narbitrary temperatures. While coherent features visible at absolute zero\nquickly smear out with rising temperature as expected, the line width of the\nmain peak is, counterintuitively, found to decrease near unitarity. We compare\nthe results to the Fermi polaron problem, for which we provide more detailed\nspectra than previously available by deriving an explicit formula for the\noverlap operator.",
        "positive": "Physics of hollow Bose-Einstein condensates: Bose-Einstein condensate shells, while occurring in ultracold systems of\ncoexisting phases and potentially within neutron stars, have yet to be realized\nin isolation on Earth due to the experimental challenge of overcoming\ngravitational sag. Motivated by the expected realization of hollow condensates\nby the space-based Cold Atomic Laboratory in microgravity conditions, we study\na spherical condensate undergoing a topological change from a filled sphere to\na hollow shell. We argue that the collective modes of the system show marked\nand robust signatures of this hollowing transition accompanied by the\nappearance of a new boundary. In particular, we demonstrate that the frequency\nspectrum of the breathing modes shows a pronounced depression as it evolves\nfrom the filled sphere limit to the hollowing transition. Furthermore, when the\ncenter of the system becomes hollow surface modes show a global restructuring\nof their spectrum due to the availability of a new, inner, surface for\nsupporting density distortions. We pinpoint universal features of this\ntopological transition as well as analyse the spectral evolution of collective\nmodes in the experimentally relevant case of a bubble-trap."
    },
    {
        "anchor": "Quantitative Studies on the Quantum Critical Regime near Superfluid to\n  Mott Insulator Transition: We investigate the critical behaviors of correlation length and critical\nexponents for strongly interacting bosons in a two-dimensional optical lattice\nvia quantum Monte Carlo simulations. By comparing the full numerical results to\nthose given by the effective theory, we quantitatively determine the critical\nregime where the universal scaling behaviors applies for both classical\nBerezinskii-Kosterlitz-Thouless transition at a finite temperature and quantum\nphase transition from superfluid to Mott insulator. Our results show that the\ncritical regime can be as large as a few lattice sites in optical lattice and\nshould be observable in present experimental conditions.",
        "positive": "Quantum caustics and the hierarchy of light cones in quenched spin\n  chains: We show that the light cone-like structures that form in spin chains after a\nquench are quantum caustics. Their natural description is in terms of\ncatastrophe theory and this implies: 1) a hierarchy of light cone structures\ncorresponding to the different catastrophes; 2) dressing by characteristic wave\nfunctions that obey scaling laws determined by the Arnol'd and Berry indices;\n3) a network of vortex-antivortex pairs in space-time inside the cone. We\nillustrate the theory by giving explicit calculations for the transverse field\nIsing model and the XY model, finding fold catastrophes dressed by Airy\nfunctions and cusp catastrophes dressed by Pearcey functions; multisite\ncorrelation functions are described by higher catastrophes such as the\nhyperbolic umbilic. Furthermore, we find that the vortex pairs created inside\nthe cone are sensitive to phase transitions in these spin models with their\nrate of production being determined by the dynamical critical exponent. More\nbroadly, this work illustrates how catastrophe theory can be applied to\nsingularities in quantum fields."
    },
    {
        "anchor": "Dynamical Hartree-Fock-Bogoliubov Theory of Vortices in Bose-Einstein\n  Condensates at Finite Temperature: We present a method utilizing the continuity equation for the condensate\ndensity to make predictions of the precessional frequency of single off-axis\nvortices and of vortex arrays in Bose-Einstein condensates at finite\ntemperature. We also present an orthogonalized Hartree-Fock-Bogoliubov (HFB)\nformalism. We solve the continuity equation for the condensate density\nself-consistently with the orthogonalized HFB equations, and find stationary\nsolutions in the frame rotating at this frequency. As an example of the utility\nof this formalism we obtain time-independent solutions for\nquasi-two-dimensional rotating systems in the co-rotating frame. We compare\nthese results with time-dependent predictions where we simulate stirring of the\ncondensate.",
        "positive": "Realising a species-selective double well with\n  multiple-radiofrequency-dressed potentials: Techniques to manipulate the individual constituents of an ultracold mixture\nare key to investigating impurity physics. In this work, we confine a mixture\nof the hyperfine ground states of Rb-87 in a double-well potential. The\npotential is produced by dressing the atoms with multiple radiofrequencies. The\namplitude and phase of each frequency component of the dressing field are\nindividually controlled to independently manipulate each species. Furthermore,\nwe verify that our mixture of hyperfine states is collisionally stable, with no\nobservable inelastic loss."
    },
    {
        "anchor": "Metal-insulator phase transition and topology in a three-component\n  system: In the framework of the tight binding approximation, we study a\nnon-interacting model on the three-component dice lattice with real\nnearest-neighbor and complex next-nearest-neighbor hopping subjected to\n$\\Lambda$- or V-type sublattice potentials. By analyzing the dispersions of\ncorresponding energy bands, we find that the system undergoes a metal-insulator\ntransition which can be modulated not only by the Fermi energy but also the\ntunable extra parameters. Furthermore, rich topological phases, including the\nones with high Hall plateau, are uncovered by calculating the associated band's\nChern number. Besides, we also analyze the edge-state spectra and discuss the\ncorrespondence between Chern numbers and the edge states by the principle of\nbulk-edge correspondence.",
        "positive": "Renormalization theory of a two dimensional Bose gas: quantum critical\n  point and quasi-condensed state: We present a renormalization group construction of a weakly interacting Bose\ngas at zero temperature in the two-dimensional continuum, both in the quantum\ncritical regime and in the presence of a condensate fraction. The construction\nis performed within a rigorous renormalization group scheme, borrowed from the\nmethods of constructive field theory, which allows us to derive explicit bounds\non all the orders of renormalized perturbation theory. Our scheme allows us to\nconstruct the theory of the quantum critical point completely, both in the\nultraviolet and in the infrared regimes, thus extending previous heuristic\napproaches to this phase. For the condensate phase, we solve completely the\nultraviolet problem and we investigate in detail the infrared region, up to\nlength scales of the order $(\\lambda^3 \\rho_0)^{-1/2}$ (here $\\lambda$ is the\ninteraction strength and $\\rho_0$ the condensate density), which is the largest\nlength scale at which the problem is perturbative in nature. We exhibit\nviolations to the formal Ward Identities, due to the momentum cutoff used to\nregularize the theory, which suggest that previous proposals about the\nexistence of a non-perturbative non-trivial fixed point for the infrared flow\nshould be reconsidered."
    },
    {
        "anchor": "Multi-vortex crystal lattices in Bose-Einstein Condensates with a\n  rotating trap: We consider vortex dynamics in the context of Bose-Einstein Condensates (BEC)\nwith a rotating trap, with or without anisotropy. Starting with the\nGross-Pitaevskii (GP) partial differential equation (PDE), we derive a novel\nreduced system of ordinary differential equations (ODEs) that describes stable\nconfigurations of multiple co-rotating vortices (vortex crystals). This\ndescription is found to be quite accurate quantitatively especially in the case\nof multiple vortices. In the limit of many vortices, BECs are known to form\nvortex crystal structures, whereby vortices tend to arrange themselves in a\nhexagonal-like spatial configuration. Using our asymptotic reduction, we derive\nthe effective vortex crystal density and its radius. We also obtain an\nasymptotic estimate for the maximum number of vortices as a function of\nrotation rate. We extend considerations to the anisotropic trap case,\nconfirming that a pair of vortices lying on the long (short) axis is linearly\nstable (unstable), corroborating the ODE reduction results with full PDE\nsimulations. We then further investigate the many-vortex limit in the case of\nstrong anisotropic potential. In this limit, the vortices tend to align\nthemselves along the long axis, and we compute the effective one-dimensional\nvortex density, as well as the maximum admissible number of vortices. Detailed\nnumerical simulations of the GP equation are used to confirm our analytical\npredictions.",
        "positive": "Effect of scattering lengths on the dynamics of a two-component\n  Bose-Einstein condensate: We examine the effect of the intra- and interspecies scattering lengths on\nthe dynamics of a two-component Bose-Einstein condensate, particularly focusing\non the existence and stability of solitonic excitations. For each type of\npossible soliton pairs stability ranges are presented in tabulated form. We\nalso compare the numerically established stability of bright-bright,\nbright-dark and dark-dark solitons with our analytical prediction and with that\nof Painlev\\'e-analysis of the dynamical equation. We demonstrate that tuning\nthe inter-species scattering length away from the predicted value (keeping the\nintra-species coupling fixed) breaks the stability of the soliton pairs."
    },
    {
        "anchor": "Long-lived universal resonant Bose gases: Quantum simulations based on near-resonance Bose gases are limited by their\nshort lifetimes due to severe atom losses. In addition to this, the recently\npredicted thermodynamical instability adds another constraint on accessing the\nresonant Bose gases. In this article, we offer a potential solution by\nproposing long-lived resonant Bose gases in both two and three dimensions,\nwhere the conventional few-body losses are strongly suppressed. We show that\nthe thermodynamical properties as well as the lifetimes of these strongly\ninteracting systems are universal, and independent of short-range physics.",
        "positive": "Thermodynamics vs. local density fluctuations in the\n  metal/Mott-insulator crossover: The crossover between a metal and a Mott insulator leads to a localization of\nfermions from delocalized Bloch states to localized states. We experimentally\nstudy this crossover using fermionic atoms in an optical lattice by measuring\nthermodynamic and local (on--site) density correlations. In the metallic phase\nat incommensurable filling we observe the violation of the local\nfluctuation--dissipation theorem indicating that the thermodynamics cannot be\nexplained by local observables. In contrast, in the Mott-insulator we observe\nthe convergence of local and thermodynamic fluctuations indicating the absence\nof long--range density-density correlations."
    },
    {
        "anchor": "Clock shifts of optical transitions in ultracold atomic gases: We calculate the shift, due to interatomic interactions, of an optical\ntransition in an atomic Fermi gas trapped in an optical lattice, as in recent\nexperiments of Campbell {\\it et al.}, Science {\\bf 324}, 360 (2009). Using a\npseudospin formalism to describe the density matrix of the internal two states\nof the optical transition, we derive a Bloch equation which incorporates both\nthe spatial inhomogeneity of the probe laser field and the interatomic\ninteractions. Expressions are given for the frequency shift as a function of\nthe pulse duration, detuning of the probe laser, and the spatial dependence of\nthe electric field of the probe beam. In the low temperature semiclassical\nregime, we find that the magnitude of the shift is proportional to the\ntemperature.",
        "positive": "Highly excited exciton-polariton condensates: Exciton-polaritons are a coherent electron-hole-photon (e-h-p) system where\ncondensation has been observed in semiconductor microcavities. In contrast to\nequilibrium Bose-Einstein condensation (BEC) for long lifetime systems,\npolariton condensates have a dynamical nonequilibrium feature owing to the\nsimilar physical structure that they have to semiconductor lasers. One of the\ndistinguishing features of a condensate to a laser is the presence of strong\ncoupling between the matter and photon fields. Irrespective of its equilibrium\nor nonequilibrium nature, exciton-polariton have been observed to maintain\nstrong coupling. We show that by investigating high density regime of\nexciton-polariton condensates, the negative branch directly observed in\nphotoluminescence. This is evidence that the present e-h-p system is still in\nthe strong coupling regime, contrary to past results where the system reduced\nto standard lasing at high density."
    },
    {
        "anchor": "Emulating twisted double bilayer graphene with a multiorbital optical\n  lattice: This work theoretically explores how to emulate twisted double bilayer\ngraphene with ultracold atoms in multiorbital optical lattices. In particular,\nthe quadratic band touching of Bernal stacked bilayer graphene is emulated\nusing a square optical lattice with $p_x$, $p_y$, and $d_{x^2-y^2}$ orbitals on\neach site, while the effects of a twist are captured through the application of\nan incommensurate potential. The quadratic band touching is stable until the\nsystem undergoes an Anderson like delocalization transition in momentum space,\nwhich occurs concomitantly with a strongly renormalized single particle\nspectrum inducing flat bands, which is a generalization of the magic-angle\ncondition realized in Dirac semimetals. The band structure is described\nperturbatively in the quasiperiodic potential strength, which captures miniband\nformation and the existence of magic-angles that qualitatively agrees with the\nexact numerical results in the appropriate regime. We identify several\nmagic-angle conditions that can either have part or all of the quadratic band\ntouching point become flat. In each case, these are accompanied by a diverging\ndensity of states and the delocalization of plane wave eigenstates. It is\ndiscussed how these transitions and phases can be observed in ultracold atom\nexperiments.",
        "positive": "Thermometry with spin-dependent lattices: We propose a method for measuring the temperature of strongly correlated\nphases of ultracold atom gases confined in spin-dependent optical lattices. In\nthis technique, a small number of \"impurity\" atoms--trapped in a state that\ndoes not experience the lattice potential--are in thermal contact with atoms\nbound to the lattice. The impurity serves as a thermometer for the system\nbecause its temperature can be straightforwardly measured using time-of-flight\nexpansion velocity. This technique may be useful for resolving many open\nquestions regarding thermalization in these isolated systems. We discuss the\ntheory behind this method and demonstrate proof-of-principle experiments,\nincluding the first realization of a 3D spin-dependent lattice in the strongly\ncorrelated regime."
    },
    {
        "anchor": "Controllable quantum spin glasses with magnetic impurities embedded in\n  quantum solids: Magnetic impurities embedded in inert solids can exhibit long coherence times\nand interact with one another via their intrinsic anisotropic dipolar\ninteraction. We argue that, as a consequence of these properties, disordered\nensembles of magnetic impurities provide an effective platform for realizing a\ncontrollable, tunable version of the dipolar quantum spin glass seen in\nLiHo$_x$Y$_{1-x}$F$_4$. Specifically, we propose and analyze a system composed\nof dysprosium atoms embedded in solid helium. We describe the phase diagram of\nthe system and discuss the realizability and detectability of the quantum spin\nglass and antiglass phases.",
        "positive": "Laser cooling for quantum gases: Laser cooling exploits the physics of light scattering to cool atomic and\nmolecular gases to close to absolute zero. It is the crucial initial step for\nessentially all atomic gas experiments in which Bose-Einstein condensation and,\nmore generally, quantum degeneracy is reached. The ongoing development of\nlaser-cooling methods has allowed more elements to be brought to quantum\ndegeneracy, with each additional atomic species offering its own experimental\nopportunities. Improved methods are opening new avenues, for example, reaching\nBose-Einstein condensation purely through laser cooling as well as the\nrealization of continuous Bose-Einstein condensation. Here we review these\nrecent innovations in laser cooling and provide an outlook on methods that may\nenable new ways of creating quantum gases."
    },
    {
        "anchor": "Direct evaporative cooling of 39K atoms to Bose-Einstein condensation: We report the realization of Bose-Einstein condensates of 39K atoms without\nthe aid of an additional atomic coolant. Our route to Bose-Einstein\ncondensation comprises Sub Doppler laser cooling of large atomic clouds with\nmore than 10^10 atoms and evaporative cooling in optical dipole traps where the\ncollisional cross section can be increased using magnetic Feshbach resonances.\nLarge condensates with almost 10^6 atoms can be produced in less than 15\nseconds. Our achievements eliminate the need for sympathetic cooling with Rb\natoms which was the usual route implemented till date due to the unfavourable\ncollisional property of 39K. Our findings simplify the experimental set-up for\nproducing Bose-Einstein condensates of 39K atoms with tunable interactions,\nwhich have a wide variety of promising applications including\natom-interferometry to studies on the interplay of disorder and interactions in\nquantum gases.",
        "positive": "Dirty bosons in a three-dimensional harmonic trap: We study a three-dimensional Bose-Einstein condensate in an isotropic\nharmonic trapping potential with an additional delta-correlated disorder\npotential at both zero and finite temperature and investigate the emergence of\na Bose-glass phase for increasing disorder strength. To this end, we revisit a\nquite recent non-perturbative approach towards the dirty boson problem, which\nrelies on the Hartree-Fock mean-field theory and is worked out on the basis of\nthe replica method, and extend it from the homogeneous case to a harmonic\nconfinement. At first, we solve the zero-temperature self-consistency equations\nfor the respective density contributions, which are obtained via the\nHartree-Fock theory within the Thomas-Fermi approximation. Additionally we use\na variational ansatz, whose results turn out to coincide qualitatively with\nthose obtained from the Thomas-Fermi approximation. In particular, a\nfirst-order quantum phase transition from the superfluid phase to the\nBose-glass phase is detected at a critical disorder strength, which agrees with\nfindings in the literature. Afterwards, we consider the three-dimensional dirty\nboson problem at finite temperature. This allows us to study the impact of both\ntemperature and disorder fluctuations on the respective components of the\ndensity as well as their Thomas-Fermi radii. In particular, we find that a\nsuperfluid region, a Bose-glass region, and a thermal region coexist for\nsmaller disorder strengths. Furthermore, depending on the respective system\nparameters, three phase transitions are detected, namely, one from the\nsuperfluid to the Bose-glass phase, another one from the Bose-glass to the\nthermal phase, and finally one from the superfluid to the thermal phase."
    },
    {
        "anchor": "Topological superfluid phases of an atomic Fermi gas with in- and\n  out-of-plane Zeeman fields and equal Rashba-Dresselhaus spin-orbit coupling: We analyze the effects of in- and out-of-plane Zeeman fields on the BCS-BEC\nevolution of a Fermi gas with equal Rashba-Dresselhaus (ERD) spin-orbit\ncoupling (SOC). We show that the ground state of the system involves novel\ngapless superfluid phases that can be distinguished with respect to the\ntopology of the momentum-space regions with zero excitation energy. For the\nBCS-like uniform superfluid phases with zero center-of-mass momentum, the zeros\nmay correspond to one or two doubly-degenerate spheres, two or four spheres,\ntwo or four concave spheroids, or one or two doubly-degenerate circles,\ndepending on the combination of Zeeman fields and SOC. Such changes in the\ntopology signal a quantum phase transition between distinct superfluid phases,\nand leave their signatures on some thermodynamic quantities. We also analyze\nthe possibility of Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)-like nonuniform\nsuperfluid phases with finite center-of-mass momentum and obtain an even richer\nphase diagram.",
        "positive": "Distortion of Interference Fringes and the Resulting Vortex Production\n  of Merging Bose-Einstein Condensates: We investigate the effects of interatomic interactions and expansion on the\ndistortion of interference fringes of a pair of initially well-separated, but\ncoherent, condensate clouds trapped in a harmonic trap. The distortion of\ninterference fringes, which can lead to the spontaneous formation of vortices\nin the atom clouds, depends crucially on two relevant parameters: the\ncenter-of-mass velocity and peak density of the initial state. We identify\nthree qualitatively distinct regimes for the interfering condensates:\ncollision, expansion, and merging, by the spatial and temporal features of the\nfringe spacings. Using a comprehensive set of numerical simulations based on\nthe Gross-Pitaevskii equation, we specify the cross-overs between these regimes\nand propose the optimal the system parameters required for dynamical\ninstabilities and vortex creation."
    },
    {
        "anchor": "An $\u03b7$-condensate of fermionic atom pairs via adiabatic state\n  preparation: We discuss how an $\\eta$-condensate, corresponding to an exact excited\neigenstate of the Fermi-Hubbard model, can be produced with cold atoms in an\noptical lattice. Using time-dependent density matrix renormalisation group\nmethods, we analyse a state preparation scheme beginning from a band insulator\nstate in an optical superlattice. This state can act as an important test case,\nboth for adiabatic preparation methods and the implementation of the many-body\nHamiltonian, and measurements on the final state can be used to help detect\nassociated errors.",
        "positive": "Dipolar Fermi gases in anisotropic traps: The quest for quantum degenerate Fermi gases interacting through the\nanisotropic and long-range dipole-dipole interaction is an exciting and fast\ndeveloping branch within the cold-atoms research program. Recent experimental\nprogress in trapping, cooling, and controlling polar molecules with large\nelectric dipole moments has, therefore, motivated much theoretical effort. In a\nrecent letter, we have briefly discussed the application of a variational\ntime-dependent Hartree-Fock approach to study theoretically both the static and\nthe dynamic properties of such a system in a cylinder-symmetric harmonic trap.\nWe focused on the hydrodynamic regime, where collisions assure the equilibrium\nlocally. Here, we present a detailed theory, extended to encompass the general\ncase of a harmonic trap geometry without any symmetry. After deriving the\nequations of motion for the gas, we explore their static solutions to\ninvestigate key properties like the aspect ratios in both real and momentum\nspace as well as the stability diagram. We find that, despite the lack of\nsymmetry of the trap, the momentum distribution remains cylinder symmetric. The\nequations of motion are then used to study the low-lying hydrodynamic\nexcitations, where, apart from the quadrupole and monopole modes, also the\nradial quadrupole mode is investigated. Furthermore, we study the\ntime-of-flight dynamics as it represents an important diagnostic tool for\nquantum gases. We find that the real-space aspect ratios are inverted during\nthe expansion, while the one in momentum space becomes asymptotically unity. In\naddition, anisotropic features of the dipole-dipole interaction are discussed\nin detail. These results could be particularly useful for future investigations\nof strongly dipolar heteronuclear polar molecules deep in the quantum\ndegenerate regime."
    },
    {
        "anchor": "Stationary States of Trapped Spin-Orbit-Coupled Bose-Einstein\n  Condensates: We numerically investigate low-energy stationary states of pseudospin-1\nBose-Einstein condensates in the presence of Rashba-Dresselhaus-type spin-orbit\ncoupling. We show that for experimentally feasible parameters and strong\nspin-orbit coupling, the ground state is a square vortex lattice irrespective\nof the nature of the spin-dependent interactions. For weak spin-orbit coupling,\nthe lowest-energy state may host a single vortex. Furthermore, we analytically\nderive constraints that explain why certain stationary states do not emerge as\nground states. Importantly, we show that the distinct stationary states can be\nobserved experimentally by standard time-of-flight spinindependent absorption\nimaging.",
        "positive": "String-Theory-Based Predictions for Nonhydrodynamic Collective Modes in\n  Strongly Interacting Fermi Gases: Very different strongly interacting quantum systems such as Fermi gases,\nquark-gluon plasmas formed in high energy ion collisions and black holes\nstudied theoretically in string theory are known to exhibit quantitatively\nsimilar damping of hydrodynamic modes. It is not known if such similarities\nextend beyond the hydrodynamic limit. Do non-hydrodynamic collective modes in\nFermi gases with strong interactions also match those from string theory\ncalculations? In order to answer this question, we use calculations based on\nstring theory to make predictions for novel types of modes outside the\nhydrodynamic regime in trapped Fermi gases. These predictions are amenable to\ndirect testing with current state-of-the-art cold atom experiments."
    },
    {
        "anchor": "Bogoliubov theory for atom scattering into separate regions: We review the Bogoliubov theory in the context of recent experiments, where\natoms are scattered from a Bose-Einstein Condensate into two well-separated\nregions. We find the full dynamics of the pair-production process, calculate\nthe first and second order correlation functions and show that the system is\nideally number-squeezed. We calculate the Fisher information to show how the\nentanglement between the atoms from the two regions changes in time. We also\nprovide a simple expression for the lower bound of the useful entanglement in\nthe system in terms of the average number of scattered atoms and the number of\nmodes they occupy. We then apply our theory to a recent \"twin-beam\" experiment\n[R. B\\\"ucker {\\it et al.}, Nat. Phys. {\\bf 7}, 608 (2011)]. The only numerical\nstep of our semi-analytical description can be easily solved and does not\nrequire implementation of any stochastic methods.",
        "positive": "Inelastic scattering of atoms in a double well: We study a mixture of two light spin-1/2 fermionic atoms and two heavy atoms\n%in a Mott state in a double well potential. Inelastic scattering processes\nbetween both atomic species excite the heavy atoms and renormalize the\ntunneling rate and the interaction of the light atoms (polaron effect). The\neffective interaction of the light atoms changes its sign and becomes\nattractive for strong inelastic scattering. This is accompanied by a crossing\nof the energy levels from singly occupied sites at weak inelastic scattering to\na doubly occupied and an empty site for stronger inelastic scattering. We are\nable to identify the polaron effect and the level crossing in the quantum\ndynamics."
    },
    {
        "anchor": "Universal impurity-induced bound state in topological superfluids: We predict a universal mid-gap bound state in topological superfluids,\ninduced by either non-magnetic or magnetic impurities in the strong scattering\nlimit. This universal state is similar to the lowest-energy Caroli-de\nGennes-Martricon bound state in a vortex core, but is bound to localized\nimpurities. We argue that the observation of such a universal bound state can\nbe a clear signature for identifying topological superfluids. We theoretically\nexamine our argument for a spin-orbit coupled ultracold atomic Fermi gas\ntrapped in a two-dimensional harmonic potential, by performing extensive\nself-consistent calculations within the mean-field Bogoliubov-de Gennes theory.\nA realistic scenario for observing universal bound state in ultracold $^{40}$K\natoms is proposed.",
        "positive": "A slow gravity compensated Atom Laser: We report on a slow guided atom laser beam outcoupled from a Bose-Einstein\ncondensate of 87Rb atoms in a hybrid trap. The acceleration of the atom laser\nbeam can be controlled by compensating the gravitational acceleration and we\nreach residual accelerations as low as 0.0027 g. The outcoupling mechanism\nallows for the production of a constant flux of 4.5x10^6 atoms per second and\ndue to transverse guiding we obtain an upper limit for the mean beam width of\n4.6 \\mu\\m. The transverse velocity spread is only 0.2 mm/s and thus an upper\nlimit for the beam quality parameter is M^2=2.5. We demonstrate the potential\nof the long interrogation times available with this atom laser beam by\nmeasuring the trap frequency in a single measurement. The small beam width\ntogether with the long evolution and interrogation time makes this atom laser\nbeam a promising tool for continuous interferometric measurements."
    },
    {
        "anchor": "Honeycomb optical lattices with harmonic confinement: We consider the fate of the Dirac points in the spectrum of a honeycomb\noptical lattice in the presence of a harmonic confining potential. By\nnumerically solving the tight binding model we calculate the density of states,\nand find that the energy dependence can be understood from analytical\narguments. In addition, we show that the density of states of the harmonically\ntrapped lattice system can be understood by application of a local density\napproximation based on the density of states of the homogeneous lattice. The\nDirac points are found to survive locally in the trap as evidenced by the local\ndensity of states. They furthermore give rise to a distinct spatial profile of\na noninteracting Fermi gas.",
        "positive": "Magnetic resonance spectroscopy and characterization of magnetic phases\n  for spinor Bose-Einstein condensates: The response of spinor Bose-Einstein condensates to dynamical modulation of\nmagnetic fields is discussed with linear response theory. As an experimentally\nmeasurable quantity, the energy absorption rate (EAR) is considered, and the\nresponse function is found to access quadratic spin correlations which come\nfrom the perturbation of the quadratic Zeeman term. By applying our formalism\nto spin-1 condensates, we demonstrate that the EAR spectrum as a function of\nthe modulation frequency is able to characterize the different magnetically\nordered phases."
    },
    {
        "anchor": "Detecting Topological phase transitions in a double kicked quantum rotor: We present a concrete theoretical proposal for detecting topological phase\ntransitions in double kicked atom-optics kicked rotors with internal spin-1/2\ndegree of freedom. The implementation utilizes a kicked Bose-Einstein\ncondensate evolving in one-dimensional momentum space. To reduce influence of\natom loss and phase decoherence we aim to keep experimental durations short\nwhile maintaining a resonant experimental protocol. Experimental limitations\ninduced by phase noise, quasimomentum distributions, symmetries, and the\nAC-Stark shift are considered. Our results thus suggest a feasible and\noptimized procedure for observing topological phase transitions in quantum\nkicked rotors.",
        "positive": "FFLO order in ultra-cold atoms in three-dimensional optical lattices: We investigate different ground-state phases of attractive spin-imbalanced\npopulations of fermions in 3-dimensional optical lattices. Detailed numerical\ncalculations are performed using Hartree-Fock-Bogoliubov theory to determine\nthe ground-state properties systematically for different values of density,\nspin polarization and interaction strength. We first consider the high density\nand low polarization regime, in which the effect of the optical lattice is most\nevident. We then proceed to the low density and high polarization regime where\nthe effects of the underlying lattice are less significant and the system\nbegins to resemble a continuum Fermi gas. We explore the effects of density,\npolarization and interaction on the character of the phases in each regime and\nhighlight the qualitative differences between the two regimes. In the\nhigh-density regime, the order is found to be of Larkin-Ovchinnikov type,\nlinearly oriented with one characteristic wave vector but varying in its\ndirection with the parameters. At lower densities the order parameter develops\nmore structures involving multiple wave vectors."
    },
    {
        "anchor": "Production of a rubidium Bose-Einstein condensate in a hybrid trap with\n  light induced atom desorption: We report on the production of a rubidium Bose-Einstein condensate in a\nsimplified vacuum apparatus. Magneto-optical traps with large numbers and\nultra-high vacuum for moderately long conservative trap lifetimes of 16 seconds\nare sequentially obtained with light induced rapid atomic vapor pressure\nmodulation. Subsequent evaporative cooling is carried out in two stages in a\nhybrid magnetic quadrupole plus optical dipole trap. High evaporation\nefficiencies are observed in both stages and $^{87}$Rb BECs with more than\n10$^5$ atoms can be reliably produced with total evaporation time of only 9.5\nseconds.",
        "positive": "Quantum properties of a binary bosonic mixture in a double well: This work contains a detailed analysis of the properties of the ground state\nof a two-component two-sites Bose-Hubbard model, which captures the physics of\na binary mixture of Bose-Einstein condensates trapped in a double-well\npotential. The atom-atom interactions within each species and among the two\nspecies are taken as variable parameters while the hopping terms are kept\nfixed. To characterize the ground state we use observables such as the\nimbalance of population and its quantum uncertainty. The quantum many-body\ncorrelations present in the system are further quantified by studying the\ndegree of condensation of each species, the entanglement between the two sites\nand the entanglement between the two species. The latter is measured by means\nof the Schmidt gap, the von Neumann entropy or the purity obtained after\ntracing out a part of the system. A number of relevant states are identified,\ne.g. Schr\\\"odinger catlike many-body states, in which the outcome of the\npopulation imbalance of both components is completely correlated, and other\nstates with even larger von Neumann entropy which have a large spread in Fock\nspace."
    },
    {
        "anchor": "Turbulence in rotating Bose-Einstein condensates: Since the idea of quantum turbulence was first proposed by Feynman, and later\nrealized in experiments of superfluid helium and Bose-Einstein condensates,\nmuch emphasis has been put in finding signatures that distinguish quantum\nturbulence from its classical counterpart. Here we show that quantum turbulence\nin rotating condensates is fundamentally different from the classical case.\nWhile rotating quantum turbulence develops a negative temperature state with\nself-organization of the kinetic energy in quantized vortices, it also displays\nan anisotropic dissipation mechanism and a different, non-Kolmogorovian,\nscaling of the energy at small scales. This scaling is compatible with Vinen\nturbulence and is also found in recent simulations of condensates with\nmulticharged vortices. An elementary explanation for the scaling is presented\nin terms of disorder in the vortices positions.",
        "positive": "A two-leg Su-Schrieffer-Heeger chain with glide reflection symmetry: The Su-Schrieffer-Heeger (SSH) model lays the foundation of many important\nconcepts in quantum topological matters. Since it tells one that topological\nstates may be distinguished by abelian geometric phases, a question naturally\narises as to what happens if one assembles two topologically distinct states.\nHere, we show that a spin-dependent double-well optical lattice allows one to\ncouple two topologically distinct SSH chains in the bulk and realise a\nglided-two-leg SSH model that respects the glide reflection symmetry. Such\nmodel gives rise to intriguing quantum phenomena beyond the paradigm of a\ntraditional SSH model. It is characterised by Wilson line that requires\nnon-abelian Berry connections, and the interplay between the glide symmetry and\ninteraction automatically leads to charge fractionalisation without jointing\ntwo lattice potentials at an interface. Our work demonstrates the power of\nultracold atoms to create new theoretical models for studying topological\nmatters."
    },
    {
        "anchor": "Phase structure of mass- and spin-imbalanced unitary Fermi gases: We study the phase diagram of mass- and spin-imbalanced unitary Fermi gases,\nin search for the emergence of spatially inhomogeneous phases. To account for\nfluctuation effects beyond the mean-field approximation, we employ\nrenormalization group techniques. We thus obtain estimates for critical values\nof the temperature, mass and spin imbalance, above which the system is in the\nnormal phase. In the unpolarized, equal-mass limit, our result for the critical\ntemperature is in accordance with state-of-the-art Monte Carlo calculations. In\naddition, we estimate the location of regions in the phase diagram where\ninhomogeneous phases are likely to exist. We show that an intriguing relation\nexists between the general structure of the many-body phase diagram and the\nbinding energies of the underlying two-body bound-state problem, which further\nsupports our findings. Our results suggest that inhomogeneous condensates form\nfor mass ratios of the spin-down and spin-up fermions greater than three. The\nextent of the inhomogeneous phase in parameter space increases with increasing\nmass imbalance.",
        "positive": "Superglass formation in an atomic BEC with competing long-range\n  interactions: The complex dynamical phases of quantum systems are dictated by atomic\ninteractions that usually evoke an emergent periodic order. Here, we study a\nquantum many-body system with two competing and substantially different\nlong-range interaction potentials where the dynamical instability towards\ndensity order can give way to a superglass phase, i. e., a superfluid\ndisordered amorphous solid, which exhibits local density modulations but no\nlong-range periodic order. We consider a two-dimensional BEC in the\nRydberg-dressing regime coupled to an optical standing wave resonator. The\ndynamic pattern formation in this system is governed by the competition between\nthe two involved interaction potentials: repulsive soft-core interactions\narising due to Rydberg dressing and infinite-range sign changing interactions\ninduced by the cavity photons. The superglass phase is found when the two\ninteraction potentials introduce incommensurate length scales. The dynamic\nformation of this peculiar phase without any externally added disorder is\ndriven by quantum fluctuations and can be attributed to frustration induced by\nthe two competing interaction energies and length scales."
    },
    {
        "anchor": "Self-trapping of a binary Bose-Einstein condensate induced by\n  interspecies interaction: The problem of self-trapping of a Bose-Einstein condensate (BEC) and a binary\nBEC in an optical lattice (OL) and double well (DW) is studied using the\nmean-field Gross-Pitaevskii equation. For both DW and OL, permanent\nself-trapping occurs in a window of the repulsive nonlinearity $g$ of the GP\nequation: $g_{c1}<g<g_{c2}$. In case of OL, the critical nonlinearities\n$g_{c1}$ and $g_{c2}$ correspond to a window of chemical potentials\n$\\mu_{c1}<\\mu<\\mu_{c2}$ defining the band gap(s) of the periodic OL. The\npermanent self-trapped BEC in an OL usually represents a breathing oscillation\nof a stable stationary gap soliton. The permanent self-trapped BEC in a DW, on\nthe other hand, is a dynamically stabilized state without any stationary\ncounterpart. For a binary BEC with intraspecies nonlinearities outside this\nwindow of nonlinearity, a permanent self trapping can be induced by tuning the\ninterspecies interaction such that the effective nonlinearities of the\ncomponents fall in the above window.",
        "positive": "Dynamics of Onsager vortex clustering in decaying turbulent polariton\n  quantum fluids: We investigate the turbulent properties of a confined driven-dissipative\npolariton quantum fluid after a pulsed excitation. Using numerical simulations,\nwe provide insight into the vortex clustering processes that emerge during the\nrelaxation dynamics of the initially injected vortex cloud. A confrontation\nbetween conservative and non-conservative dynamics reveals that the onset of\nclusterization strongly depends on the interplay between the different\ncharacteristic system lengths and time scales at stake, with an additional time\nscale due to dissipation in the non-conservative case. Quantification of the\nclustering observables allows us to numerically characterize the optimal\nconditions for observing Onsager condensation in decaying polariton systems,\ndemonstrating its experimental reachability under pulse excitation. These\nfindings hold significance for exploring the onset of turbulent dynamics in\nopen systems, spanning both classical and quantum domains."
    },
    {
        "anchor": "Thermodynamics of noninteracting bosonic gases in cubic optical lattices\n  versus ideal homogeneous Bose gases: We have studied thermodynamic properties of noninteracting gases in periodic\nlattice potential at arbitrary integer fillings and compared them with that of\nideal homogeneous gases. Deriving explicit expressions for thermodynamic\nquantities and performing exact numerical calculations we have found that the\ndependence of e.g. entropy and energy on the temperature in the normal phase is\nrather weak. In the Bose condensed phase their power dependence on the reduced\ntemperature is nearly linear, which is in contrast to that of ideal homogeneous\ngases. We evaluated the discontinuity in the slope of the specific heat which\nturned out to be approximately the same as that of the ideal homogeneous Bose\ngas for filling factor $\\nu=1$. With increasing $\\nu$ it decreases as the\ninverse of $\\nu$. These results may serve as a checkpoint for various\nexperiments on optical lattices as well as theoretical studies of weakly\ninteracting Bose systems in periodic potentials being a starting point for\nperturbative calculations.",
        "positive": "Harmonically trapped dipolar fermions in a two-dimensional square\n  lattice: We consider dipolar fermions in a two-dimensional square lattice and a\nharmonic trapping potential. The anisotropy of the dipolar interaction combined\nwith the lattice leads to transitions between phases with density order of\ndifferent symmetries. We show that the attractive part of the dipolar\ninteraction results in a superfluid phase which is suppressed by density order.\nThe trapping potential is demonstrated to make the different phases co-exist,\nforming ring and island structures. The phases with density and superfluid\norder can overlap forming regions with supersolid order."
    },
    {
        "anchor": "Time-Dependent Density Functional Theory and the Real-Time Dynamics of\n  Fermi Superfluids: I describe the Time-Dependent Superfluid Local Density Approximation, which\nis an adiabatic extension of the Density Functional Theory to superfluid Fermi\nsystems and their real-time dynamics. This new theoretical framework has been\napplied to describe a number of phenomena in cold atomic gases and nuclear\ncollective motion: excitation of the Higgs modes in strongly interacting Fermi\nsuperfluids, generation of quantized vortices, crossing and reconnection of\nvortices, excitation of the superflow at velocities above the critical\nvelocity, excitation of quantum shock waves and domain walls in the collisions\nof superfluid atomic clouds, excitation of collective states in nuclei.",
        "positive": "Microscopic characteristics and tomography scheme of the local Chern\n  marker: The concept of the local Chern marker has gained a lot of attention\nespecially in the field of ultracold quantum gases in optical lattices and\nartificial gauge fields. We investigate in further detail the microscopic\nreal-space characteristics of the local Chern marker for the two-band Harper-\nHofstadter-Hatsugai model and propose a tomographic scheme for the experimental\ndetection of an approximate local Chern marker neglecting higher orders."
    },
    {
        "anchor": "Evolution of condensate fraction during rapid lattice ramps: Combining experiments and numerical simulations, we investigate the\nredistribution of quasi-momentum in a gas of atoms trapped in an optical\nlattice when the lattice depth is rapidly reduced. We find that interactions\nlead to significant momentum redistribution on millisecond timescales, thereby\ninvalidating previous assumptions regarding adiabaticity. We show that this\nphenomenon is driven by the presence of low-momentum particle-hole excitations\nin an interacting system. Our results invalidate bandmapping as an equilibrium\nprobe in interacting gases.",
        "positive": "Evolution of an isolated monopole in a spin-1 Bose-Einstein condensate: We simulate the decay dynamics of an isolated monopole defect in the nematic\nvector of a spin-1 Bose-Einstein condensate during the polar-to-ferromagnetic\nphase transition of the system. Importantly, the decay of the monopole occurs\nin the absence of external magnetic fields and is driven principally by the\ndynamical instability due to the ferromagnetic spin-exchange interactions. An\ninitial isolated monopole is observed to relax into a polar-core spin vortex,\nthus demonstrating the spontaneous transformation of a point defect of the\npolar order parameter manifold to a line defect of the ferromagnetic manifold.\nWe also investigate the dynamics of an isolated monopole pierced by a quantum\nvortex line with winding number k. It is shown to decay into a coreless\nAnderson-Toulouse vortex if k = 1 and into a singular vortex with an empty core\nif k = 2. In both cases, the resulting vortex is also encircled by a polar-core\nvortex ring."
    },
    {
        "anchor": "An eternal discrete time crystal beating the Heisenberg limit: A discrete time crystal (DTC) repeats itself with a rigid rhythm, mimicking a\nticking clock set by the interplay between its internal structures and an\nexternal force. DTCs promise profound applications in precision time-keeping\nand other quantum techniques. However, it has been facing a grand challenge of\nthermalization. The periodic driving supplying the power may ultimately bring\nDTCs to thermal equilibrium and destroy their coherence. Here, we show that an\nall-to-all interaction delivers a DTC that evades thermalization and maintains\nquantum coherence and quantum synchronization regardless of spatial\ninhomogeneities in the driving field and the environment. Moreover, the\nsensitivity of this DTC scales with the total particle number to the power of\nthree over two, realizing a quantum device of measuring the driving frequency\nor the interaction strength beyond the Heisenberg limit. Our work paves the way\nfor designing novel non-equilibrium phases with long coherence time to advance\nquantum metrology.",
        "positive": "Energy-Resolved Information Scrambling in Energy-Space Lattices: Weakly interacting Fermi gases simulate spin-lattices in energy-space,\noffering a rich platform for investigating information spreading and spin\ncoherence in a large many-body quantum system. We show that the collective spin\nvector can be determined as a function of energy from the measured spin\ndensity, enabling general energy-space resolved protocols. We measure an\nout-of-time-order correlation function in this system and observe the energy\ndependence of the many-body coherence."
    },
    {
        "anchor": "Observation of universal dynamics in an isolated one-dimensional Bose\n  gas far from equilibrium: We provide experimental evidence of universal dynamics far from equilibrium\nduring the relaxation of an isolated one-dimensional Bose gas. Following a\nrapid cooling quench, the system exhibits universal scaling in time and space,\nassociated with the approach of a non-thermal fixed point. The time evolution\nwithin the scaling period is described by a single universal function and\nscaling exponent, independent of the specifics of the initial state. Our\nresults provide a quantum simulation in a regime, where to date no theoretical\npredictions are available. This constitutes a crucial step in the verification\nof universality far from equilibrium. If successful, this may lead to a\ncomprehensive classification of systems based on their universal properties far\nfrom equilibrium, relevant for a large variety of systems at different scales.",
        "positive": "Striped states in a many-body system of tilted dipoles: We study theoretically and experimentally the behaviour of a strongly\nconfined dipolar Bose-Einstein condensate, in the regime of quantum-mechanical\nstabilization by beyond-mean-field effects. Theoretically, we demonstrate that\nself-organized striped ground states are predicted in the framework of the\nextended Gross-Pitaevskii theory. Experimentally, by tilting the magnetic\ndipoles we show that self-organized striped states can be generated, likely in\ntheir metastable state. Matter-wave interference experiments with multiple\nstripes show that there is no long-range off-diagonal order (global phase\ncoherence). We outline a parameter range where global phase coherence could be\nestablished, thus paving the way towards the observation of supersolid states\nin this system."
    },
    {
        "anchor": "Fibonacci optical lattices for tunable quantum quasicrystals: We describe a quasiperiodic optical lattice, created by a physical\nrealization of the abstract cut-and-project construction underlying all\nquasicrystals. The resulting potential is a generalization of the Fibonacci\ntiling. Calculation of the energies and wavefunctions of ultracold atoms loaded\ninto such a lattice demonstrate a multifractal energy spectrum, a singular\ncontinuous momentum-space structure, and the existence of controllable edge\nstates. These results open the door to cold atom quantum simulation experiments\nin tunable or dynamic quasicrystalline potentials, including topological\npumping of edge states and phasonic spectroscopy.",
        "positive": "Generation of dark-bright soliton trains in superfluid-superfluid\n  counterflow: The dynamics of two penetrating superfluids exhibit an intriguing variety of\nnonlinear effects. Using two distinguishable components of a Bose-Einstein\ncondensate, we investigate the counterflow of two superfluids in a narrow\nchannel. We present the first experimental observation of trains of dark-bright\nsolitons generated by the counterflow. Our observations are theoretically\ninterpreted by three-dimensional numerical simulations for the coupled\nGross-Pitaevskii (GP) equations and the analysis of a jump in the two\nrelatively flowing components' densities. Counterflow induced modulational\ninstability for this miscible system is identified as the central process in\nthe dynamics."
    },
    {
        "anchor": "Probing two Higgs oscillations in a one-dimensional Fermi superfluid\n  with Raman-type spin-orbit coupling: We theoretically investigate the Higgs oscillation in a one-dimensional\nRaman-type spin-orbit-coupled Fermi superfluid with the time-dependent\nBogoliubov-de Gennes equations. By linearly ramping or abruptly changing the\neffective Zeeman field in both the Bardeen-Cooper-Schrieffer state and the\ntopological superfluid state, we find the amplitude of the order parameter\nexhibits an oscillating behaviour over time with two different frequencies\n(i.e., two Higgs oscillations) in contrast to the single one in a conventional\nFermi superfluid. The observed period of oscillations has a great agreement\nwith the one calculated using the previous prediction [Volkov and Kogan, J.\nExp. Theor. Phys. 38, 1018 (1974)], where the oscillating periods are now\ndetermined by the minimums of two quasi-particle spectrum in this system. We\nfurther verify the existence of two Higgs oscillations using a periodic ramp\nstrategy with theoretically calculated driving frequency. Our predictions would\nbe useful for further theoretical and experimental studies of these Higgs\noscillations in spin-orbit-coupled systems.",
        "positive": "Protocol for autonomous rearrangement of cold atoms into low-entropy\n  configurations: The preparation of low-entropy starting conditions is a key requirement for\nmany experiments involving neutral atoms. Here, we propose a method to\nautonomously assemble arbitrary spatial configurations of atoms within arrays\nof optical tweezers or lattice sites, enabled by a combination of tunneling and\nground-state laser cooling. In contrast to previous methods, our protocol does\nnot rely on either imaging or evaporative cooling. This circumvents limitations\nassociated with imaging fidelity and loss, especially in systems with small\nspatial scales, while providing a substantial improvement in speed relative to\nevaporative approaches. These features may make it well-suited for preparing\narbitrary initial conditions for Bose-Hubbard or Rydberg interacting systems."
    },
    {
        "anchor": "Bose polaron as an instance of quantum Brownian motion: We study the dynamics of a quantum impurity immersed in a Bose-Einstein\ncondensate as an open quantum system in the framework of the quantum Brownian\nmotion model. We derive a generalized Langevin equation for the position of the\nimpurity. The Langevin equation is an integrodifferential equation that\ncontains a memory kernel and is driven by a colored noise. These result from\nconsidering the environment as given by the degrees of freedom of the quantum\ngas, and thus depend on its parameters, e.g. interaction strength between the\nbosons, temperature, etc. We study the role of the memory on the dynamics of\nthe impurity. When the impurity is untrapped, we find that it exhibits a\nsuper-diffusive behavior at long times. We find that back-flow in energy\nbetween the environment and the impurity occurs during evolution. When the\nparticle is trapped, we calculate the variance of the position and momentum to\ndetermine how they compare with the Heisenberg limit. One important result of\nthis paper is that we find position squeezing for the trapped impurity at long\ntimes. We determine the regime of validity of our model and the parameters in\nwhich these effects can be observed in realistic experiments.",
        "positive": "Measurement Protocol for the Entanglement Spectrum of Cold Atoms: Entanglement, and, in particular the entanglement spectrum, plays a major\nrole in characterizing many-body quantum systems. While there has been a surge\nof theoretical works on the subject, no experimental measurement has been\nperformed to date because of the lack of an implementable measurement scheme.\nHere, we propose a measurement protocol to access the entanglement spectrum of\nmany-body states in experiments with cold atoms in optical lattices. Our scheme\neffectively performs a Ramsey spectroscopy of the entanglement Hamiltonian and\nis based on the ability to produce several copies of the state under\ninvestigation together with the possibility to perform a global swap gate\nbetween two copies conditioned on the state of an auxiliary qubit. We show how\nthe required conditional swap gate can be implemented with cold atoms, either\nby using Rydberg interactions or coupling the atoms to a cavity mode. We\nillustrate these ideas on a simple (extended) Bose-Hubbard model where such a\nmeasurement protocol reveals topological features of the Haldane phase."
    },
    {
        "anchor": "Quantum interference-induced stability of repulsively bound pairs of\n  excitations: We study the dynamics of two types of pairs of excitations which are bound\ndespite their strong repulsive interaction. One corresponds to doubly occupied\nsites in one-dimensional Bose-Hubbard systems, the so-called doublons. The\nother is pairs of neighboring excited spins in anisotropic Heisenberg spin-1/2\nchains. We investigate the possibility of decay of the bound pairs due to\nresonant scattering by a defect or due to collisions of the pairs. We find that\nthe amplitudes of the corresponding transitions are very small. This is a\nresult of destructive quantum interference and explains the stability of the\nbound pairs.",
        "positive": "Critical points of the three-dimensional Bose-Hubbard model from on-site\n  atom number fluctuations: We discuss how positions of critical points of the three-dimensional\nBose-Hubbard model can be accurately obtained from variance of the on-site atom\nnumber operator, which can be experimentally measured. The idea that we explore\nis that the derivative of the variance, with respect to the parameter driving\nthe transition, has a pronounced maximum close to critical points. We show that\nQuantum Monte Carlo studies of this maximum lead to precise determination of\ncritical points for the superfluid-Mott insulator transition in systems with\nmean number of atoms per lattice site equal to one, two, and three. We also\nextract from such data the correlation-length critical exponent through the\nfinite-size scaling analysis and discuss how the derivative of the variance can\nbe reliably computed from numerical data for the variance. The same conclusions\napply to the derivative of the nearest-neighbor correlation function, which can\nbe obtained from routinely measured time-of-flight images."
    },
    {
        "anchor": "Collective electronic excitation in a trapped ensemble of photogenerated\n  dipolar excitons and free holes revealed by inelastic light scattering: Photogenerated excitonic ensembles confined in coupled GaAs quantum wells are\nprobed by a complementary approach of emission spectroscopy and resonant\ninelastic light scattering. Lateral electrostatic trap geometries are used to\ncreate dense systems of spatially indirect excitons and excess holes with\nsimilar densities in the order of 10$^{11}$ cm$^{-2}$. Inelastic light\nscattering spectra reveal a very sharp low-lying collective mode that is\nidentified at an energy of 0.44 meV and a FWHM of only ~50 $\\mu$eV. This mode\nis interpreted as a plasmon excitation of the excess hole system coupled to the\nphotogenerated indirect excitons. The emission energy of the indirect excitons\nshifts under the application of a perpendicular applied electric field with the\nquantum-confined Stark effect unperturbed from the presence of free charge\ncarriers. Our results illustrate the potential of studying low-lying collective\nexcitations in photogenerated exciton systems to explore the many-body phase\ndiagram, related phase transitions, and interaction physics.",
        "positive": "Formation of paired phases of bosons and their excitations in a square\n  lattice: We investigate the formation of paired states of bosons in an optical\nlattice, namely, pair superfluid (PSF) and pair supersolid (PSS) in the\npresence of pair hopping as well as the next nearest neighbor (NNN) interaction\nmimicking long-range forces. Both the zero and finite temperature phase\ndiagrams are obtained using the cluster mean field theory, which includes the\neffect of correlations systematically. We also compute the low-energy\nexcitations which capture the characteristic features of such paired states and\ntheir transitions. Apart from the gapless sound mode due to the PSF order, a\ngapped mode also appears in the PSF phase, similar to the Higgs mode of the\nusual atomic superfluid (ASF). The PSF to ASF transition exhibits an intriguing\nbehavior due to the existence of a `tri-critical' point, where the nature of\ntransition changes. As a consequence of the continuous PSF-ASF transition, the\ngapped mode of both the phases becomes gapless at the critical point. For\nsufficiently strong NNN interaction strength, a PSS phase appears with\ncoexisting pair superfluidity and stripe density order. The softening of the\nroton mode as a precursor of density ordering and the appearance of a\nlow-energy gapped mode serve as robust features related to the formation of the\nPSS phase. We also investigate the melting of PSF and PSS phases to normal\nfluid at finite temperatures, particularly the melting pathway of PSS which\noccurs in atleast two steps due to the coexisting orders. Finally, we discuss\nthe possibility of emulating such exotic phases in the ongoing cold atom\nexperiments."
    },
    {
        "anchor": "Impurity in a bosonic Josephson junction: swallowtail loops, chaos,\n  self-trapping and the poor man's Dicke model: We study a model describing $N$ identical bosonic atoms trapped in a\ndouble-well potential together with a single impurity atom, comparing and\ncontrasting it throughout with the Dicke model. As the boson-impurity coupling\nstrength is varied, there is a symmetry-breaking pitchfork bifurcation which is\nanalogous to the quantum phase transition occurring in the Dicke model. Through\nstability analysis around the bifurcation point, we show that the critical\nvalue of the coupling strength has the same dependence on the parameters as the\ncritical coupling value in the Dicke model. We also show that, like the Dicke\nmodel, the mean-field dynamics go from being regular to chaotic above the\nbifurcation and macroscopic excitations of the bosons are observed. Overall,\nthe boson-impurity system behaves like a poor man's version of the Dicke model.",
        "positive": "Emergence of Metallic Quantum Solid Phase in a Rydberg-Dressed Fermi\n  Gases: We examine possible low-temperature phases of a repulsively Rydberg-dressed\nFermi gas in a three-dimensional free space. It is shown that the collective\ndensity excitations develop a roton minimum, which is softened at a wavevector\nsmaller than the Fermi wavevector when the particle density is above a critical\nvalue. The mean field calculation shows that unlike the insulating charge\ndensity waves states often observed in conventional condensed matters, a\nself-assembled metallic density wave state emerges at low temperatures. In\nparticular, the density wave state supports a Fermi surface and a\nbody-center-cubic crystal order at the same time with the estimated critical\ntemperature being about one-tenth of the non-interacting Fermi energy. Our\nresults suggest the emergency of a fermionic quantum solid that should be\nobservable in current experimental setup."
    },
    {
        "anchor": "Resonant enhancement of the FFLO-state in 3D by a one-dimensional\n  optical potential: We describe an imbalanced superfluid Fermi gas in three dimensions within the\npath-integral framework. To allow for the formation of the\nFulde-Ferell-Larkin-Ovchinnikov-state (FFLO-state), a suitable form of the\nsaddle-point is chosen, in which the pairs have a finite centre-of-mass\nmomentum. To test the correctness of this path-integral description, the\nzero-temperature phase diagram for an imbalanced Fermi gas in three dimensions\nis calculated, and compared to recent theoretical results. Subsequently, we\ninvestigate two models that describe the effect of imposing a one-dimensional\noptical potential on the 3D imbalanced Fermi gas. We show that this 1D optical\npotential can greatly enlarge the stability region of the FFLO-state, relative\nto the case of the 3D Fermi gas without 1D periodic modulation. Furthermore it\nis show that there exists a direct connection between the centre-of-mass\nmomentum of the FFLO-pairs and the wavevector of the optical potential. We\npropose that this concept can be used experimentally to resonantly enhance the\nstability region of the FFLO-state.",
        "positive": "Disorder effects on the quantum coherence of a many-boson system: The effects of disorders on the quantum coherence for many-bosons are studied\nin a double well model. For the ground state, the disorder enhances the quantum\ncoherence. In the deep Mott regime, dynamical evolution reveals periodical\ncollapses and revivals of the quantum coherence which is robust against the\ndisorder. The average over variations in both the on-site energy and the\ninteraction reveals a beat phenomenon of the coherence-decoherence oscillation\nin the temporal evolution."
    },
    {
        "anchor": "Saturation properties of helium drops from a Leading Order description: Saturation properties are directly linked to the short-range scale of the\ntwo-body interaction of the particles. The case of helium is particular, from\none hand the two-body potential has a strong repulsion at short distances. On\nthe other hand, the extremely weak binding of the helium dimer locates this\nsystem very close to the unitary limit allowing for a description based on an\neffective theory. At leading order of this theory a two- and a three-body term\nappear, each one characterized by a low energy constant. In a potential model\nthis description corresponds to a soft potential model with a two-body term\npurely attractive plus a three-body term purely repulsive constructed to\ndescribe the dimer and trimer binding energies. Here we analyse the capability\nof this model to describe the saturation properties making a direct link\nbetween the low energy scale and the short-range correlations. We will show\nthat the energy per particle, $E_N/N$, can be obtained with reasonable accuracy\nat leading order extending the validity of this approximation, characterizing\nuniversal behavior in few-boson systems close to the unitary limit, to the\nmany-body system.",
        "positive": "Non-equilibrium strong-coupling theory for a driven-dissipative\n  ultracold Fermi gas in the BCS-BEC crossover region: We theoretically investigate strong-coupling properties of an ultracold Fermi\ngas in the BCS-BEC crossover regime in the non-equilibrium steady state, being\ncoupled with two fermion baths. By developing a non-equilibrium strong-coupling\ntheory based on the combined $T$-matrix approximation with the Keldysh Green's\nfunction technique, we show that the chemical potential bias applied by the two\nbaths gives rise to the anomalous enhancement of\nFulde-Ferrell-Larkin-Ovchinnikov (FFLO) type pairing fluctuations (although the\nsystem has no spin imbalance), resulting in the re-entrant behavior of the\nnon-equilibrium superfluid phase transition in the BCS-unitary regime. These\npairing fluctuations are also found to anomalously enhance the pseudogap\nphenomenon. Since various non-equilibrium phenomena have recently been measured\nin ultracold Fermi gases, our non-equilibrium strong-coupling theory would be\nuseful to catch up this experimental development in this research field."
    },
    {
        "anchor": "Nature of polaron-molecule transition in Fermi polarons: In this work, we explore the polaron and molecule physics by utilizing a\nunified variational ansatz with up to two particle-hole(p-h)\nexcitations(V-2ph). We confirm the existence of a first-order transition in 3D\nand 2D Fermi polarons, and show that the nature of such transition lies in an\nenergy competition between systems with different momenta ${\\mathbf Q}=0$ and\n$|{\\mathbf Q}|=k_F$, here ${\\mathbf Q}$ is defined as the momentum of Fermi\npolaron system with respect to the Fermi sea of majority fermions (with Fermi\nmomentum $k_F$). The literally proposed molecule ansatz is identified as an\nasymptotic limit of $|{\\mathbf Q}|=k_F$ state in strong coupling regime, which\nimplies a huge $SO(3)$(for 3D) or $SO(2)$ (for 2D) ground state degeneracy in\nthis regime. The recognization of such degeneracy is crucially important for\nevaluating the molecule occupation in realistic systems with finite impurity\ndensity and at finite temperature. To compare with recent experiment of 3D\nFermi polarons, we have calculated various physical quantities under the V-2ph\nframework and obtained results that are in good agreements with experimental\ndata in the weak coupling and near resonance regime. Further, to check the\nvalidity of our conclusion in 2D, we have adopted a different variational\nmethod based on the Gaussian sample of high-order p-h excitations(V-Gph), and\nfound the same conclusion on the nature of polaron-molecule transition therein.\nFor 1D system, the V-2ph method predicts no sharp transition and the ground\nstate is always at ${\\mathbf Q}=0$ sector, consistent with exact Bethe ansatz\nsolution. The presence/absence of polaron-molecule transition is analyzed to be\nclosely related to the interplay effect of Pauli-blocking and p-h excitations\nin different dimensions.",
        "positive": "Periodic dynamics of fermionic superfluids in the BCS regime: We study the zero temperature non-equilibrium dynamics of a fermionic\nsuperfluid in the BCS limit and in the presence of a drive leading to a time\ndependent chemical potential $\\mu(t)$. We choose a periodic driving protocol\ncharacterized by a frequency $\\omega$ and compute the fermion density, the\nwavefunction overlap, and the residual energy of the system at the end of $N$\nperiods of the drive. We demonstrate that the BCS self-consistency condition is\ncrucial in shaping the long-time behaviour of the fermions subjected to the\ndrive and provide an analytical understanding of the behaviour of the fermion\ndensity $n_{{\\mathbf k}_F}$ (where ${\\mathbf k}_F$ is the Fermi momentum\nvector) after a drive period and for large $\\omega$. We also show that the\nmomentum distribution of the excitations generated due to such a drive bears\nthe signature of the pairing symmetry and can be used, for example, to\ndistinguish between s- and d-wave superfluids. We propose experiments to test\nour theory."
    },
    {
        "anchor": "Thermodynamic geometry of ideal quantum gases: a general framework and a\n  geometric picture of BEC-enhanced heat engines: Thermodynamic geometry provides a physically transparent framework to\ndescribe thermodynamic processes in meso- and micro-scale systems that are\ndriven by slow variations of external control parameters. Focusing on periodic\ndriving for thermal machines, we extend this framework to ideal quantum gases.\nTo this end, we show that the standard approach of equilibrium physics, where a\ngrand-canonical ensemble is used to model a canonical one by fixing the mean\nparticle number through the chemical potential, can be extended to the slow\ndriving regime in a thermodynamically consistent way. As a key application of\nour theory, we use a Lindblad-type quantum master equation to work out a\ndynamical model of a quantum many-body engine using a harmonically trapped Bose\ngas. Our results provide a geometric picture of the BEC-induced power\nenhancement that was previously predicted for this type of engine on the basis\nof an endoreversible model [New J. Phys. 24, 025001 (2022)]. Using an earlier\nderived universal trade-off relation between power and efficiency as a\nbenchmark, we further show that the Bose-gas engine can deliver significantly\nmore power at given efficiency than an equally large collection of single-body\nengines. Our work paves the way for a more general thermodynamic framework that\nmakes it possible to systematically assess the impact of quantum many-body\neffects on the performance of thermal machines.",
        "positive": "The universality of the Efimov three-body parameter: In this paper we discuss the recent discovery of the universality of the\nthree-body parameter (3BP) from Efimov physics. This new result was identified\nby recent experimental observations in ultracold quantum gases where the value\nof the s-wave scattering length, $a=a_-$, at which the first Efimov resonance\nis created was found to be nearly the same for a range of atomic species --- if\nscaled as $a_-/r_{\\rm vdW}$, where $r_{\\rm vdW}$ is the van der Waals length.\nHere, we discuss some of the physical principles related to these observations\nthat emerge from solving the three-body problem with van der Waals interactions\nin the hyperspherical formalism. We also demonstrate the strong three-body\nmultichannel nature of the problem and the importance of properly accounting\nfor nonadiabatic effects."
    },
    {
        "anchor": "Periodically-driven Kondo impurity in nonequilibrium steady states: We study the nonequilibrium dynamics of a periodically-driven anisotropic\nKondo impurity model. The periodic time dependence is introduced for a local\nmagnetic field which couples to the impurity spin and also for an in-plane\nexchange interaction. We obtain the exact results on the time evolution for\narbitrary periodic time dependence at the special point in the parameter space\nknown as the Toulouse limit. We first consider a specific case where the local\nmagnetic field is periodically switched on and off. When the driving period is\nmuch shorter than the inverse of the Kondo temperature, an intriguing\noscillating behavior (resonance phenomenon) emerges in the time average of the\nimpurity spin polarization with increasing the local magnetic field intensity.\nBy taking the high frequency limit of the external driving, we elucidate that\nthe system recovers the translational invariance in time and can be described\nby a mixture of the zero-temperature and infinite-temperature properties. In\ncertain cases, the system is governed by either the zero-temperature or\ninfinite-temperature properties, and therefore can be properly described by the\ncorresponding equilibrium state.",
        "positive": "An unsupervised deep learning algorithm for single-site reconstruction\n  in quantum gas microscopes: In quantum gas microscopy experiments, reconstructing the site-resolved\nlattice occupation with high fidelity is essential for the accurate extraction\nof physical observables. For short interatomic separations and limited\nsignal-to-noise ratio, this task becomes increasingly challenging. Common\nmethods rapidly decline in performance as the lattice spacing is decreased\nbelow half the imaging resolution. Here, we present a novel algorithm based on\ndeep convolutional neural networks to reconstruct the site-resolved lattice\noccupation with high fidelity. The algorithm can be directly trained in an\nunsupervised fashion with experimental fluorescence images and allows for a\nfast reconstruction of large images containing several thousand lattice sites.\nWe benchmark its performance using a quantum gas microscope with cesium atoms\nthat utilizes short-spaced optical lattices with lattice constant $383.5\\,$nm\nand a typical Rayleigh resolution of $850\\,$nm. We obtain promising\nreconstruction fidelities~$\\gtrsim 96\\%$ across all fillings based on a\nstatistical analysis. We anticipate this algorithm to enable novel experiments\nwith shorter lattice spacing, boost the readout fidelity and speed of\nlower-resolution imaging systems, and furthermore find application in related\nexperiments such as trapped ions."
    },
    {
        "anchor": "Matter wave Fourier optics with a strongly interacting two-dimensional\n  Fermi gas: We demonstrate and characterize an experimental technique to directly image\nthe momentum distribution of a strongly interacting two-dimensional quantum gas\nwith high momentum resolution. We apply the principles of Fourier optics to\ninvestigate three main operations on the expanding gas: focusing, collimation\nand magnification. We focus the gas in the radial plane using a harmonic\nconfining potential and thus gain access to the momentum distribution. We pulse\na different harmonic potential to stop the rapid axial expansion which allows\nus to image the momentum distribution with high resolution. Additionally, we\npropose a method to magnify the mapped momentum distribution to access\ninteresting momentum scales. All these techniques can be applied to a wide\nrange of experiments and in particular to study many-body phases of quantum\ngases.",
        "positive": "Unconventional superfluidity of fermions in Bose-Fermi mixtures: We examine two dimensional mixture of single-component fermions and dipolar\nbosons. We calculate the self-enregies of the fermions in the normal state and\nthe Cooper pair channel by including first order vertex correction to derive a\nmodified Eliashberg equation. We predict appearance of superfluids with various\nnon-standard pairing symmetries at experimentally feasible transition\ntemperatures within the strong-coupling limit of the Eliashberg equation.\nExcitations in these superfluids are anyonic and follow non-Abelian statistics."
    },
    {
        "anchor": "Ground states and dynamics of population-imbalanced Fermi condensates in\n  one dimension: By using the numerically exact density-matrix renormalization group (DMRG)\napproach, we investigate the ground states of harmonically trapped\none-dimensional (1D) fermions with population imbalance and find that the\nLarkin-Ovchinnikov (LO) state, which is a condensed state of fermion pairs with\nnonzero center-of-mass momentum, is realized for a wide range of parameters.\nThe phase diagram comprising the two phases of i) an LO state at the trap\ncenter and a balanced condensate at the periphery and ii) an LO state at the\ntrap center and a pure majority component at the periphery, is obtained. The\nreduced two-body density matrix indicates that most of the minority atoms\ncontribute to the LO-type quasi-condensate. With the time-dependent DMRG, we\nalso investigate the real-time dynamics of a system of 1D fermions in response\nto a spin-flip excitation.",
        "positive": "Light scattering in inhomogeneous Tomonaga-Luttinger liquids: We derive the dynamical structure factor for an inhomogeneous\nTomonaga-Luttinger liquid as can be formed in a confined strongly interacting\none-dimensional gas. In view of current experimental progress in the field, we\nprovide a simple analytic expression for the light-scattering cross section,\nrequiring only the knowledge of the density dependence of the ground-state\nenergy, as they can be extracted e.g. from exact or Quantum Monte Carlo\ntechniques, and a Thomas-Fermi description. We apply the result to the case of\none-dimensional quantum bosonic gases with dipolar interaction in a harmonic\ntrap, using an energy functional deduced from Quantum Monte Carlo computations.\nWe find an universal scaling behavior peculiar of the Tomonaga-Luttinger\nliquid, a signature that can be eventually probed by Bragg spectroscopy in\nexperimental realizations of such systems."
    },
    {
        "anchor": "Multigrid Algorithms for Tensor Network States: The widely used density matrix renormalization group (DRMG) method often\nfails to converge in systems with multiple length scales, such as lattice\ndiscretizations of continuum models and dilute or weakly doped lattice models.\nThe local optimization employed by DMRG to optimize the wave function is\nineffective in updating large-scale features. Here we present a multigrid\nalgorithm that solves these convergence problems by optimizing the wave\nfunction at different spatial resolutions. We demonstrate its effectiveness by\nsimulating bosons in continuous space, and study non-adiabaticity when ramping\nup the amplitude of an optical lattice. The algorithm can be generalized to\ntensor network methods, and be combined with the contractor renormalization\ngroup (CORE) method to study dilute and weakly doped lattice models.",
        "positive": "Interaction-enhanced flow of a polariton persistent current in a ring: We study the quantum hydrodynamical features of exciton-polaritons flowing\ncircularly in a ring-shaped geometry. We consider a resonant-excitation scheme\nin which the spinor polariton fluid is set into motion in both components by\nspin-to-orbital angular momentum conversion. We show that this scheme allows to\ncontrol the winding number of the fluid, and to create two circulating states\ndiffering by two units of the angular momentum. We then consider the effect of\na disorder potential, which is always present in realistic nanostructures. We\nshow that a smooth disorder is efficiently screened by the polariton-polariton\ninteractions, yielding a signature of polariton superfluidity. This effect is\nreminiscent of supercurrent in a superconducting loop."
    },
    {
        "anchor": "Density Waves in Layered Systems with Fermionic Polar Molecules: A layered system of two-dimensional planes containing fermionic polar\nmolecules can potentially realize a number of exotic quantum many-body states.\nAmong the predictions, are density-wave instabilities driven by the anisotropic\npart of the dipole-dipole interaction in a single layer. However, in typical\nmultilayer setups it is reasonable to expect that the onset and properties of a\ndensity-wave are modified by adjacent layers. Here we show that this is indeed\nthe case. For multiple layers the critical strength for the density-wave\ninstability decreases with the number of layers. The effect depends on density\nand is more pronounced in the low density regime. The lowest solution of the\ninstability corresponds to the density waves in the different layers being\nin-phase, whereas higher solutions have one or several adjancet layers that are\nout of phase. The parameter regime needed to explore this instability is within\nreach of current experiments.",
        "positive": "One- and two-dimensional solitons in spin-orbit-coupled Bose-Einstein\n  condensates with fractional kinetic energy: We address effects of spin-orbit coupling (SOC), phenomenologically added to\na two-component Bose-Einstein condensate composed of particles moving by Levy\nflights, in one- and two-dimensional (1D and 2D) settings. The corresponding\nsystem of coupled Gross-Pitaevskii equations includes fractional kinetic-energy\noperators, characterized by the Levy index, \\alpha < 2 (the normal kinetic\nenergy corresponds to \\alpha = 2). The SOC terms, with strength \\lambda,\nproduce strong effects in the 2D case: they create families of stable solitons\nof the semi-vortex (SV) and mixed-mode (MM) types in the interval of 1 < \\alpha\n< 2, where the supercritical collapse does not admit the existence of stable\nsolitons in the absence of the SOC. At \\lambda --> 0, amplitudes of these\nsolitons vanish as (\\lambda)^{1/(\\alpha - 1)}."
    },
    {
        "anchor": "Stabilization of a nonlinear bullet coexisting with a Bose-Einstein\n  condensate in a rapidly cooled magnonic system driven by a spin-orbit torque: We have recently shown that injection of magnons into a magnetic dielectric\nvia the spin-orbit torque (SOT) effect in the adjacent layer of a heavy metal\nsubjected to the action of short (0.1 $\\mu$s) current pulses allows for control\nof a magnon Bose-Einstein Condensate (BEC). Here, the BEC was formed in the\nprocess of rapid cooling (RC), when the electric current heating the sample is\nabruptly terminated. In the present study, we show that the application of a\nlonger (1.0 $\\mu$s) electric current pulse triggers the formation of a\nnonlinear localized magnonic bullet below the linear magnon spectrum. After\npulse termination, the magnon BEC, as before, is formed at the bottom of the\nlinear spectrum, but the nonlinear bullet continues to exist, stabilized for\nadditional 30 ns by the same process of RC-induced magnon condensation. Our\nresults suggest that a stimulated condensation of excess magnons to all highly\npopulated magnonic states occurs.",
        "positive": "Homogeneous and inhomogeneous magnetic phases of constrained dipolar\n  bosons: We study the emergence of several magnetic phases in dipolar bosonic gases\nsubject to three-body loss mechanism employing numerical simulations based on\nthe density matrix renormalization group(DMRG) algorithm. After mapping the\noriginal Hamiltonian in spin language, we find a strong parallelism between the\nbosonic theory and the spin-1 Heisenberg model with single ion anisotropy and\nlong-range interactions. A rich phase diagram, including ferromagnetic,\nantiferromagnetic and non-local ordered phases, emerges in the half-filled\none-dimensional case, and is preserved even in presence of a trapping\npotential."
    },
    {
        "anchor": "Turbulence in a Bose-Einstein Condensate of Dipolar Excitons in Coupled\n  Quantum Wells: The nonlinear dynamics of a Bose-Einstein condensate (BEC) of dipolar\nexcitons trapped in an external confining potential in coupled quantum wells is\nanalysed. It is demonstrated that under typical experimental conditions the\ndipolar excitons BEC can be described by a generalized Gross-Pitaevskii\nequation with the local interaction between the excitons, which depends on the\nexciton distribution function. It is shown that, if the system is pumped at\nsufficiently high frequencies, a steady turbulent state can be formed.",
        "positive": "Non-equilibrium Functional Renormalization for Driven-Dissipative\n  Bose-Einstein Condensation: We present a comprehensive analysis of critical behavior in the\ndriven-dissipative Bose condensation transition in three spatial dimensions.\nStarting point is a microscopic description of the system in terms of a\nmany-body quantum master equation, where coherent and driven-dissipative\ndynamics occur on an equal footing. An equivalent Keldysh real time functional\nintegral reformulation opens up the problem to a practical evaluation using the\ntools of quantum field theory. In particular, we develop a functional\nrenormalization group approach to quantitatively explore the universality class\nof this stationary non-equilibrium system. Key results comprise the emergence\nof an asymptotic thermalization of the distribution function, while manifest\nnon-equilibrium properties are witnessed in the response properties in terms of\na new, independent critical exponent. Thus the driven-dissipative microscopic\nnature is seen to bear observable consequences on the largest length scales.\nThe absence of two symmetries present in closed equilibrium systems -\nunderlying particle number conservation and detailed balance, respectively - is\nidentified as the root of this new non-equilibrium critical behavior. Our\nresults are relevant for broad ranges of open quantum systems on the interface\nof quantum optics and many-body physics, from exciton-polariton condensates to\ncold atomic gases."
    },
    {
        "anchor": "Orbital Feshbach Resonance: A \"Wide\" Narrow Resonance for Higher\n  Transition Temperature Fermi Superfluid: In this letter we show that the recently theoretically predicted and\nexperimentally observed \"orbital Feshbach resonance\" in alkali-earth-like\nYb-173 atom is a narrow resonance in energy, while it is hundreds Gauss wide in\nterm of magnetic field strength, taking the advantage that the magnetic moment\ndifference between the open and closed channels is quite small. Therefore this\nis an ideal platform for the experimental realization of a strongly interacting\nFermi superfluid with narrow resonance. We show that the transition temperature\nfor the Fermi superfluid in this system, especially at the BCS side of the\nresonance, is even higher than that in a wide resonance, which is also due to\nthe narrow character of this resonance. Our results will encourage experimental\nefforts to realize Fermi superfluid in the alkali-earth-like Yb-173 system, the\nproperties of which will be complementary to extensively studied Fermi\nsuperfluids nearby a wide resonance in alkali K-40 and Li-6 systems.",
        "positive": "Coherent phase slips in coupled matter-wave circuits: Quantum Phase slips are dual process of particle tunneling in coherent\nnetworks. Besides to be of central interest for condensed matter physics,\nquantum phase slips are resources that are sought to be manipulated in quantum\ncircuits. Here, we devise a specific matter-wave circuit enlightening quantum\nphase slips. Specifically, we investigate the quantum many body dynamics of two\nside-by-side ring-shaped neutral bosonic systems coupled through a weak link.\nBy imparting a suitable magnetic flux, persistent currents flow in each ring\nwith given winding numbers. We demonstrate that coherent phase slips occur as\nwinding number transfer among the two rings, with the populations in each ring\nremaining nearly constant. Such a phenomenon occurs as a result of a specific\nentanglement of circulating states, that, as such cannot be captured by a mean\nfield treatment of the system. Our work can be relevant for the observation of\nquantum phase slips in cold atoms experiments and their manipulation in\nmatter-wave circuits. To make contact with the field, we show that the\nphenomenon has clear signatures in the momentum distribution of the system\nproviding the time of flight image of the condensate."
    },
    {
        "anchor": "Coqblin-Schrieffer Model for an Ultra-cold Gas of Ytterbium atoms with\n  Metastable States: Motivated by the impressive recent advance in manipulating cold ytterbium\natoms we explore and substantiate the feasibility of realizing the\nCoqblin-Schrieffer model in a gas of cold fermionic $^{173}$Yb atoms. Making\nuse of different AC polarizabillity of the electronic ground state (electronic\nconfiguration $^1S_0$) and the long lived metastable state (electronic\nconfiguration $^3P_0$), it is substantiated that the latter can be localized\nand serve as a magnetic impurity while the former remains itinerant. The\nexchange mechanism between the itinerant $^1S_0$ and the localized $^3P_0$\natoms is analyzed and shown to be antiferromagnetic. The ensuing SU(6)\nsymmetric Coqblin-Schrieffer Hamiltonian is constructed, and, using the\ncalculated exchange constant $J$, perturbative RG analysis yield the Kondo\ntemperature $T_K$ that is experimentally accessible. A number of thermodynamic\nmeasurable observables are calculated in the weak coupling regime $T>T_K$\n(using perturbative RG analysis) and in the strong coupling regime $T<T_K$\n(employing known Bethe ansatz techniques).",
        "positive": "Is there a Mott-glass phase in a one-dimensional disordered quantum\n  fluid with linearly confining interactions?: We study a one-dimensional disordered quantum fluid with linearly confining\ninteractions (disordered Schwinger model) using bosonization and the\nnonperturbative functional renormalization group. We find that the long-range\ninteractions make the Anderson insulator (or, for bosons, the Bose-glass) fixed\npoint (corresponding to a compressible state with a gapless optical\nconductivity) unstable, even if the latter may control the flow at intermediate\nenergy scales. The stable fixed point describes an incompressible ground state\nwith a gapped optical conductivity similar to a Mott insulator. These results\ndisagree with the Gaussian variational method that predicts a Mott glass,\nnamely a state with vanishing compressibility but a gapless optical\nconductivity."
    },
    {
        "anchor": "Phase diagram of soft-core bosons in two dimensions: The low temperature phase diagram of Bose soft disks in two dimensions is\nstudied by numerical simulations. It is shown that a supersolid cluster phase\nexists, within a range of the model parameters, analogous to that recently\nobserved for a system of aligned dipoles interacting via a softened potential\nat short distance. These findings indicate that a long-range tail of the\ninteraction is unneeded to obtain such a phase, and that the soft-core\nrepulsive interaction is the minimal model for supersolidity.",
        "positive": "Polylogs, thermodynamics and scaling functions of one-dimensional\n  quantum many-body systems: We demonstrate that the thermodynamics of one-dimensional Lieb-Liniger bosons\ncan be accurately calculated in analytic fashion using the polylog function in\nthe framework of the thermodynamic Bethe ansatz. The approach does away with\nthe need to numerically solve the thermodynamic Bethe ansatz (Yang-Yang)\nequation. The expression for the equation of state allows the exploration of\nTomonaga-Luttinger liquid physics and quantum criticality in an archetypical\nquantum system. In particular, the low-temperature phase diagram is obtained,\nalong with the scaling functions for the density and compressibility. It has\nbeen shown recently by Guan and Ho (arXiv:1010.1301) that such scaling can be\nused to map out the criticality of ultracold fermionic atoms in experiments. We\nshow here how to map out quantum criticality for Lieb-Liniger bosons. More\ngenerally the polylog function formalism can be applied to a wide range of\nBethe ansatz integrable quantum many-body systems which are currently of\ntheoretical and experimental interest, such as strongly interacting\nmulti-component fermions, spinor bosons and mixtures of bosons and fermions."
    },
    {
        "anchor": "Non-thermal equilibration of a one-dimensional Fermi gas: Equilibration of an isolated Fermi gas in one spatial dimension after an\ninteraction quench is studied. Evaluating Kadanoff-Beym dynamic equations for\ncorrelation functions obtained from the two-particle-irreducible effective\naction in nonperturbative approximation, the gas is seen to evolve to states\ncharacterized by thermal as well as nonthermal momentum distributions,\ndepending on the assumed initial conditions. For total energies near the Fermi\ntemperature, stationary power laws emerge for the high-momentum tails while at\nlower momenta the distributions are of Fermi-Dirac type. The relation found\nbetween fluctuations and dissipation exhibits nonthermal final states.",
        "positive": "Local Photoemission Spectra and Effects of Spatial Inhomogeneity in the\n  BCS-BEC Crossover Regime of a Trapped Ultracold Fermi Gas: We theoretically investigate single particle excitations in the BCS\n(Bardeen-Cooper-Schrieffer)-BEC (Bose-Einstein-Condensation) crossover regime\nof an ultracold Fermi gas. Including strong pairing fluctuations within a\n$T$-matrix approximation, as well as effects of a harmonic trap potential in\nthe local density approximation, we calculate the local photoemission spectrum\nin the normal state. Recently, JILA group has measured this quantity in a\n$^{40}$K Fermi gas, in order to examine homogeneous single-particle properties\nof this system. Comparing our results with this experiment, we show that, this\nattempt indeed succeeds under the JILA's experimental condition. However, we\nalso find that the current local photoemission spectroscopy still has room for\nimprovement, in order to examine the pseudogap phenomenon predicted in the\nBCS-BEC crossover region. Since ultracold Fermi gases are always in a trap, our\nresults would be useful in applying this system to various homogeneous Fermi\nsystems, as a quantum simulator."
    },
    {
        "anchor": "Fluctuation Theory of Rashba Fermi Gases: Fermi gases with generalized Rashba spin orbit coupling inducedby a synthetic\ngauge field have the potential of realizing many interesting states such as\nrashbon condensates and topological phases. Here we develop a fluctuation\ntheory of such systems and demonstrate that beyond-Gaussian effects are\nessential to capture the physics of such systems. We obtain their phase diagram\nby constructing an approximate non-Gaussian theory. We conclusively establish\nthat spin-orbit coupling can enhance the exponentially small transition\ntemperature ($T_c$) of a weakly attracting superfluid to the order of Fermi\ntemperature, paving a pathway towards high $T_c$ superfluids.",
        "positive": "Relation connecting thermodynamics and transport of atomic unitary Fermi\n  superfluids: The shear viscosity has been shown to be equal to the product of pressure and\nrelaxation time in normal scale-invariant fluids, but the presence of\nsuperfluidity at low temperatures can alter the relation. By using the\nmean-field BCS-Leggett theory with a gauge-invariant linear response theory for\nunitary Fermi superfluids, we present an explicit relation between\nthermodynamic quantities, including the pressure and chemical potential, and\ntransport coefficients, including the shear viscosity, superfluid density, and\nanomalous shear viscosity from momentum transfer via Cooper pairs. The relation\nis modified when pairing fluctuations associated with noncondensed Cooper pairs\nare considered. Within a pairing fluctuation theory consistent with the\nBCS-Leggett ground state, we found an approximate relation for unitary Fermi\nsuperfluids. The exact mean-field relation and the approximate one with pairing\nflucutaions advance our understanding of relations between equilibrium and\ntransport quantities in superfluids, and they help determine or constrain\nquantities which can be otherwise difficult to measure."
    },
    {
        "anchor": "Quantum properties of light scattered from structured many-body phases\n  of ultracold atoms in quantum optical lattices: Quantum trapping potentials for ultracold gases change the landscape of\nclassical properties of scattered light and matter. The atoms in a quantum\nmany-body correlated phase of matter change the properties of light and vice\nversa. The properties of both light and matter can be tuned by design and\ndepend on the interplay between long-range (nonlocal) interactions mediated by\nan optical cavity and short-range processes of the atoms. Moreover, the quantum\nproperties of light get significantly altered by this interplay, leading the\nlight to have nonclassical features. Further, these nonclassical features can\nbe designed and optimised.",
        "positive": "One dimensional gas of bosons with integrable resonant interactions: We develop an exact solution to the problem of one dimensional chiral bosons\ninteracting via an s-wave Feshbach resonance. This problem is integrable, being\nthe quantum analog of a classical two-wave model solved by the inverse\nscattering method thirty years ago. Its solution describes one or two branches\nof dressed chiral right moving molecules depending on the chemical potential\n(particle density). We also briefly discuss the possibility of experimental\nrealization of such a system."
    },
    {
        "anchor": "Two-channel Bose-Hubbard model of atoms at a Feshbach resonance: Based on the analytic model of Feshbach resonances in harmonic traps\ndescribed in Phys. Rev. A 83, 030701 (2011) a Bose-Hubbard model is introduced\nthat provides an accurate description of two atoms in an optical lattice at a\nFeshbach resonance with only a small number of Bloch bands. The approach\ncircumvents the problem that the eigenenergies in the presence of a delta-like\ncoupling do not converge to the correct energies, if an uncorrelated basis is\nused. The predictions of the Bose-Hubbard model are compared to\nnon-perturbative calculations for both the stationary states and the\ntime-dependent wavefunction during an acceleration of the lattice potential.\nFor this purpose, a square-well interaction potential is introduced, which\nallows for a realistic description of Feshbach resonances within\nnon-perturbative single-channel calculations.",
        "positive": "Three-body bound states of two bosons and one impurity in one dimension: We investigate one-dimensional three-body systems composed of two identical\nbosons and one imbalanced atom (impurity) with two-body and three-body\nzero-range interactions. For the case in the absence of three-body interaction,\nwe give a complete phase diagram of the number of three-body bound states in\nthe whole region of mass ratio via the direct calculation of the\nSkornyakov-Ter-Martirosyan equations. We demonstrate that other low-lying\nthree-body bound states emerge when the mass of the impurity particle is not\nequal to another two identical particles. We can obtain not only the binding\nenergies but also the corresponding wave functions. When the mass of impurity\natom is vary large, there are at most three three-body bound states. We then\nstudy the effect of three-body zero-range interaction and unveil that it can\ninduces one more three-body bound state at a certain region of coupling\nstrength ratio under a fixed mass ratio."
    },
    {
        "anchor": "Quantum oscillations in ultracold Fermi gases : realizations with\n  rotating gases or artificial gauge fields: We consider the angular momentum of a harmonically trapped, noninteracting\nFermi gas subject to either rotation or to an artificial gauge field. The\nangular momentum of the gas is shown to display oscillations as a function of\nthe particle number or chemical potential. This phenomenon is analogous to the\nde Haas - van Alphen oscillations of the magnetization in the solid-state\ncontext. However, key differences exist between the solid-state and ultracold\natomic gases that we point out and analyze. We explore the dependence of the\nvisibility of these oscillations on the physical parameters and propose two\nexperimental protocols for their observation. Due to the very strong dependence\nof the amplitude of the oscillations on temperature, we propose their use as a\nsensitive thermometer for Fermi gases in the low temperature regime.",
        "positive": "Dominant fifth-order correlations in doped quantum anti-ferromagnets: Traditionally one and two-point correlation functions are used to\ncharacterize many-body systems. In strongly correlated quantum materials, such\nas the doped 2D Fermi-Hubbard system, these may no longer be sufficient because\nhigher-order correlations are crucial to understanding the character of the\nmany-body system and can be numerically dominant. Experimentally, such\nhigher-order correlations have recently become accessible in ultracold atom\nsystems. Here we reveal strong non-Gaussian correlations in doped quantum\nanti-ferromagnets and show that higher order correlations dominate over\nlower-order terms. We study a single mobile hole in the $t-J$ model using DMRG,\nand reveal genuine fifth-order correlations which are directly related to the\nmobility of the dopant. We contrast our results to predictions using models\nbased on doped quantum spin liquids which feature significantly reduced\nhigher-order correlations. Our predictions can be tested at the lowest\ncurrently accessible temperatures in quantum simulators of the 2D Fermi-Hubbard\nmodel. Finally, we propose to experimentally study the same fifth-order\nspin-charge correlations as a function of doping. This will help to reveal the\nmicroscopic nature of charge carriers in the most debated regime of the Hubbard\nmodel, relevant for understanding high-$T_c$ superconductivity."
    },
    {
        "anchor": "Pseudogap phenomenon in an ultracold Fermi gas with a p-wave pairing\n  interaction: We investigate single-particle properties of a one-component Fermi gas with a\ntunable p-wave interaction. Including pairing fluctuations associated with this\nanisotropic interaction within a $T$-matrix theory, we calculate the\nsingle-particle density of states, as well as the spectral weight, above the\nsuperfluid transition temperature $T_{\\rm c}$. Starting from the weak-coupling\nregime, we show that the so-called pseudogap first develops in these quantities\nwith increasing the interaction strength. However, when the interaction becomes\nstrong to some extent, the pseudogap becomes obscure to eventually disappear in\nthe strong-coupling regime. This non-monotonic interaction dependence is quite\ndifferent from the case of an s-wave interaction, where the pseudogap simply\ndevelops with increasing the interaction strength. The difference between the\ntwo cases is shown to originate from the momentum dependence of the p-wave\ninteraction, which vanishes in the low momentum limit. We also identify the\npseudogap regime in the phase diagram with respect to the temperature and the\np-wave interaction strength. Since the pseudogap is a precursor phenomenon of\nthe superfluid phase transition, our results would be useful for the research\ntoward the realization of p-wave superfluid Fermi gases.",
        "positive": "Scattering and absorption of ultracold atoms by nanotubes: We investigate theoretically how cold atoms, including Bose-Einstein\ncondensates, are scattered from, or absorbed by nanotubes with a view to\nanalysing recent experiments. In particular we consider the role of potential\nstrength, quantum reflection, atomic interactions and tube vibrations on atom\nloss rates. Lifshitz theory calculations deliver a significantly stronger\nscattering potential than that found in experiment and we discuss possible\nreasons for this. We find that the scattering potential for dielectric tubes\ncan be calculated to a good approximation using a modified pairwise summation\napproach, which is efficient and easily extendable to arbitrary geometries.\nQuantum reflection of atoms from a nanotube may become a significant factor at\nlow temperatures, especially for non-metallic tubes. Interatomic interactions\nare shown to increase the rate at which atoms are lost to the nanotube and lead\nto non-trivial dynamics. Thermal nanotube vibrations do not significantly\nincrease loss rates or reduce condensate fractions, but lower frequency\noscillations can dramatically heat the cloud."
    },
    {
        "anchor": "Exact equivalence between one-dimensional Bose gases interacting via\n  hard-sphere and zero-range potentials: We prove the equivalence between the hard-sphere Bose gas and a system with\nmomentum-dependent zero-range interactions in one spatial dimension, which we\ncall extended hard-sphere Bose gas. The two-body interaction in the latter\nmodel has the advantage of being a regular pseudopotential. The most immediate\nconsequence is the existence of its Fourier transform, permitting the\nformulation of the problem in momentum space, not possible with the original\nhard-core interaction. In addition, in the extended system, interactions are\ndefined in terms of the scattering length, positive or negative, identified\nwith the hard-sphere diameter only when it is positive. We are then able to\nobtain, directly in the thermodynamic limit, the ground state energy of the\nstrongly repulsive Lieb-Liniger gas and, more importantly, the energy of the\nlowest-lying super Tonks-Girardeau gas state with finite, strongly attractive\ninteractions, in perturbation theory from the novel extended hard-sphere Bose\ngas. Tan relations involving the large-momentum behavior of the Lieb-Liniger\ngas are also derived, and then applied to the super Tonks-Girardeau gas within\nour perturbative approach.",
        "positive": "Bosonic Fractional Quantum Hall States in Rotating Optical Lattices:\n  Projective Symmetry Group Analysis: We study incompressible ground states of bosons in a two-dimensional rotating\nsquare optical lattice. The system can be described by the Bose-Hubbard model\nin an effective uniform magnetic field present due to the lattice rotation. To\nstudy ground states of the system, we map it to a frustrated spin model,\nfollowed by Schwinger boson mean field theory and projective symmetry group\nanalysis. Using symmetry analysis we identify bosonic fractional quantum Hall\nstates, predicted for bosonic atoms in rotating optical lattices, with possible\nstable gapped spin liquid states within the Schwinger boson formalism. In\nparticular, we find that previously found fractional quantum Hall states\ninduced by the lattice potential, and with no counterpart in the continuum [G.\nM\\\"oller, and N. R. Cooper, Phys. Rev. Lett. \\textbf{103}, 105303 (2009)],\ncorrespond to \"$\\pi$ flux\" spin liquid states of the frustrated spin model."
    },
    {
        "anchor": "Condensation and quasicondensation in an elongated three-dimensional\n  Bose gas: We study the equilibrium correlations of a Bose gas in an elongated\nthree-dimensional harmonic trap using a grand-canonical classical-field method.\nWe focus in particular on the progressive transformation of the gas from the\nnormal phase, through a phase-fluctuating quasicondensate regime to the\nso-called true-condensate regime, with decreasing temperature. Choosing\nrealistic experimental parameters, we quantify the density fluctuations and\nphase coherence of the atomic field as functions of the system temperature. We\nidentify the onset of Bose condensation through analysis of both the\ngeneralized Binder cumulant appropriate to the inhomogeneous system, and the\nsuppression of the effective many-body T matrix that characterizes interactions\nbetween condensate atoms in the finite-temperature field. We find that the\nsystem undergoes a second-order transition to condensation near the critical\ntemperature for an ideal Bose gas in the strongly anisotropic three-dimensional\ngeometry, but remains in a strongly phase-fluctuating quasicondensate regime\nuntil significantly lower temperatures. We characterize the crossover from a\nquasicondensate to a true condensate by a qualitative change in the form of the\nnon-local first-order coherence function of the field, and compare our results\nto those of previous works employing a density-phase Bogoliubov-de Gennes\nanalysis.",
        "positive": "Conjectures about the ground-state energy of the Lieb-Liniger model at\n  weak repulsion: We develop an alternative description to solve the problem of the\nground-state energy of the Lieb-Liniger model that describes one-dimensional\nbosons with contact repulsion. For this integrable model we express the Lieb\nintegral equation in the representation of Chebyshev polynomials. The latter\nform is convenient to efficiently obtain very precise numerical results in the\nsingular limit of weak interaction. Such highly precise data enable us to use\nthe integer relation algorithm to discover the analytical form of the\ncoefficients in the expansion of the ground-state energy for small values of\nthe interaction parameter. We obtained the first nine terms of the expansion\nusing quite moderate numerical efforts. The detailed knowledge of behavior of\nthe ground-state energy on the interaction immediately leads to exact\nperturbative results for the excitation spectrum."
    },
    {
        "anchor": "Mesoscopic phases of dipolar ensembles with polar molecules and Rydberg\n  atoms: We discuss the realization of mesoscopic phases of dipolar gases relevant to\ncurrent experiments with cold polar molecules and Rydberg atoms confined to two\ndimensions. We predict the existence of superfluid clusters, mesoscopic\nsupersolids, and crystals for a small number of trapped particles, with no\ncounterpart in the homogeneous situation. For certain strengths of the\ndipole-dipole interactions, the stabilization of purely {\\it non-classical\ncrystals} by quantum fluctuations is possible. We propose a magnification\nscheme to detect the spatial structure of these crystalline phases.",
        "positive": "Compacton matter waves in binary Bose gases under strong nonlinear\n  management: The existence of compacton matter waves in binary mixtures of quasi\none-dimensional Bose-Einstein condensates in deep optical lattices and in the\npresence of nonlinearity management, is first demonstrated. For this, we derive\nan averaged vector discrete nonlinear Schr\\\"odinger equation (DNLSE) and show\nthat compacton solutions of different types can exist as stable excitations.\nStability properties are studied by linear analysis and by direct numerical\nintegrations of the DNLSE system and their dependence on the inter- and\nintra-species scattering lengths, investigated. We show that under proper\nmanagement conditions, compactons can be very robust excitations that can\nemerge spontaneously from generic initial conditions. A possible experimental\nsetting for compacton observation is also discussed."
    },
    {
        "anchor": "Visualizing spinon Fermi surfaces with time-dependent spectroscopy: Quantum simulation experiments have started to explore regimes that are not\naccessible with exact numerical methods. In order to probe these systems and\nenable new physical insights, the need for measurement protocols arises that\ncan bridge the gap to solid state experiments, and at the same time make\noptimal use of the capabilities of quantum simulation experiments. Here we\npropose applying time-dependent photo-emission spectroscopy, an established\ntool in solid state systems, in cold atom quantum simulators. Concretely, we\nsuggest combining the method with large magnetic field gradients, unattainable\nin experiments on real materials, to drive Bloch oscillations of spinons, the\nemergent quasiparticles of spin liquids. We show in exact diagonalization\nsimulations of the one-dimensional $t-J$ model that the spinons start to\npopulate previously unoccupied states in an effective band structure, thus\nallowing to visualize states invisible in the equilibrium spectrum. The\ndependence of the spectral function on the time after the pump pulse reveals\ncollective interactions among spinons. In numerical simulations of small\ntwo-dimensional systems, spectral weight appears at the ground state energy at\nmomentum $\\mathbf{q} = (\\pi,\\pi)$, where the equilibrium spectral response is\nstrongly suppressed up to higher energies, indicating a possible route towards\nsolving the mystery of the Fermi arcs in the cuprate materials.",
        "positive": "Momentum density and phase maps of a two-dimensional trapped\n  Bose-Einstein condensate excited by a red laser: We investigate numerically the momentum density and phase maps $-$in\ncoordinate and momentum space$-$ of a two dimensional Bose-Einstein condensate\n(BEC) excited by a moving red-detuned laser potential. The BEC is confined in a\nharmonic trap cutoff by hard walls. The system and excitation scheme are as in\nour previous work (Roger R. Sakhel {\\it et al.} to appear in J. Low Temp. Phys.\n(2013)); but with twice the number of particles and interaction strength. We\nsolve the time-dependent Gross-Pitaevskii equation numerically using the\nsplit-step Crank-Nicolson method in real time. It is demonstrated that the\nred-detuned laser has a phase-imprinting effect like a repulsive potential\nbarrier. Signatures of excitations are extracted from the dynamics of the\nmomentum densities and phase maps. Further, a new phase is defined in momentum\nspace, which is used to reveal excitations. Therefore, phase maps in coordinate\nspace and momentum space are compared for different BEC evolution times. We\nargue, that this momentum-space phase is especially important with regard to\nthe studies of BEC momentum distributions. In addition, this work presents a\nnew method of BEC interferometry and should contribute to the ongoing research\nin that field. One of our significant findings is the presence of substantial\ndifferences betwteen the momentum density obtained by a Fourier transform (FT)\nof the spatial density distribution and the one obtained from the modulus of\nthe wavefunction in momentum space; the latter is obtained by a FT of the\nspatial wavefunction."
    },
    {
        "anchor": "Ion-induced interactions in a Tomonaga-Luttinger liquid: We investigate the physics of a Tomonaga-Luttinger liquid of spin-polarized\nfermions superimposed on an ion chain. This compound system features\n(attractive) long-range interspecies interactions. By means of density matrix\nrenormalization group techniques we compute the Tomonaga-Luttinger-liquid\nparameter and speed of sound as a function of the relative atom/ion density and\nthe two quantum defect parameters, namely, the even and odd short-range phases\nwhich characterize the short-range part of the atom-ion polarization potential.\nThe presence of ions is found to allow critical tuning of the atom-atom\ninteraction, and the properties of the system are found to depend significantly\non the short-range phases due to the atom-ion interaction. These latter\ndependencies can be controlled, for instance, by manipulating the ions'\ninternal state. This allows modification of the static properties of the\nquantum liquid via external driving of the ionic impurities.",
        "positive": "Spin-driven spatial symmetry breaking of spinor condensates in a\n  double-well: The properties of an F=1 spinor Bose-Einstein condensate trapped in a\ndouble-well potential are discussed using both a mean-field two-mode approach\nand a simplified two-site Bose-Hubbard Hamiltonian. We focus in the region of\nphase space in which spin effects lead to a symmetry breaking of the system,\nfavoring the spatial localization of the condensate in one well. To model this\ntransition we derive, using perturbation theory, an effective Hamiltonian that\ndescribes N/2 spin singlets confined in a double-well potential."
    },
    {
        "anchor": "Spontanous spin squezing in a rubidium BEC: We describe an experiment where spin squeezing occurs spontaneously within a\nstandard Ramsey sequence driving a two-component Bose-Einstein condensate (BEC)\nof 87Rb atoms trapped in an elongated magnetic trap. Multiparticle entanglement\nis generated by state-dependent collisional interactions, despite the\nnear-identical scattering lengths of the spin states in 87Rb. In our\nproof-of-principle experiment, we observe a metrological spin squeezing that\nreaches 1.3+/-0.4dB for 5000 atoms, with a contrast of 90+/-1%. The method may\nbe applied to realize spin-squeezed BEC sources for atom interferometry without\nthe need for cavities, state-dependent potentials or Feshbach resonances.",
        "positive": "Spin-orbital-angular-momentum-coupled quantum gases: We briefly review the recent progress of theories and experiments on\nspin-orbital-angular-momentum (SOAM)-coupled quantum gases. The coupling\nbetween the intrinsic degree of freedom of particles and their external orbital\nmotions widely exists in universe, and leads to a broad variety of fundamental\nphenomena both in the classical physics and quantum mechanics. Recent\nrealization of synthetic SOAM coupling in cold atoms has attracted a great deal\nof attention, and stimulates a large amount of considerations on exotic quantum\nphases in both Bose and Fermi gases. In this review, we present a basic idea of\nengineering SOAM coupling in neutral atoms, starting from a semiclassical\ndescription of atom-light interaction. Unique features of the single-particle\nphysics in the presence of SOAM coupling are discussed. The intriguing\nground-state quantum phases of weakly interacting Bose gases are introduced,\nwith emphasis on a so-called angular stripe phase, which has yet been observed\nat present. It is demonstrated how to generate a stable giant vortex in a\nSOAM-coupled Fermi superfluid. We also discuss topological characters of a\nFermi superfluid in the presence of SOAM coupling. We then introduce the\nexperimental achievement of SOAM coupling in $^{87}$Rb Bose gases and its first\nobservation of phase transitions. The most recent development of SOAM-coupled\nBose gases in experiments is also summarized. Regarding the controllability of\nultracold quantum gases, it opens a new era, on the quantum simulation point of\nview, to study the fundamental physics resulted from SOAM coupling as well as\nnewly emergent quantum phases."
    },
    {
        "anchor": "Dynamical signatures of thermal spin-charge deconfinement in the doped\n  Ising model: The mechanism underlying charge transport in strongly correlated quantum\nsystems, such as doped antiferromagnetic Mott insulators, remains poorly\nunderstood. Here we study the expansion dynamics of an initially localized hole\ninside a two-dimensional (2D) Ising antiferromagnet at variable temperature.\nUsing a combination of classical Monte Carlo and a truncated basis method, we\nreveal two dynamically distinct regimes: A spin-charge confined region below a\ncritical temperature $T^*$, characterized by slow spreading, and a spin-charge\ndeconfined region above $T^*$, characterized by an unbounded diffusive\nexpansion. The deconfinement temperature $T^*\\approx 0.65 J_z$ we find is\naround the N\\'eel temperature $T_{\\rm N} = 0.567 J_z$ of the Ising background\nin 2D, but we expect $T^* < T_{\\rm N}$ in higher dimensions. In both regimes we\nfind that the mobile hole does not thermalize with the Ising spin background on\nthe considered time scales, indicating weak effective coupling of spin- and\ncharge degrees of freedom. Our results can be qualitatively understood by an\neffective parton model, and can be tested experimentally in state-of-the-art\nquantum gas microscopes.",
        "positive": "Time-dependent condensate fraction in an analytical model: We apply analytical solutions of a nonlinear boson diffusion equation (NBDE)\nthat include boundary conditions at the singularity to calculate the time\nevolution of the entropy during evaporative cooling of ultracold atoms, and the\ntime-dependent condensate fraction. For suitable initial conditions it is found\nto agree with available data on Na-23."
    },
    {
        "anchor": "Few-body physics with ultracold atomic and molecular systems in traps: Few-body physics has played a prominent role in atomic, molecular and nuclear\nphysics since the early days of quantum mechanics. It is now possible---thanks\nto tremendous progress in cooling, trapping, and manipulating ultracold\nsamples---to experimentally study few-body phenomena in trapped atomic and\nmolecular systems with unprecedented control. This review summarizes recent\nstudies of few-body phenomena in trapped atomic and molecular gases, with an\nemphasis on small trapped systems. We start by introducing the free-space\nscattering properties and then investigate what happens when two particles,\nbosons or fermions, are placed in an external confinement. Next, various\nthree-body systems are treated analytically in limiting cases. Our current\nunderstanding of larger two-component Fermi systems and Bose systems is\nreviewed, and connections with the corresponding bulk systems are established.\nLastly, future prospects and challenges are discussed. Throughout this review,\ncommonalities with other systems such as nuclei or quantum dots are\nhighlighted.",
        "positive": "Stable, mobile, dark-in-bright, dipolar Bose-Einstein condensate soliton: We demonstrate robust, stable, mobile, quasi-one-dimensional, dark-in-bright\ndipolar Bose-Einstein condensate (BEC) soliton with a notch in the central\nplane formed due to dipolar interaction for repulsive contact interaction. At\nmedium velocity the head on collision of two such solitons is found to be quasi\nelastic with practically no deformation. A proposal for creating dipolar\ndark-in-bright solitons in laboratories by phase imprinting is also discussed.\nA rich variety of such solitons can be formed in dipolar binary BEC, where one\ncan have a dark-in-bright soliton coupled to a bright soliton or two coupled\ndark-in-bright solitons. The findings are illustrated using numerical\nsimulation in three spatial dimensions employing realistic interaction\nparameters for a dipolar 164Dy BEC and a binary 164Dy-162Dy BEC."
    },
    {
        "anchor": "Emergent Weyl excitations in systems of polar particles: Weyl fermions are massless chiral particles first predicted in 1929 and once\nthought to describe neutrinos. Although never observed as elementary particles,\nquasiparticles with Weyl dispersion have recently been experimentally\ndiscovered in solid-state systems causing a furore in the research community.\nSystems with Weyl excitations can display a plethora of fascinating phenomena\nand offer great potential for improved quantum technologies. Here we show that\nWeyl excitations generically exist in three-dimensional systems of dipolar\nparticles with weakly broken time-reversal symmetry (for example, by a magnetic\nfield). They emerge as a result of dipolar-interaction-induced transfer of\nangular momentum between the $J=0$ and $J=1$ internal particle levels. We also\ndiscuss momentum-resolved Ramsey spectroscopy methods for observing Weyl\nquasiparticles in cold alkaline-earth-atom systems. Our results provide a\npathway for a feasible experimental realisation of Weyl quasiparticles and\nrelated phenomena in clean and controllable atomic systems.",
        "positive": "Liouvillian skin effects and fragmented condensates in an integrable\n  dissipative Bose-Hubbard model: Strongly interacting non-equilibrium systems are of great fundamental\ninterest, yet their inherent complexity make then notoriously hard to analyze.\nWe demonstrate that the dynamics of the Bose-Hubbard model, which by itself\nevades solvability, can be solved exactly at any interaction strength in the\npresence of loss tuned to a rate matching the hopping amplitude. Remarkably,\nthe full solvability of the corresponding Liouvillian, and the integrability of\nthe pertinent effective non-Hermitian Hamiltonian, survives the addition of\ndisorder and generic boundary conditions. By analyzing the Bethe ansatz\nsolutions we find that even weak interactions change the qualitative features\nof the system, leading to an intricate dynamical phase diagram featuring\nnon-Hermitian Mott-skin effects, disorder induced localization, highly\ndegenerate exceptional points, and a Bose glass-like phase of fragmented\ncondensates. We discuss realistic implementations of this model with cold\natoms."
    },
    {
        "anchor": "The multichannel nature of three-body recombination for ultracold\n  $^{39}$K: We develop a full multichannel spin model in momentum space to investigate\nthree-body recombination of identical alkali-metal atoms colliding in a\nmagnetic field. The model combines the exact three-atom spin structure and\nrealistic pairwise atom-atom interactions. By neglecting the interaction\nbetween two particles when the spectating particle is not in its initial spin\nstate we arrive at an approximate model. With this approximate model we achieve\nexcellent agreement with the recent precise measurement of the ground Efimov\nresonance position in potassium-39 close to 33.58 G [Chapurin $et$ $al$., Phys.\nRev. Lett. 123, 233402 (2019)]. We analyze the limitations of our approximation\nby comparing to the numerical results for the full system and find that it\nbreaks down for Feshbach resonances at larger magnetic fields in the same spin\nchannel. There the relevant three-body closed channel thresholds are much\ncloser to the open channel threshold, which enhances the corresponding\nmultichannel couplings. Therefore the neglected components of the interaction\nshould be included for those Feshbach resonances.",
        "positive": "Adiabatically tuning quantized supercurrents in an annular Bose-Einstein\n  condensate: The ability to generate and tune quantized persistent supercurrents is\ncrucial for building superconducting or atomtronic devices with novel\nfunctionalities. In ultracold atoms, previous methods for generating quantized\nsupercurrents are generally based on dynamical processes to prepare atoms in\nmetastable excited states. Here we show that arbitrary quantized circulation\nstates can be adiabatically prepared and tuned as the ground state of a\nring-shaped Bose-Einstein condensate by utilizing spin-orbital-angular-momentum\n(SOAM) coupling and an external potential. There exists superfluid hysteresis\nfor tuning supercurrents between different quantization values with nonlinear\natomic interactions, which is explained by developing a nonlinear Landau-Zener\ntheory. Our work will provide a powerful platform for studying SOAM coupled\nultracold atomic gases and building novel atomtronic circuits."
    },
    {
        "anchor": "Condensed Fraction of an Atomic Bose Gas Induced by Critical\n  Correlations: We study the condensed fraction of a harmonically-trapped atomic Bose gas at\nthe critical point predicted by mean-field (MF) theory. The non-zero condensed\nfraction $f_0$ is induced by critical correlations which increase the\ntransition temperature $T_c$ above $\\T_c^{MF}$. Unlike the $T_c$ shift in a\ntrapped gas, $f_0$ is sensitive only to the critical behaviour in the\nquasi-uniform part of the cloud near the trap centre. To leading order in the\ninteraction parameter $a/\\lambda_0$, where $a$ is the s-wave scattering length\nand $\\lambda_0$ the thermal wavelength, we expect a universal scaling $f_0\n\\propto (a/\\lambda_0)^4$. We experimentally verify this scaling using a\nFeshbach resonance to tune $a/\\lambda_0$. Further, using the local density\napproximation, we compare our measurements with the universal result obtained\nfrom Monte-Carlo simulations for a uniform system, and find excellent\nquantitative agreement.",
        "positive": "Phase separation of a two-component dipolar Bose-Einstein condensate in\n  the quasi-one-dimensional and quasi-two-dimensional regime: We consider a two-component Bose-Einstein condensate, which contains atoms\nwith magnetic dipole moments aligned along the $z$ direction (labeled as\ncomponent 1) and nonmagnetic atoms (labeled as component 2). The problem is\nstudied by means of exact numerical simulations. The effects of dipole-dipole\ninteraction on phase separations are investigated. It is shown that, in the\nquasi-one-dimensional regime, the atoms in component 2 are squeezed out when\nthe dimensionless dipolar strength parameter is small, whereas the atoms in\ncomponent 1 are pushed out instead when the parameter is large. This is in\ncontrast to the phenomena in the quasi-two-dimensional regime. These two\ncomponents are each kicked out by the other in the quasi-one-dimensional regime\nand this phenomenon is discussed as well."
    },
    {
        "anchor": "Single-site- and single-atom-resolved measurement of correlation\n  functions: Correlation functions play an important role for the theoretical and\nexperimental characterization of many-body systems. In solid-state systems,\nthey are usually determined through scattering experiments whereas in\ncold-gases systems, time-of-flight and in-situ absorption imaging are the\nstandard observation techniques. However, none of these methods allow the\nin-situ detection of spatially resolved correlation functions at the\nsingle-particle level. Here we give a more detailed account of recent advances\nin the detection of correlation functions using in-situ fluorescence imaging of\nultracold bosonic atoms in an optical lattice. This method yields single-site\nand single-atom-resolved images of the lattice gas in a single experimental\nrun, thus gaining direct access to fluctuations in the many-body system. As a\nconsequence, the detection of correlation functions between an arbitrary set of\nlattice sites is possible. This enables not only the detection of two-site\ncorrelation functions but also the evaluation of non-local correlations, which\noriginate from an extended region of the system and are used for the\ncharacterization of quantum phases that do not possess (quasi-)long-range order\nin the traditional sense.",
        "positive": "Phase Winding a Two-Component BEC in an Elongated Trap: Experimental\n  Observation of Moving Magnetic Orders and Dark-bright Solitons: We experimentally investigate the phase winding dynamics of a harmonically\ntrapped two-component BEC subject to microwave induced Rabi oscillations\nbetween two pseudospin components. While the single particle dynamics can be\nexplained by mapping the system to a two-component Bose-Hubbard model,\nnonlinearities due to the interatomic repulsion lead to new effects observed in\nthe experiments: In the presence of a linear magnetic field gradient, a\nqualitatively stable moving magnetic order that is similar to antiferromagnetic\norder is observed after critical winding is achieved. We also demonstrate how\nthe phase winding can be used as a new tool to generate copious dark-bright\nsolitons in a two-component BEC, opening the door for new experimental studies\nof these nonlinear features."
    },
    {
        "anchor": "Post-quench dynamics and pre-thermalization in a resonant Bose gas: We explore the dynamics of a resonant Bose gas following its quench to a\nstrongly interacting regime near a Feshbach resonance. For such deep quenches,\nwe utilize a self-consistent dynamic field approximation and find that after an\ninitial regime of many-body Rabi-like oscillations between the condensate and\nfinite-momentum quasiparticle pairs, at long times, the gas reaches a\npre-thermalized nonequilibrium steady state. We explore the resulting state\nthrough its broad stationary momentum distribution function, that exhibits a\npower-law high momentum tail. We study the dynamics and steady-state form of\nthe associated enhanced depletion, quench-rate dependent excitation energy,\nTan's contact, structure function and radio frequency spectroscopy. We find\nthese predictions to be in a qualitative agreement with recent experiments.",
        "positive": "Beyond the Hubbard bands in strongly correlated lattice bosons: We investigate features in the single-particle spectral function beyond the\nHubbard bands in the strongly correlated normal phase of the Bose-Hubbard\nmodel. There are two distinct classes of additional peaks generated by the\nbosonic statistics. The first type is thermally activated Hubbard \"sidebands\",\nwith the same physical origin as the zero-temperature Hubbard bands, but\ngenerated by excitations from thermally activated local occupation number\nstates. The second class are two-particle fluctuation resonances driven by the\nlattice dynamics. In the unity filling Mott insulator, this takes the form of a\nlocalized triplon combined with a dispersing holon. Both types of resonances\nalso manifest themselves in the structure factor and the interaction modulation\nspectra obtained from nonequilibrium bosonic dynamical mean-field theory\ncalculations. Our findings explain experimental lattice modulation and Bragg\nspectroscopy results, and they predict a strong temperature dependence of the\nfirst sideband, thereby opening the door to precise thermometry of strongly\ncorrelated lattice bosons."
    },
    {
        "anchor": "Universality in nonequilibrium condensation of exciton-polaritons: We investigate the process of condensation of exciton-polaritons in a\none-dimensional nanowire, predicting spontaneous formation of domains of\nuncondensed excitons and condensed polaritons. We demonstrate a universal\nscaling law for the density of domains, which results from the competition\nbetween characteristic timescales present in the system. However, we find that\nthe system does not follow the standard Kibble-\\.Zurek scenario of a\nnonequilibrium phase transition.",
        "positive": "Continuous Bose-Einstein condensation: Bose-Einstein condensates (BECs) are macroscopic coherent matter waves that\nhave revolutionized quantum science and atomic physics. They are essential to\nquantum simulation and sensing, for example underlying atom interferometers in\nspace and ambitious tests of Einstein's equivalence principle. The key to\ndramatically increasing the bandwidth and precision of such matter-wave sensors\nlies in sustaining a coherent matter wave indefinitely. Here we demonstrate\ncontinuous Bose-Einstein condensation by creating a continuous-wave (CW)\ncondensate of strontium atoms that lasts indefinitely. The coherent matter wave\nis sustained by amplification through Bose-stimulated gain of atoms from a\nthermal bath. By steadily replenishing this bath while achieving 1000x higher\nphase-space densities than previous works, we maintain the conditions for\ncondensation. This advance overcomes a fundamental limitation of all atomic\nquantum gas experiments to date: the need to execute several cooling stages\ntime-sequentially. Continuous matter-wave amplification will make possible CW\natom lasers, atomic counterparts of CW optical lasers that have become\nubiquitous in technology and society. The coherence of such atom lasers will no\nlonger be fundamentally limited by the atom number in a BEC and can ultimately\nreach the standard quantum limit. Our development provides a new, hitherto\nmissing piece of atom optics, enabling the construction of continuous coherent\nmatter-wave devices. From infrasound gravitational wave detectors to optical\nclocks, the dramatic improvement in coherence, bandwidth and precision now\nwithin reach will be decisive in the creation of a new class of quantum\nsensors."
    },
    {
        "anchor": "Equilibration and Approximate Conservation Laws: Dipole Oscillations and\n  Perfect Drag of Ultracold Atoms in a Harmonic Trap: The presence of (approximate) conservation laws can prohibit the fast\nrelaxation of interacting many-particle quantum systems. We investigate this\nphysics by studying the center-of-mass oscillations of two species of fermionic\nultracold atoms in a harmonic trap. If their trap frequencies are equal, a\ndynamical symmetry (spectrum generating algebra), closely related to Kohn's\ntheorem, prohibits the relaxation of center-of-mass oscillations. A small\ndetuning $\\delta\\omega$ of the trap frequencies for the two species breaks the\ndynamical symmetry and ultimately leads to a damping of dipole oscillations\ndriven by inter-species interactions. Using memory-matrix methods, we calculate\nthe relaxation as a function of frequency difference, particle number,\ntemperature, and strength of inter-species interactions. When interactions\ndominate, there is almost perfect drag between the two species and the\ndynamical symmetry is approximately restored. The drag can either arise from\nHartree potentials or from friction. In the latter case (hydrodynamic limit),\nthe center-of-mass oscillations decay with a tiny rate, $1/\\tau \\propto\n(\\delta\\omega)^2/\\Gamma$, where $\\Gamma$ is a single particle scattering rate.",
        "positive": "Beats, broken-symmetry superfluid on a one dimensional anyon Hubbard\n  model: By using the density matrix renormalization group and mean field methods, the\nanyon Hubbard model is studied systematically on a one dimensional lattice. The\nmodel can be expressed as a Bose-Hubbard model with a density-dependent-phase\nterm. When the phase angle is $\\theta=0$ or $\\theta=\\pi$, the model will be\nequivalent to boson and pseudo fermion models, respectively. In the mean field\nframe, we find a broken-symmetry superfluid (BSF), in which the\n$b^{\\dagger}(b)$ operators on the nearest neighborhood sites have exactly\nopposite directions and behave like a directed oscillation pattern. By the\ndensity matrix reorganization group method, in the broken-symmetry superfluid,\nboth the real and imaginary parts of the correlation $b^{\\dagger}_ib_{i+r}$\nbehave according to a {\\it beat phenomenon} with $0<\\theta<\\pi$ in the form\n$C_0e^{i k r}(-1)^{r}$ or behave like waves with different wavelengths in the\nform $C_0e^{i k r}$. The distributions of the broken-symmetry superfluid phase\nand other phases are shown in the phase diagrams with different values of\n$\\theta$ and the direct phase transition between the two types of superfluid is\nobserved. The beats phenomenon is explained by double peaks of momentum\ndistribution with two wave numbers ${k}_1$ and ${k}_2$ satisfying the condition\n$\\frac{{k}_1-{k}_2}{{k}_1+{k}_2}<\\frac{1}{3}$, which are expected to be\nobserved in the optical experiments."
    },
    {
        "anchor": "Shortcut to adiabaticity for an interacting Bose-Einstein condensate: We present an investigation of the fast decompression of a three-dimensional\n(3D) Bose-Einstein condensate (BEC) at finite temperature using an engineered\ntrajectory for the harmonic trapping potential. Taking advantage of the scaling\ninvariance properties of the time-dependent Gross-Pitaevskii equation, we\nexhibit a solution yielding a final state identical to that obtained through a\nperfectly adiabatic transformation, in a much shorter time. Experimentally, we\nperform a large trap decompression and displacement within a time comparable to\nthe final radial trapping period. By simultaneously monitoring the BEC and the\nnon-condensed fraction, we demonstrate that our specific trap trajectory is\nvalid both for a quantum interacting many-body system and a classical ensemble\nof non-interacting particles.",
        "positive": "Effective Potential for Ultracold Atoms at the Zero-Crossing of a\n  Feshbach Resonance: We consider finite-range effects when the scattering length goes to zero near\na magnetically controlled Feshbach resonance. The traditional effective-range\nexpansion is badly behaved at this point and we therefore introduce an\neffective potential that reproduces the full T-matrix. To lowest order the\neffective potential goes as momentum squared times a factor that is\nwell-defined as the scattering length goes to zero. The potential turns out to\nbe proportional to the background scattering length squared times the\nbackground effective range for the resonance. We proceed to estimate the\napplicability and relative importance of this potential for Bose-Einstein\ncondensates and for two-component Fermi gases where the attractive nature of\nthe effective potential can lead to collapse above a critical particle number\nor induce instability toward pairing and superfluidity. For broad Feshbach\nresonances the higher-order effect is completely negligible. However, for\nnarrow resonances in tightly confined samples signatures might be\nexperimentally accessible. This could be relevant for sub-optical wavelength\nmicrostructured traps at the interface of cold atoms and solid-state surfaces."
    },
    {
        "anchor": "Bayesian Optimization for Robust State Preparation in Quantum Many-Body\n  Systems: New generations of ultracold-atom experiments are continually raising the\ndemand for efficient solutions to optimal control problems. Here, we apply\nBayesian optimization to improve a state-preparation protocol recently\nimplemented in an ultracold-atom system to realize a two-particle fractional\nquantum Hall state. Compared to manual ramp design, we demonstrate the superior\nperformance of our optimization approach in a numerical simulation - resulting\nin a protocol that is 10x faster at the same fidelity, even when taking into\naccount experimentally realistic levels of disorder in the system. We\nextensively analyze and discuss questions of robustness and the relationship\nbetween numerical simulation and experimental realization, and how to make the\nbest use of the surrogate model trained during optimization. We find that\nnumerical simulation can be expected to substantially reduce the number of\nexperiments that need to be performed with even the most basic transfer\nlearning techniques. The proposed protocol and workflow will pave the way\ntoward the realization of more complex many-body quantum states in experiments.",
        "positive": "Nonequilibrium steady states of Bose-Einstein condensates with a local\n  particle loss in double potential barriers: We investigate stability of non-equilibrium steady states of Bose-Einstein\ncondensates with a local one-body loss in the presence of double potential\nbarriers. We construct an exactly solvable mean-field model, in which the local\nloss and the potential barriers take the form of a delta function. Using the\nexact solutions of our model, we show that there are parameter regions in which\ntwo steady-state solutions are dynamically stable, i.e., the model exhibits\nbistability. We also find that unidirectional hysteresis phenomena appear when\nthe local-loss rate is varied in some parameter region."
    },
    {
        "anchor": "Quantum dark solitons in ultracold one-dimensional Bose and Fermi gases: Solitons are ubiquitous phenomena that appear, among others, in the\ndescription of tsunami waves, fiber-optic communication and ultracold atomic\ngases. The latter systems turned out to be an excellent playground for\ninvestigations of matter-wave solitons in a quantum world. This Tutorial\nprovides a general overview of the ultracold contact interacting Bose and Fermi\nsystems in a one-dimensional space that can be described by the renowned\nLieb-Liniger and Yang-Gaudin models. Both the quantum many-body systems are\nexactly solvable by means of the Bethe ansatz technique, granting us a\npossibility for investigations of quantum nature of solitonic excitations. We\ndiscuss in details a specific class of quantum many-body excited eigenstates\ncalled yrast states and show that they are strictly related to quantum dark\nsolitons in the both considered Bose and Fermi systems.",
        "positive": "Systematic analysis of relative phase extraction in one-dimensional Bose\n  gases interferometry: Spatially resolved relative phase measurement of two adjacent 1D Bose gases\nis enabled by matter-wave interference upon free expansion. However,\nlongitudinal dynamics is typically ignored in the analysis of experimental\ndata. We provide an analytical formula showing a correction to the readout of\nthe relative phase due to longitudinal expansion and mixing with the common\nphase. We numerically assess the error propagation to the estimation of the\ngases' physical quantities such as correlation functions and temperature. Our\nwork characterizes the reliability and robustness of interferometric\nmeasurements, directing us to the improvement of existing phase extraction\nmethods necessary to observe new physical phenomena in cold-atomic quantum\nsimulators."
    },
    {
        "anchor": "Dynamics of quantum vortices at finite temperature: In this thesis, we perform investigations into the behaviour of\nfinite-temperature degenerate Bose gases using a classical-field formalism,\nfocussing in particular on the dynamics of quantum vortices in these systems.\nWe demonstrate that the coherence of the classical field can be characterised\nby its temporal correlations, and discuss how the phase-symmetry-broken\naverages familiar from mean-field theories emerge from the field trajectories.\nWe show that a finite-temperature condensate containing a precessing vortex in\na cylindrically symmetric trap can be realised as an ergodic equilibrium of the\nclassical-field theory, and demonstrate the identification of the rotationally\nsymmetry-broken condensate orbital and core-filling thermal component from the\nfield correlations. We then consider the nonequilibrium dynamics that result\nwhen such a precessing-vortex configuration is subjected to a static trap\nanisotropy which arrests its rotation, and observe novel coupled relaxation\ndynamics of the condensed and noncondensed components of the field. Finally, we\nconsider the nucleation of vortices in an initially zero-temperature\nquasi-two-dimensional condensate stirred by a rotating trap anisotropy. We\nquantify the emergence of a rotating thermal component of the field, which\ndrives the nucleation of vortices from condensate-surface oscillations, and\nstudy the relaxation and rotational equilibration of the initially turbulent\ncollection of vortices. We find that thermal fluctuations of the field prevent\nthe vortices from settling into a rigid crystalline lattice in this reduced\ndimensionality, and that true condensation in the field is completely destroyed\nby the disordered motion of vortices. We show, however, that the temporal\ncorrelations of the field distinguish the quasi-coherent vortex-liquid phase in\nthe trap centre from the truly thermal material in its periphery.",
        "positive": "Visualising Berry phase and diabolical points in a quantum\n  exciton-polariton billiard: Diabolical points (degeneracies) can naturally occur in spectra of\ntwo-dimensional quantum systems and classical wave resonators due to simple\nsymmetries. Geometric Berry phase is associated with these spectral\ndegeneracies. Here, we demonstrate a diabolical point and the corresponding\nBerry phase in the spectrum of hybrid light-matter quasiparticles --\nexciton-polaritons in semiconductor microcavities. It is well known that\nsufficiently strong optical pumping can drive exciton-polaritons to quantum\ndegeneracy, whereby they form a macroscopically populated quantum coherent\nstate similar to a Bose-Einstein condensate. By pumping a microcavity with a\nspatially structured light, we create a two-dimensional quantum billiard for\nthe exciton-polariton condensate and demonstrate a diabolical point in the\nspectrum of the billiard eigenstates. The fully reconfigurable geometry of the\npotential walls controlled by the optical pump enables a striking experimental\nvisualisation of the Berry phase associated with the diabolical point. The\nBerry phase is observed and measured by direct imaging of the macroscopic\nexciton-polariton wavefunctions."
    },
    {
        "anchor": "The stochastic projected Gross-Pitaevskii equation: We have achieved the first full implementation of the stochastic projected\nGross-Pitaevskii equation for a three-dimensional trapped Bose gas at finite\ntemperature. Our work advances previous applications of this theory, which have\nonly included growth processes, by implementing number-conserving scattering\nprocesses. We evaluate an analytic expression for the coefficient of the\nscattering term and compare it to that of the growth term in the experimental\nregime, showing the two coefficients are comparable in size. We give an\noverview of the numerical implementation of the deterministic and stochastic\nterms for the scattering process, and use simulations of a condensate excited\ninto a large amplitude breathing mode oscillation to characterize the\nimportance of scattering and growth processes in an experimentally accessible\nregime. We find that in such non-equilibrium regimes the scattering can\ndominate over the growth, leading to qualitatively different system dynamics.\nIn particular, the scattering causes the system to rapidly reach thermal\nequilibrium without greatly depleting the condensate, suggesting that it\nprovides a highly coherent energy transfer mechanism.",
        "positive": "Fast-forward scaling of atom-molecule conversion in Bose-Einstein\n  condensates: Robust stimulated Raman exact passages are requisite for controlling\nnonlinear quantum systems, with the wide applications ranging from ultracold\nmolecules, non-linear optics to superchemistry. Inspired by shortcuts to\nadiabaticity, we propose the fast-forward scaling of stimulated Raman adiabatic\nprocesses with the nonlinearity involved, describing the transfer from an\natomic Bose-Einstein condensate to a molecular one by controllable external\nfields. The fidelity and robustness of atom-molecule conversion are shown to\nsurpass those of conventional adiabatic passages, assisted by fast-forward\ndriving field. Finally, our results are extended to the fractional stimulated\nRaman adiabatic processes for the coherent superposition of atomic and\nmolecular states."
    },
    {
        "anchor": "High-polarization limit of the quasi-two-dimensional Fermi gas: We demonstrate that the theoretical description of current experiments of\nquasi-2D Fermi gases requires going beyond usual 2D theories. We provide such a\ntheory for the highly spin-imbalanced quasi-2D Fermi gas. For typical\nexperimental conditions, we find that the location of the recently predicted\npolaron-molecule transition is shifted to lower values of the vacuum binding\nenergy due to the interplay between transverse confinement and many-body\nphysics. The energy of the attractive polaron is calculated in the 2D-3D\ncrossover and displays a series of cusps before converging towards the 3D\nlimit. The repulsive polaron is shown to be accurately described by a 2D theory\nwith a single interaction parameter.",
        "positive": "Effects of interactions on the generalized Hong-Ou-Mandel effect: We numerically investigate the influence of interactions on the generalized\nHong-Ou-Mandel (HOM) effect for bosonic particles and show results for the\ncases of $N=2$, $N=3$ and $N=4$ bosons interacting with a beam splitter, whose\nrole is played by a $\\delta$-barrier. In particular, we focus on the effect of\nattractive interactions and compare the results with the repulsive case, as\nwell as with the analytically available results for the non-interacting case\n(that we use as a benchmark). We observe a fermionization effect both for\ngrowing repulsive and attractive interactions, i.e., the dip in the HOM\ncoincidence count is progressively smeared out, for increasing interaction\nstrengths. The role of input asymmetries is also explored."
    },
    {
        "anchor": "Dynamics of a few interacting bosons escaping from an open well: The dynamics of a few ultra-cold bosons tunneling from a one-dimensional\npotential well into open space is studied. In such a system several decay\nchannels can be distinguished, each corresponding to a different number of\nbosons escaping simultaneously. We show that as the interparticle interaction\nstrength is changed, the system undergoes transitions between distinct regimes\ncharacterized by the dominance of different decay channels. These transitions\nare reflected in the behavior of the decay rate of the system, which is\nmeasurable experimentally. By means of a simple theoretical description we show\nthat the transitions occur at the points where a new decay channel becomes\nenergetically viable. The results provide insight into the behavior of decaying\nfew-body systems and may have potential interest to experiments.",
        "positive": "Localized Higgs modes of superfluid Bose gases in optical lattices: A\n  Guzwiller mean-field study: We study effects of a potential barrier on collective modes of superfluid\nBose gases in optical lattices. We assume that the barrier is created by local\nsuppression of the hopping amplitude. When the system is in a close vicinity of\nthe Mott transition at commensurate fillings, where an approximate\nparticle-hole symmetry emerges, there exist bound states of Higgs amplitude\nmode that are localized around the barrier. By applying the Gutzwiller\nmean-field approximation to the Bose-Hubbard model, we analyze properties of\nnormal modes of the system with a special focus on the Higgs bound states. We\nshow that when the system becomes away from the Mott transition point, the\nHiggs bound states turn into quasi-bound states due to inevitable breaking of\nthe particle-hole symmetry. We use a stabilization method to compute the\nresonance energy and line width of the quasi-bound states. We compare the\nresults obtained by the Gutzwiller approach with those by the Ginzburg-Landau\ntheory. We find that the Higgs bound states survive even in a parameter region\nfar from the Mott transition, where the Ginzburg-Landau theory fails."
    },
    {
        "anchor": "Creating moving gap solitons in spin-orbit-coupled Bose-Einstein\n  condensates: A simple and efficient method to create gap solitons is proposed in a\nspin-orbit-coupled spin-1 Bose-Einstein condensate. We find that a free\nexpansion along the spin-orbit coupling dimension can generate two moving gap\nsolitons, which are identified from a generalized massive Thirring model. The\ndynamics of gap solitons can be controlled by adjusting spin-orbit coupling\nparameters.",
        "positive": "Towards quantitative precision in ultracold atoms with functional\n  renormalisation: We compute the equation of state, the gap as well as the density fluctuations\nof a two-component superfluid Fermi gas over the whole range of BEC-BCS\ncrossover at vanishing temperature within the functional renormalisation group\napproach. With an improved understanding of the relation between density and\nchemical potential, already a rather simple truncation yields a very good\nquantitative agreement with experimental data and theoretical results, in\nparticular in the unitarity limit and on the BEC side. The current approach\nutilises higher order density fluctuations as a fundamental building block for\nthe computation of the density as a function of the chemical potential. This\ncircumvents the fine-tuning problem of the density-related fundamental\nparameters on the microscopic level that has been observed in previous\napproaches. The quantitative reliability of the functional renormalisation\ngroup approach already within simple approximations opens the path towards\nprecision results in more elaborate truncations."
    },
    {
        "anchor": "Emergence of a spin microemulsion in spin-orbit coupled Bose-Einstein\n  condensates: We report the first numerical prediction of a \"spin microemulsion\" -- a phase\nwith undulating spin domains resembling classical bicontinuous\noil-water-surfactant emulsions -- in two-dimensional systems of spinor\nBose-Einstein condensates with isotropic Rashba spin-orbit coupling. Using\nfield-theoretic numerical simulations, we investigated the melting of a\nlow-temperature stripe phase with supersolid character and find that the\nstripes lose their superfluidity at elevated temperature and undergo a\nKosterlitz--Thouless-like transition into a spin microemulsion. Momentum\ndistribution calculations highlight a thermally broadened occupation of the\nRashba circle of low-energy states with macroscopic and isotropic occupation\naround the ring. We provide a finite-temperature phase diagram that positions\nthe emulsion as an intermediate, structured isotropic phase with residual\nquantum character before transitioning at higher temperature into a\nstructureless normal fluid.",
        "positive": "Bose gas in disordered, finite-layered systems: Disorder effects in the thermodynamic properties of a ideal Bose gas confined\nin a semi-infinite multi-layer structure %described by $M$ permeable barriers\nwithin a box of thickness $L$ and infinite lateral extent, are analyzed. The\nlayers are first modeled by a periodic array of $M$ Dirac delta-functions of\nequal intensity. Then, we introduce structural and compositional disorder, as\nwell as a random set of layer vacancies in the system to calculate the internal\nenergy, chemical potential and the specific heat for different configurations.\nWhereas structural and compositional disorder does not reveal a significant\nchange, a dramatic increase in the maximum of the specific heat is observed\nwhen the system is depleted a fraction of the order of $0.1$ to $0.2$ of random\nlayers compared to the original, fully periodic array. Furthermore, this\nmaximum, which is reminiscent of a Bose-Einstein condensation for an infinite\narray, occurs at higher temperatures."
    },
    {
        "anchor": "Floquet engineering a bosonic Josephson junction: We study Floquet engineering of the tunnel coupling between a pair of\none-dimensional bosonic quasi-condensates in a tilted double-well potential. By\nmodulating the energy difference between the two wells, we re-establish tunnel\ncoupling and precisely control its amplitude and phase. This allows us to\ninitiate coherence between two initially uncorrelated Bose gases and prepare\ndifferent initial states in the emerging sine-Gordon Hamiltonian. We fully\ncharacterize the Floquet system and study the dependence of both equilibrium\nproperties and relaxation on the modulation.",
        "positive": "Mean field effects on the scattered atoms in condensate collisions: We consider the collision of two Bose Einstein condensates at supersonic\nvelocities and focus on the halo of scattered atoms. This halo is the most\nimportant feature for experiments and is also an excellent testing ground for\nvarious theoretical approaches. In particular we find that the typical reduced\nBogoliubov description, commonly used, is often not accurate in the region of\nparameters where experiments are performed. Surprisingly, besides the halo pair\ncreation terms, one should take into account the evolving mean field of the\nremaining condensate and on-condensate pair creation. We present examples where\nthe difference is clearly seen, and where the reduced description still holds."
    },
    {
        "anchor": "Tunneling and Revival of Anderson Localization in Bose-Einstein\n  Condensate: We provide an analytical model to fabricate an exponential localization of a\nBose-Einstein condensate under bichromatic optical lattice. Such localization\nis famously known as Anderson localization. The degree of localization is\ninvestigated by the Participation Ratio to recognize the laser parameter domain\nfor Anderson localization. The exponential nature of the localization is\nproved, where we also identify the Localization Length. The tunneling of\nAnderson-localized condensate with time is observed, and the revival phenomenon\nof Anderson localization is reported. Slowing down of Anderson localization is\nnoticed for higher laser intensity. We also study the dynamical and structural\nstability of the condensate during Anderson localization, which suggests the\npreferred values of laser power and time instance to encounter minimal mean\ndifference in the presence of noise.",
        "positive": "Fragmentation of Spin-orbit Coupled Spinor Bose-Einstein Condensates: The fragmentation of spin-orbit coupled spin-1 Bose gas with a weak\ninteraction in external harmonic trap is explored by both exact diagonalization\nand mean-field theory. This fragmentation tendency, which originates from the\ntotal angular momentum conservation, is affected obviously by the spin-orbit\ncoupling strength and the spin-dependent interaction. Strong spin-orbit\ninteraction raises the inverse participation ratio, which describes the number\nof significantly occupied single-particle states. As the spin-dependent\ninteraction changes from anti-ferromagnetic to ferromagnetic, the peak values\nin the inverse participation ratio become lower. Without the confinement of the\nappointed total angular momentum, the condensate chooses a zero or finite total\nangular momentum ground state, which is determined by both the interaction and\nthe spin-orbit coupling strength."
    },
    {
        "anchor": "Collective modes and superfluidity of a two-dimensional ultracold Bose\n  gas: The collective modes of a quantum liquid shape and impact its properties\nprofoundly, including its emergent phenomena such as superfluidity. Here we\npresent how a two-dimensional Bose gas responds to a moving lattice potential.\nIn particular we discuss how the induced heating rate depends on the\ninteraction strength and the temperature. This study is motivated by the recent\nmeasurements of Sobirey {\\it et al.} arXiv:2005.07607 (2020), for which we\nprovide a quantitative understanding. Going beyond the existing measurements,\nwe demonstrate that this probing method allows to identify first and second\nsound in quantum liquids. We show that the two sound modes undergo\nhybridization as a function of interaction strength, which we propose to detect\nexperimentally. This gives a novel insight into the two regimes of Bose gases,\ndefined via the hierarchy of sounds modes.",
        "positive": "Quantum field theory of nematic transitions in spin orbit coupled spin-1\n  polar bosons: We theoretically study an ultra-cold gas of spin-1 polar bosons in a one\ndimensional continuum which are subject to linear and quadratic Zeeman fields\nand a Raman induced spin-orbit coupling. Concentrating on the regime in which\nthe background fields can be treated perturbatively we analytically solve the\nmodel in its low-energy sector, i.e. we characterize the relevant phases and\nthe quantum phase transitions between them. Depending on the sign of the\neffective quadratic Zeeman field $\\epsilon$, two superfluid phases with\ndistinct nematic order appear. In addition, we uncover a spin-disordered\nsuperfluid phase at strong coupling. We employ a combination of renormalization\ngroup calculations and duality transformations to access the nature of the\nphase transitions. At $\\epsilon = 0$, a line of spin-charge separated pairs of\nLuttinger liquids divides the two nematic phases and the transition to the spin\ndisordered state at strong coupling is of the Berezinskii-Kosterlitz-Thouless\ntype. In contrast, at $\\epsilon \\neq 0$, the quantum critical theory separating\nnematic and strong coupling spin disordered phases contains a Luttinger liquid\nin the charge sector that is coupled to a Majorana fermion in the spin sector\n(i.e. the critical theory at finite $\\epsilon$ maps to a quantum critical Ising\nmodel that is coupled to the charge Luttinger liquid). Due to an emergent\nLorentz symmetry, both have the same, logarithmically diverging velocity. We\ndiscuss the experimental signatures of our findings that are relevant to\nongoing experiments in ultra-cold atomic gases of $^{23}$Na."
    },
    {
        "anchor": "Spatiotemporal Quenches in Long-Range Hamiltonians: Spatiotemporal quenches are efficient at preparing ground states of critical\nHamiltonians that have emergent low-energy descriptions with Lorentz\ninvariance. The critical transverse field Ising model with nearest neighbor\ninteractions, for instance, maps to free fermions with a relativistic low\nenergy dispersion. However, spin models realized in artificial quantum\nsimulators based on neutral Rydberg atoms, or trapped ions, generically exhibit\nlong range power-law decay of interactions with $J(r) \\sim 1/r^\\alpha$ for a\nwide range of $\\alpha$. In this work, we study the fate of spatiotemporal\nquenches in these models with a fixed velocity $v$ for the propagation of the\nquench front, using the numerical time-dependent variational principle. For\n$\\alpha \\gtrsim 3$, where the critical theory is suggested to have a dynamical\ncritical exponent $z = 1$, our simulations show that optimal cooling is\nachieved when the front velocity $v$ approaches $c$, the effective speed of\nexcitations in the critical model. The energy density is inhomogeneously\ndistributed in space, with prominent hot regions populated by excitations\nco-propagating with the quench front, and cold regions populated by\ncounter-propagating excitations. Lowering $\\alpha$ largely blurs the boundaries\nbetween these regions. For $\\alpha < 3$, we find that the Doppler cooling\neffect disappears, as expected from renormalization group results for the\ncritical model which suggest a dispersion $\\omega \\sim q^z$ with $z < 1$.\nInstead, we show that excitations are controlled by two relevant length scales\nwhose ratio is related to that of the front velocity to a threshold velocity\nthat ultimately determines the adiabaticity of the quench.",
        "positive": "Simulating fermions in spin-dependent potentials with spin models on an\n  energy lattice: We study spin-1/2 fermions in spin dependent potentials under the \\emph{spin\nmodel approximation}, in which interatomic collisions that change the total\noccupation of single-particle modes are ignored. The spin model approximation\nmaps the interacting fermion problem to an ensemble of lattice spin models in\nenergy space, where spin-spin interactions are long-ranged and\nspin-anisotropic. We show that the spin model approximation is accurate for\nweak interactions compared to the harmonic oscillator frequency, and captures\nthe collective spin dynamics to timescales much longer than would be expected\nfrom perturbation theory. We explore corrections to the spin model, and the\nrelative importance of corrections when realistic anharmonic potential\ncorrections are taken into account. Additionally, we present numerical\ntechniques that are useful for analysis of spin models on an energy lattice,\nincluding enacting a change of single-particle basis on a many-body state as an\neffective time evolution, and fitting of spatially inhomogeneous long-range\ninteractions with exponentials. This latter technique is useful for\nconstructing matrix product operators for use in DMRG analyses, and may have\nbroader applicability within the tensor network community."
    },
    {
        "anchor": "The Chern Numbers of Interaction-stretched Monopoles in Spinor Bose\n  Condensates: Using the Dirac and the Yang monopole in spinor condensates as examples, we\nshow that interactions can stretch the point singularity of a monopole into an\nextended manifold, whose shape is strongly influenced by the sign of\ninteraction. The singular manifold will cause the first and second Chern number\nto assume non-integer values when it intersects the surface on which the Chern\nnumbers are calculated. This leads to a gradual decrease of the Chern numbers\nas the monopole moves away from the surface of integration, instead of the\nsudden jump characteristic of a point monopole. A gradual change in $C_2$ has\nin fact been observed in the recent experiment by Spielman's group at NIST. By\nmeasuring the range of non-integer values of the Chern numbers as the monopole\nmoves away from the surface of integration along different directions, one can\nmap out the shape of the singular manifold in the parameter space.",
        "positive": "Ground state properties of the disordered spin-one Bose-Hubbard model: a\n  stochastic mean-field theory study: We study the ground state of the disordered Bose-Hubbard model for spin-1\nparticles by means of the stochastic mean-field theory. This approach enables\nthe determination of the probability distributions of various physical\nquantities, such as the superfluid order parameter, the average site occupation\nnumber, the standard deviation of the occupation per site and the square of the\nspin operator per site. We show how a stochastic method, previously used in the\nstudy of localization, can be flexibly used to solve the relevant equations\nwith great accuracy. We have determined the phase diagram, which exhibits three\nphases: the polar superfluid, the Mott insulating and the Bose glass. A\ncomplete characterization of the physical properties of these phases has been\nestablished."
    },
    {
        "anchor": "Interaction-induced charge pumping in a topological many-body system: A topological 'Thouless' pump represents the quantised motion of particles in\nresponse to a slow, cyclic modulation of external control parameters. The\nThouless pump, like the quantum Hall effect, is of fundamental interest in\nphysics because it links physically measurable quantities, such as particle\ncurrents, to geometric properties of the experimental system, which can be\nrobust against perturbations and thus technologically useful. So far,\nexperiments probing the interplay between topology and inter-particle\ninteractions have remained relatively scarce. Here we observe a Thouless-type\ncharge pump in which the particle current and its directionality inherently\nrely on the presence of strong interactions. Experimentally, we utilise\nfermionic atoms in a dynamical superlattice which traces a pump trajectory that\nremains trivial in the non-interacting limit. Remarkably, the transferred\ncharge in the interacting system is half of its usual value in the\nnon-interacting case, in agreement with matrix-product-state simulations. Our\nexperiments suggest that Thouless charge pumps are promising platforms to gain\ninsights into interaction-driven topological transitions and topological\nquantum matter.",
        "positive": "Interaction-induced quantum phase revivals and evidence for the\n  transition to the quantum chaotic regime in 1D atomic Bloch oscillations: We study atomic Bloch oscillations in an ensemble of one-dimensional tilted\nsuperfluids in the Bose-Hubbard regime. For large values of the tilt, we\nobserve interaction-induced coherent decay and matter-wave quantum phase\nrevivals of the Bloch oscillating ensemble. We analyze the revival period\ndependence on interactions by means of a Feshbach resonance. When reducing the\nvalue of the tilt, we observe the disappearance of the quasi-periodic phase\nrevival signature towards an irreversible decay of Bloch oscillations,\nindicating the transition from regular to quantum chaotic dynamics."
    },
    {
        "anchor": "A Mixture of Bose and Fermi Superfluids: Superconductivity and superfluidity of fermionic and bosonic systems are\nremarkable many-body quantum phenomena. In liquid helium and dilute gases, Bose\nand Fermi superfluidity has been observed separately, but producing a mixture\nin which both the fermionic and the bosonic components are superfluid is\nchallenging. Here we report on the observation of such a mixture with dilute\ngases of two Lithium isotopes, 6Li and 7Li. We probe the collective dynamics of\nthis system by exciting center-of-mass oscillations that exhibit extremely low\ndamping below a certain critical velocity. Using high precision spectroscopy of\nthese modes we observe coherent energy exchange and measure the coupling\nbetween the two superfluids. Our observations can be captured theoretically\nusing a sum-rule approach that we interpret in terms of two coupled\noscillators.",
        "positive": "Lattice dynamics in an emergent Zeeman lattice: Periodic band structures are a hallmark phenomenon of condensed matter\nphysics. While often imposed by external potentials, periodicity can also arise\nthrough the interplay of couplings that are not necessarily spatially periodic\non their own. Here, we investigate dynamics in a lattice structure that emerges\nfrom the simultaneous application of Raman and radio frequency coupling to a\ndilute-gas Bose-Einstein condensate. We demonstrate a variety of techniques\nincluding Kapitza-Dirac scattering, Bloch oscillations, and lattice shaking\nwith spin and momentum resolved measurements. This combined coupling scheme\nallows for exceptional tunability and control, enabling future investigations\ninto unconventional band structures such as quasi-flat ground bands and those\nwith semimetal-like band gaps."
    },
    {
        "anchor": "Narrow-line magneto-optical trap for europium: We report on the realization of a magneto-optical trap (MOT) for europium\natoms using a narrow-line cooling transition with a natural linewidth of 97\nkHz. Our starting point is continuous capturing and cooling of optically pumped\nmetastable europium atoms. We have employed simultaneous MOT for the metastable\nand ground-state atoms. The trapped metastable atoms are successively pumped\nback to the ground state and then continuously loaded to the narrow-line MOT,\nwhere up to $4.7\\times10^7$ atoms are captured. A spin-polarized sample at a\ntemperature of $6\\,\\mathrm{\\mu K}$ and with a peak number density of\n$2.2\\times10^{11}\\,\\mathrm{cm^{-3}}$ is obtained through the compression\nprocess, resulting in a phase space density of $3\\times10^{-5}$.",
        "positive": "All-optical production and transport of a large $^6$Li quantum gas in a\n  crossed optical dipole trap: We report on an efficient production scheme for a large quantum degenerate\nsample of fermionic lithium. The approach is based on our previous work on\nnarrow-line $ 2S_{1/2}\\rightarrow 3P_{3/2} $ laser cooling resulting in a high\nphase-space density of up to $3\\times10^{-4}$. This allows utilizing a large\nvolume crossed optical dipole trap with a total power of $45\\,\\textrm{W}$,\nleading to high loading efficiency and $8\\times10^6$ trapped atoms. The same\noptical trapping configuration is used for rapid adiabatic transport over a\ndistance of $25\\,\\textrm{cm}$ in $0.9\\,\\textrm{s}$, and subsequent evaporative\ncooling. With optimized evaporation we achieve a degenerate Fermi gas with\n$1.7\\times 10^{6}$ atoms at a temperature of $60 \\, \\textrm{nK}$, corresponding\nto $T/T_{\\text{F}}=0.16\\left(2 \\right)$. Furthermore, the performance is\ndemonstrated by evaporation near a broad Feshbach resonance creating a\nmolecular Bose-Einstein condensate of $3\\times10^5$ lithium dimers."
    },
    {
        "anchor": "Bose-Einstein Condensation of Photons in a Microscopic Optical\n  Resonator: Towards Photonic Lattices and Coupled Cavities: Bose-Einstein condensation has in the last two decades been observed in cold\natomic gases and in solid-state physics quasiparticles, exciton-polaritons and\nmagnons, respectively. The perhaps most widely known example of a bosonic gas,\nphotons in blackbody radiation, however exhibits no Bose-Einstein condensation,\nbecause the particle number is not conserved and at low temperatures the\nphotons disappear in the system's walls instead of massively occupying the\ncavity ground mode. This is not the case in a small optical cavity, with a\nlow-frequency cutoff imprinting a spectrum of photon energies restricted to\nvalues well above the thermal energy. The here reported experiments are based\non a microscopic optical cavity filled with dye solution at room temperature.\nRecent experiments of our group observing Bose-Einstein condensation of photons\nin such a setup are described. Moreover, we discuss some possible applications\nof photon condensates to realize quantum manybody states in periodic photonic\nlattices and photonic Josephson devices.",
        "positive": "Supersolid phases of Rydberg-excited bosons on a triangular lattice: Recent experiments with ultracold Rydberg-excited atoms have shown that\nlong-range interactions can give rise to spatially ordered structures.\nObservation of crystalline phases in a system with Rydberg atoms loaded into an\noptical lattice seems also within reach. Here we investigate a bosonic model on\na triangular lattice suitable for description of such experiments. Numerical\nsimulations based on bosonic dynamical mean-field theory reveal a rich phase\ndiagram with different supersolid phases. Comparison with the results obtained\nfor a square lattice geometry shows qualitatively similar results in a wide\nrange of parameters, however, on a triangular lattice we do not observe the\ncheckerboard supersolid. Moreover, unlike on a square lattice we did not find a\nphase transition from uniform superfluid to supersolid induced by increase of\nthe hopping amplitude on a triangular lattice. Based on our results we propose\nan intuitive interpretation of the nature of different supersolid phases. We\nalso propose parameters for the experimental realization."
    },
    {
        "anchor": "Elementary excitations in dipolar spin-1 Bose-Einstein condensates: We have numerically solved the low-energy excitation spectra of ferromagnetic\nBose-Einstein condensates subject to dipolar interparticle interactions. The\nsystem is assumed to be harmonically confined by purely optical means, thereby\nmaintaining the spin degree of freedom of the condensate order parameter. Using\na zero-temperature spin-1 model, we solve the Bogoliubov excitations for\ndifferent spin textures, including a spin-vortex state in the absence of\nexternal magnetic fields and a rapidly rotating polarized spin texture in a\nfinite homogeneous field. In particular, we consider the effect of dipolar\ninteractions on excitations characteristic of ferromagnetic condensates. The\nenergies of spin waves and magnetic quadrupole modes are found to increase\nrapidly with the dipolar coupling strength, whereas the energies of density\noscillations change only slightly.",
        "positive": "Phase diagram of the Bose-Hubbard model on a ring-shaped lattice with\n  tunable weak links: Motivated by recent experiments on toroidal Bose-Einstein condensates in\nall-optical traps with tunable weak links, we study the one-dimensional\nBose-Hubbard model on a ring-shaped lattice with a small region of weak hopping\nintegrals using quantum Monte Carlo simulations. Besides the usual Mott\ninsulating and superfluid phases, we find a phase which is compressible but non\nsuperfluid with a local Mott region. This `local Mott' phase extends in a large\nregion of the phase diagram. These results suggest that the insulating and\nconducting phases can be tuned by a local parameter which may provide a new\ninsight to the design of atomtronic devices."
    },
    {
        "anchor": "Cold bosons in optical lattices: a tutorial for Exact Diagonalization: Exact diagonalization techniques are a powerful method for studying many-body\nproblems. Here, we apply this method to systems of few bosons in an optical\nlattice, and use it to demonstrate the emergence of interesting quantum\nphenomena like fragmentation and coherence. Starting with a standard\nBose-Hubbard Hamiltonian, we first revise the characterization of the\nsuperfluid to Mott insulator transitions. We then consider an inhomogeneous\nlattice, where one potential minimum is made much deeper than the others. The\nMott insulator phase due to repulsive on-site interactions then competes with\nthe trapping of all atoms in the deep potential. Finally, we turn our attention\nto attractively interacting systems, and discuss the appearance of strongly\ncorrelated phases and the onset of localization for a slightly biased lattice.\nThe article is intended to serve as a tutorial for exact diagonalization of\nBose-Hubbard models.",
        "positive": "Stability analysis and attractor dynamics of 3D dark solitons with\n  localized dissipation: We study the stability and the attractor dynamics of an elongated\nBose-Einstein condensate with dark or grey kink solitons in the presence of\nlocalized dissipation. To this end, the 3D Gross-Pitaevskii equation with an\nadditional imaginary potential is solved numerically. We analyze the\nsuppression of the snaking instability in dependence of the dissipation\nstrength and extract the threshold value for the stabilization of the dark\nsoliton for experimentally realistic parameters. Below the threshold value, we\nobserve the decay into a solitonic vortex. Above the stabilization threshold,\nwe observe the attractor dynamics towards the dark soliton when initially\nstarting from a grey soliton. We find that for all initial conditions the dark\nsoliton is the unique steady-state of the system - even when starting from the\nBEC ground state."
    },
    {
        "anchor": "Solitons and soliton interactions in repulsive spinor Bose-Einstein\n  condensates with non-zero background: We characterize the soliton solutions and their interactions for a system of\ncoupled evolution equations of nonlinear Schr\\\"odinger (NLS) type that models\nthe dynamics in one-dimensional repulsive Bose-Einstein condensates with spin\none, taking advantage of the representation of such model as a special\nreduction of a 2 x 2 matrix NLS system. Specifically, we study in detail the\ncase in which solutions tend to a non-zero background at space infinities.\nFirst we derive a compact representation for the multi-soliton solutions in the\nsystem using the Inverse Scattering Transform (IST). We introduce the notion of\ncanonical form of a solution, corresponding to the case when the background is\nproportional to the identity. We show that solutions for which the asymptotic\nbehavior at infinity is not proportional to the identity, referred to as being\nin non-canonical form, can be reduced to canonical form by unitary\ntransformations that preserve the symmetric nature of the solution (physically\ncorresponding to complex rotations of the quantization axes). Then we give a\ncomplete characterization of the two families of one-soliton solutions arising\nin this problem, corresponding to ferromagnetic and to polar states of the\nsystem, and we discuss how the physical parameters of the solitons for each\nfamily are related to the spectral data in the IST. We also show that any\nferromagnetic one-soliton solution in canonical form can be reduced to a single\ndark soliton of the scalar NLS equation, and any polar one-soliton solution in\ncanonical form is unitarily equivalent to a pair of oppositely polarized\ndisplaced scalar dark solitons up to a rotation of the quantization axes.\nFinally, we discuss two-soliton interactions and we present a complete\nclassification of the possible scenarios that can arise depending on whether\neither soliton is of ferromagnetic or polar type.",
        "positive": "Effective field theory for one-dimensional nonrelativistic particles\n  with contact interaction: We consider a field theory describing interacting nonrelativistic particles\nof two types, which map to each other under time reversal, with point-like\ninteraction. We identify a new type of interaction which depends on the\nrelative velocity between the particles. We compute the renormalization group\nrunning of the coupling constants and find a fixed point and a fixed line. We\nshow that the scattering amplitudes can be expressed in terms of three\nparameters. The result matches with a quantum mechanical analysis and\nrepresents the most general point-like interaction consistent with unitarity\nand time reversal invariance."
    },
    {
        "anchor": "Perturbative correction to the ground state properties of\n  one-dimensional strongly interacting bosons in a harmonic trap: We calculate the first-order perturbation correction to the ground state\nenergy and chemical potential of a harmonically trapped boson gas with contact\ninteractions about the infinite repulsion Tonks-Girardeau limit. With $c$\ndenoting the interaction strength, we find that for a large number of particles\n$N$ the $1/c$ correction to the ground state energy increases as $N^{5/2}$, in\ncontrast to the unperturbed Tonks-Girardeau value that is proportional to\n$N^2$. We describe a thermodynamic scaling limit for the trapping frequency\nthat yields an extensive ground state energy and reproduces the zero\ntemperature thermodynamics obtained by a local density approximation.",
        "positive": "Driving protocol for a Floquet topological phase without static\n  counterpart: Periodically driven systems play a prominent role in optical lattices. In\nthese ultracold atomic systems, driving is used to create a variety of\ninteresting behaviours, of which an important example is provided by\ntopological states of matter. Such Floquet topological phases have a richer\nclassification that their equilibrium counterparts. Although analogues of the\nequilibrium topological phases exist, which are characterised by a Chern\nnumber, the corresponding Hall conductivity, and protected edge states, there\nis an additional possibility. This is a phase that has vanishing Chern number\nand no Hall conductivity, but nevertheless hosts anomalous topological edge\nstates. Due to experimental difficulties associated with the observation of\nsuch a phase, it has not been experimentally realised so far. In this paper, we\nshow that optical lattices prove to be a good candidate for both its\nrealisation and subsequent observation, because they can be driven in a\ncontrolled manner. Specifically, we present a simple shaking protocol that\nserves to realise this special Floquet phase, discuss the specific properties\nthat it has, and propose a method to experimentally detect this fascinating\ntopological phase that has no counterpart in equilibrium systems."
    },
    {
        "anchor": "Particle number fluctuations in a cloven trapped Bose gas at finite\n  temperature: We study fluctuations in the atom number difference between two halves of a\nharmonically trapped Bose gas in three dimensions. We solve the problem\nanalytically for non interacting atoms. In the interacting case we find an\nanalytical solution in the Thomas-Fermi and high temperature limit in good\nagreement with classical field simulations. In the large system size limit,\nfluctuations in the number difference are maximal for a temperature $T\\simeq\n0.7 T_c$ where $T_c$ is the critical temperature, independently of the trap\nanisotropy. The occurrence of this maximum is due to an interference effect\nbetween the condensate and the non-condensed field.",
        "positive": "Ultradilute quantum liquid of dipolar atoms in a bilayer: We show that ultradilute quantum liquids can be formed with ultracold bosonic\ndipolar atoms in a bilayer geometry. Contrary to previous realizations of\nultradilute liquids, there is no need for stabilizing the system with an\nadditional repulsive short-range potential. The advantage of the proposed\nsystem is that dipolar interactions on their own are sufficient for creation of\na self-bound state and no additional short-range potential is needed for the\nstabilization. We perform quantum Monte Carlo simulations and find a rich\nground-state phase diagram that contains quantum phase transitions between\nliquid, solid, atomic gas, and molecular gas phases. The stabilization\nmechanism of the liquid phase is consistent with the microscopic scenario in\nwhich the effective dimer-dimer attraction is balanced by an effective\nthree-dimer repulsion. The equilibrium density of the liquid, which is\nextremely small, can be controlled by the interlayer distance. From the\nequation of state, we extract the spinodal density, below which the homogeneous\nsystem breaks into droplets. Our results offer a new example of a\ntwo-dimensional interacting dipolar liquid in a clean and highly controllable\nsetup."
    },
    {
        "anchor": "Quantum Membrane Phases in Synthetic Lattices of Cold Molecules or\n  Rydberg Atoms: We calculate properties of dipolar interacting ultracold molecules or Rydberg\natoms in a semi-synthetic three-dimensional configuration -- one synthetic\ndimension plus a two-dimensional real space optical lattice or periodic\nmicrotrap array -- using the stochastic Green function Quantum Monte Carlo\nmethod. Through a calculation of thermodynamic quantities and appropriate\ncorrelation functions, along with their finite size scalings, we show that\nthere is a second order transition to a low temperature phase in which\ntwo-dimensional `sheets' form in the synthetic dimension of internal rotational\nor electronic states of the molecules or Rydberg atoms, respectively.\nSimulations for different values of the interaction $V$, which acts between\natoms or molecules that are adjacent both in real and synthetic space, allow us\nto compute a phase diagram. We find a finite-temperature transition at\nsufficiently large $V$, as well as a quantum phase transition -- a critical\nvalue $V_c$ below which the transition temperature vanishes.",
        "positive": "All-optical production of a degenerate mixture of 6Li and 40K and\n  creation of heteronuclear molecules: We present the essential experimental steps of our all-optical approach to\nprepare a double-degenerate Fermi-Fermi mixture of 6Li and 40K atoms, which\nthen serves as a starting point for molecule formation. We first describe the\noptimized trap loading procedures, the internal-state preparation of the\nsample, and the combined evaporative and sympathetic cooling process. We then\ndiscuss the preparation of the sample near an interspecies Feshbach resonance,\nand we demonstrate the formation of heteronuclear molecules by a magnetic field\nramp across the resonance."
    },
    {
        "anchor": "Nonlinear quantum piston for the controlled generation of vortex rings\n  and soliton trains: We propose a simple way to generate nonlinear excitations in a controllable\nway by managing interactions in Bose-Einstein condensates. Under the action of\na quantum analogue of a classical piston the condensed atoms are pushed through\nthe trap generating vortex rings in a fully three- dimensional condensates or\nsoliton trains in quasi-one dimensional scenarios. The vortex rings form due to\ntransverse instability of the shock wave train enhanced and supported by the\nenergy transfer between waves. We elucidate in which sense the\nself-interactions within the atom cloud define the properties of generated\nvortex rings and soliton trains. Based on the quantum piston scheme we study\nthe behavior of two component Bose-Einstein condensates and analyze how the\npresence of an additional superfluid influences the generation of vortex rings\nor solitons in the other component and vice versa. Finally, we show the\ndynamical emergence of skyrmions within two component systems in the immiscible\nregime.",
        "positive": "Evolution from BCS to BEC superfluidity in the presence of spin-orbit\n  coupling: We discuss the evolution from BCS to BEC superfluids in the presence of\nspin-orbit coupling, and show that this evolution is just a crossover in the\nbalanced case. The dependence of several thermodynamic properties, such as the\nchemical potential, order parameter, pressure, entropy, isothermal\ncompressibility and spin susceptibility tensor on the spin-orbit coupling and\ninteraction parameter at low temperatures are analyzed. We studied both the\ncase of equal Rashba and Dresselhaus (ERD) and the Rashba-only (RO) spin-orbit\ncoupling. Comparisons between the two cases reveal several striking differences\nin the corresponding thermodynamic quantities. Finally we propose measuring the\nspin susceptibility as a means to detect the spin-orbit coupling effect."
    },
    {
        "anchor": "Thermal Global Expansion Coefficient Measurement for a Harmonic Trapped\n  Gas Across Bose-Einstein Condensation: We report the measurement of the global thermal expansion coefficient of a\nconfined Bose gas of $^{87}\\rm Rb$ in a harmonic potential around the\nBose-Einstein condensation transition temperature. We use the concept of global\nthermodynamic variables, previously introduced and appropriated for a\nnon-homogeneous system. We observe the behavior of the thermal expansion\ncoefficient above and below the critical temperature showing the lambda-like\nshape present in superfluid helium. The study demonstrates the potentiality of\nglobal thermodynamic variables for the investigation of properties across the\ncritical temperature and a new way to study the thermodynamic properties of the\nquantum systems.",
        "positive": "Cooper pair polaritons in cold fermionic atoms within a cavity: We formulate a Bardeen-Cooper-Schriffer (BCS) theory of quasiparticles in a\ndegenerate Fermi gas strongly coupled to photons in a optical cavity. The\nelementary photonic excitations of the system are cavity polaritons, which\nconsist of a cavity photon and an excitation of an atom within the Fermi sea.\nThe excitation of the atom out of the Fermi sea leaves behind a hole, which\ntogether results in a loosely bound Cooper pair, allowing for the system to be\nwritten by a BCS wavefunction. As the density of the excitations is increased,\nthe excited atom and hole become more strongly bound, crossing over into the\nmolecular regime. This thus realizes an alternative BCS to BEC crossover\nscenario, where the participating species are quasiparticle excitations in a\nFermi sea consisting of excited atoms and holes."
    },
    {
        "anchor": "Momentum distribution for a one-dimensional trapped gas of hard-core\n  bosons: Using the exact $N$-particle ground state wave function for a one-dimensional\ngas of hard-core bosons in a harmonic trap we develop an algorithm to compute\nthe reduced single-particle density matrix and corresponding momentum\ndistribution. Accurate numerical results are presented for up to N=8 particles,\nand the momentum distributions are compared to a recent analytic approximation.",
        "positive": "Dicke time crystals in driven-dissipative quantum many-body systems: The Dicke model -- a paradigmatic example of superradiance in quantum optics\n-- describes an ensemble of atoms which are collectively coupled to a leaky\ncavity mode. As a result of the cooperative nature of these interactions, the\nsystem's dynamics are captured by the behavior of a single mean-field,\ncollective spin. In this mean-field limit, it has recently been shown that the\ninterplay between photon losses and periodic driving of light-matter coupling\ncan lead to time-crystalline-like behavior of the collective spin. In this\nwork, we investigate whether such a Dicke time crystal is stable to\nperturbations that explicitly break the mean-field solvability of the\nconventional Dicke model. In particular, we consider the addition of\nshort-range interactions between atoms, which breaks the collective coupling\nand leads to complex many-body dynamics. In this context, the interplay between\nperiodic driving, dissipation and interactions yields a rich set of dynamical\nresponses including long-lived and metastable Dicke time crystals, where losses\ncan cool down the many-body heating resulting from the continuous pump of\nenergy from the periodic drive. Specifically, when the additional short-range\ninteractions are ferromagnetic, we observe time crystalline behavior at\nnon-perturbative values of the coupling strength, suggesting the possible\nexistence of stable dynamical order in a driven-dissipative quantum many-body\nsystem. These findings illustrate the rich nature of novel dynamical responses\nwith many-body character in quantum optics platforms."
    },
    {
        "anchor": "Ultracold Dipolar Molecules Composed of Strongly Magnetic Atoms: In a combined experimental and theoretical effort, we demonstrate a novel\ntype of dipolar system made of ultracold bosonic dipolar molecules with large\nmagnetic dipole moments. Our dipolar molecules are formed in weakly bound\nFeshbach molecular states from a sample of strongly magnetic bosonic erbium\natoms. We show that the ultracold magnetic molecules can carry very large\ndipole moments and we demonstrate how to create and characterize them, and how\nto change their orientation. Finally, we confirm that the relaxation rates of\nmolecules in a quasi-two dimensional geometry can be reduced by using the\nanisotropy of the dipole-dipole interaction and that this reduction follows a\nuniversal dipolar behavior.",
        "positive": "Non-Hamiltonian Kelvin wave generation on vortices in Bose-Einstein\n  condensates: Ultra-cold quantum turbulence is expected to decay through a cascade of\nKelvin waves. These helical excitations couple vorticity to the quantum fluid\ncausing long wavelength phonon fluctuations in a Bose-Einstein condensate. This\ninteraction is hypothesized to be the route to relaxation for turbulent tangles\nin quantum hydrodynamics. The local induction approximation is the lowest order\napproximation to the Biot-Savart velocity field induced by a vortex line and,\nbecause of its integrability, is thought to prohibit energy transfer by Kelvin\nwaves. Using the Biot-Savart description, we derive a generalization to the\nlocal induction approximation which predicts that regions of large curvature\ncan reconfigure themselves as Kelvin wave packets. While this generalization\npreserves the arclength metric, a quantity conserved under the Eulerian flow of\nvortex lines, it also introduces a non-Hamiltonian structure on the geometric\nproperties of the vortex line. It is this non-Hamiltonian evolution of\ncurvature and torsion which provides a resolution to the missing Kelvin wave\nmotion. In this work, we derive corrections to the local induction\napproximation in powers of curvature and state them for utilization in vortex\nfilament methods. Using the Hasimoto transformation, we arrive at a nonlinear\nintegro-differential equation which reduces to a modified nonlinear\nSchr\\\"odinger type evolution of the curvature and torsion on the vortex line.\nWe show that this modification seeks to disperse localized curvature profiles.\nAt the same time, the non-Hamiltonian break in integrability bolsters the\ndeforming curvature profile and simulations show that this dynamic results in\nKelvin wave propagation along the dispersive vortex medium."
    },
    {
        "anchor": "Spinless Bosons or Spin 1/2 Fermions in a 1D Harmonic Trap with\n  Repulsive Delta Function Interparticle Interaction I - General Theory: In these two papers, we solve the N body 1D harmonically trapped spinless\nBoson or spin 1/2 Fermions with repulsive delta function interaction in the\nlimit $N\\to \\infty$.",
        "positive": "Quantum scale anomaly and spatial coherence in a 2D Fermi superfluid: Quantum anomalies are violations of classical scaling symmetries caused by\nquantum fluctuations. Although they appear prominently in quantum field theory\nto regularize divergent physical quantities, their influence on experimental\nobservables is difficult to discern. Here, we discovered a striking\nmanifestation of a quantum anomaly in the momentum-space dynamics of a 2D Fermi\nsuperfluid of ultracold atoms. We measured the position and pair momentum\ndistribution of the superfluid during a breathing mode cycle for different\ninteraction strengths across the BEC-BCS crossover. Whereas the system exhibits\nself-similar evolution in the weakly interacting BEC and BCS limits, we found a\nviolation in the strongly interacting regime. The signature of scale-invariance\nbreaking is enhanced in the first-order coherence function. In particular, the\npower-law exponents that characterize long-range phase correlations in the\nsystem are modified due to this effect, indicating that the quantum anomaly has\na significant influence on the critical properties of 2D superfluids."
    },
    {
        "anchor": "Bogoliubov excitations driven by thermal lattice phonons in a quantum\n  fluid of light: The elementary excitations in weakly interacting quantum fluids have a\nnon-trivial nature which is at the basis of defining quantum phenomena such as\nsuperfluidity. These excitations and the physics they lead to have been\nexplored in closed quantum systems at thermal equilibrium both theoretically\nwithin the celebrated Bogoliubov framework, and experimentally in quantum\nfluids of ultracold atoms. Over the past decade, the relevance of Bogoliubov\nexcitations has become essential to understand quantum fluids of interacting\nphotons. Their driven-dissipative character leads to distinct properties with\nrespect to their equilibrium counterparts. For instance, the condensate\ncoupling to the photonic vacuum environment leads to a non-zero generation rate\nof elementary excitations with many striking implications. In this work,\nconsidering that quantum fluids of light are often hosted in solid-state\nsystems, we show within a joint theory-experiment analysis that the vibrations\nof the crystal constitute another environment that the condensate is\nfundamentally coupled to. This coupling leads to a unique heat transfer\nmechanism, resulting in a large generation rate of elementary excitations in\ntypical experimental conditions, and to a fundamental non-zero contribution at\nvanishing temperatures. Our work provides a complete framework for\nsolid-embedded quantum fluids of light, which is invaluable in view of\nachieving a regime dominated by photon vacuum fluctuations.",
        "positive": "Generation of spin currents by a temperature gradient in a two-terminal\n  device: Theoretical and experimental studies of the interaction between spins and\ntemperature are vital for the development of spin caloritronics, as they\ndictate the design of future devices. In this work, we propose a two-terminal\ncold-atom simulator to study that interaction. The proposed quantum simulator\nconsists of strongly interacting atoms that occupy two temperature reservoirs\nconnected by a one-dimensional link. First, we argue that the dynamics in the\nlink can be described using an inhomogeneous Heisenberg spin chain whose\ncouplings are defined by the local temperature. Second, we show the existence\nof a spin current in a system with a temperature difference by studying the\ndynamics that follows the spin-flip of an atom in the link. A temperature\ngradient accelerates the impurity in one direction more than in the other,\nleading to an overall spin current similar to the spin Seebeck effect."
    },
    {
        "anchor": "Approximate theories for binary magnetic quantum droplets: We develop two approximate theories to describe the miscible and immiscible\ndroplets that can occur in a binary mixture of highly magnetic bosonic atoms.\nIn addition to allowing simpler calculations, the approximate theories provide\ninsight into the role of quantum fluctuations in the two regimes. Results are\nvalidated by comparison to those from the extended Gross-Pitaevskii equation.\nAs an application we solve for the ground state droplets crossing the\nmiscible-immiscible transition as function of the short-ranged interspecies\ninteraction parameter. We consider regimes where the transition occurs suddenly\nor as a smooth cross-over. Using dynamical calculations we show that the\ncharacter of the transition is revealed in the number of domains produced when\nramping the droplet into the immiscible regime.",
        "positive": "Pauli crystals -- interplay of symmetries: Recently observed Pauli crystals are structures formed by trapped ultracold\natoms with the Fermi statistics. Interactions between these atoms are switched\noff, so their relative positions are determined by joined action of the\ntrapping potential and the Pauli exclusion principle. Numericalmodeling is used\nin this paper to find the Pauli crystals in a two-dimensional isotropic\nharmonic trap, three-dimensional harmonic trap, and a two-dimensional square\nwell trap. The Pauli crystals do not have the symmetry of the trap -- the\nsymmetry is broken by the measurement of positions and, in many cases, by the\nquantum state of atoms in the trap. Furthermore, the Pauli crystals are\ncompared with the Coulomb crystals formed by electrically charged trapped\nparticles. The~structure of the Pauli crystals differs from that of the Coulomb\ncrystals, this provides evidence that the exclusion principle cannot be\nreplaced by a two-body repulsive interaction but rather has to be considered to\nbe a specifically quantum mechanism leading to many-particle correlations."
    },
    {
        "anchor": "Exploring Unconventional Hubbard Models with Doubly Modulated Lattice\n  Gases: Recent experiments show that periodic modulations of cold atoms in optical\nlattices may be used to engineer and explore interesting models. We show that\ndouble modulation, combining lattice shaking and modulated interactions allows\nfor the engineering of a much broader class of lattice models with correlated\nhopping, which we study for the particular case of one-dimensional systems. We\nshow, in particular, that by using this double modulation it is possible to\nstudy Hubbard models with asymmetric hopping, which, contrary to the standard\nHubbard model, present insulating phases with both parity and string order.\nMoreover, double modulation allows for the simulation of lattice models in\nunconventional parameter regimes, as we illustrate for the case of the\nspin-$1/2$ Fermi-Hubbard model with correlated hopping, a relevant model for\ncuprate superconductors.",
        "positive": "Variational Polaron Method for Bose-Bose Mixtures: We study degenerate mixtures of \"heavy\" bosons and \"light\" superfluid bosons\nusing a variational polaron transformation. We consider the Mott\ninsulator-superfluid transition of the heavy species and find that at $T=0$\ninteraction favors the superfluid phase of the heavy species. Our analytic\nresults agree well with numerically exact quantum Monte Carlo simulations in\ntwo dimensions. We then show that in three dimensions the variational polaron\ntransformation can be combined with a Gutzwiller approximation to give good\nresults."
    },
    {
        "anchor": "Evolution of Fermion Pairing from Three to Two Dimensions: We follow the evolution of fermion pairing in the dimensional crossover from\n3D to 2D as a strongly interacting Fermi gas of $^6$Li atoms becomes confined\nto a stack of two-dimensional layers formed by a one-dimensional optical\nlattice. Decreasing the dimensionality leads to the opening of a gap in\nradio-frequency spectra, even on the BCS-side of a Feshbach resonance. The\nmeasured binding energy of fermion pairs closely follows the theoretical\ntwo-body binding energy and, in the 2D limit, the zero-temperature mean-field\nBEC-BCS theory.",
        "positive": "Angular Stripe Phase in Spin-Orbital-Angular-Momentum Coupled Bose\n  Condensates: We propose that novel superfluid with supersolid-like properties - angular\nstripe phase - can be realized in a pancake-like spin-1/2 Bose gas with\nspin-orbital-angular-momentum coupling. We predict a rich ground-state phase\ndiagram, including the vortex-antivortex pair phase, half-skyrmion phase, and\ntwo different angular stripe phases. The stripe phases feature modulated\nangular density-density correlation with sizable contrast and can occupy a\nrelatively large parameter space. The low-lying collective excitations, such as\nthe dipole and breathing modes, show distinct behaviors in different phases.\nThe existence of the novel stripe phase is also clearly indicated in the\nenergetic and dynamic instabilities of collective modes near phase transitions.\nOur predictions of the angular stripe phase could be readily examined in\ncurrent cold-atom experiments with $^{87}$Rb and $^{41}$K."
    },
    {
        "anchor": "Josephson dynamics of a spin-orbit coupled Bose-Einstein condensate in a\n  double well potential: We investigate the quantum dynamics of an experimentally realized spin-orbit\ncoupled Bose-Einstein condensate in a double well potential. The spin-orbit\ncoupling can significantly enhance the atomic inter-well tunneling. We find the\ncoexistence of internal and external Josephson effects in the system, which are\nmoreover inherently coupled in a complicated form even in the absence of\ninteratomic interactions. Moreover, we show that the spin-dependent tunneling\nbetween two wells can induce a net atomic spin current referred as spin\nJosephson effects. Such novel spin Josephson effects can be observable for\nrealistically experimental conditions.",
        "positive": "Synthetic-gauge-field-induced resonances and\n  Fulde-Ferrell-Larkin-Ovchinnikov states in a one-dimensional optical lattice: Coherent coupling generated by laser light between the hyperfine states of\natoms, loaded in a 1D optical lattice, gives rise to the \"synthetic dimension\"\nsystem which is equivalent to a Hofstadter model in a finite strip of square\nlattice. An SU(M) symmetric attractive interaction in conjunction with the\nsynthetic gauge field present in this system gives rise to unusual effects. We\nstudy the two- body problem of the system using the T-matrix formalism. We show\nthat the two-body ground states pick up a finite momentum and can transform\ninto two-body resonance like features in the scattering continuum with a large\nchange in the phase shift. As a result, even for this 1D system, a critical\namount of attraction is needed to form bound states. These phenomena have\nspectacular effects on the many body physics of the system analyzed using the\nnumerical density matrix renormalization group technique. We show that the\nFulde-Ferrell-Larkin-Ovchinnikov (FFLO) states form in the system even for a\n\"balanced\" gas and the FFLO momentum of the pairs scales linearly with flux.\nConsidering suitable measures, we investigate interesting properties of these\nstates. We also discuss a possibility of realization of a generalized\ninteresting topological model, called the Creutz ladder."
    },
    {
        "anchor": "Coherent seeding of the dynamics of a spinor Bose-Einstein condensate:\n  from quantum to classical behavior: We present experiments revealing the competing effect of quantum fluctuations\nand of a coherent seed in the dynamics of a spin-1 Bose-Einstein condensate,\nand discuss the relevance of a mean-field description of our system. We first\nexplore a near-equilibrium situation, where the mean-field equations can be\nlinearized around a fixed point corresponding to all atoms in the same Zeeman\nstate $m=0$. Preparing the system at this classical fixed point, we observe a\nreversible dynamics triggered by quantum fluctuations, which cannot be\nunderstood within a classical framework. We demonstrate that the classical\ndescription becomes accurate provided a coherent seed of a few atoms only is\npresent in the other Zeeman states $m= \\pm 1$. In a second regime characterized\nby a strong non-linearity of the mean-field equations, we observe a collapse\ndynamics driven by quantum fluctuations. This behavior cannot be accounted for\nby a classical description and persists for a large range of initial states. We\nshow that all our experimental results can be explained with a semi-classical\ndescription (truncated Wigner approximation), using stochastic classical\nvariables to model the quantum noise.",
        "positive": "Thermalization in the Quantum Ising Model - Approximations, Limits, and\n  Beyond: We present quantitative predictions for quantum simulator experiments on\nIsing models from trapped ions to Rydberg chains and show how the\nthermalization, and thus decoherence times, can be controlled by considering\ncommon, independent, and end-cap couplings to the bath. We find (i) independent\nbaths enable more rapid thermalization in comparison to a common one; (ii) the\nthermalization timescale depends strongly on the position in the Ising phase\ndiagram; (iii) for a common bath larger system sizes show a significant slow\ndown in the thermalization process; and (iv) finite-size scaling indicates a\nsubradiance effect slowing thermalization rates toward the infinite spin chain\nlimit. We find it is necessary to treat the full multi-channel Lindblad master\nequation rather than the commonly used single-channel local Lindblad\napproximation to make accurate predictions on a classical computer. This method\nreduces the number of qubits one can practically classical simulate by at least\na factor of 4, in turn showing a quantum advantage for such thermalization\nproblems at a factor of 4 smaller qubit number for open quantum systems as\nopposed to closed ones. Thus, our results encourage open quantum system\nexploration in noisy intermediate-scale quantum technologies."
    },
    {
        "anchor": "Quenched dynamics of the momentum distribution of the unitary Bose gas: We study the quenched dynamics of the momentum distribution of a unitary Bose\ngas under isotropic harmonic confinement within a time-dependent density\nfunctional approach based on our recently calculated Monte Carlo (MC) bulk\nequation of state. In our calculations the inter-atomic s-wave scattering\nlength of the trapped bosons is suddenly increased to a very large value and\nthe real-time evolution of the system is studied. Prompted by the very recent\nexperimental data of $^{85}$Rb atoms at unitarity [Nature Phys. 10, 116 (2014)]\nwe focus on the momentum distribution as a function of time. Our results\nsuggest that at low momenta, a quasi-stationary momentum distribution is\nreached after a long transient, contrary to what found experimentally for large\nmomenta which equilibrate on a time scale shorter than the one for three body\nlosses.",
        "positive": "Localization of spin mixing dynamics in a spin-1 Bose-Einstein\n  condensate: We propose to localize spin mixing dynamics in a spin-1 Bose-Einstein\ncondensate by a temporal modulation of spin exchange interaction, which is\ntunable with optical Feshbach resonance. Adopting techniques from coherent\ncontrol, we demonstrate the localization/freezing of spin mixing dynamics, and\nthe suppression of the intrinsic dynamic instability and spontaneous spin\ndomain formation in a ferromagnetically interacting condensate of $^{87}$Rb\natoms. This work points to a promising scheme for investigating the weak\nmagnetic spin dipole interaction, which is usually masked by the more dominant\nspin exchange interaction."
    },
    {
        "anchor": "Composite fermion basis for M-component Bose gases: The composite fermion (CF) formalism produces wave functions that are not\nalways linearly independent. This is especially so in the low angular momentum\nregime in the lowest Landau level, where a subclass of CF states, known as\nsimple states, gives a good description of the low energy spectrum. For the\ntwo-component Bose gas, explicit bases avoiding the large number of redundant\nstates have been found. We generalize one of these bases to the $M$-component\nBose gas and prove its validity. We also show that the numbers of linearly\nindependent simple states for different values of angular momentum are given by\ncoefficients of $q$-multinomials.",
        "positive": "Non-destructive monitoring of Bloch oscillations in an optical cavity: Bloch oscillations are a hallmark of coherent wave dynamics in periodic\npotentials. They occur as the response of quantum mechanical particles in a\nlattice if a weak force is applied. In optical lattices with their perfect\nperiodic structure they can be readily observed and employed as a quantum\nmechanical force sensor, for example, for precise measurements of the\ngravitational acceleration. However, the destructive character of the\nmeasurement process in previous experimental implementations poses serious\nlimitations for the precision of such measurements. In this article we show\nthat the use of an optical cavity operating in the regime of strong cooperative\ncoupling allows one to directly monitor Bloch oscillations of a cloud of cold\natoms in the light leaking out of the cavity. Hence, with a single atomic\nsample the Bloch oscillation dynamics can be mapped out, while in previous\nexperiments, each data point required the preparation of a new atom cloud. The\nuse of a cavity-based monitor should greatly improve the precision of Bloch\noscillation measurements for metrological purposes."
    },
    {
        "anchor": "Generation of nonground-state condensates and adiabatic paradox: The problem of resonant generation of nonground-state condensates is\naddressed aiming at resolving the seeming paradox that arises when one resorts\nto the adiabatic representation. In this picture, the eigenvalues and\neigenfunctions of a time-dependent Gross-Pitaevskii Hamiltonian are also\nfunctions of time. Since the level energies vary in time, no definite\ntransition frequency can be introduced. Hence no external modulation with a\nfixed frequency can be made resonant. Thus, the resonant generation of\nadiabatic coherent modes is impossible. However, this paradox occurs only in\nthe frame of the adiabatic picture. It is shown that no paradox exists in the\nproperly formulated diabatic representation. The resonant generation of\ndiabatic coherent modes is a well defined phenomenon. As an example, the\nequations are derived, describing the generation of diabatic coherent modes by\nthe combined resonant modulation of the trapping potential and atomic\nscattering length.",
        "positive": "Chiral Bosonic Phases on the Haldane Honeycomb Lattice: Recent experiments in ultracold atoms and photonic analogs have reported the\nimplementation of artificial gauge fields in lattice systems, facilitating the\nrealization of topological phases. Motivated by such advances, we investigate\nthe Haldane honeycomb lattice tight-binding model, for bosons with local\ninteractions at the average filling of one boson per site. We analyze the\nground state phase diagram and uncover three distinct phases: a uniform\nsuperfluid (SF), a chiral superfluid (CSF) and a plaquette Mott insulator with\nlocal current loops (PMI). Nearest-neighbor and next-nearest neighbor currents\ndistinguish CSF from SF, and the phase transition between them is first order.\nWe apply bosonic dynamical mean field theory and exact diagonalization to\nobtain the phase diagram, complementing numerics with calculations of\nexcitation spectra in strong and weak coupling perturbation theory. The\ncharacteristic density fluctuations, current correlation functions, and\nexcitation spectra are measurable in ultracold atom experiments."
    },
    {
        "anchor": "A Dynamical Self-Consistent Finite Temperature Kinetic Theory: The ZNG\n  Scheme: We review a self-consistent scheme for modelling trapped weakly-interacting\nquantum gases at temperatures where the condensate coexists with a significant\nthermal cloud. This method has been applied to atomic gases by Zaremba, Nikuni,\nand Griffin, and is often referred to as ZNG. It describes both\nmean-field-dominated and hydrodynamic regimes, except at very low temperatures\nor in the regime of large fluctuations. Condensate dynamics are described by a\ndissipative Gross-Pitaevskii equation (or the corresponding quantum\nhydrodynamic equation with a source term), while the non-condensate evolution\nis represented by a quantum Boltzmann equation, which additionally includes\ncollisional processes which transfer atoms between these two subsystems. In the\nmean-field-dominated regime collisions are treated perturbatively and the full\ndistribution function is needed to describe the thermal cloud, while in the\nhydrodynamic regime the system is parametrised in terms of a set of local\nvariables. Applications to finite temperature induced damping of collective\nmodes and vortices in the mean-field-dominated regime are presented.",
        "positive": "Spin-Imbalanced Fermi Superfluidity in a Lieb Lattice Hubbard Model: We obtain a phase diagram of the spin imbalanced Hubbard model on the Lieb\nlattice, which is known to feature a flat band in its single-particle spectrum.\nUsing the BCS mean-field theory for multiband systems, we find a variety of\nsuperfluid phases with imbalance. In particular, we find four different types\nFFLO phases, i.e. superfluid phases with periodic spatial modulation. They\ndiffer by the magnitude and direction of the centre-of-mass momentum of Cooper\npairs. We also see a large region of stable Sarma phase, where the density\nimbalance is associated with zero Cooper pair momentum. In the mechanism\nresponsible for the formation of those phases, the crucial role is played by\nthe flat band, wherein particles can readjust their density at zero energy\ncost. The multiorbital structure of the unit cell is found to stabilize the\nSarma phase by allowing for a modulation of the order parameter within a unit\ncell. We also study the effect of finite temperature and a lattice with\nstaggered hopping parameters on the behaviour of these phases."
    },
    {
        "anchor": "Resonant quantum dynamics of few ultracold bosons in periodically driven\n  finite lattices: The out-of-equilibrium dynamics of finite ultracold bosonic ensembles in\nperiodically driven one-dimensional optical lattices is investigated. Our study\nreveals that the driving enforces the bosons in different wells to oscillate\nin-phase and to exhibit a dipole-like mode. A wide range from weak-to-strong\ndriving frequencies is covered and a resonance-like behaviour of the intra-well\ndynamics is discussed. In the proximity of the resonance a rich intraband\nexcitation spectrum is observed. The single particle excitation mechanisms are\nstudied in the framework of Floquet theory elucidating the role of the driving\nfrequency. The impact of the interatomic repulsive interactions is examined in\ndetail yielding a strong influence on the tunneling period and the excitation\nprobabilities. Finally, the dependence of the resonance upon a variation of the\ntunable parameters of the optical lattice is examined. Our analysis is based on\nthe ab-initio Multi-Configuration Time-Dependent Hartree Method for bosons.",
        "positive": "Macroscopic quantum tunneling of Bose-Einstein condensates with\n  long-range interaction: The ground state of Bose-Einstein condensates with attractive particle\ninteraction is metastable. One of the decay mechanisms of the condensate is a\ncollapse by macroscopic quantum tunneling, which can be described by the bounce\ntrajectory as solution of the time-dependent Gross-Pitaevskii equation in\nimaginary time. For condensates with an electromagnetically induced\ngravity-like interaction the bounce trajectory is computed with an extended\nvariational approach using coupled Gaussian functions and simulated numerically\nexact within the mean-field approach on a space-time lattice. It is shown that\nthe variational computations converge very rapidly to the numerically exact\nresult with increasing number of Gaussians. The tunneling rate of the\ncondensate is obtained from the classical action and additional parameters of\nthe bounce trajectory. The converged variational and numerically exact results\ndrastically improve by several orders of magnitude the decay rates obtained\npreviously with a simple variational approach using a single Gaussian-type\norbital for the condensate wave function."
    },
    {
        "anchor": "Inertial and fluctuational effects on the motion of a Bose superfluid\n  vortex: We study the motion of a vortex under the influence of a harmonic force in an\napproximately two dimensional trapped Bose-condensed gas. The\nHall-Vinen-Iordanskii equations, modified to include a fluctuational force and\nan inertial mass term, are solved for the vortex motion. The mass of the vortex\nhas a strong influence on the time it takes the vortex to escape the trap.\nSince the vortex mass also depends on the trap size we have an additional\ndependence on the trap size in the escape time which we compare to the massless\ncase.",
        "positive": "Two-fluid hydrodynamics of cold atomic bosons under influence of the\n  quantum fluctuations at non-zero temperatures: Ultracold Bose atoms is the physical system, where the quantum and nonlinear\nphenomena play crucial role. Ultracold bosons are considered at the small\nfinite temperatures. Bosons are considered as two different fluids:\nBose-Einstein condensate and normal fluid (the thermal component). An extended\nhydrodynamic model is obtained for both fluids, where the pressure evolution\nequations and the pressure flux third rank tensor evolution equations are\nconsidered along with the continuity and Euler equations. It is found that the\npressure evolution equation contains zero contribution of the short-range\ninteraction. The pressure flux evolution equation contains the interaction\nwhich gives the quantum fluctuations in the zero temperature limit. Here, we\nobtain its generalization for the finite temperature. The contribution of\ninteraction in the pressure flux evolution equation which goes to zero in the\nzero temperature limit is found. The model is obtained via the straightforward\nderivation from the microscopic many-particle Schrodinger equation in the\ncoordinate representation."
    },
    {
        "anchor": "Numerical Studies on Correlations in Dynamics and Localization of Two\n  Interacting Particles in Lattices: Correlation of interacting particles is studied in their dynamics and\nlocalization in ideal and disordered lattice systems with the help of numerical\ntools. Both 1D and 2D systems are considered. In 1D lattices with long-range\nhopping, differences between dynamics of attractively and repulsively\ninteracting particles are noted. For calculations of 2D systems, a recursion\nbased numerical algorithm for two-particle Greens functions is implemented\nwhich provides accurate results. Using this algorithm, spectral properties of\n2D Hubbard and Hofstadter models is computed, along with localization\nparameters of 2D disordered systems.",
        "positive": "Pairing effects in the non-degenerate limit of the two-dimensional Fermi\n  gas: The spectral function of a spin-balanced two-dimensional Fermi gas with\nshort-range interactions is calculated by means of a quantum cluster expansion.\nGood qualitative agreement is found with a recent experiment by Feld\n$\\textit{et al.}$ [Nature (London) $\\textbf{480}$, 75 (2011)]. The effects of\npairing are clearly visible in the density of states, which displays a\nsuppression of spectral weight due to the formation of a two-body bound state.\nIn addition, the momentum distribution and the radio-frequency spectrum are\nderived, which are in excellent agreement with exact universal results. It is\ndemonstrated that in the limit of high temperature, the quasiparticle\nexcitations are well defined, allowing for a kinetic description of the gas."
    },
    {
        "anchor": "Measuring densities of cold atomic clouds smaller than the resolution\n  limit: We propose and demonstrate an experimental method to measure by absorption\nimaging the size and local column density of a cloud of atoms, even when its\nsmallest dimension is smaller than the resolution of the imaging system. To do\nthis, we take advantage of the fact that, for a given total number of atoms, a\nsmaller and denser cloud scatters less photons when the gas is optically thick.\nThe method relies on making an ansatz on the cloud shape along the unresolved\ndimension(s), and on providing an additional information such as the total\nnumber of atoms. We demonstrate the method on \\textit{in-situ} absorption\nimages of elongated 87Sr Fermi gases. We find significant non-linear\ncorrections to the estimated size and local density of the cloud compared to a\nstandard analysis. This allows us to recover an un-distorted longitudinal\ndensity profile, and to measure transverse sizes as small as one fourth of our\nimaging resolution. The ultimate limit of our method is the wavelength that is\nused for imaging.",
        "positive": "Cooperative scattering measurement of coherence in a spatially modulated\n  Bose gas: Correlations of a Bose gas released from an optical lattice are measured\nusing superradiant scattering. Conditions are chosen so that after initial\nincident light pumping at the Bragg angle for diffraction, due to matter wave\namplification and mode competition, superradiant scattering into the Bragg\ndiffracted mode is preponderant. A temporal analysis of the superradiant\nscattering gain reveals periodical oscillations and damping due to the initial\nlack of coherence between lattice sites. Such damping is used for\ncharacterizing first order spatial correlations in our system with a precision\nof one lattice period."
    },
    {
        "anchor": "Polar Molecules with Three-Body Interactions on the Honeycomb Lattice: We study the phase diagram of ultra-cold bosonic polar molecules loaded on a\ntwo-dimensional optical lattice of hexagonal symmetry controlled by external\nelectric and microwave fields. Following a recent proposal in Nature Physics\n\\textbf{3}, 726 (2007), such a system is described by an extended Bose-Hubbard\nmodel of hard-core bosons, that includes both extended two- and three-body\nrepulsions. Using quantum Monte-Carlo simulations, exact finite cluster\ncalculations and the tensor network renormalization group, we explore the rich\nphase diagram of this system, resulting from the strongly competing nature of\nthe three-body repulsions on the honeycomb lattice. Already in the classical\nlimit, they induce complex solid states with large unit cells and macroscopic\nground state degeneracies at different fractional lattice fillings. For the\nquantum regime, we obtain effective descriptions of the various phases in terms\nof emerging valence bond crystal states and quantum dimer models. Furthermore,\nwe access the experimentally relevant parameter regime, and determine the\nstability of the crystalline phases towards strong two-body interactions.",
        "positive": "Zero-temperature phase diagram of Bose-Fermi gaseous mixtures in optical\n  lattices: We study the ground state phase diagram of a mixture of bosonic and fermionic\ncold atoms confined on two- and three-dimensional optical lattices. The\ncoupling between bosonic fluctuations and fermionic atoms can be attractive or\nrepulsive and has similarities with electron-phonon coupling in crystals. We\ninvestigate behavior of the mixtures in the limit, where the Bogoliubov sound\nvelocity that dictates bosonic dynamics is comparable to the Fermi velocity,\nhence the retardation effects are important part of the physics. The dynamic\nLindhard response function of the fermionic density to changes in the bosonic\nnumber of particles above some critical frequency can alter the sign and in\nconsequence the inter-species interaction between particles becomes repulsive\nin contrast to the static limit (instantaneous and always attractive).\nConsidering the above we show that the structure of the phase diagrams\ncrucially depends on the difference in masses of the bosons and fermions. We\ndiscuss the situations where integrating out fermionic field provides an\nadditional interaction that can decrease or increase bosonic coherence."
    },
    {
        "anchor": "Spin Orbit Coupling in Periodically Driven Optical Lattices: We propose a method for the emulation of artificial spin orbit coupling in a\nsystem of ultracold, neutral atoms trapped in a tight-binding lattice. This\nscheme does not involve near-resonant laser fields, avoiding the heating\nprocesses connected to the spontaneous emission of photons. In our case, the\nnecessary spin dependent tunnel matrix elements are generated by a rapid, spin\ndependent, periodic force, which can be described in the framework of an\neffective, time averaged Hamiltonian. An additional radio frequency coupling\nbetween the spin states leads to a mixing of the spin bands.",
        "positive": "Finite-Range Corrections to the Thermodynamics of the One-Dimensional\n  Bose Gas: The Lieb-Liniger equation of state accurately describes the zero-temperature\nuniversal properties of a dilute one-dimensional Bose gas in terms of the\ns-wave scattering length. For weakly-interacting bosons we derive non-universal\ncorrections to this equation of state taking into account finite-range effects\nof the inter-atomic potential. Within the finite-temperature formalism of\nfunctional integration we find a beyond-mean-field equation of state which\ndepends on scattering length and effective range of the interaction potential.\nOur analytical results, which are obtained performing dimensional\nregularization of divergent zero-point quantum fluctuations, show that for the\none-dimensional Bose gas thermodynamic quantities like pressure and sound\nvelocity are modified by changing the ratio between the effective range and the\nscattering length."
    },
    {
        "anchor": "Correlated versus Ferromagnetic State in Repulsively Interacting\n  Two-Component Fermi Gases: Whether a spin-1/2 Fermi gas will become ferromagnetic as the strength of\nrepulsive interaction increases is a long-standing controversial issue.\nRecently this problem is studied experimentally by Jo et al, Science, 325, 1521\n(2009) in which the authors claim a ferromagnetic transition is observed. This\nwork is to point out the results of this experiment can not distinguish whether\nthe system is in a ferromagnetic state or in a non-magnetic but strongly\nshort-range correlated state. A conclusive experimental demonstration of\nferromagnetism relies on the observation of ferromagnetic domains.",
        "positive": "Excitation Spectra of one-dimensional spin-1/2 Fermi gas with an\n  attraction: Using exact Bethe ansatz solution, we rigorously study excitation spectra of\nthe spin-1/2 Fermi gas (called Yang-Gaudin model) with an attractive\ninteraction. Elementary excitations of this model involve particle-hole\nexcitations, hole excitations and adding particles in the Fermi seas of pairs\nand unpaired fermions. The gapped magnon excitations in spin sector show a\nferromagnetic coupling to the Fermi sea of the single fermions. By numerically\nand analytically solving the Bethe ansatz equations and the thermodynamic Bethe\nansatz equations of this model, we obtain excitation energies for various\npolarizations in the phase of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)-like\nstate. For a small momentum (long-wavelength limit) and in the strong\ninteraction regime, we analytically obtained their linear dispersions with\ncurvature corrections, effective masses as well as velocities in particle-hole\nexcitations of pairs and unpaired fermions. Such a type of particle-hole\nexcitations display a novel separation of collective motions of bosonic modes\nwithin paired and unpaired fermions. Finally, we also discuss magnon\nexcitations in spin sector and the application of the Bragg spectroscopy for\ntesting such separated charge excitation modes of pairs and single fermions."
    },
    {
        "anchor": "Persistent-current states originating from the Hilbert space\n  fragmentation in momentum space: Hilbert space fragmentation (HSF) is a phenomenon that the Hilbert space of\nan isolated quantum system splits into exponentially many disconnected\nsubsectors. The fragmented systems do not thermalize after long-time evolution\nbecause the dynamics are restricted to a small subsector. Inspired by recent\ndevelopments of the HSF, we construct the Hamiltonian that exhibits the HSF in\nthe momentum space. We show that persistent-current (PC) states emerge due to\nthe HSF in the momentum space. We also investigate the stability of the PC\nstates against the random potential, which breaks the structure of the HSF, and\nfind that the decay rate of the PC is almost independent of the current\nvelocity.",
        "positive": "Three-body problem in a multiband Hubbard model: We consider the three-body problem in a generic multiband lattice, and\nanalyze the dispersion of the trimer states that are made of two\nspin-$\\uparrow$ fermions and a spin-$\\downarrow$ fermion due to an onsite\nattraction in between. Based on a variational approach, we first obtain the\nexact solution in the form of a set of coupled integral equations, and then\nreduce it to an eigenvalue problem. As an illustration we apply our theory to\nthe sawtooth lattice, and numerically show that energetically-stable trimers\nare allowed in a two-band setting, which is in sharp contrast with the\nsingle-band linear-chain model. In particular we also reveal that the trimers\nhave a nearly-flat dispersion when formed in a flat band, which is unlike the\nhighly-dispersive spectrum of its dimers."
    },
    {
        "anchor": "Feshbach molecule formation through an oscillating magnetic field:\n  subharmonic resonances: The conversion of ultracold atoms to molecules via a magnetic Feshbach\nresonance with a sinusoidal modulation of the field is studied. Different\npractical realizations of this method in Bose atomic gases are analyzed. Our\nmodel incorporates many-body effects through an effective reduction of the\ncomplete microscopic dynamics. Moreover, we simulate the experimental\nconditions corresponding to the preparation of the system as a thermal gas and\nas a condensate. Some of the experimental findings are clarified. The origin of\nthe observed dependence of the production efficiency on the frequency,\namplitude, and application time of the magnetic modulation is elucidated. Our\nresults uncover also the role of the atomic density in the dynamics,\nspecifically, in the observed saturation of the atom-molecule conversion\nprocess.",
        "positive": "Emergence and disruption of spin-charge separation in one-dimensional\n  repulsive fermions: At low temperature, collective excitations of one-dimensional (1D)\ninteracting fermions exhibit spin-charge separation, a unique feature predicted\nby the Tomonaga-Luttinger liquid (TLL) theory, but a rigorous understanding\nremains challenging. Using the thermodynamic Bethe Ansatz (TBA) formalism, we\nanalytically derive universal properties of a 1D repulsive spin-1/2 Fermi gas\nwith arbitrary interaction strength. We show how spin-charge separation emerges\nfrom the exact TBA formalism, and how it is disrupted by the interplay between\nthe two degrees of freedom which brings us beyond the TLL paradigm. Based on\nthe exact low-lying excitation spectra, we further evaluate the spin and charge\ndynamical structure factors (DSFs). The peaks of the DSFs exhibit\ndistinguishable propagating velocities of spin and charge as functions of\ninteraction strength, which can be observed by Bragg spectroscopy with\nultracold atoms."
    },
    {
        "anchor": "Finite temperature instabilities of 2D dipolar Bose gas at arbitrary\n  tilt angle: Advances in creating stable dipolar Bose systems, and ingenious box traps\nhave generated tremendous interest. Theory study of dipolar bosons at finite\ntemperature (T) has been limited. Motivated by these, we study 2D dipolar\nbosons at arbitrary tilt angle, $\\theta$, using finite-T random phase\napproximation. We show that a comprehensive understanding of phases and\ninstabilities at non-zero T can be obtained on concurrently considering dipole\nstrength, density, temperature and $\\theta$. We find the system to be in a\nhomogeneous non-condensed phase that undergoes a collapse transition at large\n$\\theta$, and a finite momentum instability, signaling a striped phase, at\nlarge dipolar strength; there are important differences with the T=0 case. At T\n= 0, BEC appears at critical dipolar strength, and at critical density. Our\npredictions for polar molecule system, $^{41}K^{87}Rb$, and $^{166}Er$ may\nprovide tests of our results. Our approach may apply broadly to systems with\nlong-range, anisotropic interactions.",
        "positive": "Wannier solitons in spin-orbit-coupled Bose-Einstein condensates in\n  optical lattices with a flat-band: We investigate families of soliton solutions in a spin-orbit coupled\nBose-Einstein condensate embedded in an optical lattice, which bifurcate from\nthe nearly flat lowest band. Unlike the conventional gap solitons the obtained\nsolutions have the shape well approximated by a Wannier function (or a few\nWannier functions) of the underlying linear Hamiltonian with amplitudes varying\nalong the family and with nearly constant widths. The Wannier solitons (WSs)\nsharing all symmetries of the system Hamiltonian are found to be stable. Such\nsolutions allow for the construction of Wannier breathers, that can be viewed\nas nonlinearly coupled one-hump solitons. The breathers are well described by a\nfew-mode model and manifest stable behavior either in an oscillatory regime\nwith balanced average populations or in a self-trapping regime characterized by\nunbalanced atomic populations of the local potential minima (similarly to the\nconventional boson Josephson junction), with the frequencies controlled by the\ninter-atomic interactions."
    },
    {
        "anchor": "Particle number fractionalization of a one-dimensional atomic Fermi gas\n  with synthetic spin-orbit coupling: We propose an experimental scheme to simulate the fractionalization of\nparticle number by using a one-dimensional spin-orbit coupled ultracold\nfermionic gas. The wanted spin-orbit coupling, a kink-like potential, and a\nconjugation-symmetry-breaking mass term are properly constructed by laser-atom\ninteractions, leading to an effective low-energy relativistic Dirac Hamiltonian\nwith a topologically nontrivial background field. The designed system supports\na localized soliton excitation with a fractional particle number that is\ngenerally irrational and experimentally tunable, providing a direct realization\nof the celebrated generalized-Su-Schrieffer-Heeger model. In addition, we\nelaborate on how to detect the induced soliton mode with the FPN in the system.",
        "positive": "Color-charge separation in trapped SU(3) fermionic atoms: Cold fermionic atoms with three different hyperfine states with\n  SU(3) symmetry confined in one-dimensional optical lattices show color-charge\nseparation, generalizing the conventional spin charge separation for\ninteracting SU(2) fermions in one dimension. Through time-dependent DMRG\nsimulations, we explore the features of this phenomenon for a generalized SU(3)\nHubbard Hamiltonian. In our numerical simulations of finite size systems, we\nobserve different velocities of the charge and color degrees of freedom when a\nGaussian wave packet or a charge (color) density response to a local\nperturbation is evolved. The differences between attractive and repulsive\ninteractions are explored and we note that neither a small anisotropy of the\ninteraction, breaking the SU(3) symmetry, nor the filling impedes the basic\nobservation of these effects."
    },
    {
        "anchor": "Parallel Transport and Band Theory in Crystals: We show that different conventions for Bloch Hamiltonians on non-Bravais\nlattices correspond to different natural definitions of parallel transport of\nBloch eigenstates. Generically the Berry curvatures associated with these\nparallel transports differ, while physical quantities are naturally related to\na canonical choice of the parallel transport.",
        "positive": "Controlled localization of interacting bosons in a disordered optical\n  lattice: We show that tunneling and localization properties of interacting ultracold\natoms in an optical lattice can be controlled by adiabatically turning on a\nfast oscillatory force even in the presence of disorder. Our calculations are\nbased on the exact solution of the time-dependent Schroedinger equation, using\nthe Floquet formalism. Implications of our findings for larger systems and the\npossibility of controlling the phase diagram of disordered-interacting bosonic\nsystems are discussed."
    },
    {
        "anchor": "BCS-BEC crossover and quantum phase transition in an ultracold Fermi gas\n  under spin-orbit coupling: In this work, we study the BCS-BEC crossover and quantum phase transition in\na Fermi gas under Rashba spin-orbit coupling close to a Feshbach resonance. By\nadopting a two-channel model, we take into account of the closed channel\nmolecules, and show that combined with spin-orbit coupling, a finite background\nscattering in the open channel can lead to two branches of solution for both\nthe two-body and the many-body ground states. The branching of the two-body\nbound state solution originates from the avoided crossing between bound states\nin the open and the closed channels, respectively. For the many-body states, we\nidentify a quantum phase transition in the upper branch regardless of the sign\nof the background scattering length, which is in clear contrast to the case\nwithout spin-orbit coupling. For systems with negative background scattering\nlength in particular, we show that the bound state in the open channel, and\nhence the quantum phase transition in the upper branch, are induced by\nspin-orbit coupling. We then characterize the critical detuning of the quantum\nphase transition for both positive and negative background scattering lengths,\nand demonstrate the optimal parameters for the critical point to be probed\nexperimentally.",
        "positive": "Effective-Range Dependence of Resonantly Interacting Fermions: We extract the leading effective range corrections to the equation of state\nof the unitary Fermi gas from ab initio fixed-node quantum Monte Carlo (FNQMC)\ncalculations in a periodic box using a density functional theory (DFT), and\nshow them to be universal by considering several two-body interactions.\nFurthermore, we find that the DFT is consistent with the best available\nunbiased QMC calculations, analytic results, and experimental measurements of\nthe equation of state. We also discuss the asymptotic effective-range\ncorrections for trapped systems and present the first QMC results with the\ncorrect asymptotic scaling."
    },
    {
        "anchor": "Ultra-precise holographic beam shaping for microscopic quantum control: High-resolution addressing of individual ultracold atoms, trapped ions or\nsolid state emitters allows for exquisite control in quantum optics\nexperiments. This becomes possible through large aperture magnifying optics\nthat project microscopic light patterns with diffraction limited performance.\nWe use programmable amplitude holograms generated on a digital micromirror\ndevice to create arbitrary microscopic beam shapes with full phase and\namplitude control. The system self-corrects for aberrations of up to several\n$\\lambda$ and reduces them to $\\lambda/50$, leading to light patterns with a\nprecision on the $10^{-4}$ level. We demonstrate aberration-compensated beam\nshaping in an optical lattice experiment and perform single-site addressing in\na quantum gas microscope for $^{87}$Rb.",
        "positive": "Counter-flow instability of a quantum mixture of two superfluids: We study the instability of a mixture of two interacting counter-flowing\nsuperfluids. For a homogeneous system, we show that superfluid hydrodynamics\nleads to the existence of a dynamical instability at a critical value of the\nrelative velocity $v_{cr}$. When the interspecies coupling is small the\ncritical value approaches the value $v_{cr}=c_1+c_2$, given by the sum of the\nsound velocities of the two uncoupled superfluids, in agreement with the recent\nprediction of [1] based on Landau's argument. The crucial dependence of the\ncritical velocity on the interspecies coupling is explicitly discussed. Our\nresults agree with previous predictions for weakly interacting Bose-Bose\nmixtures and applies to Bose-Fermi superfluid mixtures as well. Results for the\nstability of transversally trapped mixtures are also presented."
    },
    {
        "anchor": "Fermionic transport in a homogeneous Hubbard model: Out-of-equilibrium\n  dynamics with ultracold atoms: Transport properties are among the defining characteristics of many important\nphases in condensed matter physics. In the presence of strong correlations they\nare difficult to predict even for model systems like the Hubbard model. In real\nmaterials they are in general obscured by additional complications including\nimpurities, lattice defects or multi-band effects. Ultracold atoms in contrast\noffer the possibility to study transport and out-of-equilibrium phenomena in a\nclean and well-controlled environment and can therefore act as a quantum\nsimulator for condensed matter systems. Here we studied the expansion of an\ninitially confined fermionic quantum gas in the lowest band of a homogeneous\noptical lattice. While we observe ballistic transport for non-interacting\natoms, even small interactions render the expansion almost bimodal with a\ndramatically reduced expansion velocity. The dynamics is independent of the\nsign of the interaction, revealing a novel, dynamic symmetry of the Hubbard\nmodel.",
        "positive": "Single-Spin Addressing in an Atomic Mott Insulator: Ultracold atoms in optical lattices are a versatile tool to investigate\nfundamental properties of quantum many body systems. In particular, the high\ndegree of control of experimental parameters has allowed the study of many\ninteresting phenomena such as quantum phase transitions and quantum spin\ndynamics. Here we demonstrate how such control can be extended down to the most\nfundamental level of a single spin at a specific site of an optical lattice.\nUsing a tightly focussed laser beam together with a microwave field, we were\nable to flip the spin of individual atoms in a Mott insulator with\nsub-diffraction-limited resolution, well below the lattice spacing. The Mott\ninsulator provided us with a large two-dimensional array of perfectly arranged\natoms, in which we created arbitrary spin patterns by sequentially addressing\nselected lattice sites after freezing out the atom distribution. We directly\nmonitored the tunnelling quantum dynamics of single atoms in the lattice\nprepared along a single line and observed that our addressing scheme leaves the\natoms in the motional ground state. Our results open the path to a wide range\nof novel applications from quantum dynamics of spin impurities, entropy\ntransport, implementation of novel cooling schemes, and engineering of quantum\nmany-body phases to quantum information processing."
    },
    {
        "anchor": "Superfluid to normal phase transition in strongly correlated bosons in\n  two and three dimensions: Using quantum Monte Carlo simulations, we investigate the finite-temperature\nphase diagram of hard-core bosons (XY model) in two- and three-dimensional\nlattices. To determine the phase boundaries, we perform a finite-size-scaling\nanalysis of the condensate fraction and/or the superfluid stiffness. We then\ndiscuss how these phase diagrams can be measured in experiments with trapped\nultracold gases, where the systems are inhomogeneous. For that, we introduce a\nmethod based on the measurement of the zero-momentum occupation, which is\nadequate for experiments dealing with both homogeneous and trapped systems, and\ncompare it with previously proposed approaches.",
        "positive": "Chemistry of a light impurity in a Bose-Einstein condensate: In ultracold atomic gases, a unique interplay arises between phenomena known\nfrom condensed matter physics, few-body physics and chemistry. Similar to an\nelectron in a solid, an impurity in an ultracold gas can get dressed by\nexcitations from the medium, forming a quasiparticle called the polaron. We\nstudy how dressing of an impurity leads to a modification of its chemical\nreactivity. Using a Gaussian state variational method in the frame of the\nimpurity, we demonstrate that three-body correlations lead to an instability of\nthe polaron. This instability is connected to an Efimov resonance, but shifted\nto smaller interactions by many-body effects, showing that polaron formation\nstimulates Efimov physics and the associated chemistry."
    },
    {
        "anchor": "Spin oscillations of the normal polarized Fermi gas at Unitarity: Using density functional theory in a time dependent approach we determine the\nfrequencies of the compressional modes of the normal phase of a Fermi gas at\nunitarity as a function of its polarization. Our energy functional accounts for\nthe typical elastic deformations exhibited by Landau theory of Fermi liquids.\nThe comparison with the available experiments is biased by important\ncollisional effects affecting both the {\\it in phase} and the {\\it out of\nphase} oscillations even at the lowest temperatures. New experiments in the\ncollisionless regime would provide a crucial test of the applicability of\nLandau theory to the dynamics of these strongly interacting normal Fermi gases.",
        "positive": "How to make a quantum black hole with ultra-cold gases: The realization of quantum field theories on an optical lattice is an\nimportant subject toward the quantum simulation. We argue that such efforts\nwould lead to the experimental realizations of quantum black holes. The basic\nidea is to construct non-gravitational systems which are equivalent to the\nquantum gravitational systems via the holographic principle. Here the\n`equivalence' means that two theories cannot be distinguished even in\nprinciple. Therefore, if the holographic principle is true, one can create\nactual quantum black holes by engineering the non-gravitational systems on an\noptical lattice. In this presentation, we consider the simplest example: the\nSachdev-Ye-Kitaev (SYK) model. We design an experimental scheme for creating\nthe SYK model with use of ultra-cold fermionic atoms such as Lithium-6."
    },
    {
        "anchor": "Geometric scale invariance as a route to macroscopic degeneracy: loading\n  a toroidal trap with a Bose or Fermi gas: An easily scalable toroidal geometry presents an opportunity for creating\nlarge scale persistent currents in Bose-Einstein condensates, for studies of\nthe Kibble-Zurek mechanism, and for investigations of toroidally trapped\ndegenerate Fermi gases. We consider in detail the process of isentropic loading\nof a Bose or Fermi gas from a harmonic trap into the scale invariant toroidal\nregime that exhibits a high degree of system invariance when increasing the\nradius of the toroid. The heating involved in loading a Bose gas is evaluated\nanalytically and numerically, both above and below the critical temperature.\nOur numerical calculations treat interactions within the\nHartree-Fock-Bogoliubov-Popov theory. Minimal change in degeneracy is observed\nover a wide range of initial temperatures, and a regime of cooling is\nidentified. The scale invariant property is further investigated analytically\nby studying the density of states of the system, revealing the robust nature of\nscale invariance in this trap, for both bosons and fermions. We give analytical\nresults for a Thomas-Fermi treatment. We calculate the heating due to loading a\nspin-polarized Fermi gas and compare with analytical results for high and low\ntemperature regimes. The Fermi gas is subjected to irreducible heating during\nloading, caused by the loss of one degree of freedom for thermalization.",
        "positive": "Phonon Laser Effect and Dicke-Hepp-Lieb Superradiant Phase Transition in\n  Magnetic Cantilever Coupled to a Bose Einstein Condensate: We propose a possibility of a phonon laser by coupling a Bose-Einstein\ncondensate to a nanomechanical cantilever with a magnetic tip. Due to the\nmagnetic coupling, atomic spin flips induce cantilever motion which can be used\nto produce a phonon laser. The system is described by the equivalent of the\nJaynes-Cummings Hamiltonian. By controlling the number of atoms and the\npopulation inversion, one can obtain either a continuous wave (cw) or transient\nlasing. The two-body atom-atom interaction is also shown to coherently\nmanipulate the lasing process. We also show that in the strong coupling limit,\nthe same system can undergo a Dicke-Hepp-Lieb superradiant phase transition.\nExotic phase diagrams can be obtained by tuning the two body atom-atom\ninteraction."
    },
    {
        "anchor": "Multimode analysis of non-classical correlations in double well\n  Bose-Einstein condensates: The observation of non-classical correlations arising in interacting two to\nsize weakly coupled Bose-Einstein condensates was recently reported by Esteve\net al. [Nature 455, 1216 (2008)]. In order to observe fluctuations below the\nstandard quantum limit, they utilized adiabatic passage to reduce the thermal\nnoise to below that of thermal equilibrium at the minimum realizable\ntemperature. We present a theoretical analysis that takes into account the\nspatial degrees of freedom of the system, allowing us to calculate the expected\ncorrelations at finite temperature in the system, and to verify the hypothesis\nof adiabatic passage by comparing the dynamics to the idealized model.",
        "positive": "Breaking inversion symmetry in a state-dependent honeycomb lattice:\n  Artificial graphene with tunable band gap: Here, we present the application of a novel method for controlling the\ngeometry of a state-dependent honeycomb lattice: The energy offset between the\ntwo sublattices of the honeycomb structure can be adjusted by rotating the\natomic quantization axis. This enables us to continuously tune between a\nhomogeneous graphene-like honeycomb lattice and a triangular lattice and to\nopen an energy gap at the characteristic Dirac points. We probe the symmetry of\nthe lattice with microwave spectroscopy techniques and investigate the behavior\nof atoms excited to the second energy band. We find a striking influence of the\nenergy gap at the Dirac cones onto the lifetimes of atoms in the excited band."
    },
    {
        "anchor": "Noise-induced transition from superfluid to vortex state in\n  two-dimensional nonequilibrium polariton condensates -- semi-analytical\n  treatment: We develop a semi-analytical description for the\nBerezinskii-Kosterlitz-Thouless (BKT) like phase transition in nonequilibrium\nBose-Einstein condensates. Our theoretical analysis is based on a noisy\ngeneralized Gross-Pitaevskii equation. Above a critical strength of the noise,\nspontaneous vortex-antivortex pairs are generated. We provide a semi-analytical\ndetermination of the transition point based on a linearized Bogoliubov\nanalysis, to which some nonlinear corrections are added. We present two\ndifferent approaches that are in agreement with our numerical calculations in a\nwide range of system parameters. We find that for small losses and not too\nsmall energy relaxation, the critical point approaches that of the equilibrium\nBKT transition. Furthermore, we find that losses tend to stabilize the ordered\nphase: keeping the other parameters constant and increasing the losses leads to\na higher critical noise strength for the spontaneous generation of\nvortex-antivortex pairs. Our theoretical analysis is relevant for experiments\non microcavity polaritons.",
        "positive": "Integrable supersymmetric chain without particle conservation: We introduce a new integrable supersymmetric lattice chain which violates\nfermion conservation and exhibits fermion-hole symmetry. The model displays\nexponential degeneracy in every eigenstate including the groundstate. This\ndegeneracy is expressed in the possibility to create any number of zero modes\nreminiscent of Cooper pairs."
    },
    {
        "anchor": "Spontaneous dipolar Bose-Einstein condensation on the surface of a\n  cylinder: We demonstrate the spontaneous formation of a Bose-Einstein condensate (BEC)\nof strongly-bound harmonically-trapped dipolar $^{164}$Dy atoms on the outer\ncurved surface of an elliptical or a circular cylinder, with a distinct\ntopology, employing the numerical solution of an improved mean-field model\nincluding a Lee-Huang-Yang-type interaction, meant to stop a collapse at high\natom density, the axis of the cylindrical-shell-shaped BEC being aligned along\nthe polarization direction of the dipolar atoms. These states are dynamically\nstable and a Gaussian initial state leads to the cylindrical-shell-shaped state\nin both imaginary-time and real-time propagation. The formation of the hollow\ncylindrical BEC by a real-time simulation starting from a solid cylindrical\nstate demonstrate the possibility of the formation of such a condensate\nexperimentally.",
        "positive": "Tuning the Kosterlitz-Thouless transition to zero temperature in\n  Anisotropic Boson Systems: We study the two-dimensional Bose-Hubbard model with anisotropic hopping.\nFocusing on the effects of anisotropy on the superfluid properties such like\nthe helicity modulus and the normal-to-superfluid\n(Berezinskii-Kosterlitz-Thouless, BKT) transition temperature, two different\napproaches are compared: Large-scale Quantum Monte Carlo simulations and the\nself-consistent harmonic approximation (SCHA). For the latter, two different\nformulations are considered, one applying near the isotropic limit and the\nother applying in the extremely anisotropic limit. Thus we find that the SCHA\nprovides a reasonable description of superfluid properties of this system\nprovided the appropriate type of formulation is employed. The accuracy of the\nSCHA in the extremely anisotropic limit, where the BKT transition temperature\nis tuned to zero (i.e. into a Quantum critical point) and therefore quantum\nfluctuations play a dominant role, is particularly striking."
    },
    {
        "anchor": "Sum rules, dipole oscillation and spin polarizability of a spin-orbit\n  coupled quantum gas: Using a sum rule approach we investigate the dipole oscillation of a\nspin-orbit coupled Bose-Einstein condensate confined in a harmonic trap. The\ncrucial role played by the spin polarizability of the gas is pointed out. We\nshow that the lowest dipole frequency exhibits a characteristic jump at the\ntransition between the stripe and spin-polarized phase. Near the second order\ntransition between the spin-polarized and the single minimum phase the lowest\nfrequency is vanishingly small for large condensates, reflecting the divergent\nbehavior of the spin polarizability. We compare our results with recent\nexperimental measurements as well as with the predictions of effective mass\napproximation.",
        "positive": "Emergent eigenstate solution and emergent Gibbs ensemble for expansion\n  dynamics in optical lattices: Within the emergent eigenstate solution to quantum dynamics [Phys. Rev. X 7,\n021012 (2017)], one can construct a local operator (an emergent Hamiltonian) of\nwhich the time-evolving state is an eigenstate. Here we show that such a\nsolution exists for the expansion dynamics of Tonks-Girardeau gases in optical\nlattices after turning off power-law (e.g., harmonic or quartic) confining\npotentials, which are geometric quenches that do not involve the boost\noperator. For systems that are initially in the ground state and undergo\ndynamical fermionization during the expansion, we show that they remain in the\nground state of the emergent local Hamiltonian at all times. On the other hand,\nfor systems at nonzero initial temperatures, the expansion dynamics can be\ndescribed constructing a Gibbs ensemble for the emergent local Hamiltonian (an\nemergent Gibbs ensemble)."
    },
    {
        "anchor": "Quasimomentum of an elementary excitation for a system of point bosons\n  under zero boundary conditions: As is known, an elementary excitation of a many-particle system with\nboundaries is not characterized by a definite momentum. We obtain the formula\nfor the quasimomentum of an elementary excitation for a one-dimensional system\nof $N$ spinless point bosons under zero boundary conditions (BCs). In this\ncase, we use the Gaudin's solutions obtained with the help of the Bethe ansatz.\nWe have also found the dispersion laws of the particle-like and hole-like\nexcitations under zero BCs. They coincide with the known dispersion laws\nobtained for periodic BCs.",
        "positive": "Resonant Spin Exchange between Heteronuclear Atoms Assisted by Periodic\n  Driving: We propose a general scheme for inducing resonant exchange between spins or\npseudo-spins of unmatched levels via periodic driving. The basic idea is\nillustrated for a system of two heteronuclear atoms, for which analytical\nresults are provided for the effective spin exchange (SE) interaction strength.\nIt is then applied to the mixture of 23Na and 87Rb atoms with a radio-frequency\n(rf) or microwave field near-resonant to the mismatched Zeeman level spacings.\nSE interaction engineered this way is applicable to ultracold quantum gas\nmixtures involving spinor Bose-Bose, Bose-Fermi, and Fermi-Fermi atoms."
    },
    {
        "anchor": "Compressibility of a fermionic Mott insulator of ultracold atoms: We characterize the Mott insulating regime of a repulsively interacting Fermi\ngas of ultracold atoms in a three-dimensional optical lattice. We use in-situ\nimaging to extract the central density of the gas, and to determine its local\ncompressibility. For intermediate to strong interactions, we observe the\nemergence of a plateau in the density as a function of atom number, and a\nreduction of the compressibility at a density of one atom per site, indicating\nthe formation of a Mott insulator. Comparisons to state-of-the-art numerical\nsimulations of the Hubbard model over a wide range of interactions reveal that\nthe temperature of the gas is of the order of, or below, the tunneling energy\nscale. Our results hold great promise for the exploration of many-body\nphenomena with ultracold atoms, where the local compressibility can be a useful\ntool to detect signatures of different phases or phase boundaries at specific\nvalues of the filling.",
        "positive": "Measuring the Hydrodynamic Linear Response of a Unitary Fermi Gas: We directly observe the hydrodynamic linear response of a unitary Fermi gas\nconfined in a box potential and subject to a spatially periodic optical\npotential that is translated into the cloud at speeds ranging from subsonic to\nsupersonic. We show that the time-dependent change of the density profile is\nsensitive to the thermal conductivity, which controls the relaxation rate of\nthe temperature gradients and hence the responses arising from adiabatic and\nisothermal compression."
    },
    {
        "anchor": "How does a magnetic trap work?: Magnetic trapping is a cornerstone for modern ultracold physics and its\napplications (e.g., quantum information processing, quantum metrology, quantum\noptics, or high-resolution spectroscopies). Here a comprehensive analysis and\ndiscussion of the basic physics behind the most commonly used magnetic traps in\nBose-Einstein condensation is presented. This analysis includes the quadrupole\ntrap, the time-averaged orbiting potential trap, and the Ioffe-Pritchard trap.\nIt is shown how the trapping conditions and efficiency of these devices can be\ndetermined from simple derivations based on classical electromagnetism, even\nthough they operate on quantum objects.",
        "positive": "Large-area $^{87}$Rb Bose-Einstein condensate in a clipped-Gaussian\n  optical dipole trap: We demonstrate a production of large-area $^{87}$Rb Bose-Einstein condensates\n(BECs) using a non-Gaussian optical dipole trap (ODT). The ODT is formed by\nfocusing a symmetrically truncated Gaussian laser beam and it is shown that the\nbeam clipping causes the trap geometry elongated and flattened along the beam\naxis direction. In the clipped-Gaussian ODT, an elongated, highly oblate BEC of\n$^{87}$Rb is generated with length and width of approximately\n$470~\\mu\\textrm{m}$ and $130~\\mu\\textrm{m}$, respectively, where the condensate\nhealing length is estimated to be $\\xi\\approx 0.25~\\mu\\textrm{m}$ at the trap\ncenter. The ODT is characterized to have a quartic trapping potential along the\nbeam axis and the atom density of the condensate is uniform within 10% over\n$1000\\xi$ in the central region. Finally, we discuss the prospect of conducting\nvortex shedding experiments using the elongated condensate."
    },
    {
        "anchor": "Spin evolution of cold atomic gases in SU(2)$\\otimes $U(1) fields: We consider response function and spin evolution in spin-orbit coupled cold\natomic gases in a synthetic gauge magnetic field influencing solely the orbital\nmotion of atoms. We demonstrate that various regimes of spin-orbit coupling\nstrength, magnetic field, and disorder can be treated within a single approach\nbased on the representation of atomic motion in terms of auxiliary collective\nclassical trajectories. Our approach allows for a unified description of\nfermionic and bosonic gases.",
        "positive": "Geodesic Paths for Quantum Many-Body Systems: We propose a method to obtain optimal protocols for adiabatic ground-state\npreparation near the adiabatic limit, extending earlier ideas from [D. A. Sivak\nand G. E. Crooks, Phys. Rev. Lett. 108, 190602 (2012)] to quantum\nnon-dissipative systems. The space of controllable parameters of isolated\nquantum many-body systems is endowed with a Riemannian quantum metric\nstructure, which can be exploited when such systems are driven adiabatically.\nHere, we use this metric structure to construct optimal protocols in order to\naccomplish the task of adiabatic ground-state preparation in a fixed amount of\ntime. Such optimal protocols are shown to be geodesics on the parameter\nmanifold, maximizing the local fidelity. Physically, such protocols minimize\nthe average energy fluctuations along the path. Our findings are illustrated on\nthe Landau-Zener model and the anisotropic XY spin chain. In both cases we show\nthat geodesic protocols drastically improve the final fidelity. Moreover, this\nhappens even if one crosses a critical point, where the adiabatic perturbation\ntheory fails."
    },
    {
        "anchor": "Polarization in a three-dimensional Fermi gas with Rabi coupling: We investigate the polarization of a two-component three-dimensional\nfermionic gas made of repulsive alkali-metal atoms. The two pseudo-spin\ncomponents correspond to two hyperfine states which are Rabi coupled. The\npresence of Rabi coupling implies that only the total number of atoms is\nconserved and a quantum phase transition between states dominated by\nspin-polarization along different axses is possible. By using a variational\nHartree-Fock scheme we calculate analytically the ground-state energy of the\nsystem and determine analytically and numerically the conditions under which\nthere is this quantum phase transition. This scheme includes the well-known\ncriterion for the Stoner instability. The obtained phase diagram clearly shows\nthat the polarized phase crucially depends on the interplay among the Rabi\ncoupling energy, the interaction energy per particle, and the kinetic energy\nper particle.",
        "positive": "Thermoelectricity modeling with cold dipole atoms in Aubry phase of\n  optical lattice: We study analytically and numerically the thermoelectric properties of a\nchain of cold atoms with dipole-dipole interactions placed in an optical\nperiodic potential. At small potential amplitudes the chain slides freely that\ncorresponds to the Kolmogorov-Arnold-Moser phase of integrable curves of a\nsymplectic map. Above a certain critical amplitude the chain is pinned by the\nlattice being in the cantori Aubry phase. We show that the Aubry phase is\ncharacterized by exceptional thermoelectric properties with the figure of merit\nZT = 25 being ten times larger than the maximal value reached in material\nscience experiments. We show that this system is well accessible for\nmagneto-dipole cold atom experiments that opens new prospects for\ninvestigations of thermoelectricity."
    },
    {
        "anchor": "An atom optics approach to studying lattice transport phenomena: We present a simple experimental scheme, based on standard atom optics\ntechniques, to design highly versatile model systems for the study of single\nparticle quantum transport phenomena. The scheme is based on a discrete set of\nfree-particle momentum states that are coupled via momentum-changing two-photon\nBragg transitions, driven by pairs of interfering laser beams. In the effective\nlattice models that are accessible, this scheme allows for single-site\ndetection, as well as site-resolved and dynamical control over all system\nparameters. We discuss two possible implementations, based on state-preserving\nBragg transitions and on state-changing Raman transitions, which respectively\nallow for the study of nearly arbitrary single particle Abelian U(1) and\nnon-Abelian U(2) lattice models.",
        "positive": "Bose polaron in spherical trap potentials: Spatial structure and quantum\n  depletion: We investigate how the presence of a localized impurity in a Bose-Einstein\ncondensate of trapped cold atoms that interact with each other weakly and\nrepulsively affects the profile of the condensed and excited components at zero\ntemperature. By solving the Gross-Pitaevskii and Bogoliubov-de Gennes\nequations, we find that an impurity-boson contact attraction (repulsion) causes\nboth components to change in spatial structure in such a way as to be enhanced\n(suppressed) around the impurity, while slightly declining (growing) in a far\nregion from the impurity. Such behavior of the quantum depletion of the\ncondensate can be understood by decomposing the impurity-induced change in the\nprofile of the excited component with respect to the radial and azimuthal\nquantum number. A significant role of the centrifugal potential and the \"hole\"\nexcitation level is thus clarified."
    },
    {
        "anchor": "Unconventional superfluidity and quantum geometry of topological bosons: We investigate superfluidity of bosons in gapped topological bands and\ndiscover a new phase that has no counterparts in the previous literature. This\nphase is characterized by a highly unconventional modulation of the order\nparameter, breaking the crystallographic symmetry, and for which the\ncondensation momentum is neither zero nor any other high-symmetry vector of the\nBrillouin zone. This unconventional structure impacts the spectrum of\nBogoliubov excitations and, consequently, the speed of sound in the system.\nEven in the case of perfectly flat bands, the speed of sound and Bogoliubov\nexcitations remain nonvanishing, provided that the underlying topology and\nquantum geometry are nontrivial. Furthermore, we derive detailed expressions\nfor the superfluid weight using the Popov hydrodynamic formalism for\nsuperfluidity and provide estimates for the Berezinskii-Kosterlitz-Thouless\ntemperature, which is significantly enhanced by the nontriviality of the\nunderlying quantum metric. These results are applicable to generic topological\nbosonic bands, with or without dispersion. To illustrate our findings, we\nemploy the Haldane model with a tunable bandwidth, including the narrow\nlowest-band case. Within this model, we also observe a re-entrant superfluid\nbehavior: As the Haldane's magnetic flux is varied, the\nBerezinskii-Kosterlitz-Thouless transition temperature initially decreases to\nalmost zero, only to resurface with renewed vigor.",
        "positive": "Angular Momentum of a Bose-Einstein Condensate in a Synthetic Rotational\n  Field: By applying a position-dependent detuning to a spin-orbit-coupled Hamiltonian\nwith equal Rashba and Dresselhaus coupling, we exploit the behavior of the\nangular momentum of a harmonically trapped Bose-Einstein condensed atomic gas\nand discuss the distinctive role of its canonical and spin components. By\ndeveloping the formalism of spinor hydrodynamics we predict the precession of\nthe dipole oscillation caused by the synthetic rotational field, in analogy\nwith the precession of the Foucault pendulum, the excitation of the scissors\nmode, following the sudden switching off of the detuning, and the occurrence of\nHall-like effects. When the detuning exceeds a critical value we observe a\ntransition from a vortex free, rigidly rotating quantum gas to a gas containing\nvortices with negative circulation which results in a significant reduction of\nthe total angular momentum."
    },
    {
        "anchor": "Shell potentials for microgravity Bose-Einstein condensates: Extending the understanding of Bose-Einstein condensate (BEC) physics to new\ngeometries and topologies has a long and varied history in ultracold atomic\nphysics. One such new geometry is that of a bubble, where a condensate would be\nconfined to the surface of an ellipsoidal shell. Study of this geometry would\ngive insight into new collective modes, self-interference effects,\ntopology-dependent vortex behavior, dimensionality crossovers from thick to\nthin shells, and the properties of condensates pushed into the ultradilute\nlimit. Here we discuss a proposal to implement a realistic experimental\nframework for generating shell-geometry BEC using radiofrequency dressing of\nmagnetically-trapped samples. Such a tantalizing state of matter is\ninaccessible terrestrially due to the distorting effect of gravity on\nexperimentally-feasible shell potentials. The debut of an orbital BEC machine\n(NASA Cold Atom Laboratory, aboard the International Space Station) has enabled\nthe operation of quantum-gas experiments in a regime of perpetual freefall, and\nthus has permitted the planning of microgravity shell-geometry BEC experiments.\nWe discuss specific experimental configurations, applicable inhomogeneities and\nother experimental challenges, and outline potential experiments.",
        "positive": "Exciton-Polariton Quantum Simulators: A quantum simulator is a purposeful quantum machine that can address complex\nquantum problems in a controllable setting and an efficient manner. This\nchapter introduces a solid-state quantum simulator platform based on\nexciton-polaritons, which are hybrid light-matter quantum quasi-particles. We\ndescribe the physical realization of an exciton-polariton quantum simulator in\nsemiconductor materials (hardware) and discuss a class of problems, which the\nexciton-polariton quantum simulators can address well (software). A current\nstatus of the experimental progress in building the quantum machine is\nreviewed, and potential applications are considered."
    },
    {
        "anchor": "Condensate formation in a dark state of a driven atom-cavity system: We demonstrate condensate formation in a dark state in an ultracold quantum\ngas coupled to a high-finesse cavity and pumped by a shaken optical lattice. We\nshow experimentally and theoretically that the atoms in the dark state display\na strong suppression of the coupling to the cavity. On the theory side, this is\nsupported by solving the dynamics of a minimal three-level model and of the\nfull atom-cavity system. The symmetry of the condensate wave function is\nanti-symmetric with respect to the potential minima of the pump lattice, and\ndisplays a staggered sign along the cavity direction. This symmetry decouples\nthe dark state from the cavity, and is preserved when the pump intensity is\nswitched off.",
        "positive": "Diffusive-to-ballistic crossover of symmetry violation in open many-body\n  systems: Conservation laws in a quantum many-body system play a direct role in its\ndynamic behavior. Understanding the effect of weakly breaking a conservation\nlaw due to coherent and incoherent errors is thus crucial, e.g., in the\nrealization of reliable quantum simulators. In this work, we perform exact\nnumerics and time-dependent perturbation theory to study the dynamics of\n\\textit{symmetry violation} in quantum many-body systems with slight coherent\n(at strength $\\lambda$) or incoherent (at strength $\\gamma$) breaking of their\nlocal and global symmetries. We rigorously prove the symmetry violation to be a\ndivergence measure in Hilbert space. Based on this, we show that symmetry\nbreaking generically leads to a crossover in the divergence growth from\ndiffusive behavior at onset times to ballistic or hyperballistic scaling at\nintermediate times, before diffusion dominates at long times. More precisely,\nwe show that for local errors the leading coherent contribution to the symmetry\nviolation cannot be of order lower than $\\propto\\lambda t^2$ while its\nleading-order incoherent counterpart is typically of order $\\propto\\gamma t$.\nThis remarkable interplay between unitary and incoherent gauge-breaking\nscalings is also observed at higher orders in projectors onto symmetry\n(super)sectors. Due to its occurrence at short times, the\ndiffusive-to-ballistic crossover is expected to be readily accessible in modern\nultracold-atom and NISQ-device experiments."
    },
    {
        "anchor": "Radiative lifetimes of dipolar excitons in double quantum-wells: Spatially indirect excitons in semiconducting double quantum wells have been\nshown to exhibit rich collective many-body behavior that result from the nature\nof the extended dipole-dipole interactions between particles. For many\nspectroscopic studies of the emission from a system of such indirect excitons,\nit is crucial to separate the single particle properties of the excitons from\nthe many-body effects arising from their mutual interactions. In particular,\nknowledge of the relation between the emission energy of indirect excitons and\ntheir radiative lifetime could be highly beneficial for control, manipulation,\nand analysis of such systems. Here we study a simple analytic approximate\nrelation between the radiative lifetime of indirect excitons and their emission\nenergy. We show, both numerically and experimentally, the validity and the\nlimits of this approximate relation. This relation between the emission energy\nand the lifetime of indirect excitons can be used to tune and determine their\nlifetime and their resulting dynamics without the need of directly measuring\nit, and as a tool for design of indirect exciton based devices.",
        "positive": "Conjectures about the structure of strong- and weak-coupling expansions\n  of a few ground-state observables in the Lieb-Liniger and Yang-Gaudin models: In this paper, we apply experimental number theory to two integrable quantum\nmodels in one dimension, the Lieb-Liniger Bose gas and the Yang-Gaudin Fermi\ngas with contact interactions. We identify patterns in weak- and\nstrong-coupling series expansions of the ground-state energy, local correlation\nfunctions and pressure. Based on the most accurate data available in the\nliterature, we make a few conjectures about their mathematical structure and\nextrapolate to higher orders."
    },
    {
        "anchor": "Magneto-optical trapping of optically pumped metastable europium: We demonstrate laser cooling and magneto-optical trapping of europium. The\natoms are optically pumped to a metastable state and then loaded from an\natomic-beam source via conventional Zeeman slowing and magneto-optical trapping\ntechniques using a $J=13/2\\leftrightarrow J=15/2$ quasi-cyclic transition. The\ntrapped populations contained up to $1\\times 10^7$ atoms, and a two-body loss\nrate is estimated as $1\\times10^{-10}\\,\\mathrm{cm^3/s}$ from the\nnon-exponential loss of atoms at high densities. We also observed leakage out\nof the quasi-cyclic transition to the two metastable states with $J=9/2$ and\n$11/2$, which is adequate to pump the laser-cooled atoms back to the $J=7/2$\nground state.",
        "positive": "$Ab\\,initio$ derivation of lattice gauge theory dynamics for cold gases\n  in optical lattices: We introduce a method for quantum simulation of U$(1)$ lattice gauge theories\ncoupled to matter, utilizing alkaline-earth(-like) atoms in state-dependent\noptical lattices. The proposal enables the study of both gauge and\nfermionic-matter fields without integrating out one of them in one and two\ndimensions. We focus on a realistic and robust implementation that utilizes the\nlong-lived metastable clock state available in alkaline-earth(-like) atomic\nspecies. Starting from an $ab\\,initio$ modelling of the experimental setting,\nwe systematically carry out a derivation of the target U$(1)$ gauge theory.\nThis approach allows us to identify and address conceptual and practical\nchallenges for the implementation of lattice gauge theories that - while\npivotal for a successful implementation - have never been rigorously addressed\nin the literature: those include the specific engineering of lattice potentials\nto achieve the desired structure of Wannier functions, and the subtleties\ninvolved in realizing the proper separation of energy scales to enable\ngauge-invariant dynamics. We discuss realistic experiments that can be carried\nout within such a platform using the fermionic isotope $^{173}$Yb, addressing\nvia simulations all key sources of imperfections, and provide concrete\nparameter estimates for relevant energy scales in both one- and two-dimensional\nsettings."
    },
    {
        "anchor": "Relaxation in an Extended Bosonic Josephson Junction: We present a detailed analysis of the relaxation dynamics in an extended\nbosonic Josephson junction. We show that stochastic classical field simulations\nusing Gross-Pitaevskii equations in three spatial dimensions reproduce the main\nexperimental findings of M. Pigneur et al., Phys. Rev. Lett. 120, 173601\n(2018). We give an analytic solution describing the short time evolution\nthrough multimode dephasing. For longer times, the observed relaxation to a\nphase locked state is caused by nonlinear dynamics beyond the sine-Gordon\nmodel, induced by the longitudinal confinement potential and persisting even at\nzero temperature. Finally, we analyze different experimentally relevant\ntrapping geometries to mitigate these effects. Our results provide the basis\nfor future experimental implementations aiming to study nonlinear and quantum\neffects of the relaxation in extended bosonic Josephson junctions.",
        "positive": "Observation of Density-Induced Tunneling: We study the dynamics of bosonic atoms in a tilted one-dimensional optical\nlattice and report on the first direct observation of density-induced\ntunneling. We show that the interaction affects the time evolution of the\ndoublon oscillation via density-induced tunneling and pinpoint its density- and\ninteraction-dependence. The experimental data for different lattice depths are\nin good agreement with our theoretical model. Furthermore, resonances caused by\nsecond-order tunneling processes are studied, where the density-induced\ntunneling breaks the symmetric behavior for attractive and repulsive\ninteractions predicted by the Hubbard model."
    },
    {
        "anchor": "Galilean boosts and superfluidity of resonantly driven polariton fluids\n  in the presence of an incoherent reservoir: We theoretically investigate how the presence of a reservoir of incoherent\nexcitations affects the superfluidity properties of resonantly driven polariton\nfluids. While in the absence of reservoir the two cases of a defect moving in a\nfluid at rest and of a fluid flowing against a static defect are linked by a\nformal Galilean transformation, here the reservoir defines a privileged\nreference frame attached to the semiconductor structure and causes markedly\ndifferent features between the two settings. The consequences on the critical\nvelocity for superfluidity are highlighted and compared to experiments in\nresonantly driven excitons polaritons.",
        "positive": "An accordion superlattice for controlling atom separation in optical\n  potentials: We propose a method for separating trapped atoms in optical lattices by large\ndistances. The key idea is the cyclic transfer of atoms between two lattices of\nvariable spacing, known as accordion lattices, each covering at least a factor\nof two in lattice spacing. By coherently loading atoms between the two\nsuperimposed potentials, we can reach, in principle, arbitrarily large atom\nseparations, while requiring only a relatively small numerical aperture.\nNumerical simulations of our `accordion superlattice' show that the atoms\nremain localised to one lattice site throughout the separation process, even\nfor moderate lattice depths. In a proof-of-principle experiment we demonstrate\nthe optical fields required for the accordion superlattice using acousto-optic\ndeflectors. The method can be applied to neutral-atom quantum computing with\noptical tweezers, as well as quantum simulation of low-entropy many-body\nstates. For instance, a unit-filling atomic Mott insulator can be coherently\nexpanded by a factor of ten in order to load an optical tweezer array with very\nhigh filling. In turn, sorted tweezer arrays can be compressed to form\nhigh-density states of ultracold atoms in optical lattices. The method can be\nalso be applied to biological systems where dynamical separation of particles\nis required."
    },
    {
        "anchor": "Photonic Architectures for Equilibrium High-Temperature Bose-Einstein\n  Condensation in Dichalcogenide Monolayers: Semiconductor-microcavity polaritons are composite quasiparticles of excitons\nand photons, emerging in the strong coupling regime. As quantum superpositions\nof matter and light, polaritons have much stronger interparticle interactions\ncompared with photons, enabling rapid equilibration and Bose-Einstein\ncondensation (BEC). Current realizations based on 1D photonic structures, such\nas Fabry-P\\'erot microcavities, have limited light-trapping ability resulting\nin picosecond polariton lifetime. We demonstrate, theoretically,\nabove-room-temperature (up to 590 K) BEC of long-lived polaritons in MoSe$_2$\nmonolayers sandwiched by simple TiO$_2$ based 3D photonic band gap (PBG)\nmaterials. The 3D PBG induces very strong coupling of 40 meV (Rabi splitting of\n62 meV) for as few as three dichalcogenide monolayers. Strong light-trapping in\nthe 3D PBG enables the long-lived polariton superfluid to be robust against\nfabrication-induced disorder and exciton line-broadening.",
        "positive": "Bogoliubov-wave turbulence in Bose-Einstein condensates: We theoretically and numerically study Bogoliubov-wave turbulence in\nthree-dimensional atomic Bose-Einstein condensates with the Gross-Pitaevskii\nequation, investigating three spectra for the macroscopic wave function, the\ndensity distribution, and the Bogoliubov-wave distribution. In this turbulence,\nBogoliubov waves play an important role in the behavior of these spectra, so\nthat we call it Bogoliubov-wave turbulence. In a previous study [D. Proment\n\\textit{et al.}, Phys. Rev. A \\textbf{80}, 051603(R) (2009)], a $-3/2$ power\nlaw in the spectrum for the macroscopic wave function was suggested by using\nweak wave turbulence theory, but we find that another $-7/2$ power law appears\nin both theoretical and numerical calculations. Furthermore, we focus on the\nspectrum for the density distribution, which can be observed in experiments,\ndiscussing the possibility of experimental observation. Through these\nanalytical and numerical calculations, we also demonstrate that the previously\nneglected condensate dynamics induced by the Bogoliubov waves is remarkably\nimportant."
    },
    {
        "anchor": "Bose-Einstein Condensation of Excitons in Cu$_2$O: Progress Over Thirty\n  Years: Experiments on Bose-Einstein condensation (BEC) of excitons in the\nsemiconductor Cu$_2$O started over thirty years ago, as one of the first\nserious attempts at exciton BEC. Early claims were based on spectroscopic\nsignatures and transport data which have since been reinterpreted, in large\npart because the Auger recombination process for excitons was not well\nunderstood. Understanding of the Auger process has also advanced, and recent\nexperiments have made significant progress toward exciton BEC. We review the\nhistory of experiments on exciton BEC in Cu$_2$O, the Auger recombination\nprocess, and the prospects for observing exciton BEC in this system in the near\nfuture.",
        "positive": "Abrupt transition between three and two-dimensional quantum turbulence: We present numerical evidence of a critical-like transition in an\nout-of-equilibrium mean-field description of a quantum system. By numerically\nsolving the Gross-Pitaevskii equation we show that quantum turbulence displays\nan abrupt change between three-dimensional (3D) and two-dimensional (2D)\nbehavior. The transition is observed both in quasi-2D flows in cubic domains\n(controlled by the amplitude of a 3D perturbation to the flow), as well as in\nflows in thin domains (controlled by the domain aspect ratio) in a\nconfiguration that mimics systems realized in laboratory experiments. In one\nregime the system displays a transfer of the energy towards smaller scales,\nwhile in the other the system displays a transfer of the energy towards larger\nscales and a coherent self-organization of the quantized vortices."
    },
    {
        "anchor": "Formation of classical crystals of dipolar particles in a helical\n  geometry: We consider crystal formation of particles with dipole-dipole interactions\nthat are confined to move in a one-dimensional helical geometry with their\ndipole moments oriented along the symmetry axis of the confining helix. The\nstable classical lowest energy configurations are found to be chain structures\nfor a large range of pitch-to-radius ratios for relatively low density of\ndipoles and a moderate total number of particles. The classical normal mode\nspectra support the chain interpretation both through structure and the\ndistinct degeneracies depending discretely on the number of dipoles per\nrevolution. A larger total number of dipoles leads to a clusterization where\nthe dipolar chains move closer to each other. This implies a change in the\nlocal density and the emergence of two length scales, one for the cluster size\nand one for the inter-cluster distance along the helix. Starting from three\ndipoles per revolution, this implies a breaking of the initial periodicity to\nform a cluster of two chains close together and a third chain removed from the\ncluster. This is driven by the competition between in-chain and out-of-chain\ninteractions, or alternatively the side-by-side repulsion and the head-to-tail\nattraction in the system. The speed of sound propagates along the chains. It is\nindependent of the number of chains although depending on geometry.",
        "positive": "Numerical Realization of Bethe Rapidities in cold quenched systems by\n  Feynman-Kac path integral method: We apply Quantum Monte Carlo technique to analyze the non equlibrium state of\na trapped 1d Bose gas just after the quenching of the confining potential. As a\nmatter of fact we solve the time dependent Schroedinger equation for the system\nof one-dimensional bosons interacting via delta potential in an infinite square\nwell (namely Lieb-Liniger model) using Feynman-Kac path integral Monte Carlo\ntechnique. These 1d systems are extremely interesting and worth investigating\nin the context of non-equilibrium dynamics of interacting many body systems.\nEven though the systems can be realized experimentally and are exactly solvable\nby Bethe Ansatz, the diffusion Monte Carlo is proven to be more efficient in\nmost circumstances than other mean value techniques as the numerical method can\nincorporate the finite interaction very easily. Using N particle ground state\nwavefunction for one-dimensional hard core bosons in a harmonic trap, we\ndevelop an algorithm to calculate density. We also observe the change in the\ndensity distribution by changing the length of the hard wall box. After an\nincrease in the box length, we still get a self-similar density distribution."
    },
    {
        "anchor": "Dark soliton decay due to trap anharmonicity in atomic Bose-Einstein\n  condensates: A number of recent experiments with nearly pure atomic Bose-Einstein\ncondensates have confirmed the predicted dark soliton oscillations when under\nharmonic trapping. However, a dark soliton propagating in an inhomogeneous\ncondensate has also been predicted to be unstable to the emission of sound\nwaves. Although harmonic trapping supports an equilibrium between the\nco-existing soliton and sound, we show that the ensuing dynamics are sensitive\nto trap anharmonicities. Such anharmonicities can break the soliton-sound\nequilibrium and lead to the net decay of the soliton on a considerably shorter\ntimescale than other dissipation mechanisms. Thus, we propose how small\nrealistic modifications to existing experimental set-ups could enable the\nexperimental observation of this decay channel.",
        "positive": "Domain formation of modulation instability in spin-orbit-Rabi coupled\n  Gross-Pitaevskii equation with cubic-quintic interactions: The effect of two- and three-body interactions on the modulation instability\n(MI) domain formation of a spin-orbit (SO) and Rabi-coupled Bose-Einstein\ncondensate is studied within a quasi-one-dimensional model. To this aim, we\nperform numerical and analytical investigations of the associated dispersion\nrelations derived from the corresponding coupled Gross-Pitaevskii equation. The\ninterplay between the linear (SO and Rabi) couplings with the nonlinear\ncubic-quintic interactions are explored in the mixture, considering miscible\nand immiscible configurations, with a focus on the impact in the analysis of\nexperimental realizations with general binary coupled systems, in which\nnonlinear interactions can be widely varied together with linear couplings."
    },
    {
        "anchor": "The equation of state of ultracold Bose and Fermi gases: a few examples: We describe a powerful method for determining the equation of state of an\nultracold gas from in situ images. The method provides a measurement of the\nlocal pressure of an harmonically trapped gas and we give several applications\nto Bose and Fermi gases. We obtain the grand-canonical equation of state of a\nspin-balanced Fermi gas with resonant interactions as a function of\ntemperature. We compare our equation of state with an equation of state\nmeasured by the Tokyo group, that reveals a significant difference in the\nhigh-temperature regime. The normal phase, at low temperature, is well\ndescribed by a Landau Fermi liquid model, and we observe a clear thermodynamic\nsignature of the superfluid transition. In a second part we apply the same\nprocedure to Bose gases. From a single image of a quasi ideal Bose gas we\ndetermine the equation of state from the classical to the condensed regime.\nFinally the method is applied to a Bose gas in a 3D optical lattice in the Mott\ninsulator regime. Our equation of state directly reveals the Mott insulator\nbehavior and is suited to investigate finite-temperature effects.",
        "positive": "Role of thermal friction in relaxation of turbulent Bose-Einstein\n  condensates: In recent experiments, the relaxation dynamics of highly oblate, turbulent\nBose-Einstein condensates (BECs) was investigated by measuring the vortex decay\nrates in various sample conditions [Phys. Rev. A $\\bf 90$, 063627 (2014)] and,\nseparately, the thermal friction coefficient $\\alpha$ for vortex motion was\nmeasured from the long-time evolution of a corotating vortex pair in a BEC\n[Phys. Rev. A $\\bf 92$, 051601(R) (2015)]. We present a comparative analysis of\nthe experimental results, and find that the vortex decay rate $\\Gamma$ is\nalmost linearly proportional to $\\alpha$. We perform numerical simulations of\nthe time evolution of a turbulent BEC using a point-vortex model equipped with\nlongitudinal friction and vortex-antivortex pair annihilation, and observe that\nthe linear dependence of $\\Gamma$ on $\\alpha$ is quantitatively accounted for\nin the dissipative point-vortex model. The numerical simulations reveal that\nthermal friction in the experiment was too strong to allow for the emergence of\na vortex-clustered state out of decaying turbulence."
    },
    {
        "anchor": "Interlayer superfluidity in bilayer systems of fermionic polar molecules: We consider fermionic polar molecules in a bilayer geometry where they are\noriented perpendicularly to the layers, which permits both low inelastic losses\nand superfluid pairing. The dipole-dipole interaction between molecules of\ndifferent layers leads to the emergence of interlayer superfluids. The\nsuperfluid regimes range from BCS-like fermionic superfluidity with a high\n$T_c$ to Bose-Einstein (quasi-)condensation of interlayer dimers, thus\nexhibiting a peculiar BCS-BEC crossover. We show that one can cover the entire\ncrossover regime under current experimental conditions.",
        "positive": "Optimal scaling of persistent currents for interacting bosons on a ring: We consider the persistent currents induced by an artificial gauge field\napplied to interacting ultra-cold bosonic atoms in a tight ring trap. Using\nboth analytical and numerical methods, we study the scaling of the persistent\ncurrent amplitude with the size of the ring. In the strongly interacting regime\nwe find a power-law scaling, in good agreement with the predictions of the\nLuttinger-liquid theory. By exploring all interaction regimes we find that the\nscaling is optimal, i.e. the current amplitude decreases slower with the system\nsize, at intermediate interactions."
    },
    {
        "anchor": "Robust Identification of Topological Phase Transition by Self-Supervised\n  Machine Learning Approach: We propose a systematic methodology to identify the topological phase\ntransition through a self-supervised machine learning model, which is trained\nto correlate system parameters to the non-local observables in time-of-flight\nexperiments of ultracold atoms. Different from the conventional supervised\nlearning approach, where the predicted phase transition point is very sensitive\nto the training region and data labeling, our self-supervised learning approach\nidentifies the phase transition point by the largest deviation of the predicted\nresults from the known system parameters and by the highest confidence through\na systematic shift of the training regions. We demonstrate the robust\napplication of this approach results in various 1D and 2D exactly solvable\nmodels, using different input features (time-of-flight images, spatial\ncorrelation function or density-density correlation function). As a result, our\nself-supervised approach should be a very general and reliable method for many\ncondensed matter or solid-state systems to observe new states of matters solely\nbased on experimental measurements, even without a priori knowledge of the\nphase transition models.",
        "positive": "String patterns in the doped Hubbard model: Understanding strongly correlated quantum many-body states is one of the most\ndifficult challenges in modern physics. For example, there remain fundamental\nopen questions on the phase diagram of the Hubbard model, which describes\nstrongly correlated electrons in solids. In this work we realize the Hubbard\nHamiltonian and search for specific patterns within the individual images of\nmany realizations of strongly correlated ultracold fermions in an optical\nlattice. Upon doping a cold-atom antiferromagnet we find consistency with\ngeometric strings, entities that may explain the relationship between hole\nmotion and spin order, in both pattern-based and conventional observables. Our\nresults demonstrate the potential for pattern recognition to provide key\ninsights into cold-atom quantum many-body systems."
    },
    {
        "anchor": "Bose-Einstein condensation of paraxial light: Photons, due to the virtually vanishing photon-photon interaction, constitute\nto very good approximation an ideal Bose gas, but owing to the vanishing\nchemical potential a (free) photon gas does not show Bose-Einstein\ncondensation. However, this is not necessarily true for a lower-dimensional\nphoton gas. By means of a fluorescence induced thermalization process in an\noptical microcavity one can achieve a thermal photon gas with freely adjustable\nchemical potential. Experimentally, we have observed thermalization and\nsubsequently Bose-Einstein condensation of the photon gas at room temperature.\nIn this paper, we give a detailed description of the experiment, which is based\non a dye-filled optical microcavity, acting as a white-wall box for photons.\nThermalization is achieved in a photon number-conserving way by photon\nscattering off the dye molecules, and the cavity mirrors both provide an\neffective photon mass and a confining potential - key prerequisites for the\nBose-Einstein condensation of photons. The experimental results are in good\nagreement with both a statistical and a simple rate equation model, describing\nthe properties of the thermalized photon gas.",
        "positive": "Few-body resonances of unequal-mass systems with infinite interspecies\n  two-body s-wave scattering length: Two-component Fermi and Bose gases with infinitely large interspecies s-wave\nscattering length $a_s$ exhibit a variety of intriguing properties. Among these\nare the scale invariance of two-component Fermi gases with equal masses, and\nthe favorable scaling of Efimov features for two-component Bose gases and\nBose-Fermi mixtures with unequal masses. This paper builds on our earlier work\n[D. Blume and K. M. Daily, arXiv:1006.5002] and presents a detailed discussion\nof our studies of small unequal-mass two-component systems with infinite $a_s$\nin the regime where three-body Efimov physics is absent. We report on\nnon-universal few-body resonances. Just like with two-body systems on\nresonance, few-body systems have a zero-energy bound state in free space and a\ndiverging generalized scattering length. Our calculations are performed within\na non-perturbative microscopic framework and investigate the energetics and\nstructural properties of small unequal-mass two-component systems as functions\nof the mass ratio $\\kappa$, and the numbers $N_{1}$ and $N_2$ of heavy and\nlight atoms. For purely attractive Gaussian two-body interactions, we find that\nthe $(N_1,N_2)=(2,1)$ and $(3,1)$ systems exhibit three-body and four-body\nresonances at mass ratios $\\kappa = 12.314(2)$ and 10.4(2), respectively. The\nthree- and four-particle systems on resonance are found to be large. This\nsuggests that the corresponding wave function has relatively small overlap with\ndeeply-bound dimers, trimers or larger clusters and that the three- and\nfour-body systems on resonance have a comparatively long lifetime. Thus, it\nseems feasible that the features discussed in this paper can be probed\nexperimentally with present-day technology."
    },
    {
        "anchor": "Macroscopic Quantum Coherence in a repulsive Bose-Einstein condensate: We consider a Bose-Einstein bicondensate (BEC) of $^{87}Rb$, trapped in two\ndifferent internal levels, in a situation where the density undergoes a\nsymmetry breaking in momentum space. This occurs for a suitable number of\ncondensed atoms within a double well dispersion curve, obtained by Raman\ncoupling two internal states with two tilted and detuned light fields. Evidence\nof bistability results from the Gross-Pitaevskii equation. By second\nquantization, we evaluate the tunneling rate between the two asymmetric states;\nthe effects of losses on coherence are also considered.",
        "positive": "Magnetic Feshbach resonances in $^{7}\\text{Li}-^{133}\\text{Cs}$ mixtures: Motivated by the prospect of observing Efimov and Bose polaron physics in\nultracold mixtures of bosonic atoms with large mass imbalance, this work\ninvestigates the magnetic Feshbach resonances between $^{7}\\text{Li}$ and\n$^{133}\\text{Cs}$. The resonances are predicted at the 1 gauss level using the\nmodel of Pires et al. [Phys. Rev. A, 90, 012710] obtained from experimental\nobservations of resonances between $^{6}\\text{Li}$ and $^{133}\\text{Cs}$. It is\nfound that a few resonances in a practical range of magnetic field intensity\ncould be used to tune the scattering length between $^{7}\\text{Li}$ and\n$^{133}\\text{Cs}$ atoms. Opportunities for observing Efimov and Bose polaron\nphysics are discussed."
    },
    {
        "anchor": "Interaction induced topological Bogoliubov excitations in a spin-orbit\n  coupled Bose-Einstein condensate: We study topologically non-trivial excitations of a weakly interacting,\nspin-orbit coupled Bose-Einstein condensate in a two-dimensional square optical\nlattice, a system recently realized in experiment [W. Sun et al., Phys. Rev.\nLett. 121, 150401 (2018)]. We focus on situations where the system is not\nsubjected to a Zeeman field and thus does not exhibit nontrivial\nsingle-particle band topology. Of special interest then is the role of particle\ninteraction as well as its interplay with the symmetry properties of the system\nin producing topologically non-trivial excitations. We find that the\nnon-interacting system possesses a rich set of symmetries, including the\n$\\mathcal{PT}$ symmetry, the modified dihedral point group symmetry $\\tilde\nD_4$ and the nonsymmorphic symmetry. These combined symmetries ensure the\nexistence of pairs of degenerate Dirac points at the edge of Brillouin zone for\nthe single-particle energy bands. In the presence of particle interaction and\nwith sufficient spin-orbit coupling, the atoms condense in a ground state with\nnet magnetization which spontaneously breaks the $\\mathcal{PT}$ and $\\tilde\nD_4$ symmetry. We demonstrate that this symmetry breaking leads to a gap\nopening at the Dirac point for the Bogoliubov spectrum and consequentially\ntopologically non-trivial excitations. We confirm the non-trivial topology by\ncalculating the Chern numbers of the lowest excitation bands and show that\ngapless edge states form at the interface of systems characterized by different\nvalues of the Chern number.",
        "positive": "Time dependent local potential in a Tomonaga-Luttinger liquid: We study the energy deposition in a one dimensional interacting quantum\nsystem with a point like potential modulated in amplitude. The point like\npotential at position $x=0$ has a constant part and a small oscillation in time\nwith a frequency $\\omega$. We use bosonization, renormalization group and\nlinear response theory to calculate the corresponding energy deposition. It\nexhibits a power law behavior as a function of the frequency that reflects the\nTomonaga-Luttinger liquid (TLL) nature of the system. Depending on the\ninteractions in the system, characterized by the TLL parameter $K$ of the\nsystem, a crossover between week and strong coupling for the backscattering due\nto the potential is possible. We compute the frequency scale $\\omega_\\ast$, at\nwhich such crossover exists. We find that the energy deposition due to the\nbackscattering shows different exponent for $K>1$ and $K<1$. We discuss\npossible experimental consequences, in the context of cold atomic gases, of our\ntheoretical results."
    },
    {
        "anchor": "Transmission of Excitations in a Spin-1 Bose-Einstein Condensate through\n  a Barrier: We investigate tunneling of excitations across a potential barrier separating\ntwo spin-1 Bose-Einstein condensates. Using the mean-field theory at the\nabsolute zero temperature, we determine transmission coefficients of\nexcitations in the saturated magnetization state and unsaturated magnetization\nstates. All excitations except the quadrupolar spin mode in the saturated\nmagnetization state show the anomalous tunneling phenomenon characterized as\nperfect tunneling in the low momentum limit through a potential barrier. The\nquadrupolar spin mode in the saturated magnetization state, whose spectrum is\nmassive, shows total reflection. We discuss properties common between\nexcitations showing the anomalous tunneling phenomenon. Excitations showing\nperfect tunneling have gapless spectrum in the absence of the magnetic field,\nand their wave functions in the low energy limit are the same as the condensate\nwave function.",
        "positive": "Hanbury Brown-Twiss correlations and multimode dynamics of quenched\n  spinor Bose-Einstein condensates: We have studied the interaction between multiple, competing spatial modes\nthat are excited by a quantum quench of an antiferromagnetic spinor\nBose-Einstein condensate. We observed Hanbury Brown-Twiss correlations and\nassociated super-Poissonian noise in the mode populations. The decay of these\ncorrelations was consistent with experimentally observed spin domain patterns.\nData were compared with a real-space Bogoliubov theory as well as numerical\nsolution of the coupled Gross-Pitaevskii equations that were seeded by quantum\nnoise via the truncated Wigner approximation. The spatial modes that were both\nobserved experimentally and deduced theoretically are intimately connected to\nthe inhomogeneous density profile of the condensate, which imparts many rich\nfeatures to the dynamics."
    },
    {
        "anchor": "Experimental verification of the area law of mutual information in a\n  quantum field simulator: Theoretical understanding of the scaling of entropies and the mutual\ninformation has led to significant advances in the research of correlated\nstates of matter, quantum field theory, and gravity. Measuring von Neumann\nentropy in quantum many-body systems is challenging as it requires complete\nknowledge of the density matrix. In this work, we measure the von Neumann\nentropy of spatially extended subsystems in an ultra-cold atom simulator of\none-dimensional quantum field theories. We experimentally verify one of the\nfundamental properties of equilibrium states of gapped quantum many-body\nsystems, the area law of quantum mutual information. We also study the\ndependence of mutual information on temperature and the separation between the\nsubsystems. Our work is a crucial step toward employing ultra-cold atom\nsimulators to probe entanglement in quantum field theories.",
        "positive": "Superstripes and the excitation spectrum of a spin-orbit-coupled\n  Bose-Einstein condensate: Using Bogoliubov theory we calculate the excitation spectrum of a spinor\nBose-Einstein condensed gas with equal Rashba and Dresselhaus spin-orbit\ncoupling in the stripe phase. The emergence of a double gapless band structure\nis pointed out as a key signature of Bose-Einstein condensation and of the\nspontaneous breaking of translational invariance symmetry. In the long\nwavelength limit the lower and upper branches exhibit, respectively, a clear\nspin and density nature. For wave vectors close to the first Brillouin zone,\nthe lower branch acquires an important density character responsible for the\ndivergent behavior of the structure factor and of the static response function,\nreflecting the occurrence of crystalline order. The sound velocities are\ncalculated as functions of the Raman coupling for excitations propagating\northogonal and parallel to the stripes. Our predictions provide new\nperspectives for the identification of supersolid phenomena in ultracold atomic\ngases."
    },
    {
        "anchor": "Transport in the 2D Fermi-Hubbard Model: Lessons from Weak Coupling: We use quantum kinetic theory to calculate the thermoelectric transport\nproperties of the 2D single band Fermi-Hubbard model in the weak coupling\nlimit. For generic filling, we find that the high-temperature limiting\nbehaviors of the electrical ($\\sim T$) and thermal ($\\sim T^2$) resistivities\npersist down to temperatures of order the hopping matrix element $T\\sim t$,\nalmost an order of magnitude below the bandwidth. At half filling, perfect\nnesting leads to anomalous low temperature scattering and nearly $T$-linear\nelectrical resistivity at all temperatures. We hypothesize that the $T$-linear\nresistivity observed in recent cold atom experiments is continuously connected\nto this weak coupling physics and suggest avenues for experimental\nverification. We find a number of other novel thermoelectric results, such as a\nlow-temperature Wiedemann-Franz law with Lorenz coefficient $5\\pi^2/36$.",
        "positive": "Bosonic Particle-Correlated States: A Nonperturbative Treatment Beyond\n  Mean Field: Many useful properties of dilute Bose gases at ultra-low temperature are\npredicted precisely by the (mean-field) product-state Ansatz, in which all\nparticles are in the same quantum state. Yet, in situations where\nparticle-particle correlations become important, the product Ansatz fails. To\ninclude correlations nonperturbatively, we consider a new set of states: the\nparticle-correlated state of $N=l\\times n$ bosons is derived by symmetrizing\nthe $n$-fold product of an $l$-particle quantum state. The particle-correlated\nstates can be simulated efficiently for large $N$, because their parameter\nspaces, which depend on $l$, do not grow with $n$. Here we formulate and\ndevelop in great detail the pure-state case for $l=2$, where the many-body\nstate is constructed from a two-particle pure state. These paired wave\nfunctions, which we call pair-correlated states (PCS), were introduced by A. J.\nLeggett [Rev. Mod. Phys. ${\\bf 73}$, 307 (2001)] as a\nparticle-number-conserving version of the Bogoliubov approximation. We present\nan iterative algorithm that solves for the reduced (marginal) density matrices\n(RDMs), i.e., the correlation functions, associated with PCS in time $O(N)$.\nThe RDMs can also be derived from the normalization factor of PCS, which is\nderived analytically in the large-$N$ limit. To test the efficacy of PCS, we\nanalyze the ground state of the two-site Bose-Hubbard model by minimizing the\nenergy of the PCS~state, both in its exact form and in its large-$N$\napproximate form, and comparing with the exact ground state. For $N=1\\,000$,\nthe relative errors of the ground-state energy for both cases are within\n$10^{-5}$ over the entire parameter region from a single condensate to a Mott\ninsulator. We present numerical results that suggest that PCS might be useful\nfor describing the dynamics in the strongly interacting regime."
    },
    {
        "anchor": "Z2 Topological insulator of ultra cold atoms in bichromatic optical\n  lattices: We investigate the effect of a strong bichromatic deformation to the\n$\\mathbb{Z}_{2}$ topological insulator in a fermionic ultracold atomic system\nproposed by B. B\\'eri and N. R. Cooper, Phys.Rev.Lett. {\\bf 107}, 145301\n(2011). Large insulating gap of this system allows for examination of strong\nperturbations. We consider bichromatic perturbation along all axes on a\ntriangular optical lattice. We find that $\\mathbb{Z}_{2}$ topological character\nof the system is robust up to a certain depth of the deformation. The lowest\nband can become topologically trivial while the lowest two bands are always\nprotected.",
        "positive": "Induced density correlations in a sonic black hole condensate: Analog black/white hole pairs, consisting of a region of supersonic flow,\nhave been achieved in a recent experiment by J. Steinhauer using an elongated\nBose-Einstein condensate. A growing standing density wave, and a checkerboard\nfeature in the density-density correlation function, were observed in the\nsupersonic region. We model the density-density correlation function, taking\ninto account both quantum fluctuations and the shot-to-shot variation of atom\nnumber normally present in ultracold-atom experiments. We find that quantum\nfluctuations alone produce some, but not all, of the features of the\ncorrelation function, whereas atom-number fluctuation alone can produce all the\nobserved features, and agreement is best when both are included. In both cases,\nthe density-density correlation is not intrinsic to the fluctuations, but\nrather is induced by modulation of the standing wave caused by the\nfluctuations."
    },
    {
        "anchor": "A variational model for the delayed collapse of Bose Einstein\n  condensates: We present an action that can be used to study variationally the collapse of\nBose Einstein condensates. This action is real, even though it includes\ndissipative terms. It adopts long range interactions between the atoms, so that\nthere is always a stable minimum of the energy, even if the remaining number of\natoms is above the number that in the case of local interactions is the\ncritical one. The proposed action incorporates the time needed for the abrupt\nand delayed onset of collapse, yielding in fact its dependence on the\nscattering length. We show that the evolution of the condensate is equivalent\nto the motion of a particle in an effective potential. The particle begins its\nmotion far from the point of stable equilibrium and it then proceeds to\noscillate about that point. We prove that the resulting large oscillations in\nthe shape of the wavefunction after the collapse have frequencies equal to\ntwice the frequencies of the traps. Our results agree with the experimental\nobservations.",
        "positive": "Multiphoton interband excitations of quantum gases in driven optical\n  lattices: We report on the observation of multiphoton interband absorption processes\nfor quantum gases in shaken light crystals. Periodic inertial forcing, induced\nby a spatial motion of the lattice potential, drives multiphoton interband\nexcitations of up to the ninth order. The occurrence of such excitation\nfeatures is systematically investigated with respect to the potential depth and\nthe driving amplitude. Ab initio calculations of resonance positions as well as\nnumerical evaluation of their strengths exhibit good agreement with\nexperimental data. In addition our findings could make it possible to reach\nnovel phases of quantum matter by tailoring appropriate driving schemes."
    },
    {
        "anchor": "Damping of Josephson oscillations in strongly correlated one-dimensional\n  atomic gases: We study Josephson oscillations of two strongly correlated one-dimensional\nbosonic clouds separated by a localized barrier. Using a quantum-Langevin\napproach and the exact Tonks-Girardeau solution in the impenetrable-boson\nlimit, we determine the dynamical evolution of the particle-number imbalance,\ndisplaying an effective damping of the Josephson oscillations which depends on\nbarrier height, interaction strength and temperature. We show that the damping\noriginates from the quantum and thermal fluctuations intrinsically present in\nthe strongly correlated gas. Thanks to the density-phase duality of the model,\nthe same results apply to particle-current oscillations in a one-dimensional\nring where a weak barrier couples different angular momentum states.",
        "positive": "Superfluid properties of bright solitons in a ring: We theoretically investigate superfluid properties of a one-dimensional\nannular superfluid with a boost. We derive the formula of the superfluid\nfraction in the one-dimensional superfluid, which was originally derived by\nLeggett in the context of supersolid. We see that the superfluid fraction given\nby Leggett's formula detects the emergence of solitons in the one-dimensional\nannular superfluid. The formation of a bright soliton at a critical interaction\nstrength decreases the superfluid fraction. At a critical boost velocity, a\nnode appears in the soliton and the superfluid fraction vanishes. With a\ntransverse dimension, the soliton alters to a more localized one and it\nundergoes dynamical instability at a critical transverse length. Consequently,\nthe superfluid fraction decreases as one increases the length up to the\ncritical length. With a potential barrier along the ring, the uniform density\nalters to an inhomogeneous configuration and it develops a soliton localized at\none of the potential minima by increasing the interaction strength."
    },
    {
        "anchor": "$\\mathbb{Z}_n$ symmetry broken supersolid in spin-orbit-coupled\n  Bose-Einstein condensates: Supersolid is an exotic state of matter characterized by both superfluid\nproperties and periodic particle density modulation, due to spontaneous\nbreaking of U(1) gauge symmetry and spatial translation symmetry, respectively.\nFor conventional supersolids,continuous translation symmetry breaking is\naccompanied by one gapless Goldstone mode in the excitation spectra. An\ninteresting question naturally arises: what is the consequence of breaking\ndiscrete translation symmetry for supersolids? In this work, we propose the\nconcept of $\\mathbb{Z}_n$ supersolid resulting from spontaneous breaking of a\ndiscrete $\\mathbb{Z}_n$ symmetry, or equivalently, a discrete translation\nsymmetry. This $\\mathbb{Z}_n$ supersolid is realized in the stripe phase of\nspin-orbit-coupled Bose-Einstein condensate under an external periodic\npotential with period $1/n$ of intrinsic stripe period. For $n\\geq2$, there are\n$n$ degenerate ground states with spontaneously broken lattice translation\nsymmetry. The low-energy excitations of $\\mathbb{Z}_n$ supersolid include a\npseudo-Goldstone mode, whose excitation gap at long wavelength limit is found\nto decrease fast with $n$. We further numerically show that, when confined in a\nharmonic trap, a spin-dependent perturbation can result in the transition\nbetween degenerate ground states of $\\mathbb{Z}_n$ supersolid. With the integer\n$n$ tunable using the experimental technique of generating subwavelength\noptical lattice, the $\\mathbb{Z}_n$ supersolid proposed here offers a cold atom\nplatform to simulate physics related with generic $\\mathbb{Z}_n$ symmetry\nbreaking, which is interesting not only in the field of cold atoms, but also in\nparticle physics and cosmology.",
        "positive": "Condensate fragmentation as a sensitive measure of the quantum many-body\n  behavior of bosons with long-range interactions: The occupation of more than one single-particle state and hence the emergence\nof fragmentation is a many-body phenomenon universal to systems of spatially\nconfined interacting bosons. In the present study, we investigate the effect of\nthe range of the interparticle interactions on the fragmentation degree of one-\nand two-dimensional systems. We solve the full many-body Schr\\\"odinger equation\nof the system using the recursive implementation of the multiconfigurational\ntime-dependent Hartree for bosons method, R-MCTDHB. The dependence of the\ndegree of fragmentation on dimensionality, particle number, areal or line\ndensity and interaction strength is assessed. It is found that for contact\ninteractions, the fragmentation is essentially density independent in two\ndimensions. However, fragmentation increasingly depends on density the more\nlong-ranged the interactions become. The degree of fragmentation is increasing,\nkeeping the particle number $N$ fixed, when the density is decreasing as\nexpected in one spatial dimension. We demonstrate that this remains,\nnontrivially, true also for long-range interactions in two spatial dimensions.\nWe, finally, find that within our fully self-consistent approach, the\nfragmentation degree, to a good approximation, decreases universally as\n$N^{-1/2}$ when only $N$ is varied."
    },
    {
        "anchor": "Rabi flopping induces spatial demixing dynamics: We experimentally investigate the mixing/demixing dynamics of Bose-Einstein\ncondensates in the presence of a linear coupling between two internal states.\nThe observed amplitude reduction of the Rabi oscillations can be understood as\na result of demixing dynamics of dressed states as experimentally confirmed by\nreconstructing the spatial profile of dressed state amplitudes. The\nobservations are in quantitative agreement with numerical integration of\ncoupled Gross-Pitaevskii equations without free parameters, which also reveals\nthe criticality of the dynamics on the symmetry of the system. Our observations\ndemonstrate new possibilities for changing effective atomic interactions and\nstudying critical phenomena.",
        "positive": "Interaction control and bright solitons in coherently-coupled\n  Bose-Einstein condensates: We demonstrate fast control of the interatomic interactions in a\nBose-Einstein condensate by coherently coupling two atomic states with intra-\nand inter-state scattering lengths of opposite signs. We measure the elastic\nand inelastic scattering properties of the system and find good agreement with\na theoretical model describing the interactions between dressed states. In the\nattractive regime, we observe the formation of bright solitons formed by\ndressed-state atoms. Finally, we study the response of the system to an\ninteraction quench from repulsive to attractive values, and observe how the\nresulting modulational instability develops into a bright soliton train."
    },
    {
        "anchor": "Observation of coherent multiorbital polarons in a two-dimensional Fermi\n  gas: We report on the experimental observation of multiorbital polarons in a\ntwo-dimensional Fermi gas of $^{173}\\mathrm{Yb}$ atoms formed by mobile\nimpurities in the metastable $^3\\mathrm{P}_0$ orbital and a Fermi sea in the\nground-state $^1\\mathrm{S}_0$ orbital. We spectroscopically probe the energies\nof attractive and repulsive polarons close to an orbital Feshbach resonance and\ncharacterize their coherence by measuring the quasiparticle residue. For all\nprobed interaction parameters, the repulsive polaron is a long-lived\nquasiparticle with a decay rate more than 2 orders of magnitude below its\nenergy. We formulate a many-body theory, which accurately treats the\ninterorbital interactions in two dimensions and agrees well with the\nexperimental results. Our work paves the way for the investigation of many-body\nphysics in multiorbital ultracold Fermi gases.",
        "positive": "Quantum Breathing of an Impurity in a One-dimensional Bath of\n  Interacting Bosons: By means of time-dependent density-matrix renormalization-group (TDMRG) we\nare able to follow the real-time dynamics of a single impurity embedded in a\none-dimensional bath of interacting bosons. We focus on the impurity breathing\nmode, which is found to be well-described by a single oscillation frequency and\na damping rate. If the impurity is very weakly coupled to the bath, a\nLuttinger-liquid description is valid and the impurity suffers an\nAbraham-Lorentz radiation-reaction friction. For a large portion of the\nexplored parameter space, the TDMRG results fall well beyond the\nLuttinger-liquid paradigm."
    },
    {
        "anchor": "Symmetry Protected Dynamical Symmetry in the Generalized Hubbard Models: In this letter we present a theorem on the dynamics of the generalized\nHubbard models. This theorem shows that the symmetry of the single particle\nHamiltonian can protect a kind of dynamical symmetry driven by the\ninteractions. Here the dynamical symmetry refers to that the time evolution of\ncertain observables are symmetric between the repulsive and attractive Hubbard\nmodels. We demonstrate our theorem with three different examples in which the\nsymmetry involves bipartite lattice symmetry, reflection symmetry and\ntranslation symmetry, respectively. Each of these examples relates to one\nrecent cold atom experiment on the dynamics in the optical lattices where such\na dynamical symmetry is manifested. These experiments include expansion\ndynamics of cold atoms, chirality of atomic motion within a synthetic magnetic\nfield and melting of charge-density-wave order. Therefore, our theorem provides\na unified view of these seemingly disparate phenomena.",
        "positive": "Inseparable time-crystal geometries on the M\u00f6bius strip: Description of periodically and resonantly driven quantum systems can lead to\nsolid state models where condensed matter phenomena can be investigated in time\nlattices formed by periodically evolving Wannier-like states. Here, we show\nthat inseparable two-dimensional time lattices with the M\\\"obius strip geometry\ncan be realized for ultra-cold atoms bouncing between two periodically\noscillating mirrors. Effective interactions between atoms loaded to a lattice\ncan be long-ranged and can be controlled experimentally. As a specific example\nwe show how to realize a Lieb lattice model with a flat band and how to control\nlong-range hopping of pairs of atoms in the model."
    },
    {
        "anchor": "Imprinting a topological interface using Zeeman shifts in an atomic\n  spinor Bose-Einstein condensate: We propose to use spatial control of the Zeeman energy shifts in an ultracold\natomic gas to engineer an interface between topologically distinct regions.\nThis provides an experimentally accessible means for studying the interface\nphysics of topological defects and textures. Using the spin-1 Bose-Einstein\ncondensate as an example, we find spinor wave functions that represent defects\nand textures continuously connecting across the interface between polar and\nferromagnetic regions induced by spatially varying Zeeman shifts. By numerical\nenergy minimization we characterize the defect core structures and determine\nthe energetic stability. The techniques proposed could potentially be used in\nthe laboratory to emulate complex interface physics arising, e.g., in\ncosmological and condensed-matter contexts in both uniform and lattice systems.",
        "positive": "Spin-dipole mode in a trapped Fermi gas near unitarity: We theoretically investigate the spin-dipole oscillation of a strongly\ninteracting Fermi gas in a harmonic trap. By using a combined diagrammatic\nstrong-coupling theory with a local density approximation and a sum rule\napproach, we clarify the temperature dependence of the spin-dipole frequency\nnear the unitarity, which is deeply related to the spin susceptibility, as well\nas pairing correlations. While the spin-dipole frequency exactly coincides with\nthe trap frequency in a non-interacting Fermi gas, it is shown to remarkably be\nenhanced in the superfluid state, because of the suppression of the spin degree\nof freedom due to the spin-singlet Cooper-pair formation. In strongly\ninteracting Fermi gases, this enhancement occurs even above the superfluid\nphase transition temperature, due to the strong pairing correlations."
    },
    {
        "anchor": "Spin current generation and relaxation in a quenched spin-orbit-coupled\n  Bose-Einstein condensate: Understanding the effects of spin-orbit coupling (SOC) and many-body\ninteractions on spin transport is important in condensed matter physics and\nspintronics. This topic has been intensively studied for spin carriers such as\nelectrons but barely explored for charge-neutral bosonic quasiparticles\n(including their condensates), which hold promises for coherent spin transport\nover macroscopic distances. Here, we explore the effects of synthetic SOC\n(induced by optical Raman coupling) and atomic interactions on the spin\ntransport in an atomic Bose-Einstein condensate (BEC), where the spin-dipole\nmode (SDM, actuated by quenching the Raman coupling) of two interacting spin\ncomponents constitutes an alternating spin current. We experimentally observe\nthat SOC significantly enhances the SDM damping while reducing the\nthermalization (the reduction of the condensate fraction). We also observe\ngeneration of BEC collective excitations such as shape oscillations. Our theory\nreveals that the SOC-modified interference, immiscibility, and interaction\nbetween the spin components can play crucial roles in spin transport.",
        "positive": "Possible critical regions for the ground state of a Bose gas in a\n  spherical trap: With the help of perturbation theory, we study the ground state of a Bose gas\nin a spherical trap, using the solution in the Thomas--Fermi approximation as\nthe zero approximation. We have found within a certain approximation that, in\nsome very narrow intervals of values of the magnetic field of a trap, the\nsolution deviates strongly from that in the Thomas--Fermi approximation. If the\nmagnetic field is equal to one of such critical values, the size (or even the\nshape) of the condensate cloud should significantly differ from the\nThomas--Fermi one."
    },
    {
        "anchor": "Precise Programmable Quantum Simulations with Optical Lattices: We present an efficient approach to precisely simulate tight binding models\nwith optical lattices, based on programmable digital-micromirror-device (DMD)\ntechniques. Our approach consists of a subroutine of Wegner-flow enabled\nprecise extraction of a tight-binding model for a given optical potential, and\na reverse engineering step of adjusting the potential for a targeting model,\nfor both of which we develop classical algorithms to achieve high precision and\nhigh efficiency. With renormalization of Wannier functions and high band\neffects systematically calibrated in our protocol, we show the tight-binding\nmodels with programmable onsite energies and tunnelings can be precisely\nsimulated with optical lattices integrated with the DMD techniques. With\nnumerical simulation, we demonstrate that our approach would facilitate quantum\nsimulation of localization physics with unprecedented programmability and\natom-based boson sampling for illustration of quantum computational advantage.\nWe expect this approach would pave a way towards large-scale and precise\nprogrammable quantum simulations based on optical lattices.",
        "positive": "Spin Transport in Cold Fermi gases: A Pseudogap Interpretation of Spin\n  Diffusion Experiments at Unitarity: We address recent spin transport experiments in ultracold unitary Fermi\ngases. We provide a theoretical understanding for how the measured temperature\ndependence of the spin diffusivity at low $T$ can disagree with the expected\nbehavior of a Fermi liquid (FL) while the spin susceptiblity(following the\nexperimental protocols) is consistent with a Fermi liquid picture. We show that\nthe experimental protocols for extracting $\\chi_s$ are based on a FL\npresumption; relaxing this leads to consistency within (but not proof of) a\npseudogap-based approach. Our tranport calculations yield insight into the\nmeasured strong suppression of the spin diffusion constant at lower $T$."
    },
    {
        "anchor": "Trimer superfluid induced by photoassocation on the state-dependent\n  optical lattice: We use the mean-field method, the Quantum Monte-carlo method and the Density\nmatrix renormalization group method to study the trimer superfluid phase and\nthe quantum phase diagram of the Bose-Hubbard model in an optical lattice, with\nexplicit trimer tunneling term.\n  Theoretically, we derive the explicit trimer hopping terms, such as\n$a_i^{3\\dagger}a_j^3$, by the Schrieffer-Wolf transformation. In practice, the\ntrimer super\\-fluid described by these terms is driven by photoassociation. The\nphase transition between the trimer super\\-fluid phase and other phases are\nalso studied. Without the on-site interaction, the phase transition between the\ntrimer superfluid phase and the Mott Insulator phase is continuous. Turning on\nthe on-site interaction, the phase transitions are first order with Mott\ninsulators of atom filling $1$ and $2$. With nonzero atom tunneling, the phase\ntransition is first order from the atom superfluid to the trimer superfluid. In\nthe trimer superfluid phase, the win\\-ding numbers can be divided by three\nwithout any remainders. In the atom superfluid and pair superfluid, the\nvorticities are $1$ and $1/2$, respectively. However, the vorticity is $1/3$\nfor the trimer superfluid. The power law decay exponents is $1/2$ for the non\ndiagonal correlation $a_i^{\\dagger 3} a_j^{3}$, i.e. the same as the exponent\nof the correlation $a_i^{\\dagger}a_j$ in hardcore bosons. The density dependent\natom-tunneling term $n_i^2a_i^{\\dagger}a_j$ and pair tunneling term\n$n_ia_i^{\\dagger2}a_j^2$ are also studied. With these terms, the phase\ntransition from the empty phase to atom superfluid is first order and different\nfrom the cases without the density dependent terms. The ef\\-fects of\ntemperature are studied. Our results will be helpful in realizing the trimer\nsuperfluid by a cold atom experiment.",
        "positive": "Propagation and amplification dynamics of 1D polariton condensates: The dynamics of propagating polariton condensates in one-dimensional\nmicrocavities is investigated through time resolved experiments. We find a\nstrong increase in the condensate intensity when it travels through the\nnon-resonantly excited area. This amplification is shown to come from bosonic\nstimulated relaxation of reservoir excitons into the polariton condensate,\nallowing for the repopulation of the condensate through non-resonant pumping.\nThus, we experimentally demonstrate a polariton amplifier with a large band\nwidth, opening the way towards the transport of polaritons with high densities\nover macroscopic distances."
    },
    {
        "anchor": "Vortices in the two-dimensional dipolar Bose gas: We present vortex solutions for the homogeneous two-dimensional Bose-Einstein\ncondensate featuring dipolar atomic interactions, mapped out as a function of\nthe dipolar interaction strength (relative to the contact interactions) and\npolarization direction. Stable vortex solutions arise in the regimes where the\nfully homogeneous system is stable to the phonon or roton instabilities. Close\nto these instabilities, the vortex profile differs significantly from that of a\nvortex in a nondipolar quantum gas, developing, for example, density ripples\nand an anisotropic core. Meanwhile, the vortex itself generates a mesoscopic\ndipolar potential which, at distance, scales as 1/r^2 and has an angular\ndependence which mimics the microscopic dipolar interaction.",
        "positive": "Quench dynamics and relaxation in isolated integrable quantum spin\n  chains: We review the dynamics after quantum quenches in integrable quantum spin\nchains. We give a pedagogical introduction to relaxation in isolated quantum\nsystems, and discuss the description of the steady state by (gen- eralized)\nGibbs ensembles. When then turn to general features in the time evolution of\nlocal observables after the quench, using a simple model of free fermions as an\nexample. In the second part we present an overview of recent progress in\ndescribing quench dynamics in two key paradigms for quantum integrable models,\nthe transverse field Ising chain and the anisotropic spin-1/2 Heisenberg chain."
    },
    {
        "anchor": "Strongly-interacting bosons at 2D-1D Dimensional Crossover: We study a two dimensional (2D) system of interacting quantum bosons,\nsubjected to a continuous periodic potential in one direction. The correlation\nof such system exhibits a dimensional crossover between a canonical 2D behavior\nwith Berezinski-Kosterlitz-Thouless (BKT) properties and a one-dimensional (1D)\nbehavior when the potential is large and splits the system in essentially\nindependent tubes. The later is in the universality class of Tomonaga-Luttinger\nliquids (TLL). Using a continuous quantum Monte Carlo method, we investigate\nthis dimensional crossover by computing longitudinal and transverse superfluid\nfraction as well as the superfluid correlation as a function of temperature,\ninteractions and potential. Especially, we find the correlation function\nevolves from BKT to TLL type, with special intermediate behaviors appearing at\nthe dimensional crossover. We discuss how the consequences of the dimensional\ncrossover can be investigated in cold atomic gases experiments.",
        "positive": "Quantum Bose Josephson Junction with binary mixtures of BECs: We study the quantum behaviour of a binary mixture of Bose-Einstein\ncondensates (BEC) in a double-well potential starting from a two-mode\nBose-Hubbard Hamiltonian. We focus on the small tunneling amplitude regime and\napply perturbation theory up to second order. Analytical expressions for the\nenergy eigenvalues and eigenstates are obtained. Then the quantum evolution of\nthe number difference of bosons between the two potential wells is fully\ninvestigated for two different initial conditions: completely localized states\nand coherent spin states. In the first case both the short and the long time\ndynamics is studied and a rich behaviour is found, ranging from small amplitude\noscillations and collapses and revivals to coherent tunneling. In the second\ncase the short-time scale evolution of number difference is determined and a\nmore irregular dynamics is evidenced. Finally, the formation of Schroedinger\ncat states is considered and shown to affect the momentum distribution."
    },
    {
        "anchor": "Collision dynamics of two-dimensional non-Abelian vortices: We study computationally the collision dynamics of vortices in a\ntwo-dimensional spin-2 Bose-Einstein condensate. In contrast to Abelian vortex\npairs, which annihilate or pass through each other, we observe non-Abelian\nvortex pairs to undergo rungihilation - an event that converts the colliding\nvortices into a rung vortex. The resulting rung defect subsequently decays to\nanother pair of non-Abelian vortices of different type, accompanied by a\nmagnetization reversal.",
        "positive": "Self-consistent spin waves in magnetized BEC: We obtain equations of quantum hydrodynamic (QHD) for magnetized spin-1\nneutral Bose-Einstein condensate (BEC). System of QHD equations contains the\nequation of magnetic moment evolution (an analog of the Bloch equation). We\naccount spin-spin interaction along with the short range interaction. We\nconsider self-consistent field approximation of QHD equations. Starting from\nQHD equation we derive the Gross-Pitaevskii equation for magnetized BEC. We\nshow that Gross-Pitaevskii equation exists under condition that the magnetic\nmoment direction is not change. Using obtained QHD equations we study the\ndispersion of collective excitation. As in electrically polarized BEC [P. A.\nAndreev, L. S. Kuz'menkov, arXiv: 1201.2440], in the magnetically polarized BEC\nthere is second wave mode (polarization mode or spin wave), in addition to the\nBogoliubov's mode. Second wave solution appears due to the magnetic moment\nevolution. The influence of magnetization on dispersion of Bogoliubov's mode is\nfound. We found strong difference of dispersion properties of waves in\nmagnetized BEC from electrically polarized BEC."
    },
    {
        "anchor": "Dynamic response of 1D bosons in a trap: We calculate the dynamic structure factor S(q,omega) of a one-dimensional\n(1D) interacting Bose gas confined in a harmonic trap. The effective\ninteraction depends on the strength of the confinement enforcing the 1D motion\nof atoms; interaction may be further enhanced by superimposing an optical\nlattice on the trap potential. In the compressible state, we find that the\nsmooth variation of the gas density around the trap center leads to softening\nof the singular behavior of S(q,omega) at Lieb-1 mode compared to the behavior\npredicted for homogeneous 1D systems. Nevertheless, the density-averaged\nresponse remains a non-analytic function of q and omega at Lieb-1 mode in the\nlimit of weak trap confinement. The exponent of the power-law non-analyticity\nis modified due to the inhomogeneity in a universal way, and thus, bears\nunambiguously the information about the (homogeneous) Lieb-Liniger model. A\nstrong optical lattice causes formation of Mott phases. Deep in the Mott\nregime, we predict a semi-circular peak in S(q,\\omega) centered at the on-site\nrepulsion energy, omega=U. Similar peaks of smaller amplitudes exist at\nmultiples of U as well. We explain the suppression of the dynamic response with\nentering into the Mott regime, observed recently by D. Clement et al., Phys.\nRev. Lett. v. 102, p. 155301 (2009), based on an f-sum rule for the\nBose-Hubbard model.",
        "positive": "Cold Fermi-gas with long range interaction in a harmonic trap: We study equilibrium density and spin density profiles for a model of cold\none-dimensional spin 1/2 fermions interacting via inverse square interaction\nand exchange in an external harmonic trap. This model is the well-known\nspin-Calogero model (sCM) and its fully nonlinear collective field theory\ndescription is known. We extend the field theory description to the presence of\nan external harmonic trap and obtain analytic results for statics and dynamics\nof the system. For instance, we find how the equilibrium density profile\nchanges upon tuning the interaction strength. The results we obtain for\nequilibrium configurations are very similar to the ones obtained recently by Ma\nand Yang [1] for a model of fermions with short ranged interactions. Our main\napproximation is the neglect of the terms of higher order in spatial\nderivatives in equations of motion - gradientless approximation [2]. Within\nthis approximation the hydrodynamic equations of motion can be written as a set\nof decoupled forced Riemann-Hopf equations for the dressed Fermi momenta of the\nmodel. This enables us to write analytical solutions for the dynamics of spin\nand charge. We describe the time evolution of the charge density when an\ninitial non-equilibrium profile is created by cooling the gas with an\nadditional potential in place and then suddenly removing the potential. We\npresent our results as a simple \"single-particle\" evolution in the phase-space\nreminiscing a similar description of the dynamics of non-interacting\none-dimensional fermions."
    },
    {
        "anchor": "Work statistics in ferromagnetic spinor Bose-Einstein condensates across\n  the quantum phase transition: Driving a quantum many-body system across the quantum phase transition (QPT)\nin finite time has been concerned in different branches of physics to explore\nvarious fundamental questions. Here, we analyze how the underlying QPT affects\nthe work distribution, when the controlling parameter of a ferromagnetic spinor\nBose-Einstein condensates is tuned through the critical point in finite time.We\nshow that the work distribution undergoes a dramatic change with increasing the\ndriving time $\\tau$, which is further captured by employing the entropy of the\nwork distribution.We observe three distinct regions in the evolution of entropy\nas a function of $\\tau$.Specifically, the entropy is insensitive to the driving\ntime in the region of very short $\\tau$. However, in the region with\nintermediate value of $\\tau$, it exhibits a universal power-law decay\nconsistent with the well-known Kibble-Zurek mechanism. For the region with\nlarge $\\tau$, the validity of the adiabatic perturbation theory leads to the\nentropy decay as $\\tau^{-2}\\ln\\tau$. Our results verify the usefulness of the\nentropy of the work distribution for understanding the critical dynamics and\nprovide an alternative way to experimentally study nonequilibrium properties in\nquantum many-body systems.",
        "positive": "Interacting quantum walk on a two-leg flux ladder: Emergence of\n  re-entrant dynamics: We study the quench dynamics of interacting bosons on a two-leg flux ladder\nby implementing the continuous-time quantum walk and explore the combined\neffect of the magnetic field and onsite interaction in the presence of uniform\nflux. We show that in the regime of weak interaction, the magnetic field\nsubstantially slows down the spreading of the particles' wavefunction during\nthe dynamics. However, in the presence of strong interaction, we obtain an\ninteresting re-entrant behaviour in the dynamics where the radial velocity\nassociated to the spreading first increases, then decreases, and increases\nagain as a function of the flux strength. We also find a re-entrant dynamics in\nthe chiral motion of the particles as a function of interaction for fixed flux\nstrengths."
    },
    {
        "anchor": "Interplay of phase separation and itinerant magnetism for correlated few\n  fermions in a double-well: We explore the stability of the phase separation phenomenon in few-fermion\nspin-$1/2$ systems confined in a double-well potential. It is shown that within\nthe SU(2) symmetric case, where the total spin is conserved, the phase\nseparation cannot be fully stabilized. An interaction regime characterized by\nmetastable phase separation emerges for intermediate interactions which is\ninherently related with ferromagnetic spin-spin correlations emanating within\neach of the wells. The breaking of the SU(2) symmetry crucially affects the\nstability properties of the system as the phase separated state can be\nstabilized even for weak magnetic potential gradients. Our results imply an\nintricate relation between the phenomena of phase separation and ferromagnetism\nthat lies beyond the view of the Stoner instability.",
        "positive": "Quantum Field Theory of Correlated Bose-Einstein condensates: I. Basic\n  Formalism: Quantum field theory of equilibrium and nonequilibrium Bose-Einstein\ncondensates is formulated so as to satisfy three basic requirements: the\nHugenholtz-Pines relation; conservation laws; identities among vertices\noriginating from Goldstone's theorem I. The key inputs are irreducible\nfour-point vertices, in terms of which we derive a closed system of equations\nfor Green's functions, three- and four-point vertices, and two-particle Green's\nfunctions. It enables us to study correlated Bose-Einstein condensates with a\ngapless branch of single-particle excitations without encountering any infrared\ndivergence. The single- and two-particle Green's functions are found to share\npoles, i.e., the structure of the two-particle Green's functions predicted by\nGavoret and Nozi\\`eres for a homogeneous condensate at $T=0$ is also shown to\npersist at finite temperatures, in the presence of inhomogeneity, and also in\nnonequilibrium situations."
    },
    {
        "anchor": "Decay of superfluid currents in the interacting one-dimensional Bose gas: We examine the superfluid properties of a 1D Bose gas in a ring trap based on\nthe model of Lieb and Liniger. While the 1D Bose gas has nonclassical\nrotational inertia and exhibits quantization of velocities, the metastability\nof currents depends sensitively on the strength of interactions in the gas: the\nstronger the interactions, the faster the current decays. It is shown that the\nLandau critical velocity is zero in the thermodynamic limit due to the first\nsupercurrent state, which has zero energy and finite probability of excitation.\nWe calculate the energy dissipation rate of ring currents in the presence of\nweak defects, which should be observable on experimental time scales.",
        "positive": "Dressed, noise- or disorder- resilient optical lattices: External noise is inherent in any quantum system, and can have especially\nstrong effects for systems exhibiting sensitive many-body phenomena. We show\nhow a dressed lattice scheme can provide control over certain types of noise\nfor atomic quantum gases in the lowest band of an optical lattice, removing the\neffects of lattice amplitude noise to first order for particular choices of the\ndressing field parameters. We investigate the non-equilibrium many-body\ndynamics for bosons and fermions induced by noise away from this parameter\nregime, and also show how the same technique can be used to reduce spatial\ndisorder in projected lattice potentials."
    },
    {
        "anchor": "Spontaneous creation of Kibble-Zurek solitons in a Bose-Einstein\n  condensate: When a system crosses a second-order phase transition on a finite timescale,\nspontaneous symmetry breaking can cause the development of domains with\nindependent order parameters, which then grow and approach each other creating\nboundary defects. This is known as Kibble-Zurek mechanism. Originally\nintroduced in cosmology, it applies both to classical and quantum phase\ntransitions, in a wide variety of physical systems. Here we report on the\nspontaneous creation of solitons in Bose-Einstein condensates via the\nKibble-Zurek mechanism. We measure the power-law dependence of defects number\nwith the quench time, and provide a check of the Kibble-Zurek scaling with the\nsonic horizon. These results provide a promising test bed for the determination\nof critical exponents in Bose-Einstein condensates.",
        "positive": "Two-step condensation of the charged Bose gas: The condensation of the spinless ideal charged Bose gas in the presence of a\nmagnetic field is revisited. The conventional approach is extended to include\nthe macroscopic occupation of excited kinetic states lying in the lowest Landau\nlevel, which plays an essential role in the case of large magnetic fields. In\nthat limit, signatures of two diffuse phase transitions (crossovers) appear in\nthe specific heat. In particular, at temperatures lower than the cyclotron\nfrequency, the system behaves as an effectively one-dimensional free boson\nsystem, with the specific heat equal to $(1/2)N k_B T$ and a gradual\ncondensation at lower temperatures."
    },
    {
        "anchor": "An Artificial Frustrated System: Cold Atoms in 2D Triangular Optical\n  Lattice: We investigate the strongly correlated effect of cold atoms in triangular\noptical lattice by dynamical cluster approximation combining with the\ncontinuous time quantum Monte Carlo method proposed recently. It is found the\ndouble occupancy is suppressed as the atomic interaction increases. By\ncalculating the density of states, we show how the system evolves from Fermi\nliquid with an obvious quasi-particle peak into Mott insulator with an opened\ngap for increasing interaction. The transition between Fermi liquid and\npseudogap shows a reentrant behavior due to the Kondo effect. At low\ntemperature, a Kondo peak appears before the splitting of the Fermi-liquid-like\npeak. The Fermi surface evolves from a circular ring with high amplitude into a\n{\\deg}at elliptical ring with low amplitude for the increasing interaction. We\ngive an experimental protocol to observe these phenomena by varying the lattice\ndepth and the atomic interaction via Feshbach resonance in future experiments.",
        "positive": "Pairing of electro-magnetic bosons under spin-orbit coupling: We discuss pairing of light-matter bosons under effective spin-orbit (SO)\ncoupling in two-dimensional semiconductors. The SO coupling is shown to induce\ndynamical broadening of a two-body bound state. Application of a transverse\nmagnetic field yields the rich Feshbach resonance phenomenology. We predict\nquantum bosonic halos with a synthetic angular momentum L=2. The d-wave-like\ndressing of the nominally s-wave bound state is induced by SO coupling to the\ncontinuum in the open channel. The fundamental properties of the emergent\nquantum number remain to be explored."
    },
    {
        "anchor": "Dilute Bose gas with correlated disorder: A Path Integral Monte Carlo\n  study: We investigate the thermodynamic properties of a dilute Bose gas in a\ncorrelated random potential using exact path integral Monte Carlo methods. The\nstudy is carried out in continuous space and disorder is produced in the\nsimulations by a 3D speckle pattern with tunable intensity and correlation\nlength. We calculate the shift of the superfluid transition temperature due to\ndisorder and we highlight the role of quantum localization by comparing the\ncritical chemical potential with the classical percolation threshold. The\nequation of state of the gas is determined in the regime of strong disorder,\nwhere superfluidity is suppressed and the normal phase exists down to very low\ntemperatures. We find a $T^2$ dependence of the energy in agreement with the\nexpected behavior in the Bose glass phase. We also discuss the major role\nplayed by the disorder correlation length and we make contact with a\nHartree-Fock mean-field approach that holds valid if the correlation length is\nvery large. The density profiles are analyzed as a function of temperature and\ninteraction strength. Effects of localization and the depletion of the order\nparameter are emphasized in the comparison between local condensate and total\ndensity. At very low temperature we find that the energy and the particle\ndistribution of the gas are very well described by the T=0 Gross-Pitaevskii\ntheory even in the regime of very strong disorder.",
        "positive": "Chaos induced breakdown of Bose-Hubbard modeling: We show that the Bose-Hubbard approximation fails due to the emergence of\nchaos, even when excited modes are far detuned and the standard validity\ncondition is satisfied. This is formally identical to the Melnikov-Arnold\nanalysis of the stochastic pump model. Previous numerical observations of\nBose-Hubbard breakdown are precisely reproduced by our simple model and can be\nattributed to many body enhancement of chaos."
    },
    {
        "anchor": "$\u03b7/s$ of the Normal Phase of Unitary Fermi Gas from $\\varepsilon$\n  Expansion: Using $\\varepsilon$-expansion technique we compute $\\eta/s$, where $\\eta$ is\nthe shear viscosity, $s$ is the entropy density, of the normal phase of unitary\nFermi gas in $d=4-\\varepsilon$ dimensions to LO in $\\varepsilon$. We use\nkinetic theory approach and solve transport equations for medium perturbed by a\nshear hydrodynamic flow. The collision integrals are calculated to\n$\\varepsilon^2$ which is LO. The LO result is temperature independent with\n$\\eta/\\rm s\\simeq (0.11/\\varepsilon^2)(\\hbar/k_B).$ The $d=3$ prediction for\n$\\eta/\\rm s$ exceeds the $\\hbar/4 \\pi k_B$ bound by a factor of about $1.4.$",
        "positive": "Ground states of dipolar spin-orbit-coupled Bose-Einstein condensates in\n  a toroidal trap: We investigate the ground-state structures of dipolar spin-orbit-coupled\nBose-Einstein condensates in a toroidal trap. Combined effects of dipole-dipole\ninteraction (DDI) and spin-orbit coupling (SOC) on the ground states of the\nsystem are discussed. A ground-state phase diagram is obtained as a function of\nthe SOC and DDI strengths. As two new degrees of freedom, the DDI and SOC can\nbe used to obtain the desired ground-state phases and to control the phase\ntransition between various ground states. In particular, the system displays\nexotic topological structures and spin textures, such as half-quantum vortex,\nvortex string, vortex necklace, complex vortex lattice including giant vortex\nand hidden antivortex chains, different skyrmions, meron\n(half-skyrmion)-antimeron (half-antiskyrmion) necklace, and composite\nmeron-antimeron lattice."
    },
    {
        "anchor": "Anderson Molecules: Atoms can form molecules if they attract each other. Here, we show that atoms\nare also able to form bound states not due to the attractive interaction but\nbecause of destructive interference. If the interaction potential changes in a\ndisordered way with a change of the distance between two atoms, Anderson\nlocalization can lead to the formation of exponentially localized bound states.\nWhile disordered interaction potentials do not exist in nature, we show that\nthey can be created by means of random modulation in time of the strength of\nthe original interaction potential between atoms and objects that we dub\nAnderson molecules can be realized in the laboratory.",
        "positive": "Compressibility and spin susceptibility in the evolution from BCS to BEC\n  superfluids: We describe the relation between the isothermal atomic compressibility and\ndensity fluctuations in mixtures of two-component fermions with population or\nmass imbalance. We derive a generalized version of the fluctuation-dissipation\ntheorem which is valid for both balanced and imbalanced Fermi-Fermi mixtures.\nFurthermore, we show that critical exponents for the compressibility can be\nextracted via an analysis of the density fluctuations when phase transitions\noccur as a function of population imbalance or interaction parameter. In\naddition, we demonstrate that in the presence of trapping potentials, the local\ncompressibility, local spin-susceptibility and local density-density\ncorrelations can be extracted from experimental data via a generalized local\nfluctuation-dissipation theorem which is valid beyond the local density\napproximation. Lastly, we use the local density approximation to calculate\ntheoretically the local compressibility, local spin-susceptibility and local\ndensity-density fluctuations to compare with experimental results as they\nbecome available."
    },
    {
        "anchor": "Resonantly Interacting Fermi-Fermi Mixture of $^{161}$Dy and $^{40}$K: We report on the realization of a Fermi-Fermi mixture of ultracold atoms that\ncombines mass imbalance, tunability, and collisional stability. In an optically\ntrapped sample of $^{161}$Dy and $^{40}$K, we identify a broad Feshbach\nresonance centered at a magnetic field of $217\\,$G. Hydrodynamic expansion\nprofiles in the resonant interaction regime reveal a bimodal behavior resulting\nfrom mass imbalance. Lifetime studies on resonance show a suppression of\ninelastic few-body processes by orders of magnitude, which we interpret as a\nconsequence of the fermionic nature of our system. The resonant mixture opens\nup intriguing perspectives for studies on novel states of strongly correlated\nfermions with mass imbalance.",
        "positive": "Bose-Einstein condensates in rotating ring-shaped lattices: a multimode\n  model: We develop a multimode model that describes the dynamics on a rotating\nBose-Einstein condensate confined by a ring-shaped optical lattice with large\nfilling numbers. The parameters of the model are obtained as a function of the\nrotation frequency using full 3D Gross-Pitaevskii simulations. From such\nnumerical calculations, we extract the velocity field induced at each site and\nanalyze the relation and the differences between the phase of the hopping\nparameter of our model and the Peierls phase. To this end, a detailed\ndiscussion of such phases is presented in geometrical terms which takes into\naccount the position of the junctions for different configurations. For\ncircularly symmetric onsite densities a simple analytical relation between the\nhopping phase and the angular momentum is found for arbitrary number of sites.\nFinally, we confront the results of the rotating multimode model dynamics with\nGross-Pitaevskii simulations finding a perfect agreement."
    },
    {
        "anchor": "Spin-sensitive atom mirror via spin-orbit interaction: Based on the spin-orbit coupling recently implemented in a neutral cold-atom\ngas, we propose a scheme to realize spin-dependent scattering of cold atoms. In\nparticular we consider a matter wave packet of cold-atom gas impinging upon a\nstep potential created by the optical light field, inside of which the atoms\nare subject to spin-orbit interaction. We show that the proposed system can act\nas a spin polarizer or spin-selective atom mirror for the incident atomic beam.\nThe principle and the operating parameter regime of the system are carefully\ndiscussed.",
        "positive": "Delocalization of a disordered bosonic system by repulsive interactions: Clarifying the interplay of interactions and disorder is fundamental to the\nunderstanding of many quantum systems, including superfluid helium in porous\nmedia, granular and thin-film superconductors, and light propagating in\ndisordered media. One central aspect for bosonic systems is the competition\nbetween disorder, which tends to localize particles, and weak repulsive\ninteractions, which instead have a delocalizing effect. Since the required\ndegree of independent control of the disorder and of the interactions is not\neasily achievable in most available physical systems, a systematic experimental\ninvestigation of this competition has so far not been possible. Here we employ\nan ultracold atomic Bose-Einstein condensate with tunable repulsive\ninteractions in a quasi-periodic lattice potential to study this interplay in\ndetail. We characterize the entire delocalization crossover through the study\nof the average local shape of the wavefunction, the spatial correlations, and\nthe phase coherence. Three different regimes are identified and compared with\ntheoretical expectations: an exponentially localized Anderson glass, the\nformation of locally coherent fragments, as well as a coherent, extended state.\nOur results illuminate the role of weak repulsive interactions on disordered\nbosonic systems and show that the system and the techniques we employ are\npromising for further investigations of disordered systems with interactions,\nalso in the strongly correlated regime."
    },
    {
        "anchor": "Double Degenerate Bose-Fermi Mixture of Strontium and Lithium: We report on the attainment of a degenerate Fermi gas of $\\rm^{6}Li$ in\ncontact with a Bose-Einstein condensate (BEC) of $^{84}$Sr. A degeneracy of\n$T/T_F=0.33(3)$ is observed with $1.6\\times10^5$ $^{6}$Li atoms in the two\nlowest energy hyperfine states together with an almost pure BEC of\n$3.1\\times10^5$ $^{84}$Sr atoms. The elastic s-wave scattering length between\n$^6$Li and $^{84}$Sr is estimated to be\n$|a_{\\rm^{6}Li-\\rm^{84}Sr}|=(7.1_{-1.7}^{+2.6})a_0$ ($a_0$ being the Bohr\nradius) from measured interspecies thermalization rates in an optical dipole\ntrap.",
        "positive": "Fermion superfluid with hybridized $s$- and $p$-wave pairings: Ever since the pioneering work of Bardeen, Cooper and Schrieffer in the\n1950s, exploring novel pairing mechanisms for fermion superfluids has become\none of the central tasks in modern physics. Here, we investigate a new type of\nfermion superfluid with hybridized $s$- and $p$-wave pairings in an ultracold\nspin-1/2 Fermi gas. Its occurrence is facilitated by the co-existence of\ncomparable $s$- and $p$-wave interactions, which is realizable in a\ntwo-component $^{40}$K Fermi gas with close-by $s$- and $p$-wave Feshbach\nresonances. The hybridized superfluid state is stable over a considerable\nparameter region on the phase diagram, and can lead to intriguing patterns of\nspin densities and pairing fields in momentum space. In particular, it can\ninduce a phase-locked $p$-wave pairing in the fermion species that has no\n$p$-wave interactions. The hybridized nature of this novel superfluid can also\nbe confirmed by measuring the $s$-wave and $p$-wave contacts, which can be\nextracted from the high-momentum tail of the momentum distribution of each spin\ncomponent. These results enrich our knowledge of pairing superfluidity in Fermi\nsystems, and open the avenue for achieving novel fermion superfluids with\nmultiple partial-wave scatterings in cold atomic gases."
    },
    {
        "anchor": "Bose polarons near quantum criticality: The emergence of quasiparticles in strongly interacting matter represents one\nof the cornerstones of modern physics. However, when different phases of matter\ncompete near a quantum critical point, the very existence of quasiparticles\ncomes under question. Here we create Bose polarons near quantum criticality by\nimmersing atomic impurities in a Bose-Einstein condensate (BEC) with\nnear-resonant interactions. Using locally-resolved radiofrequency spectroscopy,\nwe probe the energy, spectral width, and short-range correlations of the\nimpurities as a function of temperature. Far below the superfluid critical\ntemperature, the impurities form well-defined quasiparticles. However, their\ninverse lifetime, given by their spectral width, is observed to increase\nlinearly with temperature at the Planckian scale $\\frac{k_B T}{\\hbar}$, a\nhallmark of quantum critical behavior. Close to the BEC critical temperature,\nthe spectral width exceeds the binding energy of the impurities, signaling a\nbreakdown of the quasiparticle picture.",
        "positive": "Interacting multiple zero mode formulation and its application to a\n  system consisting of a dark soliton in a condensate: To formulate the zero modes in a finite-size system with spontaneous\nbreakdown of symmetries in quantum field theory is not trivial, for in the\nnaive Bogoliubov theory, one encounters difficulties such as phase diffusion,\nthe absence of a definite criterion for determining the ground state, and\ninfrared divergences. A new interacting zero mode formulation that has been\nproposed for systems with a single zero mode to avoid these difficulties is\nextended to general systems with multiple zero modes. It naturally and\ndefinitely gives the interactions among the quantized zero modes, the\nconsequences of which can be observed experimentally. In this paper, as a\ntypical example, we consider an atomic Bose-Einstein condensed system with a\ndark soliton that contains two zero modes corresponding to spontaneous\nbreakdown of the U(1) gauge and translational symmetries. Then we evaluate the\nstandard deviations of the zero mode operators and see how the mutual\ninteraction between the two zero modes affects them."
    },
    {
        "anchor": "Thermal solitons as revealed by static structure factor: We study, within a framework of the classical fields approximation, the\nstatic structure factor of a weakly interacting Bose gas at thermal\nequilibrium. As in a recent experiment (R. Schley et al., Phys. Rev. Lett. 111,\n055301 (2013)), we find that the thermal distribution of phonons in a\nthree-dimensional Bose gas follows the Planck distribution. On the other hand\nwe find a disagreement between the Planck and phonon (calculated just like for\nthe bulk gas) distributions in the case of elongated quasi-one-dimensional\nsystems. We attribute this discrepancy to the existence of spontaneous dark\nsolitons (i.e., thermal solitons as reported in T. Karpiuk et al., Phys. Rev.\nLett. 109, 205302 (2012)) in an elongated Bose gas at thermal equilibrium.",
        "positive": "Hydrodynamics of multi-component Bosonic systems: We obtain the superfluid hydrodynamic equations of a multi-component Bose gas\nwith short-ranged interactions at zero temperature under the local equilibrium\nassumption and show that the quantum pressure is generally present in the\nnonuniform case. Our approach can be extended to systems with long-range\ninteractions such as dipole-dipole interactions by treating the Hartree energy\nproperly. For a highly symmetric superfluid, we obtain the excitation spectrum\nand show that except for the density phonon, all other excitations are all\ndegenerate.The implication of our results is discussed."
    },
    {
        "anchor": "Observation of a red-blue detuning asymmetry in matter-wave\n  superradiance: We report the first experimental observations of strong suppression of\nmatter-wave superradiance using blue-detuned pump light and demonstrate a\npump-laser detuning asymmetry in the collective atomic recoil motion. In\ncontrast to all previous theoretical frameworks, which predict that the process\nshould be symmetric with respect to the sign of the pump-laser detuning, we\nfind that for condensates the symmetry is broken. With high condensate\ndensities and red-detuned light, the familiar distinctive multi-order,\nmatter-wave scattering pattern is clearly visible, whereas with blue-detuned\nlight superradiance is strongly suppressed. In the limit of a dilute atomic\ngas, however, symmetry is restored.",
        "positive": "Superfluid fraction tensor of a two-dimensional supersolid: We investigate the superfluid fraction of crystalline stationary states\nwithin the framework of mean-field Gross-Pitaevskii theory. Our primary focus\nis on a two-dimensional system with a non-local soft-core interaction, where\nthe superfluid fraction is described by a rank-2 tensor. We analyze and\nestablish connections between methods for calculating the superfluid tensor\nderived from analysis of the nonclassical translational inertia and the\neffective mass. We then apply these methods for crystalline states exhibiting\ntriangular, square, and stripe geometries across a broad range of interaction\nparameters. Factors leading to an anisotropic superfluid fraction tensor are\nalso considered. We also refine the Leggett bounds for the superfluid fraction\nto an accurate approach that involves a calculation using the density profile\nover a single unit cell. We systematically compare these bounds to our full\nnumerical results, and other results in the literature. This work is of direct\nrelevance to other supersolid systems of current interest, such as supersolids\nproduced using dipolar Bose-Einstein condensates."
    },
    {
        "anchor": "Dynamical solitons and boson fractionalization in cold-atom topological\n  insulators: We study the $\\mathbb{Z}_2$ Bose-Hubbard model at incommensurate densities,\nwhich describes a one-dimensional system of interacting bosons whose tunneling\nis dressed by a dynamical $\\mathbb{Z}_2$ field. At commensurate densities, the\nmodel is known to host intertwined topological phases, where long-range order\ncoexists with non-trivial topological properties. This interplay between\nspontaneous symmetry breaking (SSB) and topological symmetry protection gives\nrise to interesting fractional topological phenomena when the system is doped\nto certain incommensurate fillings. In particular, we hereby show how\ntopological defects in the $\\mathbb{Z}_2$ field can appear in the ground state,\nconnecting different SSB sectors. These defects are dynamical and can travel\nthrough the lattice carrying both a topological charge and a fractional\nparticle number. In the hardcore limit, this phenomenon can be understood\nthrough a bulk-defect correspondence. Using a pumping argument, we show that it\nsurvives also for finite interactions, demonstrating how boson\nfractionalization can occur in strongly-correlated bosonic systems, the main\ningredients of which have already been realized in cold-atom experiments.",
        "positive": "Direct imaging of the order parameter of an atomic superfluid using\n  matterwave optics: We propose a method to directly measure the complex phase distribution,\nsuperfluid density and velocity field in an ultracold atomic superfluid. The\nmethod consists of mapping the momentum distribution of the gas to real space\nusing matterwave focusing, and manipulating the amplitude and phase by means of\ntailor made optical potentials. This makes it possible to find analogues of\nwell-known techniques in optical microscopy such as Zernike phase contrast\nimaging, dark field imaging and schlieren imaging. Applying these ideas\ndirectly at the level of the macroscopic wavefunction of the superfluid will\nallow visualization of interesting effects such as phase fluctuations and\ntopological defects, and enable measurements of transport properties such as\nvorticity."
    },
    {
        "anchor": "Generalized HydroDynamics on an Atom Chip: The emergence of a special type of fluid-like behavior at large scales in\none-dimensional (1d) quantum integrable systems, theoretically predicted in\n2016, is established experimentally, by monitoring the time evolution of the in\nsitu density profile of a single 1d cloud of $^{87}{\\rm Rb}$ atoms trapped on\nan atom chip after a quench of the longitudinal trapping potential. The theory\ncan be viewed as a dynamical extension of the thermodynamics of Yang and Yang,\nand applies to the whole range of repulsion strength and temperature of the\ngas. The measurements, performed on weakly interacting atomic clouds that lie\nat the crossover between the quasicondensate and the ideal Bose gas regimes,\nare in very good agreement with the 2016 theory. This contrasts with the\npreviously existing 'conventional' hydrodynamic approach---that relies on the\nassumption of local thermal equilibrium---, which is unable to reproduce the\nexperimental data.",
        "positive": "Quasi 1D Bose-Einstein condensate flow past a nonlinear barrier: The problem of a quasi 1D {\\it repulsive} BEC flow past through a nonlinear\nbarrier is investigated. Two types of nonlinear barriers are considered, wide\nand short range ones. Steady state solutions for the BEC moving through a wide\nrepulsive barrier and critical velocities have been found using hydrodynamical\napproach to the 1D Gross-Pitaevskii equation. It is shown that in contrast to\nthe linear barrier case, for a wide {\\it nonlinear} barrier an interval of\nvelocities $0 < v < v_-$ {\\it always} exists, where the flow is superfluid\nregardless of the barrier potential strength. For the case of the $\\delta$\nfunction-like barrier, below a critical velocity two steady solutions exist,\nstable and unstable one. An unstable solution is shown to decay into a gray\nsoliton moving upstream and a stable solution. The decay is accompanied by a\ndispersive shock wave propagating downstream in front of the barrier."
    },
    {
        "anchor": "Time-averaged adiabatic ring potential for ultracold atoms: We report the experimental realisation of a versatile ring trap for ultracold\natoms. The ring geometry is created by the time-averaged adiabatic potential\nresulting from the application of an oscillating magnetic bias field to a rf\ndressed quadrupole trap. Lifetimes for a Bose-Einstein condensate in the ring\nexceed 11s and the ring radius was continuously varied from 50$\\mu$m to\n261$\\mu$m. An efficient method of loading the ring from a conventional TOP trap\nis presented together with a rotation scheme which introduces angular momentum\ninto the system. The ring presents an opportunity to study the superfluid\nproperties of a condensate in a multiply connected geometry and also has\napplications for matter-wave interferometry.",
        "positive": "Finite temperature correlations in the Lieb-Liniger 1D Bose gas: We address the problem of calculating finite-temperature response functions\nof an experimentally relevant low-dimensional strongly-correlated system: the\nintegrable 1D Bose gas with repulsive \\delta-function interaction (Lieb-Liniger\nmodel). Focusing on the observable dynamical density-density function, we\npresent a Bethe Ansatz-based method allowing for its accurate evaluation over a\nbroad range of momenta, frequencies, temperatures and interaction parameters,\nin finite but large systems. We show how thermal fluctuations smoothen the zero\ntemperature critical behavior and present explicit quantitative results in\nexperimentally accessible regimes."
    },
    {
        "anchor": "Counterflow instability and turbulence in a spin-1 spinor Bose--Einstein\n  condensate: We theoretically study counterflow instability and turbulence in a spin-1\nspinor Bose--Einstein condensate by the Gross--Pitaevskii equation and the\nBogoliubov--de Gennes equation. Our study considers (i) the dynamics induced by\nthe counterflow of two components with different magnetic quantum numbers,\nwhich leads to turbulence with spin degrees of freedom, and (ii) the properties\nof the turbulence. For (i), the behavior of the condensate induced by the\ncounterflow strongly depends on whether the spin-dependent interaction is\nferromagnetic or antiferromagnetic, leading to different behaviors for the\ndispersion relation and the spin density vector, $etc$. For (ii), we\nnumerically calculate the spectrum of the spin-dependent interaction energy,\nwhich also depends on the spin-dependent interaction. The spectrum of the\nspin-dependent interaction energy in the ferromagnetic case exhibits a -7/3\npower law, whereas that in the antiferromagnetic case does not. The -7/3 power\nlaw can be explained by scaling analysis.",
        "positive": "Excitation spectrum of a toroidal spin-1 Bose-Einstein condensate: We calculate analytically the Bogoliubov excitation spectrum of a toroidal\nspin-1 Bose-Einstein condensate that is subjected to a homogeneous magnetic\nfield and contains vortices with arbitrary winding numbers in the $m_F=\\pm 1$\ncomponents of the hyperfine spin. We show that a rotonlike spectrum can be\nobtained, or an initially stable condensate can be made unstable by adjusting\nthe magnitude of the magnetic field or the trapping frequencies. The structure\nof the instabilities can be analyzed by measuring the particle densities of the\nspin components. We confirm the validity of the analytical calculations by\nnumerical simulations."
    },
    {
        "anchor": "Pair Correlations in the Two-Dimensional Fermi Gas: We consider the two-dimensional Fermi gas at finite temperature with\nattractive short-range interactions. Using the virial expansion, which provides\na controlled approach at high temperatures, we determine the spectral function\nand contact for the normal state. Our calculated spectra are in qualitative\nagreement with recent photoemission measurements [M. Feld et al., Nature 480,\n75 (2011)], thus suggesting that the observed pairing gap is a feature of the\nhigh-temperature gas rather than being evidence of a pseudogap regime just\nabove the superfluid transition temperature. We further argue that the strong\npair correlations result from the fact that the crossover to bosonic dimers\noccurs at weaker interactions than previously assumed.",
        "positive": "Magnetic phase transitions of spin-1 ultracold bosons in a cubic optical\n  lattice: We investigate strongly correlated spin-1 ultracold bosons with\nantiferromagnetic interactions in a cubic optical lattice, based on bosonic\ndynamical mean-field theory. Rich phase diagrams of the system are mapped out\nat both zero and finite temperature, and in particular the existence of a\nspin-singlet condensate is established. Interestingly, at finite temperature,\nwe find that the superfluid can be heated into a Mott insulator with even (odd)\nfilling via a first- (second-) order phase transition, analogous to the\nPomeranchuk effect in $^{3}$He. Moreover, for typical experimental setups, we\nestimate the critical temperatures for different ordered phases and our results\nsuggest that direct experimental observation of these phases is promising."
    },
    {
        "anchor": "Self-accelerating beam dynamics in the space fractional Schr\u00f6dinger\n  equation: Self-accelerating beams are fascinating solutions of the Schr\\\"odinger\nequation. Thanks to their particular phase engineering, they can accelerate\nwithout the need of external potentials or applied forces. Finite-energy\napproximations of these beams have led to many applications, spanning from\nparticle manipulation to robust in vivo imaging. The most studied and\nemblematic beam, the Airy beam, has been recently investigated in the context\nof the fractional Schr\\\"odinger equation. It was notably found that the packet\nacceleration would decrease with the reduction of the fractional order. Here, I\nstudy the case of a general nth-order self-accelerating caustic beam in the\nfractional Schr\\\"odinger equation. Using a Madelung decomposition combined with\nthe wavelet transform, I derive the analytical expression of the beam's\nacceleration. I show that the non-accelerating limit is reached for infinite\nphase order or when the fractional order is reduced to 1. This work provides a\nquantitative description of self-accelerating caustic beams' properties.",
        "positive": "Superfluid, solid, and supersolid phases of dipolar bosons in a\n  quasi-one-dimensional optical lattice: We discuss a model of dipolar bosons trapped in a weakly coupled planar array\nof one-dimensional tubes. We consider the situation where the dipolar moments\nare aligned by an external field, and find a rich phase diagram as a function\nof the angle of this field exhibiting quantum phase transitions between solid,\nsuperfluid and supersolid phases. In the low energy limit, the model turns out\nto be identical to one describing quasi-one-dimensional superconductivity in\ncondensed matter systems. This opens the possibility of using bosons as a\nquantum analogue simulator of electronic systems, a scenario arising from the\nintricate relation between statistics and interactions in quasi-one-dimensional\nsystems."
    },
    {
        "anchor": "Symmetry breaking Rayleigh-Taylor instability in a two-component\n  Bose-Einstein condensate: The interfacial instability and subsequent dynamics in a phase-separated\ntwo-component Bose-Einstein condensate with rotation symmetry are studied. When\nthe interatomic interaction or the trap frequency is changed, the\nRayleigh-Taylor instability breaks the rotation symmetry of the interface,\nwhich is subsequently deformed into nonlinear patterns including mushroom\nshapes.",
        "positive": "Dynamical instability towards finite-momentum pairing in quenched BCS\n  superconducting phases: In this work we numerically investigate the fate of the\nBardeen-Cooper-Schrieffer (BCS) pairing in the presence of quenched phase under\nPeierls substitution using time-dependent real space and momentum space\nBogoliubov-de Gennes equation methods and Anderson pseudospin representation\nmethod. This kind of phase imprint can be realized by modulating electric field\nin ultracold atoms and illumining of THz optical pump pulse in solids with\nconventional and unconventional superconductors. In the case of weak phase\nimprint, the BCS pairing is stable; while in the strong phase imprint,\ninstability towards finite-momentum pairing is allowed, in which the real space\nand momentum space methods yield different results. In the pulsed gauge\npotential, we find that this instability will not happen even with much\nstronger vector potential. We also show that the uniform and staggered gauge\npotentials yield different behaviors. While the staggered potential induces\ntransition from the BCS pairing to over-damped phase, the uniform gauge may\nenhance the pairing and will not induce to the over-damped phase. These result\nmay shade light on the realization of finite momentum pairing, such as\nFulde-Ferrell-Larkin-Ovchinnikov phase with dynamical modulation."
    },
    {
        "anchor": "Spin nematic order in antiferromagnetic spinor condensates: Large spin systems can exhibit unconventional types of magnetic ordering\ndifferent from the ferromagnetic or N\\'eel-like antiferromagnetic order\ncommonly found in spin 1/2 systems. Spin-nematic phases, for instance, do not\nbreak time-reversal invariance and their magnetic order parameter is\ncharacterized by a second rank tensor with the symmetry of an ellipsoid. Here\nwe show direct experimental evidence for spin-nematic ordering in a spin-1\nBose-Einstein condensate of sodium atoms with antiferromagnetic interactions.\nIn a mean field description this order is enforced by locking the relative\nphase between spin components. We reveal this mechanism by studying the spin\nnoise after a spin rotation, which is shown to contain information hidden when\nlooking only at averages. The method should be applicable to high spin systems\nin order to reveal complex magnetic phases.",
        "positive": "Exact diagonalization study of the trionic crossover and the trion\n  liquid in the attractive three-component Hubbard model: We investigate the trion formation and the effective trionic properties in\nthe attractive Hubbard model with three fermionic colors using exact\ndiagonalization. The crossover to the trionic regime with colorless compound\nfermions upon increasing strength of the onsite attraction parameter U features\nsmoothly evolving ground state properties and exhibits clear similarities to\nthe BCS/BEC-crossover for two colors. In the excitation spectrum, there is a\nclear gap opening between a band of well-defined trions and excitations of\nbroken-up trions at U_c ~ 1.8t. This picture remains the same away from the\nSU(3)-symmetric point. The spatial pairing correlations for colored Cooper\npairs are compatible with a power-law at small attractions and change to an\nexponential decay above the trionic crossover. Furthermore, we show that the\neffective trionic liquid for U > U_c can be well modeled with spinless 'heavy'\nfermions interacting with a strong nearest neighbor repulsion."
    },
    {
        "anchor": "Intrinsic anomalous Hall effect across the magnetic phase transition of\n  a spin-orbit-coupled Bose-Einstein condensate: We study theoretically the zero temperature intrinsic anomalous Hall effect\nin an experimentally realized 2D spin-orbit coupled Bose gas. For anisotropic\natomic interactions and as the spin-orbit coupling strength increases, the\nsystem undergoes a ground state phase transition from states exhibiting a total\nin-plane magnetization to those with a perpendicular magnetization along the\n$z$ direction. We show that finite frequency, or ac, Hall responses exist in\nboth phases in the absence of an artificial magnetic field, as a result of\nfinite inter-band transitions. However, the characteristics of the anomalous\nHall responses are drastically different in these two phases because of the\ndifferent symmetries preserved by the corresponding ground states. In\nparticular, we find a finite dc Hall conductivity in one phase but not the\nother. The underlying physical reasons for this are analyzed further by\nexploring relations of the dc Hall conductivity to the system's chirality and\nBerry curvatures of the Bloch bands. Finally, we discuss an experimental method\nof probing the anomalous Hall effect in trapped systems.",
        "positive": "Ballistic atom pumps: We examine a classically-chaotic system consisting of two reservoirs of\nparticles connected by a channel containing oscillating potential-energy\nbarriers. We investigate whether such a system can preferentially pump\nparticles from one reservoir to the other, a process often called \"quantum\npumping.\" We show how to make a \"particle diode\" which under specified\nconditions permits net particle pumping in only one direction. Then we examine\nsystems having symmetric barriers. We find that if all initial particle\nenergies are considered, a system with symmetric barriers cannot preferentially\npump particles. However, if only finite initial energy bands are considered,\nthe system can create net particle transport in either direction. We study the\nsystem classically, semiclassically, and quantum mechanically, and find that\nthe quantum description cannot be fully understood without the insight gained\nfrom classical and semiclassical analysis."
    },
    {
        "anchor": "A Thouless Quantum Pump with Ultracold Bosonic Atoms in an Optical\n  Superlattice: More than 30 years ago, Thouless introduced the concept of a topological\ncharge pump that would enable the robust transport of charge through an\nadiabatic cyclic evolution of the underlying Hamiltonian. In contrast to\nclassical transport, the transported charge was shown to be quantized and\npurely determined by the topology of the pump cycle, making it robust to\nperturbations. On a fundamental level, the quantized charge transport can be\nconnected to a topological invariant, the Chern number, first introduced in the\ncontext of the integer quantum Hall effect. A Thouless quantum pump may\ntherefore be regarded as a 'dynamical' version of the integer quantum Hall\neffect. Here, we report on the realization of such a topological charge pump\nusing ultracold bosonic atoms that form a Mott insulator in a dynamically\ncontrolled optical superlattice potential. By taking in-situ images of the atom\ncloud, we observe a quantized deflection per pump cycle. We reveal the genuine\nquantum nature of the pump by showing that, in contrast to ground state\nparticles, a counterintuitive reversed deflection occurs when particles are\nprepared in the first excited band. Furthermore, we were able to directly\ndemonstrate that the system undergoes a controlled topological phase transition\nin higher bands when tuning the superlattice parameters.",
        "positive": "Preparing Quantum States by Measurement-feedback Control with Bayesian\n  Optimization: Preparation of quantum states is of vital importance for performing quantum\ncomputations and quantum simulations. In this work, we propose a general\nframework for preparing ground states of many-body systems by combining the\nmeasurement-feedback control process (MFCP) and the machine learning method.\nUsing the Bayesian optimization (BO) strategy, the efficiency of determining\nthe measurement and feedback operators in the MFCP is demonstrated. Taking the\none dimensional Bose-Hubbard model as an example, we show that BO can generate\noptimal parameters, although constrained by the operator basis, which can drive\nthe system to the low energy state with high probability in typical quantum\ntrajectories."
    },
    {
        "anchor": "Faraday and resonant waves in binary collisionally-inhomogeneous\n  Bose-Einstein condensates: We study Faraday and resonant waves in two-component quasi-one-dimensional\n(cigar-shaped) collisionally inhomogeneous Bose-Einstein condensates subject to\nperiodic modulation of the radial confinement. We show by means of extensive\nnumerical simulations that, as the system exhibits stronger spatially-localised\nbinary collisions (whose scattering length is taken for convenience to be of\nGaussian form), the system becomes effectively a linear one. In other words, as\nthe scattering length approaches a delta-function, we observe that the two\nnonlinear configurations typical for binary cigar-shaped condensates, namely\nthe segregated and the symbiotic one, turn into two overlapping Gaussian wave\nfunctions typical for linear systems, and that the instability onset times of\nthe Faraday and resonant waves become longer. Moreover, our numerical\nsimulations show that the spatial period of the excited waves (either resonant\nor Faraday ones) decreases as the inhomogeneity becomes stronger. Our results\nalso demonstrate that the topology of the ground state impacts the dynamics of\nthe ensuing density waves, and that the instability onset times of Faraday and\nresonant waves, for a given level of inhomogeneity in the two-body\ninteractions, depend on whether the initial configuration is segregated or\nsymbiotic.",
        "positive": "Matter-wave analog of an optical random laser: The accumulation of atoms in the lowest energy level of a trap and the\nsubsequent out-coupling of these atoms is a realization of a matter-wave analog\nof a conventional optical laser. Optical random lasers require materials that\nprovide optical gain but, contrary to conventional lasers, the modes are\ndetermined by multiple scattering and not a cavity. We show that a\nBose-Einstein condensate can be loaded in a spatially correlated disorder\npotential prepared in such a way that the Anderson localization phenomenon\noperates as a band-pass filter. A multiple scattering process selects atoms\nwith certain momenta and determines laser modes which represents a matter-wave\nanalog of an optical random laser."
    },
    {
        "anchor": "Quantum information entropies of ultra-cold atomic gases in a harmonic\n  trap: The position and momentum space information entropies of weakly interacting\ntrapped atomic Bose-Einstein condensates and spin-polarized trapped atomic\nFermi gases at absolute zero temperature are evaluated. We find that sum of the\nposition and momentum space information entropies of these quantum systems\ncontain $N$ atoms confined in a $D(\\le 3)$-dimensional harmonic trap has a\nuniversal form as $ S_t^{(D)} = N(a D - b \\ln N) $, where $a \\simeq 2.332$ and\n$b = 2$ for interacting bosonic systems and $a \\simeq 1.982$ and $b = 1$ for\nideal fermionic systems. These results obey the entropic uncertainty relation\ngiven by the Beckner, Bialynicki-Birula and Myceilski.",
        "positive": "Observation of canted antiferromagnetism with ultracold fermions in an\n  optical lattice: Understanding the magnetic response of the normal state of the cuprates is\nconsidered a key piece in solving the puzzle of their high-temperature\nsuperconductivity. The essential physics of these materials is believed to be\ncaptured by the Fermi-Hubbard model, a minimal model that has been realized\nwith cold atoms in optical lattices. Here we report on site-resolved\nmeasurements of the Fermi-Hubbard model in a spin-imbalanced atomic gas,\nallowing us to explore the response of the system to large effective magnetic\nfields. We observe short-range canted antiferromagnetism at half-filling with\nstronger spin correlations in the direction orthogonal to the magnetization, in\ncontrast with the spin-balanced case where identical correlations are measured\nfor any projection of the pseudospin. The rotational anisotropy of the spin\ncorrelators is found to increase with polarization and with distance between\nthe spins. Away from half-filling, the polarization of the gas exhibits\nnon-monotonic behavior with doping for strong interactions, resembling the\nbehavior of the magnetic susceptibility in the cuprates. We compare our\nmeasurements to predictions from Determinantal Quantum Monte Carlo (DQMC) and\nNumerical Linked Cluster Expansion (NLCE) algorithms and find good agreement.\nCalculations on the doped system are near the limits of these techniques,\nillustrating the value of cold atom quantum simulations for studying\nstrongly-correlated materials."
    },
    {
        "anchor": "Rayleigh-Taylor instability and mushroom-pattern formation in a\n  two-component Bose-Einstein condensate: The Rayleigh-Taylor instability at the interface in an immiscible\ntwo-component Bose-Einstein condensate is investigated using the mean-field and\nBogoliubov theories. Rayleigh-Taylor fingers are found to grow from the\ninterface and mushroom patterns are formed. Quantized vortex rings and vortex\nlines are then generated around the mushrooms. The Rayleigh-Taylor instability\nand mushroom-pattern formation can be observed in a trapped system.",
        "positive": "Energy, decay rate, and effective masses for a moving polaron in a Fermi\n  sea: Explicit results in the weakly attractive limit: We study the properties of an impurity of mass $M$ moving through a spatially\nhomogeneous three-dimensional fully polarized Fermi gas of particles of mass\n$m$. In the weakly attractive limit, where the effective coupling constant\n$g\\to0^-$ and perturbation theory can be used, both for a broad and a narrow\nFeshbach resonance, we obtain an explicit analytical expression for the complex\nenergy $\\Delta E(\\KK)$ of the moving impurity up to order two included in $g$.\nThis also gives access to its longitudinal and transverse effective masses\n$m_\\parallel^*(\\KK)$, $m_\\perp^*(\\KK)$, as functions of the impurity wave\nvector $\\KK$. Depending on the modulus of $\\KK$ and on the impurity-to-fermion\nmass ratio $M/m$ we identify four regions separated by singularities in\nderivatives with respect to $\\KK$ of the second-order term of $\\Delta E(\\KK)$,\nand we discuss the physical origin of these regions. Remarkably, the\nsecond-order term of $m_\\parallel^*(\\KK)$ presents points of\nnon-differentiability, replaced by a logarithmic divergence for $M=m$, when\n$\\KK$ is on the Fermi surface of the fermions. We also discuss the third-order\ncontribution and relevance for cold atom experiments."
    },
    {
        "anchor": "Dynamical mechanisms of vortex pinning in superfluid thin films: We characterize the mechanisms of vortex pinning in a superfluid thin film\ndescribed by the two-dimensional Gross-Pitaevskii equation. We consider a\nvortex \"scattering experiment\" whereby a single vortex in a superfluid flow\ninteracts with a circular, uniform pinning potential. By an analogy with linear\ndielectrics, we develop an analytical hydrodynamic approximation that predicts\nvortex trajectories, the vortex fixed point and the unpinning velocity. We then\nsolve the Gross-Pitaevskii equation to validate this model, and build a phase\nportrait of vortex pinning. We identify two different dynamical pinning\nmechanisms marked by distinctive phonon emission signatures: one enabled by\nacoustic radiation and another mediated by vortex dipoles nucleated within the\npin. Relative to obstacle size, we find that pinning potentials on the order of\nthe healing length are more effective for vortex capture. Our results could be\nuseful in mitigating the negative effects of drag due to vortices in superfluid\nchannels, in analogy to maximising supercurrents in type-II superconductors.",
        "positive": "Quantum melting of two-component Rydberg crystals: We investigate the quantum melting of one dimensional crystals that are\nrealized in an atomic lattice in which ground state atoms are laser excited to\ntwo Rydberg states. We focus on a regime where both, intra- and inter-state\ndensity-density interactions as well as coherent exchange interactions\ncontribute. We determine stable crystalline phases in the classical limit and\nexplore their melting under quantum fluctuations introduced by the excitation\nlaser as well as two-body exchange. We find that within a specific parameter\nrange quantum fluctuations introduced by the laser can give rise to a devil's\nstaircase structure which one might associate with transitions in the classical\nlimit. The melting through exchange interactions is shown to also proceed in a\nstep-like fashion, in case of small crystals, due to the proliferation of\nRydberg spinwaves."
    },
    {
        "anchor": "Semiclassical polaron dynamics of impurities in ultracold gases: We present a semiclassical treatment of a fermionic impurity coupled to\nBogolyubov modes of a BEC. In the lowest order approximation we find a full\nsolution of an initial value problem, which turns out to behave differently in\nthe sub- and supersonic regimes. While in the former case no impurity\ndeceleration is observed, in the latter case non-Markovian dissipation effects\nkick in resulting in slowing down of the fermion. Although this scenario is\ncompatible with the one offered by an elementary field theoretical picture at\nweak coupling, the details of the dynamics turn out to be completely different.\nFluctuation effects can be taken into account by expansion around the classical\npath. This allows for estimation of the all-important polaron radius as a\nfunction of fermion-boson coupling strength. As an application we calculate the\ndrag force which is exerted by the BEC on the impurity moving with constant\nvelocity $v$. Contrary to the perturbative result, according to which the drag\nforce is $\\sim v^4$, it turns out to be proportional to $1/v^2$ in the\nsemiclassical regime.",
        "positive": "Nonlinear Bose-Einstein-condensate Dynamics Induced by a Harmonic\n  Modulation of the s-wave Scattering Length: In a recent experiment, a Bose-Einstein condensate of Li7 has been excited by\na harmonic modulation of the atomic s-wave scattering length via Feshbach\nresonance. By combining an analytical perturbative approach with extensive\nnumerical simulations we analyze the emerging nonlinear dynamics of the system\non the mean-field Gross-Pitaevskii level at zero temperature. Resulting\nexcitation spectra are presented and prominent nonlinear features are found:\nmode coupling, higher harmonics generation and significant shifts in the\nfrequencies of collective modes. We indicate how nonlinear dynamical properties\ncould be made clearly observable in future experiments and compared to our\nresults."
    },
    {
        "anchor": "Critical Phenomena and Kibble-Zurek Scaling in the Long-Range Quantum\n  Ising Chain: We investigate an extension of the quantum Ising model in one spatial\ndimension including long-range $1 / r^{\\alpha}$ interactions in its statics and\ndynamics with possible applications from heteronuclear polar molecules in\noptical lattices to trapped ions described by two-state spin systems. We\nintroduce the statics of the system via both numerical techniques with finite\nsize and infinite size matrix product states and a theoretical approaches using\na truncated Jordan-Wigner transformation for the ferromagnetic and\nantiferromagnetic case and show that finite size effects have a crucial role\nshifting the quantum critical point of the external field by fifteen percent\nbetween thirty-two and around five-hundred spins. We numerically study the\nKibble-Zurek hypothesis in the long-range quantum Ising model with Matrix\nProduct States. A linear quench of the external field through the quantum\ncritical point yields a power-law scaling of the defect density as a function\nof the total quench time. For example, the increase of the defect density is\nslower for longer-range models and the critical exponent changes by twenty-five\nper cent. Our study emphasizes the importance of such long-range interactions\nin statics and dynamics that could point to similar phenomena in a different\nsetup of dynamical systems or for other models.",
        "positive": "Finite size correction to the thermo-magnetic properties of charged Bose\n  gas: We consider the finite size effect on thermo-magnetic properties of charged\nBose gases confined in a quasi two-dimentsional potential. A modified\nsemiclassical approach is used, taking into account the finite size correction\nto guarantee an accurate density of states. The charged spinless Bose gas shows\ndiamagnetic behavior. Temperature dependent magnetization is indicated for the\ninvestigated system that condense at a resistive critical temperature in\naccordance with the applied magnetic field."
    },
    {
        "anchor": "Interference of spin-orbit coupled Bose-Einstein condensates: Interference of atomic Bose-Einstein condensates, observed in free expansion\nexperiments, is a basic characteristic of their quantum nature. The ability to\nproduce synthetic spin-orbit coupling in Bose-Einstein condensates has recently\nopened a new research field. Here we theoretically describe interference of two\nnoninteracting spin-orbit coupled Bose-Einstein condensates in an external\nsynthetic magnetic field. We demonstrate that the spin-orbit and the Zeeman\ncouplings strongly influence the interference pattern determined by the angle\nbetween the spins of the condensates, as can be seen in time-of-flight\nexperiments. We show that a quantum backflow, being a subtle feature of the\ninterference, is, nevertheless, robust against the spin-orbit coupling and\napplied synthetic magnetic field.",
        "positive": "Sound modes in collisional superfluid Bose gases: We theoretically investigate sound modes in a weakly-interacting collisional\nBose gas in $D$ dimensions. Using the Landau's two-fluid hydrodynamics and\nworking within the Bogoliubov theory, we observe the hybridization of the first\nand second sound modes for $D\\ge 2$. To model the recent measurements of the\nsound velocities in 2D, obtained in the weakly-interacting regime and around\nthe Berezinskii-Kosterlitz-Thouless transition temperature, we derive a refined\ncalculation of the superfluid density, finding a fair agreement with the\nexperiment. In the 1D case, for which experimental results are currently\nunavailable, we find no hybridization, triggering the necessity of future\ninvestigations. Our analysis provides a systematic understanding of sound\npropagation in a collisional weakly-interacting Bose gas in $D$ dimensions."
    },
    {
        "anchor": "Two-component superfluid hydrodynamics of neutron star cores: We consider the hydrodynamics of the outer core of a neutron star under\nconditions when both neutrons and protons are superfluid. Starting from the\nequation of motion for the phases of the wave functions of the condensates of\nneutron pairs and proton pairs we derive the generalization of the Euler\nequation for a onecomponent fluid. These equations are supplemented by the\nconditions for conservation of neutron number and proton number. Of particular\ninterest is the effect of entrainment, the fact that the current of one nucleon\nspecies depends on the momenta per nucleon of both condensates. We find that\nthe nonlinear terms in the Euler-like equation contain contributions that have\nnot always been taken into account in previous applications of superfluid\nhydrodynamics. We apply the formalism to determine the frequency of\noscillations about a state with stationary condensates and states with a\nspatially uniform counterflow of neutrons and protons. The velocities of the\ncoupled sound-like modes of neutrons and protons are calculated from properties\nof uniform neutron star matter evaluated on the basis of chiral effective field\ntheory. We also derive the condition for the two-stream instability to occur.",
        "positive": "Finite temperature damping of collective modes of a BCS-BEC crossover\n  superfluid: A new mechanism is proposed to explain the puzzling damping of collective\nexcitations, which was recently observed in the experiments of strongly\ninteracting Fermi gases below the superfluid critical temperature on the\nfermionic (BCS) side of Feshbach resonance. Sound velocity, superfluid density\nand damping rate are calculated with effective field theory. We find that a\ndominant damping process is due to the interaction between superfluid phonons\nand thermally excited fermionic quasiparticles, in contrast to the previously\nproposed pair-breaking mechanism. Results from our effective model are compared\nquantitatively with recent experimental findings, showing a good agreement."
    },
    {
        "anchor": "Theory for Bose-Einstein condensation of light in nano-fabricated\n  semiconductor microcavities: We construct a theory for Bose-Einstein condensation of light in\nnano-fabricated semiconductor microcavities. We model the semiconductor by one\nconduction and one valence band which consist of electrons and holes that\ninteract via a Coulomb interaction. Moreover, we incorporate screening effects\nby using a contact interaction with the scattering length for a Yukawa\npotential and describe in this manner the crossover from exciton gas to\nelectron-hole plasma as we increase the excitation level of the semiconductor.\nWe then show that the dynamics of the light in the microcavities is damped due\nto the coupling to the semiconductor. Furthermore, we demonstrate that on the\nelectron-hole plasma side of the crossover, which is relevant for the\nBose-Einstein condensation of light, this damping can be described by a single\ndimensionless damping parameter that depends on the external pumping.\nHereafter, we propose to probe the superfluidity of light in these\nnano-fabricated semiconductor microcavities by making use of the differences in\nthe response in the normal or superfluid phase to a sudden rotation of the\ntrap. In particular, we determine frequencies and damping of the scissors modes\nthat are excited in this manner. Moreover, we show that a distinct signature of\nthe dynamical Casimir effect can be observed in the density-density\ncorrelations of the excited light fluid.",
        "positive": "Airy-averaged gradient corrections for two-dimensional fermion gases: Building on the discussion in PRA 93, 042510 (2016), we present a systematic\nderivation of gradient corrections to the kinetic-energy functional and the\none-particle density, in particular for two-dimensional systems. We derive the\nleading gradient corrections from a semiclassical expansion based on Wigner's\nphase space formalism and demonstrate that the semiclassical kinetic-energy\ndensity functional at zero temperature cannot be evaluated unambiguously. In\ncontrast, a density-potential functional description that effectively\nincorporates interactions provides unambiguous gradient corrections. Employing\nan averaging procedure that involves Airy functions, thereby partially\nresumming higher-order gradient corrections, we facilitate a smooth transition\nof the particle density into the classically forbidden region of arbitrary\nsmooth potentials. We find excellent agreement of the semiclassical\nAiry-averaged particle densities with the exact densities for very low but\nfinite temperatures, illustrated for a Fermi gas with harmonic potential\nenergy. We furthermore provide criteria for the applicability of the\nsemiclassical expansions at low temperatures. Finally, we derive a well-behaved\nground-state kinetic-energy functional, which improves on the Thomas-Fermi\napproximation."
    },
    {
        "anchor": "Two-stream instability in quasi-one-dimensional Bose-Einstein\n  condensates: We apply a kinetic model to predict the existence of an instability mechanism\nin elongated Bose-Einstein condensates. Our kinetic description, based on the\nWigner formalism, is employed to highlight the existence of unstable Bogoliubov\nwaves that may be excited in the counterpropagation configuration. We identify\na dimensionless parameter, the Mach number at T = 0, that tunes different\nregimes of stability. We also estimate the magnitude of the main parameters at\nwhich two-stream instability is expected to be observed under typical\nexperimental conditions.",
        "positive": "Universal scaling of spin mixing dynamics in a strongly interacting\n  one-dimensional Fermi gas: We study the spin-mixing dynamics of a one-dimensional strongly repulsive\nFermi gas under harmonic confinement. By employing a mapping onto an\ninhomogeneous isotropic Heisenberg model and the symmetries under particle\nexchange, we follow the dynamics till very long times. Starting from an initial\nspin-separated state, we observe superdiffusion, spin-dipolar large amplitude\noscillations and thermalization. We report a universal scaling of the\noscillations with particle number N^1/4, implying a slow-down of the motion and\nthe decrease of the zero-temperature spin drag coefficient as the particle\nnumber grows."
    },
    {
        "anchor": "Destruction of attractive bosonic cloud due to high spatial coherence in\n  tight trap: We study coherence of a trapped bosonic cloud with attractive finite-range\ninteraction in a tight harmonic trap. One-body density and pair-distribution\nfunction in the ground state for different trap sizes are calculated. We also\ncalculate healing length and the correlation length which signify the presence\nof high spatial coherence in a very tight trap leading to the destruction of\nthe condensate for a fixed particle number. This is in marked variance with the\nusual collapse of the attractive metastable condensate when N > Ncr . Thus we\ninvestigate the critical frequency and critical size of the trap for the\nexistence of attractive Bose-Einstein condensation. The finite-range\ninteraction gives a nonlocal effect in the effective many-body potential, and\nwe observe a high-density stable branch besides the known metastable branch.\nMoreover, the new branch shows universal behavior even in the very tight trap.",
        "positive": "Superfluidity fraction of few bosons in an annular geometry in the\n  presence of a rotating weak link: We report a beyond mean-field calculation of mass current and superfluidity\nfraction for a system of few bosons confined in a ring geometry in the presence\nof a rotating weak link induced by a potential barrier. We apply the\nMulticonfiguration Hartree Method for bosons to compute the ground state of the\nsystem and show the average superfluidity fraction for a wide range of\ninteraction strength and barrier height, highlighting the behavior of density\ncorrelation functions. The decrease of superfluidity fraction due to the\nincrease of barrier height is found whereas the condensation fraction depends\nexclusively on the interaction strength, showing the independence of both\nphenomena."
    },
    {
        "anchor": "Kondo Effect in a Spin-3/2 Fermi Gas: We investigate the Kondo effect of a spin-3/2 Fermi gas and give a detailed\ncalculation of the impurity resistance and ground state energy based on the s-d\nexchange model. It is found that the impurity resistance increases\nlogarithmically with the decrease of temperature in the case of\nantiferromagnetic coupling similar to the spin-1/2 system but has a larger\nresistance minimum value due to the increase of spin scattering channels. In\nthe case of antiferromagnetic interaction, the ground state is still the Kondo\nsinglet state while the septuplet state has the lowest energy for ferromagnetic\ncoupling. And with the same antiferromagnetic s-d coupling parameter, the\nenergy of the Kondo singlet state is lower than spin-1/2, which indicates that\nthe larger spin, the easier it is to enter the Kondo-screened phase. This\nprovides some theoretical support for the realization of the Kondo effect with\nultra-cold atoms.",
        "positive": "Topological order and equilibrium in a condensate of exciton-polaritons: We report the observation of the Berezinskii-Kosterlitz-Thouless transition\nfor a 2D gas of exciton-polaritons, and through the joint measurement of the\nfirst-order coherence both in space and time we bring compelling evidence of a\nthermodynamic equilibrium phase transition in an otherwise open\ndriven/dissipative system. This is made possible thanks to long polariton\nlifetimes in high-quality samples with small disorder and in a reservoir-free\nregion far away from the excitation spot, that allow topological ordering to\nprevail. The observed quasi-ordered phase, characteristic for an equilibrium 2D\nbosonic gas, with a decay of coherence in both spatial and temporal domains\nwith the same algebraic exponent, is reproduced with numerical solutions of\nstochastic dynamics, proving that the mechanism of pairing of the topological\ndefects (vortices) is responsible for the transition to the algebraic order.\nFinally, measurements in the weak-coupling regime confirm that polariton\ncondensates are fundamentally different from photon lasers and constitute\ngenuine quantum degenerate macroscopic states."
    },
    {
        "anchor": "Thermodynamics of the three-dimensional Hubbard model: Implications for\n  cooling cold atomic gases in optical lattices: We present a comprehensive study of the thermodynamic properties of the\nthree-dimensional fermionic Hubbard model, with application to cold fermionic\natoms subject to an optical lattice and a trapping potential. Our study is\nfocused on the temperature range of current experimental interest. We employ\ntwo theoretical methods - dynamical mean-field theory and high-temperature\nseries - and perform comparative benchmarks to delimitate their respective\nrange of validity. Special attention is devoted to understand the implications\nthat thermodynamic properties of this system have on cooling. Considering the\ndistribution function of local occupancies in the inhomogeneous lattice, we\nshow that, under adiabatic evolution, the variation of any observable (e.g.,\ntemperature) can be conveniently disentangled into two distinct contributions.\nThe first contribution is due to the redistribution of atoms in the trap during\nthe evolution, while the second one comes from the intrinsic change of the\nobservable. Finally, we provide a simplified picture of the cooling procedure\nrecently proposed in J.-S. Bernier et al., Phys. Rev. A 79, 061601 (2009) by\napplying this method to an idealized model.",
        "positive": "Optical lattice with heterogeneous atomic density: The possibility is considered for the formation in optical lattices of a\nheterogeneous state characterized by a spontaneous mesoscopic separation of the\nsystem into the spatial regions with different atomic densities. It is shown\nthat such states can arise, if there are repulsive interactions between atoms\nin different lattice sites and the filling factor is less than one-half."
    },
    {
        "anchor": "The internal structure of a vortex in a two-dimensional superfluid with\n  long healing length and its implications: We analyze the motion of quantum vortices in a two-dimensional spinless\nsuperfluid within Popov's hydrodynamic description. In the long healing length\nlimit (where a large number of particles are inside the vortex core) the\nsuperfluid dynamics is determined by saddle points of Popov's action, which, in\nparticular, allows for weak solutions of the Gross-Pitaevskii equation. We\nsolve the resulting equations of motion for a vortex moving with respect to the\nsuperfluid and find the reconstruction of the vortex core to be a non-analytic\nfunction of the force applied on the vortex. This response produces an\nanomalously large dipole moment of the vortex and, as a result, the spectrum\nassociated with the vortex motion exhibits narrow resonances lying {\\em within}\nthe phonon part of the spectrum, contrary to traditional view.",
        "positive": "Non-equilibrium transport in $d$-dimensional non-interacting Fermi gases: We consider a non-interacting Fermi gas in $d$ dimensions, both in the\nnon-relativistic and relativistic case. The system of size $L^{d}$ is initially\nprepared into two halves $\\mathcal{L}$ and $\\mathcal{R}$, each of them\nthermalized at two different temperatures, $T_{\\mathcal{L}}$ and\n$T_{\\mathcal{R}}$ respectively. At time $t=0$ the two halves are put in contact\nand the entire system is left to evolve unitarily. We show that, in the\nthermodynamic limit, the time evolution of the particle and energy densities is\nperfectly described by a semiclassical approach which permits to analytically\nevaluate the correspondent stationary currents. In particular, in the case of\nnon-relativistic fermions, we find a low-temperature behavior for the particle\nand energy currents which is independent from the dimensionality $d$ of the\nsystem, being proportional to the difference\n$T_{\\mathcal{L}}^{2}-T_{\\mathcal{R}}^{2}$. Only in one spatial dimension\n($d=1$), the results for the non-relativistic case agree with the massless\nrelativistic ones."
    },
    {
        "anchor": "Non-equilibrium Fractional Hall Response After a Topological Quench: We theoretically study the Hall response of a lattice system following a\nquench where the topology of a filled band is suddenly changed. In the limit\nwhere the physics is dominated by a single Dirac cone, we find that the change\nin the Hall conductivity is two-thirds of the quantum of conductivity. We\nexplore this universal behavior in the Haldane model, and discuss cold-atom\nexperiments for its observation. Beyond linear response, the Hall effect\ncrosses over from fractional to integer values. We investigate finite-size\neffects, and the role of the harmonic confinement.",
        "positive": "Bose-Einstein condensates in toroidal traps: instabilities, swallow-tail\n  loops, and self-trapping: We study the stability and dynamics of an ultra-cold bosonic gas trapped in a\ntoroidal geometry and driven by rotation, in the absence of dissipation. We\nfirst delineate, via the Bogoliubov mode expansion, the regions of stability\nand the nature of instabilities of the system for both repulsive and attractive\ninteraction strengths. To study the response of the system to variations in the\nrotation rate, we introduce a \"disorder\" potential, breaking the rotational\nsymmetry. We demonstrate the breakdown of adiabaticity as the rotation rate is\nslowly varied and find forced tunneling between the system's eigenstates. The\nnon-adiabaticity is signaled by the appearance of a swallow-tail loop in the\nlowest-energy level, a general sign of hysteresis. Then, we show that this\nsystem is in one-to-one correspondence with a trapped gas in a double-well\npotential and thus exhibits macroscopic quantum self-trapping. Finally, we show\nthat self-trapping is a direct manifestation of the behavior of the\nlowest-energy level."
    },
    {
        "anchor": "Vortex pairs in a spin-orbit coupled Bose-Einstein condensate: Static and dynamic properties of vortices in a two-component Bose-Einstein\ncondensate with Rashba spin-orbit coupling are investigated. The mass current\naround a vortex core in the plane-wave phase is found to be deformed by the\nspin-orbit coupling, and this makes the dynamics of the vortex pairs quite\ndifferent from those in a scalar Bose-Einstein condensate. The velocity of a\nvortex-antivortex pair is much smaller than that without spin-orbit coupling,\nand there exist stationary states. Two vortices with the same circulation move\naway from each other or unite to form a stationary state.",
        "positive": "Trapping Effects in Quantum Atomic Arrays: Quantum emitters, particularly atomic arrays with subwavelength lattice\nconstant, have been proposed to be an ideal platform for studying the interplay\nbetween photons and electric dipoles. In this work, motivated by the recent\nexperiment [1], we develop a microscopic quantum treatment using annihilation\nand creation operator of atoms in deep optical lattices. Using a diagrammatic\napproach on the Keldysh contour, we derive the cooperative scattering of the\nlight and obtain the general formula for the $S$ matrix. We apply our method to\nstudy the trapping effect, which is beyond previous treatment with spin\noperators. If the optical lattices are formed by light fields with magical\nwavelength, the result matches previous results using spin operators. When\nthere is a mismatch between the trapping potentials for atoms in the ground\nstate and the excited state, atomic mirrors become imperfect, with multiple\nresonances in the optical response. We further study the effect of recoil for\nlarge but finite trapping frequency. Our results are consistent with existing\nexperiments."
    },
    {
        "anchor": "Complex-valued neural operator assisted soliton identification: The numerical determination of solitary states is an important topic for such\nresearch areas as Bose-Einstein condensates, nonlinear optics, plasma physics,\netc. In this paper, we propose a data-driven approach for identifying solitons\nbased on dynamical solutions of real-time differential equations. Our approach\ncombines a machine-learning architecture called the complex-valued neural\noperator (CNO) with an energy-restricted gradient optimization. The former\nserves as a generalization of the traditional neural operator to the complex\ndomain, and constructs a smooth mapping between the initial and final states;\nthe latter facilitates the search for solitons by constraining the energy\nspace. We concretely demonstrate this approach on the quasi-one-dimensional\nBose-Einstein condensate with homogeneous and inhomogeneous nonlinearities. Our\nwork offers a new idea for data-driven effective modeling and studies of\nsolitary waves in nonlinear physical systems.",
        "positive": "Moving solitons in a one-dimensional fermionic superfluid: A fully analytical theory of a traveling soliton in a one-dimensional\nfermionic superfluid is developed within the framework of time-dependent\nself-consistent Bogoliubov-de Gennes equations, which are solved exactly in the\nAndreev approximation. The soliton manifests itself in a kink-like profile of\nthe superconducting order parameter and hosts a pair of Andreev bound states in\nits core. They adjust to soliton's motion and play an important role in its\nstabilization. A phase jump across the soliton and its energy decrease with\nsoliton's velocity and vanish at the critical velocity, corresponding to the\nLandau criterion, where the soliton starts emitting quasiparticles and becomes\nunstable. The \"inertial\" and \"gravitational\" masses of the soliton are\ncalculated and the former is shown to be orders of magnitude larger than the\nlatter. This results in a slow motion of the soliton in a harmonic trap,\nreminiscent to the observed behavior of a soliton-like texture in related\nexperiments in cold fermion gases [T. Yefsah et al., Nature 499, 426, (2013)].\nFurthermore, we calculate the full non-linear dispersion relation of the\nsoliton and solve the classical equations of motion in a trap. The strong\nnon-linearity at high velocities gives rise to anharmonic oscillatory motion of\nthe soliton. A careful analysis of this anharmonicity may provide a means to\nexperimentally measure the non-linear soliton spectrum in superfluids."
    },
    {
        "anchor": "Nano-Scale `Dark State' Optical Potentials for Cold Atoms: We discuss generation of subwavelength optical barriers on the scale of tens\nof nanometers, as conservative optical potentials for cold atoms. These arise\nfrom non-adiabatic corrections to Born-Oppenheimer potentials from dressed\n`dark states' in atomic $\\Lambda$-configurations. We illustrate the concepts\nwith a double layer potential for atoms obtained from inserting an optical\nsubwavelength barrier into a well generated by an off-resonant optical lattice,\nand discuss bound states of pairs of atoms interacting via magnetic dipolar\ninteractions. The subwavelength optical barriers represent an optical\n`Kronig-Penney' potential. We present a detailed study of the bandstructure in\noptical `Kronig-Penney' potentials, including decoherence from spontaneous\nemission and atom loss to open `bright' channels.",
        "positive": "Controllable Josephson junction for photon Bose-Einstein condensates: Josephson junctions are the basis for the most sensitive magnetic flux\ndetectors, the definition of the unit volt by the Josephson voltage standard,\nand superconducting digital and quantum computing. They result from the\ncoupling of two coherent quantum states, as they occur in superconductors,\nsuperfluids, atomic Bose-Einstein condensates, and exciton-polariton\ncondensates. In their ground state, Josephson junctions are characterised by an\nintrinsic phase jump. Controlling this phase jump is fundamental for\napplications in computing. Here, we experimentally demonstrate controllable\nphase relations between photon Bose-Einstein condensates resulting from\nparticle exchange in a thermo-optically tunable potential landscape. Our\nexperiment realises an optical analogue of a controllable 0,$\\pi$-Josephson\njunction. By connecting several junctions, we can study a reconfigurable\n4-condensate system demonstrating the potential of our approach for analog spin\nglass simulation. More generally, the combination of static and dynamic\nnanostructuring techniques introduced in our work offers a powerful platform\nfor the implementation of adaptive optical systems for paraxial light in and\noutside of thermal equilibrium."
    },
    {
        "anchor": "Compressibility of an Ultracold Fermi Gas with Repulsive Interactions: Fermi gases with repulsive interactions are characterized by measuring their\ncompressibility as a function of interaction strength. The compressibility is\nobtained from in-trap density distributions monitored by phase contrast\nimaging. For interaction parameters k_F a > 0.25 fast decay of the gas prevents\nthe observation of equilibrium profiles. For smaller interaction parameters,\nthe results are adequately described by first-order perturbation theory. A\nnovel phase contrast imaging method compensates for dispersive distortions of\nthe images.",
        "positive": "Using Random Boundary Conditions to simulate disordered quantum spin\n  models in 2D-systems: Disordered quantum antiferromagnets in two-dimensional compounds have been a\nfocus of interest in the last years due to their exotic properties. However,\nwith very few exceptions, the ground states of the corresponding Hamiltonians\nare notoriously difficult to simulate making their characterization and\ndetection very elusive, both, theoretically and experimentally. Here we propose\na method to signal quantum disordered antiferromagnets by doing exact\ndiagonalization in small lattices using random boundary conditions and\naveraging the observables of interest over the different disorder realizations.\nWe apply our method to study a Heisenberg spin-1/2 model in an anisotropic\ntriangular lattice. In this model, the competition between frustration and\nquantum fluctuations might lead to some spin liquid phases as predicted from\ndifferent methods ranging from spin wave mean field theory to 2D-DMRG or PEPS.\nOur method accurately reproduces the ordered phases expected of the model and\nsignals disordered phases by the presence of a large number of quasi degenerate\nground states together with the absence of a local order parameter. The method\npresents a weak dependence on finite size effects."
    },
    {
        "anchor": "Asymmetric population of momentum distribution by quasi-periodically\n  driving a triangular optical lattice: Ultracold atoms in periodical driven optical lattices enable us to\ninvestigate novel band structures and explore the topology of the bands. In\nthis work, we investigate the impact of the ramping process of the driving\nsignal and propose a simple but effective method to realize desired asymmetric\npopulation in momentum distribution by controlling the initial phase of the\ndriving signal. A quasi-momentum oscillation along the shaking direction in the\nframe of reference co-moving with the lattice is formed, causing the formation\nof the mix of ground energy band and first excited band in laboratory frame,\nwithin the regime that the driving frequency is far less than the coupling\nfrequency between ground band and higher energy bands. This method avoids the\nconstruction of intricate lattices or complex control sequence. With a\ntriangular lattice, we experimentally investigate the influence of the initial\nphase, frequency, amplitude of the driving signal on the population difference,\nand observe good agreement with our theoretical model. This provides guidance\non how to load a driving signal in driven optical lattice experiment and also\npotentially supplies a useful tool to form a qubit that can be used in quantum\ncomputation.",
        "positive": "Exciton-Mott Physics in Two-Dimensional Electron-Hole Systems: Phase\n  Diagram and Single-Particle Spectra: Exciton Mott physics in two-dimensional electron-hole (e-h) systems is\nstudied in the quasiequilibrium, which is the crossovers or phase transitions\nbetween the insulating exciton gas and the metallic e-h plasma. By developing a\nself-consistent screened T-matrix approximation, we succeed in obtaining the\n\"global\" phase diagram on the plane of the e-h density and the temperature as a\ncontour plot of the exciton ionization ratio. The detailed features of the\nexciton-Mott crossover at high temperature are figured out beyond the\nconventionally used concept of the Mott density. At low temperature, we find\nnot only the region unstable toward the inhomogeneity but the pure Mott\ntransition point characterized by the discontinuity in the ionization ratio.\nThe single particle spectra also exhibit interesting features reflecting the\nexcitonic correlations."
    },
    {
        "anchor": "Critical spin superflow in a spinor Bose-Einstein condensate: We investigate the critical dynamics of spin superflow in an easy-plane\nantiferromagnetic spinor Bose-Einstein condensate. Spin-dipole oscillations are\ninduced in a trapped condensate by applying a linear magnetic field gradient\nand we observe that the damping rate increases rapidly as the field gradient\nincreases above a certain critical value. The onset of dissipation is found to\nbe associated with the generation of dark-bright solitons due to the modulation\ninstability of the counterflow of two spin components. Spin turbulence emerges\nas the solitons decay because of their snake instability. We identify another\ncritical point for spin superflow, in which transverse magnon excitations are\ndynamically generated via spin-exchanging collisions, which leads to the\ntransient formation of axial polar spin domains.",
        "positive": "Nonuniform Bose-Einstein condensate. II. Doubly coherent states: We find stationary excited states of a one-dimensional system of $N$ spinless\npoint bosons with repulsive interaction and zero boundary conditions by\nnumerically solving the time-independent Gross-Pitaevskii equation. The\nsolutions are compared with the exact ones found in the Bethe-ansatz approach.\nWe show that the $j$th stationary excited state of a nonuniform condensate of\natoms corresponds to a Bethe-ansatz solution with the quantum numbers\n$n_{1}=n_{2}=\\ldots =n_{N}=j+1$. On the other hand, such $n_{1},\\ldots,n_{N}$\ncorrespond to a condensate of $N$ elementary excitations (in the present case\nthe latter are the Bogoliubov quasiparticles with the quasimomentum $\\hbar \\pi\nj/L$, where $L$ is the system size). Thus, each stationary excited state of the\ncondensate is ``doubly coherent'', since it corresponds simultaneously to a\ncondensate of $N$ atoms and a condensate of $N$ elementary excitations. We find\nthe energy $E$ and the particle density profile $\\rho (x)$ for such states. The\npossibility of experimental production of these states is also discussed."
    },
    {
        "anchor": "Re-entrant topological phase transition in a non-Hermitian quasiperiodic\n  lattice: We predict a re-entrant topological transition in a one dimensional\nnon-Hermitian quasiperiodic lattice. By considering a non-Hermitian generalized\nAubry-Andr\\'e-Harper (AAH) model with quasiperiodic potential, we show that the\nsystem first undergoes a transition from the delocalized phase to the localized\nphase and then to the delocalized phase as a function of the hermiticity\nbreaking parameter. This re-entrant delocalization-localization-delocalization\ntransition in turn results in a re-entrant topological transition identified by\nassociating the phases with spectral winding numbers. Moreover, we find that\nthese two transitions occur through intermediate phases hosting both extended\nand localized states having real and imaginary energies, respectively. We find\nthat these phases also possess non-trivial winding numbers which are different\nfrom that of the localized phase.",
        "positive": "One-dimensional transport of bosons between weakly linked reservoirs: We study a flow of ultracold bosonic atoms through a one-dimensional channel\nthat connects two macroscopic three-dimensional reservoirs of Bose-condensed\natoms via weak links implemented as potential barriers between each of the\nreservoirs and the channel. We consider reservoirs at equal chemical potentials\nso that a superflow of the quasi-condensate through the channel is driven\npurely by a phase difference, $2\\Phi$, imprinted between the reservoirs. We\nfind that the superflow never has the standard Josephson form $\\sim \\sin 2\\Phi\n$. Instead, the superflow discontinuously flips direction at $2\\Phi =\\pm\\pi$\nand has metastable branches. We show that these features are robust and not\nsmeared by fluctuations or phase slips. We describe a possible experimental\nsetup for observing these phenomena."
    },
    {
        "anchor": "Interplay of nonreciprocity and nonlinearity on mean-field energy and\n  dynamics of a Bose-Einstein condensate in a double-well potential: We investigate the mean-field energy spectrum and dynamics in a Bose-Einstein\ncondensate in a double-well potential with non-Hermiticity from the\nnonreciprocal hopping, and show that the interplay of nonreciprocity and\nnonlinearity leads to exotic properties. Under the two-mode and mean-field\napproximations, the nonreciprocal generalization of the nonlinear\nSchr\\\"{o}dinger equation and Bloch equations of motion for this system are\nobtained. We analyze the PT phase diagram and the dynamical stability of fixed\npoints. The reentrance of PT-symmetric phase and the reformation of stable\nfixed points with increasing the nonreciprocity parameter are found. Besides,\nwe uncover a linear self-trapping effect induced by the nonreciprocity. In the\nnonlinear case, the self-trapping oscillation is enhanced by the nonreciprocity\nand then collapses in the PT-broken phase, and can finally be recovered in the\nreentrant PT-symmetric phase.",
        "positive": "Fast dynamics for atoms in optical lattices: Cold atoms in optical lattices allow for accurate studies of many body\ndynamics. Rapid time-dependent modifications of optical lattice potentials may\nresult in significant excitations in atomic systems. The dynamics in such a\ncase is frequently quite incompletely described by standard applications of\ntight-binding models (such as e.g. Bose-Hubbard model or its extensions) that\ntypically neglect the effect of the dynamics on the transformation between the\nreal space and the tight-binding basis. We illustrate the importance of a\nproper quantum mechanical description using a multi-band extended Bose-Hubbard\nmodel with time-dependent Wannier functions. We apply it to situations,\ndirectly related to experiments."
    },
    {
        "anchor": "Three-body exclusion principle, duality mapping, and exact ground state\n  of a harmonically trapped, ultracold Bose gas with three-body hard-core\n  interactions in one dimension: Motivated by previous suggestions that three-body hard-core interactions in\nlower-dimensional ultracold Bose gases might provide a way for creation of\nnon-Abelian anyons, the exact ground state of a harmonically trapped 1D Bose\ngas with three-body hard-core interactions is constructed by duality mapping,\nstarting from an $N$-particle ideal gas of mixed symmetry with three-body\nnodes, which has double occupation of the lowest harmonic oscillator orbital\nand single occupation of the next $N-2$ orbitals. It has some similarity to the\nground state of a Tonks-Girardeau gas, but is more complicated. It is proved\nthat in 1D any system of $N\\ge 3$ bosons with three-body hard-core interactions\nalso has two-body soft-core interactions of generalized Lieb-Liniger delta\nfunction form, as a consequence of the topology of the configuration space of\n$N$ particles in 1D, i.e., wave functions with \\emph{only} three-body hard core\nzeroes are topologically impossible. This is in contrast with the case of 2D,\nwhere pure three-body hard-core interactions do exist, and are closely related\nto the fractional quantized Hall effect. The exact ground state is compared\nwith a previously-proposed Pfaffian-like approximate ground state, which\nsatisfies the three-body hard-core constraint but is not an exact energy\neigenstate. Both the exact ground state and the Pfaffian-like approximation\nimply two-body soft-core interactions as well as three-body hard-core\ninteractions, in accord with the general topological proof.",
        "positive": "Efimovian three-body potential from broad to narrow Feshbach resonances: We analyse the change in the hyperradial Efimovian three-body potential as\nthe two-body interaction is tuned from the broad to narrow Feshbach resonance\nregime. Here, it is known from both theory and experiment that the three-body\ndissociation scattering length $a_-$ shifts away from the universal value of\n$-9.7 \\ r_{\\mathrm{vdW}}$, with $r_{\\mathrm{vdW}} = \\frac{1}{2} \\left(m\nC_6/\\hbar^2 \\right)^{1/4}$ the two-body van der Waals range. We model the\nthree-body system using a separable two-body interaction that takes into\naccount the full zero-energy behaviour of the multichannel wave function. We\nfind that the short-range repulsive barrier in the three-body potential\ncharacteristic for single-channel models remains universal for narrow\nresonances, whilst the change in the three-body parameter originates from a\nstrong decrease in the potential depth. From an analysis of the underlying spin\nstructure we further attribute this behavior to the dominance of the two-body\ninteraction in the resonant channel compared to other background interactions."
    },
    {
        "anchor": "Spin gradient thermometry for ultracold atoms in optical lattices: We demonstrate spin gradient thermometry, a new general method of measuring\nthe temperature of ultracold atoms in optical lattices. We realize a mixture of\nspins separated by a magnetic field gradient. Measurement of the width of the\ntransition layer between the two spin domains serves as a new method of\nthermometry which is observed to work over a broad range of lattice depths and\ntemperatures, including in the Mott insulator regime. We demonstrate the\nthermometry in a system of ultracold rubidium atoms, and suggest that\ninteresting spin physics can be realized in this system. The lowest measured\ntemperature is 1 nK, indicating that the system has reached the quantum regime,\nwhere insulating shells are separated by superfluid layers.",
        "positive": "A momentum dependent optical lattice induced by artificial gauge\n  potential: We propose an experimentally feasible method to generate a one-dimensional\noptical lattice potential in an ultracold Bose gas system that depends on the\ntransverse momentum of the atoms. The optical lattice is induced by the\nartificial gauge potential generated by a periodically driven multi-laser Raman\nprocess, which depends on the transverse momentum of the atoms. We study the\nmany-body Bose-Hubbard model in an effective 1D case and show that the\nsuperfluid--Mott-insulator transition can be controlled via tuning the\ntransverse momentum of the atomic gas. We examined our prediction via a\nstrong-coupling expansion to an effective 1D Bose-Hubbard model and a quantum\nMonte Carlo calculation, and discuss possible applications of our system."
    },
    {
        "anchor": "Ground-state energy, density profiles, and momentum distribution of\n  attractively interacting 1D Fermi gases with hard-wall boundaries: a Monte\n  Carlo study: Motivated by the realization of hard-wall boundary conditions in experiments\nwith ultracold atoms, we investigate the ground-state properties of spin-1/2\nfermions with attractive interactions in a one-dimensional box. We use lattice\nMonte Carlo methods to determine essential quantities like the energy, which we\ncompute as a function of coupling strength and particle number in the regime\nfrom few to many particles. Many-fermion systems bound by hard walls display\nnon-trivial density profiles characterized by so-called Friedel oscillations\n(which are similar to those observed in harmonic traps). In non-interacting\nsystems, the characteristic length scale of the oscillations is set by (2\nkF)^(-1), where kF is the Fermi momentum, while repulsive interactions tend to\ngenerate Wigner-crystal oscillations of period (4 kF)^(-1). Based on the\nnon-interacting result, we find a remarkably simple parametrization of the\ndensity profiles of the attractively interacting case, which we generalize to\nthe one-body density matrix. While the total momentum is not a conserved\nquantity in the presence of hard walls, the magnitude of the momentum does\nprovide a good quantum number. We are therefore able to provide a detailed\ncharacterization of the (quasi-)momentum distribution, which displays rather\nrobust discontinuity at the Fermi surface. In addition, we determine the\nspatially varying on-site density-density correlation, which in turn yields\nTan's contact density and, upon integration, Tan's contact. As is well known,\nthe latter fully determines the short-range correlations and plays a crucial\nrole in a multitude of equilibrium and non-equilibrium sum rules.",
        "positive": "Observation of many-body localization in a one-dimensional system with\n  single-particle mobility edge: We experimentally study many-body localization (MBL) with ultracold atoms in\na weak one-dimensional quasiperiodic potential, which in the noninteracting\nlimit exhibits an intermediate phase that is characterized by a mobility edge.\nWe measure the time evolution of an initial charge density wave after a quench\nand analyze the corresponding relaxation exponents. We find clear signatures of\nMBL, when the corresponding noninteracting model is deep in the localized\nphase. We also critically compare and contrast our results with those from a\ntight-binding Aubry-Andr\\'{e} model, which does not exhibit a single-particle\nintermediate phase, in order to identify signatures of a potential many-body\nintermediate phase."
    },
    {
        "anchor": "Negative Absolute Temperature for Motional Degrees of Freedom: Absolute temperature, the fundamental temperature scale in thermodynamics, is\nusually bound to be positive. Under special conditions, however, negative\ntemperatures - where high-energy states are more occupied than low-energy\nstates - are also possible. So far, such states have been demonstrated in\nlocalized systems with finite, discrete spectra. Here, we were able to prepare\na negative temperature state for motional degrees of freedom. By tailoring the\nBose-Hubbard Hamiltonian we created an attractively interacting ensemble of\nultracold bosons at negative temperature that is stable against collapse for\narbitrary atom numbers. The quasi-momentum distribution develops sharp peaks at\nthe upper band edge, revealing thermal equilibrium and bosonic coherence over\nseveral lattice sites. Negative temperatures imply negative pressures and open\nup new parameter regimes for cold atoms, enabling fundamentally new many-body\nstates and counterintuitive effects such as Carnot engines above unity\nefficiency.",
        "positive": "Quantum Hall effects in fast rotating Fermi gases with anisotropic\n  dipolar interaction: We investigate fast rotating quasi-two-dimensional dipolar Fermi gases in the\nquantum Hall regime. By tuning the direction of the dipole moments with respect\nto the z-axis, the dipole-dipole interaction becomes anisotropic in the $x$-$y$\nplane. For a soft confining potential we find that, as we tilt the angle of the\ndipole moments, the system evolves from a $\\nu = 1/3$ Laughlin state with\ndipoles being polarized along the z axis to a series of ground states\ncharacterized by distinct mean total angular momentum, and finally to an\nanisotropic integer quantum Hall state. During the transition from the\nfractional regime to the integer regime, we find that the density profile of\nthe system exhibits crystal-like structures. We map out the ground states as a\nfunction of the tilt angle and the confining potential, revealing the\ncompetition of the isotropic confining potential and both the isotropic and\nanisotropic components of the dipole-dipole interaction."
    },
    {
        "anchor": "From Efimov Physics to the Bose Polaron using Gaussian States: Since the Efimov effect was introduced in 1970, a detailed theoretical\nunderstanding of Efimov physics has been developed in the few-body context.\nHowever, it has proven to be challenging to describe the role Efimov-type\ncorrelations play in many-body systems such as quenched or collapsing\nBose-Einstein condensates (BECs). To study the impact the Efimov effect can\nhave in such scenarios, we consider a light impurity immersed in a weakly\ninteracting BEC, forming a Bose polaron. In this case, the higher-order\ncorrelations are localized around the impurity, making it more feasible to\ndevelop a theoretical description. Specifically, we employ a Gaussian state\nvariational Ansatz in the reference frame of the impurity, capable of both\ncapturing the Efimov effect and the formation of the polaron cloud. We find\nthat the Efimov effect leads to a cooperative binding of bosons to the impurity\nand the formation of a many-body bound state. As a result, the polaron is not\nthe ground state, but rendered a metastable excited state which can decay into\nthese Efimov clusters. While this decay is slow for small interaction\nstrengths, it becomes more prominent as the attractive scattering length\nincreases, up to the point where the polaron becomes completely unstable. This\ncritical scattering length can be interpreted as a many-body shifted Efimov\nresonance, where the scattering of two excitations of the bath with the polaron\ncan lead to bound state formation. Compared to the few-body case, the resonance\nis shifted to smaller attractive scattering lengths due to the participation of\nthe polaron cloud in the cooperative binding process. This corresponds to an\nintriguing scenario of polaron-assisted chemistry, where many-body effects lead\nto enhanced signal of the chemical recombination process, which can be directly\nprobed in state-of-the-art experiments.",
        "positive": "State-to-state chemistry at ultra-low temperature: Fully understanding a chemical reaction on the quantum level is a\nlong-standing goal in physics and chemistry. Experimental investigation of such\nstate-to-state chemistry requires both the preparation of the reactants and the\ndetection of the products in a quantum state resolved way, which has been a\nlong term challenge. Using the high level control in the ultracold domain, we\nprepare a few-body quantum state of reactants and demonstrate state-to-state\nchemistry with unprecedented resolution. We present measurements and\naccompanying theoretical analysis for the recombination of three spin-polarized\nultracold Rb atoms forming a weakly bound Rb$_2$ dimer. Detailed insights of\nthe reaction process are obtained that suggest propensity rules for the\ndistribution of reaction products. The scheme can readily be adapted to other\nspecies and opens a door to detailed investigations of inelastic or reactive\nprocesses in domains never before accessible."
    },
    {
        "anchor": "Bose-Fermi-Hubbard model on a lattice with two nonequivalent sublattices: Phase transitions in systems described by Bose-Fermi-Hubbard model on a\nlattice with two nonequivalent sublattices are investigated in this work. The\ncase of hard-core bosons is considered and pseudospin formalism is used. Phase\ndiagrams are built in the plain of chemical potential of the bosons-bosonic\nhopping parameter. It is shown that in the case of anisotropic hopping, the\nregion of the supersolid phase existence is possible for a smaller parameter\nspace.",
        "positive": "Quantum Vortex States in Bose Hubbard Model With Rotation: We study quantum vortex states of strongly interacting bosons in a\ntwo-dimensional rotating optical lattice. The system is modeled by Bose-Hubbard\nHamiltonian with rotation. We consider lattices of different geometries, such\nas square, rectangular and triangular. Using numerical exact diagonalization\nmethod we show how the rotation introduces vortex states of different\nground-state symmetries and the transition between these states at discrete\nrotation frequencies. We show how the geometry of the lattice plays crucial\nrole in determining the maximum number of vortex states as well as the general\ncharacteristics of these states such as, the average angular momentum $<L_z>$,\nthe current at the perimeter of the lattice, phase winding, the relation\nbetween the maximum phase difference, the maximum current and also the\nsaturation of the current between the two neighboring lattice points. The\neffect of the two- and three-body interactions between the particles, both\nattractive and repulsive, also depends on the geometry of the lattice as the\ncurrent flow or the lattice current depends on the interactions. We also\nconsider the effect of the spatial inhomogeneity introduced by the presence of\nan additional confining harmonic trap potential. It is shown that the curvature\nof the trap potential and the position of the minimum of the trap potential\nwith respect to the axis of rotation or the center of the lattice have a\nsignificant effect on the general characteristics these vortex states."
    },
    {
        "anchor": "Modulational instability and soliton generation in chiral Bose-Einstein\n  condensates with zero-energy nonlinearity: By means of analytical and numerical methods, we address the modulational\ninstability (MI) in chiral condensates governed by the Gross-Pitaevskiiequation\nincluding the current nonlinearity. The analysis shows that this nonlinearity\npartly suppresses off the MI driven by the cubic self-focusing, although the\ncurrent nonlinearity is not represented in the system's energy (although it\nmodifies the momentum), hence it may be considered as zero-energy nonlinearity.\nDirect simulations demonstrate generation of trains of stochastically\ninteracting chiral solitons by MI. In the ring-shaped setup, the MI creates a\nsingle traveling solitary wave. The sign of the current nonlinearity determines\nthe direction of propagation of the emerging solitons.",
        "positive": "Dynamical Critical Behavior of an Attractive Bose-Einstein Condensate\n  Phase Transition: When matter undergoes a continuous phase transition on a finite timescale,\nthe Kibble-Zurek mechanism predicts universal scaling behavior with respect to\nstructure formation. The scaling is dependent on the universality class and is\nirrelevant to the details of the system. Here, we examine this phenomenon by\ncontrolling the timescale of the phase transition to a Bose-Einstein condensate\nusing sympathetic cooling of a ultracold Bose thermal could with tunable\ninteractions in an elongated trap. The phase transition results in a diverse\nnumber of bright solitons and grey solitons in the condensate that undergo\nattractive and repulsive interactions, respectively. The power law dependence\nof the average soliton number on the timescale of the phase transition is\nmeasured for each interaction and compared. The results support the\nKibble-Zurek mechanism, in that the scaling behavior is determined by\nuniversality and does not rely on the interaction properties."
    },
    {
        "anchor": "Rapid phase-diffusion between atomic and molecular Bose-Einstein\n  condensates: We study the collisional loss of atom-molecule coherence after coherently\ndissociating a small fraction of a molecular Bose-Einstein condensate into\natoms. The obtained $n$-atoms states are two-atom (SU(1,1)) coherent states\nwith number variance $\\Delta n\\propto n$ compared to $\\Delta n\\propto \\sqrt{n}$\nfor the spin (SU(2)) coherent states formed by coherent splitting of an atomic\ncondensate. Consequently, the Lorentzian atom-molecule phase-diffusion is\nfaster than the Gaussian phase-diffusion between separated atomic condensates,\nby a $\\sqrt{n}$ factor.",
        "positive": "Exploring the Kondo model in and out of equilibrium with alkaline-earth\n  atoms: We propose a scheme to realize the Kondo model with tunable anisotropy using\nalkaline-earth atoms in an optical lattice. The new feature of our setup is\nFloquet engineering of interactions using time-dependent Zeeman shifts, that\ncan be realized either using state-dependent optical Stark shifts or magnetic\nfields. The properties of the resulting Kondo model strongly depend on the\nanisotropy of the ferromagnetic interactions. In particular, easy-plane\ncouplings give rise to Kondo singlet formation even though microscopic\ninteractions are all ferromagnetic. We discuss both equilibrium and dynamical\nproperties of the system that can be measured with ultracold atoms, including\nthe impurity spin susceptibility, the impurity spin relaxation rate, as well as\nthe equilibrium and dynamical spin correlations between the impurity and the\nferromagnetic bath atoms. We analyze the non-equilibrium time evolution of the\nsystem using a variational non-Gaussian approach, which allows us to explore\ncoherent dynamics over both short and long timescales, as set by the bandwidth\nand the Kondo singlet formation, respectively. In the quench-type experiments,\nwhen the Kondo interaction is suddenly switched on, we find that real-time\ndynamics shows crossovers reminiscent of poor man's renormalization group flow\nused to describe equilibrium systems. For bare easy-plane ferromagnetic\ncouplings, this allows us to follow the formation of the Kondo screening cloud\nas the dynamics crosses over from ferromagnetic to antiferromagnetic behavior.\nOn the other side of the phase diagram, our scheme makes it possible to measure\nquantum corrections to the well-known Korringa law describing the temperature\ndependence of the impurity spin relaxation rate. Theoretical results discussed\nin our paper can be measured using currently available experimental techniques."
    },
    {
        "anchor": "Variational Monte Carlo method for the Baeriswyl wavefunction:\n  application to the one-dimensional bosonic Hubbard model: A variational Monte Carlo method for bosonic lattice models is introduced.\nThe method is based on the Baeriswyl projected wavefunction. The Baeriswyl\nwavefunction consists of a kinetic energy based projection applied to the\nwavefunction at infinite interaction, and is related to the shadow wavefunction\nalready used in the study of continuous models of bosons. The wavefunction at\ninfinite interaction, and the projector, are represented in coordinate space,\nleading to an expression for expectation values which can be evaluated via\nMonte Carlo sampling. We calculate the phase diagram and other properties of\nthe bosonic Hubbard model. The calculated phase diagram is in excellent\nagreement with known quantum Monte Carlo results. We also analyze correlation\nfunctions.",
        "positive": "Berezinskii-Kosterlitz-Thouless phase induced by dissipating\n  quasisolitons: We theoretically study the sound propagation in a two-dimensional weakly\ninteracting uniform Bose gas. Using the classical fields approximation we\nanalyze in detail the properties of density waves generated both in a weak and\nstrong perturbation regimes. While in the former case density excitations can\nbe described in terms of hydrodynamic or collisionless sound, the strong\ndisturbance of the system results in a qualitatively different response. We\nidentify observed structures as quasisolitons and uncover their internal\ncomplexity for strong perturbation case. For this regime quasisolitons break\ninto vortex pairs as time progresses, eventually reaching an equilibrium state.\nWe find this state, characterized by only fluctuating in time averaged number\nof pairs of opposite charge vortices and by appearance of a quasi-long-range\norder, as the Berezinskii-Kosterlitz-Thouless (BKT) phase."
    },
    {
        "anchor": "Quantum Phases of Ultracold Bosonic Atoms in a One Dimensional Optical\n  Superlattice: We analyze various quantum phases of ultracold bosonic atoms in a periodic\none dimensional optical superlattice. Our studies have been performed using the\nfinite size density matrix renormalization group (FS-DMRG) method in the\nframework of the Bose-Hubbard model. Calculations have been carried out for a\nwide range of densities and the energy shifts due to the superlattice\npotential. At commensurate fillings, we find the Mott insulator and the\nsuperfluid phases as well as Mott insulators induced by the superlattice. At a\nparticular incommensurate density, the system is found to be in the superfluid\nphase coexisting with density oscillations for a certain range of parameters of\nthe system.",
        "positive": "Bose-Einstein condensation of non-ground-state caesium atoms: Bose-Einstein condensates of ultracold atoms serve as low-entropy sources for\na multitude of quantum-science applications, ranging from quantum simulation\nand quantum many-body physics to proof-of-principle experiments in quantum\nmetrology and quantum computing. For stability reasons, in the majority of\ncases the energetically lowest-lying atomic spin state is used. Here we report\nthe Bose-Einstein condensation of caesium atoms in the Zeeman-excited mf = 2\nstate, realizing a non-ground-state Bose-Einstein condensate with tunable\ninteractions and tunable loss. We identify two regions of magnetic field in\nwhich the two-body relaxation rate is low enough that condensation is possible.\nWe characterize the phase transition and quantify the loss processes, finding\nunusually high three-body losses in one of the two regions. Our results open up\nnew possibilities for the mixing of quantum-degenerate gases, for polaron and\nimpurity physics, and in particular for the study of impurity transport in\nstrongly correlated one-dimensional quantum wires."
    },
    {
        "anchor": "Soliton appearing in boson-fermion mixture at the third order of the\n  interaction radius: In this paper we consider an ultra-cold mixture of boson and fermion atoms on\nthe basis of quantum hydrodynamics. Small perturbations in such systems are\nbeing analyzed. A possibility is shown for soliton solutions of a new type to\nappear if the third order of the interaction radius is taken into account in\nthe analysis of interactions. A fermion-fermion interaction occurs in explicit\nform if this approximation is accepted. The conditions that lead to occurrence\nof this type of soliton in a mixture of boson and fermion atoms were\ninvestigated. Restrictions on the fermion-fermion interaction were found that\nare necessary for this kind of perturbations to appear in the system.\nConditions determining whether perturbances would be a condensed soliton or a\nrarefied soliton are shown. Requirements to the experimental detection of a new\nsoliton type in boson-fermion mixture are considered.",
        "positive": "Leggett mode in a two-component Fermi gas with dipolar interactions: We develop an effective field theory to understand collective modes of a\nthree-dimensional two-component Fermi superfluid with dipolar inter-particle\ninteractions, which are modeled by an idealized separable potential. We first\nexamine the phase transition of the system at zero temperature, as the\nfermionic superfluidity is known to be characterized by two competing order\nparameters. We find that for strong interactions there exists a regime where\nthe two order parameters are out-of-phase and coupled, giving rise to an\nundamped massive Leggett mode. This is in addition to the well-known gapless\nphonon mode. We show that the Leggett mode can be seen in the spectral function\nof the in-medium Cooper pairs, and in principle could be measured through Bragg\nspectroscopy."
    },
    {
        "anchor": "Zeeman slowers made simple with permanent magnets in a Halbach\n  configuration: We describe a simple Zeeman slower design using permanent magnets. Contrary\nto common wire-wound setups no electric power and water cooling are required.\nIn addition, the whole system can be assembled and disassembled at will. The\nmagnetic field is however transverse to the atomic motion and an extra repumper\nlaser is necessary. A Halbach configuration of the magnets produces a high\nquality magnetic field and no further adjustment is needed. After optimization\nof the laser parameters, the apparatus produces an intense beam of slow and\ncold 87Rb atoms. With a typical flux of 1 - 5 \\times 10^10 atoms/s at 30 ms^-1,\nour apparatus efficiently loads a large magneto-optical trap with more than\n10^10 atoms in one second, which is an ideal starting point for degenerate\nquantum gases experiments.",
        "positive": "Manipulating dipolar and spin-exchange interactions in spin-1\n  Bose-Einstein condensates: It remains a challenge to independently manipulate the magnetic dipolar and\nthe spin-exchange interactions, which are entangled in many spin systems,\nparticularly in spin-1 Bose-Einstein condensates. For this purpose, we put\nforward a sequence of rf pulses and the periodic dynamical decoupling sequence\nof optical Feshbach resonance pulses to control the dipolar and the\nspin-exchange interactions, respectively. Our analytic results and the\nnumerical simulations demonstrate that either of the two interactions can be\nsuppressed to make the other dominate the spin dynamics; furthermore, both of\nthe interactions can be simultaneously suppressed to realize\nspinor-condensate-based magnetometers with a higher sensitivity. This\nmanipulation method may find its wide applications in magnetic resonance and\nspintronics."
    },
    {
        "anchor": "Ultracold atoms in quasi-1D traps: a step beyond the Lieb-Liniger model: Ultracold atoms placed in a tight cigar-shaped trap are usually described in\nterms of the Lieb-Liniger model. We study the extensions of this model which\narise when van der Waals interaction between atoms is taken into account. We\nfind that the corrections induced by the finite range of interactions can\nbecome especially important in the vicinity of narrow Feshbach resonances and\nsuggest realistic schemes of their experimental detection. The interplay of\nconfinement and interactions can lead to effective transparency where the\none-dimensional interactions are weak in a wide range of parameters.",
        "positive": "Dynamic density and spin responses of a superfluid Fermi gas in the\n  BCS-BEC crossover: Path integral formulation and pair fluctuation theory: We present a standard field theoretical derivation of the dynamic density and\nspin linear response functions of a dilute superfluid Fermi gas in the BCS-BEC\ncrossover in both three and two dimensions. The derivation of the response\nfunctions is based on the elegant functional path integral approach which\nallows us to calculate the density-density and spin-spin correlation functions\nby introducing the external sources for the density and the spin density. Since\nthe generating functional cannot be evaluated exactly, we consider two gapless\napproximations which ensure a gapless collective mode (Goldstone mode) in the\nsuperfluid state: the BCS-Leggett mean-field theory and the\nGaussian-pair-fluctuation (GPF) theory. In the mean-field theory, our results\nof the response functions agree with the known results from the random phase\napproximation. We further consider the pair fluctuation effects and establish a\ntheoretical framework for the dynamic responses within the GPF theory. We show\nthat the GPF response theory naturally recover three kinds of famous\ndiagrammatic contributions: the Self-Energy contribution, the Aslamazov-Lakin\ncontribution, and the Maki-Thompson contribution. We also show that unlike the\nequilibrium state, in evaluating the response functions, the linear\n(first-order) terms in the external sources as well as the induced order\nparameter perturbations should be treated carefully. In the superfluid state,\nthere is an additional order parameter contribution which ensures that in the\nstatic and long wavelength limit, the density response function recovers the\nresult of the compressibility (compressibility sum rule). We expect that the\n$f$-sum rule is manifested by the full number equation which includes the\ncontribution from the Gaussian pair fluctuations."
    },
    {
        "anchor": "From Rotating Atomic Rings to Quantum Hall States: Considerable efforts are currently devoted to the preparation of ultracold\nneutral atoms in the emblematic strongly correlated quantum Hall regime. The\nroutes followed so far essentially rely on thermodynamics, i.e. imposing the\nproper Hamiltonian and cooling the system towards its ground state. In rapidly\nrotating 2D harmonic traps the role of the transverse magnetic field is played\nby the angular velocity. For particle numbers significantly larger than unity,\nthe required angular momentum is very large and it can be obtained only for\nspinning frequencies extremely near to the deconfinement limit; consequently,\nthe required control on experimental parameters turns out to be far too\nstringent. Here we propose to follow instead a dynamic path starting from the\ngas confined in a rotating ring. The large moment of inertia of the fluid\nfacilitates the access to states with a large angular momentum, corresponding\nto a giant vortex. The initial ring-shaped trapping potential is then\nadiabatically transformed into a harmonic confinement, which brings the\ninteracting atomic gas in the desired quantum Hall regime. We provide clear\nnumerical evidence that for a relatively broad range of initial angular\nfrequencies, the giant vortex state is adiabatically connected to the bosonic\n$\\nu=1/2$ Laughlin state, and we discuss the scaling to many particles.",
        "positive": "Quantum Quench in the Transverse Field Ising chain I: Time evolution of\n  order parameter correlators: We consider the time evolution of order parameter correlation functions after\na sudden quantum quench of the magnetic field in the transverse field Ising\nchain. Using two novel methods based on determinants and form factor sums\nrespectively, we derive analytic expressions for the asymptotic behaviour of\none and two point correlators. We discuss quenches within the ordered and\ndisordered phases as well as quenches between the phases and to the quantum\ncritical point. We give detailed account of both methods."
    },
    {
        "anchor": "Collective excitations of quasi-two-dimensional trapped dipolar\n  fermions: transition from collisionless to hydrodynamic regime: We study the collective excitations of polarized single-component\nquasi-two-dimensional dipolar fermions in an isotropic harmonic trap by solving\nthe collisional Boltzmann-Vlasov (CBV) equation. We study the response to both\nmonopole and quadrupole perturbations of the trap potential and investigate the\ncharacter of excitations in each case. Simple analytic formulas are provided\nbased on the linearized scaling ansatz and accurate numerical results are\nobtained by satisfying the first eight moments of the CBV equation. Except for\nthe lowest lying monopole mode that exhibits a negligible damping in all of the\nstudied cases, the quadrupole and the higher order monopole modes undergo a\ntransition from the collisionless regime to a highly dissipative crossover\nregime and finally to the hydrodynamic regime upon increasing the dipolar\ninteraction strength. For strong vertical confinements (2D limit), we predict\nthe existence of a temperature window within which the characteristics of the\ncollective modes become temperature independent. This behavior, which is a\nunique feature of the universal near-threshold dipole-dipole scatterings,\npersists as long as the scattering energies remain in the near-threshold\nregime. The predictions of this work are expected to be in the reach of current\nexperiments.",
        "positive": "Estimating the conditions for polariton condensation in organic\n  thin-film microcavities: We examine the possibility of observing Bose condensation of a confined\ntwo-dimensional polariton gas in an organic quantum well. We deduce a suitable\nparameterization of a model Hamiltonian based upon the cavity geometry, the\nbiexciton binding energy, and similar spectroscopic and structural data. By\nconverting the sum-over-states to a semiclassical integration over\n$d$-dimensional phase space, we show that while an ideal 2-D Bose gas will not\nundergo condensation, an interacting gas with the Bogoliubov dispersion\n$H(p)\\approx s p$ close to $p=0$ will undergo Bose condensation at a given\ncritical density and temperature. We show that $T_c/\\sqrt{\\rho_c}$ is sensitive\nto both the cavity geometry and to the biexciton binding energy. In particular,\nfor strongly bound biexcitons, the non-linear interaction term appearing in the\nGross-Pitaevskii equation becomes negative and the resulting ground state will\nbe a localized soliton state rather than a delocalized Bose condensate."
    },
    {
        "anchor": "Quantum Rotor Theory of Systems of Spin-2 Bosons: We consider quantum phases of tightly-confined spin-2 bosons in an external\nfield under the presence of rotationally-invariant interactions. Generalizing\nprevious treatments, we show how this system can be mapped onto a quantum rotor\nmodel. Within the rotor framework, low-energy excitations about fragmented\nstates, which cannot be accessed within standard Bogoliubov theory, can be\nobtained. In the spatially extended system in the thermodynamic limit there\nexists a mean-field ground state degeneracy between a family of nematic states\nfor appropriate interaction parameters. It has been established that quantum\nfluctuations lift this degeneracy through the mechanism of order-by-disorder\nand select either a uniaxial or square-biaxial ground state. On the other hand,\nin the full quantum treatment of the analogous single-spatial mode problem with\nfinite particle number it is known that, due to symmetry restoring\nfluctuations, there is a unique ground state across the entire nematic region\nof the phase diagram. Within the established rotor framework we investigate the\npossible quantum phases under the presence of a quadratic Zeeman field, a\nproblem which has previously received little attention. By investigating wave\nfunction overlaps we do not find any signatures of the order-by-disorder\nphenomenon which is present in the continuum case. Motivated by this we\nconsider an alternative external potential which breaks less symmetry than the\nquadratic Zeeman field. For this case we do find the phenomenon of\norder-by-disorder in the fully quantum system. This is established within the\nrotor framework and with exact diagonalization.",
        "positive": "Orbital Feshbach Resonance with Small Energy Gap between Open and Closed\n  Channels: Recently a new type of Feshbach resonance, i.e., orbital Feshbach resonance\n(OFR) was proposed for the ultracold alkali-earth (like) atoms, and\nexperimentally observed in the ultracold gases of $^{{\\rm 173}}$Yb atoms.\nUnlike most of the magnetic Feshbach resonances of ultracold alkali atoms, when\nthe OFR of $^{{\\rm 173}}$Yb atoms appears, the energy gap between the\nthresholds of the open channel (OC) and the closed channel (CC) is much smaller\nthan the characteristic energy of the inter-atomic interaction, i.e., the van\nder Waals energy. In this paper we study the OFR in the systems with small\nCC-OC threshold gap. We show that in these systems the OFR can be induced by\nthe coupling between the OC and either an isolated bound state of the CC or the\nscattering states of the CC. Moreover, we also show that in each case the\ntwo-channel Huang-Yang pesudopoential is always applicable for the approximate\ncalculation of the low-energy scattering amplitude. Our results imply that in\nthe theoretical calculations for these systems it is appropriate to take into\naccount the contributions from the scattering states of the CC."
    },
    {
        "anchor": "Low-temperature, high-density magneto-optical trapping of potassium\n  using the open 4S-5P transition at 405 nm: We report the laser cooling and trapping of neutral potassium on an open\ntransition. Fermionic 40K is captured using a magneto-optical trap (MOT) on the\nclosed 4S-4P transition at 767 nm and then transferred, with unit efficiency,\nto a MOT on the open 4S-5P transition at 405 nm. Because the 5P state has a\nsmaller line width than the 4P state, the Doppler limit is reduced. We observe\ntemperatures as low as 63(6) microkelvin, the coldest potassium MOT reported to\ndate. The density of trapped atoms also increases, due to reduced temperature\nand reduced expulsive light forces. We measure a two-body loss coefficient of 2\nx 10^-10 cm^3/s, and estimate an upper bound of 8x10^-18 cm^2 for the\nionization cross section of the 5P state at 405 nm. The combined temperature\nand density improvement in the 405 nm MOT is a twenty-fold increase in phase\nspace density over our 767 nm MOT, showing enhanced pre-cooling for quantum gas\nexperiments. A qualitatively similar enhancement is observed in a 405 nm MOT of\nbosonic 41K.",
        "positive": "Two-orbital physics of high spin fermionic alkaline earth atoms confined\n  in a one-dimensional chain: We study the effect of the coupling between the electronic ground state of\nhigh spin alkaline-earth fermionic atoms and their metastable optically excited\nstate, when the system is confined in a one-dimensional chain, and show that\nthe system provides a possible realization of a finite momentum pairing\n(Fulde-Ferrell-Larkin-Ovchinnikov-like) state without spin- or bare mass\nimbalance. We determine the $\\beta$-functions of the renormalization group\ntrajectories for general spin and analyze the structure of the possible gapped\nand gapless states in the hydrodynamic limit. Due to the SU(N) symmetry in the\nspin space, complete mode separation can not be observed even in the fully\ngapless 2N-component Luttinger liquid state. Contrary, 4 velocities\ncharacterize the system. We solve the renormalization group equations for\nspin-9/2 strontium-87 isotope and analyze in detail its phase diagram. The\nfully gapless Luttinger liquid state does not stabilize in the two-orbital\nsystem of the $^{87}$Sr atoms, instead, different gapped non-Gaussian fixed\npoints are identified either with dominant density or superconducting\nfluctuations. The superconducting states are stable in a nontrivial shaped\nregion in the parameter space as a consequence of the coupling between the two\nelectronic states."
    },
    {
        "anchor": "Matter-wave solitons in the counterflow of two immiscible superfluids: We study formation of solitons induced by counterflows of immiscible\nsuperfluids. Our setting is based on a quasi-one-dimensional binary\nBose-Einstein condensate (BEC), composed of two immiscible components with\nlarge and small numbers of atoms in them. Assuming that the \"small\" component\nmoves with constant velocity, either by itself, or being dragged by a moving\ntrap, and intrudes into the \"large\" counterpart, the following results are\nobtained. Depending on the velocity, and on whether the small component moves\nin the absence or in the presence of the trap, two-component dark-bright\nsolitons, scalar dark solitons, or multiple dark solitons may emerge, the\nlatter outcome taking place due to breakdown of the superfluidity. We present\ntwo sets of analytical results to describe this phenomenology. In an\nintermediate velocity regime, where dark-bright solitons form, a reduction of\nthe two-component Gross-Pitaevskii system to an integrable Mel'nikov system is\ndeveloped, demonstrating that solitary waves of the former are very accurately\ndescribed by analytically available solitons of the latter. In the\nhigh-velocity regime, where the breakdown of the superfluidity induces the\nformation of dark solitons and multi-soliton trains, an effective\nsingle-component description, in which a strongly localized wave packet of the\n\"small\" component acts as an effective potential for the \"large\" one, allows us\nto estimate the critical velocity beyond which the coherent structures emerge\nin good agreement with the numerical results.",
        "positive": "Role of thermal two-phonon scattering for impurity dynamics in a\n  low-dimensional BEC: We numerically study the relaxation dynamics of a single, heavy impurity atom\ninteracting with a finite one- or two-dimensional, ultracold Bose-gas. While\nthere is a clear separation of time scales between processes resulting from\nsingle- and two-phonon scattering in three spatial dimensions, the\nthermalization in lower dimensions is dominated by two-phonon processes. This\nis due to infrared divergencies in the corresponding scattering rates in the\nthermodynamic limit, which are a manifestation of the Mermin-Wagner-Hohenberg\ntheorem. It makes it necessary to include second-order phonon scattering in\none-dimensional systems even at $T=0$ and above a crossover temperature\n$T_\\textrm{2ph}$ in two spatial dimensions. $T_\\textrm{2ph}$ scales inversely\nwith the system size and is much smaller than currently experimentally\naccessible."
    },
    {
        "anchor": "Bose-Fermi mixtures in the molecular limit: We consider a Bose-Fermi mixture in the molecular limit of the attractive\ninteraction between fermions and bosons. For a boson density smaller or equal\nto the fermion density, we show analytically how a T-matrix approach for the\nconstituent bosons and fermions recovers the expected physical limit of a\nFermi-Fermi mixture of molecules and atoms. In this limit, we derive simple\nexpressions for the self-energies, the momentum distribution function, and the\nchemical potentials. By extending these equations to a trapped system, we\ndetermine how to tailor the experimental parameters of a Bose-Fermi mixture in\norder to enhance the 'indirect Pauli exclusion effect' on the boson momentum\ndistribution function. For the homogeneous system, we present finally a\nDiffusion Monte Carlo simulation which confirms the occurrence of such a\npeculiar effect.",
        "positive": "Equation of state and Kosterlitz-Thouless transition temperature in\n  two-dimensional Fermi gases: An analytical approach: We study Fermi gases in two dimensions at low temperatures with attractive\ninteractions. Analytical results are derived for the equation of state and the\nKosterlitz-Thouless transition temperature as functions of the two-body binding\nenergy and the density of the gas. Our results for the equation of state\nstrongly deviate from the mean field predictions. However, they are in\nreasonable agreement with Monte-Carlo calculations and recent experiments with\ncold atomic gases."
    },
    {
        "anchor": "Phase diagram and multicritical behaviors of mixtures of 3D bosonic\n  gases: We investigate the Bose-Einstein condensation patterns, the critical and\nmulticritical behaviors of three-dimensional mixtures of bosonic gases with\nshort-range density-density interactions. These systems have a global U(1)+U(1)\nsymmetry, as the system Hamiltonian is invariant under independent U(1)\ntransformations acting on each species. In particular, we consider the\nthree-dimensional Bose-Hubbard model for two lattice bosonic gases coupled by\nan on-site inter-species density-density interaction. We study the phase\ndiagram and the critical behaviors along the transition lines characterized by\nthe Bose-Einstein condensation of one or both species. We present mean-field\ncalculations and numerical finite-size scaling analyses of quantum Monte Carlo\ndata. We also consider multicritical points, close to which it is possible to\nobserve the condensation of both gas components. We determine the possible\nmulticritical behaviors by using field-theoretical perturbative methods. We\nconsider the U(1)+U(1)-symmetric Landau-Ginzburg-Wilson Phi4 theory and\ndetermine the corresponding stable fixed points of the renormalization-group\nflow. The analysis predicts that, in all cases, the multicritical behavior is\nanalogous to the one that would be observed in systems of two identical gases,\nwith an additional Z_2 exchange symmetry.",
        "positive": "Many-body dark solitons in one-dimensional hard-core Bose gases: The existence and stability of solitonic states in one-dimensional repulsive\nBose-Einstein condensates is investigated within a fully many-body framework by\nconsidering the limit of infinite repulsion (Tonks-Girardeau gas). A class of\nstationary, shape-invariant states propagating at constant velocity are\nexplicitly found and compared to the known solution of the Gross-Pitaevskii\nequation. The typical features attributed to nonlinearity are thus recovered in\na purely linear theory, provided the full many-particle physics is correctly\naccounted for. However, the formation dynamics predicted by the\nGross-Pitaevskii approximation considerably differs from the exact many-body\nevolution."
    },
    {
        "anchor": "Bose-Einstein condensate in an elliptical waveguide: We investigate the effects of spatial curvature for an atomic Bose-Einstein\ncondensate confined in an elliptical waveguide. The system is well described by\nan effective 1D Gross-Pitaevskii equation with a quantum-curvature potential,\nwhich has the shape of a double-well but crucially depends on the eccentricity\nof the ellipse. The ground state of the system displays a quantum phase\ntransition from a two-peak configuration to a one-peak configuration at a\ncritical attractive interaction strength. In correspondence of this phase\ntransition the superfluid fraction strongly reduces and goes to zero for a\nsufficiently attractive Bose-Bose interaction.",
        "positive": "Minimum critical velocity of a Gaussian obstacle in a Bose-Einstein\n  condensate: When a superfluid flows past an obstacle, quantized vortices can be created\nin the wake above a certain critical velocity. In the experiment by Kwon et al.\n[Phys. Rev. A 91, 053615 (2015)], the critical velocity $v_c$ was measured for\natomic Bose-Einstein condensates (BECs) using a moving repulsive Gaussian\npotential and $v_c$ was minimized when the potential height $V_0$ of the\nobstacle was close to the condensate chemical potential $\\mu$. Here we\nnumerically investigate the evolution of the critical vortex shedding in a\ntwo-dimensional BEC with increasing $V_0$ and show that the minimum $v_c$ at\nthe critical strength $V_{0c}\\approx \\mu$ results from the local density\nreduction and vortex pinning effect of the repulsive obstacle. The spatial\ndistribution of the superflow around the moving obstacle just below $v_c$ is\nexamined. The particle density at the tip of the obstacle decreases as $V_0$\nincreases to $V_{c0}$ and at the critical strength, a vortex dipole is suddenly\nformed and dragged by the moving obstacle, indicating the onset of vortex\npinning. The minimum $v_c$ exhibits power-law scaling with the obstacle size\n$\\sigma$ as $v_c\\sim \\sigma^{-\\gamma}$ with $\\gamma\\approx 1/2$."
    },
    {
        "anchor": "3D Projection Sideband Cooling: We demonstrate 3D microwave projection sideband cooling of trapped, neutral\natoms. The technique employs state-dependent potentials that enable microwave\nphotons to drive vibration-number reducing transitions. The particular cooling\nsequence we employ uses minimal spontaneous emission, and works even for\nrelatively weakly bound atoms. We cool 76% of atoms to their 3D vibrational\nground states in a site-resolvable 3D optical lattice.",
        "positive": "Multicomponent spin mixtures of two-electron fermions: These lecture notes contain an introduction to the physics of quantum\nmixtures of ultracold atoms trapped in multiple internal states. I will discuss\nthe case of fermionic isotopes of alkaline-earth atoms, which feature an\nintrinsic SU($N$) interaction symmetry and convenient methods for the optical\nmanipulation of their nuclear spin. Some research directions will be presented,\nwith focus on experiments performed in Florence with nuclear-spin mixtures of\n$^{173}$Yb atoms in optical lattices."
    },
    {
        "anchor": "Quantum Monte Carlo calculation of the Fermi liquid parameters of the\n  two-dimensional homogeneous electron gas: Fermi liquid theory is the basic paradigm within which we understand the\nnormal behavior of interacting electron systems, but quantitative values for\nthe parameters that occur in this theory are currently unknown in many\nimportant cases. One such case is the two-dimensional homogeneous electron gas\n(2D HEG), which is realized in a wide variety of semiconductor devices. We have\nused quantum Monte Carlo (QMC) methods to calculate the Landau interaction\nfunctions between pairs of quasiparticles. We use these to study the Fermi\nliquid parameters, finding that finite-size effects represent a serious\nobstacle to the direct determination of Fermi liquid parameters in QMC\ncalculations. We have used QMC data in the literature for other properties of\nthe 2D HEG to assemble a set of \"best available\" values for the Fermi liquid\nparameters.",
        "positive": "Topological effects on transition temperatures and response functions in\n  three-dimensional Fermi superfluids: We investigate the effects of topological order on the transition\ntemperature, $T_c$, and response functions in fermionic superfluids with Rashba\nspin-orbit coupling and a transverse Zeeman field in three dimensions. Our\ncalculations, relevant to the ultracold atomic Fermi gases, include\nfluctuations beyond mean-field theory and are compatible with $f$-sum rules.\nReminiscent of the $p_x + i p_y$ superfluid, the topological phase is\nstabilized when driven away from the Bose-Einstein condensation and towards the\nBCS limit. Accordingly, while experimentally accessible, $T_c$ is significantly\nsuppressed in a topological superfluid. Above $T_c$, the spin and density\nresponse functions provide signatures of topological phases via the\nrecombination or amplification of frequency dependent peaks."
    },
    {
        "anchor": "Rashba spin-orbit coupling, strong interactions, and the BCS-BEC\n  crossover in the ground state of the two-dimensional Fermi Gas: The recent experimental realization of spin-orbit coupled Fermi gases\nprovides a unique opportunity to study the interplay between strong interaction\nand SOC in a tunable, disorder-free system. We present here precision ab initio\nnumerical results on the two-dimensional, unpolarized, uniform Fermi gas with\nattractive interactions and Rashba SOC. Using auxiliary-field quantum Monte\nCarlo and incorporating recent algorithmic advances, we carry out exact\ncalculations on sufficiently large system sizes to provide accurate results\nsystematically as a function of experimental parameters. We obtain the equation\nof state, the momentum distributions, the pseudo-spin correlations and the\npairing wave functions. Our results help illuminate the rich pairing structure\ninduced by SOC, and provide benchmarks for theory and guidance to future\nexperimental efforts.",
        "positive": "Creating big time crystals with ultracold atoms: We investigate the size of discrete time crystals s (ratio of response period\nto driving period) that can be created for a Bose-Einstein condensate (BEC)\nbouncing resonantly on an oscillating mirror. We find that time crystals can be\ncreated with sizes in the range s = 20 - 100 and that such big time crystals\nare easier to realize experimentally than a period-doubling (s = 2) time\ncrystal because they require either a larger drop height or a smaller number of\nbounces on the mirror. We also investigate the effects of having a realistic\nsoft Gaussian potential mirror for the bouncing BEC, such as that produced by a\nrepulsive light-sheet, which is found to make the experiment easier to\nimplement than a hard-wall potential mirror. Finally, we discuss the choice of\natomic system for creating time crystals based on a bouncing BEC and present an\nexperimental protocol for realizing big time crystals. Such big time crystals\nprovide a flexible platform for investigating a broad range of non-trivial\ncondensed matter phenomena in the time domain."
    },
    {
        "anchor": "Steering random walks with kicked ultracold atoms: A kicking sequence of the atom optics kicked rotor at quantum resonance can\nbe interpreted as a quantum random walk in momentum space. We show how to steer\nsuch a random walk by applying a random sequence of intensities and phases of\nthe kicking lattice chosen according to a probability distribution. This\ndistribution converts on average into the final momentum distribution of the\nkicked atoms. In particular, it is shown that a power-law distribution for the\nkicking strengths results in a L\\'evy walk in momentum space and in a power-law\nwith the same exponent in the averaged momentum distribution. Furthermore, we\ninvestigate the stability of our predictions in the context of a realistic\nexperiment with Bose-Einstein condensates.",
        "positive": "Hard-Wall Confinement of a Fractional Quantum Hall Liquid: We make use of numerical exact diagonalization calculations to explore the\nphysics of $\\nu = 1/2$ bosonic fractional quantum Hall (FQH) droplets in the\npresence of experimentally realistic cylindrically symmetric hard-wall\npotentials. This kind of confinement is found to produce very different\nmany-body spectra compared to a harmonic trap or the so-called extremely steep\nlimit. For a relatively weak confinement, the degeneracies are lifted and the\nlow-lying excited states organize themselves in energy branches that can be\nexplained in terms of their Jack polynomial representation. For a strong\nconfinement, a strong spatial deformation of the droplet is found, with an\nunexpected depletion of its central density."
    },
    {
        "anchor": "Quantum phase transition to unconventional multi-orbital superfluidity\n  in optical lattices: Orbital physics plays a significant role for a vast number of important\nphenomena in complex condensed matter systems such as high-T$_c$\nsuperconductivity and unconventional magnetism. In contrast, phenomena in\nsuperfluids -- especially in ultracold quantum gases -- are commonly well\ndescribed by the lowest orbital and a real order parameter. Here, we report on\nthe observation of a novel multi-orbital superfluid phase with a {\\it complex}\norder parameter in binary spin mixtures. In this unconventional superfluid, the\nlocal phase angle of the complex order parameter is continuously twisted\nbetween neighboring lattice sites. The nature of this twisted superfluid\nquantum phase is an interaction-induced admixture of the p-orbital favored by\nthe graphene-like band structure of the hexagonal optical lattice used in the\nexperiment. We observe a second-order quantum phase transition between the\nnormal superfluid (NSF) and the twisted superfluid phase (TSF) which is\naccompanied by a symmetry breaking in momentum space. The experimental results\nare consistent with calculated phase diagrams and reveal fundamentally new\naspects of orbital superfluidity in quantum gas mixtures. Our studies might\nbridge the gap between conventional superfluidity and complex phenomena of\norbital physics.",
        "positive": "Patterning by dynamically unstable spin-orbit-coupled Bose-Einstein\n  condensates: In a two-dimensional atomic Bose-Einstein condensate, we demonstrate Rashba\nspin-orbit coupling can always introduce dynamical instability into specific\nzero-quasimomentum states in all parameter regimes. During the evolution of the\nzero-quasimomentum states, such spin-orbit-coupling-induced instability can\nfragment the states and lead to a dynamically patterning process.\n  The features of formed patterns are identified from the symmetries of the\nBogoliubov-de Gennes Hamiltonian. We show that spin-orbit-coupled Bose-Einstein\ncondensates provide an interesting platform for the investigation of pattern\nformations."
    },
    {
        "anchor": "Dynamical topological phases in quenched spin-orbit coupled degenerate\n  Fermi gas: The spin-orbit coupled degenerate Fermi gas provides a totally new platform\nto realize topological superfluids and related topological excitations.\nPrevious studies have mainly focused on the properties of the ground state.\nHere we consider a two-dimensional Fermi gas with Rashba spin-orbit coupling\nsubject to a perpendicular Zeeman field. For this system, we have found that\nits ground state topological structure is captured by the spin texture, which\nis readily measurable in experiments. We show that, when the Zeeman field is\nsuddenly quenched, dynamical topological phases can be realized. More\nspecifically, three post-quench dynamical phases can be identified according to\nthe asymptotic behavior of the order parameter. In the undamped phase, a\npersistent oscillation of the order parameter may support a topological Floquet\nstate with multiple edge states. In the Landau damped phase, the magnitude of\nthe order parameter approaches a constant via a power-law decay, and this\nsystem can support a dynamical topological phase with a pair of edge states at\nthe boundary. In the over-damped phase, the order parameter decays to zero\nexponentially although the condensate fraction remains finite. These\npredictions can be observed in the strong coupling regime of ultracold Fermi\ngas.",
        "positive": "Simulating Wess-Zumino Supersymmetry Model in Optical Lattices: We study a cold atom-molecule mixture in two-dimensional optical lattices, in\nwhich fermionic atoms have a Dirac-type dispersion. We show that by fine-tuning\nthe atomic and molecular interactions, such mixtures can simulate Wess-Zumino\nsupersymmetry (SUSY) model, the first example of SUSY theories. At zero\ntemperature, SUSY is not spontaneously broken for this simplest SUSY model,\nwhich implies identical relativistic dispersions of the atom and its\nsuperpartner, bosonic diatom molecule. This defining signature of SUSY can be\nprobed by single particle spectroscopies. Thermal breaking of SUSY at finite\ntemperature is accompanied by a thermal Goldstone fermion, i.e., phonino\nexcitation. This and other signatures of broken SUSY can also be probed\nexperimentally."
    },
    {
        "anchor": "Effects of periodic potentials on the critical velocity of superfluid\n  Fermi gases in the BCS-BEC crossover: We study the effects of an external periodic potential on the critical\nvelocity of a superfluid Fermi gas in the crossover between the\nBardeen-Cooper-Schrieffer (BCS) phase and Bose-Einstein condensation (BEC). We\nnumerically solve the Bogoliubov-de Gennes equations to model a\nthree-dimensional (3D) gas of ultracold atoms in the superfluid phase flowing\nthrough a 1D optical lattice. We find that when the recoil energy is comparable\nto the Fermi energy, the presence of the periodic potential reduces the effect\nof pair-breaking excitations. This behavior is a consequence of the peculiar\nband structure of the quasiparticle energy spectrum in the lattice. When the\nlattice height is much larger than the Fermi energy, the periodic potential\nmakes pairs of atoms to be strongly bound even in the BCS regime and\npair-breaking excitations are further suppressed. We have also found that when\nthe recoil energy is comparable to or larger than the Fermi energy, the\ncritical velocity due to long-wavelength phonon excitations shows a\nnon-monotonic behavior along the BCS-BEC crossover.",
        "positive": "Unravelling the nonlinear ideal density response of many-body systems: Nonlinear density response theory is revisited focusing on the harmonically\nperturbed finite temperature uniform electron gas. Within the non-interacting\nlimit, brute force quantum kinetic theory calculations for the quadratic,\ncubic, quartic and quintic responses reveal a deep connection with the linear\nresponse. Careful analysis of the static long wavelength limit led us to\nconjecture a canonical non-interacting form that expresses arbitrary order\nnonlinear responses as the weighted sum of the linear responses evaluated at\nall multiple harmonics. This harmonic expansion is successfully validated\nagainst ab initio path integral Monte Carlo simulations"
    },
    {
        "anchor": "Production of large $^{41}$K Bose-Einstein condensates using D1 gray\n  molasses: We use D1 gray molasses to achieve Bose-Einstein condensation of a large\nnumber of $^{41}$K atoms in an optical dipole trap. By combining a new\nconfiguration of compressed-MOT with D1 gray molasses, we obtain a cold sample\nof $2.4\\times10^9$ atoms with a temperature as low as 42 $\\mu$K. After\nmagnetically transferring the atoms into the final glass cell, we perform a\ntwo-stage evaporative cooling. A condensate with up to $1.2\\times10^6$ atoms in\nthe lowest Zeeman state $|F=1,m_F=1\\rangle$ is achieved in the optical dipole\ntrap. Furthermore, we observe two narrow Feshbach resonances in the lowest\nhyperfine channel, which are in good agreement with theoretical predictions.",
        "positive": "Effective temperature of a superfluid flowing in a random potential: The spatial fluctuations of a superfluid flowing in a weak random potential\nare investigated. We employ classical field theory to demonstrate that the\ndisorder-averaged nonequilibrium second-order correlation of the order\nparameter at zero temperature is identical to the thermally averaged\nequilibrium counterpart of a uniform superfluid at an effective temperature.\nThe physics behind this equivalence is that scattering of a moving condensate\nby disorder has the same effect on the correlation function as equilibrium\nthermal excitations. The correlation function exhibits an exponential decay in\none dimension and a power-law decay in two dimensions. We show that the\neffective temperature can be measured in an interference experiment of\nultracold atomic gases."
    },
    {
        "anchor": "Reliability of lattice gauge theories in the thermodynamic limit: Although gauge invariance is a postulate in fundamental theories of nature\nsuch as quantum electrodynamics, in quantum-simulation implementations of gauge\ntheories it is compromised by experimental imperfections. In a recent work\n[Halimeh and Hauke,\n\\href{https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.125.030503}{Phys.\nRev. Lett. \\textbf{125}, 030503 (2020)}], it has been shown in finite-size\nspin-$1/2$ quantum link lattice gauge theories that upon introducing an\nenergy-penalty term of sufficiently large strength $V$, unitary gauge-breaking\nerrors at strength $\\lambda$ are suppressed $\\propto\\lambda^2/V^2$ up to all\naccessible evolution times. Here, we show numerically that this result extends\nto quantum link models in the thermodynamic limit and with larger spin-$S$. As\nwe show analytically, the dynamics at short times is described by an\n\\textit{adjusted} gauge theory up to a timescale that is at earliest\n$\\tau_\\text{adj}\\propto\\sqrt{V/V_0^3}$, with $V_0$ an energy factor. Moreover,\nour analytics predicts that a renormalized gauge theory dominates at\nintermediate times up to a timescale $\\tau_\\text{ren}\\propto\\exp(V/V_0)/V_0$.\nIn both emergent gauge theories, $V$ is volume-independent and scales at worst\n$\\sim S^2$. Furthermore, we numerically demonstrate that robust gauge\ninvariance is also retained through a single-body gauge-protection term, which\nis experimentally straightforward to implement in ultracold-atom setups and\nNISQ devices.",
        "positive": "Acoustic radiation from vortex-barrier interaction in atomic\n  Bose-Einstein condensate: We examine the dynamics of a vortex dipole in the Bose-Einstein condensates\n(BECs) of trapped dilute atomic gases at zero temperature in the presence of a\nGaussian barrier potential. The density-anisotropy induced by the barrier\nenhances the acoustic radiation from the vortex dipole. This is due to the\ndeviation of the condensate density from the equipotential curves and variation\nin the curvature of the vortex dipole trajectory. Due to the acoustic\nradiation, the vortex dipole dissipates energy and spirals towards the edge of\nthe condensate. As a result, we observe an increase in the vortex-antivortex\nannihilation events. To examine the effect of the Gaussian barrier, we estimate\nthe correction to the Thomas-Fermi condensate density using perturbation\nexpansion method and the results are in very good agreement with the numerical\nresults."
    },
    {
        "anchor": "Emergence of spiral dark solitons in the merging of rotating\n  Bose-Einstein condensates: Merging of isolated Bose-Einstein condensates (BECs) is an important topic\ndue to its relevance to matter-wave interferometry and the Kibble-Zurek\nmechanism. Many past research focused on merging of BECs with uniform initial\nphases. In our recent numerical study (Phys. Rev. A 97, 013612 (2018)), we\nrevealed that upon merging of rotating BECs with non-uniform initial phases,\nspiral-shaped dark solitons can emerge. These solitons facilitate angular\nmomentum transfer and allow the merged condensate to rotate even in the absence\nof quantized vortices. More strikingly, the sharp endpoints of these spiral\nsolitons can induce rotational motion in the BECs like vortices but with\neffectively a fraction of a quantized circulation. This paper reports our\nsystematic study on the merging dynamics of rotating BECs. We discuss how the\npotential barrier that initially separates the BECs can affect the profile of\nthe spiral solitons. We also show that the number of spiral solitons created in\nthe BECs matches the relative winding number of the rotating BECs. The\nunderlying mechanism of the observed soliton dynamics is explained.",
        "positive": "Sound propagation and quantum limited damping in a two-dimensional Fermi\n  gas: Strongly interacting two-dimensional Fermi systems are one of the great\nremaining challenges in many-body physics due to the interplay of strong local\ncorrelations and enhanced long-range fluctuations. Here, we probe the\nthermodynamic and transport properties of a 2D Fermi gas across the BEC-BCS\ncrossover by studying the propagation and damping of sound modes. We excite\nparticle currents by imprinting a phase step onto homogeneous Fermi gases\ntrapped in a box potential and extract the speed of sound from the frequency of\nthe resulting density oscillations. We measure the speed of sound across the\nBEC-BCS crossover and compare the resulting dynamic measurement of the equation\nof state both to a static measurement based on recording density profiles and\nto Quantum Monte Carlo calculations and find reasonable agreement between all\nthree. We also measure the damping of the sound mode, which is determined by\nthe shear and bulk viscosities as well as the thermal conductivity of the gas.\nWe find that the damping is minimal in the strongly interacting regime and the\ndiffusivity approaches the universal quantum bound $\\hbar/m$ of a perfect\nfluid."
    },
    {
        "anchor": "Phonon-induced breakdown of Thouless pumping in the Rice-Mele-Holstein\n  model: Adiabatic and periodic variation of the lattice parameters can make it\npossible to transport charge through a system even without net external\nelectric or magnetic fields, known as Thouless charge pumping. The amount of\ncharge pumped in a cycle is quantized and entirely determined by the system's\ntopology, which is robust against perturbations such as disorder and\ninteractions. However, coupling to the environment may play a vital role in\ntopological transport in many-body systems. We study the topological Thouless\npumping, where the charge carriers interact with local optical phonons. The\nsemi-classical multi-trajectory Ehrenfest method is employed to treat the\nphonon trajectories classically and charge carriers quantum mechanically. We\nfind a breakdown of the quantized charge transport in the presence of phonons.\nIt happens for any finite electron-phonon coupling strength at the resonance\ncondition when the pumping frequency matches the phonon frequency, and it takes\nfinite phonon coupling strength away from the resonance. Moreover, there exist\nparameter regimes with non-quantized negative and positive charge transport.\nThe modified effective pumping path due to electron-phonon coupling accurately\nexplains the underlying physics. In the large coupling regime where the pumping\ndisappears, the phonons are found to eliminate the staggering of the onsite\npotentials, which is necessary for the pumping protocol. Finally, we present a\nstability diagram of quantized pumping as a function of time period of pumping\nand phonon coupling strength.",
        "positive": "Breaking the resilience of a two-dimensional Bose-Einstein condensate to\n  fragmentation: A two-dimensional Bose-Einstein condensate (BEC) split by a radial potential\nbarrier is investigated. We determine on an accurate many-body level the\nsystem's ground-state phase diagram as well as a time-dependent phase diagram\nof the splitting process. Whereas the ground state is condensed for a wide\nrange of parameters, the time-dependent splitting process leads to substantial\nfragmentation. We demonstrate for the first time the dynamical fragmentation of\na BEC despite its ground state being condensed. The results are analyzed by a\nmean-field model and suggest that a large manifold of low-lying fragmented\nexcited states can significantly impact the dynamics of trapped two-dimensional\nBECs."
    },
    {
        "anchor": "Spin distillation cooling of ultracold Bose gases: We study the spin distillation of spinor gases of bosonic atoms and find two\ndifferent mechanisms in ${}^{52}$Cr and $^{23}$Na atoms, both of which can cool\neffectively. The first mechanism involves dipolar scattering into initially\nunoccupied spin states and cools only above a threshold magnetic field. The\nsecond proceeds via equilibrium relaxation of the thermal cloud into empty spin\nstates, reducing its proportion in the initial component. It cools only below a\nthreshold magnetic field. The technique was initially demonstrated\nexperimentally for a chromium dipolar gas [B. Naylor et al., Phys. Rev. Lett.\n115, 243002 (2015)], whereas here we develop the concept further and provide an\nin-depth understanding of the required physics and limitations involved.\nThrough numerical simulations, we reveal the mechanisms involved and\ndemonstrate that the spin distillation cycle can be repeated several times,\neach time resulting in a significant additional reduction of the thermal atom\nfraction. Threshold values of magnetic field and predictions for the achievable\ntemperature are also identified.",
        "positive": "From weak to strong: constrained extrapolation of perturbation series\n  with applications to dilute Fermi systems: We develop a method that uses truncation-order-dependent re-expansions\nconstrained by generic strong-coupling information to extrapolate perturbation\nseries to the nonperturbative regime. The method is first benchmarked against a\nzero-dimensional model field theory and then applied to the dilute Fermi gas in\none and three dimensions. Overall, our method significantly outperforms Pad\\'e\nand Borel extrapolations in these examples. The results for the ground-state\nenergy of the three-dimensional Fermi gas are robust with respect to changes of\nthe form of the re-expansion and compare well with quantum Monte Carlo\nsimulations throughout the BCS regime and beyond."
    },
    {
        "anchor": "Three-body scattering area for particles with infinite or zero\n  scattering length in two dimensions: We derive the asymptotic expansions of the wave function of three particles\nhaving equal mass with finite-range interactions and infinite or zero\ntwo-dimensional scattering length colliding at zero energy and zero orbital\nangular momentum, from which a three-body parameter $D$ is defined. The\ndimension of $D$ is length squared, and we call $D$ three-body scattering area.\nWe find that the ground state energy per particle of a zero-temperature dilute\nBose gas with these interactions is approximately $\\frac{\\hbar^2 D\n}{6m}\\rho^2$, where $\\rho$ is the number density of the bosons, $m$ is the mass\nof each boson, and $\\hbar$ is Planck's constant over $2\\pi$. Such a Bose gas is\nstable at $D\\geq 0$ in the thermodynamic limit, and metastable at $D<0$ in the\nharmonic trap if the number of bosons is less than $N_{cr}\\approx 3.6413\n\\sqrt{\\frac{\\hbar}{m\\omega |D|}}$, where $\\omega$ is the angular frequency of\nthe harmonic trap. If the two-body interaction supports bound states, $D$\ntypically acquires a negative imaginary part, and we find the relation between\nthis imaginary part and the amplitudes of the pair-boson production processes.\nWe derive a formula for the three-body recombination rate constant of the\nmany-boson system in terms of the imaginary part of $D$.",
        "positive": "Frictionless quantum quenches in ultracold gases: a quantum dynamical\n  microscope: In this article, a method is proposed to spatially scale up a trapped\nultracold gas while conserving the quantum correlations of the initial\nmany-body state. For systems supporting self-similar dynamics, this is achieved\nby implementing a many-body finite-time frictionless quantum quench of the\nharmonic trap which acts as a quantum dynamical microscope."
    },
    {
        "anchor": "A Model for Overscreened Kondo Effect in Ultracold Fermi Gas: The feasibility of realizing overscreened Kondo effect in ultra-cold Fermi\ngas of atoms with spin $s \\ge \\tfrac{3}{2}$ in the presence of a localized\nmagnetic impurity atom is proved realistic. Specifying to a system of ultra\ncold $^{22}$Na Fermi gas and a trapped $^{197}$Au impurity, the mechanism of\nexchange interaction between the Na and Au atoms is elucidated and the exchange\nconstant is found to be antiferromagnetic. The corresponding exchange\nHamiltonian is derived, and the Kondo temperature is estimated at the order of\n$ 1 \\mu$K.\n  Within a weak-coupling renormalization group scheme, it is shown that the\ncoupling renormalizes to the non-Fermi liquid fixed point.",
        "positive": "Gap solitons and Bloch waves of interacting bosons in one-dimensional\n  optical lattices: From the weak to the strong interaction limits: We study the gap solitons and nonlinear Bloch waves of interacting bosons in\none-dimensional optical lattices, taking into account the interaction from the\nweak to the strong limits. It is shown that composition relation between the\ngap solitons and nonlinear Bloch waves exists for the whole span of the\ninteraction strength. The linear stability analysis indicates that the gap\nsolitons are stable when their energies are near the bottom of the linear Bloch\nband gap. By increasing the interaction strength, the stable gap solitons can\nturn into unstable. It is argued that the stable gap solitons can easily be\nformed in a weakly interacting system with energies near the bottoms of the\nlower-level linear Bloch band gaps."
    },
    {
        "anchor": "Two-body recombination in a quantum mechanical lattice gas: Entropy\n  generation and probing of short-range magnetic correlations: We study entropy generation in a one-dimensional (1D) model of bosons in an\noptical lattice experiencing two-particle losses. Such heating is a major\nimpediment to observing exotic low temperature states, and \"simulating\"\ncondensed matter systems. Developing intuition through numerical simulations,\nwe present a simple empirical model for the entropy produced in this 1D\nsetting. We also explore the time evolution of one and two particle correlation\nfunctions, showing that they are robust against two-particle loss. Because of\nthis robustness, induced two-body losses can be used as a probe of short range\nmagnetic correlations.",
        "positive": "Semi-synthetic zigzag optical lattice for ultracold bosons: We consider a one-dimensional \"zigzag\" lattice, pictured as a two-site wide\nsingle strip taken from a triangular lattice, affected by a tunable homogeneous\nmagnetic flux piercing its triangular plaquettes. We focus on a semi-synthetic\nlattice produced by combining a one-dimensional spin-dependent lattice in the\nlong direction with laser-induced transitions between atomic internal states\nthat define the short synthetic dimension. In contrast to previous studies on\nsemi-synthetic lattices, the atom-atom interactions are nonlocal in both\nlattice directions. We investigate the ground-state properties of the system\nfor the case of strongly interacting bosons, and find that the interplay\nbetween the frustration induced by the magnetic field and the interactions\ngives rise to an exotic gapped phase at fractional filling factors\ncorresponding to one particle per magnetic unit cell."
    },
    {
        "anchor": "Design of a technique to measure the density of ultracold atoms in a\n  short-period optical lattice in three dimensions with single atom sensitivity: A measurement technique is described which has the potential to map the\natomic site occupancies of ultracold atoms in a short-period three-dimensional\noptical lattice. The method uses accordion and pinning lattices, together with\npolarization gradient cooling and fluorescence detection, to measure the\npositions of individual atoms within the sample in three dimensions at a\nresolution of around half the atomic resonant wavelength. The method measures\nthe site occupancy, rather than the parity of the site occupancy, of atoms in\nthe lattice. It is expected that such measurements hold significant potential\nfor the study of ultracold quantum dynamics.",
        "positive": "Superfluidity and coherence in uniform dipolar binary Bose mixtures: We investigate the superfluidity and the coherence in dipolar binary Bose\nmixtures using the hydrodynamic approach. Useful analytical formulas for the\nexcitations spectrum, the correlation function, the static structure factor,\nand the superfluid fraction are derived. We find that in the case of highly\nimbalanced mixture, the superfluidity can occur in the dilute component only at\nextremely low temperatures. The behavior of the first-order correlation\nfunction for both dipolar and nondipolar Bose mixtures is deeply analyzed. Then\nwe face the two-dimensional case which encodes a non-trivial physics due to the\nroton modes."
    },
    {
        "anchor": "Resonant demagnetization of a dipolar BEC in a 3D optical lattice: We study dipolar relaxation of a chromium BEC loaded into a 3D optical\nlattice. We observe dipolar relaxation resonances when the magnetic energy\nreleased during the inelastic collision matches an excitation towards higher\nenergy bands. A spectroscopy of these resonances for two orientations of the\nmagnetic field provides a 3D band spectroscopy of the lattice. The narrowest\nresonance is registered for the lowest excitation energy. Its line-shape is\nsensitive to the on-site interaction energy. We use such sensitivity to probe\nnumber squeezing in a Mott insulator, and we reveal the production of\nthree-body states with entangled spin and orbital degrees of freedom.",
        "positive": "Unsupervised machine learning of topological phase transitions from\n  experimental data: Identifying phase transitions is one of the key challenges in quantum\nmany-body physics. Recently, machine learning methods have been shown to be an\nalternative way of localising phase boundaries also from noisy and imperfect\ndata and without the knowledge of the order parameter. Here we apply different\nunsupervised machine learning techniques including anomaly detection and\ninfluence functions to experimental data from ultracold atoms. In this way we\nobtain the topological phase diagram of the Haldane model in a completely\nunbiased fashion. We show that the methods can successfully be applied to\nexperimental data at finite temperature and to data of Floquet systems, when\npostprocessing the data to a single micromotion phase. Our work provides a\nbenchmark for unsupervised detection of new exotic phases in complex many-body\nsystems."
    },
    {
        "anchor": "Phase-induced transport in atomic gases: from superfluid to Mott\n  insulator: Recent experimental realizations of artificial gauge fields for cold atoms\nare promising for generating steady states carrying a mass current in strongly\ncorrelated systems, such as the Bose-Hubbard model. Moreover, a homogeneous\ncondensate confined by hard-wall potentials from laser sheets has been\ndemonstrated, which provides opportunities for probing the intrinsic transport\nproperties of isolated quantum systems. Using the time-dependent Density Matrix\nRenormalization Group (TDMRG), we analyze the effect of the lattice and\ninteraction strength on the current generated by a quench in the artificial\nvector potential when the density varies from low values (continuum limit) up\nto integer filling in the Mott-insulator regime. There is no observable mass\ncurrent deep in the Mott-insulator state as one may expect. Other observable\nquantities used to characterize the quasi-steady state in the bulk of the\nsystem are the Drude weight and entanglement entropy production rate. The\nlatter in particular provides a striking signature of the superfluid-Mott\ninsulator transition. Furthermore, an interesting property of the superfluid\nstate is the formation of shock and rarefaction waves at the boundaries due to\nthe hard-wall confining potentials. We provide results for the height and the\nspeed of the shock front that propagates from the boundary toward the center of\nthe lattice. Our results should be verifiable with current experimental\ncapabilities.",
        "positive": "Effective field theory of bosons with finite-range interaction in a\n  disordered environment: We investigate the low-temperature properties of a ultracold gas made of\nbosonic alkali-metal atoms with finite-range interaction under the effect of a\ndisordered environment. The statistical characterization of the disorder is\ninvestigated within an effective-field-theory formalism for a generic spatial\ndimension $d$. Moving to $d=3$, where all the arising divergences are properly\nregularized, we focus on the depletion of both the condensate and superfluid\ndensities. At zero temperature we obtain meaningful analytical formulas for the\ncondensate fraction and the superfluid fraction which take into account the\ninterplay among scattering length, effective range, and disorder strength."
    },
    {
        "anchor": "Bond order via cavity-mediated interactions: We numerically study the phase diagram of bosons tightly trapped in the\nlowest band of an optical lattice and dispersively coupled to a single-mode\ncavity field. The dynamics is encompassed by an extended Bose-Hubbard model.\nHere, the cavity-mediated interactions are described by a two-body potential\nterm with a global range and by a correlated tunneling term where the hopping\namplitude depends on a global observable. We determine the ground state\nproperties in one dimension by means of the density matrix renormalization\ngroup algorithm, focusing on the effects due to the correlated tunneling. The\nlatter is responsible for the onset of bond orders, manifesting in one\ninsulating and two gapless bond ordered phases. We discuss the resulting phases\nfor different geometries that correspond to different relative strengths of the\ncorrelated tunneling coefficient. We finally analyze the scaling of the\nentanglement entropy in the gapless bond ordered phases that appear entirely\ndue to global interactions and determine the corresponding central charges.",
        "positive": "Quantum quench in 1D: Coherent inhomogeneity amplification and\n  'supersolitons': We study a quantum quench in a 1D system possessing Luttinger liquid (LL) and\nMott insulating ground states before and after the quench, respectively. We\nshow that the quench induces power law amplification in time of any particle\ndensity inhomogeneity in the initial LL ground state. The scaling exponent is\nset by the fractionalization of the LL quasiparticle number relative to the\ninsulator. As an illustration, we consider the traveling density waves launched\nfrom an initial localized density bump. While these waves exhibit a particular\nrigid shape, their amplitudes grow without bound."
    },
    {
        "anchor": "Gaussian-state Ansatz for the non-equilibrium dynamics of quantum spin\n  lattices: The study of non-equilibrium dynamics is one of the most important challenges\nof modern quantum many-body physics, in relationship with fundamental questions\nin quantum statistical mechanics, as well as with the fields of quantum\nsimulation and computing. In this work we propose a Gaussian Ansatz for the\nstudy of the nonequilibrium dynamics of quantum spin systems. Within our\napproach, the quantum spins are mapped onto Holstein-Primakoff bosons, such\nthat a coherent spin state -- chosen as the initial state of the dynamics --\nrepresents the bosonic vacuum. The state of the system is then postulated to\nremain a bosonic Gaussian state at all times, an assumption which is exact when\nthe bosonic Hamiltonian is quadratic; and which is justified in the case of a\nnonlinear Hamiltonian if the boson density remains moderate. We test the\naccuracy of such an Ansatz in the paradigmatic case of the $S=1/2$\ntransverse-field Ising model, in one and two dimensions, initialized in a state\naligned with the applied field. We show that the Gaussian Ansatz, when applied\nto the bosonic Hamiltonian with nonlinearities truncated to quartic order, is\nable to reproduce faithfully the evolution of the state, including its\nrelaxation to the equilibrium regime, for fields larger than the critical field\nfor the paramagnetic-ferromagnetic transition in the ground state. In\nparticular the spatio-temporal pattern of correlations reconstructed via the\nGaussian Ansatz reveals the dispersion relation of quasiparticle excitations,\nexhibiting the softening of the excitation gap upon approaching the critical\nfield. Our results suggest that the Gaussian Ansatz correctly captures the\nessential effects of nonlinearities in quantum spin dynamics; and that it can\nbe applied to the study of fundamental phenomena such as quantum thermalization\nand its breakdown.",
        "positive": "TheqQuantum acousto optic effect in Bose-Einstein condensate: We investigate the interaction between a single mode light field and an\nelongated cigar shaped Bose-Einstein condensate (BEC), subject to a temporal\nmodulation of the trap frequency in the tight confinement direction. Under\nappropriate conditions, the longitudinal sound like waves (Faraday waves) in\nthe direction of weak confinement acts as a dynamic diffraction grating for the\nincident light field analogous to the acousto-optic effect in classical optics.\nThe change in the refractive index due to the periodic modulation of the BEC\ndensity is responsible for the acousto-optic effect. The dynamics is\ncharacterised by Bragg scattering of light fom the matter wave Faraday grating\nand simultaneous Bragg scattering of the condensate atoms from the optical\ngrating formed due to the interference between the incident light and the\ndiffracted light fields. Varying the intensity of the incident laser beam we\nobserve the transition from the acousto-optic effect regime to the atomic Bragg\nscattering regime, where Rabi oscillations between two momentum levels of the\natoms are observed. We show that the acousto-optic effect is reduced as the\natomic interaction is increased."
    },
    {
        "anchor": "Spontaneous symmetry breaking and collapse in bosonic Josephson\n  junctions: We investigate an attractive atomic Bose-Einstein condensate (BEC) trapped by\na double-well potential in the axial direction and by a harmonic potential in\nthe transverse directions. We obtain numerically, for the first time, a quantum\nphase diagram which includes all the three relevant phases of the system:\nJosephson, spontaneous symmetry breaking (SSB), and collapse. We consider also\nthe coherent dynamics of the BEC and calculate the frequency of\npopulation-imbalance mode in the Josephson phase and in the SSB phase up to the\ncollapse. We show that these phases can be observed by using ultracold vapors\nof 7Li atoms in a magneto-optical trap.",
        "positive": "Renormalization in the Three-body Problem with Resonant P-wave\n  Interactions: Resonant P-wave interactions can be described by a minimal zero-range model\ndefined by a truncated effective range expansion, so that the only 2-body\ninteraction parameters are the inverse scattering volume 1/a_P and the P-wave\neffective range r_P. This minimal model can be formulated as a local quantum\nfield theory with a P-wave interaction between atom fields and a molecular\nfield. In the two-atom sector, the model is renormalizable, but it has\nunphysical behavior at high energies, because there are negative-probability\nstates with momentum scale r_P. In the sector with three atoms, two of which\nare identical, renormalization in some parity and angular-momentum channels\ninvolves an ultraviolet limit cycle, indicating asymptotic discrete scale\ninvariance. The Efimov effect occurs in the unitary limit a_P^(-1/3), r_P \\to\n0, but this limit is unphysical because there are low-energy states with\nnegative probability. The minimal model can be of physical relevance only at\nenergies small compared to the energy scale set by r_P, where the effects of\nnegative-probability states are suppressed."
    },
    {
        "anchor": "Quantum incommensurate Skyrmion crystals and Commensurate to\n  In-commensurate transitions in cold atoms and materials with spin orbit\n  couplings in a Zeeman field: In this work, we study strongly interacting spinor atoms in a lattice subject\nto a 2 dimensional (2d) anisotropic Rashba type of spin orbital coupling (SOC)\nand an Zeeman field. We find the interplay between the Zeeman field and the SOC\nprovides a new platform to host rich and novel classes of quantum commensurate\nand in-commensurate phases, excitations and phase transitions. These\ncommensurate phases include two collinear states at low and high Zeeman field,\ntwo co-planar canted states at Mirror reflected SOC parameters respectively.\nMost importantly, there are non-coplanar incommensurate Skyrmion (IC-SkX)\ncrystal phases surrounded by the 4 commensurate phases. New excitation spectra\nabove all the 5 phases, especially on the IC-SKX phase are computed. Three\ndifferent classes of quantum commensurate to in-commensurate transitions from\nthe IC-SKX to its 4 neighboring commensurate phases are identified. Finite\ntemperature behaviors and transitions are discussed. The critical temperatures\nof all the phases can be raised above that reachable by current cold atom\ncooling techniques simply by tuning the number of atoms $ N $ per site. In view\nof recent impressive experimental advances in generating 2d SOC for cold atoms\nin optical lattices, these new many-body phenomena can be explored in the\ncurrent and near future cold atom experiments. Applications to various\nmaterials such as MnSi, Fe$_{0.5}$Co$_{0.5}$Si, especially the complex\nincommensurate magnetic ordering in Li$_2$IrO$_3$ are given.",
        "positive": "Construction of quantum dark soliton in one-dimensional Bose gas: Dark soliton solutions in the one-dimensional classical nonlinear\nSchr\\\"odinger equation has been considered to be related to the yrast states\ncorresponding to the type-II excitations in the Lieb-Liniger model. However,\nthe relation is nontrivial and remains unclear because a dark soliton localized\nin space breaks the translation symmetry, while yrast states are\ntranslationally invariant. In this work, we construct a symmetry-broken quantum\nsoliton state and investigate the relation to the yrast states. By interpreting\na quantum dark soliton as a Bose-Einstein condensation to the wave function of\na classical dark soliton, we find that the quantum soliton state has a large\nweight only on the yrast states, which is analytically proved in the free-boson\nlimit and numerically verified in the weak-coupling regime. By extending these\nresults, we derive a parameter-free expression of a quantum soliton state that\nis written as a superposition of yrast states with Gaussian weights. The\ndensity profile of this quantum soliton state excellently agrees to that of the\nclassical dark soliton. The dynamics of a quantum dark soliton is also studied,\nand it turns out that the density profile of a dark soliton decays, but the\ndecay time increases as the inverse of the coupling constant in the\nweak-coupling limit."
    },
    {
        "anchor": "Analytical Investigation of Focusing Bose-Einstein condensates: The focusing of a propagating untrapped Bose-Einstein condensate is studied\ntheoretically. We use a scaling solution method comprising a time-dependent\nscaling function to analytically examine the dynamics of a falling\nBose-Einstein condensate in different regimes of propagation including the\nexpansion and compression zones. Our model is based on the Gross-Pitaevskii\nequation which involves the interparticle interactions between atoms, and\nconsequently their influence on the focused structures. We investigate the\nfocused profile characteristic factors such as the resolution and peak density\nfor various cases of the focusing optical potential parameters as well as the\nfactors associated with the moving cloud. Our results are compared with\nnumerical solutions of the Gross-Pitaevskii equation.",
        "positive": "Characterization of the energy level-structure of a trapped dipolar Bose\n  gas via mean-field parametric resonances: We report parametric resonances (PRs) in the mean-field dynamics of a\none-dimensional dipolar Bose-Einstein condensate (DBEC) in widely varying\ntrapping geometries. The chief goal is to characterize the energy levels of\nthis system by analytical methods and the significance of this study arises\nfrom the commonly known fact that in the presence of interactions the energy\nlevels of a trapped BEC are hard to calculate analytically. The latter\ncharacterization is achieved by a matching of the PR energies to energy levels\nof the confining trap using perturbative methods. Further, this work reveals\nthe role of the interplay between dipole-dipole interactions (DDI) and trapping\ngeometry in defining the energies and amplitudes of the PRs. The PRs are\ninduced by a negative Gaussian potential whose depth oscillates with time.\nMoreover, the DDI play a role in this induction. The dynamics of this system is\nmodeled by the time-dependent Gross- Pitaevskii equation (TDGPE) that is\nnumerically solved by the Crank-Nicolson method. The PRs are discussed basing\non analytical methods: first, it is shown that it is possible to reproduce PRs\nby the Lagrangian variational method that are similar to the ones obtained from\nTDGPE. Second, the energies at which the PRs arise are closely matched with the\nenergy levels of the corresponding trap calculated by time-independent\nperturbation theory. Third, the most probable transitions between the trap\nenergy levels yielding PRs are determined by time-dependent perturbation\ntheory. The most significant result of this work is that we have been able to\ncharacterize the above mentioned energy levels of a DBEC in a complex trapping\npotential."
    },
    {
        "anchor": "Quantum Brownian motion in a quasiperiodic potential: We consider a quantum particle subject to Ohmic dissipation, moving in a\nbichromatic quasiperiodic potential. In a periodic potential the particle\nundergoes a zero-temperature localization-delocalization transition as\ndissipation strength is decreased. We show that the delocalized phase is absent\nin the quasiperiodic case, even when the deviation from periodicity is\ninfinitesimal. Using the renormalization group, we determine how the effective\nlocalization length depends on the dissipation. We show that {a similar problem\ncan emerge in} the strong-coupling limit of a mobile impurity moving in a\nperiodic lattice and immersed in a one-dimensional quantum gas.",
        "positive": "Emergence of Crystalline Few-body Correlations in Mass-imbalanced Fermi\n  Polarons: Polarons can serve as an ideal platform to identify few-body correlations in\ntackling complex many-body problems. In this work, we reveal various\ncrystalline few-body correlations smoothly emergent from the mass-imbalanced\nFermi polarons in two dimensions. A unified variational approach up to three\nparticle-hole excitations allows us to extract the dominant dimer, trimer or\ntetramer correlation in a single framework. When the fermion-impurity mass\nratio is beyond certain critical value, the Fermi polaron is found to undergo a\nsmooth crossover, instead of a sharp transition, from the polaronic to trimer\nand tetramer regimes as increasing the fermion-impurity attraction. The\nemergent trimer and tetramer correlations result in the momentum-space\ncrystallization of particle-hole excitations featuring a stable diagonal or\ntriangular structure, as can be directly probed through the density-density\ncorrelation of majority fermions. Our results shed light on the intriguing\nquantum phases in the mass-imbalanced Fermi-Fermi mixtures beyond the pairing\nsuperfluid paradigm."
    },
    {
        "anchor": "Tight-Binding Kondo Model and Spin-Exchange Collision Rate of\n  Alkaline-Earth Atoms in a Mixed-Dimensional Optical Lattice: We study the two-body problem of the ultracold fermionic alkaline-earth\n(like) atoms in the electronic $^1$S$_0$ state ($g$-state) and $^3$P$_0$ state\n($e$-state), which are confined in a quasi-one-dimensional (quasi-1D) tube. In\naddition, in the axial direction, the $g$-atom experience a 1D optical lattice\nand the $e$-atom is localized by a harmonic potential. In this work, we propose\ntwo appropriate tight-binding models, which are applicable for the cases that\nthe odd-wave scattering between the $g$- and $e$-atom is negligible or not,\nrespectively. We further give a microscopic derivation for the inter-atomic\ninteraction parameters of these tight-binding models, by exactly calculating\nthe low-energy inter-atomic scattering amplitude. Our results show that, as one\ncan predict, these interaction parameters can be efficiently controlled by the\nconfinement potentials. We further exam the simple \"projection approximation\"\nwith which one derives the interaction parameters by directly projecting the 3D\nHuang-Yang pseudopotential on the ground state of the confinement and the\nlowest band of the optical lattice. We find that one should be very careful\nabout determining the interaction parameters in the tight-binding models.\nFurthermore, we calculate the spin-exchanging rate, which dependents on the\nincident quasi-momentum $k$ of the $g$-atom, for the recent experiment (L.\nRiegger, {\\it et. al.,} Phys. Rev. Lett. {\\bf 120}, 143601 (2018)) of\n$^{173}$Yb atoms in this quasi-(1+0)D system, and study finite-momentum effect\nin this experiment. Our results show that in this system the finite-momentum\neffect of the $g$-atom is very significant, and the momentum of the $g$-atoms\nin this experiment may be pretty high (already in the second Brillouin zone of\nthe optical lattice)",
        "positive": "Induced correlations between impurities in a one-dimensional quenched\n  Bose gas: We explore the time evolution of two impurities in a trapped one-dimensional\nBose gas that follows a change of the boson-impurity interaction. We study the\ninduced impurity-impurity interactions and their effect on the quench dynamics.\nIn particular, we report on the size of the impurity cloud, the\nimpurity-impurity entanglement, and the impurity-impurity correlation function.\nThe presented numerical simulations are based upon the variational multilayer\nmulticonfiguration time-dependent Hartree method for bosons. To analyze and\nquantify induced impurity-impurity correlations, we employ an effective\ntwo-body Hamiltonian with a contact interaction. We show that the effective\nmodel consistent with the mean-field attraction of two heavy impurities\nexplains qualitatively our results for weak interactions.\n  Our findings suggest that the quench dynamics in cold-atom systems can be a\ntool for studying impurity-impurity correlations."
    },
    {
        "anchor": "Interatomic collisions in two-dimensional and quasi-two-dimensional\n  confinements with spin-orbit coupling: We investigate the low-energy scattering and bound states of two\ntwo-component fermionic atoms in pure two-dimensional (2D) and quasi-2D\nconfinements with Rashba spin-orbit coupling (SOC). We find that the SOC\nqualitatively changes the behavior of the 2D scattering amplitude in the\nlow-energy limit. For quasi-2D systems we obtain the analytic expression for\nthe effective-2D scattering amplitude and the algebraic equations for the\ntwo-atom bound state energy. Based on these results, we further derive the\neffective 2D interaction potential between two ultracold atoms in the quasi-2D\nconfinement with Rashba SOC. These results are crucial for the control of the\n2D effective physics in quasi-2D geometry via the confinement intensity and the\natomic three-dimensional scattering length.",
        "positive": "Bogolon-mediated light absorption in atomic condensates of different\n  dimensionality: In the case of structureless bosons, cooled down to low temperatures, the\nabsorption of electromagnetic waves by their Bose-Einstein condensate is\nusually forbidden due to the momentum and energy conservation laws: the phase\nvelocity of the collective modes of the condensate called bogolons is\nsufficiently lower than the speed of light. Thus, only the light scattering\nprocesses persist. However, the situation might be different in the case of\ncomposite bosons or the bosons with an internal structure. Here, we develop a\nmicroscopic theory of electromagnetic power absorption by a Bose-Einstein\ncondensates of cold atoms in various dimensions, utilizing the Bogoliubov model\nof a weakly-interacting Bose gas. Thus, we address the transitions between a\ncollective coherent state of bosons and the discrete energy levels\ncorresponding to excited internal degrees of freedom of non-condensed\nindividual bosons. It is shown, that such transitions are mediated by one and\ntwo-bogolon excitations above the condensate, which demonstrate different\nefficiency at different frequencies and strongly depend on the condensate\ndensity, which influence varies depending on the dimensionality of the system."
    },
    {
        "anchor": "Controlled non-autonomous matter-wave solitons in spinor Bose-Einstein\n  condensates with spatiotemporal modulation: To study controlled evolution of non-autonomous matter-wave solitons in\nspinor Bose-Einstein condensates with spatiotemporal modulation, we focus on a\nsystem of three coupled Gross-Pitaevskii (GP) equations with\nspace-time-dependent external potentials and temporally modulated gain/loss\ndistributions. An integrability condition and a non-isospectral Lax pair for\nthe coupled GP equations are obtained. Using it, we derive an infinite set of\ndynamical invariants, the first two of which are the mass and momentum. The\nDarboux transform is used to generate one- and two-soliton solutions. Under the\naction of different external potentials and gain/loss distributions, various\nsolutions for controlled non-autonomous matter-wave solitons of both\nferromagnetic and polar types are obtained, such as self-compressed, snake-like\nand stepwise solitons, and as well as breathers. In particular, the formation\nof states resembling rogue waves, under the action of a sign-reversible\ngain-loss distribution, is demonstrated too. Shape-preserving and changing\ninteractions between two non-autonomous matter-wave solitons and bound states\nof solitons are addressed too. In this context, spin switching arises in the\npolar-ferromagnetic interaction. Stability of the non-autonomous matter-wave\nsolitons is verified by means of systematic simulations of their perturbed\nevolution.",
        "positive": "Collective excitations of a Bose-condensed gas: Fate of second sound in\n  the crossover regime between hydrodynamic and collisionless regimes: We develop the moment method for Bose-Einstein condensates (BECs) at finite\ntemperatures that enable us to study collective sound modes from the\nhydrodynamic to the collisionless regime. In particular, we investigate\ncollective excitations in a weakly interacting dilute Bose gas by applying the\nmoment method to the Zaremba-Nikuni-Griffin equation, which is the coupled\nequation of the Boltzmann equation with the generalized Gross-Pitaevskii\nequation. Utilizing the moment method, collective excitations in the crossover\nregime between the hydrodynamic and collisionless regimes are investigated in\ndetail. In the crossover regime, the second sound mode loses the weight of the\ndensity response function because of the significant coupling with incoherent\nmodes, whereas the first sound shows a distinct but broad peak structure. We\ncompare the result obtained by the moment method with that of the Landau\ntwo-fluid equations and show that the collective mode predicted by the Landau\ntwo-fluid equations well coincides with the result from the moment method even\nfar from the hydrodynamic regime, whereas clear distinction also emerges in the\nrelatively higher momentum regime."
    },
    {
        "anchor": "Condensation of quasiparticles and density modulation beyond the\n  superfluid critical velocity: We investigate the effect of a constant external velocity field on the ground\nstate of a bosonic quasiparticle Hamiltonian. Below a critical velocity the\nground state is a quasiparticle vacuum, corresponding to a pure superfluid\nphase at zero temperature. Beyond the critical velocity energy minimization\nleads to a macroscopic condensation of quasiparticles at a nonzero wave vector\nk_v parallel to the velocity v. Simultaneously, physical particles also undergo\na condensation at k_v and, to a smaller extent, at -k_v. Together with the BEC\nat k=0, the three entangled condensates give rise to density modulations of\nwave vectors k_v and 2k_v. For larger |v| our model predicts a bifurcation of\nk_v with corresponding two pure condensates and no density modulation.",
        "positive": "Dynamics of spin-momentum entanglement from superradiant phase\n  transitions: Exploring operational regimes of many-body cavity QED with multi-level atoms\nremains an exciting research frontier for their enhanced storage capabilities\nof intra-level quantum correlations. In this work, we propose an extension of a\nprototypical many-body cavity QED experiment from a two to a four-level\ndescription by optically addressing a combination of momentum and spin states\nof the ultracold atoms in the cavity. The resulting model comprises a pair of\nDicke Hamiltonians constructed from pseudo-spin operators, effectively\ncapturing two intertwined superradiant phase transitions. The phase diagram\nreveals regions featuring weak and strong entangled states of spin and momentum\natomic degrees of freedom. These states exhibit different dynamical responses,\nranging from slow to fast relaxation, with the added option of persistent\nentanglement temporal oscillations. We discuss the role of cavity losses in\nsteering the system dynamics into such entangled states and propose a readout\nscheme that leverages different light polarizations within the cavity. Our work\npaves the way to connect the rich variety of non-equilibrium phase transitions\nthat occur in many-body cavity QED to the buildup of quantum correlations in\nsystems with multi-level atom descriptions."
    },
    {
        "anchor": "Synthetic clock transitions via continuous dynamical decoupling: Decoherence of quantum systems due to uncontrolled fluctuations of the\nenvironment presents fundamental obstacles in quantum science. `Clock'\ntransitions which are insensitive to such fluctuations are used to improve\ncoherence, however, they are not present in all systems or for arbitrary system\nparameters. Here, we create a trio of synthetic clock transitions using\ncontinuous dynamical decoupling in a spin-1 Bose-Einstein condensate in which\nwe observe a reduction of sensitivity to magnetic field noise of up to four\norders of magnitude; this work complements the parallel work by Anderson et al.\n(submitted, 2017). In addition, using a concatenated scheme, we demonstrate\nsuppression of sensitivity to fluctuations in our control fields. These\nfield-insensitive states represent an ideal foundation for the next generation\nof cold atom experiments focused on fragile many-body phases relevant to\nquantum magnetism, artificial gauge fields, and topological matter.",
        "positive": "Strongly correlated states of trapped ultracold fermions in deformed\n  Landau levels: We analyze the strongly correlated regime of a two-component trapped\nultracold fermionic gas in a synthetic non-Abelian U(2) gauge potential, that\nconsists of both a magnetic field and a homogeneous spin-orbit coupling. This\ngauge potential deforms the Landau levels (LLs) with respect to the Abelian\ncase and exchanges their ordering as a function of the spin-orbit coupling. In\nview of experimental realizations, we show that a harmonic potential combined\nwith a Zeeman term, gives rise to an angular momentum term, which can be used\nto test the stability of the correlated states obtained through interactions.\nWe derive the Haldane pseudopotentials (HPs) describing the interspecies\ncontact interaction within a lowest LL approximation. Unlike ordinary\nfractional quantum Hall systems and ultracold bosons with short-range\ninteractions in the same gauge potential, the HPs for sufficiently strong\nnon-Abelian fields show an unconventional non-monotonic behaviour in the\nrelative angular momentum. Exploiting this property, we study the occurrence of\nnew incompressible ground states as a function of the total angular momentum.\nIn the first deformed Landau level (DLL) we obtain Laughlin and Jain states.\nInstead, in the second DLL three classes of stabilized states appear: Laughlin\nstates, a series of intermediate strongly correlated states and finally\nvortices of the integer quantum Hall state. Remarkably, in the intermediate\nregime, the non-monotonic HPs of the second DLL induce two-particle\ncorrelations which are reminiscent of paired states such as the Haffnian state.\nVia exact diagonalization in the disk geometry, we compute experimentally\nrelevant observables such as density profiles and correlations, and we study\nthe entanglement spectra as a further tool to characterize the obtained\nstrongly correlated states."
    },
    {
        "anchor": "The role of anisotropy in dipolar bosons in triple-well potentials: Mesoscopic samples of polarized dipolar atoms confined in three spatially\nseparated traps conform an extended Bose-Hubbard Hamiltonian in which different\nquantum phases appear depending on the competition between tunneling, on-site\nand long range inter-site dipole-dipole interactions. Here, by choosing an\nappropriate configuration of triple-wells, we analyze the role played by the\nanisotropic character inherent to the dipolar interaction in the phase diagram\nof the system. We further characterize the different phases as well as their\nboundaries by means of their entanglement properties.",
        "positive": "Autolocalization in a dipolar exciton system: We develop the autolocalization hypothesis suggested recently in [Andreev,\nPhys. Rev. Lett. 110, 146401 (2013)] to explain the formation of the\nmacroscopically ordered exciton state (MOES) in semiconductor quantum wells [L.\nV. Butov et al., Nature (London) 418, 751 (2002)]. We argue that the onset of a\nperiodical localizing potential having a macroscopic spatial period is possible\nin the systems where in addition to long-range dipolar repulsion the excitons\nexhibit resonant pairing at short distances. Our theory suggests, that the\ncentral incoherent part of each condensate in the MOES may represent a novel\nquantum molecular phase, which was predicted and discussed theoretically\nseveral years ago in the context of resonant Bose superfluids."
    },
    {
        "anchor": "Beyond-mean-field description of a trapped unitary Fermi gas with mass\n  and population imbalance: A detailed description is given of the phase diagram for a two-component\nunitary Fermi gas with mass and population imbalance, for both homogeneous and\ntrapped systems. This aims at providing quantitative benchmarks for the\nnormal-to-superfluid phase transition of a mass-imbalanced Fermi gas in the\ntemperature-polarization parameter space. A self-consistent t-matrix approach\nis adopted, which has already proven to accurately describe the thermodynamic\nproperties of the mass and population balanced unitary Fermi gas. Our results\nprovide a guideline for the ongoing experiments on heteronuclear Fermi\nmixtures.",
        "positive": "Extended Bose-Hubbard model with pair tunneling: spontaneous symmetry\n  breaking, effective ground state and fragmentation: The extended Bose-Hubbard model for a double-well potential with pair\ntunneling is studied through both exact diagonalization and mean field theory\n(MFT). When pair tunneling is strong enough, the ground state wavefunction\npredicted by the MFT is complex and doubly degenerate while the quantum ground\nstate wavefunction is always real and unique. The time reversal symmetry is\nspontaneously broken when the system transfers from the quantum ground state\ninto one of the mean field ground states upon a small perturbation. As the gap\nbetween the lowest two levels decreases exponentially with particle number, the\nrequired perturbation inducing the spontaneous symmetry breaking (SSB) is\ninfinitesimal for particle number of typical cold atom systems. The quantum\nground state is further analyzed with the Penrose-Onsager criterion, and is\nfound to be a fragmented condensate. The state also develops the pair\ncorrelation and has non-vanishing pair order parameter instead of the\nconventional single particle order parameter. When this model is generalized to\noptical lattice, a pair superfluid can be generated. The mean field ground\nstate can be regarded as effective ground state in this simple model. The\ndetailed computation for this model enables us to offer an in-depth discussion\nof the relation between SSB and effective ground state, giving a glimpse on how\nnonlinearity arises in the SSB of a quantum system."
    },
    {
        "anchor": "Quantum critical behavior at the many-body-localization transition: Phase transitions are driven by collective fluctuations of a system's\nconstituents that emerge at a critical point. This mechanism has been\nextensively explored for classical and quantum systems in equilibrium, whose\ncritical behavior is described by a general theory of phase transitions.\nRecently, however, fundamentally distinct phase transitions have been\ndiscovered for out-of-equilibrium quantum systems, which can exhibit critical\nbehavior that defies this description and is not well understood. A\nparadigmatic example is the many-body-localization (MBL) transition, which\nmarks the breakdown of quantum thermalization. Characterizing quantum critical\nbehavior in an MBL system requires the measurement of its entanglement\nproperties over space and time, which has proven experimentally challenging due\nto stringent requirements on quantum state preparation and system isolation.\nHere, we observe quantum critical behavior at the MBL transition in a\ndisordered Bose-Hubbard system and characterize its entanglement properties via\nits quantum correlations. We observe strong correlations, whose emergence is\naccompanied by the onset of anomalous diffusive transport throughout the\nsystem, and verify their critical nature by measuring their system-size\ndependence. The correlations extend to high orders in the quantum critical\nregime and appear to form via a sparse network of many-body resonances that\nspans the entire system. Our results unify the system's microscopic structure\nwith its macroscopic quantum critical behavior, and they provide an essential\nstep towards understanding criticality and universality in non-equilibrium\nsystems.",
        "positive": "$\u03b7$ Pairing of Light-Emitting Fermions: Nonequilibrium Pairing\n  Mechanism at High Temperatures: Strongly interacting fermionic atoms are shown to develop $\\eta$-pairing\nsuperfluid correlations in a nonequilibrium steady state in the presence of\nspontaneous emission of light from atoms. On the basis of the Hubbard model\nsubject to spontaneous decay between internal spin states, we show that\nprohibition of radiative decay due to the Pauli exclusion principle and\ndestructive interference between doublon-decay processes lead to nonequilibrium\n$\\eta$ pairing. Because of the non-thermal nature of the steady state, pair\ncorrelations arise even from a completely uncorrelated infinite-temperature\ninitial state, allowing coherent atom pairs to be formed at high temperatures.\nExperimental implementation with fermionic atoms in an optical lattice is\ndiscussed."
    },
    {
        "anchor": "Breaking the Fluctuation-Dissipation Relation by Universal Transport\n  Processes: Universal phenomena far from equilibrium exhibit additional independent\nscaling exponents and functions as compared to thermal universal behavior. For\nthe example of an ultracold Bose gas we simulate nonequilibrium transport\nprocesses in a universal scaling regime and show how they lead to the breaking\nof the fluctuation-dissipation relation. As a consequence, the scaling of\nspectral functions (commutators) and statistical correlations (anticommutators)\nbetween different points in time and space become linearly independent with\ndistinct dynamic scaling exponents. As a macroscopic signature of this\nphenomenon we identify a transport peak in the statistical two-point\ncorrelator, which is absent in the spectral function showing the quasiparticle\npeaks of the Bose gas.",
        "positive": "Characterizing quantum gases in time-controlled disorder realizations\n  using cross-correlations of density distributions: The role of disorder on physical systems has been widely studied in the\nmacroscopic and microscopic world. While static disorder is well understood in\nmany cases, the impact of time-dependent disorder on quantum gases is still\npoorly investigated. In our experimental setup, we introduce and characterize a\nmethod capable of producing time-controlled optical-speckle disorder.\nExperimentally, coherent light illuminates a combination of a static and a\nrotating diffuser, thereby collecting a spatially varying phase due to the\ndiffusers' structure and a temporally variable phase due to the relative\nrotation. Controlling the rotation of the diffuser allows changing the speckle\nrealization or, for future work, the characteristic time scale of the change of\nthe speckle pattern, i.e. the correlation time, matching typical time scales of\nthe quantum gases investigated. We characterize the speckle pattern ex-situ by\nmeasuring its intensity distribution cross-correlating different intensity\npatterns. In-situ, we observe its impact on a molecular Bose-Einstein\ncondensate (BEC) and cross-correlate the density distributions of BECs probed\nin different speckle realizations. As one diffuser rotates relative to the\nother around the common optical axis, we trace the optical speckle's intensity\ncross-correlations and the quantum gas' density cross-correlations. Our results\nshow comparable outcomes for both measurement methods. The setup allows us to\ntune the disorder potential adapted to the characteristics of the quantum gas.\nThese studies pave the way for investigating nonequilibrium physics in\ninteracting quantum gases using controlled dynamical-disorder potentials."
    },
    {
        "anchor": "Emergent pseudospin-1 Maxwell fermions with a threefold degeneracy in\n  optical lattices: The discovery of relativistic spin-1/2 fermions such as Dirac and Weyl\nfermions in condensed-matter or artificial systems opens a new era in modern\nphysics. An interesting but rarely explored question is whether other\nrelativistic spinal excitations could be realized with artificial systems.\nHere, we construct twoand three-dimensional tight-binding models realizable\nwith cold fermionic atoms in optical lattices, where the low energy excitations\nare effectively described by the spin-1 Maxwell equations in the Hamiltonian\nform. These relativistic (linear dispersion) excitations with unconventional\ninteger pseudospin, beyond the Dirac-Weyl-Majorana fermions, are an exotic kind\nof fermions named asMaxwell fermions.We demonstrate that the systems have rich\ntopological features. For instance, the threefold degenerate points called\nMaxwell points may have quantized Berry phases and anomalous quantum Hall\neffects with spin-momentum locking may appear in topological Maxwell insulators\nin the two-dimensional lattices. In three dimensions,Maxwell points may have\nnontrivial monopole charges of \\pm2 with two Fermi arcs connecting them, and\nthe merging of the Maxwell points leads to topological phase transitions.\nFinally, we propose realistic schemes for realizing the model Hamiltonians and\ndetecting the topological properties of the emergent Maxwell quasiparticles in\noptical lattices.",
        "positive": "Topological nodal chains in optical lattices: Topological nodal rings as the simplest topological nodal lines recently have\nbeen extensively studied in optical lattices. However, the realization of\ncomplex nodal line structures like nodal chains in this system remains a\ncrucial challenge. Here we propose an experimental scheme to realize and detect\ntopological nodal chains in optical Raman lattices. Specifically, we construct\na three-dimensional optical Raman lattice which supports next nearest-neighbor\nspin-orbit couplings and hosts topological nodal chains in its energy spectra.\nInterestingly, the realized nodal chains are protected by mirror symmetry and\ncould be tuned into a large variety of shapes, including the inner and outer\nnodal chains. We also demonstrate that the shapes of the nodal chains could be\ndetected by measuring spin polarizations. Our study opens up the possibility of\nexploring topological nodal-chain semimetal phases in optical lattices."
    },
    {
        "anchor": "Effects of long range hopping in the Bose-Hubbard model: We investigate the effects of an extended Bose-Hubbard model with a long\nrange hopping term on the Mott insulator-superfluid quantum phase transition.\nWe consider the effects of a power law decaying hopping term and show that the\nMott phase is shrinked in the parameters' space. We provide an exact solution\nfor one dimensional lattices and then two approximations for higher dimensions,\neach one valid in a specific range of the power law exponent: a continuum\napproximation and a discrete one. Finally, we extend these results to a more\nrealistic situation, where the long range hopping term is made by a power law\nfactor and a screening exponential term and study the main effects on the Mott\nlobes.",
        "positive": "Static-response theory and the roton-maxon spectrum of a flattened\n  dipolar Bose-Einstein condensate: Important information for the roton-maxon spectrum of a flattened dipolar\nBose-Einstein condensate is extracted by applying a static perturbation\nexhibiting a periodic in-plane modulation. By solving the Gross-Pitaevskii\nequation in the presence of the weak perturbation we evaluate the linear\ndensity response of the system and use it, together with sum rules, to provide\na Feynman-like upper-bound prediction for the excitation spectrum, finding\nexcellent agreement with the predictions of full Bogoliubov calculations. By\nsuddenly removing the static perturbation, while still maintaining the trap, we\nfind that the density modulations -- as well as the weights of the\nperturbation-induced side peaks of the momentum distribution -- undergo an\noscillatory behavior with double the characteristic frequency of the excitation\nspectrum. The measurement of the oscillation periods could provide an easy\ndetermination of dispersion relations."
    },
    {
        "anchor": "Dragging spin-orbit-coupled solitons by a moving optical lattice: It is known that the interplay of the spin-orbit-coupling (SOC) and\nmean-field self-attraction creates stable two-dimensional (2D) solitons (ground\nstates) in spinor Bose-Einstein condensates. However, SOC destroys the system's\nGalilean invariance, therefore moving solitons exist only in a narrow interval\nof velocities, outside of which the solitons suffer delocalization. We\ndemonstrate that the application of a relatively weak moving optical lattice\n(OL), with the 2D or quasi-1D structure, makes it possible to greatly expand\nthe velocity interval for stable motion of the solitons. The stability domain\nin the system's parameter space is identified by means of numerical methods. In\nparticular, the quasi-1D OL produces a stronger stabilizing effect than its\nfull 2D counterpart. Some features of the domain are explained analytically.",
        "positive": "Phase separation of trapped spin-imbalanced Fermi gases in\n  one-dimensional optical lattices: We calculate the density profiles of a trapped spin-imbalanced Fermi gas with\nattractive interactions in a one-dimensional optical lattice, using both the\nlocal density approximation (LDA) and density matrix renormalization group\n(DMRG) simulations. Based on the exact equation of state obtained by Bethe\nansatz, LDA predicts that the gas phase-separates into shells with a partially\npolarized core and fully paired wings, where the latter occurs below a critical\nspin polarization. This behavior is also seen in numerically exact DMRG\ncalculations at sufficiently large particle numbers. Unlike the continuum case,\nwe show that the critical polarization is a non monotonic function of the\ninteraction strength and vanishes in the limit of large interactions."
    },
    {
        "anchor": "Composite-boson approach to molecular Bose-Einstein condensates in\n  mixtures of ultracold Fermi gases: We show that an ansatz based on independent composite bosons [Phys. Rep. 463,\n215 (2008)] accurately describes the condensate fraction of molecular\nBose-Einstein condensates in ultracold Fermi gases. The entanglement between\nthe fermionic constituents of a single Feshbach molecule then governs the\nmany-particle statistics of the condensate, from the limit of strong\ninteraction to close to unitarity. This result strengthens the role of\nentanglement as the indispensable driver of composite-boson behavior. The\ncondensate fraction of fermion pairs at zero temperature that we compute\nmatches excellently previous results obtained by means of fixed-node diffusion\nMonte Carlo methods and the Bogoliubov depletion approximation. This paves the\nway towards the exploration of the BEC-BCS crossover physics in mixtures of\ncold Fermi gases with an arbitrary number of fermion pairs as well as the\nimplementation of Hong-Ou-Mandel-like interference experiments proposed within\ncoboson theory.",
        "positive": "Stability of quantised vortices in two-component condensates: Multiply quantised vortices (MQVs) within single component Bose-Einstein\ncondensates are unstable and decay rapidly. We show that MQVs can be stabilised\nby adding a small number of atoms of a second species to the vortex cores, and\nthat these atoms remain in the vortex core as the system evolves. A consequence\nof the stabilisation is that nearby co-rotating vortices can orbit in the\nopposite sense to their individual rotations when enough of the second species\nis present. This has implications concerning the imaging of vortices, as well\nas quantum turbulence and vortex nucleation in two-component condensates, such\nas those involving mixtures of $^{87}$Rb and $^{133}$Cs."
    },
    {
        "anchor": "Engineering matter interactions using squeezed vacuum: Virtually all interactions that are relevant for atomic and condensed matter\nphysics are mediated by quantum fluctuations of the electromagnetic field\nvacuum. Consequently, controlling the vacuum fluctuations can be used to\nengineer the strength and the range of interactions. Recent experiments have\nused this premise to demonstrate novel quantum phases or entangling gates by\nembedding electric dipoles in photonic cavities or waveguides, which modify the\nelectromagnetic fluctuations. Here, we show theoretically that the enhanced\nfluctuations in the anti-squeezed quadrature of a squeezed vacuum state allows\nfor engineering interactions between electric dipoles without the need for a\nphotonic structure. Thus, the strength and range of the interactions can be\nengineered in a time-dependent way by changing the spatial profile of the\nsqueezed vacuum in a travelling-wave geometry, which also allows the\nimplementation of chiral dissipative interactions. Using experimentally\nrealized squeezing parameters and including realistic losses, we predict single\natom cooperativities $C$ of up to 10 for the squeezed vacuum enhanced\ninteractions.",
        "positive": "Benchmarks of Generalized Hydrodynamics for 1D Bose Gases: Generalized hydrodynamics (GHD) is a recent theoretical approach that is\nbecoming a go-to tool for characterizing out-of-equilibrium phenomena in\nintegrable and near-integrable quantum many-body systems. Here, we benchmark\nits performance against an array of alternative theoretical methods, for an\ninteracting one-dimensional Bose gas described by the Lieb-Liniger model. In\nparticular, we study the evolution of both a localized density bump and dip,\nalong with a quantum Newton's cradle setup, for various interaction strengths\nand initial equilibrium temperatures. We find that GHD generally performs very\nwell at sufficiently high temperatures or strong interactions. For low\ntemperatures and weak interactions, we highlight situations where GHD, while\nnot capturing interference phenomena on short lengthscales, can describe a\ncoarse-grained behaviour based on convolution averaging that mimics finite\nimaging resolution in ultracold atom experiments. In a quantum Newton's cradle\nsetup based on a double-well to single-well trap quench, we find that GHD with\ndiffusive corrections demonstrates excellent agreement with the predictions of\na classical field approach."
    },
    {
        "anchor": "Beyond-mean-field effects in Rabi-coupled two-component Bose-Einstein\n  condensate: We theoretically calculate and experimentally measure the beyond-mean-field\n(BMF) equation of state in a coherently-coupled two-component Bose-Einstein\ncondensate (BEC) in the regime where averaging of the interspecies and\nintraspecies coupling constants over the hyperfine composition of the\nsingle-particle dressed state predicts the exact cancellation of the two-body\ninteraction. We show that with increasing the Rabi-coupling frequency $\\Omega$,\nthe BMF energy density crosses over from the nonanalytic Lee-Huang-Yang (LHY)\nscaling $\\propto n^{5/2}$ to an expansion in integer powers of density, where,\nin addition to a two-body BMF term $\\propto n^2 \\sqrt{\\Omega}$, there emerges a\nrepulsive three-body contribution $\\propto n^3/\\sqrt{\\Omega}$. We\nexperimentally evidence this two contributions, thanks to their different\nscaling with $\\Omega$, in the expansion of a Rabi-coupled two-component\n$^{39}$K condensate in a waveguide. By studying the expansion with and without\nRabi coupling, we reveal an important feature relevant for observing BMF\neffects and associated phenomena in mixtures with spin-asymmetric losses: Rabi\ncoupling helps preserve the spin composition and thus prevents the system from\ndrifting away from the point of vanishing mean field.",
        "positive": "Dissipative dynamics of the Josephson effect in the binary\n  Bose-condensed mixtures: The dissipative dynamics of a pointlike Josephson junction in binary\nBose-condensed mixtures is analyzed within the framework of the model of a\ntunneling Hamiltonian. The transmission of unlike particles across a junction\nis described by the different transmission amplitudes. The effective action\nthat describes the dynamics of the phase differences across the junction for\neach of two condensed components is derived employing the functional\nintegration method. In the low-frequency limit the dynamics of a Josephson\njunction can be described by two coupled equations in terms of the potential\nenergy and dissipative Rayleigh function using a mechanical analogy. The\ninterplay between mass currents of each mixture component appears in the\nsecond-order term in the tunneling amplitudes due to interspecies hybridizing\ninteraction. The asymmetric case of the binary mixtures with the different\nconcentration and order parameters is considered as well."
    },
    {
        "anchor": "Quantum groups as hidden symmetries of quantum impurities: We present an approach to interacting quantum many-body systems based on the\nnotion of quantum groups, also known as $q$-deformed Lie algebras. In\nparticular, we show that if the symmetry of a free quantum particle corresponds\nto a Lie group $G$, in the presence of a many-body environment this particle\ncan be described by a deformed group, $G_q$. Crucially, the single deformation\nparameter, $q$, contains all the information about the many-particle\ninteractions in the system. We exemplify our approach by considering a quantum\nrotor interacting with a bath of bosons, and demonstrate that extracting the\nvalue of $q$ from closed-form solutions in the perturbative regime allows one\nto predict the behavior of the system for arbitrary values of the impurity-bath\ncoupling strength, in good agreement with non-perturbative calculations.\nFurthermore, the value of the deformation parameter allows to predict at which\ncoupling strengths rotor-bath interactions result in a formation of a stable\nquasiparticle. The approach based on quantum groups does not only allow for a\ndrastic simplification of impurity problems, but also provides valuable\ninsights into hidden symmetries of interacting many-particle systems.",
        "positive": "Griffiths Physics in an Ultracold Bose Gas: Coupled XY model systems consisting of three-dimensional (3D) systems with\ndisordered interlayer physics are of significant theoretical interest. We\nrealize a set of coupled quasi-2D layers of $^{87}$Rb in the presence of\ndisordered inter-layer coupling. This is achieved with our high bandwidth\narbitrary optical lattice to obviate restrictions on the dimensionality of\ndisorder with speckle-generated optical fields. We identify phase crossover\nregions compatible with the existence of a pair of intermediate Griffiths\nphases between a thermal state and the emergence of bulk 3D superfluidity."
    },
    {
        "anchor": "Dynamics of correlations in a quasi-2D dipolar Bose gas following a\n  quantum quench: We study the evolution of correlations in a quasi-2D dipolar gas driven\nout-of-equilibrium by a sudden ramp of the interaction strength. For\nsufficiently strong ramps, the momentum distribution, excited fraction and\ndensity-density correlation function all display pronounced features that are\ndirectly related to the appearance of a roton minimum in the underlying\nspectrum. Our study suggests that the evolution of correlations following a\nquench can be used as a probe of roton-like excitations in a dipolar gas. We\nalso find that the build up of density-density correlations following a quench\noccurs much more slowly in the dipolar gas compared to a non-dipolar gas, owing\nto the long-range interactions.",
        "positive": "Topological phase transitions in ultra-cold Fermi superfluids: the\n  evolution from BCS to BEC under artificial spin-orbit fields: We discuss topological phase transitions in ultra-cold Fermi superfluids\ninduced by interactions and artificial spin orbit fields. We construct the\nphase diagram for population imbalanced systems at zero and finite\ntemperatures, and analyze spectroscopic and thermodynamic properties to\ncharacterize various phase transitions. For balanced systems, the evolution\nfrom BCS to BEC superfluids in the presence of spin-orbit effects is only a\ncrossover as the system remains fully gapped, even though a triplet component\nof the order parameter emerges. However, for imbalanced populations, spin-orbit\nfields induce a triplet component in the order parameter that produces nodes in\nthe quasiparticle excitation spectrum leading to bulk topological phase\ntransitions of the Lifshitz type. Additionally a fully gapped phase exists,\nwhere a crossover from indirect to direct gap occurs, but a topological\ntransition to a gapped phase possessing Majorana fermions edge states does not\noccur."
    },
    {
        "anchor": "Accurate multi-boson long-time dynamics in triple-well periodic traps: To solve the many-boson Schr\\\"odinger equation we utilize the\nMulticonfigurational time-dependent Hartree method for bosons (MCTDHB). To be\nable to attack larger systems and/or to propagate the solution for longer\ntimes, we implement a parallel version of the MCTDHB method thereby realizing\nthe recently proposed [Streltsov {\\it et al.} arXiv:0910.2577v1] novel idea how\nto construct efficiently the result of the action of the Hamiltonian on a\nbosonic state vector. We study the real-space dynamics of repulsive bosonic\nsystems made of N=12, 51 and 3003 bosons in triple-well periodic potentials.\nThe ground state of this system is three-fold fragmented. By suddenly strongly\ndistorting the trap potential, the system performs complex many-body quantum\ndynamics. At long times it reveals a tendency to an oscillatory behavior around\na threefold fragmented state. These oscillations are strongly suppressed and\ndamped by quantum depletions. In spite of the richness of the observed\ndynamics, the three time-adaptive orbitals of MCTDHB(M=3) are capable to\ndescribe the many-boson quantum dynamics of the system for short and\nintermediate times. For longer times, however, more self-consistent\ntime-adaptive orbitals are needed to correctly describe the non-equilibrium\nmany-body physics. The convergence of the MCTDHB($M$) method with the number\n$M$ of self-consistent time-dependent orbitals used is demonstrated.",
        "positive": "Polaronic slowing of fermionic impurities in lattice Bose-Fermi mixtures: We generalize the application of small polaron theory to ultracold gases of\nRef. [\\onlinecite{jaksch_njp1}] to the case of Bose-Fermi mixtures, where both\ncomponents are loaded into an optical lattice. In a suitable range of\nparameters, the mixture can be described within a Bogoliubov approach in the\npresence of fermionic (dynamic) impurities and an effective description in\nterms of polarons applies. In the dilute limit of the slow impurity regime, the\nhopping of fermionic particles is exponentially renormalized due to polaron\nformation, regardless of the sign of the Bose-Fermi interaction. This should\nlead to clear experimental signatures of polaronic effects, once the regime of\ninterest is reached. The validity of our approach is analyzed in the light of\ncurrently available experiments. We provide results for the hopping\nrenormalization factor for different values of temperature, density and\nBose-Fermi interaction for three-dimensional $^{87}\\rm{Rb}-^{40}\\rm{K}$\nmixtures in optical lattice."
    },
    {
        "anchor": "Measuring the Edwards-Anderson order parameter of the Bose glass: a\n  quantum gas microscope approach: With the advent of spatially resolved fluorescence imaging in quantum gas\nmicroscopes, it is now possible to directly image glassy phases and probe the\nlocal effects of disorder in a highly controllable setup. Here we present\nnumerical calculations using a spatially-resolved local mean-field theory, show\nthat it captures the essential physics of the disordered system and use it to\nsimulate the density distributions seen in single-shot fluorescence microscopy.\nFrom these simulated images we extract local properties of the phases which are\nmeasurable by a quantum gas microscope and show that unambiguous detection of\nthe Bose glass is possible. In particular, we show that experimental\ndetermination of the Edwards-Anderson order parameter is possible in a strongly\ncorrelated quantum system using existing experiments. We also suggest\nmodifications to the experiments which will allow further properties of the\nBose glass to be measured.",
        "positive": "Thermal blurring of a coherent Fermi gas: It is generally assumed that a condensate of paired fermions at equilibrium\nis characterized by a macroscopic wavefunction with a well-defined, immutable\nphase. In reality, all systems have a finite size and are prepared at non-zero\ntemperature; the condensate has then a finite coherence time, even when the\nsystem is isolated in its evolution and the particle number $N$ is fixed. The\nloss of phase memory is due to interactions of the condensate with the excited\nmodes that constitute a dephasing environment. This fundamental effect, crucial\nfor applications using the condensate of pairs' macroscopic coherence, was\nscarcely studied. We link the coherence time to the condensate phase dynamics,\nand we show with a microscopic theory that the time derivative of the\ncondensate phase operator $\\hat{\\theta}\\_0$ is proportional to a chemical\npotential operator that we construct including both the pair-breaking and\npair-motion excitation branches. In a single realization of energy $E$,\n$\\hat{\\theta}\\_0$ evolves at long times as $-2\\mu\\_{\\rm mc}(E)t/\\hbar$ where\n$\\mu\\_{\\rm mc}(E)$ is the microcanonical chemical potential; energy\nfluctuations from one realization to the other then lead to a ballistic\nspreading of the phase and to a Gaussian decay of the temporal coherence\nfunction with a characteristic time $\\propto N^{1/2}$. In the absence of energy\nfluctuations, the coherence time scales as $N$ due to the diffusive motion of\n$\\hat{\\theta}\\_0$. We propose a method to measure the coherence time with\nultracold atoms, which we predict to be tens of milliseconds for the canonical\nensemble unitary Fermi gas."
    },
    {
        "anchor": "Thermal Phase Transitions of Strongly Correlated Bosons with Spin-Orbit\n  Coupling: Experiments on ultracold atomic gases have begun to explore lattice effects\nand thermal fluctuations for two-component bosons with spin-orbit coupling\n(SOC). Motivated by this, we study a $tJ$ model of strongly correlated lattice\nbosons, with equal Rashba-Dresselhaus SOC and a uniform magnetic field. At zero\ntemperature, a Gutzwiller ansatz is shown to capture lattice variants of stripe\nsuperfluid (SF) ground states. We formulate a finite temperature generalization\nof the Gutzwiller approach and show that thermal fluctuations in the doped Mott\ninsulator drive a two-step melting of the stripe SF, revealing a wide\nintermediate regime of a normal fluid with stripe order.",
        "positive": "Spectral properties and phase diagram of correlated lattice bosons in an\n  optical cavity within the B-DMFT: We use the Bose-Hubbard model with an effective infinite-range interaction to\ndescribe the correlated lattice bosons in an optical cavity. We study both\nstatic and spectral properties of such system within the bosonic dynamical\nmean-field theory (B-DMFT), which is the state of the art method for strongly\ncorrelated bosonic systems. Both similarities and differences are found and\ndiscussed between our results and these obtained within different theoretical\nmethods and experiment."
    },
    {
        "anchor": "Spatially distributed multipartite entanglement enables\n  Einstein-Podolsky-Rosen steering of atomic clouds: A key resource for distributed quantum-enhanced protocols is entanglement\nbetween spatially separated modes. Yet, the robust generation and detection of\nnonlocal entanglement between spatially separated regions of an ultracold\natomic system remains a challenge. Here, we use spin mixing in a tightly\nconfined Bose-Einstein condensate to generate an entangled state of\nindistinguishable particles in a single spatial mode. We show experimentally\nthat this local entanglement can be spatially distributed by self-similar\nexpansion of the atomic cloud. Spatially resolved spin read-out is used to\nreveal a particularly strong form of quantum correlations known as\nEinstein-Podolsky-Rosen steering between distinct parts of the expanded cloud.\nBased on the strength of Einstein-Podolsky-Rosen steering we construct a\nwitness, which testifies up to genuine five-partite entanglement.",
        "positive": "Density-and-phase domain walls in a condensate with dynamical gauge\n  potentials: We show how one can generate domain walls that separate high- and low-density\nregions with opposite momenta in the ground state of a harmonically trapped\nBose-Einstein condensate using a density-dependent gauge potential. Within a\nGross-Pitaevskii framework, we elucidate the distinct roles of vector and\nscalar potentials and how they lead to synthetic electromagnetic fields that\nare localized at the domain wall. In particular, the kinetic energy cost of a\nsteep density gradient is compensated by an electrostatic field that pushes\nparticles away from a special value of density. We show numerically in one\ndimension that such a domain wall is more prominent for repulsive contact\ninteractions, and becomes metastable at strong electric fields through a\nfirst-order phase transition that ends at a critical point as the field is\nreduced. Our findings build on recent experimental developments and may be\nrealized with cold atoms in a shaken optical lattice, providing insights into\ncollective phenomena arising from dynamical gauge fields."
    },
    {
        "anchor": "Stabilizing persistent currents in an atomtronic Josephson junction\n  necklace: Arrays of Josephson junctions are at the forefront of research on quantum\ncircuitry for quantum computing, simulation and metrology. They provide a\ntesting bed for exploring a variety of fundamental physical effects where\nmacroscopic phase coherence, nonlinearities and dissipative mechanisms compete.\nHere we realize finite-circulation states in an atomtronic Josephson junction\nnecklace, consisting of a tunable array of tunneling links in a ring-shaped\nsuperfluid. We study the stability diagram of the atomic flow by tuning both\nthe circulation and the number of junctions. We predict theoretically and\ndemonstrate experimentally that the atomic circuit withstands higher\ncirculations (corresponding to higher critical currents) by increasing the\nnumber of Josephson links. The increased stability contrasts with the trend of\nthe superfluid fraction -- quantified by Leggett's criterion -- which instead\ndecreases with the number of junctions and the corresponding density depletion.\nOur results demonstrate atomic superfluids in mesoscopic structured ring\npotentials as excellent candidates for atomtronics applications, with prospects\ntowards the observation of non-trivial macroscopic superpositions of current\nstates.",
        "positive": "Nonlinear waves of polarization in two-component Bose-Einstein\n  condensates: Waves with different symmetries exist in two-component Bose-Einstein\ncondensates (BECs) whose dynamics is described by a system of coupled\nGross-Pitaevskii (GP) equations. A first type of waves corresponds to\nexcitations for which the motion of both components is locally in phase. In the\nsecond type of waves the two components have a counter-phase local motion. In\nthe case of different values of inter- and intra-component interaction\nconstants, the long wave-length behavior of these two modes corresponds to two\ntypes of sound with different velocities. In the limit of weak nonlinearity and\nsmall dispersion the first mode is described by the well-known Korteweg-de\nVries (KdV) equation. We show that in the same limit the second mode can be\ndescribed by the Gardner (modified KdV) equation, if the intra-component\ninteraction constants have close enough values. This leads to a rich\nphenomenology of nonlinear excitations (solitons, kinks, algebraic solitons,\nbreathers) which does not exist in the KdV description."
    },
    {
        "anchor": "Snapshot based characterization of particle currents and the Hall\n  response in synthetic flux lattices: Quantum simulators are attracting great interest because they promise insight\ninto the behavior of quantum many-body systems that are prohibitive for\nclassical simulations. The generic output of quantum simulators are snapshots,\nobtained by means of projective measurements. A central goal of theoretical\nefforts must be to predict the exact same quantities that can be measured in\nexperiments. Here, we report on the snapshot based calculation of particle\ncurrents in quantum lattice models with a conserved number of particles. It is\nshown how the full probability distribution of locally resolved particle\ncurrents can be obtained from suitable snapshot data. Moreover, we investigate\nthe Hall response of interacting bosonic flux ladders, exploiting snapshots\ndrawn from matrix-product states. Flux ladders are minimal lattice models,\nwhich enable microscopic studies of the Hall response in correlated quantum\nphases and they are successfully realized in current quantum-gas experiments.\nUsing a specific pattern of unitary two-site transformations, it is shown that\nthe Hall polarization and the Hall voltage can be faithfully computed from the\nsnapshots obtained in experimentally feasible quench and finite-bias\nsimulations.",
        "positive": "Mott-glass phase of a one-dimensional quantum fluid with long-range\n  interactions: We investigate the ground-state properties of quantum particles interacting\nvia a long-range repulsive potential ${\\cal V}_\\sigma(x)\\sim 1/|x|^{1+\\sigma}$\n($-1<\\sigma$) or ${\\cal V}_\\sigma(x)\\sim -|x|^{-1-\\sigma}$ ($-2\\leq \\sigma\n<-1$) that interpolates between the Coulomb potential ${\\cal V}_0(x)$ and the\nlinearly confining potential ${\\cal V}_{-2}(x)$ of the Schwinger model. In the\nabsence of disorder the ground state is a Wigner crystal when $\\sigma\\leq 0$.\nUsing bosonization and the nonperturbative functional renormalization group we\nshow that any amount of disorder suppresses the Wigner crystallization when\n$-3/2<\\sigma\\leq 0$; the ground state is then a Mott glass, i.e., a state that\nhas a vanishing compressibility and a gapless optical conductivity. For\n$\\sigma<-3/2$ the ground state remains a Wigner crystal."
    },
    {
        "anchor": "Finite range corrections near a Feshbach resonance and their role in the\n  Efimov effect: We have measured the binding energy of $^7$Li Feshbach molecules deep into\nthe non-universal regime by associating free atoms in a Bose-Einstein\ncondensate by modulating the magnetic field. We extract the scattering length\nfrom these measurements, correcting for non-universal short-range effects using\nseveral different methods. We find that field-dependent effective range\ncorrections agree well with the data.\n  With this more precise determination of the scattering length vs. field we\nreanalyze our previous data on the location of atom loss features produced by\nthe Efimov effect \\cite{PollackSci09} and investigate effective range\ncorrections to universal theory.",
        "positive": "Manipulation of coherent atom waves using accelerated two-dimensional\n  optical lattices: We study the dynamics of Bose-Einstein condensates in accelerated\ntwo-dimensional optical square lattices by numerically solving the\nGross-Pitaevskii equation. We consider the regime with negligible mean-field\ninteractions and examine in detail the pulses of atom clouds ejected from the\ncondensate due to Landau-Zener tunnelling. The pulses exhibit patterned\nstructures that can be understood from the momentum-space dynamics of the\ncondensate. Aside from conceiving realization of a pulsed two-dimensional atom\nlaser, we demonstrate that, by exploring the band structure of the lattice,\nLandau-Zener tunnelling and Bragg reflection of the condensate inside the\noptical lattice can provide means for manipulation of coherent atom waves."
    },
    {
        "anchor": "Strongly correlated superfluid order parameters from dc Josephson\n  supercurrents: The dc Josephson effect provides a powerful phase-sensitive tool for\ninvestigating superfluid order parameters. We report on the observation of dc\nJosephson supercurrents in strongly interacting fermionic superfluids across a\ntunnelling barrier in the absence of any applied potential difference. For\nsufficiently strong barriers, we observe a sinusoidal current-phase relation,\nin agreement with Josephson's seminal prediction. We map out the\nzero-resistance state and its breakdown as a function of junction parameters,\nextracting the Josephson critical current behaviour. By comparing our results\nwith an analytic model, we determine the pair condensate fraction throughout\nthe Bardeen-Cooper-Schrieffer - Bose-Einstein Condensation crossover. Our work\nsuggests that coherent Josephson transport may be used to pin down superfluid\norder parameters in diverse atomic systems, even in the presence of strong\ncorrelations.",
        "positive": "Effect of transverse confinement on a quasi-one dimensional dipolar Bose\n  gas: We study a gas of bosonic dipolar atoms in the presence of a transverse\nharmonic trapping potential by using an improved variational Bethe ansatz,\nwhich includes the transverse width of the atomic cloud as a variational\nparameter. Our calculations show that the system behavior evolves from\nquasi-one dimensional to a strictly one-dimensional one by changing the\natom-atom interaction, or the axial density, or the frequency of the transverse\nconfinement. Quite remarkably, in the droplet phase induced by the attractive\ndipolar interaction the system becomes sub-one dimensional when the transverse\nwidth is smaller than the characteristic length of the transverse harmonic\nconfinement."
    },
    {
        "anchor": "Speckle Imaging of Spin Fluctuations in a Strongly Interacting Fermi Gas: Spin fluctuations and density fluctuations are studied for a two-component\ngas of strongly interacting fermions along the BEC-BCS crossover. This is done\nby in-situ imaging of dispersive speckle patterns. Compressibility and magnetic\nsusceptibility are determined from the measured fluctuations. This new\nsensitive method easily resolves a tenfold suppression of spin fluctuations\nbelow shot noise due to pairing, and can be applied to novel magnetic phases in\noptical lattices.",
        "positive": "Breakdown of Fermi liquid description for strongly interacting fermions: The nature of the normal state of an ultracold Fermi gas in the BCS-BEC\ncrossover regime is an intriguing and controversial topic. While the many-body\nground state remains a condensate of paired fermions, the normal state must\nevolve from a Fermi liquid to a Bose gas of molecules as a function of the\ninteraction strength. How this occurs is still largely unknown. We explore this\nquestion with measurements of the distribution of single-particle energies and\nmomenta in a nearly homogeneous gas above $T_c$. The data fit well to a\nfunction that includes a narrow, positively dispersing peak that corresponds to\nquasiparticles and an \"incoherent background\" that can accommodate broad,\nasymmetric line shapes. We find that the quasiparticle's spectral weight\nvanishes abruptly as the strength of interactions is modified, which signals\nthe breakdown of a Fermi liquid description. Such a sharp feature is surprising\nin a crossover."
    },
    {
        "anchor": "Zero-point energy of ultracold atoms: We analyze the divergent zero-point energy of a dilute and ultracold gas of\natoms in D spatial dimensions. For bosonic atoms we explicitly show how to\nregularize this divergent contribution, which appears in the Gaussian\nfluctuations of the functional integration, by using three different\nregularization approaches: dimensional regularization, momentum-cutoff\nregularization and convergence-factor regularization. In the case of the ideal\nBose gas the divergent zero-point fluctuations are completely removed, while in\nthe case of the interacting Bose gas these zero-point fluctuations give rise to\na finite correction to the equation of state. The final convergent equation of\nstate is independent of the regularization procedure but depends on the\ndimensionality of the system and the two-dimensional case is highly nontrivial.\nWe also discuss very recent theoretical results on the divergent zero-point\nenergy of the D-dimensional superfluid Fermi gas in the BCS-BEC crossover. In\nthis case the zero-point energy is due to both fermionic single-particle\nexcitations and bosonic collective excitations, and its regularization gives\nremarkable analytical results in the BEC regime of composite bosons. We compare\nthe beyond-mean-field equations of state of both bosons and fermions with\nrelevant experimental data on dilute and ultracold atoms quantitatively\nconfirming the contribution of zero-point-energy quantum fluctuations to the\nthermodynamics of ultracold atoms at very low temperatures.",
        "positive": "Thermodynamics of a spin-1 Bose gas with fixed magnetization: We investigate the thermodynamics of a spin-1 Bose gas with fixed\nmagnetization including the quadratic Zeeman energy shift. Our calculations are\nbased on the grand canonical description for the ideal gas and the classical\nfields approximation for atoms with ferromagnetic and antiferromagnetic\ninteractions. We confirm the occurence of a double phase transition in the\nsystem that takes place due to two global constraints. We show analytically for\nthe ideal gas how critical temperatures and condensed fractions are changed by\na non-zero magnetic field. The interaction strongly affects the condensate\nscenario below the second critical temperature. The effect imposed by\ninteraction energies becomes diminished in high magnetic fields where\ncondensation, of both ferromagnetic and antiferromagnetic atoms, agree with the\nideal gas results."
    },
    {
        "anchor": "Topological soliton-polaritons in 1D systems of light and fermionic\n  matter: Quantum nonlinear optics is a quickly growing field with large technological\npromise, at the same time involving complex and novel many-body phenomena. In\nthe usual scenario, optical nonlinearities originate from the interactions\nbetween polaritons, which are hybrid quasi-particles mixing matter and light\ndegrees of freedom. Here we introduce a type of polariton which is\nintrinsically nonlinear and emerges as the natural quasi-particle in presence\nquantum degenerate fermionic matter. It is a composite object made of a fermion\ntrapped inside an optical soliton forming a topological defect in a\nspontaneously formed crystalline structure. Each of these soliton-polaritons\ncarries a $\\textbf{Z}_2$ topological quantum number, as they create a domain\nwall between two crystalline regions with opposite dimerization so that the\nfermion is trapped in an interphase state. These composite objects are formally\nequivalent to those appearing in the Su-Schrieffer-Heeger (SSH) model for\nelectrons coupled to lattice phonons.",
        "positive": "Contact Measurements on Atomic BEC: A powerful set of universal relations, centered on a quantity called the\ncontact, connects the strength of short-range two-body correlations to the\nthermodynamics of a many-body system with delta-function interactions. We\nreport on measurements of the contact, using RF spectroscopy, for an $^{85}$Rb\natomic Bose-Einstein condensate (BEC). For bosons, the fact that contact\nspectroscopy can be used to probe the gas on short timescales is useful given\nthe decreasing stability of BECs with increasing interactions. A complication\nis the added possibility, for bosons, of three-body interactions. In\ninvestigating this issue, we have located an Efimov resonance for $^{85}$Rb\natoms with loss measurements and thus determined the three-body interaction\nparameter. In our contact spectroscopy, in a region of observable\nbeyond-mean-field effects, we find no measurable contribution from three-body\nphysics."
    },
    {
        "anchor": "Extension of the Ginzburg - Landau approach for ultracold Fermi gases\n  below a critical temperature: In the context of superfluid Fermi gases, the Ginzburg - Landau (GL)\nformalism for the macroscopic wave function has been successfully extended to\nthe whole temperature range where the superfluid state exists. After reviewing\nthe formalism, we first investigate the temperature-dependent correction to the\nstandard GL expansion (which is valid close to $T_{c}$). Deviations from the\nstandard GL formalism are particularly important for the kinetic energy\ncontribution to the GL energy functional, which in turn influences the healing\nlength of the macroscopic wave function. We apply the formalism to\nvariationally describe vortices in a strong-coupling Fermi gas in the BEC-BCS\ncrossover regime, in a two-band system. The healing lengths, derived as\nvariational parameters in the vortex wave function, are shown to exhibit hidden\ncriticality well below $T_{c}$.",
        "positive": "Bulk viscosities for cold Fermi superfluids close to the unitary limit: We compute the coefficients of bulk viscosity for a non-relativistic\nsuperfluid corresponding to a fermionic system close to the unitarity limit. We\nconsider the low temperature regime assuming that the transport properties of\nthe system are dominated by phonons. To compute the coefficients of bulk\nviscosity we use kinetic theory in the relaxation time approximation and the\nlow energy effective field theory of the corresponding system. We show that the\nthree independent bulk viscosity coefficients, $\\zeta_1, \\zeta_2, \\zeta_3$,\nassociated with irreversible flows vanish for phonons with a linear dispersion\nlaw. Considering a phonon dispersion law with a cubic term in momentum we find\nthat in the conformal limit $\\zeta_1 = \\zeta_2=0$, while $\\zeta_3$ is non-zero.\nIncluding a conformal breaking term which arises for a large but finite s-wave\nscattering length, $a$, at the leading order in $1/a$ we obtain that $\\zeta_1\n\\propto 1/a$ and $\\zeta_2 \\propto 1/a^2$."
    },
    {
        "anchor": "Spin-tensor Meissner currents of ultracold bosonic gas in an optical\n  lattice: We investigate the Meissner currents of interacting bosons subjected to a\nstaggered artificial gauge field in a three-leg ribbon geometry, realized by\nspin-tensor--momentum coupled spin-1 atoms in a 1D optical lattice. By\ncalculating the current distributions using the state-of-the-art density-matrix\nrenormalization-group method, we find a rich phase diagram containing\ninteresting Meissner and vortex phases, where the currents are mirror symmetric\nwith respect to the {\\color{red}middle leg} (i.e., they flow in the same\ndirection on the two boundary legs opposite to that on the middle leg), leading\nto the spin-tensor type Meissner currents, which is very different from\npreviously observed chiral edge currents under uniform gauge field. The\ncurrents are uniform along each leg in the Meissner phase and form\nvortex-antivortex pairs in the vortex phase. Besides, the system also support a\npolarized phase that spontaneously breaks the mirror symmetry, whose ground\nstates are degenerate with currents either uniform or forming vortex-antivortex\npairs. We also discuss the experimental schemes for probing these phases. Our\nwork provides useful guidance to ongoing experimental research on synthetic\nflux ribbons and paves the way for exploring novel many-body phenomena therein.",
        "positive": "Nature of 3D Bose Gases near Resonance: In this paper, we explore the nature of three-dimensional Bose gases at large\npositive scattering lengths via resummation of dominating processes involving a\nminimum number of virtual atoms. We focus on the energetics of the nearly\nfermionized Bose gases beyond the usual dilute limit. We also find that an\nonset instability sets in at a critical scattering length, beyond which the\nnear-resonance Bose gases become strongly coupled to molecules and lose the\nmetastability. Near the point of instability, the chemical potential reaches a\nmaximum, and the effect of the three-body forces can be estimated to be around\na few percent."
    },
    {
        "anchor": "Ultracold field-linked tetratomic molecules: Ultracold polyatomic molecules offer intriguing new opportunities in cold\nchemistry, precision measurements, and quantum information processing, thanks\nto their rich internal structure. However, their increased complexity compared\nto diatomic molecules presents a formidable challenge to employ conventional\ncooling techniques. Here, we demonstrate a new approach to create ultracold\npolyatomic molecules by electroassociation in a degenerate Fermi gas of\nmicrowave-dressed polar molecules through a field-linked resonance. Starting\nfrom ground state NaK molecules, we create around $1.1\\times 10^3$ tetratomic\n(NaK)$_2$ molecules, with a phase space density of $0.040(3)$ at a temperature\nof $134(3)\\,\\text{nK}$, more than $3000$ times colder than previously realized\ntetratomic molecules. We observe a maximum tetramer lifetime of\n$8(2)\\,\\text{ms}$ in free space without a notable change in the presence of an\noptical dipole trap, indicating these tetramers are collisionally stable. The\nmeasured binding energy and lifetime agree well with parameter-free\ncalculations, which outlines pathways to further increase the lifetime of the\ntetramers. Moreover, we directly image the dissociated tetramers through\nmicrowave-field modulation to probe the anisotropy of their wave function in\nmomentum space. Our result demonstrates a universal tool for assembling\nultracold polyatomic molecules from smaller polar molecules, which is a crucial\nstep towards Bose--Einstein condensation (BEC) of polyatomic molecules and\ntowards a new crossover from a dipolar Bardeen-Cooper-Schrieffer (BCS)\nsuperfluid to a BEC of tetramers. Additionally, the long-lived FL state\nprovides an ideal starting point for deterministic optical transfer to deeply\nbound tetramer states.",
        "positive": "Two-site anyonic Josephson junction: Anyons are particles with intermediate quantum statistics whose wavefunction\nacquires a phase $e^{i\\theta}$ by particle exchange. Inspired by proposals of\nsimulating anyons using ultracold atoms trapped in optical lattices, we study a\ntwo-site anyonic Josephson junction, i.e. anyons confined in a one-dimensional\ndouble-well potential. We show, analytically and numerically, that many\nproperties of anyonic Josephson junctions, such as Josephson frequency,\nimbalanced solutions, macroscopic quantum self-trapping, coherence visibility,\nand condensate fraction, crucially depend on the anyonic angle $\\theta$. Our\ntheoretical predictions are a solid benchmark for near future experimental\nquantum simulations of anyonic matter in double-well potentials."
    },
    {
        "anchor": "Theory of a resonantly interacting impurity in a Bose-Einstein\n  condensate: We investigate a Bose-Einstein condensate in strong interaction with a single\nimpurity particle. While this situation has received considerable interest in\nrecent years, the regime of strong coupling remained inaccessible to most\napproaches due to an instability in Bogoliubov theory arising near the\nresonance. We present a nonlocal extension of Gross-Pitaevskii theory that is\nfree of such divergences and does not require the use of the Born approximation\nin any of the interaction potentials. We find a new dynamical transition regime\nbetween attractive and repulsive polarons, where an interaction quench results\nin a finite number of coherent oscillations in the density profiles of the\nmedium and in the contact parameter before equilibrium is reached.",
        "positive": "Spectral properties of the Goldstino in supersymmetric Bose-Fermi\n  mixtures: We evaluate the spectral properties of the Goldstino in a Bose-Fermi mixture\nof cold atoms and molecules whose dynamics is governed by a supersymmetric\nhamiltonian. Model independent results are obtained from sum rules obeyed by\nthe spectral function. We carry out specific calculations, at zero and finite\ntemperature, using the Random Phase Approximation, and obtain in particular\nanalytic expressions for the dispersion relation at small momentum. These\nexplicit calculations allow us to pin down more precisely the features of the\nGoldstino that can be attributed to the supersymmetry alone, together with its\nspontaneous breaking. The anomalous large effect of the Fermi sea at moderate\nand large momenta is emphasized."
    },
    {
        "anchor": "Superfluid phase transition and strong-coupling effects in an ultracold\n  Fermi gas with mass imbalance: We investigate the superfluid phase transition and effects of mass imbalance\nin the BCS (Bardeen-Cooper-Schrieffer)-BEC (Bose-Einstein condensation)\ncrossover regime of an cold Fermi gas. We point out that the Gaussian\nfluctuation theory developed by Nozi\\`eres and Schmitt-Rink and the $T$-matrix\ntheory, that are now widely used to study strong-coupling physics of cold Fermi\ngases, give unphysical results in the presence of mass imbalance. To overcome\nthis problem, we extend the $T$-matrix theory to include higher-order pairing\nfluctuations. Using this, we examine how the mass imbalance affects the\nsuperfluid phase transition. Since the mass imbalance is an important key in\nvarious Fermi superfluids, such as $^{40}$K-$^6$Li Fermi gas mixture, exciton\ncondensate, and color superconductivity in a dense quark matter, our results\nwould be useful for the study of these recently developing superfluid systems.",
        "positive": "Fermi liquid theory of ultra-cold trapped Fermi gases: Implications for\n  Pseudogap Physics and Other Strongly Correlated Phases: We show how Fermi liquid theory can be applied to ultra-cold Fermi gases,\nthereby expanding their \"simulation\" capabilities to a class of problems of\ninterest to multiple physics sub-disciplines. We introduce procedures for\nmeasuring and calculating position dependent Landau parameters. This lays the\nground work for addressing important controversial issues: (i) the suggestion\nthat thermodynamically, the normal state of a unitary gas is indistinguishable\nfrom a Fermi liquid (ii) that a fermionic system with strong repulsive contact\ninteractions is associated with either ferromagnetism or localization; this\nrelates as well to $^3$He and its p-wave superfluidity."
    },
    {
        "anchor": "Ferromagnetic to antiferromagnetic transition of one-dimensional spinor\n  Bose gases with spin-orbit coupling: We have analytically solved one-dimensional interacting two-component bosonic\ngases with spin-orbit (SO) coupling by the Bethe-ansatz method. Through a gauge\ntransformation, the effect of SO coupling is incorporated into a spin-dependent\ntwisted boundary condition. Our result shows that the SO coupling can influence\nthe eigenenergy in a periodical pattern. The interplay between interaction and\nSO coupling may induce the energy level crossing for the ground state, which\nleads to a transition from the ferromagnetic to antiferromagnetic state.",
        "positive": "Symmetry classification of uniform states in spin-2 Bose-Einstein\n  condensates and neutron $^3P_2$ superfluids: We clarify a relation between the Gross-Pitaevskii energy functional for\nspin-2 spinor Bose-Einstein condensates and the Ginzburg-Landau theory for\nneutron $^3P_2$ superfluidis (spin-triplet $P$-wave pairing with total angular\nmomentum two). We then classify all uniform states with nontrivial unbroken\nsymmetries, with the help of geometric invariant theory."
    },
    {
        "anchor": "Lattice gauge theories and string dynamics in Rydberg atom quantum\n  simulators: Gauge theories are the cornerstone of our understanding of fundamental\ninteractions among particles. Their properties are often probed in dynamical\nexperiments, such as those performed at ion colliders and high-intensity laser\nfacilities. Describing the evolution of these strongly coupled systems is a\nformidable challenge for classical computers, and represents one of the key\nopen quests for quantum simulation approaches to particle physics phenomena.\nHere, we show how recent experiments done on Rydberg atom chains naturally\nrealize the real-time dynamics of a lattice gauge theory at system sizes at the\nboundary of classical computational methods. We prove that the constrained\nHamiltonian dynamics induced by strong Rydberg interactions maps exactly onto\nthe one of a $U(1)$ lattice gauge theory. Building on this correspondence, we\nshow that the recently observed anomalously slow dynamics corresponds to a\nstring-inversion mechanism, reminiscent of the string-breaking typically\nobserved in gauge theories. This underlies the generality of this slow\ndynamics, which we illustrate in the context of one-dimensional quantum\nelectrodynamics on the lattice. Within the same platform, we propose a set of\nexperiments that generically show long-lived oscillations, including the\nevolution of particle-antiparticle pairs. Our work shows that the state of the\nart for quantum simulation of lattice gauge theories is at 51 qubits, and\nconnects the recently observed slow dynamics in atomic systems to archetypal\nphenomena in particle physics",
        "positive": "Numerical simulation of exciton dynamics in Cu2O at ultra low\n  temperatures within a potential trap: We have studied theoretically the relaxation behaviour of excitons in cuprous\noxide (Cu2O) at ultra low temperatures when excitons are confined within a\npotential trap by solving numerically the Boltzmann equation. As relaxation\nprocesses, we have included in this paper deformation potential phonon\nscattering, radiative and non-radiative decay and Auger decay. The relaxation\nkinetics has been analysed for temperatures in the range between 0.3K and 5K.\nUnder the action of deformation potential phonon scattering only, we find for\ntemperatures above 0.5K that the excitons reach local equilibrium with the\nlattice i.e. that the effective local temperature is coming down to bath\ntemperature, while below 0.5K a non-thermal energy distribution remains.\nInterestingly, for all temperatures the global spatial distribution of excitons\ndoes not reach the equilibrium distribution, but stays at a much higher\neffective temperature. If we include further a finite lifetime of the excitons\nand the two-particle Auger decay, we find that both the local and the global\neffective temperature are not coming down to bath temperature. In the first\ncase we find a Bose-Einstein condensation (BEC) to occur for all temperatures\nin the investigated range. Comparing our results with the thermal equilibrium\ncase, we find that BEC occurs for a significantly higher number of excitons in\nthe trap. This effect could be related to the higher global temperature, which\nrequires an increased number of excitons within the trap to observe the BEC. In\ncase of Auger decay, we do not find at any temperature a BEC due to the heating\nof the exciton gas."
    },
    {
        "anchor": "Quantised supercurrent decay in an annular Bose-Einstein condensate: We study the metastability and decay of multiply-charged superflow in a\nring-shaped atomic Bose-Einstein condensate. Supercurrent corresponding to a\ngiant vortex with topological charge up to q=10 is phase-imprinted optically\nand detected both interferometrically and kinematically. We observe q=3\nsuperflow persisting for up to a minute and clearly resolve a cascade of\nquantised steps in its decay. These stochastic decay events, associated with\nvortex-induced $2 \\pi$ phase slips, correspond to collective jumps of atoms\nbetween discrete q values. We demonstrate the ability to detect quantised\nrotational states with > 99 % fidelity, which allows a detailed quantitative\nstudy of time-resolved phase-slip dynamics. We find that the supercurrent\ndecays rapidly if the superflow speed exceeds a critical velocity in good\nagreement with numerical simulations, and we also observe rare stochastic phase\nslips for superflow speeds below the critical velocity.",
        "positive": "Spin-Imbalanced Pairing and Fermi Surface Deformation in Flat Bands: We study the attractive Hubbard model with spin imbalance on two lattices\nfeaturing a flat band: the Lieb and kagome lattices. We present mean-field\nphase diagrams featuring exotic superfluid phases, similar to the\nFulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, whose stability is confirmed by\ndynamical mean-field theory (DMFT). The nature of the pairing is found to be\nricher than just the Fermi surface shift responsible for the usual FFLO state.\nThe presence of a flat band allows for changes in the particle momentum\ndistributions at null energy cost. This facilitates formation of nontrivial\nsuperfluid phases via multiband Cooper pair formation: the momentum\ndistribution of the spin component in the flat band deforms to mimic the Fermi\nsurface of the other spin component residing in a dispersive band. The Fermi\nsurface of the unpaired particles that are typical for gapless superfluids\nbecomes deformed as well. The results highlight the profound effect of flat\ndispersions on Fermi surface instabilities, and provide a potential route for\nobserving spin-imbalanced superfluidity and superconductivity."
    },
    {
        "anchor": "Laser operation and Bose-Einstein condensation: analogies and\n  differences: After reviewing the interpretation of laser operation as a non-equilibrium\nBose-Einstein condensation phase transition, we illustrate the novel features\narising from the non-equilibrium nature of photon and polariton Bose-Einstein\ncondensates recently observed in experiments. We then proposea quantitative\ncriterion to experimentally assess the equilibrium vs. non-equilibrium nature\nof a specific condensation process, based on fluctuation-dissipation relations.\nThe power of this criterion is illustrated on two models which shows very\ndifferent behaviours.",
        "positive": "Metastable Bose-Einstein Condensation in a Strongly Correlated Optical\n  Lattice: We experimentally and theoretically study the peak fraction of a\nBose-Einstein condensate loaded into a cubic optical lattice as the lattice\npotential depth and entropy per particle are varied. This system is\nwell-described by the superfluid regime of the Bose-Hubbard model, which allows\nfor comparison with mean-field theories and exact quantum Monte Carlo (QMC)\nsimulations. Despite correcting for systematic discrepancies between condensate\nfraction and peak fraction, we discover that the experiment consistently shows\nthe presence of a condensate at temperatures higher than the critical\ntemperature predicted by QMC simulations. This metastability suggests that\nturning on the lattice potential is non-adiabatic. To confirm this behavior, we\ncompute the timescales for relaxation in this system, and find that\nequilibration times are comparable with the known heating rates. The similarity\nof these timescales implies that turning on the lattice potential adiabatically\nmay be impossible. Our results point to the urgent need for a better\ntheoretical and experimental understanding of the timescales for relaxation and\nadiabaticity in strongly interacting quantum gases, and the importance of\nmodel-independent probes of thermometry in optical lattices."
    },
    {
        "anchor": "High-intensity two-frequency photoassociation spectroscopy of a weakly\n  bound molecular state: theory and experiment: We investigate two-frequency photoassociation of a weakly bound molecular\nstate, focusing on a regime where the ac Stark shift is comparable to the\nhalo-state energy. In this \"high-intensity\" regime, we observe features absent\nin low-intensity two-frequency photoassociation. We experimentally measure the\nspectra of $^{86}$Sr atoms coupled to the least bound state of the\n$^{86}$Sr$_2$ ground electronic channel through an intermediate electronically\nexcited molecular state. We compare the spectra to a simple three-level model\nthat includes a two-frequency drive on each leg of the transition. With\nnumerical solution of the time-dependent Schrodinger equation, we show that\nthis model accurately captures (1) the existence of experimentally observed\nsatellite peaks that arise from nonlinear processes, (2) the locations of the\ntwo-photon peak in the spectrum, including ac Stark shifts, and (3) in some\ncases, spectral lineshapes. To better understand these numerical results, we\ndevelop an approximate treatment of this model, based on Floquet and\nperturbation theory, that gives simple formulas that accurately capture the\nhalo-state energies. We expect these expressions to be valuable tools to\nanalyze and guide future two-frequency photoassociation experiments.",
        "positive": "Borromean ground state of fermions in two dimensions: The study of quantum mechanical bound states is as old as quantum theory\nitself. Yet, it took many years to realize that three-body borromean systems\nthat are bound when any two-body subsystem is unbound are abundant in nature.\nHere we demonstrate the existence of borromean systems of spin-polarized\n(spinless) identical fermions in two spatial dimensions. The ground state with\nzero orbital (planar) angular momentum exists in a borromean window between\ncritical two- and three-body strengths. The doubly degenerate first excited\nstates of angular momentum one appears only very close to the two-body\nthreshold. They are the lowest in a possible sequence of so-called super-Efimov\nstates. While the observation of the super-Efimov scaling could be very\ndifficult, the borromean ground state should be observable in cold atomic gases\nand could be the basis for producing a quantum gas of three-body states in two\ndimensions."
    },
    {
        "anchor": "Quantum phases of atomic Fermi gases with anisotropic spin-orbit\n  coupling: We consider a general anisotropic spin-orbit coupling (SOC) and analyze the\nphase diagrams of both balanced and imbalanced Fermi gases for the entire\nBCS--Bose-Einstein condensate (BEC) evolution. In the first part, we use the\nself-consistent mean-field theory at zero temperature, and show that the\ntopological structure of the ground-state phase diagrams is quite robust\nagainst the effects of anisotropy. In the second part, we go beyond the\nmean-field description, and investigate the effects of Gaussian fluctuations\nnear the critical temperature. This allows us to derive the time-dependent\nGinzburg-Landau theory, from which we extract the effective mass of the Cooper\npairs and their critical condensation temperature in the molecular BEC limit.",
        "positive": "The Effective Interaction Strength in a Bose-Einstein Condensate of\n  Photons in a Dye-Filled Microcavity: We experimentally study Bose-Einstein condensation of photons (phBEC) in a\ndye-filled microcavity. Through multiple absorption and emission cycles the\nphotons inside the microcavity thermalize to the rovibronic temperature of the\ndye solution. Raising the photon density of the thermalized photon gas beyond\nthe critical photon density yields a macroscopic occupation of the ground\nstate, i.e. phBEC. For increasing density, we observe an increase of the\ncondensate radius which we attribute to effective repulsive interactions. For\nseveral dye concentrations we accurately determine the radius of the condensate\nas a function of the number of condensate photons, and derive an effective\ninteraction strength parameter $\\tilde{g}$. For all concentrations we find\n$\\tilde{g} \\sim 10^{-2}$, one order larger than previously reported."
    },
    {
        "anchor": "Dipolar bosons on an optical lattice ring: We consider an ultra-small system of polarized bosons on an optical lattice\nwith a ring topology interacting via long range dipole-dipole interactions.\nDipoles polarized perpendicular to the plane of the ring reveal sharp\ntransitions between different density wave phases. As the strength of the\ndipolar interactions is varied the behavior of the transitions is first-order\nlike. For dipoles polarized in the plane of the ring the transitions between\npossible phases show pronounced sensitivity to the lattice depth. The abundance\nof possible configurations may be useful for quantum information applications.",
        "positive": "Quantum Zeno effects across a parity-time symmetry breaking transition\n  in atomic momentum space: We experimentally study quantum Zeno effects in a parity-time (PT) symmetric\ncold atom gas periodically coupled to a reservoir. Based on the\nstate-of-the-art control of inter-site couplings of atoms in a momentum\nlattice, we implement a synthetic two-level system with passive PT symmetry\nover two lattice sites, where an effective dissipation is introduced through\nrepeated couplings to the rest of the lattice. Quantum Zeno (anti-Zeno) effects\nmanifest in our experiment as the overall dissipation of the two-level system\nbecoming suppressed (enhanced) with increasing coupling intensity or frequency.\nWe demonstrate that quantum Zeno regimes exist in the broken PT symmetry phase,\nand are bounded by exceptional points separating the PT symmetric and PT broken\nphases, as well as by a discrete set of critical coupling frequencies. Our\nexperiment establishes the connection between PT-symmetry-breaking transitions\nand quantum Zeno effects, and is extendable to higher dimensions or to\ninteracting regimes, thanks to the flexible control with atoms in a momentum\nlattice."
    },
    {
        "anchor": "Quantum fluctuations beyond the Gutzwiller approximation in the\n  Bose-Hubbard model: We develop a quantum many-body theory of the Bose-Hubbard model based on the\ncanonical quantization of the action derived from a Gutzwiller mean-field\nansatz. Our theory is a systematic generalization of the Bogoliubov theory of\nweakly-interacting gases. The control parameter of the theory, defined as the\nzero point fluctuations on top of the Gutzwiller mean-field state, remains\nsmall in all regimes. The approach provides accurate results throughout the\nwhole phase diagram, from the weakly to the strongly interacting superfluid and\ninto the Mott insulating phase. As specific examples of application, we study\nthe two-point correlation functions, the superfluid stiffness, the density\nfluctuations, for which quantitative agreement with available quantum Monte\nCarlo data is found. In particular, the two different universality classes of\nthe superfluid-insulator quantum phase transition at integer and non-integer\nfilling are recovered.",
        "positive": "Dynamical excitation processes and correlations of three-body\n  two-dimensional mixtures: A scheme is proposed to dynamically excite distinct eigenstate superpositions\nin three-body Bose-Fermi mixtures confined in a two-dimensional harmonic trap.\nThe system is initialized in a non-interacting state with a variable spatial\nextent, and the scattering lengths are subsequently quenched. For spatial\nwidths smaller than the three-body harmonic oscillator length, a superposition\nof trimers and atom-dimers is dynamically attained, otherwise trap states are\npredominantly populated. Accordingly, the Tan contacts evince the build-up of\nshort range two- and three-body correlations in the course of the evolution. A\nlarger spatial extent of the initial state leads to a reduction of few-body\ncorrelations, endowed however with characteristic peaks at the positions of the\navoided-crossings in the energy spectra, thereby signalling the participation\nof atom-dimers. Our results expose ways to dynamically excite selectively\ntrimers, atom-dimers and trapped few-body states characterized by substantial\ncorrelations and likely to be accessible within current experiments."
    },
    {
        "anchor": "Discrete time crystals in Bose-Einstein Condensates and\n  symmetry-breaking edge in a simple two-mode theory: Discrete time crystals (DTCs) refer to a novel many-body steady state that\nspontaneously breaks the discrete time-translational symmetry in a\nperiodically-driven quantum system. Here, we study DTCs in a Bose-Einstein\ncondensate (BEC) bouncing resonantly on an oscillating mirror, using a two-mode\nmodel derived from a standard quantum field theory. We investigate the validity\nof this model and apply it to study the long-time behavior of our system. A\nwide variety of initial states based on two Wannier modes are considered. We\nfind that in previous studies the investigated phenomena in the evolution\ntime-window ($\\lessapprox$2000 driving periods) are actually \"short-time\"\ntransient behavior though DTC formation signaled by the sub-harmonic responses\nis still shown if the inter-boson interaction is strong enough. After a much\nlonger (about 20 times) evolution time, initial states with no \"long-range\"\ncorrelations relax to a steady state, where time-symmetry breaking can be\nunambiguously defined. Quantum revivals also eventually occur. This long-time\nbehavior can be understood via the many-body Floquet quasi-eigenenergy spectrum\nof the two-mode model. A symmetry-breaking edge for DTC formation appears in\nthe spectrum for strong enough interaction, where all quasi-eigenstates below\nthe edge are symmetry-breaking while those above the edge are symmetric. The\nlate-time steady state's time-translational symmetry depends solely on whether\nthe initial energy is above or below the symmetry-breaking edge. A phase\ndiagram showing regions of symmetry-broken and symmetric phases for differing\ninitial energies and interaction strengths is presented. We find that according\nto this two-mode model, the discrete time crystal survives for times out to at\nleast 250,000 driving periods.",
        "positive": "Bose-Einstein Condensation and Spin Mixtures of Optically Trapped\n  Metastable Helium: We report the realization of a BEC of metastable helium-4 atoms (4He*) in an\nall optical potential. Up to 10^5 spin polarized 4He* atoms are condensed in an\noptical dipole trap formed from a single, focused, vertically propagating far\noff-resonance laser beam. The vertical trap geometry is chosen to best match\nthe resolution characteristics of a delay-line anode micro-channel plate\ndetector capable of registering single He* atoms. We also confirm the\ninstability of certain spin state combinations of 4He* to two-body inelastic\nprocesses, which necessarily affects the scope of future experiments using\noptically trapped spin mixtures. In order to better quantify this constraint,\nwe measure spin state resolved two-body inelastic loss rate coefficients in the\noptical trap."
    },
    {
        "anchor": "Spin domains in ground state of a trapped spin-1 condensate: A general\n  study under Thomas-Fermi approximation: Investigation of ground state structures and phase separation under\nconfinement is of great interest in spinor Bose Einstein Condensates (BEC). In\nthis paper we show that, in general, within the Thomas-Fermi (T-F)\napproximation, the phase separation scenario of stationary states can be\nobtained including all the mixed states on an equal footing for a spin-1\ncondensate for any confinement. Exact analytical expressions of energy density,\nbeing independent of local mass density for all allowed states enables this\ngeneral analysis under T-F approximation. We study here in details a particular\ncase of spherically symmetric harmonic confinement as an example and show a\nwide range of potential phase separation scenario for anti-ferromagnetic and\nferromagnetic interactions.",
        "positive": "Measure synchronization in a two-species bosonic Josephson junction: Measure synchronization (MS) in a two-species bosonic Josephson junction\n(BJJ) is studied based on semi-classical theory. Six different scenarios for\nMS, including two in the Josephson oscillation regime (0 phase mode) and four\nin the self-trapping regime ($\\pi$ phase mode), have been clearly shown.\nSystematic investigations of the common features behind these different\nscenarios have been performed. We show that the average energies of the two\nspecies merge at the MS transition point. The scaling of the power law near the\nMS transition has been verified, and the critical exponent is 1/2 for all of\nthe different scenarios for MS. We also illustrate MS in a three-dimensional\nphase space; from this illustration, more detailed information on the dynamical\nprocess can be obtained. Particularly, by analyzing the Poincare sections with\nchanging interspecies interactions, we find that the two-species BJJ exhibits\nseparatrix crossing behavior at MS transition point, and such behavior depicts\nthe general mechanism behind the different scenarios for the MS transitions.\nThe new critical behavior found in a two-species BJJ is expected to be found in\nreal systems of atomic Bose gases."
    },
    {
        "anchor": "Functional renormalization group approach to conventional theory of\n  superfluidity and beyond: Fermionic functional renormalization group (FRG) is applied to describe the\nsuperfluid phase transition of the two-component fermionic system with\nattractive contact interaction. Connection between the fermionic FRG approach\nand the Bardeen-Cooper-Schrieffer (BCS) theory with its Gorkov and\nMelik-Barkhudarov (GMB) correction is made clear, and the FRG flow of the\nfermion self-energy is also studied to go beyond the BCS+GMB theory. The\nsuperfluid transition temperature and the associated chemical potential are\ncalculated in the region of the negative scattering length using fermionic FRG.",
        "positive": "Guided atom laser: transverse mode quality and longitudinal momentum\n  distribution: We analyze the outcoupling of a matter wave into a guide by a time-dependent\nspilling of the atoms from an initially trapped Bose-Einstein condensate. This\nprocess yields intrinsically a breakdown of the adiabatic condition that\ntriggers the outcoupling of the wave function. Our analysis of the\ntime-dependent engineering and manipulation of condensates in momentum space in\nthis context enables to work out the limits due to interactions in the mode\nquality of a guided atom laser. This study is consistent with recent\nexperimental observations of low transverse excitations of guided atom lasers\nand suggests (i) an optimal strategy to realize such quasi-monomode guided atom\nlasers with, in addition, the lowest possible longitudinal velocity dispersion,\nor alternatively (ii) a strategy for engineering the atomic flux of the atom\nlaser."
    },
    {
        "anchor": "Superfluid vortex dynamics on an ellipsoid and other surfaces of\n  revolution: We study the dynamics of quantized superfluid vortices on axisymmetric\ncompact surfaces with no holes, where the total vortex charge must vanish and\nthe condition of irrotational flow forbids distributed vorticity. A conformal\ntransformation from the surface to the complex plane allows us to use familiar\nformalism to describe the motion of the quantized vortices and to find the\ntotal energy. The simplest case is a vortex dipole with unit vortex charges on\nan axisymmetric ellipsoid. We study two special symmetric vortex-dipole\nconfigurations along with a general asymmetric one.",
        "positive": "Variational calculations for anisotropic solitons in dipolar\n  Bose-Einstein condensates: We present variational calculations using a Gaussian trial function to\ncalculate the ground state of the Gross-Pitaevskii equation and to describe the\ndynamics of the quasi-two-dimensional solitons in dipolar Bose-Einstein\ncondensates. Furthermore we extend the ansatz to a linear superposition of\nGaussians improving the results for the ground state to exact agreement with\nnumerical grid calculations using imaginary time and split-operator method. We\nare able to give boundaries for the scattering length at which stable solitons\nmay be observed in an experiment. By dynamical calculations with coupled\nGaussians we are able to describe the rather complex behavior of the thermally\nexcited solitons. The discovery of dynamically stabilized solitons indicates\nthe existence of such BECs at experimentally accessible temperatures."
    },
    {
        "anchor": "Parametric Instabilities in Resonantly-Driven Bose-Einstein Condensates: Shaking optical lattices in a resonant manner offers an efficient and\nversatile method to devise artificial gauge fields and topological band\nstructures for ultracold atomic gases. This was recently demonstrated through\nthe experimental realization of the Harper-Hofstadter model, which combined\noptical superlattices and resonant time-modulations. Adding inter-particle\ninteractions to these engineered band systems is expected to lead to\nstrongly-correlated states with topological features, such as fractional Chern\ninsulators. However, the interplay between interactions and external\ntime-periodic drives typically triggers violent instabilities and\nuncontrollable heating, hence potentially ruling out the possibility of\naccessing such intriguing states of matter in experiments. In this work, we\nstudy the early-stage parametric instabilities that occur in systems of\nresonantly-driven Bose-Einstein condensates in optical lattices. We apply and\nextend an approach based on Bogoliubov theory [PRX 7, 021015 (2017)] to a\nvariety of resonantly-driven band models, from a simple shaken Wannier-Stark\nladder to the more intriguing driven-induced Harper-Hofstadter model. In\nparticular, we provide ab initio numerical and analytical predictions for the\nstability properties of these topical models. This work sheds light on general\nfeatures that could guide current experiments to stable regimes of operation.",
        "positive": "Stability and collapse of fermions in a binary dipolar boson-fermion\n  164Dy-161Dy mixture: We suggest a time-dependent mean-field hydrodynamic model for a binary\ndipolar boson-fermion mixture to study the stability and collapse of fermions\nin the $^{164}$Dy-$^{161}$Dy mixture. The condition of stability of the dipolar\nmixture is illustrated in terms of phase diagrams. A collapse is induced in a\ndisk-shaped stable binary mixture by jumping the interspecies contact\ninteraction from repulsive to attractive by the Feshbach resonance technique.\nThe subsequent dynamics is studied by solving the time-dependent mean-field\nmodel including three-body loss due to molecule formation in boson-fermion and\nboson-boson channels. Collapse and fragmentation in the fermions after\nsubsequent explosions are illustrated. The anisotropic dipolar interaction\nleads to anisotropic fermionic density distribution during collapse. The\npresent study is carried out in three-dimensional space using realistic values\nof dipolar and contact interactions."
    },
    {
        "anchor": "Universality of semisuper-Efimov effect: We study the semisuper-Efimov effect, which is found for four identical\nbosons with a resonant three-body interaction in 2D, in various systems. Based\non solutions of bound-state and renormalization-group equations, we first\ndemonstrate an emergence of the semisuper-Efimov effect in mass-imbalanced\nbosons in 2D. Compared with the Efimov and the super-Efimov effects, the mass\nratio-dependent scaling parameter is unexpectedly found to take on a finite\nvalue even for extremely mass-imbalanced situations, where the mass ratio is 0\nor $\\infty$. By a renormalization-group analysis, we also show that a weak\ntwo-body interaction sustains the semisuper-Efimov effect. Finally, we liberate\nthe universality of the semisuper-Efimov effect from 2D by showing that bosons\nwith linear-dispersion relation support the semisuper-Efimov effect in 1D.",
        "positive": "Spin-orbit coupled Bose-Einstein condensates in a double well: We study the quantum dynamics of a spin-orbit (SO) coupled Bose-Einstein\ncondensate (BEC) in a double-well potential inspired by the experimental\nprotocol recently developed by NIST group. We focus on the regime where the\nnumber of atoms is very large and perform a two-mode approximation. An\nanalytical solution of the two-site Bose-Hubbard-like Hamiltonian is found for\nseveral limiting cases, which range from a strong Raman coupling to a strong\nJosephson coupling, ending with the complete model in the presence of weak\nnonlinear interactions. Depending on the particular limit, different approaches\nare chosen: a mapping onto an SU(2) spin problem together with a\nHolstein-Primakoff transformation in the first two cases and a rotating wave\napproximation (RWA) when dealing with the complete model. The quantum evolution\nof the number difference of bosons with equal or different spin between the two\nwells is investigated in a wide range of parameters; finally the corresponding\ntotal atomic current and the spin current are computed. We show a spin\nJosephson effect which could be detected in experiments and employed to build\nup realistic devices."
    },
    {
        "anchor": "Hydrodynamic description of Hard-core Bosons on a Galileo ramp: We study the quantum evolution of a cloud of hard-core bosons loaded on a\none-dimensional optical lattice after its sudden release from a harmonic trap.\nJust after the trap has been removed, a linear ramp potential is applied,\nmimicking the so called Galileo ramp experiment. The non-equilibrium expansion\nof the bosonic cloud is elucidated through a hydrodynamical description which\nis compared to the exact numerical evolution obtained by exact diagonalization\non finite lattice sizes. The system is found to exhibit a rich behavior showing\nin particular Bloch oscillations of a self-trapped condensate and an ejected\nparticle density leading to two diverging entangled condensates. Depending on\nthe initial density of the gas different regimes of Josephson-like oscillations\nare observed. At low densities, the trapped part of the cloud is in a\nsuperfluid phase that oscillates in time as a whole. At higher densities, the\ntrapped condensate is in a mixed superfluid-Mott phase that show a breathing\nregime for steep enough potential ramps.",
        "positive": "Geometric phase driven Josephson junction: Possible experimental scheme\n  for the search of spin superfluidity: We use the Gross-Pitaevskii equation to study Josephson tunneling between two\nweakly coupled Bose-Einstein condensates, which compose spin-1 bosons. We show\nthat a rotating magnetic field on one side can produce a phase difference\nacross the junction, resulting in an oscillatory tunneling spin current.\nBesides numerical calculation, we derive analytical results in two extreme\ncases, namely the low- and high-frequency limits: in the low-frequency limit\n(magnetic field rotates adiabatically), a non-Abelian geometric phase arises\nand leads to the oscillatory spin current. By sharp contrast, the physics is\nintrinsically different in the high-frequency limit, where an average Zeeman\nenergy difference leads to an oscillatory spin current. This proposed apparatus\nshould be promising for the future experimental search of spin superfluidity."
    },
    {
        "anchor": "Super Fermi polaron and Nagaoka ferromagnetism in a two-dimesnional\n  square lattice: We consider the Fermi polaron problem of an impurity hopping around a\ntwo-dimensional square lattice and interacting with a sea of fermions at given\nfilling factor. When the interaction is attractive, we find standard Fermi\npolaron quasiparticles, categorized as attractive polarons and repulsive\npolarons. When the interaction becomes repulsive, interestingly, we observe an\nunconventional highly-excited polaron quasiparticle, sharply peaked at the\ncorner of the first Brillouin zone with momentum \\mathbf{k}=(\\pm\\pi,\\pm\\pi).\nThis super Fermi polaron branch arises from the dressing of the impurity's\nmotion with holes, instead of particles of fermions. We show that super Fermi\npolarons become increasingly well-defined with increasing impurity-fermion\nrepulsions and might be considered as a precursor of Nagaoka ferromagnetism,\nwhich would appear at sufficiently large repulsions and at large filling\nfactors. We also investigate the temperature-dependence of super Fermi polarons\nand find that they are thermally robust against the significant increase in\ntemperature.",
        "positive": "Expansion of 1D polarized superfluids: The FFLO state reveals itself: We study the expansion dynamics of a one dimensional polarized Fermi gas\nafter sudden release from confinement using both the mean-field Bogoliubov-de\nGennes and the numerically exact Time-Evolving Block Decimation methods. Our\nresults show that experimentally observable spin density modulations directly\nrelated to the presence of a Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) state\ndevelop during the expansion of the cloud, providing incontrovertible evidence\nof this long-sought state."
    },
    {
        "anchor": "Sudden and slow quenches into the antiferromagnetic phase of ultracold\n  fermions: We propose a method to reach the antiferromagnetic state of two-dimensional\nFermi gases trapped in optical lattices: Independent subsystems are prepared in\nsuitable initial states and then connected by a sudden or slow quench of the\ntunneling between the subsystems. Examples of suitable low-entropy subsystems\nare double wells or plaquettes, which can be experimentally realised in Mott\ninsulating shells using optical super-lattices. We estimate the effective\ntemperature T* of the system after the quench by calculating the distribution\nof excitations created using the spin wave approximation in a Heisenberg model.\nWe investigate the effect of an initial staggered magnetic field and find that\nfor an optimal polarisation of the initial state the effective temperature can\nbe significantly reduced from T*$\\approx$1.7 Tc at zero polarisation to\nT*<0.65Tc, where Tc is the crossover temperature to the antiferromagnetic\nstate. The temperature can be further reduced using a finite quench time. We\nalso show that T* decreases logarithmically with the linear size of the\nsubsystem.",
        "positive": "A Composite Fermion Approach to the Ultracold Dilute Fermi Gas: It is argued that the recently observed Fermi liquids in strongly interacting\nultracold Fermi gases are adiabatically connected to a projected Fermi gas.\nThis conclusion is reached by constructing a set of Jastrow wavefunctions,\nfollowing Tan's observations on the structure of the physical Hilbert space\n[Annals of Physics 323, 2952 (2008)]. The Jastrow projection merely implements\nthe Bethe-Peierls condition on the BCS and Fermi gas wavefunctions. This\nprocedure provides a simple picture of the emergence of Fermi polarons as\ncomposite fermions in the normal state of the highly polarized gas. It is also\nshown that the projected BCS wavefunction can be written as a condensate of\npairs of composite fermions (or Fermi polarons). A Hamiltonian for the\ncomposite fermions is derived. Within a mean-field theory, it is shown that the\nground state and excitations of this Hamiltonian are those of a non-interacting\nFermi gas although they are described by Jastrow-Slater wavefunctions."
    },
    {
        "anchor": "Momentum distribution of Cooper-pairs and strong-coupling effects in a\n  two-dimensional Fermi gas near the Berezinskii-Kosterlitz-Thouless transition: We investigate strong-coupling properties of a two-dimensional ultracold\nFermi gas in the normal state. Including pairing fluctuations within the\nframework of a $T$-matrix approximation, we calculate the distribution function\n$n({\\boldsymbol Q})$ of Cooper pairs in terms of the center of mass momentum\n${\\boldsymbol Q}$. In the strong-coupling regime, $n({\\boldsymbol Q}=0)$ is\nshown to exhibit a remarkable increase with decreasing the temperature in the\nlow temperature region, which agrees well with the recent experiment on a\ntwo-dimensional $^6$Li Fermi gas [M. G. Ries, {\\it et. al.}, Phys. Rev. Lett.\n{\\bf 114}, 230401 (2015)]. Our result indicates that the observed remarkable\nincrease of the number of Cooper pairs with zero center of mass momentum can be\nexplained without assuming the Berezinskii-Kosterlitz-Thouless (BKT)\ntransition, when one properly includes pairing fluctuations that are enhanced\nby the low-dimensionality of the system. Since the BKT transition is a crucial\ntopic in two-dimensional Fermi systems, our results would be useful for the\nstudy toward the realization of this quasi-long-range order in an ultracold\nFermi gas.",
        "positive": "Signatures of Coherent Vortex Structures in a Disordered 2D Quantum\n  Fluid: The emergence of coherent rotating structures is a phenomenon characteristic\nof both classical and quantum 2D turbulence. In this work we show theoretically\nthat the coherent vortex structures that emerge in decaying 2D quantum\nturbulence can approach quasi-classical rigid-body rotation, obeying the\nFeynman rule of constant average areal vortex density while remaining spatially\ndisordered. By developing a rigorous link between the velocity probability\ndistribution and the quantum kinetic energy spectrum over wavenumber $k$, we\nshow that the coherent vortex structures are associated with a $k^3$ power law\nin the infrared region of the spectrum, and a well-defined spectral peak that\nis a physical manifestation of the largest structures. We discuss the\npossibility of realizing coherent structures in Bose--Einstein condensate\nexperiments and present Gross-Pitaevskii simulations showing that this\nphenomenon, and its associated spectral signatures, can emerge dynamically from\nfeasible initial vortex configurations."
    },
    {
        "anchor": "Dark soliton-like magnetic domain walls in a two-dimensional\n  ferromagnetic superfluid: We report a stable magnetic domain wall in a uniform ferromagnetic spin-1\ncondensate, characterized by the magnetization having a dark soliton profile\nwith nonvanishing superfluid density. We find exact stationary solutions for a\nparticular ratio of interaction parameters with and without magnetic fields,\nand develop an accurate analytic solution applicable to the whole ferromagnetic\nphase. In the absence of magnetic fields, this domain wall relates various\ndistinct solitary excitations in binary condensates through $\\textrm{SO}(3)$\nspin rotations, which otherwise are unconnected. Remarkably, studying the\ndynamics of a quasi-two-dimensional (quasi-2D) system we show that standing\nwave excitations of the domain wall oscillate without decay, being stable\nagainst the snake instability. The domain wall is dynamically unstable to modes\nthat cause the magnetization to grow perpendicularly while leaving the domain\nwall unchanged. Real time dynamics in the presence of white noise reveals that\nthis \"spin twist\" instability does not destroy the topological structure of the\nmagnetic domain wall.",
        "positive": "Universal composite boson formation in strongly interacting\n  one-dimensional fermionic systems: Attractive $p$-wave one-dimensional fermions are studied in the fermionic\nTonks-Girardeau regime in which the diagonal properties are shared with those\nof an ideal Bose gas. We study the off-diagonal properties and present\nanalytical expressions for the eigenvalues of the one-body density matrix. One\nstriking aspect is the universality of the occupation numbers which are\nindependent of the specific shape of the external potential. We show that the\noccupation of natural orbitals occurs in pairs, indicating the formation of\ncomposite bosons, each consisting of two attractive fermions. The formation of\ncomposite bosons sheds light on the pairing mechanism of the system orbitals,\nyielding a total density equal to that of a Bose-Einstein condensate."
    },
    {
        "anchor": "Observation of interference between two molecular Bose-Einstein\n  condensates: We have observed interference between two Bose-Einstein condensates of weakly\nbound Feshbach molecules of fermionic $^6$Li atoms. Two condensates are\nprepared in a double-well trap and, after release from this trap, overlap in\nexpansion. We detect a clear interference pattern that unambiguously\ndemonstrates the de Broglie wavelength of molecules. We verify that only the\ncondensate fraction shows interference. For increasing interaction strength,\nthe pattern vanishes because elastic collisions during overlap remove particles\nfrom the condensate wave function. For strong interaction the condensates do\nnot penetrate each other as they collide hydrodynamically.",
        "positive": "Microscopic study of static and dynamical properties of dilute\n  one-dimensional soft bosons: We study static properties and the dynamical structure factor of\nzero-temperature dilute bosons interacting via a soft-shoulder potential in one\ndimension. Our approach is fully microscopic and employs state-of-the-art\nquantum Monte Carlo and analytic continuation techniques. By increasing the\ninteraction strength, our model reproduces the Lieb-Liniger gas, the\nTonks-Girardeau and the Hard-Rods models."
    },
    {
        "anchor": "Townes soliton and beyond: Non-miscible Bose mixtures in 2D: In these lecture notes, we discuss the physics of a two-dimensional binary\nmixture of Bose gases at zero temperature, close to the point where the two\nfluids tend to demix. We are interested in the case where one of the two fluids\n(the bath) fills the whole space, while the other one (the minority component)\ncontains a finite number of atoms. We discuss under which condition the\nminority component can form a stable, localized wave packet, which we relate to\nthe celebrated \"Townes soliton\". We discuss the formation of this soliton and\nthe transition towards a droplet regime that occurs when the number of atoms in\nthe minority component is increased. Our investigation is based on a\nmacroscopic approach based on coupled Gross-Pitaevskii equations, and it is\ncomplemented by a microscopic analysis in terms of bath-mediated interactions\nbetween the particles of the minority component.",
        "positive": "Magnetic stripe soliton and localized stripe wave in spin-1\n  Bose-Einstein condensates: The recent experimental realization of spin-orbit coupling for ultracold\natomic gases opens a new avenue for engineering solitons with internal spatial\nstructures through tuning atomic band dispersions. However, the types of the\nresulting stripe solitons in a spin-1/2 Bose-Einstein condensate (BEC) have\nbeen limited to dark-dark or bright-bright with the same density profiles for\ndifferent spins. Here we propose that general types of stripe solitons,\nincluding magnetic stripe (e.g., dark-bright) and localized stripe waves\n(neither bright nor dark), could be realized in a spin-1 BEC with widely\ntunable band dispersions through modulating the coupling between three spin\nstates and the linear momentum of atoms. \\ Surprisingly, a moving magnetic\nstripe soliton can possess both negative and positive effective masses at\ndifferent velocities, leading to a zero mass soliton at certain velocity. Our\nwork showcases the great potential of realizing novel types of solitons through\nband dispersion engineering, which may provide a new approach for exploring\nsoliton physics in many physical branches."
    },
    {
        "anchor": "Self-bound vortex lattice in a rapidly rotating quantum droplet: A rapidly rotating Bose gas in the quantum Hall limit is usually associated\nwith a melted vortex lattice. In this work, we report a self-bound and visible\ntriangular vortex lattice without melting for a two-dimensional Bose-Bose\ndroplet rotating in the quantum Hall limit, i.e., with rotation frequency\n$\\Omega$ approaching the trapping frequency $\\omega$. Increasing $\\Omega$ with\nrespect to interaction strength $U$, we find a smooth crossover of the vortex\nlattice droplet from a needling regime, as featured by small vortex cores and\nan equilibrium flat-top surface, to the lowest-Landau-level regime with\nGaussian-extended cores spreading over the whole surface. The surface density\nof such a rotating droplet is higher than that of a static one, and their ratio\nis found to be a universal function of $\\Omega/U$. We have demonstrated these\nresults by both numerical and variational methods. The results pave the way for\nfuture experimental exploration of rapidly rotating ultracold droplets into the\nquantum Hall limit.",
        "positive": "Non-local order in Mott insulators, Duality and Wilson Loops: It is shown that the Mott insulating and superfluid phases of bosons in an\noptical lattice may be distinguished by a non-local 'parity order parameter'\nwhich is directly accessible via single site resolution imaging. In one\ndimension, the lattice Bose model is dual to a classical interface roughening\nproblem. We use known exact results from the latter to prove that the parity\norder parameter exhibits long range order in the Mott insulating phase,\nconsistent with recent experiments by Endres et al. [Science 334, 200 (2011)].\nIn two spatial dimensions, the parity order parameter can be expressed in terms\nof an equal time Wilson loop of a non-trivial U(1) gauge theory in 2+1\ndimensions which exhibits a transition between a Coulomb and a confining phase.\nThe negative logarithm of the parity order parameter obeys a perimeter law in\nthe Mott insulator and is enhanced by a logarithmic factor in the superfluid."
    },
    {
        "anchor": "Superadiabatic quantum friction suppression in finite-time\n  thermodynamics: Optimal performance of thermal machines is reached by suppressing friction.\nFriction in quantum thermodynamics results from fast driving schemes that\ngenerate nonadiabatic excitations. The far-from-equilibrium dynamics of quantum\ndevices can be tailored by shortcuts to adiabaticity to suppress quantum\nfriction. We experimentally demonstrate friction-free superadiabatic strokes\nwith a trapped unitary Fermi gas as a working substance and establish the\nequivalence between the superadiabatic mean work and its adiabatic value.",
        "positive": "Polaron-like effects in a one-dimensional optical lattice: We study a highly imbalanced Fermi gas in a one-dimensional optical lattice\nfrom the polaronic point of view. The time-evolving block decimationg algorithm\nis used to calculate the ground state and dynamics of the system. We find\nqualitatively similar polaronic behaviour as in the recent experiment by\nSchirotzek et al. \\cite{Schirotzek2009a} where radio-frequency spectroscopy was\nused to observe polarons in three-dimensional space. In the weakly interacting\nlimit our exact results are in excellent agreement with a polaron ansatz, and\nin the strongly interacting limit the results match with an approximative\nsolution of the Bethe ansatz, suggesting a crossover from a quasiparticle to a\ncharge-density excitation regime."
    },
    {
        "anchor": "Kitaev ring threaded by a magnetic flux: Topological gap, Anderson\n  localization of quasiparticles, and divergence of supercurrent derivative: We study a superconducting Kitaev ring pierced by a magnetic flux, with and\nwithout disorder, in a quantum ring configuration, and in a rf-SQUID one, where\na weak link is present. In the rf-SQUID configuration, in the topological\nphase, the supercurrent shows jumps at specific values of the flux\n$\\Phi^*=\\frac{hc}{e}(1/4+n)$, with $n\\in\\mathbb{N}$. In the thermodynamic limit\n$\\Phi^*$ is constant inside the topological phase, independently of disorder,\nand we analytically predict this fact using a perturbative approach in the\nweak-link coupling. The weak link breaks the topological ground-state\ndegeneracy, and opens a spectral gap for $\\Phi\\neq \\Phi^*$, that vanishes at\n$\\Phi^*$ with a cusp providing the current jump. Looking at the quasiparticle\nexcitations, we see that they are Anderson localized, so they cannot carry a\nresistive contribution to the current, and the localization length shows a\npeculiar behavior at a flat-band point for the quasiparticles. In the absence\nof disorder, we analytically and numerically find that the chemical-potential\nderivative of the supercurrent logarithmically diverges at the\ntopological-to-trivial transition, in agreement with the transition being of\nthe second order.",
        "positive": "Temporal quantum fluctuations in the fringe-visibility of atom\n  interferometers with interacting Bose-Einstein condensate: We formulate a semiclassical approach to study the dynamics of coherence loss\nand revival in a Bose-Josephson dimer. The phase-space structure of the\nbi-modal system in the Rabi, Josephson, and Fock interaction regimes, is\nreviewed and the prescription for its WKB quantization is specified. The local\ndensity of states (LDOS) is then deduced for any given preparation from its\nsemiclassical projection onto the WKB eigenstates. The LDOS and the non-linear\nvariation of its level-spacing are employed to construct the time evolution of\nthe initial preparation and study the temporal fluctuations of interferometric\nfringe visibility. The qualitative behavior and characteristic timescales of\nthese fluctuations are set by the pertinent participation number, quantifying\nthe spectral content of the preparation. We employ this methodology to study\nthe Josephson-regime coherence dynamics of several initial state preparations,\nincluding a Twin-Fock state and three different coherent states that we denote\nas 'Zero', 'Pi', and 'Edge' (the latter two are both on-separatrix\npreparations, while the Zero is the standard ground sate preparation). We find\na remarkable agreement between the semiclassical predictions and numerical\nsimulations of the full quantum dynamics. Consequently, a characteristic\ndistinct behavior is implied for each of the different preparations."
    },
    {
        "anchor": "Stationary states and quantum quench dynamics of Bose-Einstein\n  condensates in a double-well potential: We consider the properties of stationary states and the dynamics of\nBose-Einstein condensates (BECs) in a double-well (DW) potential with pair\ntunneling by using a full quantum-mechanical treatment. Furthermore, we study\nthe quantum quench dynamics of the DW system subjected to a sudden change of\nthe Peierls phase. It is shown that strong pair tunneling evidently influences\nthe energy spectrum structure of the stationary states. For relatively weak\nrepulsive interatomic interactions, the dynamics of the DW system with a\nmaximal initial population difference evolves from Josephson oscillations to\nquantum self-trapping as one increases the pair tunneling strength, while for\nlarge repulsion the strong pair tunneling inhibits the quantum self-trapping.\nIn the case of attractive interatomic interactions, strong pair tunneling tends\nto destroy the Josephson oscillations and quantum self-trapping, and the system\neventually enters a symmetric regime of zero population difference. Finally,\nthe effect of the Peierls phase on the quantum quench dynamics of the system is\nanalyzed and discussed. These new features are remarkably different from the\nusual dynamical behaviors of a BEC in a DW potential.",
        "positive": "Quantum phase transitions of a two-leg bosonic ladder in an artificial\n  gauge field: We consider a two leg bosonic ladder in a $U(1)$ gauge field with both\ninterleg hopping and interleg repulsion. As a function of the flux, the\ninterleg interaction converts the commensurate-incommensurate transition from\nthe Meissner to a Vortex phase, into an Ising-type of transition towards a\ndensity wave phase. A disorder point is also found after which the correlation\nfunctions develop a damped sinusoid behavior signaling a melting of the vortex\nphase. We discuss the differences on the phase diagram for attractive and\nrepulsive interleg interaction. In particular, we show how repulsion favors the\nMeissner phase at low-flux and a phase with a second incommensuration in the\ncorrelation functions for intermediate flux, leading to a richer phase diagram\nthan in the case of interleg attraction. The effect of the temperature on the\nchiral current is also discussed."
    },
    {
        "anchor": "Perturbative computation of thermal characteristics of the Stoner phase\n  transition: We apply the thermal (imaginary time) perturbative expansion to the relevant\neffective field theory to compute characteristics of the phase transition to\nthe ordered state which can occur at low temperatures in the gas of\n(nonrelativistic) spin 1/2 fermions interacting through a short-range spin\nindependent repulsive binary interaction potential. We show how to obtain a\nsystematic expansion of the system's free energy depending on the densities\n$n_+$ and $n_-$ of spin-up and spin-down fermions. In this paper we truncate\nthis expansion at the second order and determine, by numerically minimizing the\nfree energy, the equilibrium proportions of $n_+$ and $n_-$ (that is, the\nsystem's polarization) as functions of the temperature, the system's overall\ndensity $n = n_+ + n_-$ and the strength of the interaction.",
        "positive": "Ewald method for polytropic potentials in arbitrary dimensionality: The Ewald summation technique is generalised to power-law 1/|r|^k potentials\nin three-, two- and one-dimensional geometries with explicit formulae for all\nthe components of the sums. The cases of short-range, long-range and \"marginal\"\ninteractions are treated separately. The jellium model, as a particular case of\na charge-neutral system, is discussed and the explicit forms of the Ewald sums\nfor such system are presented. A generalised form of the Ewald sums for a\nnoncubic (nonsquare) simulation cell for three- (two-) dimensional geometry is\nobtained and its possible field of application is discussed. A procedure for\nthe optimisation of the involved parameters in actual simulations is developed\nand an example of its application is presented."
    },
    {
        "anchor": "Coalescence of Two Impurities in a Trapped One-dimensional Bose Gas: We study the ground state of a one-dimensional (1D) trapped Bose gas with two\nmobile impurity particles. To investigate this set-up, we develop a variational\nprocedure in which the coordinates of the impurity particles are slow-like\nvariables. We validate our method using the exact results obtained for small\nsystems. Then, we discuss energies and pair densities for systems that contain\nof the order of one hundred atoms. We show that bosonic non-interacting\nimpurities cluster. To explain this clustering, we calculate and discuss\ninduced impurity-impurity potentials in a harmonic trap. Further, we compute\nthe force between static impurities in a ring ({\\it {\\`a} la} the Casimir\nforce), and contrast the two effective potentials: the one obtained from the\nmean-field approximation, and the one due to the one-phonon exchange. Our\nformalism and findings are important for understanding (beyond the polaron\nmodel) the physics of modern 1D cold-atom systems with more than one impurity.",
        "positive": "Supersolid-Superfluid phase separation in the extended Bose-Hubbard\n  model: Recent studies have suggested a new phase in the extended Bose-Hubbard model\nin one dimension at integer filling [1,2]. In this work, we show that this new\nphase is phase-separated into a supersolid and superfluid part, generated by\nmechanical instability. Numerical simulations are performed by means of the\ndensity matrix renormalization group algorithm in terms of matrix product\nstates. In the phase-separated phase and the adjacent homogeneous superfluid\nand supersolid phases, we find peculiar spatial patterns in the entanglement\nspectrum and string-order correlation functions and show that they survive in\nthe thermodynamic limit. In particular, we demonstrate that the elementary\nexcitations of the homogeneous superfluid with enhanced periodic modulations\nare phonons, find the central charge to be $c=1$, and show that the velocity of\nsound, extracted from the intrinsic level splitting for finite systems, matches\nwith the propagation velocity of local excitations in dynamical simulations.\nThis suggests that the low-energy spectrum of the phase under investigation is\neffectively captured by a spinless Luttinger liquid, for which we find\nconsistent results between the Luttinger parameter obtained from the linear\ndependence of the structure factor and the algebraic decay of the one-body\ndensity matrix."
    },
    {
        "anchor": "Simulation of two-flavors symmetry-locking phases in ultracold fermionic\n  mixtures: We describe an ultracold fermionic set-up where it is possible to synthesize\na superfluid phase with symmetry obtained by locking independent invariance\ngroups of the normal state. In this phase, named two-flavors symmetry-locking\nphase (TFSL), non-Abelian fractional vortices with semi-integer flux and\ngapless non-Abelian Goldstone modes localized on them appear. Considerations on\nthe possible experimental realization of the TFSL are also provided.",
        "positive": "Finding self-similar behavior in quantum many-body dynamics via\n  persistent homology: Inspired by topological data analysis techniques, we introduce persistent\nhomology observables and apply them in a geometric analysis of the dynamics of\nquantum field theories. As a prototype application, we consider data from a\nclassical-statistical simulation of a two-dimensional Bose gas far from\nequilibrium. We discover a continuous spectrum of dynamical scaling exponents,\nwhich provides a refined classification of nonequilibrium self-similar\nphenomena. A possible explanation of the underlying processes is provided in\nterms of mixing strong wave turbulence and anomalous vortex kinetics components\nin point clouds. We find that the persistent homology scaling exponents are\ninherently linked to the geometry of the system, as the derivation of a packing\nrelation reveals. The approach opens new ways of analyzing quantum many-body\ndynamics in terms of robust topological structures beyond standard field\ntheoretic techniques."
    },
    {
        "anchor": "Viscosity of strongly interacting quantum fluids: spectral functions and\n  sum rules: The viscosity of strongly interacting systems is a topic of great interest in\ndiverse fields.\n  We focus here on the bulk and shear viscosities of \\emph{non-relativistic}\nquantum fluids, with particular emphasis on strongly interacting ultracold\nFermi gases. We use Kubo formulas for the bulk and shear viscosity spectral\nfunctions, $\\zeta(\\omega)$ and $\\eta(\\omega)$ respectively, to derive exact,\nnon-perturbative results. Our results include: a microscopic connection between\nthe shear viscosity $\\eta$ and the normal fluid density $\\rho_n$; sum rules for\n$\\zeta(\\omega)$ and $\\eta(\\omega)$ and their evolution through the BCS-BEC\ncrossover; universal high-frequency tails for $\\eta(\\omega)$ and the dynamic\nstructure factor $S({\\bf q}, \\omega)$. We use our sum rules to show that, at\nunitarity, $\\zeta(\\omega)$ is identically zero and thus relate $\\eta(\\omega)$\nto density-density correlations. We predict that frequency-dependent shear\nviscosity $\\eta(\\omega)$ of the unitary Fermi gas can be experimentally\nmeasured using Bragg spectroscopy.",
        "positive": "Optimal Persistent Currents for Interacting Bosons on a Ring with a\n  Gauge Field: We study persistent currents for interacting one-dimensional bosons on a\ntight ring trap, subjected to a rotating barrier potential, which induces an\nartificial U(1) gauge field. We show that, at intermediate interactions, the\npersistent current response is maximal, due to a subtle interplay of effects\ndue to the barrier, the interaction and quantum fluctuations. These results are\nrelevant for ongoing experiments with ultracold atomic gases on mesoscopic\nrings."
    },
    {
        "anchor": "Atom Loss Maximum in Ultra-cold Fermi Gases: Recent experiments on atom loss in ultra-cold Fermi gases all show a maximum\nat a magnetic field below Feshbach resonance, where the s-wave scattering\nlength is large (close to inter-particle distance) and positive. These\nexperiments have been performed over a wide range of conditions, with\ntemperatures and trap depths spanning over three decades. Different groups have\ncome up with different explanations, among them the emergence of Stoner\nferromagnetism. Here, we show that this maximum is a consequence of two major\nsteps. The first is the establishment of a population of shallow dimers, which\nis the combined effect of dimer formation through three-body recombination, and\nthe dissociation of shallow dimers back to atoms through collisions. The\ndissociation process will be temperature dependent, and is affected by Pauli\nblocking at low temperatures. The second is the relaxation of shallow dimers\ninto tightly bound dimers through atom-dimer and dimer-dimer collisions.\n  We have constructed a simple set of rate equations describing these\nprocesses. Remarkably, even with only a few parameters, these equations\nreproduce the loss rate observed in all recent experiments, despite their\nwidely different experimental conditions. Our studies show that the location of\nthe maximum loss rate depends crucially on experimental parameters such as trap\ndepth and temperature. These extrinsic characters show that this maximum is not\na reliable probe of the nature of the underlying quantum states. The physics of\nour equations also explains some general trends found in current experiments.",
        "positive": "On the Bifurcation and Stability of Single and Multiple Vortex Rings in\n  Three-Dimensional Bose-Einstein Condensates: In the present work, we investigate how single- and multi-vortex-ring states\ncan emerge from a planar dark soliton in three-dimensional (3D) Bose-Einstein\ncondensates (confined in isotropic or anisotropic traps) through bifurcations.\nWe characterize such bifurcations quantitatively using a Galerkin-type\napproach, and find good qualitative and quantitative agreement with our\nBogoliubov-de Gennes (BdG) analysis. We also systematically characterize the\nBdG spectrum of the dark solitons, using perturbation theory, and obtain a\nquantitative match with our 3D BdG numerical calculations. We then turn our\nattention to the emergence of single- and multi-vortex-ring states. We\nsystematically capture these as stationary states of the system and quantify\ntheir BdG spectra numerically. We find that although the vortex ring may be\nunstable when bifurcating, its instabilities weaken and may even eventually\ndisappear, for sufficiently large chemical potentials and suitable trap\nsettings. For instance, we demonstrate the stability of the vortex ring for an\nisotropic trap in the large chemical potential regime."
    },
    {
        "anchor": "Bosonic Analogs of Fractional Quantum Hall State in the Vicinity of Mott\n  States: In the present paper, the Bose-Hubbard model (BHM) with the nearest-neighbor\n(NN) repulsions is studied from the view point of possible bosonic analogs of\nthe fractional quantum Hall (FQH) state in the vicinity of the Mott insulator\n(MI). First, by means of the Gutzwiller approximation, we obtain the phase\ndiagram of the BHM in a magnetic field. Then, we introduce an effective\nHamiltonian describing excess particles on a MI and calculate the vortex\ndensity, momentum distribution and the energy gap. These calculations indicate\nthat the vortex solid forms for small NN repulsions, but a homogeneous\nfeatureless `Bose-metal' takes the place of it as the NN repulsion increases.\nWe consider particular filling factors at which the bosonic FQH state is\nexpected to form. Chern-Simons (CS) gauge theory to the excess particle is\nintroduced, and a modified Gutzwiller wave function, which describes bosons\nwith attached flux quanta, is introduced. The energy of the excess particles in\nthe bosonic FQH state is calculated using that wave function, and it is\ncompared with the energy of the vortex solid and Bose-metal. We found that the\nenergy of the bosonic FQH state is lower than that of the Bose-metal and\ncomparable with the vortex solid. Finally, we clarify the condition that the\ncomposite fermion appears by using CS theory on the lattice that we previously\nproposed for studying the electron FQH effect.",
        "positive": "Death of soliton trains in attractive Bose-Einstein condensates: Experiments on ultra-cold attractive Bose-Einstein Condensates (BECs) have\ndemonstrated that at low dimensions atomic clouds can form localized objects,\npropagating for long times without significant changes in their shapes and\nattributed to bright matter-wave solitons, which are coherent objects. We\nconsider the dynamics of bright soliton trains from the perspective of\nmany-boson physics. The fate of matter-wave soliton trains is actually to\nquickly loose their coherence and become macroscopically fragmented BECs. The\ndeath of the coherent matter-wave soliton trains gives birth to fragmented\nobjects, whose quantum properties and experimental signatures differ\nsubstantially from what is currently assumed."
    },
    {
        "anchor": "Contact resistance and phase slips in mesoscopic superfluid atom\n  transport: We have experimentally measured transport of superfluid, bosonic atoms in a\nmesoscopic system: a small channel connecting two large reservoirs. Starting\nfar from equilibrium (superfluid in a single reservoir), we observe first\nresistive flow transitioning at a critical current into superflow,\ncharacterized by oscillations. We reproduce this full evolution with a simple\nelectronic circuit model. We compare our fitted conductance to two different\nmicroscopic phenomenological models. We also show that the oscillations are\nconsistent with LC oscillations as estimated by the kinetic inductance and\neffective capacitance in our system. Our experiment provides an attractive\nplatform to begin to probe the mesoscopic transport properties of a dilute,\nsuperfluid, Bose gas.",
        "positive": "Bose-Einstein Condensation of Photons versus Lasing and Hanbury\n  Brown-Twiss Measurements with a Condensate of Light: The advent of controlled experimental accessibility of Bose-Einstein\ncondensates, as realized with e.g. cold atomic gases, exciton-polaritons, and\nmore recently photons in a dye-filled optical microcavity, has paved the way\nfor new studies and tests of a plethora of fundamental concepts in quantum\nphysics. We here describe recent experiments studying a transition between\nlaser-like dynamics and Bose-Einstein condensation of photons in the dye\nmicrocavity system. Further, measurements of the second-order coherence of the\nphoton condensate are presented. In the condensed state we observe photon\nnumber fluctuations of order of the total particle number, as understood from\neffective particle exchange with the photo-excitable dye molecules. The\nobserved intensity fluctuation properties give evidence for Bose-Einstein\ncondensation occurring in the grand-canonical statistical ensemble regime."
    },
    {
        "anchor": "Observation of a Spinning Top in a Bose-Einstein Condensate: Boundaries strongly affect the behavior of quantized vortices in\nBose-Einstein condensates, a phenomenon particularly evident in elongated\ncigar-shaped traps where vortices tend to orient along a short direction to\nminimize energy. Remarkably, contributions to the angular momentum of these\nvortices are tightly confined to the region surrounding the core, in stark\ncontrast to untrapped condensates where all atoms contribute $\\hbar$. We\ndevelop a theoretical model and use this, in combination with numerical\nsimulations, to show that such localized vortices precess in an analogous\nmanner to that of a classical spinning top. We experimentally verify this\nspinning-top behavior with our real-time imaging technique that allows for the\ntracking of position and orientation of vortices as they dynamically evolve.\nFinally, we perform an in-depth numerical investigation of our real-time\nexpansion and imaging method, with the aim of guiding future experimental\nimplementation, as well as outlining directions for its improvement.",
        "positive": "Many-body open quantum systems beyond Lindblad master equations: Many-body quantum systems present a rich phenomenology which can be\nsignificantly altered when they are in contact with an environment. In order to\nstudy such setups, a number of approximations are usually performed, either\nconcerning the system, the environment, or both. A typical approach for large\nquantum interacting systems is to use master equations which are local,\nMarkovian, and in Lindblad form. Here, we present an implementation of the\nRedfield master equation using matrix product states and operators. We show\nthat this allows us to explore parameter regimes of the many-body quantum\nsystem and the environment which could not be probed with previous approaches\nbased on local Lindblad master equations. We also show the validity of our\nresults by comparing with the numerical exact thermofield-based chain-mapping\napproach."
    },
    {
        "anchor": "Dynamics of equilibration and collisions in ultradilute quantum droplets: Employing time-dependent density-functional theory, we have studied dynamical\nequilibration and binary head-on collisions of quantum droplets made of a\n$^{39}$K-$^{39}$K Bose mixture. The phase space of collision outcomes is\nextensively explored by performing fully three-dimensional calculations with\neffective single-component QMC based and two-components LHY-corrected\nmean-field functionals. We exhaustively explored the important effect -- not\nconsidered in previous studies -- of the initial population ratio deviating\nfrom the optimal mean-field value $N_2/N_1 = \\sqrt{a_{11} / a_{22}}$. Both\nstationary and dynamical calculations with an initial non-optimal concentration\nratio display good agreement with experiments. Calculations including\nthree-body losses acting only on the $\\left|F, m_{F}\\right\\rangle=|1,0\\rangle$\nstate show dramatic differences with those obtained with the three-body term\nacting on the total density.",
        "positive": "Theory of radio-frequency spectroscopy of impurities in quantum gases: We present a theory of radio-frequency spectroscopy of impurities interacting\nwith a quantum gas at finite temperature. By working in the canonical ensemble\nof a single impurity, we show that the impurity spectral response is directly\nconnected to the finite-temperature equation of state (free energy) of the\nimpurity. We consider two different response protocols: \"injection\", where the\nimpurity is introduced into the medium from an initially non-interacting state;\nand \"ejection\", where the impurity is ejected from an initially interacting\nstate with the medium. We show that there is a simple mapping between injection\nand ejection spectra, which is connected to the detailed balance condition in\nthermal equilibrium. To illustrate the power of our approach, we specialize to\nthe case of the Fermi polaron, corresponding to an impurity atom that is\nimmersed in a non-interacting Fermi gas. For a mobile impurity with a mass\nequal to the fermion mass, we employ a finite-temperature variational approach\nto obtain the impurity spectral response. We find a striking non-monotonic\ndependence on temperature in the impurity free energy, the contact, and the\nradio-frequency spectra. For the case of an infinitely heavy Fermi polaron, we\nderive exact results for the finite-temperature free energy, thus generalizing\nFumi's theorem to arbitrary temperature. We also determine the exact dynamics\nof the contact after a quench of the impurity-fermion interactions. Finally, we\nshow that the injection and ejection spectra obtained from the variational\napproach compare well with the exact spectra, thus demonstrating the accuracy\nof our approximate method."
    },
    {
        "anchor": "Density response of a trapped Fermi gas: a crossover from the pair\n  vibration mode to the Goldstone mode: We consider the density response of a trapped two-component Fermi gas.\nCombining the Bogoliubov-deGennes method with the random phase approximation\nallows the study of both collective and single particle excitations.\nCalculating the density response across a wide range of interactions, we\nobserve a crossover from a weakly interacting pair vibration mode to a strongly\ninteracting Goldstone mode. The crossover is associated with a depressed\ncollective mode frequency and an increased damping rate, in agreement with\ndensity response experiments performed in strongly interacting atomic gases.",
        "positive": "SU(3) symmetry in theory of a weakly interacting gas of spin-1 atoms\n  with Bose-Einstein condensate: We study a many-body system of interacting spin-1 particles in the context of\nhomogeneous gases of ultracold atoms. In general, its description requires\neight parameters among which there are three components of magnetization and\nfive parameters associated with quadrupole degrees of freedom. Based on the\nsymmetry considerations, we construct a many-body interaction Hamiltonian that\nincludes eight generators of the SU(3) group related to the above description\nparameters. The SU(3) symmetric Hamiltonian is applied to study the\nferromagnetic and quadrupolar phases of a homogeneous weakly interacting gas of\nspin-1 atoms with Bose-Einstein condensate. It is shown how the quadrupole\ndegrees of freedom entering the Hamiltonian modify the ground state and\nsingle-particle excitation spectra in comparison with those obtained from the\nHamiltonian bilinear in spin operators and not including quadrupole degrees of\nfreedom. We discuss the issue of taking into account the local character of\ninteraction to obtain the correct spectra of single-particle excitations."
    },
    {
        "anchor": "Study of unitary Bose polarons with Diffusion Monte-Carlo and\n  Gross-Pitaevskii approaches: We present a detailed study of the properties of unitary Bose polarons, i.e.,\nimpurities strongly interacting with a bath of dilute bosons via a short-range\npotential with infinite scattering length. Through a comparison with Diffusion\nMonte-Carlo calculations, we demonstrate that the Gross-Pitaevskii theory\naccurately describes the properties of a heavy impurity if the gas parameter\nremains small everywhere in the system, including the vicinity of the impurity.\nFurthermore, we investigate the effects of the finite range of the bath-bath\ninteraction potential by means of a non-local extension of the Gross-Pitaevskii\nequation and we discuss the applicability of the Born approximation.",
        "positive": "Luttinger liquid behavior of one-dimensional 3He: The ground-state properties of one-dimensional 3He are studied using quantum\nMonte Carlo methods. The equation of state is calculated in a wide range of\nphysically relevant densities and is well reproduced by a power-series fit. The\nLuttinger liquid theory is found to describe the long-range properties of the\ncorrelation function. The density dependence of the Luttinger parameter is\nexplicitly found and interestingly it shows a non-monotonic behavior. Depending\non the density, the static structure factor can be a smooth function of the\nmomentum or might contain a peak of a finite or infinite height. Although no\nphase transitions are present in the system, we identify a number of physically\ndifferent regimes, including an ideal Fermi gas, a \"Bose-gas\", a\n\"super-Tonks-Girardeau\" regime, and a \"quasi-crystal\"."
    },
    {
        "anchor": "Emergence of coherence in a uniform quasi-two-dimensional Bose gas: Phase transitions are ubiquitous in our three-dimensional world. By contrast\nmost conventional transitions do not occur in infinite uniform two-dimensional\nsystems because of the increased role of thermal fluctuations. Here we explore\nthe dimensional crossover of Bose-Einstein condensation (BEC) for a weakly\ninteracting atomic gas confined in a novel quasi-two-dimensional geometry, with\na flat in-plane trap bottom. We detect the onset of an extended phase\ncoherence, using velocity distribution measurements and matter-wave\ninterferometry. We relate this coherence to the transverse condensation\nphenomenon, in which a significant fraction of atoms accumulate in the ground\nstate of the motion perpendicular to the atom plane. We also investigate the\ndynamical aspects of the transition through the detection of topological\ndefects that are nucleated in a quench cooling of the gas, and we compare our\nresults to the predictions of the Kibble-Zurek theory for the conventional BEC\nsecond-order phase transition.",
        "positive": "Quantum versus mean-field collapse in a many-body system: The recent analysis, based on the mean-field approximation (MFA), has\npredicted that the critical quantum collapse of the bosonic wave function,\npulled to the center by the inverse-square potential in the three-dimensional\nspace, is suppressed by the repulsive cubic nonlinearity in the bosonic gas,\nthe collapsing ground state being replaced by a regular one. We demonstrate\nthat a similar stabilization acts in a quantum many-body system, beyond the\nMFA. While the collapse remains possible, repulsive two-particle interactions\ngive rise to a metastable gaseous state, which is separated by a potential\nbarrier from the collapsing regime. The stability of this state improves with\nthe increase of the number of particles. The results are produced by\ncalculations of the variational energy, with the help of the Monte Carlo\nmethod."
    },
    {
        "anchor": "Investigation of Quantum Droplet: An Analytical Approach: Recent observations of droplets in dipolar and binary Bose-Einstein\ncondensate (BEC) motivates us to study the theory of droplet formation in\ndetail. Precisely, we are interested in investigating the possibility of\ndroplet formation in a quasi-one-dimensional geometry. The recent observations\nhave concluded that the droplets are stabilized by the competition between\neffective mean-field and beyond mean-field interaction. Hence, it is possible\nto map the effective equation of motion to a cubic-quartic nonlinear\nSchr\\\"odinger equation (CQNLSE). We obtain two analytical solutions of the\nmodified Gross-Pitaevskii equation or CQNLSE and verified them numerically.\nBased on their stability we investigate the parameter regime for which droplets\ncan form. The effective potential allows us to conclude about the regions of\nsoliton domination and self-bound droplet formations.",
        "positive": "Collective excitations of a trapped Bose-Einstein condensate in the\n  presence of weak disorder and a two-dimensional optical lattice: We investigate the combined effects of weak disorder and a two-dimensional\n(2D) optical lattice on the collective excitations of a harmonically trapped\nBose-Einstein condensate (BEC) at zero temperature. Accordingly, we generalize\nthe hydrodynamic equations of superfluid for a weakly interacting Bose gas in a\n2D optical lattice to include the effects of weak disorder. Our analytical\nresults for the collective frequencies beyond the mean-field approximation\nreveal the peculiar role of disorder, interplaying with the 2D optical lattice\nand interatomic interaction, on elementary excitations along the 3D to 1D\ndimensional crossover. In particular, consequences of disorder on the phonon\npropagation and surface modes are analyzed in detail. The experimental scenario\nis also proposed."
    },
    {
        "anchor": "Strongly interacting confined quantum systems in one dimension: In one dimension, the study of magnetism dates back to the dawn of quantum\nmechanics when Bethe solved the famous Heisenberg model that describes quantum\nbehaviour in magnetic systems. In the last decade, one-dimensional systems have\nbecome a forefront area of research driven by the realization of the\nTonks-Girardeau gas using cold atomic gases. Here we prove that one-dimensional\nfermionic and bosonic systems with strong short-range interactions are solvable\nin arbitrary confining geometries by introducing a new energy-functional\ntechnique and obtaining the full spectrum of energies and eigenstates. As a\nfirst application, we calculate spatial correlations and show how both ferro-\nand anti-ferromagnetic states are present already for small system sizes that\nare prepared and studied in current experiments. Our work demonstrates the\nenormous potential for quantum manipulation of magnetic correlations at the\nmicroscopic scale.",
        "positive": "Anisotropic quantum quench in the presence of frustration or background\n  gauge fields: A probe of bulk currents and topological chiral edge modes: Bosons and fermions, in the presence of frustration or background gauge\nfields, can form manybody ground states that support equilibrium 'charge' or\n'spin' currents. Motivated by the experimental creation of frustration or\nartificial gauge fields in ultracold atomic systems, we propose a general\nscheme by which making a sudden anisotropic quench of the atom tunneling across\nthe lattice and tracking the ensuing density modulations provides a powerful\nand gauge invariant route to visualizing diverse equilibrium current patterns.\nUsing illustrative examples of trapped superfluid Bose and normal Fermi systems\nin the presence of artificial magnetic fluxes on square lattices, and\nfrustrated bosons in a triangular lattice, we show that this scheme to probe\nequilibrium bulk current order works independent of particle statistics. We\nalso show that such quenches can detect chiral edge currents in gapped\ntopological states, such as quantum Hall or quantum spin Hall insulators."
    },
    {
        "anchor": "Tetramers of two heavy and two light bosons: This article considers the bound states of two heavy and two light bosons,\nwhen a short-range force attracts the bosons of different mass, and a\nshort-range force repel the light bosons. The existence of such four-body bound\nstates results from the competition between these two forces. For a given\nstrength of the attraction, the critical strength of the repulsion necessary to\nunbind the four particles is calculated. This study is motivated by the\nexperimental realisation of impurity atoms immersed in an atomic Bose-Einstein\ncondensate, and aims at determining in which regime only one boson contributes\nto binding two impurities.",
        "positive": "Morphology of dipolar Bose droplets: The ground state of a free standing, self-bound droplet comprising four\nhundred dipolar Bose particles with aligned dipole moments, with an additional\npurely repulsive two-body interaction, is investigated by Quantum Monte Carlo\nsimulations. The focus here is on the evolution of the cluster as the effective\nrange of the repulsive interaction is varied. We identify a ``classical''\nregime, in which binding arises exclusively from the dipolar potential energy\nand the cluster is a quasi-one-dimensional filament, and a ``quantum'' regime\nof prolate droplets, held together to a significant degree by\nquantum-mechanical exchanges. The transition between the two regimes occurs\nabruptly."
    },
    {
        "anchor": "Collective behaviour of large number of vortices in the plane: We investigate the dynamics of $N$ point vortices in the plane, in the limit\nof large $N$. We consider {\\em relative equilibria}, which are rigidly rotating\nlattice-like configurations of vortices. These configurations were observed in\nseveral recent experiments [Durkin and Fajans, Phys. Fluids (2000) 12, 289-293;\nGrzybowski {\\em et.al} PRE (2001)64, 011603]. We show that these solutions and\ntheir stability are fully characterized via a related {\\em aggregation model}\nwhich was recently investigated in the context of biological swarms [Fetecau\n{\\em et.al.}, Nonlinearity (2011) 2681; Bertozzi {\\em et.al.}, M3AS (2011)]. By\nutilizing this connection, we give explicit analytic formulae for many of the\nconfigurations that have been observed experimentally. These include\nconfigurations of vortices of equal strength; the $N+1$ configurations of $N$\nvortices of equal strength and one vortex of much higher strength; and more\ngenerally, $N+K$ configurations. We also give examples of configurations that\nhave not been studied experimentally, including $N+2$ configurations where $N$\nvortices aggregate inside an ellipse. Finally, we introduce an artificial\n``damping'' to the vortex dynamics, in an attempt to explain the phenomenon of\ncrystalization that is often observed in real experiments. The diffusion breaks\nthe conservative structure of vortex dynamics so that any initial conditions\nconverge to the lattice-like relative equilibrium.",
        "positive": "Fourth cluster and virial coefficients of a unitary Fermi gas for an\n  arbitrary mass ratio: We calculate the fourth cluster coefficients of the homogeneous unitary spin\n1/2 Fermi gas as functions of the internal-state mass ratio, over intervals\nconstrained by the 3- or 4-body Efimov effect. For this we use our 2016\nconjecture (validated for equal masses by Hou and Drut in 2020) in a\nnumerically efficient formulation making the sum over angular momentum converge\nfaster, which is crucial at large mass ratio. The mean cluster coefficient,\nrelevant for equal chemical potentials, is not of constant sign and increases\nrapidly close to the Efimovian thresholds. We also get the fourth virial\ncoefficients, which we find to be very poor indicators of interaction-induced\n4-body correlations. We obtain analytically for all $n$ the cluster\ncoefficients of order $n$ + 1 for an infinity-mass impurity fermion, matching\nthe conjecture for $n=3$. Finally, in a harmonic potential, we predict a\nnon-monotonic behavior of the 3 + 1 cluster coefficient with trapping\nfrequency, near mass ratios where this coefficient vanishes in the homogeneous\ncase."
    },
    {
        "anchor": "Quantum Monte Carlo study of few- and many-body Bose systems in one and\n  two dimensions: In this Thesis, we report a detailed study of the ground-state properties of\na set of quantum few- and many-body systems in one and two dimensions with\ndifferent types of interactions by using Quantum Monte Carlo methods.\nNevertheless, the main focus of this work is the study of the ground-state\nproperties of an ultracold Bose system with dipole-dipole interaction between\nthe particles. We consider the cases where the bosons are confined to a bilayer\nand multilayer geometries, that consist of equally spaced two-dimensional\nlayers. These layers can be experimentally realized by imposing tight\nconfinement in one direction. We specifically address the study of new quantum\nphases, their properties, and transitions between them. One expects these\nsystems to have a rich collection of few- and many-body phases because the\ndipole-dipole interaction is anisotropic and quasi long-range.",
        "positive": "Protection of quantum states from disturbance due to random potential by\n  successive translation: We show a method to protect quantum states from the disturbance due to the\nrandom potential by successive rapid manipulations of the quantum states. The\nquantum states are kept undisturbed for a longer time than the case of the\nsimple trapping with a stationary potential. The effective potential, which the\nquantum states feel, becomes uniform when the velocity of the transport is\nsufficiently large. It is also shown that the alternating transport of a\nBose-Einstein condensate with the driving potential derived by fast-forward\nscaling theory [Masuda and Nakamura, Proc. R. Soc. A 466, 1135 (2010)] can\nprotect it from the disturbance."
    },
    {
        "anchor": "Universality of an impurity in a Bose-Einstein condensate: Universality is a powerful concept in physics, allowing one to construct\nphysical descriptions of systems that are independent of the precise\nmicroscopic details or energy scales. A prime example is the Fermi gas with\nunitarity limited interactions, whose universal properties are relevant to\nsystems ranging from atomic gases at microkelvin temperatures to the inner\ncrust of neutron stars. Here we address the question of whether unitary Bose\nsystems can possess a similar universality. We consider the simplest strongly\ninteracting Bose system, where we have an impurity particle (\"polaron\")\nresonantly interacting with a Bose-Einstein condensate (BEC). Focusing on the\nground state of the equal-mass system, we use a variational wave function for\nthe polaron that includes up to three Bogoliubov excitations of the BEC, thus\nallowing us to capture both Efimov trimers and associated tetramers. Unlike the\nFermi case, we find that the length scale associated with Efimov trimers (i.e.,\nthe three-body parameter) can strongly affect the polaron's behaviour, even at\nboson densities where there are no well-defined Efimov states. However, by\ncomparing our results with recent quantum Monte Carlo calculations, we argue\nthat the polaron energy is a \\emph{universal} function of the Efimov three-body\nparameter for sufficiently low boson densities. We further support this\nconclusion by showing that the energies of the deepest bound Efimov trimers and\ntetramers at unitarity are universally related to one another, regardless of\nthe microscopic model. On the other hand, we find that the quasiparticle\nresidue and effective mass sensitively depend on the coherence length $\\xi$ of\nthe BEC, with the residue tending to zero as $\\xi$ diverges, in a manner akin\nto the orthogonality catastrophe.",
        "positive": "Antiferromagnetic Order of Repulsively Interacting Fermions on Optical\n  lattices: The N\\'eel state in fermionic mixtures of two pseudospin species in an\noptical lattice is analyzed at low temperatures. Experimentally it remains a\nchallenge to demonstrate antiferromagnetic correlations in ultracold fermionic\nquantum gases. We find that, while in balanced systems the N\\'eel order\nparameter can point in any spatial direction, in imbalanced mixtures\nantiferromagnetism is strictly perpendicular to the quantization axis (i.e.,\nthe z-axis). Since, experimentally, one always has to assume some minimal\nimbalance this should have important consequences for ongoing experiments."
    },
    {
        "anchor": "Realization of a Resonant Fermi Gas with a Large Effective Range: We have measured the interaction energy and three-body recombination rate for\na two-component Fermi gas near a narrow Feshbach resonance and found both to be\nstrongly energy dependent. Even for deBroglie wavelengths greatly exceeding the\nvan der Waals length scale, the behavior of the interaction energy as a\nfunction of temperature cannot be described by atoms interacting via a contact\npotential. Rather, energy-dependent corrections beyond the scattering length\napproximation are required, indicating a resonance with an anomalously large\neffective range. For fields where the molecular state is above threshold, the\nrate of three-body recombination is enhanced by a sharp, two-body resonance\narising from the closed-channel molecular state which can be magnetically tuned\nthrough the continuum. This narrow resonance can be used to study strongly\ncorrelated Fermi gases that simultaneously have a sizeable effective range and\na large scattering length.",
        "positive": "Design and construction of a quantum matter synthesizer: The quantum matter synthesizer (QMS) is a new quantum simulation platform in\nwhich individual particles in a lattice can be resolved and re-arranged into\narbitrary patterns. The ability to spatially manipulate ultracold atoms and\ncontrol their tunneling and interactions at the single-particle level allows\nfull control of a many-body quantum system. We present the design and\ncharacterization of the QMS, which integrates into a single ultra-stable\napparatus a two-dimensional optical lattice, a moving optical tweezer array\nformed by a digital micromirror device, and site-resolved atomic imaging. We\ndemonstrate excellent mechanical stability between the lattice and tweezer\narray with relative fluctuations below 10 nm, high-speed real-time control of\nthe tweezer array at a 2.52 kHz refresh rate, and diffraction-limited imaging\nat a resolution of 655 nm. The QMS also features new technologies and schemes\nsuch as nanotextured anti-reflective windows and all-optical long-distance\ntransport of atoms."
    },
    {
        "anchor": "Evidence of superfluidity in a dipolar supersolid from non-classical\n  rotational inertia: A key manifestation of superfluidity in liquids and gases is a reduction of\nthe moment of inertia under slow rotations. Non-classical rotational effects\nhave been searched for a long time also for the elusive supersolid phase of\nmatter, in which superfluidity coexists with a lattice structure. Here we show\nthat the recently discovered supersolid phase in dipolar quantum gases features\na reduced moment of inertia. We study a peculiar rotational oscillation mode in\na harmonic potential, the scissors mode, already employed for superfluids. From\nthe measured moment of inertia, we infer a superfluid fraction that is\ndifferent from zero and of order of unity, providing direct evidence of the\nsuperfluid nature of the dipolar supersolid.",
        "positive": "Strongly interacting trapped one-dimensional quantum gases: an exact\n  solution: Quantum correlations can be used as a resource for quantum computing, eg for\nquantum state manipulation, and for quantum sensing, eg for creating\nnon-classical states which allow to achieve the quantum advantage regime. This\nreview collects the predictions coming from a family of exact solutions which\nallows to describe the many-body wavefunction of strongly correlated quantum\nfluids confined by a tight waveguide and subjected to any form of longitudinal\nconfinement. It directly describes the experiments with trapped ultracold atoms\nwhere the strongly correlated regime in one dimension has been achieved. The\nexact solution applies to bosons, fermions and mixtures. It allows to obtain\nexperimental observables such as the density profiles and momentum distribution\nat all momentum scales, beyond the Luttinger liquid approach. It also predicts\nthe exact quantum dynamics at all the times, including the small oscillations\nregime yielding the collective modes of the system and the large quench regime\nwhere the system parameters are changed considerably. The solution can be\nextended to describe finite-temperature conditions, spin and magnetization\neffects. The review illustrates the idea of the solution, presents the key\ntheoretical achievements and the main experiments on strongly correlated\none-dimensional quantum gases."
    },
    {
        "anchor": "Formation of Ultracold Fermionic NaLi Feshbach Molecules: We describe the formation of fermionic NaLi Feshbach molecules from an\nultracold mixture of bosonic 23Na and fermionic 6Li. Precise magnetic field\nsweeps across a narrow Feshbach resonance at 745 G result in a molecule\nconversion fraction of 5% for our experimental densities and temperatures,\ncorresponding to a molecule number of 5*10^4. The observed molecular decay\nifetime is 1.3 ms after removing free Li and Na atoms from the trap.",
        "positive": "Ring-shaped fractional quantum Hall liquids with hard-wall potentials: We study the physics of $\\nu=1/2$ bosonic fractional quantum Hall droplets\nconfined in a ring-shaped region delimited by two concentric cylindrically\nsymmetric hard-wall potentials. Trial wave functions based on an extension of\nthe Jack polynomial formalism including two different chiral edges are proposed\nand validated for a wide range of confinement potentials in terms of their\nexcellent overlap with the eigenstates numerically found by exact\ndiagonalization. In the presence of a single repulsive potential centered in\nthe origin, a recursive structure in the many-body spectra and a massively\ndegenerate ground state manifold are found. The addition of a second hard-wall\npotential confining the fractional quantum Hall droplet from the outside leads\nto a non-degenerate ground state containing a well defined number of quasiholes\nat the center and, for suitable potential parameters, to a clear organization\nof the excitations on the two edges. The utility of this ring-shaped\nconfiguration in view of theoretical and experimental studies of subtle aspects\nof fractional quantum Hall physics is outlined."
    },
    {
        "anchor": "Hamiltonian dynamics of two same-sign point vortices: We have studied numerically the Hamiltonian dynamics of two same-sign point\nvortices in an effectively two-dimensional, harmonically trapped Bose-Einstein\ncondensate. We have found in the phase space of the system an impenetrable wall\nthat divides the dynamics into two distinct and exhaustive types. In the\ntwo-dimensional position-coordinate space, the first type corresponds to\nintersecting single-vortex orbits and the second type to orbits that have no\npoints in common. The two types are also easily distinguished in the\ntwo-dimensional space spanned by the radial and angular velocities of the\nvortices: in the first type, both single-vortex orbits are the same simple loop\nin this two-dimensional space, whereas in the second type the two orbits\nconstitute two nonintersecting loops. The phase-space-dividing wall is distinct\nfrom the bifurcation curve of rigidly rotating states found by Navarro et al.\n[Phys. Rev. Lett. 110, 225301 (2013)].",
        "positive": "Periodic driving induced helical Floquet channels with ultracold atoms\n  in momentum space: Employing the external degrees of freedom of atoms as synthetic dimensions\nrenders easy and new accesses to quantum engineering and quantum simulation. As\na recent development, ultracold atoms suffering from two-photon Bragg\ntransitions can be diffracted into a series of discrete momentum states to form\na momentum lattice. Here we provide a detailed analysis on such a system, and,\nas a concrete example, report the observation of robust helical Floquet\nchannels, by introducing periodic driving sequences. The robustness of these\nchannels against perturbations is confirmed, as a test for their topological\norigin captured by Floquet winding numbers. The periodic switching demonstrated\nhere serves as a testbed for more complicated Floquet engieering schemes, and\noffers exciting opportunities to study novel topological physics in a many-body\nsetting with tunable interactions."
    },
    {
        "anchor": "Self-consistent Description of Bose-Bose Droplets: Modified Gapless\n  Hartree-Fock-Bogoliubov Method: We define a formalism of a self-consistent description of the ground state of\na weakly interacting Bose system, accounting for higher order terms in\nexpansion of energy in the diluteness parameter. The approach is designed to be\napplied to a Bose-Bose mixture in a regime of weak collapse where quantum\nfluctuations lead to stabilization of the system and formation of quantum\nliquid droplets. The approach is based on the Generalized Gross -- Pitaevskii\nequation accounting for quantum depletion and anomalous density terms. The\nequation is self-consistently coupled to modified Bogoliubov equations.\n  The modification we introduce resolves the longstanding issue of missing\nphonon-branch excitations when higher order terms are included. Our method\nensures a gapless phononic low-energy excitation spectrum, crucial to correctly\naccount for quantum fluctuations. We pay particular attention to the case of\ndroplets harmonically confined in some directions. The method allows to\ndetermine the Lee-Huang-Yang-type contribution to the chemical potential of\ninhomogeneous droplets when the local density approximation fails.",
        "positive": "Competing instabilities in quench experiments with ultracold Fermi gases\n  near a Feshbach resonance: Tunability of effective two body interactions near Feshbach resonances is a\npowerful experimental tool in systems of ultracold atoms. It has been used to\nexplore a variety of intriguing phenomena in recent experiments. However not\nall of the many-body properties of such systems can be understood in terms of\neffective models with contact interaction given by the scattering length of the\ntwo particles in vacuum. For example, when a two component Fermi mixture is\nquenched to the BEC side of the Feshbach resonance, a positive scattering\nlength suggests that interactions are repulsive and thus collective dynamics\nshould be dominated by the Stoner instability toward a spin polarized\nferromagnetic state. On the other hand, existence of low energy two particle\nbound states suggests a competing instability driven by molecule formation.\nCompe- tition between spontaneous magnetization and pair formation is\ndetermined by the the interplay of two-particle and many-body phenomena. In\nthese lecture notes we summarize our recent theoretical results, which analyzed\nthis competition from the point of view of unstable collective modes. We also\ncomment on the relevance of this theoretical analysis to recent experiments\nreported in Ref. (Jo, Lee, Choi, Christensen, Kim, Thywissen, Pritchard and\nKetterle, 2009)."
    },
    {
        "anchor": "Synthetic Spin-Orbit Coupling in Two-level Cold Atoms: Synthetic spin-orbit coupling (SOC) in controlled quantum systems such as\ncold atoms or trapped ions has been of great interest. Here we show, both\ntheoretically and computationally, a simplest realization of SOC using\ntwo-level cold atoms interacting with only one laser beam. The underlying\nmechanism is based upon the non-adiabatic nature of laser-atom interaction,\nwith the Rabi frequency and atom's kinetic energy being comparable to each\nother. We use the Zitterbewegung (ZB) oscillation to further illustrate the\neffects of the synthesized SOC on the quantum dynamics of the two-level cold\natoms. We expect our proposal to be of experimental interest in quantum\nsimulation of SOC-related physics.",
        "positive": "Verifying a quasi-classical spin model of perturbed quantum rewinding in\n  a Fermi gas: We systematically test a quasi-classical spin model of a large spin-lattice\nin energy space, with a tunable, reversible Hamiltonian and effective\nlong-range interactions. The system is simulated by a weakly interacting Fermi\ngas undergoing perturbed quantum rewinding using radio-frequency(RF) pulses.\nThe model reported here is found to be in a quantitative agreement with\nmeasurements of the ensemble-averaged energy-resolved spin density. This work\nelucidates the effects of RF detunings on the system and measurements, pointing\nthe way to new correlation measurement methods."
    },
    {
        "anchor": "Mean-Field Analysis of Spinor Bosons in Optical Superlattices: We study the ground-state phase diagram of spinless and spin-1 bosons in\noptical superlattices using a Bose-Hubbard Hamiltonian that includes\nspin-dependent interactions. We decouple the unit cells of the superlattice via\na mean-field approach and take into account the dynamics within the unit cell\nexactly. The system supports Mott-insulating as well as superfluid phases. The\ntransitions between these phases are second-order for spinless bosons and\nsecond- or first-order for spin-1 bosons. Anti-ferromagnetic interactions\nenergetically penalize high-spin configurations and elongate all Mott lobes,\nespecially the ones corresponding to an even atom number on each lattice site.\nWe find that the quadratic Zeeman effect lifts the degeneracy between different\npolar superfluid phases leading to additional metastable phases and first-order\nphase transitions. Finally, we show that an energy offset between the two sites\nof the unit cell induces a staircase of single-atom tunneling resonances which\nsurprisingly survives well into the superfluid regime.",
        "positive": "Collective modes of vortex lattices in two-component Bose-Einstein\n  condensates under synthetic gauge fields: We study collective modes of vortex lattices in two-component Bose-Einstein\ncondensates subject to synthetic magnetic fields in mutually parallel or\nantiparallel directions. By means of the Bogoliubov theory with the\nlowest-Landau-level approximation, we numerically calculate the excitation\nspectra for a rich variety of vortex lattices that appear commonly for parallel\nand antiparallel synthetic fields. We find that in all of these cases, there\nappear two distinct modes with linear and quadratic dispersion relations at low\nenergies, which exhibit anisotropy reflecting the symmetry of each lattice\nstructure. Remarkably, the low-energy spectra for the two types of fields are\nfound to be related to each other by simple rescaling when vortices in\ndifferent components overlap owing to an intercomponent attraction. These\nresults are consistent with an effective field theory analysis. However, the\nrescaling relations break down for interlaced vortex lattices appearing with an\nintercomponent repulsion, indicating a nontrivial effect of an intercomponent\nvortex displacement beyond the effective field theory. We also find that\nhigh-energy parts of the excitation bands exhibit line or point nodes as a\nconsequence of a fractional translation symmetry present in some of the lattice\nstructures."
    },
    {
        "anchor": "Stable periodic density waves in dipolar Bose-Einstein condensates\n  trapped in optical lattices: Density-wave patterns in (quasi-) discrete media with local interactions are\nknown to be unstable. We demonstrate that \\emph{stable} double- and triple-\nperiod patterns (DPPs and TPPs), with respect to the period of the underlying\nlattice, exist in media with nonlocal nonlinearity. This is shown in detail for\ndipolar Bose-Einstein condensates (BECs), loaded into a deep one-dimensional\n(1D) optical lattice (OL), by means of analytical and numerical methods in the\ntight-binding limit. The patterns featuring multiple periodicities are\ngenerated by the modulational instability of the continuous-wave (CW) state,\nwhose period is identical to that of the OL. The DPP and TPP emerge via phase\ntransitions of the second and first kind, respectively. The emerging patterns\nmay be stable provided that the dipole-dipole (DD) interactions are repulsive\nand sufficiently strong, in comparison with the local repulsive nonlinearity.\nWithin the set of the considered states, the TPPs realize a minimum of the free\nenergy. Accordingly, a vast stability region for the TPPs is found in the\nparameter space, while the DPP\\ stability region is relatively narrow. The same\nmechanism may create stable density-wave patterns in other physical media\nfeaturing nonlocal interactions, such as arrayed optical waveguides with\nthermal nonlinearity.",
        "positive": "Polariton-polariton interaction beyond the Born approximation: A toy\n  model study: We theoretically investigate the polariton-polariton interaction in\nmicrocavities beyond the commonly used Born approximation (i.e., mean-field),\nby adopting a toy model with a contact interaction to approximately describe\nthe attraction between electrons and holes in quantum well and by using a\nGaussian pair fluctuation theory beyond mean-field. We obtain a density or\nchemical potential independent polariton-polariton interaction strength even in\ntwo-dimensions, which result from coupling to the photon field. We show that\nquantum fluctuations lead to about a factor of two reduction in the\npolariton-polariton interaction strength within our toy model. Together with\ncorrections to the 1s exciton approximation at very strong light-matter\ncoupling, we find the polariton-polariton interaction strength under typical\nexperimental conditions is overestimated by a factor three in the widely used\ntheories, if our toy model can qualitatively simulate the polariton interaction\nin GaAs quantum wells. We compare our prediction with the most recent\nmeasurement and argue that the beyond-Born-approximation effect to the\npolariton-polariton interaction strength is crucial for a quantitative\nunderstanding of the experimental data by E. Estrecho \\textit{et al.}, Phys.\nRev. B \\textbf{100}, 035306 (2019)."
    },
    {
        "anchor": "Photonic Crystal Architecture for Room Temperature Equilibrium\n  Bose-Einstein Condensation of Exciton-Polaritons: We describe photonic crystal microcavities with very strong light-matter\ninteraction to realize room-temperature, equilibrium, exciton-polariton\nBose-Einstein condensation (BEC). This is achieved through a careful balance\nbetween strong light-trapping in a photonic band gap (PBG) and large exciton\ndensity enabled by a multiple quantum-well (QW) structure with moderate\ndielectric constant. This enables the formation of long-lived, dense 10~$\\mu$m\n- 1~cm scale cloud of exciton-polaritons with vacuum Rabi splitting (VRS) that\nis roughly 7\\% of the bare exciton recombination energy. We introduce a\nwoodpile photonic crystal made of Cd$_{0.6}$Mg$_{0.4}$Te with a 3D PBG of 9.2\\%\n(gap to central frequency ratio) that strongly focuses a planar guided optical\nfield on CdTe QWs in the cavity. For 3~nm QWs with 5~nm barrier width the\nexciton-photon coupling can be as large as $\\hbar\\Ome=$55~meV (i.e., vacuum\nRabi splitting $2\\hbar\\Ome=$110~meV). The exciton recombination energy of\n1.65~eV corresponds to an optical wavelength of 750~nm. For $N=$106 QWs\nembedded in the cavity the collective exciton-photon coupling per QW,\n$\\hbar\\Ome/\\sqrt{N}=5.4$~meV, is much larger than state-of-the-art value of\n3.3~meV, for CdTe Fabry-P\\'erot microcavity. The maximum BEC temperature is\nlimited by the depth of the dispersion minimum for the lower polariton branch,\nover which the polariton has a small effective mass $\\sim 10^{-5}m_0$ where\n$m_0$ is the electron mass in vacuum. By detuning the bare exciton\nrecombination energy above the planar guided optical mode, a larger dispersion\ndepth is achieved, enabling room-temperature BEC.",
        "positive": "Dephasing-rephasing dynamics of one-dimensional tunneling\n  quasicondensates: We study the quantum tunneling of two one-dimensional quasi-condensates made\nof alkali-metal atoms, considering two different tunneling configurations:\nside-by-side and head-to-tail. After deriving the quasiparticle excitation\nspectrum, we discuss the dynamics of the relative phase following a sudden\ncoupling of the independent subsystems. In particular, we calculate the\ncoherence factor of the system, which, due to the nonzero tunneling amplitude,\nit exhibits dephasing-rephasing oscillations instead of pure dephasing. These\noscillations are enhanced by a higher tunneling energy, and by higher system\ndensities. Our predictions provide a benchmark for future experiments at\ntemperatures below $T \\lesssim 5 \\, \\mbox{nK}$."
    },
    {
        "anchor": "Dispersion engineering in spin-orbit coupled spinor $F=1$ condensates\n  driven by negative masses: In this paper, we bring out several potential signatures of negative mass\nregimes while investigating an expanding spin-orbit (SO) coupled spinor $F=1$\nBose-Einstein condensates by analyzing the dispersion relation of the\nsingle-particle quantum system. In SO-coupled spinor condensates, a negative\nmass parameter generates a wave packet that propagates in the opposite\ndirection of the momentum. We analyze the dynamics of spin waves analytically\nand present a simple approach to investigate the expansion of spinor\ncondensates. In particular, we examine the dynamics when both masses are\nnegative, which results in the spinor condensates splitting into two\ncounter-propagating self-interfering packets (SIPs). Using numerical\nsimulations of the coupled Gross-Pitaevskii equations, we demonstrate the\ndensity expansion and self-interference patterns with and without magnetization\nfor repulsive and attractive interactions with different coupling parameters.\nThe highlight of our investigation is that we are able to unearth several\nphenomena observed in experiments, such as self-interfering packets, pileup,\nmodulation instability, slow down, self-trapping, and gap solitons. In\nparticular, the gap soliton exists at the gap created by the intersection of\ntwo negative masses.",
        "positive": "Generalized Bose-Fermi mapping and strong coupling ansatz wavefunction\n  for one dimensional strongly interacting spinor quantum gases: Quantum many-body systems in one dimension (1D) exhibit some peculiar\nproperties. In this article, we review some of our work on strongly interacting\n1D spinor quantum gas. First, we discuss a generalized Bose-Fermi mapping that\nmaps the charge degrees of freedom to a spinless Fermi gas and the spin degrees\nof freedom to a spin chain model. This also maps the strongly interacting\nsystem into a weakly interacting one, which is amenable for perturbative\ncalculations. Next, based on this mapping, we construct an ansatz wavefunction\nfor the strongly interacting system, using which many physical quantities can\nbe conveniently calculated. We showcase the usage of this ansatz wavefunction\nby considering the collective excitations and quench dynamics of a harmonically\ntrapped system."
    },
    {
        "anchor": "Interference of Holon Strings in 2D Hubbard Model: The 2D Hubbard model with large repulsion is a central and yet unsolved\nproblem in condensed matter physics for decades. The challenge appears below\nhalf filling, where the system is a doped antiferromagnet. In this regime, the\nfermion excitations are nothing like those in a Fermi liquid, which carry both\nspin and charge. Rather, they split up into holons and spinons, carrying charge\nand spin separately. Moreover, the motion of a holon is believed to stir up the\nunderlying antiferromagnetic order, leaving behind it a string of \"wrong\"\nspins. While direct observation of the holon string is difficult in electron\nsystems, it has become possible in cold atom experiments due to recent\nexperimental advances. Here, we point out the key feature of the holon strings,\ni.e. its Marshall phase, can be observed through measurements of spin\ncorrelations. Moreover, the interference of these strings leads to an\nanisotropic holon propagation clearly distinguishable than those of spinless\nfermions, as well as a large suppression of the magnetic order in the region\nswept through by the strings, as if the system is driven towards a spin liquid.\nWe further illustrate the effect of the Marshall phase by showing the motion of\na holon in the so-called $\\sigma tJ$-model where the Marshall phase is removed.",
        "positive": "Nonequilibrium dynamics in one-dimensional strongly interacting\n  two-component gases: The derivation of determinant representations for the space-, time-, and\ntemperature-dependent correlation functions of the impenetrable Gaudin-Yang\nmodel in the presence of a trapping potential is presented. These\nrepresentations are valid in both equilibrium and nonequilibrium scenarios like\nthe ones initiated by a sudden change of the confinement potential. In the\nequal-time case our results are shown to be equivalent to a multicomponent\ngeneralization of Lenard's formula from which Painlev\\'e transcendent\nrepresentations for the correlators can be obtained in the case of harmonic\ntrapping and Dirichlet and Neumann boundary conditions. For a system in the\nquantum Newton's cradle setup the determinant representations allow for an\nexact numerical investigation of the dynamics and even hydrodynamization which\nis outside the reach of Generalized Hydrodynamics or other approximate methods.\nIn the case of a sudden change in the trap's frequency we predict a many-body\nbounce effect, not present in the evolution of the density profile, which\ncauses a nontrivial periodic narrowing of the momentum distribution with\namplitude depending on the statistics of the particles."
    },
    {
        "anchor": "Topologically protected edge states in small Rydberg systems: We propose a simple setup of Rydberg atoms in a honeycomb lattice which gives\nrise to topologically protected edge states. The proposal is based on the\ncombination of dipolar exchange interaction, which couples the internal angular\nmomentum and the orbital degree of freedom of a Rydberg excitation, and a\nstatic magnetic field breaking time reversal symmetry. We demonstrate that for\nrealistic experimental parameters, signatures of topologically protected edge\nstates are present in small systems with as few as 10 atoms. Our analysis paves\nthe way for the experimental realization of Rydberg systems characterized by a\ntopological invariant, providing a promising setup for future application in\nquantum information.",
        "positive": "Optimal atomic interferometry robust to detection noise using spin-1\n  atomic condensates: Implementation of the quantum interferometry concept to spin-1 atomic\nBose-Einstein condensates is analyzed by employing a polar state evolved in\ntime. In order to identify the best interferometric configurations, the quantum\nFisher information is maximized. Three optimal configurations are identified,\namong which one was not reported in the literature yet, although it gives the\nhighest value of the quantum Fisher information in experimentally achievable\nshort time dynamics. Details of the most optimal configurations are\ninvestigated based on the error-propagation formula which includes the\ninteraction-based readout protocol to reduce the destructive effect of\ndetection noise. In order to obtain Heisenberg scaling accessible by present\nday experimental techniques, an efficient measurement and a method for the\ninversion of dynamics were developed, as necessary for the protocol's\nimplementation."
    },
    {
        "anchor": "Domain formation and universally critical dynamics through phase\n  separation in two-component Bose-Einstein condensates: We explore the defect formation and universally critical dynamics in\ntwo-dimensional (2D) two-component Bose-Einstein condensates(BECs) subjected to\ntwo types of potential traps: a homogeneous trap and a harmonic trap.We focus\non the non-equilibrium universal dynamics of the miscible-immiscible phase\ntransition with both linear and nonlinear quenching types.Although there exists\nspatial independence of the critical point, we find that the inhomogeneity of\ntrap doesn't affect the phase transition of system and the critical exponents\ncan still be explained by the homogeneous Kibble-Zurek mechanism. By analyzing\nthe Bogoliubov excitations, we establish a power-law relationship between the\ndomain correlation length, the phase transition delay, and the quench\ntime.Furthermore, through real-time simulations of phase transition dynamics,\nthe formation of domain defects and the delay of phase transition in\nnon-equilibrium dynamics are demonstrated, along with the corresponding\nuniversal scaling of correlation length and phase transition delay for various\nquench time and quench coefficients, which align well with our analytical\npredictions.Our study confirms that the universality class of two-component\nBECs remains unaffected by dimensionality, while the larger nonlinear\ncoefficients effectively suppress non-adiabatic excitations, offering a novel\nperspective for addressing adiabatic evolution.",
        "positive": "Supercurrent in a room temperature Bose-Einstein magnon condensate: We report evidence for the existence of a supercurrent of magnons in a magnon\nBose-Einstein condensate prepared in a room temperature yttrium-iron-garnet\nmagnetic film and subject to a thermal gradient. The magnon condensate is\nformed in a parametrically populated magnon gas, and its temporal evolution is\nstudied by time-, frequency- and wavector-resolved Brillouin light scattering\nspectroscopy. It has been found that local heating in the focal point of a\nprobing laser beam enhances the temporal decrease in the density of the freely\nevolving magnon condensate after the termination of the pumping pulse, but it\ndoes not alter the relaxation dynamics of the gaseous magnon phase. This\nphenomenon is understood as the appearance of a magnon supercurrent within the\ncondensate due to a temperature- and, consequently, magnetisation-gradient\ninduced phase gradient in the condensate wave function."
    },
    {
        "anchor": "Two emitters coupled to a bath with Kerr-like non-linearity: Exponential\n  decay, fractional populations, and Rabi oscillations: We consider two non-interacting two-level emitters that are coupled weakly to\na one-dimensional non-linear wave guide. Due to the Kerr-like non-linearity,\nthe wave guide considered supports -- in addition to the scattering continuum\n-- a two-body bound state. As such, the wave guide models a bath with\nnon-trivial mode structure. Solving the time-dependent Schr\\\"odinger equation,\nthe radiation dynamics of the two emitters, initially prepared in their excited\nstates, is presented. Changing the emitter frequency such that the two-emitter\nenergy is in resonance with one of the two-body bound states, radiation\ndynamics ranging from exponential decay to fractional populations to Rabi\noscillations is observed. Along with the detuning, the dependence on the\nseparation of the two emitters is investigated. Approximate reduced Hilbert\nspace formulations, which result in effective emitter-separation and momentum\ndependent interactions, elucidate the underlying physical mechanisms and\nprovide an avenue to showcase the features that would be absent if the\none-dimensional wave guide did not contain a non-linearity. Our theoretical\nfindings apply to a number of experimental platforms and the predictions can be\ntested with state-of-the-art technology. In addition, the weak-coupling\nSchr\\\"odinger equation based results provide critical guidance for the\ndevelopment of master equation approaches.",
        "positive": "Vortex lattice melting in a boson-ladder in artificial gauge field: We consider a two-leg boson ladder in an artificial U(1) gauge field and show\nthat, in the presence of interleg attractive interaction, the flux induced\nVortex state can be melted by dislocations. For increasing flux, instead of the\nMeissner to Vortex transition in the commensurate-incommensurate universality\nclass, first an Ising transition from the Meissner state to a charge density\nwave takes place, then, at higher flux, the melted Vortex phase is established\nvia a disorder point where incommensuration develops in the rung current\ncorrelation function and in momentum distribution.Finally, the quasi-long range\nordered Vortex phase is recovered for sufficiently small interaction. Our\npredictions for the observables, such as the spin current and the static\nstructure factor, could be tested in current experiments with cold atoms in\nbosonic ladders."
    },
    {
        "anchor": "Interaction induced doublons and embedded topological subspace in a\n  complete flat-band system: In this work, we investigate effects of weak interactions on a bosonic\ncomplete flat-band system. By employing a band projection method, the flat-band\nHamiltonian with weak interactions is mapped to an effective Hamiltonian. The\neffective Hamiltonian indicates that doublons behave as well-defined\nquasi-particles, which acquire itinerancy through the hopping induced by\ninteractions. When we focus on a two-particle system, from the effective\nHamiltonian, an effective subspace spanned only by doublon bases emerges. The\neffective subspace induces spreading of a single doublon and we find an\ninteresting property: The dynamics of a single doublon keeps short-range\ndensity-density correlation in sharp contrast to a conventional two-particle\nspreading. Furthermore, when introducing a modulated weak interaction, we find\nan interaction induced topological subspace embedded in the full Hilbert space.\nWe elucidate the embedded topological subspace by observing the dynamics of a\nsingle doublon, and show that the embedded topological subspace possesses a\nbulk topological invariant. We further expect that for the system with open\nboundary the embedded topological subspace has an interaction induced\ntopological edge mode described by the doublon. The bulk--edge--correspondence\nholds even for the embedded topological subspace.",
        "positive": "Hofstadter-Hubbard model with opposite magnetic fields:\n  Bardeen-Cooper-Schrieffer pairing and superfluidity in the nearly flat\n  butterfly bands: Despite the multi-band spectrum of the widely-known Hofstadter butterfly, it\nturns out that the pairing correlations of the time-reversal-symmetric\nHofstadter-Hubbard model are well-described by a single order parameter that is\nuniform in real space. By exploiting a BCS mean-field theory for the\nnearly-flat butterfly-bands regime of low magnetic-flux limit, here we reveal a\nnumber of unusual superfluid properties both in the ground state and at finite\ntemperatures. Our thorough analysis includes but is not limited to the order\nparameter, condensate and superfluid fractions, and the critical BCS and BKT\ntransition temperatures."
    },
    {
        "anchor": "Exact nonequilibrium dynamics of finite-temperature Tonks-Girardeau\n  gases: Describing finite-temperature nonequilibrium dynamics of interacting\nmany-particle systems is a notoriously challenging problem in quantum many-body\nphysics. Here we provide an exact solution to this problem for a system of\nstrongly interacting bosons in one dimension in the Tonks-Girardeau regime of\ninfinitely strong repulsive interactions. Using the Fredholm determinant\napproach and the Bose-Fermi mapping we show how the problem can be reduced to a\nsingle-particle basis, wherein the finite-temperature effects enter the\nsolution via an effective \"dressing\" of the single-particle wavefunctions by\nthe Fermi-Dirac occupation factors. We demonstrate the utility of our approach\nand its computational efficiency in two nontrivial out-of-equilibrium\nscenarios: collective breathing mode oscillations in a harmonic trap and\ncollisional dynamics in the Newton's cradle setting involving real-time\nevolution in a periodic Bragg potential.",
        "positive": "Stability Spectroscopy of Rotons in a Dipolar Bose Gas: We study the stability of a quasi-one-dimensional dipolar Bose-Einstein\ncondensate (dBEC) that is perturbed by a weak lattice potential along its axis.\nOur numerical simulations demonstrate that systems exhibiting a roton-maxon\nstructure destabilize readily when the lattice wavelength equals either half\nthe roton wavelength or a low roton subharmonic. We apply perturbation theory\nto the Gross-Pitaevskii and Bogoliubov de Gennes equations to illustrate the\nmechanisms behind the instability threshold. The features of our stability\ndiagram may be used as a direct measurement of the roton wavelength for\nquasi-one-dimensional geometries."
    },
    {
        "anchor": "Chaos synchronization in a BEC system using fuzzy logic controller: Since the presence of chaos in Bose-Einstein condensate (BEC) systems plays a\ndestructive role that can undermine the stability of the condensates,\ncontrolling the chaos is of great importance for the creation of the BEC. In\nthis paper, a fuzzy logic controller (FLC) to synchronize the chaotic dynamics\nof two identical master-slave BEC systems has been proposed. Unlike the\nconventional approaches, where expert knowledge is directly used to construct\nthe fuzzy rules and membership functions, the fuzzy rules have been constructed\nusing Lyapunov stability theorem ensuring the synchronization process. The\neffectiveness of the proposed controller has been demonstrated numerically.",
        "positive": "Tunable spin-orbit coupling and magnetic superstripe phase in a BEC: Superstripe phases in Bose-Einstein condensates (BECs), possessing both\ncrystalline structure and superfluidity, opens a new avenue for exploring\nexotic quantum matters---supersolids. However, conclusive detection and further\nexploration of a superstripe is still challenging in experiments because of its\nshort period, low visibility, fragility against magnetic field fluctuation or\nshort lifetime. Here we propose a scheme in a spin-orbit coupled BEC which\novercomes these obstacles and generates a robust magnetic superstripe phase,\nwith only spin (no total) density modulation due to the magnetic translational\nsymmetry, ready for direct real-space observation. In the scheme, two hyperfine\nspin states are individually Raman coupled with a largely-detuned third state,\nwhich induce a momentum-space separation between two lower band dispersions,\nyielding an effective spin-1/2 system with tunable spin-orbit coupling and\nZeeman fields. Without effective Zeeman fields, spin-dependent interaction\ndominates, yielding a magnetic superstripe phase with a long tunable period and\nhigh visibility. Our scheme provides a platform for observing and exploring\nexotic properties of superstripe phases as well as novel physics with tunable\nspin-orbit coupling."
    },
    {
        "anchor": "Time-resolved measurement of Landau--Zener tunneling in different bases: A comprehensive study of the tunneling dynamics of a Bose--Einstein\ncondensate in a tilted periodic potential is presented. We report numerical and\nexperimental results on time-resolved measurements of the Landau--Zener\ntunneling of ultracold atoms introduced by the tilt, which experimentally is\nrealized by accelerating the lattice. The use of different protocols enables us\nto access the tunneling probability, numerically as well as experimentally, in\ntwo different bases, namely, the adiabatic basis and the diabatic basis. The\nadiabatic basis corresponds to the eigenstates of the lattice, and the diabatic\none to the free-particle momentum eigenstates. Our numerical and experimental\nresults are compared with existing two-state Landau--Zener models.",
        "positive": "Thermodynamic contacts and breathing mode physics of 1D p-wave Fermi\n  gases in the high temperature limit: An important tool for understanding the effects of interactions in\nharmonically trapped atomic gases is the examination of their collective modes.\nOne such mode is the breathing or monopole mode, which is special as it is\nconstrained to occur at twice the harmonic trapping frequency when the\ninteractions are scale invariant. When the interactions are not scale\ninvariant, the frequency of the breathing mode will deviate from twice the trap\nfrequency. The deviation itself depends on the thermodynamic contacts, which\ndescribe how the energy changes with the interactions. In this work I examine\nhow the thermodynamic contacts and the breathing mode frequency of a\nspin-polarized one-dimensional (1D) p-wave Fermi gas depend on the 1D\nscattering volume, $\\ell$, and the effective range, $r$, in the high\ntemperature limit. Such dynamics can be studied in experiments and provide a\ntool for understanding how the dynamics depend on interactions with a finite\neffective range."
    },
    {
        "anchor": "Time-Resolved Observation of Spin-Charge Deconfinement in Fermionic\n  Hubbard Chains: Elementary particles such as the electron carry several quantum numbers, for\nexample, charge and spin. However, in an ensemble of strongly interacting\nparticles, the emerging degrees of freedom can fundamentally differ from those\nof the individual constituents. Paradigmatic examples of this phenomenon are\none-dimensional systems described by independent quasiparticles carrying either\nspin (spinon) or charge (holon). Here we report on the dynamical deconfinement\nof spin and charge excitations in real space following the removal of a\nparticle in Fermi-Hubbard chains of ultracold atoms. Using space- and\ntime-resolved quantum gas microscopy, we track the evolution of the excitations\nthrough their signatures in spin and charge correlations. By evaluating\nmulti-point correlators, we quantify the spatial separation of the excitations\nin the context of fractionalization into single spinons and holons at finite\ntemperatures.",
        "positive": "Interactions and scattering of quantum vortices in a polariton fluid: Quantum vortices, the quantized version of classical vortices, play a\nprominent role in superfluid and superconductor phase transitions. However,\ntheir exploration at a particle level in open quantum systems has gained\nconsiderable attention only recently. Here we study vortex pair interactions in\na resonant polariton fluid created in a solid-state microcavity. By tracking\nthe vortices on picosecond time scales, we reveal the role of nonlinearity, as\nwell as of density and phase gradients, in driving their rotational dynamics.\nSuch effects are also responsible for the split of composite spin-vortex\nmolecules into elementary half-vortices, when seeding opposite vorticity\nbetween the two spinorial components. Remarkably, we also observe that vortices\nplaced in close proximity experience a pull-push scenario leading to unusual\nscattering-like events that can be described by a tunable effective potential.\nUnderstanding vortex interactions can be useful in quantum hydrodynamics and in\nthe development of vortex-based lattices, gyroscopes, and logic devices."
    },
    {
        "anchor": "Atomic quantum simulation of a three-dimensional U(1) gauge-Higgs model: In this paper, we study theoretically atomic quantum simulations of a U(1)\ngauge-Higgs model on a three-dimensional (3D) spatial lattice by using an\nextended Bose-Hubbard model with intersite repulsions on a 3D optical lattice.\nHere, the phase and density fluctuations of the boson variable on each site of\nthe optical lattice describe the vector potential and the electric field on\neach link of the gauge-model lattice, respectively. The target gauge model is\ndifferent from the standard Wilson-type U(1) gauge-Higgs model because it has\nplaquette and Higgs interactions with asymmetric couplings in the space-time\ndirections. Nevertheless, the corresponding quantum simulation is still\nimportant as it provides us with a platform to study unexplored time-dependent\nphenomena characteristic of each phase in the general gauge-Higgs models. To\ndetermine the phase diagram of the gauge-Higgs model at zero temperature, we\nperform Monte-Carlo simulations of the corresponding 3+1-dimensional U(1)\ngauge-Higgs model, and obtain the confinement and Higgs phases. To investigate\nthe dynamical properties of the gauge-Higgs model, we apply the\nGross-Pitaevskii equations to the extended Bose-Hubbard model. We simulate the\ntime-evolution of an electric flux that initially is put on a straight line\nconnecting two external point charges. We also calculate the potential energy\nbetween this pair of charges and obtain the string tension in the confinement\nphase. Finally, we propose a feasible experimental setup for the atomic\nsimulations of this quantum gauge-Higgs model on the 3D optical lattice. These\nresults may serve as theoretical guides for future experiments.",
        "positive": "Nonthermal fixed points, vortex statistics, and superfluid turbulence in\n  an ultracold Bose gas: Nonthermal fixed points of the dynamics of a dilute degenerate Bose gas far\nfrom thermal equilibrium are analyzed in two and three spatial dimensions.\nUniversal power-law distributions, previously found within a nonperturbative\nquantum-field theoretical approach and recently shown to be related to vortical\ndynamics and superfluid turbulence [Phys. Rev. B 84, 020506(R) (2011)], are\nstudied in detail. The results imply an interpretation of the scaling behavior\nin terms of independent vortex excitations of the superfluid and show that the\nstatistics of topological excitations can be described in the framework of wave\nturbulence. The particular scaling exponents observed in the single-particle\nmomentum distributions are found to be consistent with irreversibility as well\nas conservation laws obeyed by the wave interactions. Moreover, long-wavelength\nacoustic excitations of the vortex-bearing condensate, driven by vortex\nannihilations, are found to follow a nonthermal power law. Considering vortex\ncorrelations in a statistical model, the long-time departure from the\nnonthermal fixed point is related to vortex-antivortex pairing. The studied\nnonthermal fixed points are accessible in cold-gas experiments. The results\nshed light on fundamental aspects of superfluid turbulence and have strong\npotential implications for related phenomena, e.g., in early-universe inflation\nor quark-gluon plasma dynamics."
    },
    {
        "anchor": "Non-local Order in Elongated Dipolar Gases: Dipolar particles in an elongated trap are expected to undergo a quantum\nphase transition from a linear to a zigzag structure with decreasing transverse\nconfinement. We derive the low energy effective theory of the transition\nshowing that in presence of quantum fluctuations the Zigzag phase can be\ncharacterized by a long ranged string order, while the local Ising correlations\ndecay as a power law. This is also confirmed using DMRG calculations on a\nmicroscopic model. The non local order in the bulk gives rise to zero energy\nstates localized at the interface between the ordered and disordered phases.\nSuch an interface naturally arises when the particles are subject to a weak\nharmonic confinement along the tube axis. We compute the signature of the edge\nstates in the single particle tunneling spectra pointing to differences between\na system with bosonic versus fermionic particles. Finally we asses the\nmagnitude of the relevant quantum fluctuations in realistic systems of dipolar\nparticles, including ultracold polar molecules as well as alkali atoms weakly\ndressed by a Rydberg excitation.",
        "positive": "Synthetic Helical Liquids with Ultracold Atoms in Optical Lattices: We discuss a platform for the synthetic realization of key physical\nproperties of helical Tomonaga Luttinger liquids (HTLLs) with ultracold\nfermionic atoms in one-dimensional optical lattices. The HTLL is a strongly\ncorrelated metallic state where spin polarization and propagation direction of\nthe itinerant particles are locked to each other. We propose an unconventional\none-dimensional Fermi-Hubbard model which, at quarter filling, resembles the\nHTLL in the long wavelength limit, as we demonstrate with a combination of\nanalytical (bosonization) and numerical (density matrix renormalization group)\nmethods. An experimentally feasible scheme is provided for the realization of\nthis model with ultracold fermionic atoms in optical lattices. Finally, we\ndiscuss how the robustness of the HTLL against back-scattering and\nimperfections, well known from its realization at the edge of two-dimensional\ntopological insulators, is reflected in the synthetic one-dimensional scenario\nproposed here."
    },
    {
        "anchor": "Exact quantum dynamics of a bosonic Josephson junction: The quantum dynamics of a one-dimensional bosonic Josephson junction is\nstudied by solving the time-dependent many-boson Schr\\\"odinger equation\nnumerically exactly. Already for weak interparticle interactions and on short\ntime scales, the commonly-employed mean-field and many-body methods are found\nto deviate substantially from the exact dynamics. The system exhibits rich\nmany-body dynamics like enhanced tunneling and a novel equilibration phenomenon\nof the junction depending on the interaction, attributed to a quick loss of\ncoherence.",
        "positive": "Local versus global equilibration near the bosonic Mott-superfluid\n  transition: We study the response of trapped two dimensional cold bosons to time\ndependent lattices. We find that in lattice ramps from 11 (superfluid,\n$\\hbar/U_{\\text{i}} = 3$ms, $\\hbar/J_{\\text{i}} = 45$ms) to 16 recoils (Mott,\n$\\hbar/U_{\\text{f}} = 2$ms, $\\hbar/J_{\\text{f}} = 130$ms) the local number\nfluctuations remains at their equilibrium values if ramps are slower than 3 ms.\nGlobal transport, however, is much slower (1s), especially in the presence of\nMott shells. This separation of timescales has practical implications for cold\natom experiments and cooling protocols."
    },
    {
        "anchor": "A dual-species Bose-Einstein condensate with attractive interspecies\n  interactions: We report on the production of a $^{41}$K-$^{87}$Rb dual-species\nBose-Einstein condensate with tunable interspecies interaction and we study the\nmixture in the attractive regime, i.e. for negative values of the interspecies\nscattering length $a_{12}$. The binary condensate is prepared in the ground\nstate and confined in a pure optical trap. We exploit Feshbach resonances for\ntuning the value of $a_{12}$. After compensating the gravitational sag between\nthe two species with a magnetic field gradient, we drive the mixture into the\nattractive regime. We let the system to evolve both in free space and in an\noptical waveguide. In both geometries, for strong attractive interactions, we\nobserve the formation of self-bound states, recognizable as quantum droplets.\nOur findings prove that robust, long-lived droplet states can be realized in\nattractive two-species mixtures, despite the two atomic components may\nexperience different potentials.",
        "positive": "Interaction-induced localization of mobile impurities in ultracold\n  systems: The impurities, introduced intentionally or accidentally into certain\nmaterials, can significantly modify their characteristics or reveal their\nintrinsic physical properties, and thus play an important role in solid-state\nphysics. Different from those static impurities in a solid, the impurities\nrealized in cold atomic systems are naturally mobile. Here we propose an\neffective theory for treating some unique behaviors exhibited by ultracold\nmobile impurities. Our theory reveals the interaction-induced transition\nbetween the extended and localized impurity states, and also explains the\nessential features obtained from several previous models in a unified way.\nBased on our theory, we predict many intriguing phenomena in ultracold systems\nassociated with the extended and localized impurities, including the formation\nof the impurity-molecules and impurity-lattices. We hope this investigation can\nopen up a new avenue for the future studies on ultracold mobile impurities."
    },
    {
        "anchor": "Single-particle versus many-body phase coherence in an interacting Fermi\n  gas: In quantum mechanics, each particle is described by a complex valued\nwave-function characterized by amplitude and phase. When many particles\ninteract each other, cooperative phenomena give rise to a quantum many-body\nstate with a specific quantum coherence. What is the interplay between\nsingle-particle's phase coherence and many-body quantum coherence? Over the\nyears, such question has been object of profound analysis in quantum physics.\nHere, we demonstrate how the time-dependent interference formed by releasing an\ninteracting degenerate Fermi gas from a specific matter-wave circuit in an\neffective magnetic field can tell apart the two notions. Single-particle phase\ncoherence, indicated by the first-order correlator, and many-body quantum\ncoherence, indicated by the density-density correlator, are displayed as\ndistinct features of the interferogram. Single particle phase coherence\nproduces spiral interference of the Fermi orbitals at intermediate times.\nMany-body quantum coherence emerges as long times interference. The interplay\nbetween single-particle coherence and many-body coherence is reflected in a\nstepwise dependence of the interference pattern on the effective magnetic\nfield.",
        "positive": "Characterizing the energy gap and demonstrating an adiabatic quench in\n  an interacting spin system: Spontaneous symmetry breaking occurs in a physical system whenever the ground\nstate does not share the symmetry of the underlying theory, e.g., the\nHamiltonian. It gives rise to massless Nambu-Goldstone modes and massive\nAnderson-Higgs modes. These modes provide a fundamental understanding of matter\nin the Universe and appear as collective phase/amplitude excitations of an\norder parameter in a many-body system. The amplitude excitation plays a crucial\nrole in determining the critical exponents governing universal non-equilibrium\ndynamics in the Kibble-Zurek mechanism (KZM). Here, we characterize the\namplitude excitations in a spin-1 condensate and measure their energy gap for\ndifferent phases of the quantum phase transition. At the quantum critical point\nof the transition, finite size effects lead to a non-zero gap. Our measurements\nare consistent with this prediction, and furthermore, we demonstrate an\nadiabatic quench through the phase transition, which is forbidden at the mean\nfield level. This work paves the way toward generating entanglement through an\nadiabatic phase transition."
    },
    {
        "anchor": "Kibble-Zurek scaling and its breakdown for spontaneous generation of\n  Josephson vortices in Bose-Einstein condensates: Atomic Bose-Einstein condensates confined to a dual-ring trap support\nJosephson vortices as topologically stable defects in the relative phase. We\npropose a test of the scaling laws for defect formation by quenching a Bose gas\nto degeneracy in this geometry. Stochastic Gross-Pitaevskii simulations reveal\na -1/4 power-law scaling of defect number with quench time for fast quenches,\nconsistent with the Kibble-Zurek mechanism. Slow quenches show stronger\nquench-time dependence that is explained by the stability properties of\nJosephson vortices, revealing the boundary of the Kibble-Zurek regime.\nInterference of the two atomic fields enables clear long-time measurement of\nstable defects, and a direct test of the Kibble-Zurek mechanism in\nBose-Einstein condensation.",
        "positive": "Cavity-mediated oscillating and trapping dynamics in a two-component\n  condensate: Cold atoms in cavity provides a new platform for exploring exotic many-body\nphases. Here we explore the dynamics of a two-component condensate coupled to a\nfinesse cavity, in which the Raman coupling is mediated by pumping laser and\ncavity mode. In this model, the energy scale of cavity mode is several order of\nmagnitude bigger than that in the condensate, thus the small fluctuations in\nthe cavity field may have important consequence in the dynamics of condensate.\nBeyond the steady-state approximaton, we show the cavity can play two different\nroles to this dynamics. In the first case, it imprints a gauge potential to the\ndynamics of condensate, giving rise to zero and $\\pi$ Josephson dynamics.\nNevertheless, in the other case, it plays the role of non-reciprocial\ntransportation between the two hyperfine states, in which the stability of the\nfixed points are tuned from elliptic to stable spiral for one of the trapped\nphase and unstable spiral for the other trapped phase, thus the oscillating\ndynamics will finally ceased. The transition between these dynamics can be\ncontrolled by the parameters of the cavity field and the driving field. Our\nresults demonstrate an novel way to engineer the dynamics of condensate by\ntuning the stability of the fixed points."
    },
    {
        "anchor": "Fractal energy spectrum of a polariton gas in a Fibonacci quasi-periodic\n  potential: We report on the study of a polariton gas confined in a quasi-periodic one\ndimensional cavity, described by a Fibonacci sequence. Imaging the polariton\nmodes both in real and reciprocal space, we observe features characteristic of\ntheir fractal energy spectrum such as the opening of mini-gaps obeying the gap\nlabeling theorem and log-periodic oscillations of the integrated density of\nstates. These observations are accurately reproduced solving an effective 1D\nSchr\\\"{o}dinger equation, illustrating the potential of cavity polaritons as a\nquantum simulator in complex topological geometries.",
        "positive": "Simulation of Dynamical Quantum Phase Transition of the 1D Transverse\n  Ising Model with a Double-chain Bose-Hubbard model: We propose a spinless Bose-Hubbard model in an one-dimensional (1D)\ndouble-chain tilted lattice at unit filling per cell. A subspace of this model\ncan be faithfully mapped to the 1D transverse Ising model through superexchange\ninteraction with second-order perturbation theory. At a valid parameter region,\nnumerical results show good agreement of these two models both on energy\nspectrums and correlation functions. And we show that the dynamical quantum\nphase transition of the effective 1D transverse Ising model can be simulated.\nWith carefully designed procedures for producing the dynamical quantum phase\ntransition of the 1D transverse Ising model from a Mott insulator, the rate\nfunction of the recurrence probability to the ground-state manifold shows the\nsame nonanalyticality at periodic time points as theory predicts. Our results\nmay give some inspirations on simulating 1D transverse Ising model with\nsuperexchange interaction and exploring its dynamical quantum phase transition\nin experiment."
    },
    {
        "anchor": "Confinement-Induced Resonances in Low-Dimensional Quantum Systems: We report on the observation of confinement-induced resonances in strongly\ninteracting quantum-gas systems with tunable interactions for one- and\ntwo-dimensional geometry. Atom-atom scattering is substantially modified when\nthe s-wave scattering length approaches the length scale associated with the\ntight transversal confinement, leading to characteristic loss and heating\nsignatures. Upon introducing an anisotropy for the transversal confinement we\nobserve a splitting of the confinement-induced resonance. With increasing\nanisotropy additional resonances appear. In the limit of a two-dimensional\nsystem we find that one resonance persists.",
        "positive": "Induced supersolidity in a Dy-Er mixture: Recent experimental realization of the heteronuclear dipolar mixture of Dy\nand Er atoms opens fascinating prospects for creating intriguing novel phases\nin dipolar quantum gases. The experimentally measured value of intra-species\n$s$-wave scattering length of $^{166}$Er condensate in a $^{164}$Dy-$^{166}$Er\nmixture is larger than its intra-species dipolar length, implies that the\n$^{166}$Er condensate itself will not be in a regime of dominated dipole-dipole\ninteraction (DDI). However, we find that the presence of $^{164}$Dy atoms with\nhigh magnetic moment induces droplet nucleation and supersolidity in $^{166}$Er\ncondensate via the long-range and anisotropic inter-species DDI. Remarkably, we\nfind that the imbalance in the magnetic dipole moment combined with its strong\nanisotropic coupling led to the emergence of unique ground state phases. The\nemerging phases include doubly superfluid states, a mixture of insulating\ndroplets and supersolid states, binary supersolids with uniform and alternating\ndomains and a combination of supersolid-superfluid mixed states. We delineate\nthe properties of all these ground state phases and construct a phase diagram.\nWe also explore the dynamical evolution across these phase boundaries via a\nlinear quench of inter-species scattering length. Although we have demonstrated\nthe result for the $^{164}$Dy-$^{166}$Er mixture, our results are generally\nvalid for other dipolar bosonic mixtures of different Dy-Er isotope\ncombinations and may become an important benchmark for future experimental\nscenarios."
    },
    {
        "anchor": "Simulation of non-Abelian lattice gauge fields with a single component\n  gas: We show that non-Abelian lattice gauge fields can be simulated with a single\ncomponent ultra-cold atomic gas in an optical lattice potential. An optical\nlattice can be viewed as a Bravais lattice with a $N$-point basis. An atom\nlocated at different points of the basis can be considered as a {\\it particle}\nin different internal states. The appropriate engineering of tunneling\namplitudes of atoms in an optical lattice allows one to realize U$(N)$ gauge\npotentials and control a mass of {\\it particles} that experience such\nnon-Abelian gauge fields. We provide and analyze a concrete example of an\noptical lattice configuration that allows for simulation of a static U(2) gauge\nmodel with a constant Wilson loop and an adjustable mass of {\\it particles}. In\nparticular, we observe that the non-zero mass creates large conductive gaps in\nthe energy spectrum, which could be important in the experimental detection of\nthe transverse Hall conductivity.",
        "positive": "Loschmidt Echo of Far-From-Equilibrium Fermionic Superfluids: Non-analyticities in the logarithm of the Loschmidt echo, known as dynamical\nquantum phase transitions [DQPTs], are a recently introduced attempt to\nclassify the myriad of possible phenomena which can occur in far from\nequilibrium closed quantum systems. In this work, we analytically investigate\nthe Loschmidt echo in nonequilibrium $s$-wave and topological $p_x+ip_y$\nfermionic superfluids. We find that the presence of non-analyticities in the\necho is not invariant under global rotations of the superfluid phase. We remedy\nthis deficiency by introducing a more general notion of a grand canonical\nLoschmidt echo. Overall, our study shows that DQPTs are not a good indicator\nfor the long time dynamics of an interacting system. In particular, there are\nno DQPTs to tell apart distinct dynamical phases of quenched BCS\nsuperconductors. Nevertheless, they can signal a quench induced change in the\ntopology and also keep track of solitons emerging from unstable stationary\nstates of a BCS superconductor."
    },
    {
        "anchor": "Dipole modes of a trapped bosonic mixture: Fate of the sum-rule approach: We present a general discussion of the dipole modes of a heteronuclear\nbosonic mixture in a harmonic trap by comparing the prediction of the sum-rule\napproach with full Gross-Pitaevskii (GP) calculations. Yet in the range of\ninteraction in which the mixture is miscible and stable at the mean field\nlevel, $g_{12}^2<g_{11}g_{22}$, we find that there are regimes where the sum\nrules displays significant deviations from the GP solution. We provide an\ninterpretation for this behavior in terms of the Ehrenfest approach, which we\nshow to be equivalent to the sum-rule approach for dipole excitations.",
        "positive": "Emergent light crystal from frustration and pump engineering: We demonstrate how pump engineering drives the emergence of\nfrustration-induced quasi-long-range order in a low-dimensional photonic cavity\narray. We consider a Lieb chain of nonlinear cavities as described by the\nBose-Hubbard model and featuring a photonic flat band in the single-particle\nspectrum. Incoherent pumping of the Lieb lattice leads to a photonic\ndensity-wave which manifests an algebraic decay of correlations with twice the\nperiod of the lattice unit cell. This work opens up new directions for the\nemergence of strongly-correlated phases in quantum optical frustrated systems\nthrough pump design."
    },
    {
        "anchor": "The Efimov effect for heteronuclear three-body systems at positive\n  scattering length and finite temperature: We study the recombination process of three atoms scattering into an atom and\ndiatomic molecule in heteronuclear mixtures of ultracold atomic gases with\nlarge and positive interspecies scattering length at finite temperature. We\ncalculate the temperature dependence of the three-body recombination rates by\nextracting universal scaling functions that parametrize the energy dependence\nof the scattering matrix. We compare our results to experimental data for the\n40K-87Rb mixture and make a prediction for 6Li-87Rb. We find that contributions\nfrom higher partial wave channels significantly impact the total rate and, in\nsystems with particularly large mass imbalance, can even obliterate the\nrecombination minima associated with the Efimov effect.",
        "positive": "Collective oscillation modes of a superfluid Bose-Fermi mixture: In this work, we present a theoretical study for the collective oscillation\nmodes, i.e. quadrupole, radial and axial mode, of a mixture of Bose and Fermi\nsuperfluids in the crossover from a Bardeen-Cooper-Schrieffer (BCS) superfluid\nto a molecular Bose-Einstein condensate (BEC) in harmonic trapping potentials\nwith cylindrical symmetry of experimental interest. To this end, we start from\nthe coupled superfluid hydrodynamic equations for the dynamics of Bose-Fermi\nsuperfluid mixtures and use the scaling theory that has been developed for a\ncoupled system. The collective oscillation modes of Bose-Fermi superfluid\nmixtures are found to crucially depend on the overlap integrals of the spatial\nderivations of density profiles of the Bose and Fermi superfluids at\nequilibrium. We not only present the explicit expressions for the overlap\ndensity integrals, as well as the frequencies of the collective modes provided\nthat the effective Bose-Fermi coupling is weak, but also test the valid regimes\nof the analytical approximations by numerical calculations in realistic\nexperimental conditions. In the presence of a repulsive Bose-Fermi interaction,\nwe find that the frequencies of the three collective modes of the Bose and\nFermi superfluids are all upshifted, and the change speeds of the frequency\nshifts in the BCS-BEC crossover can characterize the different groundstate\nphases of the Bose-Fermi superfluid mixtures for different trap geometries."
    },
    {
        "anchor": "Periodically-driven quantum systems: Effective Hamiltonians and\n  engineered gauge fields: Driving a quantum system periodically in time can profoundly alter its\nlong-time dynamics and trigger topological order. Such schemes are particularly\npromising for generating non-trivial energy bands and gauge structures in\nquantum-matter systems. Here, we develop a general formalism that captures the\nessential features ruling the dynamics: the effective Hamiltonian, but also the\neffects related to the initial phase of the modulation and the micro-motion.\nThis framework allows for the identification of driving schemes, based on\ngeneral N-step modulations, which lead to configurations relevant for quantum\nsimulation. In particular, we explore methods to generate synthetic spin-orbit\ncouplings and magnetic fields in cold-atom setups.",
        "positive": "Quantum walks in commensurate off-diagonal Aubry-Andr\u00e9-Harper model: Due to the topological nature of Aubry-Andr\\'{e}-Harper (AAH) model, exotic\nedge states have been found existing in one-dimensional periodic and\nquasiperiodic lattices. In this article, we investigate continuous-time quantum\nwalks of identical particles initially located on either edge of commensurate\nAAH lattices in detail. It is shown that the quantum walker is delocalized\namong the whole lattice until the strength of periodic modulation is strong\nenough. The inverse participation ratios (IPRs) for all of the eigenstates are\ncalculated. It is found that the localization properties of the quantum walker\nis mainly determined by the IPRs of the topologically protected edge states.\nMore interestingly, the edge states are shown to have an exotic\n`\\emph{repulsion}' effect on quantum walkers initiated from the lattice sites\ninside the bulk. Furthermore, we examine the role of nearest-neighbour\ninteraction on the quantum walks of two identical fermions. Clear enhancement\nof the `\\emph{repulsion}' effect by strong interaction has been shown."
    },
    {
        "anchor": "Intrinsic Photoconductivity of Ultracold Fermions in Optical Lattices: We report on the experimental observation of an analog to a persistent\nalternating photocurrent in an ultracold gas of fermionic atoms in an optical\nlattice. The dynamics is induced and sustained by an external harmonic\nconfinement. While particles in the excited band exhibit long-lived\noscillations with a momentum dependent frequency a strikingly different\nbehavior is observed for holes in the lowest band. An initial fast collapse is\nfollowed by subsequent periodic revivals. Both observations are fully explained\nby mapping the system onto a nonlinear pendulum.",
        "positive": "Thermal crossover, transition, and coexistence in Fermi polaronic\n  spectroscopies: We investigate thermal evolution of radio-frequency (RF) spectra of a\nspin-imbalanced Fermi gas near a Feshbach resonance in which degenerate\nFermi-polaron and classical Boltzmann-gas regimes emerge in the low-temperature\nand high-temperature limits, respectively. By using a self-consistent framework\nof strong-coupling diagrammatic approaches, both of the ejection and reserve RF\nspectra available in cold-atom experiments are analyzed. We find a variety of\ntransfers from Fermi polarons to Boltzmann gas such that a thermal crossover\nexpected in the weak-coupling regime is shifted to a sharp transition near\nunitarity and to double-peak coexistence of attractive and repulsive branches\nin the strong-coupling regime. Our theory provides semiquantitative\ndescriptions for a recent experiment on the ejection RF spectroscopy at\nunitarity [Z. Yan {\\it et al}., arXiv:1811.00481v1] and demonstrate that the RF\nspectroscopy is an essential probe to examine effects of strong correlations\nand finite temperature."
    },
    {
        "anchor": "Collective modes of a soliton train in a Fermi superfluid: We characterize the collective modes of a soliton train in a\nquasi-one-dimensional Fermi superfluid, using a mean-field formalism. In\naddition to the expected Goldstone and Higgs modes, we find novel long-lived\ngapped modes associated with oscillations of the soliton cores. The soliton\ntrain has an instability that depends strongly on the interaction strength and\nthe spacing of solitons. It can be stabilized by filling each soliton with an\nunpaired fermion, thus forming a commensurate Fulde-Ferrell-Larkin-Ovchinnikov\n(FFLO) phase. We find that such a state is always dynamically stable, which\npaves the way for realizing long-lived FFLO states in experiments via phase\nimprinting.",
        "positive": "Diffusion quantum Monte Carlo calculation of the quasiparticle effective\n  mass of the two-dimensional homogeneous electron gas: The quasiparticle effective mass is a key quantity in the physics of electron\ngases, describing the renormalization of the electron mass due to\nelectron-electron interactions. Two-dimensional electron gases are of\nfundamental importance in semiconductor physics, and there have been numerous\nexperimental and theoretical attempts to determine the quasiparticle effective\nmass in these systems. In this work we report quantum Monte Carlo results for\nthe quasiparticle effective mass of a two-dimensional homogeneous electron gas.\nOur calculations differ from previous quantum Monte Carlo work in that much\nsmaller statistical error bars have been achieved, allowing for an improved\ntreatment of finite-size effects. In some cases we have also been able to use\nlarger system sizes than previous calculations."
    },
    {
        "anchor": "Supersolid phase of Three-dimensional spin and hardcore-boson models: We study the stability of solid- and supersolid (SS) phases of a\nthree-dimensional spin- and a hardcore-Bose-Hubbard models on a body-centered\ncubic lattice. To see the quantum effects on the stability of the SS phase, we\nmodel the vacancies (interstitials) introduced in the solid, which are believed\nresponsible for the appearance of the SS phase, by spinwave bosons and adopt\nthe interaction between the condensed bosons as a criterion. A repulsive nature\nof the low-energy effective interaction is the necessary condition for a\nsecond-order solid-SS transition and, when this condition is met, normally the\nSS phase is expected. In calculating the effective interaction, we use\nexpansions from the semiclassical- (i.e. large-S) and the Ising limit combined\nwith the ladder approximation. The impact of quantum fluctuations crucially\ndepends on the energy of the solid phase and that of the superfluid phase at\nhalf filling. As an application to 4He, we study the parameter region in the\nvicinity of the fitting parameter set given by Liu and Fisher. For this\nparameters set, quantum fluctuations at the second order in 1/S destabilize the\nsolid phase, which is supposed to be stable within the mean field theory.",
        "positive": "Multidimensional hybrid Bose-Einstein condensates stabilized by\n  lower-dimensional spin-orbit coupling: We show that attractive spinor Bose-Einstein condensates under the action of\nspin-orbit coupling (SOC) and Zeeman splitting form self-sustained stable two-\nand three-dimensional (2D and 3D) states in free space, even when SOC acts in a\nlower-dimensional form. We find that two-dimensional states are stabilized by\none-dimensional (1D) SOC in a broad range of chemical potentials, for atom\nnumbers (or norm of the spinor wavefunction) exceeding a threshold value, which\nstrongly depends on the SOC strength and vanishes at a critical point. The\nzero-threshold point is a boundary between single-peaked and striped states,\nrealizing hybrids combining 2D and 1D structural features. In a vicinity of\nsuch point, an asymptotic equation describing the bifurcation of the solitons\nfrom the linear spectrum is derived and investigated analytically. We show that\nstriped 3D solitary states are as well stabilized by 2D SOC, albeit in a\nlimited range of chemical potentials and norms."
    },
    {
        "anchor": "Pairing and condensation in a resonant Bose-Fermi mixture: We study by diagrammatic methods a mixture of single-component bosons and\nfermions, with boson-fermion coupling tuned by a Fano-Feshbach resonance. For\nincreasing coupling, the growing boson-fermion pairing correlations\nprogressively reduce the boson condensation temperature and make it eventually\nvanish at a critical coupling. Such quantum critical point depends very weakly\non the population imbalance and for vanishing boson densities coincides with\nthat found for the polaron-molecule transition in a strongly imbalanced Fermi\ngas, thus bridging two quite distinct physical systems.",
        "positive": "Topological transition from superuid vortex rings to isolated knots and\n  links: Knots and links are fundamental topological objects play a key role in both\nclassical and quantum fluids. In this research, we propose a novel scheme to\ngenerate torus vortex knots and links through the reconnections of vortex rings\nperturbed by Kelvin waves in trapped Bose-Einstein condensates. We observe a\nnew phenomenon in a confined superfluid system in which the transfer of\nhelicity between knots/links and coils can occur in both directions with\ndifferent pathways. The pathways of topology transition can be controlled\nthrough designing specific initial states. The generation of a knot or link can\nbe achieved by setting the parity of the Kelvin wave number. The stability of\nknots/links can be improved greatly with tunable parameters, including the\nideal relative angle and the minimal distance between the initial vortex rings."
    },
    {
        "anchor": "Feasibility analysis of a proposed test of quantum gravity via novel\n  optical magnetometry in xenon: We present an analysis of the sensitivity limits of a proposed experimental\nsearch for quantum gravity, using a novel approach based on optical\nmagnetometry in the noble gas isotope $^{129}$Xe. The analysis relies on a\ngeneral uncertainty principle model that is consistent with most formulations\nof quantum gravity theory, where the canonical uncertainty relations are\nmodified by a leading-order correction term that is linear in momentum. In\nturn, this correction modifies the magnetic moment of the spin-polarized\n$^{129}$Xe atoms that are immersed in a magnetic field in the proposed\nexperiment, which results in a velocity-dependent variation of their Larmour\nfrequency, that is detected via two-photon laser spectroscopy. The thermal\ndistribution of atomic velocities, in conjunction with the Doppler effect, is\nused to scan the interrogating laser over different atomic velocities, and\nsearch for a corresponding variation in their Larmor frequencies. We show that\nthe existing bounds on the leading-order quantum gravity correction can be\nimproved by $10^{7}$ with existing technology, where another factor of $10^{2}$\nis possible with near-future technical capabilities.",
        "positive": "Hyperspherical explicitly correlated Gaussian approach for few-body\n  systems with finite angular momentum: Within the hyperspherical framework, the solution of the time-independent\nSchroedinger equation for a n-particle system is divided into two steps, the\nsolution of a Schroedinger like equation in the hyperangular degrees of freedom\nand the solution of a set of coupled Schroedinger like hyperradial equations.\nThe solutions to the former provide effective potentials and coupling matrix\nelements that enter into the latter set of equations. This paper develops a\ntheoretical framework to determine the effective potentials, as well as the\nassociated coupling matrix elements, for few-body systems with finite angular\nmomentum L=1 and negative and positive parity. The hyperangular channel\nfunctions are expanded in terms of explicitly correlated Gaussian basis\nfunctions and relatively compact expressions for the matrix elements are\nderived. The developed formalism is applicable to any n; however, for n greater\nor equal to 6, the computational demands are likely beyond present-day\ncomputational capabilities. A number of calculations relevant to cold atom\nphysics are presented, demonstrating that the developed approach provides a\ncomputationally efficient means to solving four-body bound and scattering\nproblems with finite angular momentum on powerful desktop computers. Details\nregarding the implementation are discussed."
    },
    {
        "anchor": "Phase Diagrams of Antiferromagnetic Spin-1 Bosons on Square Optical\n  Lattice with the Quadratic Zeeman Effect: We study the quadratic Zeeman effect (QZE) in a system of antiferromagnetic\nspin-1 bosons on a square lattice and derive the ground-state phase diagrams by\nmeans of quantum Monte Carlo simulations and mean field treatment. The QZE\nimbalances the populations of the magnetic sublevels $\\sigma=\\pm1$ and\n$\\sigma=0$, and therefore affects the magnetic and mobility properties of the\nphases. Both methods show that the tip of the even Mott lobes, stabilized by\nsinglet state, is destroyed when turning on the QZE, thus leaving the space to\nthe superfluid phase. Contrariwise, the tips of odd Mott lobes remain\nunaffected. Therefore, the Mott-superfluid transition with even filling\nstrongly depends on the strength of the QZE, and we show that the QZE can act\nas a control parameter for this transition at fixed hopping. Using quantum\nMonte Carlo simulations, we elucidate the nature of the phase transitions and\nexamine in detail the nematic order: the first-order Mott-superfluid transition\nwith even filling observed in the absence of QZE becomes second order for weak\nQZE, in contradistinction to our mean-field results which predict a first-order\ntransition in a larger range of QZE. Furthermore, a spin nematic order with\ndirector along the $z$ axis is found in the odd Mott lobes and in the\nsuperfluid phase for energetically favored $\\sigma=\\pm1$ states. In the\nsuperfluid phase with even filling, the $xy$ components of the nematic director\nremain finite only for moderate QZE.",
        "positive": "A kinetic model for very low temperature dilute Bose gases: We review recent work on a kinetic model for very low temperature dilute Bose\ngases. The brief derivation, expressions for hydrodynamics modes, and the\ncomparison with a experiment on a BEC of $^{87}{\\rm Rb}$ atoms are presented."
    },
    {
        "anchor": "Many-body effects of a two-dimensional electron gas on trion-polaritons: We theoretically investigate the trion-polariton and the effects of a\ntwo-dimensional electron gas on its single particle properties. Focussing on\nthe trion and exciton transitions, we set up an effective model and calculate\nthe optical absorption of the quantum well containing the 2DEG. Including the\nlight-matter coupling, we compute the Rabi splitting and polariton lineshapes\nas a function of 2DEG density. The role of finite temperature is investigated.\nThe spatial extent of the trion-polariton is also calculated. We find a\nsubstantial charge build-up at short distances as long as the Rabi frequency\ndoes not exceed the trion binding energy. All our calculations take into\naccount the Fermi-edge singularity and the Anderson orthogonality catastrophe.",
        "positive": "Magnetic crystals and helical liquids in alkaline-earth fermionic gases: The joint action of a synthetic gauge potential and of atomic contact\nrepulsion in a one-dimensional alkaline-earth(-like) fermionic gas with nuclear\nspin I leads to the existence of a hierarchy of fractional insulating and\nconducting states with intriguing properties. We unveil the existence and the\nfeatures of those phases by means of both analytical bosonization techniques\nand numerical methods based on the density-matrix renormalization group\nalgorithm. In particular, we show that the gapless phases can support helical\nmodes, whereas the gapped states, which appear under certain conditions, are\ncharacterised both by density and magnetic order. Several distinct features\nemerge solely for spin I larger than 1/2, thus making their study with\ncold-atoms unique. We will finally argue that these states are related to the\nproperties of an unconventional fractional quantum Hall effect in the\nthin-torus limit. The properties of this hierarchy of states can be\nexperimentally studied in state-of-the-art cold-atom laboratories."
    },
    {
        "anchor": "Modulational instability in binary spin-orbit-coupled Bose-Einstein\n  condensates: We study modulation instability (MI) of flat states in two-component\nspin-orbit-coupled (SOC) Bose-Einstein condensates (BECs) in the framework of\ncoupled Gross-Pitaevskii equations for two components of the pseudospinor wave\nfunction. The analysis is performed for equal densities of the components.\nEffects of the interaction parameters, Rabi coupling, and SOC on the MI are\ninvestigated. In particular, the results demonstrate that the SOC strongly\nalters the commonly known MI (immiscibility) condition, $g_{12} > g_{1} g_{2}$,\nfor the binary superfluid with coefficients $g_{1,2}$ and $g_{12}$ of the\nintra- and interspecies repulsive interactions. In fact, the binary BEC is\nalways subject to the MI under the action of the SOC, which implies that the\nground state of the system is plausibly represented by a striped phase.",
        "positive": "Thermodynamics of Dipolar Chain Systems: The thermodynamics of a quantum system of layers containing perpendicularly\noriented dipolar molecules is studied within an oscillator approximation for\nboth bosonic and fermionic species. The system is assumed to be built from\nchains with one molecule in each layer. We consider the effects of the\nintralayer repulsion and quantum statistical requirements in systems with more\nthan one chain. Specifically, we consider the case of two chains and solve the\nproblem analytically within the harmonic Hamiltonian approach which is accurate\nfor large dipole moments. The case of three chains is calculated numerically.\nOur findings indicate that thermodynamic observables, such as the heat\ncapacity, can be used to probe the signatures of the intralayer interaction\nbetween chains. This should be relevant for near future experiments on polar\nmolecules with strong dipole moments."
    },
    {
        "anchor": "Competition and interplay between topology and quasi-periodic disorder\n  in Thouless pumping of ultracold atoms: Robustness against perturbations lies at the heart of topological phenomena.\nIf, however, a perturbation such as disorder becomes dominant, it may cause a\ntopological phase transition between topologically non-trivial and trivial\nphases. Here we experimentally reveal the competition and interplay between\ntopology and quasi-periodic disorder in a Thouless pump realized with ultracold\natoms in an optical lattice, by creating a quasi-periodic potential from weak\nto strong regimes in a controllable manner. We demonstrate a disorder-induced\npumping in which the presence of quasi-periodic disorder can induce a\nnon-trivial pump for a specific pumping sequence, while no pump is observed in\nthe clean limit. Our highly controllable system, which can also\nstraightforwardly incorporate interatomic interaction, could be a unique\nplatform for studying various disorder-related novel effects in a wide range of\ntopological quantum phenomena.",
        "positive": "Measurement of phase fluctuations of Bose-Einstein condensates in an\n  optical lattice: Even at zero temperature, there exist phase fluctuations associated with an\narray of Bose-Einstein condensates confined in a one-dimensional optical\nlattice. We demonstrate a method to measure the phase fluctuations based on the\nFourier spectrum of the atomic density for a condensate released from the\noptical lattice. The phase variance is extracted from the relative intensities\nof different peaks in the Fourier spectrum. This method works even for high\nlattice strength where interference peaks disappear in the atomic density\ndistribution."
    },
    {
        "anchor": "Confined p-band Bose-Einstein condensates: We study bosonic atoms on the p-band of a two dimensional optical square\nlattice in the presence of a confining trapping potential. Using a mean-field\napproach, we show how the anisotropic tunneling for p-band particles affects\nthe cloud of condensed atoms by characterizing the ground state density and the\ncoherence properties of the atomic states both between sites and atomic\nflavors. In contrast to the usual results based on the local density\napproximation, the atomic density can become anisotropic. This anisotropic\neffect is especially pronounced in the limit of weak atom-atom interactions and\nof weak lattice amplitudes, i.e. when the properties of the ground state are\nmainly driven by the kinetic energies. We also investigate how the trap\ninfluences known properties of the non-trapped case. In particular, we focus on\nthe behavior of the anti-ferromagnetic vortex-antivortex order, which for the\nconfined system, is shown to disappear at the edges of the condensed cloud.",
        "positive": "Stability of vortices in exciton-polariton condensates with\n  spin-orbital-angular-momentum coupling: The existence and dynamics of stable quantized vortices is an important\nsubject of quantum many-body physics. Spin-orbital-angular-momentum coupling\n(SOAMC), a special type of spin-orbit coupling, has been experimentally\nachieved to create vortices in atomic Bose-Einstein condensate (BEC). Here, we\ngeneralize the concept of SOAMC to a two-component polariton BEC and analyze\nthe emergence and configuration of vortices under a finite-size circular\npumping. We discover that the regular configuration of vortex lattices induced\nby a finite-size circular pump is significantly distorted by the spatially\ndependent Raman coupling of SOAMC. Meanwhile, a vortex induced by SOAMC located\nat the center of the polariton cloud remains stable and pinned in place. When\nthe Raman coupling is sufficiently strong, the polariton BEC with SOAMC is torn\napart to become fragmented."
    },
    {
        "anchor": "Effects of disorder upon transport and Anderson Localization in a\n  finite, two dimensional Bose gas: Anderson localization in a two-dimensional ultracold Bose-gas has been\ndemonstrated experimentally. Atoms were released within a dumbbell-shaped\noptical trap, where the channel of variable aspect ratio provided the only path\nfor particles to travel between source and drain reservoirs. This channel can\nbe populated with columnar (repulsive) optical potential spikes of square cross\nsection with arbitrary pattern. These spikes constitute impurities, the\nscattering centres for the otherwise free propagation of the particles. This\ngeometry does not allow for classical potential trapping which can be hard to\nexclude in other experimental setups. Here we add further theoretical evidence\nfor Anderson localization in this system by comparing the transport processes\nwithin a regular and a random pattern of impurities. It is demonstrated that\nthe transport within randomly distributed impurities is suppressed and the\ncorresponding localization length becomes shorter than the channel length.\nHowever, if an equal density of impurities are distributed in a regular manner,\nthe transport is only modestly disturbed. This observation corroborates the\nconclusions of the experimental observation: the localization is indeed\nattributed to the disorder. Beyond analysing the density distribution and the\nlocalization length, we also calculate a quantum `impedance' exhibiting\nqualitatively different behaviour for regular and random impurity patterns.",
        "positive": "Tan's contact of a harmonically trapped one-dimensional Bose gas:\n  strong-coupling expansion and conjectural approach at arbitrary interactions: We study Tan's contact, i.e. the coefficient of the high-momentum tails of\nthe momentum distribution at leading order, for an interacting one-dimensional\nBose gas subjected to a harmonic confinement. Using a strong-coupling\nsystematic expansion of the ground-state energy of the homogeneous system\nstemming from the Bethe-Ansatz solution, together with the local-density\napproximation, we obtain the strong-coupling expansion for Tan's contact of the\nharmonically trapped gas. Also, we use a very accurate conjecture for the\nground-state energy of the homogeneous system to obtain an approximate\nexpression for Tan's contact for arbitrary interaction strength, thus\nestimating the accuracy of the strong-coupling expansion. Our results are\nrelevant for ongoing experiments with ultracold atomic gases."
    },
    {
        "anchor": "Quantum point spread function for imaging trapped few-body systems with\n  a quantum gas microscope: Quantum gas microscopes, which image the atomic occupations in an optical\nlattice, have opened a new avenue to the exploration of many-body lattice\nsystems. Imaging trapped systems after freezing the density distribution by\nramping up a pinning lattice leads, however, to a distortion of the original\ndensity distribution, especially when its structures are on the scale of the\npinning lattice spacing. We show that this dynamics can be described by a\nfilter, which we call in analogy to classical optics a quantum point spread\nfunction. Using a machine learning approach, we demonstrate via several\nexperimentally relevant setups that a suitable deconvolution allows for the\nreconstruction of the original density distribution. These findings are both of\nfundamental interest for the theory of imaging and of immediate importance for\ncurrent quantum gas experiments.",
        "positive": "Far-from-equilibrium field theory of many-body quantum spin systems:\n  Prethermalization and relaxation of spin spiral states in three dimensions: We study theoretically the far-from-equilibrium relaxation dynamics of spin\nspiral states in the three dimensional isotropic Heisenberg model. The\ninvestigated problem serves as an archetype for understanding quantum dynamics\nof isolated many-body systems in the vicinity of a spontaneously broken\ncontinuous symmetry. We present a field-theoretical formalism that\nsystematically improves on mean-field for describing the real-time quantum\ndynamics of generic spin-1/2 systems. This is achieved by mapping spins to\nMajorana fermions followed by a 1/N expansion of the resulting two-particle\nirreducible (2PI) effective action. Our analysis reveals rich\nfluctuation-induced relaxation dynamics in the unitary evolution of spin spiral\nstates. In particular, we find the sudden appearance of long-lived\nprethermalized plateaus with diverging lifetimes as the spiral winding is tuned\ntoward the thermodynamically stable ferro- or antiferromagnetic phases. The\nemerging prethermalized states are characterized by different bosonic modes\nbeing thermally populated at different effective temperatures, and by a\nhierarchical relaxation process reminiscent of glassy systems. Spin-spin\ncorrelators found by solving the non-equilibrium Bethe-Salpeter equation\nprovide further insight into the dynamic formation of correlations, the fate of\nunstable collective modes, and the emergence of fluctuation-dissipation\nrelations. Our predictions can be verified experimentally using recent\nrealizations of spin spiral states with ultracold atoms in a quantum gas\nmicroscope [S. Hild, et al. Phys. Rev. Lett. 113, 147205 (2014)]."
    },
    {
        "anchor": "Fulde-Ferrell Superfluids without Spin Imbalance in Driven Optical\n  Lattices: Spin-imbalanced ultracold Fermi gases have been widely studied recently as a\nplatform for exploring the long-sought Fulde-Ferrell-Larkin-Ovchinnikov\nsuperfluid phases, but so far conclusive evidence has not been found. Here we\npropose to realize an Fulde-Ferrell (FF) superfluid without spin imbalance in a\nthree-dimensional fermionic cold atom optical lattice, where $s$- and\n$p$-orbital bands of the lattice are coupled by another weak moving optical\nlattice. Such coupling leads to a spin-independent asymmetric Fermi surface,\nwhich, together with the $s$-wave scattering interaction between two spins,\nyields an FF type of superfluid pairing. Unlike traditional schemes, our\nproposal does not rely on the spin imbalance (or an equivalent Zeeman field) to\ninduce the Fermi surface mismatch and provides a completely new route for\nrealizing FF superfluids.",
        "positive": "Confinement-induced resonance in quasi-one-dimensional systems under\n  transversely anisotropic confinement: We theoretically investigate the confinement-induced resonance for\nquasi-one-dimensional quan- tum systems under transversely anisotropic\nconfinement, using a two-body s-wave scattering model in the zero-energy\ncollision limit. We predict a single resonance for any transverse anisotropy,\nwhose position shows a slight downshift with increasing anisotropy. We compare\nour prediction with the recent experimental result by Haller et al. [Phys. Rev.\nLett. 104, 153203 (2010)], in which two resonances are observed in the presence\nof transverse anisotropy. The discrepancy between theory and experiment remains\nto be resolved."
    },
    {
        "anchor": "Shock waves in colliding Fermi gases at finite temperature: We study the formation and the dynamics of a shock wave originating from the\ncollision between two ultracold clouds of strongly interacting fermions as\nobserved at a lower temperature in an experiment by Joseph et al. [Phys. Rev.\nLett. 106, 150401 (2011)]. We use the Boltzmann equation within the\ntest-particle method to describe the evolution of the system in the normal\nphase. We also show a direct comparison with the hydrodynamic approach and\ninsist on the necessity of including a shear viscosity and a thermal\nconductivity term in the equations to prevent unphysical behavior from taking\nplace.",
        "positive": "Localization of collisionally inhomogeneous condensates in a bichromatic\n  optical lattice: By direct numerical simulation and variational solution of the\n  Gross-Pitaevskii equation, we studied the stationary and dynamic\ncharacteristics of a cigar-shaped, localized, collisionally inhomogeneous\nBose-Einstein condensate trapped in a one-dimensional bichromatic\nquasi-periodic optical-lattice potential, as used in a recent experiment on the\nlocalization of a Bose-Einstein condensate\n  [Roati et al., Nature (London) {\\bf 453}, 895 (2008)]. The effective\npotential characterizing the spatially modulated nonlinearity is obtained. It\nis found that the collisional inhomogeneity has influence not only on the\ncentral region but also on the tail of the Bose-Einstein condensate. The\ninfluence depends on the sign and value of the spatially modulated nonlinearity\ncoefficient. We also demonstrate the stability of the stationary localized\nstat$ performing a standard linear stability analysis. Where possible, the\nnumerical results are shown to be in good agreement with the variational\nresults."
    },
    {
        "anchor": "Controlled flow of excitations in a ring-shaped network of Rydberg atoms: Highly excited Rydberg atoms are a powerful platform for quantum simulation\nand information processing. Here, we propose atomic ring networks to study\nchiral currents of Rydberg excitations. The currents are controlled by a phase\npattern imprinted via a Raman scheme and can persist even in the presence of\ndephasing. Depending on the interplay between the Rabi coupling of Rydberg\nstates and the dipole-dipole atom interaction, the current shows markedly\ndifferent features. The excitations propagate with a velocity displaying a\ncharacteristic peak in time, reflecting the chiral nature of the current. We\nfind that the time-averaged current in a quench behaves similarly to the\nground-state current. This analysis paves the way for the development of new\nmethods to transport information in atomic networks.",
        "positive": "Analysis of the buildup of spatiotemporal correlations and their bounds\n  outside of the light cone: In non-relativistic quantum theories the Lieb-Robinson bound defines an\neffective light cone with exponentially small tails outside of it. In this work\nwe use it to derive a bound for the time evolution of the correlation function\nof two local disjoint observables if the initial state has a power-law decay.\nWe show that the exponent of the power-law of the bound is identical to the\ninitial (equilibrium) decay. We explicitly verify this result by studying the\nfull dynamics of the susceptibilities and correlations in the exactly solvable\nLuttinger model after a sudden quench from the non-interacting to the\ninteracting model."
    },
    {
        "anchor": "Optically guided linear Mach Zehnder atom interferometer: We demonstrate a horizontal, linearly guided Mach Zehnder atom interferometer\nin an optical waveguide. Intended as a proof-of-principle experiment, the\ninterferometer utilises a Bose-Einstein condensate in the magnetically\ninsensitive |F=1,mF=0> state of Rubidium-87 as an acceleration sensitive test\nmass. We achieve a modest sensitivity to acceleration of da = 7x10^-4 m/s^2.\nOur fringe visibility is as high as 38% in this optically guided atom\ninterferometer. We observe a time-of-flight in the waveguide of over half a\nsecond, demonstrating the utility of our optical guide for future sensors.",
        "positive": "How to Directly Measure Floquet Topological Invariants in Optical\n  Lattices: The classification of topological Floquet systems with time-periodic\nHamiltonians transcends that of static systems. For example, spinless fermions\nin periodically driven two-dimensional lattices are not completely\ncharacterized by the Chern numbers of the quasienergy bands, but rather by a\nset of winding numbers associated with the quasienergy gaps. We propose a\nscheme for measuring these winding numbers in a system of fermionic cold atoms\nin a periodically driven optical lattice efficiently and directly. It is based\non the construction of a one-parameter family of experimentally feasible\ndrives, continuously connecting the Floquet system of interest to a trivial\nreference system. The winding numbers are then determined by the identification\nand the tomography of the band-touching singularities occurring on the way. As\na byproduct, we also propose a method for probing spectral properties of time\nevolution operators via a time analog of crystallography."
    },
    {
        "anchor": "Dynamical quantum Cherenkov transition of fast impurities in quantum\n  liquids: The challenge of understanding the dynamics of a mobile impurity in an\ninteracting quantum many-body medium comes from the necessity of including\nentanglement between the impurity and excited states of the environment in a\nwide range of energy scales. In this paper, we investigate the motion of a\nfinite mass impurity injected into a three-dimensional quantum Bose fluid as it\nstarts shedding Bogoliubov excitations. We uncover a transition in the dynamics\nas the impurity's velocity crosses a critical value which depends on the\nstrength of the interaction between the impurity and bosons as well as the\nimpurity's recoil energy. We find that in injection experiments, the two\nregimes differ not only in the character of the impurity velocity abatement,\nbut also exhibit qualitative differences in the Loschmidt echo, density ripples\nexcited in the BEC, and momentum distribution of scattered bosonic particles.\nThe transition is a manifestation of a dynamical quantum Cherenkov effect, and\nshould be experimentally observable with ultracold atoms using Ramsey\ninterferometry, RF spectroscopy, absorption imaging, and time-of-flight\nimaging.",
        "positive": "Long-lived non-thermal states realized by atom losses in one-dimensional\n  quasi-condensates: We investigate the cooling produced by a loss process non selective in energy\non a one-dimensional (1D) Bose gas with repulsive contact interactions in the\nquasi-condensate regime. By performing nonlinear classical field calculations\nfor a homogeneous system, we show that the gas reaches a non-thermal state\nwhere different modes have acquired different temperatures. After losses have\nbeen turned off, this state is robust with respect to the nonlinear dynamics,\ndescribed by the Gross-Pitaevskii equation. We argue that the integrability of\nthe Gross-Pitaevskii equation is linked to the existence of such long-lived\nnon-thermal states, and illustrate this by showing that such states are not\nsupported within a non-integrable model of two coupled 1D gases of different\nmasses. We go beyond a classical field analysis, taking into account the\nquantum noise introduced by the discreteness of losses, and show that the\nnon-thermal state is still produced and its non-thermal character is even\nenhanced. Finally, we extend the discussion to gases trapped in a harmonic\npotential and present experimental observations of a long-lived non-thermal\nstate within a trapped 1D quasi-condensate following an atom loss process."
    },
    {
        "anchor": "Finite-size corrections to quantized particle transport in topological\n  charge pumps: We investigate the quantization of adiabatic charge transport in the\ninsulating ground state of finite systems. Topological charge pumps are used in\nexperiments as an indicator of topological order. In the thermodynamic limit\nthe transport can be related to a topological Berry phase and is thus strictly\nquantized. This is no longer true for finite systems. We derive finite-size\ncorrections to the transport both for non-interacting and interacting systems\nand relate them to analytic properties of the single- and many-body Berry\ncurvature. We find that they depend on the details of experimental realizations\nof the pumps. While they can be non-negligible even in large systems, a proper\nchoice of the pumping protocol can suppress these corrections.",
        "positive": "Dynamics in multiple-well Bose-Einstein condensates: We study the dynamics of three-dimensional weakly linked Bose-Einstein\ncondensates using a multimode model with an effective interaction parameter.\nThe system is confined by a ring-shaped four-well trapping potential. By\nconstructing a two-mode Hamiltonian in a reduced highly symmetric phase space,\nwe examine the periodic orbits and calculate their time periods both in the\nself-trapping and Josephson regimes. The dynamics in the vicinity of the\nreduced phase space is investigated by means of a Floquet multiplier analysis,\nfinding regions of different linear stability and analyzing their implications\non the exact dynamics. The numerical exploration in an extended region of the\nphase space demonstrates that two-mode tools can also be useful for performing\na partition of the space in different regimes. Comparisons with\nGross-Pitaevskii simulations confirm these findings and emphasize the\nimportance of properly determining the effective on-site interaction parameter\ngoverning the multimode dynamics."
    },
    {
        "anchor": "Bifurcations, stability, and mode evolution in segregated condensate\n  mixtures: We present new features of low energy Bogoliubov quasiparticle excitations of\na two component Bose-Einstein condensate (TBEC) in quasi-2D geometry at zero\ntemperature using Hartree-Fock-Bogoliubov (HFB). We, in particular, consider\nthe TBECs of $^{133}$Cs~-$^{87}$Rb and $^{85}$Rb~-$^{87}$Rb, and show specific\nfeatures in the low energy excitation spectrum as a function of the interaction\nstrength. For $^{85}$Rb~-$^{87}$Rb TBEC, the appearance of a new zero energy\nmode is observed. Whereas for $^{133}$Cs~-$^{87}$Rb TBEC we report a\nbifurcation of the softened Kohn mode at the point of transition from miscible\nto immiscible domain. The lower energy mode, after the bifurcation, goes soft\nand becomes a new Goldstone mode of the system.",
        "positive": "Composite cores of monopoles and Alice rings in spin-2 Bose-Einstein\n  condensates: We show that energy relaxation causes a point defect in the uniaxial-nematic\nphase of a spin-2 Bose-Einstein condensate to deform into a spin-Alice ring\nthat exhibits a composite core structure with distinct topology at short and\nlong distances from the singular line. An outer biaxial-nematic core exhibits a\nspin half-quantum vortex structure with a uniaxial-nematic inner core. By\nnumerical simulation we demonstrate a dynamical oscillation between the\nspin-Alice ring and a split-core hedgehog configuration via the appearance of\nferromagnetic rings with associated vorticity inside an extended core region.\nWe further show that a similar dynamics is exhibited by a spin-Alice ring\nsurrounding a spin-vortex line resulting from the relaxation of a monopole\nsituated on a spin-vortex line in the biaxial-nematic phase. In the cyclic\nphase similar states are shown instead to form extended phase-mixing cores\ncontaining rings with fractional mass circulation or cores whose spatial shape\nreflect the order-parameter symmetry of cyclic inner core, depending on the\ninitial configuration."
    },
    {
        "anchor": "Synthetic tensor gauge fields: Synthetic gauge fields have provided physicists with a unique tool to explore\na wide range of fundamentally important phenomena in physics. However, only\nsynthetic vector gauge fields are currently available in experiments. The study\nof tensor gauge fields, which play a vital role in fracton phase of matter,\nremains purely theoretical. Here, we propose schemes to realize synthetic\ntensor gauge fields using techniques readily available in laboratories. A\nlattice tilted by a strong linear potential and a weak quadratic potential\nnaturally yields a rank-2 electric field for a lineon formed by a particle-hole\npair. Such a rank-2 electric field leads to a new type of Bloch oscillations,\nwhere neither a single particle nor a single hole responds but a lineon\nvibrates. A synthetic vector gauge field carrying a position-dependent phase\ncould also be implemented to produce the same synthetic tensor gauge field for\na lineon. In higher dimensions, the interplay between interactions and vector\ngauge potentials imprints a phase to the ring-exchange interaction and thus\ngenerates synthetic tensor gauge fields for planons. Such tensor gauge fields\nmake it possible to realize a dipolar Harper-Hofstadter model in laboratories.",
        "positive": "Free-fermion Entanglement Spectrum through Wannier Interpolation: Quantum Entanglement plays an ubiquitous role in theoretical physics, from\nthe characterization of novel phases of matter to understanding the efficacy of\nnumerical algorithms. As such, there have been extensive studies on the\nentanglement spectrum (ES) of free-fermion systems, particularly in the\nrelation between its spectral flow and topological charge pumping. However, far\nless has been studied about the \\emph{spacing} between adjacent entanglement\neigenenergies, which affects the truncation error in numerical computations\ninvolving Matrix Product States (MPS) or Projected Entangled-Pair States\n(PEPS). In this paper, we shall hence derive asymptotic bounds for the ES\nspacings through an interpolation argument that utilizes known results on\nWannier function decay. For translation invariant systems, the Entanglement\nenergies are shown to decay at a rate monotonically related to the complex gap\nbetween the filled and occupied bands. This interpolation also demonstrates the\none-to-one correspondence between the ES and the edge states. Our results also\nprovide asymptotic bounds for the eigenvalue distribution of certain types of\nBlock Toeplitz matrices common in physics, even for those not arising from\nentanglement calculations."
    },
    {
        "anchor": "Phase-locking matter-wave interferometer of vortex states: Matter-wave interferometer of ultracold atoms with different linear momenta\nhas been extensively studied in theory and experiment. The vortex matter-wave\ninterferometer with different angular momenta is applicable as a quantum sensor\nfor measuring the rotation, interatomic interaction, geometric phase, etc. Here\nwe report the first experimental realization of a vortex matter-wave\ninterferometer by coherently transferring the optical angular momentum to an\nultracold Bose condensate. After producing a lossless interferometer with atoms\nonly populating the two spin states, we demonstrate that the phase difference\nbetween the interferences in the two spin states is locked on $\\pi$. We also\ndemonstrate the robustness of this out-of-phase relation, which is independent\nof the angular-momentum difference between the two interfering vortex states,\nconstituent of Raman optical fields and expansion of the condensate. The\nexperimental results agree well with the calculation from the unitary evolution\nof wave packet in quantum mechanics. This work opens a new way to build a\nquantum sensor and measure the atomic correlation in quantum gases.",
        "positive": "Enhancement of spin coherence in a spin-1 Bose condensate by dynamical\n  decoupling approaches: We present a theoretical investigation on the enhancement of the spin\ncoherence with periodic, concatenated, or Uhrig dynamical decoupling $N$-pulse\nsequences in a $^{87}$Rb spin-1 Bose condensate, where the intrinsic dynamical\ninstability in such a ferromagnetically interacting condensate causes spin\ndecoherence and eventually leads to a multiple spatial-domain structure or a\nspin texture. Our results show that all the three sequences successfully\nenhance the spin coherence by pushing the wave vector of the most unstable mode\nin the condensate to a larger value. Among the three sequences with the same\nnumber of pulses, the concatenated one shows the best performance in preserving\nthe spin coherence. Interestingly, we find that all the three sequences exactly\nfollow the same enhancement law, $k_- T^{1/2} = c$, with $k_-$ the wave vector\nof the most unstable mode, $T$ the sequence period, and $c$ a\nsequence-dependent constant. Such a law between $k_-$ and $T$ is also derived\nanalytically for an attractive scalar Bose condensate subjecting to a periodic\ndynamical decoupling sequence."
    },
    {
        "anchor": "Time-resolved observation of competing attractive and repulsive\n  short-range correlations in strongly interacting Fermi gases: We exploit a time-resolved pump-probe spectroscopic technique to study the\nout-of-equilibrium dynamics of an ultracold two-component Fermi gas,\nselectively quenched to strong repulsion along the upper branch of a broad\nFeshbach resonance. For critical interactions, we find the rapid growth of\nshort-range anti-correlations between repulsive fermions to initially overcome\nconcurrent pairing processes. At longer evolution times, these two competing\nmechanisms appear to macroscopically coexist in a short-range correlated state\nof fermions and pairs, unforeseen thus far. Our work provides fundamental\ninsights into the fate of a repulsive Fermi gas, and offers new perspectives\ntowards the exploration of complex dynamical regimes of fermionic matter.",
        "positive": "Critical slowdown of non-equilibrium polaron dynamics: We study the quantum dynamics of a single impurity following its sudden\nimmersion into a Bose-Einstein condensate. The ensuing formation of the Bose\npolaron in this general setting can be seen as impurity decoherence driven by\nthe condensate, which we describe within a master equation approach. We derive\nrigorous analytical results for this decoherence dynamics, and thereby reveal\ndistinct stages of its evolution from a universal stretched exponential initial\nrelaxation to the final approach to equilibrium. The associated polaron\nformation time exhibits a strong dependence on the impurity speed and is found\nto undergo a critical slowdown around the speed of sound of the condensate.\nThis rich non-equilibrium behaviour of quantum impurities is of direct\nrelevance to recent cold atom experiments, in which Bose polarons are created\nby a sudden quench of the impurity-bath interaction."
    },
    {
        "anchor": "Phase diagram of the SU$(3)$ Fermi-Hubbard model with next-neighbor\n  interactions: We explore the zero-temperature phase diagram of a one-dimensional gas\ncomposed of three-color fermions, which interact locally and with their next\nneighbors. Using the density matrix renormalization group method and\nconsidering one-third filling, we characterize the ground state for several\nvalues of the parameters, finding diverse phases, namely: phase separation,\nspin density wave, pairing phase, a metallic phase, two different\ncharge-density waves, and a non-separable state with modulation of charge. We\nshow that the von Neumann block entropy and the fidelity susceptibility are\nuseful for estimating the borders between the phases.",
        "positive": "Magnon Condensation and Spin Superfluidity: We consider the phenomenon of Bose-Einstein condensation of quasi-equilibrium\nmagnons which leads to a spin superfluidity, the coherent quantum transfer of\nmagnetization in magnetic materials. These phenomena are beyond the classical\nLandau-Lifshitz-Gilbert paradigm. The critical conditions for excited magnon\ndensity for ferro- and antiferromagnets, bulk and thin films are estimated and\ndiscussed. The BEC should occur in the antiferromagnetic hematite at much lower\nexcited magnon density compared to the ferromagnetic YIG."
    },
    {
        "anchor": "Non-integrable dynamics of matter-wave solitons in a density-dependent\n  gauge theory: We study interactions between bright matter-wave solitons which acquire\nchiral transport dynamics due to an optically-induced density-dependent gauge\npotential. Through numerical simulations, we find that the collision dynamics\nfeature several non-integrable phenomena, from inelastic collisions including\npopulation transfer and radiation losses to short-lived bound states and\nsoliton fission. An effective quasi-particle model for the interaction between\nthe solitons is derived by means of a variational approximation, which\ndemonstrates that the inelastic nature of the collision arises from a coupling\nof the gauge field to velocities of the solitons. In addition, we derive a set\nof interaction potentials which show that the influence of the gauge field\nappears as a short-range potential, that can give rise to both attractive and\nrepulsive interactions.",
        "positive": "Topological states in two-dimensional optical lattices: We present a general analysis of two-dimensional optical lattice models that\ngive rise to topologically non-trivial insulating states. We identify the main\ningredients of the lattice models that are responsible for the non-trivial\ntopological character and argue that such states can be realized within a large\nfamily of realistic optical lattice Hamiltonians with cold atoms. We focus our\nquantitative analysis on the properties of topological states with broken\ntime-reversal symmetry specific to cold-atom settings. In particular, we\nanalyze finite-size effects, multi-orbital phenomena that give rise to a\nvariety of distinct topological states and transitions between them, the\ndependence on the trap geometry, and most importantly, the behavior of the edge\nstates for different types of soft and hard boundaries. Furthermore, we\ndemonstrate the possibility of experimentally detecting the topological states\nthrough light Bragg scattering of the edge and bulk states."
    },
    {
        "anchor": "Viability of rotation sensing using phonon interferometry in\n  Bose-Einstein condensates: We demonstrate the use of a ring-shaped Bose-Einstein condensate as a\nrotation sensor by measuring the interference between two counter-propagating\nphonon modes imprinted azimuthally around the ring. We observe rapid decay of\nthe excitations, quantified by quality factors of at most $Q \\approx 27$. We\nnumerically model our experiment using the c-field methodology, allowing us to\nestimate the parameters that maximise the performance of our sensor. We explore\nthe damping mechanisms underlying the observed phonon decay, and identify two\ndistinct Landau scattering processes that each dominate at different driving\namplitudes and temperatures. Our simulations reveal that $Q$ is limited by\nstrong damping of phonons even in the zero temperature limit. We perform an\nexperimental proof-of-principle rotation measurement using persistent currents\nimprinted around the ring. We demonstrate a rotation sensitivity of up to\n$\\Delta \\Omega \\approx 0.3$ rad/s from a single image, with a theoretically\nachievable value of $\\Delta \\Omega \\approx 0.04$ rad/s in the atomic shot-noise\nlimit. This is a significant improvement over the shot-noise-limited $\\Delta\n\\Omega \\approx 1$ rad/s sensitivity obtained by Marti et al. [Phys. Rev. A 91,\n013602 (2015)] for a similar setup.",
        "positive": "Superfluid Stiffness of a Driven Dissipative Condensate with Disorder: Observations of macroscopic quantum coherence in driven systems, e.g.\npolariton condensates, have strongly stimulated experimental as well as\ntheoretical efforts during the last decade. We address the question of whether\na driven quantum condensate is a superfluid, allowing for the effects of\ndisorder and its non-equilibrium nature. We predict that for spatial dimensions\nd<4 the superfluid stiffness vanishes once the condensate exceeds a critical\nsize, and treat in detail the case d=2. Thus a non-equilibrium condensate is\nnot a superfluid in the thermodynamic limit, even for weak disorder, although\nsuperfluid behavior would persist in small systems."
    },
    {
        "anchor": "Sudden interaction quench in the quantum sine-Gordon model: We study a sudden interaction quench in the weak-coupling regime of the\nquantum sine-Gordon model. The real time dynamics of the bosonic mode\noccupation numbers is calculated using the flow equation method. While we\ncannot prove results for the asymptotic long time limit, we can establish the\nexistence of an extended regime in time where the mode occupation numbers relax\nto twice their equilibrium values. This factor two indicates a non-equilibrium\ndistribution and is a universal feature of weak interaction quenches. The\nweak-coupling quantum sine-Gordon model therefore turns out to be on the\nborderline between thermalization and non-thermalization.",
        "positive": "Density functional theory for strongly-correlated bosonic and fermionic\n  ultracold dipolar and ionic gases: We introduce a density functional formalism to study the ground-state\nproperties of strongly-correlated dipolar and ionic ultracold bosonic and\nfermionic gases, based on the self-consistent combination of the weak and the\nstrong coupling limits. Contrary to conventional density functional approaches,\nour formalism does not require a previous calculation of the interacting\nhomogeneous gas, and it is thus very suitable to treat systems with tunable\nlong-range interactions. Due to its asymptotic exactness in the regime of\nstrong correlation, the formalism works for systems in which standard\nmean-field theories fail."
    },
    {
        "anchor": "Magnetically generated spin-orbit coupling for ultracold atoms: We present a new technique for producing two- and three-dimensional\nRashba-type spin-orbit couplings for ultracold atoms without involving light.\nThe method relies on a sequence of pulsed inhomogeneous magnetic fields\nimprinting suitable phase gradients on the atoms. For sufficiently short pulse\ndurations, the time-averaged Hamiltonian well approximates the Rashba\nHamiltonian. Higher order corrections to the energy spectrum are calculated\nexactly for spin-1/2 and perturbatively for higher spins. The pulse sequence\ndoes not modify the form of rotationally symmetric atom-atom interactions.\nFinally, we present a straightforward implementation of this pulse sequence on\nan atom chip.",
        "positive": "Controlled ordering of topological charges in an exciton-polariton chain: We demonstrate, experimentally and theoretically, controlled loading of an\nexciton-polariton vortex chain into a 1D array of trapping potentials.\nSwitching between two types of vortex chains, with topological charges of the\nsame or alternating sign, is realised by means of appropriate shaping of an\nincoherent pump beam that drives the system to the regime of bosonic\ncondensation. In analogy to spin chains, these vortex sequences realise either\na \"ferromagnetic\" or an \"anti-ferromagnetic\" order, whereby the role of spin is\nplayed by the orbital angular momentum. The \"ferromagnetic\" ordering of\nvortices is associated with the formation of a persistent chiral current. Our\nresults pave the way for controlled creation of nontrivial distributions of\norbital angular momentum and topological order in a periodic exciton-polariton\nsystem."
    },
    {
        "anchor": "Modeling atom interferometry experiments with Bose-Einstein condensates\n  in power-law potentials: Recent atom interferometry (AI) experiments involving Bose--Einstein\ncondensates (BECs) have been conducted under extreme conditions of volume and\ninterrogation time. Numerical solution of the standard mean-field theory\napplied to these experiments presents a nearly intractable challenge. We\npresent an approximate variational model that provides rapid approximate\nsolutions of the rotating-frame Gross--Pitaevskii equation for a power-law\npotential. This model is well-suited to the design and analysis of AI\nexperiments involving BECs that are split and later recombined to form an\ninterference pattern. We derive the equations of motion of the variational\nparameters for this model and illustrate how the model can be applied to the\nsequence of steps in a recent AI experiment where BECs were used to implement a\ndual-Sagnac atom interferometer rotation sensor. We use this model to\ninvestigate the impact of finite-size and interaction effects on the\nsingle-Sagnac-interferometer phase shift.",
        "positive": "Simulation of XXZ Spin Models using Sideband Transitions in Trapped\n  Bosonic Gases: We theoretically propose and experimentally demonstrate the use of motional\nsidebands in a trapped ensemble of $^{87}$Rb atoms to engineer tunable\nlong-range XXZ spin models. We benchmark our simulator by probing a\nferromagnetic to paramagnetic dynamical phase transition in the\nLipkin-Meshkov-Glick (LMG) model, a collective XXZ model plus additional\ntransverse and longitudinal fields, via Rabi spectroscopy. We experimentally\nreconstruct the boundary between the dynamical phases, which is in good\nagreement with mean-field theoretical predictions. Our work introduces new\npossibilities in quantum simulation of anisotropic spin-spin interactions and\nquantum metrology enhanced by many-body entanglement."
    },
    {
        "anchor": "Vortices in a toroidal Bose-Einstein condensate with a rotating weak\n  link: Motivated by a recent experiment [K.C. Wright et. al. Phys. Rev. Lett. 110,\n025302 (2013)], we investigate deterministic discontinuous jumps between\nquantized circulation states in a toroidally trapped Bose-Einstein condensate.\nThese phase slips are induced by vortex excitations created by a rotating weak\nlink. We analyze influence of a localized condensate density depletion and\natomic superflows, governed by the rotating barrier, on the energetic and\ndynamical stability of the vortices in the ring-shaped condensate. We simulate\nin a three-dimensional dissipative mean field model the dynamics of the\ncondensate using parameters similar to the experimental conditions. Moreover,\nwe consider the dynamics of the stirred condensate far beyond the\nexperimentally explored region and reveal surprising manifestations of complex\nvortex dynamics.",
        "positive": "Synchronization transition in dipole-coupled two-level systems with\n  positional disorder: We study the decoherence dynamics of dipole-coupled two-level quantum systems\nin Ramsey-type experiments. We focus on large networks of two-level systems,\nconfined to two spatial dimensions and with positional disorder giving rise to\ndisordered dipolar couplings. This setting is relevant for modeling the\ndecoherence dynamics of the rotational excitations of polar molecules confined\nto deep optical lattices, where disorder arises from the random filling of\nlattice sites with occupation probability $p$. We show that the decoherence\ndynamics exhibits a phase transition at a critical filling $p_c\\simeq 0.15$.\nFor $p<p_c$ the dynamics is disorder-dominated and the Ramsey interference\nsignal decays on a timescale $T_2 \\propto p^{-3/2}$. For $p>p_c$ the dipolar\ninteractions dominate the disorder, and the system behaves as a collective\nspin-ordered phase, representing synchronization of the two-level systems and\npersistent Ramsey oscillations with divergent $T_2$ for large systems. For a\nfinite number of two-level systems, $N$, the spin-ordered phase at $p> p_c$\nundergoes a crossover to a collective spin-squeezed state on a timescale\n$\\tau_{\\rm sq} \\propto \\sqrt{N}$. We develop a self-consistent mean-field\ntheory that is capable of capturing the synchronization transition at $p_c$,\nand provide an intuitive theoretical picture that describes the phase\ntransition in the long-time dynamics. We also show that the decoherence\ndynamics appear to be ergodic in the vicinity of $p_c$, the long-time behaviour\nbeing well described by the predictions of equilibrium thermodynamics. The\nresults are supported by the results of exact diagonalization studies of small\nsystems."
    },
    {
        "anchor": "Thermodynamics of spin-orbit coupled bosons in two dimensions from\n  complex Langevin: We investigate the thermal properties of interacting spin-orbit coupled\nbosons with contact interactions in two spatial dimensions. To that end, we\nimplement the complex Langevin method, motivated by the appearance of a sign\nproblem, on a square lattice with periodic boundary conditions. We calculate\nthe density equation of state non-perturbatively in a range of spin-orbit\ncouplings and chemical potentials. Our results show that mean-field solutions\ntend to underestimate the average density, especially for stronger values of\nthe spin-orbit coupling. Additionally, the finite nature of the simulation\nvolume induces the formation of pseudo-condensates. These have been observed to\nbe destroyed by the spin-orbit interactions.",
        "positive": "Superfluid phases of spin-1 bosons in cubic optical lattice: We analyze theoretically the emergence of different superfluid phases of\nspin-1 bosons in a three-dimensional cubic optical lattice by generalizing the\nrecently developed Ginzburg-Landau theory for the Bose-Hubbard model to a\nspinor Bose gas. In particular at zero temperature, our theory distinguishes\nwithin its validity range between various superfluid phases for an\nanti-ferromagnetic interaction with an external magnetic field. In addition, we\ndetermine that the superfluid-Mott insulator phase transition is of second\norder and that the transitions between the respective superfluid phases with\nanti-ferromagnetic interaction can be both of first and second order."
    },
    {
        "anchor": "Correlations of the upper branch of 1d harmonically trapped\n  two-component Fermi gases: We present highly-accurate energy spectra and eigen functions of small 1d\nharmonically trapped two-component Fermi gases with interspecies\n$\\delta$-function interactions, and analyze the correlations of the so-called\nupper branch (i.e., the branch that describes a repulsive Fermi gas consisting\nof atoms but no molecules) for positive and negative coupling constants.\nChanges of the two-body correlations as a function of the interspecies coupling\nstrength reflect the competition of the interspecies interaction and the\neffective repulsion due to the Pauli exclusion principle, and are interpreted\nas a few-body analog of a transition from a non-magnetic to a magnetic phase.\nMoreover, we show that the eigenstate $\\psi_{\\rm{adia}}$ of the infinitely\nstrongly-interacting system with $|n_1+n_2|>2$ and $|n_1-n_2| < n$ ($n_1$ and\n$n_2$ denote the number of fermions of components 1 and 2, respectively), which\nis reached experimentally by adiabatically changing the system parameters, does\nnot, as previously proposed, coincide with the wave function $\\psi_{\\rm{G}}$\nobtained by applying a generalized Fermi-Fermi mapping function to the eigen\nfunction of the non-interacting single-component Fermi gas.",
        "positive": "Mechanism of Tunneling in Interacting Open Ultracold Few-Boson Systems: We investigate the mechanism in the tunneling dynamics of open ultracold\nfew-boson systems by numerically solving the time-dependent few-boson\nSchr\\\"{o}dinger equation exactly. By starting from a weakly repulsive,\ninitially coherent two-boson system we demonstrate that the decay dynamics\nincorporate fragmentation. The wavefunction of the tunneling state exhibits a\npronounced dynamically-stable pattern which we explain by an analytical model.\nBy studying more bosons and stronger interactions we arrive to the conclusion\nthat the decay by tunneling is not a coherent process and exhibits a wealth of\nphenomena depending on the interaction between the particles."
    },
    {
        "anchor": "Thermal-assisted Anisotropy and Thermal-driven Instability in the\n  Superfluidity state of Two-Species Polar Fermi Gas: We study the superfluid state of two-species heteronuclear Fermi gases with\nisotropic contact and anisotropic long-range dipolar interactions. By\nexplicitly taking account of Fock exchange contribution, we derive\nself-consistent equations describing the pairing states in the system.\nExploiting the symmetry of the system, we developed an efficient way of solving\nthe self-consistent equations by exploiting the symmetries. We find that the\ntemperature tends to increase the anisotropy of the pairing state, which is\nrather counterintuitive. We study the anisotropic properties of the system by\nexamining the angular dependence of the number density distribution, the\nexcitation spectrum and the pair correlation function. The competing effects of\nthe contact interaction and the dipolar interaction upon the anisotropy are\nrevealed. We derive and compute the superfluid mass density $\\rho_{ij}$ for the\nsystem. Astonishingly, we find that $\\rho_{zz}$ becomes negative above some\ncertain temperature $T^*$($T<T_c$), signaling some instability of the system.\nThis suggests that the elusive FFLO state may be observed in experiments, due\nto an anisotropic state with a spontaneously generated superflow.",
        "positive": "Temperature dependence of the contact in a unitary Fermi gas: The contact ${\\cal I}$, introduced by Tan, has emerged as a key parameter\ncharacterizing universal properties of strongly interacting Fermi gases. For\nultracold Fermi gases near a Feshbach resonance, the contact depends upon two\nquantities: the interaction parameter $1/(k_F a)$, where $k_F$ is the Fermi\nwave-vector and $a$ is the $s$-wave scattering length, and the temperature\n$T/T_F$, where $T_F$ is the Fermi temperature. We present the first\nmeasurements of the temperature dependence of the contact in a unitary Fermi\ngas using Bragg spectroscopy. The contact is seen to follow the predicted decay\nwith temperature and shows how pair-correlations at high momentum persist well\nabove the superfluid transition temperature."
    },
    {
        "anchor": "Competing structures in 2D-trapped dipolar gases: We study a system of dipolar molecules confined in a two-dimensional trap and\nsubject to an optical square lattice. The repulsive long-range dipolar\ninteraction $D/r^3$ favors an equilateral triangular arrangement of the\nmolecules, which competes against the square symmetry of the underlying optical\nlattice with lattice constant $b$ and amplitude $V$. We find the minimal-energy\nstates at the commensurate density $n = 1/b^2$ and establish the complete\nsquare-to-triangular transformation pathway of the lattice with decreasing $V$\ninvolving period-doubled, solitonic, and distorted-triangular configurations.",
        "positive": "Probing thermoelectric transport with cold atoms: We propose experimental protocols to reveal thermoelectric and thermal\neffects in the transport properties of ultracold fermionic atoms, using the\ntwo-terminal setup recently realized at ETH. We show in particular that, for\ntwo reservoirs having equal particle numbers but different temperatures\ninitially, the observation of a transient particle number imbalance during\nequilibration is a direct evidence of thermoelectric (off-diagonal) transport\ncoefficients. This is a time-dependent analogue of the Seebeck effect, and a\ncorresponding analogue of the Peltier effect can be proposed. We reveal that in\naddition to the thermoelectric coupling of the constriction a thermoelectric\ncoupling also arises due to the finite dilatation coefficient of the\nreservoirs. We present a theoretical analysis of the protocols, and assess\ntheir feasibility by estimating the corresponding temperature and particle\nnumber imbalances in realistic current experimental conditions."
    },
    {
        "anchor": "Efimov states in Li-Cs mixtures within a minimal model: We use a minimal zero-range model for describing the bound state spectrum of\nthree-body states consisting of two Cesium and one Lithium atom. Using a broad\nFeshbach resonance model for the two-body interactions, we show that recent\nexperimental data can be described surprisingly well for particular values of\nthe three-body parameter that governs the short-range behavior of the atomic\npotentials and is outside the scope of the zero-range model. Studying the\nspectrum as a function of the three-body parameter suggests that the lowest\nstate seen in experiment could be influenced by finite range corrections. We\nalso consider the question of Fermi degeneracy and corresponding Pauli blocking\nof the Lithium atoms on the Efimov states.",
        "positive": "Persisting Meissner state and incommensurate phases of hard-core boson\n  ladders in a flux: The phase diagram of a half-filled hard core boson two-leg ladder in a flux\nis investigated by means of numerical simulations based on the Density Matrix\nRenormalization Group (DMRG) algorithm and bosonization. We calculate\nexperimentally accessible observables such as the momentum distribution, as\nwell as rung current, density wave and bond-order wave correlation functions,\nallowing us to identify the Mott Meissner and Mott Vortex states. We follow the\ntransition from commensurate Meissner to incommensurate Vortex state at\nincreasing interchain hopping till the critical value [Piraud et al. Phys. Rev.\nB v. 91, p. 140406 (2015)] above which the Meissner state is stable at any\nflux. For flux close to $\\pi$, and below the critical hopping, we observe the\nformation of a second incommensuration in the Mott Vortex state that could be\ndetectable in current experiments."
    },
    {
        "anchor": "Generalized cold-atom simulators for vacuum decay: Cold-atom analogue experiments are a promising new tool for studying\nrelativistic vacuum decay, allowing us to empirically probe early-Universe\ntheories in the laboratory. However, existing analogue proposals place\nstringent requirements on the atomic scattering lengths that are challenging to\nrealize experimentally. Here we generalize these proposals and show that any\nstable mixture between two states of a bosonic isotope can be used as a\nrelativistic analogue. This greatly expands the range of suitable experimental\nsetups, and will thus expedite efforts to study vacuum decay with cold atoms.",
        "positive": "General ultracold scattering formalism with isotropic spin orbit\n  coupling: A general treatment of ultracold two-body scattering in the presence of\nisotropic spin-orbit coupling (SOC) is presented. Owing to the mixing of\ndifferent partial wave channels, scattering with SOC is in general a coupled\nmultichannel problem. A systematic method is introduced to analytically solve a\nclass of coupled differential equations by recasting the coupled channel\nproblem as a simple eigenvalue problem. The exact Green's matrix in the\npresence of SOC is found, which readily gives the scattering solutions for any\ntwo identical particles in any total angular momentum subspace having\nnegligible center of mass momentum. Application of this formalism to two spin-1\nbosons shows the ubiquitous low energy threshold behavior for systems with\nisotropic SOC. A modified threshold behavior shows up, which does not occur for\nthe spin-orbit coupled spin-1/2 system. We also confirm the parity-breaking\nmechanism for the spontaneous emergency of handedness, that has been proposed\nby Duan et. al. [1]. Additionally, a two-body bound state is found for any\narbitrarily small and negative scattering length. Our study sheds light on the\nfew-body side of SOC physics and provides one step towards understanding\nultracold scattering in a non-Abelian gauge field."
    },
    {
        "anchor": "$\\mathbb{Z}_N$ gauge theories coupled to topological fermions: QED$_2$\n  with a quantum-mechanical $\u03b8$ angle: We present a detailed study of the topological Schwinger model [Phys. Rev. D\n99, 014503 (2019)], which describes (1+1) quantum electrodynamics of an Abelian\n$U(1)$ gauge field coupled to a symmetry-protected topological matter sector,\nby means of a class of $\\mathbb{Z}_N$ lattice gauge theories. Employing\ndensity-matrix renormalization group techniques that exactly implement Gauss'\nlaw, we show that these models host a correlated topological phase for\ndifferent values of $N$, where fermion correlations arise through\ninter-particle interactions mediated by the gauge field. Moreover, by a careful\nfinite-size scaling, we show that this phase is stable in the large-$N$ limit,\nand that the phase boundaries are in accordance to bosonization predictions of\nthe $U(1)$ topological Schwinger model. Our results demonstrate that\n$\\mathbb{Z}_N$ finite-dimensional gauge groups offer a practical route for an\nefficient classical simulation of equilibrium properties of electromagnetism\nwith topological fermions. Additionally, we describe a scheme for the quantum\nsimulation of a topological Schwinger model exploiting spin-changing collisions\nin boson-fermion mixtures of ultra-cold atoms in optical lattices. Although\ntechnically challenging, this quantum simulation would provide an alternative\nto classical density-matrix renormalization group techniques, providing also an\nefficient route to explore real-time non-equilibrium phenomena.",
        "positive": "Exact closed-form analytic wave functions in two dimensions:\n  Contact-interacting fermionic spinful ultracold atoms in a rapidly rotating\n  trap: Exact two-dimensional analytic wave functions for an arbitrary number $N$ of\ncontact-interacting lowest-Landau-level (LLL) spinful fermions are derived with\nthe use of combined numerical and symbolic computational approaches via\nanalysis of exact Hamiltonian numerical diagonalization data. Closed-form\nanalytic expressions are presented for two families of zero-interaction-energy\nstates at given total angular momentum and total spin $0 \\leq S \\leq N/2$ in\nthe neighborhood of the $\\nu=1$ filling, covering the range from the maximum\ndensity droplet to the first quasihole. Our theoretical predictions for\nhigher-order spatial and momentum correlations reveal intrinsic polygonal,\nmulti-ring crystalline-type structures, which can be tested with ultracold-atom\nexperiments in rapidly rotating traps, simulating quantum Hall physics\n(including quantum LLL skyrmions)."
    },
    {
        "anchor": "Excitations and impurity dynamics in a fermionic Mott insulator with\n  nearest-neighbor interactions: We study analytically and with the numerical time-evolving block decimation\nmethod the dynamics of an impurity in a bath of spinless fermions with\nnearest-neighbor interactions in a one-dimensional lattice. The bath is in a\nMott insulator state with alternating sites occupied and the impurity interacts\nwith the bath by repulsive on-site interactions. We find that when the\nmagnitudes of the on-site and nearest-neighbor interactions are close to each\nother, the system shows excitations of two qualitatively distinct types. For\nthe first type, a domain wall and an anti-domain wall of density propagate in\nopposite directions, while the impurity stays at the initial position. For the\nsecond one, the impurity is bound to the anti-domain wall while the domain wall\npropagates, an excitation where the impurity and bath are closely coupled.",
        "positive": "Nonlinear quantum model for atomic Josephson junctions with one and two\n  bosonic species: We study atomic Josephson junctions (AJJs) with one and two bosonic species\nconfined by a double-well potential. Proceeding from the second quantized\nHamiltonian, we show that it is possible to describe the zero-temperature AJJs\nmicroscopic dynamics by means of extended Bose-Hubbard (EBH) models, which\ninclude usually-neglected nonlinear terms. Within the mean-field approximation,\nthe Heisenberg equations derived from such two-mode models provide a\ndescription of AJJs macroscopic dynamics in terms of ordinary differential\nequations (ODEs). We discuss the possibility to distinguish the Rabi,\nJosephson, and Fock regimes, in terms of the macroscopic parameters which\nappear in the EBH Hamiltonians and, then, in the ODEs. We compare the\npredictions for the relative populations of the Bose gases atoms in the two\nwells obtained from the numerical solutions of the two-mode ODEs, with those\nderiving from the direct numerical integration of the Gross-Pitaevskii\nequations (GPEs). Our investigations shows that the nonlinear terms of the ODEs\nare crucial to achieve a good agreement between ODEs and GPEs approaches, and\nin particular to give quantitative predictions of the self-trapping regime."
    },
    {
        "anchor": "Realizing the Haldane Phase with Bosons in Optical Lattices: We analyze an experimentally realizable model of bosons in a zig-zag optical\nlattice, showing that by rapidly modulating the magnetic field one can tune\ninteraction parameters and realize an analog of the Haldane phase. We explain\nhow quantum gas microscopy can be used to detect this phase's non-local string\norder and its topological edge states. We model the detection process. We also\nfind that this model can display supersolid correlations, but argue that they\nonly occur at parameter values which would be challenging to realize in an\nexperiment.",
        "positive": "Level rearrangement in exotic-atom-like three-body systems: We study systems of three bosons bound by a long-range interaction\nsupplemented by a short-range potential of variable strength. This generalizes\nthe usual two-body exotic atoms where the Coulomb interaction is modified by\nnuclear forces at short distances. The energy shift due to the short-range part\nof the interaction combines two-body terms similar to the ones entering the\nTrueman-Deser formula, and three-body contributions. A sudden variation of the\nenergy levels is observed near the coupling thresholds of the short-range\npotential. But the patterns of rearrangement are significantly modified as\ncompared to the two-body case."
    },
    {
        "anchor": "Topological Creutz Ladder in a Resonantly Shaken 1D Optical Lattice: We report the experimental realization of a topological Creutz ladder for\nultracold fermionic atoms in a resonantly driven 1D optical lattice. The\ntwo-leg ladder consists of the two lowest orbital states of the optical lattice\nand the cross inter-leg links are generated via two-photon resonant coupling\nbetween the orbitals by periodic lattice shaking. The characteristic\npseudo-spin winding in the topologically non-trivial bands of the ladder system\nis demonstrated using momentum-resolved Ramsey-type interferometric\nmeasurements. We discuss a two-tone driving method to extend the inter-leg link\ncontrol and propose a topological charge pumping scheme for the Creutz ladder\nsystem.",
        "positive": "Self-oscillating pump in a topological dissipative atom-cavity system: Pumps are transport mechanisms in which direct currents result from a cyclic\nevolution of the potential. As Thouless has shown, the pumping process can have\ntopological origins, when considering the motion of quantum particles in\nspatially and temporally periodic potentials. However, the periodic evolution\nthat drives these pumps has always been assumed to be imparted from outside, as\nwas the case in the experimental systems studied so far. Here we report on an\nemergent mechanism for pumping in a quantum gas coupled to an optical\nresonator, where we observe a particle current without applying a periodic\ndrive. The pumping potential experienced by the atoms is formed by the\nself-consistent cavity field interfering with the static laser field driving\nthe atoms. Due to dissipation, the cavity field evolves between its two\nquadratures, each corresponding to a different centrosymmetric crystal\nconfiguration. This self-oscillation results in a time-periodic potential\nanalogous to that describing the transport of electrons in topological\ntight-binding models, like the paradigmatic Rice-Mele pump. In the experiment,\nwe directly follow the evolution by measuring the phase winding of the cavity\nfield with respect to the driving field and observing the atomic motion\nin-situ. The discovered mechanism combines the dynamics of topological and open\nsystems, and features characteristics of continuous dissipative time crystals."
    },
    {
        "anchor": "Persistent currents in rings of ultracold fermionic atoms: We have produced persistent currents of ultracold fermionic atoms trapped in\na ring, with lifetimes greater than 10 seconds in the strongly-interacting\nregime. These currents remain stable well into the BCS regime at sufficiently\nlow temperature. We drive a circulating BCS superfluid into the normal phase\nand back by changing the interaction strength and find that the probability for\nquantized superflow to reappear is remarkably insensitive to the time spent in\nthe normal phase and the minimum interaction strength. After ruling out\nspontaneous current formation for our experimental conditions, we argue that\nthe reappearance of superflow is due to weak damping of normal currents in this\nlimit. These results establish that ultracold fermionic atoms with tunable\ninteractions can be used to create matter-wave circuits similar to those\npreviously created with weakly-interacting bosonic atoms.",
        "positive": "Variational self-consistent theory for trapped Bose gases at finite\n  temperature: We apply the time-dependent variational principle of Balian-V\\'en\\'eroni to a\nsystem of self-interacting trapped bosons at finite temperature. The method\nleads to a set of coupled non-linear time dependent equations for the\ncondensate density, the thermal cloud and the anomalous density. We solve\nnumerically these equations in the static case for a harmonic trap. We analyze\nthe various densities as functions of the radial distance and the temperature.\nWe find an overall good qualitative agreement with recent experiments as well\nas with the results of many theoretical groups. We also discuss the behavior of\nthe anomalous density at low temperatures owing to its importance to account\nfor many-body effects."
    },
    {
        "anchor": "Optimal temperature estimation in polariton Bose-Einstein Condensate: Improving the measurement precision of temperature is very important and\nchallenging, especially in the low temperature range. Based on the existence of\ninvariant subspaces during the polariton thermalization, we propose a new way\nto enhance the measurement precision of the low temperature and obtain Landau\nbound to avoid that the measurement uncertainty of the temperature diverges as\nthe temperature approaches zero. The measurement precision of the low\ntemperature increases significantly with the number of polariton states. In\norder to resist the dissipation, the incoherent pumping is necessary for\nobtaining the information of the temperature encoded in the steady state. It\nshould be noted that too strong incoherent pumping is wasteful due to that the\nquantum Fisher information of the temperature becomes less and less dependent\non the total number of the polaritons.",
        "positive": "Instabilities of interacting matter waves in optical lattices with\n  Floquet driving: We experimentally investigate the stability of a quantum gas with repulsive\ninteractions in an optical 1D lattice subjected to periodic driving.\nExcitations of the gas in the lowest lattice band are analyzed across the\ncomplete stability diagram, from slow to fast driving frequencies and from weak\nto strong driving strengths. To interpret our results, we expand the\nestablished analysis based on parametric instabilities to include modulational\ninstabilities. Extending the concept of modulational instabilities from static\nto periodically driven systems provides a convenient mapping of the stability\nin a static system to the cases of slow and fast driving. At intermediate\ndriving frequencies, we observe an interesting competition between modulational\nand parametric instabilities. We experimentally confirm the existence of both\ntypes of instabilities in driven systems and probe their properties. Our\nresults allow us to predict stable and unstable parameter regions for the\nminimization of heating in future applications of Floquet driving."
    },
    {
        "anchor": "Vortex nucleation processes in rotating lattices of Bose-Einstein\n  condensates ruled by the on-site phases: We study the nucleation and dynamics of vortices in rotating lattice\npotentials where weakly linked condensates are formed with each condensate\nexhibiting an almost axial symmetry. Due to such a symmetry, the on-site phases\nacquire a linear dependence on the coordinates as a result of the rotation,\nwhich allows us to predict the position of vortices along the low density paths\nthat separate the sites. We first show that, for a system of atoms loaded in a\nfour-site square lattice potential, subject to a constant rotation frequency,\nthe analytical expression that we obtain for the positions of vortices of the\nstationary arrays accurately reproduces the full three-dimensional\nGross-Pitaevskii results. We then study the time-dependent vortex nucleation\nprocess when a linear ramp of the rotation frequency is applied to a lattice\nwith sixteen sites. We develop a formula for the number of nucleated vortices\nwhich turns to have a linear dependence on the rotation frequency with a\nsmaller slope than that of the standard estimate which is valid in absence of\nthe lattice. From time-dependent Gross-Pitaevskii simulations we further find\nthat the on-site populations remain almost constant during the time evolution\ninstead of spreading outwards, as expected from the action of the centrifugal\nforce. Therefore, the time-dependent phase difference between neighboring sites\nacquires a running behavior typical of a self-trapping regime. We finally show\nthat, in accordance with our predictions, this fast phase-difference evolution\nprovokes a rapid vortex motion inside the lattice. Our analytical expressions\nmay be useful for describing other vortex processes in systems with the same\non-site axial symmetry.",
        "positive": "Measuring Energy Differences by BEC Interferometry on a Chip: We investigate the use of a Bose-Einstein condensate trapped on an atom chip\nfor making interferometric measurements of small energy differences. We measure\nand explain the noise in the energy difference of the split condensates, which\nderives from statistical noise in the number difference. We also consider\nsystematic errors. A leading effect is the variation of rf magnetic field in\nthe trap with distance from the wires on the chip surface. This can produce\nenergy differences that are comparable with those due to gravity."
    },
    {
        "anchor": "Instability crossover of helical shear flow in segregated Bose-Einstein\n  condensates: We theoretically study the instability of helical shear flows, in which one\nfluid component flows along the vortex core of the other, in phase-separated\ntwo-component Bose-Einstein condensates at zero temperature. The helical shear\nflows are hydrodynamically classified into two regimes: (1) a helical vortex\nsheet, where the vorticity is localized on the cylindrical interface and the\nstability is described by an effective theory for ripple modes, and (2) a\ncore-flow vortex with the vorticity distributed in the vicinity of the vortex\ncore, where the instability phenomena are dominated only by the\nvortex-characteristic modes: Kelvin and varicose modes. The helical shear-flow\ninstability shows remarkable competition among different types of instabilities\nin the crossover regime between the two regimes.",
        "positive": "On Two-Component Dark-Bright Solitons in Three-dimensional Atomic\n  Bose-Einstein Condensates: In the present work, we revisit two-component Bose-Einstein condensates in\ntheir fully three-dimensional (3d) form. Motivated by earlier studies of\ndark-bright solitons in the 1d case, we explore the stability of these\nstructures in their fully 3d form in two variants. In one the dark soliton is\nplanar and trapping a planar bright (disk) soliton. In the other case, a dark\nspherical shell soliton creates an effective potential in which a bright\nspherical shell of atoms is trapped in the second component. We identify these\nsolutions as numerically exact states (up to a prescribed accuracy) and perform\na Bogolyubov-de Gennes linearization analysis that illustrates that both\nstructures can be dynamically stable in suitable intervals of sufficiently low\nchemical potentials. We corroborate this finding theoretically by analyzing the\nstability via degenerate perturbation theory near the linear limit of the\nsystem. When the solitary waves are found to be unstable, we explore their\ndynamical evolution via direct numerical simulations which, in turn, reveal\nnovel waveforms that are more robust. Finally, using the SO$(2)$ symmetry of\nthe model, we produce multi-dark-bright planar or shell solitons involved in\npairwise oscillatory motion."
    },
    {
        "anchor": "Bubble nucleation in a cold spin 1 gas: Cold atomic gases offer the prospect of simulating the physics of the very\nearly universe in the laboratory. In the condensate phase, the gas is described\nby a field theory with key features of high energy particle theory. This paper\ndescribes a three level system which undergoes a first order phase transition\nthrough the nucleation of bubbles. The theoretical investigation shows bubbles\nnucleating in two dimensions at non-zero temperature. There is good agreement\nbetween the bubble nucleation rates calculated from a Stochastic Projected\nGross-Pitaevskii equation and from a non-perturbative instanton method. When an\noptical box trap is included in the simulations, the bubbles nucleate\npreferentially near the walls of the trap.",
        "positive": "Contact matrix in dilute quantum systems: Contact has been well established as an important quantity to govern dilute\nquantum systems, in which the pairwise correlation at short distance traces a\nbroad range of thermodynamic properties. So far, studies have been focusing on\ncontact in individual angular momentum channels. Here, we point out that, to\nhave a complete description of the pairwise correlation in a general dilute\nquantum systems, contact should be defined as a matrix. Whereas the diagonal\nterms of such matrix include contact of all partial wave scatterings, the\noff-diagonal terms, which elude previous studies in the literature,\ncharacterise the coherence of the asymptotic pairwise wavefunction in the\nangular momentum space and determine important thermodynamic quantities\nincluding the momentum distribution. Contact matrix allows physicists to access\nunexplored connections between short-range correlations and macroscopic quantum\nphenomena. As an example, we show the direct connection between contact matrix\nand order parameters of a superfluid with mixed partial waves."
    },
    {
        "anchor": "Momentum-resolved spectroscopy of a Fermi liquid: We consider a recent momentum-resolved radio-frequency spectroscopy\nexperiment, in which Fermi liquid properties of a strongly interacting atomic\nFermi gas were studied. Here we show that by extending the Brueckner-Goldstone\nmodel, we can formulate a theory that goes beyond basic mean-field theories and\nthat can be used for studying spectroscopies of dilute atomic gases in the\nstrongly interacting regime. The model hosts well-defined quasiparticles and\nworks across a wide range of temperatures and interaction strengths. The theory\nprovides excellent qualitative agreement with the experiment. Comparing the\npredictions of the present theory with the mean-field Bardeen-Cooper-Schrieffer\ntheory yields insights into the role of pair correlations, Tan's contact, and\nthe Hartree mean-field energy shift.",
        "positive": "Ground state and collective excitations of a dipolar Bose-Einstein\n  condensate in a bubble trap: We consider the ground state and the low-lying excitations of dipolar\nBose-Einstein condensates in a bubble trap, i.e., a shell-shaped spherically\nsymmetric confining potential. By means of an appropriate Gaussian ansatz, we\ndetermine the ground-state properties in the case where the particles interact\nby means of both the isotropic and short-range contact and the anisotropic and\nlong-range dipole-dipole potential in the thin-shell limit. Moreover, with the\nground state at hand, we employ the sum-rule approach to study the monopole,\nthe two-, the three-dimensional quadrupole as well as the dipole modes. We find\nsituations in which neither the virial nor Kohn's theorem can be applied. On\ntop of that, we demonstrate the existence of anisotropic particle density\nprofiles, which are absent in the case with repulsive contact interaction only.\nThese significant deviations from what one would typically expect are then\ntraced back to both the anisotropic nature of the dipolar interaction and the\nnovel topology introduced by the bubble trap."
    },
    {
        "anchor": "Suppressing dissipation in a Floquet-Hubbard system: The concept of `Floquet engineering' relies on an external periodic drive to\nrealise novel, effectively static Hamiltonians. This technique is being\nexplored in experimental platforms across physics, including ultracold atoms,\nlaser-driven electron systems, nuclear magnetic resonance, and trapped ions.\nThe key challenge in Floquet engineering is to avoid the uncontrolled\nabsorption of photons from the drive, especially in interacting systems in\nwhich the excitation spectrum becomes effectively dense. The resulting\ndissipative coupling to higher-lying modes, such as the excited bands of an\noptical lattice, has been explored in recent experimental and theoretical\nworks, but the demonstration of a broadly applicable method to mitigate this\neffect is lacking. Here, we show how two-path quantum interference, applied to\nstrongly-correlated fermions in a driven optical lattice, suppresses\ndissipative coupling to higher bands and increases the lifetime of double\noccupancies and spin-correlations by two to three orders of magnitude.\nInterference is achieved by introducing a weak second modulation at twice the\nfundamental driving frequency with a definite relative phase. This technique is\nshown to suppress dissipation in both weakly and strongly interacting regimes\nof a driven Hubbard system, opening an avenue to realising low-temperature\nphases of matter in interacting Floquet systems.",
        "positive": "Single Impurity In Ultracold Fermi Superfluids: The role of impurities as experimental probes in the detection of quantum\nmaterial properties is well appreciated. Here we study the effect of a single\nclassical magnetic impurity in trapped ultracold Fermi superfluids. Depending\non its shape and strength, a magnetic impurity can induce single or multiple\nmid-gap bound states in a superfluid Fermi gas. The multiple mid-gap states\ncould coincide with the development of a Fulde-Ferrell-Larkin-Ovchinnikov\n(FFLO) phase within the superfluid. As an analog of the Scanning Tunneling\nMicroscope, we propose a modified RF spectroscopic method to measure the local\ndensity of states which can be employed to detect these states and other\nquantum phases of cold atoms. A key result of our self consistent Bogoliubov-de\nGennes calculations is that a magnetic impurity can controllably induce an FFLO\nstate at currently accessible experimental parameters."
    },
    {
        "anchor": "Local readout and control of current and kinetic energy operators in\n  optical lattices: Quantum gas microscopes have revolutionized quantum simulations with\nultracold atoms, allowing to measure local observables and snapshots of quantum\nstates. However, measurements so far were mostly carried out in the occupation\nbasis. Here, we demonstrate how all kinetic operators, such as kinetic energy\nor current operators, can be measured and manipulated with single bond\nresolution. Beyond simple expectation values of these observables, the\nsingle-shot measurements allow to access full counting statistics and complex\ncorrelation functions. Our work paves the way for the implementation of\nefficient quantum state tomography and hybrid quantum computing protocols for\nitinerant particles on a lattice. In addition, we demonstrate how site-resolved\nprogrammable potentials enable a spatially-selective, parallel readout in\ndifferent bases as well as the engineering of arbitrary initial states.",
        "positive": "Phonon-mediated Casimir interaction between finite mass impurities: The Casimir effect, a two-body interaction via vacuum fluctuations, is a\nfundamental property of quantum systems. In solid state physics it emerges as a\nlong-range interaction between two impurity atoms via virtual phonons. In the\nclassical limit for the impurity atoms in $D$ dimensions the interaction is\nknown to follow the universal power-law $U(r)\\sim r^{-D}$. However, for finite\nmasses of the impurity atoms on a lattice, it was predicted to be $U(r)\\sim\nr^{-2D-1}$ at large distances. We examine how one power-law can change into\nanother with increase of the impurity mass and in presence of an external\npotential. We provide the exact solution for the system in one-dimension. At\nlarge distances indeed $U(r)\\sim r^{-3}$ for finite impurity masses, while for\nthe infinite impurity masses or in an external potential it crosses over to\n$U(r)\\sim r^{-1}$ . At short distances the Casimir interaction is not universal\nand depends on the impurity mass and the external potential."
    },
    {
        "anchor": "Heterodimer of two distinguishable atoms in a one-dimensional optical\n  lattice: Within the Bose-Hubbard model, we theoretically determine the stationary\nstates of two distinguishable atoms in a one-dimensional optical lattice and\ncompare with the case of two identical bosons. A heterodimer has odd-parity\ndissociated states that do not depend on the interactions with the atoms, and\nthe lattice momenta of the two atomic species may have different averages even\nfor a bound state of the dimer. We discuss two possible methods of detecting\nthe dimer. First, the different distributions of the quasimomenta of the two\nspecies may be observed in suitable time-of-flight experiments. Also, an\nasymmetry in the line shape as a function of the modulation frequency may\nreveal the presence of the odd-parity dissociated states when a heterodimer is\ndissociated by modulating the depth of the optical lattice.",
        "positive": "Number squeezed and fragmented states of strongly interacting bosons in\n  a double well: We present a systematic study of the phenomena of number squeezing and\nfragmentation for a repulsive Bose-Einstein condensate (BEC) in a three\ndimensional double well potential over a range of interaction strengths and\nbarrier heights, including geometries that exhibit appreciable overlap in the\none-body wavefunctions localized in the left and right wells. We compute the\nproperties of the condensate with numerically exact, full dimensional path\nintegral ground state (PIGS) Quantum Monte Carlo simulations and compare with\nresults obtained from using two- and eight-mode truncated basis models. The\ntruncated basis models are found to agree with the numerically exact PIGS\nsimulations for weak interactions, but fail to correctly predict the amount of\nnumber squeezing and fragmentation exhibited by the PIGS simulations for strong\ninteractions. We find that both number squeezing and fragmentation of the BEC\nshow non-monotonic behavior at large values of interaction strength a. The\nnumber squeezing shows a universal scaling with the product of number of\nparticles and interaction strength (Na) but no such universal behavior is found\nfor fragmentation. Detailed analysis shows that the introduction of repulsive\ninteractions not only suppresses number fluctuations to enhance number\nsqueezing, but can also enhance delocalization across wells and tunneling\nbetween wells, each of which may suppress number squeezing. This results in a\ndynamical competition whose resolution shows a complex dependence on all three\nphysical parameters defining the system: interaction strength, number of\nparticles, and barrier height."
    },
    {
        "anchor": "New frontiers with quantum gases of polar molecules: The field of ultracold quantum matter has burgeoned over the last few\ndecades, thanks to the growing capabilities for atomic systems to be probed and\nmanipulated with exquisite control. Researchers can now precisely create and\nstudy quantum many-body states that are effectively isolated from the external\nenvironment. Much of the work in ultracold matter has focused on systems of\nalkali or alkaline-earth atoms, mainly due to their ease of cooling. Extending\nthis precise control to molecules has seen rapidly increasing interest and\nactivity, as molecules possess additional degrees of freedom that make them\nuseful for tests of fundamental physics, studying ultracold chemistry and\ncollisions, and engineering qualitatively new types of quantum phases and\nquantum many-body systems. Here, we review one particularly fruitful research\ndirection: the creation and manipulation of ultracold bialkali molecules. The\nrecent success in creating a quantum gas of polar molecules opens many exciting\nresearch opportunities.",
        "positive": "Density of states for the Unitary Fermi gas and the Schwarzschild black\n  hole: The density of states of a quantum system can be calculated from its\ndefinition but, in some cases, this approach is quite cumbersome.\nAlternatively, the density of states can be deduced from the microcanonical\nentropy or from the canonical partition function. After discussing the\nrelationship among these procedures, we suggest a simple numerical method,\nwhich is equivalent in the thermodynamic limit to perform a Legendre\ntransformation, to obtain the density of states from the Helmholtz free energy.\nWe apply this method to determine the many-body density of states of the\nunitary Fermi gas, a very dilute system of identical fermions interacting with\ndivergent scattering length. The unitary Fermi gas is highy symmetric due to\nthe absence of any internal scale except for the average distance between two\nparticles and, for this reason, its equation of state is called universal. In\nthe last part of the paper, by using the same thermodynamical techniques, we\nreview some properties of} the density of states of a Schwarzschild black hole,\nwhich shares with the unitary Fermi gas the problem of finding the density of\nstates directly from its definition."
    },
    {
        "anchor": "Quantum droplet of one-dimensional bosons with a three-body attraction: Ultracold atoms offer valuable opportunities where interparticle interactions\ncan be controlled at will. In particular, by extinguishing the two-body\ninteraction, one can realize unique systems governed by the three-body\ninteraction, which is otherwise hidden behind the two-body interaction. Here we\nstudy one-dimensional bosons with a weak three-body attraction and show that\nthey form few-body bound states as well as a many-body droplet stabilized by\nthe quantum mechanical effect. Their binding energies relative to that of three\nbosons are all universal and the ground-state energy of the dilute droplet is\nfound to grow exponentially as $E_N/E_3\\to\\exp(8N^2/\\sqrt3\\pi)$ with increasing\nparticle number $N\\gg1$. The realization of our system with coupled\ntwo-component bosons in an optical lattice is also discussed.",
        "positive": "Stability of spin-orbit coupled Fermi gases with population imbalance: We use the self-consistent mean-field theory to analyze the effects of\nRashba-type spin-orbit coupling (SOC) on the ground-state phase diagram of\npopulation-imbalanced Fermi gases throughout the BCS-BEC evolution. We find\nthat the SOC and population imbalance are counteracting, and that this\ncompetition tends to stabilize the uniform superfluid phase against the phase\nseparation. However, we also show that the SOC stabilizes (destabilizes) the\nuniform superfluid phase against the normal phase for low (high) population\nimbalances. In addition, we find topological quantum phase transitions\nassociated with the appearance of momentum space regions with zero\nquasiparticle energies, and study their signatures in the momentum\ndistribution."
    },
    {
        "anchor": "A differential approach to investigate universal scaling in\n  far-from-equilibrium quantum systems: Recent progress in out-of-equilibrium closed quantum systems has\nsignificantly advanced the understanding of mechanisms behind their evolution\ntowards thermalization. Notably, the concept of non-thermal fixed points\n(NTFPs) - responsible for the emergence of spatio-temporal universal scaling in\nfar-from-equilibrium systems - has played a crucial role in both theoretical\nand experimental investigations. In this work, we introduce a differential\nequation that has the universal scaling associated with NTFPs as a solution.\nThe advantage of working with a differential equation, rather than only with\nits solution, is that we can extract several insightful properties not\nnecessarily present in the solution alone. Employing two limiting cases of the\nequation, we determined the universal exponents related to the scaling using\nthe distributions near just two momentum values. We established a strong\nagreement with previous investigations by validating this approach with three\ndistinct physical systems. This consistency highlights the universal nature of\nscaling due to NTFPs and emphasizes the predictive capabilities of the proposed\ndifferential equation. Moreover, under specific conditions, the equation\npredicts a power-law related to the ratio of the two universal exponents,\nleading to implications concerning particle and energy transport. This suggests\nthat the observed power-laws in far-from-equilibrium turbulent fluids could be\nrelated to the universal scaling due to NTFPs, potentially offering new\ninsights into the study of turbulence.",
        "positive": "Third order corrections to the ground state energy of the polarized\n  diluted gas of spin $1/2$ fermions: We present the results of the computation of the third order corrections to\nthe ground state energy of the diluted polarized gas of nonrelativistic spin\n$1/2$ fermions interacting through a spin-independent repulsive two-body\npotential.\n  The corrections are computed within the effective field theory approach which\ndoes not require specifying the interaction potential explicitly but only to\ncharacterize it by only a few parameters - the scattering lengths $a_0$,\n$a_1,\\dots$ and effective radii $r_0,\\dots$ - measurable in low energy\nfermion-fermion elastic scattering.\n  The corrections are computed semi-analytically, that is are expressed in\nterms of two functions of the system's polarization.\n  The functions are given by the integrals which can be easily evaluated using\nthe Mathematica built-in routines for numerical integration."
    },
    {
        "anchor": "Synthetic Gauge Structures in Real Space in a Ring lattice: Emergence of fundamental forces from gauge symmetry is among our most\nprofound insights about the physical universe. In nature, such symmetries\nremain hidden in the space of internal degrees of freedom of subatomic\nparticles. Here we propose a way to realize and study gauge structures in real\nspace, manifest in external degrees of freedom of quantum states. We present a\nmodel based on a ring-shaped lattice potential, which allows for both Abelian\nand non-Abelian constructs. Non trivial Wilson loops are shown possible via\nphysical motion of the system. The underlying physics is based on the close\nanalogy of geometric phase with gauge potentials that has been utilized to\ncreate synthetic gauge fields with internal states of ultracold atoms. By\nscaling up to an array with spatially varying parameters, a discrete gauge\nfield can be realized in position space, and its dynamics mapped over\nmacroscopic size and time scales.",
        "positive": "Realizing and optimizing an atomtronic SQUID: We demonstrate how a toroidal Bose-Einstein condensate with a movable barrier\ncan be used to realize an atomtronic SQUID. The magnitude of the barrier\nheight, which creates the analogue of an SNS junction, is of crucial\nimportance, as well as its ramp-up and -down protocol. For too low of a\nbarrier, the relaxation of the system is dynamically suppressed, due to the\nsmall rate of phase slips at the barrier. For a higher barrier, the phase\ncoherence across the barrier is suppressed due to thermal fluctuations, which\nare included in our Truncated Wigner approach. Furthermore, we show that the\nramp-up protocol of the barrier can be improved by ramping up its height first,\nand its velocity after that. This protocol can be further improved by\noptimizing the ramp-up and ramp-down time scales, which is of direct practical\nrelevance for on-going experimental realizations."
    },
    {
        "anchor": "Vortex reconnections between coreless vortices in binary condensates: Vortex reconnections plays an important role in the turbulent flows\nassociated with the superfluids. To understand the dynamics, we examine the\nreconnections of vortex rings in the superfluids of dilute atomic gases\nconfined in trapping potentials using Gross-Petaevskii equation. Furthermore we\nstudy the reconnection dynamics of coreless vortex rings, where one of the\nspecies can act as a tracer.",
        "positive": "Bound states in Bose-Einstein condensates with radially-periodic\n  spin-orbit coupling: We consider Bose-Einstein condensate (BEC) subject to the action of\nspin-orbit-coupling (SOC) periodically modulated in the radial direction. In\ncontrast to the commonly known principle that periodic potentials do not create\nbound states, the binary BEC maintains multiple localized modes in the linear\nlimit, with their chemical potential falling into spectral gaps of the\n(numerically found) radial band structure induced by the spatial modulation of\nthe SOC. In the presence of the repulsive nonlinearity, the SOC modulation\nsupports fundamental gap solitons of the semi-vortex types, as well as\nhigher-order vortex gap solitons. The localization degree and stability of the\ngap solitons strongly depend on the location of their chemical potential in the\ngap. Stability intervals for vortex gap solitons in a broad range of the\nintrinsic vorticity, from -2 to 3, are identified. Thus, the analysis reveals\nthe previously unexplored mechanism of linear and nonlinear localization\nprovided by the spatially periodic modulation of SOC, which may be extended to\nother settings, such as those for optical beams and polaritons. Unlike the\ncommonly known quartets of eigenvalues for small perturbations, in the present\nsystem the instability is accounted for by shifted complex eigenvalue pairs."
    },
    {
        "anchor": "Finite temperature correlations in the Bose-Hubbard model: application\n  of the Gauge $P$ representation: We study ultracold Bose gases in periodic potentials as described by the\nBose-Hubbard model. In 1D and at finite temperature, we simulate ultracold Bose\ngases in imaginary time with the gauge $P$ representation. We study various\nquantities including the Luttinger parameter $K$, which is important for\nlocating the boundaries of the Mott insulator lobes, and find a simple relation\nfor the kinetic energy part of the Bose-Hubbard Hamiltonian.\n  We show that for J=0, the stepwise pattern of the average number of particles\nper lattice site versus the chemical potential vanishes at temperatures above\n$T \\approx 0.1 U$. Also, at chemical potential $\\mu=0.5 U$ and temperature\n$T=0.5 U$ by increasing $J$, the relative value of the number fluctuation\ndecreases and approaches that of a coherent state.",
        "positive": "Long time non-equilibrium dynamics of binary Bose condensates: We explore the out-of-equilibrium temporal dynamics of demixing and phase\nseparation in a two dimensional binary Bose fluid at zero temperature,\nfollowing a sudden quench across the miscible-immiscible phase boundary. On\nshort timescales, the system rapidly settles into a steady state characterized\nby short-range correlations in the relative density. The subsequent dynamics is\nextremely slow: domains of the relative density appear to grow with time,\nhowever, the rate of growth is much slower than that predicted by conventional\ntheories of phase ordering kinetics. Moreover, we find that the growth dynamics\nslows down with increasing time, and is consistent with logarithmic growth. Our\nstudy sheds light on ongoing investigations of how isolated quantum systems\napproach equilibrium, and indicates that studying the quantum phase diagram of\nthe binary Bose fluids following a quench, may be difficult due to\nequilibration problems."
    },
    {
        "anchor": "Scaling properties of the Tan's contact: embedding pairs and correlation\n  effect in the Tonks limit: We study the Tan's contact of a one dimensional quantum gas of N repulsive\nidentical bosons confined in a harmonic trap at finite temperature. This\ncanonical ensemble framework corresponds to the experimental conditions, the\nnumber of particles being fixed for each experimental sequence. We show that,\nin the strongly interacting regime, the contact rescaled by the contact at the\nTonks-Girardeau limit is an universal function of two parameters, the rescaled\ninteraction strength and temperature. This means that all pair and correlation\neffects in the Tan's contact are embedded in the Tan's contact in the\nTonks-Girardeau limit.",
        "positive": "Cluster mean-field approach with density matrix renormalization group:\n  Application to the hard-core bosonic Hubbard model on a triangular lattice: We introduce a new numerical method for the solution of self-consistent\nequations in the cluster mean-field theory. The method uses the density matrix\nrenormalization group method to solve the associated cluster problem. We obtain\nan accurate critical value of the supersolid-superfluid transitions in the\nhard-core bosonic Hubbard model on a triangular lattice, which is comparable\nwith the recent quantum Monte Carlo results. This algorithm is applicable to\nmore general classes of models with a larger number of degrees of freedom."
    },
    {
        "anchor": "Deep learning based quantum vortex detection in atomic Bose-Einstein\n  condensates: Quantum vortices naturally emerge in rotating Bose-Einstein condensates\n(BECs) and, similarly to their classical counterparts, allow the study of a\nrange of interesting out-of-equilibrium phenomena like turbulence and chaos.\nHowever, the study of such phenomena requires to determine the precise location\nof each vortex within a BEC, which becomes challenging when either only the\ncondensate density is available or sources of noise are present, as is\ntypically the case in experimental settings. Here, we introduce a machine\nlearning based vortex detector motivated by state-of-the-art object detection\nmethods that can accurately locate vortices in simulated BEC density images.\nOur model allows for robust and real-time detection in noisy and\nnon-equilibrium configurations. Furthermore, the network can distinguish\nbetween vortices and anti-vortices if the condensate phase profile is also\navailable. We anticipate that our vortex detector will be advantageous both for\nexperimental and theoretical studies of the static and dynamical properties of\nvortex configurations in BECs.",
        "positive": "Electromagnetic induced transparency and slow light in interacting\n  quantum degenerate atomic gases: We systematically develop the full quantum theory for the electromagnetic\ninduced transparency (EIT) and slow light properties in ultracold Bose and\nFermi gases. It shows a very different property from the classical theory which\nassumes frozen atomic motion. For example, the speed of light inside the atomic\ngases can be changed dramatically near the Bose-Einstein condensation\ntemperature, while the presence of the Fermi sea can destroy the EIT effect\neven at zero temperature. From experimental point of view, such quantum EIT\nproperty is mostly manifested in the counter-propagating excitation schemes in\neither the low-lying Rydberg transition with a narrow line width or in the D2\ntransitions with a very weak coupling field. We further investigate the\ninteraction effects on the EIT for a weakly interacting Bose-Einstein\ncondensate, showing an inhomogeneous broadening of the EIT profile and\nnontrivial change of the light speed due to the quantum many-body effects\nbeyond mean field energy shifts."
    },
    {
        "anchor": "Density correlations from analogue Hawking radiation in the presence of\n  atom losses: The sonic analogue of Hawking radiation can now be experimentally recreated\nin Bose-Einstein Condensates that contain an acoustic black hole. In these\nexperiments the signal strength and analogue Hawking temperature increase for\ndenser condensates, which however also suffer increased atom losses from\ninelastic collisions. To determine how these affect analogue Hawking radiation,\nwe numerically simulate creation of the latter in a Bose-Einstein Condensate in\nthe presence of atomic losses. In particular we explore modifications of\ndensity-density correlations through which the radiation has been analyzed so\nfar. We find that losses increase the contrast of the correlation signal, which\nwe attribute to heating that in turn leads to a component of stimulated\nradiation in addition to the spontaneous one. Another indirect consequence is\nthe modification of the white hole instability pattern.",
        "positive": "Pseudo-Goldstone Excitations in a Striped Bose-Einstein Condensate: Significant experimental progress has been made recently for observing\nlong-sought supersolid-like states in Bose-Einstein condensates, where spatial\ntranslational symmetry is spontaneously broken by anisotropic interactions to\nform a stripe order. Meanwhile, the superfluid stripe ground state was also\nobserved by applying a weak optical lattice that forces the symmetry breaking.\nDespite of the similarity of the ground states, here we show that these two\nsymmetry breaking mechanisms can be distinguished by their collective\nexcitation spectra. In contrast to gapless Goldstone modes of the\n\\textit{spontaneous} stripe state, we propose that the excitation spectra of\nthe \\textit{forced} stripe phase can provide direct experimental evidence for\nthe long-sought gapped pseudo-Goldstone modes. We characterize the\npseudo-Goldstone mode of such lattice-induced stripe phase through its\nexcitation spectrum and static structure factor. Our work may pave the way for\nexploring spontaneous and forced/approximate symmetry breaking mechanisms in\ndifferent physical systems."
    },
    {
        "anchor": "Solitary waves of Bose-Einstein condensed atoms confined in finite rings: Motivated by recent progress in trapping Bose-Einstein condensed atoms in\ntoroidal potentials, we examine solitary-wave solutions of the nonlinear\nSchr\\\"odinger equation subject to periodic boundary conditions. When the\ncircumference of the ring is much larger than the size of the wave, the density\nprofile is well approximated by that of an infinite ring, however the density\nand the velocity of propagation cannot vanish simultaneously. When the size of\nthe ring becomes comparable to the size of the wave, the density variation\nbecomes sinusoidal and the velocity of propagation saturates to a constant\nvalue.",
        "positive": "Dynamics of double-well Bose-Einstein Condensates subject to external\n  Gaussian white noise: Dynamical properties of the Bose-Einstein condensate in double-well potential\nsubject to Gaussian white noise are investigated by numerically solving the\ntime-dependent Gross-Pitaevskii equation. The Gaussian white noise is used to\ndescribe influence of the random environmental disturbance on the double-well\ncondensate. Dynamical evolutions from three different initial states, the\nJosephson oscillation state, the running phase and $\\pi$-mode macroscopic\nquantum self-trapping states are considered. It is shown that the system is\nrather robust with respect to the weak noise whose strength is small and change\nrate is high. If the evolution time is sufficiently long, the weak noise will\nfinally drive the system to evolve from high energy states to low energy\nstates, but in a manner rather different from the energy-dissipation effect. In\npresence of strong noise with either large strength or slow change rate, the\ndouble-well condensate may exhibit very irregular dynamical behaviors."
    },
    {
        "anchor": "Wigner crystal versus Fermionization for one-dimensional Hubbard models\n  with and without long-range interactions: The ground state properties of Hubbard model with or without long-range\ninteractions in the regime with strongly repulsive on-site interaction are\ninvestigated by means of the exact diagonalization method. We show that the\nappearance of $N$-crests in the density profile of a trapped N-fermion system\nis a natural result of \"fermionization\" between antiparallel-spin fermions in\nthe strongly repulsive limit and can not be taken as the only signature of\nWigner crystal phase, as the static structure factor does not show any\nsignature of crystallization. On the contrary, both the density distribution\nand static structure factor of Hubbard model with strong long-range\ninteractions display clear signature of Wigner crystal. Our results indicate\nthe important role of long-range interaction in the formation of Wigner\ncrystal.",
        "positive": "Coupling Navier-Stokes and Gross-Pitaevskii equations for the numerical\n  simulation of two-fluid quantum flows: Numerical methods for solving the Navier-Stokes equations for classical (or\nnormal) viscous fluids are well established. This is also the case for the\nGross-Pitaevskii equation, governing quantum inviscid flows (or superfluids) in\nthe zero temperature limit. In quantum flows, like liquid helium II at\nintermediate temperatures between zero and 2.17 K, a normal fluid and a\nsuperfluid coexist with independent velocity fields. The most advanced existing\nmodels for such systems use the Navier-Stokes equations for the normal fluid\nand a simplified description of the superfluid, based on the dynamics of\nquantized vortex filaments, with ad hoc reconnection rules. There was a single\nattempt (C. Coste, The European Physical Journal B - Condensed Matter and\nComplex Systems, 1998) to couple Navier-Stokes and Gross-Pitaevskii equations\nin a global model intended to describe the compressible two-fluid liquid helium\nII. We present in this contribution a new numerical model to couple a\nNavier-Stokes incompressible fluid with a Gross-Pitaevskii superfluid. Coupling\nterms in the global system of equations involve new definitions of the\nfollowing concepts: the regularized superfluid vorticity and velocity fields,\nthe friction force exerted by quantized vortices to the normal fluid, the\ncovariant gradient operator in the Gross-Pitaevskii based on a slip velocity\nrespecting the dynamics of vortex lines in the normal fluid. A numerical\nalgorithm based on pseudo-spectral Fourier methods is presented for solving the\ncoupled system of equations.Finally, we numerically test and validate the new\nnumerical system against well-known benchmarks for the evolution in a normal\nfluid of different types or arrangements of quantized vortices (vortex crystal,\nvortex dipole and vortex rings). The new coupling model opens new possibilities\nto revisit and enrich existing numerical results for complex quantum fluids."
    },
    {
        "anchor": "Collapse dynamics of a ${}^{176}\\textrm{Yb}\\,$-${}^{174}\\textrm{Yb}$\n  Bose-Einstein condensate: In this paper, we present a theoretical study of a two-component\nBose-Einstein condensate composed of Ytterbium (Yb) isotopes in a three\ndimensional anisotropic harmonic potential. The condensate consists of a\nmixture of ${}^{176}\\textrm{Yb}$ atoms which have a negative s-wave scattering\nlength and ${}^{174}\\textrm{Yb}$ atoms having a positive s-wave scattering\nlength. We study the ground state as well as dynamic properties of this\ntwo-component condensate. Due to the attractive interactions between\n${}^{176}\\textrm{Yb}$ atoms, the condensate of ${}^{176}\\textrm{Yb}$ undergo a\ncollapse when the particle number exceed a critical value. The critical number\nand the collapse dynamics are modified due to the presence of\n${}^{174}\\textrm{Yb}$ atoms. We use coupled two-component Gross-Pitaevskii\nequations to study the collapse dynamics. The theoretical results obtained are\nin reasonable agreement with the experimental results of Fukuhara {\\em et al.}\n[PRA{\\bf 79}, 021601(R) (2009)].",
        "positive": "Quantum Degenerate Majorana Surface Zero Modes in Two-Dimensional Space: We investigate the topological properties of spin polarized fermionic polar\nmolecules loaded in a multi-layer structure with the electric dipole moment\npolarized to the normal direction. When polar molecules are paired by\nattractive inter-layer interaction, unpaired Majorana fermions can be\nmacroscopically generated in the top and bottom layers in dilute density\nregime. We show that the resulting topological state is effectively composed by\na bundle of 1D Kitaev ladders labeled by in-plane momenta k and -k, and hence\nbelongs to BDI class characterized by the winding number Z, protected by the\ntime reversal symmetry. The Majorana surface modes exhibit a flatband at zero\nenergy, fully gapped from Bogoliubov excitations in the bulk, and hence becomes\nan idea system to investigate the interaction effects on quantum degenerate\nMajorana fermions. We further show that additional interference fringes can be\nidentified as a signature of such 2D Majorana surface modes in the\ntime-of-flight experiment."
    },
    {
        "anchor": "Magnetization relaxation and geometric forces in a Bose ferromagnet: We construct the hydrodynamic theory for spin 1/2 Bose gases at arbitrary\ntemperatures. This theory describes the coupling between the magnetization, and\nthe normal and superfluid components of the gas. In particular, our theory\ncontains the geometric forces on the particles that arise from their spin's\nadiabatic following of the magnetization texture. The phenomenological\nparameters of the hydrodynamic theory are calculated in the Bogoliubov\napproximation and using the Boltzmann equation in the relaxation-time\napproximation. We consider the topological Hall effect due to the presence of a\nskyrmion, and show that this effect manifests itself in the collective modes of\nthe system. The dissipative coupling between the magnetization and the normal\ncomponent is shown to give rise to magnetization relaxation that is fourth\norder in spatial gradients of the magnetization direction.",
        "positive": "On the viscosity to entropy density ratio for unitary Bose and Fermi\n  Gases: We calculate the ratio of the viscosity to the entropy density for both Bose\nand Fermi gases in the unitary limit using a new approach to the quantum\nstatistical mechanics of gases based on the S-matrix. In the unitary limit the\nscattering length diverges and the S-matrix equals -1. For the fermion case we\nobtain eta/s > 4.7 times the proposed lower bound of \\hbar/4 pi k_B which came\nfrom the AdS/CFT for gauge theories, consistent with the most recent\nexperiments. For the bosonic case we present evidence that the gas undergoes a\nphase transition to a strongly interacting Bose-Einstein condensate, and is a\nmore perfect fluid, with eta/s > 1.3 times the bound."
    },
    {
        "anchor": "Phase Diagram of Rydberg atoms in a nonequilibrium optical lattice: We study the quantum nonequilibrium dynamics of ultracold three-level atoms\ntrapped in an optical lattice, which are excited to their Rydberg states via a\ntwo-photon excitation with nonnegligible spontaneous emission. Rich quantum\nphases including uniform phase, antiferromagnetic phase and oscillatory phase\nare identified. We map out the phase diagram and find these phases can be\ncontrolled by adjusting the ratio of intensity of the pump light to the control\nlight, and that of two-photon detuning to the Rydberg interaction strength.\nWhen the two-photon detuning is blue-shifted and the latter ratio is less than\n1, bistability exists among the phases. Actually, this ratio controls the\nRydberg-blockade and antiblockade effect, thus the phase transition in this\nsystem can be considered as a possible approach to study both effects.",
        "positive": "Ordered phases in a bilayer system of dipolar fermions: The liquid-to-ordered phase transition in a bilayer system of fermions is\nstudied within the context of a recently proposed density-functional theory\n[Phys. Rev. A {\\bf 92}, 023614 (2015)]. In each two-dimensional layer, the\nfermions interact via a repulsive, isotropic dipolar interaction. The presence\nof a second layer introduces an attractive {\\em interlayer} interaction,\nthereby allowing for inhomogeneous density phases which would otherwise be\nenergetically unfavourable. For any fixed layer separation, we find an\ninstability to a commensurate one-dimensional stripe phase in each layer, which\nalways precedes the formation of a triangular Wigner crystal. However, at a\ncertain {\\em fixed} coupling, tuning the separation can lead to the system\nfavoring a commensurate triangular Wigner crystal, or one-dimensional stripe\nphase, completely bypassing the Fermi liquid state. While other crystalline\nsymmetries, with energies lower than the liquid phase can be found, they are\nnever allowed to form owing to their high energetic cost relative to the\ntriangular Wigner crystal and stripe phase."
    },
    {
        "anchor": "Global phase diagram of three-dimensional extended Boson Hubbard model -\n  a continuous time Quantum Monte Carlo study: We present the global phase diagram of the extended boson Hubbard model on a\nsimple cubic lattice by quantum Monte Carlo simulation with worm update\nalgorithm. Four kinds of phases are supported by this model, including\nsuperfluid, supersolid, Mott, and charge density wave (CDW) states, which are\nidentified in the phase diagram of chemical potential $\\mu$ versus nearest\nneighbor interaction V . By changing the chemical potential, a continuous\ntransition is found from the Mott phase to a superfluid phase without breaking\nthe translational symmetry. For an insulating CDW state, adding particles to it\ngives rise to a continuous transition to a supersolid phase, while removing\nparticles usually leads to a first-order one to either supersolid or superfluid\nphase. By tuning the nearest neighbor interaction, one can realize the\ntransition between two insulating phases, Mott and CDW with the same particle\ndensity, which turns out to be of the first-order. We also demonstrate that a\nsupersolid phase with average particle density less than 1/2 can exist in a\nsmall region of $\\mu$ - V phase diagram.",
        "positive": "Realizing topological states with polyatomic symmetric top molecules: We demonstrate that ultracold polyatomic symmetric top molecules, such as\nmethyl fluoride, loaded into an optical lattice and subject to DC electric and\nmicrowave field dressing, can display topological order via a self-consistent\nanalog of a proximity effect in the internal state space of the molecule. The\nnon-trivial topology arises from pairwise transitions between internal states\ninduced by dipole-dipole interactions and made resonant by the field dressing.\nTopological order is explicitly demonstrated by matrix product state\nsimulations on 1D chains. Additionally, we show that in the limit of pinned\nmolecules our description maps onto a long-range and anisotropic XYZ spin\nmodel, where Majorana fermions are zero-energy edge excitations in the case of\nnearest-neighbor couplings."
    },
    {
        "anchor": "Prominent quantum many-body scars in a truncated Schwinger model: The high level of control and precision achievable in current synthetic\nquantum matter setups has enabled first attempts at quantum-simulating various\nintriguing phenomena in condensed matter physics, including those probing\nthermalization or its absence in closed quantum systems. In a recent work\n[Desaules \\textit{et al.} [arXiv:2203.08830], we have shown that quantum\nmany-body scars -- special low-entropy eigenstates that weakly break ergodicity\nin nonintegrable systems -- arise in spin-$S$ quantum link models that converge\nto $(1+1)-$D lattice quantum electrodynamics (Schwinger model) in the\nKogut--Susskind limit $S\\to\\infty$. In this work, we further demonstrate that\nquantum many-body scars exist in a truncated version of the Schwinger model,\nand are qualitatively more prominent than their counterparts in spin-$S$\nquantum link models. We illustrate this by, among other things, performing a\nfinite-$S$ scaling analysis that strongly suggests that scarring persists in\nthe truncated Schwinger model in the limit $S\\to\\infty$. Although it does not\nasymptotically converge to the Schwinger model, the truncated formulation is\nrelevant to synthetic quantum matter experiments, and also provides fundamental\ninsight into the nature of quantum many-body scars, their connection to lattice\ngauge theories, and the thermalization dynamics of the latter. Our conclusions\ncan be readily tested in current cold-atom setups.",
        "positive": "Density fluctuations in a quasi-one-dimensional Bose gas as observed in\n  free expansion: We study, within a framework of the classical fields approximation, the\ndensity correlations of a weakly interacting expanding Bose gas for the whole\nrange of temperatures across the Bose-Einstein condensation threshold. We focus\non elongated quasi-one-dimensional systems where there is a huge discrepancy\nbetween the existing theory and experimental results (A. Perrin et al., Nature\nPhys. 8, 195 (2012)). We find that the density correlation function is not\nreduced for temperatures below the critical one as it is predicted for the\nideal gas or for a weakly interacting system within the Bogoliubov\napproximation. This behavior of the density correlations agrees with the above\nmentioned experiment with the elongated system. Although the system was much\nlarger then studied here we believe that the behavior of the density\ncorrelation function found there is quite generic. Our theoretical studies\nindicate also large density fluctuations in the trap in the quasicondensate\nregime where only phase fluctuations were expected. We argue that the enhanced\ndensity fluctuations can originate in the presence of interactions in the\nsystem, or more precisely in the existence of spontaneous dark solitons in the\nelongated gas at thermal equilibrium."
    },
    {
        "anchor": "Rabi coupled fermions in the BCS-BEC crossover: We investigate the three-dimensional BCS-BEC crossover in the presence of a\nRabi coupling which strongly affects several properties of the system, such as\nthe chemical potential, the pairing gap and the superfluid density. We\ndetermine the critical interaction strength, below which the system is normal\nalso at zero temperature. Finally, we calculate the effect of the Rabi coupling\non the critical temperature of the superfluid-to-normal phase transition by\nusing different theoretical schemes.",
        "positive": "Quantum double structure in cold atom superfluids: The theory of topological quantum computation is underpinned by two important\nclasses of models. One is based on non-abelian Chern-Simons theory, which\nyields the so-called $\\rm{SU}(2)_k$ anyon models that often appear in the\ncontext of electrically charged quantum fluids. The physics of the other is\ncaptured by symmetry broken Yang-Mills theory in the absence of a Chern-Simons\nterm, and results in the so-called quantum double models. Extensive resources\nhave been invested into the search for $\\rm{SU}(2)_k$ anyon quasi-particles; in\nparticular the so-called Ising anyons ($k=2$) of which Majorana zero modes are\nbelieved to be an incarnation. In contrast to the $\\rm{SU}(2)_k$ models,\nquantum doubles have attracted little attention in experiments despite their\npivotal role in the theory of error correction. Beyond topological error\ncorrecting codes, the appearance of quantum doubles has been limited to\ncontexts primarily within mathematical physics, and as such, they are of\nseemingly little relevance for the study of experimentally tangible systems.\nHowever, recent works suggest that quantum double anyons may be found in spinor\nBose-Einstein condensates. In light of this, the core purpose of this article\nis to provide a self-contained exposition of the quantum double structure,\nframed in the context of spinor condensates, by constructing explicitly the\nquantum doubles for various ground state symmetry groups and discuss their\nexperimental realisability. We also derive analytically an equation for the\nquantum double Clebsch-Gordan coefficients from which the relevant braid\nmatrices can be worked out. Finally, the existence of a particle-vortex duality\nis exposed and illuminated upon in this context."
    },
    {
        "anchor": "Synthetic Hall tube of interacting fermions: Motivated by a recent experiment [J. H. Han, et. al., Phys. Rev. Lett.122,\n065303 (2019)], we investigate many-body physics of interacting fermions in a\nsynthetic Hall tube, using state-of-the-art density-matrix\nrenormalization-group numerical method. Since the inter-leg couplings of this\nsynthetic Hall tube generate an interesting spin-tensor Zeeman field, exotic\ntopological and magnetic properties occur. Especially, four new quantum phases,\nsuch as nontopological spin-vector and -tensor paramagnetic insulators, and\ntopological and nontopological spin-mixed paramagnetic insulators, are\npredicted by calculating entanglement spectrum, entanglement entropies, energy\ngaps, and local magnetic orders with 3 spin-vectors and 5 spin-tensors.\nMoreover, the topologically magnetic phase transitions induced by the\ninteraction as well as the inter-leg couplings are also revealed. Our results\npave a new way to explore many-body (topological) states induced by both the\nspiral spin-vector and -tensor Zeeman fields.",
        "positive": "Topological Classification and Stability of Fermi Surfaces: In the framework of the Cartan classification of Hamiltonians, a kind of\ntopological classification of Fermi surfaces is established in terms of\ntopological charges. The topological charge of a Fermi surface depends on its\ncodimension and the class to which its Hamiltonian belongs. It is revealed that\nsix types of topological charges exist, and they form two groups with respect\nto the chiral symmetry, with each group consisting of one original charge and\ntwo descendants. It is these nontrivial topological charges which lead to the\nrobust topological protection of the corresponding Fermi surfaces against\nperturbations that preserve discrete symmetries."
    },
    {
        "anchor": "Quench-induced supercurrents in an annular Bose gas: We create supercurrents in annular two-dimensional Bose gases through a\ntemperature quench of the normal-to-superfluid phase transition. We detect the\namplitude and the chirality of these supercurrents by measuring spiral patterns\nresulting from the interference of the cloud with a central reference disk.\nThese measurements demonstrate the stochastic nature of the supercurrents. We\nfurther measure their distribution for different quench times and compare it\nwith the predictions based on the Kibble-Zurek mechanism.",
        "positive": "Two super Tonks-Girardeau states of a trapped 1D spinor Fermi gas: A harmonically trapped ultracold 1D spinor Fermi gas with a strongly\nattractive 1D even-wave interaction induced by a 3D Feshbach resonance is\nstudied. It is shown that it has two different super Tonks-Girardeau (sTG)\nenergy eigenstates which are metastable against collapse in spite of the strong\nattraction, due to their close connection with 1D hard sphere Bose gases which\nare highly excited gas-like states. One of these sTG states is a hybrid between\nan sTG gas with strong $(\\uparrow\\downarrow$ attractions and an ideal Fermi gas\nwith no $(\\uparrow\\uparrow)$ or $(\\downarrow\\downarrow)$ interactions, the sTG\ncomponent being an exact analog of the recently observed sTG state of a 1D\nultracold Bose gas. It should be possible to create it experimentally by a\nsudden switch of the $(\\uparrow\\downarrow)$ interaction from strongly repulsive\nto strongly attractive, as in the recent Innsbruck experiment on the bosonic\nsTG gas. The other is a trapped analog of a recently predicted sTG state which\nis an ultracold gas of strongly bound $(\\uparrow\\downarrow)$ fermion dimers\nwhich behave as bosons with a strongly attractive boson-boson interaction\nleading to sTG behavior. It is proved that the probability of a transition from\nthe ground state for strongly repulsive interaction to this dimer state under a\nsudden switch from strongly repulsive to strongly attractive interaction is\n$\\ll 1$, contrary to a previous suggestion."
    },
    {
        "anchor": "The extended states in disordered 1D systems in the presence of the\n  generalized $N$-mer correlations: We have been investigating the problem of the Anderson localization in a\ndisordered one dimensional tight-binding model. The disorder is created by the\ninteraction of mobile particles with other species, immobilized at random\npositions. We introduce a novel method of creating correlations in the optical\nlattices with such a kind of disorder by using two different lattices with\ncommensurate lattice lengths to hold two species of the particles. Such a\nmodel, called the generalized random $N$-mer model leads to the appearance of\nmultiple extended states in contrary to a localization of all states usually\nexpected in one dimension. We develop a method, based on properties of transfer\nmatrices which can be used to determine the presence of extended states and\ntheir energies for that class of correlations. Analytical results are compared\nwith the numerical calculations for several cases which can be realized in\ncold-atom experiments.",
        "positive": "Exactly-solvable system of one-dimensional trapped bosons with short and\n  long-range interactions: We consider trapped bosons with contact interactions as well as Coulomb\nrepulsion or gravitational attraction in one spatial dimension. The exact\nground state energy and wave function are identified in closed form together\nwith a rich phase diagram, unveiled by Monte Carlo methods, with crossovers\nbetween different regimes. A trapped McGuire quantum soliton describes the\nattractive case. Weak repulsion results in an incompressible Laughlin-like\nfluid with flat density, well reproduced by a Gross-Pitaevskii equation with\nlong-range interactions. Higher repulsion induces Friedel oscillation and the\neventual formation of a Wigner crystal."
    },
    {
        "anchor": "Monitoring currents in cold-atom circuits: Complex circuits of cold atoms can be exploited to devise new protocols for\nthe diagnostics of cold-atoms systems. Specifically, we study the quench\ndynamics of a condensate confined in a ring-shaped potential coupled with a\nrectilinear guide of finite size. We find that the dynamics of the atoms inside\nthe guide is distinctive of the states with different winding numbers in the\nring condensate. We also observe that the depletion of the density, localized\naround the tunneling region of the ring condensate, can decay in a pair of\nexcitations experiencing a Sagnac effect. In our approach, the current states\nof the condensate in the ring can be read out by inspection of the rectilinear\nguide only, leaving the ring condensate minimally affected by the measurement.\nWe believe that our results set the basis for definition of new quantum\nrotation sensors. At the same time, our scheme can be employed to explore\nfundamental questions involving dynamics of bosonic condensates.",
        "positive": "Observation of a dipolar quantum gas with metastable supersolid\n  properties: The competition of dipole-dipole and contact interactions leads to exciting\nnew physics in dipolar gases, well-illustrated by the recent observation of\nquantum droplets and rotons in dipolar condensates. We show that the\ncombination of the roton instability and quantum stabilization leads under\nproper conditions to a novel regime that presents supersolid properties, due to\nthe coexistence of stripe modulation and phase coherence. In a combined\nexperimental and theoretical analysis, we determine the parameter regime for\nthe formation of coherent stripes, whose lifetime of a few tens of milliseconds\nis limited by the eventual destruction of the stripe pattern due to three-body\nlosses. Our results open intriguing prospects for the development of long-lived\ndipolar supersolids."
    },
    {
        "anchor": "Thermodynamic properties of an interacting hard-sphere Bose gas in a\n  trap using the static fluctuation approximation: A hard-sphere (HS) Bose gas in a trap is investigated at finite temperatures\nin the weakly-interacting regime and its thermodynamic properties are evaluated\nusing the static fluctuation approximation (SFA). The energies are calculated\nwith a second-quantized many-body Hamiltonian and a harmonic oscillator wave\nfunction. The specific heat capacity, internal energy, pressure, entropy and\nthe Bose-Einstein (BE) occupation number of the system are determined as\nfunctions of temperature and for various values of interaction strength and\nnumber of particles. It is found that the number of particles plays a more\nprofound role in the determination of the thermodynamic properties of the\nsystem than the HS diameter characterizing the interaction, that the critical\ntemperature drops with the increase of the repulsion between the bosons, and\nthat the fluctuations in the energy are much smaller than the energy itself in\nthe weakly-interacting regime.",
        "positive": "Benchmarking discrete truncated Wigner approximation and neural network\n  quantum states with the exact dynamics in a Rydberg atomic chain: We benchmark the discrete truncated Wigner approximation (DTWA) and Neural\nquantum states (NQS) based on restricted Boltzmann-like machines with the exact\nexcitation and correlation dynamics in a chain of ten Rydberg atoms. The\ninitial state is where all atoms are in their electronic ground state. We\ncharacterize the excitation dynamics using the maximum and time-averaged number\nof Rydberg excitations. DTWA results are different from the exact dynamics for\nlarge Rydberg-Rydberg interactions. In contrast, by increasing the number of\nhidden spins, the NQS can be improved but still limited to short-time dynamics.\nInterestingly, irrespective of interaction strengths, the time-averaged number\nof excitations obtained using NQS is in excellent agreement with the exact\nresults. Concerning the calculation of quantum correlations, for instance,\nsecond-order bipartite and average two-site R\\'enyi entropies, NQS looks more\npromising. Finally, we discuss the existence of a power law scaling for the\ninitial growth of average two-site R\\'enyi entropy."
    },
    {
        "anchor": "Propagation of relativistic charged particles in ultracold atomic gases\n  with Bose-Einstein condensates: We study theoretically some effects produced by a propagation of the charged\nparticles in dilute gases of alkali-metal atoms in the state with Bose-Einstein\ncondensates. The energy change of the high-speed (relativistic) particle that\ncorresponds to the Cherenkov effect in the condensate is investigated. We show\nthat in the studied cases the particle can both loose and receive the energy\nfrom a gas. We find the necessary conditions for the particle acceleration in\nthe multi-component condensate. It is shown that the Cherenkov effect in\nBose-Einstein condensates can be used also for defining the spectral\ncharacteristics of atoms.",
        "positive": "Radio-frequency response and contact of impurities in a quantum gas: We investigate the radio-frequency spectroscopy of impurities interacting\nwith a quantum gas at finite temperature. In the limit of a single impurity, we\nshow using Fermi's golden rule that introducing (or injecting) an impurity into\nthe medium is equivalent to ejecting an impurity that is initially interacting\nwith the medium, since the \"injection\" and \"ejection\" spectral responses are\nsimply related to each other by an exponential function of frequency. Thus, the\nfull spectral information for the quantum impurity is contained in the\ninjection spectral response, which can be determined using a range of\ntheoretical methods, including variational approaches. We use this property to\ncompute the finite-temperature equation of state and Tan contact of the Fermi\npolaron. Our results for the contact of a mobile impurity are in excellent\nagreement with recent experiments and we find that the finite-temperature\nbehavior is qualitatively different compared to the case of infinite impurity\nmass."
    },
    {
        "anchor": "Topological charge pumping in the interacting bosonic Rice-Mele model: We investigate topological charge pumping in a system of interacting bosons\nin the tight-binding limit, described by the Rice-Mele model. An appropriate\ntopological invariant for the many-body case is the change of polarization per\npump cycle, which we compute for various interaction strengths from\ninfinite-size matrix-product-state simulations. We verify that the charge\npumping remains quantized as long as the pump cycle avoids the superfluid\nphase. In the limit of hardcore bosons, the quantized pumped charge can be\nunderstood from single-particle properties such as the integrated Berry\ncurvature constructed from Bloch states, while this picture breaks down at\nfinite interaction strengths. These two properties -- robust quantized charge\ntransport in an interacting system of bosons and the breakdown of a\nsingle-particle invariant -- could both be measured with ultracold quantum\ngases extending a previous experiment [Lohse et al., Nature Phys. 12, 350\n(2016)]. Furthermore, we investigate the entanglement spectrum of the Rice-Mele\nmodel and argue that the quantized charge pumping is encoded in a winding of\nthe spectral flow in the entanglement spectrum over a pump cycle.",
        "positive": "Strongly dipolar gases in a one-dimensional lattice: Bloch oscillations\n  and matter-wave localization: Three-dimensional quantum gases of strongly dipolar atoms can undergo a\ncrossover from a dilute gas to a dense macrodroplet, stabilized by quantum\nfluctuations. Adding a one-dimensional optical lattice creates a platform where\nquantum fluctuations are still unexplored, and a rich variety of new phases may\nbe observable. We employ Bloch oscillations as an interferometric tool to\nassess the role quantum fluctuations play in an array of quasi-two-dimensional\nBose-Einstein condensates. Long-lived oscillations are observed when the\nchemical potential is balanced between sites, in a region where a macrodroplet\nis extended over several lattice sites. Further, we observe a transition to a\nstate that is localized to a single lattice plane$-$driven purely by\ninteractions$-$marked by the disappearance of the interference pattern in the\nmomentum distribution. To describe our observations, we develop a discrete\none-dimensional extended Gross-Pitaevskii theory, including quantum\nfluctuations and a variational approach for the on-site wavefunction. This\nmodel is in quantitative agreement with the experiment, revealing the existence\nof single and multisite macrodroplets, and signatures of a two-dimensional\nbright soliton."
    },
    {
        "anchor": "Controlling coherence via tuning of the population imbalance in a\n  bipartite optical lattice: The control of transport properties is a key tool at the basis of many\ntechnologically relevant effects in condensed matter. The clean and precisely\ncontrolled environment of ultracold atoms in optical lattices allows one to\nprepare simplified but instructive models, which can help to better understand\nthe underlying physical mechanisms. Here we show that by tuning a structural\ndeformation of the unit cell in a bipartite optical lattice, one can induce a\nphase transition from a superfluid into various Mott insulating phases forming\na shell structure in the superimposed harmonic trap. The Mott shells are\nidentified via characteristic features in the visibility of Bragg maxima in\nmomentum spectra. The experimental findings are explained by Gutzwiller\nmean-field and quantum Monte Carlo calculations. Our system bears similarities\nwith the loss of coherence in cuprate superconductors, known to be associated\nwith the doping induced buckling of the oxygen octahedra surrounding the copper\nsites.",
        "positive": "Spin waves in a spin-1 Bose gas: We present a theory of spin waves in a non-condensed gas of spin-1 bosons:\nproviding both analytic calculations of the linear theory, and full numerical\nsimulations of the nonlinear response. We highlight the role of spin-dependent\ncontact interactions in the dynamics of a thermal gas. Although these\ninteractions are small compared to the thermal energy, they set the scale for\nlow energy long wavelength spin waves. In particular, we find that the polar\nstate of Rb-87 is unstable to collisional mixing of magnetic sublevels even in\nthe normal state. We augment our analytic calculations by providing full\nnumerical simulations of a trapped gas, explicitly demonstrating this\ninstability. Further we show that for strong enough anti-ferromagnetic\ninteractions, the polar gas is unstable. Finally we explore coherent population\ndynamics in a collisionless transversely polarized gas."
    },
    {
        "anchor": "Measuring second Chern number from non-adiabatic effects: The geometry and topology of quantum systems have deep connections to quantum\ndynamics. In this paper, I show how to measure the non-Abelian Berry curvature\nand its related topological invariant, the second Chern number, using dynamical\ntechniques. The second Chern number is the defining topological characteristic\nof the four-dimensional generalization of the quantum Hall effect and has\nrelevance in systems from three-dimensional topological insulators to\nYang-Mills field theory. I illustrate its measurement using the simple example\nof a spin-3/2 particle in an electric quadrupole field. I show how one can\ndynamically measure diagonal components of the Berry curvature in an\nover-complete basis of the degenerate ground state space and use this to\nextract the full non-Abelian Berry curvature. I also show that one can\naccomplish the same ideas by stochastically averaging over random initial\nstates in the degenerate ground state manifold. Finally I show how this system\ncan be manufactured and the topological invariant measured in a variety of\nrealistic systems, from superconducting qubits to trapped ions and cold atoms.",
        "positive": "Occupation-dependent particle separation in one-dimensional\n  non-Hermitian lattices: We unveil an exotic phenomenon arising from the intricate interplay between\nnon-Hermiticity and many-body physics, namely an occupation-dependent particle\nseparation for hardcore bosons in a one-dimensional lattice driven by\nuni-directional non-Hermitian pumping. Taking hardcore bosons as an example, we\nfind that a pair of particles occupying the same unit cell exhibit an opposite\nnon-Hermitian pumping direction to that of unpaired ones occupying different\nunit cells. By turning on an intracell interaction, many-body eigenstates split\nin their real energies, forming separable clusters in the complex energy plane\nwith either left-, right-, or bipolar-types of non-Hermitian skin effect\n(NHSE). The dependency of skin accumulating directions on particle occupation\nis further justified with local sublattice correlation and entanglement entropy\nof many-body eigenstates. Dynamically, this occupation-dependent NHSE manifests\nas uni- or bi-directional pumping for many-body initial states, allowing for\nspatially separating paired and unpaired particles. Similar phenomena also\napply to fermionic systems, unveiling the possibility of designing and\nexploring novel non-Hermitian phases originated from particle non-conservation\nin subsystems (e.g., orbitals, sublattices, or spin species) and their spatial\nconfigurations."
    },
    {
        "anchor": "Generalized classes of continuous symmetries in two-mode Dicke models: As recently realized experimentally [L\\'eonard et al., Nature 543, 87\n(2017)], one can engineer models with continuous symmetries by coupling two\ncavity modes to trapped atoms, via a Raman pumping geometry. Considering\nspecifically cases where internal states of the atoms couple to the cavity, we\nshow an extended range of parameters for which continuous symmetry breaking can\noccur, and we classify the distinct steady states and time-dependent states\nthat arise for different points in this extended parameter regime.",
        "positive": "Fingerprinting Rotons in a Dipolar Condensate: Super-Poissonian Peak in\n  the Atom-Number Fluctuations: We demonstrate that measurements of atom-number fluctuations in a trapped\ndipolar condensate can reveal the presence of the elusive roton excitation. The\nkey signature is a super-Poissonian peak in the fluctuations as the size of the\nmeasurement cell is varied, with the maximum occurring when the size is\ncomparable to the roton wavelength. The magnitude of this roton feature is\nenhanced with temperature. The variation in fluctuations across the condensate\ndemonstrates that the roton excitations are effectively confined to propagate\nin the densest central region, realizing a density trapped roton gas. While our\nmain results are based on full numerical solutions of the meanfield equations,\nwe also develop and validate a simple local density theory. Finally, we\nconsider fluctuations measured within a washer-shaped cell which filters out\nthe contribution of modes with nonzero angular momentum and provides a signal\nsensitive to individual roton modes."
    },
    {
        "anchor": "Observation of Atom Number Fluctuations in a Bose-Einstein Condensate: Fluctuations are a key property of both classical and quantum systems. While\nthe fluctuations are well understood for many quantum systems at zero\ntemperature, the case of an interacting quantum system at finite temperature\nstill poses numerous challenges. Despite intense theoretical investigations of\natom number fluctuations in Bose-Einstein condensates (BECs), their amplitude\nin experimentally relevant interacting systems is still poorly understood.\nMoreover, technical limitations have prevented their experimental observation\nto date. Here we report the first observation of these fluctuations. Our\nexperiments are based on a stabilization technique, which allows for the\npreparation of ultracold thermal clouds at the shot noise level, thereby\neliminating numerous technical noise sources. Furthermore, we make use of the\ncorrelations established by the evaporative cooling process to precisely\ndetermine the fluctuations and the sample temperature. This allows us to\nobserve a telltale signature: the sudden increase in fluctuations of the\ncondensate atom number close to the critical temperature.",
        "positive": "Excitation spectra of a Bose-Einstein condensate with an angular\n  spin-orbit coupling: A theoretical model of a Bose-Einstein condensate with angular spin-orbit\ncoupling has recently been proposed and it has been established that a\nhalf-skyrmion represents the ground state in a certain regime of spin-orbit\ncoupling and interaction. Here we investigate low-lying excitations of this\nphase by using the Bogoliubov method and numerical simulations of the\ntime-dependent Gross-Pitaevskii equation. We find that a sudden shift of the\ntrap bottom results in a complex two-dimensional motion of the system's center\nof mass that is markedly different from the response of a competing phase, and\ncomprises two dominant frequencies. Moreover, the breathing mode frequency of\nthe half-skyrmion is set by both the spin-orbit coupling and the interaction\nstrength, while in the competing state it takes a universal value. Effects of\ninteractions are especially pronounced at the transition between the two\nphases."
    },
    {
        "anchor": "Interaction-driven Lifshitz transition with dipolar fermions in optical\n  lattices: Anisotropic dipole-dipole interactions between ultracold dipolar fermions\nbreak the symmetry of the Fermi surface and thereby deform it. Here we\ndemonstrate that such a Fermi surface deformation induces a topological phase\ntransition -- so-called Lifshitz transition -- in the regime accessible to\npresent-day experiments. We describe the impact of the Lifshitz transition on\nobservable quantities such as the Fermi surface topology, the density-density\ncorrelation function, and the excitation spectrum of the system. The Lifshitz\ntransition in ultracold atoms can be controlled by tuning the dipole\norientation and -- in contrast to the transition studied in crystalline solids\n-- is completely interaction-driven.",
        "positive": "Nonlinear dissipative dynamics of a two-component atomic condensate\n  coupling with a continuum: We investigate the nonlinear dissipative coherence bifurcation and population\ndynamics of a two-component atomic Bose-Einstein condensate coupling with a\ncontinuum. The coupling between the two-component condensates and the continuum\nbrings effective dissipations to the two-component condensates. The steady\nstates and the coherence bifurcation depend on both dissipation and the\nnonlinear interaction between condensed atoms. The coherence among condensed\natoms may be even enhanced by the effective dissipations. The combination of\ndissipation and nonlinearity allows one to control the switching between\ndifferent self-trapped states or the switching between a self-trapped state and\na non-self-trapped state."
    },
    {
        "anchor": "Observation of tunable mobility edges in generalized Aubry-Andr\u00e9\n  lattices: Using synthetic lattices of laser-coupled atomic momentum modes, we\nexperimentally realize a recently proposed family of nearest-neighbor\ntight-binding models having quasiperiodic site energy modulation that host an\nexact mobility edge protected by a duality symmetry. These one-dimensional\ntight-binding models can be viewed as a generalization of the well-known\nAubry-Andr\\'{e} (AA) model, with an energy-dependent self duality condition\nthat constitutes an analytical mobility edge relation. By adiabatically\npreparing the lowest and highest energy eigenstates of this model system and\nperforming microscopic measurements of their participation ratio, we track the\nevolution of the mobility edge as the energy-dependent density of states is\nmodified by the model's tuning parameter. Our results show strong deviations\nfrom single-particle predictions, consistent with attractive interactions\ncausing both enhanced localization of the lowest energy state due to\nself-trapping and inhibited localization of the highest energy state due to\nscreening. This study paves the way for quantitative studies of interaction\neffects on self duality induced mobility edges.",
        "positive": "Cold atoms beyond atomic physics: In the last 25 years, much progress has been made producing and controlling\nBose-Einstein condensates (BECs) and degenerate Fermi gases. The advances in\ntrapping, cooling and tuning the interparticle interactions in these cold atom\nsystems lead to an unprecedented amount of control that one can exert over\nthem. This work aims to show that knowledge acquired studying cold atom systems\ncan be applied to other fields that share similarities and analogies with them,\nprovided that the differences are also known and taken into account. We focus\non two specific fields, nuclear physics and statistical optics. The nuclear\nphysics discussion occurs with the BCS-BEC crossover in mind, in which we\ncompare cold Fermi gases with nuclear and neutron matter and nuclei. We connect\nBECs and atom lasers through both systems' matter-wave character for the\nanalogy with statistical optics. Finally, we present some challenges that, if\nsolved, would increase our understanding of cold atom systems and, thus, the\nrelated areas."
    },
    {
        "anchor": "Tunable-spin-model generation with spin-orbit-coupled fermions in\n  optical lattices: We study the dynamical behaviour of ultracold fermionic atoms loaded into an\noptical lattice under the presence of an effective magnetic flux, induced by\nspin-orbit coupled laser driving. At half filling, the resulting system can\nemulate a variety of iconic spin-1/2 models such as an Ising model, an XY\nmodel, a generic XXZ model with arbitrary anisotropy, or a collective one-axis\ntwisting model. The validity of these different spin models is examined across\nthe parameter space of flux and driving strength. In addition, there is a\nparameter regime where the system exhibits chiral, persistent features in the\nlong-time dynamics. We explore these properties and discuss the role played by\nthe system's symmetries. We also discuss experimentally-viable implementations.",
        "positive": "Phase diagram of quasi-two-dimensional bosons in laser speckle potential: We have studied the phase diagram of a quasi-two-dimensional interacting Bose\ngas at zero temperature in the presence of random potential created by laser\nspeckles. The superfluid fraction and the fraction of particles with zero\nmomentum are obtained within the mean-field Gross-Pitaevskii theory and in\ndiffusion Monte Carlo simulations. We find a transition from the superfluid to\nthe insulating state, when the strength of the disorder grows. Estimations of\nthe critical parameters are compared with the predictions of the percolation\ntheory in the Thomas-Fermi approximation. Analytical expressions for the\nzero-momentum fraction and the superfluid fraction are derived in the limit of\nweak disorder and weak interactions within the framework of the Bogoliubov\ntheory. Limits of validity of various approximations are discussed."
    },
    {
        "anchor": "Observation of spin-orbit-dependent electron scattering using long-range\n  Rydberg molecules: We present experimental evidence for spin-orbit interaction of an electron as\nit scatters from a neutral atom. The scattering process takes place within a\nRb$_2$ ultralong-range Rydberg molecule, consisting of a Rydberg atomic core, a\nRydberg electron, and a ground state atom. The spin-orbit interaction leads to\ncharacteristic level splittings of vibrational molecular lines which we\ndirectly observe via photoassociation spectroscopy. We benefit from the fact\nthat molecular states dominated by resonant $p$-wave interaction are\nparticularly sensitive to the spin-orbit interaction. Our work paves the way\nfor studying novel spin dynamics in ultralong-range Rydberg molecules.\nFurthermore, it shows that the molecular setup can serve as a microlaboratory\nto perform precise scattering experiments in the low-energy regime of a few\nmeV.",
        "positive": "Vortex dynamics and skyrmions in four to six dimensions: Coherence\n  vortices in Bose-Einstein condensates: I point out how coherence vortices, i.e., topological defects in a\ncorrelation function, could help explore new physics if they are created in\nmatter waves. Vortex dynamics could be studied in up to six dimensions, and\nspin topological defects unseen in lower dimensions could be created. A\nrudimentary proof-of-principle experiment is sketched and simulated, in which\nthree Bose-Einstein condensates are used to create and detect coherence\nvortices."
    },
    {
        "anchor": "Conduction of Ultracold Fermions Through a Mesoscopic Channel: In a mesoscopic conductor electric resistance is detected even if the device\nis defect-free. We engineer and study a cold-atom analog of a mesoscopic\nconductor. It consists of a narrow channel connecting two macroscopic\nreservoirs of fermions that can be switched from ballistic to diffusive. We\ninduce a current through the channel and find ohmic conduction, even for a\nballistic channel. An analysis of in-situ density distributions shows that in\nthe ballistic case the chemical potential drop occurs at the entrance and exit\nof the channel, revealing the presence of contact resistance. In contrast, a\ndiffusive channel with disorder displays a chemical potential drop spread over\nthe whole channel. Our approach opens the way towards quantum simulation of\nmesoscopic devices with quantum gases.",
        "positive": "Observation of a strongly ferromagnetic spinor Bose-Einstein condensate: We report the observation of strongly ferromagnetic $F=1$ spinor\nBose-Einstein condensates of $^7$Li atoms. The condensates are generated in an\noptical dipole trap without using magnetic Feshbach resonances, so that the\ncondensates have internal spin degrees of freedom. Studying the non-equilibrium\nspin dynamics, we have measured the ferromagnetic spin interaction energy and\ndetermined the $s$-wave scattering length difference among total spin $f$\nchannels to be $a_{f=2}-a_{f=0} =-18(3)$ Bohr radius. This strong\ncollision-channel dependence leads to a large variation in the condensate size\nwith different spin composition. We were able to excite a radial monopole mode\nafter a spin-flip transition between the $|m_F=0\\rangle$ and $|m_F=1\\rangle$\nspin states. From the experiments, we estimated the scattering length ratio\n$a_{f=2}/a_{f=0}=0.27(6)$, and determined $a_{f=2}$ = 7(2) and $a_{f=0}$ =\n25(5) Bohr radii, respectively. The results indicate the spin-dependent\ninteraction energy of our system is as large as 46$\\%$ of the condensate\nchemical potential."
    },
    {
        "anchor": "Analytical solutions for two heteronuclear atoms in a ring trap: We consider two heteronuclear atoms interacting with a short-range $\\delta$\npotential and confined in a ring trap. By taking the Bethe-ansatz-type\nwavefunction and considering the periodic boundary condition properly, we\nderive analytical solutions for the heteronuclear system. The eigen-energies\nrepresented in terms of quasi-momentums can then be determined by solving a set\nof coupled equations. We present a number of results, which display different\nfeatures from the case of identical atoms. Our result can be reduced to the\nwell-known Lieb-Liniger solution when two interacting atoms have the same\nmasses.",
        "positive": "Decay of persistent currents in annular atomic superfluids: We investigate the role of vortices in the decay of persistent current states\nof annular atomic superfluids by solving numerically the Gross-Pitaevskii\nequation, and we directly compare our results with experimental data from Ref.\n[1]. We theoretically model the optical phase-imprinting technique employed to\nexperimentally excite finite-circulation states in Ref. [1] in the\nBose-Einstein condensation regime, accounting for imperfections of the optical\ngradient imprinting profile. By comparing simulations of this realistic\nprotocol to an ideal imprinting, we show that the introduced density\nexcitations arising from imperfect imprinting are mainly responsible for\nlimiting the maximum reachable winding number $w_\\mathrm{max}$ in the\nsuperfluid ring. We also investigate the effect of a point-like obstacle with\nvariable potential height $V_0$ onto the decay of circulating supercurrents.\nFor a given obstacle height, a critical circulation $w_c$ exists, such that for\nan initial circulation $w_0$ larger than $w_c$ the supercurrent decays through\nthe emission of vortices, which cross the superflow and thus induce phase\nslippage. Higher values of the obstacle height $V_0$ further favour the\nentrance of vortices, thus leading to lower values of $w_c$. Furthermore, the\nstronger vortex-defect interaction at higher $V_0$ leads to vortices that\npropagate closer to the center of the ring condensate. The combination of both\nthese effects leads to an increase of the supercurrent decay rate for\nincreasing $w_0$, in agreement with experimental observations.\n  [1]: G. Del Pace, et al., Phys. Rev. X 12, 041037 (2022)"
    },
    {
        "anchor": "Vortex generation in stirred binary Bose-Einstein condensates: The dynamical vortex production, with a trap-confining time-dependent stirred\npotential, is studied by using mass-imbalanced cold-atom coupled Bose-Einstein\ncondensates (BEC). The vortex formation is explored by considering that both\ncoupled species are confined by a pancake-like harmonic trap, slightly modified\nelliptically by a time-dependent periodic potential, with the characteristic\nfrequency enough larger than the transversal trap frequency. The approach is\napplied to the experimentally accessible binary mixtures $^{85}$Rb-$^{133}$Cs\nand $^{85}$Rb-$^{87}$Rb, which allow us to verify the effect of mass\ndifferences in the dynamics. For both species, the time evolutions of the\nrespective energy contributions, together with associated velocities, are\nstudied in order to distinguish turbulent from non-turbulent flows. By using\nthe angular momentum and moment of inertia mean values, effective classical\nrotation frequencies are suggested, which are further considered within\nsimulations in the rotating frame without the stirring potential. Spectral\nanalysis is also provided for both species, with the main focus being the\nincompressible kinetic energies. In the transient turbulent regime, before\nstable vortex patterns are produced, the characteristic $k^{-5/3}$ Kolmogorov\nbehavior is clearly identified for both species at intermediate momenta $k$\nabove the inverse Thomas-Fermi radial positions, further modified by the\nuniversal $k^{-3}$ scaling at momenta higher than the inverse of the respective\nhealing lengths.\n  Emerging from the mass-imbalanced comparison, relevant is to observe that, as\nlarger is the mass difference, much faster is the dynamical production of\nstable vortices.",
        "positive": "Analog cosmological reheating in an ultracold Bose gas: Cosmological reheating describes the transition of the post-inflationary\nuniverse to a hot and thermal state. In order to shed light on the underlying\ndynamics of this process, we propose to quantum-simulate the reheating-like\ndynamics of a generic cosmological single-field model in an ultracold Bose gas.\nIn our setup, the excitations on top of an atomic Bose-Einstein condensate play\nthe role of the particles produced by the decaying inflaton field after\ninflation. Expanding spacetime as well as the background oscillating inflaton\nfield are mimicked in the non-relativistic limit by a time dependence of the\natomic interactions, which can be tuned experimentally via Feshbach resonances.\nAs we illustrate by means of classical-statistical simulations for the case of\ntwo spatial dimensions, the dynamics of the atomic system exhibits the\ncharacteristic stages of far-from-equilibrium reheating, including the\namplification of fluctuations via parametric instabilities and the subsequent\nturbulent transport of energy towards higher momenta. The transport is governed\nby a non-thermal fixed point showing universal self-similar time evolution as\nwell as a transient regime of prescaling with time-dependent scaling exponents.\nWhile the classical-statistical simulations can capture only the earlier stages\nof the dynamics for weak couplings, the proposed experiment has the potential\nof exploring the evolution up to late times even beyond the weak coupling\nregime."
    },
    {
        "anchor": "Free expansion of quasi-2D Bose-Einstein condensates with quantized\n  vortices: We observe that a density-depleted vortex core evolves into concentric\ndensity ripples in a freely expanding quasi-two-dimensional Bose-Einstein\ncondensate. The atomic density of the expanding condensate rapidly reduces due\nto the fast expansion along the tightly confining axial direction, and thus the\ntransverse expansion of the condensate is not significantly affected by the\natom-atom interactions. We find that the observed density profiles of the\nvortex cores are in good quantitative agreement with numerical simulations\nassuming no interactions. We analyze the defocused images of the vortex cores,\nwhere defocussing is caused by the free fall of the condensate during the\nexpansion time. In the defocused images, the vortex core becomes magnified and\nappears to be filled after a certain expansion time which depends on the vortex\ncharge number.",
        "positive": "Asymptotic Bound-state Model for Feshbach Resonances: We present an Asymptotic Bound-state Model which can be used to accurately\ndescribe all Feshbach resonance positions and widths in a two-body system. With\nthis model we determine the coupled bound states of a particular two-body\nsystem. The model is based on analytic properties of the two-body Hamiltonian,\nand on asymptotic properties of uncoupled bound states in the interaction\npotentials. In its most simple version, the only necessary parameters are the\nleast bound state energies and actual potentials are not used. The complexity\nof the model can be stepwise increased by introducing threshold effects,\nmultiple vibrational levels and additional potential parameters. The model is\nextensively tested on the 6Li-40K system and additional calculations on the\n40K-87Rb system are presented."
    },
    {
        "anchor": "Two-dimensional bright and dark-in-bright dipolar Bose-Einstein\n  condensate solitons on a one-dimensional optical lattice: We study the statics and dynamics of anisotropic, stable, bright and\ndark-in-bright dipolar quasi-two-dimensional Bose-Einstein condensate (BEC)\nsolitons on a one-dimensional (1D) optical-lattice (OL) potential. These\nsolitons mobile in a plane perpendicular to the 1D OL trap can have both\nrepulsive and attractive contact interactions. The dark-in-bright solitons are\nthe excited states of the bright solitons. The solitons, when subject to a\nsmall perturbation, exhibit sustained breathing oscillation. The dark-in-bright\nsolitons can be created by phase imprinting a bright soliton. At medium\nvelocities the collision between two solitons is found to be quasi elastic.The\nresults are demonstrated by a numerical simulation of the three-dimensional\nmean-field Gross-Pitaevskii equation in three spatial dimensions employing\nrealistic interaction parameters for a dipolar $^{164}$Dy BEC.",
        "positive": "Fermi-Fermi crossover in the ground state of 1D few-body systems with\n  anomalous three-body interactions: In one spatial dimension, quantum systems with an attractive three-body\ncontact interaction exhibit a scale anomaly. In this work, we examine the\nfew-body sector for up to six particles. We study those systems with a\nself-consistent, non-perturbative, iterative method, in the subspace of zero\ntotal momentum. Exploiting the structure of the contact interaction, the method\nreduces the complexity of obtaining the wavefunction by three powers of the\ndimension of the Hilbert space. We present results on the energy, and momentum\nand spatial structure, as well as Tan's contact. We find a Fermi-Fermi\ncrossover interpolating between large, weakly bound trimers and compact, deeply\nbound trimers: at weak coupling, the behavior is captured by degenerate\nperturbation theory; at strong coupling, the system is governed by an effective\ntheory of heavy trimers (plus free particles in the case of asymmetric\nsystems). Additionally, we find that there is no trimer-trimer attraction and\ntherefore no six-body bound state."
    },
    {
        "anchor": "Synthetic superfluid chemistry with vortex-trapped quantum impurities: We explore the effect of using two-dimensional matter-wave vortices to\nconfine an ensemble of bosonic quantum impurities. This is modelled\ntheoretically using a mass-imbalanced homogeneous two component\nGross-Pitaevskii equation where each component has independent atom numbers and\nequal atomic masses. By changing the mass imbalance of our system we find the\nshape of the vortices are deformed even at modest imbalances, leading to barrel\nshaped vortices; which we quantify using a multi-component variational\napproach. The energy of impurity carrying vortex pairs are computed, revealing\na mass-dependent energy splitting. We then compute the excited states of the\nimpurity, which we in turn use to construct `covalent bonds' for vortex pairs.\nOur work opens a new route to simulating synthetic chemical reactions with\nsuperfluid systems.",
        "positive": "Engineering Photonic Floquet Hamiltonians through Fabry P\u00e9rot\n  Resonators: In this letter we analyze an optical Fabry-P\\'erot resonator as a\ntime-periodic driving of the (2D) optical field repeatedly traversing the\nresonator, uncovering that resonator twist produces a synthetic magnetic field\napplied to the light within the resonator, while mirror aberrations produce\nrelativistic dynamics, anharmonic trapping, and spacetime curvature. We develop\na Floquet formalism to compute the effective Hamiltonian for the 2D field,\ngeneralizing the idea that the intra-cavity optical field corresponds to an\nensemble of non-interacting, massive, harmonically trapped particles. This work\nilluminates the extraordinary potential of optical resonators for exploring the\nphysics of quantum fluids in gauge fields and exotic space-times."
    },
    {
        "anchor": "Comment on \"Spectral Signatures of the Fulde-Ferrell-Larkin-Ovchinnikov\n  Order Parameter in One-Dimensional Optical lattices\": Comment on \"Spectral Signatures of the Fulde-Ferrell-Larkin-Ovchinnikov Order\nParameter in One-Dimensional Optical lattices\" M. Reza Bakhtiari, M. J.\nLeskinen, and P. T\\\"orm\\\"a, Phys. Rev. lett. {\\bf 101}, 120404 (2008).",
        "positive": "Exact ordering of energy levels for one-dimensional interacting Fermi\n  gases with $SU(n)$ symmetry: Based on the exact solution of one-dimensional Fermi gas systems with $SU(n)$\nsymmetry in a hard wall, we demonstrate that we are able to sort the ordering\nof the lowest energy eigenvalues of states with all allowed permutation\nsymmetries, which can be solely marked by certain quantum numbers in the Bethe\nansatz equations. Our results give examples beyond the scope of the generalized\nLieb-Mattis theorem, which can only compare the ordering of energy levels of\nstates belonging to different symmetry classes if they are comparable according\nto the pouring principle. In the strongly interacting regime, we show that the\nordering of energy levels can be determined by an effective spin-exchange model\nand extend our results to the non-uniform system trapped in the harmonic\npotential."
    },
    {
        "anchor": "The effect of anisotropic exchange interactions and short-range\n  phenomena on superfluidity in a homogeneous dipolar Fermi gas: We develop a simple numerical method that allows us to calculate the\nBardeen-Cooper-Schriefer (BCS) superfluid transition temperature (Tc) precisely\nfor any interaction potential. We apply it to a polarised, ultracold Fermi gas\nwith long-range, anisotropic, dipolar interactions and include the effects of\nanisotropic exchange interactions. We pay particular attention to the\nshort-range behaviour of dipolar gasses and re-examine current renormalisation\nmethods. In particular, we find that dimerisation of both atoms and molecules\nsignificantly hampers the formation of a superfluid. The end result is that at\nhigh density/interaction strengths, we find Tc is orders of magnitude lower\nthan previous calculations.",
        "positive": "Vortex lines attached to dark solitons in Bose-Einstein condensates and\n  Boson-Vortex Duality in 3+1 Dimensions: We demonstrate the existence of stationary states composed of vortex lines\nattached to planar dark solitons in scalar Bose-Einstein condensates.\nDynamically stable states of this type are found at low values of the chemical\npotential in channeled condensates, where the long-wavelength instability of\ndark solitons is prevented. In oblate, harmonic traps, U-shaped vortex lines\nattached by both ends to a single planar soliton are shown to be long-lived\nstates. Our results are reported for parameters typical of current experiments,\nand open up a way to explore the interplay of different topological structures.\nThese configurations provide Dirichlet boundary conditions for vortex lines and\nthereby mimic open strings attached to D-branes in string theory. We show that\nthese similarities can be formally established by mapping the Gross-Pitaevskii\ntheory into a dual effective string theory for open strings via a boson-vortex\nduality in 3+1 dimensions. Combining a one-form gauge field living on the\nsoliton plane which couples to the endpoints of vortex lines and a two-form\ngauge field which couples to vortex lines, we obtain a gauge-invariant dual\naction of open vortex lines with their endpoints attached to dark solitons."
    },
    {
        "anchor": "Approach and separation of quantum vortices with balanced cores: Using two innovations, smooth, but distinctly different, scaling laws for the\nnumerical reconnection of pairs of initially orthogonal and anti-parallel\nquantum vortices are obtained using the three-dimensional Gross-Pitaevskii\nequations, the simplest mean-field non-linear Schr\\\"odinger equation for a\nquantum fluid. The first innovation suppresses temporal fluctuations by using\nan initial density profile that is slightly below the usual two-dimensional\nsteady-state Pad\\'e approximate profiles. The second innovation is to find the\ntrajectories of the quantum vortices from a pseudo-vorticity constructed on the\nthree-dimensional grid from the gradients of the wave function. These\ntrajectories then allow one to calculate the Frenet-Serret frames and the\ncurvature of the vortex lines. For the anti-parallel case, the scaling laws\njust before and after reconnection obey the dimensional\n$\\delta\\sim|t_r-t|^{1/2}$ prediction with temporal symmetry about the\nreconnection time $t_r$ and physical space symmetry about the $x_r$, the\nmid-point between the vortices, with extensions of the vortex lines formng the\nedges of an equilateral pyramid. For all of the orthogonal cases, before\nreconnection $\\delta_{in}\\sim(t-t_r)^{1/3}$ and after reconnection\n$\\delta_{out}\\sim(t-t_r)^{2/3}$, which are respectively slower and faster than\nthe dimensional prediction. In these cases, the reconnection takes place in a\nplane defined by the directions of the curvature and vorticity. To define the\nstructure further, lines are drawn that connect the four arms that extend from\nthe reconnection plane, four angles $\\theta_i$ between these arms are found,\nthen summed, giving $\\sum\\theta_i>360^\\circ$. This implies that the overall\nstructure is convex or hyperbolic, as opposed to the acute angles of the\nanti-parallel pyramid.",
        "positive": "Theoretical methods to treat a single dissipative bosonic mode coupled\n  globally to an interacting many body system: We present two approaches capable of describing the dynamics of an\ninteracting many body system on a lattice coupled globally to a dissipative\nbosonic mode. Physical realizations are for example ultracold atom gases in\noptical lattice coupled to a photonic mode of an optical cavity or electronic\ngases in solids coupled to THz cavity fields. The first approach, applicable\nfor large dissipation strengths and any system size, is a variant of the\nmany-body adiabatic elimination method for investigating the long time dynamics\nof the system. The second method extends the time-dependent matrix product\ntechniques to capture the global coupling of the interacting particles to the\nbosonic mode and its open nature. It gives numerically exact results for small\nto intermediate system sizes. As a benchmark for our methods we perform the\nfull quantum evolution of a Bose-Hubbard chain coupled to a cavity mode. We\nshow that important deviations from the mean-field behavior occur when\nconsidering the full atoms cavity coupling [1]."
    },
    {
        "anchor": "Exact relaxation dynamics of a localized many-body state in the 1D bose\n  gas: Through an exact method we numerically solve the time evolution of the\ndensity profile for an initially localized state in the one-dimensional bosons\nwith repulsive short-range interactions. We show that a localized state with a\ndensity notch is constructed by superposing one-hole excitations. The initial\ndensity profile overlaps the plot of the squared amplitude of a dark soliton in\nthe weak coupling regime. We observe the localized state collapsing into a flat\nprofile in equilibrium for a large number of particles such as N=1000. The\nrelaxation time increases as the coupling constant decreases, which suggests\nthe existence of off-diagonal long-range order. We show a recurrence phenomenon\nfor a small number of particles such as N=20.",
        "positive": "Topological superfluids in two-dimensional Fermi gas with Rashba\n  spin-orbit coupling: The realization of spin-orbit coupling (SOC) in ultracold atoms has triggered\nan intensive exploring of topological superfluids in the degenerate Fermi gases\nbased on mean-field theory, which has not yet been reported in experiments.\nHere, we demonstrate the topological phase transitions in the system via the\nnumerically exact quantum Monte Carlo method. Without prior assumptions, our\nunbiased real-space calculation shows that spin-orbit coupling can stabilize an\nunconventional pairing in the weak SOC regime, in which the\nFulde-Ferrell-Larkin-Ovchinnikov pairing coexists with the\nBardeen-Cooper-Schrieffer pairing. Furthermore, we use the jumps in the spin\npolarization at the time-reversal invariant momenta to qualify the topological\nphase transition, where we find the critical exponent deviated from the\nmean-field theory. Our results pave the way for the searching of unconventional\npairing and topological superfluids with degenerate Fermi gases."
    },
    {
        "anchor": "Localized modes in quasi-2D Bose-Einstein condensates with spin-orbit\n  and Rabi couplings: We consider a two-component pancake-shaped, i.e., effectively two-dimensional\n(2D), Bose-Einstein condensate (BEC) coupled by the spin-orbit (SO) and Rabi\nterms. The SO coupling adopted here is of the mixed Rashba-Dresselhaus type.\nFor this configuration, we derive a system of two 2D nonpolynomial\nSchr\\\"odinger equations (NPSEs), for both attractive and repulsive interatomic\ninteractions. In the low- and high-density limits, the system amounts to\npreviously known models, namely, the usual 2D Gross-Pitaevskii equation, or the\nSchr\\\"odinger equation with the nonlinearity of power 7/3. We present simple\napproximate localized solutions, obtained by treating the SO and Rabi terms as\nperturbations. Localized solutions of the full NPSE system are obtained in a\nnumerical form. Remarkably, in the case of the attractive nonlinearity acting\nin free space (i.e., without any 2D trapping potential), we find parameter\nregions where the SO and Rabi couplings make 2D fundamental solitons\ndynamically stable.",
        "positive": "Extended stream functions for dynamics of Bose-Einstein condensations:\n  Snake instability of dark soliton in ultra-cold atoms as an example: In this paper, we formulate extended stream functions (ESFs) to describe the\ndynamics of Bose-Einstein condensations in the two-dimensional space. The\nordinary stream function is applicable only for stationary and incompressible\nsuperfluids, whereas the ESFs can describe the dynamics of compressible and\nnon-stationary superfluids. The ESFs are composed of two stream functions,\ni.e., one describes the compressible density modulations and the other the\nincompressible rotational superflow. As an application, we study the snake\ninstability of the dark soliton in a rectangular potential in detail by the\nESFs."
    },
    {
        "anchor": "Real space mean-field theory of a spin-1 Bose gas in synthetic\n  dimensions: The internal degrees of freedom provided by ultracold atoms give a route for\nrealizing higher dimensional physics in systems with limited spatial\ndimensions. Non-spatial degrees of freedom in these systems are dubbed\n\"synthetic dimensions\". This connection is useful from an experimental\nstandpoint but complicated by the fact that interactions alter the condensate\nground state. Here we use the Gross-Pitaevskii equation to study ground state\nproperties of a spin-1 Bose gas under the combined influence of an optical\nlattice, spin-orbit coupling, and interactions at the mean field level. The\nassociated phases depend on the sign of the spin-dependent interaction\nparameter and the strength of the optical lattice potential. We find \"charge\"\nand spin density wave phases which are directly related to helical spin order\nin real space and affect the behavior of edge currents in the synthetic\ndimension. We determine the resulting phase diagram as a function of the\nspin-orbit coupling and spin-dependent interaction strength, considering both\nattractive (ferromagnetic) and repulsive (polar) spin-dependent interactions.\nOur results are applicable to current and future experiments, specifically with\n$^{87}$Rb, $^{7}$Li, $^{41}$K, and $^{23}$Na.",
        "positive": "Liquid-gas transition and coexistence in ground-state bosons with spin\n  twist: We study the thermodynamic liquid-gas transition and coexistence (LGTC) for\nground-state bosons under contact interactions. We find that the LGTC can be\nfacilitated by the mismatch of spin polarization, dubbed \"spin twist,\" between\nsingle-particle and interaction channels of bosons with spin degrees of\nfreedom. Such a spin twist uniquely stabilizes the gas phase by creating an\neffective repulsion for low-density bosons, thereby enabling LGTC in the\npresence of a quantum droplet at a much larger density. We have demonstrated\nthe scheme for binary bosons subject to Rabi coupling and magnetic detuning,\nwhere the liquid-gas transition can be conveniently tuned and their coexistence\ncan be characterized by a discontinuous density profile in a harmonic trap. The\nspin twist scheme for LGTC can be generalized to a wide class of quantum\nsystems with competing single-particle and interaction orders."
    },
    {
        "anchor": "Gradient corrections to the local density approximation in the\n  one-dimensional Bose gas: The local density approximation (LDA) is the central technical tool in the\nmodeling of quantum gases in trapping potentials. It consists in treating the\ngas as an assembly of independent mesoscopic fluid cells at equilibrium with a\nlocal chemical potential, and it is justified when the correlation length is\nlarger than the size of the cells. The LDA is often regarded as a crude\napproximation, particularly in the ground state of the one-dimensional (1D)\nBose gas, { where the correlation length is \"therefore said to be\" infinite (in\nthe sense that correlation functions decay as a power law).} Here we take\nanother look at the LDA. The local density $\\rho(x)$ is viewed as a functional\nof the trapping potential $V(x)$, to which one applies a gradient expansion.\nThe zeroth order in that expansion is the LDA. The first-order correction in\nthe gradient expansion vanishes due to reflection symmetry. At second order,\nthere are two corrections proportional to $d^2V/dx^2$ and $(dV/dx)^2$, and we\npropose a method to determine the corresponding coefficients by a perturbative\ncalculation in the Lieb-Liniger model. This leads to an expression for the\ncoefficients in terms of matrix elements of the density operator, which can in\nprinciple be evaluated numerically for an arbitrary coupling constant; here we\nshow how to efficiently evaluate the coefficient associated to the curvature of\nthe potential $d^2V/dx^2$, which dominates the deviation to LDA near local\nminima or maxima of the trapping potential. Both coefficients are evaluated\nanalytically in the limits of infinite repulsion (hard-core bosons) and small\nrepulsion (quasi-condensate).} The corrected LDA density profiles are compared\nto DMRG calculations, with significant improvement compared to zeroth-order\nLDA.",
        "positive": "Parametric amplification of vacuum fluctuations in a spinor condensate: Parametric amplification of vacuum fluctuations is crucial in modern quantum\noptics, enabling the creation of squeezing and entanglement. We demonstrate the\nparametric amplification of vacuum fluctuations for matter waves using a spinor\nF=2 Rb-87 condensate. Interatomic interactions lead to correlated pair creation\nin the m_F= +/- 1 states from an initial unstable m_F=0 condensate, which acts\nas a vacuum for m_F unequal 0. Although this pair creation from a pure m_F=0\ncondensate is ideally triggered by vacuum fluctuations, unavoidable spurious\ninitial m_F= +/- 1 atoms induce a classical seed which may become the dominant\ntriggering mechanism. We show that pair creation is insensitive to a classical\nseed for sufficiently large magnetic fields, demonstrating the dominant role of\nvacuum fluctuations. The presented system thus provides a direct path towards\nthe generation of non-classical states of matter on the basis of spinor\ncondensates."
    },
    {
        "anchor": "Hyperchaos in a Bose-Hubbard chain with Rydberg-dressed interactions: We study chaos and hyperchaos of Rydberg-dressed Bose-Einstein condensates\n(BECs) in a one-dimensional optical lattice. Due to the long-range soft-core\ninteraction between the dressed atoms, the dynamics of the BECs are described\nby the extended Bose-Hubbard model. In the mean-field regime, we analyze the\ndynamical stability of the BEC by focusing on the groundstate and localized\nstate configuration. Lyapunov exponents of the two configurations are\ncalculated by varying the soft-core interaction strength, potential bias and\nlength of the lattice. Both configurations can have multiple positive Lyapunov\nexponents, exhibiting hyperchaotic dynamics. We show the dependence of the\nnumber of the positive Lyapunov exponents and the largest Lyapunov exponent on\nthe length of the optical lattice. The largest Lyapunov exponent is directly\nproportional to areas of phase space encompassed by the associated Poincar\\'e\nsections. We demonstrate that linear and hysteresis quenches of the lattice\npotential and the dressed interaction lead to distinct dynamics due to the\nchaos and hyperchaos. Our work is relevant to current research on chaos, and\ncollective and emergent nonlinear dynamics of BECs with long-range\ninteractions.",
        "positive": "A compact experimental machine for studying tunable Bose-Bose superfluid\n  mixtures: We present a compact and versatile experimental system for producing\nBose-Bose superfluid mixtures composed of sodium and potassium atoms. The\ncompact design combines the necessary ultra-high vacuum enviroment for\nultracold atom experiments with efficient atomic fluxes by using\ntwo-dimensional magneto-optical traps as independent source of atoms. We\ndemonstrate the performance of this new machine by producing a Bose-Einstein\ncondensate of $^{23}$Na with $\\sim 1 \\times 10^{6}~$atoms. The tunability of\nNa-K bosonic mixtures is particularly interesting for studies regarding the\nnucleation of vortices and quantum turbulence. In this direction, the large\noptical access of the science chamber along the vertical direction provides the\nconditions to implement high resolution optical setups for imaging and rotating\nthe condensate with a stirring beam. We show the nucleation of a vortex lattice\nwith up to 14 vortices in the $^{23}$Na BEC, attesting the efficiency of the\nexperimental apparatus in studying the dynamics of vortices."
    },
    {
        "anchor": "Macroscopic quantum many-body tunneling of attractive Bose-Einstein\n  condensate in anharmonic trap: We study the stability of attractive atomic Bose-Einstein condensate and the\nmacroscopic quantum many-body tunneling (MQT) in the anharmonic trap. We\nutilize correlated two-body basis function which keeps all possible two-body\ncorrelations. The anharmonic parameter ($\\lambda$) is slowly tuned from\nharmonic to anharmonic. For each choice of $\\lambda$ the many-body equation is\nsolved adiabatically. The use of the van der Waals interaction gives realistic\npicture which substantially differs from the mean-field results. For weak\nanharmonicity, we observe that the attractive condensate gains stability with\nlarger number of bosons compared to that in the pure harmonic trap. The\ntransition from resonances to bound states with weak anharmonicity also differs\nsignificantly from the earlier study of Moiseyev {\\it et.al.}[J. Phys. B: At.\nMol. Opt. Phys. {\\bf{37}}, L193 (2004)]. We also study the tunneling of the\nmetastable condensate very close to the critical number $N_{cr}$ of collapse\nand observe that near collapse the MQT is the dominant decay mechanism compared\nto the two-body and three-body loss rate. We also observe the power law\nbehavior in MQT near the critical point. The results for pure harmonic trap are\nin agreement with mean-field results. However we fail to retrieve the power law\nbehavior in anharmonic trap although MQT is still the dominant decay mechanism.",
        "positive": "Effect of impurities on the transition temperature of a dilute dipolar\n  tapped Bose gase: By using two-fluid model the effect of impurities on the transition\ntemperature of a dipolar trapped Bose gas is investigated. By treating Gaussian\nspatial correlation for impurities from the interaction modified spectra of the\nsystem, the formula for the shift of transition temperature is derived. The\nshift of the transition temperature contains essentially three contributions\ndue to contact, dipole-dipole and impurity interactions. Applying our results\nto Dipolar Bose gases show that the shift of the transition temperature due to\nimpurities could be measured for isotropic trap (dipole-dipole contributions is\nzero) and Feshbach resonance technique (contact potential contribution is\nnegligible)."
    },
    {
        "anchor": "Leading gradient correction to the kinetic energy for two-dimensional\n  fermion gases: Density functional theory (DFT) is notorious for the absence of gradient\ncorrections to the two-dimensional (2D) Thomas-Fermi kinetic-energy functional;\nit is widely accepted that the 2D analog of the 3D von Weizs\\\"acker correction\nvanishes, together with all higher-order corrections. Contrary to this\nlong-held belief, we show that the leading correction to the kinetic energy\ndoes not vanish, is unambiguous, and contributes perturbatively to the total\nenergy. This insight emerges naturally in a simple extension of standard DFT,\nwhich has the effective potential energy as a functional variable on equal\nfooting with the single-particle density.",
        "positive": "Static and Dynamic Properties of Interacting Spin-1 Bosons in an Optical\n  Lattice: We study the physics of interacting spin-$1$ bosons in an optical lattice\nusing a variational Gutzwiller technique. We compute the mean-field ground\nstate wave-function and discuss the evolution of the condensate, spin, nematic,\nand singlet order parameters across the superfluid-Mott transition. We then\nextend the Gutzwiller method to derive the equations governing the dynamics of\nlow energy excitations in the lattice. Linearizing these equations, we compute\nthe excitation spectra in the superfluid and Mott phases for both ferromagnetic\nand antiferromagnetic spin-spin interactions. In the superfluid phase, we\nrecover the known excitation spectrum obtained from Bogoliubov theory. In the\nnematic Mott phase, we obtain gapped, quadratically dispersing particle and\nhole-like collective modes, whereas in the singlet Mott phase, we obtain a\nnon-dispersive gapped mode, corresponding to the breaking of a singlet pair.\nFor the ferromagnetic Mott insulator, the Gutzwiller mean-field theory only\nyields particle-hole like modes but no Goldstone mode associated with long\nrange spin order. To overcome this limitation, we supplement the Gutzwiller\ntheory with a Schwinger boson mean-field theory which captures super-exchange\ndriven fluctuations. In addition to the gapped particle-hole-like modes, we\nobtain a gapless quadratically dispersing ferromagnetic spin-wave Goldstone\nmode. We discuss the evolution of the singlet gap, particle-hole gap, and the\neffective mass of the ferromagnetic Goldstone mode as the superfluid-Mott phase\nboundary is approached from the insulating side. We discuss the relevance and\nvalidity of Gutzwiller mean-field theories to spinful systems, and potential\nextensions of this framework to include more exotic physics which appears in\nthe presence of spin-orbit coupling or artificial gauge fields."
    },
    {
        "anchor": "A one-dimensional liquid of fermions with tunable spin: Correlations in systems with spin degree of freedom are at the heart of\nfundamental phenomena, ranging from magnetism to superconductivity. The effects\nof correlations depend strongly on dimensionality, a striking example being\none-dimensional (1D) electronic systems, extensively studied theoretically over\nthe past fifty years. However, the experimental investigation of the role of\nspin multiplicity in 1D fermions - and especially for more than two spin\ncomponents - is still lacking. Here we report on the realization of 1D,\nstrongly-correlated liquids of ultracold fermions interacting repulsively\nwithin SU(N) symmetry, with a tunable number N of spin components. We observe\nthat static and dynamic properties of the system deviate from those of ideal\nfermions and, for N>2, from those of a spin-1/2 Luttinger liquid. In the\nlarge-N limit, the system exhibits properties of a bosonic spinless liquid. Our\nresults provide a testing ground for many-body theories and may lead to the\nobservation of fundamental 1D effects.",
        "positive": "Numerical simulation of two-component attractive Fermi gases based on\n  parametrized partition function: The zero-temperature and finite-temperature thermodynamics of two-component\nFermi gases with finite-range attractive interaction suffer from fermion sign\nproblem, which seems like an insurmountable problem in exact numerical\nsimulations. In a recent work, we find a reliable method to simulate the\nthermodynamic properties of single-component Fermi gases for both\nnoninteracting and repulsively interacting cases based on the method of\nparametrized partition function and the $\\xi_E$ curve of constant energy. In\nthe present work, this method is generalized to two-component Fermi gases with\nfinite-range attractive interaction, which shows clearly that our method has\ngood chance to apply to various Fermi systems. From the simulated heat\ncapacity, we find a peak at the temperature below the Fermi temperature which\nimplies the pairing of fermions with different spin. At high temperature, the\nsimulated heat capacity approaches the classical value. The reasonable result\nin this work validates the application of our method to attractive cases, which\nimplies a wide range of applications, from nuclear physics, BCS-BEC crossover,\nsuperconductivity, to neutron star, etc.."
    },
    {
        "anchor": "Dynamical transitions and quantum quenches in mean-field models: We develop a generic method to compute the dynamics induced by quenches in\ncompletely connected quantum systems. These models are expected to provide a\nmean-field description at least of the short time dynamics of finite\ndimensional system. We apply our method to the Bose-Hubbard model, to a\ngeneralized Jaynes-Cummings model, and to the Ising model in a transverse\nfield. We find that the quantum evolution can be mapped onto a classical\neffective dynamics, which involves only a few intensive observables. For some\nspecial parameters of the quench, peculiar dynamical transitions occur. They\nresult from singularities of the classical effective dynamics and are\nreminiscent of the transition recently found in the fermionic Hubbard model.\nFinally, we discuss the generality of our results and possible extensions.",
        "positive": "Phase diagram and optimal control for n-tupling discrete time crystal: A remarkable consequence of spontaneously breaking the time translational\nsymmetry in a system, is the emergence of time crystals. In periodically driven\nsystems, discrete time crystals (DTC) can be realized which have a periodicity\nthat is n times the driving period. However, all of the experimental\nobservations have been performed for period-doubling and period-tripling\ndiscrete time crystals. Novel physics can arise by simulating many-body physics\nin the time domain, which would require a genuine realisation of the n-tupling\nDTC. A system of ultra-cold bosonic atoms bouncing resonantly on an oscillating\nmirror is one of the models that can realise large period DTC. The preparation\nof DTC demands control in creating the initial distribution of the ultra-cold\nbosonic atoms along with the mirror frequency. In this work, we demonstrate\nthat such DTC is robust against perturbations to the initial distribution of\natoms. We show how Bayesian methods can be used to enhance control in the\npreparation of the initial state as well as to efficiently calculate the phase\ndiagram for such a model. Moreover, we examine the stability of DTCs by\nanalyzing quantum many-body fluctuations and show that they do not reveal\nsignatures of heating."
    },
    {
        "anchor": "Observation of ultracold atomic bubbles in orbital microgravity: Significant leaps in the understanding of quantum systems have been driven by\nthe exploration of geometry, topology, dimensionality, and interactions with\nultracold atomic ensembles. A system where atoms evolve while confined on an\nellipsoidal surface represents a heretofore unexplored geometry and topology.\nRealizing such an ultracold bubble system (potentially Bose-Einstein condensed)\nhas areas of interest including quantized-vortex flow respecting topological\nconstraints imposed by closed surfaces, new collective modes, and\nself-interference via free bubble expansion. Large ultracold bubbles, created\nby inflating smaller condensates, directly tie into Hubble-analog expansion\nphysics. Here, we report observations from the NASA Cold Atom Lab facility\naboard the International Space Station of bubbles of ultracold atoms created\nusing a radiofrequency-dressing protocol. We observe a variety of bubble\nconfigurations of differing sizes and initial temperature, and explore bubble\nthermodynamics, demonstrating significant cooling associated with inflation.\nAdditionally, we achieve partial coverings of bubble traps greater than 1 mm in\nsize with ultracold films of inferred few-$\\mu$m thickness, and we observe the\ndynamics of shell structures projected into free-evolving harmonic confinement.\nThe observations are part of the first generation of scientific measurements\nmade with ultracold atoms in space, exploiting the benefits of perpetual\nfree-fall to explore gravity-free evolution of quantum systems that are\nprohibitively difficult to create on Earth. This work points the way to\nexperiments focused on the nature of the Bose-Einstein condensed bubble, the\ncharacter of its excitations, and the role of topology in its evolution; it\nalso ushers in an era of orbital microgravity quantum-gas physics.",
        "positive": "Prethermalization in the cooling dynamics of an impurity in a BEC: We discuss the cooling dynamics of heavy impurity atoms in a Bose-Einstein\ncondensate (BEC) by emission of Cherenkov phonons from scattering with the\ncondensate. In a weakly interacting, low-temperature condensate the\nsuperfluidity of the condensate results in a separation of time-scales of the\nthermalization dynamics. Pre-thermalized states are formed with distinct\nregions of impurity momenta determined by the mass ratio of impurity and BEC\natoms. This can be employed to detect the mass renormalization of the impurity\nupon the formation of a polaron and paves the way to preparing non-equilibrium\nimpurity-momentum distributions."
    },
    {
        "anchor": "Entanglement entropy, fidelity and the phase transition of\n  one-dimensional hard-core bosonic system with three-body interactions: We study the one-dimensional hard-core Bose-Hubbard model with three-body\ninteractions. In previous work[1], the two-thirds filling solid with both\nbond-wave order (BOW) and charge-density wave order (CDW) is found and it\nundergoes a second order phase transition to the superfluid phase. However, in\nrecent work[2], we found the BOW not independent with CDW order. Thus, by\nutilizing the density matrix renormalization group, we make use of both\nentanglement entropy and fidelity susceptibility to detect the phase\ntransition. In two-thirds filling, the extreme point of the entanglement\nentropy also indicates the superfluid phase transition point. However, the\npairwise entanglement entropy drop quickly after additional critical point,\nsuch disentangled behaviour demonstrates another melting point to the CDW\nphase. Thus, a novel intermediate phase between CDW phase and superfluid phase\nis found. At last, we analyzed the half filling case with entanglement entropy.",
        "positive": "Beyond universality in three-body recombination: an Effective Field\n  Theory treatment: We discuss the impact of a finite effective range on three-body systems\ninteracting through a large two-body scattering length. By employing a\nperturbative analysis in an effective field theory well suited to this scale\nhierarchy we find that an additional three-body parameter is required for\nconsistent renormalization once range corrections are considered. This allows\nus to extend previously discussed universal relations between different\nobservables in the recombination of cold atoms to account for the presence of a\nfinite effective range. We show that such range corrections allow us to\nsimultaneously describe the positive and negative scattering-length loss\nfeatures observed in recombination with Lithium-7 atoms by the Bar-Ilan group.\nThey do not, however, significantly reduce the disagreement between the\nuniversal relations and the data of the Rice group on Lithium-7 recombination\nat positive and negative scattering lengths."
    },
    {
        "anchor": "Generalized acceleration theorem for spatiotemporal Bloch waves: A representation is put forward for wave functions of quantum particles in\nperiodic lattice potentials subjected to homogeneous time-periodic forcing,\nbased on an expansion with respect to Bloch-like states which embody both the\nspatial and the temporal periodicity. It is shown that there exists a\ngeneralization of Bloch's famous acceleration theorem which grows out of this\nrepresentation and captures the effect of a weak probe force applied in\naddition to a strong dressing force. Taken together, these elements point at a\n\"dressing and probing\" strategy for coherent wave-packet manipulation, which\ncould be implemented in present experiments with optical lattices.",
        "positive": "Virial coefficients from unified statistical thermodynamics of quantum\n  gases trapped under generic power law potential in $d$ dimension and the\n  equivalence of trapped quantum gases: From the unified statistical thermodynamics of quantum gases, the virial\ncoefficients of ideal Bose and Fermi gases which are trapped under generic\npower law potential are derived systematically. From the general result of\nvirial coefficients, one can produce the known results in $d=3$ and $d=2$. But\nmore importantly we found that, the virial coefficients of bosons and fermions\nbecome equal (except the the second virial coefficient, where the sign is\ndifferent) when we trap the gases under harmonic potential in $d=1$. This\nresult suggests the equivalence between Bose and Fermi gases which is already\nestablished for $d=1$ by M M Faruk (J Stat Phys, DOI\n10.1007/s10955-015-1344-4). Surprisingly our investigation also shows that the\nvirial coefficients of two dimensional free quantum gases are identical to the\nvirial coefficients of one dimensional harmonically trapped quantum gases."
    },
    {
        "anchor": "Feshbach resonances, weakly bound molecular states and coupled-channel\n  potentials for cesium at high magnetic fields: We explore the scattering properties of ultracold ground-state Cs atoms at\nmagnetic fields between 450 G (45 mT) and 1000 G. We identify 17 new Feshbach\nresonances, including two very broad ones near 549 G and 787 G. We measure the\nbinding energies of several different dimer states by magnetic field modulation\nspectroscopy. We use least-squares fitting to these experimental results,\ntogether with previous measurements at lower field, to determine a new\n6-parameter model of the long-range interaction potential, designated M2012.\nCoupled-channels calculations using M2012 provide an accurate mapping between\nthe s-wave scattering length and the magnetic field over the entire range of\nfields considered. This mapping is crucial for experiments that rely on precise\ntuning of the scattering length, such as those on Efimov physics.",
        "positive": "Spectral fluctuation and $\\frac{1}{f^\u03b1}$ noise in the energy\n  level statistics of interacting trapped bosons: It has been recently shown numerically that the transition from integrability\nto chaos in quantum systems and the corresponding spectral fluctuations are\ncharacterized by $\\frac{1}{f^{\\alpha}}$ noise with $1\\leq\\alpha\\leq 2$. The\nsystem of interacting trapped bosons is inhomogeneous and a complex system. The\npresence of external harmonic trap makes it more interesting as in the atomic\ntrap the bosons occupy partly degenerate single-particle states. Earlier\ntheoretical and experimental results show that at zero temperature the\nlow-lying levels are of collective nature and high-lying excitations are of\nsingle particle nature. We observe that for few bosons, $P(s)$ distribution\nshows the Shnirelman peak which exhibits a large number of quasi-degenerate\nstates. For large number of bosons the low-lying levels are strongly affected\nby the interatomic interaction and the corresponding level fluctuation shows a\ntransition to Wigner with increase in particle number. It does not follow GOE\n(Gaussian Orthogonal Ensemble) Random Matrix predictions. For high-lying levels\nwe observe the uncorrelated Poisson distribution. Thus it may be a very\nrealistic system to prove that $\\frac{1}{f^{\\alpha}}$ noise is ubiquitous in\nnature."
    },
    {
        "anchor": "Enhanced many-body effects in the excitation spectrum of a\n  weakly-interacting rotating Bose-Einstein condensate: The excitation spectrum of a highly-condensed two-dimensional trapped\nBose-Einstein condensate (BEC) is investigated within the rotating frame of\nreference. The rotation is used to transfer high-lying excited states to the\nlow-energy spectrum of the BEC. We employ many-body linear-response theory and\nshow that, once the rotation leads to a quantized vortex in the ground state,\nalready the low-energy part of the excitation spectrum shows substantial\nmany-body effects beyond the realm of mean-field theory. We demonstrate\nnumerically that the many-body effects grow with the vorticity of the ground\nstate, meaning that the rotation enhances them even for very weak repulsion.\nFurthermore, we explore the impact of the number of bosons $N$ in the\ncondensate on a low-lying single-particle excitation, which is describable\nwithin mean-field theory. Our analysis shows deviations between the many-body\nand mean-field results which clearly persist when $N$ is increased up to the\nexperimentally relevant regime, typically ranging from several thousand up to a\nmillion bosons in size. Implications are briefly discussed.",
        "positive": "Polaron in dilute 2D Bose gas at low temperatures: The properties of a Bose polaron immersed in a dilute two-dimensional medium\nat finite temperatures are discussed. Assuming that the impurity is\nweakly-coupled to the bath particles we have perturbatively calculated the\npolaron energy, effective mass, quasiparticle residue and damping rate. The\nparameters of impurity spectrum are found to be well-defined in the whole\ntemperature region whereas the pole structure of the impurity Green's function\nis visible only at absolute zero. At any finite temperatures the quasiparticle\nresidue is logarithmically divergent signalling of the branch-cut behavior of\nthe polaron propagator."
    },
    {
        "anchor": "State engineering of impurities in a lattice by coupling to a Bose gas: We investigate the localization pattern of interacting impurities, which are\ntrapped in a lattice potential and couple to a Bose gas. For small interspecies\ninteraction strengths, the impurities populate the energetically lowest Bloch\nstate or localize separately in different wells with one extra particle being\ndelocalized over all the wells, depending on the lattice depth. In contrast,\nfor large interspecies interaction strengths we find that due to the fractional\nfilling of the lattice and the competition of the repulsive contact interaction\nbetween the impurities and the attractive interaction mediated by the Bose gas,\nthe impurities localize either pairwise or completely in a single well. Tuning\nthe lattice depth, the interspecies and intraspecies interaction strength\ncorrespondingly allows for a systematic control and engineering of the two\nlocalization patterns. The sharpness of the crossover between the two states as\nwell as the broad region of their existence supports the robustness of the\nengineering. Moreover, we are able to manipulate the ground state's degeneracy\nin form of triplets, doublets and singlets by implementing different boundary\nconditions, such as periodic and hard wall boundary conditions.",
        "positive": "Dispersion and wavefunction symmetry in cold atoms experiencing\n  artificial gauge fields: We analyze the single particle quantum mechanics of an atom whose dispersion\nis modified by spin orbit coupling to Raman lasers. We calculate how the novel\ndispersion leads to unusual single particle physics. We focus on the symmetry\nof the ground state wavefunction in different potentials."
    },
    {
        "anchor": "Theory of Combined Photoassociation and Feshbach Resonances in a\n  Bose-Einstein Condensate: We model combined photoassociation and Feshbach resonances in a Bose-Einstein\ncondensate, where the shared dissociation continuum allows for quantum\ninterference in losses from the condensate, as well as a dispersive-like shift\nof resonance. A simple analytical model, based on the limit of weakly bound\nmolecules, agrees well with numerical experiments that explicitly include\ndissociation to noncondensate modes. For a resonant laser and an off-resonant\nmagnetic field, constructive interference enables saturation of the\nphotoassociation rate at user-friendly intensities, at a value set by the\ninterparticle distance. This rate limit is larger for smaller condensate\ndensities and, near the Feshbach resonance, approaches the rate limit for\nmagnetoassociation alone. Also, we find agreement with the unitary limit--set\nby the condensate size--only for a limited range of near-resonant magnetic\nfields. Finally, for a resonant magnetic field and an off-resonant laser,\nmagnetoassociation displays similar quantum interference and a dispersive-like\nshift. Unlike photoassociation, interference and the fieldshift in resonant\nmagnetoassociation is tunable with both laser intensity and detuning. Also, the\ndispersive-like shift of the Feshbach resonance depends on the size of the\nFeshbach molecule, and is a signature of non-universal physics in a strongly\ninteracting system.",
        "positive": "Tunable dual-species Bose-Einstein condensates of $^{39}$K and $^{87}$Rb: We present the production of dual-species Bose-Einstein condensates of\n$^{39}\\mathrm{K}$ and $^{87}\\mathrm{Rb}$. Preparation of both species in the\n$\\left| F=1,m_F=-1 \\right\\rangle$ state enabled us to exploit a total of three\nFesh\\-bach resonances which allows for simultaneous Feshbach tuning of the\n$^{39}\\mathrm{K}$ intraspecies and the $^{39}\\mathrm{K}$-$^{87}\\mathrm{Rb}$\ninterspecies scattering length. Thus dual-species Bose-Einstein condensates\nwere produced by sympathetic cooling of $^{39}\\mathrm{K}$ with\n$^{87}\\mathrm{Rb}$. A dark spontaneous force optical trap was used for\n$^{87}\\mathrm{Rb}$, to reduce the losses in $^{39}\\mathrm{K}$ due to\nlight-assisted collisions in the optical trapping phase, which can be of\nbenefit for other dual-species experiments. The tunability of the scattering\nlength was used to perform precision spectroscopy of the interspecies Feshbach\nresonance located at $117.56(2)\\,\\mathrm{G}$ and to determine the width of the\nresonance to $1.21(5)\\,\\mathrm{G}$ by rethermalization measurements. The\ntransition region from miscible to immiscible dual-species condensates was\ninvestigated and the interspecies background scattering length was determined\nto $28.5\\,a_\\mathrm{0}$ using an empirical model. This paves the way for\ndual-species experiments with $^{39}\\mathrm{K}$ and $^{87}\\mathrm{Rb}$ BECs\nranging from molecular physics to precision metrology."
    },
    {
        "anchor": "Self-bound Doubly-Dipolar Bose-Einstein condensates: We analyze the physics of self-bound droplets in a doubly dipolar\nBose-Einstein condensate (DDBEC) composed by particles with both electric and\nmagnetic dipole moments. Using the particularly relevant case of dysprosium, we\nshow that the anisotropy of the doubly-dipolar interaction potential is highly\nversatile and nontrivial, depending critically on the relative orientation and\nstrength between the two dipole moments. This opens novel possibilities for\nexploring intriguing quantum many-body physics. Interestingly, by varying the\nangle between the two dipoles we find a dimensional crossover from quasi\none-dimensional to quasi two-dimensional self-bound droplets. This opens a so\nfar unique scenario in condensate physics, in which a dimensional crossover is\nsolely driven by interactions in the absence of any confinement.",
        "positive": "Rydberg-dressed atoms in BCS-state: We consider a system consisting of Rydberg dressed atoms interacting with BEC\ncondensate of diatomic molecules. Using random phase approximation (RPA) we\ncalculate the effective interactions between Rydberg atoms accounting for their\nWan der Waals repulsion and exchange of virtual excitations of the condensate\nand demonstrate that total interaction can become attractive and BCS state of\nRydberg dressed atoms can be formed. Using the example of 6Li atoms we\ndemonstrate that the strength of the interactions can be controlled optically,\nand BCS regime is achievable at realistic experimental conditions."
    },
    {
        "anchor": "Macroscopic two-state systems in trapped atomic condensates: We consider a macroscopic two-sate system based on persistent current states\nof a Bose-Einstein condensate (BEC) of interacting neutral atoms confined in a\nring with a weak Josephson link. We demonstrate that macroscopic superpositions\nof different BEC flows are energetically favorable in this system. Moreover, a\nmacroscopic two-state dynamics emerges in the low energy limit. We also\ninvestigate fundamental limitations due to the noise inherent to the\ninteracting BEC of Josephson-ring geometry. We show that the coherent\nmacroscopic dynamics is readily measurable for an experimentally accessible\nrange of parameters.",
        "positive": "Exact canonic eigenstates of the truncated Bogoliubov Hamiltonian in an\n  interacting bosons gas: In a gas of $N$ weakly interacting bosons \\cite{Bogo1, Bogo2}, a truncated\ncanonic Hamiltonian $\\widetilde{h}_c$ follows from dropping all the interaction\nterms between free bosons with momentum $\\hbar\\mathbf{k}\\ne\\mathbf{0}$.\nBogoliubov Canonic Approximation (BCA) is a further manipulation, replacing the\nnumber \\emph{operator} $\\widetilde{N}_{in}$ of free particles in\n$\\mathbf{k}=\\mathbf{0}$, with the total number $N$ of bosons. BCA transforms\n$\\widetilde{h}_c$ into a different Hamiltonian\n$H_{BCA}=\\sum_{\\mathbf{k}\\ne\\mathbf{0}}\\epsilon(k)B^\\dagger_\\mathbf{k}B_\\mathbf{k}+const$,\nwhere $B^\\dagger_\\mathbf{k}$ and $B_\\mathbf{k}$ create/annihilate non\ninteracting pseudoparticles. The problem of the \\emph{exact} eigenstates of the\ntruncated Hamiltonian is completely solved in the thermodynamic limit (TL) for\na special class of eigensolutions $|\\:S,\\:\\mathbf{k}\\:\\rangle_{c}$, denoted as\n\\textquoteleft s-pseudobosons\\textquoteright, with energies\n$\\mathcal{E}_{S}(k)$ and \\emph{zero} total momentum. Some preliminary results\nare given for the exact eigenstates (denoted as \\textquoteleft\n$\\eta$-pseudobosons\\textquoteright), carrying a total momentum\n$\\eta\\hbar\\mathbf{k}$ ($\\eta=\\:1,\\:2,\\: \\dots$). A comparison is done with\n$H_{BCA}$ and with the Gross-Pitaevskii theory (GPT), showing that some\ndifferences between exact and BCA/GPT results persist even in the TL. Finally,\nit is argued that the emission of $\\eta$-pseudobosons, which is responsible for\nthe dissipation $\\acute{a}$ \\emph{la} Landau \\cite{L}, could be significantly\ndifferent from the usual picture, based on BCA pseudobosons."
    },
    {
        "anchor": "Damping of macroscopic oscillation and interference pattern in coupled\n  Gross-Pitaevskii equations without self-interaction: Quantum phenomena appear in a macroscopic scale in Bose-Einstein condensates.\nThe Gross-Pitaevskii (GP) equation describes the dynamics of the weakly\ninteracting Bose-Einstein condensates. The GP equation has a form of the\nSchroedinger equation with self-interaction. The coupled Gross-Pitaevskii\nequations are used to describe some mixtures of Bose-Einstein condensates. In\nthis paper, we will show some numerical results of coupled Gross-Pitaevskii\nequations without self-interaction, which has a form of nonlinearly-coupled\nSchroedinger equations. We demonstrate that the macroscopic oscillation and the\ninterference of two quantum wave packets decay in time owing to mutual\ninteraction, which is analogous to the decoherence in quantum mechanics of many\nparticles.",
        "positive": "Multiple self-organized phases and spatial solitons in cold atoms\n  mediated by optical feedback: We study the transverse self-structuring of a cloud of cold atoms with\neffective atomic interactions mediated by a coherent driving beam\nretro-reflected by means of a single mirror. The resulting self-structuring due\nto optomechanical forces is much richer than that of an effective-Kerr medium,\ndisplaying hexagonal, stripe and honeycomb phases depending on the interaction\nstrength parametrized by the linear susceptibility. Phase domains are described\nby real Ginzburg-Landau amplitude equations. In the stripe phase the system\nrecovers inversion symmetry. Moreover, the subcritical character of the\nhoneycomb phase allows for light-density feedback solitons functioning as\nself-sustained dark atomic traps with motion controlled by phase gradients in\nthe driving beam."
    },
    {
        "anchor": "Alternating-domain supersolids in binary dipolar condensates: Two-component dipolar condensates are now experimentally producible, and we\ntheoretically investigate the nature of supersolidity in this system. We\npredict the existence of a binary supersolid state in which the two components\nform a series of alternating domains, producing an immiscible double\nsupersolid. Remarkably, we find that a dipolar component can even induce\nsupersolidity in a nondipolar component. In stark contrast to single-component\ndipolar supersolids, alternating-domain supersolids do not require quantum\nstabilization, and the number of crystal sites is not strictly limited by the\ncondensate populations, with the density hence being substantially lower. Our\nresults are applicable to a wide range of dipole moment combinations, marking\nan important step towards long-lived bulk-supersolidity.",
        "positive": "Experimental extraction of the quantum effective action for a\n  non-equilibrium many-body system: Far-from-equilibrium situations are ubiquitous in nature. They are\nresponsible for a wealth of phenomena, which are not simple extensions of\nnear-equilibrium properties, ranging from fluid flows turning turbulent to the\nhighly organized forms of life. On the fundamental level, quantum fluctuations\nor entanglement lead to novel forms of complex dynamical behaviour in many-body\nsystems for which a description as emergent phenomena can be found within the\nframework of quantum field theory. A central quantity in these efforts,\ncontaining all information about the measurable physical properties, is the\nquantum effective action. Though the problem of non-equilibrium quantum\ndynamics can be exactly formulated in terms of the quantum effective action,\nthe solution is in general beyond capabilities of classical computers. In this\nwork, we present a strategy to determine the non-equilibrium quantum effective\naction using analog quantum simulators, and demonstrate our method\nexperimentally with a quasi one-dimensional spinor Bose gas out of equilibrium.\nBuilding on spatially resolved snapshots of the spin degree of freedom, we\ninfer the quantum effective action up to fourth order in an expansion in\none-particle irreducible correlation functions at equal times. We uncover a\nstrong suppression of the irreducible four-vertex emerging at low momenta,\nwhich solves the problem of dynamics in the highly occupied regime far from\nequilibrium where perturbative descriptions fail. Similar behaviour in this\nnon-pertubative regime has been proposed in the context of early-universe\ncosmology. Our work constitutes a new realm of large-scale analog quantum\ncomputing, where the high level of control of synthetic quantum systems\nprovides the means for the solution of long-standing theoretical problems in\nhigh-energy and condensed matter physics with an experimental approach."
    },
    {
        "anchor": "Quantum Kinetic Theory of Collisionless Superfluid Internal Convection: Superfluids can transport heat via simultaneous opposite flows of their\nspatially interpenetrating condensate and thermal components. While this\ninternal convection is usually described within Landau's phenomenological two\nfluid hydrodynamics, we apply quantum kinetic theory to a dilute Bose gas held\nbeween thermal reservoirs at different temperatures, and show that the\nphenomenon also appears in collisionless kinetic regimes, and should be\ndirectly observable in currently feasible experiments on trapped ultracold\nvapors.",
        "positive": "Multidimensional Josephson vortices in spin-orbit coupled Bose-Einstein\n  condensates: snake instability and decay through vortex dipoles: We analyze the dynamics of Josephson vortex states in two-component\nBose-Einstein condensates with Rashba-Dresselhaus spin-orbit coupling by using\nthe Gross-Pitaevskii equation. In 1D, both in homogeneous and harmonically\ntrapped systems, we report on stationary states containing doubly charged,\nstatic Josephson vortices. In multidimensional systems, we find stable\nJosephson vortices in a regime of parameters typical of current experiments\nwith $^{87}$Rb atoms. In addition, we discuss the instability regime of\nJosephson vortices in disk-shaped condensates, where the snake instability\noperates and vortex dipoles emerge. We study the rich dynamics that they\nexhibit in different regimes of the spin-orbit coupled condensate depending on\nthe orientation of the Josephson vortices."
    },
    {
        "anchor": "Polaron Interactions and Bipolarons in One-Dimensional Bose Gases in the\n  Strong Coupling Regime: Bose polarons, quasi-particles composed of mobile impurities surrounded by\ncold Bose gas, can experience strong interactions mediated by the many-body\nenvironment and form bipolaron bound states. Here we present a detailed study\nof heavy polarons in a one-dimensional Bose gas by formulating a\nnon-perturbative theory and complementing it with exact numerical simulations.\nWe develop an analytic approach for weak boson-boson interactions and\narbitrarily strong impurity-boson couplings. Our approach is based on a\nmean-field theory that accounts for deformations of the superfluid by the\nimpurities and in this way minimizes quantum fluctuations. The mean-field\nequations are solved exactly in Born-Oppenheimer (BO) approximation leading to\nan analytic expression for the interaction potential of heavy polarons which is\nfound to be in excellent agreement with quantum Monte-Carlo (QMC) results. In\nthe strong-coupling limit the potential substantially deviates from the\nexponential form valid for weak coupling and has a linear shape at short\ndistances. Taking into account the leading-order Born-Huang corrections we\ncalculate bipolaron binding energies for impurity-boson mass ratios as low as 3\nand find excellent agreement with QMC results.",
        "positive": "Realizing and detecting Stiefel-Whitney insulators in an optical Raman\n  lattice: We propose a feasible scheme to realize a four-band Stiefel-Whitney insultor\n(SWI) with spin-orbit coupled ultracold atoms in an optical Raman lattice. Four\nselected spin states are coupled by carefully designed Raman lasers, to\ngenerate the desired spin-orbit interactions with spacetime inversion symmetry.\nWe map out a phase diagram with respect to the experimental parameters, where a\nlarge topological phase region exists. We further present two distinct\ndetection methods to resolve the non-abelian band topology, in both equilibrium\nand dynamical ways. The detection relies on the spin textures extracted from\nthe time-of-flight imaging, showing the tomographic signatures in the ground\nstates and long-time averaged patterns on certain submanifold via a\nbulk-surface duality. Our work paves a realistic way to explore novel real\ntopology with quantum matters."
    },
    {
        "anchor": "Condensate of excitations in moving superfluids: A possibility of the condensation of excitations with a non-zero momentum in\nrectilinearly moving and rotating superfluid bosonic and fermionic (with Cooper\npairing) media is considered in terms of a phenomenological order-parameter\nfunctional at zero and non-zero temperature. The results might be applicable to\nthe description of bosonic systems like superfluid $^4$He, ultracold atomic\nBose gases, charged pion and kaon condensates in rotating neutron stars, and\nvarious superconducting fermionic systems with pairing, like proton and\ncolor-superconducting components in compact stars, metallic superconductors,\nand neutral fermionic systems with pairing, like the neutron component in\ncompact stars and ultracold atomic Fermi gases. Order parameters of the\n\"mother\" condensate in the superfluid and the new condensate of excitations,\ncorresponding energy gains, critical temperatures and critical velocities are\nfound.",
        "positive": "Mixed triplet and singlet pairing in multicomponent ultracold fermion\n  systems with dipolar interactions: The symmetry properties of the Cooper pairing problem for multi-component\nultra-cold dipolar molecular systems are investigated. The dipolar anisotropy\nprovides a natural and robust mechanism for both triplet and singlet Cooper\npairing to first order in the interaction strength. With a purely dipolar\ninteraction, the triplet $p_z$-like polar pairing is the most dominant. A\nshort-range attractive interaction can enhance the singlet pairing to be nearly\ndegenerate with the triplet pairing. We point out that these two pairing\nchannels can mix by developing a relative phase of $\\pm\\frac{\\pi}{2}$, thus\nspontaneously breaking time-reversal symmetry. We also suggest the possibility\nof such mixing of triplet and singlet pairing in other systems."
    },
    {
        "anchor": "Many-Body Quantum Dynamics in the Decay of Bent Dark Solitons of\n  Bose-Einstein Condensates: The beyond mean-field dynamics of a bent dark soliton embedded in a\ntwo-dimensional repulsively interacting Bose-Einstein condensate is explored.\nWe examine the case of a single bent dark soliton comparing the mean-field\ndynamics to a correlated approach, the Multi-Configuration Time-Dependent\nHartree method for Bosons. Dynamical snaking of this bent structure is\nobserved, signaling the onset of fragmentation which becomes significant during\nthe vortex nucleation. In contrast to the mean-field approximation \"filling\" of\nthe vortex core is observed, leading in turn to the formation of filled-core\nvortices, instead of the mean-field vortex-antivortex pairs. The resulting\nsmearing effect in the density is a rather generic feature, occurring when\nsolitonic structures are exposed to quantum fluctuations. Here, we show that\nthis filling owes its existence to the dynamical building of an antidark\nstructure developed in the next-to-leading order orbital. We further\ndemonstrate that the aforementioned beyond mean-field dynamics can be\nexperimentally detected using the variance of single shot measurements.\nAdditionally, a variety of excitations including vortices, oblique dark\nsolitons, and open ring dark soliton-like structures building upon higher-lying\norbitals is observed. We demonstrate that signatures of the higher-lying\norbital excitations emerge in the total density, and can be clearly captured by\ninspecting the one-body coherence. In the latter context, the localization of\none-body correlations exposes the existence of the multi-orbital\nvortex-antidark structure.",
        "positive": "Finite-temperature phases of trapped bosons in a two-dimensional\n  quasiperiodic potential: We study a system of 2D trapped bosons in a quasiperiodic potential via ab\ninitio Path Integral Monte Carlo simulations, focusing on its finite\ntemperature properties, which have not yet been explored. Alongside the\nsuperfluid, normal fluid and insulating phases, we demonstrate the existence of\na Bose glass phase, which is found to be robust to thermal fluctuations, up to\nabout half of the critical temperature of the non-interacting system. Local\nquantities in the trap are characterized by employing zonal estimators,\nallowing us to trace a phase diagram; we do so for a set of parameters within\nreach of current experiments with quasi-2D optical confinement."
    },
    {
        "anchor": "Spin dynamics in a spin-orbit coupled Fermi gas: We study the dynamics of a non-degenerate, harmonically trapped Fermi gas\nfollowing a sudden ramp of the spin-orbit coupling strength. In the\nnon-interacting limit, we solve the Boltzmann equation in the presence of spin\norbit coupling analytically, and derive expressions for the dynamics of an\narbitrary initial spin state. In particular we show that for a fully spin\npolarized initial state, the total magnetization exhibits collapse and revival\ndynamics in time with a period set by the trapping potential. In real space,\nthis corresponds to oscillations between a fully polarized state and a spin\nhelix. We numerically study the effect of interactions on the dynamics using a\ncollisionless Boltzmann equation.",
        "positive": "Squeezing in driven bimodal Bose-Einstein Condensates: Erratic driving\n  versus noise: We study the interplay of squeezing and phase randomization near the\nhyperbolic instability of a two-site Bose-Hubbard model in the Josephson\ninteraction regime. We obtain results for the quantum Zeno suppression of\nsqueezing, far beyond the previously found short time behavior. More\nimportantly, we contrast the expected outcome with the case where randomization\nis induced by erratic driving with the same fluctuations as the quantum noise\nsource, finding significant differences. These are related to the distribution\nof the squeezing factor, which has log-normal characteristics: hence its\naverage is significantly different from its median due to the occurrence of\nrare events."
    },
    {
        "anchor": "Exact solution of a generalized two-sites Bose-Hubbard model: I introduce a new parametrization of a bosonic Lax operator for the algebraic\nBethe ansatz method with the $gl(2)$-invariant $R$-matrix and use it to present\nthe exact solution of a generalized two-sites Bose-Hubbard model with\nasymmetric tunnelling. In the no interaction limit I show that the Bethe ansatz\nequations can be written as a $S^{N-1}$ sphere, where $N$ is the total number\nof atoms in the condensate.",
        "positive": "Chiral spin liquid state of strongly interacting bosons with a moat\n  dispersion: a Monte Carlo simulation: We consider a system of strongly interacting bosons in two dimensions with\nmoat band dispersion which supports an infinitely degenerate energy minimum\nalong a closed contour in the Brillouin zone. The system has been theoretically\npredicted to stabilize a chiral spin liquid (CSL) ground state. In the\nthermodynamic limit and vanishing densities, $n\\rightarrow 0$, chemical\npotential, $\\mu$, of the uniform CSL state was shown to scale with $n$ as\n$\\mu\\sim n^2\\log ^2n$. Here we perform a Monte Carlo simulation to find the\nparametric window for particle density, $n \\lesssim \\frac{k^2_0}{82 \\pi}$,\nwhere $k_0$ is the linear size of the moat (the radius for a circular moat),\nfor which the scaling $\\sim n^2\\log ^2n$ in the equation of state of the\nhomogeneous CSL is preserved. We variationally show that the uniform CSL state\nis favorable in an interval beyond the obtained scale and present a schematic\nphase diagram for the system. Our results offer some density estimates for\nobserving the low-density behavior of CSL in time-of-flight experiments with a\nrecently Floquet-engineered moat band system of ultracold atoms in Phys. Rev.\nLett. 128, 213401 (2022), and for the recent experiments on emergent excitonic\ntopological order in imbalanced electron-hole bilayers."
    },
    {
        "anchor": "Soliton-phonon scattering problem in 1D nonlinear Schr\u00f6dinger systems\n  with general nonlinearity: A scattering problem (or more precisely, a transmission-reflection problem)\nof linearized excitations in the presence of a dark soliton is considered in a\none-dimensional nonlinear Schr\\\"odinger system with a general nonlinearity: $\n\\mathrm{i}\\partial_t \\phi = -\\partial_x^2 \\phi + F(|\\phi|^2)\\phi $. If the\nsystem is interpreted as a Bose-Einstein condensate, the linearized excitation\nis a Bogoliubov phonon, and the linearized equation is the Bogoliubov equation.\nWe exactly prove that the perfect transmission of the zero-energy phonon is\nsuppressed at a critical state determined by Barashenkov's stability criterion\n[Phys. Rev. Lett. 77, (1996) 1193.], and near the critical state, the\nenergy-dependence of the reflection coefficient shows a saddle-node type\nscaling law. The analytical results are well supported by numerical calculation\nfor cubic-quintic nonlinearity. Our result gives an exact example of scaling\nlaws of saddle-node bifurcation in time-reversible Hamiltonian systems. As a\nby-product of the proof, we also give all exact zero-energy solutions of the\nBogoliubov equation and their finite energy extension.",
        "positive": "Opto-mechanical effects in self-organization of a Bose-Einstein\n  condensate in an optical cavity: The influence of mirror motion on the spatial self organization of a\nBose-Einstein condensate (BEC) in an optical cavity is studied. We show that\nthe mirror dynamics tends to destroy the process of self organization. An\nadditional external phonon pump is shown to modify the critical photon pump\nneeded to observe the onset of self organization."
    },
    {
        "anchor": "Itinerant magnetism in Weyl spin-orbit coupled Fermi gas: Magnetic ordering of itinerant fermionic systems is at the forefront of\ncondensed matter physics dating back to Stoner's instability. Spin-orbit\ncoupling (SOC) which couples two essential ingredients of an itinerant\nfermionic system, namely spin and orbital motion, opens up new horizons to this\nlong-standing problem. Here we report that the itinerant ferromagnetism is\nabsent in 3D Fermi gas with a Weyl SOC and various itinerant spin density waves\nemerge instead, which is deeply rooted in the unique symmetry and spin-momentum\nlocking effect in spin-orbit coupled systems. What is more appealing is that,\nthe strong SOC provides a new and efficient mechanism to realize itinerant spin\ndensity waves at extremely weak repulsion---a significant benefit for present\nultra-cold atom experiment. These novel phenomena can be probed by Bragg\nspectroscopy, time of flight imaging and {\\sl In-Situ } measurements in\nultra-cold atom experiment.",
        "positive": "Observation of symmetry-protected topological band with ultracold\n  fermions: Symmetry plays a fundamental role in understanding complex quantum matter,\nparticularly in classifying topological quantum phases, which have attracted\ngreat interests in the recent decade. An outstanding example is the\ntime-reversal invariant topological insulator, a symmetry-protected topological\n(SPT) phase in the symplectic class of the Altland-Zirnbauer classification. We\nreport the observation for ultracold atoms of a noninteracting SPT band in a\none-dimensional optical lattice and study quench dynamics between topologically\ndistinct regimes. The observed SPT band can be protected by a magnetic group\nand a nonlocal chiral symmetry, with the band topology being measured via Bloch\nstates at symmetric momenta. The topology also resides in far-from-equilibrium\nspin dynamics, which are predicted and observed in experiment to exhibit\nqualitatively distinct behaviors in quenching to trivial and nontrivial\nregimes, revealing two fundamental types of spin-relaxation dynamics related to\nbulk topology. This work opens the way to expanding the scope of SPT physics\nwith ultracold atoms and studying nonequilibrium quantum dynamics in these\nexotic systems."
    },
    {
        "anchor": "Ground-state multiquantum vortices in rotating two-species superfluids: We show numerically that a rotating, harmonically trapped mixture of two\nBose-Einstein-condensed superfluids can, contrary to its single-species\ncounterpart, contain a multiply quantized vortex in the ground state of the\nsystem. This giant vortex can occur without any accompanying single-quantum\nvortices, may either be coreless or have an empty core, and can be realized in\na $^{87}$Rb-$^{41}$K Bose-Einstein condensate. Our results not only provide a\nrare example of a stable, solitary multiquantum vortex but also reveal exotic\nphysics stemming from the coexistence of multiple, compositionally distinct\ncondensates in one system.",
        "positive": "Normal state properties of spin-orbit coupled Fermi gases in the upper\n  branch of energy spectrum: We investigate normal state properties of spin-orbit coupled Fermi gases with\nrepulsive s-wave interaction, in the absence of molecule formation, i.e., in\nthe so-called \"upper branch\". Within the framework of random phase\napproximation, we derive analytical expressions for the quasi-particle lifetime\n$\\tau_s$, the effective mass $m_s^*$, and the Green's function renormalization\nfactor $Z_s$ in the presence of Rashba spin-orbit coupling. In contrast to\nspin-orbit coupled electron gas with Coulomb interaction, we show that the\nmodifications are dependent on the Rashba band index s, and occur in the first\norder of the spin-orbit coupling strength. We also calculate experimental\nobservable such as spectral weight, density of state and specific heat, which\nexhibit significant differences from their counterparts without spin-orbit\ncoupling. We expect our microscopic calculations of these Fermi liquid\nparameters would have the immediate applications to the spin-orbit coupled\nFermi gases in the upper branch of the energy spectrum."
    },
    {
        "anchor": "Competition between pairing and tripling in one-dimensional fermions\n  with coexistent s- and p-wave interactions: We theoretically investigate in-medium two- and three-body correlations in\none-dimensional two-component Fermi gases with coexistent even-parity s-wave\nand odd-parity p-wave interactions. We find the solutions of the stable\nin-medium three-body cluster states such as Cooper triple by solving the\ncorresponding in-medium variational equations. We further feature the phase\ndiagram consisting of the s- and p-wave Cooper pairing phase, and Cooper\ntripling phase, in the plane of s- and p-wave pairing strengths. The Cooper\ntripling phase dominates over the pairing phases when both s- and p-wave\ninteractions are moderately strong.",
        "positive": "A strongly interacting high partial wave Bose gas: Motivated by recent experimental progress, we make an investigation of p- and\nd-wave resonant Bose gas. An explantation of the Nozieres and Schmitt-Rink\n(NSR) scheme in terms of two-channel model is provided. Different from the\ns-wave case, high partial wave interaction supports a quasi-bound state in the\nweak coupling regime. Within the NSR approximation, we study the equation of\nstate, critical temperature and particle population distributions. We clarify\nthe effect of the quasi-bound state on the phase diagram and the dimer\nproduction. A multi-critical point where normal phase, atomic superfluid phase\nand molecular superfluid phase meet is predicted within the phase diagram. We\nalso show the occurrence of a resonant conversion between solitary atoms and\ndimers when temperature kBT approximates the quasi-bound energy."
    },
    {
        "anchor": "Tunable Bose-Einstein condensation and roton-like excitation spectra\n  with dipolar exciton-polaritons in crossed fields: We develop the many-body theory of dipolar exciton-polaritons in an optical\nmicrocavity in crossed transverse electric and in-plane magnetic fields. Even\nfor relatively weak fields, we reveal the existence of two minima in the bare\nlower-polariton dispersion, which give rise to the tuneable transition between\nthe polariton Bose-Einstein condensate and that of excitons, produced by the\ncompetition between these minima. We predict that such dipolar condensate\nexhibits a roton-maxon character of the excitation spectrum, never before\nobserved for polaritons. We show that upon the transition between the two\ncondensation regimes, the weak correlations in the polariton gas give way to\nthe intermediate interparticle correlations characteristic for excitons, and\nthat the transition is accompanied by a sharp quenching of photoluminescence as\nthe lifetime is increased by several orders of magnitude. While in the\npolariton regime, the luminescence peak corresponding to the condensate is\nshifted to a non-zero angle. The angular dependence of the two-photon decay\ntime in the Hanbury Brown and Twiss experiment is calculated and used as a tool\nto evidence the formation of the macroscopically-coherent state. Our proposal\nopens opportunities towards manipulating the superfluid properties and\nextended-range dipole-dipole correlations of exciton-polariton condensates.",
        "positive": "Unitary interaction geometries in few-body systems: We consider few-body systems in which only a certain subset of the\nparticle-particle interactions is resonant. We characterize each subset by a\n{\\it unitary graph} in which the vertices represent distinguishable particles\nand the edges resonant 2-body interactions. Few-body systems whose unitary\ngraph is connected will collapse unless a repulsive 3-body interaction is\nincluded. We find two categories of graphs, distinguished by the kind of 3-body\nrepulsion necessary to stabilize the associated system. Each category is\ncharacterized by whether the graph contains a loop or not: for tree-like graphs\n(graphs containing a loop) the 3-body force renormalizing them is the same as\nin the 3-body system with two (three) resonant interactions. We show\nnumerically that this conjecture is correct for the 4-body case as well as for\na few 5-body configurations. We explain this result in the 4-body sector\nqualitatively by imposing Bethe-Peierls boundary conditions on the pertinent\nFaddeev-Yakubovsky~decomposition of the wave function."
    },
    {
        "anchor": "Tuning superfluid phases of spin-1 bosons in cubic optical lattice with\n  linear Zeeman effect: We analyze theoretically a spinor Bose gas loaded into a three-dimensional\ncubic optical lattice. In order to account for different superfluid phases of\nspin-1 bosons in the presence of an external magnetic field, we work out a\nGinzburg-Landau theory for the underlying spin-1 Bose-Hubbard model. In\nparticular at zero temperature, we determine both the Mott and the superfluid\nphases for the competition between the anti-ferromagnetic interaction and the\nlinear Zeeman effect within the validity range of the Ginzburg-Landau theory.\nMoreover, we find that the phase transition between the superfluid and Mott\ninsulator phases is of second order and that the transitions between the\nrespective superfluid phases for anti-ferromagnetic interaction can be both of\nfirst and second order.",
        "positive": "Strong-coupling Bose polarons in 1D: Condensate deformation and modified\n  Bogoliubov phonons: We discuss the interaction of a quantum impurity with a one-dimensional\ndegenerate Bose gas forming a Bose-polaron. In three spatial dimensions the\nquasiparticle is typically well described by the extended Fr\\\"ohlich model, in\nfull analogy with the solid-state counterpart. This description, which assumes\nan undepleted condensate, fails however in 1D, where the backaction of the\nimpurity on the condensate leads to a self-bound mean-field polaron for\narbitrarily weak impurity-boson interactions. We present a model that takes\ninto account this backaction and describes the impurity-condensate interaction\nas coupling to phonon-like excitations of a deformed condensate. A comparison\nof polaron energies and masses to diffusion quantum Monte-Carlo simulations\nshows very good agreement already on the level of analytical mean-field\nsolutions and is further improved when taking into account quantum\nfluctuations."
    },
    {
        "anchor": "Exotic superfluid states of lattice fermions in elongated traps: We present real-space dynamical mean-field theory calculations for\nattractively interacting fermions in three-dimensional lattices with elongated\ntraps. The critical polarization is found to be 0.8, regardless of the trap\nelongation. Below the critical polarization, we find unconventional superfluid\nstructures where the polarized superfluid and\nFulde-Ferrell-Larkin-Ovchinnikov-type states emerge across the entire core\nregion.",
        "positive": "Collective excitations and supersolid behavior of bosonic atoms inside\n  two crossed optical cavities: We discuss the nature of symmetry breaking and the associated collective\nexcitations for a system of bosons coupled to the electromagnetic field of two\noptical cavities. For the specific configuration realized in a recent\nexperiment at ETH, we show that, in absence of direct intercavity scattering\nand for parameters chosen such that the atoms couple symmetrically to both\ncavities, the system possesses an approximate $U(1)$ symmetry which holds\nasymptotically for vanishing cavity field intensity. It corresponds to the\ninvariance with respect to redistributing the total intensity $I=I_1+I_2$\nbetween the two cavities. The spontaneous breaking of this symmetry gives rise\nto a broken continuous translation-invariance for the atoms, creating a\nsupersolid-like order in the presence of a Bose-Einstein condensate. In\nparticular, we show that atom-mediated scattering between the two cavities,\nwhich favors the state with equal light intensities $I_1=I_2$ and reduces the\nsymmetry to $\\mathbf{Z}_2\\otimes \\mathbf{Z}_2$, gives rise to a finite value\n$\\sim \\sqrt{I}$ of the effective Goldstone mass. For strong atom driving, this\nlow energy mode is clearly separated from an effective Higgs excitation\nassociated with changes of the total intensity $I$. In addition, we compute the\nspectral distribution of the cavity light field and show that both the Higgs\nand Goldstone mode acquire a finite lifetime due to Landau damping at non-zero\ntemperature."
    },
    {
        "anchor": "Dissipation and fluctuations in elongated bosonic Josephson junctions: We investigate the dynamics of bosonic atoms in elongated Josephson\njunctions. We find that these systems are characterized by an intrinsic\ncoupling between the Josephson mode of macroscopic quantum tunneling and the\nsound modes. This coupling of Josephson and sound modes gives rise to a damped\nand stochastic Langevin dynamics for the Josephson degree of freedom. From a\nmicroscopic Lagrangian, we deduce and investigate the damping coefficient and\nthe stochastic noise, which includes thermal and quantum fluctuations. Finally,\nwe study the time evolution of relative-phase and population-imbalance\nfluctuations of the Josephson mode and their oscillating thermalization to\nequilibrium.",
        "positive": "Large Range of Stability of Larkin-Ovchinnikov States for Imbalanced\n  Fermi Gases in Optical Lattices: We show that Larkin-Ovchinnikov (LO) states with modulated superfluid order\nparameters have a considerably larger range of stability in a lattice than in\nthe continuum. We obtain the phase diagram for the 3D cubic attractive Hubbard\nmodel with an unequal population of up and down fermions using the\nBogoliubov-de Gennes fully self-consistent method. We find a strong modulation\nof the local polarization that should provide a distinct signature for\ndetection of the LO phase. The shell structure in the presence of a trap\ngenerates singularities in the density at the phase boundaries and provide\nadditional evidence for the LO phase. Depending on specific parameters, the LO\nground state occurs over a large range of population imbalance, involving 80%\nof the atoms in the trap, and can exist up to an entropy s ~ 0.5 k_B per\nfermion."
    },
    {
        "anchor": "Analysis of two and three dipolar bosons in a spherical harmonic trap: As dipolar gases become more readily accessible in experiment there is a need\nto develop a comprehensive theoretical framework of the few-body physics of\nthese systems. Here, we extend the coupled-pair approach developed for the\nunitary two-component Fermi gas to a few-body system of dipolar bosons in a\nspherical harmonic trap. The long range and anisotropy of the dipole-dipole\ninteraction is handled by a flexible and efficient correlated gaussian basis\nwith stochastically variational optimisation. We calculate the eigenenergy\nspectrum and structural properties of two and three trapped bosonic dipoles.\nThis demonstrates the efficiency and flexibility of the coupled-pair approach\nat dealing with systems with complex interactions.",
        "positive": "Few-fermion thermometry: Potential realization of a quantum thermometer operating in the nanokelvin\nregime, formed by a few-fermionic mixture confined in a one-dimensional\nharmonic trap, is proposed. Thermal states of the system are studied\ntheoretically from the point of view of fundamental sensitivity to temperature\nchanges. It is pointed out that the ability to control the interaction strength\nin such systems allows obtaining high-temperature sensitivity in the regime\nwhere the temperature is much lower than the characteristic temperature scale\ndetermined by a harmonic confinement. This sensitivity is very close to the\nfundamental bound that involves optimal engineering of level separations. The\nperformance of practical measurement schemes and the possible experimental\ncoupling of the thermometer to the probe are discussed."
    },
    {
        "anchor": "Transmission and Reflection of Collective Modes in Spin-1 Bose-Einstein\n  Condensate: We study tunneling properties of collective excitations in spin-1\nBose-Einstein condensates. In the absence of magnetic fields, the total\ntransmission in the long wavelength limit occurs in all kinds of excitations\nbut the quadrupolar spin mode in the ferromagnetic state. The quadrupolar spin\nmode alone shows the total reflection. A difference between those excitations\ncomes from whether the wavefunction of an excitation corresponds to that of the\ncondensate in the long wavelength limit. The correspondence results in the\ntotal transmission as in the spinless BEC.",
        "positive": "Thermodynamics of quantum gases for the entire range of temperature: We have analytically explored thermodynamics of free Bose and Fermi gases for\nthe entire range of temperature, and have extended the same for harmonically\ntrapped cases. We have obtained approximate chemical potentials of the quantum\ngases in closed forms of temperature so that the thermodynamic properties of\nthe quantum gases become plausible specially in the intermediate regime between\nthe classical and quantum limits."
    },
    {
        "anchor": "Enhanced many-body quantum scars from the non-Hermitian Fock skin effect: In contrast with extended Bloch waves, a single particle can become spatially\nlocalized due to the so-called skin effect originating from non-Hermitian\npumping. Here we show that in a wide class of kinetically constrained many-body\nsystems, the skin effect can instead manifest as dynamical amplification within\nthe Fock space, beyond the intuitively expected and previously studied particle\nlocalization and clustering. We exemplify this non-Hermitian Fock skin effect\nin an asymmetric version of the PXP model and show that it gives rise to\nergodicity-breaking eigenstates, the non-Hermitian analogs of quantum many-body\nscars. A distinguishing feature of these non-Hermitian scars is their enhanced\nrobustness against external disorders. We propose an experimental realization\nof the non-Hermitian scar enhancement in a tilted Bose-Hubbard optical lattice\nwith laser-induced loss. Our results show that the Fock skin effect provides a\npowerful tool for creating robust non-ergodic states in generic open quantum\nsystems.",
        "positive": "Local Quench, Majorana Zero Modes, and Disturbance Propagation in the\n  Ising chain: We study the generation and propagation of local perturbations in a quantum\nmany-body spin system. In particular, we study the Ising model in transverse\nfield in the presence of a local field defect at one edge. This system\npossesses a rich phase diagram with different regions characterized by the\npresence of one or two Majorana zero modes. We show that their localized\ncharacter {\\it i}) enables a characterization of the Ising phase transition\nthrough a local-only measurement performed on the edge spin, and {\\it ii})\nstrongly affects the propagation of quasiparticles emitted after the sudden\nremoval of the defect, so that the dynamics of the local magnetization show\nclear deviations from a ballistic behavior in presence of the Majorana\nfermions."
    },
    {
        "anchor": "Non-cancellation of the parity anomaly in the strong-field regime of\n  QED$_{2+1}$: Quantum fluctuations lead to an anomalous violation of parity symmetry in\nquantum electrodynamics for an even number of spatial dimensions. While the\nleading parity-odd electric current vanishes in vacuum, we uncover a\nnon-cancellation of the anomaly for strong electric fields with distinct\nmacroscopic signatures. We perform real-time lattice simulations with fully\ndynamical gauge fields and Wilson fermions in $2+1$ space-time dimensions. In\nthe static field limit, relevant at early times, we solve the problem\nanalytically. Our results point out the fundamental role of quantum anomalies\nfor strong-field phenomena, relevant for a wide range of condensed matter and\nhigh-energy applications, but also for the next generation of gauge theory\nquantum simulators.",
        "positive": "Finite temperature QMC study of the one-dimensional polarized Fermi gas: Quantum Monte Carlo (QMC) techniques are used to provide an\napproximation-free investigation of the phases of the one-dimensional\nattractive Hubbard Hamiltonian in the presence of population imbalance. The\ntemperature at which the \"Fulde-Ferrell-Larkin-Ovchinnikov\" (FFLO) phase is\ndestroyed by thermal fluctuations is determined as a function of the\npolarization. It is shown that the presence of a confining potential does not\ndramatically alter the FFLO regime, and that recent experiments on trapped\natomic gases likely lie just within the stable temperature range."
    },
    {
        "anchor": "Few-to-many particle crossover of pair excitations in a superfluid: Motivated by recent advances in the creation of few-body atomic Fermi gases\nwith attractive interactions, we study theoretically the few-to-many particle\ncrossover of pair excitations, which for large particle numbers evolve into\nmodes describing amplitude fluctuations of the superfluid order parameter (the\n\"Higgs\" modes). Our analysis is based on a Richardson-type pairing model that\ncaptures interactions between time-reversed fermion pairs. The model is\nintegrable, which allows a systematic quantitative study of the few-to-many\nparticle crossover with only minor numerical effort. We first establish a\nparity effect in the ground state energy, which is quantified by a so-called\nMatveev-Larkin parameter that generalizes the pairing gap to mesoscopic\nensembles and which behaves quantitatively differently in a few-body and a\nmany-body regime. The crossover point for this quantity is widely tunable as a\nfunction of interaction strength. We then compute the excitation spectrum and\ndemonstrate that the pair excitation energy shows a minimum that deepens with\nincreasing particle number and shifts to smaller interaction strengths,\nconsistent with the finite-size precursor of a quantum phase transition to a\nsuperfluid state. We extract a critical finite-size scaling exponent that\ncharacterizes the decrease of the gap with increasing particle number.",
        "positive": "Linear rotor in an ideal Bose gas near the threshold for binding: We study a linear rotor in a bosonic bath within the angulon formalism. Our\nfocus is on systems where isotropic or anisotropic impurity-boson interactions\nsupport a shallow bound state. To study the fate of the angulon in the vicinity\nof bound-state formation, we formulate a beyond-linear-coupling angulon\nHamiltonian. First, we use it to study attractive, spherically symmetric\nimpurity-boson interactions for which the linear rotor can be mapped onto a\nstatic impurity. The well-known polaron formalism provides an adequate\ndescription in this limit. Second, we consider anisotropic potentials, and show\nthat the presence of a shallow bound state with pronounced anisotropic\ncharacter leads to a many-body instability that washes out the angulon\ndynamics."
    },
    {
        "anchor": "Spontaneous symmetry breaking of dual-layer solitons in\n  spin-orbit-coupled Bose-Einstein condensates: It is known that stable 2D solitons of the semi-vortex (SV) and mixed-mode\n(MM) types are maintained by the interplay of the cubic attractive nonlinearity\nand spin-orbit coupling (SOC) in binary Bose-Einstein condensates. We introduce\na double-layer system, in which two binary condensates, stabilized by the SOC,\nare linearly coupled by tunneling. By means of the numerical methods, it is\nfound that symmetric two-layer solitons undergo the\nspontaneous-symmetry-breaking (SSB) bifurcation of the subcritical type. The\nbifurcation produces families of asymmetric 2D solitons, which exist up to the\nvalue of the total norm equal to the norm of the Townes solitons, above which\nthe collapse occurs. This situation terminates at a critical value of the\ninter-layer coupling, beyond which the SSB bifurcation is absent, as the\ncollapse sets in earlier. Symmetric 2D solitons that are destabilized by the\nSSB demonstrate dynamical symmetry breaking, in combination with intrinsic\noscillations of the solitons, or transition to the collapse, if the soliton's\nnorm is sufficiently large. Asymmetric MMs produced by the SSB instability\nstart spontaneous drift, in addition to the intrinsic vibrations. Consideration\nof moving 2D solitons is a nontrivial problem because SOC breaks the Galilean\ninvariance. It is found that the system supports moving MMs up to a critical\nvalue of the velocity, beyond which they undergo delocalization.",
        "positive": "dc to ac Josephson transition in a dc atom superconducting quantum\n  interference device: We analyze the effect of the barrier motion on the Bose-Hubbard Hamiltonian\nof a ring-shaped Bose-Einstein condensate interrupted by a pair of Josephson\njunctions, a configuration which is the cold atom analog of the well-known dc\nsuperconducting quantum interference device (SQUID). Such an effect is also\nshown to modify the Heisenberg equation of motion of the boson field operator\nin the two-mode approximation, where a hysteretic contribution that could\naffect the dynamics for accelerated or overlapping barriers is identified. By\nstudying the energy landscape as a function of order and control parameters, we\ndetermine the diagram with the location of the dc and ac Josephson regimes,\nalong with the critical points that are shown to depend on the junctions\nposition. We analyze the dc to ac Josephson transition for adiabatic barrier\ntrajectories that lead to a final uniform velocity, or which perform symmetric\nvelocity paths. We show that such symmetric trajectories may induce, when\nreaching the critical point, highly hysteretic oscillating return paths within\nthe dc regime, similar to the underdamped hysteresis loops arising from the\naction of a resistive flow in the ac regime. We also consider nonequilibrium\ninitial conditions resulting from a finite phase difference on either side of\nthe junctions, along with the critical features of such a parameter. An\nexcellent agreement between the Gross-Pitaevskii simulations and the two-mode\nresults is found in all cases."
    },
    {
        "anchor": "Method of difference-differential equations for some Bethe ansatz\n  solvable models: In studies of one-dimensional Bethe ansatz solvable models, a Fredholm\nintegral equation of the second kind with a difference kernel on a finite\ninterval often appears. This equation does not generally admit a closed-form\nsolution and hence its analysis is quite complicated. Here we study a family of\nsuch equations concentrating on their moments. We find exact relations between\nthe moments in the form of difference-differential equations. The latter\nresults significantly advance the analysis, enabling one to practically\ndetermine all the moments from the explicit knowledge of the lowest one. As\napplications, first we study the moments of the quasimomentum distribution in\nthe Lieb-Liniger model and find explicit analytical results. The latter moments\ndetermine several basic quantities, e.g., the $N$-body local correlation\nfunctions. We prove the equivalence between different expressions found in the\nliterature for the three-body local correlation functions and find an exact\nresult for the four-body local correlation function in terms of the moments of\nthe quasimomentum distributions. We eventually find the analytical results for\nthe three- and four-body correlation functions in the form of asymptotic series\nin the regimes of weak and strong interactions. Next, we study the exact form\nof the low-energy spectrum of a magnon (a polaron) excitation in the\ntwo-component Bose gas described by the Yang-Gaudin model. We find its explicit\nform, which depends on the moments of the quasimomentum distributions of the\nLieb-Liniger model. Then, we address a seemingly unrelated problem of\ncapacitance of a circular capacitor and express the exact result for the\ncapacitance in the parametric form. In the most interesting case of short plate\nseparations, the parametric form has a single logarithmic term. This should be\ncontrasted with the explicit result that has a complicated structure of\nlogarithms.",
        "positive": "Quantized Superfluid Vortex Rings in the Unitary Fermi Gas: In a recent article, Yefsah et al. [Nature 499, 426 (2013)] report the\nobservation of an unusual excitation in an elongated harmonically trapped\nunitary Fermi gas. After phase imprinting a domain wall, they observe\noscillations almost an order of magnitude slower than predicted by any theory\nof domain walls which they interpret as a \"heavy soliton\" of inertial mass some\n200 times larger than the free fermion mass or 50 times larger than expected\nfor a domain wall. We present compelling evidence that this \"soliton\" is\ninstead a quantized vortex ring by showing that the main aspects of the\nexperiment can be naturally explained within the framework of time-dependent\nsuperfluid DFT."
    },
    {
        "anchor": "p-wave Superfluid Phases of Fermi Molecules in a Bilayer Lattice Array: We investigate the emergence of superfluid p=p_x+ip_y phases in an ultracold\ngas of dipolar Fermi molecules lying in two parallel square lattices in 2D. As\nshown by a two body study, dipole moments oriented in opposite directions in\neach layer is the key ingredient in our mean field analysis from which\nunconventional superfluidity is predicted. The T=0 phase diagram summarizes our\nfindings: Stable and metastable superfluid phases appear as a function of the\ndipole-dipole interaction coupling parameter. A first order phase transition,\nand thus a mixture of superfluid phases at different densities, is revealed\nfrom the coexistence curves in the metastable region. Our model predicts that\nthese superfluid phases can be observed experimentally at 0.6 nK in molecules\nof NaK confined in optical lattices of size a =532nm",
        "positive": "Collective Dynamics of Bose--Einstein Condensates in Optical Cavities: Recent experiments on Bose--Einstein condensates in optical cavities have\nreported a quantum phase transition to a coherent state of the matter-light\nsystem -- superradiance. The time dependent nature of these experiments demands\nconsideration of collective dynamics. Here we establish a rich phase diagram,\naccessible by quench experiments, with distinct regimes of dynamics separated\nby non-equilibrium phase transitions. We include the key effects of cavity\nleakage and the back-reaction of the cavity field on the condensate. Proximity\nto some of these phase boundaries results in critical slowing down of the decay\nof many-body oscillations. Notably, this slow decay can be assisted by large\ncavity losses. Predictions include the frequency of collective oscillations, a\nvariety of multi-phase co-existence regions, and persistent optomechanical\noscillations described by a damped driven pendulum. These findings open new\ndirections to study collective dynamics and non-equilibrium phase transitions\nin matter-light systems."
    },
    {
        "anchor": "Effective potentials in a rotating spin-orbit-coupled spin-1 spinor\n  condensate: We theoretically study the stationary-state vortex lattice configurations of\nrotating spin-orbit- and coherently-coupled spin-1 Bose-Einstein condensates\ntrapped in quasi-two-dimensional harmonic potentials. The combined effects of\nrotation, spin-orbit and coherent couplings are analyzed systematically from\nthe single-particle perspective. Through the single-particle Hamiltonian, which\nis exactly solvable for one-dimensional coupling, under specific coupling and\nrotation strengths, we illustrate that a boson in these rotating spin-orbit-\nand coherently-coupled condensates are subjected to effective toroidal,\nsymmetric double-well, or asymmetric double-well potentials. In the presence of\nmean-field interactions, using the coupled Gross-Pitaevskii formalism at\nmoderate to high rotation frequencies, the analytically obtained effective\npotential minima and the numerically obtained coarse-grained density maxima\nposition are in excellent agreement. On rapid rotation, we further find that\nthe spin expectation per particle of an antiferromagnetic spin-1 Bose-Einstein\ncondensate approaches unity indicating a similarity in the response with\nferromagnetic spin-orbit-coupled condensates.",
        "positive": "Non-ergodic behaviour of clean Bose-Hubbard chains: We study ergodicity breaking in the clean Bose-Hubbard chain for small\nhopping strength. We see the existence of a non-ergodic regime by means of\nindicators as the half-chain entanglement entropy of the eigenstates, the\naverage level spacing ratio, {the properties of the eigenstate-expectation\ndistribution of the correlation and the scaling of the Inverse Participation\nRatio averages.} We find that this ergodicity breaking {is different from\nmany-body localization} because the average half-chain entanglement entropy of\nthe eigenstates obeys volume law. This ergodicity breaking appears unrelated to\nthe spectrum being organized in quasidegenerate multiplets at small hopping and\nfinite system sizes, so in principle it can survive also for larger system\nsizes. We find that some imbalance oscillations in time which could mark the\nexistence of a glassy behaviour in space are well described by the dynamics of\na single symmetry-breaking doublet and {quantitatively} captured by a\nperturbative effective XXZ model. We show that the amplitude of these\noscillations vanishes in the large-size limit. {Our findings are numerically\nobtained for systems with $L < 12$. Extrapolations of our scalings to larger\nsystem sizes should be taken with care, as discussed in the paper."
    },
    {
        "anchor": "Quantum Shock Waves and Population Inversion in Collisions of Ultracold\n  Atomic Clouds: Using Time-Dependent Density Matrix Renormalization Group (TDMRG) we study\nthe collision of one-dimensional atomic clouds confined in a harmonic trap and\nevolving with the Lieb-Liniger Hamiltonian. It is observed that the motion is\nessentially periodic with the clouds bouncing elastically, at least on the time\nscale of the first few oscillations that can be resolved with high accuracy.\nThis is in agreement with the results of the \"quantum Newton cradle\" experiment\nof Kinoshita et al. [Nature 440, 900 (2006)]. We compare the results for the\ndensity profile against a hydrodynamic description, or generalized nonlinear\nSchr\\\"odinger equation, with the pressure term taken from the Bethe Ansatz\nsolution of the Lieb-Liniger model. We find that hydrodynamics can describe the\nbreathing mode of a harmonically trapped cloud for arbitrary long times while\nit breaks down almost immediately for the collision of two clouds due to the\nformation of shock waves (gradient catastrophe). In the case of the clouds'\ncollision TDMRG alone allows to extract the oscillation period which is found\nto be measurably different from the breathing mode period. Concomitantly with\nthe shock waves formation we observe a local energy distribution typical of\npopulation inversion, i.e., an effective negative temperature. Our results are\nan important step towards understanding the hydrodynamics of quantum many-body\nsystems out of equilibrium and the role of integrability in their dynamics.",
        "positive": "A single impurity in an ideal atomic Fermi gas: current understanding\n  and some open problems: We briefly review some current theoretical and experimental aspects of the\nproblem of a single spinless impurity in a 3D polarised atomic Fermi gas at\nzero temperature where the interactions can be tuned using a wide Feshbach\nresonance. We show that various few-body states in vacuum composed of the\nimpurity and background gas atoms (single impurity, dimer, trimer, tetramer)\ngive rise to corresponding dressed states ({\\em polaron}, {\\em dimeron}, {\\em\ntrimeron}, {\\em tetrameron}) in the gas and inherit many of their\ncharacteristics. We study the ground state focussing on the choice of wave\nfunction and its properties. We raise a few unsolved problems: whether the\npolaron and dimeron are really separate branches, what other few-body states\nmight exist, the nature of the groundstate for large numbers of particle-hole\npairs and why is the polaron ansatz so good. We then turn to the excited\nstates, and to the calculation of the effective mass. We examine the bounds on\nthe effective mass and raise a conjecture about that of composite quasiparticle\nstates."
    },
    {
        "anchor": "Vortex patterns and the critical rotational frequency in rotating\n  dipolar Bose-Einstein condensates: Based on the two-dimensional mean-field equations for pancake-shaped dipolar\nBose-Einstein condensates in a rotating frame with both attractive and\nrepulsive dipole-dipole interaction (DDI) as well as arbitrary polarization\nangle, we study the profiles of the single vortex state and show how the\ncritical rotational frequency change with the s-wave contact interaction\nstrengths, DDI strengths and the polarization angles. In addition, we find\nnumerically that at the `magic angle' $\\vartheta=\\arccos(\\sqrt{3}/3)$, the\ncritical rotational frequency is almost independent of the DDI strength. By\nnumerically solving the dipolar GPE at high rotational speed, we identify\ndifferent patterns of vortex lattices which strongly depend on the polarization\ndirection. As a result, we undergo a study of vortex lattice structures for the\nwhole regime of polarization direction and find evidence that the vortex\nlattice orientation tends to be aligned with the direction of the dipoles.",
        "positive": "The effect of optical lattice heating on the momentum distribution of a\n  1D Bose gas: We theoretically study how excitations due to spontaneous emission and trap\nfluctuations combine with elastic collisions to change the momentum\ndistribution of a trapped non-degenerate one-dimensional (1D) Bose gas. Using\ncalculated collisional relaxation rates, we first present a semi-analytical\nmodel for the momentum distribution evolution to get insight into the main\nprocesses responsible for the system dynamics. We then present a Monte-Carlo\nsimulation that includes features that cannot be handled analytically, and\ncompare its results to experimental data. These calculations provide a baseline\nfor how integrable 1D Bose gases evolve due to heating processes in the absence\nof diffractive collisions that might thermalize the gases."
    },
    {
        "anchor": "Emergence of non-abelian magnetic monopoles in a quantum impurity\n  problem: Recently it was shown that molecules rotating in superfluid helium can be\ndescribed in terms of the angulon quasiparticles (Phys. Rev. Lett. 118, 095301\n(2017)). Here we demonstrate that in the experimentally realized regime the\nangulon can be seen as a point charge on a 2-sphere interacting with a gauge\nfield of a non-abelian magnetic monopole. Unlike in several other settings, the\ngauge fields of the angulon problem emerge in the real coordinate space, as\nopposed to the momentum space or some effective parameter space. Furthermore,\nwe find a topological transition associated with making the monopole abelian,\nwhich takes place in the vicinity of the previously reported angulon\ninstabilities. These results pave the way for studying topological phenomena in\nexperiments on molecules trapped in superfluid helium nanodroplets, as well as\non other realizations of orbital impurity problems.",
        "positive": "Single-Atom Resolved Fluorescence Imaging of an Atomic Mott Insulator: The reliable detection of single quantum particles has revolutionized the\nfield of quantum optics and quantum information processing. For several years,\nresearchers have aspired to extend such detection possibilities to larger scale\nstrongly correlated quantum systems, in order to record in-situ images of a\nquantum fluid in which each underlying quantum particle is detected. Here we\nreport on fluorescence imaging of strongly interacting bosonic Mott insulators\nin an optical lattice with single-atom and single-site resolution. From our\nimages, we fully reconstruct the atom distribution on the lattice and identify\nindividual excitations with high fidelity. A comparison of the radial density\nand variance distributions with theory provides a precise in-situ temperature\nand entropy measurement from single images. We observe Mott-insulating plateaus\nwith near zero entropy and clearly resolve the high entropy rings separating\nthem although their width is of the order of only a single lattice site.\nFurthermore, we show how a Mott insulator melts for increasing temperatures due\nto a proliferation of local defects. Our experiments open a new avenue for the\nmanipulation and analysis of strongly interacting quantum gases on a lattice,\nas well as for quantum information processing with ultracold atoms. Using the\nhigh spatial resolution, it is now possible to directly address individual\nlattice sites. One could, e.g., introduce local perturbations or access regions\nof high entropy, a crucial requirement for the implementation of novel cooling\nschemes for atoms on a lattice."
    },
    {
        "anchor": "Towards ab initio thermodynamics of the electron gas at strong\n  degeneracy: Recently a number of theoretical studies of the uniform electron gas (UEG) at\nfinite temperature have appeared that are of relevance for dense plasmas, warm\ndense matter and laser excited solids and thermodynamic density functional\ntheory simulations. In particular, restricted path integral Monte Carlo (RPIMC)\nresults became available which, however, due to the Fermion sign problem, are\nconfined to moderate quantum degeneracy, i.e. low to moderate densities. We\nhave recently developed an alternative approach---configuration PIMC [T. Schoof\n{\\em et al.}, Contrib. Plasma Phys. {\\bf 51}, 687 (2011)] that allows one to\nstudy the so far not accessible high degeneracy regime. Here we present the\nfirst step towards UEG simulations using CPIMC by studying implementation and\nperformance of the method for the model case of $N=4$ particles. We also\nprovide benchmark data for the total energy.",
        "positive": "Mixed parity pairing in a dipolar gas: We show that fermionic dipoles in a two-layer geometry form Cooper pairs with\nboth singlet and triplet components, when they are tilted with respect to the\nnormal of the planes. The mixed parity pairing arises because the interaction\nbetween dipoles in the two different layers is not inversion symmetric. We use\nan efficient eigenvalue approach to calculate the zero temperature phase\ndiagram of the system as a function of the dipole orientation and the layer\ndistance. The phase diagram contains purely triplet as well as mixed singlet\nand triplet superfluid phases. We show in detail how the pair wave function for\ndipoles residing in different layers smoothly changes from singlet to triplet\nsymmetry as the orientation of the dipoles is changed. Our results indicate\nthat dipolar quantum gases can be used to unambiguously observe mixed parity\npairing."
    },
    {
        "anchor": "Exotic Superfluid Phases in Spin Polarized Systems on Optical Lattices: Leveraging cutting-edge numerical methodologies, we study the ground state of\nthe two-dimensional spin-polarized Fermi gas in an optical lattice. We focus on\nsystems at high density and small spin polarization, corresponding to the\nparameter regime believed to be most favorable to the formation of the elusive\nFulde-Ferrell-Larkin-Ovchinnikov (FFLO) superfluid phase. Our systematic study\nof large lattice sizes, hosting nearly $500$ atoms, provides strong evidence of\nthe stability of the FFLO state in this regime, as well as a high-accuracy\ncharacterization of its properties. Our results for the density correlation\nfunction reveal the existence of density order in the system, suggesting the\npossibility of an intricate coexistence of long-range orders in the ground\nstate. The ground-state properties are seen to differ significantly from the\nstandard mean-field description, providing a compelling avenue for future\ntheoretical and experimental explorations of the interplay between interaction\nand superfluidity in an exotic phase of matter.",
        "positive": "Non-perturbative method to compute thermal correlations in\n  one-dimensional systems: We develop a highly efficient method to numerically simulate thermal\nfluctuations and correlations in non-relativistic continuous bosonic\none-dimensional systems. The method is suitable for arbitrary local\ninteractions as long as the system remains dynamically stable. We start by\nproving the equivalence of describing the systems through the transfer matrix\nformalism and a Fokker-Planck equation for a distribution evolving in space.\nThe Fokker-Planck equation is known to be equivalent to a stochastic\ndifferential (It\\={o}) equation. The latter is very suitable for computer\nsimulations, allowing the calculation of any desired correlation function. As\nan illustration, we apply our method to the case of two tunnel-coupled\nquasi-condensates of bosonic atoms. The results are compared to the predictions\nof the sine-Gordon model for which we develop analytic expressions directly\nfrom the transfer matrix formalism."
    },
    {
        "anchor": "Observation of Non-equilibrium Motion and Equilibration in Polariton\n  Rings: We present a study of the macroscopic dynamics of a polariton condensate\nformed by non-resonant optical excitation in a quasi-one-dimensional\nring-shaped microcavity. The presence of a gradient in the cavity photon energy\ncreates a macroscopic trap for the polaritons in which a single mode condensate\nis formed. With time- and energy-resolved imaging we show the role of\ninteractions in the motion of the condensate as it undergoes equilibration in\nthe ring. These experiments also give a direct measurement of the\npolariton-polariton interaction strength above the condensation threshold. Our\nobservations are compared to the open-dissipative one-dimensional\nGross-Pitaevskii equation which shows excellent qualitative agreement.",
        "positive": "Engineering topological materials in microwave cavity arrays: We present a scalable architecture for the exploration of interacting\ntopological phases of photons in arrays of microwave cavities, using\nestablished techniques from cavity and circuit quantum electrodynamics. A\ntime-reversal symmetry breaking (non-reciprocal) flux is induced by coupling\nthe microwave cavities to ferrites, allowing for the production of a variety of\ntopological band structures including the $\\alpha=1/4$ Hofstadter model.\nEffective photon-photon interactions are included by coupling the cavities to\nsuperconducting qubits, and are sufficient to produce a $\\nu=1/2$ bosonic\nLaughlin puddle. We demonstrate by exact diagonalization that this architecture\nis robust to experimentally achievable levels of disorder. These advances\nprovide an exciting opportunity to employ the quantum circuit toolkit for the\nexploration of strongly interacting topological materials."
    },
    {
        "anchor": "Editorial: Emergence in driven solid-state and cold-atom systems: We briefly summarize the current status of driven solid-state and cold-atom\nsystems, and introduce articles compiled in the Focus Section in Zeitschrift\nf\\\"ur Naturforschung A, Volume 71, Issue 10 (2016)",
        "positive": "Collective modes, stability and superfluid transition of a\n  quasi-two-dimensional dipolar Fermi gas: We examine collective modes, stability, and BCS pairing in a\nquasi-two-dimensional gas of dipolar fermions aligned by an external field. By\nusing the (conserving) Hartree-Fock approximation, which treats direct and\nexchange interactions on an equal footing, we obtain the spectrum of\nsingle-particle excitations and long wavelength collective modes (zero sound)\nin the normal phase. It appears that exchange interactions result in strong\ndamping of zero sound when the tilting angle between the dipoles and the normal\nto the plane of confinement is below some critical value. In particular, zero\nsound cannot propagate if the dipoles are perpendicular to the plane of\nconfinement. At intermediate coupling we find unstable modes that can lead\neither to collapse of the system or the formation of a density wave. The BCS\ntransition to a superfluid phase, on the other hand, occurs at arbitrarily weak\nstrengths of the dipole-dipole interaction, provided the tilting angle exceeds\na critical value. We determine the critical temperature of the transition\ntaking into account many-body effects as well as virtual transitions to higher\nexcited states in the confining potential, and discuss prospects of\nexperimental observations."
    },
    {
        "anchor": "A quantum Langevin model for non-equilibrium condensation: We develop a quantum model for non-equilibrium Bose-Einstein condensation of\nphotons and polaritons in planar microcavity devices. The model builds upon\nlaser theory and includes the spatial dynamics of the cavity field, a\nsaturation mechanism and some frequency-dependence of the gain: quantum\nLangevin equations are written for a cavity field coupled to a continuous\ndistribution of externally pumped two-level emitters with a well-defined\nfrequency. As a an example of application, the method is used to study the\nlinearised quantum fluctuations around a steady-state condensed state. In the\ngood-cavity regime, an effective equation for the cavity field only is proposed\nin terms of a stochastic Gross-Pitaevskii equation. Perspectives in view of a\nfull quantum simulation of the non-equilibrium condensation process are finally\nsketched.",
        "positive": "Dissipation-induced topological insulators: A no-go theorem and a recipe: Nonequilibrium conditions are traditionally seen as detrimental to the\nappearance of quantum-coherent many-body phenomena, and much effort is often\ndevoted to their elimination. Recently this approach has changed: It has been\nrealized that driven-dissipative dynamics could be used as a resource. By\nproper engineering of the reservoirs and their couplings to a system, one may\ndrive the system towards desired quantum-correlated steady states, even in the\nabsence of internal Hamiltonian dynamics. An intriguing category of equilibrium\nmany-particle phases are those which are distinguished by topology rather than\nby symmetry. A natural question thus arises: which of these topological states\ncan be achieved as the result of dissipative Lindblad-type (Markovian)\nevolution? Beside its fundamental importance, it may offer novel routes to the\nrealization of topologically-nontrivial states in quantum simulators,\nespecially ultracold atomic gases. Here I give a general answer for Gaussian\nstates and quadratic Lindblad evolution, mostly concentrating on the example of\n2D Chern insulator states. I prove a no-go theorem stating that a finite-range\nLindbladian cannot induce finite-rate exponential decay towards a unique\ntopological pure state above 1D. I construct a recipe for creating such state\nby exponentially-local dynamics, or a mixed state arbitrarily close to the\ndesired pure one via finite-range dynamics. I also address the cold-atom\nrealization, classification, and detection of these states. Extensions to other\ntypes of topological insulators and superconductors are also discussed."
    },
    {
        "anchor": "Quantum Walks of Two Interacting Anyons in 1D Optical Lattices: We investigate continuous-time quantum walks of two indistinguishable anyons\nin one-dimensional lattices with both on-site and nearest-neighbor interactions\nbased on the fractional Jordan-Wigner transformation. It is shown that the\ntwo-body correlations in position space are symmetric about the initial sites\nof two quantum walkers in the Bose limit ($\\chi=0$ ) and Fermi limit (\n$\\chi=1$), while in momentum space this happens only in the Bose limit. An\ninteresting asymmetry arises in the correlation for most cases with the\nstatistical parameter $\\chi$ varying in between. It turns out that the origin\nof this asymmetry comes from the fractional statistics that anyons obey. On the\nother hand, the two-body correlations of hard-core anyons in position spaceshow\nuniform behaviors from anti-bunching to co-walking regardless of the\nstatistical parameter. The momentum correlations in the case of strong\ninteraction undergo a smooth process of two stripes smoothly merging into a\nsingle one, i.e. the evolution of fermions into hard-core bosons.",
        "positive": "Generating, dragging and releasing dark solitons in elongated\n  Bose-Einstein condensates: We theoretically analyze quasi-one-dimensional Bose-Einstein condensates\nunder the influence of a harmonic trap and a narrow potential defect that moves\nthrough the atomic cloud. Performing simulations on the mean field level, we\nexplore a robust mechanism in which a single dark soliton is nucleated and\nimmediately pinned by the moving defect, making it possible to drag it to a\ndesired position and release it there. We argue on a perturbative level that a\ndefect potential which is attractive to the atoms is suitable for holding and\nmoving dark solitons. The soliton generation protocol is investigated over a\nwide range of model parameters and its success is systematically quantified by\na suitable fidelity measure, demonstrating its robustness against parameter\nvariations, but also the need for tight focusing of the defect potential.\nHolding the soliton at a stationary defect for long times may give rise to\ndynamical instabilities, whose origin we explore within a Bogoliubov-de Gennes\nlinearization analysis. We show that iterating the generation process with\nmultiple defects offers a perspective for initializing multiple soliton\ndynamics with freely chosen initial conditions."
    },
    {
        "anchor": "Spin-Orbit Coupling in Deformed Harmonic Traps: We consider a two-dimensional system of harmonically trapped particles with\npseudo-spin-$\\frac{1}{2}$ degree of freedom. This degree of freedom is coupled\nto the particle's momentum via the so-called Rashba spin-orbit interaction. We\npresent our numerical results for a single-particle and few-particle systems,\nassuming the repulsive interparticle interaction to be of zero range.",
        "positive": "Lattice-induced rapid formation of spin singlets in spin-1 spinor\n  condensates: We experimentally demonstrate that combining a cubic optical lattice with a\nspinor Bose-Einstein condensate substantially relaxes three strict constraints\nand brings spin singlets of ultracold spin-1 atoms into experimentally\naccessible regions. About 80 percent of atoms in the lattice-confined spin-1\nspinor condensate are found to form spin singlets, immediately after the atoms\ncross first-order superfluid to Mott-insulator phase transitions in a microwave\ndressing field. A phenomenological model is also introduced to well describe\nour observations without adjustable parameters."
    },
    {
        "anchor": "Non-equilibrium dynamics in dissipative Bose-Hubbard chains: Open many-body quantum systems have recently gained renewed interest in the\ncontext of quantum information science and quantum transport with biological\nclusters and ultracold atomic gases. A series of results in diverse setups is\npresented, based on a Master equation approach to describe the dissipative\ndynamics of ultracold bosons in a one-dimensional lattice. The creation of\nmesoscopic stable many-body structures in the lattice is predicted and the\nnon-equilibrium transport of neutral atoms in the regime of strong and weak\ninteractions is studied.",
        "positive": "Macroscopic Superposition of Ultracold Atoms with Orbital Degrees of\n  Freedom: We introduce higher dimensions into the problem of Bose-Einstein condensates\nin a double-well potential, taking into account orbital angular momentum. We\ncompletely characterize the eigenstates of this system, delineating new regimes\nvia both analytical high-order perturbation theory and numerical exact\ndiagonalization. Among these regimes are mixed Josephson- and Fock-like\nbehavior, crossings in both excited and ground states, and shadows of\nmacroscopic superposition states."
    },
    {
        "anchor": "Finite-size and Particle-number Effects in an Ultracold Fermi Gas at\n  Unitarity: We investigate an ultracold Fermi gas at unitarity confined in a periodic box\n$V=L^3$ using renormalization group (RG) techniques. Within this approach we\ncan quantitatively assess the long range bosonic order parameter fluctuations\nwhich dominate finite-size effects. We determine the finite-size and\nparticle-number dependence of universal quantities, such as the Bertsch\nparameter and the fermion gap. Moreover, we analyze how these universal\nobservables respond to the variation of an external pairing source. Our results\nindicate that the Bertsch parameter saturates rather quickly to its value in\nthe thermodynamic limit as a function of increasing box size. On the other\nhand, we observe that the fermion gap shows a significantly stronger dependence\non the box size, in particular for small values of the pairing source. Our\nresults may contribute to a better understanding of finite-size and\nparticle-number effects present in Monte-Carlo simulations of ultracold Fermi\ngases.",
        "positive": "Manipulation of light in a generalized coupled Nonlinear Schrodinger\n  equation: We investigate a generalized coupled nonlinear Schrodinger (GCNLS) equation\ncontaining Self-Phase Modulation (SPM), Cross-Phase Modulation (XPM) and Four\nWave Mixing (FWM) describing the propagation of electromagnetic radiation\nthrough an optical fibre and generate the associated Lax-pair. We then\nconstruct bright solitons employing gauge transformation approach. The\ncollisional dynamics of bright solitons indicates that it is not only possible\nto manipulate intensity (energy) between the two modes (optical beams), but\nalso within a given mode unlike the Manakov model which does not have the same\nfreedom. The freedom to manipulate intensity (energy) in a given mode or\nbetween two modes arises due to a suitable combination of SPM, XPM and\nFWM.While SPM and XPM are controlled by an arbitrary real parameter each, FWM\nis governed by two arbitrary complex parameters. The above model may have wider\nramifications in nonlinear optics and Bose-Einstein Condensates (BECs)."
    },
    {
        "anchor": "Realization of a sonic black hole analogue in a Bose-Einstein condensate: We have created an analogue of a black hole in a Bose-Einstein condensate. In\nthis sonic black hole, sound waves, rather than light waves, cannot escape the\nevent horizon. A step-like potential accelerates the flow of the condensate to\nvelocities which cross and exceed the speed of sound by an order of magnitude.\nThe Landau critical velocity is therefore surpassed. The point where the flow\nvelocity equals the speed of sound is the sonic event horizon. The effective\ngravity is determined from the profiles of the velocity and speed of sound. A\nsimulation finds negative energy excitations, by means of Bragg spectroscopy.",
        "positive": "Distinguishing photon and polariton lasing from GaAs microcavities by\n  spectral and temporal analysis of the two-threshold behavior: We compare polariton lasing with photon lasing of a planar GaAs/GaAlAs\nmicrocavity with zero detuning between the bare cavity mode and the bare\nexciton mode. For the emission from the lower energy-momentum dispersion branch\nwe find a two-threshold behavior of the ground state in the input-output curve\nwhere each transition is accompanied by characteristic changes of the in-plane\nmode dispersion. In particular, we show that the thresholds are unambiguously\nevidenced in the photon statistics of the emission based on the second-order\ncorrelation function. Moreover, the distinct two-threshold behavior is\nconfirmed in the evolution of the emission pulse duration."
    },
    {
        "anchor": "Atom-dimer scattering length for fermions with different masses:\n  analytical study of limiting cases: We consider the problem of obtaining the scattering length for a fermion\ncolliding with a dimer, formed from a fermion identical to the incident one and\nanother different fermion. This is done in the universal regime where the range\nof interactions is short enough so that the scattering length $a$ for non\nidentical fermions is the only relevant quantity. This is the generalization to\nfermions with different masses of the problem solved long ago by Skorniakov and\nTer-Martirosian for particles with equal masses. We solve this problem\nanalytically in the two limiting cases where the mass of the solitary fermion\nis very large or very small compared to the mass of the two other identical\nfermions. This is done both for the value of the scattering length and for the\nfunction entering the Skorniakov-Ter-Martirosian integral equation, for which\nsimple explicit expressions are obtained.",
        "positive": "Time-reversal-invariant spin-orbit-coupled bilayer Bose-Einstein\n  Condensates: Time-reversal invariance plays a crucial role for many exotic quantum phases,\nparticularly for topologically nontrivial states, in spin-orbit coupled\nelectronic systems. Recently realized spin-orbit coupled cold-atom systems,\nhowever, lack the time-reversal symmetry due to the inevitable presence of an\neffective transverse Zeeman field. We address this issue by analyzing a\nrealistic scheme to preserve time-reversal symmetry in spin-orbit coupled\nultracold atoms, with the use of Hermite-Gaussian-laser induced Raman\ntransitions that preserve spin-layer time-reversal symmetry. We find that the\nsystem's quantum states form Kramers pairs, resulting in symmetry-protected gap\nclosing of the lowest two bands at arbitrarily large Raman coupling. We also\nshow that Bose gases in this setup exhibit interaction-induced layer-stripe and\nuniform phases as well as intriguing spin-layer symmetry and spin-layer\ncorrelation."
    },
    {
        "anchor": "Comparative study of the finite-temperature thermodynamics of a unitary\n  Fermi gas: We study the finite-temperature thermodynamics of a unitary Fermi gas. The\nchemical potential, energy density and entropy are given analytically with the\nquasi-linear approximation. The ground state energy agrees with previous\ntheoretical and experimental results. Recently, the generalized exclusion\nstatistics is applied to the discussion of the finite-temperature unitary Fermi\ngas thermodynamics. A concrete comparison between the two different approaches\nis performed. Emphasis is made on the behavior of the entropy per particle. In\nphysics, the slope of entropy gives the information for the effective fermion\nmass $m^*/m$ in the low temperature strong degenerate region. Compared with\n$m^*/m \\approx 0.70<1$ given in terms of the generalized exclusion statistics,\nour quasi-linear approximation determines $m^*/m\\approx 1.11>1$.",
        "positive": "Intrinsic decoherence and purity in a Bose quantum fluid in a triple\n  well potential: We consider a quantum Bose fluid confined in a triple well potential in 1D\nwithin the exact N-body Bose-Hubbard model to investigate the phenomena of\nintrinsic decoherence and loss of purity. Our study is done by following the\ntime evolution of one-body properties in an N-particle closed environment. We\ndo an exhaustive exploration of initial conditions to characterize these\nphenomena. Here we illustrate our main findings with a set of relevant Fock and\nSU(3) coherent states. Our study shows that signatures of stationarity and\nmaximal mixing are a direct consequence of the inter-particle interactions in\nthe closed system and become evident as the number of particles is increased.\nThis fact is confirmed by quantifying the deviations from stationarity by means\nof a matrix norm."
    },
    {
        "anchor": "Optical tweezer generation using automated alignment and adaptive optics: Recent progress in quantum technologies with ultracold atoms has been\npropelled by spatially fine-tuned control of lasers and diffraction-limited\nimaging. The state-of-the-art precision of optical alignment to achieve this\nfine-tuning is reaching the limits of manual control. Here, we show how to\nautomate this process. One of the elementary techniques of manual alignment of\noptics is cross-walking of laser beams. Here, we generalize this technique to\nmulti-variable cross-walking. Mathematically, this is a variant of the\nwell-known Alternating Minimization (AM) algorithm in convex optimization and\nis closely related to the Gauss-Seidel algorithm. Therefore, we refer to our\nmulti-variable cross-walking algorithm as the modified AM algorithm. While\ncross-walking more than two variables manually is challenging, one can do this\neasily for machine-controlled variables. We apply this algorithm to\nmechanically align high numerical aperture (NA) objectives and show that we can\nproduce high-quality diffraction-limited tweezers and point spread functions\n(PSF). After a rudimentary coarse alignment, the algorithm takes about 1 hour\nto align the optics to produce high-quality tweezers. Moreover, we use the same\nalgorithm to optimize the shape of a deformable mirror along with the\nmechanical variables and show that it can be used to correct for optical\naberrations produced, for example, by glass thickness when producing tweezers\nand imaging point sources. The shape of the deformable mirror is parametrized\nusing the first 14 non-trivial Zernike polynomials, and the corresponding\ncoefficients are optimized together with the mechanical alignment variables. We\nshow PSF with a Strehl ratio close to 1 and tweezers with a Strehl ratio >0.8.\nThe algorithm demonstrates exceptional robustness, effectively operating in the\npresence of significant mechanical fluctuations induced by a noisy environment.",
        "positive": "Bose-Hubbard Models in Confining Potentials: An Inhomogeneous Mean-Field\n  Theory: We present an extensive study of Mott insulator (MI) and superfluid (SF)\nshells in Bose-Hubbard (BH) models for bosons in optical lattices with harmonic\ntraps. For this we develop an inhomogeneous mean-field theory. Our results for\nthe BH model with one type of spinless bosons agrees quantitatively with\nquantum Monte Carlo (QMC) simulations. Our approach is numerically less\nintensive than such simulations, so we are able to perform calculation on\nexperimentally realistic, large 3D systems, explore a wide range of parameter\nvalues, and make direct contact with a variety of experimental measurements. We\nalso generalize our inhomogeneous mean-field theory to study BH models with\nharmonic traps and (a) two species of bosons or (b) spin-1 bosons. With two\nspecies of bosons we obtain rich phase diagrams with a variety of SF and MI\nphases and associated shells, when we include a quadratic confining potential.\nFor the spin-1 BH model we show, in a representative case, that the system can\ndisplay alternating shells of polar SF and MI phases; and we make interesting\npredictions for experiments in such systems."
    },
    {
        "anchor": "Quasi one-dimensional Bose-Einstein condensate in gravito-optical\n  surface trap: We study both static and dynamic properties of a weakly interacting\nBose-Einstein condensate (BEC) in a quasi one-dimensional gravito-optical\nsurface trap, where the downward pull of gravity is compensated by the\nexponentially decaying potential of an evanescent wave. First, we work out\napproximate solutions of the Gross-Pitaevskii equation for both a small number\nof atoms using a Gaussian ansatz and a larger number of atoms using the\nThomas-Fermi limit. Then we confirm the accuracy of these analytical solutions\nby comparing them to numerical results. From there, we numerically analyze how\nthe BEC cloud expands non-ballistically, when the confining evanescent laser\nbeam is shut off, showing agreement between our theoretical and previous\nexperimental results. Furthermore, we analyze how the BEC cloud expands\nnon-ballistically due to gravity after switching off the evanescent laser field\nin the presence of a hard-wall mirror. There we find that the BEC shows\nsignificant self-interference patterns for a large number of atoms, whereas for\na small number of atoms, a revival of the BEC wave packet with few matter-wave\ninterference patterns is observed.",
        "positive": "Quantum anomaly and thermodynamics of one-dimensional fermions with\n  three-body interactions: We show that a system of three species of one-dimensional fermions, with an\nattractive three-body contact interaction, features a scale anomaly directly\nrelated to the anomaly of two-dimensional fermions with two-body forces. We\nshow, furthermore, that those two cases (and their multi species\ngeneralizations) are the only non-relativistic systems with contact\ninteractions that display a scale anomaly. While the two-dimensional case is\nwell-known and has been under study both experimentally and theoretically for\nyears, the one-dimensional case presented here has remained unexplored. For the\nlatter, we calculate the impact of the anomaly on the equation of state, which\nappears through the generalization of Tan's contact for three-body forces, and\ndetermine the pressure at finite temperature. In addition, we show that the\nthird-order virial coefficient is proportional to the second-order coefficient\nof the two-dimensional two-body case."
    },
    {
        "anchor": "Quantum turbulence in Bose-Einstein condensates: present status and new\n  challenges ahead: The field of quantum turbulence is related to the manifestation of turbulence\nin quantum fluids, such as liquid helium and ultracold gases. The concept of\nturbulence in quantum systems was conceived more than 70 years ago by Onsager\nand Feynman, but the study of turbulent ultracold gases is very recent.\nAlthough it is a young field, it already provides new approaches to the problem\nof turbulence. We review the advances and present status, of both theory and\nexperiments, concerning atomic Bose-Einstein condensates (BECs). We present the\ndifficulties of characterizing turbulence in trapped BECs, if compared to\nclassical turbulence or turbulence in liquid helium. We summarize the\nchallenges ahead, mostly related to the understanding of fundamental properties\nof quantum turbulence, including what is being done to investigate them.",
        "positive": "The Dissipative Bose-Hubbard Model. Methods and Examples: Open many-body quantum systems have attracted renewed interest in the context\nof quantum information science and quantum transport with biological clusters\nand ultracold atomic gases. The physical relevance in many-particle bosonic\nsystems lies in the realization of counter-intuitive transport phenomena and\nthe stochastic preparation of highly stable and entangled many-body states due\nto engineered dissipation. We review a variety of approaches to describe an\nopen system of interacting ultracold bosons which can be modeled by a\ntight-binding Hubbard approximation. Going along with the presentation of\ntheoretical and numerical techniques, we present a series of results in diverse\nsetups, based on a master equation description of the dissipative dynamics of\nultracold bosons in a one-dimensional lattice. Next to by now standard\nnumerical methods such as the exact unravelling of the master equation by\nquantum jumps for small systems and beyond mean-field expansions for larger\nones, we present a coherent-state path integral formalism based on\nFeynman-Vernon theory applied to a many-body context."
    },
    {
        "anchor": "Exact dynamics following an interaction quench in a one-dimensional\n  anyonic gas: We study the nonequilibrium quench dynamics of a one-dimensional anyonic gas.\nWe focus on the integrable anyonic Lieb-Liniger model and consider the quench\nfrom non-interacting to hard-core anyons. We study the dynamics of the local\nproperties of the system. By means of integrability-based methods we compute\nanalytically the one-body density matrix and the density-density correlation\nfunction at all times after the quench and in particular at infinite time. Our\nresults show that the system evolves from an initial state where the local\nmomentum distribution function is non-symmetric to a steady state where it\nbecomes symmetric. Furthermore, while the initial momentum distribution\nfunctions (and the equilibrium ones) explicitly depend on the anyonic\nparameter, the final ones do not. This is reminiscent of the dynamical\nfermionization observed in the context of free expansions after release from a\nconfining trap.",
        "positive": "Rydberg dressed spin-1/2 Fermi gases in one dimension: The emergent phases of strongly correlated spin-1/2 Fermi gases of Rydberg\ndressed atoms in a one dimensional optical lattice are theoretically\ninvestigated. At weak coupling a bosonization description is used to\ndemonstrate the ability to drive alternating quantum phase transitions between\ndistinct Luttinger liquids. At strong coupling the ground state develops\nnon-trivial phase separation exhibiting Luttinger liquid ''puddles'' separated\nby magnetic domain walls due to the interplay of the incommensurate filling and\nthe Rydberg core length scale. These phases can be detected in ultracold gases\nof Rydberg atoms made from $^6$Li."
    },
    {
        "anchor": "Quantum simulator of link models using spinor dipolar ultracold atoms: We propose a scheme for the quantum simulation of quantum link models in\ntwo-dimensional lattices. Our approach considers spinor dipolar gases on a\nsuitably shaped lattice, where the dynamics of particles in the different\nhyperfine levels of the gas takes place in one-dimensional chains coupled by\nthe dipolar interactions. We show that at least four levels are needed. The\npresent scheme does not require any particular fine-tuning of the parameters.\nWe perform the derivation of the parameters of the quantum link models by means\nof two different approaches, a non-perturbative one tied to angular momentum\nconservation, and a perturbative one. A comparison with other schemes for\n$(2+1)$-dimensional quantum link models present in literature is discussed.\nFinally, the extension to three-dimensional lattices is presented, and its\nsubtleties are pointed out.",
        "positive": "Tunneling dynamics of two interacting one-dimensional particles: We present one-dimensional simulation results for the cold atom tunneling\nexperiments by the Heidelberg group [G. Z\\\"urn {\\em{et al.}}, Phys. Rev. Lett.\n{\\bf{108}}, 075303 (2012) and G. Z\\\"urn {\\em{et al.}}, Phys. Rev. Lett.\n{\\bf{111}}, 175302 (2013)] on one or two $^6$Li atoms confined by a potential\nthat consists of an approximately harmonic optical trap plus a linear magnetic\nfield gradient. At the non-interacting particle level, we find that the WKB\n(Wentzel-Kramers-Brillouin) approximation may not be used as a reliable tool to\nextract the trapping potential parameters from the experimentally measured\ntunneling data. We use our numerical calculations along with the experimental\ntunneling rates for the non-interacting system to reparameterize the trapping\npotential. The reparameterized trapping potentials serve as input for our\nsimulations of two interacting particles. For two interacting (distinguishable)\natoms on the upper branch, we reproduce the experimentally measured tunneling\nrates, which vary over several orders of magnitude, fairly well. For infinitely\nstrong interaction strength, we compare the time dynamics with that of two\nidentical fermions and discuss the implications of fermionization on the\ndynamics. For two attractively-interacting atoms on the molecular branch, we\nfind that single-particle tunneling dominates for weakly-attractive\ninteractions while pair tunneling dominates for strongly-attractive\ninteractions. Our first set of calculations yields qualitative but not\nquantitative agreement with the experimentally measured tunneling rates. We\nobtain quantitative agreement with the experimentally measured tunneling rates\nif we allow for a weakened radial confinement."
    },
    {
        "anchor": "Spin-glass-like behavior in the spin turbulence of spinor Bose-Einstein\n  condensates: We study numerically the spin turbulence in spin-1 ferromagnetic spinor\nBose-Einstein condensates (BECs). Spin turbulence (ST) is characterized by a\n-7/3 power law in the spectrum of the spin-dependent interaction energy. The\ndirection of the spin density vector is spatially disordered but temporally\nfrozen in ST, showing some analogy with the spin glass state. Thus, we\nintroduce the order parameter of spin glass into ST in spinor BECs. When ST\ndevelops through some instability, the order parameter grows with a -7/3 power\nlaw, thus succeeding in describing ST well.",
        "positive": "Ground-state properties of a dilute two-dimensional Bose gas: We revisit the problem of the calculation of low-temperature properties for\nthe dilute two-dimensional Bose gas. By using Popov's hydrodynamic approach and\nperturbation theory on the one-loop level we recover not only the known\nexpansion for the ground-state energy but also calculate for the first time the\ncondensate density and Tan's contact."
    },
    {
        "anchor": "A strongly interacting gas of two-electron fermions at an orbital\n  Feshbach resonance: We report on the experimental observation of a strongly interacting gas of\nultracold two-electron fermions with orbital degree of freedom and magnetically\ntunable interactions. This realization has been enabled by the demonstration of\na novel kind of Feshbach resonance occurring in the scattering of two 173Yb\natoms in different nuclear and electronic states. The strongly interacting\nregime at resonance is evidenced by the observation of anisotropic hydrodynamic\nexpansion of the two-orbital Fermi gas. These results pave the way towards the\nrealization of new quantum states of matter with strongly correlated fermions\nwith orbital degree of freedom.",
        "positive": "Spin-1/2 fermions with attractive interaction in an optical lattice: We study attractive fermions in an optical lattice superimposed by a trapping\npotential, such that fermions may form bosonic molecules. We map the model onto\nnonlinear field equations depending on the Nambu-Gor'kov propagator. The\nresulting field equations where solved numerically by a relaxation technique\nthat allowed us to calculate the inhomogeneous densities of fermions and\ncondensed molecules at zero temperature. When the interactions between fermions\nare strong there is a competition between unbound fermions and bound molecules\nleading to an unexpected reduction of the non-homogeneous density of fermions\nat the center of the trap."
    },
    {
        "anchor": "Scattering bright solitons: quantum versus mean-field behavior: We investigate scattering bright solitons off a potential using both\nanalytical and numerical methods. Our paper focuses on low kinetic energies for\nwhich differences between the mean-field description via the Gross-Pitaevskii\nequation (GPE) and the quantum behavior are particularly large. On the\nN-particle quantum level, adding an additional harmonic confinement leads to a\nsimple signature to distinguish quantum superpositions from statistical\nmixtures. While the non-linear character of the GPE does not allow quantum\nsuperpositions, the splitting of GPE-solitons takes place only partially. When\nthe potential strength is increased, the fraction of the soliton which is\ntransmitted or reflected jumps non-continuously. We explain these jumps via\nenergy-conservation and interpret them as indications for quantum\nsuperpositions on the N-particle level. On the GPE-level, we also investigate\nthe transition from this stepwise behavior to the continuous case.",
        "positive": "Observation of two non-thermal fixed points for the same microscopic\n  symmetry: Close to equilibrium, the underlying symmetries of a system determine its\npossible universal behavior. Far from equilibrium, however, different universal\nphenomena associated with the existence of multiple non-thermal fixed points\ncan be realized for given microscopic symmetries. Here, we study this\nphenomenon using a quasi-one-dimensional spinor Bose-Einstein condensate. We\nprepare two different initial conditions and observe two distinct universal\nscaling dynamics with different exponents. Measurements of the complex-valued\norder parameter with spatial resolution allow us to characterize the\nphase-amplitude excitations for the two scenarios. Our study provides new\ninsights into the phenomenon of universal dynamics far from equilibrium and\nopens a path towards mapping out the associated basins of non-thermal fixed\npoints."
    },
    {
        "anchor": "Emergence and stability of spontaneous vortex lattices in\n  exciton-polariton condensates: The spontaneous formation of lattice structure of quantized vortices is a\ncharacteristic feature of superfluidity in closed systems under thermal\nequilibrium. In exciton-polariton Bose-Einstein condensate, which is a typical\nexample of macroscopic quantum state in open systems, spontaneous vortex\nlattices have also been proposed by not yet observed. Here, we take into\naccount the finite decay rate of exciton reservoir, and theoretically\ninvestigate the vortex structures in circularly pumped polariton Bose-Einstein\ncondensate. Our results show that a decreasing reservoir decay rate can reduce\nthe number of vortices and destabilize the lattice structure, hence is\nunfavorable to the formation and observation of vortex lattices. These\ndetrimental effects can be prevailed by applying an external angular momentum.",
        "positive": "Low-dimensional pairing fluctuations and pseudogapped photoemission\n  spectrum in a trapped two-dimensional Fermi gas: We investigate strong-coupling properties of a trapped two-dimensional normal\nFermi gas. Within the framework of a combined $T$-matrix theory with the local\ndensity approximation, we calculate the local density of states, as well as the\nphotoemission spectrum, to see how two-dimensional pairing fluctuations affect\nthese single-particle quantities. In the BCS (Bardeen-Cooper-Schrieffer)-BEC\n(Bose-Einstein condensation) crossover region, we show that the local density\nof states exhibits a dip structure in the trap center, which is more remarkable\nthan the three-dimensional case. This pseudogap phenomenon is found to\nnaturally lead to a double peak structure in the photoemission spectrum. The\npeak-to-peak energy of the spectrum at p=0 agrees well with the recent\nexperiment on a two-dimensional 40K Fermi gas [M. Feld, et al., Nature 480, 75\n(2011)]. Since pairing fluctuations are sensitive to the dimensionality of a\nsystem, our results would be useful for the study of many-body physics in the\nBCS-BEC crossover regime of a two-dimensional Fermi gas."
    },
    {
        "anchor": "Tuning Rashba and Dresselhaus spin-orbit couplings: Effects on singlet\n  and triplet condensation with Fermi atoms: We investigate the pair condensation of a two-spin-component Fermi gas in the\npresence of both Rashba and Dresselhaus spin-orbit couplings. We calculate the\ncondensate fraction in the BCS-BEC crossover both in two and in three\ndimensions by taking into account singlet and triplet pairings. These\nquantities are studied by varying the spin-orbit interaction from the case with\nthe only Rashba to the equal-Rashba-Dresselhaus one. We find that, by mixing\nthe two couplings, the singlet pairing decreases while the triplet pairing is\nsuppressed in the BCS regime and increased in the BEC regime, both in two and\nthree dimensions. At fixed spin-orbital strength, the greatest total condensate\nfraction is obtained when only one coupling (only Rashba or only Dresselhaus)\nis present.",
        "positive": "Nonequilibrium Dynamics of Ultracold Fermi Superfluids: The aim of this mini review is to survey the literature on the study of\nnonequilibrium dynamics of Fermi superfluids in the BCS and BEC limits, both in\nthe single channel and dual channel cases. The focus is on mean field\napproaches to the dynamics, with specific attention drawn to the dynamics of\nthe Ginzburg-Landau order parameters of the Fermi and composite Bose fields, as\nwell as on the microscopic dynamics of the quantum degrees of freedom. The two\napproaches are valid approximations in two different time scales of the ensuing\ndynamics. The system is presumed to evolve during and/or after a quantum quench\nin the parameter space. The quench can either be an impulse quench with\nvirtually instantaneous variation, or a periodic variation between two values.\nThe literature for the order parameter dynamics, described by the\ntime-dependent Ginzburg- Landau equations, is reviewed, and the works of the\nauthor in this area highlighted. The mixed phase regime in the dual channel\ncase is also considered, and the dual order parameter dynamics of Fermi-Bose\nmixtures reviewed. Finally, the nonequilibrium dynamics of the microscopic\ndegrees of freedom for the superfluid is reviewed for the self-consistent and\nnon self-consistent cases. The dynamics of the former can be described by the\nBogoliubov de-Gennes equations with the equilibrium BCS gap equation continued\nin time and self -consistently coupled to the BdG dynamics. The latter is a\nreduced BCS problem and can be mapped onto the dynamics of Ising and Kitaev\nmodels. This article reviews the dynamics of both impulse quenches in the\nFeshbach detuning, as well as periodic quenches in the chemical potential, and\nhighlights the author's contributions in this area of research."
    },
    {
        "anchor": "Long-range interacting quantum systems: The presence of non-local and long-range interactions in quantum systems\ninduces several peculiar features in their equilibrium and out-of-equilibrium\nbehavior. In current experimental platforms control parameters such as\ninteraction range, temperature, density and dimension can be changed. The\nexistence of universal scaling regimes, where diverse physical systems and\nobservables display quantitative agreement, generates a common framework, where\nthe efforts of different research communities can be -- in some cases\nrigorously -- connected. Still, the application of this general framework to\nparticular experimental realisations requires the identification of the regimes\nwhere the universality phenomenon is expected to appear. In the present review\nwe summarise the recent investigations of many-body quantum systems with\nlong-range interactions, which are currently realised in Rydberg atom arrays,\ndipolar systems, trapped ion setups and cold atoms in cavity experiments. Our\nmain aim is to present and identify the common and (mostly) universal features\ninduced by long-range interactions in the behaviour of quantum many-body\nsystems. We will discuss both the case of very strong non-local couplings, i.e.\nthe non-additive regime, and the one in which energy is extensive, but\nnevertheless low-energy, long wavelength properties are altered with respect to\nthe short-range limit. Cases of competition with other local effects in the\nabove mentioned setups are also reviewed.",
        "positive": "Observation of Microcanonical Atom Number Fluctuations in a\n  Bose-Einstein Condensate: Quantum systems are typically characterized by the inherent fluctuation of\ntheir physical observables. Despite this fundamental importance, the\ninvestigation of the fluctuations in interacting quantum systems at finite\ntemperature continues to pose considerable theoretical and experimental\nchallenges. Here we report the characterization of atom number fluctuations in\nweakly interacting Bose-Einstein condensates. Technical fluctuations are\nmitigated through a combination of non-destructive detection and active\nstabilization of the cooling sequence. We observe fluctuations reduced by\n\\SI{27}{\\percent} below the canonical expectation for a non-interacting gas,\nrevealing the microcanonical nature of our system. The peak fluctuations have\nnear linear scaling with atom number $\\Delta N_{0,\\mathrm{p}}^2 \\propto\nN^{1.134}$ in an experimentally accessible transition region outside the\nthermodynamic limit. Our experimental results thus set a benchmark for\ntheoretical calculations under typical experimental conditions."
    },
    {
        "anchor": "Mesoscopic transport of fermions through an engineered optical lattice\n  connecting two reservoirs: We study transport of fermions in a system composed of a short optical\nlattice connecting two finite atomic reservoirs at different filling levels.\nThe average equilibration current through the optical lattice, for strong\nlattice-reservoir coupling and finite temperatures, is calculated within the\nLandauer formalism using a nonequilibrium Green's functions approach. We\nmoreover determine quantum and thermal fluctuations in the transport and find\nsignificant shot-to-shot deviations from the average equilibration current. We\nshow how to control the atomic current by engineering specific optical lattice\npotentials without requiring site-by-site manipulations and suggest the\nrealization of a single level model. Based on this model we discuss the\nblocking effect on the atomic current resulting from weak interactions between\nthe fermions.",
        "positive": "Topological Lifshitz Transitions, Orbital Currents, and Interactions in\n  Low-dimensional Fermi Gases in Synthetic Gauge Fields: Low-dimensional systems of interacting fermions in a synthetic gauge field\nhave been experimentally realized using two-component ultra-cold Fermi gases in\noptical lattices. Using a two-leg ladder model that is relevant to these\nexperiments, we have studied the signatures of topological Lifshitz transitions\nand the effects of the inter-species interaction $U$ on the gauge-invariant\norbital current in the regime of large intra-leg hopping $\\Omega$. Focusing on\nnon-insulating regimes, we have carried out numerically exact density-matrix\nrenormalization-group (DMRG) calculations to compute the orbital current at\nfixed particle number as a function of the interaction strength and the\nsynthetic gauge flux per plaquette. Signatures of topological Lifshitz\ntransitions where the number Fermi points changes are found to persist even in\nthe presence of very strong repulsive interactions. This numerical observation\nsuggests that the orbital current can be captured by an appropriately\nrenormalized mean-field band structure, which is also described here.\nQuantitative agreement between the mean-field and the DMRG results in the\nintermediate interaction regime where $U \\lesssim \\Omega$ is demonstrated. We\nalso have observed that interactions can change the sign of the current\nsusceptibility at zero field and induce Lifshitz transitions between two\nmetallic phases, which is also captured by the mean-field theory. Correlation\neffects beyond mean-field theory in the oscillations of the local inter-leg\ncurrent are also reported. We argue that the observed robustness against\ninteractions makes the orbital current a good indicator of the topological\nLifshitz transitions."
    },
    {
        "anchor": "Role of the effective range in the density-induced BEC-BCS crossover: We elucidate the role of the effective range in the Bose-Einstein-condensate\n(BEC) to Bardeen-Cooper-Schrieffer (BCS) crossover regime of two-component\nfermions in three dimensions. In contrast to ultracold Fermi gases near the\nbroad Feshbach resonance, where the interaction can be characterized by the\ncontact-type interaction, the interaction range in general becomes important in\nthe density-induced BEC-BCS crossover discussed in the context of\ncondensed-matter and nuclear systems. Characterizing the non-local interaction\nin terms of the low-energy constants such as scattering length $a$ and\neffective range $r$, we show how the crossover phenomena are affected by\nnonzero effective ranges. In particular, we show that the superfluid order\nparameter is strongly suppressed in the high-density regime and the sound\nvelocity exhibits a non-monotonic behavior reflecting mechanical stability of\nthe system. Moreover, we point out that the high-momentum tail associated with\nthe contact parameter can be visible when the magnitude of momentum $k$ is much\nless than $1/r$.",
        "positive": "A variational approach to repulsively interacting three-fermion systems\n  in a one-dimensional harmonic trap: We study a three-body system with zero-range interactions in a\none-dimensional harmonic trap. The system consists of two spin-polarized\nfermions and a third particle which is distinct from two others (2+1 system).\nFirst we assume that the particles have equal masses. For this case the system\nin the strongly and weakly interacting limits can be accurately described using\nwave function factorized in hyperspherical coordinates. Inspired by this result\nwe propose an interpolation ansatz for the wave function for arbitrary\nrepulsive zero-range interactions. By comparison to numerical calculations, we\nshow that this interpolation scheme yields an extremely good approximation to\nthe numerically exact solution both in terms of the energies and also in the\nspin-resolved densities. As an outlook, we discuss the case of mass imbalanced\nsystems in the strongly interacting limit. Here we find spectra that\ndemonstrate that the triply degenerate spectrum at infinite coupling strength\nof the equal mass case is in some sense a singular case as this degeneracy will\nbe broken down to a doubly degenerate or non-degenerate ground state by any\nsmall mass imbalance."
    },
    {
        "anchor": "Dark-dark-soliton dynamics in two density-coupled Bose-Einstein\n  condensates: We study the 1D dynamics of dark-dark solitons in the miscible regime of two\ndensity-coupled Bose-Einstein condensates having repulsive interparticle\ninteractions within each condensate ($g>0$). By using an adiabatic perturbation\ntheory in the parameter $g_{12}/{g}$, we show that, contrary to the case of two\nsolitons in scalar condensates, the interactions between solitons are\nattractive when the interparticle interactions between condensates are\nrepulsive $g_{12}>0$. As a result, the relative motion of dark solitons with\nequal chemical potential $\\mu$ is well approximated by harmonic oscillations of\nangular frequency $w_r=(\\mu/\\hbar)\\sqrt{({8}/{15}){g_{12}}/{g}}$. We also show\nthat in finite systems, the resonance of this anomalous excitation mode with\nthe spin density mode of lowest energy gives rise to alternating dynamical\ninstability and stability fringes as a function of the perturbative parameter.\nIn the presence of harmonic trapping (with angular frequency $\\Omega$) the\nsolitons are driven by the superposition of two harmonic motions at a frequency\ngiven by $w^2=(\\Omega/\\sqrt{2})^2+w_r^2$. When $g_{12}<0$, these two\noscillators compete to give rise to an overall effective potential that can be\neither single well or double well through a pitchfork bifurcation. All our\ntheoretical results are compared with numerical solutions of the\nGross-Pitaevskii equation for the dynamics and the Bogoliubov equations for the\nlinear stability. A good agreement is found between them.",
        "positive": "Localization of excited states of Bose-Einstein Condensates in presence\n  of disorder: We study the onset of localization from excited states of trapped Bose-\nEinstein Condensates expanding in presence of Gaussian uncorrelated random\ndisorder. In 1D systems, we observe that for a fixed ratio between the disorder\nstrength and the initial energy, excited states localize exponentially with a\nlocalization length that decreases as the energy of the initial state\nincreases. Moreover, the localized state keeps the shape of the initial state\nwave function with an exponential tail. In 2D, we analyze the interplay between\nvorticiy and localization by examining the dispersion of a state containing a\nvortex on it in a disordered media. Despite localization can be associated to\nislands of constant phase, the presence of a vortex in the initial state leads\nto dislocations and phase jumps in the localized state. The study of dispersion\nof a bosonic condensate with vorticity bears similarities to the stability of\ntopological excitations in 2D p-wave fermionic superfluids."
    },
    {
        "anchor": "Nonequilibrium Josephson oscillations in Bose-Einstein condensates\n  without dissipation: We perform a detailed field theoretical study of nonequilibrium Josephson\noscillations between interacting Bose-Einstein condensates confined in a\nfinite-size double-well trap. We find that the Josephson junction can sustain\nmultiple undamped Josephson oscillations up to a characteristic time scale\n$\\tau_c$ without quasipartcles being excited in the system. This may explain\nrecent related experiments. At larger times the dynamics of the junction is\ngoverned by fast Rabi oscillations between the descrete quasiparticle levels.\nWe predict that a selftrapped BEC state will be destroyed by these Rabi\noscillations.",
        "positive": "Dynamical self-stabilization of the Mott insulator: Time evolution of\n  the density and entanglement entropy of out-of-equilibrium cold fermion gases: The time evolution of the out-of-equilibrium Mott insulator is investigated\nnumerically through calculations of space-time resolved density and entropy\nprofiles resulting from the release of a gas of ultracold fermionic atoms from\nan optical trap. For adiabatic, moderate and sudden switching-off of the\ntrapping potential, the out-of-equilibrium dynamics of the Mott insulator is\nfound to differ profoundly from that of the band insulator and the metallic\nphase, displaying a self-induced stability that is robust within a wide range\nof densities, system sizes and interaction strengths. The connection between\nthe entanglement entropy and changes of phase, known for equilibrium\nsituations, is found to extend to the out-of-equilibrium regime. Finally, the\nrelation between the system's long time behavior and the thermalization limit\nis analyzed."
    },
    {
        "anchor": "Avalanche Mechanism for the Enhanced Loss of Ultracold Atoms: In several experiments with ultracold trapped atoms, a narrow loss feature\nhas been observed near an {\\it atom-dimer resonance}, at which there is an\nEfimov trimer at the atom-dimer threshold. The conventional interpretation of\nthese loss features is that they are produced by the {\\it avalanche mechanism},\nin which the energetic atom and dimer from 3-body recombination undergo\nsecondary elastic collisions that produce additional atoms with sufficient\nenergy to escape from the trapping potential. We use Monte Carlo methods to\ncalculate the average number of atoms lost and the average heat generated by\nrecombination events in a Bose-Einstein condensate and in a thermal gas. We\nimprove on previous models by taking into account the energy-dependence of the\ncross sections, the spacial structure of the atom cloud, and the elastic\nscattering of the atoms. We show that the avalanche mechanism cannot produce a\nnarrow loss feature near the atom-dimer resonance. The number of atoms lost\nfrom a recombination event can be more than twice as large as the 3 that would\nbe obtained in the absence of secondary collisions. However the resulting loss\nfeature is broad and its peak is at a scattering length that is larger than the\natom-dimer resonance and depends on the trap depth.",
        "positive": "Static and dynamic properties of a few spin $1/2$ interacting fermions\n  trapped in an harmonic potential: We provide a detailed study of the properties of a few interacting spin $1/2$\nfermions trapped in a one-dimensional harmonic oscillator potential. The\ninteraction is assumed to be well represented by a contact delta potential.\nNumerical results obtained by means of exact diagonalization techniques are\ncombined with analytical expressions for both the non-interacting and strongly\ninteracting regime. The $N=2$ case is used to benchmark our numerical\ntechniques with the known exact solution of the problem. After a detailed\ndescription of the numerical methods, in a tutorial-like manner, we present the\nstatic properties of the system for $N=2, 3, 4$ and 5 particles, e.g.\nlow-energy spectrum, one-body density matrix, ground-state densities. Then, we\nconsider dynamical properties of the system exploring first the excitation of\nthe breathing mode, using the dynamical structure function and corresponding\nsum-rules, and then a sudden quench of the interaction strength."
    },
    {
        "anchor": "Quantum Criticality of Liquid-Gas Transition in a Binary Bose Mixture: Quantum liquid, in the form of a self-bound droplet, is stabilized by a\nsubtle balance between the mean-field contribution and quantum fluctuations.\nWhile a liquid-gas transition is expected when such a balance is broken, it\nremains elusive whether liquid-gas critical points exist in the quantum regime.\nHere we study the quantum criticality in a binary Bose mixture undergoing the\nliquid-gas transition. We show that, beyond a narrow stability window of the\nself-bound liquid, a liquid-gas coexistence persists, which eventually transits\ninto a homogeneous mixture. Importantly, we identify two distinct critical\npoints where the liquid-gas coexistence terminates. These critical points are\ncharacterized by rich critical behaviors in their vicinity, including divergent\nsusceptibility, unique phonon-mode softening, and enhanced density\ncorrelations. The liquid-gas transition and the critical points can be readily\nexplored in ultracold atoms confined to a box potential. Our work highlights\nthe thermodynamic approach as a powerful tool in revealing the quantum\nliquid-gas criticality, and paves the way for further studies of critical\nphenomena in quantum liquids.",
        "positive": "Sublattice dynamics and quantum state transfer of doublons in\n  two-dimensional lattices: We study the dynamics of two strongly-interacting fermions moving in 2D\nlattices under the action of a periodic electric field, both with and without a\nmagnetic flux. Due to the interaction, these particles bind together forming a\ndoublon. We derive an effective Hamiltonian that permits us to understand the\ninterplay between the interaction and the driving, revealing surprising effects\nthat constrain the movement of the doublons. We show that it is possible to\nconfine doublons to just the edges of the lattice, and also to a particular\nsublattice, if different sites in the unit cell have different coordination\nnumbers. Contrary to what happens in 1D systems, here we observe the\ncoexistence of both topological and Shockley-like edge states when the system\nis in a non-trivial phase."
    },
    {
        "anchor": "Experimental setup for the production of ultracold strongly correlated\n  fermionic superfluids of $^{6}$Li: We present our experimental setup to produce ultracold strongly correlated\nfermionic superfluids made of a two-component spin-mixture of $^6$Li atoms.\nEmploying standard cooling techniques, we achieve quantum degeneracy in a\nsingle-beam optical dipole trap. Our setup is capable of generating\nspin-balanced samples at temperatures as low as $T/T_F = 0.1$ containing up to\n$5 \\times 10^4$ atomic pairs. We can access different superfluid regimes by\ntuning the interparticle interactions close to a broad magnetic Feshbach\nresonance. In particular, we are able to explore the crossover from the\nmolecular Bose-Einstein condensate (BEC) to the Bardeen-Cooper-Schrieffer (BCS)\nsuperfluid regimes.",
        "positive": "Superradiant Phase Transition of Fermi Gases in a Cavity across a\n  Feshbach Resonance: In this letter we consider the superradiant phase transition of a\ntwo-component Fermi gas in a cavity across a Feshbach resonance. It is known\nthat quantum statistics plays a crucial role for the superradiant phase\ntransition in atomic gases; in contrast to bosons, in a Fermi gas this\ntransition exhibits strong density dependence. We show that across a Feshbach\nresonance, while the two-component Fermi gas passes through the BEC-BCS\ncrossover, the superradiant phase transition undergoes a corresponding\ncrossover from a fermionic behavior on the weakly interacting BCS side, to a\nbosonic behavior on the molecular BEC side. This intricate statistics crossover\nmakes the superradiance maximally enhanced either in the unitary regime for low\ndensities, in the BCS regime for moderate densities close to Fermi surface\nnesting, or in the BEC regime for high densities."
    },
    {
        "anchor": "Finite-momentum superfluidity and phase transitions in a p-wave resonant\n  Bose gas: We study a degenerate two-species gas of bosonic atoms interacting through a\np-wave Feshbach resonance as for example realized in a Rb85-Rb87 mixture. We\nshow that in addition to a conventional atomic and a p-wave molecular spinor-1\nsuperfluidity at large positive and negative detunings, respectively, the\nsystem generically exhibits a finite momentum atomic-molecular superfluidity at\nintermediate detuning around the unitary point. We analyze the detailed nature\nof the corresponding phases and the associated quantum and thermal phase\ntransitions.",
        "positive": "Quantum phases of strongly interacting Rydberg atoms in triangular\n  lattices: We present a theoretical study on the system of laser-driven strongly\ninteracting Rydberg atoms trapped in a two-dimensional triangular lattice, in\nwhich the dipole-dipole interactions between Rydberg states result in exotic\nquantum phases. By using the mean-field theory, we investigate the steady state\nsolutions and analyze their dynamical stabilities. We find that in the\nstrong-interaction limit, the dynamics of the system is chaotic and exhibits\nrandom oscillations under appropriate laser detunings. Lyapunov exponent\ncriterion is introduced to confirm the existence of this chaotic behavior. In\naddition, we present a full quantum calculation based on a six-atom model, and\nfind that the system exhibits some bi-antiferromagnetic properties in every\ntriangular cell when the one-photon detuning is exactly resonant or\nblue-shifted."
    },
    {
        "anchor": "Collisionally inhomogeneous Bose-Einstein condensates with binary and\n  three body interactions in a bichromatic optical lattice: We study the impact of collisionally inhomogeneous binary and three body\ninteraction on Bose-Einstein condensates (BECs) of a dilute gas in a\nbichromatic optical lattice. We observe that the localized matter wave density\nwhich decreases after the introduction of repulsive spatially inhomogeneous\nbinary interaction can be sustained by the addition of constant attractive\nbinary strength in equal amounts. If the balance between repulsive spatially\ninhomogeneous binary interaction and constant attractive interaction is\ndisturbed, the condensates collapse. Reversal of sign of interaction ensures\nthe longevity of BECs. Any imbalance between attractive spatially inhomogeneous\ninteraction and constant repulsive interaction either results in the collapse\nof BECs or in the occupation of the condensates at multiple sites on either\nsides. The introduction of a weak three body interaction in phase with the\nbinary interaction increases the extent of instability of BECs. Reversing the\nsign of spatially inhomogeneous and constant interaction enhances the stability\nof BECs.",
        "positive": "Emergent spacetimes from Hermitian and non-Hermitian quantum dynamics: We show that quantum dynamics of any systems with $SU(1,1)$ symmetry give\nrise to emergent Anti-de Sitter spacetimes in 2+1 dimensions (AdS$_{2+1}$).\nUsing the continuous circuit depth, a quantum evolution is mapped to a\ntrajectory in AdS$_{2+1}$. Whereas the time measured in laboratories becomes\neither the proper time or the proper distance, quench dynamics follow geodesics\nof AdS$_{2+1}$. Such a geometric approach provides a unified interpretation of\na wide range of prototypical phenomena that appear disconnected. For instance,\nthe light cone of AdS$_{2+1}$ underlies expansions of unitary fermions released\nfrom harmonic traps, the onsite of parametric amplifications, and the\nexceptional points that represent the $PT$ symmetry breaking in non-Hermitian\nsystems. Our work provides a transparent means to optimize quantum controls by\nexploiting shortest paths in the emergent spacetimes. It also allows\nexperimentalists to engineer emergent spacetimes and induce tunnelings between\ndifferent AdS$_{2+1}$."
    },
    {
        "anchor": "Statics and dynamics of quasi one-dimensional Bose-Einstein condensate\n  in harmonic and dimple trap: We investigate a quasi one-dimensional $^{87}\\text{Rb}$ Bose-Einstein\ncondensate in a harmonic trap with an additional dimple trap (dT) in the\ncenter. Within a zero-temperature Gross-Pitaevskii mean-field description we\nprovide a one-dimensional physical intuitive model, which we solve by both a\ntime-independent variational approach and numerical calculations. With this we\nobtain at first equilibrium results for the emerging condensate wave function\nwhich reveal that a dimple trap potential induces a bump or a dip in case of a\nred- or a blue-detuned Gaussian laser beam, respectively. Afterwards, we\ninvestigate how this dT induced bump/dip-imprint upon the condensate wave\nfunction evolves for two quench scenarios. At first we consider the generic\ncase that the harmonic confinement is released. During the resulting\ntime-of-flight expansion it turns out that the dT induced bump in the\ncondensate wave function remains present, whereas the dip starts decaying after\na characteristic time scale which decreases with increasing blue-detuned dT\ndepth. Secondly, once the red- or blue-detuned dT is switched off, we find that\nbright shock-waves or gray/dark bi-soliton trains emerge which oscillate within\nthe harmonic confinement with a characteristic frequency.",
        "positive": "High-momentum tail and universal relations of a Fermi gas near a\n  Raman-dressed Feshbach resonance: In a recent proposal [Jie and Zhang, Phys. Rev. A 95, 060701(R) (2017)], it\nhas been shown that center-of-mass-momentum-dependent two-body interactions can\nbe generated and tuned by Raman coupling the closed-channel bound states in a\nmagnetic Feshbach resonance. Here we investigate the universal relations in a\nthree-dimensional Fermi gas near such a laser modulated $s$-wave Feshbach\nresonance. Using the operator-product expansion approach, we find that, to\nfully describe the high-momentum tail of the density distribution up to\n$q^{-6}$ ($q$ is the relative momentum), four center-of-mass-momentum-dependent\nparameters are required, which we identify as contacts. These contacts appear\nin various universal relations connecting microscopic and thermodynamic\nproperties. One contact is related to the variation of energy with respect to\nthe inverse scattering length and determines the leading $q^{-4}$ tail of the\nhigh-momentum distribution. Another vector contact appears in the subleading\n$q^{-5}$ tail, which is related to the velocity of closed-channel molecules.\nThe other two contacts emerge in the $q^{-6}$ tail and are respectively related\nto the variation of energy with respect to the range parameter and to the\nkinetic energy of closed-channel molecules. Particularly, we find that the\n$q^{-5}$ tail and part of the $q^{-6}$ tail of the momentum distribution show\nanisotropic features. We derive the universal relations and, as a concrete\nexample, estimate the contacts for the zero-temperature superfluid ground state\nof the system using a mean-field approach."
    },
    {
        "anchor": "Delocalization of two interacting particles in the two-dimensional\n  Harper model: We study the problem of two interacting particles in a two-dimensional\nquasiperiodic potential of the Harper model. We consider an amplitude of the\nquasiperiodic potential such that in absence of interactions all eigenstates\nare exponentially localized while the two interacting particles are delocalized\nshowing anomalous subdiffusive spreading over the lattice with the spreading\nexponent $b \\approx 0.5$ instead of a usual diffusion with $b=1$. This\nspreading is stronger than in the case of a correlated disorder potential with\na one particle localization length as for the quasiperiodic potential. At the\nsame time we do not find signatures of ballistic FIKS pairs existing for two\ninteracting particles in the one-dimensional Harper model.",
        "positive": "Dynamical critical exponents in driven-dissipative quantum systems: We study the phase-ordering of parametrically and incoherently driven\nmicrocavity polaritons after an infinitely rapid quench across the critical\nregion. We confirm that the system, despite its driven-dissipative nature,\nfulfils dynamical scaling hypothesis for both driving schemes by exhibiting\nself-similar patterns for the two-point correlator at late times of the phase\nordering. We show that polaritons are characterised by the dynamical critical\nexponent z ~ 2 with topological defects playing a fundamental role in the\ndynamics, giving logarithmic corrections both to the power-law decay of the\nnumber of vortices and to the associated growth of the characteristic\nlength-scale."
    },
    {
        "anchor": "Generalized Crossover in Interacting Fermions within the Low-Energy\n  Expansion: We generalize the Bardeen-Cooper-Schrieffer-Bose-Einstein-condensation\n(BCS-BEC) crossover of two-component fermions, which is realized by tuning the\n$s$-wave scattering length $a$ between the fermions, to the case of an\narbitrary effective range $r_{\\rm e}$. By using the Nozi\\`{e}res-Schmitt-Rink\n(NSR) approach, we show another crossover by changing $r_{\\rm e}$ and present\nseveral similarities and differences between these two crossovers. Furthermore,\nthe region ($r_{\\rm e}>a/2$) where the effective range expansion breaks down\nand the Hamiltonian becomes non-Hermitian is found, being consistent with the\nWigner's causality bound. Our results are universal for low-density interacting\nfermions with low-energy constants $a$ and $r_{\\rm e}$ and are directly\nrelevant to ultracold Fermi atomic gases as well as dilute neutron matter.",
        "positive": "Quench-induced spontaneous currents in rings of ultracold fermionic\n  atoms: We have measured the rate of spontaneous current formation in ring-shaped\nensembles of fermionic $^6$Li atoms, following a thermal quench through the BCS\nsuperfluid phase transition. For the fastest quenches, the mean square winding\nnumber follows a scaling law with exponent $\\sigma$ = 0.24(2), in line with\npredictions of the Kibble-Zurek (KZ) model for mean-field BCS theory. We use a\nhybrid quench protocol involving simultaneous evaporation and interaction\nramps, with a long system lifetime allowing characterization of a different\nrate of spontaneous current formation in the slow-quench regime, where\nfinite-size effects are important. Comparing our observations to a quasi-1D\nstochastic Ginzburg-Landau model, we find quantitative agreement for fast\nquenches, but only qualitative agreement for slow quenches."
    },
    {
        "anchor": "Spectrum of density and spin density fluctuations of an attractive\n  two-dimensional Fermi gas: We leverage unbiased auxiliary-field quantum Monte Carlo methods interfaced\nwith cutting-edge analytic continuation tools to compute from first-principles\ndynamical correlations for a dilute homogeneous two-dimensional attractive\nFermi gas. Our main purpose is to quantitatively study the collective\nexcitations of the system to shed light into fermionic superfluidity in the\nstrongly correlated regime. Despite the fact that we are somewhat limited by\nfinite-size effects, our study pinpoints a clear peak in the spin channel at\nlow momentum, and we discuss the possibility that such a peak can be\ninterpreted as the Higgs mode in the superfluid. Our study is complemented by a\nsystematic comparison with the predictions of generalized random phase\napproximation, with the dual purpose to directly compare with auxiliary-field\nquantum Monte Carlo and to quantitatively study finite-size effects.",
        "positive": "Temperature Dependence of the Density and Excitations of Dipolar\n  Droplets: Droplet states of ultracold gases which are stabilized by fluctuations have\nrecently been observed for dipolar and two component Bose gases. These systems\npresent a novel form of equilibrium where an instability at the mean field\nlevel is arrested by higher order correlations making the droplet states\nsensitive probes of fluctuations. In a recent paper, we argued that thermal\nfluctuations can play an important role for droplets even at low temperatures\nwhere the non-condensed density is much smaller than the condensate density. We\nused the Hartree-Fock-Bogoliubov theory together with local density\napproximation for fluctuations to obtain a generalized Gross Pitaevskii (GP)\nequation and solved it with a Gaussian variational ansatz to show that the\ntransition between the low density and droplet states can be significantly\nmodified by the temperature. In this paper, we first solve the same GP equation\nnumerically with a time splitting spectral method to check the validity of the\nGaussian variational ansatz. Our numerical results are in good agreement with\nthe Gaussian ansatz for a large parameter regime and show that the density of\nthe gas is most strongly modified by temperature near the abrupt transition\nbetween a pancake shaped cloud and the droplet. For cigar shaped condensates,\nas in the recent Er experiments, the dependence of the density on temperature\nremains quite small throughout the smooth transition. We then consider the\neffect of temperature on the collective oscillation frequencies of the droplet\nusing both a time dependent Gaussian variational ansatz and real time numerical\nevolution. We find that the oscillation frequencies depend significantly on the\ntemperature close to the transition for the experimentally relevant temperature\nregime ($\\simeq 100$nK)."
    },
    {
        "anchor": "Hubbard models and state preparation in an optical Lieb lattice: Inspired by the growing interest in probing many-body phases in novel\ntwo-dimensional lattice geometries we investigate the properties of cold atoms\nas they could be observed in an optical Lieb lattice. We begin by computing\nWannier functions localised at individual sites for a realistic experimental\nsetup, and determining coefficients for a Hubbard-like model. Based on this, we\nshow how experiments could probe the robustness of edge states in a Lieb\nlattice with diagonal boundary conditions to the effects of interactions and\nrealise strongly correlated many-body phases in this geometry. We then\ngeneralise this to interacting particles in a half-filled 1D Lieb ladder, where\nexcitations are dominated by flat band states. We show that for strong\nattractive interactions, pair correlations are enhanced even when there is\nstrong mixing with the Dirac cone. These findings in 1D raise interesting\nquestions about the phases in the full 2D Lieb lattice which we show can be\nexplored in current experiments.",
        "positive": "Spectral Functions and rf Response of Ultracold Fermionic Atoms: We present a calculation of the spectral functions and the associated rf\nresponse of ultracold fermionic atoms near a Feshbach resonance. The single\nparticle spectra are peaked at energies that can be modeled by a modified BCS\ndispersion. However, even at very low temperatures their width is comparable to\ntheir energy, except for a small region around the dispersion minimum. The\nstructure of the excitation spectrum of the unitary gas at infinite scattering\nlength agrees with recent momentum-resolved rf spectra near the critical\ntemperature. A detailed comparison is made with momentum integrated, locally\nresolved rf spectra of the unitary gas at arbitrary temperatures and shows very\ngood agreement between theory and experiment. The pair size defined from the\nwidth of these spectra is found to coincide with that obtained from the leading\ngradient corrections to the effective field theory of the superfluid."
    },
    {
        "anchor": "Dynamic structure factors of a strongly interacting Fermi superfluid\n  near an orbital Feshbach resonance across the phase transition from BCS to\n  Sarma superfluid: We theoretically investigate dynamic structure factors of a strongly\ninteracting Fermi superfluid near an orbital Feshbach resonance with random\nphase approximation, and find their dynamical characters during the phase\ntransition between a balanced conventional Bardeen-Cooper-Schrieffer superfluid\nand a polarized Sarma superfluid by continuously varying the chemical potential\ndifference of two spin components. In a BEC-like regime of the BCS superfluid,\ndynamic structure factors can do help to distinguish the in-phase ground state\nfrom the out-of-phase metastable state by the relative location of molecular\nexcitation and Leggett mode, or the minimum energy to break a Cooper pair. In\nthe phase transition between BCS and Sarma superfluid, we find the dynamic\nstructure factor of Sarma superfluid has its own specific gapless excitation at\na small transferred momentum which is mixed with the collective phonon\nexcitation, and also a relatively strong atomic excitation at a large\ntransferred momentum because of the existence of unpaired Fermi atoms, these\nsignals can be used to differentiate Sarma superfluid from BCS superfluid.",
        "positive": "Stationary solitons in F=1 spin-orbit coupled Bose-Einstein condensates: We consider solitary wave excitations above the ground state of $F=1$\nspin-orbit coupled Bose-Einstein condensates (SOBECs). The low energy\nproperties of SOBECs in any of the three branches of the single particle\ndispersion relation can be described by suitable scalar nonlinear Schr\\\"odinger\n(NLS) equations which we obtain using multiple-scale expansions. This enables\nus to examine a variety of different configurations, such as dark solitary\nwaves associated with higher energy branches, as well as dark and bright\nstructures in the lowest branch. The lowest branch can also exhibit a\n``superstripe'' phase that supports solitary waves. In all cases, we provide\nexplicit expressions for the NLS coefficients, and confirm their validity with\nfull numerical simulations of the SOBEC system including a harmonic confining\npotential."
    },
    {
        "anchor": "Topological Excitations in Spinor Bose-Einstein Condensates: A rich variety of order parameter manifolds of multicomponent Bose-Einstein\ncondensates (BECs) admit various kinds of topological excitations, such as\nfractional vortices, monopoles, skyrmions, and knots. In this paper, we discuss\ntwo topological excitations in spinor BECs: non-Abelian vortices and knots.\nUnlike conventional vortices, non-Abelian vortices neither reconnect themselves\nnor pass through each other, but create a rung between them in a topologically\nstable manner. We discuss the collision dynamics of non-Abelian vortices in the\ncyclic phase of a spin-2 BEC. In the latter part, we show that a knot, which is\na unique topological object characterized by a linking number or a Hopf\ninvariant [$\\pi_3 (S^2)=Z$], can be created using a conventional quadrupole\nmagnetic field in a cold atomic system.",
        "positive": "Two-channel model of photoassociation in the vicinity of a Feshbach\n  resonance: We derive the two-channel (TC) description of the photoassociation (PA)\nprocess in the presence of a magnetic Feshbach resonance and compare to full\ncoupled multi-channel calculations for the scattering of $^{6}$Li-$^{87}$Rb.\nPreviously derived results [P. Pellegrini et al., Phys. Rev. Lett. 101, 053201\n(2008)] are corrected. The PA process is shown to be fully described by two\nparameters: the maximal transition rate and the point of vanishing transition\nrate. The TC approximation reproduces excellently the PA transition rates of\nthe full multi-channel calculation and reveals, e.g., that the enhancement of\nthe rate at a resonance is directly connected to the position of vanishing\nrate. For the description of two independent resonances it was found that only\nthree parameters completely characterize the PA process."
    },
    {
        "anchor": "Dynamically Slowed Collapse of a Bose-Einstein Condensate with Negative\n  Scattering Length: We rapidly change the scattering length a_s of a 87Rb Bose-Einstein\ncondensate by means of a Feshbach resonance, simultaneously releasing the\ncondensate from its harmonic trapping potential. When a_s is changed from\npositive to negative, the subsequent collapse of the condensate is stabilized\nby the kinetic energy imparted during the release, resulting in a deceleration\nof the loss rate near the resonance. We also observe an increase in the\nThomas-Fermi radius, near the resonance, that cannot be understood in terms of\na simple scaling model. Instead, we describe this behavior using the\nGross-Pitaevskii equation, including three-body recombination, and hypothesize\nthat the increase in cloud radius is due to the formation of concentric shells.",
        "positive": "Universal contact of strongly interacting fermions at finite\n  temperatures: The recently discovered universal thermodynamic behaviour of dilute, strongly\ninteracting Fermi gases also implies a universal structure in the many-body\npair-correlation function at short distances, as quantified by the contact\n${\\cal I}$. This quantity is an excellent indicator of the presence of strong\ncorrelations in these systems, which provide a highly accessible physical model\nfor other strongly correlated quantum fluids. Here we theoretically calculate\nthe temperature dependence of this universal contact for a Fermi gas in free\nspace and in a harmonic trap. At high temperatures above the Fermi degeneracy\ntemperature, $T\\gtrsim T_{F}$, we obtain a reliable non-perturbative quantum\nvirial expansion up to third order. At low temperatures we compare different\napproximate strong coupling theories. These make different predictions, which\nneed to be tested either by future experiments or advanced quantum Monte Carlo\nsimulations. We conjecture that in the universal unitarity limit, the contact\nor correlation decreases monotonically with increasing temperature, unless the\ntemperature is significantly lower than the critical temperature, $T\\ll\nT_{c}\\sim0.2T_{F}$. We also discuss briefly how to measure the universal\ncontact either in homogeneous or harmonically trapped Fermi gases."
    },
    {
        "anchor": "Enhanced Pauli blocking of light scattering in a trapped Fermi gas: Pauli blocking of spontaneous emission by a single excited-state atom has\nbeen predicted to be dramatic at low temperature when the Fermi energy\n$E_\\mathrm{F}$ exceeds the recoil energy $E_\\mathrm{R}$. The photon scattering\nrate of a ground-state Fermi gas can also be suppressed by occupation of the\nfinal states accessible to a recoiling atom, however suppression is diminished\nby scattering events near the Fermi edge. We analyze two new approaches to\nimprove the visibility of Pauli blocking in a trapped Fermi gas. Focusing the\nincident light to excite preferentially the high-density region of the cloud\ncan increase the blocking signature by 14%, and is most effective at\nintermediate temperature. Spontaneous Raman scattering between imbalanced\ninternal states can be strongly suppressed at low temperature, and is\ncompletely blocked for a final-state $E_\\mathrm{F} > 4 E_\\mathrm{R}$ in the\nhigh imbalance limit.",
        "positive": "Optical lattice for tripod-like atomic level structure: Standard optical potentials use off-resonant laser standing wave induced\nAC-Stark shift. In a recent development [Phys. Rev. Lett. {\\bf 117}, 233001\n(2016)] a three-level scheme in $\\Lambda$ configuration coupled coherently by\nresonant laser fields was introduced leading to an effective lattice with\nsubwavelength potential peaks. Here as an extension of that work to a four\nlevel atomic setup in the tripod configuration is used to create spin\n$1/2$-like two-dimensional dark-space with 1D motion and the presence of\nexternal gauge fields. Most interestingly for a possible application, the\nlifetime for a dark subspace motion is up to two orders of magnitude larger\nthan for a similar $\\Lambda$ system. The model is quite flexible leading to\nlattices with significant nearest, next-nearest, or next-next-nearest hopping\nrates, $J_1,J_2,J_3$ opening up new intriguing possibilities to study, e.g.\nfrustrated systems. The characteristic Wannier functions lead also to new type\nof inter-site interactions not realizable in typical optical lattices."
    },
    {
        "anchor": "Ground state of a mixture of two bosonic Calogero-Sutherland gases with\n  strong odd-wave interspecies attraction: A model of two Calogero-Sutherland Bose gases A and B with strong odd-wave AB\nattractions induced by a p-wave AB Feshbach resonance is studied. The ground\nstate wave function is found analytically by a Bose-Bose duality mapping, which\npermits one to accurately determine static physical properties by a Monte Carlo\nmethod. The condensation of particles or particle pairs (molecules) is tested\nby analyzing the presence of the off-diagonal long-range order in one- or\ntwo-body density matrices. The p-wave symmetry of AB interaction makes possible\nquasi-condensation of type A particles at the Fermi momentum of the B\ncomponent. The zero-temperature phase diagram is drawn in terms of densities\nand interaction strengths.",
        "positive": "Various Topological Mott insulators in strongly-interacting boson system\n  in one-dimensional superlattice: In this paper, we study a one-dimensional boson system in a superlattice\npotential.This system is experimentally feasible by using ultracold atomic\ngases,and attracts much attention these days. It is expected that the system\nhas a topological phase called topological Mott insulator (TMI). We show that\nin strongly-interacting cases, the competition between the superlattice\npotential and the on-site interaction leads to various TMIs with non-vanishing\ninteger Chern number. Compared to hard-core case, the soft-core boson system\nexhibits rich phase diagrams including various non-trivial TMIs. By using the\nexact diagonalization,we obtain detailed bulk-global phase diagrams including\nthe TMIs with high Chern numbers and also various non-topological phases. We\nalso show that in adiabatic experimental setups, the strongly-interacting\nbosonic TMIs exhibit the topological particle transfer, i.e., topological\ncharge pumping phenomenon, similarly to weakly-interacting systems. The various\nTMIs are characterized by topological charge pumping as it is closely related\nto the Chern number, and therefor the Chern number is to be observed in\nfeasible experiments."
    },
    {
        "anchor": "Radio-frequency spectroscopy of a strongly interacting spin-orbit\n  coupled Fermi gas: We investigate experimentally and theoretically radio-frequency spectroscopy\nand pairing of a spin-orbit-coupled Fermi gas of $^{40}$K atoms near a Feshbach\nresonance at $B_{0}=202.2$ G. Experimentally, the integrated spectroscopy is\nmeasured, showing characteristic blue and red shifts in the atomic and\nmolecular responses, respectively, with increasing spin-orbit coupling.\nTheoretically, a smooth transition from atomic to molecular responses in the\nmomentum-resolved spectroscopy is predicted, with a clear signature of\nanisotropic pairing at and below resonance. Our many-body prediction agrees\nqualitatively well with the observed spectroscopy near the Feshbach resonance.",
        "positive": "Self-similar expansion of the density profile in a turbulent\n  Bose-Einstein condensate: In a recent study we demonstrated the emergence of turbulence in a trapped\nBose-Einstein condensate of Rb-87 atoms. An intriguing observation in such a\nsystem is the behavior of the turbulent cloud during free expansion.The aspect\nratio of the cloud size does not change in the way one would expect for an\nordinary non-rotating (vortex-free) condensate. Here we show that the anomalous\nexpansion can be understood, at least qualitatively, in terms of the presence\nof vorticity distributed throughout the cloud, effectively counteracting the\nusual reversal of the aspect ratio seen in free time-of-flight expansion of\nnon-rotating condensates."
    },
    {
        "anchor": "Spatial Bloch oscillations of a quantum gas in a \"beat-note\"\n  superlattice: We report the experimental realization of a new kind of optical lattice for\nultra-cold atoms where arbitrarily large separation between the sites can be\nachieved without renouncing to the stability of ordinary lattices. Two\ncollinear lasers, with slightly different commensurate wavelengths and\nretroreflected on a mirror, generate a superlattice potential with a periodic\n\"beat-note\" profile where the regions with large amplitude modulation provide\nthe effective potential minima for the atoms. To prove the analogy with a\nstandard large spacing optical lattice we study Bloch oscillations of a Bose\nEinstein condensate with negligible interactions in the presence of a small\nforce. The observed dynamics between sites separated by ten microns for times\nexceeding one second proves the high stability of the potential. This novel\nlattice is the ideal candidate for the coherent manipulation of atomic samples\nat large spatial separations and might find direct application in atom-based\ntechnologies like trapped atom interferometers and quantum simulators.",
        "positive": "Role of Nambu-Goldstone modes in the fermionic superfluid point contact: In fermionic superfluids that are charge neutral, Nambu-Goldstone (NG) modes\nalso known as Anderson-Bogoliubov modes emerge as a result of spontaneous\nsymmetry breaking. Here, we discuss DC transport properties of such NG modes\nthrough a quantum point contact. We show that contrary to a naive view that\nenhancement of the phase stiffness may suppress transport of the NG modes,\nthere must be an anomalous contribution that survives at low temperature. This\ncontribution originates from the conversion process between the condensate and\nNG mode. We find that within the BCS regime the anomalous contribution is\nenhanced with increasing channel transmittance and attractive interaction, and\nleads to a temperature-dependent Lorenz number and absence of the bunching\neffect in current noise."
    },
    {
        "anchor": "Hall response of interacting bosonic atoms in strong gauge fields: from\n  condensed to FQH states: Interacting bosonic atoms under strong gauge fields undergo a series of phase\ntransitions that take the cloud from a simple Bose-Einstein condensate all the\nway to a family of fractional-quantum-Hall-type states [M. Popp, B. Paredes,\nand J. I. Cirac, Phys. Rev. A 70, 053612 (2004)]. In this work we demonstrate\nthat the Hall response of the atoms can be used to locate the phase transitions\nand characterize the ground state of the many-body state. Moreover, the same\nresponse function reveals within some regions of the parameter space, the\nstructure of the spectrum and the allowed transitions to excited states. We\nverify numerically these ideas using exact diagonalization for a small number\nof atoms, and provide an experimental protocol to implement the gauge fields\nand probe the linear response using a periodically driven optical lattice.\nFinally, we discuss our theoretical results in relation to recent experiments\nwith condensates in artificial magnetic fields [ L. J. LeBlanc, K.\nJimenez-Garcia, R. A. Williams, M. C. Beeler, A. R. Perry, W. D. Phillips, and\nI. B. Spielman, Proc. Natl. Acad. Sci. USA 109, 10811 (2012)] and we analyze\nthe role played by vortex states in the Hall response.",
        "positive": "Preparation and spectroscopy of a metastable Mott insulator state with\n  attractive interactions: We prepare and study a metastable attractive Mott insulator state formed with\nbosonic atoms in a three-dimensional optical lattice. Starting from a Mott\ninsulator with Cs atoms at weak repulsive interactions, we use a magnetic\nFeshbach resonance to tune the interactions to large attractive values and\nproduce a metastable state pinned by attractive interactions with a lifetime on\nthe order of 10 seconds. We probe the (de-)excitation spectrum via lattice\nmodulation spectroscopy, measuring the interaction dependence of two- and\nthree-body bound state energies. As a result of increased on-site three-body\nloss we observe resonance broadening and suppression of tunneling processes\nthat produce three-body occupation."
    },
    {
        "anchor": "Homogeneous Atomic Fermi Gases: We report on the creation of homogeneous Fermi gases of ultracold atoms in a\nuniform potential. In the momentum distribution of a spin-polarized gas, we\nobserve the emergence of the Fermi surface and the saturated occupation of one\nparticle per momentum state. This directly confirms Pauli blocking in momentum\nspace. For the spin-balanced unitary Fermi gas, we observe spatially uniform\npair condensates. For thermodynamic measurements, we introduce a hybrid\npotential that is harmonic in one dimension and uniform in the other two. The\nspatially resolved compressibility reveals the superfluid transition in a\nspin-balanced Fermi gas, saturation in a fully polarized Fermi gas, and strong\nattraction in the polaronic regime of a partially polarized Fermi gas.",
        "positive": "Fate of Lattice Gauge Theories Under Decoherence: A major test of the capabilities of modern quantum simulators and NISQ\ndevices is the reliable realization of gauge theories, which constitute a gold\nstandard of implementational efficacy. In addition to unavoidable unitary\nerrors, realistic experiments suffer from decoherence, which compromises gauge\ninvariance and, therefore, the gauge theory itself. Here, we study the effect\nof decoherence on the quench dynamics of a lattice gauge theory. Rigorously\nidentifying the gauge violation as a divergence measure in the gauge sectors,\nwe find at short times that it first grows diffusively $\\sim\\gamma t$ due to\ndecoherence at environment-coupling strength $\\gamma$, before unitary errors at\nstrength $\\lambda$ dominate and the violation grows ballistically\n$\\sim\\lambda^2t^2$. We further introduce multiple quantum coherences in the\ncontext of gauge theories to quantify decoherence effects. Both experimentally\naccessible measures will be of independent interest beyond the immediate\ncontext of this work."
    },
    {
        "anchor": "Measuring topology by dynamics: Chern number from linking number: Integer-valued topological indices, characterizing nonlocal properties of\nquantum states of matter, are known to directly predict robust physical\nproperties of equilibrium systems. The Chern number, e.g., determines the\nquantized Hall conductivity of an insulator. Using fermionic atoms in a\nperiodically driven optical lattice, here we demonstrate experimentally that\nthe Chern number determines also the far-from-equilibrium dynamics of a quantum\nsystem. Following the proposal of ref. [Wang et al., Phys. Rev. Lett. 118,\n185701 (2017)] and extending it to Floquet systems, we measure the linking\nnumber that characterizes the trajectories of momentum-space vortices emerging\nafter a strong quench. We observe that it directly corresponds to the\nground-state Chern number. This one-to-one relation between a dynamical and a\nstatic topological index allows us to experimentally map out the phase diagram\nof our system. Furthermore, we measure the instantaneous Chern number and show\nthat it remains zero under the unitary dynamics.",
        "positive": "Mixtures of Bose gases confined in concentrically coupled annular traps: A two-component Bose-Einstein condensate confined in an axially-symmetric\npotential with two local minima, resembling two concentric annular traps, is\ninvestigated. The system shows a number of quantum phase transitions that\nresult from the competition between phase coexistence, and radial/azimuthal\nphase separation. The ground-state phase diagram, as well as the rotational\nproperties, including the (meta)stability of currents in this system, are\nanalysed."
    },
    {
        "anchor": "Superradiant phononic emission from the analog spin ergoregion in a\n  two-component Bose-Einstein condensate: We make use of an analog gravity perspective to obtain a physical\nunderstanding of hydrodynamic instabilities stemming from the presence of\nquantized vortices in two-component atomic condensates and of their relation to\nergoregion instabilities of rotating massive objects in gravitation. In\naddition to the localized instabilities related to vortex splitting,\nconfigurations displaying dynamically unstable modes that extend well outside\nthe vortex core are found. In this case, the superradiant scattering process\ninvolves phonon emission into the much wider ergoregion of spin modes, so the\nphysics most closely resembles the one of rotating massive objects. Our results\nconfirm the potential of two-component condensates as analog models of rotating\nspace-times in different regimes of gravitational interest.",
        "positive": "Two photon conditional phase gate based on Rydberg slow light polaritons: We analyze the fidelity of a deterministic quantum phase gate for two photons\ncounterpropagating as polaritons through a cloud of Rydberg atoms under the\ncondition of electromagnetically induced transparency (EIT). We provide\nanalytical results for the phase shift of the quantum gate, and provide an\nestimation for all processes leading to a reduction to the gate fidelity.\nEspecially, the influence of losses form the intermediate level, dispersion of\nthe photon wave packet, scattering into additional polariton channels, finite\nlifetime of the Rydberg state, as well as effects of transverse size of the\nwave packets are accounted for. We show that the flatness of the effective\ninteraction, caused by the blockade phenomena, suppresses the corrections due\nto the finite transversal size. This is a strength of Rydberg-EIT setup\ncompared to other approaches. Finally, we provide the experimental requirements\nfor the realization of a high fidelity quantum phase gate using Rydberg\npolaritons."
    },
    {
        "anchor": "Supersolid formation in a quantum gas breaking continuous translational\n  symmetry: The concept of a supersolid state is paradoxical. It combines the\ncrystallization of a many-body system with dissipationless flow of the atoms it\nis built of. This quantum phase requires the breaking of two continuous\nsymmetries, the phase invariance of a superfluid and the continuous\ntranslational invariance to form the crystal,. Proposed for helium almost 50\nyears ago, experimental verification of supersolidity remains elusive. A\nvariant with only discrete translational symmetry breaking on a preimposed\nlattice structure, the `lattice supersolid', has been realized based on\nself-organization of a Bose-Einstein condensate (BEC). However, lattice\nsupersolids do not feature the continuous ground state degeneracy that\ncharacterizes the supersolid state as originally proposed. Here we report the\nrealization of a supersolid with continuous translational symmetry breaking.\nThe continuous symmetry emerges from two discrete spatial ones by symmetrically\ncoupling a BEC to the modes of two optical cavities. We establish the phase\ncoherence of the supersolid and find a high ground-state degeneracy by\nmeasuring the crystal position over many realizations through the light fields\nleaking from the cavities. These light fields are also used to monitor the\nposition fluctuations in real-time. Our concept provides a route to creating\nand studying glassy many-body systems with contrallably lifted ground-state\ndegeneracies, such as supersolids in the presence of disorder.",
        "positive": "Fermionic quantum mixtures with tunable interactions: The topic of the present lecture notes are two-species quantum mixtures\ncomposed of a deeply degenerate Fermi gas and a second component, the latter\nbeing fermionic or bosonic. A key ingredient is the possibility to tune the\n$s$-wave interaction between the different species by means of magnetically\ncontrolled Feshbach resonances, which allow us to investigate regimes of strong\ninteractions. In two case studies, we review our experiments on mixtures of\n$^6$Li fermions with fermionic $^{40}$K or bosonic $^{41}$K atoms and on\nmixtures of fermionic $^{161}$Dy with $^{40}$K atoms. We cover various topics\nof fermionic quantum many-body physics, ranging from impurity physics and\nquasiparticles over phase separation to the formation of ultracold molecules\nand progress towards novel superfluids."
    },
    {
        "anchor": "Phonon-mediated Josephson oscillations in excitonic and polaritonic\n  condensates: We analyze theoretically the role of the exciton-phonon interactions in\nphenomena related to the Josephson effect between two spatially separated\nexciton and exciton-polariton condensates. We consider the role of the\ndephasing introduced by phonons in such phenomena as Josephson tunneling,\nself-trapping and spontaneous polarization separation. In the regime of cw\npumping we find a remarkable bistability effect arising from exciton- exciton\ninteractions as well as regimes of self- sustained regular and chaotic\noscillations.",
        "positive": "Competition of superfluidity and density waves in one-dimensional\n  Bose-Fermi mixtures: We study a mixture of one-dimensional bosons and spinless fermions at\nincommensurate filling using phenomenological bosonization and Green's\nfunctions techniques. We derive the relation between the parameters of the\nmicroscopic Hamiltonian and macroscopic observables. Galilean invariance\nresults in extra constraints for the current current interactions. We obtain\nthe exact exponents for the various response functions, and show that\nsuperfluid fluctuations are enhanced by the effective boson-fermion\ndensity-density interaction and suppressed by the effective boson-fermion\ncurrent-current interaction. In the case of a bosonized model with purely\ndensity-density interaction, when the effective boson-fermion density-density\ninteraction is weak enough, the superfluid exponent of the bosons has a\nnon-monotonous variation with the ratio of the fermion velocity to the boson\nvelocity. By contrast, density-wave exponent and the exponent for fermionic\nsuperfluidity are monotonous functions of the velocity ratio."
    },
    {
        "anchor": "Bose-Einstein Condensates with Cavity-Mediated Spin-Orbit Coupling: We propose a novel scheme to generate the spin-orbit coupling for a\ncondensate placed inside an optical cavity by using a standing wave and a\ntraveling wave. It is shown that the interplay of the laser lights and the\ncavity gives rise to rich quantum phases. Our scheme also generates an\nnontrivial lattice of the magnetic flux, which may facilitate the study of the\nexotic quantum phases.",
        "positive": "Searching for Unconventional Superfluid in Excitons of Monolayer\n  Semiconductors: It is well known that two-dimensional (2D) bosons in homogeneous space cannot\nundergo real Bose-Einstein condensation, and the superfluid to normal phase\ntransition is Berezinskii-Kosterlitz-Thouless (BKT) type, associated with\nvortex-antivortex pair unbinding. Here we point out a 2D bosonic system whose\nlow energy physics goes beyond conventional paradigm of 2D {\\it homogeneous}\nbosons, i.e., intralayer excitons in monolayer transition metal\ndichalcogenides. With intrinsic valley-orbit coupling and valley Zeeman energy,\nexciton dispersion becomes linear at small momentum, giving rise to a series of\nnovel features. The critical temperature of Bose-Einstein condensation of these\nexcitons is nonzero, suggesting true long-range order in 2D homogeneous system.\nThe dispersion of Goldstone mode at long wavelength has the form\n$\\varepsilon(\\boldsymbol{q})\\sim\\sqrt{q}$, in contrast to conventional linear\nphonon spectrum. The vortex energy deviates from the usual logarithmic form\nwith respect to system size, but instead has an additional linear term.\nSuperfluid to normal phase transition is no longer BKT type for system size\nbeyond a characteristic scale, without discontinuous jump in superfluid\ndensity. With the recent experimental progress on exciton fluid at thermal\nequilibrium in monolayer semiconductors, our work points out an experimentally\naccessible system to search for unconventional 2D superfluids beyond BKT\nparadigm."
    },
    {
        "anchor": "Exact results for nonequilibrium dynamics in Wigner phase space: We study time evolution of Wigner function of an initially interacting\none-dimensional quantum gas following the switch-off of the interactions. For\nthe scenario where at $t=0$ the interactions are suddenly suppressed, we derive\na relationship between the dynamical Wigner function and its initial value. A\ntwo-particle system initially interacting through two different interactions of\nDirac delta type is examined. For a system of particles that is suddenly let to\nmove ballistically (without interactions) in a harmonic trap in d dimensions,\nand using time evolution of one-body density matrix, we derive a relationship\nbetween the time dependent Wigner function and its initial value. Using the\ninverse Wigner transform we obtain, for an initially harmonically trapped\nnoninteracting particles in $d$ dimensions, the scaling law satisfied by the\ndensity matrix at time $t$ after a sudden change of the trapping frequency.\nFinally, the effects of interactions are analyzed in the dynamical Wigner\nfunction.",
        "positive": "Kelvin-Helmholtz instability in two-component Bose gases on a lattice: We explore the stability of the interface between two phase-separated Bose\ngases in relative motion on a lattice. Gross-Pitaevskii-Bogoliubov theory and\nthe Gutzwiller ansatz are employed to study the short- and long-time stability\nproperties. The underlying lattice introduces effects of discreteness, broken\nspatial symmetry, and strong correlations, all three of which are seen to have\nconsiderable qualitative effects on the Kelvin-Helmholtz instability.\nDiscreteness is found to stabilize low flow velocities, because of the finite\nenergy associated with displacing the interface. Broken spatial symmetry\nintroduces a dependence not only on the relative flow velocity, but on the\nabsolute velocities. Strong correlations close to a Mott transition will stop\nthe Kelvin-Helmholtz instability from affecting the bulk density and creating\nturbulence; instead, the instability will excite vortices with Mott-insulator\nfilled cores."
    },
    {
        "anchor": "Classical phase-space approach for coherent matter waves: We investigate a classical phase-space approach of matter-wave propagation\nbased on the Truncated Wigner Equation (TWE). We show that such description is\nsuitable for ideal matter waves in quadratic time-dependent confinement as well\nas for harmonically trapped Bose Einstein condensates in the Thomas-Fermi\nregime. In arbitrary interacting regimes, the TWE combined with the moment\nmethod yields the low-energy spectrum of a condensate as predicted by\nindependent variational methods. TWE also gives the right breathing mode\nfrequency for long-ranged interactions decaying as $1/r^2$ in 3D and for a\ncontact potential in 2D. Quantum signatures, beyond the TWE, may only be found\nin the condensate dynamics beyond the regimes of classical phase-space\npropagation identified here.",
        "positive": "Floquet Hamiltonian Engineering of an Isolated Many-Body Spin System: Controlling interactions is the key element for quantum engineering of\nmany-body systems. Using time-periodic driving, a naturally given many-body\nHamiltonian of a closed quantum system can be transformed into an effective\ntarget Hamiltonian exhibiting vastly different dynamics. We demonstrate such\nFloquet engineering with a system of spins represented by Rydberg states in an\nultracold atomic gas. Applying a sequence of spin manipulations, we change the\nsymmetry properties of the effective Heisenberg XYZ Hamiltonian. As a\nconsequence, the relaxation behavior of the total spin is drastically modified.\nThe observed dynamics can be qualitatively captured by a semi-classical\nsimulation. Synthesising a wide range of Hamiltonians opens vast opportunities\nfor implementing quantum simulation of non-equilibrium dynamics in a single\nexperimental setting."
    },
    {
        "anchor": "Slow quench dynamics of Mott-insulating regions in a trapped Bose gas: We investigate the dynamics of Mott-insulating regions of a trapped bosonic\ngas as the interaction strength is changed linearly with time. The bosonic gas\nconsidered is loaded into an optical lattice and confined to a parabolic\ntrapping potential. Two situations are addressed: the formation of Mott domains\nin a superfluid gas as the interaction is increased, and their melting as the\ninteraction strength is lowered. In the first case, depending on the local\nfilling, Mott-insulating barriers can develop and hinder the density and energy\ntransport throughout the system. In the second case, the density and local\nenergy adjust rapidly whereas long range correlations require longer time to\nsettle. For both cases, we consider the time evolution of various observables:\nthe local density and energy, and their respective currents, the local\ncompressibility, the local excess energy, the heat and single particle\ncorrelators. The evolution of these observables is obtained using the\ntime-dependent density-matrix renormalization group technique and comparisons\nwith time-evolutions done within the Gutzwiller approximation are provided.",
        "positive": "Controlled doping of a bosonic quantum gas with single neutral atoms: We report on the experimental doping of a $^{87}$Rubidium (Rb) Bose-Einstein\ncondensate (BEC) with individual neutral $^{133}$Cesium (Cs) atoms. We discuss\nthe experimental tools and procedures to facilitate Cs-Rb interaction. First,\nwe use degenerate Raman side-band cooling of the impurities to enhance the\nimmersion efficiency for the impurity in the quantum gas. We identify the\nimmersed fraction of Cs impurities from the thermalization of Cs atoms upon\nimpinging on a BEC, where elastic collisions lead to a localization of Cs atoms\nin the Rb cloud. Second, further enhancement of the immersion probability is\nobtained by localizing the Cs atoms in a species-selective optical lattice and\nsubsequent transport into the Rb cloud. Here, impurity-BEC interaction is\nmonitored by position and time resolved three-body loss of Cs impurities\nimmersed into the BEC. This combination of experimental methods allows for the\ncontrolled doping of a BEC with neutral impurity atoms, paving the way to\nimpurity aided probing and coherent impurity-quantum bath interaction."
    },
    {
        "anchor": "Three-body losses of a polarized Fermi gas near a p-wave Feshbach\n  resonance in effective field theory: We study three-body recombination of fully spin-polarized ${}^6$Li atoms that\nare interacting resonantly in relative p-waves. Motivated by a recent\nexperiment, we focus on negative scattering volumes where three atoms recombine\ninto a deep dimer and another atom. We calculate the three-body recombination\nrate using a Faddeev equation derived from effective field theory. In\nparticular, we study the magnetic field and temperature dependences of the loss\nrate and use the recombination data to determine the effective range of the\np-wave atom-atom interaction. We also predict the existence of a shallow\nthree-body bound state that manifests itself as a prominent feature in the\nenergy-dependent three-body recombination rate.",
        "positive": "Two-species hard-core bosons on the triangular lattice: A quantum Monte\n  Carlo study: Using worm-type quantum Monte Carlo simulations, we investigate bosonic\nmixtures on the triangular lattice of two species of bosons, which interact via\nnearest-neighbour intraspecies ($V$) and onsite interspecies ($U$) repulsions.\nFor the case of symmetric hopping amplitude ($t_A/V=t_B/V$) and $U/V=1$, we\ndetermine a rich ground-state phase diagram that contains double solid, double\nsuperfluid (2SF), supersolid (SS), solid-superfluid (Solid-SF) and counterflow\nsupersolid (CSS) states. The SS, Solid-SF and CSS states exhibit spontaneous\nsymmetry breaking among the three sublattices of the triangular lattice and\nbetween the two species, which leads to nonzero crystalline density wave order\nin each species. We furthermore show that the CSS and the SS states are present\nfor $t_A/V \\neq t_B/V$, and the latter even survives up to $t_A/V \\rightarrow\n\\infty$ or $t_B/V \\rightarrow \\infty$ limit. The effects induced by the\nvariation of $U/V$ and by the imbalance of particle numbers of the two species\nare also explored."
    },
    {
        "anchor": "Localization in momentum space of ultracold atoms in incommensurate\n  lattices: We characterize the disorder induced localization in momentum space for\nultracold atoms in one-dimensional incommensurate lattices, according to the\ndual Aubry-Andr\\'e model. For low disorder the system is localized in momentum\nspace, and the momentum distribution exhibits time-periodic oscillations of the\nrelative intensity of its components. The behavior of these oscillations is\nexplained by means of a simple three-mode approximation. We predict their\nfrequency and visibility by using typical parameters of feasible experiments.\nAbove the transition the system diffuses in momentum space, and the\noscillations vanish when averaged over different realizations, offering a clear\nsignature of the transition.",
        "positive": "The mixing-spacetime symmetry in the Floquet-Bloch band theory: We discover a class of spacetime symmetries unique to time-periodic systems,\nwhich we term \"mixing symmetry\" due to its combination of space and time\ncoordinates in the symmetry transformation. We systematically enumerate the\nsymmetry groups, and classify the corresponding Floquet-Bloch band theories by\nutilizing the winding number of quasi-energy. Moreover, we provide a\ncomprehensive scheme for the experimental realization of these symmetries. The\nparticle propagator exhibits an intriguing pattern that remains invariant even\nunder transformations mixing space and time coordinates. We anticipate that\nthis distinct feature can be observed in current cold atom experiments."
    },
    {
        "anchor": "Microscopic description of exciton-polaritons in microcavities: We investigate the microscopic description of exciton-polaritons that\ninvolves electrons, holes and photons within a two-dimensional microcavity. We\nshow that in order to recover the simplified exciton-photon model that is\ntypically used to describe polaritons, one must correctly define the\nexciton-photon detuning and exciton-photon (Rabi) coupling in terms of the bare\nmicroscopic parameters. For the case of unscreened Coulomb interactions, we\nfind that the exciton-photon detuning is strongly shifted from its bare value\nin a manner akin to renormalization in quantum electrodynamics. Within the\nrenormalized theory, we exactly solve the problem of a single exciton-polariton\nfor the first time and obtain the full spectral response of the microcavity. In\nparticular, we find that the electron-hole wave function of the polariton can\nbe significantly modified by the very strong Rabi couplings achieved in current\nexperiments. Our microscopic approach furthermore allows us to obtain the\neffective interaction between identical polaritons for any light-matter\ncoupling. Crucially, we show that the standard treatment of polariton-polariton\ninteractions in the very strong coupling regime is incorrect, since it neglects\nthe light-induced modification of the exciton size and thus greatly\noverestimates the effect of Pauli exclusion on the Rabi coupling, i.e., the\nsaturation of exciton oscillator strength. Our findings thus provide the\nfoundations for understanding and characterizing exciton-polariton systems\nacross the whole range of polariton densities.",
        "positive": "Formation of stripes in a mixed-dimensional cold-atom Fermi-Hubbard\n  system: The relation between d-wave superconductivity and stripes is fundamental to\nthe understanding of ordered phases in cuprates. While experimentally both\nphases are found in close proximity, numerical studies on the related\nFermi-Hubbard model have long been investigating whether stripes precede,\ncompete or coexist with superconductivity. Such stripes are characterised by\ninterleaved charge and spin density wave ordering where fluctuating lines of\ndopants separate domains of opposite antiferromagnetic order. Here we show\nfirst signatures of stripes in a cold-atom Fermi-Hubbard quantum simulator. By\nengineering a mixed-dimensional system, we increase their typical energy scales\nto the spin exchange energy, enabling us to access the interesting crossover\ntemperature regime where stripes begin to form. We observe extended, attractive\ncorrelations between hole dopants and find an increased probability to form\nlarger structures akin to stripes. In the spin sector, we study correlation\nfunctions up to third order and find results consistent with stripe formation.\nThese higher-order correlation measurements pave the way towards an improved\nmicroscopic understanding of the emergent properties of stripes and their\nrelation to other competing phases. More generally, our approach has direct\nrelevance for newly discovered high-temperature superconducting materials in\nwhich mixed dimensions play an essential role."
    },
    {
        "anchor": "Vortex dynamics in coherently coupled Bose-Einstein condensates: In classical hydrodynamics with uniform density, vortices move with the local\nfluid velocity. This description is rewritten in terms of forces arising from\nthe interaction with other vortices. Two such positive straight vortices\nexperience a repulsive interaction and precess in a positive (anticlockwise)\nsense around their common centroid. A similar picture applies to vortices in a\ntwo-component two-dimensional uniform Bose-Einstein condensate (BEC) coherently\ncoupled through rf Rabi fields. Unlike the classical case, however, the rf Rabi\ncoupling induces an attractive interaction and two such vortices with positive\nsigns now rotate in the negative (clockwise) sense. Pairs of counter-rotating\nvortices are instead found to translate with uniform velocity perpendicular to\nthe line joining their cores. This picture is extended to a single vortex in a\ntwo-component trapped BEC. Although two uniform vortex-free components\nexperience familiar Rabi oscillations of particle-number difference, such\nbehavior is absent for a vortex in one component because of the nonuniform\nvortex phase. Instead the coherent Rabi coupling induces a periodic vorticity\ntransfer between the two components.",
        "positive": "One-dimensional multicomponent fermions with delta function interaction\n  in strong and weak coupling limits: Two-component Fermi gas: The Fredholm equations for one-dimensional two-component Fermions with\nrepulsive and with attractive delta-function interactions are solved by an\nasymptotic expansion for A) strong repulsion, B) weak repulsion, C) weak\nattraction and D) strong attraction. Consequently, we obtain the first few\nterms of the expansion of ground state energy for the Fermi gas with\npolarization for these regimes. We also prove that the two sets of the Fredhom\nequations for weakly repulsive and attractive interactions are identical as\nlong as the integration boundaries match each other between the two sides. Thus\nthe asymptotic expansions of the energies of the repulsive and attractive\nFermions are identical to all orders in this region. The identity of the\nasymptotic expansions may not mean that the energy analytically connects."
    },
    {
        "anchor": "Quantized Topological Anderson-Thouless Pump: Thouless pump with quantized transports is topologically robust against small\nperturbations and disorders, while breaks down under sufficiently strong\ndisorders. Here we propose counter-intuitive topological pumps induced by\ndisorders in noninteracting and interacting systems. We first show an extrinsic\ntopological pump driven by the on-site quasiperiodic potential for a two-loop\nsequence, where the disorder inequivalently suppresses the topology of two pump\nloops. Moreover, we reveal an intrinsic topological pump induced by the hopping\nquasiperiodic disorder from a trivial single-loop pump in the clean limit,\ndubbed the topological Anderson-Thouless pump (TATP) as a dynamical analogue of\ntopological Anderson insulators. We demonstrate that the mechanism of the TATP\nis the disorder-induced shift of gapless critical points and the TATP can even\nexhibit in the dynamic disorder and interacting cases. Finally, we extend the\nTATP to higher-order topological systems with disorder-induced quantized corner\ntransports. Our proposed TATPs present new members of the topological pump\nfamily and could be realized with ultracold atoms or photonic waveguides.",
        "positive": "Numerically exact mimicking of quantum gas microscopy for interacting\n  lattice fermions: A numerical method is presented for reproducing fermionic quantum gas\nmicroscope experiments in equilibrium. By employing nested componentwise direct\nsampling of fermion pseudo-density matrices, as they arise naturally in\ndeterminantal quantum Monte Carlo (QMC) simulations, a stream of\npseudo-snapshots of occupation numbers on large systems can be produced. There\nis a sign problem even when the conventional determinantal QMC algorithm can be\nmade sign-problem free, and every pseudo-snapshot comes with a sign and a\nreweighting factor. Nonetheless, this \"sampling sign problem\" turns out to be\nweak and manageable in a large, relevant parameter regime. The method allows to\ncompute distribution functions of arbitrary quantities defined in occupation\nnumber space and, from a practical point of view, facilitates the computation\nof complicated conditional correlation functions. While the projective\nmeasurements in quantum gas microscope experiments achieve direct sampling of\noccupation number states from the density matrix, the presented numerical\nmethod requires a Markov chain as an intermediate step and thus achieves only\nindirect sampling, but the full distribution of pseudo-snapshots after (signed)\nreweighting is identical to the distribution of snapshots from projective\nmeasurements"
    },
    {
        "anchor": "On the jets emitted by driven Bose-Einstein condensates: Features of the emission of jets by driven Bose-Einstein condensates,\ndiscovered by Clark et al. (Nature 551, 356359), can be understood by drawing\nanalogies with particle physics. In particular, the widening of the\n$\\Delta\\phi=\\pi$ peak in the angular correlation function is due to a dijet\nacollinearity, which I estimate to be about 5$^{\\circ}$ RMS. I also propose new\ncorrelation studies using observables commonly used in studies of the\nquark-gluon plasma.",
        "positive": "A nonlinear quantum piston for the controlled generation of vortex rings: We propose a simple way to manage interactions in Bose-Einstein condensates\nto generate vortex rings in a highly controllable way.\n  The vortex rings are generated under the action of a quantum analogue of a\nclassical piston pushing the condensed atoms through a small aperture."
    },
    {
        "anchor": "Atomic homodyne detection of continuous variable entangled twin-atom\n  states: Historically, the completeness of quantum theory has been questioned using\nthe concept of bipartite continuous variable entanglement. The non-classical\ncorrelations (entanglement) between the two subsystems imply that the\nobservables of one subsystem are determined by the measurement choice on the\nother, regardless of their distance. Nowadays, continuous variable entanglement\nis regarded as an essential resource allowing for quantum enhanced measurement\nresolution, the realization of quantum teleportation and quantum memories, or\nthe demonstration of the Einstein-Podolsky-Rosen paradox. These applications\nrely on techniques to manipulate and detect coherences of quantum fields, the\nquadratures. While in optics coherent homodyne detection of quadratures is a\nstandard technique, for massive particles a corresponding method was missing.\nHere we report on the realization of an atomic analog to homodyne detection for\nthe measurement of matter-wave quadratures. The application of this technique\nto a quantum state produced by spin-changing collisions in a Bose-Einstein\ncondensate reveals continuous variable entanglement, as well as the twin-atom\ncharacter of the state. With that we present a new system in which continuous\nvariable entanglement of massive particles is demonstrated. The direct\ndetection of atomic quadratures has applications not only in experimental\nquantum atom optics but also for the measurement of fields in many-body systems\nof massive particles.",
        "positive": "Optimizing the efficiency of evaporative cooling in optical dipole traps: We present a combined computational and experimental study to optimize the\nefficiency of evaporative cooling for atoms in optical dipole traps. By\nemploying a kinetic model of evaporation, we provide a strategy for determining\nthe optimal relation between atom temperature, trap depth, and average trap\nfrequency during evaporation given experimental initial conditions. We then\nexperimentally implement a highly efficient evaporation process in an optical\ndipole trap, showing excellent agreement between the theory and experiment.\nThis method has allowed the creation of pure Bose-Einstein condensates of\n$^{87}$Rb with 2$\\times 10^4$ atoms starting from only $5\\times 10^5$ atoms\ninitially loaded in the optical dipole trap, achieving an evaporation\nefficiency, $\\gamma_{eff}$, of 4.0 during evaporation."
    },
    {
        "anchor": "Realizing the Harper Hamiltonian with Laser-Assisted Tunneling in\n  Optical Lattices: We experimentally implement the Harper Hamiltonian for neutral particles in\noptical lattices using laser-assisted tunneling and a potential energy gradient\nprovided by gravity or magnetic field gradients. This Hamiltonian describes the\nmotion of charged particles in strong magnetic fields. Laser-assisted tunneling\nprocesses are characterized by studying the expansion of the atoms in the\nlattice. The band structure of this Hamiltonian should display Hofstadter's\nbutterfly. For fermions, this scheme should realize the quantum Hall effect and\nchiral edge states.",
        "positive": "Quantum dynamics of impurities in a 1D Bose gas: Using a species-selective dipole potential, we create initially localized\nimpurities and investigate their interactions with a majority species of\nbosonic atoms in a one-dimensional configuration during expansion. We find an\ninteraction-dependent amplitude reduction of the oscillation of the impurities'\nsize with no measurable frequency shift, and study it as a function of the\ninteraction strength. We discuss possible theoretical interpretations of the\ndata. We compare, in particular, with a polaronic mass shift model derived\nfollowing Feynman variational approach."
    },
    {
        "anchor": "Tunable-range, photon-mediated atomic interactions in multimode cavity\n  QED: Optical cavity QED provides a platform with which to explore quantum\nmany-body physics in driven-dissipative systems. Single-mode cavities provide\nstrong, infinite-range photon-mediated interactions among intracavity atoms.\nHowever, these global all-to-all couplings are limiting from the perspective of\nexploring quantum many-body physics beyond the mean-field approximation. The\npresent work demonstrates that local couplings can be created using multimode\ncavity QED. This is established through measurements of the threshold of a\nsuperradiant, self-organization phase transition versus atomic position.\nSpecifically, we experimentally show that the interference of near-degenerate\ncavity modes leads to both a strong and tunable-range interaction between\nBose-Einstein condensates (BECs) trapped within the cavity. We exploit the\nsymmetry of a confocal cavity to measure the interaction between real BECs and\ntheir virtual images without unwanted contributions arising from the merger of\nreal BECs. Atom-atom coupling may be tuned from short range to long range. This\ncapability paves the way toward future explorations of exotic, strongly\ncorrelated systems such as quantum liquid crystals and driven-dissipative spin\nglasses.",
        "positive": "Protocol to engineer Fulde-Ferrell-Larkin-Ovchinnikov states in a cold\n  Fermi gas: We propose a two-step experimental protocol to directly engineer\nFulde-Ferrell-Larkin-Ovchinnikov (FFLO) states in a cold two-component Fermi\ngas loaded into a quasi-one-dimensional trap. First, one uses phase imprinting\nto create a train of domain walls in a superfluid with equal number of\n$\\uparrow$- and $\\downarrow$-spins. Second, one applies a radio-frequency sweep\nto selectively break Cooper pairs near the domain walls and transfer the\n$\\uparrow$-spins to a third spin state which does not interact with the\n$\\uparrow$- and $\\downarrow$-spins. The resulting FFLO state has exactly one\nunpaired $\\downarrow$-spin in each domain wall and is stable for all values of\ndomain-wall separation and interaction strength. We show that the protocol can\nbe implemented with high fidelity at sufficiently strong interactions for a\nwide range of parameters available in present-day experimental conditions."
    },
    {
        "anchor": "Superfluid density reduction and spin-imbalanced pairing in a fermionic\n  superfluid due to dynamical boson exchange: We explore novel features of a nonrelativistic fermionic superfluid in which\nthe pairing interaction includes a contribution from the exchange of a\ndynamical bosonic mode. We show that the dynamical boson exchange (DBE), which\ncauses a retarded pairing interaction and thus violates the Galilean invariance\nof the fermion sector, generically leads to a quantum reduction of the\nsuperfluid density and hence a nonzero normal fraction even at zero\ntemperature. For spin-singlet pairing, the DBE also leads to a nonvanishing\nspin susceptibility at zero temperature, providing a mechanism for the\ncoexistence of pairing and magnetization. While these effects are negligible\nfor weak pairing, they become sizable at strong pairing. For the double\nsuperfluidity in ultracold Fermi-Bose mixtures, the superfluid density\nreduction for the fermion sector induced by the DBE just gives rise to the\nAndreev-Bashkin drag effect, indicating a strong entrainment between the two\nsuperfluid components. The DBE may also provide a new source for the superfluid\nfraction reduction of neutron matter, which is crucial for models of neutron\nstar glitches based on neutron superfluidity.",
        "positive": "Small amplitude collective modes of a finite-size unitary Fermi gas in\n  deformed traps: We have investigated collective breathing modes of a unitary Fermi gas in\ndeformed harmonic traps. The ground state is studied by the Superfluid Local\nDensity Approximation (SLDA) and small-amplitude collective modes are studied\nby the iterative Quasiparticle Random Phase Approximation (QRPA). The results\nillustrate the evolutions of collective modes of a small system in traps from\nspherical to elongated or pancake deformations. For small spherical systems,\nthe influences of different SLDA parameters are significant, and, in\nparticular, a large pairing strength can shift up the oscillation frequency of\ncollective mode. The transition currents from QRPA show that the compressional\nflow patterns are nontrivial and dependent on the deformation. Finally, the\nfinite size effects are demonstrated to be reasonable when progressing towards\nlarger systems. Our studies indicate that experiments on small and medium\nsystems are valuable for understanding effective interactions in systems with\nvarying sizes and trap deformations."
    },
    {
        "anchor": "Finite-Temperature Properties of Attractive Three-Component Fermionic\n  Atoms in Optical Lattices: We investigate the finite-temperature properties of attractive\nthree-component (colors) fermionic atoms in optical lattices using a\nself-energy functional approach. As the strength of the attractive interaction\nincreases in the low-temperature region, we observe a second-order transition\nfrom a Fermi liquid to a color superfluid (CSF), where atoms from two of the\nthree colors form Cooper pairs. In the strong attractive region, we observe a\nfirst-order transition from a CSF to a trionic state, where three atoms with\ndifferent colors form singlet bound states. A crossover between a Fermi liquid\nand a trionic state is observed in the high-temperature region. We present a\nphase diagram covering zero to finite temperatures. We demonstrate that the CSF\ntransition temperature is enhanced by the anisotropy of the attractive\ninteraction.",
        "positive": "Magnetism driven by fluctuations and frustration in synthetic triangular\n  antiferromagnets with ultracold fermions in optical lattices: Quantum simulators based on cold atomic gases can provide an ideal platform\nto study the microscopic mechanisms behind intriguing properties of solid\nmaterials and further explore novel exotic phenomena inaccessible by chemical\nsynthesis. Here we propose and theoretically analyze a coherently coupled\nbinary mixture of Fermi atoms in a triangular optical lattice as a promising\nrealization of synthetic frustrated antiferromagnets. We perform a cluster\nmean-field plus scaling analysis to show that the ground state exhibits several\nnontrivial magnetic phases and a novel spin reorientation transition caused by\nthe quantum order-by-disorder mechanism. Moreover, we find from Monte Carlo\nsimulations that thermal fluctuations induce an unexpected coexistence of\nBerezinskii-Kosterlitz-Thouless physics and long-range order in different\ncorrelators. These predictions, besides being relevant to present and future\nexperiments on triangular antiferromagnetic materials, can be tested in the\nlaboratory with the combination of the currently available techniques for cold\natoms."
    },
    {
        "anchor": "Simulation of Time-dependent Heisenberg Models in 1D: In this paper, we provide a theoretical analysis of strongly interacting\nquantum systems confined by a time-dependent external potential in one spatial\ndimension. We show that such systems can be used to simulate spin chains\ndescribed by Heisenberg Hamiltonians in which the exchange coupling constants\ncan be manipulated by time-dependent driving of the shape of the external\nconfinement. As illustrative examples, we consider a harmonic trapping\npotential with a variable frequency and an infinite square well potential with\na time-dependent barrier in the middle.",
        "positive": "Robust states of ultra-cold bosons in tilted optical lattices: We identify regular structures in the globally chaotic spectra of an\ninteracting bosonic quantum gas in tilted periodic potentials. The associated\neigenstates exhibit strong localization properties on the lattice, and are\ndynamically robust against external perturbations."
    },
    {
        "anchor": "Probing the Kondo Lattice Model with Alkaline Earth Atoms: We study transport properties of alkaline-earth atoms governed by the Kondo\nLattice Hamiltonian plus a harmonic confining potential, and suggest simple\ndynamical probes of several different regimes of the phase diagram that can be\nimplemented with current experimental techniques. In particular, we show how\nKondo physics at strong coupling, low density, and in the heavy fermion phase\nis manifest in the dipole oscillations of the conduction band upon displacement\nof the trap center.",
        "positive": "Creation of a low-entropy quantum gas of polar molecules in an optical\n  lattice: Ultracold polar molecules, with their long-range electric dipolar\ninteractions, offer a unique platform for studying correlated quantum many-body\nphenomena such as quantum magnetism. However, realizing a highly degenerate\nquantum gas of molecules with a low entropy per particle has been an\noutstanding experimental challenge. In this paper, we report the synthesis of a\nlow entropy molecular quantum gas by creating molecules at individual sites of\na three-dimensional optical lattice that is initially loaded from a low entropy\nmixture of K and Rb quantum gases. We make use of the quantum statistics and\ninteractions of the initial atom gases to load into the optical lattice,\nsimultaneously and with good spatial overlap, a Mott insulator of bosonic Rb\natoms and a single-band insulator of fermionic K atoms. Then, using\nmagneto-association and optical state transfer, we efficiently produce\nground-state molecules in the lattice at those sites that contained one Rb and\none K atom. The achieved filling fraction of 25% indicates an entropy as low as\n$2.2\\,k_B$ per molecule. This low-entropy molecular quantum gas opens the door\nto novel studies of transport and entanglement propagation in a many-body\nsystem with long-range dipolar interactions."
    },
    {
        "anchor": "Many-body quantum dynamics and induced correlations of Bose polarons: We study the ground state properties and nonequilibrium dynamics of two\nspinor bosonic impurities immersed in a one-dimensional bosonic gas upon\napplying an interspecies interaction quench. For the ground state of two\nnon-interacting impurities we reveal signatures of attractive induced\ninteractions in both cases of attractive or repulsive interspecies\ninteractions, while a weak impurity-impurity repulsion forces the impurities to\nstay apart. Turning to the quench dynamics we inspect the time-evolution of the\ncontrast unveiling the existence, dynamical deformation and the orthogonality\ncatastrophe of Bose polarons. We find that for an increasing postquench\nrepulsion the impurities reside in a superposition of two distinct two-body\nconfigurations while at strong repulsions their corresponding two-body\ncorrelation patterns show a spatially delocalized behavior evincing the\ninvolvement of higher excited states. For attractive interspecies couplings,\nthe impurities exhibit a tendency to localize at the origin and remarkably for\nstrong attractions they experience a mutual attraction on the two-body level\nthat is imprinted as a density hump on the bosonic bath.",
        "positive": "Non-Abelian gauge fields and topological insulators in shaken optical\n  lattices: Time-periodic driving like lattice shaking offers a low-demanding method to\ngenerate artificial gauge fields in optical lattices. We identify the relevant\nsymmetries that have to be broken by the driving function for that purpose and\ndemonstrate the power of this method by making concrete proposals for its\napplication to two-dimensional lattice systems: We show how to tune frustration\nand how to create and control band touching points like Dirac cones in the\nshaken kagom\\'e lattice. We propose the realization of a topological and a\nquantum spin Hall insulator in a shaken spin-dependent hexagonal lattice. We\ndescribe how strong artificial magnetic fields can be achieved for example in a\nsquare lattice by employing superlattice modulation. Finally, exemplified on a\nshaken spin-dependent square lattice, we develop a method to create strong\nnon-Abelian gauge fields."
    },
    {
        "anchor": "Mean-field study of repulsive 2D and 3D Bose polarons: The detailed mean-field treatment of the Bose polaron problem in two and\nthree dimensions is presented. Particularly, assuming that impurity is immersed\nin the dilute Bose gas and interacts with bosons via the hard-sphere two-body\npotential, we calculate the low-momentum parameters of its spectrum, namely,\nthe binding energy and the effective mass. The limits of applicability of the\nmean-field approach to a problem of mobile impurity in Bose-Einstein\ncondensates are discussed by comparing our results to the Monte Carlo\nsimulations data.",
        "positive": "Dipole-dipole interactions in optical lattices do not follow an inverse\n  cube power law: We study the effective dipole-dipole interactions in ultracold quantum gases\non optical lattices as a function of asymmetry in confinement along the\nprincipal axes of the lattice. In particular, we study the matrix elements of\nthe dipole-dipole interaction in the basis of lowest band Wannier functions\nwhich serve as a set of low-energy states for many-body physics on the lattice.\nWe demonstrate that the effective interaction between dipoles in an optical\nlattice is non-algebraic in the inter-particle separation at short to medium\ndistance on the lattice scale and has a long-range power-law tail, in contrast\nto the pure power-law behavior of the dipole-dipole interaction in free space.\nThe modifications to the free-space interaction can be sizable; we identify\ndifferences of up to 36% from the free-space interaction at the\nnearest-neighbor distance in quasi-1D arrangements. The interaction difference\ndepends essentially on asymmetry in confinement, due to the d-wave anisotropy\nof the dipole-dipole interaction. Our results do not depend on statistics,\napplying to both dipolar Bose-Einstein condensates and degenerate Fermi gases.\nUsing matrix product state simulations, we demonstrate that use of the correct\nlattice dipolar interaction leads to significant deviations from many-body\npredictions using the free-space interaction. Our results are relevant to up\nand coming experiments with ultracold heteronuclear molecules, Rydberg atoms,\nand strongly magnetic atoms in optical lattices."
    },
    {
        "anchor": "Spin and mass currents near a moving magnetic obstacle in a\n  two-component Bose-Einstein condensate: We study the spatial distributions of the spin and mass currents generated by\na moving Gaussian magnetic obstacle in a symmetric, two-component Bose-Einstein\ncondensate in two dimensions. We analytically describe the current\ndistributions for a slow obstacle and show that the spin and the mass currents\nexhibit characteristic spatial structures resembling those of electromagnetic\nfields around dipole moments. When the obstacle's velocity increases, we\nnumerically observe that the flow pattern maintains its overall structure while\nthe spin polarization induced by the obstacle is enhanced with an increased\nspin current. We investigate the critical velocity of the magnetic obstacle\nbased on the local criterion of Landau energetic instability and find that it\ndecreases almost linearly as the magnitude of the obstacle's potential\nincreases, which can be directly tested in current experiments.",
        "positive": "A Raman-induced Feshbach resonance in an effectively single-component\n  Fermi gas: Ultracold gases of interacting spin-orbit coupled fermions are predicted to\ndisplay exotic phenomena such as topological superfluidity and its associated\nMajorana fermions. Here, we experimentally demonstrate a route to\nstrongly-interacting single-component atomic Fermi gases by combining an s-wave\nFeshbach resonance (giving strong interactions) and spin-orbit coupling\n(creating an effective p-wave channel). We identify the Feshbach resonance by\nits associated atomic loss feature and show that, in agreement with our\nsingle-channel scattering model, this feature is preserved and shifted as a\nfunction of the spin-orbit coupling parameters."
    },
    {
        "anchor": "Asymmetric lineshapes of Efimov resonances in mass-imbalanced ultracold\n  gases: The resonant profile of the rate coefficient for three-body recombination\ninto a shallow dimer is investigated for mass-imbalanced systems. In the\nlow-energy limit, three atoms collide with zero-range interactions, in a regime\nwhere the scattering lengths of the heavy-heavy and the heavy-light subsystems\nare positive and negative, respectively. For this physical system, the\nadiabatic hyperspherical representation is combined with a fully semi-classical\nmethod and we show that the shallow dimer recombination spectra display an\nasymmetric lineshape that originates from the coexistence of Efimov resonances\nwith St\\\"uckelberg interference minima. These asymmetric lineshapes are\nquantified utilizing the Fano profile formula. In particular, a closed form\nexpression is derived that describes the width of the corresponding Efimov\nresonances and the Fano lineshape asymmetry parameter $q$. The profile of\nEfimov resonances exhibits a $q-$reversal effect as the inter- and\nintra-species scattering lengths vary. In the case of a diverging asymmetry\nparameter, i.e. $|q|\\to \\infty$, we show that the Efimov resonances possess\nzero width and are fully decoupled from the three-body and atom-dimer continua,\nand the corresponding Efimov metastable states behave as bound levels.",
        "positive": "Quantum pump for counter-circulations in a spinor Bose-Einstein\n  condensate: We propose a pump scheme for quantum circulations, including\ncounter-circulations for superposition states, of a spinor Bose-Einstein\ncondensate. Our scheme is efficient and can be implemented within current\nexperimental technologies and setups. It remains valid for non-classical atomic\nstates, such as pseudo-spin squeezed states and maximal entangled N-GHZ or NooN\nstates. Moreover, it is capable of transforming several enhanced sensing\nprotocols relying on reduced fluctuations from quantum correlation and\nentanglement of atomic internal states to enhanced measurement of spatial\ninterference and rotation."
    },
    {
        "anchor": "Chiral Majorana edge states in the vortex core of a $p+ip$ Fermi\n  superfluid: We study a single vortex in a two-dimensional $p+ip$ Fermi superfluid\ninteracting with a Bose-Einstein condensate. The Fermi superfluid is\ntopologically non-trivial and hosts a zero-energy Majorana bound state at the\nvortex core. Assuming a repulsive $s$-wave contact interaction between fermions\nand bosons, we find that fermions are depleted from the vortex core when the\nbosonic density becomes sufficiently large. In this case, a dynamically-driven\nlocal interface emerges between fermions and bosons, along which chiral\nMajorana edge states should appear.We examine in detail the variation of\nvortex-core structures as well as the formation of chiral Majorana edge states\nwith increasing bosonic density. In particular, when the angular momentum of\nthe vortex matches the chirality of the Fermi superfluid, the Majorana zero\nmode and normal bound states within the core continuously evolve into chiral\nMajorana edge states. Otherwise, a first-order transition occurs in the lowest\nexcited state within the core, due to the competition between counter-rotating\nnormal bound states in forming chiral Majorana edge states. Such a transition\nis manifested as a sharp peak in the excitation gap above the Majorana zero\nmode, at which point the Majorana zero mode is protected by a large excitation\ngap.Our study presents an illuminating example on how topological defects can\nbe dynamically controlled in the context of cold atomic gases.",
        "positive": "Statistical physics of Bose-Einstein condensed light in a dye\n  microcavity: We theoretically analyze the temperature behavior of paraxial light in\nthermal equilibrium with a dye-filled optical microcavity. At low temperatures\nthe photon gas undergoes Bose-Einstein condensation (BEC), and the photon\nnumber in the cavity ground state becomes macroscopic with respect to the total\nphoton number. Owing to a grandcanonical excitation exchange between the photon\ngas and the dye molecule reservoir, a regime with unusually large fluctuations\nof the condensate number is predicted for this system that is not observed in\npresent atomic physics BEC experiments."
    },
    {
        "anchor": "Symmetry and the critical phase of the two-bath spin-boson model:\n  Ground-state properties: A generalized trial wave function termed as the \"multi-D1 Ansatz\" has been\ndeveloped to study the ground state of the spin-boson model with simultaneous\ndiagonal and off-diagonal coupling in the sub-Ohmic regime. Ground-state\nproperties including the energy and the spin polarization are investigated, and\nthe results are consistent with those from the exact diagonalization and\ndensity matrix renormalization group approaches for the cases involving two\noscillators and two baths described by a continuous spectral density function.\nBreakdown of the rotational and parity symmetries along the continuous quantum\nphase transition separating the localized phase from the critical phase has\nbeen uncovered. Moreover, the phase boundary is determined accurately with the\ncorresponding symmetry parameters of the rotational and parity symmetries. A\ncritical value of the spectral exponent s* = 0.49(1) is predicted in the weak\ncoupling limit, which is in agreement with the mean-field prediction of 1/2,\nbut much smaller than the earlier literature estimate of 0.75(1).",
        "positive": "Strong-coupling Properties of a $p$-wave Interacting Fermi Gas on the\n  Viewpoint of Specific Heat at Constant Volume: We theoretically investigate the specific heat $C_V$ at constant volume in\nthe normal state of a $p$-wave interacting Fermi gas. Including fluctuations in\nthe $p$-wave Cooper channel within the framework of the strong-coupling theory\ndeveloped by Nozi\\`eres and Schmitt-Rink, we clarify how $C_V$ as a function of\ntemperature varies, as one moves from the weak-coupling regime to the\nstrong-coupling limit. In the weak-coupling regime, $C_V$ is shown to be\nenhanced by $p$-wave pairing fluctuations, near the superfluid phase transition\ntemperature $T_{\\rm c}$. Similar enhancement of $C_V(T\\simeq T_{\\rm c})$ is\nalso obtained in the strong-coupling regime, which, however, reflects that\nsystem is close an ideal Bose gas of $p$-wave two-body bound molecules. Using\nthese results, we classify the normal state into (1) the normal Fermi gas\nregime, (2) the $p$-wave molecular Bose gas regime, and (3) the region between\nthe two, where $p$-wave pairing fluctuations are dominant. Since the current\nexperiments can only access the normal phase of a $p$-wave interacting Fermi\ngas, our results would be useful for experiments to understand strong-coupling\nproperties of this Fermi system above $T_{\\rm c}$."
    },
    {
        "anchor": "A charged Coulomb Bose gas with dipole-dipole interactions: We systematically study the properties of a charged Coulomb Bose gas with\ndipole-dipole interactions in the weak coupling limit at both zero and finite\ntemperatures using the Hartree-Fock-Bogoliubov approach. We numerically analyze\nthe collective excitations, the condensate fraction, the depletion, the\nchemical potential, and the static structure factor. Moreover, we compare our\nnew findings with those of nondipolar charged Coulomb Bose gas. Our results\nreveal that the complex interplay of Coulomb and dipole-dipole interactions may\nmodify the stability, the thermodynamics and the coherence of the system.",
        "positive": "Competition between Bose Einstein Condensation and spin dynamics: We study the impact of spin-exchange collisions on the dynamics of\nBose-Einstein condensation, by rapidly cooling a chromium multi-component Bose\ngas. Despite relatively strong spin-dependent interactions, the critical\ntemperature for Bose-Einstein condensation is reached before the spin-degrees\nof freedom fully thermalize. The increase in density due to Bose-Einstein\ncondensation then triggers spin dynamics, hampering the formation of\ncondensates in spin excited states. Small metastable spinor condensates are\nnevertheless produced, and manifest strong spin fluctuations."
    },
    {
        "anchor": "Biased dynamics of the miscible-immiscible quantum phase transition in a\n  binary Bose-Einstein condensate: A quantum phase transition from the miscible to the immiscible phase of a\nquasi-one-dimensional binary Bose-Einstein condensate is driven by ramping down\nthe coupling amplitude of its two hyperfine states. It results in a random\npattern of spatial domains where the symmetry is broken separated by defects.\nIn distinction to previous studies [J. Sabbatini et al., Phys. Rev. Lett. 107,\n230402 (2011), New J. Phys. 14 095030 (2012)], we include nonzero detuning\nbetween the light field and the energy difference of the states, which provides\na bias towards one of the states. Using the truncated Wigner method, we test\nthe biased version of the quantum Kibble-Zurek mechanism [M. Rams et al., Phys.\nRev. Lett. 123, 130603 (2019)] and observe a crossover to the adiabatic regime\nwhen the quench is sufficiently fast to dominate the effect of the bias. We\nverify a universal power law for the population imbalance in the nonadiabatic\nregime both at the critical point and by the end of the ramp. Shrinking and\nannihilation of domains of the unfavourable phase after the ramp, that is,\nalready in the broken symmetry phase, enlarges the defect-free sections by the\nend of the ramp. The consequences of this phase-ordering effect can be captured\nby a phenomenological power law.",
        "positive": "Einstein-de Haas Effect in a Dipolar Fermi Gas: We show that an analogue to the classical Einstein-de Haas effect can appear\nin ultracold dipolar Fermi gases. The anisotropic nature of dipole-dipole\ninteractions can lead to a transfer of magnetization into orbital angular\nmomentum. Remarkably, distinct from a Bose-Einstein condensate, this transfer\nis accompanied by twisting motion, where individual spin components rotate in\nopposite directions with larger orbital angular momenta than the full system,\npossibly leading to easier experimental observation of the effect. This feature\nis induced by the deformation of the Fermi surface and the direction of the\ntwisting motion can be controlled by an s-wave scattering length or external\nmagnetic field, possibly providing a method of measuring scattering lengths of\nstrongly dipolar atomic species."
    },
    {
        "anchor": "Out-of-equilibrium dynamics of quantum many-body systems with long-range\n  interactions: Experimental progress in atomic, molecular, and optical platforms in the last\ndecade has stimulated strong and broad interest in the quantum coherent\ndynamics of many long-range interacting particles. The prominent collective\ncharacter of these systems enables novel non-equilibrium phenomena with no\ncounterpart in conventional quantum systems with local interactions. Much of\nthe theory work in this area either focussed on the impact of variable-range\ninteraction tails on the physics of local interactions or relied on\nmean-field-like descriptions based on the opposite limit of all-to-all\ninfinite-range interactions. In this Report, we present a systematic and\norganic review of recent advances in the field. Working with prototypical\ninteracting quantum spin lattices without disorder, our presentation hinges\nupon a versatile theoretical formalism that interpolates between the few-body\nmean-field physics and the many-body physics of quasi-local interactions. Such\na formalism allows us to connect these two regimes, providing both a formal\nquantitative tool and basic physical intuition. We leverage this unifying\nframework to review several findings of the last decade, including the peculiar\nnon-ballistic spreading of quantum correlations, counter-intuitive slowdown of\nentanglement dynamics, suppression of thermalization and equilibration,\nanomalous scaling of defects upon traversing criticality, dynamical phase\ntransitions, and genuinely non-equilibrium phases stabilized by periodic\ndriving. The style of this Report is on the pedagogical side, which makes it\naccessible to readers without previous experience in the subject matter.",
        "positive": "Dispersive hydrodynamics of nonlinear polarization waves in\n  two-component Bose-Einstein condensates: We study one dimensional mixtures of two-component Bose-Einstein condensates\nin the limit where the intra-species and inter-species interaction constants\nare very close. Near the mixing-demixing transition the polarization and the\ndensity dynamics decouple. We study the nonlinear polarization waves, show that\nthey obey a universal (i.e., parameter free) dynamical description, identify a\nnew type of algebraic soliton, explicitly write simple wave solutions, and\nstudy the Gurevich-Pitaevskii problem in this context."
    },
    {
        "anchor": "Periodically Driven Array of Single Rydberg Atoms: An array of single Rydberg atoms driven by a frequency modulated light field\nis studied. The periodic modulation effectively modifies the Rabi coupling,\nleading to unprecedented dynamics in the presence of Rydberg-Rydberg\ninteractions. They include state dependent population trapping, the Rydberg\nblockade for small and anti-blockades at large interaction strengths.\nInterestingly, the Schrieffer-wolf transformation reveals a fundamental process\nin Rydberg gases, correlated Rabi oscillations, arising from the long-range\ninteractions, provides an alternative depiction for Rydberg blockade and it\nexhibits a nontrivial behaviour in the presence of periodic modulation. The\ndynamical localization of a many body configuration in a driven Rydberg-lattice\nis discussed.",
        "positive": "Band and correlated insulators of cold fermions in a mesoscopic lattice: We investigate the transport properties of neutral, fermionic atoms passing\nthrough a one-dimensional quantum wire containing a mesoscopic lattice. The\nlattice is realized by projecting individually controlled, thin optical\nbarriers on top of a ballistic conductor. Building an increasingly longer\nlattice, one site after another, we observe and characterize the emergence of a\nband insulating phase, demonstrating control over quantum-coherent transport.\nWe explore the influence of atom-atom interactions and show that the insulating\nstate persists as contact interactions are tuned from moderately to strongly\nattractive. Using bosonization and classical Monte-Carlo simulations we analyze\nsuch a model of interacting fermions and find good qualitative agreement with\nthe data. The robustness of the insulating state supports the existence of a\nLuther-Emery liquid in the one-dimensional wire. Our work realizes a tunable,\nsite-controlled lattice Fermi gas strongly coupled to reservoirs, which is an\nideal test bed for non-equilibrium many-body physics."
    },
    {
        "anchor": "A semiclassical theory of phase-space dynamics of interacting bosons: We study the phase-space representation of dynamics of bosons in the\nsemiclassical regime where the occupation number of the modes is large. To this\nend, we employ the van Vleck-Gutzwiller propagator to obtain an approximation\nfor the Green's function of the Wigner distribution. The semiclassical analysis\nincorporates interference of classical paths and reduces to the truncated\nWigner approximation (TWA) when the interference is ignored. Furthermore, we\nidentify the Ehrenfest time after which the TWA fails. As a case study, we\nconsider a single-mode quantum nonlinear oscillator, which displays collapse\nand revival of observables. We analytically show that the interference of\nclassical paths leads to revivals, an effect that is not reproduced by the TWA\nor a perturbative analysis.",
        "positive": "Spontaneous Emission in a Matter-Wave Open Quantum System: One of the paradigms of a small quantum system in a dissipative environment\nis the decay of an excited atom undergoing spontaneous photon emission into the\nfluctuating quantum electrodynamic vacuum. Recent experiments have demonstrated\nthat the gapped photon dispersion in periodic structures can give rise to novel\nspontaneous-decay behavior including the formation of dissipative bound states.\nSo far, these effects have been restricted to the optical domain. Here, we\nexperimentally demonstrate similar behavior in a system of artificial atoms in\nan optical lattice that decay by emitting matter-wave, rather than optical,\nradiation into free space. By controlling the vacuum coupling and excitation\nenergy, we directly observe exponential and partly reversible, non-Markovian\ndynamics and detect a tunable bound state containing evanescent matter waves\nfor emission at negative excitation energies. Our system provides a flexible\nplatform for the emulation of open-system quantum electrodynamics and studies\nof dissipative many-body physics with ultracold atoms."
    },
    {
        "anchor": "Amended Proof of Pitaevskii-Stringari's Theorem: An amended proof of Pitaevskii-Stringari's theorem is given in mathematically\ncoherent manner without resorting to the Bogoliubov approximation. This\napproach is based on the orthodox quantum field theory which rigorously\nmaintains the canonical commutation relations. Moreover, we make a sound\nargument by taking the thermodynamic limit which the authors of the original\npapers did not refer to. We conclude that there is no Bose Einstein\nCondensation (BEC) as a phase transition based on the Spontaneous Symmetry\nBreaking (SSB) of the global $U(1)$ gauge symmetry in flat one dimensional\ngeometry even absolute zero temperature.",
        "positive": "Supersolid and charge density-wave states from anisotropic interaction\n  in an optical lattice: We show anisotropy of the dipole interaction between magnetic atoms or polar\nmolecules can stabilize new quantum phases in an optical lattice. Using a well\ncontrolled numerical method based on the tensor network algorithm, we calculate\nphase diagram of the resultant effective Hamiltonian in a two-dimensional\nsquare lattice - an anisotropic Hubbard model of hard-core bosons with\nattractive interaction in one direction and repulsive interaction in the other\ndirection. Besides the conventional superfluid and the Mott insulator states,\nwe find the striped and the checkerboard charge density wave states and the\nsupersolid phase that interconnect the superfluid and the striped solid states.\nThe transition to the supersolid phase has a mechanism different from the case\nof the soft-core Bose Hubbard model."
    },
    {
        "anchor": "A superheated Bose-condensed gas: Our understanding of various states of matter usually relies on the\nassumption of thermodynamic equilibrium. However, the transitions between\ndifferent phases of matter can be strongly affected by non-equilibrium\nphenomena. Here we demonstrate and explain an example of non-equilibrium\nstalling of a continuous, second-order phase transition. We create a\nsuperheated atomic Bose gas, in which a Bose-Einstein condensate (BEC) persists\nabove the equilibrium critical temperature, $T_c$, if its coupling to the\nsurrounding thermal bath is reduced by tuning interatomic interactions. For\nvanishing interactions the BEC persists in the superheated regime for a minute.\nHowever, if strong interactions are suddenly turned on, it rapidly \"boils\"\naway. Our observations can be understood within a two-fluid picture, treating\nthe condensed and thermal components of the gas as separate equilibrium systems\nwith a tuneable inter-component coupling. We experimentally reconstruct a\nnon-equilibrium phase diagram of our gas, and theoretically reproduce its main\nfeatures.",
        "positive": "Rotons and their damping in elongated dipolar Bose-Einstein condensates: We discuss finite temperature damping of rotons in elongated Bose-condensed\ndipolar gases, which are in the Thomas-Fermi regime in the tightly confined\ndirections. The presence of many branches of excitations which can participate\nin the damping process, is crucial for the Landau damping and results in\nsignificant increase of the damping rate. It is found, however, that even\nrotons with energies close to the roton gap may remain fairly stable in systems\nwith the roton gap as small as 1nK."
    },
    {
        "anchor": "Localization of Rung Pairs in Hard-core Bose-Hubbard Ladder: Quantum simulation in experiments of many-body systems may bring new\nphenomena which are not well studied theoretically. Motivated by a recent work\nof quantum simulation on a superconducting ladder circuit, we investigate the\nrung-pair localization of the Bose-Hubbard ladder model without quenched\ndisorder. Our results show that, in the hard-core limit, there exists a\nrung-pair localization both at the edges and in the bulk. Using center-of-mass\nframe, the two-particle system can be mapped to an effective single-particle\nsystem with an approximate sub-lattice symmetry. Under the condition of\nhard-core limit, the effective system is forced to have a defect at the left\nedge leading to a zero-energy flat band, which is the origin of the rung-pair\nlocalization. We also study the multi-particle dynamics of the Bose-Hubbard\nladder model, which is beyond the singleparticle picture. In this case, we find\nthat the localization can still survive despite of the existence of interaction\nbetween the pairs. Moreover, the numerical results show that the entanglement\nentropy exhibits a long-time logarithmic growth and the saturated values\nsatisfy a volume law. This phenomenon implies that the interaction plays an\nimportant role during the dynamics, although it cannot break the localization.\nOur results reveal another interesting type of disorder-free localization\nrelated to a zero-energy flat band, which is induced by on-site interaction and\nspecific lattice symmetry.",
        "positive": "Goldstone and Higgs Hydrodynamics in the BCS-BEC Crossover: We discuss the derivation of a low-energy effective field theory of phase\n(Goldstone) and amplitude (Higgs) modes of the pairing field from a microscopic\ntheory of attractive fermions. The coupled equations for Goldstone and Higgs\nfields are critically analyzed in the Bardeen-Cooper-Schrieffer (BCS) to\nBose-Einstein condensate (BEC) crossover both in three spatial dimensions and\nin two spatial dimensions. The crucial role of pair fluctuations is\ninvestigated, and the beyond-mean-field Gaussian theory of the BCS-BEC\ncrossover is compared with available experimental data of the two-dimensional\nultracold Fermi superfluid."
    },
    {
        "anchor": "Pair breaking and N\u00e9el ordering in attractive three-component Dirac\n  fermions: We employ the determinant quantum Monte Carlo method to investigate\nfinite-temperature properties of the half-filled attractive three-component\nHubbard model on a honeycomb lattice. By adjusting the anistropy of\ninteractions, the symmetry of the Hamiltonian changes from SU(3) to\nSU(2)$\\otimes$ U(1) and finally to SO(4)$\\otimes$ U(1). The system undergoes\nthe phase transition between the disorder state and the charge density wave\n(CDW) state around the SU(3) symmetric points. Away from the SU(3) symmetric\npoints and the SO(4)$\\otimes$ U(1) symmetric points, the system can enter into\nthe color density wave (color DW) phase or the color selective density wave\n(CSDW) phase. Around the SO(4)$\\otimes$ U(1) symmetric points, the pairing\norder and the CSDW order can be both detected. The pairing order is quickly\nsuppressed away from the SO(4)$\\otimes$ U(1) symmetric points because Cooper\npairs are scattered. When the anisotropy of interaction exists, N\\'eel order\nappears because the number of off-site trions $|12,3\\rangle$ is greater than\nthe number of other two types of off-site trions and off-site trions\n$|12,3\\rangle$ do not distribute randomly. The calculated entropy-temperature\nrelations show the anisotropy of interactions induced adiabatic cooling, which\nmay provide a new method to cool a system in experiments.",
        "positive": "Formation and detection of a chiral orbital Bose liquid in an optical\n  lattice: Recent experiments on $p$-orbital atomic bosons have suggested the emergence\nof a spectacular ultracold superfluid with staggered orbital currents in\noptical lattices. This raises fundamental questions like the effects of\ncollective thermal fluctuations, and how to directly observe such chiral order.\nHere, we show via Monte Carlo simulations that thermal fluctuations destroy\nthis superfluid in an unexpected two-step process, unveiling an intermediate\nnormal phase with spontaneously broken time-reversal symmetry, dubbed \"chiral\nBose liquid\". For integer fillings ($n\\geq 2$) in the chiral Mott regime,\nthermal fluctuations are captured by an effective orbital Ising model, and\nOnsager's powerful exact solution is adopted to determine the transition from\nthis intermediate liquid to the para-orbital normal phase at high temperature.\nA suitable lattice quench is designed to convert the staggered angular\nmomentum, previously thought by experts difficult to directly probe, into\ncoherent orbital oscillations, providing a smoking-gun signature of chiral\norder."
    },
    {
        "anchor": "Thermal and Quantum Fluctuation Effects in Quasiperiodic Systems in\n  External Potentials: We analyze the many-body phases of an ensemble of particles interacting via a\nLifshitz--Petrich--Gaussian pair potential in a harmonic confinement. We focus\non specific parameter regimes where we expect decagonal quasiperiodic cluster\narrangements. Performing classical Monte Carlo as well as path integral quantum\nMonte Carlo methods, we numerically simulate systems of a few thousand\nparticles including thermal and quantum fluctuations. Our findings indicate\nthat the competition between the intrinsic length scale of the harmonic\noscillator and the wavelengths associated to the minima of the pair potential\ngenerically lead to a destruction of the quasicrystalline pattern. Extensions\nof this work are also discussed.",
        "positive": "Pair-Breaking Collective Branch in BCS Superconductors and Superfluid\n  Fermi Gases: We demonstrate the existence of a collective excitation branch in the\npair-breaking continuum of superfluid Fermi gases and BCS superconductors. At\nzero temperature, we analytically continue the equation on the collective mode\nenergy in Anderson's Random Phase Approximation or Gaussian fluctuations\nthrough its branch cut associated with the continuum, and obtain the full\ncomplex dispersion relation, including in the strong coupling regime. The\nbranch exists as long as the chemical potential $\\mu$ is positive and the wave\nnumber below $\\sqrt{2m\\mu}/\\hbar$ (with m the fermion mass). In the long\nwavelength limit, the branch varies quadratically with the wave number, with a\ncomplex effective mass that we compute analytically for an arbitrary\ninteraction strength."
    },
    {
        "anchor": "Interaction-Induced Gradients Across a Confined Fermion Lattice: An imposed chemical potential gradient $A_\\uparrow=d\\mu_\\uparrow/dx$ on a\nsingle fermionic species (\"spin up\") directly produces a gradient in the\ndensity $d\\rho_\\uparrow/dx$ across a lattice. We study here the induced density\ninhomogeneity $d\\rho_\\downarrow/dx$ in the second fermionic species (\"spin\ndown\") which results from fermionic interactions $U$, even in the absence of a\nchemical potential gradient $A_\\downarrow=0$ on that species. The magnitude of\n$d\\rho_\\downarrow/dx$ acquired by the second species grows with $U$, while the\nmagnitude of $d\\rho_\\uparrow/dx$ remains relatively constant, that is, set only\nby $A_\\uparrow$. For a given $A_\\uparrow$, we find an interaction strength\n$U_*$ above which the two density gradients are equal in magnitude. We also\nevaluate the spin-spin correlations and show that, as expected,\nantiferromagnetism is most dominant at locations where the local density is\nhalf-filled. The spin polarization induced by sufficiently large gradients, in\ncombination with $U$, drives ferromagnetic behavior. In the case of repulsive\ninteractions, $d\\rho_\\downarrow/dx = -d\\rho_\\uparrow/dx$. A simple\nparticle-hole transformation determines the related effect in the case of\nattractive interactions.",
        "positive": "Splitting of singly and doubly quantized composite vortices in\n  two-component Bose-Einstein condensates: We study numerically the dynamical instabilities and splitting of singly and\ndoubly quantized composite vortices in two-component Bose-Einstein condensates\nharmonically confined to quasi two dimensions. In this system, the vortices\nbecome pointlike composite defects that can be classified in terms of an\ninteger pair $(\\kappa_1,\\kappa_2)$ of phase winding numbers. Our simulations\nbased on zero-temperature mean-field theory reveal several vortex splitting\nbehaviors that stem from the multicomponent nature of the system and do not\nhave direct counterparts in single-component condensates. By calculating the\nBogoliubov excitations of stationary axisymmetric composite vortices, we find\nnonreal excitation frequencies (dynamical instabilities) for the singly\nquantized $(1,1)$ and $(1,-1)$ vortices and for all variants of doubly\nquantized vortices, which we define by the condition\n$\\max_{j=1,2}|\\kappa_j|=2$. While the short-time predictions of the linear\nBogoliubov analysis are confirmed by direct time integration of the\nGross-Pitaevskii equations of motion, the time integration also reveals\nintricate long-time decay behavior not captured by the linearized dynamics.\nFirst, the $(1,\\pm 1)$ vortex is found to be unstable against splitting into a\n$(1,0)$ vortex and a $(0,\\pm 1)$ vortex. Second, the $(2,1)$ vortex exhibits a\ntwo-step decay process in which its initial splitting into a $(2,0)$ vortex and\na $(0,1)$ vortex is followed by the off-axis splitting of the $(2,0)$ vortex\ninto two $(1,0)$ vortices. Third, the $(2,-2)$ vortex is observed to split into\na $(-1,1)$ vortex, three $(1,0)$ vortices, and three $(0,-1)$ vortices. Each of\nthese splitting processes is the dominant decay mechanism of the respective\nstationary composite vortex for a wide range of intercomponent interaction\nstrengths and relative populations of the two condensate components and should\nbe amenable to experimental detection."
    },
    {
        "anchor": "Continuously observing a dynamically decoupled spin-1 quantum gas: We continuously observe dynamical decoupling in a spin-1 quantum gas using a\nweak optical measurement of spin precession. Continuous dynamical decoupling\naims to dramatically modify the character and energy spectrum of spin states to\nrender them insensitive to parasitic fluctuations. Continuous observation\nmeasures this new spectrum in a single-preparation of the quantum gas. The\nmeasured time-series contains seven tones, which spectrogram analysis parses as\nsplittings, coherences, and coupling strengths between the decoupled states in\nreal-time. With this we locate a regime where a transition between two states\nis decoupled from magnetic field instabilities up to fourth order,\ncomplementary to the parallel work at higher fields by Trypogeorgos et al.\n(arXiv:1706.07876). The decoupled microscale quantum gas offers magnetic\nsensitivity in a tunable band, persistent over many milliseconds: the length\nscales, frequencies, and durations relevant to many applications, including\nsensing biomagnetic phenomena such as neural spike trains.",
        "positive": "Dynamics of BEC mixtures loaded into the optical lattice in the presence\n  of linear inter-component coupling: We consider dynamics of a two-component Bose-Einstein condensate where the\ncomponents correspond to different hyperfine states of the same sort of atoms.\nExternal microwave radiation leads to resonant transitions between the states.\nThe condensate is loaded into the optical lattice. We invoke the tight-binding\napproximation and examine the interplay of spatial and internal dynamics of the\nmixture. It is shown that internal dynamics qualitatively depends on the\nintra-component interaction strength and the phase configuration of the initial\nstate. We focus attention on two intriguing phenomena occurring for certain\nparameter values. The first phenomenon is the spontaneous synchronization of\nRabi oscillations running inside neighbouring lattice sites. Another one is the\ndemixing of the condensate with formation of immiscible solitons when\nnonlinearity becomes sufficiently strong. Demixing is preceded by the transient\nregime with highly irregular behavior of the mixture."
    },
    {
        "anchor": "Dipolar condensed atomic mixtures and miscibility under rotation: By considering symmetric and asymmetric dipolar coupled mixtures (with\ndysprosium and erbium isotopes), we report a study on relevant anisotropic\neffects, related to spatial separation and miscibility, due to dipole-dipole\ninteractions (DDIs) in rotating binary dipolar Bose-Einstein condensates. The\nbinary mixtures are kept in strong pancake-like traps, with repulsive two-body\ninteractions modeled by an effective two-dimensional (2D) coupled\nGross-Pitaevskii equation. The DDI are tuned from repulsive to attractive by\nvarying the dipole polarization angle. A clear spatial separation is verified\nin the densities for attractive DDIs, being angular for symmetric mixtures and\nradial for asymmetric ones. Also relevant is the mass-imbalance sensibility\nobserved by the vortex-patterns in symmetric and asymmetric-dipolar mixtures.\nIn an extension of this study, here we show how the rotational properties and\nspatial separation of these dipolar mixture are affected by a quartic term\nadded to the harmonic trap of one of the components.",
        "positive": "Phase-separated symmetry-breaking vortex-lattice in a binary\n  Bose-Einstein condensate: We study spontaneous-symmetry-breaking circularly-asymmetric phase separation\nof vortex lattices in a rapidly rotating harmonically-trapped\nquasi-two-dimensional (quasi-2D) binary Bose-Einstein condensate (BEC) with\nrepulsive inter- and intra-species interactions. The phase separated vortex\nlattices of the components appear in different regions of space with no overlap\nbetween the vortices of the two components, which will permit an efficient\nexperimental observation of such vortices and accurate study of the effect of\natomic interaction on such vortex lattice. Such phase separation takes place\nwhen the intra-species interaction energies of the two components are equal or\nnearly equal with relatively strong inter-species repulsion. When the\nintra-species energies are equal, the two phase-separated vortex lattices have\nidentical semicircular shapes with one being the parity conjugate of the other.\nWhen the intra-species energies are nearly equal, the phase separation is also\ncomplete but the vortex lattices have different shapes. We demonstrate our\nclaim with a numerical solution of the mean-field Gross-Pitaevskii equation for\na rapidly rotating quasi-2D binary BEC."
    },
    {
        "anchor": "Thermometry and cooling of a Bose-Einstein condensate to 0.02 times the\n  critical temperature: Ultracold gases promise access to many-body quantum phenomena at convenient\nlength and time scales. However, it is unclear whether the entropy of these\ngases is low enough to realize many phenomena relevant to condensed matter\nphysics, such as quantum magnetism. Here we report reliable single-shot\ntemperature measurements of a degenerate $^{87}$Rb gas by imaging the momentum\ndistribution of thermalized magnons, which are spin excitations of the atomic\ngas. We record average temperatures as low as\n$0.022(1)_\\text{stat}(2)_\\text{sys}$ times the Bose-Einstein condensation\ntemperature, indicating an entropy per particle, $S/N\\approx0.001\\, k_B$ at\nequilibrium, that is well below the critical entropy for antiferromagnetic\nordering of a Bose-Hubbard system. The magnons themselves can reduce the\ntemperature of the system by absorbing energy during thermalization and by\nenhancing evaporative cooling, allowing low-entropy gases to be produced within\ndeep traps.",
        "positive": "Immiscibile two-component Bose Einstein condensates beyond mean-field\n  approximation: phase transitions and rotational response: We consider a two-component immiscible Bose-Einstein condensate with\ndominating intra-species repulsive density-density interactions. In the\nground-state phase of such a system only one condensates is present. This can\nbe viewed as a spontaneous breakdown of $\\mathbb{Z}_2$ symmetry. We study the\nphase diagram of the system at finite temperature beyond mean-field\napproximation. In the absence of rotation, we show that the system undergoes a\nfirst order phase transition from this ground state to a miscible two-component\nnormal fluid as temperature is increased. In the presence of rotation, the\nsystem features a competition between vortex-vortex interaction and short range\ndensity-density interactions. This leads to a rotation-driven \"mixing\" phase\ntransition in a spatially inhomogeneous state with additional broken\n$\\mathrm{U}(1)$ symmetry. Thermal fluctuations in this state lead to nematic\ntwo-component sheets of vortex liquids. At sufficiently strong inter-component\ninteraction, we find that the superfluid and $\\mathbb{Z}_2$ phase transitions\nsplit. This results in the formation of an intermediate state which breaks only\n$\\mathbb{Z}_2$ symmetry. It represents two phase separated normal fluids with\ndensity imbalance."
    },
    {
        "anchor": "Dark Continuum in the Spectral Function of the Resonant Fermi Polaron: We present controlled numerical results for the ground state spectral\nfunction of the resonant Fermi polaron in three dimensions. We establish the\nexistence of a \"dark continuum\"---a region of anomalously low spectral weight\nbetween the narrow polaron peak and the rest of the spectral continuum. The\ndark continuum develops when the s-wave scattering length is of the order of\nthe inverse Fermi wavevector, $a\\lesssim 1/k_{\\rm F}$, i.e. in the absence of a\nsmall interaction-related parameter when the spectral weight is not expected to\nfeature a near-perfect gap structure after the polaron peak.",
        "positive": "Spatial Phase Separation of a Binary Mixture in a Ring Trimer: We investigate the phase separation mechanism of bosonic binary mixtures in\nspatially-fragmented traps, evidencing the emergence of phases featuring a\ndifferent degree of mixing. The analysis is initially carried out by means of a\nsemiclassical approach which transparently shows the occurrence of critical\nphenomena. These predictions are actually corroborated by the study of\ngenuinely quantum indicators, including, but not limited to, the energy levels'\nstructure and the entanglement between the species. The scope of our work goes\nalso beyond the ground state's properties, as it comprises excited states and\nthe dynamical evolution thereof. In particular, after introducing an indicator\nto monitor the degree of mixing, we show that several dynamical regimes feature\npersistent demixing in spite of their remarkably chaotic character."
    },
    {
        "anchor": "Study of the inter-species interactions in an ultracold dipolar mixture: We experimentally and theoretically investigate the influence of the\ndipole-dipole interactions (DDIs) on the total inter-species interaction in an\nerbium-dysprosium mixture. By rotating the dipole orientation we are able to\ntune the effect of the long-range and anisotropic DDI, and therefore the\nin-trap clouds displacement. We present a theoretical description for our\nbinary system based on an extended Gross-Pitaevskii (eGP) theory, including the\nsingle-species beyond mean-field terms, and we predict a lower and an upper\nbound for the inter-species scattering length $a_{12}$. Our work is a first\nstep towards the investigation of the experimentally unexplored dipolar\nmiscibility-immiscibility phase diagram and the realization of quantum droplets\nand supersolid states with heteronuclear dipolar mixtures.",
        "positive": "Induced interactions and the superfluid transition temperature in a\n  three-component Fermi gas: We study many-body contributions to the effective interaction between\nfermions in a three-component Fermi mixture. We find that effective\ninteractions induced by the third component can lead to a phase diagram\ndifferent from that predicted if interactions with the third component are\nneglected. As a result, in a confining potential a superfluid shell structure\ncan arise even for equal populations of the components. We also find a critical\ntemperature for the BCS transition in a 6Li mixture which can deviate strongly\nfrom the one in a weakly interacting two-component system."
    },
    {
        "anchor": "Observation of Feshbach resonances between ultracold Na and Rb atoms: We have successfully prepared an optically trapped ultracold mixture of\n$^{23}$Na and $^{87}$Rb atoms and studied their interspecies Feshbach\nresonances. Using two different spin combinations, several s-wave and p-wave\nresonances are identified by observing a high inelastic loss and a temperature\nrising for both species near resonant magnetic field values. The two s-wave\nresonances observed below 500 G between atoms in the lowest energy level are\npossible candidates for Feshbach molecule association. Our results are well\ncharacterized by a coupled-channel model and are used refining the ground state\ninteraction potentials between $^{23}$Na and $^{87}$Rb. This work opens up the\nprospect for preparing ultracold ensembles of ground-state bosonic NaRb\nmolecules which are chemically stable and can provide strong dipolar\ninteractions.",
        "positive": "Photonic spectral density of coupled microwave cavities: We study a pair of anharmonic microwave cavities that is connected by an\noptical fiber. The photonic spectral density characterizes the evolution of the\ncoupled cavities after the system has been prepared in a Fock or N00N state. We\nevaluate the photonic spectral density within the recursive projection method\nand find that the anharmonicity has no substantial effect on the spectral\nproperties. In all cases the photonic spectral density has a Gaussian envelope\nfor large photon numbers."
    },
    {
        "anchor": "Numerical model of the Gross-Pitaevskii equation for rotating\n  Bose-Einstein condensates using smoothed-particle hydrodynamics: This study proposed a new numerical scheme for vortex lattice formation in a\nrotating Bose-Einstein condensate (BEC) using smoothed particle hydrodynamics\n(SPH) with an explicit real-time integration scheme. Specifically, the\nGross-Pitaevskii (GP) equation was described as a complex representation to\nobtain a pair of time-dependent equations, which were then solved\nsimultaneously following discretization based on SPH particle approximation. We\nadopt the 4th-order Runge-Kutta method for time evolution. We performed\nsimulations of a rotating Bose gas trapped in a harmonic potential, showing\nresults that qualitatively agreed with previously reported experiments and\nsimulations. The geometric patterns of formed lattices were successfully\nreproduced for several cases, for example, the hexagonal lattice observed in\nthe experiments of rotating BECs. Consequently, it was confirmed that the\nsimulation began with the periodic oscillation of the condensate, which\nattenuated and maintained a stable rotation with slanted elliptical shapes;\nhowever, the surface was excited to be unstable and generated ripples, which\ngrew into vortices and then penetrated the inside the condensate, forming a\nlattice. We confirmed that each branch point of the phase of wavefunctions\ncorresponds to each vortex. These results demonstrate our approach at a certain\ndegree of accuracy. In conclusion, we successfully developed a new SPH scheme\nfor the simulations of vortex lattice formation in rotating BECs.",
        "positive": "Bright soliton dynamics in Spin Orbit-Rabi coupled Bose-Einstein\n  condensates: We investigate the dynamics of a spin-orbit (SO) coupled BECs in a time\ndependent harmonic trap and show the dynamical system to be completely\nintegrable by constructing the Lax pair. We then employ gauge transformation\napproach to witness the rapid oscillations of the condensates for a relatively\nsmaller value of SO coupling in a time independent harmonic trap compared to\ntheir counterparts in a transient trap. Keeping track of the evolution of the\ncondensates in a transient trap during its transition from confining to\nexpulsive trap, we notice that they collapse in the expulsive trap. We further\nshow that one can manipulate the scattering length through Feshbach resonance\nto stretch the lifetime of the confining trap and revive the condensate.\nConsidering a SO coupled state as the initial state, the numerical simulation\nindicates that the reinforcement of Rabi coupling on SO coupled BECs generates\nthe striped phase of the bright solitons and does not impact the stability of\nthe condensates despite destroying the integrability of the dynamical system."
    },
    {
        "anchor": "Vortex lattices in binary Bose-Einstein condensates with dipole-dipole\n  interactions: We study the structure and stability of vortex lattices in two-component\nrotating Bose-Einstein condensates with intrinsic dipole-dipole interactions\n(DDIs) and contact interactions. To address experimentally accessible coupled\nsystems, we consider $^{164}$Dy-$^{162}$Dy and $^{168}$Er-$^{164}$Dy mixtures,\nwhich feature different miscibilities. The corresponding dipole moments are\n$\\mu_{\\mathrm{Dy}}=10\\mu_{\\mathrm{B}}$ and $\\mu_{\\mathrm{Er}}=\n7\\mu_{\\mathrm{B}}$, where $\\mu_{\\mathrm{B}}$ is the Bohr magneton. For\ncomparison, we also discuss a case where one of the species is non dipolar.\nUnder a large aspect ratio of the trap, we consider mixtures in the\npancake-shaped format, which are modeled by effective two-dimensional coupled\nGross-Pitaevskii equations, with a fixed polarization of the magnetic dipoles.\nThen, the miscibility and vortex-lattice structures are studied, by varying the\ncoefficients of the contact interactions (assuming the use of the\nFeshbach-resonance mechanism) and the rotation frequency. We present phase\ndiagrams for several types of lattices in the parameter plane of the rotation\nfrequency and ratio of inter- and intra-species scattering lengths. The vortex\nstructures are found to be diverse for the more miscible $^{164}$Dy-$^{162}$Dy\nmixture, with a variety of shapes, whereas, for the less miscible case of\n$^{168}$Er-$^{164}$Dy, the lattice patterns mainly feature circular or square\nformats.",
        "positive": "Second-Scale Nuclear Spin Coherence Time of Trapped Ultracold\n  $^{23}$Na$^{40}$K Molecules: Coherence, the stability of the relative phase between quantum states, lies\nat the heart of quantum mechanics. Applications such as precision measurement,\ninterferometry, and quantum computation are enabled by physical systems that\nhave quantum states with robust coherence. With the creation of molecular\nensembles at sub-$\\mu$K temperatures, diatomic molecules have become a novel\nsystem under full quantum control. Here, we report on the observation of stable\ncoherence between a pair of nuclear spin states of ultracold fermionic NaK\nmolecules in the singlet rovibrational ground state. Employing microwave\nfields, we perform Ramsey spectroscopy and observe coherence times on the scale\nof one second. This work opens the door for the exploration of single molecules\nas a versatile quantum memory. Switchable long-range interactions between\ndipolar molecules can further enable two-qubit gates, allowing quantum storage\nand processing in the same physical system. Within the observed coherence time,\n$10^4$ one- and two-qubit gate operations will be feasible."
    },
    {
        "anchor": "Renormalization group analysis on emergence of higher rank symmetry and\n  higher moment conservation: Higher rank symmetry and higher moment conservation have been drawn\nconsiderable attention from, e.g., subdiffusive transport to fracton\ntopological order. In this paper, we perform a one-loop renormalization group\n(RG) analysis and show how these phenomena emerge at low energies. We consider\na $d$-dimensional model of interacting bosons of d components. At\nhigher-rank-symmetric points with conserved angular moments, the $a$-th bosons\nhave kinetic energy only along the $x^a$ direction. Therefore, the symmetric\npoints look highly anisotropic and fine-tuned. By studying RG in a wide\nvicinity of the symmetric points, we find that symmetry-disallowed kinetic\nterms tend to be irrelevant within the perturbative regime, which potentially\nleads to emergent higher-rank symmetry and higher-moment conservation at the\ndeep infrared limit. While non-perturbative analysis is called for in the\nfuture, by regarding higher-rank symmetry as an emergent phenomenon, the RG\nanalysis presented in this paper holds alternative promise for realizing\nhigher-rank symmetry and higher-moment conservation in experimentally\nachievable systems.",
        "positive": "Dipolar Dynamics for Interacting Ultracold Fermions in a Trapped Optical\n  Lattice: Using the time-dependent density matrix renormalization group method, we\ncalculate transport properties of an interacting Fermi gas in an optical\nlattice with a confining trap after a sudden displacement of the trap center.\nIn the regime of attractive interactions, the dipolar motion after the\ndisplacement can be classified into underdamped oscillations and overdamped\nrelaxations, depending on the interaction strength. These numerical\ncalculations are consistent with experimental results. In the regime of\nrepulsive interactions, we predict a revival of the oscillations of the center\nof mass when the interaction strength is increased. This unique feature can be\nconsidered as a dynamical signature for the emergence of a Mott plateau for an\ninteracting trapped Fermi gas in an optical lattice."
    },
    {
        "anchor": "Collective Dipole Oscillation of a Spin-Orbit Coupled Bose-Einstein\n  Condensate: We present an experimental study of the collective dipole oscillation of a\nspin-orbit coupled Bose-Einstein condensate in a harmonic trap. Dynamics of the\ncenter-of-mass dipole oscillation is studied in a broad parameter region, as a\nfunction of spin-orbit coupling parameters as well as oscillation amplitude.\nAnharmonic properties beyond effective-mass approximation are revealed, such as\namplitude-dependent frequency and finite oscillation frequency at place with\ndivergent effective mass. These anharmonic behaviors agree quantitatively with\nvariational wave-function calculations. Moreover, we experimentally demonstrate\na unique feature of spin-orbit coupled system predicted by a sum-rule approach,\nstating that spin polarization susceptibility--a static physical quantity--can\nbe measured via dynamics of dipole oscillation. The divergence of polarization\nsusceptibility is observed at the quantum phase transition that separates\nmagnetic nonzero-momentum condensate from nonmagnetic zero-momentum phase. The\ngood agreement between the experimental and theoretical results provides a\nbench mark for recently developed theoretical approaches.",
        "positive": "Bose-Einstein Condensates in a Cavity-mediated Triple-well: We investigate the energy structures and the dynamics of a Bose-Einstein\ncondensates (BEC) in a triple-well potential coupled a high finesse optical\ncavity within a mean field approach. Due to the intrinsic atom-cavity field\nnonlinearity, several interesting phenomena arise which are the focuses of this\nwork. For the energy structure, the bistability appears in the energy levels\ndue to this atoms-cavity field nonlinearity, and the same phenomena can be\nfound in the intra-cavity photons number. With an increase of the pump-cavity\ndetunings, the higher and lower energy levels show a loop structure due to this\ncavity-mediated effects. In the dynamical process, an extensive numerical\nsimulation of localization of the BECs for atoms initially trapped in one-,\ntwo-, and three-wells are performed for the symmetric and asymmetric cases in\ndetail. It is shown that the the transition from oscillation to the\nlocalization can be modified by the cavity-mediated potential, which will\nenlarge the regions of oscillation. With the increasing of the atomic\ninteraction, the oscillation is blocked and the localization emerges. The\ncondensates atoms can be trapped either in one-, two-, or in three wells\neventually where they are initially uploaded for certain parameters. In\nparticular, we find that the transition from the oscillation to the\nlocalization is accompanied with some irregular regime where tunneling dynamics\nis dominated by chaos for this cavity-mediated system."
    },
    {
        "anchor": "Condensate fraction of cold gases in non-uniform external potential: Exact calculation of the condensate fraction in multi-dimensional\ninhomogeneous interacting Bose systems which do not possess continuous\nsymmetries is a difficult computational problem. We have developed an iterative\nprocedure which allows to calculate the condensate fraction as well as the\ncorresponding eigenfunction of the one-body density matrix. We successfully\nvalidate this procedure in diffusion Monte Carlo simulations of a Bose gas in\nan optical lattice at zero temperature. We also discuss relation between\ndifferent criteria used for testing coherence in cold Bose systems, such as\nfraction of particles that are superfluid, condensed or are in the\nzero-momentum state.",
        "positive": "Supersolidity in an elongated dipolar condensate: We present a theory for the emergence of a supersolid state in a cigar-shaped\ndipolar quantum Bose gas. Our approach is based on a reduced three-dimensional\n(3D) theory, where the condensate wavefunction is decomposed into an axial\nfield and a transverse part described variationally. This provides an accurate\nfully 3D description that is specific to the regime of current experiments and\nefficient to compute. We apply this theory to understand the phase diagram for\na gas in an infinite tube potential. We find that the supersolid transition has\ncontinuous and discontinuous regions as the averaged density varies. We develop\ntwo simplified analytic models to characterize the phase diagram and elucidate\nthe roles of quantum droplets and of the roton excitation."
    },
    {
        "anchor": "Phase vortices of the quenched Haldane Model: Using the recently developed Bloch-state tomography technique, the\nquasimomentum $\\bf k$-dependent Bloch states ${\\left( {\\sin \\left( {{\\theta\n_{\\mathbf{k}}}/2} \\right),\\; - \\cos \\left( {{\\theta _{\\mathbf{k}}}/2}\n\\right){e^{i{\\phi _{\\mathbf{k}}}}}} \\right)^T}$ of a two-band tight-binding\nmodel with two sublattices can be mapped out. We show that, if we prepare the\ninitial Bloch state as the lower-band eigenstate of a topologically trivial\nHaldane Hamiltonian $H_i$, and then quench the Haldane Hamiltonian to $H_f$,\nthe time-dependent azimuthal phase ${\\phi _{\\mathbf{k}}(t)}$ supports two types\nof vortices. The first type of vortices are static, with the corresponding\nBloch vectors pointing to the north pole ($\\theta_{\\mathbf{k}}=0$). The second\ntype of vortices are dynamical, with the corresponding Bloch vectors pointing\nto the south pole ($\\theta_{\\mathbf{k}}=\\pi$). In the $(k_x,k_y,t)$ space, the\nlinking number between the trajectories of these two types of vortices equals\nexactly to the Chern number of the lower band of $H_f$, which provides an\nalternative method to directly map out the topological phase boundaries of the\nHaldane model.",
        "positive": "The two-state Bose-Hubbard model in the hard-core boson limit:\n  Non-ergodicity and the Bose-Einstein condensation: The Bose-Einstein condensation in the hard-core boson limit (HCB) of the\nBose-Hubbard model with two local states and the particle hopping in the\nexcited band only is investigated. For the purpose of considering the\nnon-ergodicity, a single-particle spectral density is calculated in the random\nphase approximation by means of the temperature boson Green functions. The\nnon-ergodic contribution to the momentum distribution function of particles\n(connected with the static density fluctuations) increases significantly and\nbecomes comparable with the ergodic contribution in the superfluid phase near\nthe tricritical point."
    },
    {
        "anchor": "Doping a lattice-trapped bosonic species with impurities: From ground\n  state properties to correlated tunneling dynamics: We investigate the ground state properties and the nonequilibrium dynamics of\na lattice trapped bosonic mixture consisting of an impurity species and a\nfinite-sized medium. For the case of one as well as two impurities we observe\nthat, depending on the lattice depth and the interspecies interaction strength,\na transition from a strongly delocalized to a localized impurity distribution\noccurs. In the latter regime the two species phase separate, thereby forming a\nparticle-hole pair. For two impurities we find that below a critical lattice\ndepth they are delocalized among two neighboring outer lattice wells and are\ntwo-body correlated. This transition is characterized by a crossover from\nstrong to a suppressed interspecies entanglement for increasing impurity-medium\nrepulsion. Turning to the dynamical response of the mixture, upon quenching the\ninterspecies repulsion to smaller values, we reveal that the predominant\ntunneling process for a single impurity corresponds to that of a particle-hole\npair, whose dynamical stability depends strongly on the quench amplitude.\nDuring the time-evolution a significant increase of the interspecies\nentanglement is observed, caused by the build-up of a superposition of states\nand thus possesses a many-body nature. In the case of two bosonic impurities\nthe particle-hole pair process becomes unstable in the course of the dynamics\nwith the impurities aggregating in adjacent lattice sites while being strongly\ncorrelated.",
        "positive": "Detecting two-site spin-entanglement in many-body systems with local\n  particle-number fluctuations: We derive experimentally measurable lower bounds for the two-site\nentanglement of the spin-degrees of freedom of many-body systems with local\nparticle-number fluctuations. Our method aims at enabling the spatially\nresolved detection of spin-entanglement in Hubbard systems using\nhigh-resolution imaging in optical lattices. A possible application is the\nobservation of entanglement generation and spreading during spin impurity\ndynamics, for which we provide numerical simulations. More generally, the\nscheme can simplify the entanglement detection in ion chains, Rydberg atoms, or\nsimilar atomic systems."
    },
    {
        "anchor": "Nonlinear two-photon Rabi-Hubbard model: superradiance and\n  photon/photon-pair Bose-Einstein condensate: We study the ground state phase diagram of a nonlinear two-photon\nRabi-Hubbard (RH) model in one dimension using quantum Monte Carlo (QMC)\nsimulations and density matrix renormalization group (DMRG) calculations. Our\nmodel includes a nonlinear photon-photon interaction term. Absent this term,\nthe RH model has only one phase, the normal disordered phase, and suffers from\nspectral collapse at larger values of the photon-qubit interaction or\ninter-cavity photon hopping. The photon-photon interaction, no matter how\nsmall, stabilizes the system which now exhibits {\\it two} quantum phase\ntransitions: Normal phase to {\\it photon pair} superfluid (PSF) transition and\nPSF to single particle superfluid (SPSF). The discrete $Z_4$ symmetry of the\nHamiltonian spontaneously breaks in two stages: First it breaks partially as\nthe system enters the PSF and then completely breaks when the system finally\nenters the SPSF phase. We show detailed numerical results supporting this, and\nmap out the ground state phase diagram.",
        "positive": "Quantum enhanced SU(1,1) matter wave interferometry in a ring cavity: Quantum squeezed states offer metrological enhancement as compared to their\nclassical counterparts. Here, we devise and numerically explore a novel method\nfor performing SU(1,1) interferometry beyond the standard quantum limit, using\nquasi-cyclic nonlinear wave mixing dynamics of ultracold atoms in a ring\ncavity. The method is based on generating quantum correlations between many\natoms via photon mediated optomechanical interaction. Timescales of the\ninterferometer operation are here given by the inverse of photonic recoil\nfrequency, and are orders of magnitude shorter than the timescales of\ncollisional spin-mixing based interferometers. Such shorter timescales should\nenable not only faster measurement cycles, but also lower atomic losses from\nthe trap during measurement, which may lead to significant quantum metrological\ngain of matter wave interferometry in state of the art cavity setups."
    },
    {
        "anchor": "A Quantized Inter-level Character in Quantum Systems: For a quantum system subject to external parameters, the Berry phase is an\nintra-level property, which is gauge invariant module $2\\pi$ for a closed loop\nin the parameter space and generally is non-quantized. In contrast, we define a\ninter-band character $\\Theta$ for a closed loop, which is gauge invariant and\nquantized as integer values. It is a quantum mechanical analogy of the Euler\ncharacter based on the Gauss-Bonnet theorem for a manifold with a boundary. The\nrole of the Gaussian curvature is mimicked by the difference between the Berry\ncurvatures of the two levels, and the counterpart of the geodesic curvature is\nthe quantum geometric potential which was proposed to improve the quantum\nadiabatic condition. This quantized inter-band character is also generalized to\nquantum degenerate systems.",
        "positive": "Effects of quantum fluctuations on macroscopic quantum tunneling and\n  self-trapping of BEC in a double well trap: We study the influence of quantum fluctuations on the macroscopic quantum\ntunneling and self-trapping of a two-component Bose-Einstein condensate in a\ndouble-well trap. Quantum fluctuations are described by the Lee-Huang-Yang term\nin the modified Gross-Pitaevskii equation. Employing the modified\nGross-Pitaevskii equation in scalar approximation, we derive the dimer model\nusing a two-mode approximation. The frequencies of Josephson oscillations and\nself-trapping conditions under quantum fluctuations are found analytically and\nproven by numerical simulations of the modified Gross-Pitaevskii equation. The\ntunneling and localization phenomena are investigated also for the case of the\nLee-Huang-Yang fluid loaded in the double-well potential."
    },
    {
        "anchor": "Topologically Protected Vortex Knots in an Experimentally Realizable\n  System: Ordered media often support vortex structures with intriguing topological\nproperties. Here, we investigate non-Abelian vortices in tetrahedral order,\nwhich appear in the cyclic phase of spin-2 Bose--Einstein condensates and in\nthe tetrahedratic phase of bent-core nematic liquid crystals. Using these\nvortices, we construct topologically protected knots in the sense that they\ncannot decay into unlinked simple loop defects through vortex crossings and\nreconnections without destroying the phase. The discovered structures are the\nfirst examples of knots bearing such topological protection in a known\nexperimentally realizable system.",
        "positive": "Bosonic molecules in a lattice: unusual fluid phase from multichannel\n  interactions: We show that multichannel interactions significantly alter the phase diagram\nof ultracold bosonic molecules in an optical lattice. Most prominently, an\nunusual fluid region intervenes between the conventional superfluid and the\nMott insulator. In it, number fluctuations remain but phase coherence is\nsuppressed by a significant factor. This factor can be made arbitrarily large,\nat least in a two-site configuration. We calculate the phase diagram using\ncomplementary methods, including Gutzwiller mean-field and density matrix\nrenormalization group (DMRG) calculations. Although we focus on bosonic\nmolecules without dipolar interactions, we expect multichannel interactions to\nremain important for dipolar interacting and fermionic molecules."
    },
    {
        "anchor": "Formulation for zero mode of Bose-Einstein condensate beyond Bogoliubov\n  approximation: It is shown for the Bose-Einstein condensate of cold atomic system that the\nnew unperturbed Hamiltonian, which includes not only the first and second\npowers of the zero mode operators but also the higher ones, determines a unique\nand stationary vacuum at zero temperature. From the standpoint of quantum field\ntheory, it is done in a consistent manner that the canonical commutation\nrelation of the field operator is kept. In this formulation, the condensate\nphase does not diffuse and is robust against the quantum fluctuation of the\nzero mode. The standard deviation for the phase operator depends on the\ncondensed atom number with the exponent of $-1/3$, which is universal for both\nhomogeneous and inhomogeneous systems.",
        "positive": "Nonequilibrium Thermo Field Dynamics Using 4x4-Matrix Transformation for\n  System with Bose--Einstein Condensation: This study aims to construct a theoretical formulation of a nonequilibrium\nprocess for a system of Bose--Einstein condensate associated with a spontaneous\nsymmetry breakdown. For this, Thermo Field Dynamics is used. We then describe\nthe most general forms of a 4x4 transformation and an unperturbed Hamiltonian.\nAfter calculating the $4\\times 4$ self-energy and identifying its on-shell, we\nimpose the renormalization condition in which the entire on-shell self-energy\nshould vanish. This condition provides a sufficient number of independent\nequations to determine all of the parameters in an unperturbed Hamiltonian,\namong which the quantum transport equations for normal and anomalous number\ndistributions are included."
    },
    {
        "anchor": "Pair supersolid of the extended Bose-Hubbard model with atom-pair\n  hopping on the triangular Lattice: We systematically study an extended Bose-Hubbard model with atom hopping and\natom-pair hopping in the presence of a three-body constraint on the triangular\nlattice. By means of large-scale Quantum Monte Carlo simulations, the\nground-state phase diagram are studied. We find a continuous transition between\nthe atomic superfluid phase and the pair superfluid when the ratio of the\natomic hopping and the atom-pair hopping is adapted. We then focus on the\ninterplay among the atom-pair hopping, the on-site repulsion and the\nnearest-neighbor repulsion. With on-site repulsion present, we observe first\norder transitions between the Mott Insulators and pair superfluid driven by the\npair hopping. With the nearest-neighbor repulsion turning on, three typical\nsolid phases with 2/3, 1 and 4/3-filling emerge at small atom-pair hopping\nregion. A stable pair supersolid phase is found at small on-site repulsion.\nThis is due to the three-body constraint and the pair hopping, which\nessentially make the model a quasi hardcore boson system. Thus the pair\nsupersolid state emerges basing on the order-by-disorder mechanism, by which\nhardcore bosons avoid classical frustration on the triangular lattice. The\ntransition between the pair supersolid and the pair superfluid is first order,\nexcept for the particle-hole symmetric point. We compare the results with those\nobtained by means of mean-field analysis.",
        "positive": "An atomic boson sampler: A boson sampler implements a restricted model of quantum computing. It is\ndefined by the ability to sample from the distribution resulting from the\ninterference of identical bosons propagating according to programmable,\nnon-interacting dynamics. Here, we demonstrate a new combination of tools for\nimplementing boson sampling using ultracold atoms in a two-dimensional,\ntunnel-coupled optical lattice. These tools include fast and programmable\npreparation of large ensembles of nearly identical bosonic atoms\n($99.5^{+0.5}_{-1.6}\\;\\%$ indistinguishability) by means of rearrangement with\noptical tweezers and high-fidelity optical cooling, propagation for variable\nevolution time in the lattice with low loss ($5.0(2)\\;\\%$, independent of\nevolution time), and high fidelity detection of the atom positions after their\nevolution (typically $99.8(1)\\;\\%$). With this system, we study specific\ninstances of boson sampling involving up to $180$ atoms distributed among $\\sim\n1000$ sites in the lattice. Direct verification of a given boson sampling\ndistribution is not feasible in this regime. Instead, we introduce and perform\ntargeted tests to determine the indistinguishability of the prepared atoms, to\ncharacterize the applied family of single particle unitaries, and to observe\nexpected bunching features due to interference for a large range of atom\nnumbers. When extended to interacting systems, our work demonstrates the core\ncapabilities required to directly assemble ground and excited states in\nsimulations of various Hubbard models."
    },
    {
        "anchor": "Berry Curvature of interacting bosons in a honeycomb lattice: We consider soft-core bosons with onsite interaction loaded in the honeycomb\nlattice with different site energies for the two sublattices. Using both a\nmean-field approach and quantum Monte-Carlo simulations, we show that the\ntopology of the honeycomb lattice results in a non-vanishing Berry curvature\nfor the band structure of the single-particle excitations of the system. This\nBerry curvature induces an anomalous Hall effect. It is seen by studying the\ntime evolution of a wavepacket, namely a superfluid ground state in a harmonic\ntrap, subjected either to a constant force (Bloch oscillations) or to a sudden\nshift of the trap center.",
        "positive": "Cold Bose Atoms Around the Crossing of Quantum Waveguides: We show that massive low energy particles traversing a branching zone or a\ncrossing of quantum waveguides may experience a non standard trapping force\nthat cannot be derived from a potential. For interacting cold Bose atoms we\nreport on the formation of a localised Hartree ground state for three prototype\nwaveguide geometries with broken translational symmetry: a cranked L-shaped\nwaveguide L, a T-shaped waveguide T, and the crossing C of two quantum\nwaveguides. The phenomenon is kinetic energy driven and cannot be described\nwithin the Thomas-Fermi approximation. Depending on the ratio of joining\nlateral tube diameters of the respective waveguides C,L,T delocalisation\ncommences when the particle number N approaches a critical value. For the case\nof a binary mixture of two different Bose atom species A and B we observe non\nstandard trapping of both atom species for subcritical particle numbers. A\nsudden demixing quantum transition takes place as the total particle number\nN=N_{A}+N_{B} is increased at fixed mixing ratio N_{A}/N_{B}. Depending on the\nmass ratio m_{A}/m_{B} the heavier atom species delocalises first for a wide\nrange of interaction parameters. The numerical calculations are based on a\nsplitting scheme involving an analytic approximation to the short time\nasymptotics of the imaginary time quantum propagator of a single particle\nobeying to Dirichlet boundary conditions at the walls inside the respective\nwaveguides."
    },
    {
        "anchor": "Resonant Driving induced Ferromagnetism in the Fermi Hubbard Model: In this letter we consider quantum phases and the phase diagram of a Fermi\nHubbard model under periodic driving that has been realized in recent cold atom\nexperiments, in particular, when the driving frequency is resonant with the\ninteraction energy. Due to the resonant driving, the effective Hamiltonian\ncontains a correlated hopping term where the density occupation strongly\nmodifies the hopping strength. Focusing on half filling, in addition to the\ncharge and spin density wave phases, large regions of ferromagnetic phase and\nphase separation are discovered in the weakly interacting regime. The mechanism\nof this ferromagnetism is attributed to the correlated hopping because the\nhopping strength within a ferromagnetic domain is normalized to a larger value\nthan the hopping strength across the domain. Thus, the kinetic energy favors a\nlarge ferromagnetic domain and consequently drives the system into a\nferromagnetic phase. We note that this is a different mechanism in contrast to\nthe well-known Stoner mechanism for ferromagnetism where the ferromagnetism is\ndriven by interaction energy.",
        "positive": "Cluster Gutzwiller study of Bose-Hubbard ladder: ground-state phase\n  diagram and many-body Landau-Zener dynamics: We present a cluster Gutzwiller mean-field study for ground states and\ntime-evolution dynamics in the Bose-Hubbard ladder (BHL), which can be realized\nby loading Bose atoms in double-well optical lattices. In our cluster\nmean-field approach, we treat each double-well unit of two lattice sites as a\ncoherent whole for composing the cluster Gutzwiller ansatz, which may remain\nsome residual correlations in each two-site unit. For a unbiased BHL, in\naddition to conventional superfluid phase and integer Mott insulator phases, we\nfind that there are exotic fractional insulator phases if the inter-chain\ntunneling is much stronger than the intra-chain one. The fractional insulator\nphases can not be found by using a conventional mean-field treatment based upon\nthe single-site Gutzwiller ansatz. For a biased BHL, we find there appear\nsingle-atom tunneling and interaction blockade if the system is dominated by\nthe interplay between the on-site interaction and the inter-chain bias. In the\nmany-body Landau-Zener process, in which the inter-chain bias is linearly swept\nfrom negative to positive or vice versa, our numerical results are\nqualitatively consistent with the experimental observation [Nat. Phys.\n\\textbf{7}, 61 (2011)]. Our cluster bosonic Gutzwiller treatment is of\npromising perspectives in exploring exotic quantum phases and time-evolution\ndynamics of bosonic particles in superlattices."
    },
    {
        "anchor": "Thermalization kinetics of light: From laser dynamics to equilibrium\n  condensation of photons: We report a time-resolved study of the thermalization dynamics and the lasing\nto photon Bose-Einstein condensation crossover by in-\\textit{situ} monitoring\nthe photon kinetics in a dye microcavity. When the equilibration of the light\nto the dye temperature by absorption and re-emission is faster than photon loss\nin the cavity, the optical spectrum becomes Bose-Einstein distributed and\nphotons accumulate at low-energy states, forming a Bose-Einstein condensate.\nThe thermalization of the photon gas and its evolution from nonequilibrium\ninitial distributions to condensation is monitored in real-time. In contrast,\nif photons leave the cavity before they thermalize, the system operates as a\nlaser.",
        "positive": "A two-dimensional quantum gas in a magnetic trap: We present the first experimental realization of a two-dimensional quantum\ngas in a purely magnetic trap dressed by a radio frequency field in the\npresence of gravity. The resulting potential is extremely smooth and very close\nto harmonic in the two-dimensional plane of confinement. We fully characterize\nthe trap and demonstrate the confinement of a quantum gas to two dimensions.\nThe trap geometry can be modified to a large extent, in particular in a\ndynamical way. Taking advantage of this possibility, we study the monopole and\nthe quadrupole modes of a two-dimensional Bose gas."
    },
    {
        "anchor": "Coherent Manipulation of the Internal State of Ultracold\n  $^{87}$Rb$^{133}$Cs Molecules with Multiple Microwave Fields: We explore coherent multi-photon processes in $^{87}$Rb$^{133}$Cs molecules\nusing 3-level lambda and ladder configurations of rotational and hyperfine\nstates, and discuss their relevance to future applications in quantum\ncomputation and quantum simulation. In the lambda configuration, we demonstrate\nthe driving of population between two hyperfine levels of the rotational ground\nstate via a two-photon Raman transition. Such pairs of states may be used in\nthe future as a quantum memory, and we measure a Ramsey coherence time for a\nsuperposition of these states of 58(9) ms. In the ladder configuration, we show\nthat we can generate and coherently populate microwave dressed states via the\nobservation of an Autler-Townes doublet. We demonstrate that we can control the\nstrength of this dressing by varying the intensity of the microwave coupling\nfield. Finally, we perform spectroscopy of the rotational states of\n$^{87}$Rb$^{133}$Cs up to $N=6$, highlighting the potential of ultracold\nmolecules for quantum simulation in synthetic dimensions. By fitting the\nmeasured transition frequencies we determine a new value of the centrifugal\ndistortion coefficient $D_v=h\\times207.3(2)~$Hz.",
        "positive": "In situ measurement of the dynamic structure factor in ultracold quantum\n  gases: We propose an experimental setup to efficiently measure the dynamic structure\nfactor of ultracold quantum gases. Our method uses the interaction of the\ntrapped atomic system with two different cavity modes, which are driven by\nexternal laser fields. By measuring the output fields of the cavity the dynamic\nstructure factor of the atomic system can be determined. Contrary to previous\napproaches the atomic system is not destroyed during the measurement process."
    },
    {
        "anchor": "Supersolid states in a hard-core Bose-Hubbard model on a layered\n  triangular lattice: We study ground-state properties in a hard-core Bose-Hubbard model on a\nlayered triangular lattice. Combining cluster mean-field theory with the\ndensity matrix renormalization group method, we discuss the effect of the\ninterlayer coupling on the supersolid states realized in a single layered\nmodel. By examining the distributions for the particle density and superfluid\norder parameter, the rich phase diagram of the system is obtained. We find that\nthe supersolid states are widely stabilized at a commensurate filling, in\ncontrast to the case of the single layered model. The nature of the supersolid\nstates is also addressed.",
        "positive": "Vortex Tiling in a Spin-2 Spinor Bose-Einstein Condensate: We point out that the internal spin symmetry of the order parameter manifests\nitself at the core of a fractional vortex in real space without spin-orbit\ncoupling. Such symmetry breaking arises from a topological constraint and the\ncommensurability between spin symmetries of the order parameters inside and\noutside the core. Our prediction can be applied to probe the cyclic order\nparameter in a rotating spin-2 $^{87}$Rb condensate as a non-circular vortex\ncore in a biaxial nematic state."
    },
    {
        "anchor": "Critical behaviour in one dimension: unconventional pairing, phase\n  separation, BEC-BCS crossover and magnetic Lifshitz transition: We study the superconducting properties of population-imbalanced ultracold\nFermi mixtures in one-dimensional (1D) optical lattices that can be effectively\ndescribed by the spin-imbalanced attractive Hubbard model (AHM) in the presence\nof a Zeeman magnetic field. We use the mean-field theory approach to obtain the\nground state phase diagrams including some unconventional superconducting\nphases such as the Fulde--Ferrell--Larkin--Ovchinnikov (FFLO) phase, and the\n$\\eta$ phase (an extremal case of the FFLO phase), both for the case of a fixed\nchemical potential and for a fixed number of particles. It allows to determine\noptimal regimes for the FFLO phase as well as $\\eta$-pairing stability. We also\ninvestigate the evolution from the weak coupling (BCS-like limit) to the strong\ncoupling limit of tightly bound local pairs (BEC) with increasing attraction,\nat $T=0$. Finally, the obtained results show that despite of the occurrence of\nthe Lifshitz transition induced by an external magnetic field, the\nsuperconducting state can still exist in the system, at higher magnetic field\nvalues.",
        "positive": "Floquet eigenspectra of a nonlinear two-mode system under periodic\n  driving: the emergence of \"ring\" structures: We study Floquet eigenspectra of a nonlinear two-mode system under a periodic\ndriving of the off-diagonal coupling. By solving the Gross-Pitaevskii equation\nnumerically, we obtain triangular and loop structures near the crossings of\ndifferent Floquet branches. At lower driving frequencies, we find \"ring\" and\n\"double-ring\" structures which are distinct from the well-known loop structure.\nThe mechanism of the emergence of these structures is discussed and the\nparameter windows of their existence are obtained analytically. In addition, we\nstudy the evolution of the system under the driving with an adiabatic sweep and\nfind there are some dynamically unstable states in the Floquet eigenspectra\nwhich break the quantum adiabaticity."
    },
    {
        "anchor": "Measuring work and heat in ultracold quantum gases: We propose a feasible experimental scheme to direct measure heat and work in\ncold atomic setups. The method is based on a recent proposal which shows that\nwork is a positive operator valued measure (POVM). In the present contribution,\nwe demonstrate that the interaction between the atoms and the light\npolarisation of a probe laser allows us to implement such POVM. In this way the\nwork done on or extracted from the atoms after a given process is encoded in\nthe light quadrature that can be measured with a standard homodyne detection.\nThe protocol allows one to verify fluctuation theorems and study properties of\nthe non-unitary dynamics of a given thermodynamic process.",
        "positive": "Ground state properties of a one-dimensional strongly-interacting\n  Bose-Fermi mixture in a double-well potential: We calculate the reduced single-particle density matrix (RSPDM), momentum\ndistributions, natural orbitals and their occupancies, for a strongly\ninteracting one-dimensional Bose-Fermi mixture in a double-well potential with\na large central barrier. For mesoscopic systems, we find that the ground state\nproperties qualitatively differ for mixtures with even number of particles\n(both odd-odd and even-even mixtures) in comparison to mixtures with odd\nparticle numbers (odd-even and even-odd mixtures). For even mixtures the\nmomentum distribution is smooth, whereas the momentum distribution of odd\nmixtures possesses distinct modulations; the differences are observed also in\nthe off-diagonal correlations of the RSPDM, and in the occupancies of natural\norbitals. The calculation is based on a derived formula which enables efficient\ncalculation of the RSPDM for mesoscopic mixtures in various potentials."
    },
    {
        "anchor": "Comment on \"Creating artificial magnetic fields for cold atoms by\n  photon-assisted tunneling\" by Kolovsky A.R: We comment briefly on the scheme proposed in EPL 93, 20003 (2011) to produce\nsynthetic gauge fields by means of photon-assisted tunneling.",
        "positive": "Ultracold Atomic Gases in Artificial Magnetic Fields (PhD thesis): A phenomenon can hardly be found that accompanied physical paradigms and\ntheoretical concepts in a more reflecting way than magnetism. From the\nbeginnings of metaphysics and the first classical approaches to magnetic poles\nand streamlines of the field, it has inspired modern physics on its way to the\nclassical field description of electrodynamics, and further to the quantum\nmechanical description of internal degrees of freedom of elementary particles.\nMeanwhile, magnetic manifestations have posed and still do pose complex and\noften controversially debated questions. This regards so various and utterly\ndistinct topics as quantum spin systems and the grand unification theory. This\nmay be foremost caused by the fact that all of these effects are based on\ncorrelated structures, which are induced by the interplay of dynamics and\nelementary interactions. It is strongly correlated systems that certainly\nrepresent one of the most fascinating and universal fields of research. In\nparticular, low dimensional systems are in the focus of interest, as they\nreveal strongly pronounced correlations of counterintuitive nature. As regards\nthis framework, the quantum Hall effect must be seen as one of the most\nintriguing and complex problems of modern solid state physics. Even after two\ndecades and the same number of Nobel prizes, it still keeps researchers of\nnearly all fields of physics occupied. In spite of seminal progress, its\ninherent correlated order still lacks understanding on a microscopic level.\nDespite this, it is obvious that the phenomenon is thoroughly fundamental of\nnature. To resolve some puzzles of this nature is a key topic of this thesis.\n(excerpt from abstract)"
    },
    {
        "anchor": "Medium-induced bosonic clusters in a Bose-Fermi mixture: Towards\n  simulating cluster formations in neutron-rich matter: Considering bosonic atoms immersed in a dilute Fermi gas, we theoretically\ninvestigate medium-induced bosonic clusters associated with fermion-mediated\ntwo- and three-body interactions. Using the variational approach combined with\nthe fermion-mediated interactions, we numerically calculate the binding\nenergies of two- and three-body bosonic clusters in a one-dimensional system.\nIt is found that the bosonic clusters can be formed even with a repulsive\nboson-boson interaction due to the fermion-mediated interactions. Our results\nwould be relevant for ultracold atomic systems as well as analogue quantum\nsimulations of alpha clusters in neutron-rich matter.",
        "positive": "First-principles quantum dynamics for fermions: Application to molecular\n  dissociation: We demonstrate that the quantum dynamics of a many-body Fermi-Bose system can\nbe simulated using a Gaussian phase-space representation method. In particular,\nwe consider the application of the mixed fermion-boson model to ultracold\nquantum gases and simulate the dynamics of dissociation of a Bose-Einstein\ncondensate of bosonic dimers into pairs of fermionic atoms. We quantify\ndeviations of atom-atom pair correlations from Wick's factorization scheme, and\nshow that atom-molecule and molecule-molecule correlations grow with time, in\nclear departures from pairing mean-field theories. As a first-principles\napproach, the method provides benchmarking of approximate approaches and can be\nused to validate dynamical probes for characterizing strongly correlated phases\nof fermionic systems."
    },
    {
        "anchor": "Observation of a pairing pseudogap in a two-dimensional Fermi gas: Pairing of fermions is ubiquitous in nature and it is responsible for a large\nvariety of fascinating phenomena like superconductivity, superfluidity of\n$^3$He, the anomalous rotation of neutron stars, and the BEC-BCS crossover in\nstrongly interacting Fermi gases. When confined to two dimensions, interacting\nmany-body systems bear even more subtle effects, many of which lack\nunderstanding at a fundamental level. Most striking is the, yet unexplained,\neffect of high-temperature superconductivity in cuprates, which is intimately\nrelated to the two-dimensional geometry of the crystal structure. In\nparticular, the questions how many-body pairing is established at high\ntemperature and whether it precedes superconductivity are crucial to be\nanswered. Here, we report on the observation of pairing in a harmonically\ntrapped two-dimensional atomic Fermi gas in the regime of strong coupling. We\nperform momentum-resolved photoemission spectroscopy, analogous to ARPES in the\nsolid state, to measure the spectral function of the gas and we detect a\nmany-body pairing gap above the superfluid transition temperature. Our\nobservations mark a significant step in the emulation of layered\ntwo-dimensional strongly correlated superconductors using ultracold atomic\ngases.",
        "positive": "Quasi-one- and quasi-two-dimensional perfect Bose gas: the second\n  critical density and generalised condensation: In this letter we discuss a relevance of the 3D Perfect Bose gas (PBG)\ncondensation in extremely elongated vessels for the study of anisotropic\ncondensate coherence and the \"quasi-condensate\". To this end we analyze the\ncase of exponentially anisotropic (van den Berg) boxes, when there are two\ncritical densities $\\rho_c < \\rho_m$ for a generalised Bose-Einstein\nCondensation (BEC). Here $\\rho_c$ is the standard critical density for the PBG.\nWe consider three examples of anisotropic geometry: slabs, squared beams and\n\"cigars\" to demonstrate that the \"quasi-condensate\" which exists in domain\n$\\rho_c < \\rho < \\rho_m$ is in fact the van den Berg-Lewis-Pul\\'e generalised\ncondensation (vdBLP-GC) of the type III with no macroscopic occupation of any\nmode. We show that for the slab geometry the second critical density $\\rho_m$\nis a threshold between quasi- two-dimensional (quasi-2D) condensate and the\nthree dimensional (3D) regime when there is a coexistence of the\n\"quasi-condensate\" with the standard one-mode BEC. On the other hand, in the\ncase of squared beams and \"cigars\" geometries critical density $\\rho_m$\nseparates quasi-1D and 3D regimes. We calculate the value of difference between\n$\\rho_c, \\rho_m$ (and between corresponding critical temperatures $T_m, T_c$)\nto show that observed space anisotropy of the condensate coherence can be\ndescribed by a critical exponent $\\gamma(T)$ related to the anisotropic ODLRO.\nWe compare our calculations with physical results for extremely elongated traps\nthat manifest \"quasi-condensate\"."
    },
    {
        "anchor": "Beliaev damping of the Goldstone mode in atomic Fermi superfluids: Beliaev damping in a superfluid is the decay of a collective excitation into\ntwo lower frequency collective excitations; it represents the only decay mode\nfor a bosonic collective excitation in a superfluid at T = 0. The standard\ntreatment for this decay assumes a linear spectrum, which in turn implies that\nthe final state momenta must be collinear to the initial state. We extend this\ntreatment, showing that the inclusion of a gradient term in the Hamiltonian\nyields a realistic spectrum for the bosonic excitations; we then derive a\nformula for the decay rate of such excitations, and show that even moderate\nnonlinearities in the spectrum can yield substantial deviations from the\nstandard result. We apply our result to an attractive Fermi gas in the BCS-BEC\ncrossover: here the low-energy bosonic collective excitations are density\noscillations driven by the phase of the pairing order field. These collective\nexcitations, which are gapless modes as a consequence of the Goldstone\nmechanism, have a spectrum which is well established both theoretically and\nexperimentally, and whose linewidth, we show, is determined at low temperatures\nby the Beliaev decay mechanism.",
        "positive": "Fluctuation-induced and symmetry-prohibited metastabilities in spinor\n  Bose-Einstein condensates: Spinor Bose-Einstein condensates provide a unique example in which the\nBogoliubov theory fails to describe the metastability associated with\nfirst-order quantum phase transitions. This problem is resolved by developing\nthe spinor Beliaev theory which takes account of quantum fluctuations of the\ncondensate. It is these fluctuations that generate terms of higher than the\nfourth order in the order-parameter field which are needed for the first-order\nphase transitions. Besides the conventional first-order phase transitions which\nare accompanied by metastable states, we find a class of first-order phase\ntransitions which are not accompanied by metastable states. The absence of\nmetastability in these phase transitions holds to all orders of approximation\nsince the metastability is prohibited by the symmetry of the Hamiltonian at the\nphase boundary. Finally, the possibility of macroscopic quantum tunneling from\na metastable state to the ground state is discussed."
    },
    {
        "anchor": "Anderson-Bogoliubov collective excitations in superfluid Fermi gases at\n  nonzero temperatures: The Anderson-Bogoliubov branch of collective excitations in a condensed Fermi\ngas is treated using the effective bosonic action of Gaussian pair\nfluctuations. The spectra of collective excitations are treated for finite\ntemperature and momentum throughout the BCS-BEC crossover. The obtained spectra\nexplain, both qualitatively and quantitatively, recent experimental results on\nGoldstone modes in atomic Fermi superfluids.",
        "positive": "Stability Condition of a Strongly Interacting Boson-Fermion Mixture\n  across an Inter-Species Feshbach Resonance: We study the properties of dilute bosons immersed in a single component Fermi\nsea across a broad boson-fermion Feshbach resonance. The stability of the\nmixture requires that the bare interaction between bosons exceeds a critical\nvalue, which is a universal function of the boson-fermion scattering length,\nand exhibits a maximum in the unitary region. We calculate the quantum\ndepletion, momentum distribution and the boson contact parameter across the\nresonance. The transition from condensate to molecular Fermi gas is also\ndiscussed."
    },
    {
        "anchor": "Gr\u00fcneisen Parameter for Gases: The Gr\\\"uneisen ratio ($\\Gamma$), i.e.\\,the ratio of the linear thermal\nexpansivity to the specific heat at constant pressure, quantifies the degree of\nanharmonicity of the potential governing the physical properties of a system.\nWhile $\\Gamma$ has been intensively explored in solid state physics, very\nlittle is known about its behavior for gases. This is most likely due to the\ndifficulties posed to carry out both thermal expansion and specific heat\nmeasurements in gases with high accuracy as a function of pressure and\ntemperature. Furthermore, to the best of our knowledge a comprehensive\ndiscussion about the peculiarities of the Gr\\\"uneisen ratio is still lacking in\nthe literature. Here we report on a detailed and comprehensive overview of the\nGr\\\"uneisen ratio. Particular emphasis is placed on the analysis of $\\Gamma$\nfor gases. The main findings of this work are: \\emph{i)} for the Van der Waals\ngas $\\Gamma$ depends only on the co-volume $b$ due to interaction effects, it\nis smaller than that for the ideal gas ($\\Gamma$ = 2/3) and diverges upon\napproaching the critical volume; \\emph{ii)} for the Bose-Einstein condensation\nof an ideal boson gas, assuming the transition as first-order $\\Gamma$ diverges\nupon approaching a critical volume, similarly to the Van der Waals gas;\n\\emph{iii)} for $^4$He at the superfluid transition $\\Gamma$ shows a singular\nbehavior. Our results reveal that $\\Gamma$ can be used as an appropriate\nexperimental tool to explore pressure-induced critical points.",
        "positive": "The second quantization method for indistinguishable particles (Lecture\n  Notes in Physics, UFABC 2010): Contents\n  1. Creation and annihilation operators for the system of indistinguishable\nparticles 1.1 The permutation group and the states of a system of\nindistinguishable particles 1.2 Dimension of the Hilbert space of a system of\nindistinguishable particles 1.3 Definition and properties of the creation and\nannihilation operators 1.4 TheFockspace 1.5 The representations of state\nvectors and operators 1.5.1 N-particlewave-functions 1.5.2 The\nsecond-quantization representation of operators 1.5.3 Examples 1.6 Evolution of\noperators in the Heisenberg picture 1.7 Statistical operators of\nindistinguishable particles 1.7.1 The averages of the s-particle operators\n1.7.2 The general structure of the one-particle statistical operator 2\nQuadratic Hamiltonian and the diagonalization 2.1 Diagionalization of the\nHamiltonian quadratic in the fermion operators 2.2 Diagionalization of the\nHamiltonian quadratic in the boson operators 2.2.1 Diagonalization of the\nquadratic bosonic Hamiltonian possessing a zero mode 2.3 Long range order,\ncondensation and the Bogoliubov spectrum of weakly interacting Bose gas 2.3.1\nThe excitation spectrum of weakly interacting Bose gas inabox 2.3.2 The\nexcitation spectrum of an interacting Bose gas in an externalpotential 2.4 The\nJordan-Wigner transformation: fermionization of interacting 1D spin chains"
    },
    {
        "anchor": "Observation of the antiferromagnetic phase transition in the fermionic\n  Hubbard model: The fermionic Hubbard model (FHM)[1], despite its simple form, captures\nessential features of strongly correlated electron physics. Ultracold fermions\nin optical lattices[2, 3] provide a clean and well-controlled platform for\nsimulating FHM. Doping its antiferromagnetic ground state at half filling,\nvarious exotic phases are expected to arise in the FHM simulator, including\nstripe order[4], pseudogap[5], and d-wave superconductors[6], offering valuable\ninsights into high-temperature superconductivity[7{9]. Although notable\nprogress, such as the observation of antiferromagnetic correlations over\nshort[10] and extended distances[11], has been obtained, the antiferromagnetic\nphase has yet to be realized due to the significant challenges of achieving low\ntemperatures in a large and uniform quantum simulator. Here, we report the\nobservation of the antiferromagnetic phase transition in a three-dimensional\nfermionic Hubbard system comprising lithium-6 atoms in a uniform optical\nlattice with approximately 800,000 sites. When the interaction strength,\ntemperature, and doping concentration are finely tuned to approach their\nrespective critical values, sharp increases in the spin structure factor (SSF)\nare observed. These observations can be well described by a power-law\ndivergence, with a critical exponent of 1.396 from the Heisenberg universality\nclass[12]. At half filling and with optimal interaction strength, the measured\nSSF reaches 123(8), signifying the establishment of an antiferromagnetic phase.\nOur results set the stage for exploring the low-temperature phase diagram of\nFHM.",
        "positive": "Stability and excitations of a bilayer of strongly correlated dipolar\n  Bosons: We study correlation effects and excitations in a dipolar Bose gas bilayer\nwhich is modeled by a one-dimensional double well trap that determines the\nwidth of an individual layer, the distance between the two layers, and the\nheight of the barrier between them. For the ground state calculations we use\nthe hypernetted--chain Euler Lagrange method and for the calculation of the\nexcitations we use the correlated basis function method. We observe\ninstabilities both for wide, well-separated layers dominated by\n\\emph{intra-layer} attraction of the dipoles, and for narrow layers that are\nclose to each other dominated by \\emph{inter-layer} attraction. The behavior of\nthe pair distribution function leads to the interpretation that the monomer\nphase becomes unstable when pairing of two dipoles becomes energetically\nfavorable between or within layers, respectively. In both cases we observe a\ntendency towards \"rotonization\", i.e. the appearance of a soft mode with finite\nmomentum in the excitation spectrum. The dynamic structure function is not\nsimply characterized by a single excitation mode, but has a non-trivial\nmulti-peak structure that is not captured by the Bijl-Feynman approximation.\nThe dipole-dipole interaction between different layers leads to additional\ndamping compared to the damping obtained for uncoupled layers."
    },
    {
        "anchor": "Quantum state engineering of a Hubbard system with ultracold fermions: Accessing new regimes in quantum simulation requires the development of new\ntechniques for quantum state preparation. We demonstrate the quantum state\nengineering of a strongly correlated many-body state of the two-component\nrepulsive Fermi-Hubbard model on a square lattice. Our scheme makes use of an\nultralow entropy doublon band insulator created through entropy redistribution.\nAfter isolating the band insulator, we change the underlying potential to\nexpand it into a half-filled system. The final many-body state realized shows\nstrong antiferromagnetic correlations and a temperature below the exchange\nenergy. We observe an increase in entropy, which we find is likely caused by\nthe many-body physics in the last step of the scheme. This technique is\npromising for low-temperature studies of cold-atom-based lattice models.",
        "positive": "Protected quasi-locality in quantum systems with long-range interactions: We study the out-of-equilibrium dynamics of quantum systems with long-range\ninteractions. Two different models describing, respectively, interacting\nlattice bosons and spins are considered. Our study relies on a combined\napproach based on accurate many-body numerical calculations as well as on a\nquasiparticle microscopic theory. For sufficiently fast decaying long-range\npotentials, we find that the quantum speed limit set by the long-range\nLieb-Robinson bounds is never attained and a purely ballistic behavior is\nfound. For slowly decaying potentials, a radically different scenario is\nobserved. In the bosonic case, a remarkable local spreading of correlations is\nstill observed, despite the existence of infinitely fast traveling excitations\nin the system. This is in marked contrast to the spin case, where locality is\nbroken. We finally provide a microscopic justification of the different regimes\nobserved and of the origin of the protected locality in the bosonic model."
    },
    {
        "anchor": "Rebuilding of destroyed spin squeezing in noisy environments: We investigate the process of spin squeezing in a ferromagnetic dipolar\nspin-1 Bose-Einstein condensate under the driven oneaxis twisting scheme, with\nemphasis on the detrimental effect of noisy environments (stray magnetic\nfields) which completely destroy the spin squeezing. By applying concatenated\ndynamical decoupling pulse sequences with a moderate bias magnetic field to\nsuppress the effect of the noisy environments, we faithfully reconstruct the\nspin squeezing process under realistic experimental conditions. Our\nnoise-resistant method is ready to be employed to generate the spin squeezed\nstate in a dipolar spin-1 Bose-Einstein condensate and paves a feasible way to\nthe Heisenberg-limit quantum metrology",
        "positive": "Hydrodynamic Description of Spin-1 Bose-Einstein Condensates: We establish a complete set of hydrodynamic equations for a spin-1\nBose-Einstein condensate (BEC), which are equivalent to the multi-component\nGross-Pitaevskii equations and expressed in terms of only observable physical\nquantities: the spin density and the nematic (or quadrupolar) tensor in\naddition to the density and the mass current that appear in the hydrodynamic\ndescription of a scalar BEC. The obtained hydrodynamic equations involve a\ngeneralized Mermin-Ho relation that is valid regardless of the spatiotemporal\ndependence of the spin polarization. Low-lying collec- tive modes for phonons\nand magnons are reproduced by linearizing the hydrodynamic equations. We also\napply the single-mode approximation to the hydrodynamic equations and find a\ncomplete set of analytic solutions."
    },
    {
        "anchor": "Hidden vortices in a Bose-Einstein condensate in a rotating double-well\n  potential: We study vortex formation in a Bose-Einstein condensate in a rotating\ndouble-well potential. Besides the ordinary quantized vortices and elusive\nghost vortices, \"hidden\" vortices are found distributing along the central\nbarrier. These hidden vortices are invisible like ghost vortex but carry\nangular momentum. Moreover, their core size is not given by the healing length,\nbut is strongly influenced by the external potential. We find that the\nFeynman's rule can be well satisfied only after including the hidden vortices.\nThere is no critical rotating frequency for the formation of hidden vortex\nwhile there is one for the formation of ordinary visible vortices. Hidden\nvortices can be revealed in the free expansion of the Bose-Einstein\ncondensates. In addition, the hidden vortices in a Bose-Einstein condensate can\nappear in other external potentials, such as a rotating anisotropic toroidal\ntrap.",
        "positive": "Nucleation of Spontaneous Vortices in Trapped Fermi Gases Undergoing a\n  BCS-BEC Crossover: We study the spontaneous formation of vortices during the superfluid\ncondensation in a trapped fermionic gas subjected to a rapid thermal quench via\nevaporative cooling. Our work is based on the numerical solution of the time\ndependent crossover Ginzburg-Landau equation coupled to the heat diffusion\nequation. We quantify the evolution of condensate density and vortex length as\na function of a crossover phase parameter from BCS to BEC. The more interesting\nphenomena occur somewhat nearer to the BEC regime and should be experimentally\nobservable; during the propagation of the cold front, the increase in\ncondensate density leads to the formation of supercurrents towards the center\nof the condensate as well as possible condensate volume oscillations."
    },
    {
        "anchor": "Twin-atom beams: We present highly efficient emission of twin-atom beams into a single\ntransversal mode of a waveguide potential. The source is a one-dimensional\ndegenerate Bose gas in the first radially excited state. We directly measure a\nsuppression of fluctuations in the atom number difference between the beams to\n0.37(3) with respect to the classical expectation, equivalent to 0.11(2) after\ncorrecting for detection noise. Our results underline the high potential of\nultracold atomic gases as sources for quantum matter wave optics and will\nenable the implementation of schemes previously unattainable with massive\nparticles",
        "positive": "Theoretical approaches to liquid Helium: In this article, we review the main theoretical methods applied to the study\nof liquid Helium adopting a microscopic approach, that is, starting from the\nmany-particle Hamiltonian of the system. Following an introduction on the first\nearly approaches, we discuss two main issues. In the first one, we report the\nmain ingredients of a theoretical approach based on the variational method,\nwith the discussion of the high accuracy obtained with them and the related\nprogress in the design of highly accurate trial wave functions. In the second\npart, the main stochastic methods used in this study are briefly discussed.\nAltogether reflects the strong links between the study of liquid Helium and the\nprogress in the development of new and extremely powerful approaches to deal\nwith one of the most strongly quantum many-body systems in Nature."
    },
    {
        "anchor": "Repulsive dynamics of strongly attractive one-dimensional quantum gases: We analyze the dynamics of one-dimensional quantum gases with strongly\nattractive contact interactions. We specify a class of initial states for which\nattractive forces effectively act as strongly repulsive ones during the time\nevolution. Our findings extend the theoretical results on the\nsuper-Tonks-Girardeau gas to a highly nonequilibrium dynamics. The novel\nmechanism is illustrated on the prototypical problem of the domain stability in\na two-component Fermi gas. We also discuss nonlocal interactions and analyze\nuniversality of the presented results. Moreover, we use our conclusions to\nargue for the existence of metastable quantum droplets in the regime of\nstrongly attractive contact and attractive dipolar interactions.",
        "positive": "Viscous dissipation in a gas of one-dimensional fermions with generic\n  dispersion: A well-known feature of the classical monoatomic gas is that its bulk\nviscosity is strongly suppressed because the single-particle dispersion is\nquadratic. On the other hand, in condensed matter systems the effective\nsingle-particle dispersion is altered by lattice effects and interactions. In\nthis work, we study the bulk viscosity of one-dimensional Fermi gases with\ngeneric energy-momentum dispersion relations. As an application, viscous\ndissipation arising from lattice effects is analyzed for the tight-binding\nmodel. In addition, we investigate how weak interactions affect the bulk\nviscosity. Finally, we discuss viscous dissipation in the regime in which the\nFermi gas is not fully equilibrated, as can occur when the system is driven at\nfrequencies that exceed the rate of fermion backscattering. In this case, the\nFermi gas is described by three bulk viscosities, which we obtain for a generic\nsingle-particle dispersion."
    },
    {
        "anchor": "Strongly correlated Fermions strongly coupled to light: Strong quantum correlations in matter are responsible for some of the most\nextraordinary properties of material, from magnetism to high-temperature\nsuperconductivity, but their integration in quantum devices requires a strong,\ncoherent coupling with photons, which still represents a formidable technical\nchallenge in solid state systems. In cavity quantum electrodynamics, quantum\ngases such as Bose-Einstein condensates or lattice gases have been strongly\ncoupled with light. However, neither Fermionic quantum matter, comparable to\nelectrons in solids, nor atomic systems with controlled interactions, have thus\nfar been strongly coupled with photons. Here we report on the strong coupling\nof a quantum-degenerate unitary Fermi gas with light in a high finesse cavity.\nWe map out the spectrum of the coupled system and observe well resolved dressed\nstates, resulting from the strong coupling of cavity photons with each spin\ncomponent of the gas. We investigate spin-balanced and spin-polarized gases and\nfind quantitative agreement with ab-initio calculation describing light-matter\ninteraction. Our system offers complete and simultaneous control of atom-atom\nand atom-photon interactions in the quantum degenerate regime, opening a wide\nrange of perspectives for quantum simulation.",
        "positive": "Low-energy modes of spin-imbalanced Fermi gases in BCS phase: The low-energy modes of a spin-imbalanced superfluid Fermi gas in the\nBardeen-Cooper-Schrieffer (BCS) side are studied. The gas is assumed to be\nsufficiently dilute so that the pairing of atoms can be considered effective\nonly in s-wave between fermions of different internal state. The order\nparameter at equilibrium is determined by the mean-field approximation, while\nthe properties of the collective modes are calculated within a Gaussian\napproximation for the fluctuations of the order parameter. In particular we\ninvestigate the effects of asymmetry between the populations of the two\ndifferent components and of temperature on the frequency and damping of\ncollective modes. It is found that the temperature does not much affect the\nfrequency and the damping of the modes, whereas an increase of the imbalance\nshifts the frequency toward lower values and enhances the damping sensitively.\nBesides the Bogoliubov-Anderson phonons, we observe modes at zero frequency for\nfinite values of the wave-number. These modes indicate that an instability\ndevelops driving the system toward two separate phases, normal and superfluid."
    },
    {
        "anchor": "Tuning energy transport using interacting vibrational modes: We study energy transport in a chain of quantum harmonic and anharmonic\noscillators where the anharmonicity is induced by interaction between local\nvibrational states of the chain. Using adiabatic elimination and numerical\nsimulations with matrix product states, we show how strong interactions\nsignificantly slow down the relaxation dynamics (with the emergence of a new\ntime scale) and can alter the properties of the steady state. We also show that\nsteady state properties are completely different depending on the order in\nwhich the limits of infinite time and infinite interaction are taken.",
        "positive": "Single-site-resolved imaging of ultracold atoms in a triangular optical\n  lattice: We demonstrate single-site-resolved fluorescence imaging of ultracold\n$^{87}\\mathrm{Rb}$ atoms in a triangular optical lattice by employing Raman\nsideband cooling. Combining a Raman transition at the D1 line and a photon\nscattering through an optical pumping of the D2 line, we obtain images with low\nbackground noise. The Bayesian optimisation of 11 experimental parameters for\nfluorescence imaging with Raman sideband cooling enables us to achieve\nsingle-atom detection with a high fidelity of $(96.3 \\pm 1.3)$%. Single-atom\nand single-site resolved detection in a triangular optical lattice paves the\nway for the direct observation of spin correlations or entanglement in\ngeometrically frustrated systems."
    },
    {
        "anchor": "Zone-plate focusing of Bose-Einstein condensates for atom optics and\n  erasable high-speed lithography of quantum electronic components: We show that Fresnel zone plates, fabricated in a solid surface, can sharply\nfocus atomic Bose-Einstein condensates that quantum reflect from the surface or\npass through the etched holes. The focusing process compresses the condensate\nby orders of magnitude despite inter-atomic repulsion. Crucially, the focusing\ndynamics are insensitive to quantum fluctuations of the atom cloud and largely\npreserve the condensates' coherence, suggesting applications in passive\natom-optical elements, for example zone plate lenses that focus atomic matter\nwaves and light at the same point to strengthen their interaction. We explore\ntransmission zone-plate focusing of alkali atoms as a route to erasable and\nscalable lithography of quantum electronic components in two-dimensional\nelectron gases embedded in semiconductor nanostructures. To do this, we\ncalculate the density profile of a two-dimensional electron gas immediately\nbelow a patch of alkali atoms deposited on the surface of the nanostructure by\nzone-plate focusing. Our results reveal that surface-induced polarization of\nonly a few thousand adsorbed atoms can locally deplete the electron gas. We\nshow that, as a result, the focused deposition of alkali atoms by existing zone\nplates can create quantum electronic components on the 50 nm scale, comparable\nto that attainable by ion beam implantation but with minimal damage to either\nthe nanostructure or electron gas.",
        "positive": "Relaxation of phonons in the Lieb-Liniger gas by dynamical\n  refermionization: We investigate the Lieb-Liniger gas initially prepared in an\nout-of-equilibrium state that is Gaussian in terms of the phonons. Because the\nphonons are not exact eigenstates of the Hamiltonian, the gas relaxes to a\nstationary state at very long times. Thanks to integrability, that stationary\nstate needs not be a thermal state. We characterize the stationary state of the\ngas after relaxation and compute its phonon population distribution.\nTechnically, this follows from the mapping between the exact eigenstates of the\nLieb-Liniger Hamiltonian and those of a non-interacting Fermi gas -- a mapping\nprovided by the Bethe equations -- , as well as on bosonization formulas valid\nin the low-energy sector of the Hilbert space. We apply our results to the case\nwhere the initial state is an excited coherent state for a single phonon mode,\nand we compare them to exact results obtained in the hard-core limit."
    },
    {
        "anchor": "Universal tetramer and pentamer in two-dimensional fermionic mixtures: We study the emergence of universal tetramer and pentamer bound states in the\ntwo-dimensional $(N+1)$ system, which consists of $N$ identical heavy fermions\ninteracting with a light atom. We show that the critical heavy-light mass ratio\nto support a ($3+1$) tetramer below the trimer threshold is $3.38$, and to\nsupport a ($4+1$) pentamer below the tetramer threshold is $5.14$. While these\nground state tetramer and pentamer are both with zero total angular momentum,\nthey exhibit very different density distributions and correlations in momentum\nspace, due to their distinct angular momentum decompositions in the\ndimer-fermion frame. These universal bound states can be accessible by a number\nof Fermi-Fermi mixtures now realized in cold atoms laboratories, which also\nsuggest novel few-body correlations dominant in their corresponding many-body\nsystems.",
        "positive": "Multistable circular currents of polariton condensates trapped in ring\n  potentials: We demonstrate the formation and trapping of different stationary solutions,\noscillatory solutions, and rotating solutions of a polariton condensate in a\nplanar semiconductor microcavity with a built-in ring-shaped potential well.\nMultistable ring shaped solutions are trapped in shallow potential wells. These\nsolutions have the same ring shaped density distribution but different\ntopological charges, corresponding to different orbital angular momentum (OAM)\nof the emitted light. For stronger confinement potentials, besides the\nfundamental modes, higher excited (dipole) modes can also be trapped. If two\nmodes are excited simultaneously, their beating produces a complex oscillation\nand rotation dynamics. When the two modes have the same OAM, a double-ring\nsolution forms for which the density oscillates between the inner and the outer\nring. When the two modes have different OAM, a rotating solution with a\ncrescent-shaped density and fractional OAM is created."
    },
    {
        "anchor": "Non-equilibrium Enhancement of Cooper Pairing in Cold Fermion Systems: Non-equilibrium stimulation of superfluidity in trapped Fermi gases is\ndiscussed by analogy to the work of Eliashberg [G. M. Eliashberg, in\n\"Nonequilibrium Superconductivity,\" edited by D. N. Langenberg and A. I. Larkin\n(North-Holland, New York, 1986)] on the microwave enhancement of\nsuperconductivity. Optical excitation of the fermions balanced by heat loss due\nto thermal contact with a boson bath and/or evaporative cooling enables\nstationary non-equilibrium states to exist. Such a state manifests as a shift\nof the quasiparticle spectrum to higher energies and this effect effectively\nraises the pairing transition temperature. As an illustration, we calculate the\neffective enhancement of Cooper pairing and superfluidity in both the normal\nand superfluid phases for a mixture of Rb and Li in the limit of small\ndeparture from equilibrium. It is argued that in experiment the desirable\neffect is not limited to such small perturbations and the effective enhancement\nof the pairing temperature may be quite large.",
        "positive": "Observation of quasiparticle pair-production and quantum entanglement in\n  atomic quantum gases quenched to an attractive interaction: We report observation of quasiparticle pair-production and characterize\nquantum entanglement created by a modulational instability in an atomic\nsuperfluid. By quenching the atomic interaction to attractive and then back to\nweakly repulsive, we produce correlated quasiparticles and monitor their\nevolution in a superfluid through evaluating the in situ density noise power\nspectrum, which essentially measures a 'homodyne' interference between ground\nstate atoms and quasiparticles of opposite momenta. We observe large amplitude\ngrowth in the power spectrum and subsequent coherent oscillations in a wide\nspatial frequency band within our resolution limit, demonstrating coherent\nquasiparticle generation and evolution. The spectrum is observed to oscillate\nbelow a quantum limit set by the Peres-Horodecki separability criterion of\ncontinuous-variable states, thereby confirming quantum entanglement between\ninteraction quench-induced quasiparticles."
    },
    {
        "anchor": "Floquet realization and signatures of one-dimensional anyons in an\n  optical lattice: We propose a simple scheme for realizing the physics of 1D anyons with\nultracold bosonic atoms in an optical lattice. It relies on\nlattice-shaking-induced resonant tunneling against potential off-sets created\nby a combination of a lattice tilt and strong on-site interactions. No lasers\nadditional to those used for the creation of the optical lattice are required.\nWe also discuss experimental signatures of the continuous interpolation between\nbosons and fermions when the statistical angle $\\theta$ is varied from 0 to\n$\\pi$. Since the anyonic momentum distribution is not measurable in the bosonic\nrepresentation of the anyon model, we propose to use Friedel oscillations in\nsmall systems as an alternative probe.",
        "positive": "Staggered-Vortex Superfluid of Ultracold Bosons in an Optical Lattice: We show that the dynamics of cold bosonic atoms in a two-dimensional square\noptical lattice produced by a bichromatic light-shift potential is described by\na Bose-Hubbard model with an additional effective staggered magnetic field. In\naddition to the known uniform superfluid and Mott insulating phases, the\nzero-temperature phase diagram exhibits a novel kind of finite-momentum\nsuperfluid phase, characterized by a quantized staggered rotational flux. An\nextension for fermionic atoms leads to an anisotropic Dirac spectrum, which is\nrelevant to graphene and high-$T_c$ superconductors."
    },
    {
        "anchor": "Self-maintaining defect/droplets from two interacting Bose-Einstein\n  condensates: We consider two interacting Bose-Einstein condensates (BEC's) with different\nkind of the potential energy of interaction of the condensates: (a) the\nstandard potential; (b) the potential has a positive three-body and a negative\ntwo-body scattering terms and (c) the potential has a positive four-body and a\nnegative three-body scattering terms for the first BEC and a positive\nthree-body and a negative two-body scattering terms for the second BEC. It is\nshown that in these cases there exist regular spherically symmetric solutions.\nPhysically such solution is either a defect or a droplet created by the\ncondensates. The defect is a cavity filled with one BEC on the background of\nanother BEC. The droplet is an object on the background of the empty space. For\n(a) and (b) cases the obtained objects are supported by a constant external\ntrapping potential and for (c) case the droplet is a self-maintaining object\nwithout any external potential. The possibility of construction of an\nelementary logic qubit device on the basis of this droplet is discussed.",
        "positive": "Multi-band spectroscopy of inhomogeneous Mott-insulator states of\n  ultracold bosons: In this work, we use inelastic scattering of light to study the response of\ninhomogeneous Mott-insulator gases to external excitations. The experimental\nsetup and procedure to probe the atomic Mott states are presented in detail. We\ndiscuss the link between the energy absorbed by the gases and accessible\nexperimental parameters as well as the linearity of the response to the\nscattering of light. We investigate the excitations of the system in multiple\nenergy bands and a band-mapping technique allows us to identify band and\nmomentum of the excited atoms. In addition the momentum distribution in the\nMott states which is spread over the entire first Brillouin zone enables us to\nreconstruct the dispersion relation in the high energy bands using a single\nBragg excitation with a fixed momentum transfer."
    },
    {
        "anchor": "Schwinger-Keldysh approach to out of equilibrium dynamics of the Bose\n  Hubbard model with time varying hopping: We study the real time dynamics of the Bose Hubbard model in the presence of\ntime-dependent hopping allowing for a finite temperature initial state. We use\nthe Schwinger-Keldysh technique to find the real-time strong coupling action\nfor the problem at both zero and finite temperature. This action allows for the\ndescription of both the superfluid and Mott insulating phases. We use this\naction to obtain dynamical equations for the superfluid order parameter as\nhopping is tuned in real time so that the system crosses the superfluid phase\nboundary. We find that under a quench in the hopping, the system generically\nenters a metastable state in which the superfluid order parameter has an\noscillatory time dependence with a finite magnitude, but disappears when\naveraged over a period. We relate our results to recent cold atom experiments.",
        "positive": "Heteronuclear magnetisms with ultracold spinor bosonic gases in optical\n  lattices: Motivated by recent realizations of spin-1 NaRb mixtures in the experiments,\nhere we investigate heteronuclear magnetism in the Mott-insulating regime.\nDifferent from the identical mixtures where the boson (fermion) statistics only\nadmits even (odd) parity states from angular momentum composition, for\nheteronuclear atoms in principle all angular momentum states are allowed, which\ncan give rise to new magnetic phases. Various magnetic phases can be developed\nover these degenerate spaces, however, the concrete symmetry breaking phases\ndepend not only on the degree of degeneracy, but also the competitions from\nmany-body interactions. We unveil these rich phases using the bosonic dynamical\nmean-field theory approach. These phases are characterized by various orders,\nincluding spontaneous magnetization order, spin magnitude order, singlet\npairing order and nematic order, which may coexist, especially in the regime\nwith odd parity. Finally we address the possible parameter regimes for\nobserving these spin-ordered Mott phases."
    },
    {
        "anchor": "Manipulation of heteronuclear spin dynamics with microwave and vector\n  light shift: We report the observation and manipulation of heteronuclear spin dynamics in\na spin-1 mixture of ultracold $^{87}$Rb and $^{23}$Na atoms. The dynamics is\ndriven by the interspecies spin-dependent interaction and shows a pronounced\ndependence on magnetic fields with influences from both linear and quadratic\nZeeman shifts. Similar to the well-studied homonuclear cases, the interspecies\nspin dynamics can be controlled by tuning the quadratic Zeeman shift with\nfar-detuned microwave fields. In addition, we successfully realize spin\ndynamics control with vector light shifts which act as a species-selective\neffective magnetic field on $^{87}$Rb atoms. Both methods show negligible loss\nof atoms thus will be powerful techniques for investigating spin dynamics with\nfast temporal and high spatial resolutions.",
        "positive": "Pairing patterns in one-dimensional spin- and mass-imbalanced Fermi\n  gases: We study spin- and mass-imbalanced mixtures of spin-$\\tfrac{1}{2}$ fermions\ninteracting via an attractive contact potential in one spatial dimension.\nSpecifically, we address the influence of unequal particle masses on the pair\nformation by means of the complex Langevin method. By computing the\npair-correlation function and the associated pair-momentum distribution we find\nthat inhomogeneous pairing is present for all studied spin polarizations and\nmass imbalances. To further characterize the pairing behavior, we analyze the\ndensity-density correlations in momentum space, the so-called shot noise, which\nis experimentally accessible through time-of-flight imaging. At finite spin\npolarization, the latter is known to show distinct maxima at momentum\nconfigurations associated with the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)\ninstability. Besides those maxima, we find that additional features emerge in\nthe noise correlations when mass imbalance is increased, revealing the\nstability of FFLO-type correlations against mass imbalance and furnishing an\nexperimentally accessible signature to probe this type of pairing."
    },
    {
        "anchor": "Polarization-induced phase separation and re-entrant transition of two\n  component-fermions in a one-dimensional lattice: By investigating the compressibility of one-dimensional lattice fermions at\nvarious filling factors, we study the phase separation and re-entrant\ntransition within the framework of the Bethe ansatz method. We model the system\nusing the repulsive Hubbard model and calculate compressibility as a function\nof polarization for arbitrary values of chemical potential, temperature, and\ninteraction strength. For filling factors $ 0 < n < 1$, compressibility is a\nnon-monotonic function of polarization at all thermodynamic parameters. The\ncompressibility reveals a phase transition into a phase-separated state for\nboth low and intermediate temperatures at intermediate interactions as one\nincreases the polarization. For certain filling factors, we find the re-entrant\ntransition into the mixed phase at a higher polarization.",
        "positive": "Tunneling control and localization for Bose-Einstein condensates in a\n  frequency modulated optical lattice: The similarity between matter waves in periodic potential and solid-state\nphysics processes has triggered the interest in quantum simulation using\nBose-Fermi ultracold gases in optical lattices. The present work evidences the\nsimilarity between electrons moving under the application of oscillating\nelectromagnetic fields and matter waves experiencing an optical lattice\nmodulated by a frequency difference, equivalent to a spatially shaken periodic\npotential. We demonstrate that the tunneling properties of a Bose-Einstein\ncondensate in shaken periodic potentials can be precisely controlled. We take\nadditional crucial steps towards future applications of this method by proving\nthat the strong shaking of the optical lattice preserves the coherence of the\nmatter wavefunction and that the shaking parameters can be changed\nadiabatically, even in the presence of interactions. We induce reversibly the\nquantum phase transition to the Mott insulator in a driven periodic potential."
    },
    {
        "anchor": "Universal Prethermal Dynamics of Bose Gases Quenched to Unitarity: Understanding strongly correlated phases of matter, from the quark-gluon\nplasma to neutron stars, and in particular the dynamics of such systems, $e.g.$\nfollowing a Hamiltonian quench, poses a fundamental challenge in modern\nphysics. Ultracold atomic gases are excellent quantum simulators for these\nproblems, thanks to tuneable interparticle interactions and experimentally\nresolvable intrinsic timescales. In particular, they give access to the unitary\nregime where the interactions are as strong as allowed by quantum mechanics.\nFollowing years of experiments on unitary Fermi gases, unitary Bose gases have\nrecently emerged as a new experimental frontier. They promise exciting new\npossibilities, including universal physics solely controlled by the gas density\nand novel forms of superfluidity. Here, through momentum- and time-resolved\nstudies, we explore both degenerate and thermal homogeneous Bose gases quenched\nto unitarity. In degenerate samples we observe universal post-quench dynamics\nin agreement with the emergence of a prethermal state with a universal nonzero\ncondensed fraction. In thermal gases, dynamic and thermodynamic properties\ngenerically depend on both the gas density $n$ and temperature $T$, but we find\nthat they can still be expressed in terms of universal dimensionless functions.\nSurprisingly, the total quench-induced correlation energy is independent of the\ngas temperature. Our measurements provide quantitative benchmarks and new\nchallenges for theoretical understanding.",
        "positive": "Double resonances in Borromean heteronuclear triatomic systems: We investigate the occurrence of Borromean three-body continuum s-wave\nresonances, in an $\\alpha\\alpha\\beta$ system for large negative two-body\nscattering lengths. The energy and width are determined by a scaling function\nwith arguments given by energy ratios of the two-body virtual state subsystem\nenergies with the shallowest three-body bound state. The Borromean continuum\nresonances emerging from Efimov states present a peculiar behavior for trapped\nultracold atoms near a Feshbach resonance: two resonances with equal energies\nat different values of the scattering length. The corresponding three-body\nrecombination peaks should merge as the temperature is raised, with one moving\ntowards lower values of the scattering length as the other moves to larger\nvalues."
    },
    {
        "anchor": "$\\mathcal{PT}$-symmetry phase transition in a Bose-Hubbard model with\n  localized gain and loss: We study the dissipative dynamics of a one-dimensional bosonic system\ndescribed in terms of the bipartite Bose-Hubbard model with alternating gain\nand loss. This model exhibits the $\\mathcal{PT}$ symmetry under some specific\nconditions and features a $\\mathcal{PT}$-symmetry phase transition. It is\ncharacterized by an order parameter corresponding to the population imbalance\nbetween even and odd sites, similar to the continuous phase transitions in the\nHermitian realm. In the noninteracting limit, we solve the problem exactly and\ncompute the parameter dependence of the order parameter. The interacting limit\nis addressed at the mean-field level, which allows us to construct the phase\ndiagram for the model. We find that both the interaction and dissipation rates\ninduce a $\\mathcal{PT}$-symmetry breaking. On the other hand, periodic\nmodulation of the dissipative coupling in time stabilizes the\n$\\mathcal{PT}$-symmetric regime. Our findings are corroborated numerically on a\ntight-binding chain with gain and loss.",
        "positive": "Systems of vortices in a binary core-shell Bose-Einstein condensate: A trapped Bose--Einstein-condensed mixture of two types of cold atoms with\nsignificantly different masses has been simulated numerically within the\ncoupled Gross--Pitaevskii equations. A configuration consisting of a\nvortex-free core and a shell penetrated by quantum vortices is possible in the\nphase separation regime. The dynamic properties of vortices in the shell are\ndetermined by several parameters. Physically implementable parametric domains\ncorresponding to long-lived strongly nonstationary systems of several vortices\nattached to the core have been sought. A number of realistic numerical examples\nof three vortex pairs existing for many hundreds of characteristic times have\nbeen presented."
    },
    {
        "anchor": "Quantum Paddlewheel with Ultracold Atoms in Waveguides: We propose and study a quantum pump which emulates a traditional paddlewheel,\nthat can be implemented with ultracold atoms in waveguides. We use wavepacket\npropagation to study its single-mode dynamics, which also determines its\nmultimode current for mesoscopic setups. Energy flow with or without particle\ntransport is possible. The spectrum reveals unusual features such as nonuniform\nFloquet side-bands and counter-intuitive scattering. Explanations are found by\nexamining the scattering dynamics comparatively using quantum, classical and\nsemiclassical pictures, indicating a rich system and experimentally accessible\nmethod to explore quantum versus classical dynamics.",
        "positive": "Transient ordering in the Gross-Pitaevskii lattice subject to an energy\n  quench within the disordered phase: We numerically investigate heating-and-cooling quenches taking place entirely\nin the non-ordered phase of the discrete Gross-Pitaevskii equation on a\nthree-dimensional cubic lattice. In equilibrium, this system exhibits a\nU(1)-ordering phase transition at an energy density which is significantly\nlower than the minimum one during the quench. Yet, we observe that the\npost-quench relaxation is accompanied by a transient U(1) ordering, namely, the\ncorrelation length of U(1) fluctuations significantly exceeds its equilibrium\npre-quench value. The longer and the stronger the heating stage of the quench,\nthe stronger the U(1) transient ordering. We identify the origin of this\nordering with the emergence of a small group of slowly relaxing lattice sites\naccumulating a large fraction of the total energy of the system. Our findings\nsuggest that the transient ordering may be a robust feature of a broad class of\nphysical systems. This premise is consistent with the growing experimental\nevidence of the transient U(1) order in rather dissimilar settings."
    },
    {
        "anchor": "Solutions of the Schr\u00f6dinger equation for anisotropic dipole-dipole\n  interaction plus isotropic van der Waals interaction: By generalizing Bo Gao's approach [Phys. Rev. A 58, 1728 (1998)] for solving\nthe Schr\\\"{o}dinger equation for an isotropic van der Waals (vdW) potential to\nthe systems with a multi-scale anisotropic long-range interaction, we derive\nthe solutions for the Schr\\\"{o}dinger equation for an anisotropic dipole-dipole\ninteraction plus an isotropic attractive vdW potential, i.e.,\n${C_d(1-3\\cos^2\\theta)}/{r^3}-{C_6}/{r^6}$, which is projected to the subspace\nwith angular momentum $l\\leq l_{\\rm cut}$, with $l_{\\rm cut}$ being an\narbitrary angular-momentum cutoff. Here $\\theta$ is the polar angle of the\ncoordinate $\\boldsymbol{r}$ and $r=|\\boldsymbol{r}|$. The asymptotic behaviors\nof these solutions for $r\\rightarrow 0$ and $r\\rightarrow \\infty$ are obtained.\nThese results can be used in the research of collisions and chemical reactions\nbetween ultra-cold polar molecules in a static electric field. Our approach to\nderive the solutions can be applied to the systems with a general long-range\npotential $\\sum_{\\lambda= 2}^{\\lambda_{\\rm max}}\n{V_\\lambda(\\theta,\\varphi)}/{r^\\lambda}$, with $\\varphi$ being the azimuthal\nangle of $\\boldsymbol{r}$, and thus can be used in various problems on\nmolecule-molecule interaction.",
        "positive": "The three-body scattering hypervolume of identical fermions in one\n  dimension: We study the zero-energy collision of three identical spin-polarized fermions\nwith short-range interactions in one dimension. We derive the asymptotic\nexpansions of the three-body wave function when the three fermions are far\napart or one pair and the third fermion are far apart, and the three-body\nscattering hypervolume $D_F$ appears in the coefficients of such expansions. If\nthe two-body interaction is attractive and supports two-body bound states,\n$D_F$ acquires a negative imaginary part related to the amplitudes of the\noutgoing waves describing the departure of the resultant bound pair and the\nremaining free fermion. For weak interaction potentials, we derive an\napproximate formula of the hypervolume by using the Born expansion. For the\nsquare-barrier and the square-well potentials and the Gaussian potential, we\nsolve the three-body Schr\\\"{o}dinger equation to compute $D_F$ numerically. We\nalso calculate the shifts of energy and of pressure of spin-polarized\none-dimensional Fermi gases due to a nonzero $D_F$ and the three-body\nrecombination rate in one dimension."
    },
    {
        "anchor": "FACt: FORTRAN toolbox for calculating fluctuations in atomic condensates: We develop a FORTRAN code to compute fluctuations in atomic condensates\n(FACt) by solving the Bogoliubov-de Gennes (BdG) equations for two component\nBose-Einstein condensate (TBEC) in quasi two dimensions. The BdG equations are\nrecast as matrix equations and solved self consistently. The code is suitable\nfor handling quantum fluctuations as well as thermal fluctuations at\ntemperatures below the critical point of Bose-Einstein condensation. The code\nis versatile, and the ground state density profile and low energy excitation\nmodes obtained from the code can be easily adapted to compute different\nproperties of TBECs -- ground state energy, overlap integral, quasi particle\namplitudes of BdG spectrum, dispersion relation and structure factor and other\nrelated experimental observables.",
        "positive": "Josephson oscillations in split one-dimensional Bose gases: We consider the non-equilibrium dynamics of a weakly interacting Bose gas\ntightly confined to a highly elongated double well potential. We use a\nself-consistent time-dependent Hartree--Fock approximation in combination with\na projection of the full three-dimensional theory to several coupled\none-dimensional channels. This allows us to model the time-dependent splitting\nand phase imprinting of a gas initially confined to a single quasi\none-dimensional potential well and obtain a microscopic description of the\nensuing damped Josephson oscillations."
    },
    {
        "anchor": "Generation of vortices and observation of Quantum Turbulence in an\n  oscillating Bose-Einstein Condensate: We report on the experimental observation of vortex formation and production\nof tangled vortex distribution in an atomic BEC of Rb-87 atoms submitted to an\nexternal oscillatory perturbation. The oscillatory perturbations start by\nexciting quadrupolar and scissors modes of the condensate. Then regular\nvortices are observed finally evolving to a vortex tangle configuration. The\nvortex tangle is a signature of the presence of a turbulent regime in the\ncloud. We also show that this turbulent cloud has suppression of the aspect\nratio inversion typically observed in quantum degenerate bosonic gases during\nfree expansion.",
        "positive": "Kibble-Zurek dynamics in an array of coupled binary Bose condensates: Universal dynamics of spontaneous symmetry breaking is central to\nunderstanding the universal behavior of spontaneous defect formation in various\nsystem from the early universe, condensed-matter systems to ultracold atomic\nsystems. We explore the universal real-time dynamics in an array of coupled\nbinary atomic Bose-Einstein condensates in optical lattices, which undergo a\nspontaneous symmetry breaking from the symmetric Rabi oscillation to the\nbroken-symmetry self-trapping. In addition to Goldstone modes, there exist\ngapped Higgs mode whose excitation gap vanishes at the critical point. In the\nslow passage through the critical point, we analytically find that the\nsymmetry-breaking dynamics obeys the Kibble-Zurek mechanism. From the scalings\nof bifurcation delay and domain formation, we numerically extract two\nKibble-Zurek exponents $b_{1}=\\nu/(1+\\nu z)$ and $b_{2}=1/(1+\\nu z)$, which\ngive the static correlation-length critical exponent $\\nu$ and the dynamic\ncritical exponent $z$. Our approach provides an efficient way to simultaneous\ndetermination of the critical exponents $\\nu$ and $z$ for a continuous phase\ntransition."
    },
    {
        "anchor": "Rapid generation and number-resolved detection of spinor Rubidium\n  Bose-Einstein condensates: High data acquisition rates and low-noise detection of ultracold neutral\natoms present important challenges for the state tomography and interferometric\napplication of entangled quantum states in Bose-Einstein condensates. In this\narticle, we present a high-flux source of $^{87}$Rb Bose-Einstein condensates\ncombined with a number-resolving detection. We create Bose-Einstein condensates\nof $2\\times10^5$ atoms with no discernible thermal fraction within $3.3$ s\nusing a hybrid evaporation approach in a magnetic/optical trap. For the\nhigh-fidelity tomography of many-body quantum states in the spin degree of\nfreedom [arXiv:2207.01270], it is desirable to select a single mode for a\nnumber-resolving detection. We demonstrate the low-noise selection of\nsubsamples of up to $16$ atoms and their subsequent detection with a counting\nnoise below $0.2$ atoms. The presented techniques offer an exciting path\ntowards the creation and analysis of mesoscopic quantum states with\nunprecedented fidelities, and their exploitation for fundamental and\nmetrological applications.",
        "positive": "Quantum phases of spin-orbital-angular-momentum coupled bosonic gases in\n  optical lattices: Spin-orbit coupling plays an important role in understanding exotic quantum\nphases. In this work, we present a scheme to combine\nspin-orbital-angular-momentum (SOAM) coupling and strong correlations in\nultracold atomic gases. Essential ingredients of this setting is the interplay\nof SOAM coupling and Raman-induced spin-flip hopping, engineered by lasers that\ncouples different hyperfine spin states. In the presence of SOAM coupling only,\nwe find rich quantum phases in the Mott-insulating regime, which support\ndifferent types of spin defects such as spin vortex and composite vortex with\nantiferromagnetic core surrounded by the outer spin vortex. Based on an\neffective exchange model, we find that these competing spin textures are a\nresult of the interplay of Dzyaloshinskii-Moriya and Heisenberg exchange\ninteractions. In the presence of both SOAM coupling and Raman-induced spin-flip\nhopping, more many-body phases appear, including canted-antiferromagnetic and\nstripe phases. Our prediction suggests that SOAM coupling could induce rich\nexotic many-body phases in the strongly interacting regime."
    },
    {
        "anchor": "Vortex gap solitons in spin-orbit-coupled Bose-Einstein condensates with\n  competing nonlinearities: The formation and dynamics of full vortex gap solitons (FVGSs) is\ninvestigated in two-component Bose-Einstein condensates with spin-orbit\ncoupling (SOC), Zeeman splitting (ZS), and competing cubic and quintic\nnonlinear terms, while the usual kinetic energy is neglected, assuming that it\nis much smaller than the SOC and ZS terms. Unlike previous SOC system with the\ncubic-only attractive nonlinearity, in which solely semi-vortices may be\nstable, with the vorticity carried by a single component, the present system\nsupports stable FVGS states, with the vorticity present in both components\n(such states are called here full vortex solitons, to stress the difference\nfrom the half-vortices). They populate the bandgap in the system's linear\nspectrum. In the case of the cubic self-attraction and quintic repulsion,\nstable FVGSs with a positive effective mass exist near the top of the bandgap.\nOn the contrary, the system with cubic self-repulsion and quintic attraction\nproduces stable FVGSs with a negative mass near the bottom of the bandgap.\nMobility and collisions of FVGSs with different topological charges are\ninvestigated too.",
        "positive": "Thermal versus Quantum Fluctuations of Optical Lattice Fermions: We show that, for fermionic atoms in a one-dimensional optical lattice, the\nfraction of atoms in doubly occupied sites is a highly non-monotonic function\nof temperature. We demonstrate that this property persists even in the presence\nof realistic harmonic confinement, and that it leads to a suppression of\nentropy at intermediate temperatures that offers a route to adiabatic cooling.\nOur interpretation of the suppression is that such intermediate temperatures\nare simultaneously too high for quantum coherence and too low for significant\nthermal excitation of double occupancy thus offering a clear indicator of the\nonset of quantum fluctuations."
    },
    {
        "anchor": "Pair formation in quenched unitary Bose gases: We study a degenerate Bose gas quenched to unitarity by solving a many-body\nmodel including three-body losses and correlations up to second order. As the\ngas evolves in this strongly-interacting regime, the buildup of correlations\nleads to the formation of extended pairs bound purely by many-body effects,\nanalogous to the phenomenon of Cooper pairing in the BCS regime of the Fermi\ngas. Through fast sweeps away from unitarity, we detail how the correlation\ngrowth and formation of bound pairs emerge in the fraction of unbound atoms\nremaining post sweep, finding quantitative agreement with experiment. We\ncomment on the possible role of higher-order effects in explaining the\ndeviation of our theoretical results from experiment for slower sweeps and\nlonger times spent in the unitary regime.",
        "positive": "Radio-frequency evaporation in an optical dipole trap: We present an evaporative cooling technique for atoms trapped in an optical\ndipole trap that benefits from narrow optical transitions. For an appropriate\nchoice of wavelength and polarization, a single laser beam leads to opposite\nlight-shifts in two internal states of the lowest energy manifold.\nRadio-frequency coupling between these two states results in evaporative\ncooling at a constant trap stiffness. The evaporation protocol is well adapted\nto several atomic species, in particular to the case of Lanthanides such as Er,\nDy, and fermionic Yb, but also to alkali-earth metals such as fermionic Sr. We\nderive the dimensionless expressions that allow us to estimate the evaporation\nefficiency. As a concrete example, we consider the case of $^{162}$Dy and\npresent a numerical analysis of the evaporation in a dipole trap near the\n$J'=J$ optical transition at 832 nm. We show that this technique can lead to\nrunaway evaporation in a minimalist experimental setup."
    },
    {
        "anchor": "Spatiotemporal Binary Interaction and Designer quasi particle\n  condensates: We introduce a new integrable model to investigate the dynamics of two\ncomponent quasi particle condensates with spatio temporal interaction\nstrengths. We derive the associated Lax-pair of the coupled GP equation and\nconstruct matter wave solitons. We show that the spatio temporal binary\ninteraction strengths not only facilitate the stabilization of the condensates,\nbut also enables one to fabricate condensates with desirable densities,\ngeometries and properties leading to the so called \"designer quasi particle\ncondensates\".",
        "positive": "Direct Transfer of Light's Orbital Angular Momentum onto Non-resonantly\n  Excited Polariton Superfluid: Recently, exciton-polaritons in a semiconductor microcavity were found to\ncondense into a coherent ground state much like a Bose-Einstein condensate and\na superfluid. They have become a unique testbed for generating and manipulating\nquantum vortices in a driven-dissipative superfluid. Here, we generate\nexciton-polariton condensate with non-resonant Laguerre-Gaussian (LG) optical\nbeam and verify the direct transfer of light's orbital angular momentum to\nexciton-polariton quantum fluid. Quantized vortices are found in spite of large\nenergy relaxation involved in non-resonant pumping. We identified phase\nsingularity, density distribution and energy eigenstates for the vortex states.\nOur observations confirm that non-resonant optical LG beam can be used to\nmanipulate chirality, topological charge, and stability of non-equilibrium\nquantum fluid. These vortices are quite robust, only sensitive to the OAM of\nlight and not other parameters such as energy, intensity, size or shape of the\npump beam. Therefore, optical information can be transferred between photon and\nexciton-polariton with ease and the technique is potentially useful to form the\ncontrollable network of multiple topological charges even in the presence of\nspectral randomness in solid state system."
    },
    {
        "anchor": "How many particles do make a fluid? Qualifying collective behavior in\n  expanding ultracold gases: Collective phenomena in quantum many-body systems are often described in\nterms of hydrodynamics, an appropriate framework when the involved particle\nnumbers are effectively macroscopic. We propose to use experiments on expanding\nclouds of few and many interacting cold atoms to investigate the emergence of\nhydrodynamics as a function of particle number. We consider gases confined in\ntwo-dimensional elliptically-deformed traps, and we employ the manifestation of\nelliptic flow as an indicator of collective behavior. We quantify the response\nof the gas to the deformation of the trapping potential, and show how such\ninformation can be used to establish how many atoms are needed for the system\nto develop a degree of collectivity comparable to that expected in the\nhydrodynamic limit. This method permits one, in particular, to exploit\nobservations made in expanding atomic gases to shed light on the apparent\nhydrodynamic behaviour of mesoscopic systems of quarks and gluons formed in the\nscattering of light ions in high-energy collider experiments.",
        "positive": "Ultracold dipolar few-boson ensembles in a triple well trap: We investigate the ground state properties and tunneling dynamics of\nultracold dipolar bosons in a one dimensional triple well trap from a few-body\nab-initio perspective. Our focus is primarily on the distinctive features of\ndipolar bosons compared to the contact interacting bosons. Formation of\nintra-well localization is observed for very strong dipolar interaction.\nGeneral population rearangement as well as fragmentation and localization\neffects have been found, depending strongly on the particle number. The energy\nspectrum for two particles exhibits avoided crossings that lead to several\ndistinct resonances involving different bands, i.e. to an inter-band resonant\ntunneling dynamics. The corresponding mechanisms are investigated by studying\namong others the pair-probability and performing an eigenstate analysis."
    },
    {
        "anchor": "Comparing fermionic superfluids in two and three dimensions: Understanding the origins of unconventional superconductivity has been a\nmajor focus of condensed matter physics for many decades. While many questions\nremain unanswered, experiments have found that the systems with the highest\ncritical temperatures tend to be layered materials where superconductivity\noccurs in two-dimensional (2D) structures. However, to what extent the\nremarkable stability of these strongly correlated 2D superfluids is related to\ntheir reduced dimensionality is still an open question. In this work, we use\ndilute gases of ultracold fermionic atoms as a model system to directly observe\nthe influence of dimensionality on strongly interacting fermionic superfluids.\nWe achieve this by measuring the superfluid gap of a strongly correlated\nquasi-2D Fermi gas over a wide range of interaction strengths and comparing the\nresults to recent measurements in 3D Fermi gases. We find that the superfluid\ngap follows the same universal function of the interaction strength in both\nsystems, which suggests that there is no inherent difference in the stability\nof fermionic superfluidity between two- and three-dimensional quantum gases.\nFinally, we compare our data to results from solid state systems and find a\nsimilar relation between the interaction strength and the gap for a wide range\nof two- and three-dimensional superconductors.",
        "positive": "Excitations in disordered bosonic optical lattices: Spectral excitations of ultracold gases of bosonic atoms trapped in one\ndimensional optical lattices with disorder are investigated by means of the\nvariational cluster approach applied to the Bose-Hubbard model. In particular,\nqualitatively different disorder distributions typically employed in\nexperiments are considered. The computed spectra exhibit a strong dependence on\nboth the shape of the disorder distribution and the disorder strength. We\ncompare alternative results for the Mott gap obtained from its formal\ndefinition and from the minimum peak distance, which is the quantity available\nfrom experiments."
    },
    {
        "anchor": "The Bose polaron problem: effect of mass imbalance on binding energy: By means of Quantum Monte Carlo methods we calculate the binding energy of an\nimpurity immersed in a Bose-Einstein condensate at T = 0. The focus is on the\nattractive branch of the Bose polaron and on the role played by the mass\nimbalance between the impurity and the surrounding particles. For an impurity\nresonantly coupled to the bath, we investigate the dependence of the binding\nenergy on the mass ratio and on the interaction strength within the medium. In\nparticular, we determine the equation of state in the case of a static\n(infinite mass) impurity, where three-body correlations are irrelevant and the\nresult is expected to be a universal function of the gas parameter. For the\nmass ratio corresponding to $^{40}$K impurities in a gas of $^{87}$Rb atoms we\nprovide an explicit comparison with the experimental findings of a recent study\ncarried out at JILA.",
        "positive": "Bidirectional dynamic scaling in an isolated Bose gas far from\n  equilibrium: Understanding and classifying nonequilibrium many-body phenomena, analogous\nto the classification of equilibrium states of matter into universality\nclasses, is an outstanding problem in physics. Any many-body system, from\nstellar matter to financial markets, can be out of equilibrium in a myriad of\nways; since many are also difficult to experiment on, it is a major goal to\nestablish universal principles that apply to different phenomena and physical\nsystems. At the heart of the classification of equilibrium states is the\nuniversality seen in the self-similar spatial scaling of systems close to phase\ntransitions. Recent theoretical work, and first experimental evidence, suggest\nthat isolated many-body systems far from equilibrium generically exhibit\ndynamic (spatiotemporal) self-similar scaling, akin to turbulent cascades and\nthe Family-Vicsek scaling in classical surface growth. Here we observe\nbidirectional dynamic scaling in an isolated quench-cooled atomic Bose gas; as\nthe gas thermalises and undergoes Bose-Einstein condensation, it shows\nself-similar net flows of particles towards the infrared (smaller momenta) and\nenergy towards the ultraviolet (smaller lengthscales). For both infrared (IR)\nand ultraviolet (UV) dynamics we find that the scaling exponents are\nindependent of the strength of the interparticle interactions that drive the\nthermalisation."
    },
    {
        "anchor": "Effective theory and universal relations for Fermi gases near a $d$-wave\n  interaction resonance: In this work, we present an effective field theory to describe a\ntwo-component Fermi gas near a $d$-wave interaction resonance. The effective\nfield theory is renormalizable by matching with the low energy $d$-wave\nscattering phase shift. Based on the effective field theory, we derive\nuniversal properties of the Fermi gas by the operator product expansion method.\nWe find that beyond the contacts defined by adiabatic theorems, the asymptotic\nexpressions of the momentum distribution and the Raman spectroscopy involve two\nextra contacts which provide additional information of correlations of the\nsystem. Our formalism sets the stage for further explorations of many-body\neffects in a $d$-wave resonant Fermi gas. Finally we generalise our effective\nfield theory for interaction resonances of arbitrary higher partial waves.",
        "positive": "Probing spin dynamics from the Mott insulating to the superfluid regime\n  in a dipolar lattice gas: We analyze the spin dynamics of an out-of-equilibrium large spin dipolar\natomic Bose gas in an optical lattice. We observe a smooth crossover from a\ncomplex oscillatory behavior to an exponential behavior throughout the Mott to\nsuperfluid transition. While both of these regimes are well described by our\ntheoretical models, we provide data in the intermediate regime where dipolar\ninteractions, contact interactions, and super-exchange mechanisms compete. In\nthis strongly correlated regime, spin dynamics and transport are coupled, which\nchallenges theoretical models for quantum magnetism."
    },
    {
        "anchor": "BCS-BEC crossover in a two-dimensional Fermi gas: We investigate the crossover from Bardeen-Cooper-Schrieffer (BCS)\nsuperfluidity to Bose-Einstein condensation (BEC) in a two-dimensional Fermi\ngas at T=0 using the fixed-node diffusion Monte Carlo method. We calculate the\nequation of state and the gap parameter as a function of the interaction\nstrength, observing large deviations compared to mean-field predictions. In the\nBEC regime our results show the important role of dimer-dimer and atom-dimer\ninteraction effects that are completely neglected in the mean-field picture.\nResults on Tan's contact parameter associated with short-range physics are also\nreported along the BCS-BEC crossover.",
        "positive": "Two-component few-fermion mixtures in a one-dimensional trap: numerical\n  versus analytical approach: We explore a few-fermion mixture consisting of two components which are\nrepulsively interacting and confined in a one-dimensional harmonic trap.\nDifferent scenarios of population imbalance ranging from the completely\nimbalanced case where the physics of a single impurity in the Fermi-sea is\ndiscussed to the partially imbalanced and equal population configurations are\ninvestigated. For the numerical calculations the multi-configurational\ntime-dependent Hartree (MCTDH) method is employed, extending its application to\nfew-fermion systems. Apart from numerical calculations we generalize our Ansatz\nfor a correlated pair wave-function proposed in [1] for bosons to mixtures of\nfermions. From weak to strong coupling between the components the energies, the\ndensities and the correlation properties of one-dimensional systems change\nvastly with an upper limit set by fermionization where for infinite repulsion\nall fermions can be mapped to identical ones. The numerical and analytical\ntreatments are in good agreement with respect to the description of this\ncrossover. We show that for equal populations each pair of different component\natoms splits into two single peaks in the density while for partial imbalance\nadditional peaks and plateaus arise for very strong interaction strengths. The\ncase of a single impurity atom shows rich behaviour of the energy and density\nas we approach fermionization, and is directly connected to recent experiments\n[2-4]."
    },
    {
        "anchor": "An impurity in a heteronuclear two-component Bose mixture: We study the fate of an impurity in an ultracold heteronuclear Bose mixture,\nfocusing on the experimentally relevant case of a $^{41}$K-$^{87}$Rb mixture,\nwith the impurity in a $^{41}$K hyperfine state. Our work provides a\ncomprehensive description of an impurity in a BEC mixture with contact\ninteractions across its phase diagram. We present results for the miscible and\nimmiscible regimes, as well as for the impurity in a self-bound quantum\ndroplet. Here, varying the interactions, we find novel, exotic states where the\nimpurity localizes either at the center or at the surface of the droplet.",
        "positive": "Soliton Magnetization Dynamics in Spin-Orbit Coupled Bose-Einstein\n  Condensates: Ring-trapped Bose-Einstein condensates subject to spin-orbit coupling support\nlocalized dark soliton excitations that show periodic density dynamics in real\nspace. In addition to the density feature, solitons also carry a localized\npseudo-spin magnetization that exhibits a rich and tunable dynamics. Analytic\nresults for Rashba-type spin-orbit coupling and spin-invariant interactions\npredict a conserved magnitude and precessional motion for the soliton\nmagnetization that allows for the simulation of spin-related geometric phases\nrecently seen in electronic transport measurements."
    },
    {
        "anchor": "Delocalization in a partially disordered interacting many-body system: We study a partially disordered one-dimensional system with interacting\nparticles. Concretely, we impose a disorder potential to only every other site,\nfollowed by a clean site. Our numerical analysis of eigenstate properties is\nbased on the entanglement entropy and density distributions. Most importantly,\nat large disorder, there exist eigenstates with large entanglement entropies\nand significant correlations between the clean sites. These states have\nvolume-law scaling, embedded into a sea of area-law states, reminiscent of\ninverted quantum-scar states. These eigenstate features leave fingerprints in\nthe nonequilibrium dynamics even in the large-disorder regime, with a strong\ninitial-state dependence. We demonstrate that certain types of initial\ncharge-density-wave states decay significantly, while others preserve their\ninitial inhomogeneity, the latter being the typical behavior for many-body\nlocalized systems. This initial-condition dependent dynamics may give extra\ncontrol over the delocalization dynamics at large disorder strength and should\nbe experimentally feasible with ultracold atoms in optical lattices.",
        "positive": "Use of quantum quenches to probe the equilibrium current patterns of\n  ultracold atoms in an optical lattice: Atomic bosons and fermions in an optical lattice can realize a variety of\ninteresting condensed matter states that support equilibrium current patterns\nin the presence of synthetic magnetic fields or non-abelian gauge fields. As a\nroute to probing such mass currents, we propose a nonequilibrium quantum quench\nof the Hamiltonian that dynamically converts the current patterns into\nexperimentally measurable real-space density patterns. We illustrate how a\nspecific such \"unidirectional\" quench of the optical lattice can be used to\nuncover checkerboard and stripe current orders in lattice Bose superfluids and\nFermi gases, as well as chiral edge currents in an integer quantum Hall state."
    },
    {
        "anchor": "Effect of Rare Fluctuations on the Thermalization of Isolated Quantum\n  Systems: We consider the question of thermalization for isolated quantum systems after\na sudden parameter change, a so-called quantum quench. In part icular we\ninvestigate the pre-requisites for thermalization focusing on the statistical\nproperties of the time-averaged density matrix and o f the expectation values\nof observables in the final eigenstates. We find that eigenstates, which are\nrare compared to the typical ones sampled by the micro-canonical distribution,\nare responsible for the absence of thermalization of some infinite integrable\nmodels and play an important role for some non-integrable systems of finite\nsize, such as the Bose-Hubbard model. We stress the importance of finite size\neffects for the thermalization of isolated quantum systems and discuss two\nalternative scenarios for thermalization, as well as ways to prune down the\ncorrect one.",
        "positive": "Transient phases and dynamical transitions in the post quench evolution\n  of the generalized Bose-Anderson model: The exact description of the time evolution of open correlated quantum\nsystems remains one of the major challenges of the condensed matter theory,\nspecially for asymptotic long times where most numerical methods fail. Here,\nthe post-quench dynamics of the $N$-component Bose-Anderson impurity model is\nstudied in the $N\\to\\infty$ limit. The equilibrium phase diagram is similar to\nthat of the Bose-Hubbard model in that it contains local versions of the Mott\nand Bose phases. Using a numerically exact procedure we are able to study the\nreal time evolution including asymptotic long time regimes. The formation of\nlong-lived transient phases is observed for quench paths crossing foreign\nphases. For quenches inside the local Bose condensed phase, a dynamical phase\ntransition is reported, that separates the evolution towards a new equilibrium\nstate and a regime characterized at large times by a persistent phase rotation\nof the order parameter. We explain how such non-decaying mode can exist in the\npresence of a dissipative bath. We discuss the extension of our results to the\nexperimental relevant finite-$N$ case and their implication for the existence\nof non-decaying modes in generic quantum systems in the presence of a bath."
    },
    {
        "anchor": "Delocalization and superfluidity of ultracold bosonic atoms in a ring\n  lattice: Properties of bosonic atoms in small systems with a periodic quasi\none-dimensional circular toroidal lattice potential subjected to rotation are\nexamined by performing exact diagonalization in a truncated many body space.\nThe expansion of the many-body Hamiltonian is considered in terms of the first\nband Bloch functions, and no assumption regarding restriction to\nnearest-neighbor hopping (tight-binding approximation) is involved. A finite\nsize version of the zero temperature phase diagrams of Fisher et al.\n\\cite{Fisher} is obtained and the results, in remarkable quantitative\ncorrespondence with the results available for larger systems, discussed. Ground\nstate properties relating to superfluidity are examined in the context of\ntwo-fluid phenomenology. The basic tool, consisting of the intrinsic inertia\nassociated with small rotation angular velocities in the lab frame, is used to\nobtain ground state `superfluid fractions' numerically. They are analytically\nassociated with one-body, uniform solenoidal currents in the case of the\nadopted geometry. These currents are in general incoherent superpositions of\ncontributions from each eigenstate of the associated reduced one-body\ndensities, with the corresponding occupation numbers as weights. Full coherence\noccurs therefore only when only one eigenstate is occupied by all bosons. The\nobtained numerical values for the superfluid fractions remain small throughout\nthe parameter region corresponding to the `Mott insulator to superfluid'\ntransition, and saturate at unity only as the lattice is completely smoothed\nout.",
        "positive": "Recurrences in an isolated quantum many-body system: Even though the evolution of an isolated quantum system is unitary, the\ncomplexity of interacting many-body systems prevents the observation of\nrecurrences of quantum states for all but the smallest systems. For large\nsystems one can not access the full complexity of the quantum states and the\nrequirements to observe a recurrence in experiments reduces to being close to\nthe initial state with respect to the employed observable. Selecting an\nobservable connected to the collective excitations in one-dimensional\nsuperfluids, we demonstrate recurrences of coherence and long range order in an\ninteracting quantum many-body system containing thousands of particles. This\nopens up a new window into the dynamics of large quantum systems even after\nthey reached a transient thermal-like state."
    },
    {
        "anchor": "Low-dimensional physics of ultracold gases with bound states and the\n  sine-Gordon model: One-dimensional systems of interacting atoms are an ideal laboratory to study\nthe Kosterlitz-Thouless phase transition. In the renormalization group picture\nthere is essentially a two-parameter phase diagram to explore. We first present\nhow detailed experiments have shown direct evidence for the theoretical\ntreatment of this transition. Then generalization to the case of two-component\nsystems with bound state formation is discussed. Trimer formation in the\nasymmetric attractive Hubbard model involve in a crucial way this kind of\nphysics.",
        "positive": "Dynamical Friedel oscillations of a Fermi sea: We study the scenario of quenching an interaction-free Fermi sea on a\none-dimensional lattice ring by suddenly changing the potential of a site. From\nthe point-of-view of the conventional Friedel oscillation, which is a static or\nequilibrium problem, it is of interest what temporal and spatial oscillations\nthe local sudden quench will induce. Numerically, the primary observation is\nthat for a generic site, the local particle density switches between two\nplateaus periodically in time. Making use of the proximity of the realistic\nmodel to an exactly solvable model and employing the {Abel regularization} to\nassign a definite value to a divergent series, we obtain an analytical formula\nfor the heights of the plateaus, which turns out to be very accurate for sites\nnot too close to the quench site. The unexpected relevance and the incredible\naccuracy of the Abel regularization are yet to be understood. Eventually, when\nthe contribution of the defect mode is also taken into account, the plateaus\nfor those sites close to or on the quench site can also be accurately\npredicted. We have also studied the infinite lattice case. In this case,\nensuing the quench, the out-going wave fronts leave behind a stable density\noscillation pattern. Because of some interesting single-particle property, this\ndynamically generated Friedel oscillation differs from its conventional static\ncounterpart only by the defect mode."
    },
    {
        "anchor": "Universal Borromean Binding in Spin-Orbit Coupled Ultracold Fermi Gases: Borromean rings and Borromean binding, a class of intriguing phenomena as\nthree objects are linked (bound) together while any two of them are unlinked\n(unbound), widely exist in nature and have been found in systems of biology,\nchemistry and physics. Previous studies have suggested that the occurrence of\nsuch a binding in physical systems typically relies on the microscopic details\nof pairwise interaction potentials at short-range, and is therefore\nnon-universal. Here, we report a new type of Borromean binding in ultracold\nFermi gases with Rashba spin-orbit coupling, which is {\\it universal} against\nshort-range interaction details, with its binding energy only dependent on the\ns-wave scattering length and the spin-orbit coupling strength. We show that the\noccurrence of this universal Borromean binding is facilitated by the symmetry\nof the single-particle dispersion under spin-orbit coupling, and is therefore\n{\\it symmetry-selective} rather than interaction-selective. The state is robust\nover a wide range of mass ratio between composing fermions, which are\naccessible by Li-Li, K-K and K-Li mixtures in cold atoms experiments. Our\nresults reveal the importance of symmetry factor in few-body physics, and shed\nlight on the emergence of new quantum phases in a many-body system with exotic\nfew-body correlations.",
        "positive": "Optimized sympathetic cooling of atomic mixtures via fast adiabatic\n  strategies: We discuss fast frictionless cooling techniques in the framework of\nsympathetic cooling of cold atomic mixtures. It is argued that optimal cooling\nof an atomic species - in which the deepest quantum degeneracy regime is\nachieved - may be obtained by means of sympathetic cooling with another species\nwhose trapping frequency is dynamically changed to maintain constancy of the\nLewis-Riesenfeld adiabatic invariant. Advantages and limitations of this\ncooling strategy are discussed, with particular regard to the possibility of\ncooling Fermi gases to a deeper degenerate regime."
    },
    {
        "anchor": "Controlling the Floquet state population and observing micromotion in a\n  periodically driven two-body quantum system: Near-resonant periodic driving of quantum systems promises the implementation\nof a large variety of novel effective Hamiltonians. The challenge of Floquet\nengineering lies in the preparation and measurement of the desired quantum\nstate. We address these aspects in a model system consisting of interacting\nfermions in a periodically driven array of double wells created by an optical\nlattice. The singlet and triplet fractions and the double occupancy of the\nFloquet states are measured, and their behavior as a function of the\ninteraction strength is analyzed in the high- and low-frequency regimes. We\ndemonstrate full control of the Floquet state population and find suitable\nramping protocols and time-scales which adiabatically connect the initial\nground state to different targeted Floquet states. The micromotion which\nexactly describes the time evolution of the system within one driving cycle is\nobserved. Additionally, we provide an analytic description of the model and\ncompare it to numerical simulations.",
        "positive": "Catching Bethe phantoms and quantum many-body scars: Long-lived\n  spin-helix states in Heisenberg magnets: Exact solutions for quantum many-body systems are rare and provide valuable\ninsight to universal phenomena. Here we show experimentally in anisotropic\nHeisenberg chains that special helical spin patterns can have very long\nlifetimes. This finding confirms the recent prediction of phantom Bethe states,\nexact many-body eigenstates carrying finite momenta yet no energy. We\ntheoretically find analogous stable spin helices in higher dimensions and in\nother non-integrable systems, where they imply non-thermalizing dynamics\nassociated with quantum many-body scars. We use phantom spin helices to\ndirectly measure the interaction anisotropy which has a major contribution from\nshort-range off-site interactions that have not been observed before. Phantom\nhelix states open new opportunities for quantum simulations of spin physics and\nstudies of many-body dynamics."
    },
    {
        "anchor": "Stabilising Fulde-Ferrel-Larkin-Ovchinnikov Superfluidity with\n  long-range Interactions in a mixed dimensional Bose-Fermi System: We analyse the stability of inhomogeneous superfluid phases in a system\nconsisting of identical fermions confined in two layers that are immersed in a\nBose-Einstein condensate (BEC). The fermions in the two layers interact via an\ninduced interaction mediated by the BEC, which gives rise to pairing. We\npresent zero temperature phase diagrams varying the chemical potential\ndifference between the two layers and the range of the induced interaction, and\nshow that there is a large region where an inhomogeneous superfluid phase is\nthe ground state. This region grows with increasing range of the induced\ninteraction and it can be much larger than for a corresponding system with a\nshort range interaction. The range of the interaction is controlled by the\nhealing length of the BEC, which makes the present system a powerful tunable\nplatform to stabilise inhomogeneous superfluid phases. We furthermore analyse\nthe melting of the superfluid phases in the layers via phase fluctuations as\ndescribed by the Berezinskii-Kosterlitz-Thouless mechanism and show that the\nnormal, homogeneous and inhomogeneous superfluid phases meet in a tricritical\npoint. The superfluid density of the inhomogeneous superfluid phase is reduced\nby inherent gapless excitations, and we demonstrate that this leads to a\nsignificant suppression of the critical temperature as compared to the\nhomogeneous superfluid phase.",
        "positive": "Casimir force of two-component Bose-Einstein condensates confined by a\n  parallel plate geometry: Using field theory we calculate the Casimir energy and Casimir force of\ntwo-component Bose-Einstein condensates restricted between two parallel plates,\nin which Dirichlet and periodic boundary conditions applied. Our results show\nthat, in one-loop approximation, the Casimir force equals to summation of the\none of each component and it is vanishing in some cases: (i) inter-distance\nbetween two plates becomes large enough; (ii) intraspecies interaction is zero;\n(iii) interspecies interaction is full strong segregation."
    },
    {
        "anchor": "The effect of non-local derivative on Bose-Einstein condensation: In this paper, we study the effect of non-local derivative on Bose-Einstein\ncondensation. Firstly, we consider the Caputo-Fabrizio derivative of fractional\norder \\alpha to derive the eigenvalues of non-local Schr\\\"odinger equation for\na free particle in a 3D box. Afterwards, we consider 3D Bose-Einstein\ncondensation of an ideal gas with the obtained energy spectrum. Interestingly,\nin this approach the critical temperatures Tc of condensation for 1 < \\alpha <\n2 are greater than the standard one. Furthermore, the condensation in 2D is\nshown to be possible. Second and for comparison, we presented, on the basis of\na spectrum established by N. Laskin, the critical transition temperature as a\nfunction of the fractional parameter {\\alpha} for a system of free bosons\ngoverned by an Hamiltonian with power law on the moment (H~p\\alpha). In this\ncase, we have demonstrated that the transition temperature is greater than the\nstandard one. By comparing the two transition temperatures (relative to\nCaputo-Fabrizio and to Laskin), we have found for fixed \\alpha and the density\n\\rho that the transition temperature relative to Caputo-fabrizio is greater\nthan relative to Laskin.",
        "positive": "Time-of-Flight Roton Spectroscopy in Dipolar Bose-Einstein Condensates: Dipolar Bose-Einstein condensates may present a rotonlike dispersion minimum,\nwhich has yet to be observed in experiments. We discuss a simple method to\nreveal roton excitations, based on the response of quasi-two-dimensional\ndipolar condensates against a weak lattice potential. By employing numerical\nsimulations for realistic scenarios, we analyze the response of the system as a\nfunction of both the lattice spacing and the s-wave scattering length, showing\nthat the roton minimum may be readily revealed in current experiments by the\nresonant population of Bragg peaks in time-of-flight measurements."
    },
    {
        "anchor": "Pairing in Asymmetric Many-Fermion Systems: Functional Renormalisation\n  Group Approach: Functional renormalisation group approach is applied to a imbalanced many-\nfermion system with a short-range attractive force. Composite boson field is\nintroduced to describe the pairing between different flavour fermions. A set of\napproximate flow equations for the effective couplings is derived and solved.\nWe identify the critical values of mass and particle number density mismatch\nwhen the system undergoes a phase transition to a normal state and determine\nthe phase diagram both at unitary regime and nearby.",
        "positive": "Optomechanical atom-cavity interaction in the sub-recoil regime: We study the optomechanical interaction of a Bose-Einstein condensate with a\nsingle longitudinal mode of an ultra-high finesse standing wave optical\nresonator. As a unique feature the resonator combines three extreme regimes,\npreviously not realized together, i.e., strong cooperative coupling, cavity\ndominated scattering with a Purcell factor far above unity, and sub-recoil\nresolution provided by a cavity damping rate smaller than four times the single\nphoton recoil frequency. We present experimental observations in good agreement\nwith a two-mode model predicting highly non-linear dynamics with signatures as\nbistability, hysteresis, persistent oscillations, and superradiant\nback-scattering instabilities."
    },
    {
        "anchor": "On the interaction constant measurement of polarized fermions via sound\n  wave spectra obtained from hydrodynamics with the pressure evolution equation: Usually, hydrodynamic equations are restricted by the continuity and Euler\nequations. However, the account of the higher moments of the distribution\nfunction gives better description of the kinetic properties. Therefore, the\npressure tensor evolution equation (PTEE) is derived for spin polarized\ndegenerate fermions. Moreover, it is found that the pressure tensor enters the\ninteraction term generalizing the p-wave interaction in the Euler equation.\nHence, the PTEE allows to give a more accurate description of the interaction\nin Euler equation. Next, the interaction is calculated for the PTEE. The\ndeveloped model is applied to the small amplitude bulk collective excitations\nin homogeneous and trapped fermions in order to suggest the methods of\nexperimental measurement of the interaction constant of polarized fermions. It\nis demonstrated that the anisotropy in the momentum space revealing in the\ndifference of the pressures in the anisotropy direction and the perpendicular\ndirections leads to a method of detection of the interaction constant.",
        "positive": "Four-Dimensional Quantum Hall Effect with Ultracold Atoms: We propose a realistic scheme to detect the 4D quantum Hall effect using\nultracold atoms. Based on contemporary technology, motion along a synthetic\nfourth dimension can be accomplished through controlled transitions between\ninternal states of atoms arranged in a 3D optical lattice. From a\nsemi-classical analysis, we identify the linear and non-linear quantized\ncurrent responses of our 4D model, relating these to the topology of the Bloch\nbands. We then propose experimental protocols, based on current or\ncenter-of-mass-drift measurements, to extract the topological 2nd Chern number.\nOur proposal sets the stage for the exploration of novel topological phases in\nhigher dimensions."
    },
    {
        "anchor": "Structure functions of many-boson system with regard for direct three-\n  and four-particle correlations: On the basis of the expression for the density matrix of interacting Bose\nparticles in the coordinate representation with regard for the direct three-\nand four-particle correlations [I.O.\\,\\,Vakarchuk and O.I.\\,\\,Hryhorchak,\nJ.\\,\\,Phys.\\,\\,Stud.\\,\\,\\textbf{3}, 3005 (2009)], the two-, three-, and\nfour-particle structure factors of liquid $^{4}$He in a wide temperature\ninterval were calculated in the approximation \"one sum over the wave\nvector\".\\,\\,In the low-temperature limit, the expression obtained for the\ntwo-particle structure factor transforms into the well-known one.\\,\\,In the\nhigh-temperature limit, the expressions for the two-, three-, and four-particle\nstructure factors are reduced to those for the ideal Bose gas.\\,\\,The results\nobtained can be applied to calculations of the thermodynamic functions of\nliquid $^{4}$He and to the determination of the temperature dependence of the\nfirst-sound velocity in a many-boson system.",
        "positive": "Discontinuities in the First and Second Sound Velocities at the\n  Berezinskii-Kosterlitz-Thouless Transition: We calculate the temperature dependence of the first and second sound\nvelocities in the superfluid phase of a 2D dilute Bose gas by solving Landau's\ntwo fluid hydrodynamic equations. We predict the occurrence of a significant\ndiscontinuity in both velocities at the critical temperature, as a consequence\nof the jump of the superfluid density characterizing the\nBerezinskii-Kosterlitz-Thouless transition. The key role of the thermal\nexpansion coefficient is discussed. We find that second sound in this dilute\nBose gas can be easily excited through a density perturbation, thereby, making\nthe perspective of the measurement of the superfluid density particularly\nfavorable."
    },
    {
        "anchor": "Two-photon nonlinear spectroscopy of periodically trapped ultracold\n  atoms in a cavity: We study the transmission spectra of a Bose Einstein condensate confined in\nan optical lattice interacting with two modes of a cavity via nonlinear\ntwo-photon transition. In particular we show that a nonlinear two-photon\ninteraction between the superfluid (SF) phase and the Mott insulating (MI)\nphase of a Bose-Einstein condensate (BEC) and the cavity field show\nqualitatively different transmission spectra compared to the one-photon\ninteraction. We found that when the BEC is in the Mott state, the usual normal\nmode splitting present in the one-photon transition is missing in the\ntwo-photon interaction. When the BEC is in the superfluid state, the\ntransmission spectra shows the usual multiple lorentzian structure. However the\nseparation between the lorentzians for the two-photon case is much larger than\nthat for the one-photon case. This study could form the basis for\nnon-destructive high resolution Rydberg spectroscopy of ultracold atoms or\ntwo-photon spectroscopy of a gas of ultracold atomic hydrogen.",
        "positive": "Exact Numerical Results on the Ground State of Strongly Interacting\n  Fermi Gases in Two Dimensions: Exact calculations are performed on the two-dimensional strongly interacting,\nunpolarized, uniform Fermi gas with a zero-range attractive interaction. Two\nauxiliary-field approaches are employed which accelerate the sampling of\nimaginary-time paths using BCS trial wave functions and a force bias technique.\nTheir combination enables calculations on large enough lattices to reliably\ncompute ground-state properties in the thermodynamic limit. A new equation of\nstate is obtained, with a parametrization provided, which can serve as a\nbenchmark and allow accurate comparisons with experiments. The pressure,\ncontact parameter, and condensate fraction are determined systematically\nvs.~$k_F a$. The momentum distribution, pairing correlation, and the structure\nof the pair wave function are computed. The use of force bias to accelerate the\nMetropolis sampling of auxiliary-fields in determinantal approaches is\ndiscussed."
    },
    {
        "anchor": "Patterned Supersolids in Dipolar Bose Systems: We study by means of first principle Quantum Monte Carlo simulations the\nground state phase diagram of a system of dipolar bosons with aligned dipole\nmoments, and with the inclusion of a two-body repulsive potential of varying\nrange. The system is shown to display a supersolid phase in a relatively broad\nregion of the phase diagram, featuring different crystalline patterns depending\non the density and on the range of the repulsive part of the interaction\n(scattering length). The supersolid phase is sandwiched between a classical\ncrystal of parallel filaments and a homogeneous superfluid phase. We show that\na \"roton\" minimum appears in the elementary excitation spectrum of the\nsuperfluid as the system approaches crystallization.",
        "positive": "Spectroscopic probes of isolated nonequilibrium quantum matter: Quantum\n  quenches, Floquet states, and distribution functions: We investigate radio-frequency (rf) spectroscopy, metal-to-superconductor\ntunneling, and ARPES as probes of isolated out-of-equilibrium quantum systems,\nand examine the crucial role played by the nonequilibrium distribution\nfunction. As an example, we focus on the induced topological time-periodic\n(Floquet) phase in a 2D $p+ip$ superfluid, following an instantaneous quench of\nthe coupling strength. The post-quench Cooper pairs occupy a linear combination\nof \"ground\" and \"excited\" Floquet states, with coefficients determined by the\ndistribution function. While the Floquet bandstructure exhibits a single\navoided crossing relative to the equilibrium case, the distribution function\nshows a population inversion of the Floquet bands at low energies. For a\nrealization in ultracold atoms, these two features compensate, producing a bulk\naverage rf signal that is well-captured by a quasi-equilibrium approximation.\nIn particular, the rf spectrum shows a robust gap. The single crossing occurs\nbecause the quench-induced Floquet phase belongs to a particular class of\nsoliton dynamics for the BCS equation. The population inversion is a\nconsequence of this, and ensures the conservation of the pseudospin winding\nnumber. As a comparison, we compute the rf signal when only the lower Floquet\nband is occupied; in this case, the gap disappears for strong quenches. The\ntunneling signal in a solid state realization is ignorant of the distribution\nfunction, and can show wildly different behaviors. We also examine rf,\ntunneling, and ARPES for weak quenches, such that the resulting topological\nsteady-state is characterized by a constant nonequilibrium order parameter. In\na system with a boundary, tunneling reveals the Majorana edge states. However,\nthe local rf signal due to the edge states is suppressed by a factor of the\ninverse system size, and is spatially deconfined throughout the bulk of the\nsample."
    },
    {
        "anchor": "Coexistence of pairing gaps in three-component Fermi gases: We study a three-component superfluid Fermi gas in a spherically symmetric\nharmonic trap using the Bogoliubov-deGennes method. We predict a coexistence\nphase in which two pairing field order parameters are simultaneously nonzero,\nin stark contrast to studies performed for trapped gases using local density\napproximation. We also discuss the role of atom number conservation in the\ncontext of a homogeneous system.",
        "positive": "Rydberg-dressing of atoms in optical lattices: We study atoms in optical lattices whose electronic ground state is\noff-resonantly coupled to a highly excited state with strong binary\ninteractions. We present a time-dependent treatment of the resulting quantum\ndynamics, which -- contrary to recent predictions [Phys. Rev. Lett. 110, 213005\n(2013)] -- proves that the strong repulsion between the weakly admixed Rydberg\nstates does not lead to atomic trap-loss. This finding provides an important\nbasis for creating and manipulating coherent long-range interactions in optical\nlattice experiments."
    },
    {
        "anchor": "Quantum Phases of Two-Component Bosons with Spin-Orbit Coupling in\n  Optical Lattices: Ultracold bosons in optical lattices are one of the few systems where bosonic\nmatter is known to exhibit strong correlations. Here we push the frontier of\nour understanding of interacting bosons in optical lattices by adding synthetic\nspin-orbit coupling, and show that new kinds of density- and chiral-orders\ndevelop. The competition between the optical lattice period and the spin-orbit\ncoupling length -- which can be made comparable in experiments -- along with\nthe spin hybridization induced by a transverse field (i.e., Rabi coupling) and\ninterparticle interactions create a rich variety of quantum phases including\nuniform, non-uniform and phase-separated superfluids, as well as Mott\ninsulators. The spontaneous symmetry breaking phenomena at the transitions\nbetween them are explained by a two-order-parameter Ginzburg-Landau model with\nmultiparticle umklapp processes. Finally, in order to characterize each phase,\nwe calculated their experimentally measurable crystal momentum distributions.",
        "positive": "Cooling in strongly correlated optical lattices: prospects and\n  challenges: Optical lattices have emerged as ideal simulators for Hubbard models of\nstrongly correlated materials, such as the high-temperature superconducting\ncuprates. In optical lattice experiments, microscopic parameters such as the\ninteraction strength between particles are well known and easily tunable.\nUnfortunately, this benefit of using optical lattices to study Hubbard models\ncome with one clear disadvantage: the energy scales in atomic systems are\ntypically nanoKelvin compared with Kelvin in solids, with a correspondingly\nminiscule temperature scale required to observe exotic phases such as d-wave\nsuperconductivity. The ultra-low temperatures necessary to reach the regime in\nwhich optical lattice simulation can have an impact-the domain in which our\ntheoretical understanding fails-have been a barrier to progress in this field.\nTo move forward, a concerted effort to develop new techniques for cooling and,\nby extension, techniques to measure even lower temperatures. This article will\nbe devoted to discussing the concepts of cooling and thermometry, fundamental\nsources of heat in optical lattice experiments, and a review of proposed and\nimplemented thermometry and cooling techniques."
    },
    {
        "anchor": "Stability and structure of an anisotropically trapped dipolar\n  Bose-Einstein condensate: angular and linear rotons: We study theoretically Bose-Einstein condensates with polarized dipolar\ninteractions in anisotropic traps. We map the parameter space by varying the\ntrap frequencies and dipolar interaction strengths and find an irregular-shaped\nregion of parameter space in which density-oscillating condensate states occur,\nwith maximum density away from the trap center. These density-oscillating\nstates may be biconcave (red-blood-cell-shaped), or have two or four peaks. For\nall trap frequencies, the condensate becomes unstable to collapse for\nsufficiently large dipole interaction strength. The collapse coincides with the\nsoftening of an elementary excitation. When the condensate mode is\ndensity-oscillating, the character of the softening excitation is related to\nthe structure of the condensate. We classify these excitations by linear and\nangular characteristics. We also find excited solutions to the Gross-Pitaevskii\nequation, which are always unstable.",
        "positive": "Gas-to-soliton transition of attractive bosons on a spherical surface: We investigate the ground state properties of $N$ bosons with attractive\nzero-range interactions characterized by the scattering length $a>0$ and\nconfined to the surface of a sphere of radius $R$. We present the analytic\nsolution of the problem for $N=2$, mean-field analysis for $N\\rightarrow\n\\infty$, and exact diffusion Monte-Carlo results for intermediate $N$. For\nfinite $N$ we observe a smooth crossover from the uniform state in the limit\n$a/R\\gg 1$ (weak attraction) to a localized state at small $a/R$ (strong\nattraction). With increasing $N$ this crossover narrows down to a discontinuous\ntransition from the uniform state to a soliton of size $\\sim R/\\sqrt{N}$. The\ntwo states are separated by an energy barrier, tunneling under which is\nexponentially suppressed at large $N$. The system behavior is marked by a\npeculiar competition between space-curvature effects and beyond-mean-field\nterms, both breaking the scaling invariance of a two-dimensional mean-field\ntheory."
    },
    {
        "anchor": "Concavity of the collective excitation branch of a Fermi gas in the\n  BEC-BCS crossover: We study the concavity of the dispersion relation $q\\mapsto\n\\omega\\_{\\mathbf{q}}$ of the bosonic excitations of a three-dimensional\nspin-$1/2$ Fermi gas in the Random Phase Approximation (RPA). In the limit of\nsmall wave numbers $q$ we obtain analytically the spectrum up to order $5$ in\n$q$. In the neighborhood of $q=0$, a change in concavity between the convex BEC\nlimit and the concave BCS limit takes place at $\\Delta/\\mu\\simeq0.869$\n[$1/(k\\_F a)\\simeq-0.144$], where $a$ is the scattering length between opposite\nspin fermions, $k\\_F$ is the Fermi wave number and $\\Delta$ the gap according\nto BCS theory, and $\\mu$ is the chemical potential. At that point the branch is\nconcave due to a negative fifth-order term. Our results are supplemented by a\nnumerical study which shows the evolution of the border between the zone of the\n$(q,\\Delta)$ plane where $q\\mapsto \\omega\\_{\\mathbf{q}}$ is concave and the\nzone where it is convex.",
        "positive": "Two dimensional bright solitons in dipolar Bose-Einstein condensates\n  with tilted dipoles: The effect of dipolar orientation with respect to the soliton plane on the\nphysics of two-dimensional bright solitons in dipolar Bose-Einstein condensates\nis discussed. Previous studies on such a soliton involved dipoles either\nperpendicular or parallel to the condensate-plane. The tilting angle\nconstitutes an additional tuning parameter, which help us to control the\nin-plane anisotropy of the soliton as well as provides access to previously\ndisregarded regimes of interaction parameters for soliton stability. In\naddition, it can be used to drive the condensate into phonon instability\nwithout changing its interaction parameters or trap geometry. The\nphonon-instability in a homogeneous 2D condensate of tilted dipoles always\nfeatures a transient stripe pattern, which eventually breaks into a metastable\nsoliton gas. Finally, we demonstrate how a dipolar BEC in a shallow trap can\neventually be turned into a self-trapped matter wave by an adiabatic approach,\ninvolving the tuning of tilting angle."
    },
    {
        "anchor": "Doublon dynamics in the extended Fermi Hubbard model: Two fermions occupying the same site of a lattice model with strongly\nrepulsive Hubbard-type interaction U form a doublon, a long-living excitation\nthe decay of which is suppressed because of energy conservation. By means of an\nexact-diagonalization approach based on the Krylov-space technique, we study\nthe dynamics of a single doublon, of two doublons, and of a doublon in the\npresence of two additional fermions prepared locally in the initial state of\nthe extended Hubbard model. The time dependence of the expectation value of the\ndouble occupancy at the different sites of a large one-dimensional lattice is\nanalyzed by perturbative arguments. In this way the spatiotemporal evolution of\nthe doublon can be understood. The initial decay takes place on a short time\nscale 1/U, and the long-time average of the decayed fraction of the total\ndouble occupancy scales as 1/U^2 . We demonstrate how the dynamics of a doublon\nin the initial state is related to the spectrum of two-fermion excitations\nobtained from linear-response theory, we work out the difference between\ndoublons composed of fermions vs doublons composed of bosons, and we show that\ndespite the increase of phase space for inelastic decay processes, the\nstability of a doublon is enhanced by the presence of additional fermions on an\nintermediate time scale.",
        "positive": "Impenetrable SU(N) fermions in one-dimensional lattices: We study SU(N) fermions in the limit of infinite on-site repulsion between\nall species. We focus on states in which every pair of consecutive fermions\ncarries a different spin flavor. Since the particle order cannot be changed\n(because of the infinite on-site repulsion) and contiguous fermions have a\ndifferent spin flavor, we refer to the corresponding constrained model as the\nmodel of distinguishable quantum particles. We introduce an exact numerical\nmethod to calculate equilibrium one-body correlations of distinguishable\nquantum particles based on a mapping onto noninteracting spinless fermions. In\ncontrast to most many-body systems in one dimension, which usually exhibit\neither power-law or exponential decay of off-diagonal one-body correlations\nwith distance, distinguishable quantum particles exhibit a Gaussian decay of\none-body correlations in the ground state, while finite-temperature\ncorrelations are well described by stretched exponential decay."
    },
    {
        "anchor": "Complex and real unconventional Bose-Einstein condensations in high\n  orbital bands: We perform the theoretical study on the unconventional Bose-Einstein\ncondensations (UBEC) in the high bands of optical lattices observed by\nHemmerich's group. These exotic states are characterized by complex-valued\ncondensate wavefunctions with nodal points, or real-valued ones with nodal\nlines, thus are beyond the {\\it \"no-node\"} paradigm of the conventional BECs. A\nquantum phase transition is driven by the competition between the single\nparticle band and interaction energies. The complex UBECs spontaneously break\ntime-reversal symmetry, exhibiting a vortex-antivortex lattice structure.",
        "positive": "Localization of matter waves in lattice systems with moving disorder: We study the localization phenomena in a one-dimensional lattice system with\na uniformly moving disordered potential. At a low moving velocity, we find a\nsliding localized phase in which the initially localized matter wave\nadiabatically follows the moving potential without diffusion, thus resulting in\nan initial state memory in the many-body dynamics. Such an intriguing localized\nphase distinguishes itself from the standard Anderson localization in two\naspects: it is not robust against interaction, but persists in the presence of\nslowly varying perturbations. Such a sliding localized phase can be understood\nas a consequence of interference between the wavepacket paths under moving\nquasi-periodic potentials with various periods that are incommensurate with the\nlattice constant. The experimental realization and detection were also\ndiscussed.."
    },
    {
        "anchor": "Fractional quantum anomalous Hall phase for Raman superarray of Rydberg\n  atoms: Rydberg atom arrays offer promising platforms for quantum simulation of\ncorrelated quantum matter and raise great interests. This work proposes a novel\nstripe-lattice model with Raman superarray of Rydberg atoms to realize bosonic\nfractional quantum anomalous Hall (FQAH) phase. Two types of Rydberg states,\narranged in a supperarray configuration and with Raman-assisted dipole-exchange\ncouplings, are implemented to realize a minimal QAH model for hard-core bosons\npopulated into a topological flat band with large bulk gap under proper tunable\nexperimental condition. With this the bosonic FQAH phase can be further\nachieved and probed feasibly. In particular, a novel quench protocol is\nproposed to probe the fractionalized excitations by measuring the correlated\nquench dynamics featured by fractional charge tunneling between bulk and chiral\nedge modes in the open boundary.",
        "positive": "Quantum Many-Body Physics with Ultracold Polar Molecules: Nanostructured\n  Potential Barriers and Interactions: We design dipolar quantum many-body Hamiltonians that will facilitate the\nrealization of exotic quantum phases under current experimental conditions\nachieved for polar molecules. The main idea is to modulate both single-body\npotential barriers and two-body dipolar interactions on a spatial scale of tens\nof nanometers to strongly enhance energy scales and, therefore, relax\ntemperature requirements for observing new quantum phases of engineered\nmany-body systems. We consider and compare two approaches. In the first,\nnanoscale barriers are generated with standing wave optical light fields\nexploiting optical nonlinearities. In the second, static electric field\ngradients in combination with microwave dressing are used to write\nnanostructured spatial patterns on the induced electric dipole moments, and\nthus dipolar interactions. We study the formation of inter-layer and interface\nbound states of molecules in these configurations, and provide detailed\nestimates for binding energies and expected losses for present experimental\nsetups."
    },
    {
        "anchor": "Finding zeros of the Riemann zeta function by periodic driving of cold\n  atoms: The Riemann hypothesis, which states that the non-trivial zeros of the\nRiemann zeta function all lie on a certain line in the complex plane, is one of\nthe most important unresolved problems in mathematics. Inspired by the\nP\\'olya-Hilbert conjecture, we propose a new approach to finding a physical\nsystem to study the Riemann zeros, which in contrast to previous examples, is\nbased on applying a time-periodic driving field. This driving allows us to\nmould the quasienergies of the system (the analogue of the eigenenergies in the\nabsence of driving), so that they are directly governed by the zeta function.\nWe further show by numerical simulations that this allows the Riemann zeros to\nbe measured in currently accessible cold atom experiments.",
        "positive": "Cat states in a driven superfluid: role of signal shape and switching\n  protocol: We investigate the behavior of a one-dimensional Bose-Hubbard model whose\nkinetic energy is made to oscillate with zero time-average. The effective\ndynamics is governed by an atypical many-body Hamiltonian where only even-order\nhopping processes are allowed. At a critical value of the driving, the system\npasses from a Mott insulator to a superfluid formed by a cat-like superposition\nof two quasi-condensates with opposite non-zero momenta. We analyze the\nrobustness of this unconventional ground state against variations of a number\nof system parameters. In particular we study the effect of the waveform and the\nswitching protocol of the driving signal. Knowledge of the sensitivity of the\nsystem to these parameter variations allows us to gauge the robustness of the\nexotic physical behavior."
    },
    {
        "anchor": "The Massive Goldstone (Higgs) mode in two-dimensional ultracold atomic\n  lattice systems: We discuss how to reveal the massive Goldstone mode, often referred to as the\nHiggs amplitude mode, near the Superfluid-to-Insulator quantum critical point\n(QCP) in a system of two-dimensional ultracold bosonic atoms in optical\nlattices. The spectral function of the amplitude response is obtained by\nanalytic continuation of the kinetic energy correlation function calculated by\nMonte Carlo methods. Our results enable a direct comparison with the recent\nexperiment [M. Endres, T. Fukuhara, D. Pekker, M. Cheneau, P. Schau{\\ss}, C.\nGross, E. Demler, S. Kuhr, and I. Bloch, Nature 487, 454-458 (2012)], and\ndemonstrate a good agreement for temperature shifts induced by lattice\nmodulation. Based on our numerical analysis, we formulate the necessary\nconditions in terms of homogeneity, detuning from the QCP and temperature in\norder to reveal the massive Goldstone resonance peak in spectral functions\nexperimentally. We also propose to apply a local modulation at the trap center\nto overcome the inhomogeneous broadening caused by the parabolic trap\nconfinement.",
        "positive": "Quantum liquid droplets in a mixture of Bose-Einstein condensates: Quantum droplets are small clusters of atoms self-bound by the balance of\nattractive and repulsive forces. Here we report on the observation of a novel\ntype of droplets, solely stabilized by contact interactions in a mixture of two\nBose-Einstein condensates. We demonstrate that they are several orders of\nmagnitude more dilute than liquid helium by directly measuring their size and\ndensity via in situ imaging. Moreover, by comparison to a single-component\ncondensate, we show that quantum many-body effects stabilize them against\ncollapse. We observe that droplets require a minimum atom number to be stable.\nBelow, quantum pressure drives a liquid-to-gas transition that we map out as a\nfunction of interaction strength. These ultra-dilute isotropic liquids remain\nweakly interacting and constitute an ideal platform to benchmark quantum\nmany-body theories."
    },
    {
        "anchor": "Sudden jumps and plateaus in the quench dynamics of a Bloch state: We take a one-dimensional tight binding chain with periodic boundary\ncondition and put a particle in an arbitrary Bloch state, then quench it by\nsuddenly changing the potential of an arbitrary site. In the ensuing time\nevolution, the probability density of the wave function at an arbitrary site\n\\emph{jumps indefinitely between plateaus}. This phenomenon adds to a former\none in which the survival probability of the particle in the initial Bloch\nstate shows \\emph{cusps} periodically, which was found in the same scenario\n[Zhang J. M. and Yang H.-T., EPL, \\textbf{114} (2016) 60001]. The plateaus\nsupport the scattering wave picture of the quench dynamics of the Bloch state.\nUnderlying the cusps and jumps is the exactly solvable, nonanalytic dynamics of\na Luttinger-like model, based on which, the locations of the jumps and the\nheights of the plateaus are accurately predicted.",
        "positive": "Non-local emergent hydrodynamics in a long-range quantum spin system: Generic short-range interacting quantum systems with a conserved quantity\nexhibit universal diffusive transport at late times. We employ non-equilibrium\nquantum field theory and semi-classical phase-space simulations to show how\nthis universality is replaced by a more general transport process in a\nlong-range XY spin chain at infinite temperature with couplings decaying\nalgebraically with distance as $r^{-\\alpha}$. While diffusion is recovered for\n$\\alpha>1.5$, longer-ranged couplings with $0.5<\\alpha\\leq 1.5 $ give rise to\neffective classical L\\'evy flights; a random walk with step sizes drawn from a\ndistribution with algebraic tails. We find that the space-time dependent spin\ndensity profiles are self-similar, with scaling functions given by the stable\nsymmetric distributions. As a consequence, for $0.5<\\alpha\\leq1.5$\nautocorrelations show hydrodynamic tails decaying in time as\n$t^{-1/(2\\alpha-1)}$ and linear-response theory breaks down. Our findings can\nbe readily verified with current trapped ion experiments."
    },
    {
        "anchor": "Imaging the Holon String by Quantum Interference: It has been a long sought goal of Quantum Simulation to find answers to long\nstanding questions in condensed matter physics. A famous example is the ground\nand the excitations of 2D Hubbard model with strong repulsion below half\nfilling. The system is a doped antiferromagnet. It is of great interests\nbecause of its possible relation to high Tc superconductor. Theoretically, the\nfermion excitations of this model are believed to split up into holons and\nspinions, and a moving holon is believed to leave behind it a string of \"wrong\"\nspins that mismatch with the antiferromagnet background. Here, we show that the\nproperties of the ground state wavefunction and the holon excitation of the 2D\nHubbard model can be revealed in unprecedented detail using the technique of\nquantum interference in atomic physics. This is achieved by using quantum\ninterference to measure the Marshall sign of the doped antiferromanget. The\nregion of wrong Marshall sign directly reflects the spatial extent of\nfluctuating string attached to the holon.",
        "positive": "Open Fermi-Hubbard model: Landauer's vs. master equation approaches: We introduce a simple model for the quantum transport of Fermi particles\nbetween two contacts connected by a lead. It generalizes the Landauer formalizm\nby explicitly taken into account the relaxation processes in the contacts. We\ncalculate the contact resistance and non-equilibrium quasi-momentum\ndistribution of the carriers in the lead and show that they strongly depend on\nthe rate of relaxation processes."
    },
    {
        "anchor": "Atom-dimer scattering amplitude for fermionic mixtures with different\n  masses: s-wave and p-wave contributions: We study near a Feshbach resonance, as a function of the mass ratio, the\nfermion-dimer scattering amplitude in fermionic mixtures of two fermion\nspecies. When masses are equal the physical situation is known to be quite\nsimple. We show that, when the mass ratio is increased, the situation becomes\nmuch more complex. For the s-wave contribution we obtain an analytical solution\nin the asymptotic limit of very large mass ratio. In this regime the s-wave\nscattering amplitude displays a large number of zeros, essentially linked to\nthe known large value of the fermion-dimer scattering length in this regime. We\nfind by an exact numerical calculation that a zero is still present for a mass\nratio of 15. For the p-wave contribution we make our study below the mass ratio\nof 8.17, where a fermion-dimer bound state appears. We find that a strong\np-wave resonance is present at low energy, due to a virtual bound state, in the\nfermion-dimer system, which is a forerunner of the real bound state. This\nresonance becomes prominent in the mass ratio range around the one\ncorresponding to the $^{40}$K - $^6$Li mixtures, much studied experimentally.\nThis resonance should affect a number of physical properties. These include the\nequation of state of unbalanced mixtures at very low temperature but also the\nequation of state of balanced mixtures at moderate or high temperature. The\nfrequency and the damping of collective modes should also provide a convenient\nway to evidence this resonance. Finally it should be possible to modify the\neffective mass of one of the fermionic species by making use of an optical\nlattice. This would allow to study the strong dependence of the resonance as a\nfunction of the mass ratio of the two fermionic elements. In particular one\ncould check if the virtual bound state is relevant for the instabilities of\nthese mixtures.",
        "positive": "Isolated quantum heat engine: We present a theoretical and numerical analysis of a quantum system that is\ncapable of functioning as a heat engine. This system could be realized\nexperimentally using cold bosonic atoms confined to a double well potential\nthat is created by splitting a harmonic trap with a focused laser. The system\nshows thermalization, and can model a reversible heat engine cycle. This is the\nfirst demonstration of the operation of a heat engine with a finite quantum\nheat bath."
    },
    {
        "anchor": "Many-body state and dynamic behaviour of the pair-correlation function\n  of a small Bose-Einstein condensate confined in a ring potential: We investigate the many-body state and the static and the dynamic behaviour\nof the pair-correlation function of a Bose-Einstein condensate with a finite\natom number, which is confined in a quasi-one-dimensional toroidal/annular\npotential, both for repulsive, and for attractive interactions. We link the\ndynamic pair-correlation function that we evaluate with the problem of quantum\ntime crystals. For weak repulsive interatomic interactions and a finite number\nof atoms the pair-correlation function shows a periodic temporal behaviour,\nwhich disappears in the limit of a large atom number, in agreement with general\narguments. Finally we provide some insight into older results of attractive\ninteractions, where the time-crystalline behaviour exists only in the limit of\na large atom number.",
        "positive": "Ultracold bosons in the vicinity of a narrow resonance: shallow dimer\n  and recombination: The different resonant regimes that can be achieved by using a magnetic\nFeshbach resonance are analyzed with a separable two-channel model. Emphasis is\nput on the case of narrow resonances in a region of intermediate detuning where\na shallow dimer exists and an approximate law including the background\nscattering length for the three-body recombination rate is derived."
    },
    {
        "anchor": "Symmetry breaking and phase transitions in Bose-Einstein condensates\n  with spin-orbital-angular-momentum coupling: Theoretical study is presented for a spinor Bose-Einstein condensate, whose\ntwo components are coupled by copropagating Raman beams with different orbital\nangular momenta. The investigation is focused on the behavior of the ground\nstate of this condensate, depending on the atom-light coupling strength. By\nanalyzing the ground state, we have identified a number of quantum phases,\nwhich reflect the symmetries of the effective Hamiltonian and are characterized\nby the specific structure of the wave function. In addition to the well-known\nstripe, polarized and zero-momentum phases, our results show that the system\ncan support phases, whose wave function contains a complex vortex molecule.\nSuch molecule plays an important role in the continuous phase transitions of\nthe system. The predicted behavior of vortex-molecule phases can be examined in\ncold-atom experiments using currently existing techniques.",
        "positive": "Cavity-induced Fulde-Ferrell-Larkin-Ovchinnikov superfluids of ultracold\n  Fermi gases: Motivated by recent experimental advances in ultracold atomic gases placed in\ncavities, we study the influence of the atom-cavity coupling on the Fermi gases\ntrapped in optical lattices. By adiabatic elimination of the cavity photon\nfield, the atom-cavity coupling gives rise to effective long-range\ninteractions. It results in a variety of two-body scattering processes, during\nwhich the atomic pairs can acquire an additional center-of-mass momentum. This\nreveals the possibility of Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superfluids\nin which the atomic pairing momentum is nonzero. By inspecting the phase\ndiagram at the mean-field level, we confirm that the FFLO superfluid phase\ncoexists with the zero-momentum pairing, and is the ground state that hosts the\nlowest energy. Furthermore, the order parameter characterizing the\nnonzero-momentum pairing does not vanish as long as the cavity-induced\ninteraction is present."
    },
    {
        "anchor": "Detecting many-body entanglements in noninteracting ultracold atomic\n  fermi gases: We explore the possibility of detecting many-body entanglement using\ntime-of-flight (TOF) momentum correlations in ultracold atomic fermi gases. In\nanalogy to the vacuum correlations responsible for Bekenstein-Hawking black\nhole entropy, a partitioned atomic gas will exhibit particle-hole correlations\nresponsible for entanglement entropy. The signature of these momentum\ncorrelations might be detected by a sensitive TOF type experiment.",
        "positive": "Certifying the adiabatic preparation of ultracold lattice bosons in the\n  vicinity of the Mott transition: We present a joint experimental and theoretical analysis to assess the\nadiabatic experimental preparation of ultracold bosons in optical lattices\naimed at simulating the three-dimensional Bose-Hubbard model. Thermometry of\nlattice gases is realized from the superfluid to the Mott regime by combining\nthe measurement of three-dimensional momentum-space densities with ab-initio\nquantum Monte Carlo (QMC) calculations of the same quantity. The measured\ntemperatures across the superfluid-to-Mott transition are in agreement with\nisentropic lines reconstructed via QMC for the experimental parameters of\ninterest, with a conserved entropy per particle of $S/N=0.8(1) k_{B}$. In\naddition, the Fisher information associated with this thermometry method shows\nthat the latter is most accurate in the critical regime close to the Mott\ntransition, as confirmed in the experiment. These results prove that\nequilibrium states of the Bose-Hubbard model - including those in the\nquantum-critical regime above the Mott transition - can be adiabatically\nprepared in cold-atom apparatus."
    },
    {
        "anchor": "From non equilibrium quantum Brownian motion to impurity dynamics in 1D\n  quantum liquids: Impurity motion in one dimensional ultra cold quantum liquids confined in an\noptical trap has attracted much interest recently. As a step towards its full\nunderstanding, we construct a generating functional from which we derive the\nposition non equilibrium correlation function of a quantum Brownian particle\nwith general Gaussian non-factorizing initial conditions. We investigate the\nslow dynamics of a particle confined in a harmonic potential after a position\nmeasurement; the rapid relaxation of a particle trapped in a harmonic potential\nafter a quantum quench realized as a sudden change in the potential parameters;\nand the evolution of an impurity in contact with a one dimensional bosonic\nquantum gas. We argue that such an impurity-Luttinger liquid system, that has\nbeen recently realized experimentally, admits a simple modeling as quantum\nBrownian motion in a super Ohmic bath.",
        "positive": "Realization of tunnel barriers for matter waves using spatial gaps: We experimentally demonstrate the trapping of a propagating Bose-Einstein\nCondensate in a Bragg cavity produced by an attractive optical lattice with a\nsmooth envelope. As a consequence of the envelope, the band gaps become\nposition-dependent and act as mirrors of finite and velocity-dependent\nreflectivity. We directly observe both the oscillations of the wave packet\nbouncing in the cavity provided by these spatial gaps and the tunneling out for\nnarrow classes of velocity. Synchronization of different classes of velocity\ncan be achieved by proper shaping of the envelope. This technique can generate\nsingle or multiple tunnel barriers for matter waves with a tunable transmission\nprobability, equivalent to a standard barrier of submicron size."
    },
    {
        "anchor": "High-resolution imaging of Rydberg atoms in optical lattices using an\n  aspheric-lens objective in vacuum: We present a high-resolution, simple and versatile system for imaging\nultracold Rydberg atoms in optical lattices. The imaging objective is a single\naspheric lens (with a working distance of 20.6 mm and a numerical aperture (NA)\nof 0.51) placed inside the vacuum chamber. Adopting a large-working-distance\nlens leaves room for electrodes and electrostatic shields to control electric\nfields around Rydberg atoms. With this setup, we achieve an Rayleigh resolution\nof 1.10 $\\mu$m or $1.41\\lambda$ ($\\lambda=780$ nm), limited by the NA of the\naspheric lens. For systems of highly excited Rydberg states with blockade radii\ngreater than a few $\\mu$m, the resolution achieved is sufficient for studying\nmany physical processes of interest.",
        "positive": "Population imbalance in the extended Fermi-Hubbard model: We study the interplay between population imbalance in a two-component\nfermionic system and nearest-neighbor interaction using matrix product states\nmethod. Our analysis reveals the existence of a new type of\nFulde-Ferrell-Larkin-Ovchinnikov phase in the presence of competing\ninteractions. Furthermore, we find distinct evidence for the presence of hidden\norder in the system. We present an effective model to understand the emergent\noscillations in the string correlations due to the imbalance, and show how they\ncan become an efficient tool to investigate systems with imbalance."
    },
    {
        "anchor": "Loss of Conformality in Efimov Physics: The loss of conformal invariance in Efimov physics is due to the merger and\ndisappearance of an infrared and an ultraviolet fixed point of a three-body\nrenormalization group flow as the spatial dimension $d$ is varied. In the case\nof identical bosons at unitarity, it is known that there are two critical\ndimensions $d_{\\rm 1}=2.30$ and $d_{\\rm 2}=3.76$ at which there is loss of\nconformality. For $d<d_{\\rm 1}$ and $d>d_{\\rm 2}$, the beta function of the\nthree-body coupling has real roots which correspond to infrared and ultraviolet\nfixed points. The fixed points merge and disappear into the complex plane at\nthe critical dimensions $d_1$ and $d_2$. For $d_{\\rm 1}<d<d_{\\rm 2}$, the beta\nfunction has complex roots and the renormalization group flow for the\nthree-body coupling constant is a limit cycle.",
        "positive": "Incompressible Energy Spectrum from Wave Turbulence: Bose-Einstein condensates with their superfluidity property provide an\ninteresting parallel to classical fluids. Due to the Kolmogorov spectrum of\nhomogeneous turbulence the statistics of the incompressible velocity field is\nof great interest, but in superfluids obtaining quantities such as the\nstatistics of the velocity field from the macroscopic wavefunction turns out be\na complicated task; therefore, most of the work up to now has been numerical in\nnature. We made use of the Weak Wave Turbulence (WWT) theory, which provides\nthe statistics of the macroscopic wavefunction, to obtain the statistics of the\nvelocity field, which allowed us to produce a semi analytical procedure for\nextracting the incompressible energy spectrum in the WWT regime. This is done\nby introducing an auxiliary wavefunction that preserves the relevant\nstatistical and hydrodynamical properties of the condensate but with a\nhomogeneous density thus allowing for a simpler description of the velocity\nfield."
    },
    {
        "anchor": "Resonant two-site tunnelling dynamics of bosons in a tilted optical\n  superlattice: We study the non-equilibrium dynamics of a 1D Bose-Hubbard model in a\ngradient potential and a superlattice, beginning from a deep Mott insulator\nregime with an average filling of one particle per site. Studying a quench that\nis near resonance to tunnelling of the particles over two lattice sites, we\nshow how a spin model emerges consisting of two coupled Ising chains that are\ncoupled by interaction terms in a staggered geometry. We compare and contrast\nthe behavior in this case with that in a previously studied case where the\nresonant tunnelling was over a single site. Using optimized tensor network\ntechniques to calculate finite temperature behavior of the model, as well as\nfinite size scaling for the ground state, we conclude that the universality\nclass of the phase transition for the coupled chains is that of a tricritical\nIsing point. We also investigate the out-of-equilibrium dynamics after the\nquench in the vicinity of the resonance and compare dynamics with recent\nexperiments realized without the superlattice geometry. This model is directly\nrealizable in current experiments, and reflects a new general way to realize\nspin models with ultracold atoms in optical lattices.",
        "positive": "Expansion of the strongly interacting superfluid Fermi gas: symmetries\n  and self-similar regimes: We consider an expansion of the strongly interacting superfluid Fermi gas in\na vacuum, assuming absence of the trapping potential, in the so-called unitary\nregime (see, for instance, \\cite{pitaevskii2008superfluid}) when the chemical\npotential $\\mu \\propto \\hbar^2n^{2/3}/m$ where $n$ is the density of the\nBose-Einstein condensate of Cooper pairs of fermionic atoms. In low\ntemperatures, $T\\to 0$, such expansion can be described in the framework of the\nGross-Pitaevskii equation (GPE). Because of the chemical potential dependence\non the density, $\\sim n^{2/3}$, the GPE has additional symmetries, resulting in\nthe existence of the virial theorem \\cite% {vlasov1971averaged}, connecting the\nmean size of the gas cloud and its Hamiltonian. It leads asymptotically at\n$t\\to\\infty$ to the gas cloud expansion, linearly growing in time. We study\nsuch asymptotics, and reveal the perfect match between the quasi-classical\nself-similar solution and the asymptotic expansion of the non-interacting gas.\nThis match is governed by the virial theorem, derived through utilizing the\nTalanov transformation \\cite{talanov1970focusing}, which was first obtained for\nthe stationary self-focusing of light in media with a cubic nonlinearity due to\nthe Kerr effect. In the quasi-classical limit, the equations of motion coincide\nwith 3D hydrodynamics for the perfect monoatomic gas with $\\gamma=5/3$. Their\nself-similar solution describes, on the background of the gas expansion, the\nangular deformities of the gas shape in the framework of the Ermakov--Ray--Reid\ntype system."
    },
    {
        "anchor": "High-momentum tail in the Tonks-Girardeau gas under general confining\n  potentials: We prove that the ground state momentum distribution of a one-dimensional\nsystem of impenetrable bosons exhibits a $k^{-4}$ tail for any confining\npotential. We also derive an expression for easily computing the asymptotic\noccupation numbers and verify our results with an exact numerical approach.",
        "positive": "Observation of Elastic Doublon Decay in the Fermi-Hubbard Model: We investigate the decay of highly excited states of ultracold fermions in a\nthree-dimensional optical lattice. Starting from a repulsive Fermi-Hubbard\nsystem near half filling, we generate additional doubly occupied sites\n(doublons) by lattice modulation. The subsequent relaxation back to thermal\nequilibrium is monitored over time. The measured doublon lifetime covers two\norders of magnitude. In units of the tunneling time h/J it is found to depend\nexponentially on the ratio of on-site interaction energy U to kinetic energy J.\nWe argue that the dominant mechanism for the relaxation is a high order\nscattering process involving several single fermions as scattering partners. A\nmany-body calculation is carried out using diagrammatic methods, yielding good\nagreement with the data."
    },
    {
        "anchor": "Fluctuational susceptibility of ultracold bosons in the vicinity of\n  condensation: We study the behaviour of ultracold bosonic gas in the critical region above\nthe Bose-Einstein condensation in the presence of an artificial magnetic field,\n$B_\\mathrm{art}$. We show that the condensate fluctuations above the critical\ntemperature $T_c$ cause the fluctuational susceptibility, $\\chi _\\mathrm{fl}$,\nof a uniform gas to have a stronger power-law divergence than in an analogous\nsuperconducting system. Measuring such a divergence opens new ways of exploring\ncritical properties of the ultracold gas and an opportunity of an accurate\ndetermination of $T_c$. We describe a method of measuring $\\chi _\\mathrm{fl}$\nwhich requires a constant gradient in $B_\\mathrm{art}$ and suggest a way of\ncreating such a field in experiment.",
        "positive": "Electromagnetically induced transparency with Cu$_2$O excitons in the\n  presence of phonon coupling: Highly excited Rydberg states of excitons in Cu$_2$O semiconductors provide a\npromising approach to explore and control strong particle interactions in a\nsolid-state environment. A major obstacle has been the substantial absorption\nbackground that stems from exciton-phonon coupling and lies under the Rydberg\nexcitation spectrum, weakening the effects of exciton interactions. Here, we\ndemonstrate that two-photon excitation of Rydberg excitons under conditions of\nelectromagnetically induced transparency (EIT) can be used to control this\nbackground. Based on a microscopic theory that describes the known\nsingle-photon absorption spectrum, we analyze the conditions under which\ntwo-photon EIT permits separating the optical Rydberg excitation from the\nphonon-induced absorption background, and even suppressing it entirely. Our\nfindings thereby pave the way for the exploitation of Rydberg blockade with\nCu$_2$O excitons in nonlinear optics and other applications."
    },
    {
        "anchor": "Casimir forces for the ideal Bose gas in anisotropic optical lattices:\n  the effect of alternating sign upon varying dimensionality: We analyze the thermodynamic Casimir effect occurring in a gas of\nnon-interacting bosons confined by two parallel walls with a strongly\nanisotropic dispersion inherited from an underlying lattice. In the direction\nperpendicular to the confining walls the standard quadratic dispersion is\nreplaced by the term $|{\\bf p}|^{\\alpha}$ with $\\alpha \\geq 2$ treated as a\nparameter. We derive a closed, analytical expression for the Casimir force\ndepending on the dimensionality $d$ and the exponent $\\alpha$, and analyze it\nfor thermodynamic states in which the Bose-Einstein condensate is present. For\n$\\alpha\\in\\{4,6,8,\\dots\\}$ the exponent governing the decay of the Casimir\nforce with increasing distance between the walls becomes modified and the\nCasimir amplitude $\\Delta_{\\alpha}(d)$ exhibits oscillations of sign as a\nfunction of $d$. Otherwise we find that $\\Delta_{\\alpha}(d)$ features\nsingularities when viewed as a function of $d$ and $\\alpha$. Recovering the\nknown previous results for the isotropic limit $\\alpha=2$ turns out to occur\nvia a cancellation of singular terms.",
        "positive": "The bilinear-biquadratic spin-1 chain undergoing quadratic Zeeman effect: The Heisenberg model for spin-1 bosons in one dimension presents many\ndifferent quantum phases including the famous topological Haldane phase. Here\nwe study the robustness of such phases in front of a SU(2) symmetry breaking\nfield as well as the emergence of novel phases. Previous studies have analyzed\nthe effect of such uniaxial anysotropy in some restricted relevant points of\nthe phase diagram. Here we extend those studies and present the complete phase\ndiagram of the spin-1 chain with uniaxial anysotropy. To this aim, we employ\nthe density matrix renormalization group (DMRG) together with analytical\napproaches. The complete phase diagram can be realized using ultracold spinor\ngases in the Mott insulator regime under a quadratic Zeeman effect."
    },
    {
        "anchor": "Interaction of One-Dimensional Quantum Droplets with Potential Wells and\n  Barriers: We address static and dynamical properties of one-dimensional (1D) quantum\ndroplets (QDs) under the action of local potentials in the form of narrow wells\nand barriers. The QDs are governed by the 1D Gross-Pitaevskii equation\nincluding the mean-field cubic repulsive term and the beyond-mean-field\nattractive quadratic one. In the case of the well represented by the\ndelta-functional potential, three exact stable solutions are found for\nlocalized states pinned to the well. The Thomas-Fermi approximation for the\nwell and the adiabatic approximation for the collision of the QD with the\nbarrier are developed too. Collisions of incident QDs with the wells and\nbarriers are analyzed in detail by means of systematic simulations. Outcomes,\nsuch as fission of the moving QD into transmitted, reflected, and trapped\nfragments, are identified in relevant parameter planes. In particular, a\ncounter-intuitive effect of partial or full rebound of the incident QD from the\npotential well is studied in detail and qualitatively explained.",
        "positive": "Dark-bright ring solitons in Bose-Einstein condensates: We study dark-bright ring solitons in two-component Bose-Einstein\ncondensates. In the limit of large densities of the dark component, we describe\nthe soliton dynamics by means of an equation of motion for the ring radius. The\npresence of the bright, \"filling\" species is demonstrated to have a stabilizing\neffect on the ring dark soliton. Near the linear limit, we discuss the\nsymmetry-breaking bifurcations of dark-bright soliton stripes and vortex-bright\nsoliton clusters from the dark-bright ring and relate the stabilizing effect of\nfilling to changes in the bifurcation diagram. Finally, we show that\nstabilization by means of a second component is not limited to the radially\nsymmetric structures, but can also be observed in a cross-like dark-bright\nsoliton configuration."
    },
    {
        "anchor": "Continuous wave solutions in spinor Bose-Einstein condensates: We find analytic continuous wave (cw) solutions for spinor Bose-Einstein\ncondenates (BECs) in a magnetic field that are more general than those\npublished to date. For particles with spin F=1 in a homogeneous one-dimensional\ntrap, there exist cw states in which the chemical potential and wavevectors of\nthe different spin components are different from each other. We include linear\nand quadratic Zeeman splitting. Linear Zeeman splitting, if the magnetic field\nis constant and uniform, can be mathematically eliminated by a gauge\ntransformation, but quadratic Zeeman effects modify the cw solutions in a way\nsimilar to non-zero differences in the wavenumbers between the different spin\nstates. The solutions are stable fixed points within the continuous wave\nframework, and the coherent spin mixing frequencies are obtained.",
        "positive": "Dimensional crossover on multileg attractive-$U$ Hubbard ladders: We study the ground state properties of a polarized two-component Fermi gas\non multileg attractive-$U$ Hubbard ladders. Using exact diagonalization and\ndensity matrix renormalization group method simulations, we construct grand\ncanonical phase diagrams for ladder widths of up to $W=5$ and varying\nperpendicular geometries, characterizing the quasi-one-dimensional regime of\nthe dimensional crossover. We unveil a multicritical point marking the onset of\npartial polarization in those phase diagrams, a candidate regime of\nfinite-momentum pairing. We compare our findings with recent experimental and\ntheoretical studies of quasi-one-dimensional polarized Fermi gases."
    },
    {
        "anchor": "Stable-unstable transition for a Bose-Hubbard chain coupled to an\n  environment: Interactions in quantum systems may induce transitions to exotic correlated\nphases of matter which can be vulnerable to coupling to an environment. Here,\nwe study the stability of a Bose-Hubbard chain coupled to a bosonic bath at\nzero and non-zero temperature. We show that only above a critical interaction\nthe chain loses bosons and its properties are significantly affected. The\ntransition is of a different nature than the superfluid-Mott insulator\ntransition and occurs at a different critical interaction. We explain such a\nstable-unstable transition by the opening of a charge gap. The comparison of\naccurate matrix product state simulations to approximative approaches that miss\nthis transition reveals its many-body origin.",
        "positive": "Universal Five- and Six-Body Droplets Tied to an Efimov Trimer: We explore the properties of weakly bound bosonic states in the strongly\ninteracting regime. Combining a correlated-Gaussian (CG) basis set expansion\nwith a complex scaling method, we extract the energies and structural\nproperties of bosonic cluster states with $N\\le6$ for different two-body\npotentials. The identification of five- and six-body resonances attached to an\nexcited Efimov trimer provides strong support to the premise of Efimov\nuniversality in bosonic systems. Our study also reveals a rich structure of\nbosonic cluster states. Besides the lowest cluster states which behave as\nbosonic droplets, we identify cluster states weakly bound to one or two atoms\nforming effective cluster-atom \"dimers\" and cluster-atom-atom \"trimers.\" The\nexperimental signatures of these cluster states are discussed."
    },
    {
        "anchor": "Synthetic Landau levels for photons: Synthetic photonic materials are an emerging platform for exploring the\ninterface between microscopic quantum dynamics and macroscopic material\nproperties[1-5]. Photons experiencing a Lorentz force develop handedness,\nproviding opportunities to study quantum Hall physics and topological quantum\nscience[6-8]. Here we present an experimental realization of a magnetic field\nfor continuum photons. We trap optical photons in a multimode ring resonator to\nmake a two-dimensional gas of massive bosons, and then employ a non-planar\ngeometry to induce an image rotation on each round-trip[9]. This results in\nphotonic Coriolis/Lorentz and centrifugal forces and so realizes the\nFock-Darwin Hamiltonian for photons in a magnetic field and harmonic trap[10].\nUsing spatial- and energy-resolved spectroscopy, we track the resulting\nphotonic eigenstates as radial trapping is reduced, finally observing a\nphotonic Landau level at degeneracy. To circumvent the challenge of trap\ninstability at the centrifugal limit[10,11], we constrain the photons to move\non a cone. Spectroscopic probes demonstrate flat space (zero curvature) away\nfrom the cone tip. At the cone tip, we observe that spatial curvature increases\nthe local density of states, and we measure fractional state number excess\nconsistent with the Wen-Zee theory, providing an experimental test of this\ntheory of electrons in both a magnetic field and curved space[12-15]. This work\nopens the door to exploration of the interplay of geometry and topology, and in\nconjunction with Rydberg electromagnetically induced transparency, enables\nstudies of photonic fractional quantum Hall fluids[16,17] and direct detection\nof anyons[18-19].",
        "positive": "Transition from supersonic to subsonic waves in superfluid Fermi gases: We study the propagation of dispersive waves in superfluid Fermi gases in the\nBEC-BCS crossover. Unlike in other superfluid systems, where dispersive waves\nhave already been studied and observed, Fermi gases can exhibit a subsonic\ndispersion relation for which the dispersive wave pattern appears at the tail\nof the wave front. We show that this property can be used to distinguish\nbetween a subsonic and a supersonic dispersion relation at unitarity."
    },
    {
        "anchor": "Gap solitons in the spin-orbit coupled Bose-Einstein condensates: We report a diversity of stable gap solitons in a spin-orbit coupled\nBose-Einstein condensate subject to a spatially periodic Zeeman field. It is\nshown that the solitons, can be classified by the main physical symmetries they\nobey, i.e. symmetries with respect to parity (P), time (T), and internal degree\nof freedom, i.e. spin, (C) inversions. The conventional gap and gap-stripe\nsolitons are obtained in lattices with different parameters. It is shown that\nsolitons of the same type but obeying different symmetries can exist in the\nsame lattice at different spatial locations. PT and CPT symmetric solitons have\nanti-ferromagnetic structure and are characterized respectively by nonzero and\nzero total magnetizations.",
        "positive": "Cluster Mean-Field Signature of Entanglement Entropy in Bosonic\n  Superfluid-Insulator Transitions: Entanglement entropy (EE), a fundamental conception in quantum information\nfor characterizing entanglement, has been extensively employed to explore\nquantum phase transitions (QPTs). Although the conventional single-site\nmean-field (MF) approach successfully predicts the emergence of QPTs, it fails\nto include any entanglement. Here, for the first time, in the framework of a\ncluster MF treatment, we extract the signature of EE in the bosonic\nsuperfluid-insulator transitions. We consider a trimerized Kagome lattice of\ninteracting bosons, in which each trimer is treated as a cluster, and implement\nthe cluster MF treatment by decoupling all inter-trimer hopping. In addition to\nsuperfluid and integer insulator phases, we find that fractional insulator\nphases appear when the tunneling is dominated by the intra-trimer part. To\nquantify the residual bipartite entanglement in a cluster, we calculate the\nsecond-order Renyi entropy, which can be experimentally measured by quantum\ninterference of many-body twins. The second-order Renyi entropy itself is\ncontinuous everywhere, however, the continuousness of its first-order\nderivative breaks down at the phase boundary. This means that the bosonic\nsuperfluid-insulator transitions can still be efficiently captured by the\nresidual entanglement in our cluster MF treatment. Besides to the bosonic\nsuperfluid-insulator transitions, our cluster MF treatment may also be used to\ncapture the signature of EE for other QPTs in quantum superlattice models."
    },
    {
        "anchor": "Spatial pattern formation and polarization dynamics of a nonequilibrium\n  spinor polariton condensate: Quasiparticles in semiconductors -- such as microcavity polaritons -- can\nform condensates in which the steady-state density profile is set by the\nbalance of pumping and decay. By taking account of the polarization degree of\nfreedom for a polariton condensate, and considering the effects of an applied\nmagnetic field, we theoretically discuss the interplay between polarization\ndynamics, and the spatial structure of the pumped decaying condensate. If\nspatial structure is neglected, this dynamics has attractors that are linearly\npolarized condensates (fixed points), and desynchronized solutions (limit\ncycles), with a range of bistability. Considering spatial fluctuations about\nthe fixed point, the collective spin modes can either be diffusive, linearly\ndispersing, or gapped. Including spatial structure, interactions between the\nspin components can influence the dynamics of vortices; produce stable\ncomplexes of vortices and rarefaction pulses with both co- and counter-rotating\npolarizations; and increase the range of possible limit cycles for the\npolarization dynamics, with different attractors displaying different spatial\nstructures.",
        "positive": "Quantum heat engine based on a spin-orbit and Zeeman-coupled\n  Bose-Einstein condensate: We explore the potential of a spin-orbit coupled Bose-Einstein condensate for\nthermodynamic cycles. For this purpose we propose a quantum heat engine based\non a condensate with spin-orbit and Zeeman coupling as a working medium. The\ncooling and heating are simulated by contacts of the condensate with an\nexternal magnetized media and demagnetized media. We examine the condensate\nground state energy and its dependence on the strength of the synthetic\nspin-orbit and Zeeman couplings and interatomic interaction. Then we study the\nefficiency of the proposed engine. The cycle has a critical value of spin-orbit\ncoupling related to the engine maximum efficiency."
    },
    {
        "anchor": "Anomalous Diffusion in a Dynamical Optical Lattice: Motivated by experimental progress in strongly coupled atom-photon systems in\noptical cavities, we study theoretically the quantum dynamics of atoms coupled\nto a one-dimensional dynamical optical lattice. The dynamical lattice is chosen\nto have a period that is incommensurate with that of an underlying static\nlattice, leading to a dynamical version of the Aubry-Andr\\'e model which can\ncause localization of single-particle wavefunctions. We show that atomic\nwavepackets in this dynamical lattice generically spread via anomalous\ndiffusion, which can be tuned between super-diffusive and sub-diffusive\nregimes. This anomalous diffusion arises from an interplay between quantum\nlocalization and quantum fluctuations of the cavity field.",
        "positive": "Localization of a dipolar Bose-Einstein condensate in a bichromatic\n  optical lattice: By numerical simulation and variational analysis of the Gross-Pitaevskii\nequation we study the localization, with an exponential tail, of a dipolar\nBose-Einstein condensate (DBEC) of $^{52}$Cr atoms in a three-dimensional\nbichromatic optical-lattice (OL) generated by two monochromatic OL of\nincommensurate wavelengths along three orthogonal directions. For a fixed\ndipole-dipole interaction, a localized state of a small number of atoms ($\\sim\n1000$) could be obtained when the short-range interaction is not too attractive\nor not too repulsive. A phase diagram showing the region of stability of a DBEC\nwith short-range interaction and dipole-dipole interaction is given."
    },
    {
        "anchor": "Heisenberg Operator Approach for Spin Squeezing Dynamics: We reconsider the one-axis twisting Hamiltonian, which is commonly used for\ngenerating spin squeezing, and treat its dynamics within the Heisenberg\noperator approach. To this end we solve the underlying Heisenberg equations of\nmotion perturbatively and evaluate the expectation values of the resulting\ntime-dependent Heisenberg operators in order to determine approximately the\ndynamics of spin squeezing. Comparing our results with those originating from\nexact numerics reveals that they are more accurate than the commonly used\nfrozen spin approximation.",
        "positive": "Lattice generalization of the Dirac equation to general spin and the\n  role of the flat band: We provide a novel setup for generalizing the two-dimensional pseudospin\nS=1/2 Dirac equation, arising in graphene's honeycomb lattice, to general\npseudospin-S. We engineer these band structures as a nearest-neighbor hopping\nHamiltonian involving stacked triangular lattices. We obtain multi-layered low\nenergy excitations around half-filling described by a two-dimensional Dirac\nequation of the form H=v_F S\\cdot p, where S represents an arbitrary spin-S\n(integer or half-integer). For integer-S, a flat band appears, whose presence\nmodifies qualitatively the response of the system. Among physical observables,\nthe density of states, the optical conductivity and the peculiarities of Klein\ntunneling are investigated. We also study Chern numbers as well as the\nzero-energy Landau level degeneracy. By changing the stacking pattern, the\ntopological properties are altered significantly, with no obvious analogue in\nmultilayer graphene stacks."
    },
    {
        "anchor": "The Hyperfine Molecular Hubbard Hamiltonian: An ultracold gas of heteronuclear alkali dimer molecules with hyperfine\nstructure loaded into a one-dimensional optical lattice is investigated. The\n\\emph{Hyperfine Molecular Hubbard Hamiltonian} (HMHH), an effective low-energy\nlattice Hamiltonian, is derived from first principles. The large permanent\nelectric dipole moment of these molecules gives rise to long range\ndipole-dipole forces in a DC electric field and allows for transitions between\nrotational states in an AC microwave field. Additionally, a strong magnetic\nfield can be used to control the hyperfine degrees of freedom independently of\nthe rotational degrees of freedom. By tuning the angle between the DC electric\nand magnetic fields and the strength of the AC field it is possible to control\nthe number of internal states involved in the dynamics as well as the degree of\ncorrelation between the spatial and internal degrees of freedom. The HMHH's\nunique features have direct experimental consequences such as quantum\ndephasing, tunable complexity, and the dependence of the phase diagram on the\nmolecular state.",
        "positive": "Many-body delocalization with random vector potentials: We study the ergodic properties of excited states in a model of interacting\nfermions in quasi-one-dimensional chains subjected to a random vector\npotential. In the noninteracting limit, we show that arbitrarily small values\nof this complex off-diagonal disorder trigger localization for the whole\nspectrum; the divergence of the localization length in the single-particle\nbasis is characterized by a critical exponent $\\nu$ which depends on the energy\ndensity being investigated. When short-range interactions are included, the\nlocalization is lost, and the system is ergodic regardless of the magnitude of\ndisorder in finite chains. Our numerical results suggest a delocalization\nscheme for arbitrary small values of interactions. This finding indicates that\nthe standard scenario of the many-body localization cannot be obtained in a\nmodel with random gauge fields."
    },
    {
        "anchor": "Fano-Hopfield model and photonic band gaps for an arbitrary atomic\n  lattice: We study the light dispersion relation in a periodic ensemble of atoms at\nfixed positions in the Fano-Hopfield model (the atomic dipole being modeled\nwith harmonic oscillators). Compared to earlier works, we do not restrict to\ncubic lattices, and we do not regularize the theory by hand but we renormalize\nit in a systematic way using a Gaussian cut-off in momentum space. Whereas no\nomnidirectional spectral gap is known for light in a Bravais atomic lattice, we\nfind that, for a wide range of parameters, an omnidirectional gap occurs in a\ndiamond atomic lattice, which may be realized in an experiment with ultra-cold\natoms. The long-wavelength limit of the theory also provides a Lorentz-Lorenz\n(or Clausius-Mossotti) relation for an arbitrary lattice.",
        "positive": "Off-Diagonal Long-Range Order Implies Vanishing Charge Gap: For a large class of quantum many-body systems with U(1) symmetry, we prove a\ngeneral inequality that relates the (off-diagonal) long-range order with the\ncharge gap. For a system of bosons or fermions on a lattice or in the\ncontinuum, the inequality implies that a ground state with off-diagonal\nlong-range order inevitably has a vanishing charge gap, and hence is\ncharacterized by nonzero charge susceptibility. For a quantum spin system, the\ninequality implies that a ground state within a magnetization plateau cannot\nhave transverse long-range order."
    },
    {
        "anchor": "Bose-like few-fermion systems: Dealing with a few-fermion system in the canonical ensemble, rather than in\nthe grand canonical ensemble, shows that a few-fermion system with odd number\nfermions behaves differently from a few-fermion system with even number\nfermions. An even-number-fermion system behaves like a Bose system rather than\na Fermi system.",
        "positive": "Dynamical quantum phase transitions on cross-stitch flat band networks: We study the quench dynamics on cross-stitch flat band networks by a sudden\nchange of the inter-cell hopping strength $J$. For quench processes with $J$\nchanging as $J=0\\rightarrow J\\neq0$, we give the analytical expression to the\nLoschmidt echo which possesses a series of zero points at critical times\n$t^{*}$, indicating where the dynamical quantum phase transitions occur. We\nfurther study the converse quench process with $J\\neq0\\rightarrow J=0$, and\nfind a non-trivial example that the pre-quench quantum state is not an\neigenstate of the post-quench Hamiltonian, whereas the Loschmidt echo\n$\\mathcal{L}(t)\\equiv1$ during this process. For both situations, these results\nare also illustrated numerically. Finally, we give a brief discussion on the\nobservation of these predictions in the system of ultracold atoms in optical\nlattices."
    },
    {
        "anchor": "Solvable Model of a Mixture of Bose-Einstein Condensates: A mixture of two kinds of identical bosons held in a harmonic potential and\ninteracting by harmonic particle-particle interactions is discussed. This is an\nexactly-solvable model of a mixture of two trapped Bose-Einstein condensates\nwhich allows us to examine analytically various properties. Generalizing the\ntreatment in [Cohen and Lee, J. Math. Phys. {\\bf 26}, 3105 (1985)], closed form\nexpressions for the ground-state energy, wave-function, and lowest-order\ndensities are obtained and analyzed for attractive and repulsive intra-species\nand inter-species particle-particle interactions. A particular mean-field\nsolution of the corresponding Gross-Pitaevskii theory is also found\nanalytically. This allows us to compare properties of the mixture at the exact,\nmany-body and mean-field levels, both for finite systems and at the limit of an\ninfinite number of particles. We hereby prove that the exact ground-state\nenergy and lowest-order intra-species and inter-species densities converge at\nthe infinite-particle limit (when the products of the number of particles times\nthe intra-species and inter-species interaction strengths are held fixed) to\nthe results of the Gross-Pitaevskii theory for the mixture. Finally and on the\nother end, the separability of the mixture's center-of-mass coordinate is used\nto show that the Gross-Pitaevskii theory for mixtures is unable to describe the\nvariance of many-particle operators in the mixture, even in the\ninfinite-particle limit. Our analytical results show that many-body\ncorrelations exist in a mixture of Bose-Einstein condensates made of any number\nof particles. Implications are briefly discussed.",
        "positive": "Macroscopic self trapping in BECs: analysis of a dynamical quantum phase\n  transition: We consider a Bose-Einstein condensate in a double-well potential undergoing\na dynamical transition from the regime of Josephson oscillations to the regime\nof self-trapping. We analyze the statistical properties of the ground state (or\nthe highest excited state) of the Hamiltonian in these two regimes for\nattractive (repulsive) interactions. We demonstrate that it is impossible to\ndescribe the transition within the mean-field theory. In contrast, the\ntransition proceeds through a strongly correlated delocalized state, with large\nquantum fluctuations, and spontaneous breaking of the symmetry."
    },
    {
        "anchor": "Nonlinear waves in two-component Bose-Einstein condensates: Manakov\n  system and Kowalevski equations: Traveling waves in two-component Bose-Einstein condensates whose dynamics is\ndescribed by the Manakov limit of the Gross-Pitaevskii equations are considered\nin general situation with relative motion of the components when their chemical\npotentials are not equal to each other. It is shown that in this case the\nsolution is reduced to the form known in the theory of motion of S.~Kowalevski\ntop. Typical situations are illustrated by the particular cases when the\ngeneral solution can be represented in terms of elliptic functions and their\nlimits. Depending on the parameters of the wave, both density waves (with\nin-phase motions of the components) and polarization waves (with counter-phase\ntheir motions) are considered.",
        "positive": "Ultracold mixtures of atomic Li-6 and Cs-133 with tunable interactions: We report the experimental and theoretical study of two-body interactions in\na $^{6}$Li-$^{133}$Cs Fermi- Bose mixture. Using a translatable dipole trap\nsetup, we have successfully trapped the two species in the same trap with\ntemperatures of a few microkelvins. By monitoring atom number loss and\ninter-species thermalization, we identify five s-wave interspecies Feshbach\nresonances in the lowest two scattering channels. We construct a coupled\nchannels model using molecular potentials to fit and characterize these\nresonances. Two of the resonances are as wide as 60 G and thus should be\nsuitable for creating Feshbach molecules and searching for universal few-body\nscaling."
    },
    {
        "anchor": "Quantum Simulation of a Topological Mott Insulator with Rydberg Atoms in\n  a Lieb Lattice: We propose a realistic scheme to quantum simulate the so-far experimentally\nunobserved topological Mott insulator phase -- an interaction-driven\ntopological insulator -- using cold atoms in an optical Lieb lattice. To this\nend, we study a system of spinless fermions in a Lieb lattice, exhibiting\nrepulsive nearest and next-to-nearest neighbor interactions, and derive the\nassociated zero temperature phase diagram within mean-field approximation. In\nparticular, we analyze how the interactions can dynamically generate a charge\ndensity wave ordered, a nematic as well as a topologically non-trivial quantum\nanomalous Hall phase. We characterize the topology of the different phases by\nthe Chern number and discuss the possibility of phase coexistence. Based on the\nidentified phases, we propose a realistic implementation of this model using\ncold Rydberg-dressed atoms in an optical lattice. The scheme, which allows one\nto access in particular the topological Mott insulator phase, robustly and\nindependently of its exact position in parameter space, merely requires global,\nalways-on off-resonant laser coupling to Rydberg states and is feasible with\nstate-of-the-art experimental techniques.",
        "positive": "Many-Body Rate Limit on Photoassociation of a Bose-Einstein Condensate: We briefly report on zero-temperature photoassociation of a Bose-Einstein\ncondensate, focusing on the many-body rate limit for atom-molecule conversion.\nAn upgraded model that explicitly includes spontaneous radiative decay leads to\nan unanticipated shift in the position of the photoassociation resonance, which\naffects whether the rate (constant) maximizes or saturates, as well as the\nlimiting value itself. A simple analytical model agrees with numerical\nexperiments, but only for high density. Finally, an explicit comparison with\nthe two-body unitary limit, set by the size of the condensate, finds that the\nmany-body rate limit is generally more strict."
    },
    {
        "anchor": "Light-induced quantum droplet phases of lattice bosons in multimode\n  cavities: Multimode optical cavities can be used to implement interatomic interactions\nwhich are highly tunable in strength and range. For bosonic atoms trapped in an\noptical lattice, cavity-mediated interactions compete with the short-range\ninteratomic repulsion, which we study using an extended Bose-Hubbard model.\nAlready in a single-mode cavity, where the corresponding interaction has an\ninfinite range, a rich phase diagram has been experimentally observed,\nfeaturing density-wave and supersolid self-organized phases in addition to the\nusual superfluid and Mott insulator. Here we show that, for any finite range of\nthe cavity-mediated interaction, quantum self-bound droplets dominate the\nground state phase diagram. Their size and in turn density is not externally\nfixed but rather emerges from the competition between local repulsion and\nfinite-range attraction. Therefore, the phase diagram becomes very rich,\nfeaturing both compressible superfluid/supersolid as well as incompressible\nMott and density-wave droplets. Additionally, we observe droplets with a\ncompressible core and incompressible outer shells.",
        "positive": "The p=0 condensate is a myth: Analyzing some of the basic aspects of the dynamics of two bosons\n(interacting through a central force) and their importance in determining the\nground state of a system like liquid $^4He$, it is unequivocally concluded that\nour conventional belief in the existence $p=0$ condensate in the superfluid\nstate of such systems [including the state of Bose Einstein condensate (BEC) of\ntrapped dilute gases] is a myth."
    },
    {
        "anchor": "The dynamics of straight vortex filaments in a Bose-Einstein condensate\n  with a Gaussian density profile: The dynamics of interacting quantized vortex filaments in a rotating trapped\nBose-Einstein condensate, which is in the Thomas-Fermi regime at zero\ntemperature and described by the Gross-Pitaevskii equation, is considered in\nthe hydrodynamic \"anelastic\" approximation. In the presence of a smoothly\ninhomogeneous array of filaments (vortex lattice), a non-canonical Hamiltonian\nequation of motion is derived for the macroscopically averaged vorticity, with\ntaking into account the spatial non-uniformity of the equilibrium condensate\ndensity determined by the trap potential. A minimum of the corresponding\nHamiltonian describes a static configuration of deformed vortex lattice against\na given density background. The minimum condition is reduced to a vector\nnonlinear partial differential equation of the second order, for which some\napproximate and exact solutions are found. It is shown that if the condensate\ndensity has an anisotropic Gaussian profile then equation of motion for the\naveraged vorticity admits solutions in the form of a spatially uniform vector\nwith a nontrivial time dependence. An integral representation is obtained for\nthe matrix Green function determining the non-local Hamiltonian of a system of\narbitrary shaped vortex filaments in a condensate with Gaussian density. ... A\nsimple approximate expression for the two-dimensional Green function is\nsuggested at rather arbitrary density profile, and its successful comparison to\nthe exact result in the Gaussian case is done. Approximate equations of motion\nare derived which describe a long-wave dynamics of interacting vortex filaments\nin condensates with the density depending on the transverse coordinates only.",
        "positive": "Bose-Einstein Condensates on slightly asymmetric double-well potentials: An analytical insight into the symmetry breaking mechanisms underlying the\ntransition from Josephson to self-trapping regimes in Bose-Einstein condensates\nis presented. We obtain expressions for the ground state properties of the\nsystem of a gas of attractive bosons modelized by a two site Bose-Hubbard\nhamiltonian with an external bias. Simple formulas are found relating the\nappearance of fragmentation in the condensate with the large quantum\nfluctuations of the population imbalance occurring in the transition from the\nJosephson to the self-trapped regime."
    },
    {
        "anchor": "From Classical to Quantum Glasses with Ultracold Polar Molecules: The dynamics of a bilayer system of ultracold dipolar molecules exhibits\nclassical and quantum glassy behavior, characterized by long tails in the\nrelaxation time and dynamical heterogeneity. In the proposed setup, quantum\nfluctuations are of the order of thermal fluctuations and the degree of\nfrustration can tuned by the interlayer distance. We present experimental\naccessible order parameters based on marker molecules, distinguished by\nproperly chosen internal levels, and find quantum features of dynamical\nheterogeneity.",
        "positive": "A Bose-condensed, simultaneous dual species Mach-Zehnder atom\n  interferometer: This paper presents the first realisation of a simultaneous $^{87}$Rb\n-$^{85}$Rb Mach-Zehnder atom interferometer with Bose-condensed atoms. A number\nof ambitious proposals for precise terrestrial and space based tests of the\nWeak Equivalence Principle rely on such a system. This implementation utilises\nhybrid magnetic-optical trapping to produce spatially overlapped condensates\nwith a duty cycle of 20s. A horizontal optical waveguide with co-linear Bragg\nbeamsplitters and mirrors is used to simultaneously address both isotopes in\nthe interferometer. We observe a non-linear phase shift on a non-interacting\n$^{85}$Rb interferometer as a function of interferometer time, $T$, which we\nshow arises from inter-isotope scattering with the co-incident $^{87}$Rb\ninterferometer. A discussion of implications for future experiments is given."
    },
    {
        "anchor": "Quantum phase transitions in optical lattices beyond Bogoliubov\n  approximation: We study the quantum phase transition in optical lattices using ordinary Bose\nHubbard Hamiltonian within two loop approximation in variational perturbation\ntheory. We have shown that this approximation can reproduce superfluid Mott\ninsulator transition in contrast to the simple Bogoliubov or Hartee - Fock -\nPopov approximations.\n  The superfluid fraction and ground state energy per particle vs input\nparameters of the model are studied.",
        "positive": "Self-trapping under the two-dimensional spin-orbit-coupling and\n  spatially growing repulsive nonlinearity: We elaborate a method for the creation of two- and one-dimensional (2D and\n1D) self-trapped modes in binary spin-orbit (SO)-coupled Bose-Einstein\ncondensates (BECs) with the contact repulsive interaction, whose local strength\ngrows fast enough from the center to periphery. In particular, an exact\nsemi-vortex (SV) solution is found for the anti-Gaussian radial-modulation\nprofile. The exact modes are included in the numerically produced family of SV\nsolitons. Other families, in the form of mixed modes(MMs), as well as excited\nstate of SVs and MMs, are produced too. While the excited states are unstable\nin all previously studied models, they are partially stable in the present one.\nIn the 1D version of the system, exact solutions for the counterpart of the\nSVs, namely, \\textit{semi-dipole} solitons, are found too. Families of\nsemi-dipoles, as well as the 1D version of MMs, are produced numerically."
    },
    {
        "anchor": "Atomic Fermi gas at the unitary limit by quantum Monte Carlo methods:\n  Effects of the interaction range: We calculate the ground-state properties of unpolarized two-component Fermi\ngas by the diffusion quantum Monte Carlo (DMC) methods. Using an extrapolation\nto the zero effective range of the attractive two-particle interaction, we find\n$E/E_{\\rm free}$ to be 0.212(2), 0.407(2), 0.409(3) and 0.398(3) for 4, 14, 38\nand 66 atoms, respectively. Our results indicate that the dependence of the\ntotal energy on the effective range is sizable and the extrapolation is\ntherefore quite important. In order to test the quality of nodal surfaces and\nto estimate the impact of the fixed-node approximation we perform released-node\nDMC calculations for 4 and 14 atoms. Analysis of the released-node and the\nfixed-node results suggests that the main sources of the fixed-node errors are\nlong-range correlations which are difficult to sample in the released-node\napproaches due to the fast growth of the bosonic noise. Besides energies, we\nevaluate the two-body density matrix and the condensate fraction. We find that\nthe condensate fraction for the 66 atom system converges to 0.56(1) after the\nextrapolation to the zero interaction range.",
        "positive": "Dynamic structure factor and drag force in a one-dimensional\n  strongly-interacting Bose gas at finite temperature: We study the effect of thermal and quantum fluctuations on the dynamical\nresponse of a one-dimensional strongly-interacting Bose gas in a tight atomic\nwaveguide. We combine the Luttinger liquid theory at arbitrary interactions and\nthe exact Bose-Fermi mapping in the Tonks-Girardeau-impenetrable-boson limit to\nobtain the dynamic structure factor of the strongly-interacting fluid at finite\ntemperature. Then, we determine the drag force felt by a potential barrier\nmoving along the fluid in the experimentally realistic situation of finite\nbarrier width and temperature."
    },
    {
        "anchor": "Density Modulations Associated with the Dynamical Instability in the\n  Bose-Hubbard Model: A superfluid flow beyond a critical momentum in an optical lattice decays\ndrastically by the interplay between nonlinearity due to the interparticle\ninteractions in Bose-Einstein condensate and periodicity of the lattice; this\ninstability is called dynamical instability. The complex density modulational\nprofiles after the condensate becomes unstable observed experimentally is not\ncompletely understood, while the dynamical instability has been studied\ntheoretically and experimentally. In this paper, we analyze the density\nmodulation of condensates as a precursor of the dynamical instability in the\ntwo-dimensional Bose-Hubbard model. Our analysis has clarified the unexplored\nproperties of the density modulations associated with the dynamical instability\nat low filling and in a wide range of interactions, while the previous works\nhave analyzed the density modulation on the basis of Gross-Pitaevskii equation\nunder the specific condition that one-dimensional optical lattice is very\nshallow and the filling is very large. The numerical simulations based on the\ndynamical Gutzwiller approximation elucidate that the principal mode of density\nmodulation highly depends on interaction strength U and the momentum\nacceleration rate. We briefly discuss these features with the stability phase\ndiagram calculated on the basis of the Bogoliubov theory.",
        "positive": "Dynamics of a Mobile Impurity in a One-Dimensional Bose Liquid: We develop a microscopic theory of a quantum impurity propagating in a\none-dimensional Bose liquid. As a result of scattering off thermally excited\nquasiparticles, the impurity experiences the friction. We find that, at low\ntemperatures, the resulting force scales either as the fourth or the eighth\npower of temperature, depending on the system parameters. For temperatures\nhigher than the chemical potential of the Bose liquid, the friction force is a\nlinear function of temperature. Our approach enables us to find the friction\nforce in the crossover region between the two limiting cases. In the integrable\ncase, corresponding to the Yang-Gaudin model, the impurity becomes transparent\nfor quasiparticles and thus the friction force is absent. Our results could be\nfurther generalized to study other kinetic phenomena."
    },
    {
        "anchor": "Collisional dynamics of multiple dark solitons in a toroidal\n  Bose-Einstein condensate: Quasiparticle picture: We study the collisional dynamics of multiple dark solitons in a\nBose-Einstein condensate confined by a toroidal trap. We assume a tight enough\nconfinement in the radial direction to prevent possible dissipative effects due\nto the presence of solitonic vortices. Analytical expressions for the initial\norder parameters with imprinted phases are utilized to generate different\ninitial arrays of solitons, for which the time-dependent Gross-Pitaevskii\nequation is numerically solved. Given that the soliton velocity is conserved\ndue to the lack of dissipation, we are able to apply a simple quasiparticle\ndescription of the soliton dynamics. In fact, the trajectory equations are\nwritten in terms of the velocities and the angular shifts produced at each\ncollision, in analogy to the infinite one-dimensional system. To calculate the\nangular shifts, we directly extract them from the trajectories given by the\nGross-Pitaevskii simulations and, on the other hand, we show that accurate\nvalues can be analytically obtained by adapting a formula valid for the\ninfinite one-dimensional system that involves the healing length, which in our\ninhomogeneous system must be evaluated in terms of the sound velocity along the\nazimuthal direction. We further show that very good estimates of such a sound\nvelocity can be directly determined by using the ground state density profile\nand the values of the imprinted phases. We discuss the possible implementation\nof the system here proposed using the current experimental techniques.",
        "positive": "Quantum depletion of a homogeneous Bose-Einstein condensate: We have measured the quantum depletion of an interacting homogeneous\nBose-Einstein condensate, and confirmed the 70-year old theory of N.N.\nBogoliubov. The observed condensate depletion is reversibly tuneable by\nchanging the strength of the interparticle interactions. Our atomic homogeneous\ncondensate is produced in an optical-box trap, the interactions are tuned via a\nmagnetic Feshbach resonance, and the condensed fraction probed by coherent\ntwo-photon Bragg scattering."
    },
    {
        "anchor": "One-dimensional model of chiral fermions with Feshbach resonant\n  interactions: We study a model of two species of one-dimensional linearly dispersing\nfermions interacting via an s-wave Feshbach resonance at zero temperature.\nWhile this model is known to be integrable, it possesses novel features that\nhave not previously been investigated. Here, we present an exact solution based\non the coordinate Bethe Ansatz. In the limit of infinite resonance strength,\nwhich we term the strongly interacting limit, the two species of fermions\nbehave as free Fermi gases. In the limit of infinitely weak resonance, or the\nweakly interacting limit, the gases can be in different phases depending on the\ndetuning, the relative velocities of the particles, and the particle densities.\nWhen the molecule moves faster or slower than both species of atoms, the atomic\nvelocities get renormalized and the atoms may even become non-chiral. On the\nother hand, when the molecular velocity is between that of the atoms, the\nsystem may behave like a weakly interacting Lieb-Liniger gas.",
        "positive": "Shifts and widths of p-wave confinement induced resonances in atomic\n  waveguides: We develop and analyze a theoretical model to study p-wave Feshbach\nresonances of identical fermions in atomic waveguides by extending the\ntwo-channel model of A.D. Lange et. al. [Phys. Rev. A 79, 013622 (2009)] and S.\nSaeidian et. al. [Phys. Rev. A 86, 062713 (2012)]. The experimentally known\nparameters of Feshbach resonances in free space are used as input of the model.\nWe calculate the shifts and widths of p-wave magnetic Feshbach resonance of\n$^{40}$K atoms emerging in harmonic waveguides as p-wave confinement induced\nresonance (CIR). Particularly, we show a possibility to control the width and\nshift of the p-wave confinement induced resonance by the trap frequency and the\napplied magnetic field which could be used in corresponding experiments. Our\nanalysis also demonstrates the importance of the inclusion of the effective\nradius in the computational schemes for the description of the p-wave CIRs\ncontrary to the case of s-wave CIRs where the influence of this term is\nnegligible."
    },
    {
        "anchor": "A rapidly expanding Bose-Einstein condensate: an expanding universe in\n  the lab: We study the dynamics of a supersonically expanding ring-shaped Bose-Einstein\ncondensate both experimentally and theoretically. The expansion redshifts\nlong-wavelength excitations, as in an expanding universe. After expansion,\nenergy in the radial mode leads to the production of bulk topological\nexcitations -- solitons and vortices -- driving the production of a large\nnumber of azimuthal phonons and, at late times, causing stochastic persistent\ncurrents. These complex nonlinear dynamics, fueled by the energy stored\ncoherently in one mode, are reminiscent of a type of \"preheating\" that may have\ntaken place at the end of inflation.",
        "positive": "Classical bifurcation at the transition from Rabi to Josephson dynamics: We report on the experimental realization of an internal bosonic Josephson\njunction in a Rubidium spinor Bose-Einstein condensate. The measurement of the\nfull time dynamics in phase space allows the characterization of the\ntheoretically predicted $\\pi$-phase modes and quantitatively confirms\nanalytical predictions, revealing a classical bifurcation. Our results suggest\nthat this system is a model system which can be tuned from classical to the\nquantum regime and thus is an important step towards the experimental\ninvestigation of entanglement generation close to critical points."
    },
    {
        "anchor": "Narrow-linewidth cooling of $^{6}$Li atoms using the 2S-3P transition: We report on a narrow-linewidth cooling of $^{6}$Li atoms using the\n$2S_{1/2}\\to 3P_{3/2}$ transition in the ultraviolet (UV) wavelength regime. By\ncombining the traditional red magneto-optical trap (MOT) at 671 nm and the UV\nMOT at 323 nm, we obtain a cold sample of $1.3\\times10^9$ atoms with a\ntemperature of 58 $\\mu$K. Furthermore, we demonstrate a high efficiency\nmagnetic transport for $^{6}$Li atoms with the help of the UV MOT. Finally, we\nobtain $8.1\\times10^8$ atoms with a temperature of 296 $\\mu$K at a magnetic\ngradient of 198 G/cm in the science chamber with a good vacuum environment and\nlarge optical access.",
        "positive": "Rydberg tomography of an ultra-cold atomic cloud: One of the most striking features of the strong interactions between Rydberg\natoms is the dipole blockade effect, which allows only a single excitation to\nthe Rydberg state within the volume of the blockade sphere. Here we present a\nmethod that spatially visualizes this phenomenon in an inhomogeneous gas of\nultra-cold rubidium atoms. In our experiment we scan the position of one of the\nexcitation lasers across the cold cloud and determine the number of Rydberg\nexcitations detected as a function of position. Comparing this distribution to\nthe one obtained for the number of ions created by a two-photon ionization\nprocess via the intermediate 5P level, we demonstrate that the blockade effect\nmodifies the width of the Rydberg excitation profile. Furthermore, we study the\ndynamics of the Rydberg excitation and find that the timescale for the\nexcitation depends on the atomic density at the beam position."
    },
    {
        "anchor": "Quadratic-nonlinear Landau-Zener transition for association of an atomic\n  Bose-Einstein condensate with inter-particle elastic interactions included: We study the strong coupling limit of a quadratic-nonlinear Landau-Zener\nproblem for coherent photo- and magneto-association of cold atoms taking into\naccount the atom-atom, atom-molecule, and molecule-molecule elastic scattering.\nUsing an exact third-order nonlinear differential equation for the molecular\nstate probability, we develop a variational approach which enables us to\nconstruct a highly accurate and simple analytic approximation describing the\ntime dynamics of the coupled atom-molecule system. We show that the\napproximation describing time evolution of the molecular state probability can\nbe written as a sum of two distinct terms; the first one, being a solution to a\nlimit first-order nonlinear equation, effectively describes the process of the\nmolecule formation while the second one, being a scaled solution to the linear\nLandau-Zener problem (but now with negative effective Landau-Zener parameter as\nlong as the strong coupling regime is considered), corresponds to the remaining\noscillations which come up when the process of molecule formation is over.",
        "positive": "Finite-temperature behavior of the Bose polaron: We consider a mobile impurity immersed in a Bose gas at finite temperature.\nUsing perturbation theory valid for weak coupling between the impurity and the\nbosons, we derive analytical results for the energy and damping of the impurity\nfor low and high temperatures, as well as for temperatures close to the\ncritical temperature $T_c$ for Bose-Einstein condensation. These results show\nthat the properties of the impurity vary strongly with temperature. In\nparticular, the energy exhibits a non-monotonic behavior close to $T_c$, and\nthe damping rises sharply close to $T_c$. We argue that this behaviour is\ngeneric for impurities immersed in an environment undergoing a phase transition\nthat breaks a continuous symmetry. Finally, we discuss how these effects can be\ndetected experimentally."
    },
    {
        "anchor": "Realization of a Strongly Interacting Fermi Gas of Dipolar Atoms: We realize a two-component dipolar Fermi gas with tunable interactions, using\nerbium atoms. Employing a lattice-protection technique, we selectively prepare\ndeeply degenerate mixtures of the two lowest spin states and perform\nhigh-resolution Feshbach spectroscopy in an optical dipole trap. We identify a\ncomparatively broad Feshbach resonance and map the interspin scattering length\nin its vicinity. The Fermi mixture shows a remarkable collisional stability in\nthe strongly interacting regime, providing a first step towards studies of\nsuperfluid pairing, crossing from Cooper pairs to bound molecules, in presence\nof dipole-dipole interactions.",
        "positive": "Shear viscosity and spin diffusion coefficient of a two-dimensional\n  Fermi gas: Using kinetic theory, we calculate the shear viscosity and the spin diffusion\ncoefficient as well as the associated relaxation times for a two-component\nFermi gas in two dimensions, as a function of temperature, coupling strength,\npolarization, and mass ratio of the two components. It is demonstrated that the\nminimum value of the viscosity decreases with the mass ratio, since Fermi\nblocking becomes less efficient. We furthermore analyze recent experimental\nresults for the quadrupole mode of a 2D gas in terms of viscous damping\nobtaining a qualitative agreement using no fitting parameters."
    },
    {
        "anchor": "Magnetisms of spinor alkali and alkaline-earth atoms in optical lattices: We theoretically investigate zero-temperature magnetic ordering of mixtures\nof spin-1 (alkali atoms) and spin-0 (alkaline-earth atoms) bosons in a\nthree-dimensional optical lattice. With the single-mode approximation for the\nspin-1 bosons, we obtain an effective Bose-Hubbard model for describing the\nheteronuclear mixtures in optical lattices. By controlling the interspecies\ninteractions between alkali and alkaline-earth atoms, we map out complete phase\ndiagrams of the system with both positive and negative spin-dependent\ninteractions for spin-1 atoms, based on bosonic dynamical mean-field theory. We\nfind that the spin-1 components feature ferromagnetic and nematic insulating\nphases, in addition to the superfluid, depending on spin-dependent\ninteractions. Take the spin-1 alkali bosons as spin $\\uparrow$, and spin-0\nalkaline-earth bosons as spin $\\downarrow$, we observe that the system favors\nferromagnetic insulator at filling $n=1$, and unorder insulator at $n=2$.\nInterestingly, we observe a two-step Mott-insulating-superfluid phase\ntransition, as a result of mass imbalance between alkali and alkaline-earth\natoms.",
        "positive": "Non-equilibrium dynamics of coupled qubit-cavity arrays: We study the coherence and fluorescence properties of the coherently pumped\nand dissipative Jaynes-Cummings-Hubbard model describing polaritons in a\ncoupled-cavity array. At weak hopping we find strong signatures of photon\nblockade similar to single-cavity systems. At strong hopping the state of the\nphotons in the array depends on its size. While the photon blockade persists in\na dimer consisting of two coupled cavities, a coherent state forms on an\nextended lattice, which can be described in terms of a semi-classical model."
    },
    {
        "anchor": "Decay and revival of a transient trapped Fermi condensate: We study experimentally and theoretically the response of a two-component\nFermi condensate in the strongly-interacting regime to a quench of the\ninteraction strength. The quench is realized using a radio-frequency\n$\\pi$-pulse to a third internal level with a different interaction strength. We\nfind that the quench excites the monopole mode of the trap in the hydrodynamic\nregime and that an initial change of the condensate properties takes place on a\ntime scale comparable or even larger than the quasi-particle relaxation time.",
        "positive": "Two-dimensional Bose gas of tilted dipoles: roton instability and\n  condensate depletion: We predict the effect of the roton instability for a two-dimensional weakly\ninteracting gas of tilted dipoles in a single homogeneous quantum layer. Being\ntypical for strongly correlated systems, the roton phenomena appear to occur in\na weakly interacting gas. It is important that in contrast to a system of\nnormal to wide layer dipoles, breaking of the rotational symmetry for a system\nof tilted dipoles leads to the convergence of the condensate depletion even up\nto the threshold of the roton instability, with mean-field approach being\nvalid. Predicted effects can be observed in a wide class of dipolar systems. We\nsuggest observing predicted phenomena for systems of ultracold atoms and polar\nmolecules in optical lattices, and estimate optimal experimental parameters."
    },
    {
        "anchor": "Interpreting superfluid spin up through the response of the container: A recipe is presented for interpreting non-invasively the transport processes\nat work during relaxation of a cylindrical, superfluid-filled vessel, after it\nis accelerated impulsively and then allowed to respond to the viscous torque\nexerted by the contained fluid. The recipe exploits a recently published\nanalytic solution for Ekman pumping in a two-component superfluid, which treats\nthe back-reaction self-consistently in arbitrary geometry for the first time.\nThe applicability of the recipe to He II, 3He, 3He-4He mixtures and\nBose-Einstein condensates is assessed, and the effects of turbulence discussed.",
        "positive": "Sub-picosecond thermalization dynamics in condensation of strongly\n  coupled lattice plasmons: Bosonic condensates offer exciting prospects for studies of non-equilibrium\nquantum dynamics. Understanding the dynamics is particularly challenging in the\nsub-picosecond timescales typical for room temperature luminous\ndriven-dissipative condensates. Here we combine a lattice of plasmonic\nnanoparticles with dye molecule solution at the strong coupling regime, and\npump the molecules optically. The emitted light reveals three distinct regimes:\none-dimensional lasing, incomplete stimulated thermalization, and\ntwo-dimensional multimode condensation. The condensate is achieved by matching\nthe thermalization rate with the lattice size and occurs only for pump pulse\ndurations below a critical value. Our results give access to control and\nmonitoring of thermalization processes and condensate formation at\nsub-picosecond timescale."
    },
    {
        "anchor": "Anomalous transport in a topological Wannier-Stark ladder: A dc (e.g. electric) field with commensurate lattice direction turns a single\nparticle band structure in $d=3$ dimensions into an infinite set of equally\nspaced irreducible $(d-1)=2$-dimensional Wannier-Stark (WS) band structures\nthat are spatially localized along the field direction. Particle transport is\nexpected to be suppressed once the WS bands are gapped in energy. The\ntopological character of the irreducible band structure leads to\none-dimensional sets of boundary states which fill the energy gaps. As a\nresult, eigenmodes are smoothly connected in energy and space and yield\nanomalous particle transport throughout the ladder. The number of chiral\nboundary modes can be tuned by the dc field strength and manifests through the\ndistribution of dissipated energy and spatial motion, and the temperature\ndependence of angular momentum carried by particles.",
        "positive": "From the Cooper problem to canted supersolids in Bose-Fermi mixtures: We calculate the phase diagram of the Bose-Fermi Hubbard model on the 3d\ncubic lattice at fermionic half filling and bosonic unit filling by means of\nsingle-site dynamical mean-field theory. For fast bosons, this is equivalent to\nthe Cooper problem in which the bosons can induce s-wave pairing between the\nfermions. We also find miscible superfluid and canted supersolid phases\ndepending on the interspecies coupling strength. In contrast, slow bosons favor\nfermionic charge density wave structures for attractive fermionic interactions.\nThese competing instabilities lead to a rich phase diagram within reach of cold\ngas experiments."
    },
    {
        "anchor": "Variational approach for interacting ultra-cold atoms in arbitrary\n  one-dimensional confinement: Standard analytical construction of the many-body wave function of\ninteracting particles in one dimension, beyond mean-field theory, is based on\nthe Jastrow approach. The many-body interacting ground state is build up from\nthe ground state of the non-interacting system and the product of solutions of\nthe corresponding interacting two-body problem. However, this is possible only\nif the center-of-mass motion is decoupled from the mutual interactions. In our\nwork, based on the general constraints given by contact nature of the atom-atom\ninteractions, we present an alternative approach to the standard construction\nof the \\textit{pair-correlation} wave-function. Within the proposed ansatz, we\nstudy the many-body properties of trapped bosons as well as fermionic mixtures\nand we compare these predictions with the exact diagonalization approach in a\nwide range of particle numbers, interaction strengths, and different trapping\npotentials.",
        "positive": "Observation of chiral edge transport in a rapidly-rotating quantum gas: The frictionless, directional propagation of particles at the boundary of\ntopological materials is one of the most striking phenomena in transport. These\nchiral edge modes lie at the heart of the integer and fractional quantum Hall\neffects, and their extraordinary robustness against noise and disorder reflects\nthe quantization of Hall conductivity in these systems. Despite their central\nimportance, controllable injection of edge modes, and direct imaging of their\npropagation, structure, and dynamics, is challenging. Here, we demonstrate the\ndistillation of individual chiral edge states in a rapidly-rotating bosonic\nsuperfluid confined by an optical boundary. Tuning the wall sharpness, we\nreveal the smooth crossover between soft wall behaviour in which the\npropagation speed is proportional to wall steepness, and the hard wall regime\nexhibiting chiral free particles. From the skipping motion of atoms along the\nboundary, we spectroscopically infer the energy gap between the ground and\nfirst excited edge bands, and reveal its evolution from the bulk Landau level\nsplitting for a soft boundary, to the hard wall limit."
    },
    {
        "anchor": "Overflow of a dipolar exciton trap at high magnetic fields: We study laterally trapped dipolar exciton ensembles in coupled GaAs quantum\nwells at high magnetic fields in the Faraday configuration. In\nphotoluminescence experiments, we identify three magnetic field regimes. At low\nfields, the exciton density is increased by a reduced charge carrier escape\nfrom the trap, and additionally, the excitons' emission energy is corrected by\na positive diamagnetic shift. At intermediate fields, magnetic field dependent\ncorrection terms apply which follow the characteristics of a neutral\nmagnetoexciton. Due to a combined effect of an increasing binding energy and\nlifetime, the exciton density is roughly doubled from zero to about seven\nTesla. At the latter high field value, the charge carriers occupy only the\nlowest Landau level. In this situation, the exciton trap can overflow\nindependently from the electrostatic depth of the trapping potential, and the\nenergy shift of the excitons caused by the so-called quantum confined Stark\neffect is effectively compensated. Instead, the exciton energetics seem to be\ndriven by the magnetic field dependent renormalization of the many-body\ninteraction terms. In this regime, the impact of parasitic in-plane fields at\nthe edge of trapping potential is eliminated.",
        "positive": "Striped states in weakly trapped ultracold Bose gases with Rashba\n  spin-orbit coupling: The striped state of ultracold bosons with Rashba spin-orbit coupling in a\nhomogeneous infinite system has, as we show, a constant particle flow, which in\na finite-size system would accumulate particles at the boundaries; it is thus\nnot a physical steady state of the system. We propose, as a variational ansatz,\na condensate wave function for a weakly trapped system which behaves similarly\nto the striped state near the center, but does not have particle flow at the\nboundaries. This state has a line of unquantized coreless vortices. We show, by\nminimizing the total energy, that our modified striped state has lower energy\nthan the conventional striped state and it is thus a physically appropriate\nstarting point to analyze striped states in finite systems."
    },
    {
        "anchor": "Spin-tensor--momentum-coupled Bose-Einstein condensates: The recent experimental realization of spin-orbit coupling for ultracold\natomic gases provides a powerful platform for exploring many interesting\nquantum phenomena. In these studies, spin represents spin vector (spin-1/2 or\nspin-1) and orbit represents linear momentum. Here we propose a scheme to\nrealize a new type of spin-tensor--momentum coupling (STMC) in spin-1 ultracold\natomic gases. We study the ground state properties of interacting Bose-Einstein\ncondensates (BECs) with STMC and find interesting new types of stripe\nsuperfluid phases and multicritical points for phase transitions. Furthermore,\nSTMC makes it possible to study quantum states with dynamical stripe orders\nthat display density modulation with a long tunable period and high visibility,\npaving the way for direct experimental observation of a new dynamical\nsupersolid-like state.. Our scheme for generating STMC can be generalized to\nother systems and may open the door for exploring novel quantum physics and\ndevice applications.",
        "positive": "Topological Unwinding in an Exciton-Polariton Condensate Array: The phase distribution in a Bose-Einstein condensate can realize various\ntopological states which can be classified according to distinct winding\nnumbers. While states with different winding numbers are topologically\nprotected in the linear Schr\\\"odinger equation, when nonlinearities are\nintroduced, violations of the topological protection can occur, leading to\nunwinding. Exciton-polariton condensates constitute a weakly nonlinear\nopen-dissipative system that is well suited to studying such physics. Here we\nshow that a one-dimensional array of exciton-polariton condensates displays a\nspontaneous phase unwinding from a $\\pi$- to zero-state. We clarify that this\ncollective mode transition is caused by the combined effect of nonlinearity and\ntopological defects in the condensates. While the mode-switching phenomenon\npreviously observed in our experiment [C.W. Lai $\\it et \\ al.$, Nature (London)\n$\\bf 450$, 529 (2007)] was interpreted as the single-particle mode competition,\nwe offer a new explanation in terms the collective phase unwinding of\nmetastable states. Reanalyzing the experimental data, we find an evidence of\nthe collective phase unwinding. Our results open a route towards active control\nof the mode switching of exciton-polariton condensates by manipulating the\ntopological defects, which may be employed as one of the basic technologies of\nprospective quantum polaritonic devices."
    },
    {
        "anchor": "Topological turbulence in spin-orbit-coupled driven-dissipative quantum\n  fluids of light generates high angular momentum states: We demonstrate the formation of a high angular momentum turbulent state in an\nexciton-polariton quantum fluid with TE-TM Spin-Orbit Coupling (SOC). The\ntransfer of particles from quasi-resonantly cw pumped \\spl component to \\sm\ncomponent is accompanied with the generation of a turbulent gas of quantum\nvortices by inhomogeneities. We show that this system is unstable with respect\nto the formation of bogolons at a finite wave vector, controlled by the laser\ndetuning. In a finite-size cavity, the domains with this wave vector form a\nring-like structure along the border of a cavity, with a gas of mostly\nsame-sign vortices in the center. The total angular momentum is imposed by the\nsign of TE-TM SOC, the wave vector of instability, and the cavity size. This\neffect can be detected experimentally via local dispersion measurements or by\ninterference. The proposed configuration thus allows simultaneous experimental\nstudies of quantum turbulence and high-angular momentum states in\ncontinuously-pumped exciton-polariton condensates.",
        "positive": "Atomic Bright Soliton Interferometry: The properties of nonlinear interference pattern between atomic bright\nsolitons are characterized analytically, with the aid of exact solutions of\ndynamical equation in mean-field approximation. It is shown that relative\nvelocity, relative phase, and nonlinear interaction strength can be measured\nfrom the interference pattern. The nonlinear interference properties are\nproposed to design atomic soliton interferometry in Bose-Einstein condensate.\nAs an example, we apply them to measure gravity acceleration in a ultra-cold\natom systems with a high precision degree. The results are also meaningful for\nprecise measurements in optical fiber, water wave tank, plasma, and other\nnonlinear systems."
    },
    {
        "anchor": "Stable Hopf solitons in rotating Bose-Einstein condensates: We reveal that Hopf solitons can be stabilized in rotating atomic\nBose-Einstein condensate. The Hopfion is a matter-wave vortex complex which\ncarries two independent winding numbers. Such a topological solitonic structure\nresults from a superfluid flow of atoms simultaneously quantized in poloidal\nand toroidal directions. In the framework of a dissipative mean-field model we\nobserve different unstable evolution scenarios of the Hopfions. We demonstrate\nenergetic and dynamical stability of the Hopf solitons under experimentally\nfeasible conditions.",
        "positive": "Many-Body Anderson Metal-Insulator Transition using Kicked Quantum Gases: Understanding the interplay of interactions and disorder in quantum transport\nposes long-standing scientific challenges, with many-body quantum transport\nphenomena in high-dimensional disordered systems remaining largely unexplored\nexperimentally. We utilize a momentum space lattice platform using\nquasi-periodically kicked ultracold atomic gases to experimentally investigate\nmany-body effects on the three-dimensional Anderson metal-insulator transition.\nWe observe interaction-driven sub-diffusion and a divergence of delocalization\nonset time on approaching the many-body phase boundary. Mean-field numerical\nsimulations are in qualitative agreement with experimental observations."
    },
    {
        "anchor": "Frustrated superfluids in a non-Abelian flux: We study possible superfluid states of the Rashba spin-orbit coupled (SOC)\nspinor bosons with the spin anisotropic interaction $ \\lambda $ hopping in a\nsquare lattice. The frustrations from the non-abelian flux due to the SOC leads\nto novel spin-bond correlated superfluids. By using a recently developed\nsystematic \"order from quantum disorder\" analysis, we not only determine the\ntrue quantum ground state, but also evaluate the mass gap in the spin sector at\n$ \\lambda < 1 $, especially compute the the excitation spectrum of the\nGoldstone mode in the spin sector at $ \\lambda=1 $ which would be quadratic\nwithout the analysis. The analysis also leads to different critical exponents\non the two sides of the 2nd order transition driven by a roton touchdown at $\n\\lambda=1 $. The intimate analogy at $ \\lambda=1 $ with the charge neutral\nGoldstone mode in the pseudo-spin sector in the Bilayer quantum Hall systems at\nthe total filling factor $ \\nu_T=1 $ are stressed. The experimental\nimplications and detections of these novel phenomena in cold atoms loaded on a\noptical lattice are presented.",
        "positive": "Self-organised Limit-Cycles, Chaos and Phase-Slippage with a Superfluid\n  inside an Optical Resonator: We study dynamical phases of a driven Bose-Einstein condensate coupled to the\nlight field of a high-Q optical cavity. For high field seeking atoms at red\ndetuning the system is known to show a transition from a spatially homogeneous\nsteady-state to a self-organized regular lattice exhibiting super-radiant\nscattering into the cavity. For blue atom pump detuning the particles are\nrepelled from the maxima of the light-induced optical potential suppressing\nscattering. We show that this generates a new dynamical instability of the\nself-ordered phase, leading to the appearance of self-ordered stable\nlimit-cycles characterized by large amplitude self-sustained oscillations of\nboth the condensate density and cavity field. The limit-cycles evolve into\nchaotic behavior by period doubling. Large amplitude oscillations of the\ncondensate are accompanied by phase-slippage through soliton nucleation at a\nrate which increases by orders of magnitude in the chaotic regime. Different\nfrom a superfluid in a closed setup, this driven dissipative superfluid is not\ndestroyed by the proliferation of solitons since kinetic energy is removed\nthrough cavity losses."
    },
    {
        "anchor": "Probing quantum entanglement from magnetic-sublevels populations: beyond\n  spin squeezing inequalities: Spin squeezing inequalities (SSI) represent a major tool to probe quantum\nentanglement among a collection of few-level atoms, and are based on collective\nspin measurements and their fluctuations. Yet, for atomic ensembles of spin-$j$\natoms and ultracold spinor gases, many experiments can image the populations in\nall Zeeman sublevels $s=-j, -j+1, \\dots, j$, potentially revealing finer\nfeatures of quantum entanglement not captured by SSI. Here we present a\nsystematic approach which exploits Zeeman-sublevel population measurements in\norder to construct novel entanglement criteria, and illustrate our approach on\nground states of spin-1 and spin-2 Bose-Einstein condensates. Beyond these\nspecific examples, our approach allows one to infer, in a systematic manner,\nthe optimal permutationally-invariant entanglement witness for any given set of\ncollective measurements in an ensemble of $d$-level quantum systems.",
        "positive": "Quantitative semiclassical analysis of ultracold weakly interacting bose\n  gas trapped in optical boxes: In this paper, the condensate fraction and the critical atom number and its\ncorresponding critical temperature of condensate ultracold boson atoms trapped\nin optical box traps, are investigated. The semiclassical approximation is\nemployed in this study. The boxes traps are modeled by a general power-law\npotential. The deviation of the boxes traps from an ideal boxes traps are\ndiscussed. The out come results furnish useful quantitative theoretical results\nfor the future BEC experiments in such traps"
    },
    {
        "anchor": "Fermi edge polaritons in a highly degenerate 2D electron gas: a\n  diagrammatic theory: We present a theoretical study on polaritons in highly doped semiconductor\nmicrocavities. In particular, we focus on a cavity mode that is resonant with\nthe absorption threshold (`Fermi edge'). In agreement with experimental\nresults, the strong light-matter coupling is maintained under very high doping\nwithin our ladder diagram approximation. While the lower polariton is\nqualitatively unaltered, it acquires a finite lifetime due to relaxation of the\nvalence band hole if the electron density exceeds a certain critical value. On\nthe other hand the upper polariton has a finite lifetime for all densities,\nbecause it lies in the electron-hole continuum where no bound state exists. Our\ncalculations show that a narrow upper polariton quasiparticle still exists as a\nresult from the interplay between light-matter coupling and final state Coulomb\ninteraction.",
        "positive": "Ultrafast non-equilibrium dynamics of rotons in superfluid helium: Superfluid 4He, the first superfluid ever discovered, is in some ways the\nleast well understood. Unlike 3He superfluid, or the variety of Bose-Einstein\ncondensates of ultracold gases, superfluid 4He is a very dense liquid of\nstrongly interacting quasiparticles. The theory is then necessarily\nphenomenological: the quasiparticle properties are found from experiment, and\ncontroversies over their description still remain, notably regarding vortex\ndynamics and the nature of rotons and roton pair creation. It is therefore\nimportant to develop new experimental tools for probing the system far from\nequilibrium. Here we describe a method for locally perturbing the density of\nsuperfluid helium through the excitation of roton pairs with ultrashort laser\npulses. By measuring the time dependence of this perturbation, we track the\nnon-equilibrium evolution of the two-roton states on a picosecond timescale.\nOur results reveal an ultrafast cooling of hot roton pairs as they thermalize\nwith the colder gas of other quasiparticles. We anticipate that these findings,\nas well as future applications of the introduced ultrafast laser technique to\ndifferent temperature and pressure regimes in bulk liquid 4He, will stimulate\nfurther experimental and theoretical investigations towards better\nunderstanding of superfluidity."
    },
    {
        "anchor": "Selective Rotation and Attractive Persistent Currents in Anti-Dipolar\n  Ring Supersolids: A repulsively interacting Bose-Einstein condensate on a ring is well known to\nshow persistent currents. For attractive interactions, however, a bound state\nmay form that renders the rotation classical. Here we show that in a\nmultiply-connected confinement, the strong in-plane attraction of an {\\it\nanti-dipolar }condensate can form stacks of ring-shaped droplets which may\ncoherently overlap to form a supersolid along the azimuthal symmetry axis of\nthe system. Intriguingly, the functional behavior of the energy-angular\nmomentum dispersion of the anti-dipolar ring condensate differs from that of a\nusual repulsive superfluid. The periodic maxima between persistent flow and the\nnon-rotating ground state flatten significantly and the typical pronounced\ncusps in the energy dispersion also occur in the rotationally symmetric\nsupersolid state. A weak link results in the reduction of this minimum,\nshifting it to smaller angular momenta. With an asymmetric link potential one\ncan selectively induce superfluid and rigid-body rotation in different layers\nwithin the same system. This intriguing setup offers new perspectives for\natomtronics applications.",
        "positive": "Superfluid behaviour of a two-dimensional Bose gas: Two-dimensional (2D) systems play a special role in many-body physics.\nBecause of thermal fluctuations, they cannot undergo a conventional phase\ntransition associated to the breaking of a continuous symmetry. Nevertheless\nthey may exhibit a phase transition to a state with quasi-long range order via\nthe Berezinskii-Kosterlitz-Thouless (BKT) mechanism. A paradigm example is the\n2D Bose fluid, such as a liquid helium film, which cannot Bose-condense at\nnon-zero temperature although it becomes superfluid above a critical phase\nspace density. Ultracold atomic gases constitute versatile systems in which the\n2D quasi-long range coherence and the microscopic nature of the BKT transition\nwere recently explored. However, a direct observation of superfluidity in terms\nof frictionless flow is still missing for these systems. Here we probe the\nsuperfluidity of a 2D trapped Bose gas with a moving obstacle formed by a\nmicron-sized laser beam. We find a dramatic variation of the response of the\nfluid, depending on its degree of degeneracy at the obstacle location. In\nparticular we do not observe any significant heating in the central, highly\ndegenerate region if the velocity of the obstacle is below a critical value."
    },
    {
        "anchor": "Superfluid Bloch dynamics in an incommensurate lattice: We investigate the interplay of disorder and interactions in the accelerated\ntransport of a Bose-Einstein condensate through an incommensurate optical\nlattice. We show that interactions can effectively cancel the damping of Bloch\noscillations due to the disordered potential and we provide a simple model to\nqualitatively capture this screening effect. We find that the characteristic\ninteraction energy, above which interactions and disorder cooperate to enhance,\nrather than reduce, the damping of Bloch oscillations, coincides with the\naverage disorder depth. This is consistent with results of a mean-field\nsimulation.",
        "positive": "Universality of the superfluid Kelvin-Helmholtz instability by\n  single-vortex tracking: At the interface between two fluid layers in relative motion, infinitesimal\nfluctuations can be exponentially amplified, inducing vorticity and the\nbreakdown of the laminar flow. This process, known as the Kelvin-Helmholtz\ninstability, is responsible for many familiar phenomena observed in the\natmosphere, and the oceans, as well as in astrophysics, and it is one of the\nparadigmatic routes to turbulence in fluid mechanics. While in classical\nhydrodynamics the instability is ruled by universal scaling laws, to what\nextent universality emerges in quantum fluids is yet to be fully understood.\nHere, we shed light on this matter by triggering the Kelvin-Helmholtz\ninstability in atomic superfluids across widely different regimes, ranging from\nweakly-interacting bosonic to strongly-correlated fermionic pair condensates.\nUpon engineering two counter-rotating flows with tunable relative velocity, we\nobserve how their contact interface develops into an ordered circular array of\nquantized vortices, which loses stability and rolls up into clusters in close\nanalogy with classical Kelvin-Helmholtz dynamics. We extract the instability\ngrowth rates by tracking the position of individual vortices and find that they\nfollow universal scaling relations, predicted by both classical hydrodynamics\nand a microscopic point-vortex model. Our results connect quantum and classical\nfluids revealing how the motion of quantized vortices mirrors the interface\ndynamics and open the way for exploring a wealth of out-of-equilibrium\nphenomena, from vortex-matter phase transitions to the spontaneous emergence of\ntwo-dimensional quantum turbulence ."
    },
    {
        "anchor": "Exact solution for $SU(2)$-symmetry breaking bosonic mixtures at strong\n  interactions: We study the equilibrium properties of a one-dimensional mixture of two\nTonks-Girardeau gases on a ring geometry in the limit of strongly-repulsive\ninter-species interactions. We derive the exact many-body wavefunction and\ncompare it to the $SU(2)$ solution where intra- and inter-species interactions\nare also diverging but equal. We focus on the role of the $SU(2)$-symmetry\nbreaking on the behaviour of the large- and short-distance correlations by\nstudying the zero-momentum occupation number and the Tan's contact from the\nasymptotic behavior of the momentum distribution. Although the symmetry is only\nweakly broken, it has important consequences on spin correlations in the system\nas the reduction by a factor of two of the zero-momentum occupation number with\nrespect to the $SU(2)$ case in the thermodynamic limit and the decrease of the\nTan's contact.",
        "positive": "Engineering Time-Reversal Invariant Topological Insulators With\n  Ultra-Cold Atoms: Topological insulators are a broad class of unconventional materials that are\ninsulating in the interior but conduct along the edges. This edge transport is\ntopologically protected and dissipationless. Until recently, all existing\ntopological insulators, known as quantum Hall states, violated time-reversal\nsymmetry. However, the discovery of the quantum spin Hall effect demonstrated\nthe existence of novel topological states not rooted in time-reversal\nviolations. Here, we lay out an experiment to realize time-reversal topological\ninsulators in ultra-cold atomic gases subjected to synthetic gauge fields in\nthe near-field of an atom-chip. In particular, we introduce a feasible scheme\nto engineer sharp boundaries where the \"edge states\" are localized. Besides,\nthis multi-band system has a large parameter space exhibiting a variety of\nquantum phase transitions between topological and normal insulating phases. Due\nto their unprecedented controllability, cold-atom systems are ideally suited to\nrealize topological states of matter and drive the development of topological\nquantum computing."
    },
    {
        "anchor": "Two-leg ladder Bose Hubbard models with staggered fluxes: We investigate the ground state properties of ultracold atoms trapped in a\ntwo-leg ladder potential in the presence of an artificial magnetic field in a\nstaggered configuration. We focus on the strongly interacting regime and use\nthe Landau theory of phase transitions and a mean field Gutzwiller variational\nmethod to identify the stable superfluid phases and their boundaries with the\nMott-insulator regime as a function of magnetic flux. In addition, we calculate\nthe local and chiral currents of these superfluid phases, which show a\nstaggered vortex anti-vortex configuration. The analytical results are\nconfirmed by numerical simulations using a cluster mean-field theory approach.",
        "positive": "Dynamical conductivity of disordered quantum chains: We study the transport properties of a one dimensional quantum system with\ndisorder. We numerically compute the frequency dependence of the conductivity\nof a fermionic chain with nearest neighbor interaction and a random chemical\npotential by using the Chebyshev matrix product state (CheMPS) method. As a\nbenchmark, we investigate the noninteracting case first. Comparison with exact\ndiagonalization and analytical solutions demonstrates that the results of\nCheMPS are reliable over a wide range of frequencies. We then calculate the\ndynamical conductivity spectra of the interacting system for various values of\nthe interaction and disorder strengths. In the high frequency regime, the\nconductivity decays as a power law, with an interaction dependent exponent.\nThis behavior is qualitatively consistent with the bosonized field theory\npredictions, although the numerical evaluation of the exponent shows deviations\nfrom the analytically expected values. We also compute the characteristic\npinning frequency at which a peak in the conductivity appears. We confirm that\nit is directly related to the inverse of the localization length, even in the\ninteracting case. We demonstrate that the localization length follows a power\nlaw of the disorder strength with an exponent dependent on the interaction, and\nfind good quantitative agreement with the field theory predictions. In the low\nfrequency regime, we find a behavior consistent with the one of the\nnoninteracting system $\\omega^{2}(\\ln\\omega)^{2}$ independently of the\ninteraction. We discuss the consequences of our finding for experiments in cold\natomic gases."
    },
    {
        "anchor": "Vortex-antivortex physics in shell-shaped Bose-Einstein condensates: Shell-shaped hollow Bose-Einstein condensates (BECs) exhibit behavior\ndistinct from their filled counterparts and have recently attracted attention\ndue to their potential realization in microgravity settings. Here we study\ndistinct features of these hollow structures stemming from vortex physics and\nthe presence of rotation. We focus on a vortex-antivortex pair as the simplest\nconfiguration allowed by the constraints on superfluid flow imposed by the\nclosed-surface topology. In the two-dimensional limit of an infinitesimally\nthin shell BEC, we characterize the long-range attraction between the\nvortex-antivortex pair and find the critical rotation speed that stabilizes the\npair against energetically relaxing towards self-annihilation. In the\nthree-dimensional case, we contrast the bounds on vortex stability with those\nin the two-dimensional limit and the filled sphere BEC, and evaluate the\ncritical rotation speed as a function of shell thickness. We thus demonstrate\nthat analyzing vortex stabilization provides a nondestructive means of\ncharacterizing a hollow sphere BEC and distinguishing it from its filled\ncounterpart.",
        "positive": "Quantum ferrofluid turbulence: We study the elementary characteristics of turbulence in a quantum ferrofluid\nthrough the context of a dipolar Bose gas condensing from a highly\nnon-equilibrium thermal state. Our simulations reveal that the dipolar\ninteractions drive the emergence of polarized turbulence and density\ncorrugations. The superfluid vortex lines and density fluctuations adopt a\ncolumnar or stratified configuration, depending on the sign of the dipolar\ninteractions, with the vortices tending to form in the low density regions to\nminimize kinetic energy. When the interactions are dominantly dipolar, the\ndecay of vortex line length is enhanced, closely following a $t^{-3/2}$\nbehaviour. This system poses exciting prospects for realizing stratified\nquantum turbulence and new levels of generating and controlling turbulence\nusing magnetic fields."
    },
    {
        "anchor": "Disassociation of a one-dimensional cold molecule via quantum scattering: Motivated by the recent experimental developments on ultracold molecules and\natoms, we propose a simplest theoretical model to address the disassociation,\nreflection and transmission probability of a 1-dimensional cold molecule via\nquantum scattering. First, we give the Born approximation results in the weak\ninteraction regime. Then, employing the Lippmann-Schwinger equation, we give\nthe numerical solution and investigate the disassociation's dependence on the\ninjection momentum and the interaction strengths. We find that the maximum\ndisassociation rate has a limit as increasing the interaction strengths and\ninjection momentum. We expect that our model can be realized in experiments in\nthe near future.",
        "positive": "Collapse and revival dynamics of superfluids of ultracold atoms in\n  optical lattices: Recent experiments have shown a remarkable number of collapse-and-revival\noscillations of the matter-wave coherence of ultracold atoms in optical\nlattices [Will et al., Nature 465, 197 (2010)]. Using a mean-field\napproximation to the Bose-Hubbard model, we show that the visibility of\ncollapse-and-revival interference patterns reveal number squeezing of the\ninitial superfluid state. To describe the dynamics, we use an effective\nHamiltonian that incorporates the intrinsic two-body and induced three-body\ninteractions, and we analyze in detail the resulting complex pattern of\ncollapse-and-revival frequencies generated by virtual transitions to higher\nbands, as a function of lattice parameters and mean-atom number. Our work shows\nthat a combined analysis of both the multiband, non-stationary dynamics in the\nfinal deep lattice, and the number-squeezing of the initial superfluid state,\nexplains important characteristics of optical lattice collapse-and-revival\nphysics. Finally, by treating the two- and three-body interaction strengths,\nand the coefficients describing the initial superposition of number states, as\nfree parameters in a fit to the experimental data it should be possible to go\nbeyond some of the limitations of our model and obtain insight into the\nbreakdown of the mean-field theory for the initial state or the role of\nnonperturbative effects in the final state dynamics."
    },
    {
        "anchor": "Quantum spin models with long-range interactions and tunnelings: A\n  quantum Monte Carlo study: We use a quantum Monte Carlo method to investigate various classes of 2D spin\nmodels with long-range interactions at low temperatures. In particular, we\nstudy a dipolar XXZ model with U(1) symmetry that appears as a hard-core boson\nlimit of an extended Hubbard model describing polarized dipolar atoms or\nmolecules in an optical lattice. Tunneling, in such a model, is short-range,\nwhereas density-density couplings decay with distance following a cubic power\nlaw. We investigate also an XXZ model with long-range couplings of all three\nspin components - such a model describes a system of ultracold ions in a\nlattice of microtraps. We describe an approximate phase diagram for such\nsystems at zero and at finite temperature, and compare their properties. In\nparticular, we compare the extent of crystalline, super?uid, and supersolid\nphases. Our predictions apply directly to current experiments with mesoscopic\nnumbers of polar molecules and trapped ions.",
        "positive": "Probing superfluidity of Bose-Einstein condensates via laser stirring: We investigate the superfluid behavior of a Bose-Einstein condensate of\n$^6$Li molecules. In the experiment by Weimer et al., Phys. Rev. Lett. 114,\n095301 (2015) a condensate is stirred by a weak, red-detuned laser beam along a\ncircular path around the trap center. The rate of induced heating increases\nsteeply above a velocity $v_c$, which we define as the critical velocity. Below\nthis velocity, the moving beam creates almost no heating. In this paper, we\ndemonstrate a quantitative understanding of the critical velocity. Using both\nnumerical and analytical methods, we identify the non-zero temperature, the\ncircular motion of the stirrer, and the density profile of the cloud as key\nfactors influencing the magnitude of $v_c$. A direct comparison to the\nexperimental data shows excellent agreement."
    },
    {
        "anchor": "Bose-Einstein condensation of light in a cavity: The paper considers Bose-Einstein condensation (BEC) of light in a cavity\nwith medium. In the framework of two-level model we show the effect of gaseous\nmedium on the critical temperature of light condensation in the system.\nTransition of the system to the state with released light condensate is\nillustrated in consequent stages. Analytical expressions for a typical spatial\nextent of the condensed cloud of photons, as well for spectral characteristics\nof the condensate peak are derived. Energy and heat capacity of photons as\nfunctions of temperature are obtained. Finally, we demonstrate that the energy\nof light can be accumulated in the BEC state.",
        "positive": "How to directly observe Landau levels in driven-dissipative strained\n  honeycomb lattices: We study the driven-dissipative steady-state of a coherently-driven Bose\nfield in a honeycomb lattice geometry. In the presence of a suitable spatial\nmodulation of the hopping amplitudes, a valley-dependent artificial magnetic\nfield appears and the low-energy eigenmodes have the form of relativistic\nLandau levels. We show how the main properties of the Landau levels can be\nextracted by observing the peaks in the absorption spectrum of the system and\nthe corresponding spatial intensity distribution. Finally, quantitative\npredictions for realistic lattices based on photonic or microwave technologies\nare discussed."
    },
    {
        "anchor": "Quantum simulations made easy plane: Ever since Heisenberg's proposal of a quantum-mechanical origin of\nferromagnetism in 1928, the spin model named after him has been central to\nadvances in magnetism, featuring in proposals of novel many-body states such as\nantiferromagnets, emergent gauge fields in their confined (valence bond\ncrystal) and deconfined (resonating valence bond spin liquids) versions.\nBetween them, these cover much of our understanding of modern magnetism\nspecifically and topological states of matter in general. Many exciting\nphenomena predicted theoretically still await experimental realisation, and\ncold atomic systems hold the promise of acting as analogue 'quantum simulators'\nof the relevant theoretical models, for which ingenious and intricate set-ups\nhave been proposed. Here, we identify a new class of particularly simple\nquantum simulators exhibiting many such phenomena but obviating the need for\nfine-tuning and for amplifying perturbatively weak superexchange or\nlonger-range interactions. Instead they require only moderate on-site\ninteractions on top of uncorrelated, one-body hopping--ingredients already\navailable with present experimental technology. Between them, they realise some\nof the most interesting phenomena, such as emergent synthetic gauge fields,\nresonating valence bond phases, and even the celebrated yet enigmatic spin\nliquid phase of the kagome lattice.",
        "positive": "Phase diagram and non-Abelian symmetry locking for fermionic mixtures\n  with unequal interactions: The occurrence of non-Abelian symmetry-locked states in ultracold fermionic\nmixtures with four components is investigated. We study the phase diagram in\nthe presence of an attractive interaction between the species of two pairs of\nthe mixture, and general (also repulsive) interactions between the species of\neach pair. This system is physically realized, e.g., in mixtures of two\ndifferent earth-alkaline species, both of them with two hyperfine levels\nselectively populated. We find an extended region of the diagram exhibiting a\ntwo-flavors superfluid symmetry-locking (TSFL) phase. This phase is present\nalso for not too large repulsive intra-pair interactions and it is\ncharacterized by a global non-Abelian symmetry group obtained by locking\ntogether two independent invariance groups of the corresponding normal state.\nExplicit estimates are reported for the mixture of the fermionic isotopes\n$^{171}\\mathrm{Yb}$-$^{173}\\mathrm{Yb}$, indicating that the TFSL phase can be\nachieved also without tuning the interactions between $\\mathrm{Yb}$ atoms."
    },
    {
        "anchor": "Observation of counterflow superfluidity in a two-component Mott\n  insulator: The counterflow superfluidity (CSF) was predicted two decades ago.\nCounterintuitively, while both components in the CSF have fluidity, their\ncorrelated counterflow currents cancel out leading the overall system to an\nincompressible Mott insulator. However, realizing and identifying the CSF\nremain challenging due to the request on extreme experimental capabilities in a\nsingle setup. Here, we observe the CSF in a binary Bose mixture in optical\nlattices. We prepare a low-entropy spin-Mott state by conveying and merging two\nspin-1/2 bosonic atoms at every site and drive it adiabatically to the CSF at\n$\\sim$ 1 nK. Antipair correlations of the CSF are probed though a site- and\nspin-resolved quantum gas microscope in both real and momentum spaces. These\ntechniques and observations provide accessibility to the symmetry-protected\ntopological quantum matters.",
        "positive": "Observing a topological phase transition with deep neural networks from\n  experimental images of ultracold atoms: Although classifying topological quantum phases have attracted great\ninterests, the absence of local order parameter generically makes it\nchallenging to detect a topological phase transition from experimental data.\nRecent advances in machine learning algorithms enable physicists to analyze\nexperimental data with unprecedented high sensitivities, and identify quantum\nphases even in the presence of unavoidable noises. Here, we report a successful\nidentification of topological phase transitions using a deep convolutional\nneural network trained with low signal-to-noise-ratio (SNR) experimental data\nobtained in a symmetry-protected topological system of spin-orbit-coupled\nfermions. We apply the trained network to unseen data to map out a whole phase\ndiagram, which predicts the positions of the two topological phase transitions\nthat are consistent with the results obtained by using the conventional method\non higher SNR data. By visualizing the filters and post-convolutional results\nof the convolutional layer, we further find that the CNN uses the same\ninformation to make the classification in the system as the conventional\nanalysis, namely spin imbalance, but with an advantage concerning SNR. Our work\nhighlights the potential of machine learning techniques to be used in various\nquantum systems."
    },
    {
        "anchor": "Ultradilute self-bound quantum droplets in Bose-Bose mixtures at finite\n  temperature: We theoretically investigate the finite-temperature structure and collective\nexcitations of a self-bound ultradilute Bose droplet in a flat space realized\nin a binary Bose mixture with attractive inter-species interactions on the\nverge of mean-field collapse. As the droplet formation relies critically on the\nrepulsive force provided by Lee-Huang-Yang quantum fluctuations, which can be\neasily compensated by thermal fluctuations, we find a significant temperature\neffect in the density distribution and collective excitation spectrum of the\nBose droplet. A finite-temperature phase diagram as a function of the number of\nparticles is determined. We show that the critical number of particles at the\ndroplet-to-gas transition increases dramatically with increasing temperature.\nTowards the bulk threshold temperature for thermally destabilizing an\ninfinitely large droplet, we find that the excitation-forbidden,\nself-evaporation region in the excitation spectrum, predicted earlier by Petrov\nusing a zero-temperature theory, shrinks and eventually disappears. All the\ncollective excitations, including both surface modes and compressional bulk\nmodes, become softened at the droplet-to-gas transition. The predicted\ntemperature effects of a self-bound Bose droplet in this work could be\ndifficult to measure experimentally due to the lack of efficient thermometry at\nlow temperatures. However, these effects may already present in the current\ncold-atom experiments.",
        "positive": "Dynamics of Few Co-rotating Vortices in Bose-Einstein Condensates: We study the dynamics of small vortex clusters with few (2--4) co-rotating\nvortices in Bose-Einstein condensates by means of experiments, numerical\ncomputations, and theoretical analysis. All of these approaches corroborate the\ncounter-intuitive presence of a dynamical instability of symmetric vortex\nconfigurations. The instability arises as a pitchfork bifurcation at\nsufficiently large values of the angular momentum that induces the emergence\nand stabilization of asymmetric rotating vortex configurations. The latter are\nquantified in the theoretical model and observed in the experiments. The\ndynamics is explored both for the integrable two-vortex system, where a\nreduction of the phase space of the system provides valuable insight, as well\nas for the non-integrable three- (or more) vortex case, which additionally\nadmits the possibility of chaotic trajectories."
    },
    {
        "anchor": "Emergent Gauge Field for a Chiral Bound State on Curved Surface: In this letter we show that there emerges a gauge field for two attractive\nparticles moving on a curved surface when they form a chiral bound state. By\nsolving a two-body problem on a sphere, we show explicitly that the\ncenter-of-mass wave functions of such deeply bound states are monopole\nharmonics instead of spherical harmonics. This indicates that the bound state\nexperiences a gauge field identical to a magnetic monopole at the center of the\nsphere, with the monopole charge equal to the quantized relative angular\nmomentum of this bound state. We show that this emergent gauge field is due to\nthe coupling between the center-of-mass and the relative motion on curved\nsurfaces. Our results can be generalized to an arbitrary curved surface where\nthe emergent magnetic field is exactly the local Gaussian curvature. This\nresult establishes an intriguing connection between space curvature and gauge\nfield, paves an alternative way to engineer topological state with space\ncurvature, and may be observed in cold atom system.",
        "positive": "Observation of an orbital interaction-induced Feshbach resonance in\n  173-Yb: We report on the experimental observation of a novel inter-orbital Feshbach\nresonance in ultracold 173-Yb atoms, which opens the possibility of tuning the\ninteractions between the 1S0 and 3P0 metastable state, both possessing\nvanishing total electronic angular momentum. The resonance is observed at\nexperimentally accessible magnetic field strengths and occurs universally for\nall hyperfine state combinations. We characterize the resonance in the bulk via\ninter-orbital cross-thermalization as well as in a three-dimensional lattice\nusing high-resolution clock-line spectroscopy."
    },
    {
        "anchor": "Exploring the transition from BCS to unitarity without Cooper pairs: the\n  Pauli principle, normal modes and superfluidity: The transition from the weakly interacting BCS regime to the strongly\ninteracting unitary regime is explored for ultracold trapped Fermi gases\nassuming a normal mode description of the gas instead of the conventional\nCooper pairing. The Pauli principle is applied ``on paper'' by using specific\nnormal mode assignments. Energies, entropies, critical temperatures, and an\nexcitation frequency are studied and compared to existing results in the\nliterature. These normal modes have been derived analytically for N identical,\nconfined particles from a first-order L=0 group theoretic solution of a\nthree-dimensional Hamiltonian with a general two-body interaction. In previous\nstudies, normal modes were able to describe the unitary regime obtaining ground\nstate energies comparable to benchmark results and thermodynamics quantities in\nexcellent agreement with experiment. In a recent study, the behavior of the\nnormal mode frequencies was investigated for Hamiltonians with a range of\ninterparticle interaction strengths from BCS to unitarity in the first test of\nthis approach beyond the unitary regime, and a microscopic basis of the large\nexcitation gaps and universal behavior at unitarity was proposed. Based on the\nsuccess of these earlier studies, the current paper continues to explore the\nability of normal modes to describe superfluidity along the BCS to unitarity\ntransition. The results confirm earlier conclusions that the physics of\nsuperfluidity can be described using normal modes across a wide range of\ninterparticle interaction strengths and offer an alternative to the two-body\npairing models commonly used to describe superfluidity along this transition.",
        "positive": "Finite-temperature valence-bond-solid transitions and thermodynamic\n  properties of interacting SU($2N$) Dirac fermions: We investigate the SU($2N$) symmetry effects with $2N>2$ on the\ntwo-dimensional interacting Dirac fermions at finite temperatures, including\nthe valence-bond-solid transition, the Pomeranchuk effect, the compressibility\nand the uniform spin susceptibility, by performing the determinant quantum\nMonte Carlo simulations of the half-filled SU($2N$) Hubbard model on a\nhoneycomb lattice. The columnar valence-bond-solid (cVBS) phase only breaks the\nthree-fold discrete symmetry, and thus can survive at finite temperatures. The\ndisordered phase in the weak coupling regime is the thermal Dirac semi-metal\nstate, while in the strong coupling regime it is largely a Mott state in which\nthe cVBS order is thermally melted. The calculated entropy-temperature\nrelations for various values of the Hubbard interaction $U$ show that, the\nPomeranchuk effect occurs when the specific entropy is below a characteristic\nvalue of $S^*$ --- the maximal entropy per particle from the spin channel of\nlocal moments. The SU($2N$) symmetry enhances the Pomeranchuk effect, which\nfacilitates the interaction-induced adiabatic cooling. Our work sheds new light\non future explorations of novel states of matter with ultra-cold large-spin\nalkaline fermions."
    },
    {
        "anchor": "Mechanical resonances of mobile impurities in a one-dimensional quantum\n  fluid: We study a one-dimensional interacting quantum liquid hosting a pair of\nmobile impurities causing backscattering. We determine the effective retarded\ninteraction between the two impurities mediated by the liquid. We show that for\nstrong backscattering this interaction gives rise to resonances and\nantiresonances in the finite-frequency mobility of the impurity pair. At the\nantiresonances, the two impurities remain at rest even when driven by a (small)\nexternal force. At the resonances, their synchronous motion follows the\nexternal drive in phase and reaches maximum amplitude. Using a perturbative\nrenormalization group analysis in quantum tunneling across the impurities, we\nstudy the range of validity of our model. We predict that these mechanical\nantiresonances are observable in experiments on ultracold atom gases confined\nto one dimension.",
        "positive": "Universal four-body states in heavy-light mixtures with positive\n  scattering length: The number of four-body states known to behave universally is small. This\nwork adds a new class of four-body states to this relatively short list. We\npredict the existence of a universal four-body bound state for heavy-light\nmixtures consisting of three identical heavy fermions and a fourth\ndistinguishable lighter particle with mass ratio $\\kappa \\gtrsim 9.5$ and\nshort-range interspecies interaction characterized by a positive s-wave\nscattering length. The structural properties of these universal states are\ndiscussed and finite-range effects are analyzed. The bound states can be\nexperimentally realized and probed utilizing ultracold atom mixtures."
    },
    {
        "anchor": "Observation of antiferromagnetic correlations in an ultracold SU($N$)\n  Hubbard model: Mott insulators are paradigms of strongly correlated physics, giving rise to\nphases of matter with novel and hard-to-explain properties. Extending the\ntypical SU(2) symmetry of Mott insulators to SU($N$) is predicted to give\nexotic quantum magnetism at low temperatures, but understanding the effect of\nstrong quantum fluctuations for large $N$ remains an open challenge. In this\nwork, we experimentally observe nearest-neighbor spin correlations in the SU(6)\nHubbard model realized by ytterbium atoms in optical lattices. We study\none-dimensional, two-dimensional square, and three-dimensional cubic lattice\ngeometries. The measured SU(6) spin correlations are dramatically enhanced\ncompared to the SU(2) correlations, due to strong Pomeranchuk cooling. We also\npresent numerical calculations based on exact diagonalization and determinantal\nquantum Monte Carlo. The experimental data for a one-dimensional lattice agree\nwith theory, without any fitting parameters. The detailed comparison between\ntheory and experiment allows us to infer from the measured correlations a\nlowest temperature of $\\left[{0.096 \\pm 0.054 \\, \\rm{(theory)} \\pm 0.030 \\,\n\\rm{(experiment)}}\\right]/k_{\\rm B}$ times the tunneling amplitude. For two-\nand three-dimensional lattices, experiments reach entropies below where our\ncalculations converge, highlighting the experiments as quantum simulations.\nThese results open the door for the study of long-sought SU($N$) quantum\nmagnetism.",
        "positive": "A Dissipatively Stabilized Mott Insulator of Photons: Superconducting circuits are a competitive platform for quantum computation\nbecause they offer controllability, long coherence times and strong\ninteractions - properties that are essential for the study of quantum materials\ncomprising microwave photons. However, intrinsic photon losses in these\ncircuits hinder the realization of quantum many-body phases. Here we use\nsuperconducting circuits to explore strongly correlated quantum matter by\nbuilding a Bose-Hubbard lattice for photons in the strongly interacting regime.\nWe develop a versatile method for dissipative preparation of incompressible\nmany-body phases through reservoir engineering and apply it to our system to\nstabilize a Mott insulator of photons against losses. Site- and time-resolved\nreadout of the lattice allows us to investigate the microscopic details of the\nthermalization process through the dynamics of defect propagation and removal\nin the Mott phase. Our experiments demonstrate the power of superconducting\ncircuits for studying strongly correlated matter in both coherent and\nengineered dissipative settings. In conjunction with recently demonstrated\nsuperconducting microwave Chern insulators, we expect that our approach will\nenable the exploration of topologically ordered phases of matter."
    },
    {
        "anchor": "Ground state of a two component dipolar Fermi gas in a harmonic\n  potential: Interacting two component Fermi gases are at the heart of our understanding\nof macroscopic quantum phenomena like superconductivity. Changing nature of the\ninteraction is expected to head to novel quantum phases. Here we study the\nground state of a two component fermionic gas in a harmonic potential with\ndipolar and contact interactions. Using a variational Wigner function we\npresent the phase diagram of the system with equal but opposite values of the\nmagnetic moment. We identify the second order phase transition from\nparamagnetic to ferronematic phase. Moreover, we show the impact of the\nexperimentally relevant magnetic field on the stability and the magnetization\nof the system. We also investigate a two component Fermi gas with large but\nalmost equal values of the magnetic moment to study how the interplay between\ncontact and dipolar interactions affects the stability properties of the\nmixture. To be specific we discuss experimentally relevant parameters for\nultracold $^{161}$Dy.",
        "positive": "Slow quench dynamics of a trapped one-dimensional Bose gas confined to\n  an optical lattice: We analyze the effect of a linear time-variation of the interaction strength\non a trapped one-dimensional Bose gas confined to an optical lattice. The\nevolution of different observables such as the experimentally accessible onsite\nparticle distribution are studied as a function of the ramp time using\ntime-dependent exact diagonalization and density-matrix renormalization group\ntechniques. We find that the dynamics of a trapped system typically display two\nregimes: for long ramp times, the dynamics are governed by density\nredistribution, while at short ramp times, local dynamics dominate as the\nevolution is identical to that of an homogeneous system. In the homogeneous\nlimit, we also discuss the non-trivial scaling of the energy absorbed with the\nramp time."
    },
    {
        "anchor": "Bulk viscosity of resonating fermions revisited: Kubo formula, sum rule,\n  and the dimer and high-temperature limits: The bulk viscosity of two-component fermions with a zero-range interaction is\nrevisited both in two and three dimensions. We first point out that the\n\"standard\" Kubo formula employed in recent studies has flaws to give rise to an\nunphysical divergent bulk viscosity even in a limit where it is supposed to\nvanish. The corrected Kubo formula as well as the sum rule is then carefully\nrederived so as to confirm that the bulk viscosity indeed vanishes in the free,\nunitarity, and dimer limits. We also discuss that the recently found\ndiscrepancy between the Kubo formalism and the kinetic theory for the bulk\nviscosity is attributed to the fact that the quasiparticle approximation\nassumed by the latter breaks down even in the high-temperature limit.",
        "positive": "Realizing Hopf Insulators in Dipolar Spin Systems: The Hopf insulator is a weak topological insulator characterized by an\ninsulating bulk with conducting edge states protected by an integer-valued\nlinking number invariant. The state exists in three-dimensional two-band\nmodels. We demonstrate that the Hopf insulator can be naturally realized in\nlattices of dipolar-interacting spins, where spin exchange plays the role of\nparticle hopping. The long-ranged, anisotropic nature of the dipole-dipole\ninteractions allows for the precise detail required in the momentum-space\nstructure, while different spin orientations ensure the necessary structure of\nthe complex phases of the hoppings. Our model features robust gapless edge\nstates at both smooth edges, as well as sharp edges obeying a certain\ncrystalline symmetry, despite the breakdown of the two-band picture at the\nlatter. In a companion manuscript [2105.10504], we provide a specific\nexperimental blueprint for implementing our proposal using ultracold polar\nmolecules of $^{40}$K$^{87}$Rb."
    },
    {
        "anchor": "Quantum Monte Carlo simulation of three-dimensional Bose-Fermi mixtures: Exploratory simulations of Bose-Fermi mixtures on the three-dimensional\noptical lattice at finite temperature are performed by adopting the lattice\nquantum chromodynamics technique. We analyze the bosonic superfluid transition\nand its dependence on the strength of the boson-fermion coupling. The particle\ndensities and the pair occupancies are also studied to understand the effect of\nthe boson-fermion coupling to the microscopic properties of the system. Effect\nof the induced fermion-fermion interaction by the boson density fluctuation is\nclearly seen.",
        "positive": "Singlet and Triplet Superfluid Competition in a Mixture of Two-Component\n  Fermi and One-Component Dipolar Bose Gases: We consider a mixture of two-component Fermi and (one-component) dipolar Bose\ngases in which both dipolar interaction and s-wave scattering between fermions\nof opposite spins are tunable. We show that in the long wavelength limit, the\nanisotropy in the Fermi-Fermi interaction induced by phonons of the dipolar\ncondensate can strongly enhance the scattering in the triplet channel. We\ninvestigate in detail the conditions for achieving optimal critical temperature\nat which the triplet superfluid begins to compete with the singlet superfluid."
    },
    {
        "anchor": "Quantum Hall ferromagnets and transport properties of buckled Dirac\n  materials: We study the ground states and low-energy excitations of a generic Dirac\nmaterial with spin-orbit coupling and a buckling structure in the presence of a\nperpendicular magnetic field. The ground states can be classified into three\ntypes under different conditions: SU(2), easy-plane, and Ising quantum Hall\nferromagnets. For the SU(2) and the easy-plane quantum Hall ferromagnets there\nare goldstone modes in the collective excitations, while all the modes are\ngapped in an Ising-type ground state. We compare the Ising quantum Hall\nferromagnet with that of bilayer graphene and present the domain wall solution\nat finite temperatures. We then specify the phase transitions and transport\ngaps in silicene in Landau levels 0 and 1. The phase diagram strongly depends\non the magnetic field and the dielectric constant. We note that there exists\ntriple points in the phase diagrams in Landau level N = 1 that could be\nobserved in experiments.",
        "positive": "Quench-induced delocalization: We consider the evolution of an initially localized wave packet after a\nsudden change in the Hamiltonian, i.e.\\ a quench. When both bound and\nscattering eigenstates exist in the post-quench Hamiltonian, one might expect\npartial delocalization of the wave packet to ensue. Here we show that if the\nquench consists of a sudden switching-off of short-range inter-particle\ninteractions, then Tan's universal relations guarantee delocalization through\nthe high-momentum tail of the momentum distribution. Furthermore, we consider\nthe influence of the range of the interaction and show how a finite range\nalters the coupling to highly excited states. We illustrate our results using\nnumerical simulations of externally trapped particles in one dimension. If the\nexternal potential is both disordered and correlated, then the interaction\nquench leads to transport via delocalized states, showing that localization in\ndisordered systems is sensitive to non-adiabatic changes in the interactions\nbetween particles."
    },
    {
        "anchor": "Quantum phases from competing short- and long-range interactions in an\n  optical lattice: Insights into complex phenomena in quantum matter can be gained from\nsimulation experiments with ultracold atoms, especially in cases where\ntheoretical characterization is challenging. However these experiments are\nmostly limited to short-range collisional interactions. Recently observed\nperturbative effects of long-range interactions were too weak to reach novel\nquantum phases. Here we experimentally realize a bosonic lattice model with\ncompeting short- and infinite-range interactions, and observe the appearance of\nfour distinct phases - a superfluid, a supersolid, a Mott insulator and a\ncharge density wave. Our system is based on an atomic quantum gas trapped in an\noptical lattice inside a high finesse optical cavity. The strength of the\nshort-ranged on-site interactions is controlled by means of the optical lattice\ndepth. The infinite-range interaction potential is mediated by a vacuum mode of\nthe cavity and is independently controlled by tuning the cavity resonance. When\nprobing the phase transition between the Mott insulator and the charge density\nwave in real-time, we discovered a behaviour characteristic of a first order\nphase transition. Our measurements have accessed a regime for quantum\nsimulation of many-body systems, where the physics is determined by the\nintricate competition between two different types of interactions and the zero\npoint motion of the particles.",
        "positive": "Melting of a vortex matter Wigner crystal: The two-dimensional One-Component Plasma (OCP) is a foundational model of the\nstatistical mechanics of interacting particles, describing phenomena common to\nastrophysics, turbulence, and the Fractional Quantum Hall Effect (FQHE).\nDespite an extensive literature, the phase diagram of the 2D OCP is still a\nsubject of some controversy. Here we develop a \"vortex matter\" simulator to\nrealize the logarithmic-interaction OCP experimentally by exploiting the\ntopological character of quantized vortices in a thin superfluid layer.\nPrecision optical-tweezer control of the location of quantized vortices enables\ndirect preparation of the OCP ground state with or without defects, and heating\nfrom acoustic excitations allows the observation of the melting transition from\nthe solid Wigner crystal through the liquid phase. We present novel theoretical\nanalysis that is in quantitative agreement with experimental observations, and\ndemonstrates how equilibrium states are achieved through the system dynamics.\nThis allows a precise measurement of the superfluid-thermal cloud mutual\nfriction and heating coefficients. This platform provides a route towards\nsolving a number of open problems in systems with long-range interactions. At\nequilibrium, it could distinguish between the competing scenarios of grain\nboundary melting and KTHNY theory. Dynamical simulators could test the\nexistence of predicted edge-wave solitons which form a hydrodynamic analogue of\ntopological edge states in the FQHE."
    },
    {
        "anchor": "Superfluidity of identical fermions in an optical lattice: atoms and\n  polar molecules: In this work, we discuss the emergence of $p$-wave superfluids of identical\nfermions in 2D lattices. The optical lattice potential manifests itself in an\ninterplay between an increase in the density of states on the Fermi surface and\nthe modification of the fermion-fermion interaction (scattering) amplitude. The\ndensity of states is enhanced due to an increase of the effective mass of\natoms. In deep lattices, for short-range interacting atoms, the scattering\namplitude is strongly reduced compared to free space due to a small overlap of\nwavefunctions of fermions sitting in the neighboring lattice sites, which\nsuppresses the $p$-wave superfluidity. However, we show that for a moderate\nlattice depth there is still a possibility to create atomic $p$-wave\nsuperfluids with sizable transition temperatures. The situation is drastically\ndifferent for fermionic polar molecules. Being dressed with a microwave field,\nthey acquire a dipole-dipole attractive tail in the interaction potential.\nThen, due to a long-range character of the dipole-dipole interaction, the\neffect of the suppression of the scattering amplitude in 2D lattices is absent.\nThis leads to the emergence of a stable topological $p_x+ip_y$ superfluid of\nidentical microwave-dressed polar molecules.",
        "positive": "Dynamical violation of scale invariance and the dilaton in a cold Fermi\n  gas: We use the large N approximation to find an exotic phase of a cold,\ntwo-dimensional, N-component Fermi gas which exhibits dynamically broken\napproximate scale symmetry. We identify a particular weakly damped collective\nexcitation as the dilaton, the pseudo-Goldstone boson associated with the\nbroken approximate scale symmetry. We argue that the symmetry breaking phase is\nstable for a range of parameters of the theory and there is a fluctuation\ninduced first order quantum phase transition between the normal and the scale\nsymmetry breaking phases which can be driven by tuning the chemical potential.\nWe find that the compressibility of the gas at its lower critical density is\nanomalously large, 2N times that of a perfect gas at the same density."
    },
    {
        "anchor": "Heat and spin transport in a cold atomic Fermi gas: Motivated by recent experiments measuring the spin transport in ultracold\nunitary atomic Fermi gases (Sommer et al., 2011; Sommer et al., 2011), we\nexplore the theory of spin and heat transport in a three-dimensional\nspin-polarized atomic Fermi gas. We develop estimates of spin and thermal\ndiffusivities and discuss magnetocaloric effects, namely the the spin Seebeck\nand spin Peltier effects. We estimate these transport coefficients using a\nBoltzmann kinetic equation in the classical regime and present experimentally\naccessible signatures of the spin Seebeck effect. We study an exactly solvable\nmodel that illustrates the role of momentum-dependent scattering in the\nmagnetocaloric effects.",
        "positive": "Equilibrium trapping of cold atoms using dipole and radiative forces in\n  an optical trap: We report on highly effective trapping of cold atoms by a new method for a\nstable single optical trap in the near-optical resonant regime. An optical trap\nwith the near-optical resonance condition consists of not only the dipole but\nalso the radiative forces, while a trap using a far-off resonance dominates\nonly the dipole force. We estimate a near-optical resonant trap for ultracold\nrubidium atoms in the range between -0.373 and -2.23 THz from the resonance.\nThe time dependence of the trapped atoms indicates some difference of the\nstable center-of-mass positions in the near-optical resonant trap, and also\nindicates that the differences are caused by the change of the equilibrium\ncondition of the optical dipole and radiative forces. A stable position depends\nonly on laser detuning due to the change in the radiative force; however, the\nposition is ineffective against the change in the laser intensity, which\nresults in a change in the radiative force."
    },
    {
        "anchor": "Non equilibrium phase transitions and Floquet Kibble-Zurek scaling: We study the slow crossing of non-equilibrium quantum phase transitions in\nperiodically-driven systems. We explicitly consider a spin chain with a uniform\ntime-dependent magnetic field and focus on the Floquet state that is\nadiabatically connected to the ground state of the static model. We find that\nthis {\\it Floquet ground state} undergoes a series of quantum phase transitions\ncharacterized by a non-trivial topology. To dinamically probe these\ntransitions, we propose to start with a large driving frequency and slowly\ndecrease it as a function of time. Combining analytical and numerical methods,\nwe uncover a Kibble-Zurek scaling that persists in the presence of moderate\ninteractions. This scaling can be used to experimentally demonstrate\nnon-equilibrium transitions that cannot be otherwise observed.",
        "positive": "Macroscopic quantum escape of Bose-Einstein condensates: Analysis of\n  experimentally realizable quasi-one-dimensional traps: The variational-JWKB method is used to determine experimentally accessible\nmacroscopic quantum tunneling regimes of quasi-bound Bose-Einstein condensates\nin two quasi one-dimensional trap configurations. The potentials can be created\nby magnetic and optical traps, a symmetric trap from two offset Gaussian\nbarriers and a tilt trap from a linear gradient and Gaussian barrier. Scaling\nlaws in barrier parameters, ranging from inverse polynomial to square root\ntimes exponential, are calculated and used to elucidate different dynamical\nregimes, such as when classical oscillations dominate tunneling rates in the\nsymmetric trap. The symmetric trap is found to be versatile, with tunneling\ntimes at and below one second, able to hold $10^{3}$ to $10^{4}$ atoms, and\nrealizable for atoms ranging from rubidium to lithium, with unadjusted\nscattering lengths. The tilt trap produces sub-second tunneling times, is able\nto hold a few hundred atoms of lighter elements like lithium, and requiring the\nuse of Feshbach resonance to reduce scattering lengths. To explore a large\nparameter space, an extended Gaussian variational ansatz is used, which can\napproximate large traps with Thomas-Fermi profiles. Nonlinear interactions in\nthe Gross-Pitaevskii equation are shown to produce additional effective\nmean-field barriers, affecting scaling laws."
    },
    {
        "anchor": "Experimental investigation of tunneling times using Bose-Einstein\n  condensates: The time it takes a quantum system to complete a tunneling event (which in\nthe case of cross-barrier tunneling can be viewed as the time spent in a\nclassically forbidden area) is related to the time required for a state to\nevolve to an orthogonal state, and an observation, i.e., a quantum mechanical\nprojection on a particular basis, is required to distinguish one state from\nanother. We have performed time-resolved measurements of Landau-Zener tunneling\nof Bose-Einstein condensates in accelerated optical lattices, clearly resolving\nthe steplike time dependence of the band populations. The use of different\nprotocols enabled us to access the tunneling probability, in two different\nbases, namely, the adiabatic basis and the diabatic basis. The adiabatic basis\ncorresponds to the eigenstates of the lattice, and the diabatic one to the\nfreeparticle momentum eigenstates. Our findings pave the way towards more\nquantitative studies of the tunneling time for LZ transitions, which are of\ncurrent interest in the context of optimal quantum control and the quantum\nspeed limit.",
        "positive": "Comment on \"Feshbach-Einstein Condensates\" by V. G. Rousseau and P. J.\n  H. Denteneer: In a recent paper (Phys. Rev. Lett. 102, 015301 (2009), arXiv:0810.3763)\nRousseau and Denteneer claim that an unconventional \"super-Mott\" (SM) phase is\nrealized by bosons trapped in an optical lattice close to a Feshbach resonance\nwith a molecular state. The supposed SM phase, observed via quantum Monte Carlo\n(QMC) simulations of an atom-molecule Bose-Hubbard model, is an incompressible\nphase developing spontaneous atomic/molecular supercurrents which are perfectly\nanticorrelated. Here we show that the identification of this phase is based on\na misinterpretation of the estimators of superfluidity in QMC, which break down\nin the presence of coherent atom/molecule conversion. Our conclusion is that\nthe supposed SM phase is in fact a fully normal insulator."
    },
    {
        "anchor": "Normal mass density of a superfluid Fermi gas at unitarity: We calculate the normal mass density of a paired Fermi gas at unitarity. The\ndominant contribution near the superfluid transition is from fermionic\nquasiparticle excitations, and is thus sensitive to the pairing gap. A\ncomparison with the recent experiment of Sidorenkov et al. suggests that the\nsuperfluid gap near the transition temperature is larger than the BCS value,\nbut the data do not permit a quantitative inference of the gap. Calculations of\nthe quenched moment of inertia of a BCS superfluid in a harmonic trap are in\nreasonable agreement with the earlier experiment of Riedl et al.",
        "positive": "Spatially partitioned many-body vortices: A vortex in Bose-Einstein condensates is a localized object which looks much\nlike a tiny tornado storm. It is well described by mean-field theory. In the\npresent work we go beyond the current paradigm and introduce many-body\nvortices. These are made of {\\it spatially-partitioned} clouds, carry definite\ntotal angular momentum, and are fragmented rather than condensed objects which\ncan only be described beyond mean-field theory. A phase diagram based on a\nmean-field model assists in predicting the parameters where many-body vortices\noccur. Implications are briefly discussed."
    },
    {
        "anchor": "Mott insulating states and quantum phase transitions of correlated\n  SU(2N) Dirac fermions: The interplay between charge and spin degrees of freedom in strongly\ncorrelated fermionic systems, in particular of Dirac fermions, is a\nlong-standing problem in condensed matter physics. We investigate the competing\norders in the half-filled SU(2N) Hubbard model on a honeycomb lattice, which\ncan be accurately realized in optical lattices with large-spin ultra-cold\nalkaline-earth fermions. Employing large-scale projector determinant quantum\nMonte Carlo simulations, we have explored quantum phase transitions from the\ngapless Dirac semi-metals to the gapped Mott-insulating phases in the SU(4) and\nSU(6) cases. Both of these Mott-insulating states are found to be columnar\nvalence bond solid (cVBS) and to be absent of the antiferromagnetic Neel\nordering and the loop current ordering. Inside the cVBS phases, the dimer\nordering is enhanced by increasing fermion components and behaves\nnon-monotonically as the interaction strength increases. Although the\ntransitions generally should be of first order due to a cubic invariance\npossessed by the cVBS order, the coupling to gapless Dirac fermions can soften\nthe transitions to second order through a non-analytic term in the free energy.\nOur simulations provide important guidance for the experimental exploration of\nnovel states of matter with ultra-cold alkaline earth fermions.",
        "positive": "Dipolar quantum solids emerging in a Hubbard quantum simulator: In quantum mechanical many-body systems, long-range and anisotropic\ninteractions promote rich spatial structure and can lead to quantum\nfrustration, giving rise to a wealth of complex, strongly correlated quantum\nphases. Long-range interactions play an important role in nature; however,\nquantum simulations of lattice systems have largely not been able to realize\nsuch interactions. A wide range of efforts are underway to explore long-range\ninteracting lattice systems using polar molecules, Rydberg atoms, optical\ncavities, and magnetic atoms. Here, we realize novel quantum phases in a\nstrongly correlated lattice system with long-range dipolar interactions using\nultracold magnetic erbium atoms. As we tune the dipolar interaction to be the\ndominant energy scale in our system, we observe quantum phase transitions from\na superfluid into dipolar quantum solids, which we directly detect using\nquantum gas microscopy with accordion lattices. Controlling the interaction\nanisotropy by orienting the dipoles enables us to realize a variety of stripe\nordered states. Furthermore, by transitioning non-adiabatically through the\nstrongly correlated regime, we observe the emergence of a range of metastable\nstripe-ordered states. This work demonstrates that novel strongly correlated\nquantum phases can be realized using long-range dipolar interaction in optical\nlattices, opening the door to quantum simulations of a wide range of lattice\nmodels with long-range and anisotropic interactions."
    },
    {
        "anchor": "Birth of a quasi-stationary black hole in an outcoupled Bose-Einstein\n  condensate: We study the evolution of an initially confined atom condensate which is\nprogressively outcoupled by gradually lowering the confining barrier on one\nside. The goal is to identify protocols that best lead to a quasi-stationary\nsonic black hole separating regions of subsonic and supersonic flow. An optical\nlattice is found to be more efficient than a single barrier in yielding a\nlong-time stationary flow. This is best achieved if the final conduction band\nis broad and its minimum not much lower than the initial chemical potential. An\noptical lattice with a realistic Gaussian envelope yields similar results. We\nanalytically prove and numerically check that, within a spatially\ncoarse-grained description, the sonic horizon is bound to lie right at the\nenvelope maximum. We derive an analytical formula for the Hawking temperature\nin that setup.",
        "positive": "Vector solitons in a spin-orbit coupled spin-$2$ Bose-Einstein\n  condensate: Five-component minimum-energy bound states and mobile vector solitons of a\nspin-orbit-coupled quasi-one-dimensional hyperfine-spin-2 Bose-Einstein\ncondensate are studied using the numerical solution and variational\napproximation of a mean-field model. Two distinct types of solutions with\nsingle-peak and multi-peak density distribution of the components are\nidentified in different domains of interaction parameters. From an analysis of\nGalilean invariance and time-reversal symmetry of the Hamiltonian, we establish\nthat vector solitons with multi-peak density distribution preserve\ntime-reversal symmetry, but cannot propagate maintaining the shape of\nindividual components. However, those with single-peak density distribution\nviolate time-reversal symmetry of the Hamiltonian, but can propagate with a\nconstant velocity maintaining the shape of individual components."
    },
    {
        "anchor": "Dynamically observing the spectra of quantum droplets in optical lattice: Optical lattice plays an important role on stability and dynamics of quantum\ndroplets. In this letter, we investigate the Bogoliubov excitation spectrum of\nquantum droplets in optical lattice in the thermodynamic limit. We classify the\ncollective excitations as synchronous modes, Bloch phononic modes, and\nsite-density imbalanced modes. For synchronous modes, we measure the dipole\noscillation frequencies by quench dynamics with a sudden shift of the optical\nlattice, and the breathing frequencies by Floquet dynamics with a periodic\nchange of the lattice depth. Bloch phononic modes are observable from the\nLandau critical velocity of the droplets. We further discuss the instability\ninduced by the site-dependent density fluctuations, and calculate the critical\nfilling of atoms where the growth of lattice vacancy breaks down the\ntranslational symmetry of the system. This work makes essential steps towards\nmeasuring the excitation spectrum and understanding the superfluid nature of\nquantum droplets in optical lattice.",
        "positive": "Observing non-ergodicity due to kinetic constraints in tilted\n  Fermi-Hubbard chains: The thermalization of isolated quantum many-body systems is deeply related to\nfundamental questions of quantum information theory. While integrable or\nmany-body localized systems display non-ergodic behavior due to extensively\nmany conserved quantities, recent theoretical studies have identified a rich\nvariety of more exotic phenomena in between these two extreme limits. The\ntilted one-dimensional Fermi-Hubbard model, which is readily accessible in\nexperiments with ultracold atoms, emerged as an intriguing playground to study\nnon-ergodic behavior in a clean disorder-free system. While non-ergodic\nbehavior was established theoretically in certain limiting cases, there is no\ncomplete understanding of the complex thermalization properties of this model.\nIn this work, we experimentally study the relaxation of an initial\ncharge-density wave and find a remarkably long-lived initial-state memory over\na wide range of parameters. Our observations are well reproduced by numerical\nsimulations of a clean system. Using analytical calculations we further provide\na detailed microscopic understanding of this behavior, which can be attributed\nto emergent kinetic constraints."
    },
    {
        "anchor": "Phase correlations and quasicondensate in a two-dimensional ultracold\n  Fermi gas: The interplay between dimensionality, coherence and interaction in superfluid\nFermi gases is analyzed by the phase correlation function of the field of\nfermionic pairs. We calculate this phase correlation function for a\ntwo-dimensional superfluid Fermi gas with $s$-wave interactions within the\nGaussian pair fluctuation formalism. The spatial behavior of the correlation\nfunction is shown to exhibit a rapid (exponential) decay at short distances and\na characteristic algebraic decay at large distances, with an exponent matching\nthat expected from Berezinskii-Kosterlitz-Thouless theory of 2D Bose\nsuperfluids. We conclude that the Gaussian pair fluctuation approximation is\nable to capture the physics of quasi long-range order in two-dimensional Fermi\ngases.",
        "positive": "Polaron to molecule transition in a strongly imbalanced Fermi gas: A single down spin Fermion with an attractive, zero range interaction with a\nFermi sea of up-spin Fermions forms a polaronic quasiparticle. The associated\nquasiparticle weight vanishes beyond a critical strength of the attractive\ninteraction, where a many-body bound state is formed. From a variational\nwavefunction in the molecular limit, we determine the critical value for the\npolaron to molecule transition. The value agrees well with the diagrammatic\nMonte Carlo results of Prokof'ev and Svistunov and is consistent with recent\nrf-spectroscopy measurements of the quasiparticle weight by Schirotzek et. al.\nIn addition, we calculate the contact coefficient of the strongly imbalanced\ngas, using the adiabatic theorem of Tan and discuss the implications of the\npolaron to molecule transition for the phase diagram of the attractive Fermi\ngas at finite imbalance."
    },
    {
        "anchor": "All-Optical Production of quantum degeneracy and molecular BEC of $^6$Li: We achieve a highly degenerate and strongly interacting Fermi gas in a\nmixture of the two lowest hyperfine states of $^6$Li by direct evaporative\ncooling in a high power crossed optical dipole trap. The trap is loaded from a\nlarge atom number magneto-optical trap (MOT) which is realized by a laser\nsystem of 2.5-watts intracavity-frequency-doubled light output at 671 nm. With\nthis system, we also demonstrate the production of a molecular Bose-Einstein\ncondensates (mBEC), and observe the anisotropic expansion of Fermi gases in the\nso-called BEC-BCS crossover regime.",
        "positive": "Four-boson bound states from a functional renormalisation group: We use the functional renormalisation group to study the spectrum of three-\nand four-body states in bosonic systems around the unitary limit. Our effective\naction includes all energy-independent contact interactions in the four-atom\nsector and we introduce a running trimer field to eliminate couplings that\ninvolve the atom-atom-dimer channel. The results show qualitatively similar\nbehaviour to those from exact approaches. The truncated action we use leads to\noverbinding of the two four-body states seen in those treatments. It also\ngenerates a third state, although only for a very narrow range of two-body\nscattering lengths."
    },
    {
        "anchor": "Vortex precession dynamics in general radially symmetric potential traps\n  in two-dimensional atomic Bose-Einstein condensates: We consider the motion of individual two-dimensional vortices in general\nradially symmetric potentials in Bose-Einstein condensates. We find that\nalthough in the special case of the parabolic trap there is a logarithmic\ncorrection in the dependence of the precession frequency $\\omega$ on the\nchemical potential $\\mu$, this is no longer true for a general potential $V(r)\n\\propto r^p$. Our calculations suggest that for $p>2$, the precession frequency\nscales with $\\mu$ as $\\omega \\sim \\mu^{-2/p}$. This theoretical prediction is\ncorroborated by numerical computations, both at the level of spectral\n(Bogolyubov-de Gennes) stability analysis by identifying the relevant\nprecession mode dependence on $\\mu$, but also through direct numerical\ncomputations of the vortex evolution in the large $\\mu$, so-called\nThomas-Fermi, limit. Additionally, the dependence of the precession frequency\non the radius of an initially displaced from the center vortex is examined and\nthe corresponding predictions are tested against numerical results.",
        "positive": "Ferromagnetic transition of a two-component Fermi gas of Hard Spheres: We use microscopic many-body theory to analyze the problem of itinerant\nferromagnetism in a repulsive atomic Fermi gas of Hard Spheres. Using simple\narguments, we show that the available theoretical predictions for the onset of\nthe ferromagnetic transition predict a transition point at a density ($k_F a\n\\sim 1$) that is too large to be compatible with the universal low-density\nexpansion of the energy. We present new variational calculations for the\nhard-sphere Fermi gas, in the framework of Fermi hypperneted chain theory, that\nshift the transition to higher densities ($k_F a \\sim 1.8$). Backflow\ncorrelations, which are mainly active in the unpolarized system, are essential\nfor this shift."
    },
    {
        "anchor": "Signatures of non-trivial pairing in the quantum walk of two-component\n  bosons: Nearest neighbour bosons possessing only onsite interactions do not form\nonsite bound pairs in their quantum walk due to fermionization. We obtain\nsignatures of non-trivial onsite pairing in the quantum walk of strongly\ninteracting two component bosons in a one dimensional lattice. By considering\nan initial state with particles from different components located at the\nnearest-neighbour sites in the central region of the lattice, we show that in\nthe dynamical evolution of the system, competing intra- and inter-component\nonsite repulsion leads to the formation of onsite inter-component bound states.\nWe find that when the total number of particles is three, an inter-component\npair is favoured in the limit of equal intra- and inter-component interaction\nstrengths. However, when two bosons from each species are considered,\ninter-component pairs and trimer are favoured depending on the ratios of the\nintra- and inter-component interactions. In both the cases, we find that the\nquantum walks exhibit a re-entrant behaviour as a function of inter-component\ninteraction.",
        "positive": "Gravitational Caustics in an Atom Laser: Typically discussed in the context of optics, caustics are envelopes of\nclassical trajectories (rays) where the density of states diverges, resulting\nin pronounced observable features such as bright points, curves, and extended\nnetworks of patterns. Here, we generate caustics in the matter waves of an atom\nlaser, providing a striking experimental example of catastrophe theory applied\nto atom optics in an accelerated (gravitational) reference frame. We showcase\ncaustics formed by individual attractive and repulsive potentials, and present\nan example of a network generated by multiple potentials. Exploiting internal\natomic states, we demonstrate fluid-flow tracing as another tool of this\nflexible experimental platform. The effective gravity experienced by the atoms\ncan be tuned with magnetic gradients, forming caustics analogous to those\nproduced by gravitational lensing. From a more applied point of view, atom\noptics affords perspectives for metrology, atom interferometry, and\nnanofabrication. Caustics in this context may lead to quantum innovations as\nthey are an inherently robust way of manipulating matter waves."
    },
    {
        "anchor": "Phases and phase transitions of Bose condensed light: phase separation\n  effect: Recent realization of Bose-Einstein condensation of light in 2D provides a\nnew platform for studying novel phases and phase transitions. The combination\nof low effective mass of the confined light and the presence of the dye\nmolecules with randomly oriented directions of the dipolar transition engages a\ncompetition between disorder and the tendency to forming algebraic off-diagonal\norder. The phase diagram of possible phases is constructed at the mean field\nlevel. One of the phases is the condensate of photon pairs induced solely by\nthe orientational disorder. Such a {\\it geometrical } mechanism of pairing has\nno analogy in other systems. It is also found that the photon condensantion can\nproceed as a phase separation effect leading to a non-uniform distribution of\nthe condensate and dye molecules.",
        "positive": "Spin-1 Bose-Hubbard model with two- and three-body interactions: We investigated the ground state of spin-1 bosons interacting under local\ntwo- and three-body interactions in one dimension by means of the density\nmatrix renormalization group method. We found that the even-odd asymmetry will\nbe obtained or not depending on the relative values of the two- and three-body\ninteractions. The Mott insulator lobes are spin isotropic, the first showing a\ndimerized pattern and the second being composed of singlets. The three-body\ninteractions disfavor a longitudinal polar superfluid and a quantum phase\ntransition to a transverse polar superfluid occurs, which could be continuous\nor discontinuous."
    },
    {
        "anchor": "Many-body excitation spectra of trapped bosons with general interaction\n  by linear response: The linear-response theory of the multiconfigurational time-dependent Hartree\nfor bosons method for computing many-body excitations of trapped Bose-Einstein\ncondensates [Phys. Rev. A {\\bf 88}, 023606 (2013)] is implemented for systems\nwith general interparticle interaction. Illustrative numerical examples for\nrepulsive and attractive bosons are provided. The many-body linear-response\ntheory identifies the excitations not unraveled within Bogoliubov--de Gennes\nequations. The theory is herewith benchmarked against the exactly-solvable\none-dimensional harmonic-interaction model. As a complementary result, we\nrepresent the theory in a compact block-diagonal form, opening up thereby an\navenue for treating larger systems.",
        "positive": "Dissipation-assisted coherence formation in a spinor quantum gas: Dissipation affects all real-world physical systems and often induces energy\nor particle loss, limiting the efficiency of processes. Dissipation can also\nlead to the formation of dissipative structures or induce quantum decoherence.\nQuantum decoherence and dissipation are critical for quantum information\nprocessing. On the one hand, such effects can make achieving quantum\ncomputation much harder, but on the other hand, dissipation can promote quantum\ncoherence and offer control over the system. It is the latter avenue -- how\ndissipation can be exploited to promote coherence in a quantum system -- that\nis explored in this work. We report the exploration of dissipation in a\nBose-Einstein condensate (BEC) of spin-2 87Rb atoms. Through experiments and\nnumerical simulations, we show that spin-dependent particle dissipation can\ngive rise to quantum coherence and lead to the spontaneous formation of a\nmagnetic eigenstate. Although the interactions between the atomic spins are not\nferromagnetic, the spin-dependent dissipation enhances the synchronization of\nthe relative phases among five magnetic sublevels, and this effects promotes\nmagnetization."
    },
    {
        "anchor": "Application of the inhomogeneous Kibble-Zurek mechanism to quench\n  dynamics in the transition from a Mott-insulator to a superfluid in a finite\n  system: We apply the theory of inhomogeneous Kibble-Zurek mechanism to understand\nquench dynamics from the Mott insulator to the superfluid in a cold Bose gases\nconfined in both a two-dimensional optical lattice and a harmonic trap. The\nlocal quench time and the freeze-out region associated with the nonadiabatic\ntransition take a nontrivial positional dependence due to the Mott-lobe\nstructure of the ground state phase diagram of the Bose-Hubbard model. We\ndemonstrate that the quench dynamics through the time-dependent Gutzwiller\nsimulations, revealing inhomogeneous properties of the growth of the superfluid\norder parameter. The inhomogeneous Kibble-Zurek theory is applicable for the\nshallow harmonic trap.",
        "positive": "Generating topological optical flux lattices for ultracold atoms by\n  modulated Raman and radio-frequency couplings: We propose a scheme to dynamically generate optical flux lattices with\nnontrivial band topology using amplitude-modulated Raman lasers and\nradio-frequency (rf) magnetic fields. By tuning the strength of Raman and rf\nfields, three distinct phases are realized at unit filling for a unit cell.\nRespectively, these three phases correspond to normal insulator, topological\nChern insulator, and semimetal. Nearly nondispersive bands are found to appear\nin the topological phase, which promises opportunities for investigating\nstrongly correlated quantum states within a simple cold-atom setup. The\nvalidity of our proposal is confirmed by comparing the Floquet quasienergies\nfrom the evolution operator with the spectrum of the effective Hamiltonian."
    },
    {
        "anchor": "Tunable Confinement-Deconfinement Transition in an Ultracold Atom\n  Quantum Simulator: The one-dimensional lattice Schwinger model has recently been realized by\nusing bosons in optical lattices. This model contains both confinement and\ndeconfinement phases, whose phase diagram is controlled by the mass of the\nmatter field and the topological angle. Since varying the mass of matter field\nis straightforward experimentally, we propose how to tune the topological\nangle, allowing accessing the entire phase diagram. We propose that direct\nexperimental evidence of confinement and deconfinement can be obtained by\nmeasuring whether a physical charge is localized around a fixed gauge charge to\nscreen it. We also discuss the PXP model realized in the Rydberg atoms array,\nwhich is equivalent to the lattice Schwinger model when all local gauge charges\nare fixed as zero. Although the gauge charges are fixed, we can alternatively\nprobe the confinement and the deconfinement in the PXP model by studying the\nrelative motion of a pair of a physical charge and an anti-charge. Our scheme\ncan be directly implemented in these two relevant experimental platforms of\nultracold atom quantum simulators.",
        "positive": "Canonical c-field approach to interacting Bose gases: stochastic\n  interference of matter waves: We present a stochastic matter field equation for an interacting many-body\nBose system in equilibrium at ultracold finite temperature. Moreover, the\nproposed equation can be used for non-equilibrium dynamics on phenomenological\ngrounds. This stochastic differential equation is based on a field phase space\nrepresentation reflecting the underlying canonical density operator (fixed\nparticle number N). Remarkably, it allows for an efficient numerical\nimplementation. We apply our canonical c-field method to interference\nexperiments with quasi-one dimensional Bose gases. Crucial features of these\ninterference patterns are reproduced very well and also statistical properties\nin terms of distributions, e.g. for the contrasts, agree well with experimental\nresults."
    },
    {
        "anchor": "Beyond Mean-Field Low-Lying Excitations of Dipolar Bose Gases: We theoretically investigate various beyond mean-field effects on Bose gases\nat zero temperature featuring the anisotropic and long-range dipole-dipole\ninteraction in addition to the isotropic and short-range contact interaction.\nWithin the realm of the Bogoliubov-de Gennes theory, we consider static\nproperties and low-lying excitations of both homogeneous and harmonically\ntrapped dipolar bosonic gases. For the homogeneous system, the condensate\ndepletion, the ground-state energy, the equation of state, and the speed of\nsound are discussed in detail. Making use of the local density approximation,\nwe extend these results in order to study the properties of a dipolar Bose gas\nin a harmonic trap and in the regime of large particle numbers. After deriving\nthe equations of motion for the general case of a triaxial trap, we analyze the\ninfluence of quantum fluctuations on important properties of the gas, such as\nthe equilibrium configuration and the low-lying excitations in the case of a\ncylinder-symmetric trap. In addition to the monopole and quadrupole oscillation\nmodes, we also discuss the radial quadrupole mode. We find that the latter\nacquires a quantum correction exclusively due to the dipole-dipole interaction.\nAs a result, we identify the radial quadrupole as a reasonably accessible\nsource for the signature of dipolar many-body effects and stress the enhancing\ncharacter that dipolar interactions have for quantum fluctuations in the other\noscillation modes.",
        "positive": "Quantum Battery with Ultracold Atoms: Bosons vs. Fermions: We design a quantum battery made up of bosons or fermions in an\nultracold-atom setup, described by Fermi-Hubbard and Bose-Hubbard models,\nrespectively. We compare the performance of bosons and fermions to determine\nwhich can function as a quantum battery more effectively given a particular\non-site interaction and initial state temperature. The performance of a quantum\nbattery is quantified by the maximum energy stored per unit time over the\nevolution under an on-site charging Hamiltonian. We report that when the\ninitial battery state is in the ground state, fermions outperform bosons in a\ncertain configuration over a large range of on-site interactions which are\nshown analytically for a smaller number of lattice sites and numerically for a\nconsiderable number of sites. Bosons take the lead when the temperature is\ncomparatively high in the initial state for a longer range of on-site\ninteraction. We study a number of up and down fermions as well as the number of\nbosons per site to find the optimal filling factor for maximizing the average\npower of the battery. We also introduce disorder in both on-site and hopping\nparameters and demonstrate that the maximum average power is robust against\nimpurities. Moreover, we identify a range of tuning parameters in the fermionic\nand bosonic systems where the disorder-enhanced power is observed."
    },
    {
        "anchor": "Mitigating Heating of Degenerate Fermions in a Ring-Dimple Atomic Trap: We report on the impact of the extended geometry of a ring-dimple trap on\nparticle loss heating of a degenerate Fermi gas. When the Fermi level is\nslightly greater than the depth of the dimple and a non-degenerate \"halo\" is\npresent, the overall heating rate is reduced relative to the case of a bare\nring. We find that the experimentally measured heating rates for the overfilled\ndimple are in good agreement with a model of the hole-induced heating caused by\nbackground gas collisions. This suppression of the heating rate can be helpful\nfor experimental studies of fermionic superfluids in the weak pairing limit,\nwhere achieving and maintaining low temperatures over long time scales is\nessential.",
        "positive": "Fast production of ultracold sodium gases using light--induced\n  desorption and optical trapping: In this paper, we report on the production of a Bose--Einstein condensate\n(BEC) of sodium using light--induced desorption as an atomic source. We load\nabout 2X10^7 atoms in a MOT from this source with a ~6 s loading time constant.\nThe MOT lifetime can be kept around 27 s by turning off the desorbing light\nafter loading. We show that the pressure drops down by a factor of 40 in less\nthan 100 ms after the extinction of the desorbing light, restoring the low\nbackground pressure for evaporation. Using this technique, a \\na BEC with 10^4\natoms is produced after a 6 s evaporation in an optical dipole trap."
    },
    {
        "anchor": "Probing strongly interacting atomic gases with energetic atoms: We investigate properties of an energetic atom propagating through strongly\ninteracting atomic gases. The operator product expansion is used to\nsystematically compute a quasiparticle energy and its scattering rate both in a\nspin-1/2 Fermi gas and in a spinless Bose gas. Reasonable agreement with recent\nquantum Monte Carlo simulations even at a relatively small momentum k/kF>1.5\nindicates that our large-momentum expansions are valid in a wide range of\nmomentum. We also study a differential scattering rate when a probe atom is\nshot into atomic gases. Because the number density and current density of the\ntarget atomic gas contribute to the forward scattering only, its contact\ndensity (measure of short-range pair correlation) gives the leading\ncontribution to the backward scattering. Therefore, such an experiment can be\nused to measure the contact density and thus provides a new local probe of\nstrongly interacting atomic gases.",
        "positive": "Relative dynamics of quantum vortices and massive cores in binary BECs: We study the motion of superfluid vortices with filled massive cores.\nPrevious point-vortex models already pointed out the impact of the core mass on\nthe vortex dynamical properties, but relied on an assumption that is\nquestionable in many physical systems where the immiscibility condition is\nbarely satisfied: the fact that the massive core always lays at the very bottom\nof the effective confining potential constituted by the hosting vortex. Here,\nwe relax this assumption and present a new point-vortex model where quantum\nvortices are harmonically coupled to their massive cores. We thoroughly explore\nthe new dynamical regimes offered by this improved model; we then show that the\nfunctional dependence of the system normal modes on the microscopic parameters\ncan be correctly interpreted only within this new generalized framework. Our\npredictions are benchmarked against the numerical simulations of coupled\nGross-Pitaevskii equations for a realistic mixture of atomic Bose-Einstein\ncondensates."
    },
    {
        "anchor": "Three-dimensional splitting dynamics of giant vortices in Bose-Einstein\n  condensates: We study the splitting dynamics of giant vortices in dilute Bose-Einstein\ncondensates by numerically integrating the three-dimensional Gross-Pitaevskii\nequation in time. By taking advantage of tetrahedral tiling in the spatial\ndiscretization, we decrease the error and increase the reliability of the\nnumerical method. An extensive survey of vortex splitting symmetries is\npresented for different aspect ratios of the harmonic trapping potential. The\nsymmetries of the splitting patterns observed in the simulated dynamics are\nfound to be in good agreement with predictions obtained by solving the dominant\ndynamical instabilities from the corresponding Bogoliubov equations.\nFurthermore, we observe intertwining of the split vortices in prolate\ncondensates and a split-and-revival phenomenon in a spherical condensate.",
        "positive": "Analytic Vortex Dynamics in an Annular Bose-Einstein Condensate: We consider analytically the dynamics of an arbitrary number and\nconfiguration of vortices in an annular Bose-Einstein condensate obtaining\nexpressions for the free energy and vortex precession rates to logarithmic\naccuracy. We also obtain lower bounds for the lifetime of a single vortex in\nthe annulus. Our results enable a closed-form analytic treatment of\nvortex-vortex interactions in the annulus that is exact in the incompressible\nlimit. The incompressible hydrodynamics that is developed here paves the way\nfor more general analytical treatments of vortex dynamics in non-simply\nconnected geometries."
    },
    {
        "anchor": "Nonlinear management of topological solitons in a spin-orbit-coupled\n  system: We consider possibilities to control dynamics of solitons of two types,\nmaintained by the combination of cubic attraction and spin-orbit coupling (SOC)\nin a two-component system, namely, semi-dipoles (SDs) and mixed modes (MMs), by\nmaking the relative strength of the cross-attraction, gamma, a function of time\nperiodically oscillating around the critical value, gamma = 1, which is an\nSD/MM stability boundary in the static system. The structure of SDs is\nrepresented by the combination of a fundamental soliton in one component and\nlocalized dipole mode in the other, while MMs combine fundamental and dipole\nterms in each component. Systematic numerical analysis reveals a finite\nbistability region for the SDs and MMs around gamma = 1, which does not exist\nin the absence of the periodic temporal modulation (\"management\"), as well as\nemergence of specific instability troughs and stability tongues for the\nsolitons of both types, which may be explained as manifestations of resonances\nbetween the time-periodic modulation and intrinsic modes of the solitons. The\nsystem can be implemented in Bose-Einstein condensates, and emulated in\nnonlinear optical waveguides.",
        "positive": "Pairing of Fermions with Unequal Effective Charges in an Artificial\n  Magnetic Field: Artificial magnetic fields (AMFs) created for ultra cold systems depend\nsensitively on the internal structure of the atoms. In a mixture, each\ncomponent experiences a different AMF depending on its internal state. This\nenables the study of Bardeen-Cooper-Schrieffer pairing of fermions with unequal\neffective charges. In this Letter, we investigate the superconducting (SC)\ntransition of a system formed by such pairs as a function of field strength. We\nconsider a homogeneous two-component Fermi gas of unequal effective charges but\nequal densities with attractive interactions. We find that the phase diagram is\naltered drastically compared to the usual balanced charge case. First, for some\nAMFs there is no SC transition and isolated SC phases are formed, reflecting\nthe discrete Landau level (LL) structure. SC phases become reentrant both in\nAMF and temperature. For extremely high fields where both components are\nconfined to their lowest LLs, the effect of the charge imbalance is suppressed.\nCharge asymmetry reduces the critical temperature even in the low-field\nsemiclassical regime. We discuss a pair breaking mechanism due to the unequal\nLorentz forces acting on the components of the Cooper pairs to identify the\nunderlying physics."
    },
    {
        "anchor": "Testing universality of Efimov physics across broad and narrow Feshbach\n  resonances: Efimov physics is a universal phenomenon arising in quantum three-body\nsystems. For systems with resonant two-body interactions, Efimov predicted an\ninfinite series of three-body bound states with geometric scaling symmetry.\nThese Efimov states were first observed in cold Cs atoms and have since been\nreported in a variety of atomic systems. While theories predict non-universal\nbehavior for narrow Feshbach resonances, experiments on Efimov resonances are\nso far consistent with predictions based on universal theories. Here we\ndirectly compare the Efimov spectra in a $^6$Li-$^{133}$Cs mixture near two\nFeshbach resonances which are very different in their resonance strengths but\notherwise almost identical. Our result shows a clear dependence of the Efimov\nresonance positions on Feshbach resonance strength and a clear departure from\nthe universal prediction for the narrow Feshbach resonance.",
        "positive": "\u03c0-flux Dirac bosons and topological edge excitations in a bosonic\n  chiral p-wave superfluid: We study the topological properties of elementary excitations in a staggered\n$p_x \\pm i p_y$ Bose-Einstein condensate realized in recent orbital optical\nlattice experiments. The condensate wave function may be viewed as a\nconfiguration space variant of the famous $p_x+ ip_y$ momentum space order\nparameter of strontium ruthenate superconductors. We show that its elementary\nexcitation spectrum possesses Dirac bosons with $\\pi$ Berry flux. Remarkably,\nif we induce a population imbalance between the $p_x+ip_y$ and $p_x-ip_y$\ncondensate components, a gap opens up in the excitation spectrum resulting in a\nnonzero Chern invariant and topologically protected edge excitation modes. We\ngive a detailed description on how our proposal can be implemented with\nstandard experimental technology."
    },
    {
        "anchor": "Quantitative Determination of Temperature in the Approach to Magnetic\n  Order of Ultracold Fermions in an Optical Lattice: We perform a quantitative simulation of the repulsive Fermi-Hubbard model\nusing an ultracold gas trapped in an optical lattice. The entropy of the system\nis determined by comparing accurate measurements of the equilibrium double\noccupancy with theoretical calculations over a wide range of parameters. We\ndemonstrate the applicability of both high-temperature series and dynamical\nmean-field theory to obtain quantitative agreement with the experimental data.\nThe reliability of the entropy determination is confirmed by a comprehensive\nanalysis of all systematic errors. In the center of the Mott insulating cloud\nwe obtain an entropy per atom as low as 0.77kB which is about twice as large as\nthe entropy at the Neel transition. The corresponding temperature depends on\nthe atom number and for small fillings reaches values on the order of the\ntunneling energy.",
        "positive": "Spectroscopy of edge and bulk collective modes in fractional Chern\n  insulators: The exploration of atomic fractional quantum Hall (FQH) states is now within\nreach in optical-lattice experiments. While ground-state signatures have been\nobserved in a system realizing the Hofstadter-Bose-Hubbard model in a box\n[Leonard et al., Nature 2023], how to access hallmark low-energy collective\nmodes remains a central open question in this context. We introduce a\nspectroscopic scheme based on two interfering Laguerre-Gaussian beams, which\ntransfer a controlled angular momentum and energy to the system. The edge and\nbulk responses to the probe are detected through local density measurements, by\ntracking the transfer of atoms between the bulk and the edge of the FQH\ndroplet. This detection scheme is shown to simultaneously reveal two specific\nsignatures of FQH states: their chiral edge branch and their bulk magneto-roton\nmode. We numerically benchmark our method by considering few bosons in the\n$\\nu=1/2$ Laughlin ground state of the Hofstadter-Bose-Hubbard model, and\ndemonstrate that these signatures are already detectable in realistic systems\nof two bosons, provided that the box potential is larger than the droplet. Our\nwork paves the way for the detection of fractional statistics in cold atoms\nthrough edge signatures."
    },
    {
        "anchor": "Ultracold quantum gases in triangular optical lattices: Over the last years the exciting developments in the field of ultracold atoms\nconfined in optical lattices have led to numerous theoretical proposals devoted\nto the quantum simulation of problems e.g. known from condensed matter physics.\nMany of those ideas demand for experimental environments with non-cubic lattice\ngeometries. In this paper we report on the implementation of a versatile\nthree-beam lattice allowing for the generation of triangular as well as\nhexagonal optical lattices. As an important step the superfluid-Mott insulator\n(SF-MI) quantum phase transition has been observed and investigated in detail\nin this lattice geometry for the first time. In addition to this we study the\nphysics of spinor Bose-Einstein condensates (BEC) in the presence of the\ntriangular optical lattice potential, especially spin changing dynamics across\nthe SF-MI transition. Our results suggest that below the SF-MI phase\ntransition, a well-established mean-field model describes the observed data\nwhen renormalizing the spin-dependent interaction. Interestingly this opens new\nperspectives for a lattice driven tuning of a spin dynamics resonance occurring\nthrough the interplay of quadratic Zeeman effect and spin-dependent\ninteraction. We finally discuss further lattice configurations which can be\nrealized with our setup.",
        "positive": "Crow instability in unitary Fermi gas: We investigate the initiation and subsequent evolution of Crow instability in\nan inhomogeneous unitary Fermi gas using zero-temperature Galilei-invariant\nnon-linear Schr\\\"odinger equation. Considering a cigar-shaped unitary Fermi\ngas, we generate the vortex-antivortex pair either by phase-imprinting or by\nmoving a Gaussian obstacle potential. We observe that the Crow instability in a\nunitary Fermi gas leads to the decay of the vortex-antivortex pair into\nmultiple vortex rings and ultimately into sound waves."
    },
    {
        "anchor": "Large N Expansion for Strongly-coupled Boson-Fermion Mixtures: We study a many-body mixture of an equal number of bosons and two-component\nfermions with a strong contact attraction. In this system bosons and fermions\ncan be paired into composite fermions. We construct a large N extension where\nboth bosons and fermions have the extra large N degrees of freedom and the\nboson-fermion interaction is extended to a four-point contact interaction which\nis invariant under the O(N) group transformation, so that the composite\nfermions become singlet in terms of the O(N) group. It is shown that such O(N)\nsinglet fields have controllable quantum fluctuations suppressed by 1/N factors\nand yield a systematic 1/N-expansion in terms of composite fermions. We derive\nan effective action described by composite fermions up to the\nnext-to-leading-order terms in the large N expansion, and show that there can\nbe the BCS superfluidity of composite fermions at sufficiently low\ntemperatures.",
        "positive": "Evolution of an ultracold gas in a non-Abelian gauge fields: Finite\n  temperature effect: We detail the cooling mechanisms of a Fermionic strontium-87 gas in order to\nstudy its evolution under a non-Abelian gauge field. In contrast to our\nprevious work reported in Ref. [1], we emphasize here on the finite temperature\neffect of the gas. In addition, we provide the detail characterization for the\nefficiency of atoms loading in the cross-dipole trap, the quantitative\nperformance of the evaporative cooling, and the characterization of a\ndegenerate Fermi gas using a Thomas-Fermi distribution."
    },
    {
        "anchor": "Exploring emergent heterogeneous phases in strongly repulsive Fermi\n  gases: Recent experiments have revitalized the interest in a Fermi gas of ultracold\natoms with strong repulsive interactions. In spite of its seeming simplicity,\nthis system exhibits a complex behavior, resulting from the competing action of\ntwo distinct instabilities: ferromagnetism, which promotes spin\nanticorrelations and domain formation; and pairing, that renders the repulsive\nfermionic atoms unstable towards forming weakly bound bosonic molecules. The\nbreakdown of the homogeneous repulsive Fermi liquid arising from such\nconcurrent mechanisms has been recently observed in real time through\npump-probe spectroscopic techniques [A. Amico et al., Phys. Rev. Lett. 121,\n253602 (2018)]. These studies also lead to the discovery of an emergent\nmetastable many-body state, an unpredicted quantum emulsion of anticorrelated\nfermions and pairs. Here, we investigate in detail the properties of such an\nexotic regime by studying the evolution of kinetic and release energies, the\nspectral response and coherence of the unpaired fermionic population, and its\nspin-density noise correlations. All our observations consistently point to a\nlow-temperature heterogeneous phase, where paired and unpaired fermions\nmacroscopically coexist while featuring micro-scale phase separation. Our\nfindings open new appealing avenues for the exploration of quantum emulsions\nand also possibly of inhomogeneous superfluid regimes, where pair condensation\nmay coexist with magnetic order.",
        "positive": "BCS-BEC crossover induced by a synthetic non-Abelian gauge field: We investigate the ground state of interacting spin-$\\half$ fermions (3D) at\na finite density ($\\rho \\sim \\kf^3$) in the presence of a uniform non-Abelian\ngauge field. The gauge field configuration (GFC) described by a vector $\\blam\n\\equiv (\\lambda_x, \\lambda_y, \\lambda_z)$, whose magnitude $\\lambda$ determines\nthe gauge coupling strength, generates a generalized Rashba spin-orbit\ninteraction. For a weak attractive interaction in the singlet channel described\nby a small negative scattering length $(\\kf |\\as| \\lesssim 1)$, the ground\nstate in the absence of the gauge field ($\\lambda=0$) is a BCS\n(Bardeen-Cooper-Schrieffer) superfluid with large overlapping pairs. With\nincreasing gauge coupling strength, a non-Abelian gauge field engenders a\ncrossover of this BCS ground state to a BEC (Bose-Einstein condensate) ground\nstate of bosons even with a weak attractive interaction that fails to produce a\ntwo-body bound state in free vacuum. For large gauge couplings $(\\lambda/\\kf\n\\gg 1)$, the BEC attained is a condensate of bosons whose properties are solely\ndetermined by the gauge field (and not by the scattering length so long as it\nis non-zero) -- we call these bosons \"rashbons\". In the absence of interactions\n($\\as = 0^-$), the shape of the Fermi surface of the system undergoes a\ntopological transition at a critical gauge coupling $\\lambda_T$. For high\nsymmetry gauge field configurations we show that the crossover from the BCS\nsuperfluid to the rashbon BEC occurs in the regime of $\\lambda$ near\n$\\lambda_T$. In the context of cold atomic systems, this work makes an\ninteresting suggestion of obtaining\n  BCS-BEC crossover through a route other than tuning the interaction between\nthe fermions."
    },
    {
        "anchor": "Fulde-Ferrell Pairing instability in Spin-Orbit Coupled Fermi Gas: We consider finite-momentum pairing of superfluid phase in ultracold Fermi\ngas with spin-orbit coupling when subjected to an effective Zeeman field. Based\non our two body and mean field many body calculations, we show that the\nFulde-Ferrell type superfluid dominates in zero and finite temperature phase\ndiagram. We examine the origin and properties of this novel phase\nsystematically.",
        "positive": "Decoherence and entanglement in a bosonic Josephson junction:\n  Bose-enhanced quantum-Zeno control of phase-diffusion: We study the effect of decoherence on dynamical phase diffusion in the\ntwo-site Bose-Hubbard model. Starting with an odd parity excited coherent\nstate, the initial loss of single particle coherence varies from small bound\noscillations in the Rabi regime, through hyperbolic depletion in the Josephson\nregime, to a Gaussian decay in the Fock regime. The inclusion of local-site\nnoise, measuring the relative number difference between the modes, is shown to\nenhance phase-diffusion. In comparison, site-indiscriminate noise measuring the\npopulation imbalance between the two quasi-momentum modes, slows down the loss\nof single-particle coherence. Decoherence thus either enhances or suppresses\nphase-diffusion, depending on the details of system-bath coupling and the\noverlap of decoherence pointer states with collisional-entanglement pointer\nstates. The deceleration of phase-diffusion due to the coupling with the\nenvironment may be viewed as a many-body quantum-Zeno effect. The extended\neffective decay times in the presence of projective measurement, are further\nenhanced with increasing number of particles $N$, by a bosonic factor of\n$\\sqrt{N}$ in the Fock regime and $N/\\log{N}$ in the Josephson regime."
    },
    {
        "anchor": "How to experimentally detect a GGE? - Universal Spectroscopic Signatures\n  of the GGE in the Tonks gas: In this work we study the properties of the density density correlation\nfunction of the 1-D Lieb-Liniger model with infinite repulsion in the GGE\nregime. The GGE describes the equilibrated system in the long time limit after\na quench from a generic initial state. In the case that the initial and hence\nthe final state has low entropy per particle we find that the density density\ncorrelation function has a universal form, in particular it depends on a few\nparameters corresponding to \"key\" momenta and has power law dependence on the\ndistance. This provides an experimental signature of the GGE which may readily\nbe identified through spectroscopy. These signatures are universal and robust\nto initial sate preparation.",
        "positive": "Weyl Superfluidity in a Three-dimensional Dipolar Fermi Gas: Weyl superconductivity or superfluidity, a fascinating topological state of\nmatter, features novel phenomena such as emergent Weyl fermionic excitations\nand anomalies. Here we report that an anisotropic Weyl superfluid state can\narise as a low temperature stable phase in a 3D dipolar Fermi gas. A crucial\ningredient of our model is a rotating external field that generates a\ndirection-dependent two-body effective attraction. Experimental signatures are\npredicted for cold gases in radio-frequency spectroscopy. The finite\ntemperature phase diagram of this system is studied and the transition\ntemperature of the Weyl superfluidity is found to be within the experimental\nscope for atomic dipolar Fermi gases."
    },
    {
        "anchor": "Thermoviscous Hydrodynamics in Non-Degenerate Dipolar Bose Gases: We present a hydrodynamic model of ultracold, but not yet quantum condensed,\ndipolar Bosonic gases. Such systems present both $s$-wave and dipolar\nscattering, the latter of which results in anisotropic transport tensors of\nthermal conductivity and viscosity. This work presents an analytic derivation\nof the viscosity tensor coefficients, utilizing the methods established in\n[Wang et al., arXiv:2205.10465], where the thermal conductivities were derived.\nTaken together, these transport tensors then permit a comprehensive description\nof hydrodynamics that is now embellished with dipolar anisotropy. An analysis\nof attenuation in linear waves illustrates the effect of this anisotropy in\ndipolar fluids, where we find a clear dependence on the dipole orientation\nrelative to the direction of wave propagation.",
        "positive": "Experimental reconstruction of the Berry curvature in a topological\n  Bloch band: Topological properties lie at the heart of many fascinating phenomena in\nsolid state systems such as quantum Hall systems or Chern insulators. The\ntopology can be captured by the distribution of Berry curvature, which\ndescribes the geometry of the eigenstates across the Brillouin zone. Employing\nfermionic ultracold atoms in a hexagonal optical lattice, we generate\ntopological bands using resonant driving and show a full momentum-resolved\nmeasurement of the ensuing Berry curvature. Our results pave the way to explore\nintriguing phases of matter with interactions in topological band structures."
    },
    {
        "anchor": "Effective equations for repulsive quasi-1D BECs trapped with anharmonic\n  transverse potentials: One-dimensional nonlinear Schr\\\"odinger equations are derived to describe the\naxial effective dynamics of cigar-shaped atomic repulsive Bose-Einstein\ncondensates trapped with anharmonic transverse potentials. The accuracy of\nthese equations in the perturbative, Thomas-Fermi, and crossover regimes were\nverified numerically by comparing the ground-state profiles, transverse\nchemical potentials and oscillation patterns with those results obtained for\nthe full three-dimensional Gross-Pitaevskii equation. This procedure allows us\nto derive different patterns of 1D nonlinear models by the control of the\ntransverse confinement.",
        "positive": "Current and entanglement in a Bose-Hubbard lattice: We study the generation of entanglement for interacting cold atoms in an\noptical lattice. The entanglement is generated by managing the interaction\nbetween two distinct atomic species. It is found that the current of one of the\nspecies can be used as a good indicator of entanglement generation. The\nthermalization process between the species is also shown to be closely related\nto the evolution of the current."
    },
    {
        "anchor": "Creating quantum many-body scars through topological pumping of a 1D\n  dipolar gas: Quantum many-body scars, long-lived excited states of correlated quantum\nchaotic systems that evade thermalization, are of great fundamental and\ntechnological interest. We create novel scar states in a bosonic 1D quantum gas\nof dysprosium by stabilizing a super-Tonks-Girardeau gas against collapse and\nthermalization with repulsive long-range dipolar interactions. Stiffness and\nenergy density measurements show that the system is dynamically stable\nregardless of contact interaction strength. This enables us to cycle contact\ninteractions from weakly to strongly repulsive, then strongly attractive, and\nfinally weakly attractive. We show that this cycle is an energy-space\ntopological pump (due to a quantum holonomy). Iterating this cycle offers an\nunexplored topological pumping method to create a hierarchy of quantum\nmany-body scar states.",
        "positive": "Kelvin wave in miscible two-component Bose-Einstein condensates: We study the dispersion of Kelvin waves propagating along single- and\nhalf-quantum vortices in miscible two-component Bose-Einstein condensates based\non the analysis of the Bogoloubov-de Genne equation. With the help of the\ninterpolating formula connecting the dispersion relations at low- and\nhigh-wavenumber regime, we reveal the nontrivial dependence of the dispersion\nrelation of the Kelvin waves on the intercomponent interaction through the\nchange of the vortex core size of the vortical component. We also find the\nsplitting of the Kelvin mode dispersion into gapless and gapfull branches when\nboth components have overlapping single-quantized vortices."
    },
    {
        "anchor": "Fermi-Polaron in a driven-dissipative background medium: The study of polaron of an open quantum system plays an important role in\nboth verifying the effectiveness of approximate many-body theory and predicting\nnovel quantum phenomenone in open quantum systems. In a pioneering work, Piazza\net al have proposed a Fermi-polaron scheme with a lossy impurity [54], which\nexhibits a novel long-lived attractive polaron branch in the quantum Zeno\nlimit. However, we would also run into a counterpart problem that an impurity\nscatters with an open quantum bath exciting polarons, which is what we focus in\non. In this work, we conclude the molecular state under the two limits of\nvanishing small and infinite large dissipation intensity as well as the reason\nwhy the dissipation range leads to the decrease of the gap between the\nmolecular state and molecule-hole continuum in the former case by means of\nanalytically research. The spectrum functions of molecular and polaron states\nwith different dissipation range and loss rate are investigated. We find the\nspectral signals of molecular and polaron states will both diffuse firstly and\nthen revives as the dissipation is on the raise. Moreover, it is shown that the\nattractive and repulsive polarons show different response to the increasing\ndissipation range in our model. At last, we exhibit the polaron energy,\nresidue, effective mass and two-body decay for mass balanced and imbalanced\nsystems. Our results might be useful for future cold atom experiment on open\nquantum systems.",
        "positive": "Exploring topological double-Weyl semimetals with cold atoms in optical\n  lattices: We explore the topological properties of double-Weyl semimetals with cold\natoms in optical lattices. We first propose to realize a tight-binding model of\nsimulating the double-Weyl semimetal with a pair of double-Weyl points by\nengineering the atomic hopping in a three-dimensional optical lattice. We show\nthat the double-Weyl points with topological charges of \\$pm2$ behave as sink\nand source of Berry flux in momentum space connecting by two Fermi arcs and\nthey are stabilized by the \\$C_{4h}$ point-group symmetry. By applying a\nrealizable \\$C_4$ breaking term, we find that each double-Weyl point splits\ninto two single-Weyl points and obtain rich phase diagrams in the parameter\nspace spanned by the strengths of an effective Zeeman term and the \\$C_4$\nbreaking term, which contains a topological and a normal insulating phases and\ntwo topological Weyl semimetal phases with eight and four single-Weyl points,\napart from the double-Weyl semimetal phase. Furthermore, we demonstrate with\nnumerical simulations that (i) the mimicked double- and single-Weyl points can\nbe detected by measuring the atomic transfer fractions after a Bloch\noscillation; (ii) the Chern number of different quantum phases in the phase\ndiagram can be extracted from the center shift of the hybrid Wannier functions,\nwhich can be directly measured with the time-of-flight imaging; (iii) the band\ntopology of the \\$C_4$ symmetric Bloch Hamiltonian can be detected simply from\nmeasuring the spin polarization at the high symmetry momentum points with a\ncondensate in the optical lattice. The proposed system would provide a\npromising platform for elaborating the intrinsic exotic physics of double-Weyl\nsemimetals and the related topological phase transitions."
    },
    {
        "anchor": "Ground states of dipolar gases in quasi-1D ring traps: We compute the ground state of dipoles in a quasi-one-dimensional ring trap\nusing few-body techniques combined with analytic arguments. The effective\ninteraction between two dipoles depends on their center-of-mass coordinate and\ncan be tuned by varying the angle between dipoles and the plane of the ring.\nFor weak enough interactions, the state resembles a weakly interacting Fermi\ngas or an (inhomogeneous) Lieb-Liniger gas. A mapping between the Lieb-Liniger\nand the dipolar-gas parameters in and beyond the Born approximation is\nestablished, and we discuss the effect of inhomogeneities based on a\nlocal-density approximation. For strongly repulsive interactions, the system\nexhibits crystal-like localization of the particles. Their inhomogeneous\ndistribution may be understood in terms of a simple few-body model as well as a\nlocal-density approximation. In the case of partially attractive interactions,\nclustered states form for strong enough coupling, and the dependence of the\nstate on particle number and orientation angle of the dipoles is discussed\nanalytically.",
        "positive": "Bose-Einstein condensation of Efimovian triples in the unitary Bose gas: In an atomic Bose-Einstein condensate quenched to the unitary regime, we\npredict the sequential formation of a significant fraction of condensed pairs\nand triples. At short-distances, we demonstrate the two-body and Efimovian\ncharacter of the condensed pairs and triples, respectively. As the system\nevolves, the size of the condensed pairs and triples becomes comparable to the\ninterparticle distance, such that many-body effects become significant. The\nstructure of the condensed triples depends on the relative size of Efimov\nstates to density scales. Unexpectedly, we find universal condensed triples in\nthe limit where these scales are well-separated. Our findings provide a new\nframework for understanding dynamics in the unitary regime as the Bose-Einstein\ncondensation of few-body composites."
    },
    {
        "anchor": "Anderson localization and Mott insulator phase in the time domain: Particles in space periodic potentials constitute standard models for\ninvestigation of crystalline phenomena in solid state physics. Time periodicity\nof periodically driven systems is a close analogue of space periodicity of\nsolid state crystals. There is an intriguing question if solid state phenomena\ncan be observed in the time domain. Here we show that wave-packets localized on\nresonant classical trajectories of periodically driven systems are ideal\nelements to realize Anderson localization or Mott insulator phase in the time\ndomain. Uniform superpositions of the wave-packets form stationary states of a\nperiodically driven particle. However, an additional perturbation that\nfluctuates in time results in disorder in time and Anderson localization\neffects emerge. Switching to many-particle systems we observe that depending on\nhow strong particle interactions are, stationary states can be Bose-Einstein\ncondensates or single Fock states where definite numbers of particles occupy\nthe periodically evolving wave-packets. Our study shows that non-trivial\ncrystal-like phenomena can be observed in the time domain.",
        "positive": "Photonic topological Anderson insulator in a two-dimensional atomic\n  lattice: Disorder in atomic positions can induce a topologically nontrivial phase -\ntopological Anderson insulator (TAI) - for transverse electric optical\nquasimodes of a two-dimensional honeycomb lattice of immobile atoms. TAI\nrequires both time-reversal and inversion symmetries to be broken to similar\nextents. It is characterized by a nonzero topological invariant, a reduced\ndensity of states and spatially localized quasimodes in the bulk, as well as\npropagating edge states. A transition from TAI to the topological insulator\n(TI) phase can take place at a constant value of the topological invariant,\nshowing that TAI and TI represent the same topological phase."
    },
    {
        "anchor": "Universal correlations along the BEC-BCS crossover: We show that the long-distance behavior of the two-body density correlation\nfunctions and the Cooper-pair probability density of a balanced mixture of a\ntwo-component Fermi gas at $T = 0$, is universal along the BEC-BCS crossover.\nOur result is demonstrated by numerically solving the mean-field BCS model for\ndifferent finite short-range atomic interaction potentials. We find an analytic\nexpression for the correlation length in terms of the chemical potential and\nthe energy gap at zero momentum.",
        "positive": "Brueckner $G$-matrix approach to two-dimensional Fermi gases with the\n  finite-range attractive interaction: Two-dimensional spin-1/2 fermions with the finite-range interaction are\ntheoretically studied. Characterizing the attractive interaction in terms of\nthe scattering length and the effective range, we discuss the finite-range\neffects on the ground-state properties in this system. The Brueckner $G$-matrix\napproach is employed to analyze the finite-range effects on an attractive\nFermi-polaron energy and the equation of state throughout the BEC-BCS crossover\nin two dimensions, which can be realized in the population-imbalanced and\n-balanced cases between two components, respectively. The analytical formulae\nfor these ground states obtained in this study would be useful for\nunderstanding many-body phenomena with finite-range interactions in\nlow-dimensional systems."
    },
    {
        "anchor": "Equilibration rates and negative absolute temperatures for ultracold\n  atoms in optical lattices: As highly tunable interacting systems, cold atoms in optical lattices are\nideal to realize and observe negative absolute temperatures, T < 0. We show\ntheoretically that by reversing the confining potential, stable superfluid\ncondensates at finite momentum and T < 0 can be created with low entropy\nproduction for attractive bosons. They may serve as `smoking gun' signatures of\nequilibrated T < 0. For fermions, we analyze the time scales needed to\nequilibrate to T < 0. For moderate interactions, the equilibration time is\nproportional to the square of the radius of the cloud and grows with increasing\ninteraction strengths as atoms and energy are transported by diffusive\nprocesses.",
        "positive": "Atom Interferometric Imaging of Differential Potentials Using an Atom\n  Laser: Interferometry is a prime technique for modern precision measurements. Atoms,\nunlike light, have significant interactions with electric, magnetic, and\ngravitational fields, making their use in interferometric applications\nparticularly versatile. Here, we demonstrate atom interferometry to image\noptical and magnetic potential landscapes over an area exceeding $240 \\mu m\n\\times 600 \\mu m$. The differential potentials employed in our experiments\ngenerate phase imprints in an atom laser that are made visible through a Ramsey\npulse sequence. We further demonstrate how advanced pulse sequences can enhance\ndesired imaging features, e.g. to image steep potential gradients. A\ntheoretical discussion is presented that provides a semiclassical analysis and\nmatching numerics."
    },
    {
        "anchor": "Phase Imprinting in Equilibrating Fermi Gases: The Transience of Vortex\n  Rings and Other Defects: We present numerical simulations of phase imprinting experiments in ultracold\ntrapped Fermi gases which are in good agreement with recent, independent\nexperimental results. Our focus is on the sequence and evolution of defects\nusing the fermionic time-dependent Ginzburg-Landau equation, which contains\ndissipation necessary for equilibration. In contrast to other simulations we\nintroduce small, experimentally unavoidable symmetry breaking, particularly\nthat associated with thermal fluctuations and with the phase imprinting tilt\nangle, and illustrate their dramatic effects. The former causes vortex rings in\nconfined geometries to move to the trap surface and rapidly decay into more\nstable vortex lines, as appears consistent with recent experimental claims. The\nlatter aligns the precessing and relatively long-lived vortex filaments,\nrendering them difficult to distinguish from solitons.",
        "positive": "Optical lattices as a tool to study defect-induced superfluidity: We study the superfluid response, the energetic and structural properties of\na one-dimensional ultracold Bose gas in an optical lattice of arbitrary\nstrength. We use the Bose-Fermi mapping in the limit of infinitely large\nrepulsive interaction and the diffusion Monte Carlo method in the case of\nfinite interaction. For slightly incommensurate fillings we find a superfluid\nbehavior which is discussed in terms of vacancies and interstitials. It is\nshown that both the excitation spectrum and static structure factor are\ndifferent for the cases of microscopic and macroscopic fractions of defects.\nThis system provides a extremely well-controlled model for studying\ndefect-induced superfluidity."
    },
    {
        "anchor": "Trimers in the resonant 2+1 fermionic problem on a narrow Feshbach\n  resonance : Crossover from Efimovian to Hydrogenoid spectrum: We study the quantum three-body free space problem of two same-spin-state\nfermions of mass $m$ interacting with a different particle of mass $M$, on an\ninfinitely narrow Feshbach resonance with infinite s-wave scattering length.\nThis problem is made interesting by the existence of a tunable parameter, the\nmass ratio $\\alpha=m/M$. By a combination of analytical and numerical\ntechniques, we obtain a detailed picture of the spectrum of three-body bound\nstates, within {\\sl each} sector of fixed total angular momentum $l$. For\n$\\alpha$ increasing from 0, we find that the trimer states first appear at the\n$l$-dependent Efimovian threshold $\\alpha_c^{(l)}$, where the Efimov exponent\n$s$ vanishes, and that the {\\sl entire} trimer spectrum (starting from the\nground trimer state) is geometric for $\\alpha$ tending to $\\alpha_c^{(l)}$ from\nabove, with a global energy scale that has a finite and non-zero limit. For\nfurther increasing values of $\\alpha$, the least bound trimer states still form\na geometric spectrum, with an energy ratio $\\exp(2\\pi/|s|)$ that becomes closer\nand closer to unity, but the most bound trimer states deviate more and more\nfrom that geometric spectrum and eventually form a hydrogenoid spectrum.",
        "positive": "Open source Matrix Product States: Exact diagonalization and other\n  entanglement-accurate methods revisited in quantum systems: Tensor network methods as presented in our open source Matrix Product States\nsoftware have opened up the possibility to study many-body quantum physics in\none and quasi-one-dimensional systems in an easily accessible package similar\nto density functional theory codes but for strongly correlated dynamics. Here,\nwe address methods which allow one to capture the full entanglement without\ntruncation of the Hilbert space. Such methods are suitable for validation of\nand comparisons to tensor network algorithms, but especially useful in the case\nof new kinds of quantum states with high entanglement violating the truncation\nin tensor networks. Quantum cellular automata are one example for such a\nsystem, characterized by tunable complexity, entanglement, and a large spread\nover the Hilbert space. Beyond the evolution of pure states as a closed system,\nwe adapt the techniques for open quantum systems simulated via the Lindblad\nmaster equation. We present three algorithms for solving closed-system\nmany-body time evolution without truncation of the Hilbert space. Exact\ndiagonalization methods have the advantage that they not only keep the full\nentanglement but also require no approximations to the propagator. Seeking the\nlimits of a maximal number of qubits on a single core, we use Trotter\ndecompositions or Krylov approximation to the exponential of the Hamiltonian.\nAll three methods are also implemented for open systems represented via the\nLindblad master equation built from local channels. We show their convergence\nparameters and focus on efficient schemes for their implementations including\nAbelian symmetries, e.g., U(1) symmetry used for number conservation in the\nBose-Hubbard model or discrete Z2 symmetries in the quantum Ising model. We\npresent the thermalization timescale in the long-range quantum Ising model as a\nkey example of how exact diagonalization contributes to novel physics."
    },
    {
        "anchor": "BCS-BEC crossover and the disappearance of FFLO-correlations in a\n  spin-imbalanced, one-dimensional Fermi gas: We present a numerical study of the one-dimensional BCS-BEC crossover of a\nspin-imbalanced Fermi gas. The crossover is described by the Bose-Fermi\nresonance model in a real space representation. Our main interest is in the\nbehavior of the pair correlations, which, in the BCS limit, are of the\nFulde-Ferrell-Larkin-Ovchinnikov type, while in the BEC limit, a superfluid of\ndiatomic molecules forms that exhibits quasi-condensation at zero momentum. We\nuse the density matrix renormalization group method to compute the phase\ndiagram as a function of the detuning of the molecular level and the\npolarization. As a main result, we show that FFLO-like correlations disappear\nwell below full polarization close to the resonance. The critical polarization\ndepends on both the detuning and the filling.",
        "positive": "Six-dimensional time-space crystalline structures: Time crystalline structures are characterized by regularity that\nsingle-particle or many-body systems manifest in the time domain, closely\nresembling the spatial regularity of ordinary space crystals. Here we show that\ntime and space crystalline structures can be combined together and even\nsix-dimensional time-space lattices can be realized. As an example, we\ndemonstrate that such time-space crystalline structures can reveal the\nsix-dimensional quantum Hall effect quantified by the third Chern number."
    },
    {
        "anchor": "Model-independent determination of the shear viscosity of a trapped\n  unitary Fermi gas: Application to high temperature data: Determinations of the shear viscosity of trapped ultracold gases suffer from\nsystematic, uncontrolled uncertainties related to the treatment of the dilute\npart of the gas cloud. In this work we present an analysis of expansion\nexperiments based on a new method, anisotropic fluid dynamics, that\ninterpolates between Navier-Stokes fluid dynamics at the center of the cloud\nand ballistic behavior in the dilute corona. We validate the method using a\ncomparison between anisotropic fluid dynamics and numerical solutions of the\nBoltzmann equation. We then apply anisotropic fluid dynamics to the expansion\ndata reported by Cao et al. In the high temperature limit we find\n$\\eta=0.282(mT)^{3/2}$, which agrees within about 5\\% with the theoretical\nprediction $\\eta=0.269(mT)^{3/2}$.",
        "positive": "A scalable Bose-Einstein condensate Sagnac interferometer in a linear\n  trap: We demonstrate a two-dimensional atom interferometer in a harmonic magnetic\nwaveguide using a Bose-Einstein condensate. Such an interferometer could\nmeasure rotation using the Sagnac effect. Compared to free space\ninterferometers, larger interactions times and enclosed areas can in principle\nbe achieved, since the atoms are not in free fall. In this implementation, we\ninduce the atoms to oscillate along one direction by displacing the trap\ncenter. We then split and recombine the atoms along an orthogonal direction,\nusing an off-resonant optical standing wave. We enclose a maximum effective\narea of 0.1 square mm, limited by fluctuations in the initial velocity and the\ncoherence time of the interferometer. We argue that this arrangement is\nscalable to enclose larger areas by increasing the coherence time and then\nmaking repeated loops."
    },
    {
        "anchor": "Spiraling vortices in exciton-polariton condensates: We introduce the phenomenon of spiraling vortices in driven-dissipative\n(non-equilibrium) exciton-polariton condensates excited by a non-resonant pump\nbeam. At suitable low pump intensities, these vortices are shown to spiral\nalong circular trajectories whose diameter is inversely proportional to the\neffective mass of the polaritons, while the rotation period is mass\nindependent. Both diameter and rotation period are inversely proportional to\nthe pump intensity. Stable spiraling patterns in the form of complexes of\nmultiple mutually-interacting vortices are also found. At elevated pump\nintensities, which create a stronger homogeneous background, we observe more\ncomplex vortex trajectories resembling Spirograph patterns.",
        "positive": "Enhancing disorder-free localization through dynamically emergent local\n  symmetries: Disorder-free localization is a recently discovered phenomenon of\nnonergodicity that can emerge in quantum many-body systems hosting gauge\nsymmetries when the initial state is prepared in a superposition of gauge\nsuperselection sectors. Thermalization is then prevented up to all accessible\nevolution times despite the model being nonintegrable and\ntranslation-invariant. In a recent work [Halimeh, Zhao, Hauke, and Knolle,\narXiv:2111.02427], it has been shown that terms linear in the gauge-symmetry\ngenerator stabilize disorder-free localization in $\\mathrm{U}(1)$ gauge\ntheories against gauge errors that couple different superselection sectors.\nHere, we show in the case of $\\mathbb{Z}_2$ gauge theories that disorder-free\nlocalization can not only be stabilized, but also \\textit{enhanced} by the\naddition of translation-invariant terms linear in a local $\\mathbb{Z}_2$\n\\textit{pseudogenerator} that acts identically to the full generator in a\nsingle superselection sector, but not necessarily outside of it. We show\nanalytically and numerically how this leads through the quantum Zeno effect to\nthe dynamical emergence of a renormalized gauge theory with an enhanced local\nsymmetry, which contains the $\\mathbb{Z}_2$ gauge symmetry of the ideal model,\nassociated with the $\\mathbb{Z}_2$ pseudogenerator. The resulting proliferation\nof superselection sectors due to this dynamically emergent gauge theory creates\nan effective disorder greater than that in the original model, thereby\nenhancing disorder-free localization. We demonstrate the experimental\nfeasibility of the $\\mathbb{Z}_2$ pseudogenerator by providing a detailed\nreadily implementable experimental proposal for the observation of\ndisorder-free localization in a Rydberg setup."
    },
    {
        "anchor": "On the Josephson effect in a Bose-Einstein condensate subject to a\n  density dependent gauge potential: We investigate the coherent dynamics of a Bose-Einstein condensate in a\ndouble well, subject to a density dependent gauge potential. Further, we derive\nthe nonlinear Josephson equations that allow us to understand the many-body\nsystem in terms of a classical Hamiltonian that describes the motion of a\nnonrigid pendulum with an initial angular offset. Finally we analyze the\nphase-space trajectories of the system, and describe how the self-trapping is\naffected by the presence of an interacting gauge potential.",
        "positive": "Fluctuation effects in rotating Bose-Einstein condensates with broken\n  $\\mathrm{SU}(2)$ and $\\mathrm{U}(1)\\times \\mathrm{U}(1)$ symmetries in the\n  presence of intercomponent density-density interactions: Thermal fluctuations and melting transitions for rotating single-component\nsuperfluids have been intensively studied and are well understood. In contrast,\nthe thermal effects on vortex states for two-component superfluids with\ndensity-density interaction, which have a much richer variety of vortex ground\nstates, have been much less studied. Here, we investigate the thermal effects\non vortex matter in superfluids with $\\mathrm{U(1)}\\times \\mathrm{U(1)}$ broken\nsymmetries and intercomponent density-density interactions, as well as the case\nwith a larger $\\mathrm{SU(2)}$ broken symmetry obtainable from the\n$\\mathrm{U(1)}\\times \\mathrm{U(1)}$-symmetric case by tuning scattering\nlengths. In the former case we find that, in addition to first-order melting\ntransitions, the system exhibits thermally driven phase transitions between\nsquare and hexagonal lattices. Our main result, however, concerns the case\nwhere the condensate exhibits $\\mathrm{SU(2)}$-symmetry, and where vortices are\nnot topological. At finite temperature, the system exhibits effects which do\nnot have a counter-part in single component systems. Namely, it has a state\nwhere thermally averaged quantities show no regular vortex lattice, yet the\nsystem retains superfluid coherence along the axis of rotation. In such a\nstate, the thermal fluctuations result in transitions between different\n(nearly)-degenerate vortex states without undergoing a melting transition. Our\nresults apply to multi-component Bose-Einstein condensates, and we suggest how\nto experimentally detect some of these unusual effects in such systems."
    },
    {
        "anchor": "Adiabatic preparation of entangled, magnetically ordered states with\n  cold bosons in optical lattices: We analyze a scheme for preparation of magnetically ordered states of\ntwo-component bosonic atoms in optical lattices. We compute the dynamics during\nadiabatic and optimized time-dependent ramps to produce ground states of\neffective spin Hamiltonians, and determine the robustness to decoherence for\nrealistic experimental system sizes and timescales. Ramping parameters near a\nphase transition point in both effective spin-1/2 and spin-1 models produces\nentangled spin-symmetric states that have potential future applications in\nquantum enhanced measurement. The preparation of these states and their\nrobustness to decoherence is quantified by computing the Quantum Fisher\nInformation of final states. We identify that the generation of useful\nentanglement should in general be more robust to heating than it would be\nimplied by the state fidelity, with corresponding implications for practical\napplications.",
        "positive": "Systematic interpolatory ansatz for one-dimensional polaron systems: We explore a new variational principle for studying one-dimensional quantum\nsystems in a trapping potential. We focus on the Fermi polaron problem, where a\nsingle distinguishable impurity interacts through a contact potential with a\nbackground of identical fermions. We can accurately describe this system at\narbitrary finite repulsion by constructing a truncated basis containing states\nat both the limits of zero and infinite repulsion. We show how to construct\nthis basis and how to obtain energies, density matrices and correlation\nfunctions, and provide results both for a harmonic well and a double well for\nvarious particle numbers. The results are compared both with matrix product\nstates methods and with the analytical result for two particles in a harmonic\nwell."
    },
    {
        "anchor": "Mixtures of dipolar gases in two dimensions: a quantum Monte Carlo study: We studied the miscibility of two dipolar quantum gases in the limit of zero\ntemperature. The system under study is composed by a mixture of two Bose gases\nwith dominant dipolar interaction in a two-dimensional harmonic confinement.\nThe dipolar moments are considered all to be perpendicular to the plane,\nturning the dipolar potential in a purely repulsive and isotropic model. Our\nanalysis is carried out by using the diffusion Monte Carlo method which allows\nfor an exact solution to the many-body problem within some statistical noise.\nOur results show that the miscibility between the two species is rather\nconstrained as a function of the relative dipolar moments and masses of the two\ncomponents. A narrow regime is predicted where both species mix and we\nintroduce an adimensional parameter whose value predicts quite accurately the\nmiscibility of the two dipolar gases.",
        "positive": "Comment on \"Berezinskii-Kosterlitz-Thouless transition in\n  two-dimensional dipolar stripes\": In a recent article [R. Bombin, F. Mazzanti and J. Boronat, Phys. Rev. A100,\n063614 (2019)], it is contended that a two-dimensional system of dipolar\nbosons, with dipole moments aligned at particular angles with respect to the\ndirection perpendicular to the plane of motion, featuring a \"striped\"\ncrystalline ground state, in turn undergoes a Berezinskii-Kosterlitz-Thouless\nsuperfluid transition at low temperature, making it a two-dimensional\nsupersolid. We show here that the results provided therein, obtained by means\nof Quantum Monte Carlo simulations, do not actually support such a conclusion.\nRather, they are consistent with that expounded in our work [J. Low Temp. Phys.\n196, 413 (2019)], namely that the striped ground state is insulating (i.e.,\nnon-superfluid in the conventional sense), essentially behaving like a system\nof quasi-one-dimensional, parallel independent chains. We attribute the\nincorrectness of the conclusion reached by Bombin et al. to the very small\nsizes of their simulated system, which do not allow for a reliable\nextrapolation to the thermodynamic limit."
    },
    {
        "anchor": "Effect of three-body loss on itinerant ferromagnetism in an atomic Fermi\n  gas: A recent experiment has provided the first evidence for itinerant\nferromagnetism in an ultracold atomic gas of fermions with repulsive\ninteractions. However, the gas in this regime is also subject to significant\nthree-body loss. We adopt an extended Hertz-Millis theory to account for the\neffect of loss on the transition and on the ferromagnetic state. We find that\nthe losses damp quantum fluctuations and thereby significantly increase the\ncritical interaction strength needed to induce ferromagnetism. This effect may\nresolve a discrepancy between the experiment and previous theoretical\npredictions of the critical interaction strength. We further illuminate the\nimpact of loss by studying the collective spin excitations in the ferromagnet.\nEven in the fully polarized state, where loss is completely suppressed, spin\nwaves acquire a decay rate proportional to the three-body loss coefficient.",
        "positive": "Observation of scale invariance and universality in two-dimensional Bose\n  gases: The collective behavior of a many-body system near a continuous phase\ntransition is insensitive to the details of its microscopic physics[1].\nCharacteristic features near the phase transition are that the thermodynamic\nobservables follow generalized scaling laws[1]. The\nBerezinskii-Kosterlitz-Thouless (BKT) phase transition[2,3] in two-dimensional\n(2D) Bose gases presents a particularly interesting case because the marginal\ndimensionality and intrinsic scaling symmetry[4] result in a broad fluctuation\nregime which manifests itself in an extended range of universal scaling\nbehavior. Studies on BKT transition in cold atoms have stimulated great\ninterest in recent years[5-10], clear demonstration of a critical behavior near\nthe phase transition, however, has remained an elusive goal. Here we report the\nobservation of a scale-invariant, universal behavior of 2D gases through\nin-situ density and density fluctuation measurements at different temperatures\nand interaction strengths. The extracted thermodynamic functions confirm a wide\nuniversal region near the BKT phase transition, provide a sensitive test to the\nuniversality prediction by classical-field theory[11,12] and quantum Monte\nCarlo (MC) calculations[13], and point toward growing density-density\ncorrelations in the fluctuation region. Our assay raises new perspectives to\nexplore further universal phenomena in the realm of classical and quantum\ncritical physics."
    },
    {
        "anchor": "Dark solitons revealed in Lieb-Liniger eigenstates: We study how dark solitons, i.e. solutions of one-dimensional single-particle\nnonlinear time-dependent Schr\\\"odinger equation, emerge from eigenstates of a\nlinear many-body model of contact interacting bosons moving on a ring, the\nLieb-Liniger model. This long-standing problem was addressed by various groups,\nwhich presented different, seemingly unrelated, procedures to reveal the\nsolitonic waves directly from the many-body model. Here, we propose a\nunification of these results using a simple Ansatz for the many-body eigenstate\nof the Lieb-Liniger model, which gives us access to systems of hundreds of\natoms. In this approach, mean-field solitons emerge in a single-particle\ndensity through repeated measurements of particle positions in the Ansatz\nstate. The post-measurement state turns out to be a wave packet of yrast states\nof the reduced system.",
        "positive": "Lattice assisted spectroscopy: a generalized scanning tunnelling\n  microscope for ultra-cold atoms: We show that the possibility to address and image single sites of an optical\nlattice, now an experimental reality, allows to measure the frequency-resolved\nlocal particle and hole spectra of a wide variety of one- and two-dimensional\nsystems of lattice-confined strongly correlated ultracold atoms. Combining\nperturbation theory and time-dependent DMRG, we validate this scheme of\nlattice-assisted spectroscopy (LAS) on several example systems, such as the 1D\nsuperfluid and Mott insulator, with and without a parabolic trap, and finally\non edge states of the bosonic Su-Schrieffer-Heeger model. We also highlight\nextensions of our basic scheme to obtain an even wider variety of interesting\nand important frequency resolved spectra."
    },
    {
        "anchor": "Emergent isotropy of a wave-turbulent cascade in the Gross-Pitaevskii\n  model: The restoration of symmetries is one of the most fascinating properties of\nturbulence. We report a study of the emergence of isotropy in the\nGross-Pitaevskii model with anisotropic forcing. Inspired by recent\nexperiments, we study the dynamics of a Bose-Einstein condensate in a\ncylindrical box driven along the symmetry axis of the trap by a spatially\nuniform force. We introduce a measure of anisotropy $A(k,t)$ defined on the\nmomentum distributions $n(\\boldsymbol{k},t)$, and study the evolution of\n$A(k,t)$ and $n(\\boldsymbol{k},t)$ as turbulence proceeds. As the system\nreaches a steady state, the anisotropy, large at low momenta because of the\nlarge-scale forcing, is greatly reduced at high momenta. While\n$n(\\boldsymbol{k},t)$ exhibits a self-similar cascade front propagation,\n$A(k,t)$ decreases without such self-similar dynamics. Finally, our numerical\ncalculations show that the isotropy of the steady state is robust with respect\nto the amplitude of the drive.",
        "positive": "Competing instabilities at long length scales in the one-dimensional\n  Bose-Fermi-Hubbard model at commensurate fillings: We study the phase diagram of the one-dimensional Bose-Fermi-Hubbard model at\nunit filling for the scalar bosons and half filling for the $S=1/2$ fermions\nusing quantum Monte Carlo simulations. The bare interaction between the\nfermions is set to zero. A central question of our study is what type of\ninteractions can be induced between the fermions by the bosons, for both weak\nand strong interspecies coupling. We find that the induced interactions can\nlead to competing instabilities favoring phase separation, superconducting\nphases, and density wave structures, in many cases at work on length scales of\nmore than 100 sites. Marginal bosonic superfluids with a density matrix\ndecaying faster than what is allowed for pure bosonic systems with on-site\ninteractions, are also found."
    },
    {
        "anchor": "Crystalline phase for one-dimensional ultra-cold atomic bosons: We study cold atomic gases with a contact interaction and confined into\none-dimension. Crossing the confinement induced resonance the correlation\nbetween the bosons increases, and introduces an effective range for the\ninteraction potential. Using the mapping onto the sine-Gordon model and a\nHubbard model in the strongly interacting regime allows us to derive the phase\ndiagram in the presence of an optical lattice. We demonstrate the appearance of\na phase transition from a Luttinger liquid with algebraic correlations into a\ncrystalline phase with a particle on every second lattice site.",
        "positive": "Ground states of a mixture of two species of spin-1 Bose gases with\n  interspecies spin exchange in a magnetic field: We consider a mixture of two species of spin-1 atoms with both interspecies\nand intraspecies spin exchanges in a weak magnetic field. Under the usual\nsingle mode approximation, it can be reduced to a model of coupled giant spins.\nWe find most of its ground states. This is a complicated problem of energy\nminimization, with three quantum variables under constraints, i.e. the total\nspin of each species and the total spin of the whole mixture, as well as four\nparameters, including intraspecies and interspecies spin coupling strengths and\nthe magnetic field. The quantum phase diagram is very rich. Compared with the\ncase without a magnetic field, the ground states are modified by a magnetic\nfield, which also modifies the ground state boundaries or introduces new\ncrossover regimes on the phase diagram. Without interspecies spin coupling, the\nquantum phase transitions existing in absence of a magnetic field disappear\nwhen a magnetic field is applied, which leads to crossover regimes in the phase\ndiagram. Under ferromagnetic interspecies spin coupling, the ground states\nremain disentangled no matter whether there is a magnetic field. For\nantiferromagnetic interspecies spin coupling, a magnetic field entangles the\nground states in some parameter regimes. When the intraspecies spin couplings\nare both ferromagnetic, the quantum phase transition between antiferromagnetic\nand zero interspecies spin couplings survives the magnetic field. When the\nintraspecies spin couplings are both antiferromagnetic, a magnetic field\ninduces new quantum phase transitions between antiferromagnetic and zero\ninterspecies spin couplings."
    },
    {
        "anchor": "Continuous feedback on a quantum gas coupled to an optical cavity: We present an active feedback scheme acting continuously on the state of a\nquantum gas dispersively coupled to a high-finesse optical cavity. The quantum\ngas is subject to a transverse pump laser field inducing a self-organization\nphase transition, where the gas acquires a density modulation and photons are\nscattered into the resonator. Photons leaking from the cavity allow for a\nreal-time and non-destructive readout of the system. We stabilize the mean\nintra-cavity photon number through a micro-processor controlled feedback\narchitecture acting on the intensity of the transverse pump field. The feedback\nscheme can keep the mean intra-cavity photon number $n_\\text{ph}$ constant, in\na range between $n_\\text{ph}=0.17\\pm 0.04$ and $n_\\text{ph}=27.6\\pm 0.5$, and\nfor up to 4 s. Thus we can engage the stabilization in a regime where the\nsystem is very close to criticality as well as deep in the self-organized\nphase. The presented scheme allows us to approach the self-organization phase\ntransition in a highly controlled manner and is a first step on the path\ntowards the realization of many-body phases driven by tailored feedback\nmechanisms.",
        "positive": "Analytical results for the superflow of spin-orbit-coupled Bose-Einstein\n  condensates in optical lattices: In this paper, we show that for sufficiently strong atomic interactions,\nthere exist analytical solutions of current-carrying nonlinear Bloch states at\nthe Brillouin zone edge to the model of spin-orbit-coupled Bose-Einstein\ncondensates (BECs) with symmetric spin interaction loaded into optical\nlattices. These simple but generic exact solutions provide an analytical\ndemonstration of some intriguing properties which have neither an analog in the\nregular BEC lattice systems nor in the uniform spin-orbit-coupled BEC systems.\nIt is an analytical example for understanding the superfluid and other related\nproperties of the spin-orbit-coupled BEC lattice systems."
    },
    {
        "anchor": "An Example of Quantum Anomaly in the Physics of Ultra-Cold Gases: In this article, we propose an experimental scheme for observation of a\nquantum anomaly---quantum-mechanical symmetry breaking---in a two-dimensional\nharmonically trapped Bose gas. The anomaly manifests itself in a shift of the\nmonopole excitation frequency away from the value dictated by the\nPitaevskii-Rosch dynamical symmetry [L. P. Pitaevskii and A. Rosch, Phys. Rev.\nA, 55, R853 (1997)]. While the corresponding classical Gross-Pitaevskii\nequation and the derived from it hydrodynamic equations do exhibit this\nsymmetry, it is---as we show in our paper---violated under quantization. The\nresulting frequency shift is of the order of 1% of the carrier, well in reach\nfor modern experimental techniques. We propose using the dipole oscillations as\na frequency gauge.",
        "positive": "Gauge protection in non-Abelian lattice gauge theories: Protection of gauge invariance in experimental realizations of lattice gauge\ntheories based on energy-penalty schemes has recently stimulated impressive\nefforts both theoretically and in setups of quantum synthetic matter. A major\nchallenge is the reliability of such schemes in non-Abelian gauge theories\nwhere local conservation laws do not commute. Here, we show through exact\ndiagonalization that non-Abelian gauge invariance can be reliably controlled\nusing gauge-protection terms that energetically stabilize the target gauge\nsector in Hilbert space, suppressing gauge violations due to unitary\ngauge-breaking errors. We present analytic arguments that predict a\nvolume-independent protection strength $V$, which when sufficiently large leads\nto the emergence of an \\textit{adjusted} gauge theory with the same local gauge\nsymmetry up to least a timescale $\\propto\\sqrt{V/V_0^3}$. Thereafter, a\n\\textit{renormalized} gauge theory dominates up to a timescale\n$\\propto\\exp(V/V_0)/V_0$ with $V_0$ a volume-independent energy factor, similar\nto the case of faulty Abelian gauge theories. Moreover, we show for certain\nexperimentally relevant errors that single-body protection terms robustly\nsuppress gauge violations up to all accessible evolution times in exact\ndiagonalization, and demonstrate that the adjusted gauge theory emerges in this\ncase as well. These single-body protection terms can be readily implemented\nwith fewer engineering requirements than the ideal gauge theory itself in\ncurrent ultracold-atom setups and NISQ devices."
    },
    {
        "anchor": "Virial expansion for a strongly correlated Fermi system and its\n  application to ultracold atomic Fermi gases: Strongly correlated Fermi system plays a fundamental role in very different\nareas of physics, from neutron stars, quark-gluon plasmas, to high temperature\nsuperconductors. Despite the broad applicability, it is notoriously difficult\nto be understood theoretically because of the absence of a small interaction\nparameter. Recent achievements of ultracold trapped Fermi atoms near a Feshbach\nresonance have ushered in enormous changes. The unprecedented control of\ninteraction, geometry and purity in these novel systems has led to many\nexciting experimental results, which are to be urgently understood at both low\nand finite temperatures. Here we review the latest developments of virial\nexpansion for a strongly correlated Fermi gas and their applications on\nultracold trapped Fermi atoms. We show remarkable, quantitative agreements\nbetween virial predictions and various recent experimental measurements at\nabout the Fermi degenerate temperature. For equation of state, we discuss a\npractical way of determining high-order virial coefficients and use it to\ncalculate accurately the long-sought third-order virial coefficient, which is\nnow verified firmly in experiments at ENS and MIT. We discuss also virial\nexpansion of a new many-body paramter - Tan's contact. We then turn to less\nwidely discussed issues of dynamical properties. For dynamic structure factor,\nthe virial prediction agrees well with the measurement at the Swinburne\nUniversity of Technology. For single-particle spectral function, we show that\nthe expansion up to the second order accounts for the main feature of\nmomentum-resolved rf-spectroscopy for a resonantly interacting Fermi gas, as\nrecently reported by JILA. In the near future, more practical applications with\nvirial expansion are possible, owing to the ever-growing power in computation.",
        "positive": "Superconductivity and other phase transitions in a hybrid Bose-Fermi\n  mixture formed by a polariton condensate and an electron system in two\n  dimensions: Interacting Bose-Fermi systems play a central role in condensed matter\nphysics. Here, we analyze a novel Bose-Fermi mixture formed by a cavity\nexciton-polariton condensate interacting with a two-dimensional electron\nsystem. We show that that previous predictions of superconductivity [F.P.\nLaussy, Phys. Rev. Lett. 10, 104 (2010)] and excitonic supersolid formation\n[I.A. Shelykh, Phys. Rev. Lett. 14, 105 (2010)] in this system are closely\nintertwined- resembling the predictions for strongly correlated electron\nsystems such as high temperature superconductors. In stark contrast to a large\nmajority of Bose-Fermi systems analyzed in solids and ultracold atomic gases,\nthe renormalized interaction between the polaritons and electrons in our system\nis long-ranged and strongly peaked at a tunable wavevector, which can be\nrendered incommensurate with the Fermi momentum. We analyze the prospects for\nexperimental observation of superconductivity and find that critical\ntemperatures on the order of a few Kelvins can be achieved in heterostructures\nconsisting of transition metal dichalcogenide monolayers that are embedded in\nan open cavity structure. All optical control of superconductivity in\nsemiconductor heterostructures could enable the realization of new device\nconcepts compatible with semiconductor nanotechnology. In addition the\npossibility to interface quantum Hall physics, superconductivity and\nnonequilibrium polariton condensates is likely to provide fertile ground for\ninvestigation of completely new physical phenomena."
    },
    {
        "anchor": "Single-particle spectral functions in the normal phase of a\n  strongly-attractive Bose-Fermi mixture: We calculate the single-particle spectral functions and quasi-particle\ndispersions for a Bose-Fermi mixture when the boson-fermion attraction is\nsufficiently strong to suppress completely the condensation of bosons at zero\ntemperature. Within a T-matrix diagrammatic approach, we vary the boson-fermion\nattraction from the critical value where the boson condensate first disappears\nto the strongly attractive (molecular) regime and study the effect of both\nmass- and density-imbalance on the spectral weights and dispersions. An\ninteresting spectrum of particle-hole excitations mixing two different Fermi\nsurfaces is found. These unconventional excitations could be produced and\nexplored experimentally with radio-frequency spectroscopy.",
        "positive": "Learning the Fuzzy Phases of Small Photonic Condensates: Phase transitions, being the ultimate manifestation of collective behaviour,\nare typically features of many-particle systems only. Here, we describe the\nexperimental observation of collective behaviour in small photonic condensates\nmade up of only a few photons. Moreover, a wide range of both equilibrium and\nnon-equilibrium regimes, including Bose-Einstein condensation or laser-like\nemission are identified. However, the small photon number and the presence of\nlarge relative fluctuations places major difficulties in identifying different\nphases and phase transitions. We overcome this limitation by employing\nunsupervised learning and fuzzy clustering algorithms to systematically\nconstruct the fuzzy phase diagram of our small photonic condensate. Our results\nthus demonstrate the rich and complex phase structure of even small collections\nof photons, making them an ideal platform to investigate equilibrium and\nnon-equilibrium physics at the few particle level."
    },
    {
        "anchor": "Bose-Einstein condensation and/or modulation of \"displacements\" in the\n  two-state Bose-Hubbard model: Instabilities resulting in Bose-Einstein condensation and/or modulation of\n\"displacements\" in a system of quantum particles described by a two-state\nBose-Hubbard model (with an allowance for the interaction between particle\ndisplacements on different lattice sites) are investigated. A possibility of\nmodulation, which doubles the lattice constant, as well as the uniform\ndisplacement of particles from equilibrium positions are studied. Conditions\nfor realization of the mentioned instabilities and phase transitions into the\nSF phase and into the \"ordered\" phase with frozen displacements are analyzed.\nThe behaviour of order parameters is investigated and phase diagrams of the\nsystem are calculated both analytically (ground state) and numerically (at\nnon-zero temperatures). It is revealed that the SF phase can appear as an\nintermediate one between the normal and \"ordered\" phases, while a supersolid\nphase is thermodynamically unstable and does not appear. The relation of the\nobtained results to the lattices with the double-well local potentials is\ndiscussed.",
        "positive": "Preparation of the 1/2-Laughlin state with atoms in a rotating trap: Fractional quantum Hall systems are among the most exciting strongly\ncorrelated systems. Accessing them microscopically via quantum simulations with\nultracold atoms would be an important achievement toward a better understanding\nof this strongly correlated state of matter. A promising approach is to confine\na small number of bosonic atoms in a quasi-two-dimensional rotating trap, which\nmimics the magnetic field. For rotation frequencies close to the in-plane\ntrapping frequency, the ground state is predicted to be a bosonic analog of the\nLaughlin state. Here, we study the problem of the adiabatic preparation of the\nLaughlin state by ramping the rotation frequency and controlling the\nellipticity of the trapping potential. By employing adapted ramping speeds for\nrotation frequency and ellipticity, and large trap deformations, we improve the\npreparation time for high-fidelity Laughlin states by a factor of ten in\ncomparison to previous studies. With this improvement of the adiabatic protocol\nthe Laughlin state can be prepared with current experimental technology."
    },
    {
        "anchor": "Long-range s-wave interactions in Bose-Einstein Condensates: An exact\n  correspondence between truncated free energy and dynamics: We consider the Gross-Pitaevskii(GP) model of a Bose-Einstein Condensate(BEC)\nwith non-local s-wave interactions. The non-locality is represented by\ncorrections to the local GP equation. Due to such corrections to the GP\nequation, there arise corrections to the free energy functional as well. We\npresent here a proof of the exact correspondence between the free energy and\nthe dynamics for typical terms appearing while considering corrections to the\nGP equation at any order. This non-trivial correspondence can be used to study\nBECs perturbatively while going beyond the Fermi pseudopotential.",
        "positive": "Superfluid-droplet crossover in a binary boson mixture on a ring: Exact\n  diagonalization solutions for few-particle systems in one dimension: We investigate the formation of self-bound quantum droplets in a\none-dimensional binary mixture of bosonic atoms, applying the method of\nnumerical diagonalization of the full Hamiltonian. The excitation spectra and\nground-state pair correlations signal the formation of a few-boson droplet when\ncrossing the region of critical inter-species interactions. The self-binding\naffects the rotational excitations, displaying a change in the energy\ndispersion from negative curvature, associated with superfluidity in the\nmany-body limit, to a nearly parabolic curvature indicative of rigid body\nrotation. We exploit two global symmetries of the system to further analyze the\nfew-body modes in terms of transition matrix elements and breathing mode\ndynamics. The exact results are compared to the usual ad-hoc inclusion of\nhigher-order contributions in the extended Gross-Pitaevskii equation, showing a\nremarkable agreement between the few-body regime and the thermodynamic limit in\none dimension."
    },
    {
        "anchor": "Quantum catastrophes and ergodicity in the dynamics of bosonic Josephson\n  junctions: We study rainbow (fold) and cusp catastrophes that form in Fock space\nfollowing a quench in a Bose Josephson junction. In the Gross-Pitaevskii\nmean-field theory the rainbows are singular caustics, but in the\nsecond-quantized theory a Poisson resummation of the wave function shows that\nthey are described by well behaved Airy functions. The structural stability of\nthese Fock space caustics against variations in the initial conditions and\nHamiltonian evolution is guaranteed by catastrophe theory. We also show that\nthe long-time dynamics are ergodic. Our results are relevant to the question\nposed by Berry [M.V. Berry, Nonlinearity 21, T19 (2008)]: are there\ncircumstances when it is necessary to second-quantize wave theory in order to\navoid singularities?",
        "positive": "Vortex Dipole in a BEC with dipole-dipole interaction: We consider single and multiply charged quantized vortex dipole in an oblate\ndipolar Bose Einstein condensate in the Thomas-Fermi (TF) regime. We calculate\nthe critical velocity for the formation of a pair of vortices of opposite\ncharge. We find that dipolar interactions decrease the critical velocity for a\nvortex dipole nucleation."
    },
    {
        "anchor": "Collision of impurities with Bose-Einstein condensates: Quantum dynamics of impurities in a bath of bosons is a long-standing problem\nof solid-state, plasma, and atomic physics. Recent experimental and theoretical\ninvestigations with ultracold atoms focused on this problem, studying atomic\nimpurities immersed in a atomic Bose-Einstein condensate (BEC) and for various\nrelative coupling strengths tuned by the Fano-Feshbach resonance technique.\nHere we report extensive numerical simulations on a closely related problem:\nthe collision between a bosonic impurity made of few $^{41}$K atoms and a BEC\nmade of $^{87}$Rb atoms in a quasi one-dimensional configuration and under a\nweak harmonic axial confinement. For small values of the interspecies\ninteraction strength (no matter the sign of it), we find that the impurity,\nwhich starts from outside the BEC, simply oscillates back and forth the BEC\ncloud, but the frequency of oscillation depends on the interaction strength.\nFor intermediate couplings, after a few cycles of oscillation the impurity is\ncaptured by the BEC and strongly changes its amplitude of oscillation. In the\nstrong interaction regime, if the interspecies interaction is attractive, a\nlocal maximum (bright soliton) in the density of BEC occurs where the impurity\nis trapped; instead, if the interspecies interaction is repulsive, the impurity\nis not able to enter in the BEC cloud and the reflection coefficient is close\nto one. On the other hand, if the initial displacement of the impurity is\nincreased, the impurity is able to penetrate in the cloud leading to the\nappearance of a moving hole (dark soliton) in the BEC.",
        "positive": "Apparent low-energy scale invariance in two-dimensional Fermi gases: Recent experiments on a $\\2d$ Fermi gas find an undamped breathing mode at\ntwice the trap frequency over a wide range of parameters. To understand this\nseemingly scale-invariant behavior in a system with a scale, we derive two\nexact results valid across the entire BCS-BEC crossover at all temperatures.\nFirst, we relate the shift of the mode frequency from its scale-invariant value\nto $\\gamma_d \\equiv (1+2/d)P-\\rho(\\partial P/\\partial\\rho)_s$ in $d$\ndimensions. Next, we relate $\\gamma_d$ to dissipation via a new low-energy bulk\nviscosity sum rule. We argue that $\\2d$ is special, with its logarithmic\ndependence of the interaction on density, and thus $\\gamma_2$ is small in both\nthe BCS and BEC regimes, even though $P - 2\\varepsilon/d$, sensitive to the\ndimer binding energy that breaks scale invariance, is not."
    },
    {
        "anchor": "Scale-invariant phase transition of disordered bosons in one dimension: The disorder-induced quantum phase transition between superfluid and\nnon-superfluid states of bosonic particles in one dimension is generally\nexpected to be of the Berezinskii-Kosterlitz-Thouless (BKT) type. Here, we show\nthat hard-core lattice bosons with integrable power-law hopping decaying with\ndistance as $1/r^\\alpha$ - corresponding in spin language to a $XY$ model with\npower-law couplings - undergo a non-BKT continuous phase transition instead. We\nuse exact quantum Monte-Carlo methods to determine the phase diagram for\ndifferent values of the exponent $\\alpha$, focusing on the regime $\\alpha > 2$.\nWe find that the scaling of the superfluid stiffness with the system size is\nscale-invariant at the transition point for any $\\alpha\\leq 3$ - a behavior\nincompatible with the BKT scenario and typical of continuous phase transitions\nin higher dimension. By scaling analysis near the transition point, we find\nthat our data are consistent with a correlation length exponent satisfying the\nHarris bound $\\nu \\geq 2$ and demonstrate a new universal behavior of\ndisordered bosons in one dimension. For $\\alpha>3$ our data are consistent with\na BKT scenario where the liquid is pinned by infinitesimal disorder.",
        "positive": "Reply to \"Comment on `Quenches in quantum many-body systems:\n  One-dimensional Bose-Hubbard model reexamined' '': In his Comment [see preceding Comment, Phys. Rev. A 82, 037601 (2010)] on the\npaper by Roux [Phys. Rev. A 79, 021608(R) (2009)], Rigol argued that the energy\ndistribution after a quench is not related to standard statistical ensembles\nand cannot explain thermalization. The latter is proposed to stem from what he\ncalls the eigenstate thermalization hypothesis and which boils down to the fact\nthat simple observables are expected to be smooth functions of the energy. In\nthis Reply, we show that there is no contradiction or confusion between the\nobservations and discussions of Roux and the expected thermalization scenario\ndiscussed by Rigol. In addition, we emphasize a few other important aspects, in\nparticular the definition of temperature and the equivalence of ensemble, which\nare much more difficult to show numerically even though we believe they are\nessential to the discussion of thermalization. These remarks could be of\ninterest to people interested in the interpretation of the data obtained on\nfinite-size systems."
    },
    {
        "anchor": "State diagram for continuous quasi-one dimensional systems in optical\n  lattices: We studied the appearance of Mott insulator domains of hard sphere bosons on\nquasi one-dimensional optical lattices when an harmonic trap was superimposed\nalong the main axis of the system. Instead of the standard approximation\nrepresented by the Bose-Hubbard model, we described those arrangements by\ncontinuous Hamiltonians that depended on the same parameters as the\nexperimental setups. We found that for a given trap the optical potential\ndepth, $V_0$, needed to create a single connected Mott domain decreased with\nthe number of atoms loaded on the lattice. If the confinement was large enough,\nit reached a minimum when, in absence of any optical lattice, the atom density\nat the center of the trap was the equivalent of one particle per optical well.\nFor larger densities, the creation of that single domain proceeded via an\nintermediate shell structure in which Mott domains alternated with superfluid\nones.",
        "positive": "Probing Goldstino excitation through the tunneling transport in a\n  Bose-Fermi mixture with explicitly broken supersymmetry: We theoretically investigate the tunneling transport in a repulsively\ninteracting ultracold Bose-Fermi mixture. A two-terminal model is applied to\nsuch a mixture and the supersymmetric-like tunneling current through the\njunction can be induced by the bias of fermion chemical potential between two\nreservoirs. The Goldstino, which is the Nambu-Goldstone fermionic mode\nassociated with the spontaneous sypersymmetry breaking and appears as a gapped\nmode in the presence of the explicit supersymmetry breaking in existing\nBose-Fermi mixtures, is found to contribute to the tunneling transport as a\nsupercharge exchanging process. Our study provides a potential way to detect\nthe Goldstino transport in cold atom experiments."
    },
    {
        "anchor": "Properties of the Superfluid in the Disordered Bose-Hubbard Model: We investigate the properties of the superfluid phase in the\nthree-dimensional disordered Bose-Hubbard model using Quantum Monte-Carlo\nsimulations. The phase diagram is generated using Gaussian disorder on the\non-site potential. Comparisons with box and speckle disorder show qualitative\nsimilarities leading to the re-entrant behavior of the superfluid. Quantitative\ndifferences that arise are controlled by the specific shape of the disorder.\nStatistics pertaining to disorder distributions are studied for a range of\ninteraction strengths and system sizes, where strong finite-size effects are\nobserved. Despite this, both the superfluid fraction and compressibility remain\nself-averaging throughout the superfluid phase. Close to the\nsuperfluid-Bose-glass phase boundary, finite-size effects dominate but still\nsuggest that self-averaging holds. Our results are pertinent to experiments\nwith ultracold atomic gases where a systematic disorder averaging procedure is\ntypically not possible.",
        "positive": "Reversible decay of ring dark solitons: We show how boundary effects can cause a Bose-Einstein condensate to\nperiodically oscillate between a (circular) array of quantised\nvortex-antivortex pairs and a (ring) dark soliton. If the boundary is\nrestrictive enough, the ring dark soliton becomes long-lived."
    },
    {
        "anchor": "Crossover in the Efimov spectrum: A filtering method is introduced for solving the zero-range three-boson\nproblem. This scheme permits to solve the original Skorniakov Ter-Martirosian\nintegral equation for an arbitrary large Ultra-Violet cut-off and to avoid the\nThomas collapse of the three particles. The method is applied to a more general\nzero-range model including a finite background two-body scattering length and\nthe effective range. A cross-over in the Efimov spectrum is found in such\nsystems and a specific regime emerges where Efimov states are long-lived.",
        "positive": "Topological superfluids on a square optical lattice with non-Abelian\n  gauge fields: Effects of next-nearest-neighbor hopping in the BCS-BEC\n  evolution: We consider a two-component Fermi gas with attractive interactions on a\nsquare optical lattice, and study the interplay of Zeeman field, spin-orbit\ncoupling and next-nearest-neighbor hopping on the ground-state phase diagrams\nin the entire BCS-BEC evolution. In particular, we first classify and\ndistinguish all possible superfluid phases by the momentum-space topology of\ntheir zero-energy quasiparticle/quasihole excitations, and then numerically\nestablish a plethora of quantum phase transitions in between. These transitions\nare further signalled and evidenced by the changes in the corresponding\ntopological invariant of the system, \\textit{i.e.}, its Chern number. Lastly,\nwe find that the superfluid phase exhibits a reentrant structure, separated by\na fingering normal phase, the origin of which is traced back to the changes in\nthe single-particle density of states."
    },
    {
        "anchor": "Collective excitations and tunneling dynamics in long bosonic Josephson\n  junctions: We investigate the low-energy dynamics of two coupled anisotropic\nBose-Einstein condensates forming a long Josephson junction. The theoretical\nstudy is performed in the framework of the two-dimensional Gross-Pitaevskii\nequation and the Bogoliubov-de Gennes formalism. We analyze the excitation\nspectrum of the coupled Bose condensates and show how low-energy excitations of\nthe condensates lead to multiple-frequency oscillations of the atomic\npopulations in the two wells. This analysis generalizes the standard bosnic\nJosephson euqation approach. We also develop a one-dimensional hydrodynamic\nmodel of the coupled condensates, that is capable to reproduce the excitation\nspectrum and population dynamics of the system.",
        "positive": "Towards strongly correlated photons in arrays of dissipative nonlinear\n  cavities under a frequency-dependent incoherent pumping: We report a theoretical study of a quantum optical model consisting of an\narray of strongly nonlinear cavities incoherently pumped by an ensemble of\npopulation-inverted two-level atoms. Projective methods are used to eliminate\nthe atomic dynamics and write a generalized master equation for the photonic\ndegrees of freedom only, where the frequency-dependence of gain introduces\nnon-Markovian features. In the simplest single cavity configuration, this\npumping scheme gives novel optical bistability effects and allows for the\nselective generation of Fock states with a well-defined photon number. For many\ncavities in a weakly non-Markovian limit, the non-equilibrium steady state\nrecovers a Grand-Canonical statistical ensemble at a temperature determined by\nthe effective atomic linewidth. For a two-cavity system in the strongly\nnonlinear regime, signatures of a Mott state with one photon per cavity are\nfound."
    },
    {
        "anchor": "Master's Thesis: Excitation Spectrum of a Weakly Interacting Spin-Orbit\n  Coupled Bose-Einstein Condensate: A weakly interacting, spin-orbit coupled, two-component, ultracold Bose gas\nbound to a Bravais lattice is studied. Motivated by recent experimental\nadvances in the field of synthetically spin-orbit coupled, ultracold, neutral\natomic gases showing Bose-Einstein condensation, an analytic framework with\nwhich to describe such systems in the superfluid regime is presented. This is\napplied to a Rashba spin-orbit-coupled Bose gas in a two-dimensional optical\nlattice. The exotic nature of Bose-Einstein condensation in the presence of\nspin-orbit coupling is an interesting study by itself. Additionally, when the\noptical lattice is introduced, the system provides a highly controllable\nexperimental testing ground for numerous condensed matter physics phenomena.\nFive phases of the system are considered, and their excitation spectra,\ncritical superfluid velocities and free energies are found. In obtaining the\nfree energy, the effects of terms in the Hamiltonian that are linear in\nexcitation operators are included, and such terms have not been studied\npreviously in this context. Minimization of the free energy at zero temperature\nis used to confirm the phase diagrams reported in the literature, where it has\nusually been obtained by neglecting the effect of excitations. The plane and\nstripe wave phases in the phase diagram are bosonic analogues of\nFulde-Ferrell-Larkin-Ovchinnikov states in superconductors involving nonzero\ncondensate momenta.",
        "positive": "Neural Wave Functions for Superfluids: Understanding superfluidity remains a major goal of condensed matter physics.\nHere we tackle this challenge utilizing the recently developed Fermionic neural\nnetwork (FermiNet) wave function Ansatz for variational Monte Carlo\ncalculations. We study the unitary Fermi gas, a system with strong,\nshort-range, two-body interactions known to possess a superfluid ground state\nbut difficult to describe quantitatively. We demonstrate key limitations of the\nFermiNet Ansatz in studying the unitary Fermi gas and propose a simple\nmodification that outperforms the original FermiNet significantly, giving\nhighly accurate results. We prove mathematically that the new Ansatz, which\nonly differs from the original Ansatz by the method of antisymmetrization, is a\nstrict generalization of the original FermiNet architecture, despite the use of\nfewer parameters. Our approach shares several advantages with the FermiNet: the\nuse of a neural network removes the need for an underlying basis set; and the\nflexibility of the network yields extremely accurate results within a\nvariational quantum Monte Carlo framework that provides access to unbiased\nestimates of arbitrary ground-state expectation values. We discuss how the\nmethod can be extended to study other superfluids."
    },
    {
        "anchor": "Geometrizing quantum dynamics of a Bose-Einstein condensate: We show that quantum dynamics of Bose-Einstein condensates in the weakly\ninteracting regime can be geometrized by a Poincar\\'e disk. Each point on such\na disk represents a thermofield double state, the overlap between which equals\nthe metric of this hyperbolic space. This approach leads to a unique geometric\ninterpretation of stable and unstable modes as closed and open trajectories on\nthe Poincar\\'e disk, respectively. The resonant modes that follow geodesics\nnaturally equate fundamental quantities including the time, the length, and the\ntemperature. Our work suggests a new geometric framework to coherently control\nquantum systems and reverse their dynamics using SU(1,1) echoes. In the\npresence of perturbations breaking the SU(1,1) symmetry, SU(1,1) echoes deliver\na new means to measure these perturbations such as the interactions between\nexcited particles.",
        "positive": "Superfluid (Amplitude) Fluctuations Above $T_c$ in a Unitary Fermi Gas: We study the transport properties of a Fermi gas with strong attractive\ninteractions close to the unitary limit. In particular, we compute the spin\ndiffusion lifetime of the Fermi gas due to superfluid fluctuations above the\nBCS transition temperature $T_c$. To calculate the spin diffusion lifetime we\nneed the scattering amplitudes. The scattering amplitudes are dominated by the\nsuperfluid fluctuations at temperatures just above $T_c$. The normal scattering\namplitudes are calculated from the Landau parameters. These Landau parameters\nare obtained from the local version of the induced interaction model for\ncomputing Landau parameters. We also calculate the leading order finite\ntemperature correction to the diffusion lifetime. A calculation of the spin\ndiffusion coefficient is presented in the end. Upon choosing a proper value of\n$F_0^a$, we are able to present a good match between the theoretical result and\nthe experimental measurement which indicates the presence of the superfluid\nfluctuations near $T_c$."
    },
    {
        "anchor": "Universal dynamics of rogue waves in a quenched spinor Bose condensate: Isolated many-body systems far from equilibrium may exhibit scaling dynamics\nwith universal exponents indicating the proximity of the time-evolution to a\nnon-thermal fixed point. We find universal dynamics connected with the\noccurrence of extreme wave excitations in the mutually coupled magnetic\ncomponents of a spinor gas which propagate in an effectively random potential.\nThe frequency of these rogue waves is affected by the time-varying spatial\ncorrelation length of the potential, giving rise to an additional exponent\n$\\delta_\\mathrm{c} \\simeq 1/3$ for temporal scaling, which is different from\nthe exponent $\\beta_V \\simeq 1/4$ characterizing the scaling of the correlation\nlength $\\ell_V \\sim t^{\\,\\beta_V}$ in time. As a result of the caustics, i.e.,\nfocusing events, real-time instanton defects appear in the Larmor phase of the\nspin-1 system as vortices in space and time. The temporal correlations\ngoverning the instanton occurrence frequency scale as $t^{\\,\n\\delta_\\mathrm{I}}$. This suggests that the universality class of a non-thermal\nfixed point could be characterized by different, mutually related exponents\ndefining the evolution in time and space, respectively. Our results have a\nstrong relevance for understanding pattern coarsening from first principles and\npotential implications for dynamics ranging from the early universe to\ngeophysical dynamics and micro physics.",
        "positive": "Application of renormalized RPA to polarized Fermi gases: We consider a spin imbalanced Fermi gas at zero temperature in the normal\nphase on the BCS side of the BCS-BEC crossover and around unitarity. We compute\nthe critical polarization for pairing, the correlated occupation numbers and\nthe contact in an extension of particle-particle RPA (also called non\nself-consistent \\textit{T}-matrix approach or ladder approximation). The\nso-called renormalized RPA consists in computing the \\textit{T} matrix with\nself-consistently determined occupation numbers. The occupation numbers are\ndetermined either by keeping the self-energy only to first order or by\nresumming the Dyson equation. In this way, the result for the critical\npolarization, strongly overestimated in standard RPA, is clearly improved. We\nalso discuss some problems of this approach."
    },
    {
        "anchor": "Mean-field theory for the Mott insulator-paired superfluid transition in\n  the two-species Bose-Hubbard model: The standard mean-field theory for the Mott insulator-superfluid phase\ntransition is not sufficient to describe the Mott insulator-paired superfluid\nphase transition. Therefore, by restricting the two-species Bose-Hubbard\nHamiltonian to the subspace of paired particles, and using perturbation theory,\nhere we derive an analytic mean-field expression for the Mott insulator-paired\nsuperfluid transition boundary.",
        "positive": "Heat current control in trapped BEC: We investigate the heat transport and the control of heat current among two\nspatially separated trapped Bose-Einstein Condensates (BEC), each of them at a\ndifferent temperature. To allow for heat transport among the two independent\nBECs we consider a link made of two harmonically trapped impurities, each of\nthem interacting with one of the BECs. Since the impurities are spatially\nseparated, we consider long-range interactions between them, namely a\ndipole-dipole coupling. We study this system under theoretically suitable and\nexperimentally feasible assumptions/parameters. The dynamics of these\nimpurities is treated within the framework of the quantum Brownian motion\nmodel, where the excitation modes of the BECs play the role of the heat bath.\nWe address the dependence of heat current and current-current correlations on\nthe physical parameters of the system. Interestingly, we show that heat\nrectification, i.e., the unidirectional flow of heat, can occur in our system,\nwhen a periodic driving on the trapping frequencies of the impurities is\nconsidered. Therefore, our system is a possible setup for the implementation of\na phononic circuit. Motivated by recent developments on the usage of BECs as\nplatforms for quantum information processing, our work offers an alternative\npossibility to use this versatile setting for information transfer and\nprocessing, within the context of phononics, and more generally in quantum\nthermodynamics."
    },
    {
        "anchor": "Topological metal bands with double-triple-point fermions in optical\n  lattices: Novel fermionic quasiparticles with integer pseudospins in some energy bands,\nsuch as pseudospin-1 triple-point fermions, recently attract increasing\ninterest since they are beyond the conventional spin-$1/2$ Dirac and Weyl\ncounterparts. In this paper, we propose a class of pseudospin-1 fermioic\nexcitations emerging in topological metal bands, dubbed double-triple-point\n(DTP) fermions. We first present a general three-band continuum model with\n$C_4$ symmetry in three dimensions, which has three types of threefold\ndegenerate points in the bands classified by their topological charges\n$C=\\pm4,\\pm2,0$, respectively. They are dubbed DTPs as spin-1 generalization of\ndouble-Weyl points. We then construct two-dimensional and three-dimensional\ntight-binding lattice models of topological metal bands with exotic DTP\nfermions near the DTPs. In two dimensions, the band gaps close at a trivial DTP\nwith zero Berry phase, which occurs at the transition between the normal and\ntopological insulator phases. In three dimensions, the topological properties\nof three different DTP fermions in lattice systems are further investigated,\nand the effects of breaking $C_4$ symmetry are also studied, which generally\nleads to splitting each quadratic DTP into two linear triple points and gives\ntopological phase diagrams. Using ultracold fermionic atoms in optical\nlattices, the proposed models can be realized and the topological properties of\nthe DTP fermions can be detected.",
        "positive": "Instabilities of a matter wave in a matter grating: We investigate the stability of Bloch waves for a Bose-Einstein condensate\nmoving through a periodic lattice created by another condensate modulated by an\noptical lattice. We show that the coupling of phonon-antiphonon modes of the\ntwo species give rise to a very rich structure of the regimes for dynamical\ninstability, with significant differences with respect to the case of a single\ncondensate in an optical lattice. We characterize the relative weight of each\ncondensate in the mixing and discuss an analytic limit that accounts for the\nbare structure of the instability diagrams."
    },
    {
        "anchor": "Reply to the Comment by Benenti et al: Benenti et al. recently submitted a Comment (arXiv:0912.3667) on our work\n\"Coherent Ratchets in Driven Bose-Einstein condensates\". We show that the main\nclaim of the Comment is wrong, and correct some other misunderstandings\npresented there.",
        "positive": "High-fidelity rapid ground-state loading of an ultracold gas into an\n  optical lattice: A protocol is proposed for the rapid coherent loading of a Bose-Einstein\ncondensate into the ground state of an optical lattice, without residual\nexcitation associated with the breakdown of adiabaticity. The driving potential\nrequired to assist the rapid loading is derived using the fast forward\ntechnique, and generates the ground state in any desired short time. We propose\nan experimentally feasible loading scheme using a bichromatic lattice\npotential, which approximates the fast-forward driving potential with high\nfidelity."
    },
    {
        "anchor": "Landau phonon-roton theory revisited for superfluid helium 4 and Fermi\n  gases: Liquid helium and spin-1/2 cold-atom Fermi gases both exhibit in their\nsuperfluid phase two distinct types of excitations, gapless phonons and gapped\nrotons or fermionic pair-breaking excitations. In the long wavelength limit,\nrevising and extending Landau and Khalatnikov's theory initially developed for\nhelium [ZhETF 19, 637 (1949)], we obtain universal expressions for three- and\nfour-body couplings among these two types of excitations. We calculate the\ncorresponding phonon damping rates at low temperature and compare them to those\nof a pure phononic origin in high-pressure liquid helium and in strongly\ninteracting Fermi gases, paving the way to experimental observations.",
        "positive": "Bloch-Landau-Zener dynamics in single-particle Wannier-Zeeman systems: Stimulated by the experimental realization of spin-dependent tunneling via\ngradient magnetic field [Phys. Rev. Lett. 111, 225301 (2013); Phys. Rev. Lett.\n111, 185301 (2013)], we investigate dynamics of Bloch oscillations and\nLandau-Zener tunneling of single spin-half particles in a periodic potential\nunder the influence of a spin-dependent constant force. In analogy to the\nWannier-Stark system, we call our system as the Wannier-Zeeman system. If there\nis no coupling between the two spin states, the system can be described by two\ncrossing Wannier-Stark ladders with opposite tilts. The spatial crossing\nbetween two Wannier-Stark ladders becomes a spatial anti-crossing if the two\nspin states are coupled by external fields. For a wave-packet away from the\nspatial anti-crossing, due to the spin-dependent constant force, it will\nundergo spatial Landau-Zener transitions assisted by the intrinsic intra-band\nBloch oscillations, which we call the Bloch-Landau-Zener dynamics. If the\ninter-spin coupling is sufficiently strong, the system undergoes adiabatic\nBloch-Landau-Zener dynamics, in which the spin dynamics follows the local\ndressed states. Otherwise, for non-strong inter-spin couplings, the system\nundergoes non-adiabatic Bloch-Landau-Zener dynamics."
    },
    {
        "anchor": "Polarized fermions in one dimension: density and polarization from\n  complex Langevin calculations, perturbation theory, and the virial expansion: We calculate the finite-temperature density and polarization equations of\nstate of one-dimensional fermions with a zero-range interaction, considering\nboth attractive and repulsive regimes. In the path-integral formulation of the\ngrand-canonical ensemble, a finite chemical potential asymmetry makes these\nsystems intractable for standard Monte Carlo approaches due to the sign\nproblem. Although the latter can be removed in one spatial dimension, we\nconsider the one-dimensional situation in the present work to provide an\nefficient test for studies of the higher-dimensional counterparts. To overcome\nthe sign problem, we use the complex Langevin approach, which we compare here\nwith other approaches: imaginary-polarization studies, third-order perturbation\ntheory, and the third-order virial expansion. We find very good qualitative and\nquantitative agreement across all methods in the regimes studied, which\nsupports their validity.",
        "positive": "Super Efimov effect of resonantly interacting fermions in two dimensions: We study a system of spinless fermions in two dimensions with a short-range\ninteraction fine-tuned to a p-wave resonance. We show that three such fermions\nform an infinite tower of bound states of orbital angular momentum l=\\pm1 and\ntheir binding energies obey a universal doubly exponential scaling\nE_3^{(n)}\\propto\\exp(-2e^{3\\pi n/4+\\theta}) at large n. This \"super Efimov\neffect\" is found by a renormalization group analysis and confirmed by solving\nthe bound state problem. We also provide an indication that there are l=\\pm2\nfour-body resonances associated with every three-body bound state at\nE_4^{(n)}\\propto\\exp(-2e^{3\\pi n/4+\\theta-0.188}). These universal few-body\nstates may be observed in ultracold atom experiments and should be taken into\naccount in future many-body studies of the system."
    },
    {
        "anchor": "Multipolar Kondo Effect in $^1$S$_0$-$^3$P$_2$ Mixture of $^{173}$Yb\n  Atoms: Whereas in the familiar Kondo effect the exchange interaction is dipolar, it\ncan also be multipolar, as has been realized in a recent experiment. Here we\nstudy multipolar Kondo effect in a Fermi gas of cold $^{173}$Yb atoms. Making\nuse of different AC polarizability of the electronic ground state\nYb($^{1}$S$_{0}$) and the long-lived metastable state Yb$^{*}$($^{3}$P$_{2}$),\nit is suggested that the latter atoms can be localized and serve as a dilute\nconcentration of magnetic impurities while the former ones remain itinerant.\nThe exchange mechanism between the itinerant Yb and the localized Yb$^{*}$\natoms is analyzed and shown to be antiferromagnetic. The quadruple and octuple\ninteractions act to enhance the Kondo temperature $T_K$ that is found to be\nexperimentally accessible. The bare exchange Hamiltonian needs to be decomposed\ninto dipole ($d$), quadruple ($q$) and octuple ($o$) interactions in order to\nretain its form under renormalization group (RG) analysis, in which the\ncorresponding exchange constants ($\\lambda_{\\mathrm{d}}$,\n$\\lambda_{\\mathrm{q}}$ and $\\lambda_{\\mathrm{o}}$) flow independently.\nNumerical solution of the RG scaling equations reveals a few finite fixed\npoints, indicating an over-screening, which suggests a non-Fermi liquid phase.\nThe impurity contribution to the magnetic susceptibility is calculated in the\nweak coupling regime (${T}\\gg{T}_{K}$).",
        "positive": "Exact-diagonalization method for soft-core bosons in optical lattices\n  using hierarchical wavefunctions: In this work, we describe a new technique for numerical\nexact-diagonalization. The method is particularly suitable for cold bosonic\natoms in optical lattices, in which multiple atoms can occupy a lattice site.\nWe describe the use of the method for Bose-Hubbard model as an example,\nhowever, the method is general and can be applied to other lattice models. The\nproposed numerical technique focuses in detail on how to construct the basis\nstates as a hierarchy of wavefunctions. Starting from single-site Fock states\nwe construct the basis set in terms of row-states and cluster-states. This\nsimplifies the application of constraints and calculation of the Hamiltonian\nmatrix. Each step of the method can be parallelized to accelerate the\ncomputation. In addition, we have illustrated the computation of the spatial\nbipartite entanglement entropy in the correlated $\\nu =1/2$ fractional quantum\nHall state."
    },
    {
        "anchor": "A comparison between microscopic methods for finite temperature Bose\n  gases: We analyze the equilibrium properties of a weakly interacting, trapped\nquasi-one-dimensional Bose gas at finite temperatures and compare different\ntheoretical approaches. We focus in particular on two stochastic theories: a\nnumber-conserving Bogoliubov (ncB) approach and a stochastic Gross-Pitaevskii\nequation (sGPe) that have been extensively used in numerical simulations.\nEquilibrium properties like density profiles, correlation functions, and the\ncondensate statistics are compared to predictions based upon a number of\nalternative theories. We find that due to thermal phase fluctuations, and the\ncorresponding condensate depletion, the ncB approach loses its validity at\nrelatively low temperatures. This can be attributed to the change in the\nBogoliubov spectrum, as the condensate gets thermally depleted, and to large\nfluctuations beyond perturbation theory. Although the two stochastic theories\nare built on different thermodynamic ensembles (ncB: canonical, sGPe:\ngrand-canonical), they yield the correct condensate statistics in a large BEC\n(strong enough particle interactions). For smaller systems, the sGPe results\nare prone to anomalously large number fluctuations, well-known for the\ngrand-canonical, ideal Bose gas. Based on the comparison of the above theories\nto the modified Popov approach, we propose a simple procedure for approximately\nextracting the Penrose-Onsager condensate from first- and second-order\ncorrelation functions that is computationally convenient. This also clarifies\nthe link between condensate and quasi-condensate in the Popov theory of\nlow-dimensional systems.",
        "positive": "Effect of finite range interactions on roton mode softening in a\n  multi-component BEC: We consider the Gross-Pitaevskii(GP) model of a Bose-Einstein Condensate(BEC)\nfor single-component and multi-component BEC. The pseudopotential for s-wave\nscattering between atoms is taken to be of width of the order of the s-wave\nscattering length. Such an interaction giving rise to a roton minimum in the\nspectrum of elementary excitations of a single component BEC is well known.\nHowever, softening roton modes takes us in the strongly interacting BEC regime\nwhere three body losses occur. We study the roton mode softening for a\nmulti-component BEC. We show that by increasing the number of components of a\nmulti-component BEC, the roton mode can be softened at a progressively lower\nvalue of the gas parameter ($a^{3}n$), thus reducing three body losses."
    },
    {
        "anchor": "Non-universal Efimov Atom-Dimer Resonances in a Three-Component Mixture\n  of 6Li: We observed an enhanced atom-dimer relaxation due to the existence of Efimov\nstates in a three-component mixture of 6Li atoms. We measured the\nmagnetic-field dependence of the atom-dimer loss coefficient in the mixture of\natoms in state |1> and dimers formed in states |2> and |3>, and found two peaks\ncorresponding to the degeneracy points of the |23> dimer energy level and\nenergy levels of Efimov trimers. We found that the locations of these peaks\ndisagree with universal theory predictions, in a way that cannot be explained\nby non-universal two-body properties. We constructed theoretical models that\ncharacterize the non-universal three-body physics of three-component 6Li atoms\nin the low energy domain.",
        "positive": "The Role of Interaction in the Pairing of Two Spin-orbit Coupled\n  Fermions: We investigate the role of a repulsive s-wave interaction in the two-body\nproblem in the presence of spin orbit couplings, motivated by current interests\nin exploring exotic superfluid phases in spin-orbit coupled Fermi gases. For\nweak spin orbit coupling where the density of states is not significantly\naltered, we analytically show that the high-energy states become more important\nin determining the binding energy when the interaction strength decreases.\nConsequently, tuning the interaction gives rise to a rich ground state\nbehavior, including a zigzag of the ground state momentum or inducing\ntransitions among the meta-stable states. By exactly solving the two-body\nproblem for a spin-orbit coupled Fermi mixture, we demonstrate that our\nanalysis can also apply to the case when the density of states is significantly\nmodified by the spin-orbit coupling. Our findings pave the way for\nunderstanding and controlling the paring of fermions in the presence of spin\norbit couplings."
    },
    {
        "anchor": "Exact Two-Body Solutions and Quantum Defect Theory of Polar Molecular\n  Gases with Van der Waals Potentials: In a recent experiment [Matsuda et al, Science 370, 1324 (2020)], a quasi\ntwo-dimensional (2D), long-lived and strongly interacting diatomic polar\nmolecular gas was successfully prepared via controllable electric field\ntechnique. Surprisingly, the effective repulsive and attractive Van der Waals\ninteractions of two molecules would emerge when scanning the strength of the\nelectric fields. Those results were also generalized to the three-dimensional\n(3D) case in a later experiment [J. Li et al, Nature Physics 17, 1144 (2021)].\nMotivated by these experiments, in this paper we provide the two-body exact\nsolutions for the 2D and 3D Schr\\\"{o}dinger equation with isotropic Van der\nWaals potentials ($\\pm1/r^{6}$). Furthermore, base on these exact solutions, we\nbuild the analytical quantum defect theory (QDT) for quasi-2D and 3D\ngeometries, and then apply QDT to study the scattering properties and bound\nstates of two ultracold polar molecules confined in quasi-2D and 3D geometries.\nInterestingly, we find that for the attractive (repulsive) Van der Waals\npotential cases, the two-body short range potential can be approximated by an\nsquare barrier with infinity height (square potential with finite depth) which\nyields the wide (narrow) and dense (dilute) resonances of the quantum defect\nparameter. For the quasi-2D attractive case, the scattering resonances of\ndifferent partial waves can orderly happen which is featured by the phase jumps\nwhen varying the scattering energy. The analytical expansions in the low energy\nlimit shows a consistent agreement to the numerical results.",
        "positive": "Mott lobes of the $S=1$ Bose-Hubbard model with three-body interactions: Using the density matrix renormalization group method, we studied the ground\nstate of the one-dimensional $S=1$ Bose-Hubbard model with local three-body\ninteractions, which can be a superfluid or a Mott insulator state. We drew the\nphase diagram of this model for both ferromagnetic and antiferromagnetic\ninteraction. Regardless of the sign of the spin-dependent coupling, we obtained\nthat the Mott lobes area decreases as the spin-dependent strength increases,\nwhich means that the even-odd asymmetry of the two-body antiferromagnetic chain\nis absent for local three-body interactions. For antiferromagnetic coupling, we\nfound that the density drives first-order superfluid-Mott insulator transitions\nfor even and odd lobes. Ferromagnetic Mott insulator and superfluid states were\nobtained with a ferromagnetic coupling, and a tendency to a \"long-range\" order\nwas observed."
    },
    {
        "anchor": "Vortex pair dynamics in three-dimensional homogeneous dipolar\n  superfluids: The static and dynamic properties of vortices in dipolar Bose-Einstein\ncondensates (dBECs) can be considerably modified relative to their nondipolar\ncounterparts by the anisotropic and long-ranged nature of the dipole-dipole\ninteraction. Working in a uniform dBEC, we analyze the structure of single\nvortices and the dynamics of vortex pairs, investigating the deviations from\nthe nondipolar paradigm. For a straight vortex line, we find that the induced\ndipolar interaction potential is axially anisotropic when the dipole moments\nhave a nonzero projection orthogonal to the vortex line. This results in a\ncorresponding elongation of the vortex core along this projection as well as an\nanisotropic superfluid phase and enhanced compressibility in the vicinity of\nthe vortex core. Consequently, the trajectories of like-signed vortex pairs are\ndescribed by a family of elliptical and oval-like curves rather than the\nfamiliar circular orbits. Similarly for opposite-signed vortex pairs their\ntranslation speeds along the binormal are found to be dipole\ninteraction-dependent. We expect that these findings will shed light on the\nunderlying mechanisms of many-vortex phenomena in dBECs such as quantum\nturbulence, vortex reconnections, and vortex lattices.",
        "positive": "Numerical analysis of spin-orbit coupled one dimensional Fermi gas in\n  the magnetic field: We use the density matrix renormalization group method(DMRG) and the infinite\ntime evolved block decimation method(iTEBD) to investigate the ground states of\nthe spin-orbit coupled Fermi gas in a one dimensional optical lattice with a\ntransverse magnetic field. We discover that the system with attractive\ninteraction can have a polarized insulator(PI), a superconducting phase(SC), a\nLuther-Emery(LE) phase and a band insulator(BI) phase as we vary the chemical\npotential and the strength of magnetic field. We find that spin-orbit coupling\ninduces a triplet pairing order at zero momentum with the same critical\nexponent as that of the singlet pairing one in both the SC and the LE phase. In\ncontrast to the FFLO phase found in the spin imbalanced system without\nspin-orbit coupling, pairings at finite momentum in these two phases have a\nlarger exponent hence do not dictate the long range behavior. We also find good\nagreements of the dominant correlations between numerical results and the\nprediction from the bosonization method. The presence of Majorana fermions is\ntested. However, unlike results from the mean field study, we do not find\npositive evidence of Majorana fermions in our system."
    },
    {
        "anchor": "Phase Coherence and Fragmentation of Two-Component Bose-Einstein\n  Condensates Loaded in State-Dependent Optical Lattices: A binary mixture of interacting Bose-Einstein condensates (BEC) in the\npresence of fragmentation-driving external lattice potentials forms two\ninterdependent mean-field lattices made of each component. These effective\nmean-field lattices, like ordinary optical lattices, can induce additional\nfragmentation and phase coherence loss of BECs between lattice sites. In this\nstudy, we consider the nonequilibrium dynamics of two hyperfine states of\none-dimensional Bose-Einstein condensates, subjected to state-dependent optical\nlattices. Our numerical calculations using the truncated Wigner approximation\n(TWA) show that phase coherence in a mixture of two-component BECs can be lost\nnot just by optical lattices, but by mean-field lattices gradually formed by\nother components, and we reveal that such an effect of internal mean-field\nlattices, however, is limited, contrary to external optical lattices, in regard\nto phase decoherence.",
        "positive": "Measurement-induced integer families of critical dynamical scaling in\n  quantum many-body systems: A quantum many-body system can undergo transitions in the presence of\ncontinuous measurement. In this work, we find that a generic class of critical\ndynamical scaling behavior can emerge at these measurement-induced transitions.\nRemarkably, depending on the symmetry that can be respected by the system,\ndifferent integer families of dynamical scaling can emerge. The origin of these\nscaling families can be traced back to the presence of hierarchies of high\norder exceptional points in the effective non-Hermitian descriptions of the\nsystems. Direct experimental observation of this class of dynamical scaling\nbehavior can be readily achieved using ultracold atoms in optical lattices or\nthrough intermediate-scale quantum computing systems."
    },
    {
        "anchor": "Quasi-one-dimensional Bose-Einstein condensates in nonlinear lattices: We consider the three-dimensional (3D) mean-field model for the Bose-Einstein\ncondensate (BEC), with a 1D nonlinear lattice (NL), which periodically changes\nthe sign of the nonlinearity along the axial direction, and the\nharmonic-oscillator trapping potential applied in the transverse plane. The\nlattice can be created as an optical or magnetic one, by means of available\nexperimental techniques. The objective is to identify stable 3D solitons\nsupported by the setting. Two methods are developed for this purpose: The\nvariational approximation, formulated in the framework of the 3D\nGross-Pitaevskii equation, and the 1D nonpolynomial Schr\\\"{o}dinger equation\n(NPSE) in the axial direction, which allows one to predict the collapse in the\nframework of the 1D description. Results are summarized in the form of a\nstability region for the solitons in the plane of the NL strength and\nwavenumber. Both methods produce a similar form of the stability region. Unlike\ntheir counterparts supported by the NL in the 1D model with the cubic\nnonlinearity, kicked solitons of the NPSE cannot be set in motion, but the kick\nmay help to stabilize them against the collapse, by causing the solitons to\nshed excess norm. A dynamical effect specific to the NL is found in the form of\nfreely propagating small-amplitude wave packets emitted by perturbed solitons.",
        "positive": "Superfluid Quenching of the Moment of Inertia in a Strongly Interacting\n  Fermi Gas: We report on the observation of a quenched moment of inertia as resulting\nfrom superfluidity in a strongly interacting Fermi gas. Our method is based on\nsetting the hydrodynamic gas in slow rotation and determining its angular\nmomentum by detecting the precession of a radial quadrupole excitation. The\nmeasurements distinguish between the superfluid or collisional origin of\nhydrodynamic behavior, and show the phase transition."
    },
    {
        "anchor": "Gap Solitons and Bloch Waves in Nonlinear Periodic Systems: We comprehensively investigate gap solitons and Bloch waves in\none-dimensional nonlinear periodic systems. Our results show that there exists\na composition relation between them: Bloch waves at either the center or edge\nof the Brillouin zone are infinite chains composed of fundamental gap\nsolitons(FGSs). We argue that such a relation is related to the exact relation\nbetween nonlinear Bloch waves and nonlinear Wannier functions. With this\ncomposition relation, many conclusions can be drawn for gap solitons without\nany computation. For example, for the defocusing nonlinearity, there are $n$\nfamilies of FGS in the $n$th linear Bloch band gap; for the focusing case,\nthere are infinite number of families of FGSs in the semi-infinite gap and\nother gaps. In addition, the stability of gap solitons is analyzed. In\nliterature there are numerical results showing that some FGSs have cutoffs on\npropagation constant (or chemical potential), i.e. these FGSs do not exist for\nall values of propagation constant (or chemical potential) in the linear band\ngap. We offer an explanation for this cutoff.",
        "positive": "Bosonic Integer Quantum Hall States without Landau Levels on Square\n  Lattice: We study an interacting two-component hard-core bosons on square lattice for\nwhich, in the presence of staggered magnetic flux, the ground state is a\nbosonic integer quantum Hall (BIQH) state. Using a coupled-wire bosonization\napproach, we analytically show this model exhibits a BIQH state at total charge\nhalf filling associated with a symmetry-protected topological phase under\n$U(1)$ charge conservation. These theoretical expectations are verified, using\nthe infinite density matrix renormalization group method, by providing\nnumerical evidences for: (i) a quantized Hall conductance $\\sigma_{xy}=\\pm2$,\nand (ii) two counter-propagating gapless edge modes. Our model is a bosonic\ncousin of the fermionic Haldane model and serves as an additional case of\nanalogy between bosonic and fermionic quantum Hall states."
    },
    {
        "anchor": "Excitation of the Higgs Mode in a Superfluid Fermi Gas in the BCS-BEC\n  Crossover: In quantum many-body systems with spontaneous breaking of continuous\nsymmetries, Higgs modes emerge as collective amplitude oscillations of order\nparameters. Recently, Higgs mode has been observed in the ultracold Fermi gas.\nIn the present paper, we use the time-dependent Bogoliubov-de Gennes equations\nto investigate Higgs amplitude oscillations of the superfluid order parameter\nin a Fermi gas induced by a rapid change of the ${\\it s}$-wave scattering\nlength. In particular, we investigate the Higgs mode with different values of\nthe initial scattering length. We find that the energy of the Higgs mode\ncoincides with the threshold energy of the pair-breaking excitation, and\nexponent of the power-low decay of the Higgs mode $\\gamma$ continuously changes\nbetween $\\gamma=-1/2$ and $\\gamma=-3/2$ through the\nBardeen-Cooper-Schrieffer-Bose-Einstein condensation (BCS-BEC) crossover.\nMoreover, we propose the optimal ramp speed of the scattering length for\nobserving the clearest Higgs oscillations.",
        "positive": "Fate of Topology in Spin-1 Spinor Bose-Einstein Condensate: One of the excitements generated by the cold atom systems is the possibility\nto realize, and explore, varied topological phases stemming from\nmulti-component nature of the condensate. Popular examples are the\nantiferromagnetic (AFM) and the ferromagnetic (FM) phases in the\nthree-component atomic condensate with effective spin-1, to which different\ntopological manifolds can be assigned. It follows, from consideration of\nhomotopy, that different sorts of topological defects will be stable in each\nmanifold. For instance, Skyrmionic texture is believed to be a stable\ntopological object in two-dimensional AFM spin-1 condensate. Countering such\ncommon perceptions, here we show on the basis of a new wave function\ndecomposition scheme that there is no physical parameter regime wherein the\ntemporal dynamics of spin-1 condensate can be described solely within AFM or FM\nmanifold. Initial state of definite topological number prepared entirely within\none particular phase must immediately evolve into a mixed state. Accordingly,\nthe very notion of topology and topological stability within the sub-manifold\nof AFM or FM become invalid. Numerical simulation reveals the linear Zeeman\neffect to be an efficient catalyst to extract the alternate component from an\ninitial topological object prepared entirely within one particular\nsub-manifold, serving as a potential new tool for \"topology engineering\" in\nmulti-component Bose-Einstein condensates."
    },
    {
        "anchor": "Second-order interaction corrections to the Fermi surface and the\n  quasiparticle properties of dipolar fermions in three dimensions: We calculate the renormalized Fermi surface and the quasiparticle properties\nin the Fermi liquid phase of three-dimensional dipolar fermions to second order\nin the dipole-dipole interaction. Using parameters relevant to an ultracold gas\nof erbium atoms, we find that the second-order corrections typically\nrenormalize the Hartree-Fock results by less than one percent. On the other\nhand, if we use the second-order correction to the compressibility to estimate\nthe regime of stability of the system, the point of instability is already\nreached for a significantly smaller interaction strength than in the\nHartree-Fock approximation.",
        "positive": "Eliminating the wave function singularity for ultracold atoms by\n  similarity transformation: A hyperbolic singularity in the wave-function of $s$-wave interacting atoms\nis the root problem for any accurate numerical simulation. Here we apply the\ntranscorrelated method, whereby the wave-function singularity is explicitly\ndescribed by a two-body Jastrow factor, and then folded into the Hamiltonian\nvia a similarity transformation. The resulting non-singular eigenfunctions are\napproximated by stochastic Fock-space diagonalisation with energy errors\nscaling with $1/M$ in the number $M$ of single-particle basis functions. The\nperformance of the transcorrelated method is demonstrated on the example of\nstrongly correlated fermions with unitary interactions. The current method\nprovides the most accurate ground state energies so far for three and four\nfermions in a rectangular box with periodic boundary conditions."
    },
    {
        "anchor": "Many-body tunneling dynamics of Bose-Einstein condensates and vortex\n  states in two spatial dimensions: In this work, we study the out-of-equilibrium many-body tunneling dynamics of\na Bose-Einstein condensate in a two-dimensional radial double well. We\ninvestigate the impact of interparticle repulsion and compare the influence of\nangular momentum on the many-body tunneling dynamics. Accurate many-body\ndynamics are obtained by solving the full many-body Schr\\\"odinger equation. We\ndemonstrate that macroscopic vortex states of definite total angular momentum\nindeed tunnel and that, even in the regime of weak repulsions, a many-body\ntreatment is necessary to capture the correct tunneling dynamics. As a general\nrule, many-body effects set in at weaker interactions when the tunneling system\ncarries angular momentum.",
        "positive": "Generating and Manipulating Quantized Vortices On-Demand in a\n  Bose-Einstein Condensate: a Numerical Study: We numerically investigate an experimentally viable method, that we will\nrefer to as the \"chopsticks method\", for generating and manipulating on-demand\nseveral vortices in a highly oblate atomic Bose-Einstein condensate (BEC) in\norder to initialize complex vortex distributions for studies of vortex\ndynamics. The method utilizes moving laser beams (the \"chopsticks\") to\ngenerate, capture and transport vortices inside and outside the BEC. We examine\nin detail this methodology and show a wide parameter range of applicability for\nthe prototypical two-vortex case, and show case examples of producing and\nmanipulating several vortices for which there is no net circulation, equal\nnumbers of positive and negative circulation vortices, and for which there is\none net quantum of circulation. We find that the presence of dissipation can\nhelp stabilize the pinning of the vortices on their respective laser beam\npinning sites. Finally, we illustrate how to utilize laser beams as\nrepositories that hold large numbers of vortices and how to deposit individual\nvortices in a sequential fashion in the repositories in order to construct\nsuperfluid flows about the repository beams with several quanta of circulation."
    },
    {
        "anchor": "Fast frictionless dynamics as a toolbox for low-dimensional\n  Bose-Einstein condensates: A method is proposed to implement a fast frictionless dynamics in a\nlow-dimensional Bose-Einstein condensate by engineering the time-dependence of\nthe transverse confining potential in a highly anisotropic trap. The method\nexploits the inversion of the dynamical self-similar scaling law in the radial\ndegrees of freedom. We discuss the application of the method to preserve\nshort-range correlations in time of flight experiments, the implementation of\nnearly-sudden quenches of non-linear interactions, and its power to assist\nself-similar dynamics in quasi-one dimensional condensates.",
        "positive": "Chaos, Metastability and Ergodicity in Bose-Hubbard Superfluid Circuits: The hallmark of superfluidity is the appearance of metastable flow-states\nthat carry a persistent circulating current. Considering Bose-Hubbard\nsuperfluid rings, we clarify the role of \"quantum chaos\" in this context. We\nshow that the standard Landau and Bogoliubov superfluidity criteria fail for\nsuch low-dimensional circuits. We also discuss the feasibility for a coherent\noperation of a SQUID-like setup. Finally, we address the manifestation of the\nstrong many-body dynamical localization effect."
    },
    {
        "anchor": "Expansion of a quantum gas in a shell trap: We report the observation of the controlled expansion of a two-dimensional\nquantum gas confined onto a curved shell-shaped surface. We start from the\nellipsoidal geometry of a dressed quadrupole trap and introduce a novel gravity\ncompensation mechanism enabling to explore the full ellipsoid. The zero-point\nenergy of the transverse confinement manifests itself by the spontaneous\nemergence of an annular shape in the atomic distribution. The experimental\nresults are compared with the solution of the three-dimensional\nGross-Pitaevskii equation and with a two-dimensional semi-analytical model.\nThis work evidences how a hidden dimension can affect dramatically the embedded\nlow-dimensional system by inducing a change of topology.",
        "positive": "Anomalous and Quantum Hall Effects in Lossy Photonic Lattices: We theoretically discuss analogues of the anomalous and the integer quantum\nHall effect in driven-dissipative two-dimensional photonic lattices in the\npresence of a synthetic gauge field. Photons are coherently injected by a\nspatially localized pump, and the transverse shift of the in-plane light\ndistribution under the effect of an additional uniform force is considered.\nDepending on pumping parameters, the transverse shift turns out to be\nproportional either to the global Chern number (integer quantum Hall effect) or\nto the local Berry curvature (anomalous Hall effect). This suggests a viable\nroute to experimentally measure these quantities in photonic lattices."
    },
    {
        "anchor": "Synchronization of Bloch oscillations by a ring cavity: We consider Bloch oscillations of ultracold atoms stored in a one-dimensional\nvertical optical lattice and simultaneously interacting with a unidirectionally\npumped optical ring cavity whose vertical arm is collinear with the optical\nlattice. We find that the feedback provided by the cavity field on the atomic\nmotion synchronizes Bloch oscillations via a mode-locking mechanism, steering\nthe atoms to the lowest Bloch band. It also stabilizes Bloch oscillations\nagainst noise, and even suppresses dephasing due to atom-atom interactions.\nFurthermore, it generates periodic bursts of light emitted into the\ncounter-propagating cavity mode, providing a non-destructive monitor of the\natomic dynamics. All these features may be crucial for future improvements of\nthe design of atomic gravimeters based on recording Bloch oscillations.",
        "positive": "One-dimensional multicomponent Fermi gas in a trap: quantum Monte Carlo\n  study: One-dimensional world is very unusual as there is an interplay between\nquantum statistics and geometry, and a strong short-range repulsion between\natoms mimics Fermi exclusion principle, fermionizing the system. Instead, a\nsystem with a large number of components with a single atom in each, on the\nopposite acquires many bosonic properties. We study the ground-state properties\na multi-component Fermi gas trapped in a harmonic trap by fixed-node diffusion\nMonte Carlo method. We investigate how the energetic properties (energy,\ncontact) and correlation functions (density profile and momentum distribution)\nevolve as the number of components is changed. It is shown that the system\nfermionizes in the limit of strong interactions. Analytical expression are\nderived in the limit of weak interactions within the local density\napproximation for arbitrary number of components and for one plus one particle\nusing an exact solution."
    },
    {
        "anchor": "Semi-Implicit finite-difference methods to study the spin-orbit and\n  coherently coupled spinor Bose-Einstein condensates: We develop time-splitting finite difference methods, using implicit\nBackward-Euler and semi-implicit Crank-Nicolson discretization schemes, to\nstudy the spin-orbit coupled spinor Bose Einstein condensates with coherent\ncoupling in quasi-one and quasi-two-dimensional traps. The split equations\ninvolving kinetic energy and spin-orbit coupling operators are solved using\neither time-implicit Backward-Euler or semi-implicit Crank-Nicolson methods. We\nexplicitly develop the method for pseudospin-1/2, spin-1, and spin-2\ncondensates. The results for ground states obtained with time-splitting\nBackward-Euler and Crank-Nicolson methods are in excellent agreement with\ntime-splitting Fourier spectral method which is one of the popular methods to\nsolve the mean-field models for spin-orbit coupled spinor condensates. We\nconfirm the emergence of different phases in spin-orbit coupled pseudospin-1/2,\nspin-1, and spin-2 condensates with coherent coupling.",
        "positive": "Gauge matters: Observing the vortex-nucleation transition in a Bose\n  condensate: The order parameter of a quantum-coherent many-body system can include a\nphase degree of freedom, which, in the presence of an electromagnetic field,\ndepends on the choice of gauge. Because of the relationship between the phase\ngradient and the velocity, time-of-flight measurements reveal this gradient.\nHere, we make such measurements using initially trapped Bose-Einstein\ncondensates (BECs) subject to an artificial magnetic field. Vortices are\nnucleated in the BEC for artificial field strengths above a critical value,\nwhich represents a structural phase transition. By comparing to\nsuperfluid-hydrodynamic and Gross-Pitaevskii calculations, we confirmed that\nthe transition from the vortex-free state gives rise to a shear in the released\nBEC's spatial distribution, representing a macroscopic method to measure this\ntransition, distinct from direct measurements of vortex entry. Shear is also\naffected by an artificial electric field accompanying the artificial magnetic\nfield turn-off, which depends on the details of the physical mechanism creating\nthe artificial fields, and implies a natural choice of gauge. Measurements of\nthis kind offer opportunities for studying phase in less-well-understood\nquantum gas systems."
    },
    {
        "anchor": "Hofstadter Butterfly Evolution in the Space of Two-Dimensional Bravais\n  Lattices: The self-similar energy spectrum of a particle in a periodic potential under\na magnetic field, known as the Hofstadter butterfly, is determined by the\nlattice geometry as well as the external field. Recent realizations of\nartificial gauge fields and adjustable optical lattices in cold atom\nexperiments necessitate the consideration of these self-similar spectra for the\nmost general two-dimensional lattice. In a previous work, we investigated the\nevolution of the spectrum for an experimentally realized lattice which was\ntuned by changing the unit cell structure but keeping the square Bravais\nlattice fixed. We now consider all possible Bravais lattices in two dimensions\nand investigate the structure of the Hofstadter butterfly as the lattice is\ndeformed between lattices with different point symmetry groups. We model the\noptical lattice by a sinusoidal real space potential and obtain the tight\nbinding model for any lattice geometry by calculating the Wannier functions. We\nintroduce the magnetic field via Peierls substitution and numerically calculate\nthe energy spectrum. The transition between the two most symmetric lattices,\ni.e. the triangular and the square lattice displays the importance of bipartite\nsymmetry featuring deformation as well as closing of some of the major energy\ngaps. The transition from the square to rectangular and from the triangular to\ncentered rectangular lattices are analyzed in terms of coupling of\none-dimensional chains. We calculate the Chern numbers of the major gaps and\nChern number transfer between bands during the transitions. We use gap Chern\nnumbers to identify distinct topological regions in the space of Bravais\nlattices.",
        "positive": "Chaotic few-body vortex dynamics in rotating Bose--Einstein condensates: We investigate a small vortex-lattice system of four co-rotating vortices in\nan atomic Bose--Einstein condensate and find that the vortex dynamics display\nchaotic behaviour after a system quench introduced by reversing the direction\nof circulation of a single vortex through a phase-imprinting process. By\ntracking the vortex trajectories and Lyapunov exponent, we show the onset of\nchaotic dynamics is not immediate, but occurs at later times and is accelerated\nby the close-approach and separation of all vortices in a scattering event. The\ntechniques we develop could potentially be applied to create locally induced\nchaotic dynamics in larger lattice systems as a stepping stone to study the\nrole of chaotic events in turbulent vortex dynamics."
    },
    {
        "anchor": "From Anderson to anomalous localization in cold atomic gases with\n  effective spin-orbit coupling: We study the dynamics of a one-dimensional spin-orbit coupled Schrodinger\nparticle with two internal components moving in a random potential. We show\nthat this model can be implemented by the interaction of cold atoms with\nexternal lasers and additional Zeeman and Stark shifts. By direct numerical\nsimulations a crossover from an exponential Anderson-type localization to an\nanomalous power-law behavior of the intensity correlation is found when the\nspin-orbit coupling becomes large. The power-law behavior is connected to a\nDyson singularity in the density of states emerging at zero energy when the\nsystem approaches the quasi-relativistic limit of the random mass Dirac model.\nWe discuss conditions under which the crossover is observable in an experiment\nwith ultracold atoms and construct explicitly the zero-energy state, thus\nproving its existence under proper conditions.",
        "positive": "Self-consistent Keldysh approach to quenches in weakly interacting\n  Bose-Hubbard model: We present a non-equilibrium Green's functional approach to study the\ndynamics following a quench in weakly interacting Bose Hubbard model (BHM). The\ntechnique is based on the self-consistent solution of a set of equations which\nrepresents a particular case of the most general set of Hedin's equations for\nthe interacting single-particle Green's function. We use the ladder\napproximation as a skeleton diagram for the two-particle scattering amplitude\nuseful, through the self-energy in the Dyson equation, for finding the\ninteracting single-particle Green's function. This scheme is then implemented\nnumerically by a parallelized code. We exploit this approach to study the\ncorrelation propagation after a quench in the interaction parameter, for one\n(1D) and two (2D) dimensions. In particular, we show how our approach is able\nto recover the crossover from ballistic to diffusive regime by increasing the\nboson-boson interaction. Finally we also discuss the role of a thermal initial\nstate on the dynamics both for 1D and 2D Bose Hubbard models, finding that\nsurprisingly at high temperature a ballistic evolution is restored."
    },
    {
        "anchor": "Mixed partial-wave scattering with spin-orbit coupling and validity of\n  pseudo-potentials: We present exact solutions of two-body problem for spin-1/2 fermions with\nisotropic spin-orbit(SO) coupling and interacting with an arbitrary short-range\npotential. We find that in each partial-wave scattering channel, the\nparametrization of two-body wavefunction at short inter-particle distance\ndepends on the scattering amplitudes of all channels. This reveals the mixed\npartial-wave scattering induced by SO couplings. By comparing with results from\na square-well potential, we investigate the validity of original\npseudo-potential models in the presence of SO coupling. We find the s-wave\npseudo-potential provides a good approximation for low-energy solutions near\ns-wave resonances, given the length scale of SO coupling much longer than the\npotential range. However, near p-wave resonance the p-wave pseudo-potential\ngives low-energy solutions that are qualitatively different from exact ones,\nbased on which we conclude that the p-wave model can not be applied to the\nfermion system if the SO coupling strength is larger or comparable to the Fermi\nmomentum.",
        "positive": "Excitations of optomechanically driven Bose-Einstein condensates in a\n  cavity: photodetection measurements: We present a detailed study to analyse the Dicke quantum phase transition\nwithin the thermodynamic limit for an optomechanically driven Bose-Einstein\ncondensates in a cavity. The photodetection-based quantum optical measurements\nhave been performed to study the dynamics and excitations of this\noptomechanical Dicke system. For this, we discuss the eigenvalue analysis,\nfluorescence spectrum and the homodyne spectrum of the system. It has been\nshown that the normal phase is negligibly affected by the mechanical mode of\nthe mirror while it has a significant effect in the superradiant phase. We have\nobserved that the eigenvalues and both the spectra exhibit distinct features\nthat can be identified with the photonic, atomic and phononic branches. In the\nfluorescence spectra, we further observe an asymmetric coherent energy exchange\nbetween the three degrees of freedom of the system in the superradiant phase\narising as a result of optomechanical interaction and Bloch-Siegert shift."
    },
    {
        "anchor": "Universal many-body diffusion from momentum dephasing: The open dynamics of quantum many-body systems involve not only the exchange\nof energy, but also of other conserved quantities, such as momentum. This leads\nto additional decoherence, which may have a profound impact in the dynamics.\nMotivated by this, we consider a many-body system subject to total momentum\ndephasing and show that under very general conditions this leads to a diffusive\ncomponent in the dynamics of any local density, even far from equilibrium. Such\ncomponent will usually have an intricate interplay with the unitary dynamics.\nTo illustrate this, we consider the case of a superfluid and show that momentum\ndephasing introduces a damping in the sound-wave dispersion relation, similar\nto that predicted by the Navier-Stokes equation for ordinary fluids. Finally,\nwe also study the effects of dephasing in linear response, and show that it\nleads to a universal additive contribution to the diffusion constant, which can\nbe obtained from a Kubo formula.",
        "positive": "Stripe and checkerboard patterns in a stack of driven\n  quasi-one-dimensional dipolar condensates: The emergence of transient checkerboard and stripe patterns in a stack of\ndriven quasi-one-dimensional homogeneous dipolar condensates is studied. The\nparametric driving of the $s$-wave scattering length leads to the excitation of\nthe lowest collective Bogoliubov mode. The character of the lowest mode depends\ncritically on the orientation of the dipoles, corresponding to out-of-phase and\nin-phase density modulations in neighboring condensates, resulting in\ncheckerboard and stripe patterns. Further, we show that a dynamical transition\nbetween the checkerboard and stripe patterns can be realized by quenching the\ndipole orientation either linearly or abruptly once the initial pattern is\nformed via periodic driving."
    },
    {
        "anchor": "Expansion of a Bose-Einstein Condensate with Vortices: The expansion of Bose-Einstein condensates (BECs) is numerically studied.\nUsually, the aspect ratio of a condensate is inverted due to the anisotropy of\nthe uncertainty principle. In turbulent BECs, however, the aspect ratio remains\nconstant. The reason for this phenomenon is still unknown, being a challenging\ntopic in the study of quantum turbulence. Here, the two-dimensional\nGross-Pitaevskii equation is solved and the time development of the aspect\nratio and of the radii of the condensates are calculated in the presence of\nvortices. The results indicate that vortex pairs must be added to a condensate\nin order to expand it while maintaining its aspect ratio. The anisotropy due to\nthe vortex pairs competes with that due to the uncertainty principle so that\nthe aspect ratio remains constant.",
        "positive": "Self-localized state and solitons in a Bose-Einstein-condensate-impurity\n  mixture at finite temperature: We study the properties of a Bose-Einstein condensate (BEC)-impurity mixture\nat finite temperature employing the time dependent Hartree-Fock Bogoliubov\n(TDHFB) theory which is a set of coupled nonlinear equations of motion for the\ncondensate and its normal and anomalous fluctuations on the one hand, and for\nimpurity on the other. The numerical solutions of these equations in the static\nquasi-1D regime show that the thermal cloud and the anomalous density are\ndeformed as happens to the condensate and the impurity becomes less localized\nat nonzero temperatures. Effects of the BEC fluctuations on the self-trapping\nstate are studied in homogeneous weakly interacting BEC-impurity at low\ntemperature. The self-trapping threshold is also determined in such a system.\nThe formation of solitons in the BEC-impurity mixture at finite temperature is\ninvestigated. Our formalism shows several new pictures."
    },
    {
        "anchor": "Soliton Molecules In Dipolar Bose-Einstein Condensates: Dipolar interactions support the formation of inter-site soliton molecules in\na stack of quasi-1D traps. We show that the stability and properties of\nindividual solitons, and soliton molecules in such a geometry crucially depend\non the interplay between contact and dipolar interactions. In particular, two\ndifferent quasi-1D soliton regimes are possible: a 1D soliton characterized by\npurely repulsive DDI and a 3D soliton for which a sufficiently large dipole\nmoment renders the DDI attractive. Furthermore, we find that contrary to the\ncase of dimers of polar molecules, the soliton dimers exhibit a nontrivial\nbehavior of the elementary excitations that stems from the competition between\non-site and inter-site DDI. Finally, we prove the existence of soliton trimers\nin a regime where molecular trimers do not occur. We demonstrate that the\nsoliton molecules that we report are well feasible under realistic experimental\nconditions.",
        "positive": "Hartree-Fock-Bogoliubov Model and Simulation of Attractive and Repulsive\n  Bose-Einstein Condensates: We describe a model of dynamic Bose-Einstein condensates near a Feshbach\nresonance that is computationally feasible under assumptions of spherical or\ncylindrical symmetry. Simulations in spherical symmetry approximate the\nexperimentally measured time to collapse of an unstably attractive condensate\nonly when the molecular binding energy in the model is correct, demonstrating\nthat the quantum fluctuations and atom-molecule pairing included in the model\nare the dominant mechanisms during collapse. Simulations of condensates with\nrepulsive interactions find some quantitative disagreement, suggesting that\npairing and quantum fluctuations are not the only significant factors for\ncondensate loss or burst formation. Inclusion of three-body recombination was\nfound to be inconsequential in all of our simulations, though we do not\nconsider recent experiments [1] conducted at higher densities."
    },
    {
        "anchor": "In-situ Observation of Incompressible Mott-Insulating Domains of\n  Ultracold Atomic Gases: We present a direct measurement of the density profile of a two-dimensional\nMott Insulator formed by ultracold atoms in an optical lattice. High resolution\nabsorption imaging is used to probe the \"wedding-cake\" structure of a trapped\ngas as it crosses the boundary from a unit-filled Mott insulating phase to the\nsuperfluid phase at finite temperature. Detailed analysis of images yields\nmeasurements of temperature and local compressibility; for the latter we\nobserve a strong suppression deep in the Mott-insulating phase, which is\nrecovered for the superfluid and normal phases. Furthermore, we measure\nspatially resolved fluctuations in the local density, showing a suppression of\nfluctuations in the insulator. Results are consistent with the\nfluctuation-dissipation theorem for insulator, superfluid and normal gas.",
        "positive": "Spectroscopy for cold atom gases in periodically phase-modulated optical\n  lattices: The response of cold atom gases to small periodic phase modulation of an\noptical lattice is discussed. For bosonic gases, the energy absorption rate is\ngiven, within linear response theory, by imaginary part of the current\ncorrelation function. For fermionic gases in a strong lattice potential, the\nsame correlation function can be probed via the production rate double\noccupancy. The phase modulation gives thus direct access to the conductivity of\nthe system, as function of the modulation frequency. We give an example of\napplication in the case of one dimensional bosons at zero temperature and\ndiscuss the link between the phase- and amplitude-modulation."
    },
    {
        "anchor": "Striped Ferronematic ground states in a spin-orbit coupled $S=1$ Bose\n  gas: We theoretically establish the mean-field phase diagram of a homogeneous\nspin-$1$, spin-orbit coupled Bose gas as a function of the spin-dependent\ninteraction parameter, the Raman coupling strength and the quadratic Zeeman\nshift. We find that the interplay between spin-orbit coupling and\nspin-dependent interactions leads to the occurrence of ferromagnetic or\nferronematic phases which also break translational symmetry. For weak Raman\ncoupling, increasing attractive spin-dependent interactions (as in $^{87}$Rb or\n$^7$Li) induces a transition from a uniform to a stripe XY ferromagnet (with no\nnematic order). For repulsive spin-dependent interactions however (as in\n$^{23}$Na), we find a transition from an $XY$ spin spiral phase ($<S_{z} >= 0$\nand uniform total density) with uniaxial nematic order, to a biaxial\nferronematic, where the total density, spin vector and nematic director\noscillate in real space. We investigate the stability of these phases against\nthe quadratic Zeeman effect, which generally tends to favor uniform phases with\neither ferromagnetic or nematic order but not both. We discuss the relevance of\nour results to ongoing experiments on spin-orbit coupled, spinor Bose gases.",
        "positive": "Realizing and detecting a topological insulator in the AIII symmetry\n  class: Topological insulators in the AIII symmetry class lack experimental\nrealization. Moreover, fractionalization in one-dimensional topological\ninsulators has not been yet directly observed. Our work might open\npossibilities for both challenges. We propose a one-dimensional model realizing\nthe AIII symmetry class which can be realized in current experiments with\nultracold atomic gases. We further report on a distinctive property of\ntopological edge modes in the AIII class: in contrast to those in the well\nstudied BDI class, they have non-zero momentum. Exploiting this feature we\npropose a path for the detection of fractionalization. A fermion added to an\nAIII system splits into two halves localized at opposite momenta, which can be\ndetected by imaging the momentum distribution."
    },
    {
        "anchor": "Unlocked-relative-phase states in arrays of Bose-Einstein condensates: Phase engineering techniques are used to control the dynamics of\nlong-bosonic-Josephson-junction arrays built by linearly coupling Bose-Einstein\ncondensates. Just at the middle point of the underlying discrete energy band of\nthe system, unlocked-relative-phase states are shown to be stationary along\nwith the locked-relative-phase Bloch waves. In finite, experimentally-feasible\nsystems, such states find ranges of dynamical stability that depend on the\nratio of coupling to interaction energy. The same ratio determines different\ndecay regimes, which include the recurrence of staggered-soliton trains in the\ncondensates around Josephson loop currents at the junctions. These transient\nsolitons are also found in their stationary configurations, which provide\nstriped-density states by means of either dark-soliton or bright-soliton\ntrains. Additionally, the preparation of maximally out-of-phase (or splay)\nstates is demonstrated to evolve into an oscillation of the uniform density of\nthe condensates that keeps constant the total density of the system and robust\nagainst noise at low coupling.",
        "positive": "Injection of orbital angular momentum and storage of quantized vortices\n  in polariton superfluids: We report the experimental investigation and theoretical modeling of a\nrotating polariton superfluid relying on an innovative method for the injection\nof angular momentum. This novel, multi-pump injection method uses four coherent\nlasers arranged in a square, resonantly creating four polariton populations\npropagating inwards. The control available over the direction of propagation of\nthe superflows allows injecting a controllable non-quantized amount of optical\nangular momentum. When the density at the center is low enough to neglect\npolariton-polariton interactions, optical singularities, associated to an\ninterference pattern, are visible in the phase. In the superfluid regime\nresulting from the strong nonlinear polariton-polariton interaction, the\ninterference pattern disappears and only vortices with the same sign are\npersisting in the system. Remarkably the number of vortices inside the\nsuperfluid region can be controlled by controlling the angular momentum\ninjected by the pumps."
    },
    {
        "anchor": "Simulation of XXZ Spin Models using Sideband Transitions in Trapped\n  Bosonic Gases: We theoretically propose and experimentally demonstrate the use of motional\nsidebands in a trapped ensemble of $^{87}$Rb atoms to engineer tunable\nlong-range XXZ spin models. We benchmark our simulator by probing a\nferromagnetic to paramagnetic dynamical phase transition in the\nLipkin-Meshkov-Glick (LMG) model, a collective XXZ model plus additional\ntransverse and longitudinal fields, via Rabi spectroscopy. We experimentally\nreconstruct the boundary between the dynamical phases, which is in good\nagreement with mean-field theoretical predictions. Our work introduces new\npossibilities in quantum simulation of anisotropic spin-spin interactions and\nquantum metrology enhanced by many-body entanglement.",
        "positive": "Fragmentation of Spin-orbit Coupled Spinor Bose-Einstein Condensates: The fragmentation of spin-orbit coupled spin-1 Bose gas with a weak\ninteraction in external harmonic trap is explored by both exact diagonalization\nand mean-field theory. This fragmentation tendency, which originates from the\ntotal angular momentum conservation, is affected obviously by the spin-orbit\ncoupling strength and the spin-dependent interaction. Strong spin-orbit\ninteraction raises the inverse participation ratio, which describes the number\nof significantly occupied single-particle states. As the spin-dependent\ninteraction changes from anti-ferromagnetic to ferromagnetic, the peak values\nin the inverse participation ratio become lower. Without the confinement of the\nappointed total angular momentum, the condensate chooses a zero or finite total\nangular momentum ground state, which is determined by both the interaction and\nthe spin-orbit coupling strength."
    },
    {
        "anchor": "Modified Fermi-sphere, pairing gap and critical temperature for the\n  BCS-BEC crossover: We investigate the phase diagram of two-component fermions in the BCS-BEC\ncrossover. Using functional renormalization group equations we calculate the\neffect of quantum fluctuations on the fermionic self-energy parametrized by a\nwavefunction renormalization, an effective Fermi radius and the gap. This\nallows us to follow the modifications of the Fermi surface and the dispersion\nrelation for fermionic excitations throughout the whole crossover region. We\nalso determine the critical temperature of the second order phase transition to\nsuperfluidity. Our results are in agreement with BCS theory including Gorkov's\ncorrection for small negative scattering length a and with an interacting Bose\ngas for small positive a. At the unitarity point the result for the gap at zero\ntemperature agrees well with Quantum-Monte-Carlo simulations while the critical\ntemperature differs.",
        "positive": "Excitons and Cavity Polaritons for Optical Lattice Ultracold Atoms: Ultracold atoms uniformly filling an optical lattice can be treated like an\nartificial crystal. An implementation including the atomic occupation of a\nsingle excited atomic state can be represented by a two-component Bose-Hubbard\nmodel. Its phase diagram exhibits a quantum phase transition from a superfluid\nto a Mott insulator phase. The dynamics of electronic excitations governed by\nelectrostatic dipole-dipole interactions in the ordered regime can be well\ndescribed by wave-like collective excitations called excitons. Here we present\nan extensive study of such excitons for a wide range of geometries and\ndimensionality. Their lifetimes can vary over many orders of magnitude from\nmetastable propagation to superradiant decay. Particularly strong effects occur\nin one dimensional atomic chains coupled to tapered optical fibers. For an\noptical lattice within a cavity the excitons are coupled to cavity photons and\nthe resulting collective cavity QED model can be efficiently formulated in\nterms of polaritons. Their properties are explicitly calculated for different\nlattices and they constitute a non-destructive monitoring tool for important\nsystem properties. Even the formation of molecules in optical lattices\nmanifests itself in modified polariton properties as e.g. an anisotropic\noptical spectrum. Partial dissipation of the exciton energy in the lattice\nleads to heating, which can be microscopically understood through a mechanism\ntransferring atoms into higher Bloch bands via a resonant excitation transfer\namong neighboring lattice sites. The presence of lattice defects like vacancies\nin the Mott insulator induces a characteristic scattering of polaritons, which\ncan be optically observed to monitor the lattice integrity. Our models can be\napplied to simulate and understand corresponding collective phenomena in solid\ncrystals, where many effects are often masked by noise and disorder."
    },
    {
        "anchor": "Exact two-body solutions and Quantum defect theory of two dimensional\n  dipolar quantum gas: In this paper, we provide the two-body exact solutions of two dimensional\n(2D) Schr\\\"{o}dinger equation with isotropic $\\pm 1/r^3$ interactions. Analytic\nquantum defect theory are constructed base on these solutions and are applied\nto investigate the scattering properties as well as two-body bound states of\nultracold polar molecules confined in a quasi-2D geometry. Interestingly, we\nfind that for the attractive case, the scattering resonance happens\nsimultaneously in all partial waves which has not been observed in other\nsystems. The effect of this feature on the scattering phase shift across such\nresonances is also illustrated.",
        "positive": "Statics and dynamics of a self-bound dipolar matter-wave droplet: We study the statics and dynamics of a stable, mobile, self-bound\nthree-dimensional dipolar matter-wave droplet created in the presence of a tiny\nrepulsive three-body interaction. In frontal collision with an impact parameter\nand in angular collision at large velocities {along all directions} two\ndroplets behave like quantum solitons. Such collision is found to be quasi\nelastic and the droplets emerge undeformed after collision without any change\nof velocity. However, in a collision at small velocities the axisymmeric\ndipolar interaction plays a significant role and the collision dynamics is\nsensitive to the direction of motion. For an encounter along the $z$ direction\nat small velocities, two droplets, polarized along the $z$ direction, coalesce\nto form a larger droplet $-$ a droplet molecule. For an encounter along the $x$\ndirection at small velocities, the same droplets stay apart and never meet each\nother due to the dipolar repulsion. The present study is based on an analytic\nvariational approximation and a numerical solution of the mean-field\nGross-Pitaevskii equation using the parameters of $^{52}$Cr atoms."
    },
    {
        "anchor": "Rotating a supersolid dipolar gas: Distintictive features of supersolids show up in their rotational properties.\nWe calculate the moment of inertia of a harmonically trapped dipolar\nBose-Einstein condensed gas as a function of the tunable scattering length\nparameter, providing the transition from the (fully) superfluid to the\nsupersolid phase and eventually to an incoherent crystal of self-bound\ndroplets. The transition from the superfluid to the supersolid phase is\ncharacterized by a jump in the moment on inertia, revealing its first order\nnature. In the case of elongated trapping in the plane of rotation we show that\nthe the moment of inertia determines the value of the frequency of the scissors\nmode, which is significantly affected by the reduction of superfluidity in the\nsupersolid phase. The case of isotropic trapping is instead well suited to\nstudy the formation of quantized vortices, which are shown to be characterized,\nin the supersolid phase, by a sizeable deformed core, caused by the presence of\nthe sorrounding density peaks.",
        "positive": "Magnetization and collective excitations of a magnetic dipole fermion\n  gas: The ground states and collective excitations of trapped Fermion gases\nconsisting of atoms with magnetic dipole moment are studied using a\ntime-dependent density-matrix approach. The advantages of the density-matrix\napproach are that one-body and two-body observables are directly calculated\nusing one-body and two-body density matrices and that it has a clear relation\nto the Hartree-Fock (HF) and time-dependent HF theory. The HF calculations show\nthe magnetization of the gases when the dipole-dipole interaction is strong. It\nis shown that the tensor properties of the dipole-dipole interaction are\nrevealed in the excitation modes associated with spin degrees of freedom."
    },
    {
        "anchor": "Pseudogap regime of a strongly interacting two-dimensional Fermi gas\n  with and without confinement-induced effect range of interactions: We investigate theoretically the many-body pairing of a strongly correlated\ntwo-dimensional Fermi gas with and without negative confinement-induced\neffective range. Using a strong-coupling effective field theory in the normal\nstate, we show that the specific heat at constant volume can be used as a\ncharacteristic indicator of the crossover from the normal Fermi liquid to the\npseudogap state in two dimensions. We calculate the pseudogap formation\ntemperature through the specific heat at constant volume, examining the role of\na negative confinement-induced effective range on many-body pairing above the\nsuperfluid transition. We compare our results with and without effective range\nto the recent experimental measurement performed with radio-frequency\nspectroscopy in Murthy et al.[Science359, 452-455 (2018)]. Although a good\nqualitative agreement is found, we are not able to discriminate the effect of\nthe confinement-induced effect range in the experimental data.",
        "positive": "Observation of Quantum Equilibration in Dilute Bose Gases: We investigate experimentally the dynamical relaxation of a non-integrable\nquantum many-body system to its equilibrium state. A Bose-Einstein condensate\nis loaded into the first excited band of an optical lattice and let to evolve\nup to a few hundreds of milliseconds. Signs of quantum equilibration are\nobserved. There is a period of time, roughly 40 ms long, during which both the\naspect ratio of the cloud and its momentum distribution remain constant. In\nparticular, the momentum distribution has a flat top and is not a Gaussian\nthermal distribution. After this period, the cloud becomes classical as its\nmomentum distribution becomes Gaussian."
    },
    {
        "anchor": "Quantum criticality in disordered bosonic optical lattices: Using the exact Bose-Fermi mapping, we study universal properties of\nground-state density distributions and finite-temperature quantum critical\nbehavior of one-dimensional hard-core bosons in trapped incommensurate optical\nlattices. Through the analysis of universal scaling relations in the quantum\ncritical regime, we demonstrate that the superfluid to Bose glass transition\nand the general phase diagram of disordered hard-core bosons can be uniquely\ndetermined from finite-temperature density distributions of the trapped\ndisordered system.",
        "positive": "Theory of a peristaltic pump for fermionic quantum fluids: Motivated by the recent developments in fermionic cold atoms and in\nnanostructured systems, we propose the model of a peristaltic quantum pump.\nDifferently from the Thouless paradigm, a peristaltic pump is a quantum device\nthat generates a particle flux as the effect of a sliding finite-size\nmicrolattice. A one-dimensional tight-binding Hamiltonian model of this quantum\nmachine is formulated and analyzed within a lattice Green's function formalism\non the Keldysh contour. The pump observables, as e.g. the pumped particles per\ncycle, are studied as a function of the pumping frequency, the width of the\npumping potential, the particles mean free path and system temperature. The\nproposed analysis applies to arbitrary peristaltic potentials acting on\nfermionic quantum fluids confined to one dimension. These confinement\nconditions can be realized in nanostructured systems or, in a more controllable\nway, in cold atoms experiments. In view of the validation of the theoretical\nresults, we describe the outcomes of the model considering a fermionic cold\natoms system as a paradigmatic example."
    },
    {
        "anchor": "Mutual friction and diffusion of two-dimensional quantum vortices: We present a microscopic open quantum systems theory of thermally-damped\nvortex motion in oblate atomic superfluids that includes previously neglected\nenergy-damping interactions between superfluid and thermal atoms. This\nmechanism couples strongly to vortex core motion and causes dissipation of\nvortex energy due to mutual friction, as well as Brownian motion of vortices\ndue to thermal fluctuations. We derive an analytic expression for the\ndimensionless mutual friction coefficient that gives excellent quantitative\nagreement with experimentally measured values, without any fitted parameters.\nOur work closes an existing two orders of magnitude gap between dissipation\ntheory and experiments, previously bridged by fitted parameters, and provides a\nmicroscopic origin for the mutual friction and diffusion of quantized vortices\nin two-dimensional atomic superfluids.",
        "positive": "Interaction effects on $\\mathcal{PT}$-symmetry breaking transition in\n  atomic gases: Non-Hermitian systems having parity-time ($\\mathcal {PT}$) symmetry can\nundergo a transition, spontaneously breaking the symmetry. Ultracold atomic\ngases provide an ideal platform to study interaction effects on the transition.\nWe consider a model system of $N$ bosons of two components confined in a tight\ntrap. Radio frequency and laser fields are coupled to the bosons such that the\nsingle particle Non-Hermitian Hamiltonian $h_{\\mathcal PT}=-i\n\\Gamma\\sigma_z+J\\sigma_x$, which has $\\mathcal {PT}$-symmetry, can be simulated\nin a \\emph{passive} way. We show that when interatomic interactions are tuned\nto maintain the symmetry, the $\\mathcal {PT}$-symmetry breaking transition is\naffected only by the SU(2) variant part of the interactions parameterized by\n$\\delta g$. We find that the transition point $\\Gamma_{\\rm tr}$ decreases as\n$|\\delta g|$ or $N$ increases; in the large $|\\delta g|$ limit, $\\Gamma_{\\rm\ntr}$ scales as $\\sim|\\delta g|^{-(N-1)}$. We also give signatures of the\n$\\mathcal {PT}$-symmetric and the symmetry breaking phases for the interacting\nbosons in experiment."
    },
    {
        "anchor": "Diagrammatic Monte Carlo algorithm for the resonant Fermi gas: We provide a description of a diagrammatic Monte Carlo algorithm for the\nresonant Fermi gas in the normal phase. Details are given on diagrammatic\nframework, Monte Carlo moves, and incorporation of ultraviolet asymptotics.\nApart from the self-consistent bold scheme, we also describe a\nnon-self-consistent scheme, for which the ultraviolet treatment is more\ninvolved.",
        "positive": "Integrable model for density-modulated quantum condensates: solitons\n  passing through a soliton lattice: An integrable model possessing inhomogeneous ground states is proposed as an\neffective model of non-uniform quantum condensates such as supersolids and\nFulde--Ferrell--Larkin--Ovchinnikov superfluids. The model is a higher-order\nanalog of the nonlinear Schr\\\"odinger equation. We derive an $n$-soliton\nsolution via the inverse scattering theory with elliptic-functional background,\nand reveal various kinds of soliton dynamics such as dark soliton billiards,\ndislocations, gray solitons, and envelope solitons. We also provide the exact\nbosonic and fermionic quasiparticle eigenstates and clarify their tunneling\nphenomena. The solutions are expressed by a determinant of theta functions."
    },
    {
        "anchor": "Nonlinear interferometry beyond classical limit facilitated by cyclic\n  dynamics: Time-reversed evolution has substantial implications in physics, including\nprominent applications in refocusing of classical waves or spins and\nfundamental researches such as quantum information scrambling. In quantum\nmetrology, nonlinear interferometry based on time reversal protocols supports\nentanglement-enhanced measurements without requiring low-noise detection.\nDespite the broad interest in time reversal, it remains challenging to reverse\nthe quantum dynamics of an interacting many-body system as is typically\nrealized by an (effective) sign-flip of the system's Hamiltonian. Here, we\npresent an approach that is broadly applicable to cyclic systems for\nimplementing nonlinear interferometry without invoking time reversal. Inspired\nby the observation that the time-reversed dynamics drives a system back to its\nstarting point, we propose to accomplish the same by slaving the system to\ntravel along a 'closed-loop' instead of explicitly tracing back its antecedent\npath. Utilizing the quasi-periodic spin mixing dynamics in a three-mode\n$^{87}$Rb atom spinor condensate, we implement such a 'closed-loop' nonlinear\ninterferometer and achieve a metrological gain of $3.87_{-0.95}^{+0.91}$\ndecibels over the classical limit for a total of 26500 atoms. Our approach\nunlocks the high potential of nonlinear interferometry by allowing the dynamics\nto penetrate into deep nonlinear regime, which gives rise to highly entangled\nnon-Gaussian state. The idea of bypassing time reversal may open up new\nopportunities in the experimental investigation of researches that are\ntypically studied by using time reversal protocols.",
        "positive": "Matter-wave solitons and finite-amplitude Bloch waves in optical\n  lattices with a spatially modulated nonlinearity: We investigate solitons and nonlinear Bloch waves in Bose-Einstein\ncondensates trapped in optical lattices. By introducing specially designed\nlocalized profiles of the spatial modulation of the attractive nonlinearity, we\nconstruct an infinite number of exact soliton solutions in terms of the Mathieu\nand elliptic functions, with the chemical potential belonging to the\nsemi-infinite bandgap of the optical-lattice-induced spectrum. Starting from\nthe exact solutions, we employ the relaxation method to construct generic\nfamilies of soliton solutions in a numerical form. The stability of the\nsolitons is investigated through the computation of the eigenvalues for small\nperturbations, and also by direct simulations. Finally, we demonstrate a\nvirtually exact (in the numerical sense) composition relation between nonlinear\nBloch waves and solitons."
    },
    {
        "anchor": "Corrections to Local Density Approximation for superfluid trapped\n  fermionic atoms from the Wigner-Kirkwood $\\hbar$ expansion: A semiclassical second-order differential equation for the inhomogeneous\nlocal gap $\\Delta(r)$ is derived from a strict second-order $\\hbar$ expansion\nof the anomalous pairing tensor and compared with a similar equation given by\nSimonucci et al. The second-order normal density matrix is given as well.\nSeveral extra gradient terms are revealed. Second-order expressions at finite\ntemperature are given for the first time. The corresponding Ginzburg-Landau\nequation is presented and it is shown that, compared to the equation of Baranov\nand Petrov, an extra second-order gradient term is present. Applications to the\npairing gap in cold atoms in a harmonic trap are presented.",
        "positive": "Universal quantum computation and quantum error correction with\n  ultracold atomic mixtures: Quantum information platforms made great progress in the control of many-body\nentanglement and the implementation of quantum error correction, but it remains\na challenge to realize both in the same setup. Here, we propose a mixture of\ntwo ultracold atomic species as a platform for universal quantum computation\nwith long-range entangling gates, while providing a natural candidate for\nquantum error-correction. In this proposed setup, one atomic species realizes\nlocalized collective spins of tunable length, which form the fundamental unit\nof information. The second atomic species yields phononic excitations, which\nare used to entangle collective spins. Finally, we discuss a finite-dimensional\nversion of the Gottesman-Kitaev-Preskill code to protect quantum information\nencoded in the collective spins, opening up the possibility to universal\nfault-tolerant quantum computation in ultracold atom systems."
    },
    {
        "anchor": "Vortex Solutions in a Binary Immiscible Bose-Einstein Condensate: We consider the mean-field vortex solutions and their stability within a\ntwo-component Bose Einstein condensate in the immiscible limit. A variational\napproach is employed to study a system consisting of a majority component which\ncontains a single quantised vortex and a minority component which fills the\nvortex core. We show that a super-Gaussian function is a good approximation to\nthe two-component vortex solution for a range of atom numbers of the in-filling\ncomponent, by comparing the variational solutions to the full numerical\nsolutions of the coupled Gross-Pitaevskii equations. We subsequently examine\nthe stability of the vortex solutions by perturbing the in-filling component\naway from the centre of the vortex core, thereby demonstrating their stability\nto small perturbations.",
        "positive": "Robust Bilayer Charge-Pumping for Spin- and Density-Resolved Quantum Gas\n  Microscopy: Quantum gas microscopy has emerged as a powerful new way to probe quantum\nmany-body systems at the microscopic level. However, layered or efficient\nspin-resolved readout methods have remained scarce as they impose strong\ndemands on the specific atomic species and constrain the simulated lattice\ngeometry and size. Here we present a novel high-fidelity bilayer readout, which\ncan be used for full spin- and density-resolved quantum gas microscopy of\ntwo-dimensional systems with arbitrary geometry. Our technique makes use of an\ninitial Stern-Gerlach splitting into adjacent layers of a highly-stable\nvertical superlattice and subsequent charge pumping to separate the layers by\n$21\\,\\mu$m. This separation enables independent high-resolution images of each\nlayer. We benchmark our method by spin- and density-resolving two-dimensional\nFermi-Hubbard systems. Our technique furthermore enables the access to advanced\nentropy engineering schemes, spectroscopic methods or the realization of\ntunable bilayer systems."
    },
    {
        "anchor": "Long range mediated interactions in a mixed dimensional system: We present a mixed-dimensional atomic gas system to unambiguously detect and\nsystematically probe mediated interactions. In our scheme, fermionic atoms are\nconfined in two parallel planes and interact via exchange of elementary\nexcitations in a three-dimensional background gas. This interaction gives rise\nto a frequency shift of the out-of-phase dipole oscillations of the two clouds,\nwhich we calculate using a strong coupling theory taking the two-body\nmixed-dimensional scattering into account exactly. The shift is shown to be\neasily measurable for strong interactions and can be used as a probe for\nmediated interactions.",
        "positive": "Fragmentation and the Bose-glass phase transition of the disordered 1D\n  Bose gas: We investigate the superfluid-insulator quantum phase transition in a\ndisordered 1D Bose gas in the mean field limit, by studying the probability\ndistribution of the density. The superfluid phase is characterized by a\nvanishing probability to have zero density, whereas a nonzero probability marks\nthe insulator phase. This relation is derived analytically, and confirmed by a\nnumerical study. This fragmentation criterion is particularly suited for\ndetecting the phase transition in experiments. When a harmonic trap is\nincluded, the transition to the insulating phase can be extracted from the\nstatistics of the local density distribution."
    },
    {
        "anchor": "Propagation properties and stability of dark solitons in weakly\n  interacting Bose-Bose droplets: We investigate dark solitons in two-component Bose systems with competing\ninteractions in one dimension. Such a system hosts a liquid phase stabilized by\nthe beyond-mean field corrections. Using the generalized Gross-Pitaevskii\nequation, we reveal the presence of two families of solitonic solutions. The\nsolitons in both of them can be engineered to be arbitrarily wide. One family\nof solutions, however, has got an anomalous dispersion relation and our\nanalyses show one of its branches is unstable. We find the presence of a\ncritical velocity demarcating the stable from unstable solutions. Nonetheless,\ngrey anomalous solitons are able to exist inside quantum droplets and can be\ntreated as solitonic excitations thereof.",
        "positive": "Heat current control in trapped BEC: We investigate the heat transport and the control of heat current among two\nspatially separated trapped Bose-Einstein Condensates (BEC), each of them at a\ndifferent temperature. To allow for heat transport among the two independent\nBECs we consider a link made of two harmonically trapped impurities, each of\nthem interacting with one of the BECs. Since the impurities are spatially\nseparated, we consider long-range interactions between them, namely a\ndipole-dipole coupling. We study this system under theoretically suitable and\nexperimentally feasible assumptions/parameters. The dynamics of these\nimpurities is treated within the framework of the quantum Brownian motion\nmodel, where the excitation modes of the BECs play the role of the heat bath.\nWe address the dependence of heat current and current-current correlations on\nthe physical parameters of the system. Interestingly, we show that heat\nrectification, i.e., the unidirectional flow of heat, can occur in our system,\nwhen a periodic driving on the trapping frequencies of the impurities is\nconsidered. Therefore, our system is a possible setup for the implementation of\na phononic circuit. Motivated by recent developments on the usage of BECs as\nplatforms for quantum information processing, our work offers an alternative\npossibility to use this versatile setting for information transfer and\nprocessing, within the context of phononics, and more generally in quantum\nthermodynamics."
    },
    {
        "anchor": "Topological superfluidity with repulsive alkaline-earth atoms in optical\n  lattices: Topological superfluids are of technological relevance since they are\nbelieved to host Majorana bound states, a powerful resource for quantum\ncomputation and memory. Here we propose to realize topological superfluidity\nwith fermionic atoms in an optical lattice. We consider a situation where atoms\nin two internal states experience different lattice potentials: one species is\nlocalized and the other itinerant, and show how quantum fluctuations of the\nlocalized fermions give rise to an attraction and strong spin-orbit coupling in\nthe itinerant band. At low temperature, these effects stabilize a topological\nsuperfluid of mobile atoms even if their bare interactions are repulsive. This\nemergent state can be engineered with ${}^{87}$Sr atoms in a superlattice with\na dimerized unit cell. To probe its unique properties we describe protocols\nthat use high spectral resolution and controllability of the Sr clock\ntransition, such as momentum-resolved spectroscopy and supercurrent response to\na synthetic (laser-induced) magnetic field.",
        "positive": "Bath-induced band decay of a Hubbard lattice gas: Dissipation is introduced to a strongly interacting ultracold bosonic gas in\nthe Mott-insulator regime of a 3D spin-dependent optical lattice. A weakly\ninteracting superfluid comprised of atoms in a state that does not experience\nthe lattice potential acts as a dissipative bath coupled to the lattice atoms\nvia collisions. Lattice atoms are excited to higher-energy bands via Bragg\ntransitions, and the resulting bath-induced decay is measured using the atomic\nquasimomentum distribution. A competing but slower intrinsic decay mechanism\narising from collisions between lattice atoms is also investigated. The\nmeasured bath-induced decay rate is compared with the predictions of a weakly\ninteracting model with no free parameters. The presence of intrinsic decay,\nwhich cannot be accommodated within this framework, signals that strong\ninteractions may play a central role in the lattice-atom dynamics."
    },
    {
        "anchor": "The response to dynamical modulation of the optical lattice for fermions\n  in the Hubbard model: Fermionic atoms in a periodic optical lattice provide a realization of the\nsingle-band Hubbard model. Using Quantum Monte Carlo simulations along with the\nMaximum Entropy Method, we evaluate the effect of a time-dependent perturbative\nmodulation of the optical lattice amplitude on atomic correlations, revealed in\nthe fraction of doubly-occupied sites. Our treatment extends previous\napproaches which neglected the time dependence of the on-site interaction, and\nshows that this term changes the results in a quantitatively significant way.\nThe effect of modulation depends strongly on the filling-- the response of the\ndouble occupation is significantly different in the half-filled Mott insulator\nfrom the doped Fermi liquid region.",
        "positive": "Groundstate and Collective Modes of a Spin-Polarized Dipolar\n  Bose-Einstein Condensate in a Harmonic Trap: We report new results for the Thomas-Fermi groundstate and the quadrupolar\nmodes of density oscillations of a spin- polarized dipolar interacting\nBose-Einstein condensate for the case when the external magnetic field is not\norientated parallel to a principal axis of a harmonic anisotropic trap."
    },
    {
        "anchor": "Energy response and spatial alignment of the perturbed electron gas: We present extensive new \\emph{ab initio} path integral Monte Carlo (PIMC)\nsimulations of the harmonically perturbed uniform electron gas (UEG) for\ndifferent densities and temperatures. This allows us to study the linear\nresponse of the UEG with respect to different contributions to the total energy\nfor different wave numbers. We find that the induced change in the interaction\nenergy exhibits a non-monotonic behaviour, and becomes negative for\nintermediate wave numbers. This effect is strongly dependent on the coupling\nstrength and can be traced back to the spatial alignment of electrons\nintroduced in earlier works [T.~Dornheim \\emph{et al.}, Communications Physics\n\\textbf{5}, 304 (2022)]. The observed quadratic dependence on the perturbation\namplitude in the limit of weak perturbations and the quartic dependence of the\nperturbation amplitude corrections are consistent with linear and non-linear\nversions of the density stifness theorem. All PIMC simulation results are\nfreely available online and can be used to benchmark new methods, or as input\nfor other calculations.",
        "positive": "Measuring and engineering entropy and spin squeezing in weakly linked\n  Bose-Einstein condensates: We propose a method to infer the single-particle entropy of bosonic atoms in\nan optical lattice and to study the local evolution of entropy, spin squeezing,\nand entropic inequalities for entanglement detection in such systems. This\nmethod is based on experimentally feasible measurements of\nnon-nearest-neighbour coherences. We study a specific example of dynamically\ncontrolling atom tunneling between selected sites and show that this could\npotentially also improve the metrologically relevant spin squeezing."
    },
    {
        "anchor": "Double universality of a quantum phase transition in spinor condensates:\n  the Kibble-\u017burek mechanism and a conservation law: We consider a phase transition from antiferromagnetic to phase separated\nground state in a spin-1 Bose-Einstein condensate of ultracold atoms. We\ndemonstrate the occurrence of two scaling laws, for the number of spin\nfluctuations just after the phase transition, and for the number of spin\ndomains in the final, stable configuration. Only the first scaling can be\nexplained by the standard Kibble-\\.Zurek mechanism. We explain the occurrence\nof two scaling laws by a model including post-selection of spin domains due to\nthe conservation of condensate magnetization.",
        "positive": "Inertial and fluctuational effects on the motion of a Bose superfluid\n  vortex: We study the motion of a vortex under the influence of a harmonic force in an\napproximately two dimensional trapped Bose-condensed gas. The\nHall-Vinen-Iordanskii equations, modified to include a fluctuational force and\nan inertial mass term, are solved for the vortex motion. The mass of the vortex\nhas a strong influence on the time it takes the vortex to escape the trap.\nSince the vortex mass also depends on the trap size we have an additional\ndependence on the trap size in the escape time which we compare to the massless\ncase."
    },
    {
        "anchor": "Finite temperature dynamical properties of SU($N$) fermionic Hubbard\n  models in the spin-incoherent regime: We study strongly correlated Hubbard systems extended to symmetric\n$N$-component fermions. We focus on the intermediate-temperature regime between\nmagnetic superexchange and interaction energy, which is relevant to current\nultracold fermionic atom experiments. The $N$-component fermions are\nrepresented by slave particles, and, by using a diagrammatic technique based on\nthe atomic limit, spectral functions are analytically obtained as a function of\ntemperature, filling factor and the component number $N$. We also apply this\nanalytical technique to the calculation of lattice modulation experiments. We\ncompute the production rate of double occupancy induced by modulation of an\noptical lattice potential. Furthermore, we extend the analysis to take into\naccount the trapping potential by use of the local density approximation. We\nfind an excellent agreement with recent experiments on $^{173}$Yb atoms.",
        "positive": "Quantum Register of Fermion Pairs: Fermions are the building blocks of matter, forming atoms and nuclei, complex\nmaterials and neutron stars. Our understanding of many-fermion systems is\nhowever limited, as classical computers are often insufficient to handle the\nintricate interplay of the Pauli principle with strong interactions. Quantum\nsimulators based on ultracold fermionic atoms instead directly realize\nparadigmatic Fermi systems, albeit in \"analog\" fashion, without coherent\ncontrol of individual fermions. Digital qubit-based quantum computation of\nfermion models, on the other hand, faces significant challenges in implementing\nfermionic anti-symmetrization, calling for an architecture that natively\nemploys fermions as the fundamental unit. Here we demonstrate a robust quantum\nregister composed of hundreds of fermionic atom pairs trapped in an optical\nlattice. With each fermion pair forming a spin-singlet, the qubit is realized\nas a set of near-degenerate, symmetry-protected two-particle wavefunctions\ndescribing common and relative motion. Degeneracy is lifted by the atomic\nrecoil energy, only dependent on mass and lattice wavelength, thereby rendering\ntwo-fermion motional qubits insensitive against noise of the confining\npotential. We observe quantum coherence beyond ten seconds. Universal control\nis provided by modulating interactions between the atoms. Via state-dependent,\ncoherent conversion of free atom pairs into tightly bound molecules, we tune\nthe speed of motional entanglement over three orders of magnitude, yielding\n$10^4$ Ramsey oscillations within the coherence time. For site-resolved\nmotional state readout, fermion pairs are coherently split into a double well,\ncreating entangled Bell pairs. The methods presented here open the door towards\nfully programmable quantum simulation and digital quantum computation based on\nfermions."
    },
    {
        "anchor": "Strong-coupling expansion for the spin-1 Bose-Hubbard model: In this study, we perform a strong-coupling expansion up to third order of\nthe hopping parameter $t$ for the spin-1 Bose--Hubbard model with\nantiferromagnetic interaction. As expected from previous studies, the Mott\ninsulator phase is considerably more stable against the superfluid phase when\nfilling with an even number of bosons than when filling with an odd number of\nbosons. The phase-boundary curves are consistent with the perturbative\nmean-field theory in the limit of infinite dimensions. The critical value of\nthe hopping parameter $t_{\\rm C}$ at the peak of the Mott lobe depends on the\nantiferromagnetic interaction. This result indicates the reliability of the\nstrong coupling expansion when $U_2$ possesses large (intermediate) values for\nMott lobe with an even (odd) number of bosons. Moreover, in order to improve\nour results, we apply a few extrapolation methods up to infinite order in $t$.\nThe fitting results of the phase-boundary curves agree better with those of the\nperturbative mean-field approximation. In addition, the linear fit error of\n$t_{\\rm C}$ is very small for the strong antiferromagnetic interaction.",
        "positive": "Pairing and condensation in a resonant Bose-Fermi mixture: We study by diagrammatic methods a mixture of single-component bosons and\nfermions, with boson-fermion coupling tuned by a Fano-Feshbach resonance. For\nincreasing coupling, the growing boson-fermion pairing correlations\nprogressively reduce the boson condensation temperature and make it eventually\nvanish at a critical coupling. Such quantum critical point depends very weakly\non the population imbalance and for vanishing boson densities coincides with\nthat found for the polaron-molecule transition in a strongly imbalanced Fermi\ngas, thus bridging two quite distinct physical systems."
    },
    {
        "anchor": "Characteristic quantities for nonequilibrium Bose systems: The paper discusses what characteristic quantities could quantify\nnonequilibrium states of Bose systems. Among such quantities, the following are\nconsidered: effective temperature, Fresnel number, and Mach number. The\nsuggested classification of nonequilibrium states is illustrated by studying a\nBose-Einstein condensate in a shaken trap, where it is possible to distinguish\neight different nonequilibrium states: weak nonequilibrium, vortex germs,\nvortex rings, vortex lines, deformed vortices, vortex turbulence, grain\nturbulence, and wave turbulence. Nonequilibrium states are created\nexperimentally and modeled by solving the nonlinear Schr\\\"odinger equation.",
        "positive": "Thermodynamic behavior of a one-dimensional Bose gas at low temperature: We show that the chemical potential of a one-dimensional (1D) interacting\nBose gas exhibits a non-monotonic temperature dependence which is peculiar of\nsuperfluids. The effect is a direct consequence of the phononic nature of the\nexcitation spectrum at large wavelengths exhibited by 1D Bose gases. For low\ntemperatures $T$, we demonstrate that the coefficient in $T^2$ expansion of the\nchemical potential is entirely defined by the zero-temperature density\ndependence of the sound velocity. We calculate that coefficient along the\ncrossover between the Bogoliubov weakly-interacting gas and the Tonks-Girardeau\ngas of impenetrable bosons. Analytic expansions are provided in the asymptotic\nregimes. The theoretical predictions along the crossover are confirmed by\ncomparison with the exactly solvable Yang-Yang model in which the\nfinite-temperature equation of state is obtained numerically by solving\nBethe-{\\it ansatz} equations. A 1D ring geometry is equivalent to imposing\nperiodic boundary conditions and arising finite-size effects are studied in\ndetails. At $T=0$ we calculated various thermodynamic functions, including the\ninelastic structure factor, as a function of the number of atoms, pointing out\nthe occurrence of important deviations from the thermodynamic limit."
    },
    {
        "anchor": "Reversible decay of ring dark solitons: We show how boundary effects can cause a Bose-Einstein condensate to\nperiodically oscillate between a (circular) array of quantised\nvortex-antivortex pairs and a (ring) dark soliton. If the boundary is\nrestrictive enough, the ring dark soliton becomes long-lived.",
        "positive": "Tunable-range, photon-mediated atomic interactions in multimode cavity\n  QED: Optical cavity QED provides a platform with which to explore quantum\nmany-body physics in driven-dissipative systems. Single-mode cavities provide\nstrong, infinite-range photon-mediated interactions among intracavity atoms.\nHowever, these global all-to-all couplings are limiting from the perspective of\nexploring quantum many-body physics beyond the mean-field approximation. The\npresent work demonstrates that local couplings can be created using multimode\ncavity QED. This is established through measurements of the threshold of a\nsuperradiant, self-organization phase transition versus atomic position.\nSpecifically, we experimentally show that the interference of near-degenerate\ncavity modes leads to both a strong and tunable-range interaction between\nBose-Einstein condensates (BECs) trapped within the cavity. We exploit the\nsymmetry of a confocal cavity to measure the interaction between real BECs and\ntheir virtual images without unwanted contributions arising from the merger of\nreal BECs. Atom-atom coupling may be tuned from short range to long range. This\ncapability paves the way toward future explorations of exotic, strongly\ncorrelated systems such as quantum liquid crystals and driven-dissipative spin\nglasses."
    },
    {
        "anchor": "Dynamics of heat and mass transport in a quantum insulator: The real time evolution of two pieces of quantum insulators, initially at\ndifferent temperatures, is studied when they are glued together. Specifically,\neach subsystem is taken as a Bose-Hubbard model in a Mott insulator state. The\nprocess of temperature equilibration via heat transfer is simulated in real\ntime using the Minimally Entangled Typical Thermal States algorithm. The\nanalytic theory based on quasiparticles transport is also given.",
        "positive": "Thermalization of Atom-Molecule Bose Gases in a Double-Well Potential: We study the non-equiliribium dynamics of atom-molecule Bose gases in a\ndouble-well potential. In this system, the internal atom-molecule tunneling has\nsignificant influence on the dynamics. We investigate the periodicity of\ndynamics by studying the level statistics of the quantum system. We find that\nchaotic energy eigenstates arise from the competition between the interwell and\nthe atom-molecule internal tunnelings. Furthermore, we show that the physical\nquantities relax to the microcanonical averages in the full-quantum dynamics\nwhen the system is chaotic. This thermalization is caused by the verification\nof eigenstate thermalization hypothesis (ETH). We show numerically that the\nonset of ETH occurs simultaneously with that of chaos. In addition, we show\nthat the energy eigenstates become to be exponentially localized states\nsimultaneously with the onset of chaos."
    },
    {
        "anchor": "Experimental realization of a superfluid stripe phase in a\n  spin-orbit-coupled Bose-Einstein condensate enabled by momentum-space hopping: In the past few decades, the search for supersolid-like phases has attracted\ngreat attention in condensed matter and ultracold atom communities. Here we\nexperimentally demonstrate a route for realizing a superfluid stripe-phase in a\nspin-orbit coupled Bose-Einstein condensate by employing a weak optical lattice\nto induce momentum-space hopping between two spin-orbit band minima. We\ncharacterize the striped ground state as a function of lattice coupling\nstrength and spin-orbit detuning and find good agreement with mean-field\nsimulations. We observe coherent Rabi oscillations in momentum space between\ntwo band minima and demonstrate a long lifetime of the ground state. Our work\noffers an exciting new and stable experimental platform for exploring\nsuperfluid stripe-phases and their exotic excitations, which may shed light on\nthe properties of supersolid-like states.",
        "positive": "Bose-Einstein Condensation on the Surface of a Sphere: Motivated by the recent achievement of space-based Bose-Einstein condensates\n(BEC) with ultracold alkali-metal atoms under microgravity and by the proposal\nof bubble traps which confine atoms on a thin shell, we investigate the BEC\nthermodynamics on the surface of a sphere. We determine analytically the\ncritical temperature and the condensate fraction of a noninteracting Bose gas.\nThen we consider the inclusion of a zero-range interatomic potential, extending\nthe noninteracting results at zero and finite temperature. Both in the\nnoninteracting and interacting cases the crucial role of the finite radius of\nthe sphere is emphasized, showing that in the limit of infinite radius one\nrecovers the familiar two-dimensional results. We also investigate the\nBerezinski-Kosterlitz-Thouless transition driven by vortical configurations on\nthe surface of the sphere, analyzing the interplay of condensation and\nsuperfluidity in this finite-size system."
    },
    {
        "anchor": "Few-body solutions under spin-exchange interaction: magnetic bound state\n  and the Kondo screening effect: Motivated by recent progresses on ultracold alkaline-earth atoms towards the\ngoal of simulating Kondo physics, in this work we exactly solve the few-body\nproblem of one and two trapped fermions in one dimension interacting with a\nlocalized impurity under tunable spin-exchange interaction. It is found that\ndepending on the sign of the spin-exchange coupling, ferromagnetic(FM) or\nanti-ferromagnetic(AFM), the attractive and repulsive branches can hold\ndifferent magnetic structures. For the two fermions case, we demonstrate the\nKondo screening effect for the attractive branch with AFM coupling, and show\nthat such screening is absent for the ground state with FM coupling. Moreover,\nwe find a sequence of FM upper branches in the AFM coupling side. These FM\nstates are orthogonal to all other attractive branches and their wave functions\nfeature a full spin-charge separation. The effect of an additional contact\ninteraction and the extension of our results to many particles are also\ndiscussed. This work reveals the intriguing physics uniquely associated with\nthe spin-exchange interaction in the few-body point of view, which are\npromisingly to be explored in the experiment of ultracold alkaline-earth atoms.",
        "positive": "Quantum Landau damping in dipolar Bose-Einstein condensates: We consider Landau damping of elementary excitations in Bose-Einstein\ncondensates (BECs) with dipolar interactions. We discuss quantum and\nquasi-classical regimes of Landau damping. We use a generalized wave-kinetic\ndescription of BECs which, apart from the long range dipolar interactions, also\ntakes into account the quantum fluctuations and the finite energy corrections\nto short-range interactions. Such a description is therefore more general than\nthe usual mean field approximation. The present wave-kinetic approach is well\nsuited for the study of kinetic effects in BECs, such as those associated with\nLandau damping, atom trapping and turbulent diffusion. The inclusion of quantum\nfluctuations and energy corrections change the dispersion relation and the\ndamping rates, leading to possible experimental signatures of these effects.\n  Quantum Landau damping is described with generality, and particular examples\nof dipole condensates in two and three dimensions are studied. The occurrence\nof roton-maxon configurations, and their relevance to Landau damping is also\nconsidered in detail, as well as the changes introduced by the three different\nprocesses, associated with dipolar interactions, quantum fluctuations and\nfinite energy range collisions. The present approach is mainly based on a\nlinear perturbative procedure, but the nonlinear regime of Landau damping,\nwhich includes atom trapping and atom diffusion, is also briefly discussed."
    },
    {
        "anchor": "Unconventional Spin Density Waves in Dipolar Fermi Gases: The conventional spin density wave (SDW) phase (Overhauser, 1962), as found\nin antiferromagnetic metal for example (Fawcett 1988), can be described as a\ncondensate of particle-hole pairs with zero angular momentum, $\\ell=0$,\nanalogous to a condensate of particle-particle pairs in conventional\nsuperconductors. While many unconventional superconductors with Cooper pairs of\nfinite $\\ell$ have been discovered, their counterparts, density waves with\nnon-zero angular momenta, have only been hypothesized in two-dimensional\nelectron systems (Nayak, 2000). Using an unbiased functional renormalization\ngroup analysis, we here show that spin-triplet particle-hole condensates with\n$\\ell=1$ emerge generically in dipolar Fermi gases of atoms (Lu, Burdick, and\nLev, 2012) or molecules (Ospelkaus et al., 2008; Wu et al.) on optical lattice.\nThe order parameter of these exotic SDWs is a vector quantity in spin space,\nand, moreover, is defined on lattice bonds rather than on lattice sites. We\ndetermine the rich quantum phase diagram of dipolar fermions at half-filling as\na function of the dipolar orientation, and discuss how these SDWs arise amidst\ncompetition with superfluid and charge density wave phases.",
        "positive": "Excitations at the border of a condensate: We solve the Bogoliubov--de Gennes equations for an inhomogeneous condensate\nin the vicinity of a linear turning point. A stable integration scheme is\ndeveloped using a transformation into an adiabatic basis. We identify boundary\nmodes trapped in a potential whose shape is similar to a Hartree-Fock\nmean-field treatment. These modes are non-resonantly excited when bulk modes\nreflect at the turning point and contribute significantly to the spectrum of\nlocal density fluctuations."
    },
    {
        "anchor": "Condensed Groundstates of Frustrated Bose-Hubbard Models: We study theoretically the groundstates of two-dimensional Bose-Hubbard\nmodels which are frustrated by gauge fields. Motivated by recent proposals for\nthe implementation of optically induced gauge potentials, we focus on the\nsituation in which the imposed gauge fields give rise to a pattern of staggered\nfluxes, of magnitude $\\alpha$ and alternating in sign along one of the\nprincipal axes. For $\\alpha=1/2$ this model is equivalent to the case of\nuniform flux per plaquette $n_\\phi=1/2$, which, in the hard-core limit,\nrealizes the \"fully frustrated\" spin-1/2 XY model. We show that the mean-field\ngroundstates of this frustrated Bose-Hubbard model typically break\ntranslational symmetry. We introduce a general numerical technique to detect\nbroken symmetry condensates in exact diagonalization studies. Using this\ntechnique we show that, for all cases studied, the groundstate of the\nBose-Hubbard model with staggered flux $\\alpha$ is condensed, and we obtain\nquantitative determinations of the condensate fraction. We discuss the\nexperimental consequences of our results. In particular, we explain the meaning\nof gauge-invariance in ultracold atom systems subject to optically induced\ngauge potentials, and show how the ability to imprint phase patterns prior to\nexpansion can allow very useful additional information to be extracted from\nexpansion images.",
        "positive": "Spin-orbit coupling in quantum gases: Spin-orbit coupling links a particle's velocity to its quantum mechanical\nspin, and is essential in numerous condensed matter phenomena, including\ntopological insulators and Majorana fermions. In solid-state materials,\nspin-orbit coupling originates from the movement of electrons in a crystal's\nintrinsic electric field, which is uniquely prescribed. In contrast, for\nultracold atomic systems, the engineered \"material parameters\" are tuneable: a\nvariety of synthetic spin-orbit couplings can be engineered on demand using\nlaser fields. Here we outline the current experimental and theoretical status\nof spin-orbit coupling in ultracold atomic systems, discussing unique features\nthat enable physics impossible in any other known setting."
    },
    {
        "anchor": "Antiferromagnetic self-ordering of a Fermi gas in a ring cavity: We explore the density and spin self-ordering of driven spin-$1/2$\ncollisionless fermionic atoms coupled to the electromagnetic fields of a ring\nresonator. The two spin states are two-photon Raman-coupled via a pair of\ndegenerate counterpropagating cavity modes and two transverse pump fields. In\nthis one-dimensional configuration the coupled atom-field system possesses a\ncontinuous $U(1)$ translational symmetry and a discrete $\\mathbf{Z}_2$ spin\ninversion symmetry. At half filling for sufficiently strong pump strengths, the\ncombined $U(1)\\times \\mathbf{Z}_2$ symmetry is spontaneously broken at the\nonset of a superradiant phase transition to a state with self-ordered density\nand spin structures. We predominately find an antiferromagnetic lattice order\nat the cavity wavelength. The self-ordered states exhibit unexpected positive\nmomentum pair correlations between fermions with opposite spin. These strong\ncavity-mediated correlations vanish at higher pump strength.",
        "positive": "Towards a kinetic theory of a dark soliton gas in one-dimensional\n  superfluids: Soliton hydrodynamics is an appealing tool to describe strong turbulence in\nlow-dimensional systems. Strong turbulence in quasi-one dimensional\nspuerfluids, such as Bose-Einstein condensates, involves the dynamics of dark\nsolitons and, therefore, the description of a statistical ensemble of\ndark-solitons, i.e. soliton gases, is necessary. In this work, we propose a\nphase-space (kinetic) description of dark-soliton gases, introducing a kinetic\nequation that is formally similar to the Vlasov equation in plasma physics. We\nshow that the proposed kinetic theory can capture the dynamical features of\nsoliton gases and show that it sustains an acoustic mode, a fact that we\ncorroborate with the help of direct numerical simulations. Our findings\nmotivate the investigation of the microscopic structure of out-of-equilibrium\nand turbulent regimes in low-dimensional superfluids."
    },
    {
        "anchor": "Roton Instabilities and Wigner Crystallization of Rotating Dipolar\n  Fermions in the Fractional Quantum Hall Regime: We point out the possibility of occurring instabilities in Laughlin liquids\nof rotating dipolar fermions with zero thickness. Previously such a system was\npredicted to be the Laughlin liquid for filling factors being greater and equal\nto 1/7. However, from intra-Landau-level excitations of the liquid in the\nsingle-mode approximation, the roton minima become negative and Laughlin\nliquids are unstable for filling factors being less and equal to 1/7. We then\nconclude that there are correlated Wigner crystals for filling factors being\nless and equal to 1/7.",
        "positive": "Two-band superfluidity and intrinsic Josephson effect in alkaline-earth\n  Fermi gases across an orbital Feshbach resonance: We first show that the many-body Hamiltonian governing the physical\nproperties of an alkaline-earth Yb-173 Fermi gas across the recently-realized\norbital Feshbach resonance is exactly analogous to that of two-band s-wave\nsuperconductors with contact interactions: i.e., even though the free-particle\nbands have a tunable energy offset in between and are coupled by a\nJosephson-type attractive inter-band pair scattering, the intra-band\ninteractions have exactly the same strength. We then introduce two intra-band\norder parameters within the BCS mean-field approximation, and investigate the\ncompetition between their in-phase and out-of-phase (i.e., the so-called\n\\pi-phase) solutions in the entire BCS-BEC evolution at zero temperature."
    },
    {
        "anchor": "Polariton-polariton interaction beyond the Born approximation: A toy\n  model study: We theoretically investigate the polariton-polariton interaction in\nmicrocavities beyond the commonly used Born approximation (i.e., mean-field),\nby adopting a toy model with a contact interaction to approximately describe\nthe attraction between electrons and holes in quantum well and by using a\nGaussian pair fluctuation theory beyond mean-field. We obtain a density or\nchemical potential independent polariton-polariton interaction strength even in\ntwo-dimensions, which result from coupling to the photon field. We show that\nquantum fluctuations lead to about a factor of two reduction in the\npolariton-polariton interaction strength within our toy model. Together with\ncorrections to the 1s exciton approximation at very strong light-matter\ncoupling, we find the polariton-polariton interaction strength under typical\nexperimental conditions is overestimated by a factor three in the widely used\ntheories, if our toy model can qualitatively simulate the polariton interaction\nin GaAs quantum wells. We compare our prediction with the most recent\nmeasurement and argue that the beyond-Born-approximation effect to the\npolariton-polariton interaction strength is crucial for a quantitative\nunderstanding of the experimental data by E. Estrecho \\textit{et al.}, Phys.\nRev. B \\textbf{100}, 035306 (2019).",
        "positive": "Non-adiabatic quantum phase transition in a trapped spinor condensate: We study the effect of an external harmonic trapping potential on an outcome\nof the non-adiabatic quantum phase transition from an antiferromagnetic to a\nphase-separated state in a spin-1 atomic condensate. Previously, we\ndemonstrated that the dynamics of an untrapped system exhibits double\nuniversality with two different scaling laws appearing due to conservation of\nmagnetization. We show that in the presence of a trap double universality\npersists. However, the corresponding scaling exponents are strongly modified by\ntransfer of local magnetization across the system. The values of these\nexponents cannot be explained by the effect of causality alone, as in the\nspinless case. We derive the appropriate scaling laws based on a slow\ndiffusive-drift relaxation process in the local density approximation."
    },
    {
        "anchor": "Topological defects of spin-orbit coupled Bose-Einstein condensates in a\n  rotating anharmonic trap: We investigate the topological defects and spin structures of binary\nBose-Einstein condensates (BECs) with Dresselhaus spin-orbit coupling (D-SOC)\nin a rotating anharmonic trap. Our results show that for initially mixed BECs\nwithout SOC the increasing rotation frequency can lead to the structural phase\ntransition of the system. In the presence of isotropic D-SOC, the system\nsustains vortex pair,Anderson--Toulouse coreless vortices, circular vortex\nsheets, and combined vortex structures. In particular, when the rotation\nfrequency is fixed above the radial trapping frequency the strong D-SOC results\nin a peculiar topological structure which is comprised of multi-layer visible\nvortex necklaces, hidden vortex necklaces and a hidden giant vortex. In\naddition, the system exhibits rich spin textures including basic skyrmion,\nmeron cluster, skyrmion string and various skyrmion lattices. The skyrmions\nwill be destroyed in the limit of large D-SOC or rotation frequency.\nFurthermore, the effects of anisotropic D-SOC and Rashba-Dresselhaus SOC on the\ntopological structures of the system are discussed.",
        "positive": "Borromean droplet in three-component ultracold Bose gases: Borromean ring refers to a peculiar structure where three rings are linked\ntogether while any two of them are unlinked. Here we propose the realization of\nits quantum mechanical analog in a many-body system of three-component\nultracold bosons. Namely, we identify the {\\it Borromean droplet}, where only\nthe ternary bosons can form a self-bound droplet while any binary subsystems\ncannot. Its formation is facilitated by an additional attractive force induced\nby the density fluctuation of a third component, which enlarges the mean-field\ncollapse region in comparison to the binary case and renders the formation of\nBorromean droplet after incorporating the repulsive force from quantum\nfluctuations. Outside the Borromean regime, the competition between ternary and\nbinary droplets leads to an interesting phenomenon of droplet phase separation,\nmanifested by double plateaus in the density profile. We further show that the\ntransition between different droplets and gas phase can be conveniently tuned\nby boson numbers and interaction strengths. The study reveals the possibility\nof Borromean binding in the many-body world and sheds light on more intriguing\nmany-body bound state formed in multi-component systems."
    },
    {
        "anchor": "Numerical Realization of Bethe Rapidities in cold quenched systems by\n  Feynman-Kac path integral method: We apply Quantum Monte Carlo technique to analyze the non equlibrium state of\na trapped 1d Bose gas just after the quenching of the confining potential. As a\nmatter of fact we solve the time dependent Schroedinger equation for the system\nof one-dimensional bosons interacting via delta potential in an infinite square\nwell (namely Lieb-Liniger model) using Feynman-Kac path integral Monte Carlo\ntechnique. These 1d systems are extremely interesting and worth investigating\nin the context of non-equilibrium dynamics of interacting many body systems.\nEven though the systems can be realized experimentally and are exactly solvable\nby Bethe Ansatz, the diffusion Monte Carlo is proven to be more efficient in\nmost circumstances than other mean value techniques as the numerical method can\nincorporate the finite interaction very easily. Using N particle ground state\nwavefunction for one-dimensional hard core bosons in a harmonic trap, we\ndevelop an algorithm to calculate density. We also observe the change in the\ndensity distribution by changing the length of the hard wall box. After an\nincrease in the box length, we still get a self-similar density distribution.",
        "positive": "Dynamics of Ultracold Bosons in Artificial Gauge Fields: Angular\n  Momentum, Fragmentation, and the Variance of Entropy: We consider the dynamics of two-dimensional interacting ultracold bosons\ntriggered by suddenly switching on an artificial gauge field. The system is\ninitialized in the ground state of a harmonic trapping potential. As a function\nof the strength of the applied artificial gauge, we analyze the emergent\ndynamics by monitoring the angular momentum, the fragmentation as well the\nentropy and variance of the entropy of absorption or single-shot images. We\nsolve the underlying time-dependent many-boson Schr\\\"odinger equation using the\nmulticonfigurational time-dependent Hartree method for indistinguishable\nparticles (MCTDH-X). We find that the artificial gauge field implants angular\nmomentum in the system. Fragmentation -- multiple macroscopic eigenvalues of\nthe reduced one-body density matrix -- emerges in sync with the dynamics of\nangular momentum: the bosons in the many-body state develop non-trivial\ncorrelations. Fragmentation and angular momentum are experimentally difficult\nto assess; here, we demonstrate that they can be probed by statistically\nanalyzing the variance of the image entropy of single-shot images that are the\nstandard projective measurement of the state of ultracold atomic systems."
    },
    {
        "anchor": "Spin and density self-ordering in dynamic polarization gradients fields: We study the zero-temperature quantum phase diagram for a two-component\nBose-Einstein condensate in an optical cavity. The two atomic spin states are\nRaman coupled by two transverse orthogonally-polarized, blue detuned plane-wave\nlasers inducing a repulsive cavity potential. For weak pump the lasers favor a\nstate with homogeneous density and predefined uniform spin direction. When one\npump laser is polarized parallel to the cavity mode polarization, the photons\ncoherently scattered into the resonator induce a polarization gradient along\nthe cavity axis, which mediates long-range density-density, spin-density, and\nspin-spin interactions. We show that the coupled atom-cavity system implements\ncentral aspects of the $t$-$J$-$V$-$W$ model with a rich phase diagram. At the\nmean-field limit we identify at least four qualitatively distinct density- and\nspin-ordered phases including ferro- and anti-ferromagnetic order along the\ncavity axis, which can be controlled via the pump strength and detuning. A real\ntime observation of amplitude and phase of the emitted fields bears strong\nsignatures of the realized phase and allows for real-time determination of\nphase transition lines. Together with measurements of the population imbalance\nmost properties of the phase diagram can be reconstructed.",
        "positive": "Long Josephson junctions with exciton-polariton condensates: We demonstrate the possibility to build stable Josephson $\\pi$-junction\nstripes with exciton-polariton condensates. The stability of the $\\pi$-junction\nbetween arbitrary long polariton stripes is achieved at low pumping by\nbalancing the snaking instability with counter-propagating flows towards the\njunction. Not dissimilar from a dark soliton, the instability becomes relevant\nat high pumping leading to formation of vortex dipoles. The resulting\nstructures can be stabilised to produce static lattices of Josephson vortices\nin straight and ring geometries. Our results build towards realization of\nquantum technological applications based on the Josephson effect at room\ntemperature."
    },
    {
        "anchor": "Topological superfluid in a Fermi-Bose mixture with a high critical\n  temperature: We show that a two-dimensional (2D) spin-polarised Fermi gas immersed in a 3D\nBose-Einstein condensate (BEC) constitutes a very promising system to realise a\n$p_x+ip_y$ superfluid. The fermions attract each other via an induced\ninteraction mediated by the bosons, and the resulting pairing is analysed with\nretardation effects fully taken into account. This is further combined with\nBerezinskii-Kosterlitz-Thouless (BKT) theory to obtain reliable results for the\nsuperfluid critical temperature. We show that both the strength and the range\nof the induced interaction can be tuned experimentally, which can be used to\nmake the critical temperature approach the maximum value allowed by general BKT\ntheory. Moreover, this is achieved while keeping the Fermi-Bose interaction\nweak so that three-body losses are small. Our results show that realising a\ntopological superfluid with atomic Fermi-Bose mixtures is within experimental\nreach.",
        "positive": "Trapped fermions in a synthetic non-Abelian gauge field: On increasing the coupling strength ($\\lambda$) of a non-Abelian gauge field\nthat induces a generalized Rashba spin-orbit interaction, the topology of the\nFermi surface of a homogeneous gas of noninteracting fermions of density $\\rho\n\\sim \\kf^3$ undergoes a change at a critical value, $\\lambda_T \\approx \\kf$\n[Phys. Rev. B {\\bf 84}, 014512 (2011)]. In this paper we analyze how this\nphenomenon affects the size and shape of a cloud of spin-$\\half$ fermions\ntrapped in a harmonic potential such as those used in cold atom experiments. We\ndevelop an adiabatic formulation, including the concomitant Pancharatnam-Berry\nphase effects, for the one particle states in the presence of a trapping\npotential and the gauge field, obtaining approximate analytical formulae for\nthe energy levels for some high symmetry gauge field configurations of\ninterest. An analysis based on the local density approximation reveals that,\nfor a given number of particles, the cloud shrinks in a {\\em characteristic\nfashion with increasing $\\lambda$}. For an isotropic harmonic trap, the local\ndensity approximation predicts a spherical cloud for all gauge field\nconfigurations, which are anisotropic in general. We show, via a calculation of\nthe cloud shape using exact eigenstates, that for certain gauge field\nconfigurations there is systematic and observable anisotropy in the cloud shape\nthat increases with increasing gauge coupling $\\lambda$. These results should\nbe useful in the design of cold atom experiments with fermions in non-Abelian\ngauge fields. An important spin-off of our adiabatic formulation is that it\nreveals exciting possibilities for the cold-atom realization of interesting\ncondensed matter Hamiltonians (eg. quantum hall spherical geometry) by using a\nnon-Abelian gauge field in conjunction with another potential."
    },
    {
        "anchor": "Extended Bose-Hubbard model with pair hopping on the triangular lattice: We study systematically an extended Bose-Hubbard model on the triangular\nlattice by means of a meanfield method based on the Gutzwiller ansatz. Pair\nhopping terms are explicitly included and a three-body constraint is applied.\nThe ground-state phase diagram and a variety of quantum phase transitions are\ninvestigated in great detail. In particular, we show the existence and\nstability of the pair supersolid phase.",
        "positive": "Loop current states and their stability in small fractal lattices of\n  Bose-Einstein condensates: We consider a model of interacting Bose-Einstein condensates on small\nSierpinski gaskets. We study eigenstates which are characterised by cyclic\nsupercurrents per each triangular plaquette (\"loop\" states). For noninteracting\nsystems we find at least three classes of loop eigenmodes: standard; chaotic\nand periodic. Standard modes are those inherited from the basic three-site ring\nof condensates with phase differences locked to $2\\pi/3$. Standard modes become\nunstable in the interacting system but only when interaction exceeds a certain\ncritical value $u_c$. Chaotic modes are characterised by very different\ncircular currents per plaquette, so that the usual symmetry of loop currents is\nbroken. Circular supercurrents associated with chaotic modes become chaotic for\nany finite interaction, signalling the loss of coherence between the\ncondensates. Periodic modes are described by alternating populations and two\ndifferent phase differences. The modes are self-similar and are present in all\ngenerations of Sierpinskii gasket. When interaction is included, circular\ncurrent of such a mode becomes periodic in time with the amplitude growing\nlinearly with interaction. Above a critical interaction the amplitude saturates\nsignalling a transition to a macroscopic self-trapping state originally known\nfrom a usual Bose Josephson junction. We perform a systematic analysis of this\nnovel and rich physics."
    },
    {
        "anchor": "Non-equilibrium dynamics of an unstable quantum pendulum: A pendulum prepared perfectly inverted and motionless is a prototype of\nunstable equilibria and corresponds to an unstable hyperbolic fixed point in\nthe dynamical phase space. Unstable fixed points are central to understanding\nHamiltonian chaos in classical systems. In many-body quantum systems,\nmean-field approximations fail in the vicinity of unstable fixed points and\nlead to dynamics driven by quantum fluctuations. Here, we measure the\nnon-equilibrium dynamics of a many-body quantum pendulum initialized to a\nhyperbolic fixed point of the phase space. The experiment uses a spin-1 Bose\ncondensate, which exhibits Josephson dynamics in the spin populations that\ncorrespond in the mean-field limit to motion of a non-rigid mechanical\npendulum. The condensate is initialized to a minimum uncertainty spin state,\nand quantum fluctuations lead to non-linear spin evolution along a separatrix\nand non-Gaussian probability distributions that are measured to be in good\nagreement with exact quantum calculations up to 0.25 s. At longer times, atomic\nloss due to the finite lifetime of the condensate leads to larger spin\noscillation amplitudes compared to no loss case as orbits depart from the\nseparatrix. This demonstrates how decoherence of a many-body system can result\nin more apparent coherent behaviour. This experiment provides new avenues for\nstudying macroscopic spin systems in the quantum limit and for investigations\nof important topics in non-equilibrium quantum dynamics.",
        "positive": "Phase transitions of the coherently coupled two-component Bose gas in a\n  square optical lattice: We investigate properties of an ultracold, two-component bosonic gas in a\nsquare optical lattice at unit filling. In addition to density-density\ninteractions, the atoms are subject to coherent light-matter interactions that\ncouple different internal states. We examine the influence of this coherent\ncoupling on the system and its quantum phases by using Gutzwiller mean field\ntheory as well as bosonic dynamical mean field theory. We find that the\ninterplay of strong inter-species repulsion and coherent coupling affects the\nMott insulator to superfluid transition and shifts the tip of the Mott lobe\ntoward higher values of the tunneling amplitude. In the strongly interacting\nMott regime, the resulting Bose-Hubbard model can be mapped onto an effective\nspin Hamiltonian that offers additional insights into the observed phenomena."
    },
    {
        "anchor": "Intrinsic Anomalous Hall Effect in a Bosonic Chiral Superfluid: The anomalous Hall effect has had a profound influence on the understanding\nof many electronic topological materials but is much less studied in their\nbosonic counterparts. We predict that an intrinsic anomalous Hall effect exists\nin a recently realized bosonic chiral superfluid, a $p$-band Bose-Einstein\ncondensate in a 2D hexagonal boron nitride optical lattice [X. Wang et al.,\nhttps://www.nature.com/articles/s41586-021-03702-0 Nature (London) 596, 227\n(2021)]. We evaluate the frequency-dependent Hall conductivity within a\nmulti-orbital Bose-Hubbard model that accurately captures the real experimental\nsystem. We find that in the high frequency limit, the Hall conductivity is\ndetermined by finite loop current correlations on the $s$-orbital residing\nsublattice, the latter a defining feature of the system's chirality. In the\nopposite limit, the dc Hall conductivity can trace its origin back to the\nnon-interacting band Berry curvature at the condensation momentum, although the\ncontribution from atomic interactions can be significant. We discuss available\nexperimental probes to observe this intrinsic anomalous Hall effect at both\nzero and finite frequencies.",
        "positive": "Quantum critical thermal transport in the unitary Fermi gas: Strongly correlated systems are often associated with an underlying quantum\ncritical point which governs their behavior in the finite temperature phase\ndiagram. Their thermodynamical and transport properties arise from critical\nfluctuations and follow universal scaling laws. Here, we develop a microscopic\ntheory of thermal transport in the quantum critical regime expressed in terms\nof a thermal sum rule and an effective scattering time. We explicitly compute\nthe characteristic scaling functions in a quantum critical model system, the\nunitary Fermi gas. Moreover, we derive an exact thermal sum rule for heat and\nenergy currents and evaluate it numerically using the nonperturbative\nLuttinger-Ward approach. For the thermal scattering times we find a simple\nquantum critical scaling form. Together, the sum rule and the scattering time\ndetermine the heat conductivity, thermal diffusivity, Prandtl number and sound\ndiffusivity from high temperatures down into the quantum critical regime. The\nresults provide a quantitative description of recent sound attenuation\nmeasurements in ultracold Fermi gases."
    },
    {
        "anchor": "Nonequilibrium relaxation transport of ultracold atoms: We analyze the equilibration process between two either fermionic or bosonic\nreservoirs containing ultracold atoms with a fixed total number of particles\nthat are weakly connected via a few-level quantum system. We allow for both the\ntemperatures and particle densities of the reservoirs to evolve in time.\nSubsequently, linearizing the resulting equations enables us to characterize\nthe equilibration process and its time scales in terms of equilibrium reservoir\nproperties and linear-response transport coefficients. Additionally, we\ninvestigate the use of such a device as particle transistor or particle\ncapacitor and analyze its efficiency.",
        "positive": "A compact experimental machine for studying tunable Bose-Bose superfluid\n  mixtures: We present a compact and versatile experimental system for producing\nBose-Bose superfluid mixtures composed of sodium and potassium atoms. The\ncompact design combines the necessary ultra-high vacuum enviroment for\nultracold atom experiments with efficient atomic fluxes by using\ntwo-dimensional magneto-optical traps as independent source of atoms. We\ndemonstrate the performance of this new machine by producing a Bose-Einstein\ncondensate of $^{23}$Na with $\\sim 1 \\times 10^{6}~$atoms. The tunability of\nNa-K bosonic mixtures is particularly interesting for studies regarding the\nnucleation of vortices and quantum turbulence. In this direction, the large\noptical access of the science chamber along the vertical direction provides the\nconditions to implement high resolution optical setups for imaging and rotating\nthe condensate with a stirring beam. We show the nucleation of a vortex lattice\nwith up to 14 vortices in the $^{23}$Na BEC, attesting the efficiency of the\nexperimental apparatus in studying the dynamics of vortices."
    },
    {
        "anchor": "Fermionic Luttinger liquids from a microscopic perspective: We consider interacting one-dimensional, spinless Fermi gases, whose\nlow-energy properties are described by Luttinger liquid theory. We perform a\nsystematic, in-depth analysis of the relation between the macroscopic,\nphenomenological parameters of Luttinger liquid effective field theory, and the\nmicroscopic interactions of the Fermi gas. In particular, we begin by\nexplaining how to model effective interactions in one dimension, which we then\napply to the main forward scattering channel -- the interbranch collisions --\ncommon to these systems. We renormalise the corresponding interbranch\nphenomenological constants in favour of scattering phase shifts. Interestingly,\nour renormalisation procedure shows (i) how Luttinger's model arises in a\ncompletely natural way -- and not as a convenient approximation -- from\nTomonaga's model, and (ii) the reasons behind the interbranch coupling constant\nremaining unrenormalised in Luttinger's model. We then consider the so-called\nintrabranch processes, whose phenomenological coupling constant is known to be\nfixed by charge conservation, but whose microscopic origin is not well\nunderstood. We show that, contrary to general belief and common sense, the\nintrabranch interactions appearing in Luttinger liquid theory do not correspond\nto an intrabranch scattering channel, nor an energy shift due to intrabranch\ninteractions, in the microscopic theory. Instead, they are due to interbranch\nprocesses. We finally apply our results to a particular example of an exactly\nsolvable model, namely the fermionic dual to the Lieb-Liniger model in the\nTonks-Girardeau and super-Tonks-Girardeau regimes.",
        "positive": "Non-equilibrium effective field theory for absorbing state phase\n  transitions in driven open quantum spin systems: Phase transitions to absorbing states are among the simplest examples of\ncritical phenomena out of equilibrium. The characteristic feature of these\nmodels is the presence of a fluctuationless configuration which the dynamics\ncannot leave, which has proved a rather stringent requirement in experiments.\nRecently, a proposal to seek such transitions in highly tuneable systems of\ncold atomic gases offers to probe this physics and, at the same time, to\ninvestigate the robustness of these transitions to quantum coherent effects.\nHere we specifically focus on the interplay between classical and quantum\nfluctuations in a simple driven open quantum model which, in the classical\nlimit, reproduces a contact process, which is known to undergo a continuous\ntransition in the \"directed percolation\" universality class. We derive an\neffective long-wavelength field theory for the present class of open spin\nsystems and show that, due to quantum fluctuations, the nature of the\ntransition changes from second to first order, passing through a bicritical\npoint which appears to belong instead to the \"tricritical directed percolation\"\nclass."
    },
    {
        "anchor": "Breaking strong symmetries in dissipative quantum systems: Bosonic atoms\n  coupled to a cavity: In dissipative quantum systems, strong symmetries can lead to the existence\nof conservation laws and multiple steady states. In this work we investigate a\nstrong symmetry for bosonic atoms coupled to an optical cavity, an\nexperimentally relevant system, generalizing the adiabatic elimination\ntechniques and using numerically exact matrix product state methods. We show\nthat for ideal bosons coupled to the cavity multiple steady states exist and in\neach symmetry sector a dissipative phase transition occurs at a different\ncritical point. This implies that phases of very different nature can coexist.\nWe find that the introduction of a slight breaking of the strong symmetry by a\nsmall interaction term leads to a direct transition from multiple steady states\nto a unique steady state. We point out the phenomenon of dissipative freezing,\nthe breaking of the conservation law at the level of individual realizations in\nthe presence of the strong symmetry. For a small breaking of the strong\nsymmetry we see that the behavior of the individual trajectories still shows\nsome signs of this dissipative freezing before it fades out for a larger\nsymmetry breaking terms.",
        "positive": "Rabi coupled fermions in the BCS-BEC crossover: We investigate the three-dimensional BCS-BEC crossover in the presence of a\nRabi coupling which strongly affects several properties of the system, such as\nthe chemical potential, the pairing gap and the superfluid density. We\ndetermine the critical interaction strength, below which the system is normal\nalso at zero temperature. Finally, we calculate the effect of the Rabi coupling\non the critical temperature of the superfluid-to-normal phase transition by\nusing different theoretical schemes."
    },
    {
        "anchor": "Impurity Scattering in a Bose-Einstein Condensate at finite temperature: We consider the effects of finite temperature on the scattering of impurity\natoms in a BoseEinstein condensate, showing that the scattering rate is\nenhanced by the thermal atoms. Collisions can increase or decrease the impurity\nenergy. Below the Landau velocity only the first process occurs, i.e., the\ncollisions cool the condensate. Above the critical velocity the dissipative\ncollisions prevail over the cooling ones for sufficiently low temperatures.\nThese considerations are applied to a recent experiment.",
        "positive": "Dynamically Slowed Collapse of a Bose-Einstein Condensate with Negative\n  Scattering Length: We rapidly change the scattering length a_s of a 87Rb Bose-Einstein\ncondensate by means of a Feshbach resonance, simultaneously releasing the\ncondensate from its harmonic trapping potential. When a_s is changed from\npositive to negative, the subsequent collapse of the condensate is stabilized\nby the kinetic energy imparted during the release, resulting in a deceleration\nof the loss rate near the resonance. We also observe an increase in the\nThomas-Fermi radius, near the resonance, that cannot be understood in terms of\na simple scaling model. Instead, we describe this behavior using the\nGross-Pitaevskii equation, including three-body recombination, and hypothesize\nthat the increase in cloud radius is due to the formation of concentric shells."
    },
    {
        "anchor": "Emergent light crystal from frustration and pump engineering: We demonstrate how pump engineering drives the emergence of\nfrustration-induced quasi-long-range order in a low-dimensional photonic cavity\narray. We consider a Lieb chain of nonlinear cavities as described by the\nBose-Hubbard model and featuring a photonic flat band in the single-particle\nspectrum. Incoherent pumping of the Lieb lattice leads to a photonic\ndensity-wave which manifests an algebraic decay of correlations with twice the\nperiod of the lattice unit cell. This work opens up new directions for the\nemergence of strongly-correlated phases in quantum optical frustrated systems\nthrough pump design.",
        "positive": "Radio-frequency driving of an attractive Fermi gas in a one-dimensional\n  optical lattice: We investigate the response to radio-frequency driving of an ultracold gas of\nattractively interacting fermions in a one-dimensional optical lattice. We\nstudy the system dynamics by monitoring the driving-induced population transfer\nto a third state, and the evolution of the momentum density and pair\ndistributions. Depending on the frequency of the radio-frequency field, two\ndifferent dynamical regimes emerge when considering the evolution of the third\nlevel population. One regime exhibits (off)resonant many-body oscillations\nreminiscent of Rabi oscillations in a discrete two-level system, while the\nother displays a strong linear rise. Within this second regime, we connect, via\nlinear response theory, the extracted transfer rate to the system\nsingle-particle spectral function, and infer the nature of the excitations from\nBethe ansatz calculations. In addition, we show that this radio-frequency\ntechnique can be employed to gain insights into this many-body system coupling\nmechanism away from equilibrium. This is done by monitoring the momentum\ndensity redistributions and the evolution of the pair correlations during the\ndrive. Capturing such non-equilibrium physics goes beyond a linear response\ntreatment, and is achieved here by conducting time-dependent matrix product\nstate simulations."
    },
    {
        "anchor": "Collisional Cooling of Ultracold Molecules: Since the original work on Bose-Einstein condensation, quantum degenerate\ngases of atoms have allowed the quantum emulation of important systems from\ncondensed matter and nuclear physics, as well as the study of novel many-body\nstates with no analog in other fields of physics. Ultracold molecules in the\nmicro- and nano-Kelvin regimes promise to bring powerful new capabilities to\nquantum emulation and quantum computing, thanks to their rich internal degrees\nof freedom compared to atoms. They also open new possibilities for precision\nmeasurement and the study of quantum chemistry. Quantum gases of atoms were\nmade possible by collision-based cooling schemes, such as evaporative cooling.\nFor ultracold molecules, thermalization and collisional cooling have not been\nrealized. With other techniques such as supersonic jets and cryogenic buffer\ngases, studies have been limited to temperatures above 10 mK. Here we show\ncooling of NaLi molecules at micro- and nano-Kelvin temperatures through\ncollisions with ultracold Na atoms, both prepared in their stretched hyperfine\nspin states. We find a lower bound on the elastic to inelastic collision ratio\nbetween molecules and atoms greater than 50 -- large enough to support\nsustained collisional cooling. By employing two stages of evaporation, we\nincrease the phase-space density (PSD) of the molecules by a factor of 20,\nachieving temperatures as low as 220 nK. The favorable collisional properties\nof a Na and NaLi mixture show great promise for making deeply quantum\ndegenerate dipolar molecules and suggest the potential for such cooling in\nother systems.",
        "positive": "Characterizing the energy gap and demonstrating an adiabatic quench in\n  an interacting spin system: Spontaneous symmetry breaking occurs in a physical system whenever the ground\nstate does not share the symmetry of the underlying theory, e.g., the\nHamiltonian. It gives rise to massless Nambu-Goldstone modes and massive\nAnderson-Higgs modes. These modes provide a fundamental understanding of matter\nin the Universe and appear as collective phase/amplitude excitations of an\norder parameter in a many-body system. The amplitude excitation plays a crucial\nrole in determining the critical exponents governing universal non-equilibrium\ndynamics in the Kibble-Zurek mechanism (KZM). Here, we characterize the\namplitude excitations in a spin-1 condensate and measure their energy gap for\ndifferent phases of the quantum phase transition. At the quantum critical point\nof the transition, finite size effects lead to a non-zero gap. Our measurements\nare consistent with this prediction, and furthermore, we demonstrate an\nadiabatic quench through the phase transition, which is forbidden at the mean\nfield level. This work paves the way toward generating entanglement through an\nadiabatic phase transition."
    },
    {
        "anchor": "Temporal shaping and time varying orbital angular momentum of displaced\n  vortices: The fundamental mode of rotation in quantum fluids is given by a vortex,\nwhose quantized value yields the orbital angular momentum (OAM) per particle.\nIf the vortex is displaced (off-centered) from the reference point for\nrotation, the angular momentum is reduced and becomes fractional. Such\ndisplaced vortices can further exhibit a peculiar dynamics in presence of\nconfining potentials or couplings to other fields. We study analytically a\nnumber of 2D systems where displaced vortices exhibit a noteworthy dynamics,\nincluding time-varying self-sustained oscillation of the OAM, complex reshaping\nof their morphology with possible creation of vortex-antivortex pairs and\npeculiar trajectories for the vortex core with sequences of strong\naccelerations and decelerations which can even send the core to infinity and\nbring it back. Interestingly, these do not have to occur conjointly, with\ncomplex time dynamics of the vortex core and/or their wavepacket morphology\npossibly taking place without affecting the total OAM. Our results generalize\nto simple and fundamental systems a phenomenology recently reported with\nRabi-coupled bosonic fields, showing their wider relevance and opening\nprospects for new types of control and structuring of the angular momentum of\nlight and/or quantum fluids.",
        "positive": "Universal Landau-Zener regimes in dynamical topological phase\n  transitions: In finite systems driven unitarily across topological phase transitions, the\nChern number and the Bott index have been found to exhibit different behaviors\ndepending on the boundary conditions and on the commensurability of the\nlattice. For periodic boundary conditions, the Chern number does not change for\nfinite commensurate lattices (or in the thermodynamic limit). On the other\nhand, the Chern number can change for incommensurate lattices with periodic\nboundary conditions and the Bott index can change for lattices with open\nboundary conditions. Here we show that the scalings of the fields at which\nthose two indices change exhibit Landau-Zener and near-adiabatic regimes\ndepending on the speed at which the strength of the drive is ramped up and on\nthe system size. Those regimes are preceded by a regime in which the\ntopological indices do not change. The latter is the only regime that, for\nnonvanishing ramp speeds, survives in the thermodynamic limit. We then show\nthat the dc Hall response can be used to detect topological phase transitions\nindependently of the behavior of the topological indices."
    },
    {
        "anchor": "Quantum rotor theory of spinor condensates in tight traps: In this work, we theoretically construct exact mappings of many-particle\nbosonic systems onto quantum rotor models. In particular, we analyze the rotor\nrepresentation of spinor Bose-Einstein condensates. In a previous work it was\nshown that there is an exact mapping of a spin-one condensate of fixed particle\nnumber with quadratic Zeeman interaction onto a quantum rotor model. Since the\nrotor model has an unbounded spectrum from above, it has many more eigenstates\nthan the original bosonic model. Here we show that for each subset of states\nwith fixed spin F_z, the physical rotor eigenstates are always those with\nlowest energy. We classify three distinct physical limits of the rotor model:\nthe Rabi, Josephson, and Fock regimes. The last regime corresponds to a\nfragmented condensate and is thus not captured by the Bogoliubov theory. We\nnext consider the semiclassical limit of the rotor problem and make connections\nwith the quantum wave functions through use of the Husimi distribution\nfunction. Finally, we describe how to extend the analysis to higher-spin\nsystems and derive a rotor model for the spin-two condensate. Theoretical\ndetails of the rotor mapping are also provided here.",
        "positive": "Quantum diffusion with disorder, noise and interaction: Disorder, noise and interaction play a crucial role in the transport\nproperties of real systems, but they are typically hard to control and study\nboth theoretically and experimentally, especially in the quantum case. Here we\nexplore a paradigmatic problem, the diffusion of a wavepacket, by employing\nultra-cold atoms in a disordered lattice with controlled noise and tunable\ninteraction. The presence of disorder leads to Anderson localization, while\nboth interaction and noise tend to suppress localization and restore transport,\nalthough with completely different mechanisms. When only noise or interaction\nare present we observe a diffusion dynamics that can be explained by existing\nmicroscopic models. When noise and interaction are combined, we observe instead\na complex anomalous diffusion. By combining experimental measurements with\nnumerical simulations, we show that such anomalous behavior can be modeled with\na generalized diffusion equation, in which the noise- and interaction-induced\ndiffusions enter in an additive manner. Our study reveals also a more complex\ninterplay between the two diffusion mechanisms in regimes of strong interaction\nor narrowband noise."
    },
    {
        "anchor": "Influence of thermal effects on atomic Bloch oscillation: Advancements in the experimental toolbox of cold atoms have enabled the\nmeticulous control of atomic Bloch oscillation within optical lattices, thereby\nenhancing the capabilities of gravity interferometers. This work delves into\nthe impact of thermal effects on Bloch oscillation in 1D accelerated optical\nlattices aligned with gravity by varying the system's initial temperature.\nThrough the application of Raman cooling, we effectively reduce the\nlongitudinal thermal effect, stabilizing the longitudinal coherence length over\nthe timescale of its lifetime. The atomic losses over multiple Bloch\noscillation is measured, which are primarily attributed to transverse\nexcitation. Furthermore, we identify two distinct inverse scaling behaviors in\nthe oscillation lifetime scaled by the corresponding density with respect to\ntemperatures, implying diverse equilibrium processes within or outside the\nBose-Einstein condensate regime. The competition between the system's coherence\nand atomic density leads to a relatively smooth variation in the actual\nlifetime versus temperature. Our findings provide valuable insights into the\ninteraction between thermal effects and Bloch oscillation, offering avenues for\nthe refinement of quantum measurement technologies.",
        "positive": "Isolated quantum heat engine: We present a theoretical and numerical analysis of a quantum system that is\ncapable of functioning as a heat engine. This system could be realized\nexperimentally using cold bosonic atoms confined to a double well potential\nthat is created by splitting a harmonic trap with a focused laser. The system\nshows thermalization, and can model a reversible heat engine cycle. This is the\nfirst demonstration of the operation of a heat engine with a finite quantum\nheat bath."
    },
    {
        "anchor": "Correcting inconsistencies in the conventional superfluid path integral\n  scheme: In this paper we show how to redress a shortcoming of the path integral\nscheme for fermionic superfluids and superconductors. This approach is built\naround a simultaneous calculation of electrodynamics and thermodynamics. An\nimportant sum rule, the compressibility sum rule, fails to be satisfied in the\nusual calculation of the electromagnetic and thermodynamic response at the\nGaussian fluctuation level. Here we present a path integral scheme to address\nthis inconsistency. Specifically, at the leading order we argue that the\nsuperconducting gap should be calculated using a different saddle point\ncondition modified by the presence of an external vector potential. This leads\nto the well known gauge-invariant BCS electrodynamic response and is associated\nwith the usual (mean field) expression for thermodynamics. In this way the\ncompressibility sum rule is satisfied at the BCS level. Moreover, this scheme\ncan be readily extended to address arbitrary higher order fluctuation theories.\nAt any level this approach will lead to a gauge invariant and compressibility\nsum rule consistent treatment of electrodynamics and thermodynamics.",
        "positive": "Persistent currents in two-component condensates in a toroidal trap: The stability of persistent currents in a two-component Bose-Einstein\ncondensate in a toroidal trap is studied both in the miscible and immiscible\nregimes. In the miscible regime we show that superflow decay is related to\nlinear instabilities of the spin-density Bogoliubov mode. We find a region of\npartial stability, where the flow is stable in the majority component while it\ndecays in the minority component. We also characterize the dynamical\ninstability appearing for a large relative velocity between the two components.\nIn the immiscible regime the stability criterion is modified and depends on the\nspecific density distribution of the two components. The effect of a coherent\ncoupling between the two components is also discussed."
    },
    {
        "anchor": "Dynamic generation of spin-squeezed states in bosonic Josephson\n  junctions: We analyze the formation of squeezed states in a condensate of ultracold\nbosonic atoms confined by a double-well potential. The emphasis is set on the\ndynamical formation of such states from initially coherent many-body quantum\nstates. Two cases are described: the squeezing formation in the evolution of\nthe system around the stable point, and in the short time evolution in the\nvicinity of an unstable point. The latter is shown to produce highly squeezed\nstates on very short times. On the basis of a semiclassical approximation to\nthe Bose-Hubbard Hamiltonian, we are able to predict the amount of squeezing,\nits scaling with $N$ and the speed of coherent spin formation with simple\nanalytical formulas which successfully describe the numerical Bose-Hubbard\nresults. This new method of producing highly squeezed spin states in systems of\nultracold atoms is compared to other standard methods in the literature.",
        "positive": "Many-Body Rate Limit on Photoassociation of a Bose-Einstein Condensate: We briefly report on zero-temperature photoassociation of a Bose-Einstein\ncondensate, focusing on the many-body rate limit for atom-molecule conversion.\nAn upgraded model that explicitly includes spontaneous radiative decay leads to\nan unanticipated shift in the position of the photoassociation resonance, which\naffects whether the rate (constant) maximizes or saturates, as well as the\nlimiting value itself. A simple analytical model agrees with numerical\nexperiments, but only for high density. Finally, an explicit comparison with\nthe two-body unitary limit, set by the size of the condensate, finds that the\nmany-body rate limit is generally more strict."
    },
    {
        "anchor": "Antiferromagnetic correlations in two-dimensional fermionic\n  Mott-insulating and metallic phases: Near zero temperature, quantum magnetism can non-trivially arise from\nshort-range interactions, but the occurrence of magnetic order depends\ncrucially on the interplay of interactions, lattice geometry, dimensionality\nand doping. Even though the consequences of this interplay are not yet fully\nunderstood, quantum magnetism is believed to be connected to a range of complex\nphenomena in the solid state, for example, in the context of high-$T_c$\nsuperconductivity and spin liquids in frustrated lattices. Ultracold atomic\nFermi gases in optical lattices constitute an experimental system with\nunrivalled tunability and detection capabilities to explore quantum magnetism\nby analog quantum simulation. In this work, we study the emergence of\nantiferromagnetic correlations between ultracold fermionic atoms in two\ndimensions with decreasing temperature. We determine the magnetic\nsusceptibility of the Hubbard model from simultaneous measurements of the\nin-situ density of both spin components. At half-filling and strong\ninteractions our data approach the Heisenberg model of localized spins with\nantiferromagnetic correlations. Moreover, we observe the disappearance of\nmagnetic correlations when the system is doped away from half-filling. Our\nobservation of the dependence of quantum magnetism on doping paves the way for\nfuture studies on the emergence of pseudogap and pairing phenomena away from\nhalf-filling.",
        "positive": "First and second sound in a highly elongated Fermi gas at unitarity: We consider a Fermi gas at unitarity trapped by a highly elongated harmonic\npotential and solve the equations of two fluid hydrodynamics at finite\ntemperature. The propagation of sound waves as well as the discretized\nsolutions in the presence of weak axial trapping are considered. The relevant\nthermodynamic functions entering the hydrodynamic equations are discussed in\nthe superfluid and normal regimes in terms of universal scaling functions. Both\nfirst sound and second sound solutions are calculated as a function of\ntemperature and the role of the superfluid density is explicitly pointed out.\nThe density fluctuations in the second sound wave are found to be large enough\nto be measured as a consequence of the finite thermal expansion coefficient of\nthe gas. Emphasis is given to the comparison with recent experimental data."
    },
    {
        "anchor": "Superfluid Fraction and Leggett Bound in a Density Modulated Strongly\n  Interacting Fermi Gas at Zero Temperature: We calculate the superfluid fraction of an interacting Fermi gas, in the\npresence of a one-dimensional periodic potential of strength $V_0$ and\nwave-vector $q$. Special focus is given to the unitary Fermi gas, characterized\nby the divergent behavior of the s-wave scattering length. Comparison with the\nLeggett's upper bound $(\\langle n_{1D}\\rangle <1/n_{1D}>)^{-1}$, with $n_{1D}$\nthe 1D column density, explicitly shows that, differently from the case of a\ndilute interacting Bose gas, the bound significantly overestimates the value of\nthe superfluid fraction, except in the phonon regime of small $q$. Sum rule\narguments show that the combined knowledge of the Leggett bound and of the\nactual value of the superfluid fraction allows for the determination of\ncurvature effects providing the deviation of the dispersion of the\nAnderson-Bogoliubov mode from the linear phonon dependence. The comparison with\nthe predictions of the weakly interacting BCS Fermi gas points out the crucial\nrole of two-body interactions. The implications of our predictions on the\nanisotropic behavior of the sound velocity are also discussed.",
        "positive": "Path Integral Molecular Dynamics for Bosons: Trapped Bosons exhibit fundamental physical phenomena and are potentially\nuseful for quantum technologies. We present a method for simulating Bosons\nusing path integral molecular dynamics. A main challenge for simulations is\nincluding all permutations due to exchange symmetry. We show that evaluation of\nthe potential can be done recursively, avoiding explicit enumeration of\npermutations, and scales cubically with system size. The method is applied to\nBosons in a 2D trap and agrees with essentially exact results. An analysis of\nthe role of exchange with decreasing temperature is also presented."
    },
    {
        "anchor": "Reactions Between Layer-Resolved Molecules Mediated by Dipolar Exchange: Microscopic control over polar molecules with tunable interactions would\nenable realization of novel quantum phenomena. Using an applied electric field\ngradient, we demonstrate layer-resolved state preparation and imaging of\nultracold potassium-rubidium molecules confined to two-dimensional planes in an\noptical lattice. The coherence time of rotational superpositions in individual\nlayers is maximized by rotating the electric field relative to the optical trap\npolarization to achieve state-insensitive trapping. Molecules in adjacent\nlayers interact via dipolar exchange of rotational angular momentum; by\nadjusting the interaction strength between spatially separated ensembles of\nmolecules, we regulate the local chemical reaction rate. The observed resonance\nwidth of the exchange process vastly exceeds the dipolar interaction energy, an\neffect we attribute to the thermal energy. This work realizes precise control\nof interacting molecules, enabling electric field microscopy on subwavelength\nlength scales and allowing access to unexplored physics in two-dimensional\nsystems.",
        "positive": "Incompressible states of a two-component Fermi gas in a double-well\n  optical lattice: We propose a scheme to investigate the effect of frustration on the magnetic\nphase transitions of cold atoms confined in an optical lattice. We also\ndemonstrate how to get two-leg spin ladders with frustrated spin-exchange\ncoupling which display a phase transition from a spin liquid to a fully\nincompressible state. Various experimental quantities are further analyzed for\ndescribing this phase."
    },
    {
        "anchor": "Interference induced anisotropy in a two-dimensional dark state optical\n  lattice: We describe a two-dimensional optical lattice for ultracold atoms with\nspatial features below the diffraction limit created by a bichromatic optical\nstanding wave. At every point in space these fields couple the internal atomic\nstates in a three-level Lambda coupling configuration. Adiabatically following\nthe local wavefunction of the resulting dark state yields a spatially uniform\nBorn-Oppenheimer potential augmented by geometric scalar and vector potentials\nappearing due to spatially rapid changes of the wavefunction. Depending on\nsystem parameters, we find that the geometric scalar potential can interpolate\nfrom a 2D analogue of the Kronig-Penney lattice, to an array of tubes with a\nzig-zag shaped barrier. The geometric vector potential induces a spatially\nperiodic effective magnetic field (the Berry's curvature) that can be tuned to\ncause destructive interference between neighboring tubes, thereby decoupling\nthem at a critical point in parameter space. We numerically investigate the\nenergy spectrum including decay from the excited state, and find that the\nadiabatic approximation is sound for strong coupling strengths, leading to\nnegligible loss in the dark state manifold. Furthermore, the spectrum is\nwell-described by a non-Hermitian tight binding model with on-site losses, and\nhopping characterized by both loss and, surprisingly, gain.",
        "positive": "Atom-Dimer Scattering in a Three-Component Fermi Gas: Ultracold gases of three distinguishable particles with large scattering\nlengths are expected to show rich few-body physics related to the Efimov\neffect. We have created three different mixtures of ultracold 6Li atoms and\nweakly bound 6Li2 dimers consisting of atoms in three different hyperfine\nstates and studied their inelastic decay via atom-dimer collisions. We have\nfound resonant enhancement of the decay due to the crossing of Efimov-like\ntrimer states with the atom-dimer continuum in one mixture as well as minima of\nthe decay in another mixture, which we interpret as a suppression of exchange\nreactions of the type |12>+|3> -> |23>+|1>. Such a suppression is caused by\ninterference between different decay paths and demonstrates the possiblity to\nuse Efimov physics to control the rate constants for molecular exchange\nreactions in the ultracold regime."
    },
    {
        "anchor": "Theory of unitary Bose gases: We develop an analytical approach for the description of an atomic Bose gas\nat unitarity. By focusing in first instance on the evaluation of the\nsingle-particle density matrix, we derive several universal properties of the\nunitary Bose gas, such as the chemical potential, the contact, the speed of\nsound, the condensate density and the effective interatomic interaction. The\ntheory is also generalized to describe Bose gases with a finite scattering\nlength and then reduces to the Bogoliubov theory in the weak-coupling limit.",
        "positive": "Observation of many-body localization in a one-dimensional system with\n  single-particle mobility edge: We experimentally study many-body localization (MBL) with ultracold atoms in\na weak one-dimensional quasiperiodic potential, which in the noninteracting\nlimit exhibits an intermediate phase that is characterized by a mobility edge.\nWe measure the time evolution of an initial charge density wave after a quench\nand analyze the corresponding relaxation exponents. We find clear signatures of\nMBL, when the corresponding noninteracting model is deep in the localized\nphase. We also critically compare and contrast our results with those from a\ntight-binding Aubry-Andr\\'{e} model, which does not exhibit a single-particle\nintermediate phase, in order to identify signatures of a potential many-body\nintermediate phase."
    },
    {
        "anchor": "Local condensate depletion at trap center under strong interactions: Cold trapped Bose-condensed atoms, interacting via hard-sphere repulsive\npotentials are considered. Simple mean-field approximations show that the\ncondensate distribution inside a harmonic trap always has the shape of a hump\nwith the maximum condensate density occurring at the trap center. However Monte\nCarlo simulations at high density and strong interactions display the\ncondensate depletion at the trap center. The explanation of this effect of\nlocal condensate depletion at trap center is suggested in the frame of\nself-consistent theory of Bose-condensed systems. The depletion is shown to be\ndue to the existence of the anomalous average that takes into account pair\ncorrelations and appears in systems with broken gauge symmetry.",
        "positive": "Fate of Topology in Spin-1 Spinor Bose-Einstein Condensate: One of the excitements generated by the cold atom systems is the possibility\nto realize, and explore, varied topological phases stemming from\nmulti-component nature of the condensate. Popular examples are the\nantiferromagnetic (AFM) and the ferromagnetic (FM) phases in the\nthree-component atomic condensate with effective spin-1, to which different\ntopological manifolds can be assigned. It follows, from consideration of\nhomotopy, that different sorts of topological defects will be stable in each\nmanifold. For instance, Skyrmionic texture is believed to be a stable\ntopological object in two-dimensional AFM spin-1 condensate. Countering such\ncommon perceptions, here we show on the basis of a new wave function\ndecomposition scheme that there is no physical parameter regime wherein the\ntemporal dynamics of spin-1 condensate can be described solely within AFM or FM\nmanifold. Initial state of definite topological number prepared entirely within\none particular phase must immediately evolve into a mixed state. Accordingly,\nthe very notion of topology and topological stability within the sub-manifold\nof AFM or FM become invalid. Numerical simulation reveals the linear Zeeman\neffect to be an efficient catalyst to extract the alternate component from an\ninitial topological object prepared entirely within one particular\nsub-manifold, serving as a potential new tool for \"topology engineering\" in\nmulti-component Bose-Einstein condensates."
    },
    {
        "anchor": "Dynamical phase transitions, temporal orthogonality and the dynamics of\n  observables in one dimensional ultra-cold quantum gases: from the continuum\n  to the lattice: We investigate the dynamics of the rate function and of local observables\nafter a quench in models which exhibit phase transitions between a superfluid\nand an insulator in their ground states. Zeros of the return probability,\ncorresponding to singularities of the rate functions, have been suggested to\nindicate the emergence of dynamical criticality and we address the question of\nwhether such zeros can be tied to the dynamics of physically relevant\nobservables and hence order parameters in the systems. For this we first\nnumerically analyze the dynamics of a hard-core boson gas in a one-dimensional\nwaveguide when a quenched lattice potential is commensurate with the particle\ndensity. Such a system can undergo a pinning transition to an insulating state\nand we find non-analytic behavior in the evolution of the rate function which\nis indicative of dynamical phase transitions. In addition, we perform\nsimulations of the time dependence of the momentum distribution and compare the\nperiodicity of this collapse and revival cycle to that of the non-analyticities\nin the rate function: the two are found to be closely related only for deep\nquenches. We then confirm this observation by analytic calculations on a\nclosely related discrete model of hard-core bosons in the presence of a\nstaggered potential and find expressions for the rate function for the\nquenches. By extraction of the zeros of the Loschmidt amplitude we uncover a\nnon-equilibrium timescale for the emergence of non-analyticities and discuss\nits relationship with the dynamics of the experimentally relevant parity\noperator.",
        "positive": "Information theoretic measures on quantum droplets in ultracold atomic\n  systems: We consider Shannon entropy, Fisher information, R\\'enyi entropy, and Tsallis\nentropy to study the transition from localized phase to droplet phase in\nBose-Einstein condensates. Based on an effective Gross-Pitaevskii equation with\nLee-Huang-Yang correction, we calculate density distributions both in localized\nand the droplet phases and show that the entropy measures can efficiently\ndetect the transition from localized to droplet phase. We find that the Shannon\nentropies in coordinate space increase both in localized and droplet phases.\nThe increase of entropy in droplet phase is abrupt while it is gradual in\nlocalized phase. We observe an opposite trend in the case of Fisher\ninformation. These results are found to be consistent with the R\\'enyi and\nTsallis entropic measures."
    },
    {
        "anchor": "The dressed molecules theory for the quasi-two-dimensional quantum\n  anomaly: In this work, the dressed molecules theory is used to describe the\ntwo-dimensional quantum anomaly of breathing mode in the recent experimental\nsystem\\cite{Holten2018,Peppler2018}. With the aid of a beyond mean-field,\nGaussian pair fluctuation theory, we employ the dressed molecules states to\ncharacterize the axial excited states and the Feshbach molecular states, and\npropose a complete low energy effective theory. We show that, in the whole\ncrossover from a Bardeen-Cooper-Schrieffer (BCS) superfluid to a Bose-Einstein\ncondensate (BEC), our theory can describe the two-dimensional experimental\nsystems precisely in low energe region. We explain the the puzzling\nexperimental observations of the smaller than expected breathing mode frequency\nperfectly. Our establishment of the dressed molecules theory for 2D fermions is\ncrucial to understand the conformal anomaly in the quasi low-dimensional\nquantum systems.",
        "positive": "Critical velocity of a mobile impurity in one-dimensional quantum\n  liquids: We study the notion of superfluid critical velocity in one spatial dimension.\nIt is shown that for heavy impurities with mass $M$ exceeding a critical mass\n$M_\\mathrm{c}$, the dispersion develops periodic metastable branches resulting\nin dramatic changes of dynamics in the presence of an external driving force.\nIn contrast to smooth Bloch Oscillations for $M<M_\\mathrm{c}$, a heavy impurity\nclimbs metastable branches until it reaches a branch termination point or\nundergoes a random tunneling event, both leading to an abrupt change in\nvelocity and an energy loss. This is predicted to lead to a non-analytic\ndependence of the impurity drift velocity on small forces."
    },
    {
        "anchor": "Correlated Spin-Flip Tunneling in a Fermi Lattice Gas: We report the realization of correlated, density-dependent tunneling for\nfermionic 40K atoms trapped in an optical lattice. By appropriately tuning the\nfrequency difference between a pair of Raman beams applied to a spin-polarized\ngas, simultaneous spin transitions and tunneling events are induced that depend\non the relative occupations of neighboring lattice sites. Correlated spin-flip\ntunneling is spectroscopically resolved using gases prepared in opposite spin\nstates, and the inferred Hubbard interaction energy is compared with a\ntight-binding prediction. We show that the laser-induced correlated tunneling\nprocess generates doublons via loss induced by light-assisted collisions.\nFurthermore, by controllably introducing vacancies to a spin-polarized gas, we\ndemonstrate that correlated tunneling is suppressed when neighboring lattice\nsites are unoccupied.",
        "positive": "Striped Ultradilute Liquid of Dipolar Bosons in Two Dimensions: We investigate the phases of a Bose-Einstein condensate of dipolar atoms\nrestricted to move in a two-dimensional plane. The dipole moments are all\naligned in a direction tilted with respect to the plane normal. As a result of\nthe attractive and repulsive components of the dipole-dipole interaction, the\ndipolar gas has a self-bound phase, which is stabilized by quantum\nfluctuations. Furthermore, tilting the dipoles tunes the anisotropy of the\ndipole-dipole interaction, which can trigger a spatial density modulation. In\nthis work we study these two aspects and investigate the conditions for the\nformation of a self-bound and striped phase, which has been realized in\nexperiments with dipolar droplets. We use a variational method based on the\nhypernetted-chain Euler-Lagrange optimization of a Jastrow-Feenberg ansatz for\nthe many-body wave function to study the ground state properties. This method\ntakes into account quantum fluctuations in a non-perturbative way and thus can\nbe used also for strongly correlated systems."
    },
    {
        "anchor": "Effect of one-, two-, and three-body atom loss processes on\n  superpositions of phase states in Bose-Josephson junctions: In a two-mode Bose-Josephson junction formed by a binary mixture of ultracold\natoms, macroscopic superpositions of phase states are produced during the time\nevolution after a sudden quench to zero of the coupling amplitude. Using\nquantum trajectories and an exact diagonalization of the master equation, we\nstudy the effect of one-, two-, and three-body atom losses on the\nsuperpositions by analyzing separately the amount of quantum correlations in\neach subspace with fixed atom number. The quantum correlations useful for atom\ninterferometry are estimated using the quantum Fisher information. We identify\nthe choice of parameters leading to the largest Fisher information, thereby\nshowing that, for all kinds of loss processes, quantum correlations can be\npartially protected from decoherence when the losses are strongly asymmetric in\nthe two modes.",
        "positive": "Generating an effective magnetic lattice for cold atoms: We present a general scheme for synthesizing a spatially periodic magnetic\nfield, or a magnetic lattice (ML), for ultracold atoms using pulsed gradient\nmagnetic fields. Both the period and the depth of the artificial ML can be\ntuned, immune to atomic spontaneous emission often encountered in optical\nlattices. The effective Hamiltonian for our 2-dimensional ML has not been\ndiscussed previously in condensed matter physics. Its band structures show\ninteresting features which can support topologically nontrivial phases. The\ntechnical requirements for implementing our protocol are readily available in\ntoday's cold atom experiments. Realization of our proposal will significantly\nexpand the repertoire for quantum simulation with ultracold atoms."
    },
    {
        "anchor": "Structured Weyl Points in Spin-Orbit Coupled Fermionic Superfluids: We demonstrate that a Weyl point, widely examined in 3D Weyl semimetals and\nsuperfluids, can develop a pair of non-degenerate gapless spheres. Such a\nbouquet of two spheres is characterized by three distinct topological\ninvariants of manifolds with full energy gaps, i.e., the Chern number of a 0D\npoint inside one developed sphere, the winding number of a 1D loop around the\noriginal Weyl point, and the Chern number of a 2D surface enclosing the whole\nbouquet. We show that such structured Weyl points can be realized in the\nsuperfluid quasiparticle spectrum of a 3D degenerate Fermi gas subject to\nspin-orbit couplings and Zeeman fields, which supports Fulde-Ferrell\nsuperfluids as the ground state.",
        "positive": "Multiple dark-bright solitons in atomic Bose-Einstein condensates: We present experimental results and a systematic theoretical analysis of\ndark-br ight soliton interactions and multiple-dark-bright soliton complexes in\natomic t wo-component Bose-Einstein condensates. We study analytically the\ninteractions b etween two-dark-bright solitons in a homogeneous condensate and,\nthen, extend ou r considerations to the presence of the trap. An effective\nequation of motion is derived for the dark-bright soliton center and the\nexistence and stability of stationary two-dark-bright soliton states is\nillustrated (with the bright components being either in- or out-of-phase). The\nequation of motion provides the characteristic oscillation frequencies of the\nsolitons, in good agreement with the eigenfrequencies of the anomalous modes of\nthe system."
    },
    {
        "anchor": "Quantum anomalous Hall states in the $p$-orbital honeycomb optical\n  lattices: We study the quantum anomalous Hall states in the $p$-orbital bands of the\nhoneycomb optical lattices loaded with the single component fermions. Such an\neffect has not been realized in both condensed matter and cold atom systems\nyet. By applying the available experimental technique developed by Gemelke\n\\textit{et al.} to rotate each lattice site around its own center, the band\nstructures become topologically non-trivial. At a certain rotation angular\nvelocity $\\Omega$, a flat band structure appears with localized eigenstates\ncarrying chiral current moments. With imposing the soft confining potential,\nthe density profile exhibits a wedding-cake shaped distribution with insulating\nplateaus at commensurate fillings. Moreover, the inhomogeneous confining\npotential induces dissipationless circulation currents whose magnitudes and\nchiralities vary with the distance from the trap center. In the insulating\nregions the Hall conductances are quantized, and in the metallic regions the\ndirections and magnitudes of chiral currents cannot be described by the usual\nlocal-density-approximation. The quantum anomalous Hall effects are robust at\ntemperature scales small compared to band gaps, which increases the feasibility\nof experimental realizations.",
        "positive": "Observation of Attractive and Repulsive Polarons in a Bose-Einstein\n  Condensate: The problem of an impurity particle moving through a bosonic medium plays a\nfundamental role in physics. However, the canonical scenario of a mobile\nimpurity immersed in a Bose-Einstein condensate (BEC) has not yet been\nrealized. Here, we use radio frequency spectroscopy of ultracold bosonic\n$^{39}$K atoms to experimentally demonstrate the existence of a well-defined\nquasiparticle state of an impurity interacting with a BEC. We measure the\nenergy of the impurity both for attractive and repulsive interactions, and find\nexcellent agreement with theories that incorporate three-body correlations,\nboth in the weak-coupling limits and across unitarity. The spectral response\nconsists of a well-defined quasiparticle peak at weak coupling, while for\nincreasing interaction strength, the spectrum is strongly broadened and becomes\ndominated by the many-body continuum of excited states. Crucially, no\nsignificant effects of three-body decay are observed. Our results open up\nexciting prospects for studying mobile impurities in a bosonic environment and\nstrongly interacting Bose systems in general."
    },
    {
        "anchor": "Matter-wave diffraction from a quasicrystalline optical lattice: Quasicrystals are long-range ordered and yet non-periodic. This interplay\nresults in a wealth of intriguing physical phenomena, such as the inheritance\nof topological properties from higher dimensions, and the presence of\nnon-trivial structure on all scales. Here we report on the first experimental\ndemonstration of an eightfold rotationally symmetric optical lattice, realising\na two-dimensional quasicrystalline potential for ultracold atoms. Using\nmatter-wave diffraction we observe the self-similarity of this quasicrystalline\nstructure, in close analogy to the very first discovery of quasicrystals using\nelectron diffraction. The diffraction dynamics on short timescales constitutes\na continuous-time quantum walk on a homogeneous four-dimensional tight-binding\nlattice. These measurements pave the way for quantum simulations in fractal\nstructures and higher dimensions.",
        "positive": "Curved vortex surfaces in four-dimensional superfluids: II.\n  Equal-frequency double rotations: As is well-known, two-dimensional and three-dimensional superfluids under\nrotation can support topological excitations such as quantized point vortices\nand line vortices respectively. Recently, we have studied how, in a\nhypothetical four-dimensional (4D) superfluid, such excitations can be\ngeneralised to vortex planes and surfaces. In this paper, we continue our\nanalysis of skewed and curved vortex surfaces based on the 4D Gross-Pitaevskii\nequation, and show that certain types of such states can be stabilised by\nequal-frequency double rotations for suitable parameters. This work extends the\nrich phenomenology of vortex surfaces in 4D, and raises interesting questions\nabout vortex reconnections and the competition between various vortex\nstructures which have no direct analogue in lower dimensions."
    },
    {
        "anchor": "Correlation properties of a one-dimensional repulsive Bose gas at finite\n  temperature: We present a comprehensive study shedding light on how thermal fluctuations\naffect correlations in a Bose gas with contact repulsive interactions in one\nspatial dimension. The pair correlation function, the static structure factor,\nand the one-body density matrix are calculated as a function of the interaction\nstrength and temperature with the exact ab-initio Path Integral Monte Carlo\nmethod. We explore all possible gas regimes from weak to strong interactions\nand from low to high temperatures. We provide a detailed comparison with a\nnumber of theories, such as perturbative (Bogoliubov and decoherent classical),\neffective (Luttinger liquid) and exact (ground-state and thermal Bethe Ansatz)\nones. Our Monte Carlo results exhibit an excellent agreement with the tractable\nlimits and provide a fundamental benchmark for future observations which can be\nachieved in atomic gases, cavity quantum-electrodynamic and\nsuperconducting-circuit platforms.",
        "positive": "Few-Body Bound Complexes in One-dimensional Dipolar Gases and\n  Non-Destructive Optical Detection: We consider dipolar interactions between heteronuclear molecules in\nlow-dimensional geometries. The setup consists of two one-dimensional tubes. We\nstudy the stability of possible few-body complexes in the regime of repulsive\nintratube interaction, where the binding arises from intertube attraction. The\nstable dimers, trimers, and tetramers are found and we discuss their properties\nfor both bosonic and fermionic molecules. To observe these complexes we propose\nan optical non-destructive detection scheme that enables in-situ observation of\nthe creation and dissociation of the few-body complexes. A detailed description\nof the expected signal of such measurements is given using the numerically\ncalculated wave functions of the bound states. We also discuss implications on\nthe many-body physics of dipolar systems in tubular geometries, as well as\nexperimental issues related to the external harmonic confinement along the tube\nand the prospect of applying an in-tube optical lattice to increase the\neffective dipole strength."
    },
    {
        "anchor": "Analytical framework for non-equilibrium phase transition to\n  Bose--Einstein condensate: The theoretical description of non-equilibrium Bose--Einstein condensate\n(BEC) is one of the main challenges in modern statistical physics and kinetics.\nThe non-equilibrium nature of BEC makes it impossible to employ the\nwell-established formalism of statistical mechanics. We develop a framework for\nthe analytical description of a non-equilibrium phase transition to BEC that,\nin contrast to previously developed approaches, takes into account the infinite\nnumber of continuously distributed states. We consider the limit of fast\nthermalization and obtain an analytical expression for the full density matrix\nof a non-equilibrium ideal BEC which also covers the equilibrium case. For the\nparticular cases of 2D and 3D, we investigate the non-equilibrium formation of\nBEC by finding the temperature dependence of the ground state occupation and\nsecond-order coherence function. We show that for a given pumping rate, the\nmacroscopic occupation of the ground state and buildup of coherence may occur\nat different temperatures. Moreover, the buildup of coherence strongly depends\non the pumping scheme. We also investigate the condensate linewidth and show\nthat the Schawlow--Townes law holds for BEC in 3D and does not hold for BEC in\n2D.",
        "positive": "Variational approach to the ground state of an impurity in Bose-Einstein\n  condensate: In this paper we consider the effect of self-localization of a quantum\nimpurity in Bose-Einstein condensate. Space correlation function of the\nimpurity is evaluated with the help of the imaginary-time path integral\napproach. Employing the Feynman's variational method we calculate the impurity\ncorrelation function as well as the energy of the system associated with the\nimpurity. The effect of self-localization predicted before within\nGross-Pitaevskii approach is recovered by our treatment. The strong coupling\nregime with negative ground state energy is reached by variational method, and\ncorresponding correlation function is calculated."
    },
    {
        "anchor": "Efficient numerical description of the dynamics of interacting\n  multispecies quantum gases: We present a highly efficient method for the numerical solution of coupled\nGross-Pitaevskii equations describing the evolution dynamics of a multispecies\nmixture of Bose-Einstein condensates in time-dependent potentials. This method,\nbased on a grid-scaling technique, compares favorably to a more standard but\nmuch more computationally expensive solution based on a frozen-resolution grid.\nIt allows an accurate description of the long-time behavior of interacting,\nmulti-species quantum mixtures including the challenging problem of long free\nexpansions relevant for microgravity and space experiments. We demonstrate a\nsuccessful comparison to experimental measurements of a binary Rb-K mixture\nrecently performed with the payload of a sounding rocket experiment.",
        "positive": "Crossover trimers connecting continuous and discrete scaling regimes: For a system of two identical fermions and one distinguishable particle\ninteracting via a short-range potential with a large s-wave scattering length,\nthe Efimov trimers and Kartavtsev-Malykh trimers exist in different regimes of\nthe mass ratio. The Efimov trimers are known to exhibit a discrete scaling\ninvariance, while the Kartavtsev-Malykh trimers feature a continuous scaling\ninvariance. We point out that a third type of trimers, \"crossover trimers\",\nexist universally regardless of short-range details of the potential. These\ncrossover trimers have neither the discrete nor continuous scaling invariance.\nWe show that the crossover trimers continuously connect the discrete and\ncontinuous scaling regimes as the mass ratio and the scattering length are\nvaried. We identify the regions for the Kartavtsev-Malykh trimers, Efimov\ntrimers, crossover trimers, and non-universal trimers as a function of the mass\nratio and the s-wave scattering length by investigating the scaling property\nand model-independence of the trimers."
    },
    {
        "anchor": "Nonuniversal beyond mean field properties of quasi-two-dimensional\n  dipolar Bose gases: We study a quasi-two dimensional gas of bosonic dipoles, calculating the\nbeyond mean field corrections to the ground state energy and chemical potential\nneglecting the transverse mode structure. We show that the corrections are\nsensitive to the high momentum part of the interaction and cannot be expressed\nsolely in terms of the scattering length and the dipole strength. While\nnonuniversal, the correction is found to be negative, which provides an\nadditional attractive term in the extended Gross-Pitaevskii equation, enhancing\nthe roton instability.",
        "positive": "Zonal estimators for quasiperiodic bosonic many-body phases: In this work, we explore the relevant methodology for the investigation of\ninteracting systems with contact interactions, and we introduce a class of\nzonal estimators for path-integral Monte Carlo methods, designed to provide\nphysical information about limited regions of inhomogeneous systems.We\ndemonstrate the usefulness of zonal estimators by their application to a system\nof trapped bosons in a quasiperiodic potential in two dimensions, focusing on\nfinite temperature properties across a wide range of values of the potential.\nFinally, we comment on the generalization of such estimators to local\nfluctuations of the particle numbers and to magnetic ordering in\nmulti-component systems, spin systems, and systems with nonlocal interactions."
    },
    {
        "anchor": "Hysteresis of noninteracting and spin-orbit coupled atomic Fermi gases\n  with relaxation: Hysteresis can be found in driven many-body systems such as magnets and\nsuperfluids. Rate-dependent hysteresis arises when a system is driven\nperiodically while relaxing towards equilibrium. A two-state paramagnet driven\nby an oscillating magnetic field in the relaxation approximation clearly\ndemonstrates rate-dependent hysteresis. A noninteracting atomic Fermi gas in an\noptical ring potential, when driven by a periodic artificial gauge field and\nsubjected to dissipation, is shown to exhibit hysteresis loops of atomic\ncurrent due to a competition of the driving time and the relaxation time. This\nis in contrast to electronic systems exhibiting equilibrium persistent current\ndriven by magnetic flux due to rapid relaxation. Universal behavior of the\ndissipated energy in one hysteresis loop is observed in both the magnetic and\natomic systems, showing linear and inverse-linear dependence on the relaxation\ntime in the strong and weak dissipation regimes. While interactions in general\ninvalidate the framework for rate-dependent hysteresis, an atomic Fermi gas\nwith artificial spin-orbit coupling exhibits hysteresis loops of atomic\ncurrents. Cold-atoms in ring-shape potentials are thus promising in\ndemonstrating rate-dependent hysteresis and its associated phenomena.",
        "positive": "Mathematical theory and numerical methods for Bose-Einstein condensation: In this paper, we mainly review recent results on mathematical theory and\nnumerical methods for Bose-Einstein condensation (BEC), based on the\nGross-Pitaevskii equation (GPE). Starting from the simplest case with\none-component BEC of the weakly interacting bosons, we study the reduction of\nGPE to lower dimensions, the ground states of BEC including the existence and\nuniqueness as well as nonexistence results, and the dynamics of GPE including\ndynamical laws, well-posedness of the Cauchy problem as well as the finite time\nblow-up. To compute the ground state, the gradient flow with discrete\nnormalization (or imaginary time) method is reviewed and various full\ndiscretization methods are presented and compared. To simulate the dynamics,\nboth finite difference methods and time splitting spectral methods are\nreviewed, and their error estimates are briefly outlined. When the GPE has\nsymmetric properties, we show how to simplify the numerical methods. Then we\ncompare two widely used scalings, i.e. physical scaling (commonly used) and\nsemiclassical scaling, for BEC in strong repulsive interaction regime\n(Thomas-Fermi regime), and discuss semiclassical limits of the GPE. Extensions\nof these results for one-component BEC are then carried out for rotating BEC by\nGPE with an angular momentum rotation, dipolar BEC by GPE with long range\ndipole-dipole interaction, and two-component BEC by coupled GPEs. Finally, as a\nperspective, we show briefly the mathematical models for spin-1 BEC, Bogoliubov\nexcitation and BEC at finite temperature."
    },
    {
        "anchor": "Feshbach resonant scattering of three fermions in one-dimensional wells: We study the weak-tunnelling limit for a system of cold 40K atoms trapped in\na one-dimensional optical lattice close to an s-wave Feshbach resonance. We\ncalculate the local spectrum for three atoms at one site of the lattice within\na two-channel model. Our results indicate that, for this one-dimensional\nsystem, one- and two-channel models will differ close to the Feshbach\nresonance, although the two theories would converge in the limit of strong\nFeshbach coupling. We also find level crossings in the low-energy spectrum of a\nsingle well with three atoms that may lead to quantum phase transition for an\noptical lattice of many wells. We discuss the stability of the system to a\nphase with non-uniform density.",
        "positive": "Micromagnetic modeling of magnon coherent states in a nonuniform\n  magnetic field: The study of the dynamics of magnetically ordered states in strong excitation\nthrough micromagnetic modeling has become relevant due to the observation of\nmagnon Bose condensation. In particular, the question has arisen about the\npossibility of describing the coherent quantum state by the quasi-classical\nLandau-Lifshitz-Gilbert equations. We performed micromagnetic simulations of\nmagnetization precession with a high angle of deviation in an out-of-plane\nnonuniform dc field. Our results confirm the formation of coherent magnon state\nunder conditions of high excitation. This coherent state extends over long\ndistances and described by a spatially inhomogeneous amplitude and a\nhomogeneous precession phase."
    },
    {
        "anchor": "Ring model for trapped condensates with synthetic spin-orbit coupling: We derive an effective ring model in momentum space for trapped bosons with\nsynthetic spin-orbit coupling. This effective model is characterized by a\npeculiar form of the inter particle interactions, which is crucially modified\nby the external confinement. The ring model allows for an intuitive\nunderstanding of the phase diagram of trapped condensates with isotropic\nspin-orbit coupling, and in particular for the existence of skyrmion lattice\nphases. The model, which may be generally applied for spinor condensates of\narbitrary spin and spin-dependent interactions, is illustrated for the\nparticular cases of spin-1/2 and spin-1 condensates.",
        "positive": "Kardar-Parisi-Zhang universality in discrete two-dimensional\n  driven-dissipative exciton polariton condensates: The statistics of the fluctuations of quantum many-body systems are highly\nrevealing of their nature. In driven-dissipative systems displaying macroscopic\nquantum coherence, as exciton polariton condensates under incoherent pumping,\nthe phase dynamics can be mapped to the stochastic Kardar-Parisi-Zhang (KPZ)\nequation. However, in two dimensions (2D), it was theoretically argued that the\nKPZ regime may be hindered by the presence of vortices, and a non-equilibrium\nBKT behavior was reported close to condensation threshold. We demonstrate here\nthat, when a discretized 2D polariton system is considered, universal KPZ\nproperties can emerge. We support our analysis by extensive numerical\nsimulations of the discrete stochastic generalized Gross-Pitaevskii equation.\nWe show that the first-order correlation function of the condensate exhibits\nstretched exponential behaviors in space and time with critical exponents\ncharacteristic of the 2D KPZ universality class, and find that the related\nscaling function accurately matches the KPZ theoretical one, stemming from\nfunctional Renormalization Group. We also obtain the distribution of the phase\nfluctuations and find that it is non-Gaussian, as expected for a KPZ stochastic\nprocess."
    },
    {
        "anchor": "Collective many-body interaction in Rydberg dressed atoms: We present a method to control the shape and character of the interaction\npotential between cold atomic gases by weakly dressing the atomic ground state\nwith a Rydberg level. For increasing particle densities, a crossover takes\nplace from a two-particle interaction into a collective many-body interaction,\nwhere the dipole-dipole/van der Waals Blockade phenomenon between the Rydberg\nlevels plays a dominant role. We study the influence of these collective\ninteraction potential on a Bose-Einstein condensate, and present the optimal\nparameters for its experimental detection.",
        "positive": "Many-body effects in a Bose-Fermi mixture: We investigate many-body effects on a mixture of interacting bosons and\nfermions loaded in an optical lattice using a generalized dynamical mean field\ntheory combined with the numerical renormalization group. We show that strong\ncorrelation effects emerge in the presence of bosonic superfluidity, leading to\na renormalized peak structure near the Fermi level in the density of states for\nfermions. Remarkably, this kind of strong renormalization appears not only in\nthe metallic phase but also in the insulating phases of fermions such as in the\nempty/filled band limit. A systematic analysis of the relation between the\nquasiparticle weight and the strength of superfluidity reveals that the\nrenormalization effect is indeed caused by the boson degrees of freedom. It is\nfound that such renormalization is also relevant to a supersolid phase\nconsisting of a density wave ordering of fermions accompanied by bosonic\nsuperfluidity. This sheds light on the origin of the peak structure in the\nsupersolid phase."
    },
    {
        "anchor": "Green's function approach to the Bose-Hubbard model with disorder: We analyse the distinction between the three different ground states\npresented by a system of spinless bosons with short-range interactions\nsubmitted to a random potential using the disordered Bose-Hubbard model. The\ncriteria for identifying the superfluid, the Mott-insulator, and the Bose-glass\nphases at finite temperatures are discussed for small values of the kinetic\nenergy associated with the tunnelling of particles between potential wells.\nField theoretical considerations are applied in order to construct a\ndiagrammatic hopping expansion to the finite-temperature Green's function. By\nperforming a summation of subsets of diagrams we are able to find the condition\nto the long-range correlations which leads to the phase boundary between\nsuperfluid and insulating phases. The perturbative expression to the local\ncorrelations allows us to calculate an approximation to the single-particle\ndensity of states of low-energy excitations in the presence of small hopping,\nwhich characterizes unambiguously the distinction between the Mott-insulator\nand the Bose-glass phases. We obtain the phase diagram for bounded on-site\ndisorder. It is demonstrated that our analysis is capable of going beyond the\nmean-field theory results for the classification of these different ground\nstates.",
        "positive": "Sub-picosecond thermalization dynamics in condensation of strongly\n  coupled lattice plasmons: Bosonic condensates offer exciting prospects for studies of non-equilibrium\nquantum dynamics. Understanding the dynamics is particularly challenging in the\nsub-picosecond timescales typical for room temperature luminous\ndriven-dissipative condensates. Here we combine a lattice of plasmonic\nnanoparticles with dye molecule solution at the strong coupling regime, and\npump the molecules optically. The emitted light reveals three distinct regimes:\none-dimensional lasing, incomplete stimulated thermalization, and\ntwo-dimensional multimode condensation. The condensate is achieved by matching\nthe thermalization rate with the lattice size and occurs only for pump pulse\ndurations below a critical value. Our results give access to control and\nmonitoring of thermalization processes and condensate formation at\nsub-picosecond timescale."
    },
    {
        "anchor": "Universal Dimer in a Collisionally Opaque Medium: Experimental\n  Observables and Efimov Resonances: A universal dimer is subject to secondary collisions with atoms when formed\nin a cloud of ultracold atoms via three-body recombination. We show that in a\ncollisionally opaque medium, the value of the scattering length that results in\nthe maximum number of secondary collisions may not correspond to the Efimov\nresonance at the atom-dimer threshold and thus can not be automatically\nassociated with it. This result explains a number of controversies in recent\nexperimental results on universal three-body states and supports the emerging\nevidence for the significant finite range corrections to the first excited\nEfimov energy level.",
        "positive": "First order phase transitions in optical lattices with tunable\n  three-body onsite interaction: We study the two-dimensional Bose-Hubbard model in the presence of a\nthree-body interaction term, both at a mean field level and via quantum Monte\nCarlo simulations. The three-body term is tuned by coupling the triply occupied\nstates to a trapped universal trimer. We find that, for sufficiently attractive\nthree-body interaction the n = 2 Mott lobe disappears and the system displays\nfirst order phase transitions separating the n = 1 from the n = 3 lobes, and\nthe n = 1 and n = 3 Mott insulator from the superfluid. We have also analyzed\nthe effect of finite temperature and found that transitions are still of first\norder at temperatures T\\simJ where J is the hopping matrix element."
    },
    {
        "anchor": "Scissors mode of dipolar quantum droplets of dysprosium atoms: We report on the observation of the scissors mode of a single dipolar quantum\ndroplet. The existence of this mode is due to the breaking of the rotational\nsymmetry by the dipole-dipole interaction, which is fixed along an external\nhomogeneous magnetic field. By modulating the orientation of this magnetic\nfield, we introduce a new spectroscopic technique for studying dipolar quantum\ndroplets. This provides a precise probe for interactions in the system allowing\nto extract a background scattering length for \\textsuperscript{164}Dy of\n$69(4)\\,a_0$. Our results establish an analogy between quantum droplets and\natomic nuclei, where the existence of the scissors mode is also only due to\ninternal interactions. They further open the possibility to explore physics\nbeyond the available theoretical models for strongly-dipolar quantum gases.",
        "positive": "Probing Phases and Quantum Criticality using Deviations from the Local\n  Fluctuation-Dissipation Theorem: Introduction Cold atomic gases in optical lattices are emerging as excellent\nlaboratories for testing models of strongly interacting particles in condensed\nmatter physics. Currently, one of the major open questions is how to obtain the\nfinite temperature phase diagram of a given quantum Hamiltonian directly from\nexperiments. Previous work in this direction required quantum Monte Carlo\nsimulations to directly model the experimental situation in order to extract\nquantitative information, clearly defeating the purpose of an optical lattice\nemulator. Here we propose a new method that utilizes deviations from a local\nfluctuation dissipation theorem to construct a finite temperature phase\ndiagram, for the first time, from local observables accessible by in situ\nexperimental observations. Our approach extends the utility of the\nfluctuation-dissipation theorem from thermometry to the identification of\nquantum phases, associated energy scales and the quantum critical region. We\ntest our ideas using state-of-the-art large-scale quantum Monte Carlo\nsimulations of the two-dimensional Bose Hubbard model."
    },
    {
        "anchor": "Pairing patterns in polarized unitary Fermi gases above the superfluid\n  transition: We non-perturbatively study pairing in the high-temperature regime of\npolarized unitary two-component Fermi gases by extracting the pair-momentum\ndistribution and shot-noise correlations. Whereas the pair-momentum\ndistribution allows us to analyze the propagation of pairs composed of one\nspin-up and one spin-down fermion, shot-noise correlations provide us with a\ntomographic insight into pairing correlations around the Fermi surfaces\nassociated with the two species. Assuming that the dominant pairing patterns\nright above the superfluid transition also govern the formation of condensates\nin the low-temperature regime, our analysis suggests that the superfluid ground\nstate is homogeneous and of the Bardeen-Cooper-Schrieffer-type over a wide\nrange of polarizations.",
        "positive": "Scattering of matter-waves in spatially inhomogeneous environments: We study scattering of quasi one-dimensional matter-waves at an interface of\ntwo spatial domains, one with repulsive and one with attractive interatomic\ninteractions. It is shown that the incidence of a Gaussian wavepacket from the\nrepulsive to the attractive region gives rise to generation of a soliton train.\nMore specifically, the number of emergent solitons can be controlled e.g. by\nthe variation of the amplitude or the width of the incoming wavepacket.\nFurthermore, we study the reflectivity of a soliton incident from the\nattractive region to the repulsive one. We find the reflection coefficient\nnumerically and employ analytical methods, that treat the soliton as a particle\n(for moderate and large amplitudes) or a quasi-linear wavepacket (for small\namplitudes), to determine the critical soliton momentum - as function of the\nsoliton amplitude - for which total reflection is observed."
    },
    {
        "anchor": "Upper bound of one-magnon excitation and lower bound of effective mass\n  for ferromagnetic spinor Bose and Fermi gases: Using a variational method, we derive an exact upper bound for one-magnon\nexcitation energy in ferromagnetic spinor gases, which limits the quantum\ncorrections to the effective mass of a magnon to be positive. We also derive an\nupper bound for one-magnon excitation energy in lattice systems. The results\nhold for both Bose and Fermi systems in $d$ dimensions as long as the\ninteraction is local and invariant under spin rotation.",
        "positive": "Counterflow Quantum Turbulence and the Instability in Two-component\n  Bose-Einstein Condensates: We theoretically study the nonlinear dynamics of the instability of\ncounter-superflow in two miscible Bose-Einstein condensates. The condensates\nbecome unstable when the relative velocity exceeds a critical value, which is\ncalled counter-superflow instability. We reveal that the counter-superflow\ninstability can lead to quantum turbulence by numerically solving the coupled\nGross-Pitaevskii equations. The modes amplified by the instability grow into\nsolitons and decay into quantized vortices.Eventually, the vortices become\ntangled and quantum turbulence of two superfluids. We show that this process\nmay occur in experiments by investigating the dynamics in a 2D trapped system."
    },
    {
        "anchor": "Measurement of the Homogeneous Contact of a Unitary Fermi gas: By selectively probing the center of a trapped gas, we measure the local, or\nhomogeneous, contact of a unitary Fermi gas as a function of temperature. Tan's\ncontact, C, is proportional to the derivative of the energy with respect to the\ninteraction strength, and is thus an essential thermodynamic quantity for a gas\nwith short-range correlations. Theoretical predictions for the temperature\ndependence of C differ substantially, especially near the superfluid\ntransition, Tc, where C is predicted to either sharply decrease, sharply\nincrease, or change very little. For T/T_F>0.4, our measurements of the\nhomogeneous gas contact show a gradual decrease of C with increasing\ntemperature, as predicted by theory. We observe a sharp decrease in C at\nT/T_F=0.16, which may be due to the superfluid phase transition. While a sharp\ndecrease in C below Tc is predicted by some many-body theories, we find that\nnone of the predictions fully accounts for the data.",
        "positive": "Phase Diagram of Solitons in the Polar Phase of a Spin-1 Bose-Einstein\n  Condensate: We theoretically study the structure of a stationary soliton in the polar\nphase of spin-1 Bose--Einstein condensate in the presence of quadratic Zeeman\neffect at zero temperature. The phase diagram of such solitons is mapped out by\nfinding the states of minimal soliton energy in the defining range of polar\nphase. The states are assorted into normal, anti-ferromagnetic,\nbroken-axisymmetry, and ferromagnetic phases according to the number and spin\ndensities in the core. The order of phase transitions between different\nsolitons and the critical behaviour of relevant continuous transitions are\nproved within the mean-field theory."
    },
    {
        "anchor": "Coherent merging of counter-propagating exciton-polariton superfluids: We report the formation of a macroscopic coherent state emerging from\ncolliding polariton fluids. Four lasers with random relative phases, arranged\nin a square, pump resonantly a planar microcavity, creating four coherent\npolariton fluids propagating toward each other. When the density (interactions)\nincreases, the four fluids synchronise and the topological excitations (vortex\nor soliton) disappear to form a single superfluid.",
        "positive": "Superfluidity in density imbalanced bilayers of dipolar fermions: We study the zero temperature phase diagram of an imbalanced bilayer of\ndipolar fermions. We consider perpendicularly aligned identical dipoles in two\nlayers and investigate the effect of population imbalance on the ground state\nphase at different layer spacings and average densities. The attractive part of\nthe interlayer interaction could lead to the BEC-BCS crossover and the Fermi\nsurface mismatch between two layers results in interesting uniform and\nnonuniform superfluid phases, which we have investigated here using the BCS\nmean-field theory together with the superfluid-mass density criterion. The\ndensity imbalance reduces the pairing gap. At low densities, where the system\nis on the BEC side of the crossover, this reduction is quite smooth while a\ndense system rapidly becomes normal at intermediate density polarizations.\nStable homogeneous superfluidity is predicted to appear on the phase diagram\nwhen the dipolar length exceeds both the layer spacing and the average\nintralayer distance between dipoles, a regime which should be readily\naccessible experimentally. This homogeneous superfluid phase becomes unstable\nat intermediate densities and layer spacings. We have also examined that these\nuniform and inhomogeneous superfluid phases survive when the effects of\nintralayer screenings are also incorporated in the formalism."
    },
    {
        "anchor": "Hydrodynamic Instability and Turbulence in Quantum Fluids: Superfluid turbulence consisting of quantized vortices is called quantum\nturbulence (QT). Quantum turbulence and quantized vortices were discovered in\nsuperfluid $^4$He about 50 years ago, but innovation has occurred recently in\nthis field. One is in the field of superfluid helium. Statistical quantities\nsuch as energy spectra and probability distribution function of the velocity\nfield have been accessible both experimentally and numerically. Visualization\ntechnique has developed and succeeded in the direct visualization of quantized\nvortices. The other innovation is in the field of atomic Bose-Einstein\ncondensation. The modern optical technique has enabled us to control and\nvisualize directly the condensate and quantized vortices. Various kinds of\nhydrodynamic instability have been revealed. Even QT is realized\nexperimentally. This article describes such recent developments as well as the\nmotivation of studying QT.",
        "positive": "Transition from supersonic to subsonic waves in superfluid Fermi gases: We study the propagation of dispersive waves in superfluid Fermi gases in the\nBEC-BCS crossover. Unlike in other superfluid systems, where dispersive waves\nhave already been studied and observed, Fermi gases can exhibit a subsonic\ndispersion relation for which the dispersive wave pattern appears at the tail\nof the wave front. We show that this property can be used to distinguish\nbetween a subsonic and a supersonic dispersion relation at unitarity."
    },
    {
        "anchor": "Fidelity and criticality of quantum Ising chain with long-range\n  interactions: We study the criticality of long-range quantum ferromagnetic Ising chain with\nalgebraically decaying interactions $1/r^{\\alpha}$ via the fidelity\nsusceptibility based on the exact diagonalization and the density matrix\nrenormalization group techniques. We find that critical exponents change\nmonotonously from the mean-field universality class to the short-range Ising\nuniversality class for intermediate $\\alpha$, which are consistent with recent\nresults obtained from renormalization group. In addition, we determine the\ncritical values for $1.8 \\le \\alpha \\le 3$ from the finite-size scaling of the\nfidelity susceptibility. Our work provides very nice numerical data from the\nfidelity susceptibility for the quantum long-range ferromagnetic Ising chain.",
        "positive": "Mobility edge for cold atoms in laser speckle potentials: Using the transfer matrix method, we numerically compute the precise position\nof the mobility edge of atoms exposed to a laser speckle potential, and study\nits dependence vs. the disorder strength and correlation function. Our results\ndeviate significantly from previous theoretical estimates using an approximate\nself-consistent approach of localization. In particular we find that the\nposition of the mobility edge in blue-detuned speckles is much lower than in\nthe red-detuned counterpart, pointing out the crucial role played by the\nasymmetric on-site distribution of speckle patterns."
    },
    {
        "anchor": "Topological Properties of Ultracold Bosons in One-Dimensional\n  Quasiperiodic Optical Lattice: We analyze topological properties of the one-dimensional Bose-Hubbard model\nwith a quasiperiodic superlattice potential. This system can be realized in\ninteracting ultracold bosons in optical lattice in the presence of an\nincommensurate superlattice potential. We first analyze the quasiperiodic\nsuperlattice made by the cosine function, which we call Harper-like\nBose-Hubbard model. We compute the Chern number and observe a gap-closing\nbehavior as the interaction strength $U$ is changed. Also, we discuss the\nbulk-edge correspondence in our system. Furthermore, we explore the phase\ndiagram as a function of $U$ and a continuous deformation parameter $\\beta$\nbetween the Harper-like model and another important quasiperiodic lattice, the\nFibonacci model. We numerically confirm that the incommensurate charge density\nwave (ICDW) phase is topologically non-trivial and it is topologically\nequivalent in the whole ICDW region.",
        "positive": "Universal Bose Gases Near Resonance: A Rigorous Solution: We obtain a rigorous solution of universal Bose gases near resonance and\noffer an answer to one of the long-standing challenges of quantum gases at\nlarge scattering lengths, where the standard dilute theory breaks down. The\nsolution was obtained by using an $\\epsilon$ expansion near four spatial\ndimension. In dimension $d = 4 - \\epsilon$, the chemical potential of Bose\ngases near resonances is shown to approach the universal value\n$\\epsilon^{(2/(4-\\epsilon))} \\epsilon_F \\sqrt{2/3} (1 + 0.474 \\epsilon - i\n1.217 \\epsilon + ...)$, where $\\epsilon_F$ is the Fermi energy defined for a\nFermi gas of density $n$, and the condensation fraction is equal to $2/3 (1 +\n0.0877 \\epsilon + ...)$. We also discuss the implications on ultra-cold gases\nin physical dimensions."
    },
    {
        "anchor": "Thermal field theory of bosonic gases with finite-range effective\n  interaction: We study a dilute and ultracold Bose gas of interacting atoms by using an\neffective field theory which takes account finite-range effects of the\ninter-atomic potential. Within the formalism of functional integration from the\ngrand canonical partition function we derive beyond-mean-field analytical\nresults which depend on both scattering length and effective range of the\ninteraction. In particular, we calculate the equation of state of the bosonic\nsystem as a function of these interaction parameters both at zero and finite\ntemperature including one-loop Gaussian fluctuation. In the case of zero-range\neffective interaction we explicitly show that, due to quantum fluctuations, the\nbosonic system is thermodynamically stable only for very small values of the\ngas parameter. We find that a positive effective range above a critical\nthreshold is necessary to remove the thermodynamical instability of the uniform\nconfiguration. Remarkably, also for relatively large values of the gas\nparameter, our finite-range results are in quite good agreement with recent\nzero-temperature Monte Carlo calculations obtained with hard-sphere bosons.",
        "positive": "Quench Dynamics of the Gaudin-Yang Model: We study the quench dynamics of one dimensional bosons or fermion quantum\ngases with either attractive or repulsive contact interactions. Such systems\nare well described by the Gaudin-Yang model which turns out to be quantum\nintegrable. We use a contour integral approach, the Yudson approach, to expand\ninitial states in terms of Bethe Ansatz eigenstates of the Hamiltonian. Making\nuse of the contour, we obtain a complete set of eigenstates, including both\nfree states and bound states. These states constitute a larger Hilbert space\nthan described by the standard String hypothesis. We calculate the density and\nnoise correlations of several quenched systems such as a static or kinetic\nimpurity evolving in an array of particles."
    },
    {
        "anchor": "Quench dynamics of Hopf insulators: Hopf insulators are exotic topological states of matter outside the standard\nten-fold way classification based on discrete symmetries. Its topology is\ncaptured by an integer invariant that describes the linking structures of the\nHamiltonian in the three-dimensional momentum space. In this paper, we\ninvestigate the quantum dynamics of Hopf insulators across a sudden quench and\nshow that the quench dynamics is characterized by a $\\mathbb{Z}_2$ invariant\n$\\nu$ which reveals a rich interplay between quantum quench and static band\ntopology. We construct the $\\mathbb{Z}_2$ topological invariant using the loop\nunitary operator, and prove that $\\nu$ relates the pre- and post-quench Hopf\ninvariants through $\\nu=(\\mathcal{L}-\\mathcal{L}_0)\\bmod 2$. The $\\mathbb{Z}_2$\nnature of the dynamical invariant is in sharp contrast to the $\\mathbb{Z}$\ninvariant for the quench dynamics of Chern insulators in two dimensions. The\nnon-trivial dynamical topology is further attributed to the emergence of\n$\\pi$-defects in the phase band of the loop unitary. These $\\pi$-defects are\ngenerally closed curves in the momentum-time space, for example, as nodal rings\ncarrying Hopf charge.",
        "positive": "Destruction of Long-range Order by Quenching the Hopping Range in One\n  Dimension: We study the dynamics in a one dimensional hard-core Bose gas with power-law\nhopping after an abrupt reduction of the hopping range using the time-dependent\ndensity-matrix renormalization group (t-DMRG) and bosonization techniques. In\nparticular, we focus on the destruction of the Bose-Einstein condensate (BEC),\nwhich is present in the initial state in the thermodynamic limit. We argue that\nthis type of quench is akin to a sudden reduction in the effective\ndimensionality $d$ of the system (from $d > 1$ to $d = 1$). We identify two\nregimes in the evolution of the BEC fraction. For short times the decay of the\nBEC fraction is Gaussian while for intermediate to long times, it is well\ndescribed by a stretched exponential with an exponent that depends on the\ninitial effective dimensionality of the system. These results are potentially\nrelevant for cold trapped-ion experiments which can simulate an equivalent of\nhard-core bosons, i.e. spins, with tunable long-range interactions."
    },
    {
        "anchor": "Continuous atom laser with Bose-Einstein condensates involving\n  three-body interactions: We demonstrate, through numerical simulations, the emission of a coherent\ncontinuous matter wave of constant amplitude from a Bose-Einstein Condensate in\na shallow optical dipole trap. The process is achieved by spatial control of\nthe variations of the scattering length along the trapping axis, including\nelastic three body interactions due to dipole interactions. In our approach,\nthe outcoupling mechanism are atomic interactions and thus, the trap remains\nunaltered. We calculate analytically the parameters for the experimental\nimplementation of this CW atom laser.",
        "positive": "Quantum Hall effect with small numbers of vortices in Bose-Einstein\n  condensates: When vortices are displaced in Bose-Einstein condensates (BEC), the Magnus\nforce gives the system a momentum transverse in the direction to the\ndisplacement. We show that Bose-Einstein condensates (BEC) in long channels\nwith vortices exhibit a quantization of the current response with respect to\nthe spatial vortex distribution. The quantization originates from the\nwell-known topological property of the phase around a vortex --- it is an\ninteger multiple of $ 2 \\pi $. In a similar way to the integer quantum Hall\neffect, the current along the channel is related to this topological phase, and\ncan be extracted from two experimentally measurable quantities: the total\nmomentum of the BEC and the spatial distribution. The quantization is in units\nof $ m/2h $, where $ m $ is the mass of the atoms and $ h $ is Planck's\nconstant. We derive an exact vortex momentum-displacement relation for BECs in\nlong channels under general circumstances. Our results presents the possibility\nthat the configuration described here can be used as a novel way of measuring\nthe mass of the atoms in the BEC using a topological invariant of the system.\nIf an accurate determination of the plateaus are experimentally possible, this\ngives the possibility of a topological quantum mass standard and precise\ndetermination of the fine structure constant."
    },
    {
        "anchor": "Shell potentials for microgravity Bose-Einstein condensates: Extending the understanding of Bose-Einstein condensate (BEC) physics to new\ngeometries and topologies has a long and varied history in ultracold atomic\nphysics. One such new geometry is that of a bubble, where a condensate would be\nconfined to the surface of an ellipsoidal shell. Study of this geometry would\ngive insight into new collective modes, self-interference effects,\ntopology-dependent vortex behavior, dimensionality crossovers from thick to\nthin shells, and the properties of condensates pushed into the ultradilute\nlimit. Here we discuss a proposal to implement a realistic experimental\nframework for generating shell-geometry BEC using radiofrequency dressing of\nmagnetically-trapped samples. Such a tantalizing state of matter is\ninaccessible terrestrially due to the distorting effect of gravity on\nexperimentally-feasible shell potentials. The debut of an orbital BEC machine\n(NASA Cold Atom Laboratory, aboard the International Space Station) has enabled\nthe operation of quantum-gas experiments in a regime of perpetual freefall, and\nthus has permitted the planning of microgravity shell-geometry BEC experiments.\nWe discuss specific experimental configurations, applicable inhomogeneities and\nother experimental challenges, and outline potential experiments.",
        "positive": "Majorana edge-modes in a spinful particle conserving model: We show the presence of Majorana edge modes in an interacting fermionic\nladder with spin in a number conserved setting. The interchain single particle\nhopping is suppressed and only a pair hopping is present between the different\nchains of the ladder. Additionally, the hopping along the chains is spin\nimbalanced and a transverse magnetic field is applied breaking time-reversal\ninvariance. We study the robustness of the topological phase with respect to an\non-site interaction between the spin-up and spin-down fermions and the spin\ndependent imbalance of the hopping. The main result of the present work is that\nthe topological phase survives for a finite region in the parameter space in\nthe presence of interactions. The localized Majorana edge modes seems to be\nmore stable in the case when the on-site interaction is an attraction."
    },
    {
        "anchor": "Interacting Hofstadter Interface: Two-dimensional topological insulators possess conducting edge states at\ntheir boundary while being insulating in the bulk. The detection of edge states\nremains an open question in ultracold atom setups. We propose a configuration\nto implement a topological interface within the experimentally realizable\ntime-reversal invariant Hofstadter model which gives rise to a topological\nphase boundary at the center of the system, and investigate the influence of\ntwo-body interactions on the interface in a fermionic system. The interface can\nin principle be probed via the spatially resolved compressibility of the system\nby using a quantum gas microscope. Furthermore, we distinguish the phases\nthrough their Hall response and compute a local spin Chern marker which proves\nthe phase separation of two distinct topological many-body phases. The\nbulk-boundary correspondence for the interacting system is confirmed by\ncomputing the edge state spectra at the interface.",
        "positive": "Strongly correlated states of trapped ultracold fermions in deformed\n  Landau levels: We analyze the strongly correlated regime of a two-component trapped\nultracold fermionic gas in a synthetic non-Abelian U(2) gauge potential, that\nconsists of both a magnetic field and a homogeneous spin-orbit coupling. This\ngauge potential deforms the Landau levels (LLs) with respect to the Abelian\ncase and exchanges their ordering as a function of the spin-orbit coupling. In\nview of experimental realizations, we show that a harmonic potential combined\nwith a Zeeman term, gives rise to an angular momentum term, which can be used\nto test the stability of the correlated states obtained through interactions.\nWe derive the Haldane pseudopotentials (HPs) describing the interspecies\ncontact interaction within a lowest LL approximation. Unlike ordinary\nfractional quantum Hall systems and ultracold bosons with short-range\ninteractions in the same gauge potential, the HPs for sufficiently strong\nnon-Abelian fields show an unconventional non-monotonic behaviour in the\nrelative angular momentum. Exploiting this property, we study the occurrence of\nnew incompressible ground states as a function of the total angular momentum.\nIn the first deformed Landau level (DLL) we obtain Laughlin and Jain states.\nInstead, in the second DLL three classes of stabilized states appear: Laughlin\nstates, a series of intermediate strongly correlated states and finally\nvortices of the integer quantum Hall state. Remarkably, in the intermediate\nregime, the non-monotonic HPs of the second DLL induce two-particle\ncorrelations which are reminiscent of paired states such as the Haffnian state.\nVia exact diagonalization in the disk geometry, we compute experimentally\nrelevant observables such as density profiles and correlations, and we study\nthe entanglement spectra as a further tool to characterize the obtained\nstrongly correlated states."
    },
    {
        "anchor": "Edge states and topological phases in one-dimensional optical\n  superlattices: We show that one-dimensional quasi-periodic optical lattice systems can\nexhibit edge states and topological phases which are generally believed to\nappear in two-dimensional systems. When the Fermi energy lies in gaps, the\nFermi system on the optical superlattice is a topological insulator\ncharacterized by a nonzero topological invariant. The topological nature can be\nrevealed by observing the density profile of a trapped fermion system, which\ndisplays plateaus with their positions uniquely determined by the ration of\nwavelengths of the bichromatic optical lattice. The butterfly-like spectrum of\nthe superlattice system can be also determined from the finite-temperature\ndensity profiles of the trapped fermion system. This finding opens an\nalternative avenue to study the topological phases and Hofstadter-like spectrum\nin one-dimensional optical lattices.",
        "positive": "On a scale-invariant Fermi gas in a time-dependent harmonic potential: We investigate a scale-invariant two-component Fermi gas in a time-dependent\nisotropic harmonic potential. The exact time evolution of the density\ndistribution in position space in any spatial dimension is obtained. Two\nexperimentally relevant examples, an abrupt change and a periodic modulation of\nthe trapping frequency are solved. Small deviations from scale invariance and\nisotropy of the confinement are addressed within first order perturbation\ntheory. We discuss the consequences for experiments with ultracold quantum\ngases such as the excitation of a tower of undamped breathing modes and a new\nalternative for measuring the Tan contact."
    },
    {
        "anchor": "Cold Bose Atoms Around the Crossing of Quantum Waveguides: We show that massive low energy particles traversing a branching zone or a\ncrossing of quantum waveguides may experience a non standard trapping force\nthat cannot be derived from a potential. For interacting cold Bose atoms we\nreport on the formation of a localised Hartree ground state for three prototype\nwaveguide geometries with broken translational symmetry: a cranked L-shaped\nwaveguide L, a T-shaped waveguide T, and the crossing C of two quantum\nwaveguides. The phenomenon is kinetic energy driven and cannot be described\nwithin the Thomas-Fermi approximation. Depending on the ratio of joining\nlateral tube diameters of the respective waveguides C,L,T delocalisation\ncommences when the particle number N approaches a critical value. For the case\nof a binary mixture of two different Bose atom species A and B we observe non\nstandard trapping of both atom species for subcritical particle numbers. A\nsudden demixing quantum transition takes place as the total particle number\nN=N_{A}+N_{B} is increased at fixed mixing ratio N_{A}/N_{B}. Depending on the\nmass ratio m_{A}/m_{B} the heavier atom species delocalises first for a wide\nrange of interaction parameters. The numerical calculations are based on a\nsplitting scheme involving an analytic approximation to the short time\nasymptotics of the imaginary time quantum propagator of a single particle\nobeying to Dirichlet boundary conditions at the walls inside the respective\nwaveguides.",
        "positive": "Surmounting the sign problem in non-relativistic calculations: a case\n  study with mass-imbalanced fermions: The calculation of the ground state and thermodynamics of mass-imbalanced\nFermi systems is a challenging many-body problem. Even in one spatial\ndimension, analytic solutions are limited to special configurations and\nnumerical progress with standard Monte Carlo approaches is hindered by the sign\nproblem. The focus of the present work is on the further development of methods\nto study imbalanced systems in a fully non-perturbative fashion. We report our\ncalculations of the ground-state energy of mass-imbalanced fermions using two\ndifferent approaches which are also very popular in the context of the theory\nof the strong interaction (Quantum Chromodynamics, QCD): (a) the hybrid Monte\nCarlo algorithm with imaginary mass imbalance, followed by an analytic\ncontinuation to the real axis; and (b) the Complex Langevin algorithm. We cover\na range of on-site interaction strengths that includes strongly attractive as\nwell as strongly repulsive cases which we verify with non-perturbative\nrenormalization group methods and perturbation theory. Our findings indicate\nthat, for strong repulsive couplings, the energy starts to flatten out,\nimplying interesting consequences for short-range and high-frequency\ncorrelation functions. Overall, our results clearly indicate that the Complex\nLangevin approach is very versatile and works very well for imbalanced Fermi\ngases with both attractive and repulsive interactions."
    },
    {
        "anchor": "Coreless vortex dipoles and bubbles in phase-separated binary\n  condensates: Vortex dipoles are generated when an obstacle moves through a superfluid. In\ncase of phase-separated binary condensates, with appropriate interaction\nparameters in pan-cake shaped traps, we show that coreless vortex dipoles are\ncreated when a Gaussian obstacle beam traverses across them above a critical\nspeed. As the obstacle passes through the inner component, it carries along a\nbubble of the outer component. Using Thomas-Fermi approximation, we show that\nphase-separated binary condensates can either support vortices with empty or\nfilled cores. For time dependent obstacle potentials, ramped down in the\npresent case, relative energy scales of the system influence the dynamical\nevolution of the binary condensate.",
        "positive": "Efimov resonance position near a narrow Feshbach resonance in\n  $^6$Li-$^{133}$Cs mixture: In the vicinity of a narrow Feshbach resonances Efimov features are expected\nto be characterized by the resonance's properties rather than the van der Waals\nlength of the interatomic potential. Although this theoretical prediction is\nwell-established by now, it still lacks experimental confirmation. Here, we\napply our recently developed three-channel model [Yudkin and Khaykovich, Phys.\nRev. A 103, 063303 (2021)] to the experimental result obtained in a\nmass-imbalanced $^6$Li-$^{133}$Cs mixture in the vicinity of the narrowest\nresonance explored to date [Johansen at. al. Nat. Phys. 13, 731 (2017)]. We\nconfirm that the observed position of the Efimov resonance is dictated mainly\nby the resonance physics while the influence of the van der Waals tail of the\ninteratomic potential is minor. We show that the resonance position is strongly\ninfluenced by the presence of another Feshbach resonance which significantly\nalters the effective background scattering length at the narrow resonance\nposition."
    },
    {
        "anchor": "Brownian motion of a matter-wave bright soliton: realizing a quantum\n  pollen grain: Taking an open quantum systems approach, we derive a collective equation of\nmotion for the dynamics of a matter-wave bright soliton moving through a\nthermal cloud of a distinct atomic species. The reservoir interaction involves\nenergy transfer without particle transfer between the soliton and thermal\ncloud, thus damping the soliton motion without altering its stability against\ncollapse. We derive a Langevin equation for the soliton centre of mass velocity\nin the form of an Ornstein-Uhlenbeck process with analytical drift and\ndiffusion coefficients. This collective motion is confirmed by simulations of\nthe full stochastic projected Gross-Pitaevskii equation for the matter-wave\nfield. The system offers a pathway for experimentally observing the elusive\nenergy-damping reservoir interaction, and a clear realization of collective\nBrownian motion for a mesoscopic superfluid droplet.",
        "positive": "Quantum Caging in Interacting Many-Body All-Bands-Flat Lattices: We consider translationally invariant tight-binding all-bands-flat networks\nwhich lack dispersion. In a recent work [arXiv:2004.11871] we derived the\nsubset of these networks which preserves nonlinear caging, i.e. keeps compact\nexcitations compact in the presence of Kerr-like local nonlinearities. Here we\nreplace nonlinear terms by Bose-Hubbard interactions and study quantum caging.\nWe prove the existence of degenerate energy renormalized compact states for two\nand three particles, and use an inductive conjecture to generalize to any\nfinite number M of participating particles in one dimension. Our results\nexplain and generalize previous observations for two particles on a diamond\nchain [Vidal et.al. Phys. Rev. Lett. 85, 3906 (2000)]. We further prove that\nquantum caging conditions guarantee the existence of extensive sets of\nconserved quantities in any lattice dimension, as first revealed in [Tovmasyan\net al Phys. Rev. B 98, 134513 (2018)] for a set of specific networks.\nConsequently transport is realized through moving pairs of interacting\nparticles which break the single particle caging."
    },
    {
        "anchor": "Superfluid vortex dynamics in an elliptical boundary: Recent advances in cold atom platforms, providing experimental accessibility\nto real-time dynamics, have renewed interest in the motion of superfluid\nvortices in two-dimensional domains. Motivated by this development, we study\nthe dynamics of a vortex in a two-dimensional incompressible superfluid inside\nan elliptical boundary. Employing the Joukowsky conformal map from a circle to\nan ellipse, we derive an analytical expression for the complex potential\ndescribing the hydrodynamic flow around the vortex. We integrate the resulting\nequations of motion, finding that the vortex moves along a nearly (but not\nexactly) elliptical trajectory. In addition, we obtain a simple closed\nexpression for the vortex self-energy, which serves as the Hamiltonian of the\nsystem.",
        "positive": "Nonequilibrium Hole Dynamics in Antiferromagnets: Damped Strings and\n  Polarons: We develop a nonperturbative theory for hole dynamics in antiferromagnetic\nspin lattices, as described by the $t$-$J$ model. This is achieved by\ngeneralizing the selfconsistent Born approximation to nonequilibrium systems,\nmaking it possible to calculate the full time-dependent many-body wave\nfunction. Our approach reveals three distinct dynamical regimes, ultimately\nleading to the formation of magnetic polarons. Following the initial ballistic\nstage of the hole dynamics, coherent formation of string excitations gives rise\nto characteristic oscillations in the hole density. Their damping eventually\nleaves behind magnetic polarons that undergo ballistic motion with a greatly\nreduced velocity. The developed theory provides a rigorous framework for\nunderstanding nonequilibrium physics of defects in quantum magnets and\nquantitatively explains recent observations from cold-atom quantum simulations\nin the strong coupling regime."
    },
    {
        "anchor": "Engineering Time-Reversal Invariant Topological Insulators With\n  Ultra-Cold Atoms: Topological insulators are a broad class of unconventional materials that are\ninsulating in the interior but conduct along the edges. This edge transport is\ntopologically protected and dissipationless. Until recently, all existing\ntopological insulators, known as quantum Hall states, violated time-reversal\nsymmetry. However, the discovery of the quantum spin Hall effect demonstrated\nthe existence of novel topological states not rooted in time-reversal\nviolations. Here, we lay out an experiment to realize time-reversal topological\ninsulators in ultra-cold atomic gases subjected to synthetic gauge fields in\nthe near-field of an atom-chip. In particular, we introduce a feasible scheme\nto engineer sharp boundaries where the \"edge states\" are localized. Besides,\nthis multi-band system has a large parameter space exhibiting a variety of\nquantum phase transitions between topological and normal insulating phases. Due\nto their unprecedented controllability, cold-atom systems are ideally suited to\nrealize topological states of matter and drive the development of topological\nquantum computing.",
        "positive": "Fluctuation indices for atomic systems with Bose-Einstein condensate: The notion of fluctuation indices, characterizing thermodynamic stability of\nstatistical systems, is advanced. These indices are especially useful for\ninvestigating the stability of nonuniform and trapped atomic assemblies. The\nfluctuation indices are calculated for several systems with Bose-Einstein\ncondensate. It is shown that: the ideal uniform Bose-condensed gas is\nthermodynamically unstable; trapped ideal gases are stable for the confining\ndimension larger than two; trapped gases, under the confining dimension two,\nare weakly unstable; harmonically trapped gas is stable only for the spatial\ndimension three; one-dimensional harmonically trapped gas is unstable;\ntwo-dimensional gas in a harmonic trap represents a marginal case, being weakly\nunstable; interacting nonuniform three-dimensional Bose-condensed gas is\nstable. There are no thermodynamically anomalous particle fluctuations in\nstable Bose-condensed systems."
    },
    {
        "anchor": "Energy spectra and fluxes of turbulent rotating Bose-Einstein\n  condensates in two dimensions: We investigate the scaling of the energy cascade in a harmonically trapped,\nturbulent, rotating Bose-Einstein condensate (BEC) in two dimensions. We\nachieve turbulence by injecting a localized perturbation into the condensate\nand gradually increasing its rotation frequency from an initial value to a\nmaximum. The main characteristics of the resulting turbulent state depend on\nthe initial conditions, rotation frequency, and ramp-up time. We analyze the\nenergy and the fluxes of kinetic energy by considering initial profiles without\nvortices and with vortex lattices. In the case without initial vortices, we\nfind the presence of Kolmogorov-like scaling ($k^{-5/3}$) of the incompressible\nkinetic energy in the inertial range. However, with initial vortex lattices,\nthe energy spectrum follows Vinen scaling ($k^{-1}$) at transient iterations.\nFor cases with high rotating frequencies, Kolmogorov-like scaling emerges at\nlonger durations. We observe positive kinetic energy fluxes with both initial\nstates across all final frequencies, indicating a forward cascade of\nincompressible and compressible kinetic energy.",
        "positive": "Ferromagnetism of cold fermions loaded into a decorated square lattice: We investigate two-component ultracold fermions loaded into a decorated\nsquare lattice, which are described by the Hubbard model with repulsive\ninteractions and nearest neighbor hoppings. By combining the real-space\ndynamical mean-field theory with the numerical renormalization group method, we\ndiscuss how a ferromagnetically ordered ground state in the weak coupling\nregime, which originates from the existence of a dispersionless band, is\nadiabatically connected to a Heisenberg ferrimagnetic state in the strong\ncoupling limit. The effects of level splitting and hopping imbalance are also\naddressed."
    },
    {
        "anchor": "Magnetic Monopole Noise: Magnetic monopoles are hypothetical elementary particles exhibiting quantized\nmagnetic charge $m_0=\\pm(h/\\mu_0e)$ and quantized magnetic flux $\\Phi_0=\\pm\nh/e$. A classic proposal for detecting such magnetic charges is to measure the\nquantized jump in magnetic flux $\\Phi$ threading the loop of a superconducting\nquantum interference device (SQUID) when a monopole passes through it.\nNaturally, with the theoretical discovery that a plasma of emergent magnetic\ncharges should exist in several lanthanide-pyrochlore magnetic insulators,\nincluding Dy$_2$Ti$_2$O$_7$, this SQUID technique was proposed for their direct\ndetection. Experimentally, this has proven extremely challenging because of the\nhigh number density, and the generation-recombination (GR) fluctuations, of the\nmonopole plasma. Recently, however, theoretical advances have allowed the\nspectral density of magnetic-flux noise $S_{\\Phi}(\\omega,T)$ due to GR\nfluctuations of $\\pm m_*$ magnetic charge pairs to be determined. These\ntheories present a sequence of strikingly clear predictions for the\nmagnetic-flux noise signature of emergent magnetic monopoles. Here we report\ndevelopment of a high-sensitivity, SQUID based flux-noise spectrometer, and\nconsequent measurements of the frequency and temperature dependence of\n$S_{\\Phi}(\\omega,T)$ for Dy$_2$Ti$_2$O$_7$ samples. Virtually all the elements\nof $S_{\\Phi}(\\omega,T)$ predicted for a magnetic monopole plasma, including the\nexistence of intense magnetization noise and its characteristic frequency and\ntemperature dependence, are detected directly. Moreover, comparisons of\nsimulated and measured correlation functions $C_{\\Phi}(t)$ of the magnetic-flux\nnoise $\\Phi(t)$ imply that the motion of magnetic charges is strongly\ncorrelated because traversal of the same trajectory by two magnetic charges of\nsame sign is forbidden.",
        "positive": "Renormalization of the BCS-BEC crossover by order parameter fluctuations: We use the functional renormalization group approach with partial\nbosonization in the particle-particle channel to study the effect of order\nparameter fluctuations on the BCS-BEC crossover of superfluid fermions in three\ndimensions. Our approach is based on a new truncation of the vertex expansion\nwhere the renormalization group flow of bosonic two-point functions is closed\nby means of Dyson-Schwinger equations and the superfluid order parameter is\nrelated to the single particle gap via a Ward identity. We explicitly calculate\nthe chemical potential, the single-particle gap, and the superfluid order\nparameter at the unitary point and compare our results with experiments and\nprevious calculations."
    },
    {
        "anchor": "Chiral currents in Bose-Einstein condensates subject to current-density\n  interactions: Persistent currents in quasi-one-dimensional Bose-Einstein condensates become\nchiral in the presence of current-density interactions. This phenomenon is\nexplored in ultracold atoms loaded in a rotating ring geometry, where diverse\ncurrent-carrying stationary states are analytically found to generalize\npreviously known solutions to the mean-field equations of motion. Their\ndynamical stability is tested by numerical simulations that show stable\ncurrents for states with both constant and modulated density profiles, while\ndecaying currents appear only beyond a unidirectional velocity threshold.\nRecent experiments in the field make these states within experimental reach.",
        "positive": "Modeling the transport of interacting matter-waves in disorder by a\n  non-linear diffusion equation: We model the expansion of an interacting atomic Bose-Einstein condensate in a\ndisordered lattice with a nonlinear diffusion equation normally used for a\nvariety of classical systems. We find approximate solutions of the diffusion\nequation that well reproduce the experimental observations for both short and\nasymptotic expansion times. Our study establishes a connection between the\npeculiar shape of the expanding density profiles and the microscopic nonlinear\ndiffusion coefficients."
    },
    {
        "anchor": "Gauge transformations and Galilean covariance in nonlinear gauge-coupled\n  quantum fluids: We investigate certain invariance properties of quantum fluids subject to a\nnonlinear gauge potential. In particular, we derive the covariant\ntransformation laws for the nonlinear potentials under a space-time Galilean\nboost and consider U(1) gauge transformations. We find that the hydrodynamic\ncanonical field equations are form-invariant in the case of external gauge\nfunctions, but not for nonlinear gauge functionals. Hence, nonlinear gauge\npotentials are non-trivial potentials which may not be \"gauged-away\". Notably,\nfor a 1D superfluid, attempting to do so generates the gauge-pressure of the\nfluid in the Hamiltonian density. Further, we investigate how the field\nequations transform under arbitrary Galilean transformations. We find that the\nimmediate lack of Galilean covariance is restored under a suitably chosen\ntransformation rule set for the potentials, which is identical in form to that\nof a Schr\\\"odinger particle coupled to external scalar and vector potentials.",
        "positive": "Time-dependent self-trapping of Bose-Einstein Condensates in a\n  double-well potential: Based on the mean-field approximation and the phase space analysis, we\ndiscuss the dynamics of Bose-Einstein condensates in a double-well potential.\nBy applying a periodic modulation to the coupling between the condensates, we\nfind the condensates can be trapped in the time-dependent eigenstates of the\neffective Hamiltonian, we refer to this effect as time-dependent self-trapping\nof BECs. A comparison of this self-trapping with the adiabatic evolution is\nmade, finding that the adiabatic evolution beyond the traditional(linear)\nadiabatic condition can be achieved in BECs by manipulating the nonlinearity\nand the ratio of the level bias to the coupling constant. The fixed points for\nthe system are calculated and discussed."
    },
    {
        "anchor": "Signatures of the single particle mobility edge in the ground state\n  properties of Tonks-Girardeau and non-interacting Fermi gases in a\n  bichromatic potential: We explore the ground state properties of cold atomic gases, loaded into a\nbichromatic lattice, focusing on the cases of non-interacting fermions and\nhard-core (Tonks-Girardeau) bosons, trapped by the combination of two\npotentials with incommensurate periods. For such systems, two limiting cases\nhave been thoroughly established. In the tight-binding limit, the\nsingle-particle states in the lowest occupied band show a localization\ntransition, as the strength of the second potential is increased above a\ncertain threshold. In the continuous limit, when the tight-binding\napproximation does not hold anymore, a mobility edge is found, whose position\nin energy depends upon the strength of the second potential. Here, we study how\nthe crossover from the discrete to the continuum behavior occurs, and prove\nthat signatures of the localization transition and mobility edge clearly appear\nin the generic many-body properties of the systems. Specifically, we evaluate\nthe momentum distribution, which is a routinely measured quantity in\nexperiments with cold atoms, and demonstrate that, even in the presence of\nstrong boson-boson interactions, the single particle mobility edge can be\nobserved in the ground state properties.",
        "positive": "Existence, stability and nonlinear dynamics of vortices and vortex\n  clusters in anisotropic Bose-Einstein condensates: We study vortex excitations in one-component Bose-Einstein condensates, with\na special emphasis on the role of anisotropic confinement for the existence,\nstability and dynamical properties of vortices and particularly few-vortex\nclusters. Symmetry breaking features are pervasive within this system even in\nits isotropic installment, where cascades of symmetry breaking bifurcations\ngive rise to the multi-vortex clusters, but also within the anisotropic realm\nwhich naturally breaks the rotational symmetry of the multi-vortex states. Our\nfirst main tool for analyzing the system consists of a weakly nonlinear\n(bifurcation) approach which starts from the linear states of the problem and\nexamines their continuation and bifurcation into novel symmetry-broken\nconfigurations in the nonlinear case. This is first done in the isotropic limit\nand the modifications introduced by the anisotropy are subsequently presented.\nThe second main tool concerns the highly nonlinear regime where the vortices\ncan be considered as individual topologically charged \"particles\" which precess\nwithin the parabolic trap and interact with each other, similarly to fluid\nvortices. The conclusions stemming from both the bifurcation and the\ninteracting particle picture are corroborated by numerical computations which\nare also used to bridge the gap between these two opposite-end regimes."
    },
    {
        "anchor": "Interface properties in three-component Bose-Einstein condensates: Interface properties of a three-component Bose-Einstein condensate, in which\ncomponent 3 is sandwiched by components 1 and 2 at the interface, are\ninvestigated. It is shown that component 3 can serve as a surfactant: the net\ninterfacial tension is reduced by the presence of component 3. We calculate the\ninterfacial tension as a function of the interaction coefficients. The\nstability of the interface is studied by Bogoliubov analysis. When the\ninterfacial tension has a spatial gradient, interfacial flow is induced, which\nresembles the Marangoni flow.",
        "positive": "Ground-state pressure of quasi-2D Fermi and Bose gases: Using an ultracold gas of atoms, we have realized a quasi-two-dimensional\nFermi system with widely tunable s-wave interactions nearly in a ground state.\nPressure and density are measured. The experiment covers physically different\nregimes: weakly and strongly attractive Fermi gases and a Bose gas of tightly\nbound pairs of fermions. In the Fermi regime of weak interactions, the pressure\nis systematically above a Fermi-liquid-theory prediction, maybe due to\nmesoscopic effects. In the opposite Bose regime, the pressure agrees with a\nbosonic mean-field scaling in a range beyond simplest expectations. In the\nstrongly interacting regime, measurements disagree with a purely 2D model.\nReported data may serve for sensitive testing of theoretical methods applicable\nacross different quantum physics disciplines."
    },
    {
        "anchor": "Nonequilibrium Transport in a Superfluid Josephson Junction Chain: Is\n  There Negative Differential Conductivity?: We consider the far-from-equilibrium quantum transport dynamics in a 1D\nJosephson junction chain of multi-mode Bose-Einstein condensates. We develop a\ntheoretical model to examine the experiment of R. Labouvie et al. [Phys. Rev.\nLett. 115, 050601 (2015)], wherein the phenomenon of negative differential\nconductivity (NDC) was reported in the refilling dynamics of an initially\ndepleted site within the chain. We demonstrate that a unitary c-field\ndescription can quantitatively reproduce the experimental results over the full\nrange of tunnel couplings, and requires no fitted parameters. With a view\ntowards atomtronic implementations, we further demonstrate that the filling is\nstrongly dependent on spatial phase variations stemming from quantum\nfluctuations. Our findings suggest that the interpretation of the device in\nterms of NDC is invalid outside of the weak coupling regime. Within this\nrestricted regime, the device exhibits a hybrid behaviour of NDC and the AC\nJosephson effect. A simplified circuit model of the device will require an\napproach tailored to atomtronics that incorporates quantum fluctuations.",
        "positive": "Observation of Solitonic Vortices in Bose-Einstein Condensates: We observe solitonic vortices in an atomic Bose-Einstein condensate after\nfree expansion. Clear signatures of the nature of such defects are the twisted\nplanar density depletion around the vortex line, observed in absorption images,\nand the double dislocation in the interference pattern obtained through\nhomodyne techniques. Both methods allow us to determine the sign of the\nquantized circulation. Experimental observations agree with numerical\nsimulations. These solitonic vortices are the decay product of phase defects of\nthe BEC order parameter spontaneously created after a rapid quench across the\nBEC transition in a cigar-shaped harmonic trap and are shown to have a very\nlong lifetime."
    },
    {
        "anchor": "Type-II Weyl Points in Three-Dimensional Cold Atom Optical Lattices: Topological Lifshitz phase transition characterizes an abrupt change of the\ntopology of the Fermi surface through a continuous deformation of parameters.\nRecently, Lifshitz transition has been predicted to separate two types of Weyl\npoints: type-I and type-II (or called structured Weyl points), which has\nattracted considerable attention in various fields. Although recent\nexperimental investigation has seen a rapid progress on type-II Weyl points, it\nstill remains a significant challenge to observe their characteristic Lifshitz\ntransition. Here, we propose a scheme to realize both type-I and type-II Weyl\npoints in three-dimensional ultracold atomic gases by introducing an\nexperimentally feasible configuration based on current spin-orbit coupling\ntechnology. In the resultant Hamiltonian, we find three degenerate points: two\nWeyl points carrying a Chern number $-1$ and a four-fold degenerate point\ncarrying a Chern number $2$. Remarkably, by continuous tuning of a convenient\nexperimental knob, all these degenerate points can transition from type-I to\ntype-II, thereby providing an ideal platform to study different types of Weyl\npoints and directly probe their Lifshitz phase transition.",
        "positive": "Non-equilibrium time evolution and rephasing in the quantum sine-Gordon\n  model: We discuss the non-equilibrium time evolution of the phase field in the\nsine-Gordon model using two very different approaches: the truncated Wigner\napproximation and the truncated conformal space approach. We demonstrate that\nthe two approaches agree for a period covering the first few oscillations,\nthereby giving a solid theoretical prediction in the framework of sine-Gordon\nmodel, which is thought to describe the dynamics of two bosonic condensates in\nquasi-one-dimensional traps coupled via a Josephson tunneling term. We\nconclude, however, that the recently observed phase-locking behavior cannot be\nexplained in terms of homogeneous sine-Gordon dynamics, which hints at the role\nof other degrees of freedom or inhomogeneity in the experimental system."
    },
    {
        "anchor": "Asymptotically exact trial wave functions for yrast states of rotating\n  Bose gases: We revisit the composite fermion (CF) construction of the lowest angular\nmomentum yrast states of rotating Bose gases with weak short range interaction.\nFor angular momenta at and below the single vortex, $L \\leq N$, the overlaps\nbetween these trial wave functions and the corresponding exact solutions {\\it\nincrease} with increasing system size and appear to approach unity in the\nthermodynamic limit. In the special case $L=N$, this remarkable behaviour was\npreviously observed numerically. Here we present methods to address this point\nanalytically, and find strongly suggestive evidence in favour of similar\nbehaviour for all $L \\leq N$. While not constituting a fully conclusive proof\nof the converging overlaps, our results do demonstrate a striking similarity\nbetween the analytic structure of the exact ground state wave functions at $L\n\\leq N$, and that of their CF counterparts. Results are given for two different\nprojection methods commonly used in the CF approach.",
        "positive": "Behavior of the anomalous correlation function in uniform 2D Bose gas: We investigate the behavior of the anomalous correlation function in two\ndimensional Bose gas. In the local case, we find that this quantity has a\nfinite value in the limit of weak interactions at zero temperature. The effects\nof the anomalous density on some thermodynamic quantities are also considered.\nThese effects can modify in particular the chemical potential, the ground sate\nenergy, the depletion and the superfluid fraction. Our predictions are in good\nagreement with recent analytical and numerical calculations. We show also that\nthe anomalous density presents a significant importance compared to the\nnon-condensed one at zero temperature. The single-particle anomalous\ncorrelation function is expressed in two dimensional homogenous Bose gases by\nusing the density-phase fluctuation. We then confirm that the anomalous average\naccompanies in analogous manner the true condensate at zero temperature while\nit does not exist at finite temperature."
    },
    {
        "anchor": "Ground-state properties of dilute one-dimensional Bose gas with\n  three-body repulsion: We determined perturbatively the low-energy universal thermodynamics of\ndilute one-dimensional bosons with the three-body repulsive forces. The final\nresults are presented for the limit of vanishing potential range in terms of\nthree-particle scattering length. An analogue of Tan`s energy theorem for\nconsidered system is derived in generic case without assuming weakness of the\ninterparticle interaction. We also obtained an exact identity relating the\nthree-body contact to the energy density.",
        "positive": "Griffiths Phase in a Facilitated Rydberg Gas at Low Temperature: The spread of excitations by Rydberg facilitation bears many similarities to\nepidemics. Such systems can be modeled with Monte-Carlo simulations of\nclassical rate equations to great accuracy as a result of high dephasing. In\nthis paper, we analyze the dynamics of a Rydberg many-body system in the\nfacilitation regime in the limits of high and low temperatures. While in the\nhigh-temperature limit a homogeneous mean-field behaviour is recovered,\ncharacteristic effects of heterogeneity can be seen in a frozen gas. At large\ntemperatures the system displays an absorbing-state phase transition and, in\nthe presence of an additional loss channel, self-organized criticality. In a\nfrozen or low-temperature gas, excitations are constrained to a network\nresembling an Erd\\\"os-Renyi graph. We show that the absorbing-state phase\ntransition is replaced with an extended Griffiths phase, which we accurately\ndescribe by a susceptible-infected-susceptible model on the Erd\\\"os-Renyi\nnetwork taking into account Rydberg blockade. Furthermore, we expand upon an\nexisting macroscopic Langevin equation to more accurately describe the density\nof Rydberg atoms in the frozen and finite temperature regimes."
    },
    {
        "anchor": "New opportunites for interactions and control with ultracold lanthanides: Lanthanide atoms have an unusual electron configuration, with a partially\nfilled shell of $f$ orbitals. This leads to a set of characteristic properties\nthat enable enhanced control over ultracold atoms and their interactions: large\nnumbers of optical transitions with widely varying wavelengths and transition\nstrengths, anisotropic interaction properties between atoms and with light, and\na large magnetic moment and spin space present in the ground state. These\nfeatures in turn enable applications ranging from narrow-line laser cooling and\nspin manipulation to evaporative cooling through universal dipolar scattering,\nto the observation of a rotonic dispersion relation, self-bound liquid-like\ndroplets stabilized by quantum fluctuations, and supersolid states. In this\nshort review, we describe how the unusual level structure of lanthanide atoms\nleads to these key features, and provide a brief and necessarily partial\noverview of experimental progress in this rapidly developing field.",
        "positive": "Theory of the Rotating Polaron: Spectrum and Self-Localization: We study a quantum impurity possessing both translational and internal\nrotational degrees of freedom interacting with a bosonic bath. Such a system\ncorresponds to a `rotating polaron', which can be used to model, e.g., a\nrotating molecule immersed in an ultracold Bose gas or superfluid Helium. We\nderive the Hamiltonian of the rotating polaron and study its spectrum in the\nweak- and strong-coupling regimes using a combination of variational,\ndiagrammatic, and mean-field approaches. We reveal how the coupling between\nlinear and angular momenta affects stable quasiparticle states, and demonstrate\nthat internal rotation leads to an enhanced self-localization in the\ntranslational degrees of freedom."
    },
    {
        "anchor": "Feshbach spectroscopy and scattering properties of ultracold Li+Na\n  mixtures: We have observed 26 interspecies Feshbach resonances at fields up to 2050 G\nin ultracold $^6$Li+$^{23}$Na mixtures for different spin-state combinations.\nApplying the asymptotic bound-state model to assign the resonances, we have\nfound that most resonances have d-wave character. This analysis serves as\nguidance for a coupled-channel calculation, which uses modified interaction\npotentials to describe the positions of the Feshbach resonances well within the\nexperimental uncertainty and to calculate their widths. The scattering length\nderived from the improved interaction potentials is experimentally confirmed\nand deviates from previously reported values in sign and magnitude. We give\nprospects for $^7$Li+$^{23}$Na and predict broad Feshbach resonances suitable\nfor tuning.",
        "positive": "Momentum distribution of Cooper-pairs and strong-coupling effects in a\n  two-dimensional Fermi gas near the Berezinskii-Kosterlitz-Thouless transition: We investigate strong-coupling properties of a two-dimensional ultracold\nFermi gas in the normal state. Including pairing fluctuations within the\nframework of a $T$-matrix approximation, we calculate the distribution function\n$n({\\boldsymbol Q})$ of Cooper pairs in terms of the center of mass momentum\n${\\boldsymbol Q}$. In the strong-coupling regime, $n({\\boldsymbol Q}=0)$ is\nshown to exhibit a remarkable increase with decreasing the temperature in the\nlow temperature region, which agrees well with the recent experiment on a\ntwo-dimensional $^6$Li Fermi gas [M. G. Ries, {\\it et. al.}, Phys. Rev. Lett.\n{\\bf 114}, 230401 (2015)]. Our result indicates that the observed remarkable\nincrease of the number of Cooper pairs with zero center of mass momentum can be\nexplained without assuming the Berezinskii-Kosterlitz-Thouless (BKT)\ntransition, when one properly includes pairing fluctuations that are enhanced\nby the low-dimensionality of the system. Since the BKT transition is a crucial\ntopic in two-dimensional Fermi systems, our results would be useful for the\nstudy toward the realization of this quasi-long-range order in an ultracold\nFermi gas."
    },
    {
        "anchor": "Non-equilibrium and local detection of the normal fraction of a trapped\n  two-dimensional Bose gas: We propose a method to measure the normal fraction of a two-dimensional Bose\ngas, a quantity that generally differs from the non-condensed fraction. The\nidea is based on applying a spatially oscillating artificial gauge field to the\natoms. The response of the atoms to the gauge field can be read out either\nmechanically from the deposited energy into the cloud, or optically from the\nmacroscopic optical properties of the atomic gas. The local nature of the\nproposed scheme allows one to reconstruct the spatial profile of the superfluid\ncomponent; furthermore, the proposed method does not require having established\nthermal equilibrium in the gas in the presence of the gauge field. The\ntheoretical description of the system is based on a generalization of the\nDum-Olshanii theory of artificial gauge fields to the interacting many-body\ncontext. The efficiency of the proposed measurement scheme is assessed by means\nof classical field numerical simulations. An explicit atomic level scheme\nminimizing disturbing effects such as spontaneous emission and light-shifts is\nproposed for Rb 87 atoms.",
        "positive": "Ferromagnetic phase in the polarized two-species bosonic Hubbard Model: We recently studied a doped two-dimensional bosonic Hubbard model with two\nhard-core species, with different masses, using quantum Monte Carlo simulations\n[Phys. Rev. B 88, 161101(R) (2013)]. Upon doping away from half-filling, we\nfind several distinct phases, including a phase-separated ferromagnet with Mott\nbehavior for the heavy species and both Mott insulating and superfluid\nbehaviors for the light species. Introducing polarization, an imbalance in the\npopulation between species, we find a fully phase-separated ferromagnet. This\nphase exists for a broad range of temperatures and polarizations. By using\nfinite size scaling of the susceptibility, we find a critical exponent which is\nconsistent with the two-dimensional Ising universality class. Significantly,\nsince the global entropy of this phase is higher than that of the ferromagnetic\nphase with single species, its experimental observation in cold atoms may be\nfeasible."
    },
    {
        "anchor": "Ultracold atoms in a square lattice with spin-orbit coupling: Charge\n  order, superfluidity, and topological signatures: We present an $\\textit{ab initio}$, numerically exact study of attractive\nfermions in square lattices with Rashba spin-orbit coupling. The ground state\nof this system is a supersolid, with co-existing charge and superfluid order.\nThe superfluid is composed of both singlet and triplet pairs induced by\nspin-orbit coupling. We perform large-scale calculations using auxiliary-field\nquantum Monte Carlo to provide the first full, quantitative description of the\ncharge, spin, and pairing properties of the system. In addition to\ncharacterizing the exotic physics, our results will serve as essential\nhigh-accuracy benchmarks for the intense theoretical and especially\nexperimental efforts in ultracold atoms to realize and understand an expanding\nvariety of quantum Hall and topological superconductor systems.",
        "positive": "A three-dimensional steerable optical tweezer system for ultracold atoms: We present a three-dimensional steerable optical tweezer system based on two\npairs of acousto-optic deflectors. Radio frequencies used to steer the optical\ntweezers are generated by direct digital synthesis and multiple cross beam\ndipole traps can be produced through rapid frequency toggling and time\naveraging. We demonstrate production of arrays of ultracold atomic clouds in\nboth horizontal and vertical planes and use this as an indicator for the\nthree-dimensional nature of this optical tweezer system."
    },
    {
        "anchor": "Many-body tunneling dynamics of Bose-Einstein condensates and vortex\n  states in two spatial dimensions: In this work, we study the out-of-equilibrium many-body tunneling dynamics of\na Bose-Einstein condensate in a two-dimensional radial double well. We\ninvestigate the impact of interparticle repulsion and compare the influence of\nangular momentum on the many-body tunneling dynamics. Accurate many-body\ndynamics are obtained by solving the full many-body Schr\\\"odinger equation. We\ndemonstrate that macroscopic vortex states of definite total angular momentum\nindeed tunnel and that, even in the regime of weak repulsions, a many-body\ntreatment is necessary to capture the correct tunneling dynamics. As a general\nrule, many-body effects set in at weaker interactions when the tunneling system\ncarries angular momentum.",
        "positive": "Phase coherence in quasicondensate experiments: an ab initio analysis\n  via the stochastic Gross-Pitaevskii equation: We perform an ab initio analysis of the temperature dependence of the phase\ncoherence length of finite temperature, quasi-one-dimensional Bose gases\nmeasured in the experiments of Richard et al. (Phys. Rev. Lett. 91, 010405\n(2003)) and Hugbart et al. (Eur. Phys. J. D 35, 155-163 (2005)), finding very\ngood agreement across the entire observed temperature range\n($0.8<T/T_{\\phi}<28$). Our analysis is based on the one-dimensional stochastic\nGross-Pitaevskii equation, modified to self-consistently account for\ntransverse, quasi-one-dimensional effects, thus making it a valid model in the\nregime $\\mu ~ few \\hbar \\omega_\\perp$. We also numerically implement an\nalternative identification of $T_{\\phi}$, based on direct analysis of the\ndistribution of phases in a stochastic treatment."
    },
    {
        "anchor": "Phase diagram of disordered Bose-Hubbard model based on mean-field and\n  percolation analysis in two dimensions and at fixed $n=1$ filling: We present a phase diagram of Bose-Hubbard model with on-site chemical\npotential disorder at two dimensions within the scope of mean-field theory. The\nphase diagram in the disorder strength ($\\Delta$) and the on-site repulsion\n($U$) for disordered BHM at fixed filling $\\langle{n\\rangle}=1$, show\ninteresting re-entrance of superfluid phase, sandwiched between Bose-glass\nphases, as observed by the previous QMC results. We probe the Bose-glass to\nsuperfluid transition, as a percolation transition, based on the mean-field\nresults at various parts of the phase diagram using both $\\Delta$ and $U$ as\nthe tuning parameter. We argue the robustness of the re-entrant superfluid.",
        "positive": "The role of atomic interactions in cavity-induced continuous time\n  crystals: We consider continuous time-crystalline phases in dissipative many-body\nsystems of atoms in cavities, focusing on the role of short-range interatomic\ninteractions. First, we show that the latter can alter the nature of the time\ncrystal by changing the type of the underlying critical bifurcation. Second, we\ncharacterize the heating mechanism and dynamics resulting from the short-range\ninteractions and demonstrate that they make the time crystal inherently\nmetastable. We argue that this is generic for the broader class of dissipative\ntime crystals in atom-cavity systems whenever the cavity loss rate is\ncomparable to the atomic recoil energy. We observe that such a scenario for\nheating resembles the one proposed for preheating of the early universe, where\nthe oscillating coherent inflation field decays into a cascade of exponentially\ngrowing fluctuations. By extending approaches for dissipative dynamical systems\nto our many-body problem, we obtain analytical predictions for the parameters\ndescribing the phase transition and the heating rate inside the\ntime-crystalline phase. We underpin and extend the analytical predictions of\nthe heating rates with numerical simulations."
    },
    {
        "anchor": "Lattice Unruh effect and world-line entanglement for the XXZ chain: For the XXZ chain, we discuss the relation between a lattice version of Unruh\neffect and the ground-state entanglement on the basis of the corner\nHamiltonian. We find that the lattice Unruh temperature is interpreted as\n$\\beta_\\lambda = 2\\pi/a$ with an effective acceleration $a=\\pi/\\lambda$, where\n$\\lambda$ denotes the anisotropy parameter of the XXZ chain. Using quantum\nMonte Carlo simulation for the corner Hamiltonian at $\\beta_\\lambda$, we\ndemonstrate that world lines of spins surrounding the entangle point provides\nan intuitive understanding the quantum entanglement. We also propose an\nXXZ-chain analogue of the detector for the thermalized entanglement spectrum\nwith use of the angular time evolution defined by the corner Hamiltonian.",
        "positive": "A toolbox for elementary fermions with a dipolar Fermi gas in a 3D\n  optical lattice: There has been growing interest in investigating properties of elementary\nparticles predicted by the standard model. Examples of such studies include\nexploring their low-energy analogs in condensed matter system, where they arise\nas collective states or quasiparticles. Here we show that a toolbox for\nsystematically engineering the emergent elementary fermions, i.e., Dirac, Weyl\nand Majorana fermions, can be built in a single atomic system composed of a\nspinless magnetic dipolar Fermi gas in a 3D optical lattice. The designed\ndirection-dependent dipole-dipole interaction leads to both the basic building\nblock, i.e, in-plane p+ip superfluid pairing instability and the manipulating\ntool, i.e, out-of-plane Peierls instability. It is shown that the Peierls\ninstability provides a natural way of tuning the topological nature of p+ip\nsuperfluids and thus transform the fermion's nature between distinct emergent\nparticles. Our scheme should open up a new thrust towards searching for\nelementary particles through manipulating the topology."
    },
    {
        "anchor": "Local Quench, Majorana Zero Modes, and Disturbance Propagation in the\n  Ising chain: We study the generation and propagation of local perturbations in a quantum\nmany-body spin system. In particular, we study the Ising model in transverse\nfield in the presence of a local field defect at one edge. This system\npossesses a rich phase diagram with different regions characterized by the\npresence of one or two Majorana zero modes. We show that their localized\ncharacter {\\it i}) enables a characterization of the Ising phase transition\nthrough a local-only measurement performed on the edge spin, and {\\it ii})\nstrongly affects the propagation of quasiparticles emitted after the sudden\nremoval of the defect, so that the dynamics of the local magnetization show\nclear deviations from a ballistic behavior in presence of the Majorana\nfermions.",
        "positive": "Mean-field yrast spectrum of a two-component Bose gas in ring geometry:\n  persistent currents at higher angular momentum: We use analytic soliton solutions of a two-component Bose gas in ring\ngeometry to analyze the mean-field yrast spectrum of the system. We find that\nthe spectrum exhibits a surprisingly rich structure as a result of the\ninterplay of interparticle interactions and population imbalance. We discuss\nthe implication of these results in regard to the possibility of persistent\ncurrents at higher angular momenta."
    },
    {
        "anchor": "Scattering of matter wave solitons on localized potentials: We present numerical and analytical results for the reflection and\ntransmission properties of matter wave solitons impinging on localized\nscattering potentials in one spatial dimension. Our mean field analysis\nidentifies regimes where the solitons behave more like waves or more like\nparticles as a result of the interplay between the dispersive wave propagation\nand the attractive interactions between the atoms. For a bright soliton\npropagating together with a dark soliton void in a two-species Bose-Einstein\ncondensate of atoms with repulsive interactions, we find different reflection\nand transmission properties of the dark and the bright components.",
        "positive": "Strongly Correlated Quantum Gas Prepared by Direct Laser Cooling: We create a one-dimensional strongly correlated quantum gas of $^{133}$Cs\natoms with attractive interactions by direct laser cooling in 300~ms. After\ncompressing and cooling the optically trapped atoms to the vibrational ground\nstate along two tightly confined directions, the emergence of a non-Gaussian\ntime-of-flight distribution along the third, weakly confined direction reveals\nthat the system enters a quantum degenerate regime. We observe a strong\nreduction of two- and three-body spatial correlations and infer that the atoms\nare directly cooled into a highly correlated excited metastable state, known as\na super-Tonks-Girardeau gas."
    },
    {
        "anchor": "Quantised supercurrent decay in an annular Bose-Einstein condensate: We study the metastability and decay of multiply-charged superflow in a\nring-shaped atomic Bose-Einstein condensate. Supercurrent corresponding to a\ngiant vortex with topological charge up to q=10 is phase-imprinted optically\nand detected both interferometrically and kinematically. We observe q=3\nsuperflow persisting for up to a minute and clearly resolve a cascade of\nquantised steps in its decay. These stochastic decay events, associated with\nvortex-induced $2 \\pi$ phase slips, correspond to collective jumps of atoms\nbetween discrete q values. We demonstrate the ability to detect quantised\nrotational states with > 99 % fidelity, which allows a detailed quantitative\nstudy of time-resolved phase-slip dynamics. We find that the supercurrent\ndecays rapidly if the superflow speed exceeds a critical velocity in good\nagreement with numerical simulations, and we also observe rare stochastic phase\nslips for superflow speeds below the critical velocity.",
        "positive": "Bose-Einstein condensation of magnons in atomic hydrogen gas: We report on experimental observation of BEC-like behaviour of quantized\nelectron spin waves (magnons) in a dense gas of spin polarized atomic hydrogen.\nThe magnons are trapped and controlled with inhomogeneous magnetic fields, and\ndescribed by a Schr\\\"odinger-like wave equation, in analogy to the BEC\nexperiments with neutral atoms. We have observed the appearance of a sharp\nfeature in the ESR spectrum displaced from the normal spin wave spectrum. We\nbelieve that this observation corresponds to a sudden growth of the ground\nstate population of the magnons and emergence of their spontaneous coherence\nfor hydrogen gas densities exceeding a critical value, dependent on the\ntrapping potential. We interpret the results as a BEC of non-equilibrium\nmagnons which were formed by applying the rf power."
    },
    {
        "anchor": "Tan's contact in a cigar-shaped dilute Bose gas: We compute the Tan's contact of a weakly interacting Bose gas at zero\ntemperature in a cigar-shaped configuration. Using an effective one-dimensional\nGross-Pitaeskii equation and Bogoliubov theory, we derive an analytical formula\nthat interpolates between the three-dimensional and the one-dimensional\nmean-field regimes. In the strictly one-dimensional limit, we compare our\nresults with Lieb-Liniger theory. Our study can be a guide for actual\nexperiments interested in the study of Tan's contact in the dimensional\ncrossover.",
        "positive": "Squeezing oscillations in a multimode bosonic Josephson junction: Quantum simulators built from ultracold atoms promise to study quantum\nphenomena in interacting many-body systems. However, it remains a challenge to\nexperimentally prepare strongly correlated continuous systems such that the\nproperties are dominated by quantum fluctuations. Here, we show how to enhance\nthe quantum correlations in a one-dimensional multimode bosonic Josephson\njunction, which is a quantum simulator of the sine-Gordon field theory. Our\napproach is based on the ability to track the non-equilibrium dynamics of\nquantum properties. After creating a bosonic Josephson junction at the stable\nfixed point of the classical phase space, we observe squeezing oscillations in\nthe two conjugate variables. We show that the squeezing oscillation frequency\ncan be tuned by more than one order of magnitude, and we are able to achieve a\nspin squeezing close to 10 dB by utilising these oscillatory dynamics. The\nimpact of improved spin squeezing is directly revealed by detecting enhanced\nspatial phase correlations between decoupled condensates. Our work provides new\nways for engineering correlations and entanglement in the external degree of\nfreedom of interacting many-body systems."
    },
    {
        "anchor": "Dynamics and universality in noise driven dissipative systems: We investigate the dynamical properties of low dimensional systems, driven by\nexternal noise sources. Specifically we consider a resistively shunted\nJosephson junction and a one dimensional quantum liquid in a commensurate\nlattice potential, subject to $1/f$ noise. In absence of nonlinear coupling, we\nhave shown previously that these systems establish a non-equilibrium critical\nsteady state [Nature Phys. 6, 806 (2010)]. Here we use this state as the basis\nfor a controlled renormalization group analysis using the Keldysh path integral\nformulation to treat the non linearities: the Josephson coupling and the\ncommensurate lattice.\n  The analysis to first order in the coupling constant indicates transitions\nbetween superconducting and localized regimes that are smoothly connected to\nthe respective equilibrium transitions. However at second order, the back\naction of the mode coupling on the critical state leads to renormalization of\ndissipation and emergence of an effective temperature. In the Josephson\njunction the temperature is parametrically small allowing to observe a\nuniversal crossover between the superconducting and insulating regimes. The IV\ncharacteristics of the junction displays algebraic behavior controlled by the\nunderlying critical state over a wide range. In the noisy one dimensional\nliquid the generated dissipation and effective temperature are not small as in\nthe junction. We find a crossover between a quasi-localized regime dominated by\ndissipation and another dominated by temperature. However since in the thermal\nregime the thermalization rate is parametrically small, signatures of the\nnon-equilibrium critical state can be seen in transient dynamics.",
        "positive": "Quantum Hall states for $\u03b1= 1/3$ in optical lattices: We examine the quantum Hall (QH) states of the optical lattices with square\ngeometry using Bose-Hubbard model (BHM) in presence of artificial gauge field.\nIn particular, we focus on the QH states for the flux value of $\\alpha = 1/3$.\nFor this, we use cluster Gutzwiller mean-field (CGMF) theory with cluster sizes\nof $3\\times 2$ and $3\\times 3$. We obtain QH states at fillings $\\nu = 1/2, 1,\n3/2, 2, 5/2$ with the cluster size $3\\times 2$ and $\\nu = 1/3, 2/3, 1, 4/3,\n5/3, 2, 7/3, 8/3$ with $3\\times 3$ cluster. Our results show that the geometry\nof the QH states are sensitive to the cluster sizes. For all the values of\n$\\nu$, the competing superfluid (SF) state is the ground state and QH state is\nthe metastable state."
    },
    {
        "anchor": "Dynamic Structure Factor of Normal Fermi Gas from Collisionless to\n  Hydrodynamic Regime: The dynamic structure factor of a normal Fermi gas is investigated by using\nthe moment method for the Boltzmann equation. We determine the spectral\nfunction at finite temperatures over the full range of crossover from the\ncollisionless regime to the hydrodynamic regime. We find that the Brillouin\npeak in the dynamic structure factor exhibits a smooth crossover from zero to\nfirst sound as functions of temperature and interaction strength. The dynamic\nstructure factor obtained using the moment method also exhibits a definite\nRayleigh peak ($/omega /sim 0$), which is a characteristic of the hydrodynamic\nregime. We compare the dynamic structure factor obtained by the moment method\nwith that obtained from the hydrodynamic equations.",
        "positive": "Vortex conveyor belt for matter-wave coherent splitting and\n  interferometry: We numerically study a matter wave interferometer realized by splitting a\ntrapped Bose-Einstein condensate with phase imprinting. We show that a simple\nstep-like imprinting pattern rapidly decays into a string of vortices that can\ngenerate opposite velocities on the two halves of the condensate. We first\nstudy in detail the splitting and launching effect of these vortex structures,\nwhose functioning resembles the one of a conveyor belt, and we show that the\ninitial exit velocity along the vortex conveyor belt can be controlled\ncontinuously by adjusting the vortex distance. We finally characterize the\ncomplete interferometric sequence, demonstrating how the phase of the resulting\ninterference fringe can be used to measure an external acceleration. The\nproposed scheme has the potential to be developed into compact and high\nprecision accelerometers."
    },
    {
        "anchor": "Bose-Einstein condensates in an atom-optomechanical system with\n  effective global non-uniform interaction: We consider a hybrid atom-optomechanical system consisting of a mechanical\nmembrane inside an optical cavity and an atomic Bose-Einstein condensate\noutside the cavity. The condensate is confined in an optical lattice potential\nformed by a traveling laser beam reflected off one cavity mirror. We derive the\ncavity-mediated effective atom-atom interaction potential, and find that it is\nnon-uniform, site-dependent, and does not decay as the interatomic distance\nincreases. We show that the presence of this effective interaction breaks the\nZ$_2$ symmetry of the system and gives rise to new quantum phases and phase\ntransitions. When the long-range interaction dominates, the condensate breaks\nthe translation symmetry and turns into a novel self-organized lattice-like\nstate with increasing particle densities for sites farther away from the\ncavity. We present the phase diagram of the system, and investigate the\nstabilities of different phases by calculating their respective excitation\nspectra. The system can serve as a platform to explore various self-organized\nphenomena induced by the long-range interactions.",
        "positive": "Experimental generation of phase wraps for subwavelength phase\n  structures in Bose-Einstein condensate with two-dimensional optical lattice: We report an experimental demonstration of engineering phase wraps for\nsub-wavelength structure in a Bose-Einstein condensate (BEC) with\ntwo-dimensional optical lattices. A short lattice pulse is applied on BEC\nworking in the Kapitza-Dirac (or Raman-Nath) regime, which corresponds to phase\nmodulation imprint on matter wave. When the phase modulation on matter wave is\nlarger than $2\\pi$ in a lattice cell, there appears phase wraps with multiple\n$2\\pi$ jumps, generating the sub-wavelength phase structure. The phase wraps\nfor sub-wavelength structure are measured in momentum space via the\ntime-of-flight absorption image, which corresponds to converting phase\ninformation into amplitude. %Two different kinds of two-dimensional optical\nlattice are studied, which show the different subwavelength phase structure.\nMoreover, we identify an additional condition for the validity of Kapitza-Dirac\nregime, which relies crucially on the lattice configurations. This scheme can\nbe used for studying the property of optical lattices and topological defects\nin matter wave."
    },
    {
        "anchor": "Signature of Chaos and Delocalization in a Periodically Driven Many Body\n  System : An Out-of-Time-Order Correlation Study: We study out-of-time-order correlation (OTOC) for one-dimensional\nperiodically driven hardcore bosons in the presence of Aubry-Andr\\'e (AA)\npotential and show that both the spectral properties and the saturation values\nof OTOC in the steady state of these driven systems provide a clear distinction\nbetween the localized and delocalized phases of these models. Our results,\nobtained via exact numerical diagonalization of these boson chains, thus\nindicate that OTOC can provide a signature of drive induced delocalization even\nfor systems which do not have a well defined semiclassical (and/or large N)\nlimit. We demonstrate the presence of such signature by analyzing two different\ndrive protocols for hardcore bosons chains leading to distinct physical\nphenomena and discuss experiments which can test our theory.",
        "positive": "Dynamics in multiple-well Bose-Einstein condensates: We study the dynamics of three-dimensional weakly linked Bose-Einstein\ncondensates using a multimode model with an effective interaction parameter.\nThe system is confined by a ring-shaped four-well trapping potential. By\nconstructing a two-mode Hamiltonian in a reduced highly symmetric phase space,\nwe examine the periodic orbits and calculate their time periods both in the\nself-trapping and Josephson regimes. The dynamics in the vicinity of the\nreduced phase space is investigated by means of a Floquet multiplier analysis,\nfinding regions of different linear stability and analyzing their implications\non the exact dynamics. The numerical exploration in an extended region of the\nphase space demonstrates that two-mode tools can also be useful for performing\na partition of the space in different regimes. Comparisons with\nGross-Pitaevskii simulations confirm these findings and emphasize the\nimportance of properly determining the effective on-site interaction parameter\ngoverning the multimode dynamics."
    },
    {
        "anchor": "Exactly solvable Gross-Pitaevskii type equations: TWe suggest a method to construct exactly solvable Gross-Pitaevskii type\nequations, especially the variable-coefficient high-order Gross-Pitaevskii type\nequations. We show that there exists a relation between the Gross-Pitaevskii\ntype equations. The Gross-Pitaevskii equations connected by the relation form a\nfamily. In the family one only needs to solve one equation and other equations\nin the family can be solved by a transform. That is, one can construct a series\nof exactly solvable Gross-Pitaevskii type equations from one exactly solvable\nGross-Pitaevskii type equation. As examples, we consider the family of some\nspecial Gross-Pitaevskii type equations: the nonlinear Schr\\\"odinger equation,\nthe quintic Gross-Pitaevskii equation, and cubic-quintic Gross-Pitaevskii\nequation. We also construct the family of a kind of generalized\nGross-Pitaevskii type equation.",
        "positive": "Density-wave ordering in a unitary Fermi gas with photon-mediated\n  interactions: A density wave (DW) is a fundamental type of long-range order in quantum\nmatter tied to self-organization into a crystalline structure. The interplay of\nDW order with superfluidity can lead to complex scenarios that pose a great\nchallenge to theoretical analysis. In the last decades, tunable quantum Fermi\ngases have served as model systems for exploring the physics of strongly\ninteracting fermions, including most notably magnetic ordering, pairing and\nsuperfluidity, and the crossover from a Bardeen-Cooper-Schrieffer (BCS)\nsuperfluid to a Bose-Einstein condensate (BEC). Here, we realize a Fermi gas\nfeaturing both strong, tunable contact interactions and photon-mediated,\nspatially structured long-range interactions in a transversely driven\nhigh-finesse optical cavity. Above a critical long-range interaction strength\nDW order is stabilized in the system, which we identify via its superradiant\nlight scattering properties. We quantitatively measure the variation of the\nonset of DW order as the contact interaction is varied across the BCS-BEC\ncrossover, in qualitative agreement with a mean-field theory. The atomic DW\nsusceptibility varies over an order of magnitude upon tuning the strength and\nthe sign of the long-range interactions below the self-ordering threshold,\ndemonstrating independent and simultaneous control over the contact and\nlong-range interactions. Therefore, our experimental setup provides a fully\ntunable and microscopically controllable platform for the experimental study of\nthe interplay of superfluidity and DW order."
    },
    {
        "anchor": "Dressed, noise- or disorder- resilient optical lattices: External noise is inherent in any quantum system, and can have especially\nstrong effects for systems exhibiting sensitive many-body phenomena. We show\nhow a dressed lattice scheme can provide control over certain types of noise\nfor atomic quantum gases in the lowest band of an optical lattice, removing the\neffects of lattice amplitude noise to first order for particular choices of the\ndressing field parameters. We investigate the non-equilibrium many-body\ndynamics for bosons and fermions induced by noise away from this parameter\nregime, and also show how the same technique can be used to reduce spatial\ndisorder in projected lattice potentials.",
        "positive": "Overflow of a dipolar exciton trap at high magnetic fields: We study laterally trapped dipolar exciton ensembles in coupled GaAs quantum\nwells at high magnetic fields in the Faraday configuration. In\nphotoluminescence experiments, we identify three magnetic field regimes. At low\nfields, the exciton density is increased by a reduced charge carrier escape\nfrom the trap, and additionally, the excitons' emission energy is corrected by\na positive diamagnetic shift. At intermediate fields, magnetic field dependent\ncorrection terms apply which follow the characteristics of a neutral\nmagnetoexciton. Due to a combined effect of an increasing binding energy and\nlifetime, the exciton density is roughly doubled from zero to about seven\nTesla. At the latter high field value, the charge carriers occupy only the\nlowest Landau level. In this situation, the exciton trap can overflow\nindependently from the electrostatic depth of the trapping potential, and the\nenergy shift of the excitons caused by the so-called quantum confined Stark\neffect is effectively compensated. Instead, the exciton energetics seem to be\ndriven by the magnetic field dependent renormalization of the many-body\ninteraction terms. In this regime, the impact of parasitic in-plane fields at\nthe edge of trapping potential is eliminated."
    },
    {
        "anchor": "Bound impurities in a one-dimensional Bose lattice gas: low-energy\n  properties and quench-induced dynamics: We study two mobile bosonic impurities immersed in a one-dimensional optical\nlattice and interacting with a bosonic bath. We employ the exact\ndiagonalization method for small periodic lattices to study stationary\nproperties and dynamics. We consider the branch of repulsive interactions that\ninduce the formation of bound impurities, akin to the bipolaron problem. A\ncomprehensive study of ground-state and low-energy properties is presented,\nincluding the characterization of the critical strength for the formation of\nbound impurities. We also study the dynamics induced after an\ninteraction-quench to examine the stability of the bound impurities. We reveal\nthat after large interaction quenches from strong to weak interactions the\nsystem can show large oscillations over time with revivals of the dimer states.\nWe find that the oscillations are driven by selected eigenstates with\nphase-separated configurations.",
        "positive": "New States of Matter Suggested by New Topological Structures: We extend the well-known Borromean and Brunnian rings to new higher order\nversions. Then we suggest an extension of the connection between Efimov states\nin cold gases and Borromean and Brunnian rings to these new higher order links.\nThis gives rise to a whole new hierarchy of possible states with Efimov states\nat the bottom."
    },
    {
        "anchor": "Topological semimetal and superfluid of s-wave interacting fermionic\n  atoms in an orbital optical lattice: Recent advanced experimental implementations of optical lattices with highly\ntunable geometry open up new regimes for quantum many-body states of matter\nthat previously had not been accessible. Here we introduce a symmetry-based\nmethod of utilizing the geometry of optical lattice to systematically control\ntopologically non-trivial orbital hybridization. Such an orbital mixing leads\nto an unexpected and yet robust topological semimetal at single-particle level\nfor a gas of fermionic atoms. When considering s-wave attractive interaction\nbetween atoms as for instance tuned by Feshbach resonance, topological\nsuperfluid state with high Chern number is unveiled in the presence of on-site\nrotation. This state supports chiral edge excitations, manifesting its\ntopological nature. An experimental realization scheme is designed, which\nintroduces a systematic way of achieving a new universality class (such as\nChern number of 2) of orbital-hybridized topological phases beyond\ngeometrically standard optical lattices.",
        "positive": "Many Body Approach for Quartet Condensation in Strong Coupling: The theory for condensation of higher fermionic clusters is developed. Fully\nselfconsistent nonlinear equations for the quartet order parameter in strongly\ncoupled fermionic systems are established and solved. The breakdown of the\nquasiparticle picture is pointed out. Derivation of numerically tractable\napproximation is described. The momentum projected factorisation ansatz of Ref.\n\\cite{slr09} for the order parameter is employed again. As a definite example\nthe condensation of $\\alpha$ particles in nuclear matter is worked out."
    },
    {
        "anchor": "Comment on \"Creating artificial magnetic fields for cold atoms by\n  photon-assisted tunneling\" by Kolovsky A.R: We comment briefly on the scheme proposed in EPL 93, 20003 (2011) to produce\nsynthetic gauge fields by means of photon-assisted tunneling.",
        "positive": "Study of Efimov physics in two nuclear-spin sublevels of 7Li: Efimov physics in two nuclear-spin sublevels of bosonic lithium is studied\nand it is shown that the positions and widths of recombination minima and\nEfimov resonances are identical for both states within the experimental errors\nwhich indicates that the short-range physics is nuclear-spin independent. We\nalso find that the Efimov features are universally related across Feshbach\nresonances. These results crucially depend on careful mapping between the\nscattering length and the applied magnetic field which we achieve by\ncharacterization of the two broad Feshbach resonances in the different states\nby means of rf-spectroscopy of weakly bound molecules. By fitting the binding\nenergies numerically with a coupled channels calculation we precisely determine\nthe absolute positions of the Feshbach resonances and the values of the singlet\nand triplet scattering lengths."
    },
    {
        "anchor": "dc to ac Josephson transition in a dc atom superconducting quantum\n  interference device: We analyze the effect of the barrier motion on the Bose-Hubbard Hamiltonian\nof a ring-shaped Bose-Einstein condensate interrupted by a pair of Josephson\njunctions, a configuration which is the cold atom analog of the well-known dc\nsuperconducting quantum interference device (SQUID). Such an effect is also\nshown to modify the Heisenberg equation of motion of the boson field operator\nin the two-mode approximation, where a hysteretic contribution that could\naffect the dynamics for accelerated or overlapping barriers is identified. By\nstudying the energy landscape as a function of order and control parameters, we\ndetermine the diagram with the location of the dc and ac Josephson regimes,\nalong with the critical points that are shown to depend on the junctions\nposition. We analyze the dc to ac Josephson transition for adiabatic barrier\ntrajectories that lead to a final uniform velocity, or which perform symmetric\nvelocity paths. We show that such symmetric trajectories may induce, when\nreaching the critical point, highly hysteretic oscillating return paths within\nthe dc regime, similar to the underdamped hysteresis loops arising from the\naction of a resistive flow in the ac regime. We also consider nonequilibrium\ninitial conditions resulting from a finite phase difference on either side of\nthe junctions, along with the critical features of such a parameter. An\nexcellent agreement between the Gross-Pitaevskii simulations and the two-mode\nresults is found in all cases.",
        "positive": "The Snake Instability of Ring Dark Solitons in Toroidally Trapped\n  Bose-Einstein Condensates: We show that the onset of the snake instability of ring dark solitons\nrequires a broken symmetry. We also elucidate explicitly the connection between\nimaginary Bogoliubov modes and the snake instability, predicting the number of\nvortex-anti-vortex pairs produced. In addition, we propose a simple model to\ngive a physical motivation as to why the snake instability takes place.\nFinally, we show that tight confinement in a toroidal potential actually\nenhances soliton decay due to inhibition of soliton motion."
    },
    {
        "anchor": "Theory for Bose-Einstein condensation of light in nano-fabricated\n  semiconductor microcavities: We construct a theory for Bose-Einstein condensation of light in\nnano-fabricated semiconductor microcavities. We model the semiconductor by one\nconduction and one valence band which consist of electrons and holes that\ninteract via a Coulomb interaction. Moreover, we incorporate screening effects\nby using a contact interaction with the scattering length for a Yukawa\npotential and describe in this manner the crossover from exciton gas to\nelectron-hole plasma as we increase the excitation level of the semiconductor.\nWe then show that the dynamics of the light in the microcavities is damped due\nto the coupling to the semiconductor. Furthermore, we demonstrate that on the\nelectron-hole plasma side of the crossover, which is relevant for the\nBose-Einstein condensation of light, this damping can be described by a single\ndimensionless damping parameter that depends on the external pumping.\nHereafter, we propose to probe the superfluidity of light in these\nnano-fabricated semiconductor microcavities by making use of the differences in\nthe response in the normal or superfluid phase to a sudden rotation of the\ntrap. In particular, we determine frequencies and damping of the scissors modes\nthat are excited in this manner. Moreover, we show that a distinct signature of\nthe dynamical Casimir effect can be observed in the density-density\ncorrelations of the excited light fluid.",
        "positive": "Atomic Quantum Simulation of U(N) and SU(N) Non-Abelian Lattice Gauge\n  Theories: Using ultracold alkaline-earth atoms in optical lattices, we construct a\nquantum simulator for U(N) and SU(N) lattice gauge theories with fermionic\nmatter based on quantum link models. These systems share qualitative features\nwith QCD, including chiral symmetry breaking and restoration at non-zero\ntemperature or baryon density. Unlike classical simulations, a quantum\nsimulator does not suffer from sign problems and can address the corresponding\nchiral dynamics in real time."
    },
    {
        "anchor": "On the observability of Pauli crystals: The best known manifestation of the Fermi-Dirac statistics is the Pauli\nexclusion principle: no two identical fermions can occupy the same one-particle\nstate. This principle enforces high order correlations in systems of many\nidentical fermions and is responsible for a particular geometric arrangement of\ntrapped particles even when all mutual interactions are absent [1]. These\ngeometric structures, called Pauli crystals, are predicted for a system of $N$\nidentical atoms trapped in a harmonic potential. They emerge as the most\nfrequent configurations in a collection of single-shot pictures of the system.\nHere we study how fragile Pauli crystals are when realistic experimental\nlimitations are taken into account. The influence of the number of single-shots\npictures available to analysis, thermal fluctuations and finite efficiency of\ndetection are considered. The role of these sources of noise on the possibility\nof experimental observation of Pauli crystals is shown and conditions necessary\nfor the detection of the geometrical arrangements of particles are identified.",
        "positive": "Quantum field simulator for dynamics in curved spacetime: The observed large-scale structure in our Universe is seen as a result of\nquantum fluctuations amplified by spacetime evolution. This, and related\nproblems in cosmology, asks for an understanding of the quantum fields of the\nstandard model and dark matter in curved spacetime. Even the reduced problem of\na scalar quantum field in an explicitly time-dependent spacetime metric is a\ntheoretical challenge and thus a quantum field simulator can lead to new\ninsights. Here, we demonstrate such a quantum field simulator in a\ntwo-dimensional Bose-Einstein condensate with a configurable trap and\nadjustable interaction strength to implement this model system. We explicitly\nshow the realisation of spacetimes with positive and negative spatial curvature\nby wave packet propagation and confirm particle pair production in controlled\npower-law expansion of space. We find quantitative agreement with new\nanalytical predictions for different curvatures in time and space. This\nbenchmarks and thereby establishes a quantum field simulator of a new class. In\nthe future, straightforward upgrades offer the possibility to enter new, so far\nunexplored, regimes that give further insight into relativistic quantum field\ndynamics."
    },
    {
        "anchor": "Vortex dynamics of rotating dipolar Bose-Einstein condensates: We study the influence of dipole-dipole interaction on the formation of\nvortices in a rotating dipolar Bose-Einstein condensate (BEC) of $^{52}$Cr and\n$^{164}$Dy atoms in quasi two-dimensional geometry. By numerically solving the\ncorresponding time-dependent mean-field Gross-Pitaevskii equation, we show that\nthe dipolar interaction enhances the number of vortices while a repulsive\ncontact interaction increases the stability of the vortices. Further, an\nordered vortex lattice of relatively large number of vortices is found in a\nstrongly dipolar BEC.",
        "positive": "Three attractively interacting fermions in a harmonic trap: Exact\n  solution, ferromagnetism, and high-temperature thermodynamics: Three fermions with strongly repulsive interactions in a spherical harmonic\ntrap, constitute the simplest nontrivial system that can exhibit the onset of\nitinerant ferromagnetism. Here, we present exact solutions for three trapped,\nattractively interacting fermions near a Feshbach resonance. We analyze energy\nlevels on the upper branch of the resonance where the atomic interaction is\neffectively repulsive. When the s-wave scattering length a is sufficiently\npositive, three fully polarized fermions are energetically stable against a\nsingle spin-flip, indicating the possibility of itinerant ferromagnetism, as\ninferred in the recent experiment. We also investigate the high-temperature\nthermodynamics of a strongly repulsive or attractive Fermi gas using a quantum\nvirial expansion. The second and third virial coefficients are calculated. The\nresulting equations of state can be tested in future quantitative experimental\nmeasurements at high temperatures and can provide a useful benchmark for\nquantum Monte Carlo simulations."
    },
    {
        "anchor": "The inverse-square interaction phase diagram: unitarity in the bosonic\n  ground state: Ground-state properties of bosons interacting via inverse square potential\n(three dimensional Calogero-Sutherland model) are analyzed. A number of\nquantities scale with the density and can be naturally expressed in units of\nthe Fermi energy and Fermi momentum multiplied by a dimensionless constant\n(Bertsch parameter). Two analytical approaches are developed: the Bogoliubov\ntheory for weak and the harmonic approximation (HA) for strong interactions.\nDiffusion Monte Carlo method is used to obtain the ground-state properties in a\nnon-perturbative manner. We report the dependence of the Bertsch parameter on\nthe interaction strength and construct a Pad\\'e approximant which fits the\nnumerical data and reproduces correctly the asymptotic limits of weak and\nstrong interactions. We find good agreement with beyond-mean field theory for\nthe energy and the condensate fraction. The pair distribution function and the\nstatic structure factor are reported for a number of characteristic\ninteractions. We demonstrate that the system experiences a gas-solid phase\ntransition as a function of the dimensionless interaction strength. A\npeculiarity of the system is that by changing the density it is not possible to\ninduce the phase transition. We show that the low-lying excitation spectrum\ncontains plasmons in both phases, in agreement with the Bogoliubov and HA\ntheories. Finally, we argue that this model can be interpreted as a realization\nof the unitary limit of a Bose system with the advantage that the system stays\nin the genuine ground state contrarily to the metastable state realized in\nexperiments with short-range Bose gases.",
        "positive": "Acoustic radiation from vortex-barrier interaction in atomic\n  Bose-Einstein condensate: We examine the dynamics of a vortex dipole in the Bose-Einstein condensates\n(BECs) of trapped dilute atomic gases at zero temperature in the presence of a\nGaussian barrier potential. The density-anisotropy induced by the barrier\nenhances the acoustic radiation from the vortex dipole. This is due to the\ndeviation of the condensate density from the equipotential curves and variation\nin the curvature of the vortex dipole trajectory. Due to the acoustic\nradiation, the vortex dipole dissipates energy and spirals towards the edge of\nthe condensate. As a result, we observe an increase in the vortex-antivortex\nannihilation events. To examine the effect of the Gaussian barrier, we estimate\nthe correction to the Thomas-Fermi condensate density using perturbation\nexpansion method and the results are in very good agreement with the numerical\nresults."
    },
    {
        "anchor": "Fermi-Fermi crossover in the ground state of 1D few-body systems with\n  anomalous three-body interactions: In one spatial dimension, quantum systems with an attractive three-body\ncontact interaction exhibit a scale anomaly. In this work, we examine the\nfew-body sector for up to six particles. We study those systems with a\nself-consistent, non-perturbative, iterative method, in the subspace of zero\ntotal momentum. Exploiting the structure of the contact interaction, the method\nreduces the complexity of obtaining the wavefunction by three powers of the\ndimension of the Hilbert space. We present results on the energy, and momentum\nand spatial structure, as well as Tan's contact. We find a Fermi-Fermi\ncrossover interpolating between large, weakly bound trimers and compact, deeply\nbound trimers: at weak coupling, the behavior is captured by degenerate\nperturbation theory; at strong coupling, the system is governed by an effective\ntheory of heavy trimers (plus free particles in the case of asymmetric\nsystems). Additionally, we find that there is no trimer-trimer attraction and\ntherefore no six-body bound state.",
        "positive": "Thermalization of field driven quantum systems: There is much interest in how quantum systems thermalize after a sudden\nchange, because unitary evolution should preclude thermalization. The\neigenstate thermalization hypothesis resolves this because all observables for\nquantum states in a small energy window have essentially the same value; it is\nviolated for integrable systems due to the infinite number of conserved\nquantities. Here, we show that when a system is driven by a DC electric field\nthere are five generic behaviors: (i) monotonic or (ii) oscillatory approach to\nan infinite-temperature steady state; (iii) monotonic or (iv) oscillatory\napproach to a nonthermal steady state; or (v) evolution to an oscillatory\nstate. Examining the Hubbard model (which thermalizes under a quench) and the\nFalicov-Kimball model (which does not), we find both exhibit scenarios (i-iv),\nwhile only Hubbard shows scenario (v). This shows richer behavior than in\ninteraction quenches and integrability in the absence of a field plays no role."
    },
    {
        "anchor": "Destabilization effect of exchange dipole-dipole interaction on the\n  spectrum of electric dipolar ultracold Fermi gas: The self-consistent field approach for the electric dipolar ultracold\nspin-1/2 fermions is discussed. Contribution of the exchange part of the\nelectric dipole interaction is found. Hence we obtain a model of dipolar\nfermions beyond the self-consistent field approximation. It is shown that the\nexchange interaction of electric dipolar fermions depends on the\nspin-polarisation of the system. For instance the electric dipole exchange\ninteraction equals to zero for spin-unpolarised systems, namely all low laying\nquantum states occupied by two-particles with opposite spins. In opposite limit\nof the full spin polarisation of the degenerate fermions, then we have one\nparticle in each quantum states, the exchange interaction has maximum value,\nwhich is comparable with the self-consistent field part of the dipole-dipole\ninteraction. The self-consistent part of the electric dipole-dipole interaction\ngives a positive contribution into the spectrum of collective excitations,\nwhile the exchange part of the dipole-dipole interaction leads to a negative\nterm in the spectrum. At angles between the equilibrium polarisation and the\ndirection of wave propagation close to $\\pi/2$ the full dipolar part of the\nspectrum becomes negative. At the electric dipole moment of fermions of order\nof several Debay the dipolar part is large enough to exceed the Fermi pressure,\nthat reveals in an instability.",
        "positive": "Superfluidity of Bose-Einstein condensates in toroidal traps with\n  nonlinear lattices: Superfluid properties of Bose-Einstein condensates (BEC) in toroidal\nquasi-one-dimensional traps are investigated in the presence of periodic\nscattering length modulations along the ring. The existence of several types of\nstable periodic waves, ranging from almost uniform to very fragmented chains of\nweakly interacting and equally spaced solitons, is demonstrated. We show that\nthese waves may support persistent atomic currents and sound waves with spectra\nof Bogoliubov type. Fragmented condensates can be viewed as arrays of Josephson\njunctions and the current as a BEC manifestation of the dc-Josephson effect.\nThe influence of linear defects on BEC superfluidity has been also\ninvestigated. We found that for subcritical velocities, linear defects that are\nstatic with respect to the lattice (while the condensate moves in respect to\nboth the optical lattice and the defect) preserve the BEC superfluidity."
    },
    {
        "anchor": "Anderson localization of Cooper pairs and Majorana fermions in an\n  ultracold atomic Fermi gas with synthetic spin-orbit coupling: We theoretically investigate two-particle and many-particle Anderson\nlocalizations of a spin-orbit coupled ultracold atomic Fermi gas trapped in a\nquasi-periodic potential and subjected to an out-of-plane Zeeman field. We\nsolve exactly the two-particle problem in a finite length system by exact\ndiagonalization and solve approximately the many-particle problem within the\nmean-field Bogoliubov-de Gennes approach. At a small Zeeman field, the\nlocalization properties of the system are similar to that of a Fermi gas with\nconventional $s$-wave interactions. As the disorder strength increases, the\ntwo-particle binding energy increases and the fermionic superfluidity of many\nparticles disappears above a threshold. At a large Zeeman field, where the\ninteratomic interaction behaves effectively like a $p$-wave interaction, the\nbinding energy decreases with increasing disorder strength and the resulting\ntopological superfluidity shows a much more robust stability against disorder\nthan the conventional $s$-wave superfluidity. We also analyze the localization\nproperties of the emergent Majorana fermions in the topological phase. Our\nresults could be experimentally examined in future cold-atom experiments, where\nthe spin-orbit coupling can be induced artificially by using two Raman lasers,\nand the quasi-periodic potential can be created by using bichromatic optical\nlattices.",
        "positive": "Interspecies singlet pairing in a mixture of two spin-1 Bose condensates: We study the ground state properties of a mixture formed by two spin-1\ncondensates in the absence of an external magnetic field. As the collisional\nsymmetry between interspecies bosonic atoms is broken, the interspecies\ncoupling interaction ($\\beta $) and interspecies singlet pairing interaction\n($\\gamma $) arise. The ground state can be calculated using the angular\nmomentum theory analytically for $\\gamma =0$. The full quantum approach of\nexact diagonalization is adopted numerically to consider the more general case\nas $\\gamma \\neq 0$. We illustrate the competition between the two interspecies\ninteractions and find that as singlet pairing interaction dominates (or the\ntotal spin vanishes), there are still different types of singlet formations\nwhich are well determined by $\\beta $."
    },
    {
        "anchor": "Quantized squeezing and even-odd asymmetry of trapped bosons: We investigate the exact nature of the superfluid-to-Mott-insulator crossover\nfor interacting bosons on an optical lattice in a one-dimensional, harmonic\ntrap by high-precision density-matrix renormalization-group calculations. The\nresults reveal an intermediate regime characterized by a cascade of microscopic\nsteps. These arise as a consequence of individual boson \"squeezing\" events and\ndisplay an even-odd alternation dependent on the trap symmetry. We discuss the\nexperimental observation of this behavior, which is generic in an external\ntrapping potential.",
        "positive": "A thermoelectric heat engine with ultracold atoms: Thermoelectric effects, such as the generation of a particle current by a\ntemperature gradient, have their origin in a reversible coupling between heat\nand particle flows. These effects are fundamental probes for materials and have\napplications to cooling and power generation. Here we demonstrate\nthermoelectricity in a fermionic cold atoms channel, ballistic or diffusive,\nconnected to two reservoirs. We show that the magnitude of the effect and the\nefficiency of energy conversion can be optimized by controlling the geometry or\ndisorder strength. Our observations are in quantitative agreement with a\ntheoretical model based on the Landauer-Bu ttiker formalism. Our device\nprovides a controllable model-system to explore mechanisms of energy conversion\nand realizes a cold atom based heat engine."
    },
    {
        "anchor": "Dynamical realization of magnetic states in a strongly interacting Bose\n  mixture: We describe the dynamical preparation of magnetic states in a strongly\ninteracting two-component Bose gas in a harmonic trap. By mapping this system\nto an effective spin chain model, we obtain the dynamical spin densities and\nthe fidelities for a few-body system. We show that the spatial profiles transit\nbetween ferromagnetic and antiferromagnetic states as the intraspecies\ninteraction parameter is slowly increased.",
        "positive": "Simulation of the Laughlin state in an optical lattice: We analyze the proposal of achieving a Mott state of Laughlin wave functions\nin an optical lattice [M. Popp {\\it et al.}, Phys. Rev. A 70, 053612 (2004)]\nand study the consequences of considering the anharmonic corrections to each\nsingle site potential expansion that were not taken into account until now. Our\nresult is that, although the anharmonic correction reduces the maximum\nfrequency at which the system can rotate before the atoms escape from each site\n(centrifugal limit), the Laughlin state can still be achieved for a small\nnumber of particles and a realistic value of the laser intensity."
    },
    {
        "anchor": "Integer Quantum Hall State in Two-Component Bose Gases in a Synthetic\n  Magnetic Field: We study two-component (or pseudospin-1/2) Bose gases in a strong synthetic\nmagnetic field. Using exact diagonalization, we show that a bosonic analogue of\nan integer quantum Hall state with no intrinsic topological order appears at\nthe total filling factor \\nu=1+1 when the strengths of intracomponent and\nintercomponent interactions are comparable with each other. This provides a\nprime example of a symmetry-protected topological phase in a controlled setting\nof quantum gases. The real-space entanglement spectrum of this state is found\nto be comprised of counter-propagating chiral modes consistent with the edge\ntheory derived from the effective Chern-Simons theory.",
        "positive": "Dark-Bright Solitons in a Superfluid Bose-Fermi Mixture: The recent experimental realization of Bose-Fermi superfluid mixtures of\ndilute ultracold atomic gases has opened new perspectives in the study of\nquantum many-body systems. Depending on the values of the scattering lengths\nand the amount of bosons and fermions, a uniform Bose-Fermi mixture is\npredicted to exhibit a fully mixed phase, a fully separated phase or, in\naddition, a purely fermionic phase coexisting with a mixed phase. The\noccurrence of this intermediate configuration has interesting consequences when\nthe system is nonuniform. In this work we theoretically investigate the case of\nsolitonic solutions of coupled Bogoliubov-de Gennes and Gross-Pitaevskii\nequations for the fermionic and bosonic components, respectively. We show that,\nin the partially separated phase, a dark soliton in Fermi superfluid is\naccompanied by a broad bosonic component in the soliton, forming a dark-bright\nsoliton which keeps full spatial coherence."
    },
    {
        "anchor": "Crossover between Kelvin-Helmholtz and counter-superflow instabilities\n  in two-component Bose-Einstein condensates: Dynamical instabilities at the interface between two Bose--Einstein\ncondensates that are moving relative to each other are investigated using\nmean-field and Bogoliubov analyses. Kelvin--Helmholtz instability is dominant\nwhen the interface thickness is much smaller than the wavelength of the\nunstable interface mode, whereas the counter-superflow instability becomes\ndominant in the opposite case. These instabilities emerge not only in an\nimmiscible system but also in a miscible system where an interface is produced\nby external potential. Dynamics caused by these instabilities are numerically\ndemonstrated in rotating trapped condensates.",
        "positive": "Recurrence times of the Lieb-Liniger model in the weak and strong\n  coupling regimes: Quantum systems exhibit recurrence phenomena after equilibration, but it is a\ndifficult task to evaluate the recurrence time of a quantum system because it\ndrastically increases as the system size increases (usually double-exponential\nin the number of particles) and strongly depends on the initial state. Here, we\nanalytically derive the recurrence times of the Lieb-Liniger model with\nrelatively small particle numbers for the weak and strong coupling regimes. It\nturns out that these recurrence times are independent of the initial state and\nincreases only polynomially in the system size."
    },
    {
        "anchor": "Berezinskii-Kosterlitz-Thouless Transition in Two-Dimensional Dipolar\n  Stripes: A two-dimensional quantum system of dipoles, with a polarization angle not\nperpendicular to the plane, shows a transition from a gas to a stripe phase. We\nhave studied the thermal properties of these two phases using the path integral\nMonte Carlo (PIMC) method. By simulating the thermal density matrix, PIMC\nprovides exact results for magnitudes of interest such as the superfluid\nfraction and the one-body density matrix. As it is well known, in two\ndimensions the superfluid-to-normal phase transition follows the\nBerezinskii-Kosterlitz-Thouless (BKT) scenario. Our results show that both the\nanisotropic gas and the stripe phases follow the BKT scaling laws. At fixed\ndensity and increasing the tilting angle, the transition temperature decreases\nin going from the gas to the stripe phase. Superfluidity in the perpendicular\ndirection to the stripes is rather small close to the critical temperature but\nit becomes larger at lower temperatures, mainly close to the transition to the\ngas. Our results are in qualitative agreement with the supersolidity observed\nrecently in a quasi-one-dimensional array of dipolar droplets.",
        "positive": "Point bosons in a one-dimensional box: the ground state, excitations and\n  thermodynamics: We determine the ground-state energy and the effective dispersion law for a\none-dimensional system of point bosons under zero boundary conditions. The\nground-state energy is close to the value for a periodic system. But the\ndispersion law is essentially different from that for a periodic system, if the\ncoupling is weak (weak interaction or high concentration) or intermediate. We\npropose also a new method for construction of the thermodynamics for a gas of\npoint bosons. It turns out that the difference in the dispersion laws of\nsystems with periodic and zero boundary conditions does not lead to a\ndifference in the thermodynamic quantities. In addition, under zero boundary\nconditions, the microscopic sound velocity does not coincide with the\nmacroscopic one. This means that either the method of determination of $k$ in\nthe dispersion law $E(k)$ is unsuitable or the low-energy excitations are not\nphonons."
    },
    {
        "anchor": "Lattice gauge theories simulations in the quantum information era: The many-body problem is ubiquitous in the theoretical description of\nphysical phenomena, ranging from the behavior of elementary particles to the\nphysics of electrons in solids. Most of our understanding of many-body systems\ncomes from analyzing the symmetry properties of Hamiltonian and states: the\nmost striking example are gauge theories such as quantum electrodynamics, where\na local symmetry strongly constrains the microscopic dynamics. The physics of\nsuch gauge theories is relevant for the understanding of a diverse set of\nsystems, including frustrated quantum magnets and the collective dynamics of\nelementary particles within the standard model. In the last few years, several\napproaches have been put forward to tackle the complex dynamics of gauge\ntheories using quantum information concepts. In particular, quantum simulation\nplatforms have been put forward for the realization of synthetic gauge\ntheories, and novel classical simulation algorithms based on quantum\ninformation concepts have been formulated. In this review we present an\nintroduction to these approaches, illustrating the basics concepts and\nhighlighting the connections between apparently very different fields, and\nreport the recent developments in this new thriving field of research.",
        "positive": "Dynamics of a quantum phase transition in the Bose-Hubbard model:\n  Kibble-Zurek mechanism and beyond: In this paper, we study the dynamics of the Bose-Hubbard model by using\ntime-dependent Gutzwiller methods. In particular, we vary the parameters in the\nHamiltonian as a function of time, and investigate the temporal behavior of the\nsystem from the Mott insulator to the superfluid (SF) crossing a second-order\nphase transition. We first solve a time-dependent Schr\\\"odinger equation for\nthe experimental setup recently done by Braun et.al. [Proc. Nat. Acad. Sci.\n112, 3641 (2015)] and show that the numerical and experimental results are in\nfairly good agreement. However, these results disagree with the Kibble-Zurek\nscaling. From our numerical study, we reveal a possible source of the\ndiscrepancy. Next, we calculate the critical exponents of the correlation\nlength and vortex density in addition to the SF order parameter for a\nKibble-Zurek protocol. We show that beside the \"freeze\" time $\\hat{t}$, there\nexists another important time, $t_{\\rm eq}$, at which an oscillating behavior\nof the SF amplitude starts. From calculations of the exponents of the\ncorrelation length and vortex density with respect to a quench time $\\tQ$, we\nobtain a physical picture of a coarsening process. Finally, we study how the\nsystem evolves after the quench. We give a global picture of dynamics of the\nBose-Hubbard model."
    },
    {
        "anchor": "Reply to Comment on \"Quantum Entangled Dark Solitons formed by Ultracold\n  Atoms in Optical Lattices\": We reply to Jacek Dziarmaga, Piotr Deuar, and Krzysztof Sacha's comment,\narXiv:1001.1045, supporting the authors' simulations but differentiating\nbetween near-mean-field and strongly quantum regimes. We clarify that we have\nthree lines of evidence on decay of dark solitons and connect our work to\nLieb's Type-II excitations and the true meaning of a quantum dark soliton.",
        "positive": "Phase separations induced by a trapping potential in one-dimensional\n  fermionic systems as a source of core-shell structures: Ultracold fermionic gases in optical lattices give a great opportunity for\ncreating different types of novel states. One of them is phase separation\ninduced by a trapping potential between different types of superfluid phases.\nThe core-shell structures, occurring in systems with a trapping potential, are\na good example of such separations. The types and the sequences of phases which\nemerge in such structures can depend on spin-imbalance, shape of the trap and\non-site interaction strength. In this work, we investigate the properties of\nsuch structures within an attractive Fermi gas loaded in the optical lattice,\nin the presence of the trapping potential and their relations to the phase\ndiagram of the homogeneous system. Moreover, we show how external and internal\nparameters of the system and parameters of the trap influence their properties.\nIn particular, we show a possible occurrence of the core-shell structure in a\nsystem with a harmonic trap, containing the BCS and FFLO states. Additionally,\nwe find a spatial separation of two superfuild states in the system, one in the\nBCS limit as well as the other one in the tightly bound local pairs (BEC)\nregime."
    },
    {
        "anchor": "Tunable anisotropic superfluidity in an optical kagome superlattice: We study the phase diagram of the Bose-Hubbard model on the kagome lattice\nwith a broken sublattice symmetry. Such a superlattice structure can naturally\nbe created and tuned by changing the potential offset of one sublattice in the\noptical generation of the frustrated lattice. The superstructure gives rise to\na rich quantum phase diagram, which is analyzed by combining Quantum Monte\nCarlo simulations with the Generalized Effective Potential Landau Theory. Mott\nphases with non-integer filling and a characteristic order along stripes are\nfound, which show a transition to a superfluid phase with an anisotropic\nsuperfluid density. Surprisingly, the direction of the superfluid anisotropy is\nchanging between different symmetry directions as a function of the particle\nnumber or the hopping strength. Finally, we discuss characteristic signatures\nof anisotropic phases in time-of-flight absorption measurements.",
        "positive": "Two photon conditional phase gate based on Rydberg slow light polaritons: We analyze the fidelity of a deterministic quantum phase gate for two photons\ncounterpropagating as polaritons through a cloud of Rydberg atoms under the\ncondition of electromagnetically induced transparency (EIT). We provide\nanalytical results for the phase shift of the quantum gate, and provide an\nestimation for all processes leading to a reduction to the gate fidelity.\nEspecially, the influence of losses form the intermediate level, dispersion of\nthe photon wave packet, scattering into additional polariton channels, finite\nlifetime of the Rydberg state, as well as effects of transverse size of the\nwave packets are accounted for. We show that the flatness of the effective\ninteraction, caused by the blockade phenomena, suppresses the corrections due\nto the finite transversal size. This is a strength of Rydberg-EIT setup\ncompared to other approaches. Finally, we provide the experimental requirements\nfor the realization of a high fidelity quantum phase gate using Rydberg\npolaritons."
    },
    {
        "anchor": "Simulating artificial one-dimensional physics with ultra-cold fermionic\n  atoms: three exemplary themes: For over twenty years, ultra-cold atomic systems have formed an almost\nperfect arena for simulating different quantum many-body phenomena and exposing\ntheir non-obvious and very often counterintuitive features. Thanks to extremely\nprecise controllability of different parameters they are able to capture\ndifferent quantum properties which were previously recognized only as\ntheoretical curiosities. Here, we go over the current experimental progress in\nexploring the curious one-dimensional quantum world of fermions from the\nperspective of three subjectively selected trends being currently under\nvigorous experimental validation: (i) unconventional pairing in attractively\ninteracting fermionic mixtures, (ii) fermionic systems subjected to the\nartificial spin-orbit coupling, (iii) fermionic gases of atoms with high SU(N)\nsymmetry of internal states.",
        "positive": "Simulation of gauge transformations on systems of ultracold atoms: We show that gauge transformations can be simulated on systems of ultracold\natoms. We discuss observables that are invariant under these gauge\ntransformations and compute them using a tensor network ansatz that escapes the\nphase problem. We determine that the Mott-insulator-to-superfluid critical\npoint is monotonically shifted as the induced magnetic flux increases. This\nresult is stable against the inclusion of a small amount of entanglement in the\nvariational ansatz."
    },
    {
        "anchor": "Fulde-Ferrell superfluids in spinless ultracold Fermi gases: The Fulde-Ferrell (FF) superfluid phase, in which fermions form\nfinite-momentum Cooper pairings, is well studied in spin-singlet superfluids in\npast decades. Different from previous works that engineer the FF state in\nspinful cold atoms, we show that the FF state can emerge in spinless Fermi\ngases confined in optical lattice associated with nearest-neighbor\ninteractions. The mechanism of the spinless FF state relies on the split Fermi\nsurfaces by tuning the chemistry potential, which naturally gives rise to\nfinite-momentum Cooper pairings. The phase transition is accompanied by changed\nChern numbers, in which, different from the conventional picture, the band gap\ndoes not close. By beyond-mean-field calculations, we find the finite-momentum\npairing is more robust, yielding the system promising for maintaining the FF\nstate at finite temperature. Finally we present the possible realization and\ndetection scheme of the spinless FF state.",
        "positive": "Novel phases in rotating Bose-condensed gas: vortices and quantum\n  correlation: We present the exact diagonalization study of rotating Bose-condensed gas\ninteracting via finite-range Gaussian potential confined in a quasi-2D harmonic\ntrap. The system of many-body Hamiltonian matrix is diagonalized in given\nsubspaces of quantized total angular momentum to obtain the lowest-energy\neigenstate employing the beyond lowest-Landau-level approximation. In the\nco-rotating frame, the quantum mechanical stability of angular momentum states\nis discussed for the existence of phase transition between the stable states of\ninteracting system. Thereby analyzing the von Neumann entanglement entropy and\ndegree of condensation provide the information about quantum phase correlation\nin the many-body states. Calculating the conditional probability distribution,\nwe further probe the internal structure of quantum mechanically stable and\nunstable states. Much emphasis is put on finding the spatial correlation of\nbosonic atoms in the rotating system for the formation and entry of singly\nquantized vortices, and then organizing into canonical polygons with and\nwithout a central vortex at the trap center. Results are summarized in the form\nof a movie depicting the vortex patterns having discrete p-fold rotational\nsymmetry with $p = 2,3,4,5,6$."
    },
    {
        "anchor": "Polariton-Enhanced Exciton Transport: The transport distance of excitons in exciton-polariton systems has\npreviously been assumed to be very small ($\\lesssim 1~\\mu$m). The sharp spatial\nprofiles observed when generating polaritons by non-resonant optical excitation\nshow that this assumption is generally true. In this paper, however, we show\nthat the transport distances of excitons in two-dimensional planar cavity\nstructures with even a slightly polaritonic character are much longer than\nexpected ($\\approx 20~\\mu$m). Although this population of slightly polaritonic\nexcitons is normally small compared to the total population of excitons, they\ncan substantially outnumber the population of the polaritons at lower energies,\nleading to important implications for the tailoring of potential landscapes and\nthe measurement of interactions between polaritons.",
        "positive": "Non-thermal fixed points: Universal dynamics far from equilibrium: In this article we give an overview of the concept of universal dynamics near\nnon-thermal fixed points in isolated quantum many-body systems. We outline a\nnon-perturbative kinetic theory derived within a Schwinger-Keldysh closed-time\npath-integral approach, as well as a low-energy effective field theory which\nenable us to predict the universal scaling exponents characterizing the time\nevolution at the fixed point. We discuss the role of wave-turbulent transport\nin the context of such fixed points and discuss universal scaling evolution of\nsystems bearing ensembles of (quasi) topological defects. This is rounded off\nby the recently introduced concept of prescaling as a generic feature of the\nevolution towards a non-thermal fixed point."
    },
    {
        "anchor": "Anomalous buoyancy of quantum bubbles in immiscible Bose mixtures: Buoyancy is a well-known effect in immiscible binary Bose-Einstein\ncondensates. Depending on the differential confinement experienced by the two\ncomponents, a bubble of one component sitting at the center of the other\neventually floats to the surface, around which it spreads either totally or\npartially. We discuss how quantum fluctuations may significantly change the\nvolume and position of immiscible bubbles. We consider the particular case of\ntwo miscible components, forming a pseudo-scalar bubble condensate with\nenhanced quantum fluctuations (quantum bubble), immersed in a bath provided by\na third component, with which they are immiscible. We show that in such a\npeculiar effective binary mixture, quantum fluctuations change the equilibrium\nof pressures that define the bubble volume and modify as well the criterion for\nbuoyancy. Once buoyancy sets in, in contrast to the mean-field case, quantum\nfluctuations may place the bubble at an intermediate position between the\ncenter and the surface. At the surface, the quantum bubble may transition into\na floating self-bound droplet.",
        "positive": "Uncover band topology via quantized drift in two-dimensional Bloch\n  oscillations: We propose to measure band topology via quantized drift of Bloch oscillations\nin a two-dimensional Harper-Hofstadter lattice subjected to tilted fields in\nboth directions. When the difference between the two tilted fields is large,\nBloch oscillations uniformly sample all momenta, and hence the displacement in\neach direction tends to be quantized at multiples of the overall period,\nregardless of any momentum of initial state. The quantized displacement is\nrelated to a reduced Chern number defined as a line integral of Berry curvature\nin each direction, providing an almost perfect measurement of Chern number. Our\nscheme can apply to detect Chern number and topological phase transitions not\nonly for the energy-separable band, but also for energy-inseparable bands which\ncannot be achieved by conventional Thouless pumping or integer quantum Hall\neffect."
    },
    {
        "anchor": "Hierarchical dimensional crossover of an optically-trapped quantum gas\n  with disorder: Dimensionality serves as an indispensable ingredient in any attempt to\nformulate the low-dimensional physics, and studying the dimensional crossover\nat a fundamental level is challenging. The purpose of this work is to study the\nhierarchical dimensional crossovers, namely the crossover from three dimensions\n(3D) to quasi-2D and then to 1D. Our system consists of a 3D Bose-Einstein\ncondensate (BEC) trapped in an anisotropic 2D optical lattice characterized by\nthe lattice depths $V_1$ along the $x$ direction and $V_2$ along the $y$\ndirection, respectively, where the hierarchical dimensional crossover is\ncontrolled via $V_1$ and $V_2$. We analytically derive the ground-state energy,\nquantum depletion and the superfluid density of the system. Our results\ndemonstrate the 3D-quasi-2D-1D dimensional crossovers in the behavior of\nquantum fluctuations. Conditions for possible experimental realization of our\nscenario are also discussed.",
        "positive": "Ergoregion instabilities in rotating two-dimensional Bose--Einstein\n  condensates: new perspectives on the stability of quantized vortices: We investigate the stability of vortices in two-dimensional Bose--Einstein\ncondensates. In analogy with rotating spacetimes and with a careful account of\nboundary conditions, we show that the dynamical instability of multiply\nquantized vortices in trapped condensates persists in untrapped, spatially\nhomogeneous geometries and has an ergoregion nature with some modification due\nto the peculiar dispersion of Bogoliubov sound. Our results open new\nperspectives to the physics of vortices in trapped condensates, where multiply\nquantized vortices can be stabilized by interference effects and singly charged\nvortices can become unstable in suitably designed trap potentials. We show how\nsuperradiant scattering can be observed also in the short-time dynamics of\ndynamically unstable systems, providing an alternative point of view on\ndynamical (in)stability phenomena in spatially finite systems."
    },
    {
        "anchor": "Signature of Supersolidity in a Driven Cubic-Quartic Nonlinear\n  Schr\u00f6dinger Equation: We present analytical solution, which is periodic in nature, for a driven\ncubic-quartic nonlinear Schr\\\"odinger equation (DCQNLSE) placed in a\nbi-chromatic optical lattice. The solution indicates the creation of density\nwave. Since, beyond mean-field contribution in quasi one dimensional and\none-dimensional geometry differs on the even exponents of the nonlinearity thus\nwe extend our analysis towards quadratic-cubic-quartic and quadratic-cubic\nnonlinearities as well. Later, we study the dynamics of DCQNLSE. Our study\nindicates the existence of stripe phase along with considerable phase\ncoherence. These findings allow us to comment on the possible emergence of\nsupersolid phase in a condensate.",
        "positive": "Thermal friction on quantum vortices in a Bose-Einstein condensate: We investigate the dissipative dynamics of a corotating vortex pair in a\nhighly oblate axisymmetric Bose-Einstein condensate trapped in a harmonic\npotential. The initial vortex state is prepared by creating a doubly charged\nvortex at the center of the condensate and letting it dissociate into two\nsingly charged vortices. The separation of the vortex pair gradually increases\nover time and its increasing rate becomes higher with increasing the sample\ntemperature $T$. The evolution of the vortex state is well described with a\ndissipative point vortex model including longitudinal friction on the vortex\nmotion. For condensates of sodium atoms having a chemical potential of\n$\\mu\\approx k_B\\times 120$ nK, we find that the dimensionless friction\ncoefficient $\\alpha$ increases from 0.01 to 0.03 over the temperature range of\n200 nK $<T<$ 450 nK."
    },
    {
        "anchor": "Exotic many-body physics with large-spin Fermi gases: The experimental realization of quantum degenerate cold Fermi gases with\nlarge hyperfine spins opens up a new opportunity for exotic many-body physics.",
        "positive": "The internal structure of a vortex in a two-dimensional superfluid with\n  long healing length and its implications: We analyze the motion of quantum vortices in a two-dimensional spinless\nsuperfluid within Popov's hydrodynamic description. In the long healing length\nlimit (where a large number of particles are inside the vortex core) the\nsuperfluid dynamics is determined by saddle points of Popov's action, which, in\nparticular, allows for weak solutions of the Gross-Pitaevskii equation. We\nsolve the resulting equations of motion for a vortex moving with respect to the\nsuperfluid and find the reconstruction of the vortex core to be a non-analytic\nfunction of the force applied on the vortex. This response produces an\nanomalously large dipole moment of the vortex and, as a result, the spectrum\nassociated with the vortex motion exhibits narrow resonances lying {\\em within}\nthe phonon part of the spectrum, contrary to traditional view."
    },
    {
        "anchor": "Quantum droplets with magnetic vortices in spinor dipolar Bose-Einstein\n  condensates: Motivated by the recent experimental realization of a Bose-Einstein\ncondensate (BEC) of europium atoms, we investigate the self-bound droplet state\nof a europium BEC with spin degrees of freedom. Under a sufficiently weak\nmagnetic field, the droplet has a torus shape with circulating spin vectors,\nwhich is referred to as a magnetic vortex. The ground state transforms from the\ntorus to cigar shape through bistability with an increase in the magnetic\nfield. Dynamical change of the magnetic field causes the torus to rotate due to\nthe Einstein-de Haas effect. The magnetic vortices form a supersolid in a\nconfined system.",
        "positive": "Trapped-ion quantum simulation of tunable-range Heisenberg chains: Quantum-optical techniques allow for generating controllable spin-spin\ninteractions between ions, making trapped ions an ideal quantum simulator of\nHeisenberg chains. A single parameter, the detuning of the Raman coupling,\nallows to switch between ferromagnetic and antiferromagnetic chains, and to\nmodify the range of the interactions. On the antiferromagnetic side, the system\ncan be tuned from an extreme long-range limit, in which any pair of ions\ninteracts with almost equal strength, to interactions with a $1/r^3$ decay. By\nexact diagonalization, we study how a system of up to 20 ions behaves upon\ntuning the interactions. We find that it undergoes a transition from a\ndimerized state with extremely short-ranged correlations towards a state with\nquasi long-range order, that is, algebraically decaying correlations. On the\nferromagnetic side of the system, we demonstrate the feasibility of witnessing\nnon-locality of quantum correlations."
    },
    {
        "anchor": "Perfect transmission and perfect reflection of Bogoliubov quasiparticles\n  in a dynamically unstable Bose-Einstein condensate: The Nambu-Goldstone (NG) mode in a Bose-Einstein condensate (BEC) transmits a\npotential barrier with probability 1 in the zero-energy limit, which is known\nas the anomalous tunneling. In this paper, we investigate the tunneling\nproperties of quasiparticles in a dynamically unstable BEC. We prepare a\nmulti-component BEC (binary and spin-1 BEC) in a dynamically unstable state and\nsolve the tunneling problem of the spin-wave excitation from the condensate. We\nfind that the perfect transmission occurs even when the BEC is dynamically\nunstable if the spin-wave is the NG mode. Here, the mode that exhibits the\nperfect transmission is the dynamically unstable spin-wave mode, which is a\npure-imaginary-eigenvalue solution of the Bogoliubov-de Gennes equation. Hence,\nwe should take the zero-energy limit along not the real axis but the imaginary\naxis. We also demonstrate the existence of the perfect reflection of a\ndynamically unstable mode at the point where the imaginary part of the\neigenvalue takes its maximum. In this case, the incident and reflected waves\ndestructively interfere, and the amplitude of the quasiparticle wave function\nis strongly suppressed. We numerically confirm that the perfect reflection is a\ngeneric nature of dynamically unstable modes and not related to the NG mode.",
        "positive": "Light-induced gauge fields for ultracold atoms: Gauge fields are central in our modern understanding of physics at all\nscales. At the highest energy scales known, the microscopic universe is\ngoverned by particles interacting with each other through the exchange of gauge\nbosons. At the largest length scales, our universe is ruled by gravity, whose\ngauge structure suggests the existence of a particle - the graviton - that\nmediates the gravitational force. At the mesoscopic scale, solid-state systems\nare subjected to gauge fields of different nature: materials can be immersed in\nexternal electromagnetic fields, but they can also feature emerging gauge\nfields in their low-energy description. In this review, we focus on another\nkind of gauge field: those engineered in systems of ultracold neutral atoms. In\nthese setups, atoms are suitably coupled to laser fields that generate\neffective gauge potentials in their description. Neutral atoms \"feeling\"\nlaser-induced gauge potentials can potentially mimic the behavior of an\nelectron gas subjected to a magnetic field, but also, the interaction of\nelementary particles with non-Abelian gauge fields. Here, we review different\nrealized and proposed techniques for creating gauge potentials - both Abelian\nand non-Abelian - in atomic systems and discuss their implication in the\ncontext of quantum simulation. While most of these setups concern the\nrealization of background and classical gauge potentials, we conclude with more\nexotic proposals where these synthetic fields might be made dynamical, in view\nof simulating interacting gauge theories with cold atoms."
    },
    {
        "anchor": "Energy absorption spectroscopy of unitary Fermi gases in a uniform\n  potential: We propose to use the energy absorption spectroscopy to measure the kinetic\ncoefficients of unitary Fermi gases in a uniform potential. We show that in our\nscheme, the energy absorption spectrum is proportional to the dynamic structure\nfactor of the system. The profile of the spectrum depends on the shear\nviscosity $\\eta$, the thermal conductivity $\\kappa$ and the superfluid bulk\nviscosity $\\xi_3$. We show that extraction of these coefficients from the\nspectrum is achievable in present experiments.",
        "positive": "Quantum Control by Imaging : The Zeno effect in an ultracold lattice gas: We demonstrate the control of quantum tunneling in an ultracold lattice gas\nby the measurement backaction imposed by an imaging process. A {\\em in situ}\nimaging technique is used to acquire repeated images of an ultracold gas\nconfined in a shallow optical lattice. The backaction induced by these position\nmeasurements modifies the coherent quantum tunneling of atoms within the\nlattice. By smoothly varying the rate at which spatial information is extracted\nfrom the atomic ensemble, we observe the continuous crossover from the 'weak\nmeasurement regime' where position measurements have little influence on the\ntunneling dynamics, to the 'strong measurement regime' where\nmeasurement-induced localization causes a large suppression of tunneling. This\nsuppression of coherent tunneling is a manifestation of the Quantum Zeno\neffect. Our study realizes an experimental demonstration of the paradigmatic\nHeisenberg microscope in a lattice gas and sheds light on the implications of\nquantum measurement on the coherent evolution of a mesoscopic quantum system.\nIn addition, this demonstrates a powerful technique for the control of an\ninteracting many-body quantum system via spatially resolved measurement\nbackaction."
    },
    {
        "anchor": "Simulating strongly correlated multiparticle systems in a truncated\n  Hilbert space: Representing a strongly interacting multi-particle wave function in a finite\nproduct basis leads to errors. Simple rescaling of the contact interaction can\npreserve the low-lying energy spectrum and long-wavelength structure of wave\nfunctions in one-dimensional systems and thus correct for the basis set\ntruncation error. The analytic form of the rescaling is found for a\ntwo-particle system where the rescaling is exact. Detailed comparison between\nfinite Hilbert space calculations and exact results for up to 5 particles show\nthat rescaling can significantly improve the accuracy of numerical calculations\nin various external potentials. In addition to ground state energies, the\nlow-lying excitation spectrum, density profile and correlation functions are\nstudied. The results give a promising outlook for numerical simulations of\ntrapped ultracold atoms.",
        "positive": "Quantum quench in 1D: Coherent inhomogeneity amplification and\n  'supersolitons': We study a quantum quench in a 1D system possessing Luttinger liquid (LL) and\nMott insulating ground states before and after the quench, respectively. We\nshow that the quench induces power law amplification in time of any particle\ndensity inhomogeneity in the initial LL ground state. The scaling exponent is\nset by the fractionalization of the LL quasiparticle number relative to the\ninsulator. As an illustration, we consider the traveling density waves launched\nfrom an initial localized density bump. While these waves exhibit a particular\nrigid shape, their amplitudes grow without bound."
    },
    {
        "anchor": "Driven-Dissipative Supersolid in a Ring Cavity: Supersolids are characterized by the counter-intuitive coexistence of\nsuperfluid and crystalline order. Here we study a supersolid phase emerging in\nthe steady state of a driven-dissipative system. We consider a transversely\npumped Bose-Einstein condensate trapped along the axis of a ring cavity and\ncoherently coupled to a pair of degenerate counter-propagating cavity modes.\nAbove a threshold pump strength the interference of photons scattered into the\ntwo cavity modes results in an emergent superradiant lattice, which\nspontaneously breaks the continuous translational symmetry towards a periodic\natomic pattern. The crystalline steady state inherits the superfluidity of the\nBose-Einstein condensate, thus exhibiting genuine properties of a supersolid. A\ngapless collective Goldstone mode correspondingly appears in the superradiant\nphase, which can be non-destructively monitored via the relative phase of the\ntwo cavity modes on the cavity output. Despite cavity-photon losses the\nGoldstone mode remains undamped, indicating the robustness of the supersolid\nphase.",
        "positive": "Pairing Dynamics of Polar States in a Quenched p-wave Superfluid Fermi\n  Gas: We study the pairing dynamics of polar states in a single species p-wave\nsuperfluid Fermi gas following a sudden change of the interaction strength. The\nanisotropy of pair interaction together with the presence of the centrifugal\nbarrier results in profoundly different pairing dynamics compared to the s-wave\ncase. Depending on the direction of quenches, quench to the BCS regime results\nin a large oscillatory depletion of momentum occupation inside the Fermi sea or\na large filling of momentum occupation. We elucidate a crucial role of the\nresonant state supported by the centrifugal barrier in the pairing dynamics."
    },
    {
        "anchor": "Dynamics of spin-polarized impurity in ultracold Fermi gas: We show that the motion of spin-polarized impurity (ferron) in ultracold\natomic gas is characterized by a certain critical velocity which can be traced\nback to the amount of spin imbalance inside the impurity. We have calculated\nthe effective mass of ferron in two dimensions. We show that the effective mass\nscales with the surface of the ferron. We discuss the impact of these findings;\nin particular, we demonstrate that ferrons become unstable in the vicinity of a\nvortex.",
        "positive": "BEC-BCS Crossover with Feshbach Resonance for a Three-Hyperfine-Species\n  Model: We consider the behavior of an ultracold Fermi gas across a narrow Feshbach\nresonance, where the occupation of the closed channel may not be negligible.\nWhile the corrections to the single-channel formulae associated with the\nnonzero chemical potential and with particle conservation have been considered\nin the existing literature, there is a further effect, namely the\n\"inter-channel Pauli exclusion principle\" associated with the fact that a\nsingle hyperfine species may be common to the two channels. We focus on this\neffect and show that, as intuitively expected, the resulting corrections are of\norder $E_F/\\eta$, where $E_F$ is the Fermi energy of the gas in the absence of\ninteractions and $\\eta$ is the Zeeman energy difference between the two\nchannels. We also consider the related corrections to the fermionic excitation\nspectrum, and briefly discuss the collective modes of the system."
    },
    {
        "anchor": "Superglass phase of interaction-blockaded gases on a triangular lattice: We investigate the quantum phases of monodispersed bosonic gases confined to\na triangular lattice and interacting via a class of soft-shoulder potentials.\nThe latter correspond to soft-core potentials with an additional hard-core\nonsite interaction. Using exact quantum Monte Carlo simulations, we show that\nthe low temperature phases for weak and strong interactions following a\ntemperature quench are a homogeneous superfluid and a glass, respectively. The\nlatter is an insulating phase characterized by inhomogeneity in the density\ndistribution and structural disorder. Remarkably, we find that for intermediate\ninteraction strengths a {\\it superglass} occurs in an extended region of the\nphase diagram, where glassy behavior coexists with a sizable finite superfluid\nfraction. This glass phase is obtained in the absence of geometrical\nfrustration or external disorder and is a result of the competition of quantum\nfluctuations and cluster formation in the corresponding classical ground state.\nFor high enough temperature, the glass and superglass turn into a floating\nstripe solid and a supersolid, respectively. Given the simplicity and\ngenerality of the model, these phases should be directly relevant for\nstate-of-the-art experiments with Rydberg-dressed atoms in optical lattices.",
        "positive": "Two-dimensional expansion of a condensed dense Bose gas: We study the expansion dynamics of a condensate in a strongly interacting\nBose gas in the presence of an obstacle. Our focus is on the generation of\nshock waves after the Bose gas has passed the obstacle. The strongly\ninteracting Bose gas is described in the slave-boson representation. A\nsaddle-point approximation provides a nonlinear equation of motion for the\nmacroscopic wave function, analogous to the Gross-Pitaevskii equation of a\nweakly interacting Bose gas but with different nonlinearity. We compare the\nresults with the Gross-Pitaevskii dynamics of a weakly interacting Bose gas and\nfind a similar behavior with a slower behavior of the strongly interacting\nsystem."
    },
    {
        "anchor": "Quantum Kinetic Theory of Collisionless Superfluid Internal Convection: Superfluids can transport heat via simultaneous opposite flows of their\nspatially interpenetrating condensate and thermal components. While this\ninternal convection is usually described within Landau's phenomenological two\nfluid hydrodynamics, we apply quantum kinetic theory to a dilute Bose gas held\nbeween thermal reservoirs at different temperatures, and show that the\nphenomenon also appears in collisionless kinetic regimes, and should be\ndirectly observable in currently feasible experiments on trapped ultracold\nvapors.",
        "positive": "Coherent phase slips in coupled matter-wave circuits: Quantum Phase slips are dual process of particle tunneling in coherent\nnetworks. Besides to be of central interest for condensed matter physics,\nquantum phase slips are resources that are sought to be manipulated in quantum\ncircuits. Here, we devise a specific matter-wave circuit enlightening quantum\nphase slips. Specifically, we investigate the quantum many body dynamics of two\nside-by-side ring-shaped neutral bosonic systems coupled through a weak link.\nBy imparting a suitable magnetic flux, persistent currents flow in each ring\nwith given winding numbers. We demonstrate that coherent phase slips occur as\nwinding number transfer among the two rings, with the populations in each ring\nremaining nearly constant. Such a phenomenon occurs as a result of a specific\nentanglement of circulating states, that, as such cannot be captured by a mean\nfield treatment of the system. Our work can be relevant for the observation of\nquantum phase slips in cold atoms experiments and their manipulation in\nmatter-wave circuits. To make contact with the field, we show that the\nphenomenon has clear signatures in the momentum distribution of the system\nproviding the time of flight image of the condensate."
    },
    {
        "anchor": "Reliability of lattice gauge theories: Currently, there are intense experimental efforts to realize lattice gauge\ntheories in quantum simulators. Except for specific models, however, practical\nquantum simulators can never be fine-tuned to perfect local gauge invariance.\nThere is thus a strong need for a rigorous understanding of gauge-invariance\nviolation and how to reliably protect against it. As we show through analytic\nand numerical evidence, in the presence of a gauge invariance-breaking term the\ngauge violation accumulates only perturbatively at short times before\nproliferating only at very long times. This proliferation can be suppressed up\nto infinite times by energetically penalizing processes that drive the dynamics\naway from the initial gauge-invariant sector. Our results provide a theoretical\nbasis that highlights a surprising robustness of gauge-theory quantum\nsimulators.",
        "positive": "Role of fourth-order phase-space moments in collective modes of trapped\n  Fermi gases: We study the transition from hydrodynamic to collisionless behavior in\ncollective modes of ultracold trapped Fermi gases. To that end, we solve the\nBoltzmann equation for the trapped Fermi gas via the moments method. We showed\npreviously that it is necessary to go beyond second-order moments if one wants\nto reproduce the results of a numerical solution of the Boltzmann equation.\nHere, we will give the detailed description of the method including\nfourth-order moments. We apply this method to the case of realistic parameters,\nand compare the results for the radial quadrupole and scissors modes at\nunitarity to experimental data obtained by the Innsbruck group. It turns out\nthat the inclusion of fourth-order moments clearly improves the agreement with\nthe experimental data. In particular, the fourth-order moments reduce the\neffect of collisions and therefore partially compensate the effect of the\nenhanced in-medium cross section at low temperatures."
    },
    {
        "anchor": "Dipolar bright solitons and solitary vortices in a radial lattice: Stabilizing vortex solitons with high values of the topological charge, S, is\na challenging issue in optics, studies of Bose-Einstein condensates (BECs) and\nother fields. To develop a new approach to the solution of this problem, we\nconsider a two-dimensional dipolar BEC under the action of an axisymmetric\nradially periodic lattice potential, $V(r)\\sim \\cos (2r+\\delta )$, with dipole\nmoments polarized perpendicular to the system's plane, which gives rise to\nisotropic repulsive dipole-dipole interactions (DDIs). Two radial lattices are\nconsidered, with $\\delta =0$ and $\\pi $, i.e., a potential maximum or minimum\nat $r=0$, respectively. Families of vortex gapsoliton (GSs) with $S=1$ and\n$S\\geq 2$, the latter ones often being unstable in other settings, are\ncompletely stable in the present system (at least, up to $S=11$), being trapped\nin different annular troughs of the radial potential. The vortex solitons with\ndifferent $S$ may stably coexist in sufficiently far separated troughs.\nFundamental GSs, with $S=0$, are found too. In the case of $\\delta =0$, the\nfundamental solitons are ring-shaped modes, with a local minimum at $r=0.$At\n$\\delta =\\pi $, they place a density peak at the center.",
        "positive": "Critical Phenomena and Kibble-Zurek Scaling in the Long-Range Quantum\n  Ising Chain: We investigate an extension of the quantum Ising model in one spatial\ndimension including long-range $1 / r^{\\alpha}$ interactions in its statics and\ndynamics with possible applications from heteronuclear polar molecules in\noptical lattices to trapped ions described by two-state spin systems. We\nintroduce the statics of the system via both numerical techniques with finite\nsize and infinite size matrix product states and a theoretical approaches using\na truncated Jordan-Wigner transformation for the ferromagnetic and\nantiferromagnetic case and show that finite size effects have a crucial role\nshifting the quantum critical point of the external field by fifteen percent\nbetween thirty-two and around five-hundred spins. We numerically study the\nKibble-Zurek hypothesis in the long-range quantum Ising model with Matrix\nProduct States. A linear quench of the external field through the quantum\ncritical point yields a power-law scaling of the defect density as a function\nof the total quench time. For example, the increase of the defect density is\nslower for longer-range models and the critical exponent changes by twenty-five\nper cent. Our study emphasizes the importance of such long-range interactions\nin statics and dynamics that could point to similar phenomena in a different\nsetup of dynamical systems or for other models."
    },
    {
        "anchor": "Spatiotemporal scaling of two-dimensional nonequilibrium\n  exciton-polariton systems with weak interactions: We perform a numerical study on the two-dimensional nonequilibrium\nexciton-polariton systems driven by incoherent pumping based on the stochastic\ngeneralized Gross-Pitaevskii equation. We calculate the density fluctuation,\ncoherence function, and scaling function. It is found that the correlations at\nshort range agree with the Bogoliubov linear theory. While at large distance,\nboth static and dynamic correlations are characterized by the nonlinear scaling\nbehaviors of Kardar-Parisi-Zhang (KPZ) universality class, especially when the\ninteraction is weak. In this regime, scaling analyses are crucial to capture\nthe universal KPZ scaling features. In addition, the interaction between\nvortices is modified in the strong KPZ regime and leads to complex\nnonequilibrium vortex patterns.",
        "positive": "Polar molecule reactive collisions in quasi-1D systems: We study polar molecule scattering in quasi-one-dimensional geometries.\nElastic and reactive collision rates are computed as a function of collision\nenergy and electric dipole moment for different confinement strengths. The\nnumerical results are interpreted in terms of first order scattering and of\nadiabatic models. Universal dipolar scattering is also discussed. Our results\nare relevant to experiments where control of the collision dynamics through one\ndimensional confinement and an applied electric field is envisioned."
    },
    {
        "anchor": "Finite-size effects on the Bose-Einstein condensation critical\n  temperature in a harmonic trap: We obtain second and higher order corrections to the shift of the\nBose-Einstein critical temperature due to finite-size effects. The confinement\nis that of a harmonic trap with general anisotropy. Numerical work shows the\nhigh accuracy of our expressions. We draw attention to a subtlety involved in\nthe consideration of experimental values of the critical temperature in\nconnection with analytical expressions for the finite-size corrections.",
        "positive": "Interacting Bose-condensed gases: We provide an overview of the effects of interactions in Bose-condensed\ngases. We focus on phenomena that have been explored in ultracold atom\nexperiments, covering both tuneable contact interactions and dipolar\ninteractions. Our discussion includes: modifications to the ground state and\nexcitation spectrum, critical behaviour near the Bose--Einstein condensation\ntemperature, the unitary regime where the interactions are as strong as allowed\nby quantum mechanics, quantum droplets in mixtures, and supersolids in dipolar\ngases."
    },
    {
        "anchor": "Stability and Dynamics of Atom-Molecule Superfluids Near a Narrow\n  Feshbach Resonance: The recent observations of a stable molecular condensate emerging from a\ncondensate of bosonic atoms and related ``super-chemical\" dynamics have raised\nan intriguing set of questions. Here we provide a microscopic understanding of\nthis unexpected stability and dynamics in atom-molecule superfluids; we show\none essential element behind these phenomena is an extremely narrow Feshbach\nresonance in $^{133}$Cs at 19.849G. Comparing theory and experiment we\ndemonstrate how this narrow resonance enables the dynamical creation of a large\nclosed-channel molecular fraction superfluid, appearing in the vicinity of\nunitarity. Theoretically the observed superchemistry (\\textit{i.e.}, Bose\nenhanced reactions of atoms and molecules), is found to be assisted by the\nformation of Cooper pairs of bosonic atoms having opposite momenta.\nImportantly, this narrow resonance opens the possibility to explore the quantum\ncritical point of a molecular Bose superfluid and related phenomena which would\nnot be possible near a more typically broad Feshbach resonance.",
        "positive": "Subdiffusion and heat transport in a tilted 2D Fermi-Hubbard system: Using quantum gas microscopy we study the late-time effective hydrodynamics\nof an isolated cold-atom Fermi-Hubbard system subject to an external linear\npotential (a \"tilt\"). The tilt is along one of the principal directions of the\ntwo-dimensional (2D) square lattice and couples mass transport to local heating\nthrough energy conservation. We study transport and thermalization in our\nsystem by observing the decay of prepared initial density waves as a function\nof wavelength $\\lambda$ and tilt strength and find that the associated decay\ntime $\\tau$ crosses over as the tilt strength is increased from\ncharacteristically diffusive to subdiffusive with $\\tau\\propto\\lambda^4$. In\norder to explain the underlying physics we develop a hydrodynamic model that\nexhibits this crossover. For strong tilts, the subdiffusive transport rate is\nset by a thermal diffusivity, which we are thus able to measure as a function\nof tilt in this regime. We further support our understanding by probing the\nlocal inverse temperature of the system at strong tilts, finding good agreement\nwith our theoretical predictions. Finally, we discuss the relation of the\nstrongly tilted limit of our system to recently studied 1D models which may\nexhibit nonergodic dynamics."
    },
    {
        "anchor": "Lower bound for the population of hyperfine component $\u03bc=0$ particles\n  in the ground state of spin-1 condensates: An analytical expression for the lower bound of the average number of\nhyperfine component $\\mu =0$ particles in the ground state of spin-1\ncondensates (denoted as $\\overset{\\_\\_}{\\rho _{0}}$) under a magnetic field has\nbeen derived. In the derivation the total magnetization $M$ is kept rigorously\nconserved. Numerical examples are given to show the applicability of the\nanalytical expression. It was found that, in a broad domain of parameters\nspecified in the paper, the lower bound is very close to the actual\n$\\overset{\\_\\_}{\\rho _{0}}$. Thereby, in this domain, $\\overset{\\_\\_}{% \\rho\n_{0}}$ can be directly evaluated simply by using the analytical expression.",
        "positive": "Floquet approach to $\\mathbb{Z}_{2}$ lattice gauge theories with\n  ultracold atoms in optical lattices: Quantum simulation has the potential to investigate gauge theories in\nstrongly-interacting regimes, which are up to now inaccessible through\nconventional numerical techniques. Here, we take a first step in this direction\nby implementing a Floquet-based method for studying $\\mathbb{Z}_2$ lattice\ngauge theories using two-component ultracold atoms in a double-well potential.\nFor resonant periodic driving at the on-site interaction strength and an\nappropriate choice of the modulation parameters, the effective Floquet\nHamiltonian exhibits $\\mathbb{Z}_2$ symmetry. We study the dynamics of the\nsystem for different initial states and critically contrast the observed\nevolution with a theoretical analysis of the full time-dependent Hamiltonian of\nthe periodically-driven lattice model. We reveal challenges that arise due to\nsymmetry-breaking terms and outline potential pathways to overcome these\nlimitations. Our results provide important insights for future studies of\nlattice gauge theories based on Floquet techniques."
    },
    {
        "anchor": "Heating dynamics of bosonic atoms in a noisy optical lattice: We analyze the heating of interacting bosonic atoms in an optical lattice due\nto intensity fluctuations of the lasers forming the lattice. We focus in\nparticular on fluctuations at low frequencies below the band gap frequency,\nsuch that the dynamics is restricted to the lowest band. We derive stochastic\nequations of motion, and analyze the effects on different many-body states,\ncharacterizing heating processes in both strongly and weakly interacting\nregimes. In the limit where the noise spectrum is flat at low frequencies, we\ncan derive an effective Master equation describing the dynamics. We compute\nheating rates and changes to characteristic correlation functions both in the\nperturbation theory limit, and using a full time-dependent calculation of the\nstochastic many-body dynamics in 1D based on time-dependent\ndensity-matrix-renormalization-group methods.",
        "positive": "Chaoticity without thermalisation in disordered lattices: We study chaoticity and thermalization in Bose-Einstein condensates in\ndisordered lattices, described by the discrete nonlinear Schr\\\"odinger equation\n(DNLS). A symplectic integration method allows us to accurately obtain both the\nfull phase space trajectories and their maximum Lyapunov exponents (mLEs),\nwhich characterize their chaoticity. We find that disorder destroys ergodicity\nby breaking up phase space into subsystems that are effectively disjoint on\nexperimentally relevant timescales, even though energetically, classical\nlocalisation cannot occur. This leads us to conclude that the mLE is a very\npoor ergodicity indicator, since it is not sensitive to the trajectory being\nconfined to a subregion of phase space. The eventual thermalization of a BEC in\na disordered lattice cannot be predicted based only on the chaoticity of its\nphase space trajectory."
    },
    {
        "anchor": "Breakdown of Anderson localization of interacting quantum bright\n  solitons in a disorder potential: The center of mass of a bright soliton in a Bose-Einstein condensate may\nreveal Anderson localization in the presence of a weak disorder potential. We\nanalyze the effects of interactions between two bright solitons on the Anderson\nlocalization phenomenon. Perturbation calculus shows that even very weak\ninteractions modify localization properties of the system eigenstates. For\nstronger interactions, i.e. when the solitons are close to each other, the\nlocalization is totally broken. It implies that in order to experimentally\nobserve the Anderson localization effects, a single bright soliton has to be\nprepared and excitation of soliton trains must be avoided.",
        "positive": "BEC polaron in harmonic trap potential at weak coupling regime:\n  Lee-Low-Pines type approach: We have calculated the zero-temperature binding energy of a single impurity\natom immersed in a Bose-Einstein condensate of ultracold atoms that are trapped\nin an axially symmetric harmonic potential, where the impurity interacts with\nbosonic atoms in the condensate via a low-energy s-wave scattering. In this\ncase, bosons are excited around the impurity to form a quasiparticle, namely, a\nBEC polaron. We have developed a variational method, {\\it a la} Lee-Low-Pines\n(LLP) theory for electron-phonon systems, for description of the polaron with a\nconserved angular momentum around the symmetric axis. It is found in numerical\nresults that the binding energy between the impurity and the excited bosons\nbreak the degeneracy with respect to the total angular momentum of the polaron.\nThe angular momentum is partially shared by the excited bosons, which is due to\na mechanism similar to the drag effect on the polaron momentum by a phonon\ncloud in the LLP theory."
    },
    {
        "anchor": "Geometrically Frustrated Coarsening Dynamics in Spinor Bose-Fermi\n  Mixtures: Coarsening dynamics theory has successfully described the equilibration of a\nbroad class of systems.By studying the relaxation of a periodic array of\nmicrocondensates immersed in a Fermi gas which can mediate long-range spin\ninteractions to simulate frustrated classical magnets, we show that coarsening\ndynamics can be suppressed by geometrical frustration. The system is found to\neventually approach a metastable state which is robust against random field\nnoise and characterized by finite correlation lengths with the emergence of\ntopologically stable Z2 vortices. We find universal scaling laws with no\nthermal-equilibrium analog that relate the correlation lengths and the number\nof vortices to the degree of frustration in the system.",
        "positive": "Bose-glass phases of ultracold atoms due to cavity backaction: We determine the quantum ground-state properties of ultracold bosonic atoms\ninteracting with the mode of a high-finesse resonator. The atoms are confined\nby an external optical lattice, whose period is incommensurate with the cavity\nmode wave length, and are driven by a transverse laser, which is resonant with\nthe cavity mode. While for pointlike atoms photon scattering into the cavity is\nsuppressed, for sufficiently strong lasers quantum fluctuations can support the\nbuild-up of an intracavity field, which in turn amplifies quantum fluctuations.\nThe dynamics is described by a Bose-Hubbard model where the coefficients due to\nthe cavity field depend on the atomic density at all lattice sites. Quantum\nMonte Carlo simulations and mean-field calculations show that for large\nparameter regions cavity backaction forces the atoms into clusters with a\ncheckerboard density distribution. Here, the ground state lacks superfluidity\nand possesses finite compressibility, typical of a Bose-glass. This system\nconstitutes a novel setting where quantum fluctuations give rise to effects\nusually associated with disorder."
    },
    {
        "anchor": "Anomalous and Quantum Hall Effects in Lossy Photonic Lattices: We theoretically discuss analogues of the anomalous and the integer quantum\nHall effect in driven-dissipative two-dimensional photonic lattices in the\npresence of a synthetic gauge field. Photons are coherently injected by a\nspatially localized pump, and the transverse shift of the in-plane light\ndistribution under the effect of an additional uniform force is considered.\nDepending on pumping parameters, the transverse shift turns out to be\nproportional either to the global Chern number (integer quantum Hall effect) or\nto the local Berry curvature (anomalous Hall effect). This suggests a viable\nroute to experimentally measure these quantities in photonic lattices.",
        "positive": "Interface dynamics of a two-component Bose-Einstein condensate driven by\n  an external force: The dynamics of an interface in a two-component Bose-Einstein condensate\ndriven by a spatially uniform time-dependent force is studied. Starting from\nthe Gross-Pitaevskii Lagrangian, the dispersion relation for linear waves and\ninstabilities at the interface is derived by means of a variational approach. A\nnumber of diverse dynamical effects for different types of the driving force is\ndemonstrated, which includes the Rayleigh-Taylor instability for a constant\nforce, the Richtmyer-Meshkov instability for a pulse force, dynamic\nstabilization of the Rayleigh-Taylor instability and onset of the parametric\ninstability for an oscillating force. Gaussian Markovian and non-Markovian\nstochastic forces are also considered. It is found that the Markovian\nstochastic force does not produce any average effect on the dynamics of the\ninterface, while the non-Markovian force leads to exponential perturbation\ngrowth."
    },
    {
        "anchor": "Stability of a Bose-Einstein condensate in a driven optical lattice:\n  Crossover between weak and tight transverse confinement: We explore the effect of transverse confinement on the stability of a\nBose-Einstein condensate (BEC) loaded in a shaken one-dimensional or\ntwo-dimensional square lattice. We calculate the decay rate from two-particle\ncollisions. We predict that if the transverse confinement exceeds a critical\nvalue, then, for appropriate shaking frequencies, the condensate is stable\nagainst scattering into transverse directions.",
        "positive": "Realizing Exactly Solvable SU(N) Magnets with Thermal Atoms: We show that $n$ thermal fermionic alkaline-earth atoms in a flat-bottom trap\nallow one to robustly implement a spin model displaying two symmetries: the\n$S_n$ symmetry that permutes atoms occupying different vibrational levels of\nthe trap and the SU($N$) symmetry associated with $N$ nuclear spin states. The\nhigh symmetry makes the model exactly solvable, which, in turn, enables the\nanalytic study of dynamical processes such as spin diffusion in this SU($N$)\nsystem. We also show how to use this system to generate entangled states that\nallow for Heisenberg-limited metrology. This highly symmetric spin model should\nbe experimentally realizable even when the vibrational levels are occupied\naccording to a high-temperature thermal or an arbitrary non-thermal\ndistribution."
    },
    {
        "anchor": "Dynamical Detection of Topological Phase Transitions in Short-Lived\n  Atomic Systems: We demonstrate that dynamical probes provide direct means of detecting the\ntopological phase transition (TPT) between conventional and topological phases,\nwhich would otherwise be difficult to access because of loss or heating\nprocesses. We propose to avoid such heating by rapidly quenching in and out of\nthe short-lived topological phase across the transition that supports gapless\nexcitations. Following the quench, the distribution of excitations in the final\nconventional phase carries signatures of the TPT. We apply this strategy to\nstudy the TPT into a Majorana-carrying topological phase predicted in\none-dimensional spin-orbit-coupled Fermi gases with attractive interactions.\nThe resulting spin-resolved momentum distribution, computed by\nself-consistently solving the time-dependent Bogoliubov--de Gennes equations,\nexhibits Kibble-Zurek scaling and St\\\"{u}ckelberg oscillations characteristic\nof the TPT. We discuss parameter regimes where the TPT is experimentally\naccessible.",
        "positive": "Vortices in spin-orbit-coupled Bose-Einstein condensates: Realistic methods to create vortices in spin-orbit-coupled Bose-Einstein\ncondensates are discussed. It is shown that, contrary to common intuition,\nrotation of the trap containing a spin-orbit condensate does not lead to an\nequilibrium state with static vortex structures, but gives rise instead to\nnon-equilibrium behavior described by an intrinsically time-dependent\nHamiltonian. We propose here the following alternative methods to induce\nthermodynamically stable static vortex configurations: (1) to rotate both the\nlasers and the anisotropic trap; and (2) to impose a synthetic Abelian field on\ntop of synthetic spin-orbit interactions. Effective Hamiltonians for spin-orbit\ncondensates under such perturbations are derived for most currently known\nrealistic laser schemes that induce synthetic spin-orbit couplings. The\nGross-Pitaevskii equation is solved for several experimentally relevant\nregimes. The new interesting effects include spatial separation of left- and\nright-moving spin-orbit condensates, the appearance of unusual vortex\narrangements, and parity effects in vortex nucleation where the topological\nexcitations are predicted to appear in pairs. All these phenomena are shown to\nbe highly non-universal and depend strongly on a specific laser scheme and\nsystem parameters."
    },
    {
        "anchor": "Effective interaction in an unbalanced Fermion mixture: A one dimensional Fermi mixture with delta--interaction is investigated in\nthe limit of extreme imbalance. In particular we consider the cases of only one\nor two minority Fermions which interact with the Fermi-sea of the majority\nFermions. We calculate dispersion relation and polaron mass for the minority\nFermions as well as equal time density-density correlators. Within a cluster\nexpansion we derive an expression for the effective interaction potential\nbetween minority Fermions. For our calculations we use a reformulation of the\nexact wave functions, originally obtained by Yang and Gaudin by a nested Bethe\nansatz, in terms of determinants.",
        "positive": "Lattice bosons in a quasi-disordered environment: The effects of\n  next-nearest-neighbor hopping on localization and Bose-Einstein condensation: We present a theoretical study of the effects of the next-nearest-neighbor\n(NNN) hopping ($t_2$) on the properties of non-interacting bosons in optical\nlattices in the presence of an Aubry-Andr\\'{e} quasi-disorder. First we\ninvestigate, employing exact diagonalization, the effects of $t_2$ on the\nlocalization properties of a single boson. The localization is monitored using\nan entanglement measure as well as with inverse participation ratio. We find\nthat the sign of $t_2$ has a significant influence on the localization effects.\nWe also provide analytical results in support of the trends found in the\nlocalization behavior. Further, we extend these results including the effects\nof a harmonic potential which obtains in experiments. Next, we study the\neffects of $t_2$ on Bose-Einstein condensation. We find that, a positive $t_2$\nstrongly enhances the low temperature thermal depletion of the condensate while\na negative $t_2$ reduces it. It is also found that, for a fixed temperature,\nincreasing the quasi-disorder strength reduces the condensate fraction in the\nextended regime while enhancing it in the localized regime. We also investigate\nthe effects of boundary conditions and that of the phase of the AA potential on\nthe condensate. These are found to have significant effects on the condensate\nfraction in the localization transition region."
    },
    {
        "anchor": "Instabilities of vortex-ring-bright soliton in trapped binary 3D\n  Bose-Einstein condensates: Instabilities of vortex-ring-bright coherent structures in harmonically\ntrapped two-component three-dimensional Bose-Einstein condensates are studied\nnumerically within the coupled Gross-Pitaevskii equations and interpreted\nanalytically. Interestingly, the filled vortex core with a sufficiently large\namount of the bright component is observed to reduce the parametric interval of\nstability of the vortex ring. We have identified the mechanisms of several\nlinear instabilities and one nonlinear parametric instability in this\nconnection. Two of the linear instabilities are qualitatively different from\nones reported earlier, to our knowledge, and are associated with azimuthal\nmodes of $m=0$ and $m=1$, i.e., deviations of the vortex from the stationary\nring shape. Our nonlinear parametric resonance instability occurs between the\n$m=0$ and $m=2$ modes and signals the exchange of energy between them.",
        "positive": "Vortex patterns in the almost-bosonic anyon gas: We study theoretically and numerically the ground state of a gas of 2D\nabelian anyons in an external trapping potential. We treat anyon statistics in\nthe magnetic gauge picture, perturbatively around the bosonic end. This leads\nto a mean-field energy functional, whose ground state displays vortex lattices\nsimilar to those found in rotating Bose-Einstein condensates. A crucial\ndifference is however that the vortex density is proportional to the underlying\nmatter density of the gas."
    },
    {
        "anchor": "Topological pump and bulk-edge-correspondence in an extended\n  Bose-Hubbard model: An extended Bose-Hubbard model (EBHM) with three- and four-body constraints\ncan be feasible in cold atoms in an optical lattice. A rich phase structure\nincluding various symmetry-protected topological (SPT) phases is obtained\nnumerically with suitable parameter settings and particle filling. The SPT\nphase is characterized by the Berry phase as a local topological order\nparameter and the structure of the entanglement spectrum (ES). Based on the\npresence of various topological phases, separated by gapless phase boundaries,\nthe EBHM exhibits various bosonic topological pumps, which are constructed by\nconnecting the different SPT phases without gap closing. The bulk topological\npumps exhibit the plateau transitions characterized by many-body Chern numbers.\nFor the system with boundary, the center of mass (CoM) under grand canonical\nensemble elucidates the contributions of multiple edge states and reveals the\ntopology of the system. We demonstrate that the interacting bosonic pumps obey\nthe bulk-edge-correspondence.",
        "positive": "Observation of spin-orbit-dependent electron scattering using long-range\n  Rydberg molecules: We present experimental evidence for spin-orbit interaction of an electron as\nit scatters from a neutral atom. The scattering process takes place within a\nRb$_2$ ultralong-range Rydberg molecule, consisting of a Rydberg atomic core, a\nRydberg electron, and a ground state atom. The spin-orbit interaction leads to\ncharacteristic level splittings of vibrational molecular lines which we\ndirectly observe via photoassociation spectroscopy. We benefit from the fact\nthat molecular states dominated by resonant $p$-wave interaction are\nparticularly sensitive to the spin-orbit interaction. Our work paves the way\nfor studying novel spin dynamics in ultralong-range Rydberg molecules.\nFurthermore, it shows that the molecular setup can serve as a microlaboratory\nto perform precise scattering experiments in the low-energy regime of a few\nmeV."
    },
    {
        "anchor": "Superfluidity in the absence of kinetics in spin-orbit-coupled optical\n  lattices: At low temperatures bosons typically condense to minimize their\nsingle-particle kinetic energy while interactions stabilize superfluidity.\nOptical lattices with artificial spin-orbit coupling challenge this paradigm\nbecause here kinetic energy can be quenched in an extreme regime where the\nsingle-particle band flattens. To probe the fate of superfluidity in the\nabsence of kinetics we construct and numerically solve interaction-only\ntight-binding models in flat bands. We find that novel superfluid states arise\nentirely from interactions operating in quenched kinetic energy bands, thus\nrevealing a distinct and unexpected condensation mechanism. Our results have\nimportant implications for the identification of quantum condensed phases of\nultracold bosons beyond conventional paradigms.",
        "positive": "The self-energy of an impurity in an ideal Fermi gas to second order in\n  the interaction strength: We study in three dimensions the problem of a spatially homogeneous\nzero-temperature ideal Fermi gas of spin-polarized particles of mass $m$\nperturbed by the presence of a single distinguishable impurity of mass $M$. The\ninteraction between the impurity and the fermions involves only the partial\n$s$-wave through the scattering length $a$, and has negligible range $b$\ncompared to the inverse Fermi wave number $1/\\kf$ of the gas. Through the\ninteractions with the Fermi gas the impurity gives birth to a quasi-particle,\nwhich will be here a Fermi polaron (or more precisely a {\\sl monomeron}). We\nconsider the general case of an impurity moving with wave vector $\\KK\\neq\\OO$:\nThen the quasi-particle acquires a finite lifetime in its initial momentum\nchannel because it can radiate particle-hole pairs in the Fermi sea. A\ndescription of the system using a variational approach, based on a finite\nnumber of particle-hole excitations of the Fermi sea, then becomes\ninappropriate around $\\KK=\\mathbf{0}$. We rely thus upon perturbation theory,\nwhere the small and negative parameter $\\kf a\\to0^-$ excludes any branches\nother than the monomeronic one in the ground state (as e.g.\\ the dimeronic\none), and allows us a systematic study of the system. We calculate the impurity\nself-energy $\\Sigma^{(2)}(\\KK,\\omega)$ up to second order included in $a$.\nRemarkably, we obtain an analytical explicit expression for\n$\\Sigma^{(2)}(\\KK,\\omega)$ allowing us to study its derivatives in the plane\n$(K,\\omega)$. These present interesting singularities, which in general appear\nin the third order derivatives $\\partial^3 \\Sigma^{(2)}(\\KK,\\omega)$. In the\nspecial case of equal masses, $M=m$, singularities appear already in the\nphysically more accessible second order derivatives $\\partial^2\n\\Sigma^{(2)}(\\KK,\\omega)$; using a self-consistent heuristic approach based on\n$\\Sigma^{(2)}$ we then regularise the divergence of the second order derivative\n$\\partial\\_K^2 \\Delta E(\\KK)$ of the complex energy of the quasi-particle found\nin reference [C. Trefzger, Y. Castin, Europhys. Lett. {\\bf 104}, 50005 (2013)]\nat $K=\\kf$, and we predict an interesting scaling law in the neighborhood of\n$K=\\kf$. As a by product of our theory we have access to all moments of the\nmomentum of the particle-hole pair emitted by the impurity while damping its\nmotion in the Fermi sea, at the level of Fermi's golden rule."
    },
    {
        "anchor": "Implications of hydrodynamic fluctuations on the minimum shear viscosity\n  of the dilute Fermi gas at unitarity: We confirm and expand on work by Chafin and Schaefer on hydrodynamic\nfluctuations in the unitary Fermi gas. Using the result for the equation of\nstate from a recent MIT experiment, we derive lower bounds for \\eta/n and\n\\eta/s as a function of temperature. Re-analyzing recent quantum Monte Carlo\ndata for the shear-viscosity spectral function we point out a possible\nresolution for the tension between the viscosity bound \\eta/n> 0.3 from Chafin\nand Schaefer and the quantum Monte Carlo results \\eta/n<0.2$ from Wlazlowski et\nal. near the critical temperature",
        "positive": "Disorder Induced Vortex Lattice Melting in Bose-Einstein Condensate: We study the vortex lattice dynamics in presence of single impurity as well\nas random impurities or disorder. We show that in presence of a single impurity\nthe vortex lattice gets distorted and the distortion depends on the position of\nthe single impurity with respect to the positions of the vortices in the\nimpurity free Abrikosov vortex lattice and also the strength of the impurity\npotential. We then show that a new type of giant hole with hidden vortices\ninside it can be created in the vortex lattice by a cluster of impurities. In\npresence of random impurity potential or disorder the vortex lattice melts. We\nshow that the vortex lattice also melts in presence of pseudorandom potential\ngenerated by the superposition of two optical lattices. The absence of\nlong-range order in the melted vortex lattice is demonstrated from the\nstructure factor profile and the histogram of the distances between each pair\nof the vortices."
    },
    {
        "anchor": "Optical tweezer generation using automated alignment and adaptive optics: Recent progress in quantum technologies with ultracold atoms has been\npropelled by spatially fine-tuned control of lasers and diffraction-limited\nimaging. The state-of-the-art precision of optical alignment to achieve this\nfine-tuning is reaching the limits of manual control. Here, we show how to\nautomate this process. One of the elementary techniques of manual alignment of\noptics is cross-walking of laser beams. Here, we generalize this technique to\nmulti-variable cross-walking. Mathematically, this is a variant of the\nwell-known Alternating Minimization (AM) algorithm in convex optimization and\nis closely related to the Gauss-Seidel algorithm. Therefore, we refer to our\nmulti-variable cross-walking algorithm as the modified AM algorithm. While\ncross-walking more than two variables manually is challenging, one can do this\neasily for machine-controlled variables. We apply this algorithm to\nmechanically align high numerical aperture (NA) objectives and show that we can\nproduce high-quality diffraction-limited tweezers and point spread functions\n(PSF). After a rudimentary coarse alignment, the algorithm takes about 1 hour\nto align the optics to produce high-quality tweezers. Moreover, we use the same\nalgorithm to optimize the shape of a deformable mirror along with the\nmechanical variables and show that it can be used to correct for optical\naberrations produced, for example, by glass thickness when producing tweezers\nand imaging point sources. The shape of the deformable mirror is parametrized\nusing the first 14 non-trivial Zernike polynomials, and the corresponding\ncoefficients are optimized together with the mechanical alignment variables. We\nshow PSF with a Strehl ratio close to 1 and tweezers with a Strehl ratio >0.8.\nThe algorithm demonstrates exceptional robustness, effectively operating in the\npresence of significant mechanical fluctuations induced by a noisy environment.",
        "positive": "Collective dipole oscillations of a spin-orbit coupled Fermi gas: The collective dipole mode is induced and measured in a spin-orbit (SO)\ncoupled degenerate Fermi gas of $^{173}$Yb atoms. Using a differential optical\nStark shift, we split the degeneracy of three hyperfine states in the ground\nmanifold, and independently couple consecutive spin states with the equal Raman\ntransitions. A relatively long-lived spin-orbit-coupled Fermi gas, readily\nbeing realized with a narrow optical transition, allows to explore a\nsingle-minimum dispersion where three minima of spin-1 system merge into and to\nmonitor collective dipole modes of fermions in the strong coupling regime. The\nmeasured oscillation frequency of the dipole mode is compared with the\nsemi-classical calculation in the single-particle regime. Our work should pave\nthe way towards the characterization of spin-orbit-coupled fermions with large\nspin $s>\\frac{1}{2}$ in the strong coupling regime."
    },
    {
        "anchor": "Condensation Energy of a Spin-1/2 Strongly Interacting Fermi Gas: We report a measurement of the condensation energy of a two-component Fermi\ngas with tunable interactions. From the equation of state of the gas, we infer\nthe properties of the normal phase in the zero-temperature limit. By comparing\nthe pressure of the normal phase at T=0 to that of the low-temperature\nsuperfluid phase, we deduce the condensation energy, i.e. the energy gain of\nthe system in being in the superfluid rather than normal state. We compare our\nmeasurements to a ladder approximation description of the normal phase, and to\na fixed node Monte-Carlo approach, finding excellent agreement. We discuss the\nrelationship between condensation energy and pairing gap in the BEC-BCS\ncrossover.",
        "positive": "Two-dimensional network of atomtronic qubits: Through a combination of laser beams, we engineer a two-dimensional optical\nlattice of Mexican hat potentials able to host atoms in its ring-shaped wells.\nWhen tunneling can be ignored (at high laser intensities), we show that a\nwell-defined qubit can be associated with the states of the atoms trapped in\neach of the rings. Each of these two-level systems can be manipulated by a\nsuitable configuration of Raman laser beams imprinting a synthetic flux onto\neach Mexican hat cell of the lattice. Overall, we believe that the system has\nthe potential to form a scalable architecture for atomtronic flux qubits."
    },
    {
        "anchor": "Hamiltonian dynamics of two same-sign point vortices: We have studied numerically the Hamiltonian dynamics of two same-sign point\nvortices in an effectively two-dimensional, harmonically trapped Bose-Einstein\ncondensate. We have found in the phase space of the system an impenetrable wall\nthat divides the dynamics into two distinct and exhaustive types. In the\ntwo-dimensional position-coordinate space, the first type corresponds to\nintersecting single-vortex orbits and the second type to orbits that have no\npoints in common. The two types are also easily distinguished in the\ntwo-dimensional space spanned by the radial and angular velocities of the\nvortices: in the first type, both single-vortex orbits are the same simple loop\nin this two-dimensional space, whereas in the second type the two orbits\nconstitute two nonintersecting loops. The phase-space-dividing wall is distinct\nfrom the bifurcation curve of rigidly rotating states found by Navarro et al.\n[Phys. Rev. Lett. 110, 225301 (2013)].",
        "positive": "Three-body contact for fermions. I. General relations: We consider the resonant Fermi gas, that is, spin 1/2 fermions in three\ndimensions interacting by a short-range potential of large scattering length.\nWe introduce a quantity, the three-body contact, that determines several\nobservables. Within the zero-range model, the number of nearby fermion\ntriplets, the large-momentum tail of the center-of-mass momentum distribution\nof nearby fermion pairs, as well as the large-momentum tail of the two-particle\nmomentum distribution, are expressed in terms of the three-body contact. For a\nsmall finite interaction range, the formation rate of deeply bound dimers by\nthree-body recombination, as well as the three-body contribution to the\nfinite-range correction to the energy, are expressed in terms of the three-body\ncontact and of a three-body parameter. This three-body parameter, which\nvanishes in the zero-range limit, is defined through the asymptotic behavior of\nthe zero-energy scattering state at distances intermediate between the range\nand the two-body scattering length. In general, the three-body contact has\ndifferent contributions labeled by spin and angular momentum indices, and the\nthree-body parameter can depend on those indices. We also include the\ngeneralization to unequal masses for $\\uparrow$ and $\\downarrow$ particles.\nWith respect to the relation between three-body loss rate and number of nearby\ntriplets stated in [Petrov, Salomon and Shlyapnikov, PRL 93, 090404 (2004)],\nthe present work adds a derivation, expresses the proportionality factor in\nterms of the three-body parameter, and includes the general case where there\nare several contributions to the three-body contact and several three-body\nparameters."
    },
    {
        "anchor": "Scale and conformal invariance in rotating few-fermion systems: We show that rotating two-dimensional Fermi gases possess a nonrelativistic\nscale and conformal invariance at weak interactions, where the scale invariance\nof universal short-range interactions is not broken by quantum effects. We\ndemonstrate the symmetry in the excitation spectrum of few-fermion ensembles in\na harmonic trap obtained by exact diagonalization, which are constrained by the\noperator-state correspondence. The excitation spectrum is shown to split in a\nset of primary states, the energies of which correspond to scaling dimensions\nof conformal operators, and derived excited states that consist of breathing\nmodes as well as two different center-of-mass excitations, which describe\ncyclotron and guiding-center excitations of the total particle cloud.\nFurthermore, the conformal symmetry is manifest in the many-body wave function,\nwhere it dictates the form of the hyperradial component, which we demonstrate\nusing Monte Carlo sampling of few-body wave functions.",
        "positive": "Breached pair superfluidity: a brief review: Interior gap superfluidity was introduced together with Frank Wilczek. Later\non together with our collaborators, we generalized this new possibility of\nsuperfluidity to a broader concept, breach pair superfluidity. In the occasion\nto celebrate Professor Frank Wilczek's seventieth birthday and his productive\ncareer in several major areas in physics, I dedicate this note to recall the\nexciting times of developing this idea, the main aspects of the proposed phase,\nand the discussion on its stability condition."
    },
    {
        "anchor": "The in-plane gradient magnetic field induced vortex lattices in\n  spin-orbit coupled Bose-Einstein condensations: We consider the ground-state properties of the two-component spin-orbit\ncoupled ultracold bosons subject to a rotationally symmetric in-plane gradient\nmagnetic field. In the non-interacting case, the ground state supports\ngiant-vortices carrying large angular momenta without rotating the trap. The\nvorticity is highly tunable by varying the amplitudes and orientations of the\nmagnetic field. Interactions drive the system from a giant-vortex state to\nvarious configurations of vortex lattice states along a ring. Vortices exhibit\nellipse-shaped envelops with the major and minor axes determined by the\nspin-orbit coupling and healing lengths, respectively. Phase diagrams of vortex\nlattice configurations are constructed and their stabilities are analyzed.",
        "positive": "Four-Body Scale in Universal Few-Boson Systems: The role of an intrinsic four-body scale in universal few-boson systems is\nthe subject of active debate. We study these systems within the framework of\neffective field theory. For systems of up to six bosons we establish that no\nfour-body scale appears at leading order (LO). However, we find that at\nnext-to-leading (NLO) order a four-body force is needed to obtain renormalized\nresults for binding energies. With the associated parameter fixed to the\nbinding energy of the four-boson system, this force is shown to renormalize the\nfive- and six-body systems as well. We present an original ansatz for the\nshort-distance limit of the bosonic $A$-body wave function from which we\nconjecture that new $A$-body scales appear at N$^{A-3}$LO. As a specific\nexample, calculations are presented for clusters of helium atoms. Our results\napply more generally to other few-body systems governed by a large scattering\nlength, such as light nuclei and halo states, the low-energy properties of\nwhich are independent of the detailed internal structure of the constituents."
    },
    {
        "anchor": "Percolation analysis of a disordered spinor Bose gas: We study the effects of an on-site disorder potential in a gas of spinor\n(spin-1) ultracold atoms loaded in an optical lattice corresponding to both\nferromagnetic and antiferromagnetic spin dependent interactions. Starting with\na disordered spinor Bose-Hubbard model (SBHM) on a two dimensional square\nlattice, we observe the appearance of a Bose glass phase using the fraction of\nthe lattice sites having finite superfluid order parameter and non integer\nlocal densities as an indicator. A precise distinction between three different\ntypes of phases namely, superfluid (SF), Mott insulator (MI) and Bose glass\n(BG) is done via a percolation analysis thereby demonstrating that a reliable\nenumeration of phases is possible at particular values of the parameters of the\nSBHM. Finally we present the phase diagram based on the above information for\nboth antiferromagnetic and ferromagnetic interactions.",
        "positive": "Finite size effects and Hofstadter butterfly in a bosonic Mott insulator\n  with relativistic dispersion background: Gauge potentials with different configurations have been recently realized in\nthe optical lattice experiments. It is remarkable that one of the simplest\ngauge can generate particle energy spectrum with the self-similar structure\nknown as a Hofstadter butterfly. We investigate theoretically the impact of\nstrong on-site interaction on such a spectrum. In particular, it is shown that\nthe fractal structure is encoded in the quasi-particle and hole bosonic\nbranches. A square lattice and other structures (brick-wall and staggered\nmagnetic flux lattice) with relativistic energy dispersions which are currently\naccessible in the experiments are considered. Moreover, although in brick-wall\nand staggered flux lattices the quasi-particle densities of states looks\nqualitatively similar, the corresponding Hofstadter butterfly assumes different\nforms. In particular, we use a superposition of two different synthetic gauge\nfields which appears to be a generator of non-trivial phenomena in the optical\nlattice systems. The analysis is carried out within the strong coupling\nexpansion method on the finite size lattices and also at finite temperatures\nwhich are relevant for the currently made experiments."
    },
    {
        "anchor": "Entanglement and spin-squeezing without infinite-range interactions: Infinite-range interactions are known to facilitate the production of highly\nentangled states with applications in quantum information and metrology.\nHowever, many experimental systems have interactions that decay with distance,\nand the achievable benefits in this context are much less clear. Combining\nrecent exact solutions with a controlled expansion in the system size, we\nanalyze quench dynamics in Ising models with power-law ($1/r^{\\alpha}$)\ninteractions in $D$ dimensions, thereby expanding the understanding of spin\nsqueezing into a broad and experimentally relevant context. In spatially\nhomogeneous systems, we show that for small $\\alpha$ the scaling of squeezing\nwith system size is identical to the infinite-range ($\\alpha=0$) case. This\nindifference to the interaction range persists up to a critical value\n$\\alpha=2D/3$, above which squeezing degrades continuously. Boundary-induced\ninhomogeneities present in most experimental systems modify this picture, but\nit nevertheless remains qualitatively correct for finite-sized systems.",
        "positive": "Generating topological optical flux lattices for ultracold atoms by\n  modulated Raman and radio-frequency couplings: We propose a scheme to dynamically generate optical flux lattices with\nnontrivial band topology using amplitude-modulated Raman lasers and\nradio-frequency (rf) magnetic fields. By tuning the strength of Raman and rf\nfields, three distinct phases are realized at unit filling for a unit cell.\nRespectively, these three phases correspond to normal insulator, topological\nChern insulator, and semimetal. Nearly nondispersive bands are found to appear\nin the topological phase, which promises opportunities for investigating\nstrongly correlated quantum states within a simple cold-atom setup. The\nvalidity of our proposal is confirmed by comparing the Floquet quasienergies\nfrom the evolution operator with the spectrum of the effective Hamiltonian."
    },
    {
        "anchor": "Direct measurement of topological invariants in optical lattices: We propose an experimental technique for classifying the topology of band\nstructures realized in optical lattices, based on a generalization of\ntopological charge pumping in quantum Hall systems to cold atom in optical\nlattices. Time-of-flight measurement along one spatial direction combined with\nin situ detection along the transverse direction provide a direct measure of\nthe system's Chern number, as we illustrate by calculations for the Hofstadter\nlattice. Based on an analogy with Wannier functions techniques of topological\nband theory, the method is very general and also allows the measurement of\nother topological invariants, such as the $Z_2$ topological invariant of\ntime-reversal symmetric insulators.",
        "positive": "Data-driven discovery of statistically relevant information in quantum\n  simulators: Quantum simulators offer powerful means to investigate strongly correlated\nquantum matter. However, interpreting measurement outcomes in such systems\nposes significant challenges. Here, we present a theoretical framework for\ninformation extraction in synthetic quantum matter, illustrated for the case of\na quantum quench in a spinor Bose-Einstein condensate experiment. Employing\nnon-parametric unsupervised learning tools that provide different measures of\ninformation content, we demonstrate a system-agnostic approach to identify\ndominant degrees of freedom. This enables us to rank operators according to\ntheir relevance, akin to effective field theory. To characterize the\ncorresponding effective description, we then explore the intrinsic dimension of\ndata sets as a measure of the complexity of the dynamics. This reveals a\nsimplification of the data structure, which correlates with the emergence of\ntime-dependent universal behavior in the studied system. Our assumption-free\napproach can be immediately applied in a variety of experimental platforms."
    },
    {
        "anchor": "Quantum Vortex States in Bose Hubbard Model With Rotation: We study quantum vortex states of strongly interacting bosons in a\ntwo-dimensional rotating optical lattice. The system is modeled by Bose-Hubbard\nHamiltonian with rotation. We consider lattices of different geometries, such\nas square, rectangular and triangular. Using numerical exact diagonalization\nmethod we show how the rotation introduces vortex states of different\nground-state symmetries and the transition between these states at discrete\nrotation frequencies. We show how the geometry of the lattice plays crucial\nrole in determining the maximum number of vortex states as well as the general\ncharacteristics of these states such as, the average angular momentum $<L_z>$,\nthe current at the perimeter of the lattice, phase winding, the relation\nbetween the maximum phase difference, the maximum current and also the\nsaturation of the current between the two neighboring lattice points. The\neffect of the two- and three-body interactions between the particles, both\nattractive and repulsive, also depends on the geometry of the lattice as the\ncurrent flow or the lattice current depends on the interactions. We also\nconsider the effect of the spatial inhomogeneity introduced by the presence of\nan additional confining harmonic trap potential. It is shown that the curvature\nof the trap potential and the position of the minimum of the trap potential\nwith respect to the axis of rotation or the center of the lattice have a\nsignificant effect on the general characteristics these vortex states.",
        "positive": "Bright solitons in spin-orbit-coupled Bose-Einstein condensates: We study bright solitons in a Bose-Einstein condensate with a spin-orbit\ncoupling that has been realized experimentally. Both stationary bright solitons\nand moving bright solitons are found. The stationary bright solitons are the\nground states and possess well-defined spin-parity, a symmetry involving both\nspatial and spin degrees of freedom; these solitons are real valued but not\npositive definite, and the number of their nodes depends on the strength of\nspin-orbit coupling. For the moving bright solitons, their shapes are found to\nchange with velocity due to the lack of Galilean invariance in the system."
    },
    {
        "anchor": "Direct imaging of topological edge states in cold-atom systems: Detecting topological order in cold-atom experiments is an ongoing challenge,\nthe resolution of which offers novel perspectives on topological matter. In\nmaterial systems, unambiguous signatures of topological order exist for\ntopological insulators and quantum Hall devices. In quantum Hall systems, the\nquantized conductivity and the associated robust propagating edge modes -\nguaranteed by the existence of non-trivial topological invariants - have been\nobserved through transport and spectroscopy measurements. Here, we show that\noptical-lattice-based experiments can be tailored to directly visualize the\npropagation of topological edge modes. Our method is rooted in the unique\ncapability for initially shaping the atomic gas, and imaging its time-evolution\nafter suddenly removing the shaping potentials. Our scheme, applicable to an\nassortment of atomic topological phases, provides a method for imaging the\ndynamics of topological edge modes, directly revealing their angular velocity\nand spin structure.",
        "positive": "Collective excitations of quasi-two-dimensional trapped dipolar\n  fermions: transition from collisionless to hydrodynamic regime: We study the collective excitations of polarized single-component\nquasi-two-dimensional dipolar fermions in an isotropic harmonic trap by solving\nthe collisional Boltzmann-Vlasov (CBV) equation. We study the response to both\nmonopole and quadrupole perturbations of the trap potential and investigate the\ncharacter of excitations in each case. Simple analytic formulas are provided\nbased on the linearized scaling ansatz and accurate numerical results are\nobtained by satisfying the first eight moments of the CBV equation. Except for\nthe lowest lying monopole mode that exhibits a negligible damping in all of the\nstudied cases, the quadrupole and the higher order monopole modes undergo a\ntransition from the collisionless regime to a highly dissipative crossover\nregime and finally to the hydrodynamic regime upon increasing the dipolar\ninteraction strength. For strong vertical confinements (2D limit), we predict\nthe existence of a temperature window within which the characteristics of the\ncollective modes become temperature independent. This behavior, which is a\nunique feature of the universal near-threshold dipole-dipole scatterings,\npersists as long as the scattering energies remain in the near-threshold\nregime. The predictions of this work are expected to be in the reach of current\nexperiments."
    },
    {
        "anchor": "BCS-BEC Crossover in 2D Fermi Gases with Rashba Spin-Orbit Coupling: We present a systematic theoretical study of the BCS-BEC crossover in\ntwo-dimensional Fermi gases with Rashba spin-orbit coupling (SOC). By solving\nthe exact two-body problem in the presence of an attractive short-range\ninteraction we show that the SOC enhances the formation of the bound state: the\nbinding energy $E_{\\text B}$ and effective mass $m_{\\text B}$ of the bound\nstate grows along with the increase of the SOC. For the many-body problem, even\nat weak attraction, a dilute Fermi gas can evolve from a BCS superfluid state\nto a Bose condensation of molecules when the SOC becomes comparable to the\nFermi momentum. The ground-state properties and the\nBerezinskii-Kosterlitz-Thouless (BKT) transition temperature are studied, and\nanalytical results are obtained in various limits. For large SOC, the BKT\ntransition temperature recovers that for a Bose gas with an effective mass\n$m_{\\text B}$. We find that the condensate and superfluid densities have\ndistinct behaviors in the presence of SOC: the condensate density is generally\nenhanced by the SOC due to the increase of the molecule binding, the superfluid\ndensity is suppressed because of the non-trivial molecule effective mass\n$m_{\\text B}$.",
        "positive": "Faraday Waves in Bose-Einstein Condensates -- The Excitation by the\n  Modulation of the Interaction and the Potential: We numerically study the dynamics of Faraday waves for Bose-Einstein\ncondensates(BECs) trapped by anisotropic potentials using the three-dimensional\nGross-Pitaevskii equation. In previous studies, Faraday waves were excited by\nperiodic modulation of the interaction or potential; in contrast, this study\nsystematically addresses the excitations of the two methods. When the\ninteraction is modulated with a modulation frequency resonant with Faraday\nwaves, the breathing mode along the tight confinement direction is excited, and\nthe Faraday waves appear in the direction of weak confinement. A modulation\nfrequency that is not resonant with Faraday waves does not excite Faraday\nwaves. Thus, the dynamics depend on modulation frequencies. The behavior of the\ntotal energy and its decomposition characterize the dynamics. The excitation of\nFaraday waves depends on the anisotropy of the potentials as well; Faraday\nwaves are excited only for elongated BECs. We compare the differences of the\ndynamics in modulation methods. There are no qualitative differences between\nthe modulation of the interaction and potential. When the interaction and\npotential are simultaneously modulated, Faraday waves are excited but they do\nnot necessarily work additively. To understand this phenomenon as a dynamical\nsystem, we choose a few dynamical variables and follow their trajectory in a\nphase space. The trajectory characteristics of Faraday waves and the breathing\nmode show that the methods of modulation are not very relevant; determining the\ntarget mode to excite is important."
    },
    {
        "anchor": "Decay of an isolated monopole into a Dirac monopole configuration: We study numerically the detailed structure and decay dynamics of isolated\nmonopoles in conditions similar to those of their recent experimental\ndiscovery. We find that the core of a monopole in the polar phase of a spin-1\nBose-Einstein condensate contains a small half-quantum vortex ring. Well after\nthe creation of the monopole, we observe a dynamical quantum phase transition\nthat destroys the polar phase. Strikingly, the resulting ferromagnetic order\nparameter exhibits a Dirac monopole in its synthetic magnetic field.",
        "positive": "Probing multiple-frequency atom-photon interactions with ultracold atoms: We dress atoms with multiple-radiofrequency fields and investigate the\nspectrum of transitions driven by an additional probe field. A complete\ntheoretical description of this rich spectrum is presented, in which we find\nallowed transitions and determine their amplitudes using the resolvent\nformalism. Experimentally, we observe transitions up to sixth order in the\nprobe field using radiofrequency spectroscopy of Bose-Einstein condensates\ntrapped in single- and multiple-radiofrequency-dressed potentials. We find\nexcellent agreement between theory and experiment, including the prediction and\nverification of previously unobserved transitions, even in the\nsingle-radiofrequency case."
    },
    {
        "anchor": "Observation of wall-vortex composite defects in a spinor Bose-Einstein\n  condensate: We report the observation of spin domain walls bounded by half-quantum\nvortices (HQVs) in a spin-1 Bose-Einstein condensate with antiferromagnetic\ninteractions. A spinor condensate is initially prepared in the easy-plane polar\nphase, and then, suddenly quenched into the easy-axis polar phase. Domain walls\nare created via the spontaneous $\\mathbb{Z}_2$ symmetry breaking in the phase\ntransition and the walls dynamically split into composite defects due to snake\ninstability. The end points of the defects are identified as HQVs for the polar\norder parameter and the mass supercurrent in their proximity is demonstrated\nusing Bragg scattering. In a strong quench regime, we observe that singly\ncharged quantum vortices are formed with the relaxation of free wall-vortex\ncomposite defects. Our results demonstrate a nucleation mechanism for composite\ndefects via phase transition dynamics.",
        "positive": "Atom-dimer and dimer-dimer scattering in fermionic mixtures near a\n  narrow Feshbach resonance: We develop a diagrammatic approach for solving few-body problems in\nheteronuclear fermionic mixtures near a narrow interspecies Feshbach resonance.\nWe calculate s-, p-, and d-wave phaseshifts for the scattering of an atom by a\nweakly-bound dimer. The fermionic statistics of atoms and the composite nature\nof the dimer lead to a strong angular momentum dependence of the atom-dimer\ninteraction, which manifests itself in a peculiar interference of the scattered\ns- and p-waves. This effect strengthens with the mass ratio and is remarkably\npronounced in 40K-(40K-6Li) atom-dimer collisions. We calculate the scattering\nlength for two dimers formed near a narrow interspecies resonance. Finally, we\ndiscuss the collisional relaxation of the dimers to deeply bound states and\nevaluate the corresponding rate constant as a function of the detuning and\ncollision energy."
    },
    {
        "anchor": "Exotic magnetic orders for high spin ultracold fermions: We study Hubbard models for ultracold bosonic or fermionic atoms loaded into\nan optical lattice. The atoms carry a high spin $F>1/2$, and interact on site\nvia strong repulsive Van der Waals forces. Making convenient rearrangements of\nthe interaction terms, and exploiting their symmetry properties, we derive low\nenergy effective models with nearest-neighbor interactions, and their\nproperties. We apply our method to $F=3/2$, and 5/2 fermions on two-dimensional\nsquare lattice at quarter, and 1/6 fillings, respectively, and investigate\nmean-field equations for repulsive couplings. We find for $F=3/2$ fermions that\nthe plaquette state appearing in the highly symmetric SU(4) case does not\nrequire fine tuning, and is stable in an extended region of the phase diagram.\nThis phase competes with an SU(2) flux state, that is always suppressed for\nrepulsive interactions in absence of external magnetic field. The SU(2) flux\nstate has, however, lower energy than the plaquette phase, and stabilizes in\nthe presence of weak applied magnetic field. For $F=5/2$ fermions a similar\nSU(2) plaquette phase is found to be the ground state without external magnetic\nfield.",
        "positive": "Spin-Orbit Coupling Induced Resonance in an Ultracold Bose Gas: We study a two-component Bose gas with artificial spin-orbit coupling (SOC)\nwhich couples the center-of-mass momentum of atom to its internal states. We\nshow that in this system resonance can be induced by tuning SOC strength. With\na two-dimensional SOC, resonances in two scattering channels can be induced by\ntuning the aspect ratio of SOC strengths. With a three-dimensional SOC,\nresonance in all scattering channels can be induced by tuning the appropriate\nSOC strength. Similarly, we also find that in a Fermi gas with two- or\nthree-dimensional SOC resonance can be induced by tuning SOC strength."
    },
    {
        "anchor": "Analogue cosmological particle creation in an ultracold quantum fluid of\n  light: In inflationary cosmology, the rapid expansion of the early universe resulted\nin the spontaneous production of cosmological particles from vacuum\nfluctuations, observable today in the cosmic microwave background anisotropies.\nThe analogue of cosmological particle creation in a quantum fluid could provide\ninsight, but an observation has not yet been achieved. Here we report the\nspontaneous creation of analogue cosmological particles in the laboratory,\nusing a quenched 3-dimensional quantum fluid of light. We observe acoustic\npeaks in the density power spectrum, in close quantitative agreement with the\nquantum-field theoretical prediction. We find that the long-wavelength\nparticles provide a window to early times, and we apply this principle to the\ncosmic microwave background. This work introduces a new quantum fluid, as cold\nas an atomic Bose-Einstein condensate.",
        "positive": "Critical Temperature of Interacting Bose Gases in Periodic Potentials: The superfluid transition of a repulsive Bose gas in the presence of a\nsinusoidal potential which represents a simple-cubic optical lattice is\ninvestigate using quantum Monte Carlo simulations. At the average filling of\none particle per well the critical temperature has a nonmonotonic dependence on\nthe interaction strength, with an initial sharp increase and a rapid\nsuppression at strong interactions in the vicinity of the Mott transition. In\nan optical lattice the positive shift of the transition is strongly enhanced\ncompared to the homogenous gas. By varying the lattice filling we find a\ncrossover from a regime where the optical lattice has the dominant effect to a\nregime where interactions dominate and the presence of the lattice potential\nbecomes almost irrelevant."
    },
    {
        "anchor": "Superfluid (Amplitude) Fluctuations Above $T_c$ in a Unitary Fermi Gas: We study the transport properties of a Fermi gas with strong attractive\ninteractions close to the unitary limit. In particular, we compute the spin\ndiffusion lifetime of the Fermi gas due to superfluid fluctuations above the\nBCS transition temperature $T_c$. To calculate the spin diffusion lifetime we\nneed the scattering amplitudes. The scattering amplitudes are dominated by the\nsuperfluid fluctuations at temperatures just above $T_c$. The normal scattering\namplitudes are calculated from the Landau parameters. These Landau parameters\nare obtained from the local version of the induced interaction model for\ncomputing Landau parameters. We also calculate the leading order finite\ntemperature correction to the diffusion lifetime. A calculation of the spin\ndiffusion coefficient is presented in the end. Upon choosing a proper value of\n$F_0^a$, we are able to present a good match between the theoretical result and\nthe experimental measurement which indicates the presence of the superfluid\nfluctuations near $T_c$.",
        "positive": "Observation of a Degenerate Fermi Gas Trapped by a Bose-Einstein\n  Condensate: We report on the formation of a stable quantum degenerate mixture of\nfermionic $^6$Li and bosonic $^{133}$Cs in an optical trap by sympathetic\ncooling near an interspecies Feshbach resonance. New regimes of the quantum\ndegenerate mixtures are identified. With moderate attractive interspecies\ninteractions, we show that a degenerate Fermi gas of Li can be fully confined\nin the Cs condensate without external potentials. For stronger attraction where\nmean-field collapse is expected, no such instability is observed. In this case,\nwe suggest the stability is a result of dynamic equilibrium, where the\ninterspecies three-body loss prevents the collapse. Our picture is supported by\na rate equation model, and the crossover between the thermalization rate and\nthe observed inelastic loss rate in the regime where the mean-field collapse is\nexpected to occur."
    },
    {
        "anchor": "Dissipative dynamics of a driven quantum spin coupled to a bath of\n  ultracold fermions: We explore the dynamics and the steady state of a driven quantum spin coupled\nto a bath of fermions, which can be realized with a strongly imbalanced mixture\nof ultracold atoms using currently available experimental tools.\nRadio-frequency driving can be used to induce tunneling between the spin\nstates. The Rabi oscillations are modified due to the coupling of the quantum\nspin to the environment, which causes frequency renormalization and damping.\nThe spin-bath coupling can be widely tuned by adjusting the scattering length\nthrough a Feshbach resonance. When the scattering potential creates a bound\nstate, by tuning the driving frequency it is possible to populate either the\nground state, in which the bound state is filled, or a metastable state in\nwhich the bound state is empty. In the latter case, we predict an emergent\ninversion of the steady-state magnetization. Our work shows that different\nregimes of dissipative dynamics can be explored with a quantum spin coupled to\na bath of ultracold fermions.",
        "positive": "Current-Phase Relation of a Bose-Einstein Condensate Flowing Through a\n  Weak Link: We study the current-phase relation of a Bose-Einstein condensate flowing\nthrough a repulsive square barrier by solving analytically the one dimensional\nGross-Pitaevskii equation. The barrier height and width fix the current-phase\nrelation $j(\\delta\\phi)$, which tends to $j\\sim\\cos(\\delta\\phi/2)$ for weak\nbarriers and to the Josephson sinusoidal relation $j\\sim\\sin(\\delta\\phi)$ for\nstrong barriers. Between these two limits, the current-phase relation depends\non the barrier width. In particular, for wide enough barriers, we observe two\nfamilies of multivalued current-phase relations. Diagrams belonging to the\nfirst family, already known in the literature, can have two different positive\nvalues of the current at the same phase difference. The second family, new to\nour knowledge, can instead allow for three different positive currents still\ncorresponding to the same phase difference. Finally, we show that the\nmultivalued behavior arises from the competition between hydrodynamic and\nnonlinear-dispersive components of the flow, the latter due to the presence of\na soliton inside the barrier region."
    },
    {
        "anchor": "Chiral d-wave superfluid in periodically driven lattices: Chiral d-wave superfluid is a preliminary example of topological matters that\nintrinsically encodes interaction effects. It exhibits fascinating properties\nincluding a finite Chern number in the bulk and topologically protected edge\nstates, which have been invoking physicists for decades. However, unlike s-wave\nsuperfluids prevalent in nature, its existence requires a strong interaction in\nthe d-wave channel, a criterion that is difficult to access in ordinary\nsystems. So far, such an unconventional superfluid has not been discovered in\nexperiments. Here, we present a new principle for creating a two-dimensional\nchiral d-wave superfluid using periodically driven lattices. Due to an\nimprinted two-dimensional pseudospin-orbit coupling, where the sublattice index\nserves as the pseudospin, s-wave interaction between two hyperfine spin states\nnaturally creates a chiral d-wave superfluid. This scheme also allows\nphysicists to study the phase transition between the topologically distinct s-\nand d-wave superfluids by controlling the driving field or the particle\ndensity.",
        "positive": "Scaling solutions of the two fluid hydrodynamic equations in a\n  harmonically trapped gas at unitarity: We prove that the two fluid Landau hydrodynamic equations, when applied to a\ngas interacting with infinite scattering length (unitary gas) in the presence\nof harmonic trapping, admit exact scaling solutions of mixed compressional and\nsurface nature. These solutions are characterized by a linear dependence of the\nvelocity field on the spatial coordinates and a temperature independent\nfrequency which is calculated in terms of the parameters of the trap. Our\nresults are derived in the regime of small amplitude oscillations and hold both\nbelow and above the superfluid phase transition. They apply to isotropic as\nwell as to deformed configurations, thereby providing a generalization of\nCastin's theorem (Y. Castin, C. R. Phys. \\textbf{5}, 407 (2004)) holding for\nisotropic trapping. Our predictions agree with the experimental findings in\nresonantly interacting atomic Fermi gases. The breathing scaling solution, in\nthe presence of isotropic trapping, is also used to prove the vanishing of two\nbulk viscosity coefficients in the superfluid phase."
    },
    {
        "anchor": "Three-dimensional vortex structures in a rotating dipolar Bose-Einstein\n  condensate: We study the three-dimensional ground state vortex lattice structures of\npurely dipolar Bose-Einstein condensate (BEC). By using the mean-field model we\nobtain a stability diagram for the vortex states in purely dipolar BECs as a\nfunction of harmonic trap aspect ratio ($\\lambda$) and dipole-dipole\ninteraction strength ($D$) under rotation. Rotating the condensate within the\nunstable region leads to collapse, while in the stable region furnishes stable\nvortex lattices of dipolar BECs. We analyse stable vortex lattice structures by\nsolving three-dimensional time dependent Gross-Pitaevskii equation in imaginary\ntime. Further, the stability of vortex states is examined by evolution in\nreal-time. We also investigate distribution of vortices in fully anisotropic\ntrap by increasing eccentricity of the external trapping potential. Breaking up\nof the condensate in two parts has been observed with equally shared vortices\non each when the trap is sufficiently weak and the rotation frequency is high.",
        "positive": "From Non-Hermitian Linear Response to Dynamical Correlations and\n  Fluctuation-Dissipation Relations in Quantum Many-Body Systems: Quantum many-body systems are characterized by their correlations. While\nequal-time correlators and unequal-time commutators between operators are\nstandard observables, the direct access to unequal-time anti-commutators poses\na formidable experimental challenge. Here, we propose a general technique for\nmeasuring unequal-time anti-commutators using the linear response of a system\nto a non-Hermitian perturbation. We illustrate the protocol at the example of a\nBose-Hubbard model, where the approach to thermal equilibrium in a closed\nquantum system can be tracked by measuring both sides of the\nfluctuation-dissipation relation. We relate the scheme to the quantum Zeno\neffect and weak measurements, and illustrate possible implementations at the\nexample of a cold-atom system. Our proposal provides a way of characterizing\ndynamical correlations in quantum many-body systems with potential applications\nin understanding strongly correlated matter as well as for novel quantum\ntechnologies."
    },
    {
        "anchor": "Beyond-mean-field effects in mixtures: few-body and many-body aspects: The discovery of ultracold dilute liquids has significantly elevated our\ninterest in various phenomena which go under the name of beyond-mean-field\n(BMF) physics. In these lecture notes we give an elementary introduction to the\nquantum stabilization and liquefaction of a collapsing weakly interacting\nBose-Bose mixture. A detailed derivation of the leading BMF correction, also\nknown as the Lee-Huang-Yang (LHY) term, in this system is presented in a manner\nsuitable for further generalizations and extensions. Although the LHY term is a\nnonanalytic function of the density $n$, under certain conditions the leading\nBMF correction becomes analytic and can be expanded in integer powers of $n$,\neffectively introducing three-body and higher-order interactions. We discuss\nwhy and how well the Bogoliubov approach can predict these few-body\nobservables.",
        "positive": "Observing topological charges and dynamical bulk-surface correspondence\n  with ultracold atoms: In quenching a topological phase across phase transition, the dynamical\nbulk-surface correspondence emerges that the bulk topology of $d$-dimensional\n($d$D) phase relates to the nontrivial pattern of quench dynamics emerging on\n$(d-1)$D subspace, called band inversion surfaces (BISs) in momentum space.\nHere we report the first experimental observation of the dynamical bulk-surface\ncorrespondence through measuring the topological charges in a 2D quantum\nanomalous Hall model realized in an optical Raman lattice. The system can be\nquenched with respect to every spin axis by suddenly varying the two-photon\ndetuning or phases of the Raman couplings, in which the topological charges and\nBISs are measured dynamically by the time-averaged spin textures. We observe\nthat the total charges in the region enclosed by BISs define a dynamical\ntopological invariant, which equals the Chern index of the post-quench band.\nThe topological charges relate to an emergent dynamical field which exhibits\nnontrivial topology on BIS, rendering the dynamical bulk-surface\ncorrespondence. This study opens a new avenue to explore topological phases\ndynamically."
    },
    {
        "anchor": "Can angular oscillations probe superfluidity in dipolar supersolids?: Angular oscillations can provide a useful probe of the superfluid properties\nof a system. Such measurements have recently been applied to dipolar\nsupersolids, which exhibit both density modulation and phase coherence, and for\nwhich robust probes of superfluidity are particularly interesting. So far,\nthese investigations have been confined to linear droplet arrays. Here, we\nexplore angular oscillations in systems with 2D structure, which in principle\nhave greater sensitivity to superfluidity. Surprisingly, in both experiment and\nsimulation, we find that the frequency of angular oscillations remains nearly\nunchanged even when the superfluidity of the system is altered dramatically.\nThis indicates that angular oscillation measurements do not always provide a\nrobust experimental probe of superfluidity with typical experimental protocols.",
        "positive": "Vortices and turbulence in trapped atomic condensates: After over a decade of experiments generating and studying the physics of\nquantized vortices in atomic gas Bose-Einstein condensates, research is\nbeginning to focus on the roles of vortices in quantum turbulence, as well as\nother measures of quantum turbulence in atomic condensates. Such research\ndirections have the potential to uncover new insights into quantum turbulence,\nvortices and superfluidity, and also explore the similarities and differences\nbetween quantum and classical turbulence in entirely new settings. Here we\npresent a critical assessment of theoretical and experimental studies in this\nemerging field of quantum turbulence in atomic condensates."
    },
    {
        "anchor": "Effective self-similar expansion of a Bose-Einstein condensate: Free\n  space vs confined geometries: We compare the exact evolution of an expanding three-dimensional\nBose-Einstein condensate with that obtained from the effective scaling approach\nintroduced in D. Gu\\'ery-Odelin [Phys. Rev. A 66, 033613 (2002)]. This\napproach, which consists in looking for self-similar solutions to be satisfied\non average, is tested here in different geometries and configurations. We find\nthat, in case of almost isotropic traps, the effective scaling reproduces with\nhigh accuracy the exact evolution dictated by the Gross-Pitaevskii equation for\narbitrary values of the interactions, in agreement with the proof-of-concept of\nM. Modugno, G. Pagnini, and M. A. Valle-Basagoiti [Phys. Rev. A 97, 043604\n(2018)]. Conversely, it is shown that the hypothesis of universal\nself-similarity breaks down in case of strong anisotropies and trapped\ngeometries.",
        "positive": "On the ground state energy of the inhomogeneous Bose gas: Within the self-consistent Hartree-Fock approximation, an explicit expression\nfor the ground state energy of inhomogeneous Bose gas is derived as a\nfunctional of the inhomogeneous density of the Bose-Einstein condensate. The\nresults obtained are based on existence of the off-diagonal long-range order in\nthe single-particle density matrix for systems with a Bose-Einstein condensate.\nThis makes it possible to avoid the use of anomalous averages. The explicit\nform of the kinetic energy, which differs from one in the Gross-Pitaevski\napproach, is found. This form is valid beyond the Hartree-Fock approximation\nand can be applied for arbitrary strong interparticle interaction."
    },
    {
        "anchor": "Creating p-wave superfluids and topological excitations in optical\n  lattices: We propose to realize a p-wave superfluid using bosons mixed with a single\nspecies of fermions in a deep optical lattice. We analyze with a\nself-consistent method its excitation spectrum in presence of a vortex, and we\npoint out the range of interaction strengths in which the zero-energy mode with\ntopological character exists on a finite optical lattice. Lattice effects are\nstrongest close to fermionic half-filling: here the linearity of the low-lying\nspectrum is lost, and a new class of extended zero-energy modes with\ncheckerboard structure and d-wave symmetry appears.",
        "positive": "Stability and breakdown of Fermi polarons in a strongly interacting\n  Fermi-Bose mixture: We investigate the properties of a strongly interacting imbalanced mixture of\nbosonic $^{41}$K impurities immersed in a Fermi sea of ultracold $^6$Li atoms.\nThis enables us to explore the Fermi polaron scenario for large impurity\nconcentrations including the case where they form a Bose-Einstein condensate.\nThe system is characterized by means of radio-frequency injection spectroscopy\nand interspecies interactions are widely tunable by means of a\nwell-characterized Feshbach resonance. We find that the energy of the Fermi\npolarons formed in the thermal fraction of the impurity cloud remains rather\ninsensitive to the impurity concentration, even as we approach equal densities\nfor both species. The apparent insensitivity to high concentration is\nconsistent with a theoretical prediction, based on Landau's quasiparticle\ntheory, of a weak effective interaction between the polarons. The condensed\nfraction of the bosonic $^{41}$K gas is much denser than its thermal component,\nwhich leads to a break-down of the Fermi polaron description. Instead, we\nobserve a new branch in the radio-frequency spectrum with a small energy shift,\nwhich is consistent with the presence of Bose polarons formed by $^{6}$Li\nfermions inside the $^{41}$K condensate. A closer investigation of the behavior\nof the condensate by means of Rabi oscillation measurements support this\nobservation, indicating that we have realized Fermi and Bose polarons, two\nfundamentally different quasiparticles, in one cloud."
    },
    {
        "anchor": "Analytical theory of the dressed bound state in highly polarized Fermi\n  gases: We present an analytical treatment of a single \\down atom within a Fermi sea\nof \\up atoms, when the interaction is strong enough to produce a bound state,\ndressed by the Fermi sea. Our method makes use of a diagrammatic analysis, with\nthe involved diagrams taking only into account at most two particle-hole pairs\nexcitations. The agreement with existing Monte-Carlo results is excellent. In\nthe BEC limit our equation reduces exactly to the Skorniakov and\nTer-Martirosian equation. We present results when \\up and \\down atoms have\ndifferent masses, which is of interest for experiments in progress.",
        "positive": "Injection of orbital angular momentum and storage of quantized vortices\n  in polariton superfluids: We report the experimental investigation and theoretical modeling of a\nrotating polariton superfluid relying on an innovative method for the injection\nof angular momentum. This novel, multi-pump injection method uses four coherent\nlasers arranged in a square, resonantly creating four polariton populations\npropagating inwards. The control available over the direction of propagation of\nthe superflows allows injecting a controllable non-quantized amount of optical\nangular momentum. When the density at the center is low enough to neglect\npolariton-polariton interactions, optical singularities, associated to an\ninterference pattern, are visible in the phase. In the superfluid regime\nresulting from the strong nonlinear polariton-polariton interaction, the\ninterference pattern disappears and only vortices with the same sign are\npersisting in the system. Remarkably the number of vortices inside the\nsuperfluid region can be controlled by controlling the angular momentum\ninjected by the pumps."
    },
    {
        "anchor": "Non-linear stationary solutions in realistic models for analog\n  black-hole lasers: From both a theoretical and an experimental point of view, Bose-Einstein\ncondensates are good candidates for studying gravitational analogues of black\nholes and black-hole lasers. In particular, a recent experiment has shown that\na black-hole laser configuration can be created in the laboratory. However, the\nmost considered theoretical models for analog black-hole lasers are quite\ndifficult to implement experimentally. In order to fill this gap, we devote\nthis work to present more realistic models for black-hole lasers. For that\npurpose, we first prove that, by symmetrically extending every black-hole\nconfiguration, one can obtain a black-hole laser configuration with an\narbitrarily large supersonic region. Based on this result, we propose the use\nof an attractive square well and a double delta-barrier, which can be\nimplemented using standard experimental tools, for studying black-hole lasers.\nWe also compute the different stationary states of these setups, identifying\nthe true ground state of the system and discussing the relation between the\nobtained solutions and the appearance of dynamical instabilities.",
        "positive": "Synthetic magnetism for photon fluids: We develop a theory of artificial gauge fields in photon fluids for the cases\nof both second-order and third-order optical nonlinearities. This applies to\nweak excitations in the presence of pump fields carrying orbital angular\nmomentum, and is thus a type of Bogoliubov theory. The resulting artificial\ngauge fields experienced by the weak excitations are an interesting\ngeneralization of previous cases and reflect the PT-symmetry properties of the\nunderlying non-Hermitian Hamiltonian. We illustrate the observable consequences\nof the resulting synthetic magnetic fields for examples involving both\nsecond-order and third-order nonlinearities."
    },
    {
        "anchor": "Supefluidity of flat band Bose-Einstein condensates revisited: We consider the superfluid weight, speed of sound and excitation fraction of\na flat band Bose-Einstein condensate (BEC) within multiband Bogoliubov theory.\nThe superfluid weight is calculated by introducing a phase winding and\nminimizing the free energy with respect to it. We find that the superfluid\nweight has a contribution arising from the change of the condensate density and\nchemical potential upon the phase twist that has been neglected in the previous\nliterature. We also point out that the speed of sound and the excitation\nfraction are proportional to orbital-position-independent generalizations of\nthe quantum metric and the quantum distance, and reduce to the usual quantum\nmetric (Fubini-Study metric) and the Hilbert-Schmidt quantum distance only in\nspecial cases. We derive a second order perturbation correction to the\ndependence of the speed of sound on the generalized quantum metric, and show\nthat it compares well with numerical calculations. Our results provide a\nconsistent connection between flat band BEC and quantum geometry, with physical\nobservables being independent of the orbital positions as they should, and\ncomplete formulas for the evaluation of the superfluid weight within the\nBogoliubov theory. We discuss the limitations of the Bogoliubov theory in\nevaluating the superfluid weight.",
        "positive": "Stopping power of electrons in a semiconductor channel for swift point\n  charges: The nonperturbative kinetic framework for the stopping power of a\ncharged-particle system for swift point projectiles is implemented. The\npair-interaction potential energy required in this framework to two-body\nelastic scattering is based on the screened interaction energy between system\nparticles. In such an energetically optimized modeling the swift bare\nprojectile interacts with independent screened constituents of a fixed-density\ninteracting many-body target. The first-order Born momentum-transfer\n(transport) cross section is calculated and thus a comparison with stopping\ndata obtained [Phys. Rev. B {\\bf 26}, 2335 (1982)] by swift ions,\n$Z_1\\in{[9,17]}$ and $(v/v_0)\\simeq{11}$, under channeling condition in Si is\nmade. A quantitative agreement between the elastic scattering-based theoretical\nstopping and the experimentally observed reduced magnitude is found.\nConventionally, such a reduced magnitude for the observable is interpreted,\napplying an equipartition rule, as inelastic energy loss mediated by a\ncollective classical plasma-mode without momentum transfer to the valence-part.\nBeyond the leading, i.e., first-order Born-Bethe term ($Z_1^2$), the Barkas\n($Z_1^3$) and Bloch ($Z_1^4$) terms are discussed, following the arguments of\nLindhard for screened interaction. An extension to the case of stopping of warm\ndense plasma for swift charges is outlined as well."
    },
    {
        "anchor": "Quenched dynamics and spin-charge separation in an interacting\n  topological lattice: We analyze the static and dynamical properties of a one-dimensional\ntopological lattice, the fermionic Su-Schrieffer-Heeger model, in the presence\nof on-site interactions. Based on a study of charge and spin correlation\nfunctions, we elucidate the nature of the topological edge modes, which\ndepending on the sign of the interactions, either display particles of opposite\nspin on opposite edges, or a pair and a holon. This study of correlation\nfunctions also highlights the strong entanglement that exists between the\nopposite edges of the system. This last feature has remarkable consequences\nupon subjecting the system to a quench, where an instantaneous edge-to-edge\nsignal appears in the correlation functions characterizing the edge modes.\nBesides, other correlation functions are shown to propagate in the bulk\naccording to the light-cone imposed by the Lieb-Robinson bound. Our study\nreveals how one-dimensional lattices exhibiting entangled topological edge\nmodes allow for a non-trivial correlation spreading, while providing an\naccessible platform to detect spin-charge separation using state-of-the-art\nexperimental techniques.",
        "positive": "Ultra-cold Fermi gases with resonant dipole-dipole interaction: The superfluid phases in the resonant dipolar Fermi gases are investigated by\nthe standard mean-field theory. In contrast to the crossover from Bose-Einstein\ncondensation (BEC) to Bardeen-Cooper-Schrieffer (BCS) superfluid in the Fermi\ngases with the isotropic interactions, the resonant dipolar interaction leads\nto two completely different BEC phases of the tight-binding Fermi molecules on\nboth sides of the resonance, which are characterized by two order parameters\nwith the distinct internal symmetries. We point that near the resonance, the\ntwo competitive phases can coexist, and an emergent relative phase between the\ntwo order parameters spontaneously breaks the time-reversal symmetry, which\ncould be observed in the momentum resolved rf-spectroscopy."
    },
    {
        "anchor": "Reply to \"Comment on 'Kinetic theory for a mobile impurity in a\n  degenerate Tonks-Girardeau gas'\": In our recent paper [Phys. Rev. E 90, 032132 (2014)] we have studied the\ndynamics of a mobile impurity particle weakly interacting with the\nTonks-Girardeau gas and pulled by a small external force, $F$. Working in the\nregime when the thermodynamic limit is taken prior to the small force limit, we\nhave found that the Bloch oscillations of the impurity velocity are absent in\nthe case of a light impurity. Further, we have argued that for a light impurity\nthe steady state drift velocity, $V_D$, remains finite in the limit\n$F\\rightarrow 0$. These results are in contradiction with earlier works by\nGangardt, Kamenev and Schecter [Phys. Rev. Lett. 102, 070402 (2009), Annals of\nPhysics 327, 639 (2012)]. One of us (OL) has conjectured [Phys. Rev. A 91,\n040101 (2015)] that the central assumption of these works - the adiabaticity of\nthe dynamics - can break down in the thermodynamic limit. In the preceding\nComment [Phys. Rev. E 92, 016101 (2015)] Schecter, Gangardt and Kamenev have\nargued against this conjecture and in support of the existence of Bloch\noscillations and linearity of $V_D(F)$. They have suggested that the ground\nstate of the impurity-fluid system is a quasi-bound state and that this is\nsufficient to ensure adiabaticity in the thermodynamic limit. Their analytical\nargument is based on a certain truncation of the Hilbert space of the system.\nWe argue that extending the results and intuition based on their truncated\nmodel on the original many-body problem lacks justification.",
        "positive": "Effective Scaling Approach to Frictionless Quantum Quenches in Trapped\n  Bose Gases: We work out the effective scaling approach to frictionless quantum quenches\nin a one-dimensional Bose gas trapped in a harmonic trap. The effective scaling\napproach produces an auxiliary equation for the scaling parameter interpolating\nbetween the noninteracting and the Thomas-Fermi limits. This allows us to\nimplement a frictionless quench by engineering inversely the smooth trap\nfrequency, as compared to the two-jump trajectory. Our result is beneficial to\ndesign the shortcut-to-adiabaticity expansion of trapped Bose gases for\narbitrary values of interaction, and can be directly extended to the\nthree-dimensional case."
    },
    {
        "anchor": "Odd-parity topological superfluidity for fermions in a bond-centered\n  square optical lattice: We propose a physical scheme for the realization of two-dimensional\ntopological odd-parity superfluidity in a spin-independent bond-centered square\noptical lattice based upon interband fermion pairing. The D4 point-group\nsymmetry of the lattice protects a quadratic band crossing, which allows one to\nprepare a Fermi surface of spin-up fermions with odd parity close to the\ndegeneracy point. In the presence of spin-down fermions with even parity\npopulating a different energetically well separated band, odd-parity pairing is\nfavored. Strikingly, as a necessary prerequisite for pairing both Fermi\nsurfaces can be tuned to match well. As a result, topological superfluid phases\nemerge in the presence of merely s-wave interaction. Due to the Z2 symmetry of\nthese odd-parity superfluids, we infer their topological features simply from\nthe symmetry and the Fermi-surface topology as confirmed numerically.",
        "positive": "Spontaneous creation of non-zero angular momentum modes in\n  tunnel-coupled two-dimensional degenerate Bose gases: We investigate the dynamics of two tunnel-coupled two-dimensional degenerate\nBose gases. The reduced dimensionality of the clouds enables us to excite\nspecific angular momentum modes by tuning the coupling strength, thereby\ncreating striking patterns in the atom density profile. The extreme sensitivity\nof the system to the coupling and initial phase difference results in a rich\nvariety of subsequent dynamics, including vortex production, complex\noscillations in relative atom number and chiral symmetry breaking due to\ncounter-rotation of the two clouds."
    },
    {
        "anchor": "An ytterbium quantum gas microscope with narrow-line laser cooling: We demonstrate site-resolved imaging of individual bosonic\n$^{174}\\mathrm{Yb}$ atoms in a Hubbard-regime two-dimensional optical lattice\nwith a short lattice constant of 266 nm. To suppress the heating by probe light\nwith the $^1S_0$-$^1P_1$ transition of the wavelength $\\lambda$ = 399 nm for\nhigh-resolution imaging and preserve atoms at the same lattice sites during the\nfluorescence imaging, we simultaneously cool atoms by additionally applying\nnarrow-line optical molasses with the $^1S_0$-$^3P_1$ transition of the\nwavelength $\\lambda$ = 556 nm. We achieve a low temperature of $T = 7.4(1.3)\\\n\\mu\\mathrm{K}$, corresponding to a mean oscillation quantum number along the\nhorizontal axes of 0.22(4) during imaging process. We detect on average 200\nfluorescence photons from a single atom within 400 ms exposure time, and\nestimate the detection fidelity of 87(2)%. The realization of a quantum gas\nmicroscope with enough fidelity for Yb atoms in a Hubbard-regime optical\nlattice opens up the possibilities for studying various kinds of quantum\nmany-body systems such as Bose and Fermi gases, and their mixtures, and also\nlong-range-interacting systems such as Rydberg states.",
        "positive": "Realization of a cross-linked chiral ladder with neutral fermions in an\n  optical lattice by orbital-momentum coupling: We report the experimental realization of a cross-linked chiral ladder with\nultracold fermionic atoms in an optical lattice. In the ladder, the legs are\nformed by the orbital states of the optical lattice and the complex inter-leg\nlinks are generated by the orbital-changing Raman transitions that are driven\nby a moving lattice potential superimposed onto the optical lattice. The\neffective magnetic flux per ladder plaquette is tuned by the spatial\nperiodicity of the moving lattice, and the chiral currents are observed from\nthe asymmetric momentum distributions of the orbitals. The effect of the\ncomplex cross links is demonstrated in quench dynamics by measuring the\nmomentum dependence of the inter-orbital coupling strength. We discuss the\ntopological phase transition of the chiral ladder system for the variations of\nthe complex cross links."
    },
    {
        "anchor": "$n$-body anti-bunching in a degenerate Fermi gas of $^3$He* atoms: A key observable in investigations into quantum systems are the $n$-body\ncorrelation functions, which provide a powerful tool for experimentally\ndetermining coherence and directly probing the many-body wavefunction. While\nthe (bosonic) correlations of photonic systems are well explored, the\ncorrelations present in matter-wave systems, particularly for fermionic atoms,\nare still an emerging field. In this work, we use the unique single-atom\ndetection properties of $^3$He* atoms to perform simultaneous measurements of\nthe $n$-body quantum correlations, up to the fifth-order, of a degenerate Fermi\ngas. In a direct demonstration of the Pauli exclusion principle, we observe\nclear anti-bunching at all orders and find good agreement with predicted\ncorrelation volumes. Our results pave the way for using correlation functions\nto probe some of the rich physics associated with fermionic systems, such as\nd-wave pairing in superconductors.",
        "positive": "Adiabatic formation of bound states in the 1d Bose gas: We consider the 1d interacting Bose gas in the presence of time-dependent and\nspatially inhomogeneous contact interactions. Within its attractive phase, the\ngas allows for bound states of an arbitrary number of particles, which are\neventually populated if the system is dynamically driven from the repulsive to\nthe attractive regime. Building on the framework of Generalized Hydrodynamics,\nwe analytically determine the formation of bound states in the limit of\nadiabatic changes in the interactions. Our results are valid for arbitrary\ninitial thermal states and, more generally, Generalized Gibbs Ensembles."
    },
    {
        "anchor": "Production of a dual-species Bose-Einstein condensate of Rb and Cs atoms: We report the simultaneous production of Bose-Einstein condensates (BECs) of\n$^{87}$Rb and $^{133}$Cs atoms in separate optical traps. The two samples are\nmixed during laser cooling and loading but are separated by $400 \\mu$m for the\nfinal stage of evaporative cooling. This is done to avoid considerable\ninterspecies three-body recombination, which causes heating and evaporative\nloss. We characterize the BEC production process, discuss limitations, and\noutline the use of the dual-species BEC in future experiments to produce\nrovibronic ground state molecules, including a scheme facilitated by the\nsuperfluid-to-Mott-insulator (SF-MI) phase transition.",
        "positive": "Dynamics of spin-momentum entanglement from superradiant phase\n  transitions: Exploring operational regimes of many-body cavity QED with multi-level atoms\nremains an exciting research frontier for their enhanced storage capabilities\nof intra-level quantum correlations. In this work, we propose an extension of a\nprototypical many-body cavity QED experiment from a two to a four-level\ndescription by optically addressing a combination of momentum and spin states\nof the ultracold atoms in the cavity. The resulting model comprises a pair of\nDicke Hamiltonians constructed from pseudo-spin operators, effectively\ncapturing two intertwined superradiant phase transitions. The phase diagram\nreveals regions featuring weak and strong entangled states of spin and momentum\natomic degrees of freedom. These states exhibit different dynamical responses,\nranging from slow to fast relaxation, with the added option of persistent\nentanglement temporal oscillations. We discuss the role of cavity losses in\nsteering the system dynamics into such entangled states and propose a readout\nscheme that leverages different light polarizations within the cavity. Our work\npaves the way to connect the rich variety of non-equilibrium phase transitions\nthat occur in many-body cavity QED to the buildup of quantum correlations in\nsystems with multi-level atom descriptions."
    },
    {
        "anchor": "Manipulation of nonequilibrium spin dynamics of an ultracold gas in a\n  moving optical lattice: The isolation and control of disparate degrees of freedom underpin quantum\nsimulators. We advance the programmability of cold atom quantum simulators with\na first realization of the dynamic interplay of spatial and spin degrees of\nfreedom. We experimentally demonstrate that violent spatial evolutions tune\nlong-lived coherent spin dynamics and develop a model of quantum spin-mixing\nincorporating the spatial evolution via time-dependent spin-spin interactions.\nOur results open new paths towards the simulation of quantum spin models with\ntunable interactions via tailored spatial dynamics.",
        "positive": "Vortex lattices in binary Bose-Einstein condensates with dipole-dipole\n  interactions: We study the structure and stability of vortex lattices in two-component\nrotating Bose-Einstein condensates with intrinsic dipole-dipole interactions\n(DDIs) and contact interactions. To address experimentally accessible coupled\nsystems, we consider $^{164}$Dy-$^{162}$Dy and $^{168}$Er-$^{164}$Dy mixtures,\nwhich feature different miscibilities. The corresponding dipole moments are\n$\\mu_{\\mathrm{Dy}}=10\\mu_{\\mathrm{B}}$ and $\\mu_{\\mathrm{Er}}=\n7\\mu_{\\mathrm{B}}$, where $\\mu_{\\mathrm{B}}$ is the Bohr magneton. For\ncomparison, we also discuss a case where one of the species is non dipolar.\nUnder a large aspect ratio of the trap, we consider mixtures in the\npancake-shaped format, which are modeled by effective two-dimensional coupled\nGross-Pitaevskii equations, with a fixed polarization of the magnetic dipoles.\nThen, the miscibility and vortex-lattice structures are studied, by varying the\ncoefficients of the contact interactions (assuming the use of the\nFeshbach-resonance mechanism) and the rotation frequency. We present phase\ndiagrams for several types of lattices in the parameter plane of the rotation\nfrequency and ratio of inter- and intra-species scattering lengths. The vortex\nstructures are found to be diverse for the more miscible $^{164}$Dy-$^{162}$Dy\nmixture, with a variety of shapes, whereas, for the less miscible case of\n$^{168}$Er-$^{164}$Dy, the lattice patterns mainly feature circular or square\nformats."
    },
    {
        "anchor": "Adiabatic preparation of Floquet condensates: We argue that a Bose-Einstein condensate can be transformed into a Floquet\ncondensate, that is, into a periodically time-dependent many-particle state\npossessing the coherence properties of a mesoscopically occupied\nsingle-particle Floquet state. Our reasoning is based on the observation that\nthe denseness of the many-body system's quasienergy spectrum does not\nnecessarily obstruct effectively adiabatic transport. Employing the idealized\nmodel of a driven bosonic Josephson junction, we demonstrate that only a small\namount of Floquet entropy is generated when a driving force with judiciously\nchosen frequency and maximum amplitude is turned on smoothly.",
        "positive": "Topological phase transitions in tilted optical lattices: We analyze the energy spectrum and eigenstates of cold atoms in a tilted\nbrick-wall optical lattice. When the tilt is applied, the system exhibits a\nsequence of topological phase transitions reflected in an abrupt change of the\neigenstates. It is demonstrated that these topological phase transitions can be\neasily detected in a laboratory experiment by observing Bloch oscillations of\ncold atoms."
    },
    {
        "anchor": "Topological phase transitions driven by non-Abelian gauge potentials in\n  optical square lattices: We analyze a tight-binding model of ultracold fermions loaded in an optical\nsquare lattice and subjected to a synthetic non-Abelian gauge potential\nfeaturing both a magnetic field and a translationally invariant SU(2) term. We\nconsider in particular the effect of broken time-reversal symmetry and its role\nin driving non-trivial topological phase transitions. By varying the spin-orbit\ncoupling parameters, we find both a semimetal/insulator phase transition and a\ntopological phase transition between insulating phases with different numbers\nof edge states. The spin is not a conserved quantity of the system and the\ntopological phase transitions can be detected by analyzing its polarization in\ntime of flight images, providing a clear diagnostic for the characterization of\nthe topological phases through the partial entanglement between spin and\nlattice degrees of freedom.",
        "positive": "Classical field records of a quantum system: their internal consistency\n  and accuracy: We determine the regime where the widespread classical field description for\nquantum Bose gases is quantitatively accurate in 1d, 2d, and 3d by a careful\nstudy of the ideal gas limit. Numerical benchmarking in 1d shows that the ideal\ngas results carry over unchanged into the weakly interacting gas. The optimum\nhigh energy cutoff is in general shown to depend strongly on the observable in\nquestion (e.g. energy, density fluctuations, phase coherence length, condensate\nfraction). This explains the wide spread of past results. A consistent\nclassical field representation with less than 10% deviation in all typical\nobservables can be given for systems at temperatures below 0.0064 degeneracy\ntemperature in 1d, and 0.49 critical temperature in 3d. Surprisingly, this is\nnot possible for the 2d ideal gas even at zero temperature because mean\ndensity, density fluctuations and energy cannot be simultaneously matched to\nthe quantum results."
    },
    {
        "anchor": "Repulsive polarons in two-dimensional Fermi gases: We consider a single spin-down impurity atom interacting via an attractive,\nshort-range potential with a spin-up Fermi sea in two dimensions (2D).\nSimilarly to 3D, we show how the impurity can form a metastable state (the\n\"repulsive polaron\") with energy greater than that of the non-interacting\nimpurity. Moreover, we find that the repulsive polaron can acquire a finite\nmomentum for sufficiently weak attractive interactions. Even though the energy\nof the repulsive polaron can become sizeable, we argue that saturated\nferromagnetism is unfavorable in 2D because of the polaron's finite lifetime\nand small quasiparticle weight.",
        "positive": "The one-dimensional Bose-Fermi-Hubbard model in the ultrafast-fermion\n  limit: Charge density wave phase and MI - CDW phase separation: In a recent work [1] we presented results for the Bose-Fermi-Hubbard model\n(BFHM) in the limit of ultrafast fermions. The present work gives an overview\nover the used methods and an deeper insight into the implications arising from\nthe treated limit. Starting from the discussion of the phase diagram obtained\nby numerical means, we develop an analytic theory and derive an effective\nbosonic Hamiltonian. Arising issues in the Hamiltonian are overcome by\ninclusion of a back-action, renormalizing the solution of our system. Based on\na detailed analysis of the effective Hamiltonian, the phase diagram in the\nthermodynamic limit is constructed by analytic means and comparison to\nnumerical results obtained by density matrix renormalization group (DMRG)\ntechniques for the full BFHM shows a very reasonable agreement. The most\nprominent feature of the phase diagram, the existence of a phase separation\nbetween Mott insulator (MI) and charge density wave (CDW) is discussed in depth\nwith inclusion of important effects due to the boundary condition."
    },
    {
        "anchor": "Vortex Excitations of Dirac Bose-Einstein Condensates: We explore vortices in non-equilibrium Dirac Bose-Einstein condensates (Dirac\nBEC) described by a stationary Dirac Gross-Pitaevskii equations (GPE). We find\nthat the multi-component structure of Dirac equation enables the difference in\nphase winding of two condensates with respective phase winding number differing\nby one, $\\ell_a - \\ell_b = \\pm 1$. We observe three classes of vortex states\ndistinguished by their far-field behavior: A ring soliton on either of the two\ncomponents in combination with a vortex on the other component, and, in the\ncase of strong inter-component interactions, a vortex profile on both\ncomponents. The latter are multiple core vortices due to the phase winding\ndifference between the components. We also address the role of a Haldane gap on\nthese vortices, which has a similar effect than inter-component by making the\noccupation on either sublattice more costly. We employ a numerical shooting\nmethod to reliably identify vortex solutions and use it to scan large parts of\nthe phase space. We then use a classification algorithm on the integrated\nwavefunctions to establish a phase diagram of the different topological\nsectors.",
        "positive": "Quantum liquid droplets in Bose mixtures with weak disorder: We study the properties of self-bound liquid droplets of three-dimensional\nBose mixtures in a weak random potential with Gaussian correlation function at\nboth zero and finite temperatures. Using the Bogoliubov theory, we derive\nuseful formulas for the ground-state energy, the equilibrium density, the\ndepletion, and the anomalous density of the droplet. The quantum fluctuation\ninduced by the disorder known as the glassy fraction is also systematically\ncomputed. At finite temperature, we calculate the free energy, the thermal\nequilibrium density, and the critical temperature in terms of the disorder\nparameters. We show that when the strength and the correlation length of the\ndisorder potential exceed a certain critical value, the droplet evaporates and\nis eventually entirely destroyed. We calculate the density profiles of this\nexotic state by means of numerical simulations of the corresponding generalized\ndisorder Gross-Pitaevskii equation. Our predictions reveal that as the strength\nof the disorder gets larger, the atomic density varies rapidly in the plateau\nregion. We point out in addition that the peculiar interplay of the disorder\nand the repulsive Lee-Huang-Yang corrections play a pivotal role in the\ncollective modes of the self-bound droplet."
    },
    {
        "anchor": "Symmetry protected bosonic topological phase transitions: Quantum\n  Anomalous Hall system of weakly interacting spinor bosons in a square lattice: We study possible many body phenomena in the Quantum Anomalous Hall system of\nweakly interacting spinor bosons in a square lattice. There are various novel\nspin-bond correlated superfluids (SF) and quantum or topological phase\ntransitions among these SF phases. One transition is a first order one driven\nby roton droppings ( but with non-zero gaps $ \\Delta_R $ ) tuned by the Zeeman\nfield $ h $. Another is a second order bosonic Lifshitz transition with the\ndynamic exponents $ z_x=z_y=2 $ and an accompanying $ [C_4 \\times C_4]_D $\nsymmetry breaking. It is driven by the softening of the superfluid Goldstone\nmode tuned by the ratio of spin-orbit coupled (SOC) strength over the hopping\nstrength. The two phase boundaries meet at a topological tri-critical (TT)\npoint which separates the $ h=0 $ line into two SF phases with $ N=2 $ and $\nN=4 $ condensation momenta respectively. At the $ h=0 $ line where the system\nhas an anti-unitary $ Z_2 $ Reflection symmetry, there are infinite number of\nclassically degenerate family of states on both sides. We perform a systematic\norder from quantum disorder analysis to find the quantum ground states, also\ncalculate the roton gaps $ \\Delta_R $ generated by the order from disorder\nmechanism on both sides of the TT point. The $ N=2 $ and $ N=4 $ SF phases have\nthe same spin-orbital XY-AFM spin structure, respect the anti-unitary symmetry\nand break the $ [C_4 \\times C_4]_D $ symmetry, so they be distinguished only by\nthe different topology of the BEC condensation momenta instead of by any\ndifferences in the symmetry breaking patterns. All these novel quantum or\ntopological phenomena can be probed in the recent experimentally realized\nweakly interacting Quantum Anomalous Hall (QAH) model of $ ^87 Rb $ by Wu, {\\sl\net.al}, Science 354, 83-88 (2016).",
        "positive": "Cold Fermi-gas with long range interaction in a harmonic trap: We study equilibrium density and spin density profiles for a model of cold\none-dimensional spin 1/2 fermions interacting via inverse square interaction\nand exchange in an external harmonic trap. This model is the well-known\nspin-Calogero model (sCM) and its fully nonlinear collective field theory\ndescription is known. We extend the field theory description to the presence of\nan external harmonic trap and obtain analytic results for statics and dynamics\nof the system. For instance, we find how the equilibrium density profile\nchanges upon tuning the interaction strength. The results we obtain for\nequilibrium configurations are very similar to the ones obtained recently by Ma\nand Yang [1] for a model of fermions with short ranged interactions. Our main\napproximation is the neglect of the terms of higher order in spatial\nderivatives in equations of motion - gradientless approximation [2]. Within\nthis approximation the hydrodynamic equations of motion can be written as a set\nof decoupled forced Riemann-Hopf equations for the dressed Fermi momenta of the\nmodel. This enables us to write analytical solutions for the dynamics of spin\nand charge. We describe the time evolution of the charge density when an\ninitial non-equilibrium profile is created by cooling the gas with an\nadditional potential in place and then suddenly removing the potential. We\npresent our results as a simple \"single-particle\" evolution in the phase-space\nreminiscing a similar description of the dynamics of non-interacting\none-dimensional fermions."
    },
    {
        "anchor": "Thermal fading of the $1/k^4$-tail of the momentum distribution induced\n  by the hole anomaly: We study the thermal behavior of correlations in a one-dimensional Bose gas\nwith tunable interaction strength, crossing from weakly-repulsive to\nTonks-Girardeau regime. A reference temperature in this system is that of the\nhole anomaly, observed as a peak in the specific heat and a maximum in the\nchemical potential. We find that at large momenta $k$ and temperature above the\nanomaly threshold, the tail $\\mathcal{C}/k^4$ of the momentum distribution\n(proportional to the Tan contact $\\mathcal{C}$) is screened by the\n$1/|k|^3$-term due to a dramatic thermal increase of the internal energy\nemerging from the thermal occupation of spectral excitation states. The same\nfading is consistently revealed in the behavior at short distances $x$ of the\none-body density matrix (OBDM) where the $|x|^3$-dependence disappears for\ntemperatures above the anomaly. We obtain a new general analytic tail for the\nmomentum distribution and a minimum $k$ fixing its validity range, both\ncalculated with exact Bethe-Ansatz method and valid in all interaction and\nthermal regimes, crossing from the quantum to the classical gas limit. Our\npredictions are confirmed by comparison with ab-initio Path Integral Monte\nCarlo calculations for the momentum distribution and the OBDM exploring a wide\nrange of interaction strength and temperature. Our results unveil a novel\nconnection between excitations and correlations. We expect them to be of\ninterest to any cold atomic, nuclear, solid-state, electronic and spin system\nexhibiting an anomaly or a thermal second-order phase transition.",
        "positive": "Matter Wave Turbulence: Beyond Kinetic Scaling: Turbulent scaling phenomena are studied in an ultracold Bose gas away from\nthermal equilibrium. Fixed points of the dynamical evolution are characterized\nin terms of universal scaling exponents of correlation functions. The scaling\nbehavior is determined analytically in the framework of quantum field theory,\nusing a nonperturbative approximation of the two-particle irreducible effective\naction. While perturbative Kolmogorov scaling is recovered at higher energies,\nscaling solutions with anomalously large exponents arise in the infrared regime\nof the turbulence spectrum. The extraordinary enhancement in the momentum\ndependence of long-range correlations could be experimentally accessible in\ndilute ultracold atomic gases. Such experiments have the potential to provide\ninsight into dynamical phenomena directly relevant also in other present-day\nfocus areas like heavy-ion collisions and early-universe cosmology."
    },
    {
        "anchor": "Kitaev ring threaded by a magnetic flux: Topological gap, Anderson\n  localization of quasiparticles, and divergence of supercurrent derivative: We study a superconducting Kitaev ring pierced by a magnetic flux, with and\nwithout disorder, in a quantum ring configuration, and in a rf-SQUID one, where\na weak link is present. In the rf-SQUID configuration, in the topological\nphase, the supercurrent shows jumps at specific values of the flux\n$\\Phi^*=\\frac{hc}{e}(1/4+n)$, with $n\\in\\mathbb{N}$. In the thermodynamic limit\n$\\Phi^*$ is constant inside the topological phase, independently of disorder,\nand we analytically predict this fact using a perturbative approach in the\nweak-link coupling. The weak link breaks the topological ground-state\ndegeneracy, and opens a spectral gap for $\\Phi\\neq \\Phi^*$, that vanishes at\n$\\Phi^*$ with a cusp providing the current jump. Looking at the quasiparticle\nexcitations, we see that they are Anderson localized, so they cannot carry a\nresistive contribution to the current, and the localization length shows a\npeculiar behavior at a flat-band point for the quasiparticles. In the absence\nof disorder, we analytically and numerically find that the chemical-potential\nderivative of the supercurrent logarithmically diverges at the\ntopological-to-trivial transition, in agreement with the transition being of\nthe second order.",
        "positive": "Topological Supersolidity of Dipolar Fermi Gases in a Spin-Dependent\n  Optical Lattice: We investigate topological supersolidity of dipolar Fermi gases in a\nspin-dependent 2D optical lattice. Numerical results show that the topological\nsupersolid states can be synthesized via the combination of topological\nsuperfluid states with the stripe order, where the topological superfluid\nstates generated with dipolar interaction possess the $\\Delta_{x}+i\\Delta_{y}$\norder, and it is of D class topological classification. By adjusting the ratio\nbetween hopping amplitude $t_{x}/t_{y}$ and interaction strength $U$ with\ndipole orientation $\\phi \\approx \\frac{\\pi}{4}$, the system will undergo phase\ntransitions among the $p_{x}+ip_{y}$-wave topological superfluid state, the\np-wave superfluid state, and the topological supersolid state. The topological\nsupersolid state is proved to be stable by the positive sign of the inverse\ncompressibility. We design an experimental protocol to realize the staggered\nnext-next-nearest-neighbour hopping via the laser assisted tunneling technique,\nwhich is the key to synthesize topological supersolid states."
    },
    {
        "anchor": "Quantum-Fluctuation-Driven Dynamics of Droplet Splashing, Recoiling and\n  Deposition in Ultracold Binary Bose Gases: Droplet impact on a surface is practically relevant to a variety of fields in\nnature and industry, while a complete control of its outcomes remains\nchallenging due to various unmanageable factors. In this work, we propose the\nquantum simulation of droplet impact outcomes in the platform of ultracold\natoms. Specifically, we study the quantum-fluctuation-driven dynamics (QFDD) of\ntwo-dimensional Bose-Bose mixtures from an initial Townes soliton towards the\nformation of a quantum droplet. By tuning the fluctuation energy of the initial\nTownes state through its size and number, the subsequent QFDD can produce\nvarious outcomes including splashing, recoiling, and deposition, similar to\nthose in droplet impact dynamics. We have utilized the Weber number to identify\nthe thresholds of splashing and recoiling, and further established a universal\nscaling law between the maximum spreading factor and the Weber number in the\nrecoiling regime. In addition, we show that the residual QFDD in the deposition\nregime can be used to probe the collective breathing modes of a quantum\ndroplet. Our results reveal a mechanism for the droplet impact outcomes, which\ncan be directly tested in cold-atom experiments and can pave the way for\nexploring intriguing droplet dynamics in a clean and fully controlled quantum\nsetting.",
        "positive": "Quantum phases of dipolar bosons in multilayer optical lattice: We consider a minimal model to investigate the quantum phases of hardcore,\npolarized dipolar atoms confined in multilayer optical lattices. The model is a\nvariant of the extended Bose-Hubbard model, which incorporates intralayer\nrepulsion and interlayer attraction between the atoms in nearest-neighbour\nsites. We study the phases of this model emerging from the competition between\nthe attractive interlayer interaction and the interlayer hopping. Our results\nfrom the analytical and cluster-Gutzwiller mean-field theories reveal that\nmultimer formation occurs in the regime of weak intra and interlayer hopping\ndue to the attractive interaction. In addition, intralayer isotropic repulsive\ninteraction results in the checkerboard ordering of the multimers. This leads\nto an incompressible checkerboard multimer phase at half-filling. At higher\ninterlayer hopping, the multimers are destabilized to form resonating\nvalence-bond like states. Furthermore, we discuss the effects of thermal\nfluctuations on the quantum phases of the system."
    },
    {
        "anchor": "Multicriticality, Metastability, and Roton Feature in Bose-Einstein\n  Condensates with Three-Dimensional Spin-Orbit Coupling: We theoretically study homogeneously trapped atomic Bose-Einstein condensates\nwhere all three momentum components couple to a pseudo-spin-$1/2$ degree of\nfreedom. Tuning the anisotropies of spin-orbit coupling and the spin-dependent\ninteractions is shown to provide access to a rich phase diagram with a\ntetracritical point, first-order phase transitions, and multiple metastable\nphases of stripe and plane-wave character. The elementary excitation spectrum\nof the axial plane-wave phase features an anisotropic roton feature and can be\nused to probe the phase diagram. In addition to providing a versatile\nlaboratory for studying fundamental concepts in statistical physics, the\nemergence of metastable phases creates new opportunities for observing\nfalse-vacuum decay and bubble nucleation in ultra-cold-atom experiments.",
        "positive": "Quantum noise in three-dimensional BEC interferometry: We develop a theory of quantum fluctuations and squeezing in a\nthree-dimensional Bose-Einstein condensate atom interferometer with nonlinear\nlosses. We use stochastic equations in a truncated Wigner representation to\ntreat quantum noise. Our approach includes the multi-mode spatial evolution of\nspinor components and describes the many-body dynamics of a mesoscopic quantum\nsystem."
    },
    {
        "anchor": "Compressibility of a fermionic Mott insulator of ultracold atoms: We characterize the Mott insulating regime of a repulsively interacting Fermi\ngas of ultracold atoms in a three-dimensional optical lattice. We use in-situ\nimaging to extract the central density of the gas, and to determine its local\ncompressibility. For intermediate to strong interactions, we observe the\nemergence of a plateau in the density as a function of atom number, and a\nreduction of the compressibility at a density of one atom per site, indicating\nthe formation of a Mott insulator. Comparisons to state-of-the-art numerical\nsimulations of the Hubbard model over a wide range of interactions reveal that\nthe temperature of the gas is of the order of, or below, the tunneling energy\nscale. Our results hold great promise for the exploration of many-body\nphenomena with ultracold atoms, where the local compressibility can be a useful\ntool to detect signatures of different phases or phase boundaries at specific\nvalues of the filling.",
        "positive": "Density of condensate of a dilute Bose gas in improved Hartree-Fock\n  approximation: In a manner of Cornwal-Jackiw-Tomboulis effective action approach, the\ndensity of condensate of a dilute Bose gas confined between two planar walls is\ninvestigated within the framework of improved Hartree-Fock. Thereby, the\nquantum fluctuations are taken into account with presence of high-order terms\nin the momentum integrals. Our results show that the quantum fluctuations\nsignificantly belittle the density of condensate compared with square of the\nexpectation value of the field operator. The comparison with relating results\nof Gross-Pitaevskii theory is made."
    },
    {
        "anchor": "Finite Range Effects in Energies and Recombination Rates of Three\n  Identical Bosons: We investigate finite-range effects in systems with three identical bosons.\nWe calculate recombination rates and bound state spectra using two different\nfinite-range models that have been used recently to describe the physics of\ncold atomic gases near Feshbach resonances where the scattering length is\nlarge. The models are built on contact potentials which take into account\nfinite range effects; one is a two-channel model and the other is an effective\nrange expansion model implemented through the boundary condition on the\nthree-body wave function when two of the particles are at the same point in\nspace. We compare the results with the results of the ubiquitous\nsingle-parameter zero-range model where only the scattering length is taken\ninto account. Both finite range models predict variations of the well-known\ngeometric scaling factor 22.7 that arises in Efimov physics. The threshold\nvalue at negative scattering length for creation of a bound trimer moves to\nhigher or lower values depending on the sign of the effective range compared to\nthe location of the threshold for the single-parameter zero-range model. Large\neffective ranges, corresponding to narrow resonances, are needed for the\nreduction to have any noticeable effect.",
        "positive": "Disorder driven Thouless charge pump in a quasiperiodic chain: Thouless charge pump enables a quantized transport of charge through an\nadiabatic evolution of the Hamiltonian exhibiting topological phase. While this\ncharge pumping is known to be robust against the presence of weak disorder in\nthe system, it often breaks down with the increase in disorder strength. In\nthis work, however, we show that in a one dimensional Su-Schrieffer-Heeger\nlattice, a unit cell-wise staggered quasiperiodic disorder favors a quantized\ncharge pump. Moreover, we show that such quantized Thouless charge pump is\nachieved by following the standard single cycle pumping protocol which usually\nleads to a breakdown of charge pump in other known models. This unusual\nproperty is found to be due to an emergence of a trivial gapped phase from a\ntopological phase as the quasiperiodic disorder is tuned. This emergent gapped\nto gapped transition also allows us to propose a non-standard pumping scheme\nwhere a modulated disorder favors a quantized Thouless charge pump."
    },
    {
        "anchor": "Classifying Snapshots of the Doped Hubbard Model with Machine Learning: Quantum gas microscopes for ultracold atoms can provide high-resolution\nreal-space snapshots of complex many-body systems. We implement machine\nlearning to analyze and classify such snapshots of ultracold atoms.\nSpecifically, we compare the data from an experimental realization of the\ntwo-dimensional Fermi-Hubbard model to two theoretical approaches: a doped\nquantum spin liquid state of resonating valence bond type, and the geometric\nstring theory, describing a state with hidden spin order. This approach\nconsiders all available information without a potential bias towards one\nparticular theory by the choice of an observable and can therefore select the\ntheory which is more predictive in general. Up to intermediate doping values,\nour algorithm tends to classify experimental snapshots as\ngeometric-string-like, as compared to the doped spin liquid. Our results\ndemonstrate the potential for machine learning in processing the wealth of data\nobtained through quantum gas microscopy for new physical insights.",
        "positive": "Many-body effects in the excitations and dynamics of trapped\n  Bose-Einstein condensates: This review explores the dynamics and the low-energy excitation spectra of\nBose-Einstein condensates (BECs) of interacting bosons in external potential\ntraps putting particular emphasis on the emerging many-body effects beyond\nmean-field descriptions. To do so, methods have to be used that, in principle,\ncan provide numerically exact results for both the dynamics and the excitation\nspectra in a systematic manner. Numerically exact results for the dynamics are\npresented employing the well-established multicongurational time-dependent\nHartree for bosons (MCTDHB) method. The respective excitation spectra are\ncalculated utilizing the more recently introduced linear-response theory atop\nit (LR-MCTDHB). The latter theory gives rise to an, in general, non-hermitian\neigenvalue problem. The theory and its newly developed implementation are\ndescribed in detail and benchmarked towards the exactly-solvable\nharmonic-interaction model. Several applications to BECs in one- and\ntwo-dimensional potential traps are discussed. With respect to dynamics, it is\nshown that both the out-of-equilibrium tunneling dynamics and the dynamics of\ntrapped vortices are of many-body nature. Furthermore, many-body effects in the\nexcitation spectra are presented for BECs in different trap geometries. It is\ndemonstrated that even for essentially-condensed systems, the spectrum of the\nlowest-in-energy excitations computed at the many-body level can differ\nsubstantially from the standard mean-field description. In general, it is shown\nthat bosons carrying angular momentum are more sensitive to many-body effects\nthan bosons without. These effects are present in both the dynamics and the\nexcitation spectrum."
    },
    {
        "anchor": "Time crystals in a shaken atom-cavity system: We demonstrate the emergence of a time crystal of atoms in a high-finesse\noptical cavity driven by a phase-modulated transverse pump field, resulting in\na shaken lattice. This shaken system exhibits macroscopic oscillations in the\nnumber of cavity photons and order parameters at noninteger multiples of the\ndriving period, which signals the appearance of an incommensurate time crystal.\nThe subharmonic oscillatory motion corresponds to dynamical switching between\nsymmetry-broken states, which are nonequilibrium bond ordered density wave\nstates. Employing a semiclassical phase-space representation for the\ndriven-dissipative quantum dynamics, we confirm the rigidity and persistence of\nthe time crystalline phase. We identify experimentally relevant parameter\nregimes for which the time crystal phase is long-lived, and map out the\ndynamical phase diagram. We compare and contrast the incommensurate time\ncrystal with the commensurate Dicke time crystal in the amplitude-modulated\ncase.",
        "positive": "Short-range correlations and entropy in ultracold atomic Fermi gases: We relate short-range correlations in ultracold atomic Fermi gases to the\nentropy of the system over the entire temperature, $T$, vs. coupling strength,\n$-1/k_Fa$, plane. In the low temperature limit the entropy is dominated by\nphonon excitations and the correlations increase as $T^4$. In the BEC limit, we\ncalculate a boson model within the Bogoliubov approximation to show explicitly\nhow phonons enhance the fermion correlations. In the high temperature limit, we\nshow from the virial expansion that the correlations decrease as $1/T$. The\ncorrelations therefore reach a maximum at a finite temperature. We infer the\ngeneral structure of the isentropes of the Fermi gas in the $T,-1/k_Fa$ plane,\nand the temperature dependence of the correlations in the unitary, BEC, and BCS\nlimits. Our results compare well with measurements of the correlations via\nphotoassociation experiments at higher temperatures."
    },
    {
        "anchor": "Modulational instability and soliton generation in chiral Bose-Einstein\n  condensates with zero-energy nonlinearity: By means of analytical and numerical methods, we address the modulational\ninstability (MI) in chiral condensates governed by the Gross-Pitaevskiiequation\nincluding the current nonlinearity. The analysis shows that this nonlinearity\npartly suppresses off the MI driven by the cubic self-focusing, although the\ncurrent nonlinearity is not represented in the system's energy (although it\nmodifies the momentum), hence it may be considered as zero-energy nonlinearity.\nDirect simulations demonstrate generation of trains of stochastically\ninteracting chiral solitons by MI. In the ring-shaped setup, the MI creates a\nsingle traveling solitary wave. The sign of the current nonlinearity determines\nthe direction of propagation of the emerging solitons.",
        "positive": "Quantum behavior of a heavy impurity strongly coupled to a Bose gas: We investigate the problem of an infinitely heavy impurity interacting with a\ndilute Bose gas at zero temperature. When the impurity-boson interactions are\nshort ranged, we show that boson-boson interactions induce a quantum blockade\neffect, where a single boson can effectively block or screen the impurity\npotential. Since this behavior depends on the quantum granular nature of the\nBose gas, it cannot be captured within a standard classical-field description.\nUsing a combination of exact quantum Monte Carlo methods and a truncated basis\napproach, we show how the quantum correlations between bosons lead to universal\nfew-body bound states and a logarithmically slow dependence of the polaron\nground-state energy on the boson-boson scattering length. Moreover, we expose\nthe link between the polaron energy and the spatial structure of the quantum\ncorrelations, spanning the infrared to ultraviolet physics."
    },
    {
        "anchor": "Quantum optics and frontiers of physics: The third quantum revolution: The year 2015 was the International Year of Light. It marked, however, also\nthe 20th anniversary of the first observation of Bose-Einstein condensation in\natomic vapors by Eric Cornell, Carl Wieman and Wolfgang Ketterle. This\ndiscovery can be considered as one of the greatest achievements of quantum\noptics that has triggered an avalanche of further seminal discoveries and\nachievements. For this reason we devote this essay for focus issue on \"Quantum\nOptics in the International Year of Light\" to the recent revolutionary\ndevelopments in quantum optics at the frontiers of all physics: atomic physics,\nmolecular physics, condensed matter physics, high energy physics and quantum\ninformation science. We follow here the lines of the introduction to our book\n\"Ultracold atoms in optical lattices: Simulating quantum many-body systems\"\n[1]. The book, however, was published in 2012, and many things has happened\nsince then -- the present essay is therefore upgraded to include the latest\ndevelopments.",
        "positive": "Synthetic Flux Attachment: Topological field theories emerge at low energy in strongly-correlated\ncondensed matter systems and appear in the context of planar gravity. In\nparticular, the study of Chern-Simons terms gives rise to the concept of flux\nattachment when the gauge field is coupled to matter, yielding flux-charge\ncomposites. Here we investigate the generation of flux attachment in a\nBose-Einstein condensate in the presence of non-linear synthetic gauge\npotentials. In doing so, we identify the U(1) Chern-Simons gauge field as a\nsingular density-dependent gauge potential, which in turn can be expressed as a\nBerry connection. We envisage a proof-of-concept scheme where the artificial\ngauge field is perturbatively induced by an effective light-matter detuning\ncreated by interparticle interactions. At a mean field level, we recover the\naction of a \"charged\" superfluid minimally coupled to both a background and a\nChern-Simons gauge field. Remarkably, a localised density perturbation in\ncombination with a non-linear gauge potential gives rise to an effective\ncomposite boson model of fractional quantum Hall effect, displaying anyonic\nvortices."
    },
    {
        "anchor": "Violation of single-length scaling dynamics via spin vortices in an\n  isolated spin-1 Bose gas: We consider the phase ordering dynamics of an isolated quasi-two-dimensional\nspin-1 Bose gas quenched into an easy-plane ferromagnetic phase. Preparing the\ninitial system in an unmagnetized anti-ferromagnetic state the subsequent\nordering involves both polar core and Mermin-Ho spin vortices, with the ratio\nbetween the different vortices controllable by the quench parameter.\nFerromagnetic domain growth occurs as these vortices annihilate. The distinct\ndynamics of the two types of vortices means that the domain growth law is\ndetermined by two macroscopic length scales, violating the standard dynamic\nscaling hypothesis. Nevertheless we find that universality of the ordering\nprocess manifests in the decay laws for the spin vortices.",
        "positive": "Floquet analysis of time-averaged trapping potentials: Time-averaged trapping potentials have played an important role in the\ndevelopment of the field of ultracold atoms. Despite their widespread\napplication, there is not yet a complete understanding of when a system can be\nconsidered time-averaged. Here we use Floquet theory to analyse the lowest\nenergy state of time-periodic trapping potentials, and characterise the\ntransition from a localised state in a slowly moving trap to a delocalised\nstate in a rapidly oscillating time-averaged potential. We investigate how the\ndriving parameters affect the density and phase of the Floquet ground state,\nand provide a quantitative measure of the degree to which they can be\nconsidered time-averaged. We study a number of simple representative systems,\nand comment on the features affecting the experimental realisation of\ntime-averaged trapping potentials."
    },
    {
        "anchor": "Hydrodynamic modes of partially condensed Bose mixtures: We generalize the Landau-Khalatnikov hydrodynamic theory for superfluid\nhelium to two-component (binary) Bose mixtures at arbitrary temperatures. In\nparticular, we include the spin-drag terms that correspond to viscous coupling\nbetween the clouds. Therefore, our theory not only describes the usual\ncollective modes of the individual components, e.g., first and second sound,\nbut also results in new collective modes, where both constituents participate.\nWe study these modes in detail and present their dispersions using\nthermodynamic quantities obtained within the Popov approximation.",
        "positive": "Fractional domain walls from on-site softening in dipolar bosons: We study dipolar bosons in a 1D optical lattice and identify a region in\nparameter space---strong coupling but relatively weak on-site\nrepulsion---hosting a series of stable charge-density-wave (CDW) states whose\nlow-energy excitations, built from \"fractional domain walls,\" have remarkable\nsimilarities to those of non-Abelian fractional quantum Hall states. Here, a\nconventional domain wall between translated CDW's may be split by inserting\nstrings of degenerate, but inequivalent, CDW states. Outside these insulating\nregions, we find numerous supersolids as well as a superfluid regime. The\nmentioned phases should be accessible experimentally and, in particular, the\nfractional domain walls can be created in the ground state using single-site\naddressing, i.e., by locally changing the chemical potential."
    },
    {
        "anchor": "Topological Gapless Matters in Three-dimensional Ultracold Atomic Gases: Three-dimensional topological gapless matters with gapless degeneracies\nprotected by a topological invariant defined over a closed manifold in momentum\nspace have attracted considerable interest in various fields ranging from\ncondensed matter materials to ultracold atomic gases. As a highly controllable\nand disorder free system, ultracold atomic gases provide a versatile platform\nto simulate topological gapless matters. Here, the current progress in studies\nof topological gapless phenomena in three-dimensional cold atom systems is\nsummarized in the review. It is mainly focused on Weyl points, structured\n(type-II) Weyl points, Dirac points, nodal rings and Weyl exceptional rings in\ncold atoms. Since interactions in cold atoms can be controlled via Feshbach\nresonances, the progress in both superfluids for attractive interactions and\nnon-interacting cold atom gases is reviewed.",
        "positive": "Spin Hall mode in a trapped thermal Rashba gas: We theoretically investigate a two-dimensional harmonically-trapped gas of\nidentical atoms with Rashba spin-orbit coupling and no interatomic\ninteractions. In analogy with the spin Hall effect in uniform space, the gas\nexhibits a spin Hall mode. In particular, in response to a displacement of the\ncenter-of-mass of the system, spin-dipole moment oscillations occur. We\ndetermine the properties of these oscillations exactly, and find that their\namplitude strongly depends on the spin-orbit coupling strength and the quantum\nstatistics of the particles."
    },
    {
        "anchor": "Itinerant Ferromagnetism in a polarized two-component Fermi gas: We analyze when a repulsively interacting two-component Fermi gas becomes\nthermodynamically unstable against phase separation. We focus on the strongly\npolarised limit where the free energy of the homogeneous mixture can be\ncalculated accurately in terms of well-defined quasiparticles, the repulsive\npolarons. Phase diagrams as a function of polarisation, temperature, mass\nimbalance, and repulsive polaron energy, as well as scattering length and range\nparameter are provided. We show that the lifetime of the repulsive polaron\nincreases significantly with the interaction range and the mass of the minority\natoms, raising the prospects of detecting the transition to the elusive\nitinerant ferromagnetic state with ultracold atoms.",
        "positive": "Helical superfluid in a frustrated honeycomb Bose-Hubbard model: We study a \"helical\" superfluid, a nonzero-momentum condensate in a\nfrustrated bosonic model. At mean-field Bogoliubov level, such a novel state\nexhibits \"smectic\" fluctuation that are qualitatively stronger than that of a\nconventional superfluid. We develop a phase diagram and compute a variety of\nits physical properties, including the spectrum, structure factor, condensate\ndepletion, momentum distribution, all of which are qualitatively distinct from\nthat of a conventional superfluid. Interplay of fluctuations, interaction and\nlattice effects gives rise to the phenomenon of order-by-disorder, leading to a\ncrossover from the smectic superfluid regime to the anisotropic XY superfluid\nphase. We complement the microscopic lattice analysis with a field theoretic\ndescription for such a helical superfluid, which we derive from microscopics\nand justify on general symmetry grounds, reassuringly finding full consistency.\nPossible experimental realizations are discussed."
    },
    {
        "anchor": "Intra-scales energy transfer during the evolution of turbulence in a\n  trapped Bose-Einstein condensate: In turbulence phenomena, including the quantum turbulence in superfluids, an\nenergy flux flows from large to small length scales, composing a cascade of\nenergy. A universal characteristic of turbulent flows is the existence of a\nrange of scales where the energy flux is scale-invariant: this interval of\nscales is often referred to as inertial region. This property is fundamental\nas, for instance, in turbulence of classical fluids it characterizes the\nbehavior of statistical features such as spectra and structure functions. Here\nwe show that also in decaying quantum turbulence generated in trapped\nBose-Einstein condensates (BECs), intervals of momentum space where the energy\nflux is constant can be identified. Indeed, we present a procedure to measure\nthe energy flux using both the energy spectrum and the continuity equation. A\nrange of scales where the flux is constant is then determined employing two\ndistinct protocols and in the same range, the momentum distribution measured is\nconsistent with previous work. The successful identification of a region with\nconstant flux in turbulent BECs is a manifestation of the universal character\nof turbulence in these quantum systems. These measurements pave the way for\nstudies of energy conservation and dissipation in trapped atomic superfluids,\nand also analogies with the related processes that take place in ordinary\nfluids.",
        "positive": "Triplet pair correlations in {\\it s-}wave superfluids as a signature of\n  the FFLO state: We show that triplet pairing correlations are generated in purely s-waves\nsuperfluids whenever population imbalance enforces anisotropic Fulde-Ferrell\n(FF) or inhomogeneous Larkin-Ovchinikov (LO) states. The same set of\nquasiparticle states contributes to the triplet component and to the\npolarization, thus spatially correlating them. In the LO case, this set forms a\nnarrow band of Andreev states centered on the nodes of the s-wave order\nparameter. This picture naturally provides a unifying explanation of previous\nfindings that attractive p-wave interaction stabilizes FFLO states. We also\nstudy a similar triplet mixing which occurs when a balanced two-component\nsystem displays FFLO type oscillations due to a spin-dependent optical lattice.\nWe discuss how this triplet component can be measured in systems of ultra-cold\natoms using a rapid ramp across a p-wave Feshbach resonance. This should\nprovide a smoking gun signature of FFLO states."
    },
    {
        "anchor": "Generation of dark-bright soliton trains in superfluid-superfluid\n  counterflow: The dynamics of two penetrating superfluids exhibit an intriguing variety of\nnonlinear effects. Using two distinguishable components of a Bose-Einstein\ncondensate, we investigate the counterflow of two superfluids in a narrow\nchannel. We present the first experimental observation of trains of dark-bright\nsolitons generated by the counterflow. Our observations are theoretically\ninterpreted by three-dimensional numerical simulations for the coupled\nGross-Pitaevskii (GP) equations and the analysis of a jump in the two\nrelatively flowing components' densities. Counterflow induced modulational\ninstability for this miscible system is identified as the central process in\nthe dynamics.",
        "positive": "Many-body exceptional points in colliding condensates: Exceptional points describe the coalescence of the eigenmodes of a\nnon-Hermitian matrix. When an exceptional point occurs in the unitary evolution\nof a many-body system, it generically leads to a dynamical instability with a\nfinite wavevector [N. Bernier \\etal, Phys. Rev. Lett. 113, 065303 (2014)].\nHere, we study exceptional points in the context of the counterflow instability\nof colliding Bose-Einstein condensates. We show that the instability of this\nsystem is due to an exceptional point in the Bogoliubov spectrum. We further\nclarify the connection of this effect to the Landau criterion of superfluidity\nand to the scattering of classical particles. We propose an experimental set-up\nto directly probe this exceptional point, and demonstrate its feasibility with\nthe aid of numerical calculations. Our work fosters the observation of\nexceptional points in nonequilibrium many-body quantum systems."
    },
    {
        "anchor": "Proposal for interferometric detection of topological defects in\n  modulated superfluids: Attractive interactions between fermions can produce a superfluid ground\nstate, in which pairs of up and down spins swirl together in a coordinated,\ncoherent dance. How is this dance affected by an imbalance in the population of\nup and down fermions? Do the extra fermions stand on the sides, or do they\ndisrupt the dance? The most intriguing possibility is the formation of a\nmodulated superfluid state, known as an LO phase, in which the excess fermions\nself-organize into domain walls where the pairing amplitude changes sign.\nDespite fifty years of theoretical and experimental work, there has so far been\nno direct observation of an LO phase. Here we propose an experiment in which\ntwo fermion clouds, prepared with unequal population imbalances, are allowed to\nexpand and interfere. A zipper pattern in the interference fringes is\nunequivocal evidence of LO physics. Furthermore, because the experiment is\nresolved in time and in two spatial directions, we expect an observable\nsignature even at finite temperatures (when thermal fluctuations destroy\nlong-range LO order averaged over time).",
        "positive": "Collective modes of a two-dimensional Fermi gas at finite temperature: In this work we examine the breathing mode of a strongly interacting\ntwo-dimensional Fermi gas and the role of temperature on the anomalous breaking\nof scale invariance. By calculating the equation of state with different\nmany-body $T$-matrix theories and the virial expansion approach, we obtain a\nhydrodynamic equation of the harmonically trapped Fermi gas (with trapping\nfrequency $\\omega_{0}$) through the local density approximation. By solving the\nhydrodynamic equation we determine the breathing mode frequencies as functions\nof interaction strength and temperature. We find that the breathing mode\nanomaly depends sensitively on both interaction strength and temperature. In\nparticular, in the strongly interacting regime we predict a significant\ndown-shift of the breathing mode frequency, below the scale invariant value of\n$2\\omega_{0}$ for temperatures of order the Fermi temperature."
    },
    {
        "anchor": "Quantum lock-in detection of a vector light shift: We demonstrate detection of a vector light shift (VLS) using the quantum\nlock-in method. The method offers precise and accurate VLS measurement without\nbeing affected by real magnetic field fluctuations. We detect a VLS on a\nBose--Einstein condensate (BEC) of $^{87}$Rb atoms caused by an optical trap\nbeam with a resolution less than 1 Hz. We also demonstrate elimination of a VLS\nby controlling the beam polarization to realize a long coherence time of a\ntransversally polarized $F$ = 2 BEC. Quantum lock-in VLS detection should find\nwide application, including the study of spinor BECs, electric-dipole moment\nsearches, and precise magnetometry.",
        "positive": "Spin effects in Bose-Glass phases: We study the mechanism of formation of Bose glass (BG) phases in the spin-1\nBose Hubbard model when diagonal disorder is introduced. To this aim, we\nanalyze first the phase diagram in the zero-hopping limit, there disorder\ninduces superposition between Mott insulator (MI) phases with different filling\nnumbers. Then BG appears as a compressible but still insulating phase. The\nphase diagram for finite hopping is also calculated with the Gutzwiller\napproximation. The bosons' spin degree of freedom introduces another scattering\nchannel in the two-body interaction modifying the stability of MI regions with\nrespect to the action of disorder. This leads to some peculiar phenomena such\nas the creation of BG of singlets, for very strong spin correlation, or the\ndisappearance of BG phase in some particular cases where fluctuations are not\nable to mix different MI regions."
    },
    {
        "anchor": "Sisyphus cooling in a continuously loaded trap: We demonstrate continuous Sisyphus cooling combined with a continuous loading\nmechanism used to efficiently slow down and accumulate atoms from a guided\nbeam. While the loading itself is based on a single slowing step, applying a\nradio frequency field forces the atoms to repeat this step many times resulting\nin a so-called Sisyphus cooling. This extension allows efficient loading and\ncooling of atoms from a wide range of initial beam conditions. We study the\ninterplay of the continuous loading and simultaneous Sisyphus cooling in\ndifferent density regimes. In the case of a low density flux we observe a\nrelative gain in phase-space density of nine orders of magnitude. This makes\nthe presented scheme an ideal tool for reaching collisional densities enabling\nevaporative cooling - in spite of unfavourable initial conditions.",
        "positive": "Phonon Stability of Quantum Droplets in a dipolar Bose gases: Stabilized by quantum fluctuations, dipolar Bose-Einstein condensates can\nform self-bound liquidlike droplets in the mean-field unstable regime. However\nin the Bogoliubov theory, some phonon energies are imaginary in the\nlong-wavelength limit, implying dynamical instability of this system. A similar\ninstability appears in the Bogoliubov theory of a binary quantum droplet, and\nis removed due to higher-order quantum fluctuations as shown recently [1]. In\nthis work, we study the phonon energy of a dipolar quantum droplet in the\nBeliaev formalism, and find that quantum fluctuations can enhance the phonon\nstability. We obtain the anisotropic sound velocity which can be tested in\nexperiment."
    },
    {
        "anchor": "Dynamical topological invariants and reduced rate functions for\n  dynamical quantum phase transitions in two dimensions: We show that dynamical quantum phase transitions (DQPTs) in the quench\ndynamics of two-dimensional topological systems can be characterized by a\ndynamical topological invariant defined along an appropriately chosen closed\ncontour in momentum space. Such a dynamical topological invariant reflects the\nvorticity of dynamical vortices responsible for the DQPTs, and thus serves as a\ndynamical topological order parameter in two dimensions. We demonstrate that\nwhen the contour crosses topologically protected fixed points in the quench\ndynamics, an intimate connection can be established between the dynamical\ntopological order parameter in two dimensions and those in one dimension. We\nfurther define a reduced rate function of the Loschmidt echo on the contour,\nwhich features non-analyticities at critical times and is sufficient to\ncharacterize DQPTs in two dimensions. We illustrate our results using the\nHaldane honeycomb model and the quantum anomalous Hall model as concrete\nexamples, both of which have been experimentally realized using cold atoms.",
        "positive": "Controlling the scattering length of ultracold dipolar molecules: By applying a circularly polarized and slightly blue-detuned microwave field\nwith respect to the first excited rotational state of a dipolar molecule, one\ncan engineer a long-range, shallow potential well in the entrance channel of\nthe two colliding partners. As the applied microwave ac-field is increased, the\nlong-range well becomes deeper and can support a certain numbers of bound\nstates, which in turn bring the value of the molecule-molecule scattering\nlength from a large negative value to a large positive one. We adopt an\nadimensional approach where the molecules are described by a rescaled\nrotational constant $\\tilde{B} = B/s_{E_3} $ where $s_{E_3}$ is a\ncharacteristic dipolar energy. We found that molecules with $\\tilde{B} > 10^8$\nare immune to any quenching losses when a sufficient ac-field is applied, the\nratio elastic to quenching processes can reach values above $10^3$, and that\nthe value and sign of the scattering length can be tuned. The ability to\ncontrol the molecular scattering length opens the door for a rich, strongly\ncorrelated, many-body physics for ultracold molecules, similar than that for\nultracold atoms."
    },
    {
        "anchor": "Acoustic oscillations in cigar-shaped logarithmic Bose-Einstein\n  condensate in the Thomas-Fermi approximation: We consider the dynamical properties of density fluctuations in the\ncigar-shaped Bose-Einstein condensate described by the logarithmic wave\nequation with a constant nonlinear coupling by using the Thomas-Fermi and\nlinear approximations. It is shown that the propagation of small density\nfluctuations along the long axis of a condensed lump in a strongly anisotropic\ntrap is essentially one-dimensional, while the trapping potential can be\ndisregarded in the linear regime. Depending on the sign of nonlinear coupling,\nthe fluctuations either take the form of translationally symmetric pulses and\nstanding waves, or become oscillations with varying amplitudes. We also study\nthe condensate in an axial harmonic trap, by using elasticity theory's notions.\nLinear particle density and energy also behave differently depending on the\nnonlinear coupling's value. If it is negative, the density monotonously grows\nalong with lump's radius, while energy is a monotonous function of density. For\nthe positive coupling, the density is bound from above, whereas energy grows\nmonotonously as a function of density until it reaches its global maximum.",
        "positive": "Instabilities and \"phonons\" of optical lattices in hollow optical fibers: Instabilities are predicted for a sufficiently long hollow photonic optical\nfiber, or \"cavity\", containing a one dimensional Bose-gas in the presence of a\nclassical, far red-detuned, confined weak electromagnetic mode. We examine both\na single beam with Bose gas (a type of Brillouin instability) and the case of a\nstanding wave, or optical lattice. The instabilities of these driven systems\nhave pronounced spatial structure, of combined modulational instabilities in\nthe electromagnetic and Bose density fields. Near the critical wave vectors for\nthe instability the coupled modes of the BEC and light can be interpreted as\n\"phonons\" of the optical lattice. We conjecture these spatially-structured\ninstabilities for the optical lattice, which we predict at weak fields, develop\ninto the source of spatially homogeneous heating predicted for strong fields."
    },
    {
        "anchor": "Experimental Methods for Generating Two-Dimensional Quantum Turbulence\n  in Bose-Einstein Condensates: Bose-Einstein condensates of dilute gases are well-suited for investigations\nof vortex dynamics and turbulence in quantum fluids, yet there has been little\nexperimental research into the approaches that may be most promising for\ngenerating states of two-dimensional turbulence in these systems. Here we give\nan overview of techniques for generating the large and disordered vortex\ndistributions associated with two-dimensional quantum turbulence. We focus on\ndescribing methods explored in our Bose-Einstein condensation laboratory, and\ndiscuss the suitability of these methods for studying various aspects of\ntwo-dimensional quantum turbulence. We also summarize some of the open\nquestions regarding our own understanding of these mechanisms of\ntwo-dimensional quantum turbulence generation in condensates. We find that\nwhile these disordered distributions of vortices can be generated by a variety\nof techniques, further investigation is needed to identify methods for\nobtaining quasi-steady-state quantum turbulence in condensates.",
        "positive": "Quasiparticle Dispersions and Lifetimes in the Normal State of the\n  BCS-BEC Crossover: We compute the spectral density in the normal phase of an interacting\nhomogenous Fermi gas using a T-matrix approximation. We fit the quasiparticle\npeaks of the spectral density to BCS-like dispersion relations, and extract\nestimates of a \"pseudo-gap\" energy scale and an effective Fermi-wavevector as a\nfunction of interaction strength. We find that the effective Fermi-wavevector\nof the quasiparticles vanishes when the inverse scattering length exceeds some\npositive threshold. We also find that near unitarity the quasiparticle\nlifetimes, estimated from the widths of the peaks in the spectral density,\napproach values on the order of the inverse Fermi-energy. These results are\nconsistent with the \"breakdown of Fermi liquid theory\" observed in recent\nexperiments."
    },
    {
        "anchor": "Decay of Bogoliubov excitations in one-dimensional Bose gases: We study the decay of Bogoliubov quasiparticles in one-dimensional Bose\ngases. Starting from the hydrodynamic Hamiltonian, we develop a microscopic\ntheory that enables one to systematically study both the excitations and their\ndecay. At zero temperature, the leading mechanism of decay of a quasiparticle\nis disintegration into three others. We find that low-energy quasiparticles\n(phonons) decay with the rate that scales with the seventh power of momentum,\nwhereas the rate of decay of the high-energy quasiparticles does not depend on\nmomentum. In addition, our approach allows us to study analytically the\nquasiparticle decay in the whole crossover region between the two limiting\ncases. When applied to integrable models, including the Lieb-Liniger model of\nbosons with contact repulsion, our theory confirms the absence of the decay of\nquasiparticle excitations. We account for two types of integrability-breaking\nperturbations that enable finite decay: three-body interaction between the\nbosons and two-body interaction of finite range.",
        "positive": "Gauge theory description of Rydberg atom arrays with a tunable blockade\n  radius: We discuss a Rydberg atom chain with a tunable blockade radius from the gauge\ntheoretic perspective. When the blockade radius is one lattice spacing, this\nsystem can be formulated in terms of the PXP model, and there is a\n$\\mathbb{Z}_2$ Ising phase transition known to be equivalent to a\nconfinement-deconfinement transition in a gauge theory, the lattice Schwinger\nmodel. Further increasing the blockade radius, one can add a next-nearest\nneighbor (NNN) interaction into the PXP model. We discuss the interpretation of\nNNN interaction in terms of the gauge theory and how finite NNN interaction\nalters the deconfinement behavior and propose a corresponding experimental\nprotocol. When the blockade radius reaches two lattice spacing, the model\nreduces to the PPXPP model. A novel gauge theory equivalent to the PPXPP model\nis formulated, and the phases in the two formulations are delineated. These\nresults are readily explored experimentally in Rydberg quantum simulators."
    },
    {
        "anchor": "Dynamical phase transitions in quantum spin models with\n  antiferromagnetic long-range interactions: In recent years, dynamical phase transitions and out-of-equilibrium\ncriticality have been at the forefront of ultracold gases and condensed matter\nresearch. Whereas universality and scaling are established topics in\nequilibrium quantum many-body physics, out-of-equilibrium extensions of such\nconcepts still leave much to be desired. Using exact diagonalization and the\ntime-dependent variational principle in uniform martrix product states, we\ncalculate the time evolution of the local order parameter and Loschmidt return\nrate in transverse-field Ising chains with antiferromagnetic power law-decaying\ninteractions, and map out the corresponding rich dynamical phase diagram.\n\\textit{Anomalous} cusps in the return rate, which are ubiquitous at small\nquenches within the ordered phase in the case of ferromagnetic long-range\ninteractions, are absent within the accessible timescales of our simulations in\nthe antiferromagnetic case, showing that long-range interactions are not a\nsufficient condition for their appearance. We attribute this to much weaker\ndomain-wall binding in the antiferromagnetic case. For quenches across the\nquantum critical point, \\textit{regular} cusps appear in the return rate and\nconnect to the local order parameter changing sign, indicating the concurrence\nof two major concepts of dynamical phase transitions. Our results consolidate\nconclusions of previous works that a necessary condition for the appearance of\nanomalous cusps in the return rate after quenches within the ordered phase is\nfor topologically trivial local spin flips to be the energetically dominant\nexcitations in the spectrum of the quench Hamiltonian. Our findings are readily\naccessible in modern trapped-ion setups, and we outline the associated\nexperimental considerations.",
        "positive": "Propagation of collective pair excitations in disordered Bose\n  superfluids: We study the effect of disorder on the propagation of collective excitations\nin a disordered Bose superfluid. We incorporate local density depletion induced\nby strong disorder at the meanfield level, and formulate the transport of the\nexcitations in terms of a screened scattering problem. We show that the\ncompetition of disorder, screening, and density depletion induces a strongly\nnon-monotonic energy dependence of the disorder parameter. In three dimensions,\nit results in a rich localization diagram with four different classes of\nmobility spectra, characterized by either no or up to three mobility edges.\nImplications on experiments with disordered ultracold atoms are discussed."
    },
    {
        "anchor": "General relations for quantum gases in two and three dimensions.\n  Two-component fermions: We derive exact relations for $N$ spin-1/2 fermions with zero-range or\nshort-range interactions, in continuous space or on a lattice, in $2D$ or in\n$3D$, in any external potential. Some of them generalize known relations\nbetween energy, momentum distribution $n(k)$, pair distribution function\n$g^{(2)}(r)$, derivative of the energy with respect to the scattering length\n$a$. Expressions are found for the second order derivative of the energy with\nrespect to $1/a$ (or to $\\ln a$ in $2D$). Also, it is found that the leading\nenergy corrections due to a finite interaction range, are proportional to the\neffective range $r\\_e$ in $3D$ (and to $r\\_e^2$ in $2D$) with exprimable\nmodel-independent coefficients, that give access to the subleading short\ndistance behavior of $g^{(2)}(r)$ and to the subleading $1/k^6$ tail of $n(k)$.\nThis applies to lattice models for some magic dispersion relations, an example\nof which is given. Corrections to exactly solvable two-body and three-body\nproblems are obtained. For the trapped unitary gas, the variation of the\nfinite-$1/a$ and finite $r\\_e$ energy corrections within each $SO(2,1)$ energy\nladder is obtained; it gives the frequency shift and the collapse time of the\nbreathing mode. For the bulk unitary gas, we compare to fixed-node Monte Carlo\ndata, and we estimate the experimental uncertainty on the Bertsch parameter due\nto a finite $r\\_e$.",
        "positive": "Measuring second Chern number from non-adiabatic effects: The geometry and topology of quantum systems have deep connections to quantum\ndynamics. In this paper, I show how to measure the non-Abelian Berry curvature\nand its related topological invariant, the second Chern number, using dynamical\ntechniques. The second Chern number is the defining topological characteristic\nof the four-dimensional generalization of the quantum Hall effect and has\nrelevance in systems from three-dimensional topological insulators to\nYang-Mills field theory. I illustrate its measurement using the simple example\nof a spin-3/2 particle in an electric quadrupole field. I show how one can\ndynamically measure diagonal components of the Berry curvature in an\nover-complete basis of the degenerate ground state space and use this to\nextract the full non-Abelian Berry curvature. I also show that one can\naccomplish the same ideas by stochastically averaging over random initial\nstates in the degenerate ground state manifold. Finally I show how this system\ncan be manufactured and the topological invariant measured in a variety of\nrealistic systems, from superconducting qubits to trapped ions and cold atoms."
    },
    {
        "anchor": "Dominant Andreev Reflection through Nonlinear Radio-Frequency Transport: We theoretically propose the laser-induced Andreev reflection between\ntwo-component Fermi superfluid and normal states via spatially-uniform Rabi\ncouplings. By analyzing the tunneling current between the superfluid and normal\nstates up to the fourth order in the Rabi couplings, we find that the Andreev\ncurrent exhibits unconventional non-Ohmic transport at zero temperature.\nRemarkably, the Andreev current gives the only contribution in the synthetic\njunction system at zero detunings regardless of the ratio of the chemical\npotential bias to the superfluid gap, which is in sharp contrast to that in the\nconventional superconductor-normal metal junction. Our result may also pave a\nway for understanding the black hole information paradox through the Andreev\nreflection as a quantum-information mirror.",
        "positive": "On the hydrodynamics of Bose-condensed fluids subject to\n  density-dependent gauge potentials: When the energy functional of a Bose-condensed state of matter features an\neffective gauge potential which depends on the density $\\rho$ of the\ncondensate, the kinetic energy density of the matter field becomes nonlinear in\n$\\rho$ and additional flow-dependent terms enter the wave equation for the\nphase of the condensate wavefunction. To begin with, we consider a certain\nclass of density-dependent `single-component' gauge potentials, and later\nextend this class to encompass more general `multi-component' potentials. The\nnonlinear flow terms are cast into the general form of an inner-product between\nthe velocity field of the fluid and the gauge potential. This is achieved by\nintroducing a coupling matrix of dimensionless functions $\\gamma_{ij}\\left(\n\\rho \\right)$, which characterises the particular functional form of the gauge\npotential and regulates the strengths of the nonlinear terms accordingly. In\nthe momentum-transport equation of the fluid, two non-trivial terms emerge due\nto the density-dependent vector potential. A body-force of dilation appears as\na product of the gauge potential and the dilation rate of the fluid, while the\nfluid stress tensor features a flow-dependent pressure contribution given by\nthe inner-product of the gauge potential and the current density of the fluid.\nThis explicit dependence of the fluid pressure on the flow highlights the lack\nof Galilean invariance of the nonlinear fluid."
    },
    {
        "anchor": "On the theory of inhomogeneous Bose-Einstein condensation of magnons in\n  yttrium garnet: The Bose-Einstein condensation (BEC) of magnons created by a strong pumping\nin ferromagnetic thin films of yttrium iron garnet used as systems of finite\nsize is considered analytically. Such a peculiarity, typical for this magnetic\nmaterial, as the presence of a minimum in the spectrum of spin waves at a\nfinite value of the wave vector is taken into account. The definition of\nhightemperature BEC is introduced and its characteristics are discussed. A role\nof boundary conditions for spin variables is analyzed, and it is shown that in\nthe case of free spins on the boundary the magnon lattice can form in the\nsystem. The factors responsible for its appearance are discussed.",
        "positive": "Dynamical creation of entangled bosonic states in a double well: We study the creation of a bosonic N00N state from the evolution of a Fock\nstate in a double well. While noninteracting bosons disappear quickly in the\nHilbert space, the evolution under the influence of a Bose-Hubbard Hamiltonian\nis much more restricted. This restriction is caused by the fragmentation of the\nspectrum into a high-energy part with doubly degenerate levels and a\nnondegenerate low-energy part. This degeneracy suppresses transitions to states\nof the high-energy part of the spectrum. At a moderate interaction strength\nthis effect supports strongly the dynamical formation of a N00N state. The N00N\nstate is suppressed in an asymmetric double well, where the double degeneracy\nis absent."
    },
    {
        "anchor": "Spontaneous Vortex Production in Driven Condensates with Narrow Feshbach\n  Resonances: We explore the possibility that, at zero temperature, vortices can be created\nspontaneously in a condensate of cold Fermi atoms, whose scattering is\ncontrolled by a narrow Feshbach resonance, by rapid magnetic tuning from the\nBEC to BCS regime. This could be achievable with current experimental\ntechniques.",
        "positive": "Two Nambu-Goldstone zero modes for rotating Bose-Einstein condensates: We consider rotating finite size vortex arrays in Bose-Einstein condensates\nthat are confined by cylindrically symmetric external potentials. We show that\nsuch systems possess two exact Nambu-Goldstone zero modes associated with two\nspontaneously broken continuous symmetries of the system. We verify our\nanalytical result via direct numerical diagonalizations of the Bogoliubov-de\nGennes equations. We conclude by comparing rotating vortex lattices in\nsuperfluids to supersolids and discrete time crystals."
    },
    {
        "anchor": "Quantum droplet of a two-component Bose gas in an optical lattice near\n  the Mott insulator transition: We theoretically study dynamical formation of a quantum droplet in a\ntwo-component Bose-Hubbard system with an external trap potential.\nSpecifically, the superfluid in the central region surrounded by the Mott\ninsulator with double filling forms a quantum droplet, which is self-bound\nthanks to the discontinuous nature of the quantum phase transition between the\ntwo phases. We show how to induce the characteristic behavior of the droplet\nthrough the control of the trap potential by using the time-dependent\nGutzwiller simulations in a two-dimensional system. The static and dynamical\nproperties of the droplet can be described qualitatively by the effective\nGinzburg-Landau field theory with cubic-quintic nonlinearities, where the\nattractive cubic nonlinearlity emerges although all the bare interparticle\ninteractions are repulsive.",
        "positive": "Phase Estimation from Atom Position Measurements: We study the measurement of the position of atoms as a means to estimate the\nrelative phase between two Bose-Einstein condensates. First, we consider $N$\natoms released from a double-well trap, forming an interference pattern, and\nshow that a simple least-squares fit to the density gives a shot-noise limited\nsensitivity. The shot-noise limit can instead be overcome by using correlation\nfunctions of order $\\sqrt{N}$ or larger. The measurement of the\n$N\\mathrm{th}$-order correlation function allows to estimate the relative phase\nat the Heisenberg limit. Phase estimation through the measurement of the\ncenter-of-mass of the interference pattern can also provide sub-shot-noise\nsensitivity. Finally, we study the effect of the overlap between the two clouds\non the phase estimation, when Mach-Zehnder interferometry is performed in a\ndouble-well."
    },
    {
        "anchor": "Spontaneous population imbalance in two-component Bose and Fermi gases: We study two-component (or pseudo-spin-1/2) Bose or Fermi gases in one\ndimension, in which particles are convertible between the components. Through\nbosonization and numerical analyses of a simple lattice model, we demonstrate\nthat, in such gases, a strong intercomponent repulsion induces spontaneous\npopulation imbalance between the components, namely, the ferromagnetism of the\npseudo spins. The imbalanced phase contains gapless charge excitations\ncharacterized as a Tomonaga-Luttinger liquid and gapped spin excitations. We\nuncover a crucial effect of the intercomponent particle hopping on the\ntransition to the imbalanced phase. In the absence of this hopping, the\ntransition is of first order. At the transition point, the energy spectrum\nreveals certain degeneracy indicative of an emergent SU(2) symmetry. With an\ninfinitesimal intercomponent hopping, the transition becomes of Ising type. We\ndetermine the phase diagram of the model accurately and test the reliability of\nthe weak-coupling bosonization formalism.",
        "positive": "Repulsive Fermi polarons with negative effective mass: Recent LENS experiment on a 3D Fermi gas has reported a negative effective\nmass ($m^*<0$) of Fermi polarons in the strongly repulsive regime. There\nnaturally arise a question whether the negative $m^*$ is a precursor of the\ninstability towards phase separation (or itinerant ferromagnetism). In this\nwork, we make use of the exact solutions to study the ground state and\nexcitation properties of repulsive Fermi polarons in 1D, which can also exhibit\na negative $m^*$ in the super Tonks-Girardeau regime. By analyzing the total\nspin, quasi-momentum distribution and pair correlations, we conclude that the\nnegative $m^*$ is irrelevant to the instability towards ferromagnetism or phase\nseparation, but rather an intrinsic feature of collective excitations for\nfermions in the strongly repulsive regime. Surprisingly, for large and negative\n$m^*$, such excitation is accompanied with a spin density modulation when the\nmajority fermions move closer to the impurity rather than being repelled far\naway, contrary to the picture of phase separation. These results suggest an\nalternative interpretation of negative $m^*$ as observed in recent LENS\nexperiment."
    },
    {
        "anchor": "Exciting the Goldstone Modes of a Supersolid Spin-Orbit-Coupled Bose Gas: Supersolidity is deeply connected with the emergence of Goldstone modes,\nreflecting the spontaneous breaking of both phase and translational symmetry.\nHere, we propose accessible signatures of these modes in harmonically trapped\nspin-orbit-coupled Bose-Einstein condensates, where supersolidity appears in\nthe form of stripes. By suddenly changing the trapping frequency, an axial\nbreathing oscillation is generated, whose behavior changes drastically at the\ncritical Raman coupling. Above the transition, a single mode of hybridized\ndensity and spin nature is excited, while below it, we predict a beating effect\nsignaling the excitation of a Goldstone spin-dipole mode. We further provide\nevidence for the Goldstone mode associated with the translational motion of\nstripes. Our results open up new perspectives for probing supersolid properties\nin experimentally relevant configurations with both symmetric as well as highly\nasymmetric intraspecies interactions.",
        "positive": "Persisting Meissner state and incommensurate phases of hard-core boson\n  ladders in a flux: The phase diagram of a half-filled hard core boson two-leg ladder in a flux\nis investigated by means of numerical simulations based on the Density Matrix\nRenormalization Group (DMRG) algorithm and bosonization. We calculate\nexperimentally accessible observables such as the momentum distribution, as\nwell as rung current, density wave and bond-order wave correlation functions,\nallowing us to identify the Mott Meissner and Mott Vortex states. We follow the\ntransition from commensurate Meissner to incommensurate Vortex state at\nincreasing interchain hopping till the critical value [Piraud et al. Phys. Rev.\nB v. 91, p. 140406 (2015)] above which the Meissner state is stable at any\nflux. For flux close to $\\pi$, and below the critical hopping, we observe the\nformation of a second incommensuration in the Mott Vortex state that could be\ndetectable in current experiments."
    },
    {
        "anchor": "Light scattering for thermometry of fermionic atoms in an optical\n  lattice: We propose a method for measuring the temperature of fermionic atoms in an\noptical lattice potential from the intensity of the scattered light in the\nfar-field diffraction pattern. We consider a single-component gas in a\ntightly-confined two-dimensional lattice, illuminated by far off-resonant light\ndriving a cycling transition. Our calculations show that thermal correlations\nof the fermionic atoms generate fluctuations in the intensity of the\ndiffraction pattern of light scattered from the atomic lattice array and that\nthis signal can be accurately detected above the shot noise using a lens to\ncollect photons scattered in a forward direction (with the diffraction maxima\nblocked). The sensitivity of the thermometer is enhanced by an additional\nharmonic trapping potential.",
        "positive": "Momentum distribution of Vinen turbulence in trapped atomic\n  Bose-Einstein condensates: The decay of multicharged vortices in trapped Bose-Einstein condensates may\nlead to a disordered vortex state consistent with the Vinen regime of\nturbulence, characterized by an absence of large-scale flow and an\nincompressible kinetic energy spectrum $E\\propto k^{-1}$. In this work, we\nstudy numerically the dynamics of a three-dimensional harmonically trapped\nBose-Einstein condensate excited to a Vinen regime of turbulence through the\ndecay of two doubly-charged vortices. First, we study the momentum distribution\nand observe the emergence of a power-law behavior $n(k)\\propto k^{-3}$\nconsistent with the coexistence of wave turbulence. We also study the kinetic\nenergy and particle fluxes, which allows us to identify a direct particle\ncascade associated with the turbulent stage."
    },
    {
        "anchor": "Simulation of Anderson localization in two-dimensional ultracold gases\n  for point-like disorder: Anderson localization has been observed for a variety of media, including\nultracold atomic gases with speckle disorder in one and three dimensions.\nHowever, observation of Anderson localization in a two-dimensional geometry for\nultracold gases has been elusive. We show that a cause of this difficulty is\nthe relatively high percolation threshold of a speckle potential in two\ndimensions, resulting in strong classical localization. We propose a realistic\npoint-like disorder potential that circumvents this percolation limit with\nlocalization lengths that are experimentally observable. The percolation\nthreshold is evaluated for experimentally realistic parameters, and a regime of\nnegligible classical trapping is identified. Localization lengths are\ndetermined via scaling theory, using both exact scattering cross sections and\nthe Born approximation, and by direct simulation of the time-dependent\nSchr\\\"{o}dinger equation. We show that the Born approximation can underestimate\nthe localization length by four orders of magnitude at low energies, while\nexact cross sections and scaling theory provide an upper bound. Achievable\nexperimental parameters for observing localization in this system are proposed.",
        "positive": "Dynamical quantum phase transitions in discrete time crystals: Discrete time crystals are related to non-equilibrium dynamics of\nperiodically driven quantum many-body systems where the discrete time\ntranslation symmetry of the Hamiltonian is spontaneously broken into another\ndiscrete symmetry. Recently, the concept of phase transitions has been extended\nto non-equilibrium dynamics of time-independent systems induced by a quantum\nquench, i.e. a sudden change of some parameter of the Hamiltonian. There, the\nreturn probability of a system to the ground state reveals singularities in\ntime which are dubbed dynamical quantum phase transitions. We show that the\nquantum quench in a discrete time crystal leads to dynamical quantum phase\ntransitions where the return probability of a periodically driven system to a\nFloquet eigenstate before the quench reveals singularities in time. It\nindicates that dynamical quantum phase transitions are not restricted to\ntime-independent systems and can be also observed in systems that are\nperiodically driven. We discuss how the phenomenon can be observed in\nultra-cold atomic gases."
    },
    {
        "anchor": "Entanglement spectrum: Identification of the transition from\n  vortex-liquid to vortex-lattice state in a weakly interacting rotating\n  Bose-Einstein condensate: We use entanglement to investigate the transition from vortex liquid phase to\nvortex lattice phase in weakly interacting rotating Bose-Einstein condensate\n(BEC). Ground state entanglement spectrum is analyzed to distinguish these two\ndifferent phases. For the torus geometry, the low-lying part of ground state\nentanglement spectrum, as well as the behavior of its lowest level change\nclearly when the transition occurs. For the sphere geometry, the disappearance\nof entanglement gap in the conformal limit (CL) can indicate this transition.\nWe also show that the decrease of entanglement between particles can be\nregarded as a signal of the transition.",
        "positive": "How to Directly Measure Floquet Topological Invariants in Optical\n  Lattices: The classification of topological Floquet systems with time-periodic\nHamiltonians transcends that of static systems. For example, spinless fermions\nin periodically driven two-dimensional lattices are not completely\ncharacterized by the Chern numbers of the quasienergy bands, but rather by a\nset of winding numbers associated with the quasienergy gaps. We propose a\nscheme for measuring these winding numbers in a system of fermionic cold atoms\nin a periodically driven optical lattice efficiently and directly. It is based\non the construction of a one-parameter family of experimentally feasible\ndrives, continuously connecting the Floquet system of interest to a trivial\nreference system. The winding numbers are then determined by the identification\nand the tomography of the band-touching singularities occurring on the way. As\na byproduct, we also propose a method for probing spectral properties of time\nevolution operators via a time analog of crystallography."
    },
    {
        "anchor": "Fixed-node diffusion Monte Carlo study of the BCS-BEC crossover in a\n  bilayer system of fermionic dipoles: We investigate the BCS-BEC crossover in a bilayer system of fermionic dipoles\nat zero temperature using the fixed-node diffusion Monte Carlo technique. The\ndipoles are confined on two parallel planes separated by a distance $\\lambda$\nand are aligned perpendicular to the planes by an external field. The\ninterlayer pairing, which is responsible for the superfluid behavior of the\nsystem, crosses from a weak to a strong-coupling regime by reducing the\nseparation distance $\\lambda$. For a fixed in-plane density, equal in the two\nlayers, we calculate the ground-state energy, the chemical potential, the\npairing gap and the quasiparticle dispersion as a function of the interlayer\nseparation. At large $\\lambda$ one recovers the ground-state energy of a single\nlayer of fermions and at small $\\lambda$ the one of a single layer of composite\nbosons with twice the particle mass and the dipole moment. The superfluid gap\nvaries instead from the exponentially small BCS result to half of the large\ntwo-body binding energy in the BEC regime of strong interlayer pairing. Results\nare compared with the predictions of the simplest mean-field theory valid in\nthe low-density limit and deviations are observed both in the BCS regime, where\nin-plane repulsions are important, and in the BEC regime where the mean-field\napproach fails to describe the physics of composite dipolar bosons.",
        "positive": "Exact diagonalization of the truncated Bogoliubov Hamiltonian: The present short note is simply intended to communicate that I have\nanalytically diagonalized the Bogoliubov truncated Hamiltonian\n$H_c$~\\cite{Bogo1,Bogo2}, in an interacting bosonic gas. This is the natural\nprosecution of my work~\\cite{MS}, now denoted as (I), where the diagonalization\nwas performed only in the subspace corresponding to zero momentum collective\nexcitations (CE)."
    },
    {
        "anchor": "One-dimensional purely Lee-Huang-Yang fluids dominated by quantum\n  fluctuations in two-component Bose-Einstein condensates: Lee-Huang-Yang (LHY) fluids are an exotic quantum matter dominated purely by\nquantum fluctuations. Recently, the three-dimensional LHY fluids were observed\nin ultracold atoms experiments, while their low-dimensional counterparts have\nnot been well known. Herein, based on the Gross-Pitaevskii equation of\none-dimensional LHY quantum fluids in two-component Bose-Einstein condensates,\nwe reveal analytically and numerically the formation, properties, and dynamics\nof matter-wave structures therein. Considering a harmonic trap, approximate\nanalytical results are obtained based on variational approximation, and\nhigher-order nonlinear localized modes with nonzero nodes are constructed\nnumerically. Stability regions of all the LHY nonlinear localized modes are\nidentified by linear-stability analysis and direct perturbed numerical\nsimulations. Movements and oscillations of single localized mode, and\ncollisions between two modes, under the influence of different initial kicks\nare also studied in dynamical evolutions. The predicted results are available\nto quantum-gas experiments, providing a new insight into LHY physics in\nlow-dimensional settings.",
        "positive": "Polarons and dressed molecules near narrow Feshbach resonances: The properties of impurities immersed in a large Fermi sea are naturally\ndescribed in terms of dressed quasiparticles: attractive and repulsive\npolarons, and dressed molecules. Motivated by recent experiments on narrow\nFeshbach resonances, we analyze here how the quasiparticle properties are\naffected by a non-zero resonance range. We find two interesting analytic\nresults. For large range, the ground state energy close to resonance is shown\nto become perturbative in the inverse range. In the limit of broad resonance\ninstead, we provide a new Tan's relation linking the impurity ground state\nenergy $E_\\downarrow$ to the number of atoms in its dressing cloud $\\Delta N$.\nAs a corollary, at unitarity one finds $\\Delta N=-E_\\downarrow/\\epsilon_F $,\nwith $\\epsilon_F$ the Fermi energy of the bath."
    },
    {
        "anchor": "Unconventional pairing in few-fermion systems tuned by external\n  confinement: We study the ground-state properties of a two-component one-dimensional\nsystem of a few ultra-cold fermions with attractive interactions. We show that,\nby ramping up an external potential barrier felt by one of the components, it\nis possible to induce regions of exotic superfluid phases, characterized by a\ntunable finite net momentum of the Cooper pair, without changing the overall\nspin populations. We show that these phases, which are the few-body analogs of\nthe celebrated Fulde-Ferrell-Larkin-Ovchinnikov state, can be distinguished by\nanalyzing a specific two-particle correlation encoded in the noise correlation\nfunction. Our theoretical results can be addressed in current experiments with\ncold atoms confined in spin-selective optical traps.",
        "positive": "Propagation of a quantum fluid of light in a cavityless nonlinear\n  optical medium: General theory and response to quantum quenches: Making use of a generalized quantum theory of paraxial light propagation\nwhere the radiation-axis and the temporal coordinates play exchanged roles, we\ndiscuss the potential of bulk nonlinear optical media in cavityless\nconfigurations for quantum statistical mechanics studies of the conservative\nmany-body dynamics of a gas of interacting photons. To illustrate the general\nfeatures of this point of view, we investigate the response of the fluid of\nlight to the quantum quenches in the photon-photon interaction constant\nexperienced at the front and the back faces of a finite slab of weakly\nnonlinear material. Extending the standard Bogoliubov theory of dilute\nBose-Einstein condensates, peculiar features are predicted for the statistical\nproperties of the light emerging from the nonlinear medium."
    },
    {
        "anchor": "Diffraction of strongly interacting molecular Bose-Einstein condensate\n  from standing wave light pulses: We study the effects of strong inter-particle interaction on diffraction of a\nBose-Einstein condensate of $^6Li_2$ molecules from a periodic potential\ncreated by pulses of a far detuned optical standing wave. For short pulses we\nobserve the standard Kapitza-Dirac diffraction, with the contrast of the\ndiffraction pattern strongly reduced for very large interactions due to\ninteraction dependent loss processes. For longer pulses diffraction shows the\ncharacteristic for matter waves impinging on an array of tubes and coherent\nchanneling transport. We observe a slowing down of the time evolution governing\nthe population of the momentum modes caused by the strong atom interaction. A\nsimple physical explanation of that slowing down is the phase shift caused by\nthe self-interaction of the forming matter wave patterns inside the standing\nlight wave. Simple 1D mean field simulations qualitatively capture the\nphenomenon, however to quantitatively reproduce the experimental results the\nmolecular scattering length has to be multiplied by factor of 4.2. In addition,\ntwo contributions to interaction-dependent degradation of the coherent\ndiffraction patterns were identified: (i) in-trap loss of molecules during the\nlattice pulse, which involves dissociation of Feshbach molecules into free\natoms, as confirmed by radio-frequency spectroscopy and (ii) collisions between\ndifferent momentum modes during separation. This was confirmed by\ninterferometrically recombining the diffracted momenta into the zero-momentum\npeak, which consequently removed the scattering background.",
        "positive": "Many-body dark solitons in one-dimensional hard-core Bose gases: The existence and stability of solitonic states in one-dimensional repulsive\nBose-Einstein condensates is investigated within a fully many-body framework by\nconsidering the limit of infinite repulsion (Tonks-Girardeau gas). A class of\nstationary, shape-invariant states propagating at constant velocity are\nexplicitly found and compared to the known solution of the Gross-Pitaevskii\nequation. The typical features attributed to nonlinearity are thus recovered in\na purely linear theory, provided the full many-particle physics is correctly\naccounted for. However, the formation dynamics predicted by the\nGross-Pitaevskii approximation considerably differs from the exact many-body\nevolution."
    },
    {
        "anchor": "Vortices in the supersolid phase of dipolar Bose-Einstein condensates: Vortices are expected to exist in a supersolid but experimentally their\ndetection can be difficult because the vortex cores are localized at positions\nwhere the local density is very low. We address here this problem by performing\nnumerical simulations of a dipolar Bose-Einstein Condensate (BEC) in a pancake\nconfinement at $T=0$ K and study the effect of quantized vorticity on the\nphases that can be realized depending upon the ratio between dipolar and\nshort-range interaction. By increasing this ratio the system undergoes a\nspontaneous density modulation in the form of an ordered arrangement of\nmulti-atom \"droplets\". This modulated phase can be either a \"supersolid\" (SS)\nor a \"normal solid\" (NS). In the SS state droplets are immersed in a background\nof low-density superfluid and the system has a finite global superfluid\nfraction resulting in non-classical rotational inertia. In the NS state no such\nsuperfluid background is present and the global superfluid fraction vanishes.\nWe propose here a protocol to create vortices in modulated phases of dipolar\nBEC by \"freezing\" into such phases a vortex-hosting superfluid (SF) state. The\nresulting system, depending upon the interactions strengths, can be either a SS\nor a NS To discriminate between these two possible outcome of a \"freezing\"\nexperiment, we show that upon releasing of the radial harmonic confinement, the\nexpanding vortex-hosting SS shows tell-tale quantum interference effects which\ndisplay the symmetry of the vortex lattice of the originating SF, as opposed to\nthe behavior of the NS which shows instead a ballistic radial expansion of the\nindividual droplets. Such markedly different behavior might be used to prove\nthe supersolid character of rotating dipolar condensates.",
        "positive": "Super Fermi polaron and Nagaoka ferromagnetism in a two-dimesnional\n  square lattice: We consider the Fermi polaron problem of an impurity hopping around a\ntwo-dimensional square lattice and interacting with a sea of fermions at given\nfilling factor. When the interaction is attractive, we find standard Fermi\npolaron quasiparticles, categorized as attractive polarons and repulsive\npolarons. When the interaction becomes repulsive, interestingly, we observe an\nunconventional highly-excited polaron quasiparticle, sharply peaked at the\ncorner of the first Brillouin zone with momentum \\mathbf{k}=(\\pm\\pi,\\pm\\pi).\nThis super Fermi polaron branch arises from the dressing of the impurity's\nmotion with holes, instead of particles of fermions. We show that super Fermi\npolarons become increasingly well-defined with increasing impurity-fermion\nrepulsions and might be considered as a precursor of Nagaoka ferromagnetism,\nwhich would appear at sufficiently large repulsions and at large filling\nfactors. We also investigate the temperature-dependence of super Fermi polarons\nand find that they are thermally robust against the significant increase in\ntemperature."
    },
    {
        "anchor": "Mobile impurity probing a two-dimensional superfluid phase transition: The use of atomically sized quantum systems as highly sensitive measuring\ndevices represents an exciting and quickly growing research field. Here, we\nexplore the properties of a quasiparticle formed by a mobile impurity\ninteracting with a two-dimensional fermionic superfluid. The energy of the\nquasiparticle is shown to be lowered by superfluid pairing as this increases\nthe compressibility of the Fermi gas, thereby making it easier for the impurity\nto perturb its surroundings. We demonstrate that the fundamentally\ndiscontinuous nature of the superfluid to normal phase transition of a\ntwo-dimensional system, leads to a rapid increase in the quasiparticle energy\naround the critical temperature. The magnitude of this increase exhibits a\nnonmonotonic behavior as a function of the pairing strength with a sizable\nmaximum in the cross-over region, where the spatial extend of the Cooper pairs\nis comparable to the interparticle spacing.\n  Since the quasiparticle energy is measurable with present experimental\ntechniques, our results illustrate how impurities entangled with their\nenvironment can serve as useful probes for non-trivial thermal and quantum\ncorrelations.",
        "positive": "Quantum phases from competing short- and long-range interactions in an\n  optical lattice: Insights into complex phenomena in quantum matter can be gained from\nsimulation experiments with ultracold atoms, especially in cases where\ntheoretical characterization is challenging. However these experiments are\nmostly limited to short-range collisional interactions. Recently observed\nperturbative effects of long-range interactions were too weak to reach novel\nquantum phases. Here we experimentally realize a bosonic lattice model with\ncompeting short- and infinite-range interactions, and observe the appearance of\nfour distinct phases - a superfluid, a supersolid, a Mott insulator and a\ncharge density wave. Our system is based on an atomic quantum gas trapped in an\noptical lattice inside a high finesse optical cavity. The strength of the\nshort-ranged on-site interactions is controlled by means of the optical lattice\ndepth. The infinite-range interaction potential is mediated by a vacuum mode of\nthe cavity and is independently controlled by tuning the cavity resonance. When\nprobing the phase transition between the Mott insulator and the charge density\nwave in real-time, we discovered a behaviour characteristic of a first order\nphase transition. Our measurements have accessed a regime for quantum\nsimulation of many-body systems, where the physics is determined by the\nintricate competition between two different types of interactions and the zero\npoint motion of the particles."
    },
    {
        "anchor": "Superfluid signatures in a dissipative quantum point contact: We measure superfluid transport of strongly interacting fermionic lithium\natoms through a quantum point contact with local, spin-dependent particle loss.\nWe observe that the characteristic non-Ohmic superfluid transport enabled by\nhigh-order multiple Andreev reflections transitions into an excess Ohmic\ncurrent as the dissipation strength exceeds the superfluid gap. We develop a\nmodel with mean-field reservoirs connected via tunneling to a dissipative site.\nOur calculations in the Keldysh formalism reproduce the observed nonequilibrium\nparticle current, yet do not fully explain the observed loss rate or spin\ncurrent.",
        "positive": "Phase Diagram Detection via Gaussian Fitting of Number Probability\n  Distribution: We investigate the number probability density function that characterizes\nsub-portions of a quantum many-body system with globally conserved number of\nparticles. We put forward a linear fitting protocol capable of mapping out the\nground-state phase diagram of the rich one-dimensional extended Bose-Hubbard\nmodel: The results are quantitatively comparable with more sophisticated\ntraditional and machine learning techniques. We argue that the studied quantity\nshould be considered among the most informative bipartite properties, being\nmoreover readily accessible in atomic gases experiments."
    },
    {
        "anchor": "Quantum anomaly, universal relations, and breathing mode of a\n  two-dimensional Fermi gas: In this Letter, we show that the classical SO(2,1) symmetry of a harmonically\ntrapped Fermi gas in two dimensions is broken by quantum effects. The anomalous\ncorrection to the symmetry algebra is given by a two-body operator that is well\nknown as the contact. Taking into account this modification, we are able to\nderive the virial theorem for the system and a universal relation for the\npressure of a homogeneous gas. The existence of an undamped breathing mode is\nassociated with the classical symmetry. We provide an estimate for the\nanomalous frequency shift of this oscillation at zero temperature and compare\nthe result with a recent experiment by [E. Vogt et al., Phys. Rev. Lett. 108,\n070404 (2012)]. Discrepancies are attributed to finite temperature effects.",
        "positive": "Thermalization of interacting quasi-one-dimensional systems: Many experimentally relevant systems are quasi-one-dimensional, consisting of\nnearly decoupled chains. In these systems, there is a natural separation of\nscales between the strong intra-chain interactions and the weak interchain\ncoupling. When the intra-chain interactions are integrable, weak interchain\ncouplings play a crucial part in thermalizing the system. Here, we develop a\nBoltzmann-equation formalism involving a collision integral that is\nasymptotically exact for any interacting integrable system, and apply it to\ndevelop a quantitative theory of relaxation in coupled Bose gases in the\nexperimentally relevant Newton's cradle setup. We find that relaxation involves\na broad spectrum of timescales. We provide evidence that the Markov process\ngoverning relaxation at late times is gapless; thus, the approach to\nequilibrium is generally non-exponential, even for spatially uniform\nperturbations."
    },
    {
        "anchor": "Steerable optical tweezers for ultracold atom studies: We report on the implementation of an optical tweezer system for controlled\ntransport of ultracold atoms along a narrow, static confinement channel. The\ntweezer system is based on high-efficiency acousto-optical deflectors and\noffers two-dimensional control over beam position. This opens up the\npossibility for tracking the transport channel when shuttling atomic clouds\nalong the guide, forestalling atom spilling. Multiple clouds can be tracked\nindependently by time-shared tweezer beams addressing individual sites in the\nchannel. The deflectors are controlled using a multichannel direct digital\nsynthesizer, which receives instructions on a sub-microsecond time scale from a\nfield-programmable gate array. Using the tweezer system, we demonstrate\nsequential binary splitting of an ultracold $\\rm^{87}Rb$ cloud into $2^5$\nclouds.",
        "positive": "The Pairing of Spin-orbit Coupled Fermi Gas in Optical Lattice: We investigate Rashba spin-orbit coupled Fermi gases in square optical\nlattice by using the determinant quantum Monte Carlo (DQMC) simulations which\nis free of the sign-problem. We show that the Berezinskii-Kosterlitz-Thoules\nphase transition temperature is firstly enhanced and then suppressed by\nspin-orbit coupling in the strong attraction region. In the intermediate\nattraction region, spin-orbit coupling always suppresses the transition\ntemperature. We also show that the spin susceptibility becomes anisotropic and\nretains finite values at zero temperature."
    },
    {
        "anchor": "Equilibrium vortex formation in ultrarapidly rotating two-component\n  Bose-Einstein condensates: Equilibrium vortex formation in rotating binary Bose gases with a rotating\nfrequency higher than the harmonic trapping frequency is investigated\ntheoretically. We consider the system being evaporatively cooled to form\ncondensates and a combined numerical scheme is applied to ensure the binary\nsystem being in an authentic equilibrium state. To keep the system stable\nagainst the large centrifugal force of ultrafast rotation, a quartic trapping\npotential is added to the existing harmonic part. Using the Thomas-Fermi\napproximation, a critical rotating frequency \\Omega_c is derived, which\ncharacterizes the structure with or without a central density hole. Vortex\nstructures are studied in detail with rotation frequency both above and below\n?\\Omega_c and with respect to the miscible, symmetrically separated, and\nasymmetrically separated phases in their nonrotating ground-state counterparts.",
        "positive": "Semiclassical solitons in strongly correlated systems of ultracold\n  bosonic atoms in optical lattices: We investigate theoretically soliton excitations and dynamics of their\nformation in strongly correlated systems of ultracold bosonic atoms in two and\nthree dimensional optical lattices. We derive equations of nonlinear\nhydrodynamics in the regime of strong interactions and incommensurate fillings,\nwhen atoms can be treated as hard core bosons. When parameters change in one\ndirection only we obtain Korteweg-de Vries type equation away from half-filling\nand modified KdV equation at half-filling. We apply this general analysis to a\nproblem of the decay of the density step. We consider stability of one\ndimensional solutions to transverse fluctuations. Our results are also relevant\nfor understanding nonequilibrium dynamics of lattice spin models."
    },
    {
        "anchor": "Kapitza stabilization of a repulsive Bose-Einstein condensate in an\n  oscillating optical lattice: We show that the Kapitza stabilization can occur in the context of nonlinear\nquantum fields. Through this phenomenon, an amplitude-modulated lattice can\nstabilize a Bose-Einstein condensate with repulsive interactions and prevent\nthe spreading for long times. We present a classical and quantum analysis in\nthe framework of Gross-Pitaevskii equation, specifying the parameter region\nwhere stabilization occurs. Effects of nonlinearity lead to a significant\nincrease of the stability domain compared with the classical case. Our proposal\ncan be experimentally implemented with current cold atom settings.",
        "positive": "Asymmetric Particle Transport and Light-Cone Dynamics Induced by Anyonic\n  Statistics: We study the non-equilibrium dynamics of Abelian anyons in a one-dimensional\nsystem. We find that the interplay of anyonic statistics and interactions gives\nrise to spatially asymmetric particle transport together with a novel dynamical\nsymmetry that depends on the anyonic statistical angle and the sign of\ninteractions. Moreover, we show that anyonic statistics induces asymmetric\nspreading of quantum information, characterized by asymmetric light cones of\nout-of-time-ordered correlators. Such asymmetric dynamics is in sharp contrast\nwith the dynamics of conventional fermions or bosons, where both the transport\nand information dynamics are spatially symmetric. We further discuss\nexperiments with cold atoms where the predicted phenomena can be observed using\nstate-of-the-art technologies. Our results pave the way toward experimentally\nprobing anyonic statistics through non-equilibrium dynamics."
    },
    {
        "anchor": "Detecting d-wave superfluid and d-density wave states of ultracold\n  Fermions on optical lattices: We propose a pump probe experiment for detecting the d-wave superfluid and\nd-density wave phases of ultracold Fermions on an optical lattice. The pump\nconsists of periodic modulations of the optical lattice intensity which creates\nquasiparticle pairs in these systems. The changes in the momentum distribution\nunder the drive can be used to measure quasiparticle dispersion and gap\nanisotropy. Further, we show that the pattern of peaks and dips in the spin\nselective density-density correlation function provides a phase sensitive probe\nof the symmetry of the order parameter in these systems.",
        "positive": "Spin-sensitive atom mirror via spin-orbit interaction: Based on the spin-orbit coupling recently implemented in a neutral cold-atom\ngas, we propose a scheme to realize spin-dependent scattering of cold atoms. In\nparticular we consider a matter wave packet of cold-atom gas impinging upon a\nstep potential created by the optical light field, inside of which the atoms\nare subject to spin-orbit interaction. We show that the proposed system can act\nas a spin polarizer or spin-selective atom mirror for the incident atomic beam.\nThe principle and the operating parameter regime of the system are carefully\ndiscussed."
    },
    {
        "anchor": "Effects of Rashba spin-orbit coupling, Zeeman splitting and gyrotropy in\n  two-dimensional cavity polaritons under the influence of the Landau\n  quantization: GaAs-type quantum wells (QWs) with p-type valence band embedded into the\nresonators. The Landau quantization of the electrons and heavy-holes (hh) was\ninvestigated taking into account the Rashba spin-orbit coupling with\nthird-order chirality terms for hh and with nonparabolicity terms in their\ndispersion low including the Zeeman splitting (ZS) effects. The exact solutions\nfor the eigenfunctions and eigenenergies were obtained using the Rashba method\n[1]. We derive in the second quantization representation the Hamiltonians\ndescribing the Coulomb electron-electron and the electron-radiation\ninteractions and determine the magnetoexciton energy branches and the\nmagnetoexciton-photon interaction. The fifth order dispersion equation\ndescribing the energy spectrum of the cavity magnetoexciton-polariton is\ninvestigated. It takes into account the interaction of the cavity photons with\ntwo dipole-active and with two quadrupole-active 2D magnetoexciton energy\nbranches. The cavity photons have the circular polarizations oriented along\ntheir wave vectors, which has the quantized longitudinal component. The\nselection rules of the exciton-photon interaction is expressed through the\nscalar products of the two-types circular polarizations and it is related with\nthe numbers of the LQ levels of electrons and heavy-holes. It is shown that the\nRabi frequency of the polariton branches and the magnetoexciton oscillator\nstrength increase in dependence on the magnetic field strength. The optical\ngyrotropy effects may be revealed if changing the sign of the photon circular\npolarization at a given sign of the wave vector longitudinal projection or\nequivalently changing the sign of the longitudinal projection at the same\nselected light circular polarization.",
        "positive": "Imaging a single atom in a time-of-flight experiment: We perform fluorescence imaging of a single 87Rb atom after its release from\nan optical dipole trap. The time-of-flight expansion of the atomic spatial\ndensity distribution is observed by accumulating many single atom images. The\nposition of the atom is revealed with a spatial resolution close to 1\nmicrometer by a single photon event, induced by a short resonant probe. The\nexpansion yields a measure of the temperature of a single atom, which is in\nvery good agreement with the value obtained by an independent measurement based\non a release-and-recapture method. The analysis presented in this paper\nprovides a way of calibrating an imaging system useful for experimental studies\ninvolving a few atoms confined in a dipole trap."
    },
    {
        "anchor": "Breathing mode in the Bose-Hubbard chain with a harmonic trapping\n  potential: We investigate the breathing mode of harmonically trapped bosons in an\noptical lattice at small site occupancies. The Bose-Hubbard model with a\ntrapping potential is used to describe the breathing-mode dynamics initiated\nthrough weak quenches of the trap strength. We connect to results for continuum\nbosons (Lieb-Liniger and Gross-Pitaevskii results) and also present deviations\nfrom continuum physics. We take a spectral perspective, identifying the\nbreathing mode frequency with a particular energy gap in the spectrum of the\ntrapped Bose-Hubbard Hamiltonian. We present the low energy eigenspectrum of\nthe trapped many-boson system, and study overlaps of the initial state with\neigenstates of the quenched Hamiltonian. There is an intermediate interaction\nregime, between a \"free-boson\" limit and a \"free-fermion\" limit, in which the\nBose-Hubbard breathing mode frequency approaches the Gross-Pitaevskii\nprediction. In addition, we present a striking failure of the time-dependent\nGutzwiller approximation for describing breathing modes.",
        "positive": "Nonlinear phase-dynamics in a driven Bosonic Josephson junction: We study the collective dynamics of a driven two mode Bose-Hubbard model in\nthe Josephson interaction regime. The classical phase-space is mixed, with\nchaotic and regular components, that determine the dynamical nature of the\nfringe-visibility. For weak off-resonant drive, where the chaotic component is\nsmall, the many-body dynamics corresponds to that of a Kapitza pendulum, with\nthe relative-phase $\\varphi$ between the condensates playing the role of the\npendulum angle. Using a master equation approach we show that the modulation of\nthe inter-site potential barrier stabilizes the $\\varphi=\\pi$ 'inverted\npendulum' coherent state, and protects the fringe visibility."
    },
    {
        "anchor": "Miscibility-Immiscibility transition of strongly interacting bosonic\n  mixtures in optical lattices: Interaction plays key role in the mixing properties of a multi-component\nsystem. The miscibility-immiscibility transition (MIT) in a weakly interacting\nmixture of Bose gases is predominantly determined by the strengths of the intra\nand inter-component two-body contact interactions. On the other hand, in the\nstrongly interacting regime interaction induced processes become relevant.\nDespite previous studies on bosonic mixtures in optical lattices, the effects\nof the interaction induced processes on the MIT remains unexplored. In this\nwork, we investigate the MIT in the strongly interacting phases of\ntwo-component bosonic mixture trapped in a homogeneous two-dimensional square\noptical lattice. Particularly we examine the transition when both the\ncomponents are in superfluid (SF), one-body staggered superfluid (OSSF) or\nsupersolid (SS) phases. Our study prevails that, similar to the contact\ninteractions, the MIT can be influenced by competing intra and inter-component\ndensity induced tunnelings and off-site interactions. To probe the MIT in the\nstrongly interacting regime, we study the extended version of the Bose-Hubbard\nmodel with the density induced tunneling and nearest-neighbouring interaction\nterms, and focus in the regime where the hopping processes are considerably\nweaker than the on-site interaction. We solve this model through\nsite-decoupling mean-field theory with Gutzwiller ansatz and characterize the\nmiscibility through the site-wise co-existence of the two-component across the\nlattice. Our study contributes to the better understanding of miscibility\nproperties of multi-component systems in the strongly interacting regime.",
        "positive": "Route towards classical frustration and band flattening via optical\n  lattice distortion: We propose and experimentally explore a method for realizing frustrated\nlattice models using a Bose-Einstein condensate held in an optical square\nlattice. A small lattice distortion opens up an energy gap such the lowest band\nsplits into two. Along the edge of the first Brillouin zone for both bands a\nnearly flat energy-momentum dispersion is realized. For the excited band a\nhighly degenerate energy minimum arises. By loading ultracold atoms into the\nexcited band, a classically frustrated $XY$ model is formed, describing rotors\non a square lattice with competing nearest and next nearest tunnelling\ncouplings. Our experimental optical lattice provides a regime, where a fully\ncoherent Bose-Einstein condensate is observed, and a regime where frustration\nis expected. If we adiabatically tune from the condensate regime to the regime\nof frustration, the momentum spectra shows a complete loss of coherence. Upon\nslowly tuning back to the condensate regime, coherence is largely restored.\nGood agreement with model calculations is obtained."
    },
    {
        "anchor": "Dual-species Bose-Einstein condensates of $^{23}$Na and $^{41}$K with\n  tunable interactions: We report the creation of dual-species Bose-Einstein condensates (BECs) of\n$^{23}$Na and $^{41}$K. Favorable background scattering lengths enable\nefficient sympathetic cooling of $^{41}$K via forced evaporative cooling of\n$^{23}$Na in a plugged magnetic trap and an optical dipole trap. The $1/e$\nlifetime of the thermal mixture in the stretched hyperfine state exceeds 5 s in\nthe presence of background scattering. At the end of evaporation, we create\ndual BECs in the immiscible phase, with about $3\\times10^5$ $^{23}$Na atoms\nsurrounding $5\\times10^4$ $^{41}$K atoms. To further enable the tuning of the\ninterspecies interaction strength, we locate multiple Feshbach resonances at\nmagnetic fields up to 100 G. The broadest $s$-wave resonance located at 73.4(3)\nG features a favorable width of 1.8(2) G. This work sets the stage for the\ncreation of ultracold gases of strongly dipolar bosonic $^{23}$Na$^{41}$K\nmolecules as well as the exploration of many-body physics in bosonic\n$^{23}$Na-$^{41}$K mixtures.",
        "positive": "Scattering of two heavy Fermi polarons: resonances and quasibound states: Impurities in a Fermi sea, or Fermi polarons, experience a Casimir\ninteraction induced by quantum fluctuations of the medium. When there is\nshort-range attraction between impurities and fermions, also the induced\ninteraction between two impurities is strongly attractive at short distance and\noscillates in space for larger distances. We theoretically investigate the\nscattering properties and compute the scattering phase shifts and scattering\nlengths between two heavy impurities in an ideal Fermi gas at zero temperature.\nWhile the induced interaction between impurities is weakly attractive for weak\nimpurity-medium interactions, we find that impurities strongly and attractively\ninteracting with the medium exhibit resonances in the induced scattering with a\nsign change of the induced scattering length and even strong repulsion. These\nresonances occur whenever a three-body Efimov bound state appears at the\ncontinuum threshold. At energies above the continuum threshold, we find that\nthe Efimov state in medium can turn into a quasibound state with a finite decay\nwidth."
    },
    {
        "anchor": "Dynamical emergence of a Kosterlitz-Thouless transition in a disordered\n  Bose gas following a quench: We study the dynamical evolution of a two-dimensional Bose gas after a\ndisorder potential quench. Depending on the initial conditions, the system\nevolves either to a thermal or a superfluid state. Using extensive quasi-exact\nnumerical simulations, we show that the two phases are separated by a\nKosterlitz-Thouless transition. The thermalization time is shown to be longer\nin the superfluid phase, but no critical slowing down is observed at the\ntransition. The long-time phase diagram is well reproduced by a simple\ntheoretical model. The spontaneous emergence of Kosterlitz-Thouless transitions\nfollowing a quench is a generic phenomenon that should arise both in the\ncontext of non-equilibrium quantum gases and nonlinear, classical wave systems.",
        "positive": "Quantum Quench in a Harmonically Trapped One-Dimensional Bose Gas: We study the non-equilibrium dynamics of a one-dimensional Bose gas trapped\nby a harmonic potential for a quench from zero to infinite interaction. The\ndifferent thermodynamic limits required for the equilibrium pre- and\npost-quench Hamiltonians are the origin of a few unexpected phenomena that have\nno counterparts in the translational invariant setting. We find that the\ndynamics is perfectly periodic with breathing time related to the strength of\nthe trapping potential. For very short times, we observe a sudden expansion\nleading to an extreme dilution of the gas and to the emergence of slowly\ndecaying tails in the density profile. The haste of the expansion induces a\nundertow effect with a pronounced local minimum of the density at the center of\nthe trap. At half period there is a refocusing phenomenon characterized by a\nsharp central peak of the density, juxtaposed to algebraically decaying tails.\nWe finally show that the time-averaged density is correctly captured by a\ngeneralized Gibbs ensemble built with the conserved mode occupations."
    },
    {
        "anchor": "Symmetry-broken states in a system of interacting bosons on a two-leg\n  ladder with a uniform Abelian gauge field: We study the quantum phases of bosons with repulsive contact interactions on\na two-leg ladder in the presence of a uniform Abelian gauge field. The model\nrealizes many interesting states, including Meissner phases, vortex-fluids,\nvortex-lattices, charge-density-waves and the biased-ladder phase. Our work\nfocuses on the subset of these states that break a discrete symmetry. We use\ndensity matrix renormalization group simulations to demonstrate the existence\nof three vortex-lattice states at different vortex densities and we\ncharacterize the phase transitions from these phases into neighboring states.\nFurthermore, we provide an intuitive explanation of the chiral-current reversal\neffect that is tied to some of these vortex lattices. We also study a\ncharge-density-wave state that exists at 1/4 particle filling at large\ninteraction strengths and flux values close to half a flux quantum. By changing\nthe system parameters, this state can transition into a completely gapped\nvortex-lattice Mott-insulating state. We elucidate the stability of these\nphases against nearest-neighbor interactions on the rungs of the ladder\nrelevant for experimental realizations with a synthetic lattice dimension. A\ncharge-density-wave state at 1/3 particle filling can be stabilized for flux\nvalues close to half a flux-quantum and for very strong on-site interactions in\nthe presence of strong repulsion on the rungs. Finally, we analytically\ndescribe the emergence of these phases in the low-density regime, and, in\nparticular, we obtain the boundaries of the biased-ladder phase, i.e., the\nphase that features a density imbalance between the legs. We make contact to\nrecent quantum-gas experiments that realized related models and discuss\nsignatures of these quantum states in experimentally accessible observables.",
        "positive": "Spin-charge separation effects in the low-temperature transport of 1D\n  Fermi gases: We study the transport properties of a one-dimensional spinful Fermi gas,\nafter junction of two semi-infinite sub-systems held at different temperatures.\nThe ensuing dynamics is studied by analysing the space-time profiles of local\nobservables emerging at large distances $x$ and times $t$, as a function of\n$\\zeta = x/t$. At equilibrium, the system displays two distinct species of\nquasi-particles, naturally associated with different physical degrees of\nfreedom. By employing the generalised hy- drodynamic approach, we show that\nwhen the temperatures are finite no notion of separation can be attributed to\nthe quasi-particles. In this case the profiles can not be qualitatively\ndistinguished by those associated to quasi-particles of a single species that\ncan form bound states. On the contrary, signatures of separation emerge in the\nlow-temperature regime, where two distinct characteristic ve- locities appear.\nIn this regime, we analytically show that the profiles display a piece-wise\nconstant form and can be understood in terms of two decoupled Luttinger\nliquids."
    },
    {
        "anchor": "Reinforcement learning for autonomous preparation of Floquet-engineered\n  states: Inverting the quantum Kapitza oscillator: I demonstrate the potential of reinforcement learning (RL) to prepare quantum\nstates of strongly periodically driven non-linear single-particle models. The\nability of Q-Learning to control systems far away from equilibrium is exhibited\nby steering the quantum Kapitza oscillator to the Floquet-engineered stable\ninverted position in the presence of a strong periodic drive within several\nshaking cycles. The study reveals the potential of the intra-period\n(micromotion) dynamics, often neglected in Floquet engineering, to take\nadvantage over pure stroboscopic control at moderate drive frequencies. Without\nany knowledge about the underlying physical system, the algorithm is capable of\nlearning solely from tried protocols and directly from simulated noisy quantum\nmeasurement data, and is stable to noise in the initial state, and sources of\nrandom failure events in the control sequence. Model-free RL can provide new\ninsights into automating experimental setups for out-of-equilibrium systems\nundergoing complex dynamics, with potential applications in quantum\ninformation, quantum optics, ultracold atoms, trapped ions, and condensed\nmatter.",
        "positive": "Interaction-induced conducting-nonconducting transition of ultra-cold\n  atoms in 1D optical lattices: The study of time-dependent, many-body transport phenomena is increasingly\nwithin reach of ultra-cold atom experiments. We show that the introduction of\nspatially inhomogeneous interactions, e.g., generated by optically-controlled\ncollisions, induce negative differential conductance in the transport of atoms\nin 1D optical lattices. Specifically, we simulate the dynamics of interacting\nfermionic atoms via a micro-canonical transport formalism within both\nmean-field and a higher-order approximation, as well as with time-dependent\nDMRG. For weakly repulsive interactions, a quasi steady-state atomic current\ndevelops that is similar to the situation occurring for electronic systems\nsubject to an external voltage bias. At the mean-field level, we find that this\natomic current is robust against the details of how the interaction is switched\non. Further, a conducting-to-nonconducting transition exists when the\ninteraction imbalance exceeds some threshold from both our approximate and\ntime-dependent DMRG simulations. This transition is preceded by the atomic\nequivalent of negative differential conductivity observed in transport across\nsolid-state structures."
    },
    {
        "anchor": "Quantum turbulence in trapped atomic Bose-Einstein condensates: Turbulence, the complicated fluid behavior of nonlinear and statistical\nnature, arises in many physical systems across various disciplines, from tiny\nlaboratory scales to geophysical and astrophysical ones. The notion of\nturbulence in the quantum world was conceived long ago by Onsager and Feynman,\nbut the occurrence of turbulence in ultracold gases has been studied in the\nlaboratory only very recently. Albeit new as a field, it already offers new\npaths and perspectives on the problem of turbulence. Herein we review the\ngeneral properties of quantum gases at ultralow temperatures paying particular\nattention to vortices, their dynamics and turbulent behavior. We review the\nrecent advances both from theory and experiment. We highlight, moreover, the\ndifficulties of identifying and characterizing turbulence in gaseous\nBose-Einstein condensates compared to ordinary turbulence and turbulence in\nsuperfluid liquid helium and spotlight future possible directions.",
        "positive": "A cavity-induced artificial gauge field in a Bose-Hubbard ladder: We consider theoretically ultracold interacting bosonic atoms confined to\nquasi-one-dimensional ladder structures formed by optical lattices and coupled\nto the field of an optical cavity. The atoms can collect a spatial phase\nimprint during a cavity-assisted tunneling along a rung via Raman transitions\nemploying a cavity mode and a transverse running wave pump beam. By adiabatic\nelimination of the cavity field we obtain an effective Hamiltonian for the\nbosonic atoms, with a self-consistency condition. Using the numerical density\nmatrix renormalization group method, we obtain a rich steady state diagram of\nself-organized steady states. Transitions between superfluid to Mott-insulating\nstates occur, on top of which we can have Meissner, vortex liquid, and vortex\nlattice phases. Also a state that explicitly breaks the symmetry between the\ntwo legs of the ladder, namely the biased-ladder phase is dynamically\nstabilized."
    },
    {
        "anchor": "Unitary fermions and Luscher's formula on a crystal: We consider the low-energy particle-particle scattering properties in a\nperiodic simple cubic crystal. In particular, we investigate the relation\nbetween the two-body scattering length and the energy shift experienced by the\nlowest-lying unbound state when this is placed in a periodic finite box. We\nintroduce a continuum model for s-wave contact interactions that respects the\nsymmetry of the Brillouin zone in its regularisation and renormalisation\nprocedures, and corresponds to the na{\\\"i}ve continuum limit of the Hubbard\nmodel. The energy shifts are found to be identical to those obtained in the\nusual spherically symmetric renormalisation scheme upon resolving an important\nsubtlety regarding the cutoff procedure. We then particularize to the Hubbard\nmodel, and find that for large finite lattices the results are identical to\nthose obtained in the continuum limit. The results reported here are valid in\nthe weak, intermediate and unitary limits, and can be used for the extraction\nof scattering information ,via exact diagonalisation or Monte Carlo methods, of\ntwo-body systems in realistic periodic lattices.",
        "positive": "Density and spin modes in imbalanced normal Fermi gases from\n  collisionless to hydrodynamic regime: We study mass and population imbalance effect on density (in-phase) and spin\n(out-of-phase) collective modes in a two-component normal Fermi gas. By\ncalculating eigenmodes of the linearized Boltzmann equation as well as the\ndensity/spin dynamic structure factor, we show that mass and population\nimbalance effects offer a variety of collective mode crossover behaviors from\ncollisionless to hydrodynamic regimes. The mass imbalance effect shifts the\ncrossover regime to the higher-temperature, and a significant peak of the spin\ndynamic structure factor emerges only in the collisionless regime. This is in\ncontrast to the case of mass and population balanced normal Fermi gases, where\nthe spin dynamic response is always absent. Although the population imbalance\neffect does not shift the crossover regime, the spin dynamic structure factor\nsurvives both in the collisionless and hydrodynamic regimes."
    },
    {
        "anchor": "Analyzing Feshbach resonances -- A $^6$Li -$^{133}$Cs case study: We provide a comprehensive comparison of a coupled channels calculation, the\nasymptotic bound state model (ABM), and the multichannel quantum defect theory\n(MQDT). Quantitative results for $^6$Li -$^{133}$Cs are presented and compared\nto previously measured $^6$Li -$^{133}$Cs Feshbach resonances (FRs) [M. Repp et\nal., Phys. Rev. A 87 010701(R) (2013)]. We demonstrate how the accuracy of the\nABM can be stepwise improved by including magnetic dipole-dipole interactions\nand coupling to a non-dominant virtual state. We present a MQDT calculation,\nwhere magnetic dipole-dipole and second order spin-orbit interactions are\nincluded. A frame transformation formalism is introduced, which allows the\nassignment of measured FRs with only three parameters. All three models achieve\na total rms error of < 1G on the observed FRs. We critically compare the\ndifferent models in view of the accuracy for the description of FRs and the\nrequired input parameters for the calculations.",
        "positive": "Comparative study of the finite-temperature thermodynamics of a unitary\n  Fermi gas: We study the finite-temperature thermodynamics of a unitary Fermi gas. The\nchemical potential, energy density and entropy are given analytically with the\nquasi-linear approximation. The ground state energy agrees with previous\ntheoretical and experimental results. Recently, the generalized exclusion\nstatistics is applied to the discussion of the finite-temperature unitary Fermi\ngas thermodynamics. A concrete comparison between the two different approaches\nis performed. Emphasis is made on the behavior of the entropy per particle. In\nphysics, the slope of entropy gives the information for the effective fermion\nmass $m^*/m$ in the low temperature strong degenerate region. Compared with\n$m^*/m \\approx 0.70<1$ given in terms of the generalized exclusion statistics,\nour quasi-linear approximation determines $m^*/m\\approx 1.11>1$."
    },
    {
        "anchor": "Solvable Model of a Mixture of Bose-Einstein Condensates: A mixture of two kinds of identical bosons held in a harmonic potential and\ninteracting by harmonic particle-particle interactions is discussed. This is an\nexactly-solvable model of a mixture of two trapped Bose-Einstein condensates\nwhich allows us to examine analytically various properties. Generalizing the\ntreatment in [Cohen and Lee, J. Math. Phys. {\\bf 26}, 3105 (1985)], closed form\nexpressions for the ground-state energy, wave-function, and lowest-order\ndensities are obtained and analyzed for attractive and repulsive intra-species\nand inter-species particle-particle interactions. A particular mean-field\nsolution of the corresponding Gross-Pitaevskii theory is also found\nanalytically. This allows us to compare properties of the mixture at the exact,\nmany-body and mean-field levels, both for finite systems and at the limit of an\ninfinite number of particles. We hereby prove that the exact ground-state\nenergy and lowest-order intra-species and inter-species densities converge at\nthe infinite-particle limit (when the products of the number of particles times\nthe intra-species and inter-species interaction strengths are held fixed) to\nthe results of the Gross-Pitaevskii theory for the mixture. Finally and on the\nother end, the separability of the mixture's center-of-mass coordinate is used\nto show that the Gross-Pitaevskii theory for mixtures is unable to describe the\nvariance of many-particle operators in the mixture, even in the\ninfinite-particle limit. Our analytical results show that many-body\ncorrelations exist in a mixture of Bose-Einstein condensates made of any number\nof particles. Implications are briefly discussed.",
        "positive": "Scaling approach to quantum non-equilibrium dynamics of many-body\n  systems: Understanding non-equilibrium quantum dynamics of many-body systems is one of\nthe most challenging problems in modern theoretical physics. While numerous\napproximate and exact solutions exist for systems in equilibrium, examples of\nnon-equilibrium dynamics of many-body systems, which allow reliable theoretical\nanalysis, are few and far between. In this paper we discuss a broad class of\ntime-dependent interacting systems subject to external linear and parabolic\npotentials, for which the many-body Schr\\\"{o}dinger equation can be solved\nusing a scaling transformation. We demonstrate that scaling solutions exist for\nboth local and nonlocal interactions and derive appropriate self-consistency\nequations. We apply this approach to several specific experimentally relevant\nexamples of interacting bosons in one and two dimensions. As an intriguing\nresult we find that weakly and strongly interacting Bose-gases expanding from a\nparabolic trap can exhibit very similar dynamics."
    },
    {
        "anchor": "Degenerate Quantum Gases with Spin-Orbit Coupling: This review focuses on recent developments on studying synthetic spin-orbit\n(SO) coupling in ultracold atomic gases. Two types of SO coupling are\ndiscussed. One is Raman process induced coupling between spin and motion along\none of the spatial directions, and the other is Rashba SO coupling. We\nemphasize their common features in both single-particle and two-body physics\nand their consequences in many-body physics. For instance, single particle\nground state degeneracy leads to novel features of superfluidity and richer\nphase diagram; increased low-energy density-of-state enhances interaction\neffects; the absence of Galilean invariance and spin-momentum locking give rise\nto intriguing behaviors of superfluid critical velocity and novel quantum\ndynamics; and mixing of two-body singlet and triplet states yields novel\nfermion pairing structure and topological superfluids. With these examples, we\nshow that investigating SO coupling in cold atom systems can enrich our\nunderstanding of basic phenomena such as superfluidity, provide a good platform\nfor simulating condensed matter states such as topological superfluids, and\nmore importantly, result in novel quantum systems such as SO coupled unitary\nFermi gas or high spin quantum gases. Finally we also point out major\nchallenges and possible future directions.",
        "positive": "Detection and manipulation of nuclear spin states in fermionic strontium: Fermionic 87Sr has a nuclear spin of I=9/2, higher than any other element\nwith similar electronic structure. This large nuclear spin has many\napplications in quantum simulation and computation, for which preparation and\ndetection of the spin state are requirements. For an ultracold 87Sr cloud, we\nshow two complementary methods to characterize the spin-state mixture: optical\nStern-Gerlach state separation and state-selective absorption imaging. We use\nthese methods to optimize the preparation of a variety of spin-state mixtures\nby optical pumping and to measure an upper bound of the 87Sr spin relaxation\nrate."
    },
    {
        "anchor": "Quantum Rydberg Central Spin Model: We consider dynamics of a Rydberg impurity in a cloud of ultracold bosonic\natoms in which the Rydberg electron can undergo spin-changing collisions with\nsurrounding atoms. This system realizes a new type of the quantum impurity\nproblem that compounds essential features of the Kondo model, the Bose polaron,\nand the central spin model. To capture the interplay of the Rydberg-electron\nspin dynamics and the orbital motion of atoms, we employ a new variational\nmethod that combines an impurity-decoupling transformation with a Gaussian\nansatz for the bath particles. We find several unexpected features of this\nmodel that are not present in traditional impurity problems, including\ninteraction-induced renormalization of the absorption spectrum that eludes\nsimple explanations from molecular bound states, and long-lasting oscillations\nof the Rydberg-electron spin. We discuss generalizations of our analysis to\nother systems in atomic physics and quantum chemistry, where an electron\nexcitation of high orbital quantum number interacts with a spinful quantum\nbath.",
        "positive": "Reaching Fermi degeneracy via universal dipolar scattering: We report on the creation of a degenerate dipolar Fermi gas of erbium atoms.\nWe force evaporative cooling in a fully spin-polarized sample down to\ntemperatures as low as 0.2 times the Fermi temperature. The strong magnetic\ndipole-dipole interaction enables elastic collisions between identical fermions\neven in the zero-energy limit. The measured elastic scattering cross section\nagrees well with the predictions from dipolar scattering theory, which follow a\nuniversal scaling law depending only on the dipole moment and on the atomic\nmass. Our approach to quantum degeneracy proceeds with very high cooling\nefficiency and provides large atomic densities, and it may be extended to\nvarious dipolar systems."
    },
    {
        "anchor": "An Example of Quantum Anomaly in the Physics of Ultra-Cold Gases: In this article, we propose an experimental scheme for observation of a\nquantum anomaly---quantum-mechanical symmetry breaking---in a two-dimensional\nharmonically trapped Bose gas. The anomaly manifests itself in a shift of the\nmonopole excitation frequency away from the value dictated by the\nPitaevskii-Rosch dynamical symmetry [L. P. Pitaevskii and A. Rosch, Phys. Rev.\nA, 55, R853 (1997)]. While the corresponding classical Gross-Pitaevskii\nequation and the derived from it hydrodynamic equations do exhibit this\nsymmetry, it is---as we show in our paper---violated under quantization. The\nresulting frequency shift is of the order of 1% of the carrier, well in reach\nfor modern experimental techniques. We propose using the dipole oscillations as\na frequency gauge.",
        "positive": "One-dimensional Bose-Hubbard model with local three-body interactions: We employ the (dynamical) density matrix renormalization group technique to\ninvestigate the ground-state properties of the Bose-Hubbard model with\nnearest-neighbor transfer amplitudes t and local two-body and three-body\nrepulsion of strength U and W, respectively. We determine the phase boundaries\nbetween the Mott-insulating and superfluid phases for the lowest two Mott lobes\nfrom the chemical potentials. We calculate the tips of the Mott lobes from the\nTomonaga-Luttinger liquid parameter and confirm the positions of the\nKosterlitz-Thouless points from the von Neumann entanglement entropy. We find\nthat physical quantities in the second Mott lobe such as the gap and the\ndynamical structure factor scale almost perfectly in t/(U+W), even close to the\nMott transition. Strong-coupling perturbation theory shows that there is no\ntrue scaling but deviations from it are quantitatively small in the\nstrong-coupling limit. This observation should remain true in higher dimensions\nand for not too large attractive three-body interactions."
    },
    {
        "anchor": "Dynamic virial theorem at nonequilibrium and applications: We show that a variety of nonequilibrium dynamics of interacting many-body\nsystems are universally characterized by an elegant relation, which we call the\ndynamic virial theorem. The out-of-equilibrium dynamics of quantum correlations\nis entirely governed by Tan\\textquoteright s contact. It gives rise to a series\nof observable consequences and is closely related to experiments with ultracold\natoms. Especially, we show that the dynamic virial theorem provides an\nexperimentally accessible verification of maximum energy growth theorem [Qi et\nal., Phys. Rev. Lett. 126, 240401 (2021)], which is encoded in the evolution of\nthe atomic cloud size during expansion. In addition, the dynamic virial theorem\nleads to a simple thermodynamic relation of strongly interacting quantum gases\nin the framework of two-fluid hydrodynamic theory, which holds in a wide range\nof temperature. This thermodynamic relation is a kind of the out-of-equilibrium\nanalog of Tan's pressure relation at equilibrium. Our results provide\nfundamental understanding of generic behaviors of interacting many-body systems\nat nonequilibrium, and are readily examined in experiments with ultracold\natoms.",
        "positive": "Rapid-prototyping of microscopic thermal landscapes in Brillouin light\n  scattering spectroscopy: Since temperature and its spatial and temporal variations affect a wide range\nof physical properties of material systems, they can be used to create\nreconfigurable spatial structures of various types in physical and biological\nobjects. This paper presents an experimental optical setup for creating tunable\ntwo-dimensional temperature patterns on a micrometer scale. As an example of\nits practical application, we have produced temperature-induced magnetization\nlandscapes in ferrimagnetic yttrium iron garnet films and investigated them\nusing micro-focused Brillouin light scattering spectroscopy. It is shown that,\ndue to the temperature dependence of the magnon spectrum, temperature changes\ncan be visualized even for microscale thermal patterns."
    },
    {
        "anchor": "Current production in ring condensates with a weak link: We consider attractive and repulsive condensates in a ring trap stirred by a\nweak link, and analyze the spectrum of solitonic trains dragged by the link, by\nmeans of analytical expressions for the wave functions, energies and currents.\nThe precise evolution of current production and destruction in terms of defect\nformation in the ring and in terms of stirring is studied. We find that any\nexcited state can be coupled to the ground state through two proposed methods:\neither by adiabatically tuning the link's strength and velocity through precise\ncycles which avoid the critical velocities and thus unstable regions, or by\nkeeping the link still while setting an auxiliary potential and imprinting a\nnonlinear phase as the potential is turned off. We also analyze hysteresis\ncycles through the spectrum of energies and currents.",
        "positive": "Universal relations for the two-dimensional spin-1/2 Fermi gas with\n  contact interactions: We present universal relations for a two-dimensional Fermi gas with pairwise\ncontact interactions. The derivation of these relations is made possible by\nobtaining the explicit form of a generalized function -- selector -- in the\nmomentum representation. The selector implements the short-distance boundary\ncondition between two fermions in a straightforward manner, and leads to simple\nderivations of the universal relations, in the spirit of Tan's original method\nfor the three-dimensional gas."
    },
    {
        "anchor": "Collisions of three-component vector solitons in Bose-Einstein\n  condensates: Ultracold gases provide an unprecedented level of control for the\ninvestigation of soliton dynamics and collisions. We present a scheme for\ndeterministically preparing pairs of three-component solitons in a\nBose-Einstein condensate. Our method is based on local spin rotations which\nsimultaneously imprint suitable phase and density distributions. This enables\nus to observe striking collisional properties of the vector degree of freedom\nwhich naturally arises for the coherent nature of the emerging multi-component\nsolitons. We find that the solitonic properties in the quasi-one-dimensional\nsystem are quantitatively described by the integrable repulsive three-component\nManakov model.",
        "positive": "Many-body effects in the out-of-equilibrium dynamics of a composite\n  bosonic Josephson junction: The out-of-equilibrium many-body quantum dynamics of an interacting Bose gas\ntrapped in a one-dimensional composite double-well potential is studied by\nsolving the many-body Schr\\\"odinger equation numerically accurately by\nemploying the multiconfigurational time-dependent Hartree for bosons (MCTDHB)\nmethod. The composite double-well is formed by merging two deformed harmonic\nwells having a hump at their centre. We characterised the dynamics by the time\nevolution of survival probability, fragmentation, and many-particle position\nand momentum variances. Our study demonstrates the prominent role played by the\nhigher orbitals in the dynamics and thereby highlighted the necessity of a\nmany-body technique like MCTDHB which can take into account all the relevant\norbitals for the accurate description of complex many-body dynamics. Further,\nwe showed that the universality of fragmentation with respect to the number of\nparticles corresponding to a particular interaction strength is also exhibited\nby the higher-order orbitals. Therefore, it is a robust phenomenon not limited\nto systems that can be described by two orbitals only."
    },
    {
        "anchor": "Pairing imbalance in BCS-BEC crossover of inhomogeneous three-component\n  Fermi-gas in two dimensions: We in this paper investigate the phase diagram associated with the BCS-BEC\ncrossover of a three-component ultracold superfluid-Fermi-gas of different\nchemical-potentials and equal masses in two dimensions. The gap order parameter\nand number densities are found analytically by using the functional\npath-integral method. The balance of paring will be broken in the free space\ndue to the unequal chemical-potentials. We obtain the same particle\nnumber-density and condensed fraction in the BCS superfluid phase as that in a\nrecent paper (Phys. Rev. A 83, 033630), while the Sarma phase of coexistence of\nnormal and superfluid Fermi gases is the characteristics of inhomogeneous\nsystem. The minimum ratio of BCS superfluid phase becomes 1/3 in the BCS limit\ncorresponding to the zero-ratio in the two-component system in which the\ncritical point of phase separation is {\\epsilon}B/{\\epsilon}F = 2 but becomes 3\nin the three-component case.",
        "positive": "Entanglement growth in quench dynamics with variable range interactions: Studying entanglement growth in quantum dynamics provides both insight into\nthe underlying microscopic processes and information about the complexity of\nthe quantum states, which is related to the efficiency of simulations on\nclassical computers. Recently, experiments with trapped ions, polar molecules,\nand Rydberg excitations have provided new opportunities to observe dynamics\nwith long-range interactions. We explore nonequilibrium coherent dynamics after\na quantum quench in such systems, identifying qualitatively different behavior\nas the exponent of algebraically decaying spin-spin interactions in a\ntransverse Ising chain is varied. Computing the build-up of bipartite\nentanglement as well as mutual information between distant spins, we identify\nlinear growth of entanglement entropy corresponding to propagation of\nquasiparticles for shorter range interactions, with the maximum rate of growth\noccurring when the Hamiltonian parameters match those for the quantum phase\ntransition. Counter-intuitively, the growth of bipartite entanglement for\nlong-range interactions is only logarithmic for most regimes, i.e.,\nsubstantially slower than for shorter range interactions. Experiments with\ntrapped ions allow for the realization of this system with a tunable\ninteraction range, and we show that the different phenomena are robust for\nfinite system sizes and in the presence of noise. These results can act as a\ndirect guide for the generation of large-scale entanglement in such\nexperiments, towards a regime where the entanglement growth can render existing\nclassical simulations inefficient."
    },
    {
        "anchor": "Universal scaling at non-thermal fixed points of a two-component Bose\n  gas: Quasi-stationary far-from-equilibrium critical states of a two-component Bose\ngas are studied in two spatial dimensions. After the system has undergone an\ninitial dynamical instability it approaches a non-thermal fixed point. At this\ncritical point the structure of the gas is characterised by ensembles of\n(quasi-)topological defects such as vortices, skyrmions and solitons which give\nrise to universal power-law behaviour of momentum correlation functions. The\nresulting power-law spectra can be interpreted in terms of\nstrong-wave-turbulence cascades driven by particle transport into\nlong-wave-length excitations. Scaling exponents are determined on both sides of\nthe miscible-immiscible transition controlled by the ratio of the intra-species\nto inter-species couplings. Making use of quantum turbulence methods, we\nexplain the specific values of the exponents from the presence of transient\n(quasi-)topological defects.",
        "positive": "Efimov spectrum in bosonic systems with increasing number of particles: It is well-known that three-boson systems show the Efimov effect when the\ntwo-body scattering length $a$ is large with respect to the range of the\ntwo-body interaction. This effect is a manifestation of a discrete scaling\ninvariance (DSI). In this work we study DSI in the $N$-body system by analysing\nthe spectrum of $N$ identical bosons obtained with a pairwise gaussian\ninteraction close to the unitary limit. We consider different universal ratios\nsuch as $E_N^0/E_3^0$ and $E_N^1/E_N^0$, with $E_N^i$ being the energy of the\nground ($i=0$) and first-excited ($i=1$) state of the system, for $N\\le16$. We\ndiscuss the extension of the Efimov radial law, derived by Efimov for $N=3$, to\ngeneral $N$."
    },
    {
        "anchor": "Unconventional superfluidity and quantum geometry of topological bosons: We investigate superfluidity of bosons in gapped topological bands and\ndiscover a new phase that has no counterparts in the previous literature. This\nphase is characterized by a highly unconventional modulation of the order\nparameter, breaking the crystallographic symmetry, and for which the\ncondensation momentum is neither zero nor any other high-symmetry vector of the\nBrillouin zone. This unconventional structure impacts the spectrum of\nBogoliubov excitations and, consequently, the speed of sound in the system.\nEven in the case of perfectly flat bands, the speed of sound and Bogoliubov\nexcitations remain nonvanishing, provided that the underlying topology and\nquantum geometry are nontrivial. Furthermore, we derive detailed expressions\nfor the superfluid weight using the Popov hydrodynamic formalism for\nsuperfluidity and provide estimates for the Berezinskii-Kosterlitz-Thouless\ntemperature, which is significantly enhanced by the nontriviality of the\nunderlying quantum metric. These results are applicable to generic topological\nbosonic bands, with or without dispersion. To illustrate our findings, we\nemploy the Haldane model with a tunable bandwidth, including the narrow\nlowest-band case. Within this model, we also observe a re-entrant superfluid\nbehavior: As the Haldane's magnetic flux is varied, the\nBerezinskii-Kosterlitz-Thouless transition temperature initially decreases to\nalmost zero, only to resurface with renewed vigor.",
        "positive": "Liouvillian gap and single spin-flip dynamics in the dissipative\n  Fermi-Hubbard model: Motivated by recent progress in cold-atom experiments, we analyze the SU($N$)\nFermi-Hubbard model on a $d$-dimensional hypercubic lattice with two-body loss.\nBy focusing on states near the ferromagnetic steady states, we obtain the\nLiouvillian gap in closed form for any $d$ and $N$. We also investigate the\ndynamics of a ferromagnetic initial state with a single spin flip both\nanalytically and numerically. In particular, we show that, by decreasing the\nstrength of the interaction and loss, the survival probability of the spin flip\nexhibits a crossover from the power-law decay to the exponential decay. We\nexpect that our findings can be tested experimentally with ultracold\nalkaline-earth-like atoms in an optical lattice."
    },
    {
        "anchor": "Rashbon bound states associated with a spherical spin-orbit coupling in\n  an ultracold Fermi gas with an $s$-wave interaction: We investigate the formation of rashbon bound states and strong-coupling\neffects in an ultracold Fermi gas with a spherical spin-orbit interaction,\n$H_{\\rm so}=\\lambda{\\bf p}\\cdot{\\bf \\sigma}$ (where ${\\bf\n\\sigma}=(\\sigma_x,\\sigma_y,\\sigma_z)$ are Pauli matrices). Extending the\nstrong-coupling theory developed by Nozi\\`eres and Schmitt-Rink (NSR) to\ninclude this spin-orbit coupling, we determine the superfluid phase transition\ntemperature $T_{\\rm c}$, as functions of the strength of a pairing interaction\n$U_s$, as well as the spin-orbit coupling strength $\\lambda$. Evaluating poles\nof the NSR particle-particle scattering matrix describing fluctuations in the\nCooper channel, we clarify the region where rashbon bound states dominate the\nsuperfluid phase transition in the $U_{s}$-$\\lambda$ phase diagram. Since the\nantisymmetric spin-orbit interaction $H_{\\rm so}$ breaks the inversion symmetry\nof the system, rashbon bound states naturally have, not only a spin-singlet and\neven-parity symmetry, but also a spin-triplet and odd-parity symmetry. Thus,\nour results would be also useful for the study of this parity mixing effect in\nthe BCS-BEC crossover regime of a spin-orbit coupled Fermi gas.",
        "positive": "Vortex precession dynamics in general radially symmetric potential traps\n  in two-dimensional atomic Bose-Einstein condensates: We consider the motion of individual two-dimensional vortices in general\nradially symmetric potentials in Bose-Einstein condensates. We find that\nalthough in the special case of the parabolic trap there is a logarithmic\ncorrection in the dependence of the precession frequency $\\omega$ on the\nchemical potential $\\mu$, this is no longer true for a general potential $V(r)\n\\propto r^p$. Our calculations suggest that for $p>2$, the precession frequency\nscales with $\\mu$ as $\\omega \\sim \\mu^{-2/p}$. This theoretical prediction is\ncorroborated by numerical computations, both at the level of spectral\n(Bogolyubov-de Gennes) stability analysis by identifying the relevant\nprecession mode dependence on $\\mu$, but also through direct numerical\ncomputations of the vortex evolution in the large $\\mu$, so-called\nThomas-Fermi, limit. Additionally, the dependence of the precession frequency\non the radius of an initially displaced from the center vortex is examined and\nthe corresponding predictions are tested against numerical results."
    },
    {
        "anchor": "Collapse and revival dynamics of superfluids of ultracold atoms in\n  optical lattices: Recent experiments have shown a remarkable number of collapse-and-revival\noscillations of the matter-wave coherence of ultracold atoms in optical\nlattices [Will et al., Nature 465, 197 (2010)]. Using a mean-field\napproximation to the Bose-Hubbard model, we show that the visibility of\ncollapse-and-revival interference patterns reveal number squeezing of the\ninitial superfluid state. To describe the dynamics, we use an effective\nHamiltonian that incorporates the intrinsic two-body and induced three-body\ninteractions, and we analyze in detail the resulting complex pattern of\ncollapse-and-revival frequencies generated by virtual transitions to higher\nbands, as a function of lattice parameters and mean-atom number. Our work shows\nthat a combined analysis of both the multiband, non-stationary dynamics in the\nfinal deep lattice, and the number-squeezing of the initial superfluid state,\nexplains important characteristics of optical lattice collapse-and-revival\nphysics. Finally, by treating the two- and three-body interaction strengths,\nand the coefficients describing the initial superposition of number states, as\nfree parameters in a fit to the experimental data it should be possible to go\nbeyond some of the limitations of our model and obtain insight into the\nbreakdown of the mean-field theory for the initial state or the role of\nnonperturbative effects in the final state dynamics.",
        "positive": "The Pauli principle in collective motion: Reimagining and reinterpreting\n  Cooper pairs, the Fermi sea, Pauli blocking and superfluidity: Typically visualized from an independent particle viewpoint, the Pauli\nprinciple's role in collective motion is analyzed leading to a reimagination of\nthe microscopic dynamics underlying superfluidity/superconductivity and a\nreinterpretation of several interrelated phenomena: Cooper pairs, the Fermi\nsea, and Pauli blocking. The current approach, symmetry-invariant perturbation\ntheory is a first principles method with no adjustable parameters. An adiabatic\nevolution is employed to transfer the well-known Pauli restrictions for\nidentical, independent particles with two spin values to restrictions on the\ncollective modes of an ensemble of ``spin up'' ``spin down'' particles. The\ncollective modes, analytic N-body normal modes, are obtained from a group\ntheoretic exact solution of the first-order equations. Cooper pairing is\nreinterpreted not as the pairing of two fermions with total zero momentum, but\nas the convergence of the momentum of the entire ensemble to two values, +k and\n-k, as the particles in the normal mode move back and forth with a single\nfrequency and phase. The Fermi sea and Pauli blocking, commonly described using\nindependent fermions that occupy lower states to create a ``sea'' in energy\nspace and block occupation is redescribed as a collective energy phenomena of\nthe entire ensemble. Superfluidity, which has always been viewed as a\ncollective phenomena as Cooper pairs are assumed to condense into a macroscopic\noccupation of a single lowest state, is now reimagined without two-body pairing\nin real space, but as a macroscopic occupation of a low-energy phonon normal\nmode resulting in the convergence of the momentum to two equal and opposite\nvalues. The expected properties of superfluidity including the rigidity of the\nwave function, interactions between fermions in different pairs, convergence of\nthe momentum and the gap in the excitation spectrum are discussed."
    },
    {
        "anchor": "Gravity-induced accelerating expansion of excited-state Bose-Einstein\n  condensate: The Bose-Einstein condensate (BEC) of excited states, provides a different\nplatform to explore the interplay between gravity and quantum physics. In this\nLetter, we study the response of excited-state BECs to an external\ngravitational field and their dynamics under gravity when space is expanding.\nWe reveal the anomalous response of the center-of-mass of the BEC to the\ngravitational field and the exotic gravity-induced accelerating expansion\nphenomena. We demonstrate that these effects result from the interplay among\ngravity, space and quantum effects. We also propose related experiments to\nobserve these anomalies.",
        "positive": "Dynamical fermionization in a one-dimensional Bose-Fermi mixture: After release from the trap the momentum distribution of an impenetrable gas\nasymptotically approaches that of a spinless noninteracting Fermi gas in the\ninitial trap. This phenomenon is called dynamical fermionization and, very\nrecently, has been experimentally confirmed in the case of the Lieb-Liniger\nmodel in the Tonks-Girardeau regime. We prove analytically and confirm\nnumerically that following the removal of axial confinement the strongly\ninteracting Bose-Fermi mixture exhibits dynamical fermionization and the\nasymptotical momentum distribution of each component has the same shape as its\ndensity profile at $t=0$. Under a sudden change of the trap frequency to a new\nnon-zero value the dynamics of both fermionic and bosonic momentum\ndistributions presents characteristics which are similar to the case of single\ncomponent bosons experiencing a similar quench. Our results are derived using a\nproduct representation for the correlation functions which, in addition to\nanalytical considerations, can be implemented numerically very easily with\ncomplexity which scales polynomially in the number of particles."
    },
    {
        "anchor": "Bose-Einstein condensation in a magnetic double-well potential: We present the first experimental realisation of Bose-Einstein condensation\nin a purely magnetic double-well potential. This has been realised by combining\na static Ioffe-Pritchard trap with a time orbiting potential (TOP). The double\ntrap can be rapidly switched to a single harmonic trap of identical oscillation\nfrequencies thus accelerating the two condensates towards each other.\nFurthermore, we show that time averaged potentials can be used as a means to\ncontrol the radial confinement of the atoms. Manipulation of the radial\nconfinement allows vortices and radial quadrupole oscillations to be excited.",
        "positive": "Ground state properties of a one-dimensional strongly-interacting\n  Bose-Fermi mixture in a double-well potential: We calculate the reduced single-particle density matrix (RSPDM), momentum\ndistributions, natural orbitals and their occupancies, for a strongly\ninteracting one-dimensional Bose-Fermi mixture in a double-well potential with\na large central barrier. For mesoscopic systems, we find that the ground state\nproperties qualitatively differ for mixtures with even number of particles\n(both odd-odd and even-even mixtures) in comparison to mixtures with odd\nparticle numbers (odd-even and even-odd mixtures). For even mixtures the\nmomentum distribution is smooth, whereas the momentum distribution of odd\nmixtures possesses distinct modulations; the differences are observed also in\nthe off-diagonal correlations of the RSPDM, and in the occupancies of natural\norbitals. The calculation is based on a derived formula which enables efficient\ncalculation of the RSPDM for mesoscopic mixtures in various potentials."
    },
    {
        "anchor": "A supercircle description of universal three-body states in two\n  dimensions: We consider bound states of asymmetric three-body systems confined to two\ndimensions. In the universal regime, two energy ratios and two mass ratios\nprovide complete knowledge of the three-body energy measured in units of one\ntwo-body energy. The lowest number of stable bound states is produced when one\nmass is larger than two similar masses. We focus on selected asymmetric systems\nof interest in cold atom physics. The scaled three-body energy and the two\nscaled two-body energies are related through an equation for a supercircle\nwhose radius increases almost linearly with three-body energy. The exponents\nexhibit an increasing behavior with three-body energy. The mass dependence is\nhighly non-trivial. We give a simple relation that predicts the universal\nthree-body energy.",
        "positive": "From few to many bosons inside the unitary window: a transition between\n  universal to non-universal behavior: Universal behaviour in few-bosons systems close to the unitary limit, where\ntwo bosons become unbound, has been intensively investigated in recent years\nboth experimentally and theoretically. In this particular region, called the\nunitary window, details of the inter-particle interactions are not important\nand observables, such as binding energies, can be characterized by a few\nparameters. With an increasing number of particles the short-range repulsion,\npresent in all atomic, molecular or nuclear interactions, gradually induces\ndeviations from the universal behaviour. In the present letter we discuss for\nthe first time a simple way of incorporating non-universal behaviour through\none specific parameter which controls the smooth transition of the system from\nuniversal to non-universal regime. Using a system of $N$ helium atoms as an\nexample we calculate their ground state energies as trajectories within the\nunitary window and also show that the control parameters can be used to\ndetermine the energy per particle in homogeneous systems when $N \\rightarrow\n\\infty$."
    },
    {
        "anchor": "Universal Hall Response in Synthetic Dimensions: We theoretically study the Hall effect on interacting $M$-leg ladder systems,\ncomparing different measures and properties of the zero temperature Hall\nresponse in the limit of weak magnetic fields. Focusing on $SU(M)$ symmetric\ninteracting bosons and fermions, as relevant for e.g. typical synthetic\ndimensional quantum gas experiments, we identify an extensive regime in which\nthe Hall imbalance $\\Delta_{\\rm H}$ is universal and corresponds to a classical\nHall resistivity $R_{\\rm H}=-1/n$ for a large class of quantum phases. Away\nfrom this high symmetry point we observe interaction driven phenomena such as\nsign reversal and divergence of the Hall response.",
        "positive": "Superballistic center-of-mass motion in one-dimensional attractive Bose\n  gases: Decoherence-induced Gaussian random walks in velocity space: We show that the spreading of the center-of-mass density of ultracold\nattractively interacting bosons can become superballistic in the presence of\ndecoherence, via single-, two- and/or three-body losses. In the limit of weak\ndecoherence, we analytically solve the numerical model introduced in [Phys.\nRev. A 91, 063616 (2015)]. The analytical predictions allow us to identify\nexperimentally accessible parameter regimes for which we predict superballistic\nspreading of the center-of-mass density. Ultracold attractive Bose gases form\nweakly bound molecules; quantum matter-wave bright solitons. Our\ncomputer-simulations combine ideas from classical field methods (\"truncated\nWigner\") and piecewise deterministic stochastic processes. While the truncated\nWigner approach to use an average over classical paths as a substitute for a\nquantum superposition is often an uncontrolled approximation, here it predicts\nthe exact root-mean-square width when modeling an expanding Gaussian wave\npacket. In the superballistic regime, the leading-order of the spreading of the\ncenter-of-mass density can thus be modeled as a quantum superposition of\nclassical Gaussian random walks in velocity space."
    },
    {
        "anchor": "Stochastic-field approach to the quench dynamics of the one-dimensional\n  Bose polaron: We consider the dynamics of a quantum impurity after a sudden interaction\nquench into a one-dimensional degenerate Bose gas. We use the Keldysh path\nintegral formalism to derive a truncated Wigner like approach that takes the\nback action of the impurity onto the condensate into account already on the\nmean-field level and further incorporates thermal and quantum effects up to\none-loop accuracy. This framework enables us not only to calculate the real\nspace trajectory of the impurity but also the absorption spectrum. We find that\nquantum corrections and thermal effects play a crucial role for the impurity\nmomentum at weak to intermediate impurity-bath couplings.Furthermore, we see\nthe broadening of the absorption spectrum with increasing temperature.",
        "positive": "Observation of pairs of atoms at opposite momenta in an equilibrium\n  interacting Bose gas: Quantum fluctuations play a central role in the properties of quantum matter.\nIn non-interacting ensembles, they manifest as fluctuations of non-commuting\nobservables, quantified by Heisenberg inequalities. In the presence of\ninteractions, additional quantum fluctuations appear, from which many-body\ncorrelations and entanglement arise. In the context of many-body physics, the\nBogoliubov theory provides us with an illuminating microscopic picture of how\nthis occurs for weakly-interacting bosons, with the appearance of the quantum\ndepletion formed by pairs of bosons with opposite momenta. Here, we report the\nobservation of these atom pairs in the depletion of an equilibrium interacting\nBose gas. A quantitative study of atom-atom correlations, both at opposite and\nclose-by momenta, allows us to fully characterise the equilibrium many-body\nstate. We show that the atom pairs share the properties of two-mode squeezed\nstates, including relative number squeezing. Our results illustrate how\ninteracting systems acquire non-trivial quantum correlations as a result of the\ninterplay between quantum fluctuations and interactions"
    },
    {
        "anchor": "Two-dimensional spectroscopic diagnosis of quantum coherence in Fermi\n  polarons: We present a full microscopic many-body calculation of a recently-proposed\nnonlinear two-dimensional spectroscopy for Fermi polarons, and show that the\nquantum coherence between the attractive and repulsive polarons, which has\nnever been experimentally examined, can be unambiguously revealed via quantum\nbeats at the two off-diagonal crosspeaks in the two-dimensional spectrum. We\npredict that particle-hole excitations make the two crosspeaks asymmetric and\nlead to an additional side peak near the diagonal repulsive polaron peak. Our\nsimulated spectra can be readily examined in future cold-atom experiments,\nwhere the two-dimensional spectroscopy is to be implemented by using a Ramsey\ninterference sequence of rf pulses in the time domain. Our results also provide\na first-principle understanding of the recent two-dimensional coherent\nspectroscopy of interacting excitons and trions in doped monolayer transition\nmetal dichalcogenides.",
        "positive": "Angular collapse of dipolar Bose-Einstein condensates: We explore the structure and dynamics of dipolar Bose-Einstein condensates\n(DBECs) near their threshold for instability. Near this threshold a DBEC may\nexhibit nontrivial, biconcave density distributions, which are associated with\ninstability against collapse into \"angular roton\" modes. Here we discuss\nexperimental signatures of these novel features. In the first, we infer local\ncollapse of the DBEC from the experimental stability diagram. In the second, we\nexplore the dynamics of collapse and find that a nontrivial angular\ndistribution is a signature of the DBEC possessing a biconcave structure."
    },
    {
        "anchor": "Supersolid phases of dipolar bosons in optical lattices with a staggered\n  flux: We present the theoretical mean-field zero-temperature phase diagram of a\nBose-Einstein condensate (BEC) with dipolar interactions loaded into an optical\nlattice with a staggered flux. Apart from uniform superfluid, checkerboard\nsupersolid and striped supersolid phases, we identify several supersolid phases\nwith staggered vortices, which can be seen as combinations of supersolid phases\nfound in earlier work on dipolar BECs and a staggered-vortex phase found for\nbosons in optical lattices with staggered flux. By allowing for different\nphases and densities on each of the four sites of the elementary plaquette,\nmore complex phase patterns are found.",
        "positive": "Spin-orbit-coupled Bose-Einstein condensates of rotating polar molecules: An experimental proposal for realizing spin-orbit (SO) coupling of\npseudospin-1 in the ground manifold $^1\\Sigma(\\upsilon=0)$ of (bosonic)\nbialkali polar molecules is presented. The three spin components are composed\nof the ground rotational state and two substates from the first excited\nrotational level. Using hyperfine resolved Raman processes through two select\nexcited states resonantly coupled by a microwave, an effective coupling between\nthe spin tensor and linear momentum is realized. The properties of\nBose-Einstein condensates for such SO-coupled molecules exhibiting dipolar\ninteractions are further explored. In addition to the SO-coupling-induced\nstripe structures, the singly and doubly quantized vortex phases are found to\nappear, implicating exciting opportunities for exploring novel quantum physics\nusing SO-coupled rotating polar molecules with dipolar interactions."
    },
    {
        "anchor": "Weyl points and topological nodal superfluids in a face-centered cubic\n  optical lattice: We point out that a face-centered cubic (FCC) optical lattice, which can be\nrealised by a simple scheme using three lasers, provides one a highly\ncontrollable platform for creating Weyl points and topological nodal\nsuperfluids in ultracold atoms. In non-interacting systems, Weyl points\nautomatically arise in the Floquet band structure when shaking such FCC\nlattices, and sophisticated design of the tunnelling is not required. More\ninterestingly, in the presence of attractive interaction between two hyperfine\nspin states, which experience the same shaken FCC lattice, a three-dimensional\ntopological nodal superfluid emerges, and Weyl points show up as the gapless\npoints in the quasiparticle spectrum. One could either create a double Weyl\npoint of charge 2, or split it to two Weyl points of charge 1, which can be\nmoved in the momentum space by tuning the interactions. Correspondingly, the\nFermi arcs at the surface may be linked with each other or separated as\nindividual ones.",
        "positive": "Statics and dynamics of a binary dipolar Bose-Einstein condensate\n  soliton: We study the statics and dynamics of a binary dipolar Bose-Einstein\ncondensate soliton for repulsive inter- and intraspecies contact interactions\nwith the two components subject to different spatial symmetries $-$ distinct\nquasi-one-dimensional and quasi-two-dimensional shapes - using numerical\nsolution and variational approximation of a three-dimensional mean-field model.\nThe results are illustrated with realistic values of parameters in the binary\n164Dy-168Er mixture. The possibility of forming robust dipolar solitons of very\nlarge number of atoms make them of great experimental interest. The existence\nof the solitons is illustrated in terms of stability phase diagrams. Exotic\nshapes of these solitons are illustrated in isodensity plots. The variational\nresults for statics (size and chemical potential) and dynamics (small\noscillation) of the binary soliton compare well with the numerical results. A\nway of preparing and studying these solitons in laboratory is suggested."
    },
    {
        "anchor": "Strongly Interacting Quantum Gases in One-Dimensional Traps: Under the second-order degenerate perturbation theory, we show that the\nphysics of $N$ particles with arbitrary spin confined in a one dimensional trap\nin the strongly interacting regime can be described by super-exchange\ninteraction. An effective spin-chain Hamiltonian (non-translational-invariant\nSutherland model) can be constructed from this procedure. For spin-1/2\nparticles, this model reduces to the non-translational-invariant Heisenberg\nmodel, where a transition between Heisenberg anti-ferromagnetic (AFM) and\nferromagnetic (FM) states is expected to occur when the interaction strength is\ntuned from the strongly repulsive to the strongly attractive limit. We show\nthat the FM and the AFM states can be distinguished in two different methods:\nthe first is based on their distinct response to a spin-dependent magnetic\ngradient, and the second is based on their distinct momentum distribution. We\nconfirm the validity of the spin-chain model by comparison with results\nobtained from several unbiased techniques",
        "positive": "Dynamic polaron response from variational imaginary time evolution: An variational expression for the zero temperature polaron impedance is\nobtained by minimizing the free energy in a generalized quadratic Feynman\nmodel. The impedance function of the quadratic model serves as the variational\nparameter. It is shown that a very small change in the energy can be\naccompanied by a large change in the optical conductivity. This is related to\nthe insensitivity of the Jensen-Feynman free energy to the UV properties of the\nmodel. Analytic and numeric results are derived for the Fr\\\"ohlich polaron in\nweak and strong coupling. Standard results are recovered at weak coupling but,\nmore importantly, strong coupling inconsistencies are removed."
    },
    {
        "anchor": "Recovering quantum correlations in optical lattices from interaction\n  quenches: Quantum simulations with ultra-cold atoms in optical lattices open up an\nexciting path towards understanding strongly interacting quantum systems. Atom\ngas microscopes are crucial for this as they offer single-site density\nresolution, unparalleled in other quantum many-body systems. However, currently\na direct measurement of local coherent currents is out of reach. In this work,\nwe show how to achieve that by measuring densities that are altered in response\nto quenches to non-interacting dynamics, e.g., after tilting the optical\nlattice. For this, we establish a data analysis method solving the closed set\nof equations relating tunnelling currents and atom number dynamics, allowing to\nreliably recover the full covariance matrix, including off-diagonal terms\nrepresenting coherent currents. The signal processing builds upon semi-definite\noptimization, providing bona fide covariance matrices optimally matching the\nobserved data. We demonstrate how the obtained information about non-commuting\nobservables allows to lower bound entanglement at finite temperature which\nopens up the possibility to study quantum correlations in quantum simulations\ngoing beyond classical capabilities.",
        "positive": "Effective equations for repulsive quasi-1D BECs trapped with anharmonic\n  transverse potentials: One-dimensional nonlinear Schr\\\"odinger equations are derived to describe the\naxial effective dynamics of cigar-shaped atomic repulsive Bose-Einstein\ncondensates trapped with anharmonic transverse potentials. The accuracy of\nthese equations in the perturbative, Thomas-Fermi, and crossover regimes were\nverified numerically by comparing the ground-state profiles, transverse\nchemical potentials and oscillation patterns with those results obtained for\nthe full three-dimensional Gross-Pitaevskii equation. This procedure allows us\nto derive different patterns of 1D nonlinear models by the control of the\ntransverse confinement."
    },
    {
        "anchor": "Strong Boundary and Trap Potential Effects on Emergent Physics in\n  Ultra-Cold Fermionic Gases: The field of quantum simulations in ultra-cold atomic gases has been\nremarkably successful. In principle it allows for an exact treatment of a\nvariety of highly relevant lattice models and their emergent phases of matter.\nBut so far there is a lack in the theoretical literature concerning the\nsystematic study of the effects of the trap potential as well as the finite\nsize of the systems, as numerical studies of such non periodic, correlated\nfermionic lattices models are numerically demanding beyond one dimension. We\nuse the recently introduced real-space truncated unity functional\nrenormalization group to study these boundary and trap effects with a focus on\ntheir impact on the superconducting phase of the $2$D Hubbard model. We find\nthat in the experiments not only lower temperatures need to be reached compared\nto current capabilities, but also system size and trap potential shape play a\ncrucial role to simulate emergent phases of matter.",
        "positive": "Modulational instability and localized breather modes in the discrete\n  nonlinear Schr\u00f6dinger equation with helicoidal hopping: We study a one-dimensional discrete nonlinear Schr\\\"odinger model with\nhopping to the first and a selected N-th neighbor, motivated by a helicoidal\narrangement of lattice sites. We provide a detailed analysis of the\nmodulational instability properties of this equation, identifying distinctive\nmulti-stage instability cascades due to the helicoidal hopping term.\nBistability is a characteristic feature of the intrinsically localized breather\nmodes, and it is shown that information on the stability properties of weakly\nlocalized solutions can be inferred from the plane-wave modulational\ninstability results. Based on this argument, we derive analytical estimates of\nthe critical parameters at which the fundamental on-site breather branch of\nsolutions turns unstable. In the limit of large N, these estimates predict the\nemergence of an effective threshold behavior, which can be viewed as the result\nof a dimensional crossover to a two-dimensional square lattice."
    },
    {
        "anchor": "Thermodynamical properties of a trapped interacting Bose gas: The thermodynamical properties of interacting Bose atoms in a harmonic\npotential are studied within the mean-field approximation. For weak\ninteractions, the quantum statistics is equivalent to an ideal gas in an\neffective mean-field potential. The eigenvalue of the Gross-Pitaevskii equation\nis identified as the chemical potential of the ideal gas. The condensation\ntemperature and density profile of atoms are calculated. It is found that the\ncritical temperature $T_c$ decreases as the interactions increase. Below the\ncritical point, the condensation fraction exhibits a universal relation of\n$N_0/N=1-(T/T_c)^{\\gamma}$, with the index $\\gamma\\approx 2.3$ independent of\nthe interaction strength, the chemical potential, as well as the frequency of\nthe confining potential.",
        "positive": "Mass-imbalanced Three-Body Systems in Two Dimensions: We consider three-body systems in two dimensions with zero-range interactions\nfor general masses and interaction strengths. The momentum-space Schr\\\"odinger\nequation is solved numerically and in the Born-Oppenheimer (BO) approximation.\nThe BO expression is derived using separable potentials and yields a concise\nadiabatic potential between the two heavy particles. The BO potential is\nCoulomb-like and exponentially decreasing at small and large distances,\nrespectively. While we find similar qualitative features to previous studies,\nwe find important quantitative differences. Our results demonstrate that\nmass-imbalanced systems that are accessible in the field of ultracold atomic\ngases can have a rich three-body bound state spectrum in two dimensional\ngeometries. Small light-heavy mass ratios increase the number of bound states.\nFor 87Rb-87Rb-6Li and 133Cs-133Cs-6Li we find respectively 3 and 4 bound\nstates."
    },
    {
        "anchor": "An unsupervised deep learning algorithm for single-site reconstruction\n  in quantum gas microscopes: In quantum gas microscopy experiments, reconstructing the site-resolved\nlattice occupation with high fidelity is essential for the accurate extraction\nof physical observables. For short interatomic separations and limited\nsignal-to-noise ratio, this task becomes increasingly challenging. Common\nmethods rapidly decline in performance as the lattice spacing is decreased\nbelow half the imaging resolution. Here, we present a novel algorithm based on\ndeep convolutional neural networks to reconstruct the site-resolved lattice\noccupation with high fidelity. The algorithm can be directly trained in an\nunsupervised fashion with experimental fluorescence images and allows for a\nfast reconstruction of large images containing several thousand lattice sites.\nWe benchmark its performance using a quantum gas microscope with cesium atoms\nthat utilizes short-spaced optical lattices with lattice constant $383.5\\,$nm\nand a typical Rayleigh resolution of $850\\,$nm. We obtain promising\nreconstruction fidelities~$\\gtrsim 96\\%$ across all fillings based on a\nstatistical analysis. We anticipate this algorithm to enable novel experiments\nwith shorter lattice spacing, boost the readout fidelity and speed of\nlower-resolution imaging systems, and furthermore find application in related\nexperiments such as trapped ions.",
        "positive": "Bound states in the one-dimensional two-particle Hubbard model with an\n  impurity: We investigate bound states in the one-dimensional two-particle Bose-Hubbard\nmodel with an attractive ($V> 0$) impurity potential. This is a\none-dimensional, discrete analogy of the hydrogen negative ion H$^-$ problem.\nThere are several different types of bound states in this system, each of which\nappears in a specific region. For given $V$, there exists a (positive) critical\nvalue $U_{c1}$ of $U$, below which the ground state is a bound state.\nInterestingly, close to the critical value ($U\\lesssim U_{c1}$), the ground\nstate can be described by the Chandrasekhar-type variational wave function,\nwhich was initially proposed for H$^-$. For $U>U_{c1}$, the ground state is no\nlonger a bound state. However, there exists a second (larger) critical value\n$U_{c2}$ of $U$, above which a molecule-type bound state is established and\nstabilized by the repulsion. We have also tried to solve for the eigenstates of\nthe model using the Bethe ansatz. The model possesses a global $\\Zz_2$-symmetry\n(parity) which allows classification of all eigenstates into even and odd ones.\nIt is found that all states with odd-parity have the Bethe form, but none of\nthe states in the even-parity sector. This allows us to identify analytically\ntwo odd-parity bound states, which appear in the parameter regions $-2V<U<-V$\nand $-V<U<0$, respectively. Remarkably, the latter one can be \\textit{embedded}\nin the continuum spectrum with appropriate parameters. Moreover, in part of\nthese regions, there exists an even-parity bound state accompanying the\ncorresponding odd-parity bound state with almost the same energy."
    },
    {
        "anchor": "Excitation Spectrum and Superfluid Gap of an Ultracold Fermi Gas: Ultracold atomic gases are a powerful tool to experimentally study strongly\ncorrelated quantum many-body systems. In particular, ultracold Fermi gases with\ntunable interactions have allowed to realize the famous BEC-BCS crossover from\na Bose-Einstein condensate (BEC) of molecules to a Bardeen-Cooper-Schrieffer\n(BCS) superfluid of weakly bound Cooper pairs. However, large parts of the\nexcitation spectrum of fermionic superfluids in the BEC-BCS crossover are still\nunexplored. In this work, we use Bragg spectroscopy to measure the full\nmomentum-resolved low-energy excitation spectrum of strongly interacting\nultracold Fermi gases. This enables us to directly observe the smooth\ntransformation from a bosonic to a fermionic superfluid that takes place in the\nBEC-BCS crossover. We also use our spectra to determine the evolution of the\nsuperfluid gap and find excellent agreement with previous experiments and\nself-consistent T-matrix calculations both in the BEC and crossover regime.\nHowever, towards the BCS regime a calculation that includes the effects of\nparticle-hole correlations shows better agreement with our data.",
        "positive": "Rotational properties of superfluid Fermi-Bose mixtures in a tight\n  toroidal trap: We consider a mixture of a Bose-Einstein condensate, with a paired Fermi\nsuperfluid, confined in a ring potential. We start with the ground state of the\ntwo clouds, identifying the boundary between the regimes of their phase\nseparation and phase coexistence. We then turn to the rotational response of\nthe system. In the phase-separated regime, we have center of mass excitation.\nWhen the two species coexist, the spectrum has a rich structure, consisting of\ncontinuous and discontinuous phase transitions. Furthermore, for a reasonably\nlarge population imbalance it develops a clear quasi-periodic behaviour, in\naddition to the one due to the periodic boundary conditions. It is then\nfavourable for the one component to reside in a plane-wave state, with a\nhomogeneous density distribution, and the problem resembles that of a\nsingle-component system."
    },
    {
        "anchor": "Exact Results for the Boundary Energy of One-Dimensional Bosons: We study bosons in a one-dimensional hard-wall box potential. In the case of\ncontact interaction, the system is exactly solvable by the Bethe ansatz, as\nfirst shown by Gaudin in 1971. Although contained in the exact solution, the\nboundary energy in the thermodynamic limit for this problem is only\napproximately calculated by Gaudin, who found the leading order result at weak\nrepulsion. Here we derive an exact integral equation that enables one to\ncalculate the boundary energy in the thermodynamic limit at an arbitrary\ninteraction. We then solve such an equation and find the asymptotic results for\nthe boundary energy at weak and strong interactions. The analytical results\nobtained from the Bethe ansatz are in agreement with the ones found by other\ncomplementary methods, including quantum Monte Carlo simulations. We study the\nuniversality of the boundary energy in the regime of a small gas parameter by\nmaking a comparison with the exact solution for the hard rod gas.",
        "positive": "Complex contact interaction for systems with short-range two-body loss: Contact interaction is a fundamental concept that appears in various areas of\nphysics. It simplifies physical models by replacing the detailed short-range\ninteraction with a zero-range contact potential which reproduces the same\nlow-energy scattering parameter, i.e. the $s$-wave scattering length. In this\nwork, we generalize this concept to a system with short-range two-body loss. We\nshow that the short-range two-body loss can effectively be replaced by a\nzero-range complex contact potential with proper regularization characterized\nby a complex scattering length. We develop appropriate ways to regularize this\npotential in the Lindblad master equation and apply them to the dynamic problem\nof Bose-Einstein condensate with weak interaction and two-body loss."
    },
    {
        "anchor": "Noise-induced transition from superfluid to vortex state in\n  two-dimensional nonequilibrium polariton condensates: We study the Berezinskii-Kosterlitz-Thouless mechanism for vortex-antivortex\npair formation in two-dimensional superfluids for nonequilibrium condensates.\nOur numerical study is based on a classical field model for driven-dissipative\nquantum fluids that is applicable to polariton condensates. We investigate the\ncritical noise needed to create vortex-antivortex pairs in the systems,\nstarting from a state with uniform phase. The dependence of the critical noise\non the nonequilibrium and energy relaxation parameters is analyzed in detail.",
        "positive": "Shape of a sound wave in a weakly-perturbed Bose gas: We employ the Gross-Pitaevskii equation to study acoustic emission generated\nin a uniform Bose gas by a static impurity. The impurity excites a sound-wave\npacket, which propagates through the gas. We calculate the shape of this wave\npacket in the limit of long wave lengths, and argue that it is possible to\nextract properties of the impurity by observing this shape. We illustrate here\nthis possibility for a Bose gas with a trapped impurity atom -- an example of a\nrelevant experimental setup. Presented results are general for all\none-dimensional systems described by the nonlinear Schr\\\"odinger equation and\ncan also be used in nonatomic systems, e.g., to analyze light propagation in\nnonlinear optical media. Finally, we calculate the shape of the sound-wave\npacket for a three-dimensional Bose gas assuming a spherically symmetric\nperturbation."
    },
    {
        "anchor": "Dynamics for the Haldane phase in the Bilinear-Biquadratic Model: The BBM is a promising candidate to study spin-one systems and to design\nquantum simulators based on its underlying Hamiltonian. The variety of\ndifferent phases contains amongst other valuable and exotic phases the Haldane\nphase. We study the Kibble-Zurek physics of linear quenches into the Haldane\nphase. We outline ideal quench protocols to minimize defects in the final state\nwhile exploiting different linear quench protocols via the uniaxial or\ninteraction term. Furthermore, we look at the fate of the string order when\nquenching from a topologically non-trivial phase to a trivial phase. Our\nstudies show this depends significantly on the path chosen for quenching; for\nexample, we discover quenches from \\Neel{} to Haldane phase which reach a\nstring order greater than their ground state counterparts for the initial or\nfinal state at intermediate quench times.",
        "positive": "Time-resolved measurement of Landau--Zener tunneling in different bases: A comprehensive study of the tunneling dynamics of a Bose--Einstein\ncondensate in a tilted periodic potential is presented. We report numerical and\nexperimental results on time-resolved measurements of the Landau--Zener\ntunneling of ultracold atoms introduced by the tilt, which experimentally is\nrealized by accelerating the lattice. The use of different protocols enables us\nto access the tunneling probability, numerically as well as experimentally, in\ntwo different bases, namely, the adiabatic basis and the diabatic basis. The\nadiabatic basis corresponds to the eigenstates of the lattice, and the diabatic\none to the free-particle momentum eigenstates. Our numerical and experimental\nresults are compared with existing two-state Landau--Zener models."
    },
    {
        "anchor": "Density Functional of a Two-Dimensional Gas of Dipolar Atoms:\n  Thomas-Fermi-Dirac Treatment: We derive the density functional for the ground-state energy of a\ntwo-dimensional, spin-polarized gas of neutral fermionic atoms with\nmagnetic-dipole interaction, in the Thomas-Fermi-Dirac approximation. For many\natoms in a harmonic trap, we give analytical solutions for the single-particle\nspatial density and the ground-state energy, in dependence on the interaction\nstrength, and we discuss the weak-interaction limit that is relevant for\nexperiments. We then lift the restriction of full spin polarization and account\nfor a time-independent inhomogeneous external magnetic field. The field\nstrength necessary to ensure full spin polarization is derived.",
        "positive": "Berezinskii-Kosterlitz-Thouless transition of spin-1 spinor Bose gases\n  in the presence of the quadratic Zeeman effect: We numerically study the Berezinskii-Kosterlitz-Thouless (BKT) transition of\na spin-1 spinor Bose gas under the quadratic Zeeman effect. A calculation of\nthe mass and spin superfluid densities shows that (i) the BKT transition occurs\nonly when vortices are classified by the integer group $\\mathbb{Z}$, and\n$\\mathbb{Z}_2$ vortices do not contribute to the BKT transition, (ii) the two\nBKT transition temperatures for mass and spin superfluid densities are\ndifferent for a positive quadratic Zeeman effect and equal for a negative\nquadratic Zeeman effect, and (iii) the universal relation of the superfluid\ndensities at the BKT transition temperature is changed when multiple kinds of\nvortices contribute to the transition. We have further found that (iv)\nspin-singlet pairs in non-magnetic states show the\nquasi-off-diagonal-long-range order at the different temperature lower than the\nBKT transition temperature, giving the new universal relation of the superfluid\ndensity."
    },
    {
        "anchor": "Emergence of a tunable crystalline order in a Floquet-Bloch system from\n  a parametric instability: Parametric instabilities in interacting systems can lead to the appearance of\nnew structures or patterns. In quantum gases, two-body interactions are\nresponsible for a variety of instabilities that depend on the characteristics\nof both trapping and interactions. We report on the Floquet engineering of such\ninstabilities, on a Bose-Einstein condensate held in a time-modulated optical\nlattice. The modulation triggers a destabilization of the condensate into a\nstate exhibiting a density modulation with a new spatial periodicity. This new\ncrystal-like order directly depends on the modulation parameters: the interplay\nbetween the Floquet spectrum and interactions generates narrow and adjustable\ninstability regions, leading to the growth, from quantum or thermal\nfluctuations, of modes with a density modulation non commensurate with the\nlattice spacing. This study demonstrates the production of metastable exotic\nstates of matter through Floquet engineering, and paves the way for further\nstudies of dissipation in the resulting phase, and of similar phenomena in\nother geometries.",
        "positive": "Observation of Quantum Phase Transitions with Parity-Symmetry Breaking\n  and Hysteresis: Symmetry-breaking quantum phase transitions play a key role in several\ncondensed matter, cosmology and nuclear physics theoretical models. Its\nobservation in real systems is often hampered by finite temperatures and\nlimited control of the system parameters. In this work we report for the first\ntime the experimental observation of the full quantum phase diagram across a\ntransition where the spatial parity symmetry is broken. Our system is made of\nan ultra-cold gas with tunable attractive interactions trapped in a spatially\nsymmetric double-well potential. At a critical value of the interaction\nstrength, we observe a continuous quantum phase transition where the gas\nspontaneously localizes in one well or the other, thus breaking the underlying\nsymmetry of the system. Furthermore, we show the robustness of the asymmetric\nstate against controlled energy mismatch between the two wells. This is the\nresult of hysteresis associated with an additional discontinuous quantum phase\ntransition that we fully characterize. Our results pave the way to the study of\nquantum critical phenomena at finite temperature, the investigation of\nmacroscopic quantum tunneling of the order parameter in the hysteretic regime\nand the production of strongly quantum entangled states at critical points."
    },
    {
        "anchor": "Ground states and dynamics of population-imbalanced Fermi condensates in\n  one dimension: By using the numerically exact density-matrix renormalization group (DMRG)\napproach, we investigate the ground states of harmonically trapped\none-dimensional (1D) fermions with population imbalance and find that the\nLarkin-Ovchinnikov (LO) state, which is a condensed state of fermion pairs with\nnonzero center-of-mass momentum, is realized for a wide range of parameters.\nThe phase diagram comprising the two phases of i) an LO state at the trap\ncenter and a balanced condensate at the periphery and ii) an LO state at the\ntrap center and a pure majority component at the periphery, is obtained. The\nreduced two-body density matrix indicates that most of the minority atoms\ncontribute to the LO-type quasi-condensate. With the time-dependent DMRG, we\nalso investigate the real-time dynamics of a system of 1D fermions in response\nto a spin-flip excitation.",
        "positive": "Topological invariant and cotranslational symmetry in strongly\n  interacting multi-magnon systems: It is still an outstanding challenge to characterize and understand the\ntopological features of strongly interacting states such as bound-states in\ninteracting quantum systems. Here, by introducing a cotranslational symmetry in\nan interacting multi-particle quantum system, we systematically develop a\nmethod to define a Chern invariant, which is a generalization of the well-known\nThouless-Kohmoto-Nightingale-den Nijs invariant, for identifying strongly\ninteracting topological states. As an example, we study the topological\nmulti-magnon states in a generalized Heisenberg XXZ model, which can be\nrealized by the currently available experiment techniques of cold atoms [Phys.\nRev. Lett. \\textbf{111}, 185301 (2013); Phys. Rev. Lett. \\textbf{111}, 185302\n(2013)]. Through calculating the two-magnon excitation spectrum and the defined\nChern number, we explore the emergence of topological edge bound-states and\ngive their topological phase diagram. We also analytically derive an effective\nsingle-particle Hofstadter superlattice model for a better understanding of the\ntopological bound-states. Our results not only provide a new approach to\ndefining a topological invariant for interacting multi-particle systems, but\nalso give insights into the characterization and understanding of strongly\ninteracting topological states."
    },
    {
        "anchor": "Coupled Ferromagnetic and Nematic Ordering of Fermions in an Optical\n  Flux Lattice: Ultracold atoms in Raman-dressed optical lattices allow for effective\nmomentum-dependent interactions among single-species fermions originating from\nshort-range s-wave interactions. These dressed-state interactions combined with\nvery flat bands encountered in the recently introduced optical flux lattices\npush the Stoner instability towards weaker repulsive interactions, making it\naccessible with current experiments. As a consequence of the coupling between\nspin and orbital degrees of freedom, the magnetic phase features Ising nematic\norder.",
        "positive": "Exact quantum dynamics of bosons with finite-range time-dependent\n  interactions of harmonic type: The exactly solvable quantum many-particle model with harmonic one- and\ntwo-particle interaction terms is extended to include time-dependency. We show\nthat when the external trap potential and finite-range interparticle\ninteraction have a time-dependency the exact solutions of the corresponding\ntime-dependent many-boson Schr\\\"odinger equation are still available. We use\nthese exact solutions to benchmark the recently developed multiconfigurational\ntime-dependent Hartree method for bosons (MCTDHB) [Phys. Rev. Lett. {\\bf 99},\n030402 (2007), Phys. Rev. A {\\bf 77}, 033613 (2008)]. In particular, we\nbenchmark the MCTDHB method for: (i) the ground state; (ii) the breathing\nmany-body dynamics activated by a quench scenario where the interparticle\ninteraction strength is suddenly turned on to a finite value; (iii) the\nnon-equilibrium dynamic for driven scenarios where both the trap- and\ninterparticle-interaction potentials are {\\it time-dependent}. Excellent\nconvergence of the ground state and dynamics is demonstrated. The great\nrelevance of the self-consistency and time-adaptivity, which are the intrinsic\nfeatures of the MCTDHB method, is demonstrated by contrasting the MCTDHB\npredictions and those obtained within the standard full configuration\ninteraction method spanning the Fock space of the same size, but utilizing as\none-particle basis set the fixed-shape eigenstates of the one-particle\npotential. Connections of the model's results to ultra-cold Bose-Einstein\ncondensed systems are addressed."
    },
    {
        "anchor": "Gaussian trajectory description of fragmentation in an isolated spinor\n  condensate: Spin-1 Bose gases quenched to spin degeneracy exhibit fragmentation: the\nappearance of a condensate in more than one single-particle state. Due to its\nhighly entangled nature, the dynamics leading to this collective state are\nbeyond the scope of a Gaussian variational approximation of the many-body wave\nfunction. Here, we improve the performance of the Gaussian variational Ansatz\nby considering dissipation into a fictitious environment, effectively\nsuppressing entanglement within individual quantum trajectories at the expense\nof introducing a classical mixture of states. We find that this quantum\ntrajectory approach captures the dynamical formation of a fragmented\ncondensate, and analyze how much dissipation should be added to the experiment\nin order to keep a single realization in a non-fragmented state.",
        "positive": "Emergent non-trivial lattices for topological insulators: Materials with non-trivial lattice geometries allow for the creation of\nexotic states of matter like topologically insulating states. Therefore\nsearching for such materials is an important aspect of current research in\nsolid-state physics. In the field of ultracold gases there are ongoing studies\naiming to create non-trivial lattices using optical means. In this paper we\nstudy two species of fermions trapped in a square optical lattice and show how\nnon-trivial lattices can emerge due to strong interaction between atoms. We\ntheoretically investigate regimes of tunable parameters in which such\nself-assembly may take place and describe the necessary experimental\nconditions. Moreover we discuss the possibility of such emergent lattices\nhosting topologically insulating states."
    },
    {
        "anchor": "Selection Rule for Topological Amplifiers in Bogoliubov de Gennes\n  Systems: Dynamical instability is an inherent feature of bosonic systems described by\nthe Bogoliubov de Geenes (BdG) Hamiltonian. Since it causes the BdG system to\ncollapse, it is generally thought that it should be avoided. Recently, there\nhas been much effort to harness this instability for the benefit of creating a\ntopological amplifier with stable bulk bands but unstable edge modes which can\nbe populated at an exponentially fast rate. We present a theorem for\ndetermining the stability of states with energies sufficiently away from zero,\nin terms of an unconventional commutator between the number conserving part and\nnumber nonconserving part of the BdG Hamiltonian. We apply the theorem to a\ngeneralization of a model from Galilo et al. [Phys. Rev. Lett, 115,\n245302(2015)] for creating a topological amplifier in an interacting spin-1\natom system in a honeycomb lattice through a quench process. We use this model\nto illustrate how the vanishing of the unconventional commutator selects the\nsymmetries for a system so that its bulk states are stable against (weak)\npairing interactions. We find that as long as time reversal symmetry is\npreserved, our system can act like a topological amplifier, even in the\npresence of an onsite staggered potential which breaks the inversion symmetry.",
        "positive": "Fluctuations and quantum self-bound droplets in a dipolar Bose-Bose\n  mixture: We systematically investigate the properties of three-dimensional dipolar\nbinary Bose mixture at low temperatures. A set of coupled self-consistent\nequations of motion are derived for the two condensates. In the homogeneous\ncase, useful analytical formulas for the condensate depletion, the anomalous\ndensity, the ground-state energy, and the equation of state are obtained. The\ntheory is extended to the inhomogeneous case and the importance of the\ninhomogeneity is highlighted. Our results open up a new avenue for studying\ndipolar mixture droplets. Impacts of the dipole-dipole interaction on the\nstability, density profiles, and the size of the self-bound droplet are deeply\ndiscussed. The finite-temperature behavior of such a state is also examined."
    },
    {
        "anchor": "The bilinear-biquadratic spin-1 chain undergoing quadratic Zeeman effect: The Heisenberg model for spin-1 bosons in one dimension presents many\ndifferent quantum phases including the famous topological Haldane phase. Here\nwe study the robustness of such phases in front of a SU(2) symmetry breaking\nfield as well as the emergence of novel phases. Previous studies have analyzed\nthe effect of such uniaxial anysotropy in some restricted relevant points of\nthe phase diagram. Here we extend those studies and present the complete phase\ndiagram of the spin-1 chain with uniaxial anysotropy. To this aim, we employ\nthe density matrix renormalization group (DMRG) together with analytical\napproaches. The complete phase diagram can be realized using ultracold spinor\ngases in the Mott insulator regime under a quadratic Zeeman effect.",
        "positive": "Exact ordering of energy levels for one-dimensional interacting Fermi\n  gases with $SU(n)$ symmetry: Based on the exact solution of one-dimensional Fermi gas systems with $SU(n)$\nsymmetry in a hard wall, we demonstrate that we are able to sort the ordering\nof the lowest energy eigenvalues of states with all allowed permutation\nsymmetries, which can be solely marked by certain quantum numbers in the Bethe\nansatz equations. Our results give examples beyond the scope of the generalized\nLieb-Mattis theorem, which can only compare the ordering of energy levels of\nstates belonging to different symmetry classes if they are comparable according\nto the pouring principle. In the strongly interacting regime, we show that the\nordering of energy levels can be determined by an effective spin-exchange model\nand extend our results to the non-uniform system trapped in the harmonic\npotential."
    },
    {
        "anchor": "Effective three-body interactions via photon-assisted tunneling in an\n  optical lattice: We present a simple, experimentally realizable method to make coherent\nthree-body interactions dominate the physics of an ultracold lattice gas. Our\nscheme employs either lattice modulation or laser-induced tunneling to reduce\nor turn off two-body interactions in a rotating frame, promoting three-body\ninteractions arising from multi-orbital physics to leading-order processes.\nThis approach provides a route to strongly-correlated phases of lattice gases\nthat are beyond the reach of previously proposed dissipative three-body\ninteractions. In particular, we study the mean-field phase diagram for spinless\nbosons with three- and two- body interactions, and provide a roadmap to dimer\nstates of varying character in 1D. This new toolset should be immediately\napplicable in state-of-the-art cold atom experiments.",
        "positive": "Stationary and moving bright solitons in Bose-Einstein condensates with\n  spin-orbit coupling in a Zeeman field: With the discovery of various matter wave solitons in spin-orbit-coupled\nBose-Einstein condensates (BECs), exploring their properties has become\nincreasingly significant. We mainly study stationary and moving bright solitons\nin spin-orbit-coupled spin-1 BECs with or without a Zeeman field. The bright\nsolitons correspond to the plane wave (PW) and standing wave (SW) phases. With\nthe assistance of single-particle energy spectrum, we obtain the existence\ndomains of PW and SW solitons by analytical and numerical methods. The results\nindicate that the interaction between atoms is also a key factor determining\nthe existence of solitons. In addition, we systematically discuss the stability\ndomains of PW and SW solitons, and investigate the impact of different\nparameters on the stability domains. We find that PW solitons are unstable when\nthe linear Zeeman effect reaches a certain threshold, and the threshold is\ndetermined by other parameters. The linear Zeeman effect also leads to the\nalternating distribution of stable and unstable areas of SW solitons, and makes\nSW solitons stably exist in the area with stronger ferromagnetism. Finally, we\nanalyze the collision dynamics of different types of stable solitons."
    },
    {
        "anchor": "Anomalous Resistivity at Weak Coupling: Recent cold atom experiments have observed bad and strange metal behaviors in\nstrongly-interacting Fermi-Hubbard systems. Motivated by these results, we\ncalculate the thermoelectric transport properties of a 2D Fermi-Hubbard system\nin the weak coupling limit using quantum kinetic theory. We find that many\nfeatures attributed to strong correlations are also found at weak coupling. In\nparticular, for temperatures $T\\gtrsim t$ the electrical resistivity is nearly\nlinear in temperature despite the fact that the quasiparticle scattering rate\nis non-linear and changes by nearly an order of magnitude. We argue that this\nasymptotic behavior is a general feature of systems with a finite spectral\nwidth, which implies that there is no MIR bound on the resistivity in\nsingle-band models. Due to nesting, the $T$-linear resistivity persists down to\n$T=0$ at half filling. Our work sheds light on the transport regime in\nultracold atom experiments, which can differ substantially from that of\ncondensed matter systems. Disentangling these band-structure effects from the\nphysics of strong correlations is a major challenge for future experiments.",
        "positive": "Metal-Insulator-Superconductor transition of spin-3/2 atoms on optical\n  lattices: We use a slave-rotor approach within a mean-field theory to study the\ncompetition of metallic, Mott-insulating, and superconducting phases of\nspin-3/2 fermions subjected to a periodic optical lattice potential. In\naddition to the metallic, the Mott-insulating, and the superconducting phases\nthat are associated with the gauge symmetry breaking of the spinon field, we\nidentify a novel emerging superconducting phase that breaks both roton and\nspinon field gauge symmetries. This novel superconducting phase emerges as a\nresult of the competition between spin-0 singlet and spin-2 quintet interaction\nchannels naturally available for spin-3/2 systems. The two superconducting\nphases can be distinguished from each other by quasiparticle weight. We further\ndiscuss the properties of these phases for both two-dimensional square and\nthree-dimensional cubic lattices at zero and finite temperatures."
    },
    {
        "anchor": "Creating vortons and three-dimensional skyrmions from domain wall\n  annihilation with stretched vortices in Bose-Einstein condensates: We propose a mechanism to create a vorton or three-dimensional skyrmion in\nphase-separated two-component BECs with the order parameters Psi_1 and Psi_2 of\nthe two condensates. We consider a pair of a domain wall (brane) and an\nanti-domain wall (anti-brane) stretched by vortices (strings), where the Psi_2\ncomponent with a vortex winding is sandwiched by two domains of the Psi_1\ncomponent. The vortons appear when the domain wall pair annihilates.\nExperimentally, this can be realized by preparing the phase separation in the\norder Psi_1, Psi_2 and Psi_1 components, where the nodal plane of a dark\nsoliton in Psi_1 component is filled with the Psi_2 component with vorticity.\nBy selectively removing the filling Psi_2 component gradually with a resonant\nlaser beam, the collision of the brane and anti-brane can be made, creating\nvortons.",
        "positive": "Bose-Hubbard model with occupation dependent parameters: We study the ground-state properties of ultracold bosons in an optical\nlattice in the regime of strong interactions. The system is described by a\nnon-standard Bose-Hubbard model with both occupation-dependent tunneling and\non-site interaction. We find that for sufficiently strong coupling the system\nfeatures a phase-transition from a Mott insulator with one particle per site to\na superfluid of spatially extended particle pairs living on top of the Mott\nbackground -- instead of the usual transition to a superfluid of single\nparticles/holes. Increasing the interaction further, a superfluid of particle\npairs localized on a single site (rather than being extended) on top of the\nMott background appears. This happens at the same interaction strength where\nthe Mott-insulator phase with 2 particles per site is destroyed completely by\nparticle-hole fluctuations for arbitrarily small tunneling. In another regime,\ncharacterized by weak interaction, but high occupation numbers, we observe a\ndynamical instability in the superfluid excitation spectrum. The new ground\nstate is a superfluid, forming a 2D slab, localized along one spatial direction\nthat is spontaneously chosen."
    },
    {
        "anchor": "Quantum Gases in Optical Boxes: Advances in light shaping for optical trapping of neutral particles have led\nto the development of box traps for ultracold atoms and molecules. These traps\nhave allowed the creation of homogeneous quantum gases and opened new\npossibilities for studies of many-body physics. They simplify the\ninterpretation of experimental results, provide more direct connections with\ntheory, and in some cases allow qualitatively new, hitherto impossible\nexperiments. Here we review progress in this emerging field.",
        "positive": "Novel soliton in dipolar BEC caused by the quantum fluctuations: Solitons in the extended hydrodynamic model of the dipolar Bose-Einstein\ncondensate with quantum fluctuations are considered. This model includes the\ncontinuity equation for the scalar field of concentration, the Euler equation\nfor the vector field of velocity, the pressure evolution equation for the\nsecond rank tensor of pressure, and the evolution equation for the third rank\ntensor. Large amplitude soliton solution caused by the dipolar part of quantum\nfluctuations is found. It appears as the bright soliton. Hence, it is the area\nof compression of the number of particles. Moreover, it exists for the\nrepulsive short-range interaction."
    },
    {
        "anchor": "Quantum control in strongly driven optical lattices: Matter waves can be coherently and adiabatically loaded and controlled in\nstrongly driven optical lattices. This coherent control is used in order to\nmodify the modulus and the sign of the tunneling matrix element in the\ntunneling Hamiltonian. Our findings pave the way for studies of driven quantum\nsystems and new methods for engineering Hamiltonians that are impossible to\nrealize with static techniques.",
        "positive": "Double-Quantum Spin Vortices in SU(3) Spin-Orbit Coupled Bose Gases: We show that double-quantum spin vortices, which are characterized by doubly\nquantized circulating spin currents and unmagnetized filled cores, can exist in\nthe ground states of SU(3) spin-orbit coupled Bose gases. It is found that the\nSU(3) spin-orbit coupling and spin-exchange interaction play important roles in\ndetermining the ground-state phase diagram. In the case of effective\nferromagnetic spin interaction, the SU(3) spin-orbit coupling induces a\nthree-fold degeneracy to the magnetized ground state, while in the\nantiferromagnetic spin interaction case, the SU(3) spin-orbit coupling breaks\nthe ordinary phase rule of spinor Bose gases, and allows the spontaneous\nemergence of double-quantum spin vortices. This exotic topological defect is in\nstark contrast to the singly quantized spin vortices observed in existing\nexperiments, and can be readily observed by the current magnetization-sensitive\nphase-contrast imaging technique."
    },
    {
        "anchor": "Abnormal Superfluid Fraction of Harmonically Trapped Few-Fermion Systems: Superfluidity is a fascinating phenomenon that, at the macroscopic scale,\nleads to dissipationless flow and the emergence of vortices. While these\nmacroscopic manifestations of superfluidity are well described by theories that\nhave their origin in Landau's two-fluid model, our microscopic understanding of\nsuperfluidity is far from complete. Using analytical and numerical \\textit{ab\ninitio} approaches, this paper determines the superfluid fraction and local\nsuperfluid density of small harmonically trapped two-component Fermi gases as a\nfunction of the interaction strength and temperature. At low temperature, we\nfind that the superfluid fraction is, in certain regions of the parameter\nspace, negative. This counterintuitive finding is traced back to the symmetry\nof the system's ground state wave function, which gives rise to a diverging\nquantum moment of inertia $I_{\\text{q}}$. Analogous abnormal behavior of\n$I_{\\text{q}}$ has been observed in even-odd nuclei at low temperature. Our\npredictions can be tested in modern cold atom experiments.",
        "positive": "Consistent theory of self-bound quantum droplets with bosonic pairing: We revisit the Bogoliubov theory of quantum droplets proposed by Petrov\n{[}Phys. Rev. Lett. \\textbf{115}, 155302 (2015){]} for an ultracold Bose-Bose\nmixture, where the mean-field collapse is stabilized by the Lee-Huang-Yang\nquantum fluctuations. We show that a loophole in Petrov's theory, i.e., the\nignorance of the softening complex Bogoliubov spectrum, can be naturally\nremoved by the introduction of bosonic pairing. The pairing leads to weaker\nmean-field attractions, and also stronger Lee-Huang-Yang term in the case of\nunequal intraspecies interactions. As a result, the equilibrium density for the\nformation of self-bound droplets significantly decrease in the deep droplet\nregime, in agreement with a recent observation from diffusion Monte Carlo\nsimulations. Our construction of a consistent Bogoliubov theory paves the way\nto understand the puzzling low critical number of small quantum droplets\nobserved in the experiment {[}Science \\textbf{359}, 301 (2018){]}."
    },
    {
        "anchor": "Hubbard models and state preparation in an optical Lieb lattice: Inspired by the growing interest in probing many-body phases in novel\ntwo-dimensional lattice geometries we investigate the properties of cold atoms\nas they could be observed in an optical Lieb lattice. We begin by computing\nWannier functions localised at individual sites for a realistic experimental\nsetup, and determining coefficients for a Hubbard-like model. Based on this, we\nshow how experiments could probe the robustness of edge states in a Lieb\nlattice with diagonal boundary conditions to the effects of interactions and\nrealise strongly correlated many-body phases in this geometry. We then\ngeneralise this to interacting particles in a half-filled 1D Lieb ladder, where\nexcitations are dominated by flat band states. We show that for strong\nattractive interactions, pair correlations are enhanced even when there is\nstrong mixing with the Dirac cone. These findings in 1D raise interesting\nquestions about the phases in the full 2D Lieb lattice which we show can be\nexplored in current experiments.",
        "positive": "The study of random vorticity in quantum fluids through interference\n  fluctuations: We study the vortex dynamics of a quantum degenerate Bose gas through the\nintensity fluctuations of the interference from particles extracted at two\ndifferent positions. It is shown numerically with classical field simulations\nthat an interacting Bose gas with proliferating vortices exhibits long\ncorrelation times for these intensity fluctuations. This behavior is contrasted\nwith the case of a noninteracting gas, that we describe analytically, and with\nthe case of a well condensed Bose gas without vortices. We discuss the\nobservability of our predictions in quantum fluids of exciton-polaritons."
    },
    {
        "anchor": "Global superfluid phase diagram of three component fermions with\n  magnetic ordering: We investigate a three component fermion mixture in the presence of weak\nattractive interactions. We use a combination of the equation of motion and the\nGaussian variational mean-field approaches, which both allow for simultaneous\nsuperfluid and magnetic ordering in an unbiased way, and capture the interplay\nbetween the two order parameters. This interplay significantly modifies the\nphase diagram, especially the superfluid-normal phase boundaries. In the close\nvicinity of the critical temperature and for small chemical potential\nimbalances, strong particle-hole symmetry breaking leads to a phase diagram\nsimilar to the one predicted by Cherng et al. [Phys. Rev. Lett. 99, 130406\n(2007)], however, the overall phase diagram is markedly different: new chemical\npotential-driven first and second order transitions and triple points emerge as\nwell as more exotic second order multicritical points, and bicritical lines\nwith O(2,2) symmetry. We identify the terms which are necessary to capture this\ncomplex phase diagram in a Ginzburg-Landau approach, and determine the\ncorresponding coefficients.",
        "positive": "Quantum engineering of a synthetic thermal bath for bosonic atoms in a\n  one-dimensional optical lattice via Markovian feedback control: We propose and investigate a scheme for engineering a synthetic thermal bath\nfor a bosonic quantum gas in a one-dimensional optical lattice based on\nMarkovian feedback control. The performance of our scheme is quantified by the\nfidelity between the steady state of the system and the effective thermal\nstate. For double-well and triple-well systems with non-interacting particles,\nthe steady state is found to be an exact thermal state, which is attributed to\nthe fact that the transfer rates between all pairs of coupled eigenstates\nsatisfy detailed balance condition. The scenario changes when there are more\nlattice sites, where the detailed balance condition does not hold any more, but\nremains an accurate approximation. Remarkably, our scheme performs very well at\nlow and high temperature regimes, with the fidelity close to one. The\nperformance at the intermediate temperature regime (where a crossover into a\nBose condensed regime occurs) is slightly worse, and the fidelity shows a\ngentle decrease with increasing system size. We also discuss the interacting\ncases. In contrast to the non-interacting cases, the scheme is found to perform\nbetter at a higher temperature. Another difference is that the minimal\ntemperature that can be engineered is nonzero and increases with the\ninteraction strength."
    },
    {
        "anchor": "Experimental realization of an ideal Floquet disordered system: The atomic Quantum Kicked Rotor is an outstanding \"quantum simulator\" for the\nexploration of transport in disordered quantum systems. Here we study\nexperimentally the phase-shifted quantum kicked rotor, which we show to display\nproperties close to an ideal disordered quantum system, opening new windows\ninto the study of Anderson physics.",
        "positive": "Statistical physics of Bose-Einstein condensed light in a dye\n  microcavity: We theoretically analyze the temperature behavior of paraxial light in\nthermal equilibrium with a dye-filled optical microcavity. At low temperatures\nthe photon gas undergoes Bose-Einstein condensation (BEC), and the photon\nnumber in the cavity ground state becomes macroscopic with respect to the total\nphoton number. Owing to a grandcanonical excitation exchange between the photon\ngas and the dye molecule reservoir, a regime with unusually large fluctuations\nof the condensate number is predicted for this system that is not observed in\npresent atomic physics BEC experiments."
    },
    {
        "anchor": "Beyond universality in repulsive SU(N) Fermi gases: Itinerant ferromagnetism in dilute Fermi gases is predicted to emerge at\nvalues of the gas parameter where second-order perturbation theory is not\naccurate enough to properly describe the system. We have revisited perturbation\ntheory for SU(N) fermions and derived its generalization up to third order both\nin terms of the gas parameter and the polarization. Our results agree\nsatisfactorily with quantum Monte Carlo results for hard-sphere and soft-sphere\npotentials for $S = 1/2$. Although the nature of the phase transition depends\non the interaction potential, we find that for a hard-sphere potential a phase\ntransition is guaranteed to occur. While for $S= 1/2$ we observe a\nquasi-continuous transition, for spins $3/2$ and $5/2$, a first-order phase\ntransition is found. For larger spins, a double transition (combination of\ncontinuous and discontinuous) occurs. The critical density reduces drastically\nwhen the spin increases, making the phase transition more accessible to\nexperiments with ultracold dilute Fermi gases. Estimations for Fermi gases of\nYb and Sr with spin $5/2$ and $9/2$, respectively, are reported.",
        "positive": "Large-$N$ Chern insulators: lattice field theory and quantum simulation\n  approaches to correlation effects in the quantum anomalous Hall effect: Four-Fermi quantum field theories in (2+1) dimensions lie among the simplest\nmodels in high-energy physics, the understanding of which requires a\nnon-perturbative lattice formulation addressing their strongly-coupled fixed\npoints. These lattice models are also relevant in condensed matter, as they\noffer a neat playground to explore strong correlations in the quantum anomalous\nHall (QAH) effect. We give a detailed description of our multidisciplinary\napproach to understand the fate of the QAH phases as the four-Fermi\ninteractions are increased, which combines strong-coupling and\neffective-potential techniques, unveiling a rich phase diagram with large-$N$\nChern insulators and Lorentz-breaking fermion condensates. Moreover, this\ntoolbox can be enlarged with recent advances in quantum information science, as\nwe show that tensor-network algorithms based on projected entangled pairs can\nbe used to improve our understanding of the strong-coupling limit. We also\npresent a detailed scheme that uses ultra-cold atoms in optical lattices with\nsynthetic spin-orbit coupling to build quantum simulators of these four-Fermi\nmodels. This yields a promising alternative to characterise the\nstrongly-coupled fixed points and, moreover, could also explore real-time\ndynamics and finite-fermion densities."
    },
    {
        "anchor": "Quantum phase transition of Bose-Einstein condensates on a ring\n  nonlinear lattice: We study the phase transitions in a one dimensional Bose-Einstein condensate\non a ring whose atomic scattering length is modulated periodically along the\nring. By using a modified Bogoliubov method to treat such a nonlinear lattice\nin the mean field approximation, we find that the phase transitions are of\ndifferent orders when the modulation period is 2 and greater than 2. We further\nperform a full quantum mechanical treatment based on the time-evolving block\ndecimation algorithm which confirms the mean field results and reveals\ninteresting quantum behavior of the system. Our studies yield important\nknowledge of competing mechanisms behind the phase transitions and the quantum\nnature of this system.",
        "positive": "Measuring entropy and mutual information in the two-dimensional Hubbard\n  model: We measure pressure and entropy of ultracold fermionic atoms in an optical\nlattice for a range of interaction strengths, temperatures and fillings. Our\nmeasurements demonstrate that, for low enough temperatures, entropy-rich\nregions form locally in the metallic phase which are in contact with a\nMott-insulating phase featuring lower entropy. In addition, we also measure the\nreduced density matrix of a single lattice site, and from the comparison\nbetween the local and thermodynamic entropies we determine the mutual\ninformation between a single lattice site and the rest of the system. For low\nlattice fillings, we find the mutual information to be independent of\ninteraction strength, however, for half filling we find that strong\ninteractions suppress the correlations between a single site and the rest of\nthe system."
    },
    {
        "anchor": "Various Topological Mott insulators in strongly-interacting boson system\n  in one-dimensional superlattice: In this paper, we study a one-dimensional boson system in a superlattice\npotential.This system is experimentally feasible by using ultracold atomic\ngases,and attracts much attention these days. It is expected that the system\nhas a topological phase called topological Mott insulator (TMI). We show that\nin strongly-interacting cases, the competition between the superlattice\npotential and the on-site interaction leads to various TMIs with non-vanishing\ninteger Chern number. Compared to hard-core case, the soft-core boson system\nexhibits rich phase diagrams including various non-trivial TMIs. By using the\nexact diagonalization,we obtain detailed bulk-global phase diagrams including\nthe TMIs with high Chern numbers and also various non-topological phases. We\nalso show that in adiabatic experimental setups, the strongly-interacting\nbosonic TMIs exhibit the topological particle transfer, i.e., topological\ncharge pumping phenomenon, similarly to weakly-interacting systems. The various\nTMIs are characterized by topological charge pumping as it is closely related\nto the Chern number, and therefor the Chern number is to be observed in\nfeasible experiments.",
        "positive": "Supersolid-like square- and triangular-lattice crystallization of\n  dipolar droplets in a box trap: Using a beyond-mean-field model including a Lee-Huang-Yang-type interaction,\nwe demonstrate a supersolid-like spatially-periodic square- and\ntriangular-lattice crystallization of droplets in a polarized dipolar\ncondensate confined by an appropriate three-dimensional (3D) box trap. In this\npaper we consider a rectangular box (cuboid) trap, a square box (cuboid with\ntwo equal sides) trap, a cylindrical box trap and a hexagonal box (hexagonal\nprism) trap. The droplet lattice is always formed in the $x$-$y$ plane\nperpendicular to the polarization $z$ direction of dipolar atoms. In contrast\nto a harmonic trap, the box traps allow the formation of a large clean\nsupersolid-like spatially-periodic crystallization in free space without any\ndistortion. Moreover, a droplet lattice can be formed in a 3D box trap with a\nsignificantly reduced number of atoms than in a harmonic trap, which could\nfacilitate the experimental observation of droplet lattice in a box trap. With\npresent know-how such a supersolid-like crystallization of dipolar droplets in\na 3D box trap can be realized in a laboratory thus allowing the study of a\nlarge periodic lattice of dipolar droplets in free space bounded by rigid\nwalls."
    },
    {
        "anchor": "Chladni solitons and the onset of the snaking instability for dark\n  solitons in confined superfluids: Complex solitary waves composed of intersecting vortex lines are predicted in\na channeled superfluid. Their shapes in a cylindrical trap include a cross,\nspoke wheels, and Greek $\\Phi$, and trace the nodal lines of unstable vibration\nmodes of a planar dark soliton in analogy to Chladni's figures of membrane\nvibrations. The stationary solitary waves extend a family of solutions that\ninclude the previously known solitonic vortex and vortex rings. Their\nbifurcation points from the dark soliton indicating the onset of new unstable\nmodes of the snaking instability are predicted from scale separation for\nBose-Einstein condensates (BECs) and superfluid Fermi gases across the BEC--BCS\ncrossover, and confirmed by full numerical calculations. Chladni solitons could\nbe observed in ultra-cold gas experiments by seeded decay of dark solitons.",
        "positive": "Relaxation dynamics of local observables in integrable systems: We show, using the quench action approach [Caux&Essler Phys. Rev. Lett. 110\n(2013)], that the whole post-quench time evolution of an integrable system in\nthe thermodynamic limit can be computed with a minimal set of data which are\nencoded in what we denote the generalized single-particle overlap coefficient\n$s_0^{\\Psi_0}(\\lambda)$. This function can be extracted from the\nthermodynamically leading part of the overlaps between the eigenstates of the\nmodel and the initial state. For a generic global quench the shape of\n$s_0^{\\Psi_0}(\\lambda)$ in the low momentum limit directly gives the exponent\nfor the power law decay to the effective steady state. As an example we compute\nthe time evolution of the static density-density correlation in the interacting\nLieb-Liniger gas after a quench from a Bose-Einstein condensate. This shows an\napproach to equilibrium with power law $t^{-3}$ which turns out to be\nindependent of the post-quench interaction and of the considered observable."
    },
    {
        "anchor": "Cold chemistry: a few-body perspective on impurity physics of a single\n  ion in an ultracold bath: Impurity physics is a traditional topic in condensed matter physics that\nnowadays is being explored in the field of ultracold gases. Among the different\nclasses of impurities, we focus on charged impurities in an ultracold bath.\nWhen a single ion is brought in contact with an ultracold gas it is subjected\nto different reactive processes that can be understood from a cold chemistry\napproach. In this work, we present an outlook of approaches for the dynamics of\na single ion in a bath of ultracold atoms or molecules, complementing the usual\nmany-body approaches characteristic of impurity physics within condensed matter\nphysics. In particular, we focus on the evolution of a charged impurity in\ndifferent baths, including external time-dependent trapping potentials and we\nexplore the effect of the external laser sources present in ion-neutral hybrid\ntraps into the lifetime of an impurity.",
        "positive": "Higgs oscillations in a unitary Fermi superfluid: Symmetry-breaking phase transitions are central to our understanding of\nstates of matter. When a continuous symmetry is spontaneously broken, new\nexcitations appear that are tied to fluctuations of the order parameter. In\nsuperconductors and fermionic superfluids, the phase and amplitude can\nfluctuate independently, giving rise to two distinct collective branches.\nHowever, amplitude fluctuations are difficult to both generate and measure, as\nthey do not couple directly to the density of fermions and have only been\nobserved indirectly to date. Here, we excite amplitude oscillations in an\natomic Fermi gas with resonant interactions by an interaction quench.\nExploiting the sensitivity of Bragg spectroscopy to the amplitude of the order\nparameter, we measure the time-resolved response of the atom cloud, directly\nrevealing amplitude oscillations at twice the frequency of the gap. The\nmagnitude of the oscillatory response shows a strong temperature dependence,\nand the oscillations appear to decay faster than predicted by time-dependent\nBCS theory applied to our experimental setup."
    },
    {
        "anchor": "A proof to Biswas-Mitra-Bhattacharyya conjecture for ideal quantum gas\n  trapped under generic power law potential $U=\\sum_{i=1} ^d c_i |\\frac\n  {x_i}{a_i}|^{n_i}$ in $d$ dimension: The well known relation for ideal classical gas $\\Delta \\epsilon^2=kT^2 C_V$\nwhich does not remain valid for quantum system is revisited. A new connection\nis established between energy fluctuation and specific heat for quantum gases,\nvalid in the classical limit and the degenerate quantum regime as well. Most\nimportantly the proposed Biswas-Mitra-Bhattacharyya (BMB) conjecture (Biswas\n$et.$ $al.$, J. Stat. Mech. P03013, 2015.) relating hump in energy fluctuation\nand discontinuity of specific heat is proved and precised in this manuscript.",
        "positive": "Entanglement entropy in low-energy field theories at finite chemical\n  potential: We investigate the leading area-law contribution to entanglement entropy in a\nsystem described by a general Lagrangian with O(2) symmetry containing first-\nand second-order time derivatives, namely breaking the Lorentz-invariance. We\nestablish a connection between the Higgs gap present in a symmetry-broken phase\nand the area-law term for the entanglement entropy in the general,\nnon-relativistic case. Our predictions for the entanglement entropy and\ncorrelation length are successfully compared to numerical results in two\nparadigmatic systems: the Mott insulator to superfluid transition for ultracold\nlattice bosons, and the ground state of ferrimagnetic systems."
    },
    {
        "anchor": "Supersolid-like solitons in spin-orbit coupled spin-2 condensate: We study supersolid-like crystalline structures emerging in the stationary\nstates of a quasi-two-dimensional spin-orbit (SO)-coupled spin-2 condensate in\nthe ferromagnetic, cyclic, and antiferro-magnetic phases by solving a\nmean-field model.Interplay of different strengths of SO coupling and\ninteratomic interactions gives rise to a variety of non-trivial density\npatterns in the emergent solutions. For small SO-coupling strengths $\\gamma$\n($\\gamma \\approx 0.5$), the ground state is an axisymmetric multi-ring soliton\nfor polar, cyclic and weakly-ferromagnetic interactions, whereas for\nstronger-ferromagnetic interactions a circularly-asymmetric soliton emerges as\nthe ground state.Depending on the values of interaction parameters, with an\nincrease in SO-coupling strength, a stripe phase may also emerge as the ground\nstate for polar and cyclic interactions. For intermediate values of SO-coupling\nstrength ($\\gamma \\approx 1$), in addition to these solitons, one could have a\nquasi-degenerate triangular-lattice soliton in all magnetic phases. On further\nincreasing the SO-coupling strength ($\\gamma \\gtrapprox 4$), a square-lattice\nand a superstripe soliton emerge as quasi-degenerate states. The emergence of\nall these solitons can be inferred from a study of solutions of the\nsingle-particle Hamiltonian.",
        "positive": "Probing the critical exponent of superfluid fraction in a strongly\n  interacting Fermi gas: We theoretically investigate the critical behavior of second sound mode in a\nharmonically trapped ultracold atomic Fermi gas with resonant interactions.\nNear the superfluid phase transition with critical temperature $T_{c}$, the\nfrequency or the sound velocity of second sound mode depends crucially on the\ncritical exponent $\\beta$ of superfluid fraction. In an isotropic harmonic\ntrap, we predict that the mode frequency diverges like\n$(1-T/T_{c})^{\\beta-1/2}$ when $\\beta<1/2$. In a highly elongated trap, the\nspeed of second sound reduces by a factor $1/\\sqrt{2\\beta+1}$ from that in a\nhomogeneous three-dimensional superfluid. Our prediction could be readily\ntested by measurements of second sound wave propagation in a setup such as that\nexploited by Sidorenkov \\textit{et al.} {[}Nature \\textbf{498}, 78 (2013){]}\nfor resonantly interacting lithium-6 atoms, once the experimental precision is\nimproved."
    },
    {
        "anchor": "Disorder-Driven Loss of Phase Coherence in a Quasi-2D Cold Atom System: We study the order parameter of a quasi-2D gas of ultracold atoms trapped in\nan optical potential in the presence of controllable disorder. Our results show\nthat disorder drives phase fluctuations without significantly affecting the\namplitude of the quasi-condensate order parameter. This is evidence that\ndisorder can drive phase fluctuations in 2D systems, relevant to the\nphase-fluctuation mechanism for the superconductor-to-insulator phase\ntransition (SIT) in disordered 2D superconductors.",
        "positive": "Forming complex neurons by four-wave mixing in a Bose-Einstein\n  condensate: A physical artificial complex-valued neuron is formed by four-wave mixing in\na homogeneous three-dimensional Bose-Einstein condensate. Bragg beamsplitter\npulses prepare superpositions of three plane-waves states as an input- and the\nfourth wave as an output signal. The nonlinear dynamics of the non-degenerate\nfour-wave mixing process leads to Josephson-like oscillations within the closed\nfour-dimensional subspace and defines the activation function of a neuron. Due\nto the high number of symmetries, closed form solutions can be found by\nquadrature and agree with numerical simulation. The ideal behaviour of an\nisolated four-wave mixing setup is compared to a situation with additional\npopulation of rogue states. We observe a robust persistence of the main\noscillation. As an application for neural learning of this physical system, we\ntrain it on the XOR problem. After $100$ training epochs, the neuron responds\nto input data correctly at the $10^{-5}$ error level."
    },
    {
        "anchor": "Phase diagram of quantum fluids. The role of the chemical potential and\n  the phenomenon of condensation: We discuss the generic phase diagrams of pure systems that remain fluid near\nzero temperature. We call this phase a quantum fluid. We argue that the\nsignature of the transition is the change of sign of the chemical potential,\nbeing negative in the normal phase and becoming positive in the quantum fluid\nphase. We show that this change is characterized by a phenomenon that we call\ncondensation, in which a macroscopic number of particles is in their own\nmany-body ground state, a situation common to Fermi and Bose gases. We show\nthat the ideal Bose-Einstein Condensation fits in this scenario, but that it\nalso permits the occurrence of a situation that we may call \"Fermi-Dirac\nCondensation\". In addition, we argue that this phenomenon is also behind the\ndevelopment of superfluid phases in real interacting fluids. However, only\ninteracting systems may show the change from a thermal fluid to a quantum one\nas a true phase transition. As a corollary, this argument shows the necessity\nof the appearance of a \"supersolid\" phase. We also indicate how these ideas may\nbe useful in the description of of experiments with ultracold alkali gases.",
        "positive": "Observation of the Presuperfluid Regime in a Two-Dimensional Bose Gas: In complementary images of coordinate-space and momentum-space density in a\ntrapped 2D Bose gas, we observe the emergence of pre-superfluid behavior. As\nphase-space density $\\rho$ increases toward degenerate values, we observe a\ngradual divergence of the compressibility $\\kappa$ from the value predicted by\na bare-atom model, $\\kappa_{ba}$. $\\kappa/\\kappa_{ba}$ grows to 1.7 before\n$\\rho$ reaches the value for which we observe the sudden emergence of a spike\nat $p=0$ in momentum space. Momentum-space images are acquired by means of a 2D\nfocusing technique. Our data represent the first observation of non-meanfield\nphysics in the pre-superfluid but degenerate 2D Bose gas."
    },
    {
        "anchor": "Collision dynamics and entanglement generation of two initially\n  independent and indistinguishable boson pairs in one-dimensional harmonic\n  confinement: We investigate finite number effects in collisions between two states of an\ninitially well known number of identical bosons with contact interactions,\noscillating in the presence of harmonic confinement in one dimension. We\ninvestigate two N/2 (interacting) ground states, which are initially displaced\nfrom the trap center, and the effects of varying interaction strength. The\nnumerics focus on the simplest case of N=4. In the non-interacting case, such a\nsystem would display periodic oscillation with a half harmonic oscillator\nperiod (due to the left-right symmetry). With the addition contact interactions\nbetween the bosons, collisions generate entanglement between each of the states\nand distribute energy into other modes of the oscillator. We study the system\nnumerically via an exact diagonalization of the Hamiltonian with a finite\nbasis, investigating left/right number uncertainty as our primary measure of\nentanglement. Additionally we study the time-evolution and equilibration of the\nsingle-body von Neumann entropy for both the attractive and repulsive cases. We\nidentify parameter regimes for which attractive interactions create\nqualitatively different behavior to repulsive interactions, due to the presence\nof bound states (quantum solitons) and explain the processes behind this.",
        "positive": "Path-dependent correlations in dynamically tuned Ising models and its\n  short-time behavior: application of Magnus expansion: We study the buildup of antiferromagnetic (AF) correlation in the dynamically\ntuned Ising models which are realized by the Rydberg atomic system. In\nshort-time scale, we apply Magnus expansion (ME) to derive the high-order\nanalytic expression of the connected correlation functions and compare it with\nexactly numerical results for the different lattice geometries, e.g., 1D chain,\n$2 \\times n$ lattice, and $n \\times n$ lattice. It is shown that the high-order\nexpansion is required to describe accurately the buildup of AF correlation in\nthe quench dynamics. Moreover, through a 2D square lattice, we find that the\nmagnitude of AF correlation for the same Manhattan distance is proportional to\nthe number of the shortest paths in a sufficiently long time until long and\ndistinct paths are involved significantly with the buildup of the correlation.\nFinally, we propose an applicable experimental setup to realize our findings."
    },
    {
        "anchor": "1D topological chains with Majorana fermions in 2D non-topological\n  optical lattices: The recent experimental realization of 1D equal Rashba-Dresselhaus spin-orbit\ncoupling (ERD-SOC) for cold atoms provide a disorder-free platform for the\nimplementation and observation of Majorana fermions (MFs), similar to the well\nstudied solid state nanowire/superconductor heterostructures. However, the\ncorresponding 1D chains of cold atoms possess strong quantum fluctuation, which\nmay destroy the superfluids and MFs. In this Letter, we show that such 1D\ntopological chains with MFs may be on demand generated in a 2D non-topological\noptical lattice with 1D ERD-SOC by modifying local potentials on target\nlocations using experimentally already implemented atomic gas microscopes or\npatterned (e.g., double or triple well) optical lattices. All ingredients in\nour scheme have been experimentally realized and the combination of them may\npave the way for the experimental observation of MFs in a clean system.",
        "positive": "Out-of-phase oscillation between superfluid and thermal components for a\n  trapped Bose condensate under oscillatory excitation: The vortex nucleation and the emergence of quantum turbulence induced by\noscillating magnetic fields, introduced by Henn E A L, et al. 2009 (Phys. Rev.\nA 79, 043619) and Henn E A L, et al. 2009 (Phys. Rev. Lett. 103, 045301), left\na few open questions concerning the basic mechanisms causing those interesting\nphenomena. Here, we report the experimental observation of the slosh dynamics\nof a magnetically trapped $^{87}$Rb Bose-Einstein condensate (BEC) under the\ninfluence of a time-varying magnetic field. We observed a clear relative\ndisplacement in between the condensed and the thermal fraction center-of-mass.\nWe have identified this relative counter move as an out-of-phase oscillation\nmode, which is able to produce ripples on the condensed/thermal fractions\ninterface. The out-of-phase mode can be included as a possible mechanism\ninvolved in the vortex nucleation and further evolution when excited by time\ndependent magnetic fields."
    },
    {
        "anchor": "Enhancement of boson superfluidity in a one-dimensional Bose-Fermi\n  mixture: We examine the effect of boson-fermion interaction in a one-dimensional\nBose-Fermi mixture by using the density matrix renormalization group method. We\nshow that the boson superfluidity is enhanced by fermions for a weak\nboson-fermion coupling at an approximate integer boson filling factor (e.g.,\n$0.935\\le \\rho_b \\le 1.0$), and this enhancement is produced both in a fermion\nmetallic state and in a fermion insulating state. A metal-insulator phase\ntransition of fermions induced by boson-fermion interaction is observed even\nthough there is no fermion-fermion interaction in the parent Hamiltonian.\nFurthermore, we find that the boson superfluid order and density wave order can\ncoexist in a deep fermion Mott region. All these features could be measured in\nfuture experiments and open up the possibility of detecting the new physical\neffect in the Bose-Fermi mixture.",
        "positive": "Decay and fragmentation in an open Bose-Hubbard chain: We analyze the decay of ultracold atoms from an optical lattice with loss\nform a single lattice site. If the initial state is dynamically stable a\nsuitable amount of dissipation can stabilize a Bose-Einstein condensate, such\nthat it remains coherent even in the presence of strong interactions. A\ntransition between two different dynamical phases is observed if the initial\nstate is dynamically unstable. This transition is analyzed here in detail. For\nstrong interactions, the system relaxes to an entangled quantum state with\nremarkable statistical properties: The atoms bunch in a few \"breathers\" forming\nat random positions. Breathers at different positions are coherent, such that\nthey can be used in precision quantum interferometry and other applications."
    },
    {
        "anchor": "Dynamical stabilization of two-dimensional trapless Bose-Einstein\n  condensates by three-body interaction and quantum fluctuations: Analyzing a Gross-Pitaevskii equation with cubic, quartic, and quintic\nnonlinearities through analytical and numerical methods, we examine the\nstability of two-dimensional (2D) trapless Bose-Einstein condensates (BECs)\nwith two-, three-body interactions and quantum fluctuations. Applying a\nvariational approach, we derive the equation of motion and effective potential\nto discuss in detail the stability of the BECs in 2D free space. We show that\nwith the aid of quantum fluctuations it is possible to stabilize 2D trapless\nBEC without any oscillatory nonlinearities. Also, there is an enhancement of\nthe stability of the system, due to the inclusion of the three-body interaction\nand quantum fluctuations in addition to the two-body interaction. We further\nstudy the stability of 2D trapless BECs with rapid periodic temporal modulation\nof scattering length by using a Feshbach resonance. We discuss all possible\nways of stabilization of trapless BECs in 2D by three-body interaction and\nquantum fluctuations. Finally, we verify our analytical results with numerical\nsimulation using split-step Crank-Nicholson method. These match well with the\nanalytical predictions.",
        "positive": "Demagnetization dynamics of non-interacting trapped fermions: Motivated by several experimental efforts to understand spin diffusion and\ntransport in ultracold fermionic gases, we study the spin dynamics of initially\nspin-polarized ensembles of harmonically trapped non-interacting spin-1/2\nfermionic atoms, subjected to a magnetic field gradient. We obtain simple\nanalytic expressions for spin observables in the presence of both constant and\nlinear magnetic field gradients, with and without a spin-echo pulse, and at\nzero and finite temperatures. The analysis shows the relevance of spin-motional\ncoupling in the non-interacting regime where the demagnetization decay rate at\nshort times can be faster than the experimentally measured rates in the\nstrongly interacting regime under similar trapping conditions. Our calculations\nalso show that particle motion limits the ability of a spin-echo pulse to\nremove the effect of magnetic field inhomogeneity, and that a spin-echo pulse\ncan instead lead to an increased decay of magnetization at times comparable to\nthe trapping period."
    },
    {
        "anchor": "Elastic Scattering Time of Matter-Waves in Disordered Potentials: We report on an extensive study of the elastic scattering time $\\tauS$ of\nmatter-waves in optical disordered potentials. Using direct experimental\nmeasurements, numerical simulations and comparison with first-order Born\napproximation based on the knowledge of the disorder properties, we explore the\nbehavior of $\\tauS$ over more than three orders of magnitude, spanning from the\nweak to the strong scattering regime. We study in detail the location of the\ncrossover and, as a main result, we reveal the strong influence of the disorder\nstatistics, especially on the relevance of the widely used Ioffe-Regel-like\ncriterion $k\\lS\\sim 1$. While it is found to be relevant for\nGaussian-distributed disordered potentials, we observe significant deviations\nfor laser speckle disorders that are commonly used with ultracold atoms. Our\nresults are crucial for connecting experimental investigation of complex\ntransport phenomena, such as Anderson localization, to microscopic theories.",
        "positive": "Tan's adiabatic sweep theorem from the variational theorem for the\n  scattering length: It is shown that variation of the one-particle dispersion in a universal\nmany-body system enables us to obtain Tan's adiabatic sweep theorem and its\ngeneralization. The derivation is based on the Hellmann-Feynman theorem and the\nvariational theorem for the scattering length suggested in our previous paper\n[Cherny and Shanenko, Phys. Rev. E 62, 1646 (2000)]. As an example, the\nuniversal effects in the system of spinless bosons are considered. With the\nhelp of the variational theorem, we obtain the mean kinetic and interaction\nenergies and derive the virial theorem for the homogeneous and trapped bosons.\nThe results can easily be generalized to the two-component fermions with\ninteractions between opposite spins."
    },
    {
        "anchor": "Universal Properties of Fermi Gases in One-dimension: In this Rapid Communication, we investigate the universal properties of a\nspin-polarized two-component Fermi gas in one dimension (1D) using Bethe\nansatz. We discuss the quantum phases and phase transitions by obtaining exact\nresults for the equation of state, the contact, the magnetic susceptibility and\nthe contact susceptibility, giving a precise understanding of the 1D analogue\nof the Bose-Einstein condensation and Bardeen-Cooper-Schrieffer crossover in\nthree dimension (3D) and the associated universal magnetic properties. In\nparticular, we obtain the exact form of the magnetic susceptibility $\\chi \\sim\n{1}/{\\sqrt{T}}\\exp(-\\Delta/T)$ at low temperatures, where $\\Delta$ is the\nenergy gap and $T$ is the temperature. Moreover, we establish exact upper and\nlower bounds for the relation between polarization $P$ and the contact $C$ for\nboth repulsive and attractive Fermi gases. Our findings emphasize the role of\nthe pair fluctuations in strongly interacting 1D fermion systems that can shed\nlight on higher dimensions.",
        "positive": "Excitation of the Higgs Mode in a Superfluid Fermi Gas in the BCS-BEC\n  Crossover: In quantum many-body systems with spontaneous breaking of continuous\nsymmetries, Higgs modes emerge as collective amplitude oscillations of order\nparameters. Recently, Higgs mode has been observed in the ultracold Fermi gas.\nIn the present paper, we use the time-dependent Bogoliubov-de Gennes equations\nto investigate Higgs amplitude oscillations of the superfluid order parameter\nin a Fermi gas induced by a rapid change of the ${\\it s}$-wave scattering\nlength. In particular, we investigate the Higgs mode with different values of\nthe initial scattering length. We find that the energy of the Higgs mode\ncoincides with the threshold energy of the pair-breaking excitation, and\nexponent of the power-low decay of the Higgs mode $\\gamma$ continuously changes\nbetween $\\gamma=-1/2$ and $\\gamma=-3/2$ through the\nBardeen-Cooper-Schrieffer-Bose-Einstein condensation (BCS-BEC) crossover.\nMoreover, we propose the optimal ramp speed of the scattering length for\nobserving the clearest Higgs oscillations."
    },
    {
        "anchor": "Virial expansion with Feynman diagrams: We present a field theoretic method for the calculation of the second and\nthird virial coefficients b2 and b3 of 2-species fermions interacting via a\ncontact interaction. The method is mostly analytic. We find a closed expression\nfor b3 in terms of the 2 and 3-body T-matrices. We recover numerically, at\nunitarity, and also in the whole BEC-BCS crossover, previous numerical results\nfor the third virial coefficient b3.",
        "positive": "Composite cores of monopoles and Alice rings in spin-2 Bose-Einstein\n  condensates: We show that energy relaxation causes a point defect in the uniaxial-nematic\nphase of a spin-2 Bose-Einstein condensate to deform into a spin-Alice ring\nthat exhibits a composite core structure with distinct topology at short and\nlong distances from the singular line. An outer biaxial-nematic core exhibits a\nspin half-quantum vortex structure with a uniaxial-nematic inner core. By\nnumerical simulation we demonstrate a dynamical oscillation between the\nspin-Alice ring and a split-core hedgehog configuration via the appearance of\nferromagnetic rings with associated vorticity inside an extended core region.\nWe further show that a similar dynamics is exhibited by a spin-Alice ring\nsurrounding a spin-vortex line resulting from the relaxation of a monopole\nsituated on a spin-vortex line in the biaxial-nematic phase. In the cyclic\nphase similar states are shown instead to form extended phase-mixing cores\ncontaining rings with fractional mass circulation or cores whose spatial shape\nreflect the order-parameter symmetry of cyclic inner core, depending on the\ninitial configuration."
    },
    {
        "anchor": "Synthetic-gauge-field-induced resonances and\n  Fulde-Ferrell-Larkin-Ovchinnikov states in a one-dimensional optical lattice: Coherent coupling generated by laser light between the hyperfine states of\natoms, loaded in a 1D optical lattice, gives rise to the \"synthetic dimension\"\nsystem which is equivalent to a Hofstadter model in a finite strip of square\nlattice. An SU(M) symmetric attractive interaction in conjunction with the\nsynthetic gauge field present in this system gives rise to unusual effects. We\nstudy the two- body problem of the system using the T-matrix formalism. We show\nthat the two-body ground states pick up a finite momentum and can transform\ninto two-body resonance like features in the scattering continuum with a large\nchange in the phase shift. As a result, even for this 1D system, a critical\namount of attraction is needed to form bound states. These phenomena have\nspectacular effects on the many body physics of the system analyzed using the\nnumerical density matrix renormalization group technique. We show that the\nFulde-Ferrell-Larkin-Ovchinnikov (FFLO) states form in the system even for a\n\"balanced\" gas and the FFLO momentum of the pairs scales linearly with flux.\nConsidering suitable measures, we investigate interesting properties of these\nstates. We also discuss a possibility of realization of a generalized\ninteresting topological model, called the Creutz ladder.",
        "positive": "Fermi gas throughout the BCS-BEC crossover: Comparative study of\n  t-matrix approaches with various degrees of self-consistency: The diagrammatic t-matrix approximation has often been adopted to describe a\ndilute Fermi gas. This approximation, originally considered by Galitskii for a\nrepulsive inter-particle interaction (Galitskii-1958), has later been widely\nutilized for an attractive Fermi gas to describe the BCS-BEC crossover from\nstrongly overlapping Cooper pairs in weak coupling to non-overlapping composite\nbosons in strong coupling. Several variants of the $t$-matrix approximation\nhave been considered in the literature, which are distinguished by the degree\nof self-consistency allowed in the building blocks of the diagrammatic\nstructure. Here, we perform a systematic and comparative study of all possible\nvariants on the degree of self-consistency for the $t$-matrix approximation in\nan attractive Fermi gas, which enables us to confront their outcomes for\nthermodynamic and dynamical quantities on the same footing in an unbiased way.\nFor definiteness, only the normal phase above the superfluid critical\ntemperature is considered. The dispute that can be raised in this context,\nabout the adequateness of introducing progressive degrees of self-consistency\nover and above the non-self-consistent $t$-matrix approximation for an\nattractive Fermi gas, parallels the recent interest in the literature on\nassessing the importance of various degrees of self-consistency in the context\nof semiconductors and insulators."
    },
    {
        "anchor": "Large-N ground state of the Lieb-Liniger model and Yang-Mills theory on\n  a two-sphere: We derive the large particle number limit of the Bethe equations for the\nground state of the attractive one-dimensional Bose gas (Lieb-Liniger model) on\na ring and solve it for arbitrary coupling. We show that the ground state of\nthis system can be mapped to the large-N saddle point of Euclidean Yang-Mills\ntheory on a two-sphere with a U(N) gauge group, and the phase transition that\ninterpolates between the homogeneous and solitonic regime is dual to the\nDouglas-Kazakov confimenent-deconfinement phase transition.",
        "positive": "Critical velocity in resonantly driven polariton superfluids: We study the necessary condition under which a resonantly driven exciton\npolariton superfluid flowing against an obstacle can generate turbulence. The\nvalue of the critical velocity is well estimated by the transition from\nelliptic to hyperbolic of an operator following ideas developed by Frisch,\nPomeau, Rica for a superfluid flow around an obstacle, though the nature of\nequations governing the polariton superfluid is quite different. We find\nanalytical estimates depending on the pump amplitude and on the pump energy\ndetuning, quite consistent with our numerical computations."
    },
    {
        "anchor": "Controlling the Rotational and Hyperfine State of Ultracold\n  $^{87}$Rb$^{133}$Cs Molecules: We demonstrate coherent control of both the rotational and hyperfine state of\nultracold, chemically stable $^{87}$Rb$^{133}$Cs molecules with external\nmicrowave fields. We create a sample of ~2000 molecules in the lowest hyperfine\nlevel of the rovibronic ground state N = 0. We measure the transition\nfrequencies to 8 different hyperfine levels of the N = 1 state at two magnetic\nfields ~23 G apart. We determine accurate values of rotational and hyperfine\ncoupling constants that agree well with previous calculations. We observe Rabi\noscillations on each transition, allowing complete population transfer to a\nselected hyperfine level of N = 1. Subsequent application of a second microwave\npulse allows transfer of molecules back to a different hyperfine level of N =\n0.",
        "positive": "Quantum-optical magnets with competing short- and long-range\n  interactions: Rydberg-dressed spin lattice in an optical cavity: The fields of quantum simulation with cold atoms [1] and quantum optics [2]\nare currently being merged. In a set of recent pathbreaking experiments with\natoms in optical cavities [3,4] lattice quantum many-body systems with both, a\nshort-range interaction and a strong interaction potential of infinite range\n-mediated by a quantized optical light field- were realized. A theoretical\nmodelling of these systems faces considerable complexity at the interface of:\n(i) spontaneous symmetry-breaking and emergent phases of interacting many-body\nsystems with a large number of atoms $N\\rightarrow\\infty$, (ii) quantum optics\nand the dynamics of fluctuating light fields, and (iii) non-equilibrium physics\nof driven, open quantum systems. Here we propose what is possibly the simplest,\nquantum-optical magnet with competing short- and long-range interactions, in\nwhich all three elements can be analyzed comprehensively: a Rydberg-dressed\nspin lattice [5] coherently coupled to a single photon mode. Solving a set of\ncoupled even-odd sublattice Master equations for atomic spin and photon\nmean-field amplitudes, we find three key results. (R1): Superradiance and a\ncoherent photon field can coexist with spontaneously broken magnetic\ntranslation symmetry. The latter is induced by the short-range nearest-neighbor\ninteraction from weakly admixed Rydberg levels. (R2): This broken even-odd\nsublattice symmetry leaves its imprint in the light via a novel peak in the\ncavity spectrum beyond the conventional polariton modes. (R3): The combined\neffect of atomic spontaneous emission, drive, and interactions can lead to\nphases with anomalous photon number oscillations. Extensions of our work\ninclude nano-photonic crystals coupled to interacting atoms and multi-mode\nphoton dynamics in Rydberg systems."
    },
    {
        "anchor": "Machine-learning the phase diagram of a strongly-interacting Fermi gas: We determine the phase diagram of strongly correlated fermions in the\ncrossover from Bose-Einstein condensates of molecules (BEC) to Cooper pairs of\nfermions (BCS) utilizing an artificial neural network. By applying advanced\nimage recognition techniques to the momentum distribution of the fermions, a\nquantity which has been widely considered as featureless for providing\ninformation about the condensed state, we measure the critical temperature and\nshow that it exhibits a maximum on the bosonic side of the crossover.\nAdditionally, we back-analyze the trained neural network and demonstrate that\nit interprets physically relevant quantities.",
        "positive": "Disorder-controlled relaxation in a 3D Hubbard model quantum simulator: Understanding the collective behavior of strongly correlated electrons in\nmaterials remains a central problem in many-particle quantum physics. A minimal\ndescription of these systems is provided by the disordered Fermi-Hubbard model\n(DFHM), which incorporates the interplay of motion in a disordered lattice with\nlocal inter-particle interactions. Despite its minimal elements, many dynamical\nproperties of the DFHM are not well understood, owing to the complexity of\nsystems combining out-of-equilibrium behavior, interactions, and disorder in\nhigher spatial dimensions. Here, we study the relaxation dynamics of doubly\noccupied lattice sites in the three-dimensional (3D) DFHM using\ninteraction-quench measurements on a quantum simulator composed of fermionic\natoms confined in an optical lattice. In addition to observing the widely\nstudied effect of disorder inhibiting relaxation, we find that the cooperation\nbetween strong interactions and disorder also leads to the emergence of a\ndynamical regime characterized by \\textit{disorder-enhanced} relaxation. To\nsupport these results, we develop an approximate numerical method and a\nphenomenological model that each capture the essential physics of the decay\ndynamics. Our results provide a theoretical framework for a previously\ninaccessible regime of the DFHM and demonstrate the ability of quantum\nsimulators to enable understanding of complex many-body systems through minimal\nmodels."
    },
    {
        "anchor": "Atom-Number Enhancement by Shielding Atoms from Losses in Strontium\n  Magneto-Optical Traps: We present a scheme to enhance the atom number in magneto-optical traps of\nstrontium atoms operating on the 461 nm transition. This scheme consists of\nresonantly driving the $^1$S$_0\\to^3$P$_1$ intercombination line at 689 nm,\nwhich continuously populates a short-lived reservoir state and, as expected\nfrom a theoretical model, partially shields the atomic cloud from losses\narising in the 461 nm cooling cycle. We show a factor of two enhancement in the\natom number for the bosonic isotopes $^{88}$Sr and $^{84}$Sr, and the fermionic\nisotope $^{87}$Sr, in good agreement with our model. Our scheme can be applied\nin the majority of strontium experiments without increasing the experimental\ncomplexity of the apparatus, since the employed 689 nm transition is commonly\nused for further cooling. Our method should thus be beneficial to a broad range\nof quantum science and technology applications exploiting cold strontium atoms,\nand could be extended to other atomic species.",
        "positive": "Second-order interaction corrections to the Fermi surface and the\n  quasiparticle properties of dipolar fermions in three dimensions: We calculate the renormalized Fermi surface and the quasiparticle properties\nin the Fermi liquid phase of three-dimensional dipolar fermions to second order\nin the dipole-dipole interaction. Using parameters relevant to an ultracold gas\nof erbium atoms, we find that the second-order corrections typically\nrenormalize the Hartree-Fock results by less than one percent. On the other\nhand, if we use the second-order correction to the compressibility to estimate\nthe regime of stability of the system, the point of instability is already\nreached for a significantly smaller interaction strength than in the\nHartree-Fock approximation."
    },
    {
        "anchor": "Quantum phases of spinful Fermi gases in optical cavities: We explore the quantum phases emerging from the interplay between spin and\nmotional degrees of freedom of a one-dimensional quantum fluid of spinful\nfermionic atoms, effectively interacting via a photon-mediating mechanism with\ntunable sign and strength g, as it can be realized in present-day experiments\nwith optical cavities. We find the emergence, in the very same system, of spin-\nand atomic-density wave ordering, accompanied by the occurrence of\nsuperfluidity for g > 0, while cavity photons are seen to drive strong\ncorrelations at all g values, with fermionic character for g > 0, and bosonic\ncharacter for g < 0. Due to the long-range nature of interactions, to infer\nthese results we combine mean-field and exact diagonalization methods supported\nby bosonization analysis.",
        "positive": "Metastable Bose-Einstein Condensation in a Strongly Correlated Optical\n  Lattice: We experimentally and theoretically study the peak fraction of a\nBose-Einstein condensate loaded into a cubic optical lattice as the lattice\npotential depth and entropy per particle are varied. This system is\nwell-described by the superfluid regime of the Bose-Hubbard model, which allows\nfor comparison with mean-field theories and exact quantum Monte Carlo (QMC)\nsimulations. Despite correcting for systematic discrepancies between condensate\nfraction and peak fraction, we discover that the experiment consistently shows\nthe presence of a condensate at temperatures higher than the critical\ntemperature predicted by QMC simulations. This metastability suggests that\nturning on the lattice potential is non-adiabatic. To confirm this behavior, we\ncompute the timescales for relaxation in this system, and find that\nequilibration times are comparable with the known heating rates. The similarity\nof these timescales implies that turning on the lattice potential adiabatically\nmay be impossible. Our results point to the urgent need for a better\ntheoretical and experimental understanding of the timescales for relaxation and\nadiabaticity in strongly interacting quantum gases, and the importance of\nmodel-independent probes of thermometry in optical lattices."
    },
    {
        "anchor": "Two mass-imbalanced atoms in a hard-wall trap: Deep learning\n  integrability of many-body systems: The study of integrable systems has led to significant advancements in our\nunderstanding of many-body physics. We design a series of numerical experiments\nto analyze the integrability of a mass-imbalanced two-body system through\nenergy level statistics and deep learning of wavefunctions. The level spacing\ndistributions are fitted by a Brody distribution and the fitting parameter\n$\\omega$ is found to separate the integrable and non-integrable mass ratios by\na critical line $\\omega=0$. The convolutional neural network built from the\nprobability density images could identify the transition points between\nintegrable and non-integrable systems with high accuracy, yet in a much shorter\ncomputation time. A brilliant example of the network's ability is to identify a\nnew integrable mass ratio $1/3$ by learning from the known integrable case of\nequal mass, with a remarkable network confidence of $98.78\\%$. The robustness\nof our neural networks is further enhanced by adversarial learning, where\nsamples are generated by standard and quantum perturbations mixed in the\nprobability density images and the wavefunctions, respectively.",
        "positive": "Dimensional reduction of a binary Bose-Einstein condensate in mixed\n  dimensions: We present effective reduced equations for the study of a binary\nBose-Einstein condensate (BEC), where the confining potentials of the two BEC\ncomponents have distinct asymmetry so that the components belong to different\nspace dimensions as in a recent experiment [G. Lamporesi et al., Phys. Rev.\nLett. 104, 153202 (2010)]. Starting from a binary three-dimensional (3D)\nGross-Pitaevskii equation (GPE) and using a Lagrangian variational approach we\nderive a binary effective nonlinear Schroedinger equation with components in\ndifferent reduced dimensions, e. g., the first component in one dimension and\nthe second in two dimensions as appropriate to represent a cigar-shaped BEC\ncoupled to a disk-shaped BEC. We demonstrate that the effective reduced binary\nequation, which depend on the geometry of the system, is quite reliable when\ncompared with the binary 3D GPE and can be efficiently used to perform\nnumerical simulation and analytical calculation for the investigation of static\nand dynamic properties of a binary BEC in mixed dimensions."
    },
    {
        "anchor": "Thermal destabilization of self-bound ultradilute quantum droplets: We theoretically investigate the temperature effect in a Bose-Bose mixture\nwith attractive inter-species interactions, in the regime where a self-bound\nultradilute quantum droplet forms due to the subtle balance between the\nattractive mean-field force and the repulsive force provided by Lee-Huang-Yang\nquantum fluctuations. We find that in contrast to quantum fluctuations, thermal\nfluctuations destabilize the droplet state and completely destroy it above a\nthreshold temperature. We show that the threshold temperature is determined by\nthe intra-species interaction energy. For a three-dimensional Bose-Bose\nmixture, the threshold temperature is less than one-tenth of the Bose-Einstein\ncondensation temperature under the typical experimental conditions. With\nincreasing temperature, the droplet's equilibrium density gradually decreases\nand can be reduced by several tens of percent upon reaching the threshold\ntemperature. We also consider a one-dimensional quantum droplet and find a\nsimilar destabilization effect due to thermal fluctuations. The threshold\ntemperature in one dimension is roughly set by the binding energy of the\ninter-species dimer. The pronounced thermal instability of a self-bound quantum\ndroplet predicted in our work could be examined in future experiments, by\nmeasuring the temperature dependence of its central density and observing its\nsudden disappearance at the threshold temperature.",
        "positive": "Surface excitations, shape deformation and the long-time behavior in a\n  stirred Bose-Einstein condensate: The surface excitations, shape deformation and the formation of persistent\ncurrent for a Gaussian obstacle potential rotating in an highly oblate\nBose-Einstein condensate(BEC)are investigated. Vortex dipole can be produced\nand trapped in the center of the stirrer even for slow motion of the stirring\nbeam. When the barrier angular velocity is above some critical value, the\ncondensate shape can be deformed remarkably according to the rotation frequency\ndue to the existence of plenty of surface wave excitations. After a long enough\ntime, a few vortices are found to be left either trapped in the condensate or\npinned by the obstacle, a vortex dipole or several vortices can be trapped at\nthe beam center, which enables the possibility of vortex manipulation."
    },
    {
        "anchor": "Probing Entanglement in Adiabatic Quantum Optimization with Trapped Ions: Adiabatic quantum optimization has been proposed as a route to solve\nNP-complete problems, with a possible quantum speedup compared to classical\nalgorithms. However, the precise role of quantum effects, such as entanglement,\nin these optimization protocols is still unclear. We propose a setup of cold\ntrapped ions that allows one to quantitatively characterize, in a controlled\nexperiment, the interplay of entanglement, decoherence, and non-adiabaticity in\nadiabatic quantum optimization. We show that, in this way, a broad class of\nNP-complete problems becomes accessible for quantum simulations, including the\nknapsack problem, number partitioning, and instances of the max-cut problem.\nMoreover, a general theoretical study reveals correlations of the success\nprobability with entanglement at the end of the protocol. From exact numerical\nsimulations for small systems and linear ramps, however, we find no substantial\ncorrelations with the entanglement during the optimization. For the final\nstate, we derive analytically a universal upper bound for the success\nprobability as a function of entanglement, which can be measured in experiment.\nThe proposed trapped-ion setups and the presented study of entanglement address\npertinent questions of adiabatic quantum optimization, which may be of general\ninterest across experimental platforms.",
        "positive": "Majorana Fermions in Equilibrium and Driven Cold Atom Quantum Wires: We introduce a new approach to create and detect Majorana fermions using\noptically trapped 1D fermionic atoms. In our proposed setup, two internal\nstates of the atoms couple via an optical Raman transition---simultaneously\ninducing an effective spin-orbit interaction and magnetic field---while a\nbackground molecular BEC cloud generates s-wave pairing for the atoms. The\nresulting cold atom quantum wire supports Majorana fermions at phase boundaries\nbetween topologically trivial and nontrivial regions, as well as `Floquet\nMajorana fermions' when the system is periodically driven. We analyze\nexperimental parameters, detection schemes, and various imperfections."
    },
    {
        "anchor": "Superfluidity and Chaos in low dimensional circuits: The hallmark of superfluidity is the appearance of \"vortex states\" carrying a\nquantized metastable circulating current. Considering a unidirectional flow of\nparticles in a ring, at first it appears that any amount of scattering will\nrandomize the velocity, as in the Drude model, and eventually the ergodic\nsteady state will be characterized by a vanishingly small fluctuating current.\nHowever, Landau and followers have shown that this is not always the case. If\nelementary excitations (e.g. phonons) have higher velocity than that of the\nflow, simple kinematic considerations imply metastability of the vortex state:\nthe energy of the motion cannot dissipate into phonons. On the other hand if\nthis Landau criterion is violated the circulating current can decay. Below we\nshow that the standard Landau and Bogoliubov superfluidity criteria fail in\nlow-dimensional circuits. Proper determination of the superfluidity\nregime-diagram must account for the crucial role of chaos, an ingredient\nmissing from the conventional stability analysis. Accordingly, we find novel\ntypes of superfluidity, associated with irregular or chaotic or breathing\nvortex states.",
        "positive": "Density-induced geometric frustration of ultra-cold bosons in optical\n  lattices: A density-dependent gauge field may induce density-induced geometric\nfrustration, leading to a non-trivial interplay between density modulation and\nfrustration, which we illustrate for the particular case of ultra-cold bosons\nin zig-zag optical lattices with a density-dependent hopping. We show that the\ndensity-induced frustration leads in a rich landscape of quantum phases,\nincluding Mott and bond-order insulators, two-component superfluids, chiral\nsuperfluids, and partially-paired superfluids. We show as well that the\ndensity-dependent hopping results in an effective repulsive or attractive\ninteractions, and that for the latter case the vacuum may be destabilized\nleading to a strong compressibility. Finally, we discuss how the predicted\nphases may be experimentally observed and characterized in time-of-flight\nmeasurements using their characteristic signatures in the momentum\ndistribution."
    },
    {
        "anchor": "A versatile ring trap for quantum gases: We report on the confinement of a Bose-Einstein condensate in an annular trap\nwith widely tunable parameters. The trap relies on a combination of magnetic,\noptical and radio-frequency fields. The loading procedure is discussed. We\npresent annular traps with radii adjusted between 20 and 150 micrometers. We\ndemonstrate the preparation of persistent flows both with a rotating laser\nstirrer and with a global quadrupole deformation of the ring.Our setup is well\nadapted for the study of superfluid dynamics.",
        "positive": "Ground state properties and excitation spectrum of a two dimensional gas\n  of bosonic dipoles: We present a quantum Monte Carlo study of two-dimensional dipolar Bose gases\nin the limit of zero temperature. The analysis is mainly focused on the\nanisotropy effects induced in the homogeneous gas when the polarization angle\nwith respect to the plane is changed. We restrict our study to the regime where\nthe dipolar interaction is strictly repulsive, although the strength of the\npair repulsion depends on the vector interparticle distance. Our results show\nthat the effect of the anisotropy in the energy per particle scales with the\ngas parameter at low densities as expected, and that this scaling is preserved\nfor all polarization angles even at the largest densities considered here. We\nalso evaluate the excitation spectrum of the dipolar Bose gas in the context of\nthe Feynman approximation and compare the results obtained with the Bogoliubov\nones. As expected, we find that these two approximations agree at very low\ndensities, while they start to deviate from each other as the density\nincreases. For the largest densities studied, we observe a significant\ninfluence of the anisotropy of the dipole-dipole interaction in the excitation\nspectrum."
    },
    {
        "anchor": "Dimensional Effects on the Momentum distribution of Bosonic Trimer\n  States: The momentum distribution is a powerful probe of strongly-interacting systems\nthat are expected to display universal behavior. This is contained in the\ncontact parameters which relate few- and many-body properties. Here we consider\na Bose gas in two dimensions and explicitly show that the two-body contact\nparameter is universal and then demonstrate that the momentum distribution at\nnext-to-leading order has a logarithmic dependence on momentum which is vastly\ndifferent from the three-dimensional case. Based on this, we propose a scheme\nfor measuring the effective dimensionality of a quantum many-body system by\nexploiting the functional form of the momentum distribution.",
        "positive": "Dispersive hydrodynamics of nonlinear polarization waves in\n  two-component Bose-Einstein condensates: We study one dimensional mixtures of two-component Bose-Einstein condensates\nin the limit where the intra-species and inter-species interaction constants\nare very close. Near the mixing-demixing transition the polarization and the\ndensity dynamics decouple. We study the nonlinear polarization waves, show that\nthey obey a universal (i.e., parameter free) dynamical description, identify a\nnew type of algebraic soliton, explicitly write simple wave solutions, and\nstudy the Gurevich-Pitaevskii problem in this context."
    },
    {
        "anchor": "Relaxation dynamics of a Fermi gas in an optical superlattice: This paper comprises an experimental and theoretical investigation of the\ntime evolution of a Fermi gas following fast and slow quenches of a\none-dimensional optical double-well superlattice potential. We investigate both\nthe local tunneling in the connected double wells and the global dynamics\ntowards a steady state. The local observables in the steady-state resemble\nthose of an equilibrium state, whereas the global properties indicate a strong\nnon-equilibrium situation.",
        "positive": "Static and dynamic properties of a few spin $1/2$ interacting fermions\n  trapped in an harmonic potential: We provide a detailed study of the properties of a few interacting spin $1/2$\nfermions trapped in a one-dimensional harmonic oscillator potential. The\ninteraction is assumed to be well represented by a contact delta potential.\nNumerical results obtained by means of exact diagonalization techniques are\ncombined with analytical expressions for both the non-interacting and strongly\ninteracting regime. The $N=2$ case is used to benchmark our numerical\ntechniques with the known exact solution of the problem. After a detailed\ndescription of the numerical methods, in a tutorial-like manner, we present the\nstatic properties of the system for $N=2, 3, 4$ and 5 particles, e.g.\nlow-energy spectrum, one-body density matrix, ground-state densities. Then, we\nconsider dynamical properties of the system exploring first the excitation of\nthe breathing mode, using the dynamical structure function and corresponding\nsum-rules, and then a sudden quench of the interaction strength."
    },
    {
        "anchor": "Exact methods in analysis of nonequilibrium dynamics of integrable\n  models: application to the study of correlation functions in nonequilibrium\n  1D Bose gas: In this paper we study nonequilibrium dynamics of one dimensional Bose gas\nfrom the general perspective of dynamics of integrable systems. After outlining\nand critically reviewing methods based on inverse scattering transform,\nintertwining operators, q-deformed objects, and extended dynamical conformal\nsymmetry, we focus on the form-factor based approach. Motivated by possible\napplications in nonlinear quantum optics and experiments with ultracold atoms,\nwe concentrate on the regime of strong repulsive interactions. We consider\ndynamical evolution starting from two initial states: a condensate of particles\nin a state with zero momentum and a condensate of particles in a gaussian\nwavepacket in real space. Combining the form-factor approach with the method of\nintertwining operator we develop a numerical procedure which allows explicit\nsummation over intermediate states and analysis of the time evolution of\nnon-local density-density correlation functions. In both cases we observe a\ntendency toward formation of crystal-like correlations at intermediate time\nscales.",
        "positive": "Dynamic Density Response of Trapped Interacting Quantum Gases: An expression for the dynamic density response function has been obtained for\nan interacting quantum gas in Random Phase Approximation (RPA) including first\norder self and exchange contribution. It involves the single particle wave\nfunctions and eigen values. The expression simplifies when diagonal elements\nare considered. The diagonal elements of the imaginary part of Fourier\ntransformed response function is relevant in the measurement of Bragg\nscattering cross-section and in several other applications."
    },
    {
        "anchor": "Spin drag and fast response in a quantum mixture of atomic gases: By applying a sudden perturbation to one of the components of a mixture of\ntwo quantum fluids, we explore the effect on the motion of the second component\non a short time scale. By implementing perturbation theory, we prove that for\nshort times the response of the second component is fixed by the energy\nweighted moment of the crossed dynamic structure factor (crossed f-sum rule).\nWe also show that by properly monitoring the time duration of the perturbation\nit is possible to identify peculiar fast spin drag regimes, which are sensitive\nto the interaction effects in the Hamiltonian. Special focus is given to the\ncase of coherently coupled Bose-Einstein condensates, interacting Bose mixtures\nexhibiting the Andreev-Bashkin effect, normal Fermi liquids and the polaron\nproblem. The relevant excitations of the system contributing to the spin drag\neffect are identified and the contribution of the low frequency gapless\nexcitations to the f-sum rule in the density and spin channels is explicitly\ncalculated employing the proper macroscopic dynamic theories. Both spatially\nperiodic and Galilean boost perturbations are considered.",
        "positive": "An analytical approach to atomic multichannel collisions in tight\n  harmonic waveguides: We perform an analytical investigation in the framework of generalized $K$\nmatrix theory of the scattering problem in tight isotropic and harmonic\nwaveguides allowing for several open scattering channels. The scattering\nbehavior is explored for identical bosons and fermions, as well as for\ndistinguishable particles, the main aspect being the confinement-induced\nresonances (CIR) which are attributed to different partial waves. In particular\nwe present the unitarity bounds which emerge when considering a quasi one\ndimensional system. Unitarity bounds are also given for the transition\ncoefficients, which show the limitations for efficient transversal\n(de-)excitations by means of CIRs. We analyze the CIR for $d$-waves and find\nthe intriguing phenomenon of a strong transmission suppression in the presence\nof more than one open channel, which represents an interesting regime to be\napplied in the corresponding many-particle systems. The corresponding channel\nthreshold singularities are studied and it is shown that these are solely\ndetermined by the symmetry class of the partial wave."
    },
    {
        "anchor": "Nucleation in finite topological systems during continuous metastable\n  quantum phase transitions: Finite topological quantum systems can undergo continuous metastable quantum\nphase transitions to change their topological nature. Here we show how to\nnucleate the transition between ring currents and dark soliton states in a\ntoroidally trapped Bose-Einstein condensate. An adiabatic passage to wind and\nunwind its phase is achieved by explicit global breaking of the rotational\nsymmetry. This could be realized with current experimental technology.",
        "positive": "Observation of Topologically Stable 2D Skyrmions in an Antiferromagnetic\n  Spinor Bose-Einstein Condensate: We present the creation and time evolution of two-dimensional Skyrmion\nexcitations in an antiferromagnetic spinor Bose-Einstein condensate. Using a\nspin rotation method, the Skyrmion spin textures were imprinted on a sodium\ncondensate in a polar phase, where the two-dimensional Skyrmion is\ntopologically protected. The Skyrmion was observed to be stable on a short time\nscale of a few tens of ms but to have dynamical instability to deform its shape\nand eventually decay to a uniform spin texture. The deformed spin textures\nreveal that the decay dynamics involves breaking the polar phase inside the\ncondensate without having topological charge density flow through the boundary\nof the finite-sized sample. We discuss the possible formation of half-quantum\nvortices in the deformation process."
    },
    {
        "anchor": "Coherent Manipulation of the Internal State of Ultracold\n  $^{87}$Rb$^{133}$Cs Molecules with Multiple Microwave Fields: We explore coherent multi-photon processes in $^{87}$Rb$^{133}$Cs molecules\nusing 3-level lambda and ladder configurations of rotational and hyperfine\nstates, and discuss their relevance to future applications in quantum\ncomputation and quantum simulation. In the lambda configuration, we demonstrate\nthe driving of population between two hyperfine levels of the rotational ground\nstate via a two-photon Raman transition. Such pairs of states may be used in\nthe future as a quantum memory, and we measure a Ramsey coherence time for a\nsuperposition of these states of 58(9) ms. In the ladder configuration, we show\nthat we can generate and coherently populate microwave dressed states via the\nobservation of an Autler-Townes doublet. We demonstrate that we can control the\nstrength of this dressing by varying the intensity of the microwave coupling\nfield. Finally, we perform spectroscopy of the rotational states of\n$^{87}$Rb$^{133}$Cs up to $N=6$, highlighting the potential of ultracold\nmolecules for quantum simulation in synthetic dimensions. By fitting the\nmeasured transition frequencies we determine a new value of the centrifugal\ndistortion coefficient $D_v=h\\times207.3(2)~$Hz.",
        "positive": "Chiral Prethermalization in supersonically split condensates: We study the dynamics of phase relaxation between a pair of one-dimensional\ncondensates created by a supersonic unzipping of a single condensate. We use\nthe Lorentz invariance of the low energy sector of such systems to show that\ndephasing results in an unusual prethermal state, in which right- and\nleft-moving excitations have different, Doppler-shifted temperatures. The\nchirality of these modes can be probed experimentally by measuring the\ninterference fringe contrasts with the release point of the split condensates\nmoving at another supersonic velocity. Further, an accelerated motion of the\nrelease point can be used to observe a space-like analogue of the Unruh effect.\nA concrete experimental realization of the quantum zipper for a BEC of trapped\natoms on a atom chip is outlined. We interpret these results in the context of\nthe general question of the Lorentz transformation of temperature, and the\nclose analogy with the dipolar anisotropy of the Cosmic Microwave Background."
    },
    {
        "anchor": "Skin superfluid, topological Mott insulators, and asymmetric dynamics in\n  interacting non-Hermitian Aubry-Andre-Harper models: Non-Hermitian quantum many-body systems are a fascinating subject to be\nexplored. Using the generalized density matrix renormalisation group method and\ncomplementary exact diagonalization, we elucidate the many-body ground states\nand dynamics of a 1D interacting non-Hermitian Aubry-Andre-Harper model for\nbosons. We find stable ground states in the superfluid and Mott insulating\nregimes under wide range of conditions in this model. We reveal a skin\nsuperfluid state induced by the non-Hermiticity from the nonreciprocal hopping.\nWe investigate the topology of the Mott insulating phase and find its\nindependence of the non-Hermiticity. The topological Mott insulators in this\nnon-Hermitian system are characterized by four equal Chern numbers and a\nquantized shift of biorthogonal many-body polarizations. Furthermore, we show\ngeneric asymmetric expansion and correlation dynamics in the system.",
        "positive": "Random-Phase-Approximation Excitation Spectra for Bose-Hubbard Models: We obtain the excitation spectra of the following three generalized\nBose-Hubbard (BH) models: (1) a two-species generalization of the spinless BH\nmodel, (2) a single-species, spin-1 BH model, and (3) the extended Bose-Hubbard\nmodel (EBH) for spinless interacting bosons of one species. In all the phases\nof these models we provide a unified treatment of random-phase-approximation\n(RPA) excitation spectra. These spectra have gaps in all the MI phases and gaps\nin the DW phases in the EBH model; they are gapless in all the SF phases in\nthese models and in the SS phases in the EBH model. We obtain the dependence of\n(a) gaps $\\Delta$ and (b) the sound velocity $u_s$ on the parameters of these\nmodels and examine $\\Delta$ and $u_s$ as these systems go through phase\ntransitions. At the SF-MI transitions in the spin-1 BH model, $u_s$ goes to\nzero continuously (discontinuously) for MI phases with an odd (even) number of\nbosons per site; this is consistent with the natures of these transition in\nmean-field theory. In the SF phases of these models, our excitation spectra\nagree qualitatively, at weak couplings, with those that can be obtained from\nGross-Pitaevskii-type models. We compare the results of our work with earlier\nstudies of related models and discuss implications for experiments."
    },
    {
        "anchor": "Phase diagram of the Bose-Hubbard model on a ring-shaped lattice with\n  tunable weak links: Motivated by recent experiments on toroidal Bose-Einstein condensates in\nall-optical traps with tunable weak links, we study the one-dimensional\nBose-Hubbard model on a ring-shaped lattice with a small region of weak hopping\nintegrals using quantum Monte Carlo simulations. Besides the usual Mott\ninsulating and superfluid phases, we find a phase which is compressible but non\nsuperfluid with a local Mott region. This `local Mott' phase extends in a large\nregion of the phase diagram. These results suggest that the insulating and\nconducting phases can be tuned by a local parameter which may provide a new\ninsight to the design of atomtronic devices.",
        "positive": "A single impurity in an ideal atomic Fermi gas: current understanding\n  and some open problems: We briefly review some current theoretical and experimental aspects of the\nproblem of a single spinless impurity in a 3D polarised atomic Fermi gas at\nzero temperature where the interactions can be tuned using a wide Feshbach\nresonance. We show that various few-body states in vacuum composed of the\nimpurity and background gas atoms (single impurity, dimer, trimer, tetramer)\ngive rise to corresponding dressed states ({\\em polaron}, {\\em dimeron}, {\\em\ntrimeron}, {\\em tetrameron}) in the gas and inherit many of their\ncharacteristics. We study the ground state focussing on the choice of wave\nfunction and its properties. We raise a few unsolved problems: whether the\npolaron and dimeron are really separate branches, what other few-body states\nmight exist, the nature of the groundstate for large numbers of particle-hole\npairs and why is the polaron ansatz so good. We then turn to the excited\nstates, and to the calculation of the effective mass. We examine the bounds on\nthe effective mass and raise a conjecture about that of composite quasiparticle\nstates."
    },
    {
        "anchor": "Elastic and inelastic transmission in guided atom lasers: a truncated\n  Wigner approach: We study the transport properties of an ultracold gas of Bose-Einstein\ncondensate that is coupled from a magnetic trap into a one-dimensional\nwaveguide. Our theoretical approach to tackle this problem is based on the\ntruncated Wigner method for which we assume the system to consist of two\nsemi-infinite non-interacting leads and a finite interacting scattering region\nwith two constrictions modelling an atomic quantum dot. The transmission is\ncomputed in the steady-state regime and we find a good agreement between\ntruncated Wigner and Matrix-Product State calculations. We also identify clear\nsignatures of inelastic resonant scattering by analyzing the distribution of\nenergy in the transmitted atomic matter wave beam.",
        "positive": "A generalized phase space approach for solving quantum spin dynamics: Numerical techniques to efficiently model out-of-equilibrium dynamics in\ninteracting quantum many-body systems are key for advancing our capability to\nharness and understand complex quantum matter. Here we propose a new numerical\napproach which we refer to as GDTWA. It is based on a discrete semi-classical\nphase-space sampling and allows to investigate quantum dynamics in lattice spin\nsystems with arbitrary $S\\geq 1/2$. We show that the GDTWA can accurately\nsimulate dynamics of large ensembles in arbitrary dimensions. We apply it for\n$S>1/2$ spin-models with dipolar long-range interactions, a scenario arising in\nrecent experiments with magnetic atoms. We show that the method can capture\nbeyond mean-field effects, not only at short times, but it also correctly\nreproduces long time quantum-thermalization dynamics. We benchmark the method\nwith exact diagonalization in small systems, with perturbation theory for short\ntimes, and with analytical predictions made for closed system which feature\nquantum-thermalization at long times. By computing the Renyi entropy, currently\nan experimentally accessible quantifier of entanglement, we reveal that large\n$S$ systems can feature larger entanglement than corresponding $S=1/2$ systems.\nOur analyses demonstrate that the GDTWA can be a powerful tool for modeling\ncomplex spin dynamics in regimes where other state-of-the art numerical methods\nfail."
    },
    {
        "anchor": "Bond-Order Density Wave Phases in Dimerized Extended Bose-Hubbard Models: The Bose-Hubbard model (BHM) has been widely explored to develop a profound\nunderstanding of the strongly correlated behavior of interacting bosons.\nQuantum simulators not only allow the exploration of the BHM but also extend it\nto models with interesting phenomena such as gapped phases with multiple orders\nand topological phases. In this work, an extended Bose-Hubbard model involving\na dimerized one-dimensional model of long-range interacting hard-core bosons is\nstudied. Bond-order density wave phases (BODW) are characterized in terms of\ntheir symmetry breaking and topological properties. At certain fillings,\ninteractions combined with dimerized hoppings give rise to an emergent\nsymmetry-breaking leading to BODW phases, which differs from the case of\nnon-interacting models that require an explicit breaking of the symmetry.\nSpecifically, the BODW phase at filling $\\rho=1/3$ possesses no analogue in the\nnon-interacting model in terms of its symmetry-breaking properties and the unit\ncell structure. Upon changing the dimerization pattern, the system realizes\ntopologically trivial BODW phases. At filling $\\rho=1/4$, on-site density\nmodulations are shown to stabilize the topological BODW phase. Our work\nprovides the bridge between interacting and non-interacting BODW phases and\nhighlights the significance of long-range interactions in a dimerized lattice\nby showing unique BODW phases that do not exist in the non-interacting model.",
        "positive": "Vortices in spin-0 superfluids carry magnetic flux: Vortices in spin-$0$ superfluids generically carry magnetic fields inside\ntheir cores, so that even neutral superfluid vortices may be thought of as\nmagnetic flux tubes. We give a systematic analysis of this `vortex magnetic\neffect' using effective field theory, clarifying earlier literature on the\nsubject. Our analysis shows that in superfluid Helium-$4$ the vortex magnetic\neffect may be large enough to be experimentally detectable."
    },
    {
        "anchor": "Deterministic creation, pinning, and manipulation of quantized vortices\n  in a Bose-Einstein condensate: We experimentally and numerically demonstrate deterministic creation and\nmanipulation of a pair of oppositely charged singly quantized vortices in a\nhighly oblate Bose-Einstein condensate (BEC). Two identical blue-detuned,\nfocused Gaussian laser beams that pierce the BEC serve as repulsive obstacles\nfor the superfluid atomic gas; by controlling the positions of the beams within\nthe plane of the BEC, superfluid flow is deterministically established around\neach beam such that two vortices of opposite circulation are generated by the\nmotion of the beams, with each vortex pinned to the \\emph{in situ} position of\na laser beam. We study the vortex creation process, and show that the vortices\ncan be moved about within the BEC by translating the positions of the laser\nbeams. This technique can serve as a building block in future experimental\ntechniques to create, on-demand, deterministic arrangements of few or many\nvortices within a BEC for precise studies of vortex dynamics and vortex\ninteractions.",
        "positive": "Phase diagram of the 3D Anderson model for uncorrelated speckle\n  potentials: We investigate the localization properties of atoms moving in a\nthree-dimensional optical lattice in the presence of an uncorrelated disorder\npotential having the same probability distribution $P(V)$ as laser speckles. We\nfind that the disorder-averaged (single-particle) Green's function, calculated\nvia the coherent potential approximation, is in very good agreement with exact\nnumerics. Using the transfer-matrix method, we compute the phase diagram in the\nenergy-disorder plane and show that its peculiar shape can be understood from\nthe self-consistent theory of localization. In particular, we recover the large\nasymmetry in the position of the mobility edge for blue and red speckles, which\nwas recently observed numerically for correlated speckle potentials."
    },
    {
        "anchor": "Ultracold atoms and the Functional Renormalization Group: We give a self-contained introduction to the physics of ultracold atoms using\nfunctional integral techniques. Based on a consideration of the relevant length\nscales, we derive the universal effective low energy Hamiltonian describing\nultracold alkali atoms. We then introduce the concept of the effective action,\nwhich generalizes the classical action principle to full quantum status and\nprovides an intuitive and versatile tool for practical calculations. This\nframework is applied to weakly interacting degenerate bosons and fermions in\nthe spatial continuum. In particular, we discuss the related BEC and BCS\nquantum condensation mechanisms. We then turn to the BCS-BEC crossover, which\ninterpolates between both phenomena, and which is realized experimentally in\nthe vicinity of a Feshbach resonance. For its description, we introduce the\nFunctional Renormalization Group approach. After a general discussion of the\nmethod in the cold atoms context, we present a detailed and pedagogical\napplication to the crossover problem. This not only provides the physical\nmechanism underlying this phenomenon. More generally, it also reveals how the\nrenormalization group can be used as a tool to capture physics at all scales,\nfrom few-body scattering on microscopic scales, through the finite temperature\nphase diagram governed by many-body length scales, up to critical phenomena\ndictating long distance physics at the phase transition. The presentation aims\nto equip students at the beginning PhD level with knowledge on key physical\nphenomena and flexible tools for their description, and should enable to embark\nupon practical calculations in this field.",
        "positive": "Time-Dependent Density Functional Theory and the Real-Time Dynamics of\n  Fermi Superfluids: I describe the Time-Dependent Superfluid Local Density Approximation, which\nis an adiabatic extension of the Density Functional Theory to superfluid Fermi\nsystems and their real-time dynamics. This new theoretical framework has been\napplied to describe a number of phenomena in cold atomic gases and nuclear\ncollective motion: excitation of the Higgs modes in strongly interacting Fermi\nsuperfluids, generation of quantized vortices, crossing and reconnection of\nvortices, excitation of the superflow at velocities above the critical\nvelocity, excitation of quantum shock waves and domain walls in the collisions\nof superfluid atomic clouds, excitation of collective states in nuclei."
    },
    {
        "anchor": "Phonon-mediated Josephson oscillations in excitonic and polaritonic\n  condensates: We analyze theoretically the role of the exciton-phonon interactions in\nphenomena related to the Josephson effect between two spatially separated\nexciton and exciton-polariton condensates. We consider the role of the\ndephasing introduced by phonons in such phenomena as Josephson tunneling,\nself-trapping and spontaneous polarization separation. In the regime of cw\npumping we find a remarkable bistability effect arising from exciton- exciton\ninteractions as well as regimes of self- sustained regular and chaotic\noscillations.",
        "positive": "Quasi-One-Dimensional Dipolar Quantum Gases: In this letter we consider dipolar quantum gases in a quasi-one-dimensional\ntube with dipole moment perpendicular to the tube direction. We deduce the\neffective one-dimensional interaction potential and show that this potential is\nnot purely repulsive, but rather has an attractive part due to high-order\nscattering processes through transverse excited states. The attractive part can\ninduce bound state and cause scattering resonances. This represents the dipole\ninduced resonance in low-dimension. We work out an unconventional behavior of\nlow-energy phase shift for this effective potential and show how it evolves\nacross a resonance. Based on the phase shift, the interaction energy of\nspinless bosons is obtained using asymptotic Bethe ansatz. Despite of\nlong-range nature of dipolar interaction, we find that a behavior similar as\nshort-range Lieb-Linger gas emerges at the resonance regime."
    },
    {
        "anchor": "Dissipation-induced topological insulators: A no-go theorem and a recipe: Nonequilibrium conditions are traditionally seen as detrimental to the\nappearance of quantum-coherent many-body phenomena, and much effort is often\ndevoted to their elimination. Recently this approach has changed: It has been\nrealized that driven-dissipative dynamics could be used as a resource. By\nproper engineering of the reservoirs and their couplings to a system, one may\ndrive the system towards desired quantum-correlated steady states, even in the\nabsence of internal Hamiltonian dynamics. An intriguing category of equilibrium\nmany-particle phases are those which are distinguished by topology rather than\nby symmetry. A natural question thus arises: which of these topological states\ncan be achieved as the result of dissipative Lindblad-type (Markovian)\nevolution? Beside its fundamental importance, it may offer novel routes to the\nrealization of topologically-nontrivial states in quantum simulators,\nespecially ultracold atomic gases. Here I give a general answer for Gaussian\nstates and quadratic Lindblad evolution, mostly concentrating on the example of\n2D Chern insulator states. I prove a no-go theorem stating that a finite-range\nLindbladian cannot induce finite-rate exponential decay towards a unique\ntopological pure state above 1D. I construct a recipe for creating such state\nby exponentially-local dynamics, or a mixed state arbitrarily close to the\ndesired pure one via finite-range dynamics. I also address the cold-atom\nrealization, classification, and detection of these states. Extensions to other\ntypes of topological insulators and superconductors are also discussed.",
        "positive": "On the momentum of solitons and vortex rings in a superfluid: This paper is devoted to the calculation of the momentum of localized\nexcitations, such as solitons and vortex rings, moving in a superfluid. The\ndirect calculation of the momentum by integration of the mass flux density\nresults in a badly-converging integral. I suggest a method for the\nrenormalization of the integral with the explicit separation of a term related\nto the vortex line. This term can be calculated explicitly and gives the main\ncontribution for the rings whose size is large compared to the healing length.\nI compare my method with the Jones and Roberts prescription for the\nrenormalization. I investigate the case of a uniform superfluid, and that of a\nsuperfluid in a cylindrical trap. I discuss the calculation of the jump in the\nphase of the order parameter and obtain a simple estimate for this jump for a\nlarge ring in the trap."
    },
    {
        "anchor": "Relaxation of Bosons in One Dimension and the Onset of Dimensional\n  Crossover: We study ultra-cold bosons out of equilibrium in a one-dimensional (1D)\nsetting and probe the breaking of integrability and the resulting relaxation at\nthe onset of the crossover from one to three dimensions. In a quantum Newton's\ncradle type experiment, we excite the atoms to oscillate and collide in an\narray of 1D tubes and observe the evolution for up to 4.8 seconds (400\noscillations) with minimal heating and loss. By investigating the dynamics of\nthe longitudinal momentum distribution function and the transverse excitation,\nwe observe and quantify a two-stage relaxation process. In the initial stage\nsingle-body dephasing reduces the 1D densities, thus rapidly drives the 1D gas\nout of the quantum degenerate regime. The momentum distribution function\nasymptotically approaches the distribution of quasimomenta (rapidities), which\nare conserved in an integrable system. In the subsequent long time evolution,\nthe 1D gas slowly relaxes towards thermal equilibrium through the collisions\nwith transversely excited atoms. Moreover, we tune the dynamics in the\ndimensional crossover by initializing the evolution with different imprinted\nlongitudinal momenta (energies). The dynamical evolution towards the relaxed\nstate is quantitatively described by a semiclassical molecular dynamics\nsimulation.",
        "positive": "Mean-field Dynamics of Spin-Orbit Coupled Bose-Einstein Condensates: Spin-orbit coupling (SOC), the interaction between the spin and momentum of a\nquantum particle, is crucial for many important condensed matter phenomena. The\nrecent experimental realization of SOC in neutral bosonic cold atoms provides a\nnew and ideal platform for investigating spin-orbit coupled quantum many-body\nphysics. In this Letter, we derive a generic Gross-Pitaevskii equation as the\nstarting point for the study of many-body dynamics in spin-orbit coupled\nBose-Einstein condensates. We show that different laser setups for realizing\nthe same SOC may lead to different mean field dynamics. Various ground state\nphases (stripe, phase separation, etc.) of the condensate are found in\ndifferent parameter regions. A new oscillation period induced by the SOC,\nsimilar to the Zitterbewegung oscillation, is found in the center of mass\nmotion of the condensate."
    },
    {
        "anchor": "Frustration- and doping-induced magnetism in a Fermi-Hubbard simulator: Geometrical frustration in strongly correlated systems can give rise to a\nplethora of novel ordered states and intriguing magnetic phases, such as\nquantum spin liquids. Promising candidate materials for such phases can be\ndescribed by the Hubbard model on an anisotropic triangular lattice, a\nparadigmatic model capturing the interplay between strong correlations and\nmagnetic frustration. However, the fate of frustrated magnetism in the presence\nof itinerant dopants remains unclear, as well as its connection to the doped\nphases of the square Hubbard model. Here we investigate the local spin order of\na Hubbard model with controllable frustration and doping, using ultracold\nfermions in anisotropic optical lattices continuously tunable from a square to\na triangular geometry. At half-filling and strong interactions $U/t \\sim 9$, we\nobserve at the single-site level how frustration reduces the range of magnetic\ncorrelations and drives a transition from a collinear N\\'eel antiferromagnet to\na short-range correlated 120$^{\\circ}$ spiral phase. Away from half-filling,\nthe triangular limit shows enhanced antiferromagnetic correlations on the\nhole-doped side and a reversal to ferromagnetic correlations at particle\ndopings above 20%, hinting at the role of kinetic magnetism in frustrated\nsystems. This work paves the way towards exploring possible chiral ordered or\nsuperconducting phases in triangular lattices and realizing t-t' square lattice\nHubbard models that may be essential to describe superconductivity in cuprate\nmaterials.",
        "positive": "Quantum quench and non-equilibrium dynamics in lattice-confined spinor\n  condensates: We present an experimental study on non-equilibrium dynamics of a spinor\ncondensate after it is quenched across a superfluid to Mott insulator (MI)\nphase transition in cubic lattices. Intricate dynamics consisting of\nspin-mixing oscillations at multiple frequencies are observed in time\nevolutions of the spinor condensate localized in deep lattices after the\nquantum quench. Similar spin dynamics also appear after spinor gases in the MI\nphase are suddenly moved away from their ground states via quenching magnetic\nfields. We confirm these observed spectra of spin-mixing dynamics can be\nutilized to reveal atom number distributions of an inhomogeneous system, and to\nstudy transitions from two-body to many-body dynamics. Our data also imply the\nnon-equilibrium dynamics depend weakly on the quench speed but strongly on the\nlattice potential. This enables precise measurements of the spin-dependent\ninteraction, a key parameter determining the spinor physics."
    },
    {
        "anchor": "An instanton-like excitation of a discrete time crystal: Spontaneous symmetry breaking and elementary excitation are two of the\npillars of condensed matter physics that are closely related to each other. The\nsymmetry and its spontaneous breaking not only control the dynamics and\nspectrum of elementary excitations, but also determine their underlying\nstructures. In this paper, we study the excitation properties of a\nnon-equilibrium quantum matter: a discrete time crystal phase that\nspontaneously breaks the temporal translational symmetry. It is shown that such\nan intriguing symmetry breaking allows an instanton-like excitation that\nrepresents a tunneling between two \"degenerate\" time crystal phases.\nFurthermore, we also observe a dynamical transition point at which the\ninstanton \"size\" diverges, a reminiscence of the critical slowing down\nphenomenon in nonequilibrium statistic physics. A phenomenological theory has\nbeen proposed to understand the phase dynamics of the proposed system and the\nexperimental realization and detection have also been discussed.",
        "positive": "Anomalous quantum glass of bosons in a random potential in two\n  dimensions: We present a quantum Monte Carlo study of the \"quantum glass\" phase of the 2D\nBose-Hubbard model with random potentials at filling $\\rho=1$. In the narrow\nregion between the Mott and superfluid phases the compressibility has the form\n$\\kappa \\sim {\\rm exp}(-b/T^\\alpha)+c$ with $\\alpha <1$ and $c$ vanishing or\nvery small. Thus, at $T=0$ the system is either incompressible (a Mott glass)\nor nearly incompressible (a Mott-glass-like anomalous Bose glass). At stronger\ndisorder, where a glass reappears from the superfluid, we find a conventional\nhighly compressible Bose glass. On a path connecting these states, away from\nthe superfluid at larger Hubbard repulsion, a change of the disorder strength\nby only $10\\%$ changes the low-temperature compressibility by more than four\norders of magnitude, lending support to two types of glass states separated by\na phase transition or a sharp cross-over."
    },
    {
        "anchor": "Ground-state Properties of Tonks-Girardeau Gas in One Dimensional\n  Periodic Potential: The relations among the occupation number of the lowest natural orbital\n(ONLNO), momentum distributions (MD) and off-diagonal long-range element\n(ODLRE) of the reduced single-particle density matrix (RSPDM) are studied while\nTonks-Girardeau gas in one dimensional periodic potential is in the ground\nstate. For $N$-body systems of large enough, RSPDM and its lowest natural\norbital do not vary with $N$ in overlapped areas in commensurate and\nincommensurate cases correspondingly. In commensurate case, the ODLRE is\nexponential attenuation with $N$, which results in that the ONLNO and MD are\ninvariant with $N$. While in contrast, in incommensurate case, the off-diagonal\nelements are inversely proportional to $\\sqrt{N}$, which results in the\ndifferent behavior of the ONLNO and MD.",
        "positive": "Relevance of Bose-Einstein Condensation to the Interference of Two\n  Independent Bose Gases: Interference of two independently prepared ideal Bose gases is discussed, on\nthe basis of the idea of measurement-induced interference: even if the number\nof each gas is individually fixed finite and the symmetry of the system is not\nbroken, an interference pattern is observed on each single snapshot. The key\nrole is played by the Hanbury Brown and Twiss effect, which leads to an\noscillating pattern of the cloud of identical atoms. Then, how essential is the\nBose-Einstein condensation to the interference? We describe the ideal Bose\ngases trapped respectively in two spatially separated 3D harmonic traps at a\nfinite temperature as canonical ensembles with fixed numbers of atoms, and\ncompute the full statistics of the snapshot profiles of the expanding and\noverlapping gases released from the traps. We obtain a simple formula, which\nshows that the average fringe spectrum (average fringe contrast) is given by\nthe purity of each gas. The purity is known to be a good measure of\ncondensation, and this result clarifies the relevance of the condensation to\nthe interference. The fluctuation of the interference spectrum is also studied,\nand it is shown that the fluctuation is vanishingly small below the critical\ntemperature, while it is nonvanishing above. This implies that interference\npattern is certainly observed on every snapshot below the critical temperature.\nThe fact that the number of atoms is fixed in the canonical ensemble is crucial\nto this vanishing fluctuation."
    },
    {
        "anchor": "Pattern formation in one-dimensional polaron systems and temporal\n  orthogonality catastrophe: Recent studies have demonstrated that higher than two-body bath-impurity\ncorrelations are not important for quantitatively describing the ground state\nof the Bose polaron. Motivated by the above, we employ the so-called Gross\nAnsatz (GA) approach to unravel the stationary and dynamical properties of the\nhomogeneous one-dimensional Bose-polaron for different impurity momenta and\nbath-impurity couplings. We explicate that the character of the equilibrium\nstate crossovers from the quasi-particle Bose polaron regime to the\ncollective-excitation stationary dark-bright soliton for varying impurity\nmomentum and interactions. Following an interspecies interaction quench the\ntemporal orthogonality catastrophe is identified, provided that bath-impurity\ninteractions are sufficiently stronger than the intraspecies bath ones, thus\ngeneralizing the results of the confined case. This catastrophe originates from\nthe formation of dispersive shock wave structures associated with the\nzero-range character of the bath-impurity potential. For initially moving\nimpurities, a momentum transfer process from the impurity to the dispersive\nshock waves via the exerted drag force is demonstrated, resulting in a final\npolaronic state with reduced velocity. Our results clearly demonstrate the\ncrucial role of non-linear excitations for determining the behavior of the\none-dimensional Bose polaron.",
        "positive": "Pseudopotentials for Two-dimentional Ultracold Scattering in the\n  Presence of Synthetic Spin-orbit-coupling: We derive a pseudopotential in two dimensions (2D) with the presence of a 2D\nRashba spin-orbit-coupling (SOC), following the same spirit of frame\ntransformation in {[}Phys. Rev. A 95, 020702(R) (2017){]}. The frame\ntransformation correctly describes the non-trivial phase accumulation and\npartial wave couplings due to the presence of SOC and gives rise to a different\npseudopotential than the free-space one, even when the length scale of SOC is\nsignificantly larger than the two-body potential range. As an application, we\napply our pseudopotential with the Lippmann-Schwinger equation to obtain an\nanalytical scattering matrix. To demonstrate the validity, we compare our\nresults with a numerical scattering calculation of finite-range potential and\nshow perfect agreement over a wide range of scattering energy and SOC strength.\nOur results also indicate that the differences between our pseudopotential and\nthe original free-space pseudopotential are essential to reproduce scattering\nobservables correctly."
    },
    {
        "anchor": "Crafting the dynamical structure of synchronization by harnessing\n  bosonic multilevel cavity QED: Many-body cavity QED experiments are established platforms to tailor and\ncontrol the collective responses of ensembles of atoms, interacting through one\nor more common photonic modes. The rich diversity of dynamical phases they can\nhost, calls for a unified framework. Here we commence this program by showing\nthat a cavity QED simulator assembled from $N$-levels bosonic atoms, can\nreproduce and extend the possible dynamical responses of collective observables\noccurring after a quench. Specifically, by initializing the atoms in classical\nor quantum states, or by leveraging intra-levels quantum correlations, we craft\non demand the entire synchronization/desynchronization dynamical crossover of\nan exchange model for $SU(N)$ spins. We quantitatively predict the onset of\ndifferent dynamical responses by combining the Liouville-Arnold theorem on\nclassical integrability with an ansatz for reducing the collective evolution to\nan effective few-body dynamics. Among them, we discover a synchronized chaotic\nphase induced by quantum correlations and associated to a first order\nnon-equilibrium transition in the Lyapunov exponent of collective atomic\ndynamics. Our outreach includes extensions to other spin-exchange quantum\nsimulators and a universal conjecture for the dynamical reduction of\nnon-integrable all-to-all interacting systems.",
        "positive": "Breathing mode of two-dimensional atomic Fermi gases in harmonic traps: For two-dimensional (2D) atomic Fermi gases in harmonic traps, the SO(2,1)\nsymmetry is broken by the interatomic interaction explicitly via the contact\ncorrelation operator. Consequently the frequency of the breathing mode\n$\\omega_B$ of the 2D Fermi gas can be different from $2\\omega_0$, with\n$\\omega_0$ the trapping frequency of harmonic potentials. At zero temperature,\nwe use the sum rules of density correlation functions to yield upper bounds for\n$\\omega_B$. We further calculate $\\omega_B$ through the Euler equations in the\nhydrodynamic regime. The obtained value of $\\omega_B$ satisfies the upper\nbounds and shows deviation from $2\\omega_0$ which can be as large as about 8%."
    },
    {
        "anchor": "Dynamical preparation of laser-excited anisotropic Rydberg crystals in\n  2D optical lattices: We describe the dynamical preparation of anisotropic crystalline phases\nobtained by laser-exciting ultracold Alkali atoms to Rydberg p-states where\nthey interact via anisotropic van der Waals interactions. We develop a time-\ndependent variational mean field ansatz to model large, but finite\ntwo-dimensional systems in experimentally accessible parameter regimes, and we\npresent numerical simulations to illustrate the dynamical formation of\nanisotropic Rydberg crystals.",
        "positive": "Interaction-Enhanced Group Velocity of Bosons in the Flat Band of an\n  Optical Kagome Lattice: Geometric frustration of particle motion in a kagome lattice causes the\nsingle-particle band structure to have a flat s-orbital band. We probe this\nband structure by exciting a Bose-Einstein condensate into excited Bloch states\nof an optical kagome lattice, and then measuring the group velocity through the\natomic momentum distribution. We find that interactions renormalize the band\nstructure of the kagome lattice, greatly increasing the dispersion of the third\nband that, according to non-interacting band theory, should be nearly\nnon-dispersing. Measurements at various lattice depths and gas densities agree\nquantitatively with predictions of the lattice Gross-Pitaevskii equation,\nindicating that the observed distortion of band structure is caused by the\ndisortion of the overall lattice potential away from the kagome geometry by\ninteractions."
    },
    {
        "anchor": "Spin Turbulence in a Trapped Spin-1 Spinor Bose--Einstein Condensate: We numerically study spin turbulence in a two-dimensional trapped spin-1\nspinor Bose--Einstein condensate, focusing on the energy spectrum. The spin\nturbulence in the trapped system is generated by instability of the helical\nstructure of the spin density vector in the initial state. Our numerical\ncalculation finds that in the trapped system the spectrum of the spin-dependent\ninteraction energy in the ferromagnetic case exhibits a -7/3 power law, which\nwas confirmed in a uniform system by our previous study. The relation between\nthe -7/3 power law and the motion of the spin density vector is discussed by\ninvestigating the orbits of dynamical variables in the spin space.",
        "positive": "Extension of the Generalized Hydrodynamics to the Dimensional Crossover\n  Regime: In an effort to address integrability breaking in cold gas experiments, we\nextend the integrable hydrodynamics of the 1d Lieb-Liniger model with two\nadditional components representing the population of atoms in the first and\nsecond transverse excited states, thus enabling a description of quasi-1d\ncondensates. Collisions between different components are accounted for through\nthe inclusion of a Boltzmann-type collision integral in the hydrodynamic\nequation. Contrary to standard generalized hydrodynamics, our extended model\ncaptures thermalization of the condensate at a rate consistent with\nexperimental observations from a quantum Newton's cradle setup."
    },
    {
        "anchor": "Quench dynamics of a confined ultracold Fermi gas: Direct visibility of\n  the Goldstone mode in the single-particle excitations: We present a numerical study of a confined ultracold Fermi gas showing that\nthe Goldstone mode of the BCS gap is directly visible in the dynamics of the\nsingle-particle excitations. To this end, we investigate the low-energy dynamic\nresponse of a confined Fermi gas to a rapid change of the scattering length\n(i.e., an interaction quench). Based on a fully microscopic time-dependent\ndensity-matrix approach within the Bogoliubov-de Gennes formalism that includes\na 3D harmonic confinement we simulate and identify the emergence of the\nGoldstone mode in a cigar-shaped $^6$Li gas. We show that the quench leads to a\nlow-frequency in-phase oscillation of the single-particle occupations. Complete\ninversion is achieved for occupations corresponding to the lowest-lying\nsingle-particle states.",
        "positive": "Bogoliubov Theory of acoustic Hawking radiation in Bose-Einstein\n  Condensates: We apply the microscopic Bogoliubov theory of dilute Bose-Einstein\ncondensates to analyze quantum and thermal fluctuations in a flowing atomic\ncondensate in the presence of a sonic horizon. For the simplest case of a\nstep-like horizon, closed-form analytical expressions are found for the\nspectral distribution of the analog Hawking radiation and for the density\ncorrelation function. The peculiar long-distance density correlations that\nappear as a consequence of the Hawking emission features turns out to be\nreinforced by a finite initial temperature of the condensate. The analytical\nresults are in good quantitative agreement with first principle numerical\ncalculations."
    },
    {
        "anchor": "Phase separation of a two-component dipolar Bose-Einstein condensate in\n  the quasi-one-dimensional and quasi-two-dimensional regime: We consider a two-component Bose-Einstein condensate, which contains atoms\nwith magnetic dipole moments aligned along the $z$ direction (labeled as\ncomponent 1) and nonmagnetic atoms (labeled as component 2). The problem is\nstudied by means of exact numerical simulations. The effects of dipole-dipole\ninteraction on phase separations are investigated. It is shown that, in the\nquasi-one-dimensional regime, the atoms in component 2 are squeezed out when\nthe dimensionless dipolar strength parameter is small, whereas the atoms in\ncomponent 1 are pushed out instead when the parameter is large. This is in\ncontrast to the phenomena in the quasi-two-dimensional regime. These two\ncomponents are each kicked out by the other in the quasi-one-dimensional regime\nand this phenomenon is discussed as well.",
        "positive": "Quantum droplets with particle imbalance in one-dimensional optical\n  lattices: We study the formation of particle-imbalanced quantum droplets in a\none-dimensional optical lattice containing a binary bosonic mixture at zero\ntemperature. To understand the effects of the imbalance from both the few- and\nmany-body perspectives, we employ density matrix renormalization group (DMRG)\nsimulations and perform the extrapolation to the thermodynamic limit. In\ncontrast to the particle-balanced case, not all bosons are paired, resulting in\nan interplay between bound states and individual atoms that leads to intriguing\nphenomena. Quantum droplets manage to sustain a small particle imbalance,\nresulting in an effective magnetization. However, as the imbalance is further\nincreased, a critical point is eventually crossed, and the droplets start to\nexpel the excess particles while the magnetization in the bulk remains\nconstant. Remarkably, the unpaired particles on top of the quantum droplet\neffectively form a super Tonks-Girardeau (hard-rod) gas. The expulsion point\ncoincides with the critical density at which the size of the super\nTonks-Girardeau gas matches the size of the droplet."
    },
    {
        "anchor": "Eigenfunction structure and scaling of two interacting particles in the\n  one-dimensional Anderson model: The localization properties of eigenfunctions for two interacting particles\nin the one-dimensional Anderson model are studied for system sizes up to\n$N=5000$ sites corresponding to a Hilbert space of dimension $\\approx 10^7$\nusing the Green function Arnoldi method. The eigenfunction structure is\nillustrated in position, momentum and energy representation, the latter\ncorresponding to an expansion in non-interacting product eigenfunctions.\nDifferent types of localization lengths are computed for parameter ranges in\nsystem size, disorder and interaction strengths inaccessible until now. We\nconfirm that one-parameter scaling theory can be successfully applied provided\nthat the condition of $N$ being significantly larger than the one-particle\nlocalization length $L_1$ is verified. The enhancement effect of the\ntwo-particle localization length $L_2$ behaving as $L_2\\sim L_1^2$ is clearly\nconfirmed for a certain quite large interval of optimal interactions strengths.\nFurther new results for the interaction dependence in a very large interval, an\nenergy value outside the band center, and different interaction ranges are\nobtained.",
        "positive": "Solitons as the early stage of quasicondensate formation during\n  evaporative cooling: We calculate the evaporative cooling dynamics of trapped one-dimensional\nBose-Einstein condensates for parameters leading to a range of condensates and\nquasicondensates in the final equilibrium state. We confirm that solitons are\ncreated during the evaporation process, but always eventually dissipate during\nthermalisation. The distance between solitons at the end of the evaporation\nramp matches the coherence length in the final thermal state. Calculations were\nmade using the classical fields method. They bridge the gap between the phase\ndefect picture of the Kibble-Zurek mechanism and the long-wavelength phase\nfluctuations in the thermal state."
    },
    {
        "anchor": "Dynamics of Bose-Einstein condensates under anharmonic trap: The dynamics of weakly interacting three-dimensional Bose-Einstein\ncondensates (BECs), trapped in external axially symmetric plus anharmonic\ndistortion potential are studied. Within a variational approach and\ntime-dependent Gross-Pitaevskii equation, the coupled condensate width\nequations are derived. By modulating anharmonic distortion of the trapping\npotential, nonlinear features are studied numerically and illustrated\nanalytically, such as mode coupling of oscillation modes, and resonances.\nFurthermore, the stability of attractive interaction BEC in both repulsive and\nattractive anharmonic distortion is examined. We demonstrate that a small\nrepulsive and attractive anharmonic distortion is effective in reducing\n(extending) the condensate stability region since it decreases (increases) the\ncritical number of atoms in the trapping potential.",
        "positive": "Fourth cluster and virial coefficients of a unitary Fermi gas for an\n  arbitrary mass ratio: We calculate the fourth cluster coefficients of the homogeneous unitary spin\n1/2 Fermi gas as functions of the internal-state mass ratio, over intervals\nconstrained by the 3- or 4-body Efimov effect. For this we use our 2016\nconjecture (validated for equal masses by Hou and Drut in 2020) in a\nnumerically efficient formulation making the sum over angular momentum converge\nfaster, which is crucial at large mass ratio. The mean cluster coefficient,\nrelevant for equal chemical potentials, is not of constant sign and increases\nrapidly close to the Efimovian thresholds. We also get the fourth virial\ncoefficients, which we find to be very poor indicators of interaction-induced\n4-body correlations. We obtain analytically for all $n$ the cluster\ncoefficients of order $n$ + 1 for an infinity-mass impurity fermion, matching\nthe conjecture for $n=3$. Finally, in a harmonic potential, we predict a\nnon-monotonic behavior of the 3 + 1 cluster coefficient with trapping\nfrequency, near mass ratios where this coefficient vanishes in the homogeneous\ncase."
    },
    {
        "anchor": "Dynamics of spin-1 bosons in an optical lattice: spin mixing, quantum\n  phase revival spectroscopy and effective three-body interactions: We study the dynamics of spin-1 atoms in a periodic optical-lattice potential\nand an external magnetic field in a quantum quench scenario where we start from\na superfluid ground state in a shallow lattice potential and suddenly raise the\nlattice depth. The time evolution of the non-equilibrium state, thus created,\nshows collective collapse-and-revival oscillations of matter-wave coherence as\nwell as oscillations in the spin populations. We show that the complex pattern\nof these two types of oscillations reveals details about the superfluid and\nmagnetic properties of the initial many-body ground state. Furthermore, we show\nthat the strengths of the spin-dependent and spin-independent atom-atom\ninteractions can be deduced from the observations. The Hamiltonian that\ndescribes the physics of the final deep lattice not only contains two-body\ninteractions but also effective multi-body interactions, which arise due to\nvirtual excitations to higher bands. We derive these effective spin-dependent\nthree-body interaction parameters for spin-1 atoms and describe how spin-mixing\nis affected. Spinor atoms are unique in the sense that multi-body interactions\nare directly evident in the in-situ number densities in addition to the\nmomentum distributions. We treat both antiferromagnetic (e.g. $^{23}$Na atoms)\nand ferromagnetic (e.g. $^{87}$Rb and $^{41}$K) condensates.",
        "positive": "Black-hole radiation in Bose-Einstein condensates: We study the phonon fluxes emitted when the condensate velocity crosses the\nspeed of sound, i.e., in backgrounds which are analogous to that of a black\nhole. We focus on elongated one dimensional condensates and on stationary\nflows. Our theoretical analysis and numerical results are based on the\nBogoliubov-de Gennes equation without further approximation. The spectral\nproperties of the fluxes and of the long distance density-density correlations\nare obtained, both with and without an initial temperature. In realistic\nconditions, we show that the condensate temperature dominates the fluxes and\nthus hides the presence of the spontaneous emission (the Hawking effect). We\nalso explain why the temperature amplifies the long distance correlations which\nare intrinsic to this effect. This confirms that the correlation pattern offers\na neat signature of the Hawking effect. Optimal conditions for observing the\npattern are discussed, as well as correlation patterns associated with\nscattering of classical waves. Flows associated with white holes are also\nconsidered."
    },
    {
        "anchor": "Renormalized analytic solution for the enstrophy cascade in\n  two-dimensional quantum turbulence: The forward enstrophy cascade in two-dimensional quantum turbulence in a\nsuperfluid film connected to a thermal bath is investigated using a\nFokker-Planck equation based on Kosterlitz-Thouless renormalization. The\nsteady-state cascade is formed by injecting vortex pairs of large initial\nseparation at a constant rate. They diffuse with a constant flux to smaller\nscales, finally annihilating when reaching the core size. The energy spectrum\nvaries as $k^{-3}$, similar to the spectrum known for 2D classical-fluid\nenstrophy cascades. The dynamics of the cascade can also be studied, and for\nthe case of a sharply peaked initial vortex-pair distribution, it takes about\nfour eddy turnover times for the system to evolve to the decaying $k^{-3}$\ncascade, in agreement with recent computer simulations. These insights into the\nnature of the cascade also allow a better understanding of the phase-ordering\nprocess of temperature-quenched 2D superfluids, where the decay of the\nvorticity is found to proceed via the turbulent cascade. This connection with\nturbulence may be a fundamental characteristic of phase-ordering in general.",
        "positive": "Implementation of a stable, high-power optical lattice for quantum gas\n  microscopy: We describe the design and implementation of a stable high-power 1064 nm\nlaser system to generate optical lattices for experiments with ultracold\nquantum gases. The system is based on a low-noise laser amplified by an array\nof four heavily modified, high-power fiber amplifiers. The beam intensity is\nstabilized and controlled with a nonlinear feedback loop. Using real-time\nmonitoring of the resulting optical lattice, we find the stability of the\nlattice site positions to be well below the lattice spacing over the course of\nhours. The position of the harmonic trap produced by the Gaussian envelope of\nthe lattice beams is stable to about one lattice spacing and the long-term\n(six-month) relative RMS stability of the lattice spacing itself is 0.5%."
    },
    {
        "anchor": "Non-Hermitian Linear Response Theory: Linear response theory lies at the heart of quantum many-body physics because\nit builds up connections between the dynamical response to an external probe\nand correlation functions at equilibrium. Here we consider the dynamical\nresponse of a Hermitian system to a non-Hermitian probe, and we develop a\nnon-Hermitian linear response theory that can also relate this dynamical\nresponse to equilibrium properties. As an application of our theory, we\nconsider the real-time dynamics of momentum distribution induced by one-body\nand two-body dissipations. We find that, for many cases, the dynamics of\nmomentum occupation and the width of momentum distribution obey the same\nuniversal function, governed by the single-particle spectral function. We also\nfind that, for critical state with no well-defined quasi-particles, the\ndynamics are slower than normal state and our theory provides a model\nindependent way to extract the critical exponent. We apply our results to\nanalyze recent experiment on the Bose-Hubbard model and find surprising good\nagreement between theory and experiment. We also propose to further verify our\ntheory by carrying out a similar experiment on a one-dimensional Luttinger\nliquid.",
        "positive": "Dynamic response of spin-2 bosons in one-dimensional optical lattices: We investigate the spin-2 chain model corresponding to the small hopping\nlimit of the spin-2 Bose-Hubbard model using density-matrix\nrenormalization-group and time-evolution techniques. We calculate both static\ncorrelation functions and the dynamic structure factor. The dynamic structure\nfactor in the dimerized phase differs significantly between parameters near the\nSU(5)-symmetric point and those deeper in the phase where the dimerization is\nstrong. In the former case, most of the spectral weight is concentrated in a\nsingle excitation line, while in the latter case, a broad excitation continuum\nshows up. For the trimerized phase, we find gapless excitations at momenta\n$k=\\pm2\\pi/3$ in agreement with previous results, although the visibility of\nthese excitations in the dynamic spin response depends strongly on the specific\nparameters. We also consider parameters for specific atoms which may be\nrelevant for future optical-lattice experiments."
    },
    {
        "anchor": "Collective phenomena in quasi-two-dimensional fermionic polar molecules:\n  band renormalization and excitons: We theoretically analyze a quasi-two-dimensional system of fermionic polar\nmolecules in a harmonic transverse confining potential. The renormalized energy\nbands are calculated by solving the Hartree-Fock equation numerically for\nvarious trap and dipolar interaction strengths. The inter-subband excitations\nof the system are studied in the conserving time-dependent Hartree-Fock (TDHF)\napproximation from the perspective of lattice modulation spectroscopy\nexperiments. We find that the excitation spectrum consists of both\ninter-subband particle-hole excitation continuums and anti-bound excitons,\narising from the anisotropic nature of dipolar interactions. The excitonic\nmodes capture the majority of the spectral weight. We also evaluate the\ninter-subband transition rates in order to investigate the nature of the\nexcitonic modes and find that they are anti-bound states formed from\nparticle-hole excitations arising from several subbands. Our results indicate\nthat the excitonic effects are present for interaction strengths and\ntemperatures accessible in current experiments with polar molecules.",
        "positive": "Quantum fluctuations in a strongly interacting Bardeen-Cooper-Schrieffer\n  polariton condensate at thermal equilibrium: Microcavity electron-hole-photon systems in two-dimensions are long\nanticipated to exhibit a crossover from Bose-Einstein condensate (BEC) to\nBardeen-Cooper-Schrieffer (BCS) superfluid, when carrier density is tuned to\nreach the Mott transition density. Yet, theoretical understanding of such a\nBEC-BCS crossover largely relies on the mean-field framework and the nature of\nthe carriers at the crossover remains unclear to some extent. Here, motivated\nby the recent demonstration of a BCS polariton laser {[}Hu \\textit{et al.},\narXiv:1902.00142{]} and based on a simplified short-range description of the\nelectron-hole attraction, we examine the role of quantum fluctuations in an\nexciton-polariton condensate at thermal equilibrium and determine the number of\ndifferent type carriers at the crossover beyond mean-field. Near Mott density\nand with ultra-strong light-matter coupling, we find an unexpectedly large\nphase window for a strongly correlated BCS polariton condensate, where both\nfermionic Bogoliubov quasi-particles and bosonic excitons are significantly\npopulated and strongly couple to photons. We predict its photoluminescence\nspectra and show that the upper polariton energy gets notably renormalized,\ngiving rise to a high-energy side-peak at large carrier density, as observed in\nrecent experiments."
    },
    {
        "anchor": "Quantum Phases of Dipolar Bosons in Bilayer Geometry: We investigate the quantum phases of hard-core dipolar bosons confined to a\nsquare lattice in a bilayer geometry. Using exact theoretical techniques, we\ndiscuss the many-body effects resulting from pairing of particles across layers\nat finite density, including a novel pair supersolid phase, superfluid and\nsolid phases. These results are of direct relevance to experiments with polar\nmolecules and atoms with large magnetic dipole moments trapped in optical\nlattices.",
        "positive": "Fermionic condensation in ultracold atoms, nuclear matter and neutron\n  stars: We investigate the Bose-Einstein condensation of fermionic pairs in three\ndifferent superfluid systems: ultracold and dilute atomic gases, bulk neutron\nmatter, and neutron stars. In the case of dilute gases made of fermionic atoms\nthe average distance between atoms is much larger than the effective radius of\nthe inter-atomic potential. Here the condensation of fermionic pairs is\nanalyzed as a function of the s-wave scattering length, which can be tuned in\nexperiments by using the technique of Feshbach resonances from a small and\nnegative value (corresponding to the Bardeen-Cooper-Schrieffer (BCS) regime of\nCooper Fermi pairs) to a small and positive value (corresponding to the regime\nof the Bose-Einstein condensate (BEC) of molecular dimers), crossing the\nunitarity regime where the scattering length diverges. In the case of bulk\nneutron matter the s-wave scattering length of neutron-neutron potential is\nnegative but fixed, and the condensate fraction of neutron-neutron pairs is\nstudied as a function of the total neutron density. Our results clearly show a\nBCS-quasiunitary-BCS crossover by increasing the neutron density. Finally, in\nthe case of neutron stars, where again the neutron-neutron scattering length is\nnegative and fixed, we determine the condensate fraction as a function of the\ndistance from the center of the neutron star, finding that the maximum\ncondensate fraction appears in the crust of the neutron star."
    },
    {
        "anchor": "Tuning the mobility of a driven Bose-Einstein condensate via diabatic\n  Floquet bands: We study the response of ultracold atoms to a weak force in the presence of a\ntemporally strongly modulated optical lattice potential. It is experimentally\ndemonstrated that the strong ac-driving allows for a tailoring of the mobility\nof a dilute atomic Bose-Einstein condensate with the atoms moving ballistically\neither along or against the direction of the applied force. Our results are in\nagreement with a theoretical analysis of the Floquet spectrum of a model\nsystem, thus revealing the existence of diabatic Floquet bands in the atom's\nband spectra and highlighting their role in the non-equilibrium transport of\nthe atoms.",
        "positive": "Spatial tomography of individual atoms in a quantum gas microscope: We demonstrate a method to determine the position of single atoms in a\nthree-dimensional optical lattice. Atoms are sparsely loaded from a\nfar-off-resonant optical tweezer into a few vertical planes of a cubic optical\nlattice positioned near a high-resolution microscope objective. In a single\nrealization of the experiment, we pin the atoms in deep lattices and then\nacquire multiple fluorescence images with single-site resolution. The objective\nis translated between images, bringing different lattice planes of the lattice\ninto focus. The applicability of our method is assessed using simulated\nfluorescence images, where the atomic filling fraction in the lattice is\nvaried. This opens up the possibility of extending the domain of quantum\nsimulation using quantum gas microscopes from two to three dimensions."
    },
    {
        "anchor": "Higher first Chern numbers in one dimensional Bose-Fermi mixtures: We propose to use a one-dimensional system consisting of identical fermions\nin a periodically driven lattice immersed in a Bose gas, to realise topological\nsuperfluid phases with Chern numbers larger than 1. The bosons mediate an\nattractive induced interaction between the fermions, and we derive a simple\nformula to analyse the topological properties of the resulting pairing. When\nthe coherence length of the bosons is large compared to the lattice spacing and\nthere is a significant next-nearest neighbour hopping for the fermions, the\nsystem can realise a superfluid with Chern number +/- 2. We show that this\nphase is stable in a large region of the phase diagram as a function of the\nfilling fraction of the fermions and the coherence length of the bosons. Cold\natomic gases offer the possibility to realise the proposed system using\nwell-known experimental techniques.",
        "positive": "The roton-assisted chiral p-wave superfluid in a quasi-two-dimensional\n  dipolar Bose-Fermi quantum gas mixture: The chiral p-wave (p_x \\pm ip_y) superfluid has attracted significant\nattention in recent years, mainly because its vortex core supports a Majorana\nfermion which, due to its non-Abelian statistics, can be explored for\nimplementing topological quantum computation. Mixing dipolar bosons with\nfermions in quasi-two-dimensional (2D) space offers the opportunity to use the\nroton minimum as a tool for engineering the phonon-induced attractive\ninteraction between fermions. We study, within the Hartree-Fock-Bogoliubov\napproach, the p-wave superfluid pairings in a quasi-2D dipolar Bose-Fermi\nmixture. We show that enhancing the induced interaction by lowering the roton\nminimum can affect the stability property of the mixture as well as the\neffective mass of the fermions in an important way. We also show that one can\ntune the system to operate in stable regions where chiral p-wave superfluid\npairings can be resonantly enhanced by lowering the energy cost of the phonons\nnear the roton minimum."
    },
    {
        "anchor": "Quantized conductance through the quantum evaporation of bosonic atoms: We analyze theoretically the quantization of conductance occurring with cold\nbosonic atoms trapped in two reservoirs connected by a constriction with an\nattractive gate potential. We focus on temperatures slightly above the\ncondensation threshold in the reservoirs. We show that a conductance step\noccurs, coinciding with the appearance of a condensate in the constriction.\nConductance relies on a collective process involving the quantum condensation\nof an atom into an elementary excitation and the subsequent quantum evaporation\nof an atom, in contrast with ballistic fermion transport. The value of the\nbosonic conductance plateau is strongly enhanced compared to fermions and\nexplicitly depends on temperature. We highlight the role of weak repulsive\ninteractions between the bosons in preventing them from collapsing into the\nconstriction.",
        "positive": "SU(2) Ginzburg-Landau theory for degenerate Fermi gases with synthetic\n  non-Abelian gauge fields: The non-Abelian gauge fields play a key role in achieving novel quantum\nphenomena in condensed-matter and high-energy physics. Recently, the synthetic\nnon-Abelian gauge fields have been created in the neutral degenerate Fermi\ngases, and moreover, generate many exotic effects. All the previous predictions\ncan be well understood by the microscopic Bardeen-Cooper-Schrieffer theory. In\nthis work, we establish an SU(2) Ginzburg-Landau theory for degenerate Fermi\ngases with the synthetic non-Abelian gauge fields. We firstly address a\nfundamental problem how the non-Abelian gauge fields, imposing originally on\nthe Fermi atoms, affect the pairing field with no extra electric charge by a\nlocal gauge-field theory,and then obtain the first and second SU(2)\nGinzburg-Landau equations. Based on these obtained SU(2) Ginzburg-Landau\nequations, we find that the superfluid critical temperature of the intra-\n(inter-) band pairing increases (decreases) linearly, when increasing the\nstrength of the synthetic non-Abelian gauge fields. More importantly, we\npredict a novel SU(2) non-Abelian Josephson effect, which can be used to design\na new atomic superconducting quantum interference device."
    },
    {
        "anchor": "Realization of a distributed Bragg reflector for propagating guided\n  matter waves: We report on the experimental realization of a Bragg reflector for guided\nmatter waves. A Bose-Einstein condensate with controlled velocity distribution\nimpinges onto an attractive optical lattice of finite length and directly\nprobes its band structure. We study the dynamics of the scattering by this\npotential and compare the results with simple one-dimensional models. We\nemphasize the importance of taking into account the gaussian envelope of the\noptical lattice which gives rise to Bragg cavity effects. Our results are a\nfurther step towards integrated atom optics setups for quasi-cw matter waves.",
        "positive": "Quantum dark solitons in Bose gas confined in a hard wall box: Schr\\\"odinger equation for Bose gas with repulsive contact interactions in\none-dimensional space may be solved analytically with the help of the Bethe\nansatz if we impose periodic boundary conditions. It was shown that in such a\nsystem there exist many-body eigenstates directly corresponding to dark soliton\nsolutions of the mean-field equation. The system is still integrable if one\nswitches from the periodic boundary conditions to an infinite square well\npotential. The corresponding eigenstates were constructed by M. Gaudin. We\nanalyze weak interaction limit of Gaudin's solutions and identify\nparametrization of eigenstates strictly connected with single and multiple dark\nsolitons. Numerical simulations of detection of particle's positions reveal\ndark solitons in the weak interaction regime and their quantum nature in the\npresence of strong interactions."
    },
    {
        "anchor": "Collisionless sound of bosonic superfluids in lower dimensions: The superfluidity of low-temperature bosons is well established in the\ncollisional regime. In the collisionless regime, however, the presence of\nsuperfluidity is not yet fully clarified, in particular in lower spatial\ndimensions. Here we compare the Vlasov-Landau equation, which does not take\ninto account the superfluid nature of the bosonic system, with the\nAndreev-Khalatnikov equations, which instead explicitly contain a superfluid\nvelocity. We show that recent experimental data of the sound mode in a\ntwo-dimensional collisionless Bose gas of $^{87}$Rb atoms are in good agreement\nwith both theories but the sound damping is better reproduced by the Andreev\n-Khalatnikov equations below the Berezinskii-Kosterlitz-Thouless critical\ntemperature $T_c$ while above $T_c$ the Vlasov-Landau results are closer to the\nexperimental ones. For one dimensional bosonic fluids, where experimental data\nare not yet available, we find larger differences between the sound velocities\npredicted by the two transport theories and, also in this case, the existence\nof a superfluid velocity reduces the sound damping.",
        "positive": "First-order superfluid-Mott-insulator transition for quantum optical\n  switching in cavity QED arrays with two cavity modes: We theoretically investigated the ground states of coupled arrays of cavity\nquantum electrodynamical (cavity QED) systems in presence of two photon modes.\nWithin the Gutzwiller-type variational approach, we found the first-order\nquantum phase transition between Mott insulating and superfluid phases as well\nas the conventional second-order one. The first-order phase transition was\nfound only for specific types of emitter models, and its physical origin is\nclarified based on the analytic arguments which are allowed in the perturbative\nand semiclassical limits. The first-order transition of the correlated photons\nis accompanied with discontinuous change in the emitter states, not only with\nthe appearance of inter-cavity coherence in the superfluid phase. We also\ndiscuss the condition for the first-order transition to occur, which can lead\nto a strategy for future design of quantum optical switching devices with\ncavity QED arrays."
    },
    {
        "anchor": "Vortex and half-vortex dynamics in a spinor quantum fluid of interacting\n  polaritons: Spinorial or multi-component Bose-Einstein condensates may sustain fractional\nquanta of circulation, vorticant topological excitations with half integer\nwindings of phase and polarization. Matter-light quantum fluids, such as\nmicrocavity polaritons, represent a unique test bed for realising strongly\ninteracting and out-of-equilibrium condensates. The direct access to the phase\nof their wavefunction enables us to pursue the quest of whether half vortices\n---rather than full integer vortices--- are the fundamental topological\nexcitations of a spinor polariton fluid. Here, we are able to directly generate\nby resonant pulsed excitations, a polariton fluid carrying either the half or\nfull vortex states as initial condition, and to follow their coherent evolution\nusing ultrafast holography. Surprisingly we observe a rich phenomenology that\nshows a stable evolution of a phase singularity in a single component as well\nas in the full vortex state, spiraling, splitting and branching of the initial\ncores under different regimes and the proliferation of many vortex anti-vortex\npairs in self generated circular ripples. This allows us to devise the\ninterplay of nonlinearity and sample disorder in shaping the fluid and driving\nthe phase singularities dynamics",
        "positive": "Bond Order via Light-Induced Synthetic Many-body Interactions of\n  Ultracold Atoms in Optical Lattices: We show how bond order emerges due to light mediated synthetic interactions\nin ultracold atoms in optical lattices in an optical cavity. This is a\nconsequence of the competition between both short- and long-range interactions\ndesigned by choosing the optical geometry. Light induces effective many-body\ninteractions that modify the landscape of quantum phases supported by the\ntypical Bose-Hubbard model. Using exact diagonalization of small system sizes\nin one dimension, we present the many-body quantum phases the system can\nsupport via the interplay between the density and bond (or matter-wave\ncoherence) interactions. We find numerical evidence to support that dimer\nphases due to bond order are analogous to valence bond states. Different\npossibilities of light-induced atomic interactions are considered that go\nbeyond the typical atomic system with dipolar and other intrinsic interactions.\nThis will broaden the Hamiltonian toolbox available for quantum simulation of\ncondensed matter physics via atomic systems."
    },
    {
        "anchor": "Critical behavior at the spatial boundary of a trapped inhomogeneous\n  Bose-Einstein condensate: We investigate some aspects of the Bose-Einstein condensation (BEC) of\nquantum gases in the presence of inhomogeneous conditions. We consider\nthree-dimensional (3D) quantum gases trapped by an external potential when the\ntemperature is sufficiently low to show a BEC phase region around the center of\nthe trap. If the trap is sufficiently large, different phases may coexist in\ndifferent space regions, when moving from the center of the trap. We show that\nthe quantum gas develops a peculiar critical behavior at the boundary of the\nBEC region, whose scaling behavior is controlled by the universality class of\nthe homogenous BEC transition. We provide numerical evidence of this\nphenomenon, for lattice atomic gases modeled by the 3D Bose-Hubbard\nHamiltonian.",
        "positive": "Low-dimensional pairing fluctuations and pseudogapped photoemission\n  spectrum in a trapped two-dimensional Fermi gas: We investigate strong-coupling properties of a trapped two-dimensional normal\nFermi gas. Within the framework of a combined $T$-matrix theory with the local\ndensity approximation, we calculate the local density of states, as well as the\nphotoemission spectrum, to see how two-dimensional pairing fluctuations affect\nthese single-particle quantities. In the BCS (Bardeen-Cooper-Schrieffer)-BEC\n(Bose-Einstein condensation) crossover region, we show that the local density\nof states exhibits a dip structure in the trap center, which is more remarkable\nthan the three-dimensional case. This pseudogap phenomenon is found to\nnaturally lead to a double peak structure in the photoemission spectrum. The\npeak-to-peak energy of the spectrum at p=0 agrees well with the recent\nexperiment on a two-dimensional 40K Fermi gas [M. Feld, et al., Nature 480, 75\n(2011)]. Since pairing fluctuations are sensitive to the dimensionality of a\nsystem, our results would be useful for the study of many-body physics in the\nBCS-BEC crossover regime of a two-dimensional Fermi gas."
    },
    {
        "anchor": "Plasmon dispersion and Landau damping in the nonlinear quantum regime: We study the dispersion properties of electron plasma waves, or plasmons,\nwhich can be excited in quantum plasmas in the nonlinear regime. In order to\ndescribe nonlinear electron response to finite amplitude plasmons, we apply the\nVolkov approach to non-relativistic electrons. For that purpose, we use the\nSchr\\\"odinger equation and describe the electron population of a quantum plasma\nas a mixture of quantum states. Within the kinetic framework that we are able\nto derive from the Volkov solutions, we discuss the role of the wave amplitude\non the nonlinear plasma response. Finally, we focus on the quantum properties\nof nonlinear Landau damping and study the contributions of multi-plasmon\nabsorption and emission processes.",
        "positive": "Vertically-coupled dipolar exciton molecules: While the interaction potential between two dipoles residing in a single\nplane is repulsive, in a system of two vertically adjacent layers of dipoles it\nchanges from repulsive interaction in the long range to attractive interaction\nin the short range. Here we show that for dipolar excitons in semiconductor\nheterostructures, such a potential may give rise to bound states if two such\nexcitons are excited in two separate layers, leading to the formation of\nvertically coupled dipolar exciton molecules. Our calculations prove the\nexistence of such bound states and predict their binding energy as a function\nof the layers separation as well as their thermal distributions. We show that\nthese molecules should be observed in realistic systems such as semiconductor\ncoupled quantum well structures and the more recent van-der-Waals bound\nheterostructures. Formation of such molecules can lead to new effects such as a\ncollective dipolar drag between layers and new forms of multi-particle\ncorrelations, as well as to the study of dipolar molecular dynamics in a\ncontrolled system."
    },
    {
        "anchor": "Measurement of collective excitations in a spin-orbit-coupled\n  Bose-Einstein condensate: We measure the collective excitation spectrum of a spin-orbit coupled\nBose-Einstein condensate using Bragg spectroscopy. The spin-orbit coupling is\ngenerated by Raman dressing of atomic hyperfine states. When the Raman detuning\nis reduced, mode softening at a finite momentum is revealed, which provides\ninsight towards a supersolid-like phase transition. We find that for the\nparameters of our system, this softening stops at a finite excitation gap and\nis symmetric under a sign change of the Raman detuning. Finally, using a moving\nbarrier that is swept through the BEC, we also show the effect of the\ncollective excitation on the fluid dynamics.",
        "positive": "From Coherent Modes to Turbulence and Granulation of Trapped Gases: The process of exciting the gas of trapped bosons from an equilibrium initial\nstate to strongly nonequilibrium states is described as a procedure of symmetry\nrestoration caused by external perturbations. Initially, the trapped gas is\ncooled down to such low temperatures, when practically all atoms are in\nBose-Einstein condensed state, which implies the broken global gauge symmetry.\nExcitations are realized either by imposing external alternating fields,\nmodulating the trapping potential and shaking the cloud of trapped atoms, or it\ncan be done by varying atomic interactions by means of Feshbach resonance\ntechniques. Gradually increasing the amount of energy pumped into the system,\nwhich is realized either by strengthening the modulation amplitude or by\nincreasing the excitation time, produces a series of nonequilibrium states,\nwith the growing fraction of atoms for which the gauge symmetry is restored. In\nthis way, the initial equilibrium system, with the broken gauge symmetry and\nall atoms condensed, can be excited to the state, where all atoms are in the\nnormal state, with completely restored gauge symmetry. In this process, the\nsystem, starting from the regular superfluid state, passes through the states\nof vortex superfluid, turbulent superfluid, heterophase granular fluid, to the\nstate of normal chaotic fluid in turbulent regime. Both theoretical and\nexperimental studies are presented."
    },
    {
        "anchor": "Tuning the structural and dynamical properties of a dipolar\n  Bose-Einstein condensate: Ripples and instability islands: It is now well established that the stability of aligned dipolar Bose gases\ncan be tuned by varying the aspect ratio of the external harmonic confinement.\nThis paper extends this idea and demonstrates that a Gaussian barrier along the\nstrong confinement direction can be employed to tune both the structural\nproperties and the dynamical stability of an oblate dipolar Bose gas aligned\nalong the strong confinement direction. In particular, our theoretical\nmean-field analysis predicts the existence of instability islands immersed in\notherwise stable regions of the phase diagram. Dynamical studies indicate that\nthese instability islands, which can be probed experimentally with present-day\ntechnology, are associated with the going soft of a Bogoliubov--de Gennes\nexcitation frequency with radial breathing mode character. Furthermore, we find\ndynamically stable ground state densities with ripple-like oscillations along\nthe radial direction. These structured ground states exist in the vicinity of a\ndynamical radial roton-like instability.",
        "positive": "Comparison of time profiles for the magnetic transport of cold atoms: We have compared different time profiles for the trajectory of the centre of\na quadrupole magnetic trap designed for the transport of cold sodium atoms. Our\nexperimental observations show that a smooth profile characterized by an\nanalytical expression involving the error function minimizes the transport\nduration while limiting atom losses and heating of the trapped gas. Using\nnumerical calculations of single atom classical trajectories within the trap,\nwe show that this observation can be qualitatively interpreted as a trade-off\nbetween two types of losses: finite depth of the confinement and Majorana spin\nflips."
    },
    {
        "anchor": "Spin-orbit coupling induced Fulde-Ferrell-Larkin-Ovchinnikov-like Cooper\n  pairing and skyrmion-like polarization textures in trapped optical lattices: We study the interplay between the Zeeman field and spin-orbit coupling (SOC)\nin harmonically trapped Fermi gases loaded into a two-dimensional single-band\ntight-binding optical lattice. Using the Bogoliubov-de Gennes theory, we find\nthat the Zeeman field combined with a Rashba SOC gives rise to $(i)$\nFulde-Ferrell-like superfluidity and $(ii)$ skyrmion-like polarization textures\nnear the edges of the system. We also discussed the effects of interaction,\ntemperature, SOC anisotropy and Zeeman field anisotropy on the superfluid\nground state and polarization textures.",
        "positive": "Feedback-stabilized dynamical steady states in the Bose-Hubbard model: The implementation of a combination of continuous weak measurement and\nclassical feedback provides a powerful tool for controlling the evolution of\nquantum systems. In this work, we investigate the potential of this approach\nfrom three perspectives. First, we consider a double-well system in the\nclassical large-atom-number limit, deriving the exact equations of motion in\nthe presence of feedback. Second, we consider the same system in the limit of\nsmall atom number, revealing the effect that quantum fluctuations have on the\nfeedback scheme. Finally, we explore the behavior of modest sized Hubbard\nchains using exact numerics, demonstrating the near-deterministic preparation\nof number states, a tradeoff between local and non-local feedback for state\npreparation, and evidence of a feedback-driven symmetry-breaking phase\ntransition."
    },
    {
        "anchor": "Stable controllable giant vortex in a trapped Bose-Einstein condensate: In a harmonically-trapped rotating Bose-Einstein condensate (BEC), a vortex\nof large angular momentum decays to multiple vortices of unit angular momentum\nfrom an energetic consideration. We demonstrate the formation of a robust and\ndynamically stable giant vortex of large angular momentum in a harmonically\ntrapped rotating BEC with a potential hill at the center, thus forming a\nMexican hat like trapping potential. For a small inter-atomic interaction\nstrength, a highly controllable stable giant vortex appears, whose angular\nmomentum slowly increases as the angular frequency of rotation is increased. As\nthe inter-atomic interaction strength is increased beyond a critical value,\nonly vortices of unit angular momentum are formed, unless the strength of the\npotential hill at the center is also increased: for a stronger potential hill\nat the center a giant vortex is again formed. The dynamical stability of the\ngiant vortex is demonstrated by real-time propagation numerically. These giant\nvortices of large angular momentum can be observed and studied experimentally\nin a highly controlled fashion.",
        "positive": "Strongly Correlated Bosons on a Dynamical Lattice: We study a one-dimensional system of strongly correlated bosons on a\ndynamical lattice. To this end, we extend the standard Bose-Hubbard Hamiltonian\nto include extra degrees of freedom on the bonds of the lattice. We show that\nthis minimal model exhibits phenomena reminiscent of fermion-phonon models. In\nparticular, we discover a bosonic analog of the Peierls transition, where the\ntranslational symmetry of the underlying lattice is spontaneously broken. This\nprovides a dynamical mechanism to obtain a topological insulator in the\npresence of interactions, analogous to the Su-Schrieffer-Heeger model for\nelectrons. We characterize the phase diagram numerically, showing different\ntypes of bond order waves and topological solitons. Finally, we study the\npossibility of implementing the model using atomic systems."
    },
    {
        "anchor": "Dynamical features of Shannon information entropy of bosonic cloud in a\n  tight trap: We calculate Shannon information entropy of trapped interacting bosons in\nboth the position and momentum spaces, $S_r$ and $S_k$ respectively. The total\nentropy maintains the fuctional form $S=a + b \\ln N$ for repulsive bosons. At\nthe noninteracting limit the lower bound of entropic uncertainty relation is\nalso satisfied whereas the diverging behavior of $S_r$ and $S_k$ at the\ncritical point of collapse for attractive condensate accurately calculates the\nstability factor. Next we study the dynamics of Shannon information entropy\nwith varying interparticle potential. We numerically solve the time-dependent\nGross-Pitaevskii equation and study the influence of increasing nonlinearity in\nthe dynamics of entropy uncertainty relation (EUR). We observe that for small\nnonlinearity the dynamics is regular. With increase in nonlinearity although\nShannon entropy shows large variation in amplitude of the oscillation, the EUR\nis maintained throughout time for all cases and it confirms its generality. We\nalso study the dynamics in a very tight trap when the condensate becomes highly\ncorrelated and strongly inhomogeneous. Time evolution of total entropy exhibits\naperiodic and fluctuating nature in very tight trap. We also calculate\nLandsberg's order parameter for various interaction strengths which supports\nearlier observation that entropy and order are decoupled.",
        "positive": "Vortex dynamics in spin-orbit coupled Bose-Einstein condensates: I use a time-dependent Lagrangian formalism and a variational trial function\nto study the dynamics of a two-component vortex in a spin-orbit coupled\nBose-Einstein condensate (BEC). For a single-component BEC, various experiments\nhave validated this theoretical approach, for example a thermal quench that\nyields a quantized vortex in roughly 25% of trials. To be definite, I assume\nthe specific spin-orbit form used in recent NIST experiments, which introduces\na spatial asymmetry because of the external Raman laser beams. I here\ngeneralize this formalism to include a two-component order parameter that has\nquantized circulation in each component but not necessarily with the same\ncirculation. For example a singly quantized vortex in just one component yields\na BEC analog of the half-quantum vortex familiar in $^3$He-A and in $p$-wave\nchiral superconductors. This and other unusual two-component vortices have both\nperiodic trajectories and unbounded trajectories that leave the condensate,\ndepending on the initial conditions. The optimized phase of the order parameter\ninduces a term in the particle current that cancels the contribution from the\nvector potential, leaving pure circulating current around the vortex."
    },
    {
        "anchor": "Effects of three-body scattering processes on BCS-BEC crossover: We investigate the BCS-BEC crossover taking into account an additional\nthree-body interaction, which is essentially the scattering between the Cooper\npairs and the newly formed bosons. We show that if the two-body interaction is\nattractive, the presence of this additional three-body term makes the crossover\nprocess a nonreversible one. Starting from a stable Bose-Einstein condensate\n(BEC) state, crossover to BCS can be achieved; but if the BCS state is the\nstarting point, instead of a stable BEC region, what the system crosses over to\nis a metastable condensed state.",
        "positive": "Quantum phases of two-component bosons on the Harper-Hofstadter ladder: We study two-component bosons on the Harper-Hofstadter model with two legs.\nThe synthetic magnetic fields for the two types of bosons point to either the\nsame direction or opposite directions. The bosons have hardcore intra-species\ninteraction such that there can be no more than one boson of the same type on\neach lattice site. For certain filling factors in the absence of inter-species\ninteraction, each component realizes a vortex Mott insulator with rung current\nor a Meissner superfluid without rung current. The system undergoes phase\ntransitions to other phases as inter-species interaction is turned on, which\nare characterized numerically using the density matrix renormalization group\nmethod and supplemented with analytical studies when possible. The vortex Mott\ninsulator transits to a gapped Meissner phase without rung current and the\nMeissner superfluid transits to a gapped vortex phase with rung current. In\nboth cases, we observe gapped spin density wave states that break certain\n${\\mathbb Z}_{2}$ symmetries."
    },
    {
        "anchor": "Role of higher-order interactions on the modulational instability of\n  Bose-Einstein condensate trapped in a periodic optical lattice: In this paper, we investigate the impact of higher-order interactions on the\nmodulational instability (MI) of Bose-Einstein Condensates (BECs) immersed in\nan optical lattice potential. We derive the new variational equations for the\ntime evolution of amplitude, phase of modulational perturbation, and effective\npotential for the system. Through effective potential techniques, we find that\nhigh density attractive and repulsive BECs exhibit new character with direct\nimpact over the MI phenomenon. Results of intensive numerical investigations\nare presented and their convergence with the above semi analytical approach is\nbrought out.",
        "positive": "Coupled density-spin Bose-Einstein condensates dynamics and collapse in\n  systems with quintic nonlinearity: We investigate the effects of spin-orbit coupling and Zeeman splitting on the\ncoupled density-spin dynamics and collapse of the Bose-Einstein condensate\ndriven by the quintic self-attraction in the same- and cross-spin channels. The\ncharacteristic feature of the collapse is the decrease in the width as given by\nthe participation ratio of the density rather than by the expectation values of\nthe coordinate. Qualitative arguments and numerical simulations reveal the\nexistence of a critical spin-orbit coupling strength which either prohibits or\nleads to the collapse, and its dependence on other parameters, such as the\ncondensates norm, spin-dependent nonlinear coupling, and the Zeeman splitting.\nThe entire nonlinear dynamics critically depend on the initial spin sate."
    },
    {
        "anchor": "Analysis and resolution of the ground-state degeneracy of the\n  two-component Bose-Hubbard model: We study the degeneracy of the ground-state energy $E$ of the two-component\nBose-Hubbard model and of the perturbative correction $E_1$. We show that the\ndegeneracy properties of $E$ and $E_1$ are closely related to the connectivity\nproperties of the lattice. We determine general conditions under which $E$ is\nnondegenerate. This analysis is then extended to investigate the degeneracy of\n$E_1$. In this case, in addition to the lattice structure, the degeneracy also\ndepends on the number of particles present in the system. After identifying the\ncases in which $E_1$ is degenerate and observing that the standard (degenerate)\nperturbation theory is not applicable, we develop a method to determine the\nzeroth-order correction to the ground state by exploiting the symmetry\nproperties of the lattice. This method is used to implement the perturbative\napproach to the two-component Bose-Hubbard model in the case of degenerate\n$E_1$ and is expected to be a valid tool to perturbatively study the asymmetric\ncharacter of the Mott-insulator to superfluid transition between the particle\nand hole side.",
        "positive": "Toroidal Dipolar Supersolid with a Rotating Weak Link: Ring-shaped superfluids with weak links provide a perfect environment for\nstudying persistent currents and dynamic stirring protocols. Here, we\ninvestigate the effects of a weak-link system on dipolar supersolids. By\ncalculating the ground state energy at fixed angular momenta, we find that\nmetastable persistent currents may exist in the supersolid phase near the\nsuperfluid transition point. When stirring the weak link rapidly enough, we\nshow that vortices can enter the supersolid. These vortex entries cause phase\nslips, emitting solitonic excitations that interfere with the crystalline\nstructure of the supersolid, leading to a continuous melting and\nrecrystallization of the droplets. Finally, we examine the release of\nvortex-carrying supersolids from the trap, observing that the released density\nexhibits a discrete structure associated with the density modulation and a\ncentral hole resulting from the vortex core."
    },
    {
        "anchor": "Leading gradient correction to the kinetic energy for two-dimensional\n  fermion gases: Density functional theory (DFT) is notorious for the absence of gradient\ncorrections to the two-dimensional (2D) Thomas-Fermi kinetic-energy functional;\nit is widely accepted that the 2D analog of the 3D von Weizs\\\"acker correction\nvanishes, together with all higher-order corrections. Contrary to this\nlong-held belief, we show that the leading correction to the kinetic energy\ndoes not vanish, is unambiguous, and contributes perturbatively to the total\nenergy. This insight emerges naturally in a simple extension of standard DFT,\nwhich has the effective potential energy as a functional variable on equal\nfooting with the single-particle density.",
        "positive": "Optimized sympathetic cooling of atomic mixtures via fast adiabatic\n  strategies: We discuss fast frictionless cooling techniques in the framework of\nsympathetic cooling of cold atomic mixtures. It is argued that optimal cooling\nof an atomic species - in which the deepest quantum degeneracy regime is\nachieved - may be obtained by means of sympathetic cooling with another species\nwhose trapping frequency is dynamically changed to maintain constancy of the\nLewis-Riesenfeld adiabatic invariant. Advantages and limitations of this\ncooling strategy are discussed, with particular regard to the possibility of\ncooling Fermi gases to a deeper degenerate regime."
    },
    {
        "anchor": "Competition of spin and charge excitations in the Hubbard model: Motivated by recent experiments with ultracold fermionic atoms in optical\nlattices, we study finite temperature magnetic correlations, as singlet and\ntriplet correlations, and the double occupancy in the one-dimensional Hubbard\nmodel. We point out that for intermediate interaction strengths the double\noccupancy has an intriguing doubly non-monotonic temperature dependence due to\nthe competition between spin and charge modes, related to the Pomeranchuk\neffect. Furthermore, we determine properties of magnetic correlations in the\ntemperature regimes relevant for current cold atom experiments and discuss\neffects of the trap on spatially integrated observables. We estimate the\nentropy and the temperature reached in the experiment by Greif et al., Science\n340, 1307 (2013).",
        "positive": "Mixtures of dipolar gases in two dimensions: a quantum Monte Carlo study: We studied the miscibility of two dipolar quantum gases in the limit of zero\ntemperature. The system under study is composed by a mixture of two Bose gases\nwith dominant dipolar interaction in a two-dimensional harmonic confinement.\nThe dipolar moments are considered all to be perpendicular to the plane,\nturning the dipolar potential in a purely repulsive and isotropic model. Our\nanalysis is carried out by using the diffusion Monte Carlo method which allows\nfor an exact solution to the many-body problem within some statistical noise.\nOur results show that the miscibility between the two species is rather\nconstrained as a function of the relative dipolar moments and masses of the two\ncomponents. A narrow regime is predicted where both species mix and we\nintroduce an adimensional parameter whose value predicts quite accurately the\nmiscibility of the two dipolar gases."
    },
    {
        "anchor": "Scattering length of composite bosons in the 3D BCS-BEC crossover: We study the zero-temperature grand potential of a three-dimensional\nsuperfluid made of ultracold fermionic alkali-metal atoms in the BCS-BEC\ncrossover. In particular, we analyze the zero-point energy of both fermionic\nsingle-particle excitations and bosonic collective excitations. The bosonic\nelementary excitations, which are crucial to obtain a reliable equation of\nstate in the BEC regime, are obtained with a low-momentum expansion up to the\nforth order of the quadratic (Gaussian) action of the fluctuating pairing\nfield. By performing a cutoff regularization and renormalization of Gaussian\nfluctuations, we find that the scattering length $a_B$ of composite bosons,\nbound states of fermionic pairs, is given by $a_B = (2/3) a_F$, where $a_F$ is\nthe scattering length of fermions.",
        "positive": "Pair tunneling of two atoms out of a trap: A simple theory for the tunneling of two cold atoms out of a trap in the\npresence of an attractive contact force is developed. Two competing decay\nchannels, respectively for single-atom and bound-pair tunneling, contribute\nindependently to the decay law of the mean atom number in the trap. The\nsingle-atom tunneling rate is obtained through the quasiparticle wave function\nformalism. For pair tunneling an effective equation for the center-of-mass\nmotion is derived, so the calculation of the corresponding tunneling rate is\nagain reduced to a simpler one-body problem. The predicted dependence of\ntunneling rates on the interaction strength qualitatively agrees with a recent\nmeasurement of the two-atom decay time [G. Zuern, A. N. Wenz, S. Murmann, T.\nLompe, and S. Jochim, arXiv:1307.5153]."
    },
    {
        "anchor": "Stationary vortex flows and macroscopic Zeno effect in Bose-Einstein\n  condensates with localized dissipation: We theoretically demonstrate a possibility to observe the macroscopic Zeno\neffect in an effectively two-dimensional (pancake-shaped) repulsive\nBose--Einstein condensate subjected to a strong narrow dissipation. We show\nthat the dissipation can generate stable stationary nonlinear flows which bear\neither zero or non-zero topological charge (vorticity). The superfluid flows\ntowards the dissipative defect compensate the atomic losses. The macroscopic\nZeno effect manifests itself in a nonmonotonous dependence of the inward\ncurrent density on the strength of the dissipation.",
        "positive": "Interacting bosons in topological optical flux lattices: An interesting route to the realization of topological Chern bands in\nultracold atomic gases is through the use of optical flux lattices. These\nmodels differ from the tight-binding real-space lattice models of Chern\ninsulators that are conventionally studied in solid-state contexts. Instead,\nthey involve the coherent coupling of internal atomic (spin) states, and can be\nviewed as tight-binding models in reciprocal space. By changing the form of the\ncoupling and the number $N$ of internal spin states, they give rise to Chern\nbands with controllable Chern number and with nearly flat energy dispersion. We\ninvestigate in detail how interactions between bosons occupying these bands can\nlead to the emergence of fractional quantum Hall states, such as the Laughlin\nand Moore-Read states. In order to test the experimental realization of these\nphases, we study their stability with respect to band dispersion and band\nmixing. We also probe novel topological phases that emerge in these systems\nwhen the Chern number is greater than 1."
    },
    {
        "anchor": "Probing the conformal Calabrese-Cardy scaling with cold atoms: We demonstrate that current experiments using cold bosonic atoms trapped in\none-dimensional optical lattices and designed to measure the second-order Renyi\nentanglement entropy S_2, can be used to verify detailed predictions of\nconformal field theory (CFT) and estimate the central charge c. We discuss the\nadiabatic preparation of the ground state at half-filling where we expect a CFT\nwith c=1. This can be accomplished with a very small hoping parameter J, in\ncontrast to existing studies with density one where a much larger J is needed.\nWe provide two complementary methods to estimate and subtract the classical\nentropy generated by the experimental preparation and imaging processes. We\ncompare numerical calculations for the classical O(2) model with a chemical\npotential on a 1+1 dimensional lattice, and the quantum Bose-Hubbard\nHamiltonian implemented in the experiments. S_2 is very similar for the two\nmodels and follows closely the Calabrese-Cardy scaling, (c/8)\\ln(N_s), for N_s\nsites with open boundary conditions, provided that the large subleading\ncorrections are taken into account.",
        "positive": "Threshold for creating excitations in a stirred superfluid ring: We have measured the threshold for creating long-lived excitations when a\ntoroidal Bose-Einstein condensate is stirred by a rotating (optical) barrier of\nvariable height. When the barrier height is on the order of or greater than\nhalf of the chemical potential, the critical barrier velocity at which we\nobserve a change in the circulation state is much less than the speed for sound\nto propagate around the ring. In this regime we primarily observe discrete\njumps (phase slips) from the non-circulating initial state to a simple,\nwell-defined, persistent current state. For lower barrier heights, the critical\nbarrier velocity at which we observe a change in the circulation state is\nhigher, and approaches the effective sound speed for vanishing barrier height.\nThe response of the condensate in this small-barrier regime is more complex,\nwith vortex cores appearing in the bulk of the condensate. We find that the\nvariation of the excitation threshold with barrier height is in qualitative\nagreement with the predictions of an effective 1D hydrodynamic model."
    },
    {
        "anchor": "Phase separation in a spin-orbit coupled Bose-Einstein condensate: We study a spin-orbit (SO) coupled hyperfine spin-1 Bose-Einstein condensate\n(BEC) in a quasi-one-dimensional trap. For a SO-coupled BEC in a\none-dimensional box, we show that in the absence of the Rabi term, any non-zero\nvalue of SO coupling will result in a phase separation among the components for\na ferromagnetic BEC, like $^{87}$Rb. On the other hand, SO coupling favors\nmiscibility in a polar BEC, like $^{23}$Na. In the presence of a harmonic trap,\nwhich favors miscibility, a ferromagnetic BEC phase separates, provided the\nSO-coupling strength and number of atoms are greater than some critical value.\nThe Rabi term favors miscibility irrespective of the nature of the spin\ninteraction: ferromagnetic or polar.",
        "positive": "Pressure, compressibility, and contact of the two-dimensional attractive\n  Fermi gas: Using ab initio lattice methods, we calculate the finite temperature\nthermodynamics of homogeneous two-dimensional spin-1/2 fermions with attractive\nshort-range interactions. We present results for the density, pressure,\ncompressibility, and quantum anomaly (i.e. Tan's contact) for a wide range of\ntemperatures and coupling strengths, focusing on the unpolarized case. Within\nour statistical and systematic uncertainties, our prediction for the density\nequation of state differs quantitatively from the prediction by Luttinger-Ward\ntheory in the strongly coupled region of parameter space, but otherwise agrees\nwell with it. We also compare our calculations with the second- and third-order\nvirial expansion, with which they are in excellent agreement in the\nlow-fugacity regime."
    },
    {
        "anchor": "Interaction-induced localization of fermionic mobile impurities in a\n  Larkin-Ovchinnikov superfluid: We theoretically investigate the interplay between the fermionic mobile\nimpurity atoms and a Larkin-Ovchinnikov (LO) superfluid in a two dimensional\noptical lattice. We find that the impurity atoms get localized and can form\npairs when the interaction between the impurity atoms and the LO superfluid is\nstrong enough. These features are due to the phenomena of self-localization\nwhose underlying mechanism is revealed by an effective model. The impurity\natoms with finite concentrations can drive the transition from a\ntwo-dimensional-checkerboard-like LO state to a\nquasi-one-dimensional-stripe-like one. Experimental preparations to observe\nthese features are also discussed.",
        "positive": "Single particle polariton properties in doped quantum well\n  microcavities: role of the Fermi edge singularity and Anderson orthogonality\n  catastrophe: A theoretical investigation of the single particle polariton properties for a\nmicrocavity embedding a charged quantum well is presented. The electron gas\noptical susceptibility is calculated numerically using the method devised by\nCombescot and Nozi\\`eres. The role of many-body effects, such as the Fermi edge\nsingularity and Anderson orthogonality catastrophe, in the polariton formation\nis elucidated. By tuning the light-matter coupling the short time behaviour of\nthe electron gas response function is probed and comparison with earlier\nresults only using the long time response are made. Various single particle\npolariton properties such as the Rabi splitting, line shape, Hopfield\ncoefficients and effective mass are discussed. These are experimentally\naccessible quantities and thus allow for a comparison with the presented\ntheory."
    },
    {
        "anchor": "Parametric amplification of vacuum fluctuations in a spinor condensate: Parametric amplification of vacuum fluctuations is crucial in modern quantum\noptics, enabling the creation of squeezing and entanglement. We demonstrate the\nparametric amplification of vacuum fluctuations for matter waves using a spinor\nF=2 Rb-87 condensate. Interatomic interactions lead to correlated pair creation\nin the m_F= +/- 1 states from an initial unstable m_F=0 condensate, which acts\nas a vacuum for m_F unequal 0. Although this pair creation from a pure m_F=0\ncondensate is ideally triggered by vacuum fluctuations, unavoidable spurious\ninitial m_F= +/- 1 atoms induce a classical seed which may become the dominant\ntriggering mechanism. We show that pair creation is insensitive to a classical\nseed for sufficiently large magnetic fields, demonstrating the dominant role of\nvacuum fluctuations. The presented system thus provides a direct path towards\nthe generation of non-classical states of matter on the basis of spinor\ncondensates.",
        "positive": "Extended Bose Hubbard model for two leg ladder systems in artificial\n  magnetic fields: We investigate the ground state properties of ultracold atoms with long range\ninteractions trapped in a two leg ladder configuration in the presence of an\nartificial magnetic field. Using a Gross-Pitaevskii approach and a mean field\nGutzwiller variational method, we explore both the weakly interacting and\nstrongly interacting regime, respectively. We calculate the boundaries between\nthe density-wave/supersolid and the Mott-insulator/superfluid phases as a\nfunction of magnetic flux and uncover regions of supersolidity. The mean-field\nresults are confirmed by numerical simulations using a cluster mean field\napproach."
    },
    {
        "anchor": "Twisted superfluid phase in the extended one-dimensional Bose-Hubbard\n  model: In one-dimensional systems a twisted superfluid phase is found which is\ninduced by a spontaneous breaking of the time-reversal symmetry. Using the\ndensity-matrix renormalization group allows us to show that the excitation\nenergy gap closes exponentially causing a quasi-degenerate ground state. The\ntwo degenerate ground states are connected by the time-reversal symmetry which\nmanifests itself in an alternating complex phase of the long-range correlation\nfunction. The quantum phase transition to the twisted superfluid is driven by\npair tunneling processes in an extended Bose-Hubbard model. The phase\nboundaries of several other phases are discussed including a supersolid, a pair\nsuperfluid, and a pair supersolid phase as well as a highly unconventional Mott\ninsulator with a degenerate ground state and a staggered pair correlation\nfunction.",
        "positive": "$\\mathbb{Z}_n$ symmetry broken supersolid in spin-orbit-coupled\n  Bose-Einstein condensates: Supersolid is an exotic state of matter characterized by both superfluid\nproperties and periodic particle density modulation, due to spontaneous\nbreaking of U(1) gauge symmetry and spatial translation symmetry, respectively.\nFor conventional supersolids,continuous translation symmetry breaking is\naccompanied by one gapless Goldstone mode in the excitation spectra. An\ninteresting question naturally arises: what is the consequence of breaking\ndiscrete translation symmetry for supersolids? In this work, we propose the\nconcept of $\\mathbb{Z}_n$ supersolid resulting from spontaneous breaking of a\ndiscrete $\\mathbb{Z}_n$ symmetry, or equivalently, a discrete translation\nsymmetry. This $\\mathbb{Z}_n$ supersolid is realized in the stripe phase of\nspin-orbit-coupled Bose-Einstein condensate under an external periodic\npotential with period $1/n$ of intrinsic stripe period. For $n\\geq2$, there are\n$n$ degenerate ground states with spontaneously broken lattice translation\nsymmetry. The low-energy excitations of $\\mathbb{Z}_n$ supersolid include a\npseudo-Goldstone mode, whose excitation gap at long wavelength limit is found\nto decrease fast with $n$. We further numerically show that, when confined in a\nharmonic trap, a spin-dependent perturbation can result in the transition\nbetween degenerate ground states of $\\mathbb{Z}_n$ supersolid. With the integer\n$n$ tunable using the experimental technique of generating subwavelength\noptical lattice, the $\\mathbb{Z}_n$ supersolid proposed here offers a cold atom\nplatform to simulate physics related with generic $\\mathbb{Z}_n$ symmetry\nbreaking, which is interesting not only in the field of cold atoms, but also in\nparticle physics and cosmology."
    },
    {
        "anchor": "Probing open- and closed-channel p-wave resonances: We study the near-threshold molecular and collisional physics of a strong\n$^{40}$K p-wave Feshbach resonance through a combination of measurements,\nnumerical calculations, and modeling. Dimer spectroscopy employs both\nradio-frequency spin-flip association in the MHz band and resonant association\nin the kHz band. Systematic uncertainty in the measured binding energy is\nreduced by a model that includes both the Franck-Condon overlap amplitude and\ninhomogeneous broadening. Coupled-channels calculations based on mass-scaled\n$^{39}$K potentials compare well to the observed binding energies and also\nreveal a low-energy p-wave shape resonance in the open channel. Contrary to\nconventional expectation, we observe a nonlinear variation of the binding\nenergy with magnetic field, and explain how this arises from the interplay of\nthe closed-channel ramping state with the near-threshold shape resonance in the\nopen channel. We develop an analytic two-channel model that includes both\nresonances as well as the dipole-dipole interactions which, we show, become\nimportant at low energy. Using this parameterization of the energy dependence\nof the scattering phase, we can classify the studied $^{40}$K resonance as\nbroad. Throughout the paper, we compare to the well understood s-wave case, and\ndiscuss the significant role played by van der Waals physics. The resulting\nunderstanding of the dimer physics of p-wave resonances provides a solid\nfoundation for future exploration of few- and many-body orbital physics.",
        "positive": "Signatures of Coherent Vortex Structures in a Disordered 2D Quantum\n  Fluid: The emergence of coherent rotating structures is a phenomenon characteristic\nof both classical and quantum 2D turbulence. In this work we show theoretically\nthat the coherent vortex structures that emerge in decaying 2D quantum\nturbulence can approach quasi-classical rigid-body rotation, obeying the\nFeynman rule of constant average areal vortex density while remaining spatially\ndisordered. By developing a rigorous link between the velocity probability\ndistribution and the quantum kinetic energy spectrum over wavenumber $k$, we\nshow that the coherent vortex structures are associated with a $k^3$ power law\nin the infrared region of the spectrum, and a well-defined spectral peak that\nis a physical manifestation of the largest structures. We discuss the\npossibility of realizing coherent structures in Bose--Einstein condensate\nexperiments and present Gross-Pitaevskii simulations showing that this\nphenomenon, and its associated spectral signatures, can emerge dynamically from\nfeasible initial vortex configurations."
    },
    {
        "anchor": "Dynamical response of ultracold interacting fermion-boson mixtures: We analyze the dynamical response of a ultracold binary gas mixture in\npresence of strong boson-fermion couplings. Mapping the problem onto that of\nthe optical response of a metal/semiconductor electronic degrees of freedom to\nelectromagnetic perturbation we calculate the corresponding dynamic linear\nresponse susceptibility in the non-perturbative regimes of strong boson-fermion\ncoupling using diagrammatic resummation technique as well as quantum Monte\nCarlo simulations. We evaluate the Bragg spectral function as well as the\noptical conductivity and find a pseudogap, which forms in certain parameter\nregimes.",
        "positive": "Metastable supersolid in spin-orbit coupled Bose-Einstein condensates: Supersolid is a special state of matter with both superfluid properties and\nspontaneous modulation of particle density. In this paper, we focus on the\nsupersolid stripe phase realized in a spin-orbit coupled Bose-Einstein\ncondensate and explore the properties of a class of metastable supersolids. In\nparticular, we study a one-dimensional supersolid whose characteristic wave\nnumber $k$ (magnitude of wave vector) deviates from $k_{m}$, i.e., the one at\nground state. In other words, the period of density modulation is shorter or\nlonger than the one at ground state. We find that this class of supersolids can\nstill be stable if their wave numbers fall in the range $k_{c1}<k<k_{c2}$, with\ntwo thresholds $k_{c1}$ and $k_{c2}$. Stripes with $k$ outside this range\nsuffer from dynamical instability with complex Bogoliubov excitation spectrum\nat long wavelength. Experimentally, these stripes with $k$ away from $k_m$ are\naccessible by exciting the longitudinal spin dipole mode, resulting in temporal\noscillation of stripe period as well as $k$. Within the mean-field\nGross-Pitaevskii theory, we numerically confirm that for a large enough\namplitude of spin dipole oscillation, the stripe states become unstable through\nbreaking periodicity, in qualitative agreement with the existence of thresholds\nof $k$ for stable stripes. Our work extends the concept of supersolid and\nuncovers a new class of metastable supersolids to explore."
    },
    {
        "anchor": "Sustained propagation and control of topological excitations in\n  polariton superfluid: We present a simple method to compensate for losses in a polariton\nsuperfluid. Based on a weak support field, it allows for an extended\npropagation of a resonantly driven polariton superfluid at a minimal energetic\ncost. Moreover, this setup based on optical bistability, leads to a significant\nrelease of the phase constraint imposed by the resonant driving. This release,\ntogether with the macroscopic polariton propagation, offers a unique\nopportunity to study the hydrodynamics of topological excitations of polariton\nsuperfluids such as quantized vortices and dark solitons. We numerically study\nhow the coherent field supporting the superfluid flow interacts with the\nvortices and how it can be used to control them. Interestingly, we show that\nstandard hydrodynamics does not apply for this driven-dissipative fluid and new\nbehaviours are identified.",
        "positive": "Driving Quantum Correlated Atom-Pairs from a Bose-Einstein Condensate: The ability to cool quantum gases into the quantum degenerate realm has\nopened up possibilities for an extreme level of quantum-state control. In this\npaper, we investigate one such control protocol that demonstrates the resonant\namplification of quasimomentum pairs from a Bose-Einstein condensate by the\nperiodic modulation of the two-body s-wave scattering length. This shows a\ncapability to selectively amplify quantum fluctuations with a predetermined\nmomentum, where the momentum value can be spectroscopically tuned. A classical\nexternal field that excites pairs of particles with the same energy but\nopposite momenta is reminiscent of the coherently-driven nonlinearity in a\nparametric amplifier crystal in nonlinear optics. For this reason, it may be\nanticipated that the evolution will generate a squeezed matter-wave state in\nthe quasiparticle mode on resonance with the modulation frequency. Our model\nand analysis is motivated by a recent experiment by Clark et al. that observed\na time-of-flight pattern similar to an exploding firework. Since the drive is a\nhighly coherent process, we interpret the observed firework patterns as arising\nfrom a monotonic growth in the two-body correlation amplitude, so that the jets\nshould contain correlated atom pairs with nearly equal and opposite momenta. We\npropose a potential future experiment based on applying Ramsey interferometry\nto experimentally probe these pair correlations."
    },
    {
        "anchor": "Exciton-polariton X-waves in a microcavity: We investigate the possibility of creating X-waves, or localized wave\npackets, in resonantly excited exciton-polariton superfluids. We demonstrate\nthe existence of X-wave traveling solutions in the coupled exciton-photon\nsystem past the inflection point, where the effective mass of lower polaritons\nis negative in the direction perpendicular to the wavevector of the pumping\nbeam. Contrary to the case of bright solitons, X-waves do not require\nnonlinearity for sustaining their shape. Nevertheless, we show that\nnonlinearity is important for their dynamics, as it allows for their\nspontaneous formation from an initial Gaussian wave packet. Unique properties\nof exciton-polaritons may lead to applications of their X-waves in\nlong-distance signal propagation inside novel integrated optoelectronic\ncircuits based on excitons.",
        "positive": "Interaction-Induced Gradients Across a Confined Fermion Lattice: An imposed chemical potential gradient $A_\\uparrow=d\\mu_\\uparrow/dx$ on a\nsingle fermionic species (\"spin up\") directly produces a gradient in the\ndensity $d\\rho_\\uparrow/dx$ across a lattice. We study here the induced density\ninhomogeneity $d\\rho_\\downarrow/dx$ in the second fermionic species (\"spin\ndown\") which results from fermionic interactions $U$, even in the absence of a\nchemical potential gradient $A_\\downarrow=0$ on that species. The magnitude of\n$d\\rho_\\downarrow/dx$ acquired by the second species grows with $U$, while the\nmagnitude of $d\\rho_\\uparrow/dx$ remains relatively constant, that is, set only\nby $A_\\uparrow$. For a given $A_\\uparrow$, we find an interaction strength\n$U_*$ above which the two density gradients are equal in magnitude. We also\nevaluate the spin-spin correlations and show that, as expected,\nantiferromagnetism is most dominant at locations where the local density is\nhalf-filled. The spin polarization induced by sufficiently large gradients, in\ncombination with $U$, drives ferromagnetic behavior. In the case of repulsive\ninteractions, $d\\rho_\\downarrow/dx = -d\\rho_\\uparrow/dx$. A simple\nparticle-hole transformation determines the related effect in the case of\nattractive interactions."
    },
    {
        "anchor": "Exact solutions to the spin-2 Gross-Pitaevskii equations: We present several exact solutions to the coupled nonlinear Gross-Pitaevskii\nequations which describe the motion of the one-dimensional spin-2 Bose-Einstein\ncondensates. The nonlinear density-density interactions are decoupled by making\nuse of the properties of Jacobian elliptical functions. The distinct time\nfactors in each hyperfine state implies a \"Lamor\" procession in these\nsolutions. Furthermore, exact time-evolving solutions to the time-dependent\nGross-Pitaevskii equations are constructed through the spin-rotational symmetry\nof the Hamiltonian. The spin-polarizations and density distributions in the\nspin-space are analyzed.",
        "positive": "Crossover from exciton-polariton to photon Bose-Einstein condensation: BEC of exciton-polaritons and related effects such as superfluidity1,2,\nspontaneous symmetry breaking3,4 and quantised vortices5,6 open way to creation\nof novel light sources7 and optical logic elements8. Remarkable observations of\nexciton-polariton BEC in microcavities9-12 have been reported in the recent ten\nyears. Very recently, thermalisation and subsequent condensation of cavity\nphotons in a dye-filled microcavity have been observed13. Here we show that BEC\nof both exciton-polaritons and photons can be created in the same system under\ndifferent optical excitation conditions. A dynamic phase transition between a\nphoton and a polariton BEC takes place after a single high-power excitation\npulse and we find both condensed states in thermal equilibrium with the excited\nstates. At the crossover, photons and polaritons coexist, which results in a\ndecrease in the long-range spatial coherence. Build-up and successive depinning\nof polarisation is observed at the threshold of both polariton and photon\ncondensation."
    },
    {
        "anchor": "Controlling the transverse instability of dark solitons and nucleation\n  of vortices by a potential barrier: We study possibilities to suppress the transverse modulational instability\n(MI) of dark-soliton stripes in two-dimensional (2D) Bose-Einstein condensates\n(BECs) and self-defocusing bulk optical waveguides by means of quasi-1D\nstructures. Adding an external repulsive barrier potential (which can be\ninduced in BEC by a laser sheet, or by an embedded plate in optics), we\ndemonstrate that it is possible to reduce the MI wavenumber band, and even\nrender the dark-soliton stripe completely stable. Using this method, we\ndemonstrate the control of the number of vortex pairs nucleated by each spatial\nperiod of the modulational perturbation. By means of the perturbation theory,\nwe predict the number of the nucleated vortices per unit length. The analytical\nresults are corroborated by the numerical computation of eigenmodes of small\nperturbations, as well as by direct simulations of the underlying\nGross-Pitaevskii/nonlinear Schr\\\"{o}dinger equation.",
        "positive": "Anomalous frequency shifts in a one-dimensional trapped Bose gas: We consider a system of interacting bosons in one dimension at a two-body\nresonance. This system, which is weakly interacting, is known to give rise to\neffective three-particle interactions, whose dynamics is similar to that of a\ntwo-dimensional Bose gas with two-body interactions, and exhibits an identical\nscale anomaly. We consider the experimentally relevant scenario of a\nharmonically trapped system. We solve the three-body problem exactly and\nevaluate the shifts in the frequency of the lowest compressional mode with\nrespect to the dipole mode, and find that the effect of the anomaly is to\nincrease the mode's frequency. We also consider the weak-coupling regime of the\ntrapped many-boson problem and find, within the local density approximation,\nthat the frequency of the lowest compressional mode is also shifted upwards in\nthis limit. Moreover, the anomalous frequency shifts are enhanced by the higher\nparticle number to values that should be observable experimentally."
    },
    {
        "anchor": "Berezinskii-Kosterlitz-Thouless transition of two-dimensional Bose gases\n  in a synthetic magnetic field: We study the Berezinskii-Kosterlitz-Thouless transition of two-dimensional\nBose gases in a synthetic magnetic field using the standard Metropolis Monte\nCarlo method. The system is described by the frustrated XY model and the\ncritical temperature is calculated though the absence of central peak of the\nwave function in momentum space, which can be directly measured by the\ntime-of-flight absorbing imaging in cold atoms experiments. The results of our\nwork show agreement with former studies on superconducting Josephson arrays.",
        "positive": "Effective field theory for dilute Fermi systems at fourth order: We discuss high-order calculations in perturbative effective field theory for\nfermions at low energy scales. The Fermi-momentum or $k_{\\rm F} a_s$ expansion\nfor the ground-state energy of the dilute Fermi gas is calculated to fourth\norder, both in cutoff regularization and in dimensional regularization. For the\ncase of spin one-half fermions we find from a Bayesian analysis that the\nexpansion is well-converged at this order for ${| k_{\\rm F} a_s | \\lesssim\n0.5}$. Further, we show that Pad{\\'e}-Borel resummations can improve the\nconvergence for ${| k_{\\rm F} a_s | \\lesssim 1}$. Our results provide important\nconstraints for nonperturbative calculations of ultracold atoms and dilute\nneutron matter."
    },
    {
        "anchor": "Berry Phase in Atom-Molecule Conversion Systems and Fractional Monopole: We investigate the geometric phase or Berry phase of adiabatic quantum\nevolution in an atom-molecule conversion system, and find that the Berry phase\nin such system consists of two parts: the usual Berry connection term and a\nnovel term from the nonlinearity brought forth by the atom-molecule conversion.\nThe geometric phase can be viewed as the flux of the magnetic field of a\nmonopole through the surface enclosed by a closed path in parameter space. The\ncharge of the monopole, however, is found to be one third of the elementary\ncharge of the usual quantized monopole.",
        "positive": "Semiclassical Hartree-Fock theory of a rotating Bose-Einstein\n  condensation: In this paper, we investigate the thermodynamic behavior of a rotating\nBose-Einstein condensation with non-zero interatomic interactions\ntheoretically. The analysis relies on a semiclassical Hartree-Fock\napproximation where an integral is performed over the phase space and function\nof the grand canonical ensemble is derived. Subsequently, we use this result to\nderive several thermodynamic quantities including the condensate fraction,\ncritical temperature, entropy and heat capacity. Thereby, we investigate the\neffect of the rotation rate and interactions parameter on the thermodynamic\nbehavior. The role of finite size is discussed. Our approach can be extended to\nconsider the rotating condensate in optical potential."
    },
    {
        "anchor": "Observation of a dissipative time crystal in a strongly interacting\n  Rydberg gas: The notion of spontaneous symmetry breaking has been well established to\ncharacterize classical and quantum phase transitions of matter, such as in\ncondensation, crystallization or quantum magnetism. Generalizations of this\nparadigm to the time dimension can lead to an exotic dynamical phase, the time\ncrystal, which spontaneously breaks the time translation symmetry of the system\n[1]. While the existence of a continuous time crystal at equilibrium has been\nchallenged by no-go theorems [2-4], the difficulty can be circumvented by\ndissipation in an open system. Here, we report the experimental observation of\nsuch dissipative time crystalline order in a room-temperature atomic gas, where\nground-state atoms are continuously driven to Rydberg states. The emergent time\ncrystal is revealed by persistent oscillations of the photon transmission, with\nno observable damping during the measurement. We show that the observed limit\ncycles arise from the coexistence and competition between distinct Rydberg\ncomponents, in agreement with a mean-field analysis derived from the\nmicroscopic model. The nondecaying autocorrelation of the oscillation, together\nwith the robustness against temporal noises, indicates the establishment of\ntrue long-range temporal order and demonstrates the realization of a continuous\ntime crystal in our experiments.",
        "positive": "Dissipation and fluctuations in elongated bosonic Josephson junctions: We investigate the dynamics of bosonic atoms in elongated Josephson\njunctions. We find that these systems are characterized by an intrinsic\ncoupling between the Josephson mode of macroscopic quantum tunneling and the\nsound modes. This coupling of Josephson and sound modes gives rise to a damped\nand stochastic Langevin dynamics for the Josephson degree of freedom. From a\nmicroscopic Lagrangian, we deduce and investigate the damping coefficient and\nthe stochastic noise, which includes thermal and quantum fluctuations. Finally,\nwe study the time evolution of relative-phase and population-imbalance\nfluctuations of the Josephson mode and their oscillating thermalization to\nequilibrium."
    },
    {
        "anchor": "Two-point momentum correlations of few ultracold quasi-one-dimensional\n  trapped fermions: Diffraction patterns: Spatial and momentum correlations are important in the analysis of the\nquantum states and different phases of trapped ultracold atom systems as a\nfunction of the strength of interatomic interactions. Identification and\nunderstanding of spin-resolved patterns exhibited in two-point correlations,\naccessible directly by experiments, are key for uncovering the symmetry and\nstructure of the many-body wave functions of the trapped system. Using the\nconfiguration interaction method for exact diagonalization of the many-body\nHamiltonian of $N=2-4$ fermionic atoms trapped in single, double, triple, and\nquadruple wells, we analyze both two-point momentum and space correlations, as\nwell as associated noise distributions, for a broad range of interparticle\ncontact repulsion strengths and interwell separations, unveiling\ncharacteristics allowing insights into the transition, via an intermediate\nphase, from the non-interacting Bose-Einstein condensate to the weakly\ninteracting quasi-Bose-Einstein regime, and from the latter to the\nstrong-repulsion Tonks-Girardeau (TG) one. The ab-initio numerical predictions\nare shown to agree well with the results of a constructed analytical model\nemploying localized displaced Gaussian functions to represent the $N$ fermions.\nThe two-point momentum correlations are found to exhibit damped oscillatory\ndiffraction behavior. This diffraction behavior develops fully for atoms\ntrapped in a single well with strong interatomic repulsion in the TG regime, or\nfor atoms in well-separated multi-well traps. Additionally, the two-body\nmomentum correlation and noise distributions are found to exhibit\n\"shortsightedness\", with the main contribution coming from nearest-neighboring\nparticles.",
        "positive": "Thermalization of strongly interacting bosons after spontaneous\n  emissions in optical lattices: We study the out-of-equilibrium dynamics of bosonic atoms in a 1D optical\nlattice, after the ground-state is excited by a single spontaneous emission\nevent, i.e. after an absorption and re-emission of a lattice photon. This is an\nimportant fundamental source of decoherence for current experiments, and\nunderstanding the resulting dynamics and changes in the many-body state is\nimportant for controlling heating in quantum simulators. Previously it was\nfound that in the superfluid regime, simple observables relax to values that\ncan be described by a thermal distribution on experimental time-scales, and\nthat this breaks down for strong interactions (in the Mott insulator regime).\nHere we expand on this result, investigating the relaxation of the momentum\ndistribution as a function of time, and discussing the relationship to\neigenstate thermalization. For the strongly interacting limit, we provide an\nanalytical analysis for the behavior of the system, based on an effective\nlow-energy Hamiltonian in which the dynamics can be understood based on\ncorrelated doublon-holon pairs."
    },
    {
        "anchor": "Spatial Patterns of Rydberg Excitations from Logarithmic Pair\n  Interactions: The collective excitations in ensembles of dissipative, laser driven\nultracold atoms exhibit crystal-like patterns, a many-body effect of the\nRydberg blockade mechanism. These crystalline structure are revealed in\nexperiment from a post-selection of configurations with fixed numbers of\nexcitations. Here, we show that these sub-ensemble can be well represented by\nensembles of effective particles that interact via logarithmic pair potentials.\nThis allows one to study the emergent patterns with a small number of effective\nparticles to determine the phases of Rydberg crystals and to systematically\nstudy contributions from $N$-body terms.",
        "positive": "Dissipation-induced dynamical phase transition in postselected quantum\n  trajectories: It is known that effects of dissipation or measurement backreaction in\npostselected quantum trajectories are described by non-Hermitian Hamiltonian,\nbut their consequences in real-time dynamics of many-body systems are yet to be\nelucidated. Through a study of a non-Hermitian Hubbard model, we reveal a novel\ndissipation-induced dynamical phase transition in postselected quantum\ntrajectories, where time controls the strength of postselection and becomes the\nintrinsic parameter inducing the phase transition. Our findings are testable in\nultracold atom experiments and may open a new avenue in the dissipative\nengineering of quantum systems."
    },
    {
        "anchor": "From Cosmology to Cold Atoms: Observation of Sakharov Oscillations in\n  Quenched Atomic Superfluids: Sakharov oscillations, conventionally discussed in the context of early\nuniverse evolution and the anisotropy of cosmic microwave background radiation,\nis the manifestation of interfering acoustic waves synchronously generated in\nan ideal fluid. Here we report the laboratory demonstration of Sakharov\noscillations in a quenched atomic superfluid. We quench the sample by Feshbach\ntuning and monitor the subsequent density fluctuations at different time and\nlength scales by in situ imaging. Sakharov oscillations are identified as the\nmulti-peak structure in the atomic density power spectrum, resembling that of\nthe cosmic microwave background. We also observe Sakharov oscillations in the\ntime domain, from which we extract the energy dispersion of the superfluid, and\ndetermine the sonic horizon of the excitations.",
        "positive": "Phase diagrams of Bose-Hubbard model and Haldane-Bose-Hubbard model with\n  complex hopping amplitudes: In this paper, we study Bose-Hubbard models on the square and honeycomb\nlattices with complex hopping amplitudes, which are feasible by recent\nexperiments of cold atomic gases in optical lattices. To clarify phase\ndiagrams, we use an extended quantum Monte-Carlo simulations (eQMC). For the\nsystem on the square lattice, the complex hopping is realized by an artificial\nmagnetic field. We found that vortex-solid states form for certain set of\nmagnetic field, i.e., the magnetic field with the flux quanta per plaquette\n$f=p/q$, where $p$ and $q$ are co-prime natural numbers. For the system on the\nhoneycomb lattice, we add the next-nearest neighbor complex hopping. The model\nis a bosonic analog of the Haldane-Hubbard model. By means of the eQMC, we\nstudy the model with both weak and strong on-site repulsions. Numerical study\nshows that the model has a rich phase diagram. We also found that in the system\ndefined on the honeycomb lattice of the cylinder geometry, an interesting edge\nstate appears."
    },
    {
        "anchor": "Topological Quantum Phase Transition in Synthetic Non-Abelian Gauge\n  Potential: The method of synthetic gauge potentials opens up a new avenue for our\nunderstanding and discovering novel quantum states of matter. We investigate\nthe topological quantum phase transition of Fermi gases trapped in a honeycomb\nlattice in the presence of a synthetic non- Abelian gauge potential. We develop\na systematic fermionic effective field theory to describe a topological quantum\nphase transition tuned by the non-Abelian gauge potential and ex- plore its\nvarious important experimental consequences. Numerical calculations on lattice\nscales are performed to compare with the results achieved by the fermionic\neffective field theory. Several possible experimental detection methods of\ntopological quantum phase tran- sition are proposed. In contrast to condensed\nmatter experiments where only gauge invariant quantities can be measured, both\ngauge invariant and non-gauge invariant quantities can be measured by\nexperimentally generating various non-Abelian gauges corresponding to the same\nset of Wilson loops.",
        "positive": "Unraveling the Structure of Ultracold Mesoscopic Molecular Ions: We present an in-depth many-body investigation of the so-called mesoscopic\nmolecular ions that can build-up when an ion is immersed into an atomic\nBose-Einstein condensate in one dimension. To this end, we employ the\nMulti-Layer Multi-Configuration Time-Dependent Hartree method for Mixtures of\nultracold bosonic species for solving the underlying many-body Schr\\\"odinger\nequation. This enables us to unravel the actual structure of such massive\ncharged molecules from a microscopic perspective. Laying out their phase\ndiagram with respect to atom number and interatomic interaction strength, we\ndetermine the maximal number of atoms bound to the ion and reveal spatial\ndensities and molecular properties. Interestingly, we observe a strong\ninteraction-induced localization, especially for the ion, that we explain by\nthe generation of a large effective mass, similarly to ions in liquid Helium.\nFinally, we predict the dynamical response of the ion to small perturbations.\nOur results provide clear evidence for the importance of quantum correlations,\nas we demonstrate by benchmarking them with wave function ansatz classes\nemployed in the literature."
    },
    {
        "anchor": "Dissipative preparation of phase- and number-squeezed states with\n  ultracold atoms: We develop a dissipative quantum state preparation scheme for the creation of\nphase- and number-squeezed states. It utilizes ultracold atoms in a double-well\nconfiguration immersed in a background Bose-Einstein condensate, with the\nlatter consisting of an atom species different from the atoms in the double\nwell and acting as a dissipative quantum reservoir. We derive a master equation\nfor this system starting from microscopic physics, and show that squeezing\ndevelops on a time scale proportional to $1/N$, where $N$ is the number of\nparticles in the double well. This scaling, caused by bosonic enhancement,\nallows us to make the time scale for the creation of squeezed states very\nshort. The lifetime of squeezed states is limited by dephasing arising from the\nintrinsic structure of the setup. However, the dephasing can be avoided by\nstroboscopically switching the driving off and on. We show that this approach\nleads to robust stationary squeezed states. Finally, we provide the necessary\ningredients for a potential experimental implementation by specifying a\nparameter regime for rubidium atoms that leads to squeezed states.",
        "positive": "Studying Superfluid Transition of a Dilute Bose Gas by Conserving\n  Approximations: We consider the Bose-Einstein transition of homogeneous weakly interacting\nspin-0 particles based on the normal-state Phi-derivable approximation.\nSelf-consistent calculations of Green's function and the chemical potential\nwith several approximate Phi's are performed numerically as a function of\ntemperature near Tc, which exhibit qualitatively different results. The ladder\napproximation apparently shows a continuous transition with the prefactor\nc=2.94 for the transition-temperature shift given in terms of the scattering\nlength a and density n. In contrast, the second-order, particle-hole, and\nfluctuation-exchange approximations yield a first-order transition. The fact\nthat some standard Phi's predict a first-order transition challenges us to\nclarify whether or not the transition is really continuous."
    },
    {
        "anchor": "Many-body processes in black and grey matter-wave solitons: We perform a comparative beyond mean-field study of black and grey solitonic\nexcitations in a finite ensemble of ultracold bosons confined to a\none-dimensional box. An optimized density-engineering potential is developed\nand employed together with phase-imprinting to cleanly initialize grey\nsolitons. Based on our recently developed Multi-Layer Multi-Configuration\nTime-Dependent Hartree Method for Bosons, we demonstrate an enhancement of the\nquantum fluctuations limited lifetime of the soliton contrast with increasing\nsoliton velocity. A natural orbital analysis reveals a two-stage process\nunderlying the decay of the soliton contrast. The broken parity symmetry of\ngrey solitons results in a local asymmetry of the orbital mainly responsible\nfor the decay, which leads to a characteristic asymmetry of remarkably\nlocalized two-body correlations. The emergence and decay of these correlations\nas well as their displacement from the instantaneous soliton position are\nanalysed in detail. Finally, the role of phase-imprinting for the many-body\ndynamics is illuminated and additional non-local correlations in pairs of\ncounter-propagating grey solitons are unravelled.",
        "positive": "Permanent magnetic microtraps for ultracold atoms: We propose and numerically study two permanent magnetic micro-structures for\ncreating Ioffe-Pritchard microtraps. A bias magnetic field is used to vary the\ndepth, trap frequencies and the minimum of each microtrap. After the\nBose-Einstein condensation achievement, the bias magnetic field can be slowly\nremoved to increase the trap barrier heights for more efficiently holding the\nBose-Einstein condensates. Even without the external magnetic field, it is\npossible to hold ultracold atoms in the microtraps. These microtraps may also\nbe useful for single atom experiments for quantum information processing due to\ntheir very high confinement."
    },
    {
        "anchor": "Localization from quantum interference in one-dimensional disordered\n  potentials: We show that the tails of the asymptotic density distribution of a quantum\nwave packet that localizes in the the presence of random or quasiperiodic\ndisorder can be described by the diagonal term of the projection over the\neingenstates of the disordered potential. This is equivalent of assuming a\nphase randomization of the off-diagonal/interference terms. We demonstrate\nthese results through numerical calculations of the dynamics of ultracold atoms\nin the one-dimensional speckle and quasiperiodic potentials used in the recent\nexperiments that lead to the observation of Anderson localization for matter\nwaves [Billy et al., Nature 453, 891 (2008); Roati et al., Nature 453, 895\n(2008)]. For the quasiperiodic case, we also discuss the implications of using\ncontinuos or discrete models.",
        "positive": "Quantitative comparison between theoretical predictions and experimental\n  results for Bragg spectroscopy of a strongly interacting Fermi superfluid: Theoretical predictions for the dynamic structure factor of a harmonically\ntrapped Fermi superfluid near the BEC-BCS crossover are compared with recent\nBragg spectroscopy measurements at large transferred momenta. The calculations\nare based on a random-phase (or time-dependent Hartree-Fock-Gorkov)\napproximation generalized to the strongly interacting regime. Excellent\nagreement with experimental spectra at low temperatures is obtained, with no\nfree parameters. Theoretical predictions for zero-temperature static structure\nfactor are also found to agree well with the experimental results and\nindependent theoretical calculations based on the exact Tan relations. The\ntemperature dependence of the structure factors at unitarity is predicted."
    },
    {
        "anchor": "Twin matter waves for interferometry beyond the classical limit: Interferometers with atomic ensembles constitute an integral part of modern\nprecision metrology. However, these interferometers are fundamentally\nrestricted by the shot noise limit, which can only be overcome by creating\nquantum entanglement among the atoms. We used spin dynamics in Bose-Einstein\ncondensates to create large ensembles of up to $10^4$ pair-correlated atoms\nwith an interferometric sensitivity $-1.61^{+0.98}_{-1.1}$ dB beyond the shot\nnoise limit. Our proof-of-principle results point the way toward a new\ngeneration of atom interferometers.",
        "positive": "Observation of Feshbach resonances in an ${}^{167}$Er-${}^6$Li\n  Fermi-Fermi mixture: We present our experimental investigation of the interspecies Feshbach\nspectrum in a mixture of ${}^{167}$Er($F = 19/2, m_F = -19/2$)-${}^6$Li($F =\n1/2, m_F = 1/2$) atoms in the microkelvin temperature regime. These\ntemperatures are achieved by means of sympathetic cooling with ${}^{174}$Yb as\na third species. Interspecies Feshbach resonances are then identified by\ninvestigation of the Er-Li inelastic collisional properties for magnetic fields\nup to 800 G. Numerous narrow resonances as well as six resonances with widths\nabove 1 G could be identified. It is these broader resonances that hold much\npromise for interesting future investigations of, for exmample, novel\nsuperfluid states and Efimov states in large mass-imbalanced, all-fermionic\ntwo-component systems."
    },
    {
        "anchor": "\"Doubly-magic\" conditions in magic-wavelength trapping of ultracold\n  alkalis: In experiments with trapped atoms, atomic energy levels are shifted by the\ntrapping optical and magnetic fields. Regardless of this strong perturbation,\nprecision spectroscopy may be still carried out using specially crafted,\n\"magic\" trapping fields. Finding these conditions for particularly valuable\nmicrowave clock transitions in alkalis has so far remained an open challenge.\nHere I demonstrate that the microwave clock transitions for alkalis may be\nindeed made impervious to both trapping laser intensity and fluctuations of\nmagnetic fields. I consider driving multiphoton transitions between the clock\nlevels and show that these \"doubly-magic\" conditions are realized at special\nvalues of trapping laser wavelengths and fixed values of relatively weak\nmagnetic fields. This finding has implications for precision measurements and\nquantum information processing with qubits stored in hyperfine manifolds.",
        "positive": "Probing the optical conductivity of trapped charge-neutral quantum gases: We study a harmonically confined atomic gas which is subjected to an\nadditional external potential such as an optical lattice. Using a linear\nresponse formulation, we determine the response of the gas to a small,\ntime-dependent displacement of the harmonic trap and derive a simple exact\nrelation showing that the centre-of-mass position of the atomic cloud is\ndirectly related to the global optical conductivity of the system. We\ndemonstrate the usefulness of this approach by calculating the optical\nconductivity of bosonic atoms in an optical lattice. In the Mott insulating\nphase, there is clear evidence of an optical Mott gap, providing a\nproof-of-principle demonstration that the global optical conductivity gives\nhigh-quality information about the exci- tations of strongly-correlated quantum\ngases."
    },
    {
        "anchor": "Efficiency for preforming molecules from mixtures of light Fermi and\n  heavy Bose atoms in optical lattices: the strong-coupling-expansion method: We discuss the application of a strong-coupling expansion (perturbation\ntheory in the hopping) for studying light-Fermi-heavy-Bose (like\n$^{40}$K-$^{87}$Rb) mixtures in optical lattices. We use the strong-coupling\nmethod to evaluate the efficiency for pre-forming molecules, the entropy per\nparticle and the thermal fluctuations. We show that within the strong\ninteraction regime (and at high temperature), the strong-coupling expansion is\nan economical way to study this problem. In some cases, it remains valid even\ndown to low temperatures. Because the computational effort is minimal, the\nstrong-coupling approach allows us to work with much larger system sizes, where\nboundary effects can be eliminated, which is particularly important at higher\ntemperatures. Since the strong-coupling approach is so efficient and accurate,\nit allows one to rapidly scan through parameter space in order to optimize the\npre-forming of molecules on a lattice (by choosing the lattice depth and\ninterspecies attraction). Based on the strong-coupling calculations, we test\nthe thermometry scheme based on the fluctuation-dissipation theorem and find\nthe scheme gives accurate temperature estimation even at very low temperature.\nWe believe this approach and the calculation results will be useful in the\ndesign of the next generation of experiments, and will hopefully lead to the\nability to form dipolar matter in the quantum degenerate regime.",
        "positive": "Spin-orbit-coupling-assisted roton softening and superstripes in a\n  Rydberg-dressed Bose-Einstein Condensate: Rotons can exist in ultracold atomic gases either with long-range\ninteractions or with spin-orbitcoupled dispersions. We find that two different\nkinds of rotons coexist in a joint system combining long-range interactions and\nspin-orbit coupling. One roton originates from spin-orbit coupling and two\nothers come from long-range interactions. Their softening can be controlled\nseparately. The interesting new phenomenon which we find is that\nspin-orbit-coupled roton can push down the energy of one long-range-interaction\nroton. The spin-orbit coupling accelerates the softening of this roton. The\npost phase of spin-orbit-coupling-assisted roton softening and instability is\nidentified as a superstripe."
    },
    {
        "anchor": "Thermally induced coherence in a Mott insulator of bosonic atoms: Conventional wisdom is that increasing temperature causes quantum coherence\nto decrease. Using finite temperature perturbation theory and exact\ncalculations for the strongly correlated bosonic Mott insulating state we show\na practical counter-example that can be explored in optical lattice\nexperiments: the short-range coherence of the Mott insulating phase can\nincrease substantially with increasing temperature. We demonstrate that this\nphenomenon originates from thermally produced defects that can tunnel with\nease. Since the near zero temperature coherence properties have been measured\nwith high precision we expect these results to be verifiable in current\nexperiments.",
        "positive": "Atom Loss Maximum in Ultra-cold Fermi Gases: Recent experiments on atom loss in ultra-cold Fermi gases all show a maximum\nat a magnetic field below Feshbach resonance, where the s-wave scattering\nlength is large (close to inter-particle distance) and positive. These\nexperiments have been performed over a wide range of conditions, with\ntemperatures and trap depths spanning over three decades. Different groups have\ncome up with different explanations, among them the emergence of Stoner\nferromagnetism. Here, we show that this maximum is a consequence of two major\nsteps. The first is the establishment of a population of shallow dimers, which\nis the combined effect of dimer formation through three-body recombination, and\nthe dissociation of shallow dimers back to atoms through collisions. The\ndissociation process will be temperature dependent, and is affected by Pauli\nblocking at low temperatures. The second is the relaxation of shallow dimers\ninto tightly bound dimers through atom-dimer and dimer-dimer collisions.\n  We have constructed a simple set of rate equations describing these\nprocesses. Remarkably, even with only a few parameters, these equations\nreproduce the loss rate observed in all recent experiments, despite their\nwidely different experimental conditions. Our studies show that the location of\nthe maximum loss rate depends crucially on experimental parameters such as trap\ndepth and temperature. These extrinsic characters show that this maximum is not\na reliable probe of the nature of the underlying quantum states. The physics of\nour equations also explains some general trends found in current experiments."
    },
    {
        "anchor": "Anomalous oscillations of dark solitons in trapped dipolar condensates: Thanks to their immense purity and controllability, dipolar Bose-Einstein\ncondensates are an exemplar for studying fundamental non-local nonlinear\nphysics. Here we show that a family of fundamental nonlinear waves - the dark\nsolitons - are supported in trapped quasi-one-dimensional dipolar condensates\nand within reach of current experiments. Remarkably, the oscillation frequency\nof the soliton is strongly dependent on the atomic interactions, in stark\ncontrast to the non-dipolar case. The failure of a particle analogy, so\nsuccessful for dark solitons in general, to account for this behaviour implies\nthat these structures are inherently extended and non-particle-like. These\nhighly-sensitive waves may act as mesoscopic probes of the underlying quantum\nmatter field.",
        "positive": "Staggered superfluid phases of dipolar bosons in two-dimensional square\n  lattices: We study the quantum ground state of ultracold bosons in a two-dimensional\nsquare lattice. The bosons interact via the repulsive dipolar interactions and\ns-wave scattering. The dynamics is described by the extended Bose-Hubbard model\nincluding correlated hopping due to the dipolar interactions, the coefficients\nare found from the second quantized Hamiltonian using the Wannier expansion\nwith realistic parameters. We determine the phase diagram using the Gutzwiller\nansatz in the regime where the coefficients of the correlated hopping terms are\nnegative and can interfere with the tunneling due to single-particle effects.\nWe show that this interference gives rise to staggered superfluid and\nsupersolid phases at vanishing kinetic energy, while we identify parameter\nregions at finite kinetic energy where the phases are incompressible. We\ncompare the results with the phase diagram obtained with the cluster Gutzwiller\napproach and with the results found in one dimension using DMRG."
    },
    {
        "anchor": "Spin-Orbit Driven Transitions Between Mott Insulators and Finite\n  Momentum Superfluids of Bosons in Optical Lattices: Synthetic spin-orbit coupling in ultracold atomic gases can be taken to\nextremes rarely found in solids. We study a two dimensional Hubbard model of\nbosons in an optical lattice in the presence of spin-orbit coupling strong\nenough to drive direct transitions from Mott insulators to superfluids. Here we\nfind phase-modulated superfluids with finite momentum that are generated\nentirely by spin-orbit coupling. We investigate the rich phase patterns of the\nsuperfluids, which may be directly probed using time-of-flight imaging of the\nspin-dependent momentum distribution.",
        "positive": "Quasiparticle dynamics in a Bose insulator probed by inter-band Bragg\n  spectroscopy: We investigate experimentally and theoretically the dynamical properties of a\nMott insulator in decoupled one-dimensional chains. Using a theoretical\nanalysis of the Bragg excitation scheme we show that the spectrum of inter-band\ntransitions holds information on the single-particle Green's function of the\ninsulator. In particular the existence of particle-hole coherence due to\nquantum fluctuations in the Mott state is clearly seen in the Bragg spectra and\nquantified. Finally we propose a scheme to directly measure the full, momentum\nresolved spectral function as obtained in angle-resolved photoemission\nspectroscopy of solids."
    },
    {
        "anchor": "Tying Quantum Knots: Knots are familiar entities that appear at a captivating nexus of art,\ntechnology, mathematics, and science. As topologically stable objects within\nfield theories, they have been speculatively proposed as explanations for\ndiverse persistent phenomena, from atoms and molecules to ball lightning and\ncosmic textures in the universe. Recent experiments have observed knots in a\nvariety of classical contexts, including nematic liquid crystals, DNA, optical\nbeams, and water. However, no experimental observations of knots have yet been\nreported in quantum matter. We demonstrate here the controlled creation and\ndetection of knot solitons in the order parameter of a spinor Bose-Einstein\ncondensate. The experimentally obtained images of the superfluid directly\nreveal the circular shape of the soliton core and its accompanying linked\nrings. Importantly, the observed texture corresponds to a topologically\nnon-trivial element of the third homotopy group and demonstrates the celebrated\nHopf fibration, which unites many seemingly unrelated physical contexts. Our\nobservations of the knot soliton establish an experimental foundation for\nfuture studies of their stability and dynamics within quantum systems.",
        "positive": "Lack of a genuine time crystal in a chiral soliton model: In a recent publication [Phys. Rev. Lett. {\\bf 124}, 178902] \\\"Ohberg and\nWright claim that in a chiral soliton model it is possible to realize a genuine\ntime crystal which corresponds to a periodic evolution of an inhomogeneous\nprobability density in the lowest energy state. We show that this result is\nincorrect and present a solution which possesses lower energy with the\ncorresponding probability density that does not reveal any motion. It implies\nthat the authors' conclusion that a genuine time crystal can exist in the\nsystem they consider is not true."
    },
    {
        "anchor": "Dielectric response of electron-hole systems. Nondegenerate case and\n  quantum corrections: Analytical results for the dielectric function in RPA are derived for three-,\ntwo-, and one-dimensional semiconductors in the weakly-degenerate limit. Based\non this limit, quantum corrections are derived. Further attention is devoted to\nsystems with linear carrier dispersion and the resulting Dirac-cone physics.",
        "positive": "Universal Early Coarsening of Quenched Bose Gases: We investigate the early coarsening dynamics of an atomic Bose gas quenched\ninto a superfluid phase. Using a two-step quench protocol, we effectively\ncontrol the cooling rates, $r_1$ and $r_2$, during and after passing through\nthe critical region, respectively, and measure the number of quantum vortices\nspontaneously created in the system. The latter cooling rate $r_2$ regulates\nthe temperature during the condensate growth, consequently controlling the\nearly coarsening dynamics in the defect formation. We find that the defect\nnumber shows a scaling behavior with $r_2$ regardless of the initial cooling\nrate $r_1$, indicating universal coarsening dynamics in the early stage of\ncondensate growth. Our results demonstrate that early coarsening not only\nreduces the defect density but also affects its scaling with the quench rate,\nwhich is beyond the Kibble-Zurek mechanism."
    },
    {
        "anchor": "Stability of the Superfluid State in Three-Component Fermionic Optical\n  Lattice Systems: Three-component fermionic optical lattice systems are investigated in\ndynamical mean-field theory for the Hubbard model. Solving the effective\nimpurity model by means of continuous-time quantum Monte Carlo simulations in\nthe Nambu formalism, we find that the $s$-wave superfluid state proposed\nrecently is indeed stabilized in the repulsively interacting case and appears\nalong the first-order phase boundary between the metallic and paired Mott\nstates in the paramagnetic system. The BCS-BEC crossover in the three-component\nfermionic system is also addressed.",
        "positive": "Controlling dynamical entanglement in a Josephson tunneling junction: We analyze the evolution of an entangled many-body state in a Josephson\ntunneling junction. A N00N state, which is a superposition of two complementary\nFock states, appears in the evolution with sufficient probability only for a\nmoderate many-body interaction on an intermediate time scale. This time scale\nis inversely proportional to the tunneling rate. Interaction between particles\nsupports entanglement: The probability for creating an entangled state decays\nexponentially with the number of non-interacting particles, whereas it decays\nonly like the inverse square root of the number of interacting particles."
    },
    {
        "anchor": "Many-body quantum chaos in stroboscopically-driven cold atoms: In quantum chaotic systems, the spectral form factor (SFF), defined as the\nFourier transform of the two-level spectral correlation function, is known to\nfollow random matrix theory (RMT), namely a 'ramp' followed by a 'plateau' in\nsufficiently late times. Recently, a generic early-time deviation from the RMT\nbehavior, which we call the 'bump', was shown to exist in random quantum\ncircuits and spin chains as toy models for many-body quantum chaotic systems.\nHere we demonstrate the existence of the 'bump-ramp-plateau' behavior in the\nSFF for a number of paradigmatic and stroboscopically-driven 1D cold atom\nmodels: (i) Bose-Hubbard model, (ii) spin$-1/2$ Bose-Hubbard model, and (iii)\nnonintegrable spin-$1$ condensate with contact or dipolar interactions. We find\nthat the scaling of the many-body Thouless time $t_{\\textrm{Th}}$ -- the onset\nof RMT -- , and the bump amplitude are more sensitive to variations in atom\nnumber than the lattice size regardless of the hyperfine structure, the\nsymmetry classes, or the choice of driving protocol. Moreover,\n$t_{\\textrm{Th}}$ scaling and the increase of the bump amplitude in atom number\nare significantly slower in spinor gases than interacting bosons in 1D optical\nlattices, demonstrating the role of locality. We obtain universal scaling\nfunctions of SFF which suggest power-law behavior for the bump regime in\nquantum chaotic cold-atom systems, and propose an interference measurement\nprotocol.",
        "positive": "Fate of the Bose polaron at finite temperature: We consider an impurity immersed in a Bose-Einstein condensate with tunable\nboson-impurity interactions. Such a Bose polaron has recently been predicted to\nexhibit an intriguing energy spectrum at finite temperature, where the\nground-state quasiparticle evenly splits into two branches as the temperature\nis increased from zero [Guenther et al., Phys. Rev. Lett. 120, 050405 (2018)].\nTo investigate this theoretical prediction, we employ a recently developed\nvariational approach that systematically includes multi-body correlations\nbetween the impurity and the finite-temperature medium, thus allowing us to go\nbeyond previous finite-temperature methods. Crucially, we find that the number\nof quasiparticle branches is simply set by the number of hole excitations of\nthe thermal cloud, such that including up to one hole yields one splitting, two\nholes yields two splittings, and so on. Moreover, this effect is independent of\nthe impurity mass. We thus expect that the exact ground-state quasiparticle\nwill evolve into a single broad peak for temperatures $T>0$, with a broadening\nthat scales as $T^{3/4}$ at low temperatures and sufficiently weak boson-boson\ninteractions. In the zero-temperature limit, we show that our calculated\nground-state polaron energy is in excellent agreement with recent quantum Monte\nCarlo results and with experiments."
    },
    {
        "anchor": "Tunable source of correlated atom beams: We use a one-dimensional optical lattice to modify the dispersion relation of\natomic matter waves. Four-wave mixing in this situation produces atom pairs in\ntwo well defined beams. We show that these beams present a narrow momentum\ncorrelation, that their momenta are precisely tunable, and that this pair\nsource can be operated both in the regime of low mode occupancy and of high\nmode occupancy.",
        "positive": "Stability of spin-orbit coupled Fermi gases with population imbalance: We use the self-consistent mean-field theory to analyze the effects of\nRashba-type spin-orbit coupling (SOC) on the ground-state phase diagram of\npopulation-imbalanced Fermi gases throughout the BCS-BEC evolution. We find\nthat the SOC and population imbalance are counteracting, and that this\ncompetition tends to stabilize the uniform superfluid phase against the phase\nseparation. However, we also show that the SOC stabilizes (destabilizes) the\nuniform superfluid phase against the normal phase for low (high) population\nimbalances. In addition, we find topological quantum phase transitions\nassociated with the appearance of momentum space regions with zero\nquasiparticle energies, and study their signatures in the momentum\ndistribution."
    },
    {
        "anchor": "Phase Diagram of Rydberg atoms in a nonequilibrium optical lattice: We study the quantum nonequilibrium dynamics of ultracold three-level atoms\ntrapped in an optical lattice, which are excited to their Rydberg states via a\ntwo-photon excitation with nonnegligible spontaneous emission. Rich quantum\nphases including uniform phase, antiferromagnetic phase and oscillatory phase\nare identified. We map out the phase diagram and find these phases can be\ncontrolled by adjusting the ratio of intensity of the pump light to the control\nlight, and that of two-photon detuning to the Rydberg interaction strength.\nWhen the two-photon detuning is blue-shifted and the latter ratio is less than\n1, bistability exists among the phases. Actually, this ratio controls the\nRydberg-blockade and antiblockade effect, thus the phase transition in this\nsystem can be considered as a possible approach to study both effects.",
        "positive": "The Uhlmann Phase Winding in Bose-Einstein Condensates at Finite\n  Temperature: We investigate the Uhlmann phase, a generalization of the celebrated Berry\nphase, for Bose-Einstein condensates (BECs) at finite temperature. The Uhlmann\nphase characterizes topological properties of mixed states, in contrast to the\nBerry phase which is defined for pure states at zero temperature. Using the\n$SU(1,1)$ symmetry of the Bogoliubov Hamiltonian, we derive a general formula\nfor the Uhlmann phase of BECs. Numerical calculations reveal that the Uhlmann\nphase can differ from the Berry phase in the zero-temperature limit, contrary\nto previous studies. As the temperature increases, the Uhlmann phase exhibits a\nwinding behavior, and we relate the total winding degree to the Berry phase.\nThis winding indicates that the Uhlmann phase takes values on a Riemann\nsurface. Furthermore, we propose an experimental scheme to measure the Uhlmann\nphase of BECs by purifying the density matrix using an atomic interferometer."
    },
    {
        "anchor": "The effect of atom losses on the distribution of rapidities in the\n  one-dimensional Bose gas: We theoretically investigate the effects of atom losses in the\none-dimensional (1D) Bose gas with repulsive contact interactions, a famous\nquantum integrable system also known as the Lieb-Liniger gas. The generic case\nof K-body losses (K = 1,2,3,...) is considered. We assume that the loss rate is\nmuch smaller than the rate of intrinsic relaxation of the system, so that at\nany time the state of the system is captured by its rapidity distribution (or,\nequivalently, by a Generalized Gibbs Ensemble). We give the equation governing\nthe time evolution of the rapidity distribution and we propose a general\nnumerical procedure to solve it. In the asymptotic regimes of vanishing\nrepulsion -- where the gas behaves like an ideal Bose gas -- and hard-core\nrepulsion -- where the gas is mapped to a non-interacting Fermi gas -- we\nderive analytic formulas. In the latter case, our analytic result shows that\nlosses affect the rapidity distribution in a non-trivial way, the time\nderivative of the rapidity distribution being both non-linear and non-local in\nrapidity space.",
        "positive": "Propagation of Second sound in a superfluid Fermi gas in the unitary\n  limit: We study sound propagation in a uniform superfluid gas of Fermi atoms in the\nunitary limit. The existence of normal and superfluid components leads to\nappearance of two sound modes in the collisional regime, referred to as first\nand second sound. The second sound is of particular interest as it is a clear\nsignal of a superfluid component. Using Landau's two-fluid hydrodynamic theory,\nwe calculate hydrodynamic sound velocities and these weights in the density\nresponse function. The latter is used to calculate the response to a sudden\nmodification of the external potential generating pulse propagation. The\namplitude of a pulse which is proportional to the weight in the response\nfunction, is calculated the basis of the approach of Nozieres and Schmitt-Rink\n(NSR) for the BCS-BEC crossover. We show that, in a superfluid Fermi gas at\nunitarity, the second sound pulse is excited with an appreciate amplitude by\ndensity perturbations."
    },
    {
        "anchor": "Synthetic charge-flux quantum liquids: We apply rotating optical flux lattices to spinor Bose-Einstein condensates.\nDistinct quantum states emerge for fractional ratios of vortex charge density\nto optical flux density. We exhibit the calculated charge-flux states and\ndiscuss their topological structure and experimental signatures.",
        "positive": "Equation of State of a Strongly Interacting many-Boson System from an\n  Effective Interaction: A contact potential describing an effective interaction between atomic $^4$He\nreproducing the results obtained with the HFDHE2 potential by Aziz et al. is\nemployed to study the resulting equation of state by means of Quantum Monte\nCarlo calculations. \\cblack The energy per particle and the pair distribution\nfunctions were investigated as a function of the ultraviolet cutoff $\\Lambda$.\nThe results suggest that not only the mean field properties of the system, such\nas the energy and the saturation density, are correctly reproduced, but also\nvery microscopic quantities such as the pair distribution function are seen to\nconverge towards the exact results when extrapolating for\n$\\Lambda\\rightarrow\\infty$."
    },
    {
        "anchor": "Thermalized Abrikosov lattices from decaying turbulence in rotating BECs: We study the long-time decay of rotating turbulence in Bose-Einstein\ncondensates (BECs). We consider the Gross-Pitaevskii equation in a rotating\nframe of reference, and review different formulations for the Hamiltonian of a\nrotating BEC. We discuss how the energy can be decomposed, and present a method\nto generate out-of-equilibrium initial conditions. We also present a method to\ngenerate finite-temperature states of rotating BECs compatible with the\nCanonical or the Grand canonical ensembles. Finally, we integrate numerically\nrotating BECs in cigar-shaped traps. A transition is found in the system\ndynamics as the rotation rate is increased, with a final state of the decay of\nthe turbulent flow compatible with an Abrikosov lattice in a finite-temperature\nthermalized state.",
        "positive": "Spin-susceptibility of spin-orbit coupled Fermi superfluids: Under the self-consistent mean-field approach for the BCS-BEC crossover\nproblem, we derive a closed-form analytical expression for the general spin\nresponse of noncentrosymmetric Fermi superfluids with arbitrary spin-orbit\ncoupling and Zeeman fields. In addition to the paramagnetic, i.e., the Pauli\nintra-helicity and Van Vleck type inter-helicity, contributions to the\nspin-susceptibility tensor that have normal-state counterparts, we identify a\ndiamagnetic inter-helicity contribution that is unique to the superfluid state.\nOur extensive numerical calculations for the Weyl, Rashba and equal\nRashba-Dresselhaus spin-orbit couplings illustrate that it is this diamagnetic\ncontribution that grows gradually with pairing and cancels precisely the Van\nVleck contribution away from the BCS regime in general."
    },
    {
        "anchor": "A unified theory of strong coupling Bose polarons: From repulsive\n  polarons to non-Gaussian many-body bound states: We address the Bose polaron problem of a mobile impurity interacting strongly\nwith a host Bose-Einstein condensate (BEC) through a Feshbach resonance. On the\nrepulsive side at strong couplings, theoretical approaches predict two distinct\npolaron branches corresponding to attractive and repulsive polarons, but it\nremains unclear how the two are related. This is partly due to the challenges\nresulting from a competition of strongly attractive (destabilizing)\nimpurity-boson interactions with weakly repulsive (stabilizing) boson-boson\ninteractions, whose interplay is difficult to describe with contemporary\ntheoretical methods. Here we develop a powerful variational framework that\ncombines Gaussian correlations among impurity-boson scattering states,\nincluding up to an infinite number of bosonic excitations, with exact\nnon-Gaussian correlations among bosons occupying an impurity-boson bound state.\nThis variational scheme enables a full treatment of strong nonlinearities\narising in the Feshbach molecule on the repulsive side of the resonance. Within\nthis framework, we demonstrate that the interplay of impurity-induced\ninstability and stabilization by repulsive boson-boson interactions results in\na discrete set of metastable many-body bound states at intermediate energies\nbetween the attractive and repulsive polaron branches. These states exhibit\nstrong quantum statistical characteristics in the form of non-Gaussian quantum\ncorrelations, requiring non-perturbative beyond mean-field treatments for their\ncharacterization. Furthermore, these many-body bound states have sizable\nmolecular spectral weights, accessible via molecular spectroscopy techniques.\nThis work provides a unified theory of attractive and repulsive Bose polarons\non the repulsive side of the Feshbach resonance.",
        "positive": "Tunneling dynamics of correlated bosons in a double well potential: The quantum dynamics of a few bosons in a double well potential is studied\nusing a Bose Hubbard model. We consider both signs for the on-site\ninterparticle interaction and also investigated the situations where they are\nlarge and small. Interesting distinctive features are noted for the tunneling\noscillations of these bosons corresponding to the above scenarios. Further, the\nsensitivity of the particle dynamics to the initial conditions has been\nstudied. It is found that corresponding to an odd number of particles, such as\nthree (or five), an initial condition of having unequal number of particles in\nthe wells has interesting consequences, which is most discernible when the\npopulation difference between the wells is unity."
    },
    {
        "anchor": "Anomalous loss behavior in a single-component Fermi gas close to a\n  $p$-Wave Feshbach resonance: We theoretically investigate three-body losses in a single-component Fermi\ngas near a $p$-wave Feshbach resonance in the interacting, non-unitary regime.\nWe extend the cascade model introduced by Waseem \\textit{et al.} [M. Waseem, J.\nYoshida, T. Saito, and T. Mukaiyama, Phys. Rev. A \\textbf{99}, 052704 (2019)]\nto describe the elastic and inelastic collision processes. We find that the\nloss behavior exhibits a $n^3$ and an anomalous $n^2$ density dependence for a\nratio of elastic-to-inelastic collision rate larger and smaller than 1,\nrespectively. The corresponding evolutions of the energy distribution show\ncollisional cooling or evolution toward low-energetic non-thermalized steady\nstates, respectively. These findings are particularly relevant for\nunderstanding atom loss and energetic evolution of ultracold gases of fermionic\nlithium atoms in their ground state.",
        "positive": "Persistent, controllable circulation of a polariton ring condensate: Persistent circulation is a canonical effect of superfluidity. In previous\nexperiments, quantized circulation has been observed in polariton condensates,\nusually far from equilibrium, but persistent current in the absence of any\nstirring has not been seen. We report here the direct observation of persistent\ncirculation of a polariton condensate with no driving force and with no\nobservable change in time. We can cause the condensate to circulate in either\ndirection on demand using a short laser pulse, after which the condensate\ncontinues to circulate for dozens to hundreds of rotations around a ring trap\nwithout any further stimulation. Our theoretical model successfully shows how\nthe pulse, despite not carrying any angular momentum, causes the circulation."
    },
    {
        "anchor": "Solution of the Riemann problem for polarization waves in a\n  two-component Bose-Einstein condensate: We provide a classification of the possible flow of two-component\nBose-Einstein condensates evolving from initially discontinuous profiles. We\nconsider the situation where the dynamics can be reduced to the consideration\nof a single polarization mode (also denoted as \"magnetic excitation\") obeying a\nsystem of equations equivalent to the Landau-Lifshitz equation for an\neasy-plane ferro-magnet. We present the full set of one-phase periodic\nsolutions. The corresponding Whitham modulation equations are obtained together\nwith formulas connecting their solutions with the Riemann invariants of the\nmodulation equations. The problem is not genuinely nonlinear, and this results\nin a non-single-valued mapping of the solutions of the Whitham equations with\nphysical wave patterns as well as to the appearance of new elements --- contact\ndispersive shock waves --- that are absent in more standard, genuinely\nnonlinear situations. Our analytic results are confirmed by numerical\nsimulations.",
        "positive": "Analogue Stochastic Gravity in Strongly-Interacting Bose-Einstein\n  Condensates: Collective modes propagating in a moving superfluid are known to satisfy wave\nequations in a curved space time, with a metric determined by the underlying\nsuperflow. We use the Keldysh technique in a curved space-time to develop a\nquantum geometric theory of fluctuations in superfluid hydrodynamics. This\ntheory relies on a 'quantized' generalization of the two-fluid description of\nLandau and Khalatnikov, where the superfluid component is viewed as a\nquasi-classical field coupled to a normal component -- the collective\nmodes/phonons representing a quantum bath. This relates the problem in the\nhydrodynamic limit to the 'quantum friction' problem of Caldeira-Leggett type.\nBy integrating out the phonons, we derive stochastic Langevin equations\ndescribing a coupling between the superfluid component and phonons. These\nequations have the form of Euler equations with additional source terms\nexpressed through a fluctuating stress-energy tensor of phonons. Conceptually,\nthis result is similar to stochastic Einstein equations that arise in the\ntheory of stochastic gravity. We formulate the fluctuation-dissipation theorem\nin this geometric language and discuss possible physical consequences of this\ntheory."
    },
    {
        "anchor": "Dipole mode of a strongly correlated one-dimensional Bose gas in a split\n  trap: parity effect and barrier renormalization: We consider an interacting, one-dimensional Bose gas confined in a split\ntrap, obtained by an harmonic potential with a localized barrier at its center.\nWe address its quantum-transport properties through the study of dipolar\noscillations, which are induced by a sudden quench of the position of the\ncenter of the trap. We find that the dipole-mode frequency strongly depends on\nthe interaction strength between the particles, yielding information on the\nclassical screening of the barrier and on its renormalization due to quantum\nfluctuations. Furthermore, we predict a parity effect which becomes most\nprominent in the strongly correlated regime.",
        "positive": "Time-Dependent Superfluid Local Density Approximation: The time-dependent superfluid local density approximation (TDSLDA) is an\nextension of the Hohenberg-Kohn density functional theory (DFT) to\ntime-dependent phenomena in superfluid fermionic systems. Unlike linear\nresponse theory, which is only valid for weak external fields, the (TDSLDA)\napproach allows one to study non-linear excitations in fermionic superfluids,\nincluding large amplitude collective modes, and the response to strong external\nprobes. Even in the case of weak external fields, the (TDSLDA) approach is\ntechnically easier to implement. We will illustrate the implementation of the\n(TDSLDA) for the unitary Fermi gas, where dimensional arguments and Galilean\ninvariance simplify the form of the functional, and ab initio input from (QMC)\nsimulations fix the coefficients to quite high precision."
    },
    {
        "anchor": "Observation of generalized Kibble-Zurek mechanism across a first-order\n  quantum phase transition in a spinor condensate: The Kibble-Zurek mechanism provides a unified theory to describe the\nuniversal scaling laws in the dynamics when a system is driven through a\nsecond-order quantum phase transition. However, for first-order quantum phase\ntransitions, the Kibble-Zurek mechanism is usually not applicable. Here, we\nexperimentally demonstrate and theoretically analyze a power-law scaling in the\ndynamics of a spin-1 condensate across a first-order quantum phase transition\nwhen a system is slowly driven from a polar phase to an antiferromagnetic\nphase. We show that this power-law scaling can be described by a generalized\nKibble-Zurek mechanism. Furthermore, by experimentally measuring the spin\npopulation, we show the power-law scaling of the temporal onset of spin\nexcitations with respect to the quench rate, which agrees well with our\nnumerical simulation results. Our results open the door for further exploring\nthe generalized Kibble-Zurek mechanism to understand the dynamics across\nfirst-order quantum phase transitions.",
        "positive": "Damping of the Anderson-Bogolyubov mode by spin and mass imbalance in\n  Fermi mixtures: We study the temporally nonlocal contributions to the gradient expansion of\nthe pair fluctuation propagator for spin- and mass-imbalanced Fermi mixtures.\nThese terms are related to damping processes of sound-like\n(Anderson-Bogolyubov) collective modes and are relevant for the structure of\nthe complex pole of the pair fluctuation propagator. We derive conditions under\nwhich damping occurs even at zero temperature for large enough mismatch of the\nFermi surfaces. We compare our analytical results with numerically computed\ndamping rates of the Anderson-Bogolyubov mode."
    },
    {
        "anchor": "Local versus global equilibration near the bosonic Mott-superfluid\n  transition: We study the response of trapped two dimensional cold bosons to time\ndependent lattices. We find that in lattice ramps from 11 (superfluid,\n$\\hbar/U_{\\text{i}} = 3$ms, $\\hbar/J_{\\text{i}} = 45$ms) to 16 recoils (Mott,\n$\\hbar/U_{\\text{f}} = 2$ms, $\\hbar/J_{\\text{f}} = 130$ms) the local number\nfluctuations remains at their equilibrium values if ramps are slower than 3 ms.\nGlobal transport, however, is much slower (1s), especially in the presence of\nMott shells. This separation of timescales has practical implications for cold\natom experiments and cooling protocols.",
        "positive": "Universal relations for a spin-polarized Fermi gas in two dimensions: We derive the full set of universal relations for spin-polarized Fermi gases\nwith $p$-wave interaction in two dimensions, simply using the short-range\nasymptotic behavior of fermion-pair wave functions. For $p$-wave interactions,\nan additional contact related to the effective range needs to be introduced,\nbesides the one related to the scattering volume. Since the subleading tail\n($k^{-4}$) of the large-momentum distribution cannot fully be captured by the\ncontacts defined by the adiabatic relations, an extra term resulted from the\ncenter-of-mass motions of the pairs gives rise to an additional divergence in\nthe kinetic energy of the system, besides those related to the contacts\ndefined. We show in Tan's energy theorem that if only two-body correlations are\ntaken into account, all these divergences are reasonably removed, leading to a\nfinite internal energy of the system. In addition, we find that all the other\nuniversal relations, such as the high-frequency behavior of the radio-frequency\nresponse, short-range behavior of the pair correlation function, generalized\nvirial theorem, and pressure relation, remain unaffected by the center-of-mass\nmotions of the pairs, and are fully governed by the contacts defined by the\nadiabatic relations. Our results confirm the feasibility of generalizing the\ncontact theory for higher-partial-wave scatterings, and could readily be\nconfirmed in current experiments with ultracold $^{40}$K and $^{6}$Li atoms."
    },
    {
        "anchor": "Quenched Magneto-association of Ultracold Feshbach Molecules: We study enhanced magneto-association of atoms into weakly-bound molecules\nnear a Feshbach resonance using a quench preparatory stage. In anticipation of\nexperiments with NASA's Cold Atom Laboratory aboard the International Space\nStation, we assume as a baseline a dual-species ($^{87}$Rb and $^{41}$K) gas in\na parameter regime enabled by a microgravity environment. This includes\nsubnanokelvin temperatures and dual-species gases at densities as low as\n10$^8$/cm$^3$. Our studies indicate that, in such a regime, traditional\nmagneto-association schemes are inefficient due to the weak coupling between\natomic and molecular states at low-densities, thus requiring extremely long\nmagnetic field sweeps. To address this issue we propose a modified scheme where\natoms are quenched to unitarity before proceeding with magneto-association.\nThis substantially improves molecular formation, allowing for up to $80\\%$\nefficiency, and within time-scales much shorter than those associated to atomic\nand molecular losses. We show that this scheme also applies at higher\ndensities, therefore proving to be of interest to ground-based experiments as\nwell.",
        "positive": "Detecting paired and counterflow superfluidity via dipole oscillations: We suggest an experimentally feasible procedure to observe paired and\ncounterflow superfluidity in ultra-cold atom systems. We study the time\nevolution of one-dimensional mixtures of bosonic atoms in an optical lattice\nfollowing an abrupt displacement of an additional weak confining potential. We\nfind that the dynamic responses of the paired superfluid phase for attractive\ninter-species interactions and the counterflow superfluid phase for repulsive\ninteractions are qualitatively distinct and reflect the quasi long-range order\nthat characterizes these states. These findings suggest a clear experimental\nprocedure to detect these phases, and give an intuitive insight into their\ndynamics."
    },
    {
        "anchor": "Stabilization of ring dark solitons in Bose-Einstein condensates: Earlier work has shown that ring dark solitons in two-dimensional\nBose-Einstein condensate are generically unstable. In this work, we propose a\nway of stabilizing the ring dark soliton via a radial Gaussian external\npotential. We investigate the existence and stability of the ring dark soliton\nupon variations of the chemical potential and also of the strength of the\nradial potential. Numerical results show that the ring dark soliton can be\nstabilized in a suitable interval of external potential strengths and chemical\npotentials. We also explore different proposed particle pictures considering\nthe ring as a moving particle and find, where appropriate, results in very good\nqualitative and also reasonable quantitative agreement with the numerical\nfindings.",
        "positive": "Quasiparticle lifetime in ultracold fermionic mixtures with density and\n  mass imbalance: We show that atomic Fermi mixtures with density and mass imbalance exhibit a\nrich diversity of scaling laws for the quasiparticle decay rate beyond the\nquadratic energy and temperature dependence of conventional Fermi liquids. For\ncertain densities and mass ratios, the decay rate is linear whereas in other\ncases it exhibits a plateau. Remarkably, this plateau extends from the deeply\ndegenerate to the high temperature classical regime of the light species. Many\nof these scaling laws are analogous to what is found in very different systems\nincluding dirty metals, liquid metals, and high temperature plasmas. The Fermi\nmixtures can in this sense span a whole range of seemingly diverse and separate\nphysical systems. Our results are derived in the weakly interacting limit\nmaking them quantitatively reliable. The different regimes can be detected with\nradio-frequency spectroscopy."
    },
    {
        "anchor": "Geometry-induced entanglement in a mass-imbalanced few-fermion system: Many-body systems undergoing quantum phase transitions reveal substantial\ngrowth of non-classical correlations between different parties of the system.\nThis behavior is manifested by characteristic divergences of the von Neumann\nentropy. Here we show, that very similar features may be observed in\none-dimensional systems of a few strongly interacting atoms when the structural\ntransitions between different spatial orderings are driven by a varying shape\nof an external potential. When the appropriate adaptation of the finite-size\nscaling approach is performed in the vicinity of the transition point,\nfew-fermion systems display a characteristic power-law invariance of divergent\nquantities.",
        "positive": "Vortices in quantum droplets of heteronuclear Bose mixtures: We have theoretically investigated the structure of spinning self-bound\ndroplets made of $^{41}$K-$^{87}$Rb Bose mixture by solving the\nGross-Pitaevskii equation including beyond-mean-field correction in the\nLee-Huang-Yang form. The structure and energetics of vortex formation in the\nself-bound mixture have been elucidated, showing that the formation of linear\nvortices in the heavier species is energetically favoured over other\nconfigurations. A fake (partially filled) core develops as a consequence in the\nother species, resulting in a hole which might be imaged in experiments. The\ninterplay between vortices and capillary waves, which are the two ways angular\nmomentum can be stored in a swirling superfluid, is studied in detail by\ncomputing the relation between angular momentum and rotational frequency. The\nresults show intriguing similarities with the case of a prototypical\nsuperfluid, i.e. $^4$He droplets when set into rotation. A two-branches curve\nin the stability diagram, qualitatively similar to the one expected for\nclassical (incompressible and viscous) rotating liquid droplets, is obtained\nwhen vortices are present in the droplets, while prolate (i.e. non\naxi-symmetric) shapes are only permitted in vortex-free droplets."
    },
    {
        "anchor": "Influence of Rashba spin-orbit and Rabi couplings on the miscibility and\n  ground state phases of binary Bose-Einstein condensates: We study the miscibility properties and ground state phases of two-component\nspin-orbit (SO) coupled Bose-Einstein condensates (BECs) in a harmonic trap\nwith strong axial confinement. By numerically solving the coupled\nGross-Pitaevskii equations in the two-dimensional setting, we analyze the\nSO-coupled BECs for two possible permutations of the intra- and interspecies\ninteractions, namely (i) weak intra- and weak interspecies interactions (W-W)\nand (ii) weak intra- and strong interspecies interactions (W-S). Considering\nthe density overlap integral as a miscibility order parameter, we investigate\nthe miscible-immiscible transition by varying the coupling parameters. We\nobtain various ground state phases, including plane wave, half quantum vortex,\nelongated plane wave, and different stripe wave patterns for W-W interactions.\nFor finite Rabi coupling, an increase in SO coupling strength leads to the\ntransition from the fully miscible to the partially miscible state. We also\ncharacterize different ground states in the coupling parameter space using the\nroot mean square sizes of the condensate. The spin density vector for the\nground state phases exhibits density, quadrupole and dipole like spin\npolarizations. For the W-S interaction, in addition to that observed in the W-W\ncase, we witness semi vortex, mixed mode, and shell-like immiscible phases. We\nnotice a wide variety of spin polarizations, such as density, dipole,\nquadrupole, symbiotic, necklace, and stripe-like patterns for the W-S case. A\ndetailed investigation in the coupling parameter space indicates immiscible to\nmiscible state phase transition upon varying the Rabi coupling for a fixed\nRashba SO coupling. The critical Rabi coupling for the immiscible-miscible\nphase transition decreases upon increasing the SO coupling strength.",
        "positive": "Relationship between the transverse-field Ising model and the XY model\n  via the rotating-wave approximation: In a large transverse field, there is an energy cost associated with flipping\nspins along the axis of the field. This penalty can be employed to relate the\ntransverse-field Ising model in a large field to the XY model in no field (when\nmeasurements are performed at the right stroboscopic times). We describe the\ndetails for how this relationship works and, in particular, we also show under\nwhat circumstances it fails. We examine wavefunction overlap between the two\nmodels and observables, such as spin-spin Green's functions. In general, the\nmapping is quite robust at short times, but will ultimately fail if the run\ntime becomes too long. There is also a trade-off between the length of time one\ncan run a simulation out to and the time jitter of the stroboscopic\nmeasurements that must be balanced when planning to employ this mapping."
    },
    {
        "anchor": "Nonlinear waves in coherently coupled Bose-Einstein condensates: We consider a quasi-one-dimensional two-component Bose-Einstein condensate\nsubject to a coherent coupling between its components, such as realized in\nspin-orbit coupled condensates. We study how nonlinearity modifies the dynamics\nof the elementary excitations. The spectrum has two branches which are affected\nin different ways. The upper branch experiences a modulational instability\nwhich is stabilized by a long wave-short wave resonance with the lower branch.\nThe lower branch is stable. In the limit of weak nonlinearity and small\ndispersion it is described by a Korteweg-de Vries equation or by the Gardner\nequation, depending on the value of the parameters of the system.",
        "positive": "Collective P-Wave Orbital Dynamics of Ultracold Fermions: We consider the non-equilibrium orbital dynamics of spin-polarized ultracold\nfermions in the first excited band of an optical lattice. A specific lattice\ndepth and filling configuration is designed to allow the $p_x$ and $p_y$\nexcited orbital degrees of freedom to act as a pseudo-spin. Starting from the\nfull Hamiltonian for p-wave interactions in a periodic potential, we derive an\nextended Hubbard-type model that describes the anisotropic lattice dynamics of\nthe excited orbitals at low energy. We then show how dispersion engineering can\nprovide a viable route to realizing collective behavior driven by p-wave\ninteractions. In particular, Bragg dressing and lattice depth can reduce\nsingle-particle dispersion rates, such that a collective many-body gap is\nopened with only moderate Feshbach enhancement of p-wave interactions. Physical\ninsight into the emergent gap-protected collective dynamics is gained by\nprojecting the Hamiltonian into the Dicke manifold, yielding a one-axis\ntwisting model for the orbital pseudo-spin that can be probed using\nconventional Ramsey-style interferometry. Experimentally realistic protocols to\nprepare and measure the many-body dynamics are discussed, including the effects\nof band relaxation, particle loss, spin-orbit coupling, and doping."
    },
    {
        "anchor": "An analogous Wu-Yang monopole in superfluid: By identifying the Schr\\\"{o}dinger equation with the hydrodynamic equations\nin superfluid ${^3}$He, the effective potential is introduced in the\nSchr\\\"{o}dinger equation to solve the quantum pressure in steady state. The\npure gauge velocity solutions of hydrodynamic equations provide an analogous\nWu-Yang monopole potential. The two cases of velocity in superfluid are\nequivalent to the two regions of Wu-Yang monopole potential. Due to the\ncompressibility of superfluid, the physical models are limited, such as hard\ncore and harmonic oscillator. It is important that the constraint condition of\n$\\nabla\\rho\\cdot \\textbf{v}=0$ plays a key role, which determines that the\nintegral quantum numbers are selected in monopole harmonics and shows the\nspecial analogous Wu-Yang monopole. The results provide a new possibility for\nthe simulation of Wu-Yang monopole.",
        "positive": "Observation of Algebraic Time Order for Two-Dimensional Dipolar Excitons: Emergence of algebraic quasi-long-range order is a key feature of superfluid\nphase transitions at two dimensions. For this reduced dimensionality\ninteractions prevent Bose-Einstein condensation with true long range order, at\nany finite temperature. Here, we report the occurence of algebraic order in a\nstrongly interacting quantum liquid formed by dipolar excitons confined in a\nbilayer semiconductor heterostructure. We observe a transition from exponential\nto algebraic decay of the excitons temporal coherence, accompanied by a\nuniversal scaling behaviour of the equation of state. Our results provide\nstrong evidence for a Berezinskii-Kosterlitz-Thouless (BKT) transition in a\nmulti-component boson-like system governed by strong dipolar interactions."
    },
    {
        "anchor": "Breakdown of sound in superfluid helium: Like elementary particles carry energy and momentum in the Universe,\nquasiparticles are the elementary carriers of energy and momentum quanta in\ncondensed matter. And, like elementary particles, under certain conditions\nquasiparticles can be unstable and decay, emitting pairs of less energetic\nones. Pitaevskii proposed that such processes exist in superfluid helium, a\nquantum fluid where the very concept of quasiparticles was borne, and which\nprovided the first spectacular triumph of that concept. Pitaevskii's decays\nhave important consequences, including possible breakdown of a quasiparticle.\nHere, we present neutron scattering experiments, which provide evidence that\nsuch decays explain the collapsing lifetime (strong damping) of higher-energy\nphonon-roton sound-wave quasiparticles in superfluid helium. This damping\ndevelops when helium is pressurized towards crystallization or warmed towards\napproaching the superfluid transition. Our results resolve a number of puzzles\nposed by previous experiments and reveal the ubiquity of quasiparticle decays\nand their importance for understanding quantum matter.",
        "positive": "Destruction of attractive bosonic cloud due to high spatial coherence in\n  tight trap: We study coherence of a trapped bosonic cloud with attractive finite-range\ninteraction in a tight harmonic trap. One-body density and pair-distribution\nfunction in the ground state for different trap sizes are calculated. We also\ncalculate healing length and the correlation length which signify the presence\nof high spatial coherence in a very tight trap leading to the destruction of\nthe condensate for a fixed particle number. This is in marked variance with the\nusual collapse of the attractive metastable condensate when N > Ncr . Thus we\ninvestigate the critical frequency and critical size of the trap for the\nexistence of attractive Bose-Einstein condensation. The finite-range\ninteraction gives a nonlocal effect in the effective many-body potential, and\nwe observe a high-density stable branch besides the known metastable branch.\nMoreover, the new branch shows universal behavior even in the very tight trap."
    },
    {
        "anchor": "Lattice Boltzmann simulations of a two-dimensional Fermi gas at\n  unitarity: We present fully nonlinear dissipative fluid dynamics simulations of a\ntrapped two-dimensional Fermi gas at unitarity using a Lattice Boltzmann\nalgorithm. We are able to simulate non-harmonic trapping potentials,\ntemperature-dependent viscosities as well as a discretized version of the\nballistic (non-interacting) behavior. Our approach lends itself to direct\ncomparison with experimental data, opening up the possibility of a precision\ndetermination of transport coefficients in the unitary Fermi gas. Furthermore,\nwe predict the presence of a non-hydrodynamic component in the quadrupole mode,\nwhich should be observable experimentally.",
        "positive": "Many-particle Systems in One Dimension in the Harmonic Approximation: We consider energetics and structural properties of a many particle system in\none dimension with pairwise contact interactions confined in a parabolic\nexternal potential. To render the problem analytically solvable, we use the\nharmonic approximation scheme at the level of the Hamiltonian. We investigate\nthe scaling with particle number of the ground state energies for systems\nconsisting of identical bosons or fermions. We then proceed to focus on bosonic\nsystems and make a detailed comparison to known exact results in the absence of\nthe parabolic external trap for three-body systems. We also consider the\nthermodynamics of the harmonic model which turns out to be similar for bosons\nand fermions due to the lack of degeneracy in one dimension."
    },
    {
        "anchor": "Probing Goldstino excitation through the tunneling transport in a\n  Bose-Fermi mixture with explicitly broken supersymmetry: We theoretically investigate the tunneling transport in a repulsively\ninteracting ultracold Bose-Fermi mixture. A two-terminal model is applied to\nsuch a mixture and the supersymmetric-like tunneling current through the\njunction can be induced by the bias of fermion chemical potential between two\nreservoirs. The Goldstino, which is the Nambu-Goldstone fermionic mode\nassociated with the spontaneous sypersymmetry breaking and appears as a gapped\nmode in the presence of the explicit supersymmetry breaking in existing\nBose-Fermi mixtures, is found to contribute to the tunneling transport as a\nsupercharge exchanging process. Our study provides a potential way to detect\nthe Goldstino transport in cold atom experiments.",
        "positive": "Simulating and detecting artificial magnetic fields in trapped atoms: A Bose-Einstein condensate exhibiting a nontrivial phase induces an\nartificial magnetic field in immersed impurity atoms trapped in a stationary,\nring-shaped optical lattice. We present an effective Hamiltonian for the\nimpurities for two condensate setups: the condensate in a rotating ring and in\nan excited rotational state in a stationary ring. We use Bogoliubov theory to\nderive analytical formulas for the induced artificial magnetic field and the\nhopping amplitude in the limit of low condensate temperature where the impurity\ndynamics is coherent. As methods for observing the artificial magnetic field we\ndiscuss time of flight imaging and mass current measurements. Moreover, we\ncompare the analytical results of the effective model to numerical results of a\ncorresponding two-species Bose-Hubbard model. We also study numerically the\nclustering properties of the impurities and the quantum chaotic behavior of the\ntwo-species Bose-Hubbard model."
    },
    {
        "anchor": "Two-dimensional Fermi gases near a p-wave resonance: effect of quantum\n  fluctuations: We study the stability of p-wave superfluidity against quantum fluctuations\nin two-dimensional Fermi gases near a p-wave Feshbach resonance . An analysis\nis carried out in the limit when the interchannel coupling is strong. By\ninvestigating the effective potential for the pairing field via the standard\nloop expansion, we show that a homogeneous p-wave pairing state becomes\nunstable when two-loop quantum fluctuations are taken into account. This is in\ncontrast to the previously predicted $p + ip$ supefluid in the weak-coupling\nlimit [V. Gurarie et al., Phys. Rev. Lett. 94, 230403 (2005)]. It implies a\npossible onset of instability at certain intermediate interchannel coupling\nstrength. Alternatively, the instability can also be driven by lowering the\nparticle density. We also discuss the validity of our analysis.",
        "positive": "Collective modes and generation of a new vortex in a trapped Bose gas at\n  finite temperature: The dynamics of Bose-Einstein condensate (BEC) is studied at nonzero\ntemperatures using our variational time-dependent-HFB formalism. We have shown\nthat this approach is an efficient tool to study the expansion and collective\nexcitations of the condensate, the thermal cloud and the anomalous correlation\nfunction at nonzero temperatures. We have found that the condensate and the\nanomalous density have the same breathing oscillations. We have investigated,\non the other hand, the behavior of a single quantized vortex in a harmonically\ntrapped BEC at nonzero temperatures. Generalized expressions for vortex\nexcitations, vortex core size and Kelvin modes have been derived. An important\nand somehow surprising result is that the numerical solution of our equations\npredicts that the vortex core is partially filled by the thermal atoms at\nnonzero temperatures. We have shown that the effect of thermal fluctuations is\nimportant and it may lead to enhancing the size of the vortex core. The\nbehavior of the singly anomalous vortex has also been studied at nonzero\ntemperatures."
    },
    {
        "anchor": "Kondo Effect in a Spin-3/2 Fermi Gas: We investigate the Kondo effect of a spin-3/2 Fermi gas and give a detailed\ncalculation of the impurity resistance and ground state energy based on the s-d\nexchange model. It is found that the impurity resistance increases\nlogarithmically with the decrease of temperature in the case of\nantiferromagnetic coupling similar to the spin-1/2 system but has a larger\nresistance minimum value due to the increase of spin scattering channels. In\nthe case of antiferromagnetic interaction, the ground state is still the Kondo\nsinglet state while the septuplet state has the lowest energy for ferromagnetic\ncoupling. And with the same antiferromagnetic s-d coupling parameter, the\nenergy of the Kondo singlet state is lower than spin-1/2, which indicates that\nthe larger spin, the easier it is to enter the Kondo-screened phase. This\nprovides some theoretical support for the realization of the Kondo effect with\nultra-cold atoms.",
        "positive": "Far-Away-From-Equilibrium Quantum Critical Conformal Dynamics:\n  Reversibility, Thermalization, and Hydrodynamics: Generic far-away-from-equilibrium many-body dynamics involve entropy\nproduction, and hence are thermodynamically irreversible. Near quantum critical\npoints, an emergent conformal symmetry can impose strong constraints on entropy\nproduction rates, and in some cases completely forbid entropy production, which\nusually occurs for systems that deviate from quantum critical points. In this\narticle, we illustrate how the vanishing entropy production near a quantum\ncritical point results in reversible far-away-from-equilibrium dynamics at\nfinite temperatures that are otherwise irreversible. Away from the quantum\ncritical point, the quantum dynamics are damped, and our analysis directly\nrelates the thermalization time scale to the hydrodynamic viscosity near\nquantum critical points with dynamical critical exponent $z=2$. We demonstrate\nhow both controllable reversible and irreversible dynamics can be potentially\nstudied in cold gas experiments using Feshbach resonances."
    },
    {
        "anchor": "Analytical solutions for two heteronuclear atoms in a ring trap: We consider two heteronuclear atoms interacting with a short-range $\\delta$\npotential and confined in a ring trap. By taking the Bethe-ansatz-type\nwavefunction and considering the periodic boundary condition properly, we\nderive analytical solutions for the heteronuclear system. The eigen-energies\nrepresented in terms of quasi-momentums can then be determined by solving a set\nof coupled equations. We present a number of results, which display different\nfeatures from the case of identical atoms. Our result can be reduced to the\nwell-known Lieb-Liniger solution when two interacting atoms have the same\nmasses.",
        "positive": "Flat-band ferromagnetism in the multilayer Lieb optical lattice: We theoretically study magnetic properties of two-component cold fermions in\nhalf-filled multilayer Lieb optical lattices, i.e., two, three, and several\nlayers, using the dynamical mean-field theory. We clarify that the magnetic\nproperties of this system become quite different depending on whether the\nnumber of layers is odd or even. In odd-number-th layers in an odd-number-layer\nsystem, finite magnetization emerges even with an infinitesimal interaction.\nThis is a striking feature of the flatband ferromagnetic state in multilayer\nsystems as a consequence of the Lieb theorem. In contrast, in even-number\nlayers, magnetization develops from zero on a finite interaction. These\ndifferent magnetic behaviours are triggered by the flat bands in the local\ndensity of states and become identical in the limit of the infinite-layer\n(i.e., three-dimensional) system. We also address how interlayer hopping\naffects the magnetization process. Further, we point out that layer\nmagnetization, which is a population imbalance between up and down atoms on a\nlayer, can be employed to detect the emergence of the flat-band ferromagnetic\nstate without addressing sublattice magnetization."
    },
    {
        "anchor": "First and second sound in two-dimensional bosonic and fermionic\n  superfluids: We review our theoretical results about the sound propagation in\ntwo-dimensional (2D) systems of ultracold fermionic and bosonic atoms. In the\nsuperfluid phase, characterized by the spontaneous symmetry breaking of the\n$U(1)$ symmetry, there is the coexistence of first and second sound. In the\ncase of weakly-interacting repulsive bosons, we model the recent measurements\nof the sound velocities of 39K atoms in 2D obtained in the weakly-interacting\nregime and around the Berezinskii-Kosterlitz-Thouless (BKT)\nsuperfluid-to-normal transition temperature. In particular, we perform a quite\naccurate computation of the superfluid density and show that it is reasonably\nconsistent with the experiment. For superfluid attractive fermions, we\ncalculate the first and second sound velocities across the whole BCS-BEC\ncrossover. In the low-temperature regime we reproduce the recent measurements\nof first-sound speed with 6Li atoms. We also predict that only in the\nfinite-temperature BEC regime there is mixing between sound modes.",
        "positive": "A Non-Gaussian Variational Approach to Fermi Polarons in One- and\n  Two-dimensional Lattices: We study the Fermi polaron problem of one mobile spin-up impurity immersed\natop the bath consisting of spin-down fermions in one- and two-dimensional\nsquare lattices. We solve this problem by applying a variational approach with\nnon-Gaussian states after separating the impurity and the background by the\nLee-Low-Pines transformation. The ground state for a fixed total momentum can\nbe obtained via imaginary time evolution for the variational parameters. For\nthe one-dimensional case, the variational results are compared with numerical\nsolutions of the matrix product state method with excellent agreement. In\ntwo-dimensional lattices, we focus on the dilute limit, and find a\npolaron--molecule evolution in consistence with previous results obtained by\nvariational and quantum Monte Carlo methods for models in continuum space.\nComparing to previous works, our method provides the lowest ground state energy\nin the entire parameter region considered, and has an apparent advantage as it\ndoes not need to assume {\\it in priori} any specific form of the variational\nwave function."
    },
    {
        "anchor": "Robust states of ultra-cold bosons in tilted optical lattices: We identify regular structures in the globally chaotic spectra of an\ninteracting bosonic quantum gas in tilted periodic potentials. The associated\neigenstates exhibit strong localization properties on the lattice, and are\ndynamically robust against external perturbations.",
        "positive": "BEC-BCS crossover and the mobility edge: superfluid-insulator\n  transitions and reentrant superfluidity in disordered Fermi gases: A superfluid-insulator transition is known to occur in strongly disordered\nFermi gases, in both the BCS and BEC regimes; here, we address the properties\nof this transition across the BEC-BCS crossover. We argue that the critical\ndisorder strength at which superfluidity is lost changes non-monotonically with\ndetuning from Feshbach resonance, and that a reentrant superfluid phase arises\nfor detunings near the fermionic mobility edge. Our analysis of the\nintermediate regime is quantitatively valid for narrow resonances and near four\ndimensions, and provides a simple physical picture of this regime, in terms of\ntwo distinct but coexisting insulators."
    },
    {
        "anchor": "Universal scaling of three-dimensional bosonic gases in a trapping\n  potential: We investigate the critical properties of cold bosonic gases in three\ndimensions, confined by an external quadratic potential coupled to the particle\ndensity, and realistically described by the Bose-Hubbard (BH) model. The\ntrapping potential is often included in experiments with cold atoms and\nmodifies the critical finite-size scaling of the homogeneous system in a non\ntrivial way. The trap-size scaling (TSS) theory accounts for this effect\nthrough the exponent $\\theta$.\n  We perform extensive simulations of the BH model at the critical temperature,\nin the presence of harmonic traps. We find that the TSS predictions are\nuniversal once we account for the effective way in which the trap locally\nmodifies the chemical potential $\\mu$ of the system. The trap exponent for the\nBH model at $\\mu=0$ is the one corresponding to an effective quartic potential.\nAt positive $\\mu$, evidence suggests that TSS breaks down sufficiently far from\nthe centre of the trap, as the system encounters an effective phase boundary.",
        "positive": "Calorimetry of a harmonically trapped Bose gas: We experimentally study the energy-temperature relationship of a harmonically\ntrapped Bose-Einstein condensate by transferring a known quantity of energy to\nthe condensate and measuring the resulting temperature change. We consider two\nmethods of heat transfer, the first using a free expansion under gravity and\nthe second using an optical standing wave to diffract the atoms in the\npotential. We investigate the effect of interactions on the thermodynamics and\ncompare our results to various finite temperature theories."
    },
    {
        "anchor": "Formation of Feshbach molecules in the presence of artificial spin-orbit\n  coupling and Zeeman fields: We derive general conditions for the emergence of singlet Feshbach molecules\nin the presence of artificial Zeeman fields for arbritary mixtures of Rashba\nand Dresselhaus spin-orbit orbit coupling in two or three dimensions. We focus\non the formation of two-particle bound states resulting from interactions\nbetween ultra-cold spin-1/2 fermions, under the assumption that interactions\nare short-ranged and occur only in the s-wave channel. In this case, we\ncalculate explicitly binding energies of Feshbach molecules and analyze their\ndependence on spin-orbit couplings, Zeeman fields, interactions and center of\nmass momentum, paying particular attention to the experimentally relevant case\nof spin-orbit couplings with equal Rashba and Dresselhaus (ERD) amplitudes.",
        "positive": "Spontaneous formation of spin lattices in semimagnetic exciton-polariton\n  condensates: An exciton-polariton microcavity that incorporates magnetic ions can exhibit\na spontaneous self-trapping phenomenon which is an analog of the classical\npolaron effect. We investigate in detail the full model of a polariton\ncondensate that includes pumping and losses, the spin degree of freedom,\nexternal magnetic field and energy relaxation. In the quasi-one-dimensional\ncase, we show that the polaron effect can give rise to a spontaneous lattice of\nperfectly arranged polarization domains in an antiferromagnetic configuration.\nWe find that partial polarization of the condensate at moderate magnetic field\nstrengths facilitates the formation of such \"polaron lattices\", which are\nqualitatively different from self-trapped polarons that appear in a fully\npolarized condensate. Within the Bogoliubov-de Gennes approximation, we\ncalculate the instability condition which marks the appearance of the patterns.\nSurprisingly, we find that the stability condition displays a discontinuity at\nthe point of partial-full polarization threshold."
    },
    {
        "anchor": "Vibrations of a Columnar Vortex in a Trapped Bose-Einstein Condensate: We derive a governing equation for a Kelvin wave supported on a vortex line\nin a Bose-Einstein condensate, in a rotating cylindrically symmetric parabolic\ntrap. From this solution the Kelvin wave dispersion relation is determined. In\nthe limit of an oblate trap and in the absence of longitudinal trapping our\nresults are consistent with previous work. We show that the derived Kelvin wave\ndispersion in the general case is in quantitative agreement with numerical\ncalculations of the Bogoliubov spectrum and offer a significant improvement\nupon previous analytical work.",
        "positive": "Heating and Cooling in Adiabatic Mixing process: We study the effect of interaction on the temperature change in the process\nof adiabatic mixing two components of fermi gases by the real-space\nBogoliubov-de Gennes (BdG) method. We find that in the process of adiabatic\nmixing, the competition of the adiabatic expansion and the attractive\ninteraction make it possible to cool or heal the system depending on strength\nof interactions and the initial temperature. The change of temperature in a\nbulk system and a trapped system have been investigated respectively."
    },
    {
        "anchor": "Freed by interaction kinetic states in the Harper model: We study the problem of two interacting particles in a one-dimensional\nquasiperiodic lattice of the Harper model. We show that a short or long range\ninteraction between particles leads to emergence of delocalized pairs in the\nnon-interacting localized phase. The properties of these Freed by Interaction\nKinetic States (FIKS) are analyzed numerically including the advanced Arnoldi\nmethod. We find that the number of sites populated by FIKS pairs grows\nalgebraically with the system size with the maximal exponent $b=1$, up to a\nlargest lattice size $N=10946$ reached in our numerical simulations, thus\ncorresponding to a complete delocalization of pairs. For delocalized FIKS pairs\nthe spectral properties of such quasiperiodic operators represent a deep\nmathematical problem. We argue that FIKS pairs can be detected in the framework\nof recent cold atom experiments [M.~Schreiber {\\it et al.} Science {\\bf 349},\n842 (2015)] by a simple setup modification. We also discuss possible\nimplications of FIKS pairs for electron transport in the regime of\ncharge-density wave and high $T_c$ superconductivity.",
        "positive": "Diffraction-Unlimited Position Measurement of Ultracold Atoms in an\n  Optical Lattice: We consider a method of high-fidelity, spatially resolved position\nmeasurement of ultracold atoms in an optical lattice. We show that the\natom-number distribution can be nondestructively determined at a spatial\nresolution beyond the diffraction limit by tracking the progressive evolution\nof the many-body wavefunction collapse into a Fock state. We predict that the\nPauli exclusion principle accelerates the rate of wavefunction collapse of\nfermions in comparison with bosons. A possible application of our principle of\nsurpassing the diffraction limit to other imaging systems is discussed."
    },
    {
        "anchor": "Vortex-core structure in a mixture of Bose and Fermi superfluids: We study a single quantized vortex in the fermionic component of a mixture of\nFermi superfluid and Bose-Einstein condensate. As the density ratio between the\nboson and the fermion components is tuned, we identify a transition in the\nvortex-core structure, across which fermions in the vortex core become\ncompletely depleted even in the weak-coupling Bardeen-Cooper-Schrieffer regime.\nThis is accompanied by changes in key properties of the vortex state, as well\nas by the localization of the Bose-Einstein condensate in the vortex core. The\ntransition in the vortex-core structure can be experimentally probed in\nBose-Fermi superfluid mixtures by detecting the size and visibility of the\nvortices.",
        "positive": "Quantum Monte Carlo Study of a Resonant Bose-Fermi Mixture: We study a resonant Bose-Fermi mixture at zero temperature by using the\nfixed-node diffusion Monte Carlo method. We explore the system from weak to\nstrong boson-fermion interaction, for different concentrations of the bosons\nrelative to the fermion component. We focus on the case where the boson density\n$n_B$ is smaller than the fermion density $n_F$, for which a first-order\nquantum phase transition is found from a state with condensed bosons immersed\nin a Fermi sea, to a Fermi-Fermi mixture of composite fermions and unpaired\nfermions. We obtain the equation of state and the phase diagram, and we find\nthat the region of phase separation shrinks to zero for vanishing $n_B$."
    },
    {
        "anchor": "Multimer formation in 1D two-component gases and trimer phase in the\n  asymmetric attractive Hubbard model: We consider two-component one-dimensional quantum gases at special imbalanced\ncommensurabilities which lead to the formation of multimer (multi-particle\nbound-states) as the dominant order parameter. Luttinger liquid theory supports\na mode-locking mechanism in which mass (or velocity) asymmetry is identified as\nthe key ingredient to stabilize such states. While the scenario is valid both\nin the continuum and on a lattice, the effects of umklapp terms relevant for\ndensities commensurate with the lattice spacing are also mentioned. These ideas\nare illustrated and confronted with the physics of the asymmetric\n(mass-imbalanced) fermionic Hubbard model with attractive interactions and\ndensities such that a trimer phase can be stabilized. Phase diagrams are\ncomputed using density-matrix renormalization group techniques, showing the\nimportant role of the total density in achieving the novel phase. The effective\nphysics of the trimer gas is as well studied. Lastly, the effect of a parabolic\nconfinement and the emergence of a crystal phase of trimers are briefly\naddressed. This model has connections with the physics of imbalanced\ntwo-component fermionic gases and Bose-Fermi mixtures as the latter gives a\ngood phenomenological description of the numerics in the strong-coupling\nregime.",
        "positive": "Crystallization of an exciton superfluid: Indirect excitons -- pairs of electrons and holes spatially separated in\nsemiconductor bilayers or quantum wells -- are known to undergo Bose-Einstein\ncondensation and to form a quantum fluid. Here we show that this superfluid may\ncrystallize upon compression. However, further compression results in quantum\nmelting back to a superfluid. This unusual behavior is explained by the\neffective interaction potential between indirect excitons which strongly\ndeviates from a dipole potential at small distances due to many-particle and\nquantum effects. Based on first principle path integral Monte Carlo\nsimulations, we compute the complete phase diagram of this system and predict\nthe relevant parameters necessary to experimentally observe exciton\ncrystallization in semiconductor quantum wells."
    },
    {
        "anchor": "Optically guided beam splitter for propagating matter waves: We study experimentally and theoretically a beam splitter setup for guided\natomic matter waves. The matter wave is a guided atom laser that can be tuned\nfrom quasi-monomode to a regime where many transverse modes are populated, and\npropagates in a horizontal dipole beam until it crosses another horizontal beam\nat 45$^{\\rm o}$. We show that depending on the parameters of this $X$\nconfiguration, the atoms can all end up in one of the two beams (the system\nbehaves as a perfect guide switch), or be split between the four available\nchannels (the system behaves as a beam splitter). The splitting regime results\nfrom a chaotic scattering dynamics. The existence of these different regimes\nturns out to be robust against small variations of the parameters of the\nsystem. From numerical studies, we also propose a scheme that provides a robust\nand controlled beam splitter in two channels only.",
        "positive": "Two-flavor mixture of a few fermions of different mass in a\n  one-dimensional harmonic trap: A system of two species of fermions of different mass confined in a\none-dimensional harmonic trap is studied with an exact diagonalization\napproach. It is shown independently on the number of particles that a mass\ndifference between fermionic species induces a separation in the lighter flavor\nsystem. The mechanism of emerging of separated phases is explained\nphenomenologically and confirmed with the help of a direct inspection of the\nground-state of the system. Finally, it is shown that the separation driven by\na mass difference, in contrast to the separation induced by a difference of\npopulations, is robust to the interactions with thermal environment."
    },
    {
        "anchor": "Breathing mode frequency of a strongly interacting Fermi gas across the\n  2D-3D dimensional crossover: We address the interplay between dimension and quantum anomaly on the\nbreathing mode frequency of a strongly interacting Fermi gas harmonically\ntrapped at zero temperature. Using a beyond mean-field, Gaussian pair\nfluctuation theory, we employ periodic boundary conditions to simulate the\ndimensionality of the system and impose a local density approximation, with two\ndifferent schemes, to model different trapping potentials in the\ntightly-confined axial direction. By using a sum-rule approach, we compute the\nbreathing mode frequency associated with a small variation of the trapping\nfrequency along the weakly-confined transverse direction, and describe its\nbehavior as functions of the dimensionality, from two- to three-dimensions, and\nof the interaction strength. We compare our predictions with previous\ncalculations on the two-dimensional breathing mode anomaly and discuss their\npossible observation in ultracold Fermi gases of $^{6}$Li and $^{40}$K atoms.",
        "positive": "Particle correlations and evidence for dark state condensation in a cold\n  dipolar exciton fluid: In this paper we show experimental evidence of a few correlation regimes of a\ncold dipolar exciton fluid, created optically in a semiconductor bilayer\nheterostructure. In the higher temperature regime, the average interaction\nenergy between the particles shows a surprising temperature dependence which is\nan evidence for correlations beyond the mean field model. At a lower\ntemperature, there is a sharp increase in the interaction energy of optically\nactive excitons, accompanied by a strong reduction in their apparent\npopulation. This is an evidence for a sharp macroscopic transition to a dark\nstate as was suggested theoretically."
    },
    {
        "anchor": "Many-polaron description of impurities in a Bose-Einstein condensate in\n  the weak coupling regime: The weak coupling many-polaron formalism is applied to the case of the\npolaronic system consisting of impurities in a Bose-Einstein condensate. This\nallows to investigate the groundstate properties and the response of the system\nto Bragg spectroscopy. This theory is then applied to the system of\nspin-polarized fermionic lithium-6 impurities in a sodium condensate. The Bragg\nspectrum reveals a peak which corresponds to the emission of Bogoliubov\nexcitations. Both ground state properties and the response spectrum show that\nthe polaronic effect vanishes at large densities. We also look at two\npossibilities to define the polaronic effective mass and observe that this\nresults in a different quantitative behavior if multiple impurities are\ninvolved.",
        "positive": "Momentum correlations of a few ultra-cold bosons escaping from an open\n  well: The dynamical properties of a one-dimensional system of two and three bosons\nescaping from an open potential well are studied in terms of the momentum\ndistributions of particles. In the case of a two-boson system, it is shown that\nthe single- and two-particle momentum distributions undergo a specific\ntransition as the interaction strength is tuned through the point where\ntunneling switches from the pair tunneling to the sequential one.\nCharacteristic features in the momentum spectra can be used to quantitatively\ndetermine the participation of specific decay processes. A corresponding\nanalysis is also performed for the three-boson system, showing a scheme for\ngeneralizations to higher particle numbers. For completeness, the\ntime-dependent Tan's contact of the system is also examined and its dynamics is\nfound to undergo a similar transition. The results provide insight into the\ndynamics of decaying few-body systems and offer potential interest for\nexperimental research."
    },
    {
        "anchor": "Few-boson system with a single impurity: Universal bound states tied to\n  Efimov trimers: Small weakly-bound droplets determine a number of properties of ultracold\nBose and Fermi gases. For example, Efimov trimers near the atom-atom-atom and\natom-dimer thresholds lead to enhanced losses from bosonic clouds.\nGeneralizations to four- and higher-body systems have also been considered.\nMoreover, Efimov trimers have been predicted to play a role in the Bose polaron\nwith large boson-impurity scattering length. Motivated by these considerations,\nthe present work provides a detailed theoretical analysis of weakly-bound\n$N$-body clusters consisting of $N-1$ identical bosons (denoted by \"B\") of mass\n$m$ that interact with a single distinguishable impurity particle (denoted by\n\"X\") of mass $M$. The system properties are analyzed as a function of the mass\nratio $\\kappa$ (values from $\\kappa=1$ to $50$ are considered), where $\\kappa$\nis equal to $m/M$, and the two-body $s$-wave scattering length $a_{\\text{BX}}$\nbetween the bosons and the impurity. To reach the universal Efimov regime in\nwhich the size of the BBX trimer as well as those of larger clusters is much\nlarger than the length scales of the underlying interaction model, three\ndifferent approaches are considered: resonance states are determined in the\nabsence of BB and BBX interactions, bound states are determined in the presence\nof repulsive three-body boson-boson-impurity interactions, and bound states are\ndetermined in the presence of repulsive two-body boson-boson interactions. The\nuniversal regime, in which the details of the underlying interaction model\nbecome irrelevant, is identified.",
        "positive": "Stabilization of Hubbard-Thouless pumps through nonlocal fermionic\n  repulsion: Thouless pumping represents a powerful concept to probe quantized topological\ninvariants in quantum systems. We explore this mechanism in a generalized\nRice-Mele Fermi-Hubbard model characterized by the presence of competing onsite\nand intersite interactions. Contrary to recent experimental and theoretical\nresults, showing a breakdown of quantized pumping induced by the onsite\nrepulsion, we prove that sufficiently large intersite interactions allow for an\ninteraction-induced recovery of Thouless pumps. Our analysis further reveals\nthat the occurrence of stable topological transport at large interactions is\nconnected to the presence of a spontaneous bond-order-wave in the ground-state\nphase diagram of the model. Finally, we discuss a concrete experimental setup\nbased on ultracold magnetic atoms in an optical lattice to realize the newly\nintroduced Thouless pump. Our results provide a new mechanism to stabilize\nThouless pumps in interacting quantum systems."
    },
    {
        "anchor": "Effective triangular ladders with staggered flux from spin-orbit\n  coupling in 1D optical lattices: Light-induced spin-orbit coupling is a flexible tool to study quantum\nmagnetism with ultracold atoms. In this work we show that spin-orbit coupled\nBose gases in a one-dimensional optical lattice can be mapped into a two-leg\ntriangular ladder with staggered flux following a lowest-band truncation of the\nHamiltonian. The effective flux and the ratio of the tunneling strengths can be\nindependently adjusted to a wide range of values. We identify a certain regime\nof parameters where a hard-core boson approximation holds and the system\nrealizes a frustrated triangular spin ladder with tunable flux. We study the\nproperties of the effective spin Hamiltonian using the density-matrix\nrenormalization-group method and determine the phase diagram at half-filling.\nIt displays two phases: a uniform superfluid and a bond-ordered insulator. The\nlatter can be stabilized only for low Raman detuning. Finally, we provide\nexperimentally feasible trajectories across the parameter space of the SOC\nsystem that cross the predicted phase transition.",
        "positive": "Collective quantum stochastic resonance in Rydberg atoms: We study the collective response of a group of dissipative Rydberg atoms to a\nperiodic modulation of the Rydberg excitation laser. Focusing on the emergent\ncollective-jump dynamics, where the system stochastically switches between\nstates with distinct Rydberg excitations, we show that the counting statistics\nof the state switching is qualitatively changed by the periodic drive. The\nimpact is most prominent when the driving frequency is comparable to the\nemergent collective-jump rate, as the jumps tend to synchronize with the\nexternal drive, and their counting statistics exhibits a series of suppressed\nsubharmonics of the driving frequency. These phenomena are manifestations of a\nnovel type of stochastic resonance, where a cooperative collective state\nswitching is facilitated by quantum fluctuations in a many-body open system.\nSuch a collective quantum stochastic resonance further leads to an enhanced\nsignal-to-noise ratio in the power spectrum of the Rydberg excitations, for\nwhich the synchronized collective jumps are viewed as the output signal. We\nconfirm the many-body quantum nature of the resonance by devising a cluster\nmodel, under which the role of many-body correlations is analyzed by changing\nthe size of the atom clusters."
    },
    {
        "anchor": "Effect of nonzero temperature to condensed fraction of a homogeneous\n  dilute weakly interacting Bose gas: We investigate the effect of non-zero temperature to the condensate fraction\nof a homogeneous dilute weakly interacting Bose gas in very low-temperature\nregion. Within inproved Hartree-Fock approximation, the\nCornwall-Jackiw-Tomboulis effective action approach shows that the thermal\nfluctuations make the condensate fraction decrease as a second and fourth-order\npower law of temperature. The result is compared with experimental data.\nIndeed, the effect of non-infinite size of the trap is also integrated.",
        "positive": "Excited-state quantum phase transitions in spin-orbit coupled Bose gases: Excited-state quantum phase transitions depend on and reveal the structure of\nthe whole spectrum of many-body systems. While they are theoretically well\nunderstood, finding suitable signatures and detect them in actual experiments\nremains challenging. For instance, in spinor gases, excited-state phases have\nbeen identified and characterized through a topological order parameter that is\nchallenging to measure in experiments. Here, we propose the Raman-dressed\nspin-orbit coupled gas as a novel platform to explore excited-state quantum\nphase transitions. In a weakly-coupled regime, the dressed system is equivalent\nto a spinor gas with tunable spin-spin interactions. Through this equivalence\nwe are able to define a new excited-state phase of the dressed gas. The phase\nis characterize by the the behavior of the spatial density modulations, or\nstripes, induced by spin-orbit coupling, and can in principle be measured in\ncurrent state-of-the-art experiments with ultracold atoms. Conversely, we show\nthat the properties of the excited phase can be exploited to prepare stripe\nstates with large and stable density modulations."
    },
    {
        "anchor": "Minimal scattering entanglement in one-dimensional trapped gases: The prospect of controlling entanglement in interacting quantum systems\noffers a myriad of technological and scientific promises, given the progress in\nexperimental studies in systems such as ultracold trapped gases. This control\nis often challenging because of decoherence, the process by which environmental\ninteractions create spurious entanglements that can destroy the desired\nentanglement. Considering the collisional decoherence that is relevant for\nquantum measurements utilizing scattering in one-dimensional trapped gases,\nhere we derive a relationship between particle masses and wave packet widths\nthat minimizes the entanglement created during scattering. We assess the\nrelevance of our results by directly observing this relationship in the\nemergent scales of a master equation for a particle undergoing nonthermal\nscattering. Our relationship is independent of the details of the particle\ninteractions and sheds light on how to design scattering processes that\nminimize decoherence.",
        "positive": "Direct observation of Dirac cones and a flatband in a honeycomb lattice\n  for polaritons: Two-dimensional lattices of coupled micropillars etched in a planar\nsemiconductor microcavity offer a workbench to engineer the band structure of\npolaritons. We report experimental studies of honeycomb lattices where the\npolariton low-energy dispersion is analogous to that of electrons in graphene.\nUsing energy-resolved photoluminescence we directly observe Dirac cones, around\nwhich the dynamics of polaritons is described by the Dirac equation for\nmassless particles. At higher energies, we observe p orbital bands, one of them\nwith the nondispersive character of a flatband. The realization of this\nstructure which holds massless, massive and infinitely massive particles opens\nthe route towards studies of the interplay of dispersion, interactions, and\nfrustration in a novel and controlled environment."
    },
    {
        "anchor": "Bilayer fractional quantum Hall states with ultracold dysprosium: We show how dipolar interactions between dysprosium atoms in an optical\nlattice can be used to obtain fractional quantum Hall states. In our approach,\ndysprosium atoms are trapped one atom per site in a deep optical lattice with\nnegligible tunneling. Microwave and spatially dependent optical dressing fields\nare used to define an effective spin-1/2 or spin-1 degree of freedom in each\natom. Thinking of spin-1/2 particles as hardcore bosons, dipole-dipole\ninteractions give rise to boson hopping, topological flat bands with Chern\nnumber 1, and the \\nu = 1/2 Laughlin state. Thinking of spin-1 particles as\ntwo-component hardcore bosons, dipole-dipole interactions again give rise to\nboson hopping, topological flat bands with Chern number 2, and the bilayer\nHalperin (2,2,1) state. By adjusting the optical fields, we find a phase\ndiagram, in which the (2,2,1) state competes with superfluidity.\nGeneralizations to solid-state magnetic dipoles are discussed.",
        "positive": "Aharonov-Bohm caging in spin-orbit coupled exciton-polariton lattices: We study the Aharonov-Bohm (AB) caging effect in rhombic exciton-polariton\nlattices, with the Rashba-Dresselhaus spin-orbit coupling (RDSOC) in acting a\nsynthetic gauge field. The effective magnetic flux through each plaquette is\ncontrolled by the orientation of the RDSOC and geometry of the rhombic lattice.\nThe results show that the interplay of lattice geometry and the RDSOC will\ndramatically influence the energy band structure, furthermore, determining the\ntransportation properties of exciton-polariton condensates. Non-Hermitian\neffects, which arise from the polariton intrinsic loss mechanism, on the AB\ncaging is also discussed in detail. Meanwhile, the effect of disorder on the\ndynamics of AB caging is investigated, and we find that the disorder will lead\nto the inverse Anderson localization. We propose that using the AB caging\neffect allows to trap and steer the propagation of polaritons in a given\nparameter regime. Considering the specific example of a photonic liquid crystal\nmicrocavity to achieve our theoretical predictions, the AB caging could be\nswitched on and off by applying an external voltage."
    },
    {
        "anchor": "Interaction induced doublons and embedded topological subspace in a\n  complete flat-band system: In this work, we investigate effects of weak interactions on a bosonic\ncomplete flat-band system. By employing a band projection method, the flat-band\nHamiltonian with weak interactions is mapped to an effective Hamiltonian. The\neffective Hamiltonian indicates that doublons behave as well-defined\nquasi-particles, which acquire itinerancy through the hopping induced by\ninteractions. When we focus on a two-particle system, from the effective\nHamiltonian, an effective subspace spanned only by doublon bases emerges. The\neffective subspace induces spreading of a single doublon and we find an\ninteresting property: The dynamics of a single doublon keeps short-range\ndensity-density correlation in sharp contrast to a conventional two-particle\nspreading. Furthermore, when introducing a modulated weak interaction, we find\nan interaction induced topological subspace embedded in the full Hilbert space.\nWe elucidate the embedded topological subspace by observing the dynamics of a\nsingle doublon, and show that the embedded topological subspace possesses a\nbulk topological invariant. We further expect that for the system with open\nboundary the embedded topological subspace has an interaction induced\ntopological edge mode described by the doublon. The bulk--edge--correspondence\nholds even for the embedded topological subspace.",
        "positive": "Quasiparticle tunneling in a periodically driven bosonic Josephson\n  junction: A resonantly driven bosonic Josephson junction supports stable collective\nexcitations, or quasiparticles, which constitute analogs of the Trojan wave\npackets previously explored with Rydberg atoms in strong microwave fields. We\npredict a quantum beating effect between such symmetryrelated many-body Trojan\nstates taking place on time scales which are long in comparison with the\ndriving period. Within a mean-field approximation, this quantum beating can be\nregarded as a manifestation of dynamical tunneling. On the full N-particle\nlevel, the beating phenomenon leads to an experimentally feasible, robust\nstrategy for probing highly entangled mesoscopic states."
    },
    {
        "anchor": "Localization landscape for interacting Bose gases in one-dimensional\n  speckle potentials: While the properties and the shape of the ground state of a gas of ultracold\nbosons are well understood in harmonic potentials, they remain for a large part\nunknown in the case of random potentials. Here, we use the\nlocalization-landscape (LL) theory to study the properties of the solutions to\nthe Gross-Pitaevskii equation (GPE) in one-dimensional (1D) speckle potentials.\nIn the cases of attractive interactions, we find that the LL allows one to\npredict the position of the localization center of the ground state (GS) of the\nGPE. For weakly repulsive interactions, we point out that the GS of the\nquasi-1D GPE can be understood as a superposition of a finite number of\nsingle-particle states, which can be computed by exploiting the LL. For\nintermediate repulsive interactions, we introduce a Thomas-Fermi-like approach\nfor the GS which holds in the smoothing regime, well beyond the usual\napproximation involving the original potential. Moreover, we show that, in the\nLifshitz glass regime, the particle density and the chemical potential can be\nwell estimated by the LL. Our approach can be applied to any positive-valued\nrandom potential endowed with finite-range correlations and can be generalized\nto higher-dimensional systems.",
        "positive": "NOON states with ultracold bosonic atoms via resonance- and\n  chaos-assisted tunneling: We theoretically investigate the generation of microscopic atomic NOON\nstates, corresponding to the coherent |N,0> + |0,N> superposition with N ~ 5\nparticles, via collective tunneling of interacting ultracold bosonic atoms\nwithin a symmetric double-well potential in the self-trapping regime. We show\nthat a periodic driving of the double well with suitably tuned amplitude and\nfrequency parameters allows one to substantially boost this tunneling process\nwithout altering its collective character. The time scale to generate the NOON\nsuperposition, which corresponds to half the tunneling time and would be\nprohibitively large in the undriven double well for the considered atomic\npopulations, can thereby be drastically reduced, which renders the realization\nof NOON states through this protocol experimentally feasible. Resonance- and\nchaos-assisted tunneling are identified as key mechanisms in this context. A\nquantitative semiclassical evaluation of their impact onto the collective\ntunneling process allows one to determine the optimal choice for the driving\nparameters in order to generate those NOON states as fast as possible."
    },
    {
        "anchor": "p-Wave Resonant Bose Gas: A Finite-Momentum Spinor Superfluid: We show that a degenerate gas of two-species bosonic atoms interacting\nthrough a p-wave Feshbach resonance (as realized in, e.g., a 85Rb-87Rb mixture)\nexhibits a finite-momentum atomic-molecular superfluid (AMSF), sandwiched by a\nmolecular p-wave (orbital spinor) superfluid and by an s-wave atomic superfluid\nat large negative and positive detunings, respectively. The magnetic field can\nbe used to tune the modulation wave vector of the AMSF state, as well as to\ndrive quantum phase transitions in this rich system.",
        "positive": "Probing the bond order wave phase transitions of the ionic Hubbard model\n  by superlattice modulation spectroscopy: An exotic phase, the bond order wave, characterized by the spontaneous\ndimerization of the hopping, has been predicted to exist sandwiched between the\nband and Mott insulators in systems described by the ionic Hubbard model.\nDespite growing theoretical evidences, this phase still evades experimental\ndetection. Given the recent realization of the ionic Hubbard model in ultracold\natomic gases, we propose here to detect the bond order wave using superlattice\nmodulation spectroscopy. We demonstrate, with the help of time-dependent\ndensity-matrix renormalization group and bosonization, that this spectroscopic\napproach reveals characteristics of both the Ising and Kosterlitz-Thouless\ntransitions signaling the presence of the bond order wave phase. This scheme\nalso provides insights into the excitation spectra of both the band and Mott\ninsulators."
    },
    {
        "anchor": "Landauer-B\u00fcttiker equation for bosonic carriers: We study the current of Bose particles between two reservoirs connected by a\none-dimensional channel. We analyze the problem from first principles by\nconsidering a microscopic model of conductivity in the noninteracting limit.\nEquations for the transient and the stationary current are derived\nanalytically. The asymptotic current has a form similar to the\nLandauer-B\\\"uttiker equation for electronic current in mesoscopic devices.",
        "positive": "Synthetic Gauge Structures in Real Space in a Ring lattice: Emergence of fundamental forces from gauge symmetry is among our most\nprofound insights about the physical universe. In nature, such symmetries\nremain hidden in the space of internal degrees of freedom of subatomic\nparticles. Here we propose a way to realize and study gauge structures in real\nspace, manifest in external degrees of freedom of quantum states. We present a\nmodel based on a ring-shaped lattice potential, which allows for both Abelian\nand non-Abelian constructs. Non trivial Wilson loops are shown possible via\nphysical motion of the system. The underlying physics is based on the close\nanalogy of geometric phase with gauge potentials that has been utilized to\ncreate synthetic gauge fields with internal states of ultracold atoms. By\nscaling up to an array with spatially varying parameters, a discrete gauge\nfield can be realized in position space, and its dynamics mapped over\nmacroscopic size and time scales."
    },
    {
        "anchor": "Inducing Transport in a Dissipation-Free Lattice with Super Bloch\n  Oscillations: Particles in a perfect lattice potential perform Bloch oscillations when\nsubject to a constant force, leading to localization and preventing\nconductivity. For a weakly-interacting Bose-Einstein condensate (BEC) of Cs\natoms, we observe giant center-of-mass oscillations in position space with a\ndisplacement across hundreds of lattice sites when we add a periodic modulation\nto the force near the Bloch frequency. We study the dependence of these \"super\"\nBloch oscillations on lattice depth, modulation amplitude, and modulation\nfrequency and show that they provide a means to induce linear transport in a\ndissipation-free lattice. Surprisingly, we find that, for an interacting\nquantum system, super Bloch oscillations strongly suppress the appearance of\ndynamical instabilities and, for our parameters, increase the phase-coherence\ntime by more than a factor of hundred.",
        "positive": "Level statistics of the one-dimensional ionic Hubbard model: In this work we analyze the spectral level statistics of the one-dimensional\nionic Hubbard model, the Hubbard model with an alternating on-site potential.\nIn particular, we focus on the statistics of the gap ratios between consecutive\nenergy levels. This quantity is often used in order to signal whether a\nmany-body system is integrable or chaotic. A chaotic system has typically the\nstatistics of a Gaussian ensemble of random matrices while the spectral\nproperties of the integrable system follow a Poisson statistics. We find that\nwhereas the Hubbard model without alternating potential is known to be\nintegrable and its spectral properties follow a Poissonian statistics, the\npresence of an alternating potential causes a drastic change in the spectral\nproperties which resemble the one of a Gaussian ensemble of random matrices.\nHowever, to uncover this behavior one has to separately consider the blocks of\nall symmetries of the ionic Hubbard model."
    },
    {
        "anchor": "Statistical properties of the spectrum the extended Bose-Hubbard model: Motivated by the role that spectral properties play for the dynamical\nevolution of a quantum many-body system, we investigate the level spacing\nstatistic of the extended Bose-Hubbard model. In particular, we focus on the\ndistribution of the ratio of adjacent level spacings, useful at large\ninteraction, to distinguish between chaotic and non-chaotic regimes. After\nrevisiting the bare Bose-Hubbard model, we study the effect of two different\nperturbations: next-nearest neighbor hopping and nearest-neighbor interaction.\nThe system size dependence is investigated together with the effect of the\nproximity to integrable points or lines. Lastly, we discuss the consequences of\na cutoff in the number of onsite bosons onto the level statistics.",
        "positive": "Onsager vortex clusters on a sphere: We study Onsager vortex clustered states in a shell-shaped superfluid\ncontaining a large number of quantum vortices. In the incompressible limit and\nat low temperatures, the relevant problem can be boiled down to the statistical\nmechanics of neutral point vortices confined on a sphere. We analyze rotation\nfree vortex clustered states within the mean field theory in the microcanonical\nensemble. We find that the sandwich state, which involves the separating of\nvortices with opposite circulation and the clustering of vortices with same\ncirculation around the poles and the equator, is the maximum entropy vortex\ndistribution, subject to zero angular momentum constraint. The dipole momentum\nvanishes for the sandwich state and the quadrupole tensor serves as an order\nparameter to characterize the vortex cluster structure. For given finite\nangular momentum, the equilibrium vortex distribution forms a dipole structure,\ni.e., vortices with opposite sign are separated and are accumulated around the\nsouth and north pole, respectively. The conditions for the onset of clustering,\nand the exponents associated with the quadrupole moment and the dipole moment\nas functions of energy, are obtained within the mean field theory. At large\nenergies, we obtain asymptotically exact vortex density distributions using the\nstereographic projection method, which give rise the parameter bounds for the\nvortex clustered states. The analytical predictions are in excellent agreement\nwith microcanonical Monte Carlo simulations."
    },
    {
        "anchor": "Effect of Dimple Potential on Ultraslow Light in a Bose-Einstein\n  Condensate: We investigate the propagation of ultraslow optical pulse in atomic\nBose-Einstein condensate in a harmonic trap decorated with a dimple potential.\nThe role of dimple potential on the group velocity and time delay is studied.\nSince we consider the interatomic scattering interactions nonlinear Schrodinger\nequation or Gross-Pitaevskii equation is used in order to get the density\nprofile of the atomic system. We find large group delays of order 1 msec in an\natomic Bose-Einstein condensate in a harmonic trap with a deep dimple\npotential.",
        "positive": "Viscous dissipation in a gas of one-dimensional fermions with generic\n  dispersion: A well-known feature of the classical monoatomic gas is that its bulk\nviscosity is strongly suppressed because the single-particle dispersion is\nquadratic. On the other hand, in condensed matter systems the effective\nsingle-particle dispersion is altered by lattice effects and interactions. In\nthis work, we study the bulk viscosity of one-dimensional Fermi gases with\ngeneric energy-momentum dispersion relations. As an application, viscous\ndissipation arising from lattice effects is analyzed for the tight-binding\nmodel. In addition, we investigate how weak interactions affect the bulk\nviscosity. Finally, we discuss viscous dissipation in the regime in which the\nFermi gas is not fully equilibrated, as can occur when the system is driven at\nfrequencies that exceed the rate of fermion backscattering. In this case, the\nFermi gas is described by three bulk viscosities, which we obtain for a generic\nsingle-particle dispersion."
    },
    {
        "anchor": "Bosonic Kondo-Hubbard model: We study, using quantum Monte-Carlo simulations, the bosonic Kondo-Hubbard\nmodel in a two dimensional square lattice. We explore the phase diagram and\nanalyse the mobility of particles and magnetic properties. At unit filling, the\ntransition from a paramagnetic Mott insulator to a ferromagnetic superfluid\nappears continuous, contrary to what was predicted with mean field. For double\noccupation per site, both the Mott insulating and superfluid phases are\nferromagnetic and the transition is still continuous. Multiband tight binding\nHamiltonians can be realized in optical lattice experiments, which offer not\nonly the possibility of tuning the different energy scales over wide ranges,\nbut also the option of loading the system with either fermionic or bosonic\natoms.",
        "positive": "Interaction induced ferro-electricity in the rotational states of polar\n  molecules: We show that a ferro-electric quantum phase transition can be driven by the\ndipolar interaction of polar molecules in the presence a micro-wave field. The\nobtained ferro-electricity crucially depends on the harmonic confinement\npotential, and the resulting dipole moment persists even when the external\nfield is turned off adiabatically. The transition is shown to be second order\nfor fermions and for bosons of a smaller permanent dipole moment, but is first\norder for bosons of a larger moment. Our results suggest the possibility of\nmanipulating the microscopic rotational state of polar molecules by tuning the\ntrap's aspect ratio (and other mesoscopic parameters), even though the later's\nenergy scale is smaller than the former's by six orders of magnitude."
    },
    {
        "anchor": "Generation of atypical hopping and interactions by kinetic driving: We study the effect of time-periodically varying the hopping amplitude in a\none-dimensional Bose-Hubbard model, such that its time-averaged value is zero.\nEmploying Floquet theory, we derive a static effective Hamiltonian in which\nnearest-neighbor single-particle hopping processes are suppressed, but all even\nhigher-order processes are allowed. Unusual many-body features arise from the\ncombined effect of nonlocal interactions and correlated tunneling. At a\ncritical value of the driving, the system passes from a Mott insulator to a\nsuperfluid formed by two quasi-condensates with opposite nonzero momenta. This\nwork shows how driving of the hopping energy provides a novel form of Floquet\nengineering, which enables atypical Hamiltonians and exotic states of matter to\nbe produced and controlled.",
        "positive": "Strongly-Interacting Bosons in a Two-Dimensional Quasicrystal Lattice: Quasicrystals exhibit exotic properties inherited from the self-similarity of\ntheir long-range ordered, yet aperiodic, structure. The recent realization of\noptical quasicrystal lattices paves the way to the study of correlated Bose\nfluids in such structures, but the regime of strong interactions remains\nlargely unexplored, both theoretically and experimentally. Here, we determine\nthe quantum phase diagram of two-dimensional correlated bosons in an eightfold\nquasicrystal potential. Using large-scale quantum Monte Carlo calculations, we\ndemonstrate a superfluid-to-Bose glass transition and determine the critical\nline. Moreover, we show that strong interactions stabilize Mott insulator\nphases, some of which have spontaneously broken eightfold symmetry. Our results\nare directly relevant to current generation experiments and, in particular,\ndrive prospects to the observation of the still elusive Bose glass phase in two\ndimensions and exotic Mott phases."
    },
    {
        "anchor": "Bi-directional universal dynamics in a spinor Bose gas close to a\n  non-thermal fixed point: We numerically study the universal scaling dynamics of an isolated\none-dimensional ferromagnetic spin-1 Bose gas. Preparing the system in a\nfar-from-equilibrium initial state, simultaneous coarsening and refining is\nfound to enable and characterize the approach to a non-thermal fixed point. A\nmacroscopic length scale which scales in time according to $L_{\\Lambda}(t)\\sim\nt^{\\, \\beta}$, with $\\beta\\simeq 1/4$, quantifies the coarsening of the size of\nspin textures. At the same time kink-like defects populating these textures\nundergo a refining process measured by a shrinking microscopic length scale\n$L_{\\lambda}\\sim t^{\\, \\beta'}$, with $\\beta'\\simeq-0.17$. The combination of\nthese scaling evolutions enables particle and energy conservation in the\nisolated system and constitutes a bi-directional transport in momentum space.\nThe value of the coarsening exponent $\\beta$ suggests the dynamics to belong to\nthe universality class of diffusive coarsening of the one-dimensional XY-model.\nHowever, the universal momentum distribution function exhibiting non-linear\ntransport marks the distinction between diffusive coarsening and the approach\nof a non-thermal fixed point in the isolated system considered here. This\nunderlines the importance of the universal scaling function in classifying\nnon-thermal fixed points. Present-day experiments with quantum gases are\nexpected to have access to the predicted bi-directional scaling.",
        "positive": "Non-Markovian quantum friction of bright solitons in superfluids: We explore the quantum dynamics of a bright matter-wave soliton in a\nquasi-one-dimensional bosonic superfluid with attractive interactions.\nSpecifically, we focus on the dissipative forces experienced by the soliton due\nto its interaction with Bogoliubov excitations. Using the collective coordinate\napproach and the Keldysh formalism, a Langevin equation of motion for the\nsoliton is derived from the first principle. The equation contains a stochastic\nLangevin force (associated with quantum noise) and a non-local in time\ndissipative force, which appears due to inelastic scattering of Bogoliubov\nquasiparticles off of the moving soliton. It is shown that Ohmic friction\n(i.e., a term proportional to the soliton's velocity) is absent in the\nintegrable setup. However, the Markovian approximation gives rise to the\nAbraham-Lorentz force (i.e., a term proportional to the derivative of the\nsoliton's acceleration), which is known from classical electrodynamics of a\ncharged particle interacting with its own radiation. These Abraham-Lorentz\nequations famously contain a fundamental causality paradox, where the\nsoliton/particle interacts with excitations/radiation originating from future\nevents. We show, however, that the causality paradox is an artifact of the\nMarkovian approximation, and our exact non-Markovian dissipative equations give\nrise to physical trajectories. We argue that the quantum friction discussed\nhere should be observable in current quantum gas experiments."
    },
    {
        "anchor": "Energy level statistics of interacting trapped bosons: It is an well established fact that statistical properties of energy level\nspectra are the most efficient tool to characterize nonintegrable quantum\nsystems. The study of statistical properties and spectral fluctuation in the\ninteracting many boson systems have developed a new interest in this direction.\nSpecially we are interested in the weakly interacting trapped bosons in the\ncontext of Bose-Einstein condensation (BEC) as the energy spectrum shows a\ntransition from the collective to single particle nature with the increase in\nthe number of levels. However this has received less attention as it is\nbelieved that the system may exhibit Poisson like fluctuations due to the\nexistence of external harmonic trap. Here we compute numerically the energy\nlevels of the zero-temperature many-boson systems which are weakly interacting\nthrough the van der Waals potential and are in the 3D confined harmonic\npotential. We study the nearest neighbour spacing distribution and the spectral\nrigidity by unfolding the spectrum. It is found that increase in number of\nenergy levels for repulsive BEC induces a transition from a Wigner like form\ndisplaying level repulsion to Poisson distribution for P(s). It does not follow\nthe GOE prediction. For repulsive interaction, the lower levels are correlated\nand manifest level repulsion. For intermediate levels P (s) shows mixed\nstatistic which clearly signifies the existence of two energy scales: external\ntrap and interatomic interaction. Whereas for very high levels the trapping\npotential dominates, genarating Poisson distribution. Comparison with\nmean-field results for lower levels are also presented. For attractive BEC near\nthe critical point we observe the Shrielman like peak near s=0 which signifies\nthe presence of large number of quasi-degenerate states.",
        "positive": "Two dipolar atoms in a harmonic trap: Two identical dipolar atoms moving in a harmonic trap without an external\nmagnetic field are investigated. Using the algebra of angular momentum a semi -\nanalytical solutions are found. We show that the internal spin - spin\ninteractions between the atoms couple to the orbital angular momentum causing\nan analogue of Einstein - de Haas effect. We show a possibility of\nadiabatically pumping our system from the s-wave to the d-wave relative motion.\nThe effective spin-orbit coupling occurs at anti-crossings of the energy\nlevels."
    },
    {
        "anchor": "About conditions of spatial collapse in an infinite system of Bose\n  particles: Using the variational principle, we show that the condition of spatial\ncollapse in a Bose gas is not determined by the value of the scattering length\nof the interaction potential between particles contrary to the result following\nfrom the Gross--Pitaevskii equation, where the collapse should take place at a\nnegative scattering length.",
        "positive": "Tuning Dissipation and Excitations in Superfluid Fermi Gases with a\n  Moving Impurity: We develop a method to extract the dissipation for a heavy moving impurity\nimmersed in superfluid Fermi gases. The drag force is derived analytically. As\na reward, we are able to extract the dynamical structure factor, from which\ndensity excitations of the system is carefully examined. We show that\ndissipations through drag force is associated with two types of excitations,\none being single-particle and the other being collective. We map out the\ncritical velocity for dissipation across the BEC-BCS crossover, consistent with\nexisting experiments. For a magnetic impurity, we show that the dissipation is\nimmune to collective excitations. Our study clearly manifests that dissipation\nand associated excitations can be controlled by coupling superfluid Fermi gases\nwith a moving impurity, and paves the way for further exploring intriguing\nrealm of nonequilibrium phenomena and dissipation dynamics."
    },
    {
        "anchor": "An escape of vector matter-wave soliton from a parabolic trap: We show that a vector matter-wave soliton in Bose-Einstein condensate loaded\ninto an optical lattice can escape from a trap formed by a parabolic potential,\nresembling a Hawking emission. The particle-antiparticle pair is emulated by a\nlow-amplitude bright-bright soliton in two-component Bose-Einstein condensate\nwith effective masses of opposite signs. It is shown that the parabolic\npotential leads to a spatial separation of BEC components. One component with\nchemical potential in a semi-infinite gap exerts periodical oscillations, while\nthe other BEC component, with negative effective mass, escapes from the trap.\nThe mechanism of atoms transfer from one BEC component to another by spatially\nperiodic linear coupling term is discussed.",
        "positive": "Significance of dressed molecules in a quasi-two-dimensional polarized\n  Fermi gas: We investigate the properties of a spin-orbit coupled quasi-two-dimensional\nFermi gas with tunable s-wave interaction between the two spin species. By\nanalyzing the two-body bound state, we find that the population of the excited\nstates in the tightly-confined axial direction can be significant when the\ntwo-body binding energy becomes comparable or exceeds the axial confinement.\nSince the Rashba spin-orbit coupling that we study here tends to enhance the\ntwo-body binding energy, this effect can become prominent at unitarity or even\non the BCS side of the Feshbach resonance. To study the impact of these excited\nmodes along the third dimension, we adopt an effective two-dimensional\nHamiltonian in the form of a two-channel model, where the dressed molecules in\nthe closed channel consist of the conventional Feshbach molecules as well as\nthe excited states occupation in the axial direction. With properly\nrenormalized interactions between atoms and dressed molecules, we find that\nboth the density distribution and the phase structure in the trap can be\nsignificantly modified near a wide Feshbach resonance. In particular, the\nstability region of the topological superfluid phase is increased. Our findings\nare helpful for the experimental search for the topological superfluid phase in\nultra-cold Fermi gases, and have interesting implications for\nquasi-low-dimensional polarized Fermi gases in general."
    },
    {
        "anchor": "Laser Manipulation of Spin-Exchange Interaction Between Alkaline-Earth\n  Atoms in $^1$S$_0$ and $^3$P$_2$ States: Ultracold gases of fermionic alkaline-earth (like) atoms are hopeful\ncandidates for the quantum simulation of many-body physics induced by magnetic\nimpurities (e.g., the Kondo physics), because there are spin-exchange\ninteractions (SEIs) between two atoms in the electronic ground ($^1$S$_0$) and\nmetastable ($^3$P) state, respectively. Nevertheless, this SEI cannot be tuned\nvia magnetic Feshbach resonance. In this work we propose three methods to\ncontrol the SEI between one atom in the $^1$S$_0$ state and another atom in the\n$^3$P$_2$ states or $^3$P$_2$-$^3$P$_0$ dressed states, with one or two laser\nbeams.These methods are based on the spin-dependent AC-Stark shifts of the\n$^3$P$_2$ states, or the $^3$P$_2$-$^3$P$_0$ Raman coupling. We show that due\nto the structure of alkaline-earth (like) atoms, the heating effects induced by\nthe laser beams of our methods are very weak. For instance, for ultracold Yb\natoms, AC-Stark-shift difference of variant spin states of the $^3$P$_2(F=3/2)$\nlevel, or the strength of the $^3$P$_2$-$^3$P$_0$ Raman coupling, could be of\nthe order of $(2\\pi)$MHz, while the heating rate (photon scattering rate) is\nonly of the order of Hz. As a result, the Feshbach resonances, with which one\ncan efficiently control the SEI by changing the laser intensity, may be induced\nby the laser beams with low-enough heating rate, even if the scattering lengths\nof the bare inter-atomic interaction are so small that being comparable with\nthe length scale associated with the van der Waals interaction.",
        "positive": "Breaking of Goldstone modes in two component Bose-Einstein condensate: We study the decay rate $\\Gamma(k)$ of density excitations of two-component\nBose-Einstein condensates at zero temperature. Those excitations, where the two\ncomponents oscillate in phase, include the Goldstone mode resulting from\ncondensation. While within Bogoliubov approximation the density sector and the\nspin (out-of-phase) sector are independent, they couple at the three-phonon\nlevel. For a Bose-Bose mixture we find that the Belyaev decay is slightly\nmodified due to the coupling with the gapless spin mode. At the phase\nseparation point the decay rate changes instead from the standard $k^5$ to a\n$k^{5/2}$ behaviour due to the parabolic nature of the spin mode. In presence\nof coherent coupling between the two components the spin sector is gapped and,\naway from the ferromagnetic-like phase transition point, the decay of density\nmode is not affected. On the other hand at the transition point, when the spin\nfluctuations become critical, the Goldstone mode is not well defined anymore\nsince $\\Gamma(k)\\propto k$. As a consequence, we show that the friction induced\nby a moving impurity is enahnced -- a feature which could be experimentally\ntested. Our results apply to every non-linear 2-component quantum hydrodynamic\nHamiltonian which is time-reversal invariant, and possesses an $U(1)\\times\n{\\mathbf Z}_2$ symmetry."
    },
    {
        "anchor": "Doublon dynamics in the extended Fermi Hubbard model: Two fermions occupying the same site of a lattice model with strongly\nrepulsive Hubbard-type interaction U form a doublon, a long-living excitation\nthe decay of which is suppressed because of energy conservation. By means of an\nexact-diagonalization approach based on the Krylov-space technique, we study\nthe dynamics of a single doublon, of two doublons, and of a doublon in the\npresence of two additional fermions prepared locally in the initial state of\nthe extended Hubbard model. The time dependence of the expectation value of the\ndouble occupancy at the different sites of a large one-dimensional lattice is\nanalyzed by perturbative arguments. In this way the spatiotemporal evolution of\nthe doublon can be understood. The initial decay takes place on a short time\nscale 1/U, and the long-time average of the decayed fraction of the total\ndouble occupancy scales as 1/U^2 . We demonstrate how the dynamics of a doublon\nin the initial state is related to the spectrum of two-fermion excitations\nobtained from linear-response theory, we work out the difference between\ndoublons composed of fermions vs doublons composed of bosons, and we show that\ndespite the increase of phase space for inelastic decay processes, the\nstability of a doublon is enhanced by the presence of additional fermions on an\nintermediate time scale.",
        "positive": "Effects of quantum fluctuations on the low-energy collective modes of\n  two-dimensional superfluid Fermi gases from the BCS to the Bose Limit: We investigate the effects of quantum fluctuations on the low-energy\ncollective modes of two-dimensional (2D) $s$-wave Fermi superfluids from the\nBCS to the Bose limit. We compare our results to recent Bragg scattering\nexperiments in 2D box potentials, with very good agreement. We show that\nquantum fluctuations in the phase and modulus of the pairing order parameter\nare absolutely necessary to give physically acceptable chemical potential and\ndispersion relation of the low-energy collective mode throughout the BCS to\nBose evolution. Furthermore, we demonstrate that the dispersion of the\ncollective modes change from concave to convex as interactions are tuned from\nthe BCS to the Bose regime, and never crosses the two-particle continuum,\nbecause arbitrarily small attractive interactions produce bound states in 2D."
    },
    {
        "anchor": "Confinement induced interlayer molecules: a route to strong interatomic\n  interactions: We study theoretically the interaction between two species of ultracold atoms\nconfined into two layers of a finite separation, and demonstrate the existence\nof new types of confinement-induced interlayer bound and quasi-bound molecules:\nthese novel exciton-like interlayer molecules appear for both positive and\nnegative scattering lengths, and exist even for layer separations many times\nlarger than the interspecies scattering length. The lifetime of the quasi-bound\nmolecules grows exponentially with increasing layer separation, and they can\ntherefore be observed in simple shaking experiments, as we demonstrate through\ndetailed many-body calculations. These quasi-bound molecules can also give rise\nto novel interspecies Feshbach resonances, enabling one to control\ngeometrically the interaction between the two species by changing the layer\nseparation. Rather counter-intuitively, the species can be made strongly\ninteracting, by increasing their spatial separation. The separation induced\ninterlayer resonances provide a powerful tool for the experimental control of\ninterspecies interactions and enables one to realize novel quantum phases of\nmulticomponent quantum gases.",
        "positive": "Elementary Excitations in Bose-Einstein Condensates at Large Scattering\n  Lengths: We present a theoretical analysis of excitation modes in Bose-Einstein\ncondensates in ultracold alkali-metal gases for large scattering lengths and\nmomenta where corrections to the mean field approximation become important. We\nassume that the effective interaction in the metastable, single channel,\ngaseous phase has a well defined Fourier transform that scales with the\nscattering length. Based on this we show that for increasing scattering lengths\nor equivalently increasing densities the system becomes less correlated and\nthat at large values of the scattering length Bragg scattering measures\ndirectly the Fourier transform of the effective two-body potential. We\nconstruct model potentials which fit the recently measured line shifts in\n$^{85}$Rb by Papp et al. (Phys. Rev. Lett. {\\bf 101}, 135301 (2008)), and show\nthat they fix the low momentum expansion of the effective range function. We\nfind excellent agreement with the experimental data when the effective range is\n$\\ll 1$ and the coefficient of the $k^4$-term is $-7.5 \\pm 0.5$ in scattering\nlength units. The resolution in Bragg scattering experiments so far does not\nreveal details of the frequency dependence in the dynamic structure function\n$S(k,\\omega)$ and we show that the Feynman spectrum determines the measured\nline shifts. We propose the possibility of a transition to a novel density wave\nstate."
    },
    {
        "anchor": "REVIEW. Quantum optics with ultracold quantum gases: towards the full\n  quantum regime of the light-matter interaction: Although the study of ultracold quantum gases trapped by light is a prominent\ndirection of modern research, the quantum properties of light were widely\nneglected in this field. Quantum optics with quantum gases closes this gap and\naddresses phenomena, where the quantum statistical nature of both light and\nultracold matter play equally important roles. First, light can serve as a\nquantum nondemolition (QND) probe of the quantum dynamics of various ultracold\nparticles from ultracold atomic and molecular gases to nanoparticles and\nnanomechanical systems. Second, due to dynamic light-matter entanglement,\nprojective measurement-based preparation of the many-body states is possible,\nwhere the class of emerging atomic states can be designed via optical geometry.\nLight scattering constitutes such a quantum measurement with controllable\nmeasurement back-action. As in cavity-based spin squeezing, atom number\nsqueezed and Schroedinger cat states can be prepared. Third, trapping atoms\ninside an optical cavity one creates optical potentials and forces, which are\nnot prescribed but quantized and dynamical variables themselves. Ultimately,\ncavity QED with quantum gases requires a self-consistent solution for light and\nparticles, which enriches the picture of quantum many-body states of atoms\ntrapped in quantum potentials. This will allow quantum simulations of phenomena\nrelated to the physics of phonons, polarons, polaritons and other quantum\nquasiparticles.",
        "positive": "Temperature Dependence of the Density and Excitations of Dipolar\n  Droplets: Droplet states of ultracold gases which are stabilized by fluctuations have\nrecently been observed for dipolar and two component Bose gases. These systems\npresent a novel form of equilibrium where an instability at the mean field\nlevel is arrested by higher order correlations making the droplet states\nsensitive probes of fluctuations. In a recent paper, we argued that thermal\nfluctuations can play an important role for droplets even at low temperatures\nwhere the non-condensed density is much smaller than the condensate density. We\nused the Hartree-Fock-Bogoliubov theory together with local density\napproximation for fluctuations to obtain a generalized Gross Pitaevskii (GP)\nequation and solved it with a Gaussian variational ansatz to show that the\ntransition between the low density and droplet states can be significantly\nmodified by the temperature. In this paper, we first solve the same GP equation\nnumerically with a time splitting spectral method to check the validity of the\nGaussian variational ansatz. Our numerical results are in good agreement with\nthe Gaussian ansatz for a large parameter regime and show that the density of\nthe gas is most strongly modified by temperature near the abrupt transition\nbetween a pancake shaped cloud and the droplet. For cigar shaped condensates,\nas in the recent Er experiments, the dependence of the density on temperature\nremains quite small throughout the smooth transition. We then consider the\neffect of temperature on the collective oscillation frequencies of the droplet\nusing both a time dependent Gaussian variational ansatz and real time numerical\nevolution. We find that the oscillation frequencies depend significantly on the\ntemperature close to the transition for the experimentally relevant temperature\nregime ($\\simeq 100$nK)."
    },
    {
        "anchor": "Effects of Interactions on Bose-Einstein Condensation: Bose-Einstein condensation is a unique phase transition in that it is not\ndriven by inter-particle interactions, but can theoretically occur in an ideal\ngas, purely as a consequence of quantum statistics. This chapter addresses the\nquestion \\emph{`How is this ideal Bose gas condensation modified in the\npresence of interactions between the particles?' } This seemingly simple\nquestion turns out to be surprisingly difficult to answer. Here we outline the\ntheoretical background to this question and discuss some recent measurements on\nultracold atomic Bose gases that have sought to provide some answers.",
        "positive": "Reply to \"Comment on \"Dispersive Bottleneck Delaying Thermalization of\n  Turbulent Bose-Einstein Condensates\" by E. Kozik\" [arXiv:1102.2943]\": We discuss the comment [ arXiv:1102.2943] by E. Kozik about \"Dispersive\nbottleneck delaying thermalization of turbulent Bose-Einstein Condensates\n[arXiv:1007.4441]\"."
    },
    {
        "anchor": "Numerical generation of a vortex ring cascade in quantum turbulence: A symmetric anti-parallel quantum pair of vortices is simulated using the\nthree-dimensional Gross-Pitaevski equations. The initial development before\ncores interact directly demonstrates the traditional vortex dynamics of\nstretching, curvature and torsion in a manner consistent with a filament\ncalculation and simulations of the classical, ideal Euler equations. Once the\ncores begin to interact, reconnection develops in the vacuum that forms between\nthe pair. Out of the reconnection region, vortex waves are emitted with\nproperties similar to waves in the local induction approximation. These waves\npropagate down the initial vortex and deepen. When they deepen far enough,\nsecondary reconnections occur and vortex rings form. Near this time, spectra\nhave a $k^{-3}$ regime. As the vortex rings fully separate, the high wavenumber\nspectra grow until, at the final time simulated, spectra in two directions\ndevelop nearly -5/3 subranges. This occurs without the dissipation of energy.\nPreliminary analysis of the flow of energies in spectral scale and physical\nspace is discussed.",
        "positive": "Layer-by-layer assembly of multilayer optical lattices: Application to\n  displaced dice lattice: We propose methods for synthesizing multilayer optical lattices of cold atoms\nin a layer-by-layer manner, to unlock the potential of optical lattices in\nsimulating the fascinating physics of multilayer systems. Central to the\napproach is to compress the beam profile of a red-detuned Gaussian laser beam\nfrom disklike to a thin line by a telescope with two cylindrical lenses. A\nhighly tunable multilayer optical lattice is obtained by passing the compressed\nGaussian beam through an optical device consisting of beam splitters, mirrors,\nand glass plates. We illustrate the proposal with the displaced dice lattice,\nwhich is a trilayer lattice that maps to the dice lattice when projected to the\nsame layer. Both the dice model and its interesting variants may be realized.\nFor a model of fermionic cold atoms, featuring an isolated flat band between\ntwo dispersive bands, we find valley-contrasting interband transitions\ninvolving the flat band."
    },
    {
        "anchor": "Quantum hydrodynamic theory of quantum fluctuations in dipolar\n  Bose-Einstein condensate: Traditional quantum hydrodynamics of Bose-Einstein condensates (BECs) is\nrestricted by the continuity and Euler equations. It corresponds to the\nwell-known Gross-Pitaevskii equation. However, the quantum Bohm potential,\nwhich is a part of the momentum flux, has a nontrivial part with can evolve\nunder the quantum fluctuations. To cover this phenomenon in terms of\nhydrodynamic methods we need to derive equations for the momentum flux, and the\nthird rank tensor. In all equations we consider the main contribution of the\nshort-range interaction (SRI) in the first order by the interaction radius.\nDerived hydrodynamics consists of four hydrodynamic equations. The third moment\nevolution equation contains interaction leading to the quantum fluctuations. It\nincludes new interaction constant. The Gross-Pitaevskii interaction constant is\nthe integral of potential, but the second interaction constant is the integral\nof second derivative of potential. If we have dipolar BECs we deal with a\nlong-range interaction. Its contribution is proportional to the potential of\ndipole-dipole interaction (DDI). The Euler equation contains the derivative of\nthe potential. The third rank tensor evolution equation contains the third\nderivative of the potential. The quantum fluctuations lead to existence of the\nsecond wave solution. Moreover, the quantum fluctuations introduce the\ninstability of BECs. If the DDI is attractive, but being smaller then the\nrepulsive SRI presented by the first interaction constant, there is the\nlong-wavelength instability. For the repulsive DDI these is more complex\npicture. There is the small area with the long-wavelength instability which\ntransits into stability interval, where two waves exist. There is the\nshort-wavelength instability as well. These results are found for the DDI\nstrength comparable with the Gross-Pitaevskii SRI.",
        "positive": "$N$-coherence vs. $t$-coherence: An alternative route to the\n  Gross-Pitaevskii equation: We show how a candidate mean-field amplitude can be constructed from the\nexact wave function of an externally forced $N$-Boson system. The construction\nmakes use of subsidiary $(N-1)$-particle states which are propagated in time in\naddition to the true $N$-particle state, but does not involve spontaneous\nbreaking of the $U(1)$ symmetry associated with particle number conservation.\nProvided the flow in Fock space possesses a property which we call maximum\nstiffness, or $t$-coherence, the candidate amplitude actually satisfies the\ntime-dependent Gross-Pitaevskii equation, and then serves as macroscopic wave\nfunction of the forced $N$-particle system. The general procedure is\nillustrated in detail by numerical calculations performed for the model of a\ndriven bosonic Josephson junction, which allows one to keep track of all\ncontributions which usually are subject to uncontrolled assumptions. These\ncalculations indicate that macroscopic wave functions can persist even under\nconditions of strong forcing, but are rapidly destroyed upon entering a regime\nof chaotic dynamics. Our results provide a foundation for future attempts to\nmanipulate, and actively control, macroscopic wave functions by means of\npurposefully designed force protocols."
    },
    {
        "anchor": "Conditions for order and chaos in the dynamics of a trapped\n  Bose-Einstein condensate in coordinate and energy space: We investigate numerically conditions for order and chaos in the dynamics of\nan interacting Bose- Einstein condensate (BEC) confined by an external trap cut\noff by a hard-wall box potential. The BEC is stirred by a laser to induce\nexcitations manifesting as irregular spatial and energy oscillations of the\ntrapped cloud. Adding laser stirring to the external trap results in an\neffective time-varying trapping frequency in connection with the dynamically\nchanging combined external+laser potential trap. The resulting dynamics are\nanalyzed by plotting their trajectories in coordinate phase space and in energy\nspace. The Lyapunov exponents are computed to confirm the existence of chaos in\nthe latter space. Quantum effects and trap anharmonicity are demonstrated to\ngenerate chaos in energy space, thus confirming its presence and implicating\neither quantum effects or trap anharmonicity as its generator. The presence of\nchaos in energy space does not necessarily translate into chaos in coordinate\nspace. In general, a dynamic trapping frequency is found to promote chaos in a\ntrapped BEC. An apparent means to suppress chaos in a trapped BEC is achieved\nby increasing the characteristic scale of the external trap with respect to the\ncondensate size.",
        "positive": "Pattern formation of correlated impurities subjected to an\n  impurity-medium interaction pulse: We study the correlated dynamics of few interacting bosonic impurities\nimmersed in a one-dimensional harmonically trapped bosonic environment. The\nmixture is exposed to a time-dependent impurity-medium interaction pulse moving\nit across the relevant phase separation boundary. For modulation frequencies\nsmaller than the trapping one, the system successively transits through the\nmiscible/immiscible phases according to the driving of the impurity-medium\ninteractions. For strong modulations, and driving from the miscible to the\nimmiscible regime, a significant fraction of the impurities is expelled to the\nedges of the bath. They exhibit a strong localization behavior and tend to\nequilibrate. Following the reverse driving protocol, the impurities perform a\nbreathing motion while featuring a two-body clustering and the bath is split\ninto two incoherent parts. Interestingly, in both driving scenarios,\ndark-bright solitons are nucleated in the absence of correlations. A\nlocalization of the impurities around the trap center for weak\nimpurity-impurity repulsions is revealed, which subsequently disperse into the\nbath for increasing interactions."
    },
    {
        "anchor": "One-dimensional hard-core anyon gas in a harmonic trap at finite\n  temperature: We investigate the strongly interacting hard-core anyon gases in a one\ndimensional harmonic potential at finite temperature by extending thermal\nBose-Fermi mapping method to thermal anyon-ferimon mapping method. With thermal\nanyon-fermion mapping method we obtain the reduced one-body density matrix and\ntherefore the momentum distribution for different statistical parameters and\ntemperatures. At low temperature hard-core anyon gases exhibit the similar\nproperties as those of ground state, which interpolate between Bose-like and\nFermi-like continuously with the evolution of statistical properties. At high\ntemperature hard-core anyon gases of different statistical properties display\nthe same reduced one-body density matrix and momentum distribution as those of\nspin-polarized fermions. The Tan's contact of hard-core anyon gas at finite\ntemperature is also evaluated, which take the simple relation with that of\nTonks-Girardeau gas $C_b$ as $C=\\frac12(1-cos\\chi\\pi)C_b$.",
        "positive": "Theory of SU(N) Fermi liquid: We generalized the Fermi liquid theory to N component systems with SU(N)\nsymmetry. We emphasize the important role of fluctuations when N is large.\nThese fluctuations dramatically modifies the properties for repulsive Fermi\ngases, in particular the spin susceptibility."
    },
    {
        "anchor": "Dynamics of rotated spin states and magnetic ordering with two-component\n  bosonic atoms in optical lattices: The microscopic control available over cold atoms in optical lattices has\nopened new opportunities to study the properties of quantum spin models. While\na lot of attention is focussed on experimentally realizing ground or thermal\nstates via adiabatic loading, it would often be more straightforward to prepare\nspecific simple product states and to probe the properties of interacting spins\nby observing their dynamics. We explore this possibility for spin-1/2 and\nspin-1 models that can be realized with bosons in optical lattices, and which\nexhibit \\textit{XY}-ferromagnetic (or counterflow spin superfluid) phases. We\nconsider the dynamics of initial spin-rotated states corresponding to a\nmean-field version of the phases of interest. Using matrix product state\nmethods in one dimension, we compute both non-equilibrium dynamics and\nground/thermal states for these systems. We compare and contrast their\nbehaviour in terms of correlation functions and induced spin currents, which\nshould be directly observable with current experimental techniques. We find\nthat although spin correlations decay substantially at large distances and on\nlong timescales, for induction of spin currents, the rotated states behave\nsimilarly to the ground states on experimentally observable timescales.",
        "positive": "Dynamical Spectral Response of Fractonic Quantum Matter: Quantum many-body systems with fractonic excitations can realize fascinating\nphases of matter. Here, we study the low-energy excitations of a constrained\nBose-Hubbard model in one dimension, which conserves the center of mass or,\nequivalently, the dipole moment in addition to the particle number. This model\nis known to realize fractonic phases, including a dipole Mott insulator, a\ndipole Luttinger liquid, and a metastable dipole supersolid. We use tensor\nnetwork methods to compute spectral functions from the dynamical response of\nthe system and verify predictions from low-energy field theories of the\ncorresponding ground state phases. We demonstrate the existence of gapped\nexcitations compatible with strong coupling results in a dipole Mott insulator,\nlinear sound modes characteristic of a Luttinger liquid of dipoles, and soft\nquadratic modes at both zero and finite momenta in a supersolid state with\ncharge density wave order and phase coherence at non-integer filling."
    },
    {
        "anchor": "Coupled exciton-photon Bose condensate in path integral formalism: We study the behavior of exciton polaritons in an optical microcavity with an\nembedded semiconductor quantum well. We use two-component exciton-photon\napproach formulated in terms of path integral formalism. In order to describe\nspatial distributions of the exciton and photon condensate densities, the two\ncoupled equations of the Gross-Pitaevskii type are derived. For a homogeneous\nsystem, we find the noncondensate photon and exciton spectra, calculate the\ncoefficients of transformation from the exciton-photon basis to the lower-upper\npolariton basis, and obtain the exciton and photon occupation numbers of the\nlower and upper polariton branches for nonzero temperatures. For an\ninhomogeneous system, the set of coupled equations of the Bogoliubov-de-Gennes\ntype is derived. The equations govern the spectra and spatial distributions of\nnoncondensate photons and excitons.",
        "positive": "Abelian gauge potentials on cubic lattices: The study of the properties of quantum particles in a periodic potential\nsubject to a magnetic field is an active area of research both in physics and\nmathematics; it has been and it is still deeply investigated. In this review we\ndiscuss how to implement and describe tunable Abelian magnetic fields in a\nsystem of ultracold atoms in optical lattices. After discussing two of the main\nexperimental schemes for the physical realization of synthetic gauge potentials\nin ultracold set-ups, we study cubic lattice tight-binding models with\ncommensurate flux. We finally examine applications of gauge potentials in\none-dimensional rings."
    },
    {
        "anchor": "Memory of the Initial Conditions in an Incompletely-Chaotic Quantum\n  System: Universal Predictions and an Application to Cold Atoms: Two zero-range-interacting atoms in a circular, transversely harmonic\nwaveguide are used as a test-bench for a quantitative description of the\ncrossover between integrability and chaos in a quantum system with no selection\nrules. For such systems we show that the expectation value after relaxation of\na generic observable is given by a linear interpolation between its initial and\nthermal expectation values. The variable of this interpolation is universal; it\ngoverns this simple law to cover the whole spectrum of the chaotic behavior\nfrom integrable regime through the well- developed quantum chaos. The\npredictions are confirmed for the waveguide system, where the mode occupations\nand the trapping energy were used as the observables of interest; a variety of\nthe initial states and a full range of the interaction strengths have been\ntested.",
        "positive": "Large time and long distance asymptotics of the thermal correlators of\n  the impenetrable anyonic lattice gas: We study thermal correlation functions of the one-dimensional impenetrable\nlattice anyons. These correlation functions can be presented as a difference of\ntwo Fredholm determinants. To describe large time and long distance behavior of\nthese objects we use effective form factor approach. The asymptotic behavior is\ndifferent in the space-like and time-like regions. In particular, in the\ntime-like region we observe the additional power factor on top of the\nexponential decay. We argue that this result is universal as it is related to\nthe discontinuous behavior of the phase shift function of the effective\nfermions. At particular values of the anyonic parameter we recover asymptotics\nof spin-spin correlation functions in XXO quantum chain."
    },
    {
        "anchor": "Generation of vortices and observation of Quantum Turbulence in an\n  oscillating Bose-Einstein Condensate: We report on the experimental observation of vortex formation and production\nof tangled vortex distribution in an atomic BEC of Rb-87 atoms submitted to an\nexternal oscillatory perturbation. The oscillatory perturbations start by\nexciting quadrupolar and scissors modes of the condensate. Then regular\nvortices are observed finally evolving to a vortex tangle configuration. The\nvortex tangle is a signature of the presence of a turbulent regime in the\ncloud. We also show that this turbulent cloud has suppression of the aspect\nratio inversion typically observed in quantum degenerate bosonic gases during\nfree expansion.",
        "positive": "Phase Diagram for Magnon Condensate in Yttrium Iron Garnet Film: Recently, magnons, which are quasiparticles describing the collective motion\nof spins, were found to undergo Bose-Einstein condensation (BEC) at room\ntemperature in films of Yttrium Iron Garnet (YIG). Unlike other quasiparticle\nBEC systems, this system has a spectrum with two degenerate minima, which makes\nit possible for the system to have two condensates in momentum space. Recent\nBrillouin Light scattering studies for a microwave-pumped YIG film of thickness\nd=5 $\\mu$m and field H=1 kOe find a low-contrast interference pattern at the\ncharacteristic wavevector $Q$ of the magnon energy minimum. In this report, we\nshow that this modulation pattern can be quantitatively explained as due to\nnon-symmetric but coherent Bose-Einstein condensation of magnons into the two\nenergy minima. Our theory predicts a transition from a high-contrast symmetric\nphase to a low-contrast non-symmetric phase on varying the $d$ and $H$, and a\nnew type of collective oscillations."
    },
    {
        "anchor": "Transition state theory for wave packet dynamics. II. Thermal decay of\n  Bose-Einstein condensates with long-range interaction: We apply transition state theory to coupled Gaussian wave packets and\ncalculate thermal decay rates of Bose-Einstein condensates with additional\nlong-range interaction. The ground state of such a condensate is metastable if\nthe contact interaction is attractive and a sufficient thermal excitation may\nlead to its collapse. The use of transition state theory is made possible by\ndescribing the condensate within a variational framework and locally mapping\nthe variational parameters to classical phase space as has been demonstrated in\nthe preceding paper [A. Junginger, J. Main, and G. Wunner, submitted to J.\nPhys. A]. We apply this procedure to Gaussian wave packets and present results\nfor condensates with monopolar 1/r-interaction comparing decay rates obtained\nby using different numbers of coupled Gaussian trial wave functions as well as\ndifferent normal form orders.",
        "positive": "Observation of a strongly ferromagnetic spinor Bose-Einstein condensate: We report the observation of strongly ferromagnetic $F=1$ spinor\nBose-Einstein condensates of $^7$Li atoms. The condensates are generated in an\noptical dipole trap without using magnetic Feshbach resonances, so that the\ncondensates have internal spin degrees of freedom. Studying the non-equilibrium\nspin dynamics, we have measured the ferromagnetic spin interaction energy and\ndetermined the $s$-wave scattering length difference among total spin $f$\nchannels to be $a_{f=2}-a_{f=0} =-18(3)$ Bohr radius. This strong\ncollision-channel dependence leads to a large variation in the condensate size\nwith different spin composition. We were able to excite a radial monopole mode\nafter a spin-flip transition between the $|m_F=0\\rangle$ and $|m_F=1\\rangle$\nspin states. From the experiments, we estimated the scattering length ratio\n$a_{f=2}/a_{f=0}=0.27(6)$, and determined $a_{f=2}$ = 7(2) and $a_{f=0}$ =\n25(5) Bohr radii, respectively. The results indicate the spin-dependent\ninteraction energy of our system is as large as 46$\\%$ of the condensate\nchemical potential."
    },
    {
        "anchor": "Stable symmetry-protected 3D embedded solitons in Bose-Einstein\n  condensates: Embedded solitons are rare self-localized nonlinear structures that,\ncounterintuitively, survive inside a continuous background of resonant states.\nWhile this topic has been widely studied in nonlinear optics, it has received\nalmost no attention in the field of Bose-Einstein condensation. In this work,\nwe consider experimentally realizable Bose-Einstein condensates loaded in\none-dimensional optical lattices and demonstrate that they support continuous\nfamilies of stable three-dimensional (3D) embedded solitons. These solitons can\nexist inside the resonant continuous Bloch bands because they are protected by\nsymmetry. The analysis of the Bogoliubov excitation spectrum as well as the\nlong-term evolution after random perturbations proves the robustness of these\nnonlinear structures against any weak perturbation. This may open up a way for\nthe experimental realization of stable 3D matter-wave embedded solitons as well\nas for monitoring the gap-soliton to embedded-soliton transition.",
        "positive": "Elastic collision rates of spin-polarized fermions in two dimensions: We study the $p$-wave elastic collision rates in a two-dimensional\nspin-polarized ultracold Fermi gas in the presence of a $p$-wave Feshbach\nresonance. We derive the analytical relation of the elastic collision rate\ncoefficient in the close vicinity of resonance when the effective range is\ndominant. The elastic collision rate is enhanced by an exponential scaling of\n$e^{-q_{r}^{2} / q_{T}^{2}}$ towards the resonance. Here, $q_{r}$ is the\nresonant momentum and $q_T$ is the thermal momentum. An analogous expression is\nderived for the case of three dimensions successfully explains the\nthermalization rates measurement in the recent experiment~[Phys. Rev. A 88,\n012710 (2013)]. In the zero-range limit where the effective range is\nnegligible, the elastic collision rate coefficient is proportional to\ntemperature $T^2$ and scattering area $A_{p}^2$. In this limit, energy transfer\nfrom high to low velocity through $p$-wave collision is approximately\n$\\sqrt{2}$ times faster compared to the three-dimensional case. We also discuss\nthe collisional stability in the presence of three-body losses in the\nbackground scattering limit. Our results suggest that $p$-wave evaporation may\nbe performed with improved efficiency and may provide insight into the dynamics\nof the system in experiments."
    },
    {
        "anchor": "Strong-coupling dynamics of Bose-Einstein condensate in a double-well\n  trap: Dynamics of the repulsive Bose-Einstein condensate (BEC) in a double-well\ntrap is explored within the 3D time-dependent Gross-Pitaevskii equation. The\nmodel avoids numerous common approximations (two-mode treatment, time-space\nfactorization, fixed values of the chemical potential and barrier\npenetrability, etc) and thus provides a realistic description of BEC dynamics,\nincluding both weak-coupling (sub-barrier) and strong-coupling (above-barrier)\nregimes and their crossover. The strong coupling regime is achieved by\nincreasing the number $N$ of BEC atoms and thus the chemical potential. The\nevolution with $N$ of Josephson oscillations (JO) and Macroscopic Quantum\nSelf-Trapping (MQST) is examined and the crucial impact of the BEC interaction\nis demonstrated. At weak coupling, the calculations well reproduce the JO/MQST\nexperimental data. At strong coupling, with a significant overlap of the left\nand right BECs, we observe a remarkable persistence of the Josephson-like\ndynamics: the JO and MQST converge to a high-frequency JO-like mode where both\npopulation imbalance and phase difference oscillate around the zero averages.\nThe results open new avenues for BEC interferometry.",
        "positive": "Connecting Topological Anderson and Mott Insulators in Disordered\n  Interacting Fermionic Systems: The topological Anderson and Mott insulators are two phases that have so far\nbeen separately and widely explored beyond topological band insulators. Here we\ncombine the two seemingly different topological phases into a system of\nspin-1/2 interacting fermionic atoms in a disordered optical lattice. We find\nthat the topological Anderson and Mott insulators in the noninteracting and\nclean limits can be adiabatically connected without gap closing in the phase\ndiagram of our model. Lying between the two phases, we uncover a disordered\ncorrelated topological insulator, which is induced from a trivial band\ninsulator by the combination of disorder and interaction, as the generalization\nof topological Anderson insulators to the many-body interacting regime. The\nphase diagram is determined by computing various topological properties and\nconfirmed by unsupervised and automated machine learning. We develop an\napproach to provide a unified and clear description of topological phase\ntransitions driven by interaction and disorder. The topological phases can be\ndetected from disorder/interaction induced edge excitations and charge pumping\nin optical lattices."
    },
    {
        "anchor": "Sub-Poissonian number differences in four-wave mixing of matter waves: We demonstrate sub-Poissonian number differences in four-wave mixing of\nBose-Einstein condensates of metastable helium. The collision between two\nBose-Einstein condensates produces a scattering halo populated by pairs of\natoms of opposing velocities, which we divide into several symmetric zones. We\nshow that the atom number difference for opposing zones has sub-Poissonian\nnoise fluctuations whereas that of nonopposing zones is well described by shot\nnoise. The atom pairs produced in a dual number state are well adapted to sub\nshot-noise interferometry and studies of Einstein-Podolsky-Rosen-type\nnonlocality tests.",
        "positive": "Chiral $p\\pm ip$ superfluid on a sphere: We consider a spinless fermionic $p\\pm ip$ superfluid living on a\ntwo-dimensional sphere. Using superfluid hydrodynamics we show that the ground\nstate necessarily exhibits topological defects: either a pair of elementary\nvortices or a domain wall between $p\\pm ip$ phases. In the topologically\nnontrivial BCS phase we identify the chiral fermion modes localized on the\ntopological defects and compute their low-energy spectrum."
    },
    {
        "anchor": "Bosonic quantum Hall states in single-layer two-dimensional optical\n  lattices: Quantum Hall (QH) states of 2D single layer optical lattices are examined\nusing Bose-Hubbard model (BHM) in presence of artificial gauge field. We study\nthe QH states of both the homogeneous and inhomogeneous systems. For the\nhomogeneous case we use cluster Gutzwiller mean field (CGMF) theory with\ncluster sizes ranging from $2\\times 2$ to $5\\times 5$. We, then, consider the\ninhomogeneous case, which is relevant to experimental realization. In this\ncase, we use CGMF and exact diagonalization (ED). The ED studies are using\nlattice sizes ranging from $3\\times 3$ to $4\\times 12$. Our results show that\nthe geometry of the QH states are sensitive to the magnetic flux $\\alpha$ and\ncluster sizes. For homogeneous system, among various combinations of\n$1/5\\leqslant \\alpha\\leqslant 1/2$ and filling factor $\\nu$, only the QH state\nof $\\alpha=1/4$ with $\\nu=1/2$, $1$, $3/2$ and $2$ occur as ground states. For\nother combinations, the competing superfluid (SF) state is the ground state and\nQH state is metastable. For BHM with envelope potential all the QH states\nobserved in homogeneous system exist for box potentials, but none for the\nharmonic potential. The QH states also persist for very shallow Gaussian\nenvelope potential. As a possible experimental signature we study the two point\ncorrelations of the QH and SF states.",
        "positive": "Disordered quantum gases under control: When attempting to understand the role of disorder in condensed-matter\nphysics, one faces severe experimental and theoretical difficulties and many\nquestions are still open. Two of the most challenging ones, which have been\ndebated for decades, concern the effect of disorder on superconductivity and\nquantum magnetism. Recent progress in ultracold atomic gases paves the way\ntowards realization of versatile quantum simulators which will be useful to\nsolve these questions. In addition, ultracold gases offer original situations\nand viewpoints, which open new perspectives to the field of disordered systems."
    },
    {
        "anchor": "Pseudopotentials for an ultracold dipolar gas: A gas of ultracold molecules interacting via the long-range dipolar potential\noffers a highly controlled environment in which to study strongly correlated\nphases. However, at particle coalescence the divergent $1/r^3$ dipolar\npotential and associated pathological wavefunction hinder computational\nanalysis. For a dipolar gas constrained to two dimensions we overcome these\nnumerical difficulties by proposing a pseudopotential that is explicitly smooth\nat particle coalescence, resulting in a 2000-times speedup in diffusion Monte\nCarlo calculations. The pseudopotential delivers the scattering phase shifts of\nthe dipolar interaction with an accuracy of $10^{-5}$ and predicts the energy\nof a dipolar gas to an accuracy of $10^{-4}E_\\mathrm{F}$ in a diffusion Monte\nCarlo calculation.",
        "positive": "Two-body and three-body substructures served as building blocks in small\n  spin-3 condensates: It was found that stable few-body spin-structures, pairs and triplexes, may\nexist as basic constituents in small spin-3 condensates, and they will play the\nrole as building blocks when the parameters of interaction are appropriate.\nSpecific method is designed to find out these constituents."
    },
    {
        "anchor": "Effective Three-Body Interactions in Jaynes-Cummings-Hubbard Systems: A generalisation of the Jaynes-Cummings-Hubbard model for coupled-cavity\narrays is introduced, where the embedded two-level system in each cavity is\nreplaced by a $\\Xi$-type three-level system. We demonstrate that the resulting\neffective polariton-polariton interactions at each site are both two-body and\nthree-body. By tuning the ratio of the two transition dipole matrix elements,\nwe show that the strength and sign of the two-body interaction can be\ncontrolled whilst maintaining a three-body repulsion. We then proceed to\ndemonstrate how different two-body and three-body interactions alter the mean\nfield superfluid-Mott insulator phase diagram, with the possible emergence of a\npair superfluid phase in the two-body attractive regime.",
        "positive": "Finite-size effects in the two-dimensional BCS-BEC crossover: We study the finite-size effects on the BCS-BEC crossover in two dimensions,\noccurring in confined fermionic superfluids. We analyze several thermodynamic\nproperties, such as the chemical potential, the energy gap and the superfluid\ndensity, taking into account unavoidable quantum fluctuations, and, by means of\nrenormalization group procedure, we detect the putative\nBerezinskii-Kosterlitz-Thouless phase transition at finite-size."
    },
    {
        "anchor": "Rapid generation and number-resolved detection of spinor Rubidium\n  Bose-Einstein condensates: High data acquisition rates and low-noise detection of ultracold neutral\natoms present important challenges for the state tomography and interferometric\napplication of entangled quantum states in Bose-Einstein condensates. In this\narticle, we present a high-flux source of $^{87}$Rb Bose-Einstein condensates\ncombined with a number-resolving detection. We create Bose-Einstein condensates\nof $2\\times10^5$ atoms with no discernible thermal fraction within $3.3$ s\nusing a hybrid evaporation approach in a magnetic/optical trap. For the\nhigh-fidelity tomography of many-body quantum states in the spin degree of\nfreedom [arXiv:2207.01270], it is desirable to select a single mode for a\nnumber-resolving detection. We demonstrate the low-noise selection of\nsubsamples of up to $16$ atoms and their subsequent detection with a counting\nnoise below $0.2$ atoms. The presented techniques offer an exciting path\ntowards the creation and analysis of mesoscopic quantum states with\nunprecedented fidelities, and their exploitation for fundamental and\nmetrological applications.",
        "positive": "Finite-momentum Bose-Einstein condensates in shaken 2D square optical\n  lattices: We consider ultracold bosons in a 2D square optical lattice described by the\nBose-Hubbard model. In addition, an external time-dependent sinusoidal force is\napplied to the system, which shakes the lattice along one of the diagonals. The\neffect of the shaking is to renormalize the nearest-neighbor hopping\ncoefficients, which can be arbitrarily reduced, can vanish, or can even change\nsign, depending on the shaking parameter. It is therefore necessary to account\nfor higher-order hopping terms, which are renormalized differently by the\nshaking, and introduce anisotropy into the problem. We show that the\ncompetition between these different hopping terms leads to finite-momentum\ncondensates, with a momentum that may be tuned via the strength of the shaking.\nWe calculate the boundaries between the Mott-insulator and the different\nsuperfluid phases, and present the time-of-flight images expected to be\nobserved experimentally. Our results open up new possibilities for the\nrealization of bosonic analogs of the FFLO phase describing inhomogeneous\nsuperconductivity."
    },
    {
        "anchor": "Vortices in rotating Bose gas interacting via finite range Gaussian\n  potential in a quasi-two-dimensional harmonic trap: A system of harmonically trapped N=16 spin-$0$ bosons confined in quasi-$2$D\nsymmetrical $x-y$ plane interacting via a finite range repulsive Gaussian\npotential is studied under an externally impressed rotation to an over all\nangular velocity $\\Omega$ about the $z-$axis. The exact diagonalization (ED) of\n$n\\times n$ many-body Hamiltonian matrix in a given subspace of quantized total\nangular momentum $0\\le L_{z} \\le 4N$ is performed using Davidson algorithm. For\n$N=16 \\mbox{and}\\ L_{z}=32$, the dimensionality of the Hilbert space turns out\nto be $n=384559$. The trap velocity $\\Omega$ being the Langrange multiplier\nassociated with the angular momentum $L_{z}$ for the rotating systems, the\n$L_{z}-\\Omega$ phase diagram (or stability line) is drawn which determines the\ncritical angular velocities, $\\Omega_{\\bf c_{i}}, i=1,2..$, at which, for a\ngiven angular momentum $L_{z}$, the system goes through a quantum phase\ntransition. %condensate fraction, von-Neumann entropy exhibit abrupt %(quantum\nphase)jumps. Further with increase in interaction range $\\sigma$, the quantum\nmechanical coherence extends over more and more particles in the system\nresulting in an enhanced stability of the $i^{th}$ vortical state with angular\nmomentum $L_{z}\\left(\\Omega_{c_{i}}\\right)$ leading to a delayed onset of the\nthe next vortical state $L_{z}\\left(\\Omega_{c_{i+1}}\\right)$ at a higher value\nof the next critical angular velocity $\\Omega_{c_{i+1}}$. There is an increase\nin the critical angular velocity $\\left(\\Omega_{\\textbf{c}_{i}},\ni=1,2,3\\cdots\\right)$ and in the largest condensate fraction $\\lambda_{1}$,\ncalculated using single particle reduced density matrix(SPRDM) eigen-values\nwith increase in the interaction range $\\sigma$. We calculated the von-Neumann\nquantum entropy ($S_{1}$), degree of condensation ($C_{d}$) and the conditional\nprobability density (CPDs).",
        "positive": "Confined p-band Bose-Einstein condensates: We study bosonic atoms on the p-band of a two dimensional optical square\nlattice in the presence of a confining trapping potential. Using a mean-field\napproach, we show how the anisotropic tunneling for p-band particles affects\nthe cloud of condensed atoms by characterizing the ground state density and the\ncoherence properties of the atomic states both between sites and atomic\nflavors. In contrast to the usual results based on the local density\napproximation, the atomic density can become anisotropic. This anisotropic\neffect is especially pronounced in the limit of weak atom-atom interactions and\nof weak lattice amplitudes, i.e. when the properties of the ground state are\nmainly driven by the kinetic energies. We also investigate how the trap\ninfluences known properties of the non-trapped case. In particular, we focus on\nthe behavior of the anti-ferromagnetic vortex-antivortex order, which for the\nconfined system, is shown to disappear at the edges of the condensed cloud."
    },
    {
        "anchor": "Even-Odd Correlation Functions on an Optical Lattice: We study how different many body states appear in a quantum gas microscope,\nsuch as the one developed at Harvard [Bakr et al. Nature 462, 74 (2009)], where\nthe site-resolved parity of the atom number is imaged. We calculate the spatial\ncorrelations of the microscope images, corresponding to the correlation\nfunction of the parity of the number of atoms at each site. We produce analytic\nresults for a number of well-known models: noninteracting bosons, the large U\nBose-Hubbard model, and noninteracting fermions. We find that these parity\ncorrelations tend to be less strong than density-density correlations, but they\ncarry similar information.",
        "positive": "Three-component topological superfluid in one-dimensional Fermi gases\n  with spin-orbit coupling: We theoretically investigate one-dimensional three-component\nspin-orbit-coupled Fermi gases in the presence of Zeeman field. By solving the\nBogoliubov-de-Gennes equations, we obtain the phase diagram at given chemical\npotential and order parameter. We show that the system undergoes a phase\ntransition from Bardeen-Cooper-Schrieffer superfluid to topological superfluid\nas increasing the intensity of Zeeman field. By comparing to the two-component\nsystem, we find, besides the topological phase transition from the trivial\nsuperfluid to nontrivial topological superfluid, the system can always be in a\nnontrivial topological superfluid, and there are two Majorana zero energy\nregions while increasing the magnetic field. We find the three-component\nspin-orbit-coupled Fermi gases in certain parameter range is more optimizing\nfor experimental realization due to the smaller magnetic field needed. We\ntherefore propose a promising candidate for realizing topological superfluid."
    },
    {
        "anchor": "Attractive Bose-Einstein condensates in anharmonic traps: Accurate\n  numerical treatment and the intriguing physics of the variance: The dynamics of attractive bosons trapped in one dimensional anharmonic\npotentials is investigated. Particular emphasis is put on the variance of the\nposition and momentum many-particle operators. Coupling of the center-of-mass\nand relative-motion degrees-of-freedom necessitates an accurate numerical\ntreatment. The multiconfigurational time-dependent Hartree for bosons (MCTDHB)\nmethod is used, and high convergence of the energy, depletion and occupation\nnumbers, and position and momentum variances is proven numerically. We\ndemonstrate for the ground state and out-of-equilibrium dynamics, for condensed\nand fragmented condensates, for small systems and {\\it en route} to the\ninfinite-particle limit, that intriguing differences between the density and\nvariance of an attractive Bose-Einstein condensate emerge. Implications are\nbriefly discussed.",
        "positive": "Soliton trains after interaction quenches in Bose mixtures: We investigate the quench dynamics of a two-component Bose mixture and study\nthe onset of modulational instability, which leads the system far from\nequilibrium. Analogous to the single-component counterpart, this phenomenon\nresults in the creation of trains of bright solitons. We provide an analytical\nestimate of the number of solitons at long times after the quench for each of\nthe two components based on the most unstable mode of the Bogoliubov spectrum,\nwhich agrees well with our simulations for quenches to the weak attractive\nregime when the two components possess equal intraspecies interactions and loss\nrates. We also explain the significantly different soliton dynamics in a\nrealistic experimental homonuclear potassium mixture in terms of different\nintraspecies interaction and loss rates. We investigate the quench dynamics of\nthe particle number of each component estimating the characteristic time for\nthe appearance of modulational instability for a variety of interaction\nstrengths and loss rates. Finally, we evaluate the influence of the\nbeyond-mean-field contribution, which is crucial for the ground-state\nproperties of the mixture, in the quench dynamics for both the evolution of the\nparticle number and the radial width of the mixture. In particular, even for\nquenches to strongly attractive effective interactions, we do not observe the\ndynamical formation of solitonic droplets."
    },
    {
        "anchor": "Formation of matter-wave soliton trains by modulational instability: Nonlinear systems can exhibit a rich set of dynamics that are inherently\nsensitive to their initial conditions. One such example is modulational\ninstability, which is believed to be one of the most prevalent instabilities in\nnature. By exploiting a shallow zero-crossing of a Feshbach resonance, we\ncharacterize modulational instability and its role in the formation of\nmatter-wave soliton trains from a Bose-Einstein condensate. We examine the\nuniversal scaling laws exhibited by the system, and through real-time imaging,\naddress a long-standing question of whether the solitons in trains are created\nwith effectively repulsive nearest neighbor interactions, or rather, evolve\ninto such a structure.",
        "positive": "Critical temperature of noninteracting bosonic gases in cubic optical\n  lattices at arbitrary integer fillings: We have shown that the critical temperature of a Bose-Einstein condensate to\na normal phase transition of noninteracting bosons in cubic optical lattices\nhas a linear dependence on the filling factor, especially at large densities.\nThe condensed fraction exhibits a linear power law dependence on temperature in\ncontrast to the case of ideal homogeneous Bose gases."
    },
    {
        "anchor": "Vortex dynamics in lattice Bose gases in a synthesized magnetic field\n  with a random noise and a dissipation: Study by the stochastic\n  Gross-Pitaevskii equation: In this paper, we investigate vortex dynamics in a two-dimensional\nBose-Hubbard model coupled with a weak artificial magnetic field, a random\nwhite noise and a dissipation. Origin of the noise and dissipation is\nconsidered as thermal fluctuations of atoms that do not participate the\nBose-Einstein condensation (BEC). Solving a stochastic Gross-Pitaevskii\nequation to this system, we show that the interplay of the magnetic field and\nthe white noise generates vortices in the bulk of the BEC and stable steady\nstates of vortices form after a transition period. We calculate the\nincompressible part of the kinetic-energy spectrum of the BEC. In the\ntransition period, a Kolmogorov $k^{-5/3}$ spectrum appears in the infrared\nregime with the wave number $k$, $k<\\zeta^{-1}$, where $\\zeta$ is the healing\nlength, whereas in the ultraviolet region, $k>\\zeta^{-1}$, the spectrum behaves\nas $k^{-3}$. On the other hand in the steady states, another scaling low\nappears. We find a relationship between the above mentioned kinetic-energy\nspectra and the velocity of vortices. By an inverse cascade, the large velocity\nof a few created vortices develops the Kolmogorov $k^{-5/3}$ spectrum.",
        "positive": "A Non-Equilibrium Kinetic Theory for Trapped Binary Condensates: We derive a non-equilibrium finite-temperature kinetic theory for a binary\nmixture of two interacting atomic Bose-Einstein condensates and use it to\nexplore the degree of hydrodynamicity attainable in realistic experimental\ngeometries. Based on the standard separation of timescale argument of kinetic\ntheory, the dynamics of the condensates of the multi-component system are shown\nto be described by dissipative Gross-Pitaevskii equations, self-consistently\ncoupled to corresponding Quantum Boltzmann equations for the non-condensate\natoms: on top of the usual mean field contributions, our scheme identifies a\ntotal of eight distinct collisional processes, whose dynamical interplay is\nexpected to be responsible for the systems equilibration. In order to provide\ntheir first characterization, we perform a detailed numerical analysis of the\nrole of trap frequency and geometry on collisional rates for experimentally\naccessible mixtures of $^{87}$Rb-$^{41}$K and $^{87}$Rb-$^{85}$Rb, discussing\nthe extent to which the system may approach the hydrodynamic regime with regard\nto some of those processes, as a guide for future experimental investigations\nof ultracold Bose gas mixtures."
    },
    {
        "anchor": "Variational analysis of flat-top solitons in Bose-Einstein condensates: Static and dynamic properties of matter-wave solitons in dense Bose-Einstein\ncondensates, where three-body interactions play a significant role, have been\nstudied by a variational approximation (VA) and numerical simulations. For\nexperimentally relevant parameters, matter-wave solitons may acquire a flat-top\nshape, which suggests employing a super-Gaussian trial function for VA.\nComparison of the soliton profiles, predicted by VA and those found from\nnumerical solution of the governing Gross-Pitaevskii equation shows good\nagreement, thereby validating the proposed approach.",
        "positive": "Excitation spectra of many-body systems by linear response: General\n  theory and applications to trapped condensates: We derive a general linear-response many-body theory capable of computing\nexcitation spectra of trapped interacting bosonic systems, e.g., depleted and\nfragmented Bose-Einstein condensates (BECs). To obtain the linear-response\nequations we linearize the multiconfigurational time-dependent Hartree for\nbosons (MCTDHB) method, which provides a self-consistent description of\nmany-boson systems in terms of orbitals and a state vector (configurations),\nand is in principle numerically-exact. The derived linear-response many-body\ntheory, which we term LR-MCTDHB, is applicable to systems with interaction\npotentials of general form. From the numerical implementation of the LR-MCTDHB\nequations and solution of the underlying eigenvalue problem, we obtain\nexcitations beyond available theories of excitation spectra, such as the\nBogoliubov-de Gennes (BdG) equations. The derived theory is first applied to\nstudy BECs in a one-dimensional harmonic potential. The LR-MCTDHB method\ncontains the BdG excitations and, also, predicts a plethora of additional\nmany-body excitations which are out of the realm of standard linear response.\nIn particular, our theory describes the exact energy of the higher harmonic of\nthe first (dipole) excitation not contained in the BdG theory. We next study a\nBEC in a very shallow one-dimensional double-well potential. We find with\nLR-MCTDHB low-lying excitations which are not accounted for by BdG, even though\nthe BEC has only little fragmentation and, hence, the BdG theory is expected to\nbe valid. The convergence of the LR-MCTDHB theory is assessed by systematically\ncomparing the excitation spectra computed at several different levels of\ntheory."
    },
    {
        "anchor": "Density-functional theory for the spin-1 bosons in a one-dimensional\n  harmonic trap: We propose the density-functional theory for one-dimensional harmonically\ntrapped spin-1 bosons in the ground state with repulsive density-density\ninteraction and anti-ferromagnetic spin-exchange interaction. The density\ndistributions of spin singlet paired bosons and polarized bosons with different\ntotal polarization for various interaction parameters are obtained by solving\nthe Kohn-Sham equations which are derived based on the local density\napproximation and the Bethe ansatz exact results for homogeneous system.\nNon-monotonicity of the central densities is attributed to the competition\nbetween the density interaction and spin-exchange. The results reveal the phase\nseparation of the paired and polarized bosons, the density profiles of which\nrespectively approach the Tonks-Girardeau gases of Bose-Bose pairs and scalar\nbosons in the case of strong interaction. We give the R-P phase diagram at\nstrong interaction and find the critical polarization, which paves the way to\ndirect observe the exotic singlet pairing in spinor gas experimentally.",
        "positive": "Simulation method for evaporative cooling of trapped Bose gases at\n  finite temperatures: We develop a simulation method for evaporative cooling of trapped\nBose-Einstein condensate at finite temperatures using Zaremba-Nikuni-Griffin\n(ZNG) formalism. ZNG formalism includes the generalized GP equation and a\nsemiclassical kinetic equation for the thermal cloud, which treats the\nexcitations semiclassically within the Hartree Fock approximation. The\ngeneralized GP equation includes the mean field due to the thermal cloud and\nthe source term associated with collisions between the condensate and the\nthermal cloud. Our method is based on the numerical approach developed by\nJackson and Zaremba, which simulates the kinetic equation using test particles.\nA key point of our method is to mimic the evaporative cooling process by\neliminating the test particles with high energy. We show that our method\nsuccessfully describes condensate growth during evaporative cooling. We also\nnumerically simulate vortex lattice formation during evaporative cooling in the\npresence of the rotating thermal cloud."
    },
    {
        "anchor": "Effects of Efimov states on quench dynamics in a three-boson trapped\n  system: We investigate the effects of Efimov states on the post-quench dynamics of a\nsystem of three identical bosons with contact interactions, in a\nspherically-symmetric three-dimensional harmonic trap, which undergoes a quench\nin interaction strength. Using known hyperspherical solutions to the static\nthree-body problem we calculate semi-analytic results for the Ramsey signal and\nparticle separation as functions of time after the system is quenched. We\nconsider the quench from the non-interacting to strongly interacting and vice\nversa for a variety of possible Efimov state energies.",
        "positive": "Floquet operator engineering for quantum state stroboscopic\n  stabilization: Optimal control is a valuable tool for quantum simulation, allowing for the\noptimized preparation, manipulation, and measurement of quantum states. Through\nthe optimization of a time-dependent control parameter, target states can be\nprepared to initialize or engineer specific quantum dynamics. In this work, we\nfocus on the tailoring of a unitary evolution leading to the stroboscopic\nstabilization of quantum states of a Bose-Einstein condensate in an optical\nlattice. We show how, for states with space and time symmetries, such an\nevolution can be derived from the initial state-preparation controls; while for\na general target state we make use of quantum optimal control to directly\ngenerate a stabilizing Floquet operator. Numerical optimizations highlight the\nexistence of a quantum speed limit for this stabilization process, and our\nexperimental results demonstrate the efficient stabilization of a broad range\nof quantum states in the lattice."
    },
    {
        "anchor": "The Planck distribution of phonons in a Bose-Einstein condensate: The Planck distribution of photons emitted by a black body led to the\ndevelopment of quantum theory. An analogous distribution of phonons should\nexist in a Bose-Einstein condensate. We observe this Planck distribution of\nthermal phonons in a 3D condensate. This observation provides an important\nconfirmation of the basic nature of the condensate's quantized excitations. In\ncontrast to the bunching effect, the density fluctuations are seen to increase\nwith increasing temperature. This is due to the non-conservation of the number\nof phonons. In the case of rapid cooling, the phonon temperature is out of\nequilibrium with the surrounding thermal cloud. In this case, a Bose-Einstein\ncondensate is not as cold as previously thought. These measurements are enabled\nby our in situ k-space technique.",
        "positive": "Response to comment on \"Lack of a genuine time crystal in a chiral\n  soliton model\" by \u00d6hberg and Wright: In the paper [Phys. Rev. Research 2, 032038] we have analyzed a chiral\nsoliton model and shown that despite the claim of \\\"Ohberg and Wright [Phys.\nRev. Lett. 124, 178902], there is no indication that a genuine quantum time\ncrystal can be observed in the system. Here, we response to the recent comment\non our paper written by \\\"Ohberg and Wright."
    },
    {
        "anchor": "Controlling superfluid flows using dissipative impurities: We propose and analyze a protocol to create and control the superfluid flow\nin a one dimensional, weakly interacting Bose gas by noisy point contacts\ncoupled to the density of the bosons. Considering first a single contact in a\nstatic or moving condensate, we identify three different dynamical phases: I. a\nlinear response regime, where the noise induces a coherent flow in proportion\nto the strength of the noise accompanied by a counterflow of the normal\ncomponent of the gas, II. a Zeno regime with suppressed currents and negative\ndifferential current to noise characteristics, and III. for a non-vanishing\nrelative velocity, a regime of continuous soliton emission. The velocity of the\ncondensate at the dissipative impurity determines the threshold for Zeno\nsuppression of the current through the point contact, and the onset of the\nnon-stationary regime of soliton \"shooting\" from the defect. Generalizing to\ntwo point contacts in a condensate at rest we show that noise tuning can be\nemployed to control, stabilize or eventually shunt the superfluid transport of\nparticles along the segment which connects them, with perspectives for an\natomtronic analogue of a superfluid-current source for studying quantum\ntransport phenomena.",
        "positive": "Decay rates and energies of free magnons and bound states in dissipative\n  XXZ chains: Chains of coupled two-level atoms behave as 1D quantum spin systems,\nexhibiting free magnons and magnon bound states. While these excitations are\nwell studied for closed systems, little consideration has been given to how\nthey are altered by the presence of an environment. This will be especially\nimportant in systems that exhibit nonlocal dissipation, e.g. systems in which\nthe magnons decay due to optical emission. In this work, we consider free\nmagnon excitations and two-magnon bound states in an XXZ chain with nonlocal\ndissipation. We prove that whilst the energy of the bound state can lie outside\nthe two-magnon continuum of energies, the decay rate of the bound state has to\nalways lie within the two-magnon continuum of decay rates. We then derive\nanalytically the bound state solutions for a system with nearest-neighbour and\nnext-nearest-neighbour XY interaction and nonlocal dissipation, finding that\nthe inclusion of nonlocal dissipation allows more freedom in engineering the\nenergy and decay rate dispersions for the bound states. Finally, we numerically\nstudy a model of an experimental set-up that should allow the realisation of\ndissipative bound states by using Rydberg-dressed atoms coupled to a photonic\ncrystal waveguide (PCW). We demonstrate that this model can exhibit many key\nfeatures of our simpler models."
    },
    {
        "anchor": "Optical spin transport theory of spin-1/2 topological Fermi superfluids: We theoretically investigate optical (frequency-dependent) bulk spin\ntransport properties in a spin-1/2 topological Fermi superfluid. We\nspecifically consider a one-dimensional system with an interspin {\\it p}-wave\ninteraction, which can be realized in ultracold atom experiments. Developing\nthe BCS-Leggett theory to describe the Bardeen-Cooper-Schrieffer (BCS) to\nBose-Einstein condensate (BEC) evolution and the $\\mathbb{Z}_2$ topological\nphase transition in this system, we show how the spin transport reflects these\nmany-body aspects. We find that the optical spin conductivity, which is a small\nAC response of a spin current, shows the spin gapped spectrum in the wide\nparameter region and the gap closes at $\\mathbb{Z}_2$ topological phase\ntransition point. Moreover, the validity of the low-energy effective model of\nthe Majorana zero mode is discussed along the BCS-BEC evolution in connection\nwith the scale invariance at {\\it p}-wave unitarity.",
        "positive": "Hydrodynamic description of Hard-core Bosons on a Galileo ramp: We study the quantum evolution of a cloud of hard-core bosons loaded on a\none-dimensional optical lattice after its sudden release from a harmonic trap.\nJust after the trap has been removed, a linear ramp potential is applied,\nmimicking the so called Galileo ramp experiment. The non-equilibrium expansion\nof the bosonic cloud is elucidated through a hydrodynamical description which\nis compared to the exact numerical evolution obtained by exact diagonalization\non finite lattice sizes. The system is found to exhibit a rich behavior showing\nin particular Bloch oscillations of a self-trapped condensate and an ejected\nparticle density leading to two diverging entangled condensates. Depending on\nthe initial density of the gas different regimes of Josephson-like oscillations\nare observed. At low densities, the trapped part of the cloud is in a\nsuperfluid phase that oscillates in time as a whole. At higher densities, the\ntrapped condensate is in a mixed superfluid-Mott phase that show a breathing\nregime for steep enough potential ramps."
    },
    {
        "anchor": "Dissipative superfluid hydrodynamics for the unitary Fermi gas: In this work we establish constraints on the temperature dependence of the\nshear viscosity $\\eta$ in the superfluid phase of a dilute Fermi gas in the\nunitary limit. Our results are based on analyzing experiments that measure the\naspect ratio of a deformed cloud after release from an optical trap. We discuss\nhow to apply the two-fluid formalism to the unitary gas, and provide a suitable\nparametrization of the equation of state. We show that in expansion experiments\nthe difference between the normal and superfluid velocities remains small, and\ncan be treated as a perturbation. We find that expansion experiments favor a\nshear viscosity that decreases significantly in the superfluid regime. Using an\nexponential parametrization we find $\\eta(T_c/(2T_F))< 0.37\\eta (T_c/T_F)$,\nwhere $T_c$ is the critical temperature, $T_F$ is the local Fermi temperature\nof the gas.",
        "positive": "Supersolid and pair correlations of the extended Jaynes-Cummings-Hubbard\n  model on triangular lattices: We study the extended Jaynes-Cummings-Hubbard model on triangular cavity\nlattices and zigzag ladders. By using density-matrix renormalization group\nmethods, we observe various types of solids with different density patterns and\nfind evidence for light supersolids, which exist in extended regions of the\nphase diagram of the zigzag ladder. Furthermore, we observe strong pair\ncorrelations in the supersolid phase due to the interplay between the atoms in\nthe cavities and atom-photon interaction. By means of cluster mean-field\nsimulations and a scaling of the cluster size extending our analysis to\ntwo-dimensional triangular lattices, we present evidence for the emergence of a\nlight supersolid in this case also."
    },
    {
        "anchor": "Robust and Ultrafast State Preparation by Ramping Artificial Gauge\n  Potentials: The implementation of static artificial magnetic fields in ultracold atomic\nsystems has become a powerful tool, e.g. for simulating quantum-Hall physics\nwith charge-neutral atoms. Taking an interacting bosonic flux ladder as a\nminimal model, we investigate protocols for adiabatic state preparation via\nmagnetic flux ramps. Considering the fact that it is actually the artificial\nvector potential (in the form of Peierls phases) that can be experimentally\nengineered in optical lattices, rather than the magnetic field, we find that\nthe time required for adiabatic state preparation dramatically depends on which\npattern of Peierls phases is used. This can be understood intuitively by noting\nthat different patterns of time-dependent Peierls phases that all give rise to\nthe same magnetic field ramp, generally lead to different artificial electric\nfields during the ramp. Remarkably, we find that an optimal choice allows for\npreparing the ground state almost instantaneously. We relate this observation\nto shortcuts to adiabaticity via counterdiabatic driving. Our findings open new\npossibilities for robust state preparation in atomic quantum simulators.",
        "positive": "Continuous feedback on a quantum gas coupled to an optical cavity: We present an active feedback scheme acting continuously on the state of a\nquantum gas dispersively coupled to a high-finesse optical cavity. The quantum\ngas is subject to a transverse pump laser field inducing a self-organization\nphase transition, where the gas acquires a density modulation and photons are\nscattered into the resonator. Photons leaking from the cavity allow for a\nreal-time and non-destructive readout of the system. We stabilize the mean\nintra-cavity photon number through a micro-processor controlled feedback\narchitecture acting on the intensity of the transverse pump field. The feedback\nscheme can keep the mean intra-cavity photon number $n_\\text{ph}$ constant, in\na range between $n_\\text{ph}=0.17\\pm 0.04$ and $n_\\text{ph}=27.6\\pm 0.5$, and\nfor up to 4 s. Thus we can engage the stabilization in a regime where the\nsystem is very close to criticality as well as deep in the self-organized\nphase. The presented scheme allows us to approach the self-organization phase\ntransition in a highly controlled manner and is a first step on the path\ntowards the realization of many-body phases driven by tailored feedback\nmechanisms."
    },
    {
        "anchor": "Phase dependent loading of Bloch bands and Quantum simulation of\n  relativistic wave equation predictions with ultracold atoms in variably\n  shaped optical lattice potentials: The dispersion relation of ultracold atoms in variably shaped optical\nlattices can be tuned to resemble that of a relativistic particle, i.e. be\nlinear instead of the usual nonrelativistic quadratic dispersion relation of a\nfree atom. Cold atoms in such a lattice can be used to carry out quantum\nsimulations of relativistic wave equation predictions. We begin this article by\ndescribing a Raman technique that allows to selectively load atoms into a\ndesired Bloch band of the lattice near a band crossing. Subsequently, we review\ntwo recent experiments with quasirelativistic rubidium atoms in a bichromatic\nlattice, demonstrating the analogs of Klein tunneling and Veselago lensing with\nultracold atoms respectively.",
        "positive": "Double-degenerate Bose-Fermi mixture of strontium: We report on the attainment of a spin-polarized Fermi sea of 87-Sr in thermal\ncontact with a Bose-Einstein condensate (BEC) of 84-Sr. Interisotope collisions\nthermalize the fermions with the bosons during evaporative cooling. A\ndegeneracy of T/T_F=0.30(5) is reached with 2x10^4 87-Sr atoms together with an\nalmost pure 84-Sr BEC of 10^5 atoms."
    },
    {
        "anchor": "$\\mathbb{Z}_N$ gauge theories coupled to topological fermions: QED$_2$\n  with a quantum-mechanical $\u03b8$ angle: We present a detailed study of the topological Schwinger model [Phys. Rev. D\n99, 014503 (2019)], which describes (1+1) quantum electrodynamics of an Abelian\n$U(1)$ gauge field coupled to a symmetry-protected topological matter sector,\nby means of a class of $\\mathbb{Z}_N$ lattice gauge theories. Employing\ndensity-matrix renormalization group techniques that exactly implement Gauss'\nlaw, we show that these models host a correlated topological phase for\ndifferent values of $N$, where fermion correlations arise through\ninter-particle interactions mediated by the gauge field. Moreover, by a careful\nfinite-size scaling, we show that this phase is stable in the large-$N$ limit,\nand that the phase boundaries are in accordance to bosonization predictions of\nthe $U(1)$ topological Schwinger model. Our results demonstrate that\n$\\mathbb{Z}_N$ finite-dimensional gauge groups offer a practical route for an\nefficient classical simulation of equilibrium properties of electromagnetism\nwith topological fermions. Additionally, we describe a scheme for the quantum\nsimulation of a topological Schwinger model exploiting spin-changing collisions\nin boson-fermion mixtures of ultra-cold atoms in optical lattices. Although\ntechnically challenging, this quantum simulation would provide an alternative\nto classical density-matrix renormalization group techniques, providing also an\nefficient route to explore real-time non-equilibrium phenomena.",
        "positive": "Single Impurity In Ultracold Fermi Superfluids: The role of impurities as experimental probes in the detection of quantum\nmaterial properties is well appreciated. Here we study the effect of a single\nclassical magnetic impurity in trapped ultracold Fermi superfluids. Depending\non its shape and strength, a magnetic impurity can induce single or multiple\nmid-gap bound states in a superfluid Fermi gas. The multiple mid-gap states\ncould coincide with the development of a Fulde-Ferrell-Larkin-Ovchinnikov\n(FFLO) phase within the superfluid. As an analog of the Scanning Tunneling\nMicroscope, we propose a modified RF spectroscopic method to measure the local\ndensity of states which can be employed to detect these states and other\nquantum phases of cold atoms. A key result of our self consistent Bogoliubov-de\nGennes calculations is that a magnetic impurity can controllably induce an FFLO\nstate at currently accessible experimental parameters."
    },
    {
        "anchor": "Ferromagnetic Resonance in Spinor Dipolar Bose--Einstein Condensates: We used the Gross--Pitaevskii equations to investigate ferromagnetic\nresonance in spin-1 Bose--Einstein condensates with a magnetic dipole-dipole\ninteraction. By introducing the dipole interaction, we obtained equations\nsimilar to the Kittel equations used to represent ferromagnetic resonance in\ncondensed matter physics. These equations indicated that the ferromagnetic\nresonance originated from dipolar interaction, and that the resonance frequency\ndepended upon the shape of the condensate. Furthermore, spin currents driven by\nspin diffusions are characteristic of this system.",
        "positive": "Fractional Chern insulators of few bosons in a box: Hall plateaus from\n  center-of-mass drifts and density profiles: Realizing strongly-correlated topological phases of ultracold gases is a\ncentral goal for ongoing experiments. And while fractional quantum Hall states\ncould soon be implemented in small atomic ensembles, detecting their signatures\nin few-particle settings remains a fundamental challenge. In this work, we\nnumerically analyze the center-of-mass Hall drift of a small ensemble of\nhardcore bosons, initially prepared in the ground state of the\nHarper-Hofstadter-Hubbard model in a box potential. By monitoring the Hall\ndrift upon release, for a wide range of magnetic flux values, we identify an\nemergent Hall plateau compatible with a fractional Chern insulator state: the\nextracted Hall conductivity approaches a fractional value determined by the\nmany-body Chern number, while the width of the plateau agrees with the spectral\nand topological properties of the prepared ground state. Besides, a direct\napplication of Streda's formula indicates that such Hall plateaus can also be\ndirectly obtained from static density-profile measurements. Our calculations\nsuggest that fractional Chern insulators can be detected in cold-atom\nexperiments, using available detection methods."
    },
    {
        "anchor": "First-order spatial coherence measurements in a thermalized\n  two-dimensional photonic quantum gas: Phase transitions between different states of matter can profoundly modify\nthe order in physical systems, with the emergence of ferromagnetic or\ntopological order constituting important examples. Correlations allow to\nquantify the degree of order and classify different phases. Here we report\nmeasurements of first-order spatial correlations in a harmonically trapped\ntwo-dimensional photon gas below, at, and above the critical particle number\nfor Bose-Einstein condensation, using interferometric measurements of the\nemission of a dye-filled optical microcavity. For the uncondensed gas, the\ntransverse coherence decays on a length scale determined by the thermal de\nBroglie wavelength of the photons, which shows the expected scaling with\ntemperature. At the onset of Bose-Einstein condensation true long-range order\nemerges, and we observe quantum statistical effects as the thermal wave packets\noverlap. The excellent agreement with equilibrium Bose gas theory prompts\nmicrocavity photons as promising candidates for studies of critical scaling and\nuniversality in optical quantum gases.",
        "positive": "Repulsive polarons in alkaline-earth(-like) atoms across an orbital\n  Feshbach resonance: We characterize properties of the so-called repulsive polaron across the\nrecently discovered orbital Feshbach resonance in alkaline-earth(-like) atoms.\nBeing a metastable quasiparticle excitation at the positive energy, the\nrepulsive polaron is induced by the interaction between an impurity atom and a\nFermi sea. By analyzing in detail the energy, the polaron residue, the\neffective mass, and the decay rate of the repulsive polaron, we reveal\ninteresting features that are intimately related to the two-channel nature of\nthe orbital Feshbach resonance. In particular, we find that the life time of\nthe repulsive polaron is non-monotonic in the Zeeman-field detuning bewteen the\ntwo channels, and has a maximum on the BEC-side of the resonance. Further, by\nconsidering the stability of a mixture of the impurity and the majority atoms\nagainst phase separation, we show that the itin- erant ferromagnetism may exist\nnear the orbital Feshbach resonance at appropriate densities. Our results can\nbe readily probed experimentally, and have interesting implications for the\nobservation of itinerant ferromagnetism near an orbital Feshbach resonance."
    },
    {
        "anchor": "Ground-state densities of repulsive two-component Fermi gases: We investigate separations of trapped balanced two-component atomic Fermi\ngases with repulsive contact interaction. Candidates for ground-state densities\nare obtained from the imaginary-time evolution of a nonlinear\npseudo-Schr\\\"odinger equation in three dimensions, rather than from the\ncumbersome variational equations. With the underlying hydrodynamical approach,\ngradient corrections to the Thomas-Fermi approximation are conveniently\nincluded and are shown to be vital for reliable density profiles. We provide\ncritical repulsion strengths that mark the onset of phase transitions in a\nharmonic trap. We present transitions from identical density profiles of the\ntwo fermion species towards isotropic and anisotropic separations for various\nconfinements, including harmonic and double-well-type traps. Our proposed\nmethod is suited for arbitrary trap geometries and can be straightforwardly\nextended to study dynamics in the light of ongoing experiments on degenerate\nFermi gases.",
        "positive": "Plane and Stripe Wave Phases of a Spin-Orbit Coupled Bose-Einstein\n  Condensate in an Optical Lattice with a Zeeman Field: A weakly interacting, spin-orbit coupled, ultracold, dilute Bose gas on a\ntwo-dimensional square lattice with an external Zeeman field is studied. We\nexplore the plane and stripe wave phases of the system involving nonzero\ncondensate momenta, which occur when the Zeeman field is below a critical\nvalue. Their excitation spectra are found using Bogoliubov theory and by two\ndifferent routes. The validity of each method to obtain the excitation spectrum\nis discussed, and it is found that projection on the lowest single-particle\nband is an excellent approximation in the plane wave phase, while it is a poor\napproximation in the stripe wave phase. While the plane wave phase has a phonon\nminimum at its single condensate momentum, revealing a nonzero sound velocity\nof the excitations, the stripe wave phase has quadratic minima at its two\ncondensate momenta showing zero sound velocity of the excitations. We discuss\nhow the presence of more than one condensate momentum is essential for these\ndifferences between the two phases. Additionally, it is emphasized that the\nzero sound velocity in the stripe wave phase is a lattice effect, since\ncontinuum studies of the same phase have shown nonzero sound velocity."
    },
    {
        "anchor": "Spectral properties and observables in ultracold Fermi gases: We calculate non-perturbative self-consistent fermionic and bosonic spectral\nfunctions of ultra-cold Fermi gases with the spectral functional approach. This\napproach allows for a direct real-time computation of non-perturbative\ncorrelation functions, and in the present work we use spectral Dyson-Schwinger\nequations. We focus on the normal phase of the spin-balanced Fermi gas and\nprovide numerical results for the full fermionic and bosonic spectral\nfunctions. The spectral functions are then used for the determination of the\nequation of state, the Tan contact and ejection rf spectra at unitarity. These\nresults are compared to experimental data, the self-consistent T-matrix\napproach and lattice results. Our approach offers a wide range of applications,\nincluding the ab initio calculation of transport and spectral properties of the\nsuperfluid phase in the BCS-BEC crossover.",
        "positive": "Floquet FFLO superfluids and Majorana fermions in a shaken fermionic\n  optical lattice: Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superfluids, Cooper pairings with\nfinite momentum, and Majorana fermions (MFs), quasiparticles with non-Abelian\nexchange statistics, are two topics under intensive investigation in the past\nseveral decades, but unambiguous experimental evidences for them have not been\nfound yet in any physical system. Here we show that the recent experimentally\nrealized cold atom shaken optical lattice provides a new pathway to realize\nFFLO superfluids and MFs. By tuning shaken lattice parameters (shaking\nfrequency and amplitude), various coupling between the s- and p-orbitals of the\nlattice (denoted as the pseudo-spins) can be generated. We show that the\ncombination of the inverted s- and p-band dispersions, the engineered\npseudo-spin coupling, and the attractive on-site atom interaction, naturally\nallows the observation of FFLO superfluids as well as MFs in different\nparameter regions. While without interaction the system is a topological\ninsulator (TI) with edge states, the MFs in the superfluid may be found to be\nin the conduction or valence band, distinguished from previous TI-based schemes\nthat utilize edge states inside the band gap."
    },
    {
        "anchor": "Topological phases with long-range interactions: Topological phases of matter are primarily studied in systems with\nshort-range interactions. In nature, however, non-relativistic quantum systems\noften exhibit long-range interactions. Under what conditions topological phases\nsurvive such interactions, and how they are modified when they do, is largely\nunknown. By studying the symmetry-protected topological phase of an\nantiferromagnetic spin-1 chain with $1/r^{\\alpha}$ interactions, we show that\ntwo very different outcomes are possible, depending on whether or not the\ninteractions are frustrated. While non-frustrated long-range interactions can\ndestroy the topological phase for $\\alpha\\lesssim3$, the topological phase\nsurvives frustrated interactions for all $\\alpha>0$. Our conclusions are based\non strikingly consistent results from large-scale matrix-product-state\nsimulations and effective-field-theory calculations, and we expect them to hold\nfor more general interacting spin systems. The models we study can be naturally\nrealized in trapped-ion quantum simulators, opening the prospect for\nexperimental investigation of the issues confronted here.",
        "positive": "Superfluid phases of fermions with hybridized $s$ and $p$ orbitals: We explore the superfluid phases of a two-component Fermi mixture with\nhybridized orbitals in optical lattices. We show that there exists a general\nmapping of this system to the Lieb lattice. By using simple multiband models\nwith hopping between $s$ and $p$-orbital states, we show that superfluid order\nparameters can have a $\\pi$-phase difference between lattice sites, which is\ndistinct from the case with hopping between $s$-orbitals. If the population\nimbalance between the two spin species is tuned, the superfluid phase may\nevolve through various phases due to the interplay between hopping,\ninteractions and imbalance. We show that the rich behavior is observable in\nexperimentally realizable systems."
    },
    {
        "anchor": "A continuum of compass spin models on the honeycomb lattice: Quantum spin models with spatially dependent interactions, known as compass\nmodels, play an important role in the study of frustrated quantum magnetism.\nOne example is the Kitaev model on the honeycomb lattice with spin-liquid\nground states and anyonic excitations. Another example is the geometrically\nfrustrated quantum $120^\\circ$ model on the same lattice whose ground state has\nnot been unambiguously established. To generalize the Kitaev model beyond the\nexactly solvable limit and connect it with other compass models, we propose a\nnew model, dubbed \"the tripod model\", which contains a continuum of\ncompass-type models. It smoothly interpolates the Ising model, the Kitaev\nmodel, and the quantum $120^\\circ$ model by tuning a single parameter\n$\\theta'$, the angle between the three legs of a tripod in the spin space.\nHence it not only unifies three paradigmatic spin models, but also enables the\nstudy of their quantum phase transitions. We obtain the phase diagram of the\ntripod model numerically by tensor networks in the thermodynamic limit. We show\nthat the ground state of the quantum $120^\\circ$ model has long-range dimer\norder. Moreover, we find an extended spin-disordered (spin-liquid) phase\nbetween the dimer phase and an antiferromagnetic phase. The unification and\nsolution of a continuum of frustrated spin models as outline here may be useful\nto exploring new domains of other quantum spin or orbital models.",
        "positive": "High Order Momentum Modes by Resonant Superradiant Scattering: The spatial and time evolutions of superradiant scattering are studied\ntheoretically for a weak pump beam with different frequency components\ntraveling along the long axis of an elongated Bose-Einstein condensate.\nResulting from the analysis for mode competition between the different resonant\nchannels and the local depletion of the spatial distribution in the\nsuperradiant Rayleigh scattering, a new method of getting a large number of\nhigh-order forward modes by resonant frequency components of the pump beam is\nprovided, which is beneficial to a lager momentum transfer in atom manipulation\nfor the atom interferometry and atomic optics."
    },
    {
        "anchor": "The mixing-demixing phase diagram of ultracold heteronuclear mixtures in\n  a ring trimer: We derive the complete mixing-demixing phase-diagram relevant to a bosonic\nbinary mixture confined in a ring trimer and modeled within the Bose-Hubbard\npicture. The mixing properties of the two quantum fluids, which are shown to be\nstrongly affected by the fragmented character of the confining potential, are\nevaluated by means of a specific indicator imported from Statistical\nThermodynamics and are shown to depend only on two effective parameters\nincorporating the asymmetry between the heteronuclear species. To closely match\nrealistic experimental conditions, our study is extended also beyond the\npointlike approximation of potential wells by describing the systems in terms\nof two coupled Gross-Pitaevskii equations. The resulting mean-field analysis\nconfirms the rich scenario of mixing-demixing transitions of the mixture and\nalso constitutes an effective springboard towards a viable experimental\nrealization. We additionally propose an experimental realization based on a\nrealistic optical-tweezers system and on mixtures of bosonic $^{23}\\mathrm{Na}$\nand $^{39}\\mathrm{K}$, thanks to the large tunability of their intra- and\ninter-species scattering lengths.",
        "positive": "Topological Phases of Fermionic Ladders with Periodic Magnetic Fields: In recent experiments bosonic [Atala et al., Nat. Phys. 10, 588 (2014), B. K.\nStuhl et al., Science 349, 1514 (2015)] as well as fermionic ladders [M.\nMancini et al., Science 349, 1510 (2015)] with a uniform flux were studied and\ndifferent interesting many-body states were observed. Motivated by these\nexperiments, we extend the uniform synthetic magnetic field to a periodic case\nand show that a commensurate synthetic magnetic field offers an alternative\nscheme to realize topological phases in many-body systems of ultra-cold Fermi\ngases in ladder-like optical lattices. Using the exact diagonalization, we\nnumerically determine the topological band structure, edge states, non-zero\nChern numbers, Hofstadter-like-butterfly spectrum, and a complete phase diagram\nof non-interacting fermionic ladders."
    },
    {
        "anchor": "Formation and detection of a chiral orbital Bose liquid in an optical\n  lattice: Recent experiments on $p$-orbital atomic bosons have suggested the emergence\nof a spectacular ultracold superfluid with staggered orbital currents in\noptical lattices. This raises fundamental questions like the effects of\ncollective thermal fluctuations, and how to directly observe such chiral order.\nHere, we show via Monte Carlo simulations that thermal fluctuations destroy\nthis superfluid in an unexpected two-step process, unveiling an intermediate\nnormal phase with spontaneously broken time-reversal symmetry, dubbed \"chiral\nBose liquid\". For integer fillings ($n\\geq 2$) in the chiral Mott regime,\nthermal fluctuations are captured by an effective orbital Ising model, and\nOnsager's powerful exact solution is adopted to determine the transition from\nthis intermediate liquid to the para-orbital normal phase at high temperature.\nA suitable lattice quench is designed to convert the staggered angular\nmomentum, previously thought by experts difficult to directly probe, into\ncoherent orbital oscillations, providing a smoking-gun signature of chiral\norder.",
        "positive": "Mesoscopic phases of dipolar ensembles with polar molecules and Rydberg\n  atoms: We discuss the realization of mesoscopic phases of dipolar gases relevant to\ncurrent experiments with cold polar molecules and Rydberg atoms confined to two\ndimensions. We predict the existence of superfluid clusters, mesoscopic\nsupersolids, and crystals for a small number of trapped particles, with no\ncounterpart in the homogeneous situation. For certain strengths of the\ndipole-dipole interactions, the stabilization of purely {\\it non-classical\ncrystals} by quantum fluctuations is possible. We propose a magnification\nscheme to detect the spatial structure of these crystalline phases."
    },
    {
        "anchor": "Dissipative phase transitions in the fully-connected Ising model with\n  $p$-spin interaction: In this paper, we study the driven-dissipative p-spin models for $p\\geq 2$.\nIn thermodynamics limit, the equation of motion is derived by using a\nsemiclassical approach. The long-time asymptotic states are obtained\nanalytically, which exhibit multi-stability in some regions of the parameter\nspace. The steady state is unique as the number of spins is finite. But the\nthermodynamic limit of the steady-state magnetization displays nonanalytic\nbehavior somewhere inside the semiclassical multi-stable region. We find both\nthe first-order and continuous dissipative phase transitions. As the number of\nspins increases, both the Liouvillian gap and magnetization variance vanish\naccording to a power law at the continuous transition. At the first-order\ntransition, the gap vanishes exponentially accompanied by a jump of\nmagnetization in thermodynamic limit. The properties of transitions depend on\nthe symmetry and semiclassical multistability, being qualitatively different\namong $p=2$, odd $p$ ($p\\geq 3$) and even $p$ ($p\\geq 4$).",
        "positive": "Stability and Excitations of Spontaneous Vortices in Homogeneous\n  Polariton Condensates: We study the dynamics of spontaneously formed vortices in homogeneous\nmicrocavity-polariton condensates (MPCs). We find that vortices are stable and\nappear spontaneously without stirring or rotating MPCs. The dip of the vortex\ncore contains some background of reservoir polaritons and the visibility of a\nvortex is increasing with respect to the pump strength. The vortex radius is\ninversely proportional to the square root of the condensate density. Excitation\nenergies of vortices at high and low pump powers are finite and zero,\nrespectively. Vortices at low pump powers exhibit the short lifetime."
    },
    {
        "anchor": "Imaging the decay of quantized vortex rings to decipher quantum\n  dissipation: Like many quantum fluids, superfluid helium-4 (He II) can be considered as a\nmixture of two miscible fluid components: an inviscid superfluid and a viscous\nnormal fluid consisting of thermal quasiparticles [1]. A mutual friction\nbetween the two fluids can emerge due to quasiparticles scattering off\nquantized vortex lines in the superfluid [2]. This quantum dissipation\nmechanism is the key for understanding various fascinating behaviors of the\ntwo-fluid system [3,4]. However, due to the lack of experimental data for\nguidance, modeling the mutual friction between individual vortices and the\nnormal fluid remains an unsettled topic despite decades of research [5-10].\nHere we report an experiment where we visualize the motion of quantized vortex\nrings in He II by decorating them with solidified deuterium tracer particles.\nBy examining how the rings spontaneously shrink and accelerate, we provide\nunequivocal evidences showing that only a recent theory [9] which accounts for\nthe coupled motion of the two fluids with a self-consistent local friction can\nreproduce the observed ring dynamics. Our work eliminates long-standing\nambiguities in our theoretical description of the vortex dynamics in He II,\nwhich will have a far-reaching impact since similar mutual friction concept has\nbeen adopted for a wide variety of quantum two-fluid systems, including atomic\nBose-Einstein condensates (BECs) [11,12], superfluid neutron stars [13-15], and\ngravity-mapped holographic superfluid [16,17].",
        "positive": "Dynamics of Macroscopic Tunneling in Elongated BEC: We investigate macroscopic tunneling from an elongated quasi 1-d trap,\nforming a 'cigar shaped' BEC. Using recently developed formalism we get the\nleading analytical approximation for the right hand side of the potential wall,\ni.e. outside the trap, and a formalism based on Wigner functions, for the left\nside of the potential wall, i.e. inside the BEC. We then present accomplished\nresults of numerical calculations, which show a 'blip' in the particle density\ntraveling with an asymptotic shock velocity, as resulted from previous works on\na dot-like trap, but with significant differences from the latter. Inside the\nBEC a pattern of a traveling dispersive shock wave is revealed. In the\nattractive case, we find trains of bright solitons frozen near the boundary."
    },
    {
        "anchor": "Quantum Hall phase diagram of two-component Bose gases: Intercomponent\n  entanglement and pseudopotentials: We study the ground-state phase diagram of two-dimensional two-component (or\npseudospin-1/2) Bose gases in a high synthetic magnetic field in the space of\nthe total filling factor and the ratio of the intercomponent coupling\n$g_{\\uparrow\\downarrow}$ to the intracomponent one $g>0$. Using exact\ndiagonalization, we find that when the intercomponent coupling is attractive\n($g_{\\uparrow\\downarrow}<0$), the product states of a pair of nearly\nuncorrelated quantum Hall states are remarkably robust and persist even when\n$|g_{\\uparrow\\downarrow}|$ is close to $g$. This contrasts with the case of an\nintercomponent repulsion, where a variety of spin-singlet quantum Hall states\nwith high intercomponent entanglement emerge for $g_{\\uparrow\\downarrow}\\approx\ng$. We interpret this marked dependence on the sign of $g_{\\uparrow\\downarrow}$\nin light of pseudopotentials on a sphere, and also explain recent numerical\nresults in two-component Bose gases in mutually antiparallel magnetic fields\nwhere a qualitatively opposite dependence on the sign of\n$g_{\\uparrow\\downarrow}$ is found. Our results thus unveil an intriguing\nconnection between multicomponent quantum Hall systems and quantum spin Hall\nsystems in minimal setups.",
        "positive": "Interaction-induced transparency for strong-coupling polaritons: The propagation of light in strongly coupled atomic media takes place through\nthe formation of polaritons - hybrid quasi-particles resulting from a\nsuperposition of an atomic and a photonic excitation. Here we consider the\npropagation under the condition of electromagnetically-induced transparency and\nshow that a novel many-body phenomenon can appear due to strong, dissipative\ninteractions between the polaritons. Upon increasing the photon-pump strength,\nwe find a first-order transition between an opaque phase with strongly\nbroadened polaritons and a transparent phase where a long-lived polariton\nbranch with highly tunable occupation emerges. Across this non-equilibrium\nphase transition, the transparency window is reconstructed via nonlinear\ninterference effects induced by the dissipative polariton interactions. Our\npredictions are based on a systematic diagrammatic expansion of the\nnon-equilibrium Dyson equations which is quantitatively valid, even in the\nnon-perturbative regime of large single-atom cooperativities, provided the\npolariton interactions are sufficiently long ranged. Such a regime can be\nreached in photonic crystal waveguides thanks to the tunability of\ninteractions, allowing to observe the interaction-induced-transparency\ntransition even at low polariton densities."
    },
    {
        "anchor": "Spin-orbit coupled bosons in one dimension: emergent gauge field and\n  Lifshitz transition: In the presence of strong spin-independent interactions and spin-orbit\ncoupling, we show that the spinor Bose liquid confined to one spatial dimension\nundergoes an interaction- or density-tuned quantum phase transition similar to\none theoretically proposed for itinerant magnetic solid-state systems. The\norder parameter describes broken $Z_2$ inversion symmetry, with the ordered\nphase accompanied by non-vanishing momentum which is generated by fluctuations\nof an emergent dynamical gauge field at the phase transition. This quantum\nphase transition has dynamical critical exponent $z \\simeq 2$, typical of a\nLifshitz transition, but is described by a nontrivial interacting fixed point.\nFrom direct numerical simulation of the microscopic model, we extract\npreviously unknown critical exponents for this fixed point. Our model describes\na realistic situation of 1D ultracold atoms with Raman-induced spin-orbit\ncoupling, establishing this system as a platform for studying exotic critical\nbehavior of the Hertz-Millis type.",
        "positive": "Spatial structure of the pair wavefunction and the density correlation\n  functions at the BEC-BCS crossover: By an exact numerical calculation of the BCS pair wavefunction and the\ndensity correlation functions both between atoms in the same and in different\nspin states, we extract the spatial large distance behavior of the respective\nfunctions. After different initial transients, those distributions show an\nalgebraic dependence accompanied with their own exponential decay and a well\ndefined periodic oscillatory behavior. While in general, in the BCS side there\nare long-range correlations and in the BEC region the behavior is dominated by\ntight pairs formation, each distribution shows its own overall behavior. We\nderive analytic expressions for the mean pair size and the correlation lengths\nof the same and different density correlation functions. The whole analysis\nyields a quite complete description of the spatial structure of the superfluid\nalong the crossover."
    },
    {
        "anchor": "Quantum Bubbles in Microgravity: The recent developments of microgravity experiments with ultracold atoms have\nproduced a relevant boost in the study of shell-shaped ellipsoidal\nBose-Einstein condensates. For realistic bubble-trap parameters, here we\ncalculate the critical temperature of Bose-Einstein condensation, which, if\ncompared to the one of the bare harmonic trap with the same frequencies, shows\na strong reduction. We simulate the zero-temperature density distribution with\nthe Gross-Pitaevskii equation, and we study the free expansion of the hollow\ncondensate. While part of the atoms expands in the outward direction, the\ncondensate self-interferes inside the bubble trap, filling the hole in\nexperimentally observable times. For a mesoscopic number of particles in a\nstrongly interacting regime, for which more refined approaches are needed, we\nemploy quantum Monte Carlo simulations, proving that the nontrivial topology of\na thin shell allows superfluidity. Our work constitutes a reliable benchmark\nfor the forthcoming scientific investigations with bubble traps.",
        "positive": "Measuring quantized circular dichroism in ultracold topological matter: The topology of two-dimensional materials traditionally manifests itself\nthrough the quantization of the Hall conductance, which is revealed in\ntransport measurements. Recently, it was predicted that topology can also give\nrise to a quantized spectroscopic response upon subjecting a Chern insulator to\na circular drive: Comparing the frequency-integrated depletion rates associated\nwith drives of opposite orientations leads to a quantized response dictated by\nthe topological Chern number of the populated Bloch band. Here we\nexperimentally demonstrate this intriguing topological effect for the first\ntime, using ultracold fermionic atoms in topological Floquet bands. In\naddition, our depletion-rate measurements also provide a first experimental\nestimation of the Wannier-spread functional, a fundamental geometric property\nof Bloch bands. Our results establish topological spectroscopic responses as a\nversatile probe, which could be applied to access the geometry and topology of\nmany-body quantum systems, such as fractional Chern insulators."
    },
    {
        "anchor": "Phase transitions in dipolar gases in optical lattices: We investigate the phase diagrams of two-dimensional lattice dipole systems\nwith variable geometry. For bipartite square and triangular lattices with\ntunable vertical sublattice separation, we find rich phase diagrams featuring a\nsequence of easy-plane magnetically ordered phases separated by incommensurate\nspin-wave states.",
        "positive": "Potential and Feshbach $s$-wave resonances in coupled atomic collision\n  channels: We discuss $s$-wave scattering in an atomic binary collision with two coupled\nchannels, tunable by an external magnetic field, one channel open and the other\nclosed for the incident energies considered. The analysis is performed with a\nstylized model of square-well potentials. This simplification allows for a\npedagogically thorough discussion of the different scattering resonances that\nappear in coupled channels. One of the them, the potential resonances at\nvanishing energy, occur as a bound state of the coupled system emerges, in\nturned tuned at a very precise value of the external field. The other\nresonances, described by Feshbach theory, occur when the incident energy is\nnear a bound state of the closed channel, as if it were decoupled from the open\nchannel. These resonances exist for values of the external field above a\nparticular threshold value. Besides the potential intrinsic value of this study\nin a quantum mechanics course, as the analysis can be performed with minor\nnumerical calculations, it is also an aid for the understanding of current\nresearch advances in the exciting field of ultracold gases."
    },
    {
        "anchor": "Shock waves in strongly interacting Fermi gas from time-dependent\n  density functional calculations: Motivated by a recent experiment [Phys. Rev. Lett. 106, 150401 (2011)] we\nsimulate the collision between two clouds of cold Fermi gas at unitarity\nconditions by using an extended Thomas-Fermi density functional. At variance\nwith the current interpretation of the experiments, where the role of viscosity\nis emphasized, we find that a quantitative agreement with the experimental\nobservation of the dynamics of the cloud collisions is obtained within our\nsuperfluid effective hydrodynamics approach, where density variations during\nthe collision are controlled by a purely dispersive quantum gradient term. We\nalso suggest different initial conditions where dispersive density ripples can\nbe detected with the available experimental spatial resolution.",
        "positive": "Wigner Crystallization of Rotating Dipolar Fermions in the Fractional\n  Quantum Hall Regime: We show the possible existence of the Wigner crystal (WC) in the Fractional\nQuantum Hall (FQH) regime. We find that the Landau-level mixing (LLM) will\nlower the energy of the WC significantly in the high-density regime. The WC is\nlower in energy than the FQH liquid in the high-density regime. We conclude\nthat the crystal phase is expected at high density for rotating dipolar gases,\nwhich is consistent with non-rotating dipolar gases, but is inconsistent with\nthe low-density conclusion from Baranov et al. [Phys. Rev. Lett. 100, 200402\n(2008)], where the effect of LLM is ignored."
    },
    {
        "anchor": "Zero-Temperature Equation of State and Phase Diagram of Repulsive\n  Fermionic Mixtures: We compute the zero-temperature equation of state of a mixture of two\nfermionic atomic species with repulsive interspecies interactions using\nsecond-order perturbation theory. We vary the interaction strength, the\npopulation and the mass imbalance, and we analyze the competition between\ndifferent states: homogeneous, partially separated and fully separated. The\ncanonical phase diagrams are determined for various mass ratios, including the\nexperimentally relevant case of the 6Li-40K mixture. We find substantial\ndifferences with respect to the equal-mass case: phase separation occurs at\nweaker interaction strength, and the partially-separated state can be stable\neven in the limit of a large majority of heavy atoms. We highlight the effects\ndue to correlations by making comparison with previous mean-field results.",
        "positive": "Dissipative Dicke Model with Collective Atomic Decay: Bistability,\n  Noise-Driven Activation and Non-Thermal First Order Superradiance Transition: The Dicke model describes the coherent interaction of a laser-driven ensemble\nof two level atoms with a quantized light field. It is realized within cavity\nQED experiments, which in addition to the coherent Dicke dynamics feature\ndissipation due to e.g. atomic spontaneous emission and cavity photon loss.\nSpontaneous emission supports the uncorrelated decay of individual atomic\nexcitations as well as the enhanced, collective decay of an excitation that is\nshared by $N$ atoms and whose strength is determined by the cavity geometry. We\nderive a many-body master equation for the dissipative Dicke model including\nboth spontaneous emission channels and analyze its dynamics on the basis of\nHeisenberg-Langevin and stochastic Bloch equations. We find that the collective\nloss channel leads to a region of bistability between the empty and the\nsuperradiant state. Transitions between these states are driven by non-thermal,\nmarkovian noise. The interplay between dissipative and coherent elements leads\nto a genuine non-equilibrium dynamics in the bistable regime, which is\nexpressed via a non-conservative force and a multiplicative noise kernel\nappearing in the stochastic Bloch equations. We present a semiclassical\napproach, based on stochastic nonlinear optical Bloch equations, which for the\ninfinite-range Dicke Model become exact in the large-$N$-limit. The absence of\nan effective free energy functional, however, necessitates to include\nfluctuation corrections with $\\mathcal{O}(1/N)$ for finite $N<\\infty$ to locate\nthe non-thermal first-order phase transition between the superradiant and the\nempty cavity."
    },
    {
        "anchor": "Scrambled Mean Field Approach to the Quantum Dynamics of Degenerate Bose\n  Gases: We present a novel approach to modeling dynamics of trapped, degenerate,\nweakly interacting Bose gases beyond the mean field limit. We transform a\nmany-body problem to the interaction representation with respect to a suitably\nchosen part of the Hamiltonian and only then apply a multimode coherent-state\nansatz. The obtained equations are almost as simple as the Gross--Pitaevskii\nequation, but our approach captures essential features of the quantum dynamics\nsuch as the collapse of coherence.",
        "positive": "Van der Waals universality in homonuclear atom-dimer elastic collisions: The universal aspects of atom-dimer elastic collisions are investigated\nwithin the framework of Faddeev equations. The two-body interactions between\nthe neutral atoms are approximated by the separable potential approach. Our\nanalysis considers a pure van der Waals potential tail as well as soft-core van\nder Waals interactions permitting us in this manner to address the universally\ngeneral features of atom-dimer resonant spectra. In particular, we show that\nthe atom-dimer resonances are solely associated with the {\\it excited} Efimov\nstates. Furthermore, the positions of the corresponding resonances for a\nsoft-core potentials with more than 5 bound states are in good agreement with\nthe corresponding results from an infinitely deep pure van der Waals tail\npotential."
    },
    {
        "anchor": "Dark-bright solitons in Bose-Einstein condensates at finite temperatures: We study the dynamics of dark-bright solitons in binary mixtures of Bose\ngases at finite temperature using a system of two coupled dissipative\nGross-Pitaevskii equations. We develop a perturbation theory for the\ntwo-component system to derive an equation of motion for the soliton centers\nand identify different temperature-dependent damping regimes. We show that the\neffect of the bright (\"filling\") soliton component is to partially stabilize\n\"bare\" dark solitons against temperature-induced dissipation, thus providing\nlonger lifetimes. We also study analytically thermal effects on dark-bright\nsoliton \"molecules\" (i.e., two in- and out-of-phase dark-bright solitons),\nshowing that they undergo expanding oscillations while interacting. Our\nanalytical findings are in good agreement with results obtained via a\nBogoliubov-de Gennes analysis and direct numerical simulations.",
        "positive": "Realization of a fractional quantum Hall state with ultracold atoms: Strongly interacting topological matter exhibits fundamentally new phenomena\nwith potential applications in quantum information technology. Emblematic\ninstances are fractional quantum Hall states, where the interplay of magnetic\nfields and strong interactions gives rise to fractionally charged\nquasi-particles, long-ranged entanglement, and anyonic exchange statistics.\nProgress in engineering synthetic magnetic fields has raised the hope to create\nthese exotic states in controlled quantum systems. However, except for a recent\nLaughlin state of light, preparing fractional quantum Hall states in engineered\nsystems remains elusive. Here, we realize a fractional quantum Hall (FQH) state\nwith ultracold atoms in an optical lattice. The state is a lattice version of a\nbosonic $\\nu=1/2$ Laughlin state with two particles on sixteen sites. This\nminimal system already captures many hallmark features of Laughlin-type FQH\nstates: we observe a suppression of two-body interactions, we find a\ndistinctive vortex structure in the density correlations, and we measure a\nfractional Hall conductivity of $\\sigma_\\text{H}/\\sigma_0= 0.6(2)$ via the bulk\nresponse to a magnetic perturbation. Furthermore, by tuning the magnetic field\nwe map out the transition point between the normal and the FQH regime through a\nspectroscopic probe of the many-body gap. Our work provides a starting point\nfor exploring highly entangled topological matter with ultracold atoms."
    },
    {
        "anchor": "Entangled phonons in atomic Bose-Einstein condensates: We theoretically study the entanglement between phonons spontaneously\ngenerated in atomic Bose-Einstein condensates by analog Hawking and dynamical\nCasimir processes. The quantum evolution of the system is numerically modeled\nby a truncated Wigner method based on a full microscopic description of the\ncondensate and state non-separability is assessed by applying a generalized\nPeres-Horodecki criterion. The peculiar distribution of entanglement is\ndescribed in both real and momentum spaces and its robustness against\nincreasing initial temperature is investigated. Viable strategies to\nexperimentally detect the predicted phonon entanglement are briefly discussed.",
        "positive": "Regularization of fluctuations near the sonic horizon due to the quantum\n  potential and its influence on the Hawking radiation: We consider dynamics of fluctuations in transonically accelerating\nBose-Einstein condensates and luminous liquids (coherent light propagating in a\nKerr nonlinear medium) using the hydrodynamic approach. It is known that\nneglecting the quantum potential (QP) leads to a singular behavior of quantum\nand classical fluctuations in the vicinity of the Mach (sonic) horizon, which\nin turn gives rise to the Hawking radiation. The neglect of QP is well founded\nat not too small distances $|x| \\gg l_h$ from the horizon, where $l_h$ is the\nhealing length. Taking the QP into account we show that a second characteristic\nlength $l_r > l_h$ exists, such that the linear fluctuation modes become\nregularized for $|x| \\ll l_r$. At $|x| \\gg l_r$ the modes keep their singular\nbehavior, which however is influenced by the QP. As a result we find a\ndeviation of the high frequency tail of the spectrum of Hawking radiation from\nPlanck's black body radiation distribution. Similar results hold for the wave\npropagation in Kerr nonlinear media where the length $l_h$ and $l_r$ exist due\nto the nonlinearity."
    },
    {
        "anchor": "Spin-orbit-coupled topological Fulde-Ferrell states of fermions in a\n  harmonic trap: Motivated by recent experimental breakthroughs in generating spin-orbit\ncoupling in ultracold Fermi gases using Raman laser beams, we present a\nsystematic study of spin-orbit-coupled Fermi gases confined in a\nquasi-one-dimensional trap in the presence of an in-plane Zeeman field (which\ncan be realized using a finite two-photon Raman detuning). We find that a\ntopological Fulde-Ferrell state will emerge, featuring finite-momentum Cooper\npairing and zero-energy Majorana excitations localized near the edge of the\ntrap based on the self-consistent Bogoliubov-de Genes (BdG) equations. We find\nanalytically the wavefunctions of the Majorana modes. Finally using the\ntime-dependent BdG we show how the finite-momentum pairing field manifests\nitself in the expansion dynamics of the atomic cloud.",
        "positive": "Damping of elementary excitations in one-dimensional dipolar Bose gases: In the presence of dipolar interactions the excitation spectrum of a Bose gas\ncan acquire a local minimum. The corresponding quasiparticles are known as\nrotons. They are gaped and do not decay at zero temperature. Here we study the\ndecay of rotons in one-dimensional Bose gases at low temperatures. It\npredominantly occurs due to the backscattering of thermal phonons on rotons.\nThe resulting rate scales with the third power of temperature and is inversely\nproportional to the sixth power of the roton gap near the solidification phase\ntransition. The hydrodynamic approach used here enables us to find the decay\nrate for quasiparticles at practically any momenta, with minimal assumptions on\nthe exact form of the interparticle interactions. Our results are an essential\nprerequisite for the description of all the dissipative phenomena in dipolar\ngases and have direct experimental relevance."
    },
    {
        "anchor": "Atomtronics with a spin: statistics of spin transport and\n  non-equilibrium orthogonality catastrophe in cold quantum gases: We propose to investigate the full counting statistics of nonequilibrium spin\ntransport with an ultracold atomic quantum gas. The setup makes use of the spin\ncontrol available in atomic systems to generate spin transport induced by an\nimpurity atom immersed in a spin-imbalanced two-component Fermi gas. In\ncontrast to solid-state realizations, in ultracold atoms spin relaxation and\nthe decoherence from external sources is largely suppressed. As a consequence,\nonce the spin current is turned off by manipulating the internal spin degrees\nof freedom of the Fermi system, the nonequilibrium spin population remains\nconstant. Thus one can directly count the number of spins in each reservoir to\ninvestigate the full counting statistics of spin flips, which is notoriously\nchallenging in solid state devices. Moreover, using Ramsey interferometry, the\ndynamical impurity response can be measured. Since the impurity interacts with\na many-body environment that is out of equilibrium, our setup provides a way to\nrealize the non-equilibrium orthogonality catastrophe. Here, even for spin\nreservoirs initially prepared in a zero-temperature state, the Ramsey response\nexhibits an exponential decay, which is in contrast to the conventional\npower-law decay of Anderson's orthogonality catastrophe. By mapping our system\nto a multi-step Fermi sea, we are able to derive analytical expressions for the\nimpurity response at late times. This allows us to reveal an intimate\nconnection of the decay rate of the Ramsey contrast and the full counting\nstatistics of spin flips.",
        "positive": "Emergence of a Bose polaron in a small ring threaded by the\n  Aharonov-Bohm flux: The model of a ring threaded by the Aharonov-Bohm flux underlies our\nunderstanding of a coupling between gauge potentials and matter. The typical\nformulation of the model is based upon a single particle picture, and should be\nextended when interactions with other particles become relevant. Here, we\nillustrate such an extension for a particle in an Aharonov-Bohm ring subject to\ninteractions with a weakly interacting Bose gas. We show that the ground state\nof the system can be described using the Bose polaron concept -- a particle\ndressed by interactions with a bosonic environment. We connect the energy\nspectrum to the effective mass of the polaron, and demonstrate how to change\ncurrents in the system by tuning boson-particle interactions. Our results\nsuggest the Aharonov-Bohm ring as a platform for studying coherence and few- to\nmany-body crossover of quasi-particles that arise from an impurity immersed in\na medium."
    },
    {
        "anchor": "Toward an automated-algebra framework for high orders in the virial\n  expansion of quantum matter: The virial expansion provides a non-perturbative view into the thermodynamics\nof quantum many-body systems in dilute regimes. While powerful, the expansion\nis challenging as calculating its coefficients at each order $n$ requires\nanalyzing (if not solving) the quantum $n$-body problem. In this work, we\npresent a comprehensive review of automated algebra methods, which we developed\nto calculate high-order virial coefficients. The methods are computational but\nnon-stochastic, thus avoiding statistical effects; they are also for the most\npart analytic, not numerical, and amenable to massively parallel computer\narchitectures. We show formalism and results for coefficients characterizing\nthe thermodynamics (pressure, density, energy, static susceptibilities) of\nhomogeneous and harmonically trapped systems, and explain how to generalize\nthem to other observables such as the momentum distribution, Tan's contact, and\nthe structure factor.",
        "positive": "Propagation of electromagnetic waves in Bose-Einstein condensate of\n  atoms with dipole moments: We study the propagation of electromagnetic waves in the Bose-Einstein\ncondensate of atoms with both intrinsic dipole moments and those induced by the\nelectric field. The modified Gross--Pitaevskii equation is used, which takes\ninto account relaxation and interaction with the electromagnetic field. Two\ncases are considered: 1) when the dispersion curves of the electromagnetic wave\nand of the condensate excitations do not intercross and 2) when the condensate\nexcitations' spectrum has a gap and the two dispersion curves do intercross. In\nthe second case the two branches hybridize. It is shown that propagation of\nsound waves can be accompanied by oscillation of the electromagnetic field. The\nimpact is studied of the dipole-dipole interaction on the character of\nelectromagnetic and acoustic waves' propagation in the Bose-Einstein\ncondensate."
    },
    {
        "anchor": "Clock shifts of optical transitions in ultracold atomic gases: We calculate the shift, due to interatomic interactions, of an optical\ntransition in an atomic Fermi gas trapped in an optical lattice, as in recent\nexperiments of Campbell {\\it et al.}, Science {\\bf 324}, 360 (2009). Using a\npseudospin formalism to describe the density matrix of the internal two states\nof the optical transition, we derive a Bloch equation which incorporates both\nthe spatial inhomogeneity of the probe laser field and the interatomic\ninteractions. Expressions are given for the frequency shift as a function of\nthe pulse duration, detuning of the probe laser, and the spatial dependence of\nthe electric field of the probe beam. In the low temperature semiclassical\nregime, we find that the magnitude of the shift is proportional to the\ntemperature.",
        "positive": "Characterization of density oscillations in confined and degenerate\n  Fermi gases: Friedel oscillations appear in density of Fermi gases due to Pauli exclusion\nprinciple and translational symmetry breaking nearby a defect or impurity. In\nconfined Fermi gases, this symmetry breaking occurs also near to boundaries.\nHere, density oscillations of a degenerate and confined Fermi gas are\nconsidered and characterized. True nature of density oscillations are\nrepresented by analytical formulas for degenerate conditions. Analytical\ncharacterization is first done for completely degenerate case, then temperature\neffects are also incorporated with a finer approximation. Envelope functions\ndefining the upper and lower bounds of these oscillations are determined. It is\nshown that the errors of obtained expressions are negligible as long as the\nsystem is degenerate. Numbers, amplitudes, averages and spatial coordinates of\noscillations are also given by analytical expressions. The results may be\nhelpful to efficiently predict and easily calculate the oscillations in density\nand density-dependent properties of confined electrons at nanoscale."
    },
    {
        "anchor": "Engineered Nearest-Neighbour Interactions with Doubly Modulated Optical\n  Lattices: Optical lattice systems provide exceptional platforms for quantum simulation\nof many-body systems. We focus on the doubly modulated Bose-Hubbard model\ndriven by both time-dependent on-site energy and interaction, and predict the\nemergence of the nearest neighbour interaction and density-assisted tunnelling.\nBy specifically designing a bi-chromatic driving pattern for a one dimensional\nlattice, we demonstrate that the doubly modulated fields can be tuned to\nrealize desired quantum phases, e.g. the Mott insulator phase with selective\ndefects, and density wave phase.",
        "positive": "Topological Bogoliubov excitations in inversion-symmetric systems of\n  interacting bosons: On top of the mean-field analysis of a Bose-Einstein condensate, one\ntypically applies the Bogoliubov theory to analyze quantum fluctuations of the\nexcited modes. Therefore, one has to diagonalize the Bogoliubov Hamiltonian in\na symplectic manner. In our article we investigate the topology of these\nBogoliubov excitations in inversion-invariant systems of interacting bosons. We\nanalyze how the condensate influences the topology of the Bogoliubov\nexcitations. Analogously to the fermionic case, here we establish a symplectic\nextension of the polarization characterizing the topology of the Bogoliubov\nexcitations and link it to the eigenvalues of the inversion operator at the\ninversion-invariant momenta. We also demonstrate an instructive but\nexperimentally feasible example that this quantity is also related to edge\nstates in the excitation spectrum."
    },
    {
        "anchor": "Collisions of solitary waves in condensates beyond mean-field theory: Bright solitary waves in a Bose-Einstein condensate contain thousands of\nidentical atoms held together despite their only weakly attractive contact\ninteractions. They nonetheless behave like a compound object, staying whole in\ncollisions, with their collision properties strongly affected by inter-soliton\nquantum coherence. We show that separate solitary waves decohere due to phase\ndiffusion, dependent on their effective ambient temperature, after which their\ninitial mean-field relative phases are no longer well defined or relevant for\ncollisions. In this situation, collisions occur predominantly repulsively and\ncan no longer be described within mean field theory. When considering the\ntime-scales involved in recent solitary wave experiments where non-equilibrium\nphenomena play an important role, these features could explain the\npredominantly repulsive collision dynamics observed in most condensate soliton\ntrain experiments.",
        "positive": "Universal contact and collective excitations of a strongly interacting\n  Fermi gas: We study the relationship between Tan's contact parameter and the macroscopic\ndynamic properties of an ultracold trapped gas, such as the frequencies of the\ncollective oscillations and the propagation of sound in one-dimensional (1D)\nconfigurations. We find that the value of the contact, extracted from the most\nrecent low-temperature measurements of the equation of state near unitarity,\nreproduces with accuracy the experimental values of the collective frequencies\nof the radial breathing mode at the lowest temperatures. The available\nexperiment results for the 1D sound velocities near unitarity are also\ninvestigated."
    },
    {
        "anchor": "Propagation in media as a probe for topological properties: The central goal of this thesis is to develop methods to experimentally study\ntopological phases. We do so by applying the powerful toolbox of quantum\nsimulation techniques with cold atoms in optical lattices. To this day, a\ncomplete classification of topological phases remains elusive. In this context,\nexperimental studies are key, both for studying the interplay between topology\nand complex effects and for identifying new forms of topological order. It is\ntherefore crucial to find complementary means to measure topological properties\nin order to reach a fundamental understanding of topological phases. In one\ndimensional chiral systems, we suggest a new way to construct and identify\ntopologically protected bound states, which are the smoking gun of these\nmaterials. In two dimensional Hofstadter strips (i.e: systems which are very\nshort along one dimension), we suggest a new way to measure the topological\ninvariant directly from the atomic dynamics.",
        "positive": "Bose-Einstein Condensation of 84-Sr: We report Bose-Einstein condensation of 84-Sr in an optical dipole trap.\nEfficient laser cooling on the narrow intercombination line and an ideal s-wave\nscattering length allow creation of large condensates (N0 ~ 3x10^5) even though\nthe natural abundance of this isotope is only 0.6%. Condensation is heralded by\nthe emergence of a low-velocity component in time-of-flight images."
    },
    {
        "anchor": "Superfluid Stiffness of a Driven Dissipative Condensate with Disorder: Observations of macroscopic quantum coherence in driven systems, e.g.\npolariton condensates, have strongly stimulated experimental as well as\ntheoretical efforts during the last decade. We address the question of whether\na driven quantum condensate is a superfluid, allowing for the effects of\ndisorder and its non-equilibrium nature. We predict that for spatial dimensions\nd<4 the superfluid stiffness vanishes once the condensate exceeds a critical\nsize, and treat in detail the case d=2. Thus a non-equilibrium condensate is\nnot a superfluid in the thermodynamic limit, even for weak disorder, although\nsuperfluid behavior would persist in small systems.",
        "positive": "Theory of vibronic assistance in the nonequilibrium condensation of\n  exciton polaritons in optically--pumped organic single crystal microcavities: We present a reaction/diffusion model for the formation of a lower polariton\ncondensate in a micro cavity containing an organic semiconducting molecular\ncrystalline film. Our model--based upon an anthracene film sandwiched between\ntwo reflecting dielectric mirrors--consists of three coupled fields\ncorresponding to a gas of excitons created by an external driving pulse, a\nreservoir of vibron states formed by the coupling between a ground-state\nvibrational model and a cavity photon, and a lower polariton condensate. We\nshow that at finite temperature, the presence of the vibron reservoir can\naugment the exciton population such that a lower critical pumping threshold is\nrequired to achieve condensation."
    },
    {
        "anchor": "Bound states of Dipolar Bosons in One-dimensional Systems: We consider one-dimensional tubes containing bosonic polar molecules. The\nlong-range dipole-dipole interactions act both within a single tube and between\ndifferent tubes. We consider arbitrary values of the externally aligned dipole\nmoments with respect to the symmetry axis of the tubes. The few-body structures\nin this geometry are determined as function of polarization angles and dipole\nstrength by using both essentially exact stochastic variational methods and the\nharmonic approximation. The main focus is on the three, four, and five-body\nproblems in two or more tubes. Our results indicate that in the weakly-coupled\nlimit the inter-tube interaction is similar to a zero-range term with a\nsuitable rescaled strength. This allows us to address the corresponding\nmany-body physics of the system by constructing a model where bound chains with\none molecule in each tube are the effective degrees of freedom. This model can\nbe mapped onto one-dimensional Hamiltonians for which exact solutions are\nknown.",
        "positive": "Out-of-equilibrium steady states of a locally driven lossy qubit array: We find a rich variety of counterintuitive features in the steady states of a\nqubit array coupled to a dissipative source and sink at two arbitrary sites,\nusing a master equation approach. We show there are setups where increasing the\npump and loss rates establishes long-range coherence. At sufficiently strong\ndissipation, the source or sink effectively generates correlation between its\nneighboring sites, leading to a striking density-wave order for a class of\n\"resonant\" geometries. This effect can be used more widely to engineer\nnonequilibrium phases. We show the steady states are generically distinct for\nhard-core bosons and free fermions, and differ significantly from the ones\nfound before in special cases. They are explained by generally applicable\nansatzes for the long-time dynamics at weak and strong dissipation. Our\nfindings are relevant for existing photonic setups."
    },
    {
        "anchor": "Weyl spin-orbit-coupling-induced interactions in uniform and trapped\n  atomic quantum fluids: We establish through analytical and numerical studies of thermodynamic\nquantities for noninteracting atomic gases that the isotropic three-dimensional\nspin-orbit coupling, the Weyl coupling, induces interaction which counters\n\"effective\" attraction (repulsion) of the exchange symmetry present in\nzero-coupling Bose (Fermi) gas. The exact analytical expressions for the grand\npotential and hence for several thermodynamic quantities have been obtained for\nthis purpose in both uniform and trapped cases. It is enunciated that many\ninteresting features of spin-orbit coupled systems revealed theoretically can\nbe understood in terms of coupling-induced modifications in statistical\ninterparticle potential. The temperature-dependence of the chemical potential,\nspecific heat and isothermal compressibility for a uniform Bose gas is found to\nhave signature of the incipient Bose-Einstein condensation in very weak\ncoupling regime although the system does not really go in the Bose-condensed\nphase. The transition temperature in harmonically trapped case decreases with\nincrease of coupling strength consistent with the weakening of the statistical\nattractive interaction. Anomalous behavior of some thermodynamic quantities,\npartly akin to that in dimensions less than two, appears for uniform fermions\nas soon as the Fermi level goes down the Dirac point on increasing the coupling\nstrength. It is suggested that the fluctuation-dissipation theorem can be\nutilized to verify anomalous behaviors from studies of long-wavelength\nfluctuations in bunching and antibunching effects.",
        "positive": "Self-trapping dynamics in a 2D optical lattice: We describe theoretical models for the recent experimental observation of\nMacroscopic Quantum Self-Trapping (MQST) in the transverse dynamics of an\nultracold bosonic gas in a 2D lattice. The pure mean-field model based on the\nsolution of coupled nonlinear equations fails to reproduce the experimental\nobservations. It greatly overestimates the initial expansion rates at short\ntimes and predicts a slower expansion rate of the cloud at longer times. It\nalso predicts the formation of a hole surrounded by a steep square fort-like\nbarrier which was not observed in the experiment. An improved theoretical\ndescription based on a simplified Truncated Wigner Approximation (TWA), which\nadds phase and number fluctuations in the initial conditions, pushes the\ntheoretical results closer to the experimental observations but fails to\nquantitatively reproduce them. An explanation of the delayed expansion as a\nconsequence of a new type of self-trapping mechanism, where quantum\ncorrelations suppress tunneling even when there are no density gradients, is\ndiscussed and supported by numerical time-dependent Density Matrix\nRenormalization Group (t-DMRG) calculations performed in a simplified two\ncoupled tubes set-up."
    },
    {
        "anchor": "Fractional Excitations in Cold Atomic Gases: We study the behavior of excitations in the tilted one-dimensional\nBose-Hubbard model. In the phase with broken symmetry, fundamental excitations\nare domain-walls which show fractional statistics. Using perturbation theory,\nwe derive an analytic model for the time evolution of these fractional\nexcitations, and demonstrate the existence of a repulsively bound state above a\ncritical center of mass momentum. The validity of the perturbative analysis is\nconfirmed by the use of t- DMRG simulations. These findings open the path for\nexperimental detection of fractional particles in cold atomic gases.",
        "positive": "Simulation of time crystal behavior for a few boson chiral soliton model\n  in a ring: We present numerical simulations for a chiral soliton model with N=2,3 bosons\nin a ring, this being a few-particle version of our previous mean-field model\nfor a quantum time crystal. Following Syrwid, Kosior, and Sacha (SKS), the\nnotion is that a precise position measurement of one particle can lead to\nspontaneous formation of a bright soliton that in a time crystal should rotate\nintact for at least a few revolutions around the ring. In their work SKS find\nspontaneous formation of a soliton due to the position measurement, but quantum\nfluctuations cause the soliton to subsequently decay before it has a chance to\nperform even one revolution of the ring. Based on this they conclude that time\ncrystal dynamics are impossible. In contrast, for our few boson chiral soliton\nmodel, and allowing for imprecise (weak) measurements of the particle position,\nwe show that time crystal behavior is possible allowing for several revolutions\nof the spontaneously formed soliton around the ring. We therefore argue that\nour chiral soliton model can realize a quantum time crystal when weak position\nmeasurements are allowed for."
    },
    {
        "anchor": "In situ measurement of the dynamic structure factor in ultracold quantum\n  gases: We propose an experimental setup to efficiently measure the dynamic structure\nfactor of ultracold quantum gases. Our method uses the interaction of the\ntrapped atomic system with two different cavity modes, which are driven by\nexternal laser fields. By measuring the output fields of the cavity the dynamic\nstructure factor of the atomic system can be determined. Contrary to previous\napproaches the atomic system is not destroyed during the measurement process.",
        "positive": "Simulating dense QCD matter with ultracold atomic boson-fermion mixtures: We delineate, as an analog of two-flavor dense quark matter, the phase\nstructure of a many-body mixture of atomic bosons and fermions in two internal\nstates with a tunable boson-fermion attraction. The bosons b correspond to\ndiquarks, and the fermions f to unpaired quarks. For weak b-f attraction, the\nsystem is a mixture of a Bose-Einstein condensate and degenerate fermions,\nwhile for strong attraction composite b-f fermions N, analogs of the nucleon,\nare formed, which are superfluid due to the N-N attraction in the spin-singlet\nchannel. We determine the symmetry breaking patterns at finite temperature as a\nfunction of the b-f coupling strength, and relate the phase diagram to that of\ndense QCD."
    },
    {
        "anchor": "Scaling law for three-body collisions near a narrow s-wave Feshbach\n  resonance: Ultracold atomic gases provide a controllable system to study the inelastic\nprocesses for three-body systems, where the three-body recombination rate\ndepends on the scattering length scaling. Such scalings have been confirmed in\nbosonic systems with various interaction strengths, but their existence with\nfermionic atoms remains elusive. In this work, we report on an experimental\ninvestigation of the scaling law for the three-body atomic loss rate $L_3$ in a\ntwo-component $^6$Li Fermi gas with the scattering length $a<0$. The scaling\nlaw is validated within a certain range of $a$ near the narrow $s$-wave\nFeshbach resonance, where $L_3\\propto T|a|^{2.60(5)}$, and $T$ is the gas\ntemperature. The scaling law is observed to have an upper and a lower bound in\nterms of the scattering length. For the upper bound, when $a\\rightarrow\n\\infty$, the power-law scaling is suppressed by the unitary behavior of the\nresonance caused by the strong three-body collisions. For the lower bound,\n$a\\rightarrow 0$, the finite range effect modifies the scaling law by the\neffective scattering length $L_e$. These results indicate that the three-body\nrecombination rate in a fermionic system could be characterized by the scaling\nlaw associated with the generalized Efimov physics.",
        "positive": "Density redistribution effects in fermionic optical lattices: We simulate a one dimensional fermionic optical lattice to analyse heating\ndue to non-adiabatic lattice loading. Our simulations reveal that, similar to\nthe bosonic case, density redistribution effects are the major cause of heating\nin harmonic traps. We suggest protocols to modulate the local density\ndistribution during the process of lattice loading, in order to reduce the\nexcess energy. Our numerical results confirm that linear interpolation of the\ntrapping potential and/or the interaction strength is an efficient method of\ndoing so, bearing practical applications relevant to experiments."
    },
    {
        "anchor": "Control of the symmetry breaking in double-well potentials by the\n  resonant nonlinearity management: We introduce a one-dimensional model of Bose-Einstein condensates (BECs),\ncombining the double-well potential, which is a well-known setting for the\nonset of spontaneous-symmetry-breaking (SSB) effects, and time-periodic\nmodulation of the nonlinearity, which may be implemented by means of the\nFeshbach-resonance-management (FRM) technique. Both cases of the nonlinearity\nwhich is repulsive or attractive on the average are considered. In the former\ncase, the main effect produced by the application of the FRM is spontaneous\nself-trapping of the condensate in either of the two potential wells in\nparameter regimes where it would remain untrapped in the absence of the\nmanagement. In the weakly nonlinear regime, the frequency of intrinsic\noscillations in the FRM-induced trapped state is very close to half the FRM\nfrequency, suggesting that the effect is accounted for by a parametric\nresonance. In the case of the attractive nonlinearity, the FRM-induced effect\nis the opposite, i.e., enforced detrapping of a state which is self-trapped in\nits unmanaged form. In the latter case, the frequency of oscillations of the\nuntrapped mode is close to a quarter of the driving frequency, suggesting that\na higher-order parametric resonance may account for this effect.",
        "positive": "Peaks and widths of radio-frequency spectra: An analysis of the phase\n  diagram of ultra-cold Fermi gases: We provide a comprehensive theoretical study of the radio-frequency (rf)\nspectra of a two-component Fermi gas with balanced populations in the normal\nregion of the temperature-vs-coupling phase diagram. In particular, rf spectra\nare analyzed in terms of two characteristic peaks, which can be either distinct\nor overlapping. On the BEC side of the crossover, these two contributions are\nassociated with a fermionic quasi-particle peak and a bosonic-like contribution\ndue to pairing. On the BCS side of the crossover, the two peaks are instead\nassociated with interactions between particles occurring, respectively, at high\nor low relative momenta. Through this two-peak analysis, we show how and to\nwhat extent the correlation between the widths of the rf spectra and the pair\nsize, previously identified in the superfluid phase at low temperature, can be\nextended to the normal phase, as well as how the temperature-vs-coupling phase\ndiagram of the BCS-BEC crossover can be partitioned in a number of distinct\nphysical sectors. Several analytic results for the shape and widths of the rf\nspectra are also derived in appropriate temperature and coupling limits."
    },
    {
        "anchor": "Flat band induced non-Fermi liquid behavior of multicomponent fermions: We investigate multicomponent fermions in a flat band and predict\nexperimental signatures of non-Fermi liquid behavior. We use dynamical\nmean-field theory to obtain the density, double occupancy and entropy in a Lieb\nlattice for $\\mathcal{N} = 2$ and $\\mathcal{N} = 4$ components. We derive a\nmean-field scaling relation between the results for different values of\n$\\mathcal{N}$, and study its breakdown due to beyond-mean field effects. The\npredicted signatures occur at temperatures above the N\\'eel temperature and\npersist in presence of a harmonic trapping potential, thus they are observable\nwith current ultracold gas experiments.",
        "positive": "Ultrafast coherent control of spinor Bose-Einstein condensates using\n  stimulated Raman adiabatic passage: We propose the use of stimulated Raman adiabatic passage (STIRAP) to offer a\nfast high fidelity method of performing SU(2) rotations on spinor Bose Einstein\ncondensates (BEC). Past demonstrations of BEC optical control suffer from\ndifficulties arising from collective enhancement of spontaneous emission and\ninefficient two-photon transitions originating from selection rules. We present\nhere a novel scheme which allows for arbitrary coherent rotations of\ntwo-component BECs while overcoming these issues. Numerical tests of the method\nshow that for BECs of \\ce{^{87}Rb} with up to $ 10^4 $ atoms and gate times of\n$ \\SI{1}{\\micro\\second} $, decoherence due to spontaneous emission can be\nsuppressed to negligible values."
    },
    {
        "anchor": "Symmetry-breaking thermally induced collapse of dipolar Bose-Einstein\n  condensates: We investigate a Bose-Einstein condensate with additional long-range dipolar\ninteraction in a cylindrically symmetric trap within a variational framework.\nCompared to the ground state of this system, little attention has as yet been\npayed to its unstable excited states. For thermal excitations, however, the\nlatter is of great interest, because it forms the \"activated complex\" that\nmediates the collapse of the condensate. For a certain value of the s-wave\nscatting length our investigations reveal a bifurcation in the transition\nstate, leading to the emergence of two additional and symmetry-breaking excited\nstates. Because these are of lower energy than their symmetric counterpart, we\npredict the occurrence of a symmetry-breaking thermally induced collapse of\ndipolar condensates. We show that its occurrence crucially depends on the trap\ngeometry and calculate the thermal decay rates of the system within leading\norder transition state theory with the help of a uniform rate formula near the\nrank-2 saddle which allows to smoothly pass the bifurcation.",
        "positive": "Momentum distribution and contacts of one-dimensional spinless Fermi\n  gases with an attractive p-wave interaction: We present a rigorous study of momentum distribution and p-wave contacts of\none dimensional (1D) spinless Fermi gases with an attractive p-wave\ninteraction. Using the Bethe wave function, we analytically calculate the\nlarge-momentum tail of momentum distribution of the model. We show that the\nleading ($\\sim 1/p^{2}$) and sub-leading terms ($\\sim 1/p^{4}$) of the\nlarge-momentum tail are determined by two contacts $C_2$ and $C_4$, which we\nshow, by explicit calculation, are related to the short-distance behaviour of\nthe two-body correlation function and its derivatives. We show as one increases\nthe 1D scattering length, the contact $C_2$ increases monotonically from zero\nwhile $C_4$ exhibits a peak for finite scattering length. In addition, we\nobtain analytic expressions for p-wave contacts at finite temperature from the\nthermodynamic Bethe ansatz equations in both weakly and strongly attractive\nregimes."
    },
    {
        "anchor": "Interaction Effects on Number Fluctuations in a Bose-Einstein Condensate\n  of Light: We investigate the effect of interactions on condensate-number fluctuations\nin Bose-Einstein condensates. For a contact interaction we variationally obtain\nthe equilibrium probability distribution for the number of particles in the\ncondensate. To facilitate comparison with experiment, we also calculate the\nzero-time delay autocorrelation function $g^{(2)}(0)$ for different strengths\nof the interaction. Finally, we focus on the case of a condensate of photons\nand discuss possible mechanisms for the interaction.",
        "positive": "Engineering and probing non-Abelian chiral spin liquids using\n  periodically driven ultracold atoms: We propose a scheme to implement Kitaev's honeycomb model with cold atoms,\nbased on a periodic (Floquet) drive, in view of realizing and probing\nnon-Abelian chiral spin liquids using quantum simulators. We derive the\neffective Hamiltonian to leading order in the inverse-frequency expansion, and\nshow that the drive opens up a topological gap in the spectrum without mixing\nthe effective Majorana and vortex degrees of freedom. We address the challenge\nof probing the physics of Majorana fermions, while having only access to the\noriginal composite spin degrees of freedom. Specifically, we propose to detect\nthe properties of the chiral spin liquid phase using gap spectroscopy and edge\nquenches in the presence of the Floquet drive. The resulting chiral edge\nsignal, which relates to the thermal Hall effect associated with neutral\nMajorana currents, is found to be robust for realistically-prepared states. By\ncombining strong interactions with Floquet engineering, our work paves the way\nfor future studies of non-Abelian excitations and quantized thermal transport\nusing quantum simulators."
    },
    {
        "anchor": "Pairing correlations of cold fermionic gases at overflow from a narrow\n  to a wide harmonic trap: Within the context of Hartree-Fock-Bogoliubov theory, we study the behavior\nof superfluid Fermi systems when they pass from a small to a large container.\nSuch systems can be now realized thanks to recent progress in experimental\ntechniques. It will allow to better understand pairing properties at overflow\nand in general in rapidly varying external potentials.",
        "positive": "Bound vortex states and exotic lattices in multi-component Bose-Einstein\n  condensates: The role of vortex-vortex interaction: We numerically study the vortex-vortex interaction in multi-component\nhomogeneous Bose-Einstein condensates within the realm of the Gross-Pitaevskii\ntheory. We provide strong evidences that pairwise vortex interaction captures\nthe underlying mechanisms which determine the geometric configuration of the\nvortices, such as different lattices in many-vortex states, as well as the\nbound vortex states with two (dimer) or three (trimer) vortices. Specifically,\nwe discuss and apply our theoretical approach to investigate intra- and\ninter-component vortex-vortex interactions in two- and three-component\nBose-Einstein condensates, thereby shedding light on the formation of the\nexotic vortex configurations. These results correlate with current experimental\nefforts in multi-component Bose-Einstein condensates, and the understanding of\nthe role of vortex interactions in multiband superconductors."
    },
    {
        "anchor": "Intrinsic decoherence and recurrences in a large ferromagnetic $F = 1$\n  spinor Bose-Einstein condensate: Decoherence with recurrences appear in the dynamics of the one-body density\nmatrix of an $F = 1$ spinor Bose-Einstein condensate, initially prepared in\ncoherent states, in the presence of an external uniform magnetic field and\nwithin the single mode approximation. The phenomenon emerges as a many-body\neffect of the interplay of the quadratic Zeeman effect, that breaks the\nrotational symmetry, and the spin-spin interactions. By performing full quantum\ndiagonalizations very accurate time evolution of large condensates are\nanalyzed, leading to heuristic analytic expressions for the time dependence of\nthe one-body density matrix, in the weak and strong interacting regimes, for\ninitial coherent states. We are able to find accurate analytical expressions\nfor both the decoherence and the recurrence times, in terms of the number of\natoms and strength parameters, that show remarkable differences depending on\nthe strength of the spin-spin interactions. The features of the stationary\nstates in both regimes is also investigated. We discuss the nature of these\nlimits in the light of the thermodynamic limit.",
        "positive": "Vortex states and spin textures of rotating spin-orbit-coupled\n  Bose-Einstein condensates in a toroidal trap: We consider the ground-state properties of Rashba spin-orbit-coupled\npseudo-spin-1/2 Bose-Einstein condensates (BECs) in a rotating two-dimensional\n(2D) toroidal trap. In the absence of spin-orbit coupling (SOC), the increasing\nrotation frequency enhances the creation of giant vortices for the initially\nmiscible BECs, while it can lead to the formation of semiring density patterns\nwith irregular hidden vortex structures for the initially immiscible BECs.\nWithout rotation, strong 2D isotropic SOC yields a heliciform-stripe phase for\nthe initially immiscible BECs. Combined effects of rotation, SOC, and\ninteratomic interactions on the vortex structures and typical spin textures of\nthe ground state of the system are discussed systematically. In particular, for\nfixed rotation frequency above the critical value, the increasing isotropic SOC\nfavors a visible vortex ring in each component which is accompanied by a hidden\ngiant vortex plus a (several) hidden vortex ring(s) in the central region. In\nthe case of 1D anisotropic SOC, large SOC strength results in the generation of\nhidden linear vortex string and the transition from initial phase separation\n(phase mixing) to phase mixing (phase separation). Furthermore, the peculiar\nspin textures including skyrmion lattice, skyrmion pair and skyrmion string are\nrevealed in this system."
    },
    {
        "anchor": "Impact of local integrals of motion to metastable non-equilibrium states: We analyse the stationary behaviour of correlations in a strongly correlated\nBose gas out of equilibrium. The dynamics are triggered by a quench of the\ninteraction starting from the strongly interacting limit where the system is in\na perfect Mott state. Despite the complete integrability of our theoretical\ndescription, we find seemingly thermal behaviour for the experimentally\nmeasurable correlations at large interactions. Quite opposed, away from the\nstrongly interacting regime these correlation functions show highly non-thermal\nstationary values. This behaviour is explained by overlaps of the integrals of\nmotion with the observable and the initial state in an effective thermal\nensemble. These results suggest that non-equilibrium Mazur equalities are an\nefficient way to calculate short range correlations for arbitrary integrable\nmodels.",
        "positive": "Interaction between an impurity and nonlinear excitations in a polariton\n  condensate: Exploring the dynamics of a mobile impurity immersed in the field excitations\nis challenging, as it requires to account for the entanglement between the\nimpurity and the surrounding excitations. To this end, the impurity's effective\nmass has to be considered as finite, rather than infinite. Here, we\ntheoretically investigate the interaction between a finite-mass impurity and a\ndissipative soliton representing nonlinear excitations in the polariton\nBose-Einstein condensate (BEC). Using the Lagrange variational method and the\nopen-dissipative Gross-Pitaevskii equation, we analytically derive the\ninteraction phase diagram between the impurity and a dissipative bright soliton\nin the polariton BEC. Depending on the impurity mass, we find the dissipative\nsoliton colliding with the impurity can transmit through, get trapped, or be\nreflected. This work opens a new perspective in understanding the impurity\ndynamics immersed in the field excitations, as well as potential applications\nin information processing with polariton solitons."
    },
    {
        "anchor": "Pauli crystal melting in shaken optical traps: Pauli crystals are ordered geometric structures that emerge in trapped\nnoninteracting fermionic systems due to their underlying Pauli repulsion. The\ndeformation of Pauli crystals - often called melting - has been recently\nobserved in experiments, but the mechanism that leads to it remains unclear. We\naddress this question by studying the melting dynamics of N=6 fermions as a\nfunction of periodic driving and experimental imperfections in the trap\n(anisotropy and anharmonicity) by employing a combination of numerical\nsimulations and Floquet theory. Surprisingly, we reveal that the melting of\nPauli crystals is not simply a direct consequence of an increase in system\nenergy, but is instead related to the trap geometry and the population of the\nFloquet modes. We show that the melting is absent in traps without\nimperfections and triggered only by a sufficiently large shaking amplitude in\ntraps with imperfections.",
        "positive": "Crow instability in trapped Bose-Einstein condensates: We show theoretically that elongated vortex-antivortex dipoles can be created\ncontrollably in trapped Bose-Einstein condensates, using known experimental\ntechniques. Vortex dipoles of sufficient length are unstable and cascade into\nslow vortex rings which ultimately decay via sound emission. This instability\nof antiparallel vortex line elements, which self-generates Kelvin waves on\nvortex loops and in trapped atomic gases, may play a role in bridging the\nKelvin-wave and Kolmogorov-Richardson cascades of quantum turbulence."
    },
    {
        "anchor": "Optically driven rotation of exciton-polariton condensates: The rotational response of quantum condensed fluids is strikingly distinct\nfrom rotating classical fluids, especially notable for the excitation and\nordering of quantized vortex ensembles. Although widely studied in conservative\nsystems, the dynamics of rotating open-dissipative superfluids such as\nexciton-polariton condensates remain largely unexplored, as it requires\nhigh-frequency rotation whilst avoiding resonantly driving the condensate. We\ncreate a rotating polariton condensate at GHz frequencies by off-resonantly\npumping with a rotating optical stirrer composed of the time-dependent\ninterference of two frequency-offset, structured laser modes. Acquisition of\nangular momentum exceeding the critical $1\\hbar$/particle is directly measured,\naccompanied by the deterministic nucleation and capture of quantized vortices\nwith a handedness controlled by the pump rotation direction. The demonstration\nof controlled optical rotation of a spontaneously formed polariton condensate\nenables new opportunities for the study of open-dissipative superfluidity,\nordering of non-Hermitian quantized vortex matter, and topological states in a\nhighly non-linear, photonic platform.",
        "positive": "Stability of $p$-orbital Bose-Einstein condensates in optical\n  checkerboard and square lattices: We investigate $p$-orbital Bose-Einstein condensates in both the square and\ncheckerboard lattice by numerically solving the Gross-Pitaevskii equation. The\nperiodic potential for the latter lattice is taken exactly from the recent\nexperiment [Nature Phys. 7, 147 (2011)]. It is confirmed that the staggered\norbital-current state is the lowest-energy state in the $p$ band. Our numerical\ncalculation further reveals that for both lattices the staggered $p$-orbital\nstate suffers Landau instability but the situation is remarkably different for\ndynamical instability. A dynamically stable parameter region is found for the\ncheckerboard lattice, but not for the square."
    },
    {
        "anchor": "High-energy Bragg scattering measurements of a dipolar supersolid: We present an experimental and theoretical study of the high-energy\nexcitation spectra of a dipolar supersolid. Using Bragg spectroscopy, we study\nthe scattering response of the system to a high-energy probe, enabling\nmeasurements of the dynamic structure factor. We experimentally observe a\ncontinuous reduction of the response when tuning the contact interaction from\nan ordinary Bose-Einstein condensate to a supersolid state. Yet the observed\nreduction is faster than the one theoretically predicted by the\nBogoliubov-de-Gennes theory. Based on an intuitive semi-analytic model and\nreal-time simulations, we primarily attribute such a discrepancy to the\nout-of-equilibrium phase dynamics, which although not affecting the system\nglobal coherence, reduces its response.",
        "positive": "New trends in quantum integrability: Recent experiments with ultracold\n  atoms: Over the past two decades quantum engineering has made significant advances\nin our ability to create genuine quantum many-body systems using ultracold\natoms. In particular, some prototypical exactly solvable Yang-Baxter systems\nhave been successfully realized allowing us to confront elegant and\nsophisticated exact solutions of these systems with their experimental\ncounterparts. The new experimental developments show a variety of fundamental\none-dimensional (1D) phenomena, ranging from the generalized hydrodynamics to\ndynamical fermionization, Tomonaga-Luttinger liquids, collective excitations,\nfractional exclusion statistics, quantum holonomy, spin-charge separation,\ncompeting orders with high spin symmetry and quantum impurity problems. This\narticle briefly reviews these developments and provides rigorous understanding\nof those observed phenomena based on the exact solutions while highlighting the\nuniqueness of 1D quantum physics. The precision of atomic physics realizations\nof integrable many-body problems continues to inspire significant developments\nin mathematics and physics while at the same time offering the prospect to\ncontribute to future quantum technology."
    },
    {
        "anchor": "Population imbalanced lattice fermions near the BCS-BEC crossover: I.The\n  breached pair and metastable FFLO phases: We study s-wave superconductivity in the two dimensional attractive Hubbard\nmodel in an applied magnetic field, assume the extreme Pauli limit, and examine\nthe role of spatial fluctuations in the coupling regime corresponding to\nBCS-BEC crossover. We use a decomposition of the interaction in terms of an\nauxiliary pairing field, retain the static mode, and sample the pairing field\nvia Monte Carlo. The method requires iterative solution of the\nBogoliubov-de-Gennes (BdG) equations for amplitude and phase fluctuating\nconfigurations of the pairing field. We establish the full thermal phase\ndiagram of this strong coupling problem, revealing $T_c$ scales an order of\nmagnitude below the mean field estimate, highlight the spontaneous\ninhomogeneity in the field induced magnetization, and discover a strong non\nmonotonicity in the temperature dependence of the low energy density of states.\nWe compare our results to the experimental phase diagram of the imbalanced\nFermi gas at unitarity. This paper focuses on the magnetized but homogeneous\n(breached pair) superconducting state, a companion paper deals with the\nFulde-Ferrell-Larkin-Ovchinnikov (FFLO) regime.",
        "positive": "Quantum and Thermal Transitions Out of the Pair-Supersolid Phase of\n  Two-Species Bosons in Lattice: We investigate two-species bosons in a two-dimensional square lattice by\nquantum Monte Carlo method. We show that the inter-species attraction and\nnearest-neighbor intra-species repulsion results in the pair-supersolid phase,\nwhere a diagonal solid order coexists with an off-diagonal pair-superfluid\norder. The quantum and thermal transitions out of the pair-supersolid phase are\ncharacterized. It is found that there is a direct first order transition from\nthe pair-supersolid phase to the double-superfluid phase without an\nintermediate region. Furthermore, the melting of the pair-supersolid occurs in\ntwo steps. Upon heating, first the pair-superfluid is destroyed via a KT\ntransition then the solid order melts via an Ising transition"
    },
    {
        "anchor": "Sudden quench of harmonically trapped mass-imbalanced fermions: Dynamical properties of two-component mass-imbalanced few-fermion systems\nconfined in a one-dimensional harmonic trap following a sudden quench of\ninteractions are studied. It is assumed that initially the system is prepared\nin the non-interacting ground state and then, after a sudden quench of\ninteractions, the unitary evolution is governed by interacting many-body\nHamiltonian. By careful analysis of the evolution of the Loschmidt echo,\ndensity distributions of the components, and entanglement entropy between them,\nthe role of mass imbalance and particle number imbalance on the system's\nevolution stability are investigated. All the quantities studied manifest a\ndramatic dependence on the number of heavy and lighter fermions in each\ncomponent at a given quench strength. The results may have implications for\nupcoming experiments on fermionic mixtures with a well-defined and small number\nof particles.",
        "positive": "Path integral Monte Carlo ground state approach: Formalism,\n  implementation, and applications: Monte Carlo techniques have played an important role in understanding\nstrongly-correlated systems across many areas of physics, covering a wide range\nof energy and length scales. Among the many Monte Carlo methods applicable to\nquantum mechanical systems, the path integral Monte Carlo approach with its\nvariants has been employed widely. Since semi-classical or classical approaches\nwill not be discussed in this review, path integral based approaches can for\nour purposes be divided into two categories: approaches applicable to quantum\nmechanical systems at zero temperature and approaches applicable to quantum\nmechanical systems at finite temperature. While these two approaches are\nrelated to each other, the underlying formulation and aspects of the algorithm\ndiffer. This paper reviews the path integral Monte Carlo ground state (PIGS)\napproach, which solves the time-independent Schroedinger equation.\nSpecifically, the PIGS approach allows for the determination of expectation\nvalues with respect to eigen states of the few- or many-body Schroedinger\nequation provided the system Hamiltonian is known. The theoretical framework\nbehind the PIGS algorithm, implementation details, and sample applications for\nsermonic systems are presented."
    },
    {
        "anchor": "Texture control in a pseudospin Bose-Einstein condensate: We describe a wavefunction engineering approach to the formation of textures\nin a two-component nonrotated Bose-Einstein condensate. By controlling the\nphases of wavepackets that combine in a three-wave interference process, a\nballistically-expanding regular lattice-texture is generated, in which the\nphases determine the component textures. A particular example is presented of a\nlattice-texture composed of half-quantum vortices and spin-2 textures. We\ndemonstrate the lattice formation with numerical simulations of a viable\nexperiment, identifying the textures and relating their locations to a linear\ntheory of wavepacket interference.",
        "positive": "New cross-phase modulated localized solitons in coupled atomic-molecular\n  BEC: The interacting atom-molecule BEC (AMBEC) dynamics is investigated in the\nmean field ap- proach. The presence of atom-atom, atom-molecule and\nmolecule-molecule interactions, coupled with a characteristically different\ninteraction representing atom-molecule interconversion, endows this system with\nnonlinearities, which differ significantly from the standard Gross-Pitaevskii\n(GP) equation. Exact localized solutions are found to belong to two distinct\nclasses. The first ones are analogous to the soliton solutions of the weakly\ncoupled GP equation, whereas the second non- equivalent class is related to the\nsolitons of the strongly coupled BEC. Distinct parameter domains characterize\nthese solitons, some of which are analogous to the complex profile Bloch\nsolitons in magnetic systems. These localized solutions are found to represent\na variety of phenomena, which include co-existence of both atom-molecule\ncomplex and miscible-immiscible phases. Numerical sta- bility is explicitly\nchecked, as also the stability analysis based on the study of quantum\nuctuations around our solutions. We also find out the domain of modulation\ninstability in this system."
    },
    {
        "anchor": "Quench dynamics of the interacting Bose gas in one dimension: We obtain an exact expression for the time evolution of the interacting Bose\ngas following a quench from a generic initial state using the Yudson\nrepresentation for integrable systems. We study the time evolution of the\ndensity and noise correlation for a small number of bosons and their asymptotic\nbehavior for any number. We show that for any value of the coupling, as long as\nit is repulsive, the system asymptotes towards a strongly repulsive gas, while\nfor any value of an attractive coupling the long time behavior is dominated by\nthe maximal bound state. This occurs independently of the initial state and can\nbe viewed as an emerging \"dynamic universality\".",
        "positive": "Efficient production of long-lived ultracold Sr$_2$ molecules: We associate Sr atom pairs on sites of a Mott insulator optically and\ncoherently into weakly-bound ground-state molecules, achieving an efficiency\nabove 80\\%. This efficiency is 2.5 times higher than in our previous work [S.\nStellmer, B. Pasquiou, R. Grimm, and F. Schreck, Phys. Rev. Lett. 109, 115302\n(2012)] and obtained through two improvements. First, the lifetime of the\nmolecules is increased beyond one minute by using an optical lattice wavelength\nthat is further detuned from molecular transitions. Second, we compensate\nundesired dynamic light shifts that occur during the stimulated Raman adiabatic\npassage (STIRAP) used for molecule association. We also characterize and model\nSTIRAP, providing insights into its limitations. Our work shows that\nsignificant molecule association efficiencies can be achieved even for atomic\nspecies or mixtures that lack Feshbach resonances suitable for\nmagnetoassociation."
    },
    {
        "anchor": "Robust stripes in the mixed-dimensional $t-J$ model: Microscopically understanding competing orders in strongly correlated systems\nis a key challenge in modern quantum many-body physics. For example, the origin\nof stripe order and its relation to pairing in the Fermi-Hubbard model remains\none of the central questions, and may help to understand the origin of\nhigh-temperature superconductivity in cuprates. Here, we analyze stripe\nformation in the doped mixed-dimensional (mixD) variant of the $t-J$ model,\nwhere charge carriers are restricted to move only in one direction, whereas\nmagnetic $\\mathrm{SU}(2)$ interactions are two-dimensional. Using the density\nmatrix renormalization group at finite temperature, we find a stable vertical\nstripe phase in the absence of pairing, featuring incommensurate magnetic order\nand long-range charge density wave profiles over a wide range of dopings. We\nfind high critical temperatures on the order of the magnetic coupling $J$,\nhence being within reach of current quantum simulators. Snapshots of the\nmany-body state, accessible to quantum simulators, reveal hidden spin\ncorrelations in the mixD setting, whereby antiferromagnetic correlations are\nenhanced when considering purely the magnetic background. The proposed model\ncan be viewed as realizing a parent Hamiltonian of the stripe phase, whose\nhidden spin correlations lead to the predicted resilience against quantum and\nthermal fluctuations.",
        "positive": "Emergent and broken symmetries of atomic self-organization arising from\n  Gouy phase shifts in multimode cavity QED: Optical cavities can induce photon-mediated interactions among\nintracavity-trapped atoms. Multimode cavities provide the ability to tune the\nform of these interactions, e.g., by inducing a nonlocal, sign-changing term to\nthe interaction. By accounting for the Gouy phase shifts of the modes in a\nnearly degenerate, confocal, Fabry-Perot cavity, we provide a theoretical\ndescription of this interaction, along with additional experimental\nconfirmation to complement that presented in the companion paper, Ref. [1].\nFurthermore, we show that this interaction should be written in terms of a\ncomplex order parameter, allowing for a U(1)-symmetry to emerge. This symmetry\ncorresponds to the phase of the atomic density wave arising from\nself-organization when the cavity is transversely pumped above a critical\nthreshold power. We theoretically and experimentally show how this phase\ndepends on the position of the Bose-Einstein condensate (BEC) within the cavity\nand discuss mechanisms that break the U(1)-symmetry and lock this phase. We\nthen consider alternative Fabry-Perot multimode cavity geometries (i.e., beyond\nthe confocal) and schemes with more than one pump laser and show that these\nprovide additional capabilities for tuning the cavity-meditated interaction\namong atoms, including the ability to restore the U(1)-symmetry despite the\npresence of symmetry-breaking effects. These photon-mediated interactions may\nbe exploited for realizing quantum liquid crystalline states and spin glasses\nusing multimode optical cavities."
    },
    {
        "anchor": "Finite temperature expansion dynamics of Bose-Einstein condensates: We explore the effects of finite temperature on the dynamics of Bose-Einstein\ncondensates (BECs) after it is released from the confining potential. In\naddition, we examine the variation in the expansion dynamics of the BECs as the\nconfining potential is transformed from a multiply to a simply connected\ngeometry. To include the effects of finite temperatures we use the frozen\nthermal cloud approximation, and observe unique features of the condensate\ndensity distribution when released from the confining potential. We find that\nat $T\\neq 0$, during the initial stages of expansion, the multiply connected\ncondensate has more pronounced interference rings compared to the case of zero\ntemperature. Such difference in the dynamical evolution is also evident for\nsimply connected condensates.",
        "positive": "Hidden Magnetism in Periodically Modulated One Dimensional Dipolar\n  Fermions: The experimental realization of time dependent ultracold lattice systems has\npaved the way towards the implementation of new Hubbard-like Hamiltonians. We\nshow that in a one dimensional two components lattice dipolar Fermi gas the\ncompetition between long range repulsion and correlated hopping induced by\nperiodically modulated on-site interaction allows for the formation of exotic\nhidden magnetic phases. The magnetism, characterized solely by string-like\nnonlocal order parameters, manifests itself both in the charge and, noticeably,\nin the spin degrees of freedom. Such behavior is enlighten by employing both\nLuttinger theory and numerical methods. Crucially the range of parameters for\nwhich hidden magnetism is present can be reached by means of the currently\navailable experimental setups and probes."
    },
    {
        "anchor": "Loss features in ultracold $^{162}$Dy gases: two- versus three-body\n  processes: Dipolar gases like erbium and dysprosium have a dense spectrum of resonant\nloss features associated with their strong anisotropic interaction potential.\nThese resonances display various behaviours with density and temperature,\nimplying diverse microscopic properties. Here, we quantitatively investigate\nthe low-field ($B < 6\\,\\text{G}$) loss features in ultracold thermal samples of\n$^{162}$Dy, revealing two- and three-body dominated loss processes. We\ninvestigate their temperature dependence and detect a feature compatible with a\n$d$-wave Fano-Feshbach resonance, which has not been observed before. We also\nanalyse the expansion of the dipolar Bose-Einstein condensate as a function of\nthe magnetic field and interpret the changes in size close to the resonances\nwith a variation in the scattering length.",
        "positive": "Analogy of RKKY oscillations to the heat exchange in cold atoms: An oscillatory term is found in both the energy expectation and dynamics of a\nwave-packet in a time-varying harmonic trap and infinite potential well. They\nare proved to oscillate in coherence with the time lapse within each period\ndepending on both the cutoff in transition energies and the specific route via\nwhich the potential is being varied. This oscillatory term is general to\narbitrary potential forms since it derives from the interference between\ncrossed transition trajectories. Close analogy is made to the\nRuderman-Kittel-Kasuya-Yosida interaction for giant-magnetoresistance\ntrilayers, where many-body quantum interference among scattering states renders\nthe oscillation as a function of spacer width. This connection reveals the\ngenerality of quantum friction due to parasitic oscillations."
    },
    {
        "anchor": "Resonantly enhanced coherence by laser-assisted tunneling: We study quantum coherence of strongly interacting cold bosons in a\ndouble-well potential driven by a laser field. The system is initially in a\nFock state and, for either with or without a static tilting field, evolves into\nthe coherent states. The coherence is resonantly enhanced by the\nphoton-assisted tunneling. For the tilted wells, it reveals a two-branch\npattern which corresponds to the multiple photon absorption or emission,\nrespectively.",
        "positive": "Dynamic optical lattices of sub-wavelength spacing for ultracold atoms: We propose a scheme to realize lattice potentials of sub-wavelength spacing\nfor ultracold atoms. It is based on spin-dependent optical lattices with a\ntime-periodic modulation. We show that the atomic motion is well described by\nthe combined action of an effective, time-independent, lattice of small\nspacing, together with a micro-motion associated with the time-modulation. A\nnumerical simulation shows that an atomic gas can be adiabatically loaded into\nthe effective lattice ground state, for timescales comparable to the ones\nrequired for adiabatic loading of standard optical lattices. We generalize our\nscheme to a two-dimensional geometry, leading to Bloch bands with non-zero\nChern numbers. The realization of lattices of sub-wavelength spacing allows for\nthe enhancement of energy scales, which could facilitate the achievment of\nstrongly-correlated (topological) states."
    },
    {
        "anchor": "Site-resolved imaging of single atoms with a Faraday quantum gas\n  microscope: We successfully demonstrate a quantum gas microscopy using the Faraday effect\nwhich has an inherently non-destructive nature. The observed Faraday rotation\nangle reaches 3.0(2) degrees for a single atom. We reveal the non-destructive\nfeature of this Faraday imaging method by comparing the detuning dependence of\nthe Faraday signal strength with that of the photon scattering rate. We\ndetermine the atom distribution with deconvolution analysis. We also\ndemonstrate the absorption and the dark field Faraday imaging, and reveal the\ndifferent shapes of the point spread functions for these methods, which are\nfully explained by theoretical analysis. Our result is an important first step\ntowards an ultimate quantum non-demolition site-resolved imaging and\nfurthermore opens up the possibilities for quantum feedback control of a\nquantum many-body system with a single-site resolution.",
        "positive": "Quasiparticle properties of a mobile impurity in a Bose-Einstein\n  condensate: We develop a systematic perturbation theory for the quasiparticle properties\nof a single impurity immersed in a Bose-Einstein condensate. Analytical results\nare derived for the impurity energy, the effective mass, and residue to third\norder in the impurity-boson scattering length. The energy is shown to depend\nlogarithmically on the scattering length to third order, whereas the residue\nand effective mass are given by analytical power series. When the boson-boson\nscattering length equals the boson-impurity scattering length, the energy has\nthe same structure as that of a weakly interacting Bose gas, including terms of\nthe Lee-Huang-Yang and fourth order logarithmic form. Our results, which cannot\nbe obtained within the canonical Fr{\\\"o}hlich model of an impurity interacting\nwith phonons, provide valuable benchmarks for many-body theories and for\nexperiments."
    },
    {
        "anchor": "Quantum signatures of self-trapping transition in attractive lattice\n  bosons: We consider the Bose-Hubbard model describing attractive bosonic particles\nhopping across the sites of a translation-invariant lattice, and compare the\nrelevant ground-state properties with those of the corresponding\nsymmetry-breaking semiclassical nonlinear theory. The introduction of a\nsuitable measure allows us to highlight many correspondences between the\nnonlinear theory and the inherently linear quantum theory, characterized by the\nwell-known self-trapping phenomenon. In particular we demonstrate that the\nlocalization properties and bifurcation pattern of the semiclassical\nground-state can be clearly recognized at the quantum level. Our analysis\nhighlights a finite-number effect.",
        "positive": "Probing the Hall Voltage in Synthetic Quantum Systems: In the context of experimental advances in the realization of artificial\nmagnetic fields in quantum gases, we discuss feasible schemes to extend\nmeasurements of the Hall polarization to a study of the Hall voltage, allowing\nfor direct comparison with solid state systems. Specifically, for the\nparadigmatic example of interacting flux ladders, we report on characteristic\nzero crossings and a remarkable robustness of the Hall voltage with respect to\ninteraction strengths, particle fillings, and ladder geometries, which is\nunobservable in the Hall polarization. Moreover, we investigate the\nsite-resolved Hall response in spatially inhomogeneous quantum phases."
    },
    {
        "anchor": "Finite temperature vortices in a rotating Fermi gas: Vortices and vortex arrays have been used as a hallmark of superfluidity in\nrotated, ultracold Fermi gases. These superfluids can be described in terms of\nan effective field theory for a macroscopic wave function representing the\nfield of condensed pairs, analogous to the Ginzburg-Landau theory for\nsuperconductors. Here, we have established how rotation modifies this effective\nfield theory, by rederiving it starting from the action of Fermi gas in the\nrotating frame of reference. The rotation leads to the appearance of an\neffective vector potential, and the coupling strength of this vector potential\nto the macroscopic wave function depends on the interaction strength between\nthe fermions, due to a renormalization of the pair effective mass in the\neffective field theory. The mass renormalization derived here is in agreement\nwith results of functional renormalization group theory. In the extreme BEC\nregime, the pair effective mass tends to twice the fermion mass, in agreement\nwith the physical picture of a weakly interacting Bose gas of molecular pairs.\nThen, we use our macroscopic wave function description to study vortices and\nthe critical rotation frequencies to form them. Equilibrium vortex state\ndiagrams are derived, and they are in good agreement with available results of\nthe Bogoliubov - De Gennes theory and with experimental data.",
        "positive": "Integrability breakdown in longitudinaly trapped, one-dimensional\n  bosonic gases: A system of identical bosons with short-range (contact) interactions is\nstudied. Their motion is confined to one dimension by a tight lateral trapping\npotential and, additionally, subject to a weak harmonic confinement in the\nlongitudinal direction. Finite delay time associated with penetration of\nquantum particles through each other in the course of a pairwise\none-dimensional collision in the presence of the longitudinal potential makes\nthe system non-integrable and, hence, provides a mechanism for relaxation to\nthermal equilibrium. To analyse this effect quantitatively in the limit of a\nnon-degenerate gas, we develop a system of kinetic equations and solve it for\nsmall-amplitude monopole oscillations of the gas. The obtained damping rate is\nlong enough to be neglected in a realistic cold-atom experiment, and therefore\nlongitudinal trapping does not hinder integrable dynamics of atomic gases in\nthe 1D regime."
    },
    {
        "anchor": "Dynamical generation of dark solitons in spin-orbit-coupled\n  Bose-Einstein condensates: We numerically investigate the ground state, the Raman-driving dynamics and\nthe nonlinear excitations of a realized spin-orbit-coupled Bose-Einstein\ncondensate in a one-dimensional harmonic trap. Depending on the Raman coupling\nand the interatomic interactions, three ground-state phases are identified:\nstripe, plane wave and zero-momentum phases. A narrow parameter regime with\ncoexistence of stripe and zero-momentum or plane wave phases in real space is\nfound. Several sweep progresses across different phases by driving the Raman\ncoupling linearly in time is simulated and the non-equilibrium dynamics of the\nsystem in these sweeps are studied. We find kinds of nonlinear excitations,\nwith the particular dark solitons excited in the sweep from the stripe phase to\nthe plane wave or zero-momentum phase within the trap. Moreover, the number and\nthe stability of the dark solitons can be controlled in the driving, which\nprovide a direct and easy way to generate dark solitons and study their\ndynamics and interaction properties.",
        "positive": "Critical Velocity for Vortex Shedding in a Bose-Einstein Condensate: We present measurements of the critical velocity for vortex shedding in a\nhighly oblate Bose-Einstein condensate with a moving repulsive Gaussian laser\nbeam. As a function of the barrier height $V_0$, the critical velocity $v_c$\nshows a dip structure having a minimum at $V_0 \\approx \\mu $, where $\\mu$ is\nthe chemical potential of the condensate. At fixed $V_0\\approx 7\\mu$, we\nobserve that the ratio of $v_c$ to the speed of sound $c_s$ monotonically\nincreases for decreasing $\\sigma/\\xi$, where $\\sigma$ is the beam width and\n$\\xi$ is the condensate healing length. The measured upper bound for $v_c/c_s$\nis about 0.4, which is in good agreement with theoretical predictions for a\ntwo-dimensional superflow past a circular cylinder. We explain our results with\nthe density reduction effect of the soft boundary of the Gaussian obstacle,\nbased on the local Landau criterion for superfluidity."
    },
    {
        "anchor": "Effect of mediated interactions on a Hubbard chain in mixed-dimensional\n  fermionic cold atoms: Cold atom experiments can now realize mixtures where different components\nmove in different spatial dimensions. We investigate a fermion mixture where\none species is constrained to move along a one-dimensional lattice embedded in\na two-dimensional lattice populated by another species of fermions, and where\nall bare interactions are contact interactions. By focusing on the\none-dimensional fermions, we map this problem onto a model of fermions with\nnon-local interactions on a chain. The effective interaction is mediated by the\ntwo-dimensional fermions and is both attractive and retarded, the form of which\ncan be varied by changing the density of the two-dimensional fermions. By using\nthe functional renormalization group in the weak-coupling and adiabatic limit,\nwe show that the one-dimensional fermions can be controlled to be in various\ndensity-wave, or spin-singlet or triplet superconducting phases.",
        "positive": "Understanding many-body physics in one dimension from the Lieb-Liniger\n  model: This article presents an elementary introduction on various aspects of the\nprototypical integrable model the Lieb-Liniger Bose gas ranging from the\ncooperative to the collective features of many-body phenomena [1]. In 1963 Lieb\nand Liniger first solved this quantum field theory many-body problem using the\nBethe's hypothesis, i.e. a particular form of wave function introduced by Bethe\nin solving the one-dimensional Heisenberg model in 1931. Despite the\nLieb-Liniger model is arguably the simplest exactly solvable model, it exhibits\nrich quantum many-body physics in terms of the aspects of mathematical\nintegrability and physical universality. Moreover, the Yang-Yang grand\ncanonical ensemble description for the model provides us with a deep\nunderstanding of quantum statistics, thermodynamics and quantum critical\nphenomena at the many-body physics level. Recently, such fundamental physics of\nthis exactly solved model has been attracting growing interest in experiments.\nSince 2004, there have been more than 20 experimental papers that report novel\nobservations of different physical aspects of the Lieb-Liniger model in the\nlab. So far the observed results to date are seen to be in excellent agreement\nwith results obtained using the analysis of this simplest exactly solved model.\nThose experimental observations reveal the unique beauty of integrability."
    },
    {
        "anchor": "Observation of symmetry-protected topological band with ultracold\n  fermions: Symmetry plays a fundamental role in understanding complex quantum matter,\nparticularly in classifying topological quantum phases, which have attracted\ngreat interests in the recent decade. An outstanding example is the\ntime-reversal invariant topological insulator, a symmetry-protected topological\n(SPT) phase in the symplectic class of the Altland-Zirnbauer classification. We\nreport the observation for ultracold atoms of a noninteracting SPT band in a\none-dimensional optical lattice and study quench dynamics between topologically\ndistinct regimes. The observed SPT band can be protected by a magnetic group\nand a nonlocal chiral symmetry, with the band topology being measured via Bloch\nstates at symmetric momenta. The topology also resides in far-from-equilibrium\nspin dynamics, which are predicted and observed in experiment to exhibit\nqualitatively distinct behaviors in quenching to trivial and nontrivial\nregimes, revealing two fundamental types of spin-relaxation dynamics related to\nbulk topology. This work opens the way to expanding the scope of SPT physics\nwith ultracold atoms and studying nonequilibrium quantum dynamics in these\nexotic systems.",
        "positive": "Transient supersolid properties in an array of dipolar quantum droplets: We study theoretically and experimentally the emergence of supersolid\nproperties in a dipolar Bose-Einstein condensate. The theory reveals a ground\nstate phase diagram with three distinct regimes - a regular Bose-Einstein\ncondensate, incoherent and coherent arrays of quantum droplets. In the latter\nthe droplets are connected by a finite superfluid density, which leads - in\naddition to the periodic density modulation - to a robust phase coherence\nthroughout the whole system. We further theoretically demonstrate that we are\nable to dynamically approach the ground state in our experiment and that its\nlifetime is only limited by three-body losses. Experimentally we probe and\nconfirm the signatures of the phase diagram by observing the in-situ density\nmodulation as well as the phase coherence using matter wave interference."
    },
    {
        "anchor": "Mixtures of ultra-cold atoms in 1D disordered potentials: We study interacting 1D two-component mixtures of cold atoms in a random\npotential, and extend the results reported earlier [{\\it Phys. Rev. Lett.} {\\bf\n105}, 115301 (2010)]. We construct the phase diagram of a disordered Bose-Fermi\nmixture as a function of the strength of the Bose-Bose and Bose-Fermi\ninteractions, and the ratio of the bosonic sound velocity and the Fermi\nvelocity. Performing renormalization group and variational calculations, three\nphases are identified: (i) a fully delocalized two-component Luttinger liquid\nwith superfluid bosons and fermions (ii) a fully localized phase with both\ncomponents pinned by disorder, and (iii) an intermediate phase where fermions\nare localized but bosons are superfluid. Within the variational approach, each\nphase corresponds to a different level of replica symmetry breaking. In the\nfully localized phase we find that the bosonic and fermionic localization\nlengths can largely differ. We also compute the momentum distribution as well\nas the structure factor of the atoms (both experimentally accessible), and\ndiscuss how the three phases can be experimentally distinguished.",
        "positive": "Topological Euler class as a dynamical observable in optical lattices: The last years have witnessed rapid progress in the topological\ncharacterization of out-of-equilibrium systems. We report on robust signatures\nof a new type of topology -- the Euler class -- in such a dynamical setting.\nThe enigmatic invariant $(\\xi)$ falls outside conventional symmetry-eigenvalue\nindicated phases and, in simplest incarnation, is described by triples of bands\nthat comprise a gapless pair, featuring $2\\xi$ stable band nodes, and a gapped\nband. These nodes host non-Abelian charges and can be further undone by\nconverting their charge upon intricate braiding mechanisms, revealing that\nEuler class is a fragile topology. We theoretically demonstrate that quenching\nwith non-trivial Euler Hamiltonian results in stable monopole-antimonopole\npairs, which in turn induce a linking of momentum-time trajectories under the\nfirst Hopf map, making the invariant experimentally observable. Detailing\nexplicit tomography protocols in a variety of cold-atom setups, our results\nprovide a basis for exploring new topologies and their interplay with\ncrystalline symmetries in optical lattices beyond paradigmatic Chern\ninsulators."
    },
    {
        "anchor": "Generation and Decay of Two-Dimensional Quantum Turbulence in a Trapped\n  Bose-Einstein Condensate: In a recent experiment, Kwon et. al (arXiv:1403.4658 [cond-mat.quant-gas])\ngenerated a disordered state of quantum vortices by translating an oblate\nBose-Einstein condensate past a laser-induced obstacle and studying the\nsubsequent decay of vortex number. Using mean-field simulations of the\nGross-Pitaevskii equation, we shed light on the various stages of the observed\ndynamics. We find that the flow of the superfluid past the obstacle leads\ninitially to the formation of a classical-like wake, which later becomes\ndisordered. Following removal of the obstacle, the vortex number decays due to\nvortices annihilating and reaching the boundary. Our results are in excellent\nagreement with the experimental observations. Furthermore, we probe thermal\neffects through phenomenological dissipation.",
        "positive": "Theory of cold atoms: Bose-Einstein statistics: This Tutorial is the continuation of the previous tutorial part, published in\nLaser Phys. 23, 062001 (2013), where the basic mathematical techniques required\nfor an accurate description of cold atoms for both types of quantum statistics\nare expounded. In the present part, the specifics of the correct theoretical\ndescription of atoms obeying Bose-Einstein statistics are explained, including\ntrapped Bose atoms. In the theory of systems exhibiting the phenomenon of\nBose-Einstein condensation, there exists a number of delicate mathematical\npoints, whose misunderstanding often results in principally wrong conclusions.\nThis is why the consideration in the present Tutorial is sufficiently detailed\nin order that the reader could clearly understand the underlying mathematics\nand would avoid confusions."
    },
    {
        "anchor": "Manipulating multimer propagation using lattice modulation: We propose a scheme for controlling the movement of dimers, trimers, and\nother multimers in optical lattices by modulating the lattice potential. In\ndeep optical lattices the propagation of deeply bound atomic clusters is slowed\ndown by the high energy cost of virtual intermediate states. Adapting the\nwell-known method of lattice modulation spectroscopy, the movement of the\nclusters can be made resonant by utilizing sequences of bound-bound\ntransitions. Using the scheme, the mobility of each specific cluster can be\nselectively controlled by tuning the modulation frequency. We formulate a\nsimple and intuitive model and confirm the validity of the model by numerical\nsimulations of dimers and trimers in a one-dimensional optical lattice.",
        "positive": "Exact correlations in the Lieb-Liniger model and detailed balance\n  out-of-equilibrium: We study the density-density correlation function of the 1D Lieb-Liniger\nmodel and obtain an exact expression for the small momentum limit of the static\ncorrelator in the thermodynamic limit. We achieve this by summing exactly over\nthe relevant form factors of the density operator in the small momentum limit.\nThe result is valid for any eigenstate, including thermal and non-thermal\nstates. We also show that the small momentum limit of the dynamic structure\nfactors obeys a generalized detailed balance relation valid for any equilibrium\nstate."
    },
    {
        "anchor": "Longitudinal spin diffusion in a nondegenerate trapped $^{87}$Rb gas: Longitudinal spin diffusion of two pseudo-spin domains is studied in a\ntrapped $^{87}$Rb sample above quantum degeneracy, and the effect of coherence\nin the domain wall on the dynamics of the system is investigated. Coherence in\na domain wall leads to transverse-spin-mediated longitudinal spin diffusion\nthat is slower than classical predictions, as well as altering the domains'\noscillation frequency. The system also shows an instability in the longitudinal\nspin dynamics as longitudinal and transverse spin components couple, and a\nconversion of longitudinal spin to transverse spin is observed, resulting in an\nincrease in the total amount of coherence in the system.",
        "positive": "Floquet engineering from long-range to short-range interactions: Quantum simulators based on atoms or molecules often have long-range\ninteractions due to dipolar or Coulomb interactions. We present a method based\non Floquet engineering to turn a long-range interaction into a short-range one.\nBy modulating a magnetic-field gradient with one or a few frequencies, one\nreshapes the interaction profile, such that the system behaves as if it only\nhad nearest-neighbor interactions. Our approach works in both one and two\ndimensions and for both spin-1/2 and spin-1 systems. It does not require\nindividual addressing, and is applicable to all experimental systems with\nlong-range interactions: trapped ions, polar molecules, Rydberg atoms,\nnitrogen-vacancy centers, and cavity QED. Our approach allows one achieve a\nshort-range interaction without relying on Hubbard superexchange."
    },
    {
        "anchor": "Frequency combs with weakly lasing exciton-polariton condensates: We predict the spontaneous modulated emission from a pair of\nexciton-polariton condensates due to coherent (Josephson) and dissipative\ncoupling. We show that strong polariton-polariton inter- action generates\ncomplex dynamics in the weak-lasing domain way beyond Hopf bifurcations. As a\nresult, the exciton-polariton condensates exhibit self-induced oscillations and\nemit an equidistant frequency comb light spectrum. A plethora of possible\nemission spectra with asymmetric peak dis- tributions appears due to\nspontaneously broken time-reversal symmetry. The lasing dynamics is affected by\nthe shot noise arising from the influx of polaritons. That results in a complex\ninhomo- geneous line broadening.",
        "positive": "Tuning Feshbach resonance in cold atomic gases with inter-channel\n  coupling: We show that the essential properties of a Feshbach resonance in cold atomic\ngases can be tuned by dressing the atomic states in different scattering\nchannels through inter-channel couplings. Such a scheme can be readily\nimplemented in the orbital Feshbach resonance of alkaline-earth-like atoms by\ncoupling hyperfine states in the clock-state manifolds. Using $^{173}$Yb atoms\nas an example, we find that both the resonance position and the two-body\nbound-state energy depend sensitively on the inter-channel coupling strength,\nwhich offers control parameters in tuning the inter-atomic interactions. We\nalso demonstrate the dramatic impact of the dressed Feshbach resonance on\nmany-body processes such as the polaron to molecule transition and the BCS-BEC\ncrossover."
    },
    {
        "anchor": "Machine-learning enhanced dark soliton detection in Bose-Einstein\n  condensates: Most data in cold-atom experiments comes from images, the analysis of which\nis limited by our preconceptions of the patterns that could be present in the\ndata. We focus on the well-defined case of detecting dark solitons -- appearing\nas local density depletions in a Bose-Einstein condensate (BEC) -- using a\nmethodology that is extensible to the general task of pattern recognition in\nimages of cold atoms. Studying soliton dynamics over a wide range of parameters\nrequires the analysis of large datasets, making the existing\nhuman-inspection-based methodology a significant bottleneck. Here we describe\nan automated classification and positioning system for identifying localized\nexcitations in atomic BECs utilizing deep convolutional neural networks to\neliminate the need for human image examination. Furthermore, we openly publish\nour labeled dataset of dark solitons, the first of its kind, for further\nmachine learning research.",
        "positive": "Extended Bose-Hubbard model in a shaken optical lattice: We study an extended Bose-Hubbard model with next-nearest-neighbor (NNN)\nhopping in a shaken optical lattice. We show how mean-field phase diagram\nevolves with the change of NNN hopping amplitude $t_{2}$, which can be easily\ntuned via shaking amplitude. As $t_{2}$ increases, a $Z_{2}$-symmetry-breaking\nsuperfluid ($Z_{2}$SF) phase emerges at the bottom of the Mott lobs. The\ntricritical points between normal superfluid, $Z_{2}$SF, and Mott insulator\n(MI) phases are identified. We further demonstrate the tricritical point can be\ntuned to the tip of the Mott lobe, in which case a new critical behavior has\nbeen predicted. Within random-phase approximation, excitation spectra in the\nthree phases are obtained, which indicate how the phase transitions occur."
    },
    {
        "anchor": "Anomalous scaling at non-thermal fixed points of Burgers' and\n  Gross-Pitaevskii turbulence: Scaling in the dynamical properties of complex many-body systems has been of\nstrong interest since turbulence phenomena became the subject of systematic\nmathematical studies. In this article, dynamical critical phenomena far from\nequilibrium are investigated with functional renormalisation group equations.\nThe focus is set on scaling solutions of the stochastic driven-dissipative\nBurgers equation and their relation to solutions known in the literature for\nBurgers and Kardar-Parisi-Zhang dynamics. We furthermore relate superfluid as\nwell as acoustic turbulence described by the Gross-Pitaevskii model to known\nanalytic and numerical results for scaling solutions. In this way, the\ncanonical Kolmogorov exponent 5/3 for the energy cascade in superfluid\nturbulence is obtained analytically. We also get first results for anomalous\nexponents of acoustic and quantum turbulence. These are consistent with\nexisting experimental data. Our results should be relevant for future\nexperiments with, e.g., exciton-polariton condensates in solid-state systems as\nwell as with ultra-cold atomic gases.",
        "positive": "Luttinger theorem and imbalanced Fermi systems: The proof of the Luttinger theorem, which was originally given for a normal\nFermi liquid with equal spin populations formally described by the exact\nmany-body theory at zero temperature, is here extended to an approximate theory\ngiven in terms of a \"conserving\" approximation also with spin imbalanced\npopulations. The need for this extended proof, whose underlying assumptions are\nhere spelled out in detail, stems from the recent interest in superfluid\ntrapped Fermi atoms with attractive inter-particle interaction, for which the\ndifference between two spin populations can be made large enough that\nsuperfluidity is destroyed and the system remains normal even at zero\ntemperature. In this context, we will demonstrate the validity of the Luttinger\ntheorem separately for the two spin populations for any \"$\\Phi$-derivable\"\napproximation, and illustrate it in particular for the self-consistent\n$t$-matrix approximation."
    },
    {
        "anchor": "The Local Spin Structure of Large Spin Fermions: We show that large spin fermions have very rich spin structures. The local\nspin order of a spin-$f$ Fermi gas is a linear combination of $2f$\n(particle-hole) angular momentum states, $L=1,..,2f$. $L=1, 2$ represent\nferromagnetic and nematic spin order, while $L\\geq 3$ are higher spin orders\nthat has no analog in spin-1/2 systems. Each $L$ spin sector is characterized\nas $L$ pairs of antipodal points on a sphere. Model calculations show that some\nof these spin-orders have the symmetry of Platonic solid, and many of them have\nnon-abelian line defects.",
        "positive": "Homogeneous and inhomogeneous magnetic phases of constrained dipolar\n  bosons: We study the emergence of several magnetic phases in dipolar bosonic gases\nsubject to three-body loss mechanism employing numerical simulations based on\nthe density matrix renormalization group(DMRG) algorithm. After mapping the\noriginal Hamiltonian in spin language, we find a strong parallelism between the\nbosonic theory and the spin-1 Heisenberg model with single ion anisotropy and\nlong-range interactions. A rich phase diagram, including ferromagnetic,\nantiferromagnetic and non-local ordered phases, emerges in the half-filled\none-dimensional case, and is preserved even in presence of a trapping\npotential."
    },
    {
        "anchor": "Nonequilibrium dynamics of vortex arrest in a finite-temperature\n  Bose-Einstein condensate: We perform finite-temperature dynamical simulations of the arrest of a\nrotating Bose-Einstein condensate by a fixed trap anisotropy, using a\nHamiltonian classical-field method. We consider a quasi-two-dimensional\ncondensate containing a single vortex in equilibrium with a rotating thermal\ncloud. Introducing an elliptical deformation of the trapping potential leads to\nthe loss of angular momentum from the system. We identify the condensate and\nthe complementary thermal component of the nonequilibrium field, and compare\nthe evolution of their angular momenta and angular velocities. By varying the\ntrap anisotropy we alter the relative efficiencies of the vortex-cloud and\ncloud-trap coupling. For strong trap anisotropies the angular momentum of the\nthermal cloud may be entirely depleted before the vortex begins to decay. For\nweak trap anisotropies, the thermal cloud exhibits a long-lived steady state in\nwhich it rotates at an intermediate angular velocity.",
        "positive": "Spectroscopic Signatures for the Dark Bose-Einstein Condensation of\n  Spatially Indirect Excitons: We study semiconductor excitons confined in an electrostatic trap of a GaAs\nbilayer heterostructure. We evidence that optically bright excitonic states are\nstrongly depleted while cooling to sub-Kelvin temperatures. In return, the\nother accessible and optically dark states become macroscopically occupied so\nthat the overall exciton population in the trap is conserved. These combined\nbehaviours constitute the spectroscopic signature for the mostly dark\nBose-Einstein condensation of excitons, which in our experiments is restricted\nto a dilute regime within a narrow range of densities, below a critical\ntemperature of about 1K."
    },
    {
        "anchor": "Quantum simulation of non-trivial topology: We propose several designs to simulate quantum many-body systems in manifolds\nwith a non-trivial topology. The key idea is to create a synthetic lattice\ncombining real-space and internal degrees of freedom via a suitable use of\ninduced hoppings. The simplest example is the conversion of an open spin-ladder\ninto a closed spin-chain with arbitrary boundary conditions. Further\nexploitation of the idea leads to the conversion of open chains with internal\ndegrees of freedom into artificial tori and M\\\"obius strips of different kinds.\nWe show that in synthetic lattices the Hubbard model on sharp and scalable\nmanifolds with non-Euclidean topologies may be realized. We provide a few\nexamples of the effect that a change of topology can have on quantum systems\namenable to simulation, both at the single-particle and at the many-body level.",
        "positive": "Light-cone and diffusive propagation of correlations in a many-body\n  dissipative system: We analyze the propagation of correlations after a sudden interaction change\nin a strongly interacting quantum system in contact with an environment. In\nparticular, we consider an interaction quench in the Bose-Hubbard model, deep\nwithin the Mott-insulating phase, under the effect of dephasing. We observe\nthat dissipation effectively speeds up the propagation of single-particle\ncorrelations while reducing their coherence. In contrast, for two-point density\ncorrelations, the initial ballistic propagation regime gives way to diffusion\nat intermediate times. Numerical simulations, based on a time-dependent matrix\nproduct state algorithm, are supplemented by a quantitatively accurate\nfermionic quasi-particle approach providing an intuitive description of the\ninitial dynamics in terms of holon and doublon excitations."
    },
    {
        "anchor": "Topological transitions of interacting bosons in one-dimensional\n  bi-chromatic optical lattices: Ultra-cold atoms in 1D bi-chromatic lattices constitute a surprisingly simple\nsystem for the study of topological insulators. We show that topological phase\ntransitions constitute a general feature of bosons in 1D bi-chromatic lattices,\nand that these transitions may occur both as a function of the superlattice\nstrength and due to inter-site interactions. We discuss in addition the\ntopological character of incommensurate density wave phases in quasi-periodic\nlattices.",
        "positive": "Spin-incoherent one-dimensional spin-1 Bose Luttinger liquid: We investigate spin-incoherent Luttinger liquid of a one-dimensional spin-1\nBose gas in a harmonic trap. In this regime highly degenerate spin\nconfigurations emerge since the spin exchange energy is much less than the\nthermal energy of the system, while the temperature is low enough that the\nlowest energetic orbitals are occupied. As an example we numerically study the\nmomentum distribution of a one-dimensional spin-1 Bose gas in Tonks- Girardeau\ngas limit and in the sector of zero magnetization.We find that the momentum\ndistributions broaden as the number of atoms increase due to the averaging of\nspin function overlaps. Large momentum ($p$) asymptotic is analytically\nderived, showing the universal $1/p^4$ dependence. We demonstrate that the\nspin-incoherent Luttinger liquid has a momentum distribution also distinct from\nspinless bosons at finite temperature."
    },
    {
        "anchor": "Coherent ratchets in driven Bose-Einstein condensates: We study the response of a Bose-Einstein condensate to an unbiased periodic\ndriving potential. By controlling the space and time symmetries of the driving\nwe show how a directed current can be induced, producing a coherent quantum\nratchet. Weak driving induces a regular behavior that is strongly governed by\nthe interparticle interaction. Breaking both space and time symmetries is\nrequired to produce current flow. For strong driving the behavior becomes\nchaotic. The resulting effective irreversibility renders the space asymmetry\nsufficient to produce the ratchet effect, although the system is completely\ncoherent.",
        "positive": "Pump-and-probe optical transmission phase shift as a quantitative probe\n  of the Bogoliubov dispersion relation in a nonlinear channel waveguide: We theoretically investigate the dispersion relation of small-amplitude\noptical waves superimposing upon a beam of polarized monochromatic light\npropagating along a single-mode channel waveguide characterized by an\ninstantaneous and spatially local Kerr nonlinearity. These small luminous\nfluctuations propagate along the waveguide as Bogoliubov elementary excitations\non top of a one-dimensional dilute Bose quantum fluid evolve in time. They\nconsequently display a strongly renormalized dispersion law, of Bogoliubov\ntype. Analytical and numerical results are found in both the absence and the\npresence of one- and two-photon losses. Silicon and silicon-nitride waveguides\nare used as examples. We finally propose an experiment to measure this\nBogoliubov dispersion relation, based on a stimulated four-wave mixing and\ninterference spectroscopy techniques."
    },
    {
        "anchor": "Tailored particle current in an optical lattice by a weak time-symmetric\n  harmonic potential: Quantum ratchets exhibit asymptotic currents when driven by a time-periodic\npotential of zero mean if the proper spatio-temporal symmetries are broken.\nThere has been recent debate on whether directed currents may arise for\npotentials which do not break these symmetries. We show here that, in the\npresence of degeneracies in the quasienergy spectrum, long-lasting directed\ncurrents can be induced, even if the time reversal symmetry is not broken. Our\nmodel can be realized with ultracold atoms in optical lattices in the\ntight-binding regime, and we show that the time scale of the average current\ncan be controlled by extremely weak fields.",
        "positive": "Dynamics of spin-orbit coupled Bose-Einstein condensates in a random\n  potential: Disorder plays a crucial role in spin dynamics in solids and condensed matter\nsystems. We demonstrate that for a spin-orbit coupled Bose-Einstein condensate\nin a random potential two mechanisms of spin evolution, that can be\ncharacterized as \"precessional\" and \"anomalous\", are at work simultaneously.\nThe precessional mechanism, typical for solids, is due to the condensate\ndisplacement. The unconventional \"anomalous\" mechanism is due to the\nspin-dependent velocity producing the distribution of the condensate spin\npolarization. The condensate expansion is accompanied by a random displacement\nand fragmentation, where it becomes sparse, as clearly revealed in the spin\ndynamics. Thus, different stages of the evolution can be characterized by\nlooking at the condensate spin."
    },
    {
        "anchor": "Spontanous spin squezing in a rubidium BEC: We describe an experiment where spin squeezing occurs spontaneously within a\nstandard Ramsey sequence driving a two-component Bose-Einstein condensate (BEC)\nof 87Rb atoms trapped in an elongated magnetic trap. Multiparticle entanglement\nis generated by state-dependent collisional interactions, despite the\nnear-identical scattering lengths of the spin states in 87Rb. In our\nproof-of-principle experiment, we observe a metrological spin squeezing that\nreaches 1.3+/-0.4dB for 5000 atoms, with a contrast of 90+/-1%. The method may\nbe applied to realize spin-squeezed BEC sources for atom interferometry without\nthe need for cavities, state-dependent potentials or Feshbach resonances.",
        "positive": "Strongly interacting trapped one-dimensional quantum gases: an exact\n  solution: Quantum correlations can be used as a resource for quantum computing, eg for\nquantum state manipulation, and for quantum sensing, eg for creating\nnon-classical states which allow to achieve the quantum advantage regime. This\nreview collects the predictions coming from a family of exact solutions which\nallows to describe the many-body wavefunction of strongly correlated quantum\nfluids confined by a tight waveguide and subjected to any form of longitudinal\nconfinement. It directly describes the experiments with trapped ultracold atoms\nwhere the strongly correlated regime in one dimension has been achieved. The\nexact solution applies to bosons, fermions and mixtures. It allows to obtain\nexperimental observables such as the density profiles and momentum distribution\nat all momentum scales, beyond the Luttinger liquid approach. It also predicts\nthe exact quantum dynamics at all the times, including the small oscillations\nregime yielding the collective modes of the system and the large quench regime\nwhere the system parameters are changed considerably. The solution can be\nextended to describe finite-temperature conditions, spin and magnetization\neffects. The review illustrates the idea of the solution, presents the key\ntheoretical achievements and the main experiments on strongly correlated\none-dimensional quantum gases."
    },
    {
        "anchor": "Spin 1 condensates at thermal equilibrium : a $SU(3)$ coherent state\n  approach: We propose a theoretical framework based on $SU(3)$ coherent states as a\nconvenient tool to describe the collective state of a Bose-Einstein condensate\nof spin 1 atoms at thermal equilibrium. We work within the single-mode\napproximation, which assumes that all atoms condense in the same spatial mode.\nIn this system, the magnetization $m_z$ is conserved to a very good\napproximation. This conservation law is included by introducing a prior\ndistribution for $m_z$ and constructing a generalized statistical ensemble that\npreserves its first moments. In the limit of large particle numbers, we\nconstruct the partition function at thermal equilibrium and use it to compute\nvarious quantities of experimental interest, such as the probability\ndistribution function and moments of the population in each Zeeman state. When\n$N$ is large but finite (as in typical experiments, where $N\\sim 10^3-10^5$),\nwe find that fluctuations of the collective spin can be important.",
        "positive": "Momentum reconstruction and contact of the one-dimensional Bose-Fermi\n  mixture: We investigate the one-dimensional mixture of scalar bosons and spin\npolarized fermions interacting through a $\\delta$-function potential. Using a\nthermodynamic description derived by employing a lattice embedding of the\ncontinuum model and the quantum transfer matrix method we perform a detailed\nanalysis of the contact and quantum critical behaviour. We show that the\ncompressibility Wilson ratio presents anomalous enhancement at the quantum\ncritical points and that the boundaries of the quantum critical regions can be\nwell mapped by the maxima of the specific heat. As a function of the coupling\nstrength and temperature the contact presents nonmonotonic behavior. In the\nstrong coupling regime the local minimum exhibited by the contact as a function\nof temperature is accompanied by a significant momentum reconstruction at both\nlow and high momenta. This momentum reconstruction occurs as the system crosses\nthe boundary between the Tomonaga-Luttinger liquid phase to the spin-incoherent\nregime and provides an experimental signature of the transition."
    },
    {
        "anchor": "Superfluidity of Total Angular Momentum: Spontaneous symmetry breaking of a U(1) symmetry leads to superfluidity of a\ncorresponding conserved charge. We generalize the superfluidity to systems with\nU(1) symmetries acting on both matter fields and two-dimensional spatial\ncoordinates. Such systems can be effectively realized in easy-plane\nferromagnetic systems with spin-orbit coupling where the conserved charge is a\ntotal angular momentum. We clarify that under a steady injection of spin\nangular momentum, the superfluid of the total angular momentum shows spacetime\noscillations of the spin density and geometry-dependent spin hydrodynamics.\nThough a stability analysis shows that the superfluid under the spin injection\nis nonideal, the proposed spin transport persists with weak dissipation of the\nspin angular momentum. Our study broadens the comprehension of superfluidity\nand sheds new light on the interplay between symmetries and phases of matter.",
        "positive": "Soliton sheets formed by interference of Bose-Einstein condensates in\n  optical lattices: Soliton sheets which are formed by interference of Bose Einstein condensates\noccupying different single-particle states are observed in optical lattice\npotential. This structure consists of one-dimensional stationary solitons\narranged periodically along the peaks of optical lattice (y direction) with the\nphase difference between the two sides of the soliton sheets is a linear\nfunction of y in each period, so we call it soliton sheet. A y component\nvelocity difference exists between the two sides of the soliton sheet. Similar\nvelocity distributions can be produced by the alignment of an infinite number\nof isotropic vortices along the peaks of the optical lattice. Their difference\nis that the soliton sheet structure is not limited by the number of phase\nsingularities and can be generated even without phase singularities."
    },
    {
        "anchor": "Solvable model of a generic driven mixture of trapped Bose-Einstein\n  condensates and properties of a many-boson Floquet state at the limit of an\n  infinite number of particles: A solvable model of a periodically-driven trapped mixture of Bose-Einstein\ncondensates, consisting of $N_1$ interacting bosons of mass $m_1$ driven by a\nforce of amplitude $f_{L,1}$ and $N_2$ interacting bosons of mass $m_2$ driven\nby a force of amplitude $f_{L,2}$, is presented. The model generalizes the\nharmonic-interaction model for mixtures to the time-dependent domain. The\nresulting many-particle ground Floquet wavefunction and quasienergy, as well as\nthe time-dependent densities and reduced density matrices, are prescribed\nexplicitly and analyzed at the many-body and mean-field levels of theory for\nfinite systems and at the limit of an infinite number of particles. We prove\nthat the time-dependent densities per particle are given at the limit of an\ninfinite number of particles by their respective mean-field quantities, and\nthat the time-dependent reduced one-particle and two-particle density matrices\nper particle of the driven mixture are $100\\%$ condensed. Interestingly, the\nquasienergy per particle {\\it does not} coincide with the mean-field value at\nthis limit, unless the relative center-of-mass coordinate of the two\nBose-Einstein condensates is not activated by the driving forces $f_{L,1}$ and\n$f_{L,2}$. As an application, we investigate the imprinting of angular momentum\nand its fluctuations when steering a Bose-Einstein condensate by an interacting\nbosonic impurity, and the resulting modes of rotations. Whereas the expectation\nvalues per particle of the angular-momentum operator for the many-body and\nmean-field solutions coincide at the limit of an infinite number of particles,\nthe respective fluctuations can differ substantially. The results are analyzed\nin terms of the transformation properties of the angular-momentum operator\nunder translations and boosts and the interactions between the particles.\nImplications are briefly discussed.",
        "positive": "Convergence of a renormalization group approach to dimer-dimer\n  scattering: We study the convergence of a functional renormalisation group technique by\nlooking at the ratio between the fermion-fermion scattering length and the\ndimer-dimer scattering length for a system of nonrelativistic fermions. We find\nthat in a systematic expansion in powers of the fields there is a rapid\nconvergence of the result that agrees with know exact results."
    },
    {
        "anchor": "Geometry and non-adiabatic response in quantum and classical systems: In these lecture notes, partly based on a course taught at the Karpacz Winter\nSchool in March 2014, we explore the close connections between non-adiabatic\nresponse of a system with respect to macroscopic parameters and the geometry of\nquantum and classical states. We center our discussion around adiabatic gauge\npotentials, which are the generators of unitary basis transformations in\nquantum systems and generators of special canonical transformations in\nclassical systems. In quantum systems, eigenstate expectation values of these\npotentials are the Berry connections and the covariance matrix of these gauge\npotentials is the geometric tensor, whose antisymmetric part defines the Berry\ncurvature and whose symmetric part is the Fubini-Study metric tensor. In\nclassical systems one simply replaces the eigenstate expectation value by an\naverage over the micro-canonical shell. For complicated interacting systems, we\nshow that a variational principle may be used to derive approximate gauge\npotentials. We then express the non-adiabatic response of the physical\nobservables of the system through these gauge potentials, specifically\ndemonstrating the close connection of the geometric tensor to the notions of\nLorentz force and renormalized mass. We highlight applications of this\nformalism to deriving counter-diabatic (dissipationless) driving protocols in\nvarious systems, as well as to finding equations of motion for slow macroscopic\nparameters coupled to fast microscopic degrees of freedom that go beyond\nmacroscopic Hamiltonian dynamics. Finally, we illustrate these ideas with a\nnumber of simple examples and highlight a few more complicated ones drawn from\nrecent literature.",
        "positive": "Polarons and Molecules in a Two-Dimensional Fermi Gas: We study an impurity atom in a two-dimensional Fermi gas using variational\nwave functions for (i) an impurity dressed by particle-hole excitations\n(polaron) and (ii) a dimer consisting of the impurity and a majority atom. In\ncontrast to three dimensions, where similar calculations predict a sharp\ntransition to a dimer state with increasing interspecies attraction, we show\nthat the polaron ansatz always gives a lower energy. However, the exact\nsolution for a heavy impurity reveals that both a two-body bound state and\ndistortions of the Fermi sea are crucial. This reflects the importance of\nparticle-hole pairs in lower dimensions and makes simple variational\ncalculations unreliable. We show that the energy of an impurity gives important\ninformation about its dressing cloud, for which both ans\\\"atze give inaccurate\nresults."
    },
    {
        "anchor": "From weak to strong: constrained extrapolation of perturbation series\n  with applications to dilute Fermi systems: We develop a method that uses truncation-order-dependent re-expansions\nconstrained by generic strong-coupling information to extrapolate perturbation\nseries to the nonperturbative regime. The method is first benchmarked against a\nzero-dimensional model field theory and then applied to the dilute Fermi gas in\none and three dimensions. Overall, our method significantly outperforms Pad\\'e\nand Borel extrapolations in these examples. The results for the ground-state\nenergy of the three-dimensional Fermi gas are robust with respect to changes of\nthe form of the re-expansion and compare well with quantum Monte Carlo\nsimulations throughout the BCS regime and beyond.",
        "positive": "Formation and decay of Bose-Einstein condensates in an excited band of a\n  double-well optical lattice: We study the formation and collision-aided decay of an ultra-cold atomic\nBose-Einstein condensate in the first excited band of a double-well 2D-optical\nlattice with weak harmonic confinement in the perpendicular $z$ direction. This\nlattice geometry is based on an experiment by Wirth et al. The double well is\nasymmetric, with the local ground state in the shallow well nearly degenerate\nwith the first excited state of the adjacent deep well. We compare the band\nstructure obtained from a tight-binding (TB) model with that obtained\nnumerically using a plane wave basis. We find the TB model to be in\nquantitative agreement for the lowest two bands, qualitative for next two\nbands, and inadequate for even higher bands. The band widths of the excited\nbands are much larger than the harmonic oscillator energy spacing in the $z$\ndirection. We then study the thermodynamics of a non-interacting Bose gas in\nthe first excited band. We estimate the condensate fraction and critical\ntemperature, $T_c$, as functions of lattice parameters. For typical atom\nnumbers, the critical energy $k_BT_c$, with $k_B$ the Boltzmann constant, is\nlarger than the excited band widths and harmonic oscillator energy. Using\nconservation of total energy and atom number, we show that the temperature\nincreases after the lattice transformation. Finally, we estimate the time scale\nfor a two-body collision-aided decay of the condensate as a function of lattice\nparameters. The decay involves two processes, the dominant one in which both\ncolliding atoms decay to the ground band, and the second involving excitation\nof one atom to a higher band. For this estimate, we have used TB wave functions\nfor the lowest four bands, and numerical estimates for higher bands. The decay\nrate rapidly increases with lattice depth, but stays smaller than the tunneling\nrate between the $s$ and $p$ orbitals in adjacent wells."
    },
    {
        "anchor": "Efficient production of an 87Rb F = 2, mF = 2 Bose-Einstein condensate\n  in a hybrid trap: We have realized Bose-Einstein condensation (BEC) of 87Rb in the F=2, m_F=2\nhyperfine substate in a hybrid trap, consisting of a quadrupole magnetic field\nand a single optical dipole beam. The symmetry axis of the quadrupole magnetic\ntrap coincides with the optical beam axis, which gives stronger axial\nconfinement than previous hybrid traps. After loading 2x10^6 atoms at 14 muK\nfrom a quadrupole magnetic trap into the hybrid trap, we perform efficient\nforced evaporation and reach the onset of BEC at a temperature of 0.5 muK and\nwith 4x10^5 atoms. We also obtain thermal clouds of 1x10^6 atoms below 1 muK in\na pure single beam optical dipole trap, by ramping down the magnetic field\ngradient after evaporative cooling in the hybrid trap.",
        "positive": "Vortex-antivortex physics in shell-shaped Bose-Einstein condensates: Shell-shaped hollow Bose-Einstein condensates (BECs) exhibit behavior\ndistinct from their filled counterparts and have recently attracted attention\ndue to their potential realization in microgravity settings. Here we study\ndistinct features of these hollow structures stemming from vortex physics and\nthe presence of rotation. We focus on a vortex-antivortex pair as the simplest\nconfiguration allowed by the constraints on superfluid flow imposed by the\nclosed-surface topology. In the two-dimensional limit of an infinitesimally\nthin shell BEC, we characterize the long-range attraction between the\nvortex-antivortex pair and find the critical rotation speed that stabilizes the\npair against energetically relaxing towards self-annihilation. In the\nthree-dimensional case, we contrast the bounds on vortex stability with those\nin the two-dimensional limit and the filled sphere BEC, and evaluate the\ncritical rotation speed as a function of shell thickness. We thus demonstrate\nthat analyzing vortex stabilization provides a nondestructive means of\ncharacterizing a hollow sphere BEC and distinguishing it from its filled\ncounterpart."
    },
    {
        "anchor": "Finite resolution fluctuation measurements of a trapped Bose-Einstein\n  condensate: We consider the fluctuations in atom number that occur within finite-sized\nmeasurement cells in a trapped Bose-Einstein condensate (BEC). This\napproximates the fluctuation measurements made in current experiments with\nfinite resolution in situ imaging. A numerical scheme is developed to calculate\nthese fluctuations using the quasiparticle modes of a cylindrically symmetric\nthree-dimensionally trapped condensate with either contact or dipole-dipole\ninteractions (DDIs). We use this scheme to study the properties of a pancake\nshaped condensate using cylindrical cells. The extension of the theory to\nwasher shaped cells with azimuthal weighting is made and used to discriminate\nbetween the low energy roton modes in a dipolar condensate according to their\npro- jection of angular momentum. Our results are based on the Bogoliubov\napproach valid for zero and small finite temperatures.",
        "positive": "Chains with loops - synthetic magnetic fluxes and topological order in\n  one-dimensional spin systems: Engineering topological quantum order has become a major field of physics.\nMany advances have been made by synthesizing gauge fields in cold atomic\nsystems. Here, we carry over these developments to other platforms which are\nextremely well suited for quantum engineering, namely trapped ions and\nnano-trapped atoms. Since these systems are typically one-dimensional, the\naction of artificial magnetic fields has so far received little attention.\nHowever, exploiting the long-range nature of interactions, loops with\nnon-vanishing magnetic fluxes become possible even in one-dimensional settings.\nThis gives rise to intriguing phenomena, such as fractal energy spectra, flat\nbands with localized edge states, and topological many-body states. We\nelaborate on a simple scheme for generating the required artificial fluxes by\nperiodically driving an XY spin chain. Concrete estimates demonstrating the\nexperimental feasibility for trapped ions and atoms in waveguides are given."
    },
    {
        "anchor": "Many-body effects on second-order phase transitions in spinor\n  Bose-Einstein condensates and breathing dynamics: We unravel the correlation effects of the second-order quantum phase\ntransitions emerging on the ground state of a harmonically trapped spin-1 Bose\ngas, upon varying the involved Zeeman terms, as well as its breathing dynamics\ntriggered by quenching the trapping frequency. It is found that the boundaries\nof the associated magnetic phases are altered in the presence of interparticle\ncorrelations for both ferromagnetic and anti-ferromagnetic spin-spin\ninteractions, an effect which becomes more prominent in the few-body scenario.\nMost importantly, we unveil a correlation-induced shrinking of the\nanti-ferromagnetic and broken-axisymmetry phases implying that ground states\nwith bosons polarized in a single spin-component are favored. Turning to the\ndynamical response of the spinor gas it is shown that its breathing frequency\nis independent of the system parameters while correlations lead to the\nformation of filamentary patterns in the one-body density of the participating\ncomponents. The number of filaments is larger for increasing spin-independent\ninteraction strengths or for smaller particle numbers. Each filament maintains\nits coherence and exhibits an anti-correlated behavior while distinct filaments\nshow significant losses of coherence and are two-body correlated.\nInterestingly, we demonstrate that for an initial broken-axisymmetry phase an\nenhanced spin-flip dynamics takes place which can be tuned either via the\nlinear Zeeman term or the quench amplitude.",
        "positive": "Equilibration and GGE for hard wall boundary conditions: In this work we present an analysis of a quench for the repulsive\nLieb-Liniger gas confined to a large box with hard wall boundary conditions. We\nstudy the time average of local correlation functions and show that both the\nquench action approach and the GGE formalism are applicable for the long time\naverage of local correlation functions. We find that the time average of the\nsystem corresponds to an eigenstate of the Lieb-Liniger Hamiltonian and that\nthis eigenstate is related to an eigenstate of a Lieb-Liniger Hamiltonian with\nperiodic boundary conditions on an interval of twice the length and with twice\nas many particles (a doubled system). We further show that local operators with\nsupport far away from the boundaries of the hard wall have the same expectation\nvalues with respect to this eigenstate as corresponding operators for the\ndoubled system. We present an example of a quench where the gas is initially\nconfined in several moving traps and then released into a bigger container, an\napproximate description of the Newton cradle experiment. We calculate the time\naverage of various correlation functions for long times after the quench."
    },
    {
        "anchor": "Topologically protected boundary discrete time crystal for a solvable\n  model: Floquet time crystal, which breaks discrete time-translation symmetry, is an\nintriguing phenomenon in non-equilibrium systems. It is crucial to understand\nthe rigidity and robustness of discrete time crystal (DTC) phases in a\nmany-body system, and finding a precisely solvable model can pave a way for\nunderstanding of the DTC phase. Here, we propose and study a solvable spin\nchain model by mapping it to a Floquet superconductor through the Jordan-Wigner\ntransformation. The phase diagrams of Floquet topological systems are\ncharacterized by topological invariants and tell the existence of anomalous\nedge states. The sub-harmonic oscillation, which is the typical signal of the\nDTC, can be generated from such edge states and protected by topology. We also\nexamine the robustness of the DTC by adding symmetry-preserving and\nsymmetry-breaking perturbations. Our results on topologically protected DTC can\nprovide a deep understanding of the DTC when generalized to other interacting\nor dissipative systems.",
        "positive": "Counterflow and paired superfluidity in one-dimensional Bose mixtures in\n  optical lattices: We study the quantum phases of mixtures of ultra-cold bosonic atoms held in\nan optical lattice that confines motion or hopping to one spatial dimension.\nThe phases are found by using Tomonaga-Luttinger liquid theory as well as the\nnumerical method of time evolving block decimation (TEBD). We consider a binary\nmixture with repulsive intra-species interactions, and either repulsive or\nattractive inter-species interaction. For a homogeneous system, we find paired-\nand counterflow-superfluid phases at different filling and hopping energies. We\nalso predict parameter regions in which these types of superfluid order coexist\nwith charge density wave order. We show that the Tomonaga-Luttinger liquid\ntheory and TEBD qualitatively agree on the location of the phase boundary to\nsuperfluidity. We then describe how these phases are modified and can be\ndetected when an additional harmonic trap is present. In particular, we show\nhow experimentally measurable quantities, such as time-of-flight images and the\nstructure factor, can be used to distinguish the quantum phases. Finally, we\nsuggest applying a Feshbach ramp to detect the paired superfluid state, and a\n$\\pi/2$ pulse followed by Bragg spectroscopy to detect the counterflow\nsuperfluid phase."
    },
    {
        "anchor": "Oblique breathers generated by a flow of two-component Bose-Einstein\n  condensate past a polarized obstacle: We predict that oblique breathers can be generated by a flow of two-component\nBose-Einstein condensate past a polarized obstacle which attracts one component\nof the condensate and repels the other one. The breather exists if\nintra-species interaction constants differ from the inter-species interaction\nconstant and it corresponds to the nonlinear excitation of the so-called\npolarization mode with domination of the relative motion of the components.\nApproximate analytical theory is developed for the case of small-amplitude\nbreathers that is in reasonable agreement with the exact numerical results.",
        "positive": "A Full Configuration Interaction Perspective on the Homogeneous Electron\n  Gas: Highly accurate results for the homogeneous electron gas (HEG) have only been\nachieved to date within a diffusion Monte Carlo (DMC) framework. Here, we\nintroduce a newly developed stochastic technique, Full Configuration\nInteraction Quantum Monte Carlo (FCIQMC), which samples the exact wavefunction\nexpanded in plane wave Slater determinants. Despite the introduction of a basis\nset incompleteness error, we obtain a finite-basis energy which is\nsignificantly, and variationally lower than any previously published work for\nthe 54-electron HEG at $r_s$ = 0.5 a.u., in a Hilbert space of $10^{108}$\nSlater determinants. At this value of $r_s$, as well as of 1.0 a.u., we remove\nthe remaining basis set incompleteness error by extrapolation, yielding results\ncomparable or better than state-of-the-art DMC backflow energies. In doing so,\nwe demonstrate that it is possible to yield highly accurate results with the\nFCIQMC method in sizable periodic systems."
    },
    {
        "anchor": "Compacton matter waves in binary Bose gases under strong nonlinear\n  management: The existence of compacton matter waves in binary mixtures of quasi\none-dimensional Bose-Einstein condensates in deep optical lattices and in the\npresence of nonlinearity management, is first demonstrated. For this, we derive\nan averaged vector discrete nonlinear Schr\\\"odinger equation (DNLSE) and show\nthat compacton solutions of different types can exist as stable excitations.\nStability properties are studied by linear analysis and by direct numerical\nintegrations of the DNLSE system and their dependence on the inter- and\nintra-species scattering lengths, investigated. We show that under proper\nmanagement conditions, compactons can be very robust excitations that can\nemerge spontaneously from generic initial conditions. A possible experimental\nsetting for compacton observation is also discussed.",
        "positive": "Dominant fifth-order correlations in doped quantum anti-ferromagnets: Traditionally one and two-point correlation functions are used to\ncharacterize many-body systems. In strongly correlated quantum materials, such\nas the doped 2D Fermi-Hubbard system, these may no longer be sufficient because\nhigher-order correlations are crucial to understanding the character of the\nmany-body system and can be numerically dominant. Experimentally, such\nhigher-order correlations have recently become accessible in ultracold atom\nsystems. Here we reveal strong non-Gaussian correlations in doped quantum\nanti-ferromagnets and show that higher order correlations dominate over\nlower-order terms. We study a single mobile hole in the $t-J$ model using DMRG,\nand reveal genuine fifth-order correlations which are directly related to the\nmobility of the dopant. We contrast our results to predictions using models\nbased on doped quantum spin liquids which feature significantly reduced\nhigher-order correlations. Our predictions can be tested at the lowest\ncurrently accessible temperatures in quantum simulators of the 2D Fermi-Hubbard\nmodel. Finally, we propose to experimentally study the same fifth-order\nspin-charge correlations as a function of doping. This will help to reveal the\nmicroscopic nature of charge carriers in the most debated regime of the Hubbard\nmodel, relevant for understanding high-$T_c$ superconductivity."
    },
    {
        "anchor": "Dynamic high-resolution optical trapping of ultracold atoms: All light has structure, but only recently it has become possible to\nconstruct highly controllable and precise potentials so that most laboratories\ncan harness light for their specific applications. In this chapter, we review\nthe emerging techniques for high-resolution and configurable optical trapping\nof ultracold atoms. We focus on optical deflectors and spatial light modulators\nin the Fourier and direct imaging configurations. These optical techniques have\nenabled significant progress in studies of superfluid dynamics, single-atom\ntrapping, and underlie the emerging field of atomtronics. The chapter is\nintended as a complete guide to the experimentalist for understanding,\nselecting, and implementing the most appropriate optical trapping technology\nfor a given application. After introducing the basic theory of optical trapping\nand image formation, we describe each of the above technologies in detail,\nproviding a guide to the fundamental operation of optical deflectors, digital\nmicromirror devices, and liquid crystal spatial light modulators. We also\ndescribe the capabilities of these technologies for manipulation of trapped\nultracold atoms, where the potential is dynamically modified to enable\nexperiments, and where time-averaged potentials can realise more complex traps.\nThe key considerations when implementing time-averaged traps are described.",
        "positive": "Thermodynamics of spin-1/2 fermions on coarse temporal lattices using\n  automated algebra: Recent advances in automated algebra for dilute Fermi gases in the virial\nexpansion, where coarse temporal lattices were found advantageous, motivate the\nstudy of more general computational schemes that could be applied to arbitrary\ndensities, beyond the dilute limit where the virial expansion is physically\nreasonable. We propose here such an approach by developing what we call the\nQuantum Thermodynamics Computational Engine (QTCE). In QTCE, the imaginary-time\ndirection is discretized and the interaction is accounted for via a quantum\ncumulant expansion, where the coefficients are expressed in terms of\nnoninteracting expectation values. The aim of QTCE is to enable the systematic\nresolution of interaction effects at fixed temporal discretization, as in\nlattice Monte Carlo calculations, but here in an algebraic rather than\nnumerical fashion. Using this approach, in combination with numerical\nintegration techniques (both known and alternative ones proposed here), we\nexplore the thermodynamics of spin-1/2 fermions, focusing on the unitary limit\nin 3 spatial dimensions, but also exploring the effects of continuously varying\nthe spatial dimension below 3. We find that, remarkably, extremely coarse\ntemporal lattices, when suitably renormalized using known results from the\nvirial expansion, yield stable partial sums for QTCE's cumulant expansion which\nare qualitatively and quantitatively correct in wide regions, compared with\nknown experimental results."
    },
    {
        "anchor": "Creation of ultracold Sr2 molecules in the electronic ground state: We report on the creation of ultracold 84Sr2 molecules in the electronic\nground state. The molecules are formed from atom pairs on sites of an optical\nlattice using stimulated Raman adiabatic passage (STIRAP). We achieve a\ntransfer efficiency of 30% and obtain 4x10^4 molecules with full control over\nthe external and internal quantum state. STIRAP is performed near the narrow\n1S0-3P1 intercombination transition, using a vibrational level of the 0u\npotential as intermediate state. In preparation of our molecule association\nscheme, we have determined the binding energies of the last vibrational levels\nof the 0u, 1u excited-state, and the 1\\Sigma_g^+ ground-state potentials. Our\nwork overcomes the previous limitation of STIRAP schemes to systems with\nFeshbach resonances, thereby establishing a route that is applicable to many\nsystems beyond bi-alkalis.",
        "positive": "Period-doubled Bloch states in a Bose-Einstein condensate: We study systematically the period-doubled Bloch states for a weakly\ninteracting Bose-Einstein condensate in a one-dimensional optical lattice. This\nkind of state is of form $\\psi_k=e^{ikx}\\phi_k(x)$, where $\\phi_k(x)$ is of\nperiod twice the optical lattice constant. Our numerical results show how these\nnonlinear period-doubled states grow out of linear period-doubled states at a\nquarter away from the Brillouin zone center as the repulsive interatomic\ninteraction increases. This is corroborated by our analytical results. We find\nthat all nonlinear period-doubled Bloch states have both Landau instability and\ndynamical instability."
    },
    {
        "anchor": "Dipolar Drag in Bilayer Harmonically Trapped Gases: We consider two separated pancake-shaped trapped gases interacting with a\ndipolar (either magnetic or electric) force. We study how the center of mass\nmotion propagates from one cloud to the other as a consequence of the\nlong-range nature of the interaction. The corresponding dynamics is fixed by\nthe frequency difference between the in-phase and the out-of-phase center of\nmass modes of the two clouds, whose dependence on the dipolar interaction\nstrength and the cloud separation is explicitly investigated. We discuss Fermi\ngases in the degenerate as well as in the classical limit and comment on the\ncase of Bose-Einsten condensed gases.",
        "positive": "Non-equilibrium quantum dynamics and formation of the Bose polaron: Advancing our understanding of non-equilibrium phenomena in quantum many-body\nsystems remains among the greatest challenges in physics. Here, we report on\nthe experimental observation of a paradigmatic many-body problem, namely the\nnon-equilibrium dynamics of a quantum impurity immersed in a bosonic\nenvironment. We use an interferometric technique to prepare coherent\nsuperposition states of atoms in a Bose-Einstein condensate with a small\nimpurity-state component, and monitor the evolution of such quantum\nsuperpositions into polaronic quasiparticles. These results offer a systematic\npicture of polaron formation from weak to strong impurity interactions. They\nreveal three distinct regimes of evolution with dynamical transitions that\nprovide a link between few-body processes and many-body dynamics. Our\nmeasurements reveal universal dynamical behavior in interacting many-body\nsystems and demonstrate new pathways to study non-equilibrium quantum\nphenomena."
    },
    {
        "anchor": "Eightfold way to dark states in SU(3) cold gases with two-body losses: We study the quantum dynamics of a one-dimensional SU(3)-symmetric system of\ncold atoms in the presence of two-body losses. We exploit the representation\ntheory of SU(3), the so-called eightfold way, as a scheme to organize the dark\nstates of the dissipative dynamics in terms of generalized Dicke states and\nshow how they are dynamically approached, both in the weakly- and and\nstrongly-interacting and dissipative regimes. Our results are relevant for a\nwide class of alkaline-earth(-like) gases experiments, paving the way to the\ndissipative preparation and exploitation of generalized Dicke states.",
        "positive": "Zero Dimensional Polariton Laser in a Sub-Wavelength Grating Based\n  Vertical Microcavity: Semiconductor exciton-polaritons in planar microcavities form coherent\ntwo-dimensional condensates in non-equilibrium. However, coupling of multiple\nlower-dimensional polariton quantum systems, critically needed for polaritonic\nquantum device applications and novel cavity-lattice physics, has been limited\ndue to the conventional cavity structures. Here we demonstrate full confinement\nof the polaritons non-destructively using a hybrid cavity made of a\nsingle-layer sub-wavelength grating mirror and a distributed Bragg reflector.\nSingle-mode polariton lasing was observed at a chosen polarization.\nIncorporation of a designable slab mirror into the conventional vertical\ncavity, when operating in the strong-coupling regime, enables confinement,\ncontrol and coupling of polariton gasses in a scalable fashion. It may open a\ndoor to experimental implementation of polariton-based quantum photonic devices\nand coupled cavity quantum electrodynamics systems."
    },
    {
        "anchor": "Equation of State of Ultracold Fermions in the 2D BEC-BCS Crossover\n  Region: We report the experimental measurement of the equation of state of a\ntwo-dimensional Fermi gas with attractive s-wave interactions throughout the\ncrossover from a weakly coupled Fermi gas to a Bose gas of tightly bound dimers\nas the interaction strength is varied. We demonstrate that interactions lead to\na renormalization of the density of the Fermi gas by several orders of\nmagnitude. We compare our data near the ground state and at finite temperature\nto predictions for both fermions and bosons from Quantum Monte Carlo\nsimulations and Luttinger-Ward theory. Our results serve as input for\ninvestigations of close-to-equilibrium dynamics and transport in the\ntwo-dimensional system.",
        "positive": "Taming the snake instabilities in a polariton superfluid: The dark solitons observed in a large variety of nonlinear media are unstable\nagainst the modulational (snake) instabilities and can break in vortex streets.\nThis behavior has been investigated in nonlinear optical crystals and ultracold\natomic gases. However, a deep characterization of this phenomenon is still\nmissing. In a resonantly pumped 2D polariton superfluid, we use an all-optical\nimprinting technique together with the bistability of the polariton system to\ncreate dark solitons in confined channels. Due to the snake instabilities, the\nsolitons are unstable and break in arrays of vortex streets whose dynamical\nevolution is frozen by the pump-induced confining potential, allowing their\ndirect observation in our system. A deep quantitative study shows that the\nvortex street period is proportional to the quantum fluid healing length, in\nagreement with the theoretical predictions. Finally, the full control achieved\non the soliton patterns is exploited to give a proof of principle of an\nefficient, ultra-fast, analog, all-optical maze solving machine in this\nphotonic platform."
    },
    {
        "anchor": "Two-dimensional quantum droplets in binary quadrupolar condensates: We study the stability and characteristics of two-dimensional (2D)\nquasi-isotropic quantum droplets (QDs) of fundamental and vortex types, formed\nby binary Bose-Einstein condensate with magnetic quadrupole-quadrupole\ninteractions (MQQIs). The magnetic quadrupoles are built as pairs of dipoles\nand antidipoles polarized along the x-axis. The MQQIs are induced by applying\nan external magnetic field that varies along the x-axis. The system is modeled\nby the Gross-Pitaevskii equations including the MQQIs and Lee-Huang-Yang\ncorrection to the mean-field approximation. Stable 2D fundamental QDs and\nquasi-isotropic vortex QDs with topological charges S<4 are produced by means\nof the imaginary-time-integration method for configurations with the\nquadrupoles polarized parallel to the systems two-dimensional plane. Effects of\nthe norm and MQQI strength on the QDs are studied in detail. Some results,\nincluding an accurate prediction of the effective area, chemical potential, and\npeak density of QDs, are obtained in an analytical form by means of the\nThomas-Fermi approximation. Collisions between moving QDs are studied by means\nof systematic simulations.",
        "positive": "Baryon squishing in synthetic dimensions by effective $SU(M)$ gauge\n  fields: We investigate few body physics in a cold atomic system with synthetic\ndimensions (Celi et al., PRL 112, 043001 (2014)) which realizes a Hofstadter\nmodel with long-ranged interactions along the synthetic dimension. We show that\nthe problem can be mapped to a system of particles (with $SU(M)$ symmetric\ninteractions) which experience an $SU(M)$ Zeeman field at each lattice site\n{\\em and} a non-Abelian $SU(M)$ gauge potential that affects their hopping from\none site to another. This mapping brings out the possibility of generating {\\em\nnon-local} interactions (interaction between particles at different physical\nsites). It also shows that the non-Abelian gauge field, which induces a\nflavor-orbital coupling, mitigates the \"baryon breaking\" effects of the Zeeman\nfield. For $M$ particles, the $SU(M)$ singlet baryon which is site localized,\nis \"deformed\" to be a nonlocal object (\"squished\" baryon) by the combination of\nthe Zeeman and the non-Abelian gauge potential, an effect that we conclusively\ndemonstrate by analytical arguments and exact (numerical) diagonalization\nstudies. These results not only promise a rich phase diagram in the many body\nsetting, but also suggests possibility of using cold atom systems to address\nproblems that are inconceivable in traditional condensed matter systems. As an\nexample, we show that the system can be adapted to realize Hamiltonians akin to\nthe $SU(M)$ random flux model."
    },
    {
        "anchor": "Kolmogorov-Hinze scales in turbulent superfluids: When a two-component mixture of immiscible fluids is stirred, the fluids are\nsplit into smaller domains with more vigorous stirring. We numerically\ninvestigate the sizes of such domains in a fully-developed turbulent state of a\ntwo-component superfluid stirred with energy input rate $\\epsilon$. For the\nstrongly immiscible condition, the typical domain size is shown to be\nproportional to $\\epsilon^{-2/5}$, as predicted by the Kolmogorov-Hinze theory\nin classical fluids. For the weakly immiscible condition, quantum effects\nbecome pronounced and the power changes from $-2 / 5$ to $-1 / 4$.",
        "positive": "Instability and Vortex Rings Dynamics in a Three-Dimensional Superfluid\n  Flow Through a Constriction: We study the instability of a superfluid flow through a constriction in three\nspatial dimensions. We consider a Bose-Einstein condensate at zero temperature\nin two different geometries: a straight waveguide and a torus. The constriction\nconsists of a broad, repulsive penetrable barrier. In the hydrodynamic regime,\nwe find that the flow becomes unstable as soon as the velocity at the classical\n(Thomas-Fermi) surface equals the sound speed inside the constriction. At this\ncritical point, vortex rings enter inside the bulk region of the cloud. The\nnucleation and dynamics scenario is strongly affected by the presence of\nasymmetries in the velocity and density of the background condensate flow."
    },
    {
        "anchor": "Transient ordering in the Gross-Pitaevskii lattice subject to an energy\n  quench within the disordered phase: We numerically investigate heating-and-cooling quenches taking place entirely\nin the non-ordered phase of the discrete Gross-Pitaevskii equation on a\nthree-dimensional cubic lattice. In equilibrium, this system exhibits a\nU(1)-ordering phase transition at an energy density which is significantly\nlower than the minimum one during the quench. Yet, we observe that the\npost-quench relaxation is accompanied by a transient U(1) ordering, namely, the\ncorrelation length of U(1) fluctuations significantly exceeds its equilibrium\npre-quench value. The longer and the stronger the heating stage of the quench,\nthe stronger the U(1) transient ordering. We identify the origin of this\nordering with the emergence of a small group of slowly relaxing lattice sites\naccumulating a large fraction of the total energy of the system. Our findings\nsuggest that the transient ordering may be a robust feature of a broad class of\nphysical systems. This premise is consistent with the growing experimental\nevidence of the transient U(1) order in rather dissimilar settings.",
        "positive": "Dynamical Quantum Phase Transitions in Spin Chains with Long-Range\n  Interactions: Merging different concepts of non-equilibrium criticality: We theoretically study the dynamics of a transverse-field Ising chain with\npower-law decaying interactions characterized by an exponent $\\alpha$, which\ncan be experimentally realized in ion traps. We focus on two classes of\nemergent dynamical critical phenomena following a quantum quench from a\nferromagnetic initial state: The first one manifests in the time averaged order\nparameter, which vanishes at a critical transverse field. We argue that such a\ntransition occurs only for long-range interactions $\\alpha \\leq 2$ . The second\nclass corresponds to the emergence of time-periodic singularities in the return\nprobability to the ground state manifold (a.k.a. Loschmidt echo) which is\nobtained for all values of $\\alpha$ and agrees with the order parameter\ntransition for $\\alpha\\leq 2$. We characterize how the two classes of\nnonequilibrium criticality correspond to each other and give a physical\ninterpretation based on the symmetry of the time-evolved quantum states."
    },
    {
        "anchor": "Universal dynamics and non-thermal fixed points in quantum fluids far\n  from equilibrium: Closed quantum systems far from thermal equilibrium can show universal\ndynamics near attractor solutions, known as non-thermal fixed points,\ngenerically in the form of scaling behavior in space and time. A systematic\nclassification and comprehensive understanding of such scaling solutions are\ntasks of future developments in non-equilibrium quantum many-body theory. In\nthis tutorial review, we outline several analytical approaches to non-thermal\nfixed points and summarize corresponding numerical and experimental results.\nThe analytic methods include a non-perturbative kinetic theory derived within\nthe two-particle irreducible effective-action formalism, as well as a\nlow-energy effective field theory framework. As one of the driving forces of\nthis research field are numerical simulations, we summarize the main results of\nexemplary cases of universal dynamics in ultracold Bose gases. This encompasses\nquantum vortex ensembles in turbulent superfluids as well as recently observed\nreal-time instanton solutions in one-dimensional spinor condensates.",
        "positive": "Room-temperature superfluidity in a polariton condensate: Superfluidity---the suppression of scattering in a quantum fluid at\nvelocities below a critical value---is one of the most striking manifestations\nof the collective behaviour typical of Bose-Einstein condensates. This\nphenomenon, akin to superconductivity in metals, has until now only been\nobserved at prohibitively low cryogenic temperatures. For atoms, this limit is\nimposed by the small thermal de Broglie wavelength, which is inversely related\nto the particle mass. Even in the case of ultralight quasiparticles such as\nexciton-polaritons, superfluidity has only been demonstrated at liquid helium\ntemperatures. In this case, the limit is not imposed by the mass, but instead\nby the small exciton binding energy of Wannier-Mott excitons, which places the\nupper temperature limit. Here we demonstrate a transition from normal to\nsuperfluid flow in an organic microcavity supporting stable Frenkel\nexciton-polaritons at room temperature. This result paves the way not only to\ntable-top studies of quantum hydrodynamics, but also to room-temperature\npolariton devices that can be robustly protected from scattering."
    },
    {
        "anchor": "Feedback cooled Bose-Einstein condensation: near and far from\n  equilibrium: Continuously measured interacting quantum systems almost invariably heat,\ncausing loss of quantum coherence. Here, we study Bose-Einstein condensates\n(BECs) subject to repeated weak measurement of the atomic density and describe\nseveral protocols for generating a feedback signal designed to remove\nexcitations created by measurement backaction. We use a stochastic\nGross-Pitaevskii equation to model the system dynamics and find that a feedback\nprotocol utilizing momentum dependant gain and filtering can effectively cool\nboth 1D and 2D systems. The performance of these protocols is quantified in\nterms of the steady state energy, entropy, and condensed fraction. These are\nthe first feedback cooling protocols demonstrated in 2D, and in 1D our optimal\nprotocol reduces the equilibrium energy by more than a factor of 100 as\ncompared with a previous cooling protocol developed using the same methodology.\nWe also use this protocol to quench-cool 1D BECs from non-condensed highly\nexcited states and find that they rapidly condense into a far from equilibrium\nstate with energy orders of magnitude higher than the equilibrium ground state\nenergy for that condensate fraction. We explain this in terms of the\nnear-integrability of our 1D system, whereby efficiently cooled low momentum\nmodes are effectively decoupled from the energetic `reservoir' of the higher\nmomentum modes. We observe that the quench-cooled condensed states can have\nnon-zero integer winding numbers described by quantized supercurrents.",
        "positive": "Quantum tri-criticality and phase transitions in spin-orbit coupled\n  Bose-Einstein condensates: We consider a spin-orbit coupled configuration of spin-1/2 interacting bosons\nwith equal Rashba and Dresselhaus couplings. The phase diagram of the system is\ndiscussed with special emphasis to the role of the interaction treated in the\nmean-field approximation. For a critical value of the density and of the Raman\ncoupling we predict the occurrence of a characteristic tri-critical point\nseparating the spin mixed, the phase separated and the single minimum states of\nthe Bose gas. The corresponding quantum phases are investigated analyzing the\nmomentum distribution, the longitudinal and transverse spin-polarization and\nthe emergence of density fringes. The effect of harmonic trapping as well as\nthe role of the breaking of spin symmetry in the interaction Hamiltonian are\nalso discussed."
    },
    {
        "anchor": "Thermalisation of a two-dimensional photonic gas in a 'white-wall'\n  photon box: Bose-Einstein condensation, the macroscopic accumulation of bosonic particles\nin the energetic ground state below a critical temperature, has been\ndemonstrated in several physical systems. The perhaps best known example of a\nbosonic gas, blackbody radiation, however exhibits no Bose-Einstein\ncondensation at low temperatures. Instead of collectively occupying the lowest\nenergy mode, the photons disappear in the cavity walls when the temperature is\nlowered - corresponding to a vanishing chemical potential. Here we report on\nevidence for a thermalised two-dimensional photon gas with freely adjustable\nchemical potential. Our experiment is based on a dye filled optical\nmicroresonator, acting as a 'white-wall' box for photons. Thermalisation is\nachieved in a photon number-conserving way by photon scattering off the\ndye-molecules, and the cavity mirrors both provide an effective photon mass and\na confining potential - key prerequisites for the Bose-Einstein condensation of\nphotons. As a striking example for the unusual system properties, we\ndemonstrate a yet unobserved light concentration effect into the centre of the\nconfining potential, an effect with prospects for increasing the efficiency of\ndiffuse solar light collection.",
        "positive": "Non-equilibrium dynamics of the anyonic Tonks-Girardeau gas at finite\n  temperature: We derive an exact description of the non-equilibrium dynamics at finite\ntemperature for the anyonic Tonks-Girardeau gas extending the results of Atas\net al. [Phys. Rev. A 95, 043622 (2017)] to the case of arbitrary statistics.\nThe one-particle reduced density matrix is expressed as the Fredholm minor of\nan integral operator with the kernel being the one-particle Green's function of\nfree fermions at finite temperature and the statistics parameter determining\nthe constant in front of the integral operator. We show that the numerical\nevaluation of this representation using Nystr\\\"{o}m's method significantly\noutperforms the other approaches present in the literature when there are no\nanalytical expressions for the overlaps of the wave-functions. We illustrate\nthe distinctive features and novel phenomena present in the dynamics of anyonic\nsystems in two experimentally relevant scenarios: the quantum Newton's cradle\nsetting and the breathing oscillations initiated by a sudden change of the trap\nfrequency."
    },
    {
        "anchor": "Anisotropic pair-superfluidity of trapped two-component Bose gases: We theoretically investigate the pair-superfluid phase of two-component\nultracold gases with negative inter-species interactions in an optical lattice.\nWe establish the phase diagram for filling $n=1$ at zero and finite\ntemperature, by applying Bosonic Dynamical Mean-Field Theory, and confirm the\nstability of pair-superfluidity for asymmetric hopping of the two species.\nWhile the pair superfluid is found to be robust in the presence of a harmonic\ntrap, we observe that it is destroyed already by a small population imbalance\nof the two species.",
        "positive": "Thermodynamics of noninteracting bosonic gases in cubic optical lattices\n  versus ideal homogeneous Bose gases: We have studied thermodynamic properties of noninteracting gases in periodic\nlattice potential at arbitrary integer fillings and compared them with that of\nideal homogeneous gases. Deriving explicit expressions for thermodynamic\nquantities and performing exact numerical calculations we have found that the\ndependence of e.g. entropy and energy on the temperature in the normal phase is\nrather weak. In the Bose condensed phase their power dependence on the reduced\ntemperature is nearly linear, which is in contrast to that of ideal homogeneous\ngases. We evaluated the discontinuity in the slope of the specific heat which\nturned out to be approximately the same as that of the ideal homogeneous Bose\ngas for filling factor $\\nu=1$. With increasing $\\nu$ it decreases as the\ninverse of $\\nu$. These results may serve as a checkpoint for various\nexperiments on optical lattices as well as theoretical studies of weakly\ninteracting Bose systems in periodic potentials being a starting point for\nperturbative calculations."
    },
    {
        "anchor": "Universal high-momentum asymptote and thermodynamic relations in a\n  spinless Fermi gas with a resonant $p$-wave interaction: We investigate universal relations in a spinless Fermi gas near a $p$-wave\nFeshbach resonance. We show that the momentum distribution $n_{\\vec{k}}$ has an\nasymptote proportional to $k^{-2}$ with the proportionality constant--the\n$p$-wave contact-- scaling with the number of closed-channel molecules. We\nprove the adiabatic sweep theorem for a $p$-wave resonance which reveals the\nphysical meaning of the $p$-wave contact in thermodynamics. In contrast to the\nunitary Fermi gas in which Tan's contact is universal, the $p$-wave contact\ndepends on the short-range details of the interaction.",
        "positive": "Short-distance and short-time structure of a unitary Fermi gas: We consider the operator product expansions for unitarity fermions. We\ncompute the dynamic structure factor S(q,w) at large frequency and wavenumber\naway from the one-particle peak. The overall normalization of S(q,w) is\ndetermined by Tan's contact parameter, and the dependence on q and w is\nobtained in closed analytic form. We also find energy deposited into the system\nby small, rapid variations of the inverse scattering length."
    },
    {
        "anchor": "ac Stark shift and multiphoton-like resonances in low-frequency driven\n  optical lattices: We suggest that Bose-Einstein condensates in optical lattices subjected to ac\nforcing with a smooth envelope may provide detailed experimental access to\nmultiphoton-like transitions between ac-Stark-shifted Bloch bands. Such\ntransitions correspond to resonances described theoretically by avoided\nquasienergy crossings. We show that the width of such anticrossings can be\ninferred from measurements involving asymmetric pulses. We also introduce a\npulse tracking strategy for locating the particular driving amplitudes for\nwhich resonances occur. Our numerical calculations refer to a currently\nexisting experimental set-up [Haller et al., PRL 104, 200403 (2010)].",
        "positive": "Supersolid in a one-dimensional model of hard-core bosons: We study a system of hardcore boson on a one-dimensional lattice with\nfrustrated next-nearest neighbor hopping and nearest neighbor interaction. At\nhalf filling, for equal magnitude of nearest and next-nearest neighbor hopping,\nthe ground state of this system exhibits a first order phase transition from a\nBond-Ordered (BO) solid to a Charge-Density-Wave(CDW) solid as a function of\nthe nearest neighbor interaction. Moving away from half filling we investigate\nthe system at incommensurate densities, where we find a SuperSolid (SS) phase\nwhich has concurrent off-diagonal long range order and density wave order which\nis unusual in a system of hardcore bosons in one dimension. Using the\nfinite-size Density-Matrix Renormalization Group (DMRG) method, we obtain the\ncomplete phase diagram for this model."
    },
    {
        "anchor": "Spectroscopic measurement of the excitation spectrum on effectively\n  curved spacetimes in a polaritonic fluid of light: Quantum fields in regions of extreme spacetime curvature give rise to a\nwealth of effects, like Hawking radiation at the horizon of black holes. While\nquantum field theory can only be studied theoretically in black holes, it can\nbe tested in controlled laboratory experiments. Typically, a fluid accelerating\nfrom sub- to supersonic speed will create an effectively curved spacetime for\nthe acoustic field, with an apparent horizon where the speed of the fluid\nequals the speed of sound. Here we create effective curved spacetimes with a\nquantum fluid of light, with smooth and steep acoustic horizons and various\nsupersonic fluid speeds. We use a recently developed spectroscopy method to\nmeasure the spectrum of acoustic excitations on these spacetimes, thus\nobserving negative energy modes in the supersonic regions. This demonstrates\nthe potential of quantum fluids of light for the study of field theories on\ncurved spacetimes.",
        "positive": "Chiral spin superfluidity and spontaneous spin Hall effect of\n  interacting bosons: Recent experiments on ultracold atoms in optical lattices have synthesized a\nvariety of tunable bands with degenerate double-well structures in momentum\nspace. Such degeneracies in the single particle spectrum strongly enhance\nquantum fluctuations, and may lead to exotic many-body ground states. Here we\nconsider weakly interacting spinor Bose gases in such bands, and discover a\nuniversal quantum \"order by disorder\" phenomenon which selects a novel chiral\nspin superfluid with remarkable properties such as spontaneous anomalous spin\nHall effect and momentum space antiferromagnetism. For bosons in the excited\nDirac band of a hexagonal lattice, such a state supports staggered spin loop\ncurrents in real space. We show that Bloch oscillations provide a powerful\ndynamical route to quantum state preparation of such a chiral spin superfluid.\nOur predictions can be readily tested in spin resolved time-of-flight\nexperiments."
    },
    {
        "anchor": "Low-density molecular gas of tightly-bound Rashba-Dresselhaus fermions: We study interacting Rashba-Dresselhaus fermions in two spatial dimensions.\nFirst, we present a new exact solution to the two-particle pairing problem of\nspin-orbit-coupled fermions for arbitrary Rashba and Dresselhaus spin-orbit\ninteractions. An exact molecular wave function and the Green function are\nexplicitly derived along with the binding energy and the spectrum of the\nmolecular state. In the second part, we consider a thermal Boltzmann gas of\nfermionic molecules and compute the time-of-flight velocity and spin\ndistributions for a single fermion in the gas. We show that the pairing\nsignatures can be observed already in the first-moment expectation values, such\nas time-of-flight density and spin profiles.",
        "positive": "Quantum dark solitons in ultracold one-dimensional Bose and Fermi gases: Solitons are ubiquitous phenomena that appear, among others, in the\ndescription of tsunami waves, fiber-optic communication and ultracold atomic\ngases. The latter systems turned out to be an excellent playground for\ninvestigations of matter-wave solitons in a quantum world. This Tutorial\nprovides a general overview of the ultracold contact interacting Bose and Fermi\nsystems in a one-dimensional space that can be described by the renowned\nLieb-Liniger and Yang-Gaudin models. Both the quantum many-body systems are\nexactly solvable by means of the Bethe ansatz technique, granting us a\npossibility for investigations of quantum nature of solitonic excitations. We\ndiscuss in details a specific class of quantum many-body excited eigenstates\ncalled yrast states and show that they are strictly related to quantum dark\nsolitons in the both considered Bose and Fermi systems."
    },
    {
        "anchor": "Non-destructive monitoring of Bloch oscillations in an optical cavity: Bloch oscillations are a hallmark of coherent wave dynamics in periodic\npotentials. They occur as the response of quantum mechanical particles in a\nlattice if a weak force is applied. In optical lattices with their perfect\nperiodic structure they can be readily observed and employed as a quantum\nmechanical force sensor, for example, for precise measurements of the\ngravitational acceleration. However, the destructive character of the\nmeasurement process in previous experimental implementations poses serious\nlimitations for the precision of such measurements. In this article we show\nthat the use of an optical cavity operating in the regime of strong cooperative\ncoupling allows one to directly monitor Bloch oscillations of a cloud of cold\natoms in the light leaking out of the cavity. Hence, with a single atomic\nsample the Bloch oscillation dynamics can be mapped out, while in previous\nexperiments, each data point required the preparation of a new atom cloud. The\nuse of a cavity-based monitor should greatly improve the precision of Bloch\noscillation measurements for metrological purposes.",
        "positive": "Semi-vortex solitons and their excited states in spin-orbit-coupled\n  binary bosonic condensates: It is known that two-dimensional two-component fundamental solitons of the\nsemi-vortex (SV) type, with vorticities $(s_{+},s_{-})=(0,1)$ in their\ncomponents, are stable ground states (GSs) in the spin-orbit-coupled (SOC)\nbinary Bose-Einstein condensate with the contact self-attraction acting in both\ncomponents, in spite of the possibility of the critical collapse in the system.\nHowever, excited states(ESs) of the SV solitons, with the vorticity set\n$(s_{+},s_{-})=( S_{+},S_{+}+1)$ and $S_{+}=1,2,3,...$, are unstable in the\nsame system. We construct ESs of SV solitons in the SOC system with opposite\nsigns of the self-interaction in the two components. The main finding is\nstability of the ES-SV solitons, with the extra vorticity (at least) up to\n$S_{+}=6$. The threshold value of the norm for the onset of the critical\ncollapse, $N_{\\mathrm{thr}}$, in these excited states is higher than the\ncommonly known critical value, $N_{c}\\approx 5.85$,associated with the\nsingle-component Townes solitons, $N_{\\mathrm{thr}}$ increasing with the growth\nof $S_{+}$. A velocity interval for stable motion of the GS-SV solitons is\nfound too. The results suggest a solution for the challenging problem of the\ncreation of stable vortex solitons with high topological charges."
    },
    {
        "anchor": "Observation of the Mott Insulator to Superfluid Crossover of a\n  Driven-Dissipative Bose-Hubbard System: Dissipation is ubiquitous in nature and plays a crucial role in quantum\nsystems such as causing decoherence of quantum states. Recently, much attention\nhas been paid to an intriguing possibility of dissipation as an efficient tool\nfor preparation and manipulation of quantum states. Here we report the\nrealization of successful demonstration of a novel role of dissipation in a\nquantum phase transition using cold atoms. We realize an engineered dissipative\nBose-Hubbard system by introducing a controllable strength of two-body\ninelastic collision via photo-association for ultracold bosons in a\nthree-dimensional optical lattice. In the dynamics subjected to a slow\nramp-down of the optical lattice, we find that strong on-site dissipation\nfavors the Mott insulating state: the melting of the Mott insulator is delayed\nand the growth of the phase coherence is suppressed. The controllability of the\ndissipation is highlighted by quenching the dissipation, providing a novel\nmethod for investigating a quantum many-body state and its non-equilibrium\ndynamics.",
        "positive": "The role of thermal fluctuations in sound propagation in a\n  two-dimensional Fermi gas: We numerically study the transport properties of a two-dimensional Fermi gas\nin a weakly and strongly interacting regimes, in the range of temperatures\nclose to the transition to a superfluid phase. For that we excite sound waves\nin a fermionic mixture by using the phase imprinting technique, follow their\nevolution, and finally determine both their speed and attenuation. Our\nformalism incorporates thermal fluctuations via the ground canonical ensemble\ndescription and with the help of Metropolis algoritm. From numerical\nsimulations we extract temperature dependence of the sound velocity and\ndiffusivity as well as the dependence on the interaction strength. We emphasize\nthe role of virtual vortex-antivortex pairs creation in the process of sound\ndissipation."
    },
    {
        "anchor": "High Frequency Sound in a Unitary Fermi Gas: We present an experimental and theoretical study of the phonon mode in a\nunitary Fermi gas. Using two-photon Bragg spectroscopy, we measure excitation\nspectra at a momentum of approximately half the Fermi momentum, both above and\nbelow the superfluid critical temperature $T_\\mathrm{c}$. Below $T_\\mathrm{c}$,\nthe dominant excitation is the Bogoliubov-Anderson (BA) phonon mode, driven by\ngradients in the phase of the superfluid order parameter. The temperature\ndependence of the BA phonon is consistent with a theoretical model based on the\nquasiparticle random phase approximation in which the dominant damping\nmechanism is via collisions with thermally excited quasiparticles. As the\ntemperature is increased above $T_\\mathrm{c}$, the phonon evolves into a\nstrongly damped collisional mode, accompanied by an abrupt increase in spectral\nwidth. Our study reveals strong similarities between sound propagation in the\nunitary Fermi gas and liquid helium.",
        "positive": "Exploring quantum criticality based on ultracold atoms in optical\n  lattices: Critical behavior developed near a quantum phase transition, interesting in\nits own right, offers exciting opportunities to explore the universality of\nstrongly-correlated systems near the ground state. Cold atoms in optical\nlattices, in particular, represent a paradigmatic system, for which the quantum\nphase transition between the superfluid and Mott insulator states can be\nexternally induced by tuning the microscopic parameters. In this paper, we\ndescribe our approach to study quantum criticality of cesium atoms in a\ntwo-dimensional lattice based on in situ density measurements. Our research\nagenda involves testing critical scaling of thermodynamic observables and\nextracting transport properties in the quantum critical regime. We present and\ndiscuss experimental progress on both fronts. In particular, the thermodynamic\nmeasurement suggests that the equation of state near the critical point follows\nthe predicted scaling law at low temperatures."
    },
    {
        "anchor": "Emergence of Chiral Magnetism in Spinor Bose-Einstein Condensate with\n  Rashba Coupling: Hydrodynamic theory of the spinor BEC condensate with Rashba spin-orbit\ncoupling is presented. A close mathematical analogy of the Rashba-BEC model to\nthe recently developed theory of chiral magnetism is found. Hydrodynamic\nequations for mass density, superfluid velocity, and the local magnetization\nare derived. The mass current is shown to contain an extra term proportional to\nthe magnetization direction, as a result of the Rashba coupling. Elementary\nexcitations around the two known ground states of the Rashba-BEC Hamiltonian,\nthe plane-wave and the stripe states, are worked out in the hydrodynamic\nframework, highlighting the cross-coupling of spin and superflow velocity\nexcitations due to the Rashba term.",
        "positive": "Quench dynamics of a Bose-Einstein condensate under synthetic spin-orbit\n  coupling: We study the quench dynamics of a Bose-Einstein condensate under a\nRaman-assisted synthetic spin-orbit coupling. To model the dynamical process,\nwe adopt a self-consistent Bogoliubov approach, which is equivalent to applying\nthe time-dependent Bogoliubov-de-Gennes equations. We investigate the dynamics\nof the condensate fraction as well as the momentum distribution of the Bose gas\nfollowing a sudden change of system parameters. Typically, the system evolves\ninto a steady state in the long-time limit, which features an oscillating\nmomentum distribution and a stationary condensate fraction which is dependent\non the quench parameters. We investigate how different quench parameters such\nas the inter- and intra-species interactions and the spin-orbit-coupling\nparameters affect the condensate fraction in the steady state. Furthermore, we\nfind that the time average of the oscillatory momentum distribution in the\nlong-time limit can be described by a generalized Gibbs ensemble with two\nbranches of momentum-dependent Gibbs temperatures. Our study is relevant to the\nexperimental investigation of dynamical processes in a spin-orbit coupled\nBose-Einstein condensate."
    },
    {
        "anchor": "Rotating Fulde-Ferrell-Larkin-Ovchinnikov state in cold Fermi gases: We study an effect of rotation on the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)\nstate of two component Fermi superfluid gases in a toroidal trap. We\ninvestigate a stability of the FFLO states in the quasi-one-dimensional regime\non the basis of the Bogoliubov-de Gennes equation. We find that two novel FFLO\nphases, i.e., the half quantum vortex state and the intermediate state of\nFulde-Ferrell (FF) state and Larkin-Ovchinnikov (LO) state, are stabilized by\nthe rotation. The phase diagram for the FF state, LO state, intermediate state,\nand half quantum vortex state is shown in both T-P plane and T-h plane. We\ndemonstrate characteristic features of these states, such as the order\nparameter, flux quantization, and local polarization. Several related works are\ndiscussed, and the advantages of cold Fermi gases are indicated.",
        "positive": "Observation of Feshbach resonances between ultracold Na and Rb atoms: We have successfully prepared an optically trapped ultracold mixture of\n$^{23}$Na and $^{87}$Rb atoms and studied their interspecies Feshbach\nresonances. Using two different spin combinations, several s-wave and p-wave\nresonances are identified by observing a high inelastic loss and a temperature\nrising for both species near resonant magnetic field values. The two s-wave\nresonances observed below 500 G between atoms in the lowest energy level are\npossible candidates for Feshbach molecule association. Our results are well\ncharacterized by a coupled-channel model and are used refining the ground state\ninteraction potentials between $^{23}$Na and $^{87}$Rb. This work opens up the\nprospect for preparing ultracold ensembles of ground-state bosonic NaRb\nmolecules which are chemically stable and can provide strong dipolar\ninteractions."
    },
    {
        "anchor": "Beats and Expansion of Two-Component Bose-Einstein Condensates in the\n  Thomas-Fermi Limit: A unique feature of multi-component BECs is the possibility of beating\nfrequencies in collective oscillations. We analytically determine this beating\nfrequency for the two-component BEC in one-dimension. We also show that the\nThomas-Fermi approximation, where the quantum pressure is neglected, describes\nwell the expansion of the two-component condensate released from an harmonic\ntrap.",
        "positive": "Emergence of nonlinear behavior in the dynamics of ultracold bosons: We study the evolution of a system of interacting ultracold bosons, which\npresents nonlinear, chaotic, behaviors in the limit of very large number of\nparticles. Using the spectral entropy as an indicator of chaos and three\ndifferent numerical approaches : Exact diagonalization, truncated Husimi method\nand mean-field (Gross-Pitaevskii) approximation, we put into evidence the\ndestructive impact of quantum noise on the emergence of the nonlinear dynamics."
    },
    {
        "anchor": "Numerically exact approach to few-body problems far from a perturbative\n  regime: Recent developments of experimental techniques in the field of ultra-cold\ngases open a path to study the crossover from 'few' to 'many' on the quantum\nlevel. In this case, accurate description of inter-particle correlations is\nvery important since it is believed that they can be utilized by quantum\nengineers in quantum metrology, quantum thermometry, quantum heat engines, {\\it\netc}. Unfortunately, a theoretical description of these correlations is very\nchallenging since they are far beyond any variational approaches. By contrast,\nthe exact many-body description rapidly hits numerical limitations due to an\nexponential increase of the many-body Hilbert space. In this work, we brush up\na very effective method of constructing a many-body basis which originates in\nthe physical argumentation. We show that, in contrast to the commonly used\napproach of a straightforward cut-off, it enables one to perform exact\ncalculations with very limited numerical resources. As examples, we study\nquantum correlations in systems of spinless bosons and two-component mixtures\nof fermions confined in a one-dimensional harmonic trap being far from the\nperturbative regime.",
        "positive": "Stochastic Wave-Function Simulation of Irreversible Emission Processes\n  for Open Quantum Systems in a Non-Markovian Environment: When conducting the numerical simulation of quantum transport, the main\nobstacle is a rapid growth of the dimension of entangled Hilbert subspace. The\nQuantum Monte Carlo simulation techniques, while being capable of treating the\nproblems of high dimension, are hindered by the so-called \"sign problem\". In\nthe quantum transport, we have fundamental asymmetry between the processes of\nemission and absorption of environment excitations: the emitted excitations are\nrapidly and irreversibly scattered away. Whereas only a small part of these\nexcitations is absorbed back by the open subsystem, thus exercising the\nnon-Markovian self-action of the subsystem onto itself. We were able to devise\na method for the exact simulation of the dominant quantum emission processes,\nwhile taking into account the small backaction effects in an approximate\nself-consistent way. Such an approach allows us to efficiently conduct\nsimulations of real-time dynamics of small quantum subsystems immersed in\nnon-Markovian bath for large times, reaching the quasistationary regime. As an\nexample we calculate the spatial quench dynamics of Kondo cloud for a bozonized\nKodno impurity model."
    },
    {
        "anchor": "Spin Hall Effect in a Spinor Dipolar Bose-Einstein Condensate: We theoretically show that the spin Hall effect arises in a Bose-Einstein\ncondensate (BEC) of neutral atoms interacting via the magnetic dipole-dipole\ninteractions (MDDIs). Since the MDDI couples the total spin angular momentum\nand the relative orbital angular momentum of two colliding atoms, it works as a\nspin-orbit coupling. Thus, when we prepare a BEC in a magnetic sublevel $m=0$,\nthermally and quantum-mechanically excited atoms in the $m=1$ and $-1$ states\nfeel the Lorentz-like foces in the opposite directions. This is the origin for\nthe emergence of the the spin Hall effect. We define the mass-current and\nspin-current operators from the equations of continuity and calculate the spin\nHall conductivity from the off-diagonal current-current correlation function\nwithin the Bogoliubov approximation. We find that the correction of the current\noperators due to the MDDI significantly contributes to the spin Hall\nconductivity. Possible experimental situation is also discussed.",
        "positive": "The Dynamical Stripes in Spin-Orbit Coupled Bose-Einstein Condensates\n  with Josephson Junctions: The Josephson dynamics of the Bose-Einstein condensation with Raman-induced\nspin-orbit coupling is investigated. A quasi-1D trap is divided into two\nreservoirs by an optical barrier. Before the tunneling between the reservoirs\nis turned on, the system stays in its equilibrium ground state. For different\nspin-orbit coupling parameters and interaction strengthes, the ground state\ndisplays a rich phase diagram. In this work we focus on the plane wave phase\nand the stripe phase. Our calculation shows that, when the tunneling is turned\non, the plane wave phase evolves into a dynamical stripe phase, that is, the\ndensity of the particle changes from uniform to periodically modulated.\nBasically, this stripe is described by a sine function and the wave length, the\namplitude and the initial phase of the function are all varying with time. If\nthe system stays in stripe phase initially, the stripes become ``sliding\" when\nthe tunneling is turned on, which reflects the running of one of the phases of\nthe wave function."
    },
    {
        "anchor": "Particle partition entanglement of bosonic Luttinger liquids: We consider the R\\'{e}nyi entanglement entropy of bosonic Luttinger liquids\nunder a particle bipartition and demonstrate that the leading order finite-size\nscaling is logarithmic in the system size with a prefactor equal to the inverse\nLuttinger parameter. While higher order corrections involve a microscopic\nlength scale, the leading order scaling depends only on this sole dimensionless\nparameter which characterizes the low energy quantum hydrodynamics. This result\ncontrasts the leading entanglement entropy scaling under a spatial bipartition,\nfor which the coefficient is universal and independent of the Luttinger\nparameter. Using quantum Monte Carlo calculations, we explicitly confirm the\nscaling predictions of Luttinger liquid theory for the Lieb-Liniger model of\n$\\delta$-function interacting bosons in the one dimensional spatial continuum.",
        "positive": "Itinerant ferromagnetism of a dipolar Fermi gas with Raman-induced\n  spin-orbit coupling: We elucidate the itinerant ferromagnetism of a dipolar Fermi gas with a\nRaman-induced spin-orbit coupling by investigating the exotic phase diagrams at\nzero and finite temperature. It is revealed that the dipolar interaction along\nwith spin-orbit coupling can corroborate the formation of ferromagnetism and\nthe Raman coupling adversely eliminates the tendency to this ferromagnetism\ntransition, which greatly transcends the general understanding of this subject\nwith contact interaction only. We explore the ground states through the density\nand spin-flip distribution in momentum space, which exhibits novel degeneracy\nat strong Raman coupling indicated by a non-zero entropy at zero temperature.\nWe calculate the transition temperatures well within the reach of an\nexperimental system when altering the dipolar and spin-orbit coupling strength,\nwhich paves a way to the further experimental realization."
    },
    {
        "anchor": "Coherent insulator at arbitrary frequency in a driven atomtronic\n  transistor: We use numerical approach to study non-equilibrium transport of atomic gas in\na driven optical lattice atomtronic transistor. The shaken optical lattice\ntransistor displays a property of insulator within some regions of shaking\nfrequency and shaking strength. It is proved that appearance of the insulation\nis directly connected to coherence of the system. Coherence of the system is\naccompanied by coherent trapping of non-equilibrium atomic gas in one of the\noptical wells, which stops atomic currents. Comparing with the effective\nHamiltonian approach in Floquet engineering, the time-dependent Hamiltonian\napproach could be used in any frequency regime of periodically driven quantum\nsystem.",
        "positive": "Microscopic Origin and Universality Classes of the Efimov Three-Body\n  Parameter: The low-energy spectrum of three particles interacting via nearly resonant\ntwo-body interactions in the Efimov regime is set by the so-called three-body\nparameter. We show that the three-body parameter is essentially determined by\nthe zero-energy two-body correlation. As a result, we identify two classes of\ntwo-body interactions for which the three-body parameter has a universal value\nin units of their effective range. One class involves the universality of the\nthree-body parameter recently found in ultracold atom systems. The other is\nrelevant to short-range interactions that can be found in nuclear physics and\nsolid-state physics."
    },
    {
        "anchor": "Quasi-superfluid and Quasi-Mott phases of strongly interacting bosons in\n  shallow optical lattice: We explore the ground states of strongly interacting bosons in the\nvanishingly small and weak lattices using the multiconfiguration time-dependent\nHartree method for bosons (MCTDHB) which calculate numerically exact many-body\nwave function. Two new many-body phases: fragmented or quasi superfluid (QSF)\nand incomplete fragmented Mott or quasi Mott insulator (QMI) are emerged due to\nthe strong interplay between interaction and lattice depth. Fragmentation is\nutilized as a figure of merit to distinguish these two new phases. We utilize\nthe eigenvalues of the reduced one-body density matrix and define an order\nparameter that characterizes the pathway from a very weak lattice to a deep\nlattice. We provide a detailed investigation through the measures of one- and\ntwo-body correlations and information entropy. We find that the structures in\none- and two-body coherence are good markers to understand the gradual built-up\nof intra-well correlation and decay of inter-well correlation with increase in\nlattice depth.",
        "positive": "Creation and manipulation of Feshbach resonances with radio-frequency\n  radiation: We present a simple technique for studying collisions of ultracold atoms in\nthe presence of a magnetic field and radio-frequency radiation (rf). Resonant\ncontrol of scattering properties can be achieved by using rf to couple a\ncolliding pair of atoms to a bound state. We show, using the example of 6Li,\nthat in some ranges of rf frequency and magnetic field this can be done without\ngiving rise to losses. We also show that halo molecules of large spatial extent\nrequire much less rf power than deeply bound states. Another way to exert\nresonant control is with a set of rf-coupled bound states, linked to the\ncolliding pair through the molecular interactions that give rise to\nmagnetically tunable Feshbach resonances. This was recently demonstrated for\n87Rb [Kaufman et al., Phys. Rev. A 80:050701(R), 2009]. We examine the\nunderlying atomic and molecular physics which made this possible. Lastly, we\nconsider the control that may be exerted over atomic collisions by placing\natoms in superpositions of Zeeman states, and suggest that it could be useful\nwhere small changes in scattering length are required. We suggest other species\nfor which rf and magnetic field control could together provide a useful tuning\nmechanism."
    },
    {
        "anchor": "The origin of the period-$2T/7$ quasi-breathing in disk-shaped\n  Gross-Pitaevskii breathers: We address the origins of the quasi-periodic breathing observed in [Phys.\nRev.\\ X vol. 9, 021035 (2019)] in disk-shaped harmonically trapped\ntwo-dimensional Bose condensates, where the quasi-period\n$T_{\\text{quasi-breathing}}\\sim$~$2T/7$ and $T$ is the period of the harmonic\ntrap. We show that, due to an unexplained coincidence, the first instance of\nthe collapse of the hydrodynamic description, at $t^{*} =\n\\arctan(\\sqrt{2})/(2\\pi) T \\approx T/7$, emerges as a `skillful impostor' of\nthe quasi-breathing half-period $T_{\\text{quasi-breathing}}/2$. At the time\n$t^{*}$, the velocity field almost vanishes, supporting the requisite\ntime-reversal invariance. We find that this phenomenon persists for\nscale-invariant gases in all spatial dimensions, being exact in one dimension\nand, likely, approximate in all others. In $d$ dimensions, the quasi-breathing\nhalf-period assumes the form $T_{\\text{quasi-breathing}}/2 \\equiv t^{*} =\n\\arctan(\\sqrt{d})/(2\\pi) T$. Remaining unresolved is the origin of the\nperiod-$2T$ breathing, reported in the same experiment.",
        "positive": "Observation of the topological soliton state in the Su-Schrieffer-Heeger\n  model: The Su-Schrieffer-Heeger (SSH) model, which captures the most striking\ntransport properties of the conductive organic polymer $trans$-polyacetylene,\nprovides perhaps the most basic model system supporting topological\nexcitations. The alternating bond pattern of polyacetylene chains is captured\nby the bipartite sublattice structure of the SSH model, emblematic of\none-dimensional chiral symmetric topological insulators. This structure\nsupports two distinct nontrivial topological phases, which, when interfaced\nwith one another or with a topologically trivial phase, give rise to\ntopologically-protected, dispersionless boundary states. Using $^{87}$Rb atoms\nin a momentum-space lattice, we realize fully-tunable condensed matter\nHamiltonians, allowing us to probe the dynamics and equilibrium properties of\nthe SSH model. We report on the experimental quantum simulation of this model\nand observation of the localized topological soliton state through quench\ndynamics, phase-sensitive injection, and adiabatic preparation."
    },
    {
        "anchor": "Leading- and next-to-leading order semiclassical approximation to the\n  first seven virial coefficients of spin-1/2 fermions across spatial\n  dimensions: Following up on recent calculations, we investigate the leading- and\nnext-to-leading order semiclassical approximation to the virial coefficients of\na two-species fermion system with a contact interaction. Using the analytic\nresult for the second-order virial coefficient as a renormalization condition,\nwe derive expressions for up to the seventh-order virial coefficient $\\Delta\nb_7$. Our results at leading order, though approximate, furnish simple analytic\nformulas that relate $\\Delta b_n$ to $\\Delta b_2$ for arbitrary dimension,\nproviding a glimpse into the behavior of the virial expansion across dimensions\nand coupling strengths. As an application, we calculate the pressure and Tan's\ncontact of the 2D attractive Fermi gas and examine the radius of convergence of\nthe virial expansion as a function of the coupling strength.",
        "positive": "Dynamical topological phases in quenched spin-orbit coupled degenerate\n  Fermi gas: The spin-orbit coupled degenerate Fermi gas provides a totally new platform\nto realize topological superfluids and related topological excitations.\nPrevious studies have mainly focused on the properties of the ground state.\nHere we consider a two-dimensional Fermi gas with Rashba spin-orbit coupling\nsubject to a perpendicular Zeeman field. For this system, we have found that\nits ground state topological structure is captured by the spin texture, which\nis readily measurable in experiments. We show that, when the Zeeman field is\nsuddenly quenched, dynamical topological phases can be realized. More\nspecifically, three post-quench dynamical phases can be identified according to\nthe asymptotic behavior of the order parameter. In the undamped phase, a\npersistent oscillation of the order parameter may support a topological Floquet\nstate with multiple edge states. In the Landau damped phase, the magnitude of\nthe order parameter approaches a constant via a power-law decay, and this\nsystem can support a dynamical topological phase with a pair of edge states at\nthe boundary. In the over-damped phase, the order parameter decays to zero\nexponentially although the condensate fraction remains finite. These\npredictions can be observed in the strong coupling regime of ultracold Fermi\ngas."
    },
    {
        "anchor": "Quantum phase transition in a shallow one-dimensional optical lattice: In this article the extended Bose-Hubbard model describing ultra-cold atoms\nconfined in a shallow, one-dimensional optical lattice is introduced and\nstudied by the exact diagonalization approach. All parameters of the model are\nrelated to the only relevant parameter controlled experimentally -- the depth\nof the optical potential. Changes in a shape of the insulating lobe in the\nphase diagram of the system are explored and the value of the critical\ntunneling for which the system undergoes the phase transition (from the\ninsulating to the superfluid phase) is predicted. It is shown that the value of\ncritical tunneling is substantially affected by the presence of the tunnelings\nto distant sites of the optical lattice. The results may have some importance\nin upcoming experiments on quantum quench through phase transition points.",
        "positive": "Universality in rotating strongly interacting gases: We analytically determine the properties of two interacting particles in a\nharmonic trap subject to a rotation or a uniform synthetic magnetic field,\nwhere the spherical symmetry of the relative Hamiltonian is preserved.\nThermodynamic quantities such as the entropy and energy are calculated via the\nsecond order quantum cluster expansion. We find that in the strongly\ninteracting regime the energy is universal, however the entropy changes as a\nfunction of the rotation or synthetic magnetic field strength."
    },
    {
        "anchor": "Exploring the Kibble-Zurek mechanism with homogeneous Bose gases: Out-of-equilibrium phenomena is a subject of considerable interest in many\nfields of physics. Ultracold quantum gases, which are extremely clean,\nwell-isolated and highly controllable systems, offer ideal platforms to\ninvestigate this topic. The recent progress in tailoring trapping potentials\nnow allows the experimental production of homogeneous samples in custom\ngeometries, which is a key advance for studies of the emergence of coherence in\ninteracting quantum systems. Here we review recent experiments in which\ntemperature quenches have been performed across the Bose-Einstein condensation\n(BEC) phase transition in an annular geometry and in homogeneous 3D and\nquasi-2D gases. Combined, these experiments give a comprehensive picture of the\nKibble-Zurek (KZ) scenario through complementary measurements of correlation\nfunctions and topological defects density. They also allow the measurement of\nKZ scaling laws, the direct confirmation of the \"freeze-out\" hypothesis that\nunderlies the KZ theory, and the extraction of critical exponents of the\nBose-Einstein condensation transition.",
        "positive": "Universal upper bounds on the Bose-Einstein condensate and the Hubbard\n  star: For $N$ hard-core bosons on an arbitrary lattice with $d$ sites and\nindependent of additional interaction terms we prove that the hard-core\nconstraint itself already enforces a universal upper bound on the Bose-Einstein\ncondensate given by $N_{max}=(N/d)(d-N+1)$. This bound can only be attained for\none-particle states $|\\varphi\\rangle$ with equal amplitudes with respect to the\nhard-core basis (sites) and when the corresponding $N$-particle state\n$|\\Psi\\rangle$ is maximally delocalized. This result is generalized to the\nmaximum condensate possible within a given sublattice. We observe that such\nmaximal local condensation is only possible if the mode entanglement between\nthe sublattice and its complement is minimal. We also show that the maximizing\nstate $|\\Psi\\rangle$ is related to the ground state of a bosonic `Hubbard star'\nshowing Bose-Einstein condensation."
    },
    {
        "anchor": "Signatures of pairing and spin-orbit coupling in correlation functions\n  of Fermi gases: We derive expressions for spin and density correlation functions in the\n(greatly enhanced) pseudogap phase of spin-orbit coupled Fermi superfluids.\nDensity-density correlation functions are found to be relatively insensitive to\nthe presence of these Rashba effects. To arrive at spin-spin correlation\nfunctions we derive new $f$-sum rules, valid even in the absence of a spin\nconservation law. Our spin-spin correlation functions are shown to be fully\nconsistent with these $f$-sum rules. Importantly, they provide a clear\nsignature of the Rashba band-structure and separately help to establish the\npresence of a pseudogap.",
        "positive": "Protocol to engineer Fulde-Ferrell-Larkin-Ovchinnikov states in a cold\n  Fermi gas: We propose a two-step experimental protocol to directly engineer\nFulde-Ferrell-Larkin-Ovchinnikov (FFLO) states in a cold two-component Fermi\ngas loaded into a quasi-one-dimensional trap. First, one uses phase imprinting\nto create a train of domain walls in a superfluid with equal number of\n$\\uparrow$- and $\\downarrow$-spins. Second, one applies a radio-frequency sweep\nto selectively break Cooper pairs near the domain walls and transfer the\n$\\uparrow$-spins to a third spin state which does not interact with the\n$\\uparrow$- and $\\downarrow$-spins. The resulting FFLO state has exactly one\nunpaired $\\downarrow$-spin in each domain wall and is stable for all values of\ndomain-wall separation and interaction strength. We show that the protocol can\nbe implemented with high fidelity at sufficiently strong interactions for a\nwide range of parameters available in present-day experimental conditions."
    },
    {
        "anchor": "Inter-species Tunneling in One-dimensional Bose Mixtures: We study the ground-state properties and quantum dynamics of few-boson\nmixtures with strong inter-species repulsion in one-dimensional traps. If one\nspecies localizes at the center, e.g., due to a very large mass compared to the\nother component, it represents an effective barrier for the latter and the\nsystem can be mapped onto identical bosons in a double well. For weaker\nlocalization, the barrier atoms begin to respond to the light component,\nleading to an induced attraction between the mobile atoms that may even\noutweigh their bare intra-species repulsion. To explain the resulting effects,\nwe derive an effective Hubbard model for the lighter species accounting for the\nbackaction of the barrier in correction terms to the lattice parameters. Also\nthe tunneling is drastically affected: Varying the degree of localization of\nthe \"barrier\" atoms, the dynamics of intrinsically noninteracting bosons can\nchange from Rabi oscillations to effective pair tunneling. For identical\nfermions (or fermionized bosons) this leads to the tunneling of attractively\nbound pairs.",
        "positive": "Universality in Efimov associated tetramers in 4He: We calculated, using seven realistic 4He-4He potentials in the literature,\nthe Efimov spectra of the 4He trimer and tetramer and analyzed the universality\nof the systems. The three-(four-)body Schroedinger equations were solved fully\nnonadiabatically with the high-precision calculation method employed in our\nprevious work on the 4He trimer and tetramer [Phys. Rev. A 85, 022502 (2012);\n85, 062505 (2012)]. We found the following universality in the four-boson\nsystem: i) The critical scattering lengths at which the tetramer ground and\nexcited states couple to the four-body threshold are independent of the choice\nof the two-body realistic potentials in spite of the difference in the\nshort-range details and do not contradict the corresponding values observed in\nthe experiments in ultracold alkali atoms when scaled with the van der Waals\nlength r_vdW, and ii) the four-body hyperradial potential has a repulsive\nbarrier at the four-body hyperradius R_4 \\approx 3 r_vdW, which prevents the\nfour particles from getting close together to explore nonuniversal features of\nthe interactions at short distances. This result is an extension of the\nuniversality in Efimov trimers that the appearance of the repulsive barrier at\nthe three-body hyperradius R_3 \\approx 2 r_vdW makes the critical scattering\nlengths independent of the short-range details of the interactions as reported\nin the literature and also in the present work for the 4He trimer with the\nrealistic potentials."
    },
    {
        "anchor": "Beyond-mean-field stochastic corrections to the blueshift of a\n  driven-dissipative exciton-polariton condensate: In the absence of vortices or phase slips, the phase dynamics of\nexciton-polariton condensates was shown to map onto the Kardar-Parisi-Zhang\n(KPZ) equation, which describes the stochastic growth of a classical interface.\nThis implies that the coherence of such non-equilibrium quasi-condensates\ndecays in space and time following stretched exponentials, characterized by KPZ\nuniversal critical exponents. In this work, we focus on the time evolution of\nthe average phase of a one-dimensional exciton-polariton condensate in the KPZ\nregime and determine the frequency of its evolution, which is given by the\nblueshift, i.e. the non-equilibrium analog of the chemical potential. We\ndetermine the stochastic corrections to the blueshift within Bogoliubov\nlinearized theory and find that while this correction physically originates\nfrom short scale effects, and depends both on density and phase fluctuations,\nit can still be related to the effective large-scale KPZ parameters. Using\nnumerical simulations of the full dynamics, we investigate the dependence of\nthese blueshift corrections on both noise and interaction strength, and compare\nthe results to the Bogoliubov prediction. Our finding contributes both to the\nclose comparison between equilibrium and non-equilibrium condensates, and to\nthe theoretical understanding of the KPZ mapping.",
        "positive": "Correlations in lowest Landau level vortex states: We show how the configuration-space form of the Bogoliubov ground state wave\nfunction of a bosonic condensate with a single vortex in a harmonic trap can be\ndescribed in terms of bosonic Jastrow correlations. We then generalize this\nresult to study the first effects of such correlations on a mean-field vortex\nlattice state and show that the included correlations lower the energy below\nthat of the mean-field state. Although the reduction is relatively small, it is\na precursor of the more general expected effect of correlations in describing\nthe melting of the vortex lattice at large angular momentum per particle."
    },
    {
        "anchor": "Thermalization of isolated Bose-Einstein condensate under a PT-symmetric\n  environment: The postulates of the eigenstate thermalization hypothesis (ETH) express that\nthermalization occurs due to the individual eigenstate of the system's\nHamiltonian. But the ETH put no light on the dynamics that lead toward\nthermalization. In this paper, we observe the thermalization of a Bose-Einstein\nCondensate (BEC) confined in an optical lattice potential that is embedded in\nthe harmonic trap. Such optical lattice potential offers local friction to the\noscillating BEC. The spread in the temporal density plot of BEC shows the\nthermalization of the BEC. Moreover, we observe that the presence of a\nPT-symmetric potential greatly influences the BEC dynamics and the\nthermalization of the system. The presence of a PT-symmetric potential offers a\nway to manipulate the mean position of the BEC to the desired location and for\na desired length of time.",
        "positive": "Amplifying single impurities immersed in a gas of ultra cold atoms: We present a method for amplifying a single or scattered impurities immersed\nin a background gas of ultra cold atoms so that they can be optically imaged\nand spatially resolved. Our approach relies on a Raman transfer between two\nstable atomic hyperfine states that is conditioned on the presence of an\nimpurity atom. The amplification is based on the strong interaction among atoms\nexcited to Rydberg states. We perform a detailed analytical study of the\nperformance of the proposed scheme with particular emphasis on the influence of\nmany-body effects."
    },
    {
        "anchor": "Chaotic few-body vortex dynamics in rotating Bose--Einstein condensates: We investigate a small vortex-lattice system of four co-rotating vortices in\nan atomic Bose--Einstein condensate and find that the vortex dynamics display\nchaotic behaviour after a system quench introduced by reversing the direction\nof circulation of a single vortex through a phase-imprinting process. By\ntracking the vortex trajectories and Lyapunov exponent, we show the onset of\nchaotic dynamics is not immediate, but occurs at later times and is accelerated\nby the close-approach and separation of all vortices in a scattering event. The\ntechniques we develop could potentially be applied to create locally induced\nchaotic dynamics in larger lattice systems as a stepping stone to study the\nrole of chaotic events in turbulent vortex dynamics.",
        "positive": "Understanding superradiant phenomena with synthetic vector potentials in\n  atomic Bose-Einstein condensates: We theoretically investigate superradiance effects in quantum field theories\nin curved space-times by proposing an analogue model based on Bose--Einstein\ncondensates subject to a synthetic vector potential. The breaking of the\nirrotationality constraint of superfluids allows to study superradiance in\nsimple planar geometries and obtain intuitive insight in the amplified\nscattering processes at ergosurfaces. When boundary conditions are modified\nallowing for reflections, dynamical instabilities are found, similar to the\nones of ergoregions in rotating space-times. Their stabilization by horizons in\nblack hole geometries is discussed. All these phenomena are reinterpreted\nthrough an exact mapping with the physics of one-dimensional relativistic\ncharged scalar fields in electrostatic potentials. Our study provides a deeper\nunderstanding on the basic mechanisms of superradiance: by disentangling the\ndifferent ingredients at play, it shines light on some misconceptions on the\nrole of dissipation and horizons and on the competition between superradiant\nscattering and instabilities."
    },
    {
        "anchor": "Complex Langevin simulation of quantum vortices in a Bose-Einstein\n  condensate: The ab-initio simulation of quantum vortices in a Bose-Einstein condensate is\nperformed by adopting the complex Langevin techniques. We simulate the\nnonrelativistic boson field theory at finite chemical potential under rotation.\nIn the superfluid phase, vortices are generated above a critical angular\nvelocity and the circulation is clearly quantized even in the presence of\nquantum fluctuations.",
        "positive": "Dissociation of Feshbach molecules via spin-orbit coupling in ultracold\n  Fermi gases: We study the dissociation of Feshbach molecules in ultracold Fermi gases with\nspin-orbit (SO) coupling. Since SO coupling can induce quantum transition\nbetween the Feshbach molecules and the fully polarized Fermi gas, the Feshbach\nmolecules can be dissociated by the SO coupling. We experimentally realized\nthis new type of dissociation in ultracold gases of 40K atoms with SO coupling\ncreated by Raman beams, and observed that the dissociation rate is highly\nnon-monotonic on both the positive and negative Raman-detuning sides. Our\nresults show that the dissociation of Feshbach molecules can be controlled by\nnew degrees of freedoms, i.e., the SO-coupling intensity or the momenta of the\nRaman beams, as well as the detuning of the Raman beams."
    },
    {
        "anchor": "Bosonic Mott Insulator with Meissner Currents: We introduce a generic bosonic model exemplifying that (spin) Meissner\ncurrents can persist in insulating phases of matter. We consider two species of\ninteracting bosons on a lattice. Our model exhibits separation of charge (total\ndensity) and spin (relative density): The charge sector is gapped in a bosonic\nMott insulator phase with total density one, while the spin sector remains\nsuperfluid due to interspecies conversion. Coupling the spin sector to the\ngauge fields yields a spin Meissner effect reflecting the long-range spin\nsuperfluid coherence. We investigate the resulting phase diagram and describe\nother possible spin phases of matter in the Mott regime possessing chiral\ncurrents as well as a spin-density wave phase. The model presented here is\nrealizable in Josephson junction arrays and in cold atom experiments.",
        "positive": "Multistable circular currents of polariton condensates trapped in ring\n  potentials: We demonstrate the formation and trapping of different stationary solutions,\noscillatory solutions, and rotating solutions of a polariton condensate in a\nplanar semiconductor microcavity with a built-in ring-shaped potential well.\nMultistable ring shaped solutions are trapped in shallow potential wells. These\nsolutions have the same ring shaped density distribution but different\ntopological charges, corresponding to different orbital angular momentum (OAM)\nof the emitted light. For stronger confinement potentials, besides the\nfundamental modes, higher excited (dipole) modes can also be trapped. If two\nmodes are excited simultaneously, their beating produces a complex oscillation\nand rotation dynamics. When the two modes have the same OAM, a double-ring\nsolution forms for which the density oscillates between the inner and the outer\nring. When the two modes have different OAM, a rotating solution with a\ncrescent-shaped density and fractional OAM is created."
    },
    {
        "anchor": "Momentum Dependent Higher Partial Wave Interactions in Bose Einstein\n  condensate: We have investigated the role of momentum dependent s-wave and higher partial\nwave strong interactions to determine the ground state properties and the\ncolumn densities in the Bose-Einstein condensate (BEC) for large scattering\nlength (a) such that ka >>1 even for small values of momentum where the\nmomentum p=(h/2pi)k and k is the wave number. Since the scattering length is\nlarge we have included the first correction (Lee-Huang-Yang correction) both\nfor the k-dependent (s-wave + higher partial wave) interactions and\nk-independent contact interactions (s-wave). We have derived the\ntime-independent equations from the corresponding energy functionals and found\nthat the ground state properties and the column densities differ significantly\nfor these two types of interactions even for moderate values of scattering\nlength (a = 3000 a_0) in BEC of cylindrically trapped 85Rb atoms at 100 nK. The\neffect of higher partial wave (d-wave) increases with increase in a and it is >\n20% for peak density at a= 8700 a_0 which can be experimentally detected.\nDependence of column density on particle number density has been studied.\nColumn densities have been compared with experimental results.",
        "positive": "Pairing and molecule formation along the BEC-BCS crossover for finite\n  range potentials: We analyze the BCS-BEC crossover transition of a balanced two component\nmixture of fermions interacting via a finite range potential, within a mean\nfield approach. For the analysis we consider three finite range potentials\ncases describing the interaction between different Fermi species: a square\nwell, an exponential and a Yukawa potential. The T = 0 thermodynamics analysis\nalong the BCS-BEC crossover allow us to recognize the proper variables, for\nfinite range interactions, that capture the transition from a thermodynamic\nnon-universal behavior at unitarity, to its universal restoration. On the other\nside, the determination of the pair functions along the crossover suggests that\nthe smooth transition occurs always between the scattering resonance and the\nchange of sign of the chemical potential. This identification follows directly\nfrom the pair wave functions behavior, which in the BCS and BEC sides become\nexponentially localized and oscillatory slowly decaying respectively."
    },
    {
        "anchor": "The Condensation of Ideal Dunkl-Bose Gas in Power-Law Traps: We explore the phenomenon of Bose-Einstein condensation in two and\none-dimensional Dunkl-boson gases confined within a power-law potential,\nemploying the framework of Dunkl-deformed boson theory. Our investigation\ninvolves the calculation of particle numbers and phase transition temperatures\nusing the Dunkl formalism. To assess the validity of our findings, we compare\nthem with the corresponding results obtained from the standard approach. We\nfind that the impact of the Dunkl-formalism on the condensate fractions is\nsimilar in one and two-dimensional cases. However, we see that this conclusion\nis not fully valid for the phase transition temperature.",
        "positive": "Magnetic polarons in a nonequilibrium polariton condensate: We consider a condensate of exciton-polaritons in a diluted magnetic\nsemiconductor microcavity. Such system may exhibit magnetic self-trapping in\nthe case of sufficiently strong coupling between polaritons and magnetic ions\nembedded in the semiconductor. We investigate the effect of the nonequilibrium\nnature of exciton-polaritons on the physics of the resulting self-trapped\nmagnetic polarons. We find that multiple polarons can exist at the same time,\nand derive a critical condition for self-trapping which is different to the one\npredicted previously in the equilibrium case. Using the Bogoliubov-de Gennes\napproximation, we calculate the excitation spectrum and provide a physical\nexplanation in terms of the effective magnetic attraction between polaritons,\nmediated by the ion subsystem."
    },
    {
        "anchor": "A quantum degenerate Bose-Fermi mixture of $^{41}$K and $^6$Li: We report a new apparatus for the study of two-species quantum degenerate\nmixture of $^{41}$K and $^6$Li atoms. We develop and combine several advanced\ncooling techniques to achieve both large atom number and high phase space\ndensity of the two-species atom clouds. Furthermore, we build a high-efficiency\ntwo-species magnetic transport system to transfer atom clouds from the 3D\nmagneto-optical-trap chamber to a full glass science chamber of extreme high\nvacuum environment and good optical access. We perform a forced radio-frequency\nevaporative cooling for $^{41}$K atoms while the $^6$Li atoms are\nsympathetically cooled in an optically-plugged magnetic trap. Finally, we\nachieve the simultaneous quantum degeneracy for the $^{41}$K and $^6$Li atoms.\nThe Bose-Einstein condensate of $^{41}$K has 1.4$\\times$10$^5$ atoms with a\ncondensate fraction of about 62%, while the degenerate Fermi gas of $^6$Li has\na total atom number of 5.4$\\times$10$^5$ at 0.25 Fermi temperature.",
        "positive": "Functional building blocks for scalable multipartite entanglement in\n  optical lattices: Featuring excellent coherence and operated parallelly, ultracold atoms in\noptical lattices form a competitive candidate for quantum computation. For\nthis, a massive number of parallel entangled atom pairs have been realized in\nsuperlattices. However, the more formidable challenge is to scale-up and detect\nmultipartite entanglement due to the lack of manipulations over local atomic\nspins in retro-reflected bichromatic superlattices. Here we developed a new\narchitecture based on a cross-angle spin-dependent superlattice for\nimplementing layers of quantum gates over moderately-separated atoms\nincorporated with a quantum gas microscope for single-atom manipulation. We\ncreated and verified functional building blocks for scalable multipartite\nentanglement by connecting Bell pairs to one-dimensional 10-atom chains and\ntwo-dimensional plaquettes of $2\\times4$ atoms. This offers a new platform\ntowards scalable quantum computation and simulation."
    },
    {
        "anchor": "Ground state of a tightly bound composite dimer immersed in a Fermi Sea: In this paper we present a theoretical investigation for the ground state of\nan impurity immersed in a Fermi sea. The molecular regime is considered where a\ntwo-body bound state between the impurity and one of the fermions is formed.\nBoth interaction and exchange of the bound fermion take place between the dimer\nand the Fermi sea. We develop a formalism based on a two channel model allowing\nus to expand systematically the ground state energy of this immersed dimer with\nthe scattering length $a$. Working up to order $a^3$, associated to the\ncreation of two particle-hole pairs, reveals the first signature of the\ncomposite nature of the bosonic dimer. Finally, a complementary variational\nstudy provides an accurate estimate of the dimer energy even at large\nscattering length.",
        "positive": "Mesoscopic Transport and Interferometry with Wavepackets of Ultracold\n  atoms: Effects of Quantum Coherence and Interactions: We propose a way to simulate mesoscopic transport processes with\ncounter-propagating wavepackets of ultracold atoms in quasi one-dimensional\n(1D) waveguides, and show quantitative agreement with analytical results. The\nmethod allows the study of a broad range of transport processes at the level of\nindividual modes, not possible in electronic systems. Typically suppressed\neffects of quantum coherence become manifest, along with the effects of tunable\ninteractions, which can be used to develop a simpler type of sensitive atom\ninterferometer."
    },
    {
        "anchor": "Few-boson tunneling in a double well with spatially modulated\n  interaction: We study few-boson tunneling in a one-dimensional double well with a\nspatially modulated interaction. The dynamics changes from Rabi oscillations in\nthe non-interacting case to a highly suppressed tunneling for intermediate\ncoupling strengths followed by a revival near the fermionization limit. With\nextreme interaction inhomogeneity in the regime of strong correlations we\nobserve tunneling between the higher bands. The dynamics is explained on the\nbasis of the few-body spectrum and stationary eigenstates. For higher number of\nparticles, N > 2, it is shown that the inhomogeneity of the interaction can be\ntuned to generate tunneling resonances. Finally, a tilted double-well and its\ninterplay with the interaction asymmetry is discussed.",
        "positive": "Tuning across Universalities with a Driven Open Condensate: Driven-dissipative systems in two dimensions can differ substantially from\ntheir equilibrium counterparts. In particular, a dramatic loss of off-diagonal\nalgebraic order and superfluidity has been predicted to occur due to the\ninterplay between coherent dynamics and external drive and dissipation in the\nthermodynamic limit. We show here that the order adopted by the system can be\nsubstantially altered by a simple, experimentally viable, tuning of the driving\nprocess. More precisely, by considering the long-wavelength phase dynamics of a\npolariton quantum fluid in the optical parametric oscillator regime, we\ndemonstrate that simply changing the strength of the pumping mechanism in an\nappropriate parameter range can substantially alter the level of effective\nspatial anisotropy induced by the driving laser, and move the system into\ndistinct scaling regimes. These include: (i) the classic algebraically ordered\nsuperfluid below the Berezinskii-Kosterlitz-Thouless (BKT) transition, as in\nequilibrium; (ii) the non-equilibrium, long-wave-length fluctuation dominated\nKardar-Parisi-Zhang (KPZ) phase; and the two associated topological defect\ndominated disordered phases caused by proliferation of (iii) entropic BKT\nvortex-antivortex pairs or (iv) repelling vortices in the KPZ phase. Further,\nby analysing the renormalization group flow in a finite system, we examine the\nlength scales associated with these phases, and assess their observability in\ncurrent experimental conditions."
    },
    {
        "anchor": "Dynamical critical scaling of long-range interacting quantum magnets: Slow variations (quenches) of the magnetic field across the\nparamagnetic-ferromagnetic phase transition of spin systems produce heat. In\nsystems with short-range interactions the heat exhibits universal power-law\nscaling as a function of the quench rate, known as Kibble-Zurek scaling. In\nthis work we analyze slow quenches of the magnetic field in the\nLipkin-Meshkov-Glick (LMG) model, which describes fully connected quantum\nspins. We analytically determine the quantum contribution to the residual heat\nas a function of the quench rate $\\delta$ by means of a Holstein-Primakoff\nexpansion about the mean-field value. Unlike in the case of short-range\ninteractions, scaling laws in the LMG model are only found for a ramp ending at\nthe critical point. If instead the ramp is symmetric, as in the typical\nKibble-Zurek scenario, after crossing the critical point the system tends to\nreabsorb the defects formed during the first part of the ramp: the number of\nexcitations exhibits a crossover behavior as a function of $\\delta$ and tends\nto a constant in the thermodynamic limit. Previous, and seemingly\ncontradictory, theoretical studies are identified as specific limits of this\ndynamics. Our results can be tested on several experimental platforms,\nincluding quantum gases and trapped ions.",
        "positive": "Sum rules for spin-$1/2$ quantum gases in states with well-defined\n  spins: II. Spin-dependent two-body interactions: Sums of matrix elements of spin-dependent two-body momentum-independent\ninteractions and sums of their products are calculated analytically in the\nbasis of many-body states with given total spin --- the states built from spin\nand spatial wavefunctions belonging to multidimensional irreducible\nrepresentations of the symmetric group, unless the total spin has the maximal\nallowed value. As in the first part of the series [V. A. Yurovsky, Phys. Rev. A\n91, 053601 (2015)], the sum dependence on the many-body states is given by\nuniversal factors, which are independent of the Hamiltonians of non-interacting\nparticles. The sum rules are applied to perturbative analysis of energy spectra\nand to calculation of two-body spin-dependent local correlations."
    },
    {
        "anchor": "Interaction-modulated tunneling dynamics in a mixture of Bose-Einstein\n  condensates: We study the interaction-modulated tunneling dynamics of a Bose-Einstein\ncondensate (BEC) in a deep double-well potential, where the tunneling between\nthe two wells is modulated by another BEC trapped in a harmonic potential\nsymmetrically positioned at the center of the double-well potential. The\ninter-species interactions couple the dynamics of the two BECs, which give rise\nto interesting features in the tunneling oscillations. Adopting a two-mode\napproximation for the BEC in the double-well potential and coupling it with the\nGross-Pitaevskii equation of the harmonically trapped BEC, we numerically\ninvestigate the coupled dynamics of the BEC mixture, and map out the phase\ndiagram of the tunneling dynamics. We show that the dynamical back action of\nthe BEC in the harmonic trap leads to strong non-linearity in the oscillations\nof the BEC in the double-well potential, which enriches the system dynamics,\nand enhances macroscopic self trapping. The transition between the Josephson\noscillation and the self-trapping dynamics can be identified by monitoring the\noscillation frequency of the double-well BEC. Our results suggest the\npossibility of tuning the tunneling dynamics of BECs in double-well potentials.",
        "positive": "(Inverse) Magnetic Catalysis in Bose-Einstein Condensation of Neutral\n  Bound Pairs: The Bose-Einstein condensation of bound pairs made of oppositely charged\nfermions in a magnetic field is investigated. We find that the condensation\ntemperature shows the magnetic catalysis effect in weak coupling and the\ninverse magnetic catalysis effect in strong coupling. The different responses\nto the magnetic field can be attributed to the competition between the\ndimensional reduction by Landau orbitals in pairing dynamics and the anisotropy\nof the kinetic spectrum of fluctuations (bound pairs in the normal phase)"
    },
    {
        "anchor": "Signatures of bath-induced quantum avalanches in a many-body--localized\n  system: Strongly correlated systems can exhibit surprising phenomena when brought in\na state far from equilibrium. A spectacular example are quantum avalanches,\nthat have been predicted to run through a many-body--localized system and\ndelocalize it. Quantum avalanches occur when the system is locally coupled to a\nsmall thermal inclusion that acts as a bath. Here we realize an interface\nbetween a many-body--localized system and a thermal inclusion of variable size,\nand study its dynamics. We find evidence for accelerated transport into the\nlocalized region, signature of a quantum avalanche. By measuring the\nsite-resolved entropy we monitor how the avalanche travels through the\nlocalized system and thermalizes it site by site. Furthermore, we isolate the\nbath-induced dynamics by evaluating multipoint correlations between the bath\nand the system. Our results have fundamental implications on the robustness of\nmany-body--localized systems and their critical behavior.",
        "positive": "Dysprosium dipolar Bose-Einstein condensate with broad Feshbach\n  resonances: We produce Bose-Einstein condensates of $^{162}$Dy atoms employing an\ninnovative technique based on a resonator-enhanced optical trap that allows\nefficient loading from the magneto-optical trap and fast evaporation. We\ncharacterize the scattering properties of the ultracold atoms for magnetic\nfields between 6 and 30 G. In addition to the typical chaotic distribution of\nnarrow Feshbach resonances in Lanthanides, we discover two rather isolated\nbroad features at around 22 G and 27 G. A characterization using the\ncomplementary measurements of losses, thermalization, anisotropic expansion and\nmolecular binding energy points towards resonances of predominant s-wave\ncharacter. Such resonances will ease the investigation of quantum phenomena\nrelying on the interplay between dipole and contact interactions."
    },
    {
        "anchor": "Ultracold and dense samples of ground-state molecules in lattice\n  potentials: We produce an ultracold and dense sample of rovibronic ground state Cs_2\nmolecules close to the regime of quantum degeneracy, in a single hyperfine\nlevel, in the presence of an optical lattice. The molecules are individually\ntrapped, in the motional ground state of an optical lattice well, with a\nlifetime of 8 s. For preparation, we start with a zero-temperature atomic\nMott-insulator state with optimized double-site occupancy and efficiently\nassociate weakly-bound dimer molecules on a Feshbach resonance. Despite\nextremely weak Franck-Condon wavefunction overlap, the molecules are\nsubsequently transferred with >50% efficiency to the rovibronic ground state by\na stimulated four-photon process. Our results present a crucial step towards\nthe generation of Bose-Einstein condensates of ground-state molecules and, when\nsuitably generalized to polar heteronuclear molecules such as RbCs, the\nrealization of dipolar many-body quantum-gas phases in periodic potentials.",
        "positive": "Local Photoemission Spectra and Effects of Spatial Inhomogeneity in the\n  BCS-BEC Crossover Regime of a Trapped Ultracold Fermi Gas: We theoretically investigate single particle excitations in the BCS\n(Bardeen-Cooper-Schrieffer)-BEC (Bose-Einstein-Condensation) crossover regime\nof an ultracold Fermi gas. Including strong pairing fluctuations within a\n$T$-matrix approximation, as well as effects of a harmonic trap potential in\nthe local density approximation, we calculate the local photoemission spectrum\nin the normal state. Recently, JILA group has measured this quantity in a\n$^{40}$K Fermi gas, in order to examine homogeneous single-particle properties\nof this system. Comparing our results with this experiment, we show that, this\nattempt indeed succeeds under the JILA's experimental condition. However, we\nalso find that the current local photoemission spectroscopy still has room for\nimprovement, in order to examine the pseudogap phenomenon predicted in the\nBCS-BEC crossover region. Since ultracold Fermi gases are always in a trap, our\nresults would be useful in applying this system to various homogeneous Fermi\nsystems, as a quantum simulator."
    },
    {
        "anchor": "Controlled creation of a singular spinor vortex by circumventing the\n  Dirac belt trick: Persistent topological defects and textures are particularly dramatic\nconsequences of superfluidity. Among the most fascinating examples are the\nsingular vortices arising from the rotational symmetry group SO(3), with\nsurprising topological properties illustrated by Dirac's famous belt trick.\nDespite considerable interest, controlled preparation and detailed study of\nvortex lines with complex internal structure in fully three-dimensional spinor\nsystems remains an outstanding experimental challenge. Here, we propose and\nimplement a reproducible and controllable method for creating and detecting a\nsingular SO(3) line vortex from the decay of a non-singular spin texture in a\nferromagnetic spin-1 Bose--Einstein condensate. Our experiment explicitly\ndemonstrates the SO(3) character and the unique spinor properties of the\ndefect. Although the vortex is singular, its core fills with atoms in the\ntopologically distinct polar magnetic phase. The resulting stable, coherent\ntopological interface has analogues in systems ranging from condensed matter to\ncosmology and string theory.",
        "positive": "Generation of density waves in dipolar quantum gases by time-periodic\n  modulation of atomic interactions: We study the emergence of density waves in dipolar Bose-Einstein condensates\n(BEC) when the strength of dipole-dipole atomic interactions is periodically\nvaried in time. The proposed theoretical model, based on the evolution of small\nperturbations of the background density, allows to compute the growth rate of\ninstability (gain factor) for arbitrary set of input parameters, thus to\nidentify the regions of instability against density waves. We find that among\nother modes of the system the roton mode is most effectively excited due to the\ncontribution of sub-harmonics of the excitation frequency. The frequency of\ntemporal oscillations of emerging density waves coincides with the half of the\ndriving frequency, this being the hallmark of the parametric resonance, is\ncharacteristic to Faraday waves. The possibility to create density waves in\ndipolar BECs, which can persist after the emergence, has been demonstrated. The\nexistence of a stationary spatially periodic solution of the nonlocal\nGross-Pitaevskii equation has been discussed. The effect of three-body atomic\ninteractions, which is relevant to condensates with increased density, upon the\nproperties of emerging waves has been analyzed too. Significant modification of\nthe condensate's excitation spectrum owing to three-body effects is shown."
    },
    {
        "anchor": "FACt: FORTRAN toolbox for calculating fluctuations in atomic condensates: We develop a FORTRAN code to compute fluctuations in atomic condensates\n(FACt) by solving the Bogoliubov-de Gennes (BdG) equations for two component\nBose-Einstein condensate (TBEC) in quasi two dimensions. The BdG equations are\nrecast as matrix equations and solved self consistently. The code is suitable\nfor handling quantum fluctuations as well as thermal fluctuations at\ntemperatures below the critical point of Bose-Einstein condensation. The code\nis versatile, and the ground state density profile and low energy excitation\nmodes obtained from the code can be easily adapted to compute different\nproperties of TBECs -- ground state energy, overlap integral, quasi particle\namplitudes of BdG spectrum, dispersion relation and structure factor and other\nrelated experimental observables.",
        "positive": "Wall-vortex composite solitons in two-component Bose-Einstein\n  condensates: We study composite solitons, consisting of domain walls and vortex lines\nattaching to the walls in two-component Bose-Einstein condensates. When the\ntotal density of two components is homogeneous, the system can be mapped to the\nO(3) nonlinear sigma model for the pseudospin representing the two-component\norder parameter and the analytical solutions of the composite solitons can be\nobtained. Based on the analytical solutions, we discuss the detailed structure\nof the composite solitons in two-component condensates by employing the\ngeneralized nonlinear sigma model, where all degrees of freedom of the original\nGross-Pitaevskii theory are active. The density inhomogeneity results in\nreduction of the domain wall tension from that in the sigma model limit. We\nfind that the domain wall pulled by a vortex is logarithmically bent as a\nmembrane pulled by a pin, and it bends more flexibly than not only the domain\nwall in the sigma model but also the expectation from the reduced tension.\nFinally, we study the composite soliton structure for actual experimental\nsituations with trapped immiscible condensates under rotation through numerical\nsimulations of the coupled Gross-Pitaevskii equations."
    },
    {
        "anchor": "Engineering a flux-dependent mobility edge in disordered zigzag chains: There has been great interest in realizing quantum simulators of charged\nparticles in artificial gauge fields. Here, we perform the first quantum\nsimulation explorations of the combination of artificial gauge fields and\ndisorder. Using synthetic lattice techniques based on parametrically-coupled\natomic momentum states, we engineer zigzag chains with a tunable homogeneous\nflux. The breaking of time-reversal symmetry by the applied flux leads to\nanalogs of spin-orbit coupling and spin-momentum locking, which we observe\ndirectly through the chiral dynamics of atoms initialized to single lattice\nsites. We additionally introduce precisely controlled disorder in the site\nenergy landscape, allowing us to explore the interplay of disorder and large\neffective magnetic fields. The combination of correlated disorder and\ncontrolled intra- and inter-row tunneling in this system naturally supports\nenergy-dependent localization, relating to a single-particle mobility edge. We\nmeasure the localization properties of the extremal eigenstates of this system,\nthe ground state and the most-excited state, and demonstrate clear evidence for\na flux-dependent mobility edge. These measurements constitute the first direct\nevidence for energy-dependent localization in a lower-dimensional system, as\nwell as the first explorations of the combined influence of artificial gauge\nfields and engineered disorder. Moreover, we provide direct evidence for\ninteraction shifts of the localization transitions for both low- and\nhigh-energy eigenstates in correlated disorder, relating to the presence of a\nmany-body mobility edge. The unique combination of strong interactions,\ncontrolled disorder, and tunable artificial gauge fields present in this\nsynthetic lattice system should enable myriad explorations into intriguing\ncorrelated transport phenomena.",
        "positive": "The nonlinear Dirac equation in Bose-Einstein condensates: II.\n  Relativistic soliton stability analysis: The nonlinear Dirac equation for Bose-Einstein condensates in honeycomb\noptical lattices gives rise to relativistic multi-component bright and dark\nsoliton solutions. Using the relativistic linear stability equations, the\nrelativistic generalization of the Boguliubov-de Gennes equations, we compute\nsoliton lifetimes against quantum fluctuations and classify the different\nexcitation types. For a Bose-Einstein condensate of $^{87}\\mathrm{Rb}$ atoms,\nwe find that our soliton solutions are stable on time scales relevant to\nexperiments. Excitations in the bulk region far from the core of a soliton and\nbound states in the core are classified as either spin waves or as a\nNambu-Goldstone mode. Thus, solitons are topologically distinct\npseudospin-$1/2$ domain walls between polarized regions of $S_z = \\pm 1/2$.\nNumerical analysis in the presence of a harmonic trap potential reveals a\ndiscrete spectrum reflecting the number of bright soliton peaks or dark soliton\nnotches in the condensate background. For each quantized mode the chemical\npotential versus nonlinearity exhibits two distinct power law regimes\ncorresponding to the free-particle (weakly nonlinear) and soliton (strongly\nnonlinear) limits."
    },
    {
        "anchor": "The Bogoliubov inequality and the nature of Bose-Einstein condensates\n  for interacting atoms in spatial dimensions $D \\le 2$: We consider the restriction placed by the Bogoliubov inequality on the nature\nof the Bose-Einstein condensates (BECs) for interacting atoms in a spatial\ndimension D </- 2 and in the presence of an external arbitrary potential, which\nmay be a confining \"box\", a periodic, or a disordered potential. The atom-atom\ninteraction gives rise to a (gauge invariance) symmetry-breaking term that\nplaces further restrictions on BECs in the form of a consistency proviso. The\nnecessary condition for the existence of a BEC in D </- 2 in all cases is\nmacroscopic occupation of many single-particle momenta states with the origin a\nlimit point (or accumulation point) of condensates. It is shown that the nature\nof BECs for noninteracting atoms in a disordered potential is precisely the\nsame as that of BECs for interacting atoms in the absence of an external\npotential.",
        "positive": "Discrete Symmetry Breaking Transitions Between Paired Superfluids: We explore the zero-temperature phase diagram of bosons interacting via\nFeshbach resonant pairing interactions in one dimension. Using DMRG (Density\nMatrix Renormalization Group) and field theory techniques we characterize the\nphases and quantum phase transitions in this low-dimensional setting. We\nprovide a broad range of evidence in support of an Ising quantum phase\ntransition separating distinct paired superfluids, including results for the\nenergy gaps, correlation functions and entanglement entropy. In particular, we\nshow that the Ising correlation length, order parameter and critical properties\nare directly accessible from a ratio of the atomic and molecular two-point\nfunctions. We further demonstrate that both the zero-momentum occupation\nnumbers and the visibility are in accordance with the absence of a purely\natomic superfluid phase. We comment on the connection to recent studies of\nboson pairing in a generalized classical XY model."
    },
    {
        "anchor": "Full and fractional defects across the Berezinskii-Kosterlitz-Thouless\n  transition in a driven-dissipative spinor quantum fluid: We investigate the properties of a two-dimensional \\emph{spinor} microcavity\npolariton system driven by a linearly polarised continuous pump. In particular,\nwe establish the role of the elementary excitations, namely the so-called\nhalf-vortices and full-vortices; these objects carry a quantum rotation only in\none of the two, or both, spin components respectively. Our numerical analysis\nof the steady-state shows that it is only the half-vortices that are present in\nthe vortex-antivortex pairing/dissociation responsible for the\nBerezinskii-Kosterlitz-Thouless transition. These are the relevant elementary\nexcitations close to the critical point. However, by exploring the\nphase-ordering dynamics following a sudden quench across the transition we\nprove that full-vortices become the relevant excitations away from the critical\npoint in a deep quasi-ordered state at late times. The time-scales for\nhalf-vortices binding into full vortices are much faster than the\nvortex-antivortex annihilations.",
        "positive": "Quantum correlations of few dipolar bosons in a double-well trap: We consider $N$ interacting dipolar bosonic atoms at zero temperature in a\ndouble-well potential. This system is described by the two-space-mode extended\nBose-Hubbard (EBH) Hamiltonian which includes (in addition to the familiar BH\nterms) the nearest-neighbor interaction, correlated hopping and bosonic-pair\nhopping. For systems with $N=2$ and $N=3$ particles we calculate analytically\nboth the ground state and the Fisher information, the coherence visibility, and\nthe entanglement entropy that characterize the correlations of the lowest\nenergy state. The structure of the ground state crucially depends on the\ncorrelated hopping $K_c$. On one hand we find that this process makes possible\nthe occurrence of Schr\\\"odinger-cat states even if the onsite interatomic\nattraction is not strong enough to guarantee the formation of such states. On\nthe other hand, in the presence of a strong onsite attraction, sufficiently\nlarge values of $|K_c|$ destroys the cat-like state in favor of a delocalized\natomic coherent state."
    },
    {
        "anchor": "Shell-shaped Bose-Einstein condensates realized with dual-species\n  mixtures: Ultracold quantum gases confined in three-dimensional bubble traps are\npromising tools for exploring many-body effects on curved manifolds. As an\nalternative to the conventional technique of radio-frequency dressing, we\npropose to create such shell-shaped Bose-Einstein condensates in microgravity\nbased on dual-species atomic mixtures and we analyze their properties as well\nas the feasibility to realize symmetrically filled shells. Beyond similarities\nwith the radio-frequency dressing method as in the collective-excitation\nspectrum, our approach has several natural advantages like the robustness of\nthe created quantum bubbles and the possibility to magnify shell effects\nthrough an interaction-driven expansion.",
        "positive": "Excited-state quantum phase transitions and periodic dynamics: We investigate signatures of the excited-state quantum phase transition in\nthe periodic dynamics of the Lipkin-Meshkov-Glick model and the Tavis-Cummings\nmodel. In the thermodynamic limit, expectation values of observables in\neigenstates of the system can be calculated using classical trajectories.\nMotivated by this, we suggest a method based on the time evolution of the\nfinite-size system, to find singularities in observables, which arise due to\nthe excited-state quantum phase transition."
    },
    {
        "anchor": "The Universality and stability for a dilute Bose gas with a Feshbach\n  resonance: We study the bosonic atoms with a wide Feshbach resonance at zero temperature\nin terms of the renormalization group. We indicate that this system will always\ncollapse in the dilute limit. On the side with a positive scattering length,\nthe atomic superfluid is an unstable local minimum in the dilute limit and it\ndetermines the thermodynamics of this system within its lifetime. We calculate\nthe equilibrium properties at zero temperature in the unitary regime. They\nexhibit universal scaling forms in the dilute limit due to the presence of a\nnontrivial zero temperature, zero density fixed point. Moreover, we find that\nthe T=0 thermodynamics of this system in the unitary limit is exactly identical\nto the one for an ideal Fermi gas.",
        "positive": "Dynamics of phase separation in two species Bose-Einstein condensates\n  with vortices: We examine the dynamics associated with the miscibility-immiscibility\ntransition of trapped two-component Bose-Einstein condensates (TBECs) of dilute\natomic gases in presence of vortices. In particular, we consider TBECs of Rb\nhyperfine states, and Rb-Cs mixture. There is an enhancement of the\nphase-separation when the vortex is present in both condensates. In the case of\na singly charged vortex in only one of the condensates, there is enhancement\nwhen the vortex is present in the species which occupy the edges at\nphase-separation. But, suppression occurs when the vortex is in the species\nwhich occupies the core region. To examine the role of the vortex, we quench\nthe inter-species interactions to propel the TBEC from miscible to immiscible\nphase, and use the time dependent Gross-Pitaevskii equation to probe the\nphenomenon of phase-separation. We also examine the effect of higher charged\nvortex."
    },
    {
        "anchor": "Dynamics of atoms in a time-orbiting-potential trap: consequences of the\n  classical description: The classical model that describes the motion of an atom in a magnetic trap\nis solved in order to investigate the relationship between the failure of the\nusual adiabatic approximation assumption and the physical parameters of the\ntrap. This allows to evaluate the effect that reversing of the bias field\nrotation produces on the vertical position of the atomic orbit, a displacement\nthat is closely related to the adiabatic character of the trap motion. The\npresent investigation has been motivated by a similar experimental test\npreviously carried out in the actual magnetic time orbiting potential trap. We\nfind that the non-adiabatic effects provided by the classical model are\nextremely small. Thus, we conclude that the theoretical explanation of the\nexperimental measures, requires a quantum description of the dynamics in\nmagnetic traps.",
        "positive": "Parametric cooling of a degenerate Fermi gas in an optical trap: We demonstrate a novel technique for cooling a degenerate Fermi gas in a\ncrossed-beam optical dipole trap, where high-energy atoms can be selectively\nremoved from the trap by modulating the stiffness of the trapping potential\nwith anharmonic trapping frequencies. We measure the dependence of the cooling\neffect on the frequency and amplitude of the parametric modulations. It is\nfound that the large anharmonicity along the axial trapping potential allows to\ngenerate a degenerate Fermi gas with anisotropic energy distribution, in which\nthe cloud energy in the axial direction can be reduced to the ground state\nvalue."
    },
    {
        "anchor": "Realizing non-Abelian gauge potentials in optical square lattices:\n  Application to atomic Chern insulators: We describe a scheme to engineer non-Abelian gauge potentials on a square\noptical lattice using laser-induced transitions. We emphasize the case of\ntwo-electron atoms, where the electronic ground state g is laser coupled to a\nmetastable state e within a state-dependent optical lattice. In this scheme,\nthe alternating pattern of lattice sites hosting g and e states depict a\ncheckerboard structure, allowing for laser-assisted tunneling along both\nspatial directions. In this configuration, the nuclear spin of the atoms can be\nviewed as a \"flavor\" quantum number undergoing non-Abelian tunneling along\nnearest-neighbor links. We show that this technique can be useful to simulate\nthe equivalent of the Haldane quantum Hall model using cold atoms trapped in\nsquare optical lattices, offering an interesting route to realize Chern\ninsulators. The emblematic Haldane model is particularly suited to investigate\nthe physics of topological insulators, but requires, in its original form,\ncomplex hopping terms beyond nearest-neighboring sites. In general, this\ndrawback inhibits a direct realization with cold atoms, using standard\nlaser-induced tunneling techniques. We demonstrate that a simple mapping allows\nto express this model in terms of matrix hopping operators, that are defined on\na standard square lattice. This mapping is investigated for two models that\nlead to anomalous quantum Hall phases. We discuss the practical implementation\nof such models, exploiting laser-induced tunneling methods applied to the\ncheckerboard optical lattice.",
        "positive": "Observation of many-body localization of interacting fermions in a\n  quasi-random optical lattice: We experimentally observe many-body localization of interacting fermions in a\none-dimensional quasi-random optical lattice. We identify the many-body\nlocalization transition through the relaxation dynamics of an\ninitially-prepared charge density wave. For sufficiently weak disorder the time\nevolution appears ergodic and thermalizing, erasing all remnants of the initial\norder. In contrast, above a critical disorder strength a significant portion of\nthe initial ordering persists, thereby serving as an effective order parameter\nfor localization. The stationary density wave order and the critical disorder\nvalue show a distinctive dependence on the interaction strength, in agreement\nwith numerical simulations. We connect this dependence to the ubiquitous\nlogarithmic growth of entanglement entropy characterizing the generic many-body\nlocalized phase."
    },
    {
        "anchor": "Quantum Phases of Ultracold Bosonic Atoms in a One Dimensional Optical\n  Superlattice: We analyze various quantum phases of ultracold bosonic atoms in a periodic\none dimensional optical superlattice. Our studies have been performed using the\nfinite size density matrix renormalization group (FS-DMRG) method in the\nframework of the Bose-Hubbard model. Calculations have been carried out for a\nwide range of densities and the energy shifts due to the superlattice\npotential. At commensurate fillings, we find the Mott insulator and the\nsuperfluid phases as well as Mott insulators induced by the superlattice. At a\nparticular incommensurate density, the system is found to be in the superfluid\nphase coexisting with density oscillations for a certain range of parameters of\nthe system.",
        "positive": "Rapidly Rotating Fermions in an Anisotropic Trap: We consider a cold gas of non-interacting fermions in a two dimensional\nharmonic trap with two different trapping frequencies $\\omega_x \\leq \\omega_y$,\nand discuss the effect of rotation on the density profile. Depending on the\nrotation frequency $\\Omega$ and the trap anisotropy $\\omega_y/\\omega_x$, the\ndensity profile assumes two qualitatively different shapes. For small\nanisotropy ($\\omega_y/\\omega_x \\ll \\sqrt{1+4 \\Omega^2/\\omega_x^2}$), the\ndensity consists of elliptical plateaus of constant density, corresponding to\nLandau levels and is well described by a two dimensional local density\napproximation. For large anisotropy ($\\omega_y/\\omega_x \\gg \\sqrt{1+4\n\\Omega^2/\\omega_x^2}$), the density profile is Gaussian in the strong confining\ndirection and semicircular with prominent Friedel oscillations in the weak\ndirection. In this regime, a one dimensional local density approximation is\nwell suited to describe the system. The crossover between the two regimes is\nsmooth where the step structure between the Landau level edges turn into\nFriedel oscillations. Increasing the temperature causes the step structure or\nthe Friedel oscillations to wash out leaving a Boltzmann gas density profile."
    },
    {
        "anchor": "Josephson oscillations and self-trapping of superfluid fermions in a\n  double-well potential: We investigate the behaviour of a two-component Fermi superfluid in a\ndouble-well potential. We numerically solve the time dependent Bogoliubov-de\nGennes equations and characterize the regimes of Josephson oscillations and\nself-trapping for different potential barriers and initial conditions. In the\nweak link limit the results agree with a two-mode model where the relative\npopulation and the phase difference between the two wells obey coupled\nnonlinear Josephson equations. A more complex dynamics is predicted for large\namplitude oscillations and large tunneling.",
        "positive": "Dynamics of spatial coherence and momentum distribution of polaritons in\n  a semiconductor microcavity under conditions of Bose-Einstein condensation: The dynamics of spatial coherence and momentum distribution of polaritons in\nthe regime of Bose-Einstein condensation are investigated in a GaAs microcavity\nwith embedded quantum wells under nonresonant excitation with picosecond laser\npulses. It is shown that the onset of the condensate first order sparial\ncoherence is accompanied by narrowing of the polariton momentum distribution.\nAt the same time, at sufficiently high excitation densities, there is\nsignificant qualitative discrepancy between the dynamic behavior of the width\nof the polariton momentum distribution determined from direct measurements and\nthat calculated from the coherence spatial distribution. This discrepancy is\nobserved at the fast initial stage of the polariton system kinetics and,\napparently, results from the strong spatial nonuniformity of the phase of the\ncondensate wave function, which equilibrates on a much longer time scale."
    },
    {
        "anchor": "Time reversal symmetry breaking of $p$-orbital bosons in a\n  one-dimensional optical lattice: We study bosons loaded in a one-dimensional optical lattice of two-fold\n$p$-orbital degeneracy at each site. Our numerical simulations find an\nanti-ferro-orbital p$_x$+ip$_y$, a homogeneous p$_x$ Mott insulator phase and\ntwo kinds of superfluid phases distinguished by the orbital order\n(anti-ferro-orbital and para-orbital). The anti-ferro-orbital order breaks time\nreversal symmetry. Experimentally observable evidence is predicted for the\nphase transition between the two different superfluid phases. We also discover\nthat the quantum noise measurement is able to provide a concrete evidence of\ntime reversal symmetry breaking in the first Mott phase.",
        "positive": "Unconventional magnetism in imbalanced Fermi systems with magnetic\n  dipolar interactions: We study the magnetic structure of the ground state of an itinerant Fermi\nsystem of spin-\\nicefrac{1}{2} particles with magnetic dipole-dipole\ninteractions. We show that, quite generally, the spin state of particles depend\non its momentum, i.e., spin and orbital degrees of freedom are entangled and\ntaken separately are not ``good'' quantum numbers. Specifically, we consider a\nuniform system with non-zero magnetization at zero temperature. Assuming the\nmagnetization is along $z$-axis, the quantum spin states are $\\v{k}$-dependent\nlinear combinations of eigenstates of the $\\sigma_z$ Pauli matrix. This leads\nto novel spin structures in \\textit{momentum space} and to the fact that the\nFermi surfaces for ``up'' and ``down'' spins are not well defined. The system\nstill has a cylindrical axis of symmetry along the magnetization axis. We also\nshow that the self energy has a universal structure which we determine based on\nthe symmetries of the dipolar interaction and we explicitly calculated it in\nthe Hartree-Fock approximation. We show that the bare magnetic moment of\nparticles is renormalized due to particle-particle interactions and we give\norder of magnitude estimates of this renormalization effect. We estimate that\nthe above mentioned dipolar effects are small but we discuss possible scenarios\nwhere this physics may be realized in future experiments."
    },
    {
        "anchor": "Short-range quantum magnetism of ultracold fermions in an optical\n  lattice: The exchange coupling between quantum mechanical spins lies at the origin of\nquantum magnetism. We report on the observation of nearest-neighbor magnetic\nspin correlations emerging in the many-body state of a thermalized Fermi gas in\nan optical lattice. The key to obtaining short-range magnetic order is a local\nredistribution of entropy within the lattice structure. This is achieved in a\ntunable-geometry optical lattice, which also enables the detection of the\nmagnetic correlations. We load a low-temperature two-component Fermi gas with\nrepulsive interactions into either a dimerized or an anisotropic simple cubic\nlattice. For both systems the correlations manifest as an excess number of\nsinglets as compared to triplets consisting of two atoms with opposite spins.\nFor the anisotropic lattice, we determine the transverse spin correlator from\nthe singlet-triplet imbalance and observe antiferromagnetic correlations along\none spatial axis. Our work paves the way for addressing open problems in\nquantum magnetism using ultracold fermions in optical lattices as quantum\nsimulators.",
        "positive": "Reservoir-induced Thouless pumping and symmetry protected topological\n  order in open quantum chains: We introduce a classification scheme for symmetry protected topological\nphases applicable to stationary states of open systems based on a\ngeneralization of the many-body polarization. The polarization can be used to\nprobe the topological properties of non-interacting and interacting closed and\nopen systems as well and remains a meaningful quantity even in the presence of\nmoderate particle-number fluctuations. As examples, we discuss two open-system\nversions of a topological Thouless pump in the steady state of one-dimensional\nlattices driven by Markovian reservoirs. In the analogous unitary system, the\nRice-Mele model, symmetries enforce topological properties which lead to a\nnon-trivial winding of the geometric Zak phase upon cyclic variations of model\nparameters. Associated with this is a winding of the many-body polarization,\ncorresponding to a quantized transport in the bulk (Thouless pump). We here\nshow that in the open system, where the Zak phase looses its meaning, the same\nsymmetries enforce a winding of the generalized many- body polarization. This\nwinding is shown to be robust against Hamiltonian perturbations as well as\nhomogeneous dephasing and particle losses.."
    },
    {
        "anchor": "Correlated Pair Approach to Composite Boson Scattering Lengths: We derive the scattering length of composite bosons (cobosons) within the\nframework of the composite boson many-body formalism that uses correlated-pair\nstates as a basis, instead of free fermion states. The integral equation\nconstructed from this physically relevant basis makes transparent the role of\nfermion exchange in the coboson-coboson effective scattering. Three potentials\nused for Cooper pairs, fermionic-atom dimers, and semiconductor excitons are\nconsidered. While the s-wave scattering length for the BCS-like potential is\njust equal to its Born value, the other two are substantially smaller. For\nfermionic-atom dimers and semiconductor excitons, our results, calculated\nwithin a restricted correlated-pair basis, are in good agreement with those\nobtained from procedures numerically more demanding. We also propose model\ncoboson-coboson scatterings that are separable and thus easily workable, and\nthat produce scattering lengths which match quantitatively well with the\nnumerically-obtained values for all fermion mass ratios. These separable model\nscatterings can facilitate future works on many-body effects in coboson gases.",
        "positive": "Bose Gases Near Unitarity: We study the properties of strongly interacting Bose gases at the density and\ntemperature regime when the three-body recombination rate is substantially\nreduced. In this regime, one can have a Bose gas with all particles in\nscattering states (i.e. the \"upper branch\") with little loss even at unitarity\nover the duration of the experiment. We show that because of bosonic\nenhancement, pair formation is shifted to the atomic side of the original\nresonance (where scattering length $a_s<0$), opposite to the fermionic case. In\na trap, a repulsive Bose gas remains mechanically stable when brought across\nresonance to the atomic side until it reaches a critical scattering length\n$a_{s}^{\\ast}<0$. For $a_s<a_{s}^{\\ast}$, the density consists of a core of\nupper branch bosons surrounded by an outer layer of equilibrium phase. The\nconditions of low three-body recombination requires that the particle number\n$N<\\alpha (T/\\omega)^{5/2}$ in a harmonic trap with frequency $\\omega$, where\n$\\alpha$ is a constant."
    },
    {
        "anchor": "Controlling phase separation of a two-component Bose-Einstein condensate\n  by confinement: We point out that the widely accepted condition g11g22<g122 for phase\nseparation of a two-component Bose-Einstein condensate is insufficient if\nkinetic energy is taken into account, which competes against the intercomponent\ninteraction and favors phase mixing. Here g11, g22, and g12 are the intra- and\nintercomponent interaction strengths, respectively. Taking a d-dimensional\ninfinitely deep square well potential of width L as an example, a simple\nscaling analysis shows that if d=1 (d=3), phase separation will be suppressed\nas L\\rightarrow0 (L\\rightarrow\\infty) whether the condition g11g22<g122 is\nsatisfied or not. In the intermediate case of d=2, the width L is irrelevant\nbut again phase separation can be partially or even completely suppressed even\nif g11g22<g122. Moreover, the miscibility-immiscibility transition is turned\nfrom a first-order one into a second-order one by the kinetic energy. All these\nresults carry over to d-dimensional harmonic potentials, where the harmonic\noscillator length {\\xi}ho plays the role of L. Our finding provides a scenario\nof controlling the miscibility-immiscibility transition of a two-component\ncondensate by changing the confinement, instead of the conventional approach of\nchanging the values of the g's.",
        "positive": "Observation of density-dependent gauge fields in a Bose-Einstein\n  condensate based on micromotion control in a shaken two-dimensional lattice: We demonstrate a density-dependent gauge field, induced by atomic\ninteractions, for quantum gases. The gauge field results from the synchronous\ncoupling between the interactions and micromotion of the atoms in a modulated\ntwo-dimensional optical lattice. As a first step, we show that a coherent\nshaking of the lattice in two directions can couple the momentum and\ninteractions of atoms and break the four-fold symmetry of the lattice. We then\ncreate a full interaction-induced gauge field by modulating the interaction\nstrength in synchrony with the lattice shaking. When a condensate is loaded\ninto this shaken lattice, the gauge field acts to preferentially prepare the\nsystem in different quasimomentum ground states depending on the modulation\nphase. We envision that these interaction-induced fields, created by fine\ncontrol of micromotion, will provide a stepping stone to model new quantum\nphenomena within and beyond condensed matter physics."
    },
    {
        "anchor": "Interaction quantum quenches in the one-dimensional Fermi-Hubbard model\n  with spin imbalance: Using the time-dependent density matrix renormalization group method and\nexact diagonalization, we study the non-equilibrium dynamics of the\none-dimensional Fermi-Hubbard model following a quantum quench or a ramp of the\nonsite interaction strength. For quenches from the non-interacting to the\nattractive regime, we investigate the dynamical emergence of\nFulde-Ferrell-Larkin-Ovchinnikov (FFLO) correlations, which at finite spin\npolarizations are the dominant two-body correlations in the ground state, and\ntheir signatures in the pair quasi-momentum distribution function. We observe\nthat the post-quench double occupancy exhibits a maximum as the interaction\nstrength becomes of the order of the bandwidth. Finally, we study quenches and\nramps from attractive to repulsive interactions, which imprint FFLO\ncorrelations onto repulsively bound pairs. We show that a quite short ramp time\nis sufficient to wipe out the characteristic FFLO features in the post-quench\npair momentum distribution functions.",
        "positive": "Harmonically Trapped Four-Boson System: Four identical spinless bosons with purely attractive two-body short-range\ninteractions and repulsive three-body interactions under external spherically\nsymmetric harmonic confinement are considered. The repulsive three-body\npotential prevents the formation of deeply-bound states with molecular\ncharacter. The low-energy spectrum with vanishing orbital angular momentum and\npositive parity for infinitely large two-body $s$-wave scattering length is\nanalyzed in detail. Using the three-body contact, states are classified as\nuniversal, quasi-universal, or strongly non-universal. Connections with the\nzero-range interaction model are discussed. The energy spectrum is mapped out\nas a function of the two-body $s$-wave scattering length $a_s$, $a_s>0$. In the\nweakly- to medium-strongly-interacting regime, one of the states approaches the\nenergy obtained for a hard core interaction model. This state is identified as\nthe energetically lowest-lying \"BEC state\". Structural properties are also\npresented."
    },
    {
        "anchor": "Effective-range approximations for resonant scattering of cold atoms: Studies of cold atom collisions and few-body interactions often require the\nenergy dependence of the scattering phase shift, which is usually expressed in\nterms of an effective-range expansion. We use accurate coupled-channel\ncalculations on $^{6}$Li, $^{39}$K and $^{133}$Cs to explore the behavior of\nthe effective range in the vicinity of both broad and narrow Feshbach\nresonances. We show that commonly used expressions for the effective range\nbreak down dramatically for narrow resonances and near the zero-crossings of\nbroad resonances. We present an alternative parametrization of the effective\nrange that is accurate through both the pole and the zero-crossing for both\nbroad and narrow resonances. However, the effective range expansion can still\nfail at quite low collision energies, particularly around narrow resonances. We\ndemonstrate that an analytical form of an energy and magnetic field-dependent\nphase shift, based on multichannel quantum defect theory, gives accurate\nresults for the energy-dependent scattering length.",
        "positive": "Control of $^{164}$Dy Bose-Einstein condensate phases and dynamics with\n  dipolar anisotropy: We investigate the quench dynamics of quasi-one and two dimensional dipolar\nBose-Einstein condensates (dBEC) of $^{164}$Dy atoms under the influence of a\nfast rotating magnetic field. The magnetic field thus controls both the\nmagnitude and sign of the dipolar potential. We account for quantum\nfluctuations, critical to formation of exotic quantum droplet and supersolid\nphases in the extended Gross-Pitaevskii formalism, which includes the so-called\nLee-Huang-Yang (LHY) correction. An analytical variational ansatz allows us to\nobtain the phase diagrams of the superfluid and droplet phases. The crossover\nfrom the superfluid to the supersolid phase and to single and droplet arrays is\nprobed with particle number and dipolar interaction. The dipolar strength is\ntuned by rotating the magnetic field with subsequent effects on phase\nboundaries. Following interaction quenches across the aforementioned phases, we\nmonitor the dynamical formation of supersolid clusters or droplet lattices. We\ninclude losses due to three-body recombination over the crossover regime, where\nthe three-body recombination rate coefficient scales with the fourth power of\nthe scattering length ($a_s$) or the dipole length ($a_{dd}$). For fixed values\nof the dimensionless parameter, $\\epsilon_{dd} = a_{dd}/a_s$, tuning the\ndipolar anisotropy leads to an enhancement of the droplet lifetimes."
    },
    {
        "anchor": "Exact dynamics of two holes in two-leg antiferromagnetic ladders: We study the motion of holes in a mixed-dimensional setup of an\nantiferromagnetic ladder, featuring nearest neighbor hopping $t$ along the\nladders and Ising-type spin interactions along, $J_\\parallel$, and across,\n$J_\\perp$, the ladder. We determine exact solutions for the low-energy one- and\ntwo-hole eigenstates. The presence of the trans-leg spin coupling, $J_\\perp$,\nleads to a linear confining potential between the holes. As a result, holes on\nseparate legs feature a super-linear binding energy scaling as $(J_\\perp /\nt)^{2/3}$ in the strongly correlated regime of $J_\\perp,J_\\parallel \\leq t$.\nThis behavior is linked to an emergent length scale $\\lambda \\propto\n(t/J_\\perp)^{1/3}$, stemming from the linear confining potential, and which\ndescribes how the size of the two-hole molecular state diverges for\n$J_\\perp,J_\\parallel \\ll t$. On the contrary, holes on the same leg unbind at\nsufficiently low spin couplings. This is a consequence of the altered\nshort-range boundary condition for holes on the same leg, yielding an effective\nPauli repulsion between them, limiting their kinetic energy and making binding\nunfavorable. Finally, we determine the exact nonequilibrium quench dynamics\nfollowing the sudden immersion of initially localized nearest neigbhor holes.\nThe dynamics is characterized by a crossover from an initial ballistic quantum\nwalk to an aperiodic oscillatory motion around a finite average distance\nbetween the holes due to the confining potential between them. In the strongly\ncorrelated regime of low spin couplings, $J_\\perp, J_\\parallel \\leq t$, we find\nthis asymptotic distance to diverge as $t / J_\\perp$, showing a much stronger\nscaling than the eigenstates. The predicted results should be amenable to\nstate-of-the-art quantum simulation experiments using currently implemented\nexperimental techniques.",
        "positive": "Optical Lattice with Torus Topology: We propose an experimental scheme to construct an optical lattice where the\natoms are confined to the surface of a torus. This construction can be realized\nwith spatially shaped laser beams which could be realized with recently\ndeveloped high resolution imaging techniques. We numerically study the\nfeasibility of this proposal by calculating the tunneling strengths for atoms\nin the torus lattice. To illustrate the non-trivial role of topology in atomic\ndynamics on the torus, we study the quantized superfluid currents and\nfractional quantum Hall (FQH) states on such a structure. For FQH states, we\nnumerically investigate the robustness of the topological degeneracy and\npropose an experimental way to detect such a degeneracy. Our scheme for torus\nconstruction can be generalized to Riemann surfaces with higher genus for\nexploration of richer topological physics."
    },
    {
        "anchor": "Weakly bound states of two- and three-boson systems in the crossover\n  from two to three dimension: The spectrum and properties of quantum bound states is strongly dependent on\nthe dimensionality of space. How this comes about and how one may theoretically\nand experimentally study the interpolation between different dimensions is a\ntopic of great interest in different fields of physics. In this paper we study\nweakly bound states of non-relativistic two and three boson systems when\npassing continuously from a three (3D) to a two-dimensional (2D) regime within\na 'squeezed dimension' model. We use periodic boundary conditions to derive a\nsurprisingly simple form of the three-boson Schr{\\\"o}dinger equation in\nmomentum space that we solve numerically. Our results show a distinct\ndimensional crossover as three-boson states will either disappear into the\ncontinuum or merge with a 2D counterpart, and also a series of sharp\ntransitions in the ratios of three-body and two-body energies from being purely\n2D to purely 3D.",
        "positive": "Cosine Edge Mode in a Periodically Driven Quantum System: Time-periodic (Floquet) topological phases of matter exhibit bulk-edge\nrelationships that are more complex than static topological insulators and\nsuperconductors. Finding the edge modes unique to driven systems usually\nrequires numerics. Here we present a minimal two-band model of Floquet\ntopological insulators and semimetals in two dimensions where all the bulk and\nedge properties can be obtained analytically. It is based on the extended\nHarper model of quantum Hall effect at flux one half. We show that periodical\ndriving gives rise to a series of phases characterized by a pair of integers.\nThe model has a most striking feature: the spectrum of the edge modes is always\ngiven by a single cosine function, $\\omega(k_y)\\propto \\cos k_y$ where $k_y$ is\nthe wave number along the edge, as if it is freely dispersing and completely\ndecoupled from the bulk. The cosine mode is robust against the change in\ndriving parameters and persists even to semi-metallic phases with Dirac points.\nThe localization length of the cosine mode is found to contain an integer and\nin this sense quantized."
    },
    {
        "anchor": "Quantized vortices in a rotating Bose-Einstein condensate with\n  spatiotemporally modulated interaction: We present theoretical analysis and numerical studies of the quantized\nvortices in a rotating Bose-Einstein condensate with spatiotemporally modulated\ninteraction in harmonic and anharmonic potentials, respectively. The exact\nquantized vortex and giant vortex solutions are constructed explicitly by\nsimilarity transformation. Their stability behavior has been examined by\nnumerical simulation, which shows that a new series of stable vortex states\n(defined by radial and angular quantum numbers) can be supported by the\nspatiotemporally modulated interaction in this system. We find that there exist\nstable quantized vortices with large topological charges in repulsive\ncondensates with spatiotemporally modulated interaction. We also give an\nexperimental protocol to observe these vortex states in future experiments.",
        "positive": "Traces of integrability in scattering of one-dimensional dimers on a\n  barrier: We consider molecules made of two one-dimensional short-range-interacting\nbosonic atoms. We show that in the process of scattering of these molecules off\na narrow barrier, odd incident waves produce \\emph{no unbound atoms, even when\nthe incident energy exceeds the dissociation threshold}. This effect is a\nconsequence of a prohibition on chemical reactions acting in a generally\nunphysical Bethe Ansatz integrable system of a $C_{2}$-type, with which our\nsystem shares the spatially odd eigenstates. We suggest several experimental\nimplementations of the effect. We also propose to use the monomer production as\nan alternative read-out channel in an atom interferometer: unlike in the\nstandard interferometric schemes, no spatial separation of the output channels\nwill be required."
    },
    {
        "anchor": "Edge dynamics of an Integer Quantum Hall system: In this master thesis work the linear and non linear edge dynamics of a\nnon-interacting system of fermions in a Integer Quantum Hall state is\ntheoretically and numerically studied.",
        "positive": "Bosonic binary mixtures with Josephson-type interactions: Motivated by experiments in bosonic mixtures composed of a single element in\ntwo different hyperfine states, we study bosonic binary mixtures in the\npresence of Josephson interactions between species. We focus on a particular\nmodel with $O(2)$ isospin symmetry, lifted by an imbalanced population\nparametrized by a Rabi frequency, $\\Omega _{R}$, and a detuning, $\\nu $, which\ncouples the phases of both species. We have studied the model at mean-field\napproximation plus Gaussian fluctuations. We have found that both species\nsimultaneously condensate below a critical temperature $T_{c}$ and the relative\nphases are locked by the applied laser phase, $\\alpha$. Moreover, the\ncondensate fractions are strongly dependent on the ratio $\\Omega _{R}/|\\nu |$\nthat is not affected by thermal fluctuations."
    },
    {
        "anchor": "Poincar\u00e9 index formula and analogy with the Kosterlitz-Thouless\n  transition in a non-rotated cold atom Bose-Einstein condensate: A dilute gas of Bose-Einstein condensed atoms in a non-rotated and axially\nsymmetric harmonic trap is modelled by the time dependent Gross-Pitaevskii\nequation. When the angular momentum carried by the condensate does not vanish,\nthe minimum energy state describes vortices (or antivortices) that propagate\naround the trap center. The number of (anti)vortices increases with the angular\nmomentum, and they repel each other to form Abrikosov lattices. Besides\nvortices and antivortices there are also stagnation points where the superflow\nvanishes; to our knowledge the stagnation points have not been analyzed\npreviously, in the context of the Gross-Pitaevskii equation. The Poincar\\'e\nindex formula states that the difference in the number of vortices and\nstagnation points can never change. When the number of stagnation points is\nsmall, they tend to aggregate into degenerate propagating structures. But when\nthe number becomes sufficiently large, the stagnation points tend to pair up\nwith the vortex cores, to propagate around the trap center in regular lattice\narrangements. There is an analogy with the geometry of the Kosterlitz-Thouless\ntransition, with the angular momentum of the condensate as the external control\nparameter instead of the temperature.",
        "positive": "Optical excitation of nonlinear spin waves: We demonstrate a technique for exciting spin waves in an ultracold gas of\nRb-87 atoms based on tunable AC Stark potentials. This technique allows us to\nexcite normal modes of spin waves with arbitrary amplitudes in the trapped gas,\nincluding dipole, quadrupole, octupole, and hexadecapole modes. These modes\nexhibit strong nonlinearities, which manifest as amplitude dependence of the\nexcitation frequencies and departure from sinusoidal behavior. Our results are\nin good agreement with a full treatment of a quantum Boltzmann transport\nequation."
    },
    {
        "anchor": "Spin transport in a one-dimensional quantum wire: We analyze the spin transport through a finite-size one-dimensional\ninteracting wire connected to noninteracting leads. By combining\nrenormalization-group arguments with other analytic considerations such as the\nmemory function technique and instanton tunneling, we find the temperature\ndependence of the spin conductance in different parameter regimes in terms of\ninteractions and the wire length. The temperature dependence is found to be\nnonmonotonic. In particular, the system approaches perfect spin conductance at\nzero temperature for both attractive and repulsive interactions, in contrast\nwith the static spin conductivity. We discuss the connection of our results to\nrecent experiments with ultracold atoms and compare the theoretical prediction\nto experimental data in the parameter regime where temperature is the largest\nenergy scale.",
        "positive": "Quantum degenerate Fermi gas in an orbital optical lattice: Spin-polarized samples and spin mixtures of quantum degenerate fermionic\natoms are prepared in selected excited Bloch bands of an optical chequerboard\nsquare lattice. For the spin-polarized case, extreme band lifetimes above\n$10\\,$s are observed, reflecting the suppression of collisions by Pauli's\nexclusion principle. For spin mixtures, lifetimes are reduced by an order of\nmagnitude by two-body collisions between different spin components, but still\nremarkably large values of about one second are found. By analyzing momentum\nspectra, we can directly observe the orbital character of the optical lattice.\nThe observations demonstrated here form the basis for exploring the physics of\nFermi gases with two paired spin components in orbital optical lattices,\nincluding the regime of unitarity."
    },
    {
        "anchor": "Wave-packet Dynamics in Synthetic Non-Abelian Gauge Fields: It is generally admitted that in quantum mechanics, the electromagnetic\npotentials have physical interpretations otherwise absent in classical physics\nas illustrated by the Aharonov-Bohm effect. In 1984, Berry interpreted this\neffect as a geometrical phase factor. The same year, Wilczek and Zee\ngeneralized the concept of Berry phases to degenerate levels and showed that a\nnon-Abelian gauge field arises in these systems. In sharp contrast with the\nAbelian case, spatially uniform non-Abelian gauge fields can induce particle\nnoninertial motion. We explore this intriguing phenomenon with a degenerated\nFermionic atomic gas subject to a two-dimensional synthetic SU(2) non-Abelian\ngauge field. We reveal the spin Hall nature of the noninertial dynamic as well\nas its anisotropy in amplitude and frequency due to the spin texture of the\nsystem. We finally draw the similarities and differences of the observed wave\npacket dynamic and the celebrated Zitterbewegung effect of the relativistic\nDirac equation.",
        "positive": "Phases of one-dimensional SU(N) cold atomic Fermi gases --from molecular\n  Luttinger liquids to topological phases: Alkaline-earth and ytterbium cold atomic gases make it possible to simulate\nSU(N)-symmetric fermionic systems in a very controlled fashion. Such a high\nsymmetry is expected to give rise to a variety of novel phenomena ranging from\nmolecular Luttinger liquids to (symmetry- protected) topological phases. We\nreview some of the phases that can be stabilized in a one dimensional lattice.\nThe physics of this multicomponent Fermi gas turns out to be much richer and\nmore exotic than in the standard SU(2) case. For N > 2, the phase diagram is\nquite rich already in the case of the single-band model, including a molecular\nLuttinger liquid (with dominant superfluid instability in the N-particle\nchannel) for incommensurate fillings, as well as various Mott-insulating phases\noccurring at commensurate fillings. Particular attention will be paid to the\ncases with additional orbital degree of freedom (which is accessible\nexperimentally either by taking into account two atomic states or by putting\natoms in the p-band levels). We introduce two microscopic models which are\nrelevant for these cases and discuss their symmetries and strong coupling\nlimits. More intriguing phase diagrams are then presented including, for\ninstance, symmetry protected topological phases characterized by non-trivial\nedge states."
    },
    {
        "anchor": "Excitation of knotted vortex lines in matter waves: We study the creation of knotted ultracold matter waves in Bose-Einstein\ncondensates via coherent two-photon Raman transitions with a $\\Lambda$ level\nconfiguration. The Raman transition allows an indirect transfer of atoms from\nthe internal state $\\left| a \\right\\rangle$ to the target state $\\left| b\n\\right\\rangle$ via an excited state $\\left| e \\right\\rangle$, that would be\notherwise dipole-forbidden. This setup enables us to imprint three-dimensional\nknotted vortex lines embedded in the the probe field to the density in the\ntarget state. We elaborate on experimental feasibility as well as on subsequent\ndynamics of the matter wave.",
        "positive": "Observation of Massless and Massive Collective Excitations with Faraday\n  Patterns in a Two-Component Superfluid: We report on the experimental measurement of the dispersion relation of the\ndensity and spin collective excitation modes in an elongated two-component\nsuperfluid of ultracold bosonic atoms. Our parametric spectroscopic technique\nis based on the external modulation of the transverse confinement frequency,\nleading to the formation of density and spin Faraday waves. We show that the\napplication of a coherent coupling between the two components reduces the phase\nsymmetry and gives a finite mass to the spin modes."
    },
    {
        "anchor": "Universal relations for dipolar quantum gases: We establish that two-dimensional dipolar quantum gases admit a universal\ndescription, i.e., their thermodynamic properties are independent of details of\nthe interaction at short distances. The only relevant parameters are the dipole\nlength as well as the scattering length of the combined short-range plus\ndipolar interaction potential. We derive adiabatic relations that link the\nchange in the thermodynamic potentials with respect to the scattering length\nand the dipole length to a generalized Tan contact parameter and a new dipolar\ncontact, which involves an integral of a short-distance regularized pair\ndistribution function. These two quantities determine the scale anomaly in the\ndifference between pressure and energy density and also the internal energy in\nthe presence of a harmonic confinement. For a weak transverse confinement,\nconfigurations with attractive interactions appear, which lead to a\ndensity-wave instability beyond a critical strength of the dipolar interaction.\nWe show that this instability essentially coincides with the onset of a roton\nminimum in the excitation spectrum and may be understood in terms of a quantum\nanalog of the Hansen-Verlet criterion for freezing of a classical fluid.",
        "positive": "Rotational dynamics induced by low energy binary collisions of quantum\n  droplets: A theoretical analysis of the rotational dynamics induced by off axis binary\ncollisions of quantum droplets constituted by ultracold atoms is reported. We\nfocus on quantum droplets formed by degenerate dilute Bose gases made up from\nbinary mixtures of alkaline atoms under feasible experimental conditions. The\nstability of the ground state is known to be longer for the chosen\nheteronuclear gases than for the homonuclear ones. In both cases, we find out\nthat the dynamics seems to privilege a high similarity of the density of each\natomic species. However, the evolution of the phase of the corresponding order\nparameter differs significantly for heteronuclear admixtures. We evaluate the\nfidelity as a figure of merit for the overlap between the order parameters of\neach atomic species. Dynamical evidence of the differences between the phase of\nthe order parameters are predicted to manifest in their corresponding linear\nand angular momenta. We numerically verify that the total angular and linear\nmomenta are conserved both during the collision. Some direct correlations\nbetween the Weber number and the impact parameter with the distribution of the\ndynamical variables are established."
    },
    {
        "anchor": "From the Cooper problem to canted supersolids in Bose-Fermi mixtures: We calculate the phase diagram of the Bose-Fermi Hubbard model on the 3d\ncubic lattice at fermionic half filling and bosonic unit filling by means of\nsingle-site dynamical mean-field theory. For fast bosons, this is equivalent to\nthe Cooper problem in which the bosons can induce s-wave pairing between the\nfermions. We also find miscible superfluid and canted supersolid phases\ndepending on the interspecies coupling strength. In contrast, slow bosons favor\nfermionic charge density wave structures for attractive fermionic interactions.\nThese competing instabilities lead to a rich phase diagram within reach of cold\ngas experiments.",
        "positive": "Three-body correlations in a two-dimensional SU(3) Fermi gas: We consider a three-component Fermi gas that has SU(3) symmetry and is\nconfined to two dimensions (2D). For realistic cold atomic gas experiments, we\nshow that the phase diagram of the quasi-2D system can be characterized using\ntwo 2D scattering parameters: the scattering length and the effective range.\nUnlike the case in 3D, we argue that three-body bound states (trimers) in the\nquasi-2D system can be stable against three-body losses. Using a low-density\nexpansion coupled with a variational approach, we investigate the fate of such\ntrimers in the many-body system as the attractive interactions are decreased\n(or, conversely, as the density of particles is increased). We find that\nremnants of trimers can persist in the form of strong three-body correlations\nin the weak-coupling (high-density) limit."
    },
    {
        "anchor": "Confinement-induced Resonance of Alkaline-earth-metal-like Atoms in\n  Anisotropic Quasi-one-dimensional Traps: We study the confinement-induced resonance (CIR) of $^{173}$Yb atoms near an\norbital Feshbach resonance in a quasi-one-dimensional tube with transversal\nanisotropy. By solving the two-body scattering problem, we obtain the location\nof CIR for various anisotropy ratio and magnetic field. Our results show that\nthe anisotropy of the trapping potential can serve as an additional knob to\ntune the location of CIR. In particular, one can shift the location of CIR to\nthe region attainable in current experiment. We also study the energy spectrum\nof the system and analyze the properties of CIR from the perspective of bound\nstates. We find that as the orbital Feshbach resonance acquires two nearly\ndegenerate scattering channels, which in general have different threshold\nenergies, CIR takes place when the closed channel bound state energy becomes\ndegenerate with one of the thresholds.",
        "positive": "Ground-State Dirac Monopole: We show theoretically that a monopole defect, analogous to the Dirac magnetic\nmonopole, may exist as the ground state of a dilute spin-1 Bose-Einstein\ncondensate. The ground-state monopole is not attached to a single semi-infinite\nDirac string, but forms a point where the circulation of a single vortex line\nis reversed. Furthermore, the three-dimensional dynamics of this monopole\ndefect are studied after the magnetic field pinning the monopole is removed and\nthe emergence of antimonopoles is observed. Our scheme is experimentally\nrealizable with the present-day state of the art."
    },
    {
        "anchor": "Bosonic thermoelectric transport and breakdown of universality: In this paper we compare Bose transport in normal phase atomic gases with its\ncounterpart in Fermi gases, illustrating the non-universality of two\ndimensional bosonic transport associated with different dissipation mechanisms.\nNear the superfluid transition temperature $T_c$, a striking similarity between\nthe fermionic and bosonic transport emerges because super-conducting(fluid)\nfluctuation transport for Fermi gases is dominated by the bosonic, Cooper pair\ncomponent. As in fluctuation theory, one finds that the Seebeck coefficient\nchanges sign at $T_c$ and the Lorenz number approaches zero at $T_c$. Our\nfindings appear semi-quantitatively consistent with recent Bose gas\nexperiments.",
        "positive": "Generation and Dynamics of Quantized Vortices in a Unitary Fermi\n  Superfluid: Superfluidity and superconductivity are remarkable manifestations of quantum\ncoherence at a macroscopic scale. The dynamics of superfluids has dominated the\nstudy of these systems for decades now, but a comprehensive theoretical\nframework is still lacking. We introduce a local extension of the\ntime-dependent density functional theory to describe the dynamics of fermionic\nsuperfluids. Within this approach one can correctly represent vortex\nquantization, generation, and dynamics, the transition from a superfluid to a\nnormal phase and a number of other large amplitude collective modes which are\nbeyond the scope of two-fluid hydrodynamics, Ginzburg-Landau and/or\nGross-Pitaevskii approaches. We illustrate the power of this approach by\nstudying the generation of quantized vortices, vortex rings, vortex\nreconnection, and transition from a superfluid to a normal state in real time\nfor a unitary Fermi gas. We predict the emergence of a new qualitative\nphenomenon in superfluid dynamics of gases, the existence of stable\nsuperfluidity when the systems are stirred with velocities significantly\nexceeding the nominal Landau critical velocity in these systems."
    },
    {
        "anchor": "Polar molecules in bilayers with high population imbalance: We investigate a dilute Fermi gas of polar molecules confined into a bilayer\nsetup with dipole moments polarized perpendicular to the layers. In particular,\nwe consider the extreme case of population imbalance, where we have only one\nparticle in one layer and many particles in the other one. The single molecule\nis attracted by the dilute Fermi-gas through the inter-layer dipole-dipole\nforce presenting an interesting impurity problem with longrange anistropic\ninteraction. We calulate the chemical potential of the impurity, in second\norder perturbation theory and in ladder approximation with a\nBrueckner-Hartree-Fock approach. Moreover, we determine the momentum relaxation\nrate of the impurity, which is related to the \"dipolar\" drag effect. For a\nconfined system we relate the results for the chemical potential with the\nmeasurement of the collective modes of the impurity. The momentum relaxation\nrate provide instead an estimate on how quickly the oscillations are damped.",
        "positive": "Ultrastable super-Tonks-Girardeau gases under weak dipolar interactions: The highly excited super-Tonks-Girardeau (sTG) gas was recently observed to\nbe extremely stable in the presence of a weak dipolar repulsion. Here we reveal\nthe underlying reason for this mysterious phenomenon. By exactly solving the\ntrapped small clusters with both contact and dipolar interactions, we show that\nthe reason lies in the distinct spectral responses between sTG gas and its\ndecaying channel (bound state) when turn on a weak dipolar interaction.\nSpecifically, a tiny dipolar force can produce a visible energy shift for the\nlocalized bound state, but can hardly affect the extended sTG branch. As a\nresult, the avoided level crossing between two branches is greatly modified in\nboth location and width in the parameter axis of coupling strength, leading to\na more (less) stable sTG gas for a repulsive (attractive) dipolar force. These\nresults, consistent with experimental observations, are found to robustly apply\nto both bosonic and fermionic systems."
    },
    {
        "anchor": "Many-body localization in Ising models with random long-range\n  interactions: We theoretically investigate the many-body localization phase transition in a\none-dimensional Ising spin chain with random long-range spin-spin interactions,\n$V_{ij}\\propto\\left|i-j\\right|^{-\\alpha}$, where the exponent of the\ninteraction range $\\alpha$ can be tuned from zero to infinitely large. By using\nexact diagonalization, we calculate the half-chain entanglement entropy and the\nenergy spectral statistics and use them to characterize the phase transition\ntowards the many-body localization phase at infinite temperature and at\nsufficiently large disorder strength. We perform finite-size scaling to extract\nthe critical disorder strength and the critical exponent of the divergent\nlocalization length. With increasing $\\alpha$, the critical exponent\nexperiences a sharp increase at about $\\alpha=1$ and then gradually decreases\nto a value found earlier in a disordered short-ranged interacting spin chain.\nFor $\\alpha<1$, we find that the system is mostly localized and the increase in\nthe disorder strength may drive a transition between two many-body localized\nphases. In contrast, for $\\alpha>1$, the transition is from a thermalized phase\nto the many-body localization phase. Our predictions could be experimentally\ntested with ion-trap quantum emulator with programmable random long-range\ninteractions, or with randomly distributed Rydberg atoms or polar molecules in\nlattices.",
        "positive": "Gap solitons of a super-Tonks-Girardeau gas in a one-dimensional\n  periodic potential: We study the stability of gap solitons of the super-Tonks-Girardeau bosonic\ngas in one-dimensional periodic potential. The linear stability analysis\nindicates that increasing the amplitude of periodic potential or decreasing the\nnonlinear interactions, the unstable gap solitons can become stable. In\nparticular, the theoretical analysis and numerical calculations show that,\ncomparing to the lower-family of gap solitons, the higher-family of gap\nsolitons are easy to form near the bottoms of the linear Bloch band gaps. The\nnumerical results also verify that the composition relations between various\ngap solitons and nonlinear Bloch waves are general and can exist in the\nsuper-Tonks-Girardeau phase."
    },
    {
        "anchor": "Master's Thesis: Excitation Spectrum of a Weakly Interacting Spin-Orbit\n  Coupled Bose-Einstein Condensate: A weakly interacting, spin-orbit coupled, two-component, ultracold Bose gas\nbound to a Bravais lattice is studied. Motivated by recent experimental\nadvances in the field of synthetically spin-orbit coupled, ultracold, neutral\natomic gases showing Bose-Einstein condensation, an analytic framework with\nwhich to describe such systems in the superfluid regime is presented. This is\napplied to a Rashba spin-orbit-coupled Bose gas in a two-dimensional optical\nlattice. The exotic nature of Bose-Einstein condensation in the presence of\nspin-orbit coupling is an interesting study by itself. Additionally, when the\noptical lattice is introduced, the system provides a highly controllable\nexperimental testing ground for numerous condensed matter physics phenomena.\nFive phases of the system are considered, and their excitation spectra,\ncritical superfluid velocities and free energies are found. In obtaining the\nfree energy, the effects of terms in the Hamiltonian that are linear in\nexcitation operators are included, and such terms have not been studied\npreviously in this context. Minimization of the free energy at zero temperature\nis used to confirm the phase diagrams reported in the literature, where it has\nusually been obtained by neglecting the effect of excitations. The plane and\nstripe wave phases in the phase diagram are bosonic analogues of\nFulde-Ferrell-Larkin-Ovchinnikov states in superconductors involving nonzero\ncondensate momenta.",
        "positive": "Antiferromagnetic Order and Bose-Einstein Condensation in\n  Strongly-Correlated Cold-Atom Systems: Bosonic t-J Model in the Double-CP^1\n  Representation: We study the three-dimensional bosonic t-J model, i.e., the t-J model of\n\"bosonic electrons\" at finite temperatures. This model describes a system of\ncold bosonic atoms with two species in an optical lattice. The model is derived\nfrom the Hubbard model for very large on-site repulsive interaction between\nbosons of same species (hard-core nature) and also strong correlations between\ndifferent species. The operator B_{x\\sigma} for an atom at the site x with a\ntwo-component (pseudo-) spin \\sigma (=1,2) is treated as a hard-core boson\noperator, and represented by a composite of two slave particles; a spinon\ndescribed by a CP^1 field (Schwinger boson) z_{x\\sigma} and a holon described\nby a hard-core-boson field \\phi_x as B_{x\\sigma}=\\phi^\\dag_x z_{x\\sigma}.\n\\phi_x is then expressed by a pseudo-spin, which is, in turn, represented by\nanother CP^1 (pseudo) spinon w_{x\\eta} as \\phi_x = w_{x2}^\\dag w_{x1}. We then\nhave a double-CP^1 representation of the model by z_{x\\sigma} and w_{x\\eta}. By\nmeans of Monte Carlo simulations of this bosonic t-J model, we study its phase\nstructure and the possible phenomena like appearance of antiferromagnetic\nlong-range order, Bose-Einstein condensation, phase separation, etc. They\nshould be compared with the possible experimental results of a recently studied\nboson-boson mixture like ^87Rb and ^41K in an optical lattice."
    },
    {
        "anchor": "Classical crystal formation of dipoles in two dimensions: We consider a two-dimensional layer of dipolar particles in the regime of\nstrong dipole moments. Here we can describe the system using classical methods\nand determine the crystal structure that minimizes the total energy. The\ndipoles are assumed to be aligned by an external field and we consider\ndifferent orientations of the dipolar moments with respect to the\ntwo-dimensional plane of motion. We observe that when the orientation angle\nchanges away from perpendicular and towards the plane, the crystal structure\nwill change from a hexagonal form to one that has the dipoles sitting in\nequidistant rows, i.e. a striped configuration. In addition to calculating the\ncrystal unit cell, we also consider the phonon spectrum and the speed of sound.\nAs the orientation changes away from perpendicular the phonon spectrum develops\nlocal minima that are a result of the deformation to the crystal structure.",
        "positive": "Ultracold atoms in an optical lattice with dynamically variable\n  periodicity: The use of a dynamic \"accordion\" lattice with ultracold atoms is\ndemonstrated. Ultracold atoms of $^{87}$Rb are trapped in a two-dimensional\noptical lattice, and the spacing of the lattice is then increased in both\ndirections from 2.2 to 5.5 microns. Atoms remain bound for expansion times as\nshort as a few milliseconds, and the experimentally measured minimum ramp time\nis found to agree well with numerical calculations. This technique allows an\nexperiment such as quantum simulations to be performed with a lattice spacing\nsmaller than the resolution limit of the imaging system, while allowing imaging\nof the atoms at individual lattice sites by subsequent expansion of the optical\nlattice."
    },
    {
        "anchor": "Quantum Quenches in an XXZ Spin Chain from a Spatially Inhomogeneous\n  Initial State: Results are presented for the nonequilibrium dynamics of a quantum $XXZ$-spin\nchain whose spins are initially arranged in a domain wall profile via the\napplication of a magnetic field in the $z$-direction which is spatially varying\nalong the chain. The system is driven out of equilibrium in two ways: a). by\nrapidly turning off the magnetic field, b). by rapidly quenching the\ninteractions at the same time as the magnetic field is turned off. The\ntime-evolution of the domain wall profile as well as various two-point spin\ncorrelation functions is studied by the exact solution of the fermionic problem\nfor the $XX$ chain and via a bosonization approach and a mean-field approach\nfor the $XXZ$ chain. At long times the magnetization is found to equilibrate\n(reach the ground state value), while the two-point correlation functions in\ngeneral do not. In particular, for quenches within the gapless $XX$ phase, the\ntransverse spin correlation functions acquire a spatially inhomogeneous\nstructure at long times whose details depend on the initial domain wall\nprofile. The spatial inhomogeneity is also recovered for the case of classical\nspins initially arranged in a domain wall profile and shows that the\ninhomogeneities arise due to the dephasing of transverse spin components as the\ndomain wall broadens. A generalized Gibbs ensemble approach is found to be\ninadequate in capturing this spatially inhomogeneous state.",
        "positive": "Correlation functions of the Lieb-Liniger gas and the LeClair-Mussardo\n  formula: In this letter we derive formulas for multi point correlation functions, in\nthe thermodynamic limit, for the Lieb Liniger gas taken with respect to\narbitrary eigenstates. These results apply for the ground state, thermal states\nand GGE states. We obtain these correlation functions as a series of multiple\nintegrals of progressively higher dimensions. These integrals converge rapidly\nfor short distance correlation functions and low densities of particles. The\nseries derived matches exactly the LeClair Mussardo formula for correlation\nfunctions of relativistic integrable models."
    },
    {
        "anchor": "Creating a Quantum Degenerate Gas of Stable Molecules via Weak\n  Photoassociation: Quantum degenerate molecules represent a new paradigm for fundamental studies\nand practical applications. Association of already quantum degenerate atoms\ninto molecules provides a crucial shortcut around the difficulty of cooling\nmolecules to ultracold temperatures. Whereas association can be induced with\neither laser or magnetic fields, photoassociation requires impractical laser\nintensity to overcome poor overlap between the atom pair and molecular\nwavefunctions, and experiments are currently restricted to magnetoassociation.\nHere we model realistic production of a quantum degenerate gas of stable\nmolecules via two-photon photoassociation of Bose-condensed atoms. An adiabatic\nchange of the laser frequency converts the initial atomic condensate almost\nentirely into stable molecular condensate, even for low-intensity lasers.\nResults for dipolar LiNa provide an upper bound on the necessary\nphotoassociation laser intensity for alkali-metal atoms ~30 W/cm^2, indicating\na feasible path to quantum degenerate molecules beyond magnetoassociation.",
        "positive": "Geometry-induced memory effects in isolated quantum systems:\n  Observations and applications: Memory effects can lead to history-dependent behavior of a system, and they\nare ubiquitous in our daily life and have broad applications. Here we explore\npossibilities of generating memory effects in simple isolated quantum systems.\nBy utilizing geometrical effects from a class of lattices supporting flat-bands\nconsisting of localized states, memory effects could be observed in ultracold\natoms in optical lattices. As the optical lattice continuously transforms from\na triangular lattice into a kagome lattice with a flat band, history-dependent\ndensity distributions manifest quantum memory effects even in noninteracting\nsystems, including fermionic as well as bosonic systems in the proper ranges of\ntemperatures. Rapid growth in ultracold technology predicts a bright future for\nquantum memory-effect systems, and here two prototypical applications of\ngeometry-induced quantum memory effects are proposed: An accelerometer\nrecording the mechanical change rate in a coupled system and a rate-controlled\nmemvalve where the rate of ramping the lattice potential acts as a control of\nthe remnant density in the lattice."
    },
    {
        "anchor": "Resonantly Enhanced Tunneling and Transport of Ultracold Atoms on Tilted\n  Optical Lattices: We investigate the resonantly enhanced tunneling dynamics of ultracold bosons\nloaded on a tilted 1-D optical lattice, which can be used to simulate a chain\nof Ising spins and associated quantum phase transitions. The center of mass\nmotion after a sudden tilt both at commensurate and incommensurate fillings is\nobtained via analytic, time-dependent exact diagonalization and density matrix\nrenormalization group methods (adaptive t-DMRG). We identify a maximum in the\namplitude of the center of mass oscillations at the quantum critical point of\nthe effective spin system. For the dynamics of incommensurate systems, which\ncannot be mapped to a spin model, we develop an analytical approach in which\nthe time evolution is obtained by projecting onto resonant families of small\nclusters. We compare the results of this approach at low fillings to the exact\ntime evolution and find good agreement even at filling factors as large as 2/3.\nUsing this projection onto small clusters, we propose a controllable transport\nscheme applicable in the context of Atomtronic devices on optical lattices\n(`slinky scheme').",
        "positive": "Interference of Two-Dimensional Bose-Einstein Condensates in\n  Micro-Gravity: We investigate the interference of two-dimensional Bose-Einstein condensates\nin micro-gravity, which influenced by the interaction strength, initial\nmomentum, gravitational potential and phase difference. We demonstrate that the\ngravitational potential from the Earth can change the density distribution and\nphase distribution of the condensate's wave function. As time evolves, a\nportion of the gravitational potential energy of the microscopic particles can\nbe converted into kinetic energy, which changes the motion of the microscopic\nparticles, and leads to the varying of the density and phase distribution of\nthe wave function. Nevertheless, the influences of the Earth's gravity on the\nwave function can be eliminated by the micro-gravity environment, which\nconfirmed by many micro-gravity cold atom experiments. Our results present the\ninfluences of gravity and other parameters on interference of Bose-Einstein\ncondensates, which help us to reveal the intrinsic natures of the related\ntheoretical predictions and experimental phenomena. Furthermore, our work\nbuilds a bridge between the related physical phenomena and our physical\nintuition about the Bose-Einstein condensates in micro-gravity environment."
    },
    {
        "anchor": "Experimental realization of a non-magnetic one-way spin switch: Controlling magnetism through non-magnetic means is highly desirable for\nfuture electronic devices, as such means typically have ultra-low power\nrequirements and can provide coherent control. In recent years, great\nexperimental progress has been made in the field of electrical manipulation of\nmagnetism in numerous material systems. These studies generally do not consider\nthe directionality of the applied non-magnetic potentials and/or magnetism\nswitching. Here, we theoretically conceive and experimentally demonstrate a\nnon-magnetic one-way spin switch device using a spin-orbit coupled\nBose-Einstein condensate subjected to a moving spin-independent dipole\npotential. The physical foundation of this unidirectional device is based on\nthe breakdown of Galilean invariance in the presence of spin-orbit coupling.\nSuch a one-way spin switch opens an avenue for designing novel quantum devices\nwith unique functionalities and may facilitate further experimental\ninvestigations of other one-way spintronic and atomtronic devices.",
        "positive": "Emergence of dark soliton signatures in a one-dimensional unpolarized\n  attractive Fermi gas on a ring: The two-component Fermi gas with contact attractive interactions between\ndifferent spin components can be described by the Yang-Gaudin model. Applying\nthe Bethe ansatz approach, one finds analytical formulae for the system\neigenstates that are uniquely parametrized by the solutions of the\ncorresponding Bethe equations. Recent numerical studies of the so-called yrast\neigenstates, i.e. lowest energy eigenstates at a given non-zero total momentum,\nin the Yang-Gaudin model show that their spectrum resembles yrast dispersion\nrelation of the Lieb-Liniger model which in turn matches the dark soliton\ndispersion relation obtained within the nonlinear Schr\\\"{o}dinger equation. It\nwas shown that such conjecture in the case of the Lieb-Liniger model was not\naccidental and that dark soliton features emerged in the course of measurement\nof positions of particles, when the system was initially prepared in an yrast\neigenstate. Here, we demonstrate that, starting with yrast eigenstates in the\nYang-Gaudin model, the key soliton signatures are revealed by the measurement\nof pairs of fermions. We study soliton signatures in a wide range of the\ninteraction strength."
    },
    {
        "anchor": "Measuring The Heat Capacity in a Bose-Einstein Condensation using Global\n  Variables: Phase transitions are well understood and generally followed by the behavior\nof the associated thermodynamic quantities, such as in the case of the\n$\\lambda$ point superfluid transition of liquid helium, which is observed in\nits heat capacity. In the case of a trapped Bose-Einstein condensate (BEC), the\nheat capacity cannot be directly measured. In this work, we present a technique\nable to determine the global heat capacity from the density distribution of a\nweakly interacting gas trapped in an inhomogeneous potential. This approach\nrepresents an alternative to models based on local density approximation. By\ndefining a pair of global conjugate variables, we determine the total internal\nenergy and its temperature derivative, the heat capacity. We then apply the\ntechnique to a trapped $^{87}$Rb BEC a $\\lambda$-type transition dependent on\nthe atom number is observed, and the deviations from the non-interacting, ideal\ngas case are discussed. Finally we discuss the chances of using this method to\nstudy the heat capacity at $T \\rightarrow 0$.",
        "positive": "Topological Creutz Ladder in a Resonantly Shaken 1D Optical Lattice: We report the experimental realization of a topological Creutz ladder for\nultracold fermionic atoms in a resonantly driven 1D optical lattice. The\ntwo-leg ladder consists of the two lowest orbital states of the optical lattice\nand the cross inter-leg links are generated via two-photon resonant coupling\nbetween the orbitals by periodic lattice shaking. The characteristic\npseudo-spin winding in the topologically non-trivial bands of the ladder system\nis demonstrated using momentum-resolved Ramsey-type interferometric\nmeasurements. We discuss a two-tone driving method to extend the inter-leg link\ncontrol and propose a topological charge pumping scheme for the Creutz ladder\nsystem."
    },
    {
        "anchor": "Opto-mechanical effects in self-organization of a Bose-Einstein\n  condensate in an optical cavity: The influence of mirror motion on the spatial self organization of a\nBose-Einstein condensate (BEC) in an optical cavity is studied. We show that\nthe mirror dynamics tends to destroy the process of self organization. An\nadditional external phonon pump is shown to modify the critical photon pump\nneeded to observe the onset of self organization.",
        "positive": "Effects of an attractive three body interaction on a spin-1 Bose Hubbard\n  model: We study the effects of an attractive three body interaction potential on a\nspin-1 ultracold Bose gas using mean field approach (MFA). For an\nantiferromagnetic (AF) interaction, the third MI lobe is predominantly\naffected, where it completely engulfs the second and the fourth MI lobes at\nlarge values of the interaction strength. Albeit no significant change is\nobserved beyond the fourth MI lobe. The formation of the spin singlet (nematic)\nMI phase and the different order of phase transitions to the SF phase have been\ncarefully scrutinized with the help of spin eigenvalues and spin nematic order\nparameter. In the ferromagnetic case, the phase diagram shows similar features\nas that of a scalar Bose gas. We have compared our results on the MFA phase\ndiagrams for both types of the interaction potential via a perturbation\nexpansion in both the cases."
    },
    {
        "anchor": "Zero-point excitation of a circularly moving detector in an atomic\n  condensate and phonon laser dynamical instabilities: We study a circularly moving impurity in an atomic condensate for the\nrealisation of superradiance phenomena in tabletop experiments. The impurity is\ncoupled to the density fluctuations of the condensate and, in a quantum field\ntheory language, it serves as an analog of a detector for the quantum phonon\nfield. For sufficiently large rotation speeds, the zero-point fluctuations of\nthe phonon field induce a sizeable excitation rate of the detector even when\nthe condensate is initially at rest in its ground state. For spatially confined\ncondensates and harmonic detectors, such a superradiant emission of sound waves\nprovides a dynamical instability mechanism leading to a new concept of phonon\nlasing. Following an analogy with the theory of rotating black holes, our\nresults suggest a promising avenue to quantum simulate basic interaction\nprocesses involving fast moving detectors in curved space-times.",
        "positive": "Driven-dissipative many-body pairing states for cold fermionic atoms in\n  an optical lattice: We discuss the preparation of many-body states of cold fermionic atoms in an\noptical lattice via controlled dissipative processes induced by coupling the\nsystem to a reservoir. Based on a mechanism combining Pauli blocking and phase\nlocking between adjacent sites, we construct complete sets of jump operators\ndescribing coupling to a reservoir that leads to dissipative preparation of\npairing states for fermions with various symmetries in the absence of direct\ninter-particle interactions. We discuss the uniqueness of these states, and\ndemonstrate it with small-scale numerical simulations. In the late time\ndissipative dynamics, we identify a \"dissipative gap\" that persists in the\nthermodynamic limit. This gap implies exponential convergence of all many-body\nobservables to their steady state values. We then investigate how these pairing\nstates can be used as a starting point for the preparation of the ground state\nof Fermi-Hubbard Hamiltonian via an adiabatic state preparation process also\ninvolving the parent Hamiltonian of the pairing state. We also provide a\nproof-of-principle example for implementing these dissipative processes and the\nparent Hamiltonians of the pairing states, based on Yb171 atoms in optical\nlattice potentials."
    },
    {
        "anchor": "Quench Dynamics of the Anisotropic Heisenberg Model: We develop an analytic approach for the study of the quench dynamics of the\nanisotropic Heisenberg model (XXZ model) on the infinite line. We present the\nexact time-dependent wavefunctions after a quench in an integral form for any\ninitial state and for any anisotropy $\\Delta$ by means of a generalized Yudson\ncontour representation. We calculate the evolution of several observables from\ntwo particular initial states: starting with a local N\\`eel state we calculate\nthe time evolution of the antiferromagnetic order parameter--staggered\nmagnetization; starting with a state with consecutive flipped spins we\ncalculate the propagation of magnons and bound state excitations, and the\ninduced spin currents. We also show how the \"string\" solution of Bethe Ansatz\nequations emerge naturally from the contour approach. We confront our results\nwith experiments and numerical methods where possible.",
        "positive": "Simulating and exploring Weyl semimetal physics with cold atoms in a\n  two-dimensional optical lattice: We propose a scheme to simulate and explore Weyl semimetal physics with\nultracold fermionic atoms in a two-dimensional square optical lattice subjected\nto experimentally realizable spin-orbit coupling and an artificial dimension\nfrom an external parameter space, which may increase experimental feasibility\ncompared with the cases in three dimensional optical lattices. It is shown that\nthis system with a tight-binding model is able to describe essentially\nthree-dimensional Weyl semimetals with tunable Weyl points. The relevant\ntopological properties are also addressed by means of the Chern number and the\ngapless edge states. Furthermore, we illustrate that the mimicked Weyl points\ncan be experimentally detected by measuring the atomic transfer fractions in a\nBloch-Zener oscillation, and the characteristic topological invariant can be\nmeasured with the particle pumping approach."
    },
    {
        "anchor": "Distinguishing Quantum Phases through Cusps in Full Counting Statistics: Measuring physical observables requires averaging experimental outcomes over\nnumerous identical measurements. The complete distribution function of possible\noutcomes or its Fourier transform, known as the full counting statistics,\nprovides a more detailed description. This method captures the fundamental\nquantum fluctuations in many-body systems and has gained significant attention\nin quantum transport research. In this letter, we propose that cusp\nsingularities in the full counting statistics are a novel tool for\ndistinguishing between ordered and disordered phases. As a specific example, we\nfocus on the superfluid-to-Mott transition in the Bose-Hubbard model and\nintroduce $Z_A(\\alpha)=\\langle \\exp({i\\alpha \\sum_{i\\in\nA}(\\hat{n}_i}-\\overline{n}))\\rangle $ with $\\overline{n}=\\langle n_i \\rangle$.\nThrough both analytical analysis and numerical simulations, we demonstrate that\n$\\partial_\\alpha \\log Z_A(\\alpha)$ exhibits a discontinuity near $\\alpha=\\pi$\nin the superfluid phase when the subsystem size is sufficiently large, while it\nremains smooth in the Mott phase. This discontinuity can be interpreted as a\nfirst-order transition between different semi-classical configurations of\nvortices. We anticipate that our discoveries can be readily tested using\nstate-of-the-art ultracold atom and superconducting qubit platforms.",
        "positive": "Density-dependent hopping for ultracold atoms immersed in a\n  Bose-Einstein-condensate vortex lattice: Both mixtures of atomic Bose-Einstein condensates and systems with atoms\ntrapped in optical lattices have been intensely explored theoretically, mainly\ndue to the exceptional developments on the experimental side. We investigate\nthe properties of ultracold atomic impurities (bosons) immersed in a vortex\nlattice of a second Bose-condensed species. In contrast to the static\noptical-lattice configuration, the vortex lattice presents intrinsic dynamics\ngiven by its Tkachenko modes. These excitations induce additional correlations\nbetween the impurities, which consist in a long-range attractive potential and\nin a density-dependent hopping, described here in the framework of an extended\nBose-Hubbard model. We compute the quantum phase diagram of the impurity\nspecies through a Gutzwiller ansatz and through the mean-field approach, and\nseparately identify the effects of the two additional terms, i.e., the shift\nand the deformation of the Mott insulator lobes. The long-range attraction, in\nparticular, induces the existence of a triple point in the phase diagram, in\nagreement with previous quantum Monte Carlo calculations [Chaviguri \\emph{et\nal.}, Phys. Rev. A \\textbf{95}, 053639 (2017)]."
    },
    {
        "anchor": "Non-Hermitian Skin Effect In Periodically-Driven Dissipative Ultracold\n  Atoms: The non-Hermitian skin effect (NHSE), featured by the collapse of bulk-band\neigenstates into the localized boundary modes of the systems, is one of most\nstriking properties in the fields of non-Hermitian physics. Unique physical\nphenomena related to the NHSE have attracted a lot of interest, however, their\nexperimental realizations usually require nonreciprocal hopping, which faces a\ngreat challenge in ultracold-atom systems. In this work, we propose to realize\nthe NHSE in a 1D optical lattice by periodically-driven ultracold atoms in the\npresence of staggered atomic loss. By studying the effective Floquet\nHamiltonian in the high-frequency approximation, we reveal the underlying\nmechanism for the periodic-driving-induced the NHSE. We found that the robust\nNHSE can be tuned by driving phase, which is manifested by the dynamical\nlocalization. Most remarkably, we uncover the periodic-driving-induced critical\nskin effect for two coupled chains with different driving phases, accompanied\nby the appearance of size-dependent topological in-gap modes. Our studies\nprovide a feasible way for observing the NHSE and exploring corresponding\nunique physical phenomena due to the interplay of non-Hermiticity and many-body\nstatistics in ultracold-atom systems.",
        "positive": "Mean-field phase diagram of the 1-D Bose gas in a disorder potential: We study the quantum phase transition of the 1D weakly interacting Bose gas\nin the presence of disorder. We characterize the phase transition as a function\nof disorder and interaction strengths, by inspecting the long-range behavior of\nthe one-body density matrix as well as the drop in the superfluid fraction. We\nfocus on the properties of the low-energy Bogoliubov excitations that drive the\nphase transition, and find that the transition to the insulator state is marked\nby a diverging density of states and a localization length that diverges as a\npower-law with power 1. We draw the phase diagram and we observe that the\nboundary between the superfluid and the Bose glass phase is characterized by\ntwo different algebraic relations. These can be explained analytically by\nconsidering the limiting cases of zero and infinite disorder correlation\nlength."
    },
    {
        "anchor": "Bloch-Landau-Zener dynamics in single-particle Wannier-Zeeman systems: Stimulated by the experimental realization of spin-dependent tunneling via\ngradient magnetic field [Phys. Rev. Lett. 111, 225301 (2013); Phys. Rev. Lett.\n111, 185301 (2013)], we investigate dynamics of Bloch oscillations and\nLandau-Zener tunneling of single spin-half particles in a periodic potential\nunder the influence of a spin-dependent constant force. In analogy to the\nWannier-Stark system, we call our system as the Wannier-Zeeman system. If there\nis no coupling between the two spin states, the system can be described by two\ncrossing Wannier-Stark ladders with opposite tilts. The spatial crossing\nbetween two Wannier-Stark ladders becomes a spatial anti-crossing if the two\nspin states are coupled by external fields. For a wave-packet away from the\nspatial anti-crossing, due to the spin-dependent constant force, it will\nundergo spatial Landau-Zener transitions assisted by the intrinsic intra-band\nBloch oscillations, which we call the Bloch-Landau-Zener dynamics. If the\ninter-spin coupling is sufficiently strong, the system undergoes adiabatic\nBloch-Landau-Zener dynamics, in which the spin dynamics follows the local\ndressed states. Otherwise, for non-strong inter-spin couplings, the system\nundergoes non-adiabatic Bloch-Landau-Zener dynamics.",
        "positive": "Polaron-Depleton Transition in the Yrast Excitations of a\n  One-Dimensional Bose Gas with a Mobile Impurity: We present exact numerical data for the lowest-energy momentum eigenstates\n(yrast states) of a repulsive spin impurity in a one-dimensional Bose gas using\nfull configuration interaction quantum Monte Carlo (FCIQMC). As a stochastic\nextension to exact diagonalization it is well suited for the study of yrast\nstates of a lattice-renormalized model for a quantum gas. Yrast states carry\nvaluable information about the dynamic properties of slow-moving mobile\nimpurities immersed in a many-body system. Based on the energies and the first\nand second order correlation functions of yrast states, we identify different\ndynamical regimes and the transitions between them: The polaron regime, where\nthe impurity's motion is affected by the Bose gas through a renormalized\neffective mass; a regime of a gray soliton that is weakly correlated with a\nstationary impurity, and the depleton regime, where the impurity occupies a\ndark or gray soliton. Extracting the depleton effective mass reveals a super\nheavy regime where the magnitude of the (negative) depleton mass exceeds the\nmass of the finite Bose gas."
    },
    {
        "anchor": "Adiabatic Preparation of a Heisenberg Antiferromagnet Using an Optical\n  Superlattice: We analyze the possibility to prepare a Heisenberg antiferromagnet with cold\nfermions in optical lattices, starting from a band insulator and adiabatically\nchanging the lattice potential. The numerical simulation of the dynamics in 1D\nallows us to identify the conditions for success, and to study the influence\nthat the presence of holes in the initial state may have on the protocol. We\nalso extend our results to two-dimensional systems.",
        "positive": "Fermionization of a Few-Body Bose System Immersed into a Bose-Einstein\n  Condensate: We study the recently introduced self-pinning transition [Phys. Rev. Lett.\n128, 053401 (2022)] in a quasi-one-dimensional two-component quantum gas in the\ncase where the component immersed into the Bose-Einstein condensate has a\nfinite intraspecies interaction strength. As a result of the matter-wave\nbackaction, the fermionization in the limit of infinite intraspecies repulsion\noccurs via a first-order phase transition to the self-pinned state, which is in\ncontrast to the asymptotic behavior in static trapping potentials. The system\nalso exhibits an additional superfluid state for the immersed component if the\ninterspecies interaction is able to overcome the intraspecies repulsion. We\napproximate the superfluid state in an analytical model and derive an\nexpression for the phase transition line that coincides with well-known phase\nseparation criteria in binary Bose systems. The full phase diagram of the\nsystem is mapped out numerically for the case of two and three atoms in the\nimmersed component."
    },
    {
        "anchor": "Quantum quench in an atomic one-dimensional Ising chain: We study non-equilibrium dynamics for an ensemble of tilted one-dimensional\natomic Bose-Hubbard chains after a sudden quench to the vicinity of the\ntransition point of the Ising paramagnetic to anti-ferromagnetic quantum phase\ntransition. The quench results in coherent oscillations for the orientation of\neffective Ising spins, detected via oscillations in the number of\ndoubly-occupied lattice sites. We characterize the quench by varying the system\nparameters. We report significant modification of the tunneling rate induced by\ninteractions and show clear evidence for collective effects in the oscillatory\nresponse.",
        "positive": "Local Topological Markers in Odd Dimensions: Local topological markers have proven to be a valuable tool for investigating\nsystems with topologically non-trivial bands. Due to their local nature, such\nmarkers can treat translationally invariant systems and spatially inhomogeneous\nsystems on an equal footing. Among the most prevalent of these is the so-called\nChern marker, which is available for systems in two spatial dimensions. In this\npaper, we describe how to generalize this marker to 1d and 3d systems, by\nshowing that the relevant expressions accurately describe the phenomenon of\ntopological pumping given by the first and second Chern numbers in 1d and 3d\nrespectively. In addition to providing general derivations, we verify the\nmarkers by numerically considering model Hamiltonians. These results will open\nthe door for future studies including the influence of disorder on topological\npumping and topological phase transitions in odd-dimensional systems."
    },
    {
        "anchor": "Many-Body Entanglement in Short-Range Interacting Fermi Gases for\n  Metrology: We explore many-body entanglement in spinful Fermi gases with short-range\ninteractions, for metrology purposes. We characterize the emerging quantum\nphases via Density-Matrix Renormalization Group simulations and quantify their\nentanglement content for metrological usability via the Quantum Fisher\nInformation (QFI). Our study establishes a method, promoting the QFI to be an\norder parameter. Short-range interactions reveal to build up metrologically\npromising entanglement in the XY-ferromagnetic and cluster ordering, the\ncluster physics being unexplored so far.",
        "positive": "Observation of a non-Hermitian phase transition in an optical quantum\n  gas: Quantum gases of light, as photons or polariton condensates in optical\nmicrocavities, are collective quantum systems enabling a tailoring of\ndissipation from e.g. cavity loss. This makes them a tool to study dissipative\nphases, an emerging subject in quantum manybody physics. Here we experimentally\ndemonstrate a non-Hermitian phase transition of a photon Bose-Einstein\ncondensate to a new dissipative phase, characterized by a biexponential decay\nof the condensate's second-order coherence. The phase transition occurs due to\nthe emergence of an exceptional point in the quantum gas. While Bose-Einstein\ncondensation is usually connected to ordinary lasing by a smooth crossover, the\nobserved phase transition separates the novel, biexponential phase from both\nlasing and an intermediate, oscillatory condensate regime. Our findings pave\nthe way for studies of a wide class of dissipative quantum phases, for instance\nin topological or lattice systems."
    },
    {
        "anchor": "Polaronic properties of an impurity in a Bose-Einstein condensate in\n  reduced dimensions: The application of optical lattices allows a tuning of the geometry of\nBose-Einstein condensates to effectively reduced dimensions. In the context of\nsolid state physics the consideration of the low-dimensional Fr\\\"ohlich polaron\nresults in an extension of the polaronic strong coupling regime. With this\nmotivation we apply the Jensen-Feynman variational principle to calculate the\nground state properties of the polaron consisting of an impurity in a\nBose-Einstein condensate in reduced dimensions. Also the response of this\nsystem to Bragg scattering is calculated. We show that reducing the dimension\nleads to a larger amplitude of the polaronic features and is expected to\nfacilitate the experimental observation of polaronic properties. In optical\nlattices not only Feshbach resonances but also confinement-induced resonances\ncan be used to tune the polaronic coupling strength. This opens up the\npossibility to experimentally reveal the intermediate and strong polaronic\ncoupling regimes and resolve outstanding theoretical questions regarding\npolaron theory.",
        "positive": "Phase Diagram of Mixed-Dimensional Anisotropic t-J-Models: We study the phase diagram of two different mixed-dimensional\n$t-J_z-J_{\\perp}$-models on the square lattice, in which the hopping amplitude\n$t$ is only nonzero along the $x$-direction. In the first, bosonic, model, the\nspin exchange amplitude $J_{\\perp}$ is negative and isotropic along the $x$ and\n$y$ directions of the lattice, and $J_z$ is isotropic and positive. The\nlow-energy physics is characterized by spin-charge separation: the holes hop as\nfree fermions in an easy-plane ferromagnetic background. In the second model,\n$J_{\\perp}$ is restricted to the $x$-axis while $J_z$ remains isotropic and\npositive. The model is agnostic to particle statistics, and shows stripe\npatterns with anti-ferromagnetic N{\\'e}el order at low temperature and high\nhole concentrations, in resemblance of the mixed-dimensional $t-J_z$ and $t-J$\nmodels. At lower hole concentration, a very strong first order transition and\nhysteresis loop is seen extending to a remarkably high 14(1)% hole doping."
    },
    {
        "anchor": "Dynamical instability of a non-equilibrium exciton-polariton condensate: By imaging single-shot realizations of an organic polariton quantum fluid, we\nobserve the long-sought dynamical instability of non-equilibrium condensates.\nWithout any free parameters, we find an excellent agreement between the\nexperimental data and a numerical simulation of the open-dissipative\nGross-Pitaevskii equation, which allows us to draw several important\nconclusions about the physics of the system. We find that the reservoir\ndynamics are in the strongly nonadiabatic regime, which renders the complex\nGinzburg-Landau description invalid. The observed transition from stable to\nunstable fluid can only be explained by taking into account the specific form\nof reservoir-mediated instability as well as particle currents induced by the\nfinite extent of the pump spot.",
        "positive": "Superfluidity of a Raman spin-orbit-coupled Bose gas at finite\n  temperature: We investigate the superfluidity of a three-dimensional weakly interacting\nBose gas with a one-dimensional Raman-type spin-orbit coupling at both zero and\nfinite temperatures. Using the imaginary-time Green's function within the\nBogoliubov approximation, we explicitly derive analytic expressions of the\ncurrent-current response functions in the plane-wave and zero-momentum phases,\nfrom which we extract the superfluid density in the limits of long wavelength\nand zero frequency. At zero temperature, we check that the resultant superfluid\ndensity agrees exactly with our previous analytic prediction obtained from a\nphase-twist approach. Both results also satisfy a generalized Josephson\nrelation in the presence of spin-orbit coupling. At finite temperature, we find\na significant non-monotonic temperature dependence of superfluid density near\nthe transition from the plane-wave phase to the zero-momentum phase. We show\nthat this non-trivial behavior might be understood from the sound velocity,\nwhich has a similar temperature dependence. The non-monotonic temperature\ndependence is also shared by Landau critical velocity, above which the\nspin-orbit-coupled Bose gas loses its superfluidity. Our results would be\nuseful for further theoretical and experimental studies of superfluidity in\nexotic spin-orbit coupled quantum gases."
    },
    {
        "anchor": "Momentum isotropisation in random potentials: When particles are multiply scattered by a random potential, their momentum\ndistribution becomes isotropic on average. We study this quantum dynamics\nnumerically and with a master equation. We show how to measure the elastic\nscattering time as well as characteristic isotropisation times, which permit to\nreconstruct the scattering phase function, even in rather strong disorder.",
        "positive": "Polaronic effects of an impurity in a Fermi superfluid away from the BEC\n  limit: In this article we study the interaction between an impurity and the gas of\nBogoliubov excitations of a Fermi superfluid by mapping it on the polaron\nproblem for an impurity in a BEC. The description of the Fermi superfluid\nacross the BEC-BCS crossover regime is based on a recently developed effective\nfield theory presented in [Eur. Phys. J. B 88, 122 (2015)] and provides us with\nthe interaction-dependent dispersion relations for the Bogoliubov excitations.\nThe behavior of the polaronic coupling constant $\\alpha$ and of the effective\nmass of the polaron is examined in a broad window of the BEC-BCS crossover."
    },
    {
        "anchor": "Parametrically driven-dissipative three-level Dicke model: We investigate the three-level Dicke model, which describes a fundamental\nclass of light-matter systems. We determine the phase diagram in the presence\nof dissipation, which we assume to derive from photon loss. Utilizing both\nanalytical and numerical methods we characterize the incommensurate time\ncrystalline, light-induced, and light-enhanced superradiant states in the phase\ndiagram for the parametrically driven system. As a primary application, we\ndemonstrate that a shaken atom-cavity system is naturally approximated via a\nparametrically driven-dissipative three-level Dicke model.",
        "positive": "Nonlocal pair correlations in Lieb-Liniger gases: A unified\n  nonperturbative approach from weak degeneracy to high temperatures: We present analytical results for the nonlocal pair correlations in\none-dimensional bosonic systems with repulsive contact interactions that are\nuniformly valid from the classical regime of high temperatures down to weak\nquantum degeneracy entering the regime of ultralow temperatures. By using the\ninformation contained in the short-time approximations of the full many-body\npropagator, we derive results that are nonperturbative in the interaction\nparameter while covering a wide range of temperatures and densities. For the\ncase of three particles we give a simple formula for arbitrary couplings that\nis exact in the dilute limit while remaining valid up to the regime where the\nthermal de Broglie wavelength $\\lambda_T$ is of the order of the characteristic\nlength $L$ of the system. We then show how to use this result to find\nanalytical expressions for the nonlocal correlations for arbitrary but fixed\nparticle numbers $N$ including finite-size corrections. Neglecting the latter\nin the thermodynamic limit provides an expansion in the quantum degeneracy\nparameter $N\\lambda_T/L$. We compare our analytical results with numerical\nBethe ansatz calculations, finding excellent agreement."
    },
    {
        "anchor": "Atomic matter-wave revivals with definite atom number in an optical\n  lattice: We study the collapse and revival of interference patterns in the momentum\ndistribution of atoms in optical lattices, using a projection technique to\nproperly account for the fixed total number of atoms in the system. We consider\nthe common experimental situation in which weakly interacting bosons are loaded\ninto a shallow lattice, which is suddenly made deep. The collapse and revival\nof peaks in the momentum distribution is then driven by interactions in a\nlattice with essentially no tunnelling. The projection technique allows to us\nto treat inhomogeneous (trapped) systems exactly in the case that\nnon-interacting bosons are loaded into the system initially, and we use\ntime-dependent density matrix renormalization group techniques to study the\nsystem in the case of finite tunnelling in the lattice and finite initial\ninteractions. For systems of more than a few sites and particles, we find good\nagreement with results calculated via a naive approach, in which the state at\neach lattice site is described by a coherent state in the particle occupation\nnumber. However, for systems on the order of 10 lattice sites, we find\nexperimentally measurable discrepancies to the results predicted by this\nstandard approach.",
        "positive": "Phase diagram of Rydberg atoms with repulsive van der Waals interaction: We report a quantum Monte Carlo calculation of the phase diagram of bosons\ninteracting with a repulsive inverse sixth power pair potential, a model for\nassemblies of Rydberg atoms in the local van der Waals blockade regime. The\nmodel can be parametrized in terms of just two parameters, the reduced density\nand temperature. Solidification happens to the fcc phase. At zero temperature\nthe transition density is found with the diffusion Monte Carlo method at\ndensity $\\rho = 3.9 (\\hbar^2/m C_6)^{3/4} $, where $C_6$ is the strength of the\ninteraction. The solidification curve at non-zero temperature is studied with\nthe path integral Monte Carlo approach and is compared with transitions in\ncorresponding harmonic and classical crystals. Relaxation mechanisms are\nconsidered in relation to present experiments, especially pertaining to hopping\nof the Rydberg excitation."
    },
    {
        "anchor": "Quantum Many-Body Adiabaticity, Topological Thouless Pump and Driven\n  Impurity in a One-Dimensional Quantum Fluid: When it comes to applying the adiabatic theorem in practice, the key question\nto be answered is how slow \"slowly enough\" is. This question can be an\nintricate one, especially for many-body systems, where the limits of slow\ndriving and large system size may not commute. Recently we have shown how the\nquantum adiabaticity in many-body systems is related to the generalized\northogonality catastrophe [Phys. Rev. Lett. 119, 200401 (2017)]. We have proven\na rigorous inequality relating these two phenomena and applied it to establish\nconditions for the quantized transport in the topological Thouless pump. In the\npresent contribution we (i) review these developments and (ii) apply the\ninequality to establish the conditions for adiabaticity in a one-dimensional\nsystem consisting of a quantum fluid and an impurity particle pulled through\nthe fluid by an external force. The latter analysis is vital for the correct\nquantitative description of the phenomenon of quasi Bloch oscillations in a\none-dimensional translation invariant impurity-fluid system.",
        "positive": "Sarma phase in relativistic and non-relativistic systems: We investigate the stability of the Sarma phase in two-component fermion\nsystems in three spatial dimensions. For this purpose we compare\nstrongly-correlated systems with either relativistic or non-relativistic\ndispersion relation: relativistic quarks and mesons at finite isospin density\nand spin-imbalanced ultracold Fermi gases. Using a Functional Renormalization\nGroup approach, we resolve fluctuation effects onto the corresponding phase\ndiagrams beyond the mean-field approximation. We find that fluctuations induce\na second order phase transition at zero temperature, and thus a Sarma phase, in\nthe relativistic setup for large isospin chemical potential. This motivates the\ninvestigation of the cold atoms setup with comparable mean-field phase\nstructure, where the Sarma phase could then be realized in experiment. However,\nfor the non-relativistic system we find the stability region of the Sarma phase\nto be smaller than the one predicted from mean-field theory. It is limited to\nthe BEC side of the phase diagram, and the unitary Fermi gas does not support a\nSarma phase at zero temperature. Finally, we propose an ultracold quantum gas\nwith four fermion species that has a good chance to realize a zero-temperature\nSarma phase."
    },
    {
        "anchor": "Evidence of a liquid phase in interacting Bosons at intermediate\n  densities: In this paper, we present evidence for a liquid-like phase in systems of many\ninteracting Bosons at intermediate densities. The interacting Bose gas has been\nstudied extensively in the low and high density regimes, in which interactions\ndo not play a physically significant role, and the system behaves similarly to\nthe ideal quantum gas. Instead, we will turn our attention to the intermediate\ndensity regime, and report evidence that the system enters a strongly\ncorrelated phase where its behavior is markedly different from that of the\nideal quantum gas. To do so, we use the Simplified approach to the Bose gas,\nwhich was introduced by Lieb in 1963 and recently found to provide very\naccurate predictions for many-Boson systems at all densities. Using this tool,\nwe will compute predictions for the radial distribution function, structure\nfactor, condensate fraction and momentum distribution, and show that they are\nconsistent with liquid-type behavior.",
        "positive": "Effective multi-body SU($N$)-symmetric interactions of ultracold\n  fermionic atoms on a 3-D lattice: Rapid advancements in the experimental capabilities with ultracold\nalkaline-earth-like atoms (AEAs) bring to a surprisingly near term the prospect\nof performing quantum simulations of spin models and lattice field theories\nexhibiting SU($N$) symmetry. Motivated in particular by recent experiments\npreparing high density samples of strongly interacting ${}^{87}$Sr atoms in a\nthree-dimensional optical lattice, we develop a low-energy effective theory of\nfermionic AEAs which exhibits emergent multi-body SU($N$)-symmetric\ninteractions, where $N$ is the number of atomic nuclear spin levels. Our theory\nis limited to the experimental regime of (i) a deep lattice, with (ii) at most\none atom occupying each nuclear spin state on any lattice site. The latter\nrestriction is a consequence of initial ground-state preparation. We fully\ncharacterize the low-lying excitations in our effective theory, and compare\npredictions of many-body interaction energies with direct measurements of\nmany-body excitation spectra in an optical lattice clock. Our work makes the\nfirst step in enabling a controlled, bottom-up experimental investigation of\nmulti-body SU($N$) physics."
    },
    {
        "anchor": "Universal four-component Fermi gas in one dimension: A four-component Fermi gas in one dimension with a short-range four-body\ninteraction is shown to exhibit a one-dimensional analog of the BCS-BEC\ncrossover. Its low-energy physics is governed by a Tomonaga-Luttinger liquid\nwith three spin gaps. The spin gaps are exponentially small in the weak\ncoupling (BCS) limit where they arise from the charge-density-wave instability,\nand become large in the strong coupling (BEC) limit because of the formation of\ntightly-bound tetramers. We investigate the ground-state energy, the sound\nvelocity, and the gap spectrum in the BCS-BEC crossover and discuss exact\nrelationships valid in our system. We also show that a one-dimensional analog\nof the Efimov effect occurs for five bosons while it is absent for fermions.\nOur work opens up a very rich new field of universal few-body and many-body\nphysics in one dimension.",
        "positive": "Localization of solitons: linear response of the mean-field ground state\n  to weak external potentials: Two aspects of bright matter-wave solitons in weak external potentials are\ndiscussed. First, we briefly review recent results on the Anderson localization\nof an entire soliton in disordered potentials [Sacha et al. PRL 103, 210402\n(2009)], as a paradigmatic showcase of genuine quantum dynamics beyond simple\nperturbation theory. Second, we calculate the linear response of the mean-field\nsoliton shape to a weak, but otherwise arbitrary external potential, with a\ndetailed application to lattice potentials."
    },
    {
        "anchor": "Three-dimensional splitting dynamics of giant vortices in Bose-Einstein\n  condensates: We study the splitting dynamics of giant vortices in dilute Bose-Einstein\ncondensates by numerically integrating the three-dimensional Gross-Pitaevskii\nequation in time. By taking advantage of tetrahedral tiling in the spatial\ndiscretization, we decrease the error and increase the reliability of the\nnumerical method. An extensive survey of vortex splitting symmetries is\npresented for different aspect ratios of the harmonic trapping potential. The\nsymmetries of the splitting patterns observed in the simulated dynamics are\nfound to be in good agreement with predictions obtained by solving the dominant\ndynamical instabilities from the corresponding Bogoliubov equations.\nFurthermore, we observe intertwining of the split vortices in prolate\ncondensates and a split-and-revival phenomenon in a spherical condensate.",
        "positive": "Spectroscopy and spin dynamics for strongly interacting few spinor\n  bosons in one-dimensional traps: We consider a one-dimensional trapped gas of strongly interacting few spin-1\natoms which can be described by an effective spin chain Hamiltonian. Away from\nthe SU(3) integrable point, where the energy spectrum is highly degenerate, the\nrules of ordering and crossing of the energy levels and the symmetry of the\neigenstates in the regime of large but finite repulsion have been elucidated.\nWe study the spin-mixing dynamics which is shown to be very sensitive to the\nratio between the two channel interactions g0/g2 and the effective spin chain\ntransfers the quantum states more perfectly than the Heisenberg\nbilinear-biquadratic spin chain."
    },
    {
        "anchor": "Multimode N00N states in driven atomtronic circuits: We propose a method to generate multi-mode N00N states with arrays of\nultracold atoms. Our protocol requires a strong relative offset among the wells\nand a drive of the interparticle interaction at a frequency resonant with the\noffsets. The proposal is demonstrated by a numerical and a Floquet analysis of\nthe quantum dynamics of a ring-shaped atomtronics circuit made of M weakly\ncoupled optical traps. We generate a hierarchy of energy scales down to very\nfew low-energy states where N00N dynamics takes place, making multi-mode N00N\nstates appear at nearly regular time intervals. The production of multi-mode\nN00N states can be probed by time-of-flight imaging. Such states may be used to\nbuild a multiple beam splitter.",
        "positive": "Confocal shift interferometry of coherent emission from trapped dipolar\n  excitons: We introduce a confocal shift-interferometer based on optical fibers. The\npresented spectroscopy allows measuring coherence maps of luminescent samples\nwith a high spatial resolution even at cryogenic temperatures. We apply the\nspectroscopy onto electrostatically trapped, dipolar excitons in a\nsemiconductor double quantum well. We find that the measured spatial coherence\nlength of the excitonic emission coincides with the point spread function of\nthe confocal setup. The results are consistent with a temporal coherence of the\nexcitonic emission down to temperatures of 250 mK."
    },
    {
        "anchor": "Quantum correlations and degeneracy of identical bosons in a 2D harmonic\n  trap: We consider a few number of identical bosons trapped in a 2D isotropic\nharmonic potential and also the $N$-boson system when it is feasible. The\natom-atom interaction is modelled by means of a finite-range Gaussian\ninteraction. The spectral properties of the system are scrutinized, in\nparticular, we derive analytic expressions for the degeneracies and their\nbreaking for the lower-energy states at small but finite interactions. We\ndemonstrate that the degeneracy of the low-energy states is independent of the\nnumber of particles in the noninteracting limit and also for sufficiently weak\ninteractions. In the strongly interacting regime, we show how the many-body\nwave function develops holes whenever two particles are at the same position in\nspace to avoid the interaction, a mechanism reminiscent of the Tonks-Girardeau\ngas in 1D. The evolution of the system as the interaction is increased is\nstudied by means of the density profiles, pair correlations and fragmentation\nof the ground state for $N=2$, $3$, and $4$ bosons.",
        "positive": "Collective modes of a one-dimensional trapped Bose gas in the presence\n  of the anomalous density: We study the collective modes of a one-dimensional harmonically trapped\nBose-Einstein condensate in the presence of the anomalous density using the\ntime-dependent Hartree-Fock-Bogoliubov theory. Within the hydrodynamic\nequations, we derive analytical expressions for the mode frequencies and the\ndensity fluctuations of the anomalous density which constitutes the minority\ncomponent at very low temperature and feels an effective external potential\nexerted by the majority component, i.e., the condensate. On the other hand, we\nnumerically examine the temperature dependence of the breathing mode\noscillations of the condensate at finite temperature in the weak-coupling\nregime. At zero temperature, we compare our predictions with available\nexperimental data, theoretical treatments, and Monte carlo simulations in all\ninteraction regimes and the remaining hindrances are emphasized. We show that\nthe anomalous correlations have a non-negligible role on the collective modes\nat both zero and finite temperatures."
    },
    {
        "anchor": "Artificial Staggered Magnetic Field for Ultracold Atoms in Optical\n  Lattices: A time-dependent optical lattice with staggered particle current in the\ntight-binding regime was considered that can be described by a time-independent\neffective lattice model with an artificial staggered magnetic field. The low\nenergy description of a single-component fermion in this lattice at\nhalf-filling is provided by two copies of ideal two-dimensional massless Dirac\nfermions. The Dirac cones are generally anisotropic and can be tuned by the\nexternal staggered flux $\\p$. For bosons, the staggered flux modifies the\nsingle-particle spectrum such that in the weak coupling limit, depending on the\nflux $\\p$, distinct superfluid phases are realized. Their properties are\ndiscussed, the nature of the phase transitions between them is establised, and\nBogoliubov theory is used to determine their excitation spectra. Then the\ngeneralized superfluid-Mott-insulator transition is studied in the presence of\nthe staggered flux and the complete phase diagram is established. Finally, the\nmomentum distribution of the distinct superfluid phases is obtained, which\nprovides a clear experimental signature of each phase in ballistic expansion\nexperiments.",
        "positive": "Stable matter-wave soliton in the vortex core of a uniform condensate: We demonstrate a stable, mobile, dipolar or nondipolar three-dimensional\nmatter-wave soliton in the vortex core of a uniform nondipolar condensate. All\nintra- and inter-species contact interactions can be repulsive for a strongly\ndipolar soliton. For a weakly dipolar or nondipolar soliton, the intra-species\ncontact interaction in the soliton should be attractive for the formation of a\ncompact soliton. The soliton can propagate with a constant velocity along the\nvortex core without any deformation. Two such solitons undergo a quasi-elastic\ncollision at medium velocities. We illustrate the findings using realistic\ninteractions in a mean-field model of binary $^{87}$Rb-$^{85}$Rb and\n$^{87}$Rb-$^{164}$Dy systems."
    },
    {
        "anchor": "Ultrawide dark solitons and droplet-soliton coexistence in a dipolar\n  Bose gas with strong contact interactions: We look into dark solitons in a quasi-1D dipolar Bose gas and in a quantum\ndroplet. We derive the analytical solitonic solution of a Gross-Pitaevskii-like\nequation accounting for beyond mean-field effects. The results show there is a\ncertain critical value of the dipolar interactions, for which the width of a\nmotionless soliton diverges. Moreover, there is a peculiar solution of the\nmotionless soliton with a non-zero density minimum. We also present the energy\nspectrum of these solitons with an additional excitation subbranch appearing.\nFinally, we perform a series of numerical experiments revealing the coexistence\nof a dark soliton inside a quantum droplet.",
        "positive": "Expansion Dynamics of a Two-Component Quasi-One-Dimensional\n  Bose-Einstein Condensate: Phase Diagram, Self-Similar Solutions, and\n  Dispersive Shock Waves: We investigate the expansion dynamics of a Bose-Einstein condensate that\nconsists of two components and is initially confined in a quasi-one-dimensional\ntrap. We classify the possible initial states of the two-component condensate\nby taking into account the non-uniformity of the distributions of its\ncomponents and construct the corresponding phase diagram in the plane of\nnonlinear interaction constants. The differential equations that describe the\ncondensate evolution are derived by assuming that the condensate density and\nvelocity depend on the spatial coordinate quadratically and linearly,\nrespectively, what reproduces the initial equilibrium distribution of the\ncondensate in the trap in the Thomas-Fermi approximation. We obtained\nself-similar solutions of these differential equations for several important\nspecial cases and wrote out asymptotic formulas describing the condensate\nmotion on long time scales, when the condensate density becomes so low that the\ninteraction between atoms can be neglected. The problem on the dynamics of\nimmiscible components with the formation of dispersive shock waves was also\nconsidered. We compare the numerical solutions of the Gross-Pitaevskii\nequations with their approximate analytical solutions and study numerically the\nsituations when the analytical method admits no exact solutions."
    },
    {
        "anchor": "Bose-Einstein Condensates: a model system for particle solvation?: We propose that impurities in Bose-Einstein condensates can serve as a\nminimal laboratory system to explore the effects of quantum and thermal\nfluctuations on solvation. Specifically, we show that the role of quantum\nfluctuations in the formation of solvation shells and the breakdown of linear\nresponse theory can be explored in detail.",
        "positive": "Superfluid Breakdown and Multiple Roton Gaps in Spin-Orbit Coupled\n  Bose-Einstein Condensates on an Optical Lattice: We investigate the superfluid phases of a Rashba spin-orbit coupled\nBose-Einstein condensate residing on a two dimensional square optical lattice\nin the presence of an effective Zeeman field $\\Omega$. At a critical value\n$\\Omega=\\Omega_c$, the single-particle spectrum $ E_k $ changes from having a\nset of four degenerate minima to a single minimum at $k=0$, corresponding to\ncondensation at finite or zero momentum, respectively. We describe this quantum\nphase transition and the symmetry breaking of the condensate phases. We use the\nBogoliubov theory to treat the superfluid phases and determine the phase\ndiagram, the excitation spectrum and the sound velocity of the phonon\nexcitations. A novel dynamically unstable superfluid regime occurring when\n$\\Omega$ is close to $\\Omega_c$ is analytically identified and the behavior of\nthe condensate quantum depletion is discussed. Moreover, we show that there are\ntwo types of roton excitations occurring in the $\\Omega<\\Omega_c$ regime and\nobtain explicit values for the corresponding energy gaps."
    },
    {
        "anchor": "Connecting Berezinskii-Kosterlitz-Thouless and BEC phase transitions by\n  tuning interactions in a trapped gas: We study the critical point for the emergence of coherence in a harmonically\ntrapped two-dimensional Bose gas with tuneable interactions. Over a wide range\nof interaction strengths we find excellent agreement with the classical-field\npredictions for the critical point of the Berezinskii-Kosterlitz-Thouless (BKT)\nsuperfluid transition. This allows us to quantitatively show, without any free\nparameters, that the interaction-driven BKT transition smoothly converges onto\nthe purely quantum-statistical Bose-Einstein condensation (BEC) transition in\nthe limit of vanishing interactions.",
        "positive": "Fractal energy spectrum of a polariton gas in a Fibonacci quasi-periodic\n  potential: We report on the study of a polariton gas confined in a quasi-periodic one\ndimensional cavity, described by a Fibonacci sequence. Imaging the polariton\nmodes both in real and reciprocal space, we observe features characteristic of\ntheir fractal energy spectrum such as the opening of mini-gaps obeying the gap\nlabeling theorem and log-periodic oscillations of the integrated density of\nstates. These observations are accurately reproduced solving an effective 1D\nSchr\\\"{o}dinger equation, illustrating the potential of cavity polaritons as a\nquantum simulator in complex topological geometries."
    },
    {
        "anchor": "Floquet engineering to exotic topological phases in systems of cold\n  atoms: Topological phases with a widely tunable number of edge modes have been\nextensively studied as a typical class of exotic states of matter with\npotentially important applications. Although several models have been shown to\nsupport such phases, they are not easy to realize in solid-state systems due to\nthe complexity of various intervening factors. Inspired by the realization of\nsynthetic spin-orbit coupling in a cold-atom system [Z. Wu {\\it et al.},\nScience \\textbf{354}, 83 (2016)], we propose a periodic quenching scheme to\nrealize large-topological-number phases with multiple edge modes in optical\nlattices. Via introducing the periodic quenching to the Raman lattice, it is\nfound that a large number of edge modes can be induced in a controllable manner\nfrom the static topologically trivial system. Our result provides an\nexperimentally accessible method to artificially synthesize and manipulate\nexotic topological phases with large topological numbers and multiple edge\nmodes.",
        "positive": "Cooling schemes for two-component fermions in layered optical lattices: Recently, a cooling scheme for ultracold atoms in a bilayer optical lattice\nhas been proposed [A. Kantian et al., arXiv:1609.03579]. In their scheme, the\nenergy offset between the two layers is increased dynamically such that the\nentropy of one layer is transferred to the other layer. Using the\nfull-Hilbert-space approach, we compute cooling dynamics subjected to the\nscheme in order to show that their scheme fails to cool down two-component\nfermions. We develop an alternative cooling scheme for two-component fermions,\nin which the spin-exchange interaction of one layer is significantly reduced.\nUsing both full-Hilbert-space and matrix-product-state approaches, we find that\nour scheme can decrease the temperature of the other layer by roughly half."
    },
    {
        "anchor": "Synthetic Topological Vacua of Yang-Mills Fields in Bose-Einstein\n  Condensates: Topological vacua are a family of degenerate ground states of Yang-Mills\nfields with zero field strength but nontrivial topological structures. They\nplay a fundamental role in particle physics and quantum field theory, but have\nnot yet been experimentally observed. Here we report the first theoretical\nproposal and experimental realization of synthetic topological vacua with a\ncloud of atomic Bose-Einstein condensates. Our setup provides a promising\nplatform to demonstrate the fundamental concept that a vacuum, rather than\nbeing empty, has rich spatial structures. The Hamiltonian for the vacuum of\ntopological number n = 1 is synthesized and the related Hopf index is measured.\nThe vacuum of topological number n = 2 is also realized, and we find that vacua\nwith different topological numbers have distinctive spin textures and Hopf\nlinks. Our work opens up opportunities for exploring topological vacua and\nrelated long-sought-after instantons in tabletop experiments.",
        "positive": "Supersolid and solitonic phases in one-dimensional Extended Bose-Hubbard\n  model: We report our findings on quantum phase transitions in cold bosonic atoms in\na one dimensional optical lattice using the finite size density matrix\nrenormalization group method in the framework of the extended Bose-Hubbard\nmodel. We consider wide ranges of values for the filling factors and the\nnearest neighbor interactions. At commensurate fillings, we obtain two\ndifferent types of charge density wave phases and a Mott insulator phase.\nHowever, departure from commensurate fillings yield the exotic supersolid phase\nwhere both the crystalline and the superfluid orders coexist. In addition, we\nobtain signatures for solitary waves and also superfluidity."
    },
    {
        "anchor": "Estimated values of the kinetic energy for liquid $^3$He: The kinetic energy is estimated for the ground-state of liquid $^3$He at\nequilibrium density. The obtained value for this quantity, $10.16\\pm0.05$\nK/atom at density $0.0163~\\mbox{\\AA}$, is in agreement with most of the\nexperimental data found in the literature. This result resolves a long-standing\ncontroversy between experimental and theoretical values of this quantity. The\nvariational path integral method, an \"exact\" quantum Monte Carlo method\nextended for fermionic systems, is applied in the calculations. The results\nobtained are subjected only to the restrictions imposed by a chosen nodal\nstructure without any further approximation, even for quantities that do not\ncommute with the Hamiltonian. The required fixed-node approximation entails an\nimplementation that allows a more effective estimation of the quantities of\ninterest. Total and potential energies together with the radial distribution\nfunction are also computed.",
        "positive": "Radial vortex core oscillations in Bose-Einstein condensates: Dilute ultracold quantum gases form an ideal and highly tunable system in\nwhich superuidity can be studied. Recently quantum turbulence in Bose-Einstein\ncondensates was reported [PRL 103, 045310 (2009)], opening up a new\nexperimental system that can be used to study quantum turbulence. A novel\nfeature of this system is that vortex cores now have a finite size. This means\nthat the vortices are no longer one dimensional features in the condensate, but\nthat the radial behaviour and excitations might also play an important role in\nthe study of quantum turbulence in Bose-Einstein condensates. In this paper we\ninvestigate these radial modes using a simplified variational model for the\nvortex core. This study results in the frequencies of the radial modes, which\ncan be compared with the frequencies of the thoroughly studied Kelvin modes.\nFrom this comparison we find that the lowest (l=0) radial mode has a frequency\nin the same order of magnitude as the Kelvin modes. However the radial modes\nstill have a larger energy than the Kelvin modes, meaning that the Kelvin modes\nwill still constitute the preferred channel for energy decay in quantum\nturbulence."
    },
    {
        "anchor": "Materia cu\u00e1ntica en cavidades de alta reflectancia (Many-body CQED): This article gives details of the course on \"Quantum Matter in optical\nlattices and high-Q cavities\" given at the School of Physics XXVIII at UNAM in\n2021. The notes describe useful concepts for analog quantum simulation and\ndetails of models in optical lattices and high-Q cavities. The notes are in\nSpanish.\n  En este art\\'iculo se discuten algunos detalles del curso sobre \"Materia\ncu\\'antica en redes \\'opticas y cavidades de alta reflectancia (Many-body\nCQED)\" de la escuela de verano de F\\'isica XVIII (2021) en la UNAM. Se\ndescriben conceptos \\'utiles para la simulaci\\'on cu\\'antica an\\'aloga, as\\'i\ncomo se introducen detalles de modelos de materia cu\\'antica en redes \\'opticas\ny en cavidades de alta reflectancia.",
        "positive": "Spin-1 Atoms in Optical Superlattices: Single-Atom Tunneling and\n  Entanglement: We examine spinor Bose-Einstein condensates in optical superlattices\ntheoretically using a Bose-Hubbard Hamiltonian that takes spin effects into\naccount. Assuming that a small number of spin-1 bosons is loaded in an optical\npotential, we study single-particle tunneling that occurs when one lattice site\nis ramped up relative to a neighboring site. Spin-dependent effects modify the\ntunneling events in a qualitative and quantitative way. Depending on the\nasymmetry of the double well different types of magnetic order occur, making\nthe system of spin-1 bosons in an optical superlattice a model for mesoscopic\nmagnetism. We use a double-well potential as a unit cell for a one-dimensional\nsuperlattice. Homogeneous and inhomogeneous magnetic fields are applied and the\neffects of the linear and the quadratic Zeeman shifts are examined. We also\ninvestigate the bipartite entanglement between the sites and construct states\nof maximal entanglement. The entanglement in our system is due to both orbital\nand spin degrees of freedom. We calculate the contribution of orbital and spin\nentanglement and show that the sum of these two terms gives a lower bound for\nthe total entanglement."
    },
    {
        "anchor": "Landau-Zener Transitions in Chains: We determine transition probabilities in two exactly solvable multistate\nLandau-Zener (LZ) models and discuss applications of our results to the theory\nof dynamic passage through a phase transition in the dissipationless quantum\nmechanical regime. In particular, we show that statistics of particles in a new\nphase demonstrate scaling behavior. Our results also reveal a symmetry that we\nclaim is a property of a large class of multistate LZ models, whose explicit\nsolutions are not presently known. We support our arguments by direct numerical\nsimulations.",
        "positive": "Rotational pendulum dynamics of a vortex molecule in a channel geometry: A vortex molecule is a topological excitation in two coherently coupled\nsuperfluids consisting of a vortex in each superfluid connected by a domain\nwall of the relative phase, also known as a Josephson vortex. We investigate\nthe dynamics of this excitation in a quasi-two-dimensional geometry with slab\nor channel boundary conditions using an extended point vortex framework\ncomplemented by Gross-Pitaevskii simulations. Apart from translational motion\nalong the channel, the vortex molecule is found to exhibit intriguing internal\ndynamics including rotation and rotational-pendulum-like dynamics. Trajectories\nleading to a boundary-induced break-up of the vortex molecule are also\ndescribed qualitatively by the simplified model. We classify the stable and\nunstable fixed points as well as separatrices that characterize the vortex\nmolecule dynamics."
    },
    {
        "anchor": "Metastable order protected by destructive many-body interference: The phenomenon of metastability can shape dynamical processes on all temporal\nand spatial scales. Here, we induce metastable dynamics by pumping ultracold\nbosonic atoms from the lowest band of an optical lattice to an excitation band,\nvia a sudden quench of the unit cell. The subsequent relaxation process to the\nlowest band displays a sequence of stages, which include a metastable stage,\nduring which the atom loss from the excitation band is strongly suppressed.\nUsing classical-field simulations and analytical arguments, we provide an\nexplanation for this experimental observation, in which we show that the\ntransient condensed state of the atoms in the excitation band is a dark state\nwith regard to collisional decay and tunneling to a low-energy orbital.\nTherefore the metastable state is stabilized by destructive interference due to\nthe chiral phase pattern of the condensed state. Our experimental and\ntheoretical study provides a detailed understanding of the different stages of\na paradigmatic example of many-body relaxation dynamics.",
        "positive": "Broad Feshbach resonances in ultracold alkali-metal systems: A comprehensive search for \"broad\" Feshbach resonances (FRs) in all possible\ncombinations of stable alkali-metal atoms is carried out, using a multi-channel\nquantum-defect theory assisted by the analytic wave functions for a long-range\nvan-der-Waals potential. A number of new \"broad\" $s$-, $p$- and $d$-wave FRs in\nthe lowest-energy scattering channels, which are stable against two-body\ndipolar spin-flip loss, are predicted and characterized. Our results also show\nthat \"broad\" FRs of $p$- or $d$-wave type that are free of two-body loss do not\nexist between fermionic alkali-metal atoms for magnetic field up to 1000\\,G.\nThese findings constitute helpful guidance on efforts towards experimental\nstudy of high-partial-wave coupling induced many-body physics."
    },
    {
        "anchor": "Laser cooling for quantum gases: Laser cooling exploits the physics of light scattering to cool atomic and\nmolecular gases to close to absolute zero. It is the crucial initial step for\nessentially all atomic gas experiments in which Bose-Einstein condensation and,\nmore generally, quantum degeneracy is reached. The ongoing development of\nlaser-cooling methods has allowed more elements to be brought to quantum\ndegeneracy, with each additional atomic species offering its own experimental\nopportunities. Improved methods are opening new avenues, for example, reaching\nBose-Einstein condensation purely through laser cooling as well as the\nrealization of continuous Bose-Einstein condensation. Here we review these\nrecent innovations in laser cooling and provide an outlook on methods that may\nenable new ways of creating quantum gases.",
        "positive": "Spectral function of Fermi polarons at finite temperature from a\n  self-consistent many-body $T$-matrix approach in real frequency: We theoretically examine the finite-temperature spectral function of Fermi\npolarons in three dimensions, by using a self-consistent many-body $T$-matrix\ntheory in real frequency. In comparison with the previous results from a\nnon-self-consistent many-body $T$-matrix approach, we show that the treatment\nof self-consistency in the impurity Green function leads to notable changes in\nalmost all the dynamical quantities, including the vertex function, impurity\nself-energy and spectral function. Eventually, it gives rise to quantitatively\ndifferent predictions for the measurable radio-frequency spectrum and Raman\nspectrum at finite temperature. Using the recent spectroscopic measurements as\na benchmark, we find that the self-consistent many-body $T$-matrix theory\nsomehow provides a better explanation for the experimental data. The notable\ndifference in the predictions from the non-self-consistent and self-consistent\ntheories suggests that more accurate theoretical descriptions are needed, in\norder to fully account for the current spectroscopic observations on Fermi\npolarons."
    },
    {
        "anchor": "Fermi polarons and beyond: These lecture notes give a brief introduction to the so-called Fermi-polaron\nproblem, which explores the behaviour of a mobile impurity introduced into an\nideal Fermi gas. While this problem has been considered now for more than a\ndecade in ultracold atomic gases, it continues to generate surprises and\ninsights as new quantum mixtures emerge, both in atomic gases and in the solid\nstate. Here we summarise the basic theory for the Fermi polaron with a focus on\nthe three-dimensional case, although the results can be straightforwardly\ngeneralised to two dimensions. Our aim is to provide a pedagogical treatment of\nthe subject and we thus cover fundamental topics such as scattering theory and\nrenormalisation. We discuss the ground state of the Fermi polaron and how it is\nconnected to the phase diagram of the spin-imbalanced Fermi gas, and we also\ngive a brief overview of the energy spectrum and non-equilibrium dynamics.\nThroughout, we highlight how the static and dynamic behaviour of the Fermi\npolaron is well described using intuitive variational approaches.",
        "positive": "The BHL-BCL crossover: from nonlinear to linear quantum amplification: The black-hole laser (BHL) effect is the self-amplification of Hawking\nradiation between a pair of horizons which act as a resonant cavity. In a\nflowing atomic condensate, the BHL effect arises in a finite supersonic region,\nwhere Bogoliubov-Cherenkov-Landau (BCL) radiation is resonantly excited by any\nstatic perturbation. Thus, experimental attempts to produce a BHL unavoidably\ndeal with the presence of a strong BCL background, making the observation of\nthe BHL effect still a major challenge in the analogue gravity field. Here, we\nperform a theoretical study of the BHL-BCL crossover using an idealized model\nwhere both phenomena can be unambiguously isolated. By drawing an analogy with\nan unstable pendulum, we distinguish three main regimes according to the\ninterplay between quantum fluctuations and classical stimulation: quantum BHL,\nclassical BHL, and BCL. Based on quite general scaling arguments, the nonlinear\namplification of quantum fluctuations up to saturation is identified as the\nmost robust trait of a quantum BHL. A classical BHL behaves instead as a linear\nquantum amplifier, where the output is proportional to the input. The BCL\nregime also acts as a linear quantum amplifier, but its gain is exponentially\nsmaller as compared to a classical BHL. Complementary signatures of black-hole\nlasing are a decrease in the amplification for increasing BCL amplitude or a\nnonmonotonic dependence of the growth rate with respect to the background\nparameters. We also identify interesting analogue phenomena such as\nHawking-stimulated white-hole radiation or quantum BCL-stimulated Hawking\nradiation. The results of this work not only are of interest for analogue\ngravity, where they help to distinguish each phenomenon and to design\nexperimental schemes for a clear observation of the BHL effect, but they also\nopen the prospect of finding applications of analogue concepts in quantum\ntechnologies."
    },
    {
        "anchor": "Effects of spatially inhomogeneous atomic interactions on Bose-Einstein\n  condensates in optical lattices: An interplay of optical lattices and nonlinear impurities in controlling the\ndynamics of Bose-Einstein condensate bright solitons is investigated using\neffective potential approach. The ability of pushing the solitons into or away\nfrom the impurity region by changing both lattice and impurity parameters is\nsuggested. A possibility for the existence of stable fundamental gap solitons,\nwhich appear to satisfy an inverted Vakhitov-Kolokolov criterion, is examined.",
        "positive": "Coreless vorticity in multicomponent Bose and Fermi superfluids: We consider quantized vortices in two-component Bose-Einstein condensates and\nthree-component Fermi gases with attractive interactions. In these systems, the\nvortex core can be either empty (normal in the fermion case) or filled with\nanother superfluid. We determine critical values of the parameters -- chemical\npotentials, scattering lengths and, for Fermi gases, temperature -- at which a\nphase transition between the two types of vortices occurs. Population imbalance\ncan lead to superfluid core (coreless) vorticity in multicomponent superfluids\nwhich otherwise support only usual vortices. For multicomponent Fermi gases, we\nconstruct the phase diagram including regions of coreless vorticity. We extend\nour results to trapped bosons and fermions using an appropriate local\napproximation, which goes beyond the usual Thomas-Fermi approximation for\ntrapped bosons."
    },
    {
        "anchor": "Clustering of Four-Component Unitary Fermions: Ab initio nuclear physics tackles the problem of strongly interacting\nfour-component fermions. The same setting could foreseeably be probed\nexperimentally in ultracold atomic systems, where two- and three-component\nexperiments have led to major breakthroughs in recent years. Both due to the\nproblem's inherent interest and as a pathway to nuclear physics, in this Letter\nwe study four-component fermions at unitarity via the use of quantum Monte\nCarlo methods. We explore novel forms of the trial wave function and find one\nwhich leads to a ground state of the eight-particle system whose energy is\nalmost equal to that of two four-particle systems. We investigate the\nclustering properties involved and also extrapolate to the zero-range limit. In\naddition to being experimentally testable, our results impact the prospects of\ndeveloping nuclear physics as a perturbation around the unitary limit.",
        "positive": "Interaction of half-quantized vortices in two-component Bose-Einstein\n  condensates: We study the asymptotic interaction between two half-quantized vortices in\ntwo-component Bose-Einstein condensates. When two vortices in different\ncomponents are placed at distance 2R, the leading order of the force between\nthem is found to be (log R/\\xi-1/2)/R^3, in contrast to 1/R between vortices\nplaced in the same component. We derive it analytically using the Abrikosov\nansatz and the profile functions of the vortices, confirmed numerically with\nthe Gross-Pitaevskii model. We also find that the short-range cutoff of the\ninter-vortex potential linearly depends on the healing length."
    },
    {
        "anchor": "Mixed parity pairing in a dipolar gas: We show that fermionic dipoles in a two-layer geometry form Cooper pairs with\nboth singlet and triplet components, when they are tilted with respect to the\nnormal of the planes. The mixed parity pairing arises because the interaction\nbetween dipoles in the two different layers is not inversion symmetric. We use\nan efficient eigenvalue approach to calculate the zero temperature phase\ndiagram of the system as a function of the dipole orientation and the layer\ndistance. The phase diagram contains purely triplet as well as mixed singlet\nand triplet superfluid phases. We show in detail how the pair wave function for\ndipoles residing in different layers smoothly changes from singlet to triplet\nsymmetry as the orientation of the dipoles is changed. Our results indicate\nthat dipolar quantum gases can be used to unambiguously observe mixed parity\npairing.",
        "positive": "Collisions of Majorana Zero Modes: We investigate the collisions of Majorana zero modes, which are presented as\ninter-soliton collisional events in fermionic superfluids with spin-orbit\ncoupling. Our results demonstrate that, the zero energy splitting, induced by\nthe overlapping of inter-soliton Majorana wave-functions upon collision,\ngenerates an effective repulsive force for Majorana states, which in turn\nprotected themselves against into bulk excitation. As a result, the collision\nbetween solitons associated with Majorana zero modes appears to be repulsive\nand elastic, as they do not penetrate each other but instead repel without\nenergy loss. As well, similar repulsive behavior is observed in collisions\nbetween soliton-induced and defect-pinned Majorana zero modes. Our research\noffers new insights into the features of Majorana fermions, and robustness in\nthe collisions of Majorana zero modes bodes well for the prospects of\ntopological quantum computation with a multitude of Majorana qubits."
    },
    {
        "anchor": "Controllable Production of Degenerate Fermi Gases of $^6$Li Atoms in the\n  2D-3D Crossover: The many-body physics in the dimensional crossover regime attracts much\nattention in cold atom experiments, but yet to explore systematically. One of\nthe technical difficulties existed in the experiments is the lack of the\nexperimental technique to quantitatively tune the atom occupation ratio of the\ndifferent lattice bands. In this letter, we report such techniques in a process\nof transferring a 3D Fermi gas into a 1D optical lattice, where the capability\nof tuning the occupation of the energy band is realized by varying the trapping\npotentials of the optical dipole trap (ODT) and the lattice, respectively. We\ncould tune a Fermi gas with the occupation in the lowest band from unity to\n50$\\%$ quantitatively. This provides a route to experimentally study the\ndependence of many-body interaction on the dimensionality in a Fermi gas.",
        "positive": "Multivortex states and dynamics in nonequilibrium quantum fluids: In strongly nonequilibrium Bose-Einstein condensates described by the\ngeneralized Gross-Pitaevskii equation, vortex motion becomes self-accelerated\nwhile the long-range vortex-antivortex interaction appears to be repulsive. We\nnumerically study the impact of these rather unusual vortex properties on the\ndynamics of multivortex systems. We show that at strong nonequilibrium the\nrepulsion between vortices and antivortices leads to a dramatic slowdown of\ntheir annihilation. Moreover, in finite-size samples, relaxation of multivortex\nsystems can lead to the formation of metastable vortex-antivortex clusters,\nwhose shape and size depend, in particular, on the sample geometry, boundary\nconditions and deviations from equilibrium. We further demonstrate that at\nstrong nonequilibrium the interaction of self-accelerated vortices with\ninhomogeneous condensate flows can lead to generation of new vortex-antivortex\npairs."
    },
    {
        "anchor": "Fermions on a torus knot: In this work, we investigate the effects of a nontrivial topology (and\ngeometry) of a system considering \\textit{interacting} and\n\\textit{noninteracting} particle modes, which are restricted to follow a closed\npath over the torus surface. In order to present a prominent thermodynamical\ninvestigation of this system configuration, we carry out a detailed analysis\nusing statistical mechanics within the grand canonical ensemble approach to\ndeal with \\textit{noninteracting} fermions. In an analytical manner, we study\nthe following thermodynamic functions in such context: the Helmholtz free\nenergy, the mean energy, the magnetization and the susceptibility. Further, we\ntake into account the behavior of Fermi energy of the thermodynamic system.\nFinally, we briefly outline how to proceed in case of \\textit{interacting}\nfermions.",
        "positive": "Feynman path-integral treatment of the Bose polaron beyond the\n  Fr\u00f6hlich model: An impurity immersed in a Bose-Einstein condensate is no longer accurately\ndescribed by the Fr\\\"ohlich Hamiltonian as the coupling between the impurity\nand the boson bath gets stronger. We study the dominant effects of the\ntwo-phonon terms beyond the Fr\\\"ohlich model on the ground-state properties of\nthe polaron using Feynman's variational path-integral approach. The previously\nreported discrepancy in the effective mass between the renormalization group\napproach and this theory is shown to be absent in the beyond-Fr\\\"ohlich model\non the positive side of the Feshbach resonance. Self-trapping, characterized by\na sharp and dramatic increase of the effective mass, is no longer observed for\nthe repulsive polaron once the two-phonon interactions are included. For the\nattractive polaron we find a divergence of the ground-state energy and\neffective mass at weaker couplings than previously observed within the\nFr\\\"ohlich model."
    },
    {
        "anchor": "Dynamics of Dark-Bright Solitons in Cigar-Shaped Bose-Einstein\n  Condensates: We explore the stability and dynamics of dark-bright solitons in\ntwo-component elongated Bose-Einstein condensates by developing effective 1D\nvector equations as well as solving the corresponding 3D Gross-Pitaevskii\nequations. A strong dependence of the oscillation frequency and of the\nstability of the dark-bright (DB) soliton on the atom number of its components\nis found. Spontaneous symmetry breaking leads to oscillatory dynamics in the\ntransverse degrees of freedom for a large occupation of the component\nsupporting the dark soliton. Moreover, the interactions of two DB solitons are\ninvestigated with special emphasis on the importance of their relative phases.\nExperimental results showcasing dark-bright soliton dynamics and collisions in\na BEC consisting of two hyperfine states of $^{87}$Rb confined in an elongated\noptical dipole trap are presented.",
        "positive": "Are Quasiparticles and Phonons Identical in Bose--Einstein Condensates?: We study an interacting spinless Bose-Einstein condensate to clarify\ntheoretically whether the spectra of its quasiparticles (one-particle\nexcitations) and collective modes (two-particle excitations) are identical, as\nconcluded by Gavoret and Nozi\\`eres [Ann. Phys. 28, 349 (1964)]. We derive\nanalytic expressions for their first and second moments so as to extend the\nBijl-Feynman formula for the peak of the collective-mode spectrum to its width\n(inverse lifetime) and also to the one-particle channel. The obtained formulas\nindicate that the width of the collective-mode spectrum manifestly vanishes in\nthe long-wavelength limit, whereas that of the quasiparticle spectrum\napparently remains finite. We also evaluate the peaks and widths of the two\nspectra numerically for a model interaction potential in terms of the Jastrow\nwave function optimized by a variational method. It is thereby found that the\nwidth of the quasiparticle spectrum increases towards a constant as the\nwavenumber decreases. This marked difference in the spectral widths implies\nthat the two spectra are distinct. In particular, the lifetime of the\nquasiparticles remains finite even in the long-wavelength limit."
    },
    {
        "anchor": "The three-body scattering hypervolume of identical fermions in one\n  dimension: We study the zero-energy collision of three identical spin-polarized fermions\nwith short-range interactions in one dimension. We derive the asymptotic\nexpansions of the three-body wave function when the three fermions are far\napart or one pair and the third fermion are far apart, and the three-body\nscattering hypervolume $D_F$ appears in the coefficients of such expansions. If\nthe two-body interaction is attractive and supports two-body bound states,\n$D_F$ acquires a negative imaginary part related to the amplitudes of the\noutgoing waves describing the departure of the resultant bound pair and the\nremaining free fermion. For weak interaction potentials, we derive an\napproximate formula of the hypervolume by using the Born expansion. For the\nsquare-barrier and the square-well potentials and the Gaussian potential, we\nsolve the three-body Schr\\\"{o}dinger equation to compute $D_F$ numerically. We\nalso calculate the shifts of energy and of pressure of spin-polarized\none-dimensional Fermi gases due to a nonzero $D_F$ and the three-body\nrecombination rate in one dimension.",
        "positive": "Chern numbers for the two-body Hofstadter-Hubbard butterfly: We analyze the two-body spectrum within the Hofstadter-Hubbard model on a\nsquare lattice through an exact variational ansatz and study the topological\nproperties of its low-lying two-body bound-state branches. In particular we\ndiscuss how the Hofstadter-Hubbard butterfly of the two-body branches evolves\nas a function of onsite interactions and how to efficiently calculate their\nChern numbers using the Fukui-Hatsugai-Suzuki approach. Our numerical results\nare fully consistent with the simple picture that appears in the\nstrong-coupling limit, where the attraction between fermions forms a composite\nboson characterized by an effective hopping parameter and an effective\nmagnetic-flux ratio."
    },
    {
        "anchor": "Recent advances in the theory of the BCS-BEC crossover for fermionic\n  superfluidity: The BCS-BEC crossover realized experimentally with ultra-cold Fermi gases may\nbe considered as one of the important scientific achievements occurred during\nthe last several years. The flexibility for operating on these systems on the\nexperimental side and the full control of the relevant system degrees of\nfreedom on the theoretical side make quite stringent at a fundamental level the\ncomparison between the experimental data and the corresponding theoretical\ncalculations. Here, we briefly survey recent theoretical advances resting on a\ndiagrammatic approach at equilibrium that improves in a systematic way on the\nwidely used t-matrix approach, yielding a quite good comparison between theory\nand experiments for several physical quantities of interest. It is proposed\nthat the physical phenomena underlying this theoretical approach may also be\nrelevant to the superconducting phase of condensed-matter materials which\ncannot be described by the standard BCS theory.",
        "positive": "Fast long-distance transport of cold cesium atoms: Transporting cold atoms between distant sections of a vacuum system is a\ncentral ingredient in many quantum simulation experiments, in particular in\nsetups, where a large optical access and precise control over magnetic fields\nis needed. In this work, we demonstrate optical transport of cold cesium atoms\nover a total transfer distance of about $43\\,$cm in less than $30\\,$ms. The\nhigh speed is facilitated by a moving lattice, which is generated via the\ninterference of a Bessel and a Gaussian laser beam. We transport about $3\\times\n10^6$ atoms at a temperature of a few $\\mu$K with a transport efficiency of\nabout $75\\%$. We provide a detailed study of the transport efficiency for\ndifferent accelerations and lattice depths and find that the transport\nefficiency is mainly limited by the potential depth along the direction of\ngravity. To highlight the suitability of the optical-transport setup for\nquantum simulation experiments, we demonstrate the generation of a pure\nBose-Einstein condensate with about $2\\times 10^4$ atoms. We find a robust\nfinal atom number within $2\\%$ over a duration of $2.5\\,$h with a standard\ndeviation of $<5\\%$ between individual experimental realizations."
    },
    {
        "anchor": "Quantum collision theory in flat bands: We consider quantum scattering of particles in media exhibiting strong\ndispersion degeneracy. In particular, we study flat-banded lattices and\nlinearly dispersed energy bands. The former constitute a prime example of\nsingle-particle frustration while the latter show degeneracy at the few- and\nmany-particle level. We investigate both impurity and two-body scattering and\nshow that, quite generally, scattering does not occur, which we relate to the\nfact that transition matrices vanish on the energy shell. We prove that\nscattering is instead replaced by projections onto band-projected eigenstates\nof the interaction potential. We then use the general results to obtain\nlocalised flat band states that are eigenstates of impurity potentials with\nvanishing eigenvalues in one-dimensional flat bands and study the particular\ncase of a sawtooth lattice. We also uncover the relation between certain\nsolutions of one-dimensional systems that have been categorised as \"strange\",\nand the scattering states in linearly dispersed continuum systems.",
        "positive": "Exotic Superfluid Phases in Spin Polarized Systems on Optical Lattices: Leveraging cutting-edge numerical methodologies, we study the ground state of\nthe two-dimensional spin-polarized Fermi gas in an optical lattice. We focus on\nsystems at high density and small spin polarization, corresponding to the\nparameter regime believed to be most favorable to the formation of the elusive\nFulde-Ferrell-Larkin-Ovchinnikov (FFLO) superfluid phase. Our systematic study\nof large lattice sizes, hosting nearly $500$ atoms, provides strong evidence of\nthe stability of the FFLO state in this regime, as well as a high-accuracy\ncharacterization of its properties. Our results for the density correlation\nfunction reveal the existence of density order in the system, suggesting the\npossibility of an intricate coexistence of long-range orders in the ground\nstate. The ground-state properties are seen to differ significantly from the\nstandard mean-field description, providing a compelling avenue for future\ntheoretical and experimental explorations of the interplay between interaction\nand superfluidity in an exotic phase of matter."
    },
    {
        "anchor": "Designing Topological Bands in Reciprocal Space: Motivated by new capabilities to realise artificial gauge fields in ultracold\natomic systems, and by their potential to access correlated topological phases\nin lattice systems, we present a new strategy for designing topologically\nnon-trivial band structures. Our approach is simple and direct: it amounts to\nconsidering tight-binding models directly in reciprocal space. These models\nnaturally cause atoms to experience highly uniform magnetic flux density and\nlead to topological bands with very narrow dispersion, without fine-tuning of\nparameters. Further, our construction immediately yields instances of optical\nChern lattices, as well as band structures of higher Chern number, |C|>1.",
        "positive": "Observing Chiral Superfluid Order by Matter-Wave Interference: The breaking of time reversal symmetry via the spontaneous formation of\nchiral order is ubiquitous in nature. Here, we present an unambiguous\ndemonstration of this phenomenon for atoms Bose-Einstein condensed in the\nsecond Bloch band of an optical lattice. As a key tool we use a matter wave\ninterference technique, which lets us directly observe the phase properties of\nthe superfluid order parameter and allows us to reconstruct the spatial\ngeometry of certain low energy excitations, associated with the formation of\ndomains of different chirality. Our work marks a new era of optical lattices\nwhere orbital degrees of freedom play an essential role for the formation of\nexotic quantum matter, similarly as in electronic systems."
    },
    {
        "anchor": "Tunable spin-orbit coupling and magnetic superstripe phase in a BEC: Superstripe phases in Bose-Einstein condensates (BECs), possessing both\ncrystalline structure and superfluidity, opens a new avenue for exploring\nexotic quantum matters---supersolids. However, conclusive detection and further\nexploration of a superstripe is still challenging in experiments because of its\nshort period, low visibility, fragility against magnetic field fluctuation or\nshort lifetime. Here we propose a scheme in a spin-orbit coupled BEC which\novercomes these obstacles and generates a robust magnetic superstripe phase,\nwith only spin (no total) density modulation due to the magnetic translational\nsymmetry, ready for direct real-space observation. In the scheme, two hyperfine\nspin states are individually Raman coupled with a largely-detuned third state,\nwhich induce a momentum-space separation between two lower band dispersions,\nyielding an effective spin-1/2 system with tunable spin-orbit coupling and\nZeeman fields. Without effective Zeeman fields, spin-dependent interaction\ndominates, yielding a magnetic superstripe phase with a long tunable period and\nhigh visibility. Our scheme provides a platform for observing and exploring\nexotic properties of superstripe phases as well as novel physics with tunable\nspin-orbit coupling.",
        "positive": "Bose-Einstein condensation of 162Dy and 160Dy: We report Bose-Einstein condensation of two isotopes of the highly magnetic\nelement dysprosium: 162Dy and 160Dy. For 162Dy, condensates with 10^5 atoms\nform below T = 50 nK. We find the evaporation efficiency for the isotope 160Dy\nto be poor; however, by utilizing a low-field Fano-Feshbach resonance to\ncarefully change the scattering properties, it is possible to produce a\nBose-Einstein condensate of 160Dy with 10^3 atoms. The 162Dy BEC reported is an\norder of magnitude larger in atom number than that of the previously reported\n164Dy BEC, and it may be produced within 18 s."
    },
    {
        "anchor": "Quantum caustics and the hierarchy of light cones in quenched spin\n  chains: We show that the light cone-like structures that form in spin chains after a\nquench are quantum caustics. Their natural description is in terms of\ncatastrophe theory and this implies: 1) a hierarchy of light cone structures\ncorresponding to the different catastrophes; 2) dressing by characteristic wave\nfunctions that obey scaling laws determined by the Arnol'd and Berry indices;\n3) a network of vortex-antivortex pairs in space-time inside the cone. We\nillustrate the theory by giving explicit calculations for the transverse field\nIsing model and the XY model, finding fold catastrophes dressed by Airy\nfunctions and cusp catastrophes dressed by Pearcey functions; multisite\ncorrelation functions are described by higher catastrophes such as the\nhyperbolic umbilic. Furthermore, we find that the vortex pairs created inside\nthe cone are sensitive to phase transitions in these spin models with their\nrate of production being determined by the dynamical critical exponent. More\nbroadly, this work illustrates how catastrophe theory can be applied to\nsingularities in quantum fields.",
        "positive": "Conventional magnon BEC in YIG film: The conventional magnon Bose-Einstein condensation (BEC of magnons with k =\n0) is a coherent state of excited magnons described by a common wave function.\nIt was observed first in antiferromagnetic superfluid states of 3He. Here we\nreport on the discovery of a very similar magnon BEC in ferrimagnetic film at\nroom temperature. The experiments were performed in Yttrium Iron Garnet (YIG)\nfilms at a magnetic field oriented perpendicular to the film. The high-density\nquasiequilibrium state of excited magnon was formed by methods of pulse and/or\nContinuous Waves (CW) magnetic resonance. We have observed a Long Lived\nInduction Decay Signals (LLIDS), well known as a signature of spin\nsuperfluidity. We demonstrate that the BEC state may maintain permanently by\ncontinuous replenishment of magnons with a small radiofrequency (RF) field. Our\nfinding opens the way for development of potential supermagnonic applications\nat an ambient conditions."
    },
    {
        "anchor": "Self-consistent derivation of the modified Gross-Pitaevskii equation\n  with Lee-Huang-Yang correction: We consider a dilute and ultracold bosonic gas of weakly-interacting atoms.\nWithin the framework of quantum field theory we derive a zero-temperature\nmodified Gross-Pitaevskii equation with beyond-mean-field corrections due to\nquantum depletion and anomalous density. This result is obtained from the\nstationary equation of the Bose-Einstein order parameter coupled to the\nBogoliubov-de Gennes equations of the out-of-condensate field operator. We show\nthat, in the presence of a generic external trapping potential, the key steps\nto get the modified Gross-Pitaevskii equation are the semiclassical\napproximation for the Bogoliubov-de Gennes equations, a slowly-varying order\nparameter, and a small quantum depletion. In the uniform case, from the\nmodified Gross-Pitaevskii equation we get the familiar equation of state with\nLee-Huang-Yang correction.",
        "positive": "Quantum Non-equilibrium Many-Body Spin-Photon Systems: In this Ph.D. thesis dissertation concerns the quantum dynamics of\nstrongly-correlated quantum systems in out-of-equilibrium states. The research\nis neither restricted to static properties or long-term relaxation evolutions\nnor does it neglect effects on any relevant subsystem as is frequently done\nwith the environment in master equations approaches. The focus of this work is\nto explore different quantum systems during several regimes of operations, then\ndiscover results that might be of interest to quantum control, and hence to\nquantum computation and quantum information processing. Our main results can be\nsummarized as follows in three parts: Signature of Critical Dynamics, Driven\nDicke Model as a Test-bed of Ultra-Strong Coupling, and Beyond the Kibble-Zurek\nMechanism."
    },
    {
        "anchor": "Non-Hermitian Stark Many-Body Localization: Utilizing exact diagonalization (ED) techniques, we investigate a\none-dimensional, non-reciprocal, interacting hard-core boson model under a\nStark potential with tail curvature. By employing the non-zero imaginary\neigenenergies ratio, half-chain entanglement entropy, and eigenstate\ninstability, we numerically confirm that the critical points of spectral\nreal-complex (RC) transition and many-body localization (MBL) phase transition\nare not identical, and an examination of the phase diagrams reveals that the\nspectral RC transition arises before the MBL phase transition, which suggests\nthe existence of a novel non-MBL-driven spectral RC transition. These findings\nare quite unexpected, and they are entirely different from observations in\ndisorder-driven interacting non-Hermitian systems. This work provides a useful\nreference for further research on phase transitions in disorder-free\ninteracting non-Hermitian systems.",
        "positive": "Thermodynamics of one-dimensional SU(4) and SU(6) fermions with\n  attractive interactions: Motivated by advances in the manipulation and detection of ultracold atoms\nwith multiple internal degrees of freedom, we present a finite-temperature\nlattice Monte Carlo calculation of the density and pressure equations of state,\nas well as Tan's contact, of attractively interacting SU(4)- and\nSU(6)-symmetric fermion systems in one spatial dimension. We also furnish a\nnonperturbative proof of a universal relation whereby quantities computable in\nthe SU(2) case completely determine the virial coefficients of the SU($N_f$)\ncase. These one-dimensional systems are appealing because they can be\nexperimentally realized in highly constrained traps and because of the dominant\nrole played by correlations. The latter are typically nonperturbative and are\ncrucial for understanding ground states and quantum phase transitions. While\nquantum fluctuations are typically overpowered by thermal ones in one and two\ndimensions at any finite temperature, we find that quantum effects do leave\ntheir imprint in thermodynamic quantities. Our calculations show that the\nadditional degrees of freedom, relative to the SU(2) case, provide a dramatic\nenhancement of the density and pressure (in units of their noninteracting\ncounterparts) in a wide region around vanishing $\\beta\\mu$, where $\\beta$ is\nthe inverse temperature and $\\mu$ the chemical potential. As shown recently in\nexperiments, the thermodynamics we explore here can be measured in a controlled\nand precise fashion in highly constrained traps and optical lattices. Our\nresults are a prediction for such experiments in one dimension with atoms of\nhigh nuclear spin."
    },
    {
        "anchor": "Dynamical preparation of an atomic condensate in a Hofstadter band: The creation of a Hamiltonian in the quantum regime which has non-trivial\ntopological features is a central goal of the cold-atom community, enabling\nwidespread exploration of novel phases of quantum matter. A general scheme to\nsynthesize such Hamiltonians is based on dynamical modulation of optical\nlattices which thereby generate vector potentials. At the same time the\nmodulation can lead to heating and serious difficulties with equilibration.\nHere we show that these challenges can be overcome by demonstrating how a\nHofstadter Bose-Einstein condensate (BEC) can be dynamically realized, using\nexperimental protocols. From Gross-Pitaevskii simulations our study reveals a\ncomplex, multistage evolution; this includes a chaotic intermediate \"heating\"\nstage followed by a spontaneous reentrance to the BEC. The observed behavior is\nreminiscent of evolution in cosmological models.",
        "positive": "Rotational properties of non-dipolar and dipolar Bose-Einstein\n  condensates confined in annular potentials: We investigate the rotational response of both non-dipolar and dipolar\nBose-Einstein condensates confined in an annular potential. For the non-dipolar\ncase we identify certain critical rotational frequencies associated with the\nformation of vortices. For the dipolar case, assuming that the dipoles are\naligned along some arbitrary and tunable direction, we study the same problem\nas a function of the orientation angle of the dipole moment of the atoms."
    },
    {
        "anchor": "Enhanced Superexchange in a Tilted Mott Insulator: In an optical lattice entropy and mass transport by first-order tunneling is\nmuch faster than spin transport via superexchange. Here we show that adding a\nconstant force (tilt) suppresses first-order tunneling, but not spin transport,\nrealizing new features for spin Hamiltonians. Suppression of the superfluid\ntransition can stabilize larger systems with faster spin dynamics. For the\nfirst time in a many-body spin system, we vary superexchange rates by over a\nfactor of 100 and tune spin-spin interactions via the tilt. In a tilted\nlattice, defects are immobile and pure spin dynamics can be studied.",
        "positive": "Quantum quenches in the anisotropic spin-1/2 Heisenberg chain: different\n  approaches to many-body dynamics far from equilibrium: Recent experimental achievements in controlling ultracold gases in optical\nlattices open a new perspective on quantum many-body physics. In these\nexperimental setups it is possible to study coherent time evolution of isolated\nquantum systems. These dynamics reveal new physics beyond the low-energy\nproperties usually relevant in solid-state many-body systems. In this paper we\nstudy the time evolution of antiferromagnetic order in the Heisenberg chain\nafter a sudden change of the anisotropy parameter, using various numerical and\nanalytical methods. As a generic result we find that the order parameter, which\ncan show oscillatory or non-oscillatory dynamics, decays exponentially except\nfor the effectively non-interacting case of the XX limit. For weakly ordered\ninitial states we also find evidence for an algebraic correction to the\nexponential law. The study is based on numerical simulations using a numerical\nmatrix product method for infinite system sizes (iMPS), for which we provide a\ndetailed description and an error analysis. Additionally, we investigate in\ndetail the exactly solvable XX limit. These results are compared to\napproximative analytical approaches including an effective description by the\nXZ-model as well as by mean-field, Luttinger-liquid and sine-Gordon theories.\nThis reveals which aspects of non-equilibrium dynamics can as in equilibrium be\ndescribed by low-energy theories and which are the novel phenomena specific to\nquantum quench dynamics. The relevance of the energetically high part of the\nspectrum is illustrated by means of a full numerical diagonalization of the\nHamiltonian."
    },
    {
        "anchor": "Structural transitions of nearly second order in classical dipolar gases: Particles with repulsive power-law interactions undergo a transition from a\nsingle to a double chain (zigzag) by decreasing the confinement in the\ntransverse direction. We theoretically characterize this transition when the\nparticles are classical dipoles, polarized perpendicularly to the plane in\nwhich the motion occurs, and argue that this transition is of first order, even\nthough weakly. The nature of the transition is determined by the coupling\nbetween transverse and axial modes of the chain and contrasts with the\nbehaviour found in Coulomb systems, where the linear-zigzag transition is\ncontinuous and belongs to the universality class of the ferromagnetic\ntransition. Our results hold for classical systems with power-law interactions\n$1/r^\\alpha$ when $\\alpha > 2$, and show that structural transitions in dipolar\nsystems and Rydberg atoms can offer the testbed for simulating the critical\nbehaviour of magnets with lattice coupling.",
        "positive": "Efficient generation of many-body singlet states of spin-1 bosons in\n  optical superlattices: We propose an efficient stepwise adiabatic merging (SAM) method to generate\nmany-body singlet states in antiferromagnetic spin-1 bosons in concatenated\noptical superlattices with isolated double-well arrays, by adiabatically\nramping up the double-well bias. With an appropriate choice of bias sweeping\nrate and magnetic field, the SAM protocol predicts a fidelity as high as 90%\nfor a sixteen-body singlet state and even higher fidelities for smaller\neven-body singlet states. During their evolution, the spin-1 bosons exhibit\ninteresting squeezing dynamics, manifested by an odd-even oscillation of the\nexperimentally observable squeezing parameter. The generated many-body singlet\nstates may find practical applications in precision measurement of magnetic\nfield gradient and in quantum information processing."
    },
    {
        "anchor": "Motion of an Impurity in a Bose-Einstein Condensate with Weyl Spin-Orbit\n  Coupling: Non-collinear Drag Force and Anisotropic Critical Velocity: We consider the motion of a point-like impurity through a three-dimensional\ntwo-component Bose-Einstein condensate subject to Weyl spin-orbit coupling.\nUsing linear-response theory, we calculate the drag force felt by the impurity\nand the associated anisotropic critical velocity from the spectrum of\nelementary excitations. The drag force is shown to be generally not collinear\nwith the velocity of the impurity. This unusual behavior is a consequence of\ncondensation into a finite-momentum state due to the spin-orbit coupling.",
        "positive": "Non-equilibrium fixed points of coupled Ising models: Driven-dissipative systems are expected to give rise to non-equilibrium\nphenomena that are absent in their equilibrium counterparts. However, phase\ntransitions in these systems generically exhibit an effectively classical\nequilibrium behavior in spite of their non-equilibrium origin. In this paper,\nwe show that multicritical points in such systems lead to a rich and genuinely\nnon-equilibrium behavior. Specifically, we investigate a driven-dissipative\nmodel of interacting bosons that possesses two distinct phase transitions: one\nfrom a high- to a low-density phase---reminiscent of a liquid-gas\ntransition---and another to an antiferromagnetic phase. Each phase transition\nis described by the Ising universality class characterized by an (emergent or\nmicroscopic) $\\mathbb{Z}_2$ symmetry. They, however, coalesce at a\nmulticritical point, giving rise to a non-equilibrium model of coupled\nIsing-like order parameters described by a $\\mathbb{Z}_2 \\times \\mathbb{Z}_2$\nsymmetry. Using a dynamical renormalization-group approach, we show that a pair\nof non-equilibrium fixed points (NEFPs) emerge that govern the long-distance\ncritical behavior of the system. We elucidate various exotic features of these\nNEFPs. In particular, we show that a generic continuous scale invariance at\ncriticality is reduced to a discrete scale invariance. This further results in\ncomplex-valued critical exponents and spiraling phase boundaries, and it is\nalso accompanied by a complex Liouvillian gap even close to the phase\ntransition. As direct evidence of the non-equilibrium nature of the NEFPs, we\nshow that the fluctuation-dissipation relation is violated at all scales,\nleading to an effective temperature that becomes \"hotter\" and \"hotter\" at\nlonger and longer wavelengths. Finally, we argue that this non-equilibrium\nbehavior can be observed in cavity arrays with cross-Kerr nonlinearities."
    },
    {
        "anchor": "Collective Dissipative Molecule Formation in a Cavity: We propose a mechanism to realize high-yield molecular formation from\nultracold atoms. Atom pairs are continuously excited by a laser, and a\ncollective decay into the molecular ground state is induced by a coupling to a\nlossy cavity mode. Using a combination of analytical and numerical techniques,\nwe demonstrate that the molecular yield can be improved by simply increasing\nthe number of atoms, and can overcome efficiencies of state-of-the-art\nassociation schemes. We discuss realistic experimental setups for diatomic\npolar and nonpolar molecules, opening up collective light matter interactions\nas a tool for quantum state engineering, enhanced molecule formation,\ncollective dynamics, and cavity mediated chemistry.",
        "positive": "Zero-energy states in rotating trapped Bose-Einstein condensates: We have calculated low-lying quasiparticle excitation spectra of rotating\nthree-dimensional Bose-Einstein condensates. As opposed to the prediction of\nhydrodynamic continuum theories, we find a minimum in the Tkachenko mode\nspectrum at intermediate rotation frequencies of the harmonic trap. Such a\nminimum can harbour a Tkachenko quasiparticle with zero excitation energy. We\ndiscuss the experimental signatures of such a zero mode."
    },
    {
        "anchor": "Vortex lattice solutions to the Gross-Pitaevskii equation with\n  spin-orbit coupling in optical lattices: Effective spin-orbit coupling can be created in cold atom systems using\natom-light interaction. We study the BECs in an optical lattice using the\nGross-Pitaevskii equation with spin-orbit coupling. Bloch states for the linear\nequation are numerically obtained, and compared with stationary solutions to\nthe Gross-Pitaevskii equation with nonlinear terms. Various vortex lattice\nstates are found when the spin-orbit coupling is strong.",
        "positive": "$\u03c0$-junction and spontaneous current state in a superfluid Fermi gas: We discuss an idea to realize a spontaneous current in a superfluid Fermi\ngas. When a polarized Fermi superfluid ($N_\\up > N_\\dwn$, where $N_\\sigma$ is\nthe number of atoms in the hyperfine state described by pseudospin\n$\\sigma=\\uparrow, \\downarrow$.) is loaded onto a ring-shaped trap with a weak\npotential barrier, some of excess atoms ($\\Delta N=N_\\uparrow-N_\\downarrow$)\nare localized around the barrier. As shown in our previous paper [T. Kashimura,\nS. Tsuchiya, and Y. Ohashi, Phys. Rev. A \\textbf{82}, 033617 (2010)], this\npolarized potential barrier works as a $\\pi$-junction in the sense that the\nsuperfluid order parameter changes its sign across the barrier. Because of\nthis, the phase of the superfluid order parameter outside the junction is shown\nto be twisted by $\\pi$ along the ring, which naturally leads to a circulating\nsupercurrent. While the ordinary supercurrent state is obtained as a metastable\nstate, this spontaneous current state is shown to be more stable than the case\nwith no current. Our results indicate that localized excess atoms would be\nuseful for the manipulation of the superfluid order parameter in cold Fermi\ngases."
    },
    {
        "anchor": "Systematic analysis of relative phase extraction in one-dimensional Bose\n  gases interferometry: Spatially resolved relative phase measurement of two adjacent 1D Bose gases\nis enabled by matter-wave interference upon free expansion. However,\nlongitudinal dynamics is typically ignored in the analysis of experimental\ndata. We provide an analytical formula showing a correction to the readout of\nthe relative phase due to longitudinal expansion and mixing with the common\nphase. We numerically assess the error propagation to the estimation of the\ngases' physical quantities such as correlation functions and temperature. Our\nwork characterizes the reliability and robustness of interferometric\nmeasurements, directing us to the improvement of existing phase extraction\nmethods necessary to observe new physical phenomena in cold-atomic quantum\nsimulators.",
        "positive": "Emergence of turbulence in an oscillating Bose-Einstein condensate: We report on the experimental observation of vortices tangle in an atomic BEC\nof Rb-87 atoms when an external oscillatory perturbation is introduced in the\ntrap. The vortices tangle configuration is a signature of the presence of a\nturbulent regime in the cloud. We also show that this turbulent cloud has\nsuppression of the aspect ratio inversion typically observed in quantum\ndegenerate bosonic gases during free expansion. Instead, the cloud expands\nkeeping the ratio between their axis constant. Turbulence in atomic superfluids\nmay constitute an alternative system to investigate decay mechanisms as well as\nto test fundamental theoretical aspects in this field."
    },
    {
        "anchor": "BCS-BEC crossover at finite temperature in spin-orbit coupled Fermi\n  gases: By adopting a $T$-matrix-based method within the $G_0G$ approximation for the\npair susceptibility, we study the effects of the pairing fluctuation on the\nthree-dimensional spin-orbit coupled Fermi gases at finite temperature. The\ncritical temperatures of the superfluid/normal phase transition are determined\nfor three different types of spin-orbit coupling (SOC): (1) the extreme oblate\n(EO) or Rashba SOC, (2) the extreme prolate (EP) or equal Rashba-Dresselhaus\nSOC, and (3) the spherical (S) SOC. For EO- and S-type SOC, the SOC dependence\nof the critical temperature signals a crossover from BCS to BEC state; at\nstrong SOC limit, the critical temperature recover those of ideal BEC of\nrashbons. The pairing fluctuation induces a pseudogap in the fermionic\nexcitation spectrum in both superfluid and normal phases. We find that, for EO-\nand S-type SOC, even at weak coupling, sufficiently strong SOC can induce\nsizable pseudogap. Our research suggests that the spin-orbit coupled Fermi\ngases may open new means to the study of the pseudogap formation in fermionic\nsystems.",
        "positive": "Quantum algorithm for Bose-Einstein condensate quantum fluid dynamics: The dynamics of vortex solitons in a BEC superfluid is studied. A quantum\nlattice-gas algorithm (localization-based quantum computation) is employed to\nexamine the dynamical behavior of vortex soliton solutions of the\nGross-Pitaevskii equation (phi^4 interaction nonlinear Schroedinger equation).\nQuantum turbulence is studied in large grid numerical simulations: Kolmogorov\nspectrum associated with a Richardson energy cascade occurs on large flow\nscales. At intermediate scales a k^{-6} power law emerges, in a\nclassical-quantum transition from vortex filament reconnections to Kelvin\nwave-acoustic wave coupling. The spontaneous exchange of intermediate vortex\nrings is observed. Finally, at very small spatial scales a k^{-3} power law\nemerges, characterizing fluid dynamics occurring within the scale size of the\nvortex cores themselves, a characteristic Kelvin wave cascade region. Poincare\nrecurrence is studied: in the free non-interacting system, a fast Poincare\nrecurrence occurs for regular arrays of line vortices. The recurrence period is\nused to demarcate dynamics driving the nonlinear quantum fluid towards\nturbulence, since fast recurrence is an approximate symmetry of the nonlinear\nquantum fluid at early times. This class of quantum algorithms is useful for\nstudying BEC superfluid dynamics over a broad range of wave numbers, from\nquantum flow to a pseudo-classical inviscid flow regime to a Kolmogorov\ninertial subrange."
    },
    {
        "anchor": "Tunable nanomagnetism in moderately cold fermions on optical lattices: Localized defects, unavoidable in real solids, may be simulated in\n(generically defect-free) cold-atom systems, e.g., via modifications of the\noptical lattice. We study the Hubbard model on a square lattice with single\nimpurities, pairs of nearby impurities, or lines of impurities using\nnumerically exact determinantal quantum Monte Carlo simulations. In all cases,\ncorrelations on the \"impurity\" sites are enhanced either by larger on-site\ninteractions or by a reduced coupling to the environment.\n  We find highly nontrivial magnetic correlations, which persist at elevated\ntemperatures and should be accessible in cold-atom systems with current\nexperimental techniques. With improved cooling techniques, these features could\nbe followed towards generic quantum antiferromagnetism in the homogeneous\nlimit. More generally, tunable crossing points between different correlation\nfunctions could be used, in a quantum steelyard balance setup, as robust\nthermometers.",
        "positive": "Fermionic formalism for driven-dissipative multi-level systems: We present a fermionic description of non-equilibrium multi-level systems.\nOur approach uses the Keldysh path integral formalism and allows us to take\ninto account periodic drives, as well as dissipative channels. The technique is\nbased on the Majorana fermion representation of spin-1/2 models which follows\nearlier applications in the context of spin and Kondo systems. We apply this\nformalism to problems of increasing complexity: a dissipative two-level system,\na driven-dissipative multi-level atom, and a generalized Dicke model describing\nmany multi-level atoms coupled to a single cavity. We compare our theoretical\npredictions with recent QED experiments and point out the features of a\ncounter-lasing transition. Our technique provides a convenient and powerful\nframework for analyzing driven-dissipative quantum systems, complementary to\nother approaches based on the solution of Lindblad master equations."
    },
    {
        "anchor": "Dynamical Universal Behavior in Quantum Chaotic Systems: We discover numerically that a moving wave packet in a quantum chaotic\nbilliard will always evolve into a quantum state, whose density probability\ndistribution is exponential. This exponential distribution is found to be\nuniversal for quantum chaotic systems with rigorous proof. In contrast, for the\ncorresponding classical system, the distribution is Gaussian. We find that the\nquantum exponential distribution can smoothly change to the classical Gaussian\ndistribution with coarse graining.",
        "positive": "Variational theory of angulons and their rotational spectroscopy: The angulon, a quasiparticle formed by a quantum rotor dressed by the\nexcitations of a many-body bath, can be used to describe an impurity rotating\nin a fluid or solid environment. Here we propose a coherent state ansatz in the\nco-rotating frame which provides a comprehensive theoretical description of\nangulons. We reveal the quasiparticle properties, such as energies,\nquasiparticle weights and spectral functions, and show that our ansatz yields a\npersistent decrease in the impurity's rotational constant due to many-body\ndressing, consistent with experimental observations. From our study, a picture\nof the angulon emerges as an effective spin interacting with a magnetic field\nthat is self-consistently generated by the molecule's rotation. Moreover, we\ndiscuss rotational spectroscopy, which focuses on the response of rotating\nmolecules to a laser perturbation in the linear response regime. Importantly,\nwe take into account initial-state interactions that have been neglected in\nprior studies and reveal their impact on the excitation spectrum. To examine\nthe angulon instability regime, we use a single-excitation ansatz and obtain\nresults consistent with experiments, in which a broadening of spectral lines is\nobserved while phonon wings remain highly suppressed due to initial-state\ninteractions."
    },
    {
        "anchor": "Superfluidity of Bosons in Kagome Lattices with Frustration: In this letter we consider spinless bosons in a Kagome lattice with\nnearest-neighbor hopping and on-site interaction, and the sign of hopping is\ninverted by insetting a {\\pi} flux in each triangle of Kagome lattice so that\nthe lowest single particle band is perfectly flat. We show that in the high\ndensity limit, despite of the infinite degeneracy of the single particle ground\nstates, interaction will select out the Bloch state at the K point of Brillouin\nzone for boson condensation at the lowest temperature. As temperature\nincreases, the single boson superfluid order can be easily destroyed, while an\nexotic triple-boson paired superfluid order will remain. We establish that this\ntrion superfluid exists in a broad temperature regime until the temperature is\nincreased to the same order of hopping and then the system turns into normal\nphases. Finally we show that time of flight measurement of momentum\ndistribution and its noise correlation can be used to distinguish these three\nphases.",
        "positive": "Nonthermal fixed points and solitons in a one-dimensional Bose gas: Single-particle momentum spectra for a dynamically evolving one-dimensional\nBose gas are analysed in the semi-classical wave limit. Representing one of the\nsimplest correlation functions these give information about possible universal\nscaling behaviour. Motivated by the previously discovered connection between\n(quasi-)topological field configurations, strong wave turbulence, and\nnonthermal fixed points of quantum field dynamics, soliton formation is studied\nwith respect to the appearance of transient power-law spectra. A random-soliton\nmodel is developed to describe the spectra analytically, and the analogies and\ndifference between the appearing power laws and those found in a field theory\napproach to strong wave turbulence are discussed. The results open a view on\nsolitary wave dynamics from the point of view of critical phenomena far from\nthermal equilibrium and on a possibility to study this dynamics in experiment\nwithout the necessity of detecting solitons in situ."
    },
    {
        "anchor": "Conserving symmetries in Bose-Einstein condensate dynamics requires\n  many-body theory: We explain from first principles why satisfying conservation laws in Bose\nEinstein condensate dynamics requires many-body theory. For the\nGross-Pitaevskii mean-field we show analytically and numerically that\nconservation laws are violated. We provide examples for angular momentum and\nlinear momentum conservation. Arbitrarily large violations occur despite\nnegligible depletion and interaction energy. For the case of angular momentum\nwe show through extensive many-body simulations how the conservation law can be\ngradually restored on the many-body level. Implications are discussed.",
        "positive": "Quasi-long-range order in trapped two-dimensional Bose gases: We study the fate of algebraic decay of correlations in a harmonically\ntrapped two-dimensional degenerate Bose gas. The analysis is inspired by recent\nexperiments on ultracold atoms where power-law correlations have been observed\ndespite the presence of the external potential. We generalize the spin wave\ndescription of phase fluctuations to the trapped case and obtain an analytical\nexpression for the one-body density matrix within this approximation. We show\nthat algebraic decay of the central correlation function persists to lengths of\nabout 20% of the Thomas--Fermi radius. We establish that the trap-averaged\ncorrelation function decays algebraically with a strictly larger exponent\nweakly changing with trap size and find indications that the recently observed\nenhanced scaling exponents receive significant contributions from the normal\ncomponent of the gas. We discuss radial and angular correlations and propose a\nlocal correlation approximation which captures the correlations very well. Our\nanalysis goes beyond the usual local density approximation and the developed\nsummation techniques constitute a powerful tool to investigate correlations in\ninhomogeneous systems."
    },
    {
        "anchor": "Quantum phase transitions of a two-leg bosonic ladder in an artificial\n  gauge field: We consider a two leg bosonic ladder in a $U(1)$ gauge field with both\ninterleg hopping and interleg repulsion. As a function of the flux, the\ninterleg interaction converts the commensurate-incommensurate transition from\nthe Meissner to a Vortex phase, into an Ising-type of transition towards a\ndensity wave phase. A disorder point is also found after which the correlation\nfunctions develop a damped sinusoid behavior signaling a melting of the vortex\nphase. We discuss the differences on the phase diagram for attractive and\nrepulsive interleg interaction. In particular, we show how repulsion favors the\nMeissner phase at low-flux and a phase with a second incommensuration in the\ncorrelation functions for intermediate flux, leading to a richer phase diagram\nthan in the case of interleg attraction. The effect of the temperature on the\nchiral current is also discussed.",
        "positive": "Many-body Decay of the Gapped Lowest Excitation of a Bose-Einstein\n  Condensate: We study the decay mechanism of the gapped lowest-lying excitation of a\nquasi-pure box-trapped atomic Bose-Einstein condensate. Owing to the absence of\nlower-energy modes, or direct coupling to an external bath, this excitation is\nprotected against one-body (linear) decay and the damping mechanism is\nexclusively nonlinear. We develop a universal theoretical model that explains\nthis fundamental nonlinear damping as a process whereby two quanta of the\ngapped lowest excitation mode couple to a higher-energy mode, which\nsubsequently decays into a continuum. We find quantitative agreement between\nour experiments and the predictions of this model. Finally, by strongly driving\nthe system below its (lowest) resonant frequency we observe third-harmonic\ngeneration, a hallmark of nonlinear behavior."
    },
    {
        "anchor": "Pomeranchuk cooling of the SU($2N$) ultra-cold fermions in optical\n  lattices: We investigate the thermodynamic properties of a half-filled SU(2N)\nFermi-Hubbard model in the two-dimensional square lattice using the\ndeterminantal quantum Monte Carlo simulation, which is free of the fermion\n\"sign problem\". The large number of hyperfine-spin components enhances spin\nfluctuations, which facilitates the Pomeranchuk cooling to temperatures\ncomparable to the superexchange energy scale at the case of SU$(6)$. Various\nquantities including entropy, charge fluctuation, and spin correlations have\nbeen calculated.",
        "positive": "Self-amplifying Hawking radiation and its background: a numerical study: We numerically study an analogue black hole with two horizons with similar\nparameters to a recent experiment. We find that the Hawking radiation exists on\na background which contains a density oscillation, a zero-frequency ripple. The\nHawking radiation evolves from spontaneous to self-amplifying, while the\nbackground ripple grows steadily with no qualitative change. It is seen that\nthe self-amplifying Hawking radiation has a non-zero frequency. The background\nripple appears even before the inner horizon is created, in contrast to\npredictions. This work is in agreement with the recent observation of\nself-amplifying Hawking radiation, and explains some of the features seen. In\ncontrast to recent works, our study differentiates between the Hawking\nradiation observed, and the evolution of the background."
    },
    {
        "anchor": "Fractional quantum Hall states of few bosonic atoms in geometric gauge\n  fields: We employ the exact diagonalization method to analyze the possibility of\ngenerating strongly correlated states in two-dimensional clouds of ultracold\nbosonic atoms which are subjected to a geometric gauge field created by\ncoupling two internal atomic states to a laser beam. Tuning the gauge field\nstrength, the system undergoes stepwise transitions between different ground\nstates, which we describe by analytical trial wave functions, amongst them the\nPfaffian, the Laughlin, and a Laughlin quasiparticle many-body state. The\nadiabatic following of the center of mass movement by the lowest energy dressed\ninternal state, is lost by the mixing of the second internal state. This\nmixture can be controlled by the intensity of the laser field. The\nnon-adiabaticity is inherent to the considered setup, and is shown to play the\nrole of circular asymmetry. We study its influence on the properties of the\nground state of the system. Its main effect is to reduce the overlap of the\nnumerical solutions with the analytical trial expressions by occupying states\nwith higher angular momentum. Thus, we propose generalized wave functions\narising from the Laughlin and Pfaffian wave function by including components,\nwhere extra Jastrow factors appear, while preserving important features of\nthese states. We analyze quasihole excitations over the Laughlin and\ngeneralized Laughlin states, and show that they possess effective fractional\ncharge and obey anyonic statistics. Finally, we study the energy gap over the\nLaughlin state as the number of particles is increased keeping the chemical\npotential fixed. The gap is found to decrease as the number of particles is\nincreased, indicating that the observability of the Laughlin state is\nrestricted to a small number of particles.",
        "positive": "Finite-frequency normal and superfluid drag effects in two-component\n  atomic Bose-Einstein condensates: Two-component systems consisting of mutually interacting particles can\ndemonstrate both intracomponent transport effects and intercomponent\nentrainment (or drag) effects. In the presence of superfluidity, the\nintracomponent transport is characterized by dissipative conductivity and\nsuperfluid weight in the framework of two-fluid model, and intercomponent\nentrainment gives rise to normal and nondissipative drag effects. We present\nunified treatment of all these effects for spatially homogeneous two-component\natomic Bose-Einstein condensates based on the Bogoliubov theory, focusing\nspecifically on the drag effects. Calculating finite-frequency intra- and\nintercomponent conductivities with taking into account quasiparticle damping,\nwe derive and numerically check analytical Drude-like approximations applicable\nat low frequencies, and Lorentz-like approximations applicable at higher\nfrequencies in vicinity of the resonant energy of spin-to-density Bogoliubov\nquasiparticle conversion. As possible physical realizations of two-component\natomic systems, we consider three-dimensional Bose-Bose mixtures and closely\nspaced two-layered systems of magnetic dipolar atoms."
    },
    {
        "anchor": "Dissipation-facilitated molecules in a Fermi gas with non-Hermitian\n  spin-orbit coupling: We study the impact of non-Hermiticity on the molecule formation in a\ntwo-component spin-orbit-coupled Fermi gas near a wide Feshbach resonance.\nUnder an experimentally feasible configuration where the two-photon Raman\nprocess is dissipative, the Raman-induced synthetic spin-orbit coupling\nacquires a complex strength. Remarkably, dissipation of the system facilitates\nthe formation and binding of molecules, which, despite their dissipative nature\nand finite lifetime, exist over a wider parameter regime than in the\ncorresponding Hermitian system. These dissipation-facilitated molecules can be\nprobed by the inverse radio-frequency (rf) spectroscopy, provided the Raman\nlasers are blue detuned to the excited state. The effects of dissipation\nmanifest in the rf spectra as shifted peaks with broadened widths, which serve\nas a clear experimental signature. Our results, readily observable in current\ncold-atom experiments, shed light on the fascinating interplay of\nnon-Hermiticity and interaction in few- and many-body open quantum systems.",
        "positive": "Double well potentials with a quantum moat barrier or a quantum wall\n  barrier give rise to similar entangled wave functions: The solution to a problem in quantum mechanics is generally a linear\nsuperposition of states. The solutions for double well potentials epitomize\nthis property, and go even further than this: they can often be described by an\neffective model whose low energy features can be described by two states ---\none in which the particle is on one side of the barrier, and a second where the\nparticle is on the other side. Then the ground state remains a linear\nsuperposition of these two macroscopic-like states. In this paper we illustrate\nthat this property is achieved similarly with an attractive potential that\nseparates two regions of space, as opposed to the traditionally repulsive one.\nIn explaining how this comes about we revisit the concept of \"orthogonalized\nplane waves,\" first discussed in 1940 to understand electronic band structure\nin solids, along with the accompanying concept of a pseudopotential. We show\nhow these ideas manifest themselves in a simple double well potential, whose\n\"barrier\" consists of a moat instead of the conventional wall."
    },
    {
        "anchor": "Precise Programmable Quantum Simulations with Optical Lattices: We present an efficient approach to precisely simulate tight binding models\nwith optical lattices, based on programmable digital-micromirror-device (DMD)\ntechniques. Our approach consists of a subroutine of Wegner-flow enabled\nprecise extraction of a tight-binding model for a given optical potential, and\na reverse engineering step of adjusting the potential for a targeting model,\nfor both of which we develop classical algorithms to achieve high precision and\nhigh efficiency. With renormalization of Wannier functions and high band\neffects systematically calibrated in our protocol, we show the tight-binding\nmodels with programmable onsite energies and tunnelings can be precisely\nsimulated with optical lattices integrated with the DMD techniques. With\nnumerical simulation, we demonstrate that our approach would facilitate quantum\nsimulation of localization physics with unprecedented programmability and\natom-based boson sampling for illustration of quantum computational advantage.\nWe expect this approach would pave a way towards large-scale and precise\nprogrammable quantum simulations based on optical lattices.",
        "positive": "Chiral edge states and fractional charge separation in interacting\n  bosons on a Kagome lattice: We consider the extended hard-core Bose-Hubbard model on a Kagome lattice\nwith boundary conditions on two edges. We find that the sharp edges lift the\ndegeneracy and freeze the system into a striped order at 1/3 and 2/3 filling\nfor zero hopping. At small hopping strengths, holes spontaneously appear and\nseparate into fractional charges which move to the edges of the system. This\nleads to a novel edge liquid phase, which is characterized by fractional\ncharges near the edges and a finite edge compressibility but no superfluid\ndensity. The compressibility is due to excitations on the edge which display a\nchrial symmetry breaking that is reminiscent of the quantum Hall effect and\ntopological insulators. Large scale Monte Carlo simulations confirm the\nanalytical considerations."
    },
    {
        "anchor": "One-dimensional three-boson problem with two- and three-body\n  interactions: We solve the three-boson problem with contact two- and three-body\ninteractions in one dimension and analytically calculate the ground and excited\ntrimer-state energies. Then, by using the diffusion Monte Carlo technique we\ncalculate the binding energy of three dimers formed in a one-dimensional\nBose-Bose or Fermi-Bose mixture with attractive interspecies and repulsive\nintraspecies interactions. Combining these results with our three-body\nanalytics we extract the three-dimer scattering length close to the dimer-dimer\nzero crossing. In both considered cases the three-dimer interaction turns out\nto be repulsive. Our results constitute a concrete proposal for obtaining a\none-dimensional gas with a pure three-body repulsion.",
        "positive": "Yang-Gaudin model: A paradigm of many-body physics: Using Bethe's hypothesis, C N Yang exactly solved the one-dimensional (1D)\ndelta-function interacting spin-1/2 Fermi gas with an arbitrary spin-imbalance\nin 1967. At that time, using a different method, M Gaudin solved the problem of\ninteracting fermions in a spin-balanced case. Later, the 1D delta-function\ninteracting fermion problem was named as the Yang-Gaudin model. It has been in\ngeneral agreed that a key discovery of C N Yang's work was the cubic matrix\nequation for the solvability conditions. % This equation was later\nindependently found by R J Baxter for commuting transfer matrices of 2D exactly\nsolvable vertex models. % The equation has since been referred to Yang-Baxter\nequation, being the master equation to integrability. % The Yang-Baxter\nequation has been used to solve a wide range of 1D many-body problems in\nphysics, such as 1D Hubbard model, $SU(N)$ Fermi gases, Kondo impurity problem\nand strongly correlated electronic systems etc.\n  % In this paper, we will briefly discuss recent developments of the\nYang-Gaudin model on several breakthroughs of many-body phenomena, ranging from\nthe universal thermodynamics to the Luttigner liquid, the spin charge\nseparation, the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)-like pairing state and\nthe quantum criticality.\n  %\n  These developments demonstrate that the Yang-Gaudin model has laid out a\nprofound legacy of the Yang-Baxter equation."
    },
    {
        "anchor": "Anomalous breaking of scale invariance in a two-dimensional Fermi gas: The frequency of the breathing mode of a classical two dimensional Fermi gas\nin a harmonic confinement is fixed by the scale invariance of the Hamiltonian.\nScale invariance is broken on the quantum mechanical level by introducing the\ntwo dimensional scattering length as a regulator. This is an example of a\nquantum anomaly in the field of ultracold atoms and leads to a shift of the\nfrequency of the collective breathing mode of the cloud. In this work, we study\nthis anomalous frequency shift for a two component Fermi gas in the strongly\ninteracting regime. We measure significant shifts away from the scale invariant\nresult that depend strongly on both interactions and temperature. We find\nqualitative agreement with theoretical calculations at zero temperature.",
        "positive": "Quantum-fluctuation-driven crossover from a dilute Bose-Einstein\n  condensate to a macro-droplet in a dipolar quantum fluid: In a joint experimental and theoretical effort, we report on the formation of\na macro-droplet state in an ultracold bosonic gas of erbium atoms with strong\ndipolar interactions. By precise tuning of the s-wave scattering length below\nthe so-called dipolar length, we observe a smooth crossover of the ground state\nfrom a dilute Bose-Einstein condensate (BEC) to a dense macro-droplet state of\nmore than $10^4$ atoms. Based on the study of collective excitations and loss\nfeatures, we quantitative prove that quantum fluctuations stabilize the\nultracold gas far beyond the instability threshold imposed by mean-field\ninteractions. Finally, we perform expansion measurements, showing the evolution\nof the normal BEC towards a three-dimensional self-bound state and show that\nthe interplay between quantum stabilization and three-body losses gives rise to\na minimal expansion velocity at a finite scattering length."
    },
    {
        "anchor": "Expansion of harmonically trapped interacting particles and time\n  dependence of the contact: We study the expansion of an interacting atomic system at zero temperature,\nfollowing its release from an isotropic three-dimensional harmonic trap and\ncalculate the time dependence of its density and momentum distribution, with\nspecial focus on the behavior of the contact parameter. We consider different\nquantum systems, including the unitary Fermi gas of infinite scattering length,\nthe weakly interacting Bose gas, and two interacting particles with highly\nasymmetric mass imbalance. In all cases analytic results can be obtained, which\nshow that the initial value of the contact, fixing the $1/k^4$ tail of the\nmomentum distribution, disappears for large expansion times. Our results raise\nthe problem of understanding the recent experiment of Chang \\textit{et al.}\n[Phys. Rev. Lett. \\textbf{117}, 235303 (2016)] carried out on a weakly\ninteracting Bose gas of metastable $^4$He atoms, where a $1/r^4$ tail in the\ndensity distribution was observed after a large expansion time, implying the\nexistence of the $1/k^4$ tail in the asymptotic momentum distribution.",
        "positive": "Post-adiabatic Hamiltonian for low-energy excitations in a slowly\n  time-dependent BCS-BEC crossover: We develop a Hamiltonian that describes the time-dependent formation of a\nmolecular Bose-Einstein condensate (BEC) from a Bardeen-Cooper-Schrieffer (BCS)\nstate of fermionic atoms as a result of slowly sweeping through a Feshbach\nresonance. In contrast to many other calculations in the field (see e.g.\n[1-4]), our Hamiltonian includes the leading post-adiabatic effects that arise\nbecause the crossover proceeds at a non-zero sweep rate. We apply a path\nintegral approach and a stationary phase approximation for the molecular zero\nmomentum background, which is a good approximation for narrow resonances (see\ne.g. [5, 6]). We use two-body adiabatic approximations to solve the atomic\nevolution within this background. The dynamics of the non-zero momentum\nmolecular modes is solved within a dilute gas approximation and by mapping it\nonto a purely bosonic Hamiltonian. Our main result is a post-adiabatic\neffective Hamiltonian in terms of the instantaneous bosonic\n(Anderson-)Bogoliubov modes, which holds throughout the whole resonance, as\nlong as the Feshbach sweep is slow enough to avoid breaking Cooper pairs."
    },
    {
        "anchor": "Nonequilibrium Phase Diagram of a Driven-Dissipative Many-Body System: We study the nonequilibrium dynamics of a many-body bosonic system on a\nlattice, subject to driving and dissipation. The time-evolution is described by\na master equation, which we treat within a generalized Gutzwiller mean field\napproximation for density matrices. The dissipative processes are engineered\nsuch that the system, in the absence of interaction between the bosons, is\ndriven into a homogeneous steady state with off-diagonal long range order. We\ninvestigate how the coherent interaction affects qualitatively the properties\nof the steady state of the system and derive a nonequilibrium phase diagram\nfeaturing a phase transition into a steady state without long range order. The\nphase diagram exhibits also an extended domain where an instability of the\nhomogeneous steady state gives rise to a persistent density pattern with\nspontaneously broken translational symmetry. In the limit of small particle\ndensity, we provide a precise analytical description of the time-evolution\nduring the instability. Moreover, we investigate the transient following a\nquantum quench of the dissipative processes and we elucidate the prominent role\nplayed by collective topological variables in this regime.",
        "positive": "Perspectives of optical lattices with state-dependent tunneling in\n  approaching quantum magnetism in the presence of the external harmonic\n  trapping potential: We study theoretically potential advantages of two-component mixtures in\noptical lattices with state-dependent tunneling for approaching\nlong-range-order phases and detecting easy-axis antiferromagnetic correlations.\nWhile we do not find additional advantages of mixtures with large hopping\nimbalance for approaching quantum magnetism in a harmonic trap, it is shown\nthat a nonzero difference in hopping amplitudes remains highly important for a\nproper symmetry breaking in the pseudospin space for the single-site-resolution\nimaging and can be advantageously used for a significant increase of the\nsignal-to-noise ratio and thus detecting long-range easy-axis antiferromagnetic\ncorrelations in the corresponding experiments."
    },
    {
        "anchor": "Isothermal sweep theorems for ultra-cold quantum gases in a canonical\n  ensemble: After deriving the isothermal Hellmann-Feynman theorem (IHFT) that is\nsuitable for mixed states in a canonical ensemble, we use this theorem to\nobtain the isothermal magnetic-field sweep theorems for the free, average and\ntrapping energies, and for the entropy, specific heat, pressure and atomic\ncompressibility of strongly-correlated ultra-cold quantum gases. In particular,\nwe apply the sweep theorems to two-component Fermi gases in the\nweakly-interacting BCS and BEC limits, showing that the temperature dependence\nof the contact parameter can be determined by the variation of either the\nentropy or specific heat with respect to the scattering length. We also use the\nIHFT to obtain the Virial theorem in a canonical ensemble, and discuss its\nimplications for quantum gases.",
        "positive": "Topological Floquet engineering using two frequencies in two dimensions: Using two-frequency driving in two dimensions opens up new possibilites for\nFloquet engineering, which range from controlling specific symmetries to tuning\nthe properties of resonant gaps. In this work, we study two-band lattice models\nsubject to two-tone Floquet driving and analyse the resulting effective Floquet\nbandstructures both numerically and analytically. On the one hand, we extend\nthe methodology of Sandholzer et al. [10.1103/PhysRevResearch.4.013056] from\none to two dimensions and find competing topological phases in a simple Bravais\nlattice when the two resonant drives at $1\\omega$ and $2\\omega$ interfere. On\nthe other hand, we explore driving-induced symmetry breaking in the hexagonal\nlattice, in which the breaking of either inversion or time-reversal symmetry\ncan be tuned independently via the Floquet modulation. Possible applications of\nour work include a simpler generation of topological bands for ultracold atoms,\nand the realisation of non-linear Hall effects as well as Haldane's parity\nanomaly in inversion-symmetric parent lattices."
    },
    {
        "anchor": "Trapped two-component Fermi gases with up to six particles: Energetics,\n  structural properties, and molecular condensate fraction: We investigate small equal-mass two-component Fermi gases under external\nspherically symmetric confinement in which atoms with opposite spins interact\nthrough a short-range two-body model potential. We employ a non-perturbative\nmicroscopic framework, the stochastic variational approach, and determine the\nsystem properties as functions of the interspecies s-wave scattering length a,\nthe orbital angular momentum L of the system, and the numbers N1 and N2 of\nspin-up and spin-down atoms (with N1-N2 =0 or 1 and N < 7, where N=N1+N2). At\nunitarity, we determine the energies of the five- and six-particle systems for\nvarious ranges r0 of the underlying two-body model potential and extrapolate to\nthe zero-range limit. These energies serve as benchmark results that can be\nused to validate and assess other numerical approaches. We also present\nstructural properties such as the pair distribution function and the radial\ndensity. Furthermore, we analyze the one-body and two-body density matrices. A\nmeasure for the molecular condensate fraction is proposed and applied. Our\ncalculations show explicitly that the natural orbitals and the momentum\ndistributions of atomic Fermi gases approach those characteristic for a\nmolecular Bose gas if the s-wave scattering length a, a>0, is sufficiently\nsmall.",
        "positive": "Vortex dynamics and turbulence in dipolar Bose-Einstein condensates: Quantum turbulence indicators in dipolar Bose-Einstein condensed fluids,\nfollowing emissions of vortex-antivortex pairs generated by a circularly moving\ndetuned laser, are being provided by numerical simulations of the corresponding\nquasi-two-dimensional Gross-Pitaevskii formalism with repulsive contact\ninteractions combined with tunable dipole-dipole strength. The critical\nvelocities of two variants of a circularly moving obstacle are determined and\nanalyzed for vortex-antivortex nucleation in the form of regular and cluster\nemissions. The turbulent dynamical behavior is predicted to follow closely the\ninitial emission of vortex-antivortex pairs, relying on the expected\nKolmogorov's classical scaling law, which is verified by the spectral analysis\nof the incompressible part of the kinetic energy. Within our aim to provide\nfurther support in the up-to-now investigations of quantum turbulence, which\nhave been focused on non-dipolar Bose-Einstein condensates, we emphasize the\nrole of dipole-dipole interactions in the fluid dynamics."
    },
    {
        "anchor": "BCS-BEC crossover induced by a synthetic non-Abelian gauge field: We investigate the ground state of interacting spin-$\\half$ fermions (3D) at\na finite density ($\\rho \\sim \\kf^3$) in the presence of a uniform non-Abelian\ngauge field. The gauge field configuration (GFC) described by a vector $\\blam\n\\equiv (\\lambda_x, \\lambda_y, \\lambda_z)$, whose magnitude $\\lambda$ determines\nthe gauge coupling strength, generates a generalized Rashba spin-orbit\ninteraction. For a weak attractive interaction in the singlet channel described\nby a small negative scattering length $(\\kf |\\as| \\lesssim 1)$, the ground\nstate in the absence of the gauge field ($\\lambda=0$) is a BCS\n(Bardeen-Cooper-Schrieffer) superfluid with large overlapping pairs. With\nincreasing gauge coupling strength, a non-Abelian gauge field engenders a\ncrossover of this BCS ground state to a BEC (Bose-Einstein condensate) ground\nstate of bosons even with a weak attractive interaction that fails to produce a\ntwo-body bound state in free vacuum. For large gauge couplings $(\\lambda/\\kf\n\\gg 1)$, the BEC attained is a condensate of bosons whose properties are solely\ndetermined by the gauge field (and not by the scattering length so long as it\nis non-zero) -- we call these bosons \"rashbons\". In the absence of interactions\n($\\as = 0^-$), the shape of the Fermi surface of the system undergoes a\ntopological transition at a critical gauge coupling $\\lambda_T$. For high\nsymmetry gauge field configurations we show that the crossover from the BCS\nsuperfluid to the rashbon BEC occurs in the regime of $\\lambda$ near\n$\\lambda_T$. In the context of cold atomic systems, this work makes an\ninteresting suggestion of obtaining\n  BCS-BEC crossover through a route other than tuning the interaction between\nthe fermions.",
        "positive": "Bosonic Weyl excitations induced by $p$-orbital interactions in a cubic\n  optical lattice: Weyl points exist in a fascinating topological state of matter with linear\nband crossings analogous to magnetic monopoles. Tremendous efforts have been\ndevoted to investigate fermionic topological matters with Weyl points in the\nsingle-particle band dispersion. It remains elusive for realizing\ninteraction-induced Weyl points, especially for bosons. Motivated by recent\nexperimental progress in ultracold atoms, we propose a scheme to create Weyl\npoints for Bogoliubov excitations of a bosonic superfluid in a\nthree-dimensional cubic optical lattice. The unique design of the lattice leads\nto interaction-induced time-reversal symmetry breaking for a $p$-orbital\nsuperfluid, which in turn induces Weyl Bogoliubov excitations. Analogous to\nWeyl semimetals of electronic systems, the superfluid also support\ntopologically protected edge modes due to the bulk-boundary correspondence."
    },
    {
        "anchor": "Spatially varying interactions induced in atomic gases by optical\n  Feshbach resonance: Optical Feshbach resonance is capable of inducing spatially varying\ninteractions in ultra-cold atoms. Its applications to pancake-shaped clouds of\nbosons and fermions enable one to study several fresh phenomena. We examine\npossibilities of inducing counter-intuitive structures such as creating a\nsuperfluid enclave inside a Mott insulator for bosons and a normal-gas core\nenclosed by a superfluid shell for fermions. We discuss feasible experimental\nsetups and signatures of those interesting structures, which can be very\ndifferent from common structures observed in experiments so far. While a\nsuperfluid enclave in a Mott insulator can be useful for constructing atomic\ndevices for atomtronics, superconducting islands observed in scanning-tunneling\nmicroscopy of heavily underdoped high-temperature superconductors may be\nstudied with cold Fermi gases with spatially varying attractions.",
        "positive": "Weyl points in three-dimensional optical lattices: synthetic magnetic\n  monopoles in momentum space: We show that Hamiltonians with Weyl points can be realized for ultracold\natoms using laser-assisted tunneling in three-dimensional optical lattices.\nWeyl points are synthetic magnetic monopoles that exhibit a robust,\nthree-dimensional linear dispersion. They are associated with many interesting\ntopological states of matter, such as Weyl semimetals and chiral Weyl fermions.\nHowever, Weyl points have yet to be experimentally observed in any system. We\nshow that this elusive goal is well-within experimental reach with an extension\nof the techniques recently used to obtain the Harper Hamiltonian."
    },
    {
        "anchor": "Quasi-static Lineshape Theory for Rydberg Excitations: This work presents a theoretical approach for lineshapes of Rydberg\nexcitations. In particular, we introduce the quasi-static lineshape theory,\nleading to a methodic and general approach, and its validity is studied. Next,\nusing $^{84}$Sr as a prototypical scenario, we discuss the role of the thermal\natoms and core-perturber interactions, generally disregarded in Rydberg\nphysics. Finally, we present a characterization of the role of Ryderg-core\nperturber interactions based on the density and principal quantum number that,\nbeyond affecting the lineshape, could potentially apply to chemi-ionization\nreactions responsible for the decay or Rydberg atoms in high density media.",
        "positive": "Finite temperature ferromagnetic transition in coherently coupled Bose\n  gases: A paramagnetic-ferromagnetic quantum phase transition is known to occur at\nzero temperature in a two-dimensional coherently-coupled Bose mixture of dilute\nultracold atomic gases provided the interspecies interaction strength is large\nenough. Here we study the fate of such a transition at finite temperature by\nperforming numerical simulations with the stochastic (projected)\nGross-Pitaevskii formalism, which includes both thermal and beyond mean-field\neffects. By extracting the average magnetization, the magnetic fluctuations and\ncharacteristic relaxation frequency (or, critical slowing down), we identify a\nfinite temperature critical line for the transition. We find that the critical\npoint shifts linearly with temperature and, in addition, the three quantities\nused to probe the transition exhibit a temperature power-law scaling. The\nscaling of the critical slowing down is found to be consistent with thermal\ncritical exponents and is very well approximated by the square of the spin\nexcitation gap at the zero-temperature."
    },
    {
        "anchor": "Self-bound Doubly-Dipolar Bose-Einstein condensates: We analyze the physics of self-bound droplets in a doubly dipolar\nBose-Einstein condensate (DDBEC) composed by particles with both electric and\nmagnetic dipole moments. Using the particularly relevant case of dysprosium, we\nshow that the anisotropy of the doubly-dipolar interaction potential is highly\nversatile and nontrivial, depending critically on the relative orientation and\nstrength between the two dipole moments. This opens novel possibilities for\nexploring intriguing quantum many-body physics. Interestingly, by varying the\nangle between the two dipoles we find a dimensional crossover from quasi\none-dimensional to quasi two-dimensional self-bound droplets. This opens a so\nfar unique scenario in condensate physics, in which a dimensional crossover is\nsolely driven by interactions in the absence of any confinement.",
        "positive": "Collective behaviour of large number of vortices in the plane: We investigate the dynamics of $N$ point vortices in the plane, in the limit\nof large $N$. We consider {\\em relative equilibria}, which are rigidly rotating\nlattice-like configurations of vortices. These configurations were observed in\nseveral recent experiments [Durkin and Fajans, Phys. Fluids (2000) 12, 289-293;\nGrzybowski {\\em et.al} PRE (2001)64, 011603]. We show that these solutions and\ntheir stability are fully characterized via a related {\\em aggregation model}\nwhich was recently investigated in the context of biological swarms [Fetecau\n{\\em et.al.}, Nonlinearity (2011) 2681; Bertozzi {\\em et.al.}, M3AS (2011)]. By\nutilizing this connection, we give explicit analytic formulae for many of the\nconfigurations that have been observed experimentally. These include\nconfigurations of vortices of equal strength; the $N+1$ configurations of $N$\nvortices of equal strength and one vortex of much higher strength; and more\ngenerally, $N+K$ configurations. We also give examples of configurations that\nhave not been studied experimentally, including $N+2$ configurations where $N$\nvortices aggregate inside an ellipse. Finally, we introduce an artificial\n``damping'' to the vortex dynamics, in an attempt to explain the phenomenon of\ncrystalization that is often observed in real experiments. The diffusion breaks\nthe conservative structure of vortex dynamics so that any initial conditions\nconverge to the lattice-like relative equilibrium."
    },
    {
        "anchor": "Scaling and universality in two dimensions: three-body bound states with\n  short-ranged interactions: The momentum space zero-range model is used to investigate universal\nproperties of three interacting particles confined to two dimensions. The\npertinent equations are first formulated for a system of two identical and one\ndistinct particle and the two different two-body subsystems are characterized\nby two-body energies and masses. The three-body energy in units of one of the\ntwo-body energies is a universal function of the other two-body energy and the\nmass ratio. We derive convenient analytical formulae for calculations of the\nthree-body energy as function of these two independent parameters and exhibit\nthe results as universal curves. In particular, we show that the three-body\nsystem can have any number of stable bound states. When the mass ratio of the\ndistinct to identical particles is greater than 0.22 we find that at most two\nstable bound states exist, while for two heavy and one light mass an increasing\nnumber of bound states is possible. The specific number of stable bound states\ndepends on the ratio of two-body bound state energies and on the mass ratio and\nwe map out an energy-mass phase-diagram of the number of stable bound states.\nRealizable systems of both fermions and bosons are discussed in this framework.",
        "positive": "Numerical method for evolving the dipolar projected Gross-Pitaevskii\n  equation: We describe a method for evolving the projected Gross-Pitaevskii equation\n(PGPE) for an interacting Bose gas in a harmonic oscillator potential, with the\ninclusion of a long-range dipolar interaction. The central difficulty in\nsolving this equation is the requirement that the field is restricted to a\nsmall set of prescribed modes that constitute the low energy c-field region of\nthe system. We present a scheme, using a Hermite-polynomial based spectral\nrepresentation, that precisely implements this mode restriction and allows an\nefficient and accurate solution of the dipolar PGPE. We introduce a set of\nauxiliary oscillator states to perform a Fourier transform necessary to\nevaluate the dipolar interaction in reciprocal space. We extensively\ncharacterize the accuracy of our approach, and derive Ehrenfest equations for\nthe evolution of the angular momentum."
    },
    {
        "anchor": "Kibble-Zurek mechanism in a trapped ferromagnetic Bose-Einstein\n  condensate: Spontaneous spin vortex formation in the magnetic phase transition of a\ntrapped spin-1 Bose-Einstein condensate is investigated using mean-field\ntheory. In a harmonic trapping potential, an inhomogeneous atomic density leads\nto spatial variations of the critical point, magnetization time scale, and spin\ncorrelation length. The Kibble-Zurek phenomena are shown to emerge even in such\ninhomogeneous systems, when the quench of the quadratic Zeeman energy is fast\nenough. For slow quench, the magnetized region gradually expands from the\ncenter of the trap pushing out spin vortices, which hinders the Kibble-Zurek\nmechanism from occurring. A harmonic trap with a plug potential is also taken\ninto account.",
        "positive": "Josephson vortices in a long Josephson junction formed by phase twist in\n  a polariton superfluid: Quantum fluids of light are an emerging platform for energy efficient signal\nprocessing, ultra-sensitive interferometry and quantum simulators at elevated\ntemperatures. Here we demonstrate the optical control of the topological\nexcitations induced in a large polariton condensate, realising the bosonic\nanalog of a long Josephson junction and reporting the first observation of\nbosonic Josephson vortices. When a phase difference is imposed at the\nboundaries of the condensate, two extended regions become separated by a sharp\n$\\pi$-slippage of the phase and a solitonic depletion of the density, forming\nan insulating barrier with a suppressed order parameter. The superfluid\nbehavior, that is a smooth phase gradient across the system instead of the\nsharp phase jump, is recovered at higher polariton densities and it is mediated\nby the nucleation of Josephson vortices within the barrier. Our results\ncontribute to the understanding of dissipation and stability of elementary\nexcitations in macroscopic quantum systems."
    },
    {
        "anchor": "Stability limits for modes held in alternating trapping-expulsive\n  potentials: We elaborate a scheme of trapping-expulsion management (TEM), in the form of\nthe quadratic potential periodically switching between confinement and\nexpulsion, as a means of stabilization of two-dimensional dynamical states\nagainst the backdrop of the critical collapse driven by the cubic\nself-attraction with strength g. The TEM scheme may be implemented, as\nspatially or temporally periodic modulations, in optics or BEC, respectively.\nThe consideration is carried out by dint of numerical simulations and\nvariational approximation (VA). In terms of the VA, the dynamics amounts to a\nnonlinear Ermakov equation, which, in turn, is tantamount to a linear Mathieu\nequation. Stability boundaries are found as functions of g and parameters of\nthe periodic modulation of the trapping potential. Below the usual collapse\nthreshold, which is known, in the numerical form, as g < 5.85 (in the standard\nnotation), the stability is limited by the onset of the parametric resonance.\nThis stability limit, including the setup with the self-repulsive sign of the\ncubic term (g < 0), is accurately predicted by the VA. At g > 5.85, the\ncollapse threshold is found with the help of full numerical simulations. The\nrelative increase of the critical value of g above 5.85 is ~ 1.5%, which is a\nmeaningful result, even if its size is small, because the collapse threshold is\na universal constant, which is difficult to change.",
        "positive": "One-dimensional spin-1/2 fermionic gases with two-body losses: weak\n  dissipation and spin conservation: We present a theoretical analysis of the dynamics of a one-dimensional\nspin-1/2 fermionic gas subject to weak two-body losses. Our approach highlights\nthe crucial role played by spin conservation in the determination of the full\ntime evolution. We focus in particular on the dynamics of a gas that is\ninitially prepared in a Dicke state with fully-symmetric spin wavefunction, in\na band insulator, or in a Mott insulator. In the latter case, we investigate\nthe emergence of a steady symmetry-resolved purification of the gas. Our\nresults could help the modelisation and understanding of recent experiments\nwith alkaline-earth(-like) gases like ytterbium or fermionic molecules."
    },
    {
        "anchor": "Collapse of triaxial bright solitons in atomic Bose-Einstein condensates: We study triaxial bright solitons made of attractive Bose-condensed atoms\ncharacterized by the absence of confinement in the longitudinal axial direction\nbut trapped by an anisotropic harmonic potential in the transverse plane. By\nnumerically solving the three-dimensional Gross-Pitaevskii equation we\ninvestigate the effect of the transverse trap anisotropy on the critical\ninteraction strength above which there is the collapse of the condensate. The\ncomparison with previous predictions [Phys. Rev. A {\\bf 66}, 043619 (2002)]\nshows significant differences for large anisotropies.",
        "positive": "Universal three-body parameter in ultracold 4He*: We have analyzed our recently-measured three-body loss rate coefficient for a\nBose-Einstein condensate of spin-polarized metastable triplet 4He atoms in\nterms of Efimov physics. The large value of the scattering length for these\natoms, which provides access to the Efimov regime, arises from a nearby\npotential resonance. We find the loss coefficient to be consistent with the\nthree-body parameter (3BP) found in alkali-metal experiments, where Feshbach\nresonances are used to tune the interaction. This provides new evidence for a\nuniversal 3BP, the first outside the group of alkali-metal elements. In\naddition, we give examples of other atomic systems without Feshbach resonances\nbut with a large scattering length that would be interesting to analyze once\nprecise measurements of three-body loss are available."
    },
    {
        "anchor": "Density Wave Superradiance of Photonic Fluid in Frustrated Triangle\n  Lattice Cavity Arrays: The spontaneously broken of translational symmetry is usually due to the\ncompetition between local interactions and long-range interactions. However, in\nthis paper, we show how a crystalline order can be generated by the competition\nbetween local interaction and long-range correlation by frustration. Here we\npropose a positive hopping Bose Hubbard model on triangle lattices with a pair\ncreation term which comes from frustrated linked cavity arrays with degenerate\nquantum gases in them. We find by increasing the strength of pair creation term\nagainst local interaction strength, two kinds of density wave ordered\nsuperradiant photonic fluid phase can be realized and a first order transition\nbetween two different density wave ordered states is found. This proposal shows\nus a new way to produce coherent \"solid\" phase without the help of long range\ninteractions.",
        "positive": "Dissipation in 2D degenerate gases with non-vanishing rest mass: The complete set of transport coefficients for two dimensional relativistic\ndegenerate gases is derived within a relaxation approximation in kinetic\ntheory, by considering both the particle and energy frames. A thorough\ncomparison between Marle and Anderson-Witting's models is carried out, pointing\nout the drawbacks of the former when compared both to the latter and to the\nfull Boltzmann equation results in the non-degenerate limit. Such task is\naccomplished by solving the relativistic Uehling-Uhlenbeck equation, in both\nthe particle and energy frames, in order to establish the constitutive\nequations for the heat flux and the Navier tensor together with analytical\nexpressions for the transport coefficients in such representations. In\nparticular, the temperature dependence of the thermal conductivity (associated\nwith a generalized thermal force) and the bulk and shear viscosities are\nanalyzed and compared within both models and with the non-degenerate,\nnon-relativistic and ultra-relativistic limits."
    },
    {
        "anchor": "Ultra cold atoms and Bose-Einstein condensation for quantum metrology: This paper is a short introduction to cold atom physics and Bose-Einstein\ncondensation. Light forces on atoms are presented, together with laser cooling,\nand a few atom traps: the magneto-optical trap, dipole traps and magnetic\ntraps. A brief description of Bose-Einstein condensation is given together with\nsome important links with condensed matter physics. The reader is referred to\ncomprehensive reviews and to other lecture notes for further details on atom\ncooling, trapping and Bose-Einstein condensation.",
        "positive": "Variational approach to the two-dimensional Bose polaron: An impurity particle interacting with a Bose-Einstein condensate (BEC) leads\nto the formation of a quasiparticle known as the Bose polaron. We investigate\nthe properties of the two-dimensional Bose polaron, applying a variational\nansatz that contains up to three Bogoliubov excitations of the BEC. Similar to\nits three-dimensional counterpart, we observe the existence of two\nquasiparticle branches, namely the attractive and the repulsive polarons, at\ndifferent coupling strengths. We find that their energies agree well with\nrecent quantum Monte Carlo calculations. In particular, we observe that the\ninclusion of three excitations is crucial to capture the attractive polaron\nenergy towards the regime of strong attraction, where the quasiparticle\nproperties are dominated by few-body correlations. We also calculate the\nattractive polaron effective mass and residue, where we find significant\ndifferences between considering a weakly interacting Bose medium and taking the\nnon-interacting limit, signalling enhanced impurity dressing by excitations in\nthe latter case. By contrast, the spectral weight of the metastable repulsive\npolaron is largely insensitive to the interactions in the BEC and the number of\nBogoliubov excitations. Our model may be experimentally realized in dilute\natomic vapors and atomically thin semiconductors."
    },
    {
        "anchor": "Characteristic features of the Shannon information entropy of dipolar\n  Bose-Einstein condensates: Calculation of the Shannon information entropy (S) and its connection with\nthe order-disorder transition, and with inter-particle interaction provide a\nchallenging research area in the field of quantum information. Experimental\nprogress with cold trapped atoms has corroborated this interest. In the present\nwork, S is calculated for the Bose-Einstein condensate (BEC) with dominant\ndipolar interaction for different dipole strengths, trap aspect ratio and\nnumber of particles (N). Trapped dipolar bosons in an anisotropic trap provide\nan example of system where the effective interaction is strongly determined by\nthe trap geometry. The main conlcusion of the present calculation is that the\nanisotropic trap reduces the number of degrees of freedom, resulting in more\nordered configurations. The Landsberg's order parameter exhibits quick\nsaturation with the increase in scattering length in both prolate and oblate\ntraps. We also define the threshold scattering length which makes the system\ncompletely disordered. Unlike non-dipolar BEC in a spherical trap, we do not\nfind a universal linear relation between S and ln N, and we, therefore,\nintroduce a general quintic polynomial fit rather well working for a wide range\nof particle number.",
        "positive": "Robust quantum many-body scars in lattice gauge theories: Quantum many-body scarring is a paradigm of weak ergodicity breaking arising\ndue to the presence of special nonthermal many-body eigenstates that possess\nlow entanglement entropy, are equally spaced in energy, and concentrate in\ncertain parts of the Hilbert space. Though scars have been shown to be\nintimately connected to gauge theories, their stability in such experimentally\nrelevant models is still an open question, and it is generally considered that\nthey exist only under fine-tuned conditions. In this work, we show through\nKrylov-based time-evolution methods how quantum many-body scars can be made\nrobust in the presence of experimental errors through utilizing terms linear in\nthe gauge-symmetry generator or a simplified pseudogenerator in $\\mathrm{U}(1)$\nand $\\mathbb{Z}_2$ lattice gauge theories. Our findings are explained by the\nconcept of quantum Zeno dynamics. Our experimentally feasible methods can be\nreadily implemented in existing large-scale ultracold-atom quantum simulators\nand setups of Rydberg atoms with optical tweezers."
    },
    {
        "anchor": "Topological phases of lattice bosons with a dynamical gauge field: Optical lattices with a complex-valued tunnelling term have become a standard\nway of studying gauge-field physics with cold atoms. If the complex phase of\nthe tunnelling is made density-dependent, such system features even a\nself-interacting or dynamical magnetic field. In this paper we study the\nscenario of a few bosons in either a static or a dynamical gauge field by means\nof exact diagonalization. The topological structures are identified computing\ntheir Chern number. Upon decreasing the atom-atom contact interaction, the\neffect of the dynamical gauge field is enhanced, giving rise to a phase\ntransition between two topologically non-trivial phases.",
        "positive": "Polarized entangled Bose-Einstein condensation: We consider a mixture of two distinct species of atoms of pseudospin-1/2 with\nboth intraspecies and Interspecies spin-exchange interactions, and find all the\nground stats in a general case of the parameters in the effective Hamiltonian.\nIn general, corresponding to the two species and two pseudo-spin states, there\nare four orbital wave functions into which the atoms condense. We find that in\ncertain parameter regimes, the ground state is the so-called polarized\nentangled Bose-Einstein condensation, i.e. in addition to condensation of\ninterspecies singlet pairs, there are unpaired atoms with spins polarized in\nthe same direction. The interspecies entanglement and polarization\nsignificantly affect the generalized Gross-Pitaevskii equations governing the\nfour orbital wave functions into which the atoms condense, as an interesting\ninterplay between spin and orbital degrees of freedom."
    },
    {
        "anchor": "Softening of Roton and Phonon Modes in a Bose-Einstein Condensate with\n  Spin-Orbit Coupling: Roton-type excitations usually emerge from strong correlations or long-range\ninteractions, as in superfluid helium or dipolar ultracold atoms. However, in\nweakly short-range interacting quantum gas, the recently synthesized spin-orbit\n(SO) coupling can lead to various unconventional phases of superfluidity, and\ngive rise to an excitation spectrum of roton-maxon character. Using Bragg\nspectroscopy we study a SO coupled Bose-Einstein condensate of $^{87}$Rb atoms,\nand show that the excitation spectrum in a \"magnetized\" phase clearly possesses\na two-branch and roton-maxon structure. As Raman coupling strength $\\Omega$ is\ndecreased, a roton-mode softening is observed, as a precursor of the phase\ntransition to a stripe phase that spontaneously breaks spatially translational\nsymmetry. The measured roton gaps agree well with theoretical calculations.\nFurther, we determine sound velocities both in the magnetized and the\nnon-magnetized phase, and a phonon-mode softening is observed around the phase\ntransition in between. The validity of the $f$-sum rule is examined.",
        "positive": "Weak-Measurement-Induced Heating in Bose-Einstein Condensates: Ultracold atoms are an ideal platform for understanding system-reservoir\ndynamics of many-body systems. Here, we study quantum back-action in atomic\nBose-Einstein condensates, weakly interacting with a far-from resonant, i.e.,\ndispersively interacting, probe laser beam. The light scattered by the atoms\ncan be considered as a part of quantum measurement process whereby the change\nin the system state derives from measurement back-action. We experimentally\nquantify the resulting back-action in terms of the deposited energy. We model\nthe interaction of the system and environment with a generalized measurement\nprocess, leading to a Markovian reservoir. Further, we identify two systematic\nsources of heating and loss: a stray optical lattice and probe-induced light\nassisted collisions (an intrinsic atomic process). The observed heating and\nloss rates are larger for blue detuning than for red detuning, where they are\noscillatory functions of detuning with increased loss at molecular resonances\nand reduced loss between molecular resonances."
    },
    {
        "anchor": "Dynamics of a Mobile Impurity in a Two Leg Bosonic Ladder: We have analyzed the behavior of a mobile quantum impurity in a bath formed\nby a two-leg bosonic ladder by a combination of field theory\n(Tomonaga-Luttinger liquid) and numerical (Density Matrix Renormalization\nGroup) techniques. Computing the Green's function of the impurity as a function\nof time at different momenta, we find a power law decay at zero momentum, which\nsignals the breakdown of any quasi-particle description of the impurity motion.\nWe compute the exponent both for the limits of weak and strong impurity-bath\ninteractions. At small impurity-bath interaction, we find that the impurity\nexperiences the ladder as a single channel one-dimensional bath, but effective\ncoupling is reduced by a factor of $\\sqrt 2$, thus the impurity is less mobile\nin the ladder compared to a one dimensional bath. We compared the numerical\nresults for the exponent at zero momentum with a semi-analytical expression\nthat was initially established for the chain and find excellent agreement\nwithout adjustable parameters. We analyze the dependence of the exponent in the\ntransverse hopping in the bath and find surprisingly an increase of the\nexponent at variance with the naive extrapolation of the single channel regime.\nWe study the momentum dependence of the impurity Green's function and find\nthat, as for the single chain, two different regime of motion exist, one\ndominated by infrared metatrophy and a more conventional polaronic behavior. We\ncompute the critical momentum between these two regimes and compare with\nprediction based on the structure factor of the bath. In the polaronic regime\nwe also compute numerically the lifetime of the polaron. Finally we discuss how\nour results could be measured in cold atomic experiments.",
        "positive": "Asymmetric lineshapes of Efimov resonances in mass-imbalanced ultracold\n  gases: The resonant profile of the rate coefficient for three-body recombination\ninto a shallow dimer is investigated for mass-imbalanced systems. In the\nlow-energy limit, three atoms collide with zero-range interactions, in a regime\nwhere the scattering lengths of the heavy-heavy and the heavy-light subsystems\nare positive and negative, respectively. For this physical system, the\nadiabatic hyperspherical representation is combined with a fully semi-classical\nmethod and we show that the shallow dimer recombination spectra display an\nasymmetric lineshape that originates from the coexistence of Efimov resonances\nwith St\\\"uckelberg interference minima. These asymmetric lineshapes are\nquantified utilizing the Fano profile formula. In particular, a closed form\nexpression is derived that describes the width of the corresponding Efimov\nresonances and the Fano lineshape asymmetry parameter $q$. The profile of\nEfimov resonances exhibits a $q-$reversal effect as the inter- and\nintra-species scattering lengths vary. In the case of a diverging asymmetry\nparameter, i.e. $|q|\\to \\infty$, we show that the Efimov resonances possess\nzero width and are fully decoupled from the three-body and atom-dimer continua,\nand the corresponding Efimov metastable states behave as bound levels."
    },
    {
        "anchor": "Finite Temperature Phases of Two Dimensional Spin-Orbit Coupled Bosons: We determine the finite temperature phase diagram of two dimensional bosons\nwith two hyperfine (pseudo-spin) states coupled via Rashba-Dresselhaus\nspin-orbit interaction using classical field Monte Carlo calculations. For\nanisotropic spin-orbit coupling, we find a transition to a\nBerenzinskii-Kosterlitz-Thouless superfluid phase with quasi-long range order.\nWe show that the spin-order of the quasi-condensate is driven by the anisotropy\nof interparticle interaction, favoring either a homogeneous plane wave state or\nstripe phase with broken translational symmetry. Both phases show\ncharacteristic behavior in the algebraically decaying spin density correlation\nfunction. For fully isotropic interparticle interaction, our calculations\nindicate a fractionalized quasi-condensate where the mean-field degeneracy of\nplane wave and stripe phase remains robust against critical fluctuations. In\nthe case of fully isotropic spin-orbit coupling, the circular degeneracy of the\nsingle particle ground state destroys the algebraic ordered phase in the\nthermodynamic limit, but a cross-over remains for finite size systems.",
        "positive": "Quantum Phases of Self-Bound Droplets of Bose-Bose Mixtures: We systematically investigate the ground-state properties of self-bound\ndroplets of quasi-two-dimensional binary Bose gases by using the Gaussian state\ntheory. We find that quantum droplets consists two macroscopic squeezed phases\nand a macroscopic coherent phase. We map out the phase diagram and determine\nall phase boundaries via both numerical and nearly analytical methods. In\nparticular, we find three easily accessible signatures for the quantum phases\nand the stablization mechanism of the self-bound droplets by precisely\nmeasuring their radial size. Our studies indicate that binary droplets\nrepresent an ideal platform for in-depth investigations of the quantum nature\nof the droplet state."
    },
    {
        "anchor": "Zero-point energy of ultracold atoms: We analyze the divergent zero-point energy of a dilute and ultracold gas of\natoms in D spatial dimensions. For bosonic atoms we explicitly show how to\nregularize this divergent contribution, which appears in the Gaussian\nfluctuations of the functional integration, by using three different\nregularization approaches: dimensional regularization, momentum-cutoff\nregularization and convergence-factor regularization. In the case of the ideal\nBose gas the divergent zero-point fluctuations are completely removed, while in\nthe case of the interacting Bose gas these zero-point fluctuations give rise to\na finite correction to the equation of state. The final convergent equation of\nstate is independent of the regularization procedure but depends on the\ndimensionality of the system and the two-dimensional case is highly nontrivial.\nWe also discuss very recent theoretical results on the divergent zero-point\nenergy of the D-dimensional superfluid Fermi gas in the BCS-BEC crossover. In\nthis case the zero-point energy is due to both fermionic single-particle\nexcitations and bosonic collective excitations, and its regularization gives\nremarkable analytical results in the BEC regime of composite bosons. We compare\nthe beyond-mean-field equations of state of both bosons and fermions with\nrelevant experimental data on dilute and ultracold atoms quantitatively\nconfirming the contribution of zero-point-energy quantum fluctuations to the\nthermodynamics of ultracold atoms at very low temperatures.",
        "positive": "Rapid generation of all-optical $^{39}$K Bose-Einstein condensates using\n  a low-field Feshbach resonance: Ultracold potassium is an interesting candidate for quantum technology\napplications and fundamental research as it allows controlling intra-atomic\ninteractions via low-field magnetic Feshbach resonances. However, the\nrealization of high-flux sources of Bose-Einstein condensates remains\nchallenging due to the necessity of optical trapping to use magnetic fields as\nfree parameter. We investigate the production of all-optical $^{39}$K\nBose-Einstein condensates with different scattering lengths using a Feshbach\nresonance near $33$ G. By tuning the scattering length in a range between $75\\,\na_0$ and $300\\, a_0$ we demonstrate a trade off between evaporation speed and\nfinal atom number and decrease our evaporation time by a factor of $5$ while\napproximately doubling the evaporation flux. To this end, we are able to\nproduce fully condensed ensembles with $5.8\\times10^4$ atoms within $850$ ms\nevaporation time at a scattering length of $232\\, a_0$ and $1.6\\times10^5$\natoms within $3.9$ s at $158\\, a_0$, respectively. We deploy a numerical model\nto analyse the flux and atom number scaling with respect to scattering length,\nidentify current limitations and simulate the optimal performance of our setup.\nBased on our findings we describe routes towards high-flux sources of\nultra-cold potassium for inertial sensing."
    },
    {
        "anchor": "Effect of an oscillating Gaussian obstacle in a Dipolar Bose-Einstein\n  condensate: We study the dynamics of vortex dipoles in erbium ($^{168}$Er) and dysprosium\n($^{164}$Dy) dipolar Bose-Einstein condensates (BECs) by applying an\noscillating blue-detuned laser (Gaussian obstacle). For observing vortex\ndipoles, we solve a nonlocal Gross-Pitaevskii (GP) equation in quasi\ntwo-dimensions in real-time. We calculate the critical velocity for the\nnucleation of vortex dipoles in dipolar BECs with respect to dipolar\ninteraction strengths. We also show the dynamics of the group of vortex dipoles\nand rarefaction pulses in dipolar BECs. In the dipolar BECs with Gaussian\nobstacle, we observe rarefaction pulses due to the interaction of dynamically\nmigrating vortex dipoles.",
        "positive": "Vortex lattice melting in a boson-ladder in artificial gauge field: We consider a two-leg boson ladder in an artificial U(1) gauge field and show\nthat, in the presence of interleg attractive interaction, the flux induced\nVortex state can be melted by dislocations. For increasing flux, instead of the\nMeissner to Vortex transition in the commensurate-incommensurate universality\nclass, first an Ising transition from the Meissner state to a charge density\nwave takes place, then, at higher flux, the melted Vortex phase is established\nvia a disorder point where incommensuration develops in the rung current\ncorrelation function and in momentum distribution.Finally, the quasi-long range\nordered Vortex phase is recovered for sufficiently small interaction. Our\npredictions for the observables, such as the spin current and the static\nstructure factor, could be tested in current experiments with cold atoms in\nbosonic ladders."
    },
    {
        "anchor": "Torus quantum vortex knots in the Gross-Pitaevskii model for\n  Bose-Einstein condensates: We examine on the static and dynamical properties of quantum knots in a\nBose-Einstein condensate. In particular, we consider the Gross-Pitaevskii model\nand revise a technique to construct ab initio the condensate wave-function of a\ngeneric torus knot. After analysing its excitation energy, we study its\ndynamics relating the topological parameter to its translational velocity and\ncharacteristic size. We also investigate the breaking mechanisms of non\nshape-preserving torus knots confirming an evidence of universal decaying\nbehaviour previously observed.",
        "positive": "Quantum magnetism in strongly interacting one-dimensional spinor Bose\n  systems: Strongly interacting one-dimensional quantum systems often behave in a manner\nthat is distinctly different from their higher-dimensional counterparts. When a\nparticle attempts to move in a one-dimensional environment it will unavoidably\nhave to interact and 'push' other particles in order to execute a pattern of\nmotion, irrespective of whether the particles are fermions or bosons. A present\nfrontier in both theory and experiment are mixed systems of different species\nand/or particles with multiple internal degrees of freedom. Here we consider\ntrapped two-component bosons with short-range inter-species interactions much\nlarger than their intra-species interactions and show that they have novel\nenergetic and magnetic properties. In the strongly interacting regime, these\nsystems have energies that are fractions of the basic harmonic oscillator trap\nquantum and have spatially separated ground states with manifestly\nferromagnetic wave functions. Furthermore, we predict excited states that have\nperfect antiferromagnetic ordering. This holds for both balanced and imbalanced\nsystems, and we show that it is a generic feature as one crosses from few- to\nmany-body systems."
    },
    {
        "anchor": "Analogues of Josephson junctions and black hole event horizons in atomic\n  Bose-Einstein condensates: We study dynamical processes in coherently coupled atomic Bose-Einstein\ncondensates. Josephson effects in ring-shaped and dumbbell geometries are\ntheoretically investigated. Conditions for observation of the Josephson effect\nare revealed. We found that multicharged persistent current in toroidal\ncondensate can be robust even for supersonic atomic flow. In numerical\nsimulations the acoustic analogues of event horizon in quantized superflow was\nobserved. These theoretical finding open perspectives for investigation of Bose\nJosephson junctions and quantum aspects of acoustic analogue of Hawking\nradiation in existing experimental setups.",
        "positive": "Anisotropic relaxation dynamics in a dipolar Fermi gas driven out of\n  equilibrium: We report on the observation of a large anisotropy in the rethermalization\ndynamics of an ultracold dipolar Fermi gas driven out of equilibrium. Our\nsystem consists of an ultracold sample of strongly magnetic $^{167}$Er\nfermions, spin-polarized in the lowest Zeeman sublevel. In this system, elastic\ncollisions arise purely from universal dipolar scattering. Based on\ncross-dimensional rethermalization experiments, we observe a strong anisotropy\nof the scattering, which manifests itself in a large angular dependence of the\nthermal relaxation dynamics. Our result is in very good agreement with recent\ntheoretical predictions. Furthermore, we measure the rethermalization rate as a\nfunction of temperature for different angles and find that the suppression of\ncollisions by Pauli blocking is not influenced by the dipole orientation."
    },
    {
        "anchor": "Thermalization measurements on an ultracold mixture of metastable $^4$He\n  and $^{87}$Rb atoms in a quadrupole magnetic trap: Recently we have reported (Knoop et al. [arXiv:1404.4826]) on an experimental\ndetermination of metastable triplet $^4$He+$^{87}$Rb scattering length by\nperforming thermalization measurements for an ultracold mixture in a quadrupole\nmagnetic trap. Here we present our experimental apparatus and elaborate on\nthese thermalization measurements. In particular we give a theoretical\ndescription of interspecies thermalization rate for a quadrupole magnetic trap,\ni. e. in the presence of Majorana heating, and a general procedure to extract\nthe scattering length from the elastic cross section at finite temperature\nbased on knowledge of the $C_6$ coefficient alone. In addition, from our\nthermalization data we obtain an upper limit of the total interspecies two-body\nloss rate coefficient of $1.5\\times 10^{-12}$ cm$^3$s$^{-1}$.",
        "positive": "Infinite Lattices of Vortex Molecules in Rabi-Coupled Condensates: Vortex molecules can form in a two component superfluid when a Rabi field\ndrives transitions between the two components. We study the ground state of an\ninfinite system of vortex molecules in 2D, using a numerical scheme which makes\nno use of the lowest Landau level approximation. We find the ground state\nlattice geometry for different values of inter-component interactions and\nstrength of the Rabi field. In the limit of large field when molecules are\ntightly bound, we develop a complimentary analytical description. The energy\ngoverning the alignment of molecules on a triangular lattice is found to\ncorrespond to that of an infinite system of 2D quadrupoles, which may be\nwritten in terms of an elliptic function $\\mathcal{Q}(z_{ij};\\omega_1 ,\n\\omega_2 )$. This allows for a numerical evaluation of the energy which enables\nus to find the ground state configuration of the molecules."
    },
    {
        "anchor": "Ideal Weyl semimetal with 3D spin-orbit coupled ultracold quantum gas: There is an immense effort in search for various types of Weyl semimetals, of\nwhich the most fundamental phase consists of the minimal number of i.e. two\nWeyl points, but is hard to engineer in solids. Here we demonstrate how such\nfundamental Weyl semimetal can be realized in a maneuverable optical Raman\nlattice, with which the three-dimensional (3D) spin-orbit (SO) coupling is\nsynthesised for ultracold atoms. In addition, a new novel Weyl phase with\ncoexisting Weyl nodal points and nodal ring is also predicted here, and is\nshown to be protected by nontrivial linking numbers. We further propose\nfeasible techniques to precisely resolve 3D Weyl band topology through 2D\nequilibrium and dynamical measurements. This work leads to the first\nrealization of the most fundamental Weyl semimetal band and the 3D SO coupling\nfor ultracold quantum gases, which are respectively the significant issues in\nthe condensed matter and ultracold atom physics.",
        "positive": "Second-order topological corner states with ultracold atoms carrying\n  orbital angular momentum in optical lattices: We propose a realization of a two-dimensional higher-order topological\ninsulator with ultracold atoms loaded into orbital angular momentum (OAM)\nstates of an optical lattice. The symmetries of the OAM states induce relative\nphases in the tunneling amplitudes that allow to describe the system in terms\nof two decoupled lattice models. Each of these models displays one-dimensional\nedge states and zero-dimensional corner states that are correlated with the\ntopological properties of the bulk. We show that the topologically non-trivial\nregime can be explored in a wide range of experimentally feasible values of the\nparameters of the physical system. Furthermore, we propose an alternative way\nto characterize the second-order topological corner states based on the\ncomputation of the Zak's phases of the bands of first-order edge states."
    },
    {
        "anchor": "Two component Bose-Hubbard model with higher angular momentum states: We study a Bose-Hubbard Hamiltonian of ultracold two component gas of spinor\nChromium atoms. Dipolar interactions of magnetic moments while tuned resonantly\nby ultralow magnetic field can lead to spin flipping. Due to approximate axial\nsymmetry of individual lattice site, total angular momentum is conserved.\nTherefore, all changes of the spin are accompanied by the appearance of the\nangular orbital momentum. This way excited Wannier states with non vanishing\nangular orbital momentum can be created. Resonant dipolar coupling of the two\ncomponent Bose gas introduces additional degree of control of the system, and\nleads to a variety of different stable phases. The phase diagram for small\nnumber of particles is discussed.",
        "positive": "Properties of fermionic systems with the Path-integral ground state\n  method: We investigate strongly correlated many-body systems composed of bosons and\nfermions with a fully quantum treatment using the path-integral ground state\nmethod, PIGS. To account for the Fermi-Dirac statistics, we implement the\nfixed-node approximation into PIGS, which we then call FN-PIGS. In great\ndetail, we discuss the pair density matrices we use to construct the full\ndensity operator in coordinate representation, a vital ingredient of the\nmethod. We consider the harmonic oscillator as a proof-of-concept and, as a\nplatform representing quantum many-body systems, we explore helium atoms. Pure\n$^4$He systems demonstrate most of the features of the method. Complementarily,\nfor pure $^3$He, the fixed-node approximation resolves the ubiquitous sign\nproblem stemming from anti-symmetric wave functions. Finally, we investigate\n$^3$He-$^4$He mixtures, demonstrating the method's robustness. One of the main\nfeatures of FN-PIGS is its ability to estimate any property at temperature\n$T=0$ without any additional bias apart from the FN approximation; biases from\nlong simulations are also excluded. In particular, we calculate the correlation\nfunction of pairs of equal and opposite spins and precise values of the $^3$He\nkinetic energy in the mixture."
    },
    {
        "anchor": "Macroscopic boundary effects in the one-dimensional extended\n  Bose-Hubbard model: We study the effect of different open boundary conditions on the insulating\nground states of the one-dimensional extended Bose-Hubbard model at and near\nunit filling. To this end, we employ the density matrix renormalization group\nmethod with system sizes up to 250 sites. To characterize the system, various\norder parameters and entanglement entropies are calculated. When opposite edge\npotentials are added to the two ends of the chain, the inversion symmetry is\nexplicitly broken, and the regular bulk phases appear. On the other hand,\nsimple open boundary conditions often exhibit non-degenerate ground states with\na domain wall in the middle of the chain, which induces a sign-flip of an order\nparameter. Such a domain wall can lead to an algebraic behavior of the\noff-diagonals of the single particle density matrix. We show that this\nalgebraic behavior adds only a finite contribution to the entanglement entropy,\nwhich does not diverge as the system size increases. Therefore, it is not an\nindication of a superfluid phase. We confirm this picture by analytical\ncalculations based on an effective Hamiltonian for a domain wall.",
        "positive": "Self-trapping in an array of coupled 1D Bose gases: We study the transverse expansion of arrays of ultracold $^{87}$Rb atoms\nweakly confined in tubes created by a 2D optical lattice, and observe that\ntransverse expansion is delayed because of mutual atom interactions. A\nmean-field model of a coupled array shows that atoms become localized within a\nroughly square fort-like self-trapping barrier with time-evolving edges. But\nthe observed dynamics is poorly described by the mean-field model. Theoretical\nintroduction of random phase fluctuations among tubes improves the agreement\nwith experiment, but does not correctly predict the density at which the atoms\nstart to expand with larger lattice depths. Our results suggest a new type of\nself-trapping, where quantum correlations suppress tunneling even when there\nare no density gradients."
    },
    {
        "anchor": "Dynamics of defect-induced dark solitons in an exciton-polariton\n  condensate: We study theoretically the emission of dark solitons induced by a moving\ndefect in a nonresonantly pumped exciton-polariton condensate. The number of\ncreated dark solitons per unit of time is found to be strongly dependent on the\npump power. We relate the observed dynamics of this process to the oscillations\nof the drag force experienced by the condensate. We investigate the stability\nof the polariton quantum fluid and present various types of dynamics depending\non the condensate and moving obstacle parameters. Furthermore, we provide\nanalytical expressions for dark soliton dynamics using the variational method\nadapted to the non-equilibrium polariton system. The determined dynamical\nequations are found to be in excellent agreement with the results of numerical\nsimulations.",
        "positive": "Universal Hydrodynamic Transport Times in the Normal Phase of a Unitary\n  Fermi Gas: We determine the hydrodynamic relaxation times $\\tau_\\eta$ for the shear\nviscosity and $\\tau_\\kappa$ for the thermal conductivity in the normal phase of\na unitary Fermi gas confined in a box potential. Using a kinetic theory\nrelaxation model, we extract $\\tau_\\eta$ and $\\tau_\\kappa$ from the\ntime-dependent free-decay of a spatially periodic density perturbation,\nyielding the universal density-shift coefficients for the shear viscosity and\nthermal conductivity."
    },
    {
        "anchor": "Few-body states of bosons interacting with a heavy quantum impurity: We consider the problem of a fixed impurity coupled to a small number $N$ of\nnon-interacting bosons. We focus on impurity-boson interactions that are\nmediated by a closed-channel molecule, as is the case for tuneable interatomic\ninteractions in cold-atom experiments. We show that this two-channel model can\nbe mapped to a boson model with effective boson-boson repulsion, which enables\nus to solve the three-body ($N=2$) problem analytically and determine the\ntrimer energy for impurity-boson scattering lengths $a>0$. By analysing the\natom-dimer scattering amplitude, we find a critical scattering length $a^*$ at\nwhich the atom-dimer scattering length diverges and the trimer merges into the\ndimer continuum. We furthermore calculate the tetramer energy exactly for $a>0$\nand show that the tetramer also merges with the continuum at $a^*$. Indeed,\nsince the critical point $a^*$ formally resembles the unitary point $1/a = 0$,\nwe find that all higher-body bound states (involving the impurity and $N>1$\nbosons) emerge and disappear at both of these points. We show that the behavior\nat these 'multi-body resonances' is universal, since it occurs for any model\nwith an effective three-body repulsion involving the impurity. Thus, we see\nthat the fixed-impurity problem is strongly affected by a three-body parameter\neven in the absence of the Efimov effect.",
        "positive": "Harmonically trapped Bose-Bose mixtures: a quantum Monte Carlo study: We study a harmonically confined Bose-Bose mixture using quantum Monte Carlo\nmethods. Our results for the density profiles are systematically compared with\nmean-field predictions derived through the Gross-Pitaevskii equation in the\nsame conditions. The phase space as a function of the interaction strengths and\nthe relation between masses is quite rich. The miscibility criterion for the\nhomogeneous system applies rather well to the system, with some discrepancies\nclose to the critical line for separation. We observe significant differences\nbetween the mean-field results and the Monte Carlo ones, that magnify when the\nasymmetry between masses increases. In the analyzed interaction regime, we\nobserve universality of our results which extend beyond the applicability\nregime for the Gross-Pitaevskii equation."
    },
    {
        "anchor": "Simulations of non-Abelian gauge theories with optical lattices: Many phenomena occurring in strongly correlated quantum systems still await\nconclusive explanations. The absence of isolated free quarks in nature is an\nexample. It is attributed to quark confinement, whose origin is not yet\nunderstood. The phase diagram for nuclear matter at general temperatures and\ndensities, studied in heavy-ion collisions, is not settled. Finally, we have no\ndefinitive theory of high-temperature superconductivity. Though we have\ntheories that could underlie such physics, we lack the tools to determine the\nexperimental consequences of these theories. Quantum simulators may provide\nsuch tools. Here we show how to engineer quantum simulators of non-Abelian\nlattice gauge theories. The systems we consider have several applications: they\ncan be used to mimic quark confinement or to study dimer and valence-bond\nstates (which may be relevant for high-temperature superconductors).",
        "positive": "Probing quantum transport by engineering correlations in a speckle\n  potential: We develop a procedure to modify the correlations of a speckle potential.\nThis procedure, that is suitable for spatial light modulator devices, allows\none to increase the localization efficiency of the speckle in a narrow energy\nregion whose position can be easily tuned. This peculiar energy-dependent\nlocalization behavior is explored by pulling the potential through a\ncigar-shaped Bose-Einstein condensate. We show that the percentage of dragged\natoms as a function of the pulling velocity depends on the potential\ncorrelations below a threshold of the disorder strength. Above this threshold,\ninterference effects are no longer clearly observable during the condensate\ndrag."
    },
    {
        "anchor": "Quantum dark soliton (qubits) in Bose Einstein condensates: We study the possibility of using dark soliton in quasi one dimensional Bose\nEinstein condensates to produce two level system (qubits) by exploiting the\nintrinsic nonlinear and the coherent nature of the matter waves. We calculate\nthe soliton spectrum and the conditions for a qubit to exist. We also compute\nthe coupling between the phonons and the soliton and investigate the emission\nrate of the qubits in that case. Remarkably, the qubit lifetime is estimated to\nbe of the order of a few seconds, being by the dark soliton \"death\" due to\nquantum evaporation.",
        "positive": "Classical versus quantum dynamics of the atomic Josephson junction: We compare the classical (mean-field) dynamics with the quantum dynamics of\natomic Bose-Einstein condensates in double-well potentials. The quantum\ndynamics are computed using a simple scheme based upon the Raman-Nath\nequations. Two different methods for exciting a non-equilbrium state are\nconsidered: an asymmetry between the wells which is suddenly removed, and a\nperiodic time oscillating asymmetry. The first method generates wave packets\nthat lead to collapses and revivals of the expectation values of the\nmacroscopic variables, and we calculate the time scale for these revivals. The\nsecond method permits the excitation of a single energy eigenstate of the\nmany-particle system, including Schroedinger cat states. We also discuss a band\ntheory interpretation of the energy level structure of an asymmetric\ndouble-well, thereby identifying analogies to Bloch oscillations and Bragg\nresonances. Both the Bloch and Bragg dynamics are purely quantum and are not\ncontained in the mean-field treatment."
    },
    {
        "anchor": "Dynamic structure factor of two-dimensional Fermi superfluid with Rashba\n  spin-orbit coupling: We theoretically calculate the dynamic structure factor of two-dimensional\nRashba-type spinorbit coupled (SOC) Fermi superfluid with random phase\napproximation, and analyse the main characters of dynamical excitation sh own\nby both density and spin dynamic structure factor during a continuous phase\ntransition between Bardeen-Cooper-Schrieffer superfluid and topological\nsuperfluid. Generally we find three different excitations, including collective\nphonon excitation, two-atom molecular and atomic excitations, and pair-breaking\nexcitations due to two-branch structure of quasi-particle spectrum. It should\nbe emphasized that collective phonon excitation is overlapped with a gapless DD\ntype pair-breaking excitation at the critical Zeeman field hc, and is imparted\na finite width to phonon peak when transferred momentum q is around Fermi\nvector kF. At a much larger transferred momentum (q = 4kF ), the pair-breaking\nexcitation happens earlier than two-atom molecular excitation, which is\ndifferent from the conventional Fermi superfluid without SOC effect.",
        "positive": "Negative differential conductivity and quantum statistical effects in a\n  three-site Bose-Hubbard model: The use of an electron beam to remove ultracold atoms from selected sites in\nan optical lattice has opened up new opportunities to study transport in\nquantum systems [R. Labouvie {\\it et al.\\ }, Phys.\\ Rev.\\ Lett.\\ {\\bf 115},\n050601 (2015)]. Inspired by this experimental result, we examine the effects of\nnumber difference, dephasing, and initial quantum statistics on the filling of\nan initially depleted middle well in the three-well inline Bose-Hubbard model.\nWe find that the well-known phenomenon of macroscopic self-trapping is the main\ncontributor to oscillatory negative differential conductivity in our model,\nwith phase diffusion being a secondary effect. However, we find that phase\ndiffusion is required for the production of direct atomic current, with the\ncoherent process showing damped oscillatory currents. We also find that our\nresults are highly dependent on the initial quantum states of the atoms in the\nsystem."
    },
    {
        "anchor": "Creation and dynamics of two-dimensional skyrmions in antiferromagnetic\n  spin-1 Bose-Einstein condensates: We numerically simulate the creation process of two-dimensional skyrmionic\nexcitations in antiferromagnetic spin-1 Bose--Einstein condensates by solving\nthe full three-dimensional dynamics of the system from the Gross--Pitaevskii\nequation. Our simulations reproduce quantitatively the experimental results of\n[Choi et al., Phys. Rev. Lett. 108, 035301 (2012)] without any fitting\nparameters. Furthermore, we examine the stability of the skyrmion by computing\nthe temporal evolution of the condensate in a harmonic potential. The presence\nof both the quadratic Zeeman effect and dissipation in the simulations is vital\nfor reproducing the experimentally observed decay time.",
        "positive": "Quantum Degenerate Mixtures of Cs and Yb: We report the production of quantum degenerate Bose-Bose mixtures of Cs and\nYb with both attractive (Cs + $^{174}$Yb) and repulsive (Cs + $^{170}$Yb)\ninterspecies interactions. Dual-species evaporation is performed in a\nbichromatic optical dipole trap that combines light at 1070 nm and 532 nm to\nenable control of the relative trap depths for Cs and Yb. Maintaining a trap\nwhich is shallower for Yb throughout the evaporation leads to highly efficient\nsympathetic cooling of Cs for both isotopic combinations at magnetic fields\nclose to the Efimov minimum in the Cs three-body recombination rate at around\n22 G. For Cs + $^{174}$Yb, we produce quantum mixtures with typical atom\nnumbers of $N_\\mathrm{Yb} \\sim 5 \\times 10^4$ and $N_\\mathrm{Cs} \\sim 5 \\times\n10^3$. We find that the attractive interspecies interaction (characterised by\nthe scattering length $a_\\mathrm{CsYb} = -75\\,a_0$) is stabilised by the\nrepulsive intraspecies interactions. For Cs + $^{170}$Yb, we produce quantum\nmixtures with typical atom numbers of $N_\\mathrm{Yb} \\sim 4 \\times 10^4$, and\n$N_\\mathrm{Cs} \\sim 1 \\times 10^4$. Here, the repulsive interspecies\ninteraction ($a_\\mathrm{CsYb} = 96\\,a_0$) can overwhelm the intraspecies\ninteractions, such that the mixture sits in a region of partial miscibility."
    },
    {
        "anchor": "Phase separation of quantized vortices in two-component miscible\n  Bose-Einstein condensates in a two-dimensional box potential: The dynamics of quantized vortices in two-dimensional two-component miscible\nBose-Einstein condensates (BECs) trapped by a box potential has been\nnumerically studied using the Gross{ Pitaevskii model. We have discovered a\nnovel phenomenon where the vortices of the two components spatially separate\nfrom each other, which we call the phase separation of the distribution of\nvortices. This phase separation occurs when the inter-component coupling is\nstrong. Onsager vortices, on the other hand, are formed in both components when\nthe inter-component coupling is weak. We distinguish between Onsager vortices\nand phase-separated vortices by two types of effective distances between\nvortices. The dependence of the transition between the Onsager vortices and\nphase-separated vortices on the inter-component interaction is also studied.",
        "positive": "Exact Yrast Spectra of Cold Atoms on a Ring: We propose a methodology to construct excited states with a fixed angular\nmomentum, namely, \"yrast excited states\" of finite-size one-dimensional bosonic\nsystems with periodic boundary conditions. The excitation energies such as the\nfirst yrast excited energy are calculated through the system-size asymptotic\nexpansion and expressed analytically by dressed energy.\n  Interestingly, they are grouped into sets of almost degenerate energy levels.\nThe low-lying excitation spectrum near the yrast state is consistent with the $\nU(1)$ conformal field theories if the total angular momentum is given by an\nintegral multiple of particle number; i.e., if the system is supercurrent."
    },
    {
        "anchor": "Collective Motion of Polarized Dipolar Fermi Gases in the Hydrodynamic\n  Regime: Recently, a seminal STIRAP experiment allowed the creation of 40K-87Rb\nmolecules in the rovibrational ground state [K.-K. Ni et al., Science 322, 231\n(2008)]. In order to describe such a polarized dipolar Fermi gas in the\nhydrodynamic regime, we work out a variational time-dependent Hartree-Fock\napproach. With this we calculate dynamical properties of such a system as, for\ninstance, the frequencies of the low-lying excitations and the time-of-flight\nexpansion. We find that the dipole-dipole interaction induces anisotropic\nbreathing oscillations in momentum space. In addition, after release from the\ntrap, the momentum distribution becomes asymptotically isotropic, while the\nparticle density becomes anisotropic.",
        "positive": "Bose-Einstein Condensation of Excitons in Cu$_2$O: Progress Over Thirty\n  Years: Experiments on Bose-Einstein condensation (BEC) of excitons in the\nsemiconductor Cu$_2$O started over thirty years ago, as one of the first\nserious attempts at exciton BEC. Early claims were based on spectroscopic\nsignatures and transport data which have since been reinterpreted, in large\npart because the Auger recombination process for excitons was not well\nunderstood. Understanding of the Auger process has also advanced, and recent\nexperiments have made significant progress toward exciton BEC. We review the\nhistory of experiments on exciton BEC in Cu$_2$O, the Auger recombination\nprocess, and the prospects for observing exciton BEC in this system in the near\nfuture."
    },
    {
        "anchor": "Quantum quenches, sonic horizons and the Hawking radiation in a class of\n  exactly solvable models: Taking advantage of the known exact mapping of the one-dimensional Hard Core\nBose (HCB) fluid onto a non-interacting spinless fermion gas, we examine in\nfull detail a thought experiment on cold atoms confined in a\nquasi-one-dimensional trap, in order to investigate the emergence of the\nanalogue Hawking radiation. The dynamics of a gas of interacting bosons\nimpinging on an external potential is exactly tracked up to the reach of a\nstationary state. Under few strict conditions on the experimental parameters,\nthe stationary state is shown to be described asymptotically by a thermal\ndistribution, precisely at the expected (analogue) Hawking temperature.\nHowever, we find that in most experimental conditions the emerging\n`Hawking-like radiation' is not thermal. This analysis provides a novel\nmany-body microscopic interpretation of the Hawking mechanism, together with\nuseful limits and conditions for the design of future experiments in\nBose-Einstein condensates.",
        "positive": "Parallel dark soliton pair in a bistable 2D exciton-polariton superfluid: Collective excitations, such as vortex-antivortex and dark solitons, are\namong the most fascinating effects of macroscopic quantum states. However, 2D\ndark solitons are unstable and collapse into vortices due to snake\ninstabilities. Making use of the optical bistability in exciton-polariton\nmicrocavities, we demonstrate that a pair of dark solitons can be formed in the\nwake of an obstacle in a polariton flow resonantly supported by a homogeneous\nlaser beam. Unlike the purely dissipative case where the solitons are grey and\nspatially separate, here the two solitons are fully dark, rapidly align at a\nspecific separation distance and propagate parallel as long as the flow is in\nthe bistable regime. Remarkably, the use of this regime allows to avoid the\nphase fixing arising in resonant pumping regime and to circumvent the polariton\ndecay. Our work opens very wide perspectives of studying new classes of\nphase-density defects which can form in driven-dissipative quantum fluids of\nlight."
    },
    {
        "anchor": "Clock shift in a strongly interacting two-dimensional Fermi gas: We derive universal relations for the radio-frequency (rf) spectroscopy of a\ntwo-dimensional Fermi gas consisting of two spin states with a resonant S-wave\ninteraction. The rf transition rate has a high-frequency tail that is\nproportional to the contact and displays logarithmic scaling violations,\ndecreasing asymptotically like $1/(\\omega^2 \\ln^2 \\omega)$. Its coefficient is\nproportional to $\\ln^2(a_{2D}'/a_{2D})$, where $a_{2D}$ and $a_{2D}'$ are the\n2-dimensional scattering lengths associated with initial-state and final-state\ninteractions. The clock shift is proportional to the contact and to\n$\\ln(a_{2D}'/a_{2D})$. If $|\\ln(a_{2D}'/a_{2D})| \\gg 1$, the clock shift arises\nas a cancellation between much larger contributions proportional to\n$\\ln^2(a_{2D}'/a_{2D})$ from bound-bound and bound-free rf transitions.",
        "positive": "Boosting the Rotational Sensitivity of Matter-wave Interferometry with\n  Nonlinearity: We propose a mechanism to use nonlinearity arising from inter-particle\ninteractions to significantly enhance rotation sensitivity of matter-wave\ninterferometers. The method relies on modifying Sagnac interferometers by\nintroducing a weak circular lattice potential that couples modes with opposite\norbital angular momenta (OAM). The primary observable comprises of the modal\npopulation distributions measured at particular times. This provides an\nalternate mechanism for rotation sensing that requires substantially smaller\nring size, even in the linear non-interacting regime. Nonlinearity can improve\nthe sensitivity, as well as operation timescales, by several orders of\nmagnitude."
    },
    {
        "anchor": "Homogeneous one-dimensional Bose-Einstein Condensate in the Bogoliubov's\n  Regime: We analyze the corrections caused by finite size effects upon the ground\nstate properties of a homogeneous one-dimensional Bose-Einstein condensate. We\nassume from the very beginning that the Bogoliubov's formalism is valid and\nconsequently we show that in order to obtain a well defined ground state\nproperties, finite size effects of the system must be taken into account.\nIndeed, the formalism described in the present work allows to recover the usual\nproperties related to the ground state of a homogeneous one-dimensional\nBose-Einstein condensate but corrected by finite size effects of the system.\nFinally, this scenario allows us to analyze the sensitivity of the system when\nthe Bogoliubov's regime is valid and when finite size effects are present.\nThese facts open the possibility to apply these ideas to more realistic\nscenarios, e.g., low-dimensional trapped Bose-Einstein condensates.",
        "positive": "Cross-over to quasi-condensation: mean-field theories and beyond: We analyze the cross-over of a homogeneous one-dimensional Bose gas from the\nideal gas into the dense quasi-condensate phase. We review a number of\nmean-field theories, perturbative or self-consistent, and provide accurate\nevaluations of equation of state, density fluctuations, and correlation\nfunctions. A smooth crossover is reproduced by classical-field simulations\nbased on the stochastic Gross-Pitaevskii equation, and the Yang-Yang solution\nto the one-dimensional Bose gas."
    },
    {
        "anchor": "Breathing modes of repulsive polarons in Bose-Bose mixtures: We consider impurity atoms embedded in a two-component Bose-Einstein\ncondensate in a quasi-one dimensional regime. We study the effects of repulsive\ncoupling between the impurities and Bose species on the equilibrium of the\nsystem for both miscible and immiscible mixtures by numerically solving the\nunderlying coupled Gross-Pitaevskii equations. Our results reveal that the\npresence of impurities may lead to a miscible-immiscible phase transition due\nto the interaction of the impurities and the two condensates. Within the realm\nof the Bogoliubov-de Gennes equations we calculate the quantum fluctuations due\nto the different types of interactions. The breathing modes and the time\nevolution of harmonically trapped impurities in both homogeneous and\ninhomogeneous binary condensates are deeply discussed in the miscible case\nusing variational and numerical means. We show in particular that the\nself-trapping, the miscibility and the inhomogeneity of the trapped Bose\nmixture may strongly modify the low-lying excitations and the dynamical\nproperties of impurities. The presence of phonons in the homogeneous Bose\nmixture gives rise to the damping of breathing oscillations of impurities\nwidth.",
        "positive": "Phases of attractive spin-imbalanced fermions in square lattices: We determine the relative stability of different ground-state phases of\nspin-imbalanced popula- tions of attractive fermions in square lattices. The\nphases are systematically characterized by the symmetry of the order parameter\nand the real- and momentum-space structures using Hartree- Fock-Bogoliubov\ntheory. We find several type of unidirectional Larkin-Ovchinikov-type phases.\nWe discuss the effect of commensuration between the ordering wave vector and\nthe density imbalance, and describe the mechanism of Fermi surface\nreconstruction and pairing for various orders. A robust supersolid phase is\nshown to exist when the ordering wave vector is diagonally directed."
    },
    {
        "anchor": "Multi-stability in an optomechanical system with two-component\n  Bose-Einstein condensate: We investigate a system consisting of a two-component Bose-Einstein\ncondensate interacting dispersively with a Fabry-Perot optical cavity where the\ntwo components of the condensate are resonantly coupled to each other by\nanother classical field. The key feature of this system is that the atomic\nmotional degrees of freedom and the internal pseudo-spin degrees of freedom are\ncoupled to the cavity field simultaneously, hence an effective spin-orbital\ncoupling within the condensate is induced by the cavity. The interplay among\nthe atomic center- of-mass motion, the atomic collective spin and the cavity\nfield leads to a strong nonlinearity, resulting in multi- stable behavior in\nboth matter wave and light wave at the few-photon level.",
        "positive": "The nonlinear Dirac equation in Bose-Einstein condensates: Superfluid\n  fluctuations and emergent theories from relativistic linear stability\n  equations: We present the theoretical and mathematical foundations of stability analysis\nfor a Bose-Einstein condensate (BEC) at Dirac points of a honeycomb optical\nlattice. The combination of s-wave scattering for bosons and lattice\ninteraction places constraints on the mean-field description, and hence on\nvortex configurations in the Bloch-envelope function near the Dirac point. A\nfull derivation of the relativistic linear stability equations (RLSE) is\npresented by two independent methods to ensure veracity of our results.\nSolutions of the RLSE are used to compute fluctuations and lifetimes of vortex\nsolutions of the nonlinear Dirac equation, which include Mermin-Ho and\nAnderson-Toulouse skyrmions, with lifetime $\\approx 4$ seconds. Beyond vortex\nstabilities the RLSE provide insight into the character of collective\nsuperfluid excitations, which we find to encode several established theories of\nphysics. In particular, the RLSE reduce to the Andreev equations, in the\nnonrelativistic and semiclassical limits, the Majorana equation, inside vortex\ncores, and the Dirac-Bogoliubov-de Gennes equations, when nearest-neighbor\ninteractions are included. Furthermore, by tuning a mass gap, relative\nstrengths of various spinor couplings, for the small and large quasiparticle\nmomentum regimes, we obtain weak-strong Bardeen-Cooper-Schrieffer\nsuperconductivity, as well as fundamental wave equations such as Schr\\\"odinger,\nDirac, Klein-Gordon, and Bogoliubov-de Gennes equations. Our results apply\nequally to a strongly spin-orbit coupled BEC in which the Laplacian\ncontribution can be neglected."
    },
    {
        "anchor": "Bose-Hubbard ladder subject to effective magnetic field: quench dynamics\n  in a harmonic trap: Motivated by a recent experiment with optical lattices that has realized a\nladder geometry with an effective magnetic field (Atala et al., Nature Physics\n\\textbf{10}, 588 (2014)), we study the dynamics of bosons on a tight-binding\ntwo-leg ladder with complex hopping amplitudes. This system displays a quantum\nphase transition even without interactions. We study the non-equilibrium\ndynamics without and with interactions, in the presence of a harmonic trapping\npotential. In particular we consider dynamics induced by quenches of the\ntrapping potential and of the magnitude of the rung hopping. We present a\nstriking \"slowing down\" effect in the collective mode dynamics near the phase\ntransition. This manifestation of a slowing down phenomenon near a quantum\nphase transition can be visualized unusually directly: the collective mode\ndynamics can be followed experimentally in real time and real space by imaging\nthe atomic cloud.",
        "positive": "SO(3) \"Nuclear Physics\" with ultracold Gases: An ab initio calculation of nuclear physics from Quantum Chromodynamics\n(QCD), the fundamental SU(3) gauge theory of the strong interaction, remains an\noutstanding challenge. Here, we discuss the emergence of key elements of\nnuclear physics using an SO(3) lattice gauge theory as a toy model for QCD. We\nshow that this model is accessible to state-of-the-art quantum simulation\nexperiments with ultracold atoms in an optical lattice. First, we demonstrate\nthat our model shares characteristic many-body features with QCD, such as the\nspontaneous breakdown of chiral symmetry, its restoration at finite baryon\ndensity, as well as the existence of few-body bound states. Then we show that\nin the one-dimensional case, the dynamics in the gauge invariant sector can be\nencoded as a spin S=3/2 Heisenberg model, i.e., as quantum magnetism, which has\na natural realization with bosonic mixtures in optical lattices, and thus sheds\nlight on the connection between non-Abelian gauge theories and quantum\nmagnetism."
    },
    {
        "anchor": "Stable Solitons in Three Dimensional Free Space: Self-Trapped\n  Bose-Einstein Condensates with Spin-Orbit Coupling: By means of variational methods and systematic numerical analysis, we\ndemonstrate the existence of stable solitons in three-dimensional (3D) free\nspace, in the context of binary atomic condensates combining contact\nself-attraction and spin-orbit coupling, which can be engineered by available\nexperimental techniques. Depending on the relative strength of the intra- and\ninter-component attraction, the stable solitons feature a semi-vortex or\nmixed-mode structure. In spite of the fact that the local cubic self-attraction\ngives rise to the supercritical collapse in 3D, the solitons are stable against\nrandom perturbations, motion, and collisions.",
        "positive": "Topological phases in ultracold polar-molecule quantum magnets: We show how to use polar molecules in an optical lattice to engineer quantum\nspin models with arbitrary spin S >= 1/2 and with interactions featuring a\ndirection-dependent spin anisotropy. This is achieved by encoding the effective\nspin degrees of freedom in microwave-dressed rotational states of the molecules\nand by coupling the spins through dipolar interactions. We demonstrate how one\nof the experimentally most accessible anisotropies stabilizes symmetry\nprotected topological phases in spin ladders. Using the numerically exact\ndensity matrix renormalization group method, we find that these interacting\nphases -- previously studied only in the nearest-neighbor case -- survive in\nthe presence of long-range dipolar interactions. We also show how to use our\napproach to realize the bilinear-biquadratic spin-1 and the Kitaev honeycomb\nmodels. Experimental detection schemes and imperfections are discussed."
    },
    {
        "anchor": "Steering random walks with kicked ultracold atoms: A kicking sequence of the atom optics kicked rotor at quantum resonance can\nbe interpreted as a quantum random walk in momentum space. We show how to steer\nsuch a random walk by applying a random sequence of intensities and phases of\nthe kicking lattice chosen according to a probability distribution. This\ndistribution converts on average into the final momentum distribution of the\nkicked atoms. In particular, it is shown that a power-law distribution for the\nkicking strengths results in a L\\'evy walk in momentum space and in a power-law\nwith the same exponent in the averaged momentum distribution. Furthermore, we\ninvestigate the stability of our predictions in the context of a realistic\nexperiment with Bose-Einstein condensates.",
        "positive": "Particle-Localized Ground State of Atom-Molecule Bose-Einstein\n  Condensates in a Double-Well Potential: We study the effect of atom-molecule internal tunneling on the ground state\nof atom-molecule Bose-Einstein condensates in a double-well potential. In the\nabsence of internal tunneling between atomic and molecular states, the ground\nstate is symmetric, which has equal-particle populations in two wells. From the\nlinear stability analysis, we show that the symmetric stationary state becomes\ndynamically unstable at a certain value of the atom-molecule internal tunneling\nstrength. Above the critical value of the internal tunneling strength, the\nground state bifurcates to the particle-localized ground states. The origin of\nthis transition can be attributed to the effective attractive inter-atomic\ninteraction induced by the atom-molecule internal tunneling. This effective\ninteraction is similar to that familiar in the context of BCS-BEC crossover in\na Fermi gas with Feshbach resonance. Furthermore, we point out the possibility\nof reentrant transition in the case of the large detuning between the atomic\nand molecular states."
    },
    {
        "anchor": "Feedback cooling Bose gases to quantum degeneracy: Degenerate quantum gases are instrumental in advancing many-body quantum\nphysics and underpin emerging precision sensing technologies. All\nstate-of-the-art experiments use evaporative cooling to achieve the ultracold\ntemperatures needed for quantum degeneracy, yet evaporative cooling is\nextremely lossy: more than 99.9% of the gas is discarded. Such final particle\nnumber limitations constrain imaging resolution, gas lifetime, and applications\nleveraging macroscopic quantum coherence. Here we show that atomic Bose gases\ncan be cooled to quantum degeneracy using real-time feedback, an entirely new\nmethod that does not suffer the same limitations as evaporative cooling.\nThrough novel quantum-field simulations and scaling arguments, we demonstrate\nthat an initial low-condensate-fraction thermal Bose gas can be cooled to a\nhigh-purity Bose-Einstein condensate (BEC) by feedback control, with\nsubstantially lower atomic loss than evaporative cooling. Advantages of\nfeedback cooling are found to be robust to imperfect detection, finite\nresolution of the control and measurement, time delay in the control loop, and\nspontaneous emission. Using feedback cooling to create degenerate sources with\nhigh coherence and low entropy enables new capabilities in precision\nmeasurement, atomtronics, and few- and many-body quantum physics.",
        "positive": "Variational approach for impurity dynamics at finite temperature: We present a general variational principle for the dynamics of impurity\nparticles immersed in a quantum-mechanical medium. By working within the\nHeisenberg picture and constructing approximate time-dependent impurity\noperators, we can take the medium to be in any mixed state, such as a thermal\nstate. Our variational method is consistent with all conservation laws and, in\ncertain cases, it is equivalent to a finite-temperature Green's function\napproach. As a demonstration of our method, we consider the dynamics of heavy\nimpurities that have suddenly been introduced into a Fermi gas at finite\ntemperature. Using approximate time-dependent impurity operators involving only\none particle-hole excitation of the Fermi sea, we find that we can successfully\nmodel the results of recent Ramsey interference experiments on $^{40}$K atoms\nin a $^6$Li Fermi gas [M.~Cetina et al., Science \\textbf{354}, 96 (2016)]. We\nalso show that our approximation agrees well with the exact solution for the\nRamsey response of a fixed impurity at finite temperature. Our approach paves\nthe way for the investigation of impurities with dynamical degrees of freedom\nin arbitrary quantum-mechanical mediums."
    },
    {
        "anchor": "Quantum Criticality of one-dimensional multicomponent Fermi Gas with\n  Strongly Attractive Interaction: Quantum criticality of strongly attractive Fermi gas with $SU(3)$ symmetry in\none dimension is studied via the thermodynamic Bethe ansatz (TBA) equations.The\nphase transitions driven by the chemical potential $\\mu$, effective magnetic\nfield $H_1$, $H_2$ (chemical potential biases) are analyzed at the quantum\ncriticality. The phase diagram and critical fields are analytically determined\nby the thermodynamic Bethe ansatz equations in zero temperature limit. High\naccurate equations of state, scaling functions are also obtained analytically\nfor the strong interacting gases. The dynamic exponent $z=2$ and correlation\nlength exponent $\\nu=1/2$ read off the universal scaling form. It turns out\nthat the quantum criticality of the three-component gases involves a sudden\nchange of density of states of one cluster state, two or three cluster states.\nIn general, this method can be adapted to deal with the quantum criticality of\nmulti-component Fermi gases with $SU(N)$ symmetry.",
        "positive": "Tight binding models for ultracold atoms in honeycomb optical lattices: We discuss how to construct tight-binding models for ultra cold atoms in\nhoneycomb potentials, by means of the maximally localized Wannier functions\n(MLWFs) for composite bands introduced by Marzari and Vanderbilt [1]. In\nparticular, we work out the model with up to third-nearest neighbors, and\nprovide explicit calculations of the MLWFs and of the tunneling coefficients\nfor the graphene-lyke potential with two degenerate minima per unit cell.\nFinally, we discuss the degree of accuracy in reproducing the exact Bloch\nspectrum of different tight-binding approximations, in a range of typical\nexperimental parameters."
    },
    {
        "anchor": "Quantum glass of interacting bosons with off-diagonal disorder: We study disordered interacting bosons described by the Bose-Hubbard model\nwith Gaussian-distributed random tunneling amplitudes. It is shown that the\noff-diagonal disorder induces a spin-glass-like ground state, characterized by\nrandomly frozen quantum-mechanical U(1) phases of bosons. To access\ncriticality, we employ the \"$n$-replica trick\", as in the spin-glass theory,\nand the Trotter-Suzuki method for decomposition of the statistical density\noperator, along with numerical calculations. The interplay between disorder,\nquantum and thermal fluctuations leads to phase diagrams exhibiting a glassy\nstate of bosons, which are studied as a function of model parameters. The\nconsidered system may be relevant for quantum simulators of optical-lattice\nbosons, where the randomness can be introduced in a controlled way. The latter\nis supported by a proposition of experimental realization of the system in\nquestion.",
        "positive": "Zero-temperature phase diagram of hard sphere bosons in asymmetric three\n  dimensional optical lattices: We studied the superfluid-to-Mott insulator transition for bosonic hard\nspheres loaded in asymmetric three-dimensional optical lattices by means of\ndiffusion Monte Carlo calculations. The onset of the transition was monitored\nthrough the change in the chemical potential around the density corresponding\nto one particle per potential well. With this method, we were able to reproduce\nthe results given in the literature for three-dimensional symmetric lattices\nand for systems whose asymmetry makes them equivalent to a set of quasi-one\ndimensional tubes. The location of the same transition for asymmetric systems\nakin to a stack of quasi-two dimensional lattices will be also given. Our\nresults were checked against those given by a Bose-Hubbard model for similar\narrangements."
    },
    {
        "anchor": "Phase diagram of dipolar hard-core bosons on honeycomb lattice: In this paper, we study phase diagrams of dipolar hard-core boson gases on\nthe honeycomb lattice. The system is described by the Haldane-Bose-Hubbard\nmodel with complex hopping amplitudes and the nearest neighbor repulsion. By\nusing the slave-particle representation of the hard-core bosons and also the\npath-integral quantum Monte-Carlo simulations, we investigate the system and to\nshow that the systems have a rich phase diagram. There are Mott, superfluid,\nchiral superfluid, and sublattice chiral superfluid phases as well as the\ndensity-wave phase. We also found that there exists a coexisting phase of\nsuperfluid and chiral superfluid. Critical behaviors of the phase transitions\nare also clarified.",
        "positive": "Ground-states of spin-1 bosons in asymmetric double-wells: In this work we investigate the different states of a system of spin-1 bosons\nin two potential wells connected by tunneling, with spin-dependent interaction.\nThe model utilizes the well-known Bose-Hubbard Hamiltonian, adding a local\ninteraction term that depends on the modulus of the total spin in a well,\nfavoring a high- or low-spin state for different signs of the coupling\nconstant. We employ the concept of fidelity to detect critical values of\nparameters for which the ground state undergoes significant changes. The nature\nof the states is investigated through evaluation of average occupation numbers\nin the wells and of spin correlations. A more detailed analysis is done for a\ntwo-particle system, but a discussion of the three-particle case and some\nresults for larger numbers are also presented."
    },
    {
        "anchor": "Hartree shift in unitary Fermi gases: The Hartree energy shift is calculated for a unitary Fermi gas. By including\nthe momentum dependence of the scattering amplitude explicitly, the Hartree\nenergy shift remains finite even at unitarity. Extending the theory also for\nspin-imbalanced systems allows calculation of polaron properties. The results\nare in good agreement with more involved theories and experiments.",
        "positive": "Many-body approach to low-lying collective excitations in a BEC\n  approaching collapse: An approximate many-body theory incorporating two-body correlations has been\nemployed to calculate low-lying collective multipole frequencies in a\nBose-Einstein condensate containing $A$ bosons, for different values of the\ninteraction parameter $\\lambda=\\frac{Aa_{s}}{a_{ho}}$. Significant difference\nfrom the variational estimate of the Gross-Pitaevskii equation has been found\nnear the collapse region. This is attributed to two-body correlations and\nfinite range attraction of the realistic interatomic interaction. A large\ndeviation from the hydrodynamic model is also seen for the second monopole\nbreathing mode and the quadrupole mode for large positive $\\lambda$."
    },
    {
        "anchor": "Quench dynamics across the MI-SF quantum phase transition with cluster\n  mean field theory: In this work, we study the quench dynamics of quantum phases of ultracold\nneutral bosons trapped in optical lattices. We investigate the validity of the\nKibble-Zurek (KZ) scaling laws with the single-site Gutzwiller mean-field\n(SGMF) and cluster Gutzwiller mean-field (CGMF) theory. With CGMF, we note the\nevolution of the dynamical wavefunction in the ``impulse\" regime of the\nKibble-Zurek mechanism. We obtain the power law scalings for the crossover time\nand defect density with the quench rate predicted by KZ scaling laws. The\ncritical exponents obtained from dynamics are close to their equilibrium\nvalues. Furthermore, it is observed that the obtained dynamical critical\nexponent $z$ improves towards the equilibrium value with increasing cluster\nsizes in CGMF.",
        "positive": "Mobile magnetic impurities in a Fermi superfluid: a route to designer\n  molecules: A magnetic impurity in a fermionic superfluid hosts bound quasiparticle\nstates known as Yu-Shiba-Rusinov (YSR) states. We argue here that, if the\nimpurity is mobile (i.e., has a finite mass), the impurity and its bound YSR\nquasiparticle move together as a midgap molecule, which has an unusual\n\"Mexican-hat\" dispersion that is tunable via the fermion density. We map out\nthe impurity dispersion, which consists of an \"atomic\" branch (in which the\nimpurity is dressed by quasiparticle pairs) and a \"molecular\" branch (in which\nthe impurity binds a quasiparticle). We discuss the experimental realization\nand detection of midgap Shiba molecules, focusing on lithium-cesium mixtures,\nand comment on the prospects they offer for realizing exotic many-body states."
    },
    {
        "anchor": "Scattering by an oscillating barrier: quantum, classical, and\n  semiclassical comparison: We present a detailed study of scattering by an amplitude-modulated potential\nbarrier using three distinct physical frameworks: quantum, classical, and\nsemiclassical. Classical physics gives bounds on the energy and momentum of the\nscattered particle, while also providing the foundation for semiclassical\ntheory. We use the semiclassical approach to selectively add quantum-mechanical\neffects such as interference and diffraction. We find good agreement between\nthe quantum and semiclassical momentum distributions. Our methods and results\ncan be used to understand quantum and classical aspects of transport mechanisms\ninvolving time-varying potentials, such as quantum pumping.",
        "positive": "Superadiabatic quantum friction suppression in finite-time\n  thermodynamics: Optimal performance of thermal machines is reached by suppressing friction.\nFriction in quantum thermodynamics results from fast driving schemes that\ngenerate nonadiabatic excitations. The far-from-equilibrium dynamics of quantum\ndevices can be tailored by shortcuts to adiabaticity to suppress quantum\nfriction. We experimentally demonstrate friction-free superadiabatic strokes\nwith a trapped unitary Fermi gas as a working substance and establish the\nequivalence between the superadiabatic mean work and its adiabatic value."
    },
    {
        "anchor": "Dynamical quantum phase transitions in a spinor Bose-Einstein condensate\n  and criticality enhanced quantum sensing: Quantum phase transitions universally exist in the ground and excited states\nof quantum many-body systems, and they have a close relationship with the\nnonequilibrium dynamical phase transitions, which however are challenging to\nidentify. In the system of spin-1 Bose-Einstein condensates, though dynamical\nphase transitions with correspondence to equilibrium phase transitions in the\nground state and uppermost excited state have been probed, those taken place in\nintermediate excited states remain untouched in experiments thus far. Here we\nunravel that both the ground and excited-state quantum phase transitions in\nspinor condensates can be diagnosed with dynamical phase transitions. A\nconnection between equilibrium phase transitions and nonequilibrium behaviors\nof the system is disclosed in terms of the quantum Fisher information. We also\ndemonstrate that near the critical points parameter estimation beyond standard\nquantum limit can be implemented. This work not only advances the exploration\nof excited-state quantum phase transitions via a scheme that can immediately be\napplied to a broad class of few-mode quantum systems, but also provides new\nperspective on the relationship between quantum criticality and quantum\nenhanced sensing.",
        "positive": "$\\mathcal{PT}$-symmetry phase transition in a Bose-Hubbard model with\n  localized gain and loss: We study the dissipative dynamics of a one-dimensional bosonic system\ndescribed in terms of the bipartite Bose-Hubbard model with alternating gain\nand loss. This model exhibits the $\\mathcal{PT}$ symmetry under some specific\nconditions and features a $\\mathcal{PT}$-symmetry phase transition. It is\ncharacterized by an order parameter corresponding to the population imbalance\nbetween even and odd sites, similar to the continuous phase transitions in the\nHermitian realm. In the noninteracting limit, we solve the problem exactly and\ncompute the parameter dependence of the order parameter. The interacting limit\nis addressed at the mean-field level, which allows us to construct the phase\ndiagram for the model. We find that both the interaction and dissipation rates\ninduce a $\\mathcal{PT}$-symmetry breaking. On the other hand, periodic\nmodulation of the dissipative coupling in time stabilizes the\n$\\mathcal{PT}$-symmetric regime. Our findings are corroborated numerically on a\ntight-binding chain with gain and loss."
    },
    {
        "anchor": "Low-density expansions for the homogeneous dipolar Bose gas at zero\n  temperature: The low-density expansions for the energy, chemical potential, and condensate\ndepletion of the homogeneous dilute dipolar Bose gas are obtained by\nregularizing the dipole-dipole interaction at long distances. It is shown that\nthe leading term, proportional to the density, allows a simple physical\ninterpretation and consistently describes the thermodynamic stability of the\nsystem. The long-range asymptotics are obtained analytically for the normal and\nanomalous one-particle correlation functions and the pair distribution\nfunction. We discuss the properties of the two-body scattering with zero\nrelative momentum for the dipole-dipole interaction, in particular, we derive\nthe asymptotics of the wave function and a correction to the scattering length\nfor small values of the dipolar range. We show how the density expansions can\nbe derived within the Bogoliubov model of weakly interacting particles without\nany divergence from the assumption of universality of the expansions at low\ndensities.",
        "positive": "Coherent Manipulation of Orbital Feshbach Molecules of Two-Electron\n  Atoms: Ultracold molecules have experienced increasing attention in recent years.\nCompared to ultracold atoms, they possess several unique properties that make\nthem perfect candidates for the implementation of new quantum-technological\napplications in several fields, from quantum simulation to quantum sensing and\nmetrology. In particular, ultracold molecules of two-electron atoms (such as\nstrontium or ytterbium) also inherit the peculiar properties of these atomic\nspecies, above all the possibility to access metastable electronic states via\ndirect excitation on optical clock transitions with ultimate sensitivity and\naccuracy. In this paper we report on the production and coherent manipulation\nof molecular bound states of two fermionic $^{173}$Yb atoms in different\nelectronic (orbital) states $^1$S$_0$ and $^3$P$_0$ in proximity of a\nscattering resonance involving atoms in different spin and electronic states,\ncalled orbital Feshbach resonance. We demonstrate that orbital molecules can be\ncoherently photoassociated starting from a gas of ground-state atoms in a\nthree-dimensional optical lattices by observing several photoassociation and\nphotodissociation cycles. We also show the possibility to coherently control\nthe molecular internal state by using Raman-assisted transfer to swap the\nnuclear spin of one of the atoms forming the molecule, thus demonstrating a\npowerful manipulation and detection tool of these molecular bound states.\nFinally, by exploiting this peculiar detection technique we provide first\ninformation on the lifetime of the molecular states in a many-body setting,\npaving the way towards future investigations of strongly interacting Fermi\ngases in a still unexplored regime."
    },
    {
        "anchor": "Floquet analysis of the modulated two-mode Bose-Hubbard model: We study the tunneling dynamics in a time-periodically modulated two-mode\nBose-Hubbard model using Floquet theory. We consider situations where the\nsystem is in the self-trapping regime and either the tunneling amplitude, the\ninteraction strength, or the energy difference between the modes is modulated.\nIn the former two cases, the tunneling is enhanced in a wide range of\nmodulation frequencies, while in the latter case the resonance is narrow. We\nexplain this difference with the help of Floquet analysis. If the modulation\namplitude is weak, the locations of the resonances can be found using the\nspectrum of the non-modulated Hamiltonian. Furthermore, we use Floquet analysis\nto explain the coherent destruction of tunneling (CDT) occurring in a\nlarge-amplitude modulated system. Finally, we present two ways to create a NOON\nstate (a superposition of $N$ particles in mode 1 with zero particles in mode 2\nand vice versa). One is based on a coherent oscillation caused by detuning from\na partial CDT. The other makes use of an adiabatic variation of the modulation\nfrequency. This results in a Landau-Zener type of transition between the ground\nstate and a NOON-like state.",
        "positive": "Induced correlations between impurities in a one-dimensional quenched\n  Bose gas: We explore the time evolution of two impurities in a trapped one-dimensional\nBose gas that follows a change of the boson-impurity interaction. We study the\ninduced impurity-impurity interactions and their effect on the quench dynamics.\nIn particular, we report on the size of the impurity cloud, the\nimpurity-impurity entanglement, and the impurity-impurity correlation function.\nThe presented numerical simulations are based upon the variational multilayer\nmulticonfiguration time-dependent Hartree method for bosons. To analyze and\nquantify induced impurity-impurity correlations, we employ an effective\ntwo-body Hamiltonian with a contact interaction. We show that the effective\nmodel consistent with the mean-field attraction of two heavy impurities\nexplains qualitatively our results for weak interactions.\n  Our findings suggest that the quench dynamics in cold-atom systems can be a\ntool for studying impurity-impurity correlations."
    },
    {
        "anchor": "Association of Efimov trimers from a three-atom continuum: We develop an experimental technique for rf-association of Efimov trimers\nfrom three-atoms continuum. We apply it to probe the lowest accessible Efimov\nenergy level in bosonic lithium in the region where strong deviations from the\nuniversal behavior are expected, and provide quantitative study of this effect.\nPosition of the Efimov resonance at the atom-dimer threshold, measured with a\ndifferent experimental technique, concurs with the rf-association results.",
        "positive": "Precise measurements on a quantum phase transition in antiferromagnetic\n  spinor Bose-Einstein condensates: We have experimentally investigated the quench dynamics of antiferromagnetic\nspinor Bose-Einstein condensates in the vicinity of a zero temperature quantum\nphase transition at zero quadratic Zeeman shift $q$. The rate of instability\nshows good agreement with predictions based upon solutions to the Bogoliubov\nde-Gennes equations. A key feature of this work was removal of magnetic field\ninhomogeneities, resulting in a steep change in behavior near the transition\npoint. The quadratic Zeeman shift at the transition point was resolved to 250\nmilliHertz uncertainty, equivalent to an energy resolution of $k_B \\times 12$\npicoKelvin. To our knowledge, this is the first demonstration of sub-Hz\nprecision measurement of a phase transition in quantum gases. Our results point\nto the use of dynamics, rather than equilibrium studies for high precision\nmeasurements of phase transitions in quantum gases."
    },
    {
        "anchor": "Observation of a Modulational Instability in Bose-Einstein condensates: We observe the breakup dynamics of an elongated cloud of condensed $^{85}$Rb\natoms placed in an optical waveguide. The number of localized spatial\ncomponents observed in the breakup is compared with the number of solitons\npredicted by a plane-wave stability analysis of the nonpolynomial nonlinear\nSchr\\\"odinger equation, an effective one-dimensional approximation of the\nGross-Pitaevskii equation for cigar-shaped condensates. It is shown that the\nnumbers predicted from the fastest growing sidebands are consistent with the\nexperimental data, suggesting that modulational instability is the key\nunderlying physical mechanism driving the breakup.",
        "positive": "Theoretical Prediction of Non-Hermitian Skin Effect in Ultracold Atom\n  Systems: Non-Hermitian skin effect, which refers to the phenomenon that an extensive\nnumber of eigenstates are localized at the boundary, has been widely studied in\nlattice models and experimentally observed in several classical systems. In\nthis work, we predict that the existence of the non-Hermitian skin effect in\nthe dissipative ultracold fermions with spin-orbit coupling, a continuous model\nthat has been implemented by the Hong-Kong group in a recent experiment. This\nskin effect is robust against the variation of external parameters and trapping\npotentials. We further reveal a dynamic sticky effect in our system, which has\na common physical origin with the non-Hermitian skin effect. Our work paves the\nway for studying novel physical responses of non-Hermitian skin effect in\nquantum systems."
    },
    {
        "anchor": "Pseudo-gap pairing in ultracold Fermi atoms: The crossover from a BEC (Bose-Einstein condensation) to a BCS\n(Bardeen-Cooper-Schrieffer) superfluid in dilute gases of ultracold Fermi atoms\ncreates an ideal environment to enrich our knowledge of strongly correlated\nmany-body systems. These experiments are relevant to a wide range of fields\nfrom condensed matter to astrophysics. The nature of pairing in strongly\ninteracting Fermi gases can be readily studied, thus aiding our understanding\nof related problems in high-T_{c} superconductors, whose mechanism is still\nunder debate. These are not well-understood due to the large interaction\nparameter. Here, we calculate the dynamical properties of a normal, trapped,\nand strongly correlated Fermi gas, by developing a quantum cluster expansion.\nIn ultra-cold atomic physics one can measure the elementary excitations, using\nrf or Bragg spectroscopy. Our calculations for the single-particle spectral\nfunction agree with the recent measurements, and clearly demonstrate pseudogap\npairing in the strongly interacting regime.",
        "positive": "Calculating energy shifts in terms of phase shifts: To clarify the relation of energy shifts to scattering phase shifts in\none-body and many-body problems, we examine their relation in a number of\ndifferent situations. We derive, for a particle in a container of arbitrary\nshape with a short-range scattering center, a general result for the energy\neigenvalues in terms of the s-wave scattering phase shift and the eigenstates\nin the absence of the scatterer. We show that, while the energy shifts for a\nspherical container are proportional to the phase shift over large ranges,\nthose for a cubic container have a more complicated behavior. We connect our\nresult to the description of energy shifts in terms of the scattering T-matrix.\nThe general relation is extended to problems of particles in traps with\nsmoothly varying potentials, including, e.g., the interaction of a small\nneutral atom with a Rydberg atom. We then consider the many-body problem for\nparticles with a two-body interaction and show that the free energy change due\nto the interaction is proportional to an average of a generalized phase shift\nthat includes the effects of the medium. Finally, we discuss why, even though\nindividual energy levels are very sensitive to boundary conditions, the energy\nof a many-body system is not."
    },
    {
        "anchor": "Collective modes in the anisotropic unitary Fermi gas and the inclusion\n  of a backflow term: We study the collective modes of the confined unitary Fermi gas under\nanisotropic harmonic confinement as a function of the number of atoms. We use\nthe equations of extended superfluid hydrodynamics, which take into account a\ndispersive von Weizsacker-like term in the equaton of state. We also discuss\nthe inclusion of a backflow term in the extended superfluid Lagrangian and the\neffects of this anomalous term on sound waves and Beliaev damping of phonons.",
        "positive": "Nonlinear Floquet dynamics of spinor condensates in an optical cavity:\n  Cavity-amplified parametric resonance: We investigate Floquet dynamics of a cavity-spinor Bose-Einstein condensate\ncoupling system via periodic modulation of the cavity pump laser. Parametric\nresonances are predicted and we show that due to cavity feedback-induced\nnonlinearity the spin oscillation can be amplified to all orders of resonance,\nthus facilitating its detection. Real-time observation on Floquet dynamics via\ncavity output is also discussed."
    },
    {
        "anchor": "Controlling the dynamics of an open many-body quantum system with\n  localized dissipation: We experimentally investigate the action of a localized dissipative potential\non a macroscopic matter wave, which we implement by shining an electron beam on\nan atomic Bose-Einstein condensate (BEC). We measure the losses induced by the\ndissipative potential as a function of the dissipation strength observing a\nparadoxical behavior when the strength of the dissipation exceeds a critical\nlimit: for an increase of the dissipation rate the number of atoms lost from\nthe BEC becomes lower. We repeat the experiment for different parameters of the\nelectron beam and we compare our results with a simple theoretical model,\nfinding excellent agreement. By monitoring the dynamics induced by the\ndissipative defect we identify the mechanisms which are responsible for the\nobserved paradoxical behavior. We finally demonstrate the link between our\ndissipative dynamics and the measurement of the density distribution of the BEC\nallowing for a generalized definition of the Zeno effect. Due to the high\ndegree of control on every parameter, our system is a promising candidate for\nthe engineering of fully governable open quantum systems.",
        "positive": "Dynamics of spin polarization in tilted polariton rings: We have observed the effect of pseudo magnetic field originating from the\npolaritonic analog of spin-orbit coupling (TE$-$TM splitting) on a polariton\ncondensate in a ring-shaped microcavity. The effect gives rise to a stable\nfour-leaf pattern around the ring as seen from the linear polarization\nmeasurements of the condensate photoluminescence. This pattern is found to\noriginate from the interplay of the cavity potential, energy relaxation, and\nTE-TM splitting in the ring. Our observations are compared to the dissipative\none-dimensional spinor Gross-Pitaevskii equation with the TE-TM splitting\nenergy which shows good qualitative agreement."
    },
    {
        "anchor": "Bose-Einstein condensation of photons in an ideal atomic gas: We study peculiarities of Bose-Einstein condensation of photons that are in\nthermodynamic equilibrium with atoms of noninteracting gases. General equations\nof the thermodynamic equilibrium of the system under study are obtained. We\nexamine solutions of these equations in the case of high temperatures, when the\natomic components of the system can be considered as nondegenerated ideal gases\nof atoms, and the photonic component can form a state with the Bose condensate.\nTranscendental equation for transition temperature and expression for the\ndensity of condensed photons in the considered system are derived. We also\nobtain analytical solutions of the equation for the critical temperature in a\nnumber of particular cases. The existence of two regimes of Bose condensation\nof photons, which differ significantly in nature of transition temperature\ndependence on the total density of photons pumped into the system, is revealed.\nIn one case, this dependence is a traditional fractional-power law, and in\nanother one it is the logarithmic law. Applying numerical methods, we determine\nboundaries of existence and implementation conditions for different regimes of\ncondensation depending on the physical parameters of the system under study. We\nalso show that for a large range of physical systems that are in equilibrium\nwith photons (from ultracold gases of alkali metals to certain types of ideal\nplasma), the condensation of photons should occur according to the logarithmic\nregime.",
        "positive": "Squeezing of nonlinear spin observables by one axis twisting in the\n  presence of decoherence: An analytical study: In an ensemble of two-level atoms that can be described in terms of a\ncollective spin, entangled states can be used to enhance the sensitivity of\ninterferometric precision measurements. While non-Gaussian spin states can\nproduce larger quantum enhancements than spin-squeezed Gaussian states, their\nuse requires the measurement of observables that are nonlinear functions of the\nthree components of the collective spin. In this paper we develop strategies\nthat achieve the optimal quantum enhancements using non-Gaussian states\nproduced by a nonlinear one-axis-twisting Hamiltonian, and show that\nmeasurement-after-interaction techniques, known to amplify the output signals\nin quantum parameter estimation protocols, are effective in measuring nonlinear\nspin observables. Including the presence of the relevant decoherence processes\nfrom atomic experiments, we determine analytically the quantum enhancement of\nnon-Gaussian over-squeezed states as a function of the noise parameters for\narbitrary atom numbers."
    },
    {
        "anchor": "Stability of quantised vortices in two-component condensates: Multiply quantised vortices (MQVs) within single component Bose-Einstein\ncondensates are unstable and decay rapidly. We show that MQVs can be stabilised\nby adding a small number of atoms of a second species to the vortex cores, and\nthat these atoms remain in the vortex core as the system evolves. A consequence\nof the stabilisation is that nearby co-rotating vortices can orbit in the\nopposite sense to their individual rotations when enough of the second species\nis present. This has implications concerning the imaging of vortices, as well\nas quantum turbulence and vortex nucleation in two-component condensates, such\nas those involving mixtures of $^{87}$Rb and $^{133}$Cs.",
        "positive": "Quench dynamics of dipolar fermions in a one-dimensional harmonic trap: We study a system of few fermions in a one-dimensional harmonic trap, and\nfocus on the case of dipolar majority particles in contact with a single\nimpurity. The impurity is used both for quenching the system, and for tracking\nthe system evolution after the quench. Employing exact diagonalization, we\ninvestigate relaxation and thermalization properties. In the absence of dipolar\ninteractions, the system is near integrability, and the dynamics remains\noscillatory even on long time scales. On the other hand, repulsive as well as\nattractive dipolar interactions lead to quick relaxation to the diagonal\nensemble average which is significantly different from corresponding thermal\naverages. A Wigner-shaped level spacing distribution indicates level repulsion\nand thus chaotic dynamical behavior due to the presence of dipolar\ninteractions."
    },
    {
        "anchor": "Polarons and their induced interactions in highly imbalanced triple\n  mixtures: We unravel the polaronic properties of impurities immersed in a correlated\ntrapped one-dimensional (1D) Bose-Bose mixture. This setup allows for the\nimpurities to couple either attractively or repulsively to a specific host,\nthus offering a highly flexible platform for steering the emergent polaronic\nproperties. Specifically, the polaronic residue peak and strength of induced\ninteractions can be controlled by varying the coupling of the impurities to the\nindividual bosonic components. In particular, it is possible to maintain the\nquasiparticle character for larger interaction strengths as compared to the\ncase of impurities immersed in a single bosonic species. We explicate a\nhierarchy of the polaron binding energies in terms of the impurity-medium\ninteractions, thereby elucidating the identification of the polaronic\nresonances in recent experimental radiofrequency schemes. For strong attractive\nimpurity-medium couplings bipolaron formation is captured. Our findings pave\nthe way for continuously changing the quasiparticle character, under the impact\nof trap effects, while exposing the role of correlations in triple mixture\nsettings.",
        "positive": "Dispersion and wavefunction symmetry in cold atoms experiencing\n  artificial gauge fields: We analyze the single particle quantum mechanics of an atom whose dispersion\nis modified by spin orbit coupling to Raman lasers. We calculate how the novel\ndispersion leads to unusual single particle physics. We focus on the symmetry\nof the ground state wavefunction in different potentials."
    },
    {
        "anchor": "Entropy of the BEC Ground State: Correlation vs Ground State Entropy: Calculation of the entropy of an ideal Bose Einstein Condensate (BEC) in a\nthree dimensional trap reveals unusual, previously unrecognized, features of\nthe Canonical Ensemble. It is found that, for any temperature, the entropy of\nthe Bose gas is equal to the entropy of the excited particles although the\nentropy of the particles in the ground state is nonzero. We explain this by\nconsidering the correlations between the ground state particles and particles\nin the excited states. These correlations lead to a correlation entropy which\nis exactly equal to the contribution from the ground state. The correlations\nthemselves arise from the fact that we have a fixed number of particles obeying\nquantum statistics. We present results for correlation functions between the\nground and excited states in Bose gas, so to clarify the role of fluctuations\nin the system. We also report the sub-Poissonian nature of the ground state\nfluctuations.",
        "positive": "Realization of a sonic black hole analogue in a Bose-Einstein condensate: We have created an analogue of a black hole in a Bose-Einstein condensate. In\nthis sonic black hole, sound waves, rather than light waves, cannot escape the\nevent horizon. A step-like potential accelerates the flow of the condensate to\nvelocities which cross and exceed the speed of sound by an order of magnitude.\nThe Landau critical velocity is therefore surpassed. The point where the flow\nvelocity equals the speed of sound is the sonic event horizon. The effective\ngravity is determined from the profiles of the velocity and speed of sound. A\nsimulation finds negative energy excitations, by means of Bragg spectroscopy."
    },
    {
        "anchor": "Vortex gyroscope imaging of planar superfluids: We propose a robust imaging technique that makes it possible to distinguish\nvortices from antivortices in quasi-two-dimensional Bose--Einstein condensates\nfrom a single image of the density of the atoms. Tilting the planar condensate\nprior to standard absorption imaging excites a generalized gyroscopic mode of\nthe condensate revealing the sign and location of each vortex. This technique\nis anticipated to enable experimental measurement of the incompressible kinetic\nenergy spectrum of the condensate and the observation of a negative temperature\nphase transition of the vortex gas, driven by two-dimensional superfluid\nturbulence.",
        "positive": "Topological phases of dipolar particles in elongated Wannier orbitals: We show that topological phases with fractional excitations can occur in\ntwo-dimensional ultracold dipolar gases on a particular class of optical\nlattices. Due to the dipolar interaction and lattice confinement, a quantum\ndimer model emerges naturally as the effective theory describing the low-energy\nbehaviors of these systems under well-controlled approximations. The desired\nhierarchy of interaction energy scales is achieved by controlling the\nanisotropy of the orbital dimers and the dipole moments of the particles.\nExperimental realization and detection of various phases are discussed, as well\nas the possible relevance for quantum computation."
    },
    {
        "anchor": "Deconfinement Dynamics of Fractons in Tilted Bose-Hubbard Chains: Fractonic constraints can lead to exotic properties of quantum many-body\nsystems. Here, we investigate the dynamics of fracton excitations on top of the\nground states of a one-dimemnsional, dipole-conserving Bose-Hubbard model. We\nshow that nearby fractons undergo a collective motion mediated by exchanging\nvirtual dipole excitations, which provides a powerful dynamical tool to\ncharacterize the underlying ground state phases. We find that in the gapped\nMott insulating phase, fractons are confined to each other as motion requires\nthe exchange of massive dipoles. When crossing the phase transition into a\ngapless Luttinger liquid of dipoles, fractons deconfine. Their transient\ndeconfinement dynamics scales diffusively and exhibits strong but subleading\ncontributions described by a quantum Lifshitz model. We examine prospects for\nthe experimental realization in tilted Bose-Hubbard chains by numerically\nsimulating the adiabatic state preparation and subsequent time evolution, and\nfind clear signatures of the low-energy fracton dynamics.",
        "positive": "Fluctuation-damping of isolated, oscillating Bose-Einstein condensates: Experiments on the nonequilibrium dynamics of an isolated Bose-Einstein\ncondensate (BEC) in a magnetic double-well trap exhibit a puzzling divergence:\nWhile some show dissipation-free Josephson oscillations, others find strong\ndamping. Such damping in isolated BECs cannot be understood on the level of the\ncoherent Gross-Pitaevskii dynamics. Using the Keldysh functional-integral\nformalism, we describe the time-dependent system dynamics by means of a\nmulti-mode BEC coupled to fluctuations (single-particle excitations) beyond the\nGross-Pitaevskii saddle point. We find that the Josephson oscillations excite\nan excess of fluctuations when the effective Josephson frequency,\n$\\tilde{\\omega}_J$, is in resonance with the effective fluctuation energy,\n$\\tilde{\\varepsilon}_m$, where both, $\\tilde{\\omega}_J$ and\n$\\tilde{\\varepsilon}_m$, are strongly renormalized with respect to their\nnoninteracting values. Evaluating and using the model parameters for the\nrespective experiments describes quantitatively the presence or absence of\ndamping."
    },
    {
        "anchor": "Use of two-body correlated basis functions with van der Waals\n  interaction to study the shape-independent approximation for a large number\n  of trapped interacting bosons: We study the ground state and the low-lying excitations of a trapped Bose gas\nin an isotropic harmonic potential for very small ($\\sim 3$) to very large\n($\\sim 10^7$) particle numbers. We use the correlated two-body basis functions\nand the shape-dependent van der Waals interaction in our many-body\ncalculations. We present an exhaustive study of the effect of inter-atomic\ncorrelations and the accuracy of the mean-field equations considering a wide\nrange of particle numbers. We calculate the ground state energy and the\none-body density for different values of the van der Waals parameter $C_{6}$.\nWe compare our results with those of the modified Gross-Pitaevskii results, the\ncorrelated Hartree hypernetted-chain equations (which also utilize the two-body\ncorrelated basis functions), as well as of the Diffusion Monte Carlo for hard\nsphere interactions. We observe the effect of the attractive tail of the van\nder Waals potential in the calculations of the one-body density over the truly\nrepulsive zero-range potential as used in the Gross-Pitaevskii equation and\ndiscuss the finite-size effects. We also present the low-lying collective\nexcitations which are well described by a hydrodynamic model in the large\nparticle limit.",
        "positive": "Phantom energy in the nonlinear response of a quantum many-body scar\n  state: Quantum many-body scars are notable as nonthermal states that exist at high\nenergies. Here, we use attractively interacting dysprosium gases to create scar\nstates that are stable enough be driven into a strongly nonlinear regime while\nretaining their character. We uncover an emergent nonlinear many-body\nphenomenon, the effective transmutation of attractive interactions into\nrepulsive interactions. We measure how the kinetic and total energies evolve\nafter quenching the confining potential. Although the bare interactions are\nattractive, the low-energy degrees of freedom evolve as if they repel each\nother: Thus, their kinetic energy paradoxically decreases as the gas is\ncompressed. The missing ``phantom'' energy is quantified by benchmarking our\nexperimental results against generalized hydrodynamics calculations. We present\nevidence that the missing kinetic energy is stored in very high-momentum modes."
    },
    {
        "anchor": "Vortex Tiling in a Spin-2 Spinor Bose-Einstein Condensate: We point out that the internal spin symmetry of the order parameter manifests\nitself at the core of a fractional vortex in real space without spin-orbit\ncoupling. Such symmetry breaking arises from a topological constraint and the\ncommensurability between spin symmetries of the order parameters inside and\noutside the core. Our prediction can be applied to probe the cyclic order\nparameter in a rotating spin-2 $^{87}$Rb condensate as a non-circular vortex\ncore in a biaxial nematic state.",
        "positive": "Superfluidity of identical fermions in an optical lattice: atoms and\n  polar molecules: In this work, we discuss the emergence of $p$-wave superfluids of identical\nfermions in 2D lattices. The optical lattice potential manifests itself in an\ninterplay between an increase in the density of states on the Fermi surface and\nthe modification of the fermion-fermion interaction (scattering) amplitude. The\ndensity of states is enhanced due to an increase of the effective mass of\natoms. In deep lattices, for short-range interacting atoms, the scattering\namplitude is strongly reduced compared to free space due to a small overlap of\nwavefunctions of fermions sitting in the neighboring lattice sites, which\nsuppresses the $p$-wave superfluidity. However, we show that for a moderate\nlattice depth there is still a possibility to create atomic $p$-wave\nsuperfluids with sizable transition temperatures. The situation is drastically\ndifferent for fermionic polar molecules. Being dressed with a microwave field,\nthey acquire a dipole-dipole attractive tail in the interaction potential.\nThen, due to a long-range character of the dipole-dipole interaction, the\neffect of the suppression of the scattering amplitude in 2D lattices is absent.\nThis leads to the emergence of a stable topological $p_x+ip_y$ superfluid of\nidentical microwave-dressed polar molecules."
    },
    {
        "anchor": "Beyond-mean-field corrections for dipolar bosons in an optical lattice: Recent experiments with ultracold lanthanide atoms which are characterized by\na large magnetic moment have revealed the crucial importance of\nbeyond-mean-field corrections in understanding the dynamics of the gas. We\nstudy how the presence of an external optical lattice modifies the structure of\nthe corrections. We find that deep in the superfluid regime the equation of\nstate is well described by introducing an anisotropic effective mass. However,\nfor a deep lattice we find terms with anomalous density dependence which do not\narise in free space. For a one-dimensional lattice, the relative orientation of\nthe dipole axis with respect to the lattice plays a crucial role and the\nbeyond-mean-field corrections can be either enhanced or suppressed.",
        "positive": "Variational determination of approximate bright matter-wave soliton\n  solutions in anisotropic traps: We consider the ground state of an attractively-interacting atomic\nBose-Einstein condensate in a prolate, cylindrically symmetric harmonic trap.\nIf a true quasi-one-dimensional limit is realized, then for sufficiently weak\naxial trapping this ground state takes the form of a bright soliton solution of\nthe nonlinear Schroedinger equation. Using analytic variational and highly\naccurate numerical solutions of the Gross-Pitaevskii equation we systematically\nand quantitatively assess how soliton-like this ground state is, over a wide\nrange of trap and interaction strengths. Our analysis reveals that the regime\nin which the ground state is highly soliton-like is significantly restricted,\nand occurs only for experimentally challenging trap anisotropies. This result,\nand our broader identification of regimes in which the ground state is\nwell-approximated by our simple analytic variational solution, are relevant to\na range of potential experiments involving attractively-interacting\nBose-Einstein condensates."
    },
    {
        "anchor": "Enhanced visibility of the Fulde-Ferrell-Larkin-Ovchinnikov state in one\n  dimensional Bose-Fermi mixtures near the immiscibility point: Based on the matrix product states method, we investigate numerically the\nground state properties of one-dimensional mixtures of repulsive bosons and\nspin-imbalanced attractive fermions, the latter being in the\nFulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, where Cooper pairs condense at a\nfinite momentum $k=k_{FFLO}$. We find that the visibility of such a state is\ndramatically enhanced as the repulsive Bose-Fermi mixture is brought close to\nthe phase-separation point. In particular, large amplitude self-induced\noscillations with wave-vector $2k_{FFLO}$ appear in both the fermion total\ndensity and the boson density profiles, leaving sharp fingerprints in the\ncorresponding static structure factors. We show that these features remain well\nvisible in cold atoms systems trapped longitudinally by a smooth flat-bottom\npotential. Hence bosons can be used to directly reveal the modulated Fermi\nsuperfluid in experiments.",
        "positive": "Symmetry breaking in dipolar matter-wave solitons in dual-core couplers: We study effects of the spontaneous symmetry-breaking (SSB) in solitons built\nof the dipolar Bose-Einstein condensate (BEC), trapped in a dual-core system\nwith the dipole-dipole interactions (DDIs) and hopping between the cores. Two\nrealizations of such a matter-wave coupler are introduced, weakly- and\nstrongly-coupled. The former one in based on two parallel pipe-shaped traps,\nwhile the latter one is represented by a single pipe sliced by an external\nfield into parallel layers. The dipoles are oriented along axes of the pipes.\nIn these systems, the dual-core solitons feature the SSB of the supercritical\ntype and subcritical types, respectively. Stability regions are identified for\nsymmetric and asymmetric solitons, and, in addition, for non-bifurcating\nantisymmetric ones, as well as for symmetric flat states, which may also be\nstable in the strongly-coupled system, due to competition between the\nattractive and repulsive intra- and inter-core DDIs. Effects of the contact\ninteractions are considered too. Collisions between moving asymmetric solitons\nin the weakly-symmetric system feature elastic rebound, merger into a single\nbreather, and passage accompanied by excitation of intrinsic vibrations of the\nsolitons, for small, intermediate, and large collision velocities,\nrespectively. A PT-symmetric version of the weakly-coupled system is briefly\nconsidered too, which may be relevant for matter-wave lasers. Stability\nboundaries for PT-symmetric and antisymmetric solitons are identified."
    },
    {
        "anchor": "Investigating Dirty Crossover through Fidelity Susceptibility and\n  Density of States: We investigate the BCS-BEC crossover in an ultracold atomic gas in the\npresence of disorder. The disorder is incorporated in the mean-field formalism\nthrough Gaussian fluctuations. We observe evolution to an asymmetric line-shape\nof fidelity susceptibility as a function of interaction coupling with\nincreasing disorder strength which may point to an impending quantum phase\ntransition. The asymmetric line-shape is further analyzed using the statistical\ntools of skewness and kurtosis. We extend our analysis to density of states\n(DOS) for a better understanding of the crossover in the disordered\nenvironment.",
        "positive": "An Aharonov-Bohm interferometer for determining Bloch band topology: The geometric structure of an energy band in a solid is fundamental for a\nwide range of many-body phenomena in condensed matter and is uniquely\ncharacterized by the distribution of Berry curvature over the Brillouin zone.\nIn analogy to an Aharonov-Bohm interferometer that measures the magnetic flux\npenetrating a given area in real space, we realize an atomic interferometer to\nmeasure Berry flux in momentum space. We demonstrate the interferometer for a\ngraphene-type hexagonal lattice, where it has allowed us to directly detect the\nsingular $\\pi$ Berry flux localized at each Dirac point. We show that the\ninterferometer enables one to determine the distribution of Berry curvature\nwith high momentum resolution. Our work forms the basis for a general framework\nto fully characterize topological band structures and can also facilitate\nholonomic quantum computing through controlled exploitation of the geometry of\nHilbert space."
    },
    {
        "anchor": "Simultaneous Readout of Noncommuting Collective Spin Observables beyond\n  the Standard Quantum Limit: We augment the information extractable from a single absorption image of a\nspinor Bose-Einstein condensate by coupling to initially empty auxiliary\nhyperfine states. Performing unitary transformations in both, the original and\nauxiliary hyperfine manifold, enables the simultaneous measurement of multiple\nspin-1 observables. We apply this scheme to an elongated atomic cloud of $\n^{87} $Rb to simultaneously read out three orthogonal spin directions and with\nthat directly access the spatial spin structure. The readout even allows the\nextraction of quantum correlations which we demonstrate by detecting spin\nnematic squeezing without state tomography.",
        "positive": "Equilibration of a finite temperature binary Bose gas formed by\n  population transfer: We consider an equilibrium single-species homogeneous Bose gas from which a\nproportion of the atoms are instantaneously and coherently transferred to a\nsecond species, thereby forming a binary Bose gas in a non-equilibrium initial\nstate. We study the ensuing evolution towards a new equilibrium, mapping the\ndynamics and final equilibrium state out as a function of the population\ntransfer and the interspecies interactions by means of classical field methods.\nWhile in certain regimes, the condensate fractions are largely unaffected by\nthe population transfer process, in others, particularly for immiscible\ninteractions, one or both condensate fractions are vastly reduced to a new\nequilibrium value."
    },
    {
        "anchor": "On the direct diagonalization method for a few particles trapped in\n  harmonic potentials: We describe a procedure to systematically improve direct diagonalization\nresults for few-particle systems trapped in one-dimensional harmonic potentials\ninteracting by contact interactions. We start from the two-body problem to\ndefine a renormalization method for the interparticle interactions. The\nprocedure is benchmarked with state-of-the-art numerical results for three and\nfour symmetric fermions.",
        "positive": "Tensor-network study of correlation-spreading dynamics in the\n  two-dimensional Bose-Hubbard model: Recent developments in analog quantum simulators based on cold atoms and\ntrapped ions call for cross-validating the accuracy of quantum-simulation\nexperiments with use of quantitative numerical methods; however, it is\nparticularly challenging for dynamics of systems with more than one spatial\ndimension. Here we demonstrate that a tensor-network method running on\nclassical computers is useful for this purpose. We specifically analyze\nreal-time dynamics of the two-dimensional Bose-Hubbard model after a sudden\nquench starting from the Mott insulator by means of the tensor-network method\nbased on infinite projected entangled pair states. Calculated single-particle\ncorrelation functions are found to be in good agreement with a recent\nexperiment. By estimating the phase and group velocities from the\nsingle-particle and density-density correlation functions, we predict how these\nvelocities vary in the moderate interaction region, which serves as a\nquantitative benchmark for future experiments and numerical simulations."
    },
    {
        "anchor": "Enhancing sensitivity to rotations with quantum solitonic currents: Quantum mechanics is characterized by quantum coherence and entanglement.\nAfter having discovered how these fundamental concepts govern physical reality,\nscientists have been devoting intense efforts to harness them to shape future\nscience and technology. This is a highly nontrivial task because most often\nquantum coherence and entanglement are difficult to access. Here, we\ndemonstrate the enhancement of the sensitivity of a quantum many-body system\nwith specific coherence and entanglement properties. Our physical system is\nmade of strongly correlated attracting neutral bosons flowing in a ring-shaped\npotential of mesoscopic size. Because of attractive interactions, quantum\nanalogs of bright solitons are formed. As a genuine quantum-many-body feature,\nwe demonstrate that angular momentum fractionalization occurs. As a\nconsequence, the matter-wave current in our system can react to very small\nchanges of rotation or other artificial gauge fields. We work out a protocol to\nentangle such quantum solitonic currents, allowing them to operate rotation\nsensors and gyroscopes to Heisenberg-limited sensitivity.",
        "positive": "Two-Dimensional Homogeneous Fermi Gases: We report on the experimental realization of homogeneous two-dimensional (2D)\nFermi gases trapped in a box potential. In contrast to harmonically trapped\ngases, these homogeneous 2D systems are ideally suited to probe local as well\nas non-local properties of strongly interacting manybody systems. As a first\nmeasurement, we use a local probe to extract the equation of state (EOS) of a\nnon-interacting Fermi gas. We then perform matter wave focusing to extract its\nmomentum distribution and directly observe Pauli blocking in a near unity\noccupation of momentum states. Finally, we measure the momentum distribution of\nstrongly interacting homogeneous 2D gases in the crossover between attractively\ninteracting fermions and deeply-bound bosonic molecules."
    },
    {
        "anchor": "Collision of one dimensional (1D) spin polarized Fermi gases in an\n  optical lattice: In this work we analyze the dynamical behavior of the collision between two\nclouds of fermionic atoms with opposite spin polarization. By means of the\ntime-evolving block decimation (TEBD) numerical method, we simulate the\ncollision of two one-dimensional clouds in a lattice. There is a symmetry in\nthe collision behaviour between the attractive and repulsive interactions. We\nanalyze the pair formation dynamics in the collision region, providing a\nquantitative analysis of the pair formation mechanism in terms of a simple\ntwo-site model.",
        "positive": "An experimental test of the geodesic rule proposition for the non-cyclic\n  geometric phase: The geometric phase due to the evolution of the Hamiltonian is a central\nconcept in quantum physics, and may become advantageous for quantum technology.\nIn non-cyclic evolutions, a proposition relates the geometric phase to the area\nbounded by the phase-space trajectory and the shortest geodesic connecting its\nend points. The experimental verification of this geodesic rule proposition has\nremained elusive for more than three decades. Here, we report an unambiguous\nexperimental confirmation of the geodesic rule for a non-cyclic geometric phase\nby means of a spatial SU(2) matter-wave interferometer, demonstrating, with\nhigh precision, the predicted phase sign change and pi jumps. We show the\nconnection between our results and the Pancharatnam phase. Finally, we point\nout that the geodesic rule can be applied to obtain the red-shift in general\nrelativity, enabling a completely new quantum tool to measure gravity."
    },
    {
        "anchor": "Quantum kinetics of ultracold fermions coupled to an optical resonator: We study the far-from-equilibrium statistical mechanics of periodically\ndriven fermionic atoms in a lossy optical resonator. We show that the interplay\nof the Fermi surface with cavity losses leads to sub-natural cavity linewidth\nnarrowing, squeezed light, and out-of-equilibrium quantum statistics of the\natoms. Adapting the Keldysh approach, we set-up and solve a quantum kinetic\nBoltzmann equation in a systematic $1/N$ expansion with $N$ the number of\natoms. In the strict thermodynamic limit $N,V\\rightarrow \\infty$,\n$N/V=\\text{const.}$ we find the atoms (fermions or bosons) remain immune\nagainst cavity-induced heating or cooling. At next-to-leading order in $1/N$,\nwe find a \"one-way thermalization\" of the atoms determined by cavity decay. We\nargue that, in absence of an equilibrium fluctuation-dissipation relation, the\nlong-time limit $\\Delta t \\rightarrow \\infty$ does not commute with the\nthermodynamic limit $N\\rightarrow \\infty$, such that for the physically\nrelevant case of large but finite $N$, the dynamics ultimately becomes strongly\ncoupled, especially close to the superradiance phase transition.",
        "positive": "Spectral functions of a time-periodically driven Falicov-Kimball model:\n  real-space Floquet DMFT study: We present a systematic study of spectral functions of a time-periodically\ndriven Falicov-Kimball Hamiltonian. In the high-frequency limit, this system\ncan be effectively described as a Harper-Hofstadter-Falicov-Kimball model.\nUsing real-space Floquet dynamical mean-field theory (DMFT), we take into\naccount interaction effects and contributions from higher Floquet bands in a\nnon-perturbative way. Our calculations show a high degree of similarity between\nthe interacting driven system and its effective static counterpart with respect\nto spectral properties. However, as also illustrated by our results, one should\nbear in mind that Floquet DMFT describes a non-equilibrium steady state (NESS),\nwhile an effective static Hamiltonian describes an equilibrium state. We\nfurther demonstrate the possibility of using real-space Floquet DMFT to study\nedge states on a cylinder geometry."
    },
    {
        "anchor": "Measurement of the Canonical Equation of State of a Weakly Interacting\n  3D Bose Gas: Using a multiple-image reconstruction method applied to a harmonically\ntrapped Bose gas, we determine the equation of state of uniform matter across\nthe critical transition point, within the local density approximation. Our\nexperimental results provide the canonical description of pressure as a\nfunction of the specific volume, emphasizing the dramatic deviations from the\nideal Bose gas behavior caused by interactions. They also provide clear\nevidence for the non-monotonic behavior with temperature of the chemical\npotential, which is a consequence of superfluidity. The measured thermodynamic\nquantities are compared to mean-field predictions available for the interacting\nBose gas. The limits of applicability of the local density approximation near\nthe critical point are also discussed, focusing on the behavior of the\nisothermal compressibility.",
        "positive": "Ultracold atoms in U(2) non-Abelian gauge potentials preserving the\n  Landau levels: We study ultracold atoms subjected to U(2) non-Abelian potentials: we\nconsider gauge potentials having, in the Abelian limit, degenerate Landau\nlevels and we then investigate the effect of general homogeneous non-Abelian\nterms. The conditions under which the structure of degenerate Landau levels is\npreserved are classified and discussed. The typical gauge potentials preserving\nthe Landau levels are characterized by a fictitious magnetic field and by an\neffective spin-orbit interaction, e.g. obtained through the rotation of\ntwo-dimensional atomic gases coupled with a tripod scheme. The single-particle\nenergy spectrum can be exactly determined for a class of gauge potentials,\nwhose physical implementation is explicitly discussed. The corresponding Landau\nlevels are deformed by the non-Abelian contribution of the potential and their\nspin degeneracy is split. The related deformed quantum Hall states for fermions\nand bosons (in the presence of strong intra-species interaction) are determined\nfar from and at the degeneracy points of the Landau levels. A discussion of the\neffect of the angular momentum is presented, as well as results for U(3) gauge\npotentials."
    },
    {
        "anchor": "Parametric resonance of capillary waves at the interface between two\n  immiscible Bose-Einstein condensates: We study parametric resonance of capillary waves on the interface between two\nimmiscible Bose-Einstein condensates pushed towards each other by an\noscillating force. Guided by analytical models, we solve numerically the\ncoupled Gross-Pitaevskii equations for two-component Bose-Einstein condensate\nat zero temperature. We show that, at moderate amplitudes of the driving force,\nthe instability is stabilized due to non-linear modifications of the\noscillation frequency. When the amplitude of the driving force is large enough,\nwe observe detachment of droplets from the Bose-Einstein condensates, resulting\nin generation of quantum vortices (skyrmions). We analytically investigate the\nvortex dynamics, and conditions of quantized vortex generation.",
        "positive": "Limit of Spin Squeezing in Finite Temperature Bose-Einstein Condensates: We show that, at finite temperature, the maximum spin squeezing achievable\nusing interactions in Bose-Einstein condensates has a finite limit when the\natom number $N\\to \\infty$ at fixed density and interaction strength. We\ncalculate the limit of the squeezing parameter for a spatially homogeneous\nsystem and show that it is bounded from above by the initial non-condensed\nfraction."
    },
    {
        "anchor": "Probing superfluidity of a mesoscopic Tonks-Girardeau gas: We study the dynamical response of a Tonks-Girardeau gas on a ring induced by\na moving delta-barrier potential. An exact solution based on the time-dependent\nBose-Fermi mapping allows to obtain the particle current, its fluctuations and\nthe drag force acting on the barrier. The exact solution is analyzed\nnumerically as well as analytically in the perturbative regime of weak barrier\nstrength. In the weak barrier limit the stirring drives the system into a state\nwith net zero current for velocities $v$ smaller than $v_c=\\pi\\hbar /mL$, with\n$m$ the atomic mass and $L$ the ring circumference. At $v$ approaching $v_c$\nangular momentum can be transferred to the fluid and a nonzero drag force\narises. The existence of a velocity threshold for current generation indicates\nsuperfluid-like behavior of the mesoscopic Tonks-Girardeau gas, different from\nthe non-superfluid behavior predicted for Tonks-Girardeau gas in an infinite\ntube.",
        "positive": "A two-dimensional quantum gas in a magnetic trap: We present the first experimental realization of a two-dimensional quantum\ngas in a purely magnetic trap dressed by a radio frequency field in the\npresence of gravity. The resulting potential is extremely smooth and very close\nto harmonic in the two-dimensional plane of confinement. We fully characterize\nthe trap and demonstrate the confinement of a quantum gas to two dimensions.\nThe trap geometry can be modified to a large extent, in particular in a\ndynamical way. Taking advantage of this possibility, we study the monopole and\nthe quadrupole modes of a two-dimensional Bose gas."
    },
    {
        "anchor": "Landau critical velocity in weakly interacting Bose gases: The flow of a uniform Bose gas at speeds greater than the Landau critical\nvelocity, v_c, does not necessarily destroy superfluidity, but rather need only\nlead to a decrease of the superfluid mass density, {\\rho}_s. Analyzing a weakly\ninteracting Bose gas with a finite range interparticle interaction that leads\nto a Landau critical velocity at non-zero quasiparticle momentum, we explicitly\nconstruct the (non-uniform) condensate for fluid flow faster than v_c and\ncalculate the accompanying decrease in {\\rho}_s. We briefly comment on the\nrelation of the physics to other problems in superfluids, e.g., solitons, and\nvortices in Bose-Einstein condensates, and critical currents in\nsuperconductors.",
        "positive": "Critical temperature of a Bose gas in an optical lattice: We present theory for the critical temperature of a Bose gas in a combined\nharmonic lattice potential based on a mean-field description of the system. We\ndevelop practical expressions for the ideal-gas critical temperature, and\ncorrections due to interactions, the finite-size effect, and the occupation of\nexcited bands. We compare our expressions to numerical calculations and find\nexcellent agreement over a wide parameter regime."
    },
    {
        "anchor": "Solvable Model of a Generic Trapped Mixture of Interacting Bosons:\n  Many-Body and Mean-Field Properties at the Infinite-Particle Limit: A solvable model of a generic trapped bosonic mixture, $N_1$ bosons of mass\n$m_1$ and $N_2$ bosons of mass $m_2$ trapped in an harmonic potential of\nfrequency $\\omega$ and interacting by harmonic inter-particle interactions of\nstrengths $\\lambda_1$, $\\lambda_2$, and $\\lambda_{12}$, is discussed. It has\nrecently been shown for the ground state [J. Phys. A {\\bf 50}, 295002 (2017)]\nthat in the infinite-particle limit, when the interaction parameters\n$\\lambda_1(N_1-1)$, $\\lambda_2(N_2-1)$, $\\lambda_{12}N_1$, $\\lambda_{12}N_2$\nare held fixed, each of the species is $100\\%$ condensed and its density per\nparticle as well as the total energy per particle are given by the solution of\nthe coupled Gross-Pitaevskii equations of the mixture. In the present work we\ninvestigate properties of the trapped generic mixture at the infinite-particle\nlimit, and find differences between the many-body and mean-field descriptions\nof the mixture, despite each species being $100\\%$. We compute analytically and\nanalyze, both for the mixture and for each species, the center-of-mass position\nand momentum variances, their uncertainty product, the angular-momentum\nvariance, as well as the overlap of the exact and Gross-Pitaevskii\nwavefunctions of the mixture. The results obtained in this work can be\nconsidered as a step forward in characterizing how important are many-body\neffects in a fully condensed trapped bosonic mixture at the infinite-particle\nlimit.",
        "positive": "2D dilute Bose mixture at low temperatures: The thermodynamic and superfluid properties of the dilute two-dimensional\nbinary Bose mixture at low temperatures are discussed. We also considered the\nproblem of the emergence of the long-range order in these systems. All\ncalculations are performed by means of celebrated Popov's path-integral\napproach for the Bose gas with a short-range interparticle potential."
    },
    {
        "anchor": "Controlling Dipolar Exchange Interactions in a Dense 3D Array of Large\n  Spin Fermions: Dipolar interactions are ubiquitous in nature and rule the behavior of a\nbroad range of systems spanning from energy transfer in biological systems to\nquantum magnetism. Here, we study magnetization-conserving dipolar induced\nspin-exchange dynamics in dense arrays of fermionic erbium atoms confined in a\ndeep three-dimensional lattice. Harnessing the special atomic properties of\nerbium, we demonstrate control over the spin dynamics by tuning the dipole\norientation and changing the initial spin state within the large 20 spin\nhyperfine manifold. Furthermore, we demonstrate the capability to quickly turn\non and off the dipolar exchange dynamics via optical control. The experimental\nobservations are in excellent quantitative agreement with numerical\ncalculations based on discrete phase-space methods, which capture entanglement\nand beyond-mean field effects. Our experiment sets the stage for future\nexplorations of rich magnetic behaviors in long-range interacting dipoles,\nincluding exotic phases of matter and applications for quantum information\nprocessing.",
        "positive": "Competing order in two-band Bose-Hubbard chains with extended-range\n  interactions: Motivated by the recent progress in realizing and controlling extended\nBose-Hubbard systems using excitonic or atomic devices, the present Letter\ntheoretically investigates the case of a two-band Bose-Hubbard chain with\nnearest-neighbor interactions. Specifically, this study concentrates on the\nscenario where, due to the interactions, one band supports a density wave\nphase, i.e. a correlated insulating phase with spontaneous breaking of\ntranslational symmetry in the lattice, while the other band supports superfluid\nbehavior. Using the density matrix renormalization group method, we show that\nsupersolid order can emerge from such a combination, that is, an elusive\nquantum state that combines crystalline order with long-range phase coherence.\nDepending on the filling of the bands and the interband interaction strength,\nthe supersolid phase competes with phase-separation, superfluid order, or Mott\ninsulating density-wave order. As a possible setup to observe supersolidity, we\npropose the combination of a lower band supporting density-wave order and a\nthermally excited band that supports superfluidity due to weaker lattice\nconfinement."
    },
    {
        "anchor": "Spin Localization of a Fermi Polaron in a Quasirandom Optical Lattice: Recently, the topics of many-body localization (MBL) and one-dimensional\nstrongly interacting few-body systems have received a lot of interest. These\ntwo topics have been largely developed separately. However, the generality of\nthe latter as far as external potentials are concerned -- including random and\nquasirandom potentials -- and their shared spatial dimensionality, makes it an\ninteresting way of dealing with MBL in the strongly interacting regime.\nUtilising tools developed for few-body systems we look to gain insight into the\nlocalization properties of the spin in a Fermi gas with strong interactions. We\nobserve a delocalized--localized transition over a range of fillings of a\nquasirandom lattice. We find this transition to be of a different nature for\nlow and high fillings, due to the diluteness of the system for low fillings.",
        "positive": "Enhancement of condensate depletion due to spin-orbit coupling: We show that spin-orbit coupling (SOC) significantly enhances the depletion\nof a homogeneous Bose-Einstein condensate in three dimensions. With decreasing\nanisotropy of the SOC, both the quantum and thermal depletion increase. In\nparticular, different types of SOC give rise to qualitatively different\ndependences of the condensate depletion on microscopic variables including the\nscattering length, the strength of the SOC, and the temperature, which can be\ndirectly observed once these types of SOC are realized in experiments.\nMoreover, we point out that thermal depletion in three dimensions becomes\nlogarithmically divergent at any given finite temperature when both the SOC and\nthe interaction approach the isotropic limit."
    },
    {
        "anchor": "Tailoring flat bands and topological phases in a multi-strand Creutz\n  network: We prove that, a suitable correlation between the system parameters can\ntrigger topological phase transition and flat bands in a multi strand Creutz\nladder network, when a staggered second neighbor interaction is included along\nthe x axis. An appropriate change of basis maps such a finite N strand mesh\ninto N or N 1 decoupled Su Schrieffer Heeger chains, depending onNeven or odd.\nA simple intuitive method, using a real space decimation scheme turns out to be\nvery powerful in analytically extracting the flat bands, explaining their\ndegeneracy or a lifting of the same. Our results are analytically exact, and\nmay inspire experiments in photonics and ultracold atomic systems.",
        "positive": "Non-Bloch topological invariants in a non-Hermitian domain-wall system: We study non-Bloch bulk-boundary correspondence in a non-Hermitian\nSu-Schieffer-Heeger model in a domain-wall configuration where the left and\nright bulks have different parameters. Focusing on the case where chiral\nsymmetry is still conserved, we show that non-Hermitian skin effects of bulk\nstates persist in the system, while the definition of the non-Bloch winding\nnumber of either bulk depends on parameters on both sides of the boundary.\nUnder these redefined non-Bloch topological invariants, we confirm non-Bloch\nbulk-boundary correspondence under the domain-wall configuration, which\nexemplifies the impact of boundary conditions in non-Hermitian topological\nsystems."
    },
    {
        "anchor": "Generalized Crossover in Interacting Fermions within the Low-Energy\n  Expansion: We generalize the Bardeen-Cooper-Schrieffer-Bose-Einstein-condensation\n(BCS-BEC) crossover of two-component fermions, which is realized by tuning the\n$s$-wave scattering length $a$ between the fermions, to the case of an\narbitrary effective range $r_{\\rm e}$. By using the Nozi\\`{e}res-Schmitt-Rink\n(NSR) approach, we show another crossover by changing $r_{\\rm e}$ and present\nseveral similarities and differences between these two crossovers. Furthermore,\nthe region ($r_{\\rm e}>a/2$) where the effective range expansion breaks down\nand the Hamiltonian becomes non-Hermitian is found, being consistent with the\nWigner's causality bound. Our results are universal for low-density interacting\nfermions with low-energy constants $a$ and $r_{\\rm e}$ and are directly\nrelevant to ultracold Fermi atomic gases as well as dilute neutron matter.",
        "positive": "Stable multi-ring and rotating solitons in two-dimensional spin-orbit\n  coupled Bose-Einstein condensates with a radially-periodic potential: We consider two-dimensional spin-orbit coupled atomic Bose-Einstein\ncondensate in a radially-periodic potential. The system supports different\ntypes of stable self-sustained states including radially-symmetric\nvorticity-carrying modes with different topological charges in two spinor\ncomponents that may have multiring profiles and at the same time remain\nremarkably stable for repulsive interactions. Solitons of the second type show\npersistent rotation with constant angular frequency. They can be stable for\nboth repulsive and attractive interatomic interactions. Due to inequivalence\nbetween clockwise and counterclockwise rotation directions introduced by\nspin-orbit coupling, the properties of such solitons strongly differ for\npositive and negative rotation frequencies. Collision of solitons located in\nthe same or different rings is accompanied by change of the rotation frequency\nthat depends on the phase difference between colliding solitons."
    },
    {
        "anchor": "Nonequilibrium Thermo Field Dynamics Using 4x4-Matrix Transformation for\n  System with Bose--Einstein Condensation: This study aims to construct a theoretical formulation of a nonequilibrium\nprocess for a system of Bose--Einstein condensate associated with a spontaneous\nsymmetry breakdown. For this, Thermo Field Dynamics is used. We then describe\nthe most general forms of a 4x4 transformation and an unperturbed Hamiltonian.\nAfter calculating the $4\\times 4$ self-energy and identifying its on-shell, we\nimpose the renormalization condition in which the entire on-shell self-energy\nshould vanish. This condition provides a sufficient number of independent\nequations to determine all of the parameters in an unperturbed Hamiltonian,\namong which the quantum transport equations for normal and anomalous number\ndistributions are included.",
        "positive": "Lattice bosons in a quasi-disordered environment: In this paper, we study non-interacting bosons in a disordered\none-dimensional optical lattice in a harmonic potential. We consider the case\nof deterministic disorder produced by an Aubry-Andr\\'{e} potential. Using exact\ndiagonalization, we investigate both the zero temperature and the finite\ntemperature properties. We investigate the localization properties by using an\nentanglement measure. We find that the extreme sensitivity of the localization\nproperties to the number of lattice sites in finite size closed chains\ndisappear in open chains. This feature continues to be present in the presence\nof a harmonic confining potential. The disorder is found to strongly reduce the\nBose-Einstein condensation temperature and the condensate fraction in open\nchains. The low temperature thermal depletion rate of the condensate fraction\nincreases considerably with increasing disorder strength. We also find that the\ncritical disorder strength required for localization increases with increasing\nstrength of the harmonic potential. Further, we find that the low temperature\ncondensate fraction undergoes a sharp drop to 0.5 in the localization\ntransition region. The temperature dependence of the specific heat is found to\nbe only marginally affected by the disorder."
    },
    {
        "anchor": "Dynamics of a Quantum Phase Transition and Relaxation to a Steady State: We review recent theoretical work on two closely related issues: excitation\nof an isolated quantum condensed matter system driven adiabatically across a\ncontinuous quantum phase transition or a gapless phase, and apparent relaxation\nof an excited system after a sudden quench of a parameter in its Hamiltonian.\nAccordingly the review is divided into two parts. The first part revolves\naround a quantum version of the Kibble-Zurek mechanism including also phenomena\nthat go beyond this simple paradigm. What they have in common is that\nexcitation of a gapless many-body system scales with a power of the driving\nrate. The second part attempts a systematic presentation of recent results and\nconjectures on apparent relaxation of a pure state of an isolated quantum\nmany-body system after its excitation by a sudden quench. This research is\nmotivated in part by recent experimental developments in the physics of\nultracold atoms with potential applications in the adiabatic quantum state\npreparation and quantum computation.",
        "positive": "Dynamic and Energetic Stabilization of Persistent Currents in\n  Bose-Einstein Condensates: We study conditions under which vortices in a highly oblate harmonically\ntrapped Bose-Einstein condensate (BEC) can be stabilized due to pinning by a\nblue-detuned Gaussian laser beam, with particular emphasis on the potentially\ndestabilizing effects of laser beam positioning within the BEC. Our approach\ninvolves theoretical and numerical exploration of dynamically and energetically\nstable pinning of vortices with winding number up to $S=6$, in correspondence\nwith experimental observations. Stable pinning is quantified theoretically via\nBogoliubov-de Gennes excitation spectrum computations and confirmed via direct\nnumerical simulations for a range of conditions similar to those of\nexperimental observations. The theoretical and numerical results indicate that\nthe pinned winding number, or equivalently the winding number of the superfluid\ncurrent about the laser beam, decays as a laser beam of fixed intensity moves\naway from the BEC center. Our theoretical analysis helps explain previous\nexperimental observations, and helps define limits of stable vortex pinning for\nfuture experiments involving vortex manipulation by laser beams."
    },
    {
        "anchor": "Symmetry breaking in binary Bose-Einstein condensates in the presence of\n  an inhomogeneous artificial gauge field: We study a two component Bose-Einstein condensate in the presence of an\ninhomogeneous artificial gauge field. In response to this field, the condensate\nforms a localised vortex lattice structure that leads to a non-trivial symmetry\nbreaking in the phase separated regime. The underlying physical mechanism can\nbe understood by considering the energy landscape and we present a simplified\nmodel that is capable of reproducing the main features of the phase separation\ntransition. The intuition gained by numerically solving this simplified model\nis then corroborated using the analytical Thomas-Fermi model.",
        "positive": "Universality in Three- and Four-Body Bound States of Ultracold Atoms: Under certain circumstances, three or more interacting particles may form\nbound states. While the general few-body problem is not analytically solvable,\nthe so-called Efimov trimers appear for a system of three particles with\nresonant two-body interactions. The binding energies of these trimers are\npredicted to be universally connected to each other, independent of the\nmicroscopic details of the interaction. By exploiting a Feshbach resonance to\nwidely tune the interactions between trapped ultracold lithium atoms, we find\nevidence for two universally connected Efimov trimers and their associated\nfour-body bound states. A total of eleven precisely determined three- and\nfour-body features are found in the inelastic loss spectrum. Their relative\nlocations on either side of the resonance agree well with universal theory,\nwhile a systematic deviation from universality is found when comparing features\nacross the resonance."
    },
    {
        "anchor": "Probing the roton excitation spectrum of a stable dipolar Bose gas: We measure the excitation spectrum of a stable dipolar Bose--Einstein\ncondensate over a wide momentum-range via Bragg spectroscopy. We precisely\ncontrol the relative strength, $\\epsilon_{\\rm dd}$, of the dipolar to the\ncontact interactions and observe that the spectrum increasingly deviates from\nthe linear phononic behavior for increasing $\\epsilon_{\\rm dd}$. Reaching the\ndipolar dominated regime $\\epsilon_{\\rm dd}>1$, we observe the emergence of a\nroton minimum in the spectrum and its softening towards instability. We\ncharacterize how the excitation energy and the strength of the density-density\ncorrelations at the roton momentum vary with $\\epsilon_{\\rm dd}$. Our findings\nare in excellent agreement with numerical calculations based on mean-field\nBogoliubov theory. When including beyond-mean-field corrections, in the form of\na Lee-Huang-Yang potential, we observe a quantitative deviation from the\nexperiment, questioning the validity of such a description in the roton regime.",
        "positive": "Frustrated quantum antiferromagnetism with ultracold bosons in a\n  triangular lattice: We propose to realize the anisotropic triangular-lattice Bose-Hubbard model\nwith positive tunneling matrix elements by using ultracold atoms in an optical\nlattice dressed by a fast lattice oscillation. This model exhibits frustrated\nantiferromagnetism at experimentally feasible temperatures; it interpolates\nbetween a classical rotor model for weak interaction, and a quantum spin-1/2\n$XY$-model in the limit of hard-core bosons. This allows to explore\nexperimentally gapped spin liquid phases predicted recently [Schmied et al.,\nNew J. Phys. {\\bf 10}, 045017 (2008)]."
    },
    {
        "anchor": "Investigation of Feshbach Resonances in ultra-cold 40 K spin mixtures: Magnetically-tunable Feshbach resonances are an indispensable tool for\nexperiments with atomic quantum gases. We report on twenty thus far unpublished\nFeshbach resonances and twenty one further probable Feshbach resonances in spin\nmixtures of ultracold fermionic 40 K with temperatures well below 100 nK. In\nparticular, we locate a broad resonance at B=389.6 G with a magnetic width of\n26.4 G. Here 1 G=10^-4 T. Furthermore, by exciting low-energy spin waves, we\ndemonstrate a novel means to precisely determine the zero crossing of the\nscattering length for this broad Feshbach resonance. Our findings allow for\nfurther tunability in experiments with ultracold 40 K quantum gases.",
        "positive": "Universal description of three two-component fermions: A quantum mechanical three-body problem for two identical fermions of mass\n$m$ and a distinct particle of mass $m_1$ in the universal limit of zero-range\ntwo-body interaction is studied. For the unambiguous formulation of the problem\nin the interval $\\mu_r < m/m_1 \\le \\mu_c$ ($\\mu_r \\approx 8.619$ and $\\mu_c\n\\approx 13.607$) an additional parameter $b$ determining the wave function near\nthe triple-collision point is introduced; thus, a one-parameter family of\nself-adjoint Hamiltonians is defined. The dependence of the bound-state\nenergies on $m/m_1$ and $b$ in the sector of angular momentum and parity $L^P =\n1^-$ is calculated and analysed with the aid of a simple model."
    },
    {
        "anchor": "Density Waves in Layered Systems with Fermionic Polar Molecules: A layered system of two-dimensional planes containing fermionic polar\nmolecules can potentially realize a number of exotic quantum many-body states.\nAmong the predictions, are density-wave instabilities driven by the anisotropic\npart of the dipole-dipole interaction in a single layer. However, in typical\nmultilayer setups it is reasonable to expect that the onset and properties of a\ndensity-wave are modified by adjacent layers. Here we show that this is indeed\nthe case. For multiple layers the critical strength for the density-wave\ninstability decreases with the number of layers. The effect depends on density\nand is more pronounced in the low density regime. The lowest solution of the\ninstability corresponds to the density waves in the different layers being\nin-phase, whereas higher solutions have one or several adjancet layers that are\nout of phase. The parameter regime needed to explore this instability is within\nreach of current experiments.",
        "positive": "Regular and chaotic dynamics of a matter-wave soliton near the atomic\n  mirror: The dynamics of the soliton in a self-attractive Bose-Einstein condensate\nunder the gravity are investigated. First, we apply the inverse scattering\nmethod, which gives rise to equation of motion for the center-of-mass\ncoordinate of the soliton. We analyze the amplitude-frequency characteristic\nfor nonlinear resonance. Applying the Krylov-Bogoliubov method for the small\nparameters the dynamics of soliton on the phase plane are considered.\nHamiltonian chaos under the action of the gravity on the Poincar\\'e map are\nstudied."
    },
    {
        "anchor": "Phase-space stochastic quantum hydrodynamics for interacting Bose gases: Hydrodynamic theories offer successful approaches that are capable of\nsimulating the otherwise difficult-to-compute dynamics of quantum many-body\nsystems. In this work we derive, within the positive-P phase-space formalism, a\nnew stochastic hydrodynamic method for the description of interacting Bose\ngases. It goes beyond existing hydrodynamic approaches, such as superfluid\nhydrodynamics or generalized hydrodynamics, in its capacity to simulate the\nfull quantum dynamics of these systems: it possesses the ability to compute\nnon-equilibrium quantum correlations, even for short-wavelength phenomena.\nUsing this description, we derive a linearized stochastic hydrodynamic scheme\nwhich is able to simulate such non-equilibrium situations for longer times than\nthe full positive-P approach, at the expense of approximating the treatment of\nquantum fluctuations, and show that this linearized scheme can be directly\nconnected with existing Bogoliubov approaches. Furthermore, we go on to\ndemonstrate the usefulness and advantages of this formalism by exploring the\ncorrelations that arise in a quantum shock wave scenario and comparing its\npredictions to other established quantum many-body approaches.",
        "positive": "Ground state of a homogeneous Bose gas of hard spheres: The ground state of a homogeneous Bose gas of hard spheres is treated in\nself-consistent mean-field theory. It is shown that this approach provides an\naccurate description of the ground state of a Bose-Einstein condensed gas for\narbitrarily strong interactions. The results are in good agreement with Monte\nCarlo numerical calculations. Since all other mean-field approximations are\nvalid only for very small gas parameters, the present self-consistent theory is\na unique mean-field approach allowing for an accurate description of Bose\nsystems at arbitrary values of the gas parameter."
    },
    {
        "anchor": "Thermography of the superfluid transition in a strongly interacting\n  Fermi gas: Heat transport is a fundamental property of all physical systems and can\nserve as a fingerprint identifying different states of matter. In a normal\nliquid a hot spot diffuses while in a superfluid heat propagates as a wave\ncalled second sound. Despite its importance for understanding quantum\nmaterials, direct imaging of heat transport is challenging, and one usually\nresorts to detecting secondary effects, such as changes in density or pressure.\nHere we establish thermography of a strongly interacting atomic Fermi gas, a\nparadigmatic system whose properties relate to strongly correlated electrons,\nnuclear matter and neutron stars. Just as the color of a glowing metal reveals\nits temperature, the radiofrequency spectrum of the interacting Fermi gas\nprovides spatially resolved thermometry with sub-nanokelvin resolution. The\nsuperfluid phase transition is directly observed as the sudden change from\nthermal diffusion to second sound propagation, and is accompanied by a peak in\nthe second sound diffusivity. The method yields the full heat and density\nresponse of the strongly interacting Fermi gas, and therefore all defining\nproperties of Landau's two-fluid hydrodynamics. Our measurements serve as a\nbenchmark for theories of transport in strongly interacting fermionic matter.",
        "positive": "Strong Coupling Effects on the Specific Heat of an Ultracold Fermi Gas\n  in the Unitarity Limit: We investigate strong-coupling corrections to the specific heat $C_V$ in the\nnormal state of an ultracold Fermi gas in the BCS-BEC crossover region. A\nrecent experiment on a $^6$Li unitary Fermi gas [M. J. H. Ku, {\\it et. al.},\nScience {\\bf 335}, 563 (2012)] shows that $C_V$ is remarkably amplified near\nthe superfluid phase transition temperature $T_{\\rm c}$, being similar to the\nwell-known $\\lambda$-structure observed in liquid $^4$He. Including pairing\nfluctuations within the framework of the strong-coupling theory developed by\nNozi\\`eres and Schmitt-Rink, we show that strong pairing fluctuations are\nsufficient to explain the anomalous behavior of $C_V$ observed in a $^6$Li\nunitary Fermi gas near $T_{\\rm c}$. We also show that there is no contribution\nfrom {\\it stable} preformed Cooper pairs to $C_V$ at the unitarity. This\nindicates that the origin of the observed anomaly is fundamentally different\nfrom the case of liquid $^{4}$He, where {\\it stable} $^4$He Bose atoms induce\nthe $\\lambda$-structure in $C_V$ near the superfluid instability. Instead, the\norigin is the suppression of the entropy $S$, near $T_{\\rm c}$, due to the\nincrease of {\\it metastable} preformed Cooper pairs. Our results indicate that\nthe specific heat is a useful quantity to study the effects of pairing\nfluctuations on the thermodynamic properties of an ultracold Fermi gas in the\nBCS-BEC crossover region."
    },
    {
        "anchor": "Finding zeros of the Riemann zeta function by periodic driving of cold\n  atoms: The Riemann hypothesis, which states that the non-trivial zeros of the\nRiemann zeta function all lie on a certain line in the complex plane, is one of\nthe most important unresolved problems in mathematics. Inspired by the\nP\\'olya-Hilbert conjecture, we propose a new approach to finding a physical\nsystem to study the Riemann zeros, which in contrast to previous examples, is\nbased on applying a time-periodic driving field. This driving allows us to\nmould the quasienergies of the system (the analogue of the eigenenergies in the\nabsence of driving), so that they are directly governed by the zeta function.\nWe further show by numerical simulations that this allows the Riemann zeros to\nbe measured in currently accessible cold atom experiments.",
        "positive": "Hysteresis in quantized vortex shedding: It is shown using numerical simulations that flow patterns around an obstacle\npotential moving in a superfluid exhibit hysteresis. In a certain velocity\nregion, there is a bistability between stationary laminar flow and periodic\nvortex shedding. The bistability exists in two and three dimensional systems."
    },
    {
        "anchor": "Achieving the Quantum Ground State of a Mechanical Oscillator using a\n  Bose-Einstein Condensate with Back-Action and Cold Damping feedback schemes: We present a detailed study to show the possibility of approaching the\nquantum ground-state of a hybrid optomechanical quantum device formed by a\nBose-Einstein condensate (BEC) confined inside a high-finesse optical cavity\nwith an oscillatory end mirror. Cooling is achieved using two experimentally\nrealizable schemes: back-action cooling and cold damping quantum feedback\ncooling. In both the schemes, we found that increasing the two body atom-atom\ninteraction brings the mechanical oscillator to its quantum ground state. It\nhas been observed that back-action cooling is more effective in the good cavity\nlimit while the cold damping cooling scheme is more relevant in the bad cavity\nlimit. It is also shown that in the cold damping scheme, the device is more\nefficient in the presence of BEC than in the absence of BEC.",
        "positive": "High-fidelity rapid ground-state loading of an ultracold gas into an\n  optical lattice: A protocol is proposed for the rapid coherent loading of a Bose-Einstein\ncondensate into the ground state of an optical lattice, without residual\nexcitation associated with the breakdown of adiabaticity. The driving potential\nrequired to assist the rapid loading is derived using the fast forward\ntechnique, and generates the ground state in any desired short time. We propose\nan experimentally feasible loading scheme using a bichromatic lattice\npotential, which approximates the fast-forward driving potential with high\nfidelity."
    },
    {
        "anchor": "Talbot effect for exciton-polaritons: We demonstrate, experimentally and theoretically, a Talbot effect for hybrid\nlight-matter waves -- exciton-polariton condensate formed in a semiconductor\nmicrocavity with embedded quantum wells. The characteristic 'Talbot carpet' is\nproduced by loading the exciton-polariton condensate into a microstructured one\ndimensional periodic array of mesa traps, which creates an array of sources for\ncoherent polariton flow in the plane of the quantum wells. The spatial\ndistribution of the Talbot fringes outside the mesas mimics the near-field\ndiffraction of a monochromatic wave on a periodic amplitude and phase grating\nwith the grating period comparable to the wavelength. Despite the lossy nature\nof the polariton system, the Talbot pattern persists for distances exceeding\nthe size of the mesas by an order of magnitude.",
        "positive": "Vortex Rings in a Trap: We present a simple Hamiltonian description of the dynamics of a quantized\nvortex ring in a trapped superfluid, compare this description with dynamical\nsimulations, and characterize the dependence of the dynamics of the shape of\nthe trap."
    },
    {
        "anchor": "Design and characterization of a quantum heat pump in a driven quantum\n  gas: We propose the implementation of a quantum heat pump with ultracold atoms. It\nis based on two periodically driven coherently coupled quantum dots using\nultracold atoms. Each dot possesses two relevant quantum states and is coupled\nto a fermionic reservoir. The working principle is based on energy-selective\ndriving-induced resonant tunneling processes, where a particle that tunnels\nfrom one dot to the other either absorbs or emits the energy quantum\n$\\hbar\\omega$ associated with the driving frequency, depending on its energy.\nWe characterize the device using Floquet theory and compare simple analytical\nestimates to numerical simulations based on the Floquet-Born-Markov formalism.\nIn particular, we show that driving-induced heating is directly linked to the\nmicromotion of the Floquet states of the system.",
        "positive": "Critical behavior of a chiral superfluid in a bipartite square lattice: We study the critical behavior of Bose-Einstein condensation in the second\nband of a bipartite optical square lattice in a renormalization group framework\nat one-loop order. Within our field theoretical representation of the system,\nwe approximate the system as a two-component Bose gas in three dimensions. We\ndemonstrate that the system is in a different universality class than the\npreviously studied condensation in a frustrated triangular lattice due to an\nadditional Umklapp scattering term, which stabilizes the chiral superfluid\norder at low temperatures. We derive the renormalization group flow of the\nsystem and show that this order persists in the low energy limit. Furthermore,\nthe renormalization flow suggests that the phase transition from the thermal\nphase to the chiral superfluid state is first order."
    },
    {
        "anchor": "Kibble-Zurek universality in a strongly interacting Fermi superfluid: Near a continuous phase transition, systems with different microscopic\norigins display universal dynamics if their underlying symmetries are\ncompatible. In a thermally quenched system, the Kibble-Zurek mechanism for the\ncreation of topological defects unveils this universality through a\ncharacteristic power-law exponent, which captures the dependence of the defect\ndensity on the quench rate. Here, we report the observation of the Kibble-Zurek\nuniversality in a strongly interacting Fermi superfluid. As the system's\nmicroscopic description is tuned from bosonic to fermionic, the quench\nformation of vortices reveals a constant scaling exponent arising from the\n$U(1)$ gauge symmetry of the system. For rapid quenches, destructive vortex\ncollisions lead to the saturation of their densities, whose values can be\nuniversally scaled by the interaction-dependent area of the vortex cores.",
        "positive": "Self trapping in the two-dimensional Bose-Hubbard model: We study the expansion of harmonically trapped bosons in a two-dimensional\nlattice after suddenly turning off the confining potential. We show that, in\nthe presence of multiple occupancies per lattice site and strong interactions,\nthe system exhibits a clear dynamical separation into slowly and rapidly\nexpanding clouds. We discuss how this effect can be understood within a simple\npicture by invoking doublons and Bose enhancement. This picture is corroborated\nby an analysis of the momentum distribution function in the regions with slowly\nand rapidly expanding bosons."
    },
    {
        "anchor": "Ground-State Ferromagnetic Transition in Strongly Repulsive\n  One-Dimensional Fermi Gases: We prove that as a one-dimensional Fermi gas is brought across the resonance\nadiabatically from large repulsion to large attraction, the singlet ground\nstate will give way to the maximum spin state, which is the lowest energy state\namong the states accessible to the system in this process. In the presence of\ntiny symmetry breaking fields that destroy spin conservation, the singlet\nground state can evolve to the ferromagnetic state or a spin segregated state.\nWe have demonstrated these effects by exact calculations on fermion cluster\nrelevant to current experiments, and have worked out the quantum mechanical\nwavefunction that exhibits phase separation.",
        "positive": "Angular Momentum of a Bose-Einstein Condensate in a Synthetic Rotational\n  Field: By applying a position-dependent detuning to a spin-orbit-coupled Hamiltonian\nwith equal Rashba and Dresselhaus coupling, we exploit the behavior of the\nangular momentum of a harmonically trapped Bose-Einstein condensed atomic gas\nand discuss the distinctive role of its canonical and spin components. By\ndeveloping the formalism of spinor hydrodynamics we predict the precession of\nthe dipole oscillation caused by the synthetic rotational field, in analogy\nwith the precession of the Foucault pendulum, the excitation of the scissors\nmode, following the sudden switching off of the detuning, and the occurrence of\nHall-like effects. When the detuning exceeds a critical value we observe a\ntransition from a vortex free, rigidly rotating quantum gas to a gas containing\nvortices with negative circulation which results in a significant reduction of\nthe total angular momentum."
    },
    {
        "anchor": "The Dissipative Bose-Hubbard Model. Methods and Examples: Open many-body quantum systems have attracted renewed interest in the context\nof quantum information science and quantum transport with biological clusters\nand ultracold atomic gases. The physical relevance in many-particle bosonic\nsystems lies in the realization of counter-intuitive transport phenomena and\nthe stochastic preparation of highly stable and entangled many-body states due\nto engineered dissipation. We review a variety of approaches to describe an\nopen system of interacting ultracold bosons which can be modeled by a\ntight-binding Hubbard approximation. Going along with the presentation of\ntheoretical and numerical techniques, we present a series of results in diverse\nsetups, based on a master equation description of the dissipative dynamics of\nultracold bosons in a one-dimensional lattice. Next to by now standard\nnumerical methods such as the exact unravelling of the master equation by\nquantum jumps for small systems and beyond mean-field expansions for larger\nones, we present a coherent-state path integral formalism based on\nFeynman-Vernon theory applied to a many-body context.",
        "positive": "Creation and manipulation of quantized vortices in Bose-Einstein\n  condensates using reinforcement learning: We apply the technique of reinforcement learning to the control of nonlinear\nmatter waves. In this method, an agent controls the position, strength, and\nshape of an external Gaussian potential to create and manipulate quantized\nvortices in a Bose-Einstein condensate (BEC) trapped in a harmonic potential.\nThe density and velocity distributions of the BEC at each moment obtained by\nthe Gross-Pitaevskii evolution are directly input into a convolutional neural\nnetwork to determine the next action of the agent. We demonstrate that a\nstationary single-vortex state can be produced in a two-dimensional system, and\na stationary vortex-ring state can be produced in a three-dimensional system."
    },
    {
        "anchor": "Canted Antiferromagnetic Order of Imbalanced Fermi-Fermi mixtures in\n  Optical Lattices by Dynamical Mean-Field Theory: We investigate antiferromagnetic order of repulsively interacting fermionic\natoms in an optical lattice by means of Dynamical Mean-Field Theory (DMFT).\nSpecial attention is paid to the case of an imbalanced mixture. We take into\naccount the presence of an underlying harmonic trap, both in a local density\napproximation and by performing full Real-Space DMFT calculations. We consider\nthe case that the particle density in the trap center is at half filling,\nleading to an antiferromagnetic region in the center, surrounded by a Fermi\nliquid region at the edge. In the case of an imbalanced mixture, the\nantiferromagnetism is directed perpendicular to the ferromagnetic polarization\nand canted. We pay special attention to the boundary structure between the\nantiferromagnetic and the Fermi liquid phase. For the moderately strong\ninteractions considered here, no Stoner instability toward a ferromagnetic\nphase is found. Phase separation is only observed for strong imbalance and\nsufficiently large repulsion.",
        "positive": "Infrared behavior in systems with a broken continuous symmetry:\n  classical O(N) model vs interacting bosons: In systems with a spontaneously broken continuous symmetry, the perturbative\nloop expansion is plagued with infrared divergences due to the coupling between\ntransverse and longitudinal fluctuations. As a result the longitudinal\nsusceptibility diverges and the self-energy becomes singular at low energy. We\nstudy the crossover from the high-energy Gaussian regime, where perturbation\ntheory remains valid, to the low-energy Goldstone regime characterized by a\ndiverging longitudinal susceptibility. We consider both the classical linear\nO($N$) model and interacting bosons at zero temperature, using a variety of\ntechniques: perturbation theory, hydrodynamic approach (i.e., for bosons,\nPopov's theory), large-$N$ limit and non-perturbative renormalization group. We\nemphasize the essential role of the Ginzburg momentum scale $p_G$ below which\nthe perturbative approach breaks down. Even though the action of\n(non-relativistic) bosons includes a first-order time derivative term, we find\nremarkable similarities in the weak-coupling limit between the classical O($N$)\nmodel and interacting bosons at zero temperature."
    },
    {
        "anchor": "Self-oscillating pump in a topological dissipative atom-cavity system: Pumps are transport mechanisms in which direct currents result from a cyclic\nevolution of the potential. As Thouless has shown, the pumping process can have\ntopological origins, when considering the motion of quantum particles in\nspatially and temporally periodic potentials. However, the periodic evolution\nthat drives these pumps has always been assumed to be imparted from outside, as\nwas the case in the experimental systems studied so far. Here we report on an\nemergent mechanism for pumping in a quantum gas coupled to an optical\nresonator, where we observe a particle current without applying a periodic\ndrive. The pumping potential experienced by the atoms is formed by the\nself-consistent cavity field interfering with the static laser field driving\nthe atoms. Due to dissipation, the cavity field evolves between its two\nquadratures, each corresponding to a different centrosymmetric crystal\nconfiguration. This self-oscillation results in a time-periodic potential\nanalogous to that describing the transport of electrons in topological\ntight-binding models, like the paradigmatic Rice-Mele pump. In the experiment,\nwe directly follow the evolution by measuring the phase winding of the cavity\nfield with respect to the driving field and observing the atomic motion\nin-situ. The discovered mechanism combines the dynamics of topological and open\nsystems, and features characteristics of continuous dissipative time crystals.",
        "positive": "Tunneling of a few strongly repulsive hard-sphere bosons in an optical\n  lattice with tight external harmonic confinement: A quantum Monte Carlo\n  investigation in continuous space: The effect of strongly repulsive interactions on the tunneling amplitude of\nhard-sphere (HS) bosons confined in a simple cubic (sc) optical lattice plus\ntight external harmonic confinement in continuous space is investigated. The\nquantum variational Monte Carlo (VMC) and the variational path integral Monte\nCarlo (VPI) techniques are used at zero temperature. The effects of the lattice\nspacing $\\pi/k$ on the tunneling amplitude is also considered. The occupancies\nof the lattice sites as a function of the repulsion between the bosons are\nfurther revealed. Our chief result is, that for a small number of bosons (N=8)\nthe overlap of the wave functions in neighboring wells does not change with an\nincrease of the repulsive interactions and changes only minimally for a larger\nnumber of particles (N=40). The tunneling amplitude rises with a reduction in\nthe lattice spacing. In addition, the occupancy of the center of the trap\ndecreases in favor of a rise in the occupancy of the lattice sites at the edges\nof the trap with increasing HS repulsion. Further, it was found that the energy\nper particle at certain optical depths is insensitive to the number of\nparticles and variations in the HS diameter of the bosons. In order to support\nour results, we compare the VMC results with corresponding VPI results."
    },
    {
        "anchor": "Dynamics of Rapidly Rotating Bose-Einstein Quantum Droplets: This work theoretically investigates \\textcolor{black}{the stationary\nproperties} and the dynamics of the rotating quantum liquid droplets confined\nin a two-dimensional symmetric anharmonic trap. Mimicking the quantum Hall\nsystems, the modified Gross-Pitaevskii equation with the inclusion of the\nLee-Huang-Yang nonlinear interaction is analytically solved, and the role of\nthe Landau-level mixing effect is addressed. \\textcolor{black}{Via controlling\nthe nonlinear interaction and the rotation speed, the rotating quantum droplet\nwith multiply quantized vortex can be created, and the preference of the\nenergetically favored quantum states can be distinguished in the phase diagram.\nTo better interpret the underlying physics of the phase singularities, a brief\ncomparison of the rotating quantum droplet and the optical vortex is made. The\ninvestigation of the long-term evolution of the rotating quantum droplets\nconfirms the stability of the quantum states. At certain rotation speeds, the\nmulti-periodic trajectories and breathings provide evidence of the emergence of\nthe collective excitation of the surface mode in the vortex state. For quantum\ndroplets carrying multiply quantized vortex, the microscopic snapshots of the\nrotation field adjusted current density distribution show that the combined\nnonlinear interaction and the anharmonic trapping potential can provide the\nrestoring force to lead the quantum droplet to a regular and stable revolution\nand reach the dynamic equilibrium, revealing the signature of the generation of\nsuperfluids in the new kind of low-dimensional quantum liquids.",
        "positive": "Spin- and Momentum-Correlated Atom Pairs Mediated by Photon Exchange and\n  Seeded by Vacuum Fluctuations: Engineering pairs of massive particles that are simultaneously correlated in\ntheir external and internal degrees of freedom is a major challenge, yet\nessential for advancing fundamental tests of physics and quantum technologies.\nIn this Letter, we experimentally demonstrate a mechanism for generating pairs\nof atoms in well-defined spin and momentum modes. This mechanism couples atoms\nfrom a degenerate Bose gas via a superradiant photon-exchange process in an\noptical cavity, producing pairs via a single channel or two discernible\nchannels. The scheme is independent of collisional interactions, fast and\ntunable. We observe a collectively enhanced production of pairs and probe\ninterspin correlations in momentum space. We characterize the emergent pair\nstatistics and find that the observed dynamics is consistent with being\nprimarily seeded by vacuum fluctuations in the corresponding atomic modes.\nTogether with our observations of coherent many-body oscillations involving\nwell-defined momentum modes, our results offer promising prospects for\nquantum-enhanced interferometry and quantum simulation experiments using\nentangled matter waves."
    },
    {
        "anchor": "Dissipative Preparation of Antiferromagnetic Order in the Fermi-Hubbard\n  Model: The Fermi-Hubbard model is one of the key models of condensed matter physics,\nwhich holds a potential for explaining the mystery of high-temperature\nsuperconductivity. Recent progress in ultracold atoms in optical lattices has\npaved the way to studying the model's phase diagram using the tools of quantum\nsimulation, which emerged as a promising alternative to the numerical\ncalculations plagued by the infamous sign problem. However, the temperatures\nachieved using elaborate laser cooling protocols so far have been too high to\nshow the appearance of antiferromagnetic and superconducting quantum phases\ndirectly. In this work, we demonstrate that using the machinery of dissipative\nquantum state engineering, one can efficiently prepare antiferromagnetic order\nin present-day experiments with ultracold fermions. The core of the approach is\nto add incoherent laser scattering in such a way that the antiferromagnetic\nstate emerges as the dark state of the driven-dissipative dynamics. In order to\nelucidate the development of the antiferromagnetic order we employ two\ncomplementary techniques: Monte Carlo wave function simulations for small\nsystems and a recently proposed variational method for open quantum systems,\noperating in the thermodynamic limit. The controlled dissipation channels\ndescribed in this work are straightforward to add to already existing\nexperimental setups.",
        "positive": "On bifurcation of the four Liouville tori in one generalized integrable\n  model of the vortex dynamics: The article deals with a generalized mathematical model of the dynamics of\ntwo point vortices in the Bose-Einstein condensate enclosed in a harmonic trap,\nand of the dynamics of two point vortices in an ideal fluid bounded by a\ncircular region. In the case of a positive vortex pair, which is of interest\nfor physical experimental applications, a new bifurcation diagram is obtained,\nfor which the bifurcation of four tori into one is indicated. The presence of\nbifurcations of three and four tori in the integrable model of vortex dynamics\nwith positive intensities indicates a complex transition and the connection of\nbifurcation diagrams of both limit cases. Analytical results of this\npublication (the bifurcation diagram, the reduction to a system with one degree\nof freedom, the stability analysis) form the basis of computer simulation of\nabsolute dynamics of vortices in a fixed coordinate system in the case of\narbitrary values of the physical parameters of the model (the intensities, the\nvortex interaction and etc.)"
    },
    {
        "anchor": "Microscopic derivation of Hubbard parameters for cold atomic gases: We study the exact solution for two atomic particles in an optical lattice\ninteracting via a Feshbach resonance. The analysis includes the influence of\nall higher bands, as well as the proper renormalization of molecular energy in\nthe closed channel. Using an expansion in Bloch waves, we show that the problem\nreduces to a simple matrix equation, which can be solved numerically very\nefficient. This exact solution allows for the precise determination of the\nparameters in the Hubbard model and the two-particle bound state energy. We\nidentify the regime, where a single band Hubbard model fails to describe the\nscattering of the atoms as well as the bound states.",
        "positive": "Sculpting quasi one-dimensional Bose-Einstein condensate to generate\n  calibrated matter-waves: We explore theoretically how to tune the dynamics of a quasi one-dimensional\nharmonically trapped Bose-Einstein condensate (BEC) due to an additional red-\nand blue-detuned Hermite-Gaussian dimple trap (HGdT). To this end we study a\nBEC in a highly non-equilibrium state, which is not possible in a traditional\nharmonically confined trap. Our system is modeled by a time-dependent\nGross-Pitaevskii equation, which is numerically solved by the Crank-Nicolson\nmethod in both imaginary and real time. For equilibrium, we obtain a condensate\nwith two bumps/dips which are induced by the chosen TEM$_{01}$ mode for the\nred/blue-detuned HGdT, respectively. Afterwards, in time-of-flight dynamics, we\nexamine the adherence/decay of the two bumps/dips in the condensate, which are\ninduced by the still present red/blue-detuned HGdT, respectively. On the other\nhand, once the red/blue HGdT potential is switched off, shock-waves or\nbi-trains of gray/dark pair-solitons are created. During this process it is\nfound that the generation of gray/dark pair-solitons bi-trains are generic\nphenomena of collisions of moderately/fully fragmented BEC. Additionally, it\nturns out that the special shape of generated solitons in the harmonically\ntrapped BEC firmly depends upon the geometry of the HGdT."
    },
    {
        "anchor": "Geometrizing quantum dynamics of a Bose-Einstein condensate: We show that quantum dynamics of Bose-Einstein condensates in the weakly\ninteracting regime can be geometrized by a Poincar\\'e disk. Each point on such\na disk represents a thermofield double state, the overlap between which equals\nthe metric of this hyperbolic space. This approach leads to a unique geometric\ninterpretation of stable and unstable modes as closed and open trajectories on\nthe Poincar\\'e disk, respectively. The resonant modes that follow geodesics\nnaturally equate fundamental quantities including the time, the length, and the\ntemperature. Our work suggests a new geometric framework to coherently control\nquantum systems and reverse their dynamics using SU(1,1) echoes. In the\npresence of perturbations breaking the SU(1,1) symmetry, SU(1,1) echoes deliver\na new means to measure these perturbations such as the interactions between\nexcited particles.",
        "positive": "Revealing Hidden Antiferromagnetic Correlations in Doped Hubbard Chains\n  via String Correlators: Topological phases, like the celebrated Haldane phase in spin-1 chains, defy\ncharacterization through local order parameters. Instead, non-local string\norder parameters can be employed to reveal their hidden order. Similar diluted\nmagnetic correlations appear in doped one-dimensional lattice systems due to\nthe phenomenon of spin-charge separation. Here we report on the direct\nobservation of such hidden magnetic correlations via quantum gas microscopy of\nhole-doped ultracold Fermi-Hubbard chains. The measurement of non-local\nspin-density correlation functions reveals a hidden finite-range\nantiferromagnetic order, a direct consequence of spin-charge separation. Our\ntechnique demonstrates how topological order can directly be measured in\nexperiments and it can be extended to higher dimensions to study the complex\ninterplay between magnetic order and density fluctuations."
    },
    {
        "anchor": "Generalized cold-atom simulators for vacuum decay: Cold-atom analogue experiments are a promising new tool for studying\nrelativistic vacuum decay, allowing us to empirically probe early-Universe\ntheories in the laboratory. However, existing analogue proposals place\nstringent requirements on the atomic scattering lengths that are challenging to\nrealize experimentally. Here we generalize these proposals and show that any\nstable mixture between two states of a bosonic isotope can be used as a\nrelativistic analogue. This greatly expands the range of suitable experimental\nsetups, and will thus expedite efforts to study vacuum decay with cold atoms.",
        "positive": "Floquet engineering of correlated tunneling in the Bose-Hubbard model\n  with ultracold atoms: We report on the experimental implementation of tunable occupation-dependent\ntunneling in a Bose-Hubbard system of ultracold atoms via time-periodic\nmodulation of the on-site interaction energy. The tunneling rate is inferred\nfrom a time-resolved measurement of the lattice site occupation after a quantum\nquench. We demonstrate coherent control of the tunneling dynamics in the\ncorrelated many-body system, including full suppression of tunneling as\npredicted within the framework of Floquet theory. We find that the tunneling\nrate explicitly depends on the atom number difference in neighboring lattice\nsites. Our results may open up ways to realize artificial gauge fields that\nfeature density dependence with ultracold atoms."
    },
    {
        "anchor": "Detection of Spin Coherence in Cold Atoms via Faraday Rotation\n  Fluctuations: We report non-invasive detection of spin coherence in a collection of\nRaman-driven cold atoms using dispersive Faraday rotation fluctuation\nmeasurements, which opens up new possibilities of probing spin correlations in\nquantum gases and other similar systems. We demonstrate five orders of\nmagnitude enhancement of the measured signal strength than the traditional spin\nnoise spectroscopy with thermal atoms in equilibrium. Our observations are in\ngood agreement with the comprehensive theoretical modeling of the driven atoms\nat various temperatures. The extracted spin relaxation rate of cold rubidium\natoms with atom number density $\\sim$10$^9/$cm$^3$ is of the order of\n2$\\pi\\times$0.5 kHz at 150 $\\mu$K, two orders of magnitude less than $\\sim$\n2$\\pi\\times$50 kHz of a thermal atomic vapor with atom number density\n$\\sim$10$^{12}/$cm$^3$ at 373 K.",
        "positive": "Fluctuations of the order parameter of a mesoscopic Floquet condensate: We suggest that nonequilibrium Bose-Einstein condensates may occur in\ntime-periodically driven interacting Bose gases. Employing the model of a\nperiodically forced bosonic Josephson junction, we demonstrate that\nresonance-induced ground state-like many-particle Floquet states possess an\nalmost perfect degree of coherence, as corresponding to a mesoscopically\noccupied, explicitly time-dependent single-particle orbital. In marked contrast\nto the customary time-independent Bose-Einstein condensates, the order\nparameter of such systems is destroyed by violent fluctuations when the\nparticle number becomes too large, signaling the non-existence of a proper mean\nfield limit."
    },
    {
        "anchor": "Quasiperiodic and periodic extended Hatano-Nelson model: Anomalous\n  complex-real transition and non-Hermitian skin effect: We study the effect of quasiperiodic and periodic onsite potentials in a\nHatano-Nelson model with next-nearest-neighbour hopping. By considering a\nnon-reciprocal next-nearest-neighbour hopping and a quasiperiodic onsite\npotential under periodic boundary conditions, we show a breakdown of the\ntypical correspondence between the delocalization-localization and complex-real\ntransitions as a function of the potential strength. Moreover, we reveal that\nin the delocalized regime, when the potential strength increases, the\neigenstates under open boundary conditions exhibit a bidirectional\nnon-Hermitian skin effect, i.e., they tend to localize on both the edges\ninstead of localizing on either of the edges. However, when a periodic onsite\npotential is considered, the system not only exhibits a bidirectional skin\neffect but also shows a complete direction reversal of the skin effect as a\nfunction of the onsite periodic potential.",
        "positive": "Realizing the Harper model with Ultracold Atoms in a Ring Lattice: We demonstrate that all of the salient features of the Harper-Hofstadter\nmodel can be implemented with ultracold atoms trapped in a bichromatic\nring-shaped lattice. Using realistic sinusoidal lattice potentials rather than\nassume the idealized tight-binding picture, we determine the optimal conditions\nnecessary to realize the critical point where the spectrum becomes fractal, and\nidentify the nature and cause of the departures from the discrete model\npredictions. We also show that even with a commensurate ring with a few lattice\nsites, the Aubry-Andr\\'e localization transition can be realized. Localized\nstates that behave like edge states with energies that reside in the band gaps\ncan be generated by introducing a surprisingly small local perturbation within\nthe ring. Spectrum oscillation arising from complex coupling can be implemented\nby uniform rotation of the ring, but with certain significant differences that\nare explained"
    },
    {
        "anchor": "Induced supersolidity in a normal and hardcore boson mixture: It is well known that the supersolid form of matter can arise in a single\nspecies of cold bosonic atoms in an optical lattice due to long range\ninteractions. We present a scenario where a supersolid is induced in one of the\ncomponents of a mixture of two species bosonic atoms where there is no long\nrange interactions. We study a system of normal and hardcore boson mixture with\nonly the former possessing long range interactions. We consider three cases:\nthe first where the total density is commensurate and the other two where they\nare incommensurate . By suitable choices of the densities and the interaction\nstrengths of the atoms, we predict that the charge density wave and the\nsupersolid orders can be induced in the hardcore species as a result of the\ncompeting interatomic interactions.",
        "positive": "Cold Atom Quantum Simulator for Dilute Neutron Matter: The internal structure of neutron stars and the physical properties of nuclei\ndepend on the equation of state (EOS) of neutron matter. Dilute neutron matter\nis a quantum system of spin-1/2 Fermi particles interacting via s-wave\nscattering. Although a nuclear system and an ultracold atomic system have\nlength scales and energy scales that differ by several orders of magnitude,\nboth systems follow a common universal EOS considering their non-dimensional\nuniversal interaction parameters. In this study, we determine the EOS of\nneutron matter in the dilute region, where the influence of the s-wave\nscattering length is dominant but that of the effective range is small, by\nutilizing a quantum simulator of ultracold $^6$Li atoms with Feshbach\nresonance."
    },
    {
        "anchor": "Synthetic Helical Liquids with Ultracold Atoms in Optical Lattices: We discuss a platform for the synthetic realization of key physical\nproperties of helical Tomonaga Luttinger liquids (HTLLs) with ultracold\nfermionic atoms in one-dimensional optical lattices. The HTLL is a strongly\ncorrelated metallic state where spin polarization and propagation direction of\nthe itinerant particles are locked to each other. We propose an unconventional\none-dimensional Fermi-Hubbard model which, at quarter filling, resembles the\nHTLL in the long wavelength limit, as we demonstrate with a combination of\nanalytical (bosonization) and numerical (density matrix renormalization group)\nmethods. An experimentally feasible scheme is provided for the realization of\nthis model with ultracold fermionic atoms in optical lattices. Finally, we\ndiscuss how the robustness of the HTLL against back-scattering and\nimperfections, well known from its realization at the edge of two-dimensional\ntopological insulators, is reflected in the synthetic one-dimensional scenario\nproposed here.",
        "positive": "Finite-temperature trapped dipolar Bose gas: We develop a finite temperature Hartree theory for the trapped dipolar Bose\ngas. We use this theory to study thermal effects on the mechanical stability of\nthe system and density oscillating condensate states. We present results for\nthe stability phase diagram as a function of temperature and aspect ratio. In\noblate traps above the critical temperature for condensation we find that the\nHartree theory predicts significant stability enhancement over the\nsemiclassical result. Below the critical temperature we find that thermal\neffects are well described by accounting for the thermal depletion of the\ncondensate. Our results also show that density oscillating condensate states\noccur over a range of interaction strengths that broadens with increasing\ntemperature."
    },
    {
        "anchor": "The effect of anisotropic exchange interactions and short-range\n  phenomena on superfluidity in a homogeneous dipolar Fermi gas: We develop a simple numerical method that allows us to calculate the\nBardeen-Cooper-Schriefer (BCS) superfluid transition temperature (Tc) precisely\nfor any interaction potential. We apply it to a polarised, ultracold Fermi gas\nwith long-range, anisotropic, dipolar interactions and include the effects of\nanisotropic exchange interactions. We pay particular attention to the\nshort-range behaviour of dipolar gasses and re-examine current renormalisation\nmethods. In particular, we find that dimerisation of both atoms and molecules\nsignificantly hampers the formation of a superfluid. The end result is that at\nhigh density/interaction strengths, we find Tc is orders of magnitude lower\nthan previous calculations.",
        "positive": "Pair formation of hard core bosons in flat band systems: Hard core bosons in a large class of one or two dimensional flat band systems\nhave an upper critical density, below which the ground states can be described\ncompletely. At the critical density, the ground states are Wigner crystals. If\none adds a particle to the system at the critical density, the ground state and\nthe low lying multi particle states of the system can be described as a Wigner\ncrystal with an additional pair of particles. The energy band for the pair is\nseparated from the rest of the multi-particle spectrum. The proofs use a\nGerschgorin type of argument for block diagonally dominant matrices. In certain\none-dimensional or tree-like structures one can show that the pair is\nlocalised, for example in the chequerboard chain. For this one-dimensional\nsystem with periodic boundary condition the energy band for the pair is flat,\nthe pair is localised."
    },
    {
        "anchor": "Cooling and Near-equilibrium Dynamics of Atomic Gases Across the\n  Superfluid-Mott Insulator Transition: We study near-equilibrium thermodynamics of bosonic atoms in a\ntwo-dimensional optical lattice by ramping up the lattice depth to convert a\nsuperfluid into an inhomogeneous mixture of superfluid and Mott insulator.\nDetailed study of in situ density profiles shows that, first, locally adiabatic\nramps do not guarantee global thermal equilibrium. Indeed, full thermalization\nfor typical parameters only occurs for experiment times which exceed one\nsecond. Secondly, ramping non-adiabatically to the Mott insulator regime can\nresult in strong localized cooling at short times and global cooling once\nequilibrated. For an initial temperature estimated as 20 nK, we observe local\ntemperatures as low as 1.5 nK, and a final global temperature of 9 nK. Possible\ncooling mechanisms include adiabatic decompression, modification of the density\nof states near the quantum critical regime, and the Joule-Thomson effect.\n**NOTE: Following submission of arXiv:0910.1382v1, a systematic correction was\ndiscovered in the density measurement, stemming from three-body losses during\nthe imaging process. New measurements were performed, and the result is in\nsupport of the claim on the slow global dynamics. Due to the substantially\naltered methods and analysis, a new text has been posted as arXiv:1003.0855.",
        "positive": "Two-species boson mixture on a ring: A group theoretic approach to the\n  quantum dynamics of low-energy excitations: We investigate the weak excitations of a system made up of two condensates\ntrapped in a Bose-Hubbard ring and coupled by an interspecies repulsive\ninteraction. Our approach, based on the Bogoliubov approximation scheme, shows\nthat one can reduce the problem Hamiltonian to the sum of sub-Hamiltonians\n$\\hat{H}_k$, each one associated to momentum modes $\\pm k$. Each $\\hat{H}_k$ is\nthen recognized to be an element of a dynamical algebra. This uncommon and\nremarkable property allows us to present a straightforward diagonalization\nscheme, to find constants of motion, to highlight the significant microscopic\nprocesses, and to compute their time evolution. The proposed solution scheme is\napplied to a simple but still very interesting closed circuit, the trimer. The\ndynamics of low-energy excitations, corresponding to weakly-populated vortices,\nis investigated considering different choices of the initial conditions, and\nthe angular-momentum transfer between the two condensates is evidenced.\nFinally, the condition for which the spectral collapse and dynamical\ninstability are observed is derived analytically."
    },
    {
        "anchor": "Spin-1 bosons in an external magnetic field and a three body interaction\n  potential: We perform a thorough study of the effect of an external magnetic field on a\nspin-1 ultracold Bose gas via mean field approach corresponding to the both\nsigns of the spin dependent interaction. In contrast to some of the earlier\nstudies, the magnetic field in our work is included through both the hopping\nfrequencies (via Peierls coupling) and the zeeman interaction, thereby\nfacilitating an explo- ration for competition between the two. The phase\ndiagrams in the antiferromagnetic case shows that the Mott insulating (MI)\nphase with even particle occupancies is stable at low magnetic fields. At\nhigher magnetic fields, due to a competition between the hopping and the zeeman\ninteraction terms, the latter tries to destabilize the MI phase by suppressing\nthe formation of singlet pairs, while the former tends to stabilize the MI\nphase. In the ferromagnetic case, the MI lobes become more stable with\nincreasing flux strengths. Further inclusion of a three body interaction\npotential in order to ascertain its role on the phase diagram, we found that in\nabsence of the magnetic field, the MI lobes become more stable compared to the\nsuperfluid (SF) phase and the location of the transition point for the MI-SF\nphase increases with increasing the three body interaction strength. A strong\ncoupling perturbative calculation has also been done to provide a comparison\nwith our mean field phase diagrams. Lastly, with inclusion of the external\nfield, the insulating phases are found to be further stabilized by the three\nbody interaction potential.",
        "positive": "Universal Vortex Statistics and Stochastic Geometry of Bose-Einstein\n  Condensation: The cooling of a Bose gas in finite time results in the formation of a\nBose-Einstein condensate that is spontaneously proliferated with vortices. We\npropose that the vortex spatial statistics is described by a homogeneous\nPoisson point process (PPP) with a density dictated by the Kibble-Zurek\nmechanism (KZM). We validate this model using numerical simulations of the\ntwo-dimensional stochastic Gross-Pitaevskii equation (SGPE) for both a\nhomogeneous and a hard-wall trapped condensate. The KZM scaling of the average\nvortex number with the cooling rate is established along with the universal\ncharacter of the vortex number distribution. The spatial statistics between\nvortices is characterized by analyzing the two-point defect-defect correlation\nfunction, the corresponding spacing distributions, and the random tessellation\nof the vortex pattern using the Voronoi cell area statistics. Combining the PPP\ndescription with the KZM, we derive universal theoretical predictions for each\nof these quantities and find them in agreement with the SGPE simulations. Our\nresults establish the universal character of the spatial statistics of\npoint-like topological defects generated during a continuous phase transition\nand the associated stochastic geometry."
    },
    {
        "anchor": "All-optical production of a degenerate mixture of 6Li and 40K and\n  creation of heteronuclear molecules: We present the essential experimental steps of our all-optical approach to\nprepare a double-degenerate Fermi-Fermi mixture of 6Li and 40K atoms, which\nthen serves as a starting point for molecule formation. We first describe the\noptimized trap loading procedures, the internal-state preparation of the\nsample, and the combined evaporative and sympathetic cooling process. We then\ndiscuss the preparation of the sample near an interspecies Feshbach resonance,\nand we demonstrate the formation of heteronuclear molecules by a magnetic field\nramp across the resonance.",
        "positive": "Many-body localization and thermalization in disordered Hubbard chains: We study the many-body localization transition in one-dimensional Hubbard\nchains using exact diagonalization and quantum chaos indicators. We also study\ndynamics in the delocalized (ergodic) and localized phases and discuss\nthermalization and eigenstate thermalization, or the lack thereof, in such\nsystems. Consistently within the indicators and observables studied, we find\nthat ergodicity is very robust against disorder, namely, even in the presence\nof weak Hubbard interactions the disorder strength needed for the system to\nlocalize is large. We show that this robustness might be hidden by finite size\neffects in experiments with ultracold fermions."
    },
    {
        "anchor": "Autolocalization in a dipolar exciton system: We develop the autolocalization hypothesis suggested recently in [Andreev,\nPhys. Rev. Lett. 110, 146401 (2013)] to explain the formation of the\nmacroscopically ordered exciton state (MOES) in semiconductor quantum wells [L.\nV. Butov et al., Nature (London) 418, 751 (2002)]. We argue that the onset of a\nperiodical localizing potential having a macroscopic spatial period is possible\nin the systems where in addition to long-range dipolar repulsion the excitons\nexhibit resonant pairing at short distances. Our theory suggests, that the\ncentral incoherent part of each condensate in the MOES may represent a novel\nquantum molecular phase, which was predicted and discussed theoretically\nseveral years ago in the context of resonant Bose superfluids.",
        "positive": "Resonant Scattering and Microscopic Model of Spinless Fermi Gases in\n  One-dimensional Optical Lattices: We study the effective Bloch-wave scattering of a spinless Fermi gas in\none-dimensional (1D) optical lattices. By tuning the odd-wave scattering\nlength, we find multiple resonances of Bloch-waves scattering at the bottom\n(and the top) of the lowest band, beyond which an attractive (and a repulsive)\ntwo-body bound state starts to emerge. These resonances exhibit comparable\nwidths in the deep lattice limit, and the finite interaction range plays an\nessential role in determining their locations. Based on the exact two-body\nsolutions, we construct an effective microscopic model for the low-energy\nscattering of fermions. The model can reproduce not only the scattering\namplitudes of Bloch-waves at the lowest band bottom/top, but also the\nattractive/repulsive bound states within a reasonably large energy range\nbelow/above the band. These results lay the foundation for quantum simulating\ntopological states in cold Fermi gases confined in 1D optical lattices."
    },
    {
        "anchor": "Supersolid-like states in a two-dimensional trapped spin-orbit-coupled\n  spin-1 condensate: We study supersolid-like states in a quasi-two-dimensional trapped Rashba and\nDresselhaus spin-orbit (SO) coupled spin-1 condensate. For small strengths of\nSO coupling $\\gamma$ ($\\gamma \\lessapprox 0.75$), in the ferromagnetic phase,\ncircularly-symmetric $(0,\\pm 1, \\pm 2)$- and $(\\mp 1, 0,\\pm 1)$-type states are\nformed where the numbers in the parentheses denote the angular momentum of the\nvortex at the center of the components and where the upper (lower) sign\ncorrespond to Rashba (Dresselhaus) coupling; in the antiferromagnetic phase,\nonly $(\\mp 1, 0,\\pm 1)$-type states are formed. For large strengths of SO\ncoupling, supersolid-like superlattice and superstripe states are formed in the\nferromagnetic phase. In the antiferromagnetic phase, for large strengths of SO\ncoupling, supersolid-like superstripe and multi-ring states are formed. For an\nequal mixture of Rashba and Dresselhaus SO couplings, only a superstripe state\nis found. All these states are found to be dynamically stable and hence\naccessible in an experiment and will enhance the fundamental understanding of\ncrystallization onto spatially periodic states in solids.",
        "positive": "Matter-wave interferometers with trapped strongly interacting Feshbach\n  molecules: We implement two types of matter wave interferometers using trapped\nBose-condensed Feshbach molecules, from weak to strong interactions. In each\ncase, we focus on investigating interaction effects and their implications for\nthe performance. In the Ramsey-type interferometer where the interference\nbetween the two motional quantum states in an optical lattice is observed,\ninter-particle interactions are found to induce energy shifts in the states.\nConsequently, this results in a reduction of the interferometer frequency and\nintroduces a phase shift during the lattice pulses used for state manipulation.\nFurthermore, non-uniformity leads to dephasing and collisional losses of\ncondensate contribute to the degradation of contrast. In the Michelson-type\ninterferometer, where matter waves are spatially split and recombined in a\nwaveguide, interference is observed in the presence of significant interaction,\nhowever coherence degrades with increasing interaction strength. Notably,\ncoherence is also observed in thermal clouds, indicating the white-color nature\nof the implemented Michelson interferometer."
    },
    {
        "anchor": "Rydberg Electrons in a Bose-Einstein Condensate: We investigate a hybrid system composed of ultracold Rydberg atoms immersed\nin an atomic Bose-Einstein condensate (BEC). The coupling between the Rydberg\nelectrons and BEC atoms leads to the excitation of phonons, the exchange of\nwhich induces Yukawa interaction between Rydberg atoms. Due to the small\nelectron mass, the effective charge associated with this\nquasi-particle-mediated interaction can be large, while its range is equal to\nthe healing length of the BEC, which can be tuned by adjusting the scattering\nlength of the BEC atoms. We find that for small healing lengths, the distortion\nof the BEC can \"image\" the wave function density of the Rydberg electron, while\nlarge healing lengths induce an attractive Yukawa potential between the two\nRydberg atoms that can form a new type of ultra-long-range molecule. We discuss\nboth cases for a realistic system.",
        "positive": "Hard-Wall and Non-Uniform Lattice Monte Carlo Approaches to\n  One-Dimensional Fermi Gases in a Harmonic Trap: We present in detail two variants of the lattice Monte Carlo method aimed at\ntackling systems in external trapping potentials: a uniform-lattice approach\nwith hard-wall boundary conditions, and a non-uniform Gauss-Hermite lattice\napproach. Using those two methods, we compute the ground-state energy and\nspatial density profile for systems of N=4 - 8 harmonically trapped fermions in\none dimension. From the favorable comparison of both energies and density\nprofiles (particularly in regions of low density), we conclude that the\ntrapping potential is properly resolved by the hard-wall basis. Our work paves\nthe way to higher dimensions and finite temperature analyses, as calculations\nwith the hard-wall basis can be accelerated via fast Fourier transforms, the\ncost of unaccelerated methods is otherwise prohibitive due to the unfavorable\nscaling with system size."
    },
    {
        "anchor": "Mode switching dynamics in organic polariton lasing: We study the dynamics of multimode polariton lasing in organic microcavities\nby using a second-order cumulant equation approach. By inspecting the time\nevolution of the photon mode occupations, we show that if multiple lasing peaks\nare observed in time-integrated mode occupations, the reason can be either\nbi-modal lasing or temporal switching between several modes. The former takes\nplace within a narrow range of parameters while the latter occurs more widely.\nWe find that the origin of the temporal switching is different in the weak- and\nstrong-coupling regimes. At weak coupling slope efficiency is the determining\nfactor, while for strong coupling it is changes in the eigenmodes and gain\nspectrum upon pumping. This difference is revealed by investigating the\nphotoluminescence and momentum-resolved gain spectra. Our results underscore\nthe importance of understanding the time evolution of the populations when\ncharacterizing the lasing behaviour of a multimode polariton system, and show\nhow these features differ between weak and strong coupling.",
        "positive": "Particle current, noise, and counting statistics of quantum transport in\n  the presence of a single-particle loss: How dissipation affects transport is an important theme in quantum science.\nHere we theoretically investigate an impact of a single-particle loss in\nmesoscopic transport, which has been an issue in experiments of ultracold\natomic gases. By explicitly analyzing quantum point contact and quantum dot\nsystems, we obtain a cumulant generating function on the particle current whose\nformal expression turns out to be common to two systems. In terms of this\ngenerating function, behaviors of average current, particle loss rate, and\nnoises in presences of losses introduced in conduction channels are exemplified\nfor free fermions. It is shown that the current noise contains the component\nproportional to the particle loss rate, which may be measurable in experiments."
    },
    {
        "anchor": "Self-localization of polariton condensates in periodic potentials: We predict the existence of novel spatially localized states of\nexciton-polariton Bose-Einstein condensates in semiconductor microcavities with\nfabricated periodic in-plane potentials. Our theory shows that, under the\ncondition of continuous off-resonant pumping and losses associated with\npolariton decay, localization is observed for a wide range of optical pump\nparameters due to effective potentials self-induced by the polariton flows in\nthe spatially periodic system. We reveal that the self-localization of\nexciton-polaritons in the lattice may occur both in the gaps and bands of the\nsingle-particle linear spectrum, and is dominated by the effects of gain and\ndissipation rather than the applied potential, in sharp contrast to the\nconservative condensates of ultracold alkali atoms.",
        "positive": "Topological study of a Bogoliubov-de Gennes system of pseudo spin-$1/2$\n  bosons with conserved magnetization in a honeycomb lattice: We consider a Bogolibov-de Geenes (BdG) Hamiltonian, which is a non-Hermitian\nHamiltonian with pseudo-Hermiticity, for a system of (pseudo) spin-$1/2$ bosons\nin a honeycomb lattice under the condition that the population difference\nbetween the two spin components, i.e., magnetization, is a constant. Such a\nsystem is capable of acting as a topological amplifier, under time-reversal\nsymmetry, with stable bulk bands but unstable edge modes which can be populated\nat an exponentially fast rate. We quantitatively study the topological\nproperties of this model within the framework of the 38-fold way for\nnon-Hermitian systems. We find, through the symmetry analysis of the Bloch\nHamiltonian, that this model is classified either as two copies of symmetry\nclass AIII+$\\eta_-$ or two copies of symmetry class A+$\\eta$ depending on\nwhether the (total) system is time-reversal-symmetric, where $\\eta$ is the\nmatrix representing pseudo-Hermiticity and $\\eta_-$ indicates that\npseudo-Hermiticity and chiral symmetry operators anticommute. We prove, within\nthe context of non-Hermitian physics where eigenstates obey the\nbi-orthonormality relation, that a stable bulk is characterized by a single\ntopological invariant, the Chern number for the Haldane model, independent of\npairing interactions. We construct a convenient analytical description for the\nedge modes of the Haldane model in semi-infinite planes, which is expected to\nbe useful for models built upon copies of the Haldane model across a broad\narray of disciplines. We adapt the theorem in our recent work [Phys. Rev. A\n104, 013305 (2021)] to pseudo-Hermitian Hamiltonians that are less restrictive\nthan BdG Hamiltonians and apply it to highlight that the vanishing of an\nunconventional commutator between number-conserving and number-nonconserving\nparts of the Hamiltonian indicates whether a system can be made to act as a\ntopological amplifier."
    },
    {
        "anchor": "Spin-orbit coupled two-electron Fermi gases of ytterbium atoms: We demonstrate all-optical implementation of spin-orbit coupling (SOC) in a\ntwo-electron Fermi gas of $^{173}$Yb atoms by coupling two hyperfine ground\nstates with a narrow optical transition. Due to the SU($N$) symmetry of the\n$^1$S$_0$ ground-state manifold which is insensitive to external magnetic\nfields, an optical AC Stark effect is applied to split the ground spin states,\nwhich exhibits a high stability compared with experiments on alkali and\nlanthanide atoms, and separate out an effective spin-1/2 subspace from other\nhyperfine levels for the realization of SOC. The dephasing spin dynamics when a\nmomentum-dependent spin-orbit gap being suddenly opened and the asymmetric\nmomentum distribution of the spin-orbit coupled Fermi gas are observed as a\nhallmark of SOC. The realization of all-optical SOC for ytterbium fermions\nshould offer a new route to a long-lived spin-orbit coupled Fermi gas and\ngreatly expand our capability in studying novel spin-orbit physics with\nalkaline-earth-like atoms.",
        "positive": "Magnetic Phase Transition in the Ground-State Phase Diagram of Binary\n  Bose Gases in Optical Lattices: We investigate the ground-state phase diagram of interacting binary Bose\ngases trapped in two-dimensional optical lattices by means of quantum Monte\nCarlo simulations. Our simulations reveal a magnetic phase transition from a\n$x-y$ ferromagnetic-order to a spin insulator inside the Mott insulating phase\nwith two particles per site for quasi-balanced on-site inter- and\nintra-particle interactions, i.e., $U_{\\uparrow \\downarrow} \\lesssim U$. This\n3D-XY transition is characterized by the establishment of a finite local\nmagnetic moment along the $z$-axis, ferromagnetic correlations in the $x-y$\nplan and by counterflow superfluidity inside the Mott phase. When decreasing\n$U_{\\uparrow \\downarrow}/U$, this transition merges with the Mott-superfluid\ntransition and becomes first-order. The merging of the two transitions is\ninvestigated with respect to $U_{\\uparrow \\downarrow}/U$ parameter."
    },
    {
        "anchor": "Variational theory for the ground state and collective excitations of an\n  elongated dipolar condensate: We develop a variational theory for a dipolar condensate in an elongated\n(cigar shaped) confinement potential. Our formulation provides an effective\none-dimensional extended meanfield theory for the ground state and its\ncollective excitations. We apply our theory to investigate the properties of\nrotons in the system comparing the variational treatment to a full numerical\nsolution. We consider the effect of quantum fluctuations on the scattering\nlength at which the roton excitation softens to zero energy.",
        "positive": "Numerical calculation of dipolar quantum droplet stationary states: We describe and benchmark a method to accurately calculate the quantum\ndroplet states that can be produced from a dipolar Bose-Einstein condensate.\nOur approach also allows us to consider vortex states, where the atoms\ncirculate around the long-axis of the filament shaped droplet. We apply our\napproach to determine a phase diagram showing where self-bound droplets are\nstable against evaporation, and to quantify the energetics related to the\nfission of a vortex droplet into two non-vortex droplets."
    },
    {
        "anchor": "Artificial spin-orbit coupling in ultra-cold Fermi superfluids: We develop a theory for interacting fermions in the presence of spin-orbit\ncoupling and Zeeman fields, and show that many new superfluids phases, which\nare topological in nature, emerge. Depending on values of spin-orbit coupling,\nZeeman fields, and interactions, initially gapped s-wave superfluids acquire\np-wave, d-wave, f-wave and higher angular momentum components, which produce\nzeros in the excitation spectrum, rendering the superfluid gapless. Several\nmulti-critical points, which separate topological superfluid phases from normal\nor non-uniform, are accessible depending on spin-orbit coupling, Zeeman fields\nor interactions, setting the stage for the study of tunable topological\nsuperfluids.",
        "positive": "Dynamics of a Mobile Impurity in a One-Dimensional Bose Liquid: We develop a microscopic theory of a quantum impurity propagating in a\none-dimensional Bose liquid. As a result of scattering off thermally excited\nquasiparticles, the impurity experiences the friction. We find that, at low\ntemperatures, the resulting force scales either as the fourth or the eighth\npower of temperature, depending on the system parameters. For temperatures\nhigher than the chemical potential of the Bose liquid, the friction force is a\nlinear function of temperature. Our approach enables us to find the friction\nforce in the crossover region between the two limiting cases. In the integrable\ncase, corresponding to the Yang-Gaudin model, the impurity becomes transparent\nfor quasiparticles and thus the friction force is absent. Our results could be\nfurther generalized to study other kinetic phenomena."
    },
    {
        "anchor": "Many-body multi-valuedness of particle-current variance in closed and\n  open cold-atom systems: The quantum variance of an observable is a fundamental quantity in quantum\nmechanics, and the variance provides additional information other than the\naverage itself. By examining the relation between the particle-current variance\n$(\\delta J)^2$ and the average current $J$ in both closed and open interacting\nfermionic systems, we show the emergence of a multi-valued Lissajous curve\nbetween $\\delta J$ and $J$ due to interactions. As a closed system we\nconsidered the persistent current in a benzene-like lattice enclosing an\neffective magnetic flux and solved it by exact diagonalization. For the open\nsystem, the steady-state current flowing through a few lattice sites coupled to\ntwo particle reservoirs was investigated using a Lindblad equation. In both\ncases, interactions open a loop and change the topology of the corresponding\n$\\delta J$-$J$ Lissajous curve, showing that this effect is model-independent.\nWe finally discuss how the predicted phenomena can be observed in ultracold\natoms, thus offering an alternative way of probing the dynamics of many-body\nsystems.",
        "positive": "Thermodynamics of two-dimensional bosons in the lowest Landau level: We study the thermodynamics of short-range interacting, two-dimensional\nbosons constrained to the lowest Landau level. When the temperature is higher\nthan other energy scales of the problem, the partition function reduces to a\nmultidimensional complex integral that can be handled by classical Monte Carlo\ntechniques. This approach takes the quantization of the lowest Landau level\norbits fully into account. We observe that the partition function can be\nexpressed in terms of a function of a single combination of thermodynamic\nvariables, which allows us to derive exact thermodynamic relations. We\ndetermine the asymptotic behavior of this function and compute some\nthermodynamic observables numerically."
    },
    {
        "anchor": "Theory of inelastic confinement-induced resonances due to the coupling\n  of center-of-mass and relative motion: A detailed study of the anharmonicity-induced resonances caused by the\ncoupling of center-of-mass and relative motion is presented for a system of two\nultracold atoms in single-well potentials. As has been confirmed\nexperimentally, these inelastic confinement-induced resonances are of interest,\nsince they can lead to coherent molecule formation, losses, and heating in\nultracold atomic gases. A perturbative model is introduced to describe the\nresonance positions and the coupling strengths. The validity of the model and\nthe behavior of the resonances for different confinement geometries are\nanalyzed in comparison with exact numerical ab initio calculations. While such\nresonances have so far only been detected for large positive values of the\n$s$-wave scattering length, it is found that they are present also for negative\n$s$-wave scattering lengths, i. e. for attractive interactions. The possibility\nto coherently tune the resonances by a variation of the external confinement\ngeometry might pave the way for coherent molecule association where magnetic\nFeshbach resonances are inaccessible.",
        "positive": "Coupled superfluidity of binary Bose mixtures in two dimensions: We consider a two-component Bose gas in two dimensions at low temperature\nwith short-range repulsive interaction. In the coexistence phase where both\ncomponents are superfluid, inter-species interactions induce a nondissipative\ndrag between the two superfluid flows (Andreev-Bashkin effect). We show that\nthis behavior leads to a modification of the usual\nBerezinskii-Kosterlitz-Thouless (BKT) transition in two dimensions. We extend\nthe renormalization of the superfluid densities at finite temperature using the\nrenormalization group approach and find that the vortices of one component have\na large influence on the superfluid properties of the other, mediated by the\nnondissipative drag. The extended BKT flow equations indicate that the\noccurrence of the vortex unbinding transition in one of the components can\ninduce the breakdown of superfluidity also in the other, leading to a locking\nphenomenon for the critical temperatures of the two gases."
    },
    {
        "anchor": "Anomalous Transport in the Superfluid Fluctuation Regime: Motivated by a recent experiment in ultracold atoms [ S. Krinner et al.,\nProc. Natl. Acad. Sci. U.S.A 113, 8144 (2016)], we analyze transport of\nattractively interacting fermions through a one-dimensional wire near the\nsuperfluid transition. We show that in a ballistic regime where the conductance\nis quantized in the absence of interaction, the conductance is renormalized by\nsuperfluid fluctuations in reservoirs. In particular, the particle conductance\nis strongly enhanced and the plateau is blurred by emergent bosonic pair\ntransport. For spin transport, in addition to the contact resistance the wire\nitself is resistive, leading to a suppression of the measured spin conductance.\nOur results are qualitatively consistent with the experimental observations.",
        "positive": "Quantitative study of quasi-one-dimensional Bose gas experiments via the\n  stochastic Gross-Pitaevskii equation: The stochastic Gross-Pitaevskii equation is shown to be an excellent model\nfor quasi-one-dimensional Bose gas experiments, accurately reproducing the in\nsitu density profiles recently obtained in the experiments of Trebbia et al.\n[Phys. Rev. Lett. 97, 250403 (2006)] and van Amerongen et al. [Phys. Rev. Lett.\n100, 090402 (2008)], and the density fluctuation data reported by Armijo et al.\n[Phys. Rev. Lett. 105, 230402 (2010)]. To facilitate such agreement, we propose\nand implement a quasi-one-dimensional stochastic equation for the low-energy,\naxial modes, while atoms in excited transverse modes are treated as independent\nideal Bose gases."
    },
    {
        "anchor": "A mixed dimensional Bose polaron: A new generation of cold atom experiments trapping atomic mixtures in species\nselective optical potentials opens up the intriguing possibility to create\nsystems in which different atoms live in different spatial dimensions. Inspired\nby this, we investigate a mixed dimensional Bose polaron consisting of an\nimpurity particle moving in a two-dimensional (2D) layer immersed in a 3D\nBose-Einstein condensate (BEC), using a theory that includes the mixed\ndimensional vacuum scattering between the impurity and the bosons exactly. We\nshow that similarly to the pure 3D case, this system exhibits a well-defined\npolaron state for attractive boson-impurity interaction that evolves smoothly\ninto a mixed-dimensional dimer for strong attraction, as well as a well-defined\npolaron state for weak repulsive interaction, which becomes over-damped for\nstrong interaction. We furthermore find that the properties of the polaron\ndepend only weakly on the gas parameter of the BEC as long as the Bogoliubov\ntheory remains a valid description for the BEC. This indicates that higher\norder correlations between the impurity and the bosons are suppressed by the\nmixed dimensional geometry in comparison to a pure 3D system, and that the\nmixed dimensional polaron has universal properties in the unitarity limit of\nthe impurity-boson interaction.",
        "positive": "Scattering off a junction: Scattering off a potential is a fundamental problem in quantum physics. It\nhas been studied extensively with amplitudes derived for various potentials. In\nthis article, we explore a setting with no potentials, where scattering occurs\noff a junction where many wires meet. We study this problem using a\ntight-binding discretization of a star graph geometry -- one incoming wire and\n$M$ outgoing wires intersecting at a point. When an incoming wave scatters, one\npart is reflected along the same wire while the rest is transmitted along the\nothers. Remarkably, the reflectance increases monotonically with $M$, i.e., the\ngreater the number of outgoing channels, the more the particle bounces back. In\nthe $M \\rightarrow \\infty$ limit, the wave is entirely reflected back along the\nincoming wire. We rationalize this observation by establishing a quantitative\nmapping between a junction and an on-site potential. To each junction, we\nassign an equivalent potential that produces the same reflectance. As the\nnumber of wires ($M$) increases, the equivalent potential also increases. A\nrecent article by one of us has drawn an equivalence between junctions and\npotentials from the point of view of bound state formation. Our results here\nshow that the same equivalence also holds for scattering amplitudes. We verify\nour analytic results by simulating wavepacket motion through a junction. We\nextend the wavepacket approach to two dimensions where analytic solutions\ncannot be found. An incoming wave travels on a sheet and scatters off a point\nwhere many sheets intersect. Unlike in 1D, the equivalent potential is\nmomentum-dependent. Nevertheless, for any given momentum, the equivalent\npotential grows monotonically with the number of intersecting sheets. Our\nfindings can be tested in ultracold atom setups and semiconductor structures."
    },
    {
        "anchor": "Non-thermal fixed points: universality, topology, & turbulence in Bose\n  gases: In these notes we discuss recent developments in the field of non-equilibrium\nquantum dynamics. Specifically, we consider nearly coherent Bose gases brought\nfar out of equilibrium and study their behaviour in view of connections between\nuniversal properties, (quasi-)topological field configurations and turbulent\ndynamics. We demonstrate that the isolated Bose gas, on its way back to thermal\nequilibrium, can approach metastable non-equilibrium configurations and spend a\nlong time in their vicinity. In such configurations, which have been termed\nnon-thermal fixed points, the system shows universal long-range properties\nmanifest through scaling, i.e., self-similar correlations. The spatial field\npattern, at the same time, is characterized by the appearance of defects and\ndomain formation whose geometry gives rise to the particular scaling laws seen\nin the correlation functions. We obtain an overall picture which connects\nwell-known concepts for describing universal dynamics such as wave-turbulence,\nsuperfluid turbulence, and (quasi-)topological excitations. This allows to\nbring together a wide range of concepts and methods with a large spectrum of\napplications.",
        "positive": "Observation of Spin Superfluidity in a Bose Gas Mixture: The spin dynamics of a harmonically trapped Bose-Einstein condensed binary\nmixture of sodium atoms is experimentally investigated at finite temperature.\nIn the collisional regime the motion of the thermal component is shown to be\ndamped because of spin drag, while the two condensates exhibit a counter flow\noscillation without friction, thereby providing direct evidence for spin\nsuperfluidity. Results are also reported in the collisionless regime where the\nspin components of both the condensate and thermal part oscillate without\ndamping, their relative motion being driven by a mean field effect. We also\nmeasure the static polarizability of the condensed and thermal parts and we\nfind a large increase of the condensate polarizability with respect to the T=0\nvalue, in agreement with the predictions of theory."
    },
    {
        "anchor": "Hydrodynamic long-time tails after a quantum quench: After a quantum quench, a sudden change of parameters, generic many particle\nquantum systems are expected to equilibrate. A few collisions of quasiparticles\nare usually sufficient to establish approximately local equilibrium. Reaching\nglobal equilibrium is, however, much more difficult as conserved quantities\nhave to be transported for long distances to build up a pattern of fluctuations\ncharacteristic for equilibrium. Here we investigate the quantum quench of the\none-dimensional bosonic Hubbard model from infinite to finite interaction\nstrength U using semiclassical methods for weak, and exact diagonalization for\nstrong quenches. Equilibrium is approached only slowly, as t^{-1/2} with\nsubleading corrections proportional to t^{-3/4}, consistent with predictions\nfrom hydrodynamics. We show that these long-time tails determine the relaxation\nof a wide range of physical observables.",
        "positive": "Fractional quantum Hall phases of bosons with tunable interactions: From\n  the Laughlin liquid to a fractional Wigner crystal: Highly tunable platforms for realizing topological phases of matter are\nemerging from atomic and photonic systems, and offer the prospect of designing\ninteractions between particles. The shape of the potential, besides playing an\nimportant role in the competition between different fractional quantum Hall\nphases, can also trigger the transition to symmetry-broken phases, or even to\nphases where topological and symmetry-breaking order coexist. Here, we explore\nthe phase diagram of an interacting bosonic model in the lowest Landau level at\nhalf-filling as two-body interactions are tuned. Apart from the well-known\nLaughlin liquid, Wigner crystal phase, stripe, and bubble phases, we also find\nevidence of a phase that exhibits crystalline order at fractional filling per\ncrystal site. The Laughlin liquid transits into this phase when pairs of bosons\nstrongly repel each other at relative angular momentum $4\\hbar$. We show that\nsuch interactions can be achieved by dressing ground-state cold atoms with\nmultiple different-parity Rydberg states."
    },
    {
        "anchor": "Weyl Bogoliubov excitations in Bose-Hubbard extension of Weyl semimetal: In this paper, a Bose-Hubbard extension of a Weyl semimetal is proposed that\ncan be realized for ultracold atoms using laser assisted tunneling and Feshbach\nresonance technique in three dimensional optical lattices. The global phase\ndiagram is obtained consisting of a superfluid phase and various Mott insulator\nphases by using Landau theory. The Bogoliubov excitation modes for the weakly\ninteracting case have nontrivial properties (Weyl nodes, bosonic surface arc,\netc.) analogs of those in Weyl semimetals of electronic systems, which are\nsmoothly carried over to that of Bloch bands for the noninteracting case. The\nproperties of the insulating phases for the strongly interacting case are\nexplored by calculating both the quasiparticle and quasihole dispersion\nrelation, which shows two quasiparticle spectra touch at Weyl nodes.",
        "positive": "Unconventional fermionic pairing states in a monochromatically tilted\n  optical lattice: We study the one-dimensional attractive Fermionic Hubbard model under the\ninfluence of periodic driving with the time-dependent density matrix\nrenormalization group method. We show that the system can be driven into an\nunconventional pairing state characterized by a condensate made of Cooper-pairs\nwith a finite center-of-mass momentum similar to a Fulde-Ferrell state. We\nobtain results both in the laboratory and the rotating reference frames\ndemonstrating that the momentum of the condensate can be finely tuned by\nchanging the ratio between the amplitude and the frequency of the driving. In\nparticular, by quenching this ratio to the value corresponding to suppression\nof the tunnelling and the Coulomb interaction strength to zero, we are able to\n\"freeze\" the condensate. We finally study the effects of different initial\nconditions, and compare our numerical results to those obtained from a\ntime-independent Floquet theory in the large frequency regime. Our work offers\nthe possibility of engineering and controlling unconventional pairing states in\nfermionic condensates."
    },
    {
        "anchor": "Two-dimensional electron-hole system under the influence of the\n  Chern-Simons gauge field created by the quantum point vortices: In the present work the Chern-Simons(C-S) gauge field theory developed by\nJackiw and Pi [1] and widely used to explain the fractional quantum Hall\neffects, was applied to describe the two-dimensional (2D) electron-hole (e-h)\nsystem in a strong perpendicular magnetic field under the influence of the\nquantum point vortices creating the Chern-Simons(C-S) gauge field. The\ncomposite particles formed by electrons and by holes with equal integer\npositive numbers of the attached quantum point vortices are described by the\ndressed field operators, which obey to the Fermi or to the Bose statistics\ndepending on the even or odd numbers . It is shown that the phase operators as\nwell as the vector and the scalar potentials of the C-S gauge field depend on\nthe difference of the electron and of the hole density operators. They vanish\nin the mean field approximation, when the average values of the electron and of\nthe whole densities coincide. Nevertheless, even in this case, the quantum\nfluctuations of the C-S gauge field lead to new physics of the 2D e-h system.",
        "positive": "Mott lobes of the $S=1$ Bose-Hubbard model with three-body interactions: Using the density matrix renormalization group method, we studied the ground\nstate of the one-dimensional $S=1$ Bose-Hubbard model with local three-body\ninteractions, which can be a superfluid or a Mott insulator state. We drew the\nphase diagram of this model for both ferromagnetic and antiferromagnetic\ninteraction. Regardless of the sign of the spin-dependent coupling, we obtained\nthat the Mott lobes area decreases as the spin-dependent strength increases,\nwhich means that the even-odd asymmetry of the two-body antiferromagnetic chain\nis absent for local three-body interactions. For antiferromagnetic coupling, we\nfound that the density drives first-order superfluid-Mott insulator transitions\nfor even and odd lobes. Ferromagnetic Mott insulator and superfluid states were\nobtained with a ferromagnetic coupling, and a tendency to a \"long-range\" order\nwas observed."
    },
    {
        "anchor": "Ultrafast many-body interferometry of impurities coupled to a Fermi sea: The fastest possible collective response of a quantum many-body system is\nrelated to its excitations at the highest possible energy. In condensed-matter\nsystems, the corresponding timescale is typically set by the Fermi energy.\nTaking advantage of fast and precise control of interactions between ultracold\natoms, we report on the observation of ultrafast dynamics of impurities coupled\nto an atomic Fermi sea. Our interferometric measurements track the\nnon-perturbative quantum evolution of a fermionic many-body system, revealing\nin real time the formation dynamics of quasiparticles and the quantum\ninterference between attractive and repulsive states throughout the full depth\nof the Fermi sea. Ultrafast time-domain methods to manipulate and investigate\nstrongly interacting quantum gases open up new windows on the dynamics of\nquantum matter under extreme non-equilibrium conditions.",
        "positive": "Orbital magnetism of ultracold fermionic gases in a lattice: dynamical\n  mean-field approach: We study finite-temperature properties of ultracold four-component mixtures\nof alkaline-earth-like atoms in optical lattices that can be effectively\ndescribed by the two-band spin-$1/2$ Hubbard model including the Hund's\nexchange coupling term. Our main goal is to investigate the effect of exchange\ninteractions on finite-temperature magnetic phases for a wide range of lattice\nfillings. We use the dynamical mean-field theory approach and its real-space\ngeneralization to obtain finite-temperature phase diagrams including\ntransitions to magnetically-ordered phases. It allows to determine optimal\nexperimental regimes for approaching long-range ferromagnetic ordering in\nultracold gases. We also calculate the entropy in the vicinity of\nmagnetically-ordered phases, which provides quantitative predictions for\non-going and future experiments aiming at approaching and studying long-range\nordered states in optical lattices."
    },
    {
        "anchor": "Droplet Arrays in Doubly-Dipolar Bose-Einstein condensates: Gases of doubly-dipolar particles, with both magnetic and electric dipole\nmoments, offer intriguing novel possibilities. We show that the interplay\nbetween doubly-dipolar interactions, quantum stabilization, and external\nconfinement results in a rich ground-state physics of supersolids and\nincoherent droplet arrays in doubly-dipolar condensates. Our study reveals\nnovel possibilities for engineering quantum droplets and droplet supersolids,\nincluding supersolid-supersolid transitions and the realization of supersolid\narrays of pancake droplets.",
        "positive": "Majorana Zero Modes in Synthetic Dimensions: Recent experimental advances in the field of cold atoms led to the\ndevelopment of novel techniques for producing synthetic dimensions and\nsynthetic magnetic fields, thus greatly expanding the utility of cold atomic\nsystems for exploring exotic states of matter. In this paper we investigate the\npossibility of using experimentally tunable interactions in such systems to\nmimic the physics of Majorana chains, currently a subject of intense research.\nCrucially to our proposal, the interactions, which are local in space, appear\nnon-local in the synthetic dimension. We use this fact to induce coupling\nbetween counter-propagating edge modes in the quantum Hall regime. For the case\nof attractive interactions in a system composed of two tunneling-coupled\nchains, we find a gapless quasi-topological phase with a doubly-degenerate\nground state. While the total number of particles in the system is kept fixed,\nthis phase is characterized by strong fluctuations of the pair number in each\nchain. Each ground state is characterized by the parity of the total particle\nnumber in each chain, similar to Majorana wires. However, in our system this\ndegeneracy persists for periodic boundary conditions. For open boundary\nconditions there is a small splitting of this degeneracy due to the\nsingle-particle hopping at the edges. We show how subjecting the system to\nadditional synthetic flux or asymmetric potentials on the two chains can be\nused to control this nonlocal qubit. We propose experimental probes for testing\nthe nonlocal nature of such a qubit and measuring its state."
    },
    {
        "anchor": "Dynamics of spinor Bose-Einstein condensate subject to dissipation: We investigate the internal dynamics of the spinor Bose-Einstein Condensates\nsubject to dissipation by solving the Lindblad master equation. It is shown\nthat for the condensates without dissipation its dynamics always evolve along\nspecific orbital in the phase space of ($n_0$, $\\theta$) and display three\nkinds of dynamical properties including Josephson-like oscillation,\nself-trapping-like oscillation and 'running phase'. In contrast, the\ncondensates subject to dissipation will not evolve along the specific dynamical\norbital. If component-1 and component-(-1) dissipate in different rates, the\nmagnetization $m$ will not conserve and the system transits between different\ndynamical regions. The dynamical properties can be exhibited in the phase space\nof ($n_0$, $\\theta$, $m$).",
        "positive": "Spin-orbit coupled spin-1 Bose-Einstein condensate flow past an obstacle\n  in the presence of a Zeeman field: We study the dynamics of a Rashba spin-orbit coupled spin-1 ferromagnetic\nBose-Einstein condensate under a linear Zeeman magnetic field(ZF) disturbed by\na moving obstacle. The Bogoliubov excitation spectrums and corresponding\ncritical excitations in different situations are analyzed. The structure of the\ncoreless vortex or antivortex generated by the moving obstacle has been\ninvestigated. When the ZF is applied along x direction, the vortex cores for\nthe three components of a(an) vortex(antivortex) could be arranged into a\nvertical line, and their order would be reversed as the spin-orbit coupling\nincreases. When the ZF is parallel to z direction, a skyrmion-like vortex\nground state could be induced even by a static obstacle. This topological\nstructure is also found to be dynamically stable if the obstacle is moving at a\nrelatively small velocity."
    },
    {
        "anchor": "Bose-Einstein condensate in an elliptical waveguide: We investigate the effects of spatial curvature for an atomic Bose-Einstein\ncondensate confined in an elliptical waveguide. The system is well described by\nan effective 1D Gross-Pitaevskii equation with a quantum-curvature potential,\nwhich has the shape of a double-well but crucially depends on the eccentricity\nof the ellipse. The ground state of the system displays a quantum phase\ntransition from a two-peak configuration to a one-peak configuration at a\ncritical attractive interaction strength. In correspondence of this phase\ntransition the superfluid fraction strongly reduces and goes to zero for a\nsufficiently attractive Bose-Bose interaction.",
        "positive": "Quantum Phase Transition in an Antiferromagnetic Spinor Bose-Einstein\n  Condensate: We have experimentally observed the dynamics of an antiferromagnetic sodium\nBose-Einstein condensate (BEC) quenched through a quantum phase transition.\nUsing an off-resonant microwave field coupling the F = 1 and F = 2 atomic\nhyperfine levels, we rapidly switched the quadratic energy shift q from\npositive to negative values. At q = 0 the system undergoes a transition from a\npolar to antiferromagnetic phase. We measured the dynamical evolution of the\npopulation in the F = 1, m_F = 0 state in the vicinity of this transition point\nand observed a mixed state of all 3 hyperfine components for q < 0. We also\nobserved the coarsening dynamics of the instability for q<0, as it nucleated\nsmall domains that grew to the axial size of the cloud."
    },
    {
        "anchor": "Quantum state engineering of a Hubbard system with ultracold fermions: Accessing new regimes in quantum simulation requires the development of new\ntechniques for quantum state preparation. We demonstrate the quantum state\nengineering of a strongly correlated many-body state of the two-component\nrepulsive Fermi-Hubbard model on a square lattice. Our scheme makes use of an\nultralow entropy doublon band insulator created through entropy redistribution.\nAfter isolating the band insulator, we change the underlying potential to\nexpand it into a half-filled system. The final many-body state realized shows\nstrong antiferromagnetic correlations and a temperature below the exchange\nenergy. We observe an increase in entropy, which we find is likely caused by\nthe many-body physics in the last step of the scheme. This technique is\npromising for low-temperature studies of cold-atom-based lattice models.",
        "positive": "Repulsively interacting fermions in a two-dimensional deformed trap with\n  spin-orbit coupling: We investigate a two-dimensional system of with two values of the internal\n(spin) degree of freedom. It is confined by a deformed harmonic trap and\nsubject to a Zeeman field, Rashba or Dresselhaus one-body spin-orbit couplings\nand two-body short range repulsion. We obtain self-consistent mean-field\n$N$-body solutions as functions of the interaction parameters. Single-particle\nSpectra and total energies are computed and compared to the results without\ninteraction. We perform a statistical analysis for the distributions of nearest\nneighbor energy level spacings and show that quantum signatures of chaos are\nseen in certain parameters regimes. Furthermore, the effects of two-body\nrepulsion on the nearest neighbor distributions are investigated. This\nrepulsion can either promote or destroy the signatures of potential chaotic\nbehavior depending on relative strengths of parameters. Our findings support\nthe suggestion that cold atoms may be used to study quantum chaos both in the\npresence and absence of interactions."
    },
    {
        "anchor": "Non-Hermitian topological Fermi superfluid near the $p$-wave unitary\n  limit: We theoretically discuss the non-Hermitian superfluid phase transition in\none-dimensional two-component Fermi gases near the $p$-wave Feshbach resonance\naccompanied by the two-body loss associated with the dipolar relaxation. For\nthe first time we point out that this system gives us an opportunity to explore\nthe interplay among various non-trivial properties such as universal\nthermodynamics at divergent $p$-wave scattering length, topological phase\ntransition at vanishing chemical potential, and non-Hermitian\nBardeen-Cooper-Schrieffer(BCS) to Bose-Einstein condensate (BEC) transition, in\na unified manner. In the BCS phase, the loss-induced superfluid-normal\ntransition occurs when the exceptional point appears in the effective\nnon-Hermitian Hamiltonian. In the BEC phase, the diffusive gapless mode can be\nregarded as a precursor of the instability of the superfluid state. Moreover,\nwe show that the superfluid state is fragile against the two-body loss near the\ntopological phase transition point.",
        "positive": "Non-equilibrium evolution of Bose-Einstein condensate deformation in\n  temporally controlled weak disorder: We consider a time-dependent extension of a perturbative mean-field approach\nto the dirty boson problem by considering how switching on and off a weak\ndisorder potential affects the stationary state of an initially equilibrated\nBose-Einstein condensate by the emergence of a disorder-induced condensate\ndeformation. We find that in the switch on scenario the stationary condensate\ndeformation turns out to be a sum of an equilibrium part, that actually\ncorresponds to adiabatic switching on the disorder, and a dynamically-induced\npart, where the latter depends on the particular driving protocol. If the\ndisorder is switched off afterwards, the resulting condensate deformation\nacquires an additional dynamically-induced part in the long-time limit, while\nthe equilibrium part vanishes. We also present an appropriate generalization to\ninhomogeneous trapped condensates. Our results demonstrate that the condensate\ndeformation represents an indicator of the generically non-equilibrium nature\nof steady states of a Bose gas in a temporally controlled weak disorder."
    },
    {
        "anchor": "Temperature induced decay of persistent currents in a superfluid\n  ultracold gas: We study how temperature affects the lifetime of a quantized, persistent\ncurrent state in a toroidal Bose-Einstein condensate (BEC). When the\ntemperature is increased, we find a decrease in the persistent current\nlifetime. Comparing our measured decay rates to simple models of thermal\nactivation and quantum tunneling, we do not find agreement. We also measured\nthe size of hysteresis loops size in our superfluid ring as a function of\ntemperature, enabling us to extract the critical velocity. The measured\ncritical velocity is found to depend strongly on temperature, approaching the\nzero temperature mean-field solution as the temperature is decreased. This\nindicates that an appropriate definition of critical velocity must incorporate\nthe role of thermal fluctuations, something not explicitly contained in\ntraditional theories.",
        "positive": "Interfaces between Bose-Einstein and Tonks-Girardeau atomic gases: We consider one-dimensional mixtures of an atomic Bose-Einstein condensate\n(BEC) and Tonks- Giradeau (TG) gas. The mixture is modeled by a coupled system\nof the Gross-Pitaevskii equation for the BEC and the quintic nonlinear\nSchroedinger equation for the TG component. An immiscibility condition for the\nbinary system is derived in a general form. Under this condition, three types\nof BEC-TG interfaces are considered: domain walls (DWs) separating the two\ncomponents; bubble-drops (BDs), in the form of a drop of one component immersed\ninto the other (BDs may be considered as bound states of two DWs); and bound\nstates of bright and dark solitons (BDSs). The same model applies to the\ncopropagation of two optical waves in a colloidal medium. The results are\nobtained by means of systematic numerical analysis, in combination with\nanalytical Thomas-Fermi approximations (TFAs). Using both methods, families of\nDW states are produced in a generic form. BD complexes exist solely in the form\nof a TG drop embedded into the BEC background. On the contrary, BDSs exist as\nbound states of TG bright and BEC dark components, and vice versa."
    },
    {
        "anchor": "Competing magnetic orders in a bilayer Hubbard model with ultracold\n  atoms: Fermionic atoms in optical lattices have served as a compelling model system\nto study and emulate the physics of strongly-correlated matter. Driven by the\nadvances of high-resolution microscopy, the recent focus of research has been\non two-dimensional systems in which several quantum phases, such as\nanti-ferromagnetic Mott insulators for repulsive interactions and\ncharge-density waves for attractive interactions have been observed. However,\nthe aspired emulations of real materials, such as bilayer graphene, have to\ntake into account that their lattice structure composes of coupled layers and\ntherefore is not strictly two-dimensional. In this work, we realize a bilayer\nFermi-Hubbard model using ultracold atoms in an optical lattice and demonstrate\nthat the interlayer coupling controls a crossover between a planar\nanti-ferromagnetically ordered Mott insulator and a band insulator of\nspin-singlets along the bonds between the layers. Our work will enable the\nexploration of further fascinating properties of coupled-layer Hubbard models,\nsuch as theoretically predicted superconducting pairing mechanisms.",
        "positive": "Mesoscopic density grains in the 1d interacting Bose gas from the exact\n  Yang-Yang solution: Number fluctuations in a one-dimensional Bose gas consist of contributions\nfrom many smaller independent localized fluctuations, the density grains. We\nhave derived a set of extended integral equations from the Yang-Yang solution\nfor finite temperature that exactly determine all higher order moments of\nnumber fluctuations. These moments are closely related to the statistics of the\nlocalized (but not zero-range) density grains. We directly calculate the mean\noccupation of these fluctuations, and the variance, skewness, and kurtosis of\ntheir distribution across the whole parameter space of the gas. Findings\ninclude: Large mesoscopic density grains with a fat-tailed distribution in the\nthermal quasicondensate of the dilute gas and in the nonperturbative quantum\nturbulent regime; Regions of negative skewness and below-Gaussian kurtosis in a\npart of the fermionized gas, and an unexplained crossover region along $T\\sim\nT_d/\\gamma$; The existence of a peak in the density-density correlation\nfunction at finite interparticle spacing. We relate these density grain\nstatistics to measurable behavior such as the statistics of coarse imaging\nbins, and finite-size scaling of number fluctuations. We propose how to\nexperimentally test the relationship between thermodynamically independent\ndensity grains and density concentrations visible in single shot images."
    },
    {
        "anchor": "Time-optimal variational control of bright matter-wave soliton: Motivated by recent experiments, we present the time-optimal variational\ncontrol of bright matter-wave soliton trapped in a quasi-one-dimensional\nharmonic trap by manipulating the atomic attraction through Feshbach\nresonances. More specially, we first apply a time-dependent variational method\nto derive the motion equation for capturing the soliton's shape, and secondly\ncombine inverse engineering with optimal control theory to design the atomic\ninteraction for implementing time-optimal decompression. Since the time-optimal\nsolution is of bang-bang type, the smooth regularization is further adopted to\nsmooth the on-off controller out, thus avoiding the heating and atom loss,\ninduced from magnetic field ramp across a Feshbach resonance in practice.",
        "positive": "Bose-Einstein condensation in spherically symmetric traps: We present a pedagogical introduction to Bose-Einstein condensation in traps\nwith spherical symmetry, namely the spherical box and the thick shell,\nsometimes called bubble trap. In order to obtain the critical temperature for\nBose-Einstein condensation, we describe how to calculate the cumulative state\nnumber and density of states in these geometries, using numerical and\nanalytical (semi-classical) approaches. The differences in the results of both\nmethods are a manifestation of Weyl's theorem, i.e., they reveal how the\ngeometry of the trap (boundary condition) affects the number of the eigenstates\ncounted. Using the same calculation procedure, we analyzed the impact of going\nfrom three-dimensions to two-dimensions, as we move from a thick shell to a\ntwo-dimensional shell. The temperature range we obtained, for most commonly\nused atomic species and reasonable confinement volumes, is compatible with\ncurrent cold atom experiments, which demonstrates that these trapping\npotentials may be employed in experiments."
    },
    {
        "anchor": "Anisotropic Superfluidity in the Two-Species Polar Fermi Gas: We study the superfluid pairing in a two-species gas of heteronuclear\nfermionic molecules with equal density. The interplay of the isotropic s-wave\ninteraction and anisotropic long-range dipolar interaction reveals rich\nphysics. We find that the single-particle momentum distribution has a\ncharacteristic ellipsoidal shape that can be reasonably represented by a\ndeformation parameter $\\alpha$ defined similarly to the normal phase.\nInteresting momentum-dependent features of the order parameter are identified.\nWe calculate the critical temperatures of both the singlet and triplet\nsuperfluid, suggesting a possible pairing symmetry transition by tuning the\ns-wave or dipolar interaction strength.",
        "positive": "General ultracold scattering formalism with isotropic spin orbit\n  coupling: A general treatment of ultracold two-body scattering in the presence of\nisotropic spin-orbit coupling (SOC) is presented. Owing to the mixing of\ndifferent partial wave channels, scattering with SOC is in general a coupled\nmultichannel problem. A systematic method is introduced to analytically solve a\nclass of coupled differential equations by recasting the coupled channel\nproblem as a simple eigenvalue problem. The exact Green's matrix in the\npresence of SOC is found, which readily gives the scattering solutions for any\ntwo identical particles in any total angular momentum subspace having\nnegligible center of mass momentum. Application of this formalism to two spin-1\nbosons shows the ubiquitous low energy threshold behavior for systems with\nisotropic SOC. A modified threshold behavior shows up, which does not occur for\nthe spin-orbit coupled spin-1/2 system. We also confirm the parity-breaking\nmechanism for the spontaneous emergency of handedness, that has been proposed\nby Duan et. al. [1]. Additionally, a two-body bound state is found for any\narbitrarily small and negative scattering length. Our study sheds light on the\nfew-body side of SOC physics and provides one step towards understanding\nultracold scattering in a non-Abelian gauge field."
    },
    {
        "anchor": "Fermi liquid theory of ultra-cold trapped Fermi gases: Implications for\n  Pseudogap Physics and Other Strongly Correlated Phases: We show how Fermi liquid theory can be applied to ultra-cold Fermi gases,\nthereby expanding their \"simulation\" capabilities to a class of problems of\ninterest to multiple physics sub-disciplines. We introduce procedures for\nmeasuring and calculating position dependent Landau parameters. This lays the\nground work for addressing important controversial issues: (i) the suggestion\nthat thermodynamically, the normal state of a unitary gas is indistinguishable\nfrom a Fermi liquid (ii) that a fermionic system with strong repulsive contact\ninteractions is associated with either ferromagnetism or localization; this\nrelates as well to $^3$He and its p-wave superfluidity.",
        "positive": "Exciton-polariton condensates in zero-, one-, and two-dimensional\n  lattices: Microcavity exciton-polaritons are quantum quasi-particles arising from the\nstrong light-matter coupling. They have exhibited rich quantum dynamics rooted\nfrom bosonic nature and inherent non-equilibrium condition. Dynamical\ncondensation in microcavity exciton-polaritons has been observed at much\nelevated temperatures in comparison to ultrocold atom condensates. Recently, we\nhave investigated the behavior of exciton-polariton condensates in artificial\ntrap and lattice geometries in zero-dimension, one-dimension (1D) and\ntwo-dimension (2D). Coherent $\\pi$-state with p-wave order in a 1D condensate\narray and d-orbital state in a 2D square lattice are observed. We anticipate\nthat the preparation of high-orbital condensates can be further extended to\nprobe dynamical quantum phase transition in a controlled manner as quantum\nemulation applications."
    },
    {
        "anchor": "Rotating three-dimensional solitons in Bose Einstein condensates with\n  gravity-like attractive nonlocal interaction: We study formation of rotating three-dimensional high-order solitons\n(azimuthons) in Bose Einstein condensate with attractive nonlocal nonlinear\ninteraction. In particular, we demonstrate formation of toroidal rotating\nsolitons and investigate their stability. We show that variational methods\nallow a very good approximation of such solutions and predict accurately the\nsoliton rotation frequency. We also find that these rotating localized\nstructures are very robust and persist even if the initial condensate\nconditions are rather far from the exact soliton solutions. Furthermore, the\npresence of repulsive contact interaction does not prevent the existence of\nthose solutions, but allows to control their rotation. We conjecture that\nself-trapped azimuthons are generic for condensates with attractive nonlocal\ninteraction.",
        "positive": "Nonlinear quantum model for atomic Josephson junctions with one and two\n  bosonic species: We study atomic Josephson junctions (AJJs) with one and two bosonic species\nconfined by a double-well potential. Proceeding from the second quantized\nHamiltonian, we show that it is possible to describe the zero-temperature AJJs\nmicroscopic dynamics by means of extended Bose-Hubbard (EBH) models, which\ninclude usually-neglected nonlinear terms. Within the mean-field approximation,\nthe Heisenberg equations derived from such two-mode models provide a\ndescription of AJJs macroscopic dynamics in terms of ordinary differential\nequations (ODEs). We discuss the possibility to distinguish the Rabi,\nJosephson, and Fock regimes, in terms of the macroscopic parameters which\nappear in the EBH Hamiltonians and, then, in the ODEs. We compare the\npredictions for the relative populations of the Bose gases atoms in the two\nwells obtained from the numerical solutions of the two-mode ODEs, with those\nderiving from the direct numerical integration of the Gross-Pitaevskii\nequations (GPEs). Our investigations shows that the nonlinear terms of the ODEs\nare crucial to achieve a good agreement between ODEs and GPEs approaches, and\nin particular to give quantitative predictions of the self-trapping regime."
    },
    {
        "anchor": "Rosen-Zener model in cold molecule formation: The Rosen-Zener model for association of atoms in a Bose-Einstein condensate\nis studied. Using a nonlinear Volterra integral equation, we obtain an analytic\nformula for final probability of the transition to the molecular state for weak\ninteraction limit. Considering the strong coupling limit of high field\nintensities, we show that the system reveals two different time-evolution\npictures depending on the detuning of the frequency of the associating field.\nFor both limit cases we derive highly accurate formulas for the molecular state\nprobability valid for the whole range of variation of time. Using these\nformulas, we show that at large detuning regime the molecule formation process\noccurs almost non-oscillatory in time and a Rosen-Zener pulse is not able to\nassociate more than one third of atoms at any time point. The system returns to\nits initial all-atomic state at the end of the process and the maximal\ntransition probability is achieved when the field intensity reaches its peak.\nIn contrast, at small detuning the evolution of the system displays\nlarge-amplitude oscillations between atomic and molecular populations. We find\nthat the shape of the oscillations in the first approximation is defined by the\nfield detuning only. Finally, a hidden singularity of the Rosen-Zener model due\nto the specific time-variation of the field amplitude at the beginning of the\ninteraction is indicated. It is this singularity that stands for many of the\nqualitative and quantitative properties of the model. The singularity may be\nviewed as an effective resonance-touching.",
        "positive": "Scattering Hypervolume of Spin-Polarized Fermions: We analyze the collision of three identical spin-polarized fermions at zero\ncollision energy, assuming arbitrary finite-range potentials, and define the\ncorresponding three-body scattering hypervolume $D_F$. The scattering\nhypervolume $D$ was first defined for identical bosons in 2008 by one of us. It\nis the three-body analog of the two-body scattering length. We solve the\nthree-body Schr\\\"{o}dinger equation asymptotically when the three fermions are\nfar apart or one pair and the third fermion are far apart, deriving two\nasymptotic expansions of the wave function. Unlike the case of bosons for which\n$D$ has the dimension of length to the fourth power, here the $D_F$ we define\nhas the dimension of length to the eighth power. We then analyze the\ninteraction energy of three such fermions with momenta $\\hbar\\mathbf{k}_1$,\n$\\hbar\\mathbf{k}_2$ and $\\hbar\\mathbf{k}_3$ in a large periodic cubic box. The\nenergy shift due to $D_F$ is proportional to $D_F/\\Omega^2$, where $\\Omega$ is\nthe volume of the box. We also calculate the shifts of energy and pressure of\nspin-polarized Fermi gases due to a nonzero $D_F$ and the three-body\nrecombination rate of spin-polarized ultracold atomic Fermi gases at finite\ntemperatures."
    },
    {
        "anchor": "Parametrized path integral formulation for large fermion systems: The exchange antisymmetry between identical fermions gives rise to the well\nknown fermion sign problem, in the form of large cancellation between positive\nand negative contribution to the partition function, making any simulation\nmethods which directly sample this partition function exponentially difficult\nto converge. In this work, we employ path integral molecular dynamics (PIMD)\nand build upon the recently discovered fictitious particle model to investigate\nthe fermion sign problem further. We consider the validity and invalidity\ncondition for the method of parametrized path integral formulation of the\npartition function and extrapolation to circumvent the fermion sign problem.\nFor the valid region of our method, our simulation shows that we may give\naccurate prediction of the energy for large fermion systems, which is much\nbeyond the capability of the direct sampling in the traditional method. In\nparticular, we find and verify a simple universal relation for high temperature\nnoninteracting particles or strongly repulsive interacting particles at low\ntemperatures.",
        "positive": "Comprehensive Characterization of a State-of-the-Art Apparatus for Cold\n  Electromagnetic Dysprosium Dipoles: We developed a new advanced ultra-cold Dysprosium (Dy) apparatus, which\nincorporates a quantum gas microscope (QGM) with a resolution of a quarter\nmicrometer. The QGM and the cooling and trapping regions are within the same\nvacuum glass vessel assuring simple atom transport between them. We demonstrate\nthe essential experimental steps of laser and evaporative cooling, lattice\nloading, transporting and precise positioning of a cloud of the bosonic isotope\n164 Dy at the QGM focal plane. Preliminary basic characterization of the QGM\nand future plans in enabling its full capacity are outlined. We also present a\nfeasible platform for simulating complex spin models of quantum magnetism, such\nas XYZ model, by exploiting a set of closely spaced opposite parity levels in\nDy with a large magnetic and electric dipole moment. We isolate a degenerate\nisospin-1/2 system, which possesses both magnetic and electric dipole-dipole\ncoupling, containing Ising, exchange and spin-orbit terms. The last gives rise\nto a spin model with asymmetric tunable rates, dependable on the lattice\ngeometry."
    },
    {
        "anchor": "CONAN -- the cruncher of local exchange coefficients for strongly\n  interacting confined systems in one dimension: We consider a one-dimensional system of particles with strong zero-range\ninteractions. This system can be mapped onto a spin chain of the Heisenberg\ntype with exchange coefficients that depend on the external trap. In this\npaper, we present an algorithm that can be used to compute these exchange\ncoefficients. We introduce an open source code CONAN (Coefficients of\nOne-dimensional N-Atom Networks) which is based on this algorithm. CONAN works\nwith arbitrary external potentials and we have tested its reliability for\nsystem sizes up to around 35 particles. As illustrative examples, we consider a\nharmonic trap and a box trap with a superimposed asymmetric tilted potential.\nFor these examples, the computation time typically scales with the number of\nparticles as $O(N^{3.5 \\pm 0.4})$. Computation times are around 10 seconds for\n$N=10$ particles and less than 10 minutes for $N=20$ particles.",
        "positive": "Three-component Fulde-Ferrell superfluids in a two-dimensional Fermi gas\n  with spin-orbit coupling: We investigate the pairing physics of a three-component spin-orbit coupled\nFermi gas in two spatial dimensions. The three atomic hyperfine states of the\nsystem are coupled by the recently realized synthetic spin-orbit coupling\n(SOC), which mixes different hyperfine states into helicity branches in a\nmomentum-dependent manner. As a consequence, the interplay of spin-orbit\ncoupling and the hyperfine-state dependent interactions leads to the emergence\nof Fulde-Ferrell (FF) pairing states with finite center-of-mass momenta even in\nthe absence of the Fermi-surface asymmetry that is usually mandatory to\nstabilize an SOC-induced FF state. We show that, for different combinations of\nspin-dependent interactions, the ground state of the system can either be the\nconventional Bardeen-Cooper-Schrieffer pairing state with zero center-of-mass\nmomentum or be the FF pairing states. Of particular interest here is the\nexistence of a three-component FF pairing state in which every two out of the\nthree components form FF pairing. We map out the phase diagram of the system\nand characterize the properties of the three-component FF state, such as the\norder parameters, the gapless contours and the momentum distributions. Based on\nthese results, we discuss possible experimental detection schemes for the\ninteresting pairing states in the system."
    },
    {
        "anchor": "Slow relaxation and sensitivity to disorder in trapped lattice fermions\n  after a quench: We consider a system of non-interacting fermions in one dimension subject to\na single-particle potential consisting of (a) a strong optical lattice, (b) a\nharmonic trap, and (c) uncorrelated on-site disorder. After a quench, in which\nthe center of the harmonic trap is displaced, we study the occupation function\nof the fermions and the time-evolution of experimental observables.\nSpecifically, we present numerical and analytical results for the post-quench\noccupation function of the fermions, and analyse the time-evolution of the\nreal-space density profile. Unsurprisingly for a non-interacting (and therefore\nintegrable) system, the infinite-time limit of the density profile is\nnon-thermal. However, due to Bragg-localization of the higher-energy\nsingle-particle states, the approach to even this non-thermal state is\nextremely slow. We quantify this statement, and show that it implies a\nsensitivity to disorder parametrically stronger than that expected from\nAnderson localization.",
        "positive": "Spin-orbit Coupled Bose-Einstein Condensates in Spin-dependent Optical\n  Lattices: We investigate the ground-state properties of spin-orbit coupled\nBose-Einstein condensates in spin-dependent optical lattices. The competition\nbetween the spin-orbit coupling strength and the depth of the optical lattice\nleads to a rich phase diagram. Without spin-orbit coupling, the spin-dependent\noptical lattices separate the condensates into alternating spin domains with\nopposite magnetization directions. With relatively weak spin-orbit coupling,\nthe spin domain wall is dramatically changed from N\\'{e}el wall to Bloch wall.\nFor sufficiently strong spin-orbit coupling, vortex chains and antivortex\nchains are excited in the spin-up and spin-down domains respectively,\ncorresponding to the formation of a lattice composed of meron-pairs and\nantimeron-pairs in the pseudospin representation. We also discuss how to\nobserve these phenomena in real experiments."
    },
    {
        "anchor": "Controlling the pair momentum of the FFLO state in a 3D Fermi gas\n  through a 1D periodic potential: The question whether a spin-imbalanced Fermi gas can accommodate the\nFulde-Ferrell-Larkin-Ovchinnikov (FFLO) state has been the subject of intense\nstudy. This state, in which Cooper pairs obtain a nonzero momentum, has\nhitherto eluded experimental observation. Recently, we demonstrated that the\nFFLO state can be stabilized in a 3D Fermi gas, by adding a 1D periodic\npotential. Until now it was assumed that the FFLO wave vector always lies\nparallel to this periodic potential (FFLO-P). In this contribution we show\nthat, surprisingly, the FFLO wave vector can also lie skewed with respect to\nthe potential (FFLO-S). Starting from the partition sum, the saddle-point free\nenergy of the system is derived within the path-integral formalism. Minimizing\nthis free energy allows us to study the different competing ground states of\nthe system. To qualitatively understand the underlying pairing mechanism, we\nvisualize the Fermi surfaces of the spin up and spin down particles. From this\nvisualization, we find that tilting the FFLO wave vector with respect to the\ndirection of the periodic potential, can result in a larger overlap between the\npairing bands of both spin species. This skewed FFLO state can provide an\nadditional experimental signature for observing FFLO superfluidity in a 3D\nFermi gas.",
        "positive": "Quantum states of dark solitons in the 1D Bose gas: We present a series of quantum states that are characterized by dark solitons\nof the nonlinear Schr\\\"{o}dinger equation (i.e. the Gross-Pitaevskii equation)\nfor the one-dimensional (1D) Bose gas interacting through the repulsive\ndelta-function potentials. The classical solutions satisfy the periodic\nboundary conditions and we call them periodic dark solitons. Through exact\nsolutions we show corresponding aspects between the states and the solitons in\nthe weak coupling case: the quantum and classical density profiles completely\noverlap with each other not only at an initial time but also at later times\nover a long period of time, and they move together with the same speed in time;\nthe matrix element of the bosonic field operator between the quantum states has\nexactly the same profiles of the square amplitude and the phase as the\nclassical complex scalar field of a periodic dark soliton not only at the\ninitial time but also at later times, and the corresponding profiles move\ntogether for a long period of time. We suggest that the corresponding\nproperties hold rigorously in the weak coupling limit. Furthermore, we argue\nthat the lifetime of the dark soliton-like density profile in the quantum state\nbecomes infinitely long as the coupling constant approaches zero, by comparing\nit with the quantum speed limit time. Thus, we call the quantum states quantum\ndark soliton states."
    },
    {
        "anchor": "Testing the universality of the many-body metal-insulator transition by\n  time evolution of a disordered one-dimensional ultracold fermionic gas: It is now possible to study experimentally the combined effect of disorder\nand interactions in cold atom physics. Motivated by these developments we\ninvestigate the dynamics around the metal-insulator transition (MIT) in a\none-dimensional (1D) Fermi gas with short-range interactions in a quasiperiodic\npotential by the time-dependent density-matrix renormalization group (tDMRG)\ntechnique. By tuning disorder and interactions we study the MIT from the weakly\nto the strongly interacting limit. The MIT is not universal as time evolution,\nwell described by a process of anomalous diffusion, depends qualitatively on\nthe interaction strength. By using scaling ideas we relate the parameter that\ncontrols the diffusion process with the critical exponent that describes the\ndivergence of the localization length. In the limit of strong interactions\ntheoretical arguments suggest that the motion at the MIT tends to ballistic and\ncritical exponents approach mean-field predictions.",
        "positive": "Influence of global features of a Bose-Einstein condensate on the vortex\n  velocity: We study the way in which the geometry of the trapping potential affects the\nvortex velocity in a Bose-Einstein condensate confined by a toroidal trap. We\ncalculate the vortex precession velocity through a simple relationship between\nsuch a velocity and the gradient of the numerically obtained vortex energy. We\nobserve that our results correspond very closely to the velocity calculated\nthrough time evolution simulations. However, we find that the estimates derived\nfrom available velocity field formulas present appreciable differences. To\nresolve such discrepancies, we further study the induced velocity field,\nanalyzing the effect of global features of the condensate on such a field and\non the precession velocity."
    },
    {
        "anchor": "Majorana edge modes protected by emergent symmetry in a one dimensional\n  fermi gas: We show that a one dimensional ultra-cold Fermi gas with Rashba-like spin\norbit coupling, a Zeeman field and intrinsic attractive interactions exhibits a\nnovel topological superfluid state, which forms in spite of total number\nconservation and the absence of a single particle gap. Majorana zero modes are\nlocalized to the interface between a topological region in the middle of the\ntrap and trivial regions at its wings. Unlike the realization of a topological\nsuperconductor in proximity coupled nano-wires, the Majorana modes do not carry\na quantum number associated with the total fermion parity. Instead, the\ntopological degeneracy is protected by an emergent $Z_2$ symmetry present only\nat low energies. We discuss the experimental implications of the novel zero\nmodes, as manifest for example in the response to modulation of a local\npotential near the position of the Majorana bound states. For the range of\ninteraction strength corresponding to Luttinger parameter $1<K<2$ the zero\nmodes are unseperable from the gapless phonon continuum and therefore show up\nas an algebraic zero bias resonance in the response. For $K>2$, on the other\nhand the zero-mode can be detected as a sharp low frequency response at an\nenergy which generically scales with system size as $1/L^{K/2}$ and is\ntherefore parametrically separated from the phonons.",
        "positive": "Simulation of nodal-line semimetal in amplitude-shaken optical lattices: With topologcial semimetal developing, semimetal with nodal-line ring comes\ninto people's vision as a powerful candidate for practical application of\ntopological devices. We propose a method using ultracold atoms in\ntwo-dimensional amplitude-shaken bipartite hexagonal optical lattice to\nsimulate nodal-line semimetal, which can be achieved in experiment by attaching\none triangular optical lattice to a hexangonal optical lattice and periodically\nmodulating the intensity and position of the triangular lattice. By amplitude\nshaking, a time-reversal-symmetry-unstable mode is introduced into the\nbipartite optical lattice, and then the nodal-line semimetal is gotten by\nadjusting the proportion of such mode and the trivial mode of hexagonal\nlattice. Through calculating the energy spectrum of effective Hamiltonian, the\ntransformation from Dirac semimetal to nodal-line semimetal in pace with\nchanging shaking parameters is observed. We also study the change of Berry\ncurvature and Berry phase in the transformation, which provides guidance on\nmeasuring the transformation in experiment. By analyzing the symmetry of the\nsystem, the emergence of the time-reversal-symmetry-unstable mode is\nresearched. This proposal provides a way to research the pure nodal-line\nsemimetal without the influence of other bands, which may contribute to the\nstudy of those unique features of surface states and bulk states of nodal-line\nsemimetal."
    },
    {
        "anchor": "Nonlinear Hall response in the driving dynamics of ultracold atoms in\n  optical lattices: We propose that a nonlinear Hall response can be observed in Bloch\noscillations of ultracold atoms in optical lattices under the condition of\npreserved time-reversal symmetry. In the short-time limit of Bloch oscillations\ndriven by a direct current (dc) field, the nonlinear Hall current dominates,\nbeing a second-order response to the external field strength. The associated\nBerry curvature dipole, which is a second-order nonlinear coefficient of the\ndriving field, can be obtained from the oscillation of atoms. In an alternating\ncurrent (ac) driving field, the nonlinear Hall response has a double frequency\nof the driving force in the case of time-reversal symmetry.",
        "positive": "Asymmetric population of momentum distribution by quasi-periodically\n  driving a triangular optical lattice: Ultracold atoms in periodical driven optical lattices enable us to\ninvestigate novel band structures and explore the topology of the bands. In\nthis work, we investigate the impact of the ramping process of the driving\nsignal and propose a simple but effective method to realize desired asymmetric\npopulation in momentum distribution by controlling the initial phase of the\ndriving signal. A quasi-momentum oscillation along the shaking direction in the\nframe of reference co-moving with the lattice is formed, causing the formation\nof the mix of ground energy band and first excited band in laboratory frame,\nwithin the regime that the driving frequency is far less than the coupling\nfrequency between ground band and higher energy bands. This method avoids the\nconstruction of intricate lattices or complex control sequence. With a\ntriangular lattice, we experimentally investigate the influence of the initial\nphase, frequency, amplitude of the driving signal on the population difference,\nand observe good agreement with our theoretical model. This provides guidance\non how to load a driving signal in driven optical lattice experiment and also\npotentially supplies a useful tool to form a qubit that can be used in quantum\ncomputation."
    },
    {
        "anchor": "Bosonic integer quantum Hall effect in optical flux lattices: In two dimensions strongly interacting bosons in a magnetic field can realize\na bosonic integer quantum Hall state, the simplest two dimensional example of a\nsymmetry protected topological phase. We propose a realistic implementation of\nthis phase using an optical flux lattice. Through exact diagonalization\ncalculations, we show that the system exhibits a clear bulk gap and the\ntopological signature of the bosonic integer quantum Hall state. In particular,\nthe calculation of the many-body Chern number leads to a quantized Hall\nconductance in agreement with the analytical predictions. We also study the\nstability of the phase with respect to some of the experimentally relevant\nparameters.",
        "positive": "Emergence of spiral dark solitons in the merging of rotating\n  Bose-Einstein condensates: Merging of isolated Bose-Einstein condensates (BECs) is an important topic\ndue to its relevance to matter-wave interferometry and the Kibble-Zurek\nmechanism. Many past research focused on merging of BECs with uniform initial\nphases. In our recent numerical study (Phys. Rev. A 97, 013612 (2018)), we\nrevealed that upon merging of rotating BECs with non-uniform initial phases,\nspiral-shaped dark solitons can emerge. These solitons facilitate angular\nmomentum transfer and allow the merged condensate to rotate even in the absence\nof quantized vortices. More strikingly, the sharp endpoints of these spiral\nsolitons can induce rotational motion in the BECs like vortices but with\neffectively a fraction of a quantized circulation. This paper reports our\nsystematic study on the merging dynamics of rotating BECs. We discuss how the\npotential barrier that initially separates the BECs can affect the profile of\nthe spiral solitons. We also show that the number of spiral solitons created in\nthe BECs matches the relative winding number of the rotating BECs. The\nunderlying mechanism of the observed soliton dynamics is explained."
    },
    {
        "anchor": "Perturbative Approach to Superfluidity under Nonuniform Potential: A perturbative way to investigate superfluid properties of various systems\nunder nonuniform potential is presented. We derive the perturbation expansion\nof the superfluid fraction, which indicates how liquid exhibits nonclassical\nrotational inertia, in terms of the strength of nonuniform potential and find\nthat the coefficient of the leading term reflects the density fluctuation of\nthe system. Our formulation does not assume anything about Bose-Einstein\ncondensation and thus is applicable to wide variety of systems. Superfluid\nproperties of some examples including (non-)interacting Bose systems,\nespecially Bose gas in the mean field limit, (non-)interacting Fermi sytems,\nTomonaga-Luttinger liquid and spinless chiral $p$-wave superfluid are\ninvestigated.",
        "positive": "Topological influence and back-action between topological excitations: Topological objects can influence each other if the underlying homotopy\ngroups are non-Abelian. Under such circumstances, the topological charge of\neach individual object is no longer a conserved quantity and can be transformed\nto each other. Yet, we can identify the conservation law by considering the\nback-action of topological influence. We develop a general theory of\ntopological influence and back-action based on the commutators of the\nunderlying homotopy groups. We illustrate the case of the topological influence\nof a half-quantum vortex on the sign change of a point defect and point out\nthat the topological back-action from the point defect is such twisting of the\nvortex that the total twist of the vortex line carries the change in the\npoint-defect charge to conserve the total charge. We use this theory to\nclassify charge transfers in condensed matter systems and show that a\nnon-Abelian charge transfer can be realized in a spin-2 Bose-Einstein\ncondensate."
    },
    {
        "anchor": "Optimal Gaussian squeezed states for atom-interferometry in the presence\n  of phase diffusion: We optimize the signal-to-noise ratio of a Mach-Zehnder atom interferometer\nwith Gaussian squeezed input states, in the presence interactions. For weak\ninteractions, our results coincide with Phys. Rev. Lett. {\\bf 100}, 250406\n(2008), with optimal initial number-variance $\\sigma_o\\propto N^{1/3}$ and\noptimal signal-to-noise ratio $s_o\\propto N^{2/3}$ for total atom number $N$.\nAs the interaction strength $u$ increases past unity, phase-diffusion becomes\ndominant, leading to a transition in the optimal squeezing from initial\nnumber-squeezing to initial {\\it phase}-squeezing with\n$\\sigma_o\\propto\\sqrt{uN}$ and $s_o\\propto\\sqrt{N/u}$ shot-noise scaling. The\ninitial phase-squeezing translates into hold-time number-squeezing, which is\nless sensitive to interactions than coherent states and improves $s_o$ by a\nfactor of $\\sqrt{u}$.",
        "positive": "Universal contact for a Tonks-Girardeau gas at finite temperature: We determine the finite-temperature momentum distribution of a strongly\ninteracting 1D Bose gas in the Tonks-Girardeau (impenetrable-boson) limit under\nharmonic confinement, and explore its universal properties associated to the\nscale invariance of the model. We show that, at difference from the unitary\nFermi gas in three dimensions, the weight of its large-momentum tails -- given\nby the Tan's contact -- increase with temperature, and calculate the\nhigh-temperature universal second contact coefficient using a virial expansion."
    },
    {
        "anchor": "Phase Diagram of a Spin-Orbit Coupled Fermi Gases in a Bilayer Optical\n  Lattice: We investigate the stability of helical superfluid phase in a spin-orbit\ncoupled Fermi gas loaded in a bilayer optical lattice. The phase diagram of the\nsystem is constructed in the mean field framework. We investigate the\ntopological properties of the superfluid phases by a nontrivial application of\nthe Fermi surface topological invariant to our time-reversal invariant system\nwith degeneracies on the Fermi surface. We find that there is a first-order\nphase boundary in the phase diagram of half filling case and the superfluid\nphases are all topological trivial. The superfluid phase is topological\nnontrivial when the filling fraction deviates from the half filling. In the\ntopological nontrivial superfluid phase, a full pairing gap exists in the bulk\nand gapless helical Majorana edge states exist at the boundary.",
        "positive": "Transient phases and dynamical transitions in the post quench evolution\n  of the generalized Bose-Anderson model: The exact description of the time evolution of open correlated quantum\nsystems remains one of the major challenges of the condensed matter theory,\nspecially for asymptotic long times where most numerical methods fail. Here,\nthe post-quench dynamics of the $N$-component Bose-Anderson impurity model is\nstudied in the $N\\to\\infty$ limit. The equilibrium phase diagram is similar to\nthat of the Bose-Hubbard model in that it contains local versions of the Mott\nand Bose phases. Using a numerically exact procedure we are able to study the\nreal time evolution including asymptotic long time regimes. The formation of\nlong-lived transient phases is observed for quench paths crossing foreign\nphases. For quenches inside the local Bose condensed phase, a dynamical phase\ntransition is reported, that separates the evolution towards a new equilibrium\nstate and a regime characterized at large times by a persistent phase rotation\nof the order parameter. We explain how such non-decaying mode can exist in the\npresence of a dissipative bath. We discuss the extension of our results to the\nexperimental relevant finite-$N$ case and their implication for the existence\nof non-decaying modes in generic quantum systems in the presence of a bath."
    },
    {
        "anchor": "Generalized acceleration theorem for spatiotemporal Bloch waves: A representation is put forward for wave functions of quantum particles in\nperiodic lattice potentials subjected to homogeneous time-periodic forcing,\nbased on an expansion with respect to Bloch-like states which embody both the\nspatial and the temporal periodicity. It is shown that there exists a\ngeneralization of Bloch's famous acceleration theorem which grows out of this\nrepresentation and captures the effect of a weak probe force applied in\naddition to a strong dressing force. Taken together, these elements point at a\n\"dressing and probing\" strategy for coherent wave-packet manipulation, which\ncould be implemented in present experiments with optical lattices.",
        "positive": "Tuning an effective spin chain of three strongly interacting\n  one-dimensional fermions with the transversal confinement: Strongly interacting one-dimensional fermions form an effective spin chain in\nthe absence of an external lattice potential. We show that the exchange\ncoefficients of such a chain may be locally tuned by properly tailoring the\ntransversal confinement. In particular, in the vicinity of a\nconfinement-induced resonance (CIR) the exchange coefficients may have\nsimultaneously opposite ferromagnetic and antiferromagnetic characters at\ndifferent locations along the trap axis. Moreover, the local exchanges may be\nengineered to induce avoided crossings between spin states at the CIR, and\nhence a ramp across the resonance may be employed to create different spin\nstates and to induce spin dynamics in the chain. We show that such unusual spin\nchains have already been realized in the experiment of Murmann et al. [Phys.\nRev. Lett. 115, 215301 (2015)]."
    },
    {
        "anchor": "Optimizing a spin-flip Zeeman slower: We present a design of a spin-flip Zeeman slower controlled by a fast\nfeedback circuit for a sodium Bose-Einstein condensate apparatus. We also\ndemonstrate how the efficiency of the slower strongly depends on its intrinsic\nparameters, and compare these observations with a few theoretical models. Our\nfindings lead to a simple three-step procedure of designing an optimal Zeeman\nslower for neutral atoms, especially for those atomic species with high initial\nvelocities, such as sodium and lithium atoms.",
        "positive": "A Reduction-Based Strategy for Optimal Control of Bose-Einstein\n  Condensates: Applications of Bose-Einstein Condensates (BEC) often require that the\ncondensate be prepared in a specific complex state. Optimal control is a\nreliable framework to prepare such a state while avoiding undesirable\nexcitations, and, when applied to the time-dependent Gross-Pitaevskii Equation\n(GPE) model of BEC in multiple space dimensions, results in a large\ncomputational problem. We propose a control method based on first reducing the\nproblem, using a Galerkin expansion, from a PDE to a low-dimensional\nHamiltonian ODE system. We then apply a two-stage hybrid control strategy. At\nthe first stage, we approximate the control using a second Galerkin-like method\nknown as CRAB to derive a finite-dimensional nonlinear programming problem,\nwhich we solve with a differential evolution (DE) algorithm. This search method\nthen yields a candidate local minimum which we further refine using a variant\nof gradient descent. This hybrid strategy allows us to greatly reduce\nexcitations both in the reduced model and the full GPE system."
    },
    {
        "anchor": "d-Wave Superfluidity in Optical Lattices of Ultracold Polar Molecules: Recent work on ultracold polar molecules, governed by a generalization of the\nt-J Hamiltonian, suggests that molecules may be better suited than atoms for\nstudying d-wave superfluidity due to stronger interactions and larger\ntunability of the system. We compute the phase diagram for polar molecules in a\ncheckerboard lattice consisting of weakly coupled square plaquettes. In the\nsimplest experimentally realizable case where there is only tunneling and an\nXX-type spin-spin interaction, we identify the parameter regime where d-wave\nsuperfluidity occurs. We also find that the inclusion of a density-density\ninteraction destroys the superfluid phase and that the inclusion of a\nspin-density or an Ising-type spin-spin interaction can enhance the superfluid\nphase. We also propose schemes for experimentally realizing the perturbative\ncalculations exhibiting enhanced d-wave superfluidity.",
        "positive": "Phase diagram of strongly attractive $p$-orbital fermions on optical\n  lattices: We examine a system of doubly degenerate $p$-orbital polarized fermions on a\ntwo-dimensional square lattice with a strong on-site interaction. We consider\nthe system density at the half filling limit and tackle the strong attractive\ninteraction using a perturbation theory. We treat the four-site square\nplaquette interaction term generated from the directional tunneling dependence\nof $p$-orbitals using the fourth order in perturbation theory. We map the\nstrong coupling particle Hamiltonian into an effective spin-Hamiltonian and\nthen use a variational mean field approach and a linear spin-wave theory to\nstudy the phase diagram. Further, we discuss the experimental signatures of\nthese phases within the context of current cold-atom experimental techniques."
    },
    {
        "anchor": "Spontaneous Symmetry Breaking of Vortex Number in Binary Alternating\n  Current Countersuperflow: In binary superfluid counterflow systems, vortex nucleation arises as a\nconsequence of hydrodynamic instabilities when the coupling coefficient and\ncounterflow velocity exceed the critical value. When dealing with two identical\ncomponents, one might naturally anticipate that the number of vortices\ngenerated would remain equal. However, through the numerical experiments of the\nholographic model and the Gross-Pitaevskii equation, our investigation has\nunveiled a remarkable phenomenon: in Alternating Current counterflow systems,\nonce the coupling coefficient and frequency exceed certain critical values, a\nsurprising symmetry-breaking phenomenon occurs. This results in an asymmetry in\nthe number of vortices in the two components. We establish that this phenomenon\nrepresents a novel continuous phase transition, which, as indicated by the\nphase diagram, is exclusively observable in Alternating Current counterflow. We\nprovide an explanation for this intriguing phenomenon through soliton\nstructures, thereby uncovering the complex and unique characteristics of\nquantum fluid instabilities and their rich phenomena.",
        "positive": "Dynamical localization of interacting bosons in the few-body limit: The quantum kicked rotor is well-known to display dynamical localization in\nthe non-interacting limit. In the interacting case, while the mean-field\n(Gross-Pitaevskii) approximation displays a destruction of dynamical\nlocalization, its fate remains debated beyond mean-field. Here we study the\nkicked Lieb-Liniger model in the few-body limit. We show that for any\ninteraction strength, two kicked interacting bosons always dynamically\nlocalize, in the sense that the energy of the system saturates at long time.\nHowever, contrary to the non-interacting limit, the momentum distribution\n$\\Pi(k)$ of the bosons is not exponentially localized, but decays as $\\mathcal\nC/k^4$, as expected for interacting quantum particles, with Tan's contact\n$\\mathcal C$ which remains finite at long time. We discuss how our results will\nimpact the experimental study of kicked interacting bosons."
    },
    {
        "anchor": "Magnetic polarons in two-component hard core bosons: We use a high-temperature expansion to explore spin correlations around a\nsingle hole in a two- dimensional lattice filled with a hard-core two component\nbose gas. We find that the spins around the hole develop ferromagnetic order\nand quantify the degree of polarization at temperatures of order the hopping\nenergy, finding a measurably nonzero polarization. We also discuss the effect\nof fixing the overall magnetization of the system for finite-sized systems.",
        "positive": "Collective Dipole Oscillation of a Spin-Orbit Coupled Bose-Einstein\n  Condensate: We present an experimental study of the collective dipole oscillation of a\nspin-orbit coupled Bose-Einstein condensate in a harmonic trap. Dynamics of the\ncenter-of-mass dipole oscillation is studied in a broad parameter region, as a\nfunction of spin-orbit coupling parameters as well as oscillation amplitude.\nAnharmonic properties beyond effective-mass approximation are revealed, such as\namplitude-dependent frequency and finite oscillation frequency at place with\ndivergent effective mass. These anharmonic behaviors agree quantitatively with\nvariational wave-function calculations. Moreover, we experimentally demonstrate\na unique feature of spin-orbit coupled system predicted by a sum-rule approach,\nstating that spin polarization susceptibility--a static physical quantity--can\nbe measured via dynamics of dipole oscillation. The divergence of polarization\nsusceptibility is observed at the quantum phase transition that separates\nmagnetic nonzero-momentum condensate from nonmagnetic zero-momentum phase. The\ngood agreement between the experimental and theoretical results provides a\nbench mark for recently developed theoretical approaches."
    },
    {
        "anchor": "The temperature evolution of the shear viscosity in a unitary Fermi gas: We present an ab initio determination of the shear viscosity for the unitary\nFermi gas based on finite temperature quantum Monte Carlo (QMC) calculations\nand the Kubo linear-response formalism. The results are confronted with the\nbound for the shear viscosity originating from hydrodynamic fluctuations.\nAssuming smoothness of the frequency dependent shear viscosity eta(omega), we\nshow that the bound is violated in the low temperature regime and the violation\noccurs simultaneously with the onset of the Cooper paring in the system. In\norder to preserve the hydrodynamic bound in QMC eta(omega) has to possess a\nsharp structure located in the vicinity of zero frequency which is not resolved\nby an analytic continuation procedure.",
        "positive": "Observation of Efimov Universality across a Non-Universal Feshbach\n  Resonance in \\textsuperscript{39}K: We study three-atom inelastic scattering in ultracold \\textsuperscript{39}K\nnear a Feshbach resonance of intermediate coupling strength. The non-universal\ncharacter of such resonance leads to an abnormally large Efimov absolute length\nscale and a relatively small effective range $r_e$, allowing the features of\nthe \\textsuperscript{39}K Efimov spectrum to be better isolated from the\nshort-range physics. Meticulous characterization of and correction for finite\ntemperature effects ensure high accuracy on the measurements of these features\nat large-magnitude scattering lengths. For a single Feshbach resonance, we\nunambiguously locate four distinct features in the Efimov structure. Three of\nthese features form ratios that obey the Efimov universal scaling to within\n10\\%, while the fourth feature, occurring at a value of scattering length\nclosest to $r_e$, instead deviates from the universal value."
    },
    {
        "anchor": "Realizing unconventional quantum magnetism with symmetric top molecules: We demonstrate that ultracold symmetric top molecules loaded into an optical\nlattice can realize highly tunable and unconventional models of quantum\nmagnetism, such as an XYZ Heisenberg spin model. We show that anisotropic\ndipole-dipole interactions between molecules can lead to effective spin-spin\ninteractions which exchange spin and orbital angular momentum. This exchange\nproduces effective spin models which do not conserve magnetization and feature\ntunable degrees of spatial and spin-coupling anisotropy. In addition to\nderiving pure spin models when molecules are pinned in a deep optical lattice,\nwe show that models of itinerant magnetism are possible when molecules can\ntunnel through the lattice. Additionally, we demonstrate rich tunability of the\neffective models' parameters using only a single microwave frequency, in\ncontrast to proposals with $^1\\Sigma$ diatomic molecules, which often require\nmany microwave frequencies. Our results are germane not only for experiments\nwith polyatomic symmetric top molecules, such as methyl fluoride (CH$_3$F), but\nalso diatomic molecules with an effective symmetric top structure, such as the\nhydroxyl radical OH.",
        "positive": "Fractional Local Moment and High Temperature Kondo Effect in\n  Rashba-Fermi Gases: We investigate the new physics that arises when a correlated quantum impurity\nhybridizes with Fermi gas with a generalized Rashba spin-orbit coupling\nproduced via a uniform synthetic non-Abelian gauge field. We show that the\nimpurity develops a {\\it fractional} local moment which couples\nanti-ferromagnetically to the Rashba-Fermi gas. This results in a concomitant\n{\\it Kondo effect with a high temperature scale} that can be tuned by the\nstrength of the Rashba spin-orbit coupling."
    },
    {
        "anchor": "Suppressing defect production during passage through a quantum critical\n  point: We show that a closed quantum system driven through a quantum critical point\nwith two rates $\\omega_1$ (which controls its proximity to the quantum critical\npoint) and $\\omega_2$ (which controls the dispersion of the low-energy\nquasiparticles at the critical point) exhibits novel scaling laws for defect\ndensity $n$ and residual energy $Q$. We demonstrate suppression of both $n$ and\n$Q$ with increasing $\\omega_2$ leading to an alternate route to achieving\nnear-adiabaticity in a finite time for a quantum system during its passage\nthrough a critical point. We provide an exact solution for such dynamics with\nlinear drive protocols applied to a class of integrable models, supplement this\nsolution with scaling arguments applicable to generic many-body Hamiltonians,\nand discuss specific models and experimental systems where our theory may be\ntested.",
        "positive": "Three-component Fermi gas with SU(3) symmetry: BCS-BEC crossover in\n  three and two dimensions: We analyze the BCS-BEC crossover for a Fermi gas made of neutral atoms in\nthree hyperfine states with a SU(3) invariant attractive interaction. By\nsolving the extended BCS equations for the total number of particles and the\npairing gap, we calculate at zero temperature the pairing gap, the population\nimbalance, the condensate fraction and the first sound velocity of the uniform\nsystem as a function of the interaction strength in both three and two\ndimensions. Contrary to the three-dimensional case, in two dimensions the\ncondensate fraction approaches the value 1 only for an extremely large\ninteraction strength and, moreover, the sound velocity gives a clear signature\nof the disappearance of one of the three hyperfine components."
    },
    {
        "anchor": "Spin oscillations of the normal polarized Fermi gas at Unitarity: Using density functional theory in a time dependent approach we determine the\nfrequencies of the compressional modes of the normal phase of a Fermi gas at\nunitarity as a function of its polarization. Our energy functional accounts for\nthe typical elastic deformations exhibited by Landau theory of Fermi liquids.\nThe comparison with the available experiments is biased by important\ncollisional effects affecting both the {\\it in phase} and the {\\it out of\nphase} oscillations even at the lowest temperatures. New experiments in the\ncollisionless regime would provide a crucial test of the applicability of\nLandau theory to the dynamics of these strongly interacting normal Fermi gases.",
        "positive": "Probing the topology of density matrices: The mixedness of a quantum state is usually seen as an adversary to\ntopological quantization of observables. For example, exact quantization of the\ncharge transported in a so-called Thouless adiabatic pump is lifted at any\nfinite temperature in symmetry-protected topological insulators. Here, we show\nthat certain directly observable many-body correlators preserve the integrity\nof topological invariants for mixed Gaussian quantum states in one dimension.\nOur approach relies on the expectation value of the many-body\nmomentum-translation operator, and leads to a physical observable --- the\n\"ensemble geometric phase\" (EGP) --- which represents a bona fide geometric\nphase for mixed quantum states, in the thermodynamic limit. In cyclic\nprotocols, the EGP provides a topologically quantized observable which detects\nencircled spectral singularities (\"purity-gap\" closing points) of density\nmatrices. While we identify the many-body nature of the EGP as a key\ningredient, we propose a conceptually simple, interferometric setup to directly\nmeasure the latter in experiments with mesoscopic ensembles of ultracold atoms."
    },
    {
        "anchor": "Classical verification of a quantum simulator: local relaxation of a 1D\n  Bose gas: In [Nat. Phys. 8, 325-330 (2012)], Trotzky et al. utilize ultracold atoms in\nan optical lattice to simulate the local relaxation dynamics of a strongly\ninteracting Bose gas \"for longer times than present classical algorithms can\nkeep track of\". Here, I classically verify the results of this analog quantum\nsimulator by calculating the evolution of the same quasi-local observables up\nto the time at which they appear \"fully relaxed\". Using a parallel\nimplementation of the time-evolving block decimation (TEBD) algorithm to\nsimulate the system on a supercomputer, I show that local densities and\ncurrents can be calculated in a matter of days rather than weeks. The precision\nof these numerics allows me to observe deviations from the conjectured\npower-law decay and to determine the effects of the harmonic trapping\npotential. As well as providing a robust benchmark for future experimental,\ntheoretical, and numerical methods, this work serves as an example of the\nindependent verification process.",
        "positive": "Quasiparticle energy in a strongly interacting homogeneous Bose-Einstein\n  condensate: Using two-photon Bragg spectroscopy, we study the energy of particle-like\nexcitations in a strongly interacting homogeneous Bose-Einstein condensate, and\nobserve dramatic deviations from Bogoliubov theory. In particular, at large\nscattering length $a$ the shift of the excitation resonance from the\nfree-particle energy changes sign from positive to negative. For an excitation\nwith wavenumber $q$, this sign change occurs at $a \\approx 4/(\\pi q)$, in\nagreement with the Feynman energy relation and the static structure factor\nexpressed in terms of the two-body contact. For $a \\gtrsim 3/q$ we also see a\nbreakdown of this theory, and better agreement with calculations based on the\nWilson operator product expansion. Neither theory explains our observations\nacross all interaction regimes, inviting further theoretical efforts."
    },
    {
        "anchor": "Dynamical structure factor of one-dimensional Bose gases: experimental\n  signatures of beyond-Luttinger liquid physics: Interactions are known to have dramatic effects on bosonic gases in one\ndimension (1D). Not only does the ground state transform from a condensate-like\nstate to an effective Fermi sea, but new fundamental excitations, which do not\nhave any higher-dimensional equivalents, are predicted to appear. In this work,\nwe trace these elusive excitations via their effects on the dynamical structure\nfactor of 1D strongly-interacting Bose gases at low temperature. An array of 1D\nBose gases is obtained by loading a $^{87}$Rb condensate in a 2D lattice\npotential. The dynamical structure factor of the system is probed by energy\ndeposition through low-momentum Bragg excitations. The experimental signals are\ncompared to recent theoretical predictions for the dynamical structure factor\nof the Lieb-Liniger model at $T > 0$. Our results demonstrate that the main\ncontribution to the spectral widths stems from the dynamics of the\ninteraction-induced excitations in the gas, which cannot be described by the\nLuttinger liquid theory.",
        "positive": "Dark soliton collisions in superfluid Fermi gases: In this work dark soliton collisions in a one-dimensional superfluid Fermi\ngas are studied across the BEC-BCS crossover by means of a recently developed\nfinite-temperature effective field theory [S. N. Klimin, J. Tempere, G.\nLombardi, J. T. Devreese, Eur. Phys. J. B 88, 122 (2015)] . The evolution of\ntwo counter-propagating solitons is simulated numerically based on the theory's\nnonlinear equation of motion for the pair field. The resulting collisions are\nobserved to introduce a spatial shift into the trajectories of the solitons.\nThe magnitude of this shift is calculated and studied in different conditions\nof temperature and spin-imbalance. When moving away from the BEC-regime, the\ncollisions are found to become inelastic, emitting the lost energy in the form\nof small-amplitude density oscillations. This inelasticity is quantified and\nits behavior analyzed and compared to the results of other works. The\ndispersion relation of the density oscillations is calculated and is\ndemonstrated to show a good agreement with the spectrum of collective\nexcitations of the superfluid."
    },
    {
        "anchor": "Localization of a Bose-Fermi mixture in a bichromatic optical lattice: We study the localization of a cigar-shaped super-fluid Bose-Fermi mixture in\na quasi-periodic bichromatic optical lattice (OL) for inter-species attraction\nand intra-species repulsion. The mixture is described by the Gross-Pitaevskii\nequation for the bosons, coupled to a hydrodynamic mean-field equation for\nfermions at unitarity. We confirm the existence of the symbiotic localized\nstates in the Bose-Fermi mixture and Anderson localization of the Bose\ncomponent in the interacting Bose-Fermi mixture on a bichromatic OL. The phase\ndiagram in boson and fermion numbers showing the regions of the symbiotic and\nAnderson localization of the Bose component is presented. Finally, the\nstability of symbiotic and Anderson localized states is established under small\nperturbations.",
        "positive": "Quantum quench dynamics of the Luttinger model: The dynamics of the Luttinger model after a quantum quench is studied. We\ncompute in detail one and two-point correlation functions for two types of\nquenches: from a non-interacting to an interacting Luttinger model and\nvice-versa. In the former case, the non-interacting Fermi gas features in the\nmomentum distribution and other correlation functions are destroyed as time\nevolves. In the infinite-time limit, equal-time correlations are power-laws but\nthe critical exponents are found to differ from their equilibrium values. In\nall cases, we find that these correlations are well described by a generalized\nGibbs ensemble [M. Rigol et al., Phys. Rev. Lett. 98, 050405 (2007)], which\nassigns a momentum dependent temperature to each eigenmode."
    },
    {
        "anchor": "Dual-species Bose-Einstein condensate of 41K and 87Rb in a hybrid trap: We report on the production of a 41K-87Rb dual-species Bose-Einstein\ncondensate in a hybrid trap, consisting of a magnetic quadrupole and an optical\ndipole potential. After loading both atomic species in the trap, we cool down\n87Rb first by magnetic and then by optical evaporation, while 41K is\nsympathetically cooled by elastic collisions with 87Rb. We eventually produce\ntwo-component condensates with more than 10^5 atoms and tunable species\npopulation imbalance. We observe the immiscibility of the quantum mixture by\nmeasuring the density profile of each species after releasing them from the\ntrap.",
        "positive": "Quantum melting of two-component Rydberg crystals: We investigate the quantum melting of one dimensional crystals that are\nrealized in an atomic lattice in which ground state atoms are laser excited to\ntwo Rydberg states. We focus on a regime where both, intra- and inter-state\ndensity-density interactions as well as coherent exchange interactions\ncontribute. We determine stable crystalline phases in the classical limit and\nexplore their melting under quantum fluctuations introduced by the excitation\nlaser as well as two-body exchange. We find that within a specific parameter\nrange quantum fluctuations introduced by the laser can give rise to a devil's\nstaircase structure which one might associate with transitions in the classical\nlimit. The melting through exchange interactions is shown to also proceed in a\nstep-like fashion, in case of small crystals, due to the proliferation of\nRydberg spinwaves."
    },
    {
        "anchor": "Quantum and thermal fluctuations in bosonic Josephson junctions: We use the Bose-Hubbard Hamiltonian to study quantum fluctuations in\ncanonical equilibrium ensembles of bosonic Josephson junctions at relatively\nhigh temperatures, comparing the results for finite particle numbers to the\nclassical limit that is attained as $N$ approaches infinity. We consider both\nattractive and repulsive atom-atom interactions, with especial focus on the\nbehavior near the T=0 quantum phase transition that occurs, for large enough\n$N$, when attractive interactions surpass a critical level. Differences between\nBose-Hubbard results for small $N$ and those of the classical limit are quite\nsmall even when $N \\sim 100$, with deviations from the limit diminishing as\n1/N.",
        "positive": "Loschmidt Echo for quantum metrology: We propose a versatile Loschmidt echo protocol to detect and quantify\nmultiparticle entanglement. It allows us to extract the quantum Fisher\ninformation for arbitrary pure states, and finds direct application in quantum\nmetrology. In particular, the protocol applies to states that are generally\ndifficult to characterize, as non-Gaussian states, and states that are not\nsymmetric under particle exchange. We focus on atomic systems, including\ntrapped ions, polar molecules, and Rydberg atoms, where entanglement is\ngenerated dynamically via long-range interaction, and show that the protocol is\nstable against experimental detection errors."
    },
    {
        "anchor": "Quantum corrections to a spin-orbit coupled Bose-Einstein Condensate: We study systematically the quantum corrections to a weakly interacting\nBose-Einstein condensate with spin-orbit coupling. We show that quantum\nfluctuations, enhanced by the spin-orbit coupling, modify quantitatively the\nmean-field properties such as the superfluid density, spin polarizability, and\nsound velocity. We find that the phase boundary between the plane wave and zero\nmomentum phases is shifted to a smaller transverse field. We also calculate the\nBeliaev and Landau damping rates and find that the Landau process dominates the\nquasiparticle decay even at low temperature.",
        "positive": "Orbital-driven melting of a bosonic Mott insulator in a shaken optical\n  lattice: In order to study the interplay between localized and dispersive orbital\nstates in a system of ultracold atoms in an optical lattice, we investigate the\npossibility to coherently couple the lowest two Bloch bands by means of\nresonant periodic forcing. Considering bosons in one dimension, it is shown\nthat a strongly interacting Floquet system can be realized, where at every\nlattice site two (and only two) near-degenerate orbital states are relevant. By\nsmoothly tuning both states into resonance we find that the system can undergo\nan orbital-driven Mott-insulator-to-superfluid transition. As an intriguing\nconsequence of the kinetic frustration in the system, this transition can be\neither continuous or first-order, depending on parameters such as lattice depth\nand filling."
    },
    {
        "anchor": "A Mixture of Bose and Fermi Superfluids: Superconductivity and superfluidity of fermionic and bosonic systems are\nremarkable many-body quantum phenomena. In liquid helium and dilute gases, Bose\nand Fermi superfluidity has been observed separately, but producing a mixture\nin which both the fermionic and the bosonic components are superfluid is\nchallenging. Here we report on the observation of such a mixture with dilute\ngases of two Lithium isotopes, 6Li and 7Li. We probe the collective dynamics of\nthis system by exciting center-of-mass oscillations that exhibit extremely low\ndamping below a certain critical velocity. Using high precision spectroscopy of\nthese modes we observe coherent energy exchange and measure the coupling\nbetween the two superfluids. Our observations can be captured theoretically\nusing a sum-rule approach that we interpret in terms of two coupled\noscillators.",
        "positive": "Probing Confinement Through Dynamical Quantum Phase Transitions: From\n  Quantum Spin Models to Lattice Gauge Theories: Confinement is an intriguing phenomenon prevalent in condensed matter and\nhigh-energy physics. Exploring its effect on the far-from-equilibrium\ncriticality of quantum many-body systems is of great interest both from a\nfundamental and technological point of view. Here, we employ large-scale\nuniform matrix product state calculations to show that a qualitative change in\nthe type of dynamical quantum phase transitions (DQPTs) accompanies the\nconfinement-deconfinement transition in three paradigmatic models -- the\npower-law interacting quantum Ising chain, the two-dimensional quantum Ising\nmodel, and the spin-$S$ $\\mathrm{U}(1)$ quantum link model. By tuning a\nconfining parameter in these models, it is found that \\textit{branch}\n(\\textit{manifold}) DQPTs arise as a signature of (de)confinement. Whereas\nmanifold DQPTs are associated with a sign change of the order parameter, their\nbranch counterparts are not, but rather occur even when the order parameter\nexhibits considerably constrained dynamics. Our conclusions can be tested in\nmodern quantum-simulation platforms, such as ion-trap setups and cold-atom\nexperiments of gauge theories."
    },
    {
        "anchor": "Number Fluctuations of a Dipolar Condensate: Anisotropy and Slow\n  Approach to the Thermodynamic Regime: We present a theory for the number fluctuations of a quasi-two-dimensional\n(quasi-2D) dipolar Bose-Einstein condensate measured with finite resolution\ncells. We show that when the dipoles are tilted to have a component parallel to\nthe plane of the trap, the number fluctuations become anisotropic, i.e. depend\non the in-plane orientation of the measurement cell. We develop analytic\nresults for the quantum and thermal fluctuations applicable to the cell sizes\naccessible in experiments. We show that as cell size is increased the\nthermodynamic fluctuation result is approached much more slowly than in\ncondensates with short range interactions, so experiments would not require\nhigh numerical aperture imaging to observe the predicted effect.",
        "positive": "Thermodynamics of Attractive and Repulsive Fermi Gases in Two Dimensions: We study the attractive and repulsive two-component Fermi gas with spin\nimbalance in two dimensions. Using a generalized $T$-matrix approximation, we\nexamine the thermodynamic properties of both attractive and repulsive contact\ninteracting Fermi gases. The interaction strength, which is characterized by\nthe bound state energy $E_b=\\hbar^2/m a_{2d}^2$ in vacuum, can be adjusted\nthrough a Feshbach resonance. We calculate the interaction energy,\ncompressibility and spin susceptibility of the two branches of the Fermi gas.\nFor the repulsive branch, we also find a critical strength of interaction\n$a_{2d}^{(c)}$ above which this metastable thermodynamic state becomes\nunstable. This critical value depends on the temperature and the spin imbalance\n(the \"magnetization\") of the system."
    },
    {
        "anchor": "Rotating atomic quantum gases with light-induced azimuthal gauge\n  potentials and the observation of Hess-Fairbank effect: We demonstrate synthetic azimuthal gauge potentials for Bose-Einstein\ncondensates from engineering atom-light couplings. The gauge potential is\ncreated by adiabatically loading the condensate into the lowest energy\nRaman-dressed state, achieving a coreless vortex state. The azimuthal gauge\npotentials act as effective rotations and are tunable by the Raman coupling and\ndetuning. We characterize the spin textures of the dressed states, in\nagreements with the theory. The lowest energy dressed state is stable with a\n4.5-s half-atom-number-fraction lifetime. In addition, we exploit the azimuthal\ngauge potential to demonstrate the Hess-Fairbank effect, the analogue of\nMeissner effect in superconductors. The atoms in the absolute ground state has\na zero quasi-angular momentum and transits into a polar-core vortex when the\nsynthetic magnetic flux is tuned to exceed a critical value. Our demonstration\nserves as a paradigm to create topological excitations by tailoring atom-light\ninteractions where both types of SO(3) vortices in the $|\\langle\n\\vec{F}\\rangle|=1$ manifold, coreless vortices and polar-core vortices, are\ncreated in our experiment. The gauge field in the stationary Hamiltonian opens\na path to investigating rotation properties of atomic superfluids under thermal\nequilibrium.",
        "positive": "High partial-wave Feshbach resonances in an ultracold $^6$Li-$^{133}$Cs\n  mixture: We measure higher partial wave Feshbach resonances in an ultracold mixture of\nfermionic $^6$Li and bosonic $^{133}$Cs by magnetic field dependent atom-loss\nspectroscopy. For the $p$-wave Feshbach resonances we observe triplet\nstructures corresponding to different projections of the pair rotation angular\nmomentum onto the external magnetic field axis.\n  We attribute the splittings to the spin-spin and spin-rotation couplings by\nmodelling the observation using a full coupled-channel calculation. Comparison\nwith an oversimplified model, estimating the spin-rotation coupling by\ndescribing the weakly bound close-channel molecular state with the perturbative\nmultipole expansion, reveals the significant contribution of the molecular\nwavefunction at short internuclear distances. Our findings highlight the\npotential of Feshbach resonances in providing precise information on short- and\nintermediate-range molecular couplings and wavefunctions. The observed $d$-wave\nFeshbach resonances allow us to refine the LiCs singlet and triplet\nground-state molecular potential curves at large internuclear separations."
    },
    {
        "anchor": "Keldysh field theory for nonequilibrium condensation in a parametrically\n  pumped polariton system: We develop a quantum field theory for parametrically pumped polaritons using\nKeldysh Green's function techniques. By considering the mean-field and Gaussian\nfluctuations, we find that the low energy physics of the highly non-equilibrium\nphase transition to the optical parametric oscillator regime is in many ways\nsimilar to equilibrium condensation. In particular, we show that this phase\ntransition can be associated with an effective chemical potential, at which the\nsystem's bosonic distribution function diverges, and an effective temperature.\nAs in equilibrium systems, the transition is achieved by tuning this effective\nchemical potential to the energy of the lowest normal mode. Since the\noccupations of the modes are available, we determine experimentally observable\nproperties, such as the luminescence and absorption spectra.",
        "positive": "Collective oscillations in ultracold atomic gases: Using both fluid and kinetic descriptions, where repulsive forces between\nnear by atoms are included, we discuss the basic oscillations and waves of a\ncloud of ultra-cold atoms confined in a magneto-optical trap. The existence of\na hybrid mode, with properties similar to both plasma and acoustic waves is\ndescribed in detail. Tonks-Dattner resonances for confined hybrid modes in a\nspherical cloud are discussed and the prediction of a nonlinear coupling\nbetween the dipole resonanc and the hybrid modes is considered. Landau damping\nprocesses and quasi-linear diffusion in velocity space are also discussed."
    },
    {
        "anchor": "Imbalanced Feshbach-resonant Fermi gases: We present an overview of recent developments in species-imbalanced\n(\"polarized\") Feshbach-resonant Fermi gases. We summarize the current status of\nthermodynamics of these systems in terms of a phase diagram as a function of\nthe Feshbach resonance detuning, polarization and temperature. We review\ninstabilities of the s-wave superfluidity across the BEC-BCS crossover to phase\nseparation, FFLO states, polarized molecular superfluidity and the normal\nstate, driven by the species imbalance. We discuss different models and\napproximations of this system and compare their predictions to current\nexperiments.",
        "positive": "Weak Ergodicity Breaking in Non-Hermitian Many-body Systems: The recent discovery of persistent revivals in the Rydberg-atom quantum\nsimulator has revealed a weakly ergodicity-breaking mechanism dubbed quantum\nmany-body scars, which are a set of nonthermal states embedded in otherwise\nthermal spectra. Until now, such a mechanism has been mainly studied in\nHermitian systems. Here, we establish the non-Hermitian quantum many-body scars\nand systematically characterize their nature from dynamic revivals,\nentanglement entropy, physical observables, and energy level statistics.\nNotably, we find the non-Hermitian quantum many-body scars exhibit\nsignificantly enhanced coherent revival dynamics when approaching the\nexceptional point. The signatures of non-Hermitian scars switch from the\nreal-energy axis to the imaginary-energy axis after a real-to-complex spectrum\ntransition driven by increasing non-Hermiticity, where an exceptional point and\na quantum tricritical point emerge simultaneously. We further examine the\nstability of non-Hermitian quantum many-body scars against external fields,\nreveal the non-Hermitian quantum criticality and eventually set up the whole\nphase diagram. The possible connection to the open quantum many-body systems is\nalso explored. Our findings offer insights for realizing long-lived coherent\nstates in non-Hermitian many-body systems."
    },
    {
        "anchor": "Observation of a dipolar quantum gas with metastable supersolid\n  properties: The competition of dipole-dipole and contact interactions leads to exciting\nnew physics in dipolar gases, well-illustrated by the recent observation of\nquantum droplets and rotons in dipolar condensates. We show that the\ncombination of the roton instability and quantum stabilization leads under\nproper conditions to a novel regime that presents supersolid properties, due to\nthe coexistence of stripe modulation and phase coherence. In a combined\nexperimental and theoretical analysis, we determine the parameter regime for\nthe formation of coherent stripes, whose lifetime of a few tens of milliseconds\nis limited by the eventual destruction of the stripe pattern due to three-body\nlosses. Our results open intriguing prospects for the development of long-lived\ndipolar supersolids.",
        "positive": "Mobile Impurities and Orthogonality Catastrophe in two-dimensional\n  Vortex Lattices: We investigate the properties of a neutral impurity atom coupled with the\nTkachenko modes of a two-dimensional vortex lattice Bose-Einstein condensate.\nIn contrast with polarons in homogeneous condensates, the marginal\nimpurity-boson interaction in the vortex lattice leads to infrared\nsingularities in perturbation theory and to the breakdown of the quasiparticle\npicture in the low energy limit. These infrared singularities are interpreted\nin terms of a renormalization of the coupling constant, quasiparticle weight\nand effective impurity mass. The divergence of the effective mass in the low\nenergy limit gives rise to an orthogonality catastrophe which is manifested as\na power law singularity in the impurity spectral function."
    },
    {
        "anchor": "Few-body perspective of a quantum anomaly in two-dimensional Fermi gases: Quantum anomaly manifests itself in the deviation of breathing mode frequency\nfrom the scale invariant value of $2\\omega$ in two-dimensional harmonically\ntrapped Fermi gases, where $\\omega$ is the trapping frequency. Its recent\nexperimental observation with cold-atoms reveals an unexpected role played by\nthe effective range of interactions, which requires quantitative theoretical\nunderstanding. Here we provide accurate, benchmark results on quantum anomaly\nfrom a few-body perspective. We consider the breathing mode of a few trapped\ninteracting fermions in two dimensions up to six particles and present the mode\nfrequency as a function of scattering length for a wide range of effective\nrange. We show that the maximum quantum anomaly gradually reduces as effective\nrange increases while the maximum position shifts towards the weak-coupling\nlimit. We extrapolate our few-body results to the many-body limit and find a\ngood agreement with the experimental measurements. Our results may also be\ndirectly applicable to a few-fermion system prepared in microtraps and optical\ntweezers.",
        "positive": "Mean-field phase diagram of the Bose-Fermi Hubbard model: We analyze the ground state properties of Bose-Fermi mixtures using a\nmean-field treatment of the boson-fermion interaction on a simple cubic\nlattice. In the deep superfluid limit of the bosonic sector and the BCS regime\nof the fermion sector, we derive BCS-type equations to determine the phase\ndiagram of the system. We find a competition between a charge density wave and\na superconducting phase. In the opposite limit, we study the Mott insulator to\nsuperfluid transition of the bosonic sector in the presence of a staggered\ndensity-induced alternating potential provided by the fermions, and determine\nthe mean-field transition line. In the two-superfluid phase of the mixture we\nrestrict to nearest-neighbor induced interactions between the fermions and\nconsider the extended Hubbard model. We perform a mean-field analysis of the\ncritical temperature for the formation of boson-assisted $s$-, extended $s^-$-,\n$d$-, and $p$-wave pairs at fermionic half filling. We compare our results with\na recent dynamical mean-field study [Anders \\emph{et al.} Phys. Rev. Lett. {\\bf\n109}, 206401]."
    },
    {
        "anchor": "A two-state model for vortex nucleation in a rotating Bose-Einstein\n  condensate: It is well-known that a rotating Bose-Einstein condensate forms vortices to\ncarry the angular momentum. For a first vortex to nucleate at the trap center,\nthe rotational frequency must become larger than a certain critical value. The\nvortex nucleation process, however, is sensitive to the trap shape. It was\nshown earlier that for a symmetry-breaking potential that preserves parity, at\ncriticality the leading natural orbitals may become degenerate, giving rise to\na maximally entangled quantum state, found from exact solutions for just a few\nbosons. Developing an effective two-state model, we here show that in the limit\nof large particle numbers, the many-body ground state becomes either a\nso-called twin-like or a Schr\\\"odinger cat-like state. We corroborate this\nfinding by a direct comparison to the exact numerical solution of the problem,\nfeasible for moderate particle numbers within the lowest Landau level\napproximation. We show that the nature of the quantum state at criticality can\nbe controlled by both the quadrupolar deformation and the flatness of the\nconfining potential.",
        "positive": "Departing from thermality of analogue Hawking radiation in a\n  Bose-Einstein condensate: We study the quantum fluctuations in a one dimensional Bose-Einstein\ncondensate realizing an analogous acoustic black hole. The taking into account\nof evanescent channels and of zero modes makes it possible to accurately\nreproduce recent experimental measurements of the density correlation function.\nWe discuss the determination of Hawking temperature and show that in our model\nthe analogous radiation presents some significant departure from thermality."
    },
    {
        "anchor": "Toward precision Fermi liquid theory in two dimensions: The ultra-cold and weakly-coupled Fermi gas in two spatial dimensions is\nstudied in an effective field theory framework. It has long been observed that\nuniversal corrections to the energy density to two orders in the interaction\nstrength do not agree with Monte Carlo simulations in the weak-coupling regime.\nHere, universal corrections to three orders in the interaction strength are\nobtained for the first time, and are shown to provide agreement between theory\nand simulation. Special consideration is given to the scale ambiguity\nassociated with the non-trivial renormalization of the singular contact\ninteractions. The isotropic superfluid gap is obtained to next-to-leading\norder, and nonuniversal contributions to the energy density due to effective\nrange effects, p-wave interactions and three-body forces are computed. Results\nare compared with precise Monte Carlo simulations of the energy density and the\ncontact in the weakly-coupled attractive and repulsive Fermi liquid regimes. In\naddition, the known all-orders sum of ladder and ring diagrams is compared with\nMonte Carlo simulations at weak coupling and beyond.",
        "positive": "Oscillating solitons in a three component BEC: We investigate the properties of three component BEC systems with spin\nexchange interactions. We consider different coupling constants from those\nleading to exact solutions known in the literature. When two solitons collide,\nan oscillation of the emerging entities is observed. This behavior seems to be\ngeneric. A mathematical model is derived for the emerging solitons. It\ndescribes the new oscillatory phenomenon extremely well. Surprisingly, the\nmodel is exact as a solution to the initial equations. This comes as a bonus."
    },
    {
        "anchor": "Ballistic transport of a polariton ring condensate with spin precession: It is now routine to make Bose-Einstein condensates of polaritons with long\nenough lifetime and low enough disorder to travel ballistically for hundreds of\nmicrons in quasi-one-dimensional (1D) wires. We present observations of a\npolariton condensate injected at one point in a quasi-1D ring, with a\nwell-defined initial velocity and direction. A clear precession of the circular\npolarization is seen, which arises from an effective spin-orbit coupling term\nin the Hamiltonian. Our theoretical model accurately predicts the\nexperimentally observed behavior, and shows that \"zitterbewegung\" behavior\nplays a role in the motion of the polaritons.",
        "positive": "Universality of the Three-Body Parameter for Efimov States in Ultracold\n  Cesium: We report on the observation of triatomic Efimov resonances in an ultracold\ngas of cesium atoms. Exploiting the wide tunability of interactions resulting\nfrom three broad Feshbach resonances in the same spin channel, we measure\nmagnetic-field dependent three-body recombination loss. The positions of the\nloss resonances yield corresponding values for the three-body parameter, which\nin universal few-body physics is required to describe three-body phenomena and\nin particular to fix the spectrum of Efimov states. Our observations show a\nrobust universal behavior with a three-body parameter that stays essentially\nconstant."
    },
    {
        "anchor": "Superfluidity and spin superfluidity in spinor Bose gases: We show that spinor Bose gases subject to a quadratic Zeeman effect exhibit\ncoexisting superfluidity and spin superfluidity, and study the interplay\nbetween these two distinct types of superfluidity. To illustrate that the basic\nprinciples governing these two types of superfluidity are the same, we describe\nthe magnetization and particle-density dynamics in a single hydrodynamic\nframework. In this description spin and mass supercurrents are driven by their\nrespective chemical potential gradients. As an application, we propose an\nexperimentally accessible stationary state, where the two types of\nsupercurrents counterflow and cancel each other, thus resulting in no mass\ntransport. Furthermore, we propose a straightforward setup to probe spin\nsuperfluidity by measuring the in-plane magnetization angle of the whole cloud\nof atoms. We verify the robustness of these findings by evaluating the\nfour-magnon collision time, and find that the time scale for coherent\n(superfluid) dynamics is separated from that of the slower incoherent dynamics\nby one order of magnitude. Comparing the atom and magnon kinetics reveals that\nwhile the former can be hydrodynamic, the latter is typically collisionless\nunder most experimental conditions. This implies that, while our\nzero-temperature hydrodynamic equations are a valid description of spin\ntransport in Bose gases, a hydrodynamic description that treats both mass and\nspin transport at finite temperatures may not be readily feasible.",
        "positive": "Second Sound in Ultracold Atomic Gases: We provide an overview of the recent theoretical and experimental advances in\nthe study of second sound in ultracold atomic gases. Starting from the Landau\ntwo fluid hydrodynamic equations we develop the theory of first and second\nsound in various configurations characterized by different geometries and\nquantum statistics. These include the weakly interacting 3D Bose gas, the\nstrongly interacting Fermi gas at unitarity in the presence of highly elongated\ntraps and the dilute 2D Bose gas, characterized by the\nBerezinskii-Kosterlitz-Thouless transition. An explicit comparison with the\npropagation of second sound in liquid Helium is carried out to elucidate the\nmain analogies and differences. We also make an explicit comparison with the\navailable experimental data and point out the crucial role played by the\nsuperfluid density in determining the temperature dependence of the second\nsound speed."
    },
    {
        "anchor": "Collisionally Stable Gas of Bosonic Dipolar Ground State Molecules: Stable ultracold ensembles of dipolar molecules hold great promise for\nmany-body quantum physics, but high inelastic loss rates have been a\nlong-standing challenge. Recently, it was shown that gases of fermionic\nmolecules can be effectively stabilized through external fields. However, many\nquantum applications will benefit from molecular ensembles with bosonic\nstatistics. Here, we stabilize a bosonic gas of strongly dipolar NaCs molecules\nagainst inelastic losses via microwave shielding, decreasing losses by more\nthan a factor of 200 and reaching lifetimes on the scale of 1 second. We also\nmeasure high elastic scattering rates, a result of strong dipolar interactions,\nand observe the anisotropic nature of dipolar collisions. Finally, we\ndemonstrate evaporative cooling of a bosonic molecular gas to a temperature of\n36(5) nK, increasing its phase-space density by a factor of 20. This work is a\ncritical step towards the creation of a Bose-Einstein condensate of dipolar\nmolecules.",
        "positive": "BCS-BEC Crossover and the Unitary Fermi Gas: The crossover from weak coupling Bardeen-Cooper-Schrieffer (BCS) pairing to a\nBose-Einstein condensate (BEC) of tightly bound pairs, as a function of the\nattractive interaction in Fermi systems, has long been of interest to\ntheoretical physicists. The past decade has seen a series of remarkable\nexperimental developments in ultracold Fermi gases that has realized the\nBCS-BEC crossover in the laboratory, bringing with it fresh new insights into\nthe very strongly interacting unitary regime in the middle of this crossover.\nIn this review, we start with a pedagogical introduction to the crossover and\nthen focus on recent progress in the strongly interacting regime. While our\nfocus is on new theoretical developments, we also describe three key\nexperiments that probe the thermodynamics, transport and spectroscopy of the\nunitary Fermi gas. We discuss connections between the unitary regime and other\nareas of physics -- quark-gluon plasmas, gauge-gravity duality and high\ntemperature superconductivity -- and conclude with open questions about\nstrongly interacting Fermi gases."
    },
    {
        "anchor": "Realization of an Excited, Strongly-Correlated Quantum Gas Phase: Ultracold atomic physics offers myriad possibilities to study strongly\ncorrelated many-body systems in lower dimensions. Typically, only ground state\nphases are accessible. Using a tunable quantum gas of bosonic cesium atoms, we\nrealize and control in one dimensional geometry a highly excited quantum phase\nthat is stabilized in the presence of attractive interactions by maintaining\nand strengthening quantum correlations across a confinement-induced resonance.\nWe diagnose the crossover from repulsive to attractive interactions in terms of\nthe stiffness and the energy of the system. Our results open up the\nexperimental study of metastable excited many-body phases with strong\ncorrelations and their dynamical properties.",
        "positive": "Dimers, Effective Interactions, and Pauli Blocking Effects in a Bilayer\n  of Cold Fermionic Polar Molecules: We consider a bilayer setup with two parallel planes of cold fermionic polar\nmolecules when the dipole moments are oriented perpendicular to the planes. The\nbinding energy of two-body states with one polar molecule in each layer is\ndetermined and compared to various analytic approximation schemes in both\ncoordinate- and momentum-space. The effective interaction of two bound dimers\nis obtained by integrating out the internal dimer bound state wave function and\nits robustness under analytical approximations is studied. Furthermore, we\nconsider the effect of the background of other fermions on the dimer state\nthrough Pauli blocking, and discuss implications for the zero-temperature\nmany-body phase diagram of this experimentally realizable system."
    },
    {
        "anchor": "Generation and decay of persistent current in a toroidal Bose-Einstein\n  condensate: Persistent current, or \"flow without friction\", as well as quantum vortices\nare the hallmarks of superfluidity. Recently a very long-lived persistent flow\nof atoms has been experimentally observed in Bose-Einstein condensates trapped\nin a ring-shaped potential. This enables fundamental studies of superfluidity\nand may lead to applications in high-precision metrology and atomtronics. We\noverview our recent theoretical studies of the generation of the persistent\ncurrent in a stirred toroidal atomic Bose-Einstein condensate, and discuss our\nnew investigation of the hysteresis in the atomtronic circuit.",
        "positive": "Non-Linear Interference Challenging Topological Protection of Chiral\n  Edge States: We report on a non-linear scattering effect that challenges the notion of\ntopological protection for wave packets propagating in chiral edge modes.\nSpecifically, in a Floquet topological system close to resonant driving and\nwith a non-linear potential, we demonstrate how a wave packet propagating in a\nchiral edge mode may be irreversibly deflected by scattering off a localized\nwave-packet, or pass the collision region virtually unaffected in an\napproximately linear fashion. An experimentally accessible knob to tune between\nthose two scenarios is provided by the relative phase between the involved\nwave-packets. This genuinely non-linear interference phenomenon is in stark\ncontrast to linear scattering off a static impurity, which cannot destroy a\ntopological edge state. Besides corroborating our findings with numerically\nexact simulations, we propose two physical platforms where our predictions may\nbe verified with state of the art experimental techniques: First, a coupled\nwaveguide setting where non-linearity has been engineered via an\nintensity-dependent optical index. Second, a Bose-Einstein condensate of cold\natoms in an optical Honeycomb lattice governed by a non-linear Gross-Pitaevskii\nequation that effectively accounts for many-body interactions."
    },
    {
        "anchor": "Fermi-Bose mixture in mixed dimensions: One of the challenging goals in the studies of many-body physics with\nultracold atoms is the creation of a topological $p_{x} + ip_{y}$ superfluid\nfor identical fermions in two dimensions (2D). The expectations of reaching the\ncritical temperature $T_c$ through p-wave Feshbach resonance in spin-polarized\nfermionic gases have soon faded away because on approaching the resonance, the\nsystem becomes unstable due to inelastic-collision processes. Here, we consider\nan alternative scenario in which a single-component degenerate gas of fermions\nin 2D is paired via phonon-mediated interactions provided by a 3D BEC\nbackground. Within the weak-coupling regime, we calculate the critical\ntemperature $T_c$ for the fermionic pair formation, using Bethe-Salpeter\nformalism, and show that it is significantly boosted by higher-order\ndiagramatic terms, such as phonon dressing and vertex corrections. We describe\nin detail an experimental scheme to implement our proposal, and show that the\nlong-sought p-wave superfluid is at reach with state-of-the-art experiments.",
        "positive": "Quantum fluctuations beyond the Gutzwiller approximation in the\n  Bose-Hubbard model: Taking inspiration from the state-of-the art knowledge of the Bose-Hubbard\n(BH) model and recent methodological developments in its fermionic counterpart,\nthis work deals with the study of the collective dynamics of a lattice Bose gas\nbeyond the mean-field picture through a quantum description of its elementary\nexcitations. The Hamiltonian quantization, performed via a Bogoliubov\nquadratization of the BH action within the Gutzwiller approach, allows to\nexpand the effective action of the theory up to second order in the\nfluctuations around the mean-field solution, as well as to prefigure the\npossibility of identifying the main decay vertices of the collective modes and\nother effects that are not evident at the second-order level. This quantum\ndescription extends the standard Bogoliubov approach to the study of superfluid\nBose systems for comprising higher excitation branches, including the Higgs\nmode in the superfluid phase, and identifies their physical meaning together\nwith appropriate observables which could be taken into consideration for their\nexperimental characterization. The ultimate aim of the quantization procedure\nis the determination of fundamental quantities as the depletion of the\ncondensate and the effective superfluid fraction, which are not accessible by a\nmean-field description or not completely characterized in the regime of strong\ninteractions."
    },
    {
        "anchor": "Properties of dipolar bosonic quantum gases at finite temperatures: The properties of ultracold quantum gases of bosons with dipole-dipole\ninteraction is investigated at finite temperature in the frame of the\nrepresentative ensembles theory. Self-consistent coupled equations of motion\nare derived for the condensate and the non-condensate components. Corrections\ndue to the dipolar interaction to the condensate depletion, the anomalous\ndensity and thermodynamic quantities such as the ground state energy, the\nequation of state, the compressibility and the presure are calculated in the\nhomogeneous case at both zero and finite temperatures. Effects of interaction\nand temperature on the structure factor are also discussed. Within the realm of\nthe local density approximation, we generalize our results to the case of a\ntrapped dipolar gas.",
        "positive": "Particle Correlations in Bose-Einstein Condensates: The impact of interparticle correlations on the behavior of Bose-Einstein\nCondensates (BECs) is discussed using two approaches. In the first approach,\nthe wavefunction of a BEC is encoded in the $N$-particle sector of an extended\n\"catalytic state\". Going to a time-dependent interaction picture, we can\norganize the effective Hamiltonian by powers of ${N}^{-1/2}$. Requiring the\nterms of order ${N}^{1/2}$ to vanish, we get the Gross-Pitaevskii Equation.\nGoing to the next order, $N^0$, we obtain the number-conserving Bogoliubov\napproximation. Our approach allows one to stay in the Schr\\\"{o}dinger picture\nand to apply many techniques from quantum optics. Moreover, it is easier to\ntrack different orders in the Hamiltonian and to generalize to the\nmulti-component case. In the second approach, I consider a state of $N =l\\times\nn$ bosons that is derived by symmetrizing the $n$-fold tensor product of an\narbitrary $l$-boson state. Particularly, we are interested in the pure state\ncase for $l=2$, which we call the Pair-Correlated State (PCS). I show that PCS\nreproduces the number-conserving Bogoliubov approximation; moreover, it also\nworks in the strong interaction regime where the Bogoliubov approximation\nfails. For the two-site Bose-Hubbard model, I find numerically that the error\n(measured by the trace distance of the two-particle reduced density matrices)\nof PCS is less than two percent over the entire parameter space, thus making\nPCS a bridge between the superfluid and Mott insulating phases. Amazingly, the\nerror of PCS does not increase, in the time-dependent case, as the system\nevolves for longer times. I derive both time-dependent and -independent\nequations for the ground state and the time evolution of the PCS ansatz. The\ntime complexity of simulating PCS does not depend on $N$ and is linear in the\nnumber of orbitals in use."
    },
    {
        "anchor": "Propagation of phase-imprinted solitons from superfluid core to\n  Mott-insulator shell and superfluid shell: We study phase-imprinted solitons of ultracold bosons in an optical lattice\nwith a harmonic trap, which shows the superfluid (SF) and Mott-insulator (MI)\nshell structures. The earlier study [Konstantin V. Krutitsky, J. Larson, and M.\nLewenstein, Phys. Rev. A 82, 033618 (2010).] reported three types of\nphase-imprinted solitons in the Bose-Hubbard model: in-phase soliton,\nout-of-phase soliton, and wavelet. In this paper, we uncover the dynamical\nphase diagram of these phase-imprinted solitons, and find another type of the\nphase-imprinted soliton namely, the hybrid soliton. In the harmonically trapped\nsystem, the solitonic excitations created at the SF core cannot penetrate into\nthe outer SF shell. This repulsion at the surface of the outer SF shell can be\ncured by inposing a repulsive potential at the center of the trap. These\nresults can be interpreted as a kind of the impedance matching of excitations\nin BECs in terms of the effective chemical potentials or the local particle\nnumbers in the shell, and the analogous results can be observed also in the\nsound wave created by the local single-shot pulse potential.",
        "positive": "Observation of the Hanbury Brown and Twiss Effect with Ultracold\n  Molecules: Measuring the statistical correlations of individual quantum objects provides\nan excellent way to study complex quantum systems. Ultracold molecules\nrepresent a powerful platform for quantum science due to their rich and\ncontrollable internal degrees of freedom. However, the detection of\ncorrelations between single molecules in an ultracold gas has yet to be\ndemonstrated. Here we observe the Hanbury Brown and Twiss effect in a gas of\nbosonic $^{23}$Na$^{87}$Rb, enabled by the realization of a quantum gas\nmicroscope for molecules. We detect the characteristic bunching correlations in\nthe density fluctuations of a 2D molecular gas released from and subsequently\nrecaptured in an optical lattice. The quantum gas microscope allows us to\nextract the positions of individual molecules with single-site resolution. As a\nresult, we obtain a high-contrast two-molecule interference pattern with a\nvisibility of $54(13)\\%$. While these measured correlations arise purely from\nthe quantum statistics of the molecules, the demonstrated capabilities pave the\nway toward site-resolved studies of interacting molecular gases in optical\nlattices."
    },
    {
        "anchor": "Analytical and numerical study of trapped strongly correlated bosons in\n  two- and three-dimensional lattices: We study the ground-state properties of trapped inhomogeneous systems of\nhardcore bosons in two- and three-dimensional lattices. We obtain our results\nboth numerically, using quantum Monte Carlo techniques, and via several\nanalytical approximation schemes, such as the Gutzwiller-mean-field approach, a\ncluster-mean-field method and a spin-wave analysis which takes quantum\nfluctuations into account. We first study the homogeneous case, for which\nsimple analytical expressions are obtained for all observables of interest, and\ncompare the results with the numerical ones. We obtain the equation of state of\nthe system along with other thermodynamic properties such as the free energy,\nkinetic energy, superfluid density, condensate fraction and compressibility. In\nthe presence of a trap, superfluid and insulating domains coexist in the\nsystem. We show that the spin-wave-based method reproduces the quantum\nMonte-Carlo results for global as well as for local quantities with a high\ndegree of accuracy. We also discuss the validity of the local density\napproximation in those systems. Our analysis can be used to describe bosons in\noptical lattices where the onsite interaction U is much larger than the hopping\namplitude t.",
        "positive": "Relaxation dynamics of ultracold bosons in a double-well potential:\n  Thermalization and prethermalization in a nearly integrable model: We numerically investigate the relaxation dynamics in an isolated quantum\nsystem of interacting bosons trapped in a double-well potential after an\nintegrability breaking quench. Using the statistics of the spectrum, we\nidentify the postquench Hamiltonian as nonchaotic and close to integrability\nover a wide range of interaction parameters. We demonstrate that the system\nexhibits thermalization in the context of the eigenstate thermalization\nhypothesis (ETH). We also explore the possibility of an initial state to\ndelocalize with respect to the eigenstates of the postquench Hamiltonian even\nfor energies away from the middle of the spectrum. We observe distinct regimes\nof equilibration process depending on the initial energy. For low energies, the\nsystem rapidly relaxes in a single step to a thermal state. As the energy\nincreases towards the middle of the spectrum, the relaxation dynamics exhibits\nprethermalization and the lifetime of the metastable states grows. Time\nevolution of the occupation numbers and the von Neumann entropy in the\nmode-partitioned system underpins the analyses of the relaxation dynamics."
    },
    {
        "anchor": "Generation of ring dark solitons by phase engineering and their\n  oscillations in spin-1 Bose-Einstein condensates: The ring dark solitons in spin-1 $^{23}$Na and $^{87}$Rb Bose-Einstein\ncondensates are studied numerically in the framework of the time-dependent\nGross-Pitaevskii equations. By simulating the phase engineering technique in\nreal experiments, we explore the roles of the parameters characterizing the\nfar-off resonant laser pulse which can be used to generate the ring dark\nsolitons. The variations of these parameters have dramatic effect on the\nlifetime and the decay profiles of the ring dark solitons. If only one ring\ndark soliton is generated in one component of the condensate, ring dark\nsolitons in other components are inclined to be induced, resulting in a\ncoexistence state composed of interdependent ring dark solitons coming from\ndifferent components of the condensate. Ring dark solitons in this coexistence\nstate exhibit dynamical oscillations for hundreds of milliseconds. By studying\nthe lifetime and decaying profiles of ring dark solitons, we explore the\nsimilarities and differences of $^{23}$Na and $^{87}$Rb condensates. Besides,\ntaking into account the fact that the center of the ring may not be coincide\nwith that of the trap, we study the dynamics and decaying profiles of the\noff-centered ring dark solitons in the presence of symmetry breaking effect.",
        "positive": "Breakdown of macroscopic quantum self-trapping in coupled mesoscopic one\n  dimensional Bose gases: Two coupled BECs with a large population imbalance exhibit macroscopic\nquantum self-trapping (MQST) if the ratio of interaction energy to tunneling\nenergy is above a critical value. Here we investigate effect of quantum\nfluctuations on MQST. In particular, we analyze the dynamics of a system of two\nelongated Bose gases prepared with a large population imbalance, where due to\nthe quasi one dimensional character of the gas we no longer have true long\nrange order, and the effect of quantum fluctuations is much more important. We\nshow that MQST is possible in this system, but even when it is achieved it is\nnot always dynamically stable. Using this instability one can construct states\nwith sharply peaked momentum distributions around characteristic momenta\ndependent on system parameters. Our other finding is the nonmonotonic\noscillating dependence of the decay rate of the MQST on the length of the\nwires. We also address the interesting question of thermalization in this\nsystem and show that it occurs only in sufficiently long wires."
    },
    {
        "anchor": "BEC-BCS crossover and universal relations in unitary Fermi gases: The contact parameter in unitary Fermi Gases governs the short-distance,\nhigh-momentum, and high-energy properties of the system. We perform accurate\nquantum Monte Carlo calculations with highly optimized trial functions to\nprecisely determine this parameter at T=0, demonstrate its universal\napplication to a variety of observables, and determine the regions of momentum\nand energy over which the leading short-range behavior is dominant. We derive\nTan's expressions for the contact parameter using just the short-range behavior\nof the ground-state many-body wave function, and use this behavior to calculate\nthe two-body distribution function, one-body density matrix, and the momentum\ndistribution of unitary Fermi gases; providing a precise value of the contact\nparameter that can be compared to experiments.",
        "positive": "Probing polaron clouds by Rydberg atom spectroscopy: In recent years, Rydberg excitations in atomic quantum gases have become a\nsuccessful platform to explore quantum impurity problems. A single impurity\nimmersed in a Fermi gas leads to the formation of a polaron, a quasiparticle\nconsisting of the impurity being dressed by the surrounding medium. With a\nradius of about the Fermi wavelength, the density profile of a polaron cannot\nbe explored using in-situ optical imaging techniques. In this work, we propose\na new experimental measurement technique that enables the in-situ imaging of\nthe polaron cloud in ultracold quantum gases. The impurity atom is first\nexcited to an interacting state which induces the formation of a polaron cloud.\nThis is followed by the excitation of the impurity atom to a Rydberg state. Due\nto the mesoscopic interaction range of Rydberg excitations, which can be tuned\nby the principal numbers of the Rydberg state, atoms extracted from the polaron\ncloud form dimers with the impurity. By performing first principle calculations\nof the absorption spectrum based on a functional determinant approach, we show\nhow the occupation of the dimer state can be directly observed in spectroscopy\nexperiments and can be mapped onto the density profile of the gas particles,\nhence providing a direct, real-time, and in-situ measure of the polaron cloud."
    },
    {
        "anchor": "Itinerant magnetism in spin-orbit coupled Bose gases: Phases of matter are conventionally characterized by order parameters\ndescribing the type and degree of order in a system. For example, crystals\nconsist of spatially ordered arrays of atoms, an order that is lost as the\ncrystal melts. Like- wise in ferromagnets, the magnetic moments of the\nconstituent particles align only below the Curie temperature, TC. These two\nexamples reflect two classes of phase transitions: the melting of a crystal is\na first-order phase transition (the crystalline order vanishes abruptly) and\nthe onset of magnetism is a second- order phase transition (the magnetization\nincreases continuously from zero as the temperature falls below TC). Such\nmagnetism is robust in systems with localized magnetic particles, and yet rare\nin model itinerant systems where the particles are free to move about. Here for\nthe first time, we explore the itinerant magnetic phases present in a spin-1\nspin-orbit coupled atomic Bose gas; in this system, itinerant ferromagnetic\norder is stabilized by the spin-orbit coupling, vanishing in its absence. We\nfirst located a second-order phase transition that continuously stiffens until,\nat a tricritical point, it transforms into a first- order transition (with\nobserved width as small as h x 4 Hz). We then studied the long-lived metastable\nstates associated with the first-order transition. These measurements are all\nin agreement with theory.",
        "positive": "Spatially inhomogeneous phase evolution of a two-component Bose-Einstein\n  condensate: We investigate the spatially dependent relative phase evolution of an\nelongated two-component Bose-Einstein condensate. The pseudospin-1/2 system is\ncomprised of the |F=1,m_F=-1> and |F=2,m_F=+1> hyperfine ground states of 87Rb,\nwhich we magnetically trap and interrogate with radio-frequency and microwave\nfields. We probe the relative phase evolution with Ramsey interferometry and\nobserve a temporal decay of the interferometric contrast well described by a\nmean-field formalism. Inhomogeneity of the collective relative phase dominates\nthe loss of interferometric contrast, rather than decoherence or phase\ndiffusion. We demonstrate a technique to simultaneously image each state,\nyielding subpercent variations in the measured relative number while preserving\nthe spatial mode of each component. In addition, we propose a spatially\nsensitive interferometric technique to image the relative phase."
    },
    {
        "anchor": "Fermionization of two-component few-fermion systems in a one-dimensional\n  harmonic trap: The nature of strongly interacting Fermi gases and magnetism is one of the\nmost important and studied topics in condensed-matter physics. Still, there are\nmany open questions. A central issue is under what circumstances strong\nshort-range repulsive interactions are enough to drive magnetic correlations.\nRecent progress in the field of cold atomic gases allows to address this\nquestion in very clean systems where both particle numbers, interactions and\ndimensionality can be tuned. Here we study fermionic few-body systems in a one\ndimensional harmonic trap using a new rapidly converging effective-interaction\ntechnique, plus a novel analytical approach. This allows us to calculate the\nproperties of a single spin-down atom interacting with a number of spin-up\nparticles, a case of much recent experimental interest. Our findings indicate\nthat, in the strongly interacting limit, spin-up and spin-down particles want\nto separate in the trap, which we interpret as a microscopic precursor of\none-dimensional ferromagnetism in imbalanced systems. Our predictions are\ndirectly addressable in current experiments on ultracold atomic few-body\nsystems.",
        "positive": "Numerical calculation of spectral functions of the Bose-Hubbard model\n  using B-DMFT: We calculate the momentum dependent spectral function of the Bose-Hubbard\nmodel on a simple cubic lattice in three dimensions within the bosonic\ndynamical mean-field theory (B-DMFT). The continuous-time quantum Monte Carlo\nmethod is used to solve the self-consistent B-DMFT equations together with the\nmaximum entropy method for the analytic continuation to real frequencies.\nResults for weak, intermediate, and strong interactions are presented. In the\nlimit of weak and strong interactions very good agreement with results obtained\nby perturbation theory is found. By contrast, at intermediate interactions the\nresults differ significantly, indicating that in this regime perturbative\nmethods fail do describe the dynamics of interacting bosons."
    },
    {
        "anchor": "Solitons in One Dimensional Systems at BCS-BEC Crossover: We developed a comprehensive semiclassical theory of solitons in one\ndimensional systems at BCS-BEC crossover to provide a semiclassical explanation\nof their excitation spectra. Our semiclassical results agree well with the\nexact solutions on both the deep BCS and deep BEC side and explain\nqualitatively the smooth crossover between them. Especially, we showed that the\nminimum energy of the $S=1/2$ excitation is achieved exactly at the Fermi\nmomentum $k_F=\\pi n/2$, where $nm_F$ ($m_F$ is the mass of the fermionic atom)\nis the total mass density of the system. This momentum remains unchanged along\nthe whole crossover, whether the mass is contained in the bosonic molecules as\non the deep BEC side or in the fermionic atoms as on the deep BCS side. This\nphenomenon comes about as a result of a special feature of one dimensional\nsystems that the conventional quasiparticle is not stable with respect to\nsoliton formation. It is valid not only in exactly solvable models but also on\nthe level of semiclassical theory. Besides, we also resolved the inconsistency\nof existing semiclassical theory with the exact solution of soliton-like $S=0$\nexcitations on the deep BCS side by a new proposal of soliton configuration.",
        "positive": "Symmetry-protected Bose-Einstein condensation of interacting hardcore\n  Bosons: We introduce a mechanism stabilizing a one-dimensional quantum many-body\nphase, characterized by a certain wave vector $k_0$, from a $k_0$-modulated\ncoupling to a center site, via the protection of an emergent $\\mathbb Z_2$\nsymmetry. We illustrate this mechanism by constructing the solution of the full\nquantum many-body problem of hardcore bosons on a wheel geometry, which are\nknown to form a Bose-Einstein condensate. The robustness of the condensate is\nshown numerically by adding nearest-neighbor interactions to the wheel\nHamiltonian. We identify the energy scale that controls the protection of the\nemergent $\\mathbb Z_2$ symmetry. We discuss further applications such as\ngeometrically inducing finite-momentum condensates. Since our solution strategy\nis based on a generic mapping from a wheel geometry to a projected ladder, our\nanalysis can be applied to various related problems with extensively scaling\ncoordination numbers."
    },
    {
        "anchor": "Self-localized state and solitons in a Bose-Einstein-condensate-impurity\n  mixture at finite temperature: We study the properties of a Bose-Einstein condensate (BEC)-impurity mixture\nat finite temperature employing the time dependent Hartree-Fock Bogoliubov\n(TDHFB) theory which is a set of coupled nonlinear equations of motion for the\ncondensate and its normal and anomalous fluctuations on the one hand, and for\nimpurity on the other. The numerical solutions of these equations in the static\nquasi-1D regime show that the thermal cloud and the anomalous density are\ndeformed as happens to the condensate and the impurity becomes less localized\nat nonzero temperatures. Effects of the BEC fluctuations on the self-trapping\nstate are studied in homogeneous weakly interacting BEC-impurity at low\ntemperature. The self-trapping threshold is also determined in such a system.\nThe formation of solitons in the BEC-impurity mixture at finite temperature is\ninvestigated. Our formalism shows several new pictures.",
        "positive": "Dark-bright solitons in spinor polariton condensates under nonresonant\n  pumping: Adopting a mean-field Gross-Pitaevskii description for a spinor polariton\nBose-Einstein condensates under non-resonant pumping, we investigate the static\nand dynamical properties of dark-bright solitons. We derive analytically the\nequation of motion for the center of mass of the dark-bright soliton center,\nusing the Hamiltonian approach. The resulting equation captures how the\ncombination of the open-dissipative character and the spin degrees of freedom\nof a polariton Bose-Einstein condensate affects the properties of a dark-bright\nsoliton, i.e. the dark-bright soliton relaxes by blending with the background\nat a finite time. In this case, we also determine the life time of the DB\nsoliton. Further numerical solutions of the modified dissipative two-component\nGross-Pitaevskii equations are in excellent agreement with the analytical\nresults. In presence of the Langevin noise, we demonstrate that the DB solitons\ncan still propagate for a long time, which is sufficient for their experimental\nobservations within current facilities."
    },
    {
        "anchor": "Localization of spin mixing dynamics in a spin-1 Bose-Einstein\n  condensate: We propose to localize spin mixing dynamics in a spin-1 Bose-Einstein\ncondensate by a temporal modulation of spin exchange interaction, which is\ntunable with optical Feshbach resonance. Adopting techniques from coherent\ncontrol, we demonstrate the localization/freezing of spin mixing dynamics, and\nthe suppression of the intrinsic dynamic instability and spontaneous spin\ndomain formation in a ferromagnetically interacting condensate of $^{87}$Rb\natoms. This work points to a promising scheme for investigating the weak\nmagnetic spin dipole interaction, which is usually masked by the more dominant\nspin exchange interaction.",
        "positive": "Generalized ABCD propagation for interacting atomic clouds: We present a treatment of the nonlinear matter wave propagation inspired from\noptical methods, which includes interaction effects within the atom optics\nequivalent of the aberrationless approximation. The atom-optical ABCD matrix\nformalism, considered so far for non-interacting clouds, is extended\nperturbatively beyond the linear regime of propagation. This approach, applied\nto discuss the stability of a matter-wave resonator involving a free-falling\nsample, agrees very well with the predictions of the full nonlinear paraxial\nwave equation. An alternative optical treatment of interaction effects, based\non the aberrationless approximation and suitable for cylindrical paraxial beams\nof uniform linear density, is also adapted for matter waves."
    },
    {
        "anchor": "Self-evaporation dynamics of quantum droplets in a 41K-87Rb mixture: We theoretically investigate the self-evaporation dynamics of quantum\ndroplets in a 41K-87Rb mixture, in free-space. The dynamical formation of the\ndroplet and the effects related to the presence of three-body losses are\nanalyzed by means of numerical simulations. We identify a regime of parameters\nallowing for the observation of the droplet self-evaporation in a feasible\nexperimental setup.",
        "positive": "Superfluid drag of two-species Bose-Einstein condensates in optical\n  lattices: We study two-species Bose-Einstein condensates in quasi two-dimensional\noptical lattices of varying geometry and potential depth. Based on the\nnumerically exact Bloch and Wannier functions obtained using the plane-wave\nexpansion method, we quantify the drag (entrainment coupling) between the\ncondensate components. This drag originates from the (short range)\ninter-species interaction and increases with the kinetic energy. As a result of\nthe interplay between interaction and kinetic energy effects, the\nsuperfluid-drag coefficient shows a non-monotonic dependence on the lattice\ndepth. To make contact with future experiments, we quantitatively investigate\nthe drag for mass ratios corresponding to relevant atomic species."
    },
    {
        "anchor": "Self-ordered Time Crystals: Periodic Temporal Order Under Quasiperiodic\n  Driving: A discrete time crystal is a remarkable non-equilibrium phase of matter\ncharacterized by persistent sub-harmonic response to a periodic drive.\nMotivated by the question of whether such time-crystalline order can persist\nwhen the drive becomes aperiodic, we investigate the dynamics of a\nLipkin-Meshkov-Glick model under quasiperiodic kicking. Intriguingly, this\ninfinite-range-interacting spin chain can exhibit long-lived periodic\noscillations when the kicking amplitudes are drawn from the Thue-Morse sequence\n(TMS). We dub this phase a ``self-ordered time crystal\" (SOTC), and demonstrate\nthat our model hosts at least two qualitatively distinct prethermal SOTC\nphases. These SOTCs are robust to various perturbations, and they originate\nfrom the interplay of long-range interactions and the recursive structure of\nthe TMS. Our results suggest that quasiperiodic driving protocols can provide a\npromising route for realizing novel non-equilibrium phases of matter in\nlong-range interacting systems.",
        "positive": "Density-dependent synthetic magnetism for ultracold atoms in optical\n  lattices: Raman-assisted hopping can allow for the creation of density-dependent\nsynthetic magnetism for cold neutral gases in optical lattices. We show that\nthe density-dependent fields lead to a non-trivial interplay between density\nmodulations and chirality. This interplay results in a rich physics for atoms\nin two-leg ladders, characterized by a density-driven Meissner- to\nvortex-superfluid transition, and a non-trivial dependence of the density\nimbalance between the legs. Density-dependent fields also lead to intriguing\nphysics in square lattices. In particular, it leads to a density-driven\ntransition between a non-chiral and a chiral superfluid, both characterized by\nnon-trivial charge density-wave amplitude. We finally show how the physics due\nto the density-dependent fields may be easily probed in experiments by\nmonitoring the expansion of doublons and holes in a Mott insulator, which\npresents a remarkable dependence on quantum fluctuations."
    },
    {
        "anchor": "Transport coefficients from the Boson Uehling-Uhlenbeck Equation: We derive microscopic expressions for the bulk viscosity, shear viscosity and\nthermal conductivity of a quantum degenerate Bose gas above $T_C$, the critical\ntemperature for Bose-Einstein condensation. The gas interacts via a contact\npotential and is described by the Uehling-Uhlenbeck equation. To derive the\ntransport coefficients, we use Rayleigh-Schrodinger perturbation theory rather\nthan the Chapman-Enskog approach. This approach illuminates the link between\ntransport coefficients and eigenvalues of the collision operator. We find that\na method of summing the second order contributions using the fact that the\nrelaxation rates have a known limit improves the accuracy of the computations.\nWe numerically compute the shear viscosity and thermal conductivity for any\nboson gas that interacts via a contact potential. We find that the bulk\nviscosity remains identically zero as it is for the classical case.",
        "positive": "Shell-shaped atomic gases: We review the quantum statistical properties of two-dimensional shell-shaped\ngases, produced by cooling and confining atomic ensembles in thin hollow\nshells. We consider both spherical and ellipsoidal shapes, discussing at zero\nand at finite temperature the phenomena of Bose-Einstein condensation and of\nsuperfluidity, the physics of vortices, and the crossover from the\nBardeen-Cooper-Schrieffer regime to a Bose-Einstein condensate. The novel\naspects associated to the curved geometry are elucidated in comparison with\nflat two-dimensional superfluids. We also describe the hydrodynamic excitations\nand their relation with the Berezinskii-Kosterlitz-Thouless transition for\ntwo-dimensional flat and curved superfluids. In the next years, shell-shaped\natomic gases will be the leading experimental platform for investigations of\nquantum many-body physics in curved spatial domains."
    },
    {
        "anchor": "Observation of a smooth polaron-molecule transition in a degenerate\n  Fermi gas: Understanding the behavior of an impurity strongly interacting with a Fermi\nsea is a long-standing challenge in many-body physics. When the interactions\nare short-ranged, two vastly different ground states exist: a polaron\nquasiparticle and a molecule dressed by the majority atoms. In the\nsingle-impurity limit, it is predicted that at a critical interaction strength,\na first-order transition occurs between these two states. Experiments, however,\nare always conducted in the finite temperature and impurity density regime. The\nfate of the polaron-to-molecule transition under these conditions, where the\nstatistics of quantum impurities and thermal effects become relevant, is still\nunknown. Here, we address this question experimentally and theoretically. Our\nexperiments are performed with a spin-imbalanced ultracold Fermi gas with\ntunable interactions. Utilizing a novel Raman spectroscopy combined with a\nhigh-sensitivity fluorescence detection technique, we isolate the quasiparticle\ncontribution and extract the polaron energy, spectral weight, and the contact\nparameter. As the interaction strength is increased, we observe a continuous\nvariation of all observables, in particular a smooth reduction of the\nquasiparticle weight as it goes to zero beyond the transition point. Our\nobservation is in good agreement with a theoretical model where polaron and\nmolecule quasiparticle states are thermally occupied according to their quantum\nstatistics. At the experimental conditions, polaron states are hence populated\neven at interactions where the molecule is the ground state and vice versa. The\nemerging physical picture is thus that of a smooth transition between polarons\nand molecules and a coexistence of both in the region around the expected\ntransition.",
        "positive": "Discrete bright solitons in Bose-Einstein condensates and dimensional\n  reduction in quantum field theory: We first review the derivation of an effective one-dimensional (1D) discrete\nnonpolynomial Schr\\\"odinger equation from the continuous 3D Gross-Pitaevskii\nequation with transverse harmonic confinement and axial periodic potential.\nThen we study the bright solitons obtained from this discrete nonpolynomial\nequation showing that they give rise to the collapse of the condensate above a\ncritical attractive strength. We also investigate the dimensional reduction of\na bosonic quantum field theory, deriving an effective 1D nonpolynomial\nHeisenberg equation from the 3D Heisenberg equation of the continuous bosonic\nfield operator under the action of transverse harmonic confinement. Moreover,\nby taking into account the presence of an axial periodic potential we find a\ngeneralized Bose-Hubbard model which reduces to the familiar 1D Bose-Hubbard\nHamiltonian only if a strong inequality is satisfied. Remarkably, in the\nabsence of axial periodic potential our 1D nonpolynomial Heisenberg equation\ngives the generalized Lieb-Liniger theory we obtained some years ago."
    },
    {
        "anchor": "Josephson effect with superfluid fermions in the two-dimensional BCS-BEC\n  crossover: We investigate the macroscopic quantum tunneling of fermionic superfluids in\nthe two-dimensional BCS-BEC crossover by using an effective tunneling energy\nwhich explicitly depends on the condensate fraction and the chemical potential\nof the system. We compare the mean-field effective tunneling energy with the\nbeyond-mean-field one finding that the mean-field tunneling energy is not\nreliable in the BEC regime of the crossover. Then we solve the Josephson\nequations of the population imbalance and the relative phase calculating the\nfrequency of tunneling oscillation both in the linear regime and in the\nnonlinear one. Our results show that the Josephson frequency is larger in the\nintermediate regime of the BCS-BEC crossover due to the peculiar behavior of\nthe effective tunneling energy in the crossover.",
        "positive": "Emergence of a spin microemulsion in spin-orbit coupled Bose-Einstein\n  condensates: We report the first numerical prediction of a \"spin microemulsion\" -- a phase\nwith undulating spin domains resembling classical bicontinuous\noil-water-surfactant emulsions -- in two-dimensional systems of spinor\nBose-Einstein condensates with isotropic Rashba spin-orbit coupling. Using\nfield-theoretic numerical simulations, we investigated the melting of a\nlow-temperature stripe phase with supersolid character and find that the\nstripes lose their superfluidity at elevated temperature and undergo a\nKosterlitz--Thouless-like transition into a spin microemulsion. Momentum\ndistribution calculations highlight a thermally broadened occupation of the\nRashba circle of low-energy states with macroscopic and isotropic occupation\naround the ring. We provide a finite-temperature phase diagram that positions\nthe emulsion as an intermediate, structured isotropic phase with residual\nquantum character before transitioning at higher temperature into a\nstructureless normal fluid."
    },
    {
        "anchor": "Spin-dependent inelastic collisions in spin-2 Bose-Einstein condensates: We studied spin-dependent two-body inelastic collisions in F=2 87Rb\nBose-Einstein condensates both experimentally and theoretically. The 87Rb\ncondensates were confined in an optical trap and selectively prepared in\nvarious spin states in the F=2 manifold at a magnetic field of 3.0 G. Measured\natom loss rates are found to depend on spin states of colliding atoms. We\nmeasured two fundamental loss coefficients for two-body inelastic collisions\nwith the total spin of 0 and 2; the coefficients determine loss rates for all\nthe spin pairs. The experimental results for mixtures of all the spin\ncombinations are in good agreement with numerical solutions of the\nGross-Pitaevskii equations that include the effect of a magnetic field\ngradient.",
        "positive": "Grassmann phase space dynamics of strongly-correlated fermion: We discuss the numerical implementation of two related representations of\nfermionic density matrices which have been introduced in Annals of Physics 370,\n12 (2016). In both of them, the density matrix is expanded in a basis of\nBargmann coherent states with weights given by the two phase space\ndistributions. We derive the equations of motion for the distributions when\nimaginary time evolution is generated by the Hubbard Hamiltonian. One of them\nis a Grassmann Fokker-Planck equation that can be re-cast into a remarkably\nsimple It\\^{o} form involving solely complex variables. In spite of this simple\nform, we demonstrate that complications arise in numerically computing the\nexpectation value of any observable. These are due to exponential growth in the\nmatrix elements of the stochastic propagator, delicate numerical sensitivity in\nperforming primitive linear algebra operations, and the re-appearance of a sign\nproblem."
    },
    {
        "anchor": "Lattice polarons across the superfluid to Mott insulator transition: We study the physics of a mobile impurity confined in a lattice, moving\nwithin a Bose-Hubbard bath at zero temperature. Within the Quantum Gutzwiller\nformalism, we develop a beyond-Fr\\\"ohlich model of the bath-impurity\ninteraction. Results for the properties of the polaronic quasiparticle formed\nfrom the dressing of the impurity by quantum fluctuations of the bath are\npresented throughout the entire phase diagram, focusing on the quantum phase\ntransition between the superfluid and Mott insulating phases. Here we find that\nthe modification of the impurity properties is highly sensitive to the\ndifferent universality classes of the transition, providing an unambiguous\nprobe of correlations and collective modes in a quantum critical many-body\nenvironment.",
        "positive": "Unusual Zeeman-field effects in two-dimensional spin-orbit-coupled Fermi\n  superfluids: We investigate the Zeeman field effects on the bulk superfluid properties and\nthe collective modes in two-dimensional (2D) attractive atomic Fermi gases with\nRashba-type spin-orbit coupling. In the presence of a large spin-orbit\ncoupling, the system undergoes a quantum phase transition to a topological\nsuperfluid state at a critical Zeeman field. We show that the nonanalyticities\nof the thermodynamic functions as well as other physical quantities at the\nquantum phase transition originate from the infrared singularities caused by\nthe gapless fermionic spectrum. The same argument applies also to the BCS-BEC\nevolution in 2D fermionic superfluids with $p$- or d-wave pairing. The\nsuperfluid density $n_s$ and the velocity of the Goldstone sound mode $c_s$\nbehave oppositely in the normal and the topological superfluid phases: they are\nsuppressed by the Zeeman field in the normal superfluid phase, but get enhanced\nin the topological superfluid phase. The velocity of the Goldstone sound mode\nalso shows nonanalyticity at the quantum phase transition. For large Zeeman\nfield, we find $n_s\\rightarrow n$ and $c_s\\rightarrow \\upsilon_{\\rm F}$, where\n$n$ is the total fermion density and $\\upsilon_{\\rm F}$ is the Fermi velocity\nof noninteracting system. The unusual behavior of the superfluid density and\nthe collective modes can be understood by the fact that the spin-orbit-coupled\nsuperfluid state at large Zeeman field can be mapped to the $p_x+ip_y$\nsuperfluid state of spinless fermions."
    },
    {
        "anchor": "Two-dimensional dipolar Bose-Einstein condensate bright and vortex\n  solitons on one-dimensional optical lattice: By solving the three-dimensional Gross-Pitaevskii equation we generate\ntwo-dimensional axially-symmetric and anisotropic dipolar Bose-Einstein\ncondensate bright solitons, for repulsive atomic interaction, stabilized by\nonly a weak one-dimensional optical lattice (OL) aligned along and\nperpendicular, respectively, to the dipole polarization direction. In the\nformer case vortex solitons can also be created. We show that it is possible to\nmake a stable array of small interacting axially-symmetric dipolar solitons put\non alternate OL sites. Further, we demonstrate the elastic nature of the\ncollision of two such solitons.",
        "positive": "Observation of a pairing pseudogap in a two-dimensional Fermi gas: Pairing of fermions is ubiquitous in nature and it is responsible for a large\nvariety of fascinating phenomena like superconductivity, superfluidity of\n$^3$He, the anomalous rotation of neutron stars, and the BEC-BCS crossover in\nstrongly interacting Fermi gases. When confined to two dimensions, interacting\nmany-body systems bear even more subtle effects, many of which lack\nunderstanding at a fundamental level. Most striking is the, yet unexplained,\neffect of high-temperature superconductivity in cuprates, which is intimately\nrelated to the two-dimensional geometry of the crystal structure. In\nparticular, the questions how many-body pairing is established at high\ntemperature and whether it precedes superconductivity are crucial to be\nanswered. Here, we report on the observation of pairing in a harmonically\ntrapped two-dimensional atomic Fermi gas in the regime of strong coupling. We\nperform momentum-resolved photoemission spectroscopy, analogous to ARPES in the\nsolid state, to measure the spectral function of the gas and we detect a\nmany-body pairing gap above the superfluid transition temperature. Our\nobservations mark a significant step in the emulation of layered\ntwo-dimensional strongly correlated superconductors using ultracold atomic\ngases."
    },
    {
        "anchor": "Information theoretic approach to effects of spin-orbit coupling in\n  Bose-Einstein condensates: We make use of Shannon entropy ($S$) and Fisher information ($I$) to study\nthe response of atomic density profiles of a spin-orbit coupled Bose-Einstein\ncondensate to changes in the wave number ($\\kappa_L$) of the Raman laser that\ncouples two hyperfine states of atoms in the condensate. The choice for values\nof $\\kappa_L$, the so-called spin-orbit parameter, and Rabi frequency\n($\\Omega$) leads to two distinct regions in the system's energy spectrum with\ndifferent order parameters and/or probability densities. In addition, we can\nhave a spatially modulated density profile, reminiscent of the so called stripe\nphase. Our numbers for $S$ and $I$ demonstrate that for $\\kappa_L^2<\\Omega$\n(region 1) the density profile becomes localized as $\\kappa_L$ increases while\nwe observe delocalization in the density distribution for $\\kappa_L^2>\\Omega$\n(region 2) for increasing values of $\\kappa_L$. In the stripe phase the nature\nof $S$ and $I$ to changes in $\\kappa_L$ is similar to that found for the\ncondensate in region 2. The results for information theoretic quantities in the\nstripe phase are, in general, augmented compared to those of region 2. In\nparticular, the highly enhanced values of position-space Fisher information\nimply an extremely concentrated atomic density distribution to provide an\nevidence for supersolid properties of Bose-Einstein condensates in the presence\nof spin-orbit coupling.",
        "positive": "Velocity-dependent quantum phase slips in 1D atomic superfluids: Quantum phase slips are the primary excitations in one-dimensional\nsuperfluids and superconductors at low temperatures but their existence in\nultracold quantum gases has not been demonstrated yet. We now study\nexperimentally the nucleation rate of phase slips in one-dimensional\nsuperfluids realized with ultracold quantum gases, owing along a periodic\npotential. We observe a crossover between a regime of temperature-dependent\ndissipation at small velocity and interaction and a second regime of\nvelocity-dependent dissipation at larger velocity and interaction. This\nbehavior is consistent with the predicted crossover from thermally-assisted\nquantum phase slips to purely quantum phase slips."
    },
    {
        "anchor": "Dynamics of fermions in an amplitude modulated lattice: We study dynamics of fermions loaded in an optical lattice with a\nsuperimposed parabolic trap potential. In the recent Hamburg experiments\n[J.Heinze et.al., Phys. Rev. Lett. 110, 085302 (2013)] on quantum simulation of\nphotoconductivity, a modulation pulse on the optical lattice transferred part\nof the population of the lowest band to an excited band, leaving a hole in the\nparticle distribution of the lowest band. Subsequent intricate dynamics of both\nexcited particles and holes can be explained by a semiclassical approach based\non the evolution of Wigner function. Here we provide a more detailed analysis\nof the dynamics taking into account the dimensionality of the system and finite\ntemperature effects, aiming at reproducing experimental results on longer\ntimescales. A semiclassical wave packet is constructed more accurately than in\nthe previous theory. As a result, semiclassical dynamics indeed reproduces\nexperimental data and full quantum numerical calculations with much better\naccuracy. In particular, fascinating phenomenon of collapse and revival of\nholes is investigated in a more detail. We presume the experimental setup can\nbe used for deeper exploration of nonlinear waves in fermionic gases.",
        "positive": "Nonequilibrium Josephson oscillations in Bose-Einstein condensates\n  without dissipation: We perform a detailed field theoretical study of nonequilibrium Josephson\noscillations between interacting Bose-Einstein condensates confined in a\nfinite-size double-well trap. We find that the Josephson junction can sustain\nmultiple undamped Josephson oscillations up to a characteristic time scale\n$\\tau_c$ without quasipartcles being excited in the system. This may explain\nrecent related experiments. At larger times the dynamics of the junction is\ngoverned by fast Rabi oscillations between the descrete quasiparticle levels.\nWe predict that a selftrapped BEC state will be destroyed by these Rabi\noscillations."
    },
    {
        "anchor": "Critical points of the anyon-Hubbard model: Anyons are particles with fractional statistics that exhibit a nontrivial\nchange in the wavefunction under an exchange of particles. Anyons can be\nconsidered to be a general category of particles that interpolate between\nfermions and bosons. We determined the position of the critical points of the\none-dimensional anyon-Hubbard model, which was mapped to a modified\nBose-Hubbard model where the tunneling depends on the local density and the\ninterchange angle. We studied the latter model by using the density matrix\nrenormalization group method and observed that gapped (Mott insulator) and\ngapless (superfluid) phases characterized the phase diagram, regardless of the\nvalue of the statistical angle. The phase diagram for higher densities was\ncalculated and showed that the Mott lobes increase (decrease) as a function of\nthe statistical angle (global density). The position of the critical point\nseparating the gapped and gapless phases was found using quantum information\ntools, namely the block von Neumann entropy. We also studied the evolution of\nthe critical point with the global density and the statistical angle and showed\nthat the anyon-Hubbard model with a statistical angle $\\theta =\\pi/4$ is in the\nsame universality class as the Bose-Hubbard model with two body interactions.",
        "positive": "Spin 1 microcondensate in a magnetic field: semiclassics and exact\n  solution: We study a spin 1 Bose condensate small enough to be treated as a single\nmagnetic `domain': a system that we term a microcondensate. Because all\nparticles occupy a single spatial mode, this quantum many body system has a\nwell defined classical limit consisting of three degrees of freedom,\ncorresponding to the three macroscopically occupied spin states. We study both\nthe classical limit and its quantization, finding an integrable system in both\ncases. Depending on the sign of the ratio of the spin interaction energy and\nthe quadratic Zeeman energy, the classical limit displays either a separartrix\nin phase space, or Hamiltonian monodromy corresponding to non-trivial phase\nspace topology. We discuss the quantum signatures of these classical phenomena\nusing semiclassical quantization as well as an exact solution using the Bethe\nansatz."
    },
    {
        "anchor": "Singularity in the matrix of the coupled Gross-Pitaevskii equations and\n  the related state-transitions in three-species condensates: An approach is proposed to solve the coupled Gross-Pitaevskii equations (CGP)\nof the 3-species BEC in an analytical way under the Thomas-Fermi approximation\n(TFA). It was found that, when the strength of a kind of interaction increases\nand crosses over a critical value, a specific type of state-transition will\noccur and will cause a jump in the total energy. Due to the jump, the energy of\nthe lowest symmetric state becomes considerably higher. This leaves a\nparticular opportunity for the lowest asymmetric state to replace the symmetric\nstates as the ground state. It was further found that the critical values are\nrelated to the singularity of either the matrix or a sub-matrix of the CGP.\nThese critical values are not arising from the TFA but inherent in the CGP, and\nthey can be analytically expressed. Furthermore, a model (in which two kinds of\natoms separated from each other asymmetrically) has been proposed for the\nevaluation of the energy of the lowest asymmetric state. With this model the\nemergence of the asymmetric ground state is numerically confirmed under the\nTFA. The theoretical formalism of this paper is quite general and can be\ngeneralized for BEC with more than three species.",
        "positive": "Effects of finite temperature on the robustness of the Mott insulator\n  phase in pseudo one-dimensional Bose-Hubbard Model: We study the superfluid-Mott insulator (SF-MI) transition in an\none-dimensional optical lattice system, and employ the Bose-Hubbard model in\ntwo dimension with a combined potential of an optical lattice in one direction\nand a confining harmonic trap in the other direction, which we refer to as the\npseudo one-dimension Bose-Hubbard model. There some excited states with respect\nto the harmonic trap are considered. The Mott lobes shrink in the $\\mu$ and $J$\ndirections of the $\\mu$-$J$ phase diagram. The shrinkage occurs because the\ninteractions involving the excited states become weaker than that between\nparticles in the ground state. The dispersion of the in-site particle increases\nbecause the energy spacing between the eigenstates of the Hamiltonian decreases\nat finite temperature. The excited states significantly affect the robustness\nof the MI phase at finite temperate."
    },
    {
        "anchor": "Spontaneous condensation of exciton polaritons in the single-shot regime: Bose-Einstein condensate of exciton polaritons in a semiconductor microcavity\nis a macroscopically populated coherent quantum state subject to concurrent\npumping and decay. Debates about the fundamental nature of the condensed phase\nin this open quantum system still persist. Here, we gain a new insight into the\nspontaneous condensation process by imaging long-lifetime exciton polaritons in\na high-quality inorganic microcavity in the single-shot optical excitation\nregime, without averaging over multiple condensate realisations. In this highly\nnon-stationary regime, a condensate is strongly influenced by the `hot'\nincoherent reservoir, and reservoir depletion is critical for the transition to\nthe ground energy and momentum state. Condensates formed by more photonic\nexciton polaritons exhibit dramatic reservoir-induced density filamentation and\nshot-to-shot fluctuations. In contrast, condensates of more excitonic\nquasiparticles display smooth density and are second-order coherent. Our\nobservations show that the single-shot measurements offer a unique opportunity\nto study formation of macroscopic phase coherence during a quantum phase\ntransition in a solid state system.",
        "positive": "Measurement induced dynamics and stabilization of spinor condensate\n  domain walls: Weakly measuring many-body systems and allowing for feedback in real-time can\nsimultaneously create and measure new phenomena in strongly correlated quantum\nsystems. We study the dynamics of a continuously measured two-component\nBose-Einstein condensate (BEC) potentially containing a domain wall, and focus\non the trade-off between usable information obtained from measurement and\nquantum backaction. Each weakly measured system yields a measurement record\nfrom which we extract real-time dynamics of the domain wall. We show that\nquantum backaction due to measurement causes two primary effects: domain wall\ndiffusion and overall heating. The system dynamics and signal-to-noise ratio\ndepend on the choice of measurement observable. We describe a feedback protocol\nto create and stabilize a domain wall in the regime where domain walls are\nunstable, giving a prototype example of Hamiltonian engineering using\nmeasurement and feedback."
    },
    {
        "anchor": "Critical behaviours of contact near phase transitions: A central quantity of importance for ultracold atoms is contact, which\nmeasures two-body correlations at short distances in dilute systems. It appears\nin universal relations among thermodynamic quantities, such as large momentum\ntails, energy, and dynamic structure factors, through the renowned Tan\nrelations. However, a conceptual question remains open as to whether or not\ncontact can signify phase transitions that are insensitive to short-range\nphysics. Here we show that, near a continuous classical or quantum phase\ntransition, contact exhibits a variety of critical behaviors, including scaling\nlaws and critical exponents that are uniquely determined by the universality\nclass of the phase transition and a constant contact per particle. We also use\na prototypical exactly solvable model to demonstrate these critical behaviors\nin one-dimensional strongly interacting fermions. Our work establishes an\nintrinsic connection between the universality of dilute many-body systems and\nuniversal critical phenomena near a phase transition.",
        "positive": "Effect of short-range interaction for collision of ultracold dipoles: We consider the low-energy scattering of two ultracold polarized dipoles with\nboth a short-range interaction (SRI) and a weak dipole-dipole interaction (DDI)\nwhich is far away from shape-resonances. In previous analytical studies, the\nscattering amplitude in this system was often calculated via the first-order\nBorn approximation (FBA). Our results show that significant derivations from\nthis approximation can arise in some cases. In these cases, the SRI can\nsignificantly modify the inter-dipole scattering amplitudes even if the\nscattering amplitudes for the SRI alone are much smaller than the dipolar\nlength of the DDI. We further obtain approximate analytical expressions for\nthese inter-dipole scattering amplitudes."
    },
    {
        "anchor": "Determination of Chern numbers with a phase retrieval algorithm: Ultracold atoms in optical lattices form a clean quantum simulator platform\nwhich can be utilized to examine topological phenomena and test exotic\ntopological materials. Here we propose an experimental scheme to measure the\nChern numbers of two-dimensional multiband topological insulators with bosonic\natoms. We show how to extract the topological invariants out of a sequence of\ntime-of-flight images by applying a phase retrieval algorithm to matter waves.\nWe illustrate advantages of using bosonic atoms as well as efficiency and\nrobustness of the method with two prominent examples: the Harper-Hofstadter\nmodel with an arbitrary commensurate magnetic flux and the Haldane model on a\nbrick-wall lattice.",
        "positive": "Zitterbewegung with spin-orbit coupled ultracold atoms in a fluctuating\n  optical lattice: Dynamics of non-interacting ultracold atoms with artificial spin-orbit\ncoupling is considered. Spin-orbit coupling is created using two moving optical\nlattices with orthogonal polarizations. Our main goal is to study influence of\nlattice noise on Rabi oscillations. Special attention is paid to the phenomenon\nof the Zitterbewegung being trembling motion caused by Rabi transitions between\nstates with different velocities. Phase and amplitude fluctuations of lattices\nare modelled by means of the two-dimensional stochastic Ornstein-Uhlenbeck\nprocess, also known as harmonic noise. In the the noiseless case the problem is\nsolved analytically in terms of the momentum representation. It is shown that\nlattice noise significantly extends duration of the Zitterbewegung as compared\nto the noiseless case. This effect originates from noise-induced decoherence of\nRabi oscillations."
    },
    {
        "anchor": "Density Fluctuations in Uniform Quantum Gases: Analytical expressions are given for the static structure factor S(k) and the\npair correlation function g(r) for uniform ideal Bose-Einstein and Fermi-Dirac\ngases for all temperatures. In the vicinity of Bose Einstein condensation (BEC)\ntemperature, g(r) becomes long ranged and remains so in the condensed phase. In\nthe dilute gas limit, g(r) of bosons & fermions do not coincide with\nMaxwell-Boltzmann gas but exhibit bunching & anti-bunching effect respectively.\nThe width of these functions depends on the temperature and is scaled as \\surd\n(inverse atomic mass). Our numerical results provide the precise quantitative\nvalues of suppression/increase (antibunching and bunching) of the density\nfluctuations at small distances in ideal quantum gases in qualitative agreement\nwith the experimental observation for almost non-trapped dilute gases.",
        "positive": "Observation of superradiance in a phase fluctuating dipolar\n  Bose-Einstein condensate: Despite the extensive study of matter-wave superradiance in a Bose-Einstein\ncondensate (BEC) using its unique coherence property, the controllability of\nsuperradiant process has remained limited in the previous studies exploiting a\nphase-coherent condensate with isotropic contact interactions. Here, we combine\ntunable s-wave scattering with dipolar interactions in a BEC of $^{168}$Er\natoms wherein the asymmetry and threshold of superradiance are independently\ncontrolled. By changing the s-wave scattering length near the Feshbach\nresonance, we tune the superradiance threshold with increasing phase\nfluctuations. In contrast to collective light scattering from a condensate only\nwith contact interactions, we observe an asymmetric superradiant peak in a\ndipolar BEC by changing the direction of external magnetic field. This results\nfrom the anisotropic excitation spectrum induced by the dipole-dipole\ninteraction. Our observation is expected to bring forth unprecedented\napplication of matter-wave optics leading to controlled emission of matter\nwave."
    },
    {
        "anchor": "Ground-state properties of dilute spinless fermions in fractional\n  dimensions: We analyze zero-temperature universal properties of the simplest\nGalilean-invariant model of spinless low-dimensional fermions with short-range\ntwo-body interactions. In particular, it is shown that after proper\nrenormalization of the coupling constant, even the dilute system possesses rich\nphase diagram that includes the superfluid state and the metastable `upper\nbranch' behavior.",
        "positive": "Theoretical exploration of competing phases of lattice Bose gases in a\n  cavity: We consider bosonic atoms loaded into optical lattices with cavity-mediated\ninfinite-range interactions. Competing short- and global-range interactions\ncultivates a rich phase diagram. With a systematic field-theoretical\nperspective, we present an $\\emph{analytical}$ construction of global\nground-state phase diagram. We find that the infinite-range interaction\nenhances the fluctuation of the number density. In the strong coupling regime,\nwe find four branches of elementary excitations with two being \"partilce-like\"\nand two being \"hole-like\", and that the excitation gap becomes soft at the\nphase boundary between compressible phases and incompressible phases. We derive\nan effective theory describing compressible superfluid and supersolid states.\nTo complement this perturbative study, we construct a self-consistent\nmean-field theory and find numerical results consistent with our theoretical\nanalysis. We map out the phase diagram and find that a charge density wave may\nundergo a structure phase transition to a different charge density wave before\nit finally enters into the supersolid phase driven by increasing the hopping\namplitude."
    },
    {
        "anchor": "Universal Trimers induced by Spin-Orbit Coupling in Ultracold Fermi\n  Gases: In this letter we address the issue how synthetic spin-orbit (SO) coupling\ncan strongly affect three-body physics in ultracold atomic gases. We consider a\nsystem which consists of three fermionic atoms, including two spinless heavy\natoms and one spin-1/2 light atom subjected to an isotropic SO coupling. We\nfind that SO coupling can induce universal three-body bound states with\nnegative s-wave scattering length at a smaller mass ratio, where no trimer\nbound state can exist if in the absence of SO coupling. The energies of these\ntrimers are independent of high-energy cutoff, and therefore they are universal\nones. Moreover, the resulting atom-dimer resonance can be effectively\ncontrolled by SO coupling strength. Our results can be applied to systems like\n${}^6$Li and ${}^{40}$K mixture.",
        "positive": "Impossibility of the Efimov effect for p-wave interactions: Whether the Efimov effect is possible, in principle, for p-wave or higher\npartial-wave interactions is a fundamental question. Recently, there has been a\nclaim that three nonrelativistic particles with resonant p-wave interactions\nexhibit the Efimov effect. We point out that the assumed p-wave scattering\namplitude inevitably causes a negative probability. This indicates that the\nEfimov states found there cannot be realized in physical situations. We also\nrestate our previous argument that the Efimov effect, defined as an infinite\ntower of universal bound states characterized by discrete scale invariance, is\nimpossible for p-wave or higher partial-wave interactions."
    },
    {
        "anchor": "Josephson-type oscillations in spin-orbit coupled Bose-Einstein\n  condensates with nonlinear optical lattices: We consider spin-orbit coupled Bose Einstein Condensate in presence of linear\nand nonlinear optical lattices within the framework of quasi-one-dimensional\nGross-Pitaevskii equation. The population imbalance between the states changes\nperiodically with time and the oscillation amplitude depends sensitively on the\ninitial phase. The optical lattice is found to change phase velocity of the\noscillation of population imbalance. This oscillation can also be arrested\nbeyond critical values of parameters. We find that the optical lattice can\nefficiently be used to control the critical point.",
        "positive": "Quantum walks accompanied by spin flipping in one-dimensional optical\n  lattices: We investigate continuous-time quantum walks of two fermionic atoms loaded in\none-dimensional optical lattices with on-site interaction and subjected to a\nZeeman field. The quantum walks are accompanied by spin-flipping processes. We\ncalculate the time-dependent density distributions of the two fermions with\nopposite spins which are initially positioned on the center site by means of\nexact numerical method. Besides the usual fast linear expansion behavior, we\nfind an interesting spin-flipping induced localization in the time-evolution of\ndensity distributions. We show that the fast linear expansion behavior could be\nrestored by simply ramping on the Zeeman field or further increasing the\nspin-flipping strength. The intrinsic origin of this exotic phenomenon is\nattributed to the emergence of a flat band in the single particle spectrum of\nthe system. Furthermore, we investigate the effect of on-site interaction on\nthe dynamics of the quantum walkers. The two-particle correlations are\ncalculated and signal of localization is also shown therein. A simple potential\nexperimental application of this interesting phenomenon is proposed."
    },
    {
        "anchor": "Parity oscillations and photon correlation functions in the $ Z_2/U(1) $\n  Dicke model at a finite number of atoms or qubits: In this work, by using the strong coupling expansion and exact diagonization\n(ED), we study the $ Z_2/U(1) $ Dicke model with independent rotating wave (RW)\ncoupling $ g $ and counter-rotating wave (CRW) coupling $ g^{\\prime} $ at a\nfinite $ N $.\n  This model includes the four standard quantum optics model: Rabi, Dicke,\nJaynes-Cummings ( JC ) and Tavis-Cummings (TC) model as its various special\nlimits. We show that in the super-radiant phase, the system's energy levels are\ngrouped into doublets with even and odd parity.\n  Any anisotropy $ \\beta=g/g^{\\prime} \\neq 1 $ leads to the oscillation of\nparities in both the ground and excited doublets as the atom-photon coupling\nstrength increases.\n  The oscillations will be pushed to the infinite coupling strength in the\nisotropic $ Z_2 $ limit $ \\beta=1 $.\n  We find nearly perfect agreements between the strong coupling expansion and\nthe ED in the super-radiant regime.\n  We also compute the photon correlation functions, squeezing spectrum, number\ncorrelation functions which can be measured by various standard optical\ntechniques.",
        "positive": "Non-local state-swapping of polar molecules in bilayers: The observation of significant dipolar effects in gases of ultra-cold polar\nmolecules typically demands a strong external electric field to polarize the\nmolecules. We show that even in the absence of a significant polarization,\ndipolar effects may play a crucial role in the physics of polar molecules in\nbilayers, provided that the molecules in each layer are initially prepared in a\ndifferent rotational state. Then, inter-layer dipolar interactions result in a\nnon-local swap of the rotational state between molecules in different layers,\neven for weak applied electric fields. The inter-layer scattering due to the\ndipole-dipole interaction leads to a non-trivial dependence of the swapping\nrate on density, temperature, inter-layer spacing, and population imbalance.\nFor reactive molecules like KRb, chemical recombination immediately follows a\nnon-local swap and dominates the losses even for temperatures well above\nquantum degeneracy, and could be hence observed under current experimental\nconditions."
    },
    {
        "anchor": "Quenching to unitarity: Quantum dynamics in a 3D Bose gas: We study the dynamics of a dilute Bose gas at zero temperature following a\nsudden quench of the scattering length from a noninteracting Bose condensate to\nunitarity (infinite scattering length). We apply three complementary approaches\nto understand the momentum distribution and loss rates. First, using a\ntime-dependent variational ansatz for the many-body state, we calculate the\ndynamics of the momentum distribution. Second, we demonstrate that, at short\ntimes and large momenta compared to those set by the density, the physics can\nbe well understood within a simple, analytic two-body model. We derive a\nquantitative prediction for the evolution of Tan's contact, which increases\nlinearly at short times. We also study the three-body losses at finite\ndensities. Consistent with experiments, we observe lifetimes which are long\ncompared to the dynamics of large momentum modes.",
        "positive": "Variational ansatz for $p$-wave fermions confined in a one-dimensional\n  harmonic trap: We propose a very accurate and efficient variational scheme for the ground\nstate of the system of $p$-wave attractively interacting fermions confined in a\none-dimensional harmonic trap. By the construction, the method takes the\nnon-analytical part of interactions exactly into account and thus it\napproximates the true ground-state wave function in a whole range of\ninteractions very accurately. Within the method, we determine different\nproperties of the system for a different number of particles and different\ninteractions. In this way, we explore how the system and its features transit\nfrom the ideal non-interacting Fermi gas to the system of infinitely strong\nattractions. Additionally, we demonstrate that the ansatz may also be used on a\nrepulsive branch of interactions where other numerical methods break down. The\npresented method of including zero-range interactions is very universal and may\nbe easily generalized to other one-dimensional confinements."
    },
    {
        "anchor": "Quantum Oscillations between weakly coupled Bose-Einstein Condensates:\n  Evolution in a Non-degenerate Double Well: We discuss coherent atomic oscillations between two weakly coupled\nBose-Einstein condensates that are energetically different. The weak link is\nnotionally provided by a laser barrier in a (possibly asymmetric) multi-well\ntrap or by Raman coupling between condensates in different hyperfine levels.\nThe resultant boson Josephson junction dynamics is described by a double-well\nnonlinear Gross-Pitaevskii equation. On the basis of a new set of Jacobian\nelliptic function solutions, we describe the period of the oscillations as well\nas associated quantities and predict novel observable consequences of the\ninterplay of the energy difference and initial phase difference between the two\ncondensate populations.",
        "positive": "Splitting dynamics of giant vortices in dilute Bose-Einstein condensates: We study the splitting of multiply quantized vortices with large quantum\nnumbers in dilute nonrotated Bose-Einstein condensates in the zero-temperature\nlimit. The splitting is observed to result in vortex-free condensate fragments\nwhich are separated by vortex sheets. The number of these fragments is found to\nbe equal to the angular-momentum quantum number of the Bogoliubov excitation\nmode responsible for the splitting, although the formulation of the fragments\ncannot be described by small-amplitude excitations. Thus, the realization of an\nisolated giant vortex and the observation of its splitting would provide a\nmeans to directly relate the experimental data to discrete theoretical\nquantities."
    },
    {
        "anchor": "Ferroelectric quantum phase transition with cold polar molecules: We analyze a system of polar molecules in a one-dimensional optical lattice.\nBy controlling the internal structure of the polar molecules with static\nelectric and microwave fields, we demonstrate the appearance of a quantum phase\ntransition into a ferroelectric phase via spontaneous breaking of a $U(1)$\nsymmetry. The phase diagram is first analyzed within mean-field theory, while\nin a second step the results are verified by a mapping onto the Bose-Hubbard\nmodel for hard-core bosons. The latter is studied within the well-established\nbosonization procedure. We find that the ferroelectric phase is characterized\nby (quasi) long-range order for the electric dipole moments.",
        "positive": "Quantum Analogs of Classical Wakes in Bose-Einstein Condensates: We show that an elliptical obstacle moving through a Bose-Einstein condensate\ngenerates wakes of quantum vortices which resemble those of classical viscous\nflow past a cylinder or sphere. The role of ellipticity is to facilitate the\ninteraction of the vortices nucleated by the obstacle. Initial steady symmetric\nwakes lose their symmetry and form clusters of like-signed vortices, in analogy\nto the classical B\\'enard-von K\\'arm\\'an vortex street. Our findings,\ndemonstrated numerically in both two and three dimensions, confirm the\nintuition that a sufficiently large number of quanta of circulation reproduce\nclassical physics."
    },
    {
        "anchor": "Vortex-hole duality: a unified picture of weak and strong-coupling\n  regimes of bosonic ladders with flux: Two-leg bosonic ladders with flux harbor a remarkable vortex-hole duality\nbetween the weak-coupling vortex lattice superfluids and strong-coupling\ncharge-density-wave crystals. The strong-coupling crystalline states, which are\nrealized in the vicinity of $\\pi$-flux, are independent of particle statistics,\nand are related with the incompressible fractional quantum Hall states in the\nthin-cylinder limit. These fully gapped ground states, away of $\\pi$-flux,\ndevelop nonzero chiral (spin) currents. Contact-interacting quantum gases\npermit exploration of this vortex-hole duality in experiments.",
        "positive": "In-situ Observation of Incompressible Mott-Insulating Domains of\n  Ultracold Atomic Gases: We present a direct measurement of the density profile of a two-dimensional\nMott Insulator formed by ultracold atoms in an optical lattice. High resolution\nabsorption imaging is used to probe the \"wedding-cake\" structure of a trapped\ngas as it crosses the boundary from a unit-filled Mott insulating phase to the\nsuperfluid phase at finite temperature. Detailed analysis of images yields\nmeasurements of temperature and local compressibility; for the latter we\nobserve a strong suppression deep in the Mott-insulating phase, which is\nrecovered for the superfluid and normal phases. Furthermore, we measure\nspatially resolved fluctuations in the local density, showing a suppression of\nfluctuations in the insulator. Results are consistent with the\nfluctuation-dissipation theorem for insulator, superfluid and normal gas."
    },
    {
        "anchor": "A finite element toolbox for the Bogoliubov-de Gennes stability analysis\n  of Bose-Einstein condensates: We present a finite element toolbox for the computation of Bogoliubov-de\nGennes modes used to assess the linear stability of stationary solutions of the\nGross-Pitaevskii (GP) equation. Applications concern one (single GP equation)\nor two-component (a system of coupled GP equations) Bose-Einstein condensates\nin one, two and three dimensions of space. An implementation using the free\nsoftware FreeFem++ is distributed with this paper. For the computation of the\nGP stationary (complex or real) solutions we use a Newton algorithm coupled\nwith a continuation method exploring the parameter space (the chemical\npotential or the interaction constant). Bogoliubov-de Gennes equations are then\nsolved using dedicated libraries for the associated eigenvalue problem. Mesh\nadaptivity is proved to considerably reduce the computational time for cases\nimplying complex vortex states. Programs are validated through comparisons with\nknown theoretical results for simple cases and numerical results reported in\nthe literature.",
        "positive": "Observation of an Efimov spectrum in an atomic system: In 1970 V. Efimov predicted a puzzling quantum-mechanical effect that is\nstill of great interest today. He found that three particles subjected to a\nresonant pairwise interaction can join into an infinite number of loosely bound\nstates even though each particle pair cannot bind. Interestingly, the\nproperties of these aggregates, such as the peculiar geometric scaling of their\nenergy spectrum, are universal, i.e. independent of the microscopic details of\ntheir components. Despite an extensive search in many different physical\nsystems, including atoms, molecules and nuclei, the characteristic spectrum of\nEfimov trimer states still eludes observation. Here we report on the discovery\nof two bound trimer states of potassium atoms very close to the Efimov\nscenario, which we reveal by studying three-particle collisions in an ultracold\ngas. Our observation provides the first evidence of an Efimov spectrum and\nallows a direct test of its scaling behaviour, shedding new light onto the\nphysics of few-body systems."
    },
    {
        "anchor": "Life and death of the Bose polaron: Spectroscopic and interferometric measurements complement each other in\nextracting the fundamental properties of quantum many-body systems. While\nspectroscopy provides precise measurements of equilibrated energies,\ninterferometry can elucidate the dynamical evolution of the system. For an\nimpurity immersed in a bosonic medium, both are equally important for\nunderstanding the quasiparticle physics of the Bose polaron. Here, we compare\nthe interferometric and spectroscopic timescales to the underlying dynamical\nregimes of the impurity dynamics and the polaron lifetime, highlighting the\ncapability of the interferometric approach to clearly resolve polaron dynamics.\nIn particular, interferometric measurements of the coherence amplitude at\nstrong interactions reveal faster quantum dynamics at large repulsive\ninteraction strengths than at unitarity. These observations are in excellent\nagreement with a short-time theoretical prediction including both the continuum\nand the attractive polaron branch. For longer times, qualitative agreement with\na many-body theoretical prediction which includes both branches is obtained.\nMoreover, the polaron energy is extracted from interferometric measurements of\nthe observed phase velocity in agreement with previous spectroscopic results\nfrom weak to strong attractive interactions. Finally, the phase evolution\nallows for the measurement of an energetic equilibration timescale, describing\nthe initial approach of the phase velocity to the polaron energy.\nTheoretically, this is shown to lie within the regime of universal dynamics\nrevealing a fast initial evolution towards the formation of polarons. Our\nresults give a comprehensive picture of the many-body physics governing the\nBose polaron and thus validates the quasiparticle framework for further\nstudies.",
        "positive": "Production of quantum degenerate strontium gases: Larger, better,\n  faster, colder: We report on an improved scheme to generate Bose-Einstein condensates (BECs)\nand degenerate Fermi gases of strontium. This scheme allows us to create\nquantum gases with higher atom number, a shorter time of the experimental\ncycle, or deeper quantum degeneracy than before. We create a BEC of 84-Sr\nexceeding 10^7 atoms, which is a 30-fold improvement over previously reported\nexperiments. We increase the atom number of 86-Sr BECs to 2.5x10^4 (a fivefold\nimprovement), and refine the generation of attractively interacting 88-Sr BECs.\nWe present a scheme to generate 84-Sr BECs with a cycle time of 2s, which, to\nthe best of our knowledge, is the shortest cycle time of BEC experiments ever\nreported. We create deeply-degenerate 87-Sr Fermi gases with T/T_F as low as\n0.10(1), where the number of populated nuclear spin states can be set to any\nvalue between one and ten. Furthermore, we report on a total of five different\ndouble-degenerate Bose-Bose and Bose-Fermi mixtures. These studies prepare an\nexcellent starting point for applications of strontium quantum gases\nanticipated in the near future."
    },
    {
        "anchor": "Bogoliubov phonons in a Bose-Einstein condensate from the one-loop\n  perturbative renormalization group: Wilson's renormalization-group approach to the weakly-interacting\nsingle-component Bose gas is discussed within the symmetry-broken, condensate\nphase. Extending upon the work by Bijlsma and Stoof [Phys. Rev. A 54, 5085\n(1996), see http://doi.org/10.1103/PhysRevA.54.5085 ], wave-function\nrenormalization of the temporal derivative contributions to the effective\naction is included in order to capture sound-like quasiparticle excitations\nwith wave lengths larger than the healing-length scale. By means of a suitable\nrescaling scheme we achieve convergence of the coupling flows, which serve as a\nmeans to determine the condensate depletion in accordance with Bogoliubov\ntheory, as well as the interaction-induced shift of the critical temperature.",
        "positive": "Creation of p-wave Feshbach molecules in the selected angular momentum\n  states using an optical lattice: We selectively create p-wave Feshbach molecules in the $m_{l}=\\pm 1$ orbital\nangular momentum projection state of $^{6}$Li. We use an optical lattice\npotential to restrict the relative momentum of the atoms such that only the\n$m_{l}=\\pm 1$ molecular state couples to the atoms at the Feshbach resonance.\nWe observe the hollow-centered dissociation profile, which is a clear\nindication of the selective creation of p-wave molecules in the $m_{l}=\\pm1$\nstates. We also measure the dissociation energy of the p-wave molecules created\nin the optical lattice and develop a theoretical formulation to explain the\ndissociation energy as a function of the magnetic field ramp rate for\ndissociation. The capability of selecting one of the two closely-residing\np-wave Feshbach resonances is useful for the precise characterization of the\np-wave Feshbach resonances."
    },
    {
        "anchor": "Umklapp Superradiance from a Collisionless Quantum Degenerate Fermi Gas: The quantum dynamics of the electromagnetic light mode of an optical cavity\nfilled with a coherently driven Fermi gas of ultracold atoms strongly depends\non geometry of the Fermi surface. Superradiant light generation and\nself-organization of the atoms can be achieved at low pumping threshold due to\nresonant atom-photon Umklapp processes, where the fermions are scattered from\none side of the Fermi surface to the other by exchanging photon momenta. The\ncavity spectrum exhibits sidebands, that, despite strong atom-light coupling\nand cavity decay, retain narrow linewidth, due to absorptionless transparency\nwindows outside the atomic particle-hole continuum and the suppression of\ninhomogeneous broadening and thermal fluctuations in the collisionless Fermi\ngas.",
        "positive": "Strong Quantum Turbulence in Bose Einstein Condensates: By combining experiments and numerical simulations which model the dynamics\nof shaken atomic Bose-Einstein condensates, we reveal the surprising nature of\nquantum turbulence in these systems. Unlike the tangles of vortex lines\ndescribed in the superfluid helium literature, we find that our turbulent\natomic condensate contains a mixture of strong fragmented density fluctuations\nand small random vortex loops which are not homogeneously distributed. This\nunusual form of turbulence, with its own properties and scaling behaviour,\nwhich we call strong quantum turbulence, is significantly different from the\nturbulence which is observed in either classical or other quantum systems, thus\nposing a new challenge in turbulence research."
    },
    {
        "anchor": "Three-dimensional spin-orbit coupled Fermi gases: Fulde-Ferrell pairing,\n  Majorana fermions, Weyl fermions and gapless topological superfluidity: We theoretically investigate a three-dimensional Fermi gas with Rashba\nspin-orbit coupling in the presence of both out-of-plane and in-plane Zeeman\nfields. We show that, driven by a sufficiently large Zeeman field, either\nout-of-plane or in-plane, the superfluid phase of this system exhibits a number\nof interesting features, including inhomogeneous Fulde-Ferrell pairing, gapped\nor gapless topological order and exotic quasi-particle excitations known as\nWeyl fermions that have linear energy dispersions in momentum space (i.e.,\nmassless Dirac fermions). The topological superfluid phase can have either four\nor two topologically protected Weyl nodes. We present the phase diagrams at\nboth zero and finite temperatures and discuss the possibility of their\nobservation in an atomic Fermi gas with synthetic spin-orbit coupling. In this\ncontext, topological superfluid phases with an imperfect Rashba spin-orbit\ncoupling are also studied.",
        "positive": "Quantum entanglement of spin-1 bosons with coupled ground states in\n  optical lattices: We examine particle entanglement, characterized by pseudo-spin squeezing, of\nspin-1 bosonic atoms with coupled ground states in a one-dimensional optical\nlattice. Both the superfluid and Mott-insulator phases are investigated\nseparately for ferromagnetic and antiferromagnetic interactions. Mode\nentanglement is also discussed in the Mott insulating phase. The role of a\nsmall but nonzero angle between the polarization vectors of counter-propagating\nlasers forming the optical lattice on quantum correlations is investigated as\nwell."
    },
    {
        "anchor": "Bose-Einstein condensation and non-extensive statistics: We study the Bose-Einstein condensation in non-extensive statistics for a\nfree gas of bosons, and extend the results to the non-relativistic case as\nwell. We present results for the dependence of the critical temperature and the\ncondensate fraction on the entropic index, q, and show that the condensate can\nexist only for a limited range of q in both relativistic and non-relativistic\nsystems. We provide numerical results for other thermodynamics quantities like\nthe internal energy, specific heat and number fluctuations. We discuss the\nimplications for high energy physics and hadron physics. The results for the\nnon-relativistic case can be of interest in cold-atom systems.",
        "positive": "Quartet Superfluid in Two-dimensional Mass-imbalanced Fermi Mixtures: Quartet superfluid (QSF) is a distinct type of fermion superfluidity that\nexhibits high-order correlation beyond the conventional BCS pairing paradigm.\nIn this Letter, we report the emergent QSF in 2D mass-imbalanced Fermi mixtures\nwith two-body contact interactions. This is facilitated by the formation of\nquartet bound state in vacuum that consists of a light atom and three heavy\nfermions. For an optimized heavy-light number ratio $3:1$, we identify QSF as\nthe ground state in a considerable parameter regime of mass imbalance and 2D\ncoupling strength. Its unique high-order correlation can be manifested in the\nmomentum-space crystallization of pairing field and density distribution of\nheavy fermions. Our results can be readily detected in Fermi-Fermi mixtures\nnowadays realized in cold atoms laboratories, and meanwhile shed light on\nexotic superfluidity in a broad context of mass-imbalanced fermion mixtures."
    },
    {
        "anchor": "On the existence of an energy gap in one-dimensional Lesanovsky's model: We study the quantum lattice gas model in one dimension introduced by\nLesanovsky, who showed that the exact ground state and a couple of excited\nstates can be obtained analytically. The Hamiltonian of the model depends\nsolely on the parameter $z$, the meaning of which is a fugacity in the\ncorresponding classical lattice gas model. For small $z$ ($0<z<1$), we prove\nthat there is an energy gap between the ground state and the excited states by\napplying Knabe's method.",
        "positive": "Topological quantum critical points in the extended Bose-Hubbard model: The combination of topology and quantum criticality can give rise to an\nexotic mix of counterintuitive effects. Here, we show that unexpected\ntopological properties take place in a paradigmatic strongly-correlated\nHamiltonian: the 1D extended Bose-Hubbard model. In particular, we reveal the\npresence of two distinct topological quantum critical points with localized\nedge states and gapless bulk excitations. Our results show that the topological\ncritical points separate two phases, one topologically protected and the other\ntopologically trivial, both characterized by a long-range ordered string\ncorrelation function. The long-range order persists also at the topological\ncritical points and it reflects the presence of localized edge states protected\nby a finite charge gap. Finally, we introduce a super-resolution quantum gas\nmicroscopy scheme for dipolar dysprosium atoms, which provides a reliable route\ntowards the experimental study of topological quantum critical points."
    },
    {
        "anchor": "The Hofstadter Butterfly in a Dynamic Cavity-Induced Synthetic Magnetic\n  Field: Energy bands of electrons in a square lattice potential threaded by a uniform\nmagnetic field exhibit a fractal structure known as the Hofstadter butterfly.\nHere we study a Fermi gas in a 2D optical lattice within a linear cavity with a\ntilt along the cavity axis. The hopping along the cavity axis is only induced\nby resonant Raman scattering of transverse pump light into a standing wave\ncavity mode. Choosing a suitable pump geometry allows to realize the\nHofstadter-Harper model with a cavity-induced dynamical synthetic magnetic\nfield, which appears at the onset of the superradiant phase transition. The\ndynamical nature of this cavity-induced synthetic magnetic field arises from\nthe delicate interplay between collective superradiant scattering and the\nunderlying fractal band structure. Using a sixth-order expansion of the free\nenergy as function of the order parameter and by numerical simulations we show\nthat at low magnetic fluxes the superradiant ordering phase transition is first\norder, while it becomes second order for higher flux. The dynamic nature of the\nmagnetic field induces a non-trivial deformation of the Hofstadter butterfly in\nthe superradiant phase. At strong pump far above the self-ordering threshold we\nrecover the Hofstadter butterfly one would obtain in a static magnetic field.",
        "positive": "Acoustic superradiance from an optical-superradiance-induced vortex in a\n  Bose-Einstein condensate: We consider the simultaneous scattering of an angular momentum carrying\nLaguerre-Gaussian light beam and an acoustic wave from an atomic Bose-Einstein\ncondensate, under condition of optical superradiance induced vortex state. We\nderive the mean field dynamical equations of the light-superfluid system, and\nobtain the equations governing the elementary excitation of the system which\nresult in a massless Klein-Gordon equation with source terms. This equation\ndescribes the propagation of the sound wave in an effective spacetime.\nEmploying a simplifying draining bathtub model for the vortex, we investigate\nthe scattering of the acoustic wave in the vortex phase and obtain a condition\nfor the acoustic superradiance. We conclude that Laguerre-Gaussian beam induced\nsudden transition from homogeneous to vortex state in the superfluid\nsimultaneously leads to the optical and acoustic superradiance."
    },
    {
        "anchor": "Interacting bosons in generalized zig-zag and railroad-trestle models: We theoretically study the ground-state phase diagram of strongly interacting\nbosons on a generalized zig-zag ladder model, the rail-road trestle (RRT)\nmodel. By means of analytical arguments in the limits of decoupled chains and\nthe case of vanishing fillings as well as extensive DMRG calculations we\nexamine the rich interplay between frustration and interaction for various\nparameter regimes. We distinguish three different cases, the fully frustrated\nRRT model where the dispersion relation becomes doubly degenerate and an\nextensive chiral superfluid regime is found, the anti-symmetric RRT with\nalternating $\\pi$ and $0$ fluxes through the ladder plaquettes and the sawtooth\nlimit, which is closely related to the latter case. We study detailed phase\ndiagrams which include besides different single component superfluids, the\nchiral superfluid phases, the two component superfluids and different gaped\nphases, with dimer and a charge-density wave order.",
        "positive": "Thermalization, condensate growth, and defect formation in an\n  out-of-equilibrium Bose gas: We experimentally and numerically investigate thermalization processes of a\ntrapped $^{87}$Rb Bose gas, initially prepared in a non-equilibrium state\nthrough partial Bragg diffraction of a Bose-Einstein condensate (BEC). The\nsystem evolves in a Gaussian potential, where we observe the destruction of the\nBEC due to collisions, and subsequent growth of a new condensed fraction in an\noscillating reference frame. Furthermore, we occasionally observe the presence\nof defects, which we identify as gray solitons. We simulate the evolution of\nour system using the truncated Wigner method and compare the outcomes with our\nexperimental results."
    },
    {
        "anchor": "The Higgs mode in a superfluid of Dirac fermions: We study the Higgs amplitude mode in the s-wave superfluid state on the\nhoneycomb lattice inspired by recent cold atom experiments. We consider the\nattractive Hubbard model and focus on the vicinity of a quantum phase\ntransition between semi-metal and superfluid phases. On either side of the\ntransition, we find collective mode excitations that are stable against decay\ninto quasiparticle-pairs. In the semi-metal phase, the collective modes have\n\"Cooperon\" and exciton character. These modes smoothly evolve across the\nquantum phase transition, and become the Anderson-Bogoliubov mode and the Higgs\nmode of the superfluid phase. The collective modes are accommodated within a\nwindow in the quasiparticle-pair continuum, which arises as a consequence of\nthe linear Dirac dispersion on the honeycomb lattice, and allows for sharp\ncollective excitations. Bragg scattering can be used to measure these\nexcitations in cold atom experiments, providing a rare example wherein\ncollective modes can be tracked across a quantum phase transition.",
        "positive": "Two-Stage Melting in Systems of Strongly Interacting Rydberg Atoms: We analyze the ground state properties of a one-dimensional cold atomic\nsystem in a lattice, where Rydberg excitations are created by an external laser\ndrive. In the classical limit, the ground state is characterized by a complete\ndevil's staircase for the commensurate solid structures of Rydberg excitations.\nUsing perturbation theory and a mapping onto an effective low energy\nHamiltonian, we find a transition of these commensurate solids into a floating\nsolid with algebraic correlations. For stronger quantum fluctuations the\nfloating solid eventually melts within a second quantum phase transition and\nthe ground state becomes paramagnetic."
    },
    {
        "anchor": "Momentum-resolved observation of thermal and quantum depletion in an\n  interacting Bose gas: We report on the single-atom-resolved measurement of the distribution of\nmomenta $\\hbar k$ in a weakly interacting Bose gas after a 330 ms\ntime-of-flight. We investigate it for various temperatures and clearly separate\ntwo contributions to the depletion of the condensate by their $k$-dependence.\nThe first one is the thermal depletion. The second contribution falls of as\n$k^{-4}$, and its magnitude increases with the in-trap condensate density as\npredicted by the Bogoliubov theory at zero temperature. These observations\nsuggest associating it with the quantum depletion. How this contribution can\nsurvive the expansion of the released interacting condensate is an intriguing\nopen question.",
        "positive": "Exceptional Bound States and negative Entanglement Entropy: This work introduces a new class of robust states known as Exceptional\nBoundary (EB) states, which are distinct from the well-known topological and\nnon-Hermitian skin boundary states. EB states occur in the presence of\nexceptional points, which are non-Hermitian critical points where eigenstates\ncoalesce and fail to span the Hilbert space. This eigenspace defectiveness not\nonly limits the accessibility of state information, but also interplays with\nlong-range order to give rise to singular propagators only possible in\nnon-Hermitian settings. Their resultant EB eigenstates are characterized by\nrobust anomalously large or negative occupation probabilities, unlike ordinary\nFermi sea states whose probabilities lie between zero and one. EB states remain\nrobust after a variety of quantum quenches and give rise to enigmatic negative\nentanglement entropy contributions. Through suitable perturbations, the\ncoefficient of the logarithmic entanglement entropy scaling can be continuously\ntuned. EB states represent a new avenue for robustness arising from geometric\ndefectiveness, independent of topological protection or non-reciprocal pumping."
    },
    {
        "anchor": "Universality of Fragmentation in the Schr\u00f6dinger Dynamics of Bosonic\n  Josephson Junctions: The many-body Schr\\\"odinger dynamics of a one-dimensional bosonic Josephson\njunction is investigated for up to ten thousand bosons and long times. The\ninitial states are fully condensed and the interaction strength is weak. We\nreport on a universal fragmentation dynamics on the many-body level: systems\nconsisting of different numbers of particles fragment to the same value at\nconstant mean-field interaction strength. The phenomenon manifests itself in\nobservables such as the correlation functions of the system. We explain this\nuniversal fragmentation dynamics analytically based on the Bose-Hubbard model.\nWe thereby show that the extent to which many-body effects become important at\nlater times depends crucially on the initial state. Even for arbitrarily large\nparticle numbers and arbitrarily weak interaction strength the dynamics is\nmany-body in nature and the fragmentation universal. There is no weakly\ninteracting limit where the Gross-Piatevskii mean-field is valid for long\ntimes.",
        "positive": "Kitaev honeycomb and other exotic spin models with polar molecules: We show that ultracold polar molecules pinned in an optical lattice can be\nused to access a variety of exotic spin models, including the Kitaev honeycomb\nmodel. Treating each molecule as a rigid rotor, we use DC electric and\nmicrowave fields to define superpositions of rotational levels as effective\nspin degrees of freedom, while dipole-dipole interactions give rise to\ninteractions between the spins. In particular, we show that, with sufficient\nmicrowave control, the interaction between two spins can be written as a sum of\nfive independently controllable Hamiltonian terms proportional to the five\nrank-2 spherical harmonics Y_{2,q}(theta,phi), where (theta,phi) are the\nspherical coordinates of the vector connecting the two molecules. To\ndemonstrate the potential of this approach beyond the simplest examples studied\nin [S. R. Manmana et al., arXiv:1210.5518v2], we focus on the realization of\nthe Kitaev honeycomb model, which can support exotic non-Abelian anyonic\nexcitations. We also discuss the possibility of generating spin Hamiltonians\nwith arbitrary spin S, including those exhibiting SU(N=2S+1) symmetry."
    },
    {
        "anchor": "Topological Bogoliubov quasiparticles from Bose-Einstein condensate in a\n  flat band system: For bosons with flat energy dispersion, condensation can occur in different\nsymmetry sectors. Here, we consider bosons in a Kagome lattice with $\\pi$-flux\nhopping, which in the presence of mean-field interactions exhibit degenerate\ncondensates in the $\\Gamma$- and the $K$-point. We analyze the excitation above\nboth condensates and find strikingly different properties: For the $K$-point\ncondensate, the Bogoliubov-de Gennes (BdG) Hamiltonian has broken particle-hole\nsymmetry (PHS) and exhibits a topologically trivial quasiparticle band\nstructure. However, band flatness plays a key role in breaking the time\nreversal symmetry (TRS) of the BdG Hamiltonian for a $\\Gamma$-point condensate.\nConsequently, its quasiparticle band structure exhibits non-trivial topology,\ncharacterized by non-zero Chern numbers and the presence of edge states.\nAlthough quantum fluctuations energetically favor the $K$-point condensate, the\ninteresting properties of the $\\Gamma$-point condensate become relevant for\nanisotropic hopping. The topological properties of the $\\Gamma$-point\ncondensate get even richer in the presence of extended Bose-Hubbard\ninteractions. We find a topological phase transition into a topological\ncondensate characterized by high Chern number and also comment on the\nrealization and detection of such excitations.",
        "positive": "Schwinger pair production with ultracold atoms: We consider a system of ultracold atoms in an optical lattice as a quantum\nsimulator for electron-positron pair production in quantum electrodynamics\n(QED). For a setup in one spatial dimension, we investigate the nonequilibrium\nphenomenon of pair production including the backreaction leading to plasma\noscillations. Unlike previous investigations on quantum link models, we focus\non the infinite-dimensional Hilbert space of QED and show that it may be well\napproximated by experiments employing Bose-Einstein condensates interacting\nwith fermionic atoms. The calculations based on functional integral techniques\ngive a unique access to the physical parameters required to realize the QED\nphenomena in a cold atom experiment. In particular, we use our approach to\nconsider quantum link models in a yet unexplored parameter regime and give\nbounds for their ability to capture essential features of the physics. The\nresults suggest a paradigmatic change towards realizations using coherent\nmany-body states rather than single atoms for quantum simulations of\nhigh-energy particle physics phenomena."
    },
    {
        "anchor": "Antiferromagnetic noise correlations in optical lattices: We analyze how noise correlations probed by time-of-flight (TOF) experiments\nreveal antiferromagnetic (AF) correlations of fermionic atoms in\ntwo-dimensional (2D) and three-dimensional (3D) optical lattices. Combining\nanalytical and quantum Monte Carlo (QMC) calculations using experimentally\nrealistic parameters, we show that AF correlations can be detected for\ntemperatures above and below the critical temperature for AF ordering. It is\ndemonstrated that spin-resolved noise correlations yield important information\nabout the spin ordering. Finally, we show how to extract the spin correlation\nlength and the related critical exponent of the AF transition from the noise.",
        "positive": "Multi-band spectroscopy of ultracold fermions: Observation of reduced\n  tunneling in attractive Bose-Fermi mixtures: We perform a detailed experimental study of the band excitations and\ntunneling properties of ultracold fermions in optical lattices. Employing a\nnovel multi-band spectroscopy for fermionic atoms we can measure the full band\nstructure and tunneling energy with high accuracy. In an attractive Bose-Fermi\nmixture we observe a significant reduction of the fermionic tunneling energy,\nwhich depends on the relative atom numbers. We attribute this to an\ninteraction-induced increase of the lattice depth due to self-trapping of the\natoms."
    },
    {
        "anchor": "Quantum simulation of lattice gauge theories using Wilson fermions: Quantum simulators have the exciting prospect of giving access to real-time\ndynamics of lattice gauge theories, in particular in regimes that are difficult\nto compute on classical computers. Future progress towards scalable quantum\nsimulation of lattice gauge theories, however, hinges crucially on the\nefficient use of experimental resources. As we argue in this work, due to the\nfundamental non-uniqueness of discretizing the relativistic Dirac Hamiltonian,\nthe lattice representation of gauge theories allows for an optimization that up\nto now has been left unexplored. We exemplify our discussion with lattice\nquantum electrodynamics in two-dimensional space-time, where we show that the\nformulation through Wilson fermions provides several advantages over the\npreviously considered staggered fermions. Notably, it enables a strongly\nsimplified optical lattice setup and it reduces the number of degrees of\nfreedom required to simulate dynamical gauge fields. Exploiting the optimal\nrepresentation, we propose an experiment based on a mixture of ultracold atoms\ntrapped in a tilted optical lattice. Using numerical benchmark simulations, we\ndemonstrate that a state-of-the-art quantum simulator may access the Schwinger\nmechanism and map out its non-perturbative onset.",
        "positive": "Multipolar condensates and multipolar Josephson effects: When single-particle dynamics are suppressed in certain strongly correlated\nsystems, dipoles arise as elementary carriers of quantum kinetics. These\ndipoles can further condense, providing physicists with a rich realm to study\nfracton phases of matter. Whereas recent theoretical discoveries have shown\nthat an unconventional lattice model may host a dipole condensate as the ground\nstate, fundamental questions arise as to whether dipole condensation is a\ngeneric phenomenon rather than a specific one unique to a particular model and\nwhat new quantum macroscopic phenomena a dipole condensate may bring us with.\nHere, we show that dipole condensates prevail in bosonic systems. Because of a\nself-proximity effect, where single-particle kinetics inevitably induces a\nfinite order parameter of dipoles, dipole condensation readily occurs in\nconventional normal phases of bosons. Our findings allow experimentalists to\nmanipulate the phase of a dipole condensate and deliver dipolar Josephson\neffects, where supercurrents of dipoles arise in the absence of particle flows.\nThe self-proximity effects can also be utilized to produce a generic multipolar\ncondensate. The kinetics of the $n$-th order multipoles unavoidably creates a\ncondensate of the $(n+1)$-th order multipoles, forming a hierarchy of\nmultipolar condensates that will offer physicists a whole new class of\nmacroscopic quantum phenomena."
    },
    {
        "anchor": "Quantum enhanced SU(1,1) matter wave interferometry in a ring cavity: Quantum squeezed states offer metrological enhancement as compared to their\nclassical counterparts. Here, we devise and numerically explore a novel method\nfor performing SU(1,1) interferometry beyond the standard quantum limit, using\nquasi-cyclic nonlinear wave mixing dynamics of ultracold atoms in a ring\ncavity. The method is based on generating quantum correlations between many\natoms via photon mediated optomechanical interaction. Timescales of the\ninterferometer operation are here given by the inverse of photonic recoil\nfrequency, and are orders of magnitude shorter than the timescales of\ncollisional spin-mixing based interferometers. Such shorter timescales should\nenable not only faster measurement cycles, but also lower atomic losses from\nthe trap during measurement, which may lead to significant quantum metrological\ngain of matter wave interferometry in state of the art cavity setups.",
        "positive": "Onset of vortex clustering and inverse energy cascade in dissipative\n  quantum fluids: Turbulent phenomena are among the most striking effects that both classical\nand quantum fluids can exhibit. While classical turbulence is ubiquitous in\nnature, the observation of quantum turbulence requires the precise manipulation\nof quantum fluids such as superfluid helium or atomic Bose-Einstein\ncondensates. In this work we demonstrate the turbulent dynamics of a 2D quantum\nfluid of exciton-polaritons, hybrid light-matter quasiparticles, both by\nmeasuring the kinetic energy spectrum and showing the onset of vortex\nclustering. We demonstrate that the formation of clusters of quantum vortices\nis triggered by the increase of the incompressible kinetic energy per vortex,\nshowing the tendency of the vortex-gas towards highly excited configurations\ndespite the dissipative nature of our system. These results lay the basis for\nthe investigations of quantum turbulence in two-dimensional fluids of light."
    },
    {
        "anchor": "Tuning of dipolar interactions and evaporative cooling in a\n  three-dimensional molecular quantum gas: Ultracold polar molecules possess long-range, anisotropic, and tunable\ndipolar interactions, providing the opportunities to probe quantum phenomena\ninaccessible with existing cold gas platforms. However, experimental progress\nhas been hindered by the dominance of two-body loss over elastic interactions,\nwhich prevents efficient evaporative cooling. Though recent work has\ndemonstrated controlled interactions by confining molecules to a\ntwo-dimensional geometry, a general approach for tuning molecular interactions\nin a three-dimensional (3D), stable system has been lacking. Here, we\ndemonstrate tunable elastic dipolar interactions in a bulk gas of ultracold\n40K87Rb molecules in 3D, facilitated by an electric field-induced shielding\nresonance which suppresses the reactive loss by a factor of thirty. This\nimprovement in the ratio of elastic to inelastic collisions enables direct\nthermalization. The thermalization rate depends on the angle between the\ncollisional axis and the dipole orientation controlled by an external electric\nfield, a direct manifestation of the anisotropic dipolar interaction. We\nachieve evaporative cooling mediated by the dipolar interactions in three\ndimensions. This work demonstrates full control of a long-lived bulk quantum\ngas system with tunable long-range interactions, paving the way for the study\nof collective quantum many-body physics.",
        "positive": "Fate of topological states in incommensurate generalized Aubry-Andr\u00e9\n  models: We study one-dimensional optical lattices described by generalized\nAubry-Andr\\'e models that include both commensurate and incommensurate\nmodulations of the hopping amplitude. This brings together two interesting\nfeatures of this class of systems: Anderson localization and the existence of\ntopological edge states. We follow changes of the single-particle energy\nspectrum induced by variations of the system parameters, with focus on the\nsurvival of topological states in the localized regime."
    },
    {
        "anchor": "Landau-Ginzburg Perspective of Finite-Temperature Phase Diagrams of a\n  Two-Component Fermi-Bose Mixture: We consider a mixture of two-component Fermi and (one-component) bose gases\nunder the repulsive Bose-Fermi and attractive Fermi-Fermi interaction. We\nperform a systematic study of the finite-temperature phase diagrams in the\nchemical potential space, identifying, using the Landau-Ginzburg theory, the\nfeatures generic to the phase diagrams within the validity of our model. We\napply the theory to explore the physics of correlated BCS pairing among\nfermions in a tightly confined trap surrounded by a large BEC gas.",
        "positive": "Analytic Harmonic Approach to the N-body problem: We consider an analytic way to make the interacting N-body problem tractable\nby using harmonic oscillators in place of the relevant two-body interactions.\nThe two body terms of the N-body Hamiltonian are approximated by considering\nthe energy spectrum and radius of the relevant two-body problem which gives\nfrequency, center position, and zero point energy of the corresponding harmonic\noscillator. Adding external harmonic one-body terms, we proceed to solve the\nfull quantum mechanical N-body problem analytically for arbitrary masses.\nEnergy eigenvalues, eigenmodes, and correlation functions like density matrices\ncan then be computed analytically. As a first application of our formalism, we\nconsider the N-boson problem in two- and three dimensions where we fit the\ntwo-body interactions to agree with the well-known zero-range model for two\nparticles in a harmonic trap. Subsequently, condensate fractions, spectra,\nradii, and eigenmodes are discussed as function of dimension, boson number N,\nand scattering length obtained in the zero-range model. We find that energies,\nradii, and condensate fraction increase with scattering length as well as boson\nnumber, while radii decrease with increasing boson number. Our formalism is\ncompletely general and can also be applied to fermions, Bose-Fermi mixtures,\nand to more exotic geometries."
    },
    {
        "anchor": "Effective theory of two-dimensional chiral superfluids: gauge duality\n  and Newton-Cartan formulation: We present a theory of Galilean-invariant conventional and chiral $p_x \\pm\nip_y$ fermionic superfluids at zero temperature in two spatial dimensions in\nterms of a dual gauge theory. Our formulation is general coordinate invariant.\nThe parity-violating effects are encoded in the Wen-Zee term that gives rise to\nthe Hall viscosity and edge current. We show that the relativistic superfluid\nwith the Euler current reduces to the chiral superfluid in the limit\n$c\\to\\infty$. Using Newton-Cartan geometry we construct the covariant\nformulation of the effective theory and calculate the energy current.",
        "positive": "Dynamic structure factor and drag force in a one-dimensional\n  strongly-interacting Bose gas at finite temperature: We study the effect of thermal and quantum fluctuations on the dynamical\nresponse of a one-dimensional strongly-interacting Bose gas in a tight atomic\nwaveguide. We combine the Luttinger liquid theory at arbitrary interactions and\nthe exact Bose-Fermi mapping in the Tonks-Girardeau-impenetrable-boson limit to\nobtain the dynamic structure factor of the strongly-interacting fluid at finite\ntemperature. Then, we determine the drag force felt by a potential barrier\nmoving along the fluid in the experimentally realistic situation of finite\nbarrier width and temperature."
    },
    {
        "anchor": "A Kapitza Pendulum for Ultracold Atoms: We report on the experimental realization of a Kapitza pendulum for ultracold\natoms. Using time-periodic attractive and repulsive Gaussian potentials, we\ncreate an effective trap for ultracold neutral atoms in a regime where the time\naverage of the potential is equal to zero. We analyze the role of experimental\nimperfections, the stability of the trapped atomic cloud, and the magnitude of\nthe effective potential. We find good agreement with the high-frequency\nexpansion of the underlying system dynamics. Our experimental approach opens up\nnew possibilities to study Floquet systems of neutral atoms.",
        "positive": "Multimode Trapped Interferometer with Ideal Bose-Einstein Condensates: We experimentally demonstrate a multi-mode interferometer comprising a\nBose-Einstein condensate of $^{39}$K atoms trapped in a harmonic potential,\nwhere the interatomic interaction can be cancelled exploiting Feshbach\nresonances. Kapitza-Dirac diffraction from an optical lattice coherently splits\nthe BEC in multiple momentum components equally spaced that form different\ninterferometric paths, closed by the trapping harmonic potential. We\ninvestigate two different interferometric schemes, where the recombination\npulse is applied after a full or half oscillation in the confining potential.\nWe find that the relative amplitudes of the momentum components at the\ninterferometer output are sensitive to external forces, through the induced\ndisplacement of the harmonic potential with respect to the optical lattice. We\nshow how to calibrate the interferometer, fully characterize its output and\ndiscuss perspective improvements."
    },
    {
        "anchor": "Evidence for a Bose-Einstein condensate of excitons: The demonstration of Bose-Einstein condensation in atomic gases at\nmicro-Kelvin temperatures is a striking landmark while its evidence for\nsemiconductor excitons still is a long-awaited milestone. This situation was\nnot foreseen because excitons are light-mass boson-like particles with a\ncondensation expected to occur around a few Kelvins. An explanation can be\nfound in the underlying fermionic nature of excitons which rules their\ncondensation. Precisely, it was recently predicted that, at accessible\nexperimental conditions, the exciton condensate shall be \"gray\" with a dominant\ndark part coherently coupled to a weak bright component through fermion\nexchanges. This counter-intuitive quantum condensation, since excitons are\nmostly known for their optical activity, directly follows from the excitons\ninternal structure which has an optically inactive, i.e., dark, ground state.\nHere, we report compelling evidence for such a \"gray\" condensate. We use an\nall-optical approach in order to produce microscopic traps which confine a\ndense exciton gas that yet exhibits an anomalously weak photo-emission at\nsub-Kelvin temperatures. This first fingerprint for a \"gray\" condensate is then\nconfirmed by the macroscopic spatial coherence and the linear polarization of\nthe weak excitonic photoluminescence emitted from the trap, as theoretically\npredicted.",
        "positive": "Spin-orbit coupled soliton in a random potential: We investigate theoretically the dynamics of a spin-orbit coupled soliton\nformed by a self- interacting Bose-Einstein condensate immersed in a random\npotential, in the presence of an artificial magnetic field. We find that due to\nthe anomalous spin-dependent velocity, the synthetic Zeeman coupling can play a\ncritical role in the soliton dynamics by causing its localization or\ndelocalization, depending on the coupling strength and on the parameters of the\nrandom potential. The observed effects of the Zeeman coupling qualitatively\ndepend on the type of self-interaction in the condensate since the spin state\nand the self-interaction energy of the condensate are mutually related if the\ninvariance of the latter with respect to the spin rotation is lifted."
    },
    {
        "anchor": "Universal relations for spin-orbit-coupled Fermi gases in two and three\n  dimensions: We present a comprehensive derivation of a set of universal relations for\nspin-orbit-coupled Fermi gases in three or two dimension, which follow from the\nshort-range behavior of the two-body physics. Besides the adiabatic energy\nrelations, the large-momentum distribution, the grand canonical potential and\npressure relation derived in our previous work for three-dimensional systems\n{[}Phys. Rev. Lett. 120, 060408 (2018){]}, we further derive high-frequency\ntail of the radio-frequency spectroscopy and the short-range behavior of the\npair correlation function. In addition, we also extend the derivation to\ntwo-dimensional systems with Rashba type of spin-orbit coupling. To simply\ndemonstrate how the spin-orbit-coupling effect modifies the two-body\nshort-range behavior, we solve the two-body problem in the sub-Hilbert space of\nzero center-of-mass momentum and zero total angular momentum, and\nperturbatively take the spin-orbit-coupling effect into account at short\ndistance, since the strength of the spin-orbit coupling should be much smaller\nthan the corresponding scale of the finite range of interatomic interactions.\nThe universal asymptotic forms of the two-body wave function at short distance\nare then derived, which do not depend on the short-range details of interatomic\npotentials. We find that new scattering parameters need to be introduced\nbecause of spin-orbit coupling, besides the traditional $s$- and $p$-wave\nscattering length (volume) and effective ranges. This is a general and unique\nfeature for spin-orbit-coupled systems. We show how these two-body parameters\ncharacterize the universal relations in the presence of spin-orbit coupling.\nThis work probably shed light for understanding the profound properties of the\nmany-body quantum systems in the presence of the spin-orbit coupling.",
        "positive": "Stabilizing Gauge Theories in Quantum Simulators: A Brief Review: Quantum simulation is at the heart of the ongoing \"second\" quantum\nrevolution, with various synthetic quantum matter platforms realizing evermore\nexotic condensed matter and particle physics phenomena at high levels of\nprecision and control. The implementation of gauge theories on modern quantum\nsimulators is especially appealing due to three main reasons: (i) it offers a\nnew probe of high-energy physics on low-energy tabletop devices, (ii) it allows\nexploring condensed matter phenomena that are prominent in gauge theories even\nwithout a direct connection to high-energy physics, and (iii) it serves as a\nbanner of experimental benchmarking given the plethora of local constraints\narising from the gauge symmetry that need to be programmed and controlled. In\norder to faithfully model gauge-theory phenomena on a quantum simulator,\nstabilizing the underlying gauge symmetry is essential. In this brief review,\nwe outline recently developed experimentally feasible methods introduced by us\nthat have shown, in numerical and experimental benchmarks, reliable\nstabilization of quantum-simulator implementations of gauge theories. We\nexplain the mechanism behind these \\textit{linear gauge protection} schemes,\nand illustrate their power in protecting salient features such as gauge\ninvariance, disorder-free localization, quantum many-body scars, and other\nphenomena of topical interest. We then discuss their application in experiments\nbased on Rydberg atoms, superconducting qubits, and in particular ultracold\nneutral atoms in optical superlattices. We hope this review will illustrate\nsome facets of the exciting progress in stabilization of gauge symmetry and in\ngauge-theory quantum simulation in general."
    },
    {
        "anchor": "Verification of an analytic fit for the vortex core profile in\n  superfluid Fermi gases: A characteristic property of superfluidity and -conductivity is the presence\nof quantized vortices in rotating systems. To study the BEC-BCS crossover the\ntwo most common methods are the Bogoliubov-De Gennes theory and the usage of an\neffective field theory. In order to simplify the calculations for one vortex,\nit is often assumed that the hyperbolic tangent yields a good approximation for\nthe vortex structure. The combination of a variational vortex structure,\ntogether with cylindrical symmetry yields analytic (or numerically simple)\nexpressions. The focus of this article is to investigate to what extent this\nanalytic fit truly reflects the vortex structure throughout the BEC-BCS\ncrossover at finite temperatures. The vortex structure will be determined using\nthe effective field theory presented in [Eur. Phys. Journal B 88, 122 (2015)]\nand compared to the variational analytic solution. By doing this it is possible\nto see where these two structures agree, and where they differ. This comparison\nresults in a range of applicability where the hyperbolic tangent will be a good\nfit for the vortex structure.",
        "positive": "A Multi-Purpose Platform for Analog Quantum Simulation: Atom-based quantum simulators have had tremendous success in tackling\nchallenging quantum many-body problems, owing to the precise and dynamical\ncontrol that they provide over the systems' parameters. They are, however,\noften optimized to address a specific type of problems. Here, we present the\ndesign and implementation of a $^6$Li-based quantum gas platform that provides\nwide-ranging capabilities and is able to address a variety of quantum many-body\nproblems. Our two-chamber architecture relies on a robust and easy-to-implement\ncombination of gray molasses and optical transport from a laser-cooling chamber\nto a glass cell with excellent optical access. There, we first create unitary\nFermi superfluids in a three-dimensional axially symmetric harmonic trap and\ncharacterize them using in situ thermometry, reaching temperatures below 20 nK.\nThis allows us to enter the deep superfluid regime with samples of extreme\ndiluteness, where the interparticle spacing is sufficiently large for direct\nsingle-atom imaging. Secondly, we generate optical lattice potentials with\ntriangular and honeycomb geometry in which we study diffraction of molecular\nBose-Einstein condensates, and show how going beyond the Kapitza-Dirac regime\nallows us to unambiguously distinguish between the two geometries. With the\nability to probe quantum many-body physics in both discrete and continuous\nspace, and its suitability for bulk and single-atom imaging, our setup\nrepresents an important step towards achieving a wide-scope quantum simulator."
    },
    {
        "anchor": "Derivation of the effective action of a dilute Fermi gas in the unitary\n  limit of the BCS-BEC crossover: The effective action describing the gapless Nambu-Goldstone, or\nAnderson-Bogoliubov, mode of a zero-temperature dilute Fermi gas at unitarity\nis derived up to next-to-leading order in derivatives from the microscopic\ntheory. Apart from a next-to-leading order term that is suppressed in the BCS\nlimit, the effective action obtained in the strong-coupling unitary limit is\nproportional to that in the weak-coupling BCS limit.",
        "positive": "Topologically driven nonequilibrium phase transitions in diagonal\n  ensembles: We identify a new class of topologically driven phase transitions when\ncalculating the Hall conductance of two-band Chern insulators in the long-time\nlimit after a global quench of the Hamiltonian. The Hall conductance is\nexpressed as the integral of the Berry curvature in the diagonal ensemble. Even\nif the topological invariant of the wave function is conserved under unitary\nevolution, the Hall conductance as a function of the energy gap in the\npost-quench Hamiltonian displays a continuous but nonanalytic behavior, that is\nit has a logarithmically divergent derivative as the gap closes. The\ncoefficient of this logarithmic function is the ratio of the change of Chern\nnumber in the ground state of the post-quench Hamiltonian to the energy gap in\nthe initial state. This nonanalytic behavior is universal in two-band Chern\ninsulators."
    },
    {
        "anchor": "Critical Behavior and Fractality in Shallow One-Dimensional\n  Quasiperiodic Potentials: Quasiperiodic systems offer an appealing intermediate between long-range\nordered and genuine disordered systems, with unusual critical properties.\nOne-dimensional models that break the so-called self-dual symmetry usually\ndisplay a mobility edge, similarly as truly disordered systems in dimension\nstrictly higher than two. Here, we determine the critical localization\nproperties of single particles in shallow, one-dimensional, quasiperiodic\nmodels and relate them to the fractal character of the energy spectrum. On the\none hand, we determine the mobility edge and show that it separates the\nlocalized and extended phases, with no intermediate phase. On the other hand,\nwe determine the critical potential amplitude and find the universal critical\nexponent $\\nu \\simeq 1/3$. We also study the spectral Hausdorff dimension and\nshow that it is nonuniversal but always smaller than unity, hence showing that\nthe spectrum is nowhere dense. Finally, applications to ongoing studies of\nAnderson localization, Bose-glass physics, and many-body localization in\nultracold atoms are discussed.",
        "positive": "Dynamical band flipping in fermionic lattice systems: An ac-field-driven\n  change of the interaction from repulsive to attractive: We show theoretically that the sudden application of an appropriate ac field\nto correlated lattice fermions flips the band structure and effectively\nswitches the interaction from repulsive to attractive. The nonadiabatically\ndriven system is characterized by a negative temperature with a population\ninversion. We numerically demonstrate the converted interaction in an ac-driven\nHubbard model with the nonequilibrium dynamical mean-field theory solved by the\ncontinuous-time quantum Monte Carlo method. Based on this, we propose an\nefficient ramp-up protocol for ac fields that can suppress heating, which leads\nto an effectively attractive Hubbard model with a temperature below the\nsuperconducting transition temperature of the equilibrium system."
    },
    {
        "anchor": "Physics of Cold Atomic Fermi Gases: We consider a cold two-species atomic Fermi gas confined in a trap. We\ncombine the Hermitian coupling between the states (we assume them to be the\nstates with different spins) with the Cooper pairing of atoms with these\ndifferent spins. This opens up a new prospect for investigation of interplay\nbetween various phenomena involving Raman coupling (e.g., atom lasers,\ndark-state polaritons) and effects caused by Cooper pairing of particles (e.g.,\nsuperfluidity). We have obtained a threshold of transition from oscillatory to\namplifying behavior of matter waves.",
        "positive": "One-dimensional s-p superlattice: The physics of one dimensional optical superlattices with resonant $s$-$p$\norbitals is reexamined in the language of appropriate Wannier functions. It is\nshown that details of the tight binding model realized in different optical\npotentials crucially depend on the proper determination of Wannier functions.\nWe discuss the properties of a superlattice model which quasi resonantly\ncouples $s$ and $p$ orbitals and show its relation with different tight binding\nmodels used in other works."
    },
    {
        "anchor": "Non-equilibrium strong-coupling theory for a driven-dissipative\n  ultracold Fermi gas in the BCS-BEC crossover region: We theoretically investigate strong-coupling properties of an ultracold Fermi\ngas in the BCS-BEC crossover regime in the non-equilibrium steady state, being\ncoupled with two fermion baths. By developing a non-equilibrium strong-coupling\ntheory based on the combined $T$-matrix approximation with the Keldysh Green's\nfunction technique, we show that the chemical potential bias applied by the two\nbaths gives rise to the anomalous enhancement of\nFulde-Ferrell-Larkin-Ovchinnikov (FFLO) type pairing fluctuations (although the\nsystem has no spin imbalance), resulting in the re-entrant behavior of the\nnon-equilibrium superfluid phase transition in the BCS-unitary regime. These\npairing fluctuations are also found to anomalously enhance the pseudogap\nphenomenon. Since various non-equilibrium phenomena have recently been measured\nin ultracold Fermi gases, our non-equilibrium strong-coupling theory would be\nuseful to catch up this experimental development in this research field.",
        "positive": "Finite temperature correlations in the Lieb-Liniger 1D Bose gas: We address the problem of calculating finite-temperature response functions\nof an experimentally relevant low-dimensional strongly-correlated system: the\nintegrable 1D Bose gas with repulsive \\delta-function interaction (Lieb-Liniger\nmodel). Focusing on the observable dynamical density-density function, we\npresent a Bethe Ansatz-based method allowing for its accurate evaluation over a\nbroad range of momenta, frequencies, temperatures and interaction parameters,\nin finite but large systems. We show how thermal fluctuations smoothen the zero\ntemperature critical behavior and present explicit quantitative results in\nexperimentally accessible regimes."
    },
    {
        "anchor": "Investigation of the role of the Roentgen interaction in angular\n  momentum transfer within an electric Bose Einstein Condensate: The exact action of the Roentgen effect at an atomic level is investigated\nwithin the context of vortex formation using two Laguerre Gaussian beams.\nStarting from a modified Gross-Pitaevskii equation in the dipole approximation\nthat takes into account the coupling of the atomic system to the\nelectromagnetic fields the Roentgen interaction term is introduced and viewed\nwithin the context of such a Raman transition. A rigorous investigation of the\ncorresponding Rabi frequency reveals that the Roentgen term acts at different\nlevels compared to the (-d.E) term and thus would not cause any changes in a\nfully quantum mechanical treatment.",
        "positive": "Influence of a static electric field on a one-dimensional Bose-Fermi\n  mixture confined in a double potential welll: In this study, we conducted a detailed investigation into the time evolution\nof the probability density within a 1D double-well potential hosting a\nBose-Fermi mixture. This system comprised spinless bosons and spin one-half\nfermions with weak repulsive contact interactions. Notably, even at very low\neffective coupling constants, periodic probabilities were observed, indicating\ncorrelated tunneling of both bosons and fermions, leading to complete\nmiscibility, which disappears when an external electric field is turned on. The\nelectric field accentuated fermion-fermion interactions due to the Pauli\nexclusion principle, altering both boson density and interactions and leading\nto spatial redistribution of particles. These findings underscore the complex\ninterplay between interactions, external fields, and spatial distributions\nwithin confined quantum systems.\n  Our exploration of higher interaction strengths revealed conditions under\nwhich probability density functions are decoupled. Furthermore, we observed\nthat increased fermion interaction, driven by the electric field, led to higher\ntunneling frequencies for both species because of the repulsive nature of the\nboson-fermion interaction. Conversely, increased boson-boson interaction\nresulted in complete tunneling of both species, especially when boson density\nwas high, leading to effective fermion repulsion. Expanding our analysis to\nscenarios involving four bosons demonstrated that higher interaction values\ncorresponded to increased oscillation frequencies in tunneling probabilities.\nFinally, by manipulating interaction parameters and activating the electric\nfield, we achieved complete tunneling of both species, further increasing\noscillation frequencies and resulting in intervals characterized by overlapping\nprobability functions."
    },
    {
        "anchor": "Dynamical thermalization of interacting fermionic atoms in a\n  Sinai-oscillator trap: We study numerically the problem of dynamical thermalization of interacting\ncold fermionic atoms placed in an isolated Sinai-oscillator trap. This system\nis characterized by a quantum chaos regime for one-particle dynamics. We show\nthat for a many-body system of cold atoms the interactions, with a strength\nabove a certain quantum chaos border given by the Aberg criterion, lead to the\nFermi-Dirac distribution and relaxation of many-body initial states to the\nthermalized state in absence of any contact with a thermostate. We discuss the\nproperties of this dynamical thermalization and its links with the\nLoschmidt-Boltzmann dispute.",
        "positive": "Physical dipoles and second order perturbation theory for dipolar\n  fermions in two dimensions: In two dimensions the Fourier transform of the interaction between two point\ndipoles has a term which grows linearly in the modulus $| \\mathbf{\\textit{q}}\n|$ of the momentum . As a consequence, in second order perturbation theory the\nself-energy of two-dimensional dipolar fermions is ultraviolet divergent. We\nshow that for electric dipoles this divergence can be avoided if one takes into\naccount that physical dipoles consist of two opposite charges which are\nseparated by a finite distance. Using this regularization, we calculate the\nself-energy, the renormalized chemical potential, and the renormalized Fermi\nsurface of dipolar fermions in two dimensions in second order perturbation\ntheory. We find that in the Fermi liquid phase the second order corrections\nweaken first order effects."
    },
    {
        "anchor": "Achieving the quantum field theory limit in far-from-equilibrium quantum\n  link models: Realizations of gauge theories in setups of quantum synthetic matter open up\nthe possibility of probing salient exotic phenomena in condensed matter and\nhigh-energy physics, along with potential applications in quantum information\nand science technologies. In light of the impressive ongoing efforts to achieve\nsuch realizations, a fundamental question regarding quantum link model\nregularizations of lattice gauge theories is how faithfully they capture the\nquantum field theory limit of gauge theories. Recent work [Zache, Van Damme,\nHalimeh, Hauke, and Banerjee, at\nhttps://journals.aps.org/prd/abstract/10.1103/PhysRevD.106.L091502 has shown\nthrough analytic derivations, exact diagonalization, and infinite matrix\nproduct state calculations that the low-energy physics of $1+1$D\n$\\mathrm{U}(1)$ quantum link models approaches the quantum field theory limit\nalready at small link spin length $S$. Here, we show that the approach to this\nlimit also lends itself to the far-from-equilibrium quench dynamics of lattice\ngauge theories, as demonstrated by our numerical simulations of the Loschmidt\nreturn rate and the chiral condensate in infinite matrix product states, which\nwork directly in the thermodynamic limit. Similar to our findings in\nequilibrium that show a distinct behavior between half-integer and integer link\nspin lengths, we find that criticality emerging in the Loschmidt return rate is\nfundamentally different between half-integer and integer spin quantum link\nmodels in the regime of strong electric-field coupling. Our results further\naffirm that state-of-the-art finite-size ultracold-atom and NISQ-device\nimplementations of quantum link lattice gauge theories have the real potential\nto simulate their quantum field theory limit even in the far-from-equilibrium\nregime.",
        "positive": "Quench-induced delocalization: We consider the evolution of an initially localized wave packet after a\nsudden change in the Hamiltonian, i.e.\\ a quench. When both bound and\nscattering eigenstates exist in the post-quench Hamiltonian, one might expect\npartial delocalization of the wave packet to ensue. Here we show that if the\nquench consists of a sudden switching-off of short-range inter-particle\ninteractions, then Tan's universal relations guarantee delocalization through\nthe high-momentum tail of the momentum distribution. Furthermore, we consider\nthe influence of the range of the interaction and show how a finite range\nalters the coupling to highly excited states. We illustrate our results using\nnumerical simulations of externally trapped particles in one dimension. If the\nexternal potential is both disordered and correlated, then the interaction\nquench leads to transport via delocalized states, showing that localization in\ndisordered systems is sensitive to non-adiabatic changes in the interactions\nbetween particles."
    },
    {
        "anchor": "A Quantized Inter-level Character in Quantum Systems: For a quantum system subject to external parameters, the Berry phase is an\nintra-level property, which is gauge invariant module $2\\pi$ for a closed loop\nin the parameter space and generally is non-quantized. In contrast, we define a\ninter-band character $\\Theta$ for a closed loop, which is gauge invariant and\nquantized as integer values. It is a quantum mechanical analogy of the Euler\ncharacter based on the Gauss-Bonnet theorem for a manifold with a boundary. The\nrole of the Gaussian curvature is mimicked by the difference between the Berry\ncurvatures of the two levels, and the counterpart of the geodesic curvature is\nthe quantum geometric potential which was proposed to improve the quantum\nadiabatic condition. This quantized inter-band character is also generalized to\nquantum degenerate systems.",
        "positive": "Two-mode Bose gas: Beyond classical squeezing: The dynamical evolution of squeezing correlations in an ultracold\nBose-Einstein distributed across two modes is investigated theoretically in the\nframework of the Bose-Hubbard model. It is shown that the eigenstates of the\nHamiltonian do not exploit the full region allowed by Heisenberg's uncertainty\nrelation for number and phase fluctuations. The development of non-classical\ncorrelations and relative number squeezing is studied in the transition from\nthe Josephson to the Fock regime. Comparing the full quantum evolution with\nclassical statistical simulations allows to identify quantum aspects of the\nsqueezing formation. In the quantum regime, the measurement of squeezing allows\nto distinguish even and odd total particle numbers."
    },
    {
        "anchor": "Free Fermions with a Localized Source: We study an open quantum system of free fermions on an infinite lattice\ncoupled to a localized particle source. In the long time limit, the total\nnumber of fermions in the system increases linearly with growth rate dependent\non the lattice geometry and dimensionality. We express the growth rate in terms\nof lattice Green functions and derive explicit formulae in one dimension and\nfor the square lattice. The interplay between the dynamics and the coupling to\nthe environment leads, in contrast to classical systems, to a non-monotonic\ndependence of the particle growth rate on the input rate. We show that for all\nlattices the particle growth rate is inversely proportional to the input rate\nwhen the latter becomes large. This is a manifestation of the quantum Zeno\neffect.",
        "positive": "Spreading of correlations and Loschmidt echo after quantum quenches of a\n  Bose gas in the Aubry-Andr\u00e9 potential: We study the spreading of density-density correlations and the Loschmidt\necho, after different sudden quenches in an interacting one dimensional Bose\ngas on a lattice, also in the presence of a superimposed aperiodic potential.\nWe use a time dependent Bogoliubov approach to calculate the evolution of the\ncorrelation functions and employ the linked cluster expansion to derive the\nLoschmidt echo."
    },
    {
        "anchor": "Strong photon interactions from weakly interacting particles: The hybridization of light and matter excitations in the form of polaritons\nhas enabled major advances in understanding and controlling optical\nnonlinearities. Entering the quantum regime of strong interactions between\nindividual photons has however remained challenging since the strength of\nachievable polariton interactions is typically limited by the available\ninteractions in the material. Here, we investigate collisions between\ndark-state polaritons in three-level systems and discover a resonant process\nthat yields effective interactions, which are much larger than the underlying\ninteraction between their matter constituents. We systematically investigate\nthe underlying mechanism and demonstrate a substantial enhancement of polariton\ninteractions by several orders of magnitude. This suggests a promising approach\nto quantum nonlinear optics in a range of physical settings, from atomic gases\nto excitons in semiconductors and two-dimensional bilayer materials.",
        "positive": "Fourier transform spectroscopy of a spin-orbit coupled Bose gas: We describe a Fourier transform spectroscopy technique for directly measuring\nband structures, and apply it to a spin-1 spin-orbit coupled Bose-Einstein\ncondensate. In our technique, we suddenly change the Hamiltonian of the system\nby adding a spin-orbit coupling interaction and measure populations in\ndifferent spin states during the subsequent unitary evolution. We then\nreconstruct the spin and momentum resolved spectrum from the peak frequencies\nof the Fourier transformed populations. In addition, by periodically modulating\nthe Hamiltonian, we tune the spin-orbit coupling strength and use our\nspectroscopy technique to probe the resulting dispersion relation. The\nfrequency resolution of our method is limited only by the coherent evolution\ntimescale of the Hamiltonian and can otherwise be applied to any system, for\nexample, to measure the band structure of atoms in optical lattice potentials."
    },
    {
        "anchor": "Exact Dynamical Correlations of Hard-Core Anyons in One-Dimensional\n  Lattices: The dynamical correlations of a strongly correlated system is an essential\ningredient to describe its non-equilibrium properties. We present a general\nmethod to calculate exactly the dynamical correlations of hard-core anyons in\none-dimensional lattices, valid for any type of confining potential and any\ntemperature. We obtain exact explicit expressions of the Green's function, the\nspectral function, and the out-of-time-ordered correlators (OTOCs). We find\nthat the anyonic spectral function displays three main singularity lines which\ncan be explained as a double spectrum in analogy to the Lieb-Liniger gas. The\ndispersion relations of these lines can be given explicitly and they cross at a\n\\emph{hot point} $(q_m,\\omega_m)$, which induces a peak in the momentum\ndistribution function at $q_m$ and a power-law singularity in the local\nspectral function at $\\omega_m$. We also find that the anyonic statistics can\ninduces spatial asymmetry in the Green's function, its spectrum, and the OTOC.\nMoreover, the information spreading characterized by the OTOCs shows light-cone\ndynamics, asymmetric for general statistics and low temperatures, but symmetric\nat infinite temperature. Our results pave the way toward studying the\nnon-equilibrium dynamics of hard-core anyons and experimentally probing anyonic\nstatistics through spectral functions.",
        "positive": "Collisional Stability of 40K Immersed in a Strongly Interacting Fermi\n  Gas of 6Li: We investigate the collisional stability of a sample of 40K atoms immersed in\na tunable spin mixture of 6Li atoms. In this three-component Fermi-Fermi\nmixture, we find very low loss rates in a wide range of interactions as long as\nmolecule formation of 6Li is avoided. The stable fermionic mixture with two\nresonantly interacting spin states of one species together with another species\nis a promising system for a broad variety of phenomena in few- and many-body\nquantum physics."
    },
    {
        "anchor": "Superfluidity of Dirac Fermions in a Tunable Honeycomb Lattice: Cooper\n  Pairing, Collective Modes, and Critical Currents: Motivated by recent experiments on atomic Dirac fermions in a tunable\nhoneycomb optical lattice, we study the attractive Hubbard model of\nsuperfluidity in the anisotropic honeycomb lattice. At weak-coupling, we find\nthat the maximum mean field pairing transition temperature, as a function of\ndensity and interaction strength, occurs for the case with isotropic hopping\namplitudes. In this isotropic case, we go beyond mean field theory and study\ncollective fluctuations, treating both pairing and density fluctuations for\ninteraction strengths ranging from weak to strong coupling. We find evidence\nfor a sharp sound mode, together with a well-defined Leggett mode over a wide\nregion of the phase diagram. We also calculate the superfluid order parameter\nand collective modes in the presence of nonzero superfluid flow. The\nflow-induced softening of these collective modes leads to dynamical\ninstabilities involving stripe-like density modulations as well as a\nLeggett-mode instability associated with the natural sublattice symmetry\nbreaking charge-ordered state on the honeycomb lattice. The latter provides a\nnon-trivial test for the experimental realization of the one-band Hubbard\nmodel. We delineate regimes of the phase diagram where the critical current is\nlimited by depairing or by such collective instabilities, and discuss\nexperimental implications of our results.",
        "positive": "Two types of dark solitons in a spin-orbit-coupled Fermi gas: Dark solitons in quantum fluids are well known nonlinear excitations that are\nusually characterized by a single length scale associated with the underlying\nbackground fluid. We show that in the presence of spin-orbit coupling and a\nlinear Zeeman field, superfluid Fermi gases support two different types of\nnonlinear excitations featured by corresponding length scales related to the\nexistence of two Fermi surfaces. Only one of these types, which occurs for\nfinite spin-orbit coupling and a Zeeman field, survives to the topological\nphase transition, and is therefore capable to sustain Majorana zero modes. At\nthe point of the emergence of this soliton for varying the Zeeman field, the\nassociated Andreev bound states present a minigap that vanishes for practical\npurposes, in spite of lacking the reality condition of Majorana modes."
    },
    {
        "anchor": "Non-equilibrium Berezinskii-Kosterlitz-Thouless Transition in a Driven\n  Open Quantum System: The Berezinskii-Kosterlitz-Thouless mechanism, in which a phase transition is\nmediated by the proliferation of topological defects, governs the critical\nbehaviour of a wide range of equilibrium two-dimensional systems with a\ncontinuous symmetry, ranging from superconducting thin films to two-dimensional\nBose fluids, such as liquid helium and ultracold atoms. We show here that this\nphenomenon is not restricted to thermal equilibrium, rather it survives more\ngenerally in a dissipative highly non-equilibrium system driven into a\nsteady-state. By considering a light-matter superfluid of polaritons, in the\nso-called optical parametric oscillator regime, we demonstrate that it indeed\nundergoes a vortex binding-unbinding phase transition. Yet, the exponent of the\npower-law decay of the first order correlation function in the (algebraically)\nordered phase can exceed the equilibrium upper limit -- a surprising\noccurrence, which has also been observed in a recent experiment. Thus we\ndemonstrate that the ordered phase is somehow more robust against the quantum\nfluctuations of driven systems than thermal ones in equilibrium.",
        "positive": "Competing interactions in population-imbalanced two-component\n  Bose-Einstein condensates: We consider a two-component Bose-Einstein condensate with and without\nsynthetic \"spin-orbit\" interactions in two dimensions. Density- and\nphase-fluctuations of the condensate are included, allowing us to study the\nimpact of thermal fluctuations and density-density interactions on the physics\noriginating with spin-orbit interactions. In the absence of spin-orbit\ninteractions, we find that inter-component density interactions deplete the\nminority condensate. The thermally driven phase transition is driven by coupled\ndensity and phase-fluctuations, but is nevertheless shown to be a\nphase-transition in the Kosterlitz-Thouless universality class with close to\nuniversal amplitude ratios irrespective of whether both the minority- and\nmajority condensates exist in the ground state, or only one condensate exists.\nIn the presence of spin-orbit interactions we observe three separate phases,\ndepending on the strength of the spin-orbit coupling and inter-component\ndensity-density interactions: a phase-modulated phase with uniform amplitudes\nfor small intercomponent interactions, a completely imbalanced, effectively\nsingle-component, condensate for intermediate spin-orbit coupling strength and\nsuficciently large inter-component interactions, and a phase-modulated\n\\textit{and} amplitude-modulated phase for sufficiently large values of both\nthe spin-orbit coupling and the inter-component density-density interactions.\nThe phase which is modulated by a single $\\bv q$-vector only is observed to\ntransition into an isoptropic liquid through a strong de-pinning transition\nwith periodic boundary conditions, which weakens with open boundaries."
    },
    {
        "anchor": "Postquench prethermalization in a disordered quantum fluid of light: We study the coherence of a disordered and interacting quantum light field\nafter propagation along a nonlinear optical fiber. Disorder is generated by a\ncross-phase modulation with a randomized auxiliary classical light field, while\ninteractions are induced by self-phase modulation. When penetrating the fiber\nfrom free space, the incoming quantum light undergoes a disorder and\ninteraction quench. By calculating the coherence function of the transmitted\nquantum light, we show that the decoherence induced by the quench spreads in a\nlight-cone fashion in the nonequilibrium many-body quantum system, leaving the\nlatter prethermalize with peculiar features originating from disorder.",
        "positive": "Ultrafast tristable spin memory of a coherent polariton gas: Nonlinear interactions in coherent gases are not only at the origin of of\nbright and dark solitons and superfluids. At the same time, they give rise to\nphenomena such as multistability, which hold great promise for the development\nof advanced photonic and spintronic devices. In particular, spinor\nmultistability in strongly-coupled semiconductor microcavities shows that the\nspin of hundreds of exciton-polaritons can be coherently controlled, opening\nthe route to spin-optronic devices such as ultrafast spin memories, gates or\neven neuronal communication schemes. Here, we demonstrate that switching\nbetween the stable spin states of a driven polariton gas can be controlled by\nultrafast optical pulses. While such a long-lived spin memory necessarily\nrelies on strong and anisotropic spinor interactions within the coherent\npolariton gas, we also highlight the crucial role of nonlinear losses and\nformation of a non-radiative particle reservoir for ultrafast spin-switching."
    },
    {
        "anchor": "Long-time averaged dynamics of a Bose-Einstein condensate in a\n  bichromatic optical lattice with external harmonic confinement: The dynamics of a Bose-Einstein condensate are examined numerically in the\npresence of a one-dimensional bichromatic optical lattice with external\nharmonic confinement. The condensate is excited by a focusing red laser. For\nthis purpose, the time-dependent Gross Pitaevskii equation is solved using the\nCrank Nicolson method in real time. Two realizations of the optical lattice are\nconsidered, one with a rational and the other with an irrational ratio of the\ntwo constituting wave lengths. For a weak bichromatic optical lattice, the\nlong-time averaged physical observables of the condensate respond only very\nweakly (or not at all) to changes in the secondary optical lattice depth.\nHowever, for a much larger strength of the latter optical lattice, the response\nis stronger. It is found that qualitatively there is no difference between the\ndynamics of the condensate resulting from the use of a rational or irrational\nratio of the optical lattice wavelengths since the external harmonic trap\nwashes it out. It is further found that in the presence of an external harmonic\ntrap, the bichromatic optical lattice acts in favor of superflow.",
        "positive": "Thermalization in a Spin-Orbit coupled Bose gas by enhanced spin Coulomb\n  drag: An important component of the structure of the atom, the effects of\nspin-orbit coupling are present in many sub-fields of physics. Most of these\neffects are present continuously. We present a detailed study of the dynamics\nof changing the spin-orbit coupling in an ultra-cold Bose gas, coupling the\nmotion of the atoms to their spin. We find that the spin-orbit coupling greatly\nincreases the damping towards equilibrium. We interpret this damping as spin\ndrag, which is enhanced by spin-orbit coupling rate, scaled by a remarkable\nfactor of $8.9(6)$~s. We also find that spin-orbit coupling lowers the final\ntemperature of the Bose gas after thermalization."
    },
    {
        "anchor": "N\u00e9el temperature and thermodynamics of the half-filled 3D Hubbard\n  model by Diagrammatic Determinant Monte Carlo: We study thermodynamics of the 3D Hubbard model at half filling on approach\nto the N\\'eel transition by means of large-scale unbiased Diagrammatic\nDeterminant Monte Carlo simulations. We obtain the transition temperature in\nthe strongly correlated regime, as well as temperature dependence of energy,\nentropy, double occupancy, and the nearest-neighbor spin correlation function.\nOur results improve the accuracy of previous unbiased studies and present\naccurate benchmarks in the ongoing effort to realize the antiferromagnetic\nstate of matter with ultracold atoms in optical lattices.",
        "positive": "Geometric phases of a vortex in a superfluid: We consider geometric phases of mobile quantum vortices in superfluid\nBose-Einstein condensates. Haldane and Wu [Phys. Rev. Lett. 55, 2887 (1985)]\nshowed that the geometric phase, $\\gamma_{\\mathcal C}=2\\pi N_{\\mathcal C}$, of\nsuch a vortex is determined by the number of condensate atoms $N_{\\mathcal C}$\nenclosed by the vortex trajectory. Considering an experimentally realistic\nfreely orbiting vortex leads to an apparent disagreement with this prediction.\nWe resolve it using the superfluid electrodynamics picture, which allows us to\nidentify two additional contributions to the measured geometric phase; (i) a\ntopologically protected edge current of vortices at the condensate boundary,\nand (ii) a superfluid displacement current. Our results generalise to, and pave\nthe way for experimental measurements of vortex geometric phases using scalar\nand spinor Bose--Einstein condensates, and superfluid Fermi gases."
    },
    {
        "anchor": "Superfluid, staggered state, and Mott insulator of repulsively\n  interacting three-component fermionic atoms in optical lattices: We review our theoretical analysis of repulsively interacting three-component\nfermionic atoms in optical lattices. We discuss quantum phase transitions at\naround half filling with a balanced population by focusing on Mott transitions,\nstaggered ordering, and superfluidity. At half filling (with 3/2 atoms per\nsite), characteristic Mott transitions are induced by the anisotropic\ninteractions, where two-particle repulsions between any two of the three colors\nhave different strengths. At half filling, two types of staggered ordered\nstates appear at low temperatures depending on the anisotropy of the\ninteractions. As the temperature increases, phase transitions occur from the\nstaggered ordered states to the unordered Mott states. Deviating from half\nfilling, an exotic superfluid state appears close to a regime in which the Mott\ntransition occurs. We explain the origin of these phase transitions and present\nthe finite-temperature phase diagrams.",
        "positive": "Collective modes across the soliton-droplet crossover in binary Bose\n  mixtures: We study the collective modes of a binary Bose mixture across the soliton to\ndroplet crossover in a quasi one dimensional waveguide with a beyond-mean-field\nequation of state and a variational Gaussian ansatz for the scalar bosonic\nfield of the corresponding effective action. We observe a sharp difference in\nthe collective modes in the two regimes. Within the soliton regime modes vary\nsmoothly upon the variation of particle number or interaction strength. On the\ndroplet side collective modes are inhibited by the emission of particles. This\nmechanism turns out to be dominant for a wide range of particle numbers and\ninteractions. In a small window of particle number range and for intermediate\ninteractions we find that monopole frequency is likely to be observed. In the\nlast part we focus on the spin-dipole modes for the case of equal intraspecies\ninteractions and equal equilibrium particle numbers in the presence of a weak\nlongitudinal confinement. We found that such modes might be unobservable in the\nreal-time dynamics close to the equilibrium as their frequency is higher than\nthe particle emission spectrum by at least one order of magnitude in the\ndroplet phase. Our results are relevant for experiments with two-component BECs\nfor which we provide realistic parameters."
    },
    {
        "anchor": "A two-dimensional programmable tweezer array of fermions: We prepare high-filling two-component arrays of up to fifty fermionic atoms\nin optical tweezers, with the atoms in the ground motional state of each\ntweezer. Using a stroboscopic technique, we configure the arrays in various\ntwo-dimensional geometries with negligible Floquet heating. Full spin- and\ndensity-resolved readout of individual sites allows us to post-select near-zero\nentropy initial states for fermionic quantum simulation. We prepare a\ncorrelated state in a two-by-two tunnel-coupled Hubbard plaquette,\ndemonstrating all the building blocks for realizing a programmable fermionic\nquantum simulator.",
        "positive": "Coqblin-Schrieffer Model for an Ultra-cold Gas of Ytterbium atoms with\n  Metastable States: Motivated by the impressive recent advance in manipulating cold ytterbium\natoms we explore and substantiate the feasibility of realizing the\nCoqblin-Schrieffer model in a gas of cold fermionic $^{173}$Yb atoms. Making\nuse of different AC polarizabillity of the electronic ground state (electronic\nconfiguration $^1S_0$) and the long lived metastable state (electronic\nconfiguration $^3P_0$), it is substantiated that the latter can be localized\nand serve as a magnetic impurity while the former remains itinerant. The\nexchange mechanism between the itinerant $^1S_0$ and the localized $^3P_0$\natoms is analyzed and shown to be antiferromagnetic. The ensuing SU(6)\nsymmetric Coqblin-Schrieffer Hamiltonian is constructed, and, using the\ncalculated exchange constant $J$, perturbative RG analysis yield the Kondo\ntemperature $T_K$ that is experimentally accessible. A number of thermodynamic\nmeasurable observables are calculated in the weak coupling regime $T>T_K$\n(using perturbative RG analysis) and in the strong coupling regime $T<T_K$\n(employing known Bethe ansatz techniques)."
    },
    {
        "anchor": "Gauge fields for ultracold atoms in optical superlattices: We present a scheme that produces a strong U(1)-like gauge field on cold\natoms confined in a two-dimensional square optical lattice. Our proposal relies\non two essential features, a long-lived metastable excited state that exists\nfor alkaline-earth or Ytterbium atoms, and an optical superlattice. As in the\nproposal by Jaksch and Zoller [New Journal of Physics 5, 56 (2003)],\nlaser-assisted tunneling between adjacent sites creates an effective magnetic\nfield. In the tight-binding approximation, the atomic motion is described by\nthe Harper Hamiltonian, with a flux across each lattice plaquette that can\nrealistically take any value between 0 and $\\pi$. We show how to take advantage\nof the superlattice to ensure that each plaquette acquires the same phase, thus\nsimulating a uniform magnetic field. We discuss the observable consequences of\nthe artificial gauge field on non-interacting bosonic and fermionic gases. We\nalso outline how the scheme can be generalized to non-Abelian gauge fields.",
        "positive": "Superdiffusion of vortices in two-component quantum fluids of light: The quantum diffusion of a vortex in a two-component quantum fluid of light\nis investigated. In these systems, the Kerr nonlinearity promotes interactions\nbetween the photons, displaying features that are analogue of a Bose-Einstein\ncondensates. Quantum fluids of light have the advantage of simulating\nmatter-wave phenomena at room temperatures. While the analogy is true at the\nmean field level, the full quantum dynamics of an impurity in quantum fluids of\nlight of, and therefore the ability of featuring genuine quantum noise, has\nnever been considered. We numerically solve the problem by simulating a\nvortex-like impurity in the presence of noise with the Bogoliubov spectral\ndensity, and show that the vortex undergoes superdiffusion. We support our\nresults with a theory that has been previously developed for the brownian\nmotion of point-like particles."
    },
    {
        "anchor": "Response function of strongly interacting Fermi gas in a virial\n  expansion: The dynamic response functions of strongly interacting fermion gas in\nhomogeneous space are investigated in a virial expansion to second order. The\ndensity response function exhibits transition from atomic to molecular\nresponse, as the interaction strength increases and the system undergoes\nBCS-BEC crossover. The qualitative features of density and spin response agree\nwith measurements from the Bragg spectroscopy experiments. The virial response\nis exact at low density and high temperature, therefore providing a benchmark\nfor many-body response.",
        "positive": "Negative mass hydrodynamics in a Spin-Orbit--Coupled Bose-Einstein\n  Condensate: A negative effective mass can be realized in quantum systems by engineering\nthe dispersion relation. A powerful method is provided by spin-orbit coupling,\nwhich is currently at the center of intense research efforts. Here we measure\nan expanding spin-orbit coupled Bose-Einstein condensate whose dispersion\nfeatures a region of negative effective mass. We observe a range of dynamical\nphenomena, including the breaking of parity and of Galilean covariance,\ndynamical instabilities, and self-trapping. The experimental findings are\nreproduced by a single-band Gross-Pitaevskii simulation, demonstrating that the\nemerging features - shockwaves, soliton trains, self-trapping, etc. - originate\nfrom a modified dispersion. Our work also sheds new light on related phenomena\nin optical lattices, where the underlying periodic structure often complicates\ntheir interpretation."
    },
    {
        "anchor": "Parametrically excited star-shaped patterns at the interface of binary\n  Bose-Einstein condensates: A Faraday-wave-like parametric instability is investigated via mean-field and\nFloquet analysis in immiscible binary Bose-Einstein condensates. The\ncondensates form a so-called \\textit{ball-shell} structure in a two-dimensional\nharmonic trap. To trigger the dynamics, the scattering length of the core\ncondensate is periodically modulated in time. We reveal that in the dynamics\nthe interface becomes unstable towards the formation of oscillating patterns.\nThe interface oscillates sub-harmonically exhibiting an $m$-fold rotational\nsymmetry that can be controlled by maneuvering the amplitude and the frequency\nof the modulation. Using Floquet analysis we are able to predict the generated\ninterfacial tension of the mixture and derive a dispersion relation for the\nnatural frequencies of the emergent patterns. A heteronuclear system composed\nof $^{87}$Rb-$^{85}$Rb atoms can be used for the experimental realization of\nthe phenomenon, yet our results are independent of the specifics of the\nemployed atomic species {and of the parameter at which the driving is applied.",
        "positive": "Chaos synchronization in a BEC system using fuzzy logic controller: Since the presence of chaos in Bose-Einstein condensate (BEC) systems plays a\ndestructive role that can undermine the stability of the condensates,\ncontrolling the chaos is of great importance for the creation of the BEC. In\nthis paper, a fuzzy logic controller (FLC) to synchronize the chaotic dynamics\nof two identical master-slave BEC systems has been proposed. Unlike the\nconventional approaches, where expert knowledge is directly used to construct\nthe fuzzy rules and membership functions, the fuzzy rules have been constructed\nusing Lyapunov stability theorem ensuring the synchronization process. The\neffectiveness of the proposed controller has been demonstrated numerically."
    },
    {
        "anchor": "Bond order solid of two-dimensional dipolar fermions: Recent experimental realization of dipolar Fermi gases near or below quantum\ndegeneracy provides opportunity to engineer Hubbard-like models with long range\ninteractions. Motivated by these experiments, we chart out the theoretical\nphase diagram of interacting dipolar fermions on the square lattice at zero\ntemperature and half filling. We show that in addition to p-wave superfluid and\ncharge density wave order, two new and exotic types of bond order emerge\ngenerically in dipolar fermion systems. These phases feature homogeneous\ndensity but periodic modulations of the kinetic hopping energy between nearest\nor next-nearest neighbors. Similar, but manifestly different, phases of\ntwo-dimensional correlated electrons have previously only been hypothesized and\ntermed \"density waves of nonzero angular momentum\". Our results suggest that\nthese phases can be constructed flexibly with dipolar fermions, using currently\navailable experimental techniques.",
        "positive": "Confined Meson Excitations in Rydberg-Atom Arrays Coupled to a Cavity\n  Field: Confinement is a pivotal phenomenon in numerous models of high-energy and\nstatistical physics. In this study, we investigate the emergence of confined\nmeson excitations within a one-dimensional system, comprising Rydberg-dressed\natoms trapped and coupled to a cavity field. This system can be effectively\nrepresented by an Ising-Dicke Hamiltonian model. The observed ground-state\nphase diagram reveals a first-order transition from a ferromagnetic-subradiant\nphase to a paramagnetic-superradiant phase. Notably, a quench near the\ntransition point within the ferromagnetic-subradiant phase induces meson\noscillations in the spins and leads to the creation of squeezed-vacuum light\nstates. We suggest a method for the photonic characterization of these confined\nexcitations, utilizing homodyne detection and single-site imaging techniques to\nobserve the localized particles. The methodologies and results detailed in this\npaper are feasible for implementation on existing cavity-QED platforms,\nemploying Rydberg-atom arrays in deep optical lattices or optical tweezers."
    },
    {
        "anchor": "Laser Control of Singlet-Pairing Process in an Ultracold Spinor Mixture: In the mixture of ultracold spin-1 atoms of two different species A and B\n(e.g., $^{23}$Na (A) and $^{87}$Rb (B)), inter-species singlet-pairing process\n${\\rm A}_{+1}+{\\rm B}_{-1}\\rightleftharpoons {\\rm A}_{-1}+{\\rm B}_{+1}$, can be\ninduced by the spin-dependent inter-atomic interaction, where subscript $\\pm 1$\ndenotes the magnetic quantum number. Nevertheless, one cannot isolate this\nprocess from other spin-changing processes by tuning the bias real magnetic\nfield. As a result, so far the singlet-pairing process have not been clearly\nobserved in the experiments, and the measurement of the corresponding\ninteraction strength becomes difficult. In this work we propose to control the\nsinglet-pairing process via combining the real magnetic field and a\nlaser-induced species-dependent synthetic magnetic field. With our approach one\ncan significantly enhance this process and simultaneously supperess all other\nspin-changing processes. We illustrate our approach for both a confined\ntwo-atom system and a binary mixture of spinor Bose-Einstein condensates. Our\ncontrol scheme is helpful for the precise measurement of the weakly\nsinglet-pairing interaction strength and the entanglement generation of two\ndifferent atoms.",
        "positive": "Long-distance supercurrent transport in a room-temperature Bose-Einstein\n  magnon condensate: The term supercurrent relates to a macroscopic dissipation-free collective\nmotion of a quantum condensate and is commonly associated with such famous\nlow-temperature phenomena as superconductivity and superfluidity. Another type\nof motion of quantum condensates is second sound - a wave of the density of a\ncondensate. Recently, we reported on an enhanced decay of a parametrically\ninduced Bose-Einstein condensate (BEC) of magnons caused by a supercurrent\noutflow of the BEC phase from the locally heated area of a room temperature\nmagnetic film. Here, we present the direct experimental observation of a\nlong-distance spin transport in such a system. The condensed magnons being\npushed out from the potential well within the heated area form a density wave,\nwhich propagates through the BEC many hundreds of micrometers in the form of a\nspecific second sound pulse - Bogoliubov waves - and is reflected from the\nsample edge. The discovery of the long distance supercurrent transport in the\nmagnon BEC further advances the frontier of the physics of quasiparticles and\nallows for the application of related transport phenomena for low-loss data\ntransfer in perspective magnon spintronics devices."
    },
    {
        "anchor": "Stable vortex loops in two-species BECs: We consider the creation of stable, stationary closed vortex loops, analogue\nto the vortons and superconducting cosmic strings, in cold atom BEC's. We\nexplore the parameter region where these solutions are likely to exist and\ncomment on methods to create them experimentally.",
        "positive": "Goldstone modes and bifurcations in phase-separated binary condensates\n  at finite temperature: We show that the third Goldstone mode, which emerges in binary condensates at\nphase-separation, persists to higher inter-species interaction for density\nprofiles where one component is surrounded on both sides by the other\ncomponent. This is not the case with symmetry-broken density profiles where one\nspecies is to entirely to the left and the other is entirely to the right. We,\nthen, use Hartree-Fock-Bogoliubov theory with Popov approximation to examine\nthe mode evolution at $T\\neq0$ and demonstrate the existence of mode\nbifurcation near the critical temperature. The Kohn mode, however, exhibits\ndeviation from the natural frequency at finite temperatures after the phase\nseparation. This is due to the exclusion of the non-condensate atoms in the\ndynamics."
    },
    {
        "anchor": "Bound states of a localized magnetic impurity in a superfluid of paired\n  ultracold fermions: We consider a localized impurity atom that interacts with a cloud of fermions\nin the paired state. We develop an effective scattering length description of\nthe interaction between an impurity and a fermionic atom using their vacuum\nscattering length. Treating the pairing of fermions at the mean-field level, we\nshow that the impurity atom acts like a magnetic impurity in the condensed\nmatter context, and leads to the formation of a pair of Shiba bound states\ninside the superconducting gap. In addition, the impurity atom can lead to the\nformation of deeply bound states below the Fermi sea.",
        "positive": "Superfluid density of states and pseudogap phenomenon in the BCS-BEC\n  crossover regime of a superfluid Fermi gas: We investigate single-particle excitations and strong-coupling effects in the\nBCS-BEC crossover regime of a superfluid Fermi gas. Including phase and\namplitude fluctuations of the superfluid order parameter within a $T$-matrix\ntheory, we calculate the superfluid density of states (DOS), as well as\nsingle-particle spectral weight, over the entire BCS-BEC crossover region below\nthe superfluid transition temperature $T_{\\rm c}$. We clarify how the pseudogap\nin the normal state evolves into the superfluid gap, as one passes through\n$T_{\\rm c}$. While the pseudogap in DOS continuously evolves into the\nsuperfluid gap in the weak-coupling BCS regime, the superfluid gap in the\ncrossover region is shown to appear in DOS after the pseudogap disappears below\n$T_{\\rm c}$. In the phase diagram with respect to the temperature and\ninteraction strength, we determine the region where strong pairing fluctuations\ndominate over single-particle properties of the system. Our results would be\nuseful for the study of strong-coupling phenomena in the BCS-BEC crossover\nregime of a superfluid Fermi gas."
    },
    {
        "anchor": "Experimental observation of Josephson oscillations in a room-temperature\n  Bose-Einstein magnon condensate: The alternating current (ac) Josephson effect in a time-independent\nspatially-inhomogeneous setting is manifested by the occurrence of Josephson\noscillations - periodic macroscopic phase-induced collective motions of the\nquantum condensate. So far, this phenomenon was observed at cryogenic\ntemperatures in superconductors, in superfluid helium, and in Bose-Einstein\ncondensates (BECs) of trapped atoms. Here, we report on the discovery of the ac\nJosephson effect in a magnon BEC carried by a room-temperature ferrimagnetic\nfilm. The BEC is formed in a parametrically populated magnon gas in the spatial\nvicinity of a magnetic trench created by a dc electric current. The appearance\nof the Josephson effect is manifested by oscillations of the magnon BEC density\nin the trench, caused by a coherent phase shift between this BEC and the BEC in\nthe nearby regions. Our findings advance the physics of room-temperature\nmacroscopic quantum phenomena and will allow for their application for data\nprocessing in magnon spintronics devices.",
        "positive": "Few-body collective excitations beyond Kohn's theorem in quantum Hall\n  systems: A relative coordinate breathing mode in the quantum Hall system is predicted\nto exist with different behavior under either Coulomb or dipole-dipole\ninteractions. While Kohn's theorem predicts that any relative coordinate\ninteraction will fail to alter the center of mass energy spectrum, it can\naffect excitations in the relative coordinates. One such collective excitation,\nwhich we call the hyperradial breathing mode, emerges naturally from a\nfew-body, hyperspherical representation of the problem and depends on the\ninter-particle interactions, the ground state wave function, and the number of\nparticles participating in the excitation. Possible observations of this\nexcitation will be discussed in the context of both cold rotating atomic\nsimulations and conventional quantum Hall experiments."
    },
    {
        "anchor": "Raise and fall of a bright soliton in an optical lattice: We study an ultracold atomic gas with attractive interactions in a\none-dimensional optical lattice. We find that its excitation spectrum displays\na quantum soliton band, corresponding to $N$-particle bound states, and a\ncontinuum band of other, mostly extended, states. For a system of a finite\nsize, the two branches are degenerate in energy for weak interactions, while a\ngap opens above a threshold value for the interaction strength. We find that\nthe interplay between degenerate extended and bound states has important\nconsequences for both static and dynamical properties of the system. In\nparticular, the solitonic states turn out to be protected from spatial\nperturbations and random disorder. We discuss how such dynamics implies that\nour system effectively provides an example of a quantum many-body system that,\nwith the variation of the bosonic lattice filling, crosses over from integrable\nnon-ergodic to non-integrable ergodic dynamics, through non-integrable\nnon-ergodic regimes.",
        "positive": "Mixed partial-wave scattering with spin-orbit coupling and validity of\n  pseudo-potentials: We present exact solutions of two-body problem for spin-1/2 fermions with\nisotropic spin-orbit(SO) coupling and interacting with an arbitrary short-range\npotential. We find that in each partial-wave scattering channel, the\nparametrization of two-body wavefunction at short inter-particle distance\ndepends on the scattering amplitudes of all channels. This reveals the mixed\npartial-wave scattering induced by SO couplings. By comparing with results from\na square-well potential, we investigate the validity of original\npseudo-potential models in the presence of SO coupling. We find the s-wave\npseudo-potential provides a good approximation for low-energy solutions near\ns-wave resonances, given the length scale of SO coupling much longer than the\npotential range. However, near p-wave resonance the p-wave pseudo-potential\ngives low-energy solutions that are qualitatively different from exact ones,\nbased on which we conclude that the p-wave model can not be applied to the\nfermion system if the SO coupling strength is larger or comparable to the Fermi\nmomentum."
    },
    {
        "anchor": "Terahertz emission from AC Stark-split asymmetric intersubband\n  transitions: Transitions between the two states of an AC Stark-split doublet are forbidden\nin centro-symmetric systems, and thus almost impossible to observe in\nexperiments performed with atomic clouds. However, electrons trapped in\nnanoscopic heterostructures can behave as artificial atoms, with the advantage\nthat the wavefunction symmetry can be broken by using asymmetric confining\npotentials. Here we develop the many-body theory describing the intra-doublet\nemission of a resonantly pumped intersubband transition in a doped asymmetric\nquantum well, showing that in such a system the intra-doublet emission can be\norders of magnitude higher than in previously studied systems. This emission\nchannel, which lies in the terahertz range, and whose frequency depends upon\nthe pump power, opens the way to the realization of a new class of monolithic\nand tunable terahertz emitters.",
        "positive": "Dipolar Quantum Mixtures of Erbium and Dysprosium Atoms: We report on the first realization of heteronuclear dipolar quantum mixtures\nof highly magnetic erbium and dysprosium atoms. With a versatile experimental\nsetup, we demonstrate binary Bose-Einstein condensation in five different Er-Dy\nisotope combinations, as well as one Er-Dy Bose-Fermi mixture. Finally, we\npresent first studies of the interspecies interaction between the two species\nfor one mixture."
    },
    {
        "anchor": "Aberrations in (3+1)D Bragg diffraction using pulsed Gaussian laser\n  beams: We analyze the transfer function of a three-dimensional atomic Bragg\nbeamsplitter formed by two counterpropagating pulsed Gaussian laser beams. Even\nfor ultracold atomic ensembles, the transfer efficiency depends significantly\non the residual velocity of the particles as well as on losses into higher\ndiffraction orders. Additional aberrations are caused by the spatial intensity\nvariation and wavefront curvature of the Gaussian beam envelope, studied with\n(3+1)D numerical simulations. The temporal pulse shape also affects the\ntransfer efficiency significantly. Thus, we consider the practically important\nrectangular-, Gaussian-, Blackman- and hyperbolic secant pulses. For the\nlatter, we can describe the time-dependent response analytically with the\nDemkov-Kunike method. The experimentally observed stretching of the $\\pi$-pulse\ntime is explained from a renormalization of the simple Pendell\\\"osung\nfrequency. Finally, we compare the analytical predictions for the\nvelocity-dependent transfer function with effective (1+1)D numerical\nsimulations for pulsed Gaussian beams, as well as experimental data and find\nvery good agreement, considering a mixture of Bose-Einstein condensate and\nthermal cloud.",
        "positive": "Persistent current formation in a high-temperature Bose-Einstein\n  condensate: an experimental test for c-field theory: Experimental stirring of a toroidally trapped Bose-Einstein condensate at\nhigh temperature generates a disordered array of quantum vortices that decays\nvia thermal dissipation to form a macroscopic persistent current [T. W. Neely\nem et al. arXiv:1204.1102 (2012)]. We perform 3D numerical simulations of the\nexperimental sequence within the Stochastic Projected Gross-Pitaevskii equation\nusing ab initio determined reservoir parameters. We find that both damping and\nnoise are essential for describing the dynamics of the high-temperature Bose\nfield. The theory gives a quantitative account of the formation of a persistent\ncurrent, with no fitted parameters."
    },
    {
        "anchor": "Optical runaway evaporation for multi-BEC production: We report on parallel production of Bose-Einstein condensates (BECs) in\nsteerable, multi-plexed crossed optical dipole traps. Using a conventional\ntrap-weakening evaporation scheme, where the optical trapping power is lowered,\nwe obtain an array of up to four independent BECs. To improve evaporation\nefficiency, we propose to target each crossed trap site with a narrow auxiliary\nlaser beam, creating an escape channel for energetic atoms. We experimentally\ndemonstrate runaway evaporation using this scheme, which is characterized by\nvery modest weakening in atomic confinement such that high densities and\nelastic collision rates can be maintained. Based on discretely time-shared\noptical tweezers, our approach is particularly suited for addressing the\nproblem of simultaneously cooling atoms in multiple traps clouds, providing the\nfreedom to act locally and in a tailored fashion at individual trap sites.",
        "positive": "Universality of miscible-immiscible phase separation dynamics in\n  two-component Bose-Einstein condensates: We investigate the non-equilibrium dynamics across the miscible-immiscible\nphase separation in a binary mixture of Bose-Einstein condensates.\n  The excitation spectra reveal that the Landau critical velocity vanishes at\nthe critical point, where the superfluidity spontaneously breaks down.\n  We analytically extract the dynamical critical exponent $z=2$ from the Landau\ncritical velocity.\n  Moreover, by simulating the real-time dynamics across the critical point, we\nfind the average domain number and the average bifurcation delay show universal\nscaling laws with respect to the quench time.\n  We then numerically extract the static correlation length critical exponent\n$v=1/2$ and the dynamical critical exponent $z=2$ according to Kibble-Zurek\nmechanism.\n  The scaling exponents $(v=1/2, z=2)$ in the phase separation driven by\nquenching the atom-atom interaction are different from the ones $(v=1/2, z=1)$\nin the phase separation driven by quenching the Rabi coupling strength [PRL\n\\textbf{102}, 070401 (2009); PRL \\textbf{107}, 230402 (2011)].\n  Our study explores the connections between the spontaneous superfluidity\nbreakdown and the spontaneous defect formation in the phase separation\ndynamics."
    },
    {
        "anchor": "Pairing of few Fermi atoms in one dimension: We study a few Fermi atoms interacting through attractive contact forces in a\none-dimensional trap by means of numerical exact diagonalization. From the\ncombined analysis of energies and wave functions of correlated ground and\nexcited states we find evidence of BCS-like pairing even for very few atoms.\nFor moderate interaction strength, we reproduce the even-odd oscillation of the\nseparation energy observed in [G. Zuern, A. N. Wenz, S. Murmann, A.\nBergschneider, T. Lompe, and S. Jochim, Phys. Rev. Lett. 111, 175302 (2013)].\nFor strong interatomic attraction the arrangement of dimers in the trap differs\nfrom the homogeneous case as a consequence of Pauli blockade in real space.",
        "positive": "Relative Phase States in Quantum-Atom Optics: Relative phase is treated as a physical quantity for two mode systems in\nquantum atom optics, adapting the Pegg-Barnett treatment of quantum optical\nphase to define a linear Hermitian relative phase operator via first\nintroducing a complete orthonormal set of relative phase eigenstates. These\nstates are contrasted with other so-called phase states. Other approaches to\ntreating phase and previous attempts to find a Hermitian phase operator are\ndiscussed. The relative phase eigenstate has maximal two mode entanglement, it\nis a fragmented state with its Bloch vector lying inside the Bloch sphere and\nis highly spin squeezed. The relative phase states are applied to describing\ninterferometry experiments with Bose-Einstein condensates (BEC), particularly\nin the context of a proposed Heisenberg limited interferometry experiment. For\na relative phase eigenstate the fractional fluctuation in one spin operator\ncomponent perpendicular to the Bloch vector is essentially only of order 1/N,\nso if such a highly spin squeezed state could be prepared it may be useful for\nHeisenberg limited interferometry. An approach for preparing a BEC in a state\nclose to a relative phase state is suggested, based on adiabatically changing\nparameters in the Josephson Hamiltonian starting from a suitable energy\neigenstate in the Rabi regime."
    },
    {
        "anchor": "Emergent symmetries and slow quantum dynamics in a Rydberg-atom chain\n  with confinement: Rydberg atoms in optical tweezer arrays provide a playground for\nnonequilibrium quantum many-body physics. The PXP model describes the dynamics\nof such systems in the strongly interacting Rydberg blockade regime and notably\nexhibits weakly nonergodic dynamics due to quantum many-body scars. Here, we\nstudy the PXP model in a strong staggered external field, which has been\nproposed to manifest quasiparticle confinement in light of a mapping to a\nlattice gauge theory. We characterize this confining regime using both\nnumerical exact diagonalization and perturbation theory around the strong-field\nlimit. In addition to the expected emergent symmetry generated by the staggered\nfield, we find a second emergent symmetry that is special to the PXP model. The\ninterplay between these emergent symmetries and the Rydberg blockade constraint\ndramatically slows down the system's dynamics beyond naive expectations. We\ndevise a nested Schrieffer-Wolff perturbation theory to properly account for\nthe new emergent symmetry and show that this treatment is essential to\nunderstand the numerically observed relaxation time scales. We also discuss\nconnections to Hilbert space fragmentation and trace the origin of the new\nemergent symmetry to a \"nearly-$SU(2)$\" algebra discovered in the context of\nmany-body scarring.",
        "positive": "Feshbach resonances in 3He*-4He* mixtures: We discuss the stability of homonuclear and heteronuclear mixtures of 3He and\n4He atoms in the metastable 2^3S_1 state (He*) and predict positions and widths\nof Feshbach resonances by using the Asymptotic Bound-state Model (ABM). All\ncalculations are performed without fit parameters, using \\emph{ab-initio}\ncalculations of molecular potentials. One promising very broad Feshbach\nresonance (\\Delta B=72.9^{+18.3}_{-19.3} mT) is found that allows for tuning of\nthe inter-isotope scattering length."
    },
    {
        "anchor": "Bright matter-wave soliton collisions at narrow barriers: We study fast-moving bright solitons in the focusing nonlinear Schr\\\"odinger\nequation perturbed by a narrow Gaussian potential barrier. In particular, we\npresent a general and comprehensive analysis of the case where two fast-moving\nbright solitons collide at the location of the barrier. In the limiting case of\na delta-function barrier, we use a quasi-analytic method to show that the\nrelative norms of the outgoing waves depends sinusoidally on the relative phase\nof the incoming waves, and to determine whether one, or both, of the outgoing\nwaves are bright solitons. We show using numerical simulations that this\nquasi-analytic result is valid in the high velocity limit: outside this limit\nnonlinear effects introduce a skew to the phase-dependence, which we quantify.\nFinally, we numerically explore the effects of introducing a finite-width\nGaussian barrier. Our results are particularly relevant, as they can be used to\ndescribe a range of interferometry experiments using bright solitary\nmatter-waves.",
        "positive": "Expansion of matter waves in static and driven periodic potentials: We study the non-equilibrium dynamics of cold atoms held in an optical\nlattice potential. The expansion of an initially confined atom cloud occurs in\ntwo phases: an initial quadratic expansion followed by a ballistic behaviour at\nlong times. Accounting for this gives a good description of recent experimental\nresults, and provides a robust method to extract the effective intersite\ntunneling from time-of-flight measurements."
    },
    {
        "anchor": "Quantum fluctuation induced time of flight correlations of an\n  interacting trapped Bose gas: We investigate numerically the momentum correlations in a two dimensional,\nharmonically trapped interacting Bose system at $T=0$ temperature, by using a\nparticle number preserving Bogoliubov approximation. Interaction induced\nquantum fluctuations of the quasi-condensate lead to a large anti-correlation\ndip between particles of wave numbers $\\mathbf{k}$ and $-\\mathbf{k}$ for\n$|\\mathbf{k}|\\sim 1/R_c$, with $R_c$ typical size of the condensate. The\nanti-correlation dip found is a clear fingerprint of coherent quantum\nfluctuations of the condensate. In contrast, for larger wave numbers,\n$|\\mathbf{k}| >> 1/R_c$, a weak positive correlation is found between particles\nof wave numbers $\\mathbf{k}$ and $-\\mathbf{k}$, in accordance with the\nBogoliubov result for homogeneous interacting systems.",
        "positive": "Semi-Implicit finite-difference methods to study the spin-orbit and\n  coherently coupled spinor Bose-Einstein condensates: We develop time-splitting finite difference methods, using implicit\nBackward-Euler and semi-implicit Crank-Nicolson discretization schemes, to\nstudy the spin-orbit coupled spinor Bose Einstein condensates with coherent\ncoupling in quasi-one and quasi-two-dimensional traps. The split equations\ninvolving kinetic energy and spin-orbit coupling operators are solved using\neither time-implicit Backward-Euler or semi-implicit Crank-Nicolson methods. We\nexplicitly develop the method for pseudospin-1/2, spin-1, and spin-2\ncondensates. The results for ground states obtained with time-splitting\nBackward-Euler and Crank-Nicolson methods are in excellent agreement with\ntime-splitting Fourier spectral method which is one of the popular methods to\nsolve the mean-field models for spin-orbit coupled spinor condensates. We\nconfirm the emergence of different phases in spin-orbit coupled pseudospin-1/2,\nspin-1, and spin-2 condensates with coherent coupling."
    },
    {
        "anchor": "Quantum fluids of light: This article reviews recent theoretical and experimental advances in the\nfundamental understanding and active control of quantum fluids of light in\nnonlinear optical systems. In presence of effective photon-photon interactions\ninduced by the optical nonlinearity of the medium, a many-photon system can\nbehave collectively as a quantum fluid with a number of novel features stemming\nfrom its intrinsically non-equilibrium nature. We present a rich variety of\nphoton hydrodynamical effects that have been recently observed, from the\nsuperfluid flow around a defect at low speeds, to the appearance of a\nMach-Cherenkov cone in a supersonic flow, to the hydrodynamic formation of\ntopological excitations such as quantized vortices and dark solitons at the\nsurface of large impenetrable obstacles. While our review is mostly focused on\na class of semiconductor systems that have been extensively studied in recent\nyears (namely planar semiconductor microcavities in the strong light-matter\ncoupling regime having cavity polaritons as elementary excitations), the very\nconcept of quantum fluids of light applies to a broad spectrum of systems,\nranging from bulk nonlinear crystals, to atomic clouds embedded in optical\nfibers and cavities, to photonic crystal cavities, to superconducting quantum\ncircuits based on Josephson junctions. The conclusive part of our article is\ndevoted to a review of the exciting perspectives to achieve strongly correlated\nphoton gases. In particular, we present different mechanisms to obtain\nefficient photon blockade, we discuss the novel quantum phases that are\nexpected to appear in arrays of strongly nonlinear cavities, and we point out\nthe rich phenomenology offered by the implementation of artificial gauge fields\nfor photons.",
        "positive": "Thermalization and Bose-Einstein condensation of quantum light in bulk\n  nonlinear media: We study the thermalization and the Bose-Einstein condensation of a paraxial,\nspectrally narrow beam of quantum light propagating in a lossless bulk Kerr\nmedium. The spatiotemporal evolution of the quantum optical field is ruled by a\nHeisenberg equation analogous to the quantum nonlinear Schr\\\"odinger equation\nof dilute atomic Bose gases. Correspondingly, in the weak-nonlinearity regime,\nthe phase-space density evolves according to the Boltzmann equation.\nExpressions for the thermalization time and for the temperature and the\nchemical potential of the eventual Bose-Einstein distribution are found. After\ndiscussing experimental issues, we introduce an optical setup allowing the\nevaporative cooling of a guided beam of light towards Bose-Einstein\ncondensation. This might serve as a novel source of coherent light."
    },
    {
        "anchor": "Morphology of dipolar Bose droplets: The ground state of a free standing, self-bound droplet comprising four\nhundred dipolar Bose particles with aligned dipole moments, with an additional\npurely repulsive two-body interaction, is investigated by Quantum Monte Carlo\nsimulations. The focus here is on the evolution of the cluster as the effective\nrange of the repulsive interaction is varied. We identify a ``classical''\nregime, in which binding arises exclusively from the dipolar potential energy\nand the cluster is a quasi-one-dimensional filament, and a ``quantum'' regime\nof prolate droplets, held together to a significant degree by\nquantum-mechanical exchanges. The transition between the two regimes occurs\nabruptly.",
        "positive": "Hydrodynamic stabilization of self-organized criticality in a driven\n  Rydberg gas: Signatures of self-organized criticality (SOC) have recently been observed in\nan ultracold atomic gas under continuous laser excitation to\nstrongly-interacting Rydberg states [S. Helmrich et al., Nature, 577, 481--486\n(2020)]. This creates a unique possibility to study this intriguing dynamical\nphenomenon, e.g., to probe its robustness and universality, under controlled\nexperimental conditions. Here we examine the self-organizing dynamics of a\ndriven ultracold gas and identify an unanticipated feedback mechanism, which is\nespecially important for systems coupled to thermal baths. It sustains an\nextended critical region in the trap center for a notably long time via\nhydrodynamic transport of particles from the flanks of the cloud toward the\ncenter. This compensates the avalanche-induced atom loss and leads to a\ncharacteristic flat-top density profile, providing an additional experimental\nsignature for SOC and minimizing effects of inhomogeneity on the SOC features."
    },
    {
        "anchor": "Orbital optical lattices with bosons: This article provides a synopsis of our recent experimental work exploring\nBose-Einstein condensation in metastable higher Bloch bands of optical\nlattices. Bipartite lattice geometries have allowed us to implement appropriate\nband structures, which meet three basic requirements: the existence of\nmetastable excited states sufficiently protected from collisional band\nrelaxation, a mechanism to excite the atoms initially prepared in the lowest\nband with moderate entropy increase, and the possibility of cross-dimensional\ntunneling dynamics, necessary to establish coherence along all lattice axes. A\nvariety of bands can be selectively populated and a subsequent thermalisation\nprocess leads to the formation of a condensate in the lowest energy state of\nthe chosen band. As examples the 2nd, 4th and 7th bands in a bipartite square\nlattice are discussed. In the 2nd and 7th band, the band geometry can be tuned\nsuch that two inequivalent energetically degenerate energy minima arise at the\n$X_{\\pm}$-points at the edge of the 1st Brillouin zone. In this case even a\nsmall interaction energy is sufficient to lock the phase between the two\ncondensation points such that a complex-valued chiral superfluid order\nparameter can emerge, which breaks time reversal symmetry. In the 4th band a\ncondensate can be formed in the $\\Gamma$-point in the center of the 1st\nBrillouin zone, which can be used to explore topologically protected band\ntouching points. The new techniques to access orbital degrees of freedom in\nhigher bands greatly extend the class of many-body scenarios that can be\nexplored with bosons in optical lattices.",
        "positive": "Information geometry and Bose-Einstein condensation: It is a long held conjecture in the connection between information geometry\n(IG) and thermodynamics that the curvature endowed by IG diverges at phase\ntransitions. Recent work on the IG of Bose-Einstein (BE) gases challenged this\nconjecture by saying that in the limit of fugacity approaching unit -- where BE\ncondensation is expected -- curvature does not diverge, rather it converges to\nzero. However, as the discontinuous behavior that identify condensation is only\nobserved at the thermodynamic limit, a study of IG curvature at finite number\nof particles, $N$, is in order from which the thermodynamic behaviour can be\nobserved by taking the thermodynamic limit ($N\\to \\infty$) posteriorly. This\narticle presents such study, which was made possible by the recent advances\npresented in [Phys. Rev. A 104, 043318 (2021)]. We find that for a trapped gas,\nas $N$ increases, the values of curvature decrease proportionally to a power of\n$N$ while the temperature at which the maximum value of curvature occurs\napproaches the usually defined critical temperature. This means that, in the\nthermodynamic limit, curvature has a limited value where a phase transition is\nobserved, contradicting the forementioned conjecture."
    },
    {
        "anchor": "Time-of-flight imaging method to observe signatures of\n  antiferromagnetically ordered states of fermionic atoms in an optical lattice: We propose a simple method to detect the antiferromagnetic (AF) state of\nfermionic atoms in an optical lattice by combining a time-of-flight (TOF)\nimaging method and a Feshbach resonance. In this scheme, the nontrivial\ndynamics of fermionic atoms during the imaging process works as a probe with\nrespect to the breaking of the translational symmetry in the AF state. Precise\nnumerical simulations demonstrate that the characteristic oscillatory dynamics\ninduced by the scattering process that transfers an AF ordering vector appears\nin TOF images, which can be easily observed experimentally.",
        "positive": "The role of geometry in the superfluid flow of nonlocal photon fluids: Recent work has unveiled a new class of optical systems that can exhibit the\ncharacteristic features of superfluidity. One such system relies on the\nrepulsive photon-photon interaction that is mediated by a thermal optical\nnonlinearity and is therefore inherently nonlocal due to thermal diffusion.\nHere we investigate how such a nonlocal interaction, which at a first\ninspection would not be expected to lead to superfluid behavior, may be\ntailored by acting upon the geometry of the photon fluid itself. Our models and\nmeasurements show that restricting the laser profile and hence the photon fluid\nto a strongly elliptical geometry modifies thermal diffusion along the major\nbeam axis and reduces the effective nonlocal interaction length by two orders\nof magnitude. This in turn enables the system to display a characteristic trait\nof superfluid flow: the nucleation of quantized vortices in the flow past an\nextended physical obstacle. These results are general and apply to other\nnonlocal fluids, such as dipolar Bose-Einstein condensates, and show that\n\"thermal\" photon superfluids provide an exciting and novel experimental\nenvironment for probing the nature of superfluidity, with applications to the\nstudy of quantum turbulence and analogue gravity."
    },
    {
        "anchor": "Self-consistent Keldysh approach to quenches in weakly interacting\n  Bose-Hubbard model: We present a non-equilibrium Green's functional approach to study the\ndynamics following a quench in weakly interacting Bose Hubbard model (BHM). The\ntechnique is based on the self-consistent solution of a set of equations which\nrepresents a particular case of the most general set of Hedin's equations for\nthe interacting single-particle Green's function. We use the ladder\napproximation as a skeleton diagram for the two-particle scattering amplitude\nuseful, through the self-energy in the Dyson equation, for finding the\ninteracting single-particle Green's function. This scheme is then implemented\nnumerically by a parallelized code. We exploit this approach to study the\ncorrelation propagation after a quench in the interaction parameter, for one\n(1D) and two (2D) dimensions. In particular, we show how our approach is able\nto recover the crossover from ballistic to diffusive regime by increasing the\nboson-boson interaction. Finally we also discuss the role of a thermal initial\nstate on the dynamics both for 1D and 2D Bose Hubbard models, finding that\nsurprisingly at high temperature a ballistic evolution is restored.",
        "positive": "Quantum bright solitons in the Bose-Hubbard model with site-dependent\n  repulsive interactions: We introduce a one-dimensional (1D) spatially inhomogeneous Bose-Hubbard\nmodel (BHM) with the strength of the onsite repulsive interactions growing,\nwith the discrete coordinate $z_{j}$, as $|z_{j}|^{\\alpha }$ with $\\alpha >0$.\nRecently, the analysis of the mean-field (MF) counterpart of this system has\ndemonstrated self-trapping of robust unstaggered discrete solitons, under\ncondition $\\alpha >1$. Using the numerically implemented method of the density\nmatrix renormalization group (DMRG), we demonstrate that, in a certain range of\ninteraction, the BHM also self-traps, in the ground state, into a soliton-like\nconfiguration, at $\\alpha >1$, and remains weakly localized at $\\alpha <1$. An\nessential quantum feature is a residual density in the background surrounding\nthe soliton-like peak in the BHM ground state, while in the MF limit the\nfinite-density background is absent. Very strong onsite repulsion eventually\ndestroys soliton-like states, and, for integer densities, the system enters the\nMott phase with a spatially uniform density"
    },
    {
        "anchor": "Vortices in fermion droplets with repulsive dipole-dipole interactions: Vortices are found in a fermion system with repulsive dipole-dipole\ninteractions, trapped by a rotating quasi-two-dimensional harmonic oscillator\npotential. Such systems have much in common with electrons in quantum dots,\nwhere rotation is induced via an external magnetic field. In contrast to the\nCoulomb interactions between electrons, the (externally tunable) anisotropy of\nthe dipole-dipole interaction breaks the rotational symmetry of the\nHamiltonian. This may cause the otherwise rotationally symmetric exact\nwavefunction to reveal its internal structure more directly.",
        "positive": "Long-range sound-mediated dark soliton interactions in trapped atomic\n  condensates: A long-range soliton interaction is discussed whereby two or more dark\nsolitons interact in an inhomogeneous atomic condensate, modifying their\nrespective dynamics via the exchange of sound waves without ever coming into\ndirect contact. An idealized double well geometry is shown to yield perfect\nenergy transfer and complete periodic identity reversal of the two solitons.\nTwo experimentally relevant geometries are analyzed which should enable the\nobservation of this long-range interaction."
    },
    {
        "anchor": "Landau instability and mobility edges of the interacting one-dimensional\n  Bose gas in weak random potentials: We study the frictional force exerted on the trapped, interacting 1D Bose gas\nunder the influence of a moving random potential. Specifically we consider weak\npotentials generated by optical speckle patterns with finite correlation\nlength. We show that repulsive interactions between bosons lead to a superfluid\nresponse and suppression of frictional force, which can inhibit the onset of\nAnderson localisation. We perform a quantitative analysis of the Landau\ninstability based on the dynamic structure factor of the integrable\nLieb-Liniger model and demonstrate the existence of effective mobility edges.",
        "positive": "Rayleigh-Taylor instability in a phase-separated three-component\n  Bose-Einstein condensate: We investigate the Rayleigh-Taylor instability at the two interfaces in a\nphase-separated three-component Bose-Einstein condensate in the mean-field\nframework. The subsequent dynamics in the immiscible three-component condensate\nhas been studied in detail for different cases of instigating the instability\nin the system. The rotational symmetry of the system breaks when the atom-atom\ninteraction is tuned in such a way that the interface between the components\nbecomes unstable giving rise to non-linear patterns of mushroom shapes which\ngrow exponentially with time. We also identify these non-linear patterns as the\nsolutions of the angular Mathieu equation, representing the normal modes."
    },
    {
        "anchor": "Superfluid Phases of Dipolar Fermions in Harmonically Trapped Optical\n  Lattices: We describe the emergence of superfluid phases of ultracold dipolar fermions\nin optical lattices for two-dimensional systems. Considering the many-body\nscreening of dipolar interactions at intermediate and larger filling factors,\nwe show that several superfluid phases with distinct pairing symmetries\nnaturally arise in the singlet channel: local s-wave $(sl)$, extended s-wave\n$(se)$, d-wave $(d)$ or time-reversal-symmetry breaking $(sl + se \\pm\nid)$-wave. We obtain the temperature versus filling factor phase diagram and\nshow that d-wave pairing is favored near half-filling, that $(sl + se)$-wave is\nfavored near zero or full filling, and that time-reversal-breaking $(sl + se\n\\pm id)$-wave is favored in between. The inclusion of a harmonic trap reveals\nthat a sequence of phases can coexist in the cloud depending on the filling\nfactor at the center of the trap. Most notably in the spatial region where the\n$(sl + se \\pm id)$-wave superfluid occurs, spontaneous currents are generated,\nand may be detected using velocity sensitive Bragg spectroscopy.",
        "positive": "Long-lived periodic revivals of coherence in an interacting\n  Bose-Einstein condensate: We observe the coherence of an interacting two-component Bose-Einstein\ncondensate (BEC) surviving for seconds in a trapped Ramsey interferometer.\nMean-field driven collective oscillations of two components lead to periodic\ndephasing and rephasing of condensate wave functions with a slow decay of the\ninterference fringe visibility. We apply spin echo synchronous with the\nself-rephasing of the condensate to reduce the influence of state-dependent\natom losses, significantly enhancing the visibility up to 0.75 at the evolution\ntime of 1.5s. Mean-field theory consistently predicts higher visibility than\nexperimentally observed values. We quantify the effects of classical and\nquantum noise and infer a coherence time of 2.8 s for a trapped condensate of\n5.5e4 interacting atoms."
    },
    {
        "anchor": "Applications of fidelity measures to complex quantum systems: We revisit the fidelity as a measure for the stability and the complexity of\nthe quantum motion of single and many-body systems. Within the context of cold\natoms, we present on overview of applications of two fidelities which we call\nstatic and dynamical fidelity, respectively. The static fidelity applies to\nquantum problems which can be diagonalized since it is defined via the\neigenfunctions. In particular, we show that the static fidelity is a highly\neffective practical detector of avoided crossings characterizing the complexity\nof the systems and their evolutions. The dynamical fidelity is defined via the\ntime-dependent wave functions. Focussing on the quantum kicked rotor system, we\nhighlight a few practical applications of fidelity measurements in order to\nbetter understand the large variety of dynamical regimes of this paradigm of a\nlow-dimensional system with mixed regular-chaotic phase space.",
        "positive": "Microscopic Approach to Shear Viscosities in Superfluid Gases: From BCS\n  to BEC: We compute the shear viscosity, $\\eta$, at general temperatures $T$, in a\nBCS-BEC crossover scheme which is demonstrably consistent with conservation\nlaws. The study of $\\eta$ is important because it constrains microscopic\ntheories by revealing the excitation spectra. The onset of a normal state\npairing gap and the contribution from pair degrees of freedom imply that $\\eta$\nat low $T$ becomes small, rather than exhibiting the upturn predicted by most\nothers. Using the local density approximation, we find quite reasonable\nagreement with just-published experiments."
    },
    {
        "anchor": "Strongly anomalous non-thermal fixed point in a quenched two-dimensional\n  Bose gas: Universal scaling behavior in the relaxation dynamics of an isolated\ntwo-dimensional Bose gas is studied by means of semi-classical stochastic\nsimulations of the Gross-Pitaevskii model. The system is quenched far out of\nequilibrium by imprinting vortex defects into an otherwise phase-coherent\ncondensate. A strongly anomalous non-thermal fixed point is identified,\nassociated with a slowed decay of the defects in the case that the dissipative\ncoupling to the thermal background noise is suppressed. At this fixed point, a\nlarge anomalous exponent $\\eta \\simeq -3$ and, related to this, a large\ndynamical exponent $z \\simeq 5$ are identified. The corresponding power-law\ndecay is found to be consistent with three-vortex-collision induced loss. The\narticle discusses these aspects of non-thermal fixed points in the context of\nphase-ordering kinetics and coarsening dynamics, thus relating phenomenological\nand analytical approaches to classifying far-from-equilibrium scaling dynamics\nwith each other. In particular, a close connection between the anomalous\nscaling exponent $\\eta$, introduced in a quantum-field theoretic approach, and\nconservation-law induced scaling in classical phase-ordering kinetics is\nrevealed. Moreover, the relation to superfluid turbulence as well as to driven\nstationary systems is discussed.",
        "positive": "Synthetic gauge fields stabilize a chiral spin liquid phase: We calculate the phase diagram of the SU($N$) Hubbard model describing\nfermionic alkaline earth atoms in a square optical lattice with on-average one\natom per site, using a slave-rotor mean-field approximation. We find that the\nchiral spin liquid predicted for $N\\ge5$ and large interactions passes through\na fractionalized state with a spinon Fermi surface as interactions are\ndecreased before transitioning to a weakly interacting metal. We also show that\nby adding an artificial uniform magnetic field with flux per plaquette\n$2\\pi/N$, the chiral spin liquid becomes the ground state for all $N\\ge 3$ at\nlarge interactions, persists to weaker interactions, and its spin gap\nincreases, suggesting that the spin liquid physics will persist to higher\ntemperatures. We discuss potential methods to realize the artificial gauge\nfields and detect the predicted phases."
    },
    {
        "anchor": "Production of quantum degenerate mixtures of ytterbium and lithium with\n  controllable inter-species overlap: Quantum degenerate mixtures of alkali and spin-singlet atoms form the\nstarting point for studying few- and many-body physics of mass-imbalanced pairs\nas well as the production of paramagnetic polar molecules. We recently reported\nthe achievement of dual-species quantum degeneracy of a mixture of lithium and\nytterbium atoms. Here we present details of the key experimental steps for the\nall-optical preparation of these mixtures. Further we demonstrate the use of\nthe magnetic field gradient tool to compensate for the differential\ngravitational sag of the two species and control their spatial overlap.",
        "positive": "Anomalous localization and multifractality in a kicked quasicrystal: Multifractal states offer a \"third way\" for quantum matter, neither fully\nlocalized nor ergodic, exhibiting singular continuous spectra, self-similar\nwavefunctions, and transport and entanglement scaling exponents intermediate\nbetween extended and localized states. While multifractality in equilibrium\nsystems generally requires fine-tuning to a critical point, externally driven\nquantum matter can exhibit multifractal states with no equilibrium counterpart.\nWe report the experimental observation of multifractal matter and anomalous\nlocalization in a kicked Aubry-Andr\\'e-Harper quasicrystal. Our cold-atom\nrealization of this previously-unexplored model is enabled by apodized Floquet\nengineering techniques which expand the accessible phase diagram by five orders\nof magnitude. This kicked quantum quasicrystal exhibits a rich phase diagram\nincluding not only fully localized and fully delocalized phases but also an\nextended region comprising an intricate nested pattern of localized,\ndelocalized, and multifractal states. Mapping transport properties throughout\nthe phase diagram, we observe disorder-driven re-entrant delocalization and\nsub-ballistic transport, and present a theoretical explanation of these\nphenomena based on eigenstate multifractality. These results open up the\nexploration of new states of matter characterized by an intricate interplay of\nfractal structure and quantum dynamics."
    },
    {
        "anchor": "Bright soliton dynamics in Spin Orbit-Rabi coupled Bose-Einstein\n  condensates: We investigate the dynamics of a spin-orbit (SO) coupled BECs in a time\ndependent harmonic trap and show the dynamical system to be completely\nintegrable by constructing the Lax pair. We then employ gauge transformation\napproach to witness the rapid oscillations of the condensates for a relatively\nsmaller value of SO coupling in a time independent harmonic trap compared to\ntheir counterparts in a transient trap. Keeping track of the evolution of the\ncondensates in a transient trap during its transition from confining to\nexpulsive trap, we notice that they collapse in the expulsive trap. We further\nshow that one can manipulate the scattering length through Feshbach resonance\nto stretch the lifetime of the confining trap and revive the condensate.\nConsidering a SO coupled state as the initial state, the numerical simulation\nindicates that the reinforcement of Rabi coupling on SO coupled BECs generates\nthe striped phase of the bright solitons and does not impact the stability of\nthe condensates despite destroying the integrability of the dynamical system.",
        "positive": "Feshbach spectroscopy and analysis of the interaction potentials of\n  ultracold sodium: We have studied magnetic Feshbach resonances in an ultracold sample of Na\nprepared in the absolute hyperfine ground state. We report on the observation\nof three s-, eight d-, and three g-wave Feshbach resonances, including a more\nprecise determination of two known s-wave resonances, and one s-wave resonance\nat a magnetic field exceeding 200mT. Using a coupled-channels calculation we\nhave improved the sodium ground-state potentials by taking into account these\nnew experimental data, and derived values for the scattering lengths. In\naddition, a description of the molecular states leading to the Feshbach\nresonances in terms of the asymptotic-bound-state model is presented."
    },
    {
        "anchor": "Quantum Monte Carlo study of strongly interacting bosonic\n  one-dimensional systems in periodic potentials: We present diffusion Monte Carlo (DMC) and path-integral Monte Carlo (PIMC)\ncalculations of a one-dimensional Bose system with realistic interparticle\ninteractions in a periodic external potential. Our main aim is to test the\npredictions of the Luttinger liquid (LL) theory, in particular with respect to\nthe superfluid-Mott insulator transition at both zero and finite temperatures,\nin the predicted robust and fragile superfluid regimes. For that purpose, we\npresent our results of the superfluid fraction $\\rho_s/\\rho_0$, the one-body\ndensity matrix, the two-body correlation functions, and the static structure\nfactor. The DMC and PIMC results in the limit of very low temperature for\n$\\rho_s/\\rho_0$ agree, but the LL model for scaling $\\rho_s/\\rho_0$ does not\nfit the data well. The critical depth of the periodic potential is close to the\nvalues obtained for ultracold gases with different models of interaction, but\nwith the same value of the bare LL parameter, demonstrating the universality of\nLL description. Algebraic decay of correlation functions is observed in the\nsuperfluid regime and exponential decay in the Mott-insulator one, as well as\nin all regimes at finite temperature for distances larger than a characteristic\nlength.",
        "positive": "Low-dimensional physics of ultracold gases with bound states and the\n  sine-Gordon model: One-dimensional systems of interacting atoms are an ideal laboratory to study\nthe Kosterlitz-Thouless phase transition. In the renormalization group picture\nthere is essentially a two-parameter phase diagram to explore. We first present\nhow detailed experiments have shown direct evidence for the theoretical\ntreatment of this transition. Then generalization to the case of two-component\nsystems with bound state formation is discussed. Trimer formation in the\nasymmetric attractive Hubbard model involve in a crucial way this kind of\nphysics."
    },
    {
        "anchor": "Signature of existence of a BEC-type state in a dilute gas above the BEC\n  transition temperature: We study quantum coherence properties of a dilute gas at temperatures above,\nbut not much above the transition temperature of Bose-Einstein condensation\n(BEC). In such a gas, a small proportion of the atoms may possess coherence\nlengths longer than the mean neighboring-atomic distance, implying the\nexistence of quantum coherence more than that expected for thermal atoms.\nConjecturing that a part of this proportion of the atoms may lie in a BEC-type\nstate, some unexplained experimental results [Phys. Rev. A, 71, 043615 (2005)]\ncan be explained.",
        "positive": "Al'tshuler-Aronov-Spivak oscillations of bosonic matter-wave beams in\n  the presence of interaction: We theoretically study the propagation of a guided atom laser across an\nAharonov-Bohm ring which is exposed to a synthetic gauge field. The presence of\ndisorder within the ring gives rise to Al'tshuler-Aronov-Spivak oscillations,\nseen in the disorder average of the transmission as a function of the effective\ngauge flux that is contained within the ring. Those oscillations are induced by\ncoherent backscattering and represent a manifestation of weak localization.\nThrough analytical and numerical calculations that are based on the mean-field\nGross-Pitaevskii approximation for the propagating Bose-Einstein condensate, we\nshow that the presence of a very weak atom-atom interaction within the ring\nleads to an inversion of the Al'tshuler-Aronov-Spivak oscillations, in a very\nsimilar manner as for the coherent backscattering of Bose-Einstein condensates\nwithin two-dimensional disorder potentials. Numerical simulations based on the\nTruncated Wigner method reveal that this signature of weak antilocalization\nbecomes washed out if the interaction strength is increased."
    },
    {
        "anchor": "Signature of Quantum Criticality in the Density Profiles of Cold Atom\n  Systems: In recent years, there is considerable experimental effort using cold atoms\nto study strongly correlated many-body systems. One class of phenomena of\nparticularly interests is quantum critical (QC) phenomena. While prevalent in\nmany materials, these phenomena are notoriously difficult theoretical problems\ndue to the vanishing of energy scales in QC region. So far, there are no\nsystematic ways to deduce QC behavior of bulk systems from the data of trapped\natomic gases. Here, we present a simple algorithm to use the experimental\ndensity profile to determine the T=0 phase boundary of bulk systems, as well as\nthe scaling functions in QC regime. We also present another scheme for removing\nfinite size effects of the trap. We demonstrate the validity of our schemes\nusing exactly soluble models.",
        "positive": "Superfluid stiffness for the attractive Hubbard model on a honeycomb\n  optical lattice: In addition to the conventional contribution that is directly controlled by\nthe single-particle energy spectrum, the superfluid phase stiffness of a\ntwo-component Fermi gas has a geometric contribution that is governed by the\nquantum metric of the honeycomb's band structure. Here, we take both\ncontributions into account, and construct phase diagrams for the critical\nsuperfluid transition temperature as a function of the chemical potential,\nparticle filling, onsite interaction and next-nearest-neighbor hopping. Our\ntheoretical approach is based on a self-consistent solution of the BCS\nmean-field theory for the stationary Cooper pairs and the universal BKT\nrelation for the phase fluctuations."
    },
    {
        "anchor": "Dispersive detection of atomic ensembles in the presence of strong\n  lensing: We experimentally and theoretically investigate in-medium propagation effects\nof off-resonant light in dense, spatially homogeneous ultacold atomic gases.\nFocussing on frequency modulation spectroscopy as the dispersive detection tool\nof atoms, we observe that the refractive gradient-index lenses presented by\nlocalised atomic ensembles can significantly modify the interpretation of the\ndispersive signal even for large probe detuning, owing to the collective\ndispersive response of the atoms. We identify criteria for distinguishing\nbetween thin and thick atomic lenses, leading to either diffraction-dominated\nand lensing dominated regimes for the outgoing probe beams. Our findings are\nconsistent with experimental data and solutions of paraxial wave equation for\nlight propagation. Our study provides important practical insights for\ndispersive, minimally intrusive optical detection and imaging schemes of\nultracold atoms and will be valuable for choosing optimal parameter regimes in\nnumerous applications.",
        "positive": "Quantum effective action for the bosonic Josephson junction: We investigate a bosonic Josephson junction by using the path-integral\nformalism with relative phase and population imbalance as dynamical variables.\nWe derive an effective only-phase action performing functional integration over\nthe population imbalance. We then analyze the quantum effective only-phase\naction, which formally contains all the quantum corrections. To the second\norder in the derivative expansion and to the lowest order in $\\hbar$, we obtain\nthe quantum correction to the Josephson frequency of oscillation. Finally, the\nsame quantum correction is found by adopting an alternative approach. Our\npredictions are a useful theoretical tool for experiments with atomic or\nsuperconducting Josephson junctions."
    },
    {
        "anchor": "Non-Hamiltonian Dynamics of Quantized Vortices in Bose-Einstein\n  Condensates: The dynamics of quantized vortices in weakly interacting superfluids are\noften modeled by a nonlinear Schr\\\"odinger equation. In contrast, we show that\nquantized vortices in fact obey a non-Hamiltonian evolution equation, which\nenhances dispersion along the vortex line while introducing a gain mechanism.\nThis allows the vortex medium to support a helical shock front propagating\nahead of a dissipative soliton. This dynamic relaxes localized curvature events\ninto Kelvin wave packets. Consequently, a beyond local induction model provides\na pathway for decay in low-temperature quantum turbulence.",
        "positive": "Thermometry of one-dimensional Bose gases with neural networks: We design a neural network to extract and process features from absorption\nimages taken of one-dimensional Bose gases in the quasi-condensate regime.\nSpecifically, the network is trained to predict both the temperature of single\nrealizations of the system and the uncertainty thereof. For multiple\nrealizations, the individual predictions can be combined in an estimate of the\nmean temperature, improving precision. We benchmark our model on both simulated\nand experimentally measured data and compare it to the established method of\ndensity ripples thermometry. We find the predictions of the two methods\ncompatible, although the neural network reaches similar precision needing much\nfewer realizations, thus highlighting the efficiency gain achievable when\nincorporating neural networks into analysis of data from cold gas experiments.\nFurther, we study feature maps to reveal which local features of the condensate\nare extracted by the network and how said features correlate with properties of\nthe system. A similar analysis could be employed to uncover physical relations\nin more complex systems."
    },
    {
        "anchor": "Solitonic Vortices in Bose-Einstein Condensates: We analyse, theoretically and experimentally, the nature of solitonic\nvortices (SV) in an elongated Bose-Einstein condensate. In the experiment, such\ndefects are created via the Kibble-Zurek mechanism, when the temperature of a\ngas of sodium atoms is quenched across the BEC transition, and are imaged after\na free expansion of the condensate. By using the Gross-Pitaevskii equation, we\ncalculate the in-trap density and phase distributions characterizing a SV in\nthe crossover from an elongate quasi-1D to a bulk 3D regime. The simulations\nshow that the free expansion strongly amplifies the key features of a SV and\nproduces a remarkable twist of the solitonic plane due to the quantized\nvorticity associated with the defect. Good agreement is found between\nsimulations and experiments.",
        "positive": "Feynman diagrams versus Fermi-gas Feynman emulator: Precise understanding of strongly interacting fermions, from electrons in\nmodern materials to nuclear matter, presents a major goal in modern physics.\nHowever, the theoretical description of interacting Fermi systems is usually\nplagued by the intricate quantum statistics at play. Here we present a\ncross-validation between a new theoretical approach, Bold Diagrammatic Monte\nCarlo (BDMC), and precision experiments on ultra-cold atoms. Specifically, we\ncompute and measure with unprecedented accuracy the normal-state equation of\nstate of the unitary gas, a prototypical example of a strongly correlated\nfermionic system. Excellent agreement demonstrates that a series of Feynman\ndiagrams can be controllably resummed in a non-perturbative regime using BDMC.\nThis opens the door to the solution of some of the most challenging problems\nacross many areas of physics."
    },
    {
        "anchor": "The two-state Bose-Hubbard model in the hard-core boson limit:\n  Non-ergodicity and the Bose-Einstein condensation: The Bose-Einstein condensation in the hard-core boson limit (HCB) of the\nBose-Hubbard model with two local states and the particle hopping in the\nexcited band only is investigated. For the purpose of considering the\nnon-ergodicity, a single-particle spectral density is calculated in the random\nphase approximation by means of the temperature boson Green functions. The\nnon-ergodic contribution to the momentum distribution function of particles\n(connected with the static density fluctuations) increases significantly and\nbecomes comparable with the ergodic contribution in the superfluid phase near\nthe tricritical point.",
        "positive": "Fractional quantum Hall states of photons in an array of dissipative\n  coupled cavities: We report a theoretical study of the collective optical response of a\ntwo-dimensional array of nonlinear cavities in the impenetrable photon regime\nunder a strong artificial magnetic field. Taking advantage of the\nnon-equilibrium nature of the photon gas, we propose an experimentally viable\nall-optical scheme to generate and detect strongly correlated photon states\nwhich are optical analogs of the Laughlin states of fractional quantum Hall\nphysics."
    },
    {
        "anchor": "Non-equilibrium scale invariance and shortcuts to adiabaticity in a\n  one-dimensional Bose gas: We present experimental evidence for scale invariant behaviour of the\nexcitation spectrum in phase-fluctuating quasi-1d Bose gases after a rapid\nchange of the external trapping potential. Probing density correlations in free\nexpansion, we find that the temperature of an initial thermal state scales with\nthe spatial extension of the cloud as predicted by a model based on adiabatic\nrescaling of initial eigenmodes with conserved quasiparticle occupation\nnumbers. Based on this result, we demonstrate that shortcuts to adiabaticity\nfor the rapid expansion or compression of the gas do not induce additional\nheating.",
        "positive": "Probing the BCS-BEC crossover with persistent currents: We study the persistent currents of an attractive Fermi gas confined in a\ntightly-confining ring trap and subjected to an artificial gauge field all\nthrough the BCS-BEC crossover. At weak attractions, on the BCS side, fermions\ndisplay a parity effect in the persistent currents, ie their response to the\ngauge field is paramagnetic or diamagnetic depending on the number of pairs on\nthe ring. At resonance and on the BEC side of the crossover we find a doubling\nof the periodicity of the ground-state energy as a function of the artificial\ngauge field and disappearance of the parity effect, indicating that persistent\ncurrents can be used to infer the formation of tightly-bound bosonic pairs. Our\npredictions can be accessed in ultracold atoms experiments through noise\ninterferograms."
    },
    {
        "anchor": "Ion-induced interactions in a Tomonaga-Luttinger liquid: We investigate the physics of a Tomonaga-Luttinger liquid of spin-polarized\nfermions superimposed on an ion chain. This compound system features\n(attractive) long-range interspecies interactions. By means of density matrix\nrenormalization group techniques we compute the Tomonaga-Luttinger-liquid\nparameter and speed of sound as a function of the relative atom/ion density and\nthe two quantum defect parameters, namely, the even and odd short-range phases\nwhich characterize the short-range part of the atom-ion polarization potential.\nThe presence of ions is found to allow critical tuning of the atom-atom\ninteraction, and the properties of the system are found to depend significantly\non the short-range phases due to the atom-ion interaction. These latter\ndependencies can be controlled, for instance, by manipulating the ions'\ninternal state. This allows modification of the static properties of the\nquantum liquid via external driving of the ionic impurities.",
        "positive": "Superfluid-quasicrystal in a Bose-Einstein condensate: Quasicrystal is a class of ordered structures defying conventional\nclassification of solid crystals and may carry classically forbidden (e.g.,\n5-fold) rotational symmetries. In view of long-sought supersolids, a natural\nquestion is whether a superfluid can spontaneously form quasicrystalline order\nthat is not possessed by the underlying Hamiltonian, forming\n\"superfluid-quasicrystals\". Here we show that a superfluid-quasicrystal stripe\nstate with the minimal 5-fold rotational symmetry can be realized as the ground\nstate of a Bose-Einstein condensate within a practical experimental scheme.\nThere exists a rich phase diagram consisting of various\nsuperfluid-quasicrystal, supersolid, and plane-wave phases. Our scheme can be\ngeneralized for generating other higher-order (e.g., 7-fold) quasicrystal\nstates, and provides a platform for investigating such new exotic quantum\nmatter."
    },
    {
        "anchor": "Expansion dynamics of a shell-shaped Bose-Einstein condensate: Bose-Einstein condensates (BECs) confined on shell-shaped surfaces have been\nproposed as a platform for exploring many nontrivial quantum phenomena on\ncurved spaces. However, as the shell-shaped trapping potential generated with\nthe conventional radio frequency dressing method is very sensitive to gravity,\nso far experimental studies of shell BECs can only be performed in\nmicro-gravity environments. Here, we overcome this difficulty and create a\nshell BEC in the presence of Earth's gravity with immiscible dual-species BECs\nof sodium and rubidium atoms. After minimizing the displacement between the\ncenters of mass of the two BECs with a magic-wavelength optical dipole trap,\nthe interspecies repulsive interaction ensures the formation of a closed shell\nof sodium atoms with its center filled by rubidium atoms. Releasing the double\nBEC together from the trap, we observe explosion of the filled shell\naccompanied by energy transfer from the inner BEC to the shell BEC. With the\ninner BEC removed, we obtain a hollow shell BEC which shows self-interference\nas a manifestation of implosion. Our results pave an alternative way for\ninvestigating many of the intriguing physics offered by shell BECs.",
        "positive": "Transverse spin dynamics in the anisotropic Heisenberg model realized\n  with ultracold atoms: In Heisenberg models with exchange anisotropy, transverse spin components are\nnot conserved and can decay not only by transport, but also by dephasing. Here\nwe utilize ultracold atoms to simulate the dynamics of 1D Heisenberg spin\nchains, and observe fast, local spin decay controlled by the anisotropy.\nAdditionally, we directly observe an effective magnetic field created by\nsuperexchange which causes an inhomogeneous decay mechanism due to variations\nof lattice depth between chains, as well as dephasing within each chain due to\nthe twofold reduction of the effective magnetic field at the edges of the\nchains and due to fluctuations of the effective magnetic field in the presence\nof mobile holes. The latter is a new coupling mechanism between holes and\nmagnons. All these dephasing mechanisms, corroborated by extensive numerical\nsimulations, have not been observed before with ultracold atoms and illustrate\nbasic properties of the underlying Hubbard model."
    },
    {
        "anchor": "Critical dynamics at the Anderson localization mobility edge: We study the critical dynamics of matter waves at the 3D Anderson mobility\nedge in cold-atom disorder quench experiments. General scaling arguments are\nsupported by precision numerics for the spectral function, diffusion\ncoefficient, and localization length in isotropic blue-detuned speckle\npotentials. We discuss signatures of critical slowdown in the time-dependent\ncentral column density of a spreading wave packet, and evaluate the prospects\nof observing anomalous diffusion right at criticality.",
        "positive": "Bridging Effective Field Theories and Generalized Hydrodynamics: Generalized Hydrodynamics (GHD) has recently been devised as a method to\nsolve the dynamics of integrable quantum many-body systems beyond the\nmean-field approximation. In its original form, a major limitation is the\ninability to predict equal-time correlations. Here we present a new method to\ntreat thermal fluctuations of a 1D bosonic degenerate gas within the GHD\nframework. We show how the standard results using the thermodynmaic Bethe\nansatz can be obtained through sampling of collective bosonic excitations,\nrevealing the connection or duality between GHD and effective field theories\nsuch as the standard hydrodynamic equations. As an example, we study the\ndamping of a coherently excited density wave and show how equal-time phase\ncorrelation functions can be extracted from the GHD evolution. Our results\npresent a conceptually new way of treating fluctuations beyond the linearized\nregime of GHD."
    },
    {
        "anchor": "Feshbach Resonance in a Synthetic Non-Abelian Gauge Field: We study the Feshbach resonance of spin-1/2 particles in the presence of a\nuniform synthetic non-Abelian gauge field that produces spin orbit coupling\nalong with constant spin potentials. We develop a renormalizable quantum field\ntheory that includes the closed channel boson which engenders the Feshbach\nresonance, in the presence of the gauge field. By a study of the scattering of\ntwo particles in the presence of the gauge field, we show that the Feshbach\nmagnetic field, where the apparent low energy scattering length diverges,\ndepends on the conserved centre of mass momentum of the two particles. For high\nsymmetry gauge fields, such as the one which produces an isotropic Rashba spin\norbit coupling, we show that the system supports two bound states over a regime\nof magnetic fields for a negative background scattering length and resonance\nwidth comparable to the energy scale of the spin orbit coupling. We discuss the\nconsequences of these findings for the many body setting, and point out that a\nbroad resonance (width larger than spin orbit coupling energy scale) is most\nfavourable for the realization of the rashbon condensate.",
        "positive": "Observation of Dynamical Super Efimovian Expansion in a Unitary Fermi\n  Gas: We report an observation of a dynamical super Efimovian expansion in a\ntwo-component strongly interacting Fermi gas by engineering time dependent\nexternal harmonic trap frequencies. When trap frequency is followed as\n$[1/4t^2+1/t^2\\lambda\\log(t/t_*)]^{1/2}$, where $t_*$ and $\\lambda$ are two\ncontrol parameters, and the change is faster than a critical value, the\nexpansion of such the quantum gas shows a novel dynamics due to its spatial and\ndynamical scaling symmetry. A clear double-log periodicity, which is a hallmark\nof the super Efimov effect, is emergent for the cloud size in the expansion.\nThe universality of such scaling dynamics is verified both in the\nnon-interacting limit and in the unitarity limit. Observing super-Efmovian\nevolution represents a paradigm in probing universal properties and allows in a\nnew way to study many-body nonequilibrium dynamics with experiments."
    },
    {
        "anchor": "Nonlinear corrections in the quantization of a weakly nonideal Bose gas\n  at zero temperature. II. The general case: In the present paper, discussion of the canonical quantization of a weakly\nnonideal Bose gas at zero temperature within the framework of the Bogolyubov\napproach is continued. Contrary to the previous paper on this subject, here the\ntwo-body interaction potential is considered in the general form. It is shown\nthat in such a case consideration of the first nonlinear correction also leads\nto the automatic particle number conservation without any additional\nassumptions or modification of the resulting effective Hamiltonian.",
        "positive": "The BCS-BEC crossover: From ultra-cold Fermi gases to nuclear systems: This report adresses topics and questions of common interest in the fields of\nultra-cold gases and nuclear physics in the context of the BCS-BEC crossover.\nThe BCS-BEC crossover has recently been realized experimentally, and\nessentially in all of its aspects, with ultra-cold Fermi gases. This\nrealization, in turn, has raised the interest of the nuclear physics community\nin the crossover problem, since it represents an unprecedented tool to test\nfundamental and unanswered questions of nuclear many-body theory. Here, we\nfocus on the several aspects of the BCS-BEC crossover, which are of broad joint\ninterest to both ultra-cold Fermi gases and nuclear matter, and which will\nlikely help to solve in the future some open problems in nuclear physics\n(concerning, for instance, neutron stars). Similarities and differences\noccurring in ultra-cold Fermi gases and nuclear matter will then be emphasized,\nnot only about the relative phenomenologies but also about the theoretical\napproaches to be used in the two contexts. After an introduction to present the\nkey concepts of the BCS-BEC crossover, this report discusses the mean-field\ntreatment of the superfluid phase, both for homogeneous and inhomogeneous\nsystems, as well as for symmetric (spin- or isospin-balanced) and asymmetric\n(spin- or isospin-imbalanced) matter. Pairing fluctuations in the normal phase\nare then considered, with their manifestations in thermodynamic and dynamic\nquantities. The last two Sections provide a more specialized discussion of the\nBCS-BEC crossover in ultra-cold Fermi gases and nuclear matter, respectively.\nThe separate discussion in the two contexts aims at cross communicating to both\ncommunities topics and aspects which, albeit arising in one of the two fields,\nshare a strong common interest."
    },
    {
        "anchor": "Microscopic evolution of doped Mott insulators from polaronic metal to\n  Fermi liquid: The competition between antiferromagnetism and hole motion in two-dimensional\nMott insulators lies at the heart of a doping-dependent transition from an\nanomalous metal to a conventional Fermi liquid. Condensed matter experiments\nsuggest charge carriers change their nature within this crossover, but a\ncomplete understanding remains elusive. We observe such a crossover in\nFermi-Hubbard systems on a cold-atom quantum simulator and reveal the\ntransformation of multi-point correlations between spins and holes upon\nincreasing doping at temperatures around the superexchange energy. Conventional\nobservables, such as spin susceptibility, are furthermore computed from the\nmicroscopic snapshots of the system. Starting from a magnetic polaron regime,\nwe find the system evolves into a Fermi liquid featuring incommensurate\nmagnetic fluctuations and fundamentally altered correlations. The crossover is\ncompleted for hole dopings around $30\\%$. Our work benchmarks theoretical\napproaches and discusses possible connections to lower temperature phenomena.",
        "positive": "Energetics of three interacting mass-imbalanced bodies in a\n  three-dimensional spherical harmonic trap: We consider a system of three particles, either three identical bosons or two\nidentical fermions plus an impurity, within a three-dimensional isotropic trap\ninteracting via a contact interaction. Using two approaches, one using an\ninfinite sum of basis states for the wavefunction and the other a closed form\nwavefunction, we calculate the allowable energy eigenstates of the system as a\nfunction of the interaction strength, including the strongly and weakly\ninteracting limits. For the fermionic case this is done while maintaining\ngenerality regarding particle masses. We find that the two methods of\ncalculating the spectrum are in excellent agreement in the strongly interacting\nlimit. However the infinite sum approach is unable to uniquely specify the\nenergy of Efimov states, but in the strongly interacting limit there is, to a\nhigh degree of accuracy, a correspondence between the three-body parameter\nrequired by the boundary condition of the closed form approach and the\nsummation truncation order required by the summation approach. This\nspecification of the energies and wavefunctions forms the basis with which\nthermodynamic variables such as the virial coefficients or Tan contacts, or\ndynamic phenomena like quench dynamics can be calculated."
    },
    {
        "anchor": "Optical Lattice Emulators: Bose and Fermi Hubbard Models: This chapter is a pedagogical review of the Hubbard model for bosons with\nrepulsion and for fermions with attraction and repulsion primarily using two\nmethods, one chosen for its simplicity and insights (mean field theory) and the\nother chosen for its accuracy and reliability (quantum Monte Marlo methods).\nFrom a comparison of the two methods we glean valuable information into the\neffects of fluctuations that dominate quantum phase transitions. The chapter\nincludes an in-depth comparison with experiments. We conclude with a discussion\nof future developments where the technical methods expounded on here, mean\nfield theory and quantum Monte Carlo, could be useful.",
        "positive": "The Stochastic Gross-Pitaevskii Methodology: We review the stochastic Gross-Pitaevskii approach for non-equilibrium finite\ntemperature Bose gases, focussing on the formulation of Stoof; this method\nprovides a unified description of condensed and thermal atoms, and can thus\ndescribe the physics of the critical fluctuation regime. We discuss\nsimplifications of the full theory, which facilitate straightforward numerical\nimplementation, and how the results of such stochastic simulations can be\ninterpreted, including the procedure for extracting phase-coherent\n(`condensate') and density-coherent (`quasi-condensate') fractions. The power\nof this methodology is demonstrated by successful ab initio modelling of\nseveral recent atom chip experiments, with the important information contained\nin each individual realisation highlighted by analysing dark soliton decay\nwithin a phase-fluctuating condensate."
    },
    {
        "anchor": "Local energy density functional for superfluid Fermi gases from\n  effective field theory: Over the past two decades, many studies in the Density Functional Theory\ncontext revealed new aspects and properties of strongly correlated superfluid\nquantum systems in numerous configurations that can be simulated in\nexperiments. This was made possible by the generalization of the Local Density\nApproximation to superfluid systems by Bulgac in [Phys. Rev. C 65, 051305,\n(2002), Phys. Rev. A 76, 040502, (2007)]. In the presented work, we propose an\nextension of the Superfluid Local Density Approximation systematically\nimprovable and applicable to a large range of many-body quantum problems\ngetting rid of the fitting procedures of the functional parameters. It turns\nout that only the knowledge of the density dependence of the quasi-particle\nproperties, namely, the chemical potential, the effective mass, and the pairing\ngap function, are enough to obtain an explicit and accurate local functional of\nthe densities without any adjustment a posteriori. This opens the way toward an\nEffective Field Theory formulation of the Density Functional Theory in the\nsense that we obtain a universal expansion of the functional parameters\nentering in the theory as a series in pairing gap function. Finally, we discuss\npossible applications of the developed approach allowing precise analysis of\nexperimental observations. In that context, we focus our applications on the\nstatic structure properties of superfluid vortices.",
        "positive": "Symmetry-protected topological phases in lattice gauge theories:\n  topological QED$_2$: The interplay of symmetry, topology, and many-body effects in the\nclassification of possible phases of matter poses a formidable challenge that\nis attracting great attention in condensed-matter physics. Such many-body\neffects are typically induced by inter-particle interactions involving an\naction at a distance, such as the Coulomb interaction between electrons in a\nsymmetry-protected topological (SPT) phase. In this work, we show that similar\nphenomena also appear in high-energy physics, where inter-particle interactions\nare mediated by gauge bosons, and constrained by a local gauge symmetry. We\nintroduce a variant of the so-called Schwinger model, which describes quantum\nelectrodynamics in (1+1) dimensions (QED$_2$), and show that it can host SPT\nphases with a topological contribution to the vacuum {\\theta} angle, which\nleads to a new type of topological QED$_2.$ We use bosonization and\ndensity-matrix renormalization group techniques to study its rich phase diagram\nin great detail, and present a scheme for its realization in experiments of\nultra-cold atoms in optical lattices."
    },
    {
        "anchor": "Dynamics of Disordered States in the Bose-Hubbard Model with Confinement: Observations of center of mass dynamics offer a straightforward method to\nidentify strongly interacting quantum phases of atoms placed in optical\nlattices. We theoretically study the dynamics of states derived from the\ndisordered Bose-Hubbard model in a trapping potential. We find that the edge\nstates in the trap allow center of mass motion even with insulating states in\nthe center. We identify short and long-time scale mechanisms for edge state\ntransport in insulating phases. We also argue that the center of mass velocity\ncan aid in identifying a Bose-glass phase. Our zero temperature results offer\nimportant insights into mechanisms of transport of atoms in trapped optical\nlattices while putting bounds on center of mass dynamics expected at non-zero\ntemperature.",
        "positive": "Entanglement Spectroscopy and probing the Li-Haldane Conjecture in\n  Topological Quantum Matter: Topological phases are characterized by their entanglement properties, which\nis manifest in a direct relation between entanglement spectra and edge states\ndiscovered by Li and Haldane. We propose to leverage the power of synthetic\nquantum systems for measuring entanglement via the Entanglement Hamiltonian to\nprobe this relationship experimentally. This is made possible by exploiting the\nquasi-local structure of Entanglement Hamiltonians. The feasibility of this\nproposal is illustrated for two paradigmatic examples realizable with current\ntechnology, an integer quantum Hall state of non-interacting fermions on a 2D\nlattice and a symmetry protected topological state of interacting fermions on a\n1D chain. Our results pave the road towards an experimental identification of\ntopological order in strongly correlated quantum many-body systems."
    },
    {
        "anchor": "Are smooth pseudopotentials a good choice for representing short-range\n  interactions?: When seeking a numerical representation of a quantum-mechanical multiparticle\nproblem it is tempting to replace a singular short-range interaction by a\nsmooth finite-range pseudopotential. Finite basis set expansions, e.g.~in Fock\nspace, are then guaranteed to converge exponentially. The need to faithfully\nrepresent the artificial length scale of the pseudopotential, however, places a\ncostly burden on the basis set. Here we discuss scaling relations for the\nrequired size of the basis set and demonstrate the basis set convergence on the\nexample of a two-dimensional system of few fermions with short-range $s$-wave\ninteractions in a harmonic trapping potential. In particular we show that the\nnumber of harmonic-oscillator basis functions needed to reach a regime of\nexponential convergence for a Gaussian pseudopotential scales with the fourth\npower of the pseudopotential length scale, which can be improved to quadratic\nscaling when the basis functions are re-scaled appropriately. Numerical\nexamples for three fermions with up to a few hundred single-particle basis\nfunctions are presented and implications for the feasibility of accurate\nnumerical multi-particle simulations of interacting ultra-cold atom systems are\ndiscussed.",
        "positive": "Penrose-Onsager Criterion Validation in a One-Dimensional Polariton\n  Condensate: We perform quantum tomography on one-dimensional polariton condensates,\nspontaneously occurring in linear disorder valleys in a CdTe planar microcavity\nsample. By the use of optical interferometric techniques, we determine the\nfirst-order coherence function and the amplitude and phase of the order\nparameter of the condensate, providing a full reconstruction of the single\nparticle density matrix for the polariton system. The experimental data are\nused as input to theoretically test the consistency of Penrose-Onsager\ncriterion for Bose-Einstein condensation in the framework of nonequilibrium\npolariton condensates. The results confirm the pertinence and validity of the\ncriterion for a non equilibrium condensed gas."
    },
    {
        "anchor": "Quantum phases of Bose-Einstein condensates with synthetic spin -\n  orbital-angular-momentum coupling: The experimental realization of emergent spin-orbit coupling through\nlaser-induced Raman transitions in ultracold atoms paves the way for exploring\nnovel superfluid physics and simulating exotic many-body phenomena. A recent\nproposal with the use of Laguerre-Gaussian lasers enables another fundamental\ntype of coupling between spin and orbital angular momentum (SOAM) in ultracold\natoms. We hereby study quantum phases of a realistic Bose-Einstein condensate\n(BEC) with this synthetic SOAM coupling in a disk-shaped geometry, respecting\nradial inhomogeneity of the Raman coupling. We find that the experimental\nsystem naturally resides in a strongly interacting regime in which the phase\ndiagram significantly deviates from the single-particle picture. The interplay\nbetween SOAM coupling and interaction leads to rich structures in spin-resolved\nposition and momentum distributions, including a stripe phase and various types\nof immiscible states. Our results would provide a guide for an experimental\ninvestigation of SOAM-coupled BECs.",
        "positive": "Bose Condensate in the D-Dimensional Case, in Particular, for D=2.\n  Semiclassical transition to the classical thermodynamics: The number-theoretical problem of partition of an integer corresponds to\n$D=2$. This problem obeys the Bose--Eeinstein statistics, where repeated terms\nare admissible in the partition, and to the Fermi--Dirac statistics, where they\nare inadmissible. The Hougen--Watson P,Z-diagram shows that this problem splits\ninto two cases: the positive pressure domain corresponds to the Fermi system,\nand the negative, to the Bose system. This analogy can be applied to the van\nder Waals thermodynamics.\n  The thermodynamic approach is related to four potentials corresponding to the\nenergy, free energy, thermodynamic Gibbs potential, enthalpy. The important\nnotion of de Broglie's wavelength permits passing from particle to wave packet,\nin particular, to Bose and Fermi distributions.\n  Particles of ideal Bose and Fermi gases and the decay of a boson consisting\nof two fermions into separate fermions are studied. The case of finitely many\nparticles $N$ of the order of $10^2$ is considered by heuristic considerations\nlike those Fock used to derive the Hartree--Fock equation. The case of $N\\ll1$\nis studied by Gentile statistics, tropical geometry and nonstandard analysis\n(Leibnitz differential or monad). A relation for the energy of neutron\nseparation from the atomic nucleus is obtained when the atomic nucleus volume\nand de Broglie's wavelength are known. The Appendix is author's paper written\nin 1995."
    },
    {
        "anchor": "Transverse collisional instabilities of a Bose-Einstein condensate in a\n  driven one-dimensional lattice: Motivated by recent experiments, we analyse the stability of a\nthree-dimensional Bose-Einstein condensate (BEC) loaded in a periodically\ndriven one-dimensional optical lattice. Such periodically driven systems do not\nhave a thermodynamic ground state, but may have a long-lived steady state which\nis an eigenstate of a \"Floquet Hamiltonian\". We explore collisional\ninstabilities of the Floquet ground state which transfer energy into the\ntransverse modes. We calculate decay rates, finding that the lifetime scales as\nthe inverse square of the scattering length and inverse of the peak three-\ndimensional density. These rates can be controlled by adding additional\ntransverse potentials.",
        "positive": "Absence of long-range order in a triangular spin system with dipolar\n  interactions: Antiferromagnetic Heisenberg model on the triangular lattice is perhaps the\nbest known example of frustrated magnets, but it orders at low temperatures.\nRecent density matrix renormalization group (DMRG) calculations find that next\nnearest neighbor interaction $J_2$ enhances the frustration and leads to a spin\nliquid for $J_2/J_1\\in (0.08,0.15)$. In addition, DMRG study of a dipolar\nHeisenberg model with longer range interactions gives evidence for a spin\nliquid at small dipole titling angle $\\theta\\in[0,10^\\circ)$. In both cases,\nthe putative spin liquid region appears to be small. Here, we show that for the\ntriangular lattice dipolar Heisenberg model, a robust quantum paramagnetic\nphase exists in a surprisingly wide region, $\\theta\\in [0,54^\\circ)$, for\ndipoles tilted along the lattice diagonal direction. We obtain the phase\ndiagram of the model by functional renormalization group (RG) which treats all\nmagnetic instabilities on equal footing. The quantum paramagnetic phase is\ncharacterized by a smooth continuous flow of vertex functions and spin\nsusceptibility down to the lowest RG scale, in contrast to the apparent\nbreakdown of RG flow in phases with stripe or spiral order. Our finding points\nto a promising direction to search for quantum spin liquids in ultracold\ndipolar molecules."
    },
    {
        "anchor": "Tunnel-coupled optical microtraps for ultracold atoms: Arrays of individual atoms trapped in optical microtraps with\nmicrometer-scale sizes have emerged as a fundamental, versatile, and powerful\nplatform for quantum sciences and technologies. This platform enables the\nbottom-up engineering of quantum systems, offering the capability of\nlow-entropy preparation of quantum states with flexible geometry, as well as\nmanipulation and detection at the single-site level. The utilization of\nultracold itinerant atoms with tunnel coupling in optical microtraps provides\nnew opportunities for quantum simulation, enabling the exploration of exotic\nquantum states, phases, and dynamics, which would otherwise be challenging to\nachieve in conventional optical lattices due to high entropy and limited\ngeometric flexibility. Here the development of tunnel-coupled optical\nmicrotraps for the manipulation of ultracold atomic quantum systems and its\nrecent advances are briefly reviewed.",
        "positive": "Acceleration of spin-orbit coupled Bose-Einstein condensates: analytical\n  description of the emergence of Landau-Zener transitions: We analytically study the effect of gravitational and harmonic forces on\nultra-cold atoms with synthetic spin-orbit coupling (SOC). In particular, we\nfocus on the recently observed transitions between internal states induced by\nacceleration of the external modes. Our description corresponds to a\ngeneralized version of the Landau-Zener (LZ) model: the dimensionality is\nenlarged to combine the quantum treatment of the external variables with the\ninternal-state characterization; additionally, atomic-interaction effects are\nconsidered. The emergence of the basic model is analytically traced. Namely, by\nusing a sequence of unitary transformations and a subsequent reduction to the\nspin space, the SOC Hamiltonian, with the gravitational potential incorporated,\nis exactly converted into the primary LZ scenario. Moreover, the transitions\ninduced by harmonic acceleration are approximately cast into the framework of\nthe basic LZ model through a complete analytical procedure. We evaluate how the\nvalidity of our picture depends on the system preparation and on the magnitude\nof atomic-interaction effects. The identification of the regime of\napplicability and the rigorous characterization of the parameters of the\neffective model provide elements to control the transitions."
    },
    {
        "anchor": "Topological Superfluids with Finite Momentum Pairing and Majorana\n  Fermions: Majorana fermions, quantum particles that are their own anti-particles, are\nnot only of fundamental importance in elementary particle physics and dark\nmatter, but also building blocks for fault-tolerant quantum computation.\nRecently Majorana fermions have been intensively studied in solid state and\ncold atomic systems. These studies are generally based on superconducting\npairing between two Fermions with opposite momenta (\\textit{% i.e.}, zero total\nmomentum). On the other hand, finite total momentum Cooper pairings, known as\nFulde-Ferrell-Larkin-Ovchinnikov (FFLO) states, were predicted 50 years ago and\nthen widely studied in many branches of physics. However, whether FFLO\nsuperconductors can also support Majorana fermions has not been explored. Here\nwe show that Majorana fermions can exist in certain types of gapped FFLO\nstates, yielding a new topological quantum matter: topological FFLO\nsuperfluids/superconductors. We demonstrate the existence of such topological\nFFLO superfluids and the associated Majorana fermions using spin-orbit coupled\ndegenerate Fermi gases and derive their physical parameter regions. The\npotential implementation of topological FFLO superconductors in\nsemiconductor/superconductor heterostructures are also discussed.",
        "positive": "Direct imaging of a digital-micromirror device for configurable\n  microscopic optical potentials: Programable spatial light modulators (SLMs) have significantly advanced the\nconfigurable optical trapping of particles. Typically, these devices are\nutilized in the Fourier plane of an optical system, but direct imaging of an\namplitude pattern can potentially result in increased simplicity and\ncomputational speed. Here we demonstrate high-resolution direct imaging of a\ndigital micromirror device (DMD) at high numerical apertures (NA), which we\napply to the optical trapping of a Bose-Einstein condensate (BEC). We utilise a\n(1200 x 1920) pixel DMD and commercially available 0.45 NA microscope\nobjectives, finding that atoms confined in a hybrid optical/magnetic or\nall-optical potential can be patterned using repulsive blue-detuned (532 nm)\nlight with 630(10) nm full-width at half-maximum (FWHM) resolution, within 5%\nof the diffraction limit. The result is near arbitrary control of the density\nthe BEC without the need for expensive custom optics. We also introduce the\ntechnique of time-averaged DMD potentials, demonstrating the ability to produce\nmultiple grayscale levels with minimal heating of the atomic cloud, by\nutilising the high switching speed (20 kHz maximum) of the DMD. These\ntechniques will enable the realization and control of diverse optical\npotentials for superfluid dynamics and atomtronics applications with quantum\ngases. The performance of this system in a direct imaging configuration has\nwider application for optical trapping at non-trivial NAs."
    },
    {
        "anchor": "Observation of self-oscillating supersonic flow across an acoustic\n  horizon in two dimensions: Understanding the dynamics and stability of transonic flows in quantum\nfluids, especially for those beyond one spatial dimension, is an outstanding\nchallenge, with applications ranging from nonlinear optics and condensed matter\nto analogue gravity. One intriguing possibility is that a system with a\nspatially bounded supersonic flow may evolve into a self-oscillating state that\nperiodically emits solitons, in a process originating from the well-known\nLandau instability. Here, we report observation of self-oscillating supersonic\nflows in a two-dimensional atomic superfluid. By imposing a local particle sink\nwith strong loss, we induce a convergent radial flow forming an acoustic\nanalogue of a black-hole horizon and an inner horizon around the sink. The\nobserved superflow appears to be modulated by quasi-periodic bursts of\nsuperluminal signals. We measure their frequencies and find agreement with\nnumerical simulations of soliton oscillation frequencies within the black-hole\nhorizon. The presented experiment demonstrates a new method for creating\nsupersonic flows in atomic superfluids, which may find applications in quantum\nsimulations of curved spacetime, supersonic turbulence, and self-oscillating\ndynamics in dissipative many-body systems.",
        "positive": "Numerical model of the Gross-Pitaevskii equation for rotating\n  Bose-Einstein condensates using smoothed-particle hydrodynamics: This study proposed a new numerical scheme for vortex lattice formation in a\nrotating Bose-Einstein condensate (BEC) using smoothed particle hydrodynamics\n(SPH) with an explicit real-time integration scheme. Specifically, the\nGross-Pitaevskii (GP) equation was described as a complex representation to\nobtain a pair of time-dependent equations, which were then solved\nsimultaneously following discretization based on SPH particle approximation. We\nadopt the 4th-order Runge-Kutta method for time evolution. We performed\nsimulations of a rotating Bose gas trapped in a harmonic potential, showing\nresults that qualitatively agreed with previously reported experiments and\nsimulations. The geometric patterns of formed lattices were successfully\nreproduced for several cases, for example, the hexagonal lattice observed in\nthe experiments of rotating BECs. Consequently, it was confirmed that the\nsimulation began with the periodic oscillation of the condensate, which\nattenuated and maintained a stable rotation with slanted elliptical shapes;\nhowever, the surface was excited to be unstable and generated ripples, which\ngrew into vortices and then penetrated the inside the condensate, forming a\nlattice. We confirmed that each branch point of the phase of wavefunctions\ncorresponds to each vortex. These results demonstrate our approach at a certain\ndegree of accuracy. In conclusion, we successfully developed a new SPH scheme\nfor the simulations of vortex lattice formation in rotating BECs."
    },
    {
        "anchor": "A simple and efficient all-optical production of spinor condensates: We present a simple and optimal experimental scheme for an all-optical\nproduction of a sodium spinor Bose-Einstein condensate (BEC). With this scheme,\nwe demonstrate that the number of atoms in a pure BEC can be greatly boosted by\na factor of 5 in a simple setup that includes a single-beam optical trap or a\ncrossed optical trap. This optimal scheme avoids technical challenges\nassociated with some all-optical BEC methods, and can be applied to other\noptically trappable atomic species. In addition, we find a good agreement\nbetween our theoretical model and data. The upper limit for the efficiency of\nevaporative cooling in all-optical BEC approaches is also discussed.",
        "positive": "The evolution from BCS to BEC superfluidity in the presence of disorder: We describe the effects of disorder on the critical temperature of $s$-wave\nsuperfluids from the BCS to the BEC regime, with direct application to\nultracold fermions. We use the functional integral method and the replica\ntechnique to study Gaussian correlated disorder due to impurities, and we\ndiscuss how this system can be generated experimentally. In the absence of\ndisorder, the BCS regime is characterized by pair breaking and phase coherence\ntemperature scales which are essentially the same allowing strong correlations\nbetween the amplitude and phase of the order parameter for superfluidity. As\nnon-pair breaking disorder is introduced the largely overlapping Cooper pairs\nconspire to maintain phase coherence such that the critical temperature remains\nessentially unchanged, and Anderson's theorem is satisfied. However in the BEC\nregime the pair breaking and phase coherence temperature scales are very\ndifferent such that non-pair breaking disorder can affect dramatically phase\ncoherence, and thus the critical temperature, without the requirement of\nbreaking tightly-bound fermion pairs simultaneously. In this case, Anderson's\ntheorem does not apply, and the critical temperature can be more easily reduced\nin comparison to the BCS limit. Lastly, we find that the superfluid is more\nrobust against disorder in the intermediate region near unitarity between the\ntwo regimes."
    },
    {
        "anchor": "Solitons and solitary vortices in \"pancake\"-shaped Bose-Einstein\n  condensates: We study fundamental and vortical solitons in disk-morphed Bose-Einstein\ncondensates (BECs) subject to strong confinement along the axial direction.\nStarting from the three-dimensional (3D) Gross-Pitaevskii equation (GPE), we\nproceed to an effective 2D nonpolynomial Schroeodinger equation (NPSE) derived\nby means of the integration over the axial coordinate. Results produced by the\nlatter equation are in very good agreement with those obtained from the full 3D\nGPE, including cases when the formal 2D equation with the cubic nonlinearity is\nunreliable. The 2D NPSE is used to predict density profiles and dynamical\nstability of repulsive and attractive BECs with zero and finite topological\ncharge in various planar trapping configurations, including the axisymmetric\nharmonic confinement and 1D periodic potential. In particular, we find a stable\ndynamical regime that was not reported before, viz., periodic splitting and\nrecombination of trapped vortices with topological charge 2 or 3 in the\nself-attractive BEC.",
        "positive": "Propagation of First and Second Sound in a Highly-Elongated Trapped Bose\n  Condensed Gas at Finite temperatures: We study sound propagation in Bose-condensed gases in a highly-elongated\nharmonic trap at finite temperatures. This problem is studied within the\nframework of Zaremba-Nikuni-Griffin (ZNG) formalism, which consistent of a\ngeneralized Gross-Pitaevskii (GP) equation for the condensate and the kinetic\nequation for a thermal cloud. We extend the ZNG formalism to deal with a\nhighly-anisotropic trap potential, and use it to simulate sound propagation\nusing the trap parameters corresponding to the experiment on sound pulse\npropagation at finite temperature. We focus on the high-density two-fluid\nhydrodynamic regime, and explore the possibility of observing first and second\nsound pulse propagation. The results of numerical simulation are compared with\nan analyitical results derived from linearized ZNG hydrodynamic equations. We\nshow that the second sound mode makes a dominant contribution to condensate\nmotion in relatively high temperature, while the first sound mode makes an\nappreciable contribution."
    },
    {
        "anchor": "A Superradiant Topological Peierls Insulator inside an Optical Cavity: We consider a spinless ultracold Fermi gas tightly trapped along the axis of\nan optical resonator and transversely illuminated by a laser closely tuned to a\nresonator mode. At a certain threshold pump intensity the homogeneous gas\ndensity breaks a $\\mathbf{Z}_2$ symmetry towards a spatially periodic order,\nwhich collectively scatters pump photons into the cavity. We show that this\nknown self-ordering transition also occurs for low field seeking fermionic\nparticles when the laser light is blue-detuned to an atomic transition. The\nemergent superradiant optical lattice in this case is homopolar and possesses\ntwo distinct dimerizations. Depending on the spontaneously chosen dimerization\nthe resulting Bloch bands can have a non-trivial topological structure\ncharacterized by a non-vanishing Zak phase. In the case the Fermi momentum is\nclose to half the cavity-mode wavenumber, a Peierls-like instability here\ncreates a topoloical insulator with a gap at the Fermi surface, which hosts a\npair of edge states. The topological features of the system can be\nnon-destructively observed via the cavity output: the Zak phase of the bulk\ncoincides with the relative phase between laser and cavity field, while the\nfingerprint of edge states can be observed as additional broadening in a well\ndefined frequency window of the cavity spectrum.",
        "positive": "Cubic-quintic nonlinearity in superfluid Bose-Bose mixtures in optical\n  lattices: Heavy solitary waves, barrier-induced criticality, and\n  current-phase relations: We study superfluid (SF) states of strongly interacting Bose-Bose mixtures\nwith equal mass and intra-component interaction in optical lattices both in the\npresence and absence of a barrier potential (BP). We show that the SF order\nparameters obey the two-component nonlinear Schroedinger equation (NLSE) with\nnot only cubic but also quintic nonlinearity in the vicinity of the first-order\ntransitions to the Mott insulators with even fillings. In the case of no BP, we\nanalyze solitary-wave (SW) solutions of the cubic-quintic NLSE. When the SF\nstate changes from a ground state to a metastable one, a standard dark SW turns\ninto a bubble-like dark SW, which has a non-vanishing density dip and no pi\nphase kink even in the case of a standing SW. It is shown that the former and\nlatter SW are dynamically unstable against an out-of-phase fluctuation and an\nin-phase fluctuation, respectively, and the dynamical instabilities are\nweakened when one approaches the transition point. We find that the size and\nthe inertial mass of the SW diverge at the first-order transition point. We\nsuggest that the divergence of the inertial mass may be detected through\nmeasurement of the relation between the velocity and the phase jump of the SW.\nIn the presence of BP, we reveal that when the barrier strength exceeds a\ncertain critical value, the SF state that was metastable without the barrier is\ndestabilized towards complete disjunction of the SF. The presence of the\ncritical BP strength indicates that the strong BP qualitatively changes the\ncriticality near the metastability limit of the SF state. We derive critical\nbehaviors of the density, the compressibility, and the critical current near\nthe metastability limit induced by the BP. It is also found that the relation\nbetween the supercurrent and the phase jump across the BP exhibits a peculiar\nbehavior, owing to the non-topological nature of the bubble-like SW."
    },
    {
        "anchor": "Exploring ultracold collisions in $^6$Li-$^{53}$Cr Fermi mixtures:\n  Feshbach resonances and scattering properties of a novel alkali-transition\n  metal system: We investigate ultracold collisions in a novel mixture of $^6$Li and\n$^{53}$Cr fermionic atoms, discovering more than 50 interspecies Feshbach\nresonances via loss spectroscopy. Building a full coupled-channel model, we\nunambiguously characterize the $^{6}$Li-$^{53}$Cr scattering properties and\nyield predictions for other isotopic pairs. In particular, we identify various\nFeshbach resonances that enable the controlled tuning of elastic $s$- and\n$p$-wave $^{6}$Li-$^{53}$Cr interactions. Our studies thus make\nlithium-chromium mixtures emerge as optimally-suited platforms for the\nexperimental search of elusive few- and many-body regimes of highly-correlated\nfermionic matter, and for the realization of a new class of ultracold polar\nmolecules possessing both electric and magnetic dipole moments.",
        "positive": "Dynamics of quantum vortices at finite temperature: In this thesis, we perform investigations into the behaviour of\nfinite-temperature degenerate Bose gases using a classical-field formalism,\nfocussing in particular on the dynamics of quantum vortices in these systems.\nWe demonstrate that the coherence of the classical field can be characterised\nby its temporal correlations, and discuss how the phase-symmetry-broken\naverages familiar from mean-field theories emerge from the field trajectories.\nWe show that a finite-temperature condensate containing a precessing vortex in\na cylindrically symmetric trap can be realised as an ergodic equilibrium of the\nclassical-field theory, and demonstrate the identification of the rotationally\nsymmetry-broken condensate orbital and core-filling thermal component from the\nfield correlations. We then consider the nonequilibrium dynamics that result\nwhen such a precessing-vortex configuration is subjected to a static trap\nanisotropy which arrests its rotation, and observe novel coupled relaxation\ndynamics of the condensed and noncondensed components of the field. Finally, we\nconsider the nucleation of vortices in an initially zero-temperature\nquasi-two-dimensional condensate stirred by a rotating trap anisotropy. We\nquantify the emergence of a rotating thermal component of the field, which\ndrives the nucleation of vortices from condensate-surface oscillations, and\nstudy the relaxation and rotational equilibration of the initially turbulent\ncollection of vortices. We find that thermal fluctuations of the field prevent\nthe vortices from settling into a rigid crystalline lattice in this reduced\ndimensionality, and that true condensation in the field is completely destroyed\nby the disordered motion of vortices. We show, however, that the temporal\ncorrelations of the field distinguish the quasi-coherent vortex-liquid phase in\nthe trap centre from the truly thermal material in its periphery."
    },
    {
        "anchor": "Spin-Orbit Coupled One-Dimensional Fermi Gases with Infinite Repulsion: The current efforts of studying many-body effects with spin-orbit coupling\n(SOC) using alkali-metal atoms are impeded by the heating effects due to\nspontaneous emission. Here, we show that even for SOCs too weak to cause any\nheating, dramatic many-body effects can emerge in a one-dimensional(1D) spin\n1/2 Fermi gas provided the interaction is sufficiently repulsive. For weak\nrepulsion, the effect of a weak SOC (with strength $\\Omega$) is perturbative.\ninducing a weak spin spiral (with magnitude proportional to $\\Omega$). However,\nas the repulsion $g$ increases beyond a critical value ($g_c\\sim 1/\\Omega$),\nthe magnitude of the spin spiral rises rapidly to a value of order 1\n(independent of $\\Omega$). Moreover, near $g=+\\infty$, the spins of neighboring\nfermions can interfere destructively due to quantum fluctuations of particle\nmotion, strongly distorting the spin spiral and pulling the spins substantially\naway from the direction of the local field at various locations. These effects\nare consequences of the spin-charge separation in the strongly repulsive limit.\nThey will also occur in other 1D quantum gases with higher spins.",
        "positive": "Itinerant Ferromagnetism in a Fermi Gas of Ultracold Atoms: Can a gas of spin-up and spin-down fermions become ferromagnetic due to\nrepulsive interactions? This question which has not yet found a definitive\ntheoretical answer was addressed in an experiment with an ultracold\ntwo-component Fermi gas. The observation of non-monotonic behavior of lifetime,\nkinetic energy, and size for increasing repulsive interactions provides strong\nevidence for a phase transition to a ferromagnetic state. It implies that\nitinerant ferromagnetism of delocalized fermions is possible without lattice\nand band structure and validates the most basic model for ferromagnetism\nintroduced by Stoner."
    },
    {
        "anchor": "Functional renormalization and ultracold quantum gases: The method of functional renormalization is applied to the theoretical\ninvestigation of ultracold quantum gases. Flow equations are derived for a Bose\ngas with approximately pointlike interaction, for a Fermi gas with two\n(hyperfine) spin components in the Bardeen-Cooper-Schrieffer (BCS) to\nBose-Einstein condensation (BEC) crossover and for a Fermi gas with three\ncomponents. The solution of the flow equations determine the properties of\nthese systems both in the few-body regime and in thermal equilibrium.\n  For the Bose gas this covers the quantum phase diagram, the condensate and\nsuperfluid fraction, the critical temperature, the correlation length, the\nspecific heat or sound propagation. The properties are discussed both for three\nand two spatial dimensions. The discussion of the Fermi gas in the BCS-BEC\ncrossover concentrates on the effect of particle-hole fluctuations but\naddresses the complete phase diagram. For the three component fermions, the\nflow equations in the few-body regime show a limit-cycle scaling and the Efimov\ntower of three-body bound states. Applied to the case of Lithium they explain\nrecently observed three-body loss features. Extending the calculations by\ncontinuity to nonzero density, it is found that a new trion phase separates a\nBCS and a BEC phase for three component fermions close to a common resonance.\n  More formal is the derivation of a new exact flow equation for scale\ndependent composite operators. This equation allows for example a better\ntreatment of bound states.",
        "positive": "Relaxation dynamics of half-quantum vortices in a two-dimensional\n  two-component Bose-Einstein condensate: We study the relaxation dynamics of quantum turbulence in a two-component\nBose-Einstein condensate containing half-quantum vortices. We find a temporal\nscaling regime for the number of vortices and the correlation lengths that at\nearly times is strongly dependent on the relative strength of the inter-species\ninteraction. At later times we find that the scaling becomes universal,\nindependent of the inter-species interaction, and approaches that numerically\nobserved in a scalar Bose-Einstein condensate."
    },
    {
        "anchor": "Dependence of interface conductivity on relevant physical parameters in\n  polarized Fermi mixtures: We consider a mass-asymmetric polarized Fermi system in the presence of\nHartree-Fock (HF) potentials. We concentrate on the BCS regime with various\ninteraction strengths and numerically obtain the allowed values of the chemical\nand HF potentials, as well as the mass ratio. The functional dependence of the\nheat conductivity of the N-SF interface on relevant physical parameters, namely\nthe temperature, the mass ratio, and the interaction strength, is obtained. In\nparticular, we show that the interface conductivity starts to drop with\ndecreasing temperature at the temperature, $T_{\\text{m}}$, where the mean\nkinetic energy of the particles is just sufficient to overcome the SF gap. We\nobtain $T_{\\text{m}}$ as a function of the mass ratio and the interaction\nstrength. The variation of the heat conductivity, at fixed temperature, with\nthe HF potentials and the imbalance chemical potential is also obtained.\nFinally, because the range of relevant temperatures increases for larger values\nof the mass ratio, we consider the $^6\\text{Li}$-$^{40}\\text{K}$ mixture\nseparately by taking the temperature dependence of the pair potential into\naccount.",
        "positive": "Far from equilibrium quantum magnetism with ultracold polar molecules: Recent theory has indicated how to emulate tunable models of quantum\nmagnetism with ultracold polar molecules. Here we show that present molecule\noptical lattice experiments can accomplish three crucial goals for quantum\nemulation, despite currently being well below unit filling and not quantum\ndegenerate. The first is to verify and benchmark the models proposed to\ndescribe these systems. The second is to prepare correlated and possibly useful\nstates in well-understood regimes. The third is to explore many-body physics\ninaccessible to existing theoretical techniques. Our proposal relies on a\nnon-equilibrium protocol that can be viewed either as Ramsey spectroscopy or an\ninteraction quench. It uses only routine experimental tools available in any\nultracold molecule experiment."
    },
    {
        "anchor": "Local correlations in the attractive 1D Bose gas: from Bethe ansatz to\n  the Gross-Pitaevskii equation: We consider the ground-state properties of an extended one-dimensional Bose\ngas with pointwise attractive interactions. We take the limit where the\ninteraction strength goes to zero as the system size increases at fixed\nparticle density. In this limit the gas exhibits a quantum phase transition. We\ncompute local correlation functions at zero temperature, both at finite and\ninfinite size. We provide analytic formulas for the experimentally relevant\none-point functions $g_2$, $g_3$ and analyze their finite-size corrections. Our\nresults are compared to the mean-field approach based on the Gross-Pitaevskii\nequation which yields the exact results in the infinite system size limit, but\nnot for finite systems.",
        "positive": "Ground-state properties of electron-electron biwire systems: The correlation between electrons in different quantum wires is expected to\naffect the electronic properties of quantum electron-electron biwire systems.\nHere, we use the variational Monte Carlo method to study the ground-state\nproperties of parallel, infinitely thin electron-electron biwires for several\nelectron densities ($r_\\text{s}$) and interwire separations ($d$).\nSpecifically, the ground-state energy, the correlation energy, the interaction\nenergy, the pair-correlation function (PCF), the static structure factor (SSF),\nand the momentum distribution (MD) function are calculated. We find that the\ninteraction energy increases as $\\ln(d)$ for $d\\to 0$ and it decreases as\n$d^{-2}$ when $d\\to \\infty$. The PCF shows oscillatory behavior at all\ndensities considered here. As two parallel wires approach each other, interwire\ncorrelations increase while intrawire correlations decrease as evidenced by the\nbehavior of the PCF, SSF, and MD. The system evolves from two monowires of\ndensity parameter $r_\\text{s}$ to a single monowire of density parameter\n$r_\\text{s}/2$ as $d$ is reduced from infinity to zero. The MD reveals\nTomonaga-Luttinger (TL) liquid behavior with a power-law nature near\n$k_\\text{F}$ even in the presence of an extra interwire interaction between the\nelectrons in biwire systems. It is observed that when $d$ is reduced the MD\ndecreases for $k<k_\\text{F}$ and increases for $k>k_\\text{F}$, similar to its\nbehavior with increasing $r_\\text{s}$. The TL liquid exponent is extracted by\nfitting the MD data near $k_\\text{F}$, from which the TL liquid interaction\nparameter $K_{\\rho}$ is calculated. The value of the TL parameter is found to\nbe in agreement with that of a single wire for large separation between the two\nwires."
    },
    {
        "anchor": "Seeing topological order in time-of-flight measurements: In this work we provide a general methodology to directly measure topological\norder in cold atom systems. As an application we propose the realisation of a\ncharacteristic topological model, introduced by Haldane, using optical lattices\nloaded with fermionic atoms in two internal states. We demonstrate that\ntime-of-flight measurements directly reveal the topological order of the system\nin the form of momentum space skyrmions.",
        "positive": "Strong-coupling corrections to ground-state properties of a superfluid\n  Fermi gas: We theoretically present an economical and convenient way to study\nground-state properties of a strongly interacting superfluid Fermi gas. Our\nstrategy is that complicated strong-coupling calculations are used only to\nevaluate quantum fluctuation corrections to the chemical potential $\\mu$. Then,\nwithout any further strong-coupling calculations, we calculate the\ncompressibility, sound velocity, internal energy, pressure, and Tan's contact,\nfrom the calculated $\\mu$ without loss of accuracy, by using exact\nthermodynamic identities. Using a recent precise measurement of $\\mu$ in a\nsuperfluid $^6$Li Fermi gas, we show that an extended $T$-matrix approximation\n(ETMA) is suitable for our purpose, especially in the BCS-unitary regime, where\nour results indicate that many-body corrections are dominated by superfluid\nfluctuations. Since precise determinations of physical quantities are not\nalways easy in cold Fermi gas physics, our approach would greatly reduce\nexperimental and theoretical efforts toward the understanding of ground-state\nproperties of this strongly interacting Fermi system."
    },
    {
        "anchor": "Resonant atom-dimer collisions in cesium: Testing universality at\n  positive scattering lengths: We study the collisional properties of an ultracold mixture of cesium atoms\nand dimers close to a Feshbach resonance near 550G in the regime of positive\n$s$-wave scattering lengths. We observe an atom-dimer loss resonance that is\nrelated to Efimov's scenario of trimer states. The resonance is found at a\nvalue of the scattering length that is different from a previous observation at\nlow magnetic fields. This indicates non-universal behavior of the Efimov\nspectrum for positive scattering lengths. We compare our observations with\npredictions from effective field theory and with a recent model based on the\nvan der Waals interaction. We present additional measurements on pure atomic\nsamples in order to check for the presence of a resonant loss feature related\nto an avalanche effect as suggested by observations in other atomic species. We\ncould not confirm the presence of such a feature.",
        "positive": "Phase-space distributions of Bose-Einstein condensates in an optical\n  lattice: Optimal shaping and reconstruction: We apply quantum optimal control to shape the phase-space distribution of\nBose-Einstein condensates in a one-dimensional optical lattice. By a\ntime-dependent modulation of the lattice position, determined from optimal\ncontrol theory, we prepare, in the phase space of each lattice site, translated\nand squeezed Gaussian states, and superpositions of Gaussian states. Complete\nreconstruction of these non-trivial states is performed through a maximum\nlikelihood state tomography. As a practical application of our method to\nquantum simulations, we initialize the atomic wavefunction in an optimal\nFloquet-state superposition to enhance dynamical tunneling signals."
    },
    {
        "anchor": "Mini droplet, mega droplet and stripe formation in a dipolar condensate: We demonstrate mini droplet, mega droplet and stripe formation in a dipolar\n164Dy condensate, using an improved mean-field model including a\nLee-Huang-Yang-type interaction, employing a quasi-two-dimensional (quasi-2D)\ntrap in a way distinct from that in the pioneering experiment, M. A. Norcia et.\nal., Nature 596, 357 (2021), where the polarization z direction was taken to be\nperpendicular to the quasi-2D x-y plane. In the present study we take the\npolarization z direction in the quasi-2D x-z plane. Employing the same trapping\nfrequencies as in the experiment, and interchanging the frequencies along the y\nand z directions, we find the formation of mini droplets for number of atoms N\nas small as N = 1000. With the increase of number of atoms, a\nspatially-periodic supersolid-like one-dimensional array of mega droplets\ncontaining 50000 to 200000 atoms are formed along the x direction in the x-y\nplane. These mega droplets are elongated along the polarization z direction,\nconsequently, the spatially periodic arrangement of droplets appears as a\nstripe pattern in the x-z plane. To establish the supersolidity of the droplets\nwe demonstrate continued dipole-mode and scissors-mode oscillations of the\ndroplet-lattice pattern. The main findings of the present study can be tested\nexperimentally with the present know-how.",
        "positive": "Path-integral Monte Carlo worm algorithm for Bose systems with periodic\n  boundary conditions: We provide a detailed description of the path-integral Monte Carlo worm\nalgorithm used to exactly calculate the thermodynamics of Bose systems in the\ncanonical ensemble. The algorithm is fully consistent with periodic boundary\nconditions, that are applied to simulate homogeneous phases of bulk systems,\nand it does not require any limitation in the length of the Monte Carlo moves\nrealizing the sampling of the probability distribution function in the space of\npath configurations. The result is achieved adopting a representation of the\npath coordinates where only the initial point of each path is inside the\nsimulation box, the remaining ones being free to span the entire space.\nDetailed balance can thereby be ensured for any update of the path\nconfigurations without the ambiguity of the selection of the periodic image of\nthe particles involved. We benchmark the algorithm using the non-interacting\nBose gas model for which exact results for the partition function at finite\nnumber of particles can be derived. Convergence issues and the approach to the\nthermodynamic limit are also addressed for interacting systems of hard spheres\nin the regime of high density."
    },
    {
        "anchor": "Bose polaron as an instance of quantum Brownian motion: We study the dynamics of a quantum impurity immersed in a Bose-Einstein\ncondensate as an open quantum system in the framework of the quantum Brownian\nmotion model. We derive a generalized Langevin equation for the position of the\nimpurity. The Langevin equation is an integrodifferential equation that\ncontains a memory kernel and is driven by a colored noise. These result from\nconsidering the environment as given by the degrees of freedom of the quantum\ngas, and thus depend on its parameters, e.g. interaction strength between the\nbosons, temperature, etc. We study the role of the memory on the dynamics of\nthe impurity. When the impurity is untrapped, we find that it exhibits a\nsuper-diffusive behavior at long times. We find that back-flow in energy\nbetween the environment and the impurity occurs during evolution. When the\nparticle is trapped, we calculate the variance of the position and momentum to\ndetermine how they compare with the Heisenberg limit. One important result of\nthis paper is that we find position squeezing for the trapped impurity at long\ntimes. We determine the regime of validity of our model and the parameters in\nwhich these effects can be observed in realistic experiments.",
        "positive": "Quantum Monte Carlo simulations of two-dimensional repulsive Fermi gases\n  with population imbalance: The ground-state properties of two-component repulsive Fermi gases in two\ndimensions are investigated by means of fixed-node diffusion Monte Carlo\nsimulations. The energy per particle is determined as a function of the\nintercomponent interaction strength and of the population imbalance. The regime\nof universality in terms of the s-wave scattering length is identified by\ncomparing results for hard-disk and for soft-disk potentials. In the large\nimbalance regime, the equation of state turns out to be well described by a\nLandau-Pomeranchuk functional for two-dimensional polarons. To fully\ncharacterize this expansion, we determine the polarons' effective mass and\ntheir coupling parameter, complementing previous studies on their chemical\npotential. Furthermore, we extract the magnetic susceptibility from\nlow-imbalance data, finding only small deviations from the mean-field\nprediction. While the mean-field theory predicts a direct transition from a\nparamagnetic to a fully ferromagnetic phase, our diffusion Monte Carlo results\nsuggest that the partially ferromagnetic phase is stable in a narrow interval\nof the interaction parameter. This finding calls for further analyses on the\neffects due to the fixed-node constraint."
    },
    {
        "anchor": "Dynamics of a dipolar Bose-Einstein condensate in the vicinity of a\n  superconductor: We study the dynamics of a dipolar Bose-Einstein condensate, like for example\na $^{52}$Cr or $^{164}$Dy condensate, interacting with a superconducting\nsurface. The magnetic dipole moments of the atoms in the Bose-Einstein\ncondensate induce eddy currents in the superconductor. The magnetic field\ngenerated by eddy currents modifies the trapping potential such that the\ncenter-of-mass oscillation frequency is shifted. We numerically solve the\nGross-Pitaevskii equation for this system and compare the results with\nanalytical approximations. We present an approximation that gives excellent\nagreement with the numerical results. The eddy currents give rise to anharmonic\nterms, which leads to the excitation of shape fluctuations of the condensate.\nWe discuss how the strength of the excitation of such modes can be increased by\nexploiting resonances, and we examine the strength of the resonances as a\nfunction of the center-of-mass oscillation amplitude of the condensate.\nFinally, we study different orientations of the magnetic dipoles and discuss\nfavorable conditions for the experimental observation of the eddy current\neffect.",
        "positive": "Multidimensional hybrid Bose-Einstein condensates stabilized by\n  lower-dimensional spin-orbit coupling: We show that attractive spinor Bose-Einstein condensates under the action of\nspin-orbit coupling (SOC) and Zeeman splitting form self-sustained stable two-\nand three-dimensional (2D and 3D) states in free space, even when SOC acts in a\nlower-dimensional form. We find that two-dimensional states are stabilized by\none-dimensional (1D) SOC in a broad range of chemical potentials, for atom\nnumbers (or norm of the spinor wavefunction) exceeding a threshold value, which\nstrongly depends on the SOC strength and vanishes at a critical point. The\nzero-threshold point is a boundary between single-peaked and striped states,\nrealizing hybrids combining 2D and 1D structural features. In a vicinity of\nsuch point, an asymptotic equation describing the bifurcation of the solitons\nfrom the linear spectrum is derived and investigated analytically. We show that\nstriped 3D solitary states are as well stabilized by 2D SOC, albeit in a\nlimited range of chemical potentials and norms."
    },
    {
        "anchor": "Fermion pairing in mixed-dimensional atomic mixtures: We investigate the quantum phases of mixed-dimensional cold atom mixtures. In\nparticular, we consider a mixture of a Fermi gas in a two-dimensional lattice,\ninteracting with a bulk Fermi gas or a Bose-Einstein condensate in a\nthree-dimensional lattice. The effective interaction of the two-dimensional\nsystem mediated by the bulk system is determined. We perform a functional\nrenormalization group analysis, and demonstrate that by tuning the properties\nof the bulk system, a subtle competition of several superconducting orders can\nbe controlled among $s$-wave, $p$-wave, $d_{x^2-y^2}$-wave, and\n$g_{xy(x^2-y^2)}$-wave pairing symmetries. Other instabilities such as a\ncharge-density wave order are also demonstrated to occur. In particular, we\nfind that the critical temperature of the $d$-wave pairing induced by the\nnext-nearest-neighbor interactions can be an order of magnitude larger than\nthat of the same pairing induced by doping in the simple Hubbard model. We\nexpect that by combining the nearest-neighbor interaction with the\nnext-nearest-neighbor hopping (known to enhance $d$-wave pairing), an even\nhigher critical temperature may be achieved.",
        "positive": "Brillouin propagation modes of cold atoms in dissipative optical\n  lattices: An exact series expansion of the average velocity of cold atoms in\ndissipative optical lattices under probe driving, based on the amplitudes of\nthe excited atomic density waves, is derived from the semiclassical equations\nfor the phase space densities of the Zeeman ground-state sublevels. This\nexpansion permits the identification of the precise contribution to the current\nof a propagating atomic wave for the specific driving, as well as providing the\ngeneral threshold for the transition into the regime of infinite density."
    },
    {
        "anchor": "Equation of state of the one- and three-dimensional Bose-Bose gases: We calculate the equation of state of Bose-Bose gases in one and three\ndimensions in the framework of an effective quantum field theory. The\nbeyond-mean-field approximation at zero-temperature and the one-loop\nfinite-temperature results are obtained performing functional integration on a\nlocal effective action. The ultraviolet divergent zero-point quantum\nfluctuations are removed by means of dimensional regularization. We derive the\nnonlinear Schr\\\"odinger equation to describe one- and three-dimensional\nBose-Bose mixtures and solve it analytically in the one-dimensional scenario.\nThis equation supports self-trapped brightlike solitonic-droplets and\nself-trapped darklike solitons. At low temperature, we also find that the\npressure and the number of particles of symmetric quantum droplets have a\nnontrivial dependence on the chemical potential and the difference between the\nintra- and the inter-species coupling constants.",
        "positive": "Magnetic oscillations for neutral atoms subject to an electromagnetic\n  field: We show that the de Haas van Alphen effect can be induced in a two\ndimensional atomic gas by the He-McKellar-Wilkens interaction mediated via an\nelectric dipole moment. Under an appropriate field-dipole configuration, we\nshow that the neutral atoms subject to a synthetic magnetic field arrange\nthemselves in Landau levels. An experimental arrangement for observation of the\natomic analog of dHvA oscillations is proposed. In a strong effective magnetic\nfield regime we present the quantum oscillations in the energy and effective\nmagnetization of the two dimensional atomic gas. From the dHvA period we\ndetermine the area of the Fermi circle of the atomic cloud."
    },
    {
        "anchor": "Finite-temperature properties of one-dimensional hard-core bosons in a\n  quasiperiodic optical lattice: We investigate the properties of impenetrable bosons confined in a\none-dimensional lattice at finite temperature in the presence of an additional\nincommensurate periodic potential. Relying on the exact Fermi-Bose mapping, we\nstudy the effects of temperature on the one-particle density matrix and related\nquantities such as the momentum distribution function and the natural orbitals.\nWe found evidence of a finite-temperature crossover related to the\nzero-temperature superfluid-to-Bose-glass transition that induces a\ndelocalization of the lowest natural orbitals.",
        "positive": "Semiclassical polaron dynamics of impurities in ultracold gases: We present a semiclassical treatment of a fermionic impurity coupled to\nBogolyubov modes of a BEC. In the lowest order approximation we find a full\nsolution of an initial value problem, which turns out to behave differently in\nthe sub- and supersonic regimes. While in the former case no impurity\ndeceleration is observed, in the latter case non-Markovian dissipation effects\nkick in resulting in slowing down of the fermion. Although this scenario is\ncompatible with the one offered by an elementary field theoretical picture at\nweak coupling, the details of the dynamics turn out to be completely different.\nFluctuation effects can be taken into account by expansion around the classical\npath. This allows for estimation of the all-important polaron radius as a\nfunction of fermion-boson coupling strength. As an application we calculate the\ndrag force which is exerted by the BEC on the impurity moving with constant\nvelocity $v$. Contrary to the perturbative result, according to which the drag\nforce is $\\sim v^4$, it turns out to be proportional to $1/v^2$ in the\nsemiclassical regime."
    },
    {
        "anchor": "Interferometric Measurement of Local Spin-Fluctuations in a Quantum Gas: The subtle interplay between quantum statistics and interactions is at the\norigin of many intriguing quantum phenomena connected to superfluidity and\nquantum magnetism. The controlled setting of ultracold quantum gases is well\nsuited to study such quantum correlated systems. Current efforts are directed\ntowards the identification of their magnetic properties, as well as the\ncreation and detection of exotic quantum phases. In this context, it has been\nproposed to map the spin-polarization of the atoms to the state of a\nsingle-mode light beam. Here we introduce a quantum-limited interferometer\nrealizing such an atom-light interface with high spatial resolution. We measure\nthe probability distribution of the local spin-polarization in a trapped Fermi\ngas showing a reduction of spin-fluctuations by up to 4.6(3) dB below\nshot-noise in weakly interacting Fermi gases and by 9.4(8) dB for strong\ninteractions. We deduce the magnetic susceptibility as a function of\ntemperature and discuss our measurements in terms of an entanglement witness.",
        "positive": "Collective dynamics of vortices in trapped Bose-Einstein condensates: We have calculated collective mode spectra for three-dimensional, rotating\nBose-Einstein condensates in oblate harmonic traps using the microscopic\nBogoliubov-deGennes field theory. For condensates with $N_v$ vortices, $N_v$\nKelvin-Tkachenko mode branches are obtained. The features of these modes are\ncompared with those predicted by a classical point vortex model. We have\ncreated movies to visualize the motion of the vortices corresponding to the\nKelvin-Tkachenko waves."
    },
    {
        "anchor": "Two-component Bose gas trapped by harmonic and annular potentials:\n  Supercurrent, vortex flow and instability of superfluidity by Rabi coupling: In this paper, we study a system of two-component Bose gas in an artificial\nmagnetic field trapped by concentric harmonic and annular potentials,\nrespectively. The system is realized by gases with two-internal states like the\nhyperfine states of $^{87}$Rb. We are interested in effects of a Rabi\noscillation between them. Two-component Bose Hubbard model is introduced to\ndescribe the system, and Gross-Pitaevskii equations are used to study the\nsystem. We first study the Bose gas system in the annular trap by varying the\nwidth of the annulus and strength of the magnetic field, in particular, we\nfocus on the phase slip and superflow. Then we consider the coupled Bose gas\nsystem in a magnetic field. In a strong magnetic field, vortices form a\nAbrikosov triangular lattice in both Bose-Einstein condensates (BECs), and\nlocations of vortices in the BECs correlate with each other by the Rabi\ncoupling. However, as the strength of the Rabi coupling is increased, vortices\nstart to vibrate around their equilibrium locations. As the strength is\nincreased further, vortices in the harmonic trap start to move along the\nboundaries of the annulus. Finally for a large Rabi coupling, the BECs are\ndestroyed. Based on our findings about the BEC in the annular trap, we discuss\nthe origin of above mentioned phenomena.",
        "positive": "3/2-Body Correlations and Coherence in Bose-Einstein Condensates: We construct a variational wave function for the ground state of weakly\ninteracting bosons that gives a lower energy than the mean-field\nGirardeau-Arnowitt (or Hartree-Fock-Bogoliubov) theory. This improvement is\nbrought about by incorporating the dynamical 3/2-body processes where one of\ntwo colliding non-condensed particles drops into the condensate and vice versa.\nThe processes are also shown to transform the one-particle excitation spectrum\ninto a bubbling mode with a finite lifetime even in the long-wavelength limit.\nThese 3/2-body processes, which give rise to dynamical exchange of particles\nbetween the non-condensate reservoir and condensate absent in ideal gases, are\nidentified as a key mechanism for realizing and sustaining macroscopic\ncoherence in Bose-Einstein condensates."
    },
    {
        "anchor": "Classical Analog of Quantum Models in Synthetic Dimensions: We introduce a classical analog of quantum matter in ultracold molecule -- or\nRydberg atom -- synthetic dimensions, extending the Potts model to include\ninteractions J1 between atoms adjacent in both real and synthetic space and\nstudying its finite temperature properties. For intermediate values of J1, the\nresulting phases and phase diagrams are similar to those of the clock and\nVillain models, in which three phases emerge. There exists a sheet phase\nanalogous to that found in quantum synthetic dimension models between the high\ntemperature disordered phase and the low temperature ferromagnetic phase. We\nalso employ machine learning to uncover non-trivial features of the phase\ndiagram using the learning by confusion approach. The key result there is that\nthe method is able to discern several successive phase transitions.",
        "positive": "Atom-dimer scattering length for fermions with different masses:\n  analytical study of limiting cases: We consider the problem of obtaining the scattering length for a fermion\ncolliding with a dimer, formed from a fermion identical to the incident one and\nanother different fermion. This is done in the universal regime where the range\nof interactions is short enough so that the scattering length $a$ for non\nidentical fermions is the only relevant quantity. This is the generalization to\nfermions with different masses of the problem solved long ago by Skorniakov and\nTer-Martirosian for particles with equal masses. We solve this problem\nanalytically in the two limiting cases where the mass of the solitary fermion\nis very large or very small compared to the mass of the two other identical\nfermions. This is done both for the value of the scattering length and for the\nfunction entering the Skorniakov-Ter-Martirosian integral equation, for which\nsimple explicit expressions are obtained."
    },
    {
        "anchor": "Suppression of polaron self-localization by correlations: We investigate self-localization of a polaron in a homogeneous Bose-Einstein\ncondensate in one dimension. This effect, where an impurity is trapped by the\ndeformation that it causes in the surrounding Bose gas, has been first\npredicted by mean field calculations, but has not been seen in experiments. We\nstudy the system in one dimension, where, according to the mean field\napproximation, the self-localization effect is particularly robust, and present\nfor arbitrarily weak impurity-boson interactions. We address the question\nwhether self-localization is a real effect by developing a variational method\nwhich incorporates impurity-boson correlations non-perturbatively and solving\nthe resulting inhomogeneous correlated polaron equations. We find that\ncorrelations inhibit self-localization except for very strongly repulsive or\nattractive impurity-boson interactions. Our prediction for the critical\ninteraction strength for self-localization agrees with a sharp drop of the\ninverse effective mass to almost zero found in quantum Monte Carlo simulations\nof polarons in one dimension.",
        "positive": "The band structure of the whole spectrum of an N-body cold system\n  containing atoms with arbitrary integer spin and dominated by singlet pairing\n  force: The spectra of $N$-boson systems with arbitrary nonzero spin $\\mathfrak{f}$\nhave been studied. Firstly, only the singlet pairing interaction is considered,\na set of eigenstates together with the eigenenergies are analytically obtained.\nThe completeness of this set is proved. The analytical expression allows us to\nsee clearly the spin structures of various states different in $N$ and/or\n$\\mathfrak{f}$, and to find out the similarity and relationship lying among\nthem. Secondly, the effect of other interactions is evaluated via exact\nnumerical calculations on the systems with a smaller $N$. Some features and\nnotable phenomena that might emerge in high-$\\mathfrak{f}$ systems, say, the\nground band might have extremely high level density, have been discussed."
    },
    {
        "anchor": "Quantum hydrodynamic modeling of edge modes in chiral Berry plasmons: A quantum hydrodynamic model is used to study the edge modes of chiral Berry\nplasmons. The transcendental equation of the dispersion relation is solved\nnonlinearly and semi-analytically. We predict a new one-way chiral edge state\nwith the quantum effect compared to that without the quantum effect, at the\nboth side of $q=0$. Indeed, the plasmon frequencies for positive and negative\n$q$, exhibit different limits for $q\\rightarrow 0^{-}$ and $q\\rightarrow\n0^{+}$. As a result, the quantum effect enhances the chirality in the vicinity\nof $q=0$. Both counterpropagating edge modes exhibit greater confinement to the\nedge with the quantum effect. In addition, new localized edge modes are found\nwith increased Berry flux in both cases, i.e., without and with the quantum\neffect.",
        "positive": "Bloch oscillations and quench dynamics of interacting bosons in an\n  optical lattice: We study the dynamics of interacting superfluid bosons in a one dimensional\nvertical optical lattice after a sudden increase of the lattice potential\ndepth. We show that this system can be exploited to investigate the effects of\nstrong interactions on Bloch oscillations. We perform theoretical modelling of\nthis system, identify experimental challenges and explore a new regime of Bloch\noscillations characterized by interaction-induced matter-wave collapse and\nrevivals which modify the Bloch oscillations dynamics. In addition, we study\nthree dephasing mechanisms: effective three-body interactions, finite value of\ntunneling, and a background harmonic potential. We also find that the center of\nmass motion in the presence of finite tunneling goes through collapse and\nrevivals, giving an example of quantum transport where interaction induced\nrevivals are important. We quantify the effects of residual harmonic trapping\non the momentum distribution dynamics and show the occurrence of\ninteraction-modified temporal Talbot effect. Finally, we analyze the prospects\nand challenges of exploiting Bloch oscillations of cold atoms in the strongly\ninteracting regime for precision measurement of the gravitational acceleration\n$g$."
    },
    {
        "anchor": "Spin domains in ground state of a trapped spin-1 condensate: A general\n  study under Thomas-Fermi approximation: Investigation of ground state structures and phase separation under\nconfinement is of great interest in spinor Bose Einstein Condensates (BEC). In\nthis paper we show that, in general, within the Thomas-Fermi (T-F)\napproximation, the phase separation scenario of stationary states can be\nobtained including all the mixed states on an equal footing for a spin-1\ncondensate for any confinement. Exact analytical expressions of energy density,\nbeing independent of local mass density for all allowed states enables this\ngeneral analysis under T-F approximation. We study here in details a particular\ncase of spherically symmetric harmonic confinement as an example and show a\nwide range of potential phase separation scenario for anti-ferromagnetic and\nferromagnetic interactions.",
        "positive": "Propagation and jamming dynamics in Heisenberg spin ladders: We investigate the propagation dynamics of initially localized excitations in\nspin-1/2 Heisenberg ladders. We consider initial states with two overturned\nspins, either on neighboring sites on the same leg or on the two sites of a\nsingle rung, in an otherwise polarized (ferromagnetic) background. Compared to\nthe corresponding dynamics in a chain (single leg), we observe several\nadditional modes of propagation. We connect these propagation modes to features\nof the spectrum of the ladder system, and to different effective models\ncorresponding to different segments of the spectrum. In addition to the regular\npropagation modes, we observe for one mode a peculiar `jamming' dynamics where\ncomponents of the excitations remain localized in an unusual manner. A\ncomparison with the spin-1 bilinear-biquadratic chain is developed and\nexplored, where a similar phenomenon is shown to occur."
    },
    {
        "anchor": "Evolution of an attractive polarized Fermi gas: From a Fermi liquid of\n  polarons to a non-Fermi liquid at the Fulde-Ferrell-Larkin-Ovchinnikov\n  quantum critical point: The evolution of an attractive polarized two-component Fermi gas at zero\ntemperature is analyzed as its polarization is progressively decreased, from\nfull polarization (corresponding to the polaronic limit) down to a critical\npolarization when superfluidity sets in. This critical polarization and the\nnature of the associated superfluid instability are determined within a fully\nself-consistent $t$-matrix approach implemented exactly at zero temperature. In\nthis way, the polarization-vs-coupling phase diagram at zero temperature is\nconstructed throughout the whole BCS-BEC crossover. Depending on the coupling\nstrength of the inter-particle interaction between the two components, the\nsuperfluid instability can be either toward a Fulde-Ferrel-Larkin-Ovchinnikov\n(FFLO) phase or toward a standard polarized BCS phase. The evolution with\npolarization of the quasi-particle parameters in the normal Fermi gas turns out\nto be notably different in the two cases. When the instability is toward a\npolarized BCS superfluid, quasi-particles in the proximity of the two Fermi\nsurfaces remain well defined for all polarizations. When the instability is\ninstead toward an FFLO superfluid, precursor effects become apparent upon\napproaching the FFLO quantum critical point (QCP), where the quasi-particle\nresidues vanish and the effective masses diverge. This behavior leads to a\ncomplete breakdown of the quasi-particle picture characteristic of a Fermi\nliquid, similarly to what occurs in heavy-fermion materials at an\nantiferromagnetic QCP. At unitarity, the system is further investigated at\nfinite temperature, making it possible to identify a non-Fermi liquid region in\nthe temperature-vs-polarization phase diagram associated with the underlying\nFFLO QCP.",
        "positive": "Ginzburg-Landau Theory for the Jaynes-Cummings-Hubbard Model: We develop a Ginzburg-Landau theory for the Jaynes-Cummings-Hubbard model\nwhich effectively describes both static and dynamic properties of photons\nevolving in a cubic lattice of cavities, each filled with a two-level atom. To\nthis end we calculate the effective action to first-order in the hopping\nparameter. Within a Landau description of a spatially and temporally constant\norder parameter we calculate the finite-temperature mean-field quantum phase\nboundary between a Mott insulating and a superfluid phase of polaritons.\nFurthermore, within the Ginzburg-Landau description of a spatio-temporal\nvarying order parameter we determine the excitation spectra in both phases and,\nin particular, the sound velocity of light in the superfluid phase."
    },
    {
        "anchor": "Superfluid transition of a ferromagnetic Bose gas: The strongly ferromagnetic spin-1 Bose-Einstein condensate (BEC) has recently\nbeen realized with atomic $^{7}$Li. It was predicted that a strong\nferromagnetic interaction can drive the normal gas into a magnetized phase at a\ntemperature above the superfluid transition, and $^{7}$Li likely satisfies the\ncriterion. We re-examine this theoretical proposal employing the\ntwo-particle-irreducible (2PI) effective potential, and conclude that there\nexists no stable normal magnetized phase for a dilute ferromagnetic Bose gas.\nFor $^{7}$Li, we predict that the normal gas undergoes a joint first order\ntransition and jump directly into a state with finite condensate density and\nmagnetization. We estimate the size of the first order jump, and examine how a\npartial spin polarization in the initial sample affects the first order\ntransition. We propose a qualitative phase diagram at fixed temperature for the\ntrapped gas.",
        "positive": "Dark Solitons in Waveguide Polariton Fluids Shed Light on Interaction\n  Constants: We study exciton-polariton nonlinear optical fluids in a high momentum regime\nfor the first time. Defects in the fluid develop into dark solitons whose\nhealing length decreases with increasing density. We deduce interaction\nconstants for continuous wave polaritons an order of magnitude larger than with\npicosecond pulses. Time dependent measurements show a 100ps time for the\nbuildup of the interaction strength suggesting a self-generated excitonic\nreservoir as the source of the extra nonlinearity. The experimental results\nagree well with a model of coupled photons, excitons and the reservoir."
    },
    {
        "anchor": "An effective-field-theory analysis of Efimov physics in heteronuclear\n  mixtures of ultracold atomic gases: We use an effective-field-theory framework to analyze the Efimov effect in\nheteronuclear three-body systems consisting of two species of atoms with a\nlarge interspecies scattering length. In the leading-order description of this\ntheory, various three-body observables in heteronuclear mixtures can be\nuniversally parameterized by one three-body parameter. We present the\nnext-to-leading corrections, which include the effects of the finite\ninterspecies effective range and the finite intraspecies scattering length, to\nvarious three-body observables. We show that only one additional three-body\nparameter is required to render the theory predictive at this order. By\nincluding the effective range and intraspecies scattering length corrections,\nwe derive a set of universal relations that connect the different Efimov\nfeatures near the interspecies Feshbach resonance. Furthermore, we show that\nthese relations can be interpreted in terms of the running of the three-body\ncounterterms that naturally emerge from proper renormalization. Finally, we\nmake predictions for recombination observables of a number of atomic systems\nthat are of experimental interest.",
        "positive": "Universal nonanalytic behavior of the Hall conductance in a Chern\n  insulator at the topologically driven nonequilibrium phase transition: We study the Hall conductance of a Chern insulator after a global quench of\nthe Hamiltonian. The Hall conductance in the long time limit is obtained by\napplying the linear response theory to the diagonal ensemble. It is expressed\nas the integral of the Berry curvature weighted by the occupation number over\nthe Brillouin zone. We identify a topologically driven nonequilibrium phase\ntransition, which is indicated by the nonanalyticity of the Hall conductance as\na function of the energy gap m_f in the post-quench Hamiltonian H_f. The\ntopological invariant for the quenched state is the winding number of the\nGreen's function W, which equals the Chern number for the ground state of H_f.\nIn the limit that m_f goes to zero, the derivative of the Hall conductance with\nrespect to m_f is proportional to ln(|m_f|), with the constant of\nproportionality being the ratio of the change of W at m_f = 0 to the energy gap\nin the initial state. This nonanalytic behavior is universal in two-band Chern\ninsulators such as the Dirac model, the Haldane model, or the Kitaev honeycomb\nmodel in the fermionic basis."
    },
    {
        "anchor": "The eigenstate distribution fluctuation from thermal to localized\n  transitions: We study the thermalization of a quenched disordered Bose-Hubbard model. By\nconsidering the eigenstate distribution fluctuation, we show that the thermal\nto many-body localized transition is always connected to a minimum of this\ndistribution fluctuation. We also observe a Mott-localized regime, where the\nsystem fails to thermalize due to the strong on-site repulsion. At last, we\nshow how to detect this eigenstate distribution fluctuation in cold atom\nsystems, which is equivalent to measure the Loschmidt echo of the system. Our\nwork suggests a way to measure the thermal to localized transitions in\nexperiments, especially for a large system.",
        "positive": "Out-of-equilibrium dynamics of quantum many-body systems with long-range\n  interactions: Experimental progress in atomic, molecular, and optical platforms in the last\ndecade has stimulated strong and broad interest in the quantum coherent\ndynamics of many long-range interacting particles. The prominent collective\ncharacter of these systems enables novel non-equilibrium phenomena with no\ncounterpart in conventional quantum systems with local interactions. Much of\nthe theory work in this area either focussed on the impact of variable-range\ninteraction tails on the physics of local interactions or relied on\nmean-field-like descriptions based on the opposite limit of all-to-all\ninfinite-range interactions. In this Report, we present a systematic and\norganic review of recent advances in the field. Working with prototypical\ninteracting quantum spin lattices without disorder, our presentation hinges\nupon a versatile theoretical formalism that interpolates between the few-body\nmean-field physics and the many-body physics of quasi-local interactions. Such\na formalism allows us to connect these two regimes, providing both a formal\nquantitative tool and basic physical intuition. We leverage this unifying\nframework to review several findings of the last decade, including the peculiar\nnon-ballistic spreading of quantum correlations, counter-intuitive slowdown of\nentanglement dynamics, suppression of thermalization and equilibration,\nanomalous scaling of defects upon traversing criticality, dynamical phase\ntransitions, and genuinely non-equilibrium phases stabilized by periodic\ndriving. The style of this Report is on the pedagogical side, which makes it\naccessible to readers without previous experience in the subject matter."
    },
    {
        "anchor": "Spin squeezing in a spin-orbit coupled Bose-Einstein condensate: We study the spin squeezing in a spin-1/2 Bose-Einstein condensates (BEC)\nwith Raman induced spin-orbit coupling (SOC). Under the condition of two-photon\nresonance and weak Raman coupling strength, the system possesses two degenerate\nground states, using which we construct an effective two-mode model. The\nHamiltonian of the two-mode model takes the form of the one-axis-twisting\nHamiltonian which is known to generate spin squeezing. More importantly, we\nshow that the SOC provides a convenient control knob to adjust the spin\nnonlinearity responsible for spin squeezing. Specifically, the spin\nnonlinearity strength can be tuned to be comparable to the two-body\ndensity-density interaction, hence is much larger than the intrinsic\nspin-dependent interaction strength in conventional two-component BEC systems\nsuch as $^{87}$Rb and $^{23}$Na in the absence of the SOC. We confirm the spin\nsqueezing by carrying out a fully beyond-mean-field numerical calculation using\nthe truncated Wigner method. Additionally, the experimental implementation is\nalso discussed.",
        "positive": "Loading and compression of a single two-dimensional Bose gas in an\n  optical accordion: The experimental realization of 2D Bose gases with a tunable interaction\nstrength is an important challenge for the study of ultracold quantum matter.\nHere we report on the realization of an optical accordion creating a lattice\npotential with a spacing that can be dynamically tuned between 11$\\,\\mu$m and\n2$\\,\\mu$m. We show that we can load ultracold $^{87}$Rb atoms into a single\nnode of this optical lattice in the large spacing configuration and then\ndecrease nearly adiabatically the spacing to reach a strong harmonic\nconfinement with frequencies larger than $\\omega_z/2\\pi=10\\,$kHz. Atoms are\ntrapped in an additional flat-bottom in-plane potential that is shaped with a\nhigh resolution. By combining these tools we create custom-shaped uniform 2D\nBose gases with tunable confinement along the transverse direction and hence\nwith a tunable interaction strength."
    },
    {
        "anchor": "Properties of a nematic spin vortex in an antiferromagnetic spin-1\n  Bose-Einstein condensate: A spin-1 condensate with antiferromagnetic interactions supports nematic spin\nvortices in the easy-plane polar phase. These vortices have a $2\\pi$ winding of\nthe nematic director, with a core structure that depends on the quadratic\nZeeman energy. We characterize the properties of the nematic spin vortex in a\nuniform quasi-two-dimensional system. We also obtain the vortex excitation\nspectrum and use it to quantify its stability against dissociating into two\nhalf-quantum vortices, finding a parameter regime where the nematic spin vortex\nis dynamically stable. These results are supported by full dynamical\nsimulations.",
        "positive": "Correlation dynamics of dipolar bosons in 1D triple well optical lattice: The concept of spontaneous symmetry breaking and off-diagonal long-range\norder (ODLRO) are associated with Bose-Einstein condensation. However, as in\nthe system of reduced dimension the effect of quantum fluctuation is\ndominating, the concept of ODLRO becomes more interesting, especially for the\nlong-range interaction. In the present manuscript, we study the correlation\ndynamics triggered by lattice depth quench in a system of three dipolar bosons\nin a 1D triple-well optical lattice from the first principle using the\nmulticonfigurational time-dependent Hartree method for bosons (MCTDHB). Our\nmain motivation is to explore how ODLRO develops and decays with time when the\nsystem is brought out-of-equilibrium by a sudden change in the lattice depth.\nWe compare results of dipolar bosons with contact interaction. For forward\nquench $(V_{f} > V_{i})$, the system exhibits the collapse-revival dynamics in\nthe time evolution of normalized first- and second-order Glauber's correlation\nfunction, time evolution of Shannon information entropy both for the contact as\nwell as for the dipolar interaction which is reminiscent of the one observed in\nGreiner's experiment [Nature, {415}, (2002)]. We define the collapse and\nrevival time ratio as the figure of merit ($\\tau$) which can uniquely\ndistinguish the timescale of dynamics for dipolar interaction from that of\ncontact interaction. In the reverse quench process $(V_{i} > V_{f})$, for\ndipolar interaction, the dynamics is complex and the system does not exhibit\nany definite time scale of evolution, whereas the system with contact\ninteraction exhibits collapse-revival dynamics with a definite time-scale. The\nlong-range repulsive tail in the dipolar interaction inhibits the spreading of\ncorrelation across the lattice sites."
    },
    {
        "anchor": "Real-space probe for lattice quasiholes: We propose a real-space probe that is based on density measurements to\nextract distinct signatures of quasihole-like states of bosons experiencing a\nsynthetic magnetic field in a two-dimensional lattice. We numerically show that\ncertain ratios of the mean square radii of the particle cloud, obtainable\nthrough the density profile, approach the continuum values expected from\nLaughlin's ansatz wave functions quickly as the magnetic flux quanta per unit\ncell of the lattice decrease, even in a small lattice with few particles. This\nmethod could equally be used in both ultra-cold atomic and photonic systems.",
        "positive": "Time-resolved observation of competing attractive and repulsive\n  short-range correlations in strongly interacting Fermi gases: We exploit a time-resolved pump-probe spectroscopic technique to study the\nout-of-equilibrium dynamics of an ultracold two-component Fermi gas,\nselectively quenched to strong repulsion along the upper branch of a broad\nFeshbach resonance. For critical interactions, we find the rapid growth of\nshort-range anti-correlations between repulsive fermions to initially overcome\nconcurrent pairing processes. At longer evolution times, these two competing\nmechanisms appear to macroscopically coexist in a short-range correlated state\nof fermions and pairs, unforeseen thus far. Our work provides fundamental\ninsights into the fate of a repulsive Fermi gas, and offers new perspectives\ntowards the exploration of complex dynamical regimes of fermionic matter."
    },
    {
        "anchor": "Thermodynamics of Van der Waals Fluids with quantum statistics: We consider thermodynamics of the van der Waals fluid of quantum systems. We\nderive general relations of thermodynamic functions and parameters of any ideal\ngas and the corresponding van der Waals fluid. This provides unambiguous\ngeneralization of the classical van der Waals theory to quantum statistical\nsystems. As an example, we apply the van der Waals fluid with fermi statistics\nto characterize the liquid-gas critical point in nuclear matter. We also\nintroduce the Bose-Einstein condensation in the relativistic van der Waals\nboson gas, and argue, that it exhibits two-phase structure separated in space.",
        "positive": "Striped states in weakly trapped ultracold Bose gases with Rashba\n  spin-orbit coupling: The striped state of ultracold bosons with Rashba spin-orbit coupling in a\nhomogeneous infinite system has, as we show, a constant particle flow, which in\na finite-size system would accumulate particles at the boundaries; it is thus\nnot a physical steady state of the system. We propose, as a variational ansatz,\na condensate wave function for a weakly trapped system which behaves similarly\nto the striped state near the center, but does not have particle flow at the\nboundaries. This state has a line of unquantized coreless vortices. We show, by\nminimizing the total energy, that our modified striped state has lower energy\nthan the conventional striped state and it is thus a physically appropriate\nstarting point to analyze striped states in finite systems."
    },
    {
        "anchor": "Rapid ramps across the BEC-BCS crossover: a novel route to measuring the\n  superfluid gap: We investigate the response of superfluid Fermi gases to rapid changes of the\nthree-dimensional s-wave scattering length a by solving the time-dependent\nBogoliubov-de Gennes equations. In general the magnitude of the order parameter\n|\\Delta| performs oscillations, which are sometimes called the \"Higgs\" mode,\nwith the angular frequency 2 \\Delta_{gap}/ \\hbar, where \\Delta_{gap} is the gap\nin the spectrum of fermionic excitations. Firstly, we excite the oscillations\nwith a linear ramp of 1/a and study the evolution of |\\Delta|. Secondly, we\ncontinously drive the system with a sinusoidal modulation of 1/a. In the first\ncase, the oscillations in |\\Delta| damp according to a power law. In the second\ncase, the continued driving causes revivals in the oscillations. In both cases,\nthe excitation of the oscillations causes a reduction in the time-averaged\nvalue of |\\Delta|. We propose two experimental protocols, based around the two\napproaches, to measure the frequency and damping of the oscillations, and hence\n\\Delta_{gap}.",
        "positive": "Composite localized modes in discretized spin-orbit-coupled\n  Bose-Einstein condensates: We introduce a discrete model for binary spin-orbit-coupled (SOC)\nBose-Einstein condensates (BEC) trapped in a deep one-dimensional optical\nlattice. Two different types of the couplings are considered, with spatial\nderivatives acting inside each species, or between the species. The discrete\nsystem with inter-site couplings dominated by the SOC, while the usual hopping\nis negligible, \\textit{emulates} condensates composed of extremely heavy atoms,\nas well as those with opposite signs of the effective atomic masses in the two\ncomponents.\\ Stable localized composite states of miscible and immiscible types\nare constructed. The effect of the SOC on the immiscibility-miscibility\ntransition in the localized complexes, which emulates the phase transition\nbetween insulating and conducting states in semiconductors, is studied."
    },
    {
        "anchor": "Dynamical self-stabilization of the Mott insulator: Time evolution of\n  the density and entanglement entropy of out-of-equilibrium cold fermion gases: The time evolution of the out-of-equilibrium Mott insulator is investigated\nnumerically through calculations of space-time resolved density and entropy\nprofiles resulting from the release of a gas of ultracold fermionic atoms from\nan optical trap. For adiabatic, moderate and sudden switching-off of the\ntrapping potential, the out-of-equilibrium dynamics of the Mott insulator is\nfound to differ profoundly from that of the band insulator and the metallic\nphase, displaying a self-induced stability that is robust within a wide range\nof densities, system sizes and interaction strengths. The connection between\nthe entanglement entropy and changes of phase, known for equilibrium\nsituations, is found to extend to the out-of-equilibrium regime. Finally, the\nrelation between the system's long time behavior and the thermalization limit\nis analyzed.",
        "positive": "Superfluidity of a laser-stirred Bose-Einstein condensate: We study superfluidity of a cigar-shaped Bose-Einstein condensate (BEC) by\nstirring it with a Gaussian potential oscillating back and forth along the\naxial dimension of the condensate, motivated by experiments of C. Raman et al.\nPhys. Rev. Lett. 83, 2502 (1999). Using classical-field simulations and\nperturbation theory we examine the induced heating rate, based on the total\nenergy of the system, as a function of the stirring velocity $v$. We identify\nthe onset of dissipation by a sharply increasing heating rate above a velocity\n$v_c$, which we define as the critical velocity. We show that $v_c$ is\ninfluenced by the oscillating motion, the strength of the stirrer, the\ntemperature and the inhomogeneous density of the cloud. This results in a\nvanishing $v_c$ for the parameters similar to the experiments, which is\ninconsistent with the measurement of nonzero $v_c$. However, if the heating\nrate is based on the thermal fraction after a 100 ms equilibration time, our\nsimulation recovers the experimental observations. We demonstrate that this\ndiscrepancy is due to the slow relaxation of the stirred cloud and dipole mode\nexcitation of the cloud."
    },
    {
        "anchor": "Generating Symmetry-Protected Long-Range Entanglement in Many-Body\n  Systems: Entanglement between spatially distant qubits is perhaps the most\ncounterintuitive and vital resource for distributed quantum computing. However,\ndespite a few special cases, there is no known general procedure to maximally\nentangle two distant parts of an interacting many-body system. Here we present\na symmetry-based approach, whereby one applies several timed pulses to drive a\nsystem to a particular symmetry sector with maximal bipartite long-range\nentanglement. As a concrete example, we demonstrate how a simple sequence of\non-site pulses on a qubit array can efficiently produce any given number of\nstable nonlocal Bell pairs, realizable in several present-day atomic and\nphotonic experimental platforms. More generally, our approach paves a route for\nnovel state preparation by harnessing symmetry. For instance, we show how it\nenables the creation of long-sought-after superconducting $\\eta$ pairs in a\nrepulsive Hubbard model.",
        "positive": "Periodic waves in two-component Bose-Einstein condensates with repulsive\n  interactions between atoms: We consider periodic waves in miscible two-component Bose-Einstein\ncondensates with repulsive nonlinear interactions constants. Exact one-phase\nsolution is found for the case when all these constants are equal to each other\n(i.e., for Manakov limit). New types of nonlinear polarization waves are\nconsidered in detail. The connection of the solutions found with experimentally\nobserved periodic structures in two-component condensates is discussed."
    },
    {
        "anchor": "Coherent Quantum Phase Slip in two-component bosonic Atomtronic Circuits: Coherent Quantum Phase Slip consists in the coherent transfer of vortices in\nsuperfluids. We investigate this phenomenon in two miscible coherently coupled\ncomponents of a spinor Bose gas confined in a toroidal trap. After imprinting\ndifferent vortex states on each component, we demonstrate that during the whole\ndynamics the system remains in a linear superposition of two current states in\nspite of the non-linearity and can be mapped onto a linear Josephson problem.\nWe propose this system as a good candidate for the realization of a\nMooij-Harmans qubit and remark its feasibility for implementation in current\nexperiments with $^{87}\\mbox{Rb}$, since we have used values for the physical\nparameters currently available in laboratories.",
        "positive": "Quantum degenerate dipolar Fermi gas: The interplay between crystallinity and superfluidity is of great fundamental\nand technological interest in condensed matter settings. In particular,\nelectronic quantum liquid crystallinity arises in the non-Fermi liquid,\npseudogap regime neighboring a cuprate's unconventional superconducting phase.\nWhile the techniques of ultracold atomic physics and quantum optics have\nenabled explorations of the strongly correlated, many-body physics inherent in,\ne.g., the Hubbard model, lacking has been the ability to create a quantum\ndegenerate Fermi gas with interparticle interactions---such as the strong\ndipole-dipole interaction---capable of inducing analogs to electronic quantum\nliquid crystals. We report the first quantum degenerate dipolar Fermi gas, the\nrealization of which opens a new frontier for exploring strongly correlated\nphysics and, in particular, the quantum melting of smectics in the pristine\nenvironment provided by the ultracold atomic physics setting. A quantum\ndegenerate Fermi gas of the most magnetic atom 161Dy is produced by laser\ncooling to 10 uK before sympathetically cooling with ultracold, bosonic 162Dy.\nThe temperature of the spin-polarized 161Dy is a factor T/TF=0.2 below the\nFermi temperature TF=300 nK. The co-trapped 162Dy concomitantly cools to\napproximately Tc for Bose-Einstein condensation, thus realizing a novel, nearly\nquantum degenerate dipolar Bose-Fermi gas mixture."
    },
    {
        "anchor": "Bose-Einstein condensates in toroidal traps: instabilities, swallow-tail\n  loops, and self-trapping: We study the stability and dynamics of an ultra-cold bosonic gas trapped in a\ntoroidal geometry and driven by rotation, in the absence of dissipation. We\nfirst delineate, via the Bogoliubov mode expansion, the regions of stability\nand the nature of instabilities of the system for both repulsive and attractive\ninteraction strengths. To study the response of the system to variations in the\nrotation rate, we introduce a \"disorder\" potential, breaking the rotational\nsymmetry. We demonstrate the breakdown of adiabaticity as the rotation rate is\nslowly varied and find forced tunneling between the system's eigenstates. The\nnon-adiabaticity is signaled by the appearance of a swallow-tail loop in the\nlowest-energy level, a general sign of hysteresis. Then, we show that this\nsystem is in one-to-one correspondence with a trapped gas in a double-well\npotential and thus exhibits macroscopic quantum self-trapping. Finally, we show\nthat self-trapping is a direct manifestation of the behavior of the\nlowest-energy level.",
        "positive": "Measuring molecular electric dipoles using trapped atomic ions and\n  ultrafast laser pulses: We study a hybrid quantum system composed of an ion and an electric dipole.\nWe show how a trapped ion can be used to measure the small electric field\ngenerated by a classical dipole. We discuss the application of this scheme to\nmeasure the electric dipole moment of cold polar molecules, whose internal\nstate can be controlled with ultrafast laser pulses, by trapping them in the\nvicinity of a trapped ion."
    },
    {
        "anchor": "Dispersive and dissipative effects in quantum field theory in curved\n  space-time to model condensed matter systems: The two main predictions of quantum field theory in curved space-time, namely\nHawking radiation and cosmological pair production, have not been directly\ntested and involve ultra high energy configurations. As a consequence, they\nshould be considered with caution. Using the analogy with condensed matter\nsystems, their analogue versions could be tested in the lab. Moreover, the high\nenergy behavior of these systems is known and involves dispersion and\ndissipation, which regulate the theory at short distances. When considering\nexperiments which aim to test the above predictions, there will also be a\ncompetition between the stimulated emission from thermal noise and the\nspontaneous emission out of vacuum. In order to measure these effects, one\nshould thus compute the consequences of UV dispersion and dissipation, and\nidentify observables able to establish that the spontaneous emission took\nplace. In this thesis, we first analyze the effects of dispersion and\ndissipation on both Hawking radiation and pair particle production. To get\nexplicit results, we work in the context of de Sitter space. Using the extended\nsymmetries of the theory in such a background, exact results are obtained.\nThese are then transposed to the context of black holes using the\ncorrespondence between de Sitter space and the black hole near horizon region.\nTo introduce dissipation, we consider an exactly solvable model producing any\ndecay rate. We also study the quantum entanglement of the particles so\nproduced. In a second part, we consider explicit condensed matter systems,\nnamely Bose Einstein condensates and exciton-polariton systems. We analyze the\neffects of dissipation on entanglement produced by the dynamical Casimir\neffect. As a final step, we study the entanglement of Hawking radiation in the\npresence of dispersion for a generic analogue system.",
        "positive": "Topological classification of vortex-core structures of spin-1\n  Bose-Einstein condensates: We classify vortex-core structures according to the topology of the order\nparameter space. By developing a method to characterize how the order parameter\nchanges inside the vortex core. We apply this method to the spin-1\nBose-Einstein condensates and show that the vortex-core structures are\nclassified by winding numbers that are locally defined in the core region. We\nalso show that a vortex-core structure with a nontrivial winding number can be\nstabilized under a negative quadratic Zeeman effect."
    },
    {
        "anchor": "Analytical approach to the two-site Bose-Hubbard model: from Fock states\n  to Schr\u00f6dinger cat states and entanglement entropy: We study the interpolation from occupation number Fock states to\nSchr\\\"odinger cat states on systems modeled by two-mode Bose-Hubbard\nHamiltonian, like, for instance, bosons in a double well or superconducting\nCooper pair boxes. In the repulsive interaction regime, by a simplified single\nparticle description, we calculate, analytically, energy, number fluctuations,\nstability under coupling to a heat bath, entanglement entropy and Fisher\ninformation, all in terms of hypergeometric polynomials of the single particle\noverlap parameter. Our approach allows us to find how those quantities scale\nwith the number of bosons. In the attractive interaction regime we calculate\nthe same physical quantities in terms of the imbalance parameter, and find that\nthe symmetry breaking, occurring at interaction Uc, predicted by a\nsemiclassical approximation, is valid only in the limit of infinite number of\nbosons. For a large but finite number, we determine a characteristic strength\nof interaction, Uc*, which can be promoted as the crossover point from coherent\nto incoherent regimes and can be identified as the collapse threshold.\nMoreover, we find that the Fisher information is always in direct ratio to the\nvariance of on-site number of bosons, for both positive and negative\ninteractions. We finally show that the entanglement entropy is maximum close to\nUc* and exceeds its coherent value within the whole range of interaction\nbetween 2Uc and zero.",
        "positive": "Rabi Spectroscopy and Sensitivity of a Floquet Engineered Optical\n  Lattice Clock: We periodically modulate the lattice trapping potential of a $^{87}$Sr\noptical clock to Floquet engineer the clock transition. In the context of\natomic gases in lattices, Floquet engineering has been used to shape the\ndispersion and topology of Bloch quasi-energy bands. Differently from these\nprevious works manipulating the external (spatial) quasi-energies, we target\nthe internal atomic degrees of freedom. We shape Floquet spin quasi-energies\nand measure their resonance profiles with Rabi spectroscopy. We provide the\nspectroscopic sensitivity of each band by measuring the Fisher information and\nshow that this is not depleted by the Floquet dynamical modulation. The\ndemonstration that the internal degrees of freedom can be selectively\nengineered by manipulating the external degrees of freedom inaugurates a novel\ndevice with potential applications in metrology, sensing and quantum\nsimulations."
    },
    {
        "anchor": "Condensation of quasiparticles and density modulation beyond the\n  superfluid critical velocity: We investigate the effect of a constant external velocity field on the ground\nstate of a bosonic quasiparticle Hamiltonian. Below a critical velocity the\nground state is a quasiparticle vacuum, corresponding to a pure superfluid\nphase at zero temperature. Beyond the critical velocity energy minimization\nleads to a macroscopic condensation of quasiparticles at a nonzero wave vector\nk_v parallel to the velocity v. Simultaneously, physical particles also undergo\na condensation at k_v and, to a smaller extent, at -k_v. Together with the BEC\nat k=0, the three entangled condensates give rise to density modulations of\nwave vectors k_v and 2k_v. For larger |v| our model predicts a bifurcation of\nk_v with corresponding two pure condensates and no density modulation.",
        "positive": "Symmetry-induced many-body quantum interference in chaotic bosonic\n  systems: an augmented Truncated Wigner method: Although highly successful, the Truncated Wigner Approximation (TWA) does not\naccount for genuine many-body quantum interference between different solutions\nof the mean-field equations of a bosonic many-body (MB) system. This renders\nthe TWA essentially classical, where a large number of particles formally takes\nthe role of the inverse of Planck's constant $\\hbar$. The failure to describe\ngenuine interference phenomena, such as localization and scarring in Fock\nspace, can be seen as a virtue of this quasiclassical method, which thereby\nallows one to identify genuine quantum effects when being compared with \"exact\"\nquantum calculations that do not involve any a priori approximation. A rather\nprominent cause for such quantum effects that are not accounted for by the TWA\nis the constructive interference between the contributions of symmetry-related\ntrajectories, which would occur in the presence of discrete symmetries provided\nthe phase-space distribution of the initial state and the observable to be\nevaluated feature a strong localization about the corresponding symmetry\nsubspaces. Here we show how one can conceive an augmented version of the TWA\nwhich can account for this particular effect. This augmented TWA effectively\namounts to complementing conventional TWA calculations by separate Truncated\nWigner simulations that are restricted to symmetric subspaces and involve\nweight factors that account for the dynamical stability of sampling\ntrajectories with respect to perpendicular deviations from those subspaces. We\nillustrate the validity of this method at pre- as well as post-Ehrenfest time\nscales in prototypical Bose-Hubbard systems displaying chaotic classical\ndynamics, where it also reveals the existence of additional MB interference\neffects."
    },
    {
        "anchor": "Breaking inversion symmetry in a state-dependent honeycomb lattice:\n  Artificial graphene with tunable band gap: Here, we present the application of a novel method for controlling the\ngeometry of a state-dependent honeycomb lattice: The energy offset between the\ntwo sublattices of the honeycomb structure can be adjusted by rotating the\natomic quantization axis. This enables us to continuously tune between a\nhomogeneous graphene-like honeycomb lattice and a triangular lattice and to\nopen an energy gap at the characteristic Dirac points. We probe the symmetry of\nthe lattice with microwave spectroscopy techniques and investigate the behavior\nof atoms excited to the second energy band. We find a striking influence of the\nenergy gap at the Dirac cones onto the lifetimes of atoms in the excited band.",
        "positive": "Topology, edge states, and zero-energy states of ultracold atoms in 1D\n  optical superlattices with alternating onsite potentials or hopping\n  coefficients: One-dimensional superlattices with periodic spatial modulations of onsite\npotentials or tunneling coefficients can exhibit a variety of properties\nassociated with topology or symmetry. Recent developments of ring-shaped\noptical lattices allow a systematic study of those properties in superlattices\nwith or without boundaries. While superlattices with additional modulating\nparameters are shown to have quantized topological invariants in the augmented\nparameter space, we also found localized or zero-energy states associated with\nsymmetries of the Hamiltonians. Probing those states in ultracold-atoms is\npossible by utilizing recently proposed methods analyzing particle depletion or\nthe local density of states. Moreover, we summarize feasible realizations of\nconfigurable optical superlattices using currently available techniques."
    },
    {
        "anchor": "Ring solitons and soliton sacks in imbalanced fermionic systems: We show that in superfluids with fermionic imbalance and uniform ground\nstate, there are stable solitons. These solutions are formed of radial density\nmodulations resulting in nodal rings. We demonstrate that these solitons\nexhibit nontrivial soliton-soliton and soliton-vortex interactions and can form\ncomplicated bound states in the form of \"soliton sacks\". In a phase-modulating\n(Fulde-Ferrell) background, we find different solitonic states, in the form of\nstable vortex-antivortex pairs.",
        "positive": "Strongly Interacting One-Dimensional Systems with Small Mass Imbalance: We study a strongly interacting system of N identical bosons and one impurity\nin a one-dimensional trap. First, we assume that the particles have identical\nmasses and analyze the corresponding set-up. After that, we study the influence\nof a small mass asymmetry on our analysis. In particular, we discuss how the\nstructure of the wave function and the degeneracy in the impenetrable regime\ndepend on the mass ratio and the shape of the trapping potential. To illustrate\nour findings, we consider a four-body system in a box and in an oscillator. We\nshow that in the former case the system has the smallest energy when a heavy\n(light) impurity is close to the edge (center) of the trap. And we demonstrate\nthat the opposite is true in the latter case."
    },
    {
        "anchor": "Efimov physics and the three-body parameter for shallow van der Waals\n  potentials: Extremely weakly-bound three-boson systems are predicted to exhibit\nintriguing universal properties such as discrete scale invariance. Motivated by\nrecent experimental studies of the ground and excited helium trimers, this work\nanalyzes the three-body parameter and the structural properties of three helium\natoms as the s-wave scattering length is tuned artificially. Connections with\ntheoretical and experimental studies of the Efimov scenario as it pertains to\ncold atom systems are made.",
        "positive": "Synthetic magneto-hydrodynamics in Bose-Einstein condensates and routes\n  to vortex nucleation: Engineering of synthetic magnetic flux in Bose-Einstein condensates [Lin et\nal., Nature {\\bf 462}, 628 (2009)] has prospects for attaining the high vortex\ndensities necessary to emulate the fractional quantum Hall effect. We\nanalytically establish the hydrodynamical behaviour of a condensate in a\nuniform synthetic magnetic field, including its density and velocity profile.\nImportantly, we find that the onset of vortex nucleation observed\nexperimentally corresponds to a dynamical instability in the hydrodynamical\nsolutions and reveal other routes to instability and anticipated vortex\nnucleation."
    },
    {
        "anchor": "Pairing patterns in one-dimensional spin- and mass-imbalanced Fermi\n  gases: We study spin- and mass-imbalanced mixtures of spin-$\\tfrac{1}{2}$ fermions\ninteracting via an attractive contact potential in one spatial dimension.\nSpecifically, we address the influence of unequal particle masses on the pair\nformation by means of the complex Langevin method. By computing the\npair-correlation function and the associated pair-momentum distribution we find\nthat inhomogeneous pairing is present for all studied spin polarizations and\nmass imbalances. To further characterize the pairing behavior, we analyze the\ndensity-density correlations in momentum space, the so-called shot noise, which\nis experimentally accessible through time-of-flight imaging. At finite spin\npolarization, the latter is known to show distinct maxima at momentum\nconfigurations associated with the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)\ninstability. Besides those maxima, we find that additional features emerge in\nthe noise correlations when mass imbalance is increased, revealing the\nstability of FFLO-type correlations against mass imbalance and furnishing an\nexperimentally accessible signature to probe this type of pairing.",
        "positive": "Observing dipolar confinement-induced resonances in waveguides: We develop a theoretical framework for the quasi-low-dimensional\nconfinement-induced resonances (CIRs) of particles with the arbitrary\nthree-dimensional two-body interactions, based on the Huang-Yang\npseudopotential and the treatment of Feshbach resonances. Using this new\napproach, we analytically obtain some universal properties of dipolar CIRs in\nquasi-one-dimensional (1D) waveguides. We also show that the dipolar CIRs can\nbe induced by tuning the angle between the dipole moments and the waveguide,\nwhich is experimentally observable in quasi-1D Cr and Dy atomic gases. We\nexpect that these tilting angle induced CIRs will open up a new simpler way to\ncontrol the resonant scatterings in quasi-low-dimensional systems."
    },
    {
        "anchor": "Many-Body Formation and Dissociation of a Dipolar Chain Crystal: We propose an experimental scheme to effectively assemble chains of dipolar\ngases with an uniform length in a multi-layer system. The obtained dipolar\nchains can form a chain crystal with the system temperature easily controlled\nby the initial lattice potential and the external field strength during\nprocess. When the density of chains increases, we further observe a second\norder quantum phase transition for the chain crystal to be dissociated toward\nlayers of 2D crystal, where the quantum fluctuation dominates the classical\nenergy and the compressibility diverges at the phase boundary. Experimental\nimplication of such dipolar chain crystal and its quantum phase transition is\nalso discussed.",
        "positive": "Cavity Sub- and Superradiance Enhanced Ramsey Spectroscopy: Ramsey spectroscopy in large, dense ensembles of ultra-cold atoms trapped in\noptical lattices suffers from dipole-dipole interaction induced shifts and\ncollective superradiance limiting its precision and accuracy. We propose a\nnovel geometry implementing fast signal readout with minimal heating for large\natom numbers at lower densities via an optical cavity operated in the weak\nsingle atom but strong collective coupling regime. The key idea is controlled\ncollective transverse $\\pi/2$-excitation of the atoms to prepare a macroscopic\ncollective spin protected from cavity superradiance. This requires that the two\nhalves of the atomic ensemble are coupled to the cavity mode with opposite\nphase, which is naturally realized for a homogeneously filled volume covering\nodd and even sites of the cavity mode along the cavity axis. The origin of the\nsuperior precision can be traced back to destructive interference among\nsub-ensembles in the complex nonlinear collective atom field dynamics. In the\nsame configuration we find surprising regular self-pulsing of the cavity output\nfor suitable continuous illumination. Our simulations for large atom numbers\nemploying a cumulant expansion are qualitatively confirmed by a full quantum\ntreatment of smaller ensembles."
    },
    {
        "anchor": "Measuring entanglement entropy through the interference of quantum\n  many-body twins: Entanglement is one of the most intriguing features of quantum mechanics. It\ndescribes non-local correlations between quantum objects, and is at the heart\nof quantum information sciences. Entanglement is rapidly gaining prominence in\ndiverse fields ranging from condensed matter to quantum gravity. Despite this\ngenerality, measuring entanglement remains challenging. This is especially true\nin systems of interacting delocalized particles, for which a direct\nexperimental measurement of spatial entanglement has been elusive. Here, we\nmeasure entanglement in such a system of itinerant particles using quantum\ninterference of many-body twins. Leveraging our single-site resolved control of\nultra-cold bosonic atoms in optical lattices, we prepare and interfere two\nidentical copies of a many-body state. This enables us to directly measure\nquantum purity, Renyi entanglement entropy, and mutual information. These\nexperiments pave the way for using entanglement to characterize quantum phases\nand dynamics of strongly-correlated many-body systems.",
        "positive": "Localized phase structures growing out of quantum fluctuations in a\n  quench of tunnel-coupled atomic condensates: We investigate the relative phase between two weakly interacting 1D\ncondensates of bosonic atoms after suddenly switching on the tunnel-coupling.\nThe following phase dynamics is governed by the quantum sine-Gordon equation.\nIn the semiclassical limit of weak interactions, we observe the parametric\namplification of quantum fluctuations leading to the formation of breathers\nwith a finite lifetime. The typical lifetime and density of the these\n'quasibreathers' are derived employing exact solutions of the classical\nsine-Gordon equation. Both depend on the initial relative phase between the\ncondensates, which is considered as a tunable parameter."
    },
    {
        "anchor": "Illustration of universal relations for trapped four-fermion system with\n  arbitrary s-wave scattering length: A two-component four-fermion system with equal masses, interspecies s-wave\nscattering length a and vanishing intraspecies interactions under external\nspherically symmetric harmonic confinement is considered. Using a correlated\nGaussian basis set expansion approach, we determine the energies and various\nstructural properties of the energetically lowest-lying gas-like state\nthroughout the crossover for various ranges of the underlying two-body\npotential. Extrapolating to the zero-range limit, our numerical results show\nexplicitly that the total energy, the trap energy as well as certain aspects of\nthe pair distribution function and of the momentum distribution are related\nthrough the so-called integrated contact intensity I(a). Furthermore, it is\nshown explicitly that the total energy and the trap energy are related through\na generalized virial theorem that accounts for a non-zero range.",
        "positive": "Emergent structure in a dipolar Bose gas in a one-dimensional lattice: We consider an ultracold dipolar Bose gas in a one-dimensional lattice. For a\nsufficiently large lattice recoil energy, such a system becomes a series of\nnon-overlapping Bose-Einstein condensates that interact via the long-range\ndipole-dipole interaction (ddi). We model this system via a coupled set of\nnon-local Gross-Pitaevskii equations (GPEs) for lattices of both infinite and\nfinite extent. We find significantly modified stability properties in the\nlattice due to the softening of a discrete roton-like mode, as well as\n\"islands\" in parameter space where biconcave densities are predicted to exist\nthat only exist in the presence of the other condensates on the lattice. We\nsolve for the elementary excitations of the system to check the dynamical\nstability of these solutions and to uncover the nature of their collapse. By\nsolving a coupled set of GPEs exactly on a full numeric grid, we show that this\nemergent biconcave structure can be realized in a finite lattice with atomic\n$^{52}$Cr."
    },
    {
        "anchor": "Mapping out spin and particle conductances in a quantum point contact: We study particle and spin transport in a single mode quantum point contact\nusing a charge neutral, quantum degenerate Fermi gas with tunable, attractive\ninteractions. This yields the spin and particle conductance of the point\ncontact as a function of chemical potential or confinement. The measurements\ncover a regime from weak attraction, where quantized conductance is observed,\nto the resonantly interacting superfluid. Spin conductance exhibits a broad\nmaximum when varying the chemical potential at moderate interactions, which\nsignals the emergence of Cooper pairing. In contrast, the particle conductance\nis unexpectedly enhanced even before the gas is expected to turn into a\nsuperfluid, continuously rising from the plateau at 1/h for weak interactions\nto plateaux-like features at non-universal values as high as 4/h for\nintermediate interactions. For strong interactions, the particle conductance\nplateaux disappear and the spin conductance gets suppressed, confirming the\nspin-insulating character of a superfluid. Our observations document the\nbreakdown of universal conductance quantization as many-body correlations\nappear. The observed anomalous quantization challenges a Fermi liquid\ndescription of the normal phase, shedding new light on the nature of the\nstrongly attractive Fermi gases.",
        "positive": "Spin Solitons in Spin-1 Bose-Einstein Condensates: Solitons in multi-component Bose-Einstein condensates have been paid much\nattention, due to the stability and wide applications of them. The exact\nsoliton solutions are usually obtained for integrable models. In this paper, we\npresent four families of exact spin soliton solutions for non-integrable cases\nin spin-1 Bose-Einstein Condensates. The whole particle density is uniform for\nthe spin solitons, which is in sharp contrast to the previously reported\nsolitons of integrable models. The spectrum stability analysis and numerical\nsimulation indicate the spin solitons can exist stably. The spin density\nredistribution happens during the collision process, which depends on the\nrelative phase and relative velocity between spin solitons. The non-integrable\nproperties of the systems can bring spin solitons experience weak amplitude and\nlocation oscillations after collision. These stable spin soliton excitations\ncould be used to study the negative inertial mass of solitons, the dynamics of\nsoliton-impurity systems, and the spin dynamics in Bose-Einstein condensates."
    },
    {
        "anchor": "Wave function network description and Kolmogorov complexity of quantum\n  many-body systems: Programmable quantum devices are now able to probe wave functions at\nunprecedented levels. This is based on the ability to project the many-body\nstate of atom and qubit arrays onto a measurement basis which produces\nsnapshots of the system wave function. Extracting and processing information\nfrom such observations remains, however, an open quest. One often resorts to\nanalyzing low-order correlation functions - i.e., discarding most of the\navailable information content. Here, we introduce wave function networks - a\nmathematical framework to describe wave function snapshots based on network\ntheory. For many-body systems, these networks can become scale free - a\nmathematical structure that has found tremendous success in a broad set of\nfields, ranging from biology to epidemics to internet science. We demonstrate\nthe potential of applying these techniques to quantum science by introducing\nprotocols to extract the Kolmogorov complexity corresponding to the output of a\nquantum simulator, and implementing tools for fully scalable cross-platform\ncertification based on similarity tests between networks. We demonstrate the\nemergence of scale-free networks analyzing data from Rydberg quantum simulators\nmanipulating up to 100 atoms. We illustrate how, upon crossing a phase\ntransition, the system complexity decreases while correlation length increases\n- a direct signature of build up of universal behavior in data space. Comparing\nexperiments with numerical simulations, we achieve cross-certification at the\nwave-function level up to timescales of 4 $\\mu$ s with a confidence level of\n90%, and determine experimental calibration intervals with unprecedented\naccuracy. Our framework is generically applicable to the output of quantum\ncomputers and simulators with in situ access to the system wave function, and\nrequires probing accuracy and repetition rates accessible to most currently\navailable platforms.",
        "positive": "Ramsey imaging of optical traps: Mapping the potential landscape with high spatial resolution is crucial for\nquantum technologies based on ultracold atoms. Yet, imaging optical dipole\ntraps is challenging because purely optical methods, commonly used to profile\nlaser beams in free space, are not applicable in vacuum. In this work, we\ndemonstrate precise in-situ imaging of optical dipole traps by probing a\nhyperfine transition with Ramsey interferometry. Thereby, we obtain an absolute\nmap of the potential landscape with micrometer resolution and\nshot-noise-limited spectral precision. The idea of the technique is to control\nthe polarization ellipticity of the trap laser beam to induce a differential\nlight shift proportional to the trap potential. By studying the response to\npolarization ellipticity, we uncover a small but significant nonlinearity in\naddition to a dominant linear behavior, which is explained by the geometric\ndistribution of the atomic ensemble. Our technique for imaging of optical traps\ncan find wide application in quantum technologies based on ultracold atoms, as\nit applies to multiple atomic species and is not limited to a particular\nwavelength or trap geometry."
    },
    {
        "anchor": "Three-body losses of a polarized Fermi gas near a p-wave Feshbach\n  resonance in effective field theory: We study three-body recombination of fully spin-polarized ${}^6$Li atoms that\nare interacting resonantly in relative p-waves. Motivated by a recent\nexperiment, we focus on negative scattering volumes where three atoms recombine\ninto a deep dimer and another atom. We calculate the three-body recombination\nrate using a Faddeev equation derived from effective field theory. In\nparticular, we study the magnetic field and temperature dependences of the loss\nrate and use the recombination data to determine the effective range of the\np-wave atom-atom interaction. We also predict the existence of a shallow\nthree-body bound state that manifests itself as a prominent feature in the\nenergy-dependent three-body recombination rate.",
        "positive": "Angular topological superfluid and topological vortex in an ultracold\n  Fermi gas: We show that pairing in an ultracold Fermi gas under\nspin-orbital-angular-momentum coupling (SOAMC) can acquire topological\ncharacters encoded in the quantized angular degrees of freedom. The resulting\ntopological superfluid is the angular analog of its counterpart in a\none-dimensional Fermi gas with spin-orbit coupling, but characterized by a Zak\nphase defined in the angular-momentum space. Upon tuning the SOAMC parameters,\na topological phase transition occurs, which is accompanied by the closing of\nthe quasiparticle excitation gap. Remarkably, a topological vortex state can\nalso be stabilized by deforming the Fermi surface, which is topologically\nnon-trivial in both the coordinate and angular-momentum space, offering\ninteresting potentials for applications in quantum information and quantum\ncontrol. We discuss how the topological phase transition and the exotic vortex\nstate can be detected experimentally."
    },
    {
        "anchor": "Renormalization theory of a two dimensional Bose gas: quantum critical\n  point and quasi-condensed state: We present a renormalization group construction of a weakly interacting Bose\ngas at zero temperature in the two-dimensional continuum, both in the quantum\ncritical regime and in the presence of a condensate fraction. The construction\nis performed within a rigorous renormalization group scheme, borrowed from the\nmethods of constructive field theory, which allows us to derive explicit bounds\non all the orders of renormalized perturbation theory. Our scheme allows us to\nconstruct the theory of the quantum critical point completely, both in the\nultraviolet and in the infrared regimes, thus extending previous heuristic\napproaches to this phase. For the condensate phase, we solve completely the\nultraviolet problem and we investigate in detail the infrared region, up to\nlength scales of the order $(\\lambda^3 \\rho_0)^{-1/2}$ (here $\\lambda$ is the\ninteraction strength and $\\rho_0$ the condensate density), which is the largest\nlength scale at which the problem is perturbative in nature. We exhibit\nviolations to the formal Ward Identities, due to the momentum cutoff used to\nregularize the theory, which suggest that previous proposals about the\nexistence of a non-perturbative non-trivial fixed point for the infrared flow\nshould be reconsidered.",
        "positive": "Breakdown of scale invariance in a quasi-two-dimensional Bose gas due to\n  the presence of the third dimension: In this Rapid Communication, we describe how the presence of the third\ndimension may break the scale invariance in a two-dimensional Bose gas in a\npancake-shaped trap. From the two-dimensional perspective, the possibility of a\nweak spilling of the atomic density beyond the ground-state of the confinement\nalters the two-dimensional chemical potential; in turn, this correction no\nlonger supports scale invariance. We compare experimental data with numerical\nand analytic perturbative results and find a good agreement."
    },
    {
        "anchor": "Steady-state phase diagram of quantum gases in a lattice coupled to a\n  membrane: In a recent experiment [Vochezer {\\it et al.,} Phys. Rev. Lett. \\textbf{120},\n073602 (2018)], a novel kind of hybrid atom-opto-mechanical system has been\nrealized by coupling atoms in a lattice to a membrane. While such system\npromises a viable contender in the competitive field of simulating\nnon-equilibrium many-body physics, its complete steady-state phase diagram is\nstill lacking. Here we study the phase diagram of this hybrid system based on\nan atomic Bose-Hubbard model coupled to a quantum harmonic oscillator. We take\nboth the expectation value of the bosonic operator and the mechanical motion of\nthe membrane as order parameters, and thereby identify four different quantum\nphases. Importantly, we find the atomic gas in the steady state of such\nnon-equilibrium setting undergoes a superfluid-Mott-insulator transition when\nthe atom-membrane coupling is tuned to increase. Such steady-state phase\ntransition can be seen as the non-equilibrium counterpart of the conventional\nsuperfluid-Mott-insulator transition in the ground state of Bose-Hubbard model.\nFurther, no matter which phase the quantum gas is in, the mechanic motion of\nthe membrane exhibits a transition from an incoherent vibration to a coherent\none when the atom-membrane coupling increases, agreeing with the experimental\nobservations. Our present study provides a simple way to study non-equilibrium\nmany-body physics that is complementary to ongoing experiments on the hybrid\natomic and opto-mechanical systems.",
        "positive": "The true mechanism of spontaneous order from turbulence in\n  two-dimensional superfluid manifolds: In a two-dimensional (2D) turbulent fluid containing point-like vortices,\nLars Onsager predicted that adding energy to the fluid can lead to the\nformation of persistent clusters of like-signed vortices, i.e., Onsager vortex\n(OV) clusters. In the evolution of 2D superfluid turbulence in a uniform\ndisk-shaped Bose-Einstein condensate (BEC), it was discovered that a pair of OV\nclusters with opposite signs can form without any energy input. This striking\nspontaneous order was explained as due to a vortex evaporative-heating\nmechanism, i.e., annihilations of vortex-antivortex pairs which remove the\nlowest-energy vortices and thereby boost the mean energy per vortex. However,\nin our search for exotic OV states in a boundaryless 2D spherical BEC, we found\nthat OV clusters never form despite the annihilations of vortex pairs. Our\nanalysis reveals that contrary to the general belief, vortex-pair annihilation\nemits intense sound waves, which damp the motion of all vortices and hence\nsuppress the formation of OV clusters. We also present unequivocal evidences\nshowing that the true mechanism underlying the observed spontaneous OV state is\nthe escaping of vortices from the BEC boundary. Uncovering this mechanism paves\nthe way for a comprehensive understanding of emergent vortex orders in 2D\nmanifolds of superfluids driven far from equilibrium."
    },
    {
        "anchor": "Particle and pair spectra for strongly correlated Fermi gases: A\n  real-frequency solver: The strongly attractive Fermi gas in the BCS-BEC crossover is efficiently\ndescribed in terms of coupled fermions and fermion pairs, or molecules. We\ncompute the spectral functions of both fermions and pairs in the normal state\nnear the superfluid transition using a Keldysh formulation in real frequency.\nThe mutual influence between fermions and pairs is captured by solving the\nself-consistent Luttinger-Ward equations: these include both the damping of\nfermions by scattering off dressed pairs, as well as the decay of pair states\nby dissociation into two dressed fermions. The pair spectra encode contact\ncorrelations between fermions and form the basis for computing dynamical\nresponse functions and transport properties.",
        "positive": "Exact results for nonequilibrium dynamics in Wigner phase space: We study time evolution of Wigner function of an initially interacting\none-dimensional quantum gas following the switch-off of the interactions. For\nthe scenario where at $t=0$ the interactions are suddenly suppressed, we derive\na relationship between the dynamical Wigner function and its initial value. A\ntwo-particle system initially interacting through two different interactions of\nDirac delta type is examined. For a system of particles that is suddenly let to\nmove ballistically (without interactions) in a harmonic trap in d dimensions,\nand using time evolution of one-body density matrix, we derive a relationship\nbetween the time dependent Wigner function and its initial value. Using the\ninverse Wigner transform we obtain, for an initially harmonically trapped\nnoninteracting particles in $d$ dimensions, the scaling law satisfied by the\ndensity matrix at time $t$ after a sudden change of the trapping frequency.\nFinally, the effects of interactions are analyzed in the dynamical Wigner\nfunction."
    },
    {
        "anchor": "Cold Atom Qubits: We discuss a laser-trapped cold-atom superfluid qubit system. Each qubit is\nproposed as a macroscopic two-state system based on a set of Bose-Einstein\ncondensate (BEC) currents circulating in a ring, cut with a Josephson barrier.\nWe review the effective low energy description of a single BEC ring. In\nparticular, it is demonstrated that such system has a set of metastable current\nstates which, for certain range of parameters, form an effective two-state\nsystem, or a qubit. We show how this qubit can be initialized and manipulated\nwith currently available laser-trapping techniques. We also discuss mechanisms\nof coupling several such ring qubits as well as measuring individual qubit-ring\nsystems.",
        "positive": "Quantum critical behavior of ultracold atoms in two-dimensional optical\n  lattices: As the temperature of a many-body system approaches absolute zero, thermal\nfluctuations of observables cease and quantum fluctuations dominate.\nCompetition between different energies, such as kinetic energy, interactions or\nthermodynamic potentials, can induce a quantum phase transition between\ndistinct ground states. Near a continuous quantum phase transition, the\nmany-body system is quantum critical, exhibiting scale invariant and universal\ncollective behavior \\cite{Coleman05Nat, Sachdev99QPT}. Quantum criticality has\nbeen actively pursued in the study of a broad range of novel materials\n\\cite{vdMarel03Nat, Lohneysen07rmp, G08NatPhys, Sachdev08NatPhys}, and can\ninvoke new insights beyond the Landau-Ginzburg-Wilson paradigm of critical\nphenomena \\cite{Senthil04prb}. It remains a challenging task, however, to\ndirectly and quantitatively verify predictions of quantum criticality in a\nclean and controlled system. Here we report the observation of quantum critical\nbehavior in a two-dimensional Bose gas in optical lattices near the\nvacuum-to-superfluid quantum phase transition. Based on \\textit{in situ}\ndensity measurements, we observe universal scaling of the equation of state at\nsufficiently low temperatures, locate the quantum critical point, and determine\nthe critical exponents. The universal scaling laws also allow determination of\nthermodynamic observables. In particular, we observe a finite entropy per\nparticle in the critical regime, which only weakly depends on the atomic\ninteraction. Our experiment provides a prototypical method to study quantum\ncriticality with ultracold atoms, and prepares the essential tools for further\nstudy on quantum critical dynamics."
    },
    {
        "anchor": "Tunable critical supercurrent and spin-asymmetric Josephson effect in\n  superlattices: Combining the Josephson effect with magnetism, or spin dependence in general,\ncreates novel physical phenomena. The spin-asymmetric Josephson effect is a\npredicted phenomenon where a spin-dependent potential applied across a\nJosephson junction induces a spin-polarized Josephson current. Here, we propose\nan approach to observe the spin-asymmetric Josephson effect with spin-dependent\nsuperlattices, realizable, e.g., in ultracold atomic gases. We show that\nobserving this effect is feasible by studying numerically the quantum dynamics\nof the system in one dimension. Furthermore, we show that the enhancement, or\ntunability, of the critical supercurrent in ferromagnetic Josephson junctions\n[F. S. Bergeret, A. F. Volkov, and K. B. Efetov, Phys. Rev. Lett. 86, 3140\n(2001)] can be explained by the spin-asymmetric Josephson effect.",
        "positive": "Tunable topological phases with fermionic atoms in a one-dimensional\n  flux lattice: We present a simple scheme for implementing a one-dimensional (1D)\nmagnetic-flux lattice of ultracold fermionic spin-$1/2$ atoms. The resulting\ntight-binding model supports gapped and gapless topological phases, and chiral\ncurrents for Meissner and vortex phases. Its single-particle spectra exhibit\ntopological flat bands at small flux, and the flatness sensitively depends on\nhopping strength. An effective $p$-wave interaction arises in a $s$-wave paired\nsuperfluid. Treating atomic internal states as forming a synthetic dimension\nand balancing the interplay of magnetic flux and Zeeman field, our model\ndescribes a tunable topological Fermi superfluid, which paves the way towards\nexperimental explorations of non-Abelian topological matter in 1D atomic\nquantum gases."
    },
    {
        "anchor": "Reentrant Superfluidity and Pair Density Wave in Single Component\n  Dipolar Fermi Gases: We study the superfluidity of single component dipolar Fermi gases in three\ndimensions within a pairing fluctuation theory. The transition temperature\n$T_{c}$ for the dominant $p_z$ wave superfluidity exhibits a remarkable\nre-entrant behavior as a function of the pairing strength induced by the\ndipole-dipole interaction (DDI), which leads to an anisotropic pair dispersion.\nThe anisotropy and the long range nature of the DDI cause $T_c$ to vanish for a\nnarrow range of intermediate interaction strengths, where a pair density wave\nstate emerges as the ground state. The superfluid density and thermodynamics\nbelow $T_{c}$, along with the density profiles in a harmonic trap, are\ninvestigated as well, throughout the BCS-BEC crossover. Implications for\nexperiments are discussed.",
        "positive": "Impenetrable SU(N) fermions in one-dimensional lattices: We study SU(N) fermions in the limit of infinite on-site repulsion between\nall species. We focus on states in which every pair of consecutive fermions\ncarries a different spin flavor. Since the particle order cannot be changed\n(because of the infinite on-site repulsion) and contiguous fermions have a\ndifferent spin flavor, we refer to the corresponding constrained model as the\nmodel of distinguishable quantum particles. We introduce an exact numerical\nmethod to calculate equilibrium one-body correlations of distinguishable\nquantum particles based on a mapping onto noninteracting spinless fermions. In\ncontrast to most many-body systems in one dimension, which usually exhibit\neither power-law or exponential decay of off-diagonal one-body correlations\nwith distance, distinguishable quantum particles exhibit a Gaussian decay of\none-body correlations in the ground state, while finite-temperature\ncorrelations are well described by stretched exponential decay."
    },
    {
        "anchor": "Liquid crystal phases of two-dimensional dipolar gases and\n  Berezinskii-Kosterlitz-Thouless melting: Liquid crystals are phases of matter intermediate between crystals and\nliquids. Whereas classical liquid crystals have been known for a long time and\nare used in electro-optical displays, much less is known about their quantum\ncounterparts. There is growing evidence that quantum liquid crystals play a\ncentral role in many electron systems including high temperature\nsuperconductors, but a quantitative understanding is lacking due to disorder\nand other complications. Here, we analyse the quantum phase diagram of a\ntwo-dimensional dipolar gas, which exhibits stripe, nematic and supersolid\nphases. We calculate the stiffness constants determining the stability of the\nnematic and stripe phases, and the melting of the stripes set by the\nproliferation of topological defects is analysed microscopically. Our results\nfor the critical temperatures of these phases demonstrate that a controlled\nstudy of the interplay between quantum liquid and superfluid phases is within\nexperimental reach for the first time, using dipolar gases.",
        "positive": "Observation of vortices and vortex stripes in a dipolar Bose-Einstein\n  condensate: Quantized vortices are the prototypical feature of superfluidity. Pervasive\nin all natural systems, vortices are yet to be observed in dipolar quantum\ngases. Here, we exploit the anisotropic nature of the dipole-dipole interaction\nof a dysprosium Bose-Einstein condensate to induce angular symmetry breaking in\nan otherwise cylindrically symmetric pancake-shaped trap. Tilting the magnetic\nfield towards the radial plane deforms the cloud into an ellipsoid through\nmagnetostriction, which is then set into rotation. At stirring frequencies\napproaching the radial trap frequency, we observe the generation of dynamically\nunstable surface excitations, which cause angular momentum to be pumped into\nthe system through vortices. Under continuous rotation, the vortices arrange\ninto a stripe configuration along the field--in close corroboration with\nsimulations--realizing a long sought-after prediction for dipolar vortices."
    },
    {
        "anchor": "SU(4)-symmetric Hubbard model at quarter filling: Insights from the\n  dynamical mean-field approach: We apply the dynamical mean-field approach to the four-component\nSU(4)-symmetric Fermi-Hubbard model to study transitions between different\nmagnetically ordered phases as well as the hysteresis behavior in the unordered\nregime. At quarter filling (one particle per site) on the square lattice we\nidentify both the two-sublattice and plaquette-ordered antiferromagnetic phases\nwith the corresponding entropy-driven hierarchy for critical temperatures. We\nalso analyze the behavior of thermodynamic characteristics: the local double\noccupancy, compressibility, and entropy per particle, which are relevant for\nexperiments with ultracold alkaline-earth(-like) atoms in optical lattices.",
        "positive": "Transition to a Bose-Einstein condensate of excitons at sub-Kelvin\n  temperatures: Bose-Einstein condensation (BEC) is a quantum mechanical phenomenon directly\nlinked to the quantum statistics of bosons. While cold atomic gases provide a\nnew arena for exploring the nature of BEC, a long-term quest to confirm BEC of\nexcitons, quasi-Bose particles formed as a bound state of an electron-hole\npair, has been underway since its theoretical prediction in the 1960s.\nEnsembles of electrons and holes are complex quantum systems with strong\nCoulomb correlations; thus, it is non-trivial whether nature chooses a form of\nexciton BEC. Various systems have been examined in bulk and two-dimensional\nsemiconductors and also exciton-photon hybrid systems. Among them, the 1s\nparaexciton state in a single crystal of Cu2O has been a prime candidate for\nrealizing three-dimensional BEC. The large binding energy and long lifetime\nenable preparation of cold excitons in thermal equilibrium with the lattice and\ndecoupled from the radiation field. However, collisional loss severely limits\nthe conditions for reaching BEC. Such a system with a large inelastic cross\nsection is excluded in atomic BEC experiments, where a small inelastic\nscattering rate and efficient elastic scattering are necessary for evaporative\ncooling. Here we demonstrate that it is nevertheless possible to achieve BEC by\ncooling paraexcitons to sub-Kelvin temperatures in a cold phonon bath. Emission\nspectra from paraexcitons in a three-dimensional trap show an anomalous\ndistribution in a threshold-like manner at the critical number of BEC expected\nfor ideal bosons. Bosonic stimulated scattering into the condensate and\ncollisional loss compete and limit the condensate to a fraction of about 1%.\nThis observation adds a new class of experimentally accessible BEC for\nexploring a rich variety of matter phases of electron-hole ensembles."
    },
    {
        "anchor": "Visualization of Dimensional Effects in Collective Excitations of\n  Optically Trapped Quasi-Two-Dimensional Bose Gases: We analyze the macroscopic dynamics of a Bose gas axially confined in an\noptical lattice with a superimposed harmonic trap, taking into account weak\ntunneling effect. Our results show that upon transition to the\nquasi-two-dimensional (2D) regime of the trapped gas, the 3D equation of state\nand equilibrium density profile acquire corrections from 2D many-body effects.\nThe corresponding frequency shift in the transverse breathing mode is\naccessible within current facilities, suggesting a direct observation of\ndimensional effects. Comparisons with other relevant effects are also\npresented.",
        "positive": "Many-body dynamics of a Bose--Einstein condensate collapsing by quantum\n  tunneling: The dynamics of a Bose-Einstein condensate of atoms having attractive\ninteractions is studied using quantum many-body simulations. The collapse of\nthe condensate by quantum tunneling is numerically demonstrated and the\ntunneling rate is calculated. The correlation properties of the quantum\nmany-body state are investigated."
    },
    {
        "anchor": "Inhomogeneous Topological Superfluidity in One-Dimensional\n  Spin-Orbit-Coupled Fermi Gases: We theoretically predict an exotic topological superfluid state with\nspatially modulated pairing gap in one-dimensional spin-orbit-coupled Fermi\ngases. This inhomogeneous topological superfluidity is induced by applying\nsimultaneously a perpendicular Zeeman magnetic field and an equally weighted\nRashba and Dresselhaus spin-orbit coupling in one-dimensional optical lattices.\nBased on the self-consistent Bogoliubov--de Gennes theory, we confirm that this\nnovel topological phase is a unique condensation of Cooper pairs, which\nmanifests the interplay between the inhomogeneity of superfluid and its\nnontrivial topological structure. The properties of the emergent Majorana bound\nstates are investigated in detail by examining the associated $\\mathbb{Z}_{2}$\ntopological number, the eigenenergy and density of states spectra, as well as\nthe wave functions of the localized Majorana end modes. Experimental\nfeasibility of observing this new topological state of matter is also\ndiscussed.",
        "positive": "Ultradilute quantum liquid drops: Using quantum Monte Carlo methods we have studied dilute Bose-Bose mixtures\nwith attractive interspecies interaction in the limit of zero temperature. The\ncalculations are exact within some statistical noise and thus go beyond\nprevious perturbative estimations. By tuning the intensity of the attraction,\nwe observe the evolution of an $N$-particle system from a gas to a self-bound\nliquid drop. This observation agrees with recent experimental findings and\nallows for the study of an ultradilute liquid never observed before in Nature."
    },
    {
        "anchor": "Effective Spin-2 Quasi-particles at Linear Dispersive Five-fold\n  Degenerate Points with Tunable Topological Chern Numbers: In this work, which is based on spin-2 vectors and traceless spin-2 tensors,\nan effective Hamiltonian is constructed with a linearly dispersive five-fold\ndegenerate point with spin-2 vector-momentum couplings. For the model without\nspin-2 vector-tensor coupling, the topological Chern numbers of five bands are\ncalculated as 4, 2, 0, -2, -4. After including spin-2 vector-tensor coupling,\nseparate topological Chern numbers are obtained for different couplings. A\ncubic lattice of atoms with five internal states is designed to realize two\nfive-fold degenerate points. The Chern numbers of the bands can be changed by\ntuning the coupling coefficient. In this work we propose a theoretical design\nto obtain spin-2 quasi-particles.",
        "positive": "Non-equilibrium Bose-Einstein Condensation: We investigate formation of Bose-Einstein condensates under non-equilibrium\nconditions using numerical simulations of the three-dimensional\nGross-Pitaevskii equation. For this, we set initial random weakly nonlinear\nexcitations and the forcing at high wave numbers, and study propagation of the\nturbulent spectrum toward the low wave numbers. Our primary goal is to compare\nthe results for the evolving spectrum with the previous results obtained for\nthe kinetic equation of weak wave turbulence. We demonstrate existence of a\nregime for which good agreement with the wave turbulence results is found in\nterms of the main features of the previously discussed self-similar solution.\nIn particular, we find a reasonable agreement with the low-frequency and the\nhigh-frequency power-law asymptotics of the evolving solution, including the\nanomalous power-law exponent $x^* \\approx 1.24$ for the three-dimensional\nwaveaction spectrum. We also study the regimes of very weak turbulence, when\nthe evolution is affected by the discreteness of the Fourier space, and the\nstrong turbulence regime when emerging condensate modifies the wave dynamics\nand leads to formation of strongly nonlinear filamentary vortices."
    },
    {
        "anchor": "Supersolid phase in atomic gases with magnetic dipole interaction: A major obstacle for the experimental realization of a supersolid phase with\ncold atomic gases in an optical lattice is the weakness of the nearest-neighbor\ninteractions achievable via magnetic dipole-dipole interactions. In this\nletter, we show that using a large filling of atoms within each well the\ncharacteristic energy scales are strongly enhanced. Within this regime, the\nsystem is well described by the rotor model, and the qualitative behavior of\nthe phase diagram derives from mean-field theory. We find a stable supersolid\nphase for realistic parameters with chromium atoms.",
        "positive": "Thermally isolated Luttinger liquids with noisy Hamiltonians: We study the dynamics of a quantum-coherent thermally isolated Luttinger\nliquid with noisy Luttinger parameter. To characterize the fluctuations of the\nabsorbed energy in generic noise-driven systems, we first identify two types of\nenergy moments, which can help tease apart the effects of classical\n(sample-to-sample) and quantum sources of fluctuations. One type of moment\ncaptures the total fluctuations due to both sources, while the other one\ncaptures the effect of the classical source only. We then demonstrate that in\nthe Luttinger liquid case, the two types of moments agree in the thermodynamic\nlimit, indicating that the classical source dominates. In contrast to\nequilibrium thermodynamics, in this driven system the relative fluctuations of\nenergy do not decay with the system size. Additionally, we study the deviations\nof equal-time correlation functions from their ground-state value, and find a\nsimple scaling behavior."
    },
    {
        "anchor": "Floquet topological quantum phase transitions in the transverse\n  Wen-plaquette model: Our aim in this work is to study the nonequilibrium behavior of the\ntopological quantum phase transition in the transverse Wen-plaquette model. We\nshow that under the effect of a nonadiabatic driving the system exhibits a new\ntopological phase and a rich phase diagram. We define generalized topological\norder parameters by considering cycle-averaged expectation values of string\noperators in a Floquet state",
        "positive": "Nonlinear Bosonization and Refermionization in One Dimension with the\n  Keldysh Functional Integral: We develop a self-contained approach to bosonization and refermionization\nusing the Keldysh functional integral. Starting from fermionic particles, we\nbosonize the system and obtain a description in terms of the Tomonaga-Luttinger\nliquid, with, in addition, an infinite series of interaction terms arising from\nthe curvature of the fermionic particle spectrum. We explicitly calculate the\nleading interaction term and check its consistency with a different approach\nbased on the Matsubara framework, within which we calculate the second leading\ninteraction term, as well. Moreover, we bosonize weakly and strongly\ninteracting bosonic particles, and, finally, refermionize interacting phonons\ninto non-interacting fermionic quasiparticles. The work culminates in a map\nbetween bosonic and fermionic particles and effective bosonic and fermionic\nexcitations, representing phonons and fermionic quasiparticles."
    },
    {
        "anchor": "Universal contact of strongly interacting fermions at finite\n  temperatures: The recently discovered universal thermodynamic behaviour of dilute, strongly\ninteracting Fermi gases also implies a universal structure in the many-body\npair-correlation function at short distances, as quantified by the contact\n${\\cal I}$. This quantity is an excellent indicator of the presence of strong\ncorrelations in these systems, which provide a highly accessible physical model\nfor other strongly correlated quantum fluids. Here we theoretically calculate\nthe temperature dependence of this universal contact for a Fermi gas in free\nspace and in a harmonic trap. At high temperatures above the Fermi degeneracy\ntemperature, $T\\gtrsim T_{F}$, we obtain a reliable non-perturbative quantum\nvirial expansion up to third order. At low temperatures we compare different\napproximate strong coupling theories. These make different predictions, which\nneed to be tested either by future experiments or advanced quantum Monte Carlo\nsimulations. We conjecture that in the universal unitarity limit, the contact\nor correlation decreases monotonically with increasing temperature, unless the\ntemperature is significantly lower than the critical temperature, $T\\ll\nT_{c}\\sim0.2T_{F}$. We also discuss briefly how to measure the universal\ncontact either in homogeneous or harmonically trapped Fermi gases.",
        "positive": "Half-solitons in a polariton quantum fluid behave like magnetic\n  monopoles: Monopoles are magnetic charges, point-like sources of magnetic field.\nContrary to electric charges they are absent in Maxwell's equations and have\nnever been observed as fundamental particles. Quantum fluids such as spinor\nBose-Einstein condensates have been predicted to show monopoles in the form of\nexcitations combining phase and spin topologies. Thanks to its unique spin\nstructure and the direct optical control of the fluid wavefunction, an ideal\nsystem to experimentally explore this phenomenon is a condensate of\nexciton-polaritons in a semiconductor microcavity. We use this system to create\nhalf-solitons, non-linear excitations with mixed spin-phase geometry. By\ntracking their trajectory, we demonstrate that half-solitons behave as\nmonopoles, magnetic charges accelerated along an effective magnetic field\npresent in the microcavity. The field-induced spatial separation of\nhalf-solitons of opposite charges opens the way to the generation of magnetic\ncurrents in a quantum fluid."
    },
    {
        "anchor": "Decay of a Quantum Knot: We experimentally study the dynamics of quantum knots in a uniform magnetic\nfield in spin-1 Bose-Einstein condensates. The knot is created in the polar\nmagnetic phase, which rapidly undergoes a transition towards the ferromagnetic\nphase in the presence of the knot. The magnetic order becomes scrambled as the\nsystem evolves, and the knot disappears. Strikingly, over long evolution times,\nthe knot decays into a polar-core spin vortex, which is a member of a class of\nsingular SO(3) vortices. The polar-core spin vortex is stable with an observed\nlifetime comparable to that of the condensate itself. The structure is similar\nto that predicted to appear in the evolution of an isolated monopole defect,\nsuggesting a possible universality in the observed topological transition.",
        "positive": "Reinforcement Learning in Ultracold Atom Experiments: Cold atom traps are at the heart of many quantum applications in science and\ntechnology. The preparation and control of atomic clouds involves complex\noptimization processes, that could be supported and accelerated by machine\nlearning. In this work, we introduce reinforcement learning to cold atom\nexperiments and demonstrate a flexible and adaptive approach to control a\nmagneto-optical trap. Instead of following a set of predetermined rules to\naccomplish a specific task, the objectives are defined by a reward function.\nThis approach not only optimizes the cooling of atoms just as an\nexperimentalist would do, but also enables new operational modes such as the\npreparation of pre-defined numbers of atoms in a cloud. The machine control is\ntrained to be robust against external perturbations and able to react to\nsituations not seen during the training. Finally, we show that the time\nconsuming training can be performed in-silico using a generic simulation and\ndemonstrate successful transfer to the real world experiment."
    },
    {
        "anchor": "Formation of nonlinear X-waves in condensed matter systems: X-waves are an example of a localized wave packet solution of the homogeneous\nwave equation, and can potentially arise in any area of physics relating to\nwave phenomena, such as acoustics, electromagnetism, or quantum mechanics. They\nhave been predicted in condensed matter systems such as atomic Bose-Einstein\ncondensates in optical lattices, and were recently observed in\nexciton-polariton condensates. Here we show that polariton X-waves result from\nan interference between two separating wave packets that arise from the\ncombination of a locally hyperbolic dispersion relation and nonlinear\ninteractions. We show that similar X-wave structures could also be observed in\nexpanding spin-orbit coupled Bose-Einstein condensates.",
        "positive": "Superfluid Density of a Spin-orbit Coupled Bose Gas: We discuss the superfluid properties of a Bose-Einstein condensed gas with\nspin-orbit coupling, recently realized in experiments. We find a finite normal\nfluid density $\\rho_n$ at zero temperature which turns out to be a function of\nthe Raman coupling. In particular, the entire fluid becomes normal at the\ntransition point from the zero momentum to the plane wave phase, even though\nthe condensate fraction remains finite. We emphasize the crucial role played by\nthe gapped branch of the elementary excitations and discuss its contributions\nto various sum rules. Finally, we prove that an independent definition of\nsuperfluid density $\\rho_s$, using the phase twist method, satisfies the\nequality $\\rho_n+\\rho_s=\\rho$, the total density, despite the breaking of\nGalilean invariance."
    },
    {
        "anchor": "Slow quench dynamics of Mott-insulating regions in a trapped Bose gas: We investigate the dynamics of Mott-insulating regions of a trapped bosonic\ngas as the interaction strength is changed linearly with time. The bosonic gas\nconsidered is loaded into an optical lattice and confined to a parabolic\ntrapping potential. Two situations are addressed: the formation of Mott domains\nin a superfluid gas as the interaction is increased, and their melting as the\ninteraction strength is lowered. In the first case, depending on the local\nfilling, Mott-insulating barriers can develop and hinder the density and energy\ntransport throughout the system. In the second case, the density and local\nenergy adjust rapidly whereas long range correlations require longer time to\nsettle. For both cases, we consider the time evolution of various observables:\nthe local density and energy, and their respective currents, the local\ncompressibility, the local excess energy, the heat and single particle\ncorrelators. The evolution of these observables is obtained using the\ntime-dependent density-matrix renormalization group technique and comparisons\nwith time-evolutions done within the Gutzwiller approximation are provided.",
        "positive": "Nonlinear dynamics of Aharonov-Bohm cages: The interplay of $\\pi$-flux and lattice geometry can yield full localization\nof quantum dynamics in lattice systems, a striking interference phenomenon\nknown as Aharonov-Bohm caging. At the level of the single-particle energy\nspectrum, this full-localization effect is attributed to the collapse of Bloch\nbands into a set of perfectly flat (dispersionless) bands. In such lattice\nmodels, the effects of inter-particle interactions generally lead to a breaking\nof the cages, and hence, to the spreading of the wavefunction over the lattice.\nMotivated by recent experimental realizations of analog Aharonov-Bohm cages for\nlight, using coupled-waveguide arrays, we hereby demonstrate that caging always\noccurs in the presence of local nonlinearities. As a central result, we focus\non special caged solutions, which are accompanied by a breathing motion of the\nfield intensity, that we describe in terms of an effective two-mode model\nreminiscent of a bosonic Josephson junction. Moreover, we explore the quantum\nregime using small particle ensembles, and we observe quasi-caged\ncollapse-revival dynamics with negligible leakage. The results stemming from\nthis work open an interesting route towards the characterization of nonlinear\ndynamics in interacting flat band systems."
    },
    {
        "anchor": "Topological phases in small quantum Hall samples: Topological order has proven a useful concept to describe quantum phase\ntransitions which are not captured by the Ginzburg-Landau type of\nsymmetry-breaking order. However, lacking a local order parameter, topological\norder is hard to detect. One way to detect is via direct observation of anyonic\nproperties of excitations which are usually discussed in the thermodynamic\nlimit, but so far has not been realized in macroscopic quantum Hall samples.\nHere we consider a system of few interacting bosons subjected to the lowest\nLandau level by a gauge potential, and theoretically investigate vortex\nexcitations in order to identify topological properties of different ground\nstates. Our investigation demonstrates that even in surprisingly small systems\nanyonic properties are able to characterize the topological order. In addition,\nfocusing on a system in the Laughlin state, we study the robustness of its\nanyonic behavior in the presence of tunable finite-range interactions acting as\na perturbation. A clear signal of a transition to a different state is\nreflected by the system's anyonic properties.",
        "positive": "Manipulation of an elongated internal Josephson junction of bosonic\n  atoms: We report on the experimental characterization of a spatially extended\nJosephson junction realized with a coherently-coupled two-spin-component\nBose-Einstein condensate. The cloud is trapped in an elongated potential such\nthat that transverse spin excitations are frozen. We extract the non-linear\nparameter with three different manipulation protocols. The outcomes are all\nconsistent with a simple local density approximation of the spin hydrodynamics,\ni.e., of the so-called Bose-Josephson junction equations. We also identify a\nmethod to produce states with a well defined uniform magnetization."
    },
    {
        "anchor": "A simple method for generating Bose-Einstein condensates in a weak\n  hybrid trap: We report on a simple novel trapping scheme for the generation of\nBose-Einstein condensates of $^{87}$Rb atoms. This scheme employs a\nnear-infrared single beam optical dipole trap combined with a weak magnetic\nquadrupole field as used for magneto-optical trapping to enhance the\nconfinement in axial direction. Efficient forced evaporative cooling to the\nphase transition is achieved in this weak hybrid trap via reduction of the\nlaser intensity of the optical dipole trap at constant magnetic field gradient.",
        "positive": "Propagating wave-packets and quantised currents in coherently driven\n  polariton superfluids: We study the properties of propagating polariton wave-packets and their\nconnection to the stability of doubly charged vortices. Wave-packet propagation\nand related photoluminescence spectra exhibit a rich behaviour dependent on the\nexcitation regime. We show that, because of the non-quadratic polariton\ndispersion, doubly charged vortices are stable only when initiated in\nwave-packets propagating at small velocities. Vortices propagating at larger\nvelocities, or those imprinted directly into the polariton optical parametric\noscillator (OPO) signal and idler are always unstable to splitting."
    },
    {
        "anchor": "Topological States in a One-Dimensional Fermi Gas with Attractive\n  Interactions: We describe a novel topological superfluid state, which forms in a\none-dimensional Fermi gas with Rashba-like spin-orbit coupling, a Zeeman field\nand intrinsic attractive interactions. In spite of total number conservation\nand the presence of gapless excitations, Majorana-like zero modes appear in\nthis system and can be linked with interfaces between two distinct phases that\nnaturally form at different regions of the harmonic trap. As a result, the low\nlying collective excitations of the system, including the dipole oscillations\nand the long-wavelength phonons, are doubly degenerate. While backscattering\nfrom point impurities can lead to a splitting of the degeneracies that scales\nalgebraically with the system size, the smooth confining potential can only\ncause an exponentially small splitting. We show that the topological state can\nbe uniquely probed by a pumping effect induced by a slow sweep of the Zeeman\nfield from a high initial value down to zero field.",
        "positive": "Quantum simulation of conductivity plateaux and fractional quantum Hall\n  effect using ultracold atoms: We analyze the role of impurities in the fractional quantum Hall effect using\na highly controllable system of ultracold atoms. We investigate the mechanism\nresponsible for the formation of plateaux in the resistivity/conductivity as a\nfunction of the applied magnetic field in the lowest Landau level regime. To\nthis aim, we consider an impurity immersed in a small cloud of an ultracold\nquantum Bose gas subjected to an artificial magnetic field. We consider\nscenarios corresponding to experimentally realistic systems with gauge fields\ninduced either by rotation or by appropriately designed laser fields. Systems\nof this kind are adequate to simulate quantum Hall effects in ultracold atom\nsetups. We use exact diagonalization for few atoms and, to emulate transport\nequations, we analyze the time evolution of the system under a periodic\nperturbation. We provide a theoretical proposal to detect the up-to-now elusive\npresence of strongly correlated states related to fractional filling factors in\nthe context of ultracold atoms. We analyze the conditions under which these\nstrongly correlated states are associated with the presence of the\nresistivity/conductivity plateaux. Our main result is the presence of a plateau\nin a region, where the transfer between localized and non-localized particles\ntakes place, as a necessary condition to maintain a constant value of the\nresistivity/conductivity as the magnetic field increases."
    },
    {
        "anchor": "Self-trapping of excitations: Two-dimensional quasiparticle solitons in\n  an extended Bose-Hubbard dimer array: Considering a two-dimensional Bose-Hubbard spinor lattice with weak nearest\nneighbour interactions and no particle transfer between sites, we theoretically\nstudy the transport of energy from one initially excited dimer, to the rest of\nthe lattice. Beyond a critical interaction strength, low energy on-site\nexcitations are quickly dispersed throughout the array, while stronger\nexcitations are self trapped, resulting in localized energy breathers and\nsolitons. These structures are quasiparticle analogues to the discrete 2D\nsolitons in photonic lattices. Full many-body simulations additionally\ndemonstrate the localization of one-particle entropy.",
        "positive": "A semiclassical theory of phase-space dynamics of interacting bosons: We study the phase-space representation of dynamics of bosons in the\nsemiclassical regime where the occupation number of the modes is large. To this\nend, we employ the van Vleck-Gutzwiller propagator to obtain an approximation\nfor the Green's function of the Wigner distribution. The semiclassical analysis\nincorporates interference of classical paths and reduces to the truncated\nWigner approximation (TWA) when the interference is ignored. Furthermore, we\nidentify the Ehrenfest time after which the TWA fails. As a case study, we\nconsider a single-mode quantum nonlinear oscillator, which displays collapse\nand revival of observables. We analytically show that the interference of\nclassical paths leads to revivals, an effect that is not reproduced by the TWA\nor a perturbative analysis."
    },
    {
        "anchor": "Dynamical revival of phase coherence in a many-boson system: We study the quantum dynamics of cold Bose atoms in a double well. It is\nshown that self-trapping, as well as population oscillations are common\nphenomena associated to nonlinear interactions. For larger $U/t$,\nmulti-particle tunneling is damped and the quantum dynamics is dominated by the\nsingle-particle tunneling. The many-body system can be effectively described in\na truncated Fock space. It exhibits coherence-decoherence oscillations in the\ntemporal evolution. We predict a novel phenomenon of dynamical revival and\ncollapse of matter wave fields in optical lattices in regimes near the\nsuperfluid-Mott insulator phase boundary.",
        "positive": "Magnetic Feshbach resonances in $^{7}\\text{Li}-^{133}\\text{Cs}$ mixtures: Motivated by the prospect of observing Efimov and Bose polaron physics in\nultracold mixtures of bosonic atoms with large mass imbalance, this work\ninvestigates the magnetic Feshbach resonances between $^{7}\\text{Li}$ and\n$^{133}\\text{Cs}$. The resonances are predicted at the 1 gauss level using the\nmodel of Pires et al. [Phys. Rev. A, 90, 012710] obtained from experimental\nobservations of resonances between $^{6}\\text{Li}$ and $^{133}\\text{Cs}$. It is\nfound that a few resonances in a practical range of magnetic field intensity\ncould be used to tune the scattering length between $^{7}\\text{Li}$ and\n$^{133}\\text{Cs}$ atoms. Opportunities for observing Efimov and Bose polaron\nphysics are discussed."
    },
    {
        "anchor": "Superfluid--Mott insulator transition of ultracold superradiant bosons\n  in a cavity: We investigate harmonically-trapped, laser-pumped bosons with infinite-range\ninteractions induced by a dissipative high-finesse red-detuned optical cavity\nwith numerical and analytical methods. We obtain multiple cavity and atomic\nobservables as well as the full phase diagram of the system using the\nmulticonfigurational time-dependent Hartree method for indistinguishable\nparticles (MCTDH-X) approach. Besides the transition from an unorganized normal\nphase to a superradiant phase where atoms self-organize, we focus on an\nin-depth investigation of the self-organized superfluid to self-organized Mott\ninsulator phase transition in the superradiant phase as a function of the\ncavity-atom coupling. The numerical results are substantiated by an analytical\nstudy of an effective Bose-Hubbard model. We numerically analyze cavity\nfluctuations and emergent strong correlations between atoms in the many-body\nstate across the Mott transition via the atomic density distributions and\nGlauber correlation functions. Unexpectedly, the weak harmonic trap leads to\nfeatures like a lattice switching between the two symmetry-broken\n$\\mathbb{Z}_2$ configurations of the untrapped system and a reentrance of\nsuperfluidity in the Mott insulating phase. Our analytical considerations\nquantitatively explain the numerically observed correlation features.",
        "positive": "Connecting dissipation and phase slips in a Josephson junction between\n  fermionic superfluids: We study the emergence of dissipation in an atomic Josephson junction between\nweakly-coupled superfluid Fermi gases. We find that vortex-induced phase\nslippage is the dominant microscopic source of dissipation across the BEC-BCS\ncrossover. We explore different dynamical regimes by tuning the bias chemical\npotential between the two superfluid reservoirs. For small excitations, we\nobserve dissipation and phase coherence to coexist, with a resistive current\nfollowed by well-defined Josephson oscillations. We link the junction transport\nproperties to the phase-slippage mechanism, finding that vortex nucleation is\nprimarily responsible for the observed trends of conductance and critical\ncurrent. For large excitations, we observe the irreversible loss of coherence\nbetween the two superfluids, and transport cannot be described only within an\nuncorrelated phase-slip picture. Our findings open new directions for\ninvestigating the interplay between dissipative and superfluid transport in\nstrongly correlated Fermi systems, and general concepts in out-of-equlibrium\nquantum systems."
    },
    {
        "anchor": "Atomic Bloch-Zener Oscillations and St\u00fcckelberg Interferometry in\n  Optical Lattices: We report on experiments investigating quantum transport and band\ninterferometry of an atomic Bose-Einstein condensate in an optical lattice with\na two-band miniband structure, realized with a Fourier-synthesized optical\nlattice potential. Bloch-Zener oscillations, the coherent superposition of\nBloch oscillations and Landau-Zener tunneling between the two bands are\nobserved. When the relative phase between paths in different bands is varied,\nan interference signal is observed, demonstrating the coherence of the dynamics\nin the miniband system. Measured fringe patterns of this St\\\"uckelberg\ninterferometer allow to interferometrically map out the band structure of the\noptical lattice over the full Brillouin zone.",
        "positive": "A generalized Theory of Diffusion based on Kinetic Theory: We propose to use spin hydrodynamics, a two-fluid model of spin propagation,\nas a generalization of the diffusion equation. We show that in the dense limit\nspin hydrodynamics reduces to Fick's law and the diffusion equation. In the\nopposite limit spin hydrodynamics is equivalent to a collisionless Boltzmann\ntreatment of spin propagation. Spin hydrodynamics avoids unphysical effects\nthat arise when the diffusion equation is used to describe to a strongly\ninteracting gas with a dilute corona. We apply spin hydrodynamics to the\nproblem of spin diffusion in a trapped atomic gas. We find that the observed\nspin relaxation rate in the high temperature limit [Sommer et al., Nature 472,\n201 (2011)] is consistent with the diffusion constant predicted by kinetic\ntheory."
    },
    {
        "anchor": "Pair breaking and N\u00e9el ordering in attractive three-component Dirac\n  fermions: We employ the determinant quantum Monte Carlo method to investigate\nfinite-temperature properties of the half-filled attractive three-component\nHubbard model on a honeycomb lattice. By adjusting the anistropy of\ninteractions, the symmetry of the Hamiltonian changes from SU(3) to\nSU(2)$\\otimes$ U(1) and finally to SO(4)$\\otimes$ U(1). The system undergoes\nthe phase transition between the disorder state and the charge density wave\n(CDW) state around the SU(3) symmetric points. Away from the SU(3) symmetric\npoints and the SO(4)$\\otimes$ U(1) symmetric points, the system can enter into\nthe color density wave (color DW) phase or the color selective density wave\n(CSDW) phase. Around the SO(4)$\\otimes$ U(1) symmetric points, the pairing\norder and the CSDW order can be both detected. The pairing order is quickly\nsuppressed away from the SO(4)$\\otimes$ U(1) symmetric points because Cooper\npairs are scattered. When the anisotropy of interaction exists, N\\'eel order\nappears because the number of off-site trions $|12,3\\rangle$ is greater than\nthe number of other two types of off-site trions and off-site trions\n$|12,3\\rangle$ do not distribute randomly. The calculated entropy-temperature\nrelations show the anisotropy of interactions induced adiabatic cooling, which\nmay provide a new method to cool a system in experiments.",
        "positive": "Large photon number extraction from individual atoms trapped in an\n  optical lattice: The atom-by-atom characterization of quantum gases requires the development\nof novel measurement techniques. One particularly promising new technique\ndemonstrated in recent experiments uses strong fluorescent laser scattering\nfrom neutral atoms confined in a short-period optical lattice to measure the\nposition of individual atoms in the sample. A crucial condition for the\nmeasurements is that atomic hopping between lattice sites must be strongly\nsuppressed despite substantial photon recoil heating. This article models\nthree-dimensional polarization gradient cooling of atoms trapped within a\nfar-detuned optical lattice. The atomic dynamics are simulated using a hybrid\nMonte Carlo and master equation analysis in order to predict the frequency of\nprocesses which give rise to degradation or loss of the fluorescent signal\nduring measurements. It is shown, consistent with the experimental results,\nthat there exists a wide parameter range in which the lifetime of\nstrongly-fluorescing isolated lattice-trapped atoms is limited by background\ngas collisions rather than radiative processes. In these cases the total number\nof scattered photons can be as large as 10^8 per atom. The performance of the\ntechnique is related to relevant experimental parameters."
    },
    {
        "anchor": "Cooper pairing above the critical temperature in a unitary Fermi gas: We present an ab initio determination of spin responses of the unitary Fermi\ngas, based on finite temperature quantum Monte Carlo calculations and the Kubo\nlinear-response formalism. We determine the temperature dependence of the spin\nsusceptibility and the spin conductivity. We show that both quantities exhibit\nsuppression above the critical temperature of the superfluid to normal phase\ntransition due to presence of the Cooper pairs. The spin diffusion transport\ncoefficient does not display the existence of a minimum in the vicinity of the\ncritical temperature and it drops to very low values D_s approx 0.8hbar/m in\nthe superfluid phase. All these spin observables show a smooth and monotonic\nbehavior with temperature when crossing the critical temperature T_c, until the\nFermi liquid regime is attained at the temperature T*, where the pseudogap\nregime disappears.",
        "positive": "Bose Hubbard Model in a Strong Effective Magnetic Field: Emergence of a\n  Chiral Mott Insulator Ground State: Motivated by experiments on Josephson junction arrays, and cold atoms in an\noptical lattice in a synthetic magnetic field, we study the \"fully frustrated\"\nBose-Hubbard (FFBH) model with half a magnetic flux quantum per plaquette. We\nobtain the phase diagram of this model on a two-leg ladder at integer filling\nvia the density matrix renormalization group approach, complemented by Monte\nCarlo simulations on an effective classical XY model. The ground state at\nintermediate correlations is consistently shown to be a chiral Mott insulator\n(CMI) with a gap to all excitations and staggered loop currents which\nspontaneously break time reversal symmetry. We characterize the CMI state as a\nvortex supersolid or an indirect exciton condensate, and discuss various\nexperimental implications."
    },
    {
        "anchor": "Fractional quantum anomalous Hall phase for Raman superarray of Rydberg\n  atoms: Rydberg atom arrays offer promising platforms for quantum simulation of\ncorrelated quantum matter and raise great interests. This work proposes a novel\nstripe-lattice model with Raman superarray of Rydberg atoms to realize bosonic\nfractional quantum anomalous Hall (FQAH) phase. Two types of Rydberg states,\narranged in a supperarray configuration and with Raman-assisted dipole-exchange\ncouplings, are implemented to realize a minimal QAH model for hard-core bosons\npopulated into a topological flat band with large bulk gap under proper tunable\nexperimental condition. With this the bosonic FQAH phase can be further\nachieved and probed feasibly. In particular, a novel quench protocol is\nproposed to probe the fractionalized excitations by measuring the correlated\nquench dynamics featured by fractional charge tunneling between bulk and chiral\nedge modes in the open boundary.",
        "positive": "Theory of excitations of dipolar Bose-Einstein condensate at finite\n  temperature: We present a systematic study of dilute three-dimensional dipolar Bose gas\nemploying a finite temperature perturbation theory (beyond the mean field). We\nanalyze in particular the behavior of the anomalous density, we find that this\nquantity has a finite value in the limit of weak interactions at both zero and\nfinite temperatures. We show that the presence of the dipole-dipole interaction\n(DDI) enhances fluctuations, the second order correlation function and\nthermodynamic quantities such as the chemical potential, the ground state\nenergy, the compressibility and the superfluid fraction. We identify the\nvalidity criterion of the small parameter of the theory for Bose-condensed\ndipolar gases."
    },
    {
        "anchor": "Dynamical disentangling and cooling of atoms in bilayer optical lattices: We show how experimentally available bilayer lattice systems can be used to\nprepare quantum many-body states with exceptionally low entropy in one layer,\nby dynamically disentangling the two layers. This disentangling operation moves\none layer - subsystem $A$ - into a regime where excitations in $A$ develop a\nsingle-particle gap. As a result, this operation maps directly to cooling for\nsubsystem $A$, with entropy being shuttled to the other layer. For both bosonic\nand fermionic atoms, we study the dynamics of this process, and show that\ndisentangling can be realised cleanly in ongoing optical lattice experiments.\nThe corresponding entanglement entropies are directly measurable with quantum\ngas microscopes, and as a tool for producing lower-entropy states, this\ntechnique opens a range of applications beginning with simplifying production\nof anti-ferromagnetically ordered states of fermions.",
        "positive": "Strongly Interacting Two-component Coupled Bose Gas in Optical Lattices: Two-component coupled Bose gas in a 1D optical lattice is examined. In\naddition to the postulated Mott insulator and superfluid phases, multiple\nbosonic components manifest spin degrees of freedom. Coupling of the components\nin the Bose gas leads to substantial change in the previously observed spin\nphases, giving rise to new effective spin Hamiltonian and unraveling remarkable\nspin correlations. The system exhibiting ferromagnetic and non-ferromagnetic\nspin phases for on-site intra-component interaction stronger than\ninter-component interaction switches from first-order to second-order phase\ntransition between the spin phases upon introduction of coupling, on which is\ndependent the transition width. For comparable on-site inter- and intra-\ncomponent interaction, with coupling, instead of one, two spin phases emerge\nwith a second-order phase transition. Exact diagonalization and Variational\nMonte Carlo (VMC) with stochastic minimization on Entangled Plaquette State\n(EPS) bestow a unique and enhanced perspective into the system beyond the scope\nof a mean-field treatment."
    },
    {
        "anchor": "Nonequilibrium many-body steady states via Keldysh formalism: Many-body systems with both coherent dynamics and dissipation constitute a\nrich class of models which are nevertheless much less explored than their\ndissipationless counterparts. The advent of numerous experimental platforms\nthat simulate such dynamics poses an immediate challenge to systematically\nunderstand and classify these models. In particular, nontrivial many-body\nstates emerge as steady states under non-equilibrium dynamics. While these\nstates and their phase transitions have been studied extensively with mean\nfield theory, the validity of the mean field approximation has not been\nsystematically investigated. In this paper, we employ a field-theoretic\napproach based on the Keldysh formalism to study nonequilibrium phases and\nphase transitions in a variety of models. In all cases, a complete description\nvia the Keldysh formalism indicates a partial or complete failure of the mean\nfield analysis. Furthermore, we find that an effective temperature emerges as a\nresult of dissipation, and the universal behavior including the dynamics near\nthe steady state is generically described by a thermodynamic universality\nclass.",
        "positive": "Nonequilibrium noise as a probe of pair-tunneling transport in the\n  BCS--BEC Crossover: The detection of elementary carriers in transport phenomena is one of the\nmost important keys to understand non-trivial properties of strongly-correlated\nquantum matter. Here we propose a method to identify the tunneling current\ncarrier in strongly interacting fermions from nonequilibrium noise in the\nBardeen-Cooper-Schrieffer to Bose--Einstein condensate crossover. The\nnoise-to-current ratio, the Fano factor, can be a crucial probe for the current\ncarrier. Bringing strongly-correlated fermions into contact with a dilute\nreservoir produces a tunneling current in between. The associated Fano factor\nincreases from one to two as the interaction becomes stronger, reflecting the\nfact that the dominant conduction channel changes from the quasiparticle\ntunneling to the pair tunneling."
    },
    {
        "anchor": "Bosons with long range interactions on two-leg ladders in artificial\n  magnetic fields: Motivated by experiments exploring the physics of neutral atoms in artificial\nmagnetic fields, we study the ground state of bosons interacting with long\nrange dipolar interactions on a two-leg ladder. Using two complimentary\nvariational approaches, valid for weak interactions, we find rich physics\ndriven by the long range forces. Generically, long range interactions tend to\ndestroy the Meissner phase in favor of modulated density wave phases. Nearest\nneighbor interactions produce a novel interleg charge density wave phase, where\nthe total density remains uniform, but the density on each leg of the ladder is\nmodulating in space, out-of-phase with one another. At weak magnetic fields,\nnext nearest neighbor interactions lead to a fully modulated biased ladder\nphase, where all the particles are on one leg of the ladder, and the density is\nmodulating in space. This state simultaneously breaks $Z_{2}$ reflection\nsymmetry and $U(1)$ symmetry associated with translation in real space. For\nvalues of the flux near $\\phi = \\pi$, we find that a switching effect occurs\nfor arbitrarily weak interactions, where the density modulates in space, but\nthe chiral current changes sign on every plaquette. Arbitrarily weak attractive\ninteractions along the rungs destroy the Meissner phase completely, in favor of\na modulated density wave phase. Varying magnetic field produces a cascade of\nfirst order transitions between modulated density wave states with different\nwave-vectors, which manifests itself as discrete jumps in the chiral current.\nPolarizing the dipoles along the ladder direction yields a region of phase\nspace where a stable biased ladder phase occurs even at arbitrarily weak\nmagnetic fields. We discuss the experimental consequences of our work, in\nparticular, how the interleg charge density wave can manifest itself in recent\nexperiments on bosons in synthetic dimensions.",
        "positive": "Quasi-condensation in two-dimensional Fermi gases: In this paper we follow the analysis and protocols of recent experiments,\ncombined with simple theory, to arrive at a physical understanding of\nquasi-condensation in two dimensional Fermi gases. We find that\nquasi-condensation mirrors Berezinskii-Kosterlitz-Thouless behavior in many\nways, including the emergence of a strong zero momentum peak in the pair\nmomentum distribution. Importantly, the disappearance of this quasi-condensate\noccurs at a reasonably well defined crossover temperature. The resulting phase\ndiagram, pair momentum distribution, and algebraic power law decay are\ncompatible with recent experiments throughout the continuum from BEC to BCS."
    },
    {
        "anchor": "Evanescent Modes and Step-like Acoustic Black Holes: We consider a model of an acoustic black hole formed by a quasi-one\ndimensional Bose-Einstein condensate with a step-like horizon. This system is\nanalyzed by solving the corresponding Bogoliubov-de Gennes equation with an\nappropriate matching condition at the jump. When the step is between a subsonic\nand supersonic flow, a sonic horizon develops and in addition to the scattering\ncoefficients we compute the distribution of the accompanying analogue Hawking\nradiation. Additionally, in response to the abrupt variation in flow and\nnon-linear Bogoliubov dispersion relation, evanescent solutions of the\nBogoliubov-de Gennes equation also appear and decay out from the horizon. We\nbound this decay length and show that these modes produce a modulation of\nobservables outside the event horizon by their interference with outgoing\nHawking flux. We go further and find specific superpositions of ingoing\neigenmodes which exhibit coherent cancellation of the Hawking flux outside the\nhorizon but nevertheless have evanescent support outside the black hole. We\nconclude by speculating that when quasiparticle interactions are included,\nevanescent modes may yield a leakage of information across the event horizon\nvia interactions between the real outgoing Hawking flux and the virtual\nevanescent modes, and that we may expect this as a generic feature of models\nwhich break Lorentz invariance at the UV (Planck) scale.",
        "positive": "Level rearrangement in exotic-atom-like three-body systems: We study systems of three bosons bound by a long-range interaction\nsupplemented by a short-range potential of variable strength. This generalizes\nthe usual two-body exotic atoms where the Coulomb interaction is modified by\nnuclear forces at short distances. The energy shift due to the short-range part\nof the interaction combines two-body terms similar to the ones entering the\nTrueman-Deser formula, and three-body contributions. A sudden variation of the\nenergy levels is observed near the coupling thresholds of the short-range\npotential. But the patterns of rearrangement are significantly modified as\ncompared to the two-body case."
    },
    {
        "anchor": "Droplet formation in a Bose-Einstein condensate with strong\n  dipole-dipole interaction: Motivated by the recent experiment [H. Kadau \\textit{et al.},\narXiv:1508.05007 (2015)], we study roton instability and droplet formation in a\nBose-Einstein condensate of $^{164}$Dy atoms with strong magnetic dipole-dipole\ninteraction. We numerically solve the cubic-quintic Gross-Pitaevskii equation\nwith dipole-dipole interaction, and show that the three-body interaction plays\na significant role in the formation of droplet patterns. We numerically\ndemonstrate the formation of droplet patterns and crystalline structures, decay\nof droplets, and hysteresis behavior, which are in good agreement with the\nexperiment. Our numerical simulations provide the first prediction on the\nvalues of the three-body interaction in a $^{164}$Dy Bose-Einstein condensate.\nWe also predict that the droplets remain stable during the time-of-flight\nexpansion. From our results, further experiments investigating the three-body\ninteraction in dipolar quantum gases are required.",
        "positive": "Polaronic slowing of fermionic impurities in lattice Bose-Fermi mixtures: We generalize the application of small polaron theory to ultracold gases of\nRef. [\\onlinecite{jaksch_njp1}] to the case of Bose-Fermi mixtures, where both\ncomponents are loaded into an optical lattice. In a suitable range of\nparameters, the mixture can be described within a Bogoliubov approach in the\npresence of fermionic (dynamic) impurities and an effective description in\nterms of polarons applies. In the dilute limit of the slow impurity regime, the\nhopping of fermionic particles is exponentially renormalized due to polaron\nformation, regardless of the sign of the Bose-Fermi interaction. This should\nlead to clear experimental signatures of polaronic effects, once the regime of\ninterest is reached. The validity of our approach is analyzed in the light of\ncurrently available experiments. We provide results for the hopping\nrenormalization factor for different values of temperature, density and\nBose-Fermi interaction for three-dimensional $^{87}\\rm{Rb}-^{40}\\rm{K}$\nmixtures in optical lattice."
    },
    {
        "anchor": "Probe for bound states of SU(3) fermions and colour deconfinement: Fermionic artificial matter realized with cold atoms grants access to an\nunprecedented degree of control on sophisticated many-body effects with an\nenhanced flexibility of the operating conditions. We consider three-component\nfermions with attractive interactions to study the formation of complex bound\nstates whose nature goes beyond the standard fermion pairing occurring in\nquantum materials. Such systems display clear analogies with quark matter.\nHere, we address the nature of the bound states of a three-component fermionic\nsystem in a ring-shaped trap through the persistent current. In this way, we\ndemonstrate that we can distinguish between color superfluid and trionic bound\nstates. By analyzing finite temperature effects, we show how finite temperature\ncan lead to the deconfinement of bound states. For weak interactions the\ndeconfinement occurs because of scattering states. In this regime, the\ndeconfinement depends on the trade-off between interactions and thermal\nfluctuations temperature. For strong interactions the features of the\npersistent current result from the properties of a suitable gas of bound\nstates.",
        "positive": "Bose-Einstein condensates and the thin-shell limit in anisotropic bubble\n  traps: Within the many different models that appeared with the use of cold atoms to\ndesign BECs the bubble trap shaped potential has been of great interest. For\nthe anisotropic bubble trap physics in the thin-shell limit the relationship\nbetween the physical parameters and the resulting manifold geometry is yet to\nbe fully understood. In this paper, we work towards this goal showing how the\nparameters of the system must be manipulated in order to allow for a\nnon-collapsing thin-shell limit. In such a limit, a dimensional\ncompactification takes place thus leading to an effective 2D Hamiltonian which\nrelates to up-to-date bubble trap experiments. At last, our Hamiltonian is\npertubatively solved for some particular cases as applications of our theory."
    },
    {
        "anchor": "Lattice assisted spectroscopy: a generalized scanning tunnelling\n  microscope for ultra-cold atoms: We show that the possibility to address and image single sites of an optical\nlattice, now an experimental reality, allows to measure the frequency-resolved\nlocal particle and hole spectra of a wide variety of one- and two-dimensional\nsystems of lattice-confined strongly correlated ultracold atoms. Combining\nperturbation theory and time-dependent DMRG, we validate this scheme of\nlattice-assisted spectroscopy (LAS) on several example systems, such as the 1D\nsuperfluid and Mott insulator, with and without a parabolic trap, and finally\non edge states of the bosonic Su-Schrieffer-Heeger model. We also highlight\nextensions of our basic scheme to obtain an even wider variety of interesting\nand important frequency resolved spectra.",
        "positive": "Probing non-locality of interactions in a Bose-Einstein Condensate using\n  solitons: We consider a Bose-Einstein Condensate(BEC) with non-local inter-particle\ninteractions. The local Gross-Pitaevskii(GP) equation is valid for the gas\nparameter $\\nu =: a^{3} n_{0} << 1$, but for $\\nu \\rightarrow 1$, the BEC is\ndescribed by modified GP equation(MGPE). We study the exact solutions of the\nMGPE describing bright and dark solitons. It turns out that the width of these\nnon-local solitons has qualitatively similar behaviour as the modified healing\nlength due to the non-local interactions of the MGPE. We also study the effect\nof the non-locality and gas parameter({\\nu}) on the stability of the solitons\nusing the Vakhitov Kolokolov(VK) stability criterion. We show that these\nsoliton solutions are indeed stable. Further, the stability of these soliton\nsolutions gets enhanced due to the non-locality of interactions."
    },
    {
        "anchor": "Double resonance of Raman transitions in a degenerate Fermi gas: We measure momentum-resolved Raman spectra of a spin-polarized degenerate\nFermi gas of $^{173}$Yb atoms for a wide range of magnetic fields, where the\natoms are irradiated by a pair of counterpropagating Raman laser beams as in\nthe conventional spin-orbit coupling scheme. Double resonance of first- and\nsecond-order Raman transitions occurs at a certain magnetic field and the\nspectrum exhibits a doublet splitting for high laser intensities. The measured\nspectral splitting is quantitatively accounted for by the Autler-Townes effect.\nWe show that our measurement results are consistent with the spinful band\nstructure of a Fermi gas in the spatially oscillating effective magnetic field\ngenerated by the Raman laser fields.",
        "positive": "Attractive Hubbard Model on a Honeycomb Lattice: We study the attractive fermionic Hubbard model on a honeycomb lattice using\ndeterminantal quantum Monte Carlo simulations. By increasing the interaction\nstrength U (relative to the hopping parameter t) at half-filling and zero\ntemperature, the system undergoes a quantum phase transition at 5.0 < U_c/t <\n5.1 from a semi-metal to a phase displaying simultaneously superfluid behavior\nand density order. Doping away from half-filling, and increasing the\ninteraction strength at finite but low temperature T, the system always appears\nto be a superfluid exhibiting a crossover between a BCS and a molecular regime.\nThese different regimes are analyzed by studying the spectral function. The\nformation of pairs and the emergence of phase coherence throughout the sample\nare studied as U is increased and T is lowered."
    },
    {
        "anchor": "Long time non-equilibrium dynamics of binary Bose condensates: We explore the out-of-equilibrium temporal dynamics of demixing and phase\nseparation in a two dimensional binary Bose fluid at zero temperature,\nfollowing a sudden quench across the miscible-immiscible phase boundary. On\nshort timescales, the system rapidly settles into a steady state characterized\nby short-range correlations in the relative density. The subsequent dynamics is\nextremely slow: domains of the relative density appear to grow with time,\nhowever, the rate of growth is much slower than that predicted by conventional\ntheories of phase ordering kinetics. Moreover, we find that the growth dynamics\nslows down with increasing time, and is consistent with logarithmic growth. Our\nstudy sheds light on ongoing investigations of how isolated quantum systems\napproach equilibrium, and indicates that studying the quantum phase diagram of\nthe binary Bose fluids following a quench, may be difficult due to\nequilibration problems.",
        "positive": "Tonks-Girardeau gas, super-Tonks-Girardeau gas, and bound states of\n  one-dimensional bosons in a hard-wall trap: We investigate the Bose gas with repulsive or attractive interactions between\natoms in the scheme of Bethe Ansatz equation in a hard wall trap. Three typical\nquantum phases in the current research of 1D interacting cold atoms are\nclarified in terms of the energy spectrum, single particle density distribution\nand two-particle correlation function. We identify two matching points in the\nphase diagram, i.e. the TG and STG gas show the same profiles at the strongly\ninteracting point $-1/\\gamma=0$, and in the weakly interacting limit $\\gamma=0$\nthe ground states TG and BS join to each other smoothly."
    },
    {
        "anchor": "Inducing spin-order with an impurity: phase diagram of the magnetic Bose\n  polaron: We investigate the formation of magnetic Bose polaron, an impurity atom\ndressed by spin-wave excitations, in a one-dimensional spinor Bose gas. In\nterms of an effective potential model the impurity is strongly confined by the\nhost excitations which can even overcome the impurity-medium repulsion leading\nto a self-localized quasi-particle state. The phase diagram of the attractive\nand self-bound repulsive magnetic polaron, repulsive non-magnetic (Fr{\\\"\no}hlich-type) polaron and impurity-medium phase-separation regimes is explored\nwith respect to the Rabi-coupling between the spin components, spin-spin\ninteractions and impurity-medium coupling. The residue of such magnetic\npolarons decreases substantially in both strong attractive and repulsive\nbranches with strong impurity-spin interactions, illustrating significant\ndressing of the impurity. The impurity can be used to probe and maneuver the\nspin polarization of the magnetic medium while suppressing ferromagnetic\nspin-spin correlations. It is shown that mean-field theory fails as the spinor\ngas approaches immiscibility since the generated spin-wave excitations are\nprominent. Our findings illustrate that impurities can be utilized to generate\ncontrollable spin-spin correlations and magnetic polaron states which can be\nrealized with current cold atom setups.",
        "positive": "Synthetic Landau levels and spinor vortex matter on Haldane spherical\n  surface with magnetic monopole: We present a flexible scheme to realize exact flat Landau levels on curved\nspherical geometry in a system of spinful cold atoms. This is achieved by\nFloquet engineering of a magnetic quadrupole field. We show that a synthetic\nmonopole field in real space can be created. We prove that the system can be\nexactly mapped to the electron-monopole system on sphere, thus realizing\nHaldane's spherical geometry for fractional quantum Hall physics. The scheme\nworks for either bosons or fermions. We investigate the ground state vortex\npattern for an $s$-wave interacting atomic condensate by mapping this system to\nthe classical Thompson's problem. We further study the distortion and stability\nof the vortex pattern when dipolar interaction is present. Our scheme is\ncompatible with current experimental setup, and may serve as a promising route\nof investigating quantum Hall physics and exotic spinor vortex matter on curved\nspace."
    },
    {
        "anchor": "Tunneling vortex dynamics in linearly coupled Bose-Hubbard rings: The quantum dynamics of population-balanced fractional vortices and\npopulation-imbalanced vortices in an effective two-state bosonic system, made\nof two coupled discrete circuits with few sites, is addressed within the\nBose-Hubbard model. % We show that for low on-site interaction, the tunneling\nof quantized vortices between the rings performs a coherent, oscillating\ndynamics connecting current states with chiral symmetry. The vortex-flux\ntransfer dually follows the usual sinusoidal particle current of the Josephson\neffect, in good agreement with a mean-field approximation. Within such regime,\nthe switch of persistent currents in the rings resembles flux-qubit features,\nand is feasible to experimental realization. On the contrary, strong\ninteratomic interactions suppress the chiral current and lead the system into\nfragmented condensation.",
        "positive": "Analytic models for density of a ground-state spinor condensate: We demonstrate that the ground state of a trapped spin-1 and spin-2 spinor\nferromagnetic Bose-Einstein condensate (BEC) can be well approximated by a\nsingle decoupled Gross-Pitaevskii (GP) equation. Useful analytic models for the\nground-state densities of ferromagnetic BECs are obtained from the Thomas-Fermi\napproximation (TFA) to this decoupled equation. Similarly, for the ground\nstates of spin-1 anti-ferromagnetic and spin-2 anti-ferromagnetic and cyclic\nBECs, some of the spin component densities are zero which reduces the coupled\nGP equation to a simple reduced form. Analytic models for ground state\ndensities are also obtained for anti-ferromagnetic and cyclic BECs from the TFA\nto the respective reduced GP equations. The analytic densities are illustrated\nand compared with the full numerical solution of the GP equation with realistic\nexperimental parameters."
    },
    {
        "anchor": "Chern number spectrum of ultra-cold fermions in optical lattices tuned\n  independently via artificial magnetic, Zeeman and spin-orbit fields: We discuss the Chern number spectrum of ultra-cold fermions in square optical\nlattices as a function of artificial magnetic, Zeeman and spin-orbit fields\nthat can be tuned independently. We show the existence of topological quantum\nphase transitions induced by Zeeman and spin-orbit fields, where the total\nnumber and chirality of edge states change for fixed magnetic flux ratio, thus\nleading to topological-insulator phases which are different from those found at\nzero Zeeman and spin-orbit fields. We construct phase diagrams of chemical\npotential versus Zeeman field or spin-orbit coupling and characterize all\ninsulating phases by their topological invariants. Lastly, we obtain a\nstaircase structure in the filling factor versus chemical potential for various\nZeeman and spin-orbit fields, showing the existence of incompressible states at\nrational filling factors derived from a generalized Diophantine equation.",
        "positive": "Second order fluid dynamics for the unitary Fermi gas from kinetic\n  theory: We compute second order transport coefficients of the dilute Fermi gas at\nunitarity. The calculation is based on kinetic theory and the Boltzmann\nequation at second order in the Knudsen expansion. The second order transport\ncoefficients describe the shear stress relaxation time, non-linear terms in the\nstrain-stress relation, and non-linear couplings between vorticity and strain.\nAn exact calculation in the dilute limit gives $\\tau_R=\\eta/P$, where $\\tau_R$\nis the shear stress relaxation time, $\\eta$ is the shear viscosity, and $P$ is\npressure. This relation is identical to the result obtained using the\nBhatnagar-Gross-Krook (BGK) approximation to the collision term, but other\ntransport coefficients are sensitive to the exact collision integral."
    },
    {
        "anchor": "Bogolon-mediated light absorption in atomic condensates of different\n  dimensionality: In the case of structureless bosons, cooled down to low temperatures, the\nabsorption of electromagnetic waves by their Bose-Einstein condensate is\nusually forbidden due to the momentum and energy conservation laws: the phase\nvelocity of the collective modes of the condensate called bogolons is\nsufficiently lower than the speed of light. Thus, only the light scattering\nprocesses persist. However, the situation might be different in the case of\ncomposite bosons or the bosons with an internal structure. Here, we develop a\nmicroscopic theory of electromagnetic power absorption by a Bose-Einstein\ncondensates of cold atoms in various dimensions, utilizing the Bogoliubov model\nof a weakly-interacting Bose gas. Thus, we address the transitions between a\ncollective coherent state of bosons and the discrete energy levels\ncorresponding to excited internal degrees of freedom of non-condensed\nindividual bosons. It is shown, that such transitions are mediated by one and\ntwo-bogolon excitations above the condensate, which demonstrate different\nefficiency at different frequencies and strongly depend on the condensate\ndensity, which influence varies depending on the dimensionality of the system.",
        "positive": "Analytic Treatment of Kapitza-Dirac Effect: Connecting Raman-Nath and\n  Bragg Approximations: We develop an analytical approach for probability amplitudes of Kapitza-Dirac\neffect that merge together the Raman-Nath and Bragg regimes of interaction."
    },
    {
        "anchor": "S-matrix approach to quantum gases in the unitary limit II: the\n  three-dimensional case: A new analytic treatment of three-dimensional homogeneous Bose and Fermi\ngases in the unitary limit of negative infinite scattering length is presented,\nbased on the S-matrix approach to statistical mechanics we recently developed.\nThe unitary limit occurs at a fixed point of the renormalization group with\ndynamical exponent z=2 where the S-matrix equals -1. For fermions we find T_c\n/T_F is approximately 0.1. For bosons we present evidence that the gas does not\ncollapse, but rather has a critical point that is a strongly interacting form\nof Bose-Einstein condensation. This bosonic critical point occurs at n lambda^3\napproximately 1.3 where n is the density and lambda the thermal wavelength,\nwhich is lower than the ideal gas value of 2.61.",
        "positive": "Atomic momentum patterns with narrower interval: We studied the atomic momentum distribution for a superposition of Bloch\nstates spreading in the lowest band of an optical lattice after the action of\nthe standing wave pulse. By designing the imposing pulse on this superposed\nstate, an atomic momentum pattern appears with narrower interval between the\nadjacent peaks that can be far less than the double recoil momentum. The\npatterns with narrower interval come from the superposition of the action of\nthe designed pulse on many Bloch states with quasi-momenta over the first\nBrillouin zone, where for each quasi-momentum there is an interference among\nseveral lowest bands. Our experimental result of narrow interval peaks is\nconsistent with the theoretical simulation. The patterns of multi modes with\ndifferent quasi-momenta are helpful for precise measurement and atomic\nmanipulation."
    },
    {
        "anchor": "Observation of the Sign Reversal of the Magnetic Correlation in a\n  Driven-Dissipative Fermi Gas in Double Wells: We report the observation of the sign reversal of the magnetic correlation\nfrom antiferromagnetic to ferromagnetic in a dissipative Fermi gas in double\nwells, utilizing the dissipation caused by on-site two-body losses in a\ncontrolled manner. We systematically measure dynamics of the nearest-neighbor\nspin correlation in an isolated double-well optical lattice, as well as a\ncrossover from an isolated double-well lattice to a one-dimensional uniform\nlattice. In a wide range of lattice configurations over an isolated double-well\nlattice, we observe a ferromagnetic spin correlation, which is consistent with\na Dicke type of correlation expected in the long-time limit. This work\ndemonstrates the control of quantum magnetism in open quantum systems with\ndissipation.",
        "positive": "Energy of strongly attractive Bose-Fermi mixtures: We discuss how approximate theories for Bose-Fermi mixtures recover in the\nmolecular limit the expected expression for Fermi-Fermi mixtures of molecules\nand unpaired fermions. In particular, we compare the energy of the system\nresulting from a T-matrix diagrammatic approach with that obtained with\nVariational and Fixed-Node Diffusion Quantum Monte Carlo methods."
    },
    {
        "anchor": "Atomic spin-orbit coupling synthesized with magnetic-field-gradient\n  pulses: We discuss a general scheme for creating atomic spin-orbit coupling (SOC)\nsuch as the Rashba or Dresselhaus types using magnetic-field-gradient pulses.\nIn contrast to conventional schemes based on adiabatic center-of-mass motion\nwith atomic internal states restricted to a dressed-state subspace, our scheme\nworks for the complete subspace of a hyperfine-spin manifold by utilizing the\ncoupling between the atomic magnetic moment and external magnetic fields. A\nspatially dependent pulsed magnetic field acts as an internal-state-dependent\nimpulse, thereby coupling the atomic internal spin with its orbital\ncenter-of-mass motion, as in the Einstein-de Haas effect. This effective\ncoupling can be dynamically manipulated to synthesize SOC of any type (Rashba,\nDresselhaus, or any linear combination thereof). Our scheme can be realized\nwith most experimental setups of ultracold atoms and is especially suited for\natoms with zero nuclear spins.",
        "positive": "Mesoscopics of half-quantum vortex pair deconfinement in a trapped\n  spin-one condensate: Motivated by a recent experiment in an antiferromagnetic spin-1 Bose-Einstein\ncondensate of ${}^{23} \\textrm{Na}$ atoms, we study the energetical stability\nof a singly quantum vortex injected into the center of a quasi-two-dimensional\ngas with zero total spin against dissocation into a pair of half-quantum\nvortices. We find that the critical dissociation point of this\nconfinement-deconfinement type phase transition can be expressed in terms of\nthe ratio of density-density ($c_0$) and spin-spin ($c_2$) coupling constants.\nThe transition of bound to unbound vortices, in particular, sensitively depends\non (1) the ratio of system size ($R$) to density healing length ($\\xi_d$), and\n(2) the trap potential. Specifically, the critical ratio $(c_2 /\nc_0)_{\\textrm{cr}}$ increases when $R / \\xi_d$ decreases, and is relatively\nlarger in a harmonic trap than in a box trap. Dissociation is energetically\ngenerally favored for $c_2 / c_0 < (c_2 / c_0)_{\\textrm{cr}}$, which as a\ncorollary implies that vortex dissociation is observed as well for negative\n$c_2 < 0$, e.g., in a rubidium spin-1 BEC, whereas in a sodium spin-1 BEC\n($c_2>0$) it is energetically blocked above the critical ratio $(c_2 /\nc_0)_{\\textrm{cr}}$. Tuning the coupling ratio $c_2/c_0$ by using microwave\ncontrol techniques, the dependence of the deconfinement phase transition on\ncoupling parameters, density, and system size we predict, can be verified in\nexperiments with ultracold spinor gases."
    },
    {
        "anchor": "Thermodynamics of ideal Bose gas under generic power law potential in\n  $d$-dimension: Thermodynamic properties of ideal Bose gas trapped in an external generic\npower law potential are investigated systematically from the grand\nthermodynamic potential in $d$ dimensional space. The most general conditions\nfor Bose-Einstein condensate and the discontinuous conditions of heat capacity\nat the critical temperature in presence of generic power law potential are\npresented in this manuscript. The dependence of the physical quantities on\nexternal potential, particle characteristics and space dimensionality are\ndiscussed. The more general results obtained in this paper presents an unified\nillustration of Bose-Einstein condensation of ideal Bose systems as they\nreduces to the expressions and conclusions available in the literature with\nappropiate choice of power law exponent.",
        "positive": "Quasimomentum distribution and expansion of an anyonic gas: We point out that the momentum distribution is not a proper observable for a\nsystem of anyons in two-dimensions. In view of anyons as Wilczek's composite\ncharged flux-tubes, this is a consequence of the fact that the orthogonal\ncomponents of the kinetic momentum operator do not commute at the position of a\nflux tube, and thus cannot be diagonalized in the same basis. As a substitute\nfor the momentum distribution of an anyonic (spatially localized) state, we\npropose to use the asymptotic single-particle density after expansion of anyons\nin free space from the state. This definition is identical with the standard\none when the statistical parameter approaches that for bosons or fermions.\nExact examples of expansion dynamics, which underpin our proposal, and\nobservables that can be used to measure anyonic statistics, are shown."
    },
    {
        "anchor": "Inhomogeneous state of few-fermion superfluids: The few-fermion atomic gas is an ideal setting to explore inhomogeneous\nsuperfluid pairing analogous to the Larkin-Ovchinnikov state. Two up and one\ndown-spin atom is the minimal configuration that displays an inhomogeneous\npairing density whereas imbalanced systems containing more fermions present a\nmore complex pairing topology. With more than eight atoms trapped the system\napproaches the macroscopic superfluid limit. An oblate trap with a central\nbarrier offers a direct experimental probe of pairing inhomogeneity.",
        "positive": "Two-dimensional polaron spectroscopy of Fermi superfluids: Multidimensional spectroscopy is becoming an increasingly popular tool and\nthere is an ongoing effort to access electronic transitions and many-body\ndynamics in correlated materials. We apply the protocol recently proposed by\nWang to extract two-dimensional polaron spectra in a Fermi superfluid with an\nimpurity. The bath is descibed by a BCS ansatz and it assumed that the impurity\ncan scatter at most one quasiparticle pair. The spectral response contains a\nsymmetric contribution, which carries the same information as Ramsey spectra,\nand an asymmetric one. While {\\it a priori} it may seem promising to probe the\nquasiparticle gap from the asymmetric contribution, we show explicitly that\nthis is not the case and, in the absence of incoherent processes,\nmultidimensional spectroscopy does not bring much additional information. Our\ncalculation is suitable for 3D ultracold gases, but we discuss implications for\nexciton-polarons in 2D materials."
    },
    {
        "anchor": "Phonon-mediated Casimir interaction between finite mass impurities: The Casimir effect, a two-body interaction via vacuum fluctuations, is a\nfundamental property of quantum systems. In solid state physics it emerges as a\nlong-range interaction between two impurity atoms via virtual phonons. In the\nclassical limit for the impurity atoms in $D$ dimensions the interaction is\nknown to follow the universal power-law $U(r)\\sim r^{-D}$. However, for finite\nmasses of the impurity atoms on a lattice, it was predicted to be $U(r)\\sim\nr^{-2D-1}$ at large distances. We examine how one power-law can change into\nanother with increase of the impurity mass and in presence of an external\npotential. We provide the exact solution for the system in one-dimension. At\nlarge distances indeed $U(r)\\sim r^{-3}$ for finite impurity masses, while for\nthe infinite impurity masses or in an external potential it crosses over to\n$U(r)\\sim r^{-1}$ . At short distances the Casimir interaction is not universal\nand depends on the impurity mass and the external potential.",
        "positive": "Exotic phases of interacting p-band bosons: We study a model of interacting bosons that occupy the first excited p-band\nstates of a two-dimensional optical lattice. In contrast to the much studied\nsingle band Bose-Hubbard Hamiltonian, this more complex model allows for\nnon-trivial superfluid phases associated with condensation at non-zero momentum\nand staggered order of the orbital angular momentum in addition to the\nsuperfluid-Mott insulator transition. More specifically, we observe staggered\norbital angular momentum order in the Mott phase at commensurate filling and\nsuperfluidity at all densities. We also observe a transition between the\nstaggered angular momentum superfluid phase and a striped superfluid, with an\nalternation of the phase of the superfluid along one direction. The transition\nbetween these two phases was observed in a recent experiment, which is then\nqualitatively well described by our model."
    },
    {
        "anchor": "Probing magnetic order in ultracold lattice gases: A forthcoming challenge in ultracold lattice gases is the simulation of\nquantum magnetism. That involves both the preparation of the lattice atomic gas\nin the desired spin state and the probing of the state. Here we demonstrate how\na probing scheme based on atom-light interfaces gives access to the order\nparameters of nontrivial quantum magnetic phases, allowing us to characterize\nunivocally strongly correlated magnetic systems produced in ultracold gases.\nThis method, which is also nondemolishing, yields spatially resolved spin\ncorrelations and can be applied to bosons or fermions. As a proof of principle,\nwe apply this method to detect the complete phase diagram displayed by a chain\nof (rotationally invariant) spin-1 bosons.",
        "positive": "Multidimensional solitons: Well-established results and novel findings: A brief review is given of some well-known and some very recent results\nobtained in studies of two- and three-dimensional (2D and 3D) solitons. Both\nzero-vorticity (fundamental) solitons and ones carrying vorticity S = 1 are\nconsidered. Physical realizations of multidimensional solitons in atomic\nBose-Einstein condensates (BECs) and nonlinear optics are briefly discussed\ntoo. Unlike 1D solitons, which are typically stable, 2D and 3D ones are\nvulnerable to instabilities induced by the occurrence of the critical and\nsupercritical collapse, respectively, in the same 2D and 3D models that give\nrise to the solitons. Vortex solitons are subject to a still stronger splitting\ninstability. For this reason, a central problem is search for physical settings\nin which 2D and 3D solitons may be stabilized. The brief review addresses one\nwell-established topic, viz., the stabilization of the 3D and 2D states, with S\n= 0 and 1, trapped in harmonic-oscillator (HO) potentials, and another topic\nwhich was developed very recently: the stabilization of 2D and 3D free-space\nsolitons, which juxtapose components with S = 0 and (+/-)1 (semi-vortices and\nmixed modes), in a binary system with the spin-orbit coupling (SOC) between its\ncomponents. The former model is based on the single cubic nonlinear\nSchroedinger/Gross-Pitaevskii equation (NLSE/GPE), while the latter one is\nrepresented by a system of two coupled GPEs. In both cases, generic situations\nare drastically different in the 2D and 3D geometries. In the 2D settings, the\nstabilization mechanism creates a stable ground state (GS, which was absent\nwithout the stabilization), whose norm falls below the threshold value at which\nthe critical collapse sets in. In the 3D geometry, the supercritical collapse\ndoes not allow to create a GS, but metastable solitons can be constructed."
    },
    {
        "anchor": "Ground states of a mixture of two species of spin-1 Bose gases with\n  interspecies spin exchange in a magnetic field: We consider a mixture of two species of spin-1 atoms with both interspecies\nand intraspecies spin exchanges in a weak magnetic field. Under the usual\nsingle mode approximation, it can be reduced to a model of coupled giant spins.\nWe find most of its ground states. This is a complicated problem of energy\nminimization, with three quantum variables under constraints, i.e. the total\nspin of each species and the total spin of the whole mixture, as well as four\nparameters, including intraspecies and interspecies spin coupling strengths and\nthe magnetic field. The quantum phase diagram is very rich. Compared with the\ncase without a magnetic field, the ground states are modified by a magnetic\nfield, which also modifies the ground state boundaries or introduces new\ncrossover regimes on the phase diagram. Without interspecies spin coupling, the\nquantum phase transitions existing in absence of a magnetic field disappear\nwhen a magnetic field is applied, which leads to crossover regimes in the phase\ndiagram. Under ferromagnetic interspecies spin coupling, the ground states\nremain disentangled no matter whether there is a magnetic field. For\nantiferromagnetic interspecies spin coupling, a magnetic field entangles the\nground states in some parameter regimes. When the intraspecies spin couplings\nare both ferromagnetic, the quantum phase transition between antiferromagnetic\nand zero interspecies spin couplings survives the magnetic field. When the\nintraspecies spin couplings are both antiferromagnetic, a magnetic field\ninduces new quantum phase transitions between antiferromagnetic and zero\ninterspecies spin couplings.",
        "positive": "Hanbury-Brown and Twiss bunching of phonons and of the quantum depletion\n  in a strongly-interacting Bose gas: We report the realisation of a Hanbury-Brown and Twiss (HBT)-like experiment\nwith a gas of strongly interacting bosons at low temperatures. The regime of\nlarge interactions and low temperatures is reached in a three-dimensional\noptical lattice and atom-atom correlations are extracted from the detection of\nindividual metastable Helium atoms after a long free-fall. We observe a HBT\nbunching in the non-condensed fraction of the gas whose properties strongly\ndeviate from the HBT signals expected for non-interacting bosons. In addition,\nwe show that the measured correlations reflect the peculiar quantum statistics\nof atoms belonging to the quantum depletion and of the Bogoliubov phonons,\ni.e., of collective excitations of the many-body quantum state. Our results\ndemonstrate that atom-atom correlations provide information about the quantum\nstate of strongly-interacting particles, extending the interest of HBT-like\nexperiments beyond the case of non-interacting particles."
    },
    {
        "anchor": "Fermionic Sign Structure of High-order Feynman diagrams in a\n  Many-fermion System: The sign cancellation between scattering amplitudes makes fermions different\nfrom bosons. We systematically investigate Feynman diagrams' fermionic sign\nstructure in a representative many-fermion system---a uniform Fermi gas with\nYukawa interaction. We analyze the role of the crossing symmetry and the global\ngauge symmetry in the fermionic sign cancellation. The symmetry arguments are\nthen used to identify the sign-canceled groups of diagrams. Sign-structure\nanalysis has two applications. Numerically, it leads to a cluster diagrammatic\nMonte Carlo algorithm for fast diagram evaluations. The new algorithm is about\n$10^5$ times faster than the conventional approaches in the sixth order.\nFurthermore, our analysis provides important hints in constructing the relevant\neffective field theory for many-fermion systems.",
        "positive": "A Renormalization-Group Study of Interacting Bose-Einstein Condensates:\n  II. Anomalous Dimension $\u03b7$ for $d\\lesssim 4$ at Finite Temperatures: We study the anomalous dimension $\\eta$ of homogeneous interacting\nsingle-component Bose-Einstein condensates at finite temperatures for\n$d\\lesssim 4$ dimensions. This $\\eta$ is defined in terms of the one-particle\ndensity matrix $\\rho({\\bf r})\\equiv \\langle \\hat\\psi^\\dagger({\\bf\nr}_1)\\hat\\psi({\\bf r}_1+{\\bf r})\\rangle$ through its asymptotic behavior\n$\\rho({\\bf r})\\rightarrow N_{\\bf 0}/V+C r^{-d+2-\\eta}$ for $r\\rightarrow\n\\infty$, where $N_{\\bf 0}/V$ is the condensate density and $C$ is a constant.\nIt is shown that the anomalous dimension is given by $\\eta=0.181\\epsilon^2$ to\nthe leading order in $\\epsilon\\equiv d-4$. The change of the prefactor $0.181$\nfrom the value $0.02$ at the transition point of the ${\\rm O}(2)$ symmetric\n$\\phi^4$ model is attributed to the emergence of three-point vertices and the\nanomalous Green's function when $N_{\\bf 0}$ acquires a finite value."
    },
    {
        "anchor": "Imaging magnetic polarons in the doped Fermi-Hubbard model: Polarons are among the most fundamental quasiparticles emerging in\ninteracting many-body systems, forming already at the level of a single mobile\ndopant. In the context of the two-dimensional Fermi-Hubbard model, such\npolarons are predicted to form around charged dopants in an antiferromagnetic\nbackground in the low doping regime close to the Mott insulating state.\nMacroscopic transport and spectroscopy measurements related to high $T_{c}$\nmaterials have yielded strong evidence for the existence of such quasiparticles\nin these systems. Here we report the first microscopic observation of magnetic\npolarons in a doped Fermi-Hubbard system, harnessing the full single-site spin\nand density resolution of our ultracold-atom quantum simulator. We reveal the\ndressing of mobile doublons by a local reduction and even sign reversal of\nmagnetic correlations, originating from the competition between kinetic and\nmagnetic energy in the system. The experimentally observed polaron signatures\nare found to be consistent with an effective string model at finite\ntemperature. We demonstrate that delocalization of the doublon is a necessary\ncondition for polaron formation by contrasting this mobile setting to a\nscenario where the doublon is pinned to a lattice site. Our work paves the way\ntowards probing interactions between polarons, which may lead to stripe\nformation, as well as microscopically exploring the fate of polarons in the\npseudogap and bad metal phase.",
        "positive": "Gain-induced trapping of microcavity exciton polariton condensates: We have performed real and momentum space spectroscopy of exciton polariton\ncondensates in a GaAs-based microcavity under non-resonant excitation with an\nintensity stabilized laser. An effective trapping mechanism is revealed, which\nis due to the stimulated scattering gain inside the finite excitation spot\ncombined with the short lifetime. We observe several quantized modes while the\nlowest state shows Heisenberg-limited real and momentum space distributions.\nThe experimental findings are qualitatively reproduced by an open dissipative\nGross-Pitaevskii equation model."
    },
    {
        "anchor": "Local quench spectroscopy of many-body quantum systems: Quench spectroscopy is a relatively new method which enables the\ninvestigation of spectral properties of many-body quantum systems by monitoring\nthe out-of-equilibrium dynamics of real-space observables after a quench. So\nfar the approach has been devised for global quenches or using local\nengineering of momentum-resolved excitations. Here, we extend the quench\nspectroscopy method to local quenches. We show that it allows us to extract\nquantitative information about global properties of the system, and in\nparticular the elementary excitation spectrum. Using state-of-the-art numerical\nmethods, we simulate the out-of-equilibrium dynamics of a variety of quantum\nsystems following various local quench protocols and demonstrate a general\nscheme for designing an appropriate local quench protocol for any chosen model.\nWe provide detailed examples of how the local quench protocol can be realised\nin realistic current generation experiments, including ultracold atomic gases\nand trapped ion systems.",
        "positive": "Collective excitations of exciton-polariton condensates in a synthetic\n  gauge field: Collective (elementary) excitations of quantum bosonic condensates, including\ncondensates of exciton polaritons in semiconductor microcavities, are a\nsensitive probe of interparticle interactions. In anisotropic microcavities\nwith momentum-dependent TE-TM splitting of the optical modes, the excitations\ndispersions are predicted to be strongly anisotropic, which is a consequence of\nthe synthetic magnetic gauge field of the cavity, as well as the interplay\nbetween different interaction strengths for polaritons in the singlet and\ntriplet spin configurations. Here, by directly measuring the dispersion of the\ncollective excitations in a high-density optically trapped exciton-polariton\ncondensate, we observe excellent agreement with the theoretical predictions for\nspinor polariton excitations. We extract the inter- and intra-spin polariton\ninteraction constants and map out the characteristic spin textures in an\ninteracting spinor condensate of exciton polaritons."
    },
    {
        "anchor": "Compacton existence and spin-orbit density dependence in Bose-Einstein\n  condensates: We demonstrate the existence of compactons matter waves in binary mixtures of\nBose-Einstein condensates (BEC) trapped in deep optical lattices (OL) subjected\nto equal contributions of intra-species Rashba and Dresselhaus spin-orbit\ncoupling (SOC) under periodic time modulations of the intra-species scattering\nlength. We show that these modulations lead to the rescaling of the SOC\nparameters that involve the density imbalance of the two components. This gives\nrise to a density-dependent SOC parameters strongly influence the existence and\nstability of compacton matter waves. The stability of SOC-compactons is\ninvestigated both by linear stability analysis and by time integrations of the\ncoupled Gross-Pitaevskii equations. We find that SOC restricts the parameter\nranges for stable stationary SOC-compacton existence but, on the other side, it\ngives a more stringent signature of their occurrence. In particular,\nSOC-compactons should appear when the intra-species interactions and the number\nof atoms in the two components are perfectly balanced (or close to being\nbalanced for metastable cases). The possibility to use SOC-compactons as a tool\nfor indirect measurements of the number of atoms and/or the intra-species\ninteractions, is also suggested.",
        "positive": "Angle-resolved photoemission spectroscopy of a Fermi-Hubbard system: Angle-resolved photoemission spectroscopy (ARPES) measures the\nsingle-particle excitations of a many-body quantum system with both energy and\nmomentum resolution, providing detailed information about strongly interacting\nmaterials. ARPES is a direct probe of fermion pairing, and hence a natural\ntechnique to study the development of superconductivity in a variety of\nexperimental systems ranging from high temperature superconductors to unitary\nFermi gases. In these systems a remnant gap-like feature persists in the normal\nstate, which is referred to as a pseudogap. A quantitative understanding of\npseudogap regimes may elucidate details about the pairing mechanisms that lead\nto superconductivity, but developing this is difficult in real materials partly\nbecause the microscopic Hamiltonian is not known. Here we report on the\ndevelopment of ARPES to study strongly interacting fermions in an optical\nlattice using a quantum gas microscope. We benchmark the technique by measuring\nthe occupied single-particle spectral function of an attractive Fermi-Hubbard\nsystem across the BCS-BEC crossover and comparing to quantum Monte Carlo\ncalculations. We find evidence for a pseudogap in our system that opens well\nabove the expected critical temperature for superfluidity. This technique may\nalso be applied to the doped repulsive Hubbard model which is expected to\nexhibit a pseudogap at temperatures close to those achieved in recent\nexperiments."
    },
    {
        "anchor": "Stationary entanglement entropies following an interaction quench in 1D\n  Bose gas: We analyze the entanglement properties of the asymptotic steady state after a\nquench from free to hard-core bosons in one dimension. The R\\'enyi and von\nNeumann entanglement entropies are found to be extensive, and the latter\ncoincides with the thermodynamic entropy of the Generalized Gibbs Ensemble\n(GGE). Computing the spectrum of the two-point function, we provide exact\nanalytical results both for the leading extensive parts and the subleading\nterms for the entropies as well as for the cumulants of the particle number\nfluctuations. We also compare the extensive part of the entanglement entropy\nwith the thermodynamic ones, showing that the GGE entropy equal the\nentanglement one and it is the double of the diagonal entropy.",
        "positive": "Stochastic precession of the polarization in a polariton laser: Microcavity polaritons in the lasing regime undergo a spontaneous symmetry\nbreaking transition resulting in coherent emission with a well defined\npolarization. The order parameter is thus a vector describing both the laser\nglobal phase and polarization. Using an ultrafast single-shot detection\ntechnique we show that polariton lasing in GaAs-based microcavities presents a\nhigh degree of second order coherence ($g^{(2)}(\\tau=0) \\approx 1$) above\nthreshold, and that the initial polarization is stochastic, taking any possible\ndirection in the Poincar\\'e sphere (linear, elliptical or circular). Once the\npolarization direction is established, subsequent oscillations of the emission\nprobability witness the presence of an intrinsic polarization splitting. Our\nresults show the negligible role of polariton interactions in the total\nemission statistics and in the establishment of the initial polarization."
    },
    {
        "anchor": "Universal phase structure of dilute Bose gases with Rashba spin-orbit\n  coupling: A Bose gas subject to a light-induced Rashba spin-orbit coupling possesses a\ndispersion minimum on a circle in momentum space; we show that kinematic\nconstraints due to this dispersion cause interactions to renormalize to\nuniversal, angle-dependent values that govern the phase structure in the\ndilute-gas limit. We find that, regardless of microscopic interactions, (a) the\nground state involves condensation at two opposite momenta, and is, in finite\nsystems, a fragmented condensate; and (b) there is a nonzero-temperature\ninstability toward the condensation of pairs of bosons. We discuss how our\nresults can be reconciled with the qualitatively different mean-field phase\ndiagram, which is appropriate for dense gases.",
        "positive": "Study of a degenerate dipolar Fermi gas of 161Dy atoms: We study properties of a single-component (spin polarized) degenerate dipolar\nFermi gas of 161Dy atoms using a hydrodynamic description. Under\naxially-symmetric trapping we suggest reduced one- (1D) and two-dimensional\n(2D) description of the same for cigar and disk shapes, respectively. In\naddition to a complete numerical solution of the hydrodynamic model we also\nconsider a variational approximation of the same. For a trapped system under\nappropriate conditions, the variational approximation as well as the reduced 1D\nand 2D models are found to yield results for shape, size and chemical potential\nof the system in agreement with the full numerical solution of the\nthree-dimensional (3D) model. For the uniform system we consider anisotropic\nsound propagation in 3D. An analytical result for anisotropic sound propagation\nin uniform dipolar degenerate Fermi gas is found to be in agreement with\nresults of numerical simulation in 3D."
    },
    {
        "anchor": "Three in Many: Efimov physics in the presence of a Fermi sea: Motivated by recent experiments on $^{6}$Li-$^{133}$Cs atomic mixtures with\nhigh mass imbalance, we study the Efimov correlation in atomic system of two\nheavy bosons ($^{133}$Cs) immersed in a bath of light fermions ($^{6}$Li).\nUsing the Born-Oppenheimer approximation, we identify two different regimes,\ndepending on the Fermi momentum of light fermions ($k_F$) and the boson-fermion\nscattering length $a_s(<0)$, where the presence of underlying Fermi sea plays\ndistinct roles in the Efimov-type binding of bosons. Namely, in the regime\n$k_F|a_s|\\lesssim 1$ ($k_F|a_s|\\gtrsim1$), the Fermi sea induces an attractive\n(repulsive) effective interaction between bosons and thus favors (disfavors)\nthe formation of bound state, which can be seen as the Efimov trimer dressed by\nthe fermion cloud. Interestingly, this implies a non-monotonic behavior of\nthese bound states as increasing the fermion density (or $k_F$). Moreover, we\nestablish a generalized universal scaling law for the emergence/variation of\nsuch dressed Efimov bound states when incorporating a new scale ($k_F$) brought\nby the Fermi sea. These results can be directly tested in Li-Cs cold atoms\nexperiment by measuring the modified bound state spectrum and the shifted\nEfimov resonance, which manifest an emergent non-trivial Efimov correlation in\na fermionic many-body environment.",
        "positive": "Exploring quantum signatures of chaos on a Floquet synthetic lattice: Ergodicity and chaos play an integral role in the dynamical behavior of\nmany-particle systems and are crucial to the formulation of statistical\nmechanics. Still, a general understanding of how randomness and chaos emerge in\nthe dynamical evolution of closed quantum systems remains elusive. Here, we\ndevelop an experimental platform for the realization of canonical quantum\nchaotic Hamiltonians based on quantum simulation with synthetic lattices. We\nmap the angular momentum projection states of an effective quantum spin onto\nthe linear momentum states of a $^{87}$Rb Bose-Einstein condensate, which can\nalternatively be viewed as lattice sites in a synthetic dimension. This\nsynthetic lattice, with local and dynamical control of tight-binding lattice\nparameters, enables new capabilities related to the experimental study of\nquantum chaos. In particular, the capabilities of our system let us tune the\neffective size of our spin, allowing us to illustrate how classical chaos can\nemerge from a discrete quantum system. Moreover, spectroscopic control over our\nsynthetic lattice allows us to explore unique aspects of our spin's dynamics by\nmeasuring the out-of-time-ordered correlation function, and enables future\ninvestigations into entirely new classes of chaotic systems."
    },
    {
        "anchor": "Slow quench dynamics of periodically driven quantum gases: We study the evolution of bosons in a periodically driven optical lattice\nduring a slow change of the driving amplitude. Both the regime of high\nfrequency and low frequency driving are investigated. In the low frequency\nregime, resonant absorption of energy is observed. In the high frequency\nregime, the dynamics is compared to a system with an effective Hamiltonian in\nwhich the atoms are `dressed' by the driving field. This `dressing' can\ndramatically change the amplitude and sign of the effective tunneling. A\nparticular focus of this study is the investigation of the time-scales\nnecessary for the evolving quantum state to follow almost adiabatically to the\nground-state of the effective many body system.",
        "positive": "Universal Three-Body Parameter of Heavy-Heavy-Light systems with\n  negative intraspecies scattering length: The Three-Body Parameter(3BP)\n$a^{\\scriptscriptstyle(1)}_{\\scriptscriptstyle-}$ is crucial to understanding\nEfimov physics, and a universal 3BP has been shown in experiments and theory in\nultracold homonuclear gases. The 3BP of heteronuclear systems was predicted to\npossess much richer properties than the homonuclear counterparts for the large\nparameter space. In this work, we investigate the universal properties of\n$a^{\\scriptscriptstyle(1)}_{\\scriptscriptstyle-}$ for the\nHeavy-Heavy-Light(HHL) system with negative intraspecies scattering length\n$a_{\\scriptscriptstyle HH}$. We find that\n$a^{\\scriptscriptstyle(1)}_{\\scriptscriptstyle-}$ follows a universal behavior\ndetermined by the van der Waals(vdW) interaction and the mass ratio. An\nanalytic formula of $a^{\\scriptscriptstyle(1)}_{\\scriptscriptstyle-}$ is given\nas a function of $a_{\\scriptscriptstyle HH}$, which allows an intuitive\nunderstanding of how does $a^{\\scriptscriptstyle(1)}_{\\scriptscriptstyle-}$\ndepend on the mass ratio and the vdW length $r_{\\scriptscriptstyle vdW}$. In a\nspecial case, when the two heavy atoms are in resonance,\n$a^{\\scriptscriptstyle(1)}_{\\scriptscriptstyle-}$ is approximately a constant:\n$a^{\\scriptscriptstyle(1)}_{\\scriptscriptstyle-} = -(6.3\\pm0.6)\\,\nr_{\\scriptscriptstyle vdW,HL}$."
    },
    {
        "anchor": "OpenMP, OpenMP/MPI, and CUDA/MPI C programs for solving the\n  time-dependent dipolar Gross-Pitaevskii equation: We present new versions of the previously published C and CUDA programs for\nsolving the dipolar Gross-Pitaevskii equation in one, two, and three spatial\ndimensions, which calculate stationary and non-stationary solutions by\npropagation in imaginary or real time. Presented programs are improved and\nparallelized versions of previous programs, divided into three packages\naccording to the type of parallelization. First package contains improved and\nthreaded version of sequential C programs using OpenMP. Second package\nadditionally parallelizes three-dimensional variants of the OpenMP programs\nusing MPI, allowing them to be run on distributed-memory systems. Finally,\nprevious three-dimensional CUDA-parallelized programs are further parallelized\nusing MPI, similarly as the OpenMP programs. We also present speedup test\nresults obtained using new versions of programs in comparison with the previous\nsequential C and parallel CUDA programs. The improvements to the sequential\nversion yield a speedup of 1.1 to 1.9, depending on the program. OpenMP\nparallelization yields further speedup of 2 to 12 on a 16-core workstation,\nwhile OpenMP/MPI version demonstrates a speedup of 11.5 to 16.5 on a computer\ncluster with 32 nodes used. CUDA/MPI version shows a speedup of 9 to 10 on a\ncomputer cluster with 32 nodes.",
        "positive": "Artificial graphene with tunable interactions: We create an artificial graphene system with tunable interactions and study\nthe crossover from metallic to Mott insulating regimes, both in isolated and\ncoupled two-dimensional honeycomb layers. The artificial graphene consists of a\ntwo-component spin mixture of an ultracold atomic Fermi gas loaded into a\nhexagonal optical lattice. For strong repulsive interactions we observe a\nsuppression of double occupancy and measure a gapped excitation spectrum. We\npresent a quantitative comparison between our measurements and theory, making\nuse of a novel numerical method to obtain Wannier functions for complex lattice\nstructures. Extending our studies to time-resolved measurements, we investigate\nthe equilibration of the double occupancy as a function of lattice loading\ntime."
    },
    {
        "anchor": "Interaction induced mergence of Dirac points in Non-Abelian optical\n  lattices: We study the properties of an ultracold Fermi gas loaded in a square optical\nlattice and subjected to an external and classical non-Abelian gauge field. We\ncalculate the energy spectrum of the system and show that the Dirac points in\nthe energy spectrum will remain quite stable under onsite interaction of\ncertain strength. Once the on-site interaction grows stronger than a critical\nvalue, the Dirac points will no longer be stable and merge into a single hybrid\npoint. This mergence implies a quantum phase transition from a semimetallic\nphase to a band insulator. The on-site interaction between ultracold fermions\ncould be conveniently controlled by Feshbach resonances in current experiments.\nWe proposed that this remarkable interaction induced mergence of Dirac points\nmay be observed in the ultracold fermi gas experiments.",
        "positive": "Path-integral approach to the thermodynamics of bosons with memory:\n  Density and correlation functions: Expanding upon previous work, using the path-integral formalism we derive\nexpressions for the one-particle reduced density matrix and the two-point\ncorrelation function for a quadratic system of bosons that interact through a\ngeneral class of memory kernels. The results are applied to study the density,\ncondensate fraction and pair correlation function of trapped bosons\nharmonically coupled to external distinguishable masses."
    },
    {
        "anchor": "A quantum moat barrier, realized with a finite square well: The notion of a double well potential typically involves two regions of space\nseparated by a repulsive potential barrier. The solution is a wave function\nthat is suppressed in the barrier region and localized in the two surrounding\nregions. Remarkably, we illustrate that similar solutions can be achieved using\nan attractive \"barrier\" potential (a \"quantum moat\") instead of a repulsive one\n(a \"quantum wall\"). The reason this works is intimately connected to the\nconcepts of \"orthogonalized plane waves\" and the pseudopotential method, both\noriginally used to understand electronic band structures in solids. While the\nmain goal of this work is to use a simple model to demonstrate the barrier-like\nattribute of a quantum moat, we also show how the pseudopotential method is\nused to greatly improve the efficiency of constructing wave functions for this\nsystem using matrix diagonalization.",
        "positive": "Interaction-enhanced flow of a polariton persistent current in a ring: We study the quantum hydrodynamical features of exciton-polaritons flowing\ncircularly in a ring-shaped geometry. We consider a resonant-excitation scheme\nin which the spinor polariton fluid is set into motion in both components by\nspin-to-orbital angular momentum conversion. We show that this scheme allows to\ncontrol the winding number of the fluid, and to create two circulating states\ndiffering by two units of the angular momentum. We then consider the effect of\na disorder potential, which is always present in realistic nanostructures. We\nshow that a smooth disorder is efficiently screened by the polariton-polariton\ninteractions, yielding a signature of polariton superfluidity. This effect is\nreminiscent of supercurrent in a superconducting loop."
    },
    {
        "anchor": "Quasi-particle Lifetime in a Mixture of Bose and Fermi Superfluids: In this letter, to reveal the effect of quasi-particle interactions in a\nBose-Fermi superfluid mixture, we consider the lifetime of quasi-particle of\nBose superfluid due to its interaction with quasi-particles in Fermi\nsuperfluid. We find that this damping rate, i.e. inverse of the lifetime, has\nquite different threshold behavior at the BCS and the BEC side of the Fermi\nsuperfluid. The damping rate is a constant nearby the threshold momentum in the\nBCS side, while it increases rapidly in the BEC side. This is because in the\nBCS side the decay processe is restricted by constant density-of-state of\nfermion quasi-particle nearby Fermi surface, while such a restriction does not\nexist in the BEC side where the damping process is dominated by bosonic\nquasi-particles of Fermi superfluid. Our results are related to collective mode\nexperiment in recently realized Bose-Fermi superfluid mixture.",
        "positive": "One- and two-dimensional solitons in spin-orbit-coupled Bose-Einstein\n  condensates with fractional kinetic energy: We address effects of spin-orbit coupling (SOC), phenomenologically added to\na two-component Bose-Einstein condensate composed of particles moving by Levy\nflights, in one- and two-dimensional (1D and 2D) settings. The corresponding\nsystem of coupled Gross-Pitaevskii equations includes fractional kinetic-energy\noperators, characterized by the Levy index, \\alpha < 2 (the normal kinetic\nenergy corresponds to \\alpha = 2). The SOC terms, with strength \\lambda,\nproduce strong effects in the 2D case: they create families of stable solitons\nof the semi-vortex (SV) and mixed-mode (MM) types in the interval of 1 < \\alpha\n< 2, where the supercritical collapse does not admit the existence of stable\nsolitons in the absence of the SOC. At \\lambda --> 0, amplitudes of these\nsolitons vanish as (\\lambda)^{1/(\\alpha - 1)}."
    },
    {
        "anchor": "Bipartite and tripartite entanglement in a Bose-Einstein acoustic black\n  hole: We investigate quantum entanglement in an analogue black hole realized in the\nflow of a Bose-Einstein condensate. The system is described by a three-mode\nGaussian state and we construct the corresponding covariance matrix at zero and\nfinite temperature. We study associated bipartite and tripartite entanglement\nmeasures and discuss their experimental observation. We identify a simple\noptical setup equivalent to the analogue Bose-Einstein black hole which\nsuggests a new way of determining the Hawking temperature and grey-body factor\nof the system.",
        "positive": "Interaction induced topological Bogoliubov excitations in a spin-orbit\n  coupled Bose-Einstein condensate: We study topologically non-trivial excitations of a weakly interacting,\nspin-orbit coupled Bose-Einstein condensate in a two-dimensional square optical\nlattice, a system recently realized in experiment [W. Sun et al., Phys. Rev.\nLett. 121, 150401 (2018)]. We focus on situations where the system is not\nsubjected to a Zeeman field and thus does not exhibit nontrivial\nsingle-particle band topology. Of special interest then is the role of particle\ninteraction as well as its interplay with the symmetry properties of the system\nin producing topologically non-trivial excitations. We find that the\nnon-interacting system possesses a rich set of symmetries, including the\n$\\mathcal{PT}$ symmetry, the modified dihedral point group symmetry $\\tilde\nD_4$ and the nonsymmorphic symmetry. These combined symmetries ensure the\nexistence of pairs of degenerate Dirac points at the edge of Brillouin zone for\nthe single-particle energy bands. In the presence of particle interaction and\nwith sufficient spin-orbit coupling, the atoms condense in a ground state with\nnet magnetization which spontaneously breaks the $\\mathcal{PT}$ and $\\tilde\nD_4$ symmetry. We demonstrate that this symmetry breaking leads to a gap\nopening at the Dirac point for the Bogoliubov spectrum and consequentially\ntopologically non-trivial excitations. We confirm the non-trivial topology by\ncalculating the Chern numbers of the lowest excitation bands and show that\ngapless edge states form at the interface of systems characterized by different\nvalues of the Chern number."
    },
    {
        "anchor": "Enhancement of spin coherence in a spin-1 Bose condensate by dynamical\n  decoupling approaches: We present a theoretical investigation on the enhancement of the spin\ncoherence with periodic, concatenated, or Uhrig dynamical decoupling $N$-pulse\nsequences in a $^{87}$Rb spin-1 Bose condensate, where the intrinsic dynamical\ninstability in such a ferromagnetically interacting condensate causes spin\ndecoherence and eventually leads to a multiple spatial-domain structure or a\nspin texture. Our results show that all the three sequences successfully\nenhance the spin coherence by pushing the wave vector of the most unstable mode\nin the condensate to a larger value. Among the three sequences with the same\nnumber of pulses, the concatenated one shows the best performance in preserving\nthe spin coherence. Interestingly, we find that all the three sequences exactly\nfollow the same enhancement law, $k_- T^{1/2} = c$, with $k_-$ the wave vector\nof the most unstable mode, $T$ the sequence period, and $c$ a\nsequence-dependent constant. Such a law between $k_-$ and $T$ is also derived\nanalytically for an attractive scalar Bose condensate subjecting to a periodic\ndynamical decoupling sequence.",
        "positive": "Impurity in a bosonic Josephson junction: swallowtail loops, chaos,\n  self-trapping and the poor man's Dicke model: We study a model describing $N$ identical bosonic atoms trapped in a\ndouble-well potential together with a single impurity atom, comparing and\ncontrasting it throughout with the Dicke model. As the boson-impurity coupling\nstrength is varied, there is a symmetry-breaking pitchfork bifurcation which is\nanalogous to the quantum phase transition occurring in the Dicke model. Through\nstability analysis around the bifurcation point, we show that the critical\nvalue of the coupling strength has the same dependence on the parameters as the\ncritical coupling value in the Dicke model. We also show that, like the Dicke\nmodel, the mean-field dynamics go from being regular to chaotic above the\nbifurcation and macroscopic excitations of the bosons are observed. Overall,\nthe boson-impurity system behaves like a poor man's version of the Dicke model."
    },
    {
        "anchor": "Restoring quasi-reversibility with a single topological charge: We numerically study a rotating Bose-Einstein condensate placed transiently\nover the critical rotation frequency i.e. in a regime where the rotation\nfrequency is larger than the radial frequency of the confinement. We study the\nreversibility of this process depending on the strength of the interactions and\nthe presence of vortices. We find that the reversibility is broken by the\ninteractions in the absence of vortices but systematically quasi-restored in\nthe presence of a single vortex.",
        "positive": "OpenMP Fortran and C programs for solving the time-dependent\n  Gross-Pitaevskii equation in an anisotropic trap: We present new version of previously published Fortran and C programs for\nsolving the Gross-Pitaevskii equation for a Bose-Einstein condensate with\ncontact interaction in one, two and three spatial dimensions in imaginary and\nreal time, yielding both stationary and non-stationary solutions. To reduce the\nexecution time on multicore processors, new versions of parallelized programs\nare developed using Open Multi-Processing (OpenMP) interface. The input in the\nprevious versions of programs was the mathematical quantity nonlinearity for\ndimensionless form of Gross-Pitaevskii equation, whereas in the present\nprograms the inputs are quantities of experimental interest, such as, number of\natoms, scattering length, oscillator length for the trap, etc. New output files\nfor some integrated one- and two-dimensional densities of experimental interest\nare given. We also present speedup test results for the new programs."
    },
    {
        "anchor": "Thermodynamics and renormalized quasi-particles in the vicinity of the\n  dilute Bose gas quantum critical point in two dimensions: We use the functional renormalization group (FRG) to derive analytical\nexpressions for thermodynamic observables (density, pressure, entropy, and\ncompressibility) as well as for single-particle properties (wavefunction\nrenormalization and effective mass) of interacting bosons in two dimensions as\na function of temperature $T$ and chemical potential $\\mu$. We focus on the\nquantum disordered and the quantum critical regime close to the dilute Bose gas\nquantum critical point. Our approach is based on a truncated vertex expansion\nof the hierarchy of FRG flow equations and the decoupling of the two-body\ncontact interaction in the particle-particle channel using a suitable\nHubbard-Stratonovich transformation. Our analytic FRG results extend previous\nanalytical renormalization group calculations for thermodynamic observables at\n$\\mu =0$ to finite values of $\\mu$. To confirm the validity of our FRG\napproach, we have also performed quantum Monte Carlo simulations to obtain the\nmagnetization, the susceptibility, and the correlation length of the\ntwo-dimensional spin-$1/2$ quantum $XY$ model with coupling $J$ in a regime\nwhere its quantum critical behavior is controlled by the dilute Bose gas\nquantum critical point. We find that our analytical results describe the Monte\nCarlo data for $\\mu \\leq 0$ rather accurately up to relatively high\ntemperatures $T \\lesssim 0.1 J$.",
        "positive": "Nonlinear Phenomena of Ultracold Atomic Gases in Optical Lattices:\n  Emergence of Novel Features in Extended States: The system of a cold atomic gas in an optical lattice is governed by two\nfactors: nonlinearity originating from the interparticle interaction, and the\nperiodicity of the system set by the lattice. The high level of controllability\nassociated with such an arrangement allows for the study of the competition and\ninterplay between these two, and gives rise to a whole range of interesting and\nrich nonlinear effects. This review covers the basic idea and overview of such\nnonlinear phenomena, especially those corresponding to extended states. This\nincludes \"swallowtail\" loop structures of the energy band, Bloch states with\nmultiple periodicity, and those in \"nonlinear lattices\", i.e., systems with the\nnonlinear interaction term itself being a periodic function in space."
    },
    {
        "anchor": "Fulde-Ferrel-Larkin-Ovchinnikov phase in one dimensional Fermi gas with\n  attractive interactions and transverse spin-orbit coupling: We examine the existence and characteristics of the exotic\nFulde-Ferrel-Larkin-Ovchinnikov (FFLO) phase in a one-dimensional Fermi gas\nwith attractive Hubbard interactions, in the presence of spin-orbit coupling\n(SOC) and Zeeman field. We show that a robust FFLO phase can be created in the\npresence of attractive on-site interactions and Zeeman field, and that the\naddition of SOC suppresses the FFLO order and enhances the pair formation. In\nabsence of SOC, the system shows four phases: Bardeen-Cooper-Schrieffer (BCS),\nFFLO, multi- mode pairing and fully polarized phases by tuning the Zeeman field\nh, and the quantum transition between these phases is discontinuous with\nrespect to h. In the presence of SOC, the transition from the BCS to FFLO phase\nbecomes continuous. We present a complete phase diagram of this model both in\nthe presence and in the absence of SOC at quarter electron filling and also\nexplore the effect of SOC on the FFLO phase.",
        "positive": "Quantum Scattering States in a Nonlinear Coherent Medium: We present a comprehensive study of stationary states in a coherent medium\nwith a quadratic or Kerr nonlinearity in the presence of localized potentials\nin one dimension (1D) for both positive and negative signs of the nonlinear\nterm, as well as for barriers and wells. The description is in terms of the\nnonlinear Schr\\\"odinger equation (NLSE) and hence applicable to a variety of\nsystems, including interacting ultracold atoms in the mean field regime and\nlight propagation in optical fibers. We determine the full landscape of\nsolutions, in terms of a potential step and build solutions for rectangular\nbarrier and well potentials. It is shown that all the solutions can be\nexpressed in terms of a Jacobi elliptic function with the inclusion of a\ncomplex-valued phase shift. Our solution method relies on the roots of a cubic\npolynomial associated with a hydrodynamic picture, which provides a simple\nclassification of all the solutions, both bounded and unbounded, while the\nboundary conditions are intuitively visualized as intersections of phase space\ncurves. We compare solutions for open boundary conditions with those for a\nbarrier potential on a ring, and also show that numerically computed solutions\nfor smooth barriers agree qualitatively with analytical solutions for\nrectangular barriers. A stability analysis of solutions based on the Bogoliubov\nequations for fluctuations show that persistent instabilities are localized at\nsharp boundaries, and are predicated by the relation of the mean density change\nacross the boundary to the value of the derivative of the density at the edge.\nWe examine the scattering of a wavepacket by a barrier potential and show that\nat any instant the scattered states are well described by the stationary\nsolutions we obtain, indicating applications of our results and methods to\nnonlinear scattering problems."
    },
    {
        "anchor": "Effect of disorder close to the superfluid transition in a\n  two-dimensional Bose gas: We experimentally study the effect of disorder on trapped quasi\ntwo-dimensional (2D) 87Rb clouds in the vicinity of the\nBerezinskii-Kosterlitz-Thouless (BKT) phase transition. The disorder\ncorrelation length is of the order of the Bose gas characteristic length scales\n(thermal de Broglie wavelength, healing length) and disorder thus modifies the\nphysics at a microscopic level. We analyze the coherence properties of the\ncloud through measurements of the momentum distributions, for two disorder\nstrengths, as a function of its degeneracy. For moderate disorder, the\nemergence of coherence remains steep but is shifted to a lower entropy. In\ncontrast, for strong disorder, the growth of coherence is hindered. Our study\nis an experimental realization of the dirty boson problem in a well controlled\natomic system suitable for quantitative analysis.",
        "positive": "Dragging spin-orbit-coupled solitons by a moving optical lattice: It is known that the interplay of the spin-orbit-coupling (SOC) and\nmean-field self-attraction creates stable two-dimensional (2D) solitons (ground\nstates) in spinor Bose-Einstein condensates. However, SOC destroys the system's\nGalilean invariance, therefore moving solitons exist only in a narrow interval\nof velocities, outside of which the solitons suffer delocalization. We\ndemonstrate that the application of a relatively weak moving optical lattice\n(OL), with the 2D or quasi-1D structure, makes it possible to greatly expand\nthe velocity interval for stable motion of the solitons. The stability domain\nin the system's parameter space is identified by means of numerical methods. In\nparticular, the quasi-1D OL produces a stronger stabilizing effect than its\nfull 2D counterpart. Some features of the domain are explained analytically."
    },
    {
        "anchor": "Commensurate and incommensurate 1D interacting quantum systems: Single-atom imaging resolution of many-body quantum systems in optical\nlattices is routinely achieved with quantum-gas microscopes. Key to their great\nversatility as quantum simulators is the ability to use engineered light\npotentials at the microscopic level. Here, we employ dynamically varying\nmicroscopic light potentials in a quantum-gas microscope to study commensurate\nand incommensurate 1D systems of interacting bosonic Rb atoms. Such\nincommensurate systems are analogous to doped insulating states that exhibit\natom transport and compressibility. Initially, a commensurate system with unit\nfilling and fixed atom number is prepared between two potential barriers. We\ndeterministically create an incommensurate system by dynamically changing the\nposition of the barriers such that the number of available lattice sites is\nreduced while retaining the atom number. Our systems are characterised by\nmeasuring the distribution of particles and holes as a function of the lattice\nfilling, and interaction strength, and we probe the particle mobility by\napplying a bias potential. Our work provides the foundation for preparation of\nlow-entropy states with controlled filling in optical-lattice experiments.",
        "positive": "Bose-Einstein condensation of photons: We review recent work on the Bose-Einstein condensation of photons in a dye\nmicrocavity environment. Other than for material particles, as e.g. cold atomic\nBose gases, photons usually do not condense at low temperatures. For Planck's\nblackbody radiation, the most ubiquitous Bose gas, photon number and\ntemperature are not independently tunable and at low temperatures the photons\nsimply disappear in the system's walls, instead of massively occupying the\ncavity ground mode. In the here described approach, this obstacle is overcome\nby a fluorescence-induced thermalization mechanism in a dye-filled microcavity.\nExperimentally, both the thermalization of the photon gas and, at high photon\ndensities, Bose-Einstein condensation has been observed. This article describes\nthe thermalization mechanism of the photon gas in detail and summarizes so far\nperformed experimental work."
    },
    {
        "anchor": "Semiclassical dynamics of a disordered two-dimensional Hubbard model\n  with long-range interactions: Quench dynamics in a two-dimensional system of interacting fermions is\nanalyzed within the semiclassical truncated Wigner approximation (TWA). The\nmodels with short-range and long-range interactions are considered. We show\nthat in the latter case, the TWA is very accurate, becoming asymptotically\nexact in the infinite-range limit, provided that the semiclassical Hamiltonian\nis correctly identified. Within the TWA, different dynamical timescales of\ncharges and spins can be clearly distinguished. Interestingly, for a weak and\nmoderate disorder strength, we observe subdiffusive behavior of charges, while\nspins exhibit diffusive dynamics. At strong disorder, the quantum Fisher\ninformation shows logarithmic growth in time with a slower increase for charges\nthan for spins. It is shown that in contrast to the short-range model, strong\ninhomogeneities such as domain walls in the initial state can significantly\nslow down thermalization dynamics, especially at weak disorder. This behavior\ncan put additional challenges in designing cold-atom experimental protocols\naimed to analyze possible many-body localization in such systems. While within\nthis approach we cannot make any definite statements about the existence of a\nmany-body localized phase, we see a very fast crossover as a function of\ndisorder strength from rapidly thermalizing to a slow glassy like regime both\nfor the short-range and long-range models.",
        "positive": "Tan's universal contact and collective oscillations of strongly\n  interacting Fermi gases: We study strongly interacting two component Fermi gas near a Feshbach\nresonance. By using a ground state energy functional constructed based on\nasymptotic limits and Monte Carlo calculations, we calculate the contact,\nstructure factor, and collective oscillation frequencies in the BCS-BEC\ncrossover region. The calculated contact and structure factor show excellent\nagreements with recent experiments. We compare these results with a standard\nmean-field theory and find that the contact is proportional to the square of\nsuperfluid order parameter. Further, we present the chemical potential and the\npolytropic index in terms of homogenous energy and the contact."
    },
    {
        "anchor": "Mott Insulator-Superfluid Transition in a Generalized Bose-Hubbard Model\n  with Topologically Non-trivial Flat-Band: In this paper, we studied a generalized Bose-Hubbard model on a checkerboard\nlattice with topologically nontrivial flat-band. We used mean-field method to\ndecouple the model Hamiltonian and obtained phase diagram by Landau theory of\nsecond-order phase transition. We further calculate the energy gap and the\ndispersion of quasi-particle or quasi-hole in Mott insulator state and found\nthat in strong interaction limit the quasi-particles or the quasi-holes also\nhave flat bands.",
        "positive": "Mechanical resonances of mobile impurities in a one-dimensional quantum\n  fluid: We study a one-dimensional interacting quantum liquid hosting a pair of\nmobile impurities causing backscattering. We determine the effective retarded\ninteraction between the two impurities mediated by the liquid. We show that for\nstrong backscattering this interaction gives rise to resonances and\nantiresonances in the finite-frequency mobility of the impurity pair. At the\nantiresonances, the two impurities remain at rest even when driven by a (small)\nexternal force. At the resonances, their synchronous motion follows the\nexternal drive in phase and reaches maximum amplitude. Using a perturbative\nrenormalization group analysis in quantum tunneling across the impurities, we\nstudy the range of validity of our model. We predict that these mechanical\nantiresonances are observable in experiments on ultracold atom gases confined\nto one dimension."
    },
    {
        "anchor": "Polariton fluids for analogue gravity physics: Analogue gravity enables the study of fields on curved spacetimes in the\nlaboratory. There are numerous experimental platforms in which amplification at\nthe event horizon or the ergoregion has been observed. Here, we demonstrate how\noptically generating a defect in a polariton microcavity enables the creation\nof one- and two-dimensional, transsonic fluid flows. We show that this highly\ntuneable method permits the creation of sonic horizons. Furthermore, we present\na rotating geometry akin to the water-wave bathtub vortex. These experiments\nusher-in the possibility of observing stimulated as well as spontaneous\namplification by the Hawking, Penrose and Zeld'ovich effects in fluids of\nlight.",
        "positive": "The decay and collisions of dark solitons in superfluid Fermi gases: We study soliton collisions and the decay of solitons into sound in\nsuperfluid Fermi gases across the Bose-Einstein condensate to\nBardeen-Cooper-Schrieffer (BEC-BCS) crossover by performing numerical\nsimulations of the time-dependent Bogoliubov-de Gennes equations. This decay\nprocess occurs when the solitons are accelerated to the bulk pair-breaking\nspeed by an external potential. A similar decay process may occur when solitons\nare accelerated by an inelastic collision with another soliton. We find that\nsoliton collisions become increasingly inelastic as we move from the BEC to BCS\nregimes, and the excess energy is converted into sound. We interpret this\neffect as being due to evolution of Andreev bound states localized within the\nsoliton."
    },
    {
        "anchor": "Hyperchaos in a Bose-Hubbard chain with Rydberg-dressed interactions: We study chaos and hyperchaos of Rydberg-dressed Bose-Einstein condensates\n(BECs) in a one-dimensional optical lattice. Due to the long-range soft-core\ninteraction between the dressed atoms, the dynamics of the BECs are described\nby the extended Bose-Hubbard model. In the mean-field regime, we analyze the\ndynamical stability of the BEC by focusing on the groundstate and localized\nstate configuration. Lyapunov exponents of the two configurations are\ncalculated by varying the soft-core interaction strength, potential bias and\nlength of the lattice. Both configurations can have multiple positive Lyapunov\nexponents, exhibiting hyperchaotic dynamics. We show the dependence of the\nnumber of the positive Lyapunov exponents and the largest Lyapunov exponent on\nthe length of the optical lattice. The largest Lyapunov exponent is directly\nproportional to areas of phase space encompassed by the associated Poincar\\'e\nsections. We demonstrate that linear and hysteresis quenches of the lattice\npotential and the dressed interaction lead to distinct dynamics due to the\nchaos and hyperchaos. Our work is relevant to current research on chaos, and\ncollective and emergent nonlinear dynamics of BECs with long-range\ninteractions.",
        "positive": "Phonon contribution to the shear viscosity of a superfluid Fermi gas in\n  the unitarity limit: We present a detailed analysis of the contribution of small-angle\nNambu-Goldstone boson (phonon) collisions to the shear viscosity, $\\eta$, in a\nsuperfluid atomic Fermi gas close to the unitarity limit. We show that the\nexperimental values of the shear viscosity coefficient to entropy ratio,\n$\\eta/s$, obtained at the lowest reached temperature can be reproduced assuming\nthat phonons give the leading contribution to $\\eta$. The phonon contribution\nis evaluated considering $1 \\leftrightarrow 2$ processes and taking into\naccount the finite size of the experimental system. In particular, for very low\ntemperatures, $T \\lesssim 0.1 T_F$, we find that phonons are ballistic and the\ncontribution of phonons to the shear viscosity is determined by the processes\nthat take place at the interface between the superfluid and the normal phase.\nThis result is independent of the detailed form of the phonon dispersion law\nand leads to two testable predictions: the shear viscosity should correlate\nwith the size of the optical trap and it should decrease with decreasing\ntemperature. For higher temperatures the detailed form of the phonon dispersion\nlaw becomes relevant and, within our model, we find that the experimental data\nfor $\\eta/s$ can be reproduced assuming that phonons have an anomalous\ndispersion law."
    },
    {
        "anchor": "Formation of Solitonic Bound State via Light-Matter Interaction: Exchange of energy by means of light-matter interaction provides a new\ndimension to various nonlinear dynamical systems. Here, the effects of\nlight-matter interaction are investigated for a situation, where two\ncounter-propagating, orthogonally polarized laser pulses are incident on the\natomic condensate. It's observed that a localized laser pulse profile can\ninduce localized modes in Bose-Einstein condensate. A stability analysis\nperformed using Vakhitov-Kolokolov-like criterion has established that these\nlocalized modes are stable, when the atom-atom interaction is repulsive. The\ncooperative effects of light-matter interactions and atom-atom interactions on\nthe Lieb-mode have been studied in the stable region through atomic dispersion,\nrevealing the signature of bound state formation when the optical potential is\nP\\\"oschl-Teller type. The energy diagram also indicates a continuous transfer\nof energy from the laser pulses to the atoms as the light-matter interaction\nchanges its sign.",
        "positive": "Coherent excitation transport through ring-shaped networks: The coherent quantum transport of matter wave through a ring-shaped circuit\nattached to leads defines an iconic system in mesoscopic physics that has\nallowed both to explore fundamental questions in quantum science and to draw\nimportant avenues for conceiving devices of practical use.\n  Here we study the source-to-drain transport of excitations going through a\nring-network, without propagation of matter waves. We model the circuit in\nterms of a spin system with specific long-range interactions that are relevant\nfor quantum technology, such as Rydberg atoms trapped in optical tweezers or\nion traps. Inspired by the logic of rf- and dc-SQUIDs, we consider rings with\none and two local energy offsets, or detunings. As a combination of specific\nphase shifts in going though the localized detunings and as a result of\ncoherent tunneling, we demonstrate how the transport of excitations can be\ncontrolled, with a distinctive dependence on the range of interactions."
    },
    {
        "anchor": "Experimental verification of the area law of mutual information in a\n  quantum field simulator: Theoretical understanding of the scaling of entropies and the mutual\ninformation has led to significant advances in the research of correlated\nstates of matter, quantum field theory, and gravity. Measuring von Neumann\nentropy in quantum many-body systems is challenging as it requires complete\nknowledge of the density matrix. In this work, we measure the von Neumann\nentropy of spatially extended subsystems in an ultra-cold atom simulator of\none-dimensional quantum field theories. We experimentally verify one of the\nfundamental properties of equilibrium states of gapped quantum many-body\nsystems, the area law of quantum mutual information. We also study the\ndependence of mutual information on temperature and the separation between the\nsubsystems. Our work is a crucial step toward employing ultra-cold atom\nsimulators to probe entanglement in quantum field theories.",
        "positive": "Stable p-wave resonant two-dimensional Fermi-Bose dimers: We consider two-dimensional weakly-bound heterospecies molecules formed in a\nFermi-Bose mixture with attractive Fermi-Bose and repulsive Bose-Bose\ninteractions. Bosonic exchanges lead to an intermolecular attraction, which can\nbe controlled and tuned to a p-wave resonance. Such attractive fermionic\nmolecules can be realized in quasi-two-dimensional ultracold isotopic or\nheteronuclear mixtures. We show that they are stable with respect to the\nrecombination to deeply-bound molecular states and with respect to the\nformation of higher-order clusters (trimers, tetramers, etc.)"
    },
    {
        "anchor": "Strong-coupling limit in cold-molecule formation via photoassociation or\n  Feshbach resonance through Nikitin exponential resonance crossing: The strong-coupling limit of molecule formation in an atomic Bose-Einstein\ncondensate via two-mode one-color photoassociation or sweep across a Feshbach\nresonance is examined using a basic nonlinear time-dependent two-state model.\nFor the general class of term-crossing models with constant coupling, a common\nstrategy for attacking the problem is developed based on the reduction of the\ninitial system of semiclassical equations for atom-molecule amplitudes to a\nthird order nonlinear differential equation for the molecular state\nprobability. This equation provides deriving exact solution for a class of\nperiodic level-crossing models. These models reveal much in common with the\nRabi problem. Discussing the strong-coupling limit for the general case of\nvariable detuning, the equation is further truncated to a limit first-order\nnonlinear equation. Using this equation, the strong nonlinearity regime for the\nfirst Nikitin exponential-crossing model is analyzed and accurate asymptotic\nexpressions for the nonlinear transition probability to the molecular state are\nderived. It is shown that, because of a finite final detuning involved, this\nmodel displays essential deviations from the Landau-Zener behavior. In\nparticular, it is shown that in the limit of strong coupling the final\nconversion probability tends to 1/6. Thus, in this case the strong interaction\nlimit is not optimal for molecule formation. We have found that if optimal\nfield intensity is applied the molecular probability is increased up to 1/4\n(i.e., the half of the initial atomic population).",
        "positive": "Variational Bethe Ansatz approach for dipolar one-dimensional bosons: We propose a variational approximation to the ground state energy of a\none-dimensional gas of interacting bosons on the continuum based on the Bethe\nAnsatz ground state wavefunction of the Lieb-Liniger model. We apply our\nvariational approximation to a gas of dipolar bosons in the single mode\napproximation and obtain its ground state energy per unit length. This allows\nfor the calculation of the Tomonaga-Luttinger exponent as a function of density\nand the determination of the structure factor at small momenta. Moreover, in\nthe case of attractive dipolar interaction, an instability is predicted at a\ncritical density, which could be accessed in lanthanide atoms."
    },
    {
        "anchor": "Degenerate Fermi Gas of $^{87}$Sr: We report quantum degeneracy in a gas of ultra-cold fermionic $^{87}$Sr\natoms. By evaporatively cooling a mixture of spin states in an optical dipole\ntrap for 10.5\\,s, we obtain samples well into the degenerate regime with\n$T/T_F=0.26^{+.05}_{-.06}$. The main signature of degeneracy is a change in the\nmomentum distribution as measured by time-of-flight imaging, and we also\nobserve a decrease in evaporation efficiency below $T/T_F \\sim 0.5$.",
        "positive": "Supervised machine learning of ultracold atoms with speckle disorder: We analyze how accurately supervised machine learning techniques can predict\nthe lowest energy levels of one-dimensional noninteracting ultracold atoms\nsubject to the correlated disorder due to an optical speckle field. Deep neural\nnetworks with different numbers of hidden layers and neurons per layer are\ntrained on large sets of instances of the speckle field, whose energy levels\nhave been preventively determined via a high-order finite difference technique.\nThe Fourier components of the speckle field are used as feature vector to\nrepresent the speckle-field instances. A comprehensive analysis of the details\nthat determine the possible success of supervised machine learning tasks,\nnamely the depth and the width of the neural network, the size of the training\nset, and the magnitude of the regularization parameter, is presented. It is\nfound that ground state energies of previously unseen instances can be\npredicted with essentially arbitrary accuracy. First and second excited state\nenergies can be predicted too, albeit with slightly lower accuracy and using\nmore layers of hidden neurons."
    },
    {
        "anchor": "Resonant Five-body Recombination in an Ultracold Gas of Bosonic Atoms: We combine theory and experiment to investigate five-body recombination in an\nultracold gas of atomic cesium at negative scattering length. A refined\ntheoretical model, in combination with extensive laboratory tunability of the\ninteratomic interactions, enables the five-body resonant recombination rate to\nbe calculated and measured. The position of the new observed recombination\nfeature agrees with a recent theoretical prediction and supports the prediction\nof a family of universal cluster states at negative $a$ that are tied to an\nEfimov trimer.",
        "positive": "Quantum Crystals and Laughlin Droplets of Cavity Rydberg Polaritons: Synthetic quantum materials offer an exciting opportunity to explore quantum\nmany-body physics and novel states of matter under controlled conditions. In\nparticular, they provide an avenue to exchange the short length scales and\nlarge energy scales of the solid state for an engineered system with better\ncontrol over the system Hamiltonian, more accurate state preparation, and\nhigher fidelity state readout. Here we propose a unique platform to study\nquantum phases of strongly interacting photons. We introduce ideas for\ncontrolling the dynamics of individual photons by manipulating the geometry of\na multimode optical cavity, and combine them with recently established\ntechniques to mediate strong interactions between photons using Rydberg atoms.\nWe demonstrate that this approach gives rise to crystalline- and fractional\nquantum Hall- states of light, opening the door to studies of strongly\ncorrelated quantum many-body physics in a photonic material."
    },
    {
        "anchor": "Dissipative fluid dynamics for the dilute Fermi gas at unitarity: Free\n  expansion and rotation: We investigate the expansion dynamics of a dilute Fermi gas at unitarity in\nthe context of dissipative fluid dynamics. Our aim is to quantify the effects\nof shear viscosity on the time evolution of the system. We compare exact\nnumerical solutions of the equations of viscous hydrodynamics to various\napproximations that have been proposed in the literature. Our main findings\nare: i) Shear viscosity leads to characteristic features in the expansion\ndynamics; ii) a quantitative description of these effects has to include\nreheating; iii) dissipative effects are not sensitive to the equation of state\nP(n,T) as long as the universal relation P=(2/3)E is satisfied; iv) the\nexpansion dynamics mainly constrains the cloud average of the shear viscosity.",
        "positive": "Scaling behaviour of trapped bosonic particles in two dimensions at\n  finite temperature: In the framework of the trap-size scaling theory, we study the scaling\nproperties of the Bose-Hubbard model in two dimensions in the presence of a\ntrapping potential at finite temperature. In particular, we provide results for\nthe particle density and the density-density correlator at the Mott transitions\nand within the superfluid phase. For the former quantity, numerical outcomes\nare also extensively compared to Local Density Approximation predictions."
    },
    {
        "anchor": "Path integral Monte Carlo simulation of global and local superfluidity\n  in liquid $^{4}$He reservoirs separated by nanoscale apertures: We present a path integral Monte Carlo study of the global superfluid\nfraction and local superfluid density in cylindrically-symmetric reservoirs of\nliquid $^{4}$He separated by nanoaperture arrays. The superfluid response to\nboth translations along the axis of symmetry (longitudinal response) and\nrotations about the cylinder axis (transverse response) are computed, together\nwith radial and axial density distributions that reveal the microscopic\ninhomogeneity arising from the combined effects of the confining external\npotential and the $^4$He-$^4$He interatomic potentials. We make a microscopic\ndetermination of the length-scale of decay of superfluidity at the radial\nboundaries of the system by analyzing the local superfluid density distribution\nto extract a displacement length that quantifies the superfluid mass\ndisplacement away from the boundary. We find that the longitudinal superfluid\nresponse is reduced in reservoirs separated by a septum containing sufficiently\nsmall apertures compared to a cylinder with no intervening aperture array, for\nall temperatures below $T_{\\lambda}$. For a single aperture in the septum, a\nsignificant drop in the longitudinal superfluid response is seen when the\naperture diameter is made smaller than twice the empirical\ntemperature-dependent $^4$He healing length, consistent with the formation of a\nweak link between the reservoirs. Increasing the diameter of a single aperture\nor the number of apertures in the array results in an increase of the\nsuperfluid density toward the expected bulk value.",
        "positive": "Sub-Doppler cooling of sodium atoms in gray molasses: We report on the realization of sub-Doppler laser cooling of sodium atoms in\ngray molasses using the D1 optical transition ($3s\\, ^2S_{1/2} \\rightarrow 3p\\,\n^2P_{1/2}$) at 589.8 nm. The technique is applied to samples containing\n$3\\times10^9$ atoms, previously cooled to 350 $\\mu$K in a magneto-optical trap,\nand it leads to temperatures as low as 9 $\\mu$K and phase-space densities in\nthe range of $10^{-4}$. The capture efficiency of the gray molasses is larger\nthan 2/3, and we observe no density-dependent heating for densities up to\n$10^{11}$ cm$^{-3}$."
    },
    {
        "anchor": "N-body Efimov states from two-particle noise: The ground state energies of universal N-body clusters tied to Efimov\ntrimers, for N even, are shown to be encapsulated in the statistical\ndistribution of two particles interacting with a background auxiliary field at\nlarge Euclidean time when the interaction is tuned to the unitary point.\nNumerical evidence that this distribution is log-normal is presented, allowing\none to predict the ground-state energies of the N-body system.",
        "positive": "Observation of a superradiant Mott insulator in the Dicke-Hubbard model: It is well known that the bosonic Hubbard model possesses a Mott insulator\nphase. Likewise, it is known that the Dicke model exhibits a self-organized\nsuperradiant phase. By implementing an optical lattice inside of a high finesse\noptical cavity both models are merged such that an extended Hubbard model with\ncavity-mediated infinite range interactions arises. In addition to a normal\nsuperfluid phase, two superradiant phases are found, one of them coherent and\nhence superfluid and one incoherent Mott insulating."
    },
    {
        "anchor": "Vortex Nucleation in a Dissipative Variant of the Nonlinear\n  Schr\u00f6dinger Equation under Rotation: In the present work, we motivate and explore the dynamics of a dissipative\nvariant of the nonlinear Schr{\\\"o}dinger equation under the impact of external\nrotation. As in the well established Hamiltonian case, the rotation gives rise\nto the formation of vortices. We show, however, that the most unstable mode\nleading to this instability scales with an appropriate power of the chemical\npotential $\\mu$ of the system, increasing proportionally to $\\mu^{2/3}$. The\nprecise form of the relevant formula, obtained through our asymptotic analysis,\nprovides the most unstable mode as a function of the atomic density and the\ntrap strength. We show how these unstable modes typically nucleate a large\nnumber of vortices in the periphery of the atomic cloud. However, through a\npattern selection mechanism, prompted by symmetry-breaking, only few isolated\nvortices are pulled in sequentially from the periphery towards the bulk of the\ncloud resulting in highly symmetric stable vortex configurations with far fewer\nvortices than the original unstable mode. These results may be of relevance to\nthe experimentally tractable realm of finite temperature atomic condensates.",
        "positive": "$Z_2\\times Z_2$ symmetry and $Z_4$ Berry phase of bosonic ladder: Bose gas on a two-leg ladder exhibits an interesting topological phase. We\nshow the presence of a bosonic symmetry-protected-topological (SPT) phase\nprotected by $Z_2\\times Z_2$ symmetry. This symmetry leads to $Z_4$ fractional\nquantization of $Z_4$ Berry phase, that is a topological order parameter to\nidentify the bulk. Using the $Z_4$ Berry phase, we have shown that the\ninteracting bosonic system possesses rich topological phases depending on\nparticle density and strength of interaction. Based on the bulk-edge\ncorrespondence, each edge state of the SPT phases is discussed in relation to\nthe $Z_4$ Berry phases. Especially we have found an intermediate phase that is\nnot adiabatically connected to a simple adiabatic limit, that possesses\nunconventional edge states, which we have numerically demonstrate by employing\nthe density-matrix-renormalization group algorithm."
    },
    {
        "anchor": "Dipolar particles in a double-trap confinement: Response to tilting the\n  dipolar orientation: We analyze the microscopic few-body properties of dipolar particles confined\nin two parallel quasi-one-dimensional harmonic traps. In particular, we show\nthat an adiabatic rotation of the dipole orientation about the trap axes can\ndrive an initially non-localized few-fermion state into a localized state with\nstrong inter-trap pairing. For an instant, non-adiabatic rotation, however,\nlocalization is inhibited and a highly excited state is reached. This state may\nbe interpreted as the few-body analog of a super-Tonks-Girardeau state, known\nfrom one-dimensional systems with contact interactions.",
        "positive": "Topological chiral currents in the Gross-Neveu model extension: We unveil an interesting connection of Lorentz-violating quantum field\ntheories, studied in the context of the standard model extension, and\nHubbard-type models of topological crystalline phases. These models can be\ninterpreted as a regularisation of the former and, as hereby discussed,\nexplored with current quantum simulators based on ultra-cold atoms in optical\nRaman lattices. In particular, we present a complete analysis of the\nCreutz-Hubbard ladder under a generic magnetic flux, which regularises a\nGross-Neveu model extension, and presents a characteristic circulating chiral\ncurrent whose non-zero value arises from a specific violation of Lorentz\ninvariance. We present a complete phase diagram with trivial insulators,\nferromagnetic and anti-ferromagnetic phases, and current-carrying topological\ncrystalline phases. These predictions are benchmarked using tools from\ncondensed matter and quantum-information science, showing that self-consistent\nHartree-Fock and strong-coupling Dzyaloshinskii-Moriya methods capture the\nessence of the phase diagram in different regimes, which is further explored\nusing extensive numerical simulations based on matrix-product states."
    },
    {
        "anchor": "A Model for Overscreened Kondo Effect in Ultracold Fermi Gas: The feasibility of realizing overscreened Kondo effect in ultra-cold Fermi\ngas of atoms with spin $s \\ge \\tfrac{3}{2}$ in the presence of a localized\nmagnetic impurity atom is proved realistic. Specifying to a system of ultra\ncold $^{22}$Na Fermi gas and a trapped $^{197}$Au impurity, the mechanism of\nexchange interaction between the Na and Au atoms is elucidated and the exchange\nconstant is found to be antiferromagnetic. The corresponding exchange\nHamiltonian is derived, and the Kondo temperature is estimated at the order of\n$ 1 \\mu$K.\n  Within a weak-coupling renormalization group scheme, it is shown that the\ncoupling renormalizes to the non-Fermi liquid fixed point.",
        "positive": "Spin-orbit-coupled Bose-Einstein condensates held under toroidal trap: We study a quasispin-$1/2$ Bose-Einstein condensate with synthetically\ngenerated spin-orbit coupling in a toroidal trap, and show that the system has\na rich variety of ground and metastable states. As the central hole region\nincreases, i.e., the potential changes from harmonic-like to ring-like, the\ncondensate exhibits a variety of structures, such as triangular stripes,\nflower-petal patterns, and counter-circling states. We also show that the\nrotating systems have exotic vortex configurations. In the limit of a quasi-one\ndimensional ring, the quantum many-body ground state is obtained, which is\nfound to be the fragmented condensate."
    },
    {
        "anchor": "The stochastic projected Gross-Pitaevskii equation: We have achieved the first full implementation of the stochastic projected\nGross-Pitaevskii equation for a three-dimensional trapped Bose gas at finite\ntemperature. Our work advances previous applications of this theory, which have\nonly included growth processes, by implementing number-conserving scattering\nprocesses. We evaluate an analytic expression for the coefficient of the\nscattering term and compare it to that of the growth term in the experimental\nregime, showing the two coefficients are comparable in size. We give an\noverview of the numerical implementation of the deterministic and stochastic\nterms for the scattering process, and use simulations of a condensate excited\ninto a large amplitude breathing mode oscillation to characterize the\nimportance of scattering and growth processes in an experimentally accessible\nregime. We find that in such non-equilibrium regimes the scattering can\ndominate over the growth, leading to qualitatively different system dynamics.\nIn particular, the scattering causes the system to rapidly reach thermal\nequilibrium without greatly depleting the condensate, suggesting that it\nprovides a highly coherent energy transfer mechanism.",
        "positive": "Mobile impurities interacting with a few one-dimensional lattice bosons: We report a comprehensive study of the ground-state properties of one and two\nbosonic impurities immersed in small one-dimensional optical lattices loaded\nwith a few interacting bosons. We model the system with a two-component\nBose-Hubbard model and solve the problem numerically by means of the exact\ndiagonalization (ED) method. We report binding energies of one and two\nimpurities across the superfluid (SF) to Mott-insulator (MI) transition and\nconfirm the formation of two-body bound states of impurities induced by\nrepulsive interactions. In particular, we found that an insulator bath induces\ntightly bound di-impurity dimers, whereas a superfluid bath induces shallower\nbound states."
    },
    {
        "anchor": "Correlations in the low-density Fermi gas: Fermi-Liquid state,\n  Dimerization, and BCS Pairing: We present ground state calculations for low-density Fermi gases described by\ntwo model interactions, an attractive square-well potential and a Lennard-Jones\npotential, of varying strength. We use the optimized Fermi-Hypernetted Chain\nintegral equation method which has been proved to provide, in the density\nregimes of interest here, an accuracy better than one percent. We first examine\nthe low-density expansion of the energy and compare with the exact answer by\nHuang and Yang (H. Huang and C. N. Yang, {\\em Phys. Rev.\\/} {\\bf 105}, 767\n(1957)). It is shown that a locally correlated wave function of the\nJastrow-Feenberg type does not recover the quadratic term in the expansion of\nthe energy in powers of $\\a0\\KF$, where $\\a0$ is the vacuum $s$-wave scattering\nlength and $\\KF$ the Fermi wave number. The problem is cured by adding\nsecond-order perturbation corrections in a correlated basis. Going to higher\ndensities and/or more strongly coupled systems, we encounter an instability of\nthe normal state of the system which is characterized by a divergence of the\n{\\em in-medium\\/} scattering length. We interpret this divergence as a\nphonon-exchange driven dimerization of the system, similar to what one has at\nzero density when the vacuum scattering length $\\a0$ diverges. We then study,\nin the stable regime, the superfluid gap and its dependence on the density and\nthe interaction strength. We identify two different corrections to low-density\nexpansions: One is medium corrections to the pairing interaction, and the other\none finite-range corrections. We show that the most important finite-range\ncorrections are a direct manifestation of the many-body nature of the system.",
        "positive": "Formation, dynamics and stability of coreless vortex dipoles in\n  phase-separated binary condensates: We study the motion of the Gaussian obstacle potential created by blue\ndetuned laser beam through a phase-separated binary condensate in\npancake-shaped traps. For the velocity of the obstacle above a critical\nvelocity, we observe the generation of vortex dipoles in the outer component\nwhich can penetrate the inner component. This is equivalent to finite, although\nsmall, transport of outer component across the inner component. In the inner\ncomponent, the same method can lead to the formation of coreless vortex\ndipoles."
    },
    {
        "anchor": "Rotation of quantum impurities in the presence of a many-body\n  environment: We develop a microscopic theory describing a quantum impurity whose\nrotational degree of freedom is coupled to a many-particle bath. We approach\nthe problem by introducing the concept of an 'angulon' - a quantum rotor\ndressed by a quantum field - and reveal its quasiparticle properties using a\ncombination of variational and diagrammatic techniques. Our theory predicts\nrenormalisation of the impurity rotational structure, such as observed in\nexperiments with molecules in superfluid helium droplets, in terms of a\nrotational Lamb shift induced by the many-particle environment. Furthermore, we\ndiscover a rich many-body-induced fine structure, emerging in rotational\nspectra due to a redistribution of angular momentum within the quantum\nmany-body system.",
        "positive": "Fractional quantum Hall physics with ultracold Rydberg gases in\n  artificial gauge fields: We study ultracold Rydberg-dressed Bose gases subject to artificial gauge\nfields in the fractional quantum Hall (FQH) regime. The characteristics of the\nRydberg interaction gives rise to interesting many-body ground states different\nfrom standard FQH physics in the lowest Landau level (LLL). The non-local but\nrapidly decreasing interaction potential favors crystalline ground states for\nvery dilute systems. While a simple Wigner crystal becomes energetically\nfavorable compared to the Laughlin liquid for filling fractions $\\nu<1/12$, a\ncorrelated crystal of composite particles emerges already for $\\nu \\leq 1/6$\nwith a large energy gap to the simple Wigner crystal. The presence of a new\nlength scale, the Rydberg blockade radius $a_B$, gives rise to a bubble crystal\nphase for $\\nu\\lesssim 1/4$ when the average particle distance becomes less\nthan $a_B$, which describes the region of saturated, almost constant\ninteraction potential. For larger fillings indications for strongly correlated\ncluster liquids are found."
    },
    {
        "anchor": "Strongly interacting Bose-Fermi mixtures in one dimension: We study one-dimensional strongly interacting Bose-Fermi mixtures by both the\nexact Bethe-ansatz method and variational perturbation theory within the\ndegenerate ground state subspace of the system in the infinitely repulsive\nlimit. Based on the exact solution of the one-dimensional Bose-Fermi gas with\nequal boson-boson and boson-fermion interaction strengths, we demonstrate that\nthe ground state energy is degenerate for different Bose-Fermi configurations\nand the degeneracy is lifted when the interaction deviates the infinitely\ninteracting limit. We then show that the ground properties in the strongly\ninteracting regime can be well characterized by using the variational\nperturbation method within the degenerate ground state subspace, which can be\napplied to deal with more general cases with anisotropic interactions and in\nexternal traps. Our results indicate that the total ground-state density\nprofile in the strongly repulsive regime behaves like the polarized\nnoninteracting fermions, whereas the density distributions of bosons and\nfermions display different properties for different Bose-Fermi configurations\nand are sensitive to the anisotropy of interactions.",
        "positive": "Exploring the Kondo model in and out of equilibrium with alkaline-earth\n  atoms: We propose a scheme to realize the Kondo model with tunable anisotropy using\nalkaline-earth atoms in an optical lattice. The new feature of our setup is\nFloquet engineering of interactions using time-dependent Zeeman shifts, that\ncan be realized either using state-dependent optical Stark shifts or magnetic\nfields. The properties of the resulting Kondo model strongly depend on the\nanisotropy of the ferromagnetic interactions. In particular, easy-plane\ncouplings give rise to Kondo singlet formation even though microscopic\ninteractions are all ferromagnetic. We discuss both equilibrium and dynamical\nproperties of the system that can be measured with ultracold atoms, including\nthe impurity spin susceptibility, the impurity spin relaxation rate, as well as\nthe equilibrium and dynamical spin correlations between the impurity and the\nferromagnetic bath atoms. We analyze the non-equilibrium time evolution of the\nsystem using a variational non-Gaussian approach, which allows us to explore\ncoherent dynamics over both short and long timescales, as set by the bandwidth\nand the Kondo singlet formation, respectively. In the quench-type experiments,\nwhen the Kondo interaction is suddenly switched on, we find that real-time\ndynamics shows crossovers reminiscent of poor man's renormalization group flow\nused to describe equilibrium systems. For bare easy-plane ferromagnetic\ncouplings, this allows us to follow the formation of the Kondo screening cloud\nas the dynamics crosses over from ferromagnetic to antiferromagnetic behavior.\nOn the other side of the phase diagram, our scheme makes it possible to measure\nquantum corrections to the well-known Korringa law describing the temperature\ndependence of the impurity spin relaxation rate. Theoretical results discussed\nin our paper can be measured using currently available experimental techniques."
    },
    {
        "anchor": "Beliaev technique for a weakly interacting Bose gas: Aiming for simplicity of explicit equations and at the same time controllable\naccuracy of the theory we present results for all thermodynamic quantities and\ncorrelation functions for the weakly interacting Bose gas at\nshort-to-intermediate distances obtained within an improved version of\nBeliaev's diagrammatic technique. With a small symmetry breaking term Beliaev's\ndiagrammatic technique becomes regular in the infrared limit. Up to\nhigher-order terms (for which we present order-of-magnitude estimates), the\npartition function and entropy of the system formally correspond to those of a\nnon-interacting bosonic (pseudo-)Hamiltonian with a temperature dependent\nBogoliubov-type dispersion relation. Away from the fluctuation region, this\napproach provides the most accurate--in fact, the best possible within the\nBogoliubov-type pseudo-Hamiltonian framework--description of the system with\ncontrolled accuracy. It produces accurate answers for the off-diagonal\ncorrelation functions up to distances where the behaviour of correlators is\ncontrolled by generic hydrodynamic relations, and thus can be accurately\nextrapolated to arbitrarily large scales. In the fluctuation region, the\nnon-perturbative contributions are given by universal (for all weakly\ninteracting U(1) systems) constants and scaling functions, which can be\nobtained separately--by simulating classical U(1) models--and then used to\nextend the description of the weakly interacting Bose gas to the fluctuation\nregion. The theory works in all spatial dimensions and we explicitly check its\nvalidity against first-principle Monte Carlo simulations for various\nthermodynamic properties and the single-particle density matrix.",
        "positive": "Cold atoms in cavity-generated dynamical optical potentials: We review state-of-the-art theory and experiment of the motion of cold and\nultracold atoms coupled to the radiation field within a high-finesse optical\nresonator in the dispersive regime of the atom-field interaction with small\ninternal excitation. The optical dipole force on the atoms together with the\nback-action of atomic motion onto the light field gives rise to a complex\nnonlinear coupled dynamics. As the resonator constitutes an open driven and\ndamped system, the dynamics is non-conservative and in general enables cooling\nand confining the motion of polarizable particles. In addition, the emitted\ncavity field allows for real-time monitoring of the particle's position with\nminimal perturbation up to sub-wavelength accuracy. For many-body systems, the\nresonator field mediates controllable long-range atom-atom interactions, which\nset the stage for collective phenomena. Besides correlated motion of distant\nparticles, one finds critical behavior and non-equilibrium phase transitions\nbetween states of different atomic order in conjunction with superradiant light\nscattering. Quantum degenerate gases inside optical resonators can be used to\nemulate opto-mechanics as well as novel quantum phases like supersolids and\nspin glasses. Non-equilibrium quantum phase transitions, as predicted by e.g.\nthe Dicke Hamiltonian, can be controlled and explored in real-time via\nmonitoring the cavity field. In combination with optical lattices, the cavity\nfield can be utilized for non-destructive probing Hubbard physics and tailoring\nlong-range interactions for ultracold quantum systems."
    },
    {
        "anchor": "The role of real-space micromotion for bosonic and fermionic Floquet\n  fractional Chern insulators: Fractional Chern insulators are the proposed phases of matter mimicking the\nphysics of fractional quantum Hall states on a lattice without an overall\nmagnetic field. The notion of Floquet fractional Chern insulators refers to the\npotential possibilities to generate the underlying topological bandstructure by\nmeans of Floquet engineering. In these schemes, a highly controllable and\nstrongly interacting system is periodically driven by an external force at a\nfrequency such that double tunneling events during one forcing period become\nimportant and contribute to shaping the required effective energy bands. We\nshow that in the described circumstances it is necessary to take into account\nalso third order processes combining two tunneling events with interactions.\nReferring to the obtained contributions as micromotion-induced interactions, we\nfind that those interactions tend to have a negative impact on the stability of\nof fractional Chern insulating phases and discuss implications for future\nexperiments.",
        "positive": "Manipulation of coherent atom waves using accelerated two-dimensional\n  optical lattices: We study the dynamics of Bose-Einstein condensates in accelerated\ntwo-dimensional optical square lattices by numerically solving the\nGross-Pitaevskii equation. We consider the regime with negligible mean-field\ninteractions and examine in detail the pulses of atom clouds ejected from the\ncondensate due to Landau-Zener tunnelling. The pulses exhibit patterned\nstructures that can be understood from the momentum-space dynamics of the\ncondensate. Aside from conceiving realization of a pulsed two-dimensional atom\nlaser, we demonstrate that, by exploring the band structure of the lattice,\nLandau-Zener tunnelling and Bragg reflection of the condensate inside the\noptical lattice can provide means for manipulation of coherent atom waves."
    },
    {
        "anchor": "Density-wave phases of dipolar fermions in a bilayer: We investigate the phase diagram of dipolar fermions with aligned dipole\nmoments in a two-dimensional (2D) bilayer. Using a version of the\nSingwi-Tosi-Land-Sjolander scheme recently adapted to dipolar fermions in a\nsingle layer [M. M. Parish and F. M. Marchetti, Phys. Rev. Lett. 108, 145304\n(2012)], we determine the density-wave instabilities of the bilayer system\nwithin linear response theory. We find that the bilayer geometry can stabilize\nthe collapse of the 2D dipolar Fermi gas with intralayer attraction to form a\nnew density wave phase that has an orientation perpendicular to the density\nwave expected for strong intralayer repulsion. We thus obtain a quantum phase\ntransition between stripe phases that is driven by the interplay between strong\ncorrelations and the architecture of the low dimensional system.",
        "positive": "Macroscopic random Paschen-Back effect in ultracold atomic gases: We consider spin- and density-related properties of single-particle states in\na one-dimensional system with random spin-orbit coupling. We show that the\npresence of an additional Zeeman field $\\Delta$ induces both nonlinear spin\npolarization and delocalization of states localized at $\\Delta=0$,\ncorresponding to a random macroscopic analogue of the Paschen-Back effect.\nWhile the conventional Paschen-Back effect corresponds to a saturated\n$\\Delta-$dependence of the spin polarization, here the gradual suppression of\nthe spin-orbit coupling effects by the Zeeman field is responsible both for the\nspin saturation and delocalization of the particles."
    },
    {
        "anchor": "Simulation of frustrated classical XY models with ultra-cold atoms in 3D\n  triangular optical lattices: Miscellaneous magnetic systems are being recently intensively investigated\nbecause of their potential applications in modern technologies. Nonetheless, a\nmany body dynamical description of complex magnetic systems may be cumbersome,\nespecially when the system exhibits a geometrical frustration. This paper deals\nwith simulations of the classical XY model on a three dimensional triangular\nlattice with anisotropic couplings, including an analysis of the phase diagram\nand a Bogoliubov description of the dynamical stability of mean-field\nstationary solutions. We also discuss the possibilities of the realization of\nBose-Hubbard models with complex tunneling amplitudes in shaken optical\nlattices without breaking the generalized time-reversal symmetry and the\nopposite, i.e. real tunneling amplitudes in systems with the time-reversal\nsymmetry broken.",
        "positive": "Zero-temperature phase diagram of Bose-Fermi gaseous mixtures in optical\n  lattices: We study the ground state phase diagram of a mixture of bosonic and fermionic\ncold atoms confined on two- and three-dimensional optical lattices. The\ncoupling between bosonic fluctuations and fermionic atoms can be attractive or\nrepulsive and has similarities with electron-phonon coupling in crystals. We\ninvestigate behavior of the mixtures in the limit, where the Bogoliubov sound\nvelocity that dictates bosonic dynamics is comparable to the Fermi velocity,\nhence the retardation effects are important part of the physics. The dynamic\nLindhard response function of the fermionic density to changes in the bosonic\nnumber of particles above some critical frequency can alter the sign and in\nconsequence the inter-species interaction between particles becomes repulsive\nin contrast to the static limit (instantaneous and always attractive).\nConsidering the above we show that the structure of the phase diagrams\ncrucially depends on the difference in masses of the bosons and fermions. We\ndiscuss the situations where integrating out fermionic field provides an\nadditional interaction that can decrease or increase bosonic coherence."
    },
    {
        "anchor": "Bose-Einstein condensates with localized spin-orbit coupling: soliton\n  complexes and spinor dynamics: Spin-orbit (SO) coupling can be introduced in a Bose--Einstein condensate\n(BEC) as a gauge potential acting only in a localized spatial domain. Effect of\nsuch a SO \"defect\" can be understood by transforming the system to the\nintegrable vector model. The properties of the SO-BEC change drastically if the\nSO defect is accompanied by the Zeeman splitting. In such a non-integrable\nsystem, the SO defect qualitatively changes the character of soliton\ninteractions and allows for formation of stable nearly scalar soliton complexes\nwith almost all atoms concentrated in only one dark state. These solitons exist\nonly if the number of particles exceeds a threshold value. We also report on\nthe possibility of transmission and reflection of a soliton upon its scattering\non the SO defect. Scattering strongly affects the pseudo-spin polarization and\ncan induce pseudo-spin precession. The scattering can also result in almost\ncomplete atomic transfer between the dark states.",
        "positive": "Landau criterion in a Bose-Condensed Sodium Gas: In light of the experimental evidence for the existence of a superfluid\nregion in a Bose--Condensed Sodium gas a theoretical model is put forward. It\nwill be shown that the predictions of the present work do match with the extant\nexperimental readouts. As a by product we also calculate the speed of sound and\ncompare it against the current experimental results."
    },
    {
        "anchor": "Dynamics of a tunable superfluid junction: We study the population dynamics of a Bose-Einstein condensate in a\ndouble-well potential throughout the crossover from Josephson dynamics to\nhydrodynamics. At barriers higher than the chemical potential, we observe slow\noscillations well described by a Josephson model. In the limit of low barriers,\nthe fundamental frequency agrees with a simple hydrodynamic model, but we also\nobserve a second, higher frequency. A full numerical simulation of the\nGross-Pitaevskii equation giving the frequencies and amplitudes of the observed\nmodes between these two limits is compared to the data and is used to\nunderstand the origin of the higher mode. Implications for trapped matter-wave\ninterferometers are discussed.",
        "positive": "Work statistics in ferromagnetic spinor Bose-Einstein condensates across\n  the quantum phase transition: Driving a quantum many-body system across the quantum phase transition (QPT)\nin finite time has been concerned in different branches of physics to explore\nvarious fundamental questions. Here, we analyze how the underlying QPT affects\nthe work distribution, when the controlling parameter of a ferromagnetic spinor\nBose-Einstein condensates is tuned through the critical point in finite time.We\nshow that the work distribution undergoes a dramatic change with increasing the\ndriving time $\\tau$, which is further captured by employing the entropy of the\nwork distribution.We observe three distinct regions in the evolution of entropy\nas a function of $\\tau$.Specifically, the entropy is insensitive to the driving\ntime in the region of very short $\\tau$. However, in the region with\nintermediate value of $\\tau$, it exhibits a universal power-law decay\nconsistent with the well-known Kibble-Zurek mechanism. For the region with\nlarge $\\tau$, the validity of the adiabatic perturbation theory leads to the\nentropy decay as $\\tau^{-2}\\ln\\tau$. Our results verify the usefulness of the\nentropy of the work distribution for understanding the critical dynamics and\nprovide an alternative way to experimentally study nonequilibrium properties in\nquantum many-body systems."
    },
    {
        "anchor": "Interacting multiple zero mode formulation and its application to a\n  system consisting of a dark soliton in a condensate: To formulate the zero modes in a finite-size system with spontaneous\nbreakdown of symmetries in quantum field theory is not trivial, for in the\nnaive Bogoliubov theory, one encounters difficulties such as phase diffusion,\nthe absence of a definite criterion for determining the ground state, and\ninfrared divergences. A new interacting zero mode formulation that has been\nproposed for systems with a single zero mode to avoid these difficulties is\nextended to general systems with multiple zero modes. It naturally and\ndefinitely gives the interactions among the quantized zero modes, the\nconsequences of which can be observed experimentally. In this paper, as a\ntypical example, we consider an atomic Bose-Einstein condensed system with a\ndark soliton that contains two zero modes corresponding to spontaneous\nbreakdown of the U(1) gauge and translational symmetries. Then we evaluate the\nstandard deviations of the zero mode operators and see how the mutual\ninteraction between the two zero modes affects them.",
        "positive": "Magnetic-field dependent trap loss of ultracold metastable helium: We have experimentally studied the magnetic-field dependence of the decay of\na Bose-Einstein condensate of metastable 4He atoms confined in an optical\ndipole trap, for atoms in the m=+1 and m=-1 magnetic substates, and up to 450\nG. Our measurements confirm long-standing calculations of the two-body loss\nrate coefficient that show an increase above 50 G. We demonstrate that for m=-1\natoms, decay is due to three-body recombination only, with a three-body loss\nrate coefficient of 6.5(0.4)(0.6)10^(-27)cm^6s^(-1), which is interesting in\nthe context of universal few-body theory. We have also searched for a\nrecently-predicted d-wave Feshbach resonance, but did not observe it."
    },
    {
        "anchor": "Visualizing edge states with an atomic Bose gas in the quantum Hall\n  regime: We engineered a two-dimensional magnetic lattice in an elongated strip\ngeometry, with effective per-plaquette flux ~4/3 times the flux quanta. We\nimaged the localized edge and bulk states of atomic Bose-Einstein condensates\nin this strip, with single lattice-site resolution along the narrow direction.\nFurther, we observed both the skipping orbits of excited atoms traveling down\nour system's edges, analogues to edge magnetoplasmons in 2-D electron systems,\nand a dynamical Hall effect for bulk excitations. Our lattice's long direction\nconsisted of the sites of an optical lattice and its narrow direction consisted\nof the internal atomic spin states. Our technique has minimal heating, a\nfeature that will be important for spectroscopic measurements of the Hofstadter\nbutterfly and realizations of Laughlin's charge pump.",
        "positive": "Persistent oscillations of the order parameter and interaction quench\n  phase diagram for a confined Bardeen-Cooper-Schrieffer Fermi gas: We present a numerical study of the interaction quench dynamics in a\nsuperfluid ultracold Fermi gas confined in a three-dimensional cigar-shaped\nharmonic trap. In the present paper we investigate the amplitude mode of the\nsuperfluid order parameter after interaction quenches which start deep in the\nBCS phase and end in the BCS-BEC crossover regime. To this end, we exploit the\nBogoliubov-de Gennes formalism which takes the confinement potential explicitly\ninto account and provides a microscopic fully coherent description of the\nsystem. We find an anharmonic nonlinear oscillation of the modulus of the\nsuperfluid order parameter, i.e., of the Higgs mode. This oscillation persists\nfor large times with only a small amplitude modulation being visible. We\nconnect the frequency and the mean value of this oscillation with the breaking\nof Cooper pairs in the superfluid phase. Additionally, we demonstrate that the\noccurrence of this persistent oscillation is connected to the onset of chaotic\ndynamics in our model. Finally, we calculate an interaction quench phase\ndiagram of the Higgs mode for quenches on the BCS side of the BCS-BEC crossover\nand discuss its properties as a function of the aspect ratio of the\ncigar-shaped trap."
    },
    {
        "anchor": "Finite-size and Particle-number Effects in an Ultracold Fermi Gas at\n  Unitarity: We investigate an ultracold Fermi gas at unitarity confined in a periodic box\n$V=L^3$ using renormalization group (RG) techniques. Within this approach we\ncan quantitatively assess the long range bosonic order parameter fluctuations\nwhich dominate finite-size effects. We determine the finite-size and\nparticle-number dependence of universal quantities, such as the Bertsch\nparameter and the fermion gap. Moreover, we analyze how these universal\nobservables respond to the variation of an external pairing source. Our results\nindicate that the Bertsch parameter saturates rather quickly to its value in\nthe thermodynamic limit as a function of increasing box size. On the other\nhand, we observe that the fermion gap shows a significantly stronger dependence\non the box size, in particular for small values of the pairing source. Our\nresults may contribute to a better understanding of finite-size and\nparticle-number effects present in Monte-Carlo simulations of ultracold Fermi\ngases.",
        "positive": "Analog spacetimes from nonrelativistic Goldstone modes in spinor\n  condensates: It is well established that linear dispersive modes in a flowing quantum\nfluid behave as though they are coupled to an Einstein-Hilbert metric and\nexhibit a host of phenomena coming from quantum field theory in curved space,\nincluding Hawking radiation. We extend this analogy to any nonrelativistic\nGoldstone mode in a flowing spinor Bose-Einstein condensate. In addition to\nshowing the linear dispersive result for all such modes, we show that the\nquadratically dispersive modes couple to a special nonrelativistic spacetime\ncalled a Newton-Cartan geometry. The kind of spacetime (Einstein-Hilbert or\nNewton-Cartan) is intimately linked to the mean-field phase of the condensate.\nTo illustrate the general result, we further provide the specific theory in the\ncontext of a pseudo-spin-1/2 condensate where we can tune between relativistic\nand nonrelativistic geometries. We uncover the fate of Hawking radiation upon\nsuch a transition: it vanishes and remains absent in the Newton-Cartan geometry\ndespite the fact that any fluid flow creates a horizon for certain wave\nnumbers. Finally, we use the coupling to different spacetimes to compute and\nrelate various energy and momentum currents in these analog systems. While this\nresult is general, present day experiments can realize these different\nspacetimes including the magnon modes for spin-1 condensates such as $^{87}$Rb,\n$^{7}$Li, $^{41}$K (Newton-Cartan), and $^{23}$Na (Einstein-Hilbert)."
    },
    {
        "anchor": "Correlated dynamics of fermionic impurities induced by the counterflow\n  of an ensemble of fermions: We investigate the nonequilibrium quantum dynamics of a single and two heavy\nfermionic impurities being harmonically trapped and repulsively interacting\nwith a finite ensemble of majority fermions. A quench of the potential of the\nmajority species from a double-well to a harmonic trap is applied, enforcing\nits counterflow which in turn perturbs the impurities. For weak repulsions it\nis shown that the mixture undergoes a periodic mixing and demixing dynamics,\nwhile stronger interactions lead to a more pronounced dynamical spatial\nseparation. In the presence of correlations the impurity exhibits an expansion\ndynamics which is absent in the Hartree-Fock case resulting in an enhanced\ndegree of miscibility. We generalize our results to different impurity masses\nand demonstrate that the expansion amplitude of the impurity reduces for a\nlarger mass. Furthermore, we showcase that the majority species is strongly\ncorrelated and a phase separation occurs on the two-body level. Most\nimportantly, signatures of attractive impurity-impurity induced interactions\nmediated by the majority species are identified in the time-evolution of the\ntwo-body correlations of the impurities, a result that is supported by\ninspecting their spatial size.",
        "positive": "Hysteresis and metastability of Bose-Einstein condensed clouds of atoms\n  confined in ring potentials: We consider a Bose-Einstein condensed cloud of atoms which rotate in a\ntoroidal/annular potential. Assuming one-dimensional motion, we evaluate the\ncritical frequencies associated with the effect of hysteresis and the critical\ncoupling for stability of the persistent currents. We perform these\ncalculations using both the mean-field approximation and the method of\nnumerical diagonalization of the many-body Hamiltonian which includes\ncorrections due to the finiteness of the atom number."
    },
    {
        "anchor": "Bosonic Josephson effect in the Fano-Anderson model: We investigate the coherent dynamics of a non-interacting Bose-Einstein\ncondensate in a system consisting of two bosonic reservoirs coupled via a\nspatially localized mode. We describe this system by a two-terminal\nFano-Anderson model and investigate analytically the time evolution of\nobservables such as the bosonic Josephson current. In doing so, we find that\nthe Josephson current sensitively depends on the on-site energy of the\nlocalized mode. This facilitates to use this setup as a transistor for a\nBose-Einstein condensate. We identify two regimes. In one regime, the system\nexhibits well-behaved long-time dynamics with a slowly oscillating and undamped\nJosephson current. In a second regime, the Josephson current is a superposition\nof an extremely weakly damped slow oscillation and an undamped fast\noscillation. Our results are confirmed by finite-size simulations.",
        "positive": "Dipole-dipole interactions in optical lattices do not follow an inverse\n  cube power law: We study the effective dipole-dipole interactions in ultracold quantum gases\non optical lattices as a function of asymmetry in confinement along the\nprincipal axes of the lattice. In particular, we study the matrix elements of\nthe dipole-dipole interaction in the basis of lowest band Wannier functions\nwhich serve as a set of low-energy states for many-body physics on the lattice.\nWe demonstrate that the effective interaction between dipoles in an optical\nlattice is non-algebraic in the inter-particle separation at short to medium\ndistance on the lattice scale and has a long-range power-law tail, in contrast\nto the pure power-law behavior of the dipole-dipole interaction in free space.\nThe modifications to the free-space interaction can be sizable; we identify\ndifferences of up to 36% from the free-space interaction at the\nnearest-neighbor distance in quasi-1D arrangements. The interaction difference\ndepends essentially on asymmetry in confinement, due to the d-wave anisotropy\nof the dipole-dipole interaction. Our results do not depend on statistics,\napplying to both dipolar Bose-Einstein condensates and degenerate Fermi gases.\nUsing matrix product state simulations, we demonstrate that use of the correct\nlattice dipolar interaction leads to significant deviations from many-body\npredictions using the free-space interaction. Our results are relevant to up\nand coming experiments with ultracold heteronuclear molecules, Rydberg atoms,\nand strongly magnetic atoms in optical lattices."
    },
    {
        "anchor": "Topologically protected edge gap solitons of interacting Bosons in\n  one-dimensional superlattices: We comprehensively investigate the nontrivial states of interacting Bose\nsystem in one-dimensional optical superlattices under the open boundary\ncondition. Our results show that there exists a kind of stable localized\nstates: edge gap solitons. We argue that the states originate from the\neigenstates of independent edge parabolas. In particular, the edge gap solitons\nexhibit a nonzero topological invariant. The topological nature is due to the\nconnection of the present model to the quantized adiabatic particle transport\nproblem. In addition, the composition relations between the gap solitons and\nthe extend states under the open boundary condition are discussed.",
        "positive": "Computation of local exchange coefficients in strongly interacting\n  one-dimensional few-body systems: local density approximation and exact\n  results: One-dimensional multi-component Fermi or Bose systems with strong zero-range\ninteractions can be described in terms of local exchange coefficients and\nmapping the problem into a spin model is thus possible. For arbitrary external\nconfining potentials the local exchanges are given by highly non-trivial\ngeometric factors that depend solely on the geometry of the confinement through\nthe single-particle eigenstates of the external potential. To obtain accurate\neffective Hamiltonians to describe such systems one needs to be able to compute\nthese geometric factors with high precision which is difficult due to the\ncomputational complexity of the high-dimensional integrals involved. An\napproach using the local density approximation would therefore be a most\nwelcome approximation due to its simplicity. Here we assess the accuracy of the\nlocal density approximation by going beyond the simple harmonic oscillator that\nhas been the focus of previous studies and consider some double-wells of\ncurrent experimental interest. We find that the local density approximation\nworks quite well as long as the potentials resemble harmonic wells but break\ndown for larger barriers. In order to explore the consequences of applying the\nlocal density approximation in a concrete setup we consider quantum state\ntransfer in the effective spin models that one obtains. Here we find that even\nminute deviations in the local exchange coefficients between the exact and the\nlocal density approximation can induce large deviations in the fidelity of\nstate transfer for four, five, and six particles."
    },
    {
        "anchor": "Stable spin domains in a non-degenerate ultra-cold gas: We study the stability of two-domain spin structures in an ultra-cold gas of\nmagnetically trapped $^{87}$Rb atoms above quantum degeneracy. Adding a small\neffective magnetic field gradient stabilizes the domains via coherent\ncollective spin rotation effects, despite negligibly perturbing the potential\nenergy relative to the thermal energy. We demonstrate that domain stabilization\nis accomplished through decoupling the dynamics of longitudinal magnetization,\nwhich remains in time-independent domains, from transverse magnetization, which\nundergoes a purely transverse spin wave trapped within the domain wall. We\nexplore the effect of temperature and density on the steady-state domains, and\ncompare our results to a hydrodynamic solution to a quantum Boltzmann equation.",
        "positive": "Particle imbalanced weakly interacting quantum droplets in one-dimension: We explore the formation of one-dimensional two-component quantum droplets\nwith intercomponent particle imbalance using an ab-initio many-body method. It\nis shown that for moderate particle imbalance each component maintains its\ndroplet flat-top or Gaussian type character depending on the intercomponent\nattraction. Importantly, large particle imbalance leads to a flat-top shape of\nthe majority component with the minority exhibiting spatially localized\nconfigurations. The latter imprint modulations on the majority component which\nbecome more pronounced for increasing interspecies attraction. The same holds\nfor larger mass or increasing repulsion of the minority species. Such\nstructural transitions are also evident in the underlying two-body correlation\nfunctions. To interpret the origin and characteristics of these droplet states\nwe derive an effective model based on the established Lee-Huang-Yang theory\nproviding adequate qualitative analytical predictions even away from its\nexpected parametric region of validity. In contrast, the droplet character is\nfound to vanish in the presence of fermionic minority atoms. Our results pave\nthe way for unveiling complex droplet phases of matter."
    },
    {
        "anchor": "Evaporative cooling of a small number of atoms in a single-beam\n  microscopic dipole trap: We demonstrate experimentally the evaporative cooling of a few hundred\nrubidium 87 atoms in a single-beam microscopic dipole trap. Starting from 800\natoms at a temperature of 125microKelvins, we produce an unpolarized sample of\n40 atoms at 110nK, within 3s. The phase-space density at the end of the\nevaporation reaches unity, close to quantum degeneracy. The gain in phase-space\ndensity after evaporation is 10^3. We find that the scaling laws used for much\nlarger numbers of atoms are still valid despite the small number of atoms\ninvolved in the evaporative cooling process. We also compare our results to a\nsimple kinetic model describing the evaporation process and find good agreement\nwith the data.",
        "positive": "Anisotropy in s-wave Bose-Einstein condensate collisions and its\n  relationship to superradiance: We report the experimental realization of a single-species atomic four-wave\nmixing process with BEC collisions for which the angular distribution of\nscattered atom pairs is not isotropic, despite the collisions being in the\n$s$-wave regime. Theoretical analysis indicates that this anomalous behavior\ncan be explained by the anisotropic nature of the gain in the medium. There are\ntwo competing anisotropic processes: classical trajectory deflections due to\nthe mean-field potential, and Bose enhanced scattering which bears similarity\nto super-radiance. We analyse the relative importance of these processes in the\ndynamical buildup of the anisotropic density distribution of scattered atoms,\nand compare to optically pumped super-radiance."
    },
    {
        "anchor": "Dimerized Mott insulators in hexagonal optical lattices: We study bosonic atoms in optical honeycomb lattices with anisotropic\ntunneling and find dimerized Mott insulator phases with fractional filling.\nThese incompressible insulating phases are characterized by an\ninteraction-driven localization of particles in respect to the individual\ndimers and large local particle-number fluctuations within the dimers. We\ncalculate the ground-state phase diagrams and the excitation spectra using an\naccurate cluster mean-field method. The cluster treatment enables us to probe\nthe fundamental excitations of the dimerized Mott insulator where the\nexcitation gap is dominated by the intra-dimer tunneling amplitude. This allows\nthe distinction from normal Mott insulating phases gapped by the on-site\ninteraction. In addition, we present analytical results for the phase diagram\nderived by a higher-order strong-coupling perturbative expansion approach. By\ncomputing finite lattices with large diameters the influence of a harmonic\nconfinement is discussed in detail. It is shown that a large fraction of atoms\nforms the dimerized Mott insulator under experimental conditions. The necessary\nanisotropic tunneling can be realized either by periodic driving of the optical\nlattice or by engineering directly a dimerized lattice potential. The dimers\ncan be mapped to to their antisymmetric states creating a lattice with coupled\np-orbitals.",
        "positive": "Instabilities of a Filled Vortex in a Two-Component Bose-Einstein\n  Condensate: A two-component Bose-Einstein condensate of cold atoms with a strong\nintercomponent repulsion leading to the spatial separation of the components\nhas been numerically studied. Configurations with a multiple quantized vortex\nin one component, where the vortex core is filled with the other component, are\nconsidered. The effective radius of the core can exceed the width of the\ntransition layer between components, and then an analogy with a filled\ncylindrical vortex in the classical hydrodynamics of two immiscible ideal\nfluids appears. This analogy allows one to analyze the longitudinal \"sausage\"\ninstability and the transverse instability of the filled vortex in the\ncondensate caused by the \"tangential discontinuity,\" as well as the stable\nregime in the parametric gap between them. The presence of long-lived coherent\nstructures formed in some cases at the nonlinear stages of both instabilities\nis numerically discovered."
    },
    {
        "anchor": "Matter-wave solitons in the counterflow of two immiscible superfluids: We study formation of solitons induced by counterflows of immiscible\nsuperfluids. Our setting is based on a quasi-one-dimensional binary\nBose-Einstein condensate (BEC), composed of two immiscible components with\nlarge and small numbers of atoms in them. Assuming that the \"small\" component\nmoves with constant velocity, either by itself, or being dragged by a moving\ntrap, and intrudes into the \"large\" counterpart, the following results are\nobtained. Depending on the velocity, and on whether the small component moves\nin the absence or in the presence of the trap, two-component dark-bright\nsolitons, scalar dark solitons, or multiple dark solitons may emerge, the\nlatter outcome taking place due to breakdown of the superfluidity. We present\ntwo sets of analytical results to describe this phenomenology. In an\nintermediate velocity regime, where dark-bright solitons form, a reduction of\nthe two-component Gross-Pitaevskii system to an integrable Mel'nikov system is\ndeveloped, demonstrating that solitary waves of the former are very accurately\ndescribed by analytically available solitons of the latter. In the\nhigh-velocity regime, where the breakdown of the superfluidity induces the\nformation of dark solitons and multi-soliton trains, an effective\nsingle-component description, in which a strongly localized wave packet of the\n\"small\" component acts as an effective potential for the \"large\" one, allows us\nto estimate the critical velocity beyond which the coherent structures emerge\nin good agreement with the numerical results.",
        "positive": "Sudden jumps and plateaus in the quench dynamics of a Bloch state: We take a one-dimensional tight binding chain with periodic boundary\ncondition and put a particle in an arbitrary Bloch state, then quench it by\nsuddenly changing the potential of an arbitrary site. In the ensuing time\nevolution, the probability density of the wave function at an arbitrary site\n\\emph{jumps indefinitely between plateaus}. This phenomenon adds to a former\none in which the survival probability of the particle in the initial Bloch\nstate shows \\emph{cusps} periodically, which was found in the same scenario\n[Zhang J. M. and Yang H.-T., EPL, \\textbf{114} (2016) 60001]. The plateaus\nsupport the scattering wave picture of the quench dynamics of the Bloch state.\nUnderlying the cusps and jumps is the exactly solvable, nonanalytic dynamics of\na Luttinger-like model, based on which, the locations of the jumps and the\nheights of the plateaus are accurately predicted."
    },
    {
        "anchor": "Quantum bright solitons in a quasi-one-dimensional optical lattice: We study a quasi-one-dimensional attractive Bose gas confined in an optical\nlattice with a superimposed harmonic potential by analyzing the effective\none-dimensional Bose-Hubbard Hamiltonian of the system. In order to have a\nreliable description of the ground-state, that we call quantum bright soliton,\nwe use the Density-Matrix-Renormalization-Group (DMRG) technique. By comparing\nDMRG results with mean-field (MF) ones we find that beyond-mean-field effects\nbecome relevant by increasing the attraction between bosons or by decreasing\nthe frequency of the harmonic confinement. In particular we discover that,\ncontrary to the MF predictions based on the discrete nonlinear Schr\u007f\\\"odinger\nequation, quantum bright solitons are not self-trapped. We also use the\ntime-evolving-block-decimation (TEBD) method to investigate dynamical\nproperties of bright solitons when the frequency of the harmonic potential is\nsuddenly increased. This quantum quench induces a breathing mode whose period\ncrucially depends on the final strength of the super-imposed harmonic\nconfinement.",
        "positive": "Faraday and resonant waves in binary collisionally-inhomogeneous\n  Bose-Einstein condensates: We study Faraday and resonant waves in two-component quasi-one-dimensional\n(cigar-shaped) collisionally inhomogeneous Bose-Einstein condensates subject to\nperiodic modulation of the radial confinement. We show by means of extensive\nnumerical simulations that, as the system exhibits stronger spatially-localised\nbinary collisions (whose scattering length is taken for convenience to be of\nGaussian form), the system becomes effectively a linear one. In other words, as\nthe scattering length approaches a delta-function, we observe that the two\nnonlinear configurations typical for binary cigar-shaped condensates, namely\nthe segregated and the symbiotic one, turn into two overlapping Gaussian wave\nfunctions typical for linear systems, and that the instability onset times of\nthe Faraday and resonant waves become longer. Moreover, our numerical\nsimulations show that the spatial period of the excited waves (either resonant\nor Faraday ones) decreases as the inhomogeneity becomes stronger. Our results\nalso demonstrate that the topology of the ground state impacts the dynamics of\nthe ensuing density waves, and that the instability onset times of Faraday and\nresonant waves, for a given level of inhomogeneity in the two-body\ninteractions, depend on whether the initial configuration is segregated or\nsymbiotic."
    },
    {
        "anchor": "Quasi-Nambu-Goldstone Modes in Bose-Einstein Condensates: We show that quasi-Nambu-Goldstone (NG) modes, which play prominent roles in\nhigh energy physics but have been elusive experimentally, can be realized with\natomic Bose-Einstein condensates. The quasi-NG modes emerge when the symmetry\nof a ground state is larger than that of the Hamiltonian. When they appear, the\nconventional vacuum manifold should be enlarged. Consequently topological\ndefects that are stable within the conventional vacuum manifold become unstable\nand decay by emitting the quasi-NG modes. Contrary to conventional wisdom,\nhowever, we show that the topological defects are stabilized by quantum\nfluctuations that make the quasi-NG modes massive, thereby suppressing their\nemission.",
        "positive": "Verification of exceptional points in the collapse dynamics of\n  Bose-Einstein condensates: In Bose-Einstein condensates with an attractive contact interaction the\nstable ground state and an unstable excited state emerge in a tangent\nbifurcation at a critical value of the scattering length. At the bifurcation\npoint both the energies and the wave functions of the two states coalesce,\nwhich is the characteristic of an exceptional point. In numerical simulations\nsignatures of the exceptional point can be observed by encircling the\nbifurcation point in the complex extended space of the scattering length,\nhowever, this method cannot be applied in an experiment. Here we show in which\nway the exceptional point effects the collapse dynamics of the Bose-Einstein\ncondensate. The harmonic inversion analysis of the time signal given as the\nspatial extension of the collapsing condensate wave function can provide clear\nevidence for the existence of an exceptional point. This method can be used for\nan experimental verification of exceptional points in Bose-Einstein\ncondensates."
    },
    {
        "anchor": "Aharonov-Bohm Caging and Inverse Anderson transition in Ultracold Atoms: Aharonov-Bohm (AB) caging, a special flat-band localization mechanism, has\nspurred great interest in different areas of physics. AB caging can be\nharnessed to explore the rich and exotic physics of quantum transport in\nflatband systems, where geometric frustration, disorder and correlations act in\na synergetic and distinct way than in ordinary dispersive band systems. In\ncontrast to the ordinary Anderson localization, where disorder induces\nlocalization and prevents transport, in flat band systems disorder can induce\nmobility, a phenomenon dubbed inverse Anderson transition. Here, we report on\nthe experimental realization of the AB cage using a synthehtic lattice in the\nmomentum space of ultracold atoms with tailored gauge fields, demonstrate the\ngeometric localization due to the flat band and the inverse Anderson transition\nwhen correlated binary disorder is added to the system. Our experimental\nplatform in a many-body environment provides a fashiinating quantum simulator\nwhere the interplay between engineered gauge fields, localization, and\ntopological properties of flat band systems can be finely explored.",
        "positive": "Alternating-domain supersolids in binary dipolar condensates: Two-component dipolar condensates are now experimentally producible, and we\ntheoretically investigate the nature of supersolidity in this system. We\npredict the existence of a binary supersolid state in which the two components\nform a series of alternating domains, producing an immiscible double\nsupersolid. Remarkably, we find that a dipolar component can even induce\nsupersolidity in a nondipolar component. In stark contrast to single-component\ndipolar supersolids, alternating-domain supersolids do not require quantum\nstabilization, and the number of crystal sites is not strictly limited by the\ncondensate populations, with the density hence being substantially lower. Our\nresults are applicable to a wide range of dipole moment combinations, marking\nan important step towards long-lived bulk-supersolidity."
    },
    {
        "anchor": "Stability and structure of an anisotropically trapped dipolar\n  Bose-Einstein condensate: angular and linear rotons: We study theoretically Bose-Einstein condensates with polarized dipolar\ninteractions in anisotropic traps. We map the parameter space by varying the\ntrap frequencies and dipolar interaction strengths and find an irregular-shaped\nregion of parameter space in which density-oscillating condensate states occur,\nwith maximum density away from the trap center. These density-oscillating\nstates may be biconcave (red-blood-cell-shaped), or have two or four peaks. For\nall trap frequencies, the condensate becomes unstable to collapse for\nsufficiently large dipole interaction strength. The collapse coincides with the\nsoftening of an elementary excitation. When the condensate mode is\ndensity-oscillating, the character of the softening excitation is related to\nthe structure of the condensate. We classify these excitations by linear and\nangular characteristics. We also find excited solutions to the Gross-Pitaevskii\nequation, which are always unstable.",
        "positive": "Integrable two-channel p_x+ip_y-wave superfluid model: We present a new two-channel integrable model describing a system of spinless\nfermions interacting through a p-wave Feshbach resonance. Unlike the BCS-BEC\ncrossover of the s-wave case, the p-wave model has a third order quantum phase\ntransition. The critical point coincides with the deconfinement of a single\nmolecule within a BEC of bound dipolar molecules. The exact many-body\nwavefunction provides a unique perspective of the quantum critical region\nsuggesting that the size of the condensate wavefunction, that diverges\nlogarithmically with the chemical potential, could be used as an experimental\nindicator of the phase transition."
    },
    {
        "anchor": "Dynamical formation and interaction-induced stabilization of dark\n  condensates of dipolar excitons: The formation of a dense Bose-Einstein condensate in dark spin states of\ntwo-dimensional dipolar excitons is shown to be driven by a dynamical\ntransition to the long-lived dark states. The condensate is stabilized by\nstrong dipole-dipole interactions up to densities high enough for a dark\nquantum liquid to form. The persistence of dark condensation was observed in\nrecent experiments. A model describing the non-equilibrium dynamics of\nexternally driven coupled dark and bright condensates reproduces the step-like\ndependence of the exciton density on the pump power or on temperature. This\nunique condensate dynamics demonstrates the possibility of observing new\nunexpected collective phenomena in coupled condensed Bose systems, where the\nparticle number is not conserved.",
        "positive": "Shortcuts to adiabaticity for trapped ultracold gases: We study, experimentally and theoretically, the controlled transfer of\nharmonically trapped ultracold gases between different quantum states. In\nparticular we experimentally demonstrate a fast decompression and displacement\nof both a non-interacting gas and an interacting Bose-Einstein condensate which\nare initially at equilibrium. The decompression parameters are engineered such\nthat the final state is identical to that obtained after a perfectly adiabatic\ntransformation despite the fact that the fast decompression is performed in the\nstrongly non-adiabatic regime. During the transfer the atomic sample goes\nthrough strongly out-of-equilibrium states while the external confinement is\nmodified until the system reaches the desired stationary state. The scheme is\ntheoretically based on the invariants of motion and scaling equations\ntechniques and can be generalized to decompression trajectories including an\narbitrary deformation of the trap. It is also directly applicable to arbitrary\ninitial non-equilibrium states."
    },
    {
        "anchor": "Enhanced Fulde-Ferrell-Larkin-Ovchinnikov and Sarma superfluid states\n  near an orbital Feshbach resonance: We investigate the inhomogeneous Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) and\nhomogeneous Sarma superfluid states in alkaline-earth-like $^{173}$Yb atomic\ngases near an orbital Feshbach resonance at zero temperature with population\nimbalances in both the open and closed channels (or bands). We find that in\nhomogeneous space by adjusting the open-channel Zeeman energy $h_o$, both the\nSarma and Fulde-Ferrell superfluid states are greatly enhanced by the\nspin-exchange interaction while the closed-channel Zeeman energy $h_c$ remains\nsmall. In the presence of an external harmonic trap, the trapped gas features a\nshell structure of separated phases, where the Sarma phase leaves detectable\nvalley structure in the columnar-integrated momentum distribution, and the\nFulde-Ferrell state acquires enhanced spatial anisotropy. As both signatures\ncan be easily detected in time-of-flight images, our findings are helpful to\nrealize and detect the long-sought FFLO and Sarma superfluid states at the same\ntime in experiments.",
        "positive": "Hard-core Bose-Fermi mixture in one-dimensional split traps: We consider a strongly interacting one-dimensional (1D) Bose-Fermi mixture\nconfined in a hard wall trap or a harmonic oscillator trap with a tunable\n$\\delta$-function barrier at the trap center. The mixture consists of 1D Bose\ngas with repulsive interactions and of 1D noninteracting spin-aligned Fermi\ngas, both species interacting through hard-core interactions. Using a\ngeneralized Bose-Fermi mapping, we calculated the reduced single-particle\ndensity matrix and the momentum distribution of the gas as a function of\nbarrier strength and the parity of particle number. The secondary peaks in the\nmomentum distribution show remarkable correlation between particles on the two\nsides of the split."
    },
    {
        "anchor": "Pauli crystals -- interplay of symmetries: Recently observed Pauli crystals are structures formed by trapped ultracold\natoms with the Fermi statistics. Interactions between these atoms are switched\noff, so their relative positions are determined by joined action of the\ntrapping potential and the Pauli exclusion principle. Numericalmodeling is used\nin this paper to find the Pauli crystals in a two-dimensional isotropic\nharmonic trap, three-dimensional harmonic trap, and a two-dimensional square\nwell trap. The Pauli crystals do not have the symmetry of the trap -- the\nsymmetry is broken by the measurement of positions and, in many cases, by the\nquantum state of atoms in the trap. Furthermore, the Pauli crystals are\ncompared with the Coulomb crystals formed by electrically charged trapped\nparticles. The~structure of the Pauli crystals differs from that of the Coulomb\ncrystals, this provides evidence that the exclusion principle cannot be\nreplaced by a two-body repulsive interaction but rather has to be considered to\nbe a specifically quantum mechanism leading to many-particle correlations.",
        "positive": "A finite element method with mesh adaptivity for computing vortex states\n  in fast-rotating Bose-Einstein condensates: Numerical computations of stationary states of fast-rotating Bose-Einstein\ncondensates require high spatial resolution due to the presence of a large\nnumber of quantized vortices. In this paper we propose a low-order finite\nelement method with mesh adaptivity by metric control, as an alternative\napproach to the commonly used high order (finite difference or spectral)\napproximation methods. The mesh adaptivity is used with two different numerical\nalgorithms to compute stationary vortex states: an imaginary time propagation\nmethod and a Sobolev gradient descent method. We first address the basic issue\nof the choice of the variable used to compute new metrics for the mesh\nadaptivity and show that simultaneously refinement using the real and imaginary\npart of the solution is successful. Mesh refinement using only the modulus of\nthe solution as adaptivity variable fails for complicated test cases. Then we\nsuggest an optimized algorithm for adapting the mesh during the evolution of\nthe solution towards the equilibrium state. Considerable computational time\nsaving is obtained compared to uniform mesh computations. The new method is\napplied to compute difficult cases relevant for physical experiments (large\nnonlinear interaction constant and high rotation rates)."
    },
    {
        "anchor": "Thermodynamics in the vicinity of a relativistic quantum critical point\n  in 2+1 dimensions: We study the thermodynamics of the relativistic quantum O($N$) model in two\nspace dimensions. In the vicinity of the zero-temperature quantum critical\npoint (QCP), the pressure can be written in the scaling form\n$P(T)=P(0)+N(T^3/c^2)\\calF_N(\\Delta/T)$ where $c$ is the velocity of the\nexcitations at the QCP and $\\Delta$ is a characteristic zero-temperature energy\nscale. Using both a large-$N$ approach to leading order and the nonperturbative\nrenormalization group, we compute the universal scaling function $\\calF_N$. For\nsmall values of $N$ ($N\\lesssim 10$) we find that $\\calF_N(x)$ is nonmonotonous\nin the quantum critical regime ($|x|\\lesssim 1$) with a maximum near $x=0$. The\nlarge-$N$ approach -- if properly interpreted -- is a good approximation both\nin the renormalized classical ($x\\lesssim -1$) and quantum disordered\n($x\\gtrsim 1$) regimes, but fails to describe the nonmonotonous behavior of\n$\\calF_N$ in the quantum critical regime. We discuss the renormalization-group\nflows in the various regimes near the QCP and make the connection with the\nquantum nonlinear sigma model in the renormalized classical regime. We compute\nthe Berezinskii-Kosterlitz-Thouless transition temperature in the quantum O(2)\nmodel and find that in the vicinity of the QCP the universal ratio\n$\\Tkt/\\rho_s(0)$ is very close to $\\pi/2$, implying that the stiffness\n$\\rho_s(\\Tkt^-)$ at the transition is only slightly reduced with respect to the\nzero-temperature stiffness $\\rho_s(0)$. Finally, we briefly discuss the\nexperimental determination of the universal function $\\calF_2$ from the\npressure of a Bose gas in an optical lattice near the\nsuperfluid--Mott-insulator transition.",
        "positive": "Pair fraction in a finite temperature Fermi gas on the BEC side of the\n  BCS-BEC crossover: We investigate pairing in a strongly interacting two-component Fermi gas with\npositive scattering length. In this regime, pairing occurs at temperatures\nabove the superfluid critical temperature; unbound fermions and pairs coexist\nin thermal equilibrium. Measuring the total number of these fermion pairs in\nthe gas we systematically investigate the phases in the sectors of pseudogap\nand preformed-pair. Our measurements quantitatively test predictions from two\ntheoretical models. Interestingly, we find that already a model based on\nclassical atom-molecule equilibrium describes our data quite well."
    },
    {
        "anchor": "Spin-orbit-coupled Bose-Einstein-condensed atoms confined in annular\n  potentials: A spin-orbit-coupled Bose-Einstein-condensed cloud of atoms confined in an\nannular trapping potential shows a variety of phases that we investigate in the\npresent study. Starting with the non-interacting problem, the homogeneous phase\nthat is present in an untrapped system is replaced by a sinusoidal density\nvariation in the limit of a very narrow annulus. In the case of an untrapped\nsystem there is another phase with a striped-like density distribution, and its\ncounterpart is also found in the limit of a very narrow annulus. As the width\nof the annulus increases, this picture persists qualitatively. Depending on the\nrelative strength between the inter- and the intra-components, interactions\neither favor the striped phase, or suppress it, in which case either a\nhomogeneous, or a sinusoidal-like phase appears. Interactions also give rise to\nnovel solutions with a nonzero circulation.",
        "positive": "Phase diagram of a rapidly-rotating two-component Bose gas: We derive analytically the phase diagram of a two-component Bose gas confined\nin an anharmonic potential, which becomes exact and universal in the limit of\nweak interactions and small anharmonicity of the trapping potential. The\ntransitions between the different phases, which consist of vortex states of\nsingle and multiple quantization, are all continuous because of the addition of\nthe second component."
    },
    {
        "anchor": "Statics and dynamics of quasi one-dimensional Bose-Einstein condensate\n  in harmonic and dimple trap: We investigate a quasi one-dimensional $^{87}\\text{Rb}$ Bose-Einstein\ncondensate in a harmonic trap with an additional dimple trap (dT) in the\ncenter. Within a zero-temperature Gross-Pitaevskii mean-field description we\nprovide a one-dimensional physical intuitive model, which we solve by both a\ntime-independent variational approach and numerical calculations. With this we\nobtain at first equilibrium results for the emerging condensate wave function\nwhich reveal that a dimple trap potential induces a bump or a dip in case of a\nred- or a blue-detuned Gaussian laser beam, respectively. Afterwards, we\ninvestigate how this dT induced bump/dip-imprint upon the condensate wave\nfunction evolves for two quench scenarios. At first we consider the generic\ncase that the harmonic confinement is released. During the resulting\ntime-of-flight expansion it turns out that the dT induced bump in the\ncondensate wave function remains present, whereas the dip starts decaying after\na characteristic time scale which decreases with increasing blue-detuned dT\ndepth. Secondly, once the red- or blue-detuned dT is switched off, we find that\nbright shock-waves or gray/dark bi-soliton trains emerge which oscillate within\nthe harmonic confinement with a characteristic frequency.",
        "positive": "Connecting strongly correlated superfluids by a quantum point contact: Point contacts provide simple connections between macroscopic particle\nreservoirs. In electric circuits, strong links between metals, semiconductors\nor superconductors have applications for fundamental condensed-matter physics\nas well as quantum information processing. However for complex, strongly\ncorrelated materials, links have been largely restricted to weak tunnel\njunctions. Here we study resonantly interacting Fermi gases connected by a\ntunable, ballistic quantum point contact, finding a non-linear current-bias\nrelation. At low temperature, our observations agree quantitatively with a\ntheoretical model in which the current originates from multiple Andreev\nreflections. In a wide contact geometry, the competition between superfluidity\nand thermally activated transport leads to a conductance minimum. Our system\noffers a controllable platform for the study of mesoscopic devices based on\nstrongly interacting matter."
    },
    {
        "anchor": "High-precision numerical solution of the Fermi polaron problem and\n  large-order behavior of its diagrammatic series: We introduce a simple determinant diagrammatic Monte Carlo algorithm to\ncompute the ground-state properties of a particle interacting with a Fermi sea\nthrough a zero-range interaction. The fermionic sign does not cause any\nfundamental problem when going to high diagram orders, and we reach order\n$N=30$. The data reveal that the diagrammatic series diverges exponentially as\n$(-1/R)^{N}$ with a radius of convergence $R<1$. Furthermore, on the polaron\nside of the polaron-dimeron transition, the value of $R$ is determined by a\nspecial class of three-body diagrams, corresponding to repeated scattering of\nthe impurity between two particles of the Fermi sea. A power-counting argument\nexplains why finite $R$ is possible for zero-range interactions in three\ndimensions. Resumming the divergent series through a conformal mapping yields\nthe polaron energy with record accuracy.",
        "positive": "Hydrodynamic theory of motion of quantized vortex rings in trapped\n  superfluid gases: I study vortex ring oscillations in a superfluid, trapped in an elongated\ntrap, under the conditions of the Local Density Approximation. On the basis of\nthe Hamiltonian formalism I develop a hydrodynamic theory, which is valid for\nan arbitrary superfluid and depends only on the equation of state. The problem\nis reduced to an ordinary differential equation for the ring radius. The cases\nof the dilute BEC and the Fermi gas at unitarity are investigated in detail.\nSimple analytical equations for the periods of small oscillations are obtained\nand the equations of non-linear dynamics are solved in quadratures. The results\nagree with available numerical calculations. Experimental possibilities to\ncheck the predictions are discussed."
    },
    {
        "anchor": "Neural-network quantum states for a two-leg Bose-Hubbard ladder under\n  magnetic flux: Quantum gas systems are ideal analog quantum simulation platforms for\ntackling some of the most challenging problems in strongly correlated quantum\nmatter. However, they also expose the urgent need for new theoretical\nframeworks. Simple models in one dimension, well studied with conventional\nmethods, have received considerable recent attention as test cases for new\napproaches. Ladder models provide the logical next step, where established\nnumerical methods are still reliable, but complications of higher dimensional\neffects like gauge fields can be introduced. In this paper, we investigate the\napplication of the recently developed neural-network quantum states in the\ntwo-leg Bose-Hubbard ladder under strong synthetic magnetic fields. Based on\nthe restricted Boltzmann machine and feedforward neural network, we show that\nvariational neural networks can reliably predict the superfluid-Mott insulator\nphase diagram in the strong coupling limit comparable with the accuracy of the\ndensity-matrix renormalization group. In the weak coupling limit, neural\nnetworks also diagnose other many-body phenomena such as the vortex, chiral,\nand biased-ladder phases. Our work demonstrates that the two-leg Bose-Hubbard\nmodel with magnetic flux is an ideal test ground for future developments of\nneural-network quantum states.",
        "positive": "Ultracold Bosons on a Regular Spherical Mesh: I study the zero-temperature phase behavior of bosonic particles living on\nthe nodes of a regular spherical mesh (\"Platonic mesh\") and interacting through\nan extended Bose-Hubbard Hamiltonian. Only the hard-core version of the model\nis considered here, for two instances of Platonic mesh. Using the mean-field\ndecoupling approximation, I show that the system may exist in various ground\nstates, which can be regarded as analogs of gas, solid, supersolid, and\nsuperfluid. For one mesh, by comparing the theoretical results with the outcome\nof numerical diagonalization, I manage to uncover the signatures of diagonal\nand off-diagonal spatial orders in a finite quantum system."
    },
    {
        "anchor": "Transition region properties of a trapped quasi-two-dimensional\n  degenerate Bose gas: The c-field simulation technique is used to study a trapped quasi-two\ndimensional Bose gas. We calculate the central curvature of the system density\nand fluctuations of the condensate mode in the degenerate regime. These results\nprovide new understanding of the system behavior in the region of the\nsuperfluid transition.",
        "positive": "Application of the Feshbach-resonance management to a tightly confined\n  Bose-Einstein condensate: We study suppression of the collapse and stabilization of matter-wave\nsolitons by means of time-periodic modulation of the effective nonlinearity,\nusing the nonpolynomial Schroedinger equation (NPSE) for BEC trapped in a tight\ncigar-shaped potential. By means of systematic simulations, a stability region\nis identified in the plane of the modulation amplitude and frequency. In the\nlow-frequency regime, solitons feature chaotic evolution, although they remain\nrobust objects."
    },
    {
        "anchor": "Expansion dynamics in two-dimensional Bose-Hubbard lattices:\n  Bose-Einstein condensate and thermal cloud: We study the temporal expansion of an ultracold Bose gas in two-dimensional,\nsquare optical lattices. The gas is described by the Bose-Hubbard model deep in\nthe superfluid regime, with initially all bosons condensed in the central site\nof the lattice. We use the previously developed nonequilibrium propagator\nmethod for capturing the time evolution of an interacting bosonic system, where\nthe many-body Hamiltonian is represented in an appropriate local basis and the\ncorresponding field operators are separated into the classical [Bose-Einstein\ncondensate (BEC)] part and quantum mechanical fluctuations. After a quench,\ni.e. after a sudden switch of the lattice nearest-neighbor hopping, the\nexpanding, bosonic cloud separates spatially into a fast, ballistic forerunner\nand a slowly expanding central part controlled by selftrapping. We show that\nthe forerunner expansion is driven by the coherent dynamics of the BEC and that\nits velocity is consistent with the Lieb-Robinson bound. For smaller lattices\nwe analyze how quasiparticle collisions lead to enhanced condensate depletion\nand oscillation damping.",
        "positive": "Negative refraction and rotons in the relativistic Bose gas: We investigate the dispersion of a classical electromagnetic field in a\nrelativistic ideal gas of charged bosons using scalar quantum electrodynamics\nat finite temperature and charge density. We derive the effective\nelectromagnetic responses and the electromagnetic propagation modes that\ncharacterize the gas as a left-handed material with negative effective index of\nrefraction $n_{\\rm eff}=-1$ below the transverse plasmon frequency. In the\ncondensed phase, we show that the longitudinal plasmon dispersion relation\nexhibits a roton-type local minimum that disappears at the transition\ntemperature."
    },
    {
        "anchor": "Photonic topological Anderson insulator in a two-dimensional atomic\n  lattice: Disorder in atomic positions can induce a topologically nontrivial phase -\ntopological Anderson insulator (TAI) - for transverse electric optical\nquasimodes of a two-dimensional honeycomb lattice of immobile atoms. TAI\nrequires both time-reversal and inversion symmetries to be broken to similar\nextents. It is characterized by a nonzero topological invariant, a reduced\ndensity of states and spatially localized quasimodes in the bulk, as well as\npropagating edge states. A transition from TAI to the topological insulator\n(TI) phase can take place at a constant value of the topological invariant,\nshowing that TAI and TI represent the same topological phase.",
        "positive": "A generalized Lieb-Liniger model: In 1963, Lieb and Liniger solved exactly a one dimensional model of bosons\ninteracting by a repulsive \\delta-potential and calculated the ground state in\nthe thermodynamic limit. In the present work, we extend this model to a\npotential of three \\delta-functions, one of them is repulsive and the other two\nare attractive, modeling some aspects of the interaction between atoms, and\npresent an approximate solution for a dilute gas. In this limit, for low energy\nstates, the results are found to be reduced to the ones of an effective Lieb\nLiniger model with an effective \\delta-function of strength $c_{eff}$ and the\nregime of stability is identified. This may shed light on some aspects of\ninteracting bosons."
    },
    {
        "anchor": "Thermodynamics of a deeply degenerate SU($N$)-symmetric Fermi gas: Many-body quantum systems can exhibit a striking degree of symmetry\nunparalleled by their classical counterparts. While in real materials SU($N$)\nsymmetry is an idealization, this symmetry is pristinely realized in fully\ncontrollable ultracold alkaline-earth atomic gases. Here, we study an\nSU($N$)-symmetric Fermi liquid of $^{87}$Sr atoms, where $N$ can be tuned to be\nas large as 10. In the deeply degenerate regime, we show through precise\nmeasurements of density fluctuations and expansion dynamics that the large $N$\nof spin states under SU($N$) symmetry leads to pronounced interaction effects\nin a system with a nominally negligible interaction parameter. Accounting for\nthese effects we demonstrate thermometry accurate to one-hundredth of the Fermi\nenergy. We also demonstrate record speed for preparing degenerate Fermi seas,\nreaching $T/T_F = 0.12$ in under 3 s, enabled by the SU($N$) symmetric\ninteractions. This, along with the introduction of a new spin polarizing\nmethod, enables operation of a 3D optical lattice clock in the band\ninsulating-regime.",
        "positive": "Probing the quantum state of a 1D Bose gas using off-resonant light\n  scattering: We present a theoretical treatment of coherent light scattering from an\ninteracting 1D Bose gas at finite temperatures. We show how this can provide a\nnondestructive measurement of the atomic system states. The equilibrium states\nare determined by the temperature and interaction strength, and are\ncharacterized by the spatial density-density correlation function. We show how\nthis correlation function is encoded in the angular distribution of the\nfluctuations of the scattered light intensity, thus providing a sensitive,\nquantitative probe of the density-density correlation function and therefore\nthe quantum state of the gas."
    },
    {
        "anchor": "High-momentum oscillating tails of strongly interacting 1D gases in a\n  box: We study the momentum distribution of strongly interacting one-dimensional\nmixtures of particles at zero temperature in a box potential. We find that the\nmagnitude of the $1/k^4$ tail of the momentum distribution is not only due to\nshort-distance correlations, but also to the presence of the rigid walls,\nbreaking the Tan's relation relating this quantity to the adiabatic derivative\nof the energy with respect to the inverse of the interaction strength. The\nadditional contribution is a finite-size effect that includes a $k$-independent\nand an oscillating part. This latter, surprisingly, encodes information on\nlong-range spin correlations.",
        "positive": "Discrete truncated Wigner approach to dynamical phase transitions in\n  Ising models after a quantum quench: By means of the discrete truncated Wigner approximation we study dynamical\nphase transitions arising in the steady state of transverse-field Ising models\nafter a quantum quench. Starting from a fully polarized ferromagnetic initial\ncondition these transitions separate a phase with nonvanishing magnetization\nalong the ordering direction from a symmetric phase upon increasing the\ntransverse field. We consider two paradigmatic cases, a one-dimensional\nlong-range model with power-law interactions $\\propto 1/r^{\\alpha}$ decaying\nalgebraically as a function of distance $r$ and a two-dimensional system with\nshort-range nearest-neighbour interactions. In the former case we identify\ndynamical phase transitions for $\\alpha \\lesssim 2$ and we extract the critical\nexponents from a data collapse of the steady state magnetization for up to 1200\nlattice sites. We find identical exponents for $\\alpha \\lesssim 0.5$,\nsuggesting that the dynamical transitions in this regime fall into the same\nuniversality class as the nonergodic mean-field limit. The two-dimensional\nIsing model is believed to be thermalizing, which we also confirm using exact\ndiagonalization for small system sizes. Thus, the dynamical transition is\nexpected to correspond to the thermal phase transition, which is consistent\nwith our data upon comparing to equilibrium quantum Monte-Carlo simulations. We\nfurther test the accuracy of the discrete truncated Wigner approximation by\ncomparing against numerically exact methods such as exact diagonalization,\ntensor network as well as artificial neural network states and we find good\nquantitative agreement on the accessible time scales. Finally, our work\nprovides an additional contribution to the understanding of the range and the\nlimitations of qualitative and quantitative applicability of the discrete\ntruncated Wigner approximation."
    },
    {
        "anchor": "Strong interaction regime of the nonlinear Landau-Zener problem for\n  photo- and magneto-association of cold atoms: We discuss the strong interaction regime of the nonlinear Landau-Zener\nproblem coming up at coherent photo- and magneto-association of ultracold\natoms. We apply a variational approach to an exact third-order nonlinear\ndifferential equation for the molecular state probability and construct an\naccurate approximation describing the whole time dynamics of the coupled\natom-molecular system. The resultant solution improves the accuracy of the\nprevious approximation by A. Ishkhanyan et al. [J. Phys. A 39, 14887 (2006)].\nThe obtained results reveal a remarkable observation that in the strong\ncoupling limit the resonance crossing is mostly governed by the nonlinearity\nwhile the coherent atom-molecular oscillations coming up soon after the\nresonance has been crossed are principally of linear nature. This observation\nis supposed to be general for all the nonlinear quantum systems having the same\ngeneric quadratic nonlinearity, due to the basic attributes of the resonance\ncrossing processes in such systems. The constructed approximation turns out to\nhave a larger applicability range (than it was initially expected) covering the\nwhole moderate coupling regime for which the proposed solution accurately\ndescribes all the main characteristics of the system's evolution except the\namplitude of the coherent atom-molecule oscillation, which is rather\noverestimated.",
        "positive": "Introduction to quantum turbulence: The term quantum turbulence denotes the turbulent motion of quantum fluids,\nsystems such as superfluid helium and atomic Bose-Einstein condensates which\nare characterized by quantized vorticity, uperfluidity and, at finite\ntemperatures, two-fluid behavior. This article introduces their basic\nproperties, describes types and regimes of turbulence which have been observed,\nand highlights similarities and differences between quantum turbulence and\nclassical turbulence in ordinary fluids. Our aim is also to link together the\narticles of this special issue, and to provide a perspective of the future\ndevelopment of a subject which contains aspects of fluid mechanics, atomic\nphysics, condensed matter and low temperature physics."
    },
    {
        "anchor": "Fragmented condensation in Bose-Hubbard trimers with tunable tunnelling: We consider a Bose-Hubbard trimer, i.e. an ultracold Bose gas populating\nthree quantum states. The latter can be either different sites of a triple-well\npotential or three internal states of the atoms. The bosons can tunnel between\ndifferent states with variable tunnelling strength between two of them. This\nwill allow us to study; i) different geometrical configurations, i.e. from a\nclosed triangle to three aligned wells and ii) a triangular configuration with\na $\\pi$-phase, i.e. by setting one of the tunnellings negative. By solving the\ncorresponding three-site Bose-Hubbard Hamiltonian we obtain the ground state of\nthe system as a function of the trap topology. We characterise the different\nground states by means of the coherence and entanglement properties. For small\nrepulsive interactions, fragmented condensates are found for the $\\pi$-phase\ncase. These are found to be robust against small variations of the tunnelling\nin the small interaction regime. A low-energy effective many-body Hamiltonian\nrestricted to the degenerate manifold provides a compelling description of the\n$\\pi$-phase degeneration and explains the low-energy spectrum as excitations of\ndiscrete semifluxon states.",
        "positive": "Exotic vortex lattices in two-species Bose-Einstein condensates: We numerically investigate vortex lattices in rotating two-component\nBose-Einstein condensates in which the two components have unequal atomic\nmasses and interact attractively with each other. For sufficiently strong\nattraction, the system is found to exhibit exotic ground-state structures in a\nharmonic trap, such as lattices having a square geometry or consisting of\ntwo-quantum vortices. The obtained states satisfy the Feynman relation, and\nthey can be realized with current experimental techniques."
    },
    {
        "anchor": "Shear viscosity of p-wave superfluid Fermi gas with weak interaction at\n  low temperatures: The shear viscosity tensor of the superfluid Fermi gas in p-wave state with\nweak interaction is calculated at low temperatures, by using the Boltzmann\nequation approach. We consider the transition probabilities for the binary,\ndecay and coalescence processes. We show that only the binary processes are\ndominated at low temperatures and the components of shear viscosity {\\eta}_xy,\n{\\eta}_xx, {\\eta}_yy are proportional to (1/T)^2, and {\\eta}_xz, {\\eta}_yz and\n{\\eta}_zz are proportional to (1/T)^4 and (1/T)^6, respectively.",
        "positive": "Dimensional crossover of nonrelativistic bosons: We investigate how confining a transverse spatial dimension influences the\nfew- and many-body properties of non-relativistic bosons with pointlike\ninteractions. Our main focus is on the dimensional crossover from three to two\ndimensions, which is of relevance for ultracold atom experiments. Using\nFunctional Renormalization Group equations and T-matrix calculations we study\nhow the phase transition temperature changes as a function of the spatial\nextent of the transverse dimension and relate the 3D and 2D s-wave scattering\nlengths. The analysis reveals how the properties of the lower-dimensional\nsystem are inherited from the higher-dimensional one during the renormalization\ngroup evolution. We limit the discussion to confinements in a potential well\nwith periodic boundary conditions and argue why this qualitatively captures the\nphysics of other compactifications such as transverse harmonic confinement as\nin cold atom experiments."
    },
    {
        "anchor": "Microwave control of coupling parameters in spinor alkali condensates: We propose a protocol which utilises radio frequency magnetic pulses in order\nto tune the effective two-particle scattering amplitudes for alkali atoms in\nthe $F=1$ hyperfine ground state. Unlike the Feshbach resonance method, the\nproposed protocol preserves with controllable accuracy the global rotational\nsymmetry in the spin space offering access to a broad region of the phase\ndiagram of the rotationally-symmetric spinor Bose condensate. Examples of\n$^{41}$K and $^{7}$Li are considered and it is shown that for these atoms\nsufficient variation in the effective coupling constants can be achieved in\norder to explore phase transitions between different symmetry-broken phases of\nthe condensate.",
        "positive": "Universal probes for antiferromagnetic correlations and entropy in cold\n  fermions on optical lattices: We determine antiferromagnetic (AF) signatures in the half-filled Hubbard\nmodel at strong coupling on a cubic lattice and in lower dimensions. Upon\ncooling, the transition from the charge-excitation regime to the AF Heisenberg\nregime is signaled by a universal minimum of the double occupancy at entropy\ns=S/(N k_B)=s*=ln(2) per particle and a linear increase of the next-nearest\nneighbor (NNN) spin correlation function for s<s*. This crossover, driven by a\ngain in kinetic exchange energy, appears as the essential AF physics relevant\nfor current cold-atom experiments. The onset of long-range AF order (at low s\non cubic lattices) is hardly visible in nearest-neighbor spin correlations\nversus s, but could be detected in spin correlations at or beyond NNN\ndistances."
    },
    {
        "anchor": "Hydrodynamic model of BEC with anisotropic short range interaction and\n  the bright solitons in the repulsive BEC: The quantum hydrodynamic model is developed for the axial symmetric\nanisotropic short-range interaction. The quantum stress tensor presents the\ninteraction. It is derived up to the third order by the interaction radius. The\nfirst order by the interaction radius contains the isotropic part only. It\nleads to the interaction in the Gross-Pitaevskii approximation. Terms existing\nin the third order by the interaction radius are caused by the isotropic and\nnonisotropic parts of the interaction. Each of them introduces the interaction\nconstant. Therefore, three interaction constants are involved in the model.\nAtoms, except the alkali and alkali-earth atoms, can have anisotropic potential\nof interaction, particularly it is demonstrated for the lanthanides. The\nshort-wavelength instability caused by the nonlocal terms appears in the\nBogoliubov spectrum. Conditions for the stable and unstable behaviour are\ndescribed. Bright solitons in the repulsive BEC are studied under influence of\nthe anisotropic short-range interaction in the BEC of one species. Area of\nexistence of this bright solitons corresponds to the area of the instability of\nthe Bogoliubov spectrum. Approximate reduction of the nonlocal nonlinearity to\nthe quintic nonlinearity at the description of the bright solitons is\ndemonstrated either.",
        "positive": "Macroscopic quantum escape of Bose-Einstein condensates: Analysis of\n  experimentally realizable quasi-one-dimensional traps: The variational-JWKB method is used to determine experimentally accessible\nmacroscopic quantum tunneling regimes of quasi-bound Bose-Einstein condensates\nin two quasi one-dimensional trap configurations. The potentials can be created\nby magnetic and optical traps, a symmetric trap from two offset Gaussian\nbarriers and a tilt trap from a linear gradient and Gaussian barrier. Scaling\nlaws in barrier parameters, ranging from inverse polynomial to square root\ntimes exponential, are calculated and used to elucidate different dynamical\nregimes, such as when classical oscillations dominate tunneling rates in the\nsymmetric trap. The symmetric trap is found to be versatile, with tunneling\ntimes at and below one second, able to hold $10^{3}$ to $10^{4}$ atoms, and\nrealizable for atoms ranging from rubidium to lithium, with unadjusted\nscattering lengths. The tilt trap produces sub-second tunneling times, is able\nto hold a few hundred atoms of lighter elements like lithium, and requiring the\nuse of Feshbach resonance to reduce scattering lengths. To explore a large\nparameter space, an extended Gaussian variational ansatz is used, which can\napproximate large traps with Thomas-Fermi profiles. Nonlinear interactions in\nthe Gross-Pitaevskii equation are shown to produce additional effective\nmean-field barriers, affecting scaling laws."
    },
    {
        "anchor": "Effective dynamics of a tracer particle in a dense homogeneous quantum\n  gas: We investigate the mean field regime of the dynamics of a tracer particle in\na homogenous quantum gas. For a bosonic gas, we show that this regime is\nconstrained by the well known requirement of an appropriate mean field scaling\nof the interaction. For fermions, however, we find an important qualitative\ndifference. Not only are fermions much more homogeneously distributed than\nbosons but also deviations from the mean are due only to fast degrees of\nfreedom in the gas. This observation leads to an explanation of why a tracer\nparticle behaves freely in the dense homogeneous fermion gas despite of a\nnon-scaled interaction, i.e., despite of non-vanishing statistical\nfluctuations. Finally, we indicate how the gained insight can be rigorously\njustified.",
        "positive": "Trap Frequency Measurement with a Pulsed Atom Laser: We describe a novel method of single-shot trap frequency measurement for a\nconfined Bose-Einstein Condensate, which uses an atom laser to repeatedly\nsample the mean velocity of trap oscillations as a function of time. The method\nis able to determine the trap frequency to an accuracy of 39~ppm (16~mHz) in a\nsingle experimental realization, improving on the literature by a factor of\nthree. Further, we show that by employing a reconstructive aliasing approach\nour method can be applied to trap frequencies more than a factor of 3 greater\nthan the sampling frequency."
    },
    {
        "anchor": "One- and two-dimensional reductions of the mean-field description of\n  degenerate Fermi gases: We study collective behavior of Fermi gases trapped in various external\npotentials, including optical lattices (OLs), in the framework of the\nmean-field (hydrodynamic) description. Using the variational method, we derive\neffective dynamical equations for the one- and two-dimensional (1D and 2D)\nsettings from the general 3D mean-field equation. The respective confinement is\nprovided by trapping potentials with the cylindrical and planar symmetry,\nrespectively. The resulting equations are nonpolynomial Schr% \\\"{o}dinger\nequations (NPSEs) coupled to equations for the local transverse size of the\ntrapped states. Numerical simulations demonstrate close agreement of results\nproduced by the underlying 3D equation and the effective low-dimensional ones.\nWe consider the ground state in these settings. In particular, analytical\nsolutions are obtained for the effectively 2D non-interacting Fermi gas.\nDifferences between the 1D and 2D configurations are highlighted. Finally, we\nanalyze the dependence of the 1D and 2D density patterns of the trapped gas, in\nthe presence of the OL, on the strengths of the confining and OL potentials,\nand on the scattering length which determines the strength of interactions\nbetween non-identical fermions.",
        "positive": "Collective modes of trapped spinor Bose condensates: We study the richer structures of quasi-one-dimensional Bogoliubov-de Genes\ncollective excitations of F = 1 spinor Bose-Einstein condensate in a harmonic\ntrap potential loaded in an optical lattice. Employing a perturbative method we\nreport general analytical expressions for the confined collective polar and\nferromagnetic Goldstone modes. In both cases the excited eigenfrequencies are\ngiven as function of the 1D effective coupling constants, trap frequency and\noptical lattice parameters. It is shown that the main contribution of the\noptical lattice laser intensity is to shift the confined phonon frequencies.\nMoreover, for high intensities, the excitation spectrum becomes independent of\nthe self-interaction parameters. We reveal some features of the evolution for\nthe Goldstone modes as well as the condensate densities from the ferromagnetic\nto the polar phases."
    },
    {
        "anchor": "Scalable, ab initio protocol for quantum simulating SU($N$)$\\times$U(1)\n  Lattice Gauge Theories: We propose a protocol for the scalable quantum simulation of\nSU($N$)$\\times$U(1) lattice gauge theories with alkaline-earth like atoms in\noptical lattices in both one- and two-dimensional systems. The protocol\nexploits the combination of naturally occurring SU($N$) pseudo-spin symmetry\nand strong inter-orbital interactions that is unique to such atomic species. A\ndetailed ab initio study of the microscopic dynamics shows how gauge invariance\nemerges in an accessible parameter regime, and allows us to identify the main\nchallenges in the simulation of such theories. We provide quantitative results\nabout the requirements in terms of experimental stability in relation to\nobserving gauge invariant dynamics, a key element for a deeper analysis on the\nfunctioning of such class of theories in both quantum simulators and computers.",
        "positive": "Prospects for thermalization of microwave-shielded ultracold molecules: We study anisotropic thermalization in dilute gases of microwave shielded\npolar molecular fermions. For collision energies above the threshold regime, we\nfind that thermalization is suppressed due to a strong preference for forward\nscattering and a reduction in total cross section with energy, significantly\nreducing the efficiency of evaporative cooling. We perform close-coupling\ncalculations on the effective potential energy surface derived by Deng et al.\n[Phys. Rev. Lett. 130, 183001 (2023)], to obtain accurate 2-body elastic\ndifferential cross sections across a range of collision energies. We use\nGaussian process regression to obtain a global representation of the\ndifferential cross section, over a wide range of collision angles and energies.\nThe route to equilibrium is then analyzed with cross-dimensional\nrethermalization experiments, quantified by a measure of collisional efficiency\ntoward achieving thermalization."
    },
    {
        "anchor": "Fractional Quantum Hall states in the vicinity of Mott plateaus: We perform variational Monte-Carlo calculations to show that bosons in a\nrotating optical lattice will form analogs of fractional quantum Hall states\nwhen the tunneling is sufficiently weak compared to the interactions and the\ndeviation of density from an integer is commensurate with the effective\nmagnetic field. We compare the energies of superfluid and correlated states to\none-another and to the energies found in full configuration-interaction\ncalculations on small systems. We look at overlaps between our variational\nstates and the exact ground-state, characterizing the ways in which fractional\nquantum Hall effect correlations manifest themselves near the Mott insulating\nstate. We explore the experimental signatures of these states.",
        "positive": "Generation, propagation and control of quantized vortices and dark\n  solitons in polariton superfluids: Exciton-polaritons are quasi-particles arising from the strong coupling\nregime between excitons and photons. In planar microcavitites, phenomena such\nas superfluidity or Bose-Einstein condensation can be observed. Those systems\nhave demonstrated to be very efficient in the hydrodynamic generation of\ntopological excitations, such as vortex-antivortex pairs or dark solitons.\nHowever, the lifetime and motion of those excitations were limited by the\ndriven dissipative nature of the system. In this thesis, we present a rich\nvariety of results about the generation and control of such topological\nexcitations. Taking advantage of the optical bistability present in our system,\nwe were able to greatly enhanced the propagation length of vortices and\nsolitons generated in the wake of a structural defect, revealing in the mean\ntime an unexpected binding mechanism of the solitons which propagate parallel.\nThis behaviour was recovered in a specifically designed experiment, where we\nartificially imprint dark soliton pairs on demand on a polariton superfluid.\nThe adaptability of our technique allowed for a detailed study of this\nphenomenon, that we directly connected to the driven-dissipative nature of our\nsystem. Finally, confined dark solitons were generated within guided intensity\nchannels on a static polariton fluid. The absence of flow lead to the\ndevelopment of transverse snake instabilities of which we studied the\ninteresting properties."
    },
    {
        "anchor": "Extracting Dynamical Green's Function of Ultracold Quantum Gases via\n  Electromagnetically Induced Transparency: The essential quantum many-body physics of an ultracold quantum gas relies on\nthe single-particle Green's functions.\\ We demonstrate that it can be extracted\nby the spectrum of electromagnetically induced transparency (EIT).\\ The\nsingle-particle Green's function can be reconstructed by the measurements of\nfrequency moments in EIT spectroscopy.\\ This optical measurement provides an\nefficient and nondestructive method to reveal the many-body properties, and we\npropose an experimental setup to realize it.\\ Finite temperature and finite\nsize effects are discussed, and we demonstrate the reconstruction steps of\nGreen's function for the examples of three-dimensional Mott-insulator phase and\none-dimensional Luttinger liquid.",
        "positive": "Strain and pseudo-magnetic fields in optical lattices from\n  density-assisted tunneling: Applying time-periodic modulations is routinely used to control and design\nsynthetic matter in quantum-engineered settings. In lattice systems, this\napproach is explored to engineer band structures with non-trivial topological\nproperties, but also to generate exotic interaction processes. A prime example\nis density-assisted tunneling, by which the hopping amplitude of a particle\nbetween neighboring sites explicitly depends on their respective occupations.\nHere, we show how density-assisted tunneling can be tailored in view of\nsimulating the effects of strain in synthetic graphene-type systems.\nSpecifically, we consider a mixture of two atomic species on a honeycomb\noptical lattice: one species forms a Bose-Einstein condensate in an anisotropic\nharmonic trap, whose inhomogeneous density profile induces an effective\nuniaxial strain for the second species through density-assisted tunneling\nprocesses. In direct analogy with strained graphene, the second species\nexperiences a pseudo magnetic field, hence exhibiting relativistic Landau\nlevels and the valley Hall effect. Our proposed scheme introduces a unique\nplatform for the investigation of strain-induced gauge fields and their\npossible interplay with quantum fluctuations and collective excitations."
    },
    {
        "anchor": "Driven dipole oscillations and the lowest energy excitations of strongly\n  interacting lattice bosons in a harmonic trap: We show that the analysis of the time evolution of the occupation of site and\nmomentum modes of harmonically trapped lattice hard-core bosons, under driven\ndipole oscillations, allows one to determine the energy of the lowest\none-particle excitations of the system in equilibrium. The analytic solution of\na single particle in the absence of a lattice is used to identify which\nfunction of those time-dependent observables is best fit for the analysis, as\nwell as to relate the dynamic response of the system to its single-particle\nspectrum. In the presence of the lattice and of multiple particles, a much\nricher and informative dynamical response is observed under the drive.",
        "positive": "Quantum and thermal fluctuations in two-component Bose gases: We study the effects of quantum and thermal fluctuations on Bose-Bose\nmixtures at finite temperature employing the time-dependent\nHartree-Fock-Bogoliubov (TDHFB) theory. The theory governs selfconsistently the\nmotion of the condensates, the noncondensates and of the anomalous components\non an equal footing. The finite temperature criterion for the phase separation\nis established. We numerically analyze the temperature dependence of different\ndensities for both miscible and immiscible mixtures. We show that the degree of\nthe overlap between the two condensates and the thermal clouds is lowered and\nthe relative motion of the centers-of-mass of the condensed and thermal\ncomponents is strongly damped due to the presence of the pair anomalous\nfluctuations. Our results are compared with previous theoretical and\nexperimental findings. On the other hand, starting from our TDHFB equations, we\ndevelop a random-phase theory for the elementary excitations in a homogeneous\nmixture. We find that the normal and anomalous fluctuations may lead to enhance\nthe excitations and the thermodynamics of the system."
    },
    {
        "anchor": "Dispersive optical detection of magnetic Feshbach resonances in\n  ultracold gases: Magnetically tunable Feshbach resonances in ultracold atomic systems are\nchiefly identified and characterized through time consuming atom loss\nspectroscopy. We describe an off-resonant dispersive optical probing technique\nto rapidly locate Feshbach resonances and demonstrate the method by locating\nfour resonances of $^{87}$Rb, between the $|\\rm{F} = 1, \\rm{m_F}=1 \\rangle$ and\n$|\\rm{F} = 2, \\rm{m_F}=0 \\rangle$ states. Despite the loss features being\n$\\lesssim0.1$ G wide, we require only 21 experimental runs to explore a\nmagnetic field range >18 G, where $1~\\rm{G}=10^{-4}$ T. The resonances consist\nof two known s-wave features in the vicinity of 9 G and 18 G and two previously\nunobserved p-wave features near 5 G and 10 G. We further utilize the dispersive\napproach to directly characterize the two-body loss dynamics for each Feshbach\nresonance.",
        "positive": "Robustness and observability of rotating vortex-lattices in an\n  exciton-polariton condensate: Exciton-polariton condensates display a variety of intriguing pattern-forming\nbehaviors, particularly when confined in potential traps. It has previously\nbeen predicted that triangular lattices of vortices of the same sign will form\nspontaneously as the result of surface instabilities in a harmonic trap.\nHowever, natural disorder, deviation of the external potential from circular\nsymmetry, or higher-order terms modifying the dynamical equations may all have\ndetrimental effects and destabilize the circular trajectories of vortices. Here\nwe address these issues, by characterizing the robustness of the vortex lattice\nagainst disorder and deformations of the trapping potential. Since most\nexperiments use time integrated measurements it would be hard to observe\ndirectly the rotating vortex lattices or distinguish them from vortex-free\nstates. We suggest how these difficulties can be overcome and present an\nexperimentally viable interference-imaging scheme that would allow the\ndetection of rotating vortex lattices."
    },
    {
        "anchor": "Quasi-compactons and bistability in exciton-polariton condensates: We address stationary patterns in exciton-polariton condensates supported by\na narrow external pump beam, and we discover that even in the absence of\ntrapping potentials, such condensates may support stable localized stationary\ndissipative solutions (quasi-compactons), whose field decays faster than\nexponentially or even vanishes everywhere outside the pump spot. More general\nconditions lead to dissipative solitons which may display bistability. The\nbistability in exciton-polariton condensates, which manifests itself in\nsimultaneous existence of two stable and one unstable localized solitons with\ndifferent amplitudes, widths, and exciton-photon fractions under the same\nphysical conditions, strongly depends on the width of pump beam and is found to\ndisappear for sufficiently narrow pump beams.",
        "positive": "Trap anharmonicity and sloshing mode of a Fermi gas: For a gas trapped in a harmonic potential, the sloshing (or Kohn) mode is\nundamped and its frequency coincides with the trap frequency, independently of\nthe statistics, interaction and temperature of the gas. However, experimental\ntrap potentials have usually Gaussian shape and anharmonicity effects appear as\nthe temperature and, in the case of Fermions, the filling of the trap are\nincreased. We study the sloshing mode of a degenerate Fermi gas in an\nanharmonic trap within the Boltzmann equation, including in-medium effects in\nboth the transport and collision terms. The calculated frequency shifts and\ndamping rates of the sloshing mode due to the trap anharmonicity are in\nsatisfactory agreement with the available experimental data. We also discuss\nhigher-order dipole, octupole, and bending modes and show that the damping of\nthe sloshing mode is caused by its coupling to these modes."
    },
    {
        "anchor": "Nonlinear waves in two-component Bose-Einstein condensates: Manakov\n  system and Kowalevski equations: Traveling waves in two-component Bose-Einstein condensates whose dynamics is\ndescribed by the Manakov limit of the Gross-Pitaevskii equations are considered\nin general situation with relative motion of the components when their chemical\npotentials are not equal to each other. It is shown that in this case the\nsolution is reduced to the form known in the theory of motion of S.~Kowalevski\ntop. Typical situations are illustrated by the particular cases when the\ngeneral solution can be represented in terms of elliptic functions and their\nlimits. Depending on the parameters of the wave, both density waves (with\nin-phase motions of the components) and polarization waves (with counter-phase\ntheir motions) are considered.",
        "positive": "Quantum many-body effects on Rydberg excitons in cuprous oxide: We investigate quantum many-body effects on Rydberg excitons in cuprous oxide\ninduced by the surrounding electron-hole plasma. Line shifts and widths are\ncalculated by full diagonalisation of the plasma Hamiltonian and compared to\nresults in first order perturbation theory, and the oscillator strength of the\nexciton lines is analysed."
    },
    {
        "anchor": "Observing phase jumps of solitons in Bose-Einstein condensates: The phase difference of the macroscopic wave function is a unique structure\nof the soliton in an atomic Bose--Einstein condensate (BEC). However,\nexperiments on ultracold atoms so far have observed the valley of the density\nprofile to study the dynamics of solitons. We propose a method to observe the\nphase difference of a soliton in a BEC by using an interference technique with\nRaman and rf pulses. We introduce a phase jump factor, which is an indicator to\nmeasure the phase difference between two points. It is demonstrated by using\nthe projected Gross--Pitaevskii equation that an interference density ratio,\nthe density ratio of two-component BECs after the Raman and rf pulses,\nreproduces the phase jump factor well. This technique will become an\nalternative method to study the decay and breakdown of a phase imprinted\nsoliton in atomic BECs.",
        "positive": "Floquet edge states in a harmonically driven integer quantum Hall system: Recent theoretical work on time-periodically kicked Hofstadter model found\nrobust counter-propagating edge modes. It remains unclear how ubiquitously such\nanomalous modes can appear, and what dictates their robustness against\ndisorder. Here we shed further light on the nature of these modes by analyzing\na simple type of periodic driving where the hopping along one spatial direction\nis modulated sinusoidally with time while the hopping along the other spatial\ndirection is kept constant. We obtain the phase diagram for the quasienergy\nspectrum at flux 1/3 as the driving frequency $\\omega$ and the hopping\nanisotropy are varied. A series of topologically distinct phases with\ncounter-propagating edge modes appear due to the harmonic driving, similar to\nthe case of a periodically kicked system studied earlier. We analyze the time\ndependence of the pair of Floquet edge states localized at the same edge, and\ncompare their Fourier components in the frequency domain. In the limit of small\nmodulation, one of the Floquet edge mode within the pair can be viewed as the\nedge mode originally living in the other energy gap shifted in quasienergy by\n$\\hbar \\omega$, i.e., by absorption or emission of a \"photon\" of frequency\n$\\omega$. Our result suggests that counter-propagating Floquet edge modes are\ngeneric features of periodically driven integer quantum Hall systems, and not\ntied to any particular driving protocol. It also suggests that the Floquet edge\nmodes would remain robust to any static perturbations that do not destroy the\nchiral edge modes of static quantum Hall states."
    },
    {
        "anchor": "Universal Scaling of the Dynamic BKT Transition in Quenched 2D Bose\n  Gases: While renormalization group theory is a fully established method to capture\nequilibrium phase transitions, the applicability of RG theory to universal\nnon-equilibrium behavior remains elusive. Here we address this question by\nmeasuring the non-equilibrium dynamics triggered by a quench from superfluid to\nthermal phase across the Berezinskii-Kosterlitz-Thouless transition in a 2D\nBose gas. We quench the system by splitting the 2D gas in two and probe the\nrelaxation dynamics by measuring the phase correlation function and vortex\ndensity via matter-wave interferometry. The dynamics occur via a two-step\nprocess of rapid phonon thermalization followed by slow dynamic vortex\nunbinding. We demonstrate universal scaling laws for the algebraic exponents\nand vortex density, supported by classical-field simulations, and show their\nagreement with the real-time RG theory.",
        "positive": "Dynamical instability towards finite-momentum pairing in quenched BCS\n  superconducting phases: In this work we numerically investigate the fate of the\nBardeen-Cooper-Schrieffer (BCS) pairing in the presence of quenched phase under\nPeierls substitution using time-dependent real space and momentum space\nBogoliubov-de Gennes equation methods and Anderson pseudospin representation\nmethod. This kind of phase imprint can be realized by modulating electric field\nin ultracold atoms and illumining of THz optical pump pulse in solids with\nconventional and unconventional superconductors. In the case of weak phase\nimprint, the BCS pairing is stable; while in the strong phase imprint,\ninstability towards finite-momentum pairing is allowed, in which the real space\nand momentum space methods yield different results. In the pulsed gauge\npotential, we find that this instability will not happen even with much\nstronger vector potential. We also show that the uniform and staggered gauge\npotentials yield different behaviors. While the staggered potential induces\ntransition from the BCS pairing to over-damped phase, the uniform gauge may\nenhance the pairing and will not induce to the over-damped phase. These result\nmay shade light on the realization of finite momentum pairing, such as\nFulde-Ferrell-Larkin-Ovchinnikov phase with dynamical modulation."
    },
    {
        "anchor": "Reservoir interactions of a vortex in a trapped 3D Bose-Einstein\n  condensate: We simulate the dissipative evolution of a vortex in a trapped\nfinite-temperature dilute-gas Bose-Einstein condensate using first-principles\nopen-systems theory. Simulations of the complete stochastic projected\nGross-Pitaevskii equation for a partially condensed Bose gas containing a\nsingle quantum vortex show that the transfer of condensate energy to the\nincoherent thermal component without population transfer provides an important\nchannel for vortex decay. For the lower temperatures considered, this effect is\nsignificantly larger that the population transfer process underpinning the\nstandard theory of vortex decay, and is the dominant determinant of the vortex\nlifetime. A comparison with the Zaremba-Nikuni-Griffin kinetic (two-fluid)\ntheory further elucidates the role of the particle transfer interaction, and\nsuggests the need for experimental testing of reservoir interaction theory. The\ndominance of this particular energetic decay mechanism for this open quantum\nsystem should be testable with current experimental setups, and its observation\nwould have broad implications for the dynamics of atomic matter waves and\nexperimental studies of dissipative phenomena.",
        "positive": "Interference, spectral momentum correlations, entanglement, and Bell\n  inequality for a trapped interacting ultracold atomic dimer: Analogies with\n  biphoton interferometry: Elucidating similarities and differences between quantum-optics biphoton\ninterference phenomena and the quantum physics of quasi-one-dimensional\ndouble-well optically-trapped ultracold neutral bosonic or fermionic atoms, we\nshow that the analog of the optical biphoton joint-coincidence spectral\ncorrelations, studied with massless non-interacting biphotons emanating from\nEPR-Bell-Bohm single-occupancy sources, corresponds to a distinct contribution\nin the total second-order momentum correlations of the massive, interacting,\nand time-evolving ultracold atoms. This single-occupancy contribution can be\nextracted from the total second-order momentum correlation function measured in\ntime-of-flight experiments, which for the trapped atomic system contains, in\ngeneral, a double-occupancy, NOON, component. The dynamics of the two-particle\nsystem are modeled by a Hubbard Hamiltonian. This partial coincidence spectrum\nis a cosine-square quantum beating dependent on the difference of the momenta\nof the two particles, while the corresponding coincidence probability proper,\nfamiliar from its role in describing the Hong-Ou-Mandel coincidence dip of\noverlapping photons, results from an integration over the particle momenta.\nBecause the second-order momentum correlations are mirrored in the\ntime-of-flight spectra in space, our theoretical findings provide impetus for\ntime-of-flight experimental protocols for emulating with (massive) ultracold\natoms venerable optical interferometries that use two space-time separated and\nentangled (massless) photons or double-slit optical sources. The implementation\nof such developments will facilitate testing of fundamental aspects and enable\napplications of quantum physics with trapped massive ultracold atoms, that is,\ninvestigations of nonlocality and violation of Bell inequalities, entanglement,\nand quantum information science."
    },
    {
        "anchor": "Quantum nanofriction in trapped ion chains with a topological defect: Trapped ion systems constitute a well controllable scenario for the study and\nemulation of nanofriction, and in particular of Frenkel-Kontorova-like models.\nThis is in particular the case when a topological defect is created in a zigzag\nion Coulomb crystal, which results in an Aubry transition from free sliding to\npinned phase as a function of the trap aspect ratio. We explore the quantum\neffects of the Aubry transition by means of an effective simplified model, in\nwhich the defect is treated like a single quantum particle that experiences an\neffective Peierls-Nabarro potential and a position-dependent mass. We\ndemonstrate the relevance of quantum tunneling in a finite range of aspect\nratios close the critical point, showing that the quantum effects may be\nobserved in the kink dynamics for sufficiently low temperatures. Finally, we\ndiscuss the requirements to reveal quantum effects at the Aubry transition in\nfuture experiments on trapped ions.",
        "positive": "Effects of periodic potentials on the critical velocity of superfluid\n  Fermi gases in the BCS-BEC crossover: We study the effects of an external periodic potential on the critical\nvelocity of a superfluid Fermi gas in the crossover between the\nBardeen-Cooper-Schrieffer (BCS) phase and Bose-Einstein condensation (BEC). We\nnumerically solve the Bogoliubov-de Gennes equations to model a\nthree-dimensional (3D) gas of ultracold atoms in the superfluid phase flowing\nthrough a 1D optical lattice. We find that when the recoil energy is comparable\nto the Fermi energy, the presence of the periodic potential reduces the effect\nof pair-breaking excitations. This behavior is a consequence of the peculiar\nband structure of the quasiparticle energy spectrum in the lattice. When the\nlattice height is much larger than the Fermi energy, the periodic potential\nmakes pairs of atoms to be strongly bound even in the BCS regime and\npair-breaking excitations are further suppressed. We have also found that when\nthe recoil energy is comparable to or larger than the Fermi energy, the\ncritical velocity due to long-wavelength phonon excitations shows a\nnon-monotonic behavior along the BCS-BEC crossover."
    },
    {
        "anchor": "Functional renormalization group approach to interacting bosons at zero\n  temperature: We investigate the single-particle spectral density of interacting bosons\nwithin the non-perturbative functional renormalization group technique. The\nflow equations for a Bose gas are derived in a scheme which treats the\ntwo-particle density-density correlations exactly but neglects irreducible\ncorrelations among three and more particles. These flow equations are solved\nwithin a truncation which allows to extract the complete frequency and momentum\nstructure of the normal and anomalous self-energies. Both the asymptotic small\nmomentum regime, where perturbation regime fails, as well as the perturbative\nregime at larger momenta are well described within a single unified approach.\nThe self-energies do not exhibit any infrared divergences, satisfy the U(1)\nsymmetry constraints, and are in accordance with the Nepomnyashchy relation\nwhich states that the anomalous self-energy vanishes at zero momentum and zero\nfrequency. From the self-energies we extract the single-particle spectral\ndensity of the two-dimensional Bose gas. The dispersion is found to be of the\nBogoliubov form and shows the crossover from linear Goldstone modes to the\nquadratic behavior of quasi-free bosons. The damping of the quasiparticles is\nfound to be in accordance with the standard Beliaev damping. We furthermore\nrecover the exact asymptotic limit of the propagators derived by Gavoret and\nNozieres and discuss the nature of the non-analyticities of the self-energies\nin the very small momentum regime.",
        "positive": "Clustered Superfluids in the One Dimensional Bose-Hubbard model with\n  extended correlated hopping: Bosonic lattice systems with non-trivial interactions represent an intriguing\nplatform to study exotic phases of matter. Here, we study the effects of\nextended correlated hopping processes in a system of bosons trapped in a\nlattice geometry. The interplay between single particle tunneling terms,\ncorrelated hopping processes and on-site repulsion is studied by means of a\ncombination of exact diagonalization, strong coupling expansion and cluster\nmean field theory. We identify a rich ground state phase diagram where, apart\nthe usual Mott and superfluid states, superfluid phases with interesting\nclustering properties occur."
    },
    {
        "anchor": "Elementary excitations in spinor polariton- electron systems: We consider effective interactions in a 2D hybrid polariton- electron system\nand calculate dispersion of elementary excitations accounting the spin degree\nof freedom of the particles. Due to the crucial role played by the exchange\nterm in polariton- electron interactions the dispersions of this system become\nspin- dependent and show unusual behavior. The coupling of the excitations of\nthe condensate with 2D plasmon can result in appearence of roton minimum in the\ndispersion and destruction of the condensate for close enough situated quantum\nwells with electrons and excitons.",
        "positive": "Evolution of an isolated monopole in a spin-1 Bose-Einstein condensate: We simulate the decay dynamics of an isolated monopole defect in the nematic\nvector of a spin-1 Bose-Einstein condensate during the polar-to-ferromagnetic\nphase transition of the system. Importantly, the decay of the monopole occurs\nin the absence of external magnetic fields and is driven principally by the\ndynamical instability due to the ferromagnetic spin-exchange interactions. An\ninitial isolated monopole is observed to relax into a polar-core spin vortex,\nthus demonstrating the spontaneous transformation of a point defect of the\npolar order parameter manifold to a line defect of the ferromagnetic manifold.\nWe also investigate the dynamics of an isolated monopole pierced by a quantum\nvortex line with winding number k. It is shown to decay into a coreless\nAnderson-Toulouse vortex if k = 1 and into a singular vortex with an empty core\nif k = 2. In both cases, the resulting vortex is also encircled by a polar-core\nvortex ring."
    },
    {
        "anchor": "Dirac-Weyl fermions with arbitrary spin in two-dimensional optical\n  superlattices: Dirac-Weyl fermions are massless relativistic particles with a well-defined\nhelicity which arise in the context of high-energy physics. Here we propose a\nquantum simulation of these paradigmatic fermions using multicomponent\nultracold atoms in a two-dimensional square optical lattice. We find that\nlaser-assisted spin-dependent hopping, specifically tuned to the\n$(2s+1)$-dimensional representations of the $\\mathfrak{su}$(2) Lie algebra,\ndirectly leads to a regime where the emerging massless excitations correspond\nto Dirac-Weyl fermions with arbitrary pseudospin $s$. We show that this\nplatform hosts two different phases: a semimetallic phase that occurs for\nhalf-integer $s$, and a metallic phase that contains a flat zero-energy band at\ninteger $s$. These phases host a variety of interesting effects, such as a very\nrich anomalous quantum Hall effect and a remarkable multirefringent Klein\ntunneling. In addition we show that these effects are directly related to the\nnumber of underlying Dirac-Weyl species and zero modes.",
        "positive": "Two-body relaxation in a Fermi gas at a p-wave Feshbach resonance: We systematically studied the two-body loss in a two-component Fermi gas of\n$^6$Li atoms near a p-wave Feshbach resonance. The two-body loss rate constants\nwere measured for various temperatures and magnetic fields using atoms trapped\nin three-dimensional and quasi-two-dimensional traps. Our results were nicely\nreproduced by a theoretical model that incorporates the two-body loss as an\nimaginary part to the inverse of the scattering volume in the scattering\namplitude expression. The observed loss suppression in quasi-two-dimensional\ntraps may provide a promising strategy to realize a p-wave superfluid in a\nsystem of ultracold atoms."
    },
    {
        "anchor": "Metallic state in bosonic systems with continuously degenerate minima: In systems above one dimension a continuously degenerate minimum of the\nsingle particle dispersion is realized due to one or a combination of\nsystem-parameters such as lattice structure, isotropic spin-orbit coupling, and\ninteractions. A unit codimension of the dispersion-minima leads to a divergent\ndensity of states which enhances the effects of interactions, and may lead to\nnovel states of matter as exemplified by Luttinger liquids in one dimensional\nbosonic systems. Here we show that in dilute, homogeneous bosonic systems above\none dimension, weak, spin-independent, inter-particle interactions stabilize a\nmetallic state at zero temperature in the presence of a curved manifold of\ndispersion minima. In this metallic phase the system possesses a quasi\nlong-range order with non-universal scaling exponents. At a fixed positive\ncurvature of the manifold, increasing either the dilution or the interaction\nstrength destabilizes the metallic state towards charge density wave states\nthat break one or more symmetries. The magnitude of the wave vector of the\ndominant charge density wave state is controlled by the product of the mean\ndensity of bosons and the curvature of the manifold. We obtain the zero\ntemperature phase diagram, and identify the phase boundary.",
        "positive": "Catalyzation of supersolidity in binary dipolar condensates: Breakthrough experiments have newly explored the fascinating physics of\ndipolar quantum droplets and supersolids. The recent realization of dipolar\nmixtures opens further intriguing possibilities. We show that under rather\ngeneral conditions, the presence of a second component catalyzes droplet\nnucleation and supersolidity in an otherwise unmodulated condensate. Droplet\ncatalyzation in miscible mixtures, which may occur even for a surprisingly\nsmall impurity doping, results from a local roton instability triggered by the\ndoping-dependent modification of the effective dipolar strength. The\ncatalyzation mechanism may trigger the formation of a two-fluid supersolid,\ncharacterized by a generally different superfluid fraction of each component,\nwhich opens intriguing possibilities for the future study of spin physics in\ndipolar supersolids."
    },
    {
        "anchor": "Anomalous momentum diffusion in a dissipative many-body system: Decoherence is ubiquitous in quantum physics, from the conceptual foundations\nto quantum information processing or quantum technologies, where it is a threat\nthat must be countered. While decoherence has been extensively studied for\nsimple, well-isolated systems such as single atoms or ions, much less is known\nfor many-body systems where inter-particle correlations and interactions can\ndrastically alter the dissipative dynamics. Here we report an experimental\nstudy of how spontaneous emission destroys the spatial coherence of a gas of\nstrongly interacting bosons in an optical lattice. Instead of the standard\nmomentum diffusion expected for independent atoms, we observe an anomalous\nsub-diffusive expansion, associated with a universal slowing down $\\propto\n1/t^{1/2}$ of the decoherence dynamics. This algebraic decay reflects the\nemergence of slowly-relaxing many-body states, akin to sub-radiant states of\nmany excited emitters. These results, supported by theoretical predictions,\nprovide an important benchmark in the understanding of open many-body systems.",
        "positive": "Quantum quench phase diagrams of an s-wave BCS-BEC condensate: We study the dynamic response of an s-wave BCS-BEC (atomic-molecular)\ncondensate to detuning quenches within the two channel model beyond the weak\ncoupling BCS limit. At long times after the quench, the condensate ends up in\none of three main asymptotic states (nonequilibrium phases), which are\nqualitatively similar to those in other fermionic condensates defined by a\nglobal complex order parameter. In phase I the amplitude of the order parameter\nvanishes as a power law, in phase II it goes to a nonzero constant, and in\nphase III it oscillates persistently. We construct exact quench phase diagrams\nthat predict the asymptotic state (including the many-body wavefunction)\ndepending on the initial and final detunings and on the Feshbach resonance\nwidth. Outside of the weak coupling regime, both the mechanism and the time\ndependence of the relaxation of the amplitude of the order parameter in phases\nI and II are modified. Also, quenches from arbitrarily weak initial to\nsufficiently strong final coupling do not produce persistent oscillations in\ncontrast to the behavior in the BCS regime. The most remarkable feature of\ncoherent condensate dynamics in various fermion superfluids is an effective\nreduction in the number of dynamic degrees of freedom as the evolution time\ngoes to infinity. As a result, the long time dynamics can be fully described in\nterms of just a few new collective dynamical variables governed by the same\nHamiltonian only with \"renormalized\" parameters. Combining this feature with\nthe integrability of the underlying (e.g. the two channel) model, we develop\nand consistently present a general method that explicitly obtains the exact\nasymptotic state of the system."
    },
    {
        "anchor": "Enhancing variational Monte Carlo using a programmable quantum simulator: Programmable quantum simulators based on Rydberg atom arrays are a\nfast-emerging quantum platform, bringing together long coherence times,\nhigh-fidelity operations, and large numbers of interacting qubits\ndeterministically arranged in flexible geometries. Today's Rydberg array\ndevices are demonstrating their utility as quantum simulators for studying\nphases and phase transitions in quantum matter. In this paper, we show that\nunprocessed and imperfect experimental projective measurement data can be used\nto enhance in silico simulations of quantum matter, by improving the\nperformance of variational Monte Carlo simulations. As an example, we focus on\ndata spanning the disordered-to-checkerboard transition in a $16 \\times 16$\nsquare lattice array [S. Ebadi et al. Nature 595, 227 (2021)] and employ\ndata-enhanced variational Monte Carlo to train powerful autoregressive\nwavefunction ans\\\"atze based on recurrent neural networks (RNNs). We observe\nuniversal improvements in the convergence times of our simulations with this\nhybrid training scheme. Notably, we also find that pre-training with\nexperimental data enables relatively simple RNN ans\\\"atze to accurately capture\nphases of matter that are not learned with a purely variational training\napproach. Our work highlights the promise of hybrid quantum--classical\napproaches for large-scale simulation of quantum many-body systems, combining\nautoregressive language models with experimental data from existing quantum\ndevices.",
        "positive": "Observation of dynamical topology in 1D: Nontrivial topology in lattices is characterized by invariants--such as the\nZak phase for one dimensional (1D) lattices--derived from wave functions\ncovering the Brillouin zone. We realized the 1D bipartite Rice-Mele (RM)\nlattice using ultracold $^{87}$Rb and focus on lattice configurations\npossessing various combinations of chiral, time-reversal and particle-hole\nsymmetries. We quenched between configurations and used a form of quantum state\ntomography, enabled by diabatically tuning lattice parameters, to directly\nfollow the time evolution of the Zak phase as well as a chiral winding number.\nThe Zak phase evolves continuously; however, when chiral symmetry transiently\nappears in the out-of-equilibrium system, the chiral winding number is well\ndefined and can take on different integer values. When quenching between two\nconfigurations obeying all three symmetries the Zak phase is time independent;\nwe confirm the contrasting prediction of [M. McGinley and N. R.Cooper, PRL 121\n090401 (2018)] that chiral symmetry is periodically restored, at which times\nthe winding number changes by $\\pm 2$, yielding values that are not present in\nthe native RM Hamiltonian."
    },
    {
        "anchor": "Fluctuation based interpretable analysis scheme for quantum many-body\n  snapshots: Microscopically understanding and classifying phases of matter is at the\nheart of strongly-correlated quantum physics. With quantum simulations, genuine\nprojective measurements (snapshots) of the many-body state can be taken, which\ninclude the full information of correlations in the system. The rise of deep\nneural networks has made it possible to routinely solve abstract processing and\nclassification tasks of large datasets, which can act as a guiding hand for\nquantum data analysis. However, though proven to be successful in\ndifferentiating between different phases of matter, conventional neural\nnetworks mostly lack interpretability on a physical footing. Here, we combine\nconfusion learning with correlation convolutional neural networks, which yields\nfully interpretable phase detection in terms of correlation functions. In\nparticular, we study thermodynamic properties of the 2D Heisenberg model,\nwhereby the trained network is shown to pick up qualitative changes in the\nsnapshots above and below a characteristic temperature where magnetic\ncorrelations become significantly long-range. We identify the full counting\nstatistics of nearest neighbor spin correlations as the most important quantity\nfor the decision process of the neural network, which go beyond averages of\nlocal observables. With access to the fluctuations of second-order correlations\n-- which indirectly include contributions from higher order, long-range\ncorrelations -- the network is able to detect changes of the specific heat and\nspin susceptibility, the latter being in analogy to magnetic properties of the\npseudogap phase in high-temperature superconductors. By combining the confusion\nlearning scheme with transformer neural networks, our work opens new directions\nin interpretable quantum image processing being sensible to long-range order.",
        "positive": "Polaron in almost ideal molecular Bose-Einstein condensate: We discuss properties of a single impurity atom immersed in the spin-$1/2$\ndilute Fermi gas with equal populations of two species in the deep\nBose-Einstein condensate (BEC) phase. In this limit, when an almost undepleted\nBEC of the tightly bound molecules of spin-up and spin-down fermions is formed,\nwe calculate the parameters of an impurity spectrum. It is justified that the\nleading-order contribution to the impurity energy, while being determined by\nthe two- and three-body scattering processes, is dominated by the former ones."
    },
    {
        "anchor": "Non-integer Floquet Sidebands Spectroscopy: In the quantum system under periodical modulation, the particle can be\nexcited by absorbing the laser photon with the assistance of integer Floquet\nphotons, so that the Floquet sidebands appear. Here, we experimentally observe\nnon-integer Floquet sidebands (NIFBs) emerging between the integer ones while\nincreasing the strength of the probe laser in the optical lattice clock system.\nThen, we propose the Floquet channel interference hypothesis (FCIH) which\nsurprisingly matches quantitatively well with both experimental and numerical\nresults. With its help, we found both Rabi and Ramsey spectra are very\nsensitive to the initial phase and exhibit additional two symmetries. More\nimportantly, the height of Ramsey NIFBs is comparable to the integer one at\nlarger $g/\\omega_s$ which indicates an exotic phenomenon beyond the\nperturbative description. Our work provides new insight into the spectroscopy\nof the Floquet system and has potential application in quantum technology.",
        "positive": "Mott Insulator to Superfluid transition in Bose-Bose mixtures in a\n  two-dimensional lattice: We perform a numeric study (Worm algorithm Monte Carlo simulations) of\nultracold two-component bosons in two-dimensional optical lattices. We study\nhow the Mott insulator to superfluid transition is affected by the presence of\na second superfluid bosonic species. We find that, at fixed interspecies\ninteraction, the upper and lower boundaries of the Mott lobe are differently\nmodified. The lower boundary is strongly renormalized even for relatively low\nfilling factor of the second component and moderate (interspecies) interaction.\nThe upper boundary, instead, is affected only for large enough filling of the\nsecond component. Whereas boundaries are renormalized we find evidence of\npolaron-like excitations. Our results are of interest for current experimental\nsetups."
    },
    {
        "anchor": "Superconductivity and other phase transitions in a hybrid Bose-Fermi\n  mixture formed by a polariton condensate and an electron system in two\n  dimensions: Interacting Bose-Fermi systems play a central role in condensed matter\nphysics. Here, we analyze a novel Bose-Fermi mixture formed by a cavity\nexciton-polariton condensate interacting with a two-dimensional electron\nsystem. We show that that previous predictions of superconductivity [F.P.\nLaussy, Phys. Rev. Lett. 10, 104 (2010)] and excitonic supersolid formation\n[I.A. Shelykh, Phys. Rev. Lett. 14, 105 (2010)] in this system are closely\nintertwined- resembling the predictions for strongly correlated electron\nsystems such as high temperature superconductors. In stark contrast to a large\nmajority of Bose-Fermi systems analyzed in solids and ultracold atomic gases,\nthe renormalized interaction between the polaritons and electrons in our system\nis long-ranged and strongly peaked at a tunable wavevector, which can be\nrendered incommensurate with the Fermi momentum. We analyze the prospects for\nexperimental observation of superconductivity and find that critical\ntemperatures on the order of a few Kelvins can be achieved in heterostructures\nconsisting of transition metal dichalcogenide monolayers that are embedded in\nan open cavity structure. All optical control of superconductivity in\nsemiconductor heterostructures could enable the realization of new device\nconcepts compatible with semiconductor nanotechnology. In addition the\npossibility to interface quantum Hall physics, superconductivity and\nnonequilibrium polariton condensates is likely to provide fertile ground for\ninvestigation of completely new physical phenomena.",
        "positive": "Multi-Particle Tunneling Transport at Strongly-Correlated Interfaces: We elucidate the multi-particle transport of pair- and spin-tunnelings in\nstrongly correlated interfaces. Not only usual single-particle tunneling but\nalso interaction-induced multi-particle tunneling processes naturally arise\nfrom a conventional microscopic model without any empirical parameters, through\nthe overlap of the many-body wave functions around the interface. We\ndemonstrate how anomalous tunneling currents occur in a strongly interacting\nsystem due to the pair-tunneling process which we derived microscopically. Our\nformulation is useful for junction systems in various disciplines, including\natomtronics, spintronics, and nuclear reactions."
    },
    {
        "anchor": "$Ab\\,initio$ derivation of lattice gauge theory dynamics for cold gases\n  in optical lattices: We introduce a method for quantum simulation of U$(1)$ lattice gauge theories\ncoupled to matter, utilizing alkaline-earth(-like) atoms in state-dependent\noptical lattices. The proposal enables the study of both gauge and\nfermionic-matter fields without integrating out one of them in one and two\ndimensions. We focus on a realistic and robust implementation that utilizes the\nlong-lived metastable clock state available in alkaline-earth(-like) atomic\nspecies. Starting from an $ab\\,initio$ modelling of the experimental setting,\nwe systematically carry out a derivation of the target U$(1)$ gauge theory.\nThis approach allows us to identify and address conceptual and practical\nchallenges for the implementation of lattice gauge theories that - while\npivotal for a successful implementation - have never been rigorously addressed\nin the literature: those include the specific engineering of lattice potentials\nto achieve the desired structure of Wannier functions, and the subtleties\ninvolved in realizing the proper separation of energy scales to enable\ngauge-invariant dynamics. We discuss realistic experiments that can be carried\nout within such a platform using the fermionic isotope $^{173}$Yb, addressing\nvia simulations all key sources of imperfections, and provide concrete\nparameter estimates for relevant energy scales in both one- and two-dimensional\nsettings.",
        "positive": "Quantum states of p-band bosons in optical lattices: We study a gas of repulsively interacting bosons in the first excited band of\nan optical lattice. We explore this p-band physics both within the framework of\na standard mean-field theory as well as with the more accurate generalized\nGutzwiller ansatz. We find the phase diagrams for two- and three-dimensional\nsystems and characterize the first Mott-states in detail. Furthermore, we find\nthat even though the p-band model has strongly anisotropic kinetic energies and\ninter-flavor interaction terms are missing in the lowest band theory, the\nmean-field theory becomes useful quite rapidly once the transition from the\nMott-insulator to the superfluid is crossed."
    },
    {
        "anchor": "Novel $p$-wave superfluids of fermionic polar molecules: We show that recently suggested subwavelength lattices offer remarkable\nprospects for the observation of novel superfluids of fermionic polar\nmolecules. It becomes realistic to obtain a topological $p$-wave superfluid of\nmicrowave-dressed polar molecules in 2D lattices at temperatures of the order\nof tens of nanokelvins, which is promising for topologically protected quantum\ninformation processing. Another foreseen novel phase is an interlayer $p$-wave\nsuperfluid of polar molecules in a bilayer geometry.",
        "positive": "A Monte Carlo wavefunction description of losses in a 1D Bose gas and\n  cooling to the ground state by quantum feedback: The effect of atom losses on a homogeneous one-dimensional Bose gas lying\nwithin the quasi-condensate regime is investigated using a Monte Carlo\nwavefunction approach. The evolution of the system is calculated, conditioned\nby the loss sequence, namely the times of individual losses and the position of\nthe removed atoms. We describe the gas within the linearized Bogoliubov\napproach. For each mode, we find that, for a given quantum trajectory, the\nstate of the system converges towards a coherent state, i.e. the ground state,\ndisplaced in phase space. Provided losses are recorded with a temporal and\nspatially resolved detector, we show that quantum feedback can be implemented\nand cooling to the ground state of one or several modes can be realized."
    },
    {
        "anchor": "Cavity Optomechanics with a Bose-Einstein Condensate: Normal Mode\n  Splitting: We study the normal mode splitting in a system consisting of a Bose Einstein\ncondensates (BECs) trapped inside a Fabry Perot cavity driven by a single mode\nlaser field. We analyze the variations in frequency and damping rate of the\ncollective density excitation of a BEC imparted by the optical field. We study\nthe occurrence of normal mode splitting which appears as consequences of the\nhybridization of the fluctuations of the intracavity field and the condensate\nmode. It is shown that normal mode splitting vanishes for weak coupling between\nthe condensate mode and the intracavity field. Moreover, we investigate the\nnormal mode splitting in the transmission spectrum of the cavity field.",
        "positive": "Spontaneous ferromagnetism in the spinor Bose gas with Rashba spin-orbit\n  coupling: We show that in the two-component Bose gas with Rashba spin-orbit coupling an\narbitrarily small attractive interaction between bosons with opposite spin\ninduces spontaneous ferromagnetism below a finite critical temperature $T_c$.\nIn the ferromagnetic phase the single-particle spectrum exhibits a unique\nminimum in momentum space in the direction of the magnetization. For\nsufficiently small temperatures below $T_c$ the bosons eventually condense into\nthe unique state at the bottom of the spectrum, forming a ferromagnetic\nBose-Einstein condensate."
    },
    {
        "anchor": "Light self-trapping in a large cloud of cold atoms: We show that, for a near-resonant propagating beam, a large cloud of cold\n87Rb atoms acts as a saturable Kerr medium and produces self-trapping of light.\nBy side fluorescence imaging we monitor the transverse size of the beam and,\ndepending on the sign of the laser detuning with respect to the atomic\ntransition, we observe self-focusing or -defocusing, with the waist remaining\nstationary for an appropriate choice of parameters. We analyze our observations\nby using numerical simulations based on a simple 2-level atom model.",
        "positive": "Damping of long wavelength collective modes in spinor Bose-Fermi\n  mixtures: Using an effective field theory we describe the low energy bosonic\nexcitations in a three dimensional ultra-cold mixture of spin-1 bosons and\nspin-1/2 fermions. We establish an interesting fermionic excitation induced\ngeneric damping of the usual undamped long wavelength bosonic collective\nGoldstone modes. Two states with bosons forming either a ferromagnetic or polar\nsuperfluid are studied. The linear dispersion of the bosonic Bogoliubov\nexcitations is preserved with a renormalized sound velocity. For the polar\nsuperfluid we find both gapless modes (density and spin) are damped, whereas in\nthe ferromagnetic superfluid we find the density (spin) mode is (not) damped.\nWe argue quite generally that this holds for any mixture of bosons and fermions\nthat are coupled through at least a density-density interaction. We discuss the\nimplications of our many-body interaction results for experiments on Bose-Fermi\nmixtures."
    },
    {
        "anchor": "Confinement in 1+1D $\\mathbb{Z}_2$ Lattice Gauge Theories at Finite\n  Temperature: Confinement is a paradigmatic phenomenon of gauge theories, and its\nunderstanding lies at the forefront of high-energy physics. Here, we study\nconfinement in a simple one-dimensional \\Zt lattice gauge theory at finite\ntemperature and filling, which is within the reach of current cold-atom and\nsuperconducting-qubit platforms. By employing matrix product states (MPS)\ncalculations, we investigate the decay of the finite-temperature Green's\nfunction and uncover a smooth crossover between the confined and deconfined\nregimes. This is furthermore confirmed by considering the Friedel oscillations\nand string length distributions obtained from snapshots sampled from MPS, both\nof which are experimentally readily available. Finally, we verify that confined\nmesons remain well-defined at finite temperature by probing their quench\ndynamics with exact diagonalization. Our results shed new light on confinement\nat finite temperature from an experimentally relevant standpoint.",
        "positive": "Antiferrosmectic ground state of two-component dipolar Fermi gases -- an\n  analog of meson condensation in nuclear matter: We show that an antiferrosmectic-C phase has lower energy at high densities\nthan the non-magnetized Fermi gas and ferronematic phases in an ultracold gas\nof fermionic atoms, or molecules, with large magnetic dipole moments. This\nphase, which is analogous to meson condensation in dense nuclear matter, is a\none-dimensional periodic structure in which the fermions localize in layers\nwith their pseudospin direction aligned parallel to the layers, and staggered\nlayer by layer."
    },
    {
        "anchor": "Critical dynamics and tree-like spatiotemporal patterns in\n  exciton-polaritoncondensates: We study nonresonantly pumped exciton-polariton system in the vicinity of the\ndynamical instability threshold. We find that the system exhibits unique and\nrich dynamics, which leads to spatiotemporal pattern formation. The patterns\nhave a tree-like structure and are reminiscent of structures that appear in a\nvariety of soft matter systems. Within the approximation of slow and fast time\nscales, we show that the polariton model exhibits self-replication point in\nanalogy to reaction-diffusion systems.",
        "positive": "Ground State Energy of Hydrogen-Like Ions in Quantum Plasmas: Using the asymptotic iteration method (AIM) we investigate the variation in\nthe 1s energy levels of hydrogen and helium-like static ions in fully\ndegenerate electron gas. The semiclassical Thomas-Fermi (TF), Shukla-Eliasson\n(SE) and corrected Shukla-Eliasson (cSE) models are compared. It is remarked\nthat these models merge into the vacuum level for hydrogen and helium-like ions\nin the dilute classical electron gas regime. While in the TF model hydrogen\nground state level lifts monotonically towards the continuum limit with\nincrease in the electron concentration, in the SE and cSE models universal\nbound stabilization valley through the energy minimization occurs at a\nparticular electron concentration range for the hydrogen-like ion which for cSE\nmodel closely matches the electron concentrations in typical metals. The later\nstabilizing mechanism appears to be due to the interaction between plasmon\nexcitations and the Fermi lengthscales in metallic density regime. In the case\nof helium-like ions, however, no such stability mechanism is found. The\napplication of cSE model with electron exchange and correlation effects reveals\nthat cSE model qualitatively accounts for the number-density and lattice\nparameters of elemental metals within the framework of free electron\nassumption. According to the cSE model of static charge screening a simple\nmetal-insulator transition criterion is defined. Current investigation may\nfurther elucidate the underlying physical mechanisms in the formation and\ndielectric properties of metallic compounds."
    },
    {
        "anchor": "Stable non-equilibrium Fulde-Ferrell-Larkin-Ovchinnikov state in a\n  spin-imbalanced driven-dissipative Fermi gas loaded on a three-dimensional\n  cubic optical lattice: We theoretically investigate a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) type\nsuperfluid phase transition in a driven-dissipative two-component Fermi gas.\nThe system is assumed to be in the non-equilibrium steady state, which is tuned\nby adjusting the chemical potential difference between two reservoirs that are\ncoupled with the system. Including pairing fluctuations by extending the\nstrong-coupling theory developed in the thermal-equilibrium state by Nozieres\nand Schmitt-Rink to this non-equilibrium case, we show that a non-equilibrium\nFFLO (NFFLO) phase transition can be realized without spin imbalance, under the\nconditions that (1) the two reservoirs imprint a two-edge structure on the\nmomentum distribution of Fermi atoms, and (2) the system is loaded on a\nthree-dimensional cubic optical lattice. While the two edges work like two\nFermi surfaces with different sizes, the role of the optical lattice is to\nprevent the NFFLO long-range order from destruction by NFFLO pairing\nfluctuations. We also draw the non-equilibrium mean-field phase diagram in\nterms of the chemical potential difference between the two reservoirs, a\nfictitious magnetic field to tune the spin imbalance of the system, and the\nenvironmental temperature of the reservoirs, to clarify the relation between\nthe NFFLO state and the ordinary thermal-equilibrium FFLO state discussed in\nspin-imbalanced Fermi gases.",
        "positive": "Fermi surface deformations and pairing in mixtures of dipolar and\n  non-dipolar fermions: We study mass-imbalanced two-component Fermi mixtures, where one of the\ncomponents consists of dipolar fermions. We specifically study the mass\nimbalances corresponding to the atomic ${}^{163}$Dy-${}^{40}$K and\n${}^{53}$Cr-${}^{6}$Li mixtures. We study the onset of the $s$-wave superfluid\nphase, as a function of population imbalance and the dipolar interaction\nstrength. We find the critical temperature and the Fermi surface deformations\nat the transition to depend on the dipolar interaction strength, where the\ncritical temperature increases (decreases) with dipolar interaction strength\nfor a majority (minority) of dipolar atoms. We present momentum distributions\nof both components where the Fermi surface deformations are visible."
    },
    {
        "anchor": "Quantum Cherenkov transition of finite momentum Bose polarons: We investigate the behavior of a finite-momentum impurity immersed in a\nweakly interacting three-dimensional Bose-Einstein condensate (BEC) of\nultra-cold atoms, giving a detailed account of the dynamical quantum Cherenkov\ntransition discussed in Ref. [arXiv:2101.00030]. Using a time-dependent\nvariational approach, we identify a transition in the far-from-equilibrium\ndynamics of the system after the attractive short-range impurity-boson\ninteraction is quenched on. The transition occurs as the impurity's velocity\ncrosses an interaction-dependent critical value, and manifests in the long-time\nbehavior of the Loschmidt echo and average impurity velocity. This behavior is\nalso reflected in the finite momentum ground state of the system, where the\ngroup velocity of the interaction-dressed impurity loses it's dependence on the\ntotal momentum of the system as the critical point is crossed. The transition\nwe discuss should be experimentally observable via a variety of common\nprotocols in ultracold atomic systems such as time-of-flight imaging, RF\nspectroscopy, Ramsey interferometry, and absorption imaging.",
        "positive": "Ground-State Magnetization in Mixtures of a Few Ultra-Cold Fermions in\n  One-Dimensional Traps: Ground-state properties of a few spin-$1/2$ ultra-cold fermions confined in a\none-dimensional trap are studied by the exact diagonalization method. In\ncontrast to previous studies, it is not assumed that the projection of a spin\nof individual particles is fixed. Therefore, the spin is treated as an\nadditional degree of freedom and the global magnetization of the system is\nestablished spontaneously. Depending on the shape of the trap, inter-particle\ninteractions, and an external magnetic field, the phase diagram of the system\nis determined. It is shown that, for particular confinements, some values of\nthe magnetization cannot be reached by the ground-state of the system."
    },
    {
        "anchor": "Controlling disorder with periodically modulated interactions: We investigate a celebrated problem of one dimensional tight binding model in\nthe presence of disorder leading to Anderson localization from a novel\nperspective. A binary disorder is assumed to be created by immobile heavy\nparticles for the motion of the lighter, mobile species in the limit of no\ninteraction between mobile particles. Fast periodic modulations of interspecies\ninteractions allow us to produce an effective model with small diagonal and\nlarge off-diagonal disorder unexplored in cold atoms experiments. We present an\nexpression for an approximate Anderson localization length and verify the\nexistence of the well known extended resonant mode and analyze the influence of\nnonzero next-nearest neighbor hopping terms. We point out that periodic\nmodulation of interaction allow disorder to work as a tunable band-pass filter\nfor momenta.",
        "positive": "Fate of topological states and mobility edges in one-dimensional slowly\n  varying incommensurate potentials: We investigate the interplay between disorder and superconducting pairing for\na one-dimensional $p$-wave superconductor subject to slowly varying\nincommensurate potentials with mobility edges. With amplitude increments of the\nincommensurate potentials, the system can undergo a transition from a\ntopological phase to a topologically trivial localized phase. Interestingly, we\nfind that there are four mobility edges in the spectrum when the strength of\nthe incommensurate potential is below a critical threshold, and a novel\ntopologically nontrivial localized phase emerges in a certain region. We reveal\nthis energy-dependent metal-insulator transition by applying several numerical\ndiagnostic techniques, including the inverse participation ratio, the density\nof states and the Lyapunov exponent. Nowadays, precise control of the\nbackground potential and the $p$-wave superfluid can be realized in the\nultracold atomic systems, we believe that these novel mobility edges can be\nobserved experimentally."
    },
    {
        "anchor": "Quantum magnetism of ultra-cold fermion systems with the symplectic\n  symmetry: We numerically study quantum magnetism of ultra-cold alkali and\nalkaline-earth fermion systems with large hyperfine spin $F=3/2$, which are\ncharacterized by a generic $Sp(N)$ symmetry with N=4. The methods of exact\ndiagonalization (ED) and density-matrix-renormalization-group are employed for\nthe large size one-dimensional (1D) systems, and ED is applied to a\ntwo-dimensional (2D) square lattice on small sizes. We focus on the magnetic\nexchange models in the Mott-insulating state at quarter-filling. Both 1D and 2D\nsystems exhibit rich phase diagrams depending on the ratio between the spin\nexchanges $J_0$ and $J_2$ in the bond spin singlet and quintet channels,\nrespectively. In 1D, the ground states exhibit a long-range-ordered\ndimerization with a finite spin gap at $J_0/J_2>1$, and a gapless spin liquid\nstate at $J_0/J_2 \\le 1$, respectively. In the former and latter cases, the\ncorrelation functions exhibit the two-site and four-site periodicities,\nrespectively. In 2D, various spin correlation functions are calculated up to\nthe size of $4\\times 4$. The Neel-type spin correlation dominates at large\nvalues of $J_0/J_2$, while a $2\\times 2$ plaquette correlation is prominent at\nsmall values of this ratio. Between them, a columnar spin-Peierls dimerization\ncorrelation peaks. We infer the competitions among the plaquette ordering, the\ndimer ordering, and the Neel ordering in the 2D system.",
        "positive": "Non-local double-path Casimir phase in atom interferometers: We present a quantum open system theory of atom interferometers evolving in\nthe quantized electromagnetic field bounded by an ideal conductor. Our\ntreatment reveals an unprecedented feature of matter-wave propagation, namely\nthe appearance of a non-local double-path phase coherence. Such a non-local\nphase arises from the coarse-graining over the quantized electromagnetic field\nand internal atomic degrees of freedom, yielding a non-Hamiltonian evolution of\nthe atomic waves moving in presence of correlated quantum dipole and field\nfluctuations. We develop a diagrammatic interpretation of this phase, and\nestimate it for realistic experimental parameters."
    },
    {
        "anchor": "Scaling Flows and Dissipation in the Dilute Fermi Gas at Unitarity: We describe recent attempts to extract the shear viscosity of the dilute\nFermi gas at unitarity from experiments involving scaling flows. A scaling flow\nis a solution of the hydrodynamic equations that preserves the shape of the\ndensity distribution. The scaling flows that have been explored in the\nlaboratory are the transverse expansion from a deformed trap (\"elliptic flow\"),\nthe expansion from a rotating trap, and collective oscillations. We discuss\nadvantages and disadvantages of the different experiments, and point to\nimprovements of the theoretical analysis that are needed in order to achieve\ndefinitive results. A conservative bound based on the current data is that the\nminimum of the shear viscosity to entropy density ration is that eta/s is less\nor equal to 0.5 hbar/k_B.",
        "positive": "Third order corrections to the ground state energy of the polarized\n  diluted gas of spin $1/2$ fermions: We present the results of the computation of the third order corrections to\nthe ground state energy of the diluted polarized gas of nonrelativistic spin\n$1/2$ fermions interacting through a spin-independent repulsive two-body\npotential.\n  The corrections are computed within the effective field theory approach which\ndoes not require specifying the interaction potential explicitly but only to\ncharacterize it by only a few parameters - the scattering lengths $a_0$,\n$a_1,\\dots$ and effective radii $r_0,\\dots$ - measurable in low energy\nfermion-fermion elastic scattering.\n  The corrections are computed semi-analytically, that is are expressed in\nterms of two functions of the system's polarization.\n  The functions are given by the integrals which can be easily evaluated using\nthe Mathematica built-in routines for numerical integration."
    },
    {
        "anchor": "Observation of the universal jump across the\n  Berezinskii-Kosterlitz-Thouless transition in two-dimensional Bose gases: The physics in two-dimensional (2D) systems is very different from what we\nobserve in three-dimensional (3D) systems. Thermal fluctuations in 2D systems\nare enhanced, and they prevent the conventional Bose-Einstein condensation\n(BEC) at non-zero temperatures by destroying the long-range order. However, a\nphase transition to a superfluid phase is still expected to occur in a 2D\nsystem along with an emergence of a quasi-long-range order, explained by the\nBerezinskii-Kosterlitz-Thouless (BKT) mechanism. Within the BKT mechanism, a\nuniversal jump of the superfluid density in a 2D Bosonic system was\ntheoretically predicted by Nelson and Kosterlitz, and was first observed in 2D\n\\textsuperscript{4}He films by Bishop and Reppy. Recent experiments in trapped\nultracold 2D Bose gas systems have shown signatures of the BKT transition, and\nits superfluidity. However, the universal jump in the superfluid density was\nnot observed in these systems. Here we report the first observation of the\nuniversal jump in the superfluid density using an optically trapped ultracold\n2D Bose gas. The measured superfluid phase space density at the BKT transition\nagrees well with the predicted value within our measurement uncertainty.\nAdditionally, we measure the phase fluctuations in our density profiles to show\nthat the BKT transition occurs first, followed by the BEC transition.",
        "positive": "Adiabatic passage through chaos: We study the process of nonlinear stimulated Raman adiabatic passage within a\nclassical mean-fieldframework. Depending on the sign of interaction, the\nbreakdown of adiabaticity in the interactingnonintegrable system is not related\nto bifurcations in the energy landscape, but rather to the emergence\nofquasistochastic motion that drains the followed quasistationary state.\nConsequently, faster sweep rate,rather than quasistatic variation of\nparameters, is better for adiabaticity"
    },
    {
        "anchor": "Gray molasses cooling of $^{39}$K to a high phase-space density: We present new techniques in cooling 39K atoms using laser light close to the\nD1 transition. First, a new compressed-MOT configuration is taking advantage of\ngray molasses type cooling induced by blue-detuned D1 light. It yields an\noptimized density of atoms. Then, we use pure D1 gray molasses to further cool\nthe atoms to an ultra-low temperature of 6\\,$\\mu$K. The resulting phase-space\ndensity is $2 \\times 10^{-4}$ and will ease future experiments with ultracold\npotassium. As an example, we use it to directly load up to $3\\times 10^7$ atoms\nin a far detuned optical trap, a result that opens the way to the all-optical\nproduction of potassium degenerate gases.",
        "positive": "A comparative study of deconvolution techniques for quantum-gas\n  microscope images: Quantum-gas microscopes are used to study ultracold atoms in optical lattices\nat the single particle level. In these system atoms are localised on lattice\nsites with separations close to or below the diffraction limit. To determine\nthe lattice occupation with high fidelity, a deconvolution of the images is\noften required. We compare three different techniques, a local iterative\ndeconvolution algorithm, Wiener deconvolution and the Lucy-Richardson\nalgorithm, using simulated microscope images. We investigate how the\nreconstruction fidelity scales with varying signal-to-noise ratio, lattice\nfilling fraction, varying fluorescence levels per atom, and imaging resolution.\nThe results of this study identify the limits of singe-atom detection and\nprovide quantitative fidelities which are applicable for different atomic\nspecies and quantum-gas microscope setups."
    },
    {
        "anchor": "Criticality in Trapped Atomic Systems: We discuss generic limits posed by the trap in atomic systems on the accurate\ndetermination of critical parameters for second-order phase transitions, from\nwhich we deduce optimal protocols to extract them. We show that under current\nexperimental conditions the in-situ density profiles are barely suitable for an\naccurate study of critical points in the strongly correlated regime. Contrary\nto recent claims, the proper analysis of time-of-fight images yields critical\nparameters accurately.",
        "positive": "Quantum simulation of exotic PT-invariant topological nodal loop bands\n  with ultracold atoms in an optical lattice: Since the well-known PT symmetry has its fundamental significance and\nimplication in physics, where PT denotes the combined operation of\nspace-inversion P and time-reversal T, it is extremely important and intriguing\nto completely classify exotic PT-invariant topological metals and to physically\nrealize them. Here we, for the first time, establish a rigorous classification\nof topological metals that are protected by the PT symmetry using KO-theory. As\na physically realistic example, a PT-invariant nodal loop (NL) model in a 3D\nBrillouin zone is constructed, whose topological stability is revealed through\nits PT-symmetry-protected nontrivial Z2 topological charge. Based on these\nexact results, we propose an experimental scheme to realize and to detect\ntunable PT-invariant topological NL states with ultracold atoms in an optical\nlattice, in which atoms with two hyperfine spin states are loaded in a\nspin-dependent 3D OL and two pairs of Raman lasers are used to create\nout-of-plane spin-flip hopping with site-dependent phase. Such a realistic\ncold-atom setup can yield topological NL states, having a tunable ring-shaped\nband-touching line with the two-fold degeneracy in the bulk spectrum and\nnon-trivial surface states. The states are actually protected by the combined\nPT symmetry even in the absence of both P and T symmetries, and are\ncharacterized by a Z2-type invariant (a quantized Berry phase). Remarkably, we\ndemonstrate with numerical simulations that (i) the characteristic NL can be\ndetected by measuring the atomic transfer fractions in a Bloch-Zener\noscillation; (ii) the topological invariant may be measured based on the\ntime-of-flight imaging; and (iii) the surface states may be probed through\nBragg spectroscopy. The present proposal for realizing topological NL states in\ncold atom systems may provide a unique experimental platform for exploring\nexotic PT-invariant topological physics."
    },
    {
        "anchor": "Quantum hydrodynamic approximations to the finite temperature trapped\n  Bose gases: For the quantum kinetic system modelling the Bose-Einstein Condensate that\naccounts for interactions between condensate and excited atoms, we use the\nChapman-Enskog expansion to derive its hydrodynamic approximations, include\nboth Euler and Navier-Stokes approximations. The hydrodynamic approximations\ndescribe not only the macroscopic behavior of the BEC but also its coupling\nwith the non-condensates, which agrees with Landau's two fluid theory.",
        "positive": "Instability of superfluid Fermi gases induced by a roton-like density\n  mode in optical lattices: We study the stability of superfluid Fermi gases in deep optical lattices in\nthe BCS--Bose-Einstein condensation (BEC) crossover at zero temperature. Within\nthe tight-binding attractive Hubbard model, we calculate the spectrum of the\nlow-energy Anderson-Bogoliubov (AB) mode as well as the single-particle\nexcitations in the presence of superfluid flow in order to determine the\ncritical velocities. To obtain the spectrum of the AB mode, we calculate the\ndensity response function in the generalized random-phase approximation\napplying the Green's function formalism developed by C\\^ot\\'e and Griffin to\nthe Hubbard model. We find that the spectrum of the AB mode is separated from\nthe particle-hole continuum having the characteristic rotonlike minimum at\nshort wavelength due to the strong charge-density-wave fluctuations. The energy\nof the rotonlike minimum decreases with increasing the lattice velocity and it\nreaches zero at the critical velocity which is smaller than the pair breaking\nvelocity. This indicates that the superfluid state is energetically unstable\ndue to the spontaneous emission of the short-wavelength rotonlike excitations\nof the AB mode instead due to pair-breaking. We determine the critical\nvelocities as functions of the interaction strength across the BCS-BEC\ncrossover regime."
    },
    {
        "anchor": "Directed transport in driven optical lattices by phase generation: We examine the dynamics of ultracold atoms held in optical lattice\npotentials. By controlling the switching of a periodic driving potential we\nshow how a phase-induced renormalization of the intersite tunneling can be used\nto produce directed motion and control wavepacket spreading. We further show\nhow this generation of a synthetic gauge potential can be used to split and\nrecombine wavepackets, providing an attractive route to implementing quantum\ncomputing tasks.",
        "positive": "A modular implementation of an effective interaction approach for\n  harmonically trapped fermions in 1D: We introduce a generic and accessible implementation of an exact\ndiagonalization method for studying few-fermion models. Our aim is to provide a\ntestbed for the newcomers to the field as well as a stepping stone for trying\nout novel optimizations and approximations. This userguide consists of a\ndescription of the algorithm, and several examples in varying orders of\nsophistication. In particular, we exemplify our routine using an\neffective-interaction approach that fixes the low-energy physics. We benchmark\nthis approach against the existing data, and show that it is able to deliver\nstate-of-the-art numerical results at a significantly reduced computational\ncost."
    },
    {
        "anchor": "Chiral f-wave Topological Superuid in Triangular Optical Lattices: We demonstrate that an exotically chiral f-wave topological superfluid can be\ninduced in coldfermionic-atom triangular optical lattices through the\nlaser-field-generated effective non-Abelian gauge field, controllable Zeeman\nfields and s-wave Feshbach resonance. We find that the chiral f-wave\ntopological superfluid is characterized by three gapless Majorana edge states\nlocated on the boundary of the system. More interestingly, these Majorana edge\nstates degenerate into one Majorana fermion bound to each vortex in the\nsuperfluid. Our proposal enlarges topological superfluid family and specifies a\nunique experimentally controllable system to study the Majorana fermion\nphysics.",
        "positive": "Dynamics for partially coherent Bose-Einstein condensates in double\n  wells: The dynamical properties of partially coherent Bose-Einstein condensates in\ndouble wells are investigated in three typical regimes. In the extreme Fock\nregime, the time evolution of the degree of coherence is shown to decay\nrapidly. In the Rabi regime, a relation between the amplitude of Rabi\noscillation and the degree of coherence is obtained, which is expected to\ndetermine the degree of coherence by measuring the amplitude of Rabi\noscillation. The study on the self-trapping phenomena in the Josephson regime\nexhibits that both the degree of coherence and the initial relative phase can\naffect the final particle distribution."
    },
    {
        "anchor": "Fractional quantum Hall states of a Bose gas with spin-orbit coupling: We study the fractional quantum Hall phases of a pseudospin-1/2 Bose gas in\nan artificial gauge field. In addition to an external magnetic field, the gauge\nfield also mimics an intrinsic spin-orbit coupling of the Rashba type. While\nthe spin degeneracy of the Landau levels is lifted by the spin-orbit coupling,\nthe crossing of two Landau levels at certain coupling strengths gives rise to a\nnew degeneracy. We therefore take into account two Landau levels, and perform\nexact diagonalization of the many-body Hamiltonian. We study and characterize\nthe quantum Hall phases which occur in the vicinity of the degeneracy point.\nNotably, we describe the different states appearing at the Laughlin filling,\n\\nu=1/2. While for this filling incompressible phases disappear at the\ndegeneracy point, denser systems at \\nu=3/2 and \\nu=2 are found to be clearly\ngapped. For filling factors \\nu=2/3 and \\nu=4/3, we discuss the connection of\nthe exact ground state to the non-Abelian spin singlet states, obtained as the\nground state of k+1 body contact interactions.",
        "positive": "Elementary Excitations in a BEC with Isotropic Harmonic Trap: Bogoliubov\n  Equations versus Hydrodynamic Formalism: The elementary excitations for a BEC trapped by means of an isotropic\nharmonic oscillator are studied in the present work. The analysis of these\nperturbations is done in the context of the Bogoliubov equations and not\nresorting to the hydrodynamic version. The comparison between these two\napproaches will allow us to deduce a parameter explaining the role that the\nscattering length and the trap play in the way in which the frequency of these\nelementary excitations acquires information about the angular momentum of the\ncorresponding solutions. It will be shown that outside the validity realm of\nthe Thomas_fermi approximation the frequencies of the perturbations cannot\ninherit the information of the angular momentum codified in the functions\nescribing the elementary excitations."
    },
    {
        "anchor": "Temporal and spatio-temporal correlation functions for trapped Bose\n  gases: Density correlations unambiguously reveal the quantum nature of matter. Here,\nwe study correlations between measurements of density in cold-atom clouds at\ndifferent times at one position, and also at two separated positions. We take\ninto account the effects of finite-size and -duration measurements made by\nlight beams passing through the atom cloud. We specialise to the case of Bose\ngases in harmonic traps above critical temperature, for weakly-perturbative\nmeasurements. For overlapping measurement regions, shot-noise correlations\nrevive after a trap oscillation period. For non-overlapping regions, bosonic\ncorrelations dominate at long times, and propagate at finite speeds. Finally,\nwe give a realistic measurement protocol for performing such experiments.",
        "positive": "Exploring multi-band excitations of interacting Bose gases in a 1D\n  optical lattice by coherent scattering: We use a coherent Bragg diffraction method to impart an external momentum to\nultracold bosonic atoms trapped in a one-dimensional optical lattice. This\nmethod is based on the application of a single light pulse, with conditions\nwhere scattering of photons can be resonantly amplified by the atomic density\ngrating. An oscillatory behavior of the momentum distribution resulting from\nthe time evolution in the lattice potential is then observed. By measuring the\noscillating frequencies, we extract multi-band energy structures of\nsingle-particle excitations with zero pseudo-momentum transfer for a wide range\nof lattice depths. The excitation energy structures reveal the interaction\neffect through the whole range of lattice depth."
    },
    {
        "anchor": "Time crystal platform: from quasi-crystal structures in time to systems\n  with exotic interactions: Time crystals are quantum many-body systems which, due to interactions\nbetween particles, are able to spontaneously self-organize their motion in a\nperiodic way in time by analogy with the formation of crystalline structures in\nspace in condensed matter physics. In solid state physics properties of space\ncrystals are often investigated with the help of external potentials that are\nspatially periodic and reflect various crystalline structures. A similar\napproach can be applied for time crystals, as periodically driven systems\nconstitute counterparts of spatially periodic systems, but in the time domain.\nHere we show that condensed matter problems ranging from single particles in\npotentials of quasi-crystal structure to many-body systems with exotic\nlong-range interactions can be realized in the time domain with an appropriate\nperiodic driving. Moreover, it is possible to create molecules where atoms are\nbound together due to destructive interference if the atomic scattering length\nis modulated in time.",
        "positive": "Magnetic Quantum Phases of Ultracold Dipolar Gases in an Optical\n  Superlattice: We propose an effective Ising spin chain constructed with dipolar quantum\ngases confined in a one-dimensional optical superlattice. Mapping the motional\ndegrees of freedom of a single particle in the lattice onto a pseudo-spin\nresults in effective transverse and longitudinal magnetic fields. This\neffective Ising spin chain exhibits a quantum phase transition from a\nparamagnetic to a single-kink phase as the dipolar interaction increases.\nParticularly in the single-kink phase,a magnetic kink arises in the effective\nspin chain and behaves as a quasi-particle in a pinning potential exerted by\nthe longitudinal magnetic field. Being realizable with current experimental\ntechniques, this effective Ising chain presents a unique platform for emulating\nthe quantum phase transition as well as the magnetic kink effects in the\nIsing-spin chain and enriches the toolbox for quantum emulation of spin models\nby ultracold quantum gases."
    },
    {
        "anchor": "Dynamical symmetry and breathers in a two-dimensional Bose gas: A fluid is said to be \\emph{scale-invariant} when its interaction and kinetic\nenergies have the same scaling in a dilation operation. In association with the\nmore general conformal invariance, scale invariance provides a dynamical\nsymmetry which has profound consequences both on the equilibrium properties of\nthe fluid and its time evolution. Here we investigate experimentally the\nfar-from-equilibrium dynamics of a cold two-dimensional rubidium Bose gas. We\noperate in the regime where the gas is accurately described by a classical\nfield obeying the Gross--Pitaevskii equation, and thus possesses a dynamical\nsymmetry described by the Lorentz group SO(2,1). With the further\nsimplification provided by superfluid hydrodynamics, we show how to relate the\nevolutions observed for different initial sizes, atom numbers, trap frequencies\nand interaction parameters by a scaling transform. Finally we show that some\nspecific initial shapes - uniformly-filled triangles or disks - may lead to a\nperiodic evolution, corresponding to a novel type of breather for the\ntwo-dimensional Gross--Pitaevskii equation.",
        "positive": "Strong optical self-focusing effect in coherent light scattering with\n  condensates: We present a theoretical investigation of optical self-focusing effects in\nlight scattering with condensates. Using long (>200 \\mu s), red-detuned pulses\nwe show numerically that a non-negligible self-focusing effect is present that\ncauses rapid optical beam width reduction as the scattered field propagates\nthrough a medium with an inhomogeneous density distribution. The rapid growth\nof the scattered field intensity and significant local density feedback\npositively to further enhance the wave generation process and condensate\ncompression, leading to highly efficient collective atomic recoil motion."
    },
    {
        "anchor": "Fractional angular momentum in cold atom systems: The quantum statistics of bosons or fermions are manifest through even or odd\nrelative angular momentum of a pair. We show theoretically that, under certain\nconditions, a pair of certain test particles immersed in a fractional quantum\nHall state possesses, effectively, a fractional relative angular momentum,\nwhich can be interpreted in terms of fractional braid statistics. We propose\nthat the fractionalization of the angular momentum can be detected directly\nthrough the measurement of the pair correlation function in rotating ultra-cold\natomic systems in the fractional quantum Hall regime. Such a measurement will\nalso provide direct evidence for the effective magnetic field, resulting from\nBerry phases arising from attached vortices, and of excitations with fractional\nparticle number, analogous to fractional charge of electron fractional quantum\nHall effect.",
        "positive": "Non-Perturbative Dynamical Effects in Nearly Scale Invariant Systems:\n  The Action of Breaking Scale Invariance: In this work we develop a general formalism that categorizes the action of\nbroken scale invariance on the non-equilibrium dynamics of non-relativistic\nquantum systems. This approach is equally applicable to both strongly and\nweakly interacting systems. We show that any small deviation from the strongly\ninteracting fixed point, in three spatial dimensions, leads to non-pertubative\neffects in the long time dynamics, dramatically altering the dynamics observed\nat the scale invariant fixed point. As a concrete example, we apply this\napproach to the non-equilibrium dynamics for the interacting two-body problem,\nand for a non-interacting quantum gas in the presence of an impurity, both in\nthree spatial dimensions. Slightly away from the resonantly-interacting scale\ninvariant fixed point, we show that the dynamics are altered by a\nnon-perturbative log-periodic beat. The presence of the beat depends only on\ndeviating from the resonant fixed point, while the frequency depends on the\nmicroscopic parameters of the system."
    },
    {
        "anchor": "Coherent molecule formation in anharmonic potentials near\n  confinement-induced resonances: We perform a theoretical and experimental study of a system of two ultracold\natoms with tunable interaction in an elongated trapping potential. We show that\nthe coupling of center-of-mass and relative motion due to an anharmonicity of\nthe trapping potential leads to a coherent coupling of a state of an unbound\natom pair and a molecule with a center of mass excitation. By performing the\nexperiment with exactly two particles we exclude three-body losses and can\ntherefore directly observe coherent molecule formation. We find quantitative\nagreement between our theory of inelastic confinement-induced resonances and\nthe experimental results. This shows that the effects of center-of-mass to\nrelative motion coupling can have a significant impact on the physics of\nquasi-1D quantum systems.",
        "positive": "Observation of pair condensation in the quasi-2D BEC-BCS crossover: The condensation of fermion pairs lies at the heart of superfluidity.\nHowever, for strongly correlated systems with reduced dimensionality the\nmechanisms of pairing and condensation are still not fully understood. In our\nexperiment we use ultracold atoms as a generic model system to study the phase\ntransition from a normal to a condensed phase in a strongly interacting\nquasi-two-dimensional Fermi gas. Using a novel method, we obtain the in situ\npair momentum distribution of the strongly interacting system and observe the\nemergence of a low-momentum condensate at low temperatures. By tuning\ntemperature and interaction strength we map out the phase diagram of the\nquasi-2D BEC-BCS crossover."
    },
    {
        "anchor": "Controlled Transport between Fermi Superfluids Through a Quantum Point\n  Contact: Recent advances in experimental techniques allow one to create a quantum\npoint contact between two Fermi superfluids in cold atomic gases with a tunable\ntransmission coefficient. In this Letter we propose that three distinct\nbehaviors of charge transports between two Fermi superfluids can be realized in\nthis single setup, which are the multiple Andreev reflection, the self-trapping\nand the Josephson oscillation. We investigate the dynamics of atom number\ndifference between two reservoirs for different initial conditions and\ndifferent transmission coefficients, and present a coherent picture of how the\ncrossover between different regimes takes place. Our results can now be\ndirectly verified in current experimental system.",
        "positive": "Challenges and constraints of dynamically emerged source and sink in\n  atomtronic circuits: From closed-system to open-system approaches: While batteries offer electronic source and sink in electronic devices,\natomic analogues of source and sink and their theoretical descriptions have\nbeen a challenge in cold-atom systems. Here we consider dynamically emerged\nlocal potentials as controllable source and sink for bosonic atoms. Although a\nsink potential can collect bosons in equlibrium and indicate its usefulness in\nthe adiabatic limit, sudden switching of the potential exhibits low\neffectiveness in pushing bosons into it. This is due to conservation of energy\nand particle in isolated systems such as cold atoms. By varying the potential\ndepth and interaction strength, the systems can further exhibit averse\nresponse, where a deeper emerged potential attracts less bosonic atoms into it.\nTo explore possibilities for improving the effectiveness, we investigate what\ntypes of system-environment coupling can help bring bosons into a dynamically\nemerged sink, and a Lindblad operator corresponding to local cooling is found\nto serve the purpose."
    },
    {
        "anchor": "Stability Spectroscopy of Rotons in a Dipolar Bose Gas: We study the stability of a quasi-one-dimensional dipolar Bose-Einstein\ncondensate (dBEC) that is perturbed by a weak lattice potential along its axis.\nOur numerical simulations demonstrate that systems exhibiting a roton-maxon\nstructure destabilize readily when the lattice wavelength equals either half\nthe roton wavelength or a low roton subharmonic. We apply perturbation theory\nto the Gross-Pitaevskii and Bogoliubov de Gennes equations to illustrate the\nmechanisms behind the instability threshold. The features of our stability\ndiagram may be used as a direct measurement of the roton wavelength for\nquasi-one-dimensional geometries.",
        "positive": "Perron-Frobenius theorem on the superfluid transition of an ultracold\n  Fermi gas: The Perron-Frobenius theorem is applied to identify the superfluid transition\nof a two-component Fermi gas with a zero-range s-wave interaction. According to\nthe quantum cluster expansion method of Lee and Yang, the grand partition\nfunction is expressed by the Lee-Yang contracted 0-graphs. A singularity of an\ninfinite series of ladder-type Lee-Yang contracted 0-graphs is analyzed. We\npoint out that the singularity is governed by the Perron-Frobenius eigenvalue\nof a certain primitive matrix which is defined in terms of the two-body cluster\nfunctions and the Fermi distribution functions. As a consequence, it is found\nthat there exists a unique fugacity at the phase transition point, which\nimplies that there is no fragmentation of Bose-Einstein condensates of dimers\nand Cooper pairs at the ladder-approximation level of Lee-Yang contracted\n0-graphs. An application to a Bose-Einstein condensate of strongly bounded\ndimers is also made."
    },
    {
        "anchor": "Frustration induced Itinerant Ferromagnetism of Fermions in Optical\n  Lattice: When the Fermi Hubbard model was first introduced sixty years ago, one of the\noriginal motivations was to understand correlation effects in itinerant\nferromagnetism. In the past two decades, ultracold Fermi gas in an optical\nlattice has been used to study the Fermi Hubbard model. However, the metallic\nferromagnetic correlation was observed only in a recent experiment using\nfrustrated lattices, and its underlying mechanism is not clear yet. In this\nletter, we point out that, under the particle--hole transformation, the\nsingle-particle ground state can exhibit double degeneracy in such a frustrated\nlattice. Therefore, the low-energy state exhibits valley degeneracy,\nreminiscent of multi-orbit physics in ferromagnetic transition metals. The\nlocal repulsive interaction leads to the valley Hund's rule, responsible for\nthe observed ferromagnetism. We generalize this mechanism to distorted\nhoneycomb lattices and square lattices with flux. This mechanism was first\ndiscussed by M\\\"uller-Hartmann in a simpler one-dimension model. However, this\nmechanism has not been widely discussed and has not been related to\nexperimental observations before. Hence, our study not only explains the\nexperimental findings but also enriches our understanding of itinerant\nferromagnetism.",
        "positive": "Beating dark-dark solitons and Zitterbewegung in spin-orbit coupled\n  Bose-Einstein condensates: We present families of beating dark-dark solitons in spin-orbit (SO) coupled\nBose-Einstein condensates. These families consist of solitons residing\nsimultaneously in the two bands of the energy spectrum. The soliton components\nare characterized by two different spatial and temporal scales, which are\nidentified by a multiscale expansion method. The solitons are \"beating\" ones,\nas they perform density oscillations with a characteristic frequency, relevant\nto Zitterbewegung (ZB). We find that spin oscillations may occur, depending on\nthe parity of each soliton branch, which consequently lead to ZB oscillations\nof the beating dark solitons. Analytical results are corroborated by numerical\nsimulations, illustrating the robustness of the solitons."
    },
    {
        "anchor": "Phase separation of multicomponent excitonic Bose-Einstein condensates: For the observation of Bose-Einstein condensation, excitons in cuprous oxide\nare regarded as promising candidates due to their large binding energy and long\nlifetime. High particle densities may be achieved by entrapment in a stress\ninduced potential. We consider a multi-component gas of interacting para- and\northoexcitons in cuprous oxide confined in a three-dimensional potential trap.\nBased on the Hartree-Fock-Bogoliubov theory, we calculate density profiles as\nwell as decay luminescence spectra which exhibit signatures of the separation\nof the Bose-condensed phases.",
        "positive": "Stability of dynamical quantum phase transitions in quenched topological\n  insulators: From multiband to disordered systems: Dynamical quantum phase transitions (DQPTs) represent a counterpart in\nnon-equilibrium quantum time evolution of thermal phase transitions at\nequilibrium, where real time becomes analogous to a control parameter such as\ntemperature. In quenched quantum systems, recently the occurrence of DQPTs has\nbeen demonstrated, both with theory and experiment, to be intimately connected\nto changes of topological properties. Here, we contribute to broadening the\nsystematic understanding of this relation between topology and DQPTs to\nmulti-orbital and disordered systems. Specifically, we provide a detailed\nergodicity analysis to derive criteria for DQPTs in all spatial dimensions, and\nconstruct basic counter-examples to the occurrence of DQPTs in multi-band\ntopological insulator models. As a numerical case study illustrating our\nresults, we report on microscopic simulations of the quench dynamics in the\nHarper-Hofstadter model. Furthermore, going gradually from multi-band to\ndisordered systems, we approach random disorder by increasing the (super) unit\ncell within which random perturbations are switched on adiabatically. This\nleads to an intriguing order of limits problem which we address by extensive\nnumerical calculations on quenched one-dimensional topological insulators and\nsuperconductors with disorder."
    },
    {
        "anchor": "Quantum geometry and flat band Bose-Einstein condensation: We study the properties of a weakly interacting Bose-Einstein condensate\n(BEC) in a flat band lattice system by using multiband Bogoliubov theory, and\ndiscover fundamental connections to the underlying quantum geometry. In a flat\nband, the speed of sound and the quantum depletion of the condensate are\ndictated by the quantum geometry, and a finite quantum distance between the\ncondensed and other states guarantees stability of the BEC. Our results reveal\nthat a suitable quantum geometry allows one to reach the strong quantum\ncorrelation regime even with weak interactions.",
        "positive": "Manipulation of a Bose-Einstein condensate by a time-averaged orbiting\n  potential using phase jumps of the rotating field: We report on the manipulation of the center-of-mass motion (`sloshing') of a\nBose Einstein condensate in a time-averaged orbiting potential (TOP) trap. We\nstart with a condensate at rest in the center of a static trapping potential.\nWhen suddenly replacing the static trap with a TOP trap centered about the same\nposition, the condensate starts to slosh with an amplitude much larger than the\nTOP micromotion. We show, both theoretically and experimentally, that the\ndirection of sloshing is related to the initial phase of the rotating magnetic\nfield of the TOP. We show further that the sloshing can be quenched by applying\na carefully timed and sized jump in the phase of the rotating field."
    },
    {
        "anchor": "Formation of Matter-Wave Polaritons in an Optical Lattice: The polariton, a quasiparticle formed by strong coupling of a photon to a\nmatter excitation, is a fundamental ingredient of emergent photonic quantum\nsystems ranging from semiconductor nanophotonics to circuit quantum\nelectrodynamics. Exploiting the interaction between polaritons has led to the\nrealization of superfluids of light as well as of strongly correlated phases in\nthe microwave domain, with similar efforts underway for microcavity\nexciton-polaritons. Here, we develop an ultracold-atom analogue of an\nexciton-polariton system in which interacting polaritonic phases can be studied\nwith full tunability and without dissipation. In our optical-lattice system,\nthe exciton is replaced by an atomic excitation, while an atomic matter wave is\nsubstituted for the photon under a strong dynamical coupling. We access the\nband structure of the matter-wave polariton spectroscopically by coupling the\nupper and lower polariton branches, and explore polaritonic many-body transport\nin the superfluid and Mott-insulating regimes, finding quantitative agreement\nwith our theoretical expectations. Our work opens up novel possibilities for\nstudies of polaritonic quantum matter.",
        "positive": "Rebuilding of destroyed spin squeezing in noisy environments: We investigate the process of spin squeezing in a ferromagnetic dipolar\nspin-1 Bose-Einstein condensate under the driven oneaxis twisting scheme, with\nemphasis on the detrimental effect of noisy environments (stray magnetic\nfields) which completely destroy the spin squeezing. By applying concatenated\ndynamical decoupling pulse sequences with a moderate bias magnetic field to\nsuppress the effect of the noisy environments, we faithfully reconstruct the\nspin squeezing process under realistic experimental conditions. Our\nnoise-resistant method is ready to be employed to generate the spin squeezed\nstate in a dipolar spin-1 Bose-Einstein condensate and paves a feasible way to\nthe Heisenberg-limit quantum metrology"
    },
    {
        "anchor": "Anisotropic acoustics in dipolar Fermi gases: We consider plane wave modes in ultracold, but not quantum degenerate,\ndipolar Fermi gases in the hydrodynamic limit. Longitudinal waves present\nanisotropies in both the speed of sound and their damping, and experience a\nsmall, undulatory effect in their flow velocity. Two distinct types of shear\nwaves appear, a ``familiar\" one, and another that is accompanied by nontrivial\ndensity and temperature modulations. We propose these shear modes as an\nexperimental means to measure the viscosity coefficients, including their\nanisotropies.",
        "positive": "Competition between Bose Einstein Condensation and spin dynamics: We study the impact of spin-exchange collisions on the dynamics of\nBose-Einstein condensation, by rapidly cooling a chromium multi-component Bose\ngas. Despite relatively strong spin-dependent interactions, the critical\ntemperature for Bose-Einstein condensation is reached before the spin-degrees\nof freedom fully thermalize. The increase in density due to Bose-Einstein\ncondensation then triggers spin dynamics, hampering the formation of\ncondensates in spin excited states. Small metastable spinor condensates are\nnevertheless produced, and manifest strong spin fluctuations."
    },
    {
        "anchor": "Matter-wave recombiners for trapped Bose-Einstein condensates: Interferometry with trapped atomic Bose-Einstein condensates (BECs) requires\nthe development of techniques to recombine the two paths of the interferometer\nand map the accumulated phase difference to a measurable atom number\ndifference. We have implemented and compared two recombining procedures in a\ndouble-well based BEC interferometer. The first procedure utilizes the bosonic\nJosephson effect and controlled tunneling of atoms through the potential\nbarrier, similar to laser light in an optical fibre coupler. The second one\nrelies on the interference of the reflected and transmitted parts of the BEC\nwavefunction when impinging on the potential barrier, analogous to light\nimpinging on a half-silvered mirror. Both schemes were implemented\nsuccessfully, yielding an interferometric contrast of about 20% and 42%\nrespectively. Building efficient matter wave recombiners represents an\nimportant step towards the coherent manipulation of external quantum\nsuperposition states of BECs.",
        "positive": "Magnetization relaxation and geometric forces in a Bose ferromagnet: We construct the hydrodynamic theory for spin 1/2 Bose gases at arbitrary\ntemperatures. This theory describes the coupling between the magnetization, and\nthe normal and superfluid components of the gas. In particular, our theory\ncontains the geometric forces on the particles that arise from their spin's\nadiabatic following of the magnetization texture. The phenomenological\nparameters of the hydrodynamic theory are calculated in the Bogoliubov\napproximation and using the Boltzmann equation in the relaxation-time\napproximation. We consider the topological Hall effect due to the presence of a\nskyrmion, and show that this effect manifests itself in the collective modes of\nthe system. The dissipative coupling between the magnetization and the normal\ncomponent is shown to give rise to magnetization relaxation that is fourth\norder in spatial gradients of the magnetization direction."
    },
    {
        "anchor": "Low-energy scatterings and pseudopotential of polarized quadrupoles: We investigate the low-energy scattering properties of two identical\nparticles interacting via the polarized quadrupolar interaction. It is shown\nthat a series of $s$- and $p$-wave resonances appear for identical bosons and\nfermions, respectively, as the strength of the quadrupolar interaction\nincreases. Interestingly, scattering resonances also appear on the generalized\nscattering length corresponding to the coupling between the $s$ and $d$ waves.\nThis observation inspires us to propose a new pseudopotential for the\nquadupolar interaction. We also explore the bound-state properties of two\nparticles in both free space and harmonic traps.",
        "positive": "Generating soliton trains through Floquet engineering: We study a gas of interacting ultracold bosons held in a parabolic trap in\nthe presence of an optical lattice potential. Treating the system as a\ndiscretised Gross-Pitaevskii model, we show how Floquet engineering, by rapidly\n``shaking'' the lattice, allows the ground-state of the system to be converted\ninto a train of bright solitons by inverting the sign of the hopping energy. We\nstudy how the number of solitons produced depends on the system's nonlinearity\nand the curvature of the trap, show how the technique can be applied both in\nthe high and low driving-frequency regimes, and demonstrate the phenomenon's\nstability against noise. We conclude that the Floquet approach is a useful and\nstable method of preparing solitons in cold atom systems."
    },
    {
        "anchor": "Critical velocity of a two-dimensional superflow past a potential\n  barrier of arbitrary penetrability: We theoretically investigate the critical velocity for dissipationless motion\nof a two-dimensional superfluid past a static potential barrier of large width.\nThe circular-shaped barrier provides a comprehensive analytical framework for\nthe critical speed, for which we derive closed-form expressions using the\nhydraulic approximation, the hodograph method, and Janzen-Rayleigh expansions\nof the velocity potential. These analytical estimates are shown to be in good\nagreement with the numerical results of an imaginary-time integration of the\nfull wave equation. In contrast to most of the state of the art, our study is\nnot restricted to an impenetrable potential barrier nor to a quartic\ninteraction Hamiltonian, which enables realistic modeling of recent experiments\nwith atomic Bose-Einstein condensates and paraxial superfluids of light in two\ndimensions.",
        "positive": "The confinement induced resonance in spin-orbit coupled cold atoms with\n  Raman coupling: We investigate the confinement induced resonance in spin-orbit coupled cold\natoms with Raman coupling. We find that the quasi-bound levels induced by the\nspin-orbit coupling and Raman coupling result in the Feshbach-type resonances.\nFor sufficiently large Raman coupling, the bound states in one dimension exist\nonly for sufficiently strong attractive interaction. Furthermore, the bound\nstates in quasi-one dimension exist only for sufficient large ratio of the\nlength scale of confinement to three dimensional s-wave scattering length. The\nRaman coupling substantially changes the confinement-induced resonance\nposition. We give a proposal to realize confinement induced resonance by\nincreasing the Raman coupling strength in experiments."
    },
    {
        "anchor": "Moving obstacle potential in a spin-orbit-coupled Bose-Einstein\n  condensate: We investigate the dynamics around an obstacle potential moving in the\nplane-wave state of a pseudospin-$1/2$ Bose-Einstein condensate with Rashba\nspin-orbit coupling. We numerically investigate the dynamics of the system and\nfind that it depends not only on the velocity of the obstacle but also\nsignificantly on the direction of obstacle motion, which are verified by a\nBogoliubov analysis. The excitation diagram with respect to the velocity and\ndirection is obtained. The dependence of the critical velocity on the strength\nof the spin-orbit coupling and the size of the obstacle is also investigated.",
        "positive": "Synthetic gauge field in two interacting ultracold atomic gases without\n  an optical lattice: A 2D Fock-state lattice (FSL is constructed from the many-body states of two\ninteracting two-mode quantum gases. By periodically driving the interspecies\ninteractions and pulsing the tunneling between the two modes of each gas, a\nsynthetic gauge field is generated. We derive an effective Hamiltonian in the\nshort pulse limit which resembles the Harper-Hofstadter Hamiltonian where the\nmagnetic flux per plaquette is controlled by the ratio of the interaction\nenergy and the driving frequency. The quasispectrum of the Floquet operator of\nthe driving sequence shows the celebrated Hofstadter's butterfly pattern as\nwell as the existence of edge states. From the calculation of the local Chern\nmarker, we establish that the FSL has non-trivial topology and by simulating\nthe dynamics of the edge states, show that they exhibit chirality. Finally, the\ninclusion of the intraspecies interactions creates an overall harmonic trap in\nthe lattice and introduces the nonlinear effect of macroscopic quantum\nself-trapping which is shown to hinder the movement along the edge of the\nlattice. This work introduces a new avenue to explore synthetic gauge fields\nand provides a link between non-trivial condensed matter systems and quantum\ngases."
    },
    {
        "anchor": "Designing Arbitrary One-dimensional Potentials on an Atom Chip: We use laser light shaped by a digital micro-mirror device to realize\narbitrary optical dipole potentials for one-dimensional (1D) degenerate Bose\ngases of 87Rb trapped on an atom chip. Superposing optical and magnetic\npotentials combines the high flexibility of optical dipole traps with the\nadvantages of magnetic trapping, such as effective evaporative cooling and the\napplication of radio-frequency dressed state potentials. As applications, we\npresent a 160 ${\\mu}$m long box-like potential with a central tuneable barrier,\na box-like potential with a sinusoidally modulated bottom and a linear\nconfining potential. These potentials provide new tools to investigate the\ndynamics of 1D quantum systems and will allow us to address exciting questions\nin quantum thermodynamics and quantum simulations.",
        "positive": "Dynamics of Bright Soliton Under Cubic-Quartic Interactions in Quasi\n  One-Dimensional Geometry: Recent inspection of liquid-like state in ultracold atomic gases due to the\nstabilization mechanism through the delicate balance between effective\nmean-field and beyond mean-field (BMF) interactions, has motivated us to study\nthe modified/extended Gross-Pitaevskii (eGP) equation which includes the BMF\ncontribution. In this article, we focus on variational analysis of solitonic\nregime with eGP equation while the soliton is subjected to an obstacle. This\nreveals different scattering scenarios of the soliton with explicit dependence\nof the BMF interaction. The results show the existence of tunneling, partial\nand complete trappings, in different parameter domains. These observations are\nfurther corroborated by the fast-Fourier transform method. In the later part we\nalso extend our analysis to trapped systems. The controlled trapping in defect\npotential and its release can be potentially useful for quantum information\nstorage."
    },
    {
        "anchor": "$p$ orbitals in 3D lattices; fermions, bosons and (exotic) models of\n  magnetism: We demonstrate how different types of $SU(3)$ Heisenberg models can be\nimplemented with the use of the $p$ orbitals of three dimensional optical\nlattices. By considering a Mott insulator with unit filling, the dynamics is\nwell described by an effective model derived from the perturbative treatment of\nthe tunneling elements relative to the onsite interaction terms. This yields\nsystems with degrees of freedom that are generators of the $SU(3)$ group, which\nextends the Heisenberg models frequently used to analyze quantum magnetism. Due\nto the different character of interactions in the bosonic and fermionic cases,\nthe choice of atom determines what type of anisotropies will appear in the\ncouplings of the corresponding effective Hamiltonians. Experimental schemes for\ndetection and manipulation of these systems are presented, and properties of\nthe ground states of selected examples are discussed.",
        "positive": "Interplay of coherent and dissipative dynamics in condensates of light: Based on the Lindblad master equation approach we obtain a detailed\nmicroscopic model of photons in a dye-filled cavity, which features\ncondensation of light. To this end we generalise a recent non-equilibrium\napproach of Kirton and Keeling such that the dye-mediated contribution to the\nphoton-photon interaction in the light condensate is accessible due to an\ninterplay of coherent and dissipative dynamics. We describe the steady-state\nproperties of the system by analysing the resulting equations of motion of both\nphotonic and matter degrees of freedom. In particular, we discuss the existence\nof two limiting cases for steady states: photon Bose-Einstein condensate and\nlaser-like. In the former case, we determine the corresponding dimensionless\nphoton-photon interaction strength by relying on realistic experimental data\nand find a good agreement with previous theoretical estimates. Furthermore, we\ninvestigate how the dimensionless interaction strength depends on the\nrespective system parameters."
    },
    {
        "anchor": "The Contact in the BCS-BEC crossover for finite range interacting\n  ultracold Fermi gases: Using mean-field theory for the Bardeen-Cooper-Schriefer (BCS) to the\nBose-Einstein condensate (BEC) crossover we investigate the ground state\nthermodynamic properties of an interacting homogeneous Fermi gas. The\ninteratomic interactions modeled through a finite range potential allows us to\nexplore the entire region from weak to strong interacting regimes with no\napproximations. To exhibit the thermodynamic behavior as a function of the\npotential parameters in the whole crossover region, we concentrate in studying\nthe contact variable, the thermodynamic conjugate of the inverse of the s-wave\nscattering length. Our analysis allows us to validate the mean-field approach\nacross the whole crossover. It also leads to predict a quantum transition-like\nin the case when the potential range becomes large. This finding is a direct\nconsequence of the k-dependent energy gap for finite interaction range\npotentials.",
        "positive": "Quantum dynamics of impurities in a Bose-Einstein condensate: We study the quantum dynamics of the two impurities in a trapped\nquasi-one-dimensional Bose-Einstein condensate (BEC). We explore the effect of\nimpurity-BEC and impurity-impurity interaction strengths on the dynamics of\nimpurities inside the Bose-Einstein condensate. By studying the\nauto-correlation function of impurities and the BEC, we analyze and quantify\nthe trapping of impurities inside the BEC. We find out that for the small value\nof inter-species coupling strength the BEC starts to oscillate inside the trap.\nFor mild coupling strengths, attractive and repulsive impurities are captured\nafter a few cycles of oscillation inside the BEC. In the strong interaction\nstrength regime, the to-and-fro motion of impurities is suppressed quite fast.\nOur conclusion indicates that quench dynamics can be a tool for studying\nimpurity BEC interactions or impurity-impurity interactions. Our analysis shows\nthat the generation of phonon, shock waves, soliton trains, and self-trapping\nis strongly dependent on the impurity-BEC coupling coefficient."
    },
    {
        "anchor": "Landau damping in a collisionless dipolar Bose gas: We present a theory for the Landau damping of low energy quasi-particles in a\ncollisionless, quasi-2D dipolar Bose gas and produce expressions for the\ndamping rate in uniform and non-uniform systems. Using simple energy-momentum\nconservation arguments, we show that in the homogeneous system, the nature of\nthe low energy dispersion in a dipolar Bose gas severely inhibits Landau\ndamping of long wave-length excitations. For a gas with contact and dipolar\ninteractions, the damping rate for phonons tends to decrease with increasing\ndipolar interactions; for strong dipole-dipole interactions, phonons are\nvirtually undamped over a broad range of temperature. The damping rate for\nmaxon-roton excitations is found to be significantly larger than the damping\nrate for phonons.",
        "positive": "Color Superfluid and Trionic State of Attractive Three-Component Lattice\n  Fermionic Atoms at Finite Temperatures: We investigate the finite-temperature properties of attractive\nthree-component (colors) fermionic atoms in optical lattices using a\nself-energy functional approach. As the strength of the attractive interaction\nincreases in the low temperature region, a second-order transition occurs from\na Fermi liquid to a color superfluid (CSF). In the strong attractive region, a\nfirst-order transition occurs from a CSF to a trionic state. In the high\ntemperature region, a crossover between a Fermi liquid and a trionic state is\nobserved with increasing the strength of the attractive interaction. The\ncrossover region for fixed temperature is almost independent of filling."
    },
    {
        "anchor": "Bilayer superfluidity of fermionic polar molecules: many body effects: We study the BCS superfluid transition in a single-component fermionic gas of\ndipolar particles loaded in a tight bilayer trap, with the electric dipole\nmoments polarized perpendicular to the layers. Based on the detailed analysis\nof the interlayer scattering, we calculate the critical temperature of the\ninterlayer superfluid pairing transition when the layer separation is both\nsmaller (dilute regime) and of the order or larger (dense regime) than the mean\ninterparticle separation in each layer. Our calculations go beyond the standard\nBCS approach and include the many-body contributions resulting in the mass\nrenormalization, as well as additional contributions to the pairing\ninteraction. We find that the many-body effects have a pronounced effect on the\ncritical temperature, and can either decrease (in the very dilute limit) or\nincrease (in the dense and moderately dilute limits) the transition temperature\nas compared to the BCS approach.",
        "positive": "Site-resolved imaging of ytterbium atoms in a two-dimensional optical\n  lattice: We report a high-resolution microscope system for imaging ultracold ytterbium\natoms trapped in a two-dimensional optical lattice. By using the ultraviolet\nstrong transition combined with a solid immersion lens and high-resolution\noptics, our system resolved individual sites in an optical lattice with a\n544-nm spacing. Without any cooling mechanism during the imaging process, the\ndeep potential required to contain the atoms was realized using a combination\nof a shallow ground-state and a deep excited-state potentials. The lifetime and\nlimitations of this setup were studied in detail."
    },
    {
        "anchor": "Strong coupling Bose polarons in a BEC: We use a non-perturbative renormalization group approach to develop a unified\npicture of the Bose polaron problem, where a mobile impurity is strongly\ninteracting with a surrounding Bose-Einstein condensate (BEC). A detailed\ntheoretical analysis of the phase diagram is presented and the\npolaron-to-molecule transition is discussed. For attractive polarons we argue\nthat a description in terms of an effective Fr\\\"ohlich Hamiltonian with\nrenormalized parameters is possible. Its strong coupling regime is realized\nclose to a Feshbach resonance, where we predict a sharp increase of the\neffective mass. Already for weaker interactions, before the polaron mass\ndiverges, we predict a transition to a regime where states exist below the\npolaron energy and the attractive polaron is no longer the ground state. On the\nrepulsive side of the Feshbach resonance we recover the repulsive polaron,\nwhich has a finite lifetime because it can decay into low-lying molecular\nstates. We show for the entire range of couplings that the polaron energy has\nlogarithmic corrections in comparison with predictions by the mean-field\napproach. We demonstrate that they are a consequence of the polaronic mass\nrenormalization which is due to quantum fluctuations of correlated phonons in\nthe polaron cloud.",
        "positive": "Optical lattices as a tool to study defect-induced superfluidity: We study the superfluid response, the energetic and structural properties of\na one-dimensional ultracold Bose gas in an optical lattice of arbitrary\nstrength. We use the Bose-Fermi mapping in the limit of infinitely large\nrepulsive interaction and the diffusion Monte Carlo method in the case of\nfinite interaction. For slightly incommensurate fillings we find a superfluid\nbehavior which is discussed in terms of vacancies and interstitials. It is\nshown that both the excitation spectrum and static structure factor are\ndifferent for the cases of microscopic and macroscopic fractions of defects.\nThis system provides a extremely well-controlled model for studying\ndefect-induced superfluidity."
    },
    {
        "anchor": "Thermodynamics and magnetic properties of the anisotropic 3D Hubbard\n  model: We study the 3D Hubbard model with anisotropic nearest neighbor tunneling\namplitudes using the dynamical cluster approximation and compare the results\nwith a quantum simulation experiment using ultracold fermions in an optical\nlattice, focussing on magnetic correlations. We find that the short-range spin\ncorrelations are significantly enhanced in the direction with stronger\ntunneling amplitudes. Our results agree with the experimental observations and\nshow that the experimental temperature is lower than the strong tunneling\namplitude. We characterize the system by examining the spin correlations beyond\nneighboring sites and determine the distribution of density, entropy and spin\ncorrelation in the trapped system. We furthermore investigate the dependence of\nthe critical entropy at the N\\'eel transition on anisotropy.",
        "positive": "Second root of dilute Bose-Fermi mixtures: We discuss an equilibrium mean-field properties of mixtures consisting of\nbosons and spin-polarized fermionic atoms with a point-like interaction in an\narbitrary dimension $2<d<4$. Particularly, we discuss except the standard\nweak-coupling limit of the system with slightly depleted Bose condensate and\nalmost ideal Fermi gas, the (meta)stable phase with dimers composed exactly of\none boson and one fermion. The peculiarities of the fermion-dimer and the\nboson-dimer three-body effective interactions and their impact on the\nthermodynamic stability of the dilute Bose-Fermi mixtures are elucidated."
    },
    {
        "anchor": "Controlling entanglement in a triple-well system of dipolar atoms: We study the dynamics of entanglement and atomic populations of ultracold\ndipolar bosons in an aligned three-well potential described by an extended\nBose-Hubbard model. We focus on a sufficiently strong interacting regime where\nthe couplings are tuned to obtain an integrable system, in which the time\nevolution exhibits a resonant behavior that can be exactly predicted. Within\nthis framework, we propose a protocol that includes an integrability breaking\nstep by tilting the edge wells for a short time through an external field,\nallowing the production of quantum states with a controllable degree of\nentanglement. We analyze this protocol for different initial states and show\nthe formation of highly entangled states as well as NOON-like states. These\nresults offer valuable insights into how entanglement can be controlled in\nultracold atom systems that may be useful for the proposals of new quantum\ndevices.",
        "positive": "Quantum quench in a p + i p superfluid: Winding numbers and topological\n  states far from equilibrium: We study the non-adiabatic dynamics of a 2D p+ip superfluid following a\nquantum quench of the BCS coupling constant. The model describes a topological\nsuperconductor with a non-trivial BCS (trivial BEC) phase appearing at weak\n(strong) coupling strengths. We extract the exact long-time asymptotics of the\norder parameter \\Delta(t) by exploiting the integrability of the classical\np-wave Hamiltonian, which we establish via a Lax construction. Three different\ntypes of behavior can occur depending upon the strength and direction of the\nquench. In phase I, the order parameter asymptotes to zero. In phase II,\n\\Delta(t) goes to a non-zero constant. Phase III is characterized by persistent\noscillations of \\Delta(t). For quenches within I and II, we determine the\ntopological character of the asymptotic states. We show that two different\nformulations of the bulk topological winding number, although equivalent in the\nground state, must be regarded as independent out of equilibrium. The first\nnumber Q characterizes the Anderson pseudospin texture of the initial state; we\nshow that it is conserved. For non-zero Q, this leads to the prediction of a\n\"gapless topological\" state when \\Delta(t) goes to zero. The presence or\nabsence of Majorana edge modes in a sample with a boundary is encoded in the\nsecond winding number W, formulated in terms of the retarded Green's function.\nWe show that W can change following a quench across the quantum critical point.\nWe discuss the implications for the (dis)appearance of Majorana edge modes.\nFinally, we show that the parity of zeros in the bulk out-of-equilibrium Cooper\npair distribution function constitutes a Z2-valued quantum number, which is\nnon-zero whenever W differs from Q. The pair distribution can in principle be\nmeasured using RF spectroscopy in an ultracold atom realization, allowing\ndirect experimental detection of the bulk Z2 number."
    },
    {
        "anchor": "Controlled generation of momentum states in a high-finesse ring cavity: A Bose-Einstein condensate in a high-finesse ring cavity scatters the photons\nof a pump beam into counterpropagating cavity modes, populating a\nbi-dimensional momentum lattice. A high-finesse ring cavity with a sub-recoil\nlinewidth allows to control the quantized atomic motion, selecting particular\ndiscrete momentum states and generating atom-photon entanglement. The\nsemiclassical and quantum model for the 2D collective atomic recoil lasing\n(CARL) are derived and the superradiant and good-cavity regimes discussed. For\npump incidence perpendicular to the cavity axis, the momentum lattice is\nsymmetrically populated. Conversely, for oblique pump incidence the motion\nalong the two recoil directions is unbalanced and different momentum states can\nbe populated on demand by tuning the pump frequency.",
        "positive": "Resonant control of polar molecules in an optical lattice: We study the resonant control of two nonreactive polar molecules in an\noptical lattice site, focussing on the example of RbCs. Collisional control can\nbe achieved by tuning bound states of the intermolecular dipolar potential, by\nvarying the applied electric field or trap frequency. We consider a wide range\nof electric fields and trapping geometries, showing that a three-dimensional\noptical lattice allows for significantly wider avoided crossings than free\nspace or quasi-two dimensional geometries. Furthermore, we find that dipolar\nconfinement induced resonances can be created with reasonable trapping\nfrequencies and electric fields, and have widths that will enable useful\ncontrol in forthcoming experiments."
    },
    {
        "anchor": "Quantum fluctuations inhibit symmetry breaking in the HMF model: It is widely believed that mean-field theory is exact for a wide-range of\nclassical long-range interacting systems. Is this also true once quantum\nfluctuations have been accounted for? As a test case we study the Hamiltonian\nMean Field (HMF) model for a system of indistinguishable bosons which is\npredicted (according to mean-field theory) to undergo a second-order quantum\nphase transition at zero temperature. The ordered phase is characterized by a\nspontaneously broken $O(2)$ symmetry, which, despite occurring in a\none-dimensional model, is not ruled out by the Mermin-Wagner theorem due to the\npresence of long-range interactions. Nevertheless, a spontaneously broken\nsymmetry implies gapless Goldstone modes whose large fluctuations can restore\nbroken symmetries. In this work, we study the influence of quantum fluctuations\nby projecting the Hamiltonian onto the continuous subspace of symmetry breaking\nmean-field states. We find that the energetic cost of gradients in the center\nof mass wavefunction inhibit the breaking of the $O(2)$ symmetry, but that the\nenergetic cost is very small --- scaling as $\\mathcal{O}(1/N^2)$. Nevertheless,\nfor any finite $N$, no matter how large, this implies that the ground state has\na restored $O(2)$ symmetry. Implications for the finite temperature phases, and\nclassical limit, of the HMF model are discussed.",
        "positive": "Core filling and snaking instability of dark solitons in spin-imbalanced\n  superfluid Fermi gases: We use the time-dependent Bogoliubov de Gennes equations to study dark\nsolitons in three-dimensional spin-imbalanced superfluid Fermi gases. We\nexplore how the shape and dynamics of dark solitons are altered by the presence\nof excess unpaired spins which fill their low-density core. The unpaired\nparticles broaden the solitons and suppress the transverse snake instability.\nWe discuss ways of observing these phenomena in cold atom experiments."
    },
    {
        "anchor": "Magnetic domains in 2D moir\u00e9 lattices with square and hexagonal\n  symmetry: We report the persistence of magnetic domains lying in moir\\'e patterns with\nsquare and hexagonal symmetries. Our investigation is based on the dynamical\ndescription of two magnetic domains represented by a two species bosonic\nmixture of $^{87}$Rb ultracold atoms, being each specie initially localized in\nthe left and right halves of a moir\\'e lattice defined by a specific angle\n$\\theta$. To demonstrate the persistence of such initial domains, we follow the\ntime evolution of the superfluid spin texture, and in particular, the\nmagnetization on each halve. The two-component superfluid, confined in the\nmoir\\'e pattern plus a harmonic trap, was described through the time dependent\nGross-Pitaevskii coupled equations for moir\\'e lattices having $90 \\times 90$\nsites. Results showed the existence of rotation-angle-dependent structures for\nwhich the initial magnetic domain is preserved for both, square and hexagonal\nmoir\\'e patterns; above $\\theta >10^\\circ$ the initial magnetic domain is never\ndestroyed. Stationary magnetic states for a single component Bose condensate\nallowed us to identify the lattice parameter associated with moir\\'e crystals\nthat emerge for twisting angles belonging to the intervals $\\theta \\in\n\\left(0^\\circ ,30^\\circ \\right)$ and $\\theta \\in \\left(0^\\circ ,45^\\circ\n\\right)$ for hexagonal and square geometries respectively.",
        "positive": "Domain formation of modulation instability in spin-orbit-Rabi coupled\n  Gross-Pitaevskii equation with cubic-quintic interactions: The effect of two- and three-body interactions on the modulation instability\n(MI) domain formation of a spin-orbit (SO) and Rabi-coupled Bose-Einstein\ncondensate is studied within a quasi-one-dimensional model. To this aim, we\nperform numerical and analytical investigations of the associated dispersion\nrelations derived from the corresponding coupled Gross-Pitaevskii equation. The\ninterplay between the linear (SO and Rabi) couplings with the nonlinear\ncubic-quintic interactions are explored in the mixture, considering miscible\nand immiscible configurations, with a focus on the impact in the analysis of\nexperimental realizations with general binary coupled systems, in which\nnonlinear interactions can be widely varied together with linear couplings."
    },
    {
        "anchor": "Creating quantum many-body scars through topological pumping of a 1D\n  dipolar gas: Quantum many-body scars, long-lived excited states of correlated quantum\nchaotic systems that evade thermalization, are of great fundamental and\ntechnological interest. We create novel scar states in a bosonic 1D quantum gas\nof dysprosium by stabilizing a super-Tonks-Girardeau gas against collapse and\nthermalization with repulsive long-range dipolar interactions. Stiffness and\nenergy density measurements show that the system is dynamically stable\nregardless of contact interaction strength. This enables us to cycle contact\ninteractions from weakly to strongly repulsive, then strongly attractive, and\nfinally weakly attractive. We show that this cycle is an energy-space\ntopological pump (due to a quantum holonomy). Iterating this cycle offers an\nunexplored topological pumping method to create a hierarchy of quantum\nmany-body scar states.",
        "positive": "From Few to Many: Observing the Formation of a Fermi Sea One Atom at a\n  Time: Knowing when a physical system has reached sufficient size for its\nmacroscopic properties to be well described by many-body theory is difficult.\nWe investigate the crossover from few to many-body physics by studying quasi\none-dimensional systems of ultracold atoms consisting of a single impurity\ninteracting with an increasing number of identical fermions. We measure the\ninteraction energy of such a system as a function of the number of majority\natoms for different strengths of the interparticle interaction. As we increase\nthe number of majority atoms one by one we observe the fast convergence of the\nnormalized interaction energy towards a many-body limit calculated for a single\nimpurity immersed in a Fermi sea of majority particles."
    },
    {
        "anchor": "Confinement-Induced Resonance with Weak Background Interaction: We studied the scattering problem of two distinguishable atoms with unequal\nmass, where one atom (atom $\\alpha$) is trapped in a quasi-one-dimensional\n(quasi-1D) tube and the other one (atom $\\beta$) is localized by a 3D harmonic\ntrap. We show that in such a system if atom $\\alpha$ is much heavier than\n$\\beta$, confinement-induced resonance (CIR) can appear when the 3D $s$-wave\nscattering length $a_s$ of these two atoms is much smaller than the\ncharacteristic lengths (CLs) of the confinements, for either $a_s>0$ or\n$a_s<0$. This is quite different from the usual CIRs which occurs only when\n$a_s$ is comparable with the CL of confinement. Moreover, the CIRs we find are\nbroad enough that can serve as a tool for the control of effective inter-atomic\ninteraction. We further show the mechanism of these CIRs via the\nBorn-Oppenheimer approximation. Our results can be used for the realization of\nstrongly-interacting systems with ultracold atoms with weak 3D background\ninteraction (i.e., small $a_s$), e.g., the realization of ultracold gases with\nstrong spin-dependent interaction at zero magnetic fields.",
        "positive": "Topological charge pumping with subwavelength Raman lattices: Recent experiments demonstrated deeply subwavelength lattices using atoms\nwith $N$ internal states Raman-coupled with lasers of wavelength $\\lambda$. The\nresulting unit cell was $\\lambda/2N$ in extent, an $N$-fold reduction compared\nto the usual $\\lambda/2$ periodicity of an optical lattice. For resonant Raman\ncoupling, this lattice consists of $N$ independent sinusoidal potentials (with\nperiod $\\lambda/2$) displaced by $\\lambda/2N$ from each other. We show that\ndetuning from Raman resonance induces tunneling between these potentials.\nPeriodically modulating the detuning couples the $s$- and $p$-bands of the\npotentials, creating a pair of coupled subwavelength Rice--Mele chains. This\noperates as a novel topological charge pump that counter-intuitively can give\nhalf the displacement per pump cycle of each individual Rice--Mele chain\nseparately. We analytically describe this behavior in terms of infinite-system\nChern numbers, and numerically identify the associated finite-system edge\nstates."
    },
    {
        "anchor": "Linear response study of collisionless spin drag: In this work we are concerned with the understanding of the collisionless\ndrag or entrainment between two superfluids, also called Andreev-Bashkin\neffect, in terms of current response functions. The drag density is shown to be\nproportional to the cross transverse current-current response function, playing\nthe role of a normal component for the single species superfluid density. We\ncan in this way link the existence of finite entrainment with the exhaustion of\nthe energy-weighted sum rule in the spin channel. The formalism is then used to\nreproduce some known results for a weakly interacting Bose-Bose mixture.\nFinally we include the drag effect to determine the beyond mean-field\ncorrection on the speed of sound and on the spin dipole excitations for a\nhomogeneous and trapped gas, respectively.",
        "positive": "Non-equilibrium phases of Fermi gas inside a cavity with imbalanced\n  pumping: In this work, we investigate the non-equilibrium dynamics of one-dimensional\nspinless fermions loaded in a cavity with imbalanced pumping lasers. Our study\nis motivated by previous work on a similar setup using bosons, and we explore\nthe unique properties of fermionic systems in this context. By considering the\nimbalance in the pumping, we find that the system exhibits multiple\nsuperradiant steady phases and an unstable phase. Furthermore, by making use of\nthe hysteresis structure of superradiant phases, we propose a unidirectional\ntopological pumping. Unlike the usual topological pumping in which the driving\nprotocol breaks time reversal symmetry, the driving protocol can be time\nreversal invariant in our proposal."
    },
    {
        "anchor": "Antiferromagnetism with Ultracold Atoms: We use ultracold spin--1/2 atomic fermions ($^6$Li) to realize the Hubbard\nmodel on a three-dimensional (3D) optical lattice. At relatively high\ntemperatures and at densities near half-filling, we show that the gas forms a\nMott insulator with unordered spins. To observe antiferromagnetic order that is\npredicted to occur at lower temperatures, we developed the compensated optical\nlattice method to evaporatively cool atoms in the lattice. This cooling has\nenabled the detection of short-range magnetic order by spin-sensitive Bragg\nscattering of light.",
        "positive": "Competition between pairing and ferromagnetic instabilities in ultracold\n  Fermi gases near Feshbach resonances: We study the quench dynamics of a two-component ultracold Fermi gas from the\nweak into the strong interaction regime, where the short time dynamics are\ngoverned by the exponential growth rate of unstable collective modes. We obtain\nan effective interaction that takes into account both Pauli blocking and the\nenergy dependence of the scattering amplitude near a Feshbach resonance. Using\nthis interaction we analyze the competing instabilities towards Stoner\nferromagnetism and pairing."
    },
    {
        "anchor": "Gradient corrections to the local density approximation for trapped\n  superfluid Fermi gases: Two species superfluid Fermi gas is investigated on the BCS side up to the\nFeshbach resonance. Using the Greens's function technique gradient corrections\nare calculated to the generalized Thomas-Fermi theory including Cooper pairing.\nTheir relative magnitude is found to be measured by the small parameter\n$(d/R_{TF})^4$, where $d$ is the oscillator length of the trap potential and\n$R_{TF}$ is the radial extension of the density $n$ in the Thomas-Fermi\napproximation. In particular at the Feshbach resonance the universal %constant\n$A_{TF}$ has the %correction in the center $A=A_{TF}+A_2(d/R_{TF})^4+\\...$\ncorrections to the local density approximation are calculated and a universal\nprefactor $\\kappa_W=7/27$ is derived for the von Weizs\\\"acker type correction\n$\\kappa_W(\\hbar^2/2m)(\\nabla^2 n^{1/2}/n^{1/2})$.",
        "positive": "Quantum Quench of the \"Speed of Light\": Quantum Dynamical Universality\n  Classes and Short-time Universal Behavior: A long-lived prethermal state may emerge upon a sudden quench of a quantum\nsystem. In this paper, we study a quantum quench of an initial {\\it critical}\nstate, and show that the resulting prethermal state exhibits a genuinely\nquantum and dynamical universal behavior. Specifically, we consider a scenario\nwhere the \"speed of light\" characterizing the propagation of local\nperturbations is suddenly quenched at criticality. We also find that the system\napproaches the prethermal state in a universal way described by a new exponent\nthat characterizes a kind of quantum aging."
    },
    {
        "anchor": "Thermodynamics and structural transition of binary atomic Bose-Fermi\n  mixtures in box or harmonic potentials: A path-integral study: Experimental realizations of a variety of atomic binary Bose-Fermi mixtures\nhave brought opportunities for studying composite quantum systems with\ndifferent spin-statistics. The binary atomic mixtures can exhibit a structural\ntransition from a mixture into phase separation as the boson-fermion\ninteraction increases. By using a path-integral formalism to evaluate the grand\npartition function and thermodynamic grand potential, we obtain the effective\npotential of binary Bose-Fermi mixtures. Thermodynamic quantities in a broad\nrange of temperatures and interactions are also derived. The structural\ntransition can be identified as a loop of the effective potential curve, and\nthe volume fraction of phase separation can be determined by the lever rule.\nFor $^6$Li-$^7$Li and $^6$Li-$^{41}$K mixtures, we present the phase diagrams\nof the mixtures in a box potential at zero and finite temperatures. Due to the\nflexible densities of atomic gases, the construction of phase separation is\nmore complicated when compared to conventional liquid or solid mixtures where\nthe individual densities are fixed. For harmonically trapped mixtures, we use\nthe local density approximation to map out the finite-temperature density\nprofiles and present typical trap structures, including the mixture, partially\nseparated phases, and fully separated phases.",
        "positive": "Superfluidity vs prethermalisation in a nonlinear Floquet system: We show that superfluidity can be used to prevent thermalisation in a\nnonlinear Floquet system. Generically, periodic driving boils an interacting\nsystem to a featureless infinite temperature state. Fast driving is a known\nstrategy to postpone Floquet heating with a large but always finite boiling\ntime. In contrast, using a nonlinear periodically-driven system on a lattice,\nwe show the existence of a continuous class of initial states which do not\nthermalise at all. This absence of thermalisation is associated to the\nexistence and persistence of a stable superflow motion."
    },
    {
        "anchor": "Simulating frustrated magnetism with spinor Bose gases: Although there is a broad consensus on the fact that critical behavior in\nstacked triangular Heisenberg antiferromagnets --an example of frustrated\nmagnets with competing interactions-- is described by a Landau-Ginzburg-Wilson\nHamiltonian with O(3)$\\times$O(2) symmetry, the nature of the phase transition\nin three dimensions is still debated. We show that spin-one Bose gases provide\nus with a simulator of the O(3)$\\times$O(2) model. Using a\nrenormalization-group approach, we argue that the transition is weakly first\norder and shows pseudoscaling behavior, and give estimates of the\npseudocritical exponent $\\nu$ in $^{87}$Rb, $^{41}$K and $^7$Li atom gases\nwhich can be tested experimentally.",
        "positive": "Stochastic Projected Gross-Pitaevskii equation for spinor and\n  multi-component condensates: A stochastic Gross-Pitaevskii equation is derived for partially condensed\nBose gas systems subject to binary contact interactions. The theory we present\nprovides a classical-field theory suitable for describing dissipative dynamics\nand phase transitions of spinor and multi-component Bose gas systems comprised\nof an arbitrary number of distinct interacting Bose fields. A new class of\ndissipative processes involving distinguishable particle interchange between\ncoherent and incoherent regions of phase-space is identified. The formalism and\nits implications are illustrated for two-component mixtures and spin-1\nBose-Einstein condensates. For systems comprised of atoms of equal mass, with\nthermal reservoirs that are close to equilibrium, the dissipation rates of the\ntheory are reduced to analytical expressions that may be readily evaluated. The\nunified treatment of binary contact interactions presented here provides a\ntheory with broad relevance for quasi-equilibrium and far-from-equilibrium\nBose-Einstein condensates."
    },
    {
        "anchor": "Trapping Effects in Quantum Atomic Arrays: Quantum emitters, particularly atomic arrays with subwavelength lattice\nconstant, have been proposed to be an ideal platform for studying the interplay\nbetween photons and electric dipoles. In this work, motivated by the recent\nexperiment [1], we develop a microscopic quantum treatment using annihilation\nand creation operator of atoms in deep optical lattices. Using a diagrammatic\napproach on the Keldysh contour, we derive the cooperative scattering of the\nlight and obtain the general formula for the $S$ matrix. We apply our method to\nstudy the trapping effect, which is beyond previous treatment with spin\noperators. If the optical lattices are formed by light fields with magical\nwavelength, the result matches previous results using spin operators. When\nthere is a mismatch between the trapping potentials for atoms in the ground\nstate and the excited state, atomic mirrors become imperfect, with multiple\nresonances in the optical response. We further study the effect of recoil for\nlarge but finite trapping frequency. Our results are consistent with existing\nexperiments.",
        "positive": "Robust sub-shot-noise measurement via Rabi-Josephson oscillations in\n  bimodal Bose-Einstein condensates: Mach-Zehnder atom interferometry requires hold-time phase-squeezing to attain\nreadout accuracy below the standard quantum limit. This increases its\nsensitivity to phase-diffusion, restoring shot-noise scaling of the optimal\nsignal-to-noise ratio, $s_o$, in the presence of interactions. The\ncontradiction between the preparations required for readout accuracy and\nrobustness to interactions, is removed by monitoring Rabi-Josephson\noscillations instead of relative-phase oscillations during signal acquisition.\nOptimizing $s_o$ with a Gaussian squeezed input, we find that hold-time number\nsqueezing satisfies both demands and that sub-shot-noise scaling is retained\neven for strong interactions."
    },
    {
        "anchor": "Using superlattice potentials to probe long-range magnetic correlations\n  in optical lattices: In Pedersen et al. (2011) we proposed a method to utilize a temporally\ndependent superlattice potential to mediate spin-selective transport, and\nthereby probe long and short range magnetic correlations in optical lattices.\nSpecifically this can be used for detecting antiferromagnetic ordering in\nrepulsive fermionic optical lattice systems, but more generally it can serve as\na means of directly probing correlations among the atoms by measuring the mean\nvalue of an observable, the number of double occupied sites. Here, we provide a\ndetailed investigation of the physical processes which limit the effectiveness\nof this \"conveyer belt method\". Furthermore we propose a simple ways to improve\nthe procedure, resulting in an essentially perfect (error-free) probing of the\nmagnetic correlations. These results shows that suitably constructed\nsuperlattices constitute a promising way of manipulating atoms of different\nspin species as well as probing their interactions.",
        "positive": "Hydrodynamic relaxation of spin helices: Motivated by recent cold atom experiments, we study the relaxation of spin\nhelices in quantum XXZ spin chains. The experimentally observed relaxation of\nspin helices follows scaling laws that are qualitatively different from\nlinear-response transport. We construct a theory of the relaxation of helices,\ncombining generalized hydrodynamics (GHD) with diffusive corrections and the\nlocal density approximation. Although helices are far from local equilibrium\n(so GHD need not apply a priori), our theory reproduces the experimentally\nobserved relaxational dynamics of helices. In particular, our theory explains\nthe existence of temporal regimes with apparent anomalous diffusion, as well as\nthe asymmetry between positive and negative anisotropy regimes."
    },
    {
        "anchor": "Propagation and amplification dynamics of 1D polariton condensates: The dynamics of propagating polariton condensates in one-dimensional\nmicrocavities is investigated through time resolved experiments. We find a\nstrong increase in the condensate intensity when it travels through the\nnon-resonantly excited area. This amplification is shown to come from bosonic\nstimulated relaxation of reservoir excitons into the polariton condensate,\nallowing for the repopulation of the condensate through non-resonant pumping.\nThus, we experimentally demonstrate a polariton amplifier with a large band\nwidth, opening the way towards the transport of polaritons with high densities\nover macroscopic distances.",
        "positive": "New perspectives on superfluidity in resonantly--driven polariton fluids: In this paper we discuss, within the Gross--Pitaevskii framework,\nsuperfluidity, soliton nucleation, and instabilities in a non-equilibrium\npolariton fluid injected by a spatially localized and continuous-wave coherent\npump and flowing against a defect located outside the pump spot. In contrast to\nequilibrium condensates, the steady-state solutions of the driven-dissipative\nequations in this specific geometry hardly show a clean superfluid flow around\nthe defect and rather feature a crossover from shallow to deep soliton-like\nperturbation. This is explained in terms of the properties of one-dimensional\nflows, in particular their weak dependence on the pump parameters and their\nrapid transition to a super-sonic regime under the effect of the quantum\npressure; such a highly nonlinear behaviour calls for quantitative experimental\ntests of the underlying Gross--Pitaevskii equation. The role of disorder and of\na incoherent reservoir in inducing non-stationary behaviours with moving\nvortices is also highlighted."
    },
    {
        "anchor": "Effects of dipole-dipole interaction between cigar-shaped BECs of cold\n  alkali atoms: Towards inverse-squared interactions: We show that the dipole-dipole coupling between Wannier modes in cigar-shaped\nBose-Einstein condensates (BECs) is significantly enhanced while the\nshort-range coupling strongly suppressed. As a result, the dipole-dipole\ninteraction can become the dominant interaction between ultracold alkali Bose\natoms. In the long length limit of a cigar-shaped BEC, the resulting effective\none-dimensional models possess an effective inverse squared interacting\npotential, the Calogero-Sutherland potential, which plays a fundamental role in\nmany fields of contemporary physics; but its direct experimental realization\nhas been a challenge for a long time. We propose to realize the\nCalogero-Sutherland model in ultracold alkali Bose atoms and study the effects\nof the dipole-dipole interaction.",
        "positive": "Effective field theory of a vortex lattice in a bosonic superfluid: Using boson-vortex duality, we formulate a low-energy effective theory of a\ntwo-dimensional vortex lattice in a bosonic Galilean-invariant compressible\nsuperfluid. The excitation spectrum contains a gapped Kohn mode and an\nelliptically polarized Tkachenko mode that has quadratic dispersion relation at\nlow momenta. External rotation breaks parity and time-reversal symmetries and\ngives rise to Hall responses. We extract the particle number current and stress\ntensor linear responses and investigate the relations between them that follow\nfrom Galilean symmetry. We argue that elementary particles and vortices do not\ncouple to the spin connection which suggests that the Hall viscosity at zero\nfrequency and momentum vanishes in a vortex lattice."
    },
    {
        "anchor": "Model for two-body collisions between ultracold dipolar molecules around\n  a F\u00f6rster resonance in an electric field: We propose a one-channel, simple model to describe the dynamics of ultracold\ndipolar molecules around a F\\\"orster resonance. Slightly above a specific\nelectric field, a collisional shielding can take place, suppressing the\nmolecular losses in a gas. The overall description of the quantum physical\nmechanism comes back to the dynamics on a unique energy surface, which depends\non the relative distance and angular approach of the molecules. This surface\nenables to interpret how the dipole moments of the molecules are induced and\ninterlocked by the electric field and the dipole-dipole interaction during the\nprocess, especially when the shielding is triggered. Averaging the relative\nangular motion over a unique partial wave (the lowest one when the ultracold\nregime is reached), the model reproduces well the behaviour of the rate\ncoefficients observed experimentally and predicted theoretically [Matsuda et\nal., Science 370, 1324 (2020); Li et al., Nat. Phys. 17, 1144 (2021)]. This\neconomic model encapsulates the main physics of the quantum process. Therefore,\nit can be used as an alternative to a full quantum dynamical treatment and is\npromising for future studies of collisions involving more bodies.",
        "positive": "Compressibility and entropy of cold fermions in one dimensional optical\n  lattices: We calculate several thermodynamic quantities for repulsively interacting\none-dimensional fermions.We solve the Hubbard model at both zero and finite\ntemperatures using the Bethe-ansatz method. For arbitrary values of the\nchemical potential, we calculate the particle number density, the double\noccupancy, various compressibilities, and the entropy as a function of\ntemperature and interaction. We find that these thermodynamic quantities show a\ncharacteristic behavior so that measurements of these quantities can be used as\na detection of temperature, the metal-insulator transition, and metallic and\ninsulating phases in the trap environment. Further, we discuss an experimental\nscheme to extract these thermodynamic quantities from the column density\nprofiles. The entropy and the compressibility of the entire trapped atomic\ncloud also reveal characteristic features indicating whether insulating and/or\nmetallic phases coexist in the trap."
    },
    {
        "anchor": "Chaotic delocalization of two interacting particles in the classical\n  Harper model: We study the problem of two interacting particles in the classical Harper\nmodel in the regime when one-particle motion is absolutely bounded inside one\ncell of periodic potential. The interaction between particles breaks\nintegrability of classical motion leading to emergence of Hamiltonian dynamical\nchaos. At moderate interactions and certain energies above the mobility edge\nthis chaos leads to a chaotic propulsion of two particles with their diffusive\nspreading over the whole space both in one and two dimensions. At the same time\nthe distance between particles remains bounded by one or two periodic cells\ndemonstrating appearance of new composite quasi-particles called chaons. The\neffect of chaotic delocalization of chaons is shown to be rather general being\npresent for Coulomb and short range interactions. It is argued that such\ndelocalized chaons can be observed in experiments with cold atoms and ions in\noptical lattices.",
        "positive": "Effect of transverse confinement on a quasi-one dimensional dipolar Bose\n  gas: We study a gas of bosonic dipolar atoms in the presence of a transverse\nharmonic trapping potential by using an improved variational Bethe ansatz,\nwhich includes the transverse width of the atomic cloud as a variational\nparameter. Our calculations show that the system behavior evolves from\nquasi-one dimensional to a strictly one-dimensional one by changing the\natom-atom interaction, or the axial density, or the frequency of the transverse\nconfinement. Quite remarkably, in the droplet phase induced by the attractive\ndipolar interaction the system becomes sub-one dimensional when the transverse\nwidth is smaller than the characteristic length of the transverse harmonic\nconfinement."
    },
    {
        "anchor": "Three-component Ultracold Fermi Gases with Spin-Orbit Coupling: We investigate the pairing physics in a three-component Fermi-Fermi mixture,\nwhere a few impurities are immersed in a non-interacting spin-$\\frac{1}{2}$\nFermi gas with synthetic spin-orbit coupling (SOC), and interact attractively\nwith one spin species in the Fermi gas. Due to the interplay of SOC and\nspin-selective interaction, the molecular state intrinsically acquires a\nnon-zero center-of-mass momentum, which results in a new type of Fulde-Ferrell\n(FF) pairing in spin-orbit coupled Fermi systems. The existence of the Fermi\nsea can also lead to the competition between FF-like molecular states with\ndifferent center-of-mass momenta, which corresponds to a first-order transition\nbetween FF phases in the thermodynamic limit. As the interaction strength is\ntuned, a polaron-molecule transition occurs in the highly imbalanced system,\nwhere the boundary varies non-monotonically with SOC parameters and gives rise\nto the reentrance of polaron states. The rich physics in this system can be\nprobed using existing experimental techniques.",
        "positive": "Dynamics of exciton-polaritons in a Josephson double dimer: We study the dynamics of exciton-polaritons in a double-well configuration.\nThe system consists of two weakly coupled Bose-Josephson junctions, each\ncorresponding to a different circular polarization of the polaritons, forming a\n{\\it Josephson double dimer}. We show that the Josephson oscillation between\nthe wells is strongly coupled to the polarization rotation and that\nconsequently Josephson excitation is periodically exchanged between the two\npolarizations. Linearized analysis agrees well with numerical simulations using\ntypical experimental parameters."
    },
    {
        "anchor": "Intra- and interband excitations induced residue decay of the Bose\n  polaron in a one-dimensional double-well: We investigate the polaronic properties of a single impurity immersed in a\nweakly interacting bosonic environment confined within a one-dimensional\ndouble-well potential using an exact diagonalization approach. We find that an\nincrease of the impurity-bath coupling results in a vanishing residue,\nsignifying the occurrence of the polaron orthogonality catastrophe. Asymptotic\nconfigurations of the systems' ground state wave function in the strongly\ninteracting regime are obtained by means of a Schmidt decomposition, which in\nturn accounts for the observed orthogonality catastrophe of the polaron. We\nexemplify that depending on the repulsion of the Bose gas, three distinct\nresidue behaviors appear with respect to the impurity-bath coupling. These\nresidue regimes are characterized by two critical values of the bosonic\nrepulsion and originate from the interplay between the intra- and the interband\nexcitations of the impurity. Moreover, they can be clearly distinguished in the\ncorresponding species reduced density matrices with the latter revealing a\nphase separation on either the one- or the two-body level. The impact of the\ninterspecies mass-imbalance on the impurity's excitation processes is\nappreciated yielding an interaction shift of the residue regions. Our results\nexplicate the interplay of intra- and interband excitation processes for the\npolaron generation in multiwell traps and for designing specific polaron\nentangled states motivating their exposure in current experiments.",
        "positive": "The universality of the Efimov three-body parameter: In this paper we discuss the recent discovery of the universality of the\nthree-body parameter (3BP) from Efimov physics. This new result was identified\nby recent experimental observations in ultracold quantum gases where the value\nof the s-wave scattering length, $a=a_-$, at which the first Efimov resonance\nis created was found to be nearly the same for a range of atomic species --- if\nscaled as $a_-/r_{\\rm vdW}$, where $r_{\\rm vdW}$ is the van der Waals length.\nHere, we discuss some of the physical principles related to these observations\nthat emerge from solving the three-body problem with van der Waals interactions\nin the hyperspherical formalism. We also demonstrate the strong three-body\nmultichannel nature of the problem and the importance of properly accounting\nfor nonadiabatic effects."
    },
    {
        "anchor": "Pseudogap phenomena in ultracold atomic Fermi gases: The pairing and superfluid phenomena in a two-component ultracold atomic\nFermi gas is an analogue of Cooper pairing and superconductivity in an electron\nsystem, in particular, the high $T_c$ superconductors. Owing to the various\ntunable parameters that have been made accessible experimentally in recent\nyears, atomic Fermi gases can be explored as a prototype or quantum simulator\nof superconductors. It is hoped that, utilizing such an analogy, the study of\natomic Fermi gases may shed light to the mysteries of high $T_c$\nsuperconductivity. One obstacle to the ultimate understanding of high $T_c$\nsuperconductivity, from day one of its discovery, is the anomalous yet\nwidespread pseudogap phenomena, for which a consensus is yet to be reached\nwithin the physics community, after over 27 years of intensive research\nefforts. In this article, we shall review the progress in the study of\npseudogap phenomena in atomic Fermi gases in terms of both theoretical\nunderstanding and experimental observations. We show that there is strong,\nunambiguous evidence for the existence of a pseudogap in strongly interacting\nFermi gases. In this context, we shall present a pairing fluctuation theory of\nthe pseudogap physics and show that it is indeed a strong candidate theory for\nhigh $T_c$ superconductivity.",
        "positive": "Gap solitons and Bloch waves of interacting bosons in one-dimensional\n  optical lattices: From the weak to the strong interaction limits: We study the gap solitons and nonlinear Bloch waves of interacting bosons in\none-dimensional optical lattices, taking into account the interaction from the\nweak to the strong limits. It is shown that composition relation between the\ngap solitons and nonlinear Bloch waves exists for the whole span of the\ninteraction strength. The linear stability analysis indicates that the gap\nsolitons are stable when their energies are near the bottom of the linear Bloch\nband gap. By increasing the interaction strength, the stable gap solitons can\nturn into unstable. It is argued that the stable gap solitons can easily be\nformed in a weakly interacting system with energies near the bottoms of the\nlower-level linear Bloch band gaps."
    },
    {
        "anchor": "Elementary modes of excitation caused by the quadratic Zeeman term and\n  the sensitivity of spin structures of small spin-2 condensates against the\n  magnetic field: The response of spin-2 small condensates to an external magnetic field $B$ is\nstudied. The parameters of the interaction are considered as variable. The\nemphasis is placed on clarifying the modes of excitation caused by the\nquadratic Zeeman term. The theoretical method used is beyond the mean field\ntheory. A set of eigenstates with the $U(5)\\supset SO(5)\\supset SO(3)$ symmetry\nis introduced to facilitate the analysis. To obtain a quantitative evaluation\non the response, the fidelity susceptibility and the $B$ -dependent average\npopulations of spin-components have been calculated. Mostly the particle number\nN=30 is assumed. The effect with a larger or smaller $N$ is also considered. It\nwas found that the sensitivity of the response depends strongly both on the\ninteraction and on the inherent symmetry.",
        "positive": "Coherent light scattering from a two-dimensional Mott insulator: We experimentally demonstrate coherent light scattering from an atomic Mott\ninsulator in a two-dimensional lattice. The far-field diffraction pattern of\nsmall clouds of a few hundred atoms was imaged while simultaneously laser\ncooling the atoms with the probe beams. We describe the position of the\ndiffraction peaks and the scaling of the peak parameters by a simple analytic\nmodel. In contrast to Bragg scattering, scattering from a single plane yields\ndiffraction peaks for any incidence angle. We demonstrate the feasibility of\ndetecting spin correlations via light scattering by artificially creating a\none-dimensional antiferromagnetic order as a density wave and observing the\nappearance of additional diffraction peaks."
    },
    {
        "anchor": "Six-dimensional time-space crystalline structures: Time crystalline structures are characterized by regularity that\nsingle-particle or many-body systems manifest in the time domain, closely\nresembling the spatial regularity of ordinary space crystals. Here we show that\ntime and space crystalline structures can be combined together and even\nsix-dimensional time-space lattices can be realized. As an example, we\ndemonstrate that such time-space crystalline structures can reveal the\nsix-dimensional quantum Hall effect quantified by the third Chern number.",
        "positive": "Orbital superfluidity in the $P$-band of a bipartite optical square\n  lattice: The successful emulation of the Hubbard model in optical lattices has\nstimulated world wide efforts to extend their scope to also capture more\ncomplex, incompletely understood scenarios of many-body physics. Unfortunately,\nfor bosons, Feynmans fundamental \"no-node\" theorem under very general\ncircumstances predicts a positive definite ground state wave function with\nlimited relevance for many-body systems of interest. A promising way around\nFeynmans statement is to consider higher bands in optical lattices with more\nthan one dimension, where the orbital degree of freedom with its intrinsic\nanisotropy due to multiple orbital orientations gives rise to a structural\ndiversity, highly relevant, for example, in the area of strongly correlated\nelectronic matter. In homogeneous two-dimensional optical lattices, lifetimes\nof excited bands on the order of a hundred milliseconds are possible but the\ntunneling dynamics appears not to support cross-dimensional coherence. Here we\nreport the first observation of a superfluid in the $P$-band of a bipartite\noptical square lattice with $S$-orbits and $P$-orbits arranged in a\nchequerboard pattern. This permits us to establish full cross-dimensional\ncoherence with a life-time of several ten milliseconds. Depending on a small\nadjustable anisotropy of the lattice, we can realize real-valued striped\nsuperfluid order parameters with different orientations $P_x \\pm P_y$ or a\ncomplex-valued $P_x \\pm i P_y$ order parameter, which breaks time reversal\nsymmetry and resembles the $\\pi$-flux model proposed in the context of high\ntemperature superconductors. Our experiment opens up the realms of orbital\nsuperfluids to investigations with optical lattice models."
    },
    {
        "anchor": "Bose polaron in spherical trap potentials: Spatial structure and quantum\n  depletion: We investigate how the presence of a localized impurity in a Bose-Einstein\ncondensate of trapped cold atoms that interact with each other weakly and\nrepulsively affects the profile of the condensed and excited components at zero\ntemperature. By solving the Gross-Pitaevskii and Bogoliubov-de Gennes\nequations, we find that an impurity-boson contact attraction (repulsion) causes\nboth components to change in spatial structure in such a way as to be enhanced\n(suppressed) around the impurity, while slightly declining (growing) in a far\nregion from the impurity. Such behavior of the quantum depletion of the\ncondensate can be understood by decomposing the impurity-induced change in the\nprofile of the excited component with respect to the radial and azimuthal\nquantum number. A significant role of the centrifugal potential and the \"hole\"\nexcitation level is thus clarified.",
        "positive": "Rayleigh surface wave interaction with 2D exciton Bose-Einstein\n  condensate: We describe the interaction of the Rayleigh surface acoustic wave (SAW)\ntraveling on the semiconductor substrate and interacting with excitonic gas in\na double quantum well located on the substrate surface. We study the SAW\nattenuation and its velocity renormalization due to coupling with excitons.\nBoth the deformation potential and piezoelectric mechanisms of the SAW-exciton\ninteraction are considered. We focus our attention on the frequency and\nexcitonic density dependencies of the SAW absorption coefficient and velocity\nrenormalization at temperatures both above and well below the critical\ntemperature of Bose-Einstein condensation of excitonic gas. We demonstrate that\nthe SAW attenuation and velocity renormalization are strongly different below\nand above the critical temperature."
    },
    {
        "anchor": "Conformal-invariance of 2D quantum turbulence in an exciton-polariton\n  fluid of light: The similarities of quantum turbulence with classical hydrodynamics allow\nquantum fluids to provide essential models of their classical analogue, paving\nthe way for fundamental advances in physics and technology. Recently,\nexperiments on 2D quantum turbulence observed the clustering of same-sign\nvortices in strong analogy with the inverse energy cascade of classical fluids.\nHowever, self-similarity of the turbulent flow, a fundamental concept in the\nstudy of classical turbulence, has so far remained largely unexplored in\nquantum systems. Here, thanks to the unique features of exciton-polaritons, we\nmeasure the scale invariance of velocity circulations and show that the cascade\nprocess follows the universal scaling of critical phenomena in 2D. We\ndemonstrate this behaviour from the statistical analysis of the experimentally\nmeasured incompressible velocity field and the microscopic imaging of the\nquantum fluid. These results can find wide application in both quantum and\nclassical 2D turbulence.",
        "positive": "Bosonic fractional quantum Hall states in driven optical lattices: Strong synthetic magnetic fields have been successfully implemented in\nperiodically driven optical lattices. However, the interplay of the driving and\ninteractions introduces detrimental heating, and for this reason it is still\nchallenging to reach a fractional quantum Hall state in cold-atom setup. By\nperforming a numerical study, we investigate stability of a bosonic Laughlin\nstate in a small atomic sample exposed to driving. We identify an optimal\nregime of microscopic parameters, in particular interaction strength $U$ and\nthe driving frequency $\\omega$, such that the stroboscopic dynamics supports\nthe basic $\\nu = 1/2$ Laughlin state. Moreover, we explore slow ramping of a\ndriving term and show that the considered protocol allows for the preparation\nof the Laughlin state on experimentally realistic time scales."
    },
    {
        "anchor": "Interaction-controlled impurity transport in trapped mixtures of\n  ultracold bosons: We explore the dynamical transport of an impurity between different embedding\nmajority species which are spatially separated in a double well. The transfer\nand storage of the impurity is triggered by dynamically changing the\ninteraction strengths between the impurity and the two majority species. We\nfind a simple but efficient protocol consisting of linear ramps of\nmajority-impurity interactions at designated times to pin or unpin the\nimpurity. Our study of this highly imbalanced few-body triple mixture is\nconducted with the multi-layer multi-configuration time-dependent Hartree\nmethod for atomic mixtures which accounts for all interaction-induced\ncorrelations. We analyze the dynamics in terms of single-particle densities,\nentanglement growth and provide an effective potential description involving\nmean-fields of the interacting components. The majority components remain\nself-trapped in their individual wells at all times, which is a crucial element\nfor the effectiveness of our protocol. During storage times each component\nperforms low-amplitude dipole oscillations in a single well. Unexpectedly, the\ninter-species correlations possess a stabilizing impact on the transport and\nstorage properties of the impurity particle.",
        "positive": "Floquet Engineering of Haldane Chern Insulators and Chiral bosonic phase\n  transitions: The realization of synthetic gauge fields has attracted a lot of attention\nrecently in relation with periodically driven systems and the Floquet theory.\nIn ultra-cold atom systems in optical lattices and photonic networks, this\nallows to simulate exotic phases of matter such as quantum Hall phases,\nanomalous quantum Hall phases and analogs of topological insulators. In this\npaper, we apply the Floquet theory to engineer anisotropic Haldane models on\nthe honeycomb lattice and two-leg ladder systems. We show that these\nanisotropic Haldane models still possess a topologically non-trivial band\nstructure associated with chiral edge modes (without the presence of a net unit\nflux in a unit cell), then referring to the quantum anomalous Hall effect.\nFocusing on (interacting) boson systems in s-wave bands of the lattice, we show\nhow to engineer through the Floquet theory, a quantum phase transition between\na uniform superfluid and a BEC (Bose-Einstein Condensate) analog of FFLO\n(Fulde-Ferrell-Larkin-Ovchinnikov) states, where bosons condense at non-zero\nwave-vectors. We perform a Ginzburg-Landau analysis of the quantum phase\ntransition on the graphene lattice, and compute observables such as chiral\ncurrents and the momentum distribution. The results are supported by exact\ndiagonalization calculations and compared with those of the isotropic\nsituation. The validity of high-frequency expansion in the Floquet theory is\nalso tested using time-dependent simulations for various parameters of the\nmodel. Last, we show that the anisotropic choice for the effective vector\npotential allows a bosonization approach in equivalent ladder (strip)\ngeometries."
    },
    {
        "anchor": "Singular mean-field states: A brief review of recent results: This article provides a focused review of recent findings which demonstrate,\nin some cases quite counter-intuitively, the existence of bound states with a\nsingularity of the density pattern at the center, while the states are\nphysically meaningful because their total norm converges. One model of this\ntype is based on the 2D Gross-Pitaevskii equation (GPE) which combines the\nattractive potential ~ 1/r^2 and the quartic self-repulsive nonlinearity,\ninduced by the Lee-Huang-Yang effect (quantum fluctuations around the\nmean-field state). The GPE demonstrates suppression of the 2D quantum collapse,\ndriven by the attractive potential, and emergence of a stable ground state\n(GS), whose density features an integrable singularity ~1/r^{4/3} at r --> 0.\nModes with embedded angular momentum exist too, and they have their stability\nregions. A counter-intuitive peculiarity of the model is that the GS exists\neven if the sign of the potential is reversed from attraction to repulsion,\nprovided that its strength is small enough. This peculiarity finds a relevant\nexplanation. The other model outlined in the review includes 1D, 2D, and 3D\nGPEs, with the septimal (seventh-order), quintic, and cubic self-repulsive\nterms, respectively. These equations give rise to stable singular solitons,\nwhich represent the GS for each dimension D, with the density singularity\n~1/r^{2/(4-D). Such states may be considered as a result of screening of a\n\"bare\" delta-functional attractive potential by the respective nonlinearity.",
        "positive": "Dirac fields in curved spacetime as Fermi-Hubbard model with non unitary\n  tunnelings: In this article we show that a Dirac Hamiltonian in a curved background\nspacetime can be interpreted, when discretized, as a tight binding\nFermi-Hubbard model with non unitary tunnelings. We find the form of the\nnonunitary tunneling matrices in terms of the metric tensor. The main\nmotivation behind this exercise is the feasibility of such Hamiltonians by\nmeans of laser assisted tunnelings in cold atomic experiments. The mapping thus\nprovide a physical interpretation of such Hamiltonians. We demonstrate the use\nof the mapping on the example of time dependent metric in 2+1 dimensions.\nStudying the spin dynamics, we find qualitative agreement with known\ntheoretical predictions, namely the particle pair creation in expanding\nuniverse."
    },
    {
        "anchor": "Observation of universal Kibble-Zurek scaling in an atomic Fermi\n  superfluid: Half a century ago, T. Kibble proposed a scenario for topological defect\nformation from symmetry breaking during the expansion of the early Universe. W.\nZurek later crystallized the concept to superfluid helium, predicting a\npower-law relation between the number of quantum vortices and the rate at which\nthe system passes through the lambda transition. Here, we report the\nobservation of Kibble-Zurek scaling in a homogeneous, strongly interacting\nFermi gas undergoing a superfluid phase transition. We investigate the\nsuperfluid transition using two distinct control parameters: temperature and\ninteraction strength. The microscopic physics of condensate formation is\nmarkedly different for the two quench parameters, signaled by their two orders\nof magnitude difference in the condensate formation timescale. However,\nregardless of the thermodynamic direction in which the system passes through a\nphase transition, the Kibble-Zurek exponent is identically observed to be about\n0.68 and shows good agreement with theoretical predictions that describe\nsuperfluid phase transitions. This work demonstrates the gedanken experiment\nZurek proposed for liquid helium that shares the same universality class with\nstrongly interacting Fermi gases.",
        "positive": "Rotating quantum droplets confined in a harmonic potential: We investigate the rotational properties of a two-component, two-dimensional\nself-bound quantum droplet, which is confined in a harmonic potential and\ncompare them with the well-known problem of a single-component atomic gas with\ncontact interactions. For a fixed value of the trap frequency, choosing some\nrepresentative values of the atom number, we determine the lowest-energy state,\nas the angular momentum increases. For a sufficiently small number of atoms,\nthe angular momentum is carried via center-of-mass excitation. For larger\nvalues, when the angular momentum is sufficiently small, we observe vortex\nexcitation instead. Depending on the actual atom number, one or more vortices\nenter the droplet. Beyond some critical value of the angular momentum, however,\nthe droplet does not accommodate more vortices and the additional angular\nmomentum is carried via center-of-mass excitation in a \"mixed\" state. Finally,\nthe excitation spectrum is also briefly discussed."
    },
    {
        "anchor": "Quantum phases of quadrupolar Fermi gases in coupled one-dimensional\n  systems: Following the recent proposal to create quadrupolar gases [S.G. Bhongale et\nal., Phys. Rev. Lett. 110, 155301 (2013)], we investigate what quantum phases\ncan be created in these systems in one dimension. We consider a geometry of two\ncoupled one-dimensional systems, and derive the quantum phase diagram of\nultra-cold fermionic atoms interacting via quadrupole-quadrupole interaction\nwithin a Tomonaga-Luttinger-liquid framework. We map out the phase diagram as a\nfunction of the distance between the two tubes and the angle between the\ndirection of the tubes and the quadrupolar moments. The latter can be\ncontrolled by an external field. We show that there are two magic angles\n$\\theta^{c}_{B,1}$ and $\\theta^{c}_{B,2}$ between $0$ to $\\pi/2$, where the\nintratube quadrupolar interactions vanish and change signs. Adopting a\npseudo-spin language with regards to the two 1D systems, the system undergoes a\nspin-gap transition and displays a zig-zag density pattern, above\n$\\theta^{c}_{B,2}$ and below $\\theta^{c}_{B,1}$. Between the two magic angles,\nwe show that polarized triplet superfluidity and a planar spin-density wave\norder compete with each other. The latter corresponds to a bond order solid in\nhigher dimensions. We demonstrate that this order can be further stabilized by\napplying a commensurate periodic potential along the tubes.",
        "positive": "Renormalization group analysis on emergence of higher rank symmetry and\n  higher moment conservation: Higher rank symmetry and higher moment conservation have been drawn\nconsiderable attention from, e.g., subdiffusive transport to fracton\ntopological order. In this paper, we perform a one-loop renormalization group\n(RG) analysis and show how these phenomena emerge at low energies. We consider\na $d$-dimensional model of interacting bosons of d components. At\nhigher-rank-symmetric points with conserved angular moments, the $a$-th bosons\nhave kinetic energy only along the $x^a$ direction. Therefore, the symmetric\npoints look highly anisotropic and fine-tuned. By studying RG in a wide\nvicinity of the symmetric points, we find that symmetry-disallowed kinetic\nterms tend to be irrelevant within the perturbative regime, which potentially\nleads to emergent higher-rank symmetry and higher-moment conservation at the\ndeep infrared limit. While non-perturbative analysis is called for in the\nfuture, by regarding higher-rank symmetry as an emergent phenomenon, the RG\nanalysis presented in this paper holds alternative promise for realizing\nhigher-rank symmetry and higher-moment conservation in experimentally\nachievable systems."
    },
    {
        "anchor": "Stability of High-Density Two-Dimensional Excitons against a Mott\n  Transition in High Magnetic Fields Probed by Coherent Terahertz Spectroscopy: We have performed time-resolved terahertz absorption measurements on\nphotoexcited electron-hole pairs in undoped GaAs quantum wells in magnetic\nfields. We probed both unbound- and bound-carrier responses via cyclotron\nresonance and intraexciton resonance, respectively. The stability of excitons,\nmonitored as the pair density was systematically increased, was found to\ndramatically increase with increasing magnetic field. Specifically, the\n1$s$-2$p_-$ intraexciton transition at 9 T persisted up to the highest density,\nwhereas the 1$s$-2$p$ feature at 0 T was quickly replaced by a free-carrier\nDrude response. Interestingly, at 9 T, the 1$s$-2$p_-$ peak was replaced by\nfree-hole cyclotron resonance at high temperatures, indicating that 2D\nmagnetoexcitons do dissociate under thermal excitation, even though they are\nstable against a density-driven Mott transition.",
        "positive": "Thermal Ising transition in two-dimensional SU(3) Fermi lattice gases\n  with population imbalance: We focus on three-component SU(3) Fermi gases loaded into a square optical\nlattice, with population imbalance between one component and the others. At\nstrong coupling the system is described by the SU(3) Heisenberg model with an\nexternal field that couples to the population imbalance. We discuss the ground\nstate at the mean-field level and then analyze the thermal fluctuations with\nthe semi-classical Monte Carlo method. The interplay of interactions,\npopulation imbalance and thermal fluctuations gives rise to a phase transition\nlinked to the breaking of an emergent Ising symmetry, despite the absence of\nfrustration. This represents a new scenario of discrete symmetry breaking in\nlow-dimensional systems with continuous symmetries. Possible implementations\nwith cold alkaline-earth(-like) atoms are discussed."
    },
    {
        "anchor": "Quantum fluctuations on top of a $\\mathcal{PT}$-symmetric Bose-Einstein\n  Condensate: We investigate the effects of quantum fluctuations in a\nparity-time($\\mathcal{PT}$) symmetric two-species Bose-Einstein\nCondensate(BEC). It is found that the $\\mathcal{PT}$-symmetry, though preserved\nby the macroscopic condensate, can be spontaneously broken by its Bogoliubov\nquasi-particles under quantum fluctuations. The associated\n$\\mathcal{PT}$-breaking transitions in the Bogoliubov spectrum can be\nconveniently tuned by the interaction anisotropy in spin channels and the\nstrength of $\\mathcal{PT}$ potential. In the $\\mathcal{PT}$-unbroken regime,\nthe real Bogoliubov modes are generally gapped, in contrast to the gapless\nphonon mode in Hermitian case. Moreover, the presence of $\\mathcal{PT}$\npotential is found to enhance the mean-field collapse and thereby intrigue the\ndroplet formation after incorporating the repulsive force from quantum\nfluctuations. These remarkable interplay effects of $\\mathcal{PT}$-symmetry and\ninteraction can be directly probed in cold atoms experiments, which shed light\non related quantum phenomena in general $\\mathcal{PT}$-symmetric systems.",
        "positive": "Dimensional reduction in Bose-Einstein condensed clouds of atoms\n  confined in tight potentials of any geometry and any interaction strength: Motivated by numerous experiments on Bose-Einstein condensed atoms which have\nbeen performed in tight trapping potentials of various geometries (elongated\nand/or toroidal/annular), we develop a general method which allows us to reduce\nthe corresponding three-dimensional Gross-Pitaevskii equation for the order\nparameter into an effectively one-dimensional equation, taking into account the\ninteractions (i.e., treating the width of the transverse profile variationally)\nand the curvature of the trapping potential. As an application of our model we\nconsider atoms which rotate in a toroidal trapping potential. We evaluate the\nstate of lowest energy for a fixed value of the angular momentum within various\napproximations of the effectively one-dimensional model and compare our results\nwith the full solution of the three-dimensional problem, thus getting evidence\nfor the accuracy of our model."
    },
    {
        "anchor": "String-Theory-Based Predictions for Nonhydrodynamic Collective Modes in\n  Strongly Interacting Fermi Gases: Very different strongly interacting quantum systems such as Fermi gases,\nquark-gluon plasmas formed in high energy ion collisions and black holes\nstudied theoretically in string theory are known to exhibit quantitatively\nsimilar damping of hydrodynamic modes. It is not known if such similarities\nextend beyond the hydrodynamic limit. Do non-hydrodynamic collective modes in\nFermi gases with strong interactions also match those from string theory\ncalculations? In order to answer this question, we use calculations based on\nstring theory to make predictions for novel types of modes outside the\nhydrodynamic regime in trapped Fermi gases. These predictions are amenable to\ndirect testing with current state-of-the-art cold atom experiments.",
        "positive": "Ab-initio Quantum Monte Carlo study of ultracold atomic mixtures: In this thesis, the properties of mixtures of Bose-Einstein condensates at $T\n= 0$ have been investigated using quantum Monte Carlo (QMC) methods and Density\nFunctional Theory (DFT) with the aim of understanding physics beyond the\nmean-field theory in Bose-Bose mixtures."
    },
    {
        "anchor": "Berry phase for a Bose gas on a one-dimensional ring: We study a system of strongly interacting one-dimensional (1D) bosons on a\nring pierced by a synthetic magnetic flux tube. By the Fermi-Bose mapping, this\nsystem is related to the system of spin-polarized non-interacting electrons\nconfined on a ring and pierced by a solenoid (magnetic flux tube). On the ring\nthere is an external localized delta-function potential barrier $V(\\phi)=g\n\\delta(\\phi-\\phi_0)$. We study the Berry phase associated to the adiabatic\nmotion of delta-function barrier around the ring as a function of the strength\nof the potential $g$ and the number of particles $N$. The behavior of the Berry\nphase can be explained via quantum mechanical reflection and tunneling through\nthe moving barrier which pushes the particles around the ring. The barrier\nproduces a cusp in the density to which one can associate a missing charge\n$\\Delta q$ (missing density) for the case of electrons (bosons, respectively).\nWe show that the Berry phase (i.e., the Aharonov-Bohm phase) cannot be\nidentified with the quantity $\\Delta q/\\hbar \\oint \\mathbf{A}\\cdot\nd\\mathbf{l}$. This means that the missing charge cannot be identified as a\n(quasi)hole. We point out to the connection of this result and recent studies\nof synthetic anyons in noninteracting systems. In addition, for bosons we study\nthe weakly-interacting regime, which is related to the strongly interacting\nelectrons via Fermi-Bose duality in 1D systems.",
        "positive": "Complex Langevin and other approaches to the sign problem in quantum\n  many-body physics: We review the theory and applications of complex stochastic quantization to\nthe quantum many-body problem. Along the way, we present a brief overview of a\nnumber of ideas that either ameliorate or in some cases altogether solve the\nsign problem, including the classic reweighting method, alternative\nHubbard-Stratonovich transformations, dual variables (for bosons and fermions),\nMajorana fermions, density-of-states methods, imaginary asymmetry approaches,\nand Lefschetz thimbles. We discuss some aspects of the mathematical\nunderpinnings of conventional stochastic quantization, provide a few\npedagogical examples, and summarize open challenges and practical solutions for\nthe complex case. Finally, we review the recent applications of complex\nLangevin to quantum field theory in relativistic and nonrelativistic quantum\nmatter, with an emphasis on the nonrelativistic case."
    },
    {
        "anchor": "Unruh effect for interacting particles with ultracold atoms: The Unruh effect is a quantum relativistic effect where the accelerated\nobserver perceives the vacuum as a thermal state. Here we propose the\nexperimental realization of the Unruh effect for interacting ultracold fermions\nin optical lattices by a sudden quench resulting in vacuum acceleration with\nvarying interactions strengths in the real temperature background. We observe\nthe inversion of statistics for the low lying excitations in the Wightman\nfunction as a result of competition between the spacetime and BCS Bogoliubov\ntransformations. This paper opens up new perspectives for simulators of quantum\ngravity.",
        "positive": "Contact matrix in dilute quantum systems: Contact has been well established as an important quantity to govern dilute\nquantum systems, in which the pairwise correlation at short distance traces a\nbroad range of thermodynamic properties. So far, studies have been focusing on\ncontact in individual angular momentum channels. Here, we point out that, to\nhave a complete description of the pairwise correlation in a general dilute\nquantum systems, contact should be defined as a matrix. Whereas the diagonal\nterms of such matrix include contact of all partial wave scatterings, the\noff-diagonal terms, which elude previous studies in the literature,\ncharacterise the coherence of the asymptotic pairwise wavefunction in the\nangular momentum space and determine important thermodynamic quantities\nincluding the momentum distribution. Contact matrix allows physicists to access\nunexplored connections between short-range correlations and macroscopic quantum\nphenomena. As an example, we show the direct connection between contact matrix\nand order parameters of a superfluid with mixed partial waves."
    },
    {
        "anchor": "Medium-induced Interaction Between Impurities in a Bose-Einstein\n  Condensate: We consider two heavy particles immersed in a Bose-Einstein condensate in\nthree dimensions and compute their mutual interaction induced by excitations of\nthe medium. For an ideal Bose gas, the induced interaction is Newtonian up to a\nshift in distance which depends on the coupling strength between impurities and\nBosons. For a real BEC, we find that on short distances, the induced potential\nis dominated by three-body physics of a single Boson bound to the impurities,\nleading to an Efimov potential. At large distances of the order of the healing\nlength, a Yukawa potential emerges instead. In particular, we find that both\nregimes are realized for all impurity-boson couplings and determine the\ncorresponding crossover scales. The transition from the real to the ideal\ncondensate at low gas parameters is investigated.",
        "positive": "Splitting of topological charge pumping in an interacting two-component\n  fermionic Rice-Mele Hubbard model: A Thouless pump transports an integer amount of charge when pumping\nadiabatically around a singularity. We study the splitting of such a critical\npoint into two separate critical points by adding a Hubbard interaction.\nFurthermore, we consider extensions to a spinful Rice-Mele model, namely a\nstaggered magnetic field or an Ising-type spin coupling, further reducing the\nspin symmetry. The resulting models additionally allow for the transport of a\nsingle charge in a two-component system of spinful fermions, whereas in the\nabsence of interactions, zero or two charges are pumped. In the SU(2)-symmetric\ncase, the ionic Hubbard model is visited once along pump cycles that enclose a\nsingle singularity. Adding a staggered magnetic field additionally transports\nan integer amount of spin while the Ising term realizes a pure charge pump. We\nemploy real-time simulations in finite and infinite systems to calculate the\nadiabatic charge and spin transport, complemented by the analysis of gaps and\nthe many-body polarization to confirm the adiabatic nature of the pump. The\nresulting charge pumps are expected to be measurable in finite-pumping speed\nexperiments in ultra-cold atomic gases, for which the SU(2) invariant version\nis the most promising path. We discuss the implications of our results for a\nrelated quantum-gas experiment by Walter et al. [arXiv:2204.06561]."
    },
    {
        "anchor": "Topological Floquet engineering of a 1D optical lattice via resonantly\n  shaking with two harmonic frequencies: We investigate the topological properties of a resonantly shaken\none-dimensional optical lattice system, where the lattice position is\nperiodically driven with two harmonic frequencies to generate one- and\ntwo-photon couplings between the two lowest orbitals. In a two-band\napproximation, we numerically show that degenerate edge states appear under a\ncertain driving condition and that the corresponding topological phase is\nprotected by the chiral symmetry of the periodically driven system. The\nsystem's micromotion is characterized with oscillating Zak phases and we find\nthat the Zak phases are quantized only at the time when the chiral symmetry\ncondition is explicitly satisfied. Finally, we describe the topological charge\npumping effect which arises when the driving parameters are slowly modulated\naround a critical point, and investigate its adiabaticity for increasing the\nmodulation frequency.",
        "positive": "Phase diffusion in stationary state of nonequilibrium Bose gas: Properties of low energy spectrum of elementary excitations in nonequilibrium\nBose gas in stationary state with the dynamical equilibrium of outgoing and\nincoming of particles are studied. It is shown that due to the noise effect,\ntypical for nonequilibrium systems, this spectrum has a diffusion character, in\ncontradiction with the thermodynamically equilibrium systems, where this\nspectrum has a sound form."
    },
    {
        "anchor": "Non-Hermitian Absorption Spectroscopy: While non-Hermitian Hamiltonians have been experimentally realized in cold\natom systems, it remains an outstanding open question of how to experimentally\nmeasure their complex energy spectra in momentum space for a realistic system\nwith boundaries. The existence of non-Hermitian skin effects may make the\nquestion even more difficult to address given the fact that energy spectra for\na system with open boundaries are dramatically different from those in momentum\nspace; the fact may even lead to the notion that momentum-space band structures\nare not experimentally accessible for a system with open boundaries. Here, we\ngeneralize the widely used radio-frequency spectroscopy to measure both real\nand imaginary parts of complex energy spectra of a non-Hermitian quantum system\nfor either bosonic or fermionic atoms. By weakly coupling the energy levels of\na non-Hermitian system to auxiliary energy levels, we theoretically derive a\nformula showing that the decay of atoms on the auxiliary energy levels reflects\nthe real and imaginary parts of energy spectra in momentum space. We further\nprove that measurement outcomes are independent of boundary conditions in the\nthermodynamic limit, providing strong evidence that the energy spectrum in\nmomentum space is experimentally measurable. We finally apply our non-Hermitian\nabsorption spectroscopy protocol to the Hatano-Nelson model and non-Hermitian\nWeyl semimetals to demonstrate its feasibility.",
        "positive": "Casimir force of two-component Bose-Einstein condensates confined by a\n  parallel plate geometry: Using field theory we calculate the Casimir energy and Casimir force of\ntwo-component Bose-Einstein condensates restricted between two parallel plates,\nin which Dirichlet and periodic boundary conditions applied. Our results show\nthat, in one-loop approximation, the Casimir force equals to summation of the\none of each component and it is vanishing in some cases: (i) inter-distance\nbetween two plates becomes large enough; (ii) intraspecies interaction is zero;\n(iii) interspecies interaction is full strong segregation."
    },
    {
        "anchor": "Ferromagnetic--nematic order and strongly correlated phases of fermions\n  in optical flux lattices: We study a model of a 2D ultracold atomic gas subject to an \"optical flux\nlattice\": a laser configuration where Raman-dressed atoms experience a strong\nartificial magnetic field. This leads to a bandstructure of narrow energy bands\nwith non-zero Chern numbers. We consider the case of two-level (spin-$1/2$)\nfermionic atoms in this lattice, interacting via a repulsive $s$-wave contact\ninteraction. Atoms restricted to the lowest band are described by an effective\nmodel of spinless fermions with interactions that couple states in a\nmomentum-dependent manner across the Brillouin zone; a consequence of the Raman\ndressing of the two spin states. We present the results of detailed exact\ndiagonalization studies of the many-body states for a range of filling factors,\n$\\nu$. First, we present evidence for the existence of a phase with coupled\nferromagnetic--nematic ordering, which was previously suggested by a mean-field\nanalysis. Second, we present evidence indicating the presence of a\nLaughlin-like fractional quantum Hall state occurring at filling factor $\\nu =\n1/3$. Finally, we observe a charge density wave state at $\\nu=1/2$, which we\nare able to cleanly distinguish from the Laughlin-like state by its\ntranslational symmetry breaking and relatively small participation ratio.",
        "positive": "Equilibrium Phases of Tilted Dipolar Lattice Bosons: The recent advances in creating nearly degenerate quantum dipolar gases in\noptical lattices are opening the doors for the exploration of equilibrium\nphysics of quantum systems with anisotropic and long-range dipolar\ninteractions. In this paper we study the zero- and finite-temperature phase\ndiagrams of a system of hard-core dipolar bosons at half-filling, trapped in a\ntwo-dimensional optical lattice. The dipoles are aligned parallel to one\nanother and tilted out of the optical lattice plane by means of an external\nelectric field. At zero-temperature, the system is a superfluid at all tilt\nangles $\\theta$ provided that the strength of dipolar interaction is below a\ncritical value $V_c(\\theta)$. Upon increasing the interaction strength while\nkeeping $\\theta$ fixed, the superfluid phase is destabilized in favor of a\ncheckerboard or a stripe solid depending on the tilt angle. We explore the\nnature of the phase transition between the two solid phases and find evidence\nof a micro-emulsion phase, following the Spivak-Kivelson scenario, separating\nthese two solid phases. Additionally, we study the stability of these quantum\nphases against thermal fluctuations and find that the stripe solid is the most\nrobust, making it the best candidate for experimental observation."
    },
    {
        "anchor": "Polaron in the dilute critical Bose condensate: The properties of impurity immersed in the dilute $D$-dimensional Bose gas at\ntemperatures close to the second-order phase transition point are considered.\nParticularly by means of the $1/N$-expansion we calculated the leading-order\npolaron energy and the damping rate in the limit of vanishing boson-boson\ninteraction. It is show that the perturbative effective mass and the\nquasiparticle residue diverge logarithmically in the long-length limit\nsignalling the non-analytic behavior of impurity spectrum and a non-pole\nstructure of a polaron Green's function in the infrared region, respectively.",
        "positive": "Concept of contact spectrum and its applications in atomic quantum Hall\n  states: A unique feature of ultracold atoms is the separation of length scales,\n$r_0\\ll k_F^{-1}$, where $k_F$ and $r_0$ are the Fermi momentum characterizing\nthe average particle distance and the range of interaction between atoms\nrespectively. For $s$-wave scattering, Shina Tan discovered that such\ndiluteness leads to universal relations, all of which are governed by contact,\namong a wide range of thermodynamic quantities. Here, we show that the concept\nof contact can be generalized to an arbitrary partial-wave scattering. Contact\nof all partial-wave scatterings form a contact spectrum, which establishes\nuniversal thermodynamic relations with notable differences from those in the\npresence of $s$-wave scattering alone. Moreover, such a contact spectrum has an\ninteresting connection with a special bipartite entanglement spectrum of atomic\nquantum Hall states, and enables an intrinsic probe of these highly correlated\nstates using two-body short-ranged correlations."
    },
    {
        "anchor": "Hyperspherical explicitly correlated Gaussian approach for few-body\n  systems with finite angular momentum: Within the hyperspherical framework, the solution of the time-independent\nSchroedinger equation for a n-particle system is divided into two steps, the\nsolution of a Schroedinger like equation in the hyperangular degrees of freedom\nand the solution of a set of coupled Schroedinger like hyperradial equations.\nThe solutions to the former provide effective potentials and coupling matrix\nelements that enter into the latter set of equations. This paper develops a\ntheoretical framework to determine the effective potentials, as well as the\nassociated coupling matrix elements, for few-body systems with finite angular\nmomentum L=1 and negative and positive parity. The hyperangular channel\nfunctions are expanded in terms of explicitly correlated Gaussian basis\nfunctions and relatively compact expressions for the matrix elements are\nderived. The developed formalism is applicable to any n; however, for n greater\nor equal to 6, the computational demands are likely beyond present-day\ncomputational capabilities. A number of calculations relevant to cold atom\nphysics are presented, demonstrating that the developed approach provides a\ncomputationally efficient means to solving four-body bound and scattering\nproblems with finite angular momentum on powerful desktop computers. Details\nregarding the implementation are discussed.",
        "positive": "Probing Phase Fluctuations in a 2D Degenerate Bose Gas by Free Expansion: We measure the power spectrum of the density distribution of a freely\nexpanding 2D degenerate Bose gas, where irregular density modulations gradually\ndevelop due to the initial phase fluctuations in the sample. The spectrum has\nan oscillatory shape, where the peak positions are found to be independent of\ntemperature and show scaling behavior in the course of expansion. The relative\nintensity of phase fluctuations is estimated from the normalized spectral peak\nstrength and observed to decrease at lower temperatures, confirming the thermal\nnature of the phase fluctuations. We investigate the relaxation dynamics of\nnonequilibrium states using the power spectrum. Free vortices are observed with\nring-shaped density ripples in a perturbed sample after a long relaxation time."
    },
    {
        "anchor": "Mobile impurity in a Fermi sea from the functional renormalization group\n  analytically continued to real time: Motivated by experiments with cold atoms, we investigate a mobile impurity\nimmersed in a Fermi sea in three dimensions at zero temperature by means of the\nfunctional renormalization group. We first perform the derivative expansion of\nthe effective action to calculate the ground state energy and Tan's contact\nacross the polaron-molecule transition for several mass imbalances. Next we\nstudy quasiparticle properties of the impurity by using a real-time method\nrecently developed in nuclear physics, which allows one to go beyond the\nderivative expansion. We obtain the spectral function of the polaron, the\neffective mass and quasiparticle weight of attractive and repulsive polarons,\nand clarify how they are affected by mass imbalances.",
        "positive": "Exact Tkachenko modes and their damping in the vortex lattice regime of\n  rapidly rotating bosons: We have found an exact analytical solution of the Bogoliubov-de Gennes\nequations for the Tkachenko modes of the vortex lattice in the lowest Landau\nlevel (LLL) in the thermodynamic limit at any momenta and calculated their\ndamping rates. At finite temperatures both Beliaev and Landau damping leads to\nmomentum independent damping rates in the low-energy limit, which shows that at\nsufficiently low energies Tkachenko modes become strongly damped. We then found\nthat the mean square fluctuations of the density grow logarithmically at large\ndistances, which indicates that the state is ordered in the vortex lattice only\non a finite (although exponentially large) distance scale and introduces a\nlow-momentum cut-off. Using this circumstance we showed that at finite\ntemperatures the one-body density matrix undergoes an exponential decay at\nlarge distances."
    },
    {
        "anchor": "Spin dynamics of two bosons in an optical lattice site: a role of\n  anharmonicity and anisotropy of the trapping potential: We study a spin dynamics of two magnetic Chromium atoms trapped in a single\nsite of a deep optical lattice in a resonant magnetic field. Dipole-dipole\ninteractions couple spin degrees of freedom of the two particles to their\nmotion in the site. The motion is quantized, therefore a trap geometry combined\nwith two-body contact s-wave interactions influence a spin dynamics through the\nenergy spectrum of the two atom system. Anharmonicity and anisotropy of the\nsite results in a `fine' structure of two body eigenenergies. The structure can\nbe easily resolved by a weak magnetic dipole-dipole interactions. As an example\nwe examine the effect of anharmonicity and anisotropy of the binding potential\non the Einstein-de Haas effect. We show that the weak dipolar interactions\nprovide a perfect tool for a precision spectroscopy of the energy spectrum of\nthe interacting few particle system.",
        "positive": "Characteristics of Two-Dimensional Quantum Turbulence in a Compressible\n  Superfluid: Under suitable forcing a fluid exhibits turbulence, with characteristics\nstrongly affected by the fluid's confining geometry. Here we study\ntwo-dimensional quantum turbulence in a highly oblate Bose-Einstein condensate\nin an annular trap. As a compressible quantum fluid, this system affords a rich\nphenomenology, allowing coupling between vortex and acoustic energy.\nSmall-scale stirring generates an experimentally observed disordered vortex\ndistribution that evolves into large-scale flow in the form of a persistent\ncurrent. Numerical simulation of the experiment reveals additional\ncharacteristics of two-dimensional quantum turbulence: spontaneous clustering\nof same-circulation vortices, and an incompressible energy spectrum with\n$k^{-5/3}$ dependence for low wavenumbers $k$ and $k^{-3}$ dependence for high\n$k$."
    },
    {
        "anchor": "Floquet Engineering Ultracold Polar Molecules to Simulate Topological\n  Insulators: We present a quantitative, near-term experimental blueprint for the quantum\nsimulation of topological insulators using lattice-trapped ultracold polar\nmolecules. In particular, we focus on the so-called Hopf insulator, which\nrepresents a three-dimensional topological state of matter existing outside the\nconventional tenfold way and crystalline-symmetry-based classifications of\ntopological insulators. Its topology is protected by a \\emph{linking number}\ninvariant, which necessitates long-range spin-orbit coupled hoppings for its\nrealization. While these ingredients have so far precluded its realization in\nsolid state systems and other quantum simulation architectures, in a companion\nmanuscript [1901.08597] we predict that Hopf insulators can in fact arise\nnaturally in dipolar interacting systems. Here, we investigate a specific such\narchitecture in lattices of polar molecules, where the effective `spin' is\nformed from sublattice degrees of freedom. We introduce two techniques that\nallow one to optimize dipolar Hopf insulators with large band gaps, and which\nshould also be readily applicable to the simulation of other exotic\nbandstructures. First, we describe the use of Floquet engineering to control\nthe range and functional form of dipolar hoppings and second, we demonstrate\nthat molecular AC polarizabilities (under circularly polarized light) can be\nused to precisely tune the resonance condition between different rotational\nstates. To verify that this latter technique is amenable to current generation\nexperiments, we calculate from first principles the AC polarizability for\n$\\sigma^+$ light for ${}^{40}$K$^{87}$Rb. Finally, we show that experiments are\ncapable of detecting the unconventional topology of the Hopf insulator by\nvarying the termination of the lattice at its edges, which gives rise to three\ndistinct classes of edge mode spectra.",
        "positive": "Strongly bound fermion pairs on a ring: a composite-boson approach: Particles made of two fermions can in many cases be treated as elementary\nbosons, but the conditions for this treatment to be valid are nontrivial. The\nso-called \"coboson formalism\" is a powerful tool to tackle compositeness\neffects relevant for instance for exciton physics and ultracold atomic dimers.\nA key element of this theory is an ansatz for the ground state of N pairs,\nbuilt from the single-pair ground state combined with the exclusion principle.\nWe show that this ansatz can fail in one-dimensional systems which fulfill the\nconditions expected to make the ansatz valid. Nevertheless, we also explain how\ncoboson theory can recover the correct ground state. Thus, our work highlights\nlimitations and strengths of the formalism and leads to a better treatment of\ncomposite bosons."
    },
    {
        "anchor": "Ultracold Feshbach molecules in an orbital optical lattice: Quantum gas systems provide a unique experimental platform to study a\nfundamental paradigm of quantum many-body physics: the crossover between\nBose-Einstein condensed (BEC) molecular pairs and Bardeen Cooper Schrieffer\n(BCS) superfluidity. Some studies have considered quantum gas samples confined\nin optical lattices, however, focusing on the case, when only the lowest Bloch\nband is populated, such that orbital degrees of freedom are excluded. In this\nwork, for the first time, ultracold Feshbach molecules of fermionic $^{40}K$\natoms are selectively prepared in the second Bloch band of an optical square\nlattice, covering a wide range of interaction strengths including the regime of\nunitarity. Binding energies and band relaxation dynamics are measured by means\nof a method resembling mass spectrometry. The longest lifetimes arise for\nstrongly interacting Feshbach molecules at the onset of unitarity with values\naround 300 ms for the lowest band and 100 ms for the second band. In the case\nof strong confinement in a deep lattice potential, we observe bound dimers also\nfor negative values of the s-wave scattering length, extending previous\nfindings for molecules in the lowest band. Our work prepares the stage for\norbital BEC-BCS crossover physics.",
        "positive": "Equation of state and self-bound droplet in Rabi-coupled Bose mixtures: Laser induced transitions between internal states of atoms have been playing\na fundamental role to manipulate atomic clouds for many decades. In absence of\ninteractions each atom behaves independently and their coherent quantum\ndynamics is described by the Rabi model. Since the experimental observation of\nBose condensation in dilute gases, static and dynamical properties of\nmulticomponent quantum gases have been extensively investigated. Moreover, at\nvery low temperatures quantum fluctuations crucially affect the equation of\nstate of many-body systems. Here we study the effects of quantum fluctuations\non a Rabi-coupled two-component Bose gas of interacting alkali atoms. The\ndivergent zero-point energy of gapless and gapped elementary excitations of the\nuniform system is properly regularized obtaining a meaningful analytical\nexpression for the beyond-mean-field equation of state. In the case of\nattractive inter-particle interaction we show that the quantum pressure arising\nfrom Gaussian fluctuations can prevent the collapse of the mixture with the\ncreation of a self-bound droplet. We characterize the droplet phase and\ndiscover an energetic instability above a critical Rabi frequency provoking the\nevaporation of the droplet. Finally, we suggest an experiment to observe such\nquantum droplets using Rabi-coupled internal states of $^{39}$K atoms."
    },
    {
        "anchor": "Dipole Oscillations in Fermionic Mixtures: We study dipole oscillations in a general fermionic mixture: starting from\nthe Boltzmann equation, we classify the different solutions in the parameter\nspace through the number of real eigenvalues of the small oscillations matrix.\nWe discuss how this number can be computed using the Sturm algorithm and its\nrelation with the properties of the Laplace transform of the experimental\nquantities. After considering two components in harmonic potentials having\ndifferent trapping frequencies, we study dipole oscillations in three-component\nmixtures. Explicit computations are done for realistic experimental setups\nusing the classical Boltzmann equation without intra-species interactions. A\nbrief discussion of the application of this classification to general\ncollective oscillations is also presented.",
        "positive": "Revealing the Superfluid Lambda Transition in the Universal\n  Thermodynamics of a Unitary Fermi Gas: We have observed the superfluid phase transition in a strongly interacting\nFermi gas via high-precision measurements of the local compressibility, density\nand pressure down to near-zero entropy. Our data completely determine the\nuniversal thermodynamics of strongly interacting fermions without any fit or\nexternal thermometer. The onset of superfluidity is observed in the\ncompressibility, the chemical potential, the entropy, and the heat capacity. In\nparticular, the heat capacity displays a characteristic lambda-like feature at\nthe critical temperature of $T_c/T_F = 0.167(13)$. This is the first clear\nthermodynamic signature of the superfluid transition in a spin-balanced atomic\nFermi gas. Our measurements provide a benchmark for many-body theories on\nstrongly interacting fermions, relevant for problems ranging from\nhigh-temperature superconductivity to the equation of state of neutron stars."
    },
    {
        "anchor": "Dynamics of pattern-loaded fermions in bichromatic optical lattices: Motivated by experiments in Munich (M. Schreiber et. al. Science\n\\textbf{349}, 842), we study the dynamics of interacting fermions initially\nprepared in charge density wave states in one-dimensional bichromatic optical\nlattices. The experiment sees a marked lack of thermalization, which has been\ntaken as evidence for an interacting generalization of Anderson localization,\ndubbed \"many-body localization\". We model the experiments using an interacting\nAubry-Andre model and develop a computationally efficient low-density cluster\nexpansion to calculate the even-odd density imbalance as a function of\ninteraction strength and potential strength. Our calculations agree with the\nexperimental results and shed light on the phenomena. We also explore a\ntwo-dimensional generalization. The cluster expansion method we develop should\nhave broad applicability to similar problems in non-equilibrium quantum\nphysics.",
        "positive": "Interaction induced fractionalization and topological superconductivity\n  in the polar molecules anisotropic $t-J$ model: We show that the interplay between antiferromagnetic interaction and hole\nmotion gives rise to a topological superconducting phase. This is captured by\nthe one dimensional anisotropic $t-J$ model which can be experimentally\nachieved with ultracold polar molecules trapped onto an optical lattice. As a\nfunction of the anisotropy strength we find that different quantum phases\nappear, ranging from a gapless Luttinger liquid to spin gapped conducting and\nsuperconducting regimes. In presence of appropriate $z$-anisotropy, we also\nprove that a phase characterized by non-trivial topological order takes place.\nThe latter is described uniquely by a finite non local string parameter and\npresents robust edge spin fractionalization. These results allow to explore\nquantum phases of matter where topological superconductivity is induced by the\ninteraction."
    },
    {
        "anchor": "Temporal bistability in the dissipative Dicke-Bose-Hubbard system: We consider a driven-dissipative system consisting of an atomic Bose-Einstein\ncondensates loaded into a two-dimensional Hubbard lattice and coupled to a\nsingle mode of an optical cavity. Due to the interplay between strong,\nrepulsive atomic interaction and the atom-cavity coupling, the system exhibits\nseveral phases of atoms and photons including the atomic superfluid (SF) and\nsupersolid (SS). We investigate the dynamical behaviour of the system, where we\ninclude dissipation by means of Lindblad master equation formalism. Due to the\ndiscontinuous nature of the Dicke transition for strong atomic repulsion, we\nfind extended co-existence region of different phases. We investigate the\nresulting switching dynamics, particularly between the coexisting SF and SS\nphases, which eventually becomes damped by the dissipation.",
        "positive": "A proposed signature of Anderson localization and correlation-induced\n  delocalization in an N-leg optical lattice: We propose a realization of the one-dimensional random dimer model and\ncertain N-leg generalizations using cold atoms in an optical lattice. We show\nthat these models exhibit multiple delocalization energies that depend strongly\non the symmetry properties of the corresponding Hamiltonian and we provide\nanalytical and numerical results for the localization length as a function of\nenergy. We demonstrate that the N-leg systems possess similarities with their\n1D ancestors but are demonstrably distinct. The existence of critical\ndelocalization energies leads to dips in the momentum distribution which serve\nas a clear signal of the localization-delocalization transition. These momentum\ndistributions are different for models with different group symmetries and are\nidentical for those with the same symmetry."
    },
    {
        "anchor": "Vortex generation in a superfluid gas of dipolar chains in crossed\n  electric and magnetic fields: Crossed electric and magnetic fields influence dipolar neutral particles in\nthe same way as the magnetic field influences charged particles. The effect of\ncrossed fields is proportional to the dipole moment of the particle (inherent\nor induced). We show that this effect is quite spectacular in a multilayer\nsystem of polar molecules. In this system molecules may bind in chains. At low\ntemperature the gas of chains becomes the superfluid one. The crossed fields\nthen induce vortices in the superfluid gas of chains. The density of vortices\nis proportional to the number of particles in the chain. The effect can be used\nfor monitoring the formation and destruction of chains in multilayer dipolar\ngases.",
        "positive": "Condensation versus Long-range Interaction: Competing Quantum Phases in\n  Bosonic Optical Lattice Systems at Near-resonant Rydberg Dressing: Recent experiments have shown that (quasi-)crystalline phases of\nRydberg-dressed quantum many-body systems in optical lattices (OL) are within\nreach. Rydberg systems naturally possess strong long-range interactions due to\nthe large polarizability of Rydberg atoms. Thus a wide range of quantum phases\nhave been predicted, such as a devil's staircase of lattice incommensurate\ndensity wave phases as well as more exotic lattice supersolid order for bosonic\nsystems, as considered in our work. Guided by results in the \"frozen\" gas\nlimit, we study the ground state phase diagram at finite hopping amplitudes and\nin the vicinity of resonant Rydberg driving, while fully including the\nlong-range tail of the van der Waals interaction. Simulations within real-space\nbosonic dynamical mean-field theory (RB-DMFT) yield an extension of the devil's\nstaircase into the supersolid regime where the competition of condensation and\ninteraction leads to a sequence of crystalline phases."
    },
    {
        "anchor": "Majorana fermions in one-dimensional spin-orbit coupled Fermi gases: We theoretically study trapped one-dimensional Fermi gases in the presence of\nspin-orbit coupling induced by Raman lasers. The gas changes from a\nconventional (non-topological) superfluid to a topological superfluid as one\nincreases the intensity of the Raman lasers above a critical chemical-potential\ndependent value. Solving the Bogoliubov-de Gennes equations self-consistently,\nwe calculate the density of states in real and momentum space at finite\ntemperatures. We study Majorana fermions (MFs) which appear at the boundaries\nbetween topologically trivial and topologically non-trivial regions. We\nlinearize the trap near the location of a MF, finding an analytic expression\nfor the localized MF wavefunction and the gap between the MF state and other\nedge states.",
        "positive": "Balls and Walls: A Compact Unary Coding for Bosonic States: We introduce a unary coding of bosonic occupation states based on the famous\n\"balls and walls\" counting for the number of configurations of $N$\nindistinguishable particles on $L$ distinguishable sites. Each state is\nrepresented by an integer with a human readable bit string that has a\ncompositional structure allowing for the efficient application of operators\nthat locally modify the number of bosons. By exploiting translational and\ninversion symmetries, we identify a speedup factor of order $L$ over current\nmethods when generating the basis states of bosonic lattice models. The unary\ncoding is applied to a one-dimensional Bose-Hubbard Hamiltonian with up to\n$L=N=20$, and the time needed to generate the ground state block is reduced to\na fraction of the diagonalization time. For the ground state symmetry resolved\nentanglement, we demonstrate that variational approaches restricting the local\nbosonic Hilbert space could result in an error that scales with system size."
    },
    {
        "anchor": "Anomalous tunneling of collective excitations and effects of superflow\n  in the polar phase of a spin-1 spinor Bose-Einstein condensate: We investigate tunneling properties of collective modes in the polar phase of\na spin-1 spinor Bose-Einstein condensate. This spinor BEC state has two kinds\nof gapless modes, i.e., Bogoliubov mode and spin-wave. Within the framework of\nthe mean-field theory at T=0, we show that these Goldstone modes exhibit the\nperfect transmission in the low-energy limit. Their anomalous tunneling\nbehaviors still hold in the presence of superflow, except in the critical\ncurrent state. In the critical current state, while the tunneling of Bogoliubov\nmode is accompanied by finite reflection, the spin-wave still exhibit the\nperfect transmission, unless the strengths of a spin-dependent and\nspin-independent interactions take the same value.",
        "positive": "Atomtronic circuits: from many-body physics to quantum technologies: Atomtronics is an emerging field that aims to manipulate ultracold atom\nmoving in matter wave circuits for both fundamental studies in quantum science\nand technological applications. In this colloquium, we review recent progress\nin matter-wave circuitry and atomtronics-based quantum technology. After a\nshort introduction to the basic physical principles and the key experimental\ntechniques needed to realize atomtronic systems, we describe the physics of\nmatter-waves in simple circuits such as ring traps and two-terminal systems.\nThe main experimental observations and outstanding questions are discussed. We\nalso present possible applications to a broad range of quantum technologies,\nfrom quantum sensing with atom interferometry to future quantum simulation and\nquantum computation architectures."
    },
    {
        "anchor": "Zero-temperature equation of state of a two-dimensional bosonic quantum\n  fluid with finite-range interaction: We derive the two-dimensional equation of state for a bosonic system of\nultracold atoms interacting with a finite-range effective interaction. Within a\nfunctional integration approach, we employ an hydrodynamic parametrization of\nthe bosonic field to calculate the superfluid equations of motion and the\nzero-temperature pressure. The ultraviolet divergences, naturally arising from\nthe finite-range interaction, are regularized with an improved dimensional\nregularization technique.",
        "positive": "Non-Markovian polaron dynamics in a trapped Bose-Einstein condensate: We study the dynamics of an impurity embedded in a trapped Bose-Einstein\ncondensate (Bose polaron), by recalling the quantum Brownian motion model. It\nis crucial that the model considers a parabolic trapping potential to resemble\nthe experimental conditions. Thus, we detail here how the formal derivation\nchanges due to the gas trap, in comparison to the homogeneous gas. We first\nfind that the presence of a gas trap leads to a new form of the bath-impurity\ncoupling constant and a larger degree in the super-ohmicity of the spectral\ndensity. This is manifested as a different dependence of the system dynamics on\nthe past history. To quantify this, we introduce several techniques to compare\nthe different amount of memory effects arising in the homogeneous and\ninhomogeneous gas. We find that it is higher in the second case. Moreover, we\ncalculate the position variance of the impurity, represenitng a measurable\nquantity. We show that the impurity experiences super-diffusion and genuine\nposition squeezing. Wdetail how both effects can be enhanced or inhibited by\ntuning the Bose-Einstein condensate trap frequency."
    },
    {
        "anchor": "Antiferromagnetic Spatial Ordering in a Quenched One-dimensional Spinor\n  Gas: We have experimentally observed the emergence of spontaneous\nantiferromagnetic spatial order in a sodium spinor Bose-Einstein condensate\nthat was quenched through a magnetic phase transition. For negative values of\nthe quadratic Zeeman shift, a gas initially prepared in the F = 1, mF = 0 state\ncollapsed into a dynamically evolving superposition of all 3 spin projections,\nmF = 0, +/-1. The quench gave rise to rich, nonequilibrium behavior where both\nnematic and magnetic spin waves were generated. We characterized the\nspatiotemporal evolution through two particle correlations between atoms in\neach pair of spin states. These revealed dramatic differences between the\ndynamics of the spin correlations and those of the spin populations.",
        "positive": "Unexpectedly Slow Two Particle Decay of Ultra-Dense Excitons in Cuprous\n  Oxide: For an ultra-dense exciton gas in cuprous oxide (Cu$_2$O), exciton-exciton\ninteractions are the dominant cause of exciton decay. This study demonstrates\nthat the accepted Auger recombination model overestimates the exciton decay\nrate following intense two photon excitation. Two exciton decay is relevant to\nthe search for collective quantum behavior of excitons in bulk systems. These\nresults suggest the existence of a new high density regime of exciton behavior."
    },
    {
        "anchor": "$\u03b7/s$ of the Normal Phase of Unitary Fermi Gas from $\\varepsilon$\n  Expansion: Using $\\varepsilon$-expansion technique we compute $\\eta/s$, where $\\eta$ is\nthe shear viscosity, $s$ is the entropy density, of the normal phase of unitary\nFermi gas in $d=4-\\varepsilon$ dimensions to LO in $\\varepsilon$. We use\nkinetic theory approach and solve transport equations for medium perturbed by a\nshear hydrodynamic flow. The collision integrals are calculated to\n$\\varepsilon^2$ which is LO. The LO result is temperature independent with\n$\\eta/\\rm s\\simeq (0.11/\\varepsilon^2)(\\hbar/k_B).$ The $d=3$ prediction for\n$\\eta/\\rm s$ exceeds the $\\hbar/4 \\pi k_B$ bound by a factor of about $1.4.$",
        "positive": "Bosons in a two-dimensional bichromatic quasiperiodic potential:\n  Analysis of the disorder in the Bose-Hubbard parameters and phase diagrams: Experimental realizations of disorder in optical lattices generate a\ndistribution of the Bose-Hubbard (BH) parameters, like on-site potentials,\nhopping strengths, and interaction energies. We analyze this distribution for\nbosons in a bichromatic quasi-periodic potential by determining the generalized\nWannier functions and calculating the corresponding BH parameters. Using a\nlocal mean-field cluster analysis, we study the effect of the corresponding\ndisorder on the phase diagrams. We find a substantial amount of disorder in the\nhopping strengths, which produces strong deviations from the phase diagram of\nthe disordered BH model with solely random on-site potentials."
    },
    {
        "anchor": "Quantitative analysis of $p$-wave three-body losses via cascade process: We describe the three-body loss coefficient of identical fermions with\n$p$-wave interactions using a set of rate equations in which three-body\nrecombination happens via an indirect process. Our theoretical treatment\nexplains experimental results just above the universal scaling law regime of\nweak interactions. Furthermore, we theoretically extend and experimentally\nverify the rate equation model for the case of atoms trapped in two dimensions.\nMoreover, we find that the three-body loss coefficient in a two-dimensional\ntrap is proportional to $A_{p}^{3}$ in the weakly interacting regime, where\n$A_{p}$ is the scattering area. Our results are useful in understanding\nthree-body physics with $p$-wave interactions.",
        "positive": "Magnetic lattices for ultracold atoms and degenerate quantum gases: We review recent developments in the use of magnetic lattices as a\ncomplementary tool to optical lattices for trapping periodic arrays of\nultracold atoms and degenerate quantum gases. Recent advances include the\nrealisation of Bose-Einstein condensation in multiple sites of a magnetic\nlattice of one-dimensional microtraps, the trapping of ultracold atoms in\nsquare and triangular magnetic lattices, and the fabrication of magnetic\nlattice structures with sub-micron period suitable for quantum tunnelling\nexperiments. Finally, we describe a proposal to utilise long-range interacting\nRydberg atoms in a large spacing magnetic lattice to create interactions\nbetween atoms on neighbouring sites."
    },
    {
        "anchor": "Symmetry breaking in a localized interacting binary BEC in a\n  bi-chromatic optical lattice: By direct numerical simulation of the time-dependent Gross-Pitaevskii\nequation using the split-step Fourier spectral method we study different\naspects of the localization of a cigar-shaped interacting binary\n(two-component) Bose-Einstein condensate (BEC) in a one-dimensional\nbi-chromatic quasi-periodic optical-lattice potential, as used in a recent\nexperiment on the localization of a BEC [Roati et al., Nature 453, 895 (2008)].\nWe consider two types of localized states: (i) when both localized components\nhave a maximum of density at the origin x=0, and (ii) when the first component\nhas a maximum of density and the second a minimum of density at x=0. In the\nnon-interacting case the density profiles are symmetric around x=0. We\nnumerically study the breakdown of this symmetry due to inter-species and\nintra-species interaction acting on the two components. Where possible, we have\ncompared the numerical results with a time-dependent variational analysis. We\nalso demonstrate the stability of the localized symmetry-broken BEC states\nunder small perturbation.",
        "positive": "Energy-resolved spin correlation measurements: Decoding transverse spin\n  dynamics in weakly interacting Fermi gases: We study transverse spin dynamics on a microscopic level by measuring\nenergy-resolved spin correlations in weakly interacting Fermi gases (WIFGs).\nThe trapped cloud behaves as a many-body spin-lattice in energy space with\neffective long-range interactions, simulating a collective Heisenberg model. We\nobserve the flow of correlations in energy space in this quasi-continuous\nsystem, revealing the connection between the evolution of the magnetization and\nthe localization or spread of correlations. This work highlights energy-space\ncorrelation as a new observable in quantum phase transition studies of WIFGs,\ndecoding system features that are hidden in macroscopic measurements."
    },
    {
        "anchor": "Ab initio methods for finite temperature two-dimensional Bose gases: The stochastic Gross-Pitaevskii equation and modified Popov theory are shown\nto provide an ab initio description of finite temperature, weakly-interacting\ntwo-dimensional Bose gas experiments. Using modified Popov theory, a systematic\napproach is developed in which the momentum cut-off inherent to classical field\nmethods is removed as a free parameter. This is shown to yield excellent\nagreement with the recent experiment of Hung et al. [Nature, 470, 236 (2011)],\nverifying that the stochastic Gross-Pitaevskii equation captures the observed\nuniversality and scale-invariance.",
        "positive": "Bose-Einstein Condensate in Weak 3d Isotropic Speckle Disorder: The effect of a weak three-dimensional (3d) isotropic laser speckle disorder\non various thermodynamic properties of a dilute Bose gas is considered at zero\ntemperature. First, we summarize the derivation of the autocorrelation function\nof laser speckles in 1d and 2d following the seminal work of Goodman. The goal\nof this discussion is to show that a Gaussian approximation of this function,\nproposed in some recent papers, is inconsistent with the general background of\nlaser speckle theory. Then we propose a possible experimental realization for\nan isotropic 3d laser speckle potential and derive its corresponding\nautocorrelation function. Using a Fourier transform of that function, we\ncalculate both condensate depletion and sound velocity of a Bose-Einstein\ncondensate as disorder ensemble averages of such a weak laser speckle potential\nwithin a perturbative solution of the Gross-Pitaevskii equation. By doing so,\nwe reproduce the expression of the normalfluid density obtained earlier within\nthe treatment of Landau. This physically transparent derivation shows that\ncondensate particles, which are scattered by disorder, form a gas of\nquasiparticles which is responsible for the normalfluid component."
    },
    {
        "anchor": "Blocked populations in ring-shaped optical lattices: We study a special dynamical regime of a Bose-Einstein condensate in a\nring-shaped lattice where the populations in each site remain constant during\nthe time evolution. The states in this regime are characterized by equal\noccupation numbers in alternate wells and non-trivial phases, while the phase\ndifferences between neighboring sites evolve in time yielding persistent\ncurrents that oscillate around the lattice. We show that the velocity\ncirculation around the ring lattice alternates between two values determined by\nthe number of wells and with a specific time period that is only driven by the\nonsite interaction energy parameter. In contrast to the self-trapping regime\npresent in optical lattices, the occupation number at each site does not show\nany oscillation and the particle imbalance does not possess a lower bound for\nthe phenomenon to occur. These findings are predicted with a multimode model\nand confirmed by full three-dimensional Gross-Pitaevskii simulations using an\neffective onsite interaction energy parameter.",
        "positive": "Evidence of attraction between charge-carriers in a doped Mott insulator: Recent progress in optically trapped ultracold atomic gases is now making it\npossible to access microscopic observables in doped Mott insulators, which are\nthe parent states of high-temperature superconductors. This makes it possible\nto address longstanding questions about the temperature scales at which\nattraction between charge carriers are present, and their mechanism.\nControllable theoretical results for this problem are not available at low\ntemperature due to the sign problem. In this work, we employ worm-algorithm\nMonte Carlo to obtain completely unbiased results for two charge carriers in a\nMott insulator. Our method gives access to lower temperatures than what is\ncurrently possible in experiments, and provides evidence for attraction between\ndopants at a temperature scale that is now feasible in ultracold atomic\nsystems. We also report on spin-correlations in the presence of charge\ncarriers, which are directly comparable to experiments."
    },
    {
        "anchor": "Highly excited exciton-polariton condensates: Exciton-polaritons are a coherent electron-hole-photon (e-h-p) system where\ncondensation has been observed in semiconductor microcavities. In contrast to\nequilibrium Bose-Einstein condensation (BEC) for long lifetime systems,\npolariton condensates have a dynamical nonequilibrium feature owing to the\nsimilar physical structure that they have to semiconductor lasers. One of the\ndistinguishing features of a condensate to a laser is the presence of strong\ncoupling between the matter and photon fields. Irrespective of its equilibrium\nor nonequilibrium nature, exciton-polariton have been observed to maintain\nstrong coupling. We show that by investigating high density regime of\nexciton-polariton condensates, the negative branch directly observed in\nphotoluminescence. This is evidence that the present e-h-p system is still in\nthe strong coupling regime, contrary to past results where the system reduced\nto standard lasing at high density.",
        "positive": "Dynamical structure factors of a two-dimensional Fermi superfluid within\n  random phase approximation: Based on random phase approximation (RPA), we numerically calculate dynamical\nstructure factors of a balanced two-dimensional (2D) Fermi superfluid, and\ndiscuss their energy, momentum and interaction strength dependence in the 2D\nBEC-BCS crossover. At a small transferred momentum, a stable Higgs mode is\nobserved in the unitary 2D Fermi superfluid gas where the particle-hole\nsymmetry is not satisfied. Stronger interaction strength will make the\nvisibility of the dispersion of Higgs mode harder to be observed. We also\ndiscuss the dimension effect and find that the signal of the Higgs mode in two\ndimension is more obvious than that in 3D case. At a large transferred momentum\nregime, stronger interaction strength will induce the weight of the molecules\nexcitation increasing, while in verse the atomic one decreasing, which shows\nthe pairing information of Fermi superfluid. The theoretical results\nqualitatively agree with the corresponding Quantum Monte Carlo data."
    },
    {
        "anchor": "Propagation of first and second sound in a two-dimensional Fermi\n  superfluid: Sound propagation is a macroscopic manifestation of the interplay between the\nequilibrium thermodynamics and the dynamical transport properties of fluids.\nHere, for a two-dimensional system of ultracold fermions, we calculate the\nfirst and second sound velocities across the whole BCS-BEC crossover and we\nanalyze the system response to an external perturbation. In the low-temperature\nregime we reproduce the recent measurements [Phys Rev. Lett. {\\bf 124}, 240403\n(2020)] of the first sound velocity, which, due to the decoupling of density\nand entropy fluctuations, is the sole mode excited by a density probe.\nConversely, a heat perturbation excites only the second sound, which, being\nsensitive to the superfluid depletion, vanishes in the deep BCS regime, and\njumps discontinuously to zero at the Berezinskii-Kosterlitz-Thouless superfluid\ntransition. A mixing between the modes occurs only in the finite-temperature\nBEC regime, where our theory converges to the purely bosonic results.",
        "positive": "Observation of antiferromagnetic correlations in an ultracold SU($N$)\n  Hubbard model: Mott insulators are paradigms of strongly correlated physics, giving rise to\nphases of matter with novel and hard-to-explain properties. Extending the\ntypical SU(2) symmetry of Mott insulators to SU($N$) is predicted to give\nexotic quantum magnetism at low temperatures, but understanding the effect of\nstrong quantum fluctuations for large $N$ remains an open challenge. In this\nwork, we experimentally observe nearest-neighbor spin correlations in the SU(6)\nHubbard model realized by ytterbium atoms in optical lattices. We study\none-dimensional, two-dimensional square, and three-dimensional cubic lattice\ngeometries. The measured SU(6) spin correlations are dramatically enhanced\ncompared to the SU(2) correlations, due to strong Pomeranchuk cooling. We also\npresent numerical calculations based on exact diagonalization and determinantal\nquantum Monte Carlo. The experimental data for a one-dimensional lattice agree\nwith theory, without any fitting parameters. The detailed comparison between\ntheory and experiment allows us to infer from the measured correlations a\nlowest temperature of $\\left[{0.096 \\pm 0.054 \\, \\rm{(theory)} \\pm 0.030 \\,\n\\rm{(experiment)}}\\right]/k_{\\rm B}$ times the tunneling amplitude. For two-\nand three-dimensional lattices, experiments reach entropies below where our\ncalculations converge, highlighting the experiments as quantum simulations.\nThese results open the door for the study of long-sought SU($N$) quantum\nmagnetism."
    },
    {
        "anchor": "Condensates Breaking Up Under Rotation: The ground state of a rotating Bose-Einstein condensate trapped in a\ntwo-dimensional anharmonic--anisotropic potential is analyzed numerically at\nthe limit of an infinite number of particles. We find that the density breaks\nup along the $x$ direction in position space and along the $p_y$ direction in\nmomentum space together with the acquisition of angular momentum. Side by side,\nthe anisotropies of the many-particle position variances along the $x$ and $y$\ndirections and of the many-particle momentum variances along the $p_y$ and\n$p_x$ directions become opposite when computed at the many-body and mean-field\nlevels of theory. All in all, the rotating bosons are found to possess unique\ncorrelations at the limit of an infinite number of particles, both in position\nand momentum spaces, although their many-body and mean-field energies per\nparticle and densities per particle coincide and the condensate fraction is\n100\\%. Implications are briefly discussed.",
        "positive": "Hydrodynamic spectrum of a superfluid in an elongated trap: --In this article we study the hydrodynamic spectrum of a superfluid confined\nin a cylindrical trap. We show that the dispersion relation $\\omega$(q) of the\nphonon branch scales like $\\sqrt$ q at large q, leading to a vanishingly small\nsuperfluid critical velocity. In practice the critical velocity is set by the\nbreakdown of the hydrodynamic approximation. For a broad class of superfluids,\nthis entails a reduction of the critical velocity by a factor ($\\omega$ $\\perp$\n/\\\"i1/2c) 1/3 with respect to the free-space prediction (here $\\omega$ $\\perp$\nis the trapping frequency and \\\"i1/2c the chemical potential of the cloud)."
    },
    {
        "anchor": "Study of Bose-Einstein condensation using generalized canonical\n  partition function: We open a new discussion of generalized canonical partition function in\nstandard statistical mechanics and apply it for the study of Bose-Einstein\ncondensation. We discuss the possible cases for the generalized canonical\npartition function and arrives at a conclusion that the system of trapped bose\ngas will not be existing at absolute zero. We analyse the present study with an\nexperimental result and point out the general difficulties in the analyses of\nexperimental observations, which can possibly suppress the effect of\ngeneralized canonical partition function over standard canonical partition\nfunction. We mention that the experimental studies with ideal condensates at\nabsolute zero with an unbiased approach towards the traditional Bose-Einstein\ncondensation theory can bring out the effect of generalized canonical partition\nfunction.",
        "positive": "Phase structure of mass- and spin-imbalanced unitary Fermi gases: We study the phase diagram of mass- and spin-imbalanced unitary Fermi gases,\nin search for the emergence of spatially inhomogeneous phases. To account for\nfluctuation effects beyond the mean-field approximation, we employ\nrenormalization group techniques. We thus obtain estimates for critical values\nof the temperature, mass and spin imbalance, above which the system is in the\nnormal phase. In the unpolarized, equal-mass limit, our result for the critical\ntemperature is in accordance with state-of-the-art Monte Carlo calculations. In\naddition, we estimate the location of regions in the phase diagram where\ninhomogeneous phases are likely to exist. We show that an intriguing relation\nexists between the general structure of the many-body phase diagram and the\nbinding energies of the underlying two-body bound-state problem, which further\nsupports our findings. Our results suggest that inhomogeneous condensates form\nfor mass ratios of the spin-down and spin-up fermions greater than three. The\nextent of the inhomogeneous phase in parameter space increases with increasing\nmass imbalance."
    },
    {
        "anchor": "Frustration and glassiness in spin models with cavity-mediated\n  interactions: We show that the effective spin-spin interaction between three-level atoms\nconfined in a multimode optical cavity is long-ranged and sign-changing, like\nthe RKKY interaction; therefore, ensembles of such atoms subject to frozen-in\npositional randomness can realize spin systems having disordered and frustrated\ninteractions. We argue that, whenever the atoms couple to sufficiently many\ncavity modes, the cavity-mediated interactions give rise to a spin glass. In\naddition, we show that the quantum dynamics of cavity-confined spin systems is\nthat of a Bose-Hubbard model with strongly disordered hopping but no on-site\ndisorder; this model exhibits a random-singlet glass phase, absent in\nconventional optical-lattice realizations. We briefly discuss experimental\nsignatures of the realizable phases.",
        "positive": "Dissipative dynamics and cooling rates of trapped impurity atoms\n  immersed in a reservoir gas: We study the dissipative dynamics of neutral atoms in anisotropic harmonic\npotentials, immersed in a reservoir species that is not trapped by the harmonic\npotential. Considering initial motional excitation of the atoms along one\ndirection, we explore the resulting spontaneous emission of reservoir\nexcitations, across a range of trap parameters from strong to weak radial\nconfinement. In different limits these processes are useful as a basis for\nanalogies to laser cooling, or as a means to introduce controlled dissipation\nto many-body dynamics. For realistic experimental parameters, we analyse the\ndistribution of the atoms during the decay and determine the effects of heating\narising from a finite temperature reservoir."
    },
    {
        "anchor": "Analysis of shape change of droplet in dipolar Bose-Hubbard model: The long-range and anisotropic nature of the dipolar interaction provides the\nso-called supersolid phases in Bose-Einstein condensates (BECs) in an optical\nlattice. However, in a certain area of dipole interaction parameters, BECs can\nform into a droplet. In this paper, in order to qualitatively understand the\ndroplet formations, we propose a toy model that allows us to estimate the size\nand shape of droplets in dipolar Bose-Hubbard system in the optical lattice. We\ncompare results of the toy model with numerical solutions of the mean-field\ncalculation.",
        "positive": "Cooperatively-enhanced precision of hybrid light-matter sensors: We consider a hybrid system of matter and light as a sensing device and\nquantify the role of cooperative effects. The latter generically enhance the\nprecision with which modifications of the effective light-matter coupling\nconstant can be measured. In particular, considering a fundamental model of $N$\nqubits coupled to a single electromagnetic mode, we show that the ultimate\nbound for the precision shows double-Heisenberg scaling:\n$\\Delta\\theta\\propto1/(Nn)$, with $N$ and $n$ being the number of qubits and\nphotons, respectively. Moreover, even using classical states and measuring only\none subsystem, a Heisenberg-times-shot-noise scaling, i.e. $1/(N\\sqrt{n})$ or\n$1/(n\\sqrt{N})$, is reached. As an application, we show that a Bose-Einstein\ncondensate trapped in a double-well potential within an optical cavity can\ndetect the gravitational acceleration $g$ with the relative precision of\n$\\Delta g/g\\simeq10^{-9}\\text{Hz}^{-1/2}$. The analytical approach presented in\nthis study takes into account the leakage of photons through the cavity\nmirrors, and allows to determine the sensitivity when $g$ is inferred via\nmeasurements on atoms or photons."
    },
    {
        "anchor": "Quasihole dynamics as a detection tool for quantum Hall phases: Existing techniques for synthesizing gauge fields are able to bring a\ntwo-dimensional cloud of harmonically trapped bosonic atoms into a regime where\nthe occupied single-particle states are restricted to the lowest Landau level\n(LLL). Repulsive short-range interactions drive various transitions from fully\ncondensed into strongly correlated states. In these different phases we study\nthe response of the system to quasihole excitations induced by a laser beam. We\nfind that in the Laughlin state the quasihole performs a coherent constant\nrotation around the center, ensuring conservation of angular momentum. This is\ndistinct to any other regime with higher density, where the quasihole is found\nto decay. At a characteristic time, the decay process is reversed, and revivals\nof the quasihole can be observed in the density. Measuring the period and\nposition of the revival can be used as a spectroscopic tool to identify the\nstrongly correlated phases in systems with a finite number of atoms.",
        "positive": "Universal Dynamics of a Degenerate Bose Gas Quenched to Unitarity: Motivated by an unexpected experimental observation from the Cambridge group,\n[Eigen {\\it et al.,} Nature {\\bf563}, 221 (2018)], we study the evolution of\nthe momentum distribution of a degenerate Bose gas quenched from the weakly\ninteracting to the unitarity regime. For the two-body problem, we establish a\nrelation that connects the momentum distribution at a long time to a\nsub-leading term in the initial wave function. For the many-body problem, we\nemploy the time-dependent Bogoliubov variational wave function and find that,\nin certain momentum regimes, the momentum distribution at long times displays\nthe same exponential behavior found by the experiment. Moreover, we find that\nthis behavior is universal and independent of the short-range details of the\ninteraction potential. Consistent with the relation found in the two-body\nproblem, we also numerically show that this exponential form is hidden in the\nsame sub-leading term of the Bogoliubov wave function in the initial stages.\nOur results establish a consistent picture to understand the universal dynamics\nobserved in the Cambridge experiment."
    },
    {
        "anchor": "Single-exposure absorption imaging of ultracold atoms using deep\n  learning: Absorption imaging is the most common probing technique in experiments with\nultracold atoms. The standard procedure involves the division of two frames\nacquired at successive exposures, one with the atomic absorption signal and one\nwithout. A well-known problem is the presence of residual structured noise in\nthe final image, due to small differences between the imaging light in the two\nexposures. Here we solve this problem by performing absorption imaging with\nonly a single exposure, where instead of a second exposure the reference frame\nis generated by an unsupervised image-completion autoencoder neural network.\nThe network is trained on images without absorption signal such that it can\ninfer the noise overlaying the atomic signal based only on the information in\nthe region encircling the signal. We demonstrate our approach on data captured\nwith a quantum degenerate Fermi gas. The average residual noise in the\nresulting images is below that of the standard double-shot technique. Our\nmethod simplifies the experimental sequence, reduces the hardware requirements,\nand can improve the accuracy of extracted physical observables. The trained\nnetwork and its generating scripts are available as an open-source repository\n(http://absDL.github.io/).",
        "positive": "Imaginary time crystal of thermal quantum matter: Spontaneous symmetry breaking is responsible for rich quantum phenomena from\ncrystalline structures to superconductivity. This concept was boldly extended\nto the breaking of time translation, opening an avenue to finding exotic phases\nof quantum matter with collective time modulation and correlation. Here we\nreport that a thermally open quantum ensemble manifests in the dual space of\nimaginary time with crystalline ordering due to a bath-induced retarded\ninteraction. Exact quantum Monte Carlo simulations are performed to show that\nthis imaginary time crystal phase exhibits characteristic ground-state and\nthermal properties absent in conventional quantum manybody systems, especially\nthe striking temperature-oscillating behavior of its physical observables."
    },
    {
        "anchor": "Hysteresis in a quantized, superfluid atomtronic circuit: Atomtronics is an emerging interdisciplinary field that seeks new\nfunctionality by creating devices and circuits where ultra-cold atoms, often\nsuperfluids, play a role analogous to the electrons in electronics. Hysteresis\nis widely used in electronic circuits, e.g., it is routinely observed in\nsuperconducting circuits and is essential in rf-superconducting quantum\ninterference devices [SQUIDs]. Furthermore, hysteresis is as fundamental to\nsuperfluidity (and superconductivity) as quantized persistent currents,\ncritical velocity, and Josephson effects. Nevertheless, in spite of multiple\ntheoretical predictions, hysteresis has not been previously observed in any\nsuperfluid, atomic-gas Bose-Einstein condensate (BEC). Here we demonstrate\nhysteresis in a quantized atomtronic circuit: a ring of superfluid BEC\nobstructed by a rotating weak link. We directly detect hysteresis between\nquantized circulation states, in contrast to superfluid liquid helium\nexperiments that observed hysteresis directly in systems where the quantization\nof flow could not be observed and indirectly in systems that showed quantized\nflow. Our techniques allow us to tune the size of the hysteresis loop and to\nconsider the fundamental excitations that accompany hysteresis. The results\nsuggest that the relevant excitations involved in hysteresis are vortices and\nindicate that dissipation plays an important role in the dynamics. Controlled\nhysteresis in atomtronic circuits may prove to be a crucial feature for the\ndevelopment of practical devices, just as it has in electronic circuits like\nmemory, digital noise filters (e.g., Schmitt triggers), and magnetometers\n(e.g., SQUIDs).",
        "positive": "Wannier functions using a discrete variable representation for optical\n  lattices: We propose a numerical method using the discrete variable representation\n(DVR) for constructing real-valued Wannier functions localized in a unit cell\nfor both symmetric and asymmetric periodic potentials. We apply these results\nto finding Wannier functions for ultracold atoms trapped in laser-generated\noptical lattices. Following Kivelson \\cite{kivelson_wannier_1982}, for a\nsymmetric lattice with inversion symmetry, we construct Wannier functions as\neigen states of the position operators $\\hat x$, $\\hat y$ and $\\hat z$\nrestricted to single-particle Bloch functions belonging to one or more bands.\nTo ensure that the Wannier functions are real-valued, we numerically obtain the\nband structure and real-valued eigen states using a uniform Fourier grid DVR.\nWe then show by a comparison of tunneling energies, that the Wannier functions\nare accurate for both inversion symmetric and asymmetric potentials to better\nthan ten significant digits when using double-precision arithmetic. The\ncalculations are performed for an optical lattice with double-wells per unit\ncell with tunable asymmetry along the $x$ axis and a single sinusoidal\npotential along the perpendicular directions. Localized functions at the two\npotential minima within each unit cell are similarly constructed, but using a\nsuperposition of single-particle solutions from the two lowest bands. We\nfinally use these localized basis functions to determine the two-body\ninteraction energies in the Bose-Hubbard (BH) model, and show the dependence of\nthese energies on lattice asymmetry."
    },
    {
        "anchor": "Vortices in dipolar condensates with dominant dipolar interactions: We present full three-dimensional numerical calculations of single vortex\nstates in rotating dipolar condensates. We consider a Bose-Einstein condensate\nof 52Cr atoms with dipole-dipole and s-wave contact interactions confined in an\naxially symmetric harmonic trap. We obtain the vortex states by numerically\nsolving the Gross-Pitaevskii equation in the rotating frame with no further\napproximations. We investigate the properties of a single vortex and calculate\nthe critical angular velocity for different values of the s-wave scattering\nlength. We show that, whereas the standard variational approach breaks down in\nthe limit of pure dipolar interactions, exact solutions of the Gross-Pitaevskii\nequation can be obtained for values of the s-wave scattering length down to\nzero. The energy barrier for the nucleation of a vortex is calculated as a\nfunction of the vortex displacement from the rotation axis for different values\nof the angular velocity of the rotating trap.",
        "positive": "Multi-Component Quantum Gases in Spin-Dependent Hexagonal Lattices: Periodicity is one of the most fundamental structural characteristics of\nsystems occurring in nature. The properties of these systems depend strongly on\nthe symmetry of the underlying periodic structure. In solid state materials -\nfor example - the static and transport properties as well as the magnetic and\nelectronic characteristics are crucially influenced by the crystal symmetry. In\nthis context, hexagonal structures play an extremely important role and lead to\nnovel physics like that of carbon nanotubes or graphene. Here we report on the\nfirst realization of ultracold atoms in a spin-dependent optical lattice with\nhexagonal symmetry. We show how combined effects of the lattice and\ninteractions between atoms lead to a forced antiferromagnetic N\\'eel order when\ntwo spin-components localize at different lattice sites. We also demonstrate\nthat the coexistence of two components - one Mott-insulating and the other one\nsuperfluid - leads to the formation of a forced supersolid. Our observations\nare consistent with theoretical predictions using Gutzwiller mean-field theory."
    },
    {
        "anchor": "Odd-frequency Two Particle Bose-Einstein Condensate: We introduce the concept of the {\\em odd-frequency} Bose Einstein Condensate\n(BEC), characterized by the odd frequency/time two-boson expectation value. To\nillustrate the concept of odd frequency BEC we present simple classification of\npair boson condensates that explicitly permits this state. We point qualitative\ndifferences of odd-frequency BEC with conventional BEC and introduce the order\nparameter and wave function for the odd-frequency BEC.",
        "positive": "Thermodynamics of inhomogenous imperfect quantum gases in harmonic traps: We discuss thermodynamic properties of harmonically trapped imperfect quantum\ngases. The spatial inhomogeneity of these systems imposes a redefinition of the\nmean-field interparticle potential energy as compared to the homogeneous case.\nIn our approach, it takes the form $\\frac{a}{2} N^2 \\, \\omega^d$, where $N$ is\nthe number of particles, $\\omega$ - the harmonic trap frequency, $d$ - system's\ndimensionality, and $a$ is a parameter characterizing the interparticle\ninteraction. We provide arguments that this model corresponds to the limiting\ncase of a long-ranged interparticle potential of vanishingly small amplitude.\nThis conclusion is drawn from a computation similar to the well-known Kac\nscaling procedure, which is presented here in a form adapted to the case of an\nisotropic harmonic trap. We show that within our model, the imperfect gas of\ntrapped repulsive bosons undergoes the Bose-Einstein condensation provided\n$d>1$. The main result of our analysis is that in $d=1$ the gas of attractive\nimperfect fermions with $a=-a_{F}<0$ is thermodynamically equivalent to the gas\nof repulsive bosons with $a=a_{B}>0$ provided the parameters $a_{F}$ and\n$a_{B}$ fulfill the relation $a_{B}+a_{F}=\\hbar$. This result supplements\nsimilar recent conclusion about thermodynamic equivalence of two-dimensional\nuniform imperfect repulsive Bose and attractive Fermi gases."
    },
    {
        "anchor": "Dynamical nonlinear excitations induced by interaction quench in a\n  two-dimensional box-trapped Bose-Einstein condensate: Manipulating nonlinear excitations, including solitons and vortices, is an\nessential topic in quantum many-body physics. A recent progress in this\ndirection is a new protocol proposed in [Phys. Rev. Res. 2, 043256 (2020)] to\nproduce dark solitons in a one-dimensional atomic Bose-Einstein condensate\n(BEC) by quenching inter-atomic interaction. Motivated by this work, we\ngeneralize the protocol to a two-dimensional BEC and investigate the general\nscenario of its post-quench dynamics. For an isotropic disk trap with a\nhard-wall boundary, we find that successive inward-moving ring dark solitons\n(RDSs) can be induced from the edge, and the number of RDSs can be controlled\nby tuning the ratio of the after- and before-quench interaction strength across\ndifferent critical values. The role the quench played on the profiles of the\ndensity, phase, and sound velocity is also investigated. Due to the snake\ninstability, the RDSs then become vortex-antivortex pairs with peculiar\ndynamics managed by the initial density and the after-quench interaction. By\ntuning the geometry of the box traps, demonstrated as polygonal ones, more\nsubtle dynamics of solitons and vortices are enabled. Our proposed protocol and\nthe discovered rich dynamical effects on nonlinear excitations can be realized\nin future cold-atom experiments.",
        "positive": "Imaginary spin-orbital coupling in parity-time symmetric systems with\n  momentum-dependent gain and loss: Spin-orbital coupling (SOC) and parity-time ($\\mathcal{PT}$) symmetry both\nhave attracted paramount research interest in condensed matter physics, cold\natom physics, optics and acoustics to develop spintronics, quantum computation,\nprecise sensors and novel functionalities. Natural SOC is an intrinsic\nrelativistic effect. However, there is an increasing interest in synthesized\nSOC nowadays. Here, we show that in a $\\mathcal{PT}$-symmetric spin-1/2 system,\nthe momentum-dependent balanced gain and loss can synthesize a new type of SOC,\nwhich we call imaginary SOC. The imaginary SOC can substantially change the\nenergy spectrum of the system. Firstly, we show that it can generate a pure\nreal energy spectrum with a double-valleys structure. Therefore, it has the\nability to generate supersolid stripe states. Especially, the imaginary SOC\nstripe state can have a high contrast of one. Moreover, the imaginary SOC can\nalso generate a spectrum with tunable complex energy band, in which the waves\nare either amplifying or decaying. Thus, the imaginary SOC would also find\napplications in the engineering of $\\mathcal{PT}$-symmetry-based coherent wave\namplifiers/absorbers. Potential experimental realizations of imaginary SOC are\nproposed in cold atomic gases and systems of coupled waveguides constituted of\nnonlocal gain and loss."
    },
    {
        "anchor": "Bayesian Optimization of Bose-Einstein Condensates: Machine Learning methods are emerging as faster and efficient alternatives to\nnumerical simulation techniques. The field of Scientific Computing has started\nadopting these data-driven approaches to faithfully model physical phenomena\nusing scattered, noisy observations from coarse-grained grid-based simulations.\nIn this paper, we investigate data-driven modelling of Bose-Einstein\nCondensates (BECs). In particular, we use Gaussian Processes (GPs) to model the\nground state wave function of BECs as a function of scattering parameters from\nthe dimensionless Gross Pitaveskii Equation (GPE). Experimental results\nillustrate the ability of GPs to accurately reproduce ground state wave\nfunctions using a limited number of data points from simulations. Consistent\nperformance across different configurations of BECs, namely Scalar and\nVectorial BECs generated under different potentials, including harmonic, double\nwell and optical lattice potentials pronounces the versatility of our method.\nComparison with existing data-driven models indicates that our model achieves\nsimilar accuracy with only a small fraction 1/50th of data points used by\nexisting methods, in addition to modelling uncertainty from data. When used as\na simulator post-training, our model generates ground state wave functions $36\n\\times $ faster than Trotter Suzuki, a numerical approximation technique that\nuses Imaginary time evolution. Our method is quite general; with minor changes\nit can be applied to similar quantum many-body problems.",
        "positive": "Two-body bound and edge states in the extended SSH Bose-Hubbard model: We study the bosonic two-body problem in a Su-Schrieffer-Heeger dimerized\nchain with on-site and nearest-neighbor interactions. We find two classes of\nbound states. The first, similar to the one induced by on-site interactions,\nhas its center of mass on the strong link, whereas the second, existing only\nthanks to nearest-neighbors interactions, is centered on the weak link. We\nidentify energy crossings between these states and analyse them using exact\ndiagonalization and perturbation theory. In the presence of open boundary\nconditions, novel strongly-localized edge-bound states appear in the spectrum\nas a consequence of the interplay between lattice geometry, on-site and\nnearest-neighbor interactions. Contrary to the case of purely on-site\ninteractions, such EBS persist even in the strongly interacting regime."
    },
    {
        "anchor": "Efimov physics from the functional renormalization group: Few-body physics related to the Efimov effect is discussed using the\nfunctional renormalization group method. After a short review of\nrenormalization in its modern formulation we apply this formalism to the\ndescription of scattering and bound states in few-body systems of identical\nbosons and distinguishable fermions with two and three components. The Efimov\neffect leads to a limit cycle in the renormalization group flow. Recently\nmeasured three-body loss rates in an ultracold Fermi gas $^6$Li atoms are\nexplained within this framework. We also discuss briefly the relation to the\nmany-body physics of the BCS-BEC crossover for two-component fermions and the\nformation of a trion phase for the case of three species.",
        "positive": "Non-Galilean response of Rashba coupled Fermi gases: We consider the effect of a momentum kick on the ground state of a\nnon-interacting two-dimensional Fermi gas subject to Rashba spin-orbit\ncoupling. Although the total momentum is a constant of motion, the gas does not\nobey the rules of Galilean relativity. Upon imprinting a small overall velocity\nto the non-interacting gas, we find that the Fermi sea is deformed in a\nnon-trivial way. We also consider a weakly repulsive Fermi gas, and find, from\nits Hartree shift, that the total ground state of the system may change into a\ndeformed, finite momentum ground state as the repulsion is increased beyond a\ncritical value, without the need of any external Zeeman fields. We also discuss\npossible experimental signatures of these effects."
    },
    {
        "anchor": "Bose-Fermi transmutation for one-dimensional harmonic trap: Using Density Matrix renormalization group (DMRG), we study the ground state\nproperties of spin one-half fermions and scalar bosons in the soft-core limit,\nwith weak s-wave inter and intra species interactions. We considered the system\nsubject to one-dimensional (1D) optical lattice and a superimposed potential at\nzero temperature, in the framework of Bose-Fermi-Hubbard model. We found that\nfor certain fillings and interaction parameters, a transmutation occurs between\nthe ground states of bosons and fermions when the densities are exchanged. We\ntoo report that the density distributions of bosons and fermions overlap with\neach other in a bosonic and fermionic Mott plateau, when the interaction\nparameters fulfill the relationship $U_{BB}>U_{BF}<U_{BF}$. We also find that\nthe fermions are repelled out of the central region of the trap for\nsufficiently strong $U_{FF}$ interaction, exhibiting phase separation of Bose\nand Fermi components.",
        "positive": "Stability change of a multi-charged vortex due to coupling with\n  quadrupole mode: We have studied collective modes of quasi-2D Bose-Einstein condensates with\nmultiply-charged vortices using a variational approach. Two of the four\ncollective modes considered exhibit coupling between the vortex dynamics and\nthe large-scale motion of the cloud. The vortex presence causes a shift in all\nfrequencies of collective modes even for the ones that do not couple\ndynamically with the vortex-core. The coupling between vortex and large-scale\ncollective excitations can induce the multi-charged vortex to decay into\nsingly-charged vortices with the quadrupole mode being one possible channel for\nsuch a decay. Therefore a thorough study was done about the possibility to\nprevent the vortex decay by applying a Gaussian potential with its width\nproportional to the vortex-core radius and varying its height. In such way, we\ncreated a stability diagram of height versus interaction strength which has\nstable regions due the static Gaussian potential. Furthermore, by using a\nsinusoidal time-modulation around the average height of the Gaussian potential,\nwe have obtained a diagram for the parametric resonance which can prevent the\nvortex decay in regions where static potential can not."
    },
    {
        "anchor": "Phase Space Crystal Vibrations: Chiral Edge States with Preserved\n  Time-reversal Symmetry: It was recently discovered that atoms subject to a time-periodic drive can\ngive rise to a crystal structure in phase space. In this work, we point out the\natom-atom interactions give rise to collective phonon excitations of\nphase-space crystal via a pairing interaction with intrinsically complex phases\nthat can lead to a phonon Chern insulator, accompanied by topologically robust\nchiral transport along the edge of the phase-space crystal. This topological\nphase is realized even in scenarios where the time-reversal transformation is a\nsymmetry, which is surprising because the breaking of time-reversal symmetry is\na strict precondition for topological chiral transport in the standard setting\nof real-space crystals. Our work has also important implications for the\ndynamics of 2D charged particles in a strong magnetic field.",
        "positive": "Momentum-dependent pseudo-spin dimers of coherently coupled bosons in\n  optical lattices: We study the two-body bound and scattering states of two particles in a one\ndimensional optical lattice in the presence of a coherent coupling between two\ninternal atomic levels. Due to the interplay between periodic potential,\ninteractions and coherent coupling, the internal structure of the bound states\ndepends on their center of mass momentum. This phenomenon corresponds to an\neffective momentum-dependent magnetic field for the dimer pseudo-spin, which\ncould be observed in a chirping of the precession frequency during Bloch\noscillations. The essence of this effect can be easily interpreted in terms of\nan effective bound state Hamiltonian. Moreover for indistinguishable bosons,\nthe two-body eigenstates can present simultaneously attractive and repulsive\nbound-state nature or even bound and scattering properties."
    },
    {
        "anchor": "Stable, mobile, dark-in-bright, dipolar Bose-Einstein condensate soliton: We demonstrate robust, stable, mobile, quasi-one-dimensional, dark-in-bright\ndipolar Bose-Einstein condensate (BEC) soliton with a notch in the central\nplane formed due to dipolar interaction for repulsive contact interaction. At\nmedium velocity the head on collision of two such solitons is found to be quasi\nelastic with practically no deformation. A proposal for creating dipolar\ndark-in-bright solitons in laboratories by phase imprinting is also discussed.\nA rich variety of such solitons can be formed in dipolar binary BEC, where one\ncan have a dark-in-bright soliton coupled to a bright soliton or two coupled\ndark-in-bright solitons. The findings are illustrated using numerical\nsimulation in three spatial dimensions employing realistic interaction\nparameters for a dipolar 164Dy BEC and a binary 164Dy-162Dy BEC.",
        "positive": "Melting of a vortex matter Wigner crystal: The two-dimensional One-Component Plasma (OCP) is a foundational model of the\nstatistical mechanics of interacting particles, describing phenomena common to\nastrophysics, turbulence, and the Fractional Quantum Hall Effect (FQHE).\nDespite an extensive literature, the phase diagram of the 2D OCP is still a\nsubject of some controversy. Here we develop a \"vortex matter\" simulator to\nrealize the logarithmic-interaction OCP experimentally by exploiting the\ntopological character of quantized vortices in a thin superfluid layer.\nPrecision optical-tweezer control of the location of quantized vortices enables\ndirect preparation of the OCP ground state with or without defects, and heating\nfrom acoustic excitations allows the observation of the melting transition from\nthe solid Wigner crystal through the liquid phase. We present novel theoretical\nanalysis that is in quantitative agreement with experimental observations, and\ndemonstrates how equilibrium states are achieved through the system dynamics.\nThis allows a precise measurement of the superfluid-thermal cloud mutual\nfriction and heating coefficients. This platform provides a route towards\nsolving a number of open problems in systems with long-range interactions. At\nequilibrium, it could distinguish between the competing scenarios of grain\nboundary melting and KTHNY theory. Dynamical simulators could test the\nexistence of predicted edge-wave solitons which form a hydrodynamic analogue of\ntopological edge states in the FQHE."
    },
    {
        "anchor": "Increasing Quantum Degeneracy by Heating a Superfluid: We consider a uniform superfluid confined in two compartments connected by a\nsuperleak and initially held at equal temperatures. If one of the two\ncompartments is heated, a fraction of the superfluid will flow through the\nsuperleak. We show that, under certain thermodynamic conditions, the atoms flow\nfrom the hotter to the colder compartment, contrary to what happens in the\nfountain effect observed in superfluid Helium. This flow causes quantum\ndegeneracy to increase in the colder compartment. In superfluid Helium, this\nnovel thermomechanical effect takes place in the phonon regime of very low\ntemperatures. In dilute quantum gases, it occurs at all temperatures below Tc .\nThe increase in quantum degeneracy reachable through the adiabatic displacement\nof the wall separating the two compartments is also discussed.",
        "positive": "Chaos and two-level dynamics of the Atomtronic Quantum Interference\n  Device: We study the Atomtronics Quantum Interference Device employing a\nsemiclassical perspective. We consider an $M$ site ring that is described by\nthe Bose-Hubbard Hamiltonian. Coherent Rabi oscillations in the flow of the\ncurrent are feasible, with an enhanced frequency due to to chaos-assisted\ntunneling. We highlight the consequences of introducing a weak-link into the\ncircuit. In the latter context we clarify the phase-space considerations that\nare involved in setting up an effective \"systems plus bath\" description in\nterms of Josephson-Caldeira-Leggett Hamiltonian."
    },
    {
        "anchor": "Composite Fermions and their Pair States in a Strongly-Coupled Fermi\n  Liquid: Our goal is to understand the phenomena arising in optical lattice fermions\nat low temperature in an external magnetic field. Varying the field, the\nattraction between any two fermions can be made arbitrarily strong, where\ncomposite bosons form via so-called Feshbach resonances. By setting up\nstrong-coupling equations for fermions, we find that in spatial dimension $d>2$\nthey couple to bosons which dress up fermions and lead to new massive composite\nfermions. At low enough temperature, we obtain the critical temperature at\nwhich composite bosons undergo the Bose-Einstein condensate (BEC), leading to\nBEC-dressing massive fermions. These form tightly bound pair states which are\nnew bosonic quasi-particles producing a BEC-type condensate. A quantum critical\npoint is found and the formation of condensates of complex quasi-particles is\nspeculated over.",
        "positive": "Bose-Einstein condensation of 86Sr: We report on the attainment of Bose-Einstein condensation of 86Sr. This\nisotope has a scattering length of about +800 a0 and thus suffers from fast\nthree-body losses. To avoid detrimental atom loss, evaporative cooling is\nperformed at low densities around 3x10^12 cm^-3 in a large volume optical\ndipole trap. We obtain almost pure condensates of 5x10^3 atoms."
    },
    {
        "anchor": "Bose-Einstein Condensates in Non-abelian Gauge Fields: The recent success of the NIST group in generating abelian gauge field in\ncold atoms has created opportunities to simulate electronic transports in\nsolids using atomic gases. Very recently, the NIST group has also announced in\na DARPA Meeting the creation of non-abelian gauge fields in a pseudo spin-1/2\nBose gas. While there have been considerable theoretical activities in\nsynthetic gauge fields, non-abelian fields have not been generated until now.\nHere, we show that in a non-abelian gauge field, a spinor condensate will\ndevelop a spontaneous stripe structure in each spin component, reflecting a\nground state made up of two non-orthogonal dressed states with different\nmomenta. Depending on interactions, this ground state can reduce back to a\nsingle dressed state. These momentum carrying stripes are the {\\em macroscopic}\nbosonic counterpart of the spin-orbit phenomena in fermions that are being\nactively studied in electron physics today.",
        "positive": "Spin-charge-density wave in a squircle-like Fermi surface for ultracold\n  atoms: We derive and discuss an experimentally realistic model describing ultracold\natoms in an optical lattice including a commensurate, but staggered, Zeeman\nfield. The resulting band structure is quite exotic; fermions in the third band\nhave an unusual rounded picture-frame Fermi surface (essentially two concentric\nsquircles), leading to imperfect nesting. We develop a generalized\nSO(3,1)xSO(3,1) theory describing the spin and charge degrees of freedom\nsimultaneously, and show that the system can develop a coupled\nspin-charge-density wave order. This ordering is absent in studies of the\nHubbard model that treat spin and charge density separately."
    },
    {
        "anchor": "Quantum Breathing of an Impurity in a One-dimensional Bath of\n  Interacting Bosons: By means of time-dependent density-matrix renormalization-group (TDMRG) we\nare able to follow the real-time dynamics of a single impurity embedded in a\none-dimensional bath of interacting bosons. We focus on the impurity breathing\nmode, which is found to be well-described by a single oscillation frequency and\na damping rate. If the impurity is very weakly coupled to the bath, a\nLuttinger-liquid description is valid and the impurity suffers an\nAbraham-Lorentz radiation-reaction friction. For a large portion of the\nexplored parameter space, the TDMRG results fall well beyond the\nLuttinger-liquid paradigm.",
        "positive": "The effect of non-local derivative on Bose-Einstein condensation: In this paper, we study the effect of non-local derivative on Bose-Einstein\ncondensation. Firstly, we consider the Caputo-Fabrizio derivative of fractional\norder \\alpha to derive the eigenvalues of non-local Schr\\\"odinger equation for\na free particle in a 3D box. Afterwards, we consider 3D Bose-Einstein\ncondensation of an ideal gas with the obtained energy spectrum. Interestingly,\nin this approach the critical temperatures Tc of condensation for 1 < \\alpha <\n2 are greater than the standard one. Furthermore, the condensation in 2D is\nshown to be possible. Second and for comparison, we presented, on the basis of\na spectrum established by N. Laskin, the critical transition temperature as a\nfunction of the fractional parameter {\\alpha} for a system of free bosons\ngoverned by an Hamiltonian with power law on the moment (H~p\\alpha). In this\ncase, we have demonstrated that the transition temperature is greater than the\nstandard one. By comparing the two transition temperatures (relative to\nCaputo-Fabrizio and to Laskin), we have found for fixed \\alpha and the density\n\\rho that the transition temperature relative to Caputo-fabrizio is greater\nthan relative to Laskin."
    },
    {
        "anchor": "Symmetry properties of the ground state of the system of interacting\n  spinless bosons: We perform the symmetry analysis of the properties of the ground state of a\nfinite system of interacting spinless bosons for the three most symmetric\nboundary conditions (BCs): zero BCs with spherical and circular symmetries, as\nwell as periodic BCs. The symmetry of the system can lead to interesting\nproperties. For instance, the density of a periodic Bose system is an exact\nconstant: $\\rho(\\textbf{r})=const$. Moreover, under the perfect spherical\nsymmetry of BCs, the crystalline state cannot produce the Bragg peaks. The main\nresult of the article is that symmetry properties and general\nquantum-mechanical theorems admit equally both crystalline and liquid ground\nstate for a Bose system of any density.",
        "positive": "Quantum Hydrodynamics in One Dimension beyond the Luttinger Liquid: Recent years have seen the development of a rich phenomenology beyond the\nLuttinger Liquid model of one dimensional quantum fluids, arising from\ninteractions between the elementary phonon excitations. It has been known for\nsome time, however, that the straightforward inclusion of these interactions\npresents technical difficulties that have necessitated approaches based on\nrefermionization or effective impurity models.\n  In this work we show that the nonlinear extensions of the Luttinger model are\ntractable in the phonon basis. We present a calculation of the singularities\npresent in the zero temperature dynamical structure factor in the semiclassical\nlimit where the phonon dispersion is strong.\n  A unitary transformation decouples interactions between left-- and\nright--moving phonons, leaving a nonlinear chiral Hamiltonian. At low momenta,\nthis Hamiltonian has a spectrum bounded above and below by thresholds\nidentified with phonon and soliton excitations in the semiclassical limit. The\nchiral dynamical structure factor therefore has support only in this region,\nwith power law singularities at the thresholds originating in the Anderson\northogonality catastrophe, which we calculate analytically. The dynamical\nstructure factor for the original nonchiral Hamiltonian is a convolution of\nthis chiral correlator with a power law arising from the left--right\ndecoupling."
    },
    {
        "anchor": "Bloch oscillations of spin-orbit-coupled cold atoms in an optical\n  lattice and spin current generation: We study the Bloch oscillation dynamics of a spin-orbit-coupled cold atomic\ngas trapped inside a one-dimensioanl optical lattice. The eigenspectra of the\nsystem is identified as two interpenetrating Wannier-Stark ladder. Based on\nthat, we carefully analyzed the Bloch oscillation dynamics and found out that\nintraladder coupling between neighboring rungs of Wannier-Stark ladder give\nrise to ordinary Bloch oscillation while interladder coupling lead to small\namplitude high frequency oscillation superimposed on it. Specifically\nspin-orbit interaction breaks Galilean invariance, which can be reflected by\nout-of-phase oscillation of the two spin components in the accelerated frame.\nThe possibility of generating spin current in this system are also explored.",
        "positive": "Efimov physics beyond universality: We provide an exact solution of the Efimov spectrum in ultracold gases within\nthe standard two-channel model for Feshbach resonances. It is shown that the\nfinite range in the Feshbach coupling makes the introduction of an adjustable\nthree-body parameter obsolete. The solution explains the empirical relation\nbetween the scattering length a_- where the first Efimov state appears at the\natom threshold and the van der Waals length l_vdw for open channel dominated\nresonances. There is a continuous crossover to the closed channel dominated\nlimit, where the scale in the energy level diagram as a function of the inverse\nscattering length 1/a is set by the intrinsic length r* associated with the\nFeshbach coupling. Our results provide a number of predictions for\nnon-universal ratios between energies and scattering lengths that can be tested\nin future experiments."
    },
    {
        "anchor": "Infinitely-long-range nonlocal potentials and the Bose-Einstein\n  supersolid phase: It is shown, with the aid of the Bogoliubov inequality, that a Bose-Einstein\ncondensate has the Bloch form and represents a self-organized supersolid\nprovided the interaction between the condensate atoms is nonlocal and of\ninfinitely long-range.",
        "positive": "Hydrodynamic Relaxation in a Strongly Interacting Fermi Gas: We measure the free decay of a spatially periodic density profile in a normal\nfluid strongly interacting Fermi gas, which is confined in a box potential.\nThis spatial profile is initially created in thermal equilibrium by a\nperturbing potential. After the perturbation is abruptly extinguished, the\ndominant spatial Fourier component exhibits an exponentially decaying\n(thermally diffusive) mode and a decaying oscillatory (first sound) mode,\nenabling independent measurement of the thermal conductivity and the shear\nviscosity directly from the time-dependent evolution."
    },
    {
        "anchor": "Skyrmion-antiSkyrmion pairs in Ultracold Atomic Gases: We study theoretically the dynamics of two-component Bose-Einstein\ncondensates in two dimensions, which admit topological excitations related to\nthe Skyrmions of nuclear physics. We show that there exists a branch of\nuniformly propagating solitary waves characterised by a conserved momentum.\nThese excitations exhibit a cross-over from spatially extended spin-wave states\nat low momentum to a localised \"spin-wave droplet\" at intermediate momentum; at\nstill higher momentum, the configuration evolves continuously into a\nSkyrmion-antiSkyrmion pair. We discuss how these solitary waves can be\ngenerated and studied in experiment.",
        "positive": "Driving quantized vortices with quantum vacuum fluctuations: We propose to use a rotating corrugated material plate in order to stir,\nthrough the Casimir-Polder interaction, quantized vortices in an harmonically\ntrapped Bose-Einstein condensate. The emergence of such vortices within the\ncondensate cannot be explained with a computation of the Casimir-Polder\npotential based on the pairwise summation approach or on the proximity force\napproximation. It thus appears as a genuine signature of non-trivial geometry\neffects on the electromagnetic vacuum fluctuations, which fully exploits the\nsuperfluid nature of the sample. In order to discuss quantitatively the\ngeneration of Casimir-driven vortices, we derive an exact non-perturbative\ntheory of the Casimir-Polder potential felt by the atoms in front of the\ngrating. Our numerical results for a Rb condensate close to a Si grating show\nthat the resulting quantum vacuum torque is strong enough to provide a\ncontactless transfer of angular momentum to the condensate and generate\nquantized vortices under realistic experimental conditions at separation\ndistances around $3$ microns."
    },
    {
        "anchor": "Robustness of gauge-invariant dynamics against defects in ultracold-atom\n  gauge theories: Recent years have seen strong progress in quantum simulation of gauge-theory\ndynamics using ultracold-atom experiments. A principal challenge in these\nefforts is the certification of gauge invariance, which has recently been\nrealized in [B.~Yang et al., arXiv:2003.08945]. One major but poorly\ninvestigated experimental source of gauge-invariance violation is an imperfect\npreparation of the initial state. Using the time-dependent density-matrix\nrenormalization group, we analyze the robustness of gauge-invariant dynamics\nagainst potential preparation defects in the above ultracold-atom\nimplementation of a $\\mathrm{U}(1)$ gauge theory. We find defects related to an\nerroneous initialization of matter fields to be innocuous, as the associated\ngauge-invariance violation remains strongly localized throughout the time\nevolution. A defect due to faulty initialization of the gauge field leads to a\nmild proliferation of the associated violation. Furthermore, we characterize\nthe influence of immobile and mobile defects by monitoring the spread of\nentanglement entropy. Overall, our results indicate that the aforementioned\nexperimental realization exhibits a high level of fidelity in the gauge\ninvariance of its dynamics at all evolution times. Our work provides strong\nevidence that ultracold-atom setups can serve as an extremely reliable\nframework for the quantum simulation of gauge-theory dynamics.",
        "positive": "Anharmonicity-Induced Criticality of Collective Excitation in a Trapped\n  Bose-Einstein Condensate: We investigate the low energy excitations of a dilute atomic Bose gas\nconfined in a anharmonic trap interacting with repulsive forces. The dispersion\nlaw of both surface and compression modes are derived and analyzed for large\nnumbers of atoms in the trap, which show two branches of excitation and appear\na two critical value. For a upper limit, BEC can be unstable with respect to\nsome specific collective excitation, while for the lower limit, the frequency\nof collective excitation under anharmonic influence can be effectively lower\nthan that without anharmonicity. Our work reveals the key role played by the\nanharmonicity and interatomic forces which introduce a rich structure in the\ndynamic behavior of these new many-body systems."
    },
    {
        "anchor": "Efimov Physics in 6Li Atoms: A new narrow 3-atom loss resonance associated with an Efimov trimer crossing\nthe 3-atom threshold has recently been discovered in a many-body system of\nultracold 6Li atoms in the three lowest hyperfine spin states at a magnetic\nfield near 895 G. O'Hara and coworkers have used measurements of the 3-body\nrecombination rate in this region to determine the complex 3-body parameter\nassociated with Efimov physics. Using this parameter as the input, we calculate\nthe universal predictions for the spectrum of Efimov states and for the 3-body\nrecombination rate in the universal region above 600 G where all three\nscattering lengths are large. We predict an atom-dimer loss resonance at (672\n+/- 2) G associated with an Efimov trimer disappearing through an atom-dimer\nthreshold. We also predict an interference minimum in the 3-body recombination\nrate at (759 +/- 1) G where the 3-spin mixture may be sufficiently stable to\nallow experimental study of the many-body system.",
        "positive": "Breakdown of the superfluidity of a matter wave in a random environment: We consider a guided Bose-Einstein matter wave flowing through a disordered\npotential. We determine the critical velocity at which superfluidity is broken\nand compute its statistical properties. They are shown to be connected to\nextreme values of the random potential. Experimental implementations of this\nphysics are discussed."
    },
    {
        "anchor": "Superoperators vs. Trajectories for Matrix Product State Simulations of\n  Open Quantum System: A Case Study: Quantum trajectories and superoperator algorithms implemented within the\nmatrix product state (MPS) framework are powerful tools to simulate the\nreal-time dynamics of open dissipative quantum systems. As for the unitary\ncase, the reachable time-scales as well as system sizes are limited by the\n(possible) build-up of entanglement entropy. The aforementioned methods\nconstitute complementary approaches how Lindblad master equations can be\nintegrated relying either on a quasi-exact representation of the full density\nmatrix or a stochastic unraveling of the density matrix in terms of pure\nstates. In this work, we systematically benchmark both methods by studying the\ndynamics of a Bose-Hubbard chain in the presence of local as well as global\ndephasing. The build-up as well as system-size scaling of entanglement entropy\nstrongly depends on the method and the parameter regime and we discuss the\napplicability of the methods for these cases as well as study the distribution\nof observables and time discretization errors that can become a limiting factor\nfor global dissipation.",
        "positive": "Collinear Four-Wave Mixing of Two-Component Matter Waves: We demonstrate atomic four-wave mixing of two-component matter waves in a\ncollinear geometry. Starting from a single-species Bose-Einstein condensate,\nseed and pump modes are prepared through microwave state transfer and\nstate-selective Kapitza-Dirac diffraction. Four-wave mixing then populates the\ninitially empty output modes. Simulations based on a coupled-mode expansion of\nthe Gross-Pitaevskii equation are in very good agreement with the experimental\ndata. We show that four-wave mixing can play an important role in studies of\nbosonic mixtures in optical lattices. Moreover our system should be of interest\nin the context of quantum atom optics."
    },
    {
        "anchor": "Studies of Single Component Fermi Gas near a $P$-wave Resonance with\n  Lowest Order Constrained Variational Method: We study single component Fermi gas near a $p$-wave resonance with the lowest\norder constrained variational (LOCV) method. We obtain the energy per particle\nfor the ground state of single component Fermi gas near a $p$-wave resonance\nwith LOCV method. We also calculate compressibility of the single component\nFermi gas near a $p$-wave resonance and it shows that near the $p$-wave\nresonance, the system would lose its stability and collapse. The two $p$-wave\ncontacts are also obtained and their variation tendencies with interaction\nstrength are consistent with recent experimental results.",
        "positive": "For high-precision bosonic Josephson junctions, many-body effects matter: Typical treatments of superconducting or superfluid Josephson junctions rely\non mean-field or two-mode models; we explore many-body dynamics of an isolated,\nultracold, Bose-gas long Josephson junction using time-evolving block\ndecimation simulations. We demonstrate that with increasing repulsive\ninteraction strength, localized dynamics emerge that influence macroscopic\ncondensate behavior and can lead to formation of solitons that directly oppose\nthe symmetry of the junction. Initial state population and phase yield insight\ninto dynamic tunneling regimes of a quasi one-dimensional double well\npotential, from Josephson oscillations to macroscopic self-trapping. Population\nimbalance simulations reveal substantial deviation of many-body dynamics from\nmean-field Gross-Pitaevskii predictions, particularly as the barrier height and\ninteraction strength increase. In addition, the sudden approximation supports\nlocalized particle-hole formation after a diabatic quench, and correlation\nmeasures unveil a new dynamic regime: the Fock flashlight."
    },
    {
        "anchor": "Energy relaxation in the Gross-Pitaevskii equation: We introduce a dissipation term in the Gross-Pitaevskii equation that\ndescribes the stimulated relaxation of condensed bosons due to scattering with\na different type of particles. This situation applies to Bose-Einstein\ncondensates of quasi-particles in the solid state, such as magnons and\nexcitons. Our model is compatible with the phenomenology of superfluidity:\nsupercurrents are stable up to a critical speed and decay when they are faster.",
        "positive": "Non-equilibrium transport in $d$-dimensional non-interacting Fermi gases: We consider a non-interacting Fermi gas in $d$ dimensions, both in the\nnon-relativistic and relativistic case. The system of size $L^{d}$ is initially\nprepared into two halves $\\mathcal{L}$ and $\\mathcal{R}$, each of them\nthermalized at two different temperatures, $T_{\\mathcal{L}}$ and\n$T_{\\mathcal{R}}$ respectively. At time $t=0$ the two halves are put in contact\nand the entire system is left to evolve unitarily. We show that, in the\nthermodynamic limit, the time evolution of the particle and energy densities is\nperfectly described by a semiclassical approach which permits to analytically\nevaluate the correspondent stationary currents. In particular, in the case of\nnon-relativistic fermions, we find a low-temperature behavior for the particle\nand energy currents which is independent from the dimensionality $d$ of the\nsystem, being proportional to the difference\n$T_{\\mathcal{L}}^{2}-T_{\\mathcal{R}}^{2}$. Only in one spatial dimension\n($d=1$), the results for the non-relativistic case agree with the massless\nrelativistic ones."
    },
    {
        "anchor": "Periodic dynamics of fermionic superfluids in the BCS regime: We study the zero temperature non-equilibrium dynamics of a fermionic\nsuperfluid in the BCS limit and in the presence of a drive leading to a time\ndependent chemical potential $\\mu(t)$. We choose a periodic driving protocol\ncharacterized by a frequency $\\omega$ and compute the fermion density, the\nwavefunction overlap, and the residual energy of the system at the end of $N$\nperiods of the drive. We demonstrate that the BCS self-consistency condition is\ncrucial in shaping the long-time behaviour of the fermions subjected to the\ndrive and provide an analytical understanding of the behaviour of the fermion\ndensity $n_{{\\mathbf k}_F}$ (where ${\\mathbf k}_F$ is the Fermi momentum\nvector) after a drive period and for large $\\omega$. We also show that the\nmomentum distribution of the excitations generated due to such a drive bears\nthe signature of the pairing symmetry and can be used, for example, to\ndistinguish between s- and d-wave superfluids. We propose experiments to test\nour theory.",
        "positive": "Vortex reconnections in atomic condensates at finite temperature: The study of vortex reconnections is an essential ingredient of understanding\nsuperfluid turbulence, a phenomenon recently also reported in trapped atomic\nBose-Einstein condensates. In this work we show that, despite the established\ndependence of vortex motion on temperature in such systems, vortex\nreconnections are actually temperature independent on the typical length/time\nscales of atomic condensates. Our work is based on a dissipative\nGross-Pitaevskii equation for the condensate, coupled to a semiclassical\nBoltzmann equation for the thermal cloud (the Zaremba-Nikuni-Griffin\nformalism). Comparison to vortex reconnections in homogeneous condensates\nfurther show reconnections to be insensitive to the inhomogeneity in the\nbackground density."
    },
    {
        "anchor": "Boundary central charge from bulk odd viscosity - chiral superfluids: We derive a low energy effective field theory for chiral superfluids, which\naccounts for both spontaneous symmetry breaking and fermionic ground-state\ntopology. Using the theory, we show that the odd (or Hall) viscosity tensor, at\nsmall wave-vector, contains a dependence on the chiral central charge $c$ of\nthe boundary degrees of freedom, as well as additional non-universal\ncontributions. We identify related bulk observables which allow for a bulk\nmeasurement of $c$. In Galilean invariant superfluids, only the particle\ncurrent and density responses to strain and electromagnetic fields are\nrequired. To complement our results, the effective theory is benchmarked\nagainst a perturbative computation within a canonical microscopic model.",
        "positive": "Condensation and superfluidity of $SU(N)$ Bose gas: We perform the comprehensive comparison of properties of the condensate and\nsuperfluid densities for the $N$-component three-dimensional Bose gas with the\nsymmetric inter- and intraspecies short-range interaction between particles. In\nparticular, based on the large-$N$ expansion approach for many-boson systems we\nobtain general expression for density of the superfluid component that at very\nlow temperatures reproduce the well-know Landau's formula and non-trivially\nincludes the thermal fluctuations in the finite-temperature region, and compare\nit to the condensate density calculated previously. The numerically evaluated\ntemperature dependencies are in a qualitatively good agreement with the results\nof Monte Carlo simulations."
    },
    {
        "anchor": "Quantum theory of bright matter wave solitons in harmonic confinement: This paper investigates bright quantum-matter-wave solitons beyond the\nGross-Pitaevskii equation (GPE). As proposals for interferometry and creating\nnonlocal quantum superpositions have been formed, it has become necessary to\ninvestigate effects not present in mean-field models. We investigate the effect\nof harmonic confinement on the internal degrees of freedom, as the ratio of\nzero-point harmonic oscillator length to classical soliton length, for\ndifferent numbers of atoms. We derive a first-order energy correction for the\naddition of a harmonic potential to the many-body wave function and use this to\ncreate a variational technique based on energy minimization of this wave\nfunction for an arbitrary number of atoms, and include numerics based on\ndiagonalization of the Hamiltonian in a basis of harmonic oscillator Fock\nstates. Finally we compare agreement between a Hartree product ground state and\nthe Bethe ansatz solution with a Gaussian envelope localizing the center of\nmass and show a region of good agreement.",
        "positive": "Nonrelativistic Banks-Casher relation and random matrix theory for\n  multi-component fermionic superfluids: We apply QCD-inspired techniques to study nonrelativistic N-component\ndegenerate fermions with attractive interactions. By analyzing the\nsingular-value spectrum of the fermion matrix in the Lagrangian, we derive\nseveral exact relations that characterize the spontaneous symmetry breaking\nU(1)xSU(N)$\\to$Sp(N) through bifermion condensates. These are nonrelativistic\nanalogues of the Banks-Casher relation and the Smilga-Stern relation in QCD.\nNon-local order parameters are also introduced and their spectral\nrepresentations are derived, from which a nontrivial constraint on the phase\ndiagram is obtained. The effective theory of soft collective excitations is\nderived and its equivalence to random matrix theory is demonstrated in the\nepsilon-regime. We numerically confirm the above analytical predictions in\nMonte Carlo simulations."
    },
    {
        "anchor": "Resonant Hawking radiation in Bose-Einstein condensates: We study double-barrier interfaces separating regions of asymptotically\nsubsonic and supersonic flow of Bose condensed atoms. These setups contain at\nleast one black hole sonic horizon from which the analog of Hawking radiation\nshould be generated and emitted against the flow in the subsonic region.\nMultiple coherent scattering by the double-barrier structure strongly modulates\nthe transmission probability of phonons, rendering it very sensitive to their\nfrequency. As a result, resonant tunneling occurs with high probability within\na few narrow frequency intervals. This gives rise to highly non-thermal spectra\nwith sharp peaks. We find that these peaks are mostly associated to decaying\nresonances and only occasionally to dynamical instabilities. Even at achievable\nnonzero temperatures, the radiation peaks can be dominated by the spontaneous\nemission, i.e. enhanced zero-point fluctuations, and not, as often in analog\nmodels, by stimulated emission.",
        "positive": "Coherent Backscattering in Fock Space: a Signature of Quantum Many-Body\n  Interference in Interacting Bosonic Systems: We predict a generic manifestation of quantum interference in many-body\nbosonic systems resulting in a coherent enhancement of the average return\nprobability in Fock space. This enhancement is both robust with respect to\nvariations of external parameters and genuinely quantum insofar as it cannot be\ndescribed within mean-field approaches. As a direct manifestation of the\nsuperposition principle in Fock space, it arises when many-body equilibration\ndue to interactions sets in. Using a semiclassical approach based on\ninterfering paths in Fock space, we calculate the magnitude of the\nbackscattering peak and its dependence on gauge fields that break time-reversal\ninvariance. We confirm our predictions by comparing them to exact quantum\nevolution probabilities in Bose-Hubbard models, and discuss the relevance of\nour findings in the context of many-body thermalization."
    },
    {
        "anchor": "Many-body molecule formation at a domain wall in a one-dimensional\n  strongly interacting ultracold Fermi gas: We analyze how the presence of the bound state on top of strong\nintercomponent contact repulsion affects the dynamics of a two-component\nultracold Fermi gas confined in a one-dimensional harmonic trap. By performing\nfull many-body numerical calculations, we retrieve dynamics of an initially\nphase separated state that has been utilized to excite the spin-dipole mode in\nexperimental settings. We observe an appearance of pairing correlations at the\ndomain wall, heralding the onset of a molecular faction at the interlayer\nbetween the components. We find that such a mechanism can be responsible for\nthe stabilization of the phase separation.",
        "positive": "Properties of a Bose Gas in the Presence of Disorder (Laurea thesis): The phenomenon of Bose-Einstein condensation and superfluidity in a Bose gas\nwith disorder is investigated. Diffusion Monte Carlo (DMC) method is used to\ncalculate superfluid and condensate fraction of the system as a function of\ndensity and strength of disorder at zero temperature. The algorithm and\nimplementation of the Diffusion Monte Carlo method is explained in details.\nBogoliubov theory is developed for the analytical description of the problem.\nGround state energy, superfluid fraction and condensate fraction are\ncalculated. It is shown that same results for the superfluid fraction can be\nobtained in a perturbative manner from Gross-Pitaevskii equation. Ground state\nenergy, obtained from DMC calculations, is compared to predictions of\nBogoliubov theory, which are found to be valid in the regime, when the strength\nof disorder is small. It is shown that \"unusual\" situation, when the superfluid\nfraction is smaller than the condensate fraction, can be realized in this\nsystem."
    },
    {
        "anchor": "Emergent inflation of the Efimov spectrum under three-body spin-exchange\n  interactions: One of the most fascinating predictions of few-body quantum physics is the\nEfimov effect, a universal accumulation of an infinite geometric series of\nthree-body bound states at a two-body scattering resonance. Ever since the\nfirst experimental observation of such an Efimov state, the precise\ncharacterization of their physical properties has continued to challenge\nfew-body theory. This is demonstrated most strongly by the lithium few-body\npuzzle, a remarkable theoretical discrepancy with the observed Efimov spectrum\nin $^7 \\text{Li}$. Here, we resolve this long-standing puzzle, demonstrating\nthat the discrepancy arises out of the presence of strong non-universal\nthree-body spin-exchange interactions. This conclusion is obtained from a\nthorough numerical solution of the quantum mechanical three-body problem,\nincluding precise interatomic interactions and all spin degrees of freedom for\nthree alkali-metal atoms. Our results show excellent agreement with the\nexperimental data regarding both the Efimov spectrum and the absolute rate\nconstants of three-body recombination, and in addition reveal a general product\npropensity for such triatomic reactions in the Paschen-Back regime, stemming\nfrom Wigner's spin conservation rule.",
        "positive": "Localization by Dissipative Disorder: a Deterministic Approach to\n  Position Measurements: We propose an approach to position measurements based on the hypothesis that\nthe action of a position detector on a quantum system can be effectively\ndescribed by a dissipative disordered potential. We show that such kind of\npotential is able, via the dissipation-induced Anderson localization, to\ncontemporary localize the wavefunction of the system and to dissipate\ninformation to modes bounded to the detector. By imposing a diabaticity\ncondition we demonstrate that the dissipative dynamics between the modes of the\nsystem leads to a localized energy exchange between the detector and the rest\nof the environment -the \"click\" of the detector- thus providing a complete\ndeterministic description of a position measurement. We finally numerically\ndemonstrate that our approach is consistent with the Born probability rule."
    },
    {
        "anchor": "Efimov Enhanced Kondo Effect in Alkaline and Alkaline-Earth Atomic Gas\n  Mixture: Recent experiment has observed Feshbach resonances between alkaline and\nalkaline-earth atoms. These Feshbach resonances are insensitive to the nuclear\nspin of alkaline-earth atoms. Ultilizing this feature, we propose to take this\nsystem as a candidate to perform quantum simulation of the Kondo effect. An\nalkaline atom can form a molecule with an alkaline-earth atom with different\nnuclear spins, which plays the role of spin-exchange scattering responsible for\nthe Kondo effect. Furthermore, we point out that the existence of three-body\nbound state and atom-molecule resonance due to the Efimov effect can enhance\nthis spin-exchange scattering, and therefore enhance the Kondo effect. We\ndiscuss this mechanism first with a three-body problem in free space, and then\ndemonstrate that the same mechanism still holds when the alkaline atom is\nlocalized by an external trap and becomes an impurity embedded in the\nalkaline-earth atomic gases.",
        "positive": "Pseudopotential for the 2D contact interaction: We propose a smooth pseudopotential for the contact interaction acting\nbetween ultracold atoms confined to two dimensions. The pseudopotential\nreproduces the scattering properties of the repulsive contact interaction up to\n200 times more accurately than a hard disk potential, and in the attractive\nbranch gives a 10-fold improvement in accuracy over the square well potential.\nFurthermore, the new potential enables diffusion Monte Carlo simulations of the\nultracold gas to be run 15 times quicker than was previously possible."
    },
    {
        "anchor": "Equations of Motion for the Out-of-Equilibrium Dynamics of Isolated\n  Quantum Systems from the Projection Operator Technique: We present a rigorous framework to obtain evolution equations for the\nmomentum distribution and higher order correlation functions in weakly\ninteracting systems based on the Projection Operator Technique. These equations\ncan be numerically solved in an efficient way. We compare the solution of the\nequations with known results for 1D models and find an excellent agreement.",
        "positive": "Trapped unitary two-component Fermi gases with up to ten particles: The properties of two-component Fermi gases with zero-range interactions are\nuniversal. We use an explicitly correlated Gaussian basis set expansion\napproach to investigate small equal-mass two-component Fermi gases under\nspherically symmetric external harmonic confinement. At unitarity, we determine\nthe ground state energy for systems with up to ten particles interacting\nthrough finite-range two-body potentials for both even and odd number of\nparticles. We extrapolate the energies to the zero-range limit using a novel\nscheme that removes the linear and, in some cases, also the quadratic\ndependence of the ground state energies on the two-body range. Our extrapolated\nzero-range energies are compared with results from the literature. We also\ncalculate the two-body Tan contact and structural properties."
    },
    {
        "anchor": "Spin-incoherent Luttinger liquid of one-dimensional SU($\u03ba$)\n  fermions: We theoretically investigate one-dimensional (1D) SU($\\kappa$) fermions in\nthe regime of spin-incoherent Luttinger liquid. We specifically focus on the\nTonks-Girardeau gas limit where its density is sufficiently low that effective\nrepulsions between atoms become infinite. In such case, spin exchange energy of\n1D SU($\\kappa$) fermions vanishes and all spin configurations are degenerate,\nwhich automatically puts them into spin-incoherent regime. In this limit, we\nare able to express the single-particle density matrices in terms of those of\nanyons. This allows us to numerically simulate the number of particles up to\n$N=32$. We numerically calculate single-particle density matrices in two cases:\n(1) equal populations for each spin components (balanced) and (2) all $S_z$\nmanifolds included. In contrast to noninteracting multi-component fermions, the\nmomentum distributions are broadened due to strong interactions. As $\\kappa$\nincreases, the momentum distributions are less broadened for fixed $N$, while\nthey are more broadened for fixed number of particle per spin component. We\nthen compare numerically calculated high momentum tails with analytical\npredictions which are proportional to $1/p^4$, in good agreement. Thus, our\ntheoretical study provides a comparison with the experiments of repulsive\nmulticomponent alkaline-earth fermions with a tunable SU($\\kappa$)\nspin-symmetry in the spin-incoherent regime.",
        "positive": "Spin-polarized droplets in the unitary Fermi gas: We demonstrate the existence of a new type of spatially localized excitations\nin the unitary Fermi gas: spin polarized droplets with a peculiar internal\nstructure involving the abrupt change of the pairing phase at the surface of\nthe droplet. It resembles the structure of the Josephson-$\\pi$ junction\noccurring when a slice of a ferromagnet is sandwiched between two\nsuperconductors. The stability of the impurity is enhanced by the mutual\ninterplay between the polarization effects and the pairing field, resulting in\nan exceptionally long-lived state. The prospects for its realization in\nexperiment are discussed."
    },
    {
        "anchor": "Magnetic resonance spectroscopy and characterization of magnetic phases\n  for spinor Bose-Einstein condensates: The response of spinor Bose-Einstein condensates to dynamical modulation of\nmagnetic fields is discussed with linear response theory. As an experimentally\nmeasurable quantity, the energy absorption rate (EAR) is considered, and the\nresponse function is found to access quadratic spin correlations which come\nfrom the perturbation of the quadratic Zeeman term. By applying our formalism\nto spin-1 condensates, we demonstrate that the EAR spectrum as a function of\nthe modulation frequency is able to characterize the different magnetically\nordered phases.",
        "positive": "On the Efimov Effect in Higher Partial Waves: Using the framework of effective field theory, we present a detailed study of\nthe Efimov effect in higher partial waves for systems of two identical\nparticles and a third distinguishable particle. Depending on the total angular\nmomentum $L$, the two identical particles must be bosons or fermions. We derive\nanalytical expressions for the elastic and inelastic atom-dimer scattering\ncross sections as well as the atom-dimer relaxation rate at the dimer breakup\nthreshold. For the experimentally most relevant case of P-waves, we numerically\ncalculate the atom-dimer scattering cross sections and relaxation rates as a\nfunction of the scattering length, three-body parameter, and mass ratio for\nenergies away from the breakup threshold."
    },
    {
        "anchor": "Spectral density, Levinson's theorem, and the extra term in the second\n  virial coefficient for 1D delta-function potential: In contrast with the 3D result, the Beth-Uhlenbeck (BU) formula in 1D\ncontains an extra -1/2 term. The origin of this -1/2 term is explained using a\nspectral density approach. To be explicit, a delta-function potential is used\nto show that the correction term arises from a pole of the density of states at\nzero energy. The spectral density method shows that this term is actually an\nartifact of the non-normalizability of the scattering states and an infrared\ncutoff regularization scheme has to be used to get the correct result in 1D.\nThe formal derivation of the BU formula would miss this term since it ignores\nthe effects of the boundary terms. While the result is shown for the\ndelta-function potential, the method and result are valid for more general\npotentials. Additionally, the 1D Levinson's theorem can be extracted from the\nspectral density method using the asymptotic form of general potentials. The\nimportance of the result lies in the fact that all these correction terms in 1D\nhave a universal source: a pole at zero energy. Similar calculations using\nquantum field theoretical approaches (without explicit infrared cutoff\nregularization schemes) also show the same subtleties with the correction term\noriginating from the zero energy scattering states (appendix A).",
        "positive": "Matter-wave lensing of shell-shaped Bose-Einstein condensates: Motivated by the recent experimental realization of ultracold quantum gases\nin shell topology, we propose a straightforward implementation of matter-wave\nlensing techniques for shell-shaped Bose-Einstein condensates. This approach\nallows to significantly extend the observation time of the condensate shell\nduring its free expansion and enables the study of novel quantum many-body\neffects on curved geometries. With both analytical and numerical methods we\nderive optimal parameters for realistic lensing schemes to conserve the shell\nshape of the condensate for times up to hundreds of milliseconds."
    },
    {
        "anchor": "Sub-nK thermometry of an interacting $d$-dimensional homogeneous Bose\n  gas: We propose experimentally feasible means for non-destructive thermometry of\nhomogeneous Bose Einstein condensates in different spatial dimensions\n($d\\in\\{1,2,3\\}$). Our impurity based protocol suggests that the fundamental\nerror bound on thermometry at the sub nano Kelvin domain depends highly on the\ndimension, in that the higher the dimension the better the precision.\nFurthermore, sub-optimal thermometry of the condensates by using measurements\nthat are experimentally feasible is explored. We specifically focus on\nmeasuring position and momentum of the impurity that belong to the family of\nGaussian measurements. We show that, generally, experimentally feasible\nmeasurements are far from optimal, except in 1D, where position measurements\nare indeed optimal. This makes realistic experiments perform very well at few\nnano Kelvin temperatures for all dimensions, and at sub nano Kelvin\ntemperatures in the one dimensional scenario. These results take a significant\nstep towards experimental realisation of probe-based quantum thermometry of\nBose Einstein condensates, as it deals with them in one, two and three\ndimensions and uses feasible measurements applicable in current experimental\nsetups.",
        "positive": "The imbalanced antiferromagnet in an optical lattice: We study the rich properties of the imbalanced antiferromagnet in an optical\nlattice. We present its phase diagram, discuss spin waves and explore the\nemergence of topological excitations in two dimensions, known as merons, which\nare responsible for a Kosterlitz-Thouless transition that has never\nunambiguously been observed."
    },
    {
        "anchor": "Inserting single Cs atoms into an ultracold Rb gas: We report on the controlled insertion of individual Cs atoms into an\nultracold Rb gas at about 400 nK. This requires to combine the techniques\nnecessary for cooling, trapping and manipulating single laser cooled atoms\naround the Doppler temperature with an experiment to produce ultracold\ndegenerate quantum gases. In our approach, both systems are prepared in\nseparated traps and then combined. Our results pave the way for coherent\ninteraction between a quantum gas and a single or few neutral atoms of another\nspecies.",
        "positive": "Degenerate Bose gases with uniform loss: We theoretically investigate a weakly-interacting degenerate Bose gas coupled\nto an empty Markovian bath. We show that in the universal phononic limit the\nsystem evolves towards an asymptotic state where an emergent temperature is set\nby the quantum noise of the outcoupling process. For situations typically\nencountered in experiments, this mechanism leads to significant cooling. Such\ndissipative cooling supplements conventional evaporative cooling and dominates\nin settings where thermalization is highly suppressed, such as in a\none-dimensional quasicondensate."
    },
    {
        "anchor": "Dynamical mean-field driven spinor condensate physics beyond the\n  single-mode approximation: $^{23}$Na spin-1 Bose-Einstein condensates are used to experimentally\ndemonstrate that mean-field physics beyond the single-mode approximation can be\nrelevant during the non-equilibrium dynamics. The experimentally observed spin\noscillation dynamics and associated dynamical spatial structure formation\nconfirm theoretical predictions that are derived by solving a set of coupled\nmean-field Gross-Pitaevskii equations [J. Jie et al., Phys. Rev. A 102, 023324\n(2020)]. The experiments rely on microwave dressing of the $f=1$ hyperfine\nstates, where $f$ denotes the total angular momentum of the $^{23}$Na atom. The\nfact that beyond single-mode approximation physics at the mean-field level,\ni.e., spatial mean-field dynamics that distinguishes the spatial density\nprofiles associated with different Zeeman levels, can -- in certain parameter\nregimes -- have a pronounced effect on the dynamics when the spin healing\nlength is comparable to or larger than the size of the Bose-Einstein condensate\nhas implications for using Bose-Einstein condensates as models for quantum\nphase transitions and spin squeezing studies as well as for non-linear SU(1,1)\ninterferometers.",
        "positive": "Extending rotational coherence of interacting polar molecules in a\n  spin-decoupled magic trap: Superpositions of rotational states in polar molecules induce strong,\nlong-range dipolar interactions. Here we extend the rotational coherence by\nnearly one order of magnitude to 8.7(6) ms in a dilute gas of polar\n$^{23}$Na$^{40}$K molecules in an optical trap. We demonstrate spin-decoupled\nmagic trapping, which cancels first-order and reduces second-order differential\nlight shifts. The latter is achieved with a dc electric field that decouples\nnuclear spin, rotation and trapping light field. We observe density-dependent\ncoherence times, which can be explained by dipolar interactions in the bulk\ngas."
    },
    {
        "anchor": "Entanglement and correlations in an exactly-solvable model of a\n  Bose-Einstein condensate in a cavity: An exactly solvable model of a trapped interacting Bose-Einstein condensate\n(BEC) coupled in the dipole approximation to a quantized light mode in a cavity\nis presented. The model can be seen as a generalization of the\nharmonic-interaction model for a trapped BEC coupled to a bosonic bath. After\nobtaining the ground-state energy and wavefunction in closed form, we focus on\ncomputing the correlations in the system. The reduced one-particle density\nmatrices of the bosons and the cavity are constructed and diagonalized\nanalytically, and the von Neumann entanglement entropy of the BEC and the\ncavity is also expressed explicitly as a function of the number and mass of the\nbosons, frequencies of the trap and cavity, and the cavity-boson coupling\nstrength. The results allow one to study the impact of the cavity on the bosons\nand vice versa on an equal footing. As an application we investigate a specific\ncase of basic interest for itself, namely, non-interacting bosons in a cavity.\nWe find that both the bosons and the cavity develop correlations in a\ncomplementary manner while increasing the coupling between them. Whereas the\ncavity wavepacket broadens in Fock space, the BEC density saturates in real\nspace. On the other hand, while the cavity depletion saturates, and hence does\nthe BEC-cavity entanglement entropy, the BEC becomes strongly correlated and\neventually increasingly fragmented. The latter phenomenon implies single-trap\nfragmentation of otherwise ideal bosons, where their induced long-range\ninteraction is mediated by the cavity. Finally, as a complimentary\ninvestigation, the mean-field equations for the BEC-cavity system are solved\nanalytically as well, and the breakdown of mean-field theory for the cavity and\nthe bosons with increasing coupling is discussed. Further applications are\nenvisaged.",
        "positive": "Optimizing optical potentials with physics-inspired learning algorithms: We present our new experimental and theoretical framework which combines a\nbroadband superluminescent diode (SLED/SLD) with fast learning algorithms to\nprovide speed and accuracy improvements for the optimization of 1D optical\ndipole potentials, here generated with a Digital Micromirror Device (DMD). To\ncharacterize the setup and potential speckle patterns arising from coherence,\nwe compare the superluminescent diode to a single-mode laser by investigating\ninterference properties. We employ Machine Learning (ML) tools to train a\nphysics-inspired model acting as a digital twin of the optical system\npredicting the behavior of the optical apparatus including all its\nimperfections. Implementing an iterative algorithm based on Iterative Learning\nControl (ILC) we optimize optical potentials an order of magnitude faster than\nheuristic optimization methods. We compare iterative model-based offline\noptimization and experimental feedback-based online optimization. Our methods\nprovide a new route to fast optimization of optical potentials which is\nrelevant for the dynamical manipulation of ultracold gases."
    },
    {
        "anchor": "Polaron residue and spatial structure in a Fermi gas: We study the problem of a mobile impurity of mass $M$ interacting {\\sl via} a\ns-wave broad or narrow Feshbach resonance with a Fermi sea of particles of mass\n$m$. Truncating the Hilbert space to at most one pair of particle-hole\nexcitations of the Fermi sea, we determine ground state properties of the\npolaronic branch other than its energy, namely the polaron quasiparticle\nresidue $Z$, and the impurity-to-fermion pair correlation function $G(x)$. We\nshow that $G(x)$ deviates from unity at large distances as $-(A\\_4+B\\_4 \\cos 2\nk\\_F x)/(k\\_F x)^4$, where $k\\_F$ is the Fermi momentum; since $A\\_4>0$ and\n$B\\_4>0$, the polaron has a diverging rms radius and exhibits Friedel-like\noscillations. In the weakly attractive limit, we obtain analytical results,\nthat in particular detect the failure of the Hilbert space truncation for a\ndiverging mass impurity, as expected from Anderson orthogonality catastrophe;\nat distances between $\\sim 1/k\\_F$ and the asymptotic distance where the\n$1/x^4$ law applies, they reveal that $G(x)$ exhibits an intriguing multiscale\nstructure.",
        "positive": "Penetration of a vortex dipole across an interface of Bose-Einstein\n  condensates: The dynamics of a vortex dipole in a quasi-two dimensional two-component\nBose-Einstein condensate are investigated. A vortex dipole is shown to\npenetrate the interface between the two components when the incident velocity\nis sufficiently large. A vortex dipole can also disappear or disintegrate at\nthe interface depending on its velocity and the interaction parameters."
    },
    {
        "anchor": "Correlation functions and momentum distribution of one-dimensional\n  hard-core anyons in optical lattices: We address the problem of calculating the correlation functions in a system\nof one-dimensional hard-core anyons that can be experimentally realized in\noptical lattices. Using the summation of form factors we have obtained Fredholm\ndeterminant representations for the time-, space-, and temperature-dependent\nGreen's functions which are particularly suited to numerical investigations. In\nthe static case we have also derived the large distance asymptotic behavior of\nthe correlators and computed the momentum distribution function at zero and\nfinite temperature. We present extensive numerical results highlighting the\ncharacteristic features of one-dimensional systems with fractional statistics.",
        "positive": "Spin-Injection Spectroscopy of a Spin-Orbit Coupled Fermi Gas: The coupling of the spin of electrons to their motional state lies at the\nheart of recently discovered topological phases of matter. Here we create and\ndetect spin-orbit coupling in an atomic Fermi gas, a highly controllable form\nof quantum degenerate matter. We reveal the spin-orbit gap via spin-injection\nspectroscopy, which characterizes the energy-momentum dispersion and spin\ncomposition of the quantum states. For energies within the spin-orbit gap, the\nsystem acts as a spin diode. To fully inhibit transport, we open an additional\nspin gap, thereby creating a spin-orbit coupled lattice whose spinful band\nstructure we probe. In the presence of s-wave interactions, such systems should\ndisplay induced p-wave pairing, topological superfluidity, and Majorana edge\nstates."
    },
    {
        "anchor": "Wave functions of the super Tonks-Girardeau gas and the trapped 1D hard\n  sphere Bose gas: Recent theoretical and experimental results demonstrate a close connection\nbetween the super Tonks-Girardeau (sTG) gas and a 1D hard sphere Bose (HSB) gas\nwith hard sphere diameter nearly equal to the 1D scattering length $a_{1D}$ of\nthe sTG gas, a highly excited gas-like state with nodes only at interparticle\nseparations $|x_{j\\ell}|=x_{node}\\approx a_{1D}$. It is shown herein that when\nthe coupling constant $g_B$ in the Lieb-Liniger interaction\n$g_B\\delta(x_{j\\ell})$ is negative and $|x_{12}|\\ge x_{node}$, the sTG and HSB\nwave functions for $N=2$ particles are not merely similar, but identical; the\nonly difference between the sTG and HSB wave functions is that the sTG wave\nfunction allows a small penetration into the region $|x_{12}|<x_{node}$,\nwhereas for a HSB gas with hard sphere diameter $a_{h.s.}=x_{node}$, the HSB\nwave function vanishes when all $|x_{12}|<a_{h.s.}$. Arguments are given\nsuggesting that the same theorem holds also for $N>2$. The sTG and HSB wave\nfunctions for N=2 are given exactly in terms of a parabolic cylinder function,\nand for $N\\ge 2$, $x_{node}$ is given accurately by a simple parabola. The\nmetastability of the sTG phase generated by a sudden change of the coupling\nconstant from large positive to large negative values is explained in terms of\nthe very small overlap between the ground state of the Tonks-Girardeau gas and\ncollapsed cluster states.",
        "positive": "Keldysh approach for non-equilibrium phase transitions in quantum\n  optics: beyond the Dicke model in optical cavities: We investigate non-equilibrium phase transitions for driven atomic ensembles,\ninteracting with a cavity mode, coupled to a Markovian dissipative bath. In the\nthermodynamic limit and at low-frequencies, we show that the distribution\nfunction of the photonic mode is thermal, with an effective temperature set by\nthe atom-photon interaction strength. This behavior characterizes the static\nand dynamic critical exponents of the associated superradiance transition.\nMotivated by these considerations, we develop a general Keldysh path integral\napproach, that allows us to study physically relevant nonlinearities beyond the\nidealized Dicke model. Using standard diagrammatic techniques, we take into\naccount the leading-order corrections due to the finite number of atoms N. For\nfinite N, the photon mode behaves as a damped, classical non-linear oscillator\nat finite temperature. For the atoms, we propose a Dicke action that can be\nsolved for any N and correctly captures the atoms' depolarization due to\ndissipative dephasing."
    },
    {
        "anchor": "Controlled localization of interacting bosons in a disordered optical\n  lattice: We show that tunneling and localization properties of interacting ultracold\natoms in an optical lattice can be controlled by adiabatically turning on a\nfast oscillatory force even in the presence of disorder. Our calculations are\nbased on the exact solution of the time-dependent Schroedinger equation, using\nthe Floquet formalism. Implications of our findings for larger systems and the\npossibility of controlling the phase diagram of disordered-interacting bosonic\nsystems are discussed.",
        "positive": "Universal nature and finite-range corrections in elastic atom-dimer\n  scattering below the dimer breakup threshold: We investigate universal behavior in elastic atom-dimer scattering below the\ndimer breakup threshold calculating the atom-dimer effective-range function\n$ak\\cot\\delta$. Using the He-He system as a reference, we solve the\nSchr\\\"odinger equation for a family of potentials having different values of\nthe two-body scattering length $a$ and we compare our results to the universal\nzero-range form deduced by Efimov,\n$ak\\cot\\delta=c_1(ka)+c_2(ka)\\cot[s_0\\ln(\\kappa_*a)+\\phi(ka)]$, for selected\nvalues of the three-body parameter $\\kappa_*$. Using the parametrization of the\nuniversal functions $c_1,c_2,\\phi$ given in the literature, a good agreement\nwith the universal formula is obtained after introducing a particular type of\nfinite-range corrections. Furthermore, we show that the same parametrization\ndescribes a very different system: nucleon-deuteron scattering below the\ndeuteron breakup threshold. Our analysis confirms the universal character of\nthe process, and relates the pole energy in the effective-range function of\nnucleon-deuteron scattering to the three-body parameter $\\kappa_*$."
    },
    {
        "anchor": "Universality in ultradilute liquid Bose-Bose mixtures: We have studied dilute Bose-Bose mixtures of atoms with attractive\ninterspecies and repulsive intraspecies interactions using quantum Monte Carlo\nmethods at $T=0$. Using a number of models for interactions, we determine the\nrange of validity of the universal equation of state of the symmetric liquid\nmixture as a function of two parameters: the $s$-wave scattering length and the\neffective range of the interaction potential. It is shown that the\nLee-Huang-Yang correction is sufficient only for extremely dilute liquids with\nthe additional restriction that the range of the potential is small enough.\nBased on the quantum Monte Carlo equation of state we develop a new density\nfunctional which goes beyond the Lee-Huang-Yang term and use it together with\nlocal density approximation to determine density profiles of realistic\nself-bound drops.",
        "positive": "Localization of a Bose-Einstein condensate in a bichromatic optical\n  lattice: By direct numerical simulation of the time-dependent Gross-Pitaevskii\nequation we study different aspects of the localization of a non-interacting\nideal Bose-Einstein condensate (BEC) in a one-dimensional bichromatic\nquasi-periodic optical-lattice potential. Such a quasi-periodic potential, used\nin a recent experiment on the localization of a BEC [Roati et al., Nature 453,\n895 (2008)], can be formed by the superposition of two standing-wave polarized\nlaser beams with different wavelengths. We investigate the effect of the\nvariation of optical amplitudes and wavelengths on the localization of a\nnon-interacting BEC. We also simulate the non-linear dynamics when a\nharmonically trapped BEC is suddenly released into a quasi-periodic potential,\n{as done experimentally in a laser speckle potential [Billy et al., Nature 453,\n891 (2008)]$ We finally study the destruction of the localization in an\ninteracting BEC due to the repulsion generated by a positive scattering length\nbetween the bosonic atoms."
    },
    {
        "anchor": "Emergence of crystalline steady state in a driven superfluid: The spontaneous emergence of structures from initially homogenous systems\nbelongs to the most striking topics in natural science. Systems driven into\ndeeply nonlinear regimes are theoretically difficult to describe and can\nproduce states that do not exist in equilibrium. We observe the emergence of a\nstable square lattice density modulation from an initially homogenous,\ntwo-dimensional, radially symmetric Bose-Einstein condensate when periodically\ndriving the two-particle interaction. We show theoretically that this state can\nbe understood as an attractive fixed point of coupled nonlinear amplitude\nequations, which result from phonon-phonon interactions. As a self-stabilized\nstate characterized by spontaneously broken translational symmetry, our results\nestablish a novel quantum material related to supersolids.",
        "positive": "Mott criticality and pseudogap in Bose-Fermi mixtures: We study the Mott transition of a mixed Bose-Fermi system of ultracold atoms\nin an optical lattice, where the number of (spinless) fermions and bosons adds\nup to one atom per lattice, n_F+n_B=1. For weak interactions, a Fermi surface\ncoexists with a Bose-Einstein condensate while for strong interaction the\nsystem is incompressible but still characterized by a Fermi surface of\ncomposite fermions. At the critical point, the spectral function of the\nfermions, A(k,w), exhibits a pseudo-gapped behavior, rising as |w| at the Fermi\nmomentum, while in the Mott phase it is fully gapped. Taking into account the\ninteraction between the critical modes leads at very low temperatures either to\np-wave pairing or the transition is driven weakly first order. The same\nmechanism should also be important in antiferromagnetic metals with a small\nFermi surface."
    },
    {
        "anchor": "Dynamical sign reversal of magnetic correlations in dissipative Hubbard\n  models: In quantum magnetism, the virtual exchange of particles mediates an\ninteraction between spins. Here, we show that an inelastic Hubbard interaction\nfundamentally alters the magnetism of the Hubbard model due to dissipation in\nspin-exchange processes, leading to sign reversal of magnetic correlations in\ndissipative quantum dynamics. This mechanism is applicable to both fermionic\nand bosonic Mott insulators, and can naturally be realized with ultracold atoms\nundergoing two-body inelastic collisions. The dynamical reversal of magnetic\ncorrelations can be detected by using a double-well optical lattice or\nquantum-gas microscopy, the latter of which facilitates the detection of the\nmagnetic correlations in one-dimensional systems because of spin-charge\nseparation. Our results open a new avenue toward controlling quantum magnetism\nby dissipation.",
        "positive": "Competition and interplay between topology and quasi-periodic disorder\n  in Thouless pumping of ultracold atoms: Robustness against perturbations lies at the heart of topological phenomena.\nIf, however, a perturbation such as disorder becomes dominant, it may cause a\ntopological phase transition between topologically non-trivial and trivial\nphases. Here we experimentally reveal the competition and interplay between\ntopology and quasi-periodic disorder in a Thouless pump realized with ultracold\natoms in an optical lattice, by creating a quasi-periodic potential from weak\nto strong regimes in a controllable manner. We demonstrate a disorder-induced\npumping in which the presence of quasi-periodic disorder can induce a\nnon-trivial pump for a specific pumping sequence, while no pump is observed in\nthe clean limit. Our highly controllable system, which can also\nstraightforwardly incorporate interatomic interaction, could be a unique\nplatform for studying various disorder-related novel effects in a wide range of\ntopological quantum phenomena."
    },
    {
        "anchor": "Validity of single-channel model for a spin-orbit coupled atomic Fermi\n  gas near Feshbach resonances: We theoretically investigate a Rashba spin-orbit coupled Fermi gas near\nFeshbach resonances, by using mean-field theory and a two-channel model that\ntakes into account explicitly Feshbach molecules in the close channel. In the\nabsence of spin-orbit coupling, when the channel coupling $g$ between the\nclosed and open channels is strong, it is widely accepted that the two-channel\nmodel is equivalent to a single-channel model that excludes Feshbach molecules.\nThis is the so-called broad resonance limit, which is well-satisfied by\nultracold atomic Fermi gases of $^{6}$Li atoms and $^{40}$K atoms in current\nexperiments. Here, with Rashba spin-orbit coupling we find that the condition\nfor equivalence becomes much more stringent. As a result, the single-channel\nmodel may already be insufficient to describe properly an atomic Fermi gas of\n$^{40}$K atoms at a moderate spin-orbit coupling. We determine a characteristic\nchannel coupling strength $g_{c}$ as a function of the spin-orbit coupling\nstrength, above which the single-channel and two-channel models are\napproximately equivalent. We also find that for narrow resonance with small\nchannel coupling, the pairing gap and molecular fraction is strongly suppressed\nby SO coupling. Our results can be readily tested in $^{40}$K atoms by using\noptical molecular spectroscopy.",
        "positive": "Formation of classical crystals of dipolar particles in a helical\n  geometry: We consider crystal formation of particles with dipole-dipole interactions\nthat are confined to move in a one-dimensional helical geometry with their\ndipole moments oriented along the symmetry axis of the confining helix. The\nstable classical lowest energy configurations are found to be chain structures\nfor a large range of pitch-to-radius ratios for relatively low density of\ndipoles and a moderate total number of particles. The classical normal mode\nspectra support the chain interpretation both through structure and the\ndistinct degeneracies depending discretely on the number of dipoles per\nrevolution. A larger total number of dipoles leads to a clusterization where\nthe dipolar chains move closer to each other. This implies a change in the\nlocal density and the emergence of two length scales, one for the cluster size\nand one for the inter-cluster distance along the helix. Starting from three\ndipoles per revolution, this implies a breaking of the initial periodicity to\nform a cluster of two chains close together and a third chain removed from the\ncluster. This is driven by the competition between in-chain and out-of-chain\ninteractions, or alternatively the side-by-side repulsion and the head-to-tail\nattraction in the system. The speed of sound propagates along the chains. It is\nindependent of the number of chains although depending on geometry."
    },
    {
        "anchor": "Microscopic picture of superfluid $^4$He: We elucidate the microscopic quantum mechanism of superfluid $^4$He by\nuncovering a novel characteristic of its many-body energy levels. At\ntemperature below the transition point, the system's low-lying levels exhibit a\nfundamental grouping behavior, wherein each level belongs exclusively to a\nsingle group. In a superflow state, the system establishes thermal equilibrium\nwith its surroundings on a group-specific basis. Specifically, the levels of a\nselected group, initially occupied, become thermally populated, while the\nremaining groups of levels stay vacant due to absence of transitions between\ngroups. The macroscopic properties of the system, such as its superflow\nvelocity and thermal energy density, are statistically determined by the\nthermal distribution of the occupied group. Additionally, we infer that the\nthermal energy of a superflow has an unusual relationship with flow velocity,\nsuch that the larger the flow velocity, the smaller the thermal energy. This\nrelationship is responsible for a range of intriguing phenomena, including the\nmechano-caloric effect and the fountain effect, which highlight a fundamental\ncoupling between the thermal motion and hydrodynamic motion of the\nsystem.Furthermore, we present experimental evidence of a counterintuitive\nself-heating effect in $^4$He superflows, confirming that a $^4$He superflow\ncarries significant thermal energy related to its velocity.",
        "positive": "Free Fock parafermions in the tight-binding model with dissipation: Parafermions that generalize (Majorana or usual) fermions appear as\ninteracting quasi-particles because of their nature. Although attempts to\ndevelop models with free (non-interacting) parafermions have been undertaken,\nexisting proposals require unphysical conditions such as realizing purely\nnon-Hermitian systems. Here we present a way for the realization of free Fock\nparafermions in the tight-binding model with controlled dissipation of a very\nsimple form. Introducing dissipation transforms an originally non-integrable\nquantum model to an exactly solvable classical one."
    },
    {
        "anchor": "Dynamics of vortex dipoles in anisotropic Bose-Einstein condensates: We study the motion of a vortex dipole in a Bose-Einstein condensate confined\nto an anisotropic trap. We focus on a system of ordinary differential equations\ndescribing the vortices' motion, which is in turn a reduced model of the\nGross-Pitaevskii equation describing the condensate's motion. Using a sequence\nof canonical changes of variables, we reduce the dimension and simplify the\nequations of motion. We uncover two interesting regimes. Near a family of\nperiodic orbits known as guiding centers, we find that the dynamics is\nessentially that of a pendulum coupled to a linear oscillator, leading to\nstochastic reversals in the overall direction of rotation of the dipole. Near\nthe separatrix orbit in the isotropic system, we find other families of\nperiodic, quasi-periodic, and chaotic trajectories. In a neighborhood of the\nguiding center orbits, we derive an explicit iterated map that simplifies the\nproblem further. Numerical calculations are used to illustrate the phenomena\ndiscovered through the analysis. Using the results from the reduced system we\nare able to construct complex periodic orbits in the original, partial\ndifferential equation, mean-field model for Bose-Einstein condensates, which\ncorroborates the phenomenology observed in the reduced dynamical equations.",
        "positive": "Evolution of the Hofstadter butterfly in a tunable optical lattice: Recent advances in realizing artificial gauge fields on optical lattices\npromise experimental detection of topologically non-trivial energy spectra.\nSelf-similar fractal energy structures generally known as Hofstadter\nbutterflies depend sensitively on the geometry of the underlying lattice, as\nwell as the applied magnetic field. The recent demonstration of an adjustable\nlattice geometry [L. Tarruell \\textit{et al.}, Nature 483, 302--305 (2012)]\npresents a unique opportunity to study this dependence. In this paper, we\ncalculate the Hofstadter butterflies that can be obtained in such an adjustable\nlattice and find three qualitatively different regimes. We show that the\nexistence of Dirac points at zero magnetic field does not imply the topological\nequivalence of spectra at finite field. As the real-space structure evolves\nfrom the checkerboard lattice to the honeycomb lattice, two square lattice\nHofstadter butterflies merge to form a honeycomb lattice butterfly. This\nmerging is topologically non-trivial, as it is accomplished by sequential\nclosings of gaps. Ensuing Chern number transfer between the bands can be probed\nwith the adjustable lattice experiments. We also calculate the Chern numbers of\nthe gaps for qualitatively different spectra and discuss the evolution of\ntopological properties with underlying lattice geometry."
    },
    {
        "anchor": "Quantum incommensurate Skyrmion crystals and Commensurate to\n  In-commensurate transitions in cold atoms and materials with spin orbit\n  couplings in a Zeeman field: In this work, we study strongly interacting spinor atoms in a lattice subject\nto a 2 dimensional (2d) anisotropic Rashba type of spin orbital coupling (SOC)\nand an Zeeman field. We find the interplay between the Zeeman field and the SOC\nprovides a new platform to host rich and novel classes of quantum commensurate\nand in-commensurate phases, excitations and phase transitions. These\ncommensurate phases include two collinear states at low and high Zeeman field,\ntwo co-planar canted states at Mirror reflected SOC parameters respectively.\nMost importantly, there are non-coplanar incommensurate Skyrmion (IC-SkX)\ncrystal phases surrounded by the 4 commensurate phases. New excitation spectra\nabove all the 5 phases, especially on the IC-SKX phase are computed. Three\ndifferent classes of quantum commensurate to in-commensurate transitions from\nthe IC-SKX to its 4 neighboring commensurate phases are identified. Finite\ntemperature behaviors and transitions are discussed. The critical temperatures\nof all the phases can be raised above that reachable by current cold atom\ncooling techniques simply by tuning the number of atoms $ N $ per site. In view\nof recent impressive experimental advances in generating 2d SOC for cold atoms\nin optical lattices, these new many-body phenomena can be explored in the\ncurrent and near future cold atom experiments. Applications to various\nmaterials such as MnSi, Fe$_{0.5}$Co$_{0.5}$Si, especially the complex\nincommensurate magnetic ordering in Li$_2$IrO$_3$ are given.",
        "positive": "Nonlocal field theory of quasiparticle scattering in dipolar\n  Bose-Einstein condensates: We consider the propagation of quasiparticle excitations in a dipolar\nBose-Einstein condensate, and derive a nonlocal field theory of quasiparticle\nscattering at a stepwise inhomogeneity of the sound speed, obtained by tuning\nthe contact coupling part of the interaction on one side of the barrier. To\nsolve this problem $ab$ $initio$, i.e., without prior assumptions on the form\nof the solutions, we reformulate the dipolar Bogoliubov-de Gennes equation as a\nsingular integral equation. The latter is of a $novel$ $hypersingular$ type, in\nhaving a kernel which is hypersingular at only two isolated points. Deriving\nits solution, we show that the integral equation reveals a continuum of\nevanescent channels at the sound barrier which is absent for a purely\ncontact-interaction condensate. We furthermore demonstrate that by performing a\ndiscrete approximation for the kernel, one achieves an excellent solution\naccuracy for already a moderate number of discretization steps. Finally, we\nshow that the non-monotonic nature of the system dispersion, corresponding to\nthe emergence of a roton minimum in the excitation spectrum, results in\npeculiar features of the transmission and reflection at the sound barrier which\nare nonexistent for contact interactions."
    },
    {
        "anchor": "Statistical mechanics of one-dimensional quantum droplets: We study the statistical mechanics and the dynamical relaxation process of\nmodulationally unstable one-dimensional quantum droplets described by a\nmodified Gross-Pitaevskii equation. To determine the classical partition\nfunction thereof, we leverage the semi-analytical transfer integral operator\n(TIO) technique. The latter predicts a distribution of the observed wave\nfunction amplitudes and yields two-point correlation functions providing\ninsights into the emergent dynamics involving quantum droplets. We compare the\nensuing TIO results with the probability distributions obtained at large times\nof the modulationally unstable dynamics as well as with the equilibrium\nproperties of a suitably constructed Langevin dynamics. We find that the\ninstability leads to the spontaneous formation of quantum droplets featuring\nmultiple collisions and by which are found to coalesce at large evolution\ntimes. Our results from the distinct methodologies are in good agreement aside\nfrom the case of low temperatures in the special limit where the droplet\nwidens. In this limit, the distribution acquires a pronounced bimodal\ncharacter, exhibiting a deviation between the TIO solution and the Langevin\ndynamics.",
        "positive": "Superfluid fraction of interacting bosonic gases: The superfluid fraction $f$ of a quantum fluid is defined in terms of the\nresponse of the system to a weak and constant drag. Notably, Leggett long ago\nderived two simple expressions providing a rigorous upper bound and a heuristic\nlower bound for $f$. Here we study the superfluid fraction of bosonic gases in\nvarious two-dimensional potentials, such as regular optical lattices and\ndisordered speckles, by solving the Gross-Pitaevskii equation and performing\nDiffusion Monte Carlo simulations. We show that under conditions relevant for\nmost ultracold experiments the bounds proposed by Leggett provide a\nsurprisingly narrow bracketing of the exact value of the superfluid fraction."
    },
    {
        "anchor": "Dispersion relation of a polaron in the Yang-Gaudin Bose gas: We study a one-dimensional Bose gas with two internal states described by the\nYang-Gaudin model and calculate analytically the dispersion relation of a\npolaron quasiparticle, which is the lowest excitation branch. We study the\ndispersion in the thermodynamic limit in the regimes of weak and strong\ninteraction without limitations on the momentum. At weak interaction the\npolaron dispersion is in the vicinity of the dark soliton one; we calculate the\nleading deviation in the parametric form. At strong interaction we find an\nansatz for the explicit form of the polaron dispersion. It has the form of a\npower series of the sine function of the momentum with interaction-dependent\ncoefficients. By increasing the power of the series, the corresponding\ncoefficients show faster decay and thus one practically needs only a few of\nthem; we give the results for the first three. The coefficients of the series\nare connected to the Maclaurin series of the polaron dispersion and thus it is\nsufficient to calculate latter quantity to automatically find the power series\nresult for the dispersion at all momenta. The derived results for the\ndispersion can be used to obtain explicit expressions for the exponents of the\npower-law singularities in the response functions at the spectral edge.",
        "positive": "Direct observation of incommensurate magnetism in Hubbard chains: The interplay between magnetism and doping is at the origin of exotic\nstrongly correlated electronic phases and can lead to novel forms of magnetic\nordering. One example is the emergence of incommensurate spin-density waves\nwith a wave vector that does not match the reciprocal lattice. In one dimension\nthis effect is a hallmark of Luttinger liquid theory, which also describes the\nlow energy physics of the Hubbard model. Here we use a quantum simulator based\non ultracold fermions in an optical lattice to directly observe such\nincommensurate spin correlations in doped and spin-imbalanced Hubbard chains\nusing fully spin and density resolved quantum gas microscopy. Doping is found\nto induce a linear change of the spin-density wave vector in excellent\nagreement with Luttinger theory predictions. For non-zero polarization we\nobserve a decrease of the wave vector with magnetization as expected from the\nHeisenberg model in a magnetic field. We trace the microscopic origin of these\nincommensurate correlations to holes, doublons and excess spins which act as\ndelocalized domain walls for the antiferromagnetic order. Finally, when\ninducing interchain coupling we observe fundamentally different spin\ncorrelations around doublons indicating the formation of a magnetic polaron."
    },
    {
        "anchor": "Landau Levels in Strained Optical Lattices: We propose a hexagonal optical lattice system with spatial variations in the\nhopping matrix elements. Just like in the valley Hall effect in strained\nGraphene, for atoms near the Dirac points the variations in the hopping matrix\nelements can be described by a pseudo-magnetic field and result in the\nformation of Landau levels. We show that the pseudo-magnetic field leads to\nmeasurable experimental signatures in momentum resolved Bragg spectroscopy,\nBloch oscillations, cyclotron motion, and quantization of in-situ densities.\nOur proposal can be realized by a slight modification of existing experiments.\nIn contrast to previous methods, pseudo-magnetic fields are realized in a\ncompletely static system avoiding common heating effects and therefore opening\nthe door to studying interaction effects in Landau levels with cold atoms.",
        "positive": "Thermodynamics of rotating Bose gases in a trap: Novel ground state properties of rotating Bose gases have been intensively\nstudied in the context of neutral cold atoms. We investigate the rotating Bose\ngas in a trap from a thermodynamic perspective, taking the charged ideal Bose\ngas in magnetic field (which is equivalent to a neutral gas in a synthetic\nmagnetic field) as an example. It is indicated that the Bose-Einstein\ncondensation temperature is irrelevant to the magnetic field, conflicting with\nestablished intuition that the critical temperature decreases with the field\nincreasing. The specific heat and Landau diamagnetization also exhibit\nintriguing behaviors. In contrast, we demonstrate that the condensation\ntemperature for neutral Bose gases in a rotating frame drops to zero in the\nfast rotation limit, signaling a non-condensed quantum phase in the ground\nstate."
    },
    {
        "anchor": "Entangled Collective Spin States of Two Species Ultracold atoms in a\n  Ring: We study the general quantum Hamiltonian that can be realized with two\nspecies of mutually interacting degenerate ultracold atoms in a ring-shaped\ntrap, with the options of rotation and an azimuthal lattice. We examine the\nspectrum and the states with a collective spin picture in a Dicke state basis.\nThe system can generate states with a high degree of entanglement gauged by the\nvon Neumann entropy. The Hamiltonian has two components, a linear part that can\nbe controlled and switched on via rotation or the azimuthal lattice, and an\ninteraction-dependent quadratic part. Exact solutions are found for the\nquadratic part for equal strengths of intra-species and the inter-species\ninteractions, but for generally different particle numbers in the two species.\nThe quadratic Hamiltonian has a degenerate ground state when the two species\nhave unequal number of particles, but non-degenerate when equal. We determine\nthe impact on the entanglement entropy of deviations from equal particle\nnumbers as well as deviations from the assumption of equal interaction\nstrengths. Limiting cases are shown to display features of a beam-splitter and\nspin-squeezing that can find utility in interferometry. The density of states\nfor the full Hamiltonian shows features as of phase transition in varying\nbetween linear and quadratic limits.",
        "positive": "Influence of periodically modulated cavity field on the generation of\n  atomic-squeezed states: We investigate the influence of periodically time-modulated cavity frequency\non the generation of atomic squeezed states for a collection of N two-level\natoms confined in a non-stationary cavity with a moving mirror. We show that\nthe two-photon character of the field generated from the vacuum state of field\nplays a significant role in producing the atomic or spin squeezed states. We\nfurther show that the maximum amount of persistent atomic squeezing is obtained\nfor the initial cavity field prepared in the vacuum state."
    },
    {
        "anchor": "Compressibility and the Equation of State of an Optical Quantum Gas in a\n  Box: The compressibility of a medium, quantifying its response to mechanical\nperturbations, is a fundamental property determined by the equation of state.\nFor gases of material particles, studies of the mechanical response are well\nestablished, in fields from classical thermodynamics to cold atomic quantum\ngases. Here we demonstrate a measurement of the compressibility of a\ntwo-dimensional quantum gas of light in a box potential and obtain the equation\nof state for the optical medium. The experiment is carried out in a\nnanostructured dye-filled optical microcavity. We observe signatures of\nBose-Einstein condensation at high phase-space densities in the finite-size\nsystem. Strikingly, upon entering the quantum degenerate regime, the measured\ndensity response to an external force sharply increases, hinting at the\npeculiar prediction of an infinite compressibility of the deeply degenerate\nBose gas.",
        "positive": "Immiscible and miscible states in binary condensates in the ring\n  geometry: We report detailed investigation of the existence and stability of mixed and\ndemixed modes in binary atomic Bose-Einstein condensates with repulsive\ninteractions in a ring-trap geometry. The stability of such states is examined\nthrough eigenvalue spectra for small perturbations, produced by the\nBogoliubov-de Gennes equations, and directly verified by simulations based on\nthe coupled Gross-Pitaevskii equations, varying inter- and intra-species\nscattering lengths so as to probe the entire range of miscibility-immiscibility\ntransitions. In the limit of the one-dimensional (1D) ring, i.e., a very narrow\none, stability of mixed states is studied analytically, including\nhidden-vorticity (HV) modes, i.e., those with opposite vorticities of the two\ncomponents and zero total angular momentum. The consideration of demixed 1D\nstates reveals, in addition to stable composite single-peak structures, double-\nand triple-peak ones, above a certain particle-number threshold. In the 2D\nannular geometry, stable demixed states exist both in radial and azimuthal\nconfigurations. We find that stable radially-demixed states can carry arbitrary\nvorticity and, counter-intuitively, the increase of the vorticity enhances\nstability of such states, while unstable ones evolve into randomly oscillating\nangular demixed modes. The consideration of HV states in the 2D geometry\nexpands the stability range of radially-demixed states."
    },
    {
        "anchor": "Finite-size scaling behavior of Bose-Einstein condensation in the 1D\n  Bose gas: Through exact numerical solutions we show Bose-Einstein condensation (BEC)\nfor the one-dimensional (1D) bosons with repulsive short-range interactions at\nzero temperature by taking a particular large size limit. Following the\nPenrose-Onsager criterion of BEC, we define condensate fraction by the fraction\nof the largest eigenvalue of the one-particle reduced density matrix. % We show\nthe finite-size scaling behavior such that condensate fraction is given by a\nscaling function of one-variable: interaction parameter multiplied by a power\nof particle number. Condensate fraction is nonzero and constant for any large\nvalue of particle number or system size, if the interaction parameter is\nproportional to the negative power of particle number. %Here the interaction\nparameter is defined by the coupling constant of the delta-function potentials\ndevided by the density. %With the scaling behavior we derive various\nthemodynamic limits where condensate fraction is constant for any large system\nsize; for instance, it is the case even in the system of a finite particle\nnumber.",
        "positive": "Harmonically trapped Fermi gas: Temperature dependence of the Tan\n  contact: Ultracold atomic gases with short-range interactions are characterized by a\nnumber of universal species-independent relations. Many of these relations\ninvolve the two-body Tan contact. Employing the canonical ensemble, we\ndetermine the Tan contact for small harmonically trapped two-component Fermi\ngases at unitarity over a wide range of temperatures, including the zero and\nhigh temperature regimes. A cluster expansion that describes the properties of\nthe N-particle system in terms of those of smaller subsystems is introduced and\nshown to provide an accurate description of the contact in the high temperature\nregime. Finite-range corrections are quantified and the role of the Fermi\nstatistics is elucidated by comparing results for Fermi, Bose and Boltzmann\nstatistics."
    },
    {
        "anchor": "Local Non-Hermitian Hamiltonian Formalism for Dissipative Fermionic\n  Systems and Loss-Induced Population Increase in Fermi Superfluids: Non-Hermitian Hamiltonian (NHH) is an effective formalism for open quantum\nsystems. In common wisdom, when the system is described by the Lindblad master\nequation, the NHH obtained by neglecting its jump term is believed to be a good\napproximation for a timescale sufficiently shorter than the inverse of the\ndissipation rate. We challenge this common wisdom and develop a scheme to\nobtain an appropriate NHH from the original master equation for dissipative\nfermionic systems. This NHH, called the local NHH, describes the loss process\nin each individual mode locally. As a concrete example, we justify our new\nscheme using fermionic superfluid under one-body loss. Furthermore, we find\nloss-induced population increase in the long time evolution due to the\ndissipation-induced phase locking between the pairing gap and the anomalous\nfield.",
        "positive": "Macroscopic properties of triplon Bose-Einstein condensates: Magnetic insulators can be characterized by a gap separating the singlet\nground state from the lowest energy triplet, S=1 excitation. If the gap can be\nclosed by the Zeeman interaction in applied magnetic field, the resulting S=1\nquasiparticles, triplons, can have concentrations sufficient to undergo the\nBose-Einstein condensates transition. We consider macroscopic properties of the\ntriplon Bose-Einstein condensates in the Hartree-Fock-Bogoliubov approximation\ntaking into account the anomalous averages. We prove that these averages play\nthe qualitative role in the condensate properties. As a result, we show that\nwith the increase in the external magnetic field at a given temperature, the\ncondensate demonstrates an instability related to the appearance of nonzero\nphonon damping and a change in the characteristic dependence of the speed of\nsound on the magnetic field. The calculated magnetic susceptibility diverges\nwhen the external magnetic field approaches this instability threshold,\nproviding a tool for the experimental verification of this approach."
    },
    {
        "anchor": "Simulation of non-Abelian lattice gauge fields with a single component\n  gas: We show that non-Abelian lattice gauge fields can be simulated with a single\ncomponent ultra-cold atomic gas in an optical lattice potential. An optical\nlattice can be viewed as a Bravais lattice with a $N$-point basis. An atom\nlocated at different points of the basis can be considered as a {\\it particle}\nin different internal states. The appropriate engineering of tunneling\namplitudes of atoms in an optical lattice allows one to realize U$(N)$ gauge\npotentials and control a mass of {\\it particles} that experience such\nnon-Abelian gauge fields. We provide and analyze a concrete example of an\noptical lattice configuration that allows for simulation of a static U(2) gauge\nmodel with a constant Wilson loop and an adjustable mass of {\\it particles}. In\nparticular, we observe that the non-zero mass creates large conductive gaps in\nthe energy spectrum, which could be important in the experimental detection of\nthe transverse Hall conductivity.",
        "positive": "Pairing correlations in a trapped one-dimensional Fermi gas: We use a BCS-type variational wavefunction to study attractively-interacting\nquasi one-dimensional (1D) fermionic atomic gases, motivated by cold-atom\nexperiments that access the 1D regime using an anisotropic harmonic trapping\npotential (with trapping frequencies $\\omega_x = \\omega_y \\gg \\omega_z$) that\nconfines the gas to a cigar-shaped geometry. To handle the presence of the trap\nalong the $z$-direction, we construct our variational wavefunction from the\nharmonic oscillator Hermite functions that are the eigenstates of the\nsingle-particle problem. Using an analytic determination of the effective\ninteraction among harmonic oscillator states along with a numerical solution of\nthe resulting variational equations, we make specific experimental predictions\nfor how pairing correlations would be revealed in experimental probes like the\nlocal density and the momentum correlation function."
    },
    {
        "anchor": "Resonances in ultracold dipolar atomic and molecular gases: A previously developed approach for the numerical treatment of two particles\nthat are confined in a finite optical-lattice potential and interact via an\narbitrary isotropic interaction potential has been extended to incorporate an\nadditional anisotropic dipole-dipole interaction. The interplay of a model but\nrealistic short-range Born-Oppenheimer potential and the dipole-dipole\ninteraction for two confined particles is investigated. A variation of the\nstrength of the dipole-dipole interaction leads to diverse resonance phenomena.\nIn a harmonic confinement potential some resonances show similarities to\n$s$-wave scattering resonances while in an anharmonic trapping potential like\nthe one of an optical lattice inelastic confinement-induced dipolar resonances\noccur. The latter are due to a coupling of the relative and center-of-mass\nmotion caused by the anharmonicity of the external confinement.",
        "positive": "Variance of a Trapped Bose-Einstein Condensate: The ground state of a Bose-Einstein condensate in a two-dimensional trap\npotential is analyzed numerically at the infinite-particle limit. It is shown\nthat the anisotropy of the many-particle position variance along the $x$ and\n$y$ axes can be opposite when computed at the many-body and mean-field levels\nof theory. This is despite the system being $100\\%$ condensed, and the\nrespective energies per particle and densities per particle to coincide."
    },
    {
        "anchor": "Fermionic Superfluid from a Bilayer Band Insulator in an Optical Lattice: We propose a model to realize a fermionic superfluid state in an optical\nlattice circumventing the cooling problem. Our proposal exploits the idea of\ntuning the interaction in a characteristically low entropy state, a\nband-insulator in an optical bilayer system, to obtain a superfluid. By\nperforming a detailed analysis of the model including fluctuations and\naugmented by a variational quantum Monte Carlo calculations of the ground\nstate, we show that the superfluid state obtained has high transition\ntemperature of the order of the hopping energy. Our system is designed to\nsuppress other competing orders such as a charge density wave. We suggest a\nlaboratory realization of this model via an orthogonally shaken optical lattice\nbilayer.",
        "positive": "Hofstadter-Hubbard model with opposite magnetic fields:\n  Bardeen-Cooper-Schrieffer pairing and superfluidity in the nearly flat\n  butterfly bands: Despite the multi-band spectrum of the widely-known Hofstadter butterfly, it\nturns out that the pairing correlations of the time-reversal-symmetric\nHofstadter-Hubbard model are well-described by a single order parameter that is\nuniform in real space. By exploiting a BCS mean-field theory for the\nnearly-flat butterfly-bands regime of low magnetic-flux limit, here we reveal a\nnumber of unusual superfluid properties both in the ground state and at finite\ntemperatures. Our thorough analysis includes but is not limited to the order\nparameter, condensate and superfluid fractions, and the critical BCS and BKT\ntransition temperatures."
    },
    {
        "anchor": "Collective excitations and tunneling dynamics in long bosonic Josephson\n  junctions: We investigate the low-energy dynamics of two coupled anisotropic\nBose-Einstein condensates forming a long Josephson junction. The theoretical\nstudy is performed in the framework of the two-dimensional Gross-Pitaevskii\nequation and the Bogoliubov-de Gennes formalism. We analyze the excitation\nspectrum of the coupled Bose condensates and show how low-energy excitations of\nthe condensates lead to multiple-frequency oscillations of the atomic\npopulations in the two wells. This analysis generalizes the standard bosnic\nJosephson euqation approach. We also develop a one-dimensional hydrodynamic\nmodel of the coupled condensates, that is capable to reproduce the excitation\nspectrum and population dynamics of the system.",
        "positive": "Tight-binding models in a quasiperiodic optical lattice: This paper describes how one can use four standing wave laser fields to\nrealize a two dimensional optical quasicrystal with eight-fold symmetry,\nclosely related to the well-known octagonal or Ammann-Beenker tiling\nquasicrystal. We describe the structure and its properties, and the effective\ntight-binding model for atoms in this optical quasicrystal. Such a system, if\nrealized experimentally, should provide valuable insights into the quantum\nproperties of quasicrystals."
    },
    {
        "anchor": "AC Stark Effect in Ultracold Polar RbCs Molecules: We investigate the effect of far-off-resonant trapping light on ultracold\nbosonic RbCs molecules. We use kHz-precision microwave spectroscopy to measure\nthe differential AC Stark shifts between the ground and first excited\nrotational levels of the molecule with hyperfine-state resolution. We\ndemonstrate through both experiment and theory that coupling between\nneighboring hyperfine states manifests in rich structure with many avoided\ncrossings. This coupling may be tuned by rotating the polarization of the\nlinearly polarized trapping light. A combination of spectroscopic and\nparametric heating measurements allows complete characterization of the\nmolecular polarizability at a wavelength of 1550~nm in both the ground and\nfirst excited rotational states.",
        "positive": "Chiral magnetic effect in three-dimensional optical lattices: Although Weyl semimetals have been extensively studied for exploring rich\ntopological physics, the direct observation of the celebrated chiral magnetic\neffect (CME) associated with the so-called dipolar chiral anomaly has long\nintrigued and challenged physicists, still remaining elusive in nature. Here we\npropose a feasible scheme for experimental implementation of ultracold atoms\nthat may enable us to probe the CME with a pure topological current in an\nartificial Weyl semimetal. The paired Weyl points with the dipolar chiral\nanomaly emerge in the presence of the well-designed spin-orbital coupling and\nlaser-assisted tunneling. Both of the two artificial fields are readily\nrealizable and highly tunable via current optical techniques using ultracold\natoms trapped in three-dimensional optical lattices, providing a reliable way\nfor manipulating Weyl points in the momentum-energy space. By applying a weak\nartificial magnetic field, the system processes an auxiliary current originated\nfrom the topology of a paired Weyl points, namely, the pure CME current. This\ntopological current can be extracted from measuring the center-of-mass motion\nof ultracold atoms, which may pave the way to directly and unambiguously\nobserve the CME in experiments."
    },
    {
        "anchor": "Antiferromagnetic Heisenberg Spin Chain of a Few Cold Atoms in a\n  One-Dimensional Trap: We report on the deterministic preparation of antiferromagnetic Heisenberg\nspin chains consisting of up to four fermionic atoms in a one-dimensional trap.\nThese chains are stabilized by strong repulsive interactions between the two\nspin components without the need for an external periodic potential. We\nindependently characterize the spin configuration of the chains by measuring\nthe spin orientation of the outermost particle in the trap and by projecting\nthe spatial wave function of one spin component on single-particle trap levels.\nOur results are in good agreement with a spin-chain model for fermionized\nparticles and with numerically exact diagonalizations of the full few-fermion\nsystem.",
        "positive": "Motion of vortices in inhomogeneous Bose-Einstein condensates: We derive a general and exact equation of motion for a quantised vortex in an\ninhomogeneous two-dimensional Bose-Einstein condensate. This equation expresses\nthe velocity of a vortex as a sum of local ambient density and phase gradients\nin the vicinity of the vortex. We perform Gross-Pitaevskii simulations of\nsingle vortex dynamics in both harmonic and hard-walled disk-shaped traps, and\nfind excellent agreement in both cases with our analytical prediction. The\nsimulations reveal that, in a harmonic trap, the main contribution to the\nvortex velocity is an induced ambient phase gradient, a finding that\ncontradicts the commonly quoted result that the local density gradient is the\nonly relevant effect in this scenario. We use our analytical vortex velocity\nformula to derive a point-vortex model that accounts for both density and phase\ncontributions to the vortex velocity, suitable for use in inhomogeneous\ncondensates. Although good agreement is obtained between Gross-Pitaevskii and\npoint-vortex simulations for specific few-vortex configurations, the effects of\nnonuniform condensate density are in general highly nontrivial, and are thus\ndifficult to efficiently and accurately model using a simplified point-vortex\ndescription."
    },
    {
        "anchor": "Short note on the excitonic Mott phase: An exciton gas on a lattice is analyzed in terms of a convergent hopping\nexpansion. For a given chemical potential our calculation provides a sufficient\ncondition for the hopping rate to obtain an exponential decay of the exciton\ncorrelation function. This result indicates the existence of a Mott phase in\nwhich strong fluctuations destroy the long range correlations in the exciton\ngas at any temperature, either by thermal or by quantum fluctuations.",
        "positive": "Dynamics of a cold trapped ion in a Bose-Einstein condensate: We investigate the interaction of a laser-cooled trapped ion (Ba$^+$ or\nRb$^+$) with an optically confined $^{87}$Rb Bose-Einstein condensate (BEC).\nThe system features interesting dynamics of the ion and the atom cloud as\ndetermined by their collisions and their motion in their respective traps.\nElastic as well as inelastic processes are observed and their respective cross\nsections are determined. We demonstrate that a single ion can be used to probe\nthe density profile of an ultracold atom cloud."
    },
    {
        "anchor": "Spontaneous generation of quantum turbulence through the decay of a\n  giant vortex in a two-dimensional superfluid: We show the generation of two-dimensional quantum turbulence through\nsimulations of a giant vortex decay in a trapped Bose-Einstein condensate.\nWhile evaluating the incompressible kinetic energy spectra of the quantum fluid\ndescribed by the Gross-Pitaevskii equation, a bilinear form in a log-log plot\nis verified. A characteristic scaling behavior for small momenta shows\nresemblance to the Kolmogorov $k^{-5/3}$ law, while for large momenta it\nreassures the universal behavior of the core-size $k^{-3}$ power-law. This\nindicates a mechanism of energy transportation consistent with an inverse\ncascade. The feasibility of the described physical system with the currently\navailable experimental techniques to create giant vortices opens up a new route\nto explore quantum turbulence.",
        "positive": "Self-bound droplets in quasi-two-dimensional dipolar condensates: We study the ground-state properties of self-bound dipolar droplets in\nquasi-two-dimensional geometry by using the Gaussian state theory. We show that\nthere exist two quantum phases corresponding to the macroscopic squeezed vacuum\nand squeezed coherent states. We further show that the radial size versus atom\nnumber curve exhibits a double-dip structure, as a result of the multiple\nquantum phases. In particular, we find that the critical atom number for the\nself-bound droplets is determined by the quantum phases, which allows us to\ndistinguish the quantum state and validates the Gaussian state theory."
    },
    {
        "anchor": "The Chern Numbers of Interaction-stretched Monopoles in Spinor Bose\n  Condensates: Using the Dirac and the Yang monopole in spinor condensates as examples, we\nshow that interactions can stretch the point singularity of a monopole into an\nextended manifold, whose shape is strongly influenced by the sign of\ninteraction. The singular manifold will cause the first and second Chern number\nto assume non-integer values when it intersects the surface on which the Chern\nnumbers are calculated. This leads to a gradual decrease of the Chern numbers\nas the monopole moves away from the surface of integration, instead of the\nsudden jump characteristic of a point monopole. A gradual change in $C_2$ has\nin fact been observed in the recent experiment by Spielman's group at NIST. By\nmeasuring the range of non-integer values of the Chern numbers as the monopole\nmoves away from the surface of integration along different directions, one can\nmap out the shape of the singular manifold in the parameter space.",
        "positive": "Tunable dipolar resonances and Einstein-de Haas effect in a Rb-87 atoms\n  condensate: We study a spinor condensate of Rb-87 atoms in F = 1 hyperfine state confined\nin an optical dipole trap. Putting initially all atoms in mF = 1 component we\nobserve a significant transfer of atoms to other, initially empty Zeeman states\nexclusively due to dipolar forces. Because of conservation of a total angular\nmomentum the atoms going to other Zeeman components acquire an orbital angular\nmomentum and circulate around the center of the trap. This is a realization of\nEinstein-de Haas effect in a system of cold gases. We show that the transfer of\natoms via dipolar interaction is possible only when the energies of the initial\nand the final sates are equal. This condition can be fulfilled utilizing a\nresonant external magnetic field, which tunes energies of involved states via\nthe linear Zeeman effect. We found that there are many final states of\ndifferent spatial density which can be tuned selectively to the initial state.\nWe show a simple model explaining high selectivity and controllability of weak\ndipolar interactions in the condensate of Rb-87 atoms."
    },
    {
        "anchor": "On the order of BEC transition in weakly interacting gases predicted by\n  mean-field theory: Predictions from Hartree-Fock (HF), Popov (P), Yukalov-Yukalova (YY) and\n$t$-matrix approximations regarding the thermodynamics from the normal to the\nBEC phase in weakly interacting Bose gases are considered. By analyzing the\ndependence of the chemical potential $\\mu$ on temperature $T$ and particle\ndensity $\\rho$ we show that none of them predicts a second-order phase\ntransition as required by symmetry-breaking general considerations. In this\nwork we find that the isothermal compressibility $\\kappa_{T}$ predicted by\nthese theories does not diverge at criticality as expected in a true\nsecond-order phase transition. Moreover the isotherms $\\mu=\\mu(\\rho,T)$\ntypically exhibit a non-singled valued behavior in the vicinity of the BEC\ntransition, a feature forbidden by general thermodynamic principles. This\nbehavior can be avoided if a first order phase transition is appealed. The\nfacts described above show that although these mean field approximations give\ncorrect results near zero temperature they are endowed with thermodynamic\nanomalies in the vicinity of the BEC transition. We address the implications of\nthese results in the interpretation of current experiments with ultracold\ntrapped alkali gases.",
        "positive": "Exotic quantum spin models in spin-orbit-coupled Mott insulators: We study cold atoms in an optical lattice with synthetic spin-orbit coupling\nin the Mott-insulator regime. We calculate the parameters of the corresponding\ntight-binding model using Peierls substitution and \"localized Wannier states\nmethod\" and derive the low-energy spin Hamiltonian for fermions and bosons. The\nspin Hamiltonian is a combination of Heisenberg model, quantum compass model\nand Dzyaloshinskii-Moriya interactions and it has a rich classical phase\ndiagram with collinear, spiral and vortex phases."
    },
    {
        "anchor": "Bogoliubov theory of a Bose-Einstein condensate of rigid rotor molecules: We consider a BEC of rigid rotor molecules confined to quasi-2d through\nharmonic trapping. The molecules are subjected to an external electric field\nwhich polarizes the gas, and the molecules interact via dipole-dipole\ninteractions. We present a description of the ground state and low-energy\nexcitations of the system including an analysis of the mean-field energy,\npolarization, and stability. Under large electric fields the gas becomes fully\npolarized and we reproduce a well known density-wave instability which arises\nin polar BECs. Under smaller applied electric fields the gas develops an\nin-plane polarization leading to the emergence of a new global instability as\nthe molecules \"tilt\". The character of these instabilities is clarified by\nmeans of momentum-space density-density structure factors. A peak at zero\nmomentum in the spin-spin structure factor for the in-plane component of the\npolarization indicates that the tilt instability is a global phonon-like\ninstability.",
        "positive": "Comment on \"Quantum entangled dark solitons formed by ultracold atoms in\n  optical lattices\": We demonstrate that knowledge of two body correlation functions like g2(x) is\ninsufficient to draw conclusions about whether solitons fill in or not in\nindividual experimental runs. In our example, g2 is filled in, while the\nsoliton is not."
    },
    {
        "anchor": "OpenMP solver for rotating spin-one spin-orbit- and Rabi-coupled\n  Bose-Einstein condensates: We present OpenMP version of a Fortran program for solving the\nGross-Pitaevskii equation for a harmonically trapped three-component rotating\nspin-1 spinor Bose-Einstein condensate (BEC) in two spatial dimensions with or\nwithout spin-orbit (SO) and Rabi couplings. The program uses either Rashba or\nDresselhaus SO coupling. We use the split-step Crank-Nicolson discretization\nscheme for imaginary- and real-time propagation to calculate stationary states\nand BEC dynamics, respectively.",
        "positive": "Precise photoexcitation measurement of Tan's contact in the entire\n  BCS-BEC crossover: We study two-body correlations in a spin-balanced ultracold harmonically\ntrapped Fermi gas of $^6$Li atoms in the crossover from the\nBardeen-Cooper-Schrieffer (BCS) to the Bose-Einstein-Condensate (BEC) regime.\nFor this, we precisely measure Tan's contact using a novel method based on\nphotoexcitation of atomic pairs, which was recently proposed by Wang et al.\n[Phys. Rev. A 104 063309 (2021)]. We map out the contact in the entire phase\ndiagram of the BCS-BEC crossover for various temperatures and interaction\nstrengths, probing regions in phase-space that have not been investigated yet.\nOur measurements reach an uncertainty of $\\approx 2 \\%$ and thus represent a\nprecise quantitative benchmark. We compare our data to theoretical predictions\nand interpolations and localize the regions in phase space where the latter\ngive valid results. In regions where the contact is already well known we find\nexcellent agreement with our measurements. Thus, our results demonstrate that\nphotoinduced loss is a precise probe to measure quantum correlations in a\nstrongly interacting Fermi gas."
    },
    {
        "anchor": "Reentrance of Bose-Einstein condensation in spinor atomic gases in\n  magnetic field: We calculate the Bose-Einstein condensation (BEC) temperature of spin-1\natomic bosons in external magnetic field, taking into account the influence of\nthe quadratic Zeeman effect. In case that the quadratic Zeeman coefficient is\npositive, the BEC temperature exhibits a nontrivial dependance on the magnetic\nfield and a magnetic-field-induced reentrant phenomenon of BEC is observed.\nThis phenomenon could be well understood by the competition between the linear\nand quadratic Zeeman effects. Reentrance of BEC in a trapped spinor Bose gas is\nalso discussed.",
        "positive": "Spectrum and quench-induced dynamics of spin-orbit coupled quantum\n  droplets: We investigate the ground state and dynamics of one-dimensional spin-orbit\ncoupled (SOC) quantum droplets within the extended Gross-Pitaevskii approach.\nAs the SOC wavenumber increases, stripe droplet patterns emerge, with a\nflat-top background, for larger particle numbers. The surface energy decays\nfollowing a power-law with respect to the interactions. At small SOC\nwavenumbers, a transition from Gaussian to flat-top droplets occurs for either\na larger number of atoms or reduced intercomponent attraction. The excitation\nspectrum shows that droplets for relatively small SOC wavenumbers are stable,\notherwise stripe droplets feature instabilities as a function of the particle\nnumber or the interactions. We also witness rich droplet dynamical features\nusing velocity imprinting and abrupt changes in the intercomponent interaction\nor the SOC parameters. Characteristic responses include breathing oscillations,\nexpansion, symmetric and asymmetric droplet fragmentation, admixtures of single\nand stripe droplet branches, and erratic spatial distributions suggesting the\ntriggering of relevant instabilities. Our results reveal the controlled\ndynamical generation and stability properties of stripe droplets that should be\ndetectable in current cold-atom experiments."
    },
    {
        "anchor": "Quantum dynamics of local phase differences between reservoirs of driven\n  interacting bosons separated by simple aperture arrays: We present a derivation of the effective action for the relative phase of\ndriven, aperture-coupled reservoirs of weakly-interacting condensed bosons from\na (3+1)-D microscopic model with local U(1) gauge symmetry. We show that\ninclusion of local chemical potential and driving velocity fields as a gauge\nfield allows derivation of the hydrodynamic equations of motion for the driven\nmacroscopic phase differences across simple aperture arrays. For a single\naperture, the current-phase equation for driven flow contains sinusoidal,\nlinear, and current-bias contributions. We compute the renormalization group\n(RG) beta function of the periodic potential in the effective action for small\ntunneling amplitudes and use this to analyze the temperature dependence of the\nlow-energy current-phase relation, with application to the transition from\nlinear to sinusoidal current-phase behavior observed in experiments by\nHoskinson et al. \\cite{packard} for liquid $^{4}$He driven through nanoaperture\narrays. Extension of the microscopic theory to a two-aperture array shows that\ninterference between the microscopic tunneling contributions for individual\napertures leads to an effective coupling between apertures which amplifies the\nJosephson oscillations in the array. The resulting multi-aperture current-phase\nequations are found to be equivalent to a set of equations for coupled pendula,\nwith microscopically derived couplings.",
        "positive": "Bloch-Zener oscillations across a merging transition of Dirac points: Bloch oscillations are a powerful tool to investigate spectra with Dirac\npoints. By varying band parameters, Dirac points can be manipulated and merged\nat a topological transition towards a gapped phase. Under a constant force, a\nFermi sea initially in the lower band performs Bloch oscillations and may Zener\ntunnel to the upper band mostly at the location of the Dirac points. The\ntunneling probability is computed from the low energy universal Hamiltonian\ndescribing the vicinity of the merging. The agreement with a recent experiment\non cold atoms in an optical lattice is very good."
    },
    {
        "anchor": "Shapiro steps in driven atomic Josephson junctions: We study driven atomic Josephson junctions realized by coupling two\ntwo-dimensional atomic clouds with a tunneling barrier. By moving the barrier\nat a constant velocity, dc and ac Josephson regimes are characterized by a zero\nand nonzero atomic density difference across the junction, respectively. Here,\nwe monitor the dynamics resulting in the system when, in addition to the above\nconstant velocity protocol, the position of the barrier is periodically driven.\nWe demonstrate that the time-averaged particle imbalance features a step-like\nbehavior that is the analog of Shapiro steps observed in driven superconducting\nJosephson junctions. The underlying dynamics reveals an intriguing interplay of\nthe vortex and phonon excitations, where Shapiro steps are induced via\nsuppression of vortex growth. We study the system with a classical-field\ndynamics method, and benchmark our findings with a driven circuit dynamics.",
        "positive": "Characteristic temperatures of a triplon system of dimerized quantum\n  magnets: Exploiting the analogy between ultracold atomic gases and the system of\ntriplons, we study magneto-thermodynamic properties of dimerized quantum\nmagnets in the framework of Bose -Einstein condensation (BEC). Particularly,\nintroducing the inversion (or Joule - Thomson) temperature $T_{JT}$ as the\npoint where Joule - Thomson coefficient of an isenthalpic process changes its\nsign, we show that for a simple paramagnet, this temperature is infinite, while\nfor three-dimensional (3D) dimerized quantum magnets it is finite and always\nlarger than the critical temperature $T_c$ of BEC. Below the inversion\ntemperature $T<T_{JT}$ the system of triplons may be in a liquid phase, which\nundergoes a transition into a superfluid phase at $T\\le T_c<T_{JT}$. The\ndependence of the inversion temperature on the external magnetic field $T_{JT}\n(H)$ has been calculated for quantum magnets of TlCuCl$_3$ and\nSr$_3$Cr$_2$O$_8$."
    },
    {
        "anchor": "BCS-BEC quantum phase transition and collective excitations in\n  two-dimensional Fermi gases with p- and d-wave pairings: It is generally believed that the BCS-BEC evolution in fermionic systems with\ns-wave pairing is a smooth crossover. However, for nonzero\norbital-angular-momentum pairing such as p- or d-wave pairing, the system\nundergoes a quantum phase transition at the point where the chemical potential\n$\\mu$ vanishes. In this paper, we study the BCS-BEC quantum phase transition\nand the collective excitations associated with the order-parameter fluctuations\nin two-dimensional fermionic systems with p- and d-wave pairings. We show that\nthe quantum phase transition in such systems can be generically traced back to\nthe infrared behavior of the fermionic excitation at $\\mu=0$: $E_{\\bf k}\\sim\nk^l$, where $l=1,2$ is the quantum number of the orbital angular momentum. The\nnonanalyticity of the thermodynamic quantities is due to the infrared\ndivergence caused by the fermionic excitation at $\\mu=0$. As a result, the\nevolution of the Anderson-Bogoliubov mode is not smooth: Its velocity is\nnonanalytical across the quantum phase transition.",
        "positive": "Scanning electron microscopy of Rydberg-excited Bose-Einstein\n  condensates: We report on the realization of high resolution electron microscopy of\nRydberg-excited ultracold atomic samples. The implementation of an ultraviolet\nlaser system allows us to excite the atom, with a single-photon transition, to\nRydberg states. By using the electron microscopy technique during the Rydberg\nexcitation of the atoms, we observe a giant enhancement in the production of\nions. This is due to $l$-changing collisions, which broaden the Rydberg level\nand therefore increase the excitation rate of Rydberg atoms. Our results pave\nthe way for the high resolution spatial detection of Rydberg atoms in an atomic\nsample."
    },
    {
        "anchor": "Snell's Law for a vortex dipole in a Bose-Einstein condensate: A quantum vortex dipole, comprised of a closely bound pair of vortices of\nequal strength with opposite circulation, is a spatially localized travelling\nexcitation of a planar superfluid that carries linear momentum, suggesting a\npossible analogy with ray optics. We investigate numerically and analytically\nthe motion of a quantum vortex dipole incident upon a step-change in the\nbackground superfluid density of an otherwise uniform two-dimensional\nBose-Einstein condensate. Due to the conservation of fluid momentum and energy,\nthe incident and refracted angles of the dipole satisfy a relation analogous to\nSnell's law, when crossing the interface between regions of different density.\nThe predictions of the analogue Snell's law relation are confirmed for a wide\nrange of incident angles by systematic numerical simulations of the\nGross-Piteavskii equation. Near the critical angle for total internal\nreflection, we identify a regime of anomalous Snell's law behaviour where the\nfinite size of the dipole causes transient capture by the interface.\nRemarkably, despite the extra complexity of the surface interaction, the\nincoming and outgoing dipole paths obey Snell's law.",
        "positive": "Anisotropic polarizability of erbium atoms: We report on the determination of the dynamical polarizability of ultracold\nerbium atoms in the ground and in one excited state at three different\nwavelengths, which are particularly relevant for optical trapping. Our study\ncombines experimental measurements of the light shift and theoretical\ncalculations. In particular, our experimental approach allows us to isolate the\ndifferent contributions to the polarizability, namely the isotropic scalar and\nanisotropic tensor part. For the latter contribution, we observe a clear\ndependence of the atomic polarizability on the angle between the\nlaser-field-polarization axis and the quantization axis, set by the external\nmagnetic field. Such an angle-dependence is particularly pronounced in the\nexcited-state polarizability. We compare our experimental findings with the\ntheoretical values, based on semi-empirical electronic-structure calculations\nand we observe a very good overall agreement. Our results pave the way to\nexploit the anisotropy of the tensor polarizability for spin-selective\npreparation and manipulation."
    },
    {
        "anchor": "Normal modes for N identical particles: A study of the evolution of\n  collective behavior from few-body to many-body: Normal mode dynamics are ubiquitous underlying the motions of diverse systems\nfrom rotating stars to crystal structures. These behaviors are composed of\nsimple collective motions of particles which move with the same frequency and\nphase, thus encapsulating many-body effects into simple dynamic motions. In\nregimes such as the unitary regime for ultracold Fermi gases, a single\ncollective mode can dominate, leading to simple behavior as seen in\nsuperfluidity. I investigate the evolution of collective motion as a function\nof N for five types of normal modes obtained from an L=0 group theoretic\nsolution of a general Hamiltonian for confined, identical particles. I show\nusing simple analytic forms that the collective behavior of few-body systems,\nwith the well known motions of molecular equivalents such as ammonia and\nmethane, evolves smoothly to the collective motions expected for large N\nensembles. The transition occurs at quite low values of N. I study a\nHamiltonian known to support collective behavior, the Hamiltonian for Fermi\ngases in the unitary regime. I analyze the evolution of both frequencies and\nthe coefficients that mix the radial and angular coordinates which both depend\non interparticle interactions. This analysis reveals two phenomena that could\ncontribute to the viability of collective behavior. First the mixing\ncoefficients go to zero or unity, i.e. no mixing, as N becomes large resulting\nin solutions that do not depend on the details of the interparticle potential\nas expected for this unitary regime, and that manifest the symmetry of an\nunderlying approximate Hamiltonian. Second, the five normal mode frequencies\nwhich are all close for low values of N, separate as N increases, creating\nlarge gaps that can, in principle, offer stability to collective behavior if\nmechanisms to prevent the transfer of energy to other modes exist (such as low\ntemperature) or can be constructed.",
        "positive": "Statistically induced Phase Transitions and Anyons in 1D Optical\n  Lattices: Anyons - particles carrying fractional statistics that interpolate between\nbosons and fermions - have been conjectured to exist in low dimensional\nsystems. In the context of the fractional quantum Hall effect (FQHE),\nquasi-particles made of electrons take the role of anyons whose statistical\nexchange phase is fixed by the filling factor. Here we propose an experimental\nsetup to create anyons in one-dimensional lattices with fully tuneable exchange\nstatistics. In our setup, anyons are created by bosons with\noccupation-dependent hopping amplitudes, which can be realized by assisted\nRaman tunneling. The statistical angle can thus be controlled in situ by\nmodifying the relative phase of external driving fields. This opens the\nfascinating possibility of smoothly transmuting bosons via anyons into fermions\nand of inducing a phase transition by the mere control of the particle\nstatistics as a free parameter. In particular, we demonstrate how to induce a\nquantum phase transition from a superfluid into an exotic Mott-like state where\nthe particle distribution exhibits plateaus at fractional densities."
    },
    {
        "anchor": "Conjectures about the ground-state energy of the Lieb-Liniger model at\n  weak repulsion: We develop an alternative description to solve the problem of the\nground-state energy of the Lieb-Liniger model that describes one-dimensional\nbosons with contact repulsion. For this integrable model we express the Lieb\nintegral equation in the representation of Chebyshev polynomials. The latter\nform is convenient to efficiently obtain very precise numerical results in the\nsingular limit of weak interaction. Such highly precise data enable us to use\nthe integer relation algorithm to discover the analytical form of the\ncoefficients in the expansion of the ground-state energy for small values of\nthe interaction parameter. We obtained the first nine terms of the expansion\nusing quite moderate numerical efforts. The detailed knowledge of behavior of\nthe ground-state energy on the interaction immediately leads to exact\nperturbative results for the excitation spectrum.",
        "positive": "Quantum Transport of Bosonic Cold Atoms in Double Well Optical Lattices: We numerically investigate, using the time evolving block decimation\nalgorithm, the quantum transport of ultra-cold bosonic atoms in a double well\noptical lattice through slow and periodic modulation of the lattice parameters\n(intra- and inter-well tunneling, chemical potential, etc.). The transport of\natoms does not depend on the rate of change of the parameters (as along as the\nchange is slow) and can distribute atoms in optical lattices at the quantized\nlevel without involving external forces. The transport of atoms depends on the\natom filling in each double well and the interaction between atoms. In the\nstrongly interacting region, the bosonic atoms share the same transport\nproperties as non-interacting fermions with quantized transport at the half\nfilling and no atom transport at the integer filling. In the weakly interacting\nregion, the number of the transported atoms is proportional to the atom\nfilling. We show the signature of the quantum transport from the momentum\ndistribution of atoms that can measured in the time of flight image. A\nsemiclassical transport model is developed to explain the numerically observed\ntransport of bosonic atoms in the non-interacting and strongly interacting\nlimits. The scheme may serve as an quantized battery for atomtronics\napplications."
    },
    {
        "anchor": "Probing chiral edge dynamics and bulk topology of a synthetic Hall\n  system: Quantum Hall systems are characterized by the quantization of the Hall\nconductance -- a bulk property rooted in the topological structure of the\nunderlying quantum states. In condensed matter devices, material imperfections\nhinder a direct connection to simple topological models. Artificial systems,\nsuch as photonic platforms or cold atomic gases, open novel possibilities by\nenabling specific probes of topology or flexible manipulation e.g. using\nsynthetic dimensions. However, the relevance of topological properties requires\nthe notion of a bulk, which was missing in previous works using synthetic\ndimensions of limited sizes. Here, we realize a quantum Hall system using\nultracold dysprosium atoms, in a two-dimensional geometry formed by one spatial\ndimension and one synthetic dimension encoded in the atomic spin $J=8$. We\ndemonstrate that the large number of magnetic sublevels leads to distinct bulk\nand edge behaviors. Furthermore, we measure the Hall drift and reconstruct the\nlocal Chern marker, an observable that has remained, so far, experimentally\ninaccessible. In the center of the synthetic dimension -- a bulk of 11 states\nout of 17 -- the Chern marker reaches 98(5)\\% of the quantized value expected\nfor a topological system. Our findings pave the way towards the realization of\ntopological many-body phases.",
        "positive": "Bose polaron in spherically symmetric trap potentials: Ground states\n  with zero and lower angular momenta: Single-atomic impurities immersed in a dilute Bose gas in the spherically\nsymmetric harmonic trap potentials are studied at zero temperature. In order to\nfind the ground state of the polarons, we present a conditional variational\nmethod with fixed expectation values of the total angular momentum operators,\n$\\hat{J}^2$ and $\\hat{J}_z$, of the system, using a cranking\ngauge-transformation for bosons to move them in the frame co-rotating with the\nimpurity. In the formulation, the expectation value $\\langle \\hat{J^2}\\rangle$\nis shown to be shared in impurity and bosons, but the value $\\langle\n\\hat{J}_z\\rangle$ is carried by the impurity due to the rotational symmetry. We\nalso analyze the ground-state properties numerically obtained in this\nvariational method for the system of the attractive impurity-boson interaction,\nand find that excited boson distributions around the impurity overlap largely\nwith impurity's wave function in their quantum-number spaces and also in the\nreal space because of the attractive interaction employed."
    },
    {
        "anchor": "Superfluid properties of a honeycomb dipolar supersolid: Recent breakthrough experiments on dipolar condensates have reported the\ncreation of supersolids, including two-dimensional arrays of quantum droplets.\nDroplet arrays are, however, not the only possible non-trivial density\narrangement resulting from the interplay of mean-field instability and quantum\nstabilization. Several other possible density patterns may occur in trapped\ncondensates at higher densities, including the so-called honeycomb supersolid,\na phase that exists, as it is also the case of a triangular droplet supersolid,\nin the thermodynamic limit. We show that compared to droplet supersolids,\nhoneycomb supersolids have a much-enhanced superfluid fraction while keeping a\nlarge density contrast, and constitute in this sense a much better dipolar\nsupersolid. However, in contrast to droplet supersolids, quantized vortices\ncannot be created in a honeycomb supersolid without driving a transition into a\nso-called labyrinthic phase. We show that the reduced moment of inertia, and\nwith it the superfluid fraction, can be however reliably probed by studying the\ndynamics following a scissors-like perturbation.",
        "positive": "Non-linear mixing of Bogoliubov modes in a bosonic Josephson junction: We revisit the dynamics of a Bose-Einstein condensate in a double-well\npotential, from the regime of Josephson plasma oscillations to the\nself-trapping regime, by means of the Bogoliubov quasiparticle projection\nmethod. For very small imbalance between left and right wells only the lowest\nBogoliubov mode is significantly occupied. In this regime the system performs\nplasma oscillations at the corresponding frequency, and the evolution of the\ncondensate is characterized by a periodic transfer of population between the\nground and the first excited state. As the initial imbalance is increased, more\nexcited modes -- though initially not macroscopically occupied -- get coupled\nduring the evolution of the system. Since their population also varies with\ntime, the frequency spectrum of the imbalance turns out to be still peaked\naround a single frequency, which is continuously shifted towards lower values.\nThe nonlinear mixing between Bogoliubov modes eventually drives the system into\nthe the self-trapping regime, when the population of the ground state can be\ntransferred completely to the excited states at some time during the evolution.\nFor simplicity, here we consider a one-dimensional setup, but the results are\nexpected to hold also in higher dimensions."
    },
    {
        "anchor": "Fast thermalization and Helmholtz oscillations of an ultracold Bose gas: We analyze theoretically the transport properties of a weakly-interacting\nultracold Bose gas enclosed in two reservoirs connected by a constriction. We\nassume that the transport of the superfluid part is hydrodynamic, and we\ndescribe the ballistic transport of the normal part using the Landauer-Buttiker\nformalism. Modeling the coupled evolution of the phase, atom number, and\ntemperature mismatches between the reservoirs, we predict that Helmholtz\n(plasma) oscillations, induced by an initial imbalance in atom numbers, can be\nobserved at non-zero temperatures below Tc. We show that, because of its strong\ncompressibility, the ultracold Bose gas is characterized by a fast\nthermalization compared to the damping time for plasma oscillations,\naccompanied by a fast transfer of the normal component through the\nconstriction. This fast thermalization also affects the gas above Tc, where we\npresent an explicit comparison to the ideal fermionic case.",
        "positive": "Non-equilibrium steady states and critical slowing down in the\n  dissipative Bose-Hubbard model: Motivated by recent experiments, we study the properties of large\nBose-Hubbard chains with single-particle losses at one site using classical\nfield methods. We construct and validate a compact effective model that reduces\ncomputations to only a few sites. We show that in the mean-field approach the\ndescription captures the stationary states of the dissipative mode very well.\nNot only is there a good quantitative agreement in the hysteresis loop, the\ndark soliton state can be reproduced as well due to the the preservation of the\n$U(1)$ symmetry. Bimodality of the steady states, observed on longer\ntimescales, is studied using the truncated Wigner method. We compare the\nswitching statistics and derive the effective Liouvillian gap in function of\nthe tunneling, showing that the effective description underestimates\nfluctuations."
    },
    {
        "anchor": "Induced interactions in dilute atomic gases and liquid helium mixtures: In dilute mixtures of two atomic gases, interactions between two minority\natoms acquire a contribution due to interaction with the majority component.\nUsing thermodynamic arguments, we derive expressions for this induced\ninteraction for both fermions and bosons for arbitrary strength of the\ninteraction between the two components. Implications of the work for the theory\nof dilute solutions of $^3$He in liquid $^4$He are discussed.",
        "positive": "Giant Vortex Clusters in a Two-Dimensional Quantum Fluid: Adding energy to a system through transient stirring usually leads to more\ndisorder. In contrast, point-like vortices in a bounded two-dimensional fluid\nare predicted to reorder above a certain energy, forming persistent vortex\nclusters. Here we realize experimentally these vortex clusters in a planar\nsuperfluid: a $^{87}$Rb Bose-Einstein condensate confined to an elliptical\ngeometry. We demonstrate that the clusters persist for long times, maintaining\nthe superfluid system in a high energy state far from global equilibrium. Our\nexperiments explore a regime of vortex matter at negative absolute\ntemperatures, and have relevance to the dynamics of topological defects,\ntwo-dimensional turbulence, and systems such as helium films, nonlinear optical\nmaterials, fermion superfluids, and quark-gluon plasmas."
    },
    {
        "anchor": "Majorana corner pairs in a two-dimensional $s$-wave cold atomic\n  superfluid: We propose a method to prepare Majorana pairs at the corners of imprinted\ndefects on a two-dimensional cold atom optical lattice with $s$-wave superfluid\npairing. Different from previous proposals that manipulate the effective Dirac\nmasses, our scheme relies on the sign flip of the spin-orbit coupling at the\ncorners, which can be tuned in experiments by adjusting the angle of incident\nRaman lasers. The Majorana corner pairs are found to be located at the\ninterface between two regimes with opposite spin orbit coupling strengths in an\nanticlockwise direction and are robust against certain symmetry-persevered\nperturbations. Our work provides a new way for implementing and manipulating\nMajorana pairs with existing cold-atom techniques.",
        "positive": "Light scattering from ultracold gases in disordered optical lattices: We consider a gas of bosons in a bichromatic optical lattice at finite\ntemperatures. As the amplitude of the secondary lattice grows, the\nsingle-particles eigenstates become localized. We calculate the canonical\npartition function using exact methods for the noninteracting and strongly\ninteracting limit and analyze the statistical properties of the superfluid\nphase, localized phase and the strongly interacting gas. We show that those\nphases may be distinguished in experiment using off-resonant light scattering."
    },
    {
        "anchor": "What can we learn from diffusion about Anderson localization of a\n  degenerate Fermi gas?: Disorder can fundamentally modify the transport properties of a system. A\nstriking example is Anderson localization, suppressing transport due to\ndestructive interference of propagation paths. In inhomogeneous many-body\nsystems, not all particles are localized for finite-strength disorder, and the\nsystem can become partially diffusive. Unravelling the intricate signatures of\nlocalization from such observed diffusion is a long-standing problem. Here, we\nexperimentally study a degenerate, spin-polarized Fermi gas in a disorder\npotential formed by an optical speckle pattern. We record the diffusion in the\ndisordered potential upon release from an external confining potential. We\ncompare different methods to analyze the resulting density distributions,\nincluding a new method to capture particle dynamics by evaluating\nabsorption-image statistics. Using standard observables, such as diffusion\nexponent and coefficient, localized fraction, or localization length, we find\nthat some show signatures for a transition to localization above a critical\ndisorder strength, while others show a smooth crossover to a modified diffusion\nregime. In laterally displaced disorder, we spatially resolve different\ntransport regimes simultaneously which allows us to extract the subdiffusion\nexponent expected for weak localization. Our work emphasizes that the\ntransition toward localization can be investigated by closely analyzing the\nsystem's diffusion, offering ways of revealing localization effects beyond the\nsignature of exponentially decaying density distribution.",
        "positive": "Interaction-induced excited-band condensate in a double-well optical\n  lattice: We show theoretically that interaction effects in a double-well optical\nlattice can induce condensates in an excited band. For a symmetric double-well\nlattice, bosons condense into the bottom of the excited band at the edge of the\nBrillouin Zone if the chemical potential is above a critical value. For an\nasymmetric lattice, a condensate with zero momentum is automatically induced in\nthe excited band by the condensate in the lowest band. This is due to a\ncombined effect of interaction and lattice potential, which reduces the band\ngap and breaks the inversion symmetry. Our work can be generalized to a\nsuperlattice composed of multiple-well potentials at each lattice site, where\ncondensates can be induced in even higher bands."
    },
    {
        "anchor": "Surface Effects in the Unitary Fermi Gas: We study the extended Thomas-Fermi (ETF) density functional of the superfluid\nunitary Fermi gas. This functional includes a gradient term which is essential\nto describe accurately the surface effects of the system, in particular with a\nsmall number of atoms, where the Thomas-Fermi (local density) approximation\nfails. We find that our ETF functional gives density profiles which are in good\nagreement with recent Monte Carlo results and also with a more sophisticated\nsuperfluid density functional based on Bogoliubov-de Gennes equations. In\naddition, by using extended hydrodynamics equations of superfluids, we\ncalculate the frequencies of collective surface oscillations of the unitary\nFermi gas, showing that quadrupole and octupole modes strongly depend on the\nnumber of trapped atoms.",
        "positive": "Localization-delocalization Transition in an electromagnetically induced\n  photonic lattice: We investigate the localization-delocalization transition (LDT) in an\nelectromagnetically induced photonic lattice. A four-level tripod-type scheme\nin atomic ensembles is proposed to generate an effective photonic moir\\'{e}\nlattice through the electromagnetically induced transparency (EIT) mechanism.\nBy taking advantage of the tunable atomic coherence, we show that both periodic\n(commensurable) and aperiodic (incommensurable) structure can be created in\nsuch a photonic moir\\'{e} lattice via adjusting the twist angle between two\nsuperimposed periodic patterns with square primitive. Furthermore, we also find\nthat by tuning the amplitudes of these two superimposed periodic patterns, the\nlocalization-delocalization transition occurs for the light propagating in the\naperiodic moir\\'{e} lattice. Such localization is shown to link the fact that\nthe flat bands of moir\\'{e} lattice support quasi-nondiffracting localized\nmodes and thus induce the localization of the initially localized beam. It\nwould provide a promising approach to control the light propagation via the\nelectromagnetically induced photonic lattice."
    },
    {
        "anchor": "Prethermalization in the cooling dynamics of an impurity in a BEC: We discuss the cooling dynamics of heavy impurity atoms in a Bose-Einstein\ncondensate (BEC) by emission of Cherenkov phonons from scattering with the\ncondensate. In a weakly interacting, low-temperature condensate the\nsuperfluidity of the condensate results in a separation of time-scales of the\nthermalization dynamics. Pre-thermalized states are formed with distinct\nregions of impurity momenta determined by the mass ratio of impurity and BEC\natoms. This can be employed to detect the mass renormalization of the impurity\nupon the formation of a polaron and paves the way to preparing non-equilibrium\nimpurity-momentum distributions.",
        "positive": "Spatial inversion symmetry breaking of vortex current in biased-ladder\n  superfluid: We investigate the quench dynamics of interacting bosons on a two-leg ladder\nin presence of a uniform Abelian gauge field. The model hosts a variety of\nemergent quantum phases, and we focus on the superfluid biased-ladder phase\nbreaking the $Z_{2}$ symmetry of two legs. We observe an asymmetric spreading\nof vortex current and particle density, i.e., the current behaves particle-like\non the right and wave-like on the left, indicating spontaneous breaking of the\nspatial inversion symmetry. By decreasing the repulsion strength, it is found\nthe particle-like current is more robust than the wave-like one. The evolution\nof entanglement entropy manifests logarithmic growth with time suggesting\nmany-body localization matters."
    },
    {
        "anchor": "Nonlinear Atom-Photon Interaction Induced Population Inversion and\n  Inverted Quantum Phase Transition of Bose-Einstein Condensate in an Optical\n  Cavity: In this paper we explore the rich structure of macroscopic many-particle\nquantum states for Bose- Einstein condensate in an optical cavity with the\ntunable nonlinear atom-photon interaction [Nature (London) 464, 1301 (2010)].\nPopulation inversion, bistable normal phases and the coexistence of\nnormal{superradiant phases are revealed by adjusting of the experimentally\nrealizable interaction strength and pump-laser frequency. For the negative\n(effective) cavity-frequency we observe remark- ably an inverted quantum phase\ntransition (QPT) from the superradiant to normal phases with the increase of\natom-field coupling, which is just opposite to the QPT in the normal Dicke\nmodel. The bistable macroscopic states are derived analytically in terms of the\nspin-coherent-state variational method by taking into account of both normal\nand inverted pseudospin states.",
        "positive": "Realization of a Townes soliton in a two-component planar Bose gas: Most experimental observations of solitons are limited to one-dimensional\n(1D) situations, where they are naturally stable. For instance, in 1D cold Bose\ngases, they exist for any attractive interaction strength $g$ and particle\nnumber $N$. By contrast, in two dimensions, solitons appear only for discrete\nvalues of $gN$, the so-called Townes soliton being the most celebrated example.\nHere, we use a two-component Bose gas to prepare deterministically such a\nsoliton: Starting from a uniform bath of atoms in a given internal state, we\nimprint the soliton wave function using an optical transfer to another state.\nWe explore various interaction strengths, atom numbers and sizes, and confirm\nthe existence of a solitonic behaviour for a specific value of $gN$ and\narbitrary sizes, a hallmark of scale invariance."
    },
    {
        "anchor": "The Gor'kov and Melik-Barkhudarov correction to an imbalanced Fermi gas\n  in the presence of impurities: The effects of induced interactions are calculated in both clean and dirty\nsituations, for balanced and imbalanced Fermi gases. We investigate the effects\nof nonmagnetic impurities on the induced interactions corrections to the\ntransition temperature in the case of a balanced gas, and to the tricritical\npoint in the case of an imbalanced Fermi gas at unitarity. We find that\nimpurities act in detriment of the induced interactions, or particle-hole\nfluctuations, for the transition temperature and the tricritical point. For\nlarge impurity parameter, the particle-hole fluctuations are strongly\nsuppressed. We have also found the Chandrasekhar-Clogston limit of an\nimbalanced Fermi gas at unitarity considering the effects of the induced\ninteractions, both in the pure and impurity regimes.",
        "positive": "Generation of dispersive shock waves by the flow of a Bose-Einstein\n  condensate past a narrow obstacle: We study the flow of a quasi-one-dimensional Bose-Einstein condensate\nincident onto a narrow obstacle. We consider a configuration in which a\ndispersive shock is formed and propagates upstream away from the obstacle while\nthe downstream flow reaches a supersonic velocity, generating a sonic horizon.\nConditions for obtaining this regime are explicitly derived and the accuracy of\nour analytical results is confirmed by numerical simulations."
    },
    {
        "anchor": "Exact surface-wave spectrum of a dilute quantum liquid: We consider a dilute gas of bosons with repulsive contact interactions,\ndescribed on the mean-field level by the Gross-Pitaevskii equation, and bounded\nby an impenetrable \"hard\" wall (either rigid or flexible). We solve the\nBogoliubov-de Gennes equations for excitations on top of the Bose-Einstein\ncondensate analytically, by using matrix-valued hypergeometric functions. This\nleads to the exact spectrum of gapless Bogoliubov excitations localized near\nthe boundary. The dispersion relation for the surface excitations represents\nfor small wavenumbers $k$ a ripplon mode with fractional power law dispersion\nfor a flexible wall, and a phonon mode (linear dispersion) for a rigid wall.\nFor both types of excitation we provide, for the first time, the exact\ndispersion relations of the dilute quantum liquid for all $k$ along the\nsurface, extending to $k \\rightarrow \\infty$. The small wavelength excitations\nare shown to be bound to the surface with a maximal binding energy $\\Delta=\n\\frac18 (\\sqrt{17}-3)^2 mc^2 \\simeq 0.158\\, mc^2$, which both types of\nexcitation asymptotically approach, where $m$ is mass of bosons and $c$ bulk\nspeed of sound. We demonstrate that this binding energy is close to the\nexperimental value obtained for surface excitations of helium II confined in\nnanopores, reported in Phys. Rev. B 88, 014521 (2013).",
        "positive": "Incompressibility Estimates for the Laughlin Phase: This paper has its motivation in the study of the Fractional Quantum Hall\nEffect. We consider 2D quantum particles submitted to a strong perpendicular\nmagnetic field, reducing admissible wave functions to those of the Lowest\nLandau Level. When repulsive interactions are strong enough in this model,\nhighly correlated states emerge, built on Laughlin's famous wave function. We\ninvestigate a model for the response of such strongly correlated ground states\nto variations of an external potential. This leads to a family of variational\nproblems of a new type. Our main results are rigorous energy estimates\ndemonstrating a strong rigidity of the response of strongly correlated states\nto the external potential. In particular we obtain estimates indicating that\nthere is a universal bound on the maximum local density of these states in the\nlimit of large particle number. We refer to these as incompressibility\nestimates."
    },
    {
        "anchor": "A note on Fermi energy of Fermi gas trapped under generic power law\n  potential in $d$-dimension: Average energy per fermion in case of Fermi gas with any kinematic\ncharacteristic, trapped under most general power law potential in $d$ dimension\nhas been calculated at zero temperature. In a previous paper (M. Acharyya, Eur.\nJ Phys. 31 L89 (2010)) it was shown, in case of free ideal Fermi gas as\ndimension increases average energy approaches to Fermi energy and in infinite\ndimension average energy becomes equal to Fermi energy at $T=0$. In this letter\nit is shown that, for trapped system at finite dimension the average energy\ndepends on power law exponent, but as dimension tends to infinity average\nenergy coincides with Fermi energy for any power law exponent. The result\nobtained in this manuscript is more general as we can describe free system as\nwell as any trapped system with appropriate choice of power law exponent and\ntrue for any kinematic parameter.",
        "positive": "Decay of Resonance Structure and Trapping Effect in Potential Scattering\n  Problem of Self-Focusing Wave Packet: Potential scattering problems governed by the time-dependent Gross-Pitaevskii\nequation are investigated numerically for various values of coupling constants.\nThe initial condition is assumed to have the Gaussian-type envelope, which\ndiffers from the soliton solution. The potential is chosen to be a box or well\ntype. We estimate the dependences of reflectance and transmittance on the width\nof the potential and compare these results with those given by the stationary\nSchr\\\"odinger equation. We attribute the behaviors of these quantities to the\nlimitation on the width of the nonlinear wave packet. The coupling constant and\nthe width of the potential play an important role in the distribution of the\nwaves appearing in the final state of scattering."
    },
    {
        "anchor": "Spin Susceptibility Above the Superfluid Onset in Ultracold Fermi Gases: Ultracold atomic Fermi gases can be tuned to interact strongly, where they\ndisplay spectroscopic signatures above the superfluid transition reminiscent of\nthe pseudogap in cuprates. However, the extent of the analogy can be\nquestioned, since thermodynamic quantities in the low temperature\nspin-imbalanced normal state can be described successfully using Fermi liquid\ntheory. Here we present spin susceptibility measurements across the interaction\nstrength-temperature phase diagram using a novel radiofrequency technique with\nultracold $^6\\textrm{Li}$ gases. For all significant interaction strengths and\nat all temperatures we find the spin susceptibility is reduced compared with\nthe equivalent value for a non-interacting Fermi gas, with the low temperature\nresults consistent with previous studies. However, our measurements extend to\nhigher temperatures, where we find that the reduction persists consistently\nwith a mean-field scenario. At unitarity, we can use the local density\napproximation to extract the spin susceptibility for the uniform gas, which is\nwell described by mean-field models at temperatures from the superfluid\ntransition to the Fermi temperature.",
        "positive": "Experimental realization of strong effective magnetic fields in an\n  optical lattice: We use Raman-assisted tunneling in an optical superlattice to generate large\ntunable effective magnetic fields for ultracold atoms. When hopping in the\nlattice, the accumulated phase shift by an atom is equivalent to the\nAharonov-Bohm phase of a charged particle exposed to a staggered magnetic field\nof large magnitude, on the order of one flux quantum per plaquette. We study\nthe ground state of this system and observe that the frustration induced by the\nmagnetic field can lead to a degenerate ground state for non-interacting\nparticles. We provide a measurement of the local phase acquired from\nRaman-induced tunneling, demonstrating time-reversal symmetry breaking of the\nunderlying Hamiltonian. Furthermore, the quantum cyclotron orbit of single\natoms in the lattice exposed to the magnetic field is directly revealed."
    },
    {
        "anchor": "Expansion dynamics of interacting bosons in homogeneous lattices in one\n  and two dimensions: We experimentally and numerically investigate the expansion of initially\nlocalized ultracold bosons in homogeneous one- and two-dimensional optical\nlattices. We find that both dimensionality and interaction strength crucially\ninfluence these non-equilibrium dynamics. While the atoms expand ballistically\nin all integrable limits, deviations from these limits dramatically suppress\nthe expansion and lead to the appearance of almost bimodal cloud shapes,\nindicating diffusive dynamics in the center surrounded by ballistic wings. For\nstrongly interacting bosons, we observe a dimensional crossover of the dynamics\nfrom ballistic in the one-dimensional hard-core case to diffusive in two\ndimensions, as well as a similar crossover when higher occupancies are\nintroduced into the system.",
        "positive": "Characteristic temperature for the immiscible-miscible transition of\n  binary condensates in optical lattices: We study a two-species Bose-Einstein condensates confined in\nquasi-two-dimensional (quasi-2D) optical lattices at finite temperatures,\nemploying the Hartree-Fock-Bogoliubov theory with the Popov approximation. We\nexamine the role of thermal fluctuations on the ground-state density\ndistributions, and the quasiparticle mode evolution. At zero temperature, the\ngeometry of the ground-state in the immiscible domain is side-by-side. Our\nresults show that the thermal fluctuations enhance the miscibility of the\ncondensates, and at a characteristic temperature the system becomes miscible\nwith rotationally symmetric overlapping density profiles. This\nimmiscible-miscible transition is accompanied by a discontinuity in the\nexcitation spectrum, and the low-lying quasiparticle modes such as slosh mode\nbecomes degenerate at the characteristic temperature."
    },
    {
        "anchor": "Emergence of multi-body interactions in few-atom sites of a fermionic\n  lattice clock: Alkaline-earth (AE) atoms have metastable clock states with minute-long\noptical lifetimes, high-spin nuclei, and SU($N$)-symmetric interactions that\nuniquely position them for advancing atomic clocks, quantum information\nprocessing, and quantum simulation. The interplay of precision measurement and\nquantum many-body physics is beginning to foster an exciting scientific\nfrontier with many opportunities. Few particle systems provide a window to view\nthe emergence of complex many-body phenomena arising from pairwise\ninteractions. Here, we create arrays of isolated few-body systems in a\nfermionic ${}^{87}$Sr three-dimensional (3D) optical lattice clock and use high\nresolution clock spectroscopy to directly observe the onset of both elastic and\ninelastic multi-body interactions. These interactions cannot be broken down\ninto sums over the underlying pairwise interactions. We measure\nparticle-number-dependent frequency shifts of the clock transition for atom\nnumbers $n$ ranging from 1 to 5, and observe nonlinear interaction shifts,\nwhich are characteristic of SU($N$)-symmetric elastic multi-body effects. To\nstudy inelastic multi-body effects, we use these frequency shifts to isolate\n$n$-occupied sites and measure the corresponding lifetimes. This allows us to\naccess the short-range few-body physics free from systematic effects\nencountered in a bulk gas. These measurements, combined with theory, elucidate\nan emergence of multi-body effects in few-body systems of sites populated with\nground-state atoms and those with single electronic excitations. By connecting\nthese few-body systems through tunneling, the favorable energy and timescales\nof the interactions will allow our system to be utilized for studies of\nhigh-spin quantum magnetism and the Kondo effect.",
        "positive": "Spontaneous generation of dark-bright and dark-antidark solitons upon\n  quenching a particle-imbalanced bosonic mixture: We unveil the dynamical formation of multiple localized structures in the\nform of dark-bright and dark-antidark solitary waves that emerge upon quenching\na one-dimensional particle-imbalanced Bose-Bose mixture. Interspecies\ninteraction quenches drive the system out-of-equilibrium while the so-called\nmiscible/immiscible threshold is crossed in a two directional manner.\nDark-bright entities are spontaneously generated for quenches towards the phase\nseparated regime and dark-antidark states are formed in the reverse process.\nThe distinct mechanisms of creation of the aforementioned states are discussed\nin detail and their controlled generation is showcased. In both processes, it\nis found that the number of solitary waves generated is larger for larger\nparticle imbalances, a result that is enhanced for stronger postquench\ninterspecies interactions. Additionally the confining geometry highly affects\nthe production of both types of states with a decaying solitary wave formation\noccurring for tighter traps. Furthermore, in both of the aforementioned\ntransitions, the breathing frequencies measured for the species differ\nsignificantly for highly imbalanced mixtures. Finally, the robustness of the\ndynamical formation of dark-bright and dark-antidark solitons is also\ndemonstrated in quasi one-dimensional setups."
    },
    {
        "anchor": "Expansion dynamics in the one-dimensional Fermi-Hubbard model: Expansion dynamics of interacting fermions in a lattice are simulated within\nthe one-dimensional (1D) Hubbard model, using the essentially exact\ntime-evolving block decimation (TEBD) method. In particular, the expansion of\nan initial band-insulator state is considered. We analyze the simulation\nresults based on the dynamics of a two-site two-particle system, the so-called\nHubbard dimer. Our findings describe essential features of a recent experiment\non the expansion of a Fermi gas in a two-dimensional lattice. We show that the\nHubbard-dimer dynamics, combined with a two-fluid model for the paired and\nnon-paired components of the gas, gives an efficient description of the full\ndynamics. This should be useful for describing dynamical phenomena of strongly\ninteracting Fermions in a lattice in general.",
        "positive": "Rapid generation of metastable helium Bose-Einstein condensates: We report the realisation of Bose-Einstein condensation (BEC) of metastable\nhelium atoms using an in-vacuum coil magnetic trap and a crossed beam optical\ndipole trap. A novel quadrupole-Ioffe configuration (QUIC) magnetic trap made\nfrom in-vacuum hollow copper tubes provides fast switching times while\ngenerating traps with a 10G bias, without compromising optical access. The bias\nenables in-trap 1D doppler cooling to be used, which is the only cooling stage\nbetween the magneto-optic trap (MOT) and the optical dipole trap. This allows\ndirect transfer to the dipole trap without the need for any additional\nevaporative cooling in the magnetic trap. The entire experimental sequence\ntakes 3.3 seconds, with essentially pure BECs observed with $\\sim 10^6$ atoms\nafter evaporative cooling in the dipole trap."
    },
    {
        "anchor": "Thermalization near integrability in a dipolar quantum Newton's cradle: Isolated quantum many-body systems with integrable dynamics generically do\nnot thermalize when taken far from equilibrium. As one perturbs such systems\naway from the integrable point, thermalization sets in, but the nature of the\ncrossover from integrable to thermalizing behavior is an unresolved and\nactively discussed question. We explore this question by studying the dynamics\nof the momentum distribution function in a dipolar quantum Newton's cradle\nconsisting of highly magnetic dysprosium atoms. This is accomplished by\ncreating the first one-dimensional Bose gas with strong magnetic dipole-dipole\ninteractions. These interactions provide tunability of both the strength of the\nintegrability-breaking perturbation and the nature of the near-integrable\ndynamics. We provide the first experimental evidence that thermalization close\nto a strongly interacting integrable point occurs in two steps:\nprethermalization followed by near-exponential thermalization. Exact numerical\ncalculations on a two-rung lattice model yield a similar two-timescale process,\nsuggesting that this is generic in strongly interacting near-integrable models.\nMoreover, the measured thermalization rate is consistent with a parameter-free\ntheoretical estimate, based on identifying the types of collisions that\ndominate thermalization. By providing tunability between regimes of integrable\nand nonintegrable dynamics, our work sheds light both on the mechanisms by\nwhich isolated quantum many-body systems thermalize, and on the temporal\nstructure of the onset of thermalization.",
        "positive": "Quench-induced supercurrents in an annular Bose gas: We create supercurrents in annular two-dimensional Bose gases through a\ntemperature quench of the normal-to-superfluid phase transition. We detect the\namplitude and the chirality of these supercurrents by measuring spiral patterns\nresulting from the interference of the cloud with a central reference disk.\nThese measurements demonstrate the stochastic nature of the supercurrents. We\nfurther measure their distribution for different quench times and compare it\nwith the predictions based on the Kibble-Zurek mechanism."
    },
    {
        "anchor": "Itinerant ferromagnetism of a repulsive atomic Fermi gas: a quantum\n  Monte Carlo study: We investigate the phase diagram of a two-component repulsive Fermi gas at\nT=0 by means of quantum Monte Carlo simulations. For a given value of the\npositive s-wave scattering length, both purely repulsive and purely attractive\nmodel potentials are considered in order to analyze the limits of the universal\nregime where the details of interatomic forces can be neglected. The equation\nof state of both balanced and unbalanced systems is calculated as a function of\nthe interaction strength and the critical density for the onset of\nferromagnetism is determined. The energy per particle of the strongly polarized\ngas is calculated and parametrized in terms of the physical properties of\nrepulsive polarons, which are relevant for the stability of the fully\nmagnetized ferromagnetic state. Finally, we analyze the phase diagram in the\npolarization/interaction plane under the assumption that only phases with\nhomogeneous magnetization can be produced.",
        "positive": "Observation of Nagaoka Polarons in a Fermi-Hubbard Quantum Simulator: Quantum interference can deeply alter the nature of many-body phases of\nmatter. In the paradigmatic case of the Hubbard model, Nagaoka famously proved\nthat introducing a single itinerant charge can transform a paramagnetic\ninsulator into a ferromagnet through path interference. However, a microscopic\nobservation of such kinetic magnetism induced by individually imaged dopants\nhas been so far elusive. Here we demonstrate the emergence of Nagaoka polarons\nin a Hubbard system realized with strongly interacting fermions in a triangular\noptical lattice. Using quantum gas microscopy, we reveal these polarons as\nextended ferromagnetic bubbles around particle dopants arising from the local\ninterplay of coherent dopant motion and spin exchange. In contrast, kinetic\nfrustration due to the triangular geometry promotes antiferromagnetic polarons\naround hole dopants, as proposed by Haerter and Shastry. Our work augurs the\nexploration of exotic quantum phases driven by charge motion in strongly\ncorrelated systems and over sizes that are challenging for numerical\nsimulation."
    },
    {
        "anchor": "Tan relations in one dimension: We derive exact relations that connect the universal $C/k^4$-decay of the\nmomentum distribution at large $k$ with both thermodynamic properties and\ncorrelation functions of two-component Fermi gases in one dimension with\ncontact interactions. The relations are analogous to those obtained by Tan in\nthe three-dimensional case and are derived from an operator product expansion\nof the one- and two-particle density matrix. They extend earlier results by\nOlshanii and Dunjko [Phys. Rev. Lett. 91, 090401 (2003)] for the bosonic\nLieb-Liniger gas. As an application, we calculate the pair distribution\nfunction at short distances and the dimensionless contact in the limit of\ninfinite repulsion. The ground state energy approaches a universal constant in\nthis limit, a behavior that also holds in the three-dimensional case. In both\none and three dimensions, a Stoner instability to a saturated ferromagnet for\nrepulsive fermions with zero range interactions is ruled out at any finite\ncoupling.",
        "positive": "Intermittent emission of particles from a Bose-Einstein condensate in a\n  one-dimensional lattice: We investigate particle emission from a Bose-Einstein condensate with\nperiodically modulated interactions in a one-dimensional lattice. Within\nperturbative analysis, which leads to instabilities for discrete modes, we\nobtain the main regimes where the system can emit a large particle jet, and\nfind that the emission is distinctly intermittent rather than continuous. The\ntime evolution of the trapped particles exhibits a stair-like decay, and a\nlarger drive induces a more significant intermittency. We further shed light on\nthe dynamics of the stimulating process, and demonstrate that instead of a real\nsuspension, the intermittency represents a build-up stage of the system. The\ntheoretical framework might be generalized to the explorations on multiple-site\nsystems with analogous configurations and couplings, and offer new insights\ninto other fundamental nonequilibrium problems."
    },
    {
        "anchor": "Bose-Fermi mixtures in the molecular limit: We consider a Bose-Fermi mixture in the molecular limit of the attractive\ninteraction between fermions and bosons. For a boson density smaller or equal\nto the fermion density, we show analytically how a T-matrix approach for the\nconstituent bosons and fermions recovers the expected physical limit of a\nFermi-Fermi mixture of molecules and atoms. In this limit, we derive simple\nexpressions for the self-energies, the momentum distribution function, and the\nchemical potentials. By extending these equations to a trapped system, we\ndetermine how to tailor the experimental parameters of a Bose-Fermi mixture in\norder to enhance the 'indirect Pauli exclusion effect' on the boson momentum\ndistribution function. For the homogeneous system, we present finally a\nDiffusion Monte Carlo simulation which confirms the occurrence of such a\npeculiar effect.",
        "positive": "Absence of Landau damping in driven three-component Bose-Einstein\n  condensate in optical lattices: We explore the quantum many-body physics of a three-component Bose-Einstein\ncondensate (BEC) in an optical lattices driven by laser fields in $V$ and\n$\\Lambda$ configurations. We obtain exact analytical expressions for the energy\nspectrum and amplitudes of elementary excitations, and discover symmetries\namong them. We demonstrate that the applied laser fields induce a gap in the\notherwise gapless Bogoliubov spectrum. We find that Landau damping of the\ncollective modes above the energy of the gap is carried by laser-induced roton\nmodes and is considerably suppressed compared to the phonon-mediated damping\nendemic to undriven scalar BECs."
    },
    {
        "anchor": "Radio-Frequency Manipulation of Fano-Feshbach Resonances in an Ultracold\n  Fermi Gas of $^{40}$K: Experimental control of magnetic Fano-Feshbach resonances in ultracold\n$^{40}$K Fermi gases, using radio-frequency (RF) fields, is demonstrated.\nSpectroscopic measurements are made of three molecular levels within 50 MHz of\nthe atomic continuum, along with their variation with magnetic field. Modifying\nthe scattering properties by an RF field is shown by measuring the loss profile\nversus magnetic field. This work provides the high accuracy locations of ground\nmolecular states near the s-wave Fano-Feshbach resonance, which can be used to\nstudy the crossover regime from a Bose-Einstein condensate to a\nBardeen-Cooper-Schrieffer superfluid in presence of an RF field.",
        "positive": "Energy-space random walk in a driven disordered Bose gas: Motivated by the experimental observation [1] that driving a non-interacting\nBose gas in a 3D box with weak disorder leads to power-law energy growth, $E\n\\propto t^{\\eta}$ with $\\eta=0.46(2)$, and compressed-exponential momentum\ndistributions that show dynamic scaling, we perform systematic numerical and\nanalytical studies of this system. Schr\\\"odinger-equation simulations reveal a\ncrossover from $\\eta \\approx 0.5$ to $\\eta \\approx 0.4$ with increasing\ndisorder strength, hinting at the existence of two different dynamical regimes.\nWe present a semi-classical model that captures the simulation results and\nallows an understanding of the dynamics in terms of an energy-space random\nwalk, from which a crossover from $E \\propto t^{1/2}$ to $E \\propto t^{2/5}$\nscaling is analytically obtained. The two limits correspond to the random walk\nbeing limited by the rate of the elastic disorder-induced scattering or the\nrate at which the drive can change the system's energy. Our results provide the\ntheoretical foundation for further experiments."
    },
    {
        "anchor": "Topological orbital ladders: We unveil a topological phase of interacting fermions on a two-leg ladder of\nunequal parity orbitals, derived from the experimentally realized double-well\nlattices by dimension reduction. $Z_2$ topological invariant originates simply\nfrom the staggered phases of $sp$-orbital quantum tunneling, requiring none of\nthe previously known mechanisms such as spin-orbit coupling or artificial gauge\nfield. Another unique feature is that upon crossing over to two dimensions with\ncoupled ladders, the edge modes from each ladder form a parity-protected flat\nband at zero energy, opening the route to strongly correlated states controlled\nby interactions. Experimental signatures are found in density correlations and\nphase transitions to trivial band and Mott insulators.",
        "positive": "Matter waves in two-dimensional arbitrary atomic crystals: We present a general scheme to realize a cold-atom quantum simulator of\nbidimensional atomic crystals. Our model is based on the use of two\nindependently trapped atomic species: the first one, subject to a strong\nin-plane confinement, constitutes a two-dimensional matter wave which interacts\nonly with atoms of the second species, deeply trapped around the nodes of a\ntwo-dimensional optical lattice. By introducing a general analytic approach we\nshow that the system Green function can be exactly determined, allowing for the\ninvestigation of the matter-wave transport properties. We propose some\nillustrative applications to both Bravais (square, triangular) and non-Bravais\n(graphene, kagom\\'e) lattices, studying both ideal periodic systems and\nexperimental-size and disordered ones. Some remarkable spectral properties of\nthese atomic artificial lattices are pointed out, such as the emergence of\nsingle and multiple gaps, flat bands, and Dirac cones. All these features can\nbe manipulated via the interspecies interaction, which proves to be widely\ntunable due to the interplay between scattering length and confinements."
    },
    {
        "anchor": "Two component quantum walk in one-dimensional lattice with hopping\n  imbalance: We investigate the two-component quantum walk in one-dimensional lattice. We\nshow that the inter-component interaction strength together with the hopping\nimbalance between the components exhibit distinct features in the quantum walk\nfor different initial states. When the walkers are initially on the same site,\nboth the slow and fast particles perform independent particle quantum walks\nwhen the interaction between them is weak. However, stronger inter-particle\ninteractions result in quantum walks by the repulsively bound pair formed\nbetween the two particles. For different initial states when the walkers are on\ndifferent sites initially, the quantum walk performed by the slow particle is\nalmost independent of that of the fast particle, which exhibits reflected and\ntransmitted components across the particle with large hopping strength for weak\ninteractions. Beyond a critical value of the interaction strength, the wave\nfunction of the fast particle ceases to penetrate through the slow particle\nsignalling a spatial phase separation. However, when the two particles are\ninitially at the two opposite edges of the lattice, then the interaction\nfacilitates the complete reflection of both of them from each other. We analyze\nthe above mentioned features by examining various physical quantities such as\nthe on-site density evolution, two-particle correlation functions and\ntransmission coefficients.",
        "positive": "Drude weight and the many-body quantum metric in one-dimensional Bose\n  systems: We study the effect of quantum geometry on the many-body ground state of\none-dimensional interacting bosonic systems. We find that the Drude weight is\ngiven by the sum of the kinetic energy and a term proportional to the many-body\nquantum metric of the ground state. Notably, the many-body quantum metric\ndetermines the upper bound of the Drude weight. We validate our results on the\nCreutz ladder, a flat band model, using exact diagonalization at half and unit\ndensities. Our work sheds light on the importance of the many-body quantum\ngeometry in one-dimensional interacting bosonic systems."
    },
    {
        "anchor": "Ultracold Lattice Gases with Periodically Modulated Interactions: We show that a time-dependent magnetic field inducing a periodically\nmodulated scattering length may lead to interesting novel scenarios for cold\ngases in optical lattices, characterized by a nonlinear hopping depending on\nthe number difference at neighboring sites. We discuss the rich physics\nintroduced by this hopping, including pair superfluidity, exactly defect-free\nMott-insulator states for finite hopping, and pure holon and doublon\nsuperfluids. We also address experimental detection, showing that the\nintroduced nonlinear hopping may lead in harmonically trapped gases to abrupt\ndrops in the density profile marking the interface between different superfluid\nregions.",
        "positive": "Phase space monitoring of exciton-polariton multistability: Dynamics of exciton-polariton multistability is theoretically investigated.\nPhase portraits are used as a tool to enlighten the microscopic phenomena which\ninfluence spin multistability of a confined polariton field as well as\nultrafast reversible spin switching. The formation of a non-radiative\nreservoir, due to polariton pairing into biexcitons is found to play the lead\nrole in the previously reported spin switching experiments. Ways to tailor this\nreservoir formation are discussed in order to obtain optimal spin switching\nreliability."
    },
    {
        "anchor": "Unifying treatment of nonequilibrium and unstable dynamics of cold\n  bosonic atom system with time-dependent order parameter in Thermo Filed\n  Dynamics: The coupled equations which describe the temporal evolution of the\nBose-Einstein condensed system are derived in the framework of nonequilibrium\nThermo Field Dynamics. The key element is that they are not the naive\nassemblages of presumable equations, but are the self-consistent ones derived\nby appropriate renormalization conditions. While the order parameter is\ntime-dependent, an explicit quasiparticle picture is constructed by a\ntime-dependent expansion. Our formulation is valid even for the system with a\nunstable condensate, and describes the condensate decay caused by the Landau\ninstability as well as by the dynamical one.",
        "positive": "Measurement of the excitation spectrum of a dipolar gas in the\n  macrodroplet regime: The excitation spectrum of a cigar-shaped strongly dipolar quantum gas at the\ncrossover from a Bose-Einstein condensate to a trapped macrodroplet is\npredicted to exhibit peculiar features - a strong upward shift of low momentum\nexcitation energies together with a strong multi-band response for high\nmomenta. By performing Bragg spectroscopy over a wide range of momenta, we\nobserve both key elements and also confirm the predicted stiffening of\nexcitation modes when approaching the macrodroplet regime. Our measurements are\nin good agreement with numerical calculations taking into account finite size\neffects."
    },
    {
        "anchor": "Ferromagnetism in a Repulsive Atomic Fermi Gas with Correlated Disorder: We investigate the zero-temperature ferromagnetic behavior of a two-component\nrepulsive Fermi gas in the presence of a correlated random field that\nrepresents an optical speckle pattern. The density is tuned so that the\n(noninteracting) Fermi energy is close to the mobility edge of the Anderson\nlocalization transition. We employ quantum Monte Carlo simulations to determine\nvarious ground-state properties, including the equation of state, the magnetic\nsusceptibility, and the energy of an impurity immersed in a polarized Fermi gas\n(repulsive polaron). In the weakly interacting limit, the magnetic\nsusceptibility is found to be suppressed by disorder. However, it rapidly\nincreases with the interaction strength, and it diverges at a much weaker\ninteraction strength compared to the clean gas. Both the transition from the\nparamagnetic phase to the partially ferromagnetic phase, and the one from the\npartially to the fully ferromagnetic phase are strongly favored by disorder,\nindicating a case of order induced by disorder.",
        "positive": "On the Josephson effect in a Bose-Einstein condensate subject to a\n  density dependent gauge potential: We investigate the coherent dynamics of a Bose-Einstein condensate in a\ndouble well, subject to a density dependent gauge potential. Further, we derive\nthe nonlinear Josephson equations that allow us to understand the many-body\nsystem in terms of a classical Hamiltonian that describes the motion of a\nnonrigid pendulum with an initial angular offset. Finally we analyze the\nphase-space trajectories of the system, and describe how the self-trapping is\naffected by the presence of an interacting gauge potential."
    },
    {
        "anchor": "Observation of topological phase with critical localization in a\n  quasi-periodic lattice: Disorder and localization have dramatic influence on the topological\nproperties of a quantum system. While strong disorder can close the band gap\nthus depriving topological materials of topological features, disorder may also\ninduce topology from trivial band structures, wherein topological invariants\nare shared by completely localized states in real space. Here we experimentally\ninvestigate a fundamentally distinct scenario where a topological phase is\nidentified in a critically localized regime, with eigenstates neither fully\nextended nor completely localized. Adopting the technique of momentum-lattice\nengineering for ultracold atoms, we implement a one-dimensional, generalized\nAubry-Andr\\'e model with off-diagonal quasi-periodic disorder in momentum\nspace, and characterize its localization and topological properties through\ndynamic observables. We then demonstrate the impact of interactions on the\ncritically localized topological state, as a first experimental endeavour\ntoward the clarification of many-body critical phase, the critical analogue of\nthe many-body localized state.",
        "positive": "BCS-BEC crossover in three-dimensional Fermi gases with spherical\n  spin-orbit coupling: We present a systematic theoretical study of the BCS-BEC crossover problem in\nthree-dimensional atomic Fermi gases at zero temperature with a spherical\nspin-orbit coupling which can be generated by a synthetic non-Abelian gauge\nfield coupled to neutral fermions. Our investigations are based on the path\nintegral formalism which is a powerful theoretical scheme for the study of the\nproperties of the bound state, the superfluid ground state, and the collective\nexcitations in the BCS-BEC crossover. At large spin-orbit coupling, the system\nenters the BEC state of a novel type of bound state (referred to as rashbon)\nwhich possesses a non-trivial effective mass. Analytical results and\ninteresting universal behaviors for various physical quantities at large\nspin-orbit coupling are obtained. Our theoretical predictions can be tested in\nfuture experiments of cold Fermi gases with three-dimensional spherical\nspin-orbit coupling."
    },
    {
        "anchor": "Open source Matrix Product States: Opening ways to simulate entangled\n  many-body quantum systems in one dimension: Numerical simulations are a powerful tool to study quantum systems beyond\nexactly solvable systems lacking an analytic expression. For one-dimensional\nentangled quantum systems, tensor network methods, amongst them Matrix Product\nStates (MPSs), have attracted interest from different fields of quantum physics\nranging from solid state systems to quantum simulators and quantum computing.\nOur open source MPS code provides the community with a toolset to analyze the\nstatics and dynamics of one-dimensional quantum systems. Here, we present our\nopen source library, Open Source Matrix Product States (OSMPS), of MPS methods\nimplemented in Python and Fortran2003. The library includes tools for ground\nstate calculation and excited states via the variational ansatz. We also\nsupport ground states for infinite systems with translational invariance.\nDynamics are simulated with different algorithms, including three algorithms\nwith support for long-range interactions. Convenient features include built-in\nsupport for fermionic systems and number conservation with rotational\n$\\mathcal{U}(1)$ and discrete $\\mathbb{Z}_2$ symmetries for finite systems, as\nwell as data parallelism with MPI. We explain the principles and techniques\nused in this library along with examples of how to efficiently use the general\ninterfaces to analyze the Ising and Bose-Hubbard models. This description\nincludes the preparation of simulations as well as dispatching and\npost-processing of them.",
        "positive": "Yang-Yang thermometry and momentum distribution of a trapped\n  one-dimensional Bose gas: We describe the use of the exact Yang-Yang solutions for the one-dimensional\nBose gas to enable accurate kinetic-energy thermometry based on the\nroot-mean-square width of an experimentally measured momentum distribution.\nFurthermore, we use the stochastic projected Gross-Pitaevskii theory to provide\nthe first quantitative description of the full momentum distribution\nmeasurements of Van Amerongen et al., Phys. Rev. Lett. 100, 090402 (2008). We\nfind the fitted temperatures from the stochastic projected Gross-Pitaevskii\napproach are in excellent agreement with those determined by Yang-Yang\nkinetic-energy thermometry."
    },
    {
        "anchor": "Fermionic superfluidity and spontaneous superflows in optical lattices: We study superfluidity of strongly repulsive fermionic atoms in optical\nlattices. The atoms are paired up through a correlated tunneling mechanism,\nwhich induces superfluidity when repulsive nearest-neighbor interactions are\nincluded in the Hubbard model. This paired superfluid is a metastable state\nwhich persists for a long time as the pair-broken process is severely\nsuppressed. The mean-field phase diagram and low energy excitations are\ninvestigated in a square lattice system. Intriguingly, spontaneous superflows\nmay appear in the ground state of a triangular optical lattice system due to\nantiferromagnetic frustration.",
        "positive": "Analogue Hawking radiation in an exactly solvable model of BEC: Hawking radiation, the spontaneous emission of thermal photons from an event\nhorizon, is one of the most intriguing and elusive predictions of field theory\nin curved spacetimes. A formally analogue phenomenon occurs at the supersonic\ntransition of a fluid: in this respect, ultracold gases stand out among the\nmost promising systems but the theoretical modelling of this effect has always\nbeen carried out in semiclassical approximation, borrowing part of the analysis\nfrom the gravitational analogy. Here we discuss the exact solution of a\none-dimensional Bose gas flowing against an obstacle, showing that spontaneous\nphonon emission (the analogue of Hawking radiation) is predicted without\nreference to the gravitational analogy. Long after the creation of the\nobstacle, the fluid settles into a stationary state displaying the emission of\nsound waves (phonons) in the upstream direction. A careful analysis shows that\na precise correspondence between this phenomenon and the spontaneous emission\nof radiation from an event horizon requires additional conditions to be met in\nfuture experiments aimed at identifying the occurrence of the Hawking-like\nmechanism in Bose-Einstein condensates."
    },
    {
        "anchor": "Nonlinear Dynamics of Ultra-Cold Gas: Collapse of Bose Gas With\n  Attractive Interaction: Solutions for the Nonlinear Schr\u007fodinger equation for collapsing Bose gas\nwith attraction. This is a copy of the paper published in 1992 in Proceedings\nof NATO Advanced Research workshop on Singularities in Fluids, Plasmas and\nOptics (Heraklion, Greece) edited by R.E. Caflisch and G.C. Papanicolaou\n(Kluwer Academic).",
        "positive": "Radiative lifetimes of dipolar excitons in double quantum-wells: Spatially indirect excitons in semiconducting double quantum wells have been\nshown to exhibit rich collective many-body behavior that result from the nature\nof the extended dipole-dipole interactions between particles. For many\nspectroscopic studies of the emission from a system of such indirect excitons,\nit is crucial to separate the single particle properties of the excitons from\nthe many-body effects arising from their mutual interactions. In particular,\nknowledge of the relation between the emission energy of indirect excitons and\ntheir radiative lifetime could be highly beneficial for control, manipulation,\nand analysis of such systems. Here we study a simple analytic approximate\nrelation between the radiative lifetime of indirect excitons and their emission\nenergy. We show, both numerically and experimentally, the validity and the\nlimits of this approximate relation. This relation between the emission energy\nand the lifetime of indirect excitons can be used to tune and determine their\nlifetime and their resulting dynamics without the need of directly measuring\nit, and as a tool for design of indirect exciton based devices."
    },
    {
        "anchor": "Suppression and Control of Pre-thermalization in Multi-component Fermi\n  Gases Following a Quantum Quench: We investigate the mechanisms of control and suppression of\npre-thermalization in $N$-component alkaline earth gases. To this end, we\ncompute the short-time dynamics of the instantaneous momentum distribution and\nthe relative population for different initial conditions after an interaction\nquench, accounting for the 11 peffect of initial interactions. We find that\nswitching on an interaction that breaks the SU$(N)$ symmetry of the initial\nHamiltonian, thus allowing for the occurrence of spin-changing collisions, does\nnot necessarily lead to a suppression of pre-thermalization. However, the\nsuppression will be most effective in the presence of SU$(N)$-breaking\ninteractions provided the number of components $N \\ge 4$ and the initial state\ncontains a population imbalance that breaks the SU$(N)$ symmetry. We also find\nthe conditions on the imbalance initial state that allow for a pre-thermal\nstate to be stabilized for a certain time. Our study highlights the important\nrole played by the initial state in the pre-thermalization dynamics of\nmulticomponent Fermi gases. It also demonstrates that alkaline-earth Fermi\ngases provide an interesting playground for the study and control of\npre-thermalization.",
        "positive": "Detecting Topological phase transitions in a double kicked quantum rotor: We present a concrete theoretical proposal for detecting topological phase\ntransitions in double kicked atom-optics kicked rotors with internal spin-1/2\ndegree of freedom. The implementation utilizes a kicked Bose-Einstein\ncondensate evolving in one-dimensional momentum space. To reduce influence of\natom loss and phase decoherence we aim to keep experimental durations short\nwhile maintaining a resonant experimental protocol. Experimental limitations\ninduced by phase noise, quasimomentum distributions, symmetries, and the\nAC-Stark shift are considered. Our results thus suggest a feasible and\noptimized procedure for observing topological phase transitions in quantum\nkicked rotors."
    },
    {
        "anchor": "Nonlinear management of topological solitons in a spin-orbit-coupled\n  system: We consider possibilities to control dynamics of solitons of two types,\nmaintained by the combination of cubic attraction and spin-orbit coupling (SOC)\nin a two-component system, namely, semi-dipoles (SDs) and mixed modes (MMs), by\nmaking the relative strength of the cross-attraction, gamma, a function of time\nperiodically oscillating around the critical value, gamma = 1, which is an\nSD/MM stability boundary in the static system. The structure of SDs is\nrepresented by the combination of a fundamental soliton in one component and\nlocalized dipole mode in the other, while MMs combine fundamental and dipole\nterms in each component. Systematic numerical analysis reveals a finite\nbistability region for the SDs and MMs around gamma = 1, which does not exist\nin the absence of the periodic temporal modulation (\"management\"), as well as\nemergence of specific instability troughs and stability tongues for the\nsolitons of both types, which may be explained as manifestations of resonances\nbetween the time-periodic modulation and intrinsic modes of the solitons. The\nsystem can be implemented in Bose-Einstein condensates, and emulated in\nnonlinear optical waveguides.",
        "positive": "Matter wave propagation above a step potential within the\n  cubic-nonlinear Schr\u00f6dinger equation: We analyze the matter wave transmission above a step potential within the\nframework of the cubic-nonlinear Schr\\\"odinger equation. We present a\ncomprehensive analysis of the corresponding stationary problem based on an\nexact second-order nonlinear differential equation for the probability density.\nThe exact solution of the problem in terms of the Jacobi elliptic sn-function\nis presented and analyzed. Qualitatively distinct types of wave propagation\npicture are classified depending on the input parameters of the system.\nAnalyzing the 2D space of involved dimensionless parameters, the nonlinearity\nand the reflecting potential's height/depth given in the units of the chemical\npotential, we show that the region of the parameters that does not sustain\nrestricted solutions is given by a closed curve consisting of a segment of an\nelliptic curve and two line intervals. We show that there exists a specific\nsingular point, belonging to the elliptic curve, which causes a jump from one\nevolution scenario to another one. The position of this point is determined and\nthe peculiarities of the evolution scenarios (oscillatory, non-oscillatory and\ndiverging) for all the allowed regions of involved parameters are described and\nanalyzed in detail."
    },
    {
        "anchor": "Stability and dynamics across magnetic phases of vortex-bright type\n  excitations in spinor Bose-Einstein condensates: The static properties, i.e., existence and stability, as well as the\nquench-induced dynamics of vortex-bright type excitations in two-dimensional\nharmonically confined spin-1 Bose-Einstein condensates are investigated.\nLinearly stable vortex-bright-vortex and bright-vortex-bright solutions arise\nin both antiferromagnetic and ferromagnetic spinor gases upon quadratic Zeeman\nenergy shift variations. Their deformations across the relevant transitions are\nexposed and discussed in detail evincing also that emergent instabilities can\nlead to pattern formation. Spatial elongations, precessional motion and\nspiraling of the nonlinear excitations when exposed to finite temperatures and\nupon crossing the distinct phase boundaries, via quenching of the quadratic\nZeeman coefficient, are unveiled. Spin-mixing processes triggered by the quench\nlead, among others, to changes in the waveform of the ensuing configurations.\nOur findings reveal an interplay between pattern formation and spin-mixing\nprocesses being accessible in contemporary cold atom experiments.",
        "positive": "Effects of a rotating periodic lattice on coherent quantum states in a\n  ring topology: The case of positive nonlinearity: We study the landscape of solutions of the coherent quantum states in a ring\nshaped lattice potential in the context of ultracold atoms with an effective\npositive nonlinearity induced by interatomic interactions. The exact analytical\nsolutions in the absence of lattice are used as a starting point and the\ntransformation of those solutions is mapped as the lattice is introduced and\nstrengthened. This approach allows a simple classification of all the solutions\ninto states with periods commensurate/incommensruate with the lattice period\nand those with/without nodes. Their origins are traced to the primary\ndispersion curve and the swallowtail branches of the lattice-free spectrum. The\ncommensurate states tend to remain delocalized with increasing lattice depth,\nwhereas the incommensurate ones may be localized. The symmetry and stability\nproperties of the solutions are examined and correlated with branch energies.\nThe crucial importance of rotation is highlighted by its utility in\ncontinuously transforming solutions and accessing in a finite ring with a few\nsites the full spectrum of nonlinear Bloch waves on an infinite lattice."
    },
    {
        "anchor": "Hydrodynamic fluctuations and the minimum shear viscosity of the dilute\n  Fermi gas at unitarity: We study hydrodynamic fluctuations in a non-relativistic fluid. We show that\nin three dimensions fluctuations lead to a minimum in the shear viscosity to\nentropy density ratio $\\eta/s$ as a function of the temperature. The minimum\nprovides a bound on $\\eta/s$ which is independent of the conjectured bound in\nstring theory, $\\eta/s \\geq \\hbar/(4\\pi k_B)$, where $s$ is the entropy\ndensity. For the dilute Fermi gas at unitarity we find $\\eta/s\\gsim 0.2\\hbar$.\nThis bound is not universal -- it depends on thermodynamic properties of the\nunitary Fermi gas, and on empirical information about the range of validity of\nhydrodynamics. We also find that the viscous relaxation time of a hydrodynamic\nmode with frequency $\\omega$ diverges as $1/\\sqrt{\\omega}$, and that the shear\nviscosity in two dimensions diverges as $\\log(1/ \\omega)$.",
        "positive": "Induced two-body scattering resonances from a square-well potential with\n  oscillating depth: In systems of ultracold atoms, pairwise interactions can be resonantly\nenhanced by a new mechanism which does not rely upon a magnetic Feshbach\nresonance. In this mechanism, interactions are controlled by tuning the\nfrequency of an oscillating parallel component of the magnetic field close to\nthe Bohr frequency for the transition to a two-atom bound state. The real part\nof the s-wave scattering length $a$ has a resonance as a function of the\noscillation frequency near the Bohr frequency. The resonance parameters can be\ncontrolled by varying the amplitude of the oscillating field. The amplitude\nalso controls the imaginary part of $a$ which arises predominantly because the\noscillating field converts atom pairs into molecules. For the case of a shallow\nbound state in the scattering channel, the dimensionless resonance parameters\nare universal functions of the dimensionless oscillation amplitude."
    },
    {
        "anchor": "Non classical velocity statistics in a turbulent atomic Bose Einstein\n  condensate: In a recent experiment Paoletti et al (Phys. Rev. Lett. 101, 154501, 2008)\nmonitored the motion of tracer particles in turbulent superfluid helium and\ninferred that the velocity components do not obey the Gaussian statistics\nobserved in ordinary turbulence. Motivated by their experiment, we create a\nsmall turbulent state in an atomic Bose-Einstein condensate, which enables us\nto compute directly the velocity field, and we find similar non-classical\npower-law tails. Our result thus suggests that non-Gaussian turbulent velocity\nstatistics describe a fundamental property of quantum fluids. We also track the\ndecay of the vortex tangle in the presence of the thermal cloud.",
        "positive": "Realization of a Cold Mixture of Fermionic Chromium and Lithium Atoms: We report on the production of a novel cold mixture of fermionic $^{53}$Cr\nand $^{6}$Li atoms delivered by two Zeeman-slowed atomic beams and collected\nwithin a magneto-optical trap (MOT). For lithium, we obtain clouds of up to $4\n\\,10^8$ atoms at temperatures of about $500\\,\\mu$K. A gray optical molasses\nstage allows us to decrease the gas temperature down to $45(5)\\,\\mu$K. For\nchromium, we obtain MOTs comprising up to $1.5\\, 10^6$ atoms. The availability\nof magnetically trappable metastable $D$-states, from which $P$-state atoms can\nradiatively decay onto, enables to accumulate into the MOT quadrupole samples\nof up to $10^7$ $^{53}$Cr atoms. After repumping $D$-state atoms back into the\ncooling cycle, a final cooling stage decreases the chromium temperature down to\n$145(5)\\,\\mu$K. While the presence of a lithium MOT decreases the lifetime of\nmagnetically trapped $^{53}$Cr atoms, we obtain, within a 5 seconds duty cycle,\nsamples of about $4\\, 10^6$ chromium and $1.5\\,10^8$ lithium atoms. Our work\nprovides a crucial step towards the production of degenerate Cr-Li Fermi\nmixtures."
    },
    {
        "anchor": "Collision of two self-trapped atomic matter wave packets in an optical\n  ring cavity: The interaction between atomic Bose-Einstein condensate (BEC) and light field\nin an optical ring cavity gives rise to many interesting phenomena such as\nsupersolid and movable self-trapped matter wave packets. Here we examined the\ncollision of two self-trapped atomic matter wave packets in an optical ring\ncavity, and abundant colliding phenomena have been found in the system.\nDepending on the magnitude of colliding velocity, the collision dynamics\nexhibit very different features compared with the cavity-free case. When the\ninitial colliding velocities of the two wave packets are small, they\ncorrelatedly oscillate around their initial equilibrium positions with a small\namplitude. Increasing the collision velocity leads to severe scattering of the\nBEC atoms; after the collision, the two self-trapped wave packets usually break\ninto small pieces. Interestingly, we found that such a medium velocity\ncollision is of great phase sensitivity, which may make the system useful in\nprecision matter wave interferometry. When the colliding velocity is further\nincreased, in the bad cavity limit, the two wave packets collide phenomenally\nsimilar to two classical particles -- they firstly approach each other, then\nseparate with their shape virtually maintained. However, beyond the bad cavity\nlimit, they experience severe spatial spreading.",
        "positive": "Quantum Monte Carlo study of the visibility of one-dimensional\n  Bose-Fermi mixtures: The study of ultracold optically trapped atoms has opened new vistas in the\nphysics of correlated quantum systems. Much attention has now turned to\nmixtures of bosonic and fermionic atoms. A central puzzle is the disagreement\nbetween the experimental observation of a reduced bosonic visibility ${\\cal\nV}_b$, and quantum Monte Carlo (QMC) calculations which show ${\\cal V}_b$\nincreasing. In this paper, we present QMC simulations which evaluate the\ndensity profiles and ${\\cal V}_b$ of mixtures of bosons and fermions in\none-dimensional optical lattices. We resolve the discrepancy between theory and\nexperiment by identifying parameter regimes where ${\\cal V}_b$ is reduced, and\nwhere it is increased. We present a simple qualitative picture of the different\nresponse to the fermion admixture in terms of the superfluid and\nMott-insulating domains before and after the fermions are included. Finally, we\nshow that ${\\cal V}_b$ exhibits kinks which are tied to the domain evolution\npresent in the pure case, and also additional structure arising from the\nformation of boson-fermion molecules, a prediction for future experiments."
    },
    {
        "anchor": "Population dynamics in Floquet realisation of Harper-Hofstadter\n  Hamiltonian: We study the recent Floquet-realisation of the Harper-Hofstadter model in a\ngas of cold bosonic atoms. We study in detail the scattering processes in this\nsystem in the weakly interacting regime due to the interplay of particle\ninteractions and the explicit time dependence of the Floquet states that lead\nto band transitions and heating. We focus on the experimentally used parameters\nand explicitly model the transverse confining direction. Based on transition\nrates computed within the Floquet-Fermi golden rule we obtain band population\ndynamics which are in agreement with the dynamics observed in experiment.\nFinally, we discuss whether and how photon-assisted collisions that may be the\nsource heating and band population dynamics might be suppressed in the\nexperimental setup by appropriate design of the transverse confining potential.\nThe suppression of such processes will become increasingly important as the\nexperiments progress into simulating strongly interacting systems in the\npresence of artificial gauge fields.",
        "positive": "Universal composite boson formation in strongly interacting\n  one-dimensional fermionic systems: Attractive $p$-wave one-dimensional fermions are studied in the fermionic\nTonks-Girardeau regime in which the diagonal properties are shared with those\nof an ideal Bose gas. We study the off-diagonal properties and present\nanalytical expressions for the eigenvalues of the one-body density matrix. One\nstriking aspect is the universality of the occupation numbers which are\nindependent of the specific shape of the external potential. We show that the\noccupation of natural orbitals occurs in pairs, indicating the formation of\ncomposite bosons, each consisting of two attractive fermions. The formation of\ncomposite bosons sheds light on the pairing mechanism of the system orbitals,\nyielding a total density equal to that of a Bose-Einstein condensate."
    },
    {
        "anchor": "Strongly correlated one-dimensional Bose-Fermi quantum mixtures:\n  symmetry and correlations: We consider multi-component quantum mixtures (bosonic, fermionic, or mixed)\nwith strongly repulsive contact interactions in a one-dimensional harmonic\ntrap. In the limit of infinitely strong repulsion and zero temperature, using\nthe class-sum method, we study the symmetries of the spatial wave function of\nthe mixture. We find that the ground state of the system has the most symmetric\nspatial wave function allowed by the type of mixture. This provides an example\nof the generalized Lieb-Mattis theorem. Furthermore, we show that the symmetry\nproperties of the mixture are embedded in the large-momentum tails of the\nmomentum distribution, which we evaluate both at infinite repulsion by an exact\nsolution and at finite interactions using a numerical DMRG approach. This\nimplies that an experimental measurement of the Tan's contact would allow to\nunambiguously determine the symmetry of any kind of multi-component mixture.",
        "positive": "Tunable space-time crystal in room-temperature magnetodielectrics: We report the experimental realization of a space-time crystal with tunable\nperiodicity in time and space in the magnon Bose-Einstein Condensate (BEC),\nformed in a room-temperature Yttrium Iron Garnet (YIG) film by radio-frequency\nspace-homogeneous magnetic field. The magnon BEC is prepared to have a well\ndefined frequency and non-zero wavevector. We demonstrate how the crystalline\n\"density\" as well as the time and space textures of the resulting crystal may\nbe tuned by varying the experimental parameters: external static magnetic\nfield, temperature, thickness of the YIG film and power of the radio-frequency\nfield. The proposed space-time crystals provide a new dimension for exploring\ndynamical phases of matter and can serve as a model nonlinear Floquet system,\nthat brings in touch the rich fields of classical nonlinear waves, magnonics\nand periodically driven systems."
    },
    {
        "anchor": "Relaxation dynamics of conserved quantities in a weakly non-integrable\n  one-dimensional Bose gas: In this work we report preliminary results on the relaxational dynamics of\none dimensional Bose gases, as described by the Lieb-Liniger model, upon\nrelease from a parabolic trap. We explore the effects of integrability and\nintegrability breaking upon these dynamics by placing the gas post-release in\nan integrability breaking one-body cosine potential of variable amplitude. By\nstudying the post-quench evolution of the conserved charges that would exist in\nthe purely integrable limit, we begin to quantify the effects of the weak\nbreaking of integrability on the long time thermalization of the gas.",
        "positive": "Observation of Density-Induced Tunneling: We study the dynamics of bosonic atoms in a tilted one-dimensional optical\nlattice and report on the first direct observation of density-induced\ntunneling. We show that the interaction affects the time evolution of the\ndoublon oscillation via density-induced tunneling and pinpoint its density- and\ninteraction-dependence. The experimental data for different lattice depths are\nin good agreement with our theoretical model. Furthermore, resonances caused by\nsecond-order tunneling processes are studied, where the density-induced\ntunneling breaks the symmetric behavior for attractive and repulsive\ninteractions predicted by the Hubbard model."
    },
    {
        "anchor": "The creation of two-dimensional composite solitons in spin-orbit-coupled\n  self-attractive Bose-Einstein condensates in free space: It is commonly known that two-dimensional mean-field models of optical and\nmatter waves with the cubic self-attraction cannot produce stable solitons in\nfree space because of the occurrence of the collapse in the same setting. By\nmeans of the numerical analysis and variational approximation, we demonstrate\nthat the two-component model of the Bose-Einstein condensate, with the\nspin-orbit Rashba coupling and cubic attractive interactions, gives rise to\nsolitary-vortex complexes of two types: semi-vortices (SVs, with a vortex in\none component and a fundamental soliton in the other), and mixed modes (MMs,\nwith topological charges 0 and +1/-1 mixed in both components). These two-\ndimensional composite modes can be created using the trapping\nharmonic-oscillator (HO) potential, but remain stable in the free space, if the\ntrap is gradually removed. The SVs and MMs realize the ground state of the\nsystem, provided that the self-attraction in the two components is,\nrespectively, stronger or weaker than the cross-attraction between them. The\nSVs and MMs which are not the ground state are subject to a drift instability.\nIn the free space (in the absence of the HO trap), modes of both types\ndegenerate into unstable Townes solitons when their norms attain the respective\ncritical values, while there is no lower existence threshold for the stable\nmodes. Moving free-space stable solitons are also found in the present\nnon-Galilean-invariant system, up to a critical velocity. Collisions between\ntwo moving solitons lead to their merger into a single one.",
        "positive": "Short note on the Rabi model: The spectral density of the Rabi model is calculated exactly within a\ncontinued fraction approach. It is shown that the method yields a convergent\nsolution."
    },
    {
        "anchor": "Metrology and Many-Body Physics with Ultracold Metastable Helium: Ultracold dilute gases provide ideal settings for measurements of atomic\nstructure. Helium has an internal structure sufficiently simple to permit\nhighly accurate predictions of its resonances and transition rates. Precise\nlaser spectroscopy of helium thus yields empirical constraints on such\ncalculations. These are desirable in the ongoing investigations seeking to\nreconcile the disagreement between independent determinations of nuclear charge\nradius data in both hydrogenic and helium atoms. Either the size of these\nparticles are truly constant and quantum electrodynamics (QED) is flawed, or\nthe theory is correct and some new physics is at play at the atomic scale.\n  Ultracold bose gases also serve as ideal testing ground to better understand\nthe physics of Bose-Einstein condensation, superfluidity, and the effects of\nweak interactions in condensed-matter systems. The large internal energy of\nhelium's metastable excited state enables the measurement of the momentum of\nsingle atoms, providing a new lens through which to examine both\nweakly-interacting and strongly-correlated systems. This feature is employed to\ninvestigate the quantum depletion of a BEC after expansion into the far-field.\nFinally, the appendix reports on early progress towards the realization of an\noptical lattice trap for helium.",
        "positive": "Bright solitons in quasi-one dimensional dipolar condensates with\n  spatially modulated interactions: We introduce a model for the condensate of dipolar atoms or molecules, in\nwhich the dipole-dipole interaction (DDI) is periodically modulated in space,\ndue to a periodic change of the local orientation of the permanent dipoles,\nimposed by the corresponding structure of an external field (the necessary\nfield can be created, in particular, by means of magnetic lattices, which are\navailable to the experiment). The system represents a realization of a nonlocal\nnonlinear lattice, which has a potential to support various spatial modes. By\nmeans of numerical methods and variational approximation (VA), we construct\nbright one-dimensional solitons in this system, and study their stability. In\nmost cases, the VA provides good accuracy, and correctly predicts the stability\nby means of the Vakhitov-Kolokolov (VK)\\ criterion. It is found that the\nperiodic modulation may destroy some solitons, which exist in the usual setting\nwith unmodulated DDI, and can create stable solitons in other cases, not\nverified in the absence of modulations. Unstable solitons typically transform\ninto persistent localized breathers. The solitons are often mobile, with\ninelastic collisions between them leading to oscillating localized modes."
    },
    {
        "anchor": "Berezinskii-Kosterlitz-Thouless transition in the\n  time-reversal-symmetric Hofstadter-Hubbard model: Assuming that two-component Fermi gases with opposite artificial magnetic\nfields on a square optical lattice are well-described by the so-called\ntime-reversal-symmetric Hofstadter-Hubbard model, we explore the thermal\nsuperfluid properties along with the critical Berezinskii-Kosterlitz-Thouless\n(BKT) transition temperature in this model over a wide-range of its parameters.\nIn particular, since our self-consistent BCS-BKT approach takes the multi-band\nbutterfly spectrum explicitly into account, it unveils how dramatically the\ninter-band contribution to the phase stiffness dominates the intra-band one\nwith an increasing interaction strength for any given magnetic flux.",
        "positive": "A Dynamical Self-Consistent Finite Temperature Kinetic Theory: The ZNG\n  Scheme: We review a self-consistent scheme for modelling trapped weakly-interacting\nquantum gases at temperatures where the condensate coexists with a significant\nthermal cloud. This method has been applied to atomic gases by Zaremba, Nikuni,\nand Griffin, and is often referred to as ZNG. It describes both\nmean-field-dominated and hydrodynamic regimes, except at very low temperatures\nor in the regime of large fluctuations. Condensate dynamics are described by a\ndissipative Gross-Pitaevskii equation (or the corresponding quantum\nhydrodynamic equation with a source term), while the non-condensate evolution\nis represented by a quantum Boltzmann equation, which additionally includes\ncollisional processes which transfer atoms between these two subsystems. In the\nmean-field-dominated regime collisions are treated perturbatively and the full\ndistribution function is needed to describe the thermal cloud, while in the\nhydrodynamic regime the system is parametrised in terms of a set of local\nvariables. Applications to finite temperature induced damping of collective\nmodes and vortices in the mean-field-dominated regime are presented."
    },
    {
        "anchor": "Dynamic response of 1D bosons in a trap: We calculate the dynamic structure factor S(q,omega) of a one-dimensional\n(1D) interacting Bose gas confined in a harmonic trap. The effective\ninteraction depends on the strength of the confinement enforcing the 1D motion\nof atoms; interaction may be further enhanced by superimposing an optical\nlattice on the trap potential. In the compressible state, we find that the\nsmooth variation of the gas density around the trap center leads to softening\nof the singular behavior of S(q,omega) at Lieb-1 mode compared to the behavior\npredicted for homogeneous 1D systems. Nevertheless, the density-averaged\nresponse remains a non-analytic function of q and omega at Lieb-1 mode in the\nlimit of weak trap confinement. The exponent of the power-law non-analyticity\nis modified due to the inhomogeneity in a universal way, and thus, bears\nunambiguously the information about the (homogeneous) Lieb-Liniger model. A\nstrong optical lattice causes formation of Mott phases. Deep in the Mott\nregime, we predict a semi-circular peak in S(q,\\omega) centered at the on-site\nrepulsion energy, omega=U. Similar peaks of smaller amplitudes exist at\nmultiples of U as well. We explain the suppression of the dynamic response with\nentering into the Mott regime, observed recently by D. Clement et al., Phys.\nRev. Lett. v. 102, p. 155301 (2009), based on an f-sum rule for the\nBose-Hubbard model.",
        "positive": "Nonlinear spin diffusion and spin rotation in a trapped Fermi gas: Transverse spin diffusion in a polarized, interacting Fermi gas leads to the\nLeggett-Rice effect, where the spin current precesses around the local\nmagnetization. With a spin-echo sequence both the transverse diffusivity and\nthe spin-rotation parameter $\\gamma$ are obtained; the sign of $\\gamma$ reveals\nthe repulsive or attractive character of the effective interaction. In a\ntrapped Fermi gas the spin diffusion equations become nonlinear, and their\nnumerical solution exhibits an inhomogeneous spin state even at the spin echo\ntime. While the microscopic diffusivity and $\\gamma$ increase at weak coupling,\ntheir apparent values inferred from the trap-averaged magnetization saturate in\nagreement with a recent experiment for a dilute ultracold Fermi gas."
    },
    {
        "anchor": "Chiral Ladders and the Edges of Chern Insulators: The realization and detection of topological phases with ultracold atomic\ngases is at the frontier of current theoretical and experimental research.\nHere, we identify cold atoms in optical ladders subjected to synthetic magnetic\nfields as readily realizable bridges between one-dimensional spin-orbit (time\nreversal) topological insulators and two-dimensional Chern insulators. We\nreveal three instances of their promising potential: i) they realize spin-orbit\ncoupling, with the left-right leg degree of freedom playing the role of an\neffective spin, ii) their energy bands and eigenstates exactly reproduce the\ntopological chiral edge modes of two-dimensional Chern insulators, and iii)\nthey can be tailored to realize a topological phase transition from a trivial\nto a topological insulating phase. We propose realistic schemes to observe the\nchiral and topological properties of ladder systems with current optical\nlattice-based experiments. Our findings open a door to the exploration of the\nphysics of the edges of Chern insulators and to the realization of spin-orbit\ncoupling and topological superfluid phases with ultracold atomic gases.",
        "positive": "Spatial interference from well-separated condensates: We use magnetic levitation and a variable-separation dual optical plug to\nobtain clear spatial interference between two condensates axially separated by\nup to 0.25 mm -- the largest separation observed with this kind of\ninterferometer. Clear planar fringes are observed using standard (i.e.\nnon-tomographic) resonant absorption imaging. The effect of a weak inverted\nparabola potential on fringe separation is observed and agrees well with\ntheory."
    },
    {
        "anchor": "The Bose polaron problem: effect of mass imbalance on binding energy: By means of Quantum Monte Carlo methods we calculate the binding energy of an\nimpurity immersed in a Bose-Einstein condensate at T = 0. The focus is on the\nattractive branch of the Bose polaron and on the role played by the mass\nimbalance between the impurity and the surrounding particles. For an impurity\nresonantly coupled to the bath, we investigate the dependence of the binding\nenergy on the mass ratio and on the interaction strength within the medium. In\nparticular, we determine the equation of state in the case of a static\n(infinite mass) impurity, where three-body correlations are irrelevant and the\nresult is expected to be a universal function of the gas parameter. For the\nmass ratio corresponding to $^{40}$K impurities in a gas of $^{87}$Rb atoms we\nprovide an explicit comparison with the experimental findings of a recent study\ncarried out at JILA.",
        "positive": "Galilean boosts and superfluidity of resonantly driven polariton fluids\n  in the presence of an incoherent reservoir: We theoretically investigate how the presence of a reservoir of incoherent\nexcitations affects the superfluidity properties of resonantly driven polariton\nfluids. While in the absence of reservoir the two cases of a defect moving in a\nfluid at rest and of a fluid flowing against a static defect are linked by a\nformal Galilean transformation, here the reservoir defines a privileged\nreference frame attached to the semiconductor structure and causes markedly\ndifferent features between the two settings. The consequences on the critical\nvelocity for superfluidity are highlighted and compared to experiments in\nresonantly driven excitons polaritons."
    },
    {
        "anchor": "Localization of excited states of Bose-Einstein Condensates in presence\n  of disorder: We study the onset of localization from excited states of trapped Bose-\nEinstein Condensates expanding in presence of Gaussian uncorrelated random\ndisorder. In 1D systems, we observe that for a fixed ratio between the disorder\nstrength and the initial energy, excited states localize exponentially with a\nlocalization length that decreases as the energy of the initial state\nincreases. Moreover, the localized state keeps the shape of the initial state\nwave function with an exponential tail. In 2D, we analyze the interplay between\nvorticiy and localization by examining the dispersion of a state containing a\nvortex on it in a disordered media. Despite localization can be associated to\nislands of constant phase, the presence of a vortex in the initial state leads\nto dislocations and phase jumps in the localized state. The study of dispersion\nof a bosonic condensate with vorticity bears similarities to the stability of\ntopological excitations in 2D p-wave fermionic superfluids.",
        "positive": "Faraday patterns in spin-orbit coupled Bose-Einstein condensates: We study the Faraday patterns generated by spin-orbit-coupling induced\nparametric resonance in a spinor Bose-Einstein condensate with repulsive\ninteraction. The collective elementary excitations of the Bose-Einstein\ncondensate, including density waves and spin waves, are coupled as the result\nof the Raman-induced spin-orbit coupling and a quench of the relative phase of\ntwo Raman lasers without the modulation of any of the system's parameters. We\nobserved several higher parametric resonance tongues at integer multiples of\nthe driving frequency and investigated the interplay between Faraday\ninstabilities and modulation instabilities when we quench the\nspin-orbit-coupled Bose-Einstein condensate from zero-momentum phase to\nplane-wave phase. If the detuning is equal to zero, the wave number of\ncombination resonance barely changes as the strength of spin-orbit coupling\nincreases. If the detuning is not equal to zero after a quench, a single\ncombination resonance tongue will split into two parts."
    },
    {
        "anchor": "Spectroscopic probes of quantum many-body correlations in polariton\n  microcavities: We investigate the many-body states of exciton-polaritons that can be\nobserved by pump-probe spectroscopy. Here, a weak-probe `spin-down' polariton\nis introduced into a coherent state of `spin-up' polaritons created by a strong\npump. We show that the $\\downarrow$ impurities become dressed by excitations of\nthe $\\uparrow$ medium, and form new polaronic quasiparticles that feature\ntwo-point and three-point many-body quantum correlations, which, in the low\ndensity regime, arise from coupling to the vacuum biexciton and triexciton\nstates respectively. In particular, we find that these correlations generate\nadditional branches and avoided crossings in the $\\downarrow$ optical\ntransmission spectrum that have a characteristic dependence on the\n$\\uparrow$-polariton density. Our results thus demonstrate a way to directly\nobserve correlated many-body states in an exciton-polariton system that go\nbeyond classical mean-field theories.",
        "positive": "Topological Superfluid in one-dimensional Ultracold Atomic System with\n  Spin-Orbit Coupling: We propose a one-dimensional Hamiltonian $H_{1D}$ which supports Majorana\nfermions when $d_{x^{2}-y^{2}}$-wave superfluid appears in the ultracold atomic\nsystem and obtain the phase-separation diagrams both for the\ntime-reversal-invariant case and time-reversal-symmetry-breaking case. From the\nphase-separation diagrams, we find that the single Majorana fermions exist in\nthe topological superfluid region, and we can reach this region by tuning the\nchemical potential $\\mu$ and spin-orbit coupling $\\alpha_{R}$. Importantly, the\nspin-orbit coupling has realized in ultracold atoms by the recent experimental\nachievement of synthetic gauge field, therefore, our one-dimensional ultra-cold\natomic system described by $H_{1D}$ is a promising platform to find the\nmysterious Majorana fermions."
    },
    {
        "anchor": "Synthetic spin-orbit coupling in ultracold $\u039b$-type atoms: We consider the simulation of non-abelian gauge potentials in ultracold atom\nsystems with atom-field interaction in the $\\Lambda$ configuration where two\ninternal states of an atom are coupled to a third common one with a detuning.\nWe find the simulated non-abelian gauge potentials can have the same structures\nas those simulated in the tripod configuration if we parameterize Rabi\nfrequencies properly, which means we can design spin-orbit coupling simulation\nschemes based on those proposed in the tripod configuration. We show the\nsimulated spin-orbit coupling in the $\\Lambda$ configuration can only be of a\nform similar to $p_{x}\\sigma_{y}$ even when the Rabi frequencies are not much\nsmaller than the detuning.",
        "positive": "Tan contact and universal high momentum behavior of the fermion\n  propagator in the BCS-BEC crossover: We derive the universal high momentum factorization of the fermion\nself-energy in the BCS-BEC crossover of ultracold atoms using nonperturbative\nquantum field theoretical methods. This property is then employed to compute\nthe Tan contact as a function of interaction strength, temperature, chemical\npotential and Fermi momentum. We clarify the mechanism of the factorization\nfrom an analysis of the self-consistent Schwinger-Dyson equation for the\nfermion propagator, and compute the perturbative contact on the BCS and BEC\nsides within this framework. A Functional Renormalization Group approach is\nthen put forward, which allows to determine the contact over the whole\ncrossover and, in particular, for the Unitary Fermi gas. We present numerical\nresults from an implementation of the Renormalization Group equations within a\nbasic truncation scheme."
    },
    {
        "anchor": "Optomechanical atom-cavity interaction in the sub-recoil regime: We study the optomechanical interaction of a Bose-Einstein condensate with a\nsingle longitudinal mode of an ultra-high finesse standing wave optical\nresonator. As a unique feature the resonator combines three extreme regimes,\npreviously not realized together, i.e., strong cooperative coupling, cavity\ndominated scattering with a Purcell factor far above unity, and sub-recoil\nresolution provided by a cavity damping rate smaller than four times the single\nphoton recoil frequency. We present experimental observations in good agreement\nwith a two-mode model predicting highly non-linear dynamics with signatures as\nbistability, hysteresis, persistent oscillations, and superradiant\nback-scattering instabilities.",
        "positive": "Self-bound droplets of a dilute magnetic quantum liquid: Self-bound many-body systems are formed through a balance of attractive and\nrepulsive forces and occur in many physical scenarios. Liquid droplets are an\nexample of a self-bound system, formed by a balance of the mutual attractive\nand repulsive forces that derive from different components of the\ninter-particle potential. It has been suggested that self-bound ensembles of\nultracold atoms should exist for atom number densities that are 10^8 times\nlower than in a helium droplet, which is formed from a dense quantum liquid.\nHowever, such ensembles have been elusive up to now because they require forces\nother than the usual zero-range contact interaction, which is either attractive\nor repulsive but never both. On the basis of the recent finding that an\nunstable bosonic dipolar gas can be stabilized by a repulsive many-body term,\nit was predicted that three-dimensional self-bound quantum droplets of magnetic\natoms should exist. Here we report the observation of such droplets in a\ntrap-free levitation field. We find that this dilute magnetic quantum liquid\nrequires a minimum, critical number of atoms, below which the liquid evaporates\ninto an expanding gas as a result of the quantum pressure of the individual\nconstituents. Consequently, around this critical atom number we observe an\ninteraction-driven phase transition between a gas and a self-bound liquid in\nthe quantum degenerate regime with ultracold atoms. These droplets are the\ndilute counterpart of strongly correlated self-bound systems such as atomic\nnuclei and helium droplets."
    },
    {
        "anchor": "Quantum phases of hard-core bosons on 2D lattices with anisotropic\n  dipole-dipole interaction: By using an unbiased quantum Monte Carlo method, we investigate the hard-core\nBose-Hubbard model on a square lattice with anisotropic dipole-dipole\ninteraction. To study the effect of the anisotropy, dipole moments are assumed\nto be polarized in the $y$ direction on the two-dimensional (2D) $xy$ plane. To\nperform efficient simulations of long-range interacting systems, we use the\nworm algorithm with an O(N) Monte Carlo method. We obtain the ground-state\nphase diagram that includes a superfluid phase and a striped solid phase at\nhalf-filling as two main phases. In addition to these two main phases, we find\na small region where there are multi plateaus in the particle density for small\nhopping amplitudes. In this region, the number of plateaus increases as the\nsystem size increases. This indicates the appearance of numerous competing\nground states due to frustrated interactions. In our simulations, we find no\nevidence of a supersolid phase.",
        "positive": "Exploring phonon-like interactions in one-dimensional Bose-Fermi\n  mixtures: With the objective of simulating the physical behavior of electrons in a\ndynamic background, we investigate a cold atomic Bose-Fermi mixture confined in\nan optical lattice potential solely affecting the bosons. The bosons, residing\nin the deep superfluid regime, inherit the periodicity of the optical lattice,\nsubsequently serving as a dynamic potential for the polarized fermions. Owing\nto the atom-phonon interaction between the fermions and the condensate, the\ncoupled system exhibits a Berezinskii-Kosterlitz-Thouless transition from a\nLuttinger liquid to a Peierls phase. However, under sufficiently strong\nBose-Fermi interaction, the Peierls phase loses stability, leading to either a\ncollapsed or a separated phase. We find that the primary function of the\noptical lattice is to stabilize the Peierls phase. Furthermore, the presence of\na confining harmonic trap induces a diverse physical behavior, surpassing what\nis observed for either bosons or fermions individually trapped. Notably, under\nattractive Bose-Fermi interaction, the insulating phase may adopt a fermionic\nwedding-cake-like configuration, reflecting the dynamic nature of the\nunderlying lattice potential. Conversely, for repulsive interaction, the trap\ndestabilizes the Peierls phase, causing the two species to separate."
    },
    {
        "anchor": "Spontaneous quantum superradiant emission in atomic Bose-Einstein\n  condensates subject to a synthetic vector potential: We theoretically investigate the spontaneous quantum emission of phonon pairs\nby superradiant processes in an atomic Bose-Einstein condensate subject to a\nsynthetic vector potential. Within the analog gravity perspective, this effect\ncorresponds to the spontaneous emission of radiation from the ergosurface of\nrotating black holes. A general input-output formalism is built and used to\ncharacterize the spectral and correlation properties of the emission.\nExperimentally accessible signatures of the emission are pointed out in the\ncorrelation functions of the atomic gas.",
        "positive": "Oscillons in coupled Bose-Einstein condensates: Long-lived, spatially localized, and temporally oscillating nonlinear\nexcitations are predicted by numerical simulation of coupled Gross-Pitaevskii\nequations. These oscillons closely resemble the time-periodic breather\nsolutions of the sine-Gordon equation but decay slowly by radiating Bogoliubov\nphonons. Their time-dependent profile is closely matched with solutions of the\nsine-Gordon equation, which emerges as an effective field theory for the\nrelative phase of two linearly coupled Bose fields in the weak-coupling limit.\nFor strong coupling the long-lived oscillons persist and involve both relative\nand total phase fields. The oscillons decay via Bogoliubov phonon radiation\nthat is increasingly suppressed for decreasing oscillon amplitude.\nPossibilities for creating oscillons are addressed in atomic gas experiments by\ncollision of oppositely charged Bose-Josephson vortices and direct phase\nimprinting."
    },
    {
        "anchor": "Stripe and checkerboard patterns in a stack of driven\n  quasi-one-dimensional dipolar condensates: The emergence of transient checkerboard and stripe patterns in a stack of\ndriven quasi-one-dimensional homogeneous dipolar condensates is studied. The\nparametric driving of the $s$-wave scattering length leads to the excitation of\nthe lowest collective Bogoliubov mode. The character of the lowest mode depends\ncritically on the orientation of the dipoles, corresponding to out-of-phase and\nin-phase density modulations in neighboring condensates, resulting in\ncheckerboard and stripe patterns. Further, we show that a dynamical transition\nbetween the checkerboard and stripe patterns can be realized by quenching the\ndipole orientation either linearly or abruptly once the initial pattern is\nformed via periodic driving.",
        "positive": "Formation of ultracold weakly bound dimers of bosonic\n  $^{23}\\textrm{Na}^{39}\\textrm{K}$: We create weakly bound bosonic $^{23}\\textrm{Na}^{39}\\textrm{K}$ molecules in\na mixture of ultracold $^{23}\\textrm{Na}$ and $^{39}\\textrm{K}$. The creation\nis done in the vicinity of a so far undetected Feshbach resonance at about\n$196\\,\\text{G}$ which we identify in this work by atom-loss spectroscopy. We\ninvestigate the involved molecular state by performing destructive radio\nfrequency binding energy measurements. For the constructive molecule creation\nwe use radio frequency pulses with which we assemble up to $6000$ molecules. We\nanalyze the molecule creation efficiency as a function of the radio frequency\npulse duration and the atom number ratio between $^{23}\\textrm{Na}$ and\n$^{39}\\textrm{K}$. We find an overall optimal efficiency of $6\\,\\%$ referring\nto the $^{39}\\textrm{K}$ atom number. The measured lifetime of the molecules in\nthe bath of trapped atoms is about $0.3\\,\\textrm{ms}$."
    },
    {
        "anchor": "Anderson localization of a weakly interacting one dimensional Bose gas: We consider the phase coherent transport of a quasi one-dimensional beam of\nBose-Einstein condensed particles through a disordered potential of length L.\nAmong the possible different types of flow identified in [T. Paul et al., Phys.\nRev. Lett. 98, 210602 (2007)], we focus here on the supersonic stationary\nregime where Anderson localization exists. We generalize the diffusion\nformalism of Dorokhov-Mello-Pereyra-Kumar to include interaction effects. It is\nshown that interactions modify the localization length and also introduce a\nlength scale L* for the disordered region, above which most of the realizations\nof the random potential lead to time dependent flows. A Fokker-Planck equation\nfor the probability density of the transmission coefficient that takes this new\neffect into account is introduced and solved. The theoretical predictions are\nverified numerically for different types of disordered potentials. Experimental\nscenarios for observing our predictions are discussed.",
        "positive": "Impurity effects on the quantum coherence of a few-boson system: The impurity effects on the quantum coherence of a few-boson system are\nstudied within the two-site Hubbard model. Periodical collapses and revivals of\ncoherence occur in the presence of either polarized or unpolarized fermionic\nimpurities. The relative strength $U_{BF}/U_{BB}$ of the boson-fermion versus\nthe boson-boson interactions plays a key role in the coherence revivals. As the\naverage filling of the impurity increases, the coherence revivals remain nearly\nunaffected for $U_{BF}/U_{BB}=z$ ($z\\in Z$ is an integer) while the odd revival\npeaks are damped for $U_{BF}/U_{BB}=z+1/2$, in agreement with the experimental\nobservations. For unpolarized fermionic impurities, the coherence revivals are\nirrelevant to the strength of the fermion-fermion interactions."
    },
    {
        "anchor": "Realization of tunnel barriers for matter waves using spatial gaps: We experimentally demonstrate the trapping of a propagating Bose-Einstein\nCondensate in a Bragg cavity produced by an attractive optical lattice with a\nsmooth envelope. As a consequence of the envelope, the band gaps become\nposition-dependent and act as mirrors of finite and velocity-dependent\nreflectivity. We directly observe both the oscillations of the wave packet\nbouncing in the cavity provided by these spatial gaps and the tunneling out for\nnarrow classes of velocity. Synchronization of different classes of velocity\ncan be achieved by proper shaping of the envelope. This technique can generate\nsingle or multiple tunnel barriers for matter waves with a tunable transmission\nprobability, equivalent to a standard barrier of submicron size.",
        "positive": "Collective excitations in two-dimensional harmonically trapped quantum\n  droplets: The collective excitation modes in quantum droplets trapped in a\ntwo-dimensional harmonic potential in the context of symmetric weakly\ninteracting binary bosonic mixtures are studied. By utilizing the linearization\ntechnique, the time-dependent extended Gross-Pitaevskii equation, and a\nsum-rule approach with a variational approximation, the ground state properties\nand collective excitations of such a two-dimensional quantum system are\ninvestigated for various system parameters. We present comprehensive analysis\nand calculations on the effect of the confinement strength and anisotropy of\nthe trapping potential, the number of atoms in the droplet, and the collective\nexcitation modes. The radius of the droplet, as well as the chemical potential,\nis non-monotonically related to the number of atoms in the droplet, and the\nconfinement tends to shift the minimum values towards the ideal gas limit. The\nexcitation frequency peaks, which are prominent in a self-bounded droplet,\nbecome less pronounced and smoother when subjected to a strong trapping\npotential. The sum-rule approach fails to reproduce the breathing mode\nfrequency for a moderate number of atoms in a weak trapping potential, however,\nworks perfectly well in a strong confinement. It was found that the anisotropy\nin the trap eliminates the degeneracy between the quadrupole and scissors modes\nthat occurs in an isotropic trap, causing the frequencies of these two modes to\nimmediately diverge from each other for any degree of anisotropy. These\nfindings provide valuable insights into the unique characteristics and behavior\nof quantum droplets, offering potential implications for future research and\napplications in the dynamic behaviors of intriguing quantum droplets."
    },
    {
        "anchor": "Collision of one-dimensional fermion clusters: We study cluster-cluster collisions in one-dimensional Fermi systems with\nparticular emphasis on the non-trivial quantum effects of the collision\ndynamics. We adopt the Fermi-Hubbard model and the time-dependent density\nmatrix renormalization group method to simulate collision dynamics between two\nfermion clusters of different spin states with contact interaction. It is\nelucidated that the quantum effects become extremely strong with the\ninteraction strength, leading to the transmittance much more enhanced than\nexpected from semiclassical approximation. We propose a concise model based on\none-to-one collisions, which unveils the origin of the quantum effects and also\nexplains the overall properties of the simulation results clearly. Our concise\nmodel can quite widely describe the one-dimensional collision dynamics with\ncontact interaction. Some potential applications, such as repeated collisions,\nare addressed.",
        "positive": "Controllable fusion of electromagnetic bosons in two-dimensional\n  semiconductors: We propose a physical principle for implementation of controllable\ninteractions of identical electromagnetic bosons (excitons or polaritons) in\ntwo-dimensional (2D) semiconductors. The key ingredients are tightly bound\nbiexcitons and in-plane anisotropy of the host structure due to, e.g., a\nuniaxial strain. We show that anisotropy-induced splitting of the radiative\nexciton doublet couples the biexciton state to continua of boson scattering\nstates. As a result, two-body elastic scattering of bosons may be resonantly\namplified when energetically tuned close to the biexciton by applying a\ntransverse magnetic field or tuning the coupling with the microcavity photon\nmode. At the resonance, bosonic fields undergo quantum reaction of fusion\naccompanied by their squeezing. For excitons, we predict giant molecules\n(Feshbach dimers) which can be obtained from a biexciton via rapid adiabatic\nsweeping of the magnetic field across the resonance. The molecules possess\nnon-trivial entanglement properties. Our proposal holds promise for the\nstrongly-correlated photonics and quantum chemistry of light."
    },
    {
        "anchor": "Center-of-mass-momentum-dependent interaction between ultracold atoms: We show that a type of two-body interaction, which depends on the momentum of\nthe center of mass (COM) of these two particles, can be realized in ultracold\natom gases with a laser-modulated magnetic Feshbach resonance (MFR). Here the\nMFR is modulated by two laser beams propagating along different directions,\nwhich can induce Raman transition between two-body bound states. The Doppler\neffect causes the two-atom scattering length to be strongly dependent on the\nCOM momentum of these two atoms. As a result, the effective two-atom\ninteraction is COM-momentum dependent, while the one-atom free Hamiltonian is\nstill the simple kinetic energy p^2/(2m).",
        "positive": "Sound emission and annihilations in a programmable quantum vortex\n  collider: In quantum fluids, the quantisation of circulation forbids the diffusion of a\nvortex swirling flow seen in classical viscous fluids. Yet, a quantum vortex\naccelerating in a superfluid may lose its energy into acoustic radiation, in a\nsimilar way an electric charge decelerates upon emitting photons. The\ndissipation of vortex energy underlies central problems in quantum\nhydrodynamics, such as the decay of quantum turbulence, highly relevant to\nsystems as varied as neutron stars, superfluid helium and atomic condensates. A\ndeep understanding of the elementary mechanisms behind irreversible vortex\ndynamics has been a goal for decades, but it is complicated by the shortage of\nconclusive experimental signatures. Here, we address this challenge by\nrealising a programmable quantum vortex collider in a planar, homogeneous\natomic Fermi superfluid with tunable inter-particle interactions. We create\non-demand vortex configurations and monitor their evolution, taking advantage\nof the accessible time and length scales of our ultracold Fermi gas.\nEngineering collisions within and between vortex-antivortex pairs allows us to\ndecouple relaxation of the vortex energy due to sound emission and interactions\nwith normal fluid, i.e. mutual friction. We directly visualise how the\nannihilation of vortex dipoles radiates a sound pulse in the superfluid.\nFurther, our few-vortex experiments extending across different superfluid\nregimes suggest that fermionic quasiparticles localised inside the vortex core\ncontribute significantly to dissipation, opening the route to exploring new\npathways for quantum turbulence decay, vortex by vortex."
    },
    {
        "anchor": "Selective Population of Edge States in a 2D Topological Band System: We consider a system of interacting spin-one atoms in a hexagonal lattice\nunder the presence of a synthetic gauge field. Quenching the quadratic Zeeman\nfield is shown to lead to a dynamical instability of the edge modes. This, in\nturn, leads to a spin current along the boundary of the system which grows\nexponentially fast in time following the quench. Tuning the magnitude of the\nquench can be used to selectively populate edge modes of different momenta.\nImplications of the intrinsic symmetries of Hamiltonian on the dynamics are\ndiscussed. The results hold for atoms with both antiferromagnetic and\nferromagnetic interactions.",
        "positive": "A long-lived Higgs mode in a two-dimensional confined Fermi gas: The Higgs mode corresponds to the collective motion of particles due to the\nvibrations of an invisible field. It plays a fundamental role for our\nunderstanding of both low and high energy physics, giving elementary particles\ntheir mass and leading to collective modes in condensed matter and nuclear\nsystems. The Higgs mode has been observed in a limited number of table-top\nsystems, where it however is characterised by a short lifetime due to decay\ninto a continuum of modes. A major goal which has remained elusive so far, is\ntherefore to realise a long-lived Higgs mode in a controllable system. Here, we\nshow how an undamped Higgs mode can be observed unambiguously in a Fermi gas in\na two-dimensional trap, close to a quantum phase transition between a normal\nand a superfluid phase. We develop a first-principles theory of the pairing and\nthe associated collective modes, which is quantitatively reliable when the\npairing energy is much smaller than the trap level spacing, yet simple enough\nto allow the derivation of analytical results. The theory includes the trapping\npotential exactly, which is demonstrated to stabilize the Higgs mode by making\nits decay channels discrete. Our results show how atoms in micro-traps can\nunravel properties of a long-lived Higgs mode, including the role of\nconfinement and finite size effects."
    },
    {
        "anchor": "Chiral orbital order of interacting bosons without higher bands: Ultracold atoms loaded into higher Bloch bands provide an elegant setting for\nrealizing many-body quantum states that spontaneously break time-reversal\nsymmetry through the formation of chiral orbital order. The applicability of\nthis strategy remains nonetheless limited due to the finite lifetime of atoms\nin high-energy bands. Here we introduce an alternative framework, suitable for\nbosonic gases, which builds on assembling square plaquettes pierced by a\n$\\pi$-flux (half a magnetic-flux quantum). This setting is shown to be formally\nequivalent to an interacting bosonic gas loaded into $p$ orbitals, and we\nexplore the consequences of the resulting chiral orbital order, both for weak\nand strong onsite interactions. We demonstrate the emergence of a chiral\nsuperfluid vortex lattice, exhibiting a long-lived gapped collective mode that\nis characterized by local chiral currents. This chiral superfluid phase is\nshown to undergo a phase transition to a chiral Mott insulator for sufficiently\nstrong interactions. Our work establishes coupled $\\pi$-flux plaquettes as a\npractical route for the emergence of orbital order and chiral phases of matter.",
        "positive": "Bose-Einstein condensation of photons in an optical microcavity: Bose-Einstein condensation, the macroscopic ground state accumulation of\nparticles with integer spin (bosons) at low temperature and high density, has\nbeen observed in several physical systems, including cold atomic gases and\nsolid state physics quasiparticles. However, the most omnipresent Bose gas,\nblackbody radiation (radiation in thermal equilibrium with the cavity walls)\ndoes not show this phase transition, because the chemical potential of photons\nvanishes and, when the temperature is reduced, photons disappear in the cavity\nwalls. Theoretical works have considered photon number conserving\nthermalization processes, a prerequisite for Bose-Einstein condensation, using\nCompton scattering with a gas of thermal electrons, or using photon-photon\nscattering in a nonlinear resonator configuration. In a recent experiment, we\nhave observed number conserving thermalization of a two-dimensional photon gas\nin a dye-filled optical microcavity, acting as a 'white-wall' box for photons.\nHere we report on the observation of a Bose-Einstein condensation of photons in\na dye-filled optical microcavity. The cavity mirrors provide both a confining\npotential and a non-vanishing effective photon mass, making the system formally\nequivalent to a two-dimensional gas of trapped, massive bosons. By multiple\nscattering off the dye molecules, the photons thermalize to the temperature of\nthe dye solution (room temperature). Upon increasing the photon density we\nobserve the following signatures for a BEC of photons: Bose-Einstein\ndistributed photon energies with a massively populated ground state mode on top\nof a broad thermal wing, the phase transition occurring both at the expected\nvalue and exhibiting the predicted cavity geometry dependence, and the ground\nstate mode emerging even for a spatially displaced pump spot."
    },
    {
        "anchor": "Crossover between integer and fractional vortex lattices in coherently\n  coupled two-component Bose-Einstein condensates: We study effects of the internal coherent (Rabi) coupling in vortex lattices\nin two-component BECs under rotation. We find how the vortex lattices without\nthe Rabi coupling known before are connected to the Abrikosov lattice of\ninteger vortices with increasing the Rabi coupling. We find that 1) for small\nRabi couplings, fractional vortices in triangular or square lattice for small\nor large inter-component coupling constitute hexamers or tetramers, namely\nmulti-dimer bound states made of six or four vortices, respectively, 2) these\nbound states are broken into a set of dimers at intermediate Rabi couplings,\nand 3) vortices change their partners in various ways depending on the\ninter-component coupling to organize themselves for constituting the Abrikosov\nlattice of integer vortices at strong Rabi couplings.",
        "positive": "Revisiting the Vashishta-Singwi dielectric scheme for the warm dense\n  uniform electron fluid: The finite temperature version of the Vashishta-Singwi (VS) dielectric scheme\nfor the paramagnetic warm dense uniform electron fluid is revisited correcting\nfor an earlier thermodynamic derivative error. The VS scheme handles quantum\nmechanical effects at the level of the random phase approximation and treats\ncorrelations via the density expansion of a generalized\nSingwi-Tosi-Land-Sj\\\"olander (STLS) closure that inserts a parameter determined\nby enforcing the compressibility sum rule. Systematic comparison with\nquasi-exact results, based on quantum Monte Carlo simulations, reveals a\nstructural superiority of the VS scheme towards strong coupling and a\nthermodynamic superiority of the STLS scheme courtesy of a favorable\ncancellation of errors. Guidelines are provided for the construction of\ndielectric schemes that are expected to be more accurate but computationally\ncostly."
    },
    {
        "anchor": "Spin and Charge Resolved Quantum Gas Microscopy of Antiferromagnetic\n  Order in Hubbard Chains: The repulsive Hubbard Hamiltonian is one of the foundational models\ndescribing strongly correlated electrons and is believed to capture essential\naspects of high temperature superconductivity. Ultracold fermions in optical\nlattices allow for the simulation of the Hubbard Hamiltonian with a unique\ncontrol over kinetic energy, interactions and doping. A great challenge is to\nreach the required low entropy and to observe antiferromagnetic spin\ncorrelations beyond nearest neighbors, for which quantum gas microscopes are\nideal. Here we report on the direct, single-site resolved detection of\nantiferromagnetic correlations extending up to three sites in spin-$1/2$\nHubbard chains, which requires an entropy well below $s^*=\\ln(2)$. Finally, the\nsimultaneous detection of spin and density opens the route towards the study of\nthe interplay between magnetic ordering and doping in various dimensions.",
        "positive": "Polarons and Molecules in a Fermi Gas with Orbital Feshbach Resonance: We study the impurity problem in a gas of $^{173}$Yb atoms near the recently\ndiscovered orbital Feshbach resonance. In an orbital Feshbach resonance, atoms\nin the electronic ground state $^1S_0$ interact with those in the long-lived\nexcited $^3P_0$ state with magnetically tunable interactions. We consider an\nimpurity atom with a given hyperfine spin in the $^3P_0$ state interacting with\na single-component Fermi sea of atoms in the ground $^1S_0$ manifold. Close to\nthe orbital Feshbach resonance, the impurity can induce collective\nparticle-hole excitations out of the Fermi sea, which can be regarded as the\npolaron state. While as tuning toward the BEC regime of the resonance, a\nmolecular state becomes the ground state of the system. We show that a polaron\nto molecule transition exists in $^{173}$Yb atoms close to the orbital Feshbach\nresonance. Furthermore, due to the spin-exchange nature of the orbital Feshbach\nresonance, the formation of both the polaron and the molecule involve\nspin-flipping processes with interesting density distributions among the\nrelevant hyperfine spin states. We show that the polaron to molecule transition\ncan be detected using Raman spectroscopy."
    },
    {
        "anchor": "Variational calculations for anisotropic solitons in dipolar\n  Bose-Einstein condensates: We present variational calculations using a Gaussian trial function to\ncalculate the ground state of the Gross-Pitaevskii equation and to describe the\ndynamics of the quasi-two-dimensional solitons in dipolar Bose-Einstein\ncondensates. Furthermore we extend the ansatz to a linear superposition of\nGaussians improving the results for the ground state to exact agreement with\nnumerical grid calculations using imaginary time and split-operator method. We\nare able to give boundaries for the scattering length at which stable solitons\nmay be observed in an experiment. By dynamical calculations with coupled\nGaussians we are able to describe the rather complex behavior of the thermally\nexcited solitons. The discovery of dynamically stabilized solitons indicates\nthe existence of such BECs at experimentally accessible temperatures.",
        "positive": "Mott insulating states and quantum phase transitions of correlated\n  SU(2N) Dirac fermions: The interplay between charge and spin degrees of freedom in strongly\ncorrelated fermionic systems, in particular of Dirac fermions, is a\nlong-standing problem in condensed matter physics. We investigate the competing\norders in the half-filled SU(2N) Hubbard model on a honeycomb lattice, which\ncan be accurately realized in optical lattices with large-spin ultra-cold\nalkaline-earth fermions. Employing large-scale projector determinant quantum\nMonte Carlo simulations, we have explored quantum phase transitions from the\ngapless Dirac semi-metals to the gapped Mott-insulating phases in the SU(4) and\nSU(6) cases. Both of these Mott-insulating states are found to be columnar\nvalence bond solid (cVBS) and to be absent of the antiferromagnetic Neel\nordering and the loop current ordering. Inside the cVBS phases, the dimer\nordering is enhanced by increasing fermion components and behaves\nnon-monotonically as the interaction strength increases. Although the\ntransitions generally should be of first order due to a cubic invariance\npossessed by the cVBS order, the coupling to gapless Dirac fermions can soften\nthe transitions to second order through a non-analytic term in the free energy.\nOur simulations provide important guidance for the experimental exploration of\nnovel states of matter with ultra-cold alkaline earth fermions."
    },
    {
        "anchor": "A recipe for topological observables of density matrices: Meaningful topological invariants for mixed quantum states are challenging to\nidentify as there is no unique way to define them, and most choices do not\ndirectly relate to physical observables. Here, we propose a simple pragmatic\napproach to construct topological invariants of mixed states while preserving a\nconnection to physical observables, by continuously deforming known topological\ninvariants for pure (ground) states. Our approach relies on expectation values\nof many-body operators, with no reference to single-particle (e.g., Bloch)\nwavefunctions. To illustrate it, we examine extensions to mixed states of\n$U(1)$ geometric (Berry) phases and their corresponding topological invariant\n(winding or Chern number). We discuss measurement schemes, and provide a\ndetailed construction of invariants for thermal or more general mixed states of\nquantum systems with (at least) $U(1)$ charge-conservation symmetry, such as\nquantum Hall insulators.",
        "positive": "Many-body Landau-Zener Transition in Cold Atom Double Well Optical\n  Lattices: Ultra-cold atoms in optical lattices provide an ideal platform for exploring\nmany-body physics of a large system arising from the coupling among a series of\nsmall identical systems whose few-body dynamics is exactly solvable. Using\nLandau-Zener (LZ) transition of bosonic atoms in double well optical lattices\nas an experimentally realizable model, we investigate such few to many body\nroute by exploring the relation and difference between the small few-body (in\none double well) and the large many-body (in double well lattice)\nnon-equilibrium dynamics of cold atoms in optical lattices. We find the\nmany-body coupling between double wells greatly enhances the LZ transition\nprobability. The many-body dynamics in the double well lattice shares both\nsimilarity and difference from the few-body dynamics in one and two double\nwells. The sign of the on-site interaction plays a significant role on the\nmany-body LZ transition. Various experimental signatures of the many-body LZ\ntransition, including atom density, momentum distribution, and density-density\ncorrelation, are obtained."
    },
    {
        "anchor": "Spontaneous Peierls dimerization and emergent bond order in\n  one-dimensional dipolar gases: We investigate the effect of dipolar interactions in one-dimensional systems\nin connection with the possibility of observing exotic many-body effects with\ntrapped atomic and molecular dipolar gases. By combining analytical and\nnumerical methods, we show how the competition between short- and long-range\ninteractions gives rise to frustrating effects which lead to the stabilization\nof spontaneously dimerized phases characterized by a bond-ordering. This\ngenuine quantum order is sharply distinguished from Mott and spin-density wave\nphases, and can be unambiguously probed by measuring non local order parameters\nin-situ imaging techniques.",
        "positive": "Low-Dimensional Fluctuations and Pseudogap in Gaudin-Yang Fermi Gases: Pseudogap is a ubiquitous phenomenon in strongly correlated systems such as\nhigh-$T_{\\rm c}$ superconductors, ultracold atoms and nuclear physics. While\npairing fluctuations inducing the pseudogap are known to be enhanced in\nlow-dimensional systems, such effects have not been explored well in one of the\nmost fundamental 1D models, that is, Gaudin-Yang model. In this work, we show\nthat the pseudogap effect can be visible in the single-particle excitation in\nthis system using a diagrammatic approach. Fermionic single-particle spectra\nexhibit a unique crossover from the double-particle dispersion to pseudogap\nstate with increasing the attractive interaction and the number density at\nfinite temperature. Surprisingly, our results of thermodynamic quantities in\nunpolarized and polarized gases show an excellent agreement with the recent\nquantum Monte Carlo and complex Langevin results, even in the region where the\npseudogap appears."
    },
    {
        "anchor": "Two-dimensional exciton-polariton interactions beyond the Born\n  approximation: We provide a many-body theory for the interactions of two-dimensional\nexcitons and polaritons beyond the Born approximation. Taking into account\nGaussian quantum fluctuations via the Bogoliubov theory, we find that the\ntwo-body interaction strength in two-dimensions has an inverse logarithmic\ndependence on the scattering length and ground state energy. This leads to a\nvanishing exciton interaction strength in the zero-momentum limit but a finite\npolariton interaction strength due to strong light-matter coupling. We also\nderive the exact Tan relations for exciton-polaritons and calculate Tan's\ncontact coefficient. We show the polariton interaction strength and Tan's\ncontact both exhibit an anomalous enhancement at red photon-exciton detuning\nwhen the scattering length is large. Our predictions may provide a\nqualitatively correct guide for studies of exciton and polariton\nnonlinearities, and suggest a route to achieving strongly nonlinear polariton\ngases.",
        "positive": "Anisotropic Ginzburg-Landau and Lawrence-Doniach Models for Layered\n  Ultracold Fermi Gases: We study the anisotropic Ginzburg-Landau and Lawrence-Doniach models\ndescribing a layered superfluid ultracold Fermi gas in optical lattices. We\nderive the coefficients of the anisotropic Ginzburg-Landau and the mass tensor\nas a function of anisotropy, filling and interaction, showing that near the\nunitary limit the effective anisotropy of the masses is significantly reduced.\nThe anisotropy parameter is shown to vary in realistic setups in a wide range\nof values. We also derive the Lawrence-Doniach model - often used to describe\nthe 2D-3D dimensional crossover in layered superconductors - for a layered\nultracold Fermi gas, obtaining a relation between the interlayer Josephson\ncouplings and the Ginzburg-Landau masses. Comparing to the Ginzburg-Landau\ndescription, we find that the region of validity of the Lawrence-Doniach model\nis near the unitary limit."
    },
    {
        "anchor": "Statistical properties of spectra in harmonically trapped spin-orbit\n  coupled systems: We compute single-particle energy spectra for a one-body hamiltonian\nconsisting of a two-dimensional deformed harmonic oscillator potential, the\nRashba spin-orbit coupling and the Zeeman term. To investigate the statistical\nproperties of the obtained spectra as functions of deformation, spin-orbit and\nZeeman strengths we examine the distributions of the nearest neighbor spacings.\nWe find that the shapes of these distributions depend strongly on the three\npotential parameters. We show that the obtained shapes in some cases can be\nwell approximated with the standard Poisson, Brody and Wigner distributions.\nThe Brody and Wigner distributions characterize irregular motion and help\nidentify quantum chaotic systems. We present a special choices of deformation\nand spin-orbit strengths without the Zeeman term which provide a fair\nreproduction of the fourth-power repelling Wigner distribution. By adding the\nZeeman field we can reproduce a Brody distribution, which is known to describe\na transition between the Poisson and linear Wigner distributions.",
        "positive": "Density waves and jet emission asymmetry in Bose Fireworks: A Bose condensate subject to a periodic modulation of the two-body\ninteractions was recently observed to emit matter-wave jets resembling\n\"fireworks\" [Nature 551, 356(2017)]. In this paper, combining experiment with\nnumerical simulation, we demonstrate that these \"Bose fireworks\" represent a\nlate stage in a complex time evolution of the driven condensate. We identify a\n\"density wave\" stage which precedes jet emission and results from interference\nof matterwaves. The density waves self-organize and self-amplify without the\nbreaking of long range translational symmetry. Importantly, this density wave\nstructure deterministically establishes the template for the subsequent\npatterns of the emitted jets. Our simulations, in good agreement with\nexperiment, also address the apparent asymmetry in the jet pattern and show it\nis fully consistent with momentum conservation."
    },
    {
        "anchor": "Flow enhanced pairing and other novel effects in Fermi gases in\n  synthetic gauge fields: Recent experiments on fermions in synthetic gauge fields result in systems\nwith a spin-orbit coupling along one spatial axis, a detuning field, and a\nZeeman field. We show theoretically that the presence of all three results in\ninteresting and unusual phenomena in such systems in the presence of a contact\nsinglet attraction between the fermions (described by a scattering length). For\ntwo particles, bound states appear over certain range of the centre of mass\nmomenta when a critical positive scattering length is attained, with the\ndeepest bound state appearing at a nonzero centre of mass momentum. For the\ncentre of mass momenta without a bound state, the gauge field induces a\nresonance like feature in the scattering continuum resulting in a large\nscattering phase shift. For many particles, we demonstrate that the system, in\na parameter range, shows flow enhanced pairing, i.e., a more robust superfluid\nat finite centre of mass momentum. Yet another regime of parameters offers the\nopportunity to study strongly interacting normal states of spin-orbit coupled\nfermionic systems utilizing the resonance like feature induced by the synthetic\ngauge field.",
        "positive": "Tan's contact of a harmonically trapped one-dimensional Bose gas:\n  strong-coupling expansion and conjectural approach at arbitrary interactions: We study Tan's contact, i.e. the coefficient of the high-momentum tails of\nthe momentum distribution at leading order, for an interacting one-dimensional\nBose gas subjected to a harmonic confinement. Using a strong-coupling\nsystematic expansion of the ground-state energy of the homogeneous system\nstemming from the Bethe-Ansatz solution, together with the local-density\napproximation, we obtain the strong-coupling expansion for Tan's contact of the\nharmonically trapped gas. Also, we use a very accurate conjecture for the\nground-state energy of the homogeneous system to obtain an approximate\nexpression for Tan's contact for arbitrary interaction strength, thus\nestimating the accuracy of the strong-coupling expansion. Our results are\nrelevant for ongoing experiments with ultracold atomic gases."
    },
    {
        "anchor": "Detecting One-Dimensional Dipolar Bosonic Crystal Orders via Full\n  Distribution Functions: We explore the groundstates of a few dipolar bosons in optical lattices with\nincommensurate filling. The competition of kinetic, potential, and interaction\nenergies leads to the emergence of a variety of crystal state orders with\ncharacteristic one- and two-body densities. We probe the transitions between\nthese orders and construct the emergent state diagram as a function of the\ndipolar interaction strength and the lattice depth. We show that the crystal\nstate orders can be observed using the full distribution functions of the\nparticle number extracted from simulated single-shot images.",
        "positive": "Spinless Bosons or Spin 1/2 Fermions in a 1D Harmonic Trap with\n  Repulsive Delta Function Interparticle Interaction I - General Theory: In these two papers, we solve the N body 1D harmonically trapped spinless\nBoson or spin 1/2 Fermions with repulsive delta function interaction in the\nlimit $N\\to \\infty$."
    },
    {
        "anchor": "Unravelling Interaction and Temperature Contributions in Unpolarized\n  Trapped Fermionic Atoms in the BCS Regime: In the BCS limit density profiles for unpolarized trapped fermionic clouds of\natoms are largely featureless. Therefore, it is a delicate task to analyze them\nin order to quantify their respective interaction and temperature\ncontributions. Temperature measurements have so far been mostly considered in\nan indirect way, where one sweeps isentropically from the BCS to the BEC limit.\nInstead we suggest here a direct thermometry, which relies on measuring the\ncolumn density and comparing the obtained data with a Hartree-Bogoliubov\nmean-field theory combined with a local density approximation. In case of an\nattractive interaction between two-components of $^{6}$Li atoms trapped in a\ntri-axial harmonic confinement we show that minimizing the error within such an\nexperiment-theory collaboration turns out to be a reasonable criterion for\nanalyzing in detail measured densities and, thus, for ultimately determining\nthe sample temperatures. The findings are discussed in view of various possible\nsources of errors.",
        "positive": "Many-Body Quantum Dynamics of a Bosonic Josephson Junction with a\n  Finite-Range Interaction: The out-of-equilibrium quantum dynamics of a Bose gas trapped in an\nasymmetric double well and interacting with a finite-range interaction has been\nstudied in real space by solving the time-dependent many-body Schr\\\"odinger\nequation numerically accurately using the multiconfigurational time-dependent\nHartree method for bosons (MCTDHB). We have focused on the weakly interacting\nlimit where the system is essentially condensed. We have examined the impact of\nthe range of the interaction on the dynamics of the system, both at the\nmean-field and many-body levels. Explicitly, we have studied the maximal and\nthe minimal values of the many-body position variance in each cycle of\noscillation, and the overall pace of its growth. We find that the range of the\ninteraction affects the dynamics of the system differently for the right well\nand the left well. We have also examined the infinite-particle limit and find\nthat even there, the impact of the range of the interaction can only be\ndescribed by a many-body theory such as MCTDHB."
    },
    {
        "anchor": "SU(N) magnetism in chains of ultracold alkaline-earth-metal atoms: Mott\n  transitions and quantum correlations: We investigate one dimensional SU$(N)$ Hubbard chains at zero temperature,\nwhich can be emulated with ultracold alkaline earth atoms, by using the density\nmatrix renormalization group (DMRG), Bethe ansatz (BA), and bosonization. We\ncompute experimental observables and use the DMRG to benchmark the accuracy of\nthe Bethe ansatz for $N>2$ where the BA is only approximate. In the worst case,\nwe find a relative error $\\epsilon \\lesssim 4%$ in the BA ground state energy\nfor $N \\leq 4$ at filling 1/N, which is due to the fact that BA improperly\ntreats the triply and higher occupied states. Using the DMRG for $N \\leq 4$ and\nthe BA for large $N$, we determine the regimes of validity of strong- and\nweak-coupling perturbation theory for all values of $N$ and in particular, the\nparameter range in which the system is well described by a SU$(N)$ Heisenberg\nmodel at filling 1/N. We find this depends only weakly on $N$. We investigate\nthe Berezinskii-Kosterlitz-Thouless phase transition from a Luttinger liquid to\na Mott-insulator by computing the fidelity susceptibility and the Luttinger\nparameter $K_\\rho$ at 1/N filling. The numerical findings give strong evidence\nthat the fidelity susceptibility develops a minimum at a critical interaction\nstrength which is found to occur at a finite positive value for $N>2$.",
        "positive": "Rabi-coupling driven motion of a soliton in a Bose-Einstein condensate: We study the motion of a self-attractive Bose-Einstein condensate with\npseudo-spin 1/2 driven by a synthetic Rabi (Zeeman-like) field. This field\ntriggers the pseudo-spin dynamics resulting in a density redistribution between\nits components and, as a consequence, in changes of the overall density\ndistribution. In the presence of an additional external potential, the latter\nproduces a net force acting on the condensate and activates its displacement.\nAs an example, here we consider the case of a one-dimensional condensate in a\nrandom potential."
    },
    {
        "anchor": "Isotropic contact forces in arbitrary representation: heterogeneous\n  few-body problems and low dimensions: The Bethe-Peierls asymptotic approach which models pairwise short-range\nforces by contact conditions is introduced in arbitrary representation for\nspatial dimensions less than or equal to 3. The formalism is applied in various\nsituations and emphasis is put on the momentum representation. In the presence\nof a transverse harmonic confinement, dimensional reduction toward\ntwo-dimensional (2D) or one-dimensional (1D) physics is derived within this\nformalism. The energy theorem relating the mean energy of an interacting system\nto the asymptotic behavior of the one-particle density matrix illustrates the\nmethod in its second quantized form. Integral equations that encapsulate the\nBethe-Peierls contact condition for few-body systems are derived. In three\ndimensions, for three-body systems supporting Efimov states, a nodal condition\nis introduced in order to obtain universal results from the Skorniakov\nTer-Martirosian equation and the Thomas collapse is avoided. Four-body bound\nstate eigenequations are derived and the 2D '3+1' bosonic ground state is\ncomputed as a function of the mass ratio.",
        "positive": "Spin-Imbalanced Fermi Superfluidity in a Lieb Lattice Hubbard Model: We obtain a phase diagram of the spin imbalanced Hubbard model on the Lieb\nlattice, which is known to feature a flat band in its single-particle spectrum.\nUsing the BCS mean-field theory for multiband systems, we find a variety of\nsuperfluid phases with imbalance. In particular, we find four different types\nFFLO phases, i.e. superfluid phases with periodic spatial modulation. They\ndiffer by the magnitude and direction of the centre-of-mass momentum of Cooper\npairs. We also see a large region of stable Sarma phase, where the density\nimbalance is associated with zero Cooper pair momentum. In the mechanism\nresponsible for the formation of those phases, the crucial role is played by\nthe flat band, wherein particles can readjust their density at zero energy\ncost. The multiorbital structure of the unit cell is found to stabilize the\nSarma phase by allowing for a modulation of the order parameter within a unit\ncell. We also study the effect of finite temperature and a lattice with\nstaggered hopping parameters on the behaviour of these phases."
    },
    {
        "anchor": "Quantum Information Approach to Rotating Bose-Einstein Condensate: We investigate the 2D weakly interacting Bose-Einstein condensate in a\nrotating trap by the tools of quantum information theory. The critical\nexponents of the ground state fidelity susceptibility and the correlation\nlength of the system are obtained for the quantum phase transition when the\nfrst vortex is formed. We also find the single-particle entanglement can be an\nindicator of the angular momentums for some real ground states. The\nsingle-particle entanglement of fractional quantum Hall states such as Laughlin\nstate and Pfaffian state is also studied.",
        "positive": "Dissipation-induced squeezing: We present a method for phase and number squeezing in two-mode Bose systems\nusing dissipation. The effectiveness of this method is demonstrated by\nconsidering cold Bose gases trapped in a double-well potential. The extension\nof our formalism to an optical lattice gives control of the phase boundaries of\nthe steady-state phase diagram, and we discover a new phase characterized by a\nnon-zero condensate fraction and thermal-like particle-number statistics. We\nalso show how to perform amplitude squeezing in a single-mode system using\ndissipation."
    },
    {
        "anchor": "Behavior of heat capacity of an attractive Bose-Einstein Condensate\n  approaching collapse: We report calculation of heat capacity of an attractive Bose-Einstein\ncondensate, with the number N of bosons increasing and eventually approaching\nthe critical number Ncr for collapse, using the correlated potential harmonics\n(CPH) method. Boson pairs interact via the realistic van der Waals potential.\nIt is found that the transition temperature Tc increases initially slowly, then\nrapidly as N becomes closer to Ncr . The peak value of heat capacity for a\nfixed N increases slowly with N, for N far away from Ncr . But after reaching a\nmaximum, it starts decreasing when N approaches Ncr . The effective potential\ncalculated by CPH method provides an insight into this strange behavior.",
        "positive": "Multicomponent spin mixtures of two-electron fermions: These lecture notes contain an introduction to the physics of quantum\nmixtures of ultracold atoms trapped in multiple internal states. I will discuss\nthe case of fermionic isotopes of alkaline-earth atoms, which feature an\nintrinsic SU($N$) interaction symmetry and convenient methods for the optical\nmanipulation of their nuclear spin. Some research directions will be presented,\nwith focus on experiments performed in Florence with nuclear-spin mixtures of\n$^{173}$Yb atoms in optical lattices."
    },
    {
        "anchor": "Vortex stream generation and enhanced propagation in a polariton\n  superfluid: In this work, we implement a new experimental configuration which exploits\nthe specific properties of the optical bistability exhibited by the polariton\nsystem and we demonstrate the generation of a superfluid turbulent flow in the\nwake of a potential barrier. The propagation and direction of the turbulent\nflow are sustained by a support beam on distances an order of magnitude longer\nthan previously reported. This novel technique is a powerful tool for the\ncontrolled generation and propagation of quantum turbulences and paves the way\nto the study of the hydrodynamic of quantum turbulence in driven-dissipative 2D\npolariton systems.",
        "positive": "Adiabatic Control of Atomic Dressed States for Transport and Sensing: We describe forms of adiabatic transport that arise for dressed-state atoms\nin optical lattices. Focussing on the limit of weak tunnel-coupling between\nnearest-neighbour lattice sites, we explain how adiabatic variation of optical\ndressing allows control of atomic motion between lattice sites: allowing\nadiabatic particle transport in a direction that depends on the internal state,\nand force measurements via spectroscopic preparation and readout. For uniformly\nfilled bands these systems display topologically quantised particle transport."
    },
    {
        "anchor": "Theory of the spectral function of Fermi polarons at finite temperature: We develop a general theory of Fermi polarons at nonzero temperature,\nincluding particle-hole excitations of the Fermi sea shake-up to arbitrarily\nhigh orders. The exact set of equations of the spectral function is derived by\nusing both Chevy ansatz and diagrammatic approach, and their equivalence is\nclarified to hold in free space only, with an unregularized infinitesimal\ninteraction strength. The correction to the polaron spectral function arising\nfrom two-particle-hole excitations is explicitly examined, for an exemplary\ncase of Fermi polarons in one-dimensional optical lattices. We find\nquantitative improvements at low temperatures with the inclusion of\ntwo-particle-hole excitations, in both polaron energies and decay rates. Our\nexact theory of Fermi polarons with arbitrary orders of particle-hole\nexcitations might be used to better understand the intriguing polaron dynamical\nresponses in two or three dimensions, whether in free space or within lattices.",
        "positive": "The dynamics of a single trapped ion in a high density media: a\n  stochastic approach: Based on the Langevin equation, a stochastic formulation is implemented to\ndescribe the dynamics of a trapped ion in a bath of ultracold atoms, including\nan excess of micromotion. The ion dynamics is described following a hybrid\nanalytical-numerical approach in which the ion is treated as a classical\nimpurity in a thermal bath. As a result, the ion energy's time evolution and\ndistribution are derived from studying the sympathetic cooling process.\nFurthermore, the ion dynamics under different stochastic noise terms is also\nconsidered to gain information on the bath properties' role in the system's\nenergy transfer processes. Finally, the results obtained from this formulation\nare contrasted with those obtained with a more traditional Monte Carlo\napproach."
    },
    {
        "anchor": "Identifying Quantum Phase Transitions using Artificial Neural Networks\n  on Experimental Data: Machine learning techniques such as artificial neural networks are currently\nrevolutionizing many technological areas and have also proven successful in\nquantum physics applications. Here we employ an artificial neural network and\ndeep learning techniques to identify quantum phase transitions from single-shot\nexperimental momentum-space density images of ultracold quantum gases and\nobtain results, which were not feasible with conventional methods. We map out\nthe complete two-dimensional topological phase diagram of the Haldane model and\nprovide an accurate characterization of the superfluid-to-Mott-insulator\ntransition in an inhomogeneous Bose-Hubbard system. Our work points the way to\nunravel complex phase diagrams of general experimental systems, where the\nHamiltonian and the order parameters might not be known.",
        "positive": "Random spin textures in turbulent spinor Bose-Einstein condensates: We numerically investigate the stationary turbulent states of spin-1\nBose-Einstein condensates under continuous spin driving. We analyze the\nentanglement entropy and magnetization correlation function to demonstrate the\nisotropic nature of the intricate spin texture that is generated in the\nnonequilibrium steady state. We observe a $-7/3$ power-law behavior in the\nspin-dependent interaction energy spectrum. To gain further insight into the\nstatistical properties of the spin texture, we introduce a spin state ensemble\nobtained through position projection, revealing its close resemblance to the\nHaar random ensemble for spin-1 systems. We also present the probability\ndistribution of the spin vector magnitude in the turbulent condensate, which\ncan be tested in experiments. Our numerical study highlights the\ncharacteristics of stationary turbulence in the spinor BEC system and confirms\nprevious experimental findings by Hong et al. [Phys. Rev. A 108, 013318\n(2023)]."
    },
    {
        "anchor": "Finding self-similar behavior in quantum many-body dynamics via\n  persistent homology: Inspired by topological data analysis techniques, we introduce persistent\nhomology observables and apply them in a geometric analysis of the dynamics of\nquantum field theories. As a prototype application, we consider data from a\nclassical-statistical simulation of a two-dimensional Bose gas far from\nequilibrium. We discover a continuous spectrum of dynamical scaling exponents,\nwhich provides a refined classification of nonequilibrium self-similar\nphenomena. A possible explanation of the underlying processes is provided in\nterms of mixing strong wave turbulence and anomalous vortex kinetics components\nin point clouds. We find that the persistent homology scaling exponents are\ninherently linked to the geometry of the system, as the derivation of a packing\nrelation reveals. The approach opens new ways of analyzing quantum many-body\ndynamics in terms of robust topological structures beyond standard field\ntheoretic techniques.",
        "positive": "Dipolar-Induced Resonance for Ultracold Bosons in a Quasi-1D Optical\n  Lattice: We study the role of the Dipolar-Induced Resonance (DIR) in a\nquasi-one-dimensional system of ultracold bosons. We first describe the effect\nof the DIR on two particles in a harmonic trap. Then, we consider a deep\noptical lattice loaded with ultracold dipolar bosons. In order to describe this\nsystem, we introduce a novel atom-dimer extended Bose-Hubbard model, which is\nthe minimal model correctly accounting for the DIR. We analyze the impact of\nthe DIR on the phase diagram at T=0 by exact diagonalization of a small-sized\nsystem. We show that the DIR strongly affects this phase diagram. In\nparticular, we predict the mass density wave to occur in a narrow domain\ncorresponding to weak nearest-neighbor interactions, and the occurrence of a\ncollapse phase for stronger dipolar interactions."
    },
    {
        "anchor": "Negative refraction in the relativistic electron gas: We show that a gas of relativistic electrons is a left-handed material at low\nfrequencies by computing the effective electric permittivity and effective\nmagnetic permeability that appear in Maxwell's equations in terms of the\nresponses appearing in the constitutive relations, and showing that the former\nare both negative below the {\\it same} frequency, which coincides with the\nzero-momentum frequency of longitudinal plasmons. We also show, by explicit\ncomputation, that the photonic mode of the electromagnetic radiation does not\ndissipate energy, confirming that it propagates in the gas with the speed of\nlight in vacuum, and that the medium is transparent to it. We then combine\nthose results to show that the gas has a negative effective index of refraction\n$n_{\\rm eff}=-1$. We illustrate the consequences of this fact for Snell's law,\nand for the reflection and transmission coefficients of the gas.",
        "positive": "Tunneling control in an integrable model for Bose-Einstein Condensate in\n  a triple well potential: In this work we show the simplest and integrable model for Bose-Einstein\ncondensates loaded in a triple well potential where the tunneling between two\nwells can be controlled by the other well showing a behavior similar to an\nelectronic field effect transistor. Using a classical analysis, the Hamilton's\nequation are obtained, a threshold indicating a discontinuous phase transition\nis presented and the classical dynamics is computed. Then, the quantum dynamics\nis investigated using direct diagonalisation. We find well agreement in both\nthese analysis. Based on our results, the switching scheme for tunneling is\nshown and the experimental feasibility is discussed."
    },
    {
        "anchor": "Numerical modeling of exciton-polariton Bose--Einstein condensate in a\n  microcavity: A novel, optimized numerical method of modeling of an exciton-polariton\nsuperfluid in a semiconductor microcavity was proposed. Exciton-polaritons are\nspin-carrying quasiparticles formed from photons strongly coupled to excitons.\nThey possess unique properties, interesting from the point of view of\nfundamental research as well as numerous potential applications. However, their\nnumerical modeling is challenging due to the structure of nonlinear\ndifferential equations describing their evolution. In this paper, we propose to\nsolve the equations with a modified Runge--Kutta method of 4th order, further\noptimized for efficient computations. The algorithms were implemented in form\nof C++ programs fitted for parallel environments and utilizing vector\ninstructions. The programs form the EPCGP suite which have been used for\ntheoretical investigation of exciton-polaritons.",
        "positive": "Pattern Formation in Quantum Ferrofluids: from Supersolids to\n  Superglasses: Pattern formation is a ubiquitous phenomenon observed in nonlinear and\nout-of-equilibrium systems. In equilibrium, quantum ferrofluids formed from\nultracold atoms were recently shown to spontaneously develop coherent density\npatterns, manifesting a supersolid. We theoretically investigate the phase\ndiagram of such quantum ferrofluids in oblate trap geometries and find an even\nwider range of exotic states of matter. Two-dimensional supersolid crystals\nformed from individual ferrofluid quantum droplets dominate the phase diagram\nat low densities. For higher densities we find honeycomb and labyrinthine\nstates, as well as a pumpkin phase. We discuss scaling relations which allow us\nto find these phases for a wide variety of trap geometries, interaction\nstrengths, and atom numbers. Our study illuminates the origin of the various\npossible patterns of quantum ferrofluids and shows that their occurrence is\ngeneric of strongly dipolar interacting systems stabilized by beyond mean-field\neffects."
    },
    {
        "anchor": "Enhancing disorder-free localization through dynamically emergent local\n  symmetries: Disorder-free localization is a recently discovered phenomenon of\nnonergodicity that can emerge in quantum many-body systems hosting gauge\nsymmetries when the initial state is prepared in a superposition of gauge\nsuperselection sectors. Thermalization is then prevented up to all accessible\nevolution times despite the model being nonintegrable and\ntranslation-invariant. In a recent work [Halimeh, Zhao, Hauke, and Knolle,\narXiv:2111.02427], it has been shown that terms linear in the gauge-symmetry\ngenerator stabilize disorder-free localization in $\\mathrm{U}(1)$ gauge\ntheories against gauge errors that couple different superselection sectors.\nHere, we show in the case of $\\mathbb{Z}_2$ gauge theories that disorder-free\nlocalization can not only be stabilized, but also \\textit{enhanced} by the\naddition of translation-invariant terms linear in a local $\\mathbb{Z}_2$\n\\textit{pseudogenerator} that acts identically to the full generator in a\nsingle superselection sector, but not necessarily outside of it. We show\nanalytically and numerically how this leads through the quantum Zeno effect to\nthe dynamical emergence of a renormalized gauge theory with an enhanced local\nsymmetry, which contains the $\\mathbb{Z}_2$ gauge symmetry of the ideal model,\nassociated with the $\\mathbb{Z}_2$ pseudogenerator. The resulting proliferation\nof superselection sectors due to this dynamically emergent gauge theory creates\nan effective disorder greater than that in the original model, thereby\nenhancing disorder-free localization. We demonstrate the experimental\nfeasibility of the $\\mathbb{Z}_2$ pseudogenerator by providing a detailed\nreadily implementable experimental proposal for the observation of\ndisorder-free localization in a Rydberg setup.",
        "positive": "The Massive Goldstone (Higgs) mode in two-dimensional ultracold atomic\n  lattice systems: We discuss how to reveal the massive Goldstone mode, often referred to as the\nHiggs amplitude mode, near the Superfluid-to-Insulator quantum critical point\n(QCP) in a system of two-dimensional ultracold bosonic atoms in optical\nlattices. The spectral function of the amplitude response is obtained by\nanalytic continuation of the kinetic energy correlation function calculated by\nMonte Carlo methods. Our results enable a direct comparison with the recent\nexperiment [M. Endres, T. Fukuhara, D. Pekker, M. Cheneau, P. Schau{\\ss}, C.\nGross, E. Demler, S. Kuhr, and I. Bloch, Nature 487, 454-458 (2012)], and\ndemonstrate a good agreement for temperature shifts induced by lattice\nmodulation. Based on our numerical analysis, we formulate the necessary\nconditions in terms of homogeneity, detuning from the QCP and temperature in\norder to reveal the massive Goldstone resonance peak in spectral functions\nexperimentally. We also propose to apply a local modulation at the trap center\nto overcome the inhomogeneous broadening caused by the parabolic trap\nconfinement."
    },
    {
        "anchor": "Measuring spin correlations in optical lattices using superlattice\n  potentials: We suggest two experimental methods for probing both short- and long-range\nspin correlations of atoms in optical lattices using superlattice potentials.\nThe first method involves an adiabatic doubling of the periodicity of the\nunderlying lattice to probe neighboring singlet (triplet) correlations for\nfermions (bosons) by the occupation of the new vibrational ground state. The\nsecond method utilizes a time-dependent superlattice potential to generate\nspin-dependent transport by any number of prescribed lattice sites, and probes\ncorrelations by the resulting number of doubly occupied sites. For\nexperimentally relevant parameters, we demonstrate how both methods yield large\nsignatures of antiferromagnetic (AF) correlations of strongly repulsive\nfermionic atoms in a single shot of the experiment. Lastly, we show how this\nmethod may also be applied to probe d-wave pairing, a possible ground state\ncandidate for the doped repulsive Hubbard model.",
        "positive": "Inflationary Dynamics and Particle Production in a Toroidal\n  Bose-Einstein Condensate: We present a theoretical study of the dynamics of a Bose-Einstein condensate\n(BEC) trapped inside an expanding toroid that can realize an analogue\ninflationary universe. As the system expands, we find that phonons in the BEC\nundergo redshift and damping due to quantum pressure effects. We predict that\nrapidly expanding toroidal BEC's can exhibit spontaneous particle creation, and\nstudy this phenomenon in the context of an initial coherent state wavefunction.\nWe show how particle creation would be revealed in the atom density and density\ncorrelations, and discuss connections to the cosmological theory of inflation."
    },
    {
        "anchor": "A Hydrodynamical Description of Bose Liquid with Fractional Exclusion\n  Statistics: Hydrodynamical systems are usually taken as chaotic systems with fast\nrelaxations. It is counter intuitive for \"ideal\" gas to have a hydrodynamical\ndescription. We find that a hydrodynamical model of one-dimensional $|\\Phi|^6$\ntheory shares the same ground state density profile, density-wave excitation,\nas well as the similar dynamical and statistical properties with the\nCalogero-Sutherland model in thermodynamic limit when their interaction\nstrengths matches each other. The interaction strength g0 in the\n$|\\Phi|^6$theory is then the index of fractional statistics. Although the model\nis interacting in Bose liquid sense, but it shows integrability with periodical\ncoherent evolution. We also discussed the fractional statistics emerges from\nthe $|\\Phi|^6$ theory.",
        "positive": "Interaction-induced instability and chaos in the photoassociative\n  stimulated Raman adiabatic passage from atomic to molecular Bose-Einstein\n  condensates: We study the effect of interactions on the conversion of atomic -to molecular\nBose-Einstein condensates via stimulated Raman adiabatic passage. Both\nenergetic instability during avoided crossings and dynamical instability during\nchaotic intervals limit adiabaticity and impose {\\em low} sweep-rate boundaries\non the efficiency of the process. For the diabatic traverse of avoided\ncrossings, we find a reciprocal power-law dependence of the final unconverted\npopulation on sweep rate. For the traverse of chaos, we find a sharp low-rate\nboundary determined by the dynamical instability parameters. The interplay of\nthese two mechanisms determines which instability controls the failure of\nmolecular production. A judicious choice of sweep parameters is hence required\nto restore the process efficiency."
    },
    {
        "anchor": "Cooling Atomic Gases With Disorder: Cold atomic gases have proven capable of emulating a number of fundamental\ncondensed matter phenomena including Bose-Einstein condensation, the Mott\ntransition, Fulde-Ferrell-Larkin-Ovchinnikov pairing and the quantum Hall\neffect. Cooling to a low enough temperature to explore magnetism and exotic\nsuperconductivity in lattices of fermionic atoms remains a challenge. We\npropose a method to produce a low temperature gas by preparing it in a\ndisordered potential and following a constant entropy trajectory to deliver the\ngas into a non-disordered state which exhibits these incompletely understood\nphases. We show, using quantum Monte Carlo simulations, that we can approach\nthe Ne\\'el temperature of the three-dimensional Hubbard model for\nexperimentally achievable parameters. Recent experimental estimates suggest the\nrandomness required lies in a regime where atom transport and equilibration are\nstill robust.",
        "positive": "Beyond superfluidity in driven non-equilibrium Bose-Einstein condensates: The phenomenon of superfluidity in open Bose-Einstein condensates (BEC) is\nanalysed numerically and analytically. It is found that a superfluid phase is\nfeasible even above the speed of sound, when forces due to inhomogeneous\nnon-equilibrium processes oppose the contributions of homogeneous processes.\nFurthermore a regime of accelerating impurities can be observed for particular\npumping/decay strategies. All findings are derived within the complex\nGross-Pitaevskii (GP) theory with creation and annihilation terms. Utilising\nthis framework the effective force acting on an impurity as it moves with\nvelocity v through the open condensate can be calculated. The result shows that\nthe force is continuously increasing/decreasing with increasing velocity\nstarting from the state of zero motion at v = 0, a property that can be traced\ndown to the additional homogeneous annihilation/creation term in the extended\nGP model. Our findings stand in stark contrast to the concept of a topological\nphase transition to frictionless flow below a critical velocity as observed for\nequilibrium Bose-Einstein condensates analytically, numerically and for trapped\natoms experimentally."
    },
    {
        "anchor": "Quantum holonomy in Lieb-Liniger model: We examine a parametric cycle in the N-body Lieb-Liniger model that starts\nfrom the free system and goes through Tonks-Girardeau and super-Tonks-Girardeau\nregimes and comes back to the free system. We show the existence of exotic\nquantum holonomy, whose detailed workings are analysed with the specific sample\nof two- and three body systems. The classification of eigenstates based on\nclustering structure naturally emerges from the analysis.",
        "positive": "Observation of Four-body Ring-exchange Interactions and Anyonic\n  Fractional Statistics: Ring exchange is an elementary interaction for modeling unconventional\ntopological matters which hold promise for efficient quantum information\nprocessing. We report the observation of four-body ring-exchange interactions\nand the topological properties of anyonic excitations within an ultracold atom\nsystem. A minimum toric code Hamiltonian in which the ring exchange is the\ndominant term, was implemented by engineering a Hubbard Hamiltonian that\ndescribes atomic spins in disconnected plaquette arrays formed by two\northogonal superlattices. The ring-exchange interactions were resolved from the\ndynamical evolutions in the spin orders, matching well with the predicted\nenergy gaps between two anyonic excitations of the spin system. A braiding\noperation was applied to the spins in the plaquettes and an induced phase\n$1.00(3)\\pi$ in the four-spin state was observed, confirming\n$\\frac{1}{2}$-anynoic statistics. This work represents an essential step\ntowards studying topological matters with many-body systems and the\napplications in quantum computation and simulation."
    },
    {
        "anchor": "Exact spectral function of a Tonks-Girardeau gas in a lattice: The single-particle spectral function of a strongly correlated system is an\nessential ingredient to describe its dynamics and transport properties. We\ndevelop a general method to calculate the exact spectral function of a strongly\ninteracting one-dimensional Bose gas in the Tonks-Girardeau regime, valid for\nany type of confining potential, and apply it to bosons on a lattice to obtain\nthe full spectral function, at all energy and momentum scales. We find that it\ndisplays three main singularity lines. The first two can be identified as the\nanalogs of Lieb-I and Lieb-II modes of a uniform fluid; the third one, instead,\nis specifically due to the presence of the lattice. We show that the spectral\nfunction displays a power-law behaviour close to the Lieb-I and Lieb-II\nsingularities, as predicted by the non-linear Luttinger liquid description, and\nobtain the exact exponents. In particular, the Lieb-II mode shows a divergence\nin the spectral function, differently from what happens in the dynamical\nstructure factor, thus providing a route to probe it in experiments with\nultracold atoms.",
        "positive": "Universal thermodynamics of an SU($N$) Fermi-Hubbard Model: The SU(2) symmetric Fermi-Hubbard model (FHM) plays an essential role in\nstrongly correlated fermionic many-body systems. In the one particle per site\nand strongly interacting limit ${U/t \\gg 1}$, it is effectively described by\nthe Heisenberg Hamiltonian. In this limit, enlarging the spin and extending the\ntypical SU(2) symmetry to SU($N$) has been predicted to give exotic phases of\nmatter in the ground state, with a complicated dependence on $N$. This raises\nthe question of what -- if any -- are the finite-temperature signatures of\nthese phases, especially in the currently experimentally relevant regime near\nor above the superexchange energy. We explore this question for thermodynamic\nobservables by numerically calculating the thermodynamics of the SU($N$) FHM in\nthe two-dimensional square lattice near densities of one particle per site,\nusing determinant Quantum Monte Carlo and Numerical Linked Cluster Expansion.\nInterestingly, we find that for temperatures above the superexchange energy,\nwhere the correlation length is short, the energy, number of on-site pairs, and\nkinetic energy are universal functions of $N$. Although the physics in the\nregime studied is well beyond what can be captured by low-order\nhigh-temperature series, we show that an analytic description of the scaling is\npossible in terms of only one- and two-site calculations."
    },
    {
        "anchor": "Proposal for simulating quantum spin models with Dzyaloshinskii-Moriya\n  interaction using Rydberg atoms, and construction of asymptotic quantum\n  many-body scar states: We propose a method to realize tunable quantum spin models with\nDzyaloshinskii-Moriya interaction (DMI) in Rydberg atom quantum simulators. Our\nscheme uses a two-photon Raman transition and transformation to the\nspin-rotating frame. We investigate the properties of the model including only\nthe DMI and Zeeman energy, which can be experimentally realized in our scheme.\nWe show that the model accommodates exact and asymptotic quantum many-body\nscars exhibiting nonergodic dynamics.",
        "positive": "Observation of Bose-Einstein Condensation of Dipolar Molecules: Ensembles of particles governed by quantum mechanical laws exhibit\nfascinating emergent behavior. Atomic quantum gases, liquid helium, and\nelectrons in quantum materials all show distinct properties due to their\ncomposition and interactions. Quantum degenerate samples of bosonic dipolar\nmolecules promise the realization of novel phases of matter with tunable\ndipolar interactions and new avenues for quantum simulation and quantum\ncomputation. However, rapid losses, even when reduced through collisional\nshielding techniques, have so far prevented cooling to a Bose-Einstein\ncondensate (BEC). In this work, we report on the realization of a BEC of\ndipolar molecules. By strongly suppressing two- and three-body losses via\nenhanced collisional shielding, we evaporatively cool sodium-cesium (NaCs)\nmolecules to quantum degeneracy. The BEC reveals itself via a bimodal\ndistribution and a phase-space-density exceeding one. BECs with a condensate\nfraction of 60(10) % and a temperature of 6(2) nK are created and found to be\nstable with a lifetime close to 2 seconds. This work opens the door to the\nexploration of dipolar quantum matter in regimes that have been inaccessible so\nfar, promising the creation of exotic dipolar droplets, self-organized crystal\nphases, and dipolar spin liquids in optical lattices."
    },
    {
        "anchor": "Quantum quench dynamics of tilted dipolar bosons in 2D optical lattices: We investigate the quench dynamics of the dipolar bosons in two dimensional\noptical lattice of square geometry using the time dependent Gutzwiller method.\nThe system exhibits different density orders like the checkerboard and the\nstriped pattern, depending upon the polarization angle of the dipoles. We\nquench the hopping parameter across the striped density wave (SDW) to striped\nsupersolid (SSS) phase transition, and obtain the scaling laws for the\ncorrelation length and topological vortex density, as function of the quench\nrate. The results are reminiscent of the Kibble-Zurek mechanism (KZM). We also\ninvestigate the dynamics from the striped supersolid phase to the checkerboard\nsupersolid phase, obtained by quenching the dipole tilt angle $\\theta$. This is\na first order structural quantum phase transition, and we study the\nnon-equilibrium dynamics from the perspective of the KZM. In particular, we\nfind the number of the domains with checkerboard order follows a power law\nscaling with the quench rate. This indicates the applicability of the KZM to\nthis first order quantum phase transition.",
        "positive": "Stability and decay of Bloch oscillations in presence of time-dependent\n  nonlinearity: We consider Bloch oscillations of Bose-Einstein condensates in presence of a\ntime-modulated s-wave scattering length. Generically, interaction leads to\ndephasing and decay of the wave packet. Based on a cyclic-time argument, we\nfind---additionally to the linear Bloch oscillation and a rigid soliton\nsolution---an infinite family of modulations that lead to a periodic time\nevolution of the wave packet. In order to quantitatively describe the dynamics\nof Bloch oscillations in presence of time-modulated interactions, we employ two\ncomplementary methods: collective-coordinates and the linear stability analysis\nof an extended wave packet. We provide instructive examples and address the\nquestion of robustness against external perturbations."
    },
    {
        "anchor": "Mesoscopic spin transport between strongly interacting Fermi gases: We investigate a mesoscopic spin current for strongly interacting Fermi gases\nthrough a quantum point contact. Under the situation where spin polarizations\nin left and right reservoirs are same in magnitude but opposite in sign, we\ncalculate the contribution of quasiparticles to the current by means of the\nlinear response theory and many-body $T$-matrix approximation. For a small\nspin-bias regime, the current in the vicinity of the superfluid transition\ntemperature is strongly suppressed due to the formation of pseudogaps. For a\nlarge spin-bias regime where the gases become highly polarized, on the other\nhand, the current is affected by the enhancement of a minority density of\nstates due to Fermi polarons. We also discuss the broadening of a quasiparticle\npeak associated with an attractive polaron at a large momentum, which is\nrelevant to the enhancement.",
        "positive": "Anderson localization of matter waves in tailored disordered potentials: We show that, in contrast to immediate intuition, Anderson localization of\nnoninteracting particles induced by a disordered potential in free space can\nincrease (i.e., the localization length can decrease) when the particle energy\nincreases, for appropriately tailored disorder correlations. We predict the\neffect in one, two, and three dimensions, and propose a simple method to\nobserve it using ultracold atoms placed in optical disorder. The increase of\nlocalization with the particle energy can serve to discriminate quantum versus\nclassical localization."
    },
    {
        "anchor": "Momentum distribution of a dilute unitary Bose gas with three-body\n  losses: Using Boltzmann's equation, we study the effect of three-body losses on the\nmomentum distribution of a homogeneous unitary Bose gas in the dilute limit\nwhere quantum correlations are negligible. We calculate the momentum\ndistribution of the gas and show that inelastic collisions are quantitatively\nas important as a second order virial correction.",
        "positive": "Manipulating atom-number distributions and detecting spatial\n  distributions in lattice-confined spinor gases: We present an experimental study demonstrating the manipulation of\natom-number distributions of spinor gases after nonequilibrium quantum quenches\nacross superfluid to Mott-insulator phase transitions in cubic optical\nlattices. Our data indicate that atom distributions in individual Mott lobes\ncan be tuned by properly designing quantum quench sequences, which suggests\nmethods of maximizing the fraction of atoms in Mott lobes of even occupation\nnumbers and has applications in attaining different quantum magnetic phases\nincluding massively entangled states. Spatial distributions of gases in\nthree-dimensional lattices are derived from the observed number distributions,\nwhich reveal complex spatial dynamics during the quantum quenches. Qualitative\nagreements are also found between our experimental data and numerical\nsimulations based on time-dependent Gutzwiller approximations in\ntwo-dimensional systems."
    },
    {
        "anchor": "Tuning the Tricritical Point with Spin-orbit Coupling in Polarized\n  Fermionic Condensates: We investigate a two-component atomic Fermi gas with population imbalance in\nthe presence of Rashba-type spin-orbit coupling (SOC). As a competition between\nSOC and population imbalance, the finite-temperature phase diagram reveals a\nlarge varieties of new features, including the expanding of the superfluid\nstate regime and the shrinking of both the phase separation and the normal\nregimes. For sufficiently strong SOC, the phase separation region disappears,\ngiving way to the superfluid state. We find that the tricritical point moves\ntoward regime of low temperature, high magnetic field, and high polarization as\nthe SOC increases.",
        "positive": "Drag in Bose-Fermi Mixtures: We use kinetic theory to model the dynamics of a small Bose condensed cloud\nof heavy particles moving through a larger degenerate Fermi gas of light\nparticles. Varying the Bose-Fermi interaction, we find a crossover between bulk\nand surface dominated regimes -- where scattering occurs throughout the Bose\ncloud, or solely on the surface. We calculate the damping and frequency shift\nof the dipole mode in a harmonic trap as a function of the magnetic field\ncontrolling an inter-species Feshbach resonance. We find excellent agreement\nbetween our stochastic model and the experimental studies of Cs-Li mixtures."
    },
    {
        "anchor": "Tuning linear response dynamics near the Dirac points in the bosonic\n  Mott insulator: Optical lattice systems offer the possibility of creating and tuning Dirac\npoints which are present in the tight-binding lattice dispersions. For example,\nsuch a behavior can be achieved in the staggered flux lattice or honeycomb type\nof lattices. Here we focus on the strongly correlated bosonic dynamics in the\nvicinity of Dirac points. In particular, we investigate bosonic Mott insulator\nphase in which quasiparticle excitations have a simple particle-hole\ninterpretation. We show that linear response dynamics around Dirac points, can\nbe significantly engineered at least in two ways: by the type of external\nperturbation or by changing the lattice properties. The key role is played by\nthe interband transitions. Moreover, we explain that the behavior of these\ntransitions is directly connected to different energy scales of the effective\nhopping amplitudes for particles and holes. Presented in this work theoretical\nstudy about tunability of linear response dynamics near the Dirac points can be\ndirectly simulated in the optical lattice systems.",
        "positive": "Inelastic collision dynamics of a single cold ion immersed in a\n  Bose-Einstein condensate: We investigate inelastic collision dynamics of a single cold ion in a\nBose-Einstein condensate. We observe rapid ion-atom-atom three-body\nrecombination leading to formation of weakly bound molecular ions followed by\nsecondary two-body molecule-atom collisions quenching the rovibrational states\ntowards deeper binding energies. In contrast to previous studies exploiting\nhybrid ion traps, we work in an effectively field-free environment and generate\na free low-energy ionic impurity directly from the atomic ensemble via Rydberg\nexcitation and ionization. This allows us to implement an energy-resolved\nfield-dissociation technique to trace the relaxation dynamics of the\nrecombination products. Our observations are in good agreement with numerical\nsimulations based on Langevin capture dynamics and provide complementary means\nto study stability and reaction dynamics of ionic impurities in ultracold\nquantum gases."
    },
    {
        "anchor": "Persistent currents in a two-component Bose-Einstein condensate confined\n  in a ring potential: We present variational and numerical solutions for the problem of stability\nof persistent currents in a two-component Bose-Einstein condensate of\ndistinguishable atoms which rotate in a ring potential. We consider the general\nclass of solutions of constant density in the two components separately, thus\nproviding an alternative approach of the solution of the same problem given\nrecently by Zhigang Wu and Eugene Zaremba [Phys. Rev. A {\\bf 88}, 063640\n(2013)]. Our approach provides a physically transparent solution of this\ndelicate problem. Finally, we give a unified and simple picture of the\nlowest-energy state of the system for large values of the coupling.",
        "positive": "Quantum spin dynamics of individual neutral impurities coupled to a\n  Bose-Einstein condensate: We report on spin dynamics of individual, localized neutral impurities\nimmersed in a Bose-Einstein condensate. Single Cesium atoms are transported\ninto a cloud of Rubidium atoms, thermalize with the bath, and the ensuing\nspin-exchange between localized impurities with quasi-spin $F_i=3$ and bath\natoms with $F_b=1$ is resolved. Comparing our data to numerical simulations of\nspin dynamics we find that, for gas densities in the BEC regime, the dynamics\nis dominated by the condensed fraction of the cloud. We spatially resolve the\ndensity overlap of impurities and gas by the spin-population of impurities.\nFinally we trace the coherence of impurities prepared in a coherent\nsuperposition of internal states when coupled to a gas of different densities.\nFor our choice of states we show that, despite high bath densities and thus\nfast thermalization rates, the impurity coherence is not affected by the bath,\nrealizing a regime of sympathetic cooling while maintaining internal state\ncoherence. Our work paves the way toward non-destructive probing of quantum\nmany-body systems via localized impurities."
    },
    {
        "anchor": "Interaction-induced Bloch Oscillation in a Harmonically Trapped and\n  Fermionized Quantum Gas in One Dimension: Motivated by a recent experiment by F. Meinert et al, arxiv:1608.08200, we\nstudy the dynamics of an impurity moving in the background of a harmonically\ntrapped one-dimensional Bose gas in the hard-core limit. We show that due to\nthe hidden \"lattice\" structure of background bosons, the impurity effectively\nfeels a quasi-periodic potential via impurity-boson interactions that can drive\nthe Bloch oscillation under an external force, even in the absence of real\nlattice potentials. Meanwhile, the inhomogeneous density of trapped bosons\nimposes an additional harmonic potential to the impurity, resulting in a\nsimilar oscillation dynamics but with different periods and amplitudes. We show\nthat the sign and the strength of impurity-boson coupling can significantly\naffect above two potentials so as to determine the impurity dynamics.",
        "positive": "Bose-Einstein condensation in multilayers: The critical BEC temperature $T_{c}$ of a non interacting boson gas in a\nlayered structure like those of cuprate superconductors is shown to have a\nminimum $T_{c,m}$, at a characteristic separation between planes $a_{m}$. It is\nshown that for $a<a_{m}$, $T_{c}$ increases monotonically back up to the ideal\nBose gas $T_{0}$ suggesting that a reduction in the separation between planes,\nas happens when one increases the pressure in a cuprate, leads to an increase\nin the critical temperature. For finite plane separation and penetrability the\nspecific heat as a function of temperature shows two novel crests connected by\na ridge in addition to the well-known BEC peak at $T_{c}$ associated with the\n3D behavior of the gas. For completely impenetrable planes the model reduces to\nmany disconnected infinite slabs for which just one hump survives becoming a\npeak only when the slab widths are infinite."
    },
    {
        "anchor": "Collective spin modes of a trapped quantum ferrofluid: We report on the observation of a collective spin mode in a spinor\nBose-Einstein condensate. Initially, all spins point perpendicular to the\nexternal magnetic field. The lowest energy mode consists in a sinusoidal\noscillation of the local spin around its original axis, with an oscillation\namplitude that linearly depends on the spatial coordinates. The frequency of\nthe oscillation is set by the zero-point kinetic energy of the BEC. The\nobservations are in excellent agreement with hydrodynamic equations. The\nobserved spin mode has a universal character, independent of the atomic spin\nand spin-dependent contact interactions.",
        "positive": "Realizing one-dimensional topological superfluids with ultracold atomic\n  gases: We propose an experimental implementation of a topological superfluid with\nultracold fermionic atoms. An optical superlattice is used to juxtapose a 1D\ngas of fermionic atoms and a 2D conventional superfluid of condensed Feshbach\nmolecules. The latter acts as a Cooper pair reservoir and effectively induces a\nsuperfluid gap in the 1D system. Combined with a spin-dependent optical lattice\nalong the 1D tube and laser-induced atom tunneling, we obtain a topological\nsuperfluid phase. In the regime of weak couplings to the molecular fl eld and\nfor a uniform gas the atomic system is equivalent to Kitaev's model of a p-wave\nsuperfluid. Using a numerical calculation we show that the topological\nsuperfluidity is robust beyond the perturbative limit and in the presence of a\nharmonic trap. Finally we describe how to investigate some physical properties\nof the Majorana fermions located at the topological superfluid boundaries. In\nparticular we discuss how to prepare and detect a given Majorana edge state."
    },
    {
        "anchor": "Emulating Solid-State Physics with a Hybrid System of Ultracold Ions and\n  Atoms: We propose and theoretically investigate a hybrid system composed of a\ncrystal of trapped ions coupled to a cloud of ultracold fermions. The ions form\na periodic lattice and induce a band structure in the atoms. This system\ncombines the advantages of scalability and tunability of ultracold atomic\nsystems with the high fidelity operations and detection offered by trapped ion\nsystems. It also features close analogies to natural solid-state systems, as\nthe atomic degrees of freedom couple to phonons of the ion lattice, thereby\nemulating a solid-state system. Starting from the microscopic many-body\nHamiltonian, we derive the low energy Hamiltonian including the atomic band\nstructure and give an expression for the atom-phonon coupling. We discuss\npossible experimental implementations such as a Peierls-like transition into a\nperiod-doubled dimerized state.",
        "positive": "Dynamics of Uniform Quantum Gases, II: Magnetic Susceptibility: A general expression for temperature-dependent magnetic susceptibility of\nquantum gases composed of particles possessing both charge and spin degrees of\nfreedom has been obtained within the framework of the generalized random-phase\napproximation. The conditions for the existence of dia-, para-, and\nferro-magnetism have been analyzed in terms of a parameter involving\nsingle-particle charge and spin. The zero-temperature limit retrieves the\nexpressions for the Landau and the Pauli susceptibilities for an electron gas.\nIt is found for a Bose gas that on decreasing the temperature, it passes either\nthrough a diamagnetic incomplete Meissner-effect regime or through a\nparamagnetic-ferromagnetic large magnetization fluctuation regime before going\nto the Meissner phase at BEC critical temperature."
    },
    {
        "anchor": "Ultra-cold bosons in zig-zag optical lattices: Ultra-cold bosons in zig-zag optical lattices present a rich physics due to\nthe interplay between frustration, induced by lattice geometry, two-body\ninteraction and three-body constraint. Unconstrained bosons may develop chiral\nsuperfluidity and a Mott-insulator even at vanishingly small interactions.\nBosons with a three-body constraint allow for a Haldane-insulator phase in\nnon-polar gases, as well as pair-superfluidity and density wave phases for\nattractive interactions. These phases may be created and detected within the\ncurrent state of the art techniques.",
        "positive": "Effect of three-body loss on itinerant ferromagnetism in an atomic Fermi\n  gas: A recent experiment has provided the first evidence for itinerant\nferromagnetism in an ultracold atomic gas of fermions with repulsive\ninteractions. However, the gas in this regime is also subject to significant\nthree-body loss. We adopt an extended Hertz-Millis theory to account for the\neffect of loss on the transition and on the ferromagnetic state. We find that\nthe losses damp quantum fluctuations and thereby significantly increase the\ncritical interaction strength needed to induce ferromagnetism. This effect may\nresolve a discrepancy between the experiment and previous theoretical\npredictions of the critical interaction strength. We further illuminate the\nimpact of loss by studying the collective spin excitations in the ferromagnet.\nEven in the fully polarized state, where loss is completely suppressed, spin\nwaves acquire a decay rate proportional to the three-body loss coefficient."
    },
    {
        "anchor": "Simulating the Berezinskii-Kosterlitz-Thouless Transition with Complex\n  Langevin: Numerical simulations of the full quantum properties of interacting many-body\nsystems by means of field-theoretic Monte-Carlo techniques are often limited\ndue to a sign problem. Here we simulate properties of a dilute two-dimensional\nBose gas in the vicinity of the Berezinskii-Kosterlitz-Thouless (BKT)\ntransition by means of the Complex Langevin (CL) algorithm, thereby extending\nour previous CL study of the three-dimensional Bose gas to the\nlower-dimensional case. The purpose of the paper is twofold. On the one hand,\nit adds to benchmarking of the CL method and thus contributes to further\nexploring the range of applicability of the method. With the respective\nresults, the universality of the equation of state is recovered, as well as the\nlong-wave-length power-law dependence of the single-particle momentum spectrum\nbelow the BKT transition. Analysis of the rotational part of the current\ndensity corroborates vortex unbinding in crossing the transition. Beyond these\nmeasures of consistency we compute quantum corrections to the critical density\nand chemical potential in the weakly coupled regime. Our results show a shift\nof these quantities to lower values as compared to those obtained from\nclassical field theory. It points in the opposite direction as compared to the\nshift of the critical density found by means of the path-integral Monte-Carlo\nmethod at larger values of the coupling. Our simulations widen the perspective\nfor precision comparisons with experiment.",
        "positive": "Topological charge pumping in spin-dependent superlattices with glide\n  symmetry: Topological charge pumping represents an important quantum phenomenon that\nshows the fundamental connection to the topological properties of dynamical\nsystems. Here, we introduce a pumping process in a spin-dependent double-well\noptical lattice with glide symmetry. In the dynamic process, the glide symmetry\nprotects the band touching points and topological properties of the system are\ncharacterised by the non-Abelian Berry curvature. By engineering suitable form\nof interaction between different spin components, the model not only\ndemonstrates topological phase transition, but also shows hybridisation between\nthe spatial and temporal domain with novel topological features captured by the\nWilson line along the synthetic directions. Our work provides a new model based\non ultracold atoms towards the implementation of versatile topological matters\nand topological phenomena."
    },
    {
        "anchor": "Realistic Time-Reversal Invariant Topological Insulators With Neutral\n  Atoms: We lay out an experiment to realize time-reversal invariant topological\ninsulators in alkali atomic gases. We introduce an original method to\nsynthesize a gauge field in the near-field of an atom-chip, which effectively\nmimics the effects of spin-orbit coupling and produces quantum spin-Hall\nstates. We also propose a feasible scheme to engineer sharp boundaries where\nthe hallmark edge states are localized. Our multi-band system has a large\nparameter space exhibiting a variety of quantum phase transitions between\ntopological and normal insulating phases. Due to their remarkable versatility,\ncold-atom systems are ideally suited to realize topological states of matter\nand drive the development of topological quantum computing.",
        "positive": "Phonon instability and self-organized structures in multi-layer stacks\n  of confined dipolar Bose-Einstein condensates in optical lattices: In calculations to date [1,2] of multi-layer stacks of dipolar condensates,\ncreated in one-dimensional optical lattices, the condensates have been assumed\nto be two-dimensional. In a real experiment, however, the condensates do not\nextend to infinity in the oblate direction, but have to be confined by a trap\npotential, too. By three-dimensional numerical simulations of this realistic\nexperimental situation we find a crucial dependence of the phonon instability\nboundary on the number of layers. Moreover, near the boundary of the phonon\ninstability, a variety of structured ground-state wave functions emerges, which\nmay indicate the onset of a roton instability [3,4]."
    },
    {
        "anchor": "Heat and spin transport in a cold atomic Fermi gas: Motivated by recent experiments measuring the spin transport in ultracold\nunitary atomic Fermi gases (Sommer et al., 2011; Sommer et al., 2011), we\nexplore the theory of spin and heat transport in a three-dimensional\nspin-polarized atomic Fermi gas. We develop estimates of spin and thermal\ndiffusivities and discuss magnetocaloric effects, namely the the spin Seebeck\nand spin Peltier effects. We estimate these transport coefficients using a\nBoltzmann kinetic equation in the classical regime and present experimentally\naccessible signatures of the spin Seebeck effect. We study an exactly solvable\nmodel that illustrates the role of momentum-dependent scattering in the\nmagnetocaloric effects.",
        "positive": "Discrete time crystals in Bose-Einstein Condensates and\n  symmetry-breaking edge in a simple two-mode theory: Discrete time crystals (DTCs) refer to a novel many-body steady state that\nspontaneously breaks the discrete time-translational symmetry in a\nperiodically-driven quantum system. Here, we study DTCs in a Bose-Einstein\ncondensate (BEC) bouncing resonantly on an oscillating mirror, using a two-mode\nmodel derived from a standard quantum field theory. We investigate the validity\nof this model and apply it to study the long-time behavior of our system. A\nwide variety of initial states based on two Wannier modes are considered. We\nfind that in previous studies the investigated phenomena in the evolution\ntime-window ($\\lessapprox$2000 driving periods) are actually \"short-time\"\ntransient behavior though DTC formation signaled by the sub-harmonic responses\nis still shown if the inter-boson interaction is strong enough. After a much\nlonger (about 20 times) evolution time, initial states with no \"long-range\"\ncorrelations relax to a steady state, where time-symmetry breaking can be\nunambiguously defined. Quantum revivals also eventually occur. This long-time\nbehavior can be understood via the many-body Floquet quasi-eigenenergy spectrum\nof the two-mode model. A symmetry-breaking edge for DTC formation appears in\nthe spectrum for strong enough interaction, where all quasi-eigenstates below\nthe edge are symmetry-breaking while those above the edge are symmetric. The\nlate-time steady state's time-translational symmetry depends solely on whether\nthe initial energy is above or below the symmetry-breaking edge. A phase\ndiagram showing regions of symmetry-broken and symmetric phases for differing\ninitial energies and interaction strengths is presented. We find that according\nto this two-mode model, the discrete time crystal survives for times out to at\nleast 250,000 driving periods."
    },
    {
        "anchor": "Chemistry of a light impurity in a Bose-Einstein condensate: In ultracold atomic gases, a unique interplay arises between phenomena known\nfrom condensed matter physics, few-body physics and chemistry. Similar to an\nelectron in a solid, an impurity in an ultracold gas can get dressed by\nexcitations from the medium, forming a quasiparticle called the polaron. We\nstudy how dressing of an impurity leads to a modification of its chemical\nreactivity. Using a Gaussian state variational method in the frame of the\nimpurity, we demonstrate that three-body correlations lead to an instability of\nthe polaron. This instability is connected to an Efimov resonance, but shifted\nto smaller interactions by many-body effects, showing that polaron formation\nstimulates Efimov physics and the associated chemistry.",
        "positive": "Weakly interacting disordered Bose gases out of equilibrium: from\n  multiple scattering to superfluidity: We explore the quench dynamics of a two-dimensional, weakly interacting\ndisordered Bose gas for various relative strengths of interactions and\ndisorder. This allows us to identify two well distinct out-of-equilibrium\nregimes. When interactions are smaller than the disorder, the gas experiences\nmultiple scattering and exhibits a short-range spatial coherence. At short time\nthis coherence is only smoothly affected by interactions, via a diffusion\nprocess of the particles' energies. When interactions are larger than the\ndisorder, scattering ceases and the gas behaves more and more like a fluid,\nultimately like a superfluid at low energy. In the superfluid regime, the gas\nexhibits a long-range algebraic coherence, characteristic of a pre-thermal\nregime in disorder."
    },
    {
        "anchor": "Three interacting atoms in a one-dimensional trap: A benchmark system\n  for computational approaches: We provide an accurate calculation of the energy spectrum of three atoms\ninteracting through a contact force in a one-dimensional harmonic trap,\nconsidering both spinful fermions and spinless bosons. We use fermionic\nenergies as a benchmark for exact-diagonalization technique (also known as full\nconfiguration interaction), which is found to slowly converge in the case of\nstrong interatomic attraction.",
        "positive": "Properties of phonon modes of ion trap quantum computer in the Aubry\n  phase: We study analytically and numerically the properties of phonon modes in an\nion quantum computer. The ion chain is placed in a harmonic trap with an\nadditional periodic potential which dimensionless amplitude $K$ determines\nthree main phases available for quantum computations: at zero $K$ we have the\ncase of Cirac-Zoller quantum computer, below a certain critical amplitude\n$K<K_c$ the ions are in the Kolmogorov-Arnold-Moser (KAM) phase, with\ndelocalized phonon modes and free chain sliding, and above the critical\namplitude $K>K_c$ ions are in the pinned Aubry phase with a finite frequency\ngap protecting quantum gates from temperature and other external fluctuations.\nFor the Aubry phase, in contrast to the Cirac-Zoller and KAM phases, the phonon\ngap remains independent of the number of ions placed in the trap keeping a\nfixed ion density around the trap center. We show that in the Aubry phase the\nphonon modes are much better localized comparing to the Cirac-Zoller and KAM\ncases. Thus in the Aubry phase the recoil pulses lead to local oscillations of\nions while in other two phases they spread rapidly over the whole ion chains\nmaking them rather sensible to external fluctuations. We argue that the\nproperties of localized phonon modes and phonon gap in the Aubry phase provide\nadvantages for the ion quantum computations in this phase with a large number\nof ions."
    },
    {
        "anchor": "Ultracold bosons in the vicinity of a narrow resonance: shallow dimer\n  and recombination: The different resonant regimes that can be achieved by using a magnetic\nFeshbach resonance are analyzed with a separable two-channel model. Emphasis is\nput on the case of narrow resonances in a region of intermediate detuning where\na shallow dimer exists and an approximate law including the background\nscattering length for the three-body recombination rate is derived.",
        "positive": "Cluster stability driven by quantum fluctuations: By means of an accurate path-integral Monte Carlo we investigate a\ntwo-dimensional ensemble of particles interacting via a\nLifshitz-Petrich-Gaussian potential. In particular, analysing structures\ndescribed by a commensurate ratio between the two wave numbers that mark the\npattern, the Lifshitz-Petrich-Gaussian boson model may display a stable and\nwell-defined stripe phase lacking any global phase coherence but featuring a\nsuperfluid signal along the stripe direction only. Upon increasing quantum\nfluctuations and quantum-mechanical exchange of bosons, the double-degeneration\nof the negative minima in the Fourier transform of the potential is removed at\nthe expense of a density modulation peculiar to a cluster triangular crystal.\nWe also show that this last structure possess all features adhering to the\ndefinition of a supersolid phase."
    },
    {
        "anchor": "Observation of Fermi surface deformation in a dipolar quantum gas: The deformation of a Fermi surface is a fundamental phenomenon leading to a\nplethora of exotic quantum phases. Understanding these phases, which play\ncrucial roles in a wealth of systems, is a major challenge in atomic and\ncondensed-matter physics. Here, we report on the observation of a Fermi surface\ndeformation in a degenerate dipolar Fermi gas of erbium atoms. The deformation\nis caused by the interplay between strong magnetic dipole-dipole interaction\nand the Pauli exclusion principle. We demonstrate the many-body nature of the\neffect and its tunability with the Fermi energy. Our observation provides basis\nfor future studies on anisotropic many-body phenomena in normal and superfluid\nphases.",
        "positive": "Experimental Evidence for Inhomogeneous-Pumping and Energy-Dependent\n  Effects in Photon Bose-Einstein Condensation: Light thermalised at room temperature in an optically pumped, dye-filled\nmicrocavity resembles a model system of non-interacting Bose-Einstein\ncondensation in the presence of dissipation. We have experimentally\ninvestigated some of the steady-state properties of this unusual state of light\nand found features which do not match the available theoretical descriptions.\nWe have seen that the critical pump power for condensation depends on the pump\nbeam geometry, being lower for smaller pump beams. Far below threshold, both\nintracavity photon number and thermalised photon cloud size depend on pump beam\nsize, with optimal coupling when pump beam matches the thermalised cloud size.\nWe also note that the critical pump power for condensation depends on the\ncavity cutoff wavelength and longitudinal mode number, which suggests that\nenergy-dependent thermalisation and loss mechanisms are important."
    },
    {
        "anchor": "Mesoscopic superpositions of Tonks-Girardeau states and the Bose-Fermi\n  mapping: We study a one dimensional gas of repulsively interacting ultracold bosons\ntrapped in a double-well potential as the atom-atom interactions are tuned from\nzero to infinity. We concentrate on the properties of the excited states which\nevolve from the so-called NOON states to the NOON Tonks-Girardeau states. The\nrelation between the latter and the Bose-Fermi mapping limit is explored. We\nstate under which conditions NOON Tonks-Girardeau states, which are not\npredicted by the Bose-Fermi mapping, will appear in the spectrum.",
        "positive": "Momentum-space atom correlations in a Mott insulator: We report on the investigation of the three-dimensional single-atom-resolved\ndistributions of bosonic Mott insulators in momentum-space. Firstly, we measure\nthe two-body and three-body correlations deep in the Mott regime, finding a\nperfectly contrasted bunching whose periodicity reproduces the reciprocal\nlattice. In addition, we show that the two-body correlation length is inversely\nproportional to the in-trap size of the Mott state with a pre-factor in\nagreement with the prediction for an incoherent state occupying a uniformly\nfilled lattice. Our findings indicate that the momentum-space correlations of a\nMott insulator at small tunnelling is that of a many-body ground-state with\nGaussian statistics. Secondly, in the Mott insulating regime with increasing\ntunnelling, we extract the spectral weight of the quasi-particles from the\nmomentum density profiles. On approaching the transition towards a superfluid,\nthe momentum spread of the spectral weight is found to decrease as a result of\nthe increased mobility of the quasi-particles in the lattice. While the shapes\nof the observed spectral weight agree with the ones predicted by perturbative\nmany-body calculations, the fitted mobilities are larger than the theoretical\nones. This discrepancy is similar to that previously reported on the\ntime-of-flight visibility."
    },
    {
        "anchor": "Spin and charge modulations in a single hole doped Hubbard ladder --\n  verification with optical lattice experiments: We show that pronounced modulations in spin and charge densities can be\ninduced by the insertion of a single hole in an otherwise half-filled 2-leg\nHubbard ladder. Accompanied with these modulations is a loosely bound structure\nof the doped charge with a spin-1/2, in contrast to the tightly bound case\nwhere such modulations are absent. These behaviors are caused by the\ninterference of the Berry phases associated a string of flipped spins (or\n\"phase strings\") left behind as a hole travels through a spin bath with a\nshort-range anti-ferromagnetic order. The key role of the phase strings is also\nreflected in how the system respond to increasing spin polarization, increasing\nthe on-site repulsion, addition of a second hole, and increasing asymmetry\nbetween intra- and inter-chain hopping. Remarkably, all these properties\npersist down to ladders as short as $\\sim 10$ sites. They can therefore be\nstudied in cold atom experiments using the recently developed fermion\nmicroscope.",
        "positive": "Impurity in a Bose-Einstein condensate and the Efimov effect: We investigate the zero-temperature properties of an impurity particle\ninteracting with a Bose-Einstein condensate (BEC), using a variational\nwavefunction that includes up to two Bogoliubov excitations of the BEC. This\nallows one to capture three-body Efimov physics, as well as to recover the\nfirst non-trivial terms in the weak-coupling expansion. We show that the energy\nand quasiparticle residue of the dressed impurity (polaron) are significantly\nlowered by three-body correlations, even for weak interactions where there is\nno Efimov trimer state in a vacuum. For increasing attraction between the\nimpurity and the BEC, we observe a smooth crossover from atom to Efimov trimer,\nwith a superposition of states near the Efimov resonance. We furthermore\ndemonstrate that three-body loss does not prohibit the experimental observation\nof these effects. Our results thus suggest a route to realizing Efimov physics\nin a stable quantum many-body system for the first time."
    },
    {
        "anchor": "Relaxation of a high-energy quasiparticle in a one-dimensional Bose gas: We evaluate the relaxation rate of high-energy quasiparticles in a weakly\ninteracting one-dimensional Bose gas. Unlike in higher dimensions, the rate is\na nonmonotonic function of temperature, with a maximum at the crossover to the\nstate of suppressed density fluctuations. At the maximum, the relaxation rate\nmay significantly exceed its zero-temperature value. We also find the\ndependence of the differential inelastic scattering rate on the transferred\nenergy. This rate yields information about temperature dependence of local pair\ncorrelations.",
        "positive": "The Wavefunction of the Collapsing Bose-Einstein Condensate: Bose-Einstein condensates with tunable interatomic interactions have been\nstudied intensely in recent experiments. The investigation of the collapse of a\ncondensate following a sudden change in the nature of the interaction from\nrepulsive to attractive has led to the observation of a remnant condensate that\ndid not undergo further collapse. We suggest that this high-density remnant is\nin fact the absolute minimum of the energy, if the attractive atomic\ninteractions are nonlocal, and is therefore inherently stable. We show that a\nvariational trial function consisting of a superposition of two distinct\ngaussians is an accurate representation of the wavefunction of the ground state\nof the conventional local Gross-Pitaevskii field equation for an attractive\ncondensate and gives correctly the points of emergence of instability. We then\nuse such a superposition of two gaussians as a variational trial function in\norder to calculate the minima of the energy when it includes a nonlocal\ninteraction term. We use experimental data in order to study the long range of\nthe nonlocal interaction, showing that they agree very well with a\ndimensionally derived expression for this range."
    },
    {
        "anchor": "Pseudogap Effects of Fermi Gases in the Presence of A Strong Effective\n  Magnetic Field: We address the important question of how to characterize the normal state of\nfermionic superfluids under the influence of a strong effective magnetic field,\nimplemented through rapid rotation or novel artificial field techniques. We\nconsider the effects of crossing from BCS to BEC and the role of non-condensed\npairs, or pseudogap effects. Using a simple extension of Gor'kov theory we\ndemonstrate how these pairs organize above the transition $T_c$ into precursors\nof a vortex configuration, which are associated with distortions of the ideal\nAbrikosov lattice. This non-uniform normal state appears to enable \"Bose\ncondensation\" in a field which is otherwise problematic due to the effective\none-dimensionality of Landau level dispersion.",
        "positive": "Dynamical quantum phase transitions on cross-stitch flat band networks: We study the quench dynamics on cross-stitch flat band networks by a sudden\nchange of the inter-cell hopping strength $J$. For quench processes with $J$\nchanging as $J=0\\rightarrow J\\neq0$, we give the analytical expression to the\nLoschmidt echo which possesses a series of zero points at critical times\n$t^{*}$, indicating where the dynamical quantum phase transitions occur. We\nfurther study the converse quench process with $J\\neq0\\rightarrow J=0$, and\nfind a non-trivial example that the pre-quench quantum state is not an\neigenstate of the post-quench Hamiltonian, whereas the Loschmidt echo\n$\\mathcal{L}(t)\\equiv1$ during this process. For both situations, these results\nare also illustrated numerically. Finally, we give a brief discussion on the\nobservation of these predictions in the system of ultracold atoms in optical\nlattices."
    },
    {
        "anchor": "Synthetic magnetic fields for cold erbium atoms: The implementation of the fractional quantum Hall effect in ultracold atomic\nquantum gases remains, despite substantial advances in the field, a major\nchallenge. Since atoms are electrically neutral, a key ingredient is the\ngeneration of sufficiently strong artificial gauge fields. Here we\ntheoretically investigate the synthetization of such fields for bosonic erbium\natoms by phase imprinting with two counterpropagating optical Raman beams.\nGiven the nonvanishing orbital angular momentum of the rare-earth atomic\nspecies erbium in the electronic ground state and the availability of\nnarrow-line transitions, heating from photon scattering is expected to be lower\nthan in atomic alkali-metal species. We give a parameter regime for which\nstrong synthetic magnetic fields with good spatial homogeneity are predicted.\nWe also estimate the size of the Laughlin gap expected from the s-wave\ncontribution of the interactions for typical experimental parameters of a\ntwo-dimensional atomic erbium microcloud. Our analysis shows that cold\nrare-earth atomic ensembles are highly attractive candidate systems for\nexperimental explorations of the fractional quantum Hall regime.",
        "positive": "High temperature thermodynamics of fermionic alkaline earth atoms in\n  optical lattices: We calculate experimentally relevant properties of trapped fermionic alkaline\nearth atoms in an optical lattice, modeled by the SU(N) Hubbard model. Our\ncalculation is accurate when the temperature is much larger than the tunneling\nrate, similar to current regimes in ultracold atom experiments. In addition to\nexploring the Mott insulator-metal crossover, we calculate final temperatures\nachieved by the standard experimental protocol of adiabatically ramping from a\nnon-interacting gas, as a function of initial gas temperature and final state\nlattice parameters. Of particular experimental interest, we find that\nincreasing $N$ gives substantially \\textit{colder} Mott insulators, up to more\nthan a factor of five for relevant parameters. This cooling happens for all\n$N$, fixing the initial entropy, or for all $N \\lsim 20$ (the exact value\ndepends on dimensionality), fixing the initial temperature."
    },
    {
        "anchor": "The nature of self-localization of Bose-Einstein condensates in deep\n  optical lattices: We analyze the nature of a novel type of self-trapping transition called\nself-localization (SL) of Bose-Einstein condensates in one-dimensional optical\nlattices in the presence of weak local dissipation. SL has recently been\nobserved in several studies based upon the discrete nonlinear Schr\\\"odinger\nequation (DNLS), however, its origin is hitherto an open question. We show that\nSL is based upon a self-trapping crossover in the system. Furthermore, we\nestablish that the origin of the crossover is the Peierls-Nabarro barrier, an\nenergy threshold describing the stability of self-trapped states. Beyond the\nmean-field description the crossover becomes even sharper which is also\nreflected by a sudden change of the coherence of the condensate. While we\nexpect that the crossover can be readily studied in current experiments in deep\noptical lattices, our results allow for the preparation of robust and long-time\ncoherent quantum states.",
        "positive": "Thermometry for Laughlin States of Ultracold Atoms: Cooling atomic gases into strongly correlated quantum phases requires\nestimates of the entropy to perform thermometry and establish viability. We\nconstruct an ansatz partition function for models of Laughlin states of atomic\ngases by combining high temperature series expansions with exact\ndiagonalization. Using the ansatz we find that entropies required to observe\nLaughlin correlations with bosonic gases are within reach of current cooling\ncapabilities."
    },
    {
        "anchor": "Nonlinear looped band structure of Bose-Einstein condensates in an\n  optical lattice: We study experimentally the stability of excited, interacting states of\nbosons in a double-well optical lattice in regimes where the nonlinear\ninteractions are expected to induce \"swallowtail\" looped band structure. By\ncarefully preparing different initial coherent states and observing their\nsubsequent decay, we observe distinct decay rates that provide direct evidence\nfor multivalued, looped band structure. The double well lattice both stabilizes\nthe looped band structure and allows for dynamic preparation of different\ninitial states, including states within the loop structure. We confirm our\nstate preparation procedure with dynamic Gross-Pitaevskii calculations. The\nexcited loop states are found to be more stable than dynamically unstable\nground states, but decay faster than expected based on a mean-field stability\ncalculation, indicating the importance of correlations beyond a mean field\ndescription.",
        "positive": "Polarized Fermi gases at finite temperature in the BCS-BEC crossover: We consider a polarized Fermi gas in the BCS-BEC crossover region above the\ncritical temperature within a T matrix formalism. By treating the mean-field\nlike shift of the quasiparticle energies in a self-consistent manner, we avoid\nthe known pathological behavior of the standard Nozieres-Schmitt-Rink approach\nin the polarized case, i.e., the polarization has the right sign and the spin\npolarizability is positive. The momentum distributions of the correlated system\nare computed and it is shown that, in the zero-temperature limit, they satisfy\nthe Luttinger theorem. Results for the phase diagram, the spin susceptibility,\nand the compressibility are discussed."
    },
    {
        "anchor": "Dipole-dipole frequency shifts in multilevel atoms: Dipole-dipole interactions lead to frequency shifts that are expected to\nlimit the performance of next-generation atomic clocks. In this work, we\ncompute dipolar frequency shifts accounting for the intrinsic atomic multilevel\nstructure in standard Ramsey spectroscopy. When interrogating the transitions\nfeaturing the smallest Clebsch-Gordan coefficients, we find that a simplified\ntwo-level treatment becomes inappropriate, even in the presence of large Zeeman\nshifts. For these cases, we show a net suppression of dipolar frequency shifts\nand the emergence of dominant non-classical effects for experimentally relevant\nparameters. Our findings are pertinent to current generations of optical\nlattice and optical tweezer clocks, opening a way to further increase their\ncurrent accuracy, and thus their potential to probe fundamental and many-body\nphysics.",
        "positive": "Electrodynamic duality and vortex unbinding in driven-dissipative\n  condensates: We investigate the superfluid properties of two-dimensional driven Bose\nliquids, such as polariton condensates, using their long-wavelength description\nin terms of a compact Kardar-Parisi-Zhang (KPZ) equation for the phase\ndynamics. We account for topological defects (vortices) in the phase field\nthrough a duality mapping between the compact KPZ equation and a theory of\nnon-linear electrodynamics coupled to charges. Using the dual theory we derive\nrenormalization group equations that describe vortex unbinding in these media.\nWhen the non-equilibirum drive is turned off, the KPZ non-linearity {\\lambda}\nvanishes and the RG flow gives the usual Kosterlitz-Thouless (KT) transition.\nOn the other hand, with non-linearity {\\lambda} > 0 vortices always unbind,\neven if the same system with {\\lambda} = 0 is superfluid. We predict the finite\nsize scaling behavior of the superfluid stiffness in the crossover governed by\nvortex unbinding showing its clear distinction from the scaling associated with\nthe KT transition."
    },
    {
        "anchor": "Vortex detection in atomic Bose-Einstein condensates using neural\n  networks trained on synthetic images: Quantum vortices in atomic Bose-Einstein condensates (BECs) are topological\ndefects characterized by quantized circulation of particles around them. In\nexperimental studies, vortices are commonly detected by time-of-flight imaging,\nwhere their density-depleted cores are enlarged. In this work, we describe a\nmachine learning-based method for detecting vortices in experimental BEC\nimages, particularly focusing on turbulent condensates containing irregularly\ndistributed vortices. Our approach employs a convolutional neural network (CNN)\ntrained solely on synthetic simulated images, eliminating the need for manual\nlabeling of the vortex positions as ground truth. We find that the CNN achieves\naccurate vortex detection in real experimental images, thereby facilitating\nanalysis of large experimental datasets without being constrained by specific\nexperimental conditions. This novel approach represents a significant\nadvancement in studying quantum vortex dynamics and streamlines the analysis\nprocess in the investigation of turbulent BECs.",
        "positive": "High-frequency approximation for periodically driven quantum systems\n  from a Floquet-space perspective: We derive a systematic high-frequency expansion for the effective Hamiltonian\nand the micromotion operator of periodically driven quantum systems. Our\napproach is based on the block diagonalization of the quasienergy operator in\nthe extended Floquet Hilbert space by means of degenerate perturbation theory.\nThe final results are equivalent to those obtained within a different approach\n[Phys.\\ Rev.\\ A {\\bf 68}, 013820 (2003), Phys.\\ Rev.\\ X {\\bf 4}, 031027 (2014)]\nand can also be related to the Floquet-Magnus expansion [J.\\ Phys.\\ A {\\bf 34},\n3379 (2000)]. We discuss that the dependence on the driving phase, which\nplagues the latter, can lead to artifactual symmetry breaking. The\nhigh-frequency approach is illustrated using the example of a periodically\ndriven Hubbard model. Moreover, we discuss the nature of the approximation and\nits limitations for systems of many interacting particles."
    },
    {
        "anchor": "Wave chaos in the non-equilibrium dynamics of the Gross-Pitaevskii\n  equation: The Gross-Pitaevskii equation (GPE) plays an important role in the\ndescription of Bose-Einstein condensates (BECs) at the mean-field level. The\nGPE belongs to the class of non-linear Schr\\\"odinger equations which are known\nto feature dynamical instability and collapse for attractive non-linear\ninteractions. We show that the GPE with repulsive non-linear interactions\ntypical for BECs features chaotic wave dynamics. We find positive Lyapunov\nexponents for BECs expanding in periodic and aperiodic smooth external\npotentials as well as disorder potentials. Our analysis demonstrates that wave\nchaos characterized by the exponential divergence of nearby initial\nwavefunctions is to be distinguished from the notion of non-integrability of\nnon-linear wave equations. We discuss the implications of these observations\nfor the limits of applicability of the GPE, the problem of Anderson\nlocalization, and the properties of the underlying many-body dynamics.",
        "positive": "Ferromagnetism of the Repulsive Atomic Fermi Gas: three-body\n  recombination and domain formation: The simplest model for itinerant ferromagnetism, the Stoner model, has so far\neluded experimental observation in repulsive ultracold fermions due to rapid\nthree-body recombination at large scattering lengths. Here we show that a\nferromagnetic phase can be stabilised by imposing a moderate optical lattice.\nThe reduced kinetic energy drop upon formation of a polarized phase in an\noptical lattice extends the ferromagnetic phase to smaller scattering lengths\nwhere three-body recombination is small enough to permit experimental detection\nof the phase. We also show, using time dependent density functional theory,\nthat in such a setup ferromagnetic domains emerge rapidly from a paramagnetic\ninitial state."
    },
    {
        "anchor": "Shape and size measurements of nonequilibrium Bose-Einstein condensates\n  using image processing: Bose-Einstein condensates have been the subject of intense research in recent\nyears due to their potential applications in quantum computing and many other\nareas. However, measuring the shape and size of out-of-equilibrium\nBose-Einstein condensates is a challenging task that requires sophisticated\nimage processing techniques. We propose to study perturbed BEC based on general\nconcepts of analysis, which are widely used in the image processing community.\nThe mathematical basis underlying the algorithms is quite general and\nindependent of the type of image studied. The morphological changes observed in\nthe perturbed atomic clouds as a result of excitation amplitude were observed\nin a consistent manner. And the spatial expansion of the atomic clouds under\nfree fall shows some symmetry, but it was only observed under certain\nconditions",
        "positive": "What can we learn from the experiment of electrostatic conveyer for\n  excitons?: Motivated by the experiment of electrostatic conveyer for indirect excitons\n[A. G. Winbow, et al., Phys. Rev. Lett. 106, 196806 (2011)], we studied the\nexciton patterns to understand the exciton dynamics. By analyzing the exciton\ndiffusion, we found that the patterns were from two kinds of excitons\napproximately. The patterns near the laser spot came from the hot excitons\nwhich can be taken as classical particles. However, the patterns far from the\nlaser spot were formed by the cooled excitons or coherent excitons. Considering\nthe Bosonic excitons with the limited lifetime and the interactions, we set up\na time-dependent nonlinear Schr\\\"odinger equation including the non-Hermitian\ndissipation to depict the coherent exciton dynamics. The real-time and\nimaginary-time evolutions were used alternately to solve the Schr\\\"odinger\nequation to study the exciton diffusion accompanied by the exciton cooling in\nthe moving lattices. By calculating the escape probability, we got\ntheoretically the transport distances of the coherent excitons in the conveyer\nwhich is consistent with the experimental data. The exciton cooling speed was\nfound to be the key element to the coherent exciton transport. Moreover, the\nplateau in the average transport distance as a function of the conveyer\namplitude cannot be explained by the dynamical localization-delocalization\ntransition due to the disorder."
    },
    {
        "anchor": "Efficient many-body non-Markovian dynamics of organic polaritons: We show how to simulate a model of many molecules with both strong coupling\nto many vibrational modes and collective coupling to a single photon mode. We\ndo this by combining process tensor matrix product operator methods with a\nmean-field approximation which reduces the dimension of the problem. We analyze\nthe steady-state of the model under incoherent pumping to determine the\ndependence of the polariton lasing threshold on cavity detuning, light-matter\ncoupling strength, and environmental temperature. Moreover, by measuring\ntwo-time correlations, we study quadratic fluctuations about the mean-field to\ncalculate the photoluminescence spectrum. Our method enables one to simulate\nmany-body systems with strong coupling to multiple environments, and to extract\nboth static and dynamical properties.",
        "positive": "High-temperature limit of the resonant Fermi gas: We use the virial expansion to investigate the behavior of the two-component,\nattractive Fermi gas in the high-temperature limit, where the system smoothly\nevolves from weakly attractive fermions to weakly repulsive bosonic dimers as\nthe short-range attraction is increased. We present a new formalism for\ncomputing the virial coefficients that employs a diagrammatic approach to the\ngrand potential and allows one to easily include an effective range $R^*$ in\nthe interaction. In the limit where the thermal wavelength $\\lambda \\ll R^*$,\nthe calculation of the virial coefficients is perturbative even at unitarity\nand the system resembles a weakly interacting Bose-Fermi mixture for all\nscattering lengths $a$. By interpolating from the perturbative limits\n$\\lambda/|a| \\gg 1$ and $R^*/\\lambda \\gg 1$, we estimate the value of the\nfourth virial coefficient at unitarity for $R^*=0$ and we find that it is close\nto the value obtained in recent experiments. We also derive the equations of\nstate for the pressure, density and entropy, as well as the spectral function\nat high temperatures."
    },
    {
        "anchor": "Quantum phases of spin-orbital-angular-momentum coupled bosonic gases in\n  optical lattices: Spin-orbit coupling plays an important role in understanding exotic quantum\nphases. In this work, we present a scheme to combine\nspin-orbital-angular-momentum (SOAM) coupling and strong correlations in\nultracold atomic gases. Essential ingredients of this setting is the interplay\nof SOAM coupling and Raman-induced spin-flip hopping, engineered by lasers that\ncouples different hyperfine spin states. In the presence of SOAM coupling only,\nwe find rich quantum phases in the Mott-insulating regime, which support\ndifferent types of spin defects such as spin vortex and composite vortex with\nantiferromagnetic core surrounded by the outer spin vortex. Based on an\neffective exchange model, we find that these competing spin textures are a\nresult of the interplay of Dzyaloshinskii-Moriya and Heisenberg exchange\ninteractions. In the presence of both SOAM coupling and Raman-induced spin-flip\nhopping, more many-body phases appear, including canted-antiferromagnetic and\nstripe phases. Our prediction suggests that SOAM coupling could induce rich\nexotic many-body phases in the strongly interacting regime.",
        "positive": "Evolution of Higgs mode in a Fermion Superfluid with Tunable\n  Interactions: In this letter we present a coherent picture for the evolution of Higgs mode\nin both neutral and charged $s$-wave fermion superfluids, as the strength of\nattractive interaction between fermions increases from the BCS to the BEC\nregime. In the case of neutral fermionic superfluid, such as ultracold\nfermions, the Higgs mode is pushed to higher energy while at the same time,\ngradually loses its spectral weight as interaction strength increases toward\nthe BEC regime, because the system is further tuned away from Lorentz\ninvariance. On the other hand, when damping is taken into account, Higgs mode\nis significantly broadened due to coupling to phase mode in the whole BEC-BCS\ncrossover. In the charged case of electron superconductor, the Anderson-Higgs\nmechanism gaps out the phase mode and suppresses the coupling between the Higgs\nand the phase modes, and consequently, stabilizes the Higgs mode."
    },
    {
        "anchor": "Repulsive Fermi polarons in a resonant mixture of ultracold ${}^6$Li\n  atoms: We employ radio-frequency spectroscopy to investigate a polarized\nspin-mixture of ultracold ${}^6$Li atoms close to a broad Feshbach scattering\nresonance. Focusing on the regime of strong repulsive interactions, we observe\nwell-defined coherent quasiparticles even for unitarity-limited interactions.\nWe characterize the many-body system by extracting the key properties of\nrepulsive Fermi polarons: the energy $E_+$, the effective mass $m^*$, the\nresidue $Z$ and the decay rate $\\Gamma$. Above a critical interaction, $E_+$ is\nfound to exceed the Fermi energy of the bath while $m^*$ diverges and even\nturns negative, thereby indicating that the repulsive Fermi liquid state\nbecomes energetically and thermodynamically unstable.",
        "positive": "Robust Finite-Temperature Many-Body Scarring on a Quantum Computer: Mechanisms for suppressing thermalization in disorder-free many-body systems,\nsuch as Hilbert space fragmentation and quantum many-body scars, have recently\nattracted much interest in foundations of quantum statistical physics and\npotential quantum information processing applications. However, their\nsensitivity to realistic effects such as finite temperature remains largely\nunexplored. Here, we have utilized IBM's Kolkata quantum processor to\ndemonstrate an unexpected robustness of quantum many-body scars at finite\ntemperatures when the system is prepared in a thermal Gibbs ensemble. We\nidentify such robustness in the PXP model, which describes quantum many-body\nscars in experimental systems of Rydberg atom arrays and ultracold atoms in\ntilted Bose--Hubbard optical lattices. By contrast, other theoretical models\nwhich host exact quantum many-body scars are found to lack such robustness, and\ntheir scarring properties quickly decay with temperature. Our study sheds light\non the important differences between scarred models in terms of their algebraic\nstructures, which impacts their resilience to finite temperature."
    },
    {
        "anchor": "Collective excitations in Bose-Fermi mixtures: We investigate collective excitations of density fluctuations and a dynamic\ndensity structure factor in a mixture of Bose and Fermi gases in a normal\nphase. With decreasing temperature, we find that the frequency of the\ncollective excitation deviates from that of the hydrodynamic sound mode. Even\nat temperature much lower than the Fermi temperature, the collective mode\nfrequency does not reach the collisionless limit analogous to zero sound in a\nFermi gas, because of collisions between bosons and fermions.",
        "positive": "Sudden and slow quenches into the antiferromagnetic phase of ultracold\n  fermions: We propose a method to reach the antiferromagnetic state of two-dimensional\nFermi gases trapped in optical lattices: Independent subsystems are prepared in\nsuitable initial states and then connected by a sudden or slow quench of the\ntunneling between the subsystems. Examples of suitable low-entropy subsystems\nare double wells or plaquettes, which can be experimentally realised in Mott\ninsulating shells using optical super-lattices. We estimate the effective\ntemperature T* of the system after the quench by calculating the distribution\nof excitations created using the spin wave approximation in a Heisenberg model.\nWe investigate the effect of an initial staggered magnetic field and find that\nfor an optimal polarisation of the initial state the effective temperature can\nbe significantly reduced from T*$\\approx$1.7 Tc at zero polarisation to\nT*<0.65Tc, where Tc is the crossover temperature to the antiferromagnetic\nstate. The temperature can be further reduced using a finite quench time. We\nalso show that T* decreases logarithmically with the linear size of the\nsubsystem."
    },
    {
        "anchor": "How creating one additional well can generate Bose-Einstein condensation: The realization of Bose-Einstein condensation in ultracold trapped gases has\nled to a revival of interest in that fascinating quantum phenomenon. This\nexperimental achievement necessitated both extremely low temperatures and\nsufficiently weak interactions. Particularly in reduced spatial dimensionality\neven an infinitesimal interaction immediately leads to a departure to\nquasi-condensation. We propose a system of strongly interacting bosons which\novercomes those obstacles by exhibiting a number of intriguing related\nfeatures: (i) The tuning of just a single control parameter drives a transition\nfrom quasi-condensation to complete condensation, (ii) the destructive\ninfluence of strong interactions is compensated by the respective increased\nmobility, (iii) topology plays a crucial role since a crossover from one- to\n`infinite'-dimensionality is simulated, (iv) a ground state gap opens which\nmakes the condensation robust to thermal noise. Remarkably, all these features\ncan be derived by analytical and exact numerical means despite the\nnon-perturbative character of the system.",
        "positive": "Temperature-induced miscibility of impurities in trapped Bose gases: We study the thermal properties of impurities embedded in a repulsive Bose\ngas under a harmonic trapping potential. In order to obtain exact structural\nproperties in this inhomogeneous many-body system, we resort to the\npath-integral Monte Carlo method. We find that, at low temperatures, a single\nimpurity is expelled to the edges of the bath cloud if the impurity-boson\ncoupling constant is larger than the boson-boson one. However, when the\ntemperature is increased, but still in the Bose-condensed phase, the impurity\noccupies the core of the trap and, thus, the system becomes miscible. This\nthermal-induced miscibility transition is also observed for a finite\nconcentration of impurities in this inhomogeneous system. We find that the\ntransition temperature for miscibility depends on the impurity-boson\ninteraction and we indicate a novel nondestructive method to measure the\ntemperature of a system based on the studied phenomenon."
    },
    {
        "anchor": "Perturbation-induced defects in trapped superfluids exhibit generic\n  behavior: We investigate equilibration processes shortly after sudden perturbations are\napplied to ultracold trapped superfluids. We show the similarity of phase\nimprinting and localized density depletion perturbations, both of which\ninitially are found to produce \"phase walls\". These planar defects are\nassociated with a sharp gradient in the phase. Importantly they relax following\na quite general sequence. Our studies, based on simulations of the complex\ntime-dependent Ginzburg-Landau equation, address the challenge posed by these\nexperiments: how a superfluid eventually eliminates a spatially extended planar\ndefect. The processes involved are necessarily more complex than equilibration\ninvolving simpler line vortices. An essential mechanism for relaxation involves\nrepeated formation and loss of vortex rings near the trap edge.",
        "positive": "Twisted behavior of dipolar BECs: Dipole-dipole interaction beyond the\n  self-consistent field approximation and exchange electric dipole interaction: Dipole-dipole interaction is a long-range interaction, hence we could expect\nthat the self-consistent field approximation might be applied. In most cases it\nis correct, but dipolar BECs reveal a surprise. Structure of the\nself-consistent field term requires that interacting particles are in different\nquantum states, while in BECs all particles in a single quantum state. This\nfact requires to consider the two-particle polarisation, which describes\ndipole-dipole interaction, in more details. We present this consideration and\nshow an astonishing result that the two-particle quantum correlation in dipolar\nBECs reveals in the same form as the self-consistent field term."
    },
    {
        "anchor": "Cold atoms in rotating optical lattice with nearest neighbour\n  interaction: Extended Bose Hubbard models with nearest neighbour interaction describe\nminimally the effect of long range interaction on ultra cold atoms in deep\noptical lattices. Rotation of such optical lattices subject such neutral cold\natoms to the effect of an artificial magnetic field. The modification of the\nphase boundaries of the density wave and Mott Insulator phases due to this\nrotation are shown to be related to the edge spectrum of spinorial and scalar\nHarper equation. Corresponding profiles of the checkerboard vortex states with\nsublattice modulated superfluid order parameter near density wave phase\nboundary are calculated.",
        "positive": "Quantum fluctuations in one-dimensional supersolids: In one-dimension, quantum fluctuations prevent the appearance of long-range\norder in a supersolid, and only quasi long-range order can survive. We derive\nthis quantum critical behavior and study its influence on the superfluid\nresponse and properties of the solid. The analysis is based on an effective\nlow-energy description accounting for the two coupled Goldstone modes. We find\nthat the quantum phase transition from the superfluid to the supersolid is\nshifted by quantum fluctuations from its mean-field prediction. However, for\ncurrent experimental parameters with dipolar atomic gases, this shift is not\nobservable and the transition appears to be mean-field like."
    },
    {
        "anchor": "Temperature-dependent excitation spectra of ultra-cold bosons in optical\n  lattices: Trapping ultra-cold atoms in optical lattices provides a unique environment\nfor investigating quantum phase transitions between strongly correlated\nsuperfluid and Mott insulator phases. One of the major complications in the\nanalysis of experiments is establishing of criteria for identifying the\nsuperfluid phase. Sharp features occurring while entering ordered state have\nbeen recognized as a signature of superfluidity. In the present work it is\nshown that sharp peaks are not necessarily a reliable diagnostic of phase\ncoherence in these systems. Using the combined Bogoliubov method and the\nquantum rotor approach for phase variables, we calculate the momentum and\nenergy-resolved single-particle spectral function $A(\\mathbf{k}\\omega)$ at\narbitrary temperature $T$ and its shape in the presence of the superfluid\nphase. We find that in the two-dimensional system even at $T>0$, where\ncondensate fraction vanishes, the remnants of the sharp coherence peak in\n$A(\\mathbf{k}\\omega)$ are present. In contrast, such a feature is not observed\nfor the bosons loaded in the three-dimensional lattice.",
        "positive": "The Boson-Hubbard Model on a Kagome Lattice with Sextic Ring-Exchange\n  Terms: High order ring-exchange interactions are crucial for the study of quantum\nfluctuations on highly frustrated systems. We present the first exact quantum\nMonte Carlo study of a model of hard-core bosons with sixth order ring-exchange\ninteractions on a two-dimensional kagome lattice. By using the Stochastic Green\nFunction algorithm, we show that the system becomes unstable in the limit of\nlarge ring-exchange interactions. It undergoes a phase separation at all\nfillings, except at 1/3 and 2/3 fillings for which the superfluid density\nvanishes and an unusual mixed valence bond and charge density ordered solid is\nformed."
    },
    {
        "anchor": "Disordered insulator in an optical lattice: Disorder can profoundly affect the transport properties of a wide range of\nquantum materials. Presently, there is significant disagreement regarding the\neffect of disorder on transport in the disordered Bose-Hubbard (DBH) model,\nwhich is the paradigm used to theoretically study disorder in strongly\ncorrelated bosonic systems. We experimentally realize the DBH model by using\noptical speckle to introduce precisely known, controllable, and fine-grained\ndisorder to an optical lattice5. Here, by measuring the dissipation strength\nfor transport, we discover a disorder-induced SF-to-insulator (IN) transition\nin this system, but we find no evidence for an IN-to-SF transition. Emergence\nof the IN at disorder strengths several hundred times the tunnelling energy\nagrees with a predicted SF--Bose glass (BG) transition from recent quantum\nMonte Carlo (QMC) work. Both the SF--IN transition and correlated changes in\nthe atomic quasimomentum distribution--which verify a simple model for the\ninterplay of disorder and interactions in this system--are phenomena new to the\nunit filling regime explored in this work, compared with the high filling limit\nprobed previously. We find that increasing disorder strength generically leads\nto greater dissipation in the regime of mixed SF and Mott-insulator (MI)\nphases, excluding predictions of a disorder-induced, or \"re-entrant,\" SF (RSF).\nWhile the absence of an RSF may be explained by the effect of finite\ntemperature, we strongly constrain theories by measuring bounds on the entropy\nper particle in the disordered lattice.",
        "positive": "Quantum dynamics of few dipolar bosons in a double-well potential: We study the few-body dynamics of dipolar bosons in one-dimensional\ndouble-wells. Increasing the interaction strength, by investigating one-body\nobservables, we study in the considered few-body systems tunneling\noscillations, self-trapping and the regime exhibting an equilibrating\nbehaviour. The corresponding two-body correlation dynamics exhibits a strong\ninterplay between the interatomic correlation due to non-local nature of the\nrepulsion and the inter-well coherence. We also study the link between the\ncorrelation dynamics and the occupation of natural orbitals of the one-body\ndensity matrix."
    },
    {
        "anchor": "Quantum Treatment for Bose-Einstein Condensation in Non-Equilibrium\n  Systems: We develop an approach based on stochastic quantum trajectories for an\nincoherently pumped system of interacting bosons relaxing their energy in a\nthermal reservoir. Our approach enables the study of the versatile coherence\nproperties of the system. We apply the model to exciton polaritons in a\nsemiconductor microcavity. Our results demonstrate the onset of macroscopic\noccupation in the lowest-energy mode accompanied by the establishment of both\ntemporal and spatial coherence. We show that temporal coherence exhibits a\ntransition from a thermal to coherent statistics and the spatial coherence\nreveals off-diagonal long-range order.",
        "positive": "Rotating Bose gas dynamically entering the lowest Landau level: Motivated by recent experiments, we model the dynamics of a condensed Bose\ngas in a rotating anisotropic trap, where the equations of motion are analogous\nto those of charged particles in a magnetic field. As the rotation rate is\nramped from zero to the trapping frequency, the condensate stretches along one\ndirection and is squeezed along another, becoming long and thin. When the trap\nanisotropy is slowly switched off on a particular timescale, the condensate is\nleft in the lowest Landau level. We use a time dependent variational approach\nto quantify these dynamics and give intuitive arguments about the structure of\nthe condensate wavefunction. This preparation of a lowest Landau level\ncondensate can be an important first step in realizing bosonic analogs of\nquantum Hall states."
    },
    {
        "anchor": "Spatial correlation of two-dimensional Bosonic multi-mode condensates: We studied the spatial coherence of a Bosonic two-dimensional multi-mode\ncondensate both through measurements and simulations. It is shown that\ncondensates with a constant spatial density must be described as the\nsuperposition of several quantized modes which reduces the overall coherence.\nIn this case, the spatial coherence can appear to decay faster than allowed by\nthe Berezinskii-Kosterlitz-Thouless (BKT) theory. However, we find through\nspectroscopic measurements that the individual modes show a slower decay of the\nspatial coherence than the overall system.",
        "positive": "High-field instability of field-induced triplon Bose-Einstein condensate: We study properties of magnetic field-induced Bose-Einstein condensate of\ntriplons as a function of temperature and the field within the\nHartree-Fock-Bogoliubov approach including the anomalous density. We show that\nthe magnetization is continuous across the transition, in agreement with the\nexperiment. In sufficiently strong fields the condensate becomes unstable due\nto triplon-triplon repulsion. As a result, the system is characterized by two\ncritical magnetic fields: one producing the condensate and the other destroying\nit. We show that nonparabolic triplon dispersion arising due to the gapped bare\nspectrum and the crystal structure has a strong influence on the phase diagram."
    },
    {
        "anchor": "Emergent Infrared Conformal Dynamics in Strongly Interacting Quantum\n  Gases: Conformal dynamics can appear in quantum gases when the interactions are fine\ntuned to be scale symmetric. One well-known example of such a system is a\nthree-dimensional Fermi gas at a Feshbach resonance. In this letter, we\nillustrate how conformal dynamics can also emerge in the infrared limit in\none-dimensional harmonically trapped Fermi gases, even though the system may\nnot have exactly scale symmetric interactions. The conformal dynamics are\ninduced by strong renormalization effects due to the nearby infrared stable\nscale invariant interaction. When the system approaches the infrared limit, or\nwhen the external harmonic trapping frequency $\\omega_f \\rightarrow 0$, the\ndynamics are characterized by a unique vanishingly small dissipation rate,\n$\\Gamma \\propto \\omega_f$, rather than a constant as in generic interacting\nsystems. We also examine the work done in a two-quench protocol, $W$, and the\naverage power $\\mathcal{P}$. In one dimension, the average power, $\\mathcal{P}\n\\propto \\omega_f$, becomes vanishingly small in the infrared limit, a signature\nof emergent conformal dynamics.",
        "positive": "Monte Carlo study of quantum phase transitions at zero temperature: In this Ph.D. thesis quantum Monte Carlo methods are applied to investigate\nthe properties of a number of ultracold quantum systems. In Chapter 1 we\ndiscuss the analytical approaches and approximations used in the subsequent\nChapters; also we describe the general concepts of the two-particle scattering\nproblem as a tool to construct Jastrow terms in trial wave functions. Chapter 2\nexplains in details the Quantum Monte Carlo methods employed in our\ncalculations from the theoretical and practical points of view. In Chapter 3 we\nexplain the Ewald summation technique, applied to a power-law 1/|r|k\ninteraction potential, and a generic approach to obtain the Ewald terms. The\nobtained expressions of this analytic work are implemented into simulations of\ndifferent physically relevant systems (Rydberg atoms and Yukawa particles).\nChapter 5 is devoted to the modelling of a system, governed by the model\npotential between Rydberg atoms $1/r^6$. The phase diagram of the system is\nobtained for a relevant range of densities and temperatures, combining quantum\nsimulations at low temperature and classical treatment at higher temperature. A\nspecial attention is paid to the classical description of this system, composed\nof Rydberg atoms, and its comparison to the quantum system. In Chapter 4 we\npresent the simulation of a system with the Yukawa interaction potential. The\nfollowing Chapter 6 presents the results of the Quantum Monte Carlo simulations\nof molecular para-hydrogen at zero and finite temperatures, performed in our\nGroup. Conclusions are drawn in Chapter 7."
    },
    {
        "anchor": "On-demand generation of dark-bright soliton trains in Bose-Einstein\n  condensates: The controlled creation of dark-bright (DB) soliton trains in multi-component\nBose-Einstein condensates (BECs) is a topic of ongoing interest. In this work\nwe generalize earlier findings on the creation of dark soliton trains in\nsingle-component BECs [A. Romero-Ros et al., Phys. Rev. A 103, 023329 (2021)]\nto two-component BECs. By choosing suitable filled box-type initial\nconfigurations (FBTCs) and solving the direct scattering problem for the\ndefocusing vector nonlinear Schr\\\"odinger equation with nonzero boundary\nconditions we obtain analytical expressions for the DB soliton solutions\nproduced by a general FBTC. It is found that the size of the initial box and\nthe amount of filling directly affects the number, size, and velocity of the\nsolitons, while the initial phase determines the parity (even or odd) of the\nsolutions. Our analytical results are compared to direct numerical integration\nof the coupled Gross-Pitaevskii equations, both in the absence and in the\npresence of a harmonic trap, and an excellent agreement between the two is\ndemonstrated.",
        "positive": "Properties of the Superfluid in the Disordered Bose-Hubbard Model: We investigate the properties of the superfluid phase in the\nthree-dimensional disordered Bose-Hubbard model using Quantum Monte-Carlo\nsimulations. The phase diagram is generated using Gaussian disorder on the\non-site potential. Comparisons with box and speckle disorder show qualitative\nsimilarities leading to the re-entrant behavior of the superfluid. Quantitative\ndifferences that arise are controlled by the specific shape of the disorder.\nStatistics pertaining to disorder distributions are studied for a range of\ninteraction strengths and system sizes, where strong finite-size effects are\nobserved. Despite this, both the superfluid fraction and compressibility remain\nself-averaging throughout the superfluid phase. Close to the\nsuperfluid-Bose-glass phase boundary, finite-size effects dominate but still\nsuggest that self-averaging holds. Our results are pertinent to experiments\nwith ultracold atomic gases where a systematic disorder averaging procedure is\ntypically not possible."
    },
    {
        "anchor": "Sub-Doppler laser cooling of fermionic 40K atoms in three-dimensional\n  gray optical molasses: We demonstrate sub-Doppler cooling of 40K on the D_1 atomic transition. Using\na gray molasses scheme, we efficiently cool a compressed cloud of 6.5x10^8\natoms from ~ 4\\mK to 20uK in 8 ms. After transfer in a quadrupole magnetic\ntrap, we measure a phase space density of ~10^-5. This technique offers a\npromising route for fast evaporation of fermionic 40K.",
        "positive": "Observation of 2D Mott insulator and $\u03c0$-superfluid quantum phase\n  transition in shaking optical lattice: The Mott insulator and superfluid phase transition is one of the most\nprominent phenomena in ultracold atoms. In this work, we report the observation\nof a novel 2D quantum phase transition between Mott insulator and $\\pi$\nsuperfluid in a shaking optical lattice. In the deep optical lattice regime,\nthe lowest $s$-band can be tuned to Mott phase, while the higher $p_{x,y}$\nbands are itinerant for having larger bandwidth. Through a shaking technique\ncoupling the $s$ orbital to $p_{x,y}$ orbital states, we experimentally observe\nthe transition between the states of the $s$ and $p_{x,y}$ bands, leading to a\nquantum phase transition from 2D $s$-orbital Mott phase to the\n$p_{x,y}$-orbital superfluid which condensed at $(\\pi,\\pi)$ momentum."
    },
    {
        "anchor": "Protection of quantum states from disturbance due to random potential by\n  successive translation: We show a method to protect quantum states from the disturbance due to the\nrandom potential by successive rapid manipulations of the quantum states. The\nquantum states are kept undisturbed for a longer time than the case of the\nsimple trapping with a stationary potential. The effective potential, which the\nquantum states feel, becomes uniform when the velocity of the transport is\nsufficiently large. It is also shown that the alternating transport of a\nBose-Einstein condensate with the driving potential derived by fast-forward\nscaling theory [Masuda and Nakamura, Proc. R. Soc. A 466, 1135 (2010)] can\nprotect it from the disturbance.",
        "positive": "Ground states of trapped spin-1 condensates in magnetic field: We consider a spin-1 Bose-Einstein condensate trapped in a harmonic potential\nunder the influence of a homogeneous magnetic field. We investigate spatial and\nspin structure of the mean-field ground states under constraints on the number\nof atoms and the total magnetization. We show that the trapping potential can\nmake the antiferromagnetic condensate separate into three, and ferromagnetic\ncondensate into two distinct phases. In the ferromagnetic case, the\nmagnetization is located in the center of the harmonic trap, while in the\nantiferromagnetic case magnetized phases appear in the outer regions. We\ndescribe how the transition from the Thomas-Fermi regime to the single-mode\napproximation regime with decreasing number of atoms results in the\ndisappearance of the domains. We suggest that the ground states can be created\nin experiment by adiabatically changing the magnetic field strength."
    },
    {
        "anchor": "Effect of disorder on topological charge pumping in the Rice-Mele model: Recent experiments with ultracold quantum gases have successfully realized\ninteger-quantized topological charge pumping in optical lattices. Motivated by\nthis progress, we study the effects of static disorder on topological Thouless\ncharge pumping. We focus on the half-filled Rice-Mele model of free spinless\nfermions and consider random diagonal disorder. In the instantaneous basis, we\ncompute the polarization, the entanglement spectrum, and the local Chern\nmarker. As a first main result, we conclude that the space-integrated local\nChern marker is best suited for a quantitative determination of topological\ntransitions in a disordered system. In the time-dependent simulations, we use\nthe time-integrated current to obtain the pumped charge in slowly periodically\ndriven systems. As a second main result, we observe and characterize a\ndisorder-driven breakdown of the quantized charge pump. There is an excellent\nagreement between the static and the time-dependent ways of computing the\npumped charge. The topological transition occurs well in the regime where all\nstates are localized on the given system sizes and is therefore not tied to a\ndelocalization-localization transition of Hamiltonian eigenstates. For\nindividual disorder realizations, the breakdown of the quantized pumping occurs\nfor parameters where the spectral bulk gap inherited from the band gap of the\nclean system closes, leading to a globally gapless spectrum. As a third main\nresult and with respect to the analysis of finite-size systems, we show that\nthe disorder average of the bulk gap severely overestimates the stability of\nquantized pumping. A much better estimate is the typical value of the\ndistribution of energy gaps, also called mode of the distribution.",
        "positive": "Observation of transverse condensation via Hanbury Brown--Twiss\n  correlations: A fundamental property of a three-dimensional Bose-Einstein condensate (BEC)\nis long-range coherence, however, in systems of lower dimensionality, not only\nis the long range coherence destroyed, but additional states of matter are\npredicted to exist. One such state is a `transverse condensate', first\npredicted by van Druten and Ketterle [Phys. Rev. Lett. 79, 549 (1997)], in\nwhich the gas condenses in the transverse dimensions of a highly anisotropic\ntrap while remaining thermal in the longitudinal dimension. Here we detect the\ntransition from a three-dimensional thermal gas to a gas undergoing transverse\ncondensation by probing Hanbury Brown--Twiss correlations."
    },
    {
        "anchor": "Finite temperature effective field theory and two-band superfluidity in\n  Fermi gases: We develop a description of fermionic superfluids in terms of an effective\nfield theory for the pairing order parameter. Our effective field theory\nimproves on the existing Ginzburg - Landau theory for superfluid Fermi gases in\nthat it is not restricted to temperatures close to the critical temperature.\nThis is achieved by taking into account long-range fluctuations to all orders.\nThe results of the present effective field theory compare well with the results\nobtained in the framework of the Bogoliubov - de Gennes method. The advantage\nof an effective field theory over Bogoliubov - de Gennes calculations is that\nmuch less computation time is required. In the second part of the paper, we\nextend the effective field theory to the case of a two-band superfluid. The\npresent theory allows us to reveal the presence of two healing lengths in the\ntwo-band superfluids, to analyze the finite-temperature vortex structure in the\nBEC-BCS crossover, and to obtain the ground state parameters and spectra of\ncollective excitations. For the Leggett mode our treatment provides an\ninterpretation of the observation of this mode in two-band superconductors.",
        "positive": "Oscillatory pairing amplitude and magnetic compressible-incompressible\n  transitions in imbalanced fermionic superfluids in optical lattices of\n  elongated tubes: We study two-species fermion gases with attractive interaction in\ntwo-dimensional optical lattices producing an array of elongated tube\nconfinements. Focusing on the interplay of Cooper pairing, spin imbalance (or\nmagnetization) and intertube tunneling, we find the pairing gap can exhibit\noscillatory behavior both along and across the tubes, reminiscent of a\nFulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase. We obtain a Bose-Hubbard-like\nphase diagram that shows that the magnetization of the system undergoes an\nincompressible-compressible transition as a function of magnetic field and\nintertube tunneling strength. We find the parity of tube-filling imbalance in\nincompressible states is protected by that of the oscillatory pairing gap.\nFinally, we discuss signatures of this transition and thus (indirectly) of the\nFFLO pairing in cold atom experiments."
    },
    {
        "anchor": "On the thermodynamics of fermions at any temperature based on\n  parametrized partition function: In this work we study the recently developed parametrized partition function\nformulation and show how we can infer the thermodynamic properties of fermions\nbased on numerical simulation of bosons and distinguishable particles at\nvarious temperatures. In particular, we show that in the three dimensional\nspace defined by energy, temperature and the parameter characterizing\nparametrized partition function, we can map the energies of bosons and\ndistinguishable particles to fermionic energies through constant-energy\ncontours. We apply this idea to both noninteracting and interacting Fermi\nsystems and show it is possible to infer the fermionic energies at all\ntemperatures, thus providing a practical and efficient approach to obtain\nthermodynamic properties of Fermi systems with numerical simulation. As an\nexample, we present energies and heat capacities for 10 noninteracting fermions\nand 10 interacting fermions (more fermions are provided in the appendix) and\nshow good agreement with the analytical result for noninteracting case.",
        "positive": "Incommensurate phases of a bosonic two-leg ladder under a flux: A boson two--leg ladder in the presence of a synthetic magnetic flux is\ninvestigated by means of bosonization techniques and Density Matrix\nRenormalization Group (DMRG). We follow the quantum phase transition from the\ncommensurate Meissner to the incommensurate vortex phase with increasing flux\nat different fillings. When the applied flux is $\\rho \\pi$ and close to it,\nwhere $\\rho$ is the filling per rung, we find a second incommensuration in the\nvortex state that affects physical observables such as the momentum\ndistribution, the rung-rung correlation function and the spin-spin and\ncharge-charge static structure factors."
    },
    {
        "anchor": "Superfluid to normal fluid phase transition in the Bose gas trapped in\n  two dimensional optical lattices at finite temperature: We develop the Hartree-Fock-Bogoliubov theory at finite temperature for Bose\ngas trapped in the two dimensional optical lattices. The on-site energy is\nconsidered low enough that the gas presents superfluid properties. We obtain\nthe condensate density as function of the temperature neglecting the anomalous\ndensity in the thermodynamics equations. The condensate fraction provide two\ncritical temperature. Below the temperature $T_{C1}$ there is one condensate\nfraction. Above two possible fractions merger up to the critical temperature\n$T_{C2}$. Then the gas provides an first order transition at temperature above\n$T_{C2}$ where the condensate fraction is null. We resume by a\nfinite-temperature phase diagram where can be identify three domains: the\nnormal fluid, the superfluid and the superfluid with two possible condensate\nfractions.",
        "positive": "Phase-slippage and self-trapping in a self-induced bosonic Josephson\n  junction: A dipolar condensate confined in a toroidal trap constitutes a self-induced\nJosepshon junction when the dipoles are oriented perpendicularly to the trap\nsymmetry axis and the s-wave scattering length is small enough. The ring-shaped\ndouble-well potential coming from the anisotropic character of the mean-field\ndipolar interaction is robust enough to sustain self-trapping dynamics, which\ntakes place when the initial population imbalance between the two wells is\nlarge. We show that in this system the self-trapping regime is directly related\nto a vortex-induced phase-slip dynamics. A vortex and antivortex are\nspontaneously nucleated in the low density regions, before a minimum of the\npopulation imbalance is reached, and then cross the toroidal section in\nopposite directions through the junctions.This vortex dynamics yields a phase\nslip between the two weakly linked condensates causing an inversion of the\nparticle flux."
    },
    {
        "anchor": "Damping of macroscopic oscillation and interference pattern in coupled\n  Gross-Pitaevskii equations without self-interaction: Quantum phenomena appear in a macroscopic scale in Bose-Einstein condensates.\nThe Gross-Pitaevskii (GP) equation describes the dynamics of the weakly\ninteracting Bose-Einstein condensates. The GP equation has a form of the\nSchroedinger equation with self-interaction. The coupled Gross-Pitaevskii\nequations are used to describe some mixtures of Bose-Einstein condensates. In\nthis paper, we will show some numerical results of coupled Gross-Pitaevskii\nequations without self-interaction, which has a form of nonlinearly-coupled\nSchroedinger equations. We demonstrate that the macroscopic oscillation and the\ninterference of two quantum wave packets decay in time owing to mutual\ninteraction, which is analogous to the decoherence in quantum mechanics of many\nparticles.",
        "positive": "Universality of the unitary Fermi gas: A few-body perspective: We revisit the properties of the two-component Fermi gas with short-range\ninteractions in three dimensions, in the limit where the s-wave scattering\nlength diverges. Such a unitary Fermi gas possesses universal thermodynamic and\ndynamical observables that are independent of any interaction length scale.\nFocusing on trapped systems of N fermions, where N$\\leq10$, we investigate how\nwell we can determine the zero-temperature behavior of the many-body system\nfrom published few-body data on the ground-state energy and the contact. For\nthe unpolarized case, we find that the Bertsch parameters extracted from\ntrapped few-body systems all lie within 15% of the established value.\nFurthermore, the few-body values for the contact are well within the range of\nvalues determined in the literature for the many-body system. In the limit of\nlarge spin polarization, we obtain a similar accuracy for the polaron energy,\nand we estimate the polaron's effective mass from the dependence of its energy\non N. We also compute an upper bound for the squared wave-function overlap\nbetween the unitary Fermi system and the non-interacting ground state, both for\nthe trapped and uniform cases. This allows us to prove that the trapped\nunpolarised ground state at unitarity has zero overlap with its non-interacting\ncounterpart in the many-body limit N$\\to \\infty$."
    },
    {
        "anchor": "Rotational properties of dipolar Bose-Einstein condensates confined in\n  anisotropic harmonic potentials: We study the rotational properties of a dipolar Bose-Einstein condensate\nconfined in a quasi-two- dimensional anisotropic trap, for an arbitrary\norientation of the dipoles with respect to their plane of motion. Within the\nmean-field approximation we find that the lowest-energy state of the system\ndepends strongly on the relative strength between the dipolar and the contact\ninteractions, as well as on the size and the orientation of the dipoles, and\nthe size and the orientation of the deformation of the trapping potential.",
        "positive": "Higher-order local and non-local correlations for 1D strongly\n  interacting Bose gas: The correlation function is an important quantity in the physics of ultracold\nquantum gases because it provides information about the quantum many-body wave\nfunction beyond the simple density profile. In this paper we first study the\n$M$-body local correlation functions, $g_M$, of the one-dimensional (1D)\nstrongly repulsive Bose gas within the Lieb-Liniger model using the analytical\nmethod proposed by Gangardt and Shlyapnikov [1,2]. In the strong repulsion\nregime the 1D Bose gas at low temperatures is equivalent to a gas of ideal\nparticles obeying the non-mutual generalized exclusion statistics (GES) with a\nstatistical parameter $\\alpha =1-2/\\gamma$, i.e. the quasimomenta of $N$\nstrongly interacting bosons map to the momenta of $N$ free fermions via\n$k_i\\approx \\alpha k_i^F $ with $i=1,\\ldots, N$. Here $\\gamma$ is the\ndimensionless interaction strength within the Lieb-Liniger model. We rigorously\nprove that such a statistical parameter $\\alpha$ solely determines the\nsub-leading order contribution to the $M$-body local correlation function of\nthe gas at strong but finite interaction strengths. We explicitly calculate the\ncorrelation functions $g_M$ in terms of $\\gamma$ and $\\alpha$ at zero, low, and\nintermediate temperatures. For $M=2$ and $3$ our results reproduce the known\nexpressions for $g_{2}$ and $g_{3}$ with sub-leading terms (see for instance\n[3-5]). We also express the leading order of the short distance\n\\emph{non-local} correlation functions\n$\\langle\\Psi^\\dagger(x_1)\\cdots\\Psi^\\dagger(x_M)\\Psi(y_M)\\cdots\\Psi(y_1)\\rangle$\nof the strongly repulsive Bose gas in terms of the wave function of $M$ bosons\nat zero collision energy and zero total momentum. Here $\\Psi(x)$ is the boson\nannihilation operator. These general formulas of the higher-order local and\nnon-local correlation functions of the 1D Bose gas provide new insights into\nthe many-body physics."
    },
    {
        "anchor": "Fractional quantum Hall states of bosons on cones: Motivated by a recent experiment which synthesizes Landau levels for photons\non cones [Schine {\\em et al.}, Nature 534, 671 (2016)], and more generally the\ninterest in understanding gravitational responses of quantum Hall states, we\nstudy fractional quantum Hall states of bosons on cones. A variety of trial\nwave functions for conical systems are constructed and compared with exact\ndiagonalization results. The tip of a cone is a localized geometrical defect\nwith singular curvature which can modify the density profiles of quantum Hall\nstates. The density profiles on cones can be used to extract some universal\ninformation about quantum Hall states. The values of certain quantities are\ncomputed numerically using the density profiles of some quantum Hall states and\nthey agree with analytical predictions.",
        "positive": "Transport measurement of the orbital Kondo effect with ultracold atoms: The Kondo effect in condensed-matter systems manifests itself most sharply in\ntheir transport measurements. Here we propose an analogous transport signature\nof the orbital Kondo effect realized with ultracold atoms. Our system consists\nof imbalanced Fermi seas of two components of fermions and an impurity atom of\ndifferent species which is confined by an isotropic potential. We first apply a\n\\pi/2 pulse to transform two components of fermions into two superposition\nstates. Their interactions with the impurity atom then cause a \"transport\" of\nfermions from majority to minority superposition states, whose numbers can be\nmeasured after applying another 3\\pi/2 pulse. In particular, when the\ninteraction of one component of fermions with the impurity atom is tuned close\nto a confinement-induced p-wave or higher partial-wave resonance, the resulting\nconductance is shown to exhibit the Kondo signature, i.e., universal\nlogarithmic growth by lowering the temperature. The proposed transport\nmeasurement will thus provide a clear evidence of the orbital Kondo effect\naccessible in ultracold atom experiments and pave the way for developing new\ninsights into Kondo physics."
    },
    {
        "anchor": "Universal Tomonaga-Luttinger liquid phases in one-dimensional strongly\n  attractive SU(N) fermionic cold atoms: A simple set of algebraic equations is derived for the exact low-temperature\nthermodynamics of one-dimensional multi-component strongly attractive fermionic\natoms with enlarged SU(N) spin symmetry and Zeeman splitting. Universal\nmulti-component Tomonaga-Luttinger liquid (TLL) phases are thus determined. For\nlinear Zeeman splitting, the physics of the gapless phase at low temperatures\nbelongs to the universality class of a two-component asymmetric TLL\ncorresponding to spin-neutral N-atom composites and spin-(N-1)/2 single atoms.\nThe equation of states is also obtained to open up the study of multi-component\nTLL phases in 1D systems of N-component Fermi gases with population imbalance.",
        "positive": "Self-trapping under the two-dimensional spin-orbit-coupling and\n  spatially growing repulsive nonlinearity: We elaborate a method for the creation of two- and one-dimensional (2D and\n1D) self-trapped modes in binary spin-orbit (SO)-coupled Bose-Einstein\ncondensates (BECs) with the contact repulsive interaction, whose local strength\ngrows fast enough from the center to periphery. In particular, an exact\nsemi-vortex (SV) solution is found for the anti-Gaussian radial-modulation\nprofile. The exact modes are included in the numerically produced family of SV\nsolitons. Other families, in the form of mixed modes(MMs), as well as excited\nstate of SVs and MMs, are produced too. While the excited states are unstable\nin all previously studied models, they are partially stable in the present one.\nIn the 1D version of the system, exact solutions for the counterpart of the\nSVs, namely, \\textit{semi-dipole} solitons, are found too. Families of\nsemi-dipoles, as well as the 1D version of MMs, are produced numerically."
    },
    {
        "anchor": "Organic polariton lasing and the weak- to strong-coupling crossover: Following experimental realizations of room temperature polariton lasing with\norganic molecules, we present a microscopic model that allows us to explore the\ncrossover from weak to strong matter-light coupling. We consider a\nnon-equilibrium Dicke-Holstein model, including both strong coupling to\nvibrational modes and strong matter-light coupling, providing the phase diagram\nof this model in the thermodynamic limit. We discuss the mechanism of polariton\nlasing, uncovering a process of self-tuning, and identify the relation and\ndistinction between regular dye lasers and organic polariton lasers.",
        "positive": "Separation induced resonances in quasi-one-dimensional ultracold atomic\n  gases: We study the effective one-dimensional (1D) scattering of two distinguishable\natoms confined individually by {\\em separated} transverse harmonic traps. With\nequal trapping frequency for two s-wave interacting atoms, we find that by\ntuning the trap separations, the system can undergo {\\em double} 1D scattering\nresonance, named as the separation induced resonance(SIR), when the ratio\nbetween the confinement length and s-wave scattering length is within\n$(0.791,1.46]$. Near SIR, the scattering property shows unique dependence on\nthe resonance position. The universality of a many-body system on scattering\nbranch near SIR is demonstrated by studying the interaction effect of a\nlocalized impurity coupled with a Fermi sea of light atoms in a quasi-1D trap."
    },
    {
        "anchor": "Quantum-granularity effect in the formation of supermixed solitons in\n  ring lattices: We investigate a notable class of states peculiar to a bosonic binary mixture\nfeaturing repulsive intraspecies and attractive interspecies couplings. We\nevidence that, for small values of the hopping amplitudes, one can access\nparticular regimes marked by the fact that the interwell boson transfer occurs\nin a jerky fashion. This property is shown to be responsible for the emergence\nof a staircase-like structure in the phase diagram of a mixture confined in a\nring trimer and to strongly resemble the mechanism of the superfluid-Mott\ninsulator transition. Under certain conditions, in fact, we show that it is\npossible to interpret the interspecies attraction as an effective chemical\npotential and the supermixed soliton as an effective particle reservoir. Our\ninvestigation is developed both within a fully quantum approach based on the\nanalysis of several quantum indicators and by means of a simple analytical\napproximation scheme capable of capturing the essential features of this\nultraquantum effect.",
        "positive": "Effective theory of chiral two-dimensional superfluids: We construct, to leading orders in the momentum expansion, an effective\ntheory of a chiral $p_x + ip_y$ two-dimensional fermionic superfluid at zero\ntemperature that is consistent with nonrelativistic general coordinate\ninvariance. This theory naturally incorporates the parity and time reversal\nviolating effects such as the Hall viscosity and the edge current. The particle\nnumber current and stress tensor are computed and their linear response to\nelectromagnetic and gravitational sources is calculated. We also consider an\nisolated vortex in a chiral superfluid and identify the leading chirality\neffect in the density depletion profile."
    },
    {
        "anchor": "Beyond the Hubbard bands in strongly correlated lattice bosons: We investigate features in the single-particle spectral function beyond the\nHubbard bands in the strongly correlated normal phase of the Bose-Hubbard\nmodel. There are two distinct classes of additional peaks generated by the\nbosonic statistics. The first type is thermally activated Hubbard \"sidebands\",\nwith the same physical origin as the zero-temperature Hubbard bands, but\ngenerated by excitations from thermally activated local occupation number\nstates. The second class are two-particle fluctuation resonances driven by the\nlattice dynamics. In the unity filling Mott insulator, this takes the form of a\nlocalized triplon combined with a dispersing holon. Both types of resonances\nalso manifest themselves in the structure factor and the interaction modulation\nspectra obtained from nonequilibrium bosonic dynamical mean-field theory\ncalculations. Our findings explain experimental lattice modulation and Bragg\nspectroscopy results, and they predict a strong temperature dependence of the\nfirst sideband, thereby opening the door to precise thermometry of strongly\ncorrelated lattice bosons.",
        "positive": "D-brane solitons and boojums in field theory and Bose-Einstein\n  condensates: In certain field theoretical models, composite solitons consisting of a\ndomain wall and vortex lines attached to the wall have been referred to as\nD-brane solitons. We show that similar composite solitons can be realized in\nphase-separated two-component Bose-Einstein condensates. We discuss the\nsimilarities and differences between topological solitons in the Abelian-Higgs\nmodel and those in two-component Bose-Einstein condensates. Based on the\nformulation of gauge theory, we introduce the \"boojum charge\" to characterize\nthe \"D-brane soliton\" in Bose-Einstein condensates."
    },
    {
        "anchor": "Giant increase of temporal coherence in optically trapped polariton\n  condensate: Coherent bosonic ensembles offer the promise of harnessing quantum effects in\nphotonic and quantum circuits. In the dynamic equilibrium regime, the\napplication of polariton condensates is hindered by exciton-polariton\nscattering induced de-coherence in the presence of a dark exciton reservoir. By\nspatially separating the condensate from the reservoir, we drive the system\ninto the weak interaction regime, where the ensemble coherence time exceeds the\nindividual particle lifetime by nearly three orders of magnitude. The observed\nnanosecond coherence provides an upper limit for polariton self-interactions.\nIn contrast to conventional photon lasers, we observe an increased contribution\nfrom the super-Poissonian component of the condensate to the overall particle\nnumber fluctuations. Coupled with the recent emergence of a quantum regime in\npolaritonics, coherence times extended to several nanoseconds favour the\nrealization of quantum information protocols.",
        "positive": "Emergent Mott-insulators at non-integer fillings and devil's staircase\n  induced by attractive interaction in many-body polarons: We investigate the ground state properties of an ultracold atom system\nconsisting of many-body polarons, quasiparticles formed by impurity atoms in\noptical lattices immersing in a Bose-Einstein condensate. We find the\nnearest-neighbor attractive interaction between polarons can give rise to rich\nphysics that is peculiar to this system. In a relatively shallow optical\nlattice, the attractive interaction can drive the system being in a self-bound\nsuperfluid phase with its particle density distribution manifesting a\nself-concentrated structure. While in a relatively deep optical lattice, the\nattractive interaction can drive the system forming the Mott-insulator phase\neven though the global filling factor is not integer. Interestingly, in the\nMott-insulator regime, the system can support a series of different\nMott-insulators with their effective density manifesting a devil's staircase\nstructure with respect to the strength of attractive interaction. Detailed\nestimation on relevant experimental parameters shows that these rich physics\ncan be readily observed in current experimental setups."
    },
    {
        "anchor": "Beyond braid statistics: Constructing a lattice model for anyons with\n  exchange statistics intrinsic to one dimension: Anyons obeying fractional exchange statistics arise naturally in two\ndimensions: hard-core two-body constraints make the configuration space of\nparticles not simply-connected. The braid group describes how\ntopologically-inequivalent exchange paths can be associated to non-trivial\ngeometric phases for abelian anyons. Braid-anyon exchange statistics can also\nbe found in one dimension (1D), but this requires broken Galilean invariance to\ndistinguish different ways for two anyons to exchange. However, recently it was\nshown that an alternative form of exchange statistics can occur in 1D because\nhard-core three-body constraints also make the configuration space not\nsimply-connected. Instead of the braid group, the topology of exchange paths\nand their associated non-trivial geometric phases are described by the traid\ngroup. In this article we propose a first concrete model realizing this\nalternative form of anyonic exchange statistics. Starting from a bosonic\nlattice model that implements the desired geometric phases with\nnumber-dependent Peierls phases, we then define anyonic operators so that the\nkinetic energy term in the Hamiltonian becomes local and quadratic with respect\nto them. The ground-state of this traid-anyon-Hubbard model exhibits several\nindications of exchange statistics intermediate between bosons and fermions, as\nwell as signs of emergent approximate Haldane exclusion statistics. The\ncontinuum limit results in a Galilean invariant Hamiltonian with eigenstates\nthat correspond to previously constructed continuum wave functions for traid\nanyons. This provides not only an a-posteriori justification of our lattice\nmodel, but also shows that our construction serves as an intuitive approach to\ntraid anyons, i.e. anyons intrinsic to 1D.",
        "positive": "Bright solitons in a spin-tensor-momentum-coupled Bose-Einstein\n  condensate: Synthetic spin-tensor-momentum coupling has recently been proposed to realize\nin atomic Bose-Einstein condensates. Here we study bright solitons in\nBose-Einstein condensates with spin-tensor-momentum coupling and spin-orbit\ncoupling. The properties and dynamics of spin-tensor-momentum-coupled and\nspin-orbit-coupled bright solitons are identified to be different. We\ncontribute the difference to the different symmetries."
    },
    {
        "anchor": "Energy spectrum of a harmonically trapped two-atom system with\n  spin-orbit coupling: Ultracold atomic gases provide a novel platform with which to study\nspin-orbit coupling, a mechanism that plays a central role in the nuclear shell\nmodel, atomic fine structure and two-dimensional electron gases. This paper\nintroduces a theoretical framework that allows for the efficient determination\nof the eigenenergies and eigenstates of a harmonically trapped two-atom system\nwith short-range interaction subject to an equal mixture of Rashba and\nDresselhaus spin-orbit coupling created through Raman coupling of atomic\nhyperfine states. Energy spectra for experimentally relevant parameter\ncombinations are presented and future extensions of the approach are discussed.",
        "positive": "Phase diagram, band structure and density of states in two-dimensional\n  attractive Fermi-Hubbard model with Rashba spin-orbit coupling: Based on the two-dimensional (2D) attractive Fermi-Hubbard model with Rashba\nspin-orbit coupling (SOC), the SOC strength and Zeeman field dependences of the\nphase diagram are investigated by calculating the pairing gap\nself-consistently. The results reveal that the phase transition from the BCS\nsuperfluid to the topological superfluid happens under proper Zeeman field\nstrength and SOC strength. In particular, in contrast to the BCS superfluid\ndecreasing monotonically as the SOC strength increasing, the topological\nsuperfluid region shows a dome with the SOC strength increasing. An optimal\nregion in the phase diagram to find the topological superfluid can be found,\nwhich is important to realize the topological superfluid in optical lattice\nexperimentally. Then we obtain the change of both band structure and density of\nstates (DOS) during the topological phase transition, and explain the four\npeaks of DOS in the topological superfluid by the topology change of the\nlow-energy branch of quasiparticle energy spectra. Moreover, the topological\nsuperfluid can be suppressed by the doping concentration."
    },
    {
        "anchor": "Universal thermodynamics of a two-dimensional Bose gas: Using renormalization-group arguments we show that the low-temperature\nthermodynamics of a three- or two-dimensional dilute Bose gas is fully\ndetermined by a universal scaling function $\\calF_d(\\mu/k_BT,\\tilde g(T))$ once\nthe mass $m$ and the s-wave scattering length $a_d$ of the bosons are known\n($d$ is the space dimension). Here $\\mu$ and $T$ denote the chemical potential\nand temperature of the gas, and the temperature-dependent dimensionless\ninteraction constant $\\tilde g(T)$ is a function of $ma_d^2k_BT/\\hbar^2$. We\ncompute the scaling function $\\calF_2$ using a nonperturbative\nrenormalization-group approach and find that both the $\\mu/k_BT$ and $\\tilde\ng(T)$ dependencies are in very good agreement with recent experimental data\nobtained for a quasi-two-dimensional Bose gas with or without optical lattice.\nWe also show that the nonperturbative renormalization-group estimate of the\nBerezinskii-Kosterlitz-Thouless transition temperature compares well with the\nresult obtained from a quantum Monte Carlo simulation of an effective classical\nfield theory.",
        "positive": "Strongly interacting impurities in a dilute Bose condensate: An impurity in a Bose gas is commonly referred to as Bose polaron. For a\ndilute Bose gas its properties are expected to be universal, that is dependent\nonly on a few parameters characterizing the boson-impurity interactions. When\nboson-impurity interactions are weak, it has been known for some time that the\nproperties of the polaron depend only on the scattering length of these\ninteractions. In this paper which accompanies and extends Ref. [Phys. Rev.\nLett. 126, 123403 (2021)] (where some of these results have already been\nreported) we examine stronger boson-impurity interactions, keeping their range\nfinite. We demonstrate that for attractive interactions between impurity and\nthe bosons up to and including the unitary point of these interactions, all\nstatic properties of a Bose polaron in a dilute Bose gas can be calculated in\nterms of the scattering length and an additional parameter which characterizes\nthe range of the impurity-boson interactions. We show that our approach to this\nproblem is valid if this parameter does not deviate too much from the\nscattering length of intra-boson interactions, with the precise criterion given\nin the text. We produce explicit expressions for the energy and other\nproperties of polaron for the case when the impurity-boson scattering length is\ntuned to unitarity, and we also provide the first correction away from it."
    },
    {
        "anchor": "Quadrature interferometry for nonequilibrium ultracold bosons in optical\n  lattices: We develop an interferometric technique for making time-resolved measurements\nof field-quadrature operators for nonequilibrium ultracold bosons in optical\nlattices. The technique exploits the internal state structure of magnetic atoms\nto create two subsystems of atoms in different spin states and lattice sites. A\nFeshbach resonance turns off atom-atom interactions in one spin subsystem,\nmaking it a well-characterized reference state, while atoms in the other\nsubsystem undergo nonequilibrium dynamics for a variable hold time. Interfering\nthe subsystems via a second beam-splitting operation, time-resolved quadrature\nmeasurements on the interacting atoms are obtained by detecting relative spin\npopulations. The technique can provide quadrature measurements for a variety of\nHamiltonians and lattice geometries (e.g., cubic, honeycomb, superlattices),\nincluding systems with tunneling, spin-orbit couplings using artificial gauge\nfields, and higher-band effects. Analyzing the special case of a deep lattice\nwith negligible tunneling, we obtain the time evolution of both quadrature\nobservables and their fluctuations. As a second application, we show that the\ninterferometer can be used to measure atom-atom interaction strengths with\nsuper-Heisenberg scaling n^(-3/2) in the mean number of atoms per lattice site\nn, and standard quantum limit scaling M^(-1/2) in the number of lattice sites\nM. In our analysis, we require M >> 1 and for realistic systems n is small, and\ntherefore the scaling in total atom number N = nM is below the Heisenberg\nlimit; nevertheless, measurements testing the scaling behaviors for\ninteraction-based quantum metrologies should be possible in this system.",
        "positive": "Characterizing quantum gases in time-controlled disorder realizations\n  using cross-correlations of density distributions: The role of disorder on physical systems has been widely studied in the\nmacroscopic and microscopic world. While static disorder is well understood in\nmany cases, the impact of time-dependent disorder on quantum gases is still\npoorly investigated. In our experimental setup, we introduce and characterize a\nmethod capable of producing time-controlled optical-speckle disorder.\nExperimentally, coherent light illuminates a combination of a static and a\nrotating diffuser, thereby collecting a spatially varying phase due to the\ndiffusers' structure and a temporally variable phase due to the relative\nrotation. Controlling the rotation of the diffuser allows changing the speckle\nrealization or, for future work, the characteristic time scale of the change of\nthe speckle pattern, i.e. the correlation time, matching typical time scales of\nthe quantum gases investigated. We characterize the speckle pattern ex-situ by\nmeasuring its intensity distribution cross-correlating different intensity\npatterns. In-situ, we observe its impact on a molecular Bose-Einstein\ncondensate (BEC) and cross-correlate the density distributions of BECs probed\nin different speckle realizations. As one diffuser rotates relative to the\nother around the common optical axis, we trace the optical speckle's intensity\ncross-correlations and the quantum gas' density cross-correlations. Our results\nshow comparable outcomes for both measurement methods. The setup allows us to\ntune the disorder potential adapted to the characteristics of the quantum gas.\nThese studies pave the way for investigating nonequilibrium physics in\ninteracting quantum gases using controlled dynamical-disorder potentials."
    },
    {
        "anchor": "Realization of a Strongly Interacting Fermi Gas of Dipolar Atoms: We realize a two-component dipolar Fermi gas with tunable interactions, using\nerbium atoms. Employing a lattice-protection technique, we selectively prepare\ndeeply degenerate mixtures of the two lowest spin states and perform\nhigh-resolution Feshbach spectroscopy in an optical dipole trap. We identify a\ncomparatively broad Feshbach resonance and map the interspin scattering length\nin its vicinity. The Fermi mixture shows a remarkable collisional stability in\nthe strongly interacting regime, providing a first step towards studies of\nsuperfluid pairing, crossing from Cooper pairs to bound molecules, in presence\nof dipole-dipole interactions.",
        "positive": "Relaxation of Fermionic Excitations in a Strongly Attractive Fermi Gas\n  in an Optical Lattice: We theoretically study the relaxation of high energy single particle\nexcitations into molecules in a system of attractive fermions in an optical\nlattice, both in the superfluid and the normal phase. In a system characterized\nby an interaction scale $U$ and a tunneling rate $t$, we show that the\nrelaxation rate scales as $\\sim Ct\\exp(-\\alpha U^2/t^2)$ in the large $U/t$\nlimit. We obtain explicit expressions for the exponent $\\alpha$, both in the\nlow temperature superfluid phase and the high temperature phase with pairing\nbut no coherence between the molecules. We find that the relaxation rate\ndecreases both with temperature and deviation of the fermion density from\nhalf-filling. We show that quasiparticle and phase degrees of freedom are\neffectively decoupled within experimental timescales allowing for observation\nof ordered states even at high total energy of the system."
    },
    {
        "anchor": "One-Dimensional Integrable Spinor BECs Mapped to Matrix Nonlinear\n  Schr\u00f6dinger Equation and Solution of Bogoliubov Equation in These Systems: In this short note, we construct mappings from one-dimensional integrable\nspinor BECs to matrix nonlinear Schr\\\"odinger equation, and solve the\nBogoliubov equation of these systems. A map of spin-$n$ BEC is constructed from\nthe $2^n$-dimensional spinor representation of irreducible tensor operators of\n$so(2n+1)$. Solutions of Bogoliubov equation are obtained with the aid of the\ntheory of squared Jost functions.",
        "positive": "Chiral orbital magnetism of $p$-orbital bosons in optical lattices: Chiral magnetism is a fascinating quantum phenomena that has been found in\nlow-dimensional magnetic materials. It is not only interesting for\nunderstanding the concept of chirality, but also important for potential\napplications in spintronics. Past studies show that chiral magnets require both\nlack of the inversion symmetry and spin-orbit coupling to induce the\nDzyaloshinskii-Moriya (DM) interaction. Here we report that the combination of\ninversion symmetry breaking and quantum degeneracy of orbital degrees of\nfreedom will provide a new paradigm to achieve the chiral orbital magnetism. By\nmeans of the density matrix renormalization group (DMRG) calculation, we\ndemonstrate that the chiral orbital magnetism can be found when considering\nbosonic atoms loaded in the $p$-band of an optical lattice in the Mott regime.\nThe high tunability of our scheme is also illustrated through simply\nmanipulating the inversion symmetry of the system for the cold atom\nexperimental conditions."
    },
    {
        "anchor": "1D quasicrystals and topological markers: Local topological markers are effective tools for determining the topological\nproperties of both homogeneous and inhomogeneous systems. The Chern marker is\nan established topological marker that has previously been shown to effectively\nreveal the topological properties of 2D systems. In an earlier work, the\npresent authors have developed a marker that can be applied to 1D\ntime-dependent systems which can be used to explore their topological\nproperties, like charge pumping under the presence of disorder. In this paper,\nwe show how to alter the 1D marker so that it can be applied to quasiperiodic\nand aperiodic systems. We then verify its effectiveness against different\nquasicrystal Hamiltonians, some which have been addressed in previous studies\nusing existing methods, and others which possess topological structures that\nhave been largely unexplored. We also demonstrate that the altered 1D marker\ncan be productively applied to systems that are fully aperiodic.",
        "positive": "Spin exchange-enabled quantum simulator for large-scale non-Abelian\n  gauge theories: A central requirement for the faithful implementation of large-scale lattice\ngauge theories (LGTs) on quantum simulators is the protection of the underlying\ngauge symmetry. Recent advancements in the experimental realizations of\nlarge-scale LGTs have been impressive, albeit mostly restricted to Abelian\ngauge groups. Guided by this requirement for gauge protection, we propose an\nexperimentally feasible approach to implement large-scale non-Abelian\n$\\mathrm{SU}(N)$ and $\\mathrm{U}(N)$ LGTs with dynamical matter in $d+1$D,\nenabled by two-body spin-exchange interactions realizing local emergent\ngauge-symmetry stabilizer terms. We present two concrete proposals for $2+1$D\n$\\mathrm{SU}(2)$ and $\\mathrm{U}(2)$ LGTs, including dynamical matter and\ninduced plaquette terms, that can be readily implemented in current\nultracold-molecule and next-generation ultracold-atom platforms. We provide\nnumerical benchmarks showcasing experimentally accessible dynamics, and\ndemonstrate the stability of the underlying non-Abelian gauge invariance. We\ndevelop a method to obtain the effective gauge-invariant model featuring the\nrelevant magnetic plaquette and minimal gauge-matter coupling terms. Our\napproach paves the way towards near-term realizations of large-scale\nnon-Abelian quantum link models in analog quantum simulators."
    },
    {
        "anchor": "Bose-Einstein condensation temperature of weakly interacting atoms: The critical temperature of Bose-Einstein condensation essentially depends on\ninternal properties of the system as well as on the geometry of a trapping\npotential. The peculiarities of defining the phase transition temperature of\nBose-Einstein condensation for different systems are reviewed, including\nhomogenous Bose gas, trapped Bose atoms, and bosons in optical lattices. The\nmethod of self-similar approximants, convenient for calculating critical\ntemperature, is briefly delineated.",
        "positive": "Ultracold Fermi Gases with Emergent SU(N) Symmetry: We review recent experimental and theoretical progress on ultracold\nalkaline-earth Fermi gases with emergent SU$(N)$ symmetry. Emphasis is placed\non describing the ground-breaking experimental achievements of recent years.\nThe latter include the cooling to below quantum degeneracy of various isotopes\nof ytterbium and strontium, the demonstration of optical Feshbach resonances\nand the optical Stern-Gerlach effect, the realization of a Mott insulator of\n$^{173}$Yb atoms, the creation of various kinds of Fermi-Bose mixtures and the\nobservation of many-body physics in optical lattice clocks. On the theory side,\nwe survey the zoo of phases that have been predicted for both gases in a trap\nand loaded into an optical lattice, focusing on two and three-dimensional\nsystems. We also discuss some of the challenges that lie ahead for the\nrealization of such phases, such as reaching the temperature scale required to\nobserve magnetic and more exotic quantum orders, and dealing with collisional\nrelaxation of excited electronic levels."
    },
    {
        "anchor": "Vortex Lattice Formation in Spin-Orbit-Coupled Spin-2 Bose-Einstein\n  Condensate Under Rotation: We investigate the vortex lattice configuration in a rotating spin\norbit-coupled spin-2 Bose-Einstein condensate confined in a\nquasi-two-dimensional harmonic trap. By considering the interplay between\nrotation frequency, spin-orbit couplings, and inter atomic interactions, we\nexplore a variety of vortex lattice structures emerging as a ground state\nsolution. Our study focuses on the combined effects of spin-orbit coupling and\nrotation, analyzed by using the variational method for the single-particle\nHamiltonian. We observe that the interplay between rotation and Rashba\nspin-orbit coupling gives rise to different effective potentials for the\nbosons. Specifically, at higher rotation frequencies, isotropic spin-orbit\ncoupling leads to an effective toroidal potential, while fully anisotropic\nspin-orbit coupling results in a symmetric double-well potential. To obtain\nthese findings, we solve the five coupled Gross-Pitaevskii equations for the\nspin-2 BEC with spin-orbit coupling under rotation. Notably, we find that the\nantiferromagnetic, cyclic, and ferromagnetic phases exhibit similar behavior at\nhigher rotation.",
        "positive": "Can we swim in superfluids?: Numerical demonstration of self-propulsion\n  in a Bose-Einstein condensate: It is numerically investigated whether a deformable object can propel itself\nin a superfluid. Articulated bodies and multi-component condensates are\nexamined as swimmers. An articulated two-body swimmer cannot obtain locomotion\nwithout emitting excitations. More flexible swimmers can do so without the need\nto excite waves."
    },
    {
        "anchor": "Feshbach Loss Spectroscopy in an Ultracold $^{23}$Na and $^{40}$K\n  Mixture: We perform Feshbach spectroscopy in an ultracold mixture of $^{23}$Na and\n$^{40}$K with different spin-state combinations. We have observed 24 new\ninterspecies Feshbach resonances at magnetic field up to 350 G. A full\ncoupled-channel calculation is performed to assign these resonances. Among\nthem, 12 resonances are identified as d-wave Feshbach resonances. These d-wave\nFeshbach resonances are about 5 G systematically smaller than the predications\nbased on previous model potential. Taking into account these new experimental\nresults, we improve the Born-Oppenheimer potentials between Na and K, and\nachieve good agreement between the theory and experiment for all the observed\nFeshbach resonances.",
        "positive": "Imaging of quantum Hall states in ultracold atomic gases: We examine off-resonant light scattering from ultracold atoms in the quantum\nHall regime. When the light scattering is spin dependent, we show that images\nformed in the far field can be used to distinguish states of the system. The\nspatial dependence of the far-field images is determined by the two-particle\nspin-correlation functions, which the images are related to by a\ntransformation. Quasiholes in the system appear in images of the density formed\nby collecting the scattered light with a microscope, where the quasihole\nstatistics are revealed by the reduction in density at the quasihole position."
    },
    {
        "anchor": "Z2 characterization for three-dimensional multiband Hubbard models: We introduce three numerical methods for characterizing the topological\nphases of three-dimensional multiband Hubbard models based on twisted boundary\nconditions, Wilson loops, as well as the local topological marker. We focus on\nthe half-filled, three-dimensional time-reversal-invariant Hofstadter model\nwith finite spin-orbit coupling. Besides the weak and strong topological\ninsulator phases we find a nodal line semimetal in the parameter regime between\nthe two three-dimensional topological insulator phases. Using dynamical\nmean-field theory combined with the topological Hamiltonian approach we find\nstabilization of these three-dimensional topological states due to the Hubbard\ninteraction. We study surface states which exhibit an asymmetry between left\nand right surface originating from the broken parity symmetry of the system.\nOur results set the stage for further research on inhomogeneous\nthree-dimensional topological systems, proximity effects, topological Mott\ninsulators, non-trivially linked nodal line semimetals and circuit-based\nquantum simulators.",
        "positive": "Perfect screening of the inter-polaronic interaction: We consider heavy particles immersed in a Fermi sea of light fermions, and\nstudy the interaction between the heavy particles induced by the surrounding\nlight fermions. With the Born-Oppenheimer method, we analytically show that the\ninduced interaction between N heavy particles vanishes for any N in the limit\nof high light-fermion density. The induced interaction vanishes even in the\nunitarity regime. This suggests that the formation of N-body bound states\nassociated with the Efimov effect is suppressed in the presence of the dense\nFermi sea. We ascribe the vanishing induced interaction to the screening effect\nin the neutral Fermi system."
    },
    {
        "anchor": "Theory of Interacting Cavity Rydberg Polaritons: Photonic materials are an emerging platform to explore quantum matter and\nquantum dynamics. The development of Rydberg electromagnetically induced\ntransparency provided a clear route to strong interactions between individual\noptical photons. In conjunction with carefully designed optical resonators, it\nis now possible to achieve extraordinary control of the properties of\nindividual photons, introducing tunable gauge fields whilst imbuing the photons\nwith mass and embedding them on curved spatial manifolds. Building on work\nformalizing Rydberg-mediated interactions between propagating photons, we\ndevelop a theory of interacting Rydberg polaritons in multimode optical\nresonators, where the strong interactions are married with tunable\nsingle-particle properties to build and probe exotic matter. In the presence of\nstrong coupling between the resonator field and a Rydberg-dressed atomic\nensemble, a quasiparticle called the \"cavity Rydberg polariton\" emerges. We\ninvestigate its properties, finding that it inherits both the fast dynamics of\nits photonic constituents and the strong interactions of its atomic\nconstituents. We develop tools to properly renormalize the interactions when\npolaritons approach each other, and investigate the impact of atomic motion on\nthe coherence of multi-mode polaritons, showing that most channels for\natom-polariton cross-thermalization are strongly suppressed. Finally, we\npropose to harness the repeated diffraction and refocusing of the optical\nresonator to realize interactions which are local in momentum space. This work\npoints the way to efficient modeling of polaritonic quantum materials in\nproperly renormalized strongly interacting effective theories, thereby enabling\nexperimental studies of photonic fractional quantum Hall fluids and crystals,\nplus photonic quantum information processors and repeaters.",
        "positive": "Imaginary Potential Induced Quantum Coherence for Bose-Einstein\n  Condensates: The role of complex potentials in single-body Schr\\H{o}dinger equation has\nbeen studied intensively. We study the quantum coherence for degenerate Bose\ngases in complex potentials, when the exchange symmetry of identical bosons is\nconsidered. For initially independent Bose-Einstein condensates, it is shown\nthat even very weak imaginary potential can induce perfect quantum coherence\nbetween different condensates. The scheme to observe imaginary potential\ninduced quantum coherence is discussed."
    },
    {
        "anchor": "Influence of quantum fluctuations on the superfluid critical velocity of\n  a one-dimensional Bose gas: The mean-field Gross-Pitaevskii equation with repulsive interactions exhibits\nfrictionless flow when stirred by an obstacle below a critical velocity. Here\nwe go beyond the mean-field approximation to examine the influence of quantum\nfluctuations on this threshold behaviour in a one-dimensional Bose gas in a\nring. Using the truncated Wigner approximation, we perform simulations of\nensembles of trajectories where the Bose gas is stirred with a repulsive\nobstacle below the mean-field critical velocity. We observe the probabilistic\nformation of grey solitons which subsequently decay, leading to an increase in\nthe momentum of the fluid. The formation of the first soliton leads to a\nsoliton cascade, such that the fluid rapidly accelerates to minimise the speed\ndifference with the obstacle. We measure the initial rate of momentum transfer,\nand relate it to macroscopic tunnelling between quantised flow states in the\nring.",
        "positive": "Many-body localization of one-dimensional degenerate Fermi gases with\n  cavity-assisted non-local quasiperiodic interactions: The localization properties of one-dimensional degenerate Fermi gases with\ncavity-assisted non-local quasiperiodic interactions are numerically studied.\nAlthough the cavity-induced interaction is typically nonlocal, it is proved\nthat the eigenstate thermalization hypothesis (ETH) is still applicable in our\nsystem depending on the system parameters. We also find the segment of the\nspectrum corresponding to infinite effective temperature varies for different\nsystem parameters, which indicates the spectral range employed in the spectral\nstatistical analysis should be varied accordingly. The features of many-body\nlocalization (MBL) are numerically identified by analyzing the spectral\nstatistics and the entanglement entropy using exact diagonalization. These\nfeatures are further confirmed by our time evolution results. In addition, the\nnumber of cavity photons are found stable over long time dynamics in the MBL\nphase. Such a feature can not only be utilized to nondestructively diagnose the\nMBL phase by monitoring the number of leaking photons from the cavity, but\nleveraged for constructing a device to produce a stable number of photons."
    },
    {
        "anchor": "Evolution of temporal coherence in confined polariton condensates: We study the influence of spatial confinement on the second-order temporal\ncoherence of the emission from a semiconductor microcavity in the strong\ncoupling regime. The confinement, provided by etched micropillars, has a\nfavorable impact on the temporal coherence of solid state quasi-condensates\nthat evolve in our device above threshold. By fitting the experimental data\nwith a microscopic quantum theory based on a quantum jump approach, we\nscrutinize the influence of pump power and confinement and find that\nphonon-mediated transitions are enhanced in the case of a confined structure,\nin which the modes split into a discrete set. By increasing the pump power\nbeyond the condensation threshold, temporal coherence significantly improves in\ndevices with increased spatial confinement, as revealed in the transition from\nthermal to coherent statistics of the emitted light.",
        "positive": "Spontaneous formation of polar superfluid droplets in a p-wave\n  interacting Bose gas: We study the quantum fluctuations in the condensates of a mixture of bosonic\natoms and molecules with interspecies p-wave interaction. Our analysis shows\nthat the quantum phase of coexisting atomic and molecular condensates is\nunstable at the mean-field level. Unlike the mixture of s-wave interaction, the\nLee-Huang-Yang correction of p-wave interaction is unexpectedly found here to\nexhibit an opposite sign with respect to its mean-field term above a critical\nparticle density. This quantum correction to the mean-field energy provides a\nremarkable mechanism to self-stabilize the phase. The order parameter of this\nsuperfluid phase carries opposite finite momenta for the two atomic species\nwhile the molecular component is a polar condensate. Such a correlated order\nspontaneously breaks a rich set of global U(1) gauge, atomic spin, spatial\nrotation and translation, and time-reversal symmetries. For potential\nexperimental observation, the phenomenon of anisotropic polar superfluid\ndroplets is predicted to occur, when the particle number is kept finite."
    },
    {
        "anchor": "Observation of Two Sound Modes in a Binary Superfluid Gas: We study the propagation of sound waves in a binary superfluid gas with two\nsymmetric components. The binary superfluid is constituted using a\nBose-Einstein condensate of $^{23}$Na in an equal mixture of two hyperfine\nground states. Sound waves are excited in the condensate by applying a local\nspin-dependent perturbation with a focused laser beam. We identify two distinct\nsound modes, referred to as density sound and spin sound, where the densities\nof the two spin components oscillate in phase and out of phase, respectively.\nThe observed sound propagation is explained well by the two-fluid hydrodynamics\nof the binary superfluid. The ratio of the two sound velocities is precisely\nmeasured with no need for absolute density calibration, and we find it in\nquantitatively good agreement with known interaction properties of the binary\nsystem.",
        "positive": "Single-Spin Addressing in an Atomic Mott Insulator: Ultracold atoms in optical lattices are a versatile tool to investigate\nfundamental properties of quantum many body systems. In particular, the high\ndegree of control of experimental parameters has allowed the study of many\ninteresting phenomena such as quantum phase transitions and quantum spin\ndynamics. Here we demonstrate how such control can be extended down to the most\nfundamental level of a single spin at a specific site of an optical lattice.\nUsing a tightly focussed laser beam together with a microwave field, we were\nable to flip the spin of individual atoms in a Mott insulator with\nsub-diffraction-limited resolution, well below the lattice spacing. The Mott\ninsulator provided us with a large two-dimensional array of perfectly arranged\natoms, in which we created arbitrary spin patterns by sequentially addressing\nselected lattice sites after freezing out the atom distribution. We directly\nmonitored the tunnelling quantum dynamics of single atoms in the lattice\nprepared along a single line and observed that our addressing scheme leaves the\natoms in the motional ground state. Our results open the path to a wide range\nof novel applications from quantum dynamics of spin impurities, entropy\ntransport, implementation of novel cooling schemes, and engineering of quantum\nmany-body phases to quantum information processing."
    },
    {
        "anchor": "Realizing a scalable building block of a U(1) gauge theory with cold\n  atomic mixtures: In the fundamental laws of physics, gauge fields mediate the interaction\nbetween charged particles. An example is quantum electrodynamics -- the theory\nof electrons interacting with the electromagnetic field -- based on U(1) gauge\nsymmetry. Solving such gauge theories is in general a hard problem for\nclassical computational techniques. While quantum computers suggest a way\nforward, it is difficult to build large-scale digital quantum devices required\nfor complex simulations. Here, we propose a fully scalable analog quantum\nsimulator of a U(1) gauge theory in one spatial dimension. To engineer the\nlocal gauge symmetry, we employ inter-species spin-changing collisions in an\natomic mixture. We demonstrate the experimental realization of the elementary\nbuilding block as a key step towards a platform for large-scale quantum\nsimulations of continuous gauge theories.",
        "positive": "Observation of spin-exchange dynamics between itinerant and localized\n  $^{171}\\mathrm{Yb}$ atoms: We report on the observation of the spin-exchange dynamics of\n$^{171}\\mathrm{Yb}$ atoms in the ground state $^1\\mathrm{S}_0$ and in the\nmetastable state $^3\\mathrm{P}_0$. We implement the mixed-dimensional\ntwo-orbital system using a near-resonant and magic-wavelength optical lattices,\nwhere the $^1\\mathrm{S}_0$ and $^3\\mathrm{P}_0$ atoms are itinerant in a\none-dimensional tube and localized in three dimensions, respectively. By\nexploiting an optical Stern-Gerlach method, we observe the spin depolarization\nof the $^1\\mathrm{S}_0$ atoms induced by the spin-exchange interaction with the\n$^3\\mathrm{P}_0$ atom. Our work could open the way to the quantum simulation of\nthe Kondo effect."
    },
    {
        "anchor": "Reentrant transition of bosons in a quasiperiodic potential: We investigate the behavior of a two dimensional array of Bose-Einstein\ncondensate tubes described by means of a Bose-Hubbard Hamiltonian. Using a\nWannier function expansion for the wavefunction in each tube, we compute the\nBose-Hubbard parameters related to two different longitudinal potentials,\nperiodic and quasiperiodic. We predict that - upon increasing the external\npotential strength along the direction of the tubes - the condensate can\nexperience a reentrant transition between a Mott insulating phase and the\nsuperfluid one.",
        "positive": "Complex Langevin study for polarons in an attractively interacting\n  one-dimensional two-component Fermi gas: We investigate a polaronic excitation in a one-dimensional spin-1/2 Fermi gas\nwith contact attractive interactions, using the complex Langevin method, which\nis a promising approach to evade a possible sign problem in quantum Monte Carlo\nsimulations. We found that the complex Langevin method works correctly in a\nwide range of temperature, interaction strength, and population imbalance. The\nFermi polaron energy extracted from the two-point imaginary Green's function is\nnot sensitive to the temperature and the impurity concentration in the\nparameter region we considered. Our results show a good agreement with the\nsolution of the thermodynamic Bethe ansatz at zero temperature."
    },
    {
        "anchor": "Feshbach spectroscopy of an ultracold $^{41}$K-$^6$Li mixture and\n  $^{41}$K atoms: We have observed 69 $^{41}$K-$^6$Li interspecies Feshbach resonances\nincluding 13 elastic p-wave resonances and 6 broad d-wave resonances of\n$^{41}$K atoms in different spin-state combinations at fields up to 600~G.\nMulti-channel quantum defect theory calculation is performed to assign these\nresonances and the results show perfect agreement with experimental values\nafter improving input parameters. The observed broad p- and d- wave resonances\ndisplay a full resolved multiplet structure. They may serve as important\nsimulators to nonzero partial wave dominated physics.",
        "positive": "Clock shifts in a Fermi gas interacting with a minority component: a\n  soluble model: We consider the absorption spectrum of a Fermi gas mixed with a minority\nspecies when majority fermions are transferred to another internal state by an\nexternal probe. In the limit when the minority species is much more massive\nthan the majority one, we show that the minority species may be treated as\nstatic impurities and the problem can be solved in closed form. The analytical\nresults bring out the importance of vertex corrections, which change\nqualitatively the nature of the absorption spectrum. It is demonstrated that\nlarge line shifts are not associated with resonant interactions in general. We\nalso show that the commonly used ladder approximation fails when the majority\ncomponent is degenerate for large mass ratios between the minority and majority\nspecies and that bubble diagrams, which correspond to the creation of many\nparticle--hole pairs, must be taken into account. We carry out detailed\nnumerical calculations, which confirm the analytical insights and we point out\nthe connection to shadowing phenomena in nuclear physics."
    },
    {
        "anchor": "Vortex trimer in three-component Bose-Einstein condensates: Vortex trimer is predicted in three-component Bose-Einstein condensates with\ninternal coherent couplings. The molecule is made by three constituent vortices\nwhich are bounded by domain walls of the relative phases. We show that the\nshape and the size of the molecule can be controlled by changing the internal\ncoherent couplings.",
        "positive": "Analytical thermodynamics of a strongly attractive three-component Fermi\n  gas in one dimension: Ultracold three-component atomic Fermi gases in one dimension are expected to\nexhibit rich physics due to the presence of trions and different pairing\nstates. Quantum phase transitions from the trion state into a paired phase and\na normal Fermi liquid occur at zero temperature. We derive the analytical\nthermodynamics of strongly attractive three-component one-dimensional fermions\nwith SU(3) symmetry via the thermodynamic Bethe ansatz method in unequal Zeeman\nsplitting fields $H_1$ and $H_2$. We find explicitly that for low temperature\nthe system acts like either a two-component or a three-component\nTomonaga-Luttinger liquid dependent on the system parameters. The phase\ndiagrams for the chemical potential and specific heat are presented for\nillustrative values of the Zeeman splitting. We also demonstrate that crossover\nbetween different Tomonaga-Luttinger liquid phases evolve singular behaviour in\nspecific heat and entropy as the temperature tends to zero. Beyond\nTomonaga-Luttinger liquid physics, we obtain the equation of state which\nprovides a precise description of universal thermodynamics and quantum\ncriticality in three-component strongly attractive Fermi gases."
    },
    {
        "anchor": "Delocalization in a partially disordered interacting many-body system: We study a partially disordered one-dimensional system with interacting\nparticles. Concretely, we impose a disorder potential to only every other site,\nfollowed by a clean site. Our numerical analysis of eigenstate properties is\nbased on the entanglement entropy and density distributions. Most importantly,\nat large disorder, there exist eigenstates with large entanglement entropies\nand significant correlations between the clean sites. These states have\nvolume-law scaling, embedded into a sea of area-law states, reminiscent of\ninverted quantum-scar states. These eigenstate features leave fingerprints in\nthe nonequilibrium dynamics even in the large-disorder regime, with a strong\ninitial-state dependence. We demonstrate that certain types of initial\ncharge-density-wave states decay significantly, while others preserve their\ninitial inhomogeneity, the latter being the typical behavior for many-body\nlocalized systems. This initial-condition dependent dynamics may give extra\ncontrol over the delocalization dynamics at large disorder strength and should\nbe experimentally feasible with ultracold atoms in optical lattices.",
        "positive": "Short-time universal scaling in an isolated quantum system after a\n  quench: Renormalization-group methods provide a viable approach for investigating the\nemergent collective behavior of classical and quantum statistical systems in\nboth equilibrium and nonequilibrium conditions. Within this approach we\ninvestigate here the dynamics of an isolated quantum system represented by a\nscalar $\\phi^4$ theory after a global quench of the potential close to a\ndynamical critical point. We demonstrate that, within a pre-thermal regime, the\ntime dependence of the relevant correlations is characterized by a short-time\nuniversal exponent, which we calculate at the lowest order in a dimensional\nexpansion."
    },
    {
        "anchor": "Relaxation in dipolar spin ladders: from pair production to false-vacuum\n  decay: Ultracold dipolar particles pinned in optical lattices or tweezers provide an\nexcellent platform for studying out-of-equilibrium quantum magnetism with\ndipole-mediated couplings. Starting with an initial state with spins of\nopposite orientation in each of the legs of a ladder lattice, we show that spin\nrelaxation displays an unexpected dependence on inter-leg distance and dipole\norientation. This intricate dependence, stemming from the interplay between\nintra- and inter-leg interactions, results in three distinct dynamical regimes:\n(i) ergodic, characterized by the fast relaxation towards equilibrium of\ncorrelated pairs of excitations generated at exponentially fast rates from the\ninitial state; (ii) metastable, in which the state is quasi-localized in the\ninitial state and only decays at exceedingly long timescales, resembling false\nvacuum decay; and, surprisingly, (iii) partially-relaxed, with coexisting fast\npartial relaxation and very long-lived partial quasi-localization. Realizing\nthese intriguing dynamics is within reach of current state-of-the-art\nexperiments in dipolar gases.",
        "positive": "Interlayer superfluidity in bilayer systems of fermionic polar molecules: We consider fermionic polar molecules in a bilayer geometry where they are\noriented perpendicularly to the layers, which permits both low inelastic losses\nand superfluid pairing. The dipole-dipole interaction between molecules of\ndifferent layers leads to the emergence of interlayer superfluids. The\nsuperfluid regimes range from BCS-like fermionic superfluidity with a high\n$T_c$ to Bose-Einstein (quasi-)condensation of interlayer dimers, thus\nexhibiting a peculiar BCS-BEC crossover. We show that one can cover the entire\ncrossover regime under current experimental conditions."
    },
    {
        "anchor": "Majorana Modes in Driven-Dissipative Atomic Superfluids With Zero Chern\n  Number: We investigate dissipation-induced p-wave paired states of fermions in two\ndimensions and show the existence of spatially separated Majorana zero modes in\na phase with vanishing Chern number. We construct an explicit and natural model\nof a dissipative vortex that traps a single of these modes, and establish its\ntopological origin by mapping the problem to a chiral one-dimensional wire\nwhere we observe a non-equilibrium topological phase transition characterized\nby an abrupt change of a topological invariant (winding number). We show that\nthe existence of a single Majorana zero mode in the vortex core is intimately\ntied to the dissipative nature of our model. Engineered dissipation opens up\npossibilities for experimentally realizing such states with no Hamiltonian\ncounterpart.",
        "positive": "Improving the Gutzwiller Ansatz with Matrix Product States: The Gutzwiller variational wavefunction (GVW) is commonly employed to capture\ncorrelation effects in condensed matter systems such as ferromagnets, ultracold\nbosonic gases, correlated superconductors, etc. By noticing that the\ngrand-canonical and number-conserving Gutzwiller Ans\\\"atze are in fact the\nzero-order approximation of an expansion in the truncation parameter of a\nMatrix Product State (MPS), we argue that MPSs, and the algorithms used to\noperate on them, are not only flexible computational tools but also a unifying\ntheoretical framework that can be used to generalize and improve on the GVW. In\nfact, we show that a number-conserving GVW is less efficient in capturing the\nground state of a quantum system than a more general MPS which can be optimized\nwith comparable computational resources. Moreover, we suggest a corrected\ntime-dependent density matrix renormalization group algorithm that ensures the\nconservation of the expectation value of the number of particles when a GVW or\na MPS are not explicitly number-conserving. The GVW dynamics obtained with our\nalgorithm compares very well with the exact one in 1D. Most importantly, the\nalgorithm works in any dimension for a GVW. We thus expect it to be of great\nvalue in the study of the dynamics of correlated quantum systems."
    },
    {
        "anchor": "Optical cooling and trapping of highly magnetic atoms: The benefits of a\n  spontaneous spin polarization: From the study of long-range-interacting systems to the simulation of gauge\nfields, open-shell Lanthanide atoms with their large magnetic moment and narrow\noptical transitions open novel directions in the field of ultracold quantum\ngases. As for other atomic species, the magneto-optical trap (MOT) is the\nworking horse of experiments but its operation is challenging, due to the large\nelectronic spin of the atoms. Here we present an experimental study of\nnarrow-line Dysprosium MOTs. We show that the combination of radiation pressure\nand gravitational forces leads to a spontaneous polarization of the electronic\nspin. The spin composition is measured using a Stern-Gerlach separation of spin\nlevels, revealing that the gas becomes almost fully spin-polarized for large\nlaser frequency detunings. In this regime, we reach the optimal operation of\nthe MOT, with samples of typically $3\\times 10^8$ atoms at a temperature of\n15\\,$\\mu$K. The spin polarization reduces the complexity of the radiative\ncooling description, which allows for a simple model accounting for our\nmeasurements. We also measure the rate of density-dependent atom losses,\nfinding good agreement with a model based on light-induced Van der Waals\nforces. A minimal two-body loss rate $\\beta\\sim 2\\times10^{-11}\\,$cm$^{3}$/s is\nreached in the spin-polarized regime. Our results constitute a benchmark for\nthe experimental study of ultracold gases of magnetic Lanthanide atoms.",
        "positive": "Experimental realization of a two-dimensional synthetic spin-orbit\n  coupling in ultracold Fermi gases: Spin-orbit coupling (SOC) is central to many physical phenomena, including\nfine structures of atomic spectra and quantum topological matters. Whereas SOC\nis in general fixed in a physical system, atom-laser interaction provides\nphysicists a unique means to create and control synthetic SOC for ultracold\natoms \\cite{Dalibard}. Though significant experimental progresses have been\nmade, a bottleneck in current studies is the lack of a two-dimensional (2D)\nsynthetic SOC, which is crucial for realizing high-dimensional topological\nmatters. Here, we report the experimental realization of 2D SOC in ultracold\n$^{40}$K Fermi gases using three lasers, each of which dresses one atomic\nhyperfine spin state. Through spin injection radio-frequency (rf) spectroscopy,\nwe probe the spin-resolved energy dispersions of dressed atoms, and observe a\nhighly controllable Dirac point created by the 2D SOC. Our work paves the way\nfor exploring high-dimensional topological matters in ultracold atoms using\nRaman schemes."
    },
    {
        "anchor": "Strongly correlated gases of Rydberg-dressed atoms: quantum and\n  classical dynamics: We discuss techniques to generate long-range interactions in a gas of\ngroundstate alkali atoms, by weakly admixing excited Rydberg states with laser\nlight. This provides a tool to engineer strongly correlated phases with reduced\ndecoherence from inelastic collisions and spontaneous emission. As an\nillustration, we discuss the quantum phases of dressed atoms with dipole-dipole\ninteractions confined in a harmonic potential, as relevant to experiments. We\nshow that residual spontaneous emission from the Rydberg state acts as a\nheating mechanism, leading to a quantum-classical crossover.",
        "positive": "Anyonic statistics of quantum impurities in two dimensions: We demonstrate that identical impurities immersed in a two-dimensional\nmany-particle bath can be viewed as flux-tube-charged-particle composites\ndescribed by fractional statistics. In particular, we find that the bath\nmanifests itself as an external magnetic flux tube with respect to the\nimpurities, and hence the time-reversal symmetry is broken for the effective\nHamiltonian describing the impurities. The emerging flux tube acts as a\nstatistical gauge field after a certain critical coupling. This critical\ncoupling corresponds to the intersection point between the quasiparticle state\nand the phonon wing, where the angular momentum is transferred from the\nimpurity to the bath. This amounts to a novel configuration with emerging\nanyons. The proposed setup paves the way to realizing anyons using electrons\ninteracting with superfluid helium or lattice phonons, as well as using atomic\nimpurities in ultracold gases."
    },
    {
        "anchor": "The Aubry-Andr\u00e9 model as the hobbyhorse for understanding localization\n  phenomenon: We present a thorough pedagogical analysis of the single particle\nlocalization phenomenon in a quasiperiodic lattice in one dimension.\nDescription of disorder in the lattice is represented by the Aubry-Andr\\'e\nmodel. Characterization of localization is performed through the analysis of\nboth, stationary and dynamical properties. The stationary properties\ninvestigated are the inverse participation ratio (IPR), the normalized\nparticipation ratio (NPR) and the energy spectrum as a function of the disorder\nstrength. As expected, the distinctive Hofstadter pattern is found. Two\ndynamical quantities allow discerning the localization phenomenon, being the\nspreading of an initially localized state and the evolution of population\nimbalance in even and odd sites across the lattice.",
        "positive": "Thermodynamics and spin-charge separation of one-dimensional strongly\n  repulsive three-component fermions: The low temperature thermodynamics of one-dimensional strongly repulsive\nSU(3) fermions in the presence of a magnetic field is investigated via the\nYang-Yang thermodynamic Bethe ansatz method. The analytical free energy and\nmagnetic properties of the model at low temperatures in a weak magnetic field\nare derived via the Wiener-Hopf method. It is shown that the low energy physics\ncan be described by spin-charge separated conformal field theories of an\neffective Tomonaga-Luttinger liquid and an antiferromagnetic SU(3) Heisenberg\nspin chain. Beyond the Tomonaga-Luttinger liquid regime, the equation of state\nis given in terms of the polylog function for a weak external field. The\nresults obtained are essential for further study of quantum criticality in\nstrongly repulsive three-component fermions."
    },
    {
        "anchor": "Signature of reentrant localization in collisional inhomogeneous\n  spin-orbit coupled condensates: We study the localization transition in a spin-orbit (SO) coupled binary\nBose-Einstein condensates (BECs) with collisional inhomogeneous interaction\ntrapped in a one-dimensional quasiperiodic potential. Our numerical analysis\nshows that the competition between the quasiperiodic disorder and inhomogeneous\ninteraction leads to a reentrant localization transition as the interaction\nstrength is tuned from attractive to repulsive in nature. Further, we analyse\nthe combined effect of the SO and Rabi coupling strengths on the localization\ntransition for different interaction strengths and obtain signatures of\nreentrant localization transition as function of SO coupling in the regime of\nweak interactions. We complement our numerical observation with the analytical\nmodel using the variational approach. At the end we show how the reentrant\nlocalization is manifested in the quench dynamics of the condensate. Our study\nprovides an indirect approach to achieve localization transition without tuning\nthe quasiperiodic potential strength, rather by tuning the inhomogeneous\ninteraction.",
        "positive": "Properties of spin-polarized impurities -- ferrons, in the unitary Fermi\n  gas: A new excitation mode has been predicted to exist in the unitary Fermi gas.\nIt has a form of a spin-polarized impurity, which was dubbed as ferron. It is\ncharacterized by a closed nodal surface of the pairing field surrounding a\npartially spin-polarized superfluid region, where the phase differs by $\\pi$.\nIn this paper, we discuss the effect of temperature on the generation of the\nferron and the adiabaticity of the spin-polarizing potential together with\nferron's ground state properties."
    },
    {
        "anchor": "Boson-vortex duality in compressible spin-orbit coupled BECs: Using a (1+2)-dimensional boson-vortex duality between non-linear\nelectrodynamics and a two-component compressible Bose-Einstein condensate (BEC)\nwith spin-orbit (SO) coupling, we obtain generalised versions of the\nhydrodynamic continuity and Euler equations where the phase defect and\nnon-defect degrees of freedom enter separately. We obtain the generalised\nMagnus force on vortices under SO coupling, and associate the linear\nconfinement of vortices due to SO coupling with instanton fluctuations of the\ndual theory.",
        "positive": "A New Non-Abelian Topological Phase of Cold Fermi Gases in Anisotropic\n  and Spin-Dependent Optical Lattices: To realize non-Abelian s-wave topological superfluid (TS) of cold Fermi\ngases, generally a Zeeman magnetic field larger than superfluid pairing gap is\nnecessary. In this paper we find that using an anisotropic and spin-dependent\noptical lattice (ASDOL) to trap gases, a new non-Abelian TS phase appears, in\ncontrast to an isotropic and spin-independent optical lattice. A characteristic\nof this new non-Abelian TS is that Zeeman magnetic field can be smaller than\nthe superfluid pairing gap. By self-consistently solving pairing gap equation\nand considering the competition against normal state and phase separation, this\nnew phase is also stable. Thus an ASDOL supplies a convenient route to realize\nTS. We also investigate edge states and the effects of a harmonic trap\npotential."
    },
    {
        "anchor": "Engineering photon statistics in a spinor polariton condensate: We implement full polarization tomography on the photon correlations in a\nspinor exciton-polariton condensate. Our measurements reveal condensate\npseudospin mean-field dynamics spanning from stochastic switching between\nlinear polarization components, limit cycles, and stable fixed points, and\ntheir intrinsic relation to the condensate photon statistics. We optically\nharness the cavity birefringence, polariton interactions, and the optical\norientation of the photoexcited exciton background to engineer photon\nstatistics with precise control. Our results demonstrate a smooth transition\nfrom a highly coherent to a super-thermal state of the condensate polarization\ncomponents.",
        "positive": "Pair density waves and vortices in an elongated two-component Fermi gas: We study the vortex structures of a two-component Fermi gas experiencing a\nuniform effective magnetic field in an anisotropic trap that interpolates\nbetween quasi-one dimensional (1D) and quasi-two dimensional (2D). At a fixed\nchemical potential, reducing the anisotropy (or equivalently increasing the\nattractive interactions or increasing the magnetic field) leads to\ninstabilities towards pair density waves, and vortex lattices. Reducing the\nchemical potential stabilizes the system. We calculate the phase diagram, and\nexplore the density and pair density. The structures are similar to those\npredicted for superfluid Bose gases. We further calculate the paired fraction,\nshowing how it depends on chemical potential and anisotropy."
    },
    {
        "anchor": "Nonperturbative renormalization-group approach to strongly-correlated\n  lattice bosons: We present a nonperturbative renormalization-group approach to the\nBose-Hubbard model. By taking as initial condition of the renormalization-group\nflow the (local) limit of decoupled sites, we take into account both local and\nlong-distance fluctuations in a nontrivial way. This approach yields a phase\ndiagram in very good quantitative agreement with quantum Monte Carlo\nsimulations, and reproduces the two universality classes of the\nsuperfluid--Mott-insulator transition. The critical behavior near the\nmulticritical points, where the transition takes place at constant density,\nagrees with the original predictions of Fisher {\\it et al.} [Phys. Rev. B {\\bf\n40}, 546 (1989)] based on simple scaling arguments. At a generic transition\npoint, the critical behavior is mean-field like with logarithmic corrections in\ntwo dimensions. In the weakly-correlated superfluid phase (far away from the\nMott insulating phase), the renormalization-group flow is controlled by the\nBogoliubov fixed point down to a characteristic (Ginzburg) momentum scale $k_G$\nwhich is much smaller than the inverse healing length $k_h$. In the vicinity of\nthe multicritical points, when the density is commensurate, we identify a sharp\ncrossover from a weakly- to a strongly-correlated superfluid phase where the\ncondensate density and the superfluid stiffness are strongly suppressed and\nboth $k_G$ and $k_h$ are of the order of the inverse lattice spacing.",
        "positive": "Fast dynamics for atoms in optical lattices: Cold atoms in optical lattices allow for accurate studies of many body\ndynamics. Rapid time-dependent modifications of optical lattice potentials may\nresult in significant excitations in atomic systems. The dynamics in such a\ncase is frequently quite incompletely described by standard applications of\ntight-binding models (such as e.g. Bose-Hubbard model or its extensions) that\ntypically neglect the effect of the dynamics on the transformation between the\nreal space and the tight-binding basis. We illustrate the importance of a\nproper quantum mechanical description using a multi-band extended Bose-Hubbard\nmodel with time-dependent Wannier functions. We apply it to situations,\ndirectly related to experiments."
    },
    {
        "anchor": "Bose-Einstein condensation in canonical ensemble with fixed total\n  momentum: We consider Bose-Einstein condensation of noninteracting homogeneous\nthree-dimensional gas in canonical ensemble when both particle number $N$ and\ntotal momentum $\\mathbf{P}$ of all particles are fixed. Using the saddle point\nmethod, we derive the large-$N$ analytical approximations for partition\nfunction, free energy, and statistical distributions of occupation numbers of\ndifferent single-particle energy levels. At temperatures below the critical\npoint of phase transition, we predict, in some ranges of $\\mathbf{P}$,\nfragmentation of the condensate, when more than one single-particle level is\nmacroscopically occupied. The occupation number distributions have\napproximately Gaussian shapes for the levels hosting the condensate, and\nexponential shapes for other, noncondensate levels. Our analysis demonstrates\nbreaking of Galilean invariance of moving finite-temperature many-particle\nsystem in the presence of Bose-Einstein condensation and extends the theory of\nmoving and rotating quantum systems to the finite-temperature large-$N$ limit.",
        "positive": "Topological phonons in arrays of ultracold dipolar particles: The notion of topology in physical systems is associated with the existence\nof a nonlocal ordering that is insensitive to a large class of perturbations.\nThis brings robustness to the behaviour of the system and can serve as a ground\nfor developing new fault-tolerant applications. We discuss how to design and\nstudy a large variety of topology-related phenomena for phonon-like collective\nmodes in arrays of ultracold polarized dipolar particles. These modes are\ncoherently propagating vibrational excitations, corresponding to oscillations\nof particles around their equilibrium positions, which exist in the regime\nwhere long-range interactions dominate over single-particle motion. We\ndemonstrate that such systems offer a distinct and versatile tool to\ninvestigate a wide range of topological effects in a single experimental setup\nwith a chosen underlying crystal structure by simply controlling the anisotropy\nof the interactions via the orientation of the external polarizing field. Our\nresults show that arrays of dipolar particles provide a promising unifying\nplatform to investigate topological phenomena with phononic modes."
    },
    {
        "anchor": "Spontaneous rotating vortex rings in a parametrically driven polariton\n  fluid: We present the theoretical prediction of spontaneous rotating vortex rings in\na parametrically driven quantum fluid of polaritons -- coherent superpositions\nof coupled quantum well excitons and microcavity photons. These rings arise not\nonly in the absence of any rotating drive, but also in the absence of a\ntrapping potential, in a model known to map quantitatively to experiments. We\nbegin by proposing a novel parametric pumping scheme for polaritons, with\ncircular symmetry and radial currents, and characterize the resulting\nnonequilibrium condensate. We show that the system is unstable to spontaneous\nbreaking of circular symmetry via a modulational instability, following which a\nvortex ring with large net angular momentum emerges, rotating in one of two\ntopologically distinct states. Such rings are robust and carry distinctive\nexperimental signatures, and so they could find applications in the new\ngeneration of polaritonic devices.",
        "positive": "Far-from-equilibrium quantum many-body dynamics: The theory of real-time quantum many-body dynamics as put forward in Ref.\n[arXiv:0710.4627] is evaluated in detail. The formulation is based on a\ngenerating functional of correlation functions where the Keldysh contour is\nclosed at a given time. Extending the Keldysh contour from this time to a later\ntime leads to a dynamic flow of the generating functional. This flow describes\nthe dynamics of the system and has an explicit causal structure. In the present\nwork it is evaluated within a vertex expansion of the effective action leading\nto time evolution equations for Green functions. These equations are applicable\nfor strongly interacting systems as well as for studying the late-time\nbehaviour of nonequilibrium time evolution. For the specific case of a bosonic\nN-component phi^4 theory with contact interactions an s-channel truncation is\nidentified to yield equations identical to those derived from the 2PI effective\naction in next-to-leading order of a 1/N expansion. The presented approach\nallows to directly obtain non-perturbative dynamic equations beyond the widely\nused 2PI approximations."
    },
    {
        "anchor": "Magnetic Impurities in Two-Dimensional Superfluid Fermi Gas with\n  Spin-Orbit Coupling: We consider magnetic impurities in a two dimensional superfluid Fermi gas in\nthe presence of spin-orbit coupling. By using the methods of t-matrix and\nGreen's function, we find spin-orbit coupling has some dramatic impacts on the\neffects of magnetic impurities. For the single impurity problem, the number of\nbound states localized around the magnetic impurity is doubled. For the finite\nconcentration $n$ of impurities, the energy gap is reduced and the density of\nstates in the gapless region is greatly modified.",
        "positive": "Magnetic field dependence of Raman coupling in Alkali atoms: We calculate the magnetic field dependence of Rabi rates for two-photon\noptical Raman processes in alkali atoms. Due to a decoupling of the nuclear and\nelectronic spins, these rates fall with increasing field. At the typical\nmagnetic fields of alkali atom Feshbach resonances (B\\sim 200G-1200G), the\nRaman rates have the same order of magnitude as their zero field values,\nsuggesting one can combine Raman-induced gauge fields/spin-orbital coupling\nwith strong Feshbach-induced interactions. The exception is $^6$Li, where there\nis a factor of 7 suppression in the Raman coupling, compared to its already\nsmall zero-field value."
    },
    {
        "anchor": "Measuring work and heat in ultracold quantum gases: We propose a feasible experimental scheme to direct measure heat and work in\ncold atomic setups. The method is based on a recent proposal which shows that\nwork is a positive operator valued measure (POVM). In the present contribution,\nwe demonstrate that the interaction between the atoms and the light\npolarisation of a probe laser allows us to implement such POVM. In this way the\nwork done on or extracted from the atoms after a given process is encoded in\nthe light quadrature that can be measured with a standard homodyne detection.\nThe protocol allows one to verify fluctuation theorems and study properties of\nthe non-unitary dynamics of a given thermodynamic process.",
        "positive": "Localization and shock waves in curved manifolds for the\n  Gross-Pitaevskii equation: We investigate the dynamics of a Bose-Einstein condensate in a progressively\nbended three dimensional cigar shaped potential. The interplay between geometry\nand nonlinearity is considered. At high curvature, topological localization\noccurs and becomes frustrated by the generation of curved dispersive\nshock-waves when the strength of nonlinearity is increased. The analysis is\nsupported by four-dimensional parallel simulations."
    },
    {
        "anchor": "Emergent patterns in a spin-orbit coupled spin-2 Bose-Einstein\n  condensate: The ground-state phases of a spin-orbit (SO) coupled atomic spin-2\nBose-Einstein condensate (BEC) are studied. Interesting density patterns\nspontaneously formed are widespread due to the competition between SO coupling\nand spin-dependent interactions like in a SO coupled spin-1 condensate. Unlike\nthe case of spin-1 condensates, which are characterized by either ferromagnetic\nor polar phase in the absence of SO, spin-2 condensates can take a cyclic\nphase, where we find the patterns formed due to SO are square or triangular in\ntheir spin component densities for axial symmetric SO interaction. Both\npatterns are found to continuously evolve into striped forms with increased\nasymmetry of the SO coupling.",
        "positive": "Berezinskii-Kosterlitz-Thouless phase induced by dissipating\n  quasisolitons: We theoretically study the sound propagation in a two-dimensional weakly\ninteracting uniform Bose gas. Using the classical fields approximation we\nanalyze in detail the properties of density waves generated both in a weak and\nstrong perturbation regimes. While in the former case density excitations can\nbe described in terms of hydrodynamic or collisionless sound, the strong\ndisturbance of the system results in a qualitatively different response. We\nidentify observed structures as quasisolitons and uncover their internal\ncomplexity for strong perturbation case. For this regime quasisolitons break\ninto vortex pairs as time progresses, eventually reaching an equilibrium state.\nWe find this state, characterized by only fluctuating in time averaged number\nof pairs of opposite charge vortices and by appearance of a quasi-long-range\norder, as the Berezinskii-Kosterlitz-Thouless (BKT) phase."
    },
    {
        "anchor": "Zero-temperature phase diagram of Yukawa bosons: We study the zero-temperature phase diagram of bosons interacting via\nscreened Coulomb (Yukawa) potential by means of the diffusion Monte Carlo\nmethod. The Yukawa potential is used as a model interaction in the neutron\nmatter, dusty plasmas and charged colloids. As shown by D. S. Petrov et al.\n[Phys. Rev. Lett. 99, 130407 (2007)], interactions between weakly bound\nmolecules of heavy and light fermionic atoms are described by an effective\nYukawa potential with a strength related to the heavy-light mass ratio M/m\nwhich might lead to crystallization in a two-dimensional geometry if the mass\nratio of heavy-light fermions exceeds a certain critical value. In the present\nwork we do a thorough study of the quantum three-dimensional Yukawa system. For\nstrong interactions (equivalently, large mass ratios) the system experiences\nseveral phase transitions as the density is increased, passing from gas to\nsolid and to gas phase again. Weakly interacting Yukawa particles do not\ncrystallize at any density. We find the minimal interaction strength at which\nthe crystallization happens. In terms of the two-component fermionic system,\nthis strength corresponds to a heavy-light mass ratio of M/m ~ 180, so that it\nis impossible to realize the gas-crystal transition in a conventional bulk\nsystem. For the Yukawa model of fermionic mixtures we also analyze the\npossibility of building molecular systems with very large effective mass ratios\nby confining the heavy component to a sufficiently deep optical lattice. We\nshow how the effective mass of the heavy component can be made arbitrarily\nlarge by increasing the lattice depth, thus leading to a tunable effective mass\nratio that can be used to realize a molecular superlattice.",
        "positive": "Lattice-induced rapid formation of spin singlets in spin-1 spinor\n  condensates: We experimentally demonstrate that combining a cubic optical lattice with a\nspinor Bose-Einstein condensate substantially relaxes three strict constraints\nand brings spin singlets of ultracold spin-1 atoms into experimentally\naccessible regions. About 80 percent of atoms in the lattice-confined spin-1\nspinor condensate are found to form spin singlets, immediately after the atoms\ncross first-order superfluid to Mott-insulator phase transitions in a microwave\ndressing field. A phenomenological model is also introduced to well describe\nour observations without adjustable parameters."
    },
    {
        "anchor": "Nonequilibrium Phase Transition of Interacting Bosons in an Intra-Cavity\n  Optical Lattice: We investigate the nonlinear light-matter interaction of a Bose-Einstein\ncondensate trapped in an external periodic potential inside an optical cavity\nwhich is weakly coupled to vacuum radiation modes and driven by a transverse\npump field. Based on a generalized Bose-Hubbard model which incorporates a\nsingle cavity mode, we include the collective backaction of the atoms on the\ncavity light field and determine the nonequilibrium quantum phases within the\nnonperturbative bosonic dynamical mean-field theory.With the system parameters\nadapted to recent experiments, we find a quantum phase transition from a normal\nphase to a self-organized superfluid phase, which is related to the\nHepp-Lieb-Dicke superradiance phase transition. For even stronger pumping, a\nself-organized Mott insulator phase arises.",
        "positive": "A coordinate Bethe ansatz approach to the calculation of equilibrium and\n  nonequilibrium correlations of the one-dimensional Bose gas: We use the coordinate Bethe ansatz to exactly calculate matrix elements\nbetween eigenstates of the Lieb-Liniger model of one-dimensional bosons\ninteracting via a two-body delta-potential. We investigate the static\ncorrelation functions of the zero-temperature ground state and their dependence\non interaction strength, and analyze the effects of system size in the\ncrossover from few-body to mesoscopic regimes for up to seven particles. We\nalso obtain time-dependent nonequilibrium correlation functions for five\nparticles following quenches of the interaction strength from two distinct\ninitial states. One quench is from the non-interacting ground state and the\nother from a correlated ground state near the strongly interacting\nTonks-Girardeau regime. The final interaction strength and conserved energy are\nchosen to be the same for both quenches. The integrability of the model highly\nconstrains its dynamics, and we demonstrate that the time-averaged correlation\nfunctions following quenches from these two distinct initial conditions are\nboth nonthermal and moreover distinct from one another."
    },
    {
        "anchor": "Nonlinear dependence observed in quadrupolar collective excitation of a\n  trapped BEC: We report the experimental observation of the collective excitations induced\nin a magnetically trapped 87Rb Bose-Einstein condensate. Low-lying mode\nexcitations were studied by tracking the condensate's center-of-mass\ndisplacement, and its aspect ratio as a function of the hold time in the trap.\nWe were able to partially control the modes onset by modulating the amplitude\nof the additional field gradient used to excite the BEC. The measured\nexcitation frequencies were found to be in good agreement with the literature.\nWe have also found that the modulation amplitude was able to change the phase\nof the center-of-mass oscillation. Finally, an interesting, non-linear\ndependence was observed on the condensate aspect ratio as a function of the\nperturbing amplitude which induces the quadrupolar mode.",
        "positive": "Smooth, holographically generated ring trap for the investigation of\n  superfluidity in ultracold atoms: We discuss the suitability of holographically generated optical potentials\nfor the investigation of superfluidity in ultracold atoms. By using a spatial\nlight modulator and a feedback enabled algorithm we generate a smooth ring with\nvariable bright regions that can be dynamically rotated to stir ultracold atoms\nand induce superflow. We also comment on its future integration into a cold\natoms experiment."
    },
    {
        "anchor": "Magnetic control of polariton spin transport: We show the full control of the polarization dynamics of a propagating\nexciton-polariton condensate in a planar microcavity by using a magnetic field\napplied in the Voigt geometry. The change of the spin-beat frequency, the\nsuppression of the optical spin Hall effect and the rotation of the\npolarization pattern by the magnetic field are theoretically reproduced by\naccounting for the magneto-induced mixing of exciton-polariton and dark, spin\nforbidden, exciton states.",
        "positive": "Comparative Study of BCS-BEC Crossover Theories above $T_c$: the Nature\n  of the Pseudogap in Ultra-Cold Atomic Fermi Gases: This paper presents a comparison of two finite-temperature BCS-Bose Einstein\ncondensation (BEC) crossover theories above the transition temperature:\nNozieres Schmitt-Rink (NSR) theory and finite $T$-extended BCS-Leggett theory.\nThe comparison is cast in the form of numerical studies of the behavior of the\nfermionic spectral function both theoretically and as constrained by\n(primarily) radio frequency (RF) experiments. Both theories include pair\nfluctuations and exhibit pseudogap effects, although the nature of this\npseudogap is very different. The pseudogap in finite $T$-extended BCS-Leggett\ntheory is found to follow a BCS-like dispersion which, in turn, is associated\nwith a broadened BCS-like self energy, rather more similar to what is observed\nin high temperature superconductors (albeit, for a d-wave case). The fermionic\nquasi-particle dispersion is different in NSR theory and the damping is\nconsiderably larger. We argue that the two theories are appropriate in\ndifferent temperature regimes with the BCS-Leggett approach more suitable\nnearer to condensation. There should, in effect, be little difference at higher\n$T$ as the pseudogap becomes weaker and where the simplifying approximations\nused in the BCS-Leggett approach break down. On the basis of\nmomentum-integrated radio frequency studies of unpolarized gases, it would be\ndifficult to distinguish which theory is the better. A full comparison for\npolarized gases is not possible since there is claimed to be inconsistencies in\nthe NSR approach (not found in the BCS-Leggett scheme). Future experiments\nalong the lines of momentum resolved experiments look to be very promising in\ndistinguishing the two theories."
    },
    {
        "anchor": "Pseudogap phenomenon and effects of population imbalance in the normal\n  state of a unitary Fermi gas: We investigate strong-coupling corrections to single-particle excitations in\nthe normal state of a spin-polarized unitary Fermi gas. Within the framework of\nan extended T-matrix approximation, we calculate the single-particle density of\nstates, as well as the single-particle spectral weight, to show that the\nso-called pseudogap phenomenon gradually disappears with increasing the\nmagnitude of an effective magnetic field. In the highly spin-polarized regime,\nthe calculated spin-polarization rate as a function of the effective magnetic\nfield agrees well with the recent experiment on a 6Li Fermi gas. Although this\nexperiment has been considered to be incompatible with the existence of the\npseudogap in an unpolarized Fermi gas, our result clarifies that the observed\nspin-polarization rate in the highly spin-polarized regime and the pseudogap in\nthe unpolarized limit can be explained in a consistent manner, when one\ncorrectly includes effects of population imbalance on single-particle\nexcitations. Since it is a crucial issue to clarify whether the pseudogap\nexists or not in the BCS (Bardeen-Cooper-Schrieffer)-BEC (Bose-Einstein\ncondensation) crossover regime of an ultracold Fermi gas, our results would be\nuseful for the understanding of this strongly interacting fermion system.",
        "positive": "Excitonic states of an impurity in a Fermi gas: We study excitonic states of an atomic impurity in a Fermi gas, i.e., bound\nstates consisting of the impurity and a hole. Previous studies considered bound\nstates of the impurity with particles from the Fermi sea where the holes only\nformed part of the particle-hole dressing. Within a two-channel model, we find\nthat, for a wide range of parameters, excitonic states are not ground but\nmetastable states. We further calculate the decay rates of the excitonic states\nto polaronic and dimeronic states and find they are long lived, scaling as\n$\\Gamma^{\\rm{Exc}}_ {\\rm{Pol}} \\propto ( \\Delta\\omega)^{5.5}$ and\n$\\Gamma^{\\rm{Exc}}_ {\\rm{Dim}} \\propto (\\Delta\\omega)^{4}$. We also find that a\nnew continuum of exciton-particle states should be considered alongside the\npreviously known dimeron-hole continuum in spectroscopic measurements. Excitons\nmust therefore be considered as a new ingredient in the study of metastable\nphysics currently being explored experimentally."
    },
    {
        "anchor": "Thermodynamics of spin-orbit-coupled Bose-Einstein condensates: In this paper we develop a quantum field approach to reveal the thermodynamic\nproperties of the trapped BEC with the equal Rashba and Dresselhaus spin-orbit\ncouplings. In the experimentally-feasible regime, the phase transition from the\nseparate phase to the single minimum phase can be well driven by the tunable\ntemperature. Moreover, the critical temperature, which is independent of the\ntrapped potential, can be derived exactly. At the critical point, the specific\nheat has a large jump and can be thus regarded as a promising candidate to\ndetect this temperature-driven phase transition. In addition, we obtain the\nanalytical expressions for the specific heat and the entropy in the different\nphases. In the single minimum phase, the specific heat as well as the entropy\nare governed only by the Rabi frequency. However, in the separate phase with\nlower temperature, we find that they are determined only by the strength of\nspin-orbit coupling. Finally, the effect of the effective atom interaction is\nalso addressed. In the separate phase, this effective atom interaction affects\ndramatically on the critical temperature and the corresponding thermodynamic\nproperties.",
        "positive": "Experimentally accessible invariants encoded in interparticle\n  correlations of harmonically trapped ultra-cold few-fermion mixtures: System of a two-flavor mixture of ultra-cold fermions confined in a\none-dimensional harmonic trap is studied in the frame of the center of mass. We\npresent a numerical method of obtaining energetic spectra in this frame for an\narbitrary mass ratio of fermionic species. We identify a specific invariant\nencoded in many-body correlations which enable one to determine an eigenstate\nof the Hamiltonian and to label excitations of the center of mass. The tool\npresented may be particularly useful in experimental analysis of the\ninterparticle interactions which do not affect the center of mass excitations\nin a harmonic potential."
    },
    {
        "anchor": "Solution of the BEC to BCS Quench in One Dimension: A gas of interacting fermions confined in a quasi one-dimensional geometry\nshows a BEC to BCS crossover upon slowly driving its coupling constant through\na confinement-induced resonance. On one side of the crossover the fermions form\ntightly-bound bosonic molecules behaving as a repulsive Bose gas, while on the\nother they form Cooper pairs, whose size is much larger than the average\ninter-particle distance. Here we consider the situation arising when the\ncoupling constant is varied suddenly from the BEC to the BCS value. Namely, we\nstudy a BEC-to-BCS quench. By exploiting a suitable continuum limit of recently\ndiscovered solvable quenches in the Hubbard model, we show that the local\nstationary state reached at large times after the quench can be determined\nexactly by means of the Quench Action approach. We provide an\nexperimentally-accessible characterisation of the stationary state by computing\nlocal pair correlation function as well as the quasi-particle distribution\nfunctions. We find that the steady state is increasingly dominated by two\nparticle spin singlet bound states for stronger interaction strength but that\nbound state formation is inhibited at larger BEC density. The bound state\nrapidity distribution displays quartic power law decay suggesting a violation\nof Tan's contact relations.",
        "positive": "Single-Particle Momentum Distributions of Efimov States in Mixed-Species\n  Systems: We solve the three-body bound state problem in three dimensions for mass\nimbalanced systems of two identical bosons and a third particle in the\nuniversal limit where the interactions are assumed to be of zero-range. The\nsystem displays the Efimov effect and we use the momentum-space wave equation\nto derive formulas for the scaling factor of the Efimov spectrum for any mass\nratio assuming either that two or three of the two-body subsystems have a bound\nstate at zero energy. We consider the single-particle momentum distribution\nanalytically and numerically and analyse the tail of the momentum distribution\nto obtain the three-body contact parameter. Our finding demonstrate that the\nfunctional form of the three-body contact term depends on the mass ratio and we\nobtain an analytic expression for this behavior. To exemplify our results, we\nconsider mixtures of Lithium with either two Caesium or Rubium atoms which are\nsystems of current experimental interest."
    },
    {
        "anchor": "Dynamics of quantum double dark-solitons and an exact finite-size\n  scaling of Bose-Einstein condensation: We show several novel aspects in the exact non-equilibrium dynamics of\nquantum double dark-soliton states in the Lieb-Liniger model for the\none-dimensional Bose gas with repulsive interactions. We also show an exact\nfinite-size scaling of the fraction of the Bose-Einstein condensation (BEC) in\nthe ground state, which should characterize the quasi-BEC in quantum double\ndark-soliton states that we assume to occur in the weak coupling regime. First,\nwe show the exact time evolution of the density profile in the quantum state\nassociated with a quantum double dark-soliton by the Bethe ansatz. Secondly, we\nderive a kind of macroscopic quantum wave-function effectively by exactly\nevaluating the square amplitude and phase profiles of the matrix element of the\nfield operator between the quantum double dark-soliton states. The profiles are\nclose to those of dark-solitons particularly in the weak-coupling regime. Then,\nthe scattering of two notches in the quantum double dark-soliton state is\nexactly demonstrated. It is suggested from the above observations that the\nquasi-BEC should play a significant role in the dynamics of quantum double\ndark-soliton states. If the condensate fraction is close to 1, the quantum\nstate should be well approximated by the quasi-BEC state where the mean-field\npicture is valid.",
        "positive": "The cold-atom elevator: From edge-state injection to the preparation of\n  fractional Chern insulators: Optical box traps for cold atoms offer new possibilities for quantum-gas\nexperiments. Building on their exquisite spatial and temporal control, we\npropose to engineer system-reservoir configurations using box traps, in view of\npreparing and manipulating topological atomic states in optical lattices.\nFirst, we consider the injection of particles from the reservoir to the system:\nthis scenario is shown to be particularly well suited to activate\nenergy-selective chiral edge currents, but also, to prepare fractional Chern\ninsulating ground states. Then, we devise a practical evaporative-cooling\nscheme to effectively cool down atomic gases into topological ground states.\nOur open-system approach to optical-lattice settings provides a new path for\nthe investigation of ultracold quantum matter, including strongly-correlated\nand topological phases."
    },
    {
        "anchor": "mm-wave Rydberg-Rydberg resonances as a witness of intermolecular\n  coupling in the arrested relaxation of a molecular ultracold plasma: Out-of-equilibrium, strong correlation in a many-body system triggers\nemergent properties that can act in important ways to constrain the natural\ndissipation of energy and matter. Networks of atoms, intricately engineered to\narrange positions and tune interaction energies, exhibit striking dynamics.\nBut, strong correlation itself can also act to restrict available phase space.\nRelaxation confined by strong correlation gives rise to scale invariance and\ndensity distributions characteristic of self-organized criticality. For some\ntime, we have observed signs of self-organization in the avalanche, bifurcation\nand quench of a state-selected Rydberg gas of nitric oxide to form an\nultracold, strongly correlated ultracold plasma. The robust arrested relaxation\nof this system forms a disordered state with quantum-mechanical properties that\nappear to support a coherent destruction of transport. Work reported here\nfocuses on initial stages of avalanche and quench, using the mm-wave\nspectroscopy of an embedded quantum probe to characterize the intermolecular\ninteraction dynamics associated with the evolution to plasma. Double-resonance\nexcitation prepares a Rydberg gas of nitric oxide composed of a single selected\nstate, $n_0f(2)$. Penning ionization, followed by an avalanche of\nelectron-Rydberg collisions, forms a plasma of NO$^+$ ions and weakly bound\nelectrons, in which a residual population of $n_0$ Rydberg molecules evolves to\nhigh-$\\ell$. At long times, $n_0\\ell(2) \\rightarrow (n_0 \\pm 1)d(2)$ depletion\nresonances signal collision-free energy redistribution in the basis of\ncentral-field Rydberg states. The widths and asymmetries of Fano lineshapes\nwitness the degree to which coupling to the arrested bath broadens the bright\nstate as well as how bright-state predissociation mixes the network of levels\nin the localized ensemble.",
        "positive": "Tunneling theory of two interacting atoms in a trap: A theory for the tunneling of one atom out of a trap containing two\ninteracting cold atoms is developed. The quasiparticle wave function, dressed\nby the interaction with the companion atom in the trap, replaces the\nnon-interacting orbital at resonance in the tunneling matrix element. The\ncomputed tunneling time for two 6Li atoms agrees with recent experimental\nresults [G. Zuern, F. Serwane, T. Lompe, A. N. Wenz, M. G. Ries, J. E. Bohn,\nand S. Jochim, arXiv:1111.2727], unveiling the `fermionization' of the wave\nfunction and a novel two-body effect."
    },
    {
        "anchor": "A high-flux source system for matter-wave interferometry exploiting\n  tunable interactions: Atom interferometers allow determining inertial effects to high accuracy.\nQuantum-projection noise as well as systematic effects impose demands on large\natomic flux as well as ultra-low expansion rates. Here we report on a high-flux\nsource of ultra-cold atoms with free expansion rates near the Heisenberg limit\ndirectly upon release from the trap. Our results are achieved in a\ntime-averaged optical dipole trap and enabled through dynamic tuning of the\natomic scattering length across two orders of magnitude interaction strength\nvia magnetic Feshbach resonances. We demonstrate BECs with more than $6\\times\n10^{4}$ particles after evaporative cooling for $170$ ms and their subsequent\nrelease with a minimal expansion energy of $4.5$ nK in one direction. Based on\nour results we estimate the performance of an atom interferometer and compare\nour source system to a high performance chip-trap, as readily available for\nultra-precise measurements in micro-gravity environments.",
        "positive": "Condensate formation in a dark state of a driven atom-cavity system: We demonstrate condensate formation in a dark state in an ultracold quantum\ngas coupled to a high-finesse cavity and pumped by a shaken optical lattice. We\nshow experimentally and theoretically that the atoms in the dark state display\na strong suppression of the coupling to the cavity. On the theory side, this is\nsupported by solving the dynamics of a minimal three-level model and of the\nfull atom-cavity system. The symmetry of the condensate wave function is\nanti-symmetric with respect to the potential minima of the pump lattice, and\ndisplays a staggered sign along the cavity direction. This symmetry decouples\nthe dark state from the cavity, and is preserved when the pump intensity is\nswitched off."
    },
    {
        "anchor": "Quantum Computation and Quantum Simulation with Ultracold Molecules: Ultracold molecules confined in optical lattices or tweezer traps can be used\nto process quantum information and simulate the behaviour of many-body quantum\nsystems. Molecules offer several advantages for these applications. They have a\nlarge set of stable states with strong transitions between them and long\ncoherence times. They can be prepared in a chosen state with high fidelity, and\nthe state populations can be measured efficiently. They have controllable\nlong-range dipole-dipole interactions that can be used to entangle pairs of\nmolecules and generate interesting many-body states. We review the advances\nthat have been made and the challenges still to overcome, and describe the new\nideas that will unlock the full potential of the field.",
        "positive": "Above threshold scattering about a Feshbach resonance for ultracold\n  atoms in an optical collider: Ultracold atomic gases have realised numerous paradigms of condensed matter\nphysics where control over interactions has crucially been afforded by tunable\nFeshbach resonances. So far, the characterisation of these Feshbach resonances\nhas almost exclusively relied on experiments in the threshold regime near zero\nenergy. Here we use a laser-based collider to probe a narrow magnetic Feshbach\nresonance of rubidium above threshold. By measuring the overall atomic loss\nfrom colliding clouds as a function of magnetic field, we track the\nenergy-dependent resonance position. At higher energy, our collider scheme\nbroadens the loss feature, making the identification of the narrow resonance\nchallenging. However, we observe that the collisions give rise to shifts in the\ncentre-of-mass positions of outgoing clouds. The shifts cross zero at the\nresonance and this allows us to accurately determine its location well above\nthreshold. Our inferred resonance positions are in excellent agreement with\ntheory."
    },
    {
        "anchor": "Metrologically useful states of spin-1 Bose condensates with macroscopic\n  magnetization: We study theoretically the usefulness of spin-1 Bose condensates with\nmacroscopic magnetization in a homogeneous magnetic field for quantum\nmetrology. We demonstrate Heisenberg scaling of the quantum Fisher information\nfor states in thermal equilibrium. The scaling applies to both\nantiferromagnetic and ferromagnetic interactions. The effect preserves as long\nas fluctuations of magnetization are sufficiently small. Scaling of the quantum\nFisher information with the total particle number is derived within the\nmean-field approach in the zero temperature limit and exactly in the high\nmagnetic field limit for any temperature. The precision gain is intuitively\nexplained owing to subtle features of the quasi-distribution function in phase\nspace.",
        "positive": "Conductivity spectrum of ultracold atoms in an optical lattice: We measure the conductivity of neutral fermions in a cubic optical lattice.\nUsing in-situ fluorescence microscopy, we observe the alternating current\nresultant from a single-frequency uniform force applied by displacement of a\nweak harmonic trapping potential. In the linear response regime, a\nneutral-particle analogue of Ohm's law gives the conductivity as the ratio of\ntotal current to force. For various lattice depths, temperatures, interaction\nstrengths, and fillings, we measure both real and imaginary conductivity, up to\na frequency sufficient to capture the transport dynamics within the lowest\nband. The spectral width of the real conductivity reveals the current\ndissipation rate in the lattice, and the integrated spectral weight is related\nto thermodynamic properties of the system through a sum rule. The global\nconductivity decreases with increased band-averaged effective mass, which at\nhigh temperatures approaches a T-linear regime. Relaxation of current is\nobserved to require a finite lattice depth, which breaks Galilean invariance\nand enables damping through collisions between fermions."
    },
    {
        "anchor": "Simulating Chiral Magnetic and Separation Effects with Spin-Orbit\n  Coupled Atomic Gases: The chiral magnetic and chiral separation effects---quantum-anomaly-induced\nelectric current and chiral current along an external magnetic field in\nparity-odd quark-gluon plasma---have received intense studies in the community\nof heavy-ion collision physics. We show that analogous effects occur in\nrotating trapped Fermi gases with Weyl-Zeeman spin-orbit coupling where the\nrotation plays the role of an external magnetic field. These effects can induce\na mass quadrupole in the atomic cloud along the rotation axis which may be\ntested in future experiments. Our results suggest that the spin-orbit coupled\natomic gases are potential simulators of the chiral magnetic and separation\neffects.",
        "positive": "Exact periodic and solitonic states in the spinor condensates: We propose a method to analytically solve the one-dimensional coupled\nnonlinear Gross-Pitaevskii equations which govern the motion of the spinor\nBose-Einstein condensates. In a uniform external potential, the Hamiltonian\ncomprises the kinetic energy, the linear and the quadratic Zeeman energies.\nSeveral classes of exact periodic and solitonic solutions, either in real or in\ncomplex forms, are obtained for both the F=1 and F=2 condensates. These\nsolutions are general that contain neither approximations nor constraints on\nthe system parameters."
    },
    {
        "anchor": "Supersymmetric waves in Bose-Fermi mixtures: Interacting Bose-Fermi mixtures possess a fermionic (super)symmetry when\nbosons and fermions in the mixture have equal masses, and when the interaction\nstrengths are appropriately tuned. This symmetry is spontaneously broken in the\nground state of the mixture, leading to a novel Goldstone mode with fermionic\nstatistics and quadratic dispersion. Here we examine the effect of explicit\nsymmetry-breaking perturbations on the Goldstone mode. When the symmetry is not\nexact and the system is allowed to deviate from the symmetric point, we find\nthat the Goldstone mode acquires an energy gap. We show that the excitations\nmanifest themselves as a non-analyticity of the thermodynamic pressure.",
        "positive": "Mixing, demixing, and structure formation in a binary dipolar\n  Bose-Einstein condensate: We study static properties of disk-shaped binary dipolar Bose-Einstein\ncondensates of $^{168}$Er-$^{164}$Dy and $^{52}$Cr-$^{164}$Dy mixtures under\nthe action of inter- and intra-species contact and dipolar interactions and\ndemonstrate the effect of dipolar interaction using the mean-field approach.\nThroughout this study we use realistic values of inter- and intra-species\ndipolar interactions and the intra-species scattering lengths and consider the\ninter-species scattering length as a parameter. The stability of the binary\nmixture is illustrated through phase plots involving number of atoms of the\nspecies. The binary system always becomes unstable as the number of atoms\nincreases beyond a certain limit. As the inter-species scattering length\nincreases corresponding to more repulsion, an overlapping mixed state of the\ntwo species changes to a separated demixed configuration. During transition\nfrom a mixed to a demixed configuration as the inter-species scattering length\nis increased for parameters just below the stability line, the binary\ncondensate shows special structures in density in the form of\nred-blood-cell-like biconcave and Saturn-ring-like shapes, which are direct\nmanifestations of dipolar interaction."
    },
    {
        "anchor": "Density profiles and collective modes of a Bose-Einstein condensate with\n  light-induced spin-orbit coupling: The phases of a Bose-Einstein condensate (BEC) with light-induced spin-orbit\ncoupling (SOC) are studied within the mean-field approximation. The mixed BEC\nphase, in which the system condenses in a superposition of two plane wave\nstates, is found to be stable for sufficiently small light-atom coupling,\nbecoming unstable in a continuous fashion with increasing light-atom coupling.\nThe structure of the phase diagram at fixed chemical potential for bosons with\nSOC is shown to imply an unusual density dependence for a trapped mixed BEC\nphase, with the density of one dressed spin state increasing with increasing\nradius, providing a unique experimental signature of this state. The collective\nBogoliubov sound mode is shown to also provide a signature of the mixed BEC\nstate, vanishing as the boundary to the regime of phase separation is\napproached.",
        "positive": "Study of unitary Bose polarons with Diffusion Monte-Carlo and\n  Gross-Pitaevskii approaches: We present a detailed study of the properties of unitary Bose polarons, i.e.,\nimpurities strongly interacting with a bath of dilute bosons via a short-range\npotential with infinite scattering length. Through a comparison with Diffusion\nMonte-Carlo calculations, we demonstrate that the Gross-Pitaevskii theory\naccurately describes the properties of a heavy impurity if the gas parameter\nremains small everywhere in the system, including the vicinity of the impurity.\nFurthermore, we investigate the effects of the finite range of the bath-bath\ninteraction potential by means of a non-local extension of the Gross-Pitaevskii\nequation and we discuss the applicability of the Born approximation."
    },
    {
        "anchor": "Quantum phases of lattice dipolar bosons coupled to a high-finesse\n  cavity: Two types of long range interactions, dipolar interaction and cavity-mediated\ninteraction lead to exotic quantum phases. Both interactions have been realized\nand observed in optical lattice setups. Here, we study quantum phases of\ndipolar bosons trapped in optical lattices and coupled to a high-finesse cavity\nwhere both dipolar interaction and cavity-mediated interaction coexist. We\nperform quantum Monte Carlo simulations, and find that the checkerboard solid\nis enhanced and the checkerboard supersolid phase can exist in a wide range of\ndensities (e.g. $ 0.27\\lesssim n\\lesssim0.73 $). Our unbiased numerical results\nsuggest that both solid and supersolid phases can be achieved experimentally\nwith magnetic atoms coupled to a cavity.",
        "positive": "Exact Spectral Function of One-Dimensional Bose Gases: Strong correlation in one-dimensional (1D) quantum systems drastically\nchanges their dynamic and transport properties in the presence of the\ninteraction. In this letter, combining quantum integrable theory with numerics,\nwe exactly compute the spectral function of 1D Lieb-Liniger gas at a many-body\nlevel of large scales. It turns out that a full capture of the power-law\nsingularities in the vicinities of thresholds requires system size as large as\nthousands of particles. Our research essentially confirms the validity of the\nnonlinear Tomonaga-Luttinger liquid and provides a reliable technique for\nstudying critical behaviour emerged only in thermodynamic limit."
    },
    {
        "anchor": "Viscous Properties of a Degenerate One-Dimensional Fermi Gas: We study the viscous properties of a system of weakly interacting\nspin-$\\frac{1}{2}$ fermions in one dimension. Accounting for the effect of\ninteractions on the quasiparticle energy spectrum, we obtain the bulk viscosity\nof this system at low temperatures. Our result is valid for frequencies that\nare small compared with the rate of fermion backscattering. For frequencies\nlarger than this exponentially small rate, the excitations of the system become\ndecoupled from the center of mass motion, and the fluid is described by\ntwo-fluid hydrodynamics. We calculate the three transport coefficients required\nto describe viscous dissipation in this regime.",
        "positive": "Time-Reversal-Invariant Hofstadter-Hubbard Model with Ultracold Fermions: We consider the time-reversal-invariant Hofstadter-Hubbard model which can be\nrealized in cold atom experiments. In these experiments, an additional\nstaggered potential and an artificial Rashba--type spin-orbit coupling are\navailable. Without interactions, the system exhibits various phases such as\ntopological and normal insulator, metal as well as semi--metal phases with two\nor even more Dirac cones. Using a combination of real-space dynamical\nmean-field theory and analytical techniques, we discuss the effect of on-site\ninteractions and determine the corresponding phase diagram. In particular, we\ninvestigate the semi--metal to antiferromagnetic insulator transition and the\nstability of different topological insulator phases in the presence of strong\ninteractions. We compute spectral functions which allow us to study the edge\nstates of the strongly correlated topological phases."
    },
    {
        "anchor": "Mean-field predictions for a dipolar Bose-Einstein condensate with\n  $^{164}$Dy: We study dipolar Bose-Einstein condensates for a realistic set of parameters\nclose to actual experimental setups with dysprosium. Our analysis is based on\nthe extended Gross-Pitaevskii equation, which we solve numerically exact on a\nthree-dimensional grid. We present stability and phase diagrams, and study the\nexpansion dynamics of dipolar condensates. Our calculations show signatures of\nthe dipole-dipole interaction in terms of structured states and a deviation of\nthe well-known inversion of the aspect ratio of the cloud during a time of\nflight.",
        "positive": "Trapping Centers at the Superfluid-Mott-insulator Criticality:\n  Transition between Charge-quantized States: Under the conditions of superfluid-Mott-insulator criticality in two\ndimensions, the trapping centers--i.e., local potential wells and bumps--are\ngenerically characterized by an integer charge corresponding to the number of\ntrapped particles (if positive) or holes (if negative). Varying the strength of\nthe center leads to a transition between two competing ground states with\ncharges differing by $\\pm 1$. The hallmark of the transition scenario is a\nsplitting of the number density distortion, $\\delta n(r)$, into a half-integer\ncore and a large halo carrying the complementary charge of $\\pm 1/2$. The sign\nof the halo changes across the transition and the radius of the halo, $r_0$,\ndiverges on the approach to the critical strength of the center, $V = V_c$, by\nthe law $r_0 \\propto |V-V_c|^{-\\tilde{\\nu}}$, with $\\tilde{\\nu} \\approx\n2.33(5)$."
    },
    {
        "anchor": "Spinor Bose gas in an elongated trap: We examine a spinor Bose gas confined by an elongated trap. Since a\nspin-independent energy is much higher than a spin-dependent energy in alkali\nspecies, the system exhibits different properties by changing a radial\nconfinement. We show that if a spin-dependent coupling is positive, a\nspin-liquid condensate, which breaks the charge U(1) symmetry but preserves the\nspin rotational symmetry, can be realized in an intermediate confinement\nregime. Properties of the spin-liquid condensate are visible if a temperature\nis lower than a spin gap to characterize the spin-disorder property. If a\ntemperature is higher than the gap but lower than a spin-dependent coupling, on\nthe other hand, a regime in which a spin sector is described by a semiclassical\nwave emerges. A characterization in each regime by means of correlation\nfunctions and topological solitons is also discussed.",
        "positive": "Many-body interferometry of magnetic polaron dynamics: The physics of quantum impurities coupled to a many-body environment is among\nthe most important paradigms of condensed matter physics. In particular, the\nformation of polarons, quasiparticles dressed by the polarization cloud, is key\nto the understanding of transport, optical response, and induced interactions\nin a variety of materials. Despite recent remarkable developments in ultracold\natoms and solid-state materials, the direct measurement of their ultimate\nbuilding block, the polaron cloud, has remained a fundamental challenge. We\npropose and anlalyze a unique platform to probe time-resolved dynamics of\npolaron-cloud formation with an interferometric protocol. We consider an\nimpurity atom immersed in a two-component Bose-Einstein condensate, where the\nimpurity generates spin-wave excitations that can be directly measured by the\nRamsey interference of surrounding atoms. The dressing by spin waves leads to\nthe formation of magnetic polarons and reveals a unique interplay between few-\nand many-body physics that is signified by single- and multi-frequency\noscillatory dynamics corresponding to the formation of many-body bound states.\nFinally, we discuss concrete experimental implementations in ultracold atoms."
    },
    {
        "anchor": "Self-bound clusters of one-dimensional fermionic mixtures: Diffusion Monte Carlo calculations on the possibility of having self-bound\none-dimen\\-sional droplets of SU(6) $\\times$ SU(2) ultracold fermionic mixtures\nare presented. We found that, even though arrangements with attractive\ninteractions with only two spin types are not self-bound, mixtures with at\nleast three kinds of fermions form stable small drops. However, that\nstabilization decreases for very tight confinements, where a universal behavior\nis found for Fermi-Fermi and Fermi-Boson clusters including attractive and\nrepulsive interactions.",
        "positive": "Exotic superfluid states of lattice fermions in elongated traps: We present real-space dynamical mean-field theory calculations for\nattractively interacting fermions in three-dimensional lattices with elongated\ntraps. The critical polarization is found to be 0.8, regardless of the trap\nelongation. Below the critical polarization, we find unconventional superfluid\nstructures where the polarized superfluid and\nFulde-Ferrell-Larkin-Ovchinnikov-type states emerge across the entire core\nregion."
    },
    {
        "anchor": "A Raman-induced Feshbach resonance in an effectively single-component\n  Fermi gas: Ultracold gases of interacting spin-orbit coupled fermions are predicted to\ndisplay exotic phenomena such as topological superfluidity and its associated\nMajorana fermions. Here, we experimentally demonstrate a route to\nstrongly-interacting single-component atomic Fermi gases by combining an s-wave\nFeshbach resonance (giving strong interactions) and spin-orbit coupling\n(creating an effective p-wave channel). We identify the Feshbach resonance by\nits associated atomic loss feature and show that, in agreement with our\nsingle-channel scattering model, this feature is preserved and shifted as a\nfunction of the spin-orbit coupling parameters.",
        "positive": "Bose-Einstein statistics for a finite number of particles: This article presents a study of the grand canonical Bose-Einstein (BE)\nstatistics for a finite number of particles in an arbitrary quantum system. The\nthermodynamical quantities that identify BE condensation -- namely, the\nfraction of particles in the ground state and the specific heat -- are\ncalculated here exactly in terms of temperature and fugacity. These\ncalculations are complemented by a numerical calculation of fugacity in terms\nof the number of particles, without taking the thermodynamic limit. The main\nadvantage of this approach is that it does not rely on approximations made in\nthe vicinity of the usually defined critical temperature, rather it makes\ncalculations with arbitrary precision possible, irrespective of temperature.\nGraphs for the calculated thermodynamical quantities are presented in\ncomparison to the results previously obtained in the thermodynamic limit. In\nparticular, it is observed that for the gas trapped in a 3-dimensional box the\nderivative of specific heat reaches smaller values than what was expected in\nthe thermodynamic limit -- here, this result is also verified with analytical\ncalculations. This is an important result for understanding the role of the\nthermodynamic limit in phase transitions and makes possible to further study BE\nstatistics without relying neither on the thermodynamic limit nor on\napproximations near critical temperature."
    },
    {
        "anchor": "Quantum Many-Body Scars in Optical Lattices: The concept of quantum many-body scars has recently been put forward as a\nroute to describe weak ergodicity breaking and violation of the Eigenstate\nThermalization Hypothesis. We propose a simple setup to generate quantum\nmany-body scars in a doubly modulated Bose-Hubbard system which can be readily\nimplemented in cold atomic gases. The dynamics are shown to be governed by\nkinetic constraints which appear via density assisted tunneling in a\nhigh-frequency expansion. We find the optimal driving parameters for the\nkinetically constrained hopping which leads to small isolated subspaces of\nscared eigenstates. The experimental signatures and the transition to fully\nthermalizing behavior as a function of driving frequency are analyzed.",
        "positive": "Simulation of two-flavors symmetry-locking phases in ultracold fermionic\n  mixtures: We describe an ultracold fermionic set-up where it is possible to synthesize\na superfluid phase with symmetry obtained by locking independent invariance\ngroups of the normal state. In this phase, named two-flavors symmetry-locking\nphase (TFSL), non-Abelian fractional vortices with semi-integer flux and\ngapless non-Abelian Goldstone modes localized on them appear. Considerations on\nthe possible experimental realization of the TFSL are also provided."
    },
    {
        "anchor": "Josephson tunneling of dark solitons in a double-well potential: We study the dynamics of matter waves in an effectively one-dimensional\nBose-Einstein condensate in a double well potential. We consider in particular\nthe case when one of the double wells confines excited states. Similarly to the\nknown ground state oscillations, the states can tunnel between the wells\nexperiencing the physics known for electrons in a Josephson junction, or be\nself-trapped. As the existence of dark solitons in a harmonic trap are\ncontinuations of such non-ground state excitations, one can view the\nJosephson-like oscillations as tunnelings of dark solitons. Numerical existence\nand stability analysis based on the full equation is performed, where it is\nshown that such tunneling can be stable. Through a numerical path following\nmethod, unstable tunneling is also obtained in different parameter regions. A\ncoupled-mode system is derived and compared to the numerical observations.\nRegions of (in)stability of Josephson tunneling are discussed and highlighted.\nFinally, we outline an experimental scheme designed to explore such dark\nsoliton dynamics in the laboratory.",
        "positive": "Exploring competing density order in the ionic Hubbard model with\n  ultracold fermions: We realize and study the ionic Hubbard model using an interacting\ntwo-component gas of fermionic atoms loaded into an optical lattice. The\nbipartite lattice has honeycomb geometry with a staggered energy-offset that\nexplicitly breaks the inversion symmetry. Distinct density-ordered phases are\nidentified using noise correlation measurements of the atomic momentum\ndistribution. For weak interactions the geometry induces a charge density wave.\nFor strong repulsive interactions we detect a strong suppression of doubly\noccupied sites, as expected for a Mott insulating state, and the externally\nbroken inversion symmetry is not visible anymore in the density distribution.\nThe local density distributions in different configurations are characterized\nby measuring the number of doubly occupied lattice sites as a function of\ninteraction and energy-offset. We further probe the excitations of the system\nusing direction dependent modulation spectroscopy and discover a complex\nspectrum, which we compare with a theoretical model."
    },
    {
        "anchor": "Spectral properties and phase diagram of correlated lattice bosons in an\n  optical cavity within the B-DMFT: We use the Bose-Hubbard model with an effective infinite-range interaction to\ndescribe the correlated lattice bosons in an optical cavity. We study both\nstatic and spectral properties of such system within the bosonic dynamical\nmean-field theory (B-DMFT), which is the state of the art method for strongly\ncorrelated bosonic systems. Both similarities and differences are found and\ndiscussed between our results and these obtained within different theoretical\nmethods and experiment.",
        "positive": "Integrated coherent matter wave circuits: An integrated coherent matter wave circuit is a single device, analogous to\nan integrated optical circuit, in which coherent de Broglie waves are created\nand then launched into waveguides where they can be switched, divided,\nrecombined, and detected as they propagate. Applications of such circuits\ninclude guided atom interferometers, atomtronic circuits, and precisely\ncontrolled delivery of atoms. Here we report experiments demonstrating\nintegrated circuits for guided coherent matter waves. The circuit elements are\ncreated with the painted potential technique, a form of time-averaged optical\ndipole potential in which a rapidly-moving, tightly-focused laser beam exerts\nforces on atoms through their electric polarizability. The source of coherent\nmatter waves is a Bose-Einstein condensate (BEC). We launch BECs into painted\nwaveguides that guide them around bends and form switches, phase coherent\nbeamsplitters, and closed circuits. These are the basic elements that are\nneeded to engineer arbitrarily complex matter wave circuitry."
    },
    {
        "anchor": "Degeneracies in trapped two-component Fermi gases: We report on previously unobserved inter-system degeneracies in two-component\nequal-mass Fermi gases with interspecies zero-range interactions under\nisotropic harmonic confinement. Over the past 10 years, two-component Fermi\ngases consisting of $n_1$ spin-up and $n_2$ spin-down atoms with interspecies\nzero-range interactions have become a paradigm for modeling condensed matter\nsystems, nuclear matter and neutron matter. We show that the eigen energies of\nthe $(n_1+1,n_2-1)$ system are degenerate with the eigen energies of the\n$(n_1,n_2)$ system for any s-wave scattering length $a_s$, including infinitely\nlarge, positive and negative $a_s$. The existence of the inter-system\ndegeneracies is demonstrated explicitly for few-body systems with $n_1+n_2=4,\n5$ and 6. The degeneracies and associated symmetries are explained within a\ngroup theoretical framework.",
        "positive": "Nonequilibrium thermodynamics and optimal cooling of a dilute atomic gas: Characterizing and optimizing thermodynamic processes far from equilibrium is\na challenge. This is especially true for nanoscopic systems made of few\nparticles. We here theoretically and experimentally investigate the\nnonequilibrium dynamics of a gas of few noninteracting Cesium atoms confined in\na nonharmonic optical dipole trap and exposed to degenerate Raman sideband\ncooling pulses. We determine the axial phase-space distribution of the atoms\nafter each Raman cooling pulse by tracing the evolution of the gas with\nposition-resolved fluorescence imaging. We evaluate from it the entropy\nproduction and the statistical length between each cooling steps. A single\nRaman pulse leads to a nonequilibrium state that does not thermalize on its\nown, due to the absence of interparticle collisions. Thermalization may be\nachieved by combining free phase-space evolution and trains of cooling pulses.\nWe minimize the entropy production to a target thermal state to specify the\noptimal spacing between a sequence of equally spaced pulses and achieve in this\nway optimal thermalization. We finally use the statistical length to verify a\nrefined version of the second law of thermodynamics. Altogether, these findings\nprovide a general, theoretical and experimental, framework to analyze and\noptimize far-from-equilibrium processes of few-particle systems."
    },
    {
        "anchor": "A compact and fast magnetic coil for the interaction manipulation of\n  quantum gases with Feshbach resonances: Cold atom experiments commonly use broad magnetic Feshbach resonances to\nmanipulate the interaction between atoms. In order to induce quantum dynamics\nby a change of the interaction strength, rapid ($\\sim\\mu s$) magnetic field\nchanges over several tens of Gauss are required. Here we present a compact\ndesign of a coil and its control circuit for a change of the magnetic field up\nto $36G$ in $3\\mu s$. The setup comprises two concentric solenoids with minimal\nspace requirements, which can be readily added to existing apparatuses. This\ndesign makes the observation of non-equilibrium physics with broad Feshbach\nresonances accessible.",
        "positive": "Supersolidity in Two-Dimensional Trapped Dipolar Droplet Arrays: We theoretically investigate the ground states and the spectrum of elementary\nexcitations across the superfluid to droplet crystallization transition of an\noblate dipolar Bose-Einstein condensate. We systematically identify regimes\nwhere spontaneous rotational symmetry breaking leads to the emergence of a\nsupersolid phase with characteristic collective excitations, such as the Higgs\namplitude mode. Furthermore, we study the dynamics across the transition and\nshow how these supersolids can be realized with standard protocols in\nstate-of-the-art experiments."
    },
    {
        "anchor": "Quantum Phases and Collective Excitations in Bose-Hubbard Models with\n  Staggered Magnetic Flux: We study the quantum phases of a Bose-Hubbard model with staggered magnetic\nflux in two dimensions, as has been realized recently [Aidelsburger {\\it et\nal.}, PRL, {\\bf 107}, 255301 (2011)]. Within mean field theory, we show how the\nstructure of the condensates evolves from weak to strong coupling limit,\nexhibiting a tricritical point at the Mott-superfluid transition. Non-trivial\ntopological structures (Dirac points) in the quasi-particle (hole) excitations\nin the Mott state are found within random phase approximation and we discuss\nhow interaction modifies their structures. Excitation gap in the Mott state\ncloses at different ${\\bf k}$ points when approaching the superfluid states,\nwhich is consistent with the findings of mean field theory.",
        "positive": "Coupled Hydrodynamics in Dipole-Conserving Quantum Systems: We investigate the coupled dynamics of charge and energy in interacting\nlattice models with dipole conservation. We formulate a generic hydrodynamic\ntheory for this combination of fractonic constraints and numerically verify its\napplicability to the late-time dynamics of a specific bosonic quantum system by\ndeveloping a microscopic non-equilibrium quantum field theory. Employing a\nself-consistent $1/N$ approximation in the number of field components, we\nextract all entries of a generalized diffusion matrix and determine their\ndependence on microscopic model parameters. We discuss the relation of our\nresults to experiments in ultracold atom quantum simulators."
    },
    {
        "anchor": "Frustration-induced supersolids in the absence of inter-site\n  interactions: We discuss a mechanism for the realization of supersolids in lattices in the\nabsence of intersite interactions that surprisingly works as well at unit\nfilling. This mechanism, that we study for the case of the sawtooth lattice, is\nbased on the existence of frustrated and unfrustrated plaquettes. For\nsufficiently large interactions and frustration the particles gather\npreferentially at unfrustrated plaquettes breaking spontaneously translational\ninvariance, resulting in a supersolid. We show that for the sawtooth lattice\nthe supersolid exists for a large region of parameters for densities above half\nfilling. Our results open a feasible path for realizing supersolids in existing\nultracold atomic gases in optical lattices without the need for long-range\ninteractions.",
        "positive": "Gap solitons in the spin-orbit coupled Bose-Einstein condensates: We report a diversity of stable gap solitons in a spin-orbit coupled\nBose-Einstein condensate subject to a spatially periodic Zeeman field. It is\nshown that the solitons, can be classified by the main physical symmetries they\nobey, i.e. symmetries with respect to parity (P), time (T), and internal degree\nof freedom, i.e. spin, (C) inversions. The conventional gap and gap-stripe\nsolitons are obtained in lattices with different parameters. It is shown that\nsolitons of the same type but obeying different symmetries can exist in the\nsame lattice at different spatial locations. PT and CPT symmetric solitons have\nanti-ferromagnetic structure and are characterized respectively by nonzero and\nzero total magnetizations."
    },
    {
        "anchor": "Bose-enhanced relaxation of driven atom-molecule condensates: Motivated by recent experiments we study the interconversion between\nultracold atomic and molecular condensates, quantifying the resulting\noscillations and their slow decay. We find that near equilibrium the dominant\ndamping source is the decay of condensed molecules into non-condensed pairs,\nwith a pair kinetic energy that is resonant with the frequency of the\noscillating atom-molecule interconversions. The decay, however, is\nnon-exponential, as strong population of the resonant pairs leads to Bose\nenhancement. Introducing an oscillating magnetic field, which periodically\nmodulates the molecular binding energy, enhances the oscillations at short\ntimes. However, the resulting enhancement of the pair-production process\nresults in an accelerated decay which rapidly cuts off the initial oscillation\ngrowth.",
        "positive": "Orthogonal and antiparallel vortex tubes and energy cascades in quantum\n  turbulence: We investigate the dynamics of energy cascades in quantum turbulence by\ndirectly observing the vorticity distributions in numerical simulations of the\nGross-Pitaevskii equation. By Fourier filtering each scale of the vorticity\ndistribution, we find that antiparallel vortex tubes at a large scale generate\nsmall-scale vortex tubes orthogonal to those at the large scale, which is a\nmanifestation of the energy cascade from large to small scales. We reveal the\ndynamics of quantized vortex lines in these processes."
    },
    {
        "anchor": "Superfluid Fermi atomic gas as a quantum simulator for the study of\n  neutron-star equation of state: We theoretically propose an idea to use an ultracold Fermi gas as a quantum\nsimulator for the study of the neutron-star equation of state (EoS) in the\nlow-density region. Our idea is different from the standard quantum simulator\nthat heads for {\\it perfect} replication of another system, such as a Hubbard\nmodel discussed in high-$T_{\\rm c}$ cuprates. Instead, we use the {\\it\nsimilarity} between two systems, and theoretically make up for the difference\nbetween them. That is, (1) we first show that the strong-coupling theory\ndeveloped by Nozi\\`eres-Schmitt Rink (NSR) can quantitatively explain the\nrecent EoS experiment on a $^6$Li superfluid Fermi gas in the BCS\n(Bardeen-Cooper-Schrieffer)-unitary limit far below the superfluid phase\ntransition temperature $T_{\\rm c}$. This region is considered to be very\nsimilar to the low density region (crust regime) of a neutron star (where a\nnearly unitary $s$-wave neutron superfluid is expected). (2) We then\ntheoretically compensate the difference that, while the effective range $r_{\\rm\neff}$ is negligibly small in a superfluid $^6$Li Fermi gas, it cannot be\nignored ($r_{\\rm eff}=2.7$ fm) in a neutron star, by extending the NSR theory\nto include effects of $r_{\\rm eff}$. The calculated EoS when $r_{\\rm eff}=2.7$\nfm is shown to agree well with the previous neutron-star EoS in the low density\nregion predicted in nuclear physics. Our idea indicates that an ultracold\natomic gas may more flexibly be used as a quantum simulator for the study of\nother complicated quantum many-body systems, when we use, not only the\nexperimental high tunability, but also the recent theoretical development in\nthis field. Since it is difficult to directly observe a neutron-star interior,\nour idea would provide a useful approach to the exploration for this mysterious\nastronomical object.",
        "positive": "Spin drag in an ultracold Fermi gas on the verge of a ferromagnetic\n  instability: Recent experiments [Jo et al., Science 325, 1521 (2009)] have presented\nevidence of ferromagnetic correlations in a two-component ultracold Fermi gas\nwith strong repulsive interactions. Motivated by these experiments we consider\nspin drag, i.e., frictional drag due to scattering of particles with opposite\nspin, in such systems. We show that when the ferromagnetic state is approached\nfrom the normal side, the spin drag relaxation rate is strongly enhanced near\nthe critical point. We also determine the temperature dependence of the spin\ndiffusion constant. In a trapped gas the spin drag relaxation rate determines\nthe damping of the spin dipole mode, which therefore provides a precursor\nsignal of the ferromagnetic phase transition that may be used to experimentally\ndetermine the proximity to the ferromagnetic phase."
    },
    {
        "anchor": "Quantum Monte Carlo calculation of the zero-temperature phase diagram of\n  the two-component fermionic hard-core gas in two dimensions: Motivated by potential realizations in cold-atom or cold-molecule systems, we\nhave performed quantum Monte Carlo simulations of two-component gases of\nfermions in two dimensions with hard-core interactions. We have determined the\ngross features of the zero-temperature phase diagram, by investigating the\nrelative stabilities of paramagnetic and ferromagnetic fluids and crystals. We\nhave also examined the effect of including a pairwise, long-range r^(-3)\npotential between the particles. Our most important conclusion is that there is\nno region of stability for a ferromagnetic fluid phase, even if the long-range\ninteraction is present. We also present results for the pair-correlation\nfunction, static structure factor, and momentum density of two-dimensional\nhard-core fluids.",
        "positive": "2DEG on a cylindrical shell with a screw dislocation: A two dimensional electron gas on a cylindrical surface with a screw\ndislocation is considered. More precisely, we investigate how both the geometry\nand the deformed potential due to a lattice distortion affect the Landau levels\nof such system. The case showing the deformed potential can be thought in the\ncontext of 3D common semiconductors where the electrons are confined on a\ncylindrical shell. We will show that important quantitative differences exist\ndue to this lattice distortion. For instance, the effective cyclotron frequency\nis diminished by the deformed potential, which in turn enhances the Hall\nconductivity."
    },
    {
        "anchor": "A Hermite-Pad\u00e9 perspective on Gell-Mann--Low renormalization group: an\n  application to the correlation function of Lieb-Liniger gas: While Pad\\'e approximation is a general method for improving convergence of\nseries expansions, Gell-Mann--Low renormalization group normally relies on the\npresence of special symmetries. We show that in the single-variable case, the\nlatter becomes an integral Hermite-Pad\\'e approximation, needing no special\nsymmetries. It is especially useful for interpolating between expansions for\nsmall values of a variable and a scaling law of known exponent for large\nvalues. As an example, we extract the scaling-law prefactor for the one-body\ndensity matrix of the Lieb-Liniger gas. Using a new result for the 4th-order\nterm in the short-distance expansion, we find a remarkable agreement with known\nab initio numerical results.",
        "positive": "Phase correlations and quasicondensate in a two-dimensional ultracold\n  Fermi gas: The interplay between dimensionality, coherence and interaction in superfluid\nFermi gases is analyzed by the phase correlation function of the field of\nfermionic pairs. We calculate this phase correlation function for a\ntwo-dimensional superfluid Fermi gas with $s$-wave interactions within the\nGaussian pair fluctuation formalism. The spatial behavior of the correlation\nfunction is shown to exhibit a rapid (exponential) decay at short distances and\na characteristic algebraic decay at large distances, with an exponent matching\nthat expected from Berezinskii-Kosterlitz-Thouless theory of 2D Bose\nsuperfluids. We conclude that the Gaussian pair fluctuation approximation is\nable to capture the physics of quasi long-range order in two-dimensional Fermi\ngases."
    },
    {
        "anchor": "Momentum-resolved Raman spectroscopy of non-interacting ultracold Fermi\n  gas: We report the experiment on probing the one-body spectral function in a\ntrapped non-interacting $^{40}$K Fermi gas by means of the momentum-resolved\nRaman spectroscopy The experimental result is in good agreement with the\nexpected quadratic dispersion in the non-interacting regime. Through the\ncomparison with the radio-frequency spectrum, we found that the Raman spectrum\nshows some new characteristics.",
        "positive": "Total momentum and thermodynamic phases of quantum systems: The total momentum of $N$ interacting bosons or fermions in a cube equipped\nwith periodic boundary conditions is a conserved quantity. Its eigenvalues\nfollow a probability distribution, determined by the thermal equilibrium state.\nWhile in non-interacting systems the distribution is normal with variance $\\sim\nN$, interaction couples the single-particle momenta, so that the distribution\nof their sum is unpredictable, except for some implications of Galilean\ninvariance. First, we present these implications which are strong in 1D,\nmoderately strong in 2D, and weak in 3D. Then, we speculate about the possible\nform of the distribution in fluids, crystals, and superfluids. The existence of\nphonons suggests that the total momentum can remain finite when $N\\to\\infty$.\nWe argue that in fluids the finite momenta distribute continuously, but their\nintegrated probability is smaller than 1, because the momentum can also tend to\ninfinity with $N$. In the fluid-crystal transition we expect that the total\nmomentum becomes finite with full probability and distributed over a lattice,\nand that in the fluid-superfluid transition a delta peak appears only at zero\ntotal momentum. Based on this picture, we discuss the superfluid flow in both\nthe frictionless and the dissipative cases, and derive a temperature-dependent\ncritical velocity. Finally, we show that Landau's criterion for excitations in\nmoving superfluids is an in some cases correct result of an erroneous\nderivation."
    },
    {
        "anchor": "Collective, Coherent, and Ultrastrong Coupling of 2D Electrons with\n  Terahertz Cavity Photons: Nonperturbative coupling of light with condensed matter in an optical cavity\nis expected to reveal a host of coherent many-body phenomena and states. In\naddition, strong coherent light-matter interaction in a solid-state environment\nis of great interest to emerging quantum-based technologies. However, creating\na system that combines a long electronic coherence time, a large dipole moment,\nand a high cavity quality ($Q$) factor has been a challenging goal. Here, we\nreport collective ultrastrong light-matter coupling in an ultrahigh-mobility\ntwo-dimensional electron gas in a high-$Q$ terahertz photonic-crystal cavity in\na quantizing magnetic field, demonstrating a cooperativity of $\\sim$360. The\nsplitting of cyclotron resonance (CR) into the lower and upper polariton\nbranches exhibited a $\\sqrt{n_\\mathrm{e}}$-dependence on the electron density\n($n_\\mathrm{e}$), a hallmark of collective vacuum Rabi splitting. Furthermore,\na small but definite blue shift was observed for the polariton frequencies due\nto the normally negligible $A^2$ term in the light-matter interaction\nHamiltonian. Finally, the high-$Q$ cavity suppressed the superradiant decay of\ncoherent CR, which resulted in an unprecedentedly narrow intrinsic CR linewidth\nof 5.6 GHz at 2 K. These results open up a variety of new possibilities to\ncombine the traditional disciplines of many-body condensed matter physics and\ncavity-based quantum optics.",
        "positive": "Antiferromagnetic behavior in self-bound one-dimensional composite\n  bosons: The structure of self-bound one-dimensional droplets containing a mixture of\nYtterbium fermionic isotopes ($^{173}$Yb, $^{171}$Yb) is calculated by means of\na diffusion Monte Carlo technique. We considered only balanced setups in which\nall the atoms of one isotope are spin-polarized, while the atoms of the other\ncan have up to three different spin values, that difference being a necessary\nrequirement to achieve stable systems. Our results indicate that these droplets\nconsist of consecutive \"molecules\" made up of one $^{173}$Yb and one $^{171}$Yb\natom. In other words, we have up to three different kinds of composite bosons,\ncorresponding to the number of spin components in the non-polarized isotope.\nThe fermionic nature of those Yb atoms makes pairs with identical spin\ncomposition avoid each other, creating a Pauli-like-hole filed by another\nmolecule in which at least one of the Yb atoms has a different spin from that\nof their closest neighbors. This effective repulsion is akin to an\nantiferromagnetic short-range interaction between different kinds of composite\nbosons."
    },
    {
        "anchor": "Spontaneous emissions and thermalization of cold bosons in optical\n  lattices: We study the thermalization of excitations generated by spontaneous emission\nevents for cold bosons in an optical lattice. Computing the dynamics described\nby the many-body master equation, we characterize equilibration timescales in\ndifferent parameter regimes. For simple observables, we find regimes in which\nthe system relaxes rapidly to values in agreement with a thermal distribution,\nand others where thermalization does not occur on typical experimental\ntimescales. Because spontaneous emissions lead effectively to a local quantum\nquench, this behavior is strongly dependent on the low-energy spectrum of the\nHamiltonian, and undergoes a qualitative change at the Mott\nInsulator-superfluid transition point. These results have important\nimplications for the understanding of thermalization after localized quenches\nin isolated quantum gases, as well as the characterization of heating in\nexperiments.",
        "positive": "Roton immiscibility in a two-component dipolar Bose gas: We characterize the immiscibility-miscibility transition (IMT) of a\ntwo-component Bose-Einstein condensate (BEC) with dipole-dipole interactions.\nIn particular, we consider the quasi-two dimensional geometry, where a strong\ntrapping potential admits only zero-point motion in the trap direction, while\nthe atoms are more free to move in the transverse directions. We employ the\nBogoliubov treatment of the two-component system to identify both the\nwell-known long-wavelength IMT in addition to a roton-like IMT, where the\ntransition occurs at finite-wave number and is reminiscent of the roton\nsoftening in the single component dipolar BEC. Additionally, we verify the\nexistence of the roton IMT in the fully trapped, finite systems by direct\nnumerical simulation of the two-component coupled non-local Gross-Pitaevskii\nequations."
    },
    {
        "anchor": "Finite Temperature Phase Transition in a Cross-Dimensional Triangular\n  Lattice: Atomic many-body phase transitions and quantum criticality have recently\nattracted much attention in non-standard optical lattices. Here we perform an\nexperimental study of finite-temperature superfluid transition of bosonic atoms\nconfined in a three dimensional triangular lattice, whose structure can be\ncontinuously deformed to dimensional crossover regions including quasi-one and\ntwo dimensions. This non-standard lattice system provides a versatile platform\nto investigate many-body correlated phases. For the three dimensional case, we\nfind that the finite temperature superfluid transition agrees quantitatively\nwith the Gutzwiller mean field theory prediction, whereas tuning towards\nreduced dimensional cases, both quantum and thermal fluctuation effects are\nmore dramatic, and the experimental measurement for the critical point becomes\nstrongly deviated from the mean field theory. We characterize the fluctuation\neffects in the whole dimension crossover process. Our experimental results\nimply strong many-body correlations in the system beyond mean field\ndescription, paving a way to study quantum criticality near Mott-superfluid\ntransition in finite temperature dimension-crossover lattices.",
        "positive": "Tamm's surface states and Bose-Einstein condensation: We calculate and discuss the effects on the thermodynamic properties of a 3D\nBose gas caused by a gap $\\Delta$ in the energy of the particles constituting\nthe gas that without the gap behaves like an ideal Bose gas. Explicit formulae\nwith arbitrary $\\Delta$ values are discussed for: the critical temperature\nwhich increases as the gap grows; the condensate fraction; the internal energy;\nand the constant-volume specific heat found to possess a jump-discontinuity for\nany $\\Delta$ different from zero. Three dimensional infinite ideal Bose gas\nresults are recovered when we the energy gap goes to zero."
    },
    {
        "anchor": "Emergence of the Unconventional Type-II Nambu-Goldstone Modes with\n  Topological Origin in Bose Superfluids: The Nambu-Goldstone (NG) modes in a nonrelativistic system can be classified\ninto two types from their characteristic features: being of either an odd (type\nI) or an even (type II) power energy-momentum dispersion. Conventionally, the\ntype-II NG modes may universally arise from spontaneous breaking of\nnoncommutative symmetry pairs. Here, we predict a novel type of quadratically\ndispersed NG modes that emerges in mixed $s$ and $p$ band Bose superfluids in\nan optical lattice and, unlike the conventional type-II NG modes, cannot be\nsolely interpreted with the celebrated symmetry-based argument. Instead, we\nshow that the existence of such modes has a profound connection to the\ntopological transition on projective complex order-parameter space. The\ndetection scheme is also proposed. Our Letter reveals a new universal mechanism\nfor emergence of type-II NG modes, which bridges intrinsically the Landau\nsymmetry-breaking and topological theories.",
        "positive": "Dissipation induced macroscopic entanglement in an open optical lattice: We introduce a method for the dissipative preparation of strongly correlated\nquantum states of ultracold atoms in an optical lattice via localized particle\nloss. The interplay of dissipation and interactions enables different types of\ndynamics. This ushers a new line of experimental methods to maintain the\ncoherence of a Bose-Einstein condensate or to deterministically generate\nmacroscopically entangled quantum states."
    },
    {
        "anchor": "Collective Dynamics and Atom Loss in Bright Soliton Matter Waves: Motivated by recent experiments, we model the dynamics of bright solitons\nformed by cold gases in quasi-1D traps. A dynamical variational ansatz captures\nthe far-from equilibrium excitations of these solitons. Due to a separation of\nscales, the radial and axial modes decouple, allowing for closed-form\napproximations for the dynamics. We explore how soliton dynamics influence atom\nloss, and find that the time-averaged loss is largely insensitive to the degree\nof excitation. The variational approach enables us to perform high precision\ncalculations of the critical atom number (ie. the maximum number of atoms that\ncan exist in a single soliton before the attractive forces overwhelm quantum\npressure, leading to collapse).",
        "positive": "Interferometry using Adiabatic Passage in Dilute Gas Bose-Einstein\n  Condensates: We theoretically examine three-well interferometry in Bose-Einstein\ncondensates using adiabatic passage. Specifically, we demonstrate that a\nfractional coherent transport adiabatic passage protocol enables stable spatial\nsplitting in the presence of nonlinear interactions. A reversal of this\nprotocol produces a coherent recombination of the BEC with a phase-dependent\npopulation of the three wells. The effect of nonlinear interactions on the\ninterferometric measurement is quantified and found to lead to an enhancement\nin sensitivity for moderate interaction strengths."
    },
    {
        "anchor": "Effect of anisotropic spin-orbit coupling on condensation and\n  superfluidity of a two dimensional Fermi gases: We investigated the ground state properties of a two dimensional Fermi\nsuperfluid with an anisotropic spin-orbit coupling (SOC) using path-integral\nfield theoretical method. Within the framework of mean-field theory, we\nobtained the condensed fraction including contributions from both singlet and\ntriple pairing fields. We found that for small interaction parameters and large\nanisotropic parameters, the total condensed fraction changes non-monotonically\nwhen increasing the strength of SOC and has a global maximum. But this feature\ndisappears with decreasing the anisotropic parameter and increasing the\ninteraction parameter. However, condensed fraction always decrease with\nincreasing the anisotropic parameters. Because of the anisotropy of the SOC,\nthe superfluid fraction becomes a tensor. We obtained the superfluid fraction\ntensor by deriving the effective action of the phase field of the order\nparameter. Our numerical results show that for small interaction parameters and\nlarge anisotropic parameters, superfluid fraction of the $x$ component\n$\\rho_{x}$ has a minimum as a function of the SOC strength. And this minimum of\n$\\rho_{x}$ disappears when decreasing the anisotropic parameters. In the strong\ninteraction regime, $\\rho_{x}$ always decreases with increasing the strength of\nSOC. While for the $y$ component of the superfluid fraction $\\rho_{y}$, no\nmatter how large the interaction parameters and anisotropic parameters are, it\nalways has a minimum as a function of the SOC strength. As a function of the\nanisotropic parameter, for strong SOC strength, $\\rho_{x}<\\rho_{y}$ with\n$\\rho_{x}$ having a minimum. For small SOC parameters $\\rho_{x}>\\rho_{y}$ with\n$\\rho_{y}$ developing a minimum only in the weak interaction limit.",
        "positive": "Emergent glassy behavior in a kagome Rydberg atom array: We present large-scale quantum Monte Carlo simulation results on a realistic\nHamiltonian of kagome-lattice Rydberg atom arrays. Although the system has no\nintrinsic disorder, intriguingly, our analyses of static and dynamic properties\non large system sizes reveal \\textit{emergent} glassy behavior in a region of\nparameter space located between two valence bond solid phases. The extent of\nthis glassy region is demarcated using the Edwards-Anderson order parameter,\nand its phase transitions to the two proximate valence bond solids -- as well\nas the crossover towards a trivial paramagnetic phase -- are identified. We\ndemonstrate the intrinsically slow (imaginary) time dynamics deep inside the\nglassy phase and discuss experimental considerations for detecting such a\nquantum disordered phase with numerous nearly degenerate local minima. Our\nproposal paves a new route to the study of real-time glassy phenomena and\nhighlights the potential for quantum simulation of a distinct phase of quantum\nmatter beyond solids and liquids in current-generation Rydberg platforms."
    },
    {
        "anchor": "Precision Test of the Limits to Universality in Few-Body Physics: We perform precise studies of two- and three-body interactions near an\nintermediate-strength Feshbach resonance in $^{39}\\mathrm{K}$ at\n$33.5820(14)\\thinspace$G. Precise measurement of dimer binding energies,\nspanning three orders of magnitude, enables the construction of a complete\ntwo-body coupled-channel model for determination of the scattering lengths with\nan unprecedented low uncertainty. Utilizing an accurate scattering length map,\nwe measure the precise location of the Efimov ground state to test van der\nWaals universality. Precise control of the sample's temperature and density\nensures that systematic effects on the Efimov trimer state are well understood.\nWe measure the ground Efimov resonance location to be at $-14.05(17)$ times the\nvan der Waals length $r_{\\mathrm{vdW}}$, significantly deviating from the value\nof $-9.7 \\thinspace r_{\\mathrm{vdW}}$ predicted by van der Waals universality.\nWe find that a refined multichannel three-body model, built on our measurement\nof two-body physics, can account for this difference and even successfully\npredict the Efimov inelasticity parameter $\\eta$.",
        "positive": "Energy eigenfunctions of the 1D Gross-Pitaevskii equation: We developed a new and powerful algorithm by which numerical solutions for\nexcited states in a gravito optical surface trap have been obtained. They\nrepresent solutions in the regime of strong nonlinearities of the\nGross--Pitaevskii equation. In this context we also shortly review several\napproaches which allow, in principle, for calculating excited state solutions.\nIt turns out that without modifications these are not applicable to strongly\nnonlinear Gross-Pitaevskii equations. The importance of studying excited states\nof Bose-Einstein condensates is also underlined by a recent experiment of\nB\\\"ucker et al in which vibrational state inversion of a Bose-Einstein\ncondensate has been achieved by transferring the entire population of the\ncondensate to the first excited state. Here, we focus on demonstrating the\napplicability of our algorithm for three different potentials by means of\nnumerical results for the energy eigenstates and eigenvalues of the 1D\nGrosss-Pitaevskii-equation. We compare the numerically found solutions and find\nout that they completely agree with the case of known analytical solutions."
    },
    {
        "anchor": "Many-body delocalization with random vector potentials: We study the ergodic properties of excited states in a model of interacting\nfermions in quasi-one-dimensional chains subjected to a random vector\npotential. In the noninteracting limit, we show that arbitrarily small values\nof this complex off-diagonal disorder trigger localization for the whole\nspectrum; the divergence of the localization length in the single-particle\nbasis is characterized by a critical exponent $\\nu$ which depends on the energy\ndensity being investigated. When short-range interactions are included, the\nlocalization is lost, and the system is ergodic regardless of the magnitude of\ndisorder in finite chains. Our numerical results suggest a delocalization\nscheme for arbitrary small values of interactions. This finding indicates that\nthe standard scenario of the many-body localization cannot be obtained in a\nmodel with random gauge fields.",
        "positive": "Reactive collisions in confined geometries: We consider low energy threshold reactive collisions of particles interacting\nvia a van der Waals potential at long range in the presence of external\nconfinement and give analytic formulas for the confinement modified scattering\nin such circumstances. The reaction process is described in terms of the short\nrange reaction probability. Quantum defect theory is used to express elastic\nand inelastic or reaction collision rates analytically in terms of two\ndimensionless parameters representing phase and reactivity. We discuss the\nmodifications to Wigner threshold laws for quasi-one-dimensional and\nquasi-two-dimensional geometries. Confinement-induced resonances are suppressed\ndue to reactions and are completely absent in the universal limit where the\nshort-range loss probability approaches unity."
    },
    {
        "anchor": "Fluctuations and phase transitions in Larkin-Ovchinnikov liquid crystal\n  states of population-imbalanced resonant Fermi gas: Motivated by a realization of imbalanced Feshbach-resonant atomic Fermi\ngases, we formulate a low-energy theory of the Fulde-Ferrell and the\nLarkin-Ovchinnikov (LO) states and use it to analyze fluctuations, stability,\nand phase transitions in these enigmatic finite momentum-paired superfluids.\nFocusing on the unidirectional LO pair-density wave state, that spontaneously\nbreaks the continuous rotational and translational symmetries, we show that it\nis characterized by two Goldstone modes, corresponding to a superfluid phase\nand a smectic phonon. Because of the liquid-crystalline \"softness\" of the\nlatter, at finite temperature the 3d state is characterized by a vanishing LO\norder parameter, quasi-Bragg peaks in the structure and momentum distribution\nfunctions, and a \"charge\"-4, paired Cooper-pairs, off-diagonal-long-range\norder, with a superfluid-stiffness anisotropy that diverges near a transition\ninto a nonsuperfluid state. In addition to conventional integer vortices and\ndislocations the LO superfluid smectic exhibits composite half-integer\nvortex-dislocation defects. A proliferation of defects leads to a rich variety\nof descendant states, such as the \"charge\"-4 superfluid and Fermi-liquid\nnematics and topologically ordered nonsuperfluid states, that generically\nintervene between the LO state and the conventional superfluid and the\npolarized Fermi-liquid at low and high imbalance, respectively. The fermionic\nsector of the LO gapless superconductor is also quite unique, exhibiting a\nFermi surface of Bogoliubov quasiparticles associated with the Andreev band of\nstates, localized on the array of the LO domain-walls.",
        "positive": "Quantum state manipulation and science of ultracold molecules: An increasingly large variety of molecular species are being cooled down to\nlow energies in recent years, and innovative ideas and powerful techniques\ncontinue to emerge to gain ever more precise control of molecular motion. In\nthis brief review we focus our discussions on two widely employed cooling\ntechniques that have brought molecular gases into the quantum regime:\nassociation of ultracold atomic gases into quantum gases of molecules and\ndirect laser cooling of molecules. These advances have brought into reality our\ncapability to prepare and manipulate both internal and external states of\nmolecules quantum mechanically, opening the field of cold molecules to a wide\nrange of scientific explorations."
    },
    {
        "anchor": "Multidimensional Josephson vortices in spin-orbit coupled Bose-Einstein\n  condensates: snake instability and decay through vortex dipoles: We analyze the dynamics of Josephson vortex states in two-component\nBose-Einstein condensates with Rashba-Dresselhaus spin-orbit coupling by using\nthe Gross-Pitaevskii equation. In 1D, both in homogeneous and harmonically\ntrapped systems, we report on stationary states containing doubly charged,\nstatic Josephson vortices. In multidimensional systems, we find stable\nJosephson vortices in a regime of parameters typical of current experiments\nwith $^{87}$Rb atoms. In addition, we discuss the instability regime of\nJosephson vortices in disk-shaped condensates, where the snake instability\noperates and vortex dipoles emerge. We study the rich dynamics that they\nexhibit in different regimes of the spin-orbit coupled condensate depending on\nthe orientation of the Josephson vortices.",
        "positive": "Comment on \"Interface tension of Bose-Einstein condensates\" by Bert Van\n  Schaeybroeck, Phys. Rev. A 78, 023624-9 (2008): The purpose of the comment is to point out that the leading term of the\nGinzburg-Landau nonanalytical correction to the interface tension of\nBose-Einstein condensates with strong segregation and the surface tension of\nextreme type-I superconductors are described by a common coefficient derived\nfrom the universal equation for the phase boundary. The agreement between the\nnumerical value of the coefficients gives a hint that this can be an exact\nresult which deserves to be checked. The outcome will be of interest for\nphysicists working in both fields."
    },
    {
        "anchor": "New type of crossover physics in three-component Fermi gases: A three-component Fermi gas near a broad Feshbach resonance does not have a\nuniversal ground state due to the Thomas collapse, while it does near a narrow\nFeshbach resonance. We explore its universal phase diagram in the plane of the\ninverse scattering length 1/akF and the resonance range RkF. For a large RkF,\nthere exists a Lifshitz transition between superfluids with and without an\nunpaired Fermi surface as a function of 1/akF. With decreasing RkF, the Fermi\nsurface coexisting with the superfluid can change smoothly from that of atoms\nto trimers (\"atom-trimer continuity\"), corresponding to the quark-hadron\ncontinuity in a dense nuclear matter. Eventually, there appears a finite window\nin 1/akF where the superfluid is completely depleted by the trimer Fermi gas,\nwhich gives rise to a pair of quantum critical points. The boundaries of these\nthree quantum phases are determined in regions where controlled analyses are\npossible and are also evaluated based on a mean-field plus trimer model.",
        "positive": "Ground-state properties of Dipolar Bose polarons: We consider a quantum impurity immersed in a dipolar Bose Einstein condensate\nand study the properties of the emerging polaron. We calculate the energy,\neffective mass and quasi-particle residue of the dipolar polaron and\ninvestigate their behaviour with respect to the strength of zero-range contact\nand a long-range dipolar interactions among the condensate atoms and with the\nimpurity. While quantum fluctuations in the case of pure contact interactions\ntypically lead to an increase of the polaron energy, dipole-dipole interactions\nare shown to cause a sign reversal. The described signatures of dipolar\ninteractions are shown to be observable with current experimental capabilities\nbased on quantum gases of atoms with large magnetic dipole moments such as\nErbium or Dysprosium condensates."
    },
    {
        "anchor": "Dissipative shock waves generated by a quantum-mechanical piston: The piston shock problem is a prototypical example of strongly nonlinear\nfluid flow that enables the experimental exploration of fluid dynamics in\nextreme regimes. Here we investigate this problem for a nominally\ndissipationless, superfluid Bose-Einstein condensate and observe rich dynamics\nincluding the formation of a plateau region, a non-expanding shock front, and\nrarefaction waves. Many aspects of the observed dynamics follow predictions of\nclassical dissipative---rather than superfluid dispersive---shock theory. The\nemergence of dissipative-like dynamics is attributed to the decay of large\namplitude excitations at the shock front into turbulent vortex excitations\nwhich allow us to invoke an eddy viscosity hypothesis. Our experimental\nobservations are accompanied by numerical simulations of the mean field,\nGross-Pitaevskii equation that exhibit quantitative agreement with no fitting\nparameters. This work provides an avenue for the investigation of quantum shock\nwaves and turbulence in channel geometries, which are currently the focus of\nintense research efforts.",
        "positive": "Collective fermion excitation in a warm massless Dirac system: Basing on a self-consistent method, we predict theoretically that there\noccurs not only a normal (quasi) fermion mode, but also a collective fermion\nmode, plasmino, in a warm 2D massless Dirac system, especially in a warm\nintrinsic graphene system. Results of Landau damping show that both fermion and\nplasmino are well defined modes. We find that there are sharp differences\nbetween the discussed system and the QCD/QED system. Firstly, the thermal mass\nis proportional to $\\alpha_g^{3/4}T$ but not $\\alpha_g T$. Secondly, at\n$0<q<q_c$, the fermion channel and plasmino channel are nearly degenerate and\nfurthermore, the energy difference between fermion and plasmino becomes more\nand more larger with increasing $q$ at the region $q>q_c$. Thirdly, the fermion\nbehaves as a \"relativity particles\" with none zero mass and the plasmino\nexhibits an anormal dispersion at moderate momentum."
    },
    {
        "anchor": "Complex Langevin approach to interacting Bose gases: Quantitative numerical analyses of interacting dilute Bose-Einstein\ncondensates are most often based on semi-classical approximations. Since the\ncomplex-valued field-theoretic action of the Bose gas does not offer itself to\nthe direct application of standard Monte Carlo techniques, simulations beyond\ntheir scope by now almost exclusively rely on quantum-mechanical techniques.\nHere we explore an alternative approach based on a Langevin-type sampling in an\nextended state space, known as complex Langevin (CL) algorithm. While the use\nof the CL technique has a long-standing history in high-energy physics, in\nparticular in the simulation of QCD at finitebaryon density, applications to\nultracold atoms are still in their infancy. Here we examine the applicability\nof the CL approach for a one- and two-component, three-dimensional\nnon-relativistic Bose gas in thermal equilibrium, below and above the\nBose-Einstein phase transition. By comparison with analytic descriptions at the\nGaussian level, including Bogoliubov and Hartree-Fock theory, we find that the\nmethod allows computing reliably and efficiently observables in the regime of\nexperimentally accessible parameters. Close to the transition, quantum\ncorrections lead to a shift of the critical temperature which we reproduce\nwithin the numerical range known in the literature. With this work, we aim to\nprovide a first test of CL as a potential out-of-the-box tool for the\nsimulation of experimentally realistic situations, including trapping\ngeometries and multicomponent/-species models.",
        "positive": "Attractive Solution of Binary Bose Mixtures: Liquid-Vapor Coexistence\n  and Critical Point: We study the thermodynamic behavior of attractive binary Bose mixtures using\nexact path-integral Monte-Carlo methods. Our focus is on the regime of\ninterspecies interactions where the ground state is in a self-bound liquid\nphase, stabilized by beyond mean-field effects. We calculate the isothermal\ncurves in the pressure vs density plane for different values of the attraction\nstrength and establish the extent of the coexistence region between liquid and\nvapor using the Maxwell construction. Notably, within the coexistence region,\nBose-Einstein condensation occurs in a discontinuous way as the density jumps\nfrom the normal gas to the superfluid liquid phase. Furthermore, we determine\nthe critical point where the line of first-order transition ends and\ninvestigate the behavior of the density discontinuity in its vicinity. We also\npoint out that the density discontinuity at the transition could be observed in\nexperiments of mixtures in traps."
    },
    {
        "anchor": "Feshbach resonances in an ultracold $^{7}$Li-$^{133}$Cs Bose-Bose\n  mixture: We present a study of interspecies Feshbach resonances in ultracold\n$^{7}$Li-$^{133}$Cs Bose-Bose mixtures. We locate ten interspecies resonances\nin three different spin-state combinations. By comparing to coupled-channel\ncalculations, we assign six of the resonances to $s$-wave channels and the rest\nto $p$-wave channels. We use the $s$-wave resonances to refine the ground-state\npotentials of LiCs in the coupled-channel calculations and then obtain an\naccurate characterization of the scattering and bound-state properties of the\nmixtures. Our results will be useful for future experiments with ultracold\n$^{7}$Li-$^{133}$Cs mixtures.",
        "positive": "Continuous symmetry breaking and a new universality class in 1D\n  long-range interacting quantum systems: Continuous symmetry breaking (CSB) in low-dimensional systems, forbidden by\nthe Mermin-Wagner theorem for short-range interactions, may take place in the\npresence of slowly decaying long-range interactions. Nevertheless, there is no\nstringent bound on how slowly interactions should decay to give rise to CSB in\n1D quantum systems at zero temperature. Here, we study a long-range interacting\nspin chain with $U(1)$ symmetry and power-law interactions\n$V(r)\\sim1/r^\\alpha$, directly relevant to ion-trap experiments. Using\nbosonization and renormalization group theory, we find CSB for $\\alpha$ smaller\nthan a critical exponent $\\alpha_c(\\le 3)$ depending on the microscopic\nparameters of the model. Furthermore, the transition from the gapless XY phase\nto the gapless CSB phase is mediated by the breaking of conformal symmetry due\nto long-range interactions, and is described by a new universality class akin\nto the Berezinskii-Kosterlitz-Thouless transition. Our analytical findings are\nin good agreement with a numerical calculation. Signatures of the CSB phase\nshould be accessible in existing trapped-ion experiments."
    },
    {
        "anchor": "Accuracy of quantum simulators with ultracold dipolar molecules: a\n  quantitative comparison between continuum and lattice descriptions: With rapid progress in control and manipulation of ultracold magnetic atoms\nand dipolar molecules, the quantum simulation of lattice models with strongly\ninteracting dipole-dipole interactions (DDI) and high densities is now within\nexperimental reach. This rapid development raises the issue about the validity\nof quantum simulation in such regimes. In this study, we address this question\nby performing a full quantitative comparison between the continuum description\nof a one-dimensional gas of dipolar bosons in an optical lattice, and the\nsingle-band Bose-Hubbard lattice model that it quantum simulates. By comparing\nenergies and density distributions, and by calculating direct overlaps between\nthe continuum and lattice many-body wavefunctions, we demonstrate that in\nregimes of strong DDI and high densities the continuum system fails to recreate\nthe desired lattice model. Two-band Hubbard models become necessary to reduce\nthe discrepancy observed between continuum and lattice descriptions, but\nappreciable deviations in the density profile still remain. Our study\nelucidates the role of strong DDI in generating physics beyond lowest-band\ndescriptions and should offer a guideline for the calibration of near-term\ndipolar quantum simulators.",
        "positive": "Glassy disorder-induced effects in noisy dynamics of Bose-Hubbard and\n  Fermi-Hubbard systems: We address the effects of quenched disorder averaging in the time-evolution\nof systems of ultracold atoms in optical lattices in the presence of noise,\nimposed by of an environment. For bosonic systems governed by the Bose-Hubbard\nHamiltonian, we quantify the response of disorder in Hamiltonian parameters in\nterms of physical observables, including bipartite entanglement in the ground\nstate and report the existence of disorder-induced enhancement in weakly\ninteracting cases. For systems of two-species fermions described by the\nFermi-Hubbard Hamiltonian, we find similar results. In both cases, our\ndynamical calculations show no appreciable change in the effects of disorder\nfrom that of the initial state of the evolution. We explain our findings in\nterms the statistics of the disorder in the parameters and the behaviour of the\nobservables with the parameters."
    },
    {
        "anchor": "Superfluidity of strongly correlated bosons in two- and\n  three-dimensional traps: We analyze the superfluid phase transition of harmonically confined bosons\nwith long-range interaction in both two and three dimensions in a broad\nparameter range from weak to strong coupling. We observe that the onset of\nsuperfluidity occurs in $3D$ at significantly lower temperatures compared to\n$2D$. This is demonstrated to be a quantum degeneracy effect. In addition, the\nspatial distribution of superfluidity across the shells of the clusters is\ninvestigated. It is found that superfluidity is substantially reduced in the\nouter layers due to increased correlation effects.",
        "positive": "An Effective Series Expansion to the Equation of State of Unitary Fermi\n  Gases: Using universal properties and a basic statistical mechanical approach, we\npropose a general equation of state for unitary Fermi gases. The universal\nequation of state is written as a series solution to a self consistent integral\nequation where the general solution is a linear combination of Fermi functions.\nFirst, by truncating our series solution to four terms with already known exact\ntheoretical inputs at limiting cases, namely the first \\emph{three} virial\ncoefficients and using the Bertsch parameter as a free parameter, we find a\ngood agreement with experimental measurements in the entire temperature region\nin the normal state. This analytical equation of state agrees with experimental\ndata up to the fugacity $z = 18$, which is a vast improvement over the other\nanalytical equations of state available where the agreements is \\emph{only} up\nto $z \\approx 7$. Second, by truncating our series solution to four terms again\nusing first \\emph{four} virial coefficients, we find the Bertsch parameter $\\xi\n=0.35$, which is in good agreement with the direct experimental measurement of\n$\\xi =0.37$. This second form of equation of state shows a good agreement with\nself-consistent T-matrix calculations in the normal phase."
    },
    {
        "anchor": "Quantum Monte Carlo study of ultracold gases (PhD thesis): This Dissertation presents results of a thorough study of ultracold bosonic\nand fermionic gases in three-dimensional and quasi-one-dimensional systems.\nAlthough the analyses are carried out within various theoretical frameworks\n(Gross-Pitaevskii, Bethe ansatz, local density approximation, etc.) the main\ntool of the study is the Quantum Monte Carlo method in different modifications\n(variational Monte Carlo, diffusion Monte Carlo, fixed-node Monte Carlo\nmethods). We benchmark our Monte Carlo calculations by recovering known\nanalytical results (perturbative theories in dilute limits, exactly solvable\nmodels, etc.) and extend calculations to regimes, where the results are so far\nunknown. In particular we calculate the equation of state and correlation\nfunctions for gases in various geometries and with various interatomic\ninteractions.",
        "positive": "Effect of non-local interactions on the vortex solution in Bose-Einstein\n  Condensates: We consider the Gross-Pitaevskii (GP) model of a Bose-Einstein Condensate\n(BEC) to study a single vortex line in the presence of non-local repulsive\ns-wave scattering. We show that in addition to the vortex solution with core\nwidth of the order of the healing length, there exists a vortex solution whose\nwidth is a microscopic length scale of the order of s-wave scattering length\nand is independent of the healing length. We compare the two classes of vortex\nsolution and show the region where one can possibly observe the vortex whose\nwidth is of the order of scattering length."
    },
    {
        "anchor": "Ultracold bosonic scattering dynamics off a repulsive barrier: coherence\n  loss at the dimensional crossover: We explore the impact of dimensionality on the scattering of a small bosonic\nensemble in an elongated harmonic trap off a centered repulsive barrier,\nthereby taking particle correlations into account. The loss of coherence as\nwell as the oscillation of the center of mass are studied and we analyze the\ninfluence of both particle and spatial correlations. Two different mechanisms\nof coherence losses in dependence of the aspect ratio are found. For small\naspect ratios, loss of coherence between the region close to the barrier and\nouter regions occurs, due to spatial correlations, and for large aspect ratios,\nincoherence between the two density fragments of the left and right side of the\nbarrier arises, due to particle correlations. Apart form the decay of the\ncenter of mass motion induced by the reflection and transmission, further\neffects due to the particle and spatial correlations are explored. For tight\ntransversal traps, the amplitude of the center of mass oscillation experiences\na weaker damping, which can be traced back to the population of a second\nnatural orbital, and for a weaker transversal confinement, we detect a strong\ndecay, due to the possibility of transferring energy to transversal excited\nmodes. These effects are enhanced if the aspect ratio is integer valued.",
        "positive": "Simulation and detection of Weyl fermions in ultracold Fermi gases with\n  Raman-assisted spin-orbit coupling: Weyl fermion, also referred to as pseudo-magnetic monopole in momentum space,\nis an undiscovered massless elementary particle with half-integer spin\npredicted according to relativistic quantum field theory. Motivated by the\nrecent experimental observation of Weyl semimetal band in ultracold Bose gases\nwith Raman-assisted 3D spin-orbit coupling, we investigate the properties and\npossible observation of Weyl fermions in the low-energy quasi-particle\nexcitations of ultracold Fermi gases. Following a previous suggestion that the\nexisting Raman lattice scheme can be readily generalized to fermionic systems,\nhere we discuss the movement of the Weyl points in the Brillouin Zone, as well\nas the creation and annihilation of Weyl fermions by adjusting the effective\nZeeman field. The relevant topological properties are also demonstrated by\ncalculating the Chern number. Furthermore, we propose how to experimentally\nverify the existence of the Weyl fermions and the associated quantum phase\ntransition via density profile measurements."
    },
    {
        "anchor": "Ground states of atomic Fermi gases in a two-dimensional optical lattice\n  with and without population imbalance: We study the ground state phase diagram of population balanced and imbalanced\nultracold atomic Fermi gases with a short range attractive interaction\nthroughout the crossover from BCS to Bose-Einstein condensation (BEC), in a\ntwo-dimensional optical lattice (2DOL) comprised of two lattice and one\ncontinuum dimensions. We find that the mixing of lattice and continuum\ndimensions, together with population imbalance, has an extraordinary effect on\npairing and the superfluidity of atomic Fermi gases. In the balanced case, the\nsuperfluid ground state prevails the majority of the phase space. However, for\nrelatively small lattice hopping integral $t$ and large lattice constant $d$, a\npair density wave (PDW) emerges unexpectedly at intermediate coupling strength,\nand the nature of the in-plane and overall pairing changes from particle-like\nto hole-like in the BCS and unitary regimes, associated with an abnormal\nincrease in the Fermi volume with the pairing strength. In the imbalanced case,\nthe stable polarized superfluid phase shrinks to only a small portion of the\nentire phase space spanned by $t$, $d$, imbalance $p$ and interaction strength\n$U$, mainly in the bosonic regime of low $p$, moderately strong pairing, and\nrelatively large $t$ and small $d$. Due to the Pauli exclusion between paired\nand excessive fermions within the confined momentum space, a PDW phase emerges\nand the overall pairing evolves from particle-like into hole-like, as the\npairing strength grows stronger in the BEC regime. In both cases, the ground\nstate property is largely governed by the Fermi surface topology. These\nfindings are very different from the cases of pure 3D continuum, 3D lattice or\n1DOL.",
        "positive": "Analytical solutions of the coupled Gross-Pitaevskii equations for the\n  three-species Bose-Einstein condensates: The coupled Gross-Pitaevskii equations for the g.s. of the three-species\ncondensates (3-BEC) have been solved analytically under the Thomas-Fermi\napproximation. Six types of spatial configurations in miscible phase are found.\nThe whole parameter-space has been divided into zones each supports a specific\nconfiguration (miscible or immiscible). The borders of the zones are described\nby analytical formulae. Due to the division, the variation of the spatial\nconfiguration against the parameters can be visualized, and the effects of the\nparameters can be thereby understood. There are regions in the parameter-space\nwhere the configuration is highly sensitive to the parameters. These regions\nare tunable and valuable for the determination of the parameters."
    },
    {
        "anchor": "Observation of scaling in the dynamics of a strongly quenched quantum\n  gas: We report on the experimental observation of scaling in the time evolution\nfollowing a sudden quench into the vicinity of a quantum critical point. The\nexperimental system, a two-component Bose gas with coherent exchange between\nthe constituents, allows for the necessary high level of control of parameters\nas well as the access to time-resolved spatial correlation functions. The\ntheoretical analysis reveals that when quenching the system close to the\ncritical point, the energy introduced by the quench leads to a short-time\nevolution exhibiting crossover reminiscent of the finite-temperature critical\nproperties in the system's universality class. Observing the time evolution\nafter a quench represents a paradigm shift in accessing and probing\nexperimentally universal properties close to a quantum critical point and\nallows in a new way benchmarking of quantum many-body theory with experiments.",
        "positive": "Anyon braiding on a fractal lattice with a local Hamiltonian: There is a growing interest in searching for topology in fractal dimensions\nwith the aim of finding different properties and advantages compared to the\ninteger dimensional case. It has previously been shown that the Laughlin state\ncan be adapted to fractal lattices. A key element in doing so is to replace the\nuniform background charge by a background charge that resides only on the\nlattice sites. This motivates the study of Hofstadter type models on fractal\nlattices, in which the magnetic field is present only at the lattice sites.\nHere, we study such models for hardcore bosons on finite lattices derived from\nthe Sierpinski carpet and on square lattices with open boundary conditions. We\nfind that the system sizes that we can investigate with exact diagonalization\nare generally too small to judge whether these local models are topological or\nnot. Studying the particle densities on the lattices derived from the\nSierpinski carpet, we find that the densities tend to accumulate in the regions\nthat are locally similar to a square lattice. Such accumulation seems to be\nincompatible with the uniform densities in fractional quantum Hall systems,\nwhich might suggest that the models are not topological. Our computations\nprovide guidance for future searches for topology in finite systems. We also\npropose a scheme to implement both fractal lattices and our proposed local\nHamiltonian with ultracold atoms in optical lattices, which could allow for\nquantum simulators to go beyond the numerical results presented here."
    },
    {
        "anchor": "Dynamics of the corotating vortices in dipolar Bose-Einstein condensates\n  in the presence of dissipation: We study the dynamics of a single and a corotating vortex pair in a dipolar\nBose-Einstein condensate in the framework of dissipative Gross-Pitaevskii\nequation. This simple model enables us to simulate the effect of finite\ntemperature on the vortex dynamics. We study the effect of dipolar interactions\non the dynamics of a single vortex in the presence of phenomenological\ndissipation. In the case of a corotating vortex pair, an initial asymmetry in\nthe locations of the vortices can lead to different decay rates for the\nconstituent vortices as is the case for the condensates interacting via pure\ncontact interactions. We observe that the anisotropic interaction between the\ncomponent vortices manifests itself as the perceptible difference in the\ntrajectories traversed by the vortices in the condensate at finite\ntemperatures.",
        "positive": "Unconventional pairings of spin-orbit coupled attractive degenerate\n  Fermi gas in a one dimensional optical lattice: Understanding novel pairings in attractive degenerate Fermi gases is crucial\nfor exploring rich superfluid physics. In this report, we reveal unconventional\npairings induced by spin-orbit coupling (SOC) in a one-dimensional optical\nlattice, using a state-of-the-art density-matrix renormalization group method.\nWhen both bands are partially occupied, we find a strong competition between\nthe interband Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) and intraband\nBardeen-Cooper-Schrieffer (BCS) pairings. In particular, for the weak and\nmoderate SOC strengths, these two pairings can coexist, giving rise to a new\nphase called the FFLO-BCS phase, which exhibits a unique three-peak structure\nin pairing momentum distribution. For the strong SOC strength, the intraband\nBCS pairing always dominates in the whole parameter regime, including the half\nfilling. We figure out the whole phase diagrams as functions of filling factor,\nSOC strength, and Zeeman field. Our results are qualitatively different from\nrecent mean-field predictions. Finally, we address that our predictions could\nbe observed in a weaker trapped potential."
    },
    {
        "anchor": "Buckling transitions and clock order of two-dimensional Coulomb crystals: Crystals of repulsively interacting ions in planar traps form hexagonal\nlattices, which undergo a buckling instability towards a multi-layer structure\nas the transverse trap frequency is reduced. Numerical and experimental results\nindicate that the new structure is composed of three planes, whose separation\nincreases continuously from zero. We study the effects of thermal and quantum\nfluctuations by mapping this structural instability to the six-state clock\nmodel. A prominent implication of this mapping is that at finite temperature,\nfluctuations split the buckling instability into two thermal transitions,\naccompanied by the appearance of an intermediate critical phase. This phase is\ncharacterized by quasi-long-range order in the spatial tripartite pattern. It\nis manifested by broadened Bragg peaks at new wave vectors, whose line-shape\nprovides a direct measurement of the temperature dependent exponent $\\eta(T)$\ncharacteristic of the power-law correlations in the critical phase. A quantum\nphase transition is found at the largest value of the critical transverse\nfrequency: here the critical intermediate phase shrinks to zero. Moreover,\nwithin the ordered phase, we predict a crossover from classical to quantum\nbehavior, signifying the emergence of an additional characteristic scale for\nclock order. We discuss experimental realizations with trapped ions and\npolarized dipolar gases, and propose that within accessible technology, such\nexperiments can provide a direct probe of the rich phase diagram of the quantum\nclock model, not easily observable in condensed matter analogues. Therefore,\nthis works highlights the potential for ionic and dipolar systems to serve as\nsimulators for complex models in statistical mechanics and condensed matter\nphysics.",
        "positive": "Strongly interacting spin-orbit coupled Bose-Einstein condensates in one\n  dimension: We theoretically study dilute superfluidity of spin-1 bosons with\nantiferromagnetic interactions and synthetic spin-orbit coupling (SOC) in a\none-dimensional lattice. Employing a combination of density matrix\nrenormalization group and quantum field theoretical techniques we demonstrate\nthe appearance of a robust superfluid spin-liquid phase in which the\nspin-sector of this spinor Bose-Einstein condensate remains quantum disordered\neven after introducing quadratic Zeeman and helical magnetic fields. Despite\nremaining disordered, the presence of these symmetry breaking fields lifts the\nperfect spin-charge separation and thus the nematic correlators obey power-law\nbehavior. We demonstrate that, at strong coupling, the SOC induces a charge\ndensity wave state that is not accessible in the presence of linear and\nquadratic Zeeman fields alone. In addition, the SOC induces oscillations in the\nspin and nematic expectation values as well as the bosonic Green's function.\nThese non-trivial effects of a SOC are suppressed under the application of a\nlarge quadratic Zeeman field. We discuss how our results could be observed in\nexperiments on ultracold gases of $^{23}$Na in an optical lattice."
    },
    {
        "anchor": "Single-Particle properties of a strongly-interacting Bose-Fermi mixture\n  with mass and population imbalance: We theoretically investigate strong-coupling properties of a Bose-Fermi\nmixture. In the mass- and population-balanced case, two of the authors have\nshown that a strong hetero-pairing interaction in this mixture brings about\ncoupling phenomena between Fermi atomic excitations and Bose atomic and\ncomposite molecular excitations, that appear as an anomalous multiple peak\nstructure in the single-particle spectral weight (SW). [D. Kharga, {\\it et.\nal.}, J. Phys. Soc. Jpn. {\\bf 86}, 084301 (2017)]. In this paper, extending\nthis previous work, we show that, although these many-body phenomena are\nsensitive to mass and population imbalances between the Bose and Fermi\ncomponents, SW still exhibits the multiple peak structure in a moderately\nmass-imbalanced $^{87}$Rb-$^{40}$K and $^{23}$Na-$^{40}$K mixtures. We also\npoint out that the photoemission spectrum is a useful quantity to observe this\nspectral anomaly. Since a real trapped Bose-Fermi mixture is usually\naccompanied by mass and (local) population imbalance, our results would\ncontribute to the study of a strongly interacting Bose-Fermi mixture, under\nrealistic imbalanced conditions.",
        "positive": "Mixture of two unequally charged superfluids in a magnetic field: The artificial magnetic fields engineered for ultra cold gases depend on the\ninternal structure of the neutral atoms. Therefore the components of a mixture\ncomposed of two atomic gases can exhibit a different response to an artificial\nmagnetic field. Such a mixture can be interpreted as a mixture of two atomic\ngases, carrying different synthetic charges. In this article, we consider such\nmixtures of two superfluids with unequal synthetic charges in a ring trap\nsubject to a uniform artificial magnetic field. The charge imbalance in such a\nmixture changes the distribution of excited particles over angular momentum\nstates compared to that of an equally charged mixture. This microscopic\ndifference exhibits macroscopic consequences; such as the occurrence of an\nangular momentum transfer between two unequally charged components. Due to the\ninter-fluid atomic interactions in a ring, the angular momentum transfer can\ncreate a counter flowing persistent current in the weakly charged superfluid.\nEven in the limiting case of a charged and an uncharged superfluid mixture, a\npersistent current can be induced in the uncharged superfluid, despite the fact\nthat it is not directly coupled to the magnetic field. The stability analysis\nshows that the induction depends on the interplay between inter-fluid\ninteraction and the applied magnetic field. We obtain instability boundaries of\nthe system and construct phase diagrams as a function of the inter-fluid\ninteraction and the magnetic field. We investigate these properties employing\nthe Bogoliubov approximation."
    },
    {
        "anchor": "Torquing the Condensate: Angular Momentum Transport in Bose-Einstein\n  Condensates by Solitonic \"Corkscrew\": When rotating classical fluid drops merge together, angular momentum can be\nadvected from one to another due to the viscous shear flow at the drop\ninterface. It remains elusive what the corresponding mechanism is in inviscid\nquantum fluids such as Bose-Einstein condensates (BECs). Here we report our\ntheoretical study of an initially static BEC merging with a rotating BEC in\nthree-dimensional space along the rotational axis. We show that a soliton sheet\nresembling a \"corkscrew\" spontaneously emerges at the interface. Rapid angular\nmomentum transfer at a constant rate universally proportional to the initial\nangular momentum density is observed. Strikingly, this transfer does not\nnecessarily involve fluid advection or drifting of the quantized vortices. We\nreveal that the solitonic corkscrew can exert a torque that directly creates\nangular momentum in the static BEC and annihilates angular momentum in the\nrotating BEC. Uncovering this intriguing angular momentum transport mechanism\nmay benefit our understanding of various coherent matter-wave systems, spanning\nfrom atomtronics on chips to dark matter BECs at cosmic scales.",
        "positive": "Contact Measurements on Atomic BEC: A powerful set of universal relations, centered on a quantity called the\ncontact, connects the strength of short-range two-body correlations to the\nthermodynamics of a many-body system with delta-function interactions. We\nreport on measurements of the contact, using RF spectroscopy, for an $^{85}$Rb\natomic Bose-Einstein condensate (BEC). For bosons, the fact that contact\nspectroscopy can be used to probe the gas on short timescales is useful given\nthe decreasing stability of BECs with increasing interactions. A complication\nis the added possibility, for bosons, of three-body interactions. In\ninvestigating this issue, we have located an Efimov resonance for $^{85}$Rb\natoms with loss measurements and thus determined the three-body interaction\nparameter. In our contact spectroscopy, in a region of observable\nbeyond-mean-field effects, we find no measurable contribution from three-body\nphysics."
    },
    {
        "anchor": "Quasiparticle nature of the Bose polaron at finite temperature: The Bose polaron has attracted theoretical and experimental interest because\nthe mobile impurity is surrounded by a bath that undergoes a\nsuperfluid-to-normal phase transition. Although many theoretical works have\nstudied this system in its ground state, only few analyze its behavior at\nfinite temperature. We have studied the effect of temperature on a Bose polaron\nsystem performing ab-initio Path Integral Monte Carlo simulations. This method\nis able to approach the critical temperature without losing accuracy, in\ncontrast with perturbative approximations. We have calculated the polaron\nenergy for the repulsive and attractive branches and we have observed an\nasymmetric behavior between the two branches. When the potential is repulsive,\nthe polaron energy decreases when the temperature increases, and contrariwise\nfor the attractive branch. Our results for the effective mass and the dynamical\nstructure factor of the polaron show unambiguously that its quasiparticle\nnature disappears close to the critical temperature, in agreement with recent\nexperimental findings. Finally, we have also estimated the fraction of bosons\nin the condensate as well as the superfluid fraction, and we have concluded\nthat the impurity hinders the condensation of the rest of bosons.",
        "positive": "Spin-dependent Bragg spectroscopy of a spinor Bose gas: We develop a general theory of spin-dependent Bragg spectroscopy for spinor\nBose-Einstein condensates. This spectroscopy involves using a density and\nspin-coupled optical probe to excite the system. We show that within the linear\nresponse regime the momentum or energy transferred by the probe is determined\nby a set of density and spin-density dynamic structure factors. We derive a set\nof $f$-sum rules that provide rigorous constraints for the first energy moments\nof these structure factors. As an application we compute the dynamic structure\nfactors for cases within all four distinct phases of a spin-1 condensate using\nBogoliubov theory. Our results demonstrate that spin-dependent Bragg\nspectroscopy can be used to selectively investigate the various phonon and\nmagnon excitation branches and will be a useful tool for advancing our\nunderstanding of spinor condensates."
    },
    {
        "anchor": "The Efimov effect in lithium 6: We analyse the recent experiments investigating the low-energy physics of\nthree lithium 6 atoms in different internal states with resonant two-body\nscattering lengths. All observed features are qualitatively consistent with the\nexpected Efimov effect, i.e. the effective universal three-body attraction that\narises for large values of the scattering lengths. However, we find that a\nquantitative description at negative energy requires non-universal two- and\nthree-body corrections due to presently unknown behaviour at short distance. An\nattempt to implement these corrections is made through energy-dependent\nparameters fitted to the experimental data.",
        "positive": "Realizing topological states with polyatomic symmetric top molecules: We demonstrate that ultracold polyatomic symmetric top molecules, such as\nmethyl fluoride, loaded into an optical lattice and subject to DC electric and\nmicrowave field dressing, can display topological order via a self-consistent\nanalog of a proximity effect in the internal state space of the molecule. The\nnon-trivial topology arises from pairwise transitions between internal states\ninduced by dipole-dipole interactions and made resonant by the field dressing.\nTopological order is explicitly demonstrated by matrix product state\nsimulations on 1D chains. Additionally, we show that in the limit of pinned\nmolecules our description maps onto a long-range and anisotropic XYZ spin\nmodel, where Majorana fermions are zero-energy edge excitations in the case of\nnearest-neighbor couplings."
    },
    {
        "anchor": "Thermalization Dynamics of Two Correlated Bosonic Quantum Wires After a\n  Split: Coherently splitting a one-dimensional Bose gas provides an attractive,\nexperimentally estab- lished platform to investigate many-body quantum\ndynamics. At short enough times, the dynamics is dominated by the dephasing of\nsingle quasi-particles, and well described by the relaxation to- wards a\ngeneralized Gibbs ensemble corresponding to the free Luttinger theory. At later\ntimes on the other hand, the approach to a thermal Gibbs ensemble is expected\nfor a generic, interacting quantum system. Here, we go one step beyond the\nquadratic Luttinger theory and include the lead- ing phonon-phonon\ninteractions. By applying kinetic theory and non-equilibrium Dyson-Schwinger\nequations, we analyze the full relaxation dynamics beyond dephasing and\ndetermine the asymptotic thermalization process in the two-wire system for a\nsymmetric splitting protocol. The major ob- servables are the different phonon\noccupation functions and the experimentally accessible coherence factor, as\nwell as the phase correlations between the two wires. We demonstrate that,\ndepending on the splitting protocol, the presence of phonon collisions can have\nsignificant influence on the asymptotic evolution of these observables, which\nmakes the corresponding thermalization dynamics experimentally accessible.",
        "positive": "The Quantum Echo in Two-Component Bose-Einstein Condensates: The development of ultracold atom technology has enabled the precise\ninvestigations on quantum dynamics of quantum gases. Recently, inspired by\nexperimental advancement, the $SU(1,1)$ echo, akin to the well-known $SU(2)$\nspin echo, has been proposed for single-component Bose-Einstein condensate\n(BEC). In this paper, we investigate the possibility of quantum echo in the\nmore intricate two-component BEC by fully exploiting its underlying symmetry,\nwhich is the Lie group $Sp(4,R)$. We demonstrate that quantum echo can occur\nfor the two-component BEC by applying a driving protocol consisting of two\nsteps in each period. The first step can be any Bogoliubov Hamiltonian, while\nthe second step is a Hamiltonian with interactions turned off, which plays a\nsimilar role as the $\\pi$-pulse in spin echo. We confirm our theoretical\nresults with numerical calculations for different examples of two-component\nBEC. We further consider the effect of interactions between the excited boson\nmodes on the quantum echo process and discuss the possible experiment\nimplementation of this quantum echo."
    },
    {
        "anchor": "Quadratic scaling path integral molecular dynamics for fictitious\n  identical particles and its application to fermion systems: Recently, fictitious identical particles have provided a promising way to\novercome the fermion sign problem and have been used in path integral Monte\nCarlo (PIMC) to accurately simulate warm dense matter with up to 1000 electrons\n(T. Dornheim et al., arXiv:2311.08098 (2023)). The inclusion of fictitious\nidentical particles in path integral molecular dynamics (PIMD) can provide\nanother way to simulate fermion systems. In a recent paper (J. Chem. Phys. 159,\n154107 (2023)), Feldman and Hirshberg improved the recursive formula for PIMD\nof N identical bosons, significantly reducing the computational complexity from\n$O(PN^3)$ to $O(N^2+PN)$. In this paper, we extend this latest recursive\nformula for bosons to PIMD of fictitious identical particles to improve the\nefficiency of simulating fermion systems. We also provide the virial estimator\nfor calculating energy by using the recursive technique. As an example, we use\nthe quadratic scaling PIMD for fictitious identical particles to study the\nsimulation of hundreds of fermions in a two-dimensional periodic potential, in\nthe hope of providing a simulation tool for two-dimensional Fermi-Hubbard model\nand other strongly correlated fermion systems, such as the simulation of\nultracold fermionic gases in optical lattices.",
        "positive": "Three-dimensional vortex-bright solitons in a spin-orbit coupled\n  spin-$1$ condensate: We demonstrate stable and metastable vortex-bright solitons in a\nthree-dimensional spin-orbit-coupled three-component hyperfine spin-1\nBose-Einstein condensate (BEC) using numerical solution and variational\napproximation of a mean-field model. The spin-orbit coupling provides\nattraction to form vortex-bright solitons in both attractive and repulsive\nspinor BECs. The ground state of these vortex-bright solitons is axially\nsymmetric for weak polar interaction. For a sufficiently strong ferromagnetic\ninteraction, we observe the emergence of a fully asymmetric vortex-bright\nsoliton as the ground state. We also numerically investigate moving solitons.\nThe present mean-field model is not Galilean invariant, and we use a\nGalilean-transformed mean-field model for generating the moving solitons."
    },
    {
        "anchor": "Gapless topological Fulde-Ferrell superfluidity induced by in-plane\n  Zeeman field: Topological superfluids are recently discovered quantum matters that host\ntopologically protected gapless edge states known as Majorana fermions - exotic\nquantum particles that act as their own anti-particles and obey non-Abelian\nstatistics. Their realizations are believed to lie at the heart of future\ntechnologies such as fault-tolerant quantum computation. To date, the most\nefficient scheme to create topological superfluids and Majorana fermions is\nbased on the Sau-Lutchyn-Tewari-Das Sarma model with a Rashba-type spin-orbit\ncoupling on the }\\textbf{\\textit{x-y}}\\textbf{ plane and a large out-of-plane\n(perpendicular) Zeeman field along the }\\textbf{\\textit{z}}\\textbf{-direction.\nHere we propose an alternative setup, where the topological superfluid phase is\ndriven by applying an in-plane Zeeman field. This scheme offers a number of new\nfeatures, notably Cooper pairings at finite centre-of-mass momentum (i.e.,\nFulde-Ferrell pairing) and gapless excitations in the bulk. As a result, a\nnovel gapless topological quantum matter with inhomogeneous pairing order\nparameter appears. It features unidirected Majorana surface states at\nboundaries, which propagate in the same direction and connect two Weyl nodes in\nthe bulk. We demonstrate the emergence of such an exotic topological matter and\nthe associated Majorana fermions in spin-orbit coupled atomic Fermi gases and\ndetermine its parameter space. The implementation of our scheme in\nsemiconductor/superconductor heterostructures is briefly discussed.",
        "positive": "Spontaneous formation of Kagom\u00e9 lattice in two-dimensional Rydberg\n  atoms: Two-dimensional Rydberg atoms are modeled at low temperatures by means of the\nclassical Monte Carlo method. The Coulomb repulsion of charged ions competing\nwith the repulsive van der Waals long-range tail is modeled by a number of\ninteraction potentials. We find that under specific conditions the usual\ntriangular crystal becomes unstable with respect to more exotic lattices such\nas Kagom\\'e, flower, molecular crystal and rectangular chain packings.\nGround-state configurations are obtained by means of the annealing procedure\nand their stability is additionally studied by the normal modes analysis. While\ncommonly the square lattice is mechanically unstable due to softening of the\nshear modulus, we were able to find a specific set of parameters for which the\nsquare lattice can be made stable."
    },
    {
        "anchor": "Meron Ground State of Rashba Spin-Orbit-Coupled Dipolar Bosons: We study the effects of dipolar interactions on a Bose-Einstein condensate\nwith synthetically generated Rashba spin-orbit coupling. The dipolar\ninteraction we consider includes terms that couple spin and orbital angular\nmomentum in a way perfectly congruent with the single-particle Rashba coupling.\nWe show that this internal spin-orbit coupling plays a crucial role in the rich\nground-state phase diagram of the trapped condensate. In particular, we predict\nthe emergence of a thermodynamically stable ground state with a meron spin\nconfiguration.",
        "positive": "Accelerating many-body entanglement generation by dipolar interactions\n  in the Bose-Hubbard model: The spin squeezing protocols allow the dynamical generation of massively\ncorrelated quantum many-body states, which can be utilized in\nentanglement-enhanced metrology and technologies. We study a quantum simulator\ngenerating twisting dynamics realized in a two-component Bose-Hubbard model\nwith dipolar interactions. We show that the interplay of contact and long-range\ndipolar interactions between atoms in the superfluid phase activates the\nanisotropic two-axis counter-twisting mechanism, accelerating the spin\nsqueezing dynamics and allowing the Heisenberg-limited accuracy in\nspectroscopic measurements."
    },
    {
        "anchor": "Collective mode evidence of high-spin bosonization in a trapped\n  one-dimensional atomic Fermi gas with tunable spin: We calculate the frequency of collective modes of a one-dimensional\nrepulsively interacting Fermi gas with high-spin symmetry confined in harmonic\ntraps at zero temperature. This is a system realizable with fermionic\nalkaline-earth-metal atoms such as $^{173}$Yb, which displays an exact\nSU($\\kappa$) spin symmetry with $\\kappa\\geqslant2$ and behaves like a spinless\ninteracting Bose gas in the limit of infinite spin components\n$\\kappa\\rightarrow\\infty$, namely high-spin bosonization. We solve the\nhomogeneous equation of state of the high-spin Fermi system by using Bethe\nansatz technique and obtain the density distribution in harmonic traps based on\nlocal density approximation. The frequency of collective modes is calculated by\nexactly solving the zero-temperature hydrodynamic equation. In the limit of\nlarge number of spin-components, we show that the mode frequency of the system\napproaches to that of a one-dimensional spinless interacting Bose gas, as a\nresult of high-spin bosonization. Our prediction of collective modes is in\nexcellent agreement with a very recent measurement for a Fermi gas of\n$^{173}$Yb atoms with tunable spin confined in a two-dimensional tight optical\nlattice.",
        "positive": "Efimov physics in the complex plane: Efimov effect is characterized by an infinite number of three-body bound\nstates following a universal geometric scaling law at two-body resonances. In\nthis paper, we investigate the influence of two-body loss which can be\ndescribed by a complex scattering length $a_c$ on these states. Interestingly,\nbecause of the complexity of the scattering length $a_c$, the trimer energy is\nno longer constrained on the negative real axis, and it is allowed to have a\nnonvanishing imaginary part and a real part which may exceed the three-body or\nthe atom-dimer scattering threshold. Indeed, by taking the\n$^{133}$Cs-$^{133}$Cs-$^6$Li system as a concrete example, we calculate the\ntrimer energies by solving the generalized Skorniakov-Ter-Martirosian equation\nand find such three-body bound states with energies that have positive real\nparts and obey a generalized geometric scaling law. Remarkably, we also find\nthat in some regions these three-body bound states have longer lifetimes\ncompared with the corresponding two-body bound states. The lifetimes for these\ntrimer states can even tend to infinity. Our work paves the way for the future\nexploration of few-body bound states in the complex plane."
    },
    {
        "anchor": "Emergent pseudospin-1 Maxwell fermions with a threefold degeneracy in\n  optical lattices: The discovery of relativistic spin-1/2 fermions such as Dirac and Weyl\nfermions in condensed-matter or artificial systems opens a new era in modern\nphysics. An interesting but rarely explored question is whether other\nrelativistic spinal excitations could be realized with artificial systems.\nHere, we construct twoand three-dimensional tight-binding models realizable\nwith cold fermionic atoms in optical lattices, where the low energy excitations\nare effectively described by the spin-1 Maxwell equations in the Hamiltonian\nform. These relativistic (linear dispersion) excitations with unconventional\ninteger pseudospin, beyond the Dirac-Weyl-Majorana fermions, are an exotic kind\nof fermions named asMaxwell fermions.We demonstrate that the systems have rich\ntopological features. For instance, the threefold degenerate points called\nMaxwell points may have quantized Berry phases and anomalous quantum Hall\neffects with spin-momentum locking may appear in topological Maxwell insulators\nin the two-dimensional lattices. In three dimensions,Maxwell points may have\nnontrivial monopole charges of \\pm2 with two Fermi arcs connecting them, and\nthe merging of the Maxwell points leads to topological phase transitions.\nFinally, we propose realistic schemes for realizing the model Hamiltonians and\ndetecting the topological properties of the emergent Maxwell quasiparticles in\noptical lattices.",
        "positive": "Revivals in the attractive BEC in a double-well potential and their\n  decoherence: We study the dynamics of ultracold attractive atoms in a weakly linked two\npotential wells. We consider an unbalanced initial state and monitor dynamics\nof the population difference between the two wells. The average imbalance\nbetween wells undergoes damped oscillations, like in a classical counterpart,\nbut then it revives almost to the initial value. We explain in details the\nwhole behavior using three different models of the system. Furthermore we\ninvestigate the sensitivity of the revivals on the decoherence caused by one-\nand three-body losses. We include the dissipative processes using appropriate\nmaster equations and solve them using the stochastic wave approximation method."
    },
    {
        "anchor": "Collisionless sound in a uniform two-dimensional Bose gas: Using linear response theory within the Random Phase Approximation, we\ninvestigate the propagation of sound in a uniform two dimensional (2D) Bose gas\nin the collisionless regime. We show that the sudden removal of a static\ndensity perturbation produces a damped oscillatory behavior revealing that\nsound can propagate also in the absence of collisions, due to mean-field\ninteraction effects. Our analysis points out the crucial role played by Landau\ndamping. We support our predictions by performing numerical simulations with\nthe stochastic (projected) Gross-Pitaevskii equation. The results are\nconsistent with the recent experimental observation of sound in a weakly\ninteracting 2D Bose gas both below and above the superfluid\nBerezinskii-Kosterlitz-Thouless transition.",
        "positive": "Exact Diagonalisation of Photon Bose-Einstein Condensates with\n  Thermo-Optic Interaction: Although photon Bose-Einstein condensates have already been used for studying\nmany interesting effects, the precise role of the photon-photon interaction is\nnot fully clarified up to now. In view of this, it is advantageous that these\nsystems allow measuring both the intensity of the light leaking out of the\ncavity and its spectrum at the same time. Therefore, the photon-photon\ninteraction strength can be determined once via analysing the condensate\nbroadening and once via examining the interaction-induced modifications of the\ncavity modes. As the former method depends crucially on the concrete shape of\nthe trapping potential and the spatial resolution of the used camera,\ninterferometric methods promise more precise measurements. To this end, the\npresent paper works out the impact of the photon-photon interaction upon the\ncavity modes. A quantum mechanical description of the photon-photon\ninteraction, including the thermal cloud, builds the theoretical backbone of\nthe method. An exact diagonalisation approach introduced here exposes how the\neffective photon-photon interaction modifies both the spectrum and the width of\nthe photon gas. A comparison with a variational approach based on the\nGross-Pitaevskii equation quantifies the contribution of the thermal cloud in\nthe respective applications."
    },
    {
        "anchor": "Quantum entanglement due to modulated Dynamical Casimir Effect: We study the creation and entanglement of quasiparticle pairs due to a\nperiodic variation of the mode frequencies of a homogeneous quantum system.\nDepending on the values of the parameters describing the periodic modulation,\nthe number of created pairs either oscillates or, in a narrow resonant\nfrequency interval, grows exponentially in time. For a system initially in a\nthermal state, we determine in which cases the final state is quantum\nmechanically entangled, i.e., where the bipartite state is nonseparable. We\ninclude some weak dissipation, expected to be found in any experimental setup,\nand study the corresponding reduction of the quantum entanglement. Our findings\nare used to interpret the results of two recent experiments.",
        "positive": "Stroboscopic versus non-stroboscopic dynamics in the Floquet realization\n  of the Harper-Hofstadter Hamiltonian: We study the stroboscopic and non-stroboscopic dynamics in the Floquet\nrealization of the Harper-Hofstadter Hamiltonian. We show that the former\nproduces the evolution expected in the high-frequency limit only for\nobservables which commute with the operator to which the driving protocol\ncouples. On the contrary, non-stroboscopic dynamics is capable of capturing the\nevolution governed by the Floquet Hamiltonian of any observable associated with\nthe effective high-frequency model. We provide exact numerical simulations for\nthe dynamics of the density operator following a quantum cyclotron orbit on a\n$2\\times 2$ plaquette, as well as the chiral current operator flowing along the\nlegs of a $2\\times 20$ ladder. The exact evolution is compared with its\nstroboscopic and non-stroboscopic counterparts, including finite-frequency\ncorrections."
    },
    {
        "anchor": "Exact Quantum Many-Body Scar States in the Rydberg-Blockaded Atom Chain: A recent experiment in the Rydberg atom chain observed unusual oscillatory\nquench dynamics with a charge density wave initial state, and theoretical works\nidentified a set of many-body \"scar states\" showing nonthermal behavior in the\nHamiltonian as potentially responsible for the atypical dynamics. In the same\nnonintegrable Hamiltonian, we discover several eigenstates at \\emph{infinite\ntemperature} that can be represented exactly as matrix product states with\nfinite bond dimension, for both periodic boundary conditions (two exact $E = 0$\nstates) and open boundary conditions (two $E = 0$ states and one each $E = \\pm\n\\sqrt{2}$). This discovery explicitly demonstrates violation of strong\neigenstate thermalization hypothesis in this model and uncovers exact quantum\nmany-body scar states. These states show signatures of translational symmetry\nbreaking with period-2 bond-centered pattern, despite being in one dimension at\ninfinite temperature. We show that the nearby many-body scar states can be well\napproximated as \"quasiparticle excitations\" on top of our exact $E = 0$ scar\nstates, and propose a quasiparticle explanation of the strong oscillations\nobserved in experiments.",
        "positive": "Quantum Many-Body Calculations using Body-Centered Cubic Lattices: It is often computationally advantageous to model space as a discrete set of\npoints forming a lattice grid. This technique is particularly useful for\ncomputationally difficult problems such as quantum many-body systems. For\nreasons of simplicity and familiarity, nearly all quantum many-body\ncalculations have been performed on simple cubic lattices. Since the removal of\nlattice artifacts is often an important concern, it would be useful to perform\ncalculations using more than one lattice geometry. In this work we show how to\nperform quantum many-body calculations using auxiliary-field Monte Carlo\nsimulations on a three-dimensional body-centered cubic (BCC) lattice. As a\nbenchmark test we compute the ground state energy of 33 spin-up and 33\nspin-down fermions in the unitary limit, which is an idealized limit where the\ninteraction range is zero and scattering length is infinite. As a fraction of\nthe free Fermi gas energy $E_{\\rm FG}$, we find that the ground state energy is\n$E_0/E_{\\rm FG}= 0.369(2), 0.371(2),$ using two different definitions of the\nfinite-system energy ratio. This is in excellent agreement with recent results\nobtained on a cubic lattice \\cite{He:2019ipt}. We find that the computational\neffort and performance on a BCC lattice is approximately the same as that for a\ncubic lattice with the same number of lattice points. We discuss how the\nlattice simulations with different geometries can be used to constrain the size\nlattice artifacts in simulations of continuum quantum many-body systems."
    },
    {
        "anchor": "Thermodynamic contacts and breathing mode physics of 1D p-wave Fermi\n  gases in the high temperature limit: An important tool for understanding the effects of interactions in\nharmonically trapped atomic gases is the examination of their collective modes.\nOne such mode is the breathing or monopole mode, which is special as it is\nconstrained to occur at twice the harmonic trapping frequency when the\ninteractions are scale invariant. When the interactions are not scale\ninvariant, the frequency of the breathing mode will deviate from twice the trap\nfrequency. The deviation itself depends on the thermodynamic contacts, which\ndescribe how the energy changes with the interactions. In this work I examine\nhow the thermodynamic contacts and the breathing mode frequency of a\nspin-polarized one-dimensional (1D) p-wave Fermi gas depend on the 1D\nscattering volume, $\\ell$, and the effective range, $r$, in the high\ntemperature limit. Such dynamics can be studied in experiments and provide a\ntool for understanding how the dynamics depend on interactions with a finite\neffective range.",
        "positive": "Coexistence of Bose condensation and pairing in Boson mixtures: We consider the problem when there are two kinds of Bosons with an attraction\nbetween them. We find the system to consist of two Bose condensates with an\nadditional pairing order between the Bosons. The properties of this state are\ndiscussed."
    },
    {
        "anchor": "Finite-range effects in the unitary Fermi polaron: Quantum Monte Carlo techniques are employed to study the properties of\npolarons in an ultracold Fermi gas, at $T= 0,$ and in the unitary regime using\nboth a zero-range model and a square-well potential. For a fixed density, the\npotential range is varied and results are extrapolated and compared against a\nzero-range model. A discussion regarding the choice of an interacting potential\nwith a finite range is presented. We compute the polaron effective mass, the\npolaron binding energy, and the effective coupling between them. The latter is\nobtained using the Landau-Pomeranchuk's weakly interacting quasiparticle model.\nThe contact parameter is estimated by fitting the pair distribution function of\natoms in different spin states.",
        "positive": "Non-linear dynamical response of interacting bosons to synthetic\n  electric field: We theoretically study the non-linear response of interacting neutral bosonic\ngas in a synthetically driven one-dimensional optical lattice. In particular,\nwe examine the bosonic analogue of electronic higher harmonic generation in a\nstrong time-dependent synthetic vector potential manifesting itself as the\nsynthetic electric field. We show that the vector potential can generate\nreasonably high harmonics in the insulating regime, while the superfluid regime\nexhibits only a few harmonics. In the insulating regime, the number of\nharmonics increases with the increase in the strength of the vector potential.\nThis originates primarily due to the field-driven resonant and non-resonant\nexcitations in the neutral Mott state and their recombination with the ground\nstate. If the repulsive interaction between two atoms ($U$) is close to the\nstrength of the gauge potential ($A_0$), the resonant quasiparticle-quasihole\npairs on nearest-neighbor sites, namely dipole states are found to a play a\ndominant role in the generating higher harmonics. However, in the strong-field\nlimit $A_0\\gg U$, the nonresonant states where quasiparticle-quasihole pairs\nare not on nearest-neighbor sites give rise to higher harmonics."
    },
    {
        "anchor": "Orbital order of spinless fermions near an optical Feshbach resonance: We study the quantum phases of a three-color Hubbard model that arises in the\ndynamics of the p-band orbitals of spinless fermions in an optical lattice.\nStrong, color-dependent interactions are induced by an optical Feshbach\nresonance. Starting from the microscopic scattering properties of ultracold\natoms, we derive the orbital exchange constants at 1/3 filling on the cubic\noptical lattice. Using this, we compute the phase diagram in a Gutzwiller\nansatz. We find novel phases with 'axial orbital order' in which pz and px +\nipy (or px - ipy) orbitals alternate.",
        "positive": "Shear Viscosity in the Strong Interaction Regime of a p-wave Superfluid\n  Fermi Gas: The $p$-wave superfluid state is a promising spin-triplet and non $s$-wave\npairing state in an ultracold Fermi gas. In this work we study the\nlow-temperature shear viscosity of a one-component $p$-wave superfluid Fermi\ngas, by means of Kubo formalism. Our study is done in the strong-coupling limit\nwhere Fermi superfluid reduces into a system of composite bosons. Taking into\naccount ${{p}_{x}}$-wave Cooper channel in the self-energy, the viscous\nrelaxation rates are determined. The relaxation rates related to these\ninteractions are calculated as a function of temperature. Their temperature\ndependence is different from the $s$-wave superfluid Fermi gas, and this is due\nto the anisotropic pairing interaction in the $p$-wave superfluid. Our results\ncontribute to understand how this anisotropy affects transport properties of\nthis unconventional superfluid Fermi gas in low temperature limit."
    },
    {
        "anchor": "Topologically driven Rabi-oscillating interference dislocation: Quantum vortices are the quantized version of classical vortices. Their\ncenter is a phase singularity or vortex core around which the flow of particles\nas a whole circulates and is typical in superfluids, condensates and optical\nfields. However, the exploration of the motion of the phase singularities in\ncoherently-coupled systems is still underway. We theoretically analyze the\npropagation of an interference dislocation in the regime of strong coupling\nbetween light and matter, with strong mass imbalance, corresponding to the case\nof microcavity exciton-polaritons. To this end, we utilize combinations of\nvortex and tightly focused Gaussian beams, which are introduced through\nresonant pulsed pumping. We show that a dislocation originates from\nself-interference fringes, due to the non-parabolic dispersion of polaritons\ncombined with moving Rabi-oscillating vortices. The morphology of singularities\nis analyzed in the Poincar\\'{e} space for the pseudospin associated to the\npolariton states. The resulting beam carries orbital angular momentum with\ndecaying oscillations due to the loss of overlap between the normal modes of\nthe polariton system.",
        "positive": "Classical phase-space approach for coherent matter waves: We investigate a classical phase-space approach of matter-wave propagation\nbased on the Truncated Wigner Equation (TWE). We show that such description is\nsuitable for ideal matter waves in quadratic time-dependent confinement as well\nas for harmonically trapped Bose Einstein condensates in the Thomas-Fermi\nregime. In arbitrary interacting regimes, the TWE combined with the moment\nmethod yields the low-energy spectrum of a condensate as predicted by\nindependent variational methods. TWE also gives the right breathing mode\nfrequency for long-ranged interactions decaying as $1/r^2$ in 3D and for a\ncontact potential in 2D. Quantum signatures, beyond the TWE, may only be found\nin the condensate dynamics beyond the regimes of classical phase-space\npropagation identified here."
    },
    {
        "anchor": "Ultracold Dipolar Gases in Optical Lattices: This tutorial is a theoretical work, in which we study the physics of\nultra-cold dipolar bosonic gases in optical lattices. Such gases consist of\nbosonic atoms or molecules that interact via dipolar forces, and that are\ncooled below the quantum degeneracy temperature, typically in the nK range.\nWhen such a degenerate quantum gas is loaded into an optical lattice produced\nby standing waves of laser light, new kinds of physical phenomena occur. These\nsystems realize then extended Hubbard-type models, and can be brought to a\nstrongly correlated regime. The physical properties of such gases, dominated by\nthe long-range, anisotropic dipole-dipole interactions, are discussed using the\nmean-field approximations, and exact Quantum Monte Carlo techniques (the Worm\nalgorithm).",
        "positive": "Multi-ring, stripe, and super-lattice solitons in a spin-orbit coupled\n  spin-1 condensate: We demonstrate exotic stable quasi-two-dimensional solitons in a Rashba or a\nDresselhaus spin-orbit (SO) coupled hyperfine spin-1 ($F=1$) trap-less\nantiferromagnetic Bose-Einstein condensate using the mean-field\nGross-Pitaevskii equation. For weak SO coupling, the solitons are of the\n$(-1,0,+1)$ or $(+1,0,-1)$ type with intrinsic vorticity, for Rashba or\nDresselhaus SO coupling, where the numbers in the parentheses denote angular\nmomentum in spin components $F_z= +1,0,-1$, respectively. For intermediate SO\ncoupling, the solitons have multi-ring structure maintaining the\nabove-mentioned vortices in respective components. For larger SO coupling,\nsuperlattice solitons with a square-lattice structure in total density are\nfound in addition to stripe solitons with stripe pattern in component densities\nwith no periodic modulation in total density."
    },
    {
        "anchor": "Disordered one-dimensional Bose-Fermi mixtures: The Bose-Fermi glass: We analyze an interacting Bose-Fermi mixture in a 1D disordered potential\nusing a combination of renormalization group and variational methods. We obtain\nthe complete phase diagram in the incommensurate case as a function of bosonic\nand inter-species interaction strengths, in the weak disorder limit. We find\nthat the system is characterized by several phase transitions between\nsuperfluid and various glassy insulating states, including a new Bose-Fermi\nglass phase, where both species are coupled and localized. We show that the\ndynamical structure factor, as measured through Bragg scattering experiments,\ncan distinguish between the various localized phases and probe their dynamics.",
        "positive": "Non-equilibrium dynamics of fluctuations in an ultra-cold atomic mixture: We investigate an ultra-cold mixture of Bose gases interacting via\nspin-changing collisions by studying the dynamics of spin fluctuations. The\nexperimental implementation employs $^{23}$Na and $^{7}$Li atoms, which are\nprepared out of equilibrium across a wide range of initial conditions. We\nidentify three regimes in the dynamics of the system for different initial\nstates: a long-lived metastable regime, an instability range with strong growth\nof fluctuations, and a fast relaxing regime approaching thermal equilibrium.\nTheoretical modelling of the data allows us to reconstruct effective potentials\nwhich characterize the different dynamical regimes of the system."
    },
    {
        "anchor": "Collisionally inhomogeneous Bose-Einstein condensates with binary and\n  three body interactions in a bichromatic optical lattice: We study the impact of collisionally inhomogeneous binary and three body\ninteraction on Bose-Einstein condensates (BECs) of a dilute gas in a\nbichromatic optical lattice. We observe that the localized matter wave density\nwhich decreases after the introduction of repulsive spatially inhomogeneous\nbinary interaction can be sustained by the addition of constant attractive\nbinary strength in equal amounts. If the balance between repulsive spatially\ninhomogeneous binary interaction and constant attractive interaction is\ndisturbed, the condensates collapse. Reversal of sign of interaction ensures\nthe longevity of BECs. Any imbalance between attractive spatially inhomogeneous\ninteraction and constant repulsive interaction either results in the collapse\nof BECs or in the occupation of the condensates at multiple sites on either\nsides. The introduction of a weak three body interaction in phase with the\nbinary interaction increases the extent of instability of BECs. Reversing the\nsign of spatially inhomogeneous and constant interaction enhances the stability\nof BECs.",
        "positive": "Stimulated Thermalization of a Parametrically Driven Magnon Gas as a\n  Prerequisite for Bose-Einstein Magnon Condensation: Thermalization of a parametrically driven magnon gas leading to the formation\nof a Bose-Einstein condensate at the bottom of a spin-wave spectrum was studied\nby time- and wavevector-resolved Brillouin light scattering spectroscopy. It\nhas been found that the condensation is preceded by the conversion of initially\npumped magnons into a second group of frequency degenerated magnons, which\nappear due to parametrically stimulated scattering of the initial magnons to a\nshort-wavelength spectral region. In contrast to the first magnon group, which\nwavevectors are orthogonal to the wavevectors of the magnons at the lowest\nenergy states, the secondary magnons can effectively scatter to the bottom of\nthe spectrum and condense there."
    },
    {
        "anchor": "Curvature Induced Topological Defects of $p$-wave Superfluid on a Sphere: We study the ground state of spinless fermions living on a sphere across\n$p$-wave Feschbach resonances. By construsting a microscopic model of fermions\non a general curved surface, we show that the Guassian curvature induces an\nemergent magnetic field coupled to the $p\\pm ip$ order parameters. In the case\nof a sphere, the magnetic field corresponds to a Dirac monopole field, which\ncauses topological defects in the superfluid ground state. Using the BCS mean\nfield theory, we calculate its many-body ground state self consistently and\ngive the phase diagram. The ground state may exhibit two types of topological\ndefects, two voritces on the south and north pole or a domain wall which\nseparates $p_\\theta+ ip_\\phi$ and $p_\\theta-ip_\\phi$ superfluids.",
        "positive": "Dynamical mean-field theory for light fermion--heavy boson mixtures on\n  optical lattices: We theoretically analyze Fermi-Bose mixtures consisting of light fermions and\nheavy bosons that are loaded into optical lattices (ignoring the trapping\npotential). To describe such mixtures, we consider the Fermi-Bose version of\nthe Falicov-Kimball model on a periodic lattice. This model can be exactly\nmapped onto the spinless Fermi-Fermi Falicov-Kimball model at zero temperature\nfor all parameter space as long as the mixture is thermodynamically stable. We\nemploy dynamical mean-field theory to investigate the evolution of the\nFermi-Bose Falicov-Kimball model at higher temperatures. We calculate spectral\nmoment sum rules for the retarded Green's function and self-energy, and use\nthem to benchmark the accuracy of our numerical calculations, as well as to\nreduce the computational cost by exactly including the tails of infinite\nsummations or products. We show how the occupancy of the bosons,\nsingle-particle many-body density of states for the fermions, momentum\ndistribution, and the average kinetic energy evolve with temperature. We end by\nbriefly discussing how to experimentally realize the Fermi-Bose Falicov-Kimball\nmodel in ultracold atomic systems."
    },
    {
        "anchor": "Quantum Many-Body Scarring in $2+1$D Gauge Theories with Dynamical\n  Matter: Quantum many-body scarring (QMBS) has emerged as an intriguing paradigm of\nweak ergodicity breaking in nonintegrable quantum many-body models,\nparticularly lattice gauge theories (LGTs) in $1+1$ spacetime dimensions.\nHowever, an open question is whether QMBS exists in higher-dimensional LGTs\nwith dynamical matter. Given that nonergodic dynamics in $d{=}1$ spatial\ndimension tend to vanish in $d{>}1$, it is important to probe this question.\nUsing matrix product state techniques for both finite and infinite systems, we\nshow that QMBS occurs in the $2{+}1$D $\\mathrm{U}(1)$ quantum link model (QLM),\nas evidenced in persistent coherent oscillations in local observables, a marked\nslowdown in the growth of the bipartite entanglement entropy, and revivals in\nthe fidelity. Interestingly, we see that QMBS is more robust when the matter\ndegrees of freedom are bosonic rather than fermionic. Our results further shed\nlight on the intimate connection between gauge invariance and QMBS, and\nhighlight the persistence of scarring in higher spatial dimensions. Our\nfindings can be tested in near-term analog and digital quantum simulators, and\nwe demonstrate their accessibility on a recently proposed cold-atom analog\nquantum simulator.",
        "positive": "Quench dynamics of Rydberg-dressed bosons on two-dimensional square\n  lattices: We study the dynamics of bosonic atoms on a two-dimensional square lattice,\nwhere atomic interactions are long-ranged with either a box or soft-core shape.\nThe latter can be realized through laser dressing ground-state atoms to\nelectronically excited Rydberg states. When the range of interactions is equal\nor larger than the lattice constant, the system is governed by an extended\nBose-Hubbard model. We propose a quench process by varying the atomic hopping\nlinearly across phase boundaries of the Mott insulator-supersolid and\nsupersolid-superfluid phases. Starting from a Mott insulating state, the\ndynamical evolution of the superfluid order parameter exhibits a universal\nbehaviour at the early stage, largely independent of interactions. The\ndynamical evolution is significantly altered by strong, long-range interactions\nat later times. Particularly, we demonstrate that density wave excitation is\nimportant when the quench rate is small. Moreover, we show that the quench\ndynamics can be analyzed through time-of-flight images, i.e., measuring the\nmomentum distribution and noise correlations."
    },
    {
        "anchor": "Tan's contact scaling behaviour for trapped Lieb-Liniger bosons: from\n  two to many: We show that the contact parameter of N harmonically-trapped interacting 1D\nbosons at zero temperature can be analytically and accurately obtained by a\nsimple rescaling of the exact two-boson solution, and that N-body effects can\nbe almost factorized. The small deviations observed between our analytical\nresults and DMRG calculations are more pronounced when the interaction energy\nis maximal (i.e. at intermediate interaction strengths) but they remain bounded\nby the large-N local-density approximation obtained from the Lieb-Liniger\nequation of state stemming from the Bethe Ansatz. The rescaled two-body\nsolution is so close to the exact ones, that is possible, within a simple\nexpression interpolating the rescaled two-boson result to the local-density, to\nobtain N-boson contact and ground state energy functions in very good agreement\nwith DMRG calculations. Our results suggest a change of paradigm in the study\nof interacting quantum systems, giving to the contact parameter a more\nfundamental role than energy.",
        "positive": "Spin nematic order in antiferromagnetic spinor condensates: Large spin systems can exhibit unconventional types of magnetic ordering\ndifferent from the ferromagnetic or N\\'eel-like antiferromagnetic order\ncommonly found in spin 1/2 systems. Spin-nematic phases, for instance, do not\nbreak time-reversal invariance and their magnetic order parameter is\ncharacterized by a second rank tensor with the symmetry of an ellipsoid. Here\nwe show direct experimental evidence for spin-nematic ordering in a spin-1\nBose-Einstein condensate of sodium atoms with antiferromagnetic interactions.\nIn a mean field description this order is enforced by locking the relative\nphase between spin components. We reveal this mechanism by studying the spin\nnoise after a spin rotation, which is shown to contain information hidden when\nlooking only at averages. The method should be applicable to high spin systems\nin order to reveal complex magnetic phases."
    },
    {
        "anchor": "Spin-Induced Orbital Frustration in a Hexagonal Optical Lattice: Complex lattices provide a versatile ground for fascinating quantum many-body\nphysics. Here, we propose an exotic mechanics for generating orbital\nfrustration in hexagonal lattices. We study two-component (pseudospin-$1/2$)\nBose gases in $p$-orbital bands of two-dimensional hexagonal lattices, and find\nthat the system exhibits previously untouched orbital frustration as a result\nof the interplay of spin and orbital degrees of freedom, in contrast to normal\nIsing-type orbital ordering of spinless $p$-orbital band bosons in\ntwo-dimensional hexagonal lattices. Based on the classification by symmetry\nanalysis, we find the interplay of orbital frustration and strong interaction\nleads to exotic Mott and superfluid phases with spin-orbital intertwined\norders, in spite of the complete absence of spin-orbital interaction in the\nHamiltonian. Our study implies many-body correlations in a multi-orbital\nsetting could induce rich spin-orbital intertwined physics in complex lattice\nstructures.",
        "positive": "Relativistic quantum effects of Dirac particles simulated by ultracold\n  atoms: Quantum simulation is a powerful tool to study a variety of problems in\nphysics, ranging from high-energy physics to condensed-matter physics. In this\narticle, we review the recent theoretical and experimental progress in quantum\nsimulation of Dirac equation with tunable parameters by using ultracold neutral\natoms trapped in optical lattices or subject to light-induced synthetic gauge\nfields. The effective theories for the quasiparticles become relativistic under\ncertain conditions in these systems, making them ideal platforms for studying\nthe exotic relativistic effects. We focus on the realization of one, two, and\nthree dimensional Dirac equations as well as the detection of some relativistic\neffects, including particularly the well-known Zitterbewegung effect and Klein\ntunneling. The realization of quantum anomalous Hall effects is also briefly\ndiscussed."
    },
    {
        "anchor": "Topological Bose-Mott Insulators in a One-Dimensional Optical\n  Superlattice: We study topological properties of the Bose-Hubbard model with repulsive\ninteractions in a one-dimensional optical superlattice. We find that the Mott\ninsulator states of the single-component (two-component) Bose-Hubbard model\nunder fractional fillings are topological insulators characterized by a nonzero\ncharge (or spin) Chern number with nontrivial edge states. For ultracold atomic\nexperiments, we show that the topological Chern number can be detected through\nmeasuring the density profiles of the bosonic atoms in a harmonic trap.",
        "positive": "Photon-induced sideband transitions in a many-body Landau-Zener process: We investigate the many-body Landau-Zener (LZ) process in a two-site\nBose-Hubbard model driven by a time-periodic field. We find that the driving\nfield may induce sideband transitions in addition to the main LZ transitions.\nThese photon-induced sideband transitions are a signature of the\nphoton-assisted tunneling in our many-body LZ process. In the strong\ninteraction regime, we develop an analytical theory for understanding the\nsideband transitions, which is confirmed by our numerical simulation.\nFurthermore, we discuss the quantization of the driving field. In the effective\nmodel of the quantized driving field, the sideband transitions can be\nunderstood as the LZ transitions between states of different \"photon\" numbers."
    },
    {
        "anchor": "Exploring the thermodynamics of a two-dimensional Bose gas: Using \\emph{in situ} measurements on a quasi two-dimensional, harmonically\ntrapped $^{87}$Rb gas, we infer various equations of state for the equivalent\nhomogeneous fluid. From the dependence of the total atom number and the central\ndensity of our clouds with the chemical potential and temperature, we obtain\nthe equations of state for the pressure and the phase-space density. Then using\nthe approximate scale invariance of this two-dimensional system, we determine\nthe entropy per particle. We measure values as low as $0.06\\,\\kB$ in the\nstrongly degenerate regime, which shows that a 2D Bose gas can constitute an\nefficient coolant for other quantum fluids. We also explain how to disentangle\nthe various contributions (kinetic, potential, interaction) to the energy of\nthe trapped gas using a time-of-flight method, from which we infer the\nreduction of density fluctuations in a non fully coherent cloud.",
        "positive": "Mitigating Heating of Degenerate Fermions in a Ring-Dimple Atomic Trap: We report on the impact of the extended geometry of a ring-dimple trap on\nparticle loss heating of a degenerate Fermi gas. When the Fermi level is\nslightly greater than the depth of the dimple and a non-degenerate \"halo\" is\npresent, the overall heating rate is reduced relative to the case of a bare\nring. We find that the experimentally measured heating rates for the overfilled\ndimple are in good agreement with a model of the hole-induced heating caused by\nbackground gas collisions. This suppression of the heating rate can be helpful\nfor experimental studies of fermionic superfluids in the weak pairing limit,\nwhere achieving and maintaining low temperatures over long time scales is\nessential."
    },
    {
        "anchor": "Vortex pump for Bose-Einstein condensates utilizing a time-averaged\n  orbiting potential trap: We show that topological vortex pumping can be implemented for a dilute\nBose-Einstein condensate confined in a magnetic time-averaged orbiting\npotential trap with axial optical confinement. Contrary to earlier proposals\nfor the vortex pump, we do not employ an additional optical potential to trap\nthe condensate in the radial direction, but instead, the radial confinement is\nprovided by the magnetic field throughout the pumping cycle. By performing\nnumerical simulations based on the spin-1 Gross-Pitaevskii equation, we find\nthat several pumping cycles can be carried out to produce a highly charged\nvortex before a majority of the particles escape from the trap or before the\nvortex splits into singly charged vortices. On the other hand, we observe that\nan additional, relatively weak optical plug potential is efficient in\npreventing splitting and reducing particle loss. With these results, we hope to\nbring the vortex pump closer to experimental realization.",
        "positive": "Local manipulation of quantum magnetism in 1D ultracold Fermi gases\n  across narrow resonances: Effective range is a quantity to characterize the energy dependence in\ntwo-body scattering strength, and is widely used in cold atomic systems\nespecially across narrow resonances. Here we show that the effective range can\nsignificantly modify the magnetic property of one-dimensional (1D) spin-$1/2$\nfermions in the strongly repulsive regime. In particular, the effective range\nbreaks the large spin degeneracy in the hard-core limit, and induces a\nHeisenberg exchange term in the spin chain that is much more sensitive to the\nlocal density than that induced by the bare coupling. With an external harmonic\ntrap, this leads to a very rich magnetic pattern where the anti-ferromagnetic\n(AFM) and ferromagnetic (FM) correlations can coexist and distribute in highly\ntunable regions across the trap. Finally, we propose to detect the\nrange-induced magnetic order in the tunneling experiment. Our results can be\ndirectly tested in 1D Fermi gases across narrow resonance, and suggest a\nconvenient route towards the local manipulation of quantum magnetism in cold\natoms."
    },
    {
        "anchor": "Phase diagrams of 2D and 3D disordered Bose gases in the local density\n  approximation: We study the superfluid transitions in bidimensional (2D) and tridimensional\n(3D) disordered and interacting Bose gases. We work in the limit of long-range\ncorrelated disorder such that it can be treated in the local density\napproximation. We present the superfluid transition curves both in the\ndisorder-temperature plane well as in the disorder-entropy plane in 2D and 3D\nBose gases. Surprisingly, we find that a small amount of disorder is always\nfavorable to the apparition of a superfluid. Our results offer a quantitative\ncomparison with recent experiments in 2D disordered ultra-cold gases, for which\nno exact theory exists.",
        "positive": "Multifractals Competing with Solitons on Fibonacci Optical Lattice: We study the stationary states for the nonlinear Schr\\\"odinger equation on\nthe Fibonacci lattice which is expected to be realized by Bose-Einstein\ncondensates loaded into an optical lattice. When the model does not have a\nnonlinear term, the wavefunctions and the spectrum are known to show fractal\nstructures. Such wavefunctions are called critical. We present a phase diagram\nof the energy spectrum for varying the nonlinearity. It consists of three\nportions, a forbidden region, the spectrum of critical states, and the spectrum\nof stationary solitons. We show that the energy spectrum of critical states\nremains intact irrespective of the nonlinearity in the sea of a large number of\nstationary solitons."
    },
    {
        "anchor": "Topological phase transitions generated by the order from quantum\n  disorder: The order from quantum disorder (OFQD) phenomenon was first discovered in\nquantum spin systems in geometric frustrated lattice. Similar phenomenon was\nalso discovered in interacting bosonic systems or quantum spin systems with\nspin-orbit coupling in a bipartite lattice. Here we show that the OFQD also\nleads to a topological phase transition. We demonstrate this new connection in\nthe experimentally realized weakly interacting Quantum Anomalous Hall system of\nspinor bosons in an optical lattice. There are two classes of topological\nphenomena: the first class is a perturbative one smoothly connected to the\nnon-interacting limit. The second one is a non-perturbative one which has no\nanalog in the non-interacting limit. Their experimental detections are also\ndiscussed.",
        "positive": "Inhomogeneous Pseudogap Phenomenon in the BCS-BEC Crossover Regime of a\n  Trapped Superfluid Fermi Gas: We investigate pseudogap phenomena in the unitarity limit of a trapped\nsuperfluid Fermi gas. Including effect of strong pairing fluctuations within a\n$T$-matrix approximation, as well as effects of a harmonic trap within the\nlocal density approximation (LDA), we calculate the local superfluid density of\nstates below the superfluid phase transition temperature $T_{\\rm c}$. We show\nthat the spatial region where single-particle excitations are dominated by the\npseudogap may still exist even below $T_{\\rm c}$, due to inhomogeneous pairing\nfluctuations caused by the trap potential. From the temperature dependence of\nthe pseudogapped density of states, we identify the pseudogap regime of the\nunitarity Fermi gas with respect to the temperature and spatial position. We\nalso show that the combined $T$-matrix theory with the LDA can quantitatively\nexplain the local pressure which was recently observed in the unitarity limit\nof a $^6$Li Fermi gas."
    },
    {
        "anchor": "Chiral Bosonic Phases on the Haldane Honeycomb Lattice: Recent experiments in ultracold atoms and photonic analogs have reported the\nimplementation of artificial gauge fields in lattice systems, facilitating the\nrealization of topological phases. Motivated by such advances, we investigate\nthe Haldane honeycomb lattice tight-binding model, for bosons with local\ninteractions at the average filling of one boson per site. We analyze the\nground state phase diagram and uncover three distinct phases: a uniform\nsuperfluid (SF), a chiral superfluid (CSF) and a plaquette Mott insulator with\nlocal current loops (PMI). Nearest-neighbor and next-nearest neighbor currents\ndistinguish CSF from SF, and the phase transition between them is first order.\nWe apply bosonic dynamical mean field theory and exact diagonalization to\nobtain the phase diagram, complementing numerics with calculations of\nexcitation spectra in strong and weak coupling perturbation theory. The\ncharacteristic density fluctuations, current correlation functions, and\nexcitation spectra are measurable in ultracold atom experiments.",
        "positive": "Thermometry and cooling of a Bose-Einstein condensate to 0.02 times the\n  critical temperature: Ultracold gases promise access to many-body quantum phenomena at convenient\nlength and time scales. However, it is unclear whether the entropy of these\ngases is low enough to realize many phenomena relevant to condensed matter\nphysics, such as quantum magnetism. Here we report reliable single-shot\ntemperature measurements of a degenerate $^{87}$Rb gas by imaging the momentum\ndistribution of thermalized magnons, which are spin excitations of the atomic\ngas. We record average temperatures as low as\n$0.022(1)_\\text{stat}(2)_\\text{sys}$ times the Bose-Einstein condensation\ntemperature, indicating an entropy per particle, $S/N\\approx0.001\\, k_B$ at\nequilibrium, that is well below the critical entropy for antiferromagnetic\nordering of a Bose-Hubbard system. The magnons themselves can reduce the\ntemperature of the system by absorbing energy during thermalization and by\nenhancing evaporative cooling, allowing low-entropy gases to be produced within\ndeep traps."
    },
    {
        "anchor": "Dimensional crossover of Bose-Einstein condensation phenomena in quantum\n  gases confined within slab geometries: We investigate systems of interacting bosonic particles confined within\nslab-like boxes of size L^2 x Z with Z<<L, at their three-dimensional (3D) BEC\ntransition temperature T_c, and below T_c where they experience a quasi-2D\nBerezinskii-Kosterlitz-Thouless transition (at T_BKT < T_c depending on the\nthickness Z). The low-temperature phase below T_BKT shows quasi-long-range\norder: the planar correlations decay algebraically as predicted by the 2D\nspin-wave theory. This dimensional crossover, from a 3D behavior for T > T_c to\na quasi-2D critical behavior for T < T_BKT, can be described by a transverse\nfinite-size scaling limit in slab geometries. We also extend the discussion to\nthe off-equilibrium behavior arising from slow time variations of the\ntemperature across the BEC transition. Numerical evidence of the 3D->2D\ndimensional crossover is presented for the Bose-Hubbard model defined in\nanisotropic L^2 x Z lattices with Z<<L.",
        "positive": "Higher-order topological Peierls insulator in a two-dimensional\n  atom-cavity system: In this work, we investigate a two-dimensional system of ultracold bosonic\natoms inside an optical cavity, and show how photon-mediated interactions give\nrise to a plaquette-ordered bond pattern in the atomic ground state. The latter\ncorresponds to a 2D Peierls transition, generalizing the spontaneous bond\ndimmerization driven by phonon-electron interactions in the 1D\nSu-Schrieffer-Heeger (SSH) model. Here the bosonic nature of the atoms plays a\ncrucial role to generate the phase, as similar generalizations with fermionic\nmatter do not lead to a plaquette structure. Similar to the SSH model, we show\nhow this pattern opens a non-trivial topological gap in 2D, resulting in a\nhigher-order topological phase hosting corner states, that we characterize by\nmeans of a many-body topological invariant and through its entanglement\nstructure. Finally, we demonstrate how this higher-order topological Peierls\ninsulator can be readily prepared in atomic experiments through adiabatic\nprotocols. Our work thus shows how atomic quantum simulators can be harnessed\nto investigate novel strongly-correlated topological phenomena beyond those\nobserved in natural materials."
    },
    {
        "anchor": "Neural Wave Functions for Superfluids: Understanding superfluidity remains a major goal of condensed matter physics.\nHere we tackle this challenge utilizing the recently developed Fermionic neural\nnetwork (FermiNet) wave function Ansatz for variational Monte Carlo\ncalculations. We study the unitary Fermi gas, a system with strong,\nshort-range, two-body interactions known to possess a superfluid ground state\nbut difficult to describe quantitatively. We demonstrate key limitations of the\nFermiNet Ansatz in studying the unitary Fermi gas and propose a simple\nmodification that outperforms the original FermiNet significantly, giving\nhighly accurate results. We prove mathematically that the new Ansatz, which\nonly differs from the original Ansatz by the method of antisymmetrization, is a\nstrict generalization of the original FermiNet architecture, despite the use of\nfewer parameters. Our approach shares several advantages with the FermiNet: the\nuse of a neural network removes the need for an underlying basis set; and the\nflexibility of the network yields extremely accurate results within a\nvariational quantum Monte Carlo framework that provides access to unbiased\nestimates of arbitrary ground-state expectation values. We discuss how the\nmethod can be extended to study other superfluids.",
        "positive": "Probing quantum entanglement from magnetic-sublevels populations: beyond\n  spin squeezing inequalities: Spin squeezing inequalities (SSI) represent a major tool to probe quantum\nentanglement among a collection of few-level atoms, and are based on collective\nspin measurements and their fluctuations. Yet, for atomic ensembles of spin-$j$\natoms and ultracold spinor gases, many experiments can image the populations in\nall Zeeman sublevels $s=-j, -j+1, \\dots, j$, potentially revealing finer\nfeatures of quantum entanglement not captured by SSI. Here we present a\nsystematic approach which exploits Zeeman-sublevel population measurements in\norder to construct novel entanglement criteria, and illustrate our approach on\nground states of spin-1 and spin-2 Bose-Einstein condensates. Beyond these\nspecific examples, our approach allows one to infer, in a systematic manner,\nthe optimal permutationally-invariant entanglement witness for any given set of\ncollective measurements in an ensemble of $d$-level quantum systems."
    },
    {
        "anchor": "Correlation Effects in the Quench-Induced Phase Separation Dynamics of a\n  Two-Species Ultracold Quantum Gas: We explore the quench dynamics of a binary Bose-Einstein condensate crossing\nthe miscibility-immiscibility threshold and vice versa, both within and in\nparticular beyond the mean-field approximation. Increasing the interspecies\nrepulsion leads to the filamentation of the density of each species, involving\nshorter wavenumbers and longer spatial scales in the many-body approach. These\nfilaments appear to be strongly correlated and exhibit domain-wall structures.\nFollowing the reverse quench process multiple dark-antidark solitary waves are\nspontaneously generated and subsequently found to decay in the many-body\nscenario. We simulate single-shot images to connect our findings to possible\nexperimental realizations. Finally, the growth rate of the variance of a sample\nof single-shots probes the degree of entanglement inherent in the system.",
        "positive": "Time-dependent entropy of a cooling Bose gas: Exact analytic solutions of a nonlinear boson diffusion equation with\nsuitable initial conditions that account for evaporative cooling of ultracold\natoms, plus boundary conditions at the singularity $\\epsilon=\\mu<0$ are\npresented, and used to calculate the time-dependent entropy of a cold quantum\ngas."
    },
    {
        "anchor": "Enhanced fermion pairing and superfluidity by an imaginary magnetic\n  field: We show that an imaginary magnetic field(IMF), which can be generated in\nnon-Hermitian systems with spin-dependent dissipations, can greatly enhance the\ns-wave pairing and superfluidity of spin-1/2 fermions, in distinct contrast to\nthe effect of a real magnetic field. The enhancement can be attributed to the\nincreased coupling constant in low-energy space and the reduced spin gap in\nforming singlet pairs. We have demonstrated this effect in a number of\ndifferent fermion systems with and without spin-orbit coupling, using both the\ntwo-body exact solution and many-body mean-field theory. Our results suggest an\nalternative route towards strong fermion superfluid with high superfluid\ntransition temperature.",
        "positive": "Probing Atomic Majorana Fermions in Optical Lattices: We introduce a one-dimensional system of fermionic atoms in an optical\nlattice whose phase diagram includes topological states of different symmetry\nclasses. These states can be identified by their zero-energy edge modes which\nare Majorana fermions. We propose several universal methods of detecting the\nMajorana edge states, based on their genuine features: zero-energy, localized\ncharacter of the wave functions, and induced non-local fermionic correlations."
    },
    {
        "anchor": "Quantum liquid droplets in a mixture of Bose-Einstein condensates: Quantum droplets are small clusters of atoms self-bound by the balance of\nattractive and repulsive forces. Here we report on the observation of a novel\ntype of droplets, solely stabilized by contact interactions in a mixture of two\nBose-Einstein condensates. We demonstrate that they are several orders of\nmagnitude more dilute than liquid helium by directly measuring their size and\ndensity via in situ imaging. Moreover, by comparison to a single-component\ncondensate, we show that quantum many-body effects stabilize them against\ncollapse. We observe that droplets require a minimum atom number to be stable.\nBelow, quantum pressure drives a liquid-to-gas transition that we map out as a\nfunction of interaction strength. These ultra-dilute isotropic liquids remain\nweakly interacting and constitute an ideal platform to benchmark quantum\nmany-body theories.",
        "positive": "Theory of degenerate Bose gas without anomalous averages: Theory of a weakly non-ideal Bose gas in the canonical ensemble is developed\nwithout assumption of the C-number representation of the creation and\nannihilation operators with zero momentum. It is shown that the pole of the\n\"density-density\" Green function exactly coincides with the Bogolybov's\nphonon-roton spectrum of excitations. At the same time in the one-particle\nexcitation spectrum a gap exists. The value of this gap is connected with the\ndensity of particles in the \"condensate\"."
    },
    {
        "anchor": "Isentropic Curves at Magnetic Phase Transitions: Experiments on cold atom systems in which a lattice potential is ramped up on\na confined cloud have raised intriguing questions about how the temperature\nvaries along isentropic curves, and how these curves intersect features in the\nphase diagram. In this paper, we study the isentropic curves of two models of\nmagnetic phase transitions- the classical Blume-Capel Model (BCM) and the Fermi\nHubbard Model (FHM). Both Mean Field Theory (MFT) and Monte Carlo (MC) methods\nare used. The isentropic curves of the BCM generally run parallel to the phase\nboundary in the Ising regime of low vacancy density, but intersect the phase\nboundary when the magnetic transition is mainly driven by a proliferation of\nvacancies. Adiabatic heating occurs in moving away from the phase boundary. The\nisentropes of the half-filled FHM have a relatively simple structure, running\nparallel to the temperature axis in the paramagnetic phase, and then curving\nupwards as the antiferromagnetic transition occurs. However, in the doped case,\nwhere two magnetic phase boundaries are crossed, the isentrope topology is\nconsiderably more complex.",
        "positive": "Universal bound states of one-dimensional bosons with two- and\n  three-body attractions: When quantum particles are confined into lower dimensions, an effective\nthree-body interaction inevitably arises and may cause significant\nconsequences. Here we study bosons in one dimension with weak two-body and\nthree-body interactions, predict the existence of two three-body bound states\nwhen both interactions are attractive, and determine their binding energies as\nuniversal functions of the two-body and three-body scattering lengths. We also\nshow that an infinitesimal three-body attraction induces an excited bound state\nonly for 3, 39, or more bosons. Our findings herein have direct relevance to a\nbroad range of quasi-one-dimensional systems realized with ultracold atoms."
    },
    {
        "anchor": "A new effective interaction for the trapped fermi gas: the BEC-BCS\n  crossover: We extend a recently introduced separable interaction for the unitary trapped\nFermi gas to all values of the scattering length. We derive closed expressions\nfor the interaction matrix elements and the two-particle eigenvectors and\nanalytically demonstrate the convergence of this interaction to the zero-range\ntwo-body pseudopotential for s-wave scattering. We apply this effective\ninteraction to the three- and four-particle systems along the BEC-BCS\ncrossover, and find that their low-lying energies exhibit convergence in the\nregularization parameter that is much faster than for the conventional\nrenormalized contact interaction. We find similar convergence properties of the\nthree-particle free energy at unitarity.",
        "positive": "Analytical approach to relaxation dynamics of condensed Bose gases: The temporal evolution of a perturbation of the equilibrium distribution of a\ncondensed Bose gas is investigated using the kinetic equation which describes\ncollision between condensate and noncondensate atoms. The dynamics is studied\nin the low momentum limit where an analytical treatment is feasible. Explicit\nresults are given for the behavior at large times in different temperature\nregimes."
    },
    {
        "anchor": "Single-site-resolved measurement of the current statistics in optical\n  lattices: At present, great effort is spent on the experimental realization of gauge\nfields for quantum many-body systems in optical lattices. At the same time, the\nsingle-site-resolved detection of individual atoms has become a new powerful\nexperimental tool. We discuss a protocol for the single-site resolved\nmeasurement of the current statistics of quantum many-body systems, which makes\nuse of a bichromatic optical superlattice and single-site detection. We\nillustrate the protocol by a numerical study of the current statistics for\ninteracting bosons in one and two dimensions and discuss the role of the\non-site interactions for the current pattern and the ground-state symmetry for\nsmall two-dimensional lattices with artificial magnetic fields.",
        "positive": "Fragmented Many-body States of Spin-2 Bose Gas: We investigate the fragmented many-body ground states of a spin-2 Bose gas in\nzero magnetic field.\\ We point out that the exact ground state is not simply an\naverage over rotationally-invariant mean-field states, in contrast to the\nspin-1 case with even number of particles N.\\ We construct the exact ground\nstates and compare them with the angular-averaged polar and cyclic states.\\ The\nangular-averaged polar states fail to retrieve the exact eigenstate at $N$\n$\\ge$ $6$ while angular-averaged cyclic states sustain only for N with a\nmultiple of $3$.\\ We calculate the density matrices and two-particle density\nmatrices to show how deviant the angular-averaged state is from the exact one."
    },
    {
        "anchor": "Self-bound crystals of antiparallel dipolar mixtures: Recent experiments have created supersolids of dipolar quantum droplets. The\nresulting crystals lack, however, a genuine cohesive energy and are maintained\nby the presence of an external confinement, bearing a resemblance to the case\nof ion Coulomb crystals. We show that a mixture of two antiparallel dipolar\ncondensates allows for the creation of potentially large, self-bound crystals\nwhich, resembling ionic crystals in solid-state physics, are maintained by the\nmutual dipolar attraction between the components, with no need of transversal\nconfinement. This opens intriguing novel possibilities, including\nthree-dimensionally self-bound droplet-ring structures, stripe/labyrinthic\npatterns, and self-bound crystals of droplets surrounded by an interstitial\nsuperfluid, resembling the case of superfluid Helium in porous media.",
        "positive": "Violation of Cauchy-Schwarz inequalities by spontaneous Hawking\n  radiation in resonant boson structures: The violation of a classical Cauchy-Schwarz (CS) inequality is identified as\nan unequivocal signature of spontaneous Hawking radiation in sonic black holes.\nThis violation can be particularly large near the peaks in the radiation\nspectrum emitted from a resonant boson structure forming a sonic horizon. As a\nfunction of the frequency-dependent Hawking radiation intensity, we analyze the\ndegree of CS violation and the maximum violation temperature for a double\nbarrier structure separating two regions of subsonic and supersonic condensate\nflow. We also consider the case where the resonant sonic horizon is produced by\na space-dependent contact interaction. In some cases, CS violation can be\nobserved by direct atom counting in a time-of-flight experiment. We show that\nnear the conventional zero-frequency radiation peak, the decisive CS violation\ncannot occur."
    },
    {
        "anchor": "Metastability of quantum droplet clusters: We show that metastable ring-shaped clusters can be constructed from\ntwo-dimensional quantum droplets in systems described by the Gross-Pitaevskii\nequations augmented with Lee-Huang-Yang quantum corrections. The clusters\nexhibit dynamical behaviours ranging from contraction to rotation with\nsimultaneous periodic pulsations, or expansion, depending on the initial radius\nof the necklace pattern and phase shift between adjacent quantum droplets. We\nshow that, using an energy-minimization analysis, one can predict equilibrium\nvalues of the cluster radius that correspond to rotation without radial\npulsations. In such a regime, the clusters evolve as metastable states,\nwithstanding abrupt variations in the underlying scattering lengths and keeping\ntheir azimuthal symmetry in the course of evolution, even in the presence of\nconsiderable perturbations.",
        "positive": "Yang-Yang method for the thermodynamics of one-dimensional\n  multi-component interacting fermions: Using Yang and Yang's particle-hole description, we present a thorough\nderivation of the thermodynamic Bethe ansatz equations for a general\n$SU(\\kappa)$ fermionic system in one-dimension for both the repulsive and\nattractive regimes under the presence of an external magnetic field. These\nequations are derived from Sutherland's Bethe ansatz equations by using the\nspin-string hypothesis. The Bethe ansatz root patterns for the attractive case\nare discussed in detail. The relationship between the various phases of the\nmagnetic phase diagrams and the external magnetic fields is given for the\nattractive case. We also give a quantitative description of the ground state\nenergies for both strongly repulsive and strongly attractive regimes."
    },
    {
        "anchor": "Adiabatically tuning quantized supercurrents in an annular Bose-Einstein\n  condensate: The ability to generate and tune quantized persistent supercurrents is\ncrucial for building superconducting or atomtronic devices with novel\nfunctionalities. In ultracold atoms, previous methods for generating quantized\nsupercurrents are generally based on dynamical processes to prepare atoms in\nmetastable excited states. Here we show that arbitrary quantized circulation\nstates can be adiabatically prepared and tuned as the ground state of a\nring-shaped Bose-Einstein condensate by utilizing spin-orbital-angular-momentum\n(SOAM) coupling and an external potential. There exists superfluid hysteresis\nfor tuning supercurrents between different quantization values with nonlinear\natomic interactions, which is explained by developing a nonlinear Landau-Zener\ntheory. Our work will provide a powerful platform for studying SOAM coupled\nultracold atomic gases and building novel atomtronic circuits.",
        "positive": "Deterministic Preparation of a Tunable Few-Fermion System: Systems consisting of few interacting fermions are the building blocks of\nmatter with atoms and nuclei being the most prominent examples. We have created\nan artificial few-body quantum system with complete control over the system's\nquantum state using ultracold fermionic atoms in an optical dipole trap. We\ndeterministically prepare ground state systems consisting of one to ten\nparticles with fidelities of ~ 90%. We can tune the inter-particle interactions\nto arbitrary values using a Feshbach resonance and have observed the\ninteraction-induced energy shift for a pair of repulsively interacting atoms.\nWith this work, quantum simulation of strongly correlated fewbody systems has\nbecome possible. In addition, these microscopic quantum systems can be used as\nbuilding blocks for scalable quantum information processing."
    },
    {
        "anchor": "Exploring emergent heterogeneous phases in strongly repulsive Fermi\n  gases: Recent experiments have revitalized the interest in a Fermi gas of ultracold\natoms with strong repulsive interactions. In spite of its seeming simplicity,\nthis system exhibits a complex behavior, resulting from the competing action of\ntwo distinct instabilities: ferromagnetism, which promotes spin\nanticorrelations and domain formation; and pairing, that renders the repulsive\nfermionic atoms unstable towards forming weakly bound bosonic molecules. The\nbreakdown of the homogeneous repulsive Fermi liquid arising from such\nconcurrent mechanisms has been recently observed in real time through\npump-probe spectroscopic techniques [A. Amico et al., Phys. Rev. Lett. 121,\n253602 (2018)]. These studies also lead to the discovery of an emergent\nmetastable many-body state, an unpredicted quantum emulsion of anticorrelated\nfermions and pairs. Here, we investigate in detail the properties of such an\nexotic regime by studying the evolution of kinetic and release energies, the\nspectral response and coherence of the unpaired fermionic population, and its\nspin-density noise correlations. All our observations consistently point to a\nlow-temperature heterogeneous phase, where paired and unpaired fermions\nmacroscopically coexist while featuring micro-scale phase separation. Our\nfindings open new appealing avenues for the exploration of quantum emulsions\nand also possibly of inhomogeneous superfluid regimes, where pair condensation\nmay coexist with magnetic order.",
        "positive": "Vortices and vortex states in Rashba spin-orbit-coupled condensates: The Rashba spin-orbit coupling is equivalent to the finite Yang-Mills flux of\na static SU(2) gauge field. It gives rise to the protected edge states in\ntwo-dimensional topological band-insulators, much like magnetic field yields\nthe integer quantum Hall effect. An outstanding question is which collective\ntopological behaviors of interacting particles are made possible by the Rashba\nspin-orbit coupling. Here we addresses one aspect of this question by exploring\nthe Rashba SU(2) analogues of vortices in superconductors. Using the\nLandau-Ginzburg approach and conservation laws, we classify the prominent\ntwo-dimensional condensates of two- and three-component spin-orbit-coupled\nbosons, and characterize their vortex excitations. There are two prominent\ntypes of condensates that take advantage of the Rashba spin-orbit coupling.\nTheir vortices exist in multiple flavors whose number is determined by the spin\nrepresentation, and interact among themselves through logarithmic or linear\npotentials as a function of distance. The vortices that interact linearly\nexhibit confinement and asymptotic freedom similar to quarks in quantum\nchromodynamics. One of the two condensate types supports small metastable\nneutral quadruplets of vortices, and their tiles as metastable vortex lattices.\nQuantum melting of such vortex lattices could give rise to non-Abelian\nfractional topological insulators, SU(2) analogues of fractional quantum Hall\nstates. The physical systems in which these states could exist are trapped two-\nand three-component bosonic ultra-cold atoms subjected to artificial gauge\nfields, as well as solid-state quantum wells made either from Kondo insulators\nsuch as SmB$_6$ or conventional topological insulators interfaced with\nconventional superconductors."
    },
    {
        "anchor": "Self-accelerating beam dynamics in the space fractional Schr\u00f6dinger\n  equation: Self-accelerating beams are fascinating solutions of the Schr\\\"odinger\nequation. Thanks to their particular phase engineering, they can accelerate\nwithout the need of external potentials or applied forces. Finite-energy\napproximations of these beams have led to many applications, spanning from\nparticle manipulation to robust in vivo imaging. The most studied and\nemblematic beam, the Airy beam, has been recently investigated in the context\nof the fractional Schr\\\"odinger equation. It was notably found that the packet\nacceleration would decrease with the reduction of the fractional order. Here, I\nstudy the case of a general nth-order self-accelerating caustic beam in the\nfractional Schr\\\"odinger equation. Using a Madelung decomposition combined with\nthe wavelet transform, I derive the analytical expression of the beam's\nacceleration. I show that the non-accelerating limit is reached for infinite\nphase order or when the fractional order is reduced to 1. This work provides a\nquantitative description of self-accelerating caustic beams' properties.",
        "positive": "Universal relations and normal phase of an ultracold Fermi gas with\n  coexisting $s$- and $p$-wave interactions: We study the universal relations and normal-phase thermodynamics of a\ntwo-component ultracold Fermi gas with coexisting $s$- and $p$-wave\ninteractions. Due to the orthogonality of two-body wave functions of different\nscattering channels, the universal thermodynamic relations of the system appear\nto be direct summations of contributions from each partial-wave scattering\nchannels. These universal relations are dictated by a set of contacts, which\ncan be associated with either $s$- or $p$-wave interactions. Interestingly, due\nto the interplay of $s$- and $p$-wave interactions on the many-body level, the\ncontacts, and hence all the relevant thermodynamic quantities, behave\ndifferently from those with only $s$- or $p$-wave interactions. These are\nmanifest in our numerical calculations based on second-order virial expansions\nfor $^{40}$K atoms under typical experimental parameters. A particularly\ninteresting finding is that, due to the coexistence of $s$- and $p$-wave\nscatterings, the interaction energy of the repulsive branch features abrupt\nchanges across the $p$-wave resonances. Our results can be readily checked\nexperimentally for $^{40}$K atoms near the $198$G $p$-wave Feshbach resonance,\nwhere multiple partial-wave scatterings naturally coexist."
    },
    {
        "anchor": "Reentrant behavior of the breathing-mode-oscillation frequency in a\n  one-dimensional Bose gas: We calculate the breathing mode frequency $\\omega$ in a one-dimensional Bose\ngas confined to a harmonic trap of frequency $\\omega_z$. We predict Exciting\ntemporal oscillations of the density distribution is a high-precision method\nfor probing ultracold trapped atomic gases. Interaction effects in their\nmany-body dynamics are particularly puzzling and counter-intuitive in one\nspatial dimension (1D) due to enhanced quantum correlations. We consider 1D\nquantum Bose gas in a parabolic trap at zero temperature and explain,\nanalytically and numerically, how oscillation frequency depends on the number\nof particles, their repulsion and the trap strength. We identify the frequency\nwith the energy difference between the ground state and a particular excited\nstate. This way we avoided resolving the dynamical evolution of the system,\nsimplifying the problem immensely. We find an excellent quantitative agreement\nof our results with the data from the Innsbruck experiment [Science 325, 1224\n(2009)].",
        "positive": "Metastable states and macroscopic quantum tunneling in a cold atom\n  Josephson ring: We study macroscopic properties of a system of weakly interacting neutral\nbosons confined in a ring-shaped potential with a Josephson junction. We derive\nan effective low energy action for this system and evaluate its properties. In\nparticular we find that the system possesses a set of metastable\ncurrent-carrying states and evaluate the rates of transitions between these\nstates due to macroscopic quantum tunneling. Finally we discuss signatures of\ndifferent metastable states in the time-of-flight images and argue that the\neffect is observable within currently available experimental technique."
    },
    {
        "anchor": "Rotational states of an asymmetric vortex pair with mass imbalance in\n  binary condensates: We consider massive vortices in binary condensates, where the immiscibility\ncondition entails the trapping of the minority component in the vortex cores of\nthe majority component. We study such vortices by means of a 2D point-like\nmodel, and show how the relevant dynamical equations exhibit vortex-pair\nsolutions characterized by different vortex masses and circular orbits of\ndifferent radii $a$ and $b$. These solutions are validated by the simulations\nof the Gross-Pitaevskii equations for binary condensates. After examining the\nproperties of vortex-pair rotational frequency $\\Omega$ as a function of the\nvortex masses for a given pair geometry, we define the rotational-state diagram\n$\\cal D$, describing all the possible vortex-pair solutions in terms of the\norbit radii at given $\\Omega$. This includes solutions with equal-mass pairs\nbut $a \\ne b$ or with one of the two masses (or both) equal to zero. Also, we\nanalytically find the minimum value of $\\Omega$ for the existence of such\nsolutions, and obtain numerically the critical frequency $\\Omega_c$ below which\n$\\cal D$ changes its structure and the transition to an unstable vortex-pair\nregime takes place. Our work highlights an indirect measurement scheme to infer\nthe vortex masses from orbits radii $a$ and $b$, and a link between the vortex\nmasses and the vortex-pair small-oscillation properties.",
        "positive": "Schrieffer-Wolff Transformation for Periodically Driven Systems:\n  Strongly Correlated Systems with Artificial Gauge Fields: We generalize the Schrieffer-Wolff transformation to periodically driven\nsystems using Floquet theory. The method is applied to the periodically driven,\nstrongly interacting Fermi-Hubbard model, for which we identify two regimes\nresulting in different effective low-energy Hamiltonians. In the nonresonant\nregime, we realize an interacting spin model coupled to a static gauge field\nwith a nonzero flux per plaquette. In the resonant regime, where the Hubbard\ninteraction is a multiple of the driving frequency, we derive an effective\nHamiltonian featuring doublon association and dissociation processes. The\nground state of this Hamiltonian undergoes a phase transition between an\nordered phase and a gapless Luttinger liquid phase. One can tune the system\nbetween different phases by changing the amplitude of the periodic drive."
    },
    {
        "anchor": "Simulation and measurement of the fractional particle number in\n  one-dimensional optical lattices: We propose a scheme to mimic and directly measure the fractional particle\nnumber in a generalized Su-Schrieffer-Heeger model with ultracold fermions in\none-dimensional optical lattices. We show that the fractional particle number\nin this model can be simulated in the momentum-time parameter space in terms of\nBerry curvature without a spatial domain wall. In this simulation, a hopping\nmodulation is adiabatically tuned to form a kink-type configuration and the\ninduced current plays the role of an analogous soliton distributing in the time\ndomain, such that the mimicked fractional particle number is expressed by the\nparticle transport. Two feasible experimental setups of optical lattices for\nrealizing the required Su-Schrieffer-Heeger Hamiltonian with tunable parameters\nand time-varying hopping modulation are presented. We also show practical\nmethods for measuring the particle transport in the proposed cold atom systems\nby numerically calculating the shift of the Wannier center and the center of\nmass of an atomic cloud.",
        "positive": "Experimental Results Related to Discrete Nonlinear Schr\u00f6dinger\n  Equations: In this chapter, we discuss experiments that realize the discrete nonlinear\nSchr\\\"odinger (DNLS) equations. The relevance of such descriptions arises from\nthe competition of three common features: nonlinearity, dispersion, and a\nmedium to large level of (periodic, quasiperiodic, or random) discreteness in\nspace. DNLS equations have been especially prevalent in atomic and molecular\nphysics in the study of Bose-Einstein condensates in optical lattices or\nsuperlattices; and in nonlinear optics in the description of pulse propagation\nin waveguide arrays and photorefractive crystals. New experiments in both\nnonlinear optics and Bose-Einstein condensation provide new challenges for DNLS\nmodels, and DNLS and related equations have also recently been used to make\nimportant predictions in novel physical settings such as the study of composite\nmetamaterials and arrays of superconducting devices."
    },
    {
        "anchor": "Thermodynamic signatures of the polaron-molecule transition in a Fermi\n  gas: We consider the highly spin-imbalanced limit of a two-component Fermi gas,\nwhere there is a small density of $\\downarrow$ impurities attractively\ninteracting with a sea of $\\uparrow$ fermions. In the single-impurity limit at\nzero temperature, there exists the so-called polaron-molecule transition, where\nthe impurity sharply changes its character by binding a $\\uparrow$ fermion at\nsufficiently strong attraction. Using a recently developed variational\napproach, we calculate the thermodynamic properties of the impurity, and we\nshow that the transition becomes a smooth crossover at finite temperature due\nto the thermal occupation of excited states in the impurity spectral function.\nHowever, remnants of the single-impurity transition are apparent in the\nmomentum-resolved spectral function, which can in principle be probed with\nRaman spectroscopy. We furthermore show that the Tan contact exhibits a\ncharacteristic non-monotonic dependence on temperature that provides a\nsignature of the zero-temperature polaron-molecule transition. For a finite\nimpurity density, we argue that descriptions purely based on the behavior of\nthe Fermi polaron are invalid near the polaron-molecule transition, since\ncorrelations between impurities cannot be ignored. In particular, we show that\nthe spin-imbalanced system undergoes phase separation at low temperatures due\nto the strong attraction between $\\uparrow\\downarrow$ molecules induced by the\nFermi sea. Thus, we find that the impurity spectrum and the induced\nimpurity-impurity interactions are key to understanding the phase diagram of\nthe spin-imbalanced Fermi gas.",
        "positive": "Frustrated Bose-Einstein condensates with non-collinear orbital ordering: We investigate the unconventional Bose-Einstein condensations (BEC) with the\norbital degree of freedom in the 3D cubic optical lattice, which give rise to\nvarious exotic features absent in conventional scalar and spinor BECs. Orbital\nangular momentum moments are formed on lattice sites breaking time-reversal\nsymmetry spontaneously. Furthermore, they exhibit orbital frustrations and\ndevelop a chiral ordering selected by the \"order-from-disorder\" mechanism."
    },
    {
        "anchor": "Two-stream instability in quasi-one-dimensional Bose-Einstein\n  condensates: We apply a kinetic model to predict the existence of an instability mechanism\nin elongated Bose-Einstein condensates. Our kinetic description, based on the\nWigner formalism, is employed to highlight the existence of unstable Bogoliubov\nwaves that may be excited in the counterpropagation configuration. We identify\na dimensionless parameter, the Mach number at T = 0, that tunes different\nregimes of stability. We also estimate the magnitude of the main parameters at\nwhich two-stream instability is expected to be observed under typical\nexperimental conditions.",
        "positive": "Dynamic freezing of strongly correlated ultracold bosons: We study the non-equilibrium dynamics of ultracold bosons in an optical\nlattice with a time dependent hopping amplitude J(t)=J_0 +\\delta J \\cos(\\omega\nt) which takes the system from a superfluid phase near the Mott-superfluid\ntransition (J= J_0+\\delta J) to a Mott phase (J=J_0-\\delta J) and back through\na quantum critical point (J=J_c) and demonstrate dynamic freezing of the boson\nwavefunction at specific values of \\omega. At these values, the wavefunction\noverlap F (defect density P=1-F) approaches unity (zero). We provide a\nqualitative explanation of the freezing phenomenon, show it's robustness\nagainst quantum fluctuations and the presence of a trap, compute residual\nenergy and superfluid order parameter for such dynamics, and suggest\nexperiments to test our theory."
    },
    {
        "anchor": "Superradiant phase transition with cavity assisted dynamical spin-orbit\n  coupling: Superradiant phase transition represents an important quantum phenomenon that\nshows the collective excitations based on the coupling between atoms and cavity\nmodes. The spin-orbit coupling is another quantum effect which induced from the\ninteraction of the atom internal degrees of freedom and momentum of\ncenter-of-mass. In this work, we consider the cavity assisted dynamical\nspin-orbit coupling which comes from the combination of these two effects. It\ncan induce a series of interesting quantum phenomena, such as the flat spectrum\nand the singularity of the excitation energy spectrum around the critical point\nof quantum phase transition. We further discuss the influence of atom decay and\nnonlinear coupling to the phase diagram. The atom decay suppresses the\nsingularity of the phase diagram and the nonlinear coupling can break the\nsymmetric properties of the phase transition. Our work provide the theoretical\nmethods to research the rich quantum phenomena in this dynamic many-body\nsystems.",
        "positive": "All-optical cooling of Fermi gases via Pauli inhibition of spontaneous\n  emission: A technique is proposed to cool Fermi gases to the regime of quantum\ndegeneracy based on the expected inhibition of spontaneous emission due to the\nPauli principle. The reduction of the linewidth for spontaneous emission\noriginates a corresponding reduction of the Doppler temperature, which under\nspecific conditions may give rise to a runaway process through which fermions\nare progressively cooled. The approach requires a combination of a\nmagneto-optical trap as a cooling system and an optical dipole trap to enhance\nquantum degeneracy. This results in expected Fermi degeneracy factors $T/T_F$\ncomparable to the lowest values recently achieved, with potential for a direct\nimplementation in optical lattices. The experimental demonstration of this\ntechnique should also indirectly provide a macroscopic manifestation of the\nPauli exclusion principle at the atomic physics level."
    },
    {
        "anchor": "Strongly interacting Bose-Fermi mixture: mediated interaction, phase\n  diagram and sound propagation: Motivated by recent surprising experimental findings, we develop a\nstrong-coupling theory for Bose-Fermi mixtures capable of treating resonant\ninter-species interactions while satisfying the compressibility sum rule. We\nshow that the mixture can be stable at large interaction strengths close to\nresonance, in agreement with the experiment but at odds with the widely used\nperturbation theory. We also calculate the sound velocity of the Bose gas in\nthe $^{133}$Cs-$^6$Li mixture, again finding good agreement with the\nexperimental observations both at weak and strong interactions. A central\ningredient of our theory is the generalization of a fermion mediated\ninteraction to strong Bose-Fermi scatterings and to finite frequencies. This\nfurther leads to a predicted hybridization of the sound modes of the Bose and\nFermi gases, which can be directly observed using Bragg spectroscopy.",
        "positive": "Quantum fluctuations and Gross-Pitaevskii theory: Using the linearized version of the time dependent Gross-Pitaevskii equation\nwe calculate the dynamic response of a Bose-Einstein condensed gas to periodic\ndensity and particle perturbations. The zero temperature limit of the\nfluctuation-dissipation theorem is used to evaluate the corresponding quantum\nfluctuations induced by the elementary excitations in the ground state. In\nuniform conditions the predictions of Bogoliubov theory, including the infrared\ndivergency of the particle distribution function and the quantum depletion of\nthe condensate, are exactly reproduced by Gross-Pitaevskii theory. Results are\nalso given for the crossed particle-density response function and the extension\nof the formalism to non uniform systems is discussed. The generalization of the\nGross-Pitaevskii equation to include beyond mean field effects is finally\nconsidered and an explicit result for the chemical potential is found, in\nagreement with the prediction of Lee-Huang-Yang theory."
    },
    {
        "anchor": "Quantum dynamics of impenetrable SU(N) fermions in one-dimensional\n  lattices: We study quantum quench dynamics in the Fermi-Hubbard model, and its SU($N$)\ngeneralizations, in one-dimensional lattices in the limit of infinite onsite\nrepulsion between all flavors. We consider families of initial states with\ngeneralized Neel order, namely, initial state in which there is a periodic\n$N$-spin pattern with consecutive fermions carrying distinct spin flavors. We\nintroduce an exact approach to describe the quantum evolution of those systems,\nand study two unique transient phenomena that occur during expansion dynamics\nin finite lattices. The first one is the dynamical emergence of Gaussian\none-body correlations during the melting of sharp (generalized) Neel domain\nwalls. Those correlations resemble the ones in the ground state of the SU($N$)\nmodel constrained to the same spin configurations. This is explained using an\nemergent eigenstate solution to the quantum dynamics. The second phenomenon is\nthe transformation of the quasimomentum distribution of the expanding strongly\ninteracting SU($N$) gas into the rapidity distribution after long times.\nFinally, we study equilibration in SU($N$) gasses and show that observables\nafter equilibration are described by a generalized Gibbs ensemble. Our approach\ncan be used to benchmark analytical and numerical calculations of dynamics of\nstrongly correlated SU($N$) fermions at large $U$.",
        "positive": "Layered Quantum Hall Insulators with Ultracold Atoms: We consider a generalization of the 2-dimensional (2D) quantum-Hall insulator\nto a non-compact, non-Abelian gauge group, the Heisenberg-Weyl group. We show\nthat this kind of insulator is actually a layered 3D insulator with nontrivial\ntopology. We further show that nontrivial combinations of quantized transverse\nconductivities can be engineered with the help of a staggered potential. We\ninvestigate the robustness and topological nature of this conductivity and\nconnect it to the surface modes of the system. We also propose a simple\nexperimental realization with ultracold atoms in 3D confined to a 2D square\nlattice with the third dimension being mapped to a gauge coordinate."
    },
    {
        "anchor": "Entropy production within a pulsed Bose-Einstein condensate: We suggest to subject anharmonically trapped Bose-Einstein condensates to\nsinusoidal forcing with a smooth, slowly changing envelope, and to measure the\ncoherence of the system after such pulses. In a series of measurements with\nsuccessively increased maximum forcing strength one then expects an adiabatic\nreturn of the condensate to its initial state as long as the pulses remain\nsufficiently weak. In contrast, once the maximum driving amplitude exceeds a\ncertain critical value there should be a drastic loss of coherence, reflecting\nsignificant heating induced by the pulse. This predicted experimental signature\nis traced to the loss of an effective adiabatic invariant, and to the ensuing\nbreakdown of adiabatic motion of the system's Floquet state when the many-body\ndynamics become chaotic. Our scenario is illustrated with the help of a\ntwo-site model of a forced bosonic Josephson junction, but should also hold for\nother, experimentally accessible configurations.",
        "positive": "Phase diagram of a non-Abelian Aubry-Andr\u00e9-Harper model with $p$-wave\n  superfluidity: We theoretically study a one-dimensional quasi-periodic Fermi system with\ntopological $p$-wave superfluidity, which can be deduced from a topologically\nnon-trivial tight-binding model on the square lattice in a uniform magnetic\nfield and subject to a non-Abelian gauge field. The system may be regarded a\nnon-Abelian generalization of the well-known Aubry-Andr\\'e-Harper model. We\ninvestigate its phase diagram as functions of the strength of the\nquasi-disorder and the amplitude of the $p$-wave order parameter, through a\nnumber of numerical investigations, including a multifractal analysis. There\nare four distinct phases separated by three critical lines, i.e., two phases\nwith all extended wave-functions (I and IV), a topologically trivial phase (II)\nwith all localized wave-functions and a critical phase (III) with all\nmultifractal wave-functions. The phase I is related to the phase IV by duality.\nIt also seems to be related to the phase II by duality. Our proposed phase\ndiagram may be observable in current cold-atom experiments, in view of\nsimulating non-Abelian gauge fields and topological insulators/superfluids with\nultracold atoms."
    },
    {
        "anchor": "Roton-type mode softening in a quantum gas with cavity-mediated\n  long-range interactions: Long-range interactions in quantum gases are predicted to give rise to an\nexcitation spectrum of roton character, similar to that observed in superfluid\nhelium. We investigate the excitation spectrum of a Bose-Einstein condensate\nwith cavity-mediated long-range interactions, which couple all particles to\neach other. Increasing the strength of the interaction leads to a softening of\nan excitation mode at a finite momentum, preceding a superfluid to supersolid\nphase transition. We study the mode softening spectroscopically across the\nphase transition using a variant of Bragg spectroscopy. The measured spectrum\nis in very good agreement with ab initio calculations and, at the phase\ntransition, a diverging susceptibility is observed. The work paves the way\ntowards quantum simulation of long-range interacting many-body systems.",
        "positive": "Hydrodynamics of vortices in Bose-Einstein condensates: A defect-gauge\n  field approach: This work rectifies the hydrodynamic equations commonly used to describe the\nsuperfluid velocity field in such a way that vortex dynamics are also taken\ninto account. In the field of quantum turbulence, it is of fundamental\nimportance to know the correct form of the equations which play similar roles\nto the Navier-Stokes equation in classical turbulence. Here, such equations are\nobtained by carefully taking into account the frequently overlooked multivalued\nnature of the $U(1)$ phase field. Such an approach provides exact analytical\nexplanations to some numerically observed features involving the dynamics of\nquantum vortices in Bose-Einstein condensates, such as the universal $t^{1/2}$\nbehavior of reconnecting vortex lines. It also expands these results beyond the\nGross-Pitaevskii theory so that some features can be generalized to other\nsystems such as superfluid $^{4}$He, dipolar condensates, and mixtures of\ndifferent superfluid systems."
    },
    {
        "anchor": "Interferometric determination of the s- and d-wave scattering amplitudes\n  in $^{87}$Rb: We demonstrate an interference method to determine the low-energy elastic\nscattering amplitudes of a quantum gas. We linearly accelerate two ultracold\natomic clouds up to energies of 1.2 mK and observe the collision halo by direct\nimaging in free space. From the interference between $s$- and $d$- partial\nwaves in the differential scattering pattern we extract the corresponding phase\nshifts. The method does not require knowledge of the atomic density. This\nallows us to infer accurate values for the $s$- and d-wave scattering\namplitudes from the zero-energy limit up to the first Ramsauer minimum using\nonly the Van der Waals $C_{6}$ coefficient as theoretical input. For the\n$^{87}$Rb triplet potential, the method reproduces the scattering length with\nan accuracy of 6%.",
        "positive": "Dirac Equation For Cold Atoms In Artificial Curved Spacetimes: We argue that the Fermi-Hubbard Hamiltonian describing the physics of\nultracold atoms on optical lattices in the presence of artificial non-Abelian\ngauge fields, is exactly equivalent to the gauge theory Hamiltonian describing\nDirac fermions in the lattice. We show that it is possible to couple the Dirac\nfermions to an \"artificial\" gravitational field, i.e. to consider the Dirac\nphysics in a curved spacetime. We identify the special class of spacetime\nmetrics that admit a simple realization in terms of a Fermi-Hubbard model\nsubjected to an artificial SU(2) field, corresponding to position dependent\nhopping matrices. As an example, we discuss in more detail the physics of the\n2+1D Rindler metric, its possible experimental realization and detection."
    },
    {
        "anchor": "Mean field effects on the scattered atoms in condensate collisions: We consider the collision of two Bose Einstein condensates at supersonic\nvelocities and focus on the halo of scattered atoms. This halo is the most\nimportant feature for experiments and is also an excellent testing ground for\nvarious theoretical approaches. In particular we find that the typical reduced\nBogoliubov description, commonly used, is often not accurate in the region of\nparameters where experiments are performed. Surprisingly, besides the halo pair\ncreation terms, one should take into account the evolving mean field of the\nremaining condensate and on-condensate pair creation. We present examples where\nthe difference is clearly seen, and where the reduced description still holds.",
        "positive": "Collective properties of quantum matter: from Hawking radiation\n  analogues to quantum Hall effect in graphene: The work is divided in three parts. We devote the first part to the study of\nanalog Hawking radiation in Bose-Einstein condensates. We study numerically the\nbirth of a sonic black hole in an outcoupled Bose-Einstein condensate after\nrelaxing the confinement provided by an optical lattice. We also study possible\nsignatures of spontaneous Hawking radiation. We propose that the violation of\nCS inequalities is a smoking gun of the presence of the Hawking effect. We\ncompare this criterion with the presence of entaglement, finding that both are\nequivalent under usual assumptions. Finally, we study a different gravitational\nanalogue: the so-called black-hole laser. The most interesting result is the\nappearance of a regime of continuous and periodic emission of solitons,\nproviding the most strong analogue with optical lasers. In the second part, we\nanalyze the effect of the introduction of a short Bragg pulse in a thermal\ncloud. We show that the induced periodic density pattern decays to the\nequilibrium profile. However, instead of the usual collisional relaxation, the\nmechanism responsible for the decay is the thermal disorder of the particles,\nwith a characteristic time that only depends on the temperature. We find a very\ngood agreement with actual experimental data. In the last part, we switch to a\nvery different system: the $\\nu=0$ quantum Hall state of bilayer graphene.\nAfter re-deriving the corresponding mean-field phase diagram, we compute the\ncollective modes within the zero Landau level. Among the most remarkable\nresults, we have found that at the boundary between the FLP and the F phases a\ngapless mode appears resulting from an accidental symmetry that can be regarded\nas a remanent of a broken $SO(5)$ symmetry. On the other hand, the CAF and PLP\nphases can present dynamical instabilities. We straightforwardly extend the\nprevious results to monolayer graphene."
    },
    {
        "anchor": "Interaction-driven dynamical quantum phase transitions in a strongly\n  correlated bosonic system: We study dynamical quantum phase transitions (DQPTs) in the extended\nBose-Hubbard model after a sudden quench of the nearest-neighbor interaction\nstrength. Using the time-dependent density matrix renormalization group, we\ndemonstrate that interaction-driven DQPTs can appear after quenches between two\ntopologically trivial insulating phases -- a phenomenon that has so far only\nbeen studied between gapped and gapless phases. These DQPTs occur when the\ninteraction strength crosses a certain threshold value that does not coincide\nwith the equilibrium phase boundaries, which is in contrast to quenches that\ninvolve a change of topology. In order to elucidate the nonequilibrium\nexcitations during the time evolution, we define a new set of string and parity\norder parameters. We find a close connection between DQPTs and these newly\ndefined order parameters for both types of quenches. In the interaction-driven\ncase, the order parameter exhibits a singularity at the time of the DQPT only\nwhen the quench parameter is close to the threshold value. Finally, the\ntimescales of DQPTs are scrutinized and different kinds of power laws are\nrevealed for the topological and interaction-driven cases.",
        "positive": "Quantum phase transition in an atom-molecule conversion system with\n  atomic hopping: The quantum phase transition in an atom-molecule conversion system with\natomic hopping between different hyperfine states is studied. In mean field\napproximation, we give the phase diagram whose phase boundary only depends on\nthe atomic hopping strength and the atom-molecule energy detuning but not on\nthe atomic interaction. Such a phase boundary is further confirmed by the\nfidelity of the ground state and the energy gap between the first-excited state\nand the ground one. In comparison to mean field approximation, we also study\nthe quantum phase transition in full quantum method, where the phase boundary\ncan be affected by the particle number of the system. Whereas, with the help of\nfinite-size scaling behaviors of energy gap, fidelity susceptibility and the\nfirst-order derivative of entanglement entropy, we show that one can obtain the\nsame phase boundary by the MFA and full quantum methods in the limit of\n$N\\rightarrow \\infty$. Additionally, our results show that the quantum phase\ntransition can happens at the critical value of the atomic hopping strength\neven if the atom-molecule energy detuning is fixed on a certain value, which\nprovides one a new way to control the quantum phase transition."
    },
    {
        "anchor": "Dynamical evolutions in non-Hermitian triple-well system with complex\n  potential: We investigate the dynamical properties for non-Hermitian triple-well system\nwith a loss in the middle well. When chemical potentials in two end wells are\nuniform and nonlinear interactions are neglected, there always exists a dark\nstate, whose eigenenergy becomes zero, and the projections onto which do not\nchange over time and the loss factor. The increasing of loss factor only makes\nthe damping form from the oscillating decay to over-damping decay. However,\nwhen the nonlinear interaction is introduced, even interactions in the two end\nwells are also uniform, the projection of the dark state will be obviously\ndiminished. Simultaneously the increasing of loss factor will also aggravate\nthe loss. In this process the interaction in the middle well plays no role.\nWhen two chemical potentials or interactions in two end wells are not uniform\nall disappear with time. In addition, when we extend the triple-well system to\na general (2n + 1)-well, the loss is reduced greatly by the factor 1=2n in the\nabsence of the nonlinear interaction.",
        "positive": "Low-Lying Excitation Modes of Trapped Dipolar Fermi Gases: From\n  Collisionless to Hydrodynamic Regime: By means of the Boltzmann-Vlasov kinetic equation we investigate dynamical\nproperties of a trapped, one-component Fermi gas at zero temperature, featuring\nthe anisotropic and long-range dipole-dipole interaction. To this end, we\ndetermine an approximate solution by rescaling both space and momentum\nvariables of the equilibrium distribution, thereby obtaining coupled ordinary\ndifferential equations for the corresponding scaling parameters. Based on\nprevious results on how the Fermi sphere is deformed in the hydrodynamic regime\nof a dipolar Fermi gas, we are able to implement the relaxation-time\napproximation for the collision integral. Then, we proceed by linearizing the\nequations of motion around the equilibrium in order to study both the\nfrequencies and the damping of the low-lying excitation modes all the way from\nthe collisionless to the hydrodynamic regime. Our theoretical results are\nexpected to be relevant for understanding current experiments with trapped\ndipolar Fermi gases."
    },
    {
        "anchor": "Temperature-dependent periodicity of the persistent current in strongly\n  interacting systems: The persistent current in small isolated rings enclosing magnetic flux is the\ncurrent circulating in equilibrium in the absence of an external excitation.\nWhile initially studied in superconducting and normal metals, recently, atomic\npersistent currents have been generated in ultracold gases spurring a new wave\nof theoretical investigations. Nevertheless, our understanding of the\npersistent currents in interacting systems is far from complete, especially at\nfinite temperatures. Here we consider the fermionic one-dimensional Hubbard\nmodel and show that in the strong-interacting limit, the current can change its\nflux period and sign (diamagnetic or paramagnetic) as a function of\ntemperature, features that cannot be explained within the single-particle or\nLuttinger liquid techniques. Also, the magnitude of the current can\ncounterintuitively increase with temperature, in addition to presenting\ndifferent rates of decay depending on the polarization of the system. Our work\nhighlights the properties of the strongly-interacting multi-component systems\nwhich are missed by conventional approximation techniques, but can be important\nfor the interpretation of experiments on persistent currents in ultracold\ngases.",
        "positive": "Weakly-interacting Bose-Bose mixtures from the functional\n  renormalisation group: We provide a detailed presentation of the functional renormalisation group\n(FRG) approach for weakly-interacting Bose-Bose mixtures, including a complete\ndiscussion on the RG equations. To test this approach, we examine thermodynamic\nproperties of balanced three-dimensional Bose-Bose gases at zero and finite\ntemperatures and find a good agreement with related works. We also study\nground-state energies of repulsive Bose polarons by examining mixtures in the\nlimit of infinite population imbalance. Finally, we discuss future applications\nof the FRG to novel problems in Bose-Bose mixtures and related systems."
    },
    {
        "anchor": "Quantum Many-Body Scars and Quantum Criticality: In this letter, we study the PXP Hamiltonian with an external magnetic field\nthat exhibits both quantum scar states and quantum criticality. It is known\nthat this model hosts a series of quantum many-body scar states violating\nquantum thermalization at zero magnetic field, and it also exhibits an Ising\nquantum phase transition driven by finite magnetic field. Although the former\ninvolves the properties of generic excited states and the latter concerns the\nlow-energy physics, we discover two surprising connections between them,\ninspired by the observation that both states possess log-volume law\nentanglement entropies. First, we show that the quantum many-body scar states\ncan be tracked to a set of quantum critical states, whose nature can be\nunderstood as pair-wisely occupied Fermi sea states. Second, we show that the\npartial violation of quantum thermalization diminishes in the quantum critical\nregime. We envision that these connections can be extended to general\nsituations and readily verified in existing cold atom experimental platforms.",
        "positive": "Collective many-body bounce in the breathing-mode oscillations of a\n  Tonks-Girardeau gas: We analyse the breathing-mode oscillations of a harmonically quenched\nTonks-Giradeau (TG) gas using an exact finite-temperature dynamical theory. We\npredict a striking collective manifestation of impenetrability---a collective\nmany-body bounce effect. The effect, while being invisible in the evolution of\nthe in-situ density profile of the gas, can be revealed through a nontrivial\nperiodic narrowing of its momentum distribution, taking place at twice the rate\nof the fundamental breathing-mode frequency. We identify physical regimes for\nobserving the many-body bounce and construct the respective nonequilibrium\nphase diagram as a function of the quench strength and the initial temperature\nof the gas. We also develop a finite-temperature hydrodynamic theory of the TG\ngas, wherein the many-body bounce is explained by an increased thermodynamic\npressure of the gas during the isentropic compression, which acts as a\npotential barrier at the inner turning points of the breathing cycle."
    },
    {
        "anchor": "Single-domain Bose condensate magnetometer achieves energy resolution\n  per bandwidth below $\\hbar$: We present a magnetic sensor with energy resolution per bandwidth $E_R <\n\\hbar$. We show how a $^{87}\\mathrm{Rb}$ single domain spinor Bose-Einstein\ncondensate, detected by non-destructive Faraday-rotation probing, achieves\nsingle shot dc magnetic sensitivity of $72(8)~\\mathrm{fT}$ measuring a volume\n$V= 1091(30)~\\mu\\mathrm{m}^3$ for $3.5~\\mathrm{s}$, and thus $E_R =\n0.075(16)~\\hbar$. We measure experimentally the condensate volume, spin\ncoherence time, and readout noise, and use phase-space methods, backed by 3+1D\nmean-field simulations, to compute the spin noise. Contributions to the spin\nnoise include one-body and three-body losses and shearing of the projection\nnoise distribution, due to competition of ferromagnetic contact interactions\nand quadratic Zeeman shifts. Nonetheless, the fully-coherent nature of the\nsingle-domain, ultracold two-body interactions allows the system to escape the\ncoherence vs.~density trade-off that imposes an energy resolution limit on\ntraditional spin-precession sensors. We predict that other Bose-condensed\nalkalis, especially the antiferromagnetic $^{23}\\mathrm{Na}$, can further\nimprove the energy resolution of this method.",
        "positive": "Cloud shape of a molecular Bose-Einstein condensate in a disordered\n  trap: a case study of the dirty boson problem: We investigate, both experimentally and theoretically, the static geometric\nproperties of a harmonically trapped Bose-Einstein condensate of ${}^6$Li$_2$\nmolecules in laser speckle potentials. Experimentally, we measure the in-situ\ncolumn density profiles and the corresponding transverse cloud widths over many\nlaser speckle realizations. We compare the measured widths with a theory that\nis non-perturbative with respect to the disorder and includes quantum\nfluctuations. Importantly, for small disorder strengths we find quantitative\nagreement with the perturbative approach of Huang and Meng, which is based on\nBogoliubov theory. For strong disorder our theory perfectly reproduces the\ngeometric mean of the measured transverse widths. However, we also observe a\nsystematic deviation of the individual measured widths from the theoretically\npredicted ones. In fact, the measured cloud aspect ratio monotonously decreases\nwith increasing disorder strength, while the theory yields a constant ratio. We\nattribute this discrepancy to the utilized local density approximation, whose\npossible failure for strong disorder suggests a potential future improvement."
    },
    {
        "anchor": "Repulsive dynamics of strongly attractive one-dimensional quantum gases: We analyze the dynamics of one-dimensional quantum gases with strongly\nattractive contact interactions. We specify a class of initial states for which\nattractive forces effectively act as strongly repulsive ones during the time\nevolution. Our findings extend the theoretical results on the\nsuper-Tonks-Girardeau gas to a highly nonequilibrium dynamics. The novel\nmechanism is illustrated on the prototypical problem of the domain stability in\na two-component Fermi gas. We also discuss nonlocal interactions and analyze\nuniversality of the presented results. Moreover, we use our conclusions to\nargue for the existence of metastable quantum droplets in the regime of\nstrongly attractive contact and attractive dipolar interactions.",
        "positive": "Quantum Capillary Waves at the Superfluid--Mott Insulator Interface: We discuss quantum fluctuations of the interface between a superfluid and a\nMott-insulating state of ultracold atoms in a trap. The fluctuations of the\nboundary are due to a new type of surface modes, whose spectrum is similar (but\nnot identical) to classical capillary waves. The corresponding quantum\ncapillary length sets the scale for the penetration of the superfluid into the\nMott-insulating regime by the proximity effect and may be on the order of\nseveral lattice spacings. It determines the typical magnitude of the interface\nwidth due to quantum fluctuations, which may be inferred from single site\nimaging of ultracold atoms in an optical lattice."
    },
    {
        "anchor": "Phonon-polaritons in Bose-Einstein condensates induced by Casimir-Polder\n  interaction with graphene: We consider the mechanical coupling between a two-dimensional Bose-Einstein\ncondensate with a graphene sheet via the vacuum fluctuations of the\nelectromagnetic field which are at the origin of the so-called Casimir-Polder\npotential. By deriving a self-consistent set of equations governing the\ndynamics of the condensate and the flexural (out-of-plane) modes of the\ngraphene, we can show the formation of a new type of purely acoustic\nquasi-particle excitation, a phonon-polariton resulting from the coherent\nsuperposition of quanta of flexural and Bogoliubov modes.",
        "positive": "Self-consistent theory of a homogeneous binary Bose mixture with strong\n  repulsive interspecies interaction: Multicomponent quantum gases are ideal platforms to study fundamental\nphenomena arising from the mutual interaction between different constituents.\nParticularly, due to the repulsive interactions between two species, the system\nmay exhibit a phase separation. We develop a mean-field-based theory for a\ntwo-component Bose mixture, which is equivalent to the Hartree-Fock-Bogoliubov\napproximation, and derive analytical expressions for the phase boundary and\nmiscibility. The majority of existing theories, which are valid only for weakly\ninteracting Bose gases, predict that the phase boundary is determined by the\ncriterion $g_{ab}\\leqslant\\sqrt{g_{aa} g_{bb}}$ (where $g_{ab}$ is a coupling\nconstant between the components $a$ and $b$). We show that in the\nBose-Einstein-condensation phase ($T\\leqslant T_c$) the system may remain in a\nstable and miscible phase also for larger values of $g_{ab}$, depending on the\ngas parameter $\\gamma$ and temperature."
    },
    {
        "anchor": "Bose-Einstein condensates in an eightfold symmetric optical lattice: We investigate the properties of Bose-Einstein condensates (BECs) in a\ntwo-dimensional quasi-periodic optical lattice (OL) with eightfold rotational\nsymmetry by numerically solving the Gross-Pitaevskii equation. In a stationary\nexternal harmonic trapping potential, we first analyze the evolution of\nmatter-wave interference pattern from periodic to quasi-periodic as the OL is\nchanged continuously from four-fold periodic and eight-fold quasi-periodic. We\nalso investigate the transport properties during this evolution for different\ninteratomic interaction and lattice depth, and find that the BEC crosses over\nfrom ballistic diffusion to localization. Finally, we focus on the case of\neightfold symmetric lattice and consider a global rotation imposed by the\nexternal trapping potential. The BEC shows vortex pattern with eightfold\nsymmetry for slow rotation, becomes unstable for intermediate rotation, and\nexhibits annular solitons with approximate axial symmetry for fast rotation.\nThese results can be readily demonstrated in experiments using the same\nconfiguration as in Phys. Rev. Lett. 122, 110404 (2019).",
        "positive": "Soliton Dimer-soliton scattering in coupled Quasi-one-dimensional\n  Dipolar Bose-Einstein Condensates: We discuss scattering between a bright soliton and a soliton dimer in coupled\nquasi-one-dimensional dipolar Bose-Einstein condensates. The dimer is formed by\neach soliton from both tubes due to the attractive inter-layer dipole-dipole\ninteraction. The dipoles within each tube repel each other, and a stable,\nbright soliton is stabilized via attractive contact interactions. In general,\nthe scattering is inelastic, transferring the kinetic energy into internal\nmodes of both soliton dimer and single soliton. Our studies reveal rich\nscattering scenarios, including dimer-soliton repulsion at small initial\nvelocities, exchange of atoms between dimer and single soliton and soliton\nfusion at intermediate velocities. Interestingly, for some particular initial\nvelocities, the dimer-soliton scattering results in a state of two dimers. At\nlarge initial velocities, the scattering is elastic as expected."
    },
    {
        "anchor": "Periodic driving induced helical Floquet channels with ultracold atoms\n  in momentum space: Employing the external degrees of freedom of atoms as synthetic dimensions\nrenders easy and new accesses to quantum engineering and quantum simulation. As\na recent development, ultracold atoms suffering from two-photon Bragg\ntransitions can be diffracted into a series of discrete momentum states to form\na momentum lattice. Here we provide a detailed analysis on such a system, and,\nas a concrete example, report the observation of robust helical Floquet\nchannels, by introducing periodic driving sequences. The robustness of these\nchannels against perturbations is confirmed, as a test for their topological\norigin captured by Floquet winding numbers. The periodic switching demonstrated\nhere serves as a testbed for more complicated Floquet engieering schemes, and\noffers exciting opportunities to study novel topological physics in a many-body\nsetting with tunable interactions.",
        "positive": "Detecting quantum phase transitions in the quasi-stationary regime of\n  Ising chains: Recently, single-site observables have been shown to be useful for the\ndetection of dynamical criticality due to an emergence of a universal\ncritically-prethermal temporal regime in the magnetization [arXiv:2105.05986].\nHere, we explore the potential of single-site observables as probes of quantum\nphase transitions in integrable and nonintegrable transverse-field Ising chains\n(TFIC). We analytically prove the requirement of zero modes for a\nquasi-stationary temporal regime to emerge at a bulk probe site, and show how\nthis regime gives rise to a non-analytic behavior in the dynamical order\nprofiles. Our $t$-DMRG calculations verify the results of the quench mean-field\ntheory for near-integrable TFIC both with finite-size and finite-time scaling\nanalyses. We find that both finite-size and finite-time analyses suggest a\ndynamical critical point for a strongly nonintegrable and locally connected\nTFIC. We finally demonstrate the presence of a quasi-stationary regime in the\npower-law interacting TFIC, and extract local dynamical order profiles for TFIC\nin the long-range Ising universality class with algebraic light cones."
    },
    {
        "anchor": "Fast control of topological vortex formation in BEC by counter-diabatic\n  driving: Topological vortex formation has been known as the simplest method for vortex\nformation in BEC of alkali atoms. This scheme requires inversion of the bias\nmagnetic field along the axis of the condensate, which leads to atom loss when\nthe bias field crosses zero. In this Letter, we propose a scheme with which the\natom loss is greatly suppressed by adding counter-diabatic magnetic field. A\nnaive counter-diabatic field violates the Maxwell equations and we need to\nintroduce an approximation to make it physically feasible. The resulting field\nrequires an extra currents, which is experimentally challenging. Finally we\nsolve this problem by applying a gauge transformation so that the\ncounter-diabatic field is generated by controlling the original trap field with\nthe additional control of the bias field.",
        "positive": "Self-Bound Quantum Droplet with Internal Stripe Structure in 1D\n  Spin-Orbit-Coupled Bose Gas: We study the quantum-droplet state in a 3-dimensional (3D) Bose gas in the\npresence of 1D spin-orbit-coupling and Raman coupling, especially the stripe\nphase with density modulation, by numerically computing the ground state energy\nincluding the mean-field energy and Lee-HuangYang correction. In this droplet\nstate, the stripe can exist in a wider range of Raman coupling, compared with\nthe BEC-gas state. More intriguingly, both spin-orbit-coupling and Raman\ncoupling strengths can be used to tune the droplet density."
    },
    {
        "anchor": "Experimental Observation of Curved Light-Cones in a Quantum Field\n  Simulator: We investigate signal propagation in a quantum field simulator of the\nKlein-Gordon model realized by two strongly coupled parallel one-dimensional\nquasi-condensates. By measuring local phononic fields after a quench, we\nobserve the propagation of correlations along sharp light-cone fronts. If the\nlocal atomic density is inhomogeneous, these propagation fronts are curved. For\nsharp edges, the propagation fronts are reflected at the system's boundaries.\nBy extracting the space-dependent variation of the front velocity from the\ndata, we find agreement with theoretical predictions based on curved geodesics\nof an inhomogeneous metric. This work extends the range of quantum simulations\nof non-equilibrium field dynamics in general spacetime metrics.",
        "positive": "Controlling spontaneous-emission noise in measurement-based feedback\n  cooling of a Bose-Einstein Condensate: Off-resonant optical imaging is the most popular method for continuous\nmonitoring of a Bose-Einstein condensate (BEC). However, the disturbance caused\nby scattered photons places a serious limitation on the lifetime of such\ncontinuously-monitored condensates. In this paper, we demonstrate that a new\nchoice of feedback control can overcome the heating effects of the measurement\nbackaction. In particular, we show that the measurement backaction caused by\noff-resonant optical imaging is a multimode quantum-field effect, as the entire\nheating process is not seen in single-particle or mean-field models of the\nsystem. Correctly simulating such continuously-monitored systems is only\npossible using the number-phase Wigner (NPW) particle filter, which is a hybrid\nbetween the leading techniques for simulating non-equilibrium dynamics in\ncondensates and particle filters for simulating high-dimensional non-Gaussian\nfilters in the field of engineering. The new control scheme will enable\nlong-term continuous measurement and feedback on one of the leading platforms\nfor precision measurement and the simulation of quantum fields, allowing for\nthe possibility of single-shot experiments, adaptive measurements and robust\nstate-preparation and manipulation."
    },
    {
        "anchor": "Finite temperature damping of collective modes of a BCS-BEC crossover\n  superfluid: A new mechanism is proposed to explain the puzzling damping of collective\nexcitations, which was recently observed in the experiments of strongly\ninteracting Fermi gases below the superfluid critical temperature on the\nfermionic (BCS) side of Feshbach resonance. Sound velocity, superfluid density\nand damping rate are calculated with effective field theory. We find that a\ndominant damping process is due to the interaction between superfluid phonons\nand thermally excited fermionic quasiparticles, in contrast to the previously\nproposed pair-breaking mechanism. Results from our effective model are compared\nquantitatively with recent experimental findings, showing a good agreement.",
        "positive": "Change in the adiabatic invariant in a nonlinear Landau-Zener problem: We study a nonlinear generalization of the Landau-Zener resonance-crossing\nproblem relevant to coherent photo- and magneto-association of ultracold atoms.\nDue to the structure of the corresponding classical phase space, the adiabatic\ntheorem breaks down even at very small sweep rates, and the adiabatic\napproximation diverges because of the crossing of a separatrix. First, by\nintroducing a complex term into the Hamiltonian of the system, we eliminate\nthis divergence and construct a valid zero-order approximation. Further, taking\ninto account that the molecular conversion efficiency and the change of the\nclassical adiabatic invariant at the separatrix crossing are related\nquantities, we calculate the change of the action for the situation when the\nsystem starts from the all-atomic state that corresponds to the case of zero\ninitial action. The absolute error of the presented formula for the change in\nthe action is of the order of or less than 10^-4."
    },
    {
        "anchor": "Dynamical phase transition in the open Dicke model: The Dicke model with a weak dissipation channel is realized by coupling a\nBose-Einstein condensate to an optical cavity with ultra-narrow bandwidth. We\nexplore the dynamical critical properties of the Hepp-Lieb-Dicke phase\ntransition by performing quenches across the phase boundary. We observe\nhysteresis in the transition between a homogeneous phase and a self-organized\ncollective phase with an enclosed loop area showing power law scaling with\nrespect to the quench time, which suggests an interpretation within a general\nframework introduced by Kibble and Zurek. The observed hysteretic dynamics is\nwell reproduced by numerically solving the mean field equation derived from a\ngeneralized Dicke Hamiltonian. Our work promotes the understanding of\nnonequilibrium physics in open many-body systems with infinite range\ninteractions.",
        "positive": "Observation of dense collisional soliton complexes in a two-component\n  Bose-Einstein condensate: We present an experimental and theoretical study of hydrodynamic phenomena in\na two-component atomic Bose-Einstein condensate emerging from the imprinting of\na periodic spin pattern. By employing a microwave pulse-based winding\ntechnique, we prepare a tunable initial state which evolves into an array of\nsolitary waves. We observe the ensuing dynamics, including shape deformations,\nthe emergence of dark-antidark solitons, apparent spatial frequency tripling,\nand decay and revival of contrast related to soliton collisions. For the\ndensest arrays, we obtain soliton complexes where solitons undergo continued\ncollisions for long evolution times providing an avenue towards the\ninvestigation of soliton gases in atomic condensates."
    },
    {
        "anchor": "Effective field theory and dispersion law of the phonons of a\n  non-relativistic superfluid: We study the recently proposed effective field theory for the phonon of an\narbitrary non-relativistic superfluid. After computing the one-loop phonon\nself-energy, we obtain the low temperature T contributions to the phonon\ndispersion law at low momentum, and see that the real part of those can be\nparametrized as a thermal correction to the phonon velocity. Because the\nphonons are the quanta of the sound waves, at low momentum their velocity\nshould agree with the speed of sound. We find that our results match at order\nT^4ln(T) with those predicted by Andreev and Khalatnikov for the speed of\nsound, derived from the superfluid hydrodynamical equations and the phonon\nkinetic theory. We get also higher order corrections of order T^4, which are\nnot reproduced pushing naively the kinetic theory computation. Finally, as an\napplication, we consider the cold Fermi gas in the unitarity limit, and find a\nuniversal expression for the low T relative correction to the speed of sound\nfor these systems.",
        "positive": "Ab initio interaction potentials and scattering lengths for ultracold\n  mixtures of metastable helium and alkali-metal atoms: We have obtained accurate ab initio quartet potentials for the diatomic\nmetastable triplet helium + alkali-metal (Li, Na, K, Rb) systems, using\nall-electron restricted open-shell coupled cluster singles and doubles with\nnoniterative triples corrections [CCSD(T)] calculations and accurate\ncalculations of the long-range $C_6$ coefficients. These potentials provide\naccurate ab initio quartet scattering lengths, which for these many-electron\nsystems is possible, because of the small reduced masses and shallow potentials\nthat results in a small amount of bound states. Our results are relevant for\nultracold metastable triplet helium + alkali-metal mixture experiments."
    },
    {
        "anchor": "Interactive optomechanical coupling with nonlinear polaritonic systems: We study a system of interacting matter quasiparticles strongly coupled to\nphotons inside an optomechanical cavity. The resulting normal modes of the\nsystem are represented by hybrid polaritonic quasiparticles, which acquire\neffective nonlinearity. Its strength is influenced by the presence of the\nmechanical mode and depends on the resonance frequency of the cavity. This\nleads to an interactive type of optomechanical coupling, being distinct from\nthe previously studied dispersive and dissipative couplings in optomechanical\nsystems. The emergent interactive coupling is shown to generate effective\noptical nonlinearity terms of high order, being quartic in the polariton\nnumber. We consider particular systems of exciton-polaritons and dipolaritons,\nand show that the induced effective optical nonlinearity due to the interactive\ncoupling can exceed in magnitude the strength of Kerr nonlinear terms, such as\nthose arising from polariton-polariton interactions. As applications, we show\nthat the higher order terms give rise to localized bright flat top solitons,\nwhich may form spontaneously in polariton condensates.",
        "positive": "Phases, instabilities and excitations in a two-component lattice model\n  with photon-mediated interactions: Engineering long-range interacting spin systems with ultra cold atoms offers\nthe possibility to explore exotic magnetically ordered phases in\nstrongly-correlated scenarios. Quantum gases in optical cavities provide a\nversatile experimental platform to further engineer photon-mediated\ninteractions and access the underlying microscopic processes by probing the\ncavity field. Here, we study a two-component spin Bose-Hubbard system with\ncavity-mediated interactions. We provide a comprehensive overview of its phase\ndiagram and transitions in experimentally relevant regimes. The interplay of\ndifferent energy scales yields a rich phase diagram with superfluid and\ninsulating phases exhibiting density modulation or spin ordering. In\nparticular, the combined effect of contact and global-range interactions gives\nrise to an antiferromagnetically ordered phase for arbitrarily small\nspin-dependent light-matter coupling, while long-range and inter-spin contact\ninteractions introduce regions of instability and phase separation in the phase\ndiagram. We further study the low energy excitations above the\nantiferrogmagnetic phase. Besides particle-hole branches, it hosts\nspin-exchange excitations with a tunable energy gap. The studied lattice model\ncan be readily realized in cold-atom experiments with optical cavities."
    },
    {
        "anchor": "Selective distillation phenomenon in two-species Bose-Einstein\n  condensates in open boundary optical lattices: We investigate the formation of discrete breathers (DBs) and the dynamics of\nthe mixture of two-species Bose-Einstein condensates (BECs) in open boundary\noptical lattices using the discrete nonlinear Schr\\\"{o}dinger equations. The\nresults show that the coupling of intra- and interspecies interaction can lead\nto the existence of pure single-species DBs and symbiotic DBs (i.e.,\ntwo-species DBs). Furthermore, we find that there is a selective distillation\nphenomenon in the dynamics of the mixture of two-species BECs. One can\nselectively distil one species from the mixture of two-species BECs and can\neven control dominant species fraction by adjusting the intra- and interspecies\ninteraction in optical lattices. Our selective distillation mechanism may find\npotential application in quantum information storage and quantum information\nprocessing based on multi-species atoms.",
        "positive": "Vibrational state inversion of a Bose-Einstein condensate: optimal\n  control and state tomography: We present theoretical and experimental results on high-fidelity transfer of\na trapped Bose-Einstein condensate into its first vibrationally excited\neigenstate. The excitation is driven by mechanical motion of the trap, along a\ntrajectory obtained from optimal control theory. Excellent agreement between\ntheory and experiment is found over a large range of parameters. We develop an\napproximate model to map the dynamics of the many-body condensate wave function\nto a driven two-level system."
    },
    {
        "anchor": "Anomalous minimum in the shear viscosity of a Fermi gas: We measure the static shear viscosity $\\eta$ in a two-component Fermi gas\nnear a broad collisional (Feshbach) resonance, as a function of interaction\nstrength and energy. We find that $\\eta$ has both a quadratic and a linear\ndependence on the interaction strength $1/({k_{FI}a})$, where $a$ is the s-wave\nscattering length and $k_{FI}$ is the Fermi wave vector for an ideal gas at the\ntrap center. For energies above the superfluid transition, the minimum in\n$\\eta$ as a function of interaction strength is significantly shifted toward\nthe BEC side of resonance, to $1/(k_{FI}a)\\simeq 0.25$.",
        "positive": "$p$-wave chiral superfluidity from an $s$-wave interacting atomic Fermi\n  gas: Chiral $p$-wave superfluids are fascinating topological quantum states of\nmatter that have been found in the liquid $^3$He-A phase and arguably in the\nelectronic Sr$_2$RuO$_4$ superconductor. They are shown fundamentally related\nto the fractional $5/2$ quantum Hall state which supports fractional exotic\nexcitations. A common understanding is that such states require spin-triplet\npairing of fermions due to $p$-wave interaction. Here we report by controlled\ntheoretical approximation that a center-of-mass Wannier $p$-wave chiral\nsuperfluid state can arise from spin-singlet pairing for an $s$-wave\ninteracting atomic Fermi gas in an optical lattice. Despite a conceptually\ndifferent origin, it shows topological properties similar to the conventional\nchiral $p$-wave state. These include a non-zero Chern number and the appearance\nof chiral fermionic zero modes bounded to domain walls. Several signature\nquantities are calculated for the cold atom experimental condition."
    },
    {
        "anchor": "Beyond mean-field corrections to the quasiparticle spectrum of\n  superfluid Fermi gases: We investigate the fermionic quasiparticle branch of superfluid Fermi gases\nin the BCS-BEC crossover and calculate the quasiparticle lifetime and energy\nshift due to its coupling with the collective mode. The only close-to-resonance\nprocess that low-energy quasiparticles can undergo at zero temperature is the\nemission of a bosonic excitation from the phononic branch. Close to the minimum\nof the branch we find that the quasiparticles remain undamped, allowing us to\ncompute corrections to experimentally relevant quantities such as the energy\ngap, location of the minimum, effective mass, and Landau critical velocity.",
        "positive": "Thermalization in a quasi-1D ultracold bosonic gas: We study the collisional processes that can lead to thermalization in\none-dimensional systems. For two body collisions excitations of transverse\nmodes are the prerequisite for energy exchange and thermalzation. At very low\ntemperatures excitations of transverse modes are exponentially suppressed,\nthermalization by two body collisions stops and the system should become\nintegrable. In quantum mechanics virtual excitations of higher radial modes are\npossible. These virtually excited radial modes give rise to effective\nthree-body velocity-changing collisions which lead to thermalization. We show\nthat these three-body elastic interactions are suppressed by pairwise quantum\ncorrelations when approaching the strongly correlated regime. If the relative\nmomentum $k$ is small compared to the two-body coupling constant $c$ the\nthree-particle scattering state is suppressed by a factor of $(k/c)^{12}$,\nwhich is proportional to $\\gamma ^{12}$, that is to the square of the\nthree-body correlation function at zero distance in the limit of the\nLieb-Liniger parameter $\\gamma \\gg 1$. This demonstrates that in one\ndimensional quantum systems it is not the freeze-out of two body collisions but\nthe strong quantum correlations which ensures absence of thermalization on\nexperimentally relevant time scales."
    },
    {
        "anchor": "Realization of Qi-Wu-Zhang model in spin-orbit-coupled ultracold\n  fermions: Based on the optical Raman lattice technique, we experimentally realize the\nQi-Wu-Zhang model for quantum anomalous Hall phase in ultracold fermions with\ntwo-dimensional (2D) spin-orbit (SO) coupling. We develop a novel protocol of\npump-probe quench measurement to probe, with minimal heating, the resonant spin\nflipping on particular quasi-momentum subspace called band-inversion surfaces.\nWith this protocol we demonstrate the first Dirac-type 2D SO coupling in a\nfermionic system, and detect non-trivial band topology by observing the change\nof band-inversion surfaces as the two-photon detuning varies. The non-trivial\nband topology is also observed by slowly loading the atoms into optical Raman\nlattices and measuring the spin textures. Our results show solid evidence for\nthe realization of the minimal SO-coupled quantum anomalous Hall model, which\ncan provide a feasible platform to investigate novel topological physics\nincluding the correlation effects with SO-coupled ultracold fermions.",
        "positive": "Breathing mode of a quantum droplet in a quasi-one-dimensional dipolar\n  Bose gas: We investigate the breathing mode and the stability of a quantum droplet in a\ntightly trapped one-dimensional dipolar gas of bosonic atoms. When the droplet\nwith a flat-top density profile is formed, the breathing mode frequency scales\nas the inverse of the number of atoms in the cloud. This is straightforwardly\nderived within a phenomenological hydrodynamical approach and confirmed using\nboth a variational method based on a generalized Gross-Pitaevskii action\nfunctional and the sum-rule approach. We extend our analysis also to the\npresence of axial confinement showing the effect of the trap on the density\nprofile and therefore on the breathing mode frequency scaling. Our analysis\nconfirms the stability of the quantum droplet against the particles emission\nwhen the flat-top density profile is observed. Our results can be used as a\nguide to the experimental investigations of collective modes to detect the\nformation of quantum droplets in quasi-one-dimensional dipolar gases."
    },
    {
        "anchor": "Spin-Nematic Squeezed Vacuum in a Quantum Gas: Using squeezed states it is possible to surpass the standard quantum limit of\nmeasurement uncertainty by reducing the measurement uncertainty of one property\nat the expense of another complementary property. Squeezed states were first\ndemonstrated in optical fields and later with ensembles of pseudo spin-1/2\natoms using non-linear atom-light interactions. Recently, collisional\ninteractions in ultracold atomic gases have been used to generate a large\ndegree of quadrature spin squeezing in two-component Bose condensates. For\npseudo spin-1/2 systems, the complementary properties are the different\ncomponents of the total spin vector <S>, which fully characterize the state on\nan SU(2) Bloch sphere. Here, we measure squeezing in a spin-1 Bose condensate,\nan SU(3) system, which requires measurement of the rank-2 nematic or quadrupole\ntensor <Q_ij> as well to fully characterize the state. Following a quench\nthrough a nematic to ferromagnetic quantum phase transition, squeezing is\nobserved in the variance of the quadratures up to -8.3(-0.7 +0.6) dB\n(-10.3(-0.9 +0.7) dB corrected for detection noise) below the standard quantum\nlimit. This spin-nematic squeezing is observed for negligible occupation of the\nsqueezed modes and is analogous to optical two-mode vacuum squeezing. This work\nhas potential applications to continuous variable quantum information and\nquantum-enhanced magnetometry.",
        "positive": "Robust platform for engineering pure-quantum-state transitions in\n  polariton condensates: We report on pure-quantum-state polariton condensates in optical annular\ntraps. The study of the underlying mechanism reveals that the polariton\nwavefunction always coalesces in a single pure-quantum-state that,\ncounter-intuitively, is always the uppermost confined state with the highest\noverlap to the exciton reservoir. The tunability of such states combined with\nthe short polariton lifetime allows for ultrafast transitions between coherent\nmesoscopic wavefunctions of distinctly different symmetries rendering optically\nconfined polariton condensates a promising platform for applications such as\nmany-body quantum circuitry and continuous-variable quantum processing."
    },
    {
        "anchor": "From Planar Solitons to Vortex Rings and Lines: Cascade of Solitonic\n  Excitations in a Superfluid Fermi Gas: We follow the time evolution of a superfluid Fermi gas of resonantly\ninteracting $^6$Li atoms after a phase imprint. Via tomographic imaging, we\nobserve the formation of a planar dark soliton, its subsequent snaking, and its\ndecay into a vortex ring, which in turn breaks to finally leave behind a single\nsolitonic vortex. In intermediate stages we find evidence for an exotic\nstructure resembling the $\\Phi$-soliton, a combination of a vortex ring and a\nvortex line. Direct imaging of the nodal surface reveals its undulation\ndynamics and its decay via the puncture of the initial soliton plane. The\nobserved evolution of the nodal surface represents dynamics beyond superfluid\nhydrodynamics, calling for a microscopic description of unitary fermionic\nsuperfluids out of equilibrium.",
        "positive": "Dissipative Quantum Vortices and Superradiant Scattering: Inspired by Analogue Gravity, superradiance has been previously investigated\nin Bose-Einstein condensates (BECs). In this work, we revisit this problem by\nintroducing dissipation to the system. After establishing the possibility of\nquantum vortices in dissipative BECs, we analyze the propagation of elementary\nexcitations and demonstrate the existence of superradiant modes which can be\ninterpreted in terms of the dissipation of ``antiparticles\". Our findings\nsupport the possibility of superradiant scattering around dissipative quantum\nvortices and paves the way for future experimental realization of the\nphenomenon."
    },
    {
        "anchor": "Towards ab initio thermodynamics of the electron gas at strong\n  degeneracy: Recently a number of theoretical studies of the uniform electron gas (UEG) at\nfinite temperature have appeared that are of relevance for dense plasmas, warm\ndense matter and laser excited solids and thermodynamic density functional\ntheory simulations. In particular, restricted path integral Monte Carlo (RPIMC)\nresults became available which, however, due to the Fermion sign problem, are\nconfined to moderate quantum degeneracy, i.e. low to moderate densities. We\nhave recently developed an alternative approach---configuration PIMC [T. Schoof\n{\\em et al.}, Contrib. Plasma Phys. {\\bf 51}, 687 (2011)] that allows one to\nstudy the so far not accessible high degeneracy regime. Here we present the\nfirst step towards UEG simulations using CPIMC by studying implementation and\nperformance of the method for the model case of $N=4$ particles. We also\nprovide benchmark data for the total energy.",
        "positive": "Nonlinear Bose-Einstein-condensate Dynamics Induced by a Harmonic\n  Modulation of the s-wave Scattering Length: In a recent experiment, a Bose-Einstein condensate of Li7 has been excited by\na harmonic modulation of the atomic s-wave scattering length via Feshbach\nresonance. By combining an analytical perturbative approach with extensive\nnumerical simulations we analyze the emerging nonlinear dynamics of the system\non the mean-field Gross-Pitaevskii level at zero temperature. Resulting\nexcitation spectra are presented and prominent nonlinear features are found:\nmode coupling, higher harmonics generation and significant shifts in the\nfrequencies of collective modes. We indicate how nonlinear dynamical properties\ncould be made clearly observable in future experiments and compared to our\nresults."
    },
    {
        "anchor": "Natural and unnatural parity states of small trapped equal-mass\n  two-component Fermi gases at unitarity and fourth-order virial coefficient: Equal-mass two-component Fermi gases under spherically symmetric external\nharmonic confinement with large s-wave scattering length are considered. Using\nthe stochastic variational approach, we determine the lowest 286 and 164\nrelative eigenenergies of the (2,2) and (3,1) systems at unitarity as a\nfunction of the range $r_0$ of the underlying two-body potential and\nextrapolate to the $r_0 \\rightarrow 0$ limit. Our calculations include all\nstates with vanishing and finite angular momentum $L$ (and natural and\nunnatural parity $\\Pi$) with relative energy up to $10.5 \\hbar \\Omega$, where\n$\\Omega$ denotes the angular trapping frequency of the external confinement.\nOur extrapolated zero-range energies are estimated to have uncertainties of\n0.1% or smaller. The (2,2) and (3,1) energies are used to determine the\nfourth-order virial coefficient of the trapped unitary two-component Fermi gas\nin the low-temperature regime. Our results are compared with recent predictions\nfor the fourth-order virial coefficient of the homogeneous system. We also\ncalculate small portions of the energy spectra of the (3,2) and (4,1) systems\nat unitarity.",
        "positive": "Quantifying hole-motion-induced frustration in doped antiferromagnets by\n  Hamiltonian reconstruction: Unveiling the microscopic origins of quantum phases dominated by the\ninterplay of spin and motional degrees of freedom constitutes one of the\ncentral challenges in strongly correlated many-body physics. When holes move\nthrough an antiferromagnetic spin background, they displace the positions of\nspins, which in turn induces effective frustration in the magnetic environment.\nHowever, a concrete characterization of this effect in a quantum many-body\nsystem is still an unsolved problem. Here we introduce a Hamiltonian\nreconstruction scheme that allows for a precise quantification of\nhole-motion-induced frustration. In particular, we access non-local correlation\nfunctions through projective measurements of the many-body state, from which\neffective spin-Hamiltonians can be recovered after detaching the magnetic\nbackground from dominant charge fluctuations. The scheme is applied to systems\nof mixed dimensionality, where holes are restricted to move in one dimension\n(1D), but $\\mathrm{SU}(2)$ superexchange is two-dimensional (2D). We\ndemonstrate that hole motion drives the spin background into a highly\nfrustrated spin liquid regime, reminiscent of Anderson's resonating valence\nbond paradigm in doped cuprates. We exemplify the direct applicability of the\nreconstruction scheme to ultracold atom experiments by recovering effective\nspin-Hamiltonians of experimentally obtained 1D Fermi-Hubbard snapshots. Our\nmethod can be generalized to fully 2D systems, enabling an unprecedented\nmicroscopic perspective on the doped Hubbard model."
    },
    {
        "anchor": "Dynamics of a Pair of Overlapping Polar Bright Solitons in Spin-1\n  Bose-Einstein Condensates: We analyze the dynamics of both population and spin densities, emerging from\nthe spatial overlap between two distinct polar bright solitons in Spin-1 Spinor\nCondensates. The dynamics of overlapping solitons in scalar condensates\nexhibits soliton fusion, atomic switching from one soliton to another and\nrepulsive dynamics depending on the extent of overlap and the relative phase\nbetween the solitons. The scalar case also helps us understand the dynamics of\nthe vector solitons. In the spinor case, non-trivial dynamics emerge in spatial\nand spin degrees of freedom. In the absence of spin changing collisions, we\nobserve Josephson-like oscillations in the population dynamics of each spin\ncomponent. In this case, the population dynamics is independent of the relative\nphase, but the dynamics of the spin-density vector depends on it. The latter\nalso witnesses the appearance of oscillating domain walls. The pair of\noverlapping polar solitons emerge as four ferromagnetic solitons irrespective\nof the initial phase difference for identical spin-dependent and\nspin-independent interaction strengths. But the dynamics of final solitons\ndepends explicitly on the relative phase. Depending on the ratio of\nspin-dependent and spin-independent interaction strengths, a pair of\noscillatons can also emerge as the final state. Then, increasing the extent of\noverlap may lead to the simultaneous formation of both a stationary\nferromagnetic soltion and a pair of oscillatons depending on the relative\nphase.",
        "positive": "Detecting D-Wave Pairing and Collective Modes in Fermionic Condensates\n  with Bragg Scattering: We show how the appearance of d-wave pairing in fermionic condensates\nmanifests itself in inelastic light scattering. Specifically, we calculate the\nBragg scattering intensity from the dynamic structure factor and the spin\nsusceptibility, which can be inferred from spin flip Raman transitions. This\ninformation provides a precise tool with which we can identify nontrivial\ncorrelations in the state of the system beyond the information contained in the\ndensity profile imaging alone. Due to the lack of Coulomb effects in neutral\nsuperfluids, this is also an opportunity to observe the Anderson-Bogoliubov\ncollective mode."
    },
    {
        "anchor": "The influence of sublattice bias on superfluid to Mott insulator\n  transitions: We model the superfluid to Mott insulator transition for a Bose gas on a\nlattice with two inequivalent sublattices. Using the Gutzwiller ansatz, we\nproduce phase diagrams and provide an understanding of the interplay between\nsuperfluidity on each sublattice. We explore how the Mott lobes split, and\ndescribe the experimental signatures.",
        "positive": "Spinor Bose gases: Explorations of symmetries, magnetism and quantum\n  dynamics: Spinor Bose gases form a family of quantum fluids manifesting both magnetic\norder and superfluidity. This article reviews experimental and theoretical\nprogress in understanding the static and dynamic properties of these fluids.\nThe connection between system properties and the rotational symmetry properties\nof the atomic states and their interactions are investigated. Following a\nreview of the experimental techniques used for characterizing spinor gases,\ntheir mean-field and many-body ground states, both in isolation and under the\napplication of symmetry-breaking external fields, are discussed. These states\nserve as the starting point for understanding low-energy dynamics, spin\ntextures and topological defects, effects of magnetic dipole interactions, and\nvarious non-equilibrium collective spin-mixing phenomena. The paper aims to\nform connections and establish coherence among the vast range of works on\nspinor Bose gases, so as to point to open questions and future research\nopportunities."
    },
    {
        "anchor": "Classical dynamics of the optomechanical modes of a Bose-Einstein\n  condensate in a ring cavity: We consider a cavity optomechanical system consisting of a Bose-Einstein\ncondensate (BEC) interacting with two counterpropagating traveling-wave modes\nin an optical ring cavity. In contrast to the more familiar case where the\ncondensate is driven by the standing-wave field of a high-$Q$ Fabry-P{\\'e}rot\ncavity we find that both symmetric and antisymmetric collective density side\nmodes of the BEC are mechanically excited by the light field. In the\nsemiclassical, mean-field limit where the light field and the zero-momentum\nmode of the condensate are treated classically the system is found to exhibit a\nrich multistable behavior, including the appearance of isolated branches of\nsolutions (isolas). We also present examples of the dynamics of the system as\ninput parameters such as the frequency of the driving lasers are varied.",
        "positive": "Interferometry of non-Abelian band singularities and Euler class\n  topology: In systems with a real Bloch Hamiltonian band nodes can be characterised by a\nnon-Abelian frame-rotation charge. The ability of these band nodes to\nannihilate pairwise is path dependent, since by braiding nodes in adjacent gaps\nthe sign of their charges can be changed. Here, we theoretically construct and\nnumerically confirm two concrete methods to experimentally probe these\nnon-Abelian braiding processes and charges in ultracold atomic systems. We\nconsider a coherent superposition of two bands that can be created by moving\natoms through the band singularities at some angle in momentum space. Analyzing\nthe dependency on the frame charges, we demonstrate an interferometry scheme\npassing through two band nodes, which reveals the relative frame charges and\nallows for measuring the multi-gap topological invariant. The second method\nrelies on a single wavepacket probing two nodes sequentially, where the frame\ncharges can be determined from the band populations. Our results present a\nfeasible avenue for measuring non-Abelian charges of band nodes and the\nexperimental verification of braiding procedures directly, which can be applied\nin a variety of settings including the recently discovered anomalous\nnon-Abelian phases arising under periodic driving."
    },
    {
        "anchor": "Kibble-Zurek Dynamics in a Trapped Ultracold Bose Gas: The dynamical evolution of an inhomogeneous ultracold atomic gas quenched at\ndifferent controllable rates through the Bose-Einstein condensation phase\ntransition is studied numerically in the premise of a recent experiment in an\nanisotropic harmonic trap. Our findings based on the stochastic (projected)\nGross-Pitaevskii equation are shown to be consistent at early times with the\npredictions of the homogeneous Kibble-Zurek mechanism. This is demonstrated by\ncollapsing the early dynamical evolution of densities, spectral functions and\ncorrelation lengths for different quench rates, based on an appropriate\ncharacterization of the distance to criticality felt by the quenched system.\nThe subsequent long-time evolution, beyond the identified dynamical critical\nregion, is also investigated by looking at the behaviour of the density\nwavefront evolution and the corresponding phase ordering dynamics.",
        "positive": "Exploring the Thermodynamics of a Universal Fermi Gas: From sand piles to electrons in metals, one of the greatest challenges in\nmodern physics is to understand the behavior of an ensemble of strongly\ninteracting particles. A class of quantum many-body systems such as neutron\nmatter and cold Fermi gases share the same universal thermodynamic properties\nwhen interactions reach the maximum effective value allowed by quantum\nmechanics, the so-called unitary limit [1,2]. It is then possible to simulate\nsome astrophysical phenomena inside the highly controlled environment of an\natomic physics laboratory. Previous work on the thermodynamics of a\ntwo-component Fermi gas led to thermodynamic quantities averaged over the trap\n[3-5], making it difficult to compare with many-body theories developed for\nuniform gases. Here we develop a general method that provides for the first\ntime the equation of state of a uniform gas, as well as a detailed comparison\nwith existing theories [6,14]. The precision of our equation of state leads to\nnew physical insights on the unitary gas. For the unpolarized gas, we prove\nthat the low-temperature thermodynamics of the strongly interacting normal\nphase is well described by Fermi liquid theory and we localize the superfluid\ntransition. For a spin-polarized system, our equation of state at zero\ntemperature has a 2% accuracy and it extends the work of [15] on the phase\ndiagram to a new regime of precision. We show in particular that, despite\nstrong correlations, the normal phase behaves as a mixture of two ideal gases:\na Fermi gas of bare majority atoms and a non-interacting gas of dressed\nquasi-particles, the fermionic polarons [10,16-18]."
    },
    {
        "anchor": "Supersolidity of dipolar Bose-Einstein condensates induced by coupling\n  to fermions: We study a mixture of a dipolar condensate and a degenerate Fermi gas in a\nquasi-one-dimensional geometry. We demonstrate that the presence of fermions\nmay drastically change the behavior of a dipolar condensate. For strong enough\nboson-fermion attraction a dipolar Bose-Fermi droplet appears in the mixture\nand a roton excitation develops in the Bogoliubov excitations spectrum. As\nshown analytically and by solving numerically the coupled set of extended\nGross-Pitaevski and Hartree-Fock equations for bosonic and fermionic\ncomponents, respectively, roton instability mechanism leads to the formation of\nsupersolid phase in a Bose-Einstein condensate. Scaling arguments show that\nalthough the dysprosium atoms are considered to demonstrate the appearance of\nthe supersolid phase, such a phase can be observed with less magnetic atoms\nlike chromium and even rubidium.",
        "positive": "Dynamical Phase Diagram of Ultracold Josephson Junctions: We provide a complete study of the phase diagram characterising the distinct\ndynamical regimes emerging in a three-dimensional Josephson junction in an\nultracold quantum gas. Considering trapped ultracold superfluids separated into\ntwo reservoirs by a barrier of variable height and width, we analyse the\npopulation imbalance dynamics following a variable initial population mismatch.\nWe demonstrate that as the chemical potential difference is increased, the\nsystem transitions from Josephson plasma oscillations to either a dissipative\n(in the limit of low and narrow barriers) or a self-trapped regime (for large\nand wider barriers), with a crossover between the dissipative and the\nself-trapping regimes which we explore and characterize for the first time.\nThis work, which extends beyond the validity of the standard two-mode model,\nconnects the role of the barrier width, vortex rings and associated acoustic\nemission with different regimes of the superfluid dynamics across the junction,\nestablishing a framework for its experimental observation, which is found to be\nwithin current experimental reach."
    },
    {
        "anchor": "First-principles quantum dynamics for fermions: Application to molecular\n  dissociation: We demonstrate that the quantum dynamics of a many-body Fermi-Bose system can\nbe simulated using a Gaussian phase-space representation method. In particular,\nwe consider the application of the mixed fermion-boson model to ultracold\nquantum gases and simulate the dynamics of dissociation of a Bose-Einstein\ncondensate of bosonic dimers into pairs of fermionic atoms. We quantify\ndeviations of atom-atom pair correlations from Wick's factorization scheme, and\nshow that atom-molecule and molecule-molecule correlations grow with time, in\nclear departures from pairing mean-field theories. As a first-principles\napproach, the method provides benchmarking of approximate approaches and can be\nused to validate dynamical probes for characterizing strongly correlated phases\nof fermionic systems.",
        "positive": "Beyond Gross-Pitaevskii equation for 1D gas: quasiparticles and solitons: Describing properties of a strongly interacting quantum many-body system\nposes a serious challenge both for theory and experiment. In this work, we\nstudy excitations of one-dimensional repulsive Bose gas for arbitrary\ninteraction strength using a hydrodynamic approach. We use linearization to\nstudy particle (type-I) excitations and numerical minimization to study hole\n(type-II) excitations. We observe a good agreement between our approach and\nexact solutions of the Lieb-Liniger model for the particle modes and\ndiscrepancies for the hole modes. Therefore, the hydrodynamical equations find\nto be useful for long-wave structures like phonons and of a limited range of\napplicability for short-wave ones like narrow solitons. We discuss potential\nfurther applications of the method."
    },
    {
        "anchor": "Hartree-Fock-Bogoliubov Theory of Dipolar Fermi Gases: We construct a fully self-consistent Hartree-Fock-Bogoliubov theory that\ndescribes a spinless Fermi gas with long-range interaction. We apply this\ntheory to a system of uniform dipolar fermionic polar molecules, which has\nattracted much attention recently, due to rapid experimental progress in\nachieving such systems. By calculating the anisotropic superfluid order\nparameter, and the critical temperature $T_{c}$, we show that, \"hign $T_c$\"\nsuperfluid can be achieved with a quite modest value of interaction strength\nfor polar molecules. In addition, we also show that the presence of the Fock\nexchange interaction enhances superfluid pairing.",
        "positive": "Observation of Stable Jones-Roberts Solitons in Bose-Einstein\n  Condensates: We experimentally generate two-dimensional Jones-Roberts solitons in a\nthree-dimensional atomic Bose-Einstein condensate by imprinting a triangular\nphase pattern. By monitoring their dynamics we observe that this kind of\nsolitary waves are resistant to both dynamic (snaking) and thermodynamic\ninstabilities, that usually are known to strongly limit the lifetime of dark\nplane solitons in dimensions higher than one. We additionally find signatures\nof a possible dipole-like interaction between them. Our results confirm that\nJones-Roberts solitons are stable solutions of the non-linear Schr\\\"odinger\nequation in higher dimensions and promote these excitations for applications\nbeyond matter wave physics, like energy and information transport in noisy and\ninhomogeneous environments."
    },
    {
        "anchor": "BCS-BEC crossover and quantum phase transition in an ultracold Fermi gas\n  under spin-orbit coupling: In this work, we study the BCS-BEC crossover and quantum phase transition in\na Fermi gas under Rashba spin-orbit coupling close to a Feshbach resonance. By\nadopting a two-channel model, we take into account of the closed channel\nmolecules, and show that combined with spin-orbit coupling, a finite background\nscattering in the open channel can lead to two branches of solution for both\nthe two-body and the many-body ground states. The branching of the two-body\nbound state solution originates from the avoided crossing between bound states\nin the open and the closed channels, respectively. For the many-body states, we\nidentify a quantum phase transition in the upper branch regardless of the sign\nof the background scattering length, which is in clear contrast to the case\nwithout spin-orbit coupling. For systems with negative background scattering\nlength in particular, we show that the bound state in the open channel, and\nhence the quantum phase transition in the upper branch, are induced by\nspin-orbit coupling. We then characterize the critical detuning of the quantum\nphase transition for both positive and negative background scattering lengths,\nand demonstrate the optimal parameters for the critical point to be probed\nexperimentally.",
        "positive": "Dynamical hadron formation in long-range interacting quantum spin chains: The study of confinement in quantum spin chains has seen a large surge of\ninterest in recent years. It is not only important for understanding a range of\neffective one-dimensional condensed matter realizations, but also shares some\nof the non-perturbative physics with quantum chromodynamics (QCD) which makes\nit a prime target for current quantum simulation efforts. In analogy with QCD,\nthe confinement-induced two-particle boundstates that appear in these models\nare dubbed mesons. Here, we study scattering events due to meson collisions in\na quantum spin chain with long-range interactions such that two mesons have an\nextended interaction. We show how novel hadronic boundstates, e.g. with four\nconstituent particles akin to tetraquarks, may form dynamically in fusion\nevents. In a natural collision their signal is weak as elastic meson scattering\ndominates. However, we propose two controllable protocols which allow for a\nclear observation of dynamical hadron formation. We discuss how this physics\ncan be simulated in trapped ion or Rydberg atom set-ups."
    },
    {
        "anchor": "Characterizing fractional topological phases of lattice bosons near the\n  first Mott lobe: The Bose-Hubbard model subjected to an effective magnetic field hosts a\nplethora of phases with different topological orders when tuning the chemical\npotential. Using the density matrix renormalization group method, we identify\nseveral gapped phases near the first Mott lobe at strong interactions. They are\nconnected by a particle-hole symmetry to a variety of quantum Hall states\nstabilized at low fillings. We characterize phases of both particle and hole\ntype and identify signatures compatible with Laughlin, Moore-Read, and Bosonic\nInteger Quantum Hall states by calculating the quantized Hall conductance and\nby extracting the topological entanglement entropy. Furthermore, we analyze the\nentanglement spectrum of a Laughlin state of bosonic particles and holes for a\nrange of interaction strengths, as well as the entanglement spectrum of a\nMoore-Read state. These results further corroborate the existence of\ntopological states at high fillings, close to the first Mott lobe, as hole\nanalogues of the respective low-filling states.",
        "positive": "Topology of Quantum Grey Soliton in Multi-Component Inhomogeneous\n  Bose-Einstein Condensates: We study the dispersion mechanism of Lieb mode excitations of both single and\nmulti component ultra-cold atomic Bose gas, subject to a harmonic confinement\nthrough chirp management. It is shown that in some parameter domain, the\nhole-like excitations lead to the soliton's negative mass regime, arising due\nto the coupling between chirp momentum and Kohn mode. In low momenta region the\ntrap considerably affects the dispersion of the grey soliton, which opens a new\nwindow to observe Lieb-mode excitations. Further, we extend our analysis to\nbinary condensate, which yields usual shape compatible grey-bright soliton\npairs. The inter-species interaction induces a shift in the Lieb-mode\nexcitations, where the pair can form a bound state. We emphasize that the\npresent model provides an opportunity to study such excitations in the low\nmomenta regime, as well as the formation of bound state in binary condensate."
    },
    {
        "anchor": "Observation of many-body scarring in a Bose--Hubbard quantum simulator: The ongoing quest for understanding nonequilibrium dynamics of complex\nquantum systems underpins the foundation of statistical physics as well as the\ndevelopment of quantum technology. Quantum many-body scarring has recently\nopened a window into novel mechanisms for delaying the onset of thermalization\nby preparing the system in special initial states, such as the $\\mathbb{Z}_2$\nstate in a Rydberg atom system. Here we realize many-body scarring in a\nBose-Hubbard quantum simulator from previously unknown initial conditions such\nas the unit-filling state. We develop a quantum-interference protocol for\nmeasuring the entanglement entropy and demonstrate that scarring traps the\nmany-body system in a low-entropy subspace. Our work makes the resource of\nscarring accessible to a broad class of ultracold-atom experiments, and it\nallows one to explore the relation of scarring to constrained dynamics in\nlattice gauge theories, Hilbert space fragmentation, and disorder-free\nlocalization.",
        "positive": "Superfluid to Bose-glass transition in a 1D weakly interacting Bose gas: We study the one-dimensional Bose gas in spatially correlated disorder at\nzero temperature, using an extended density-phase Bogoliubov method. We analyze\nin particular the decay of the one-body density matrix and the behaviour of the\nBogoliubov excitations across the phase boundary. We observe that the\ntransition to the Bose glass phase is marked by a power-law divergence of the\ndensity of states at low energy. A measure of the localization length displays\na power-law energy dependence in both regions, with the exponent equal to -1 at\nthe boundary. We draw the phase diagram of the superfluid-insulator transition\nin the limit of small interaction strength."
    },
    {
        "anchor": "Dissipative preparation of Chern insulators: Engineered dissipation can be employed to prepare interesting quantum many\nbody states in a non-equilibrium fashion. The basic idea is to obtain the state\nof interest as the unique steady state of a quantum master equation,\nirrespective of the initial state. Due to a fundamental competition of topology\nand locality, the dissipative preparation of gapped topological phases with a\nnon-vanishing Chern number has so far remained elusive. Here, we study the open\nquantum system dynamics of fermions on a two-dimensional lattice in the\nframework of a Lindblad master equation. In particular, we discover a mechanism\nto dissipatively prepare a topological steady state with non-zero Chern number\nby means of short-range system bath interaction. Quite remarkably, this gives\nrise to a stable topological phase in a non-equilibrium phase diagram. We\ndemonstrate how our theoretical construction can be implemented in a\nmicroscopic model that is experimentally feasible with cold atoms in optical\nlattices.",
        "positive": "Ground state and rotational properties of two-dimensional self-bound\n  quantum droplets: We consider a two-dimensional self-bound quantum droplet, which consists of a\nmixture of two Bose-Einstein condensates. We start with the ground state, and\nthen turn to the rotational response of this system, in the presence of an\nexternal (harmonic) potential. We identify various phases, depending on the\natom number, the strength of the external confinement and the angular momentum.\nThese include center of mass excitation, ghost vortices, as well as vortices of\nsingle and multiple quantization. According to our results, this is an\nexcellent system for the study of superfluid states."
    },
    {
        "anchor": "Experimental verification of a reversed Clausius inequality in an\n  isolated system: The second law of thermodynamics is a fundamental law of Nature. It is almost\nuniversally associated with the Clausius inequality that lower bounds a change\nin entropy by the ratio of supplied heat and temperature. However, this result\npresupposes that a system is in contact with a heat bath that drives it to a\nthermal state. For isolated systems that are moved from an initial equilibrium\nstate by a dissipative heat exchange, the Clausius inequality has been\npredicted to be reversed. We here experimentally investigate the nonequilibrium\nthermodynamics of an isolated dilute gas of ultracold Cesium atoms that can be\neither thermalized or pushed out of equilibrium by means of laser cooling\ntechniques. We determine in both cases the phase-space dynamics by tracing the\nevolution of the gas with position-resolved fluorescence imaging, from which we\nevaluate all relevant thermodynamic quantities. Our results confirm the\nvalidity of the usual Clausius inequality for the first process and of the\nreversed Clausius inequality for the second transformation.",
        "positive": "Propagation front of correlations in an interacting Bose gas: We analyze the quench dynamics of a one-dimensional bosonic Mott insulator\nand focus on the time evolution of density correlations. For these we identify\na pronounced propagation front, the velocity of which, once correctly\nextrapolated at large distances, can serve as a quantitative characteristic of\nthe many-body Hamiltonian. In particular, the velocity allows the weakly\ninteracting regime, which is qualitatively well described by free bosons, to be\ndistinguished from the strongly interacting one, in which pairs of distinct\nquasiparticles dominate the dynamics. In order to describe the latter case\nanalytically, we introduce a general approximation to solve the Bose-Hubbard\nHamiltonian based on the Jordan-Wigner fermionization of auxiliary particles.\nThis approach can also be used to determine the ground-state properties. As a\ncomplement to the fermionization approach, we derive explicitly the\ntime-dependent many-body state in the noninteracting limit and compare our\nresults to numerical simulations in the whole range of interactions of the\nBose-Hubbard model."
    },
    {
        "anchor": "The Unitary Fermi Gas in a Harmonic Trap and its Static Response: We use harmonically trapped systems to find the leading gradient corrections\nof the supefluid local density approximation (SLDA) - a density functional\ntheory (DFT) describing the unitary Fermi gas (UFG). We find the leading order\ncorrection to be negative, and predict the q^2 coefficient of the long-range\nstatic response c = 1.5(3) - a factor of two smaller than predicted by\nmean-field theory - thereby establishing a new and experimentally measurably\nuniversal constant.",
        "positive": "Mesoscopic transport of fermions through an engineered optical lattice\n  connecting two reservoirs: We study transport of fermions in a system composed of a short optical\nlattice connecting two finite atomic reservoirs at different filling levels.\nThe average equilibration current through the optical lattice, for strong\nlattice-reservoir coupling and finite temperatures, is calculated within the\nLandauer formalism using a nonequilibrium Green's functions approach. We\nmoreover determine quantum and thermal fluctuations in the transport and find\nsignificant shot-to-shot deviations from the average equilibration current. We\nshow how to control the atomic current by engineering specific optical lattice\npotentials without requiring site-by-site manipulations and suggest the\nrealization of a single level model. Based on this model we discuss the\nblocking effect on the atomic current resulting from weak interactions between\nthe fermions."
    },
    {
        "anchor": "Condensate fraction in metallic superconductors and ultracold atomic\n  vapors: We investigate the condensate density and the condensate fraction of\nconduction electrons in weak-coupling superconductors by using the BCS theory\nand the concept of off-diagonal-long-range-order. We discuss the analytical\nformula of the zero-temperature condensate density of Cooper pairs as a\nfunction of Debye frequency and energy gap, and calculate the condensate\nfraction for some metals. We study the density of Cooper pairs also at finite\ntemperature showing its connection with the gap order parameter and the effects\nof the electron-phonon coupling. Finally, we analyze similarities and\ndifferences between superconductors and ultracold Fermi atoms in the\ndetermination of their condensate density by using the BCS theory.",
        "positive": "Collisional stability of localized Yb(${}^3\\mathrm{P}_2$) atoms immersed\n  in a Fermi sea of Li: We establish an experimental method for a detailed investigation of inelastic\ncollisional properties between ytterbium (Yb) in the metastable\n${}^3\\mathrm{P}_2$ state and ground state lithium (Li). By combining an optical\nlattice and a direct excitation to the ${}^3\\mathrm{P}_2$ state we achieve high\nselectivity on the collisional partners. Using this method we determine\ninelastic loss coefficients in collisions between\n$^{174}$Yb(${}^3\\mathrm{P}_2$) with magnetic sublevels of $m_J=0$ and $-2$ and\nground state $^6$Li to be $(4.4\\pm0.3)\\times10^{-11}~\\mathrm{cm}^3/\\mathrm{s}$\nand $(4.7\\pm0.8)\\times10^{-11}~\\mathrm{cm}^3/\\mathrm{s}$, respectively. Absence\nof spin changing processes in Yb(${}^3\\mathrm{P}_2$)-Li inelastic collisions at\nlow magnetic fields is confirmed by inelastic loss measurements on the $m_J=0$\nstate. We also demonstrate that our method allows us to look into loss\nprocesses in few-body systems separately."
    },
    {
        "anchor": "Momentum-space engineering of gaseous Bose-Einstein condensates: We show how the momentum distribution of gaseous Bose--Einstein condensates\ncan be shaped by applying a sequence of standing-wave laser pulses. We present\na theory, whose validity for was demonstrated in an earlier experiment [L.\\\nDeng, et al., \\prl {\\bf 83}, 5407 (1999)], of the effect of a two-pulse\nsequence on the condensate wavefunction in momentum space. We generalize the\nprevious result to the case of $N$ pulses of arbitrary intensity separated by\narbitrary intervals and show how these parameters can be engineered to produce\na desired final momentum distribution. We find that several momentum\ndistributions, important in atom-interferometry applications, can be engineered\nwith high fidelity with two or three pulses.",
        "positive": "Fermi-Hubbard physics with atoms in an optical lattice: The Fermi-Hubbard model is a key concept in condensed matter physics and\nprovides crucial insights into electronic and magnetic properties of materials.\nYet, the intricate nature of Fermi systems poses a barrier to answer important\nquestions concerning d-wave superconductivity and quantum magnetism. Recently,\nit has become possible to experimentally realize the Fermi-Hubbard model using\na fermionic quantum gas loaded into an optical lattice. In this atomic approach\nto the Fermi-Hubbard model the Hamiltonian is a direct result of the optical\nlattice potential created by interfering laser fields and short-ranged\nultracold collisions. It provides a route to simulate the physics of the\nHamiltonian and to address open questions and novel challenges of the\nunderlying many-body system. This review gives an overview of the current\nefforts in understanding and realizing experiments with fermionic atoms in\noptical lattices and discusses key experiments in the metallic,\nband-insulating, superfluid and Mott-insulating regimes."
    },
    {
        "anchor": "Symmetry breaking, Josephson oscillation and self-trapping in a\n  self-bound three-dimensional quantum ball: We study spontaneous symmetry breaking (SSB), Josephson oscillation, and\nself-trapping in a stable, mobile, three-dimensional matter-wave spherical\nquantum ball self-bound by attractive two-body and repulsive three-body\ninteractions. The SSB is realized by a parity-symmetric (a) one-dimensional\n(1D) double-well potential and (b) a 1D Gaussian potential, both along the $z$\naxis and no potential along the $x$ and $y$ axes. In the presence of each of\nthese potentials, the symmetric ground state dynamically evolves into a\ndoubly-degenerate SSB ground state. If the SSB ground state in the double well,\npredominantly located in the first well ($z>0$), is given a small displacement,\nthe quantum ball oscillates with a self-trapping in the first well. For a\nmedium displacement one encounters an asymmetric Josephson oscillation. The\nasymmetric oscillation is a consequence of SSB. The study is performed by a\nvariational and numerical solution of a non-linear mean-field model with 1D\nparity-symmetric perturbations.",
        "positive": "Bose-Einstein condensation and/or modulation of \"displacements\" in the\n  two-state Bose-Hubbard model: Instabilities resulting in Bose-Einstein condensation and/or modulation of\n\"displacements\" in a system of quantum particles described by a two-state\nBose-Hubbard model (with an allowance for the interaction between particle\ndisplacements on different lattice sites) are investigated. A possibility of\nmodulation, which doubles the lattice constant, as well as the uniform\ndisplacement of particles from equilibrium positions are studied. Conditions\nfor realization of the mentioned instabilities and phase transitions into the\nSF phase and into the \"ordered\" phase with frozen displacements are analyzed.\nThe behaviour of order parameters is investigated and phase diagrams of the\nsystem are calculated both analytically (ground state) and numerically (at\nnon-zero temperatures). It is revealed that the SF phase can appear as an\nintermediate one between the normal and \"ordered\" phases, while a supersolid\nphase is thermodynamically unstable and does not appear. The relation of the\nobtained results to the lattices with the double-well local potentials is\ndiscussed."
    },
    {
        "anchor": "Interacting polariton fluids in a monolayer of tungsten disulfide: Atomically thin transition metal dichalcogenides (TMDs) possess a number of\nproperties that make them attractive for realizing room-temperature polariton\ndevices. An ideal platform for manipulating polariton fluids within monolayer\nTMDs is that of Bloch surface waves, which confine the electric field to a\nsmall volume near the surface of a dielectric mirror. Here we demonstrate that\nmonolayer tungsten disulfide ($\\text{WS}_2$) can sustain Bloch surface wave\npolaritons (BSWPs) with a Rabi splitting of 43 meV and propagation constants\nreaching 33 $\\mu$m. In addition, we evidence strong polariton-polariton\nnonlinearities within BSWPs, which manifest themselves as a reversible\nblueshift of the lower polariton resonance by up to 12.9$\\pm$0.5 meV. Such\nnonlinearities are at the heart of polariton devices and have not yet been\ndemonstrated in TMD polaritons. As a proof of concept, we use the nonlinearity\nto implement a nonlinear polariton source. Our results demonstrate that BSWPs\nusing TMDs can support long-range propagation combined with strong\nnonlinearities, enabling potential applications in integrated optical\nprocessing and polaritonic circuits.",
        "positive": "Mesoscopic dynamics of fermionic cold atoms ---Quantitative analysis of\n  transport coefficients and relaxation times---: We give a quantitative analysis of the dynamical properties of fermionic cold\natomic gases in normal phase, such as the shear viscosity, heat conductivity,\nand viscous relaxation times, using the novel microscopic expressions derived\nby the renormalization group (RG) method, where the Boltzmann equation is\nfaithfully solved to extract the hydrodynamics without recourse to any ansatz.\nIn particular, we examine the quantum statistical effects, temperature\ndependence, and scattering-length dependence of the transport coefficients and\nthe viscous relaxation times. The numerical calculation shows that the relation\n$\\tau_\\pi=\\eta/P$, which is derived in the relaxation-time approximation (RTA)\nand is used in most of the literature, turns out to be satisfied quite well,\nwhile the similar relation for the viscous relaxation time $\\tau_J$ of the heat\nconductivity is satisfied only approximately with a considerable error."
    },
    {
        "anchor": "Quantized Adiabatic Transport in Momentum Space: Though topological aspects of energy bands are known to play a key role in\nquantum transport in solid-state systems, the implications of Floquet band\ntopology for transport in momentum space (i.e., acceleration) are not explored\nso far. Using a ratchet accelerator model inspired by existing cold-atom\nexperiments, here we characterize a class of extended Floquet bands of\none-dimensional driven quantum systems by Chern numbers, reveal topological\nphase transitions therein, and theoretically predict the quantization of\nadiabatic transport in momentum space. Numerical results confirm our theory and\nindicate the feasibility of experimental studies.",
        "positive": "Competing ground states of strongly correlated bosons in the\n  Harper-Hofstadter-Mott model: Using an efficient cluster approach, we study the physics of two-dimensional\nlattice bosons in a strong magnetic field in the regime where the tunneling is\nmuch weaker than the on-site interaction strength. We study both dilute, hard\ncore bosons at filling factors much smaller than unity occupation per site, and\nthe physics in the vicinity of the superfluid-Mott lobes as the density is\ntuned away from unity. For hardcore bosons, we carry out extensive numerics for\na fixed flux per plaquette $\\phi=1/5$ and $\\phi = 1/3$. At large flux, the\nlowest energy state is a strongly correlated superfluid, analogous to He-$4$,\nin which the order parameter is dramatically suppressed, but non-zero. At\nfilling factors $\\nu=1/2,1$, we find competing incompressible states which are\nmetastable. These appear to be commensurate density wave states. For small\nflux, the situation is reversed, and the ground state at $\\nu = 1/2$ is an\nincompressible density-wave solid. Here, we find a metastable lattice\nsupersolid phase, where superfluidity and density-wave order coexist. We then\nperform careful numerical studies of the physics near the vicinity of the Mott\nlobes for $\\phi = 1/2$ and $\\phi = 1/4$. At $\\phi = 1/2$, the superfluid ground\nstate has commensurate density-wave order. At $\\phi = 1/4$, incompressible\nphases appear outside the Mott lobes at densities $n = 1.125$ and $n = 1.25$,\ncorresponding to filling fractions $\\nu = 1/2$ and $1$ respectively. These\nphases, which are absent in single-site mean-field theory are metastable, and\nhave slightly higher energy than the superfluid, but the energy difference\nbetween them shrinks rapidly with increasing cluster size, suggestive of an\nincompressible ground state. We thus explore the interplay between Mott\nphysics, magnetic Landau levels, and superfluidity, finding a rich phase\ndiagram of competing compressible and incompressible states."
    },
    {
        "anchor": "Collective modes of p-wave superfluid Fermi gases in BEC phase: The low-energy modes of a superfluid atomic Fermi gas at zero temperature are\ninvestigated. The Bose-Einstein-condensate (BEC) side of the superfluid phase\nis studied in detail. The atoms are assumed to be in only one internal state,\nso that for a sufficiently diluted gas the pairing of fermions can be\nconsidered effective in the l=1 channel only. In agreement with previous works\non p-wave superfluidity in Fermi systems, it is found that the $p_x+ip_y$ phase\nrepresents the lowest energy state in both the Bardeen-Cooper-Schrieffer (BCS)\nand BEC sides. Our calculations show that at low energy three branches of\ncollective modes can emerge, with different species of dispersion relations: a\nphonon-like mode, a single-particle-like mode and a gapped mode. A comparison\nwith the Bogoliubov excitations of the corresponding spinor Bose condensate is\nmade. They reproduce the dispersion relations of the excitation modes of the\np-wave superfluid Fermi gas to a high accuracy.",
        "positive": "Superfluid vortex dynamics on a torus and other toroidal surfaces of\n  revolution: The superfluid flow velocity is proportional to the gradient of the phase of\nthe superfluid order parameter, leading to the quantization of circulation\naround a vortex core. In this work, we study the dynamics of a superfluid film\non the surface of a torus. Such a compact surface allows only configurations of\nvortices with zero net vorticity. We derive analytic expressions for the flow\nfield, the total energy, and the time-dependent dynamics of the vortex cores.\nThe local curvature of the torus and the presence of non-contractable loops on\nthis multiply connected surface alter both the superfluid flow and the vortex\ndynamics. Finally we consider more general surfaces of revolution, called\ntoroids."
    },
    {
        "anchor": "Quench dynamics of mass-imbalanced three-body fermionic systems in a\n  spherical trap: We consider a system of two identical fermions of general mass interacting\nwith a third distinguishable particle via a contact interaction within an\nisotropic three-dimensional harmonic trap. We calculate time-dependent\nobservables of the system after it is quenched in s-wave scattering length. To\ndo this we use exact closed form mass-imbalanced hyperspherical solutions to\nthe static three-body problem. These exact solutions enable us to calculate two\ntime-dependent observables, the Ramsey signal and particle separation, after\nthe system undergoes a quench from non-interacting to the unitary regime or\nvice-versa.",
        "positive": "Effective two-mode description of a few ultra-cold bosons in a\n  double-well potential: We present a construction of an improved two-mode model for modeling the\ndynamics of interacting ultra-cold bosons confined in a one-dimensional double\nwell trap. Unlike in the typically used two-mode model based on the lowest\nsingle-particle eigenstates of the external potential, the improved model uses\na basis of properly chosen effective wave functions originating in the\nmany-body model. Accuracy of the improved model is examined and it is shown\nthat within a certain limit of inter-particle interaction strength, the model\nrecovers an exact evolution of the wells' populations much more closely than\nthe traditional two-mode model."
    },
    {
        "anchor": "Induced interactions for ultracold Fermi gases in optical lattices: We investigate the effect of optical lattices on the BCS superfluidity by\nusing the Gorkov--Melik-Barkhudarov (GMB) correction for a two-component Fermi\ngas. We find that the suppression of the order parameter is strongly enhanced\nby the lattice effects. The predictions made by the GMB corrections are in\nqualitative and, for the cases studied, quantitative agreement with previous\nquantum Monte Carlo results. We discuss how the GMB correction extends the\nvalidity of the mean-field theory to a wider range of tunable optical lattice\nsystems in different dimensions.",
        "positive": "Vinen turbulence via the decay of multicharged vortices in trapped\n  atomic Bose-Einstein condensates: We investigate a procedure to generate turbulence in a trapped Bose-Einstein\ncondensate which takes advantage of the decay of multicharged vortices. We show\nthat the resulting singly-charged vortices twist around each other, intertwined\nin the shape of helical Kelvin waves, which collide and undergo vortex\nreconnections, creating a disordered vortex state. By examining the velocity\nstatistics, the energy spectrum, the correlation functions and the temporal\ndecay, and comparing these properties with the properties of ordinary\nturbulence and observations in superfluid helium, we conclude that this\ndisordered vortex state can be identified with the `Vinen' regime of turbulence\nwhich has been discovered in the context of superfluid helium."
    },
    {
        "anchor": "Quantum tricriticality at the superfluid-insulator transition of binary\n  Bose mixtures: Quantum criticality near a tricritical point (TCP) is studied in the\ntwo-component Bose-Hubbard model on square lattices. The existence of quantum\nTCP on a boundary of superfluid-insulator transition is confirmed by quantum\nMonte Carlo simulations. Moreover, we analytically derive the quantum\ntricritical behaviors on the basis of an effective field theory. We find two\nsignificant features of the quantum tricriticality, that are the chemical\npotential dependence of the superfluid transition temperature and a strong\ndensity fluctuation. We suggest that these features are directly observable in\nexisting experimental setups of Bose-Bose mixtures in optical lattices.",
        "positive": "Bragg spectroscopy of clean and disordered lattice bosons in one\n  dimension: a spectral fingerprint of the Bose glass: We study the dynamic structure factor of a one-dimensional Bose gas confined\nin an optical lattice and modeled by the Bose-Hubbard Hamiltonian, using a\nvariety of numerical and analytical approaches. The dynamic structure factor,\nexperimentally measurable by Bragg spectroscopy, is studied in three relevant\ncases: in the clean regime, featuring either a superfluid or a Mott phase; and\nin the presence of two types of (quasi-)disordered external potentials: a\nquasi-periodic potential obtained from a bichromatic superlattice and a\nrandom-box disorder - both featuring a Bose glass phase. In the clean case, we\nshow the emergence of a gapped doublon mode (corresponding to a repulsively\nbound state) for incommensurate filling, well separated from the low-energy\nacoustic mode. In the disordered case, we show that the dynamic structure\nfactor provides a direct insight into the spatial structure of the excitations,\nunveiling their localized nature, which represents a fundamental signature of\nthe Bose glass phase. Furthermore, it provides a clear fingerprint of the very\nnature of the localization mechanism which differs for the two kinds of\ndisorder potentials we consider. In special cases, the dynamic structure factor\nmay provide an estimate of the position of the localization transition from\nsuperfluid to Bose glass, in a complementary manner to the information deduced\nfrom the momentum distribution."
    },
    {
        "anchor": "Unravelling the nonlinear ideal density response of many-body systems: Nonlinear density response theory is revisited focusing on the harmonically\nperturbed finite temperature uniform electron gas. Within the non-interacting\nlimit, brute force quantum kinetic theory calculations for the quadratic,\ncubic, quartic and quintic responses reveal a deep connection with the linear\nresponse. Careful analysis of the static long wavelength limit led us to\nconjecture a canonical non-interacting form that expresses arbitrary order\nnonlinear responses as the weighted sum of the linear responses evaluated at\nall multiple harmonics. This harmonic expansion is successfully validated\nagainst ab initio path integral Monte Carlo simulations",
        "positive": "Quasicontinuous horizontally guided atom laser: coupling spectrum and\n  flux limits: We study in detail the flux properties of a radiofrequency outcoupled\nhorizontally guided atom laser, following the scheme demonstrated in [Guerin W\net al. 2006 Phys. Rev. Lett. 97 200402]. Both the outcoupling spectrum (flux of\nthe atom laser versus rf frequency of the outcoupler) and the flux limitations\nimposed to operate in the quasicontinuous regime are investigated. These\naspects are studied using a quasi-1D model, whose predictions are shown to be\nin fair agreement with the experimental observations. This work allows us to\nidentify the operating range of the guided atom laser and to confirm its good\npromises in view of studying quantum transport phenomena."
    },
    {
        "anchor": "Full counting statistics and phase diagram of a dissipative Rydberg gas: Ultra-cold gases excited to strongly interacting Rydberg states are a\npromising system for quantum simulations of many-body systems. For off-resonant\nexcitation of such systems in the dissipative regime, highly correlated\nmany-body states exhibiting, among other characteristics, intermittency and\nmulti-modal counting distributions are expected to be created. So far,\nexperiments with Rydberg atoms have been carried out in the resonant,\nnon-dissipative regime. Here we realize a dissipative gas of rubidium Rydberg\natoms and measure its full counting statistics for both resonant and\noff-resonant excitation. We find strongly bimodal counting distributions in the\noff-resonant regime that are compatible with intermittency due to the\ncoexistence of dynamical phases. Moreover, we measure the phase diagram of the\nsystem and find good agreement with recent theoretical predictions. Our results\npave the way towards detailed studies of many-body effects in Rydberg gases.",
        "positive": "Spinor self-ordering of a quantum gas in a cavity: We observe the joint spin-spatial (spinor) self-organization of a\ntwo-component BEC strongly coupled to an optical cavity. This unusual\nnonequilibrium Hepp-Lieb-Dicke phase transition is driven by an off-resonant\ntwo-photon Raman transition formed from a classical pump field and the emergent\nquantum dynamical cavity field. This mediates a spinor-spinor interaction that,\nabove a critical strength, simultaneously organizes opposite spinor states of\nthe BEC on opposite checkerboard configurations of an emergent 2D lattice. The\nresulting spinor density-wave polariton condensate is observed by directly\ndetecting the atomic spin and momentum state and by holographically\nreconstructing the phase of the emitted cavity field. The latter provides a\ndirect measure of the spin state, and a spin-spatial domain wall is observed.\nThe photon-mediated spin interactions demonstrated here may be engineered to\ncreate dynamical gauge fields and quantum spin glasses."
    },
    {
        "anchor": "Superfluidity in Bose-Hubbard circuits: A semiclassical theory is provided for the metastability regime-diagram of\natomtronic superfluid circuits. Such circuits typically exhibit\nhigh-dimensional chaos; and non-linear resonances that couple the Bogoliubov\nexcitations manifest themselves. Contrary to the expectation these resonances\ndo not originate from the familiar Beliaev and Landau damping terms. Rather,\nthey are described by a variant of the Cherry Hamiltonian of celestial\nmechanics. Consequently we study the induced decay process, and its dependence\non the number of sites and of condensed particles.",
        "positive": "Quantum Chaos of Unitary Fermi Gases in Strong Pairing Fluctuation\n  Region: The growth rate of the out-of-time-ordered correlator in a N-flavor Fermi gas\nis investigated and the Lyapunove exponent $\\lambda_L$ is calculated to the\norder of $1/N$. We find that the Lyapunove exponent monotonically increases as\nthe the interaction strength increases from the BCS limit to the unitary\nregion. At the unitarity the Lyapunove exponent increases while the temperature\ndrops and it can reach to the order of $\\lambda_L\\sim T$ around the critical\ntemperature for the $N=1$ case. The system scrambles faster for stronger\npairing fluctuations. At the BCS limit, the Lyapunov exponent behaviors as\n$\\lambda_L\\propto e^{\\mu/T} a^2_s T^2/N$."
    },
    {
        "anchor": "Specific heat and effects of pairing fluctuations in the BCS-BEC\n  crossover regime of an ultracold Fermi gas: We investigate the specific heat at constant volume $C_V$ in the BCS\n(Bardeen-Cooper-Schrieffer)-BEC (Bose-Einstein condensation) crossover regime\nof an ultracold Fermi gas above the superfluid phase transition temperature\n$T_{\\rm c}$. Within the framework of the strong-coupling theory developed by\nNozi\\`eres and Schmitt-Rink, we show that this thermodynamic quantity is\nsensitive to the stability of preformed Cooper pairs. That is, while\n$C_V(T\\gesim T_{\\rm c})$ in the unitary regime is remarkably enhanced by {\\it\nmetastable} preformed Cooper pairs or pairing fluctuations, it is well\ndescribed by that of an ideal Bose gas of long-lived {\\it stable} molecules in\nthe strong-coupling BEC regime. Using these results, we identify the region\nwhere the system may be viewed as an almost ideal Bose gas of stable pairs, as\nwell as the pseudogap regime where the system is dominated by metastable\npreformed Cooper pairs, in the phase diagram of an ultracold Fermi gas with\nrespect to the strength of a pairing interaction and the temperature. We also\nshow that the calculated specific heat agrees with the recent experiment on a\n$^6$Li unitary Fermi gas. Since the formation of preformed Cooper pairs is a\ncrucial key in the BCS-BEC crossover phenomenon, our results would be helpful\nin considering how fluctuating preformed Cooper pairs appear in a Fermi gas, to\neventually become stable, as one passes through the BCS-BEC crossover region.",
        "positive": "Dynamics of the relativistic Gross-Pitaevskii equation with harmonic\n  potential: Following the variational approach: The role of the collective excitations as well as the free expansion dynamics\nprovide a key diagnostic tools for trapped Bose-Einstein condensations. Based\non such dynamics we proposed to study the relativistic version of them in the\ncontext of a macroscopic occupation of the ground-state for spin-0 particles.\nTherefore we used the Higgs model where the external trap is introduced by a\nnon-minimal coupling. Along with variational method, we obtained a nonlinear\ncoupling between dipolar and monopolar modes. Furthermore, the free expansion\nis no longer ballistic reaching a relativistic confinement."
    },
    {
        "anchor": "Composite boson signature in the interference pattern of atomic dimer\n  condensates: We predict the existence of high frequency modes in the interference pattern\nof two condensates made of fermionic-atom dimers. These modes, which result\nfrom fermion exchanges between condensates, constitute a striking signature of\nthe dimer composite nature. From the 2-coboson spatial correlation function,\nthat we derive analytically, and the Shiva diagrams that visualize many-body\neffects specific to composite bosons, we identify the physical origin of these\nhigh frequency modes and determine the conditions to see them experimentally by\nusing bound fermionic-atom pairs trapped on optical lattice sites. The dimer\ngranularity which appears in these modes comes from Pauli blocking that\nprevents two dimers to be located at the same lattice site.",
        "positive": "Relaxation of phonons in the Lieb-Liniger gas by dynamical\n  refermionization: We investigate the Lieb-Liniger gas initially prepared in an\nout-of-equilibrium state that is Gaussian in terms of the phonons. Because the\nphonons are not exact eigenstates of the Hamiltonian, the gas relaxes to a\nstationary state at very long times. Thanks to integrability, that stationary\nstate needs not be a thermal state. We characterize the stationary state of the\ngas after relaxation and compute its phonon population distribution.\nTechnically, this follows from the mapping between the exact eigenstates of the\nLieb-Liniger Hamiltonian and those of a non-interacting Fermi gas -- a mapping\nprovided by the Bethe equations -- , as well as on bosonization formulas valid\nin the low-energy sector of the Hilbert space. We apply our results to the case\nwhere the initial state is an excited coherent state for a single phonon mode,\nand we compare them to exact results obtained in the hard-core limit."
    },
    {
        "anchor": "Quench-induced spontaneous currents in rings of ultracold fermionic\n  atoms: We have measured the rate of spontaneous current formation in ring-shaped\nensembles of fermionic $^6$Li atoms, following a thermal quench through the BCS\nsuperfluid phase transition. For the fastest quenches, the mean square winding\nnumber follows a scaling law with exponent $\\sigma$ = 0.24(2), in line with\npredictions of the Kibble-Zurek (KZ) model for mean-field BCS theory. We use a\nhybrid quench protocol involving simultaneous evaporation and interaction\nramps, with a long system lifetime allowing characterization of a different\nrate of spontaneous current formation in the slow-quench regime, where\nfinite-size effects are important. Comparing our observations to a quasi-1D\nstochastic Ginzburg-Landau model, we find quantitative agreement for fast\nquenches, but only qualitative agreement for slow quenches.",
        "positive": "Single-particle spectral density of the unitary Fermi gas: Novel\n  approach based on the operator product expansion, sum rules and the maximum\n  entropy method: Making use of the operator product expansion, we derive a general class of\nsum rules for the imaginary part of the single-particle self-energy of the\nunitary Fermi gas. The sum rules are analyzed numerically with the help of the\nmaximum entropy method, which allows us to extract the single-particle spectral\ndensity as a function of both energy and momentum. These spectral densities\ncontain basic information on the properties of the unitary Fermi gas, such as\nthe dispersion relation and the superfluid pairing gap, for which we obtain\nreasonable agreement with the available results based on quantum Monte-Carlo\nsimulations."
    },
    {
        "anchor": "Analysis of non-Markovian coupling of a lattice-trapped atom to free\n  space: Behavior analogous to that of spontaneous emission in photonic band gap\nmaterials has been predicted for an atom-optical system consisting of an atom\nconfined in a well of a state-dependent optical lattice that is coupled to free\nspace through an internal-state transition [de Vega et al., Phys. Rev. Lett.\n101, 260404 (2008)]. Using the Weisskopf-Wigner approach and considering a\none-dimensional geometry, we analyze the properties of this system in detail,\nincluding the evolution of the lattice-trapped population, the momentum\ndistribution of emitted matter waves, and the detailed structure of an\nevanescent matter-wave state below the continuum boundary. We compare and\ncontrast our findings for the transition from Markovian to non-Markovian\nbehaviors to those previously obtained for three dimensions.",
        "positive": "Optimal configurations and \"Pauli crystals\" of quantum clusters: Broken rotational and translational symmetries are the hallmarks of solid\nstate materials. In contrast, quantum liquids and gases do not exhibit such\nproperties. However, if we regard the logarithm of the absolute square of a\nquantum liquid as an energy ${\\cal E}= -{\\rm ln}|\\Psi|^2$, a geometric pattern\nnaturally occurs at the minimum, i.e. the optimal configuration. Such geometric\npatterns have recently been studied for non-interacting fermions, and have been\nnamed \"Pauli crystals\". However, such patterns exist in all interacting gases\n(Bose or Fermi), independent of statistics. Here, we present an algorithm to\ndetermine the optimal configurations of quantum clusters solely from the images\nof their densities and without theoretical inputs. We establish its validity by\nrecovering a number of exact results, showing that it can identify the changes\nin the cluster's ground state which corresponds to phase transitions in bulk\nsystems."
    },
    {
        "anchor": "Spin Liquid Condensate of Spinful Bosons: We introduce the concept of a bosonic spin liquid condensate (SLC), where\nspinful bosons in a lattice form a zero-temperature spin disordered charge\ncondensate that preserves the spin rotation symmetry, but breaks the U(1)\nsymmetry due to a spinless order parameter with charge one. It has an energy\ngap to all the spin excitations. We show that such SLC states can be realized\nin a system of spin $S\\ge 2$ bosons. In particular, we analyze the SLC phase\ndiagram in the spin 2 case using a mean-field variational wave function method.\nWe show there is a direct analogy between the SLC and the\nresonating-valence-bond (RVB) state.",
        "positive": "Extracting the Quantum Geometric Tensor of an Optical Raman Lattice by\n  Bloch State Tomography: In Hilbert space, the geometry of the quantum state is identified by the\nquantum geometric tensor (QGT), whose imaginary part is the Berry curvature and\nreal part is the quantum metric tensor. Here, we propose and experimentally\nimplement a complete Bloch state tomography to directly measure eigenfunction\nof an optical Raman lattice for ultracold atoms. Through the measured\neigenfunction, the distribution of the complete QGT in the Brillouin zone is\nreconstructed, with which the topological invariants are extracted by the Berry\ncurvature and the distances of quantum states in momentum space are measured by\nthe quantum metric tensor. Further, we experimentally test a predicted\ninequality between the Berry curvature and quantum metric tensor, which reveals\na deep connection between topology and geometry."
    },
    {
        "anchor": "Phase diagrams of Bose-Hubbard model and antiferromagnetic spin-1/2\n  models on a honeycomb lattice: Motivated by the recent experimental realization of the Haldane model by\nultracold fermions in an optical lattice, we investigate phase diagrams of the\nhard-core Bose-Hubbard model on a honeycomb lattice. This model is closely\nrelated with a spin-1/2 antiferromagnetic (AF) quantum spin model.\nNearest-neighbor (NN) hopping amplitude is positive and it prefers an AF\nconfigurations of phases of Bose-Einstein condensates. On the other hand, an\namplitude of the next-NN hopping depends on an angle variable as in the Haldane\nmodel. Phase diagrams are obtained by means of an extended path-integral\nMonte-Carlo simulations. Besides the AF state, a 120$^o$-order state, there\nappear other phases including a Bose metal in which no long-range orders exist.",
        "positive": "Dimensional crossover and cold-atom realization of topological Mott\n  insulators: We propose a cold-atom setup which allows for a dimensional crossover from a\ntwo-dimensional quantum spin Hall insulating phase to a three-dimensional\nstrong topological insulator by tuning the hopping between the layers. We\nfurther show that additional Hubbard onsite interactions can give rise to spin\nliquid-like phases: weak and strong topological Mott insulators. They represent\nthe celebrated paradigm of a quantum state of matter which merely exists\nbecause of the interplay of the non-trivial topology of the band structure and\nstrong interactions. While the theoretical understanding of this phase has\nremained elusive, our proposal shall help to shed some light on this exotic\nstate of matter by paving the way for a controlled experimental investigation\nin optical lattices."
    },
    {
        "anchor": "Thermal fluctuations and quantum phase transition in antiferromagnetic\n  Bose-Einstein condensates: We develop a method for investigating nonequilibrium dynamics of an ultracold\nsystem that is initially at thermal equilibrium. Our procedure is based on the\nclassical fields approximation with appropriately prepared initial state. As an\napplication of the method, we investigate the influence of thermal fluctuations\non the quantum phase transition from an antiferromagnetic to phase separated\nground state in a spin-1 Bose-Einstein condensate of ultracold atoms. We find\nthat at temperatures significantly lower than the critical condensation\ntemperature $T_c$ the scaling law for the number of created spin defects\nremains intact.",
        "positive": "Scalable cold-atom quantum simulator for two-dimensional QED: We propose a scalable analog quantum simulator for quantum electrodynamics\n(QED) in two spatial dimensions. The setup for the U(1) lattice gauge field\ntheory employs inter-species spin-changing collisions in an ultra-cold atomic\nmixture trapped in an optical lattice. Building on the previous one-dimensional\nimplementation scheme of Ref. [1] we engineer spatial plaquette terms for\nmagnetic fields, thus solving a major obstacle towards experimental\nrealizations of realistic gauge theories in higher dimensions. We apply our\napproach to pure gauge theory and discuss how the phenomenon of confinement of\nelectric charges can be described by the quantum simulator."
    },
    {
        "anchor": "Non-equilibrium fluctuations and metastability arising from non-additive\n  interactions in dissipative multi-component Rydberg gases: We study the out-of-equilibrium dynamics of dissipative gases of atoms\nexcited to two or more high-lying Rydberg states. This situation bears\ninteresting similarities to classical binary (in general $p$-ary) mixtures of\nparticles. The effective forces between the components are determined by the\ninter-level and intra-level interactions of Rydberg atoms. These systems permit\nto explore new parameter regimes which are physically inaccessible in a\nclassical setting, for example one in which the mixtures exhibit non-additive\ninteractions. In this situation the out-of-equilibrium evolution is\ncharacterized by the formation of metastable domains that reach partial\nequilibration long before the attainment of stationarity. In experimental\nsettings with mesoscopic sizes, this collective behavior may in fact take the\nappearance of dynamic symmetry breaking.",
        "positive": "Broad Feshbach resonance in the 6Li-40K mixture: We study the widths of interspecies Feshbach resonances in a mixture of the\nfermionic quantum gases 6Li and 40K. We develop a model to calculate the width\nand position of all available Feshbach resonances for a system. Using the model\nwe select the optimal resonance to study the 6Li/40K mixture. Experimentally,\nwe obtain the asymmetric Fano lineshape of the interspecies elastic cross\nsection by measuring the distillation rate of 6Li atoms from a potassium-rich\n6Li/40K mixture as a function of magnetic field. This provides us with the\nfirst experimental determination of the width of a resonance in this mixture,\nDelta B=1.5(5) G. Our results offer good perspectives for the observation of\nuniversal crossover physics using this mass-imbalanced fermionic mixture."
    },
    {
        "anchor": "Phase diagram of spatiotemporal instabilities in a large magneto-optical\n  trap: Large clouds of cold atoms prepared in a magneto-optical trap are known to\npresent spatiotemporal instabilities when the frequency of the trapping lasers\nis brought close to the atomic resonance. This system bears similarities with\ntrapped plasmas where the role of the Coulomb interaction is played by the\nexchange of scattered photons, and astrophysical objects such as stars whose\nsize is dependent on radiative forces. We present in this paper a study of the\nphase-space of such instabilities, and reveal different dynamical regimes.\nThree dimensional simulations of the highly nonlinear atomic dynamics permit a\ndetailed analysis of the experimental observations.",
        "positive": "Heavy polarons in ultracold atomic Fermi superfluids at the BEC-BCS\n  crossover: formalism and applications: We investigate the system of a heavy impurity embedded in a paired\ntwo-component Fermi gas at the crossover from a Bose-Einstein condensate (BEC)\nto a Bardeen--Cooper--Schrieffer (BCS) superfluid via an extension of the\nfunctional determinant approach (FDA). FDA is an exact numerical approach\napplied to study manifestations of Anderson\\textquoteright s orthogonality\ncatastrophe (OC) in the system of a static impurity immersed in an ideal Fermi\ngas. Here, we extend the FDA to a strongly correlated superfluid background\ndescribed by a BCS mean-field wavefunction. In contrast to the ideal Fermi gas\ncase, the pairing gap in the BCS superfluid prevents the OC and leads to\ngenuine polaron signals in the spectrum. Thus, our exactly solvable model can\nprovide a deeper understanding of polaron physics. In addition, we find that\nthe polaron spectrum can be used to measure the superfluid pairing gap, and in\nthe case of a magnetic impurity, the energy of the sub-gap Yu-Shiba-Rusinov\n(YSR) bound state. Our theoretical predictions can be examined with\nstate-of-art cold-atom experiments."
    },
    {
        "anchor": "Adiabatic spin-dependent momentum transfer in an SU(N) degenerate Fermi\n  gas: We introduce a spin-orbit coupling scheme, where a retro-reflected laser beam\nselectively diffracts two spin components in opposite directions. Spin\nsensitivity is provided by sweeping through a magnetic-field sensitive\ntransition while dark states ensure that spontaneous emission remains low. The\nscheme is adiabatic and thus inherently robust. This tailored spin-orbit\ncoupling allows simultaneous measurements of the spin and momentum\ndistributions of a strontium degenerate Fermi gas, and thus opens the path to\nmomentum-resolved spin correlation measurements on SU(N) quantum magnets.",
        "positive": "Evidences for interaction-induced Haldane fractional exclusion\n  statistics in one and higher dimensions: Haldane fractional exclusion statistics (FES) has a long history of intense\nstudies, but its realization in physical systems is rare. Here we study\nrepulsively interacting Bose gases at and near a quantum critical point, and\nfind evidences that such strongly correlated gases obey simple non-mutual FES\nover a wide range of interaction strengths in both one and two dimensions.\nBased on exact solutions in one dimension, quantum Monte Carlo simulations and\nexperiments in both dimensions, we show that the thermodynamic properties of\nthese interacting gases, including entropy per particle, density and pressure,\nare essentially equivalent to those of non-interacting particles with FES.\nAccordingly, we establish a simple interaction-to-FES mapping that reveals the\nstatistical nature of particle-hole symmetry breaking induced by interaction in\nsuch quantum many-body systems. Whereas strongly interacting Bose gases reach\nfull fermionization in one dimension, they exhibit incomplete fermionization in\ntwo dimensions. Our results open a route to understanding correlated\ninteracting systems via non-interacting particles with FES in arbitrary\ndimensions."
    },
    {
        "anchor": "Atomic Bright Soliton Interferometry: The properties of nonlinear interference pattern between atomic bright\nsolitons are characterized analytically, with the aid of exact solutions of\ndynamical equation in mean-field approximation. It is shown that relative\nvelocity, relative phase, and nonlinear interaction strength can be measured\nfrom the interference pattern. The nonlinear interference properties are\nproposed to design atomic soliton interferometry in Bose-Einstein condensate.\nAs an example, we apply them to measure gravity acceleration in a ultra-cold\natom systems with a high precision degree. The results are also meaningful for\nprecise measurements in optical fiber, water wave tank, plasma, and other\nnonlinear systems.",
        "positive": "The Fermi liquid theory with fractional exclusion statistics: The Fermi liquid theory may provide a good description of the thermodynamic\nproperties of an interacting particle system when the interaction between the\nparticles contributes to the total energy of the system with a quantity which\nmay depend on the total particle number, but does not depend on the\ntemperature. In such a situation, the ideal part of the Hamiltonian, i.e. the\nenergy of the system without the interaction energy, also provides a good\ndescription of the system's thermodynamics.\n  If the total interaction energy of the system, being a complicated function\nof the particle populations, is temperature dependent, then the Landau's\nquasiparticle gas cannot describe accurately the thermodynamics of the system.\n  A general solution to this problem is presented in this paper, in which the\nquasiparticle energies are redefined in such a way that the total energy of the\nsystem is identical to the sum of the energies of the quasiparticles. This\nimplies also that the thermodynamic properties of the system and those of the\nquasiparticle gas are identical.\n  By choosing a perspective in which the quasiparticle energies are fixed while\nthe density of states along the quasiparticle axis vary, we transform our\nquasiparticle system into an ideal gas which obey fractional exclusion\nstatistics."
    },
    {
        "anchor": "Close-coupled model of Feshbach resonances in ultracold $^3$He* and\n  $^4$He* atomic Collisions: Helium atoms in the metastable $2^3{S_{1}}$ state (He$^*$) have unique\nadvantages for ultracold atomic experiments. However, there is no known\naccessible Feshbach resonance in He$^*$, which could be used to manipulate the\nscattering length and hence unlock several new experimental possiblities.\nPrevious experimental and theoretical studies for He$^*$ have produced\ncontradictory results. We aimed to resolve this discrepancy with a theoretical\nsearch for Feshbach resonances, using a new close-coupled model of He$^*$\ncollisions in the presence of an external magnetic field. Several resonances\nwere detected and the existing literature discrepancy was resolved. Although\nnone of the resonances identified are readily experimentally useable, an\ninteresting non-Feshbach scattering length variation with magnetic field was\nobserved in heteronuclear collisions, at field strengths that are\nexperimentally accessible.",
        "positive": "Condensation and superfluidity of dilute Bose gases with finite-range\n  interaction: We investigate an ultracold and dilute Bose gas by taking into account a\nfinite-range two-body interaction. The coupling constants of the resulting\nLagrangian density are related to measurable scattering parameters by following\nthe effective-field-theory approach. A perturbative scheme is then developed up\nto the Gaussian level, where both quantum and thermal fluctuations are\ncrucially affected by finite-range corrections. In particular, the relation\nbetween spontaneous symmetry breaking and the onset of superfluidity is\nemphasized by recovering the renowned Landau's equation for the superfluid\ndensity in terms of the condensate one."
    },
    {
        "anchor": "Spin-1 Bose Hubbard model with nearest neighbour extended interaction: We have studied a spinor (F = 1) Bose gas in presence of the density-density\ninteraction through the mean field approach and the perturbation theory for\neither sign of the spin dependent interaction, namely the antiferromagnetic\n(AF) and the ferromagnetic cases. In the AF case, the charge density wave (CDW)\nphase appears to be sandwiched between the Mott insulating (MI) and the\nsupersolid phases for small values of the extended interaction strength. But\nthe CDW phase completely occupies the MI lobe when the extended interaction\nstrength is larger than a certain critical value related to the width of the MI\nlobes and hence opens up the possibilities of spin singlet and nematic CDW\ninsulating phases. In the ferromagnetic case, the phase diagram shows similar\nfeatures as that of the AF case and are in complete agreement with a spin-0\nBose gas. The perturbation expansion calculations nicely corroborate the mean\nfield phase results in both these cases. Further, we extend our calculations in\npresence of a harmonic confinement and obtained the momentum distribution\nprofile that is related to the absorption spectra in order to distinguish\nbetween different phases.",
        "positive": "Spin squeezing in Bose-Einstein condensates: Limits imposed by\n  decoherence and non-zero temperature: We consider dynamically generated spin squeezing in interacting bimodal\ncondensates. We show that particle losses and non-zero temperature effects in a\nmultimode theory completely change the scaling of the best squeezing for large\natom numbers. We present the new scalings and we give approximate analytical\nexpressions for the squeezing in the thermodynamic limit. Besides reviewing our\nrecent theoretical results, we give here a simple physical picture of how\ndecoherence acts to limit the squeezing. We show in particular that under\ncertain conditions the decoherence due to losses and non-zero temperatureacts\nas a simple dephasing."
    },
    {
        "anchor": "Direct Measurement of the Zak phase in Topological Bloch Bands: Geometric phases that characterize the topological properties of Bloch bands\nplay a fundamental role in the modern band theory of solids. Here we report on\nthe direct measurement of the geometric phase acquired by cold atoms moving in\none-dimensional optical lattices. Using a combination of Bloch oscillations and\nRamsey interferometry, we extract the Zak phase - the Berry phase acquired\nduring an adiabatic motion of a particle across the Brillouin zone - which can\nbe viewed as an invariant characterizing the topological properties of the\nband. For a dimerized optical lattice, which models polyacetylene, we measure a\ndifference of the Zak phase equal to phi_Zak=0.97(2)pi for the two possible\npolyacetylene phases with different dimerization. This indicates that the two\ndimerized phases belong to different topological classes, such that for a\nfilled band, domain walls have fractional quantum numbers. Our work establishes\na new general approach for probing the topological structure of Bloch bands in\noptical lattices.",
        "positive": "The thermodynamic origin of the Contact and its relation to the gap in\n  the BEC-BCS crossover: As can be inferred from present experiments in ultracold gases, the\nscattering length is a quantity that determines the thermodynamic state of the\ngas. As such, there exists a conjugate thermodynamic to it. Here, we show that\nthe recently introduced \"contact\" is the conjugate of the inverse of the\nscattering length. We find that this identification allows for a derivation of\nessentially all the known results regarding the contact. Using the mean-field\ntheory for the Bose-Einstein (BEC) to Bardeen-Cooper-Schriefer (BCS) crossover,\nwe also find that the contact is proportional to the square of the gap. We\nanalyze in detail both a homogenous balanced mixture of fermions and its\ninhomogenous counterpart in a harmonic trap."
    },
    {
        "anchor": "Simple method for producing Bose-Einstein condensates of metastable\n  helium using a single beam optical dipole trap: We demonstrate a simple scheme to reach Bose-Einstein condensation (BEC) of\nmetastable triplet helium atoms using a single beam optical dipole trap with\nmoderate power of less than 3 W. Our scheme is based on RF-induced evaporative\ncooling in a quadrupole magnetic trap and transfer to a single beam optical\ndipole trap that is located below the magnetic trap center. We transfer 1x10^6\natoms into the optical dipole trap, with an initial temperature of 14 \\mu K,\nand observe efficient forced evaporative cooling both in a hybrid trap, in\nwhich the quadrupole magnetic trap operates just below the levitation gradient,\nand in the pure optical dipole trap, reaching the onset of BEC with 2x10^5\natoms and a pure BEC of 5x10^4 atoms. Our work shows that a single beam hybrid\ntrap can be applied for a light atom, for which evaporative cooling in the\nquadrupole magnetic trap is strongly limited by Majorana spin-flips, and the\nvery small levitation gradient limits the axial confinement in the hybrid trap.",
        "positive": "Statistical transmutation in Floquet driven optical lattices: We show that interacting bosons in a periodically-driven two dimensional (2D)\noptical lattice may effectively exhibit fermionic statistics. The phenomenon is\nsimilar to the celebrated Tonks-Girardeau regime in 1D. The Floquet band of a\ndriven lattice develops the moat shape, i.e. a minimum along a closed contour\nin the Brillouin zone. Such degeneracy of the kinetic energy favors fermionic\nquasiparticles. The statistical transmutation is achieved by the Chern-Simons\nflux attachment similar to the fractional quantum Hall case. We show that the\nvelocity distribution of the released bosons is a sensitive probe of the\nfermionic nature of their stationary Floquet state."
    },
    {
        "anchor": "Laser cooling of a potassium-argon gas mixture using collisional\n  redistribution of radiation: We study laser cooling of atomic gases by collisional redistribution, a\ntechnique applicable to ultradense atomic ensembles at a pressure of a few\nhundred bar. Frequent collisions of an optically active atom with a buffer gas\nshift atoms into resonance with a far red detuned laser beam, while spontaneous\ndecay occurs close to the unperturbed resonance frequency. In such an\nexcitation cycle, a kinetic energy of the order of the thermal energy kT is\nextracted from the sample. Here we report of recent experiments investigating\nthe cooling of a potassium-argon gas mixture, which compared to an\nrubidium-argon mixture investigated in earlier experiments has a smaller fine\nstructure of the optically active alkali atom. We observe a relative cooling of\nthe potassium-argon gas mixture by 120 K.",
        "positive": "Bosonic superfluid transport in a quantum point contact: We present a microscopic theory of heat and particle transport of an\ninteracting, low temperature Bose-Einstein condensate in a quantum point\ncontact. We show that, in contrast to charged, fermionic superconductors,\nbosonic systems feature tunneling processes of condensate elements, leading to\nthe presence of odd-order harmonics in the AC Josephson current. A crucial role\nis played by an anomalous tunneling process where condensate elements are\ncoherently converted into phonon excitations, leading to even-order harmonics\nin the AC currents as well as a DC contribution. At low bias, we find\ndissipative components obeying Ohm's law, and bias-independent nondissipative\ncomponents, in sharp contrast to fermionic superconductors. Analyzing the DC\ncontribution, we find zero thermopower and Lorenz number at zero temperature, a\nbreakdown of the bosonic Wiedemann-Franz law. These results highlight\nimportance of the anomalous tunneling process inherent to charge neutral\nsuperfluids. The consequences could readily be observed in existing cold-atom\ntransport setups."
    },
    {
        "anchor": "Collision dynamics of two-dimensional non-Abelian vortices: We study computationally the collision dynamics of vortices in a\ntwo-dimensional spin-2 Bose-Einstein condensate. In contrast to Abelian vortex\npairs, which annihilate or pass through each other, we observe non-Abelian\nvortex pairs to undergo rungihilation - an event that converts the colliding\nvortices into a rung vortex. The resulting rung defect subsequently decays to\nanother pair of non-Abelian vortices of different type, accompanied by a\nmagnetization reversal.",
        "positive": "Superfluidity in atomic Fermi gases: In a trapped atomic Fermi gas, one can tune continuously via a Feshbach\nresonance the effective pairing interaction between fermionic atoms from very\nweak to very strong. As a consequence, the low temperature superfluidity\nevolves continuously from the BCS type in the weak interaction limit to that of\nBose-Einstein condensation in the strong pairing limit, exhibiting a BCS-BEC\ncrossover. In this paper, we review recent experimental progress in atomic\nFermi gases which elucidates the nature of the superfluid phase as the\ninteraction is continuously tuned. Of particular interest is the intermediate\nor crossover regime where the $s$-wave scattering length diverges. We will\npresent an intuitive pairing fluctuation theory, and show that this theory is\nin quantitative agreement with existing experiments in cold atomic Fermi gases."
    },
    {
        "anchor": "Spinor dynamics in a mixture of spin-1 and spin-2 Bose-Einstein\n  condensates: The spinor dynamics of Bose-Einstein condensates of 87Rb atoms with hyperfine\nspins 1 and 2 were investigated. A technique of simultaneous Ramsey\ninterferometry was developed for individual control of the vectors of two spins\nwith almost the same Zeeman splittings. The mixture of spinor condensates is\ngenerated in the transversely polarized spin-1 and the longitudinally polarized\nspin-2 states. The time evolution of the spin-1 condensate exhibits dephasing\nand rephasing of the Larmor precession due to the interaction with the spin-2\ncondensate. The scattering lengths between spin-1 and -2 atoms were estimated\nby comparison with the numerical simulation using the Gross-Pitaevskii\nequation. The proposed technique is expected to facilitate the further study of\nmultiple spinor condensates.",
        "positive": "Non-exponential decay in Floquet-Bloch bands: Exponential decay laws describe systems ranging from unstable nuclei to\nfluorescent molecules, in which the probability of jumping to a lower-energy\nstate in any given time interval is static and history-independent. These\ndecays, involving only a metastable state and fluctuations of the quantum\nvacuum, are the most fundamental nonequilibrium process, and provide a\nmicroscopic model for the origins of irreversibility. Despite the fact that the\napparently universal exponential decay law has been precisely tested in a\nvariety of physical systems, it is a surprising truth that quantum mechanics\nrequires that spontaneous decay processes have non-exponential time dependence\nat both very short and very long times. Cold-atom experiments both classic and\nrecent have proven to be powerful probes of fundamental decay processes; in\nthis paper, we propose the use of Bose condensates in Floquet-Bloch bands as a\nprobe of long-time non-exponential decay in single isolated emitters. We\nidentify a range of parameters that should enable observation of long-time\ndeviations, and experimentally demonstrate a key element of the scheme: tunable\ndecay between quasienergy bands in a driven optical lattice."
    },
    {
        "anchor": "Delocalization of ultracold atoms in a disordered potential due to light\n  scattering: We numerically study the expansion dynamics of ultracold atoms in a\none-dimensional disordered potential in the presence of a weak position\nmeasurement of the atoms. We specifically consider this position measurement to\nbe realized by a combination of an external laser and a periodic array of\noptical microcavities along a waveguide. The position information is acquired\nthrough the scattering of a near-resonant laser photon into a specific\neigenmode of one of the cavities. The time evolution of the atomic density in\nthe presence of this light scattering mechanism is described within a Lindblad\nmaster equation approach, which is numerically implemented using the Monte\nCarlo wave function technique. We find that an arbitrarily weak rate of photon\nemission leads to a breakdown of Anderson localization of the atoms.",
        "positive": "Density-wave-type supersolid of two-dimensional tilted dipolar bosons: We predict a stable density-waves-type supersolid phase of a dilute gas of\ntilted dipolar bosons in a two-dimensional (2D) geometry. This many-body phase\nis manifested by the formation of the stripe pattern and elasticity coexisting\ntogether with the Bose-Einstein condensation and superfluidity at zero\ntemperature. With the increasing the tilting angle the type of the\ngas-supersolid transition changes from the first order to the second one\ndespite the 2D character of the system, whereas the anisotropy and many-body\nstabilizing interactions play crucial role. Our approach is based on the\nnumerical analysis of the phase diagram using the simulated annealing method\nfor a free-energy functional. The predicted supersolid effect can be realized\nin a variety of experimental setups ranging from excitons in heterostructures\nto cold atoms and polar molecules in optical potentials."
    },
    {
        "anchor": "Prethermalization Revealed by the Relaxation Dynamics of Full\n  Distribution Functions: We detail the experimental observation of the non-equilibrium many-body\nphenomenon prethermalization. We study the dynamics of a rapidly and coherently\nsplit one-dimensional Bose gas. An analysis based on the use of full quantum\nmechanical probability distributions of matter wave interference contrast\nreveals that the system evolves towards a quasi-steady state. This state, which\ncan be characterized by an effective temperature, is not the final thermal\nequilibrium state. We compare the evolution of the system to an integrable\nTomonaga-Luttinger liquid model and show that the system dephases to a\nprethermalized state rather than undergoing thermalization towards a final\nthermal equilibrium state.",
        "positive": "Quantum Elliptic Vortex in a Nematic-Spin Bose-Einstein Condensate: We find a novel topological defect in a spin-nematic superfluid\ntheoretically. A quantized vortex spontaneously breaks its axisymmetry, leading\nto an elliptic vortex in nematic-spin Bose-Einstein condensates with small\npositive quadratic Zeeman effect. The new vortex is considered the Joukowski\ntransform of a conventional vortex. Its oblateness grows when the Zeeman length\nexceeds the spin healing length. This structure is sustained by balancing the\nhydrodynamic potential and the elasticity of a soliton connecting two spin\nspots, which are observable by in situ magnetization imaging. The theoretical\nanalysis clearly defines the difference between half quantum vortices of the\npolar and antiferromagnetic phases in spin-1 condensates."
    },
    {
        "anchor": "Collisional losses of ultracold molecules due to intermediate complex\n  formation: Understanding the sources of losses and chemical reactions of ultracold\nalkali-metal molecules is among the critical elements needed for their\napplication in precision measurements and quantum technologies. Recent\nexperiments with nonreactive systems have reported unexpectedly large loss\nrates, posing a challenge for theoretical explanation. Here, we examine the\ndynamics of intermediate four-atom complexes formed in bimolecular collisions.\nWe calculate the nuclear spin--rotation, spin--spin, and quadrupole coupling\nconstants for bialkali tetramers using ab intio quantum-chemical methods. We\nshow that the nuclear spin--spin and quadrupole couplings are strong enough to\ncouple different rotational manifolds to increase the density of states and\nlifetimes of the collision complexes, which is consistent with experimental\nresults. We propose further experiments to confirm our predictions.",
        "positive": "Trion and Dimer Formation of Three-Color Fermions: We study the problem of three ultracold fermions in different hyperfine\nstates loaded into a lattice with spatial dimension D=1,2. We consider\nSU(3)-symmetric attractive interactions and also eventually include a\nthree-body constraint, which mimics the effect of three-body losses in the\nstrong-loss regime. We combine exact diagonalization with the Lanczos\nalgorithm, and evaluate both the eigenvalues and the eigenstates of the\nproblem. In D=1, we find that the ground state is always a three-body bound\nstate (trion) for arbitrarily small interaction, while in D=2, due to the\nstronger influence of finite-size effects, we are not able to provide\nconclusive evidence of the existence of a finite threshold for trion formation.\nOur data are however compatible with a threshold value which vanishes\nlogarithmically with the size of the system. Moreover we are able to identify\nthe presence of a fine structure inside the spectrum, which is associated with\noff-site trionic states. The characterization of these states shows that only\nthe long-distance behavior of the eigenstate wavefunctions provides clear-cut\nsignatures about the nature of bound states and that onsite observables are not\nenough to discriminate between them. The inclusion of a three-body constraint\ndue to losses promotes these off-site trions to the role of lowest energy\nstates, at least in the strong-coupling regime."
    },
    {
        "anchor": "Finite Temperature Phase Transitions in the SU$(N)$ Hubbard model: We investigate the SU($N$) Hubbard model for the multi-component fermionic\noptical lattice system, combining dynamical mean-field theory with the\ncontinuous-time quantum Monte Carlo method. We obtain the finite temperature\nphase diagrams with $N\\le 6$ and find that low temperature properties depends\non the parity of the components. The magnetically ordered state competes with\nthe correlated metallic state in the system with the even number of components\n$(N\\ge 4)$, yielding the first-order phase transition. It is also clarified\nthat, in the odd-component system, the ordered state is realized at relatively\nlower temperatures and the critical temperature is constant in the strong\ncoupling limit.",
        "positive": "Turbulence in a Bose-Einstein Condensate of Dipolar Excitons in Coupled\n  Quantum Wells: The nonlinear dynamics of a Bose-Einstein condensate (BEC) of dipolar\nexcitons trapped in an external confining potential in coupled quantum wells is\nanalysed. It is demonstrated that under typical experimental conditions the\ndipolar excitons BEC can be described by a generalized Gross-Pitaevskii\nequation with the local interaction between the excitons, which depends on the\nexciton distribution function. It is shown that, if the system is pumped at\nsufficiently high frequencies, a steady turbulent state can be formed."
    },
    {
        "anchor": "Crossed optical cavities with large mode diameters: We report on a compact, ultrahigh-vacuum compatible optical assembly to\ncreate large-scale, two-dimensional optical lattices for use in experiments\nwith ultracold atoms. The assembly consists of an octagon-shaped spacer made\nfrom ultra-low-expansion glass, to which we optically contact four fused-silica\ncavity mirrors, making it highly mechanically and thermally stable. The mirror\nsurfaces are nearly plane-parallel which allows us to create two perpendicular\ncavity modes with diameters $\\sim$1 mm. Such large mode diameters are desirable\nto increase the optical lattice homogeneity, but lead to strong angular\nsensitivities of the coplanarity between the two cavity modes. We demonstrate a\nprocedure to precisely position each mirror substrate that achieves a deviation\nfrom coplanarity of $d = 1(5)$ $\\mu$m. Creating large optical lattices at\narbitrary visible and near infrared wavelengths requires significant power\nenhancements to overcome limitations in the available laser power. The cavity\nmirrors have a customized low-loss mirror coating that enhances the power at a\nset of relevant wavelengths from the visible to the near infrared by up to\nthree orders of magnitude.",
        "positive": "Density Oscillations Induced by Individual Ultracold Two-Body Collisions: Access to single-particle momenta provides new means of studying the dynamics\nof a few interacting particles. In a joint theoretical and experimental effort,\nwe observe and analyze the effects of a finite number of ultracold two-body\ncollisions on the relative and single-particle densities by quenching two\nultracold atoms with an initial narrow wave packet into a wide trap with an\ninverted aspect ratio. The experimentally observed spatial oscillations of the\nrelative density are reproduced by a parameter-free zero-range theory and\ninterpreted in terms of cross-dimensional flux. We theoretically study the\nlong-time dynamics and find that the system does not approach its thermodynamic\nlimit. The setup can be viewed as an advanced particle collider that allows one\nto watch the collision process itself."
    },
    {
        "anchor": "Topologically induced avoided band crossing in an optical chequerboard\n  lattice: We report on the condensation of bosons in the 4th band of an optical\nchequerboard lattice providing a topologically induced avoided band crossing\ninvolving the 2nd, 3rd, and 4th Bloch bands. When the condensate is slowly\ntuned through the avoided crossing, accelerated band relaxation arises and the\nzero momentum approximately $C4$-invariant condensate wave function acquires\nfinite momentum order and reduced $C2$ symmetry. For faster tuning Landau-Zener\noscillations between different superfluid orders arise, which are used to\ncharacterize the avoided crossing.",
        "positive": "Composite boson description of a low density gas of excitons: Ground state properties of a fermionic Coulomb gas are calculated using the\nfixed-node diffusion Monte Carlo method. The validity of the composite boson\ndescription is tested for different densities. We extract the exciton-exciton\n$s$-wave scattering length by solving the four-body problem in a harmonic trap\nand mapping the energy to that of two trapped bosons. The equation of state is\nconsistent with the Bogoliubov theory for composite bosons interacting with the\nobtained $s$-wave scattering length. The perturbative expansion at low density\nhas contributions physically coming from (a) exciton binding energy, (b)\nmean-field Gross-Pitaevskii interaction between excitons, (c) quantum depletion\nof the excitonic condensate (Lee-Huang-Yang terms for composite bosons). In\naddition, for low densities we find a good agreement with the Bogoliubov\nbosonic theory for the condensate fraction of excitons. The equation of state\nin the opposite limit of large density is found to be well described by the\nperturbative theory including (a) mixture of two ideal Fermi gases (b) exchange\nenergy. We find that for low densities both energetic and coherent properties\nare correctly described by the picture of composite bosons (excitons)."
    },
    {
        "anchor": "Subcritical temperature in Bose-Einstein condensates of chiral molecules: Bose-Einstein condensation of a sample of non-interacting chiral molecules\nleads to a non zero optical activity of the condensate and also to a\nsubcritical temperature in the heat capacity. This is due to the internal\nstructure of the molecule which, in our model, is considered as a simple\ntwo-state system, characterized by tunneling and parity violation. The\npredicted singular behavior found for the specific heat, below the condensation\ntemperature, sheds some light on the existence of the so far elusive parity\nviolation energy difference between enantiomers.",
        "positive": "Superfluid critical velocity of an elongated harmonically trapped\n  Bose-Einstein condensate: We numerically model experiments on the superfluid critical velocity of an\nelongated, harmonically trapped Bose-Einstein condensate as reported by [P.\nEngels and C. Atherton, Phys. Rev. Lett. 99, 160405 (2007)]. These experiments\nswept an obstacle formed by an optical dipole potential through the long axis\nof the condensate at constant velocity. Their results found an increase in the\nresulting density fluctuations of the condensate above an obstacle velocity of\n$v\\approx 0.3$ mm/s, suggestive of a superfluid critical velocity substantially\nless than the average speed of sound. However, our analysis shows that the that\nthe experimental observations of Engels and Atherton are in fact consistent\nwith a superfluid critical velocity equal to the local speed of sound. We\nconstruct a model of energy transfer to the system based on the local density\napproximation to explain the experimental observations, and propose and\nsimulate experiments that sweep potentials through harmonically trapped\ncondensates at a constant fraction of the local speed of sound. We find that\nthis leads to a sudden onset of excitations above a critical fraction, in\nagreement with the Landau criterion for superfluidity."
    },
    {
        "anchor": "Effects of disorder upon transport and Anderson Localization in a\n  finite, two dimensional Bose gas: Anderson localization in a two-dimensional ultracold Bose-gas has been\ndemonstrated experimentally. Atoms were released within a dumbbell-shaped\noptical trap, where the channel of variable aspect ratio provided the only path\nfor particles to travel between source and drain reservoirs. This channel can\nbe populated with columnar (repulsive) optical potential spikes of square cross\nsection with arbitrary pattern. These spikes constitute impurities, the\nscattering centres for the otherwise free propagation of the particles. This\ngeometry does not allow for classical potential trapping which can be hard to\nexclude in other experimental setups. Here we add further theoretical evidence\nfor Anderson localization in this system by comparing the transport processes\nwithin a regular and a random pattern of impurities. It is demonstrated that\nthe transport within randomly distributed impurities is suppressed and the\ncorresponding localization length becomes shorter than the channel length.\nHowever, if an equal density of impurities are distributed in a regular manner,\nthe transport is only modestly disturbed. This observation corroborates the\nconclusions of the experimental observation: the localization is indeed\nattributed to the disorder. Beyond analysing the density distribution and the\nlocalization length, we also calculate a quantum `impedance' exhibiting\nqualitatively different behaviour for regular and random impurity patterns.",
        "positive": "Two interacting fermions in a 1D harmonic trap: matching the Bethe\n  ansatz and variational approaches: In this work, combining the Bethe ansatz approach with the variational\nprinciple, we calculate the ground state energy of the relative motion of a\nsystem of two fermions with spin up and down interacting via a delta-function\npotential in a 1D harmonic trap. Our results show good agreement with the\nanalytical solution of the problem, and provide a starting point for the\ninvestigation of more complex few-body systems where no exact theoretical\nsolution is available."
    },
    {
        "anchor": "Cluster Mean-Field Signature of Entanglement Entropy in Bosonic\n  Superfluid-Insulator Transitions: Entanglement entropy (EE), a fundamental conception in quantum information\nfor characterizing entanglement, has been extensively employed to explore\nquantum phase transitions (QPTs). Although the conventional single-site\nmean-field (MF) approach successfully predicts the emergence of QPTs, it fails\nto include any entanglement. Here, for the first time, in the framework of a\ncluster MF treatment, we extract the signature of EE in the bosonic\nsuperfluid-insulator transitions. We consider a trimerized Kagome lattice of\ninteracting bosons, in which each trimer is treated as a cluster, and implement\nthe cluster MF treatment by decoupling all inter-trimer hopping. In addition to\nsuperfluid and integer insulator phases, we find that fractional insulator\nphases appear when the tunneling is dominated by the intra-trimer part. To\nquantify the residual bipartite entanglement in a cluster, we calculate the\nsecond-order Renyi entropy, which can be experimentally measured by quantum\ninterference of many-body twins. The second-order Renyi entropy itself is\ncontinuous everywhere, however, the continuousness of its first-order\nderivative breaks down at the phase boundary. This means that the bosonic\nsuperfluid-insulator transitions can still be efficiently captured by the\nresidual entanglement in our cluster MF treatment. Besides to the bosonic\nsuperfluid-insulator transitions, our cluster MF treatment may also be used to\ncapture the signature of EE for other QPTs in quantum superlattice models.",
        "positive": "Spin-Orbit Coupling and Spin Textures in Optical Superlattices: We proposed and demonstrated a new approach for realizing spin orbit coupling\nwith ultracold atoms. We use orbital levels in a double well potential as\npseudospin states. Two-photon Raman transitions between left and right wells\ninduce spin-orbit coupling. This scheme does not require near resonant light,\nfeatures adjustable interactions by shaping the double well potential, and does\nnot depend on special properties of the atoms. A pseudospinor Bose-Einstein\ncondensate spontaneously acquires an antiferromagnetic pseudospin texture which\nbreaks the lattice symmetry similar to a supersolid."
    },
    {
        "anchor": "Adiabatic loading of one-dimensional SU(N) alkaline earth fermions in\n  optical lattices: Ultracold fermionic alkaline earth atoms confined in optical lattices realize\nHubbard models with internal SU(N) symmetries, where N can be as large as ten.\nSuch systems are expected to harbor exotic magnetic physics at temperatures\nbelow the superexchange energy scale. Employing quantum Monte Carlo simulations\nto access the low-temperature regime, we show that after adiabatically loading\na weakly interacting gas into the strongly interacting regime of an optical\nlattice, the final temperature decreases with increasing N. Furthermore, we\nestimate the temperature scale required to probe correlations associated with\nlow-temperature SU(N) magnetism. Our findings are encouraging for the\nexploration of exotic large-N magnetic states in ongoing experiments.",
        "positive": "Vortex lattices in three-component Bose-Einstein condensates under\n  rotation: simulating colorful vortex lattices in a color superconductor: We study vortex lattices in three-component BECs under rotation, where three\nkinds of fractional vortices winding one of three components are present.\nUnlike the cases of two-component BECs where the phases of square and\ntriangular lattices are present depending on the intercomponent coupling\nconstant and the rotation speed, we find triangular ordered \"colorful\" vortex\nlattices where three kind of fractional vortices are placed in order without\ndefects, in all parameter region where the inter-component coupling g' is less\nthan the intra-component coupling g. When g > g' on the other hand, we find the\nphase separation; In a region where one component is present, the other two\ncomponents must vanish, where we find ghost vortices in these two components\nwhose positions are separated. In the boundary g = g', the accidental U(3)\nsymmetry is present, in which case two vortices in different components are\nclose to each other in some regions."
    },
    {
        "anchor": "Probing nearest-neighbor correlations of ultracold fermions in an\n  optical lattice: We demonstrate a probe for nearest-neighbor correlations of fermionic quantum\ngases in optical lattices. It gives access to spin and density configurations\nof adjacent sites and relies on creating additional doubly occupied sites by\nperturbative lattice modulation. The measured correlations for different\nlattice temperatures are in good agreement with an ab initio calculation\nwithout any fitting parameters. This probe opens new prospects for studying the\napproach to magnetically ordered phases.",
        "positive": "Dynamical Zeeman resonance in spin-orbit-coupled spin-1 Bose gases: We predict a dynamical resonant effect, which is driven by externally applied\nlinear and quadratic Zeeman fields, in a spin-orbit-coupled spin-1\nBose-Einstein condensate. The Bose-Einstein condensate is assumed to be\ninitialized in some superposed state of Zeeman sublevels and subject to a\nsudden shift of the trapping potential. It is shown that the time-averaged\ncenter-of-mass oscillation and the spin polarizations of the Bose-Einstein\ncondensate exhibit remarkable resonant peaks when the Zeeman fields are tuned\nto certain strengths. The underlying physics behind this resonance can be\ntraced back to the out-of-phase interference of the dynamical phases carried by\ndifferent spinorbit states. By analyzing the single particle spectrum, the\nresonant condition is summarized as a simple algebraic relation, connecting the\nstrengths of the linear and quadratic Zeeman fields. This property is\npotentially applicable in quantum information and quantum precision\nmeasurement."
    },
    {
        "anchor": "Scale invariance and universality in a cold gas of indirect excitons: We address theoretically the puzzling similarity observed in the\nthermodynamic behaviour of independent clouds of cold dipolar excitons in\ncoupled semiconductor quantum wells. We argue that the condensation of\nself-trapped exciton gas starts at the same critical temperature in all traps\ndue to the specific scaling rule. As a consequence of the reduced\ndimensionality of the system, the scaling parameters appear to be insensitive\nto disorder.",
        "positive": "Noise-induced transition from superfluid to vortex state in\n  two-dimensional nonequilibrium polariton condensates -- semi-analytical\n  treatment: We develop a semi-analytical description for the\nBerezinskii-Kosterlitz-Thouless (BKT) like phase transition in nonequilibrium\nBose-Einstein condensates. Our theoretical analysis is based on a noisy\ngeneralized Gross-Pitaevskii equation. Above a critical strength of the noise,\nspontaneous vortex-antivortex pairs are generated. We provide a semi-analytical\ndetermination of the transition point based on a linearized Bogoliubov\nanalysis, to which some nonlinear corrections are added. We present two\ndifferent approaches that are in agreement with our numerical calculations in a\nwide range of system parameters. We find that for small losses and not too\nsmall energy relaxation, the critical point approaches that of the equilibrium\nBKT transition. Furthermore, we find that losses tend to stabilize the ordered\nphase: keeping the other parameters constant and increasing the losses leads to\na higher critical noise strength for the spontaneous generation of\nvortex-antivortex pairs. Our theoretical analysis is relevant for experiments\non microcavity polaritons."
    },
    {
        "anchor": "Algebraic order and the Berezinskii-Kosterlitz-Thouless transition in an\n  exciton-polariton gas: We observe quasi-long range coherence in a two-dimensional condensate of\nexciton-polaritons. Our measurements are the first to confirm that the spatial\ncorrelation algebraically decays with a slow power-law, whose exponent\nquantitatively behaves as predicted by the Berezinskii-Kosterlitz-Thouless\ntheory. The exciton-polaritons are created by non-resonant optical pumping of a\nmicro-cavity sample with embedded GaAs quantum-wells at liquid helium\ntemperature. Michelson interference is used to measure the coherence of the\nphotons emitted by decaying exciton-polaritons.",
        "positive": "SU(3) truncated Wigner approximation for strongly interacting Bose gases: We develop and utilize the SU(3) truncated Wigner approximation (TWA) in\norder to analyze far-from-equilibrium quantum dynamics of strongly interacting\nBose gases in an optical lattice. Specifically, we explicitly represent the\ncorresponding Bose--Hubbard model at an arbitrary filling factor with\nrestricted local Hilbert spaces in terms of SU(3) matrices. Moreover, we\nintroduce a discrete Wigner sampling technique for the SU(3) TWA and examine\nits performance as well as that of the SU(3) TWA with the Gaussian\napproximation for the continuous Wigner function. We directly compare outputs\nof these two approaches with exact computations regarding dynamics of the\nBose--Hubbard model at unit filling with a small size and that of a\nfully-connected spin-1 model with a large size. We show that both approaches\ncan quantitatively capture quantum dynamics on a timescale of $\\hbar/(Jz)$,\nwhere $J$ and $z$ denote the hopping energy and the coordination number. We\napply the two kinds of SU(3) TWA to dynamical spreading of a two-point\ncorrelation function of the Bose--Hubbard model on a square lattice with a\nlarge system size, which has been measured in recent experiments. Noticeable\ndeviations between the theories and experiments indicate that proper inclusion\nof effects of the spatial inhomogeneity, which is not straightforward in our\nformulation of the SU(3) TWA, may be necessary."
    },
    {
        "anchor": "Confined Quasiparticle Dynamics in Long-Range Interacting Quantum Spin\n  Chains: We study the quasiparticle excitation and quench dynamics of the\none-dimensional transverse-field Ising model with power-law ($1/r^{\\alpha}$)\ninteractions. We find that long-range interactions give rise to a confining\npotential, which couples pairs of domain walls (kinks) into bound\nquasiparticles, analogous to mesonic bound states in high-energy physics. We\nshow that these quasiparticles have signatures in the dynamics of order\nparameters following a global quench and the Fourier spectrum of these order\nparameters can be expolited as a direct probe of the masses of the confined\nquasiparticles. We introduce a two-kink model to qualitatively explain the\nphenomenon of long-range-interaction induced confinement, and to quantitatively\npredict the masses of the bound quasiparticles. Furthermore, we illustrate that\nthese quasiparticle states can lead to slow thermalization of one-point\nobservables for certain initial states. Our work is readily applicable to\ncurrent trapped-ion experiments.",
        "positive": "Large-Scale $2+1$D $\\mathrm{U}(1)$ Gauge Theory with Dynamical Matter in\n  a Cold-Atom Quantum Simulator: A major driver of quantum-simulator technology is the prospect of probing\nhigh-energy phenomena in synthetic quantum matter setups at a high level of\ncontrol and tunability. Here, we propose an experimentally feasible realization\nof a large-scale $2+1$D $\\mathrm{U}(1)$ gauge theory with dynamical matter and\ngauge fields in a cold-atom quantum simulator with spinless bosons. We present\nthe full mapping of the corresponding Gauss's law onto the bosonic\ncomputational basis. We then show that the target gauge theory can be\nfaithfully realized and stabilized by an emergent gauge protection term in a\ntwo-dimensional single-species Bose--Hubbard optical Lieb superlattice with two\nspatial periods along either direction, thereby requiring only moderate\nexperimental resources already available in current cold-atom setups. Using\ninfinite matrix product states, we calculate numerical benchmarks for adiabatic\nsweeps and global quench dynamics that further confirm the fidelity of the\nmapping. Our work brings quantum simulators of gauge theories a significant\nstep forward in terms of investigating particle physics in higher spatial\ndimensions, and is readily implementable in existing cold-atom platforms."
    },
    {
        "anchor": "Coherence Properties of the Repulsive Anyon-Hubbard Dimer: One-dimensional anyonic models of the Hubbard type show intriguing\nground-state properties, effectively transmuting between Bose-Einstein and\nFermi-Dirac statistics. The simplest model that one can investigate is an\nanyonic version of the bosonic Josephson junction, the repulsive anyon-Hubbard\ndimer. In the following we find an exact duality relation to the Bethe-solvable\nBose-Hubbard dimer, which is well known from quantum optics and information\ntheory and has interesting connections to spin squeezing and entangled coherent\nstates. Conversely, we show that the anyonic Hubbard dimer has nontrivial\ncoherence properties that emerge from the anyonic statistics. In particular, we\nfind that coherences can be suppressed and amplified and show that these\nfeatures are remarkably robust against additional repulsive on-site\ninteractions highlighting the distinct nature of anyons.",
        "positive": "Dynamics and Density Correlations in Matter Wave Jet Emission of a\n  Driven Condensate: Emission of matter wave jets has been recently observed in a Bose-Einstein\ncondensate confined by a cylindrical box potential, induced by a periodically\nmodulated inter-particle interaction (Nature {\\bf 551}, 356 (2017)). In this\npaper we apply the time-dependent Bogoliubov theory to study the quantum\ndynamics and the correlation effects observed in this highly non-equilibrium\nphenomenon. Without any fitting parameter, our theoretical calculations on the\nnumber of ejected atoms and the angular density correlations are in excellent\nquantitative agreement with the experimental measurements. The exponential\ngrowth in time of the ejected atoms can be understood in terms of a dynamical\ninstability associated with the modulation of the interaction. We interpret the\nangular density correlation of the jets as the Hanbury-Brown-Twiss effect\nbetween the excited quasi-particles with different angular momenta, and our\ntheory explains the puzzling observation of the asymmetric density correlations\nbetween the jets with the same and opposite momenta. Our theory can also\nidentify the main factors that control the height and width of the peaks in the\ndensity correlation function, which can be directly verified in future\nexperiments."
    },
    {
        "anchor": "Quantized Topological Anderson-Thouless Pump: Thouless pump with quantized transports is topologically robust against small\nperturbations and disorders, while breaks down under sufficiently strong\ndisorders. Here we propose counter-intuitive topological pumps induced by\ndisorders in noninteracting and interacting systems. We first show an extrinsic\ntopological pump driven by the on-site quasiperiodic potential for a two-loop\nsequence, where the disorder inequivalently suppresses the topology of two pump\nloops. Moreover, we reveal an intrinsic topological pump induced by the hopping\nquasiperiodic disorder from a trivial single-loop pump in the clean limit,\ndubbed the topological Anderson-Thouless pump (TATP) as a dynamical analogue of\ntopological Anderson insulators. We demonstrate that the mechanism of the TATP\nis the disorder-induced shift of gapless critical points and the TATP can even\nexhibit in the dynamic disorder and interacting cases. Finally, we extend the\nTATP to higher-order topological systems with disorder-induced quantized corner\ntransports. Our proposed TATPs present new members of the topological pump\nfamily and could be realized with ultracold atoms or photonic waveguides.",
        "positive": "Roton in a few-body dipolar system: We solve numerically exactly the many-body 1D model of bosons interacting via\nshort-range and dipolar forces and moving in the box with periodic boundary\nconditions. We show that the lowest energy states with fixed total momentum can\nbe smoothly transformed from the typical states of collective character to\nstates resembling single particle excitations. In particular, we identify the\ncelebrated roton state. The smooth transition is realized by simultaneous\ntuning short-range interactions and adjusting a trap geometry. With our methods\nwe study the weakly interacting regime as well as the regime beyond the range\nof validity of the Bogoliubov approximation."
    },
    {
        "anchor": "Large-$N$ properties of a non-ideal Bose gas: We rigorously discuss the large-$N$ thermodynamics of a Bose gas with a\nshort-range two-body potential. Considering the system as a mixture of $N$\nidentical components with symmetrical interaction we calculated numerically the\ntemperature dependence of the leading-order corrections to the depletion of\nBose-Einstein condensate and to the isothermal compressibility.",
        "positive": "One-dimensional model of chiral fermions with Feshbach resonant\n  interactions: We study a model of two species of one-dimensional linearly dispersing\nfermions interacting via an s-wave Feshbach resonance at zero temperature.\nWhile this model is known to be integrable, it possesses novel features that\nhave not previously been investigated. Here, we present an exact solution based\non the coordinate Bethe Ansatz. In the limit of infinite resonance strength,\nwhich we term the strongly interacting limit, the two species of fermions\nbehave as free Fermi gases. In the limit of infinitely weak resonance, or the\nweakly interacting limit, the gases can be in different phases depending on the\ndetuning, the relative velocities of the particles, and the particle densities.\nWhen the molecule moves faster or slower than both species of atoms, the atomic\nvelocities get renormalized and the atoms may even become non-chiral. On the\nother hand, when the molecular velocity is between that of the atoms, the\nsystem may behave like a weakly interacting Lieb-Liniger gas."
    },
    {
        "anchor": "Symmetry breaking in the collisions of double channel BEC solitons: We investigate an attractive Bose-Einstein condensate in two coupled one\ndimensional channels. In this system a stable double channel soliton can be\nformed. It is symmetric for small interaction parameters and asymmetric for\nlarge ones. We study this symmetry breaking phenomenon in detail. Next, we\ninvestigate the dynamics of symmetric double channel soliton collisions. For\nsufficiently strong interactions we observe spontaneous symmetry breaking\nduring the collision. Approximate considerations based on two different\nmethods, Bogoliubov and variational, are used to describe this effect. The\nresults are compatible.",
        "positive": "Quantum interferometry at zero and finite temperature with two-mode\n  bosonic Josephson junctions: We analyze phase interferometry realized with a bosonic Josephson junction\nmade of trapped dilute and ultracold atoms. By using a suitable phase\nsensitivity indicator we study the zero temperature junction states useful to\nachieve sub shot-noise precisions. Sub shot-noise phase shift sensitivities can\nbe reached even at finite temperature under a suitable choice of the junction\nstate. We infer a scaling law in terms of the size system (that is, the number\nof particles) for the temperature at which the shot-noise limit is not overcome\nanymore"
    },
    {
        "anchor": "Rayleigh-Taylor instability and mushroom-pattern formation in a\n  two-component Bose-Einstein condensate: The Rayleigh-Taylor instability at the interface in an immiscible\ntwo-component Bose-Einstein condensate is investigated using the mean-field and\nBogoliubov theories. Rayleigh-Taylor fingers are found to grow from the\ninterface and mushroom patterns are formed. Quantized vortex rings and vortex\nlines are then generated around the mushrooms. The Rayleigh-Taylor instability\nand mushroom-pattern formation can be observed in a trapped system.",
        "positive": "Tetramers of two heavy and two light bosons: This article considers the bound states of two heavy and two light bosons,\nwhen a short-range force attracts the bosons of different mass, and a\nshort-range force repel the light bosons. The existence of such four-body bound\nstates results from the competition between these two forces. For a given\nstrength of the attraction, the critical strength of the repulsion necessary to\nunbind the four particles is calculated. This study is motivated by the\nexperimental realisation of impurity atoms immersed in an atomic Bose-Einstein\ncondensate, and aims at determining in which regime only one boson contributes\nto binding two impurities."
    },
    {
        "anchor": "Resonant dynamics of strongly interacting SU($n$) fermionic atoms in a\n  synthetic flux ladder: We theoretically study the dynamics of $n$-level spin-orbit coupled\nalkaline-earth fermionic atoms with SU($n$) symmetric interactions. We consider\nthree dimensional lattices with tunneling along one dimension, and the internal\nlevels treated as a synthetic dimension, realizing an $n$-leg flux ladder.\nLaser driving is used to couple the internal levels and to induce an effective\nmagnetic flux through the ladder. We focus on the dense and strongly\ninteracting regime, where in the absence of flux the system behaves as a Mott\ninsulator with suppressed motional dynamics. At integer and fractional ratios\nof the laser Rabi frequency to the onsite interactions, the system exhibits\nresonant features in the dynamics. These resonances occur when interactions\nhelp overcome kinetic constraints upon the tunneling of atoms, thus enabling\nmotion. Different resonances allow for the development of complex chiral\ncurrent patterns. The resonances resemble the ones appearing in the\nlongitudinal Hall resistance when the magnetic field is varied. We characterize\nthe dynamics by studying the system's long-time relaxation behavior as a\nfunction of flux, number of internal levels $n$, and interaction strength. We\nobserve a series of non-trivial pre-thermal plateaus caused by the emergence of\nresonant processes at successive orders in perturbation theory. We discuss\nprotocols to observe the predicted phenomena under current experimental\nconditions.",
        "positive": "Tunneling Time of Bose-Einstein Condensates on Real Time Stochastic\n  Approach: We study tunneling processes of Bose-Einstein condensate (BEC) on the real\ntime stochastic approach and reveal some properties of their tunneling time. An\nimportant result is that the tunneling time decreases as the repulsive\ninteratomic interaction becomes stronger. Furthermore, the tunneling time in a\nstrong interaction region is not much affected by the potential height and is\nrepresented by an almost constant function. We also obtain the other related\ntimes such as the hesitating and interaction ones and investigate their\ndependence on the interaction strength. Finally, we calculate the mean arrival\ntime of BEC wave packet and show the large displacement of its peak position."
    },
    {
        "anchor": "Error estimates and specification parameters for functional\n  renormalization: We present a strategy for estimating the error of truncated functional flow\nequations. While the basic functional renormalization group equation is exact,\napproximated solutions by means of truncations do not only depend on the choice\nof the retained information, but also on the precise definition of the\ntruncation. Therefore, results depend on specification parameters that can be\nused to quantify the error of a given truncation. We demonstrate this for the\nBCS-BEC crossover in ultracold atoms. Within a simple truncation the precise\ndefinition of the frequency dependence of the truncated propagator affects the\nresults, indicating a shortcoming of the choice of a frequency independent\ncutoff function.",
        "positive": "Thermalization of a weakly interacting Bose gas in a disordered trap: Previously we numerically showed that thermalization can occur in an\noscillating Bose-Einstein condensate (BEC) with a disordered harmonic trap when\nhealing length $\\xi$ of the condensate is shorter than the correlation length\n$\\sigma_{D}$ of the disorder [see, for example, the experiment reported in\nPhys. Rev. A \\textbf{82}, 033603 (2010)]. In this work, we investigate the\nweakly interacting or Anderson localization regime $\\xi>\\sigma_{D}$ and show\nthat the oscillating BEC can also exhibit a relaxation process from\nnonequilibrium to equilibrium. In such an isolated quantum system, energy and\nparticle number are conserved and the irreversible evolution towards\nthermodynamic equilibrium is induced by the disorder. The thermodynamic\nequilibrium is evidenced by the maximized entropy $S\\left[n_{k}\\right]$ in\nwhich the waveaction spectrum $n_{k}$ follows the Rayleigh-Jeans distribution.\nBesides, unlike a monotonic irreversible process of thermalization to\nequilibrium, the Fermi-Pasta-Ulam-Tsingou recurrence arises in this system,\nmanifested by the oscillation of the non-equilibrium entropy."
    },
    {
        "anchor": "Formation of stripes in a mixed-dimensional cold-atom Fermi-Hubbard\n  system: The relation between d-wave superconductivity and stripes is fundamental to\nthe understanding of ordered phases in cuprates. While experimentally both\nphases are found in close proximity, numerical studies on the related\nFermi-Hubbard model have long been investigating whether stripes precede,\ncompete or coexist with superconductivity. Such stripes are characterised by\ninterleaved charge and spin density wave ordering where fluctuating lines of\ndopants separate domains of opposite antiferromagnetic order. Here we show\nfirst signatures of stripes in a cold-atom Fermi-Hubbard quantum simulator. By\nengineering a mixed-dimensional system, we increase their typical energy scales\nto the spin exchange energy, enabling us to access the interesting crossover\ntemperature regime where stripes begin to form. We observe extended, attractive\ncorrelations between hole dopants and find an increased probability to form\nlarger structures akin to stripes. In the spin sector, we study correlation\nfunctions up to third order and find results consistent with stripe formation.\nThese higher-order correlation measurements pave the way towards an improved\nmicroscopic understanding of the emergent properties of stripes and their\nrelation to other competing phases. More generally, our approach has direct\nrelevance for newly discovered high-temperature superconducting materials in\nwhich mixed dimensions play an essential role.",
        "positive": "Feshbach Resonance in a Tight-Binding Model: The physics of Feshbach resonance is analyzed using an analytic expression\nfor the $s$-wave scattering phase-shift and the scattering length $a$ which we\nderive within a two-channel tight-binding model. Employing a unified treatment\nof bound states and resonances in terms of the Jost function, it is shown that\nfor strong inter-channel coupling, Feshbach resonance can occur even when the\nclosed channel does not have a bound state. This may extend the range of\nultra-cold atomic systems that can be manipulated by Feshbach resonance. The\ndependence of the sign of $a$ on the coupling strength in the unitary limit is\nelucidated. As a by-product, analytic expressions are derived for the\nbackground scattering length, the external magnetic field at which resonance\noccurs, and the energy shift $\\varepsilon-\\varepsilon_B$, where $\\varepsilon$\nis the scattering energy and $\\varepsilon_B$ is the bound state energy in the\nclosed channel (when there is one)."
    },
    {
        "anchor": "Poincar\u00e9 crystal on the one-dimensional lattice: In this paper, we develop the quantum theory of particles that has discrete\nPoincar\\'{e} symmetry on the one-dimensional Bravais lattice. We review the\nrecently discovered discrete Lorentz symmetry, which is the unique Lorentz\nsymmetry that coexists with the discrete space translational symmetry on a\nBravais lattice. The discrete Lorentz transformations and spacetime\ntranslations form the discrete Poincar\\'{e} group, which are represented by\nunitary operators in a quantum theory. We find the conditions for the existence\nof representation, which are expressed as the congruence relation between\nquasi-momentum and quasi-energy. We then build the Lorentz-invariant many-body\ntheory of indistinguishable particles by expressing both the unitary operators\nand Floquet Hamiltonians in terms of the field operators. Some typical\nHamiltonians include the long-range hopping which fluctuates as the distance\nbetween sites increases. We calculate the Green's functions of the lattice\ntheory. The spacetime points where the Green's function is nonzero display a\nlattice structure. During the propagation, the particles stay localized on a\nsingle or a few sites to preserve the Lorentz symmetry.",
        "positive": "Two-superfluid Model of Two-component Bose-Einstein Condensates; First\n  Sound and Second Sound: Superfluid $^4$He at a finite temperature is described by the two-fluid model\nwith the normal fluid component and the superfluid component.We formulate the\ntwo-fluid model for two-component BECs, namely two-superfluid model, starting\nfrom the coupled Gross-Pitaevskii equations.The two-superfluid model well\ncorresponds to the two-fluid model in superfluid $^4$He.In a special condition,\nthe two sound modes in the two-superfluid model behave like first and second\nsounds in the two-fluid model of superfluid $^4$He."
    },
    {
        "anchor": "Universal impurity-induced bound state in topological superfluids: We predict a universal mid-gap bound state in topological superfluids,\ninduced by either non-magnetic or magnetic impurities in the strong scattering\nlimit. This universal state is similar to the lowest-energy Caroli-de\nGennes-Martricon bound state in a vortex core, but is bound to localized\nimpurities. We argue that the observation of such a universal bound state can\nbe a clear signature for identifying topological superfluids. We theoretically\nexamine our argument for a spin-orbit coupled ultracold atomic Fermi gas\ntrapped in a two-dimensional harmonic potential, by performing extensive\nself-consistent calculations within the mean-field Bogoliubov-de Gennes theory.\nA realistic scenario for observing universal bound state in ultracold $^{40}$K\natoms is proposed.",
        "positive": "Cavity Optomechanics with Ultra Cold Atoms in Synthetic Abelian and\n  Non-Abelian Gauge Field: In this article we present a pedagogical discussion of some of the\noptomechanical properties of a high finesse cavity loaded with ultracold atoms\nin laser induced synthetic gauge fields of different types. Essentially, the\nsubject matter of this article is an amalgam of two sub-fields of atomic\nmolecular and optical (AMO) physics namely, the cavity optomechanics with\nultracold atoms and ultracold atoms in synthetic gauge field. After providing a\nbrief introduction to either of these fields we shall show how and what\nproperties of these trapped ultracold atoms can be studied by looking at the\ncavity (optomechanical or transmission) spectrum. In presence of abelian\nsynthetic gauge field we discuss the cold-atom analogue of Shubnikov de Haas\noscillation and its detection through cavity spectrum. Then, in the presence of\na non-abelian synthetic gauge field (spin-orbit coupling), we see when the\nelectromagnetic field inside the cavity is quantized, it provides a quantum\noptical lattice for the atoms, leading to the formation of different quantum\nmagnetic phases. We also discuss how these phases can be explored by studying\nthe cavity transmission spectrum."
    },
    {
        "anchor": "Flow-Induced Charge Modulation in Superfluid Atomic Fermions Loaded into\n  an Optical Kagome Lattice: We study the superfluid state of atomic fermions in a tunable optical kagome\nlattice motivated by recent experiments. We show that imposed superflow induces\nspatial modulations in the density and order parameter of the pair condensate\nand leads to a charge modulated superfluid state analogous to a supersolid\nstate. The spatial modulations in the superfluid emerge due to the geometric\neffect of the kagome lattice that introduces anisotropy in hopping amplitudes\nof fermion pairs in the presence of superflow. We also study superflow\ninstabilities and find that the critical current limited by the dynamical\ninstability is quite enhanced due to the large density of states associated\nwith the flatband. The charge modulated superfluid state can sustain high\ntemperatures close to the transition temperature that is also enhanced due to\nthe flatband, and is therefore realizable in experiments.",
        "positive": "Fragmented Condensate in a Two-Component Bose Gas with $p$-wave\n  Interactions: In this Letter, we discuss the effects of $p$-wave attractive interaction in\na spin-$1/2$ Bose gas. With a repulsive $s$-wave background interaction, we\nshow that for weak $p$-wave attraction, one obtains a standard Bose-Einstein\ncondensate at zero momentum with spins fully polarized. Upon increasing the\n$p$-wave attraction, a fragmented condensate state with singlet pair formation\nand $p$-wave correlation emerges. We determine the transition point and\ninvestigate the properties of the fragmented condensate using an ansatz wave\nfunction. We construct the relevant Gross-Pitaevskii equations for the\nfragmented condensate and show that the sound velocities are anisotropic and\nmay vanish in specific directions. Based on the many-body wave function, we\nalso discuss the low-energy spin excitations of the system."
    },
    {
        "anchor": "Tunneling of polarized fermions in 3D double wells: We study the tunneling of a spin polarized Fermi gas in a three-dimensional\ndouble well potential, focusing on the time dynamics starting from an initial\nstate in which there is an imbalance in the number of particles in the two\nwells. Although fermions in different doublets of the double well tunnel with\ndifferent frequencies, we point out that (incoherent) oscillations of a large\nnumber of particles can arise, as a consequence of the presence of transverse\ndegrees of freedom. Estimates of the doublet structure and of the occupation of\ntransverse eigenstates for a realistic experimental setup are provided.",
        "positive": "Electronic properties and polaronic dynamics of semi-Dirac system within\n  ladder approximation: We investigate the electronic properties of the semi-Dirac system and its\npolaronic dynamics when coupled with a fermi bath with quadratic dispersion.\nThe electronic anisotropic transport properties and the semiclassical dynamics\nof the semi-Dirac system are studied, including the density-of-states,\nconductivity, transport relaxation rate, specific heat, electrical current\ndenity, and free energy. The attractive polaron formed as the semi-Dirac\nimpurity dressed with the particle-hole excitations in a two-dimensional system\nare studied both analytically and numerically. The pair propagator,\nself-energy, spectral function are being detailly calculated and discussed."
    },
    {
        "anchor": "Quantum Mechanics with a Momentum-Space Artificial Magnetic Field: The Berry curvature is a geometrical property of an energy band which acts as\na momentum space magnetic field in the effective Hamiltonian describing\nsingle-particle quantum dynamics. We show how this perspective may be exploited\nto study systems directly relevant to ultracold gases and photonics. Given the\nexchanged roles of momentum and position, we demonstrate that the global\ntopology of momentum space is crucially important. We propose an experiment to\nstudy the Harper-Hofstadter Hamiltonian with a harmonic trap that will\nillustrate the advantages of this approach and that will also constitute the\nfirst realization of magnetism on a torus.",
        "positive": "Emergence of Classical Rotation in Superfluid Bose-Einstein Condensates: Phase transitions can modify quantum behaviour on mesoscopic scales and give\naccess to new and unusual quantum dynamics. Here we investigate the superfluid\nproperties of a rotating two-component Bose--Einstein condensate as a function\nof changes in the interaction energy and in particular through the phase\ntransition from miscibility to immiscibility. We show that the breaking of one\nof the hallmarks of superfluid flow, namely the quantisation condition on\ncirculation, is continuous throughout an azimuthal phase separation process and\ndisplays intriguing density dynamics. We find that the resulting currents are\nstable for long times and possess a phase boundary that exhibits classical\nsolid body rotation, despite the quantum nature of superfluid flow. To support\nthis co-existence of classical and quantum behaviour the system develops a\nunique velocity flow profile, which includes unusual radial flow in regions\nnear the phase boundary."
    },
    {
        "anchor": "Nonsmooth and level-resolved dynamics illustrated with the tight binding\n  model: We point out that in the first order time-dependent perturbation theory, the\ntransition probability may behave nonsmoothly in time and have kinks\nperiodically. Moreover, the detailed temporal evolution can be sensitive to the\nexact locations of the eigenvalues in the continuum spectrum, in contrast to\ncoarse-graining ideas. Underlying this nonsmooth and level-resolved dynamics is\na simple equality about the sinc function $\\sinc x \\equiv \\sin x / x$. These\nphysical effects appear in many systems with approximately equally spaced\nspectra, and is also robust for larger-amplitude coupling beyond the domain of\nperturbation theory. We use a one-dimensional periodically driven tight-binding\nmodel to illustrate these effects, both within and outside the perturbative\nregime.",
        "positive": "Fluctuation-induced and symmetry-prohibited metastabilities in spinor\n  Bose-Einstein condensates: Spinor Bose-Einstein condensates provide a unique example in which the\nBogoliubov theory fails to describe the metastability associated with\nfirst-order quantum phase transitions. This problem is resolved by developing\nthe spinor Beliaev theory which takes account of quantum fluctuations of the\ncondensate. It is these fluctuations that generate terms of higher than the\nfourth order in the order-parameter field which are needed for the first-order\nphase transitions. Besides the conventional first-order phase transitions which\nare accompanied by metastable states, we find a class of first-order phase\ntransitions which are not accompanied by metastable states. The absence of\nmetastability in these phase transitions holds to all orders of approximation\nsince the metastability is prohibited by the symmetry of the Hamiltonian at the\nphase boundary. Finally, the possibility of macroscopic quantum tunneling from\na metastable state to the ground state is discussed."
    },
    {
        "anchor": "Strongly correlated phases in rapidly rotating Bose gases: We consider a system of trapped spinless bosons interacting with a repulsive\npotential and subject to rotation. In the limit of rapid rotation and small\nscattering length, we rigorously show that the ground state energy converges to\nthat of a simplified model Hamiltonian with contact interaction projected onto\nthe Lowest Landau Level. This effective Hamiltonian models the bosonic analogue\nof the Fractional Quantum Hall Effect (FQHE). For a fixed number of particles,\nwe also prove convergence of states; in particular, in a certain regime we show\nconvergence towards the bosonic Laughlin wavefunction. This is the first\nrigorous justification of the effective FQHE Hamiltonian for rapidly rotating\nBose gases. We review previous results on this effective Hamiltonian and\noutline open problems.",
        "positive": "Quasiparticle decay in a one-dimensional Bose-Fermi mixture: In a one-dimensional weakly interacting Bose-Fermi mixture one branch of\nelementary excitations is well described by the Bogoliubov spectrum. Here we\nuse the microscopic theory to study the decay of such quasiparticle\nexcitations. The main scattering process which leads to their decay is the\nbackscattering of a Bogoliubov quasiparticle off the Fermi sea, where a\nparticle-hole pair is excited. For a low-momentum quasiparticle (phonon) of\nmomentum $q$, we find that the decay rate scales as $q^3$ provided $q$ is\nsmaller than the Fermi momentum $k_F$, while in the opposite case the decay\nbehaves as $q^2$. If the ratio of the masses of fermions and bosons equals to\nthe ratio of the boson-fermion and the boson-boson interaction strengths, the\ndecay rate changes dramatically. It scales as $q^7$ for $q<k_F$ while we find\n$q^6$ scaling at $q>k_F$. For a high momentum Bogoliubov quasiparticle, we find\na constant decay rate for $q<k_F$, while it scales as $1/q$ for $q>k_F$. We\nalso find an analytic expression for the decay rate in the crossover region\nbetween low and high momenta. The decay rate is a continuous, but nonanalytic\nfunction of the momentum at $q=k_F$. In the special case when the parameters of\nour system correspond to the integrable model, we observe that the decay rate\nvanishes."
    },
    {
        "anchor": "Fermi super-Tonks-Girardeau state for attractive Fermi gases in an\n  optical lattice: We demonstrate that a kind of highly excited state of strongly attractive\nHubbard model, named of Fermi super-Tonks-Girardeau state, can be realized in\nthe spin-1/2 Fermi optical lattice system by a sudden switch of interaction\nfrom the strongly repulsive regime to the strongly attractive regime. In\ncontrast to the ground state of the attractive Hubbard model, such a state is\nthe lowest scattering state with no pairing between attractive fermions. With\nthe aid of Bethe-ansatz method, we calculate energies of both the Fermi\nTonks-Girardeau gas and the Fermi super-Tonks-Girardeau state of spin-1/2\nultracold fermions and show that both energies approach to the same limit as\nthe strength of the interaction goes to infinity. By exactly solving the quench\ndynamics of the Hubbard model, we demonstrate that the Fermi\nsuper-Tonks-Girardeau state can be transferred from the initial repulsive\nground state very efficiently. This allows the experimental study of properties\nof Fermi super-Tonks-Girardeau gas in optical lattices.",
        "positive": "Observation of Half Quantum Vortices in an Exciton-Polariton Condensate: Singly quantized vortices have been already observed in many systems\nincluding the superfluid helium, Bose Einstein condensates of dilute atomic\ngases, and condensates of exciton polaritons in the solid state. Two\ndimensional superfluids carrying spin are expected to demonstrate a different\ntype of elementary excitations referred to as half quantum vortices\ncharacterized by a pi rotation of the phase and a pi rotation of the\npolarization vector when circumventing the vortex core. We detect half quantum\nvortices in an exciton-polariton condensate by means of polarization resolved\ninterferometry, real space spectroscopy and phase imaging. Half quantum\nvortices coexist with single quantum vortices in our sample."
    },
    {
        "anchor": "Stable dilute supersolid of two-dimensional dipolar bosons: We consider two-dimensional bosonic dipoles oriented perpendicularly to the\nplane. On top of the usual two-body contact and long-range dipolar interactions\nwe add a contact three-body repulsion as expected, in particular, for dipoles\nin the bilayer geometry with tunneling. The three-body repulsion is crucial for\nstabilizing the system, and we show that our model allows for stable continuous\nspace supersolid states in the dilute regime and calculate the zero-temperature\nphase diagram.",
        "positive": "Vortex structures of a two-component BEC for large anisotropies: We calculate the vortex structures of an elongated two-component\nBose-Einstein condensate. We study how these structures depend on the\nintra-component and inter-component interaction strengths. We present analytic\nand numeric results respectively at weak and strong interactions; finding\nlattices with different interlocking geometries: triangular, square,\nrectangular and double-core."
    },
    {
        "anchor": "Rotating a Bose-Einstein condensate by shaking an anharmonic\n  axisymmetric magnetic potential: We present an experimental method for rotating a Bose-Einstein condensate\ntrapped in an axisymmetric magnetic potential. This method is based on the\nanharmonicity of the trapping potential, which couples the center-of-mass\nmotion of the condensate to its internal motion. By circularly shaking the\ntrapping potential, we generate a circular center-of-mass motion of the\ncondensate around the trap center. The circulating condensate undergoes\nrotating shape deformation and eventually relaxes into a rotating condensate\nwith a vortex lattice. We discuss the vortex nucleation mechanism and in\nparticular, the role of the thermal cloud in the relaxation process. Finally,\nwe investigate the dependence of the vortex nucleation on the elliptical\npolarization of the trap shaking. The response of the condensate is asymmetric\nwith respect to the sign of the shaking polarization, demonstrating the gauge\nfield effect due to the spin texture of the condensate in the magnetic\npotential.",
        "positive": "First-order Bose-Einstein condensation with three-body interacting\n  bosons: Bose-Einstein condensation, observed in either strongly interacting liquid\nhelium or weakly interacting atomic Bose gases, is widely known to be a\nsecond-order phase transition. Here, we predict a first-order Bose-Einstein\ncondensation in a cloud of harmonically trapped bosons interacting with both\nattractive two-body interaction and repulsive three-body interaction,\ncharacterized respectively by an $s$-wave scattering length $a<0$ and a\nthree-body scattering hypervolume $D>0$. It happens when the harmonic trapping\npotential is weak, so with increasing temperature the system changes from a\nlow-temperature liquid-like quantum droplet to a normal gas, and therefore\nexperiences a first-order liquid-to-gas transition. At large trapping\npotential, however, the quantum droplet can first turn into a superfluid gas,\nrendering the condensation transition occurred later from a superfluid gas to a\nnormal gas smooth. We determine a rich phase diagram and show the existence of\na tri-critical point, where the three phases - quantum droplet, superfluid gas\nand normal gas - meet together. We argue that an ensemble of spin-polarized\ntritium atoms could be a promising candidate to observe the predicted\nfirst-order Bose-Einstein condensation, across which the condensate fraction or\ncentral condensate density jumps to zero and the surface-mode frequencies\ndiverge."
    },
    {
        "anchor": "Collective pairing of resonantly coupled microcavity polaritons: We consider the possible phases of microcavity polaritons tuned near a\nbipolariton Feshbach resonance. We show that, as well as the regular polariton\nsuperfluid phase, a \"molecular\" superfluid exists, with (quasi-)long-range\norder only for pairs of polaritons. We describe the experimental signatures of\nthis state. Using variational approaches we find the phase diagram (critical\ntemperature, density and exciton-photon detuning). Unlike ultracold atoms, the\nmolecular superfluid is not inherently unstable, and our phase diagram suggests\nit is attainable in current experiments.",
        "positive": "High-momentum tails as magnetic structure probes for strongly-correlated\n  $SU(\u03ba)$ fermionic mixtures in one-dimensional traps: A universal $k^{-4}$ decay of the large-momentum tails of the momentum\ndistribution, fixed by Tan's contact coefficients, constitutes a direct\nsignature of strong correlations in a short-range interacting quantum gas. Here\nwe consider a repulsive multicomponent Fermi gas under harmonic confinement, as\nin the experiment of Pagano et al. [Nat. Phys. {\\bf 10}, 198 (2014)], realizing\na gas with tunable $SU(\\kappa)$ symmetry. We exploit an exact solution at\ninfinite repulsion to show a direct correspondence between the value of the\nTan's contact for each of the $\\kappa$ components of the gas and the Young\ntableaux for the $S_N$ permutation symmetry group identifying the magnetic\nstructure of the ground-state. This opens a route for the experimental\ndetermination of magnetic configurations in cold atomic gases, employing only\nstandard (spin-resolved) time-of-flight techniques. Combining the exact result\nwith matrix-product-states simulations, we obtain the Tan's contact at all\nvalues of repulsive interactions. We show that a local density approximation\n(LDA) on the Bethe-Ansatz equation of state for the homogeneous mixture is in\nexcellent agreement with the results for the harmonically confined gas. At\nstrong interactions, the LDA predicts a scaling behavior of the Tan's contact.\nThis provides a useful analytical expression for the dependence on the number\nof fermions, number of components and on interaction strength. Moreover, using\na virial approach in the limit of infinite interactions, we show that the\ncontact increases with the temperature and the number of components. At zero\ntemperature, we predict that the weight of the momentum distribution tails\nincreases with interaction strength and the number of components if the\npopulation per component is kept constant. This latter property was\nexperimentally observed in Ref.~[Nat. Phys. {\\bf 10}, 198 (2014)]."
    },
    {
        "anchor": "Traveling Majorana solitons in a one-dimensional spin-orbit coupled\n  Fermi superfluid: We investigate traveling solitons of a one-dimensional spin-orbit coupled\nFermi superfluid in both topologically trivial and non-trivial regimes by\nsolving the static and time-dependent Bogoliubov-de Gennes equations. We find a\ncritical velocity $v_{h}$ for traveling solitons that is much smaller than the\nvalue predicted using the Landau criterion due to the presence of spin-orbit\ncoupling, which strongly upshifts the energy level of the soliton-induced\nAndreev bound states towards the quasi-particle scattering continuum. Above\n$v_{h}$, our time-dependent simulations in harmonic traps indicate that\ntraveling solitons decay by radiating sound waves. In the topological phase, we\npredict the existence of peculiar Majorana solitons, which host two Majorana\nfermions and feature a phase jump of $\\pi$ across the soliton, irrespective of\nthe velocity of travel. These unusual properties of Majorana solitons may open\nan alternative way to manipulate Majorana fermions for fault-tolerant\ntopological quantum computations.",
        "positive": "Localization and criticality in antiblockaded 2D Rydberg atom arrays: Controllable Rydberg atom arrays have provided new insights into fundamental\nproperties of quantum matter both in and out of equilibrium. In this work, we\nstudy the effect of experimentally relevant positional disorder on Rydberg\natoms trapped in a 2D square lattice under anti-blockade (facilitation)\nconditions. We show that the facilitation conditions lead the connectivity\ngraph of a particular subspace of the full Hilbert space to form a 2D Lieb\nlattice, which features a singular flat band. Remarkably, we find three\ndistinct regimes as the disorder strength is varied: a critical regime, a\ndelocalized but nonergodic regime, and a regime with a disorder-induced flat\nband. The critical regime's existence depends crucially upon the singular flat\nband in our model, and is absent in any 1D array or ladder system. We propose\nto use quench dynamics to probe the three different regimes experimentally."
    },
    {
        "anchor": "Drag force on a moving impurity in a spin-orbit coupled Bose-Einstein\n  condensate: We investigate the drag force on a moving impurity in a spin-orbit coupled\nBose-Einstein condensate. We prove rigorously that the superfluid critical\nvelocity is zero when the impurity moves in all but one directions, in contrast\nto the case of liquid helium and superconductor where it is finite in all\ndirections. We also find that when the impurity moves in all directions except\ntwo special ones, the drag force has nonzero transverse component at small\nvelocity. When the velocity becomes large and the states of the upper band are\nalso excited, the transverse force becomes very small due to opposite\ncontributions of the two bands. The characteristics of the superfluid critical\nvelocity and the transverse force are results of the order by disorder\nmechanism in spin-orbit coupled boson systems.",
        "positive": "Fermi Gases in the Two-Dimensional to Quasi-Two-Dimensional Crossover: We tune the dimensionality of pancake-shaped strongly-interacting $^6$Li\nFermi gas clouds from two-dimensional (2D) to quasi-2D, by controlling the\nratio of the radial Fermi energy $E_F$ to the harmonic oscillator energy\n$h\\nu_z$ in the tightly confined direction. In the 2D regime, where\n$E_F<<h\\nu_z$, the measured radio frequency resonance spectra are in agreement\nwith 2D-BCS theory. In the quasi-2D regime, where $E_F\\simeq h\\nu_z$, the\nmeasured spectra deviate significantly from 2D-BCS theory. For both regimes,\nthe measured cloud radii disagree with 2D-BCS mean field theory, but agree\napproximately with predictions using a free energy derived from the\nBethe-Goldstone equation."
    },
    {
        "anchor": "Phase structure of the interacting Su-Schrieffer-Heeger model and the\n  relationship with the Gross-Neveu model on lattice: The $N$-flavor interacting Su-Schrieffer-Heeger (i-SSH) model realizable in\ncold-atoms in an optical lattice is studied. We clarify the relationship\nbetween the i-SSH model and the Chiral-Gross-Neveu-Wilson (CGNW) model.\nFollowing the previous study of the CGNW model in the high-energy physics\ncommunity, the groundstate phases of the i-SSH model are investigated and\ninterpreted from the view of the phases of the CGNW model. The interaction\neffect on the i-SSH model, belonging to the topological BDI class, is grasped\nby following the view of the dynamical breakdown of chiral symmetry in the CGNW\nmodel. Furthermore, we compare the large-$N$ groundstate phase diagram with\nthat of the $N=1$ case obtained by exact diagonalization and then propose a\ntable-top cold-atom quantum simulator to test the model.",
        "positive": "Out-of-equilibrium dynamics of a Bose Einstein condensate in a\n  periodically driven band system: We report on the out-of-equilibrium dynamics of a Bose-Einstein condensate\n(BEC) placed in an optical lattice whose phase is suddenly modulated. The\nfrequency and the amplitude of modulation are chosen to ensure a negative\nrenormalized tunneling rate. Under these conditions, staggered states are\nnucleated by a spontaneous four wave mixing mechanism. The nucleation time is\nexperimentally studied as a function of the renormalized tunnel rate, the\natomic density and the modulation frequency. Our results are quantitatively\nwell accounted for by a Truncated Wigner approach and reveal the nucleation of\ngap solitons after the quench. We discuss the role of quantum versus thermal\nfluctuations in the nucleation process and experimentally address the limit of\nthe effective Hamiltonian approach."
    },
    {
        "anchor": "Resonantly Interacting Fermi-Fermi Mixture of $^{161}$Dy and $^{40}$K: We report on the realization of a Fermi-Fermi mixture of ultracold atoms that\ncombines mass imbalance, tunability, and collisional stability. In an optically\ntrapped sample of $^{161}$Dy and $^{40}$K, we identify a broad Feshbach\nresonance centered at a magnetic field of $217\\,$G. Hydrodynamic expansion\nprofiles in the resonant interaction regime reveal a bimodal behavior resulting\nfrom mass imbalance. Lifetime studies on resonance show a suppression of\ninelastic few-body processes by orders of magnitude, which we interpret as a\nconsequence of the fermionic nature of our system. The resonant mixture opens\nup intriguing perspectives for studies on novel states of strongly correlated\nfermions with mass imbalance.",
        "positive": "Quantum correlations and spatial localization in one-dimensional\n  ultracold bosonic mixtures: We present the complete phase diagram for one-dimensional binary mixtures of\nbosonic ultracold atomic gases in a harmonic trap. We obtain exact results with\ndirect numerical diagonalization for small number of atoms, which permits us to\nquantify quantum many-body correlations. The quantum Monte Carlo method is used\nto calculate energies and density profiles for larger system sizes. We study\nthe system properties for a wide range of interaction parameters. For the\nextreme values of these parameters, different correlation limits can be\nidentified, where the correlations are either weak or strong. We investigate in\ndetail how the correlation evolve between the limits. For balanced mixtures in\nthe number of atoms in each species, the transition between the different\nlimits involves sophisticated changes in the one- and two-body correlations.\nParticularly, we quantify the entanglement between the two components by means\nof the von Neumann entropy. We show that the limits equally exist when the\nnumber of atoms is increased, for balanced mixtures. Also, the changes in the\ncorrelations along the transitions among these limits are qualitatively\nsimilar. We also show that, for imbalanced mixtures, the same limits with\nsimilar transitions exist. Finally, for strongly imbalanced systems, only two\nlimits survive, i.e., a miscible limit and a phase-separated one, resembling\nthose expected with a mean-field approach."
    },
    {
        "anchor": "Motional Coherence of Fermions Immersed in a Bose Gas: We prepare a superposition of two motional states by addressing lithium atoms\nimmersed in a Bose-Einstein condensate of sodium with a species-selective\npotential. The evolution of the superposition state is characterized by the\npopulations of the constituent states as well as their coherence. The latter we\nextract employing a novel scheme analogous to the spin-echo technique.\nComparing the results directly to measurements on freely-evolving fermions\nallows us to isolate the decoherence effects induced by the bath. In our\nsystem, the decoherence time is close to the maximal possible value since the\ndecoherence is dominated by population relaxation processes. The measured data\nare in good agreement with a theoretical model based on Fermi's golden rule.",
        "positive": "Coupled Atomic Wires in a Synthetic Magnetic Field: We propose and study systems of coupled atomic wires in a perpendicular\nsynthetic magnetic field as a platform to realize exotic phases of quantum\nmatter. This includes (fractional) quantum Hall states in arrays of many wires\ninspired by the pioneering work [Kane et al. PRL {\\bf{88}}, 036401 (2002)], as\nwell as Meissner phases and Vortex phases in double-wires. With one continuous\nand one discrete spatial dimension, the proposed setup naturally complements\nrecently realized discrete counterparts, i.e. the Harper-Hofstadter model and\nthe two leg flux ladder, respectively. We present both an in-depth theoretical\nstudy and a detailed experimental proposal to make the unique properties of the\nsemi-continuous Harper-Hofstadter model accessible with cold atom experiments.\nFor the minimal setup of a double-wire, we explore how a sub-wavelength spacing\nof the wires can be implemented. This construction increases the relevant\nenergy scales by at least an order of magnitude compared to ordinary optical\nlattices, thus rendering subtle many-body phenomena such as Lifshitz\ntransitions in Fermi gases observable in an experimentally realistic parameter\nregime. For arrays of many wires, we discuss the emergence of Chern bands with\nreadily tunable flatness of the dispersion and show how fractional quantum Hall\nstates can be stabilized in such systems. Using for the creation of optical\npotentials Laguerre-Gauss beams that carry orbital angular momentum, we detail\nhow the coupled atomic wire setups can be realized in non-planar geometries\nsuch as cylinders, discs, and tori."
    },
    {
        "anchor": "Self-consistent time-dependent harmonic approximation for the\n  sine-Gordon model out of equilibrium: We derive a self-consistent time-dependent harmonic approximation for the\nquantum sine-Gordon model out of equilibrium and apply the method to the\ndynamics of tunnel-coupled one-dimensional Bose gases. We determine the time\nevolution of experimentally relevant observables and in particular derive\nresults for the probability distribution of subsystem phase fluctuations. We\ninvestigate the regime of validity of the approximation by applying it to the\nsimpler case of a nonlinear harmonic oscillator, for which numerically exact\nresults are available. We complement our self-consistent harmonic approximation\nby exact results at the free fermion point of the sine-Gordon model.",
        "positive": "Thermodynamics, contact and density profiles of the repulsive\n  Gaudin-Yang model: We address the problem of computing the thermodynamic properties of the\nrepulsive one-dimensional two-component Fermi gas with contact interaction,\nalso known as the Gaudin-Yang model. Using a specific lattice embedding and the\nquantum transfer matrix we derive an exact system of only two nonlinear\nintegral equations for the thermodynamics of the homogeneous model which is\nvalid for all temperatures and values of the chemical potential, magnetic field\nand coupling strength. This system allows for an easy and extremely accurate\ncalculation of thermodynamic properties circumventing the difficulties\nassociated with the truncation of the thermodynamic Bethe ansatz system of\nequations. We present extensive results for the densities, polarization,\nmagnetic susceptibility, specific heat, interaction energy, Tan contact and\nlocal correlation function of opposite spins. Our results show that at low and\nintermediate temperatures the experimentally accessible contact is a\nnon-monotonic function of the coupling strength. As a function of the\ntemperature the contact presents a pronounced local minimum in the\nTonks-Girardeau regime which signals an abrupt change of the momentum\ndistribution in a small interval of temperature. The density profiles of the\nsystem in the presence of a harmonic trapping potential are computed using the\nexact solution of the homogeneous model coupled with the local density\napproximation. We find that at finite temperature the density profile presents\na double shell structure (partially polarized center and fully polarized wings)\nonly when the polarization in the center of the trap is above a critical value\nwhich is monotonically increasing with temperature."
    },
    {
        "anchor": "Fluctuations of spinor Bose-Einstein condensates: We develop theory for fluctuations in atom number and spin within\nfinite-sized cells of a spinor Bose-Einstein condensate. This theory provides a\nmodel of measurements that can be performed in current experiments using finite\nresolution in situ imaging. We develop analytic results for quantum and\nthermodynamic limits of the fluctuations and apply our theory to the four\nequilibrium phases of a spin-1 condensate. We then validate these limits and\nexamine the behaviour over a wide parameter regime using numerical calculations\nspecialised to the case of a spinor condensate confined to be\nquasi-two-dimensional (quasi-2D).",
        "positive": "Self-consistent field theory of polarized BEC: dispersion of collective\n  excitation: We suggest the construction of a set of the quantum hydrodynamics equations\nfor the Bose-Einstein condensate (BEC), where atoms have the electric dipole\nmoment. The contribution of the dipole-dipole interactions (DDI) to the Euler\nequation is obtained. Quantum equations for the evolution of medium\npolarization are derived. Developing mathematical method allows to study effect\nof interactions on the evolution of polarization. The developing method can be\napplied to various physical systems in which dynamics is affected by the DDI.\nDerivation of Gross-Pitaevskii equation for polarized particles from the\nquantum hydrodynamics is described. We showed that the Gross-Pitaevskii\nequation appears at condition when all dipoles have the same direction which\ndoes not change in time. Comparison of the equation of the electric dipole\nevolution with the equation of the magnetization evolution is described.\nDispersion of the collective excitations in the dipolar BEC, either affected or\nnot affected by the uniform external electric field, is considered using our\nmethod. We show that the evolution of polarization in the BEC leads to the\nformation of a novel type of the collective excitations. Detailed description\nof the dispersion of collective excitations is presented. We also consider the\nprocess of wave generation in the polarized BEC by means of a monoenergetic\nbeam of neutral polarized particles. We compute the possibilities of the\ngeneration of Bogoliubov and polarization modes by the dipole beam."
    },
    {
        "anchor": "Von K\u00e1rm\u00e1n vortex street in a Bose-Einstein condensate: Vortex shedding from an obstacle potential moving in a Bose-Einstein\ncondensate is investigated. Long-lived alternately aligned vortex pairs are\nfound to form in the wake, as for the von K\\'arm\\'an vortex street in classical\nviscous fluids. Various patterns of vortex shedding are systematically studied\nand the drag force on the obstacle is calculated. It is shown that the\nphenomenon can be observed in a trapped system.",
        "positive": "Collapse and revival oscillations as a probe for the tunneling amplitude\n  in an ultra-cold Bose gas: We present a theoretical study of the quantum corrections to the revival time\ndue to finite tunneling in the collapse and revival of matter wave interference\nafter a quantum quench. We study hard-core bosons in a superlattice potential\nand the Bose-Hubbard model by means of exact numerical approaches and\nmean-field theory. We consider systems without and with a trapping potential\npresent. We show that the quantum corrections to the revival time can be used\nto accurately determine the value of the hopping parameter in experiments with\nultracold bosons in optical lattices."
    },
    {
        "anchor": "Bose Einstein condensation and ferromagnetism of low density Bose gas of\n  particles with arbitrary spin: Properties of the ground state and the spectrum of elementary excitations are\ninvestigated for the low density ultracold spinor 3D Bose gas of particles with\narbitrary nonzero spin. Gross-Pitaevskii equations are derived. Within the\nframework of the considering interaction Hamiltonian it is shown that the\nground state spin structure and spin part of the chemical potential is\ndetermined by the renormalized interaction, being defined by the contribution\nof the virtual large momenta. The ferromagnetic structure of the ground state,\nand the equation of the phase, density, and spin dynamics are obtained from\nGross-Pitaevskii equations.",
        "positive": "Spin-Dipole Oscillation and Polarizability of a Binary Bose-Einstein\n  Condensate near the Miscible-Immiscible Phase Transition: We report on the measurement of the spin-dipole (SD) polarizability and of\nthe frequency of the SD oscillation of a two-component Bose-Einstein condensate\nof sodium atoms occupying the $|3^2S_{1/2}, F=1, m_F=\\pm1\\rangle$ hyperfine\nstates. This binary spin-mixture presents the important properties of being, at\nthe same time, fully miscible and rid of the limit set by buoyancy. It is also\ncharacterized by a huge enhancement of the SD polarizability and by the\nconsequent softening of the frequency of the SD oscillation, due to the\nvicinity to the transition to the immiscible phase. The experimental data are\nsuccessfully compared with the predictions of theory."
    },
    {
        "anchor": "Real-Time Dynamics of an Impurity in an Ideal Bose Gas in a Trap: We investigate the behavior of a harmonically trapped system consisting of an\nimpurity in a dilute ideal Bose gas after the boson-impurity interaction is\nsuddenly switched on. As theoretical framework, we use a field theory approach\nin the space-time domain within the T-matrix approximation. We establish the\nform of the corresponding T-matrix and address the dynamical properties of the\nsystem. As a numerical application, we consider a simple system of a weakly\ninteracting impurity in one dimension where the interaction leads to\noscillations of the impurity density. Moreover, we show that the amplitude of\nthe oscillations can be driven by periodically switching the interaction on and\noff.",
        "positive": "Quench Dynamics of Finite Bosonic Ensembles in Optical Lattices with\n  Spatially Modulated Interactions: The nonequilibrium quantum dynamics of few boson ensembles which experience a\nspatially modulated interaction strength and are confined in finite optical\nlattices is investigated. We utilize a cosinusoidal spatially modulated\neffective interaction strength which is characterized by its wavevector,\ninhomogeneity amplitude, interaction offset and a phase. Performing quenches\neither on the wavevector or the phase of the interaction profile an enhanced\nimbalance of the interatomic repulsion between distinct spatial regions of the\nlattice is induced. Following both quench protocols triggers various tunneling\nchannels and a rich excitation dynamics consisting of a breathing and a cradle\nmode. All modes are shown to be amplified for increasing inhomogeneity\namplitude of the interaction strength. Especially the phase quench induces a\ndirectional transport enabling us to discern energetically, otherwise,\ndegenerate tunneling pathways. Moreover, a periodic population transfer between\ndistinct momenta for quenches of increasing wavevector is observed, while a\ndirected occupation of higher momenta can be achieved following a phase quench.\nFinally, during the evolution regions of partial coherence are revealed between\nthe predominantly occupied wells."
    },
    {
        "anchor": "Probing non-Abelian statistics of Majorana fermions in ultracold atomic\n  superfluid: We propose an experiment to directly probe the non-Abelian statistics of\nMajorana fermions by braiding them in an s-wave superfluid of ultracold atoms.\nWe show different orders of braiding operations give orthogonal output states\nthat can be distinguished through Raman spectroscopy. Realization of Majorana\nbound states in an s-wave superfluid requires strong spin-orbital coupling and\na controllable Zeeman field in the perpendicular direction. We present a simple\nlaser configuration to generate the artificial spin-orbital coupling and the\nrequired Zeeman field in the dark state subspace.",
        "positive": "On the Bifurcation and Stability of Single and Multiple Vortex Rings in\n  Three-Dimensional Bose-Einstein Condensates: In the present work, we investigate how single- and multi-vortex-ring states\ncan emerge from a planar dark soliton in three-dimensional (3D) Bose-Einstein\ncondensates (confined in isotropic or anisotropic traps) through bifurcations.\nWe characterize such bifurcations quantitatively using a Galerkin-type\napproach, and find good qualitative and quantitative agreement with our\nBogoliubov-de Gennes (BdG) analysis. We also systematically characterize the\nBdG spectrum of the dark solitons, using perturbation theory, and obtain a\nquantitative match with our 3D BdG numerical calculations. We then turn our\nattention to the emergence of single- and multi-vortex-ring states. We\nsystematically capture these as stationary states of the system and quantify\ntheir BdG spectra numerically. We find that although the vortex ring may be\nunstable when bifurcating, its instabilities weaken and may even eventually\ndisappear, for sufficiently large chemical potentials and suitable trap\nsettings. For instance, we demonstrate the stability of the vortex ring for an\nisotropic trap in the large chemical potential regime."
    },
    {
        "anchor": "Hong-Ou-Mandel atom interferometry in tunnel-coupled optical tweezers: The quantum statistics of atoms is typically observed in the behavior of an\nensemble via macroscopic observables. However, quantum statistics modifies the\nbehavior of even two particles, inducing remarkable consequences that are at\nthe heart of quantum science. Here we demonstrate near-complete control over\nall the internal and external degrees of freedom of two laser-cooled 87Rb atoms\ntrapped in two optical tweezers. This full controllability allows us to\nimplement a massive-particle analog of a Hong-Ou-Mandel interferometer where\natom tunneling plays the role of a photon beamsplitter. We use the\ninterferometer to probe the effect of quantum statistics on the two-atom\ndynamics under tunable initial conditions, chosen to adjust the degree of\natomic indistinguishability. Our work thereby establishes laser-cooled atoms in\noptical tweezers as a new route to bottom-up engineering of scalable,\nlow-entropy quantum systems.",
        "positive": "Density-and-phase domain walls in a condensate with dynamical gauge\n  potentials: We show how one can generate domain walls that separate high- and low-density\nregions with opposite momenta in the ground state of a harmonically trapped\nBose-Einstein condensate using a density-dependent gauge potential. Within a\nGross-Pitaevskii framework, we elucidate the distinct roles of vector and\nscalar potentials and how they lead to synthetic electromagnetic fields that\nare localized at the domain wall. In particular, the kinetic energy cost of a\nsteep density gradient is compensated by an electrostatic field that pushes\nparticles away from a special value of density. We show numerically in one\ndimension that such a domain wall is more prominent for repulsive contact\ninteractions, and becomes metastable at strong electric fields through a\nfirst-order phase transition that ends at a critical point as the field is\nreduced. Our findings build on recent experimental developments and may be\nrealized with cold atoms in a shaken optical lattice, providing insights into\ncollective phenomena arising from dynamical gauge fields."
    },
    {
        "anchor": "Generating mesoscopic Bell states via collisions of distinguishable\n  quantum bright solitons: We investigate numerically the collisions of two distinguishable quantum\nmatter-wave bright solitons in a one-dimensional harmonic trap. We show that\nsuch collisions can be used to generate mesoscopic Bell states which can\nreliably be distinguished from statistical mixtures. Calculation of the\nrelevant s-wave scattering lengths predicts that such states could potentially\nbe realized in quantum-degenerate mixtures of 85Rb and 133Cs. In addition to\nfully quantum simulations for two distinguishable two-particle solitons, we use\na mean-field description supplemented by a stochastic treatment of quantum\nfluctuations in the soliton's center of mass: We demonstrate the validity of\nthis approach by comparison to a mathematically rigorous effective potential\ntreatment of the quantum many-particle problem.",
        "positive": "Zero and First Sound in Normal Fermi Systems: On the basis of a moment method, general solutions of a linearized Boltzmann\nequation for a normal Fermi system are investigated. In particular, we study\nthe sound velocities and damping rates as functions of the temperature and the\ncoupling constant. In the extreme limits of collisionless and hydrodynamic\nregimes, eigenfrequency of sound mode obtained from the moment equations\nreproduces the well-known results of zero sound and first sound. In addition,\nthe moment method can describe crossover between those extreme limits at finite\ntemperatures. Solutions of the moment equations also involve a thermal\ndiffusion mode. From solutions of these equations, we discuss excitation\nspectra corresponding to the particle-hole continuum as well as collective\nexcitations. We also discuss a collective mode in a weak coupling case."
    },
    {
        "anchor": "Engineering Bright Solitons to Enhance the Stability of Two-Component\n  Bose-Einstein Condensates: We consider a system of coupled Gross-Pitaevskii (GP) equations describing a\nbinary quasi-one-dimensional Bose-Einstein condensate (BEC) with intrinsic\ntime-dependent attractive interactions, placed in a time-dependent expulsive\nparabolic potential, in a special case when the system is integrable (a\ndeformed Manakov's system). Since the nonlinearity in the integrable system\nwhich represents binary attractive interactions exponentially decays with time,\nsolitons are also subject to decay. Nevertheless, it is shown that the\nrobustness of bright solitons can be enhanced in this system, making their\nrespective lifetime longer, by matching the time dependence of the interaction\nstrength (adjusted with the help of the Feshbach-resonance management) to the\ntime modulation of the strength of the parabolic potential. The analytical\nresults, and their stability, are corroborated by numerical simulations. In\nparticular, we demonstrate that the addition of random noise does not impact\nthe stability of the solitons.",
        "positive": "Ferroelectric nano-traps for polar molecules: We propose and analyze an electrostatic-optical nano-scale trap for cold\ndiatomic polar molecules. The main ingredient of our proposal is an\nsquare-array of ferroelectric nano-rods {with alternating polarization}. We\nshow that, in contrast to electrostatic traps using the linear Stark effect, a\nquadratic Stark potential supports long-lived trapped states. The molecules are\nkept at a fixed height from the nano-rods by a standing-wave optical dipole\ntrap. For the molecules and materials considered, we find that nano-traps with\ntrap frequency up to 1MHz, ground-state width $\\sim20$nm with lattice\nperiodicity of $\\sim 200$nm. Analyzing the loss mechanisms due to\nnon-adiabaticity, surface-induced radiative transitions, and laser-induced\ntransitions, we show the existence of trapped states with life-time $\\sim 1$s,\ncompetitive with current traps created via optical mechanisms. As an\napplication we extend our discussion to an 1D array of nano-traps to simulate\nof a long-range spin Hamiltonian in our structure."
    },
    {
        "anchor": "Magneto-optical trapping of optically pumped metastable europium: We demonstrate laser cooling and magneto-optical trapping of europium. The\natoms are optically pumped to a metastable state and then loaded from an\natomic-beam source via conventional Zeeman slowing and magneto-optical trapping\ntechniques using a $J=13/2\\leftrightarrow J=15/2$ quasi-cyclic transition. The\ntrapped populations contained up to $1\\times 10^7$ atoms, and a two-body loss\nrate is estimated as $1\\times10^{-10}\\,\\mathrm{cm^3/s}$ from the\nnon-exponential loss of atoms at high densities. We also observed leakage out\nof the quasi-cyclic transition to the two metastable states with $J=9/2$ and\n$11/2$, which is adequate to pump the laser-cooled atoms back to the $J=7/2$\nground state.",
        "positive": "Resonant Superfluidity in an Optical Lattice: We study a system of ultracold fermionic Potassium (40K) atoms in a\nthree-dimensional optical lattice in the vicinity of an s-wave Feshbach\nresonance. Close to resonance, the system is described by a multi-band\nBose-Fermi Hubbard Hamiltonian. We derive an effective lowest-band Hamiltonian\nin which the effect of the higher bands is incorporated by a self-consistent\nmean-field approximation. The resulting model is solved by means of Generalized\nDynamical Mean-Field Theory. In addition to the BEC/BCS crossover we find a\nphase transition to a fermionic Mott insulator at half filling, induced by the\nrepulsive fermionic background scattering length. We also calculate the\ncritical temperature of the BEC/BCS-state and find it to be minimal at\nresonance."
    },
    {
        "anchor": "Anomalous quantum-reflection of Bose-Einstein condensates as a\n  self-screening effect: We discuss the effect of anomalous quantum-reflection of Bose-Einstein\ncondensates as a screening effect, that is created by the condensate itself. We\nderive an effective, time-independent single-mode approach, that allows us to\ndefine different paths of reflection. We compare our theory with experimental\nresults.",
        "positive": "Polaritonic ultracold reactions: cavity controlled molecular\n  photoassociation: We introduce a prototypical model for cavity polaritonic control of ultracold\nphotochemistry by considering the resonant vibrational strong coupling of a\nrubidium dimer to a terahertz cavity. We demonstrate that at avoided crossings\nbetween a vibrational excitation and the vacuum photon absorption, the\nresulting polaritonic states between the molecule and photons can efficiently\ncontrol the molecular vibrational Franck-Condon (FC) factors. Due to the\nentanglement between light and matter, FC factor is transferred from one\npolaritonic branch to other, leading to a polariton with a substantially\nenhanced FC factor. Utilizing this polariton state for photoassociation results\nin the enhanced formation of ultracold molecules. This work suggests a path to\ncontrolling photoassociation with cavity vacuum fields, and lays the ground for\nthe emerging subfield of polaritonic ultracold chemistry."
    },
    {
        "anchor": "Mean-field regime and Thomas-Fermi approximations of trapped\n  Bose-Einstein condensates with higher order interactions in one and two\n  dimensions: We derive rigorously one- and two-dimensional mean-field equations for cigar-\nand pancake-shaped Bose-Einstein condensates (BEC) with higher order\ninteractions (HOI). We show how the higher order interaction modifies the\ncontact interaction of the strongly confined particles. Surprisingly, we find\nthat the usual Gaussian profile assumption for the strongly confining direction\nis inappropriate for the cigar-shaped BEC case, and a Thomas-Fermi type profile\nshould be adopted instead. Based on the derived mean field equations, the\nThomas-Fermi densities are analyzed in presence of the contact interaction and\nHOI. For both box and harmonic traps in one, two and three dimensions, we\nidentify the analytical Thomas-Fermi densities, which depend on the competition\nbetween the contact interaction and the HOI.",
        "positive": "A coherent superposition of Feshbach dimers and Efimov trimers: A powerful experimental technique to study Efimov physics at positive\nscattering lengths is demonstrated. We use the Feshbach dimers as a local\nreference for Efimov trimers by creating a coherent superposition of both\nstates. Measurement of its coherent evolution provides information on the\nbinding energy of the trimers with unprecedented precision and yields access to\npreviously inaccessible parameters of the system such as the Efimov trimers'\nlifetime and the elastic processes between atoms and the constituents of the\nsuperposition state. We develop a comprehensive data analysis suitable for\nnoisy experimental data that confirms the trustworthiness of our demonstration."
    },
    {
        "anchor": "Mobile impurity in a Bose-Einstein condensate and the orthogonality\n  catastrophe: We analyze the properties of an impurity in a dilute Bose-Einstein condensate\n(BEC). First the quasiparticle residue of a static impurity in an ideal BEC is\nshown to vanish with increasing particle number as a stretched exponential,\nleading to a bosonic orthogonality catastrophe. Then we introduce a variational\nansatz, which recovers this exact result and describes the macroscopic dressing\nof the impurity including its back-action onto the BEC as well as boson-boson\nrepulsion beyond the Bogoliubov approximation. This ansatz predicts that the\northogonality catastrophe also occurs for mobile impurities, whenever the BEC\nbecomes ideal. Finally, we show that our ansatz agrees well with experimental\nresults.",
        "positive": "Liquid crystal phases of ultracold dipolar fermions on a lattice: Motivated by the search for quantum liquid crystal phases in a gas of\nultracold atoms and molecules, we study the density wave and nematic\ninstabilities of dipolar fermions on the two-dimensional square lattice (in the\n$x-y$ plane) with dipoles pointing to the $z$ direction. We determine the phase\ndiagram using two complimentary methods, the Hatree-Fock mean field theory and\nthe linear response analysis of compressibility. Both give consistent results.\nIn addition to the staggered ($\\pi$, $\\pi$) density wave, over a finite range\nof densities and hopping parameters, the ground state of the system first\nbecomes nematic and then smectic, when the dipolar interaction strength is\nincreased. Both phases are characterized by the same broken four-fold (C$_4$)\nrotational symmetry. The difference is that the nematic phase has a closed\nFermi surface but the smectic does not. The transition from the nematic to the\nsmectic phase is associated with a jump in the nematic order parameter. This\njump is closely related to the van Hove singularities. We derive the kinetic\nequation for collective excitations in the normal isotropic phase and find that\nthe zero sound mode is strongly Landau damped and thus is not a well defined\nexcitation. Experimental implications of our results are discussed."
    },
    {
        "anchor": "Critical temperature in the BCS-BEC crossover with spin-orbit coupling: We review the study of the superfluid phase transition in a system of\nfermions whose interaction can be tuned continuously along the crossover from\nBardeen-Cooper-Schrieffer (BCS) superconducting phase to a Bose-Einstein\ncondensate (BEC), also in the presence of a spin-orbit coupling. Below a\ncritical temperature the system is characterized by an order parameter.\nGenerally a mean field approximation cannot reproduce the correct behavior of\nthe critical temperature $T_c$ over the whole crossover. We analyze the crucial\nrole of quantum fluctuations beyond the mean-field approach useful to find\n$T_c$ along the crossover in the presence of a spin-orbit coupling, within a\npath integral approach. A formal and detailed derivation for the set of\nequations useful to derive $T_c$ is performed in the presence of Rashba,\nDresselhaus and Zeeman couplings. In particular in the case of only Rashba\ncoupling, for which the spin-orbit effects are more relevant, the two-body\nbound state exists for any value of the interaction, namely in the full\ncrossover. As a result the effective masses of the emerging bosonic excitations\nare finite also in the BCS regime.",
        "positive": "Induced supersolidity in a Dy-Er mixture: Recent experimental realization of the heteronuclear dipolar mixture of Dy\nand Er atoms opens fascinating prospects for creating intriguing novel phases\nin dipolar quantum gases. The experimentally measured value of intra-species\n$s$-wave scattering length of $^{166}$Er condensate in a $^{164}$Dy-$^{166}$Er\nmixture is larger than its intra-species dipolar length, implies that the\n$^{166}$Er condensate itself will not be in a regime of dominated dipole-dipole\ninteraction (DDI). However, we find that the presence of $^{164}$Dy atoms with\nhigh magnetic moment induces droplet nucleation and supersolidity in $^{166}$Er\ncondensate via the long-range and anisotropic inter-species DDI. Remarkably, we\nfind that the imbalance in the magnetic dipole moment combined with its strong\nanisotropic coupling led to the emergence of unique ground state phases. The\nemerging phases include doubly superfluid states, a mixture of insulating\ndroplets and supersolid states, binary supersolids with uniform and alternating\ndomains and a combination of supersolid-superfluid mixed states. We delineate\nthe properties of all these ground state phases and construct a phase diagram.\nWe also explore the dynamical evolution across these phase boundaries via a\nlinear quench of inter-species scattering length. Although we have demonstrated\nthe result for the $^{164}$Dy-$^{166}$Er mixture, our results are generally\nvalid for other dipolar bosonic mixtures of different Dy-Er isotope\ncombinations and may become an important benchmark for future experimental\nscenarios."
    },
    {
        "anchor": "Experimental realization of spin-tensor momentum coupling in ultracold\n  Fermi gases: We experimentally realize the spin-tensor momentum coupling (STMC) using the\nthree ground Zeeman states coupled by three Raman laser beams in ultracold\natomic system of $^{40}$K Fermi atoms. This new type of STMC consists of two\nbright-state bands as a regular spin-orbit coupled spin-1/2 system and one\ndark-state middle band. Using radio-frequency spin-injection spectroscopy, we\ninvestigate the energy band of STMC. It is demonstrated that the middle state\nis a dark state in the STMC system. The realized energy band of STMC may open\nthe door for further exploring exotic quantum matters.",
        "positive": "Critical Velocity and Arrest of a Superfluid in a Point-Like Disordered\n  Potential: Superfluid flow past a potential barrier is a well studied problem in\nultracold Bose gases, however, fewer studies have considered the case of flow\nthrough a disordered potential. Here we consider the case of a superfluid\nflowing through a channel containing multiple point-like barriers, randomly\nplaced to form a disordered potential. We begin by identifying the relationship\nbetween the relative position of two point-like barriers and the critical\nvelocity of such an arrangement. We then show that there is a mapping between\nthe critical velocity of a system with two obstacles, and a system with a large\nnumber of obstacles. By establishing an initial superflow through a point-like\ndisordered potential, moving faster than the critical velocity, we study how\nthe superflow is arrested through the nucleation of vortices and the breakdown\nof superfluidity, a problem with interesting connections to quantum turbulence\nand coarsening. We calculate the vortex decay rate as the width of the barriers\nis increased, and show that vortex pinning becomes a more important effect for\nthese larger barriers."
    },
    {
        "anchor": "Suppression of Density Fluctuations in a Quantum Degenerate Fermi Gas: We study density profiles of an ideal Fermi gas and observe Pauli suppression\nof density fluctuations (atom shot noise) for cold clouds deep in the quantum\ndegenerate regime. Strong suppression is observed for probe volumes containing\nmore than 10,000 atoms. Measuring the level of suppression provides sensitive\nthermometry at low temperatures. After this method of sensitive noise\nmeasurements has been validated with an ideal Fermi gas, it can now be applied\nto characterize phase transitions in strongly correlated many-body systems.",
        "positive": "Capturing the re-entrant behaviour of one-dimensional Bose-Hubbard model: The Bose Hubbard model (BHM) is an archetypal quantum lattice system\nexhibiting a quantum phase transition between its superfluid (SF) and\nMott-insulator (MI) phase. Unlike in higher dimensions the phase diagram of the\nBHM in one dimension possesses regions in which increasing the hopping\namplitude can result in a transition from MI to SF and then back to a MI. This\ntype of re-entrance is well known in classical systems like liquid crystals yet\nits origin in quantum systems is still not well understood. Moreover, this\nunusual re-entrant character of the BHM is not easily captured in approximate\nanalytical or numerical calculations. Here we study in detail the predictions\nof three different and widely used approximations; a multi-site mean-field\ndecoupling, a finite-sized cluster calculation, and a real-space\nrenormalization group (RG) approach. It is found that mean-field calculations\ndo not reproduce re-entrance while finite-sized clusters display a precursor to\nre-entrance. Here we show for the first time that RG does capture the\nre-entrant feature and constitutes one of the simplest approximation able to do\nso. The differing abilities of these approaches reveals the importance of\ndescribing short-ranged correlations relevant to the kinetic energy of a MI in\na particle-number symmetric way."
    },
    {
        "anchor": "Universal many-body response of heavy impurities coupled to a Fermi sea: In this work we discuss the dynamical response of heavy quantum impurities\nimmersed in a Fermi gas at zero and at finite temperature. Studying both the\nfrequency and the time domain allows one to identify interaction regimes that\nare characterized by distinct many-body dynamics. From this theoretical study a\npicture emerges in which impurity dynamics is universal on essentially all time\nscales, and where the high-frequency few-body response is related to the\nlong-time dynamics of the Anderson orthogonality catastrophe by Tan relations.\nOur theoretical description relies on different and complementary approaches:\nfunctional determinants give an exact numerical solution for time- and\nfrequency-resolved responses, bosonization provides analytical expressions at\nlow temperatures, and the theory of Toeplitz determinants allows one to\nanalytically predict response up to high temperatures. Using these approaches\nwe predict the thermal decoherence rate and prove that within the considered\nmodel the fastest rate of long-time decoherence is given by $\\gamma=\\pi\nk_BT/4$. We show that Feshbach resonances in cold atomic systems give access to\nnew interaction regimes where quantum effects prevail even in the thermal\nregime of many-body dynamics. The key signature of this phenomenon is a\ncrossover between exponential decay rates of the real-time Ramsey signal. It is\nshown that the physics of the orthogonality catastrophe is experimentally\nobservable up to temperatures $T/T_F\\lesssim 0.2$ where it leaves its\nfingerprint in a power-law temperature dependence of thermal spectral weight\nand we review how this phenomenon is related to the physics of heavy ions in\nliquid $^3$He and the formation of Fermi polarons. The presented results are in\nexcellent agreement with recent experiments on LiK mixtures, and we predict\nseveral phenomena that can be tested using currently available experimental\ntechnology.",
        "positive": "The rise and fall of patterns in driven-dissipative Rydberg polaritons: Spatial structures commonly emerge in interacting nonlinear systems. In this\nstudy, we focus on the out-of-equilibrium dynamics of the recently-established\nplatform of Rydberg exciton-polaritons, fueled by their characteristic\nlong-range non-local interactions, in the presence of an external drive and\ndissipation. Our work elucidates how modulational instability sets off\nspontaneous density pattern formations in a Rydberg polariton system with\ncharacteristic scales in the micron range. Under conditions of an unstable\nflattop state, we track the evolution of the polariton ensemble, showing the\nemergence of meta-stable patterns and their collapse in the long-time limit. We\ntrace this phenomenon back to the destructive interference between the\npolariton state and the pump in a driven ensemble. Finally, we map out\nconditions that allow stable patterns to form under incoherent pumping. These\nfindings provide new opportunities for exploring the emerging field of\nlong-range interacting gases through Rydberg exciton-polaritons."
    },
    {
        "anchor": "Scattering of solitons in binary Bose-Einstein condensates with\n  spin-orbit and Rabi couplings: In this paper we study the scattering of solitons in a binary Bose-Einstein\nCondensate (BEC) including SO- and Rabi-couplings. To this end, we derive a\nreduced ODE model in view to provide a variational description of the\ncollisional dynamics. Also, we assume negative intra- and inter-component\ninteraction strengths, such that one obtains localized solutions even in\nabsence of external potentials. By performing extensive numerical simulations\nof this model we observe that, for specific conditions, the final propagation\nvelocity of the scattered solitons could be highly sensitive to small changes\nin the initial conditions, being a possible signature of chaos. Additionally,\nthere are infinitely many intervals of regularity emerging from the obtained\nchaotic-like regions and forming a fractal-like structure of\nreflection/transmission windows. Finally, we investigate how the value of the\nspin-orbit coupling strength changes the critical velocities, which are\nminimum/maximum values for the occurrence of solitons bound-states, as well as\nthe fractal-like structure.",
        "positive": "su(N) Mermin-Ho relation: The Mermin-Ho relation expresses the vorticity of a coreless su(2) vortex in\nterms of the spin-1 or l vector which characterizes fully polarized superfluid\ntextures. We generalize it to an su(N) vortex which is applicable to\narbitrarily polarized superfluid textures with higher spin or angular momentum.\nThe obtained relation is expressed in terms of the mean-field generators and\ntheir structure factors."
    },
    {
        "anchor": "Quasiparticle properties of an impurity in a Fermi gas: We report on a study of a spin-down impurity strongly coupled to a spin-up\nFermi sea (a so-called Fermi polaron) with the diagrammatic Monte-Carlo\n(DiagMC) technique. Conditions of zero temperature and three dimensions are\nconsidered for an ultracold atomic gas with resonant interactions in the\nzero-range limit. A Feynman diagrammatic series is developed for the one-body\nand two-body propagators providing information about the polaron and molecule\nchannel respectively. The DiagMC technique allows us to reach diagram orders\nthat are high enough for extrapolation to infinite order. The robustness of the\nextracted results is examined by checking various resummation techniques and by\nrunning the simulations with various choices for the propagators and vertex\nfunctions. It turns out that dressing the lines in the diagrams as much as\npossible is not always the optimal choice. We also identify classes of dominant\ndiagrams for the one-body and two-body self-energy in the region of strong\ninteraction. These dominant diagrams turn out to be the leading processes of\nthe strong-coupling limit. The quasiparticle energies and $Z$-factor are\nobtained as a function of the interaction strength. We find that the DiagMC\nresults for the molecule and polaron properties are very similar to those\nobtained with a variational ansatz. Surprisingly, this variational ansatz gives\nvery good predictions for the quasiparticle residue even when this residue is\nsignificantly smaller than one.",
        "positive": "Momentum-resolved Raman spectroscopy of bound molecules in ultracold\n  Fermi gas: The binding energy of Feshbach molecules from a two component Fermi gas of\n$^{40}$K atoms has been experimentally measured with the momentum-resolved\nRaman spectroscopy. Comparing with the radio-frequency spectroscopy, in the\npresent experiment the signal of unpaired (free atoms) and the bound molecules\ncan be directly observed and the binding energy can be simultaneously\ndetermined in a single running experiment. The energy-momentum dispersion\nspectra of the strongly interacting ultracold Fermi gas in BEC side are also\nmeasured and reconstructed. The present experimental technology of the\nmomentum-resolved Raman spectroscopy can be easily extended to perform\nspatially momentum-resolved Raman spectroscopy and to obtain the response\nspectra of a homogeneous system in the local density approximation."
    },
    {
        "anchor": "Correlation effects and collective excitations in bosonic bilayers: role\n  of quantum statistics, superfluidity and dimerization transition: A two-component two-dimensional (2D) dipolar bosonic system in the bilayer\ngeometry is considered. By performing quantum Monte Carlo simulations in a wide\nrange of layer spacings we analyze in detail the pair correlation functions,\nthe static response function, the kinetic and interaction energies. By reducing\nthe layer spacing we observe a transition from weakly to strongly bound dimer\nstates. The transition is accompanied by the onset of short-range correlations,\nsuppression of the superfluid response, and rotonization of the excitation\nspectrum. A dispersion law and a dynamic structure factor for the {\\em\nin-phase} (symmetric) and {\\em out-of-phase} (antisymmetric) collective modes,\nduring the dimerization, is studied in detail with the stochastic\nreconstruction method and the method of moments. The antisymmetric mode\nspectrum is most strongly influenced by suppression of the inlayer\nsuperfluidity (specified by the superfluid fraction $\\gamma_s=\\rho_s/\\rho$). In\na pure superfluid/normal phase only an acoustic/optical(gapped) mode is\nrecovered. In a partially superfluid phase, both are present simultaneously,\nand the dispersion splits into two branches corresponding to a normal and a\nsuperfluid component. The spectral weight of the acoustic mode scales linearly\nwith $\\gamma_s$. This weight transfers to the optical branch when $\\gamma_s$ is\nreduced due to formation of dimer states. In summary, we demonstrate how the\ninterlayer dimerization in dipolar bilayers can be uniquely identified by\nstatic and dynamic properties.",
        "positive": "Ground state of a resonantly interacting Bose gas: We show that a two-channel mean-field theory for a Bose gas near a Feshbach\nresonance allows for an analytic computation of the chemical potential, and\ntherefore the universal constant \\beta, at unitarity. To improve on this\nmean-field theory, which physically neglects condensate depletion, we study a\nvariational Jastrow ansatz for the ground-state wave function and use the\nhypernetted-chain approximation to minimize the energy for all positive values\nof the scattering length. We also show that other important physical quantities\nsuch as Tan's contact and the condensate fraction can be directly obtained from\nthis approach."
    },
    {
        "anchor": "Rydberg impurity in a Fermi gas: Quantum statistics and rotational\n  blockade: We consider the quench of an atomic impurity via a single Rydberg excitation\nin a degenerate Fermi gas. The Rydberg interaction with the background gas\nparticles induces an ultralong-range potential that binds particles to form\ndimers, trimers, tetramers, etc. Such oligomeric molecules were recently\nobserved in atomic Bose-Einstein condensates. In this work, we demonstrate with\na functional determinant approach that quantum statistics and fluctuations have\nobservable spectral consequences. We show that the occupation of molecular\nstates is predicated on the Fermi statistics, which suppresses molecular\nformation in an emergent molecular shell structure. At large gas densities this\nleads to spectral narrowing, which can serve as a probe of the quantum gas\nthermodynamic properties.",
        "positive": "Cavity optomechanical detection of persistent currents and solitons in a\n  bosonic ring condensate: We present numerical simulations of the cavity optomechanical detection of\npersistent currents and bright solitons in an atomic Bose-Einstein condensate\nconfined in a ring trap. This work describes a novel technique that measures\ncondensate rotation in situ, in real-time, and with minimal destruction, in\ncontrast to currently used methods, all of which destroy the condensate\ncompletely. For weakly repulsive inter-atomic interactions, the analysis of\npersistent currents extends our previous few-mode treatment of the condensate\n[P. Kumar et al. Phys. Rev. Lett. 127, 113601 (2021)] to a stochastic\nGross-Pitaevskii simulation. For weakly attractive atomic interactions, we\npresent the first analysis of optomechanical detection of matter-wave soliton\nmotion. We provide optical cavity transmission spectra containing signatures of\nthe condensate rotation, sensitivity as a function of the system response\nfrequency, and atomic density profiles quantifying the effect of the\nmeasurement backaction on the condensate. We treat the atoms at a mean-field\nlevel and the optical field classically, account for damping and noise in both\ndegrees of freedom, and investigate the linear as well as nonlinear response of\nthe configuration. Our results are consequential for the characterization of\nrotating matter waves in studies of atomtronics, superfluid hydrodynamics, and\nmatter-wave soliton interferometry."
    },
    {
        "anchor": "Composite-boson approach to molecular Bose-Einstein condensates in\n  mixtures of ultracold Fermi gases: We show that an ansatz based on independent composite bosons [Phys. Rep. 463,\n215 (2008)] accurately describes the condensate fraction of molecular\nBose-Einstein condensates in ultracold Fermi gases. The entanglement between\nthe fermionic constituents of a single Feshbach molecule then governs the\nmany-particle statistics of the condensate, from the limit of strong\ninteraction to close to unitarity. This result strengthens the role of\nentanglement as the indispensable driver of composite-boson behavior. The\ncondensate fraction of fermion pairs at zero temperature that we compute\nmatches excellently previous results obtained by means of fixed-node diffusion\nMonte Carlo methods and the Bogoliubov depletion approximation. This paves the\nway towards the exploration of the BEC-BCS crossover physics in mixtures of\ncold Fermi gases with an arbitrary number of fermion pairs as well as the\nimplementation of Hong-Ou-Mandel-like interference experiments proposed within\ncoboson theory.",
        "positive": "Phase-Sensitive Detection for Unconventional Bose-Einstein Condensations: We propose a phase-sensitive detection scheme to identify the unconventional\n$p_{x}\\pm ip_{y}$ symmetry of the condensate wavefunctions of bosons, which\nhave already been proposed and realized in high bands in optical lattices.\nUsing the impulsive Raman operation combining with time-of-flight imaging, the\noff-diagonal correlation functions in momentum space give rise to the relative\nphase information between different components of condensate wavefunctions.\nThis scheme is robust against the interaction and interband effects, and\nprovides smoking gun evidence for unconventional Bose-Einstein condensations\nwith nontrivial condensation symmetries."
    },
    {
        "anchor": "Lifetime of double occupancies in the Fermi-Hubbard model: We investigate the decay of artificially created double occupancies in a\nrepulsive Fermi-Hubbard system in the strongly interacting limit using\ndiagrammatic many-body theory and experiments with ultracold fermions on\noptical lattices. The lifetime of the doublons is found to scale exponentially\nwith the ratio of the on-site repulsion to the bandwidth. We show that the\ndominant decay process in presence of background holes is the excitation of a\nlarge number of particle hole pairs to absorb the energy of the doublon. We\nalso show that the strongly interacting nature of the background state is\ncrucial in obtaining the correct estimate of the doublon lifetime in these\nsystems. The theoretical estimates and the experimental data are in fair\nquantitative agreement.",
        "positive": "Ginzburg-Landau effective action approach to disordered Bose-Hubbard\n  Model: We study the phase transition from Mott insulator (MI) to Bose glass (BG) of\na disordered Bose-Hubbard model within the framework of Ginzburg-Landau\neffective action approach. By treating MI as unperturbed ground state and\nperforming a systematic expansion with respect to tunneling matrix element, we\nextend such a field-theoretic method into the disordered lattice Bose systems.\nTo the lowest order, a second order phase transition is confirmed to happen\nhere and the corresponding phase boundary equation coincides with the previous\nmean-field approximation result. Keeping all the terms second order in hopping\nparameter, we obtain the beyond mean-field results of MI-BG phase boundary of\n2D and 3D disordered Bose-Hubbard models. Our analytic predictions are in\nagreement with recent semianalytic results."
    },
    {
        "anchor": "Radiofrequency spectroscopy of a linear array of Bose-Einstein\n  condensates in a magnetic lattice: We report site-resolved radiofrequency spectroscopy measurements of\nBose-Einstein condensates of 87Rb atoms in about 100 sites of a one-dimensional\n10 micron-period magnetic lattice produced by a grooved magnetic film plus bias\nfields. Site-to-site variations of the trap bottom, atom temperature,\ncondensate fraction and chemical potential indicate that the magnetic lattice\nis remarkably uniform, with variations in trap bottoms of only +/- 0.4 mG. At\nthe lowest trap frequencies (radial and axial frequencies 1.5 kHz and 260 Hz,\nrespectively), temperatures down to 0.16 microkelvin are achieved in the\nmagnetic lattice and at the smallest trap depths (50 kHz) condensate fractions\nup to 80% are observed. With increasing radial trap frequency (up to 20 kHz, or\naspect ratio up to about 80) large condensate fractions persist and the highly\nelongated clouds approach the quasi-1D Bose gas regime. The temperature\nestimated from analysis of the spectra is found to increase by a factor of\nabout five which may be due to suppression of rethermalising collisions in the\nquasi-1D Bose gas. Measurements for different holding times in the lattice\nindicate a decay of the atom number with a half-life of about 0.9 s due to\nthree-body losses and the appearance of a high temperature (about 1.5\nmicrokelvin) component which is attributed to atoms that have acquired energy\nthrough collisions with energetic three-body decay products.",
        "positive": "Resonant collisional shielding of reactive molecules using electric\n  fields: Full control of molecular interactions, including reactive losses, would open\nnew frontiers in quantum science. Here, we demonstrate extreme tunability of\nchemical reaction rates by using an external electric field to shift excited\ncollision channels of ultracold molecules into degeneracy with the initial\ncollision channel. In this situation, resonant dipolar interactions mix the\nchannels at long range, dramatically altering the intermolecular potential. We\nprepare fermionic potassium-rubidium (KRb) molecules in their first excited\nrotational state and observe a three orders-of-magnitude modulation of the\nchemical reaction rate as we tune the electric field strength by a few percent\nacross resonance. In a quasi-two-dimensional geometry, we accurately determine\nthe contributions from the three lowest angular momentum projections of the\ncollisions. Using the resonant features, we shield the molecules from loss and\nsuppress the reaction rate by up to an order of magnitude below the background\nvalue, realizing a long-lived sample of polar molecules in large electric\nfields."
    },
    {
        "anchor": "Magnetically generated spin-orbit coupling for ultracold atoms: We present a new technique for producing two- and three-dimensional\nRashba-type spin-orbit couplings for ultracold atoms without involving light.\nThe method relies on a sequence of pulsed inhomogeneous magnetic fields\nimprinting suitable phase gradients on the atoms. For sufficiently short pulse\ndurations, the time-averaged Hamiltonian well approximates the Rashba\nHamiltonian. Higher order corrections to the energy spectrum are calculated\nexactly for spin-1/2 and perturbatively for higher spins. The pulse sequence\ndoes not modify the form of rotationally symmetric atom-atom interactions.\nFinally, we present a straightforward implementation of this pulse sequence on\nan atom chip.",
        "positive": "Few-Boson Processes in the Presence of an Attractive Impurity under\n  One-Dimensional Confinement: We consider a few-boson system confined to one dimension with a single\ndistinguishable particle of lesser mass. All particle interactions are modeled\nwith $\\delta$-functions, but due to the mass imbalance the problem is\nnonintegrable. Universal few-body binding energies, atom-dimer and atom-trimer\nscattering lengths are all calculated in terms of two parameters, namely the\nmass ratio: $m_{\\text{L}}/m_{\\text{H}}$, and ratio\n$g_{\\text{HH}}/g_{\\text{HL}}$ of the $\\delta$-function couplings. We\nspecifically identify the values of these ratios for which the atom-dimer or\natom-trimer scattering lengths vanish or diverge. We identify regions in this\nparameter space in which various few-body inelastic process become\nenergetically allowed. In the Tonks-Girardeau limit ($g_{\\text{HH}}\\rightarrow\n\\infty$), our results are relevant to experiments involving trapped fermions\nwith an impurity atom."
    },
    {
        "anchor": "Spin and topological order in a periodically driven spin chain: The periodically driven quantum Ising chain has recently attracted a large\nattention in the context of Floquet engineering. In addition to the common\nparamagnet and ferromagnet, this driven model can give rise to new topological\nphases. In this work we systematically explore its quantum phase diagram, by\nexamining the properties of its Floquet ground state. We specifically focus on\ndriving protocols with time-reversal invariant points, and demonstrate the\nexistence of an infinite number of distinct phases. These phases are separated\nby second-order quantum phase transitions, accompanied by continuous changes of\nlocal and string order parameters, as well as sudden changes of a topological\nwinding number and of the number of protected edge states. When one of these\nphase transitions is adiabatically crossed, the correlator associated to the\norder parameter is nonvanishing over a length scale which shows a Kibble-Zurek\nscaling. In some phases, the Floquet ground state spontaneously breaks the\ndiscrete time-translation symmetry of the Hamiltonian. Our findings provide a\nbetter understanding of topological phases in periodically driven clean\nintegrable models.",
        "positive": "Fermi-to-Bose crossover in a trapped quasi-2D gas of fermionic atoms: Physics of many-body systems where particles are restricted to move in two\nspatial dimensions is challenging and even controversial: On one hand, neither\nlong-range order nor Bose condensation may appear in infinite uniform 2D\nsystems at finite temperature, on the other hand this does not prohibit\nsuperfluidity or superconductivity. Moreover, 2D superconductors, such as\ncuprates, are among the systems with highest critical temperatures. Ultracold\natoms are a platform for studying 2D physics. Uniquely to other physical\nsystems, quantum statistics may be completely changed in an ultracold gas: an\natomic Fermi gas may be smoothly crossed over into a gas of Bose molecules (or\ndimers) by tuning interatomic interactions. We review recent experiments where\nsuch crossover has been demonstrated as well as critical phenomena in the\nFermi-to-Bose crossover. We also present simple theoretical models describing\nthe gas at different points of the crossover and compare the data to these and\nmore advanced models."
    },
    {
        "anchor": "Dilute Bose gas with correlated disorder: A Path Integral Monte Carlo\n  study: We investigate the thermodynamic properties of a dilute Bose gas in a\ncorrelated random potential using exact path integral Monte Carlo methods. The\nstudy is carried out in continuous space and disorder is produced in the\nsimulations by a 3D speckle pattern with tunable intensity and correlation\nlength. We calculate the shift of the superfluid transition temperature due to\ndisorder and we highlight the role of quantum localization by comparing the\ncritical chemical potential with the classical percolation threshold. The\nequation of state of the gas is determined in the regime of strong disorder,\nwhere superfluidity is suppressed and the normal phase exists down to very low\ntemperatures. We find a $T^2$ dependence of the energy in agreement with the\nexpected behavior in the Bose glass phase. We also discuss the major role\nplayed by the disorder correlation length and we make contact with a\nHartree-Fock mean-field approach that holds valid if the correlation length is\nvery large. The density profiles are analyzed as a function of temperature and\ninteraction strength. Effects of localization and the depletion of the order\nparameter are emphasized in the comparison between local condensate and total\ndensity. At very low temperature we find that the energy and the particle\ndistribution of the gas are very well described by the T=0 Gross-Pitaevskii\ntheory even in the regime of very strong disorder.",
        "positive": "Pair Correlations in the Two-Dimensional Fermi Gas: We consider the two-dimensional Fermi gas at finite temperature with\nattractive short-range interactions. Using the virial expansion, which provides\na controlled approach at high temperatures, we determine the spectral function\nand contact for the normal state. Our calculated spectra are in qualitative\nagreement with recent photoemission measurements [M. Feld et al., Nature 480,\n75 (2011)], thus suggesting that the observed pairing gap is a feature of the\nhigh-temperature gas rather than being evidence of a pseudogap regime just\nabove the superfluid transition temperature. We further argue that the strong\npair correlations result from the fact that the crossover to bosonic dimers\noccurs at weaker interactions than previously assumed."
    },
    {
        "anchor": "Localization and topological transitions in generalized non-Hermitian\n  SSH models: We study the localization and topological transitions of the generalized\nnon-Hermitian SSH models, where the non-Hermiticities are introduced by the\ncomplex quasiperiodic hopping and the nonreciprocal hopping. We elucidate the\nuniversality of the models and how many models can be mapped to them. Under the\nopen boundary condition, two delocalization transitions are found due to the\ncompetition between the Anderson localization and the boundary localization\nfrom the nontrivial edge states and the non-Hermitian skin effect. Under the\nperiodic boundary condition, only one delocalization transition is found due to\nthe disappearance of the non-Hermitian skin effect. The winding numbers of\nenergy and the Lyapunov exponents in analytical form are obtained to exactly\ncharacterize the two deloaclizateon transitions. It finds that the\ndelocalization transitions don't accompany the topological transition.\nFurthermore, the large on-site non-Hermiticity and the large nonreciprocal\nhopping are all detrimental to the topological transitions. However, the large\nnonreciprocal hopping enhances the Anderson localizations. The above analyses\nare verified by calculating the energy gap and the inverse of the participation\nratio numerically.",
        "positive": "Macroscopic quantum coherence in spinor condensates confined in an\n  anisotropic potential: We investigate the macroscopic quantum coherence of a spin-1 Rb condensate\nconfined in an anisotropic potential. Under the single-mode approximation, we\nshow that the system can be modeled as a biaxial quantum magnet due to the\ninterplay between the magnetic dipole-dipole interaction and the anisotropic\npotential. By applying a magnetic field along the hard-axis, we show that the\ntunneling splitting oscillates as a function of the field strength. We also\npropose an experimental scheme to detect the oscillatory behavior of the\ntunneling splitting by employing the Landau-Zener tunneling."
    },
    {
        "anchor": "Spin Josephson effects of spin-orbit-coupled Bose-Einstein condensates\n  in a non-Hermitian double well: In this paper, we investigate the spin and tunneling dynamics of a\nspin-orbit-coupled noninteracting Bose-Einstein condensate in a periodically\ndriven non-Hermitian double-well potential. Under high-frequency driving, we\nobtain the effective time-averaged Hamiltonian by using the standard\ntime-averaging method, and analytically calculate the Floquet quasienergies,\nrevealing that the parity-time (PT)-breaking phase transition appears even for\narbitrarily small non-Hermitian parameters when the spin-orbit coupling\nstrength takes half-integer value, irrespective of the values of other\nparameters used. When the system is PT-symmetric with balanced gain and loss,\nwe find numerically and analytically that in the broken PT-symmetric regions,\nthere will exist the net spin current together with a vanishing atomic current,\nif we drop the contribution of the exponential growth of the norm to the\ncurrent behaviors. When the system is non-PT-symmetric, though the\nquasienergies are partial complex, a stable net spin current can be generated\nby controlling the periodic driving field, which is accompanied by a spatial\nlocalization of the condensate in the well with gain. The results deepen the\nunderstanding of non-Hermitian physics and could be useful for engineering a\nvariety of devices for spintronics.",
        "positive": "Calculation of the critical temperature of a dilute Bose gas in the\n  Bogoliubov approximation: Following an earlier calculation in 3D, we calculate the 2D critical\ntemperature of a dilute, translation-invariant Bose gas using a variational\nformulation of the Bogoliubov approximation introduced by Critchley and Solomon\nin 1976. This provides the first analytical calculation of the\nKosterlitz-Thouless transition temperature that includes the constant in the\nlogarithm."
    },
    {
        "anchor": "Superfluid weight and Berezinskii-Kosterlitz-Thouless temperature of\n  spin-imbalanced and spin-orbit-coupled Fulde-Ferrell phases in lattice\n  systems: We study the superfluid weight $D^s$ and Berezinskii-Kosterlitz-Thouless\n(BKT) transition temperatures $T_{BKT}$ in case of exotic Fulde-Ferrell (FF)\nsuperfluid states in lattice systems. We consider spin-imbalanced systems with\nand without spin-orbit coupling (SOC) accompanied with in-plane Zeeman field.\nBy applying mean-field theory, we derive general equations for $D^s$ and\n$T_{BKT}$ in the presence of SOC and the Zeeman fields for 2D Fermi-Hubbard\nlattice models, and apply our results to a 2D square lattice. We show that\nconventional spin-imbalanced FF states without SOC can be observed at finite\ntemperatures and that FF phases are further stabilized against thermal\nfluctuations by introducing SOC. We also propose how topologically non-trivial\nSOC-induced FF phases could be identified experimentally by studying the total\ndensity profiles. Furthermore, the relative behavior of transverse and\nlongitudinal superfluid weight components and the role of the geometric\nsuperfluid contribution are discussed.",
        "positive": "Dynamics of a Bose-Einstein Condensate of Excited Magnons: The emergence of a non-equilibrium Bose-Einstein-like condensation of magnons\nin rf-pumped magnetic thin films has recently been experimentally observed. We\npresent here a complete theoretical description of the non-equilibrium\nprocesses involved. It it demonstrated that the phenomenon is another example\nof the presence of a Bose-Einstein-like condensation in non-equilibrium\nmany-boson systems embedded in a thermal bath, better referred-to as\nFr\\\"{o}hlich-Bose-Einstein condensation. The complex behavior emerges after a\nthreshold of the exciting intensity is attained. It is inhibited at higher\nintensities when the magnon-magnon interaction drives the magnons to internal\nthermalization. The observed behavior of the relaxation to equilibrium after\nthe end of the pumping pulse is also accounted for and the different processes\nfully described."
    },
    {
        "anchor": "Density functional theory versus quantum Monte Carlo simulations of\n  Fermi gases in the optical-lattice arena: We benchmark the ground state energies and the density profiles of atomic\nrepulsive Fermi gases in optical lattices computed via Density Functional\nTheory (DFT) against the results of diffusion Monte Carlo (DMC) simulations.\nThe main focus is on a half-filled one-dimensional optical lattices, for which\nthe DMC simulations performed within the fixed-node approach provide unbiased\nresults. This allows us to demonstrate that the local spin-density\napproximation (LSDA) to the exchange-correlation functional of DFT is very\naccurate in the weak and intermediate interactions regime, and also to\nunderline its limitations close to the strongly-interacting Tonks-Girardeau\nlimit and in very deep optical lattices. We also consider a three dimensional\noptical lattice at quarter filling, showing also in this case the high accuracy\nof the LSDA in the moderate interaction regime. The one-dimensional data\nprovided in this study may represent a useful benchmark to further develop DFT\nmethods beyond the LSDA and they will hopefully motivate experimental studies\nto accurately measure the equation of state of Fermi gases in\nhigher-dimensional geometries.",
        "positive": "Vortex excitation in a stirred toroidal Bose-Einstein condensate: Motivated by the recent experiment [Wright et al., Phys. Rev. A 88, 063633\n(2013)], we investigate formation of vortices in an annular BEC stirred by a\nnarrow blue-detuned optical beam. In the framework of a two-dimensional mean\nfield model, we study the dissipative dynamics of the condensate with\nparameters matched to the experimental conditions. Vortex-antivortex pairs\nappear near the center of the stirrer in the bulk of the condensate for slow\nmotion of the stirring beam. When the barrier angular velocity is above some\ncritical value, an outer edge surface mode develops and breaks into the\nvortices entering the condensate annulus. We determine the conditions for\ncreation of the vortex excitations in the stirred toroidal condensate and\ncompare our results with the experimental observations."
    },
    {
        "anchor": "Topological Uniform Superfluid and FFLO Phases in 3D to 1D crossover of\n  spin-orbit coupled Fermi gases: We consider the quasi-one dimensional system realized by an array of weakly\ncoupled parallel one-dimensional \"tubes\" in a two-dimensional lattice which\npermits free motion of atoms in an axial direction in the presence of a Zeeman\nfield, Rashba type spin orbit coupling (SOC), and an s-wave attractive\ninteraction, while the radial motion is tightly confined. We solve the\nzero-temperature (T=0) Bogoliubov-de Gennes (BdG) equations for the quasi-1D\nFermi gas with the dispersion modified by tunneling between the tubes, and show\nthat the T=0 phase diagram hosts the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)\nphase with non-zero center of mass momentum Cooper pairs for small values of\nthe SOC while for larger values of the SOC and high Zeeman fields the uniform\nsuperfluid phase with zero center of mass momentum Cooper pairs has an\ninstability towards the topological uniform superfluid phase with Majorana\nfermions at the tube ends. Also, we show that tuning the two-dimensional\noptical lattice strength in this model allows one to explore the crossover\nbehaviors of the phases during the transition between the 3D and the 1D system\nand in general the FFLO (for small SOC) and the topological uniform superfluid\nphase (for large SOC) are favored as the system becomes more one-dimensional.\nWe also find evidence of the existence of a Zeeman tuned topological quantum\nphase transition (TQPT) within the FFLO phase itself and for large values of\nthe Zeeman field and small SOC the TQPT gives rise to a topologically distinct\nFFLO phase.",
        "positive": "Pure Mott phases in confined ultracold atomic systems: We propose a novel scheme for confining atoms to optical lattices by\nengineering a spatially-inhomogeneous hopping matrix element in the\nHubbard-model (HM) description, a situation we term off-diagonal confinement\n(ODC). We show, via an exact numerical solution of the boson HM with ODC, that\nthis scheme possesses distinct advantages over the conventional method of\nconfining atoms using an additional trapping potential, including the presence\nof incompressible Mott phases at commensurate filling and a phase diagram that\nis similar to the uniform HM. The experimental implementation of ODC will thus\nallow a more faithful realization of correlated phases of interest in cold atom\nexperiments."
    },
    {
        "anchor": "Helical Floquet Channels in 1D Lattices: We show how dispersionless channels exhibiting perfect spin-momentum locking\ncan arise in a 1D lattice model. While such spectra are forbidden by fermion\ndoubling in static 1D systems, here we demonstrate their appearance in the\nstroboscopic dynamics of a periodically driven system. Remarkably, this\nphenomenon does not rely on any adiabatic assumptions, in contrast to the well\nknown Thouless pump and related models of adiabatic spin pumps. The proposed\nsetup is shown to be experimentally feasible with state of the art techniques\nused to control ultracold alkaline earth atoms in optical lattices.",
        "positive": "Effective approach to impurity dynamics in one-dimensional trapped Bose\n  gases: We investigate a temporal evolution of an impurity atom in a one-dimensional\ntrapped Bose gas following a sudden change of the boson-impurity interaction\nstrength. Our focus is on the effects of inhomogeneity due to the harmonic\nconfinement. These effects can be described by an effective one-body model\nwhere both the mass and the spring constant are renormalized. This is in\ncontrast to the classic renormalization, which addresses only the mass. We\npropose an effective single-particle Hamiltonian and apply the multilayer\nmulticonfiguration time-dependent Hartree method for bosons to explore its\nvalidity. Numerical results suggest that the effective mass is smaller than the\nimpurity mass, which means that it cannot straightforwardly be extracted from\ntranslationally invariant models."
    },
    {
        "anchor": "Effect of Feshbach Resonance on the Entropy Production in the ultra cold\n  Bosonic Atoms: The entropy of the coexisting gas of ultra cold fermionic atoms and Bosonic\nmolecular condensate confined in a magnetic trap has been calculated from\nequation of motion approaches. We have found that the entropy production\ndepends not only to the Feshbach resonance and but also under certain limits to\nRabi type oscillation and Bose Josephson junction type oscillation.",
        "positive": "Metal-Mott Insulator Transition and Spin Exchange of Two-Component Fermi\n  Gas with Spin-Orbit Coupling in Two-Dimension Square Optical Lattices: Effects of spin-orbit coupling (SOC) on metal-Mott insulator transition\n(MMIT) and spin exchange physics (SEP) of two-component Fermi gases in\ntwo-dimension half-filling square optical lattices are investigated. In the\nframe of Kotliar and Ruckenstein slave boson and the second order perturbation\ntheory, the phase boundary of paramagnetic MMIT and spin exchange Hamiltonian\nare calculated. In addition by adopting two mean-field ansatzs including\nantiferromagnetic, ferromagnetic and spiral phases, we find that SOC can drive\na quantum phase transition from antiferromagnet to spiral phase."
    },
    {
        "anchor": "Polarization of a quasi two-dimensional repulsive Fermi gas with Rashba\n  spin-orbit coupling: a variational study: Motivated by the remarkable experimental control of synthetic gauge fields in\nultracold atomic systems, we investigate the effect of an artificial Rashba\nspin-orbit coupling on the spin polarization of a two-dimensional repulsive\nFermi gas. By using a variational many-body wavefunction, based on a suitable\nspinorial structure, we find that the polarization properties of the system are\nindeed controlled by the interplay between spin-orbit coupling and repulsive\ninteraction. In particular, two main effects are found: 1) The Rashba coupling\ndetermines a gradual increase of the degree of polarization beyond the critical\nrepulsive interaction strength, at variance with conventional 2D Stoner\ninstability. 2) The critical interaction strength, above which finite\npolarization is developed, shows a dependence on the Rashba coupling, i.e. it\nis enhanced in case the Rashba coupling exceeds a critical value. A simple\nanalytic expression for the critical interaction strength is further derived in\nthe context of our variational formulation, which allows for a straightforward\nand insightful analysis of the present problem.",
        "positive": "Entanglement and spin squeezing in non-Hermitian phase transitions: We show that non-Hermitian dynamics generate substantial entanglement in\nmany-body systems. We consider the non-Hermitian Lipkin-Meshkov-Glick model and\nshow that its phase transition occurs with maximum multiparticle entanglement:\nthere is full N-particle entanglement at the transition, in contrast to the\nHermitian case. The non-Hermitian model also exhibits more spin squeezing than\nthe Hermitian model, showing that non-Hermitian dynamics are useful for quantum\nmetrology. Experimental implementations with trapped ions and cavity QED are\ndiscussed."
    },
    {
        "anchor": "Dicke-type phase transition in a spin-orbit coupled Bose-Einstein\n  condensate: Spin-orbit coupled Bose-Einstein condensates (BECs) provide a powerful tool\nto investigate interesting gauge-field related phenomena. We study the ground\nstate properties of such a system and show that it can be mapped to the\nwell-known Dicke model in quantum optics, which describes the interactions\nbetween an ensemble of atoms and an optical field. A central prediction of the\nDicke model is a quantum phase transition between a superradiant phase and a\nnormal phase. Here we detect this transition in a spin-orbit coupled BEC by\nmeasuring various physical quantities across the phase transition. These\nquantities include the spin polarization, the relative occupation of the nearly\ndegenerate single particle states, the quantity analogous to the photon field\noccupation, and the period of a collective oscillation (quadrupole mode). The\napplicability of the Dicke model to spin-orbit coupled BECs may lead to\ninteresting applications in quantum optics and quantum information science.",
        "positive": "Collective excitations of dipolar gases based on local tunneling in\n  superlattices: The collective dynamics of a dipolar fermionic quantum gas confined in a\none-dimensional double-well superlattice is explored. The fermionic gas resides\nin a paramagnetic-like ground state in the weak interaction regime, upon which\na new type of collective dynamics is found when applying a local perturbation.\nThis dynamics is composed of the local tunneling of fermions in separate\nsupercells, and is a pure quantum effect, with no classical counterpart. Due to\nthe presence of the dipolar interactions the local tunneling transports through\nthe entire superlattice, giving rise to a collective dynamics. A well-defined\nmomentum-energy dispersion relation is identified in the ab-initio simulations\ndemonstrating the phonon-like behavior. The phonon-like characteristic is also\nconfirmed by an analytical description of the dynamics within a semiclassical\npicture."
    },
    {
        "anchor": "Damping of Josephson oscillations in strongly correlated one-dimensional\n  atomic gases: We study Josephson oscillations of two strongly correlated one-dimensional\nbosonic clouds separated by a localized barrier. Using a quantum-Langevin\napproach and the exact Tonks-Girardeau solution in the impenetrable-boson\nlimit, we determine the dynamical evolution of the particle-number imbalance,\ndisplaying an effective damping of the Josephson oscillations which depends on\nbarrier height, interaction strength and temperature. We show that the damping\noriginates from the quantum and thermal fluctuations intrinsically present in\nthe strongly correlated gas. Thanks to the density-phase duality of the model,\nthe same results apply to particle-current oscillations in a one-dimensional\nring where a weak barrier couples different angular momentum states.",
        "positive": "Counterflow of spontaneous mass currents in trapped spin-orbit coupled\n  Fermi gases: We use the Bogoliubov-de Gennes formalism and study the ground-state phases\nof trapped spin-orbit coupled Fermi gases in two dimensions. Our main finding\nis that the presence of a symmetric (Rashba type) spin-orbit coupling\nspontaneously induces counterflowing mass currents in the vicinity of the trap\nedge, i.e. $\\uparrow$ and $\\downarrow$ particles circulate in opposite\ndirections with equal speed. These currents flow even in noninteracting\nsystems, but their strength decreases toward the molecular BEC limit, which can\nbe achieved either by increasing the spin-orbit coupling or the interaction\nstrength. These currents are also quite robust against the effects of\nasymmetric spin-orbit couplings in $x$ and $y$ directions, gradually reducing\nto zero as the spin-orbit coupling becomes one dimensional. We compare our\nresults with those of chiral p-wave superfluids/superconductors."
    },
    {
        "anchor": "Bound Dimers in Bilayers of Cold Polar Molecules: The exploration of cold polar molecules in different geometries is a rapidly\ndeveloping experimental and theoretical pursuit. Recently, the implementation\nof optical lattices has enabled confinement in stacks of planes, the number of\nwhich is also controllable. Here we consider the bound state structure of two\npolar molecules confined in two adjacent planes as function of the polarization\nangle of the dipole moment of the molecules. We prove analytically and present\nnumerical evidence for the existence of bound states for arbitrary dipole\nmoments and polarization directions in this two-dimensional geometry. The\nspatial structure of the bound states is dominated by two-dimensional s- and\np-waves, where the latter exceeds 40 percent over a large range of polarization\nangles for intermediate or strong dipole strength. Finally, we consider the\ninfluence of the dimer bound states on the potential many-body ground-state of\nthe system.",
        "positive": "The Gor'kov and Melik-Barkhudarov correction to the mean-field critical\n  field transition to Fulde-Ferrell-Larkin-Ovchinnikov states: The Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states, characterized by Cooper\npairs condensed at finite-momentum are, at the same time, exotic and elusive.\nIt is partially due to the fact that the FFLO states allow superconductivity to\nsurvive even in strong magnetic fields at the mean-field level. The effects of\ninduced interactions at zero temperature are calculated in both clean and dirty\ncases, and it is found that the critical field at which the quantum phase\ntransition to an FFLO state occurs at the mean-field level is strongly\nsuppressed in imbalanced Fermi gases. This strongly shrinks the phase space\nregion where the FFLO state is unstable and more exotic ground state is to be\nfound. In the presence of high level impurities, this shrinkage may destroy the\nFFLO state completely."
    },
    {
        "anchor": "Feedback-enhanced algorithm for aberration correction of holographic\n  atom traps: We show that a phase-only spatial light modulator can be used to generate\nnon-trivial light distributions suitable for trapping ultracold atoms, when the\nhologram calculation is included within a simple and robust feedback loop that\ncorrects for imperfect device response and optical aberrations. This correction\nreduces the discrepancy between target and experimental light distribution to\nthe level of a few percent (RMS error). We prove the generality of this\nalgorithm by applying it to a variety of target light distributions of\nrelevance for cold atomic physics.",
        "positive": "Universal Dynamics at the Lowest Temperatures: High-performance graphical processing units (GPU) are used for the repeated\nparallelised propagation of non-linear partial differential equations on large\nspatio-temporal grids. The main challenge results as a combination of the\nrequirement of large grids for exploring scaling over several orders of\nmagnitude, both in space and time, and the need for high statistics in\naveraging over many runs, in computing correlation functions for highly\nfluctuating quantum many-body states. With our simulations, we explore the\ndynamics of complex quantum systems far from equilibrium, with the aim of\nclassifying their universal characteristics such as scaling exponents near\nnon-thermal fixed points. Our results are strongly relevant for the development\nof synthetic quantum systems when exploring the respective physics in the\nlaboratory."
    },
    {
        "anchor": "Growth dynamics of a Bose-Einstein condensate in a dimple trap without\n  cooling: We study the formation of a Bose-Einstein condensate in a cigar-shaped\nthree-dimensional harmonic trap, induced by the controlled addition of an\nattractive \"dimple\" potential along the weak axis. In this manner we are able\nto induce condensation without cooling due to a localized increase in the phase\nspace density. We perform a quantitative analysis of the thermodynamic\ntransformation in both the sudden and adiabatic regimes for a range of dimple\nwidths and depths. We find good agreement with equilibrium calculations based\non self-consistent semiclassical Hartree-Fock theory describing the condensate\nand thermal cloud. We observe there is an optimal dimple depth that results in\na maximum in the condensate fraction. We also study the non-equilibrium\ndynamics of condensate formation in the sudden turn-on regime, finding good\nagreement for the observed time dependence of the condensate fraction with\ncalculations based on quantum kinetic theory.",
        "positive": "Two Cold Atoms in a Time-Dependent Harmonic Trap in One Dimension: We analyze the dynamics of two atoms with a short-ranged pair interaction in\na one-dimensional harmonic trap with time-dependent frequency. Our analysis is\nfocused on two representative cases: (i) a sudden change of the trapping\nfrequency from one value to another, and (ii) a periodic trapping frequency. In\ncase (i), the dynamics of the interacting and the corresponding non-interacting\nsystems turn out to be similar. In the second case, however, the interacting\nsystem can behave quite differently, especially close to parametric resonance.\nFor instance, in the regions where such resonance occurs we find that the\ninteraction can significantly reduce the rate of energy increase. The\nimplications for applications of our findings to cool or heat the system are\nalso dicussed."
    },
    {
        "anchor": "Competing exotic quantum phases of spin-$1/2$ ultra-cold lattice bosons\n  with extended spin interactions: Advances in pure optical trapping techniques now allow the creation of\ndegenerate Bose gases with internal degrees of freedom. Systems such as\n${}^{87}$Rb, $^{39}$K or ${}^{23}$Na in the $F=1$ hyperfine state offer an\nideal platform for studying the interplay of superfluidity and quantum\nmagnetism. Motivated by the experimental developments, we study ground state\nphases of a two-component Bose gas loaded on an optical lattice. The system is\ndescribed effectively by the Bose-Hubbard Hamiltonian with onsite and near\nneighbor spin-spin interactions. An important feature of our investigation is\nthe inclusion of interconversion (spin flip) terms between the two species,\nwhich has been observed in optical lattice experiments. Using mean-field theory\nand quantum Monte Carlo simulations, we map out the phase diagram of the\nsystem. A rich variety of phases is identified, including antiferromagnetic\n(AF) Mott insulators, ferromagnetic and AF superfluids.",
        "positive": "Reproducible mesoscopic superpositions of Bose-Einstein condensates and\n  mean-field chaos: In a parameter regime for which the mean-field (Gross-Pitaevskii) dynamics\nbecomes chaotic, mesoscopic quantum superpositions in phase space can occur in\na double-well potential which is shaken periodically. For experimentally\nrealistic initial states like the ground state of some 100 atoms, the emergence\nof mesoscopic quantum superpositions in phase space is investigated\nnumerically. It is shown to be reproducible even if the initial conditions\nslightly change. While the final state is not a perfect superposition of two\ndistinct phase-states, the superposition is reached an order of magnitude\nfaster than in the case of the collapse and revival phenomenon. Furthermore, a\ngenerator of entanglement is identified."
    },
    {
        "anchor": "Efimov trimers under strong confinement: The dimensionality of a system can fundamentally impact the behaviour of\ninteracting quantum particles. Classic examples range from the fractional\nquantum Hall effect to high temperature superconductivity. As a general rule,\none expects confinement to favour the binding of particles. However,\nattractively interacting bosons apparently defy this expectation: while three\nidentical bosons in three dimensions can support an infinite tower of Efimov\ntrimers, only two universal trimers exist in the two dimensional case. We\nreveal how these two limits are connected by investigating the problem of three\nidentical bosons confined by a harmonic potential along one direction. We show\nthat the confinement breaks the discrete Efimov scaling symmetry and destroys\nthe weakest bound trimers. However, the deepest bound Efimov trimer persists\nunder strong confinement and hybridizes with the quasi-two-dimensional trimers,\nyielding a superposition of trimer configurations that effectively involves\ntunnelling through a short-range repulsive barrier. Our results suggest a way\nto use strong confinement to engineer more stable Efimov-like trimers, which\nhave so far proved elusive.",
        "positive": "Phase diagram of imbalanced fermions in optical lattices: The zero-temperature phase diagrams of imbalanced fermions in 3D optical\nlattices are investigated to evaluate the validity of the Fermi-Hubbard model.\nIt is found that depending on the filling factor, s-wave scattering strength\nand lattice potential, the system may fall into the normal($N$) phase,\nmagnetized superfluid(SF$_M$) or phase separation of $N$ and BCS state. By\ntuning these parameters, the superfluidity could be favorable by enhanced\neffective couplings or suppressed by the increased band gap. The phase profiles\nin the presence of a harmonic trap are also investigated under LDA, which show\nsome exotic shell structures compared to those without the optical lattice."
    },
    {
        "anchor": "Higher-order and fractional discrete time crystals in Floquet-driven\n  Rydberg atoms: Higher-order and fractional discrete time crystals (DTCs) are exotic phases\nof matter where the discrete time translation symmetry is broken into\nhigher-order and non-integer category. Generation of these unique DTCs has been\nwidely studied theoretically in different systems. However, no current\nexperimental methods can probe these higher-order and fractional DTCs in any\nquantum many-body systems. We demonstrate an experimental approach to observe\nhigher-order and fractional DTCs in Floquet-driven Rydberg atomic gases. We\nhave discovered multiple $n$-DTCs with integer values of $n$ = 2, 3, and 4, and\nothers ranging up to 14, along with fractional $n$-DTCs with $n$ values beyond\nthe integers. The system response can transition between adjacent integer DTCs,\nduring which the fractional DTCs are investigated. Study of higher-order and\nfractional DTCs expands fundamental knowledge of non-equilibrium dynamics and\nis promising for discovery of more complex temporal symmetries beyond the\nsingle discrete time translation symmetry.",
        "positive": "Three-body and Coulomb interactions in a quasi two-dimensional dipolar\n  Bose condensed gas: In this paper, we studied a dilute quasi two-dimensional dipolar\nBose-condensed with two- and three-body contact, and Coulomb interactions using\nthe Hartree-Fock-Bogoliubov-Popov approximation. We analyze numerically the\neffects of three-body contact, and Coulomb interactions on the energy spectrum,\nthe quantum and thermal noncondensate fraction of the system. We show that\nincreasing the three-body contact and Coulomb interactions leads to the\nappearance of rotonization and condensate instability at stronger dipole-dipole\ninteraction. Also we find that the temperature dependence of the thermal\nnoncondensate fraction is linear at low temperature."
    },
    {
        "anchor": "Magnetic solitons in an immiscible two-component Bose-Einstein\n  condensate: We investigate magnetic solitons in an immiscible binary Bose-Einstein\ncondensate (BEC), where the intraspecies interactions are slightly weaker than\nthe interspecies interactions. While their density and phase profiles are\nanalogous to dark-bright solitons, other characteristic properties such as\nvelocities, widths, total density depletions, and in-trap oscillations are\ndifferent. In the low velocity regime, a magnetic soliton reduces to a\ntraveling pair of magnetic domain walls. Collisional behaviors of the solitons\nare also briefly discussed. We further demonstrate that these solitonic states\ncan be realized in a quasi-one-dimensional (quasi-1D) spin-1 ferromagnetic BEC\nwith weak spin interaction, e.g., a Rb87 BEC.",
        "positive": "Turbulence scaling laws across the superfluid to supersolid transition: We investigate quantum turbulence in a two-dimensional trapped supersolid and\ndemonstrate that both the wave and vortex turbulence involve triple rather than\ndual cascades, as in a superfluid. Because of the presence of a second gapless\nmode associated with translation symmetry breaking, a new $k^{-13/3}$ scaling\nlaw is predicted to occur in the wave turbulence. Simultaneous fast\nvortex-antivortex creation and annihilation in the interior of the oscillating\nsupersolid results in a $k^{-1}$ scaling law in the vortex turbulence.\nNumerical simulations based on the Gross-Pitaevskii equation confirmed the\npredictions."
    },
    {
        "anchor": "Topological Bands for Ultracold Atoms: There have been significant recent advances in realizing bandstructures with\ngeometrical and topological features in experiments on cold atomic gases. We\nprovide an overview of these developments, beginning with a summary of the key\nconcepts of geometry and topology for Bloch bands. We describe the different\nmethods that have been used to generate these novel bandstructures for cold\natoms, as well as the physical observables that have allowed their\ncharacterization. We focus on the physical principles that underlie the\ndifferent experimental approaches, providing a conceptual framework within\nwhich to view these developments. However, we also describe how specific\nexperimental implementations can influence physical properties. Moving beyond\nsingle-particle effects, we describe the forms of inter-particle interactions\nthat emerge when atoms are subjected to these energy bands, and some of the\nmany-body phases that may be sought in future experiments.",
        "positive": "Comment on \"Dispersive bottleneck delaying thermalization of turbulent\n  Bose-Einstein Condensates\" by Krstulovic and Brachet [arXiv:1007.4441]: We reveal the connection of the recent numerical observations of Krstulovic\nand Brachet [arXiv:1007.4441] with the general theory of relaxation kinetics of\nthe strongly non-equilibrium Bose-Einstein condensates."
    },
    {
        "anchor": "Solitary-wave solutions in binary mixtures of Bose-Einstein condensates\n  under periodic boundary conditions: We derive solitary-wave solutions within the mean-field approximation in\nquasi-one-dimensional binary mixtures of Bose-Einstein condensates under\nperiodic boundary conditions, for the case of an effective repulsive\ninteratomic interaction. The particular gray-bright solutions that give the\nglobal energy minima are determined. Their characteristics and the associated\ndispersion relation are derived. In the case of weak coupling, we diagonalize\nthe Hamiltonian analytically to obtain the full excitation spectrum of\n\"quantum\" solitary-wave solutions.",
        "positive": "Radio-frequency spectroscopy of weakly bound molecules in spin-orbit\n  coupled atomic Fermi gases: We investigate theoretically radio-frequency spectroscopy of weakly bound\nmolecules in an ultracold spin-orbit-coupled atomic Fermi gas. We consider two\ncases with either equal Rashba and Dresselhaus coupling or pure Rashba\ncoupling. The former system has been realized very recently at Shanxi\nUniversity [Wang et al., arXiv:1204.1887] and MIT [Cheuk et al.,\narXiv:1205.3483]. We predict realistic radio-frequency signals for revealing\nthe unique properties of anisotropic molecules formed by spin-orbit coupling."
    },
    {
        "anchor": "Quantum Monte Carlo simulations of thermodynamic properties of\n  attractive SU($3$) Dirac fermions: We employ the determinant quantum Monte Carlo method to study the\nfinite-temperature properties of the half-filled attractive SU($3$) Hubbard\nmodel on a honeycomb lattice. We calculate the phase diagram in which the phase\nboundary separates the disordered phase and the charge-density-wave (CDW) phase\nand the transition temperature $T_{\\text{tr}}(|U|)$ varies non-monotonically\nwith attractive Hubbard interaction $|U|$. As the Hubbard $|U|$ increases at\nconstant temperature $T<\\text{max}(T_{\\text{tr}}(|U|))$, the system first\nundergoes a transition from thermal Dirac semimetal phase to CDW phase, and\neventually the CDW state is thermally melted at a strong Hubbard $|U|$ where\nthe system enters a trion liquid phase. In between the two transition points\nthe non-monotonic $|U|$ dependence of CDW order strength is strikingly\ndifferent from the zero-temperature monotonic behavior. In the trion CDW state\nwhere off-site trions arise from quantum fluctuations (a fermion inside an\non-site trion hops to a nearest-neighbor site), the simulated triple occupancy\nat constant Hubbard $|U|$ surprisingly increases with temperature, implying\nthat the formation of off-site trions is suppressed by the thermal\ndelocalization of on-site trions. We have also calculated the\nentropy-temperature relations for various attractive Hubbrad interactions,\nwhich exhibit the prominent characteristic of the Pomeranchuk effect. Our work\nhas revealed that the formation of on-site and off-site trions has significant\nconsequences for thermodynamic properties of SU(3) Dirac fermions.",
        "positive": "Improved optical standing-wave beam splitters for dilute Bose-Einstein\n  condensates: Bose-Einstein condensate (BEC)-based atom interferometry exploits low\ntemperatures and long coherence lengths to facilitate high-precision\nmeasurements. Progress in atom interferometry promises improvements in\nnavigational devices like gyroscopes and accelerometers, as well as\napplications in fundamental physics such as accurate determination of physical\nconstants. Previous work demonstrates that beam splitters and mirrors for\ncoherent manipulation of dilute BEC momentum in atom interferometers can be\nimplemented with sequences of non-resonant standing-wave light pulses. While\nprevious work focuses on the optimization of the optical pulses' amplitude and\nduration to produce high-order momentum states with high fidelity, we explore\nhow varying the shape of the optical pulses affects optimal beam-splitter\nperformance, as well as the effect of pulse shape on the sensitivity of\noptimized parameters in achieving high fidelity in high-momentum states. In\nsimulations of two-pulse beam splitters utilizing optimized square, triangle,\nand sinc-squared pulse shapes applied to dilute BECs, we, in some cases, reduce\nparameter sensitivity by an order of magnitude while maintaining fidelity."
    },
    {
        "anchor": "Complex and real unconventional Bose-Einstein condensations in high\n  orbital bands: We perform the theoretical study on the unconventional Bose-Einstein\ncondensations (UBEC) in the high bands of optical lattices observed by\nHemmerich's group. These exotic states are characterized by complex-valued\ncondensate wavefunctions with nodal points, or real-valued ones with nodal\nlines, thus are beyond the {\\it \"no-node\"} paradigm of the conventional BECs. A\nquantum phase transition is driven by the competition between the single\nparticle band and interaction energies. The complex UBECs spontaneously break\ntime-reversal symmetry, exhibiting a vortex-antivortex lattice structure.",
        "positive": "Equilibration Dynamics of Strongly Interacting Bosons in 2D Lattices\n  with Disorder: Motivated by recent optical lattice experiments [J.-y. Choi et al., Science\n352, 1547 (2016)], we study the dynamics of strongly interacting bosons in the\npresence of disorder in two dimensions. We show that Gutzwiller mean-field\ntheory (GMFT) captures the main experimental observations, which are a result\nof the competition between disorder and interactions. Our findings highlight\nthe difficulty in distinguishing glassy dynamics, which can be captured by\nGMFT, and many-body localization, which cannot be captured by GMFT, and\nindicate the need for further experimental studies of this system."
    },
    {
        "anchor": "Interaction-induced quantum phase revivals and evidence for the\n  transition to the quantum chaotic regime in 1D atomic Bloch oscillations: We study atomic Bloch oscillations in an ensemble of one-dimensional tilted\nsuperfluids in the Bose-Hubbard regime. For large values of the tilt, we\nobserve interaction-induced coherent decay and matter-wave quantum phase\nrevivals of the Bloch oscillating ensemble. We analyze the revival period\ndependence on interactions by means of a Feshbach resonance. When reducing the\nvalue of the tilt, we observe the disappearance of the quasi-periodic phase\nrevival signature towards an irreversible decay of Bloch oscillations,\nindicating the transition from regular to quantum chaotic dynamics.",
        "positive": "Efimov three-body states on top of a Fermi sea: The stabilization of Cooper pairs of bound electrons in the background of a\nFermi sea is the origin of superconductivity and the paradigmatic example of\nthe striking influence of many-body physics on few-body properties. In the\nquantum-mechanical three-body problem the famous Efimov effect yields\nunexpected scaling relations among a tower of universal states. These seemingly\nunrelated problems can now be studied in the same setup thanks to the success\nof ultracold atomic gas experiments. In light of the tremendous effect of a\nbackground Fermi sea on two-body properties, a natural question is whether a\nbackground can modify or even destroy the Efimov effect. Here we demonstrate\nhow the generic problem of three interacting particles changes when one\nparticle is embedded in a background Fermi sea, and show that Efimov scaling\npersists. It is found in a scaling that relates the three-body physics to the\nbackground density of fermionic particles."
    },
    {
        "anchor": "Anomalous Dimers in Quantum Mixtures near Broad Resonances: Pauli\n  Blocking, Fermi Surface Dynamics and Implications: We study the energetics and dispersion of anomalous dimers that are induced\nby the Pauli blocking effect in a quantum Fermi gas of majority atoms near\ninterspecies resonances. Unlike in vacuum, we find that both the sign and\nmagnitude of the dimer masses are tunable via Feshbach resonances. We also\ninvestigate the effects of particle-hole fluctuations on the dispersion of\ndimers and demonstrate that the particle-hole fluctuations near a Fermi surface\n(with Fermi momentum $\\hbar k_F$) generally reduce the effective two-body\ninteractions and the binding energy of dimers. Furthermore, in the limit of\nlight minority atoms the particle-hole fluctuations disfavor the formation of\ndimers with a total momentum $\\hbar k_F$, because near $\\hbar k_F$ the modes\nwhere the dominating particle-hole fluctuations appear are the softest. Our\ncalculation suggests that near broad interspecies resonances when the\nminority-majority mass ratio $m_B/m_F$ is smaller than a critical value\n(estimated to be 0.136), dimers in a finite-momentum channel are energetically\nfavored over dimers in the zero-momentum channel. We apply our theory to\nquantum gases of $^{6}$Li$^{40}$K, $^{6}$Li$^{87}$Rb, $^{40}$K$^{87}$Rb and\n$^{6}$Li$^{23}$Na near broad interspecies resonances, and discuss the\nlimitations of our calculations and implications.",
        "positive": "Non-perturbative method to compute thermal correlations in\n  one-dimensional systems: A brief overview: We develop a highly efficient method to numerically simulate thermal\nfluctuations and correlations in non-relativistic continuous bosonic\none-dimensional systems. We start by noticing the equivalence of their\ndescription through the transfer matrix formalism and a Fokker-Planck equation\nfor a distribution evolving in space. The corresponding stochastic differential\n(It\\={o}) equation is very suitable for computer simulations, allowing the\ncalculation of arbitrary correlation functions. As an illustration, we apply\nour method to the case of two tunnel-coupled quasicondensates of bosonic atoms."
    },
    {
        "anchor": "Dynamics of Vortex Dipoles in Confined Bose-Einstein Condensates: We present a systematic theoretical analysis of the motion of a pair of\nstraight counter-rotating vortex lines within a trapped Bose-Einstein\ncondensate. We introduce the dynamical equations of motion, identify the\nassociated conserved quantities, and illustrate the integrability of the\nensuing dynamics. The system possesses a stationary equilibrium as a special\ncase in a class of exact solutions that consist of rotating guiding-center\nequilibria about which the vortex lines execute periodic motion; thus, the\ngeneric two-vortex motion can be classified as quasi-periodic. We conclude with\nan analysis of the linear and nonlinear stability of these stationary and\nrotating equilibria.",
        "positive": "Emergence of Quintet Superfluidity in the Chain of Partially Polarized\n  Spin-3/2 Ultracold Atom: The system of ultracold atoms with hyperfine spin $F=3/2$ might be unstable\nagainst the formation of quintet pairs if the interaction is attractive in the\nquintet channel. We have investigated the behavior of correlation functions in\na model including only s-wave interactions at quarter filling by large-scale\ndensity-matrix renormalization-group simulations. We show that the correlations\nof quintet pairs become quasi-long-ranged, when the system is partially\npolarized, leading to the emergence of various mixed superfluid phases in which\nBCS-like pairs carrying different magnetic moment coexist."
    },
    {
        "anchor": "Finite-rate quenches of site bias in the Bose-Hubbard dimer: For a Bose-Hubbard dimer, we study quenches of the site energy imbalance,\ntaking a highly asymmetric Hamiltonian to a fully symmetric one. The ramp is\ncarried out over a finite time that interpolates between the instantaneous and\nadiabatic limits. We provide results for the excess energy of the final state\ncompared to the ground state energy of the final Hamiltonian, as a function of\nthe quench rate. This excess energy serves as the analog of the defect density\nthat is considered in the Kibble-Zurek picture of ramps across phase\ntransitions. We also examine the fate of quantum `self-trapping' when the ramp\nis not instantaneous.",
        "positive": "Faraday waves on a bubble Bose-Einstein condensed binary mixture: By studying the dynamic stability of Bose-Einstein condensed binary mixtures\ntrapped on the surface of an ideal two-dimensional spherical bubble, we show\nhow the Rabi coupling between the species can modulate the interactions leading\nto parametric resonances. In this spherical geometry, the discrete unstable\nangular modes drive both phase separations and spatial patterns, with Faraday\nwaves emerging and coexisting with an immiscible phase. Noticeable is the fact\nthat, in the context of discrete kinetic energy spectrum, the only parameters\nto drive the emergence of Faraday waves are the $s-wave$ contact interactions\nand the Rabi coupling. Once analytical solutions for population dynamics are\nobtained, the stability of homogeneous miscible species is investigated through\nBogoliubov-de Gennes and Floquet methods, with predictions being analysed by\nfull numerical solutions applied to the corresponding time-dependent coupled\nformalism."
    },
    {
        "anchor": "Exact results for polaron and molecule in one-dimensional spin-1/2 Fermi\n  gas: Using exact Bethe ansatz (BA) solutions, we show that a spin-down fermion\nimmersed into a fully polarized spin-up Fermi sea with a weak attraction is\ndressed by the surrounding spin-up fermions to form the one-dimensional analog\nof a polaron. As the attraction becomes strong, the spin-down fermion binds\nwith one spin-up fermion to form a tightly bound molecule. Throughout the whole\ninteraction regime, a crossover from the polaron to a molecule state is fully\ndemonstrated through exact results of the excitation spectrum, the effective\nmass, binding energy and kinetic energy. Furthermore, a clear distinction\nbetween the polaron and molecule is conceived by the probability distribution,\nsingle particle reduced density matrix and density-density correlations, which\nare calculated directly from the Bethe ansatz wave function. Such a\npolaron-molecule crossover presents a universal nature of an impurity immersed\ninto a fermionic medium with an attraction in one dimension.",
        "positive": "Exploring vortex formation in rotating Bose-Einstein condensates beyond\n  mean-field regime: The production of quantized vortices having diverse structures is a\nremarkable effect of rotating Bose-Einstein condensates. Vortex formation\ndescribed by the mean-field theory is valid only in the regime of weak\ninteractions. The exploration of the rich and diverse physics of strongly\ninteracting BEC requires a more general approach. This study explores the\nvortex formation of strongly interacting and rapidly rotating BEC from a\ngeneral ab initio many-body perspective. We demonstrate that the quantized\nvortices form various structures that emerge from an intricate interplay\nbetween the angular momentum and many-body interaction. We examine the distinct\nimpact of the angular velocity and interaction energy on the vortex formation.\nOur analysis shows that, while the angular rotation generally augments the\nvortex formation, the interactions can enhance as well as impede the vortices\nproduction."
    },
    {
        "anchor": "Helical spin textures in dipolar Bose-Einstein condensates: We numerically study elongated helical spin textures in ferromagnetic spin-1\nBose-Einstein condensates subject to dipolar interparticle forces. Stationary\nstates of the Gross-Pitaevskii equation are solved and analyzed for various\nvalues of the helical wave vector and dipolar coupling strength. We find two\nhelical spin textures which differ by the nature of their topological defects.\nThe spin structure hosting a pair of Mermin-Ho vortices with opposite mass\nflows and aligned spin currents is stabilized for a nonzero value of the\nhelical wave vector.",
        "positive": "Correspondence between dark solitons and the type II excitations of\n  Lieb-Liniger model: A one-dimensional model of bosons with repulsive short-range interactions,\nsolved analytically by Lieb and Liniger many years ago, predicts existence of\ntwo branches of elementary excitations. One of them represents Bogoliubov\nphonons, the other, as suggested by some authors, might be related to dark\nsolitons. On the other hand, it has been already demonstrated within a\nframework of the classical field approximation that quasi-one-dimensional\ninteracting Bose gas at equilibrium exhibits excitations which are phonons and\ndark solitons. By showing that statistical distributions of dark solitons\nobtained within the classical field approximation match the distributions of\nquasiparticles of the second kind derived from fully quantum description we\ndemonstrate that type II excitations in the Lieb-Liniger model are, indeed,\nquantum solitons."
    },
    {
        "anchor": "Multiorder topological superfluid phase transitions in a two-dimensional\n  optical superlattice: Higher-order topological superfluids have gapped bulk and symmetry-protected\nMajorana zero modes with various localizations. Motivated by recent advances,\nwe present a proposal for synthesizing multi-order topological superfluids that\nsupport various Majorana zero modes in ultracold atomic gases. For this\npurpose, we use the two-dimensional optical superlattice that introduces a\nspatial modulation to the spin-orbit coupling in one direction, providing an\nextra degree of freedom for the emergent higher-order topological state. We\nfind the topologically trivial superfluids, first-order and second-order\ntopological superfluids, as well as different topological phase transitions\namong them with respect to the experimentally tunable parameters. Besides the\nconventional transition characterized by the Chern number associated with the\nbulk gap closing and reopening, we find the system can support the topological\nsuperfluids with Majorana corner modes, but the topological phase transition\nundergoes no gap-closing of bulk bands. Instead, the transition is refined by\nthe quadrupole moment and signaled out by the gap-closing of edge states. The\nproposal is based on the $s$-wave interaction and is valid using existing\nexperimental techniques, which unifies multi-order topological phase\ntransitions in a simple but realistic system.",
        "positive": "Ground-state properties of dilute Bose systems with synthetic dispersion\n  laws: Experimental advances in synthesizing spin-orbit couplings in cold atomic\nBose gases promise to create single-particle dispersion laws featuring energy\nminima that are degenerate on a ring or a sphere in momentum space. We show\nthat for arbitrary space dimensionality the ground-state properties of a dilute\nsystem of spin-orbit coupled Bose particles with such dispersion and\nshort-range repulsive interactions are universal: the chemical potential\nexhibits a quadratic dependence on the particle density as found in a\none-dimensional free Fermi gas."
    },
    {
        "anchor": "Time dependent local potential in a Tomonaga-Luttinger liquid: We study the energy deposition in a one dimensional interacting quantum\nsystem with a point like potential modulated in amplitude. The point like\npotential at position $x=0$ has a constant part and a small oscillation in time\nwith a frequency $\\omega$. We use bosonization, renormalization group and\nlinear response theory to calculate the corresponding energy deposition. It\nexhibits a power law behavior as a function of the frequency that reflects the\nTomonaga-Luttinger liquid (TLL) nature of the system. Depending on the\ninteractions in the system, characterized by the TLL parameter $K$ of the\nsystem, a crossover between week and strong coupling for the backscattering due\nto the potential is possible. We compute the frequency scale $\\omega_\\ast$, at\nwhich such crossover exists. We find that the energy deposition due to the\nbackscattering shows different exponent for $K>1$ and $K<1$. We discuss\npossible experimental consequences, in the context of cold atomic gases, of our\ntheoretical results.",
        "positive": "Thermal Phase Transitions of Strongly Correlated Bosons with Spin-Orbit\n  Coupling: Experiments on ultracold atomic gases have begun to explore lattice effects\nand thermal fluctuations for two-component bosons with spin-orbit coupling\n(SOC). Motivated by this, we study a $tJ$ model of strongly correlated lattice\nbosons, with equal Rashba-Dresselhaus SOC and a uniform magnetic field. At zero\ntemperature, a Gutzwiller ansatz is shown to capture lattice variants of stripe\nsuperfluid (SF) ground states. We formulate a finite temperature generalization\nof the Gutzwiller approach and show that thermal fluctuations in the doped Mott\ninsulator drive a two-step melting of the stripe SF, revealing a wide\nintermediate regime of a normal fluid with stripe order."
    },
    {
        "anchor": "Few-to-many particle crossover of pair excitations in a superfluid: Motivated by recent advances in the creation of few-body atomic Fermi gases\nwith attractive interactions, we study theoretically the few-to-many particle\ncrossover of pair excitations, which for large particle numbers evolve into\nmodes describing amplitude fluctuations of the superfluid order parameter (the\n\"Higgs\" modes). Our analysis is based on a Richardson-type pairing model that\ncaptures interactions between time-reversed fermion pairs. The model is\nintegrable, which allows a systematic quantitative study of the few-to-many\nparticle crossover with only minor numerical effort. We first establish a\nparity effect in the ground state energy, which is quantified by a so-called\nMatveev-Larkin parameter that generalizes the pairing gap to mesoscopic\nensembles and which behaves quantitatively differently in a few-body and a\nmany-body regime. The crossover point for this quantity is widely tunable as a\nfunction of interaction strength. We then compute the excitation spectrum and\ndemonstrate that the pair excitation energy shows a minimum that deepens with\nincreasing particle number and shifts to smaller interaction strengths,\nconsistent with the finite-size precursor of a quantum phase transition to a\nsuperfluid state. We extract a critical finite-size scaling exponent that\ncharacterizes the decrease of the gap with increasing particle number.",
        "positive": "Spatial order in a two-dimensional spin-orbit-coupled spin-1/2\n  condensate: superlattice, multi-ring and stripe formation: We demonstrate the formation of stable spatially-ordered states in a {\\it\nuniform} and also {\\it trapped} quasi-two-dimensional (quasi-2D) Rashba or\nDresselhaus spin-orbit (SO) coupled pseudo spin-1/2 Bose-Einstein condensate\nusing the mean-field Gross-Pitaevskii equation. For weak SO coupling, one can\nhave a circularly-symmetric $(0,+1)$- or $(0,-1)$-type multi-ring state with\nintrinsic vorticity, for Rashba or Dresselhaus SO coupling, respectively, where\nthe numbers in the parentheses denote the net angular momentum projection in\nthe two components, in addition to a circularly-asymmetric degenerate state\nwith zero net angular momentum projection. For intermediate SO couplings, in\naddition to the above two types, one can also have states with stripe pattern\nin component densities with no periodic modulation in total density. The stripe\nstate continues to exist for large SO coupling. In addition, a new\nspatially-periodic state appears in the uniform system: a superlattice state,\npossessing some properties of a supersolid, with a square-lattice pattern in\ncomponent densities and also in total density. In a trapped system the\nsuperlattice state is slightly different with multi-ring pattern in component\ndensity and a square-lattice pattern in total density. For an equal mixture of\nRashba and Dresselhaus SO couplings, in both uniform and trapped systems, only\nstripe states are found for all strengths of SO couplings. In a uniform system\nall these states are quasi-2D solitonic states."
    },
    {
        "anchor": "Observation of the Berezinskii-Kosterlitz-Thouless Phase Transition in\n  an Ultracold Fermi Gas: We experimentally investigate the first-order correlation function of a\ntrapped Fermi gas in the two-dimensional BEC-BCS crossover. We observe a\ntransition to a low-temperature superfluid phase with algebraically decaying\ncorrelations. We show that the spatial coherence of the entire trapped system\ncan be characterized by a single temperature-dependent exponent. We find the\nexponent at the transition to be constant over a wide range of interaction\nstrengths across the crossover. This suggests that the phase transitions in\nboth the bosonic regime and the strongly interacting crossover regime are of\nBerezinskii-Kosterlitz-Thouless-type and lie within the same universality\nclass. On the bosonic side of the crossover, our data are well-described by\nQuantum Monte Carlo calculations for a Bose gas. In contrast, in the strongly\ninteracting regime, we observe a superfluid phase which is significantly\ninfluenced by the fermionic nature of the constituent particles.",
        "positive": "Perfect-fluid behavior of a dilute Fermi gas near unitary: We present an ab initio calculation of the shear viscosity as a function of\ninteraction strength in a two-component unpolarized Fermi gas near the unitary\nlimit, within a finite temperature quantum Monte Carlo (QMC) framework and\nusing the Kubo linear-response formalism. The shear viscosity decreases as we\ntune the interaction strength 1/ak_F from the Bardeen-Cooper-Schrieffer side of\nthe Feshbach resonance towards Bose-Einstein condensation limit and it acquires\nthe smallest value for 1/ak_F approx 0.4, with a minimum value of (eta/s)_min\napprox 0.2 hbar/k_B, which is about twice as small as the value reported for\nexperiments in quark-gluon plasma (eta/s)_QGP lesssim 0.4 hbar/k_B. The Fermi\ngas near unitarity thus emerges as the most \"perfect fluid\" observed so far in\nnature. The clouds of dilute Fermi gas near unitarity exhibit the unusual\nattribute that, for the sizes realized so far in the laboratory or larger (less\nthan 10^9 atoms), can sustain quantum turbulence below the critical\ntemperature, but at the same time the classical turbulence is suppressed in the\nnormal phase."
    },
    {
        "anchor": "Isentropes of spin-1 bosons in an optical lattice: We analyze the effects of adiabatic ramping of optical lattices on the\ntemperature of spin-1 bosons in a homogeneous lattice. Using mean-field theory,\nwe present the isentropes in the temperature-interaction strength ($T,U_0$)\nplane for ferromagnetic, antiferromagnetic, and zero spin couplings. Following\nthe isentropic lines, temperature changes can be determined during adiabatic\nloading of current experiments. We show that the heating-cooling separatrix\nlies on the superfluid-Mott phase boundary with cooling occuring within the\nsuperfluid and heating in the Mott insulator, and quantify the effects of spin\ncoupling on the heating rate. We find that the mean-field isentropes for low\ninitial entropy terminate at the superfluid-Mott insulator phase boundary.",
        "positive": "Creating exotic condensates via quantum-phase-revival dynamics in\n  engineered lattice potentials: In the field of ultracold atoms in optical lattices a plethora of phenomena\ngoverned by the hopping energy $J$ and the interaction energy $U$ have been\nstudied in recent years. However, the trapping potential typically present in\nthese systems sets another energy scale and the effects of the corresponding\ntime scale on the quantum dynamics have rarely been considered. Here we study\nthe quantum collapse and revival of a lattice Bose-Einstein condensate (BEC) in\nan arbitrary spatial potential, focusing on the special case of harmonic\nconfinement. Analyzing the time evolution of the single-particle density\nmatrix, we show that the physics arising at the (temporally) recurrent quantum\nphase revivals is essentially captured by an effective single particle theory.\nThis opens the possibility to prepare exotic non-equilibrium condensate states\nwith a large degree of freedom by engineering the underlying spatial lattice\npotential."
    },
    {
        "anchor": "Ultracold heteronuclear three-body systems: How diabaticity limits the\n  universality of recombination into shallow dimers: The mass-imbalanced three-body recombination process that forms a shallow\ndimer is shown to possess a rich Efimov-St\\\"uckelberg landscape, with\ncorresponding spectra that differ fundamentally from the homonuclear case. A\nsemi-analytical treatment of the three-body recombination predicts an unusual\nspectra with intertwined resonance peaks and minima, and yields in-depth\ninsight into the behavior of the corresponding Efimov spectra. In particular,\nthe patterns of the Efimov-St\\\"uckelberg landscape are shown to depend\ninherently on the degree of diabaticity of the three-body collisions, which\nstrongly affects the universality of the heteronuclear Efimov states.",
        "positive": "From multimode to monomode guided atom lasers: an entropic analysis: We have experimentally demonstrated a high level of control of the mode\npopulations of guided atom lasers (GALs) by showing that the entropy per\nparticle of an optically GAL, and the one of the trapped Bose Einstein\ncondensate (BEC) from which it has been produced are the same. The BEC is\nprepared in a crossed beam optical dipole trap. We have achieved isentropic\noutcoupling for both magnetic and optical schemes. We can prepare GAL in a\nnearly pure monomode regime (85 % in the ground state). Furthermore, optical\noutcoupling enables the production of spinor guided atom lasers and opens the\npossibility to tailor their polarization."
    },
    {
        "anchor": "Capillary Flotation in a System of Two Immiscible Bose-Einstein\n  Condensates: A spatially inhomogeneous, trapped two-component Bose-Einstein condensate of\ncold atoms in the phase separation mode has been numerically simulated. It has\nbeen demonstrated for the first time that the surface tension between the\ncomponents makes possible the existence of drops of a denser phase floating on\nthe surface of a less dense phase. Depending on the harmonic trap anisotropy\nand other system parameters, a stable equilibrium of the drop is achieved\neither at the poles or at the equator. The drop flotation sometimes persists\neven in the presence of an attached quantized vortex.",
        "positive": "Quasi-one-dimensional spin-orbit- and Rabi-coupled bright dipolar\n  Bose-Einstein-condensate solitons: We study the formation of stable bright solitons in quasi-one-dimensional\n(quasi-1D) spin-orbit- (SO-) and Rabi-coupled two pseudospinor dipolar\nBose-Einstein condensates (BECs) of 164 Dy atoms in the presence of repulsive\ncontact interactions. As a result of the combined attraction-repulsion effect\nof both interactions and the addition of SO and Rabi couplings, two kinds of\nground states in the form of self-trapped bright solitons can be formed, a\nplane-wave soliton (PWS) and a stripe soliton (SS). These quasi-1D solitons\ncannot exist in a condensate with purely repulsive contact interactions and SO\nand Rabi couplings (no dipole). Neglecting the repulsive contact interactions,\nour findings also show the possibility of creating PWSs and SSs. When the\nstrengths of the two interactions are close to each other, the SS develops an\noscillatory instability indicating a possibility of a breather solution,\neventually leading to its destruction. We also obtain a phase diagram showing\nregions where the solution is a PWS or SS."
    },
    {
        "anchor": "Preparing Atomic Topological Quantum Matter by Adiabatic Nonunitary\n  Dynamics: Motivated by the outstanding challenge of realizing low-temperature states of\nquantum matter in synthetic materials, we propose and study an experimentally\nfeasible protocol for preparing topological states such as Chern insulators. By\ndefinition, such (non-symmetry protected) topological phases cannot be attained\nwithout going through a phase transition in a closed system, largely preventing\ntheir preparation in coherent dynamics. To overcome this fundamental caveat, we\npropose to couple the target system to a conjugate system, so as to prepare a\nsymmetry protected topological phase in an extended system by intermittently\nbreaking the protecting symmetry. Finally, the decoupled conjugate system is\ndiscarded, thus projecting onto the desired topological state in the target\nsystem. By construction, this protocol may be immediately generalized to the\nclass of invertible topological phases, characterized by the existence of an\ninverse topological order. We illustrate our findings with microscopic\nsimulations on an experimentally realistic Chern insulator model of ultracold\nfermionic atoms in a driven spin-dependent hexagonal optical lattice.",
        "positive": "Microscopic derivation of multi-channel Hubbard models for ultracold\n  nonreactive molecules in an optical lattice: Recent experimental advances in the cooling and manipulation of bialkali\ndimer molecules have enabled the production of gases of ultracold molecules\nthat are not chemically reactive. It has been presumed in the literature that\nin the absence of an electric field the low-energy scattering of such\nnonreactive molecules (NRMs) will be similar to atoms, in which a single\n$s$-wave scattering length governs the collisional physics. However, in Ref.\n[1], it was argued that the short-range collisional physics of NRMs is much\nmore complex than for atoms, and that this leads to a many-body description in\nterms of a multi-channel Hubbard model. In this work, we show that this\nmulti-channel Hubbard model description of NRMs in an optical lattice is robust\nagainst the approximations employed in Ref. [1] to estimate its parameters. We\ndo so via an exact, albeit formal, derivation of a multi-channel resonance\nmodel for two NRMs from an ab initio description of the molecules in terms of\ntheir constituent atoms. We discuss the regularization of this two-body\nmulti-channel resonance model in the presence of a harmonic trap, and how its\nsolutions form the basis for the many-body model of Ref. [1]. We also\ngeneralize the derivation of the effective lattice model to include multiple\ninternal states (e.g., rotational or hyperfine). We end with an outlook to\nfuture research."
    },
    {
        "anchor": "Universal Short Range Correlations in Bosonic Helium Clusters: Short-range correlations in bosonic Helium clusters, composed of $^4$He\natoms, are studied utilizing the generalized contact formalism. The emergence\nof universal $n$-body short range correlations is formulated and demonstrated\nnumerically via Monte Carlo simulations. The values of the $n$-particle\ncontacts are evaluated for $n\\le5$. In the thermodynamic limit, the two-body\ncontact is extracted from available experimental measurements of the static\nstructure factor of liquid $^4$He at high momenta, and found in a good\nagreement with the value extracted from our calculations.",
        "positive": "The Equation of State of a Low-Temperature Fermi Gas with Tunable\n  Interactions: Interacting fermions are ubiquitous in nature and understanding their\nthermodynamics is an important problem. We measure the equation of state of a\ntwo-component ultracold Fermi gas for a wide range of interaction strengths at\nlow temperature. A detailed comparison with theories including Monte-Carlo\ncalculations and the Lee-Huang-Yang corrections for low-density bosonic and\nfermionic superfluids is presented. The low-temperature phase diagram of the\nspin imbalanced gas reveals Fermi liquid behavior of the partially polarized\nnormal phase for all but the weakest interactions. Our results provide a\nbenchmark for many-body theories and are relevant to other fermionic systems\nsuch as the crust of neutron stars."
    },
    {
        "anchor": "Supersolid phases of lattice dipoles tilted in three-dimensions: By means of quantum Monte Carlo simulations we study phase diagrams of\ndipolar bosons in a square optical lattice. The dipoles in the system are\nparallel to each other and their orientation can be fixed in any direction of\nthe three-dimensional space. Starting from experimentally tunable parameters\nlike scattering length and dipolar interaction strength, we derive the\nparameters entering the effective Hamiltonian. Depending on the direction of\nthe dipoles, various types of supersolids (e.g. checkerboard, stripe) and\nsolids (checkerboard, stripe, diagonal stripe, and an incompressible phase) can\nbe stabilized. Remarkably, we find a cluster supersolid characterized by the\nformation of horizontal clusters of particles. These clusters order along a\ndirection at an angle with the horizontal. Moreover, we find what we call a\ngrain-boundary superfluid. In this phase, regions with solid order are\nseparated by extended defects -- grain boundaries -- which support\nsuperfluidity. We also investigate the robustness of the stripe supersolid\nagainst thermal fluctuations. Finally, we comment on the experimental\nrealization of the phases found.",
        "positive": "Pseudogap temperature and effects of a harmonic trap in the BCS-BEC\n  crossover regime of an ultracold Fermi gas: We theoretically investigate excitation properties in the pseudogap regime of\na trapped Fermi gas. Using a combined $T$-matrix theory with the local density\napproximation, we calculate strong-coupling corrections to single-particle\nlocal density of states (LDOS), as well as the single-particle local spectral\nweight (LSW). Starting from the superfluid phase transition temperature $T_{\\rm\nc}$, we clarify how the pseudogap structures in these quantities disappear with\nincreasing the temperature. As in the case of a uniform Fermi gas, LDOS and LSW\ngive different pseudogap temperatures $T^*$ and $T^{**}$ at which the pseudogap\nstructures in these quantities completely disappear. Determining $T^*$ and\n$T^{**}$ over the entire BCS (Bardeen-Cooper-Schrieffer)-BEC (Bose-Einstein\ncondensate) crossover region, we identify the pseudogap regime in the phase\ndiagram with respect to the temperature and the interaction strength. We also\nshow that the so-called back-bending peak recently observed in the\nphotoemission spectra by JILA group may be explained as an effect of pseudogap\nphenomenon in the trap center. Since strong pairing fluctuations, spatial\ninhomogeneity, and finite temperatures, are important keys in considering real\ncold Fermi gases, our results would be useful for clarifying normal state\nproperties of this strongly interacting Fermi system."
    },
    {
        "anchor": "Fermi-Liquid Behavior of the Normal Phase of a Strongly Interacting Gas\n  of Cold Atoms: We measure the magnetic susceptibility of a Fermi gas with tunable\ninteractions in the low-temperature limit and compare it to quantum Monte Carlo\ncalculations. Experiment and theory are in excellent agreement and fully\ncompatible with the Landau theory of Fermi liquids. We show that these measure-\nments shed new light on the nature of the excitations of the normal phase of a\nstrongly interacting Fermi gas.",
        "positive": "Magnetic dipolar interaction between hyperfine clock states in a planar\n  alkali Bose gas: In atomic systems, clock states feature a zero projection of the total\nangular momentum and thus a low sensitivity to magnetic fields. This makes them\nwidely used for metrological applications like atomic fountains or gravimeters.\nHere, we show that a mixture of two such non-magnetic states still display\nmagnetic dipole-dipole interactions. Using high resolution spectroscopy of a\nplanar gas of $^{87}$Rb atoms with a controlled in-plane shape, we explore the\neffective isotropic and extensive character of these interactions and\ndemonstrate their tunability. Our measurements set strong constraints on the\nrelative values of the s-wave scattering lengths $a_{ij}$ involving the two\nclock states."
    },
    {
        "anchor": "A Hubbard model for ultracold bosonic atoms interacting via\n  zero-point-energy induced three-body interactions: We show that for ultra-cold neutral bosonic atoms held in a three-dimensional\nperiodic potential or optical lattice, a Hubbard model with dominant,\nattractive three-body interactions can be generated. In fact, we derive that\nthe effect of pair-wise interactions can be made small or zero starting from\nthe realization that collisions occur at the zero-point energy of an optical\nlattice site and the strength of the interactions is energy dependent from\neffective-range contributions. We determine the strength of the two- and\nthree-body interactions for scattering from van-der-Waals potentials and near\nFano-Feshbach resonances. For van-der-Waals potentials, which for example\ndescribe scattering of alkaline-earth atoms, we find that the pair-wise\ninteraction can only be turned off for species with a small negative scattering\nlength, leaving the $^{88}$Sr isotope a possible candidate. Interestingly, for\ncollisional magnetic Feshbach resonances this restriction does not apply and\nthere often exist magnetic fields where the two-body interaction is small. We\nillustrate this result for several known narrow resonances between alkali-metal\natoms as well as chromium atoms. Finally, we compare the size of the three-body\ninteraction with hopping rates and describe limits due to three-body\nrecombination.",
        "positive": "Hybrid OpenMP/MPI programs for solving the time-dependent\n  Gross-Pitaevskii equation in a fully anisotropic trap: We present hybrid OpenMP/MPI (Open Multi-Processing/Message Passing\nInterface) parallelized versions of earlier published C programs (D. Vudragovic\net al., Comput. Phys. Commun. 183, 2021 (2012)) for calculating both stationary\nand non-stationary solutions of the time-dependent Gross-Pitaevskii (GP)\nequation in three spatial dimensions. The GP equation describes the properties\nof dilute Bose-Einstein condensates at ultra-cold temperatures. Hybrid versions\nof programs use the same algorithms as the C ones, involving real- and\nimaginary-time propagation based on a split-step Crank-Nicolson method, but\nconsider only a fully-anisotropic three-dimensional GP equation, where\nalgorithmic complexity for large grid sizes necessitates parallelization in\norder to reduce execution time and/or memory requirements per node. Since\ndistributed memory approach is required to address the latter, we combine MPI\nprograming paradigm with existing OpenMP codes, thus creating fully flexible\nparallelism within a combined distributed/shared memory model, suitable for\ndifferent modern computer architectures. The two presented C/OpenMP/MPI\nprograms for real- and imaginary-time propagation are optimized and accompanied\nby a customizable makefile. We present typical scalability results for the\nprovided OpenMP/MPI codes and demonstrate almost linear speedup until\ninter-process communication time starts to dominate over calculation time per\niteration. Such a scalability study is necessary for large grid sizes in order\nto determine optimal number of MPI nodes and OpenMP threads per node."
    },
    {
        "anchor": "Quantum gases in optical lattices: The experimental realization of correlated quantum phases with ultracold\ngases in optical lattices and their theoretical understanding has witnessed\nremarkable progress during the last decade. In this review we introduce basic\nconcepts and tools to describe the many-body physics of quantum gases in\noptical lattices. This includes the derivation of effective lattice\nHamiltonians from first principles and an overview of the emerging quantum\nphases. Additionally, state-of-the-art numerical tools to quantitatively treat\nbosons or fermions on different lattices are introduced.",
        "positive": "Lifshitz Point in the Phase Diagram of Resonantly Interacting\n  $^6Li$-$^{40}K$ Mixtures: We consider a strongly interacting ${}^{6}$Li-${}^{40}$K mixture, which is\nimbalanced both in the masses and the densities of the two fermionic species.\nAt present, it is the experimentalist's favorite for reaching the superfluid\nregime. We construct an effective thermodynamic potential that leads to\nexcellent agreement with Monte Carlo results for the normal state. We use it to\ndetermine the universal phase diagram of the mixture in the unitarity limit,\nwhere we find, in contrast to the mass-balanced case, the presence of a\nLifshitz point. This point is characterized by the effective mass of the Cooper\npairs becoming negative, which signals an instability towards a supersolid\nphase."
    },
    {
        "anchor": "Collective emission of matter-wave jets from driven Bose-Einstein\n  condensates: Scattering is an elementary probe for matter and its interactions in all\nareas of physics. Ultracold atomic gases provide a powerful platform in which\ncontrol over pair-wise interactions empowers us to investigate scattering in\nquantum many-body systems. Past experiments on colliding Bose-Einstein\ncondensates have revealed many important features, including matter-wave\ninterference, halos of scattered atoms, four-wave mixing, and correlations\nbetween counter-propagating pairs. However, a regime with strong stimulation of\nspontaneous collisions analogous to superradiance has proven elusive. Here we\naccess that regime, finding that runaway stimulated collisions in condensates\nwith modulated interaction strength cause the emission of matter-wave jets\nwhich resemble fireworks. Jets appear only above a threshold modulation\namplitude and their correlations are invariant even as the ejected atom number\ngrows exponentially. Hence, we show that the structures and occupations of the\njets stem from the quantum fluctuations of the condensate. Our findings\ndemonstrate the conditions for runaway stimulated collisions and reveal the\nquantum nature of the matter-wave emission.",
        "positive": "Quantum dark solitons in the 1D Bose gas and the superfluid velocity: We give explicit connections of quantum one-hole excited states to classical\nsolitons for the one-dimensional Bose gas with repulsive short-range\ninteractions. We call the quantum states connected to classical solitons the\nquantum soliton states. We show that the matrix element of the canonical field\noperator between quantum soliton states with $N-1$ and $N$ particles is given\nby a dark soliton of the Gross-Pitaevskii equation in the weak coupling case.\nWe suggest that the matrix element corresponds to the order parameter of BEC in\nthe quantum soliton state. The result should be useful in the study of\nmany-body effects in Bose-Einstein condensation and superfluids. For instance,\nwe derive the superfluid velocity for a quantum soliton state."
    },
    {
        "anchor": "Three-dimensional numerical simulation of long-lived quantum vortex\n  knots and links in a trapped Bose-Einstein condensate: Dynamics of simplest vortex knots, unknots, and links of torus type inside an\natomic Bose-Einstein condensate in anisotropic harmonic trap at zero\ntemperature has been numerically simulated using three-dimensional\nGross-Pitaevskii equation. The lifetime for such quasi-stationary rotating\nvortex structures has been found quite long in wide parametric domains of the\nsystem. This result is in qualitative agreement with a previous prediction\nbased on a simplified one-dimensional model approximately describing dynamics\nof vortex filaments [V.P. Ruban, JETP 126, 397 (2018)].",
        "positive": "Thermal phase transitions for Dicke-type models in the ultra-strong\n  coupling limit: We consider the Dicke model in the ultra-strong coupling limit to investigate\nthermal phase transitions and their precursors at finite particle numbers $N$\nfor bosonic and fermionic systems. We derive partition functions with\ndegeneracy factors that account for the number of configurations and derive\nexplicit expressions for the Landau free energy. This allows us to discuss the\ndifference between the original Dicke (fermionic) and the bosonic case. We find\na crossover between these two cases that shows up, e.g., in the specific heat."
    },
    {
        "anchor": "Damping-free collective oscillations of a driven two-component Bose gas\n  in optical lattices: We explore quantum many-body physics of a driven Bose-Einstein condensate in\noptical lattices. The laser field induces a gap in the generalized Bogoliubov\nspectrum proportional to the effective Rabi frequency. The lowest lying modes\nin a driven condensate are characterized by zero group velocity and non-zero\ncurrent. Thus, the laser field induces roton modes, which carry interaction in\na driven condensate. We show that collective excitations below the energy of\nthe laser-induced gap remain undamped, while above the gap they are\ncharacterized by a significantly suppressed Landau damping rate.",
        "positive": "Observation of Bose-Einstein Condensation in a Strong Synthetic Magnetic\n  Field: Extensions of Berry's phase and the quantum Hall effect have led to the\ndiscovery of new states of matter with topological properties. Traditionally,\nthis has been achieved using gauge fields created by magnetic fields or spin\norbit interactions which couple only to charged particles. For neutral\nultracold atoms, synthetic magnetic fields have been created which are strong\nenough to realize the Harper-Hofstadter model. Despite many proposals and major\nexperimental efforts, so far it has not been possible to prepare the ground\nstate of this system. Here we report the observation of Bose-Einstein\ncondensation for the Harper-Hofstadter Hamiltonian with one-half flux quantum\nper lattice unit cell. The diffraction pattern of the superfluid state directly\nshows the momentum distribution on the wavefuction, which is gauge-dependent.\nIt reveals both the reduced symmetry of the vector potential and the twofold\ndegeneracy of the ground state. We explore an adiabatic many-body state\npreparation protocol via the Mott insulating phase and observe the superfluid\nground state in a three-dimensional lattice with strong interactions."
    },
    {
        "anchor": "Nonlinear Scattering of a Bose-Einstein Condensate on a Rectangular\n  Barrier: We consider the nonlinear scattering and transmission of an atom laser, or\nBose-Einstein condensate (BEC) on a finite rectangular potential barrier. The\nnonlinearity inherent in this problem leads to several new physical features\nbeyond the well-known picture from single-particle quantum mechanics. We find\nnumerical evidence for a denumerably infinite string of bifurcations in the\ntransmission resonances as a function of nonlinearity and chemical potential,\nwhen the potential barrier is wide compared to the wavelength of oscillations\nin the condensate. Near the bifurcations, we observe extended regions of\nnear-perfect resonance, in which the barrier is effectively invisible to the\nBEC. Unlike in the linear case, it is mainly the barrier width, not the height,\nthat controls the transmission behavior. We show that the potential barrier can\nbe used to create and localize a dark soliton or dark soliton train from a\nphonon-like standing wave.",
        "positive": "Proof of Bose condensation for weakly interacting lattice bosons: A weakly interacting Bose gas on a simple cubic lattice is considered. We\nprove the existence of the standard or zero-mode Bose condensation at\nsufficiently low temperature. This result is valid for sufficiently small\ninteraction potential and small values of chemical potential. Our method\nexploits infrared bound for the suitable two-point Bogolyubov's inner product.\nWe do not use the reflection positivity or some expansion methods."
    },
    {
        "anchor": "Quantum metric contribution to the pair mass in spin-orbit coupled Fermi\n  superfluids: As a measure of the quantum distance between Bloch states in the Hilbert\nspace, the quantum metric was introduced to solid-state physics through the\nreal part of the so-called geometric Fubini-Study tensor, the imaginary part of\nwhich corresponds to the Berry curvature measuring the emergent gauge field in\nmomentum space. Here, we first derive the Ginzburg-Landau theory near the\ncritical superfluid transition temperature, and then identify and analyze the\ngeometric effects on the effective mass tensor of the Cooper pairs. By showing\nthat the quantum metric contribution accounts for a sizeable fraction of the\npair mass in a surprisingly large parameter regime throughout the BCS-BEC\ncrossover, we not only reveal the physical origin of its governing role in the\nsuperfluid density tensor but also hint at its plausible roles in many other\nobservables as well.",
        "positive": "Dynamics of a coupled spin vortex pair in dipolar spinor Bose-Einstein\n  condensates: The collisional and magnetic field quench dynamics of a coupled spin-vortex\npair in dipolar spinor Bose-Einstein condensates in a double well potential are\nnumerically investigated in the mean field theory. Upon a sudden release of the\npotential barrier the two layers of condensates collide with each other in the\ntrap center with the chirality of the vortex pair exchanged after each\ncollision, showing the typical signature of in-phase collision for the parallel\nspin vortex phase, and out-of-phase collision for the antiparallel phase. When\nquenching the transverse magnetic field, the vortex center in the\nsingle-layered condensate starts to make a helical motion with oval-shaped\ntrajectories and the displacement of the center position is found to exhibit a\ndamped simple harmonic oscillation with an intrinsic frequency and damping\nrate. The oscillation mode of the spin vortex pair may be tuned by the initial\nmagnetic field and the height of the Gaussian barrier, e.g. the gyrotropic\nmotions for parallel spin vortex pair are out of sync with each other in the\ntwo layers, while those for the antiparallel pair exhibit a\ndouble-helix-structure with the vortex centers moving opposite to each other\nwith the same amplitude."
    },
    {
        "anchor": "Nonlocal interactions in a BEC: an Analogue Gravity perspective: We add a minimal correction term to the local Gross-Pitaevskii equation to\nrepresent non-locality in the interactions. We show that the effective minimal\nnon-locality can make the healing length decrease more rapidly with the\nincrease of $s$-wave scattering length leaving the expression of the velocity\nof sound unaltered. We discuss the implication of this result for a\nBose-Einstein Condensate (BEC) being used as an analogue gravity system. The\npresented result is important in the context of condensed matter physics as\nwell because one can considerably change the size of a quantized vortex at\nfinite $s$-wave scattering length by tuning the healing length.",
        "positive": "Quantum gas microscopy of an attractive Fermi-Hubbard system: The attractive Fermi-Hubbard model is the simplest theoretical model for\nstudying pairing and superconductivity of fermions on a lattice. Although its\ns-wave pairing symmetry excludes it as a microscopic model for high-temperature\nsuperconductivity, it exhibits much of the relevant phenomenology, including a\nshort-coherence length at intermediate coupling and a pseudogap regime with\nanomalous properties. Here we study an experimental realization of this model\nusing a two-dimensional (2D) atomic Fermi gas in an optical lattice. Our\nsite-resolved measurements on the normal state reveal checkerboard\ncharge-density-wave correlations close to half-filling. A \"hidden\" SU(2)\npseudo-spin symmetry of the Hubbard model at half-filling guarantees superfluid\ncorrelations in our system, the first evidence for such correlations in a\nsingle-band Hubbard system of ultracold fermions. Compared to the paired atom\nfraction, we find the charge-density-wave correlations to be a much more\nsensitive thermometer, useful for optimizing cooling into superfluid phases in\nfuture experiments."
    },
    {
        "anchor": "Feshbach-Stabilized Insulator of Bosons in Optical Lattices: Feshbach resonances - namely resonances between an unbound two-body state\n(atomic state) and a bound (molecular) state, differing in magnetic moment -\nare a unique tool to tune the interaction properties of ultracold atoms. Here\nwe show that the spin-changing interactions, coherently coupling the atomic and\nmolecular state, can act as a novel mechanism to stabilize an insulating phase\n- the Feshbach insulator - for bosons in an optical lattice close to a narrow\nFeshbach resonance. Making use of quantum Monte Carlo simulations and\nmean-field theory, we show that the Feshbach insulator appears around the\nresonance, preventing the system from collapsing when the effective atomic\nscattering length becomes negative. On the atomic side of the resonance, the\ntransition from condensate to Feshbach insulator has a characteristic\nfirst-order nature, due to the simultaneous loss of coherence in the atomic and\nmolecular components. These features appear clearly in the ground-state phase\ndiagram of e.g. $^{87}$Rb around its 414 G resonance, and they are therefore\ndirectly amenable to experimental observation.",
        "positive": "Emission of Spin-correlated Matter-wave Jets from Spinor Bose-Einstein\n  Condensates: We report the observation of matter-wave jet emission in a strongly\nferromagnetic spinor Bose-Einstein condensate of $^7$Li atoms. Directional\natomic beams with $|{F=1,m_F=1}\\rangle$ and $|{F=1,m_F=-1}\\rangle$ spin states\nare generated from $|{F=1,m_F=0}\\rangle$ state condensates, or vice versa. This\nresults from collective spin-mixing scattering events, where spontaneously\nproduced pairs of atoms with opposite momentum facilitates additional\nspin-mixing collisions as they pass through the condensates. The matter-wave\njets of different spin states ($|{F=1,m_F=\\pm1}\\rangle$) can be a macroscopic\nEinstein-Podolsky-Rosen state with spacelike separation. Its spin-momentum\ncorrelations are studied by using the angular correlation function for each\nspin state. Rotating the spin axis, the inter-spin and intra-spin momentum\ncorrelation peaks display a high contrast oscillation, indicating collective\ncoherence of the atomic ensembles. We provide numerical calculations that\ndescribe the experimental results at a quantitative level and can identify its\nentanglement after 100~ms of a long time-of-flight."
    },
    {
        "anchor": "Driven Bose-Hubbard Model with a Parametrically Modulated Harmonic Trap: We investigate a one-dimensional Bose-Hubbard model in a parametrically\ndriven global harmonic trap. The delicate interplay of both the local atom\ninteraction and the global driving allows to control the dynamical stability of\nthe trapped quantum many-body state. The mechanism is illustrated for weak\ninteraction by a discretized Gross-Pitaevskii equation within a Gaussian\nvariational ansatz, yielding to a Mathieu equation for the condensate width.\nThe parametric resonance condition can be tuned by the atom interaction\nstrength. For stronger interaction, this mechanism is confirmed by results of\nthe numerically exact time-evolving block decimation scheme. The global\nmodulation also induces an effective time-independent inhomogeneous hopping\nstrength for the atoms.",
        "positive": "Interorbital Interactions in an SU(2)xSU(6)-Symmetric Fermi-Fermi\n  Mixture: We characterize inter- and intraisotope interorbital interactions between\natoms in the 1S0 ground state and the 3P0 metastable state in interacting\nFermi-Fermi mixtures of 171Yb and 173Yb. We perform high-precision clock\nspectroscopy to measure interaction-induced energy shifts in a deep 3D optical\nlattice and determine the corresponding scattering lengths. We find the elastic\ninteraction of the interisotope mixtures 173Yb_e-171Yb_g and 173Yb_g-171Yb_e to\nbe weakly attractive and very similar, while the corresponding two-body loss\ncoefficients differ by more than two orders of magnitude. By comparing\ndifferent spin mixtures we experimentally demonstrate the SU(2)xSU(6) symmetry\nof all elastic and inelastic interactions. Furthermore, we measure the\nspin-exchange interaction in 171Yb and confirm its previously observed\nantiferromagnetic nature."
    },
    {
        "anchor": "Fractional quantization of the topological charge pumping in a\n  one-dimensional superlattice: A one-dimensional quantum charge pump transfers a quantized charge in each\npumping cycle. This quantization is topologically robust being analogous to the\nquantum Hall effect. The charge transferred in a fraction of the pumping period\nis instead generally unquantized. We show, however, that with specific\nsymmetries in parameter space the charge transferred at well-defined fractions\nof the pumping period is quantized as integer fractions of the Chern number. We\nillustrate this in a one-dimensional Harper-Hofstadter model and show that the\nfractional quantization of the topological charge pumping is independent of the\nspecific boundary conditions taken into account. We further discuss the\nrelevance of this phenomenon for cold atomic gases in optical superlattices.",
        "positive": "Superfluid to Mott insulator transition in the one-dimensional\n  Bose-Hubbard model for arbitrary integer filling factors: We study the quantum phase transition between the superfluid and the Mott\ninsulator in the one-dimensional (1D) Bose-Hubbard model. Using the\ntime-evolving block decimation method, we numerically calculate the tunneling\nsplitting of two macroscopically distinct states with different winding\nnumbers. From the scaling of the tunneling splitting with respect to the system\nsize, we determine the critical point of the superfluid to Mott insulator\ntransition for arbitrary integer filling factors. We find that the critical\nvalues versus the filling factor in 1D, 2D, and 3D are well approximated by a\nsimple analytical function. We also discuss the condition for determining the\ntransition point from a perspective of the instanton method."
    },
    {
        "anchor": "Dissipative nonlinear waves in a gravitating quantum fluid: Nonlinear wave propagation is studied analytically in a dissipative,\nself-gravitating Bose Einstein condensate, in the framework of Gross-Pitaevskii\nmodel. The linear dispersion relation shows that the effect of dissipation is\nto suppress dynamical instabilities that destabilize the system. The small\namplitude analysis using reductive perturbation technique is found to yield a\nmodified form of KdV equation. The soliton energy, amplitude and velocity are\nfound to decay with time, whereas the soliton width increases, such that the\nsoliton exists for a finite time only",
        "positive": "Coleman-Weinberg mechanism in spinor Bose-Einstein condensates: It is argued that a continuous quantum phase transition between different\nordered phases in spinor Bose-Einstein condensates predicted by the mean-field\ntheory is vulnerable to quantum fluctuations. By analyzing Lee-Huang-Yang\ncorrections in the condensate, we demonstrate that the so-called\nColeman-Weinberg mechanism takes place in such a transition, that is, the\ntransition becomes of the first order by quantum fluctuations. A jump to be\nexpected in this first-order transition is induced by a correction from density\nfluctuations despite a transition between different magnetic properties with\nkeeping condensation. We exemplify this with an experimentally relevant case\nand show that a measurement of a condensate depletion can be utilized to\nconfirm the first-order transition."
    },
    {
        "anchor": "Atom chips with two-dimensional electron gases: theory of near surface\n  trapping and ultracold-atom microscopy of quantum electronic systems: We show that current in a two-dimensional electron gas (2DEG) can trap\nultracold atoms $<1 \\mu$m away with orders of magnitude less spatial noise than\na metal trapping wire. This enables the creation of hybrid systems, which\nintegrate ultracold atoms with quantum electronic devices to give extreme\nsensitivity and control: for example, activating a single quantized conductance\nchannel in the 2DEG can split a Bose-Einstein condensate (BEC) for atom\ninterferometry. In turn, the BEC offers unique structural and functional\nimaging of quantum devices and transport in heterostructures and graphene.",
        "positive": "Density-induced processes in quantum gas mixtures in optical lattices: We show that off-site processes and multi-orbital physics have a crucial\nimpact on the phase diagram of quantum gas mixtures in optical lattices. In\nparticular, we discuss Bose-Fermi mixtures where the intra- and interspecies\ninteractions induce competing density-induced hopping processes, the so-called\nbond-charge interactions. Furthermore, higher bands strongly influence\ntunneling and on-site interactions. We apply a multi-orbital\ninteraction-induced dressing of the lowest band which leads to renormalized\nhopping processes. These corrections give rise to an extended Hubbard model\nwith intrinsically occupation-dependent parameters. The resulting decrease of\nthe tunneling competes with a decrease of the total on-site interaction energy\nboth affecting the critical lattice depth of the superfluid to Mott insulator\ntransition. In contrast to the standard Bose-Fermi-Hubbard model, we predict a\nlarge shift of the transition to shallower lattice depths with increasing\nBose-Fermi attraction. The applied theoretical model allows an accurate\nprediction of the modified tunneling amplitudes and the critical lattice depth\nboth recently observed experimentally."
    },
    {
        "anchor": "Exotic Vortex Lattices in Binary Repulsive Superfluids: We investigate a mixture of two repulsively interacting superfluids with\ndifferent constituent particle masses: $m_1\\ne m_2$. Solutions to the\nGross-Pitaevskii equation for homogeneous infinite vortex lattices predict the\nexistence of rich vortex lattice configurations, a number of which correspond\nto Platonic and Archimedean planar tilings. Some notable geometries include the\nsnub-square, honeycomb, kagome, and herringbone lattice configurations. We\npresent a full phase diagram for the case $m_2/m_1 = 2$ and list a number of\ngeometries that are found for higher integer mass ratios.",
        "positive": "Squeezed Ground States in a Spin-1 Bose-Einstein Condensate: We generate spin squeezed ground states in an atomic spin-1 Bose-Einstein\ncondensate tuned nearthe quantum critical point between the polar and\nferromagnetic quantum phases of the interactingspin ensemble. In contrast to\ntypical non-equilibrium methods for preparing atomic squeezed statesby\nquenching through a quantum phase transition, squeezed ground states are\ntime-stationary andremain squeezed for the lifetime of the condensate. A\nsqueezed ground state with a metrologicalimprovement up to 6-8 dB and a\nconstant squeezing angle maintained over 2 s is demonstrated."
    },
    {
        "anchor": "Universality of three-body systems in 2D: parametrization of the bound\n  states energies: Universal properties of mass-imbalanced three-body systems in 2D are studied\nusing zero-range interactions in momentum space. The dependence of the\nthree-particle binding energy on the parameters (masses and two-body energies)\nis highly non-trivial even in the simplest case of two identical particles and\na distinct one. This dependence is parametrized for ground and excited states\nin terms of {\\itshape supercircles} functions in the most general case of three\ndistinguishable particles.",
        "positive": "Beyond mean-field dynamics in open Bose-Hubbard chains: We investigate the effects of phase noise and particle loss on the dynamics\nof a Bose-Einstein condensate in an optical lattice. Starting from the\nmany-body master equation, we discuss the applicability of generalized\nmean-field approximations in the presence of dissipation as well as methods to\nsimulate quantum effects beyond mean-field by including higher-order\ncorrelation functions. It is shown that localized particle dissipation leads to\nsurprising dynamics, as it can suppress decay and restore the coherence of a\nBose-Einstein condensate. These effects can be applied to engineer coherent\nstructures such as stable discrete breathers and dark solitons."
    },
    {
        "anchor": "Topological phase transitions in ultra-cold Fermi superfluids: the\n  evolution from BCS to BEC under artificial spin-orbit fields: We discuss topological phase transitions in ultra-cold Fermi superfluids\ninduced by interactions and artificial spin orbit fields. We construct the\nphase diagram for population imbalanced systems at zero and finite\ntemperatures, and analyze spectroscopic and thermodynamic properties to\ncharacterize various phase transitions. For balanced systems, the evolution\nfrom BCS to BEC superfluids in the presence of spin-orbit effects is only a\ncrossover as the system remains fully gapped, even though a triplet component\nof the order parameter emerges. However, for imbalanced populations, spin-orbit\nfields induce a triplet component in the order parameter that produces nodes in\nthe quasiparticle excitation spectrum leading to bulk topological phase\ntransitions of the Lifshitz type. Additionally a fully gapped phase exists,\nwhere a crossover from indirect to direct gap occurs, but a topological\ntransition to a gapped phase possessing Majorana fermions edge states does not\noccur.",
        "positive": "Elastic scattering of a Bose-Einstein condensate at a potential\n  landscape: We investigate the elastic scattering of Bose-Einstein condensates at shallow\nperiodic and disorder potentials. We show that the collective scattering of the\nmacroscopic quantum object couples to internal degrees of freedom of the\nBose-Einstein condensate such that the Bose-Einstein condensate gets depleted.\nAs a precursor for the excitation of the Bose-Einstein condensate we observe\nwave chaos within a mean-field theory."
    },
    {
        "anchor": "Universal Relations for Fermions with Large Scattering Length: The behavior of fermions with two spin states that interact with a large\nscattering length is constrained by universal relations that hold for any state\nof the system. These relations involve a central property of the system called\nthe contact, which measures the number of pairs of fermions with different\nspins that have small separations. The contact controls the thermodynamics of\nthe system as well as the large-momentum and high-frequency tails of\ncorrelation functions. This review summarizes the current theoretical and\nexperimental status of these universal relations.",
        "positive": "Miscibility in coupled dipolar and non-dipolar Bose-Einstein condensates: We perform a full three-dimensional study on miscible-immiscible conditions\nfor coupled dipolar and non-dipolar Bose-Einstein condensates (BEC), confined\nwithin anisotropic traps. Without loosing general miscibility aspects that can\noccur for two-component mixtures, our main focus was on the atomic\nerbium-dysprosium ($^{168}$Er-$^{164}$Dy) and dysprosium-dysprosium\n($^{164}$Dy-$^{162}$Dy) mixtures. Our analysis for pure-dipolar BEC was limited\nto coupled systems confined in pancake-type traps, after considering a study on\nthe stability regime of such systems. In case of non-dipolar systems with\nrepulsive contact intneeractions we are able to extend the miscibility analysis\nto coupled systems with cigar-type symmetries. For a coupled condensate with\nrepulsive inter- and intra-species two-body interactions, confined by an\nexternal harmonic trap, the transition from a miscible to an immiscible phase\nis verified to be much softer than in the case the system is confined by a\nsymmetric hard-wall potential. Our results, presented by density plots, are\npointing out the main role of the trap symmetry and inter-species interaction\nfor the miscibility. A relevant parameter to measure the overlap between the\ntwo densities was defined and found appropriate to quantify the miscibility of\na coupled system."
    },
    {
        "anchor": "Comment on Influence of induced interactions on superfluid properties of\n  quasi-two-dimensional dilute Fermi gases with spin-orbit coupling: In an article in 2013, Caldas et al. [Phys. Rev. A 88, 023615 (2013)] derived\nanalytical expressions of the induced interaction within the scheme of Gorkov\nand Melik-Barkhudrov in quasi-two-dimensional Fermi gases with Rashba\nspin-orbit coupling (SOC). They claimed that the induced interaction is exactly\nthe same as the one for the case without SOC when the SOC is weak, and in the\nregion of strong SOC, it starts from a reduced value and then recovers the\nvalue for the zero SOC in the limit of large SOC. We point out that their\ncalculations contain the critical errors and inconsistencies that significantly\naffect the basis of these claims.",
        "positive": "Spin squeezing in mixed-dimensional anisotropic lattice models: We describe a theoretical scheme for generating scalable spin squeezing with\nnearest-neighbour interactions between spin-1/2 particles in a 3D lattice,\nwhich are naturally present in state-of-the-art 3D optical lattice clocks. We\npropose to use strong isotropic Heisenberg interactions within individual\nplanes of the lattice, forcing the constituent spin-1/2s to behave as large\ncollective spins. These large spins are then coupled with XXZ anisotropic\ninteractions along a third direction of the lattice. This system can be\nrealized via superexchange interactions in a 3D optical lattice subject to an\nexternal linear potential, such as gravity, and in the presence of spin-orbit\ncoupling (SOC) to generate spin anisotropic interactions. We show there is a\nwide range of parameters in this setting where the spin squeezing improves with\nincreasing system size even in the presence of holes."
    },
    {
        "anchor": "Accelerated Bose-Einstein condensates in a double-well potential: Devices based on ultracold atoms moving in an accelerating optical lattice or\ndouble-well potential are a promising tool for precise measurements of\nfundamental physical constants as well as for the construction of sensors.\nHere, we carefully analyze the model of a couple of BECs separated by a barrier\nin an accelerated field and we show how the observable quantities, mainly the\nperiod of the beating motion or of the phase-shift, are related to the physical\nparameters of the model as well as to the energy of the initial state.",
        "positive": "Producing and storing spin-squeezed states and\n  Greenberger-Horne-Zeilinger states in a one-dimensional optical lattice: We study the dynamical generation and storage of spin squeezed states, as\nwell as more entangled states up to macroscopic superpositions, in a system\ncomposed of a few ultra-cold atoms trapped in a one-dimensional optical\nlattice. The system, initially in the superfluid phase with each atom in a\nsuperposition of two internal states, is first dynamically entangled by\natom-atom interactions then adiabatically brought to the Mott-insulator phase\nwith one atom per site where the quantum correlations are stored. Exact\nnumerical diagonalization allows us to explore the structure of the stored\nstates by looking at various correlation functions, on site and between\ndifferent sites, both at zero temperature and at finite temperature, as it\ncould be done in an experiment with a quantum-gas microscope."
    },
    {
        "anchor": "Noise correlations of a strongly attractive spin-1/2 Fermi gas in an\n  optical lattice: We calculate density-density correlations of an expanding gas of strongly\nattractive ultra-cold spin-1/2 fermions in an optical lattice. The phase\ndiagram of the tightly bound fermion pairs exhibits a Bose-Einstein condensed\nstate and a Mott insulating state with a single molecule per lattice site. We\nstudy the effects of quantum fluctuations on the correlations in both phases\nand show that they are especially important in the Bose-Einstein condensate\nstate, leading to the appearance of singular peaks. In the Mott insulating\nstate the correlations are characterized by sharp dips. This can be utilized in\nexperiments to distinguish between these two phases.",
        "positive": "Thermodynamics and static response of anomalous 1D fermions via quantum\n  Monte Carlo in the worldline representation: A system of three-species fermions in one spatial dimension (1D) with a\ncontact three-body interaction is known to display a scale anomaly. This\nanomaly is identical to that of a two-dimensional (2D) system of two-species\nfermions. The exact relation between those two systems, however, is limited to\nthe two-particle sector of the 2D case and the three-particle sector of the 1D\ncase. Here, we implement a non-perturbative Monte Carlo approach, based on the\nworldline representation, to calculate the thermodynamics and static response\nof three-species fermions in 1D, thus tackling the many-body sector of the\nproblem. We determine the energy, density, and pressure equations of state, and\nthe compressibility and magnetic susceptibility for a wide range of\ntemperatures and coupling strengths. We compare our results with the\nthird-order virial expansion."
    },
    {
        "anchor": "A strongly interacting Sarma superfluid near orbital Feshbach resonances: We investigate the nature of superfluid pairing in a strongly interacting\nFermi gas near orbital Feshbach resonances with spin-population imbalance in\nthree dimensions, which can be well described by a two-band or two-channel\nmodel. We show that a Sarma superfluid with gapless single-particle excitations\nis favored in the closed channel at large imbalance. It is thermodynamically\nstable against the formation of an inhomogeneous Fulde\\textendash\nFerrell\\textendash Larkin\\textendash Ovchinnikov superfluid and features a\nwell-defined Goldstone-Anderson-Bogoliubov phonon mode and a massive Leggett\nmode as collective excitations at low momentum. At large momentum, the Leggett\nmode disappears and the phonon mode becomes damped at zero temperature, due to\nthe coupling to the particle-hole excitations. We discuss possible experimental\nobservation of a strongly interacting Sarma superfluid with ultracold\nalkaline-earth-metal Fermi gases.",
        "positive": "From few to many body degrees of freedom: Here, I focus on the use of microscopic, few-body techniques that are\nrelevant in the many-body problem. These methods can be divided into indirect\nand direct. In particular, indirect methods are concerned with the\nsimplification of the many-body problem by substituting the full, microscopic\ninteractions by pseudopotentials which are designed to reproduce collisional\ninformation at specified energies, or binding energies in the few-body sector.\nThese simplified interactions yield more tractable theories of the many-body\nproblem, and are equivalent to effective field theory of interactions. Direct\nmethods, which so far are most useful in one spatial dimension, have the goal\nof attacking the many-body problem at once by using few-body information only.\nHere, I will present non-perturbative direct methods to study one-dimensional\nfermionic and bosonic gases in one dimension."
    },
    {
        "anchor": "On Many Body System Interactions: We discuss possible relationships between geometric and topological\ninteractions on one side and physical interactions on the other side.",
        "positive": "Drag-induced dynamical formation of dark solitons in Bose mixture on a\n  ring: Andreev-Bashkin drag plays a very important role in multiple areas like\nsuperfluid mixtures, superconductors and dense nuclear matter. Here, we point\nout that the drag phenomenon can be also important in physics of solitons,\nubiquitous objects arising in a wide array of fields ranging from tsunami waves\nand fiber-optic communication to biological systems. So far, fruitful studies\nwere conducted in ultracold atomic systems where nontrivial soliton dynamics\noccurred due to inter-component density-density interaction. In this work we\nshow that current-current coupling between components (Andreev-Bashkin drag)\ncan lead to a substantially different kind of effects, unsupported by\ndensity-density interactions, such as a drag-induced dark soliton generation.\nThis also points out that soliton dynamics can be used as a tool to\nexperimentally study the dissipationless drag effect."
    },
    {
        "anchor": "Finite temperature stability and dimensional crossover of exotic\n  superfluidity in lattices: We investigate exotic paired states of spin-imbalanced Fermi gases in\nanisotropic lattices, tuning the dimension between one and three. We calculate\nthe finite temperature phase diagram of the system using real-space dynamical\nmean-field theory in combination with the quantum Monte Carlo method. We find\nthat regardless of the intermediate dimensions examined, the\nFulde-Ferrell-Larkin-Ovchinnikov (FFLO) state survives to reach about one third\nof the BCS critical temperature of the spin-density balanced case. We show how\nthe gapless nature of the state found is reflected in the local spectral\nfunction. While the FFLO state is found at a wide range of polarizations at low\ntemperatures across the dimensional crossover, with increasing temperature we\nfind out strongly dimensionality-dependent melting characteristics of shell\nstructures related to harmonic confinement. Moreover, we show that intermediate\ndimension can help to stabilize an extremely uniform finite temperature FFLO\nstate despite the presence of harmonic confinement.",
        "positive": "Momentum distribution of 1D Bose gases at the quasi-condensation\n  crossover: theoretical and experimental investigation: We investigate the momentum distribution of weakly interacting 1D Bose gases\nat thermal equilibrium both experimentally and theoretically. Momentum\ndistribution of single 1D Bose gases is measured using a focusing technique,\nwhose resolution we improve via a guiding scheme. The momentum distribution\ncompares very well with quantum Monte Carlo calculations for the Lieb-Liniger\nmodel at finite temperature, allowing for an accurate thermometry of the gas\nthat agrees with (and improves upon) the thermometry based on in situ density\nfluctuation measurements. The quasi-condensation crossover is investigated via\ntwo different experimental parameter sets, corresponding to the two different\nsides of the crossover. Classical field theory is expected to correctly\ndescribe the quasi-condensation crossover of weakly interacting gases. We\nderive the condition of validity of the classical field theory, and find that,\nin typical experiments, interactions are too strong for this theory to be\naccurate. This is confirmed by a comparison between the classical field\npredictions and the numerically exact quantum Monte Carlo calculations."
    },
    {
        "anchor": "Finite-size effects on the cluster expansions for quantum gases in\n  restricted geometries: We have analytically obtained 1-particle density matrices for ideal Bose and\nFermi gases in both the 3-D box geometries and the harmonically trapped\ngeometries for the entire range of temperature. We have obtained quantum\ncluster expansions of the grand free energies in closed forms for the same\nsystems in the restricted geometries. We have proposed a theorem (with a proof)\nabout the generic form of the quantum cluster integral. We also have considered\nshort ranged interactions in our analyses for the quasi 1-D cases of Bose and\nFermi gases in the box geometries. Our theoretical results are exact, and are\ndirectly useful for understanding finite-size effects on quantum cluster\nexpansion of Bose and Fermi gases in the restricted geometries. Our results\nwould be relevant in the context of experimental study of spatial correlations\nin ultra-cold systems of dilute Bose and Fermi gases of alkali atoms (i) in 3-D\nmagneto-optical box traps with quasi-uniform potential around the center [1],\nand (ii) in 3-D harmonic traps [2, 3].",
        "positive": "Dissipation-enhanced collapse singularity of a nonlocal fluid of light\n  in a hot atomic vapor: We study the out-of-equilibrium dynamics of a two-dimensional paraxial fluid\nof light using a near-resonant laser propagating through a hot atomic vapor. We\nobserve a double shock-collapse instability: a shock (gradient catastrophe) for\nthe velocity, as well as an annular (ring-shaped) collapse singularity for the\ndensity. We find experimental evidence that this instability results from the\ncombined effect of the nonlocal photon-photon interaction and the linear photon\nlosses. The theoretical analysis based on the method of characteristics reveals\nthe main counterintuitive result that dissipation (photon losses) is\nresponsible for an unexpected enhancement of the collapse instability. Detailed\nanalytical modeling makes it possible to evaluate the nonlocality range of the\ninteraction. The nonlocality is controlled by adjusting the atomic vapor\ntemperature and is seen to increase dramatically when the atomic density\nbecomes much larger than one atom per cubic wavelength. Interestingly, such a\nlarge range of the nonlocal photon-photon interaction has not been observed in\nan atomic vapor so far and its microscopic origin is currently unknown."
    },
    {
        "anchor": "Fusion channels of non-Abelian anyons from angular-momentum and\n  density-profile measurements: We present a method to characterize non-Abelian anyons that is based only on\nstatic measurements and that does not rely on any form of interference. For\ngeometries where the anyonic statistics can be revealed by rigid rotations of\nthe anyons, we link this property to the angular momentum of the initial state.\nWe test our method on the paradigmatic example of the Moore-Read state, that is\nknown to support excitations with non-Abelian statistics of Ising type. As an\nexample, we reveal the presence of different fusion channels for two such\nexcitations, a defining feature of non-Abelian anyons. This is obtained by\nmeasuring density-profile properties, like the mean square radius of the system\nor the depletion generated by the anyons. Our study paves the way to novel\nmethods for characterizing non-Abelian anyons, both in the experimental and\ntheoretical domains.",
        "positive": "Superfluid properties of bright solitons in a ring: We theoretically investigate superfluid properties of a one-dimensional\nannular superfluid with a boost. We derive the formula of the superfluid\nfraction in the one-dimensional superfluid, which was originally derived by\nLeggett in the context of supersolid. We see that the superfluid fraction given\nby Leggett's formula detects the emergence of solitons in the one-dimensional\nannular superfluid. The formation of a bright soliton at a critical interaction\nstrength decreases the superfluid fraction. At a critical boost velocity, a\nnode appears in the soliton and the superfluid fraction vanishes. With a\ntransverse dimension, the soliton alters to a more localized one and it\nundergoes dynamical instability at a critical transverse length. Consequently,\nthe superfluid fraction decreases as one increases the length up to the\ncritical length. With a potential barrier along the ring, the uniform density\nalters to an inhomogeneous configuration and it develops a soliton localized at\none of the potential minima by increasing the interaction strength."
    },
    {
        "anchor": "Bosonic molecules in a lattice: unusual fluid phase from multichannel\n  interactions: We show that multichannel interactions significantly alter the phase diagram\nof ultracold bosonic molecules in an optical lattice. Most prominently, an\nunusual fluid region intervenes between the conventional superfluid and the\nMott insulator. In it, number fluctuations remain but phase coherence is\nsuppressed by a significant factor. This factor can be made arbitrarily large,\nat least in a two-site configuration. We calculate the phase diagram using\ncomplementary methods, including Gutzwiller mean-field and density matrix\nrenormalization group (DMRG) calculations. Although we focus on bosonic\nmolecules without dipolar interactions, we expect multichannel interactions to\nremain important for dipolar interacting and fermionic molecules.",
        "positive": "Non-Universal Equation of State of the Two-Dimensional Bose Gas: For a dilute two-dimensional Bose gas the universal equation of state has a\nlogarithmic dependence on the s-wave scattering length. Here we derive\nnon-universal corrections to this equation of state taking account finite-range\neffects of the inter-atomic potential. Our beyond-mean-field analytical results\nare obtained performing dimensional regularization of divergent zero-point\nquantum fluctuations within the finite-temperature formalism of functional\nintegration. In particular, we find that in the grand canonical ensemble the\npressure has a nonpolynomial dependence on the finite- range parameter and it\nis a highly nontrivial function of chemical potential and temperature."
    },
    {
        "anchor": "Laser cooling to quantum degeneracy: We report on Bose-Einstein condensation (BEC) in a gas of strontium atoms,\nusing laser cooling as the only cooling mechanism. The condensate is formed\nwithin a sample that is continuously Doppler cooled to below 1\\muK on a\nnarrow-linewidth transition. The critical phase-space density for BEC is\nreached in a central region of the sample, in which atoms are rendered\ntransparent for laser cooling photons. The density in this region is enhanced\nby an additional dipole trap potential. Thermal equilibrium between the gas in\nthis central region and the surrounding laser cooled part of the cloud is\nestablished by elastic collisions. Condensates of up to 10^5 atoms can be\nrepeatedly formed on a timescale of 100ms, with prospects for the generation of\na continuous atom laser.",
        "positive": "Nonlinear standing waves in an array of coherently coupled Bose-Einstein\n  condensates: Stationary solitary waves are studied in an array of $M$ linearly-coupled\none-dimensional Bose-Einstein condensates (BECs) by means of the\nGross-Pitaevskii equation. Solitary wave solutions with the character of\noverlapping dark solitons, Josephson vortex - antivortex arrays, and arrays of\nhalf-dark solitons are constructed for $M>2$ from known solutions for two\ncoupled BECs. Additional solutions resembling vortex dipoles and rarefaction\npulses are found numerically. Stability analysis of the solitary waves reveals\nthat overlapping dark solitons can become unstable and susceptible to decay\ninto arrays of Josephson vortices. The Josephson vortex arrays have mixed\nstability but for all parameters we find at least one stationary solitary wave\nconfiguration that is dynamically stable. The different families of nonlinear\nstanding waves bifurcate from one another. In particular we demonstrate that\nJosephson-vortex arrays bifurcate from dark soliton solutions at instability\nthresholds. The stability thresholds for dark soliton and Josephson-vortex type\nsolutions are provided, suggesting the feasibility of realization with optical\nlattice experiments."
    },
    {
        "anchor": "Dissipation in a Finite Temperature Atomic Josephson Junction: We numerically demonstrate and characterize the emergence of distinct\ndynamical regimes of a finite temperature bosonic superfluid in an elongated\nJosephson junction generated by a thin Gaussian barrier over the entire\ntemperature range where a well-formed condensate can be clearly identified.\nAlthough the dissipation arising from the coupling of the superfluid to the\ndynamical thermal cloud increases with increasing temperature as expected, the\nimportance of this mechanism is found to depend on two physical parameters\nassociated (i) with the initial chemical potential difference, compared to some\ncharacteristic value, and (ii) the ratio of the thermal energy to the barrier\namplitude. The former determines whether the superfluid Josephson dynamics are\ndominated by gradually damped plasma-like oscillations (for relatively small\ninitial population imbalances), or whether dissipation at early times is\ninstead dominated by vortex- and sound-induced dissipation (for larger initial\nimbalances). The latter defines the effect of the thermal cloud on the\ncondensate dynamics, with a reversal of roles, i.e. the condensate being driven\nby the oscillating thermal cloud, being observed when the thermal particles\nacquire enough energy to overcome the barrier. Our findings are within current\nexperimental reach in ultracold superfluid junctions.",
        "positive": "Skyrmion-string defects with arbitrary topological charges in spinor\n  Bose-Einstein condensates: Under the presence of external magnetic fields with cylindrical symmetry,\nSkyrmion-string defects with arbitrary topological charges are shown to appear\nin spinor $F = 1$ Bose-Einstein condensates. We show that, depending on the\nmagnetic field boundary condition, the topological spin texture, at the planes\nperpendicular to the cylindrical axis, can take zero, half integer, or\narbitrary values between $-1/2$ and $1/2$. We argue that these are true\ntopological defects since their charge is independent of the spatial location\nof the singularity and since the total Skyrmion charge is the sum of the\nindividual charges of the defects present. Our findings are obtained by\nnumerically solving the corresponding fully coupled Gross-Pitaevskii equations\nwithout any symmetry assumptions. We analyze, both, polar $^{23}$Na and\nferromagnetic $^{87}$Rb condensates."
    },
    {
        "anchor": "Topological superfluids on a square optical lattice with non-Abelian\n  gauge fields: Effects of next-nearest-neighbor hopping in the BCS-BEC\n  evolution: We consider a two-component Fermi gas with attractive interactions on a\nsquare optical lattice, and study the interplay of Zeeman field, spin-orbit\ncoupling and next-nearest-neighbor hopping on the ground-state phase diagrams\nin the entire BCS-BEC evolution. In particular, we first classify and\ndistinguish all possible superfluid phases by the momentum-space topology of\ntheir zero-energy quasiparticle/quasihole excitations, and then numerically\nestablish a plethora of quantum phase transitions in between. These transitions\nare further signalled and evidenced by the changes in the corresponding\ntopological invariant of the system, \\textit{i.e.}, its Chern number. Lastly,\nwe find that the superfluid phase exhibits a reentrant structure, separated by\na fingering normal phase, the origin of which is traced back to the changes in\nthe single-particle density of states.",
        "positive": "Dipolar Stabilization of an Attractive Bose Gas in a One Dimensional\n  Lattice: We experimentally show that dipolar interaction can stabilize otherwise\nunstable many-body systems like an attractive Bose gas. In a one dimensional\nlattice the repulsive dipolar on-site interaction balances negative scattering\nlengths up to -17 Bohr radii and stabilizes the chromium Bose-Einstein\ncondensate. For reduced lattice depths, the dipolar stabilization turns into\ndestabilization. We probe the full cross-over between the two regimes and our\nresults are in excellent agreement with theoretical calculations, which reveal\nsignificant dipolar inter-site interactions."
    },
    {
        "anchor": "Dynamical many-body delocalization transition of a Tonks gas in a\n  quasi-periodic driving potential: The quantum kicked rotor is well-known for displaying dynamical (Anderson)\nlocalization. It has recently been shown that a periodically kicked Tonks gas\nwill always localize and converge to a finite energy steady-state. This\nsteady-state has been described as being effectively thermal with an effective\ntemperature that depends on the parameters of the kick. Here we study a\ngeneralization to a quasi-periodic driving with three frequencies which,\nwithout interactions, has a metal-insulator Anderson transition. We show that a\nquasi-periodically kicked Tonks gas goes through a dynamical many-body\ndelocalization transition when the kick strength is increased. The localized\nphase is still described by a low effective temperature, while the delocalized\nphase corresponds to an infinite-temperature phase, with the temperature\nincreasing linearly in time. At the critical point, the momentum distribution\nof the Tonks gas displays different scaling at small and large momenta\n(contrary to the non-interacting case), signaling a breakdown of the\none-parameter scaling theory of localization.",
        "positive": "A grand-canonical approach to the disordered Bose gas: We study the problem of disordered interacting bosons within grand-canonical\nthermodynamics and Bogoliubov theory. We compute the fractions of condensed and\nnon-condensed particles and corrections to the compressibility and the speed of\nsound due to interaction and disorder. There are two small parameters, the\ndisorder strength compared to the chemical potential and the dilute-gas\nparameter."
    },
    {
        "anchor": "Seeing spin dynamics in atomic gases: The dynamics of internal spin, electronic orbital, and nuclear motion states\nof atoms and molecules have preoccupied the atomic and molecular physics\ncommunity for decades. Increasingly, such dynamics are being examined within\nmany-body systems composed of atomic and molecular gases. Our findings\nsometimes bear close relation to phenomena observed in condensed-matter\nsystems, while on other occasions they represent truly new areas of\ninvestigation. I discuss several examples of spin dynamics that occur within\nspinor Bose-Einstein gases, highlighting the advantages of spin-sensitive\nimaging for understanding and utilizing such dynamics.",
        "positive": "Z2 Topological insulator of ultra cold atoms in bichromatic optical\n  lattices: We investigate the effect of a strong bichromatic deformation to the\n$\\mathbb{Z}_{2}$ topological insulator in a fermionic ultracold atomic system\nproposed by B. B\\'eri and N. R. Cooper, Phys.Rev.Lett. {\\bf 107}, 145301\n(2011). Large insulating gap of this system allows for examination of strong\nperturbations. We consider bichromatic perturbation along all axes on a\ntriangular optical lattice. We find that $\\mathbb{Z}_{2}$ topological character\nof the system is robust up to a certain depth of the deformation. The lowest\nband can become topologically trivial while the lowest two bands are always\nprotected."
    },
    {
        "anchor": "Quantum phase transition of cold atoms in the bilayer hexagonal optical\n  lattices: We propose a scheme to investigate the quantum phase transition of cold atoms\nin the bilayer hexagonal optical lattices. Using the quantum Monte Carlo\nmethod, we calculate the ground state phase diagrams which contain an\nantiferromagnet, a solid, a superfluid, a fully polarized state and a\nsupersolid. We find there is a supersolid emerging in a proper parameter space,\nwhere the diagonal long range order coexists with off-diagonal long range\norder. We show that the bilayer optical lattices can be realized by coupling\ntwo monolayer optical lattices and give an experimental protocol to observe\nthose novel phenomena in the real experiments.",
        "positive": "Emergence of a new pair-coherent phase in many-body quenches of\n  repulsive bosons: We investigate the dynamical mode population statistics and associated first-\nand second-order coherence of an interacting bosonic two-mode model when the\npair-exchange coupling is quenched from negative to positive values. It is\nshown that for moderately rapid second-order transitions, a new pair-coherent\nphase emerges on the positive coupling side in an excited state, which is not\nfragmented as the ground-state single-particle density matrix would prescribe\nit to be."
    },
    {
        "anchor": "Symbiotic solitons in a quasi-one- and quasi-two-dimensional spin-1\n  condensates: We study the formation of spin-1 symbiotic spinor solitons in a quasi-one-\n(quasi-1D) and quasi-two-dimensional (quasi-2D) hyper-fine spin $F=1$\nferromagnetic Bose-Einstein condensate (BEC). The symbiotic solitons\nnecessarily have a repulsive intraspecies interaction and are bound due to an\nattractive interspecies interaction. Due to a collapse instability in higher\ndimensions, an additional spin-orbit coupling is necessary to stabilize a\nquasi-2D symbiotic spinor soliton. Although a quasi-1D symbiotic soliton has a\nsimple Gaussian-type density distribution, novel spatial periodic structure in\ndensity is found in quasi-2D symbiotic SO-coupled spinor solitons. For a weak\nSO coupling, the quasi-2D solitons are of the $(-1, 0, +1)$ or $(+1, 0, -1)$\ntype with intrinsic vorticity and multi-ring structure, for Rashba or\nDresselhaus SO coupling, respectively, where the numbers in the parentheses are\nangular momenta projections in spin components $F_z = +1, 0, -1$, respectively.\nFor a strong SO coupling, stripe and superlattice solitons, respectively, with\na stripe and square-lattice modulation in density, are found in addition to the\nmulti-ring solitons. The stationary states were obtained by imaginary-time\npropagation of a mean-field model; dynamical stability of the solitons was\nestablished by real-time propagation over a long period of time. The\npossibility of the creation of such a soliton by removing the trap of a\nconfined spin-1 BEC in a laboratory is also demonstrated.",
        "positive": "Countersuperflow instability in miscible two-component Bose-Einstein\n  condensates: We study theoretically the instability of countersuperflow, i.e., two\ncounterpropagating miscible superflows, in uniform two-component Bose-Einstein\ncondensates. Countersuperflow instability causes mutual friction between the\nsuperfluids, causing a momentum exchange between the two condensates, when the\nrelative velocity of the counterflow exceeds a critical value. The momentum\nexchange leads to nucleation of vortex rings from characteristic density\npatterns due to the nonlinear development of the instability. Expansion of the\nvortex rings drastically accelerates the momentum exchange, leading to a highly\nnonlinear regime caused by intervortex interaction and vortex reconnection\nbetween the rings. For a sufficiently large interaction between the two\ncomponents, rapid expansion of the vortex rings causes isotropic turbulence and\nthe global relative motion of the two condensates relaxes. The maximum vortex\nline density in the turbulence is proportional to the square of the relative\nvelocity."
    },
    {
        "anchor": "Quantum many-body scars in the Bose-Hubbard model with a three-body\n  constraint: We uncover the exact athermal eigenstates in the Bose-Hubbard (BH) model with\na three-body constraint, motivated by the exact construction of quantum\nmany-body scar (QMBS) states in the $S=1$ $XY$ model. These states are\ngenerated by applying an $\\rm SU(2)$ ladder operator consisting of a linear\ncombination of two-particle annihilation operators to the fully occupied state.\nBy using the improved Holstein-Primakoff expansion, we clarify that the QMBS\nstates in the $S=1$ $XY$ model are equivalent to those in the constrained BH\nmodel with additional correlated hopping terms. We also find that, in the\nstrong-coupling limit of the constrained BH model, the QMBS state exists as the\nlowest-energy eigenstate of the effective model in the highest-energy sector.\nThis fact enables us to prepare the QMBS states in a certain adiabatic process\nand opens up the possibility of observing them in ultracold-atom experiments.",
        "positive": "On the long-term stability of space-time crystals: We investigate a space-time crystal in a superfluid Bose gas. Using a\nwell-controlled periodic drive we excite only one crystalline mode in the\nsystem, which can be accurately modeled in the rotating frame of the drive.\nUsing holographic imaging we observe the stability of the crystal over an\nextended period of time and show the robustness of its structure in both space\nand time. By introducing a fourth-order term in the Hamiltonian we show that\nthe crystal stabilizes at a fixed number of quanta. The results of the model\nare compared to the experimental data and show good agreement, with a small\nnumber of free parameters. The results yield insights in the long-term\nstability of the crystal, which can only be obtained by the combination of the\nextended control in the experiment and the nearly ab-initio character of the\nmodel. From the model we derive a phase diagram of the system, which can be\nexploited in the future to study the phase transitions for this new state of\nmatter in even more detail."
    },
    {
        "anchor": "Effect of spin-orbit coupling on tunnelling escape of Bose-Einstein\n  condensate: We theoretically investigate quantum tunnelling escape of a spin-orbit (SO)\ncoupled Bose-Einstein condensate (BEC) from a trapping well. The condensate is\ninitially prepared in a quasi-one-dimensional harmonic trap. Depending on the\nsystem parameters, the ground state can fall in different phases --- single\nminimum, separated or stripe. Then, suddenly the trapping well is opened at one\nside. The subsequent dynamics of the condensate is studied by solving nonlinear\nSchr\\\"{o}dinger equations. We found that the diverse phases will greatly change\nthe tunneling escape behavior of SO coupled BECs. In single minimum and\nseparated phases, the condensate escapes the trapping well continuously, while\nin stripe phase it escapes the well as an array of pulses. We also found that\nSO coupling has a suppressing effect on the tunnelling escape of atoms.\nEspecially, for BECs without inter-atom interaction, the tunnelling escape can\nbe almost completely eliminated when the system is tuned near the transition\npoint between single minimum and stripe phase. Our work thus suggests that SO\ncoupling may be a useful tool to control the tunnelling dynamic of BECs, and\npotentially be applied in realization of atom lasers and matter wave switches.",
        "positive": "Experimental realisation of the topological Haldane model: The Haldane model on the honeycomb lattice is a paradigmatic example of a\nHamiltonian featuring topologically distinct phases of matter. It describes a\nmechanism through which a quantum Hall effect can appear as an intrinsic\nproperty of a band-structure, rather than being caused by an external magnetic\nfield. Although an implementation in a material was considered unlikely, it has\nprovided the conceptual basis for theoretical and experimental research\nexploring topological insulators and superconductors. Here we report on the\nexperimental realisation of the Haldane model and the characterisation of its\ntopological band-structure, using ultracold fermionic atoms in a periodically\nmodulated optical honeycomb lattice. The model is based on breaking\ntime-reversal symmetry as well as inversion symmetry. The former is achieved\nthrough the introduction of complex next-nearest-neighbour tunnelling terms,\nwhich we induce through circular modulation of the lattice position. For the\nlatter, we create an energy offset between neighbouring sites. Breaking either\nof these symmetries opens a gap in the band-structure, which is probed using\nmomentum-resolved interband transitions. We explore the resulting\nBerry-curvatures of the lowest band by applying a constant force to the atoms\nand find orthogonal drifts analogous to a Hall current. The competition between\nboth broken symmetries gives rise to a transition between topologically\ndistinct regimes. By identifying the vanishing gap at a single Dirac point, we\nmap out this transition line experimentally and quantitatively compare it to\ncalculations using Floquet theory without free parameters. We verify that our\napproach, which allows for dynamically tuning topological properties, is\nsuitable even for interacting fermionic systems. Furthermore, we propose a\ndirect extension to realise spin-dependent topological Hamiltonians."
    },
    {
        "anchor": "Non-Hermitian skin effect in one-dimensional interacting Bose gas: Non-Hermitian skin effect (NHSE) is a unique feature studied extensively in\nnon-interacting non-Hermitian systems. In this work, we extend the NHSE\noriginally discovered in non-interacting systems to interacting many-body\nsystems by investigating an exactly solvable non-Hermitian model, i.e., the\nprototypical Lieb-Liniger Bose gas with imaginary vector potential. We show\nthat this non-Hermitian many-body model can also be exactly solved through\nBethe ansatz. By solving the Bethe ansatz equations accurately, the explicit\neigenfunction is obtained, and the model's density profiles and momentum\ndistributions are calculated to characterize the NHSE quantitatively. We find\nthat the NHSE is gradually suppressed on the repulsive side but does not vanish\nas the repulsive interaction strength increases. On the attractive side, the\nNSHE for bound-state solutions is enhanced as interaction strength grows. In\ncontrast, for the scattering state the NHSE shows a non-monotonic behavior in\nthe attractive side. Our work provides the first example of the NHSE in exactly\nsolvable many-body systems, and we envision that it can be extended to other\nnon-Hermitian many-body systems, especially to integrable models.",
        "positive": "Bosonic Functional Determinant Approach and its Application to Polaron\n  Spectra: The functional determinant approach (FDA) is a simple method to compute\nexactly certain observables for ideal quantum systems and has been successfully\napplied to the Fermi polaron problem to obtain the dynamical overlap and\nspectral function. Unfortunately, its application to Bosonic ultracold gases is\nprohibited by the failure of the grand canonical ensemble for these systems. In\nthis paper, we show how to circumvent this problem and develop a Bosonic FDA.\nThis yields exact injection and ejection spectra for ideal Bose polarons at\narbitrary temperatures. While coherent features visible at absolute zero\nquickly smear out with rising temperature as expected, the line width of the\nmain peak is, counterintuitively, found to decrease near unitarity. We compare\nthe results to the Fermi polaron problem, for which we provide more detailed\nspectra than previously available by deriving an explicit formula for the\noverlap operator."
    },
    {
        "anchor": "Nonlinear synthetic gauge potentials and sonic horizons in Bose-Einstein\n  condensates: Phonons in a Bose-Einstein condensate can be made to behave as if they\npropagate in curved spacetime by controlling the condensate flow speed.\nSeemingly disconnected to this, artificial gauge potentials can be induced in\ncharge neutral atomic condensates by for instance coupling two atomic levels to\na laser field. Here we connect these two worlds and show that synthetic\ninteracting gauge fields, i.e., density-dependent gauge potentials, induce a\nnon-trivial spacetime structure for the phonons. This allows for the creation\nof new spacetime geometries which depend not on the flow speed of the\ncondensate but on an easily controlled transverse laser phase. Using this, we\nshow how to create artificial black holes in a stationary condensate, we\nsimulate charge in a Reissner-Nordstr\\\"om black hole and induce cosmological\nhorizons by creating de Sitter spacetimes. We then show how to combine this de\nSitter spacetime with a black hole, which also opens up the possibility to\nstudy in experiments its quantum stability.",
        "positive": "Observation of Dirac Monopoles in a Synthetic Magnetic Field: Magnetic monopoles --- particles that behave as isolated north or south\nmagnetic poles --- have been the subject of speculation since the first\ndetailed observations of magnetism several hundred years ago. Numerous\ntheoretical investigations and hitherto unsuccessful experimental searches have\nfollowed Dirac's 1931 development of a theory of monopoles consistent with both\nquantum mechanics and the gauge invariance of the electromagnetic field. The\nexistence of even a single Dirac magnetic monopole would have far-reaching\nphysical consequences, most famously explaining the quantization of electric\ncharge. Although analogues of magnetic monopoles have been found in exotic\nspin-ices and other systems, there has been no direct experimental observation\nof Dirac monopoles within a medium described by a quantum field, such as\nsuperfluid helium-3. Here we demonstrate the controlled creation of Dirac\nmonopoles in the synthetic magnetic field produced by a spinor Bose-Einstein\ncondensate. Monopoles are identified, in both experiments and matching\nnumerical simulations, at the termini of vortex lines within the condensate. By\ndirectly imaging such a vortex line, the presence of a monopole may be\ndiscerned from the experimental data alone. These real-space images provide\nconclusive and long-awaited experimental evidence of the existence of Dirac\nmonopoles. Our result provides an unprecedented opportunity to observe and\nmanipulate these quantum-mechanical entities in a controlled environment."
    },
    {
        "anchor": "Dark soliton decay due to trap anharmonicity in atomic Bose-Einstein\n  condensates: A number of recent experiments with nearly pure atomic Bose-Einstein\ncondensates have confirmed the predicted dark soliton oscillations when under\nharmonic trapping. However, a dark soliton propagating in an inhomogeneous\ncondensate has also been predicted to be unstable to the emission of sound\nwaves. Although harmonic trapping supports an equilibrium between the\nco-existing soliton and sound, we show that the ensuing dynamics are sensitive\nto trap anharmonicities. Such anharmonicities can break the soliton-sound\nequilibrium and lead to the net decay of the soliton on a considerably shorter\ntimescale than other dissipation mechanisms. Thus, we propose how small\nrealistic modifications to existing experimental set-ups could enable the\nexperimental observation of this decay channel.",
        "positive": "Magnetic domain growth in a ferromagnetic Bose-Einstein condensate:\n  Effects of current: Magnetic domain patterns in a ferromagnetic Bose-Einstein condensate (BEC)\nshow different properties depending on the quadratic Zeeman effect and\ndissipation. Another important factor that affects domain patterns and domain\ngrowth is superfluid flow of atoms. Domain growth in a ferromagnetic BEC with\nnegative quadratic Zeeman energy is characterized by the same growth law as\n(classical) binary fluid in the inertial hydrodynamic regime. In the absence of\nthe superfluid flow, the domain growth law for negative quadratic Zeeman energy\nis the same as that of scalar conserved fields such as binary alloys."
    },
    {
        "anchor": "Emergent Quasicrystalline Symmetry in Light-Induced Quantum Phase\n  Transitions: The discovery of quasicrystals with crystallographically forbidden rotational\nsymmetries has changed the notion of the ordering in materials, yet little is\nknown about the dynamical emergence of such exotic forms of order. Here we\ntheoretically study a nonequilibrium cavity-QED setup realizing a\nzero-temperature quantum phase transition from a homogeneous Bose-Einstein\ncondensate to a quasicrystalline phase via collective superradiant light\nscattering. Across the superradiant phase transition, collective light\nscattering creates a dynamical, quasicrystalline optical potential for the\natoms. Remarkably, the quasicrystalline potential is \"emergent\" as its\neight-fold rotational symmetry is not present in the Hamiltonian of the system,\nrather appears solely in the low-energy states. For sufficiently strong\ntwo-body contact interactions between atoms, a quasicrystalline order is\nstabilized in the system, while for weakly interacting atoms the condensate is\nlocalized in one or few of the deepest minima of the quasicrystalline\npotential.",
        "positive": "Geometric scale invariance as a route to macroscopic degeneracy: loading\n  a toroidal trap with a Bose or Fermi gas: An easily scalable toroidal geometry presents an opportunity for creating\nlarge scale persistent currents in Bose-Einstein condensates, for studies of\nthe Kibble-Zurek mechanism, and for investigations of toroidally trapped\ndegenerate Fermi gases. We consider in detail the process of isentropic loading\nof a Bose or Fermi gas from a harmonic trap into the scale invariant toroidal\nregime that exhibits a high degree of system invariance when increasing the\nradius of the toroid. The heating involved in loading a Bose gas is evaluated\nanalytically and numerically, both above and below the critical temperature.\nOur numerical calculations treat interactions within the\nHartree-Fock-Bogoliubov-Popov theory. Minimal change in degeneracy is observed\nover a wide range of initial temperatures, and a regime of cooling is\nidentified. The scale invariant property is further investigated analytically\nby studying the density of states of the system, revealing the robust nature of\nscale invariance in this trap, for both bosons and fermions. We give analytical\nresults for a Thomas-Fermi treatment. We calculate the heating due to loading a\nspin-polarized Fermi gas and compare with analytical results for high and low\ntemperature regimes. The Fermi gas is subjected to irreducible heating during\nloading, caused by the loss of one degree of freedom for thermalization."
    },
    {
        "anchor": "Diffusion Monte Carlo methods for Spin-Orbit-Coupled ultracold Bose\n  gases: We present two Diffusion Monte Carlo (DMC) algorithms for systems of\nultracold quantum gases featuring synthetic spin-orbit interactions. The first\none is a discrete spin generalization of the T- moves spin-orbit DMC, which\nprovides an upper bound to the fixed-phase energy. The second is a\nspin-integrated DMC method which recovers the fixed-phase property by avoiding\nthe definition of the effective Hamiltonian involved in the T-moves approach.\nThe latter is a more accurate method but it is restricted to spin-independent\ntwo-body interactions. We report a comparison between both algorithms for\ndifferent systems. As a check of the efficiency of both methods, we compare the\nDMC energies with results obtained with other numerical methods, finding\nagreement between both estimation",
        "positive": "Truncated correlation hierarchy schemes for driven-dissipative multimode\n  quantum systems: We present a method to describe driven-dissipative multi-mode systems by\nconsidering a truncated hierarchy of equations for the correlation functions.\nWe consider two hierarchy truncation schemes with a global cutoff on the\ncorrelation order, which is the sum of the exponents of the operators involved\nin the correlation functions: a 'hard' cutoff corresponding to an expansion\naround the vacuum, which applies to a regime where the number of excitations\nper site is small; a 'soft' cutoff which corresponds to an expansion around\ncoherent states, which can be applied for large excitation numbers per site.\nThis approach is applied to describe the bunching-antibunching transition in\nthe driven-dissipative Bose-Hubbard model for photonic systems. The results\nhave been successfully benchmarked by comparison with calculations based on the\ncorner-space renormalization method in 1D and 2D systems. The regime of\nvalidity and strengths of the present truncation methods are critically\ndiscussed."
    },
    {
        "anchor": "Short-range correlations in dilute atomic Fermi gases with spin-orbit\n  coupling: We study the short-range correlation strength of three dimensional spin half\ndilute atomic Fermi gases with spin-orbit coupling. The interatomic interaction\nis modeled by the contact pseudopotential. In the high temperature limit, we\nderive the expression for the second order virial expansion of the\nthermodynamic potential via the ladder diagrams. We further evaluate the second\norder virial expansion in the limit that the spin-orbit coupling constants are\nsmall, and find that the correlation strength between the fermions increases as\nthe forth power of the spin-orbit coupling constants. At zero temperature, we\nconsider the cases in which there are symmetric spin-orbit couplings in two or\nthree directions. In such cases, there is always a two-body bound state of zero\nnet momentum. In the limit that the average interparticle distance is much\nlarger than the dimension of the two-body bound state, the system primarily\nconsists of condensed bosonic molecules that fermions pair to form; we find\nthat the correlation strength also becomes bigger compared to that in the\nabsence of spin-orbit coupling. Our results indicate that generic spin-orbit\ncoupling enhances the short-range correlations of the Fermi gases. Measurement\nof such enhancement by photoassociation experiment is also discussed.",
        "positive": "Solitons in Tonks-Girardeau gas with dipolar interactions: The existence of bright solitons in the model of the Tonks-Girardeau (TG) gas\nwith dipole-dipole (DD) interactions is reported. The governing equation is\ntaken as the quintic nonlinear Schr\\\"{o}dinger equation (NLSE) with the\nnonlocal cubic term accounting for the DD attraction. In different regions of\nthe parameter space (the dipole moment and atom number), matter-wave solitons\nfeature flat-top or compacton-like shapes. For the flat-top states, the NLSE\nwith the local cubic-quintic (CQ) nonlinearity is shown to be a good\napproximation. Specific dynamical effects are studied assuming that the\nstrength of the DD interactions is ramped up or drops to zero. Generation of\ndark-soliton pairs in the gas shrinking under the action of the intensifying DD\nattraction is observed. Dark solitons exhibit the particle-like collision\nbehavior. Peculiarities of dipole solitons in the TG gas are highlighted by\ncomparison with the NLSE including the local CQ terms. Collisions between the\nsolitons are studied too. In many cases, the collisions result in merger of the\nsolitons into a breather, due to strong attraction between them."
    },
    {
        "anchor": "Finite temperature superfluid transition of strongly-correlated lattice\n  bosons in various geometries: We study finite-temperature properties of the strongly interacting bosons in\nthree-dimensional lattices by employing the combined Bogoliubov method and the\nquantum rotor approach. Based on the mapping of the Bose-Hubbard Hamiltonian of\nstrongly interacting bosons onto U(1) phase action, we study their\nthermodynamic phase diagrams for several lattice geometries including; simple\ncubic, body- as well as face-centered lattices. The quantitative values for the\nphase boundaries obtained here may be used as a reference for emulation of the\nBose-Hubbard model on a variety of optical lattice structures in order to\ndemonstrate experimental-theoretical consistency for the numerical values\nregarding the location of the critical points.",
        "positive": "Functional renormalization group approach to the BCS-BEC crossover: The phase transition to superfluidity and the BCS-BEC crossover for an\nultracold gas of fermionic atoms is discussed within a functional\nrenormalization group approach. Non-perturbative flow equations, based on an\nexact renormalization group equation, describe the scale dependence of the\nflowing or average action. They interpolate continuously from the microphysics\nat atomic or molecular distance scales to the macroscopic physics at much\nlarger length scales, as given by the interparticle distance, the correlation\nlength, or the size of the experimental probe. We discuss the phase diagram as\na function of the scattering length and the temperature and compute the gap,\nthe correlation length and the scattering length for molecules. Close to the\ncritical temperature, we find the expected universal behavior. Our approach\nallows for a description of the few-body physics (scattering and molecular\nbinding) and the many-body physics within the same formalism."
    },
    {
        "anchor": "Observation of bound state self-interaction in a nano-eV atom collider: Quantum mechanical scattering resonances for colliding particles occur when a\ncontinuum scattering state couples to a discrete bound state between them. The\ncoupling also causes the bound state to interact with itself via the continuum\nand leads to a shift in the bound state energy, but, lacking knowledge of the\nbare bound state energy, measuring this self-energy via the resonance position\nhas remained elusive. Here, we report on the direct observation of\nself-interaction by using a nano-eV atom collider to track the position of a\nmagnetically-tunable Feshbach resonance through a parameter space spanned by\nenergy and magnetic field. Our system of potassium and rubidium atoms displays\na strongly non-monotonic resonance trajectory with an exceptionally large\nself-interaction energy arising from an interplay between the Feshbach bound\nstate and a different, virtual bound state at a fixed energy near threshold.",
        "positive": "Multi-particle quantum walks and Fisher information in one-dimensional\n  lattices: Recent experiments on quantum walks (QWs) of a single and two particles\ndemonstrated subtle quantum statistics-dependent walks in one-dimensional (1D)\nlattices. However the roles of interaction and quantum statistics in such a\nkind of walks are little known at a many-body level. In this letter, using\ntime-evolving block decimation algorithm and many-body perturbation theory we\nrigorously study QWs, Bloch oscillations and quantum Fisher informations (FIs)\nfor three indistinguishable bosons and fermions in 1D lattices. We show that\nsuch strongly correlated many-body QWs not only give rise to\nstatistics-and-interaction-dependent ballistic transports of scattering states,\ntwo- and three-body bound states, but also present a quantum enhanced precision\nmeasurement of the gravitational force. It turns out that in contrast to the\nwalks of the fermions, the QWs of three bosons exhibit richer dynamics of\nco-walkings and competitive Bloch oscillations, which remarkably present a\nsurprising time scaling $t^3$ of FI below a characteristic time $t_0$ and\nsaturate to the fundamental limit of $t^2$ for $t>t_0$."
    },
    {
        "anchor": "Oblique Half-Solitons and their Generation in Exciton-Polariton\n  Condensates: We describe oblique half-solitons, a new type of topological defects in a two\ndimensional spinor Bose Einstein condensate. A realistic protocol based on the\noptical spin Hall effect is proposed toward their generation within an\nexciton-polariton system.",
        "positive": "Non-local quantum fluctuations and fermionic superfluidity in the\n  imbalanced attractive Hubbard model: We study fermionic superfluidity in strongly anisotropic optical lattices\nwith attractive interactions utilizing the cluster DMFT method, and focusing in\nparticular on the role of non-local quantum fluctuations. We show that\nnon-local quantum fluctuations impact the BCS superfluid transition\ndramatically. Moreover, we show that exotic superfluid states with delicate\norder parameter structure, such as the Fulde-Ferrell-Larkin-Ovchinnikov phase\ndriven by spin population imbalance, can emerge even in the presence of such\nstrong fluctuations."
    },
    {
        "anchor": "Many body population trapping in ultracold dipolar gases: A system of interacting dipoles is of paramount importance for understanding\nof many-body physics. The interaction between dipoles is {\\it anisotropic} and\n{\\it long-range}. While the former allows to observe rich effects due to\ndifferent geometries of the system, long-range ($1/r^3$) interactions lead to\nstrong correlations between dipoles and frustration. In effect, interacting\ndipoles in a lattice form a paradigmatic system with strong correlations and\nexotic properties with possible applications in quantum information\ntechnologies, and as quantum simulators of condensed matter physics, material\nscience, etc. Notably, such a system is extremely difficult to model due to a\nproliferation of interaction induced multi-band excitations for sufficiently\nstrong dipole-dipole interactions. In this article we develop a consistent\ntheoretical model of interacting polar molecules in a lattice by applying the\nconcepts and ideas of ionization theory which allows us to include highly\nexcited Bloch bands. Additionally, by involving concepts from quantum optics\n(population trapping), we show that one can induce frustration and engineer\nexotic states, such as Majumdar-Ghosh state, or vector-chiral states in such a\nsystem.",
        "positive": "Evidence of superfluidity in a dipolar supersolid from non-classical\n  rotational inertia: A key manifestation of superfluidity in liquids and gases is a reduction of\nthe moment of inertia under slow rotations. Non-classical rotational effects\nhave been searched for a long time also for the elusive supersolid phase of\nmatter, in which superfluidity coexists with a lattice structure. Here we show\nthat the recently discovered supersolid phase in dipolar quantum gases features\na reduced moment of inertia. We study a peculiar rotational oscillation mode in\na harmonic potential, the scissors mode, already employed for superfluids. From\nthe measured moment of inertia, we infer a superfluid fraction that is\ndifferent from zero and of order of unity, providing direct evidence of the\nsuperfluid nature of the dipolar supersolid."
    },
    {
        "anchor": "Comment on \"Topological Pumping in a Floquet-Bloch Band\": This manuscript is a comment about a published article in PRL 129, 053201\n(2022) by J. Minguzzi et al.",
        "positive": "Potential insights into non-equilibrium behavior from atomic physics: This chapter seeks to outline a few basic problems in quantum statistical\nphysics where recent experimental advances from the atomic physics community\noffer the hope of dramatic progress. The focus is on nonequilibrium situations\nwhere the powerful concepts and methods of equilibrium statistical physics and\n\"linear response\" theory (for small deviations from equilibrium) are not\napplicable. The problems discussed here are chosen in part because they have a\nhigh degree of \"universality\" or generality across different microscopic\nsituations, as the major challenge in nonequilibrium statistical physics, both\nquantum and classical, has been to find principles as general as the basic\nprinciples of equilibrium statistical physics or linear response."
    },
    {
        "anchor": "A quantum storm in a teacup: The past decade has seen atomic Bose-Einstein condensates emerge as a\npromising prototype system to explore the quantum mechanical form of\nturbulence, buoyed by a powerful experimental toolbox to control and manipulate\nthe fluid, and the amenity to describe the system from first-principles. This\narticle presents an overview of quantum turbulence in atomic condensates, from\nits history and fundamental motivations, its characteristics and key results to\ndate, and finally to some promising future directions.",
        "positive": "Dipole Interaction Mediated Laser Cooling of Polar Molecules to\n  Ultra-cold Temperatures: We present a method to design a finite decay rate for excited rotational\nstates in polar molecules. The setup is based on a hybrid system of polar\nmolecules with atoms driven into a Rydberg state. The atoms and molecules are\ncoupled via the strong dipolar exchange interaction between two rotation levels\nof the polar molecule and two Rydberg states. Such a controllable decay rate\nopens the way to optically pump the hyperfine levels of polar molecules and it\nenables the application of conventional laser cooling techniques for cooling\npolar molecules into quantum degeneracy."
    },
    {
        "anchor": "Spontaneous Four-Wave Mixing of de Broglie Waves: Beyond Optics: We investigate the atom-optical analog of degenerate four-wave mixing of\nphotons by colliding two Bose-Einstein condensates (BECs) of metastable helium\nand measuring the resulting momentum distribution of the scattered atoms with a\ntime and space resolved detector. For the case of photons, phase matching\nconditions completely define the final state of the system, and in the case of\ntwo colliding BECs, simple analogy implies a spherical momentum distribution of\nscattered atoms. We find, however, that the final momenta of the scattered\natoms instead lie on an ellipsoid whose radii are smaller than the initial\ncollision momentum. Numerical and analytical calculations agree well with the\nmeasurements, and reveal the interplay between many-body effects, mean-field\ninteraction, and the anisotropy of the source condensate.",
        "positive": "Fluctuation driven topological transition of binary condensates in\n  optical lattices: We show the emergence of a third Goldstone mode in binary condensates at the\nphase-separation in quasi-1D optical lattices. We develop the coupled discrete\nnonlinear Schr\\\"odinger equations (DNLSEs) using Hartree-Fock-Bogoliubov theory\nwith Popov approximation in the Bose-Hubbard model to investigate the mode\nevolution at zero temperature. In particular, as the system is driven from\nmiscible to immiscible phase. We demonstrate that the position swapping of the\nspecies in $^{87}$Rb-$^{85}$Rb system is accompanied by a discontinuity in the\nexcitation spectrum. Our results show that in quasi-1D optical lattices, the\npresence of the fluctuations dramatically change the geometry of the ground\nstate density profile of TBEC."
    },
    {
        "anchor": "The uncertainty product of an out-of-equilibrium many-particle system: In the present work we show, analytically and numerically, that the variance\nof many-particle operators and their uncertainty product for an\nout-of-equilibrium Bose-Einstein condensate (BEC) can deviate from the outcome\nof the time-dependent Gross-Pitaevskii dynamics, even in the limit of infinite\nnumber of particles and at constant interaction parameter when the system\nbecomes 100% condensed. We demonstrate our finding on the dynamics of the\ncenter-of-mass position--momentum uncertainty product of a freely expanding as\nwell as of a trapped BEC. This time-dependent many-body phenomenon is explained\nby the existence of time-dependent correlations which manifest themselves in\nthe system's reduced two-body density matrix used to evaluate the uncertainty\nproduct. Our work demonstrates that one has to use a many-body propagation\ntheory to describe an out-of-equilibrium BEC, even in the infinite particle\nlimit.",
        "positive": "Multi-mode Bose-Hubbard model for quantum dipolar gases in confined\n  geometries: We theoretically consider ultracold polar molecules in a wave guide. The\nparticles are bosons, they experience a periodic potential due to an optical\nlattice oriented along the wave guide and are polarised by an electric field\northogonal to the guide axis. The array is mechanically unstable by opening the\ntransverse confinement in the direction orthogonal to the polarizing electric\nfield and can undergo a transition to a double-chain (zigzag) structure. For\nthis geometry we derive a multi-mode generalized Bose-Hubbard model for\ndetermining the quantum phases of the gas at the mechanical instability taking\ninto account the quantum fluctuations in all directions of space. Our model\nlimits the dimension of the numerically relevant Hilbert subspace by means of\nan appropriate decomposition of the field operator, which is obtained from a\nfield theoretical model of the linear-zigzag instability. We determine the\nphase diagrams of small systems using exact diagonalization and find that, even\nfor tight transverse confinement, the aspect ratio between the two transverse\ntrap frequencies controls not only the classical but also the quantum\nproperties of the ground state in a non-trivial way. Convergence tests at the\nlinear-zigzag instability demonstrate that our multi-mode generalized\nBose-Hubbard model can catch the essential features of the quantum phases of\ndipolar gases in confined geometries with a limited computational effort."
    },
    {
        "anchor": "Spontaneous inhomogeneous phases in ultracold dipolar Fermi gases: We study the collapse of ultracold fermionic gases into inhomogeneous states\ndue to strong dipolar interaction in both 2D and 3D. Depending on the\ndimensionality, we find that two different types of inhomogeneous states are\nstabilized once the dipole moment reaches a critical value $d>d_c$: the {\\it\nstripe phase} and {\\it phase separation} between high and low densities. In 2D,\nwe prove that the stripe phase is always favored for $d\\gtrsim d_c$, regardless\nof the microscopic details of the system. In 3D, the one-loop perturbative\ncalculation suggests that the same type of instability leads to phase\nseparation. Experimental detection and finite-temperature effects are\ndiscussed.",
        "positive": "Momentum Resolved Optical Lattice Modulation Spectroscopy for Bose\n  Hubbard Model: We propose a new method of optical lattice modulation spectroscopy for\nstudying the spectral function of ultracold bosons in an optical lattice. We\nshow that different features of the single particle spectral function in\ndifferent quantum phases can be obtained by measuring the change in momentum\ndistribution after the modulation. In the Mott phase, this gives information\nabout the momentun dependent gap to particle-hole excitations as well as their\nspectral weight. In the superfluid phase, one can obtain the spectrum of the\ngapless Bogoliubov quasiparticles as well as the gapped amplitude fluctuations.\nThe distinct evolution of the response with modulation frequency in the two\nphases can be used to identify these phases and the quantum phase transition\nseparating them."
    },
    {
        "anchor": "An extended representation of three spin component Bose Einstein\n  Condensate solitons: We consider a three spin component Bose Einstein Condensate as described by\nas many coupled nonlinear Schroedinger equations. For a very special ratio of\nthe coupling constants, exact N soliton solutions to this set of equations are\nknown. Here we find a simple representation including the N = 1 solution based\non the symmetry of the equations. This symmetry is described by a linear\noperator, the nonlinearity of NLS notwithstanding. Our useful representation\nopens the door to the nonintegrable case of general coupling constants. A new\nclass of solutions is found.",
        "positive": "Dynamical Casimir Effect in Superradiant Light Scattering by\n  Bose-Einstein Condensate in an Optomechanical Cavity: We investigate the effects of dynamical Casimir effect in superradiant light\nscattering by Bose-Einstein condensate in an optomechanical cavity. The system\nis studied using both classical and quantized mirror motions. The cavity\nfrequency is harmonically modulated in time for both the cases. The main\nquantity of interest is the number of intracavity scattered photons. The system\nhas been investigated under the weak and strong modulation. It has been\nobserved that the amplitude of the scattered photons is more for the classical\nmirror motion than the quantized mirror motion. Also, initially, the amplitude\nof scattered photons is high for lower modulation amplitude than higher\nmodulation amplitude. We also found that the behaviour of the plots are similar\nunder strong and weak modulation for the quantized mirror motion."
    },
    {
        "anchor": "Higher-order topological quantum paramagnets: Quantum paramagnets are strongly-correlated phases of matter where competing\ninteractions frustrate magnetic order down to zero temperature. In certain\ncases, quantum fluctuations induce instead topological order, supporting, in\nparticular, fractionalized quasi-particle excitations. In this work, we\ninvestigate paradigmatic spin models and show how magnetic frustration can also\ngive rise to higher-order topological properties. We first study the frustrated\nHeisenberg model in a square lattice, where a plaquette valence bond solid\nappears through the spontaneous breaking of translational invariance. Despite\nthe amount of effort that has been devoted to study this phase, its topological\nnature has so far been overlooked. By means of tensor network simulations, we\nestablish how such state belongs to a higher-order symmetry-protected\ntopological phase, where long-range plaquette order and non-trivial topology\ncoexist. This interplay allows the system to support excitations that would be\nabsent otherwise, such as corner-like states in the bulk attached to dynamical\ntopological defects. Finally, we demonstrate how this higher-order topological\nquantum paramagnet can also be induced by dipolar interactions, indicating the\npossibility to directly observe this phase using atomic quantum simulators.",
        "positive": "Magnetic ordering of three-component ultracold fermionic mixtures in\n  optical lattices: We study finite-temperature magnetic phases of three-component mixtures of\nultracold fermions with repulsive interactions in optical lattices with simple\ncubic or square geometry by means of dynamical mean-field theory (DMFT). We\nfocus on the case of one particle per site (1/3 band filling) at moderate\ninteraction strength, where we observe a sequence of thermal phase transitions\ninto two- and three-sublattice ordered states by means of the unrestricted\nreal-space generalization of DMFT. From our quantitative analysis we conclude\nthat long-range ordering in three-component mixtures should be observable at\ncomparable temperatures as in two-component mixtures."
    },
    {
        "anchor": "A dual-species Bose-Einstein condensate with attractive interspecies\n  interactions: We report on the production of a $^{41}$K-$^{87}$Rb dual-species\nBose-Einstein condensate with tunable interspecies interaction and we study the\nmixture in the attractive regime, i.e. for negative values of the interspecies\nscattering length $a_{12}$. The binary condensate is prepared in the ground\nstate and confined in a pure optical trap. We exploit Feshbach resonances for\ntuning the value of $a_{12}$. After compensating the gravitational sag between\nthe two species with a magnetic field gradient, we drive the mixture into the\nattractive regime. We let the system to evolve both in free space and in an\noptical waveguide. In both geometries, for strong attractive interactions, we\nobserve the formation of self-bound states, recognizable as quantum droplets.\nOur findings prove that robust, long-lived droplet states can be realized in\nattractive two-species mixtures, despite the two atomic components may\nexperience different potentials.",
        "positive": "Black-Hole evaporation and Quantum-depletion in Bose-Einstein\n  condensates: We study the analogy between the Hawking radiation in Black-Holes and the\nQuantum depletion process of a Bose-Einstein condensate by using the Bogoliubov\ntransformations method. We find that the relation between the Bogoliubov\ncoefficients is similar in both cases (in the appropriate regimes). We then\nconnect the condensate variables with those associated to the Black-Hole,\ndemonstrating then that the zero temperature regime of the condensate is\nequivalent to the existence of an event horizon in gravity."
    },
    {
        "anchor": "Observation of the density dependence of the closed-channel fraction of\n  a $^6$Li superfluid: Atomic Fermi gases provide an ideal platform for studying the pairing and\nsuperfluid physics, using a Feshbach resonance between closed channel molecular\nstates and open channel scattering states. Of particular interest is the\nstrongly interacting regime. We show that the closed-channel fraction $Z_{cc}$\nprovides an effective probe for the important many-body interacting effects,\nespecially through its density dependence, which is absent from two-body\ntheoretical predictions. Here we measure $Z_{cc}$ as a function of interaction\nstrength and the Fermi temperature $T_\\text{F}$ in a trapped $^6$Li superfluid\nthroughout the entire BCS--BEC crossover, in quantitative agreement with theory\nwhen important thermal contributions outside the superfluid core are taken into\naccount. Away from the deep BEC regime, the fraction $Z_{cc}$ is sensitive to\n$T_\\text{F}$. In particular, our data show $Z_{cc} \\propto T_\\text{F}^{\\alpha}$\nwith $\\alpha=1/2$ at unitarity, in quantitative agreement with calculations of\na two-channel pairing fluctuation theory, and $\\alpha$ increases rapidly into\nthe BCS regime, reflecting many-body interaction effects as predicted.",
        "positive": "Wigner distribution functions for complex dynamical systems: the\n  emergence of the Wigner-Boltzmann equation: The equation of motion for the reduced Wigner function of a system coupled to\nan external quantum system is presented for the specific case when the external\nquantum system can be modeled as a set of harmonic oscillators. The result is\nderived from the Wigner function formulation of the Feynman-Vernon influence\nfunctional theory. It is shown how the true self-energy for the equation of\nmotion is connected with the influence functional for the path integral.\nExplicit expressions are derived in terms of the bare Wigner propagator.\nFinally, we show under which approximations the resulting equation of motion\nreduces to the Wigner-Boltzmann equation."
    },
    {
        "anchor": "Collapse instability of solitons in the nonpolynomial Schr\u00f6dinger\n  equation with dipole-dipole interactions: A model of the Bose-Einstein condensate (BEC) of dipolar atoms, confined in a\ncombination of a cigar-shaped trap and optical lattice acting in the axial\ndirection, is studied in the framework of the one-dimensional (1D)\nnonpolynomial Schr\\\"{o}dinger equation (NPSE) with additional terms describing\nlong-range dipole-dipole (DD) interactions. The NPSE makes it possible to\ndescribe the collapse of localized modes, which was experimentally observed in\nthe self-attractive BEC confined in tight traps, in the framework of the 1D\ndescription. We study the influence of the DD interactions on the dynamics of\nbright solitons, especially as concerns their collapse-induced instability.\nBoth attractive and repulsive contact and DD interactions are considered. The\nresults are summarized in the form of stability/collapse diagrams in a\nrespective parametric space. In particular, it is shown that the attractive DD\ninteractions may prevent the collapse instability in the condensate with\nattractive contact interactions.",
        "positive": "Quantum-statistics-induced flow patterns in driven ideal Fermi gases: While classical or quantum interacting liquids become turbulent under\nsufficiently strong driving, it is not obvious what flow pattern an ideal\nquantum gas develops under similar conditions. Unlike classical noninteracting\nparticles which exhibit rather trivial flow, ideal fermions have to satisfy the\nexclusion principle, which acts as a form of collective repulsion. We thus\nstudy the flow of an ideal Fermi gas as it is driven out of a narrow orifice of\nwidth comparable to the Fermi wavelength, employing both a microcanonical\napproach to transport, and solving a Lindblad equation for Markovian driving\nleads. Both methods are in good agreement and predict an outflowing current\ndensity with a complex microscopic pattern of vorticity in the steady state.\nApplying a bias of the order of the chemical potential results in a short-range\ncorrelated antiferromagnetic vorticity pattern, corresponding to local moments\nof the order of a tenth of a magneton, $e\\hbar/2m$, if the fermions are\ncharged. The latter may be detectable by magnetosensitive spectroscopy in\nstrongly driven cold gases (atoms) or clean electronic nanostructures\n(electrons)."
    },
    {
        "anchor": "Ballistic atom pumps: We examine a classically-chaotic system consisting of two reservoirs of\nparticles connected by a channel containing oscillating potential-energy\nbarriers. We investigate whether such a system can preferentially pump\nparticles from one reservoir to the other, a process often called \"quantum\npumping.\" We show how to make a \"particle diode\" which under specified\nconditions permits net particle pumping in only one direction. Then we examine\nsystems having symmetric barriers. We find that if all initial particle\nenergies are considered, a system with symmetric barriers cannot preferentially\npump particles. However, if only finite initial energy bands are considered,\nthe system can create net particle transport in either direction. We study the\nsystem classically, semiclassically, and quantum mechanically, and find that\nthe quantum description cannot be fully understood without the insight gained\nfrom classical and semiclassical analysis.",
        "positive": "Two-dimensional non-Hermitian skin effect in an ultracold Fermi gas: The concept of non-Hermiticity has expanded the understanding of band\ntopology leading to the emergence of counter-intuitive phenomena. One example\nis the non-Hermitian skin effect (NHSE), which involves the concentration of\neigenstates at the boundary. However, despite the potential insights that can\nbe gained from high-dimensional non-Hermitian quantum systems in areas like\ncurved space, high-order topological phases, and black holes, the realization\nof this effect in high dimensions remains unexplored. Here, we create a\ntwo-dimensional (2D) non-Hermitian topological band for ultracold fermions in\nspin-orbit-coupled optical lattices with tunable dissipation, and\nexperimentally examine the spectral topology in the complex eigenenergy plane.\nWe experimentally demonstrate pronounced nonzero spectral winding numbers when\nthe dissipation is added to the system, which establishes the existence of 2D\nskin effect. We also demonstrate that a pair of exceptional points (EPs) are\ncreated in the momentum space, connected by an open-ended bulk Fermi arc, in\ncontrast to closed loops found in Hermitian systems. The associated EPs emerge\nand shift with increasing dissipation, leading to the formation of the Fermi\narc. Our work sets the stage for further investigation into simulating\nnon-Hermitian physics in high dimensions and paves the way for understanding\nthe interplay of quantum statistics with NHSE."
    },
    {
        "anchor": "Universal equation of state and pseudogap in the two-dimensional Fermi\n  gas: We determine the thermodynamic properties and the spectral function for a\nhomogeneous two-dimensional Fermi gas in the normal state using the\nLuttinger-Ward, or self-consistent T-matrix, approach. The density equation of\nstate deviates strongly from that of the ideal Fermi gas even for moderate\ninteractions, and our calculations suggest that temperature has a pronounced\neffect on the pressure in the crossover from weak to strong coupling,\nconsistent with recent experiments. We also compute the superfluid transition\ntemperature for a finite system in the crossover region. There is a pronounced\npseudogap regime above the transition temperature: the spectral function shows\na Bogoliubov-like dispersion with back-bending, and the density of states is\nsignificantly suppressed near the chemical potential. The contact density at\nlow temperatures increases with interaction and compares well with both\nexperiment and zero-temperature Monte Carlo results.",
        "positive": "Non-local Order in Elongated Dipolar Gases: Dipolar particles in an elongated trap are expected to undergo a quantum\nphase transition from a linear to a zigzag structure with decreasing transverse\nconfinement. We derive the low energy effective theory of the transition\nshowing that in presence of quantum fluctuations the Zigzag phase can be\ncharacterized by a long ranged string order, while the local Ising correlations\ndecay as a power law. This is also confirmed using DMRG calculations on a\nmicroscopic model. The non local order in the bulk gives rise to zero energy\nstates localized at the interface between the ordered and disordered phases.\nSuch an interface naturally arises when the particles are subject to a weak\nharmonic confinement along the tube axis. We compute the signature of the edge\nstates in the single particle tunneling spectra pointing to differences between\na system with bosonic versus fermionic particles. Finally we asses the\nmagnitude of the relevant quantum fluctuations in realistic systems of dipolar\nparticles, including ultracold polar molecules as well as alkali atoms weakly\ndressed by a Rydberg excitation."
    },
    {
        "anchor": "Realization of an atomic quantum Hall system in four dimensions: Topological states of matter lie at the heart of our modern understanding of\ncondensed matter systems. In two-dimensional (2D) quantum Hall insulators, the\nnon-trivial topology, defined by the first Chern number, manifests as a\nquantized Hall conductance and protected ballistic edge modes. Besides\ntopological insulators and Weyl semi-metals experimentally realized in 3D\nmaterials, a large variety of topological systems, theoretically predicted in\ndimensions $D > 3$, remains unexplored - among them a generalization of the\nquantum Hall effect in 4D. So far, topological properties linked with the 4D\nHall effect have been revealed via geometrical charge pump experiments in 2D\nsystems. A truly 4D Hall system has also been realized using electronic\ncircuits - however, no direct evidence of topological quantization has been\nreported. Here, we engineer an atomic quantum Hall system evolving in 4D, by\ncoupling with light fields two spatial dimensions and two synthetic ones\nencoded in the electronic spin $J = 8$ of dysprosium atoms. We measure the\ncharacteristic properties of a 4D quantum Hall system, namely the quantization\nof its electromagnetic non-linear response by a second Chern number, and the\nspecial nature of its 3D hyperedge modes, which combine ballistic motion along\none orientation and insulating behaviour in the two remaining directions. We\nalso probe low-lying excitations, revealing non-planar cyclotron orbits in\ncontrast with their circular equivalents in $D\\leq3$. Our findings pave the way\nto the exploration of interacting quantum Hall systems in 4D, from the\ninvestigation of strongly-correlated liquids to the simulation of high-energy\nmodels in link with quantum gravity and Yang-Mills field theory.",
        "positive": "Quantisation and its breakdown in a Hubbard-Thouless pump: Geometric properties of waves and wave functions can explain the appearance\nof integer-valued observables throughout physics. For example, these\n'topological' invariants describe the plateaux observed in the quantised Hall\neffect and the pumped charge in its dynamic analogon, the Thouless pump.\nHowever, the presence of interparticle interactions can profoundly affect the\ntopology of a material, invalidating the idealised formulation in terms of\nBloch waves. Despite pioneering experiments in solid state systems, photonic\nwaveguides, and optical lattices, the study of topological insulators under\nvariation of inter-particle interactions has proven challenging. Here, we\nexperimentally realise a topological Thouless pump with tuneable Hubbard\ninteractions in an optical lattice and observe regimes with robust pumping, as\nwell as an interaction-induced breakdown. We confirm the pump's robustness\nagainst interactions that are smaller than the protecting gap, which holds true\nfor both repulsive and attractive Hubbard $U$. Furthermore, we identify that\nbound pairs of fermions are responsible for quantised transport at strongly\nattractive $U$, supported by measurements of pair fraction and adiabaticity.\nFor strong repulsive interactions, on the contrary, topological pumping breaks\ndown. Yet, we can reinstate quantised pumping by modifying the pump trajectory\nwhile starting from the same initial state. Our experiments pave the way for\ninvestigating interacting topological insulators, including edge effects and\ninteraction-induced topological phases."
    },
    {
        "anchor": "Nanoplasmonic planar traps - a tool for engineering p-wave interactions: Engineering strong p-wave interactions between fermions is one of the\nchallenges in modern quantum physics. Such interactions are responsible for a\nplethora of fascinating quantum phenomena such as topological quantum liquids\nand exotic superconductors. In this letter we propose to combine recent\ndevelopments of nanoplasmonics with the progress in realizing laser-induced\ngauge fields. Nanoplasmonics allows for strong confinement leading to a\ngeometric resonance in the atom-atom scattering. In combination with the\nlaser-coupling of the atomic states, this is shown to result in the desired\ninteraction. We illustrate how this scheme can be used for the stabilization of\nstrongly correlated fractional quantum Hall states in ultracold fermionic\ngases.",
        "positive": "Projective phase measurements in one-dimensional Bose gases: We consider time-of-flight measurements in split one-dimensional Bose gases.\nIt is well known that the low-energy sector of such systems can be described in\nterms of two compact phase fields $\\hat{\\phi}_{a,s}(x)$. Building on existing\nresults in the literature we discuss how a single projective measurement of the\nparticle density after trap release is in a certain limit related to the\neigenvalues of the vertex operator $e^{i\\hat{\\phi}_a(x)}$. We emphasize the\ntheoretical assumptions underlying the analysis of \"single-shot\" interference\npatterns and show that such measurements give direct access to multi-point\ncorrelation functions of $e^{i\\hat{\\phi}_a(x)}$ in a substantial parameter\nregime. For experimentally relevant situations, we derive an expression for the\nmeasured particle density after trap release in terms of convolutions of the\neigenvalues of vertex operators involving both sectors of the two-component\nLuttinger liquid that describes the low-energy regime of the split condensate.\nThis opens the door to accessing properties of the symmetric sector via an\nappropriate analysis of existing experimental data."
    },
    {
        "anchor": "Emergent eigenstate solution and emergent Gibbs ensemble for expansion\n  dynamics in optical lattices: Within the emergent eigenstate solution to quantum dynamics [Phys. Rev. X 7,\n021012 (2017)], one can construct a local operator (an emergent Hamiltonian) of\nwhich the time-evolving state is an eigenstate. Here we show that such a\nsolution exists for the expansion dynamics of Tonks-Girardeau gases in optical\nlattices after turning off power-law (e.g., harmonic or quartic) confining\npotentials, which are geometric quenches that do not involve the boost\noperator. For systems that are initially in the ground state and undergo\ndynamical fermionization during the expansion, we show that they remain in the\nground state of the emergent local Hamiltonian at all times. On the other hand,\nfor systems at nonzero initial temperatures, the expansion dynamics can be\ndescribed constructing a Gibbs ensemble for the emergent local Hamiltonian (an\nemergent Gibbs ensemble).",
        "positive": "Magnetic phases of spin-3/2 fermions on a spatially anisotropic square\n  lattice: We study the magnetic phase diagram of spin-3/2 fermions in a spatially\nanisotropic square optical lattice at quarter filling (corresponding to one\nparticle per lattice site). In the limit of the large on-site repulsion the\nsystem can be mapped to the so-called Sp(N) Heisenberg spin model with N=4. We\nanalyze the Sp(N) spin model with the help of the large-N field-theoretical\napproach and show that the effective theory corresponds to the Sp(N) extension\nof the CP^{N-1} model, with the Lorentz invariance generically broken. We\nobtain the renormalization flow of the model couplings and show that although\nthe Sp(N) terms are seemingly irrelevant, their presence leads to a\nrenormalization of the CP^{N-1} part of the action, driving a phase transition.\nWe further consider the influence of the external magnetic field (the quadratic\nZeeman effect), and present the qualitative analysis of the ground state phase\ndiagram."
    },
    {
        "anchor": "The anisotropic Harper-Hofstadter-Mott model: competition between\n  condensation and magnetic fields: We derive the reciprocal cluster mean-field method to study the\nstrongly-interacting bosonic Harper-Hofstadter-Mott model. The system exhibits\na rich phase diagram featuring band insulating, striped superfluid, and\nsupersolid phases. Furthermore, for finite hopping anisotropy we observe\ngapless uncondensed liquid phases at integer fillings, which are analyzed by\nexact diagonalization. The liquid phases at fillings 1 and 3 exhibit the same\nband fillings as the fermionic integer quantum Hall effect, while the phase at\nfilling 2 is CT-symmetric with zero charge response. We discuss how these\nphases become gapped on a quasi-one-dimensional cylinder, leading to a\nquantized Hall response, which we characterize by introducing a suitable\nmeasure for non-trivial many-body topological properties. Incompressible\nmetastable states at fractional filling are also observed, indicating competing\nfractional quantum Hall phases. The combination of reciprocal cluster\nmean-field and exact diagonalization yields a promising method to analyze the\nproperties of bosonic lattice systems with non-trivial unit cells in the\nthermodynamic limit.",
        "positive": "Onset of the Limit Cycle and Universal Three-Body Parameter in Efimov\n  Physics: The Efimov effect is the only experimentally realized universal phenomenon\nthat exhibits the renormalization-group limit cycle with the three-body\nparameter parametrizing a family of universality classes. Recent experiments in\nultracold atoms have unexpectedly revealed that the three-body parameter itself\nis universal when measured in units of an effective range. By performing an\nexact functional renormalization-group analysis with various finite-range\ninteraction potentials, we demonstrate that the onset of the\nrenormalization-group flow into the limit cycle is universal, regardless of\nshort-range details, which connects the missing link between the two\nuniversalities of the Efimov physics. A close connection between the\ntopological property of the limit cycle and few-body physics is also\ndelineated."
    },
    {
        "anchor": "Finite-Temperature Density-Functional Theory of Bose-Einstein\n  Condensates: The thermodynamic approach to density functional theory (DFT) is used to\nderive a versatile theoretical framework for the treatment of\nfinite-temperature (and in the limit, zero temperature) Bose-Einstein\ncondensates (BECs). The simplest application of this framework, using the\noverall density of bosons alone, would yield the DFT of Nunes (1999). It is\nargued that a significant improvement in accuracy may be obtained by using\nadditional density fields: the condensate amplitude and the anomalous density.\nThus, two advanced schemes are suggested, one corresponding to a generalized\ntwo-fluid model of condensate systems, and another scheme which explicitly\naccounts for anomalous density contributions and anomalous effective\npotentials. The latter reduces to the Hartree-Fock-Bogoliubov approach in the\nlimit of weak interactions. For stronger interactions, a local density\napproximation is suggested, but its implementation requires accurate data for\nthe thermodynamic properties of uniform interacting BEC systems, including\nfictitious perturbed states of such systems. Provided that such data becomes\navailable, e.g., from quantum Monte Carlo computation, DFT can be used to\nobtain high-accuracy theoretical results for the equilibrium states of BECs of\nvarious geometries and external potentials.",
        "positive": "Phase Separation of Multi-Component Bose-Einstein Condensates of Trapped\n  Atoms and Molecules with a Homonuclear Feshbach Resonance: We investigate phase separation of Bose-Einstein condensates (BECs) of\ntwo-component atoms and one-component molecules with a homonuclear Feshbach\nresonance. We develop a full model for dilute atomic and molecular gases\nincluding correlation of the Feshbach resonance and all kinds of interparticle\ninteractions, and numerically calculate order parameters of the BECs in\nspherical harmonic oscillator traps at zero temperature with the Bogoliubov's\nclassical field approximation. As a result, we find out that the Feshbach\nresonance can induce two types of phase separation. The actual phase structures\nand density profiles of the trapped gases are predicted in the whole parameter\nregion, from the atom dominant regime to the molecule dominant regime. We focus\non the role of the molecules in the phase separation. Especially in the atom\ndominant regime, the role of the molecules is described through effective\ninteractions derived from our model. Furthermore we show that a perturbative\nand semi-classical limit of our model reproduces the conventional atomic BEC\n(single-channel) model."
    },
    {
        "anchor": "Spectral response and contact of the unitary Fermi gas: We measure radiofrequency (rf) spectra of the homogeneous unitary Fermi gas\nat temperatures ranging from the Boltzmann regime through quantum degeneracy\nand across the superfluid transition. For all temperatures, a single spectral\npeak is observed. Its position smoothly evolves from the bare atomic resonance\nin the Boltzmann regime to a frequency corresponding to nearly one Fermi energy\nat the lowest temperatures. At high temperatures, the peak width reflects the\nscattering rate of the atoms, while at low temperatures, the width is set by\nthe size of fermion pairs. Above the superfluid transition, and approaching the\nquantum critical regime, the width increases linearly with temperature,\nindicating non-Fermi-liquid behavior. From the wings of the rf spectra, we\nobtain the contact, quantifying the strength of short-range pair correlations.\nWe find that the contact rapidly increases as the gas is cooled below the\nsuperfluid transition.",
        "positive": "Caustics in quantum many-body dynamics: We describe a new class of nonequilibrium quantum many-body phenomena in the\nform of networks of caustics that dominate the many-body wavefunction in the\nsemiclassical regime following a sudden quench. It includes the light cone-like\npropagation of correlations as a particular case. Caustics are singularities\nformed by the birth and death of waves and form a hierarchy of universal\npatterns whose natural mathematical description is via catastrophe theory.\nExamples in classical waves range from rainbows and gravitational lensing in\noptics to tidal bores and rogue waves in hydrodynamics. Quantum many-body\ncaustics are discretized by second-quantization (``quantum catastrophes'') and\nlive in Fock space which can potentially have many dimensions. We illustrate\nthese ideas using the Bose Hubbard dimer and trimer models which are simple\nenough that the caustic structure can be elucidated from first principles and\nyet run the full range from integrable to nonintegrable dynamics. The dimer\ngives rise to discretized versions of fold and cusp catastrophes whereas the\ntrimer allows for higher catastrophes including the codimension-3 hyperbolic\nand elliptic umbilics which are organized by, and projections of, an\n8-dimensional corank-2 catastrophe known as $X_9$. These results describe a\nhitherto unrecognized form of universality in quantum dynamics organized by\nsingularities that manifest as strong fluctuations in mode population\nprobabilities."
    },
    {
        "anchor": "Mapping trapped atomic gas with spin-orbit coupling to quantum Rabi-like\n  model: We construct a connection of the ultracold atomic system in a harmonic trap\nwith Raman-induced spin-orbit coupling to the quantum Rabi-like model. By\nmapping the trapped atomic system to a Rabi-like model, we can get the exact\nsolution of the Rabi-like model following the methods to solve the quantum Rabi\nmodel. The existence of such a mapping implies that we can study the basic\nmodel in quantum optics by using trapped atomic gases with spin-orbit coupling.",
        "positive": "Mobile vector soliton in a spin-orbit coupled spin-$1$ condensate: We study the formation of bound states and three-component bright vector\nsolitons in a quasi-one-dimensional spin-orbit-coupled hyperfine spin $f=1$\nBose-Einstein condensate using numerical solution and variational approximation\nof a mean-field model. In the antiferromagnetic domain, the solutions are\ntime-reversal symmetric, and the component densities have multi-peak structure.\nIn the ferromagnetic domain, the solutions violate time-reversal symmetry, and\nthe component densities have single-peak structure. The dynamics of the system\nis not Galelian invariant. From an analysis of Galelian invariance, we\nestablish that the single-peak ferromagnetic vector solitons are true solitons\nand can move maintaining constant component densities, whereas the\nantiferromagnetic solitons cannot move with constant component densities."
    },
    {
        "anchor": "Probing topology by \"heating\": Quantized circular dichroism in ultracold\n  atoms: We reveal an intriguing manifestation of topology, which appears in the\ndepletion rate of topological states of matter in response to an external\ndrive. This phenomenon is presented by analyzing the response of a generic 2D\nChern insulator subjected to a circular time-periodic perturbation: due to the\nsystem's chiral nature, the depletion rate is shown to depend on the\norientation of the circular shake. Most importantly, taking the difference\nbetween the rates obtained from two opposite orientations of the drive, and\nintegrating over a proper drive-frequency range, provides a direct measure of\nthe topological Chern number of the populated band ($\\nu$): this \"differential\nintegrated rate\" is directly related to the strength of the driving field\nthrough the quantized coefficient $\\eta_0\\!=\\!\\nu /\\hbar^2$. Contrary to the\ninteger quantum Hall effect, this quantized response is found to be non-linear\nwith respect to the strength of the driving field and it explicitly involves\ninter-band transitions. We investigate the possibility of probing this\nphenomenon in ultracold gases and highlight the crucial role played by edge\nstates in this effect. We extend our results to 3D lattices, establishing a\nlink between depletion rates and the non-linear photogalvanic effect predicted\nfor Weyl semimetals. The quantized circular dichroism revealed in this work\ndesignates depletion-rate measurements as a universal probe for topological\norder in quantum matter.",
        "positive": "Dynamics and interaction of vortex lines in an elongated Bose-Einstein\n  condensate: We study the real-time dynamics of vortex lines in a large elongated\nBose-Einstein condensate (BEC) of sodium atoms using a stroboscopic technique.\nVortices are spontaneously produced via the Kibble-Zurek mechanism in a quench\nacross the BEC transition and then they slowly precess keeping their\norientation perpendicular to the long axis of the trap as expected for\nsolitonic vortices in a highly anisotropic condensate. Good agreement with\ntheoretical predictions is found for the precession period as a function of the\norbit amplitude and the number of condensed atoms. In configurations with two\nor more vortex lines, we see signatures of vortex-vortex interaction in the\nshape and visibility of the orbits. In addition, when more than two vortices\nare present, their decay is faster than the thermal decay observed for one or\ntwo vortices. The possible role of vortex reconnection processes is discussed."
    },
    {
        "anchor": "Universality of isolated $N$-body resonances at large scattering length: Non Efimovian $N$-body resonances are investigated in the regime of a large\ntwo-body s wave scattering length. In view of a universal description of\nlow-energy bound and quasi-bound states, a contact model is introduced. The\nmodeling requires two parameters in addition to the scattering length. Using a\nmodified scalar product, the contact model provides a normalization of bound\nstates, possibly not square-integrable, that coincides with that of the\ncorresponding finite range model.",
        "positive": "Half-skyrmion and meron pair in spinor condensates: We propose a simple experimental scheme to generate spin textures in the\nground state of interacting ultracold bosonic atoms loaded in a two-dimensional\nharmonic trap. Our scheme is based on two co-propagating Laguerre-Gauss laser\nbeams illuminating the atoms and coupling two of their internal ground state\nZeeman sublevels. Using a Gross-Pitaevskii description, we show that the ground\nstate of the atomic system has different topological properties depending on\nthe interaction strength and the laser beam intensity. A half-skyrmion state\ndevelops at low interactions while a meron pair develops at large interactions."
    },
    {
        "anchor": "Rapidity distribution within the defocusing non-linear Schr\u00f6dinger\n  equation model: We consider the classical field integrable system whose evolution equation is\nthe nonlinear Schr\\\"odinger equation with defocusing non-linearities, which is\nthe classical limit of the quantum Lieb-Liniger model. We propose a simple\nderivation of the relation between two sets of conserved quantities: on the one\nhand the trace of the monodromy matrix, parameterized by the spectral parameter\nand introduced in the inverse-scattering framework, and on the other hand the\nrapidity distribution, a concept imported from the Lieb-Liniger model. To do so\nwe use the definition of the rapidity distribution as the asymptotic momentum\ndistribution after an expansion. More precisely we use thought experiments\nimplementing an expansion and we present two different ways to derive our\nresult, based on different thought experiments which lead to different\ncalculations.",
        "positive": "Dynamical Kosterlitz-Thouless Theory for Two-Dimensional Ultracold\n  Atomic Gases: In this letter we develop a theory for the first and second sound in a\ntwo-dimensional atomic superfluid across the superfluid transition based on the\ndynamic Koterlitz-Thouless theory. We employ a set of modified two-fluid\nhydrodynamic equations which incorporate the dynamics of the quantised\nvortices, rather than the conventional ones for a three-dimensional superfluid.\nAs far as the sound dispersion equation is concerned, the modification is\nessentially equivalent to replacing the static superfluid density with a\nfrequency dependent one, renormalised by the frequency dependent \"dielectric\nconstant\" of the vortices. This theory has two direct consequences. First,\nbecause the renormalised superfluid density at finite frequencies does not\ndisplay discontinuity across the superfluid transition, in contrast to the\nstatic superfluid density, the sound velocities vary smoothly across the\ntransition. Second, the theory includes dissipation due to free vortices, and\nthus naturally describes the sound-to-diffusion crossover for the second sound\nin the normal phase. With only one fitting parameter, our theory gives a\nperfect agreement with the experimental measurements of sound velocities across\nthe transition, as well as the quality factor in the vicinity of the\ntransition. The predictions from this theory can be further verified by future\nexperiments."
    },
    {
        "anchor": "Circumnavigating an ocean of incompressible light: This is a popular science article to appear on the \"Il Nuovo Saggiatore\"\nmagazine of the Italian Physical Society. It aims at introducing a broad\naudience of physicists to the most recent trends in many-body physics of\ndegenerate quantum gases with a special attention to quantum fluids of light\nand the quest towards quantum Hall liquids of light.",
        "positive": "Hydrodynamics of compressible superfluids in confined geometries: We present a study of the hydrodynamics of compressible superfluids in\nconfined geometries. We use a perturbative procedure in terms of the\ndimensionless expansion parameter $(v/v_s)^2$ where $v$ is the typical speed of\nthe flow and $v_s$ the speed of sound. A zero value of this parameter\ncorresponds to the incompressible limit. We apply the procedure to two specific\nproblems: the case of a trapped superfluid with a gaussian profile of the local\ndensity, and that of a superfluid confined in a rotating obstructed cylinder.\nWe find that the corrections due to finite compressibility which are, as\nexpected, negligible for liquid He, are important but amenable to the\nperturbative treatment for typical ultracold atomic systems."
    },
    {
        "anchor": "Pseudogap phenomena in a two-dimensional ultracold Fermi gas near the\n  Berezinskii-Kosterlitz-Thouless transition: We investigate single-particle excitations and strong-coupling effects in a\ntwo-dimensional Fermi gas. Including pairing fluctuations within a Gaussian\nfluctuation theory, we calculate the density of states $\\rho(\\omega)$ near the\nBerezinskii-Kosterlitz-Thouless (BKT) transition temperature $T_{\\rm BKT}$.\nNear $T_{\\rm BKT}$, we show that superfluid fluctuations induce a pseudogap in\n$\\rho(\\omega)$. The pseudogap structure is very similar to the BCS superfluid\ndensity of states, although the superfluid order parameter is absent in the\npresent two-dimensional case. Since a two-dimensional $^{40}$K Fermi gas has\nrecently been realized, our results would contribute to the understanding of\nsingle-particle properties near the BKT instability.",
        "positive": "Hamiltonian Learning in Quantum Field Theories: We discuss Hamiltonian learning in quantum field theories as a protocol for\nsystematically extracting the operator content and coupling constants of\neffective field theory Hamiltonians from experimental data. Learning the\nHamiltonian for varying spatial measurement resolutions gives access to field\ntheories at different energy scales, and allows to learn a flow of Hamiltonians\nreminiscent of the renormalization group. Our method, which we demonstrate in\nboth theoretical studies and available data from a quantum gas experiment,\npromises new ways of addressing the emergence of quantum field theories in\nquantum simulation experiments."
    },
    {
        "anchor": "Quadratic fractional solitons: We introduce a system combining the quadratic self-attractive or composite\nquadratic-cubic nonlinearity, acting in the combination with the fractional\ndiffraction, which is characterized by its L\\'{e}vy index $\\alpha $. The model\napplies to a gas of quantum particles moving by L\\'{e}vy flights, with the\nquadratic term representing the Lee-Huang-Yang correction to the mean-field\ninteractions. A family of fundamental solitons is constructed in a numerical\nform, while the dependence of its norm on the chemical potential characteristic\nis obtained in an exact analytical form. The family of \\textit{quasi-Townes\nsolitons}, appearing in the limit case of $\\alpha =1/2$, is investigated by\nmeans of a variational approximation. A nonlinear lattice, represented by\nspatially periodical modulation of the quadratic term, is briefly addressed\ntoo. The consideration of the interplay of competing quadratic (attractive) and\ncubic (repulsive) terms with a lattice potential reveals families of single-,\ndouble-, and triple-peak gap solitons (GSs) in two finite bandgaps. The\ncompeting nonlinearity gives rise to alternating regions of stability and\ninstability of the GS, the stability intervals shrinking with the increase of\nthe number of peaks in the GS.",
        "positive": "MCTDH-X: The multiconfigurational time-dependent Hartree method for\n  indistinguishable particles software: We introduce and describe the multiconfigurational time-depenent Hartree for\nindistinguishable particles (MCTDH-X) software. This powerful tool allows the\ninvestigation of ground state properties and dynamics of interacting quantum\nmany-body systems in different spatial dimensions. The MCTDH-X software is a\nset of programs and scripts to compute, analyze, and visualize solutions for\nthe time-dependent and time-independent many-body Schr\\\"{o}dinger equation for\nindistinguishable quantum particles. As the MCTDH-X software represents a\ngeneral solver for the Schr\\\"{o}dinger equation, it is applicable to a wide\nrange of problems in the fields of atomic, optical, molecular physics as well\nas condensed matter systems. In particular, it can be used to study\nlight-matter interactions, correlated dynamics of electrons, as well as some\naspects related to quantum information and computing. The MCTDH-X software\nsolves a set of non-linear coupled working equations based on the application\nof the variational principle to the Schr\\\"{o}dinger equation. These equations\nare obtained by using an ansatz for the many-body wavefunction that is a\ntime-dependent expansion in a set of time-dependent many-body basis states. The\ntime-dependence of the basis set enables MCTDH-X to deal with quantum dynamics\nat a superior accuracy as compared to, for instance, exact diagonalization\napproaches. Herein, we give an introduction to the MCTDH-X software via an\neasy-to-follow tutorial with a focus on accessibility. We use the double well\nto illustrate the fermionization of bosonic particles, the crystallization of\nfermionic particles, characteristics of the superfluid and Mott-insulator\nquantum phases in Hubbard models, and even dynamical quantum phase transitions.\nOur tutorial guides the potential user to apply the MCTDH-X software also to\nmore complex systems."
    },
    {
        "anchor": "Non-equilibrium dynamics induced by miscible-immiscible transition in\n  binary Bose-Einstein condensates: The non-equilibrium spatial dynamics in a two-component Bose-Einstein\ncondensate were excited by controlled miscible-immiscible transition, in which\nimmiscible condensates with domain structures are transferred to the miscible\ncondensates by changing the internal state of 87Rb atoms. The subsequent\nevolution exhibits the oscillation of spatial structures involving component\nmixing and separation. We show that the larger total energy of the miscible\nsystem results in a higher oscillation frequency. This investigation introduces\na new technique to control the miscibility and the spatial degrees of freedom\nin atomic Bose-Einstein condensates.",
        "positive": "Effective control of chemical potentials by Rabi coupling with rf-fields\n  in ultracold mixtures: We show that a linear term coupling the atoms of an ultracold binary mixture\nprovides a simple method to induce an effective and tunable population\nimbalance between them. This term is easily realized by a Rabi coupling between\ndifferent hyperfine levels of the same atomic species. The resulting effective\nimbalance holds for one-particle states dressed by the Rabi coupling and\nobtained diagonalizing the mixing matrix of the Rabi term. This way of\ncontrolling the chemical potentials applies for both bosonic and fermionic\natoms and it allows also for spatially and temporally dependent imbalances. As\na first application, we show that, in the case of two attractive fermionic\nhyperfine levels with equal chemical potentials and coupled by the Rabi pulse,\nthe same superfluid properties of an imbalanced binary mixture are recovered.\nWe finally discuss the properties of m-species mixtures in the presence of\nSU(m)-invariant interactions."
    },
    {
        "anchor": "Design of a technique to measure the density of ultracold atoms in a\n  short-period optical lattice in three dimensions with single atom sensitivity: A measurement technique is described which has the potential to map the\natomic site occupancies of ultracold atoms in a short-period three-dimensional\noptical lattice. The method uses accordion and pinning lattices, together with\npolarization gradient cooling and fluorescence detection, to measure the\npositions of individual atoms within the sample in three dimensions at a\nresolution of around half the atomic resonant wavelength. The method measures\nthe site occupancy, rather than the parity of the site occupancy, of atoms in\nthe lattice. It is expected that such measurements hold significant potential\nfor the study of ultracold quantum dynamics.",
        "positive": "WKB approach and quantum corrections to classical dynamics in the\n  Josephson problem: We apply a many-body Wentzel-Kramers-Brillouin (WKB) approach to determine\nthe leading quantum corrections to the semiclassical dynamics of the Josephson\nmodel, describing interacting bosons able to tunnel between two localized\nstates. The semiclassical dynamics is known to divide between regular\noscillations and self-trapped oscillations where the sign of the imbalance\nremains fixed. In both cases, the WKB wave functions are matched to Airy\nfunctions, yielding a modified Bohr-Sommerfeld quantization condition. At the\ncritical energy dividing normal and self-trapped oscillations, the WKB wave\nfunctions should instead be matched to parabolic cylinder functions, leading to\na quantization formula that is not just the Bohr-Sommerfeld formula, and\nrecovering the known logarithmic quantum break times at this energy. This work\nthus provides another illustration of the usefulness of the WKB approach in\ncertain many-body problems."
    },
    {
        "anchor": "Deep inelastic collision of two-dimensional anisotropic dipolar\n  condensate solitons: The possibility of generating stable anisotropic solitons in dipolar\nBose-Einstein condensates (BECs) leads to a different scenario not possible in\na nondipolar BEC with contact interaction. We study the statics and dynamics of\nanisotropic bright solitons in quasi-two-dimensional BECs consisting of\npolarized dipolar atoms.We study the collision dynamics of two such solitons at\ndifferent velocities for different angles between the polarization and\ncollision directions. The collision is found to be quasi elastic at large\nvelocities. At small velocities the collision is inelastic leading to the\nformation of a coalesced soliton in an excited scissors mode, monopole mode or\nquadrupole mode. Also, at small velocities, after collision, a large change of\ndirection of motion of the solitons is possible. The investigation is performed\nthrough a numerical solution of the underlying mean-field Gross-Pitaevskii\nequation.",
        "positive": "Finite-range effects in the two-dimensional repulsive Fermi polaron: We study the repulsive Fermi polaron in a two-component, two-dimensional\nsystem of fermionic atoms inspired by the results of a recent experiment with\n$^{173}$Yb atoms [N. Darkwah Oppong \\textit{et al.}, Phys. Rev. Lett.\n\\textbf{122}, 193604 (2019)]. We use the diffusion Monte Carlo method to report\nproperties such as the polaron energy and the quasi-particle residue that have\nbeen measured in that experiment. To provide insight on the quasi-particle\ncharacter of the problem, we also report results for the effective mass. We\nshow that the effective range, together with the scattering length, is needed\nin order to reproduce the experimental results. Using different model\npotentials for the interaction between the Fermi sea and the impurity, we show\nthat it is possible to establish a regime of universality, in terms of these\ntwo parameters, that includes the whole experimental regime. This illustrates\nthe relevance of quantum fluctuations and beyond mean-field effects to\ncorrectly describe the Fermi polaron problem."
    },
    {
        "anchor": "Thermodynamic signatures for topological phase transitions to Majorana\n  and Weyl superfluids in ultracold Fermi gases: We discuss the thermodynamic signatures for the topological phase transitions\ninto Majorana and Weyl superfluid phases in ultracold Fermi gases in two and\nthree dimensions in the presence of Rashba spin-orbit coupling and a Zeeman\nfield. We analyze the thermodynamic properties exhibiting the distinct nature\nof the topological phase transitions linked with the Majorana fermions (2D\nFermi gas) and Weyl fermions (3D Fermi gas) which can be observed\nexperimentally, including pressure, chemical potential, isothermal\ncompressibility, entropy, and specific heat, as a function of the interaction\nand the Zeeman field at both zero and finite temperatures. We conclude that\namong the various thermodynamic quantities, the isothermal compressibility and\nthe chemical potential as a function of the artificial Zeeman field have the\nstrongest signatures of the topological transitions in both two and three\ndimensions.",
        "positive": "A fermionic impurity in a dipolar quantum droplet: In this article we develop the framework to describe Bose-Fermi mixtures of\nmagnetic atoms, focusing on the interaction of bosonic self-bound dipolar\nquantum droplets with a small number of fermions. We find an attractive\ninteraction potential due to the dipolar interaction with several bound states,\nwhich can be occupied by one fermion each, resulting in a very weak back-action\non the bosons. We conclude, that these impurities might act as unique probes\ngiving access to inherent properties of dipolar quantum droplets."
    },
    {
        "anchor": "Advances in precision contrast interferometry with Yb Bose-Einstein\n  condensates: Using a three-path contrast interferometer (CI) geometry and laser-pulse\ndiffraction gratings, we create the first matter-wave interferometer with\nytterbium (Yb) atoms. We present advances in contrast interferometry relevant\nto high-precision measurements. By comparing to a traditional atom\ninterferometer, we demonstrate the immunity of the CI to vibrations for long\ninteraction times (> 20 ms). We characterize and demonstrate control over the\ntwo largest systematic effects for a high-precision measurement of the fine\nstructure constant via photon recoil with our interferometer: diffraction\nphases and atomic interactions. Diffraction phases are an important systematic\nfor most interferometers using large-momentum transfer beam splitters; atomic\ninteractions are a key concern for any BEC interferometer. Finally, we consider\nthe prospects for a future sub-part per billion photon recoil measurement using\na Yb CI.",
        "positive": "Bose-Einstein Condensation of Europium: We report the realization of a Bose-Einstein condensate of europium atoms,\nwhich is a strongly dipolar species with unique properties, a highly symmetric\n$[\\mathrm{Xe}]\\ 4f^7 6s^2\\ {}^8\\mathrm{S}_{7/2}$ electronic ground state and a\nhyperfine structure. By means of evaporative cooling in a crossed optical\ndipole trap, we produced a condensate of ${}^{151}$Eu containing up to $5\\times\n10^4$ atoms. The scattering length of ${}^{151}$Eu was estimated to be $a_s =\n110(4)\\, a_\\mathrm{B}$ by comparing the velocities of expansion of condensates\nwith different orientations of the atomic magnetic moments. We observed\ndeformation of the condensate in the vicinity of the Feshbach resonance at\n$1.32\\,\\mathrm{G}$ with a width of $10\\,\\mathrm{mG}$."
    },
    {
        "anchor": "Mass and chirality inversion of a Dirac cone pair in St\u00fcckelberg\n  interferometry: We show that a St\\\"{u}ckelberg interferometer made of two massive Dirac cones\ncan reveal information on band eigenstates such as the chirality and mass sign\nof the cones. For a given spectrum with two gapped cones, we propose several\nlow-energy Hamiltonians differing by their eigenstates properties. The\ncorresponding inter-band transition probability is affected by such differences\nin its interference fringes being shifted by a new phase of geometrical origin.\nThis phase can be a useful bulk probe for topological band structures realized\nwith artificial crystals.",
        "positive": "The Molecular Hubbard Hamiltonian: Field Regimes and Molecular Species: The molecular Hubbard Hamiltonian (MHH) naturally arises for ultracold ground\nstate polar alkali dimer molecules in optical lattices. We show that, unlike\nultracold atoms, different molecules display different many-body phases due to\nintrinsic variances in molecular structure even when the molecular symmetry is\nthe same. We also demonstrate a wide variety of experimental controls on\n$^1\\Sigma$ molecules via external fields, including applied static electric and\nmagnetic fields, an AC microwave field, and the polarization and strength of\noptical lattice beams. We provide explicit numerical calculations of the\nparameters of the MHH, including tunneling and direct and exchange\ndipole-dipole interaction energies, for the molecules {$^{6}$Li$^{133}$Cs},\n$^{23}$Na$^{40}$K, $^{87}$Rb$^{133}$Cs, $^{40}$K$^{87}$Rb, and\n{$^{6}$Li$^{23}$Na} in weak and strong applied electric fields. As case studies\nof many-body physics, we use infinite-size matrix product state methods to\nexplore the quantum phase transitions from the superfluid phase to half-filled\nand third-filled crystalline phases in one dimension."
    },
    {
        "anchor": "Preparation and spectroscopy of a metastable Mott insulator state with\n  attractive interactions: We prepare and study a metastable attractive Mott insulator state formed with\nbosonic atoms in a three-dimensional optical lattice. Starting from a Mott\ninsulator with Cs atoms at weak repulsive interactions, we use a magnetic\nFeshbach resonance to tune the interactions to large attractive values and\nproduce a metastable state pinned by attractive interactions with a lifetime on\nthe order of 10 seconds. We probe the (de-)excitation spectrum via lattice\nmodulation spectroscopy, measuring the interaction dependence of two- and\nthree-body bound state energies. As a result of increased on-site three-body\nloss we observe resonance broadening and suppression of tunneling processes\nthat produce three-body occupation.",
        "positive": "Townes soliton and beyond: Non-miscible Bose mixtures in 2D: In these lecture notes, we discuss the physics of a two-dimensional binary\nmixture of Bose gases at zero temperature, close to the point where the two\nfluids tend to demix. We are interested in the case where one of the two fluids\n(the bath) fills the whole space, while the other one (the minority component)\ncontains a finite number of atoms. We discuss under which condition the\nminority component can form a stable, localized wave packet, which we relate to\nthe celebrated \"Townes soliton\". We discuss the formation of this soliton and\nthe transition towards a droplet regime that occurs when the number of atoms in\nthe minority component is increased. Our investigation is based on a\nmacroscopic approach based on coupled Gross-Pitaevskii equations, and it is\ncomplemented by a microscopic analysis in terms of bath-mediated interactions\nbetween the particles of the minority component."
    },
    {
        "anchor": "Numerical solution of the Boltzmann equation for trapped Fermi gases\n  with in-medium effects: Using the test-particle method, we solve numerically the Boltzmann equation\nfor an ultra-cold gas of trapped fermions with realistic particle number and\ntrap geometry in the normal phase. We include a mean-field potential and\nin-medium modifications of the cross-section obtained within a T matrix\nformalism. After some tests showing the reliability of our procedure, we apply\nthe method to realistic cases of practical interest, namely the anisotropic\nexpansion of the cloud and the radial quadrupole mode oscillation. Our results\nare in good agreement with experimental data. Although the in-medium effects\nsignificantly increase the collision rate, we find that they have only a\nmoderate effect on the anisotropic expansion and on frequency and damping rate\nof the quadrupole mode.",
        "positive": "Exact one-particle density matrix for SU($N$) fermionic matter-waves in\n  the strong repulsive limit: We consider a gas of repulsive $N$-component fermions confined in a\nring-shaped potential, subject to an effective magnetic field. For large\nrepulsion strengths, we work out a Bethe ansatz scheme to compute the two-point\ncorrelation matrix and then the one-particle density matrix. Our results holds\nin the mesoscopic regime of finite but sufficiently large number of particles\nand system size that are not accessible by numerics. We access the momentum\ndistribution of the system and analyse its specific dependence of interaction,\nmagnetic field and number of components $N$. In the context of cold atoms, the\nexact computation of the correlation matrix to determine the interference\npatterns that are produced by releasing cold atoms from ring traps is carried\nout."
    },
    {
        "anchor": "Engineering and Revealing Dirac Strings in Spinor Condensates: Artificial monopoles have been engineered in various systems, yet there has\nbeen no systematic study on the singular vector potentials associated with the\nmonopole field. We show that the Dirac string, the line singularity of the\nvector potential, can be engineered, manipulated, and made manifest in a spinor\natomic condensate. We elucidate the connection among spin, orbital degrees of\nfreedom, and the artificial gauge, and reveal that there exists a mapping\nbetween the vortex filament and the Dirac string. We also devise a proposal\nwhere preparing initial spin states with relevant symmetries can result in\ndifferent vortex patterns, revealing an underlying correspondence between the\ninternal spin states and the spherical vortex structures. Such a mapping also\nleads to a new way of constructing monopole harmonics. Our observation provides\nsignificant insights in quantum matter possessing internal symmetries in curved\nspaces.",
        "positive": "Basis for time crystal phenomena in ultra-cold atoms bouncing on an\n  oscillating mirror: We consider classical dynamics of a 1D system of $N$ particles bouncing on an\noscillating mirror in the presence of gravitational field. The particles behave\nlike hard balls and they are resonantly driven by the mirror. We identify the\nmanifolds the particles move on and derive the effective secular Hamiltonian\nfor resonant motion of the particles. Proper choice of time periodic\noscillations of the mirror allows for engineering of the effective behaviour of\nthe particles. In particular, the system can behave like a $N$-dimensional\nfictitious particle moving in an $N$-dimensional crystalline structure. Our\nclassical analysis constitutes a basis for quantum research of novel time\ncrystal phenomena in ultra-cold atoms bouncing on an oscillating atom mirror."
    },
    {
        "anchor": "Fidelity plateaus from correlated noise in isolated few-level quantum\n  systems: We show that, in an isolated two-level quantum system described by a\ntime-dependent Hamiltonian, correlated noise in the Hamiltonian's parameters\ncan lead to an arbitrarily long plateau in the state-preparation fidelity as a\nfunction of elapsed time. We explain the formation of this plateau using the\nBloch-sphere representation, deriving analytical expressions for its start and\nend times and its height. We also briefly discuss the extent to which this\nphenomenon is expected to be visible in more general quantum systems with $N>2$\nlevels.",
        "positive": "Mobile impurities in integrable models: We use a mobile impurity or depleton model to study elementary excitations in\none-dimensional integrable systems. For Lieb-Liniger and bosonic Yang-Gaudin\nmodels we express two phenomenological parameters characterising renormalised\ninter- actions of mobile impurities with superfluid background: the number of\ndepleted particles, $N$ and the superfluid phase drop $\\pi J$ in terms of the\ncorresponding Bethe Ansatz solution and demonstrate, in the leading order, the\nabsence of two-phonon scattering resulting in vanishing rates of inelastic\nprocesses such as viscosity experienced by the mobile impurities"
    },
    {
        "anchor": "Observation of local temporal correlations in trapped quantum gases: We measure the temporal pair correlation function $g^{(2)}(\\tau)$ of a\ntrapped gas of bosons above and below the critical temperature for\nBose-Einstein condensation. The measurement is performed {\\it in situ} using a\nlocal, time-resolved single-atom sensitive probing technique. Third and fourth\norder correlation functions are also extracted. We develop a theoretical model\nand compare it with our experimental data, finding good quantitative agreement\nand highlighting the role of interactions. Our results promote temporal\ncorrelations as new observables to study the dynamics of ultracold quantum\ngases.",
        "positive": "Mean-field transport of a Bose-Einstein condensate: The expansion of an initially confined Bose-Einstein condensate into either\nfree space or a tilted optical lattice is investigated in a mean-field\napproach. The effect of the interactions is to enhance or suppress the\ntransport depending on the sign and strength of the interactions. These effects\nare discusses in detail in view of recent experiments probing non-equilibrium\ntransport of ultracold quantum gases."
    },
    {
        "anchor": "Trimer liquids and crystals of polar molecules in coupled wires: We investigate the pairing and crystalline instabilities of bosonic and\nfermionic polar molecules confined to a ladder geometry. By means of analytical\nand quasi-exact numerical techniques, we show that gases of composite molecular\ndimers as well as trimers can be stabilized as a function of the density\ndifference between the wires. A shallow optical lattice can pin both liquids,\nrealizing crystals of composite bosons or fermions. We show that these exotic\nquantum phases should be realizable under current experimental conditions in\nfinite-size confining potentials.",
        "positive": "Spin mixing and protection of ferromagnetism in a spinor dipolar\n  condensate: We study spin mixing dynamics in a chromium dipolar Bose-Einstein Condensate,\nafter tilting the atomic spins by an angle $\\theta$ with respect to the\nmagnetic field. Spin mixing is triggered by dipolar coupling, but, once\ndynamics has started, it is mostly driven by contact interactions. For the\nparticular case $\\theta=\\pi/2$, an external spin-orbit coupling term induced by\na magnetic gradient is required to enable the dynamics. Then the initial\nferromagnetic character of the gas is locally preserved, an unexpected feature\nthat we attribute to large spin-dependent contact interactions."
    },
    {
        "anchor": "Internal Josephson Oscillations for Distinct Momenta Bose-Einstein\n  Condensates: The internal Josephson oscillations between an atomic Bose-Einstein\ncondensate (BEC) and a molecular one are studied for atoms in a square optical\nlattice subjected to a staggered gauge field. The system is described by a\nBose-Hubbard model with complex and anisotropic hopping parameters that are\ndifferent for each species, i.e., atoms and molecules. When the flux per\nplaquette for each species is small, the system oscillates between two\nconventional zero-momentum condensates. However, there is a regime of\nparameters in which Josephson oscillations between a vortex-carrying atomic\ncondensate (finite momentum BEC) and a conventional zero-momentum molecular\ncondensate may be realized. The experimental observation of the oscillations\nbetween these qualitatively distinct BEC's is possible with state-of-the-art\nRamsey interference techniques.",
        "positive": "Orbital physics of polar Fermi molecules: We study a system of polar dipolar fermions in a two-dimensional optical\nlattice and show that multi-band Fermi-Hubbard model is necessary to discuss\nsuch system. By taking into account both on-site, and long-range interactions\nbetween different bands, as well as occupation-dependent inter- and intra-band\ntunneling, we predict appearance of novel phases in the strongly-interacting\nlimit."
    },
    {
        "anchor": "Higher Order Quantum Ghost Imaging with Ultra-Cold Atoms: Ghost imaging is a quantum optics technique that uses correlations between\ntwo beams to reconstruct an image in one beam from photons that do not interact\nwith the object being imaged. While pairwise (second order) correlations are\nusually used to create the image, higher order correlations can be utilized to\nimprove the performance of ghost imaging. In this paper, we demonstrate higher\norder atomic ghost imaging, using entangled ultracold metastable helium atoms\nfrom an s-wave collision halo. We construct higher order ghost images up to 5th\norder and show that using higher order correlations can improve the visibility\nof the images without impacting the resolution. This is the first demonstration\nof higher order ghost imaging with massive particles and the first higher order\nghost imaging protocol of any type using a quantum source.",
        "positive": "Superfluid filaments of dipolar bosons in free space: We systematically investigate the zero temperature phase diagram of bosons\ninteracting via dipolar interactions in three dimensions in free space via path\nintegral Monte Carlo simulations with few hundreds of particles and periodic\nboundary conditions based on the worm algorithm. Upon increasing the strength\nof the dipolar interaction and at sufficiently high densities we find a wide\nregion where filaments are stabilized along the direction of the external\nfield. Most interestingly by computing the superfluid fraction we conclude that\nsuperfluidity is anisotropic and is greatly suppressed along the orthogonal\nplane. Finally we perform simulations at finite temperature confirming the\nstability of filaments against thermal fluctuations and provide an estimate of\nthe superfluid fraction in the weak coupling limit in the framework of the\nLandau two-fluid model."
    },
    {
        "anchor": "Pinpointing Feshbach Resonances and Testing Efimov Universalities in\n  $^{39}$K: Using a combination of bound-state spectroscopy and loss spectroscopy, we\npinpoint eight intrastate Feshbach resonances in $^{39}$K, as well as six\npreviously unexplored interstate ones. We also perform a detailed\ncharacterization of four of the intrastate resonances and two of the interstate\nones. We carry out coupled-channel scattering calculations and find good\nagreement with experiment. The combination of experiment and theory provides a\nfaithful map of the scattering length $a$ and permits precision measurements of\nthe signatures of Efimov physics across four intermediate-strength resonances.\nWe measure the modulation of the $a^4$ scaling of the three-body loss\ncoefficient for both $a<0$ and $a>0$, as well as the many-body loss dynamics at\nunitarity (where $a$ diverges). The absolute positions of the observed Efimov\nfeatures confirm a ubiquitous breakdown of Efimov--van-der-Waals universality\nin $^{39}$K, while their relative positions are in agreement with the universal\nEfimov ratios. The loss dynamics at the three broadest Feshbach resonances are\nuniversal within experimental uncertainties, consistent with observing little\nvariation in the Efimov width parameters.",
        "positive": "Multimode model for an atomic Bose-Einstein condensate in a ring-shaped\n  optical lattice: We study the population dynamics of a ring-shaped optical lattice with a high\nnumber of particles per site and a low, below ten, number of wells. Using a\nlocalized on-site basis defined in terms of stationary states, we were able to\nconstruct a multiple-mode model depending on relevant hopping and on-site\nenergy parameters. We show that in case of two wells, our model corresponds\nexactly to the latest improvement of the two-mode model. We derive a formula\nfor the self-trapping period, which turns out to be chiefly ruled by the\non-site interaction energy parameter. By comparing to time dependent\nGross-Pitaevskii simulations, we show that the multimode model results can be\nenhanced in a remarkable way over all the regimes by only renormalizing such a\nparameter. Finally, using a different approach which involves only the ground\nstate density, we derive an effective interaction energy parameter that shows\nto be in accordance with the renormalized one."
    },
    {
        "anchor": "Synthetic 3D Spin-Orbit Coupling: We describe a method for creating a three-dimensional analogue to Rashba\nspin-orbit coupling in systems of ultracold atoms. This laser induced coupling\nuses Raman transitions to link four internal atomic states with a tetrahedral\ngeometry, and gives rise to a Dirac point that is robust against environmental\nperturbations. We present an exact result showing that such a spin-orbit\ncoupling in a fermionic system always rise to a molecular bound state.",
        "positive": "Localization of weakly interacting Bose gas in quasiperiodic potential: We study the localization properties of weakly interacting Bose gas in a\nquasiperiodic potential commonly known as Aubry-Andr\\'e model. Effect of\ninteraction on localization is investigated by computing the `superfluid\nfraction' and `inverse participation ratio'. For interacting Bosons the inverse\nparticipation ratio increases very slowly after the localization transition due\nto `multisite localization' of the wave function. We also study the\nlocalization in Aubry-Andr\\'e model using an alternative approach of classical\ndynamical map, where the localization is manifested by chaotic classical\ndynamics. For weakly interacting Bose gas, Bogoliubov quasiparticle spectrum\nand condensate fraction are calculated in order to study the loss of coherence\nwith increasing disorder strength. Finally we discuss the effect of trapping\npotential on localization of matter wave."
    },
    {
        "anchor": "Topological phase transitions in four dimensions: We show that four-dimensional systems may exhibit a topological phase\ntransition analogous to the well-known Berezinskii-Kosterlitz-Thouless vortex\nunbinding transition in two-dimensional systems. The realisation of an\nengineered quantum system, where the predicted phase transition shall occur, is\nalso presented. We study a suitable generalization of the sine-Gordon model in\nfour dimensions and the renormalization group flow equation of its couplings,\nshowing that the critical value of the frequency is the square of the\ncorresponding value in $2D$. The value of the anomalous dimension at the\ncritical point is determined ($\\eta=1/32$) and a conjecture for the universal\njump of the superfluid stiffness ($4/\\pi^2$) presented.",
        "positive": "Three two-component fermions with contact interactions: correct\n  formulation and energy spectrum: Properties of two identical particles of mass $m$ and a distinct particle of\nmass $m_1$ in the universal low-energy limit of zero-range two-body interaction\nare studied in different sectors of total angular momentum $L$ and parity $P$.\nFor the unambiguous formulation of the problem in the interval $\\mu_r(L^P) <\nm/m_1 \\le \\mu_c(L^P)$ ($\\mu_r(1^-) \\approx 8.619$ and $\\mu_c(1^-) \\approx\n13.607$, $\\mu_r(2^+) \\approx 32.948$ and $\\mu_c(2^+) \\approx 38.630$,~etc.) in\neach $L^P$ sector an additional parameter $b$ determining the wave function\nnear the triple-collision point is introduced; thus, a one-parameter family of\nself-adjoint Hamiltonians is defined. Within the framework of this formulation,\ndependence of the bound-state energies on $m/m_1$ and $b$ in the sector of\nangular momentum and parity $L^P$ is calculated for $L \\le 5$ and analysed with\nthe aid of a simple model. A number of the bound states for each $L^P$ sector\nis analysed and presented in the form of `phase diagrams' in the plane of two\nparameters $m/m_1$ and $b$."
    },
    {
        "anchor": "Topological Classification and Stability of Fermi Surfaces: In the framework of the Cartan classification of Hamiltonians, a kind of\ntopological classification of Fermi surfaces is established in terms of\ntopological charges. The topological charge of a Fermi surface depends on its\ncodimension and the class to which its Hamiltonian belongs. It is revealed that\nsix types of topological charges exist, and they form two groups with respect\nto the chiral symmetry, with each group consisting of one original charge and\ntwo descendants. It is these nontrivial topological charges which lead to the\nrobust topological protection of the corresponding Fermi surfaces against\nperturbations that preserve discrete symmetries.",
        "positive": "Incoherent excitation and switching of spin states in exciton-polariton\n  condensates: We investigate, theoretically and numerically, the spin dynamics of a\ntwo-component exciton-polariton condensate created and sustained by\nnon-resonant spin-polarized optical pumping of a semiconductor microcavity.\nUsing the open-dissipative mean-field model, we show that the existence of well\ndefined phase-locked steady states of the condensate may lead to efficient\nswitching and control of spin (polarization) states with a non-resonant\nexcitation. Spatially inhomogeneous pulsed excitations can cause symmetry\nbreaking in the pseudo-spin structure of the condensate and lead to formation\nof non-trivial spin textures. Our model is universally applicable to two weakly\ncoupled polariton condensates, and therefore can also describe the behaviour of\ncondensate populations and phases in 'double-well' type potentials."
    },
    {
        "anchor": "Exploring the Single-Particle Mobility Edge in a One-Dimensional\n  Quasiperiodic Optical Lattice: A single-particle mobility edge (SPME) marks a critical energy separating\nextended from localized states in a quantum system. In one-dimensional systems\nwith uncorrelated disorder, a SPME cannot exist, since all single-particle\nstates localize for arbitrarily weak disorder strengths. However, if\ncorrelations are present in the disorder potential, the localization transition\ncan occur at a finite disorder strength and SPMEs become possible. In this\nwork, we find experimental evidence for the existence of such a SPME in a\none-dimensional quasi-periodic optical lattice. Specifically, we find a regime\nwhere extended and localized single-particle states coexist, in good agreement\nwith theoretical simulations, which predict a SPME in this regime.",
        "positive": "Thermodynamic equivalence of two-dimensional imperfect attractive Fermi\n  and repulsive Bose gases: We consider two-dimensional imperfect attractive Fermi and repulsive Bose\ngases consisting of spinless point particles whose total interparticle\ninteraction energy is represented by $a N^2/2 V$ with $a=-a_{F}\\leq 0$ for\nfermions, and $a=a_{B}\\geq 0$ for bosons. We show that in spite of the\nattraction the thermodynamics of $d=2$ imperfect Fermi gas remains well defined\nfor $0 \\leq a_{F}\\leq a_{0}=h^2/2\\pi m$, and is exactly the same as the one of\nthe repulsive imperfect Bose gas with $a_{B}=a_{0}-a_{F}$. In particular, for\n$a_{F}=a_{0}$ one observes the thermodynamic equivalence of the attractive\nimperfect Fermi gas and the ideal Bose gas."
    },
    {
        "anchor": "Systems of vortices in a binary core-shell Bose-Einstein condensate: A trapped Bose--Einstein-condensed mixture of two types of cold atoms with\nsignificantly different masses has been simulated numerically within the\ncoupled Gross--Pitaevskii equations. A configuration consisting of a\nvortex-free core and a shell penetrated by quantum vortices is possible in the\nphase separation regime. The dynamic properties of vortices in the shell are\ndetermined by several parameters. Physically implementable parametric domains\ncorresponding to long-lived strongly nonstationary systems of several vortices\nattached to the core have been sought. A number of realistic numerical examples\nof three vortex pairs existing for many hundreds of characteristic times have\nbeen presented.",
        "positive": "Quantum critical behavior of the superfluid-Mott glass transition: We investigate the zero-temperature superfluid to insulator transitions in a\ndiluted two-dimensional quantum rotor model with particle-hole symmetry. We map\nthe Hamiltonian onto a classical $(2+1)$-dimensional XY model with columnar\ndisorder which we analyze by means of large-scale Monte Carlo simulations. For\ndilutions below the lattice percolation threshold, the system undergoes a\ngeneric superfluid-Mott glass transition. In contrast to other quantum phase\ntransitions in disordered systems, its critical behavior is of conventional\npower-law type with universal (dilution-independent) critical exponents\n$z=1.52(3)$, $\\nu=1.16(5)$, $\\beta/\\nu= 0.48(2)$, $\\gamma/\\nu=2.52(4)$, and\n$\\eta=-0.52(4)$. These values agree with and improve upon earlier Monte-Carlo\nresults [Phys. Rev. Lett. 92, 015703 (2004)] while (partially) excluding other\nfindings in the literature. As a further test of universality, we also consider\na soft-spin version of the classical Hamiltonian. In addition, we study the\npercolation quantum phase transition across the lattice percolation threshold;\nits critical behavior is governed by the lattice percolation exponents in\nagreement with recent theoretical predictions. We relate our results to a\ngeneral classification of phase transitions in disordered systems, and we\nbriefly discuss experiments."
    },
    {
        "anchor": "Majorana edge states in two atomic wires coupled by pair-hopping: We present evidence for the existence of Majorana edge states in a number\nconserving theory describing a system of spinless fermions on two wires that\nare coupled by a pair hopping. Our analysis is based on the combination of a\nqualitative low energy approach and numerical techniques using the Density\nMatrix Renormalization Group. We also discuss an experimental realization of\npair-hopping interactions in cold atom gases confined in optical lattices, and\nits possible alternative applications to quantum simulation.",
        "positive": "Fate of the Mollow triplet in strongly-coupled atomic arrays: Subwavelength arrays of quantum emitters have emerged as an interesting\nplatform displaying prominent collective effects. Here we study such arrays\nunder coherent driving, realizing an open quantum many-body problem in a\nstrongly non-linear regime. We show that the combination of dipolar\ninteractions and regular geometry have a dramatic effect on the spectrum of\nemitted light: the famous Mollow triplet characterizing the emission of a\nsingle atom develops a structured broadening with flat sidebands, with a\nbandwidth determined by the dipolar interactions. This emission spectrum\ncharacterizes atomic arrays and distinguishes them from disordered ensembles as\nwell as non-interacting emitters. Our predictions are based on a novel\ndynamical mean-field theory (DMFT) approach to the problem, paving the way for\nfurther studies of these systems."
    },
    {
        "anchor": "Casimir effect in a dilute Bose gas in canonical ensemble within\n  improved Hartree-Fock approximation: The Casimir effect in a dilute Bose gas confined between two planar walls is\ninvestigated in the canonical ensemble at zero temperature by means of\nCornwall-Jackiw-Tomboulis effective action approach within the improved\nHartree-Fock approximation. Our results show that: (i) the Casimir energy and\nthe resulting Casimir force in the canonical ensemble remarkably differ from\nthose in the grand canonical ensemble; (ii) when the distance between two\nplanar walls increases, the Casimir energy and Casimir force decay in\naccordance with a half-integer power law in the canonical ensemble instead of\nan integer power law in the grand canonical ensemble.",
        "positive": "Low-momentum dynamic structure factor of a strongly interacting Fermi\n  gas at finite temperature: A two-fluid hydrodynamic description: We provide a description of the dynamic structure factor of a homogeneous\nunitary Fermi gas at low momentum and low frequency, based on the dissipative\ntwo-fluid hydrodynamic theory. The viscous relaxation time is estimated and is\nused to determine the regime where the hydrodynamic theory is applicable and to\nunderstand the nature of sound waves in the density response near the\nsuperfluid phase transition. By collecting the best knowledge on the shear\nviscosity and thermal conductivity known so far, we calculate the various\ndiffusion coefficients and obtain the damping width of the (first and second)\nsounds. We find that the damping width of the first sound is greatly enhanced\nacross the superfluid transition and very close to the transition the second\nsound might be resolved in the density response for the transferred momentum up\nto the half of Fermi momentum. Our work is motivated by the recent measurement\nof the local dynamic structure factor at low momentum at Swinburne University\nof Technology and the on-going experiment on sound attenuation of a homogeneous\nunitary Fermi gas at Massachusetts Institute of Technology. We discuss how the\nmeasurement of the velocity and damping width of the sound modes in\nlow-momentum dynamic structure factor may lead to an improved determination of\nthe universal superfluid density, shear viscosity and thermal conductivity of a\nunitary Fermi gas."
    },
    {
        "anchor": "Two supersolid phases in hard-core extended Bose-Hubbard model: The effect of the next-nearest-neighbor (nnn) tunneling on the hard-core\nextended Bose-Hubbard model on square lattices is investigated. By means of the\ncluster mean-field theory, the ground-state phase diagrams are determined. When\na modest nnn tunneling is introduced, depending on its sign, two distinct\nsupersolid states with checkerboard crystal structures are found away from\nhalf-filing. The characters of various phase transitions out of these two\nsupersolid states are discussed. In particular, for the case with kinetic\nfrustration, the existence of a half supersolid phase possessing both solid and\nunconventional superfluid orders is established. Our work hence sheds light on\nthe search of this interesting supersolid phase in real ultracold lattice gases\nwith frustrated tunnelings.",
        "positive": "Parton theory of magnetic polarons: Mesonic resonances and signatures in\n  dynamics: When a mobile hole is moving in an anti-ferromagnet it distorts the\nsurrounding Neel order and forms a magnetic polaron. Such interplay between\nhole motion and anti-ferromagnetism is believed to be at the heart of high-Tc\nsuperconductivity in cuprates. We study a single hole described by the t-Jz\nmodel with Ising interactions between the spins in 2D. This situation can be\nexperimentally realized in quantum gas microscopes. When the hole hopping is\nmuch larger than couplings between the spins, we find strong evidence that\nmagnetic polarons can be understood as bound states of two partons, a spinon\nand a holon carrying spin and charge quantum numbers respectively. We introduce\na microscopic parton description which is benchmarked by comparison with\nresults from advanced numerical simulations. Using this parton theory, we\npredict a series of excited states that are invisible in the spectral function\nand correspond to rotational excitations of the spinon-holon pair. This is\nreminiscent of mesonic resonances observed in high-energy physics, which can be\nunderstood as rotating quark antiquark pairs. We also apply the strong coupling\nparton theory to study far-from equilibrium dynamics of magnetic polarons\nobservable in current experiments with ultracold atoms. Our work supports\nearlier ideas that partons in a confining phase of matter represent a useful\nparadigm in condensed-matter physics and in the context of high-Tc\nsuperconductivity. While direct observations of spinons and holons in real\nspace are impossible in traditional solid-state experiments, quantum gas\nmicroscopes provide a new experimental toolbox. We show that, using this\nplatform, direct observations of partons in and out-of equilibrium are\npossible. Extensions of our approach to the t-J model are also discussed. Our\npredictions in this case are relevant to current experiments with quantum gas\nmicroscopes for ultracold atoms."
    },
    {
        "anchor": "Loading Ultracold Gases in Topological Floquet Bands: Current and\n  Center-of-Mass Responses: Topological band structures can be designed by subjecting lattice systems to\ntime-periodic modulations, as was recently demonstrated in cold atoms and\nphotonic crystals. However, changing the topological nature of Floquet Bloch\nbands from trivial to non-trivial, by progressively launching the\ntime-modulation, is necessarily accompanied with gap-closing processes: this\nhas important consequences for the loading of particles into a target Floquet\nband with non-trivial topology, and hence, on the subsequent measurements. In\nthis work, we analyse how such loading sequences can be optimized in view of\nprobing the topology of Floquet bands through transport measurements. In\nparticular, we demonstrate the robustness of center-of-mass responses, as\ncompared to current responses, which present important irregularities due to an\ninterplay between the micro-motion of the drive and inter-band interference\neffects. The results presented in this work illustrate how probing the\ncenter-of-mass displacement of atomic clouds offers a reliable method to detect\nthe topology of Floquet bands, after realistic loading sequences.",
        "positive": "Field-theoretical study of the Bose polaron: We study the properties of the Bose polaron, an impurity strongly interacting\nwith a Bose-Einstein condensate, using a field-theoretic approach and make\npredictions for the spectral function and various quasiparticle properties that\ncan be tested in experiment. We find that most of the spectral weight is\ncontained in a coherent attractive and a metastable repulsive polaron branch.\nWe show that the qualitative behavior of the Bose polaron is well described by\na non-selfconsistent T-matrix approximation by comparing analytical results to\nnumerical data obtained from a fully selfconsistent T-matrix approach. The\nlatter takes into account an infinite number of bosons excited from the\ncondensate."
    },
    {
        "anchor": "Bogoliubov-de Gennes theory of the \"snake\" instability of gray solitons\n  in higher dimensions: Gray solitons are a one-parameter family of solutions to the one-dimensional\nnon-linear Schr\\\"odinger equation (NLSE) with positive cubic nonlinearity, as\nfound in repulsively interacting dilute Bose-Einstein condensates or\nelectromagnetic waves in the visible spectrum in waveguides described by\nGross-Pitaevskii mean field theory. In two dimensions these solutions to the\nNLSE appear as a line or plane of depressed condensate density or light\nintensity, but numerical solutions show that this line is dynamically unstable\nto `snaking': the initially straight line of density or intensity minimum\nundulates with exponentially growing amplitude. To assist future studies of\nquantum mechanical instability beyond mean field theory, we here pursue an\napproximate analytical description of the snake instability within\nBogoliubov-de Gennes perturbation theory. Within this linear approximation the\ntwo-dimensional result applies trivially to three dimensions as well,\ndescribing buckling modes of the low-density plane. We extend the analytical\nresults of Kuznetsov and Turitsyn [Sov. Phys. JETP \\textbf{67}, 1583 (1988)] to\nshorter wavelengths of the `snake' modulation and show to what extent the snake\nmode can be described accurately as a parametric instability, in which the\nposition and grayness parameter of the initial soliton simply become dependent\non the transverse dimension(s). We find that the parametric picture remains\naccurate up to second order in the snaking wave number, if the snaking soliton\nis also dressed by an outward-propagating sound wave, but that beyond second\norder in the snaking wave number the parametric description breaks down.",
        "positive": "Mean-field and stability analysis of two-dimensional flowing soft-core\n  bosons modeling a supersolid: The soft-core boson system is one of the simplest models of supersolids,\nwhich have both off-diagonal long-range order (Bose-Einstein condensation) and\ndiagonal long-range order (crystalline order). Although this model has been\nstudied from various points of view, studies of the stability of\ncurrent-flowing states are lacking. Solving the Gross-Pitaevskii and Bogoliubov\nequations, we obtain excitation spectra in superfluid, supersolid, and stripe\nphases. On the basis of the results of the excitation spectra, we present a\nstability phase diagram that shows the region of the metastable superflow\nstates for each phase."
    },
    {
        "anchor": "Rabi flopping induces spatial demixing dynamics: We experimentally investigate the mixing/demixing dynamics of Bose-Einstein\ncondensates in the presence of a linear coupling between two internal states.\nThe observed amplitude reduction of the Rabi oscillations can be understood as\na result of demixing dynamics of dressed states as experimentally confirmed by\nreconstructing the spatial profile of dressed state amplitudes. The\nobservations are in quantitative agreement with numerical integration of\ncoupled Gross-Pitaevskii equations without free parameters, which also reveals\nthe criticality of the dynamics on the symmetry of the system. Our observations\ndemonstrate new possibilities for changing effective atomic interactions and\nstudying critical phenomena.",
        "positive": "Cold atoms at unitarity and inverse square interaction: Consider two identical atoms in a spherical harmonic oscillator interacting\nwith a zero-range interaction which is tuned to produce an s-wave zero-energy\nbound state. The quantum spectrum of the system is known to be exactly\nsolvable. We note that the same partial wave quantum spectrum is obtained by\nthe one-dimensional scale-invariant inverse square potential. Long known as the\nCalogero-Sutherland-Moser (CSM) model, it leads to Fractional Exclusion\nStatistics (FES) of Haldane and Wu. The statistical parameter is deduced from\nthe analytically calculated second virial coefficient. When FES is applied to a\nFermi gas at unitarity, it gives good agreement with experimental data without\nthe use of any free parameter."
    },
    {
        "anchor": "Three Dimensional Raman Cooling using Velocity Selective Rapid Adiabatic\n  Passage: We present a new and efficient implementation of Raman cooling of trapped\natoms. It uses Raman pulses with an appropriate frequency chirp to realize a\nvelocity selective excitation through a rapid adiabatic passage. This method\nallows to address in a single pulse a large number of non zero atomic velocity\nclasses and it produces a nearly unity transfer efficiency. We demonstrate this\ncooling method using cesium atoms in a far-detuned crossed dipole trap.\nThree-dimensional cooling of $1 \\times 10^{5}$ atoms down to $2 \\mu$K is\nperformed in 100 ms. In this preliminary experiment the final atomic density is\n$1.3\\times 10^{12}$ at/cm$^3$ (within a factor of 2) and the phase-space\ndensity increase over the uncooled sample is 20. Numerical simulations indicate\nthat temperatures below the single photon recoil temperature should be\nachievable with this method.",
        "positive": "Coherent control of phase diffusion in a Bosonic Josephson junction by\n  scattering length modulation: By means of a temporal-periodic modulation of the s-wave scattering length, a\nprocedure to control the evolution of an initial atomic coherent state\nassociated with a Bosonic Josephson junction is presented. The scheme developed\nhas a remarkable advantage of avoiding the quantum collapse of the state due to\nphase and number diffusion. This kind of control could prove useful for atom\ninterferometry using BECs, where the interactions limit the evolution time\nstage within the interferometer, and where the modulation can be induced via\nmagnetic Feshbach resonances as recently experimentally demonstrated."
    },
    {
        "anchor": "Spontaneous symmetry breaking in frustrated triangular atom arrays due\n  to cooperative light scattering: We demonstrate the presence of an optical phase transition with\nfrustration-induced spontaneous symmetry breaking in a triangular planar atomic\narray due to cooperative light-mediated interactions. We show how the array\ngeometry of triangle unit cells at low light intensities leads to degenerate\ncollective radiative excitations forming nearly flat bands. We drive degenerate\npairs of collective excitations to be equally populated in both cases of the\natomic polarization in the lattice plane and perpendicular to it. At higher\nintensities, above specific threshold values, this symmetry in the populations\nis spontaneously broken. We also develop an effective few-mode model that\nprovides semianalytic descriptions of the symmetry-breaking threshold and\ninfinite-lattice limit phase transition. Surprisingly, we find how excitations\ndue to dipolar interactions correspond to optical analogs of those found in\nfrustrated magnets and superfluids, with closely related symmetry-breaking\nmechanisms despite the significant physical differences between these systems,\nopening potential for simulating even quantum magnetism. Transmitted light\nthrough the array conveys information about symmetry breaking in the hysteresis\nbehavior of the spectrum. Moreover, in a Mott-insulator state, the atomic\npositions are subject to zero-point quantum fluctuations. Interpreting each\nstochastic realization as a light-induced quantum measurement of the atomic\nposition configuration, we find how strong nonlinearities and even weak\nposition uncertainties lead to considerable measurement-induced symmetry\nbreaking, while ensemble-averaging over many realizations restores the original\nsymmetry and the unbroken state. Larger position uncertainty results in the\nformation of domains of different broken symmetries.",
        "positive": "Observation of superfluidity in a strongly correlated two-dimensional\n  Fermi gas: Understanding how strongly correlated two-dimensional (2D) systems can give\nrise to unconventional superconductivity with high critical temperatures is one\nof the major unsolved problems in condensed matter physics. Ultracold 2D Fermi\ngases have emerged as clean and controllable model systems to study the\ninterplay of strong correlations and reduced dimensionality, but direct\nevidence of superfluidity in these systems has been missing. Here, we\ndemonstrate superfluidity in an ultracold 2D Fermi gas by moving a periodic\npotential through the system and observing no dissipation below a critical\nvelocity v$_{\\rm c}$. We measure v$_{\\rm c}$ as a function of interaction\nstrength and find a maximum in the crossover regime between bosonic and\nfermionic superfluidity. Our measurement establishes ultracold Fermi gases as a\npowerful tool for studying the influence of reduced dimensionality on strongly\ncorrelated superfluids."
    },
    {
        "anchor": "Hanle model of a spin-orbit coupled Bose-Einstein condensate of excitons\n  in semiconductor quantum wells: We present a theoretical model of a driven-dissipative spin-orbit coupled\nBose-Einstein condensate of indirect excitons in semiconductor quantum wells\n(QW's). Our steady-state solution of the problem shares analogies with the\nHanle effect in an optical orientation experiment. The role of the spin pump in\nour case is played by boson stimulated scattering into the linearly-polarized\nground state and the depolarization occurs as a result of long-range exchange\ninteraction between electrons and holes. Our theory agrees with the recent\nexperiment [A. A. High et al., Phys. Rev. Lett. 110, 246403 (2013)], where\nspontaneous emergence of spatial coherence and polarization texture have been\nobserved. As a complementary test, we discuss a configuration where an external\nmagnetic field is applied in the structure plane.",
        "positive": "Exact analytical solution for density matrix of a non-equilibrium\n  polariton Bose-Einstein condensate: In this letter, we give an analytical quantum description of a\nnon-equilibrium polariton Bose-Einstein condensate (BEC) based on the solution\nof the master equation for the full polariton density matrix in the limit of\nfast thermalization. We find the density matrix of a non-equilibrium BEC, that\ntakes into account quantum correlations between all polariton states. We show\nthat the formation of BEC is accompanied by the build-up of cross-correlations\nbetween the ground state and the excited states reaching their highest values\nat the condensation threshold. Despite the non-equilibrium nature of polariton\nsystems, we show the average population of polariton states exhibits the\nBose-Einstein distribution with an almost zero effective chemical potential\nabove the condensation threshold similar to an equilibrium BEC. We demonstrate\nthat above threshold the effective temperature of polariton condensate drops\nbelow the reservoir temperature."
    },
    {
        "anchor": "Exact solution of the three-boson problem at vanishing energy: A zero range approach is used to model resonant two-body interactions between\nthree identical bosons. A dimensionless phase parametrizes the three-body\nboundary condition while the scattering length enters the Bethe-Peierls\nboundary condition. The model is solved exactly at zero energy for any value of\nthe scattering length, positive or negative. From this solution, an analytical\nexpression for the rate of three-body recombination to the universal shallow\ndimer is extracted.",
        "positive": "Persistent currents in dipolar Bose-Einstein condensates confined in\n  annular potentials: We consider a dipolar Bose-Einstein condensate confined in an annular\npotential, with all the dipoles being aligned along some arbitrary direction.\nIn addition to the dipole-dipole interaction, we also assume a zero-range\nhard-core potential. We investigate the stability of the system against\ncollapse, as well as the stability of persistent currents as a function of the\norientation of the dipoles and of the strength of the hard-core interaction."
    },
    {
        "anchor": "Quantized superfluid vortex dynamics on cylindrical surfaces and planar\n  annuli: Superfluid vortex dynamics on an infinite cylinder differs significantly from\nthat on a plane. The requirement that a condensate wave function be single\nvalued upon once encircling the cylinder means that such a single vortex cannot\nremain stationary. Instead, it acquires one of a series of quantized\ntranslational velocities around the circumference, the simplest being $\\pm\n\\hbar/(2MR)$, with $M$ the mass of the superfluid particles and $R$ the radius\nof the cylinder. A generalization to a finite cylinder automatically includes\nthese quantum-mechanical effects through the pairing of the single vortex and\nits image in either the top or bottom end of the surface. The dynamics of a\nsingle vortex on this surface provides a hydrodynamic analog of Laughlin\npumping. The interaction energy for two vortices on an infinite cylinder is\nproportional to the classical stream function $\\chi({\\bf r}_{12})$, and it\ncrosses over from logarithmic to linear when the intervortex separation ${\\bf\nr}_{12}$ becomes larger than the cylinder radius. An Appendix summarizes the\nconnection to an earlier study of Ho and Huang for one or more vortices on an\ninfinite cylinder. A second Appendix reviews the topologically equivalent\nplanar annulus, where such quantized vortex motion has no offset, but Laughlin\npumping may be more accessible to experimental observation.",
        "positive": "Observation of Efimov Resonances in a Mixture with Extreme Mass\n  Imbalance: We observe two consecutive heteronuclear Efimov resonances in an ultracold\nLi-Cs mixture by measuring three-body loss coefficients as a function of\nmagnetic field near a Feshbach resonance. The first resonance is detected at a\nscattering length of $a_-^{(1)}=-320(10)~a_0$ corresponding to $\\sim 7 $ ($\\sim\n3$) times the Li-Cs (Cs-Cs) van der Waals range. The second resonance appears\nat $5.8(1.0) a_-^{(1)}$ close to the unitarity-limited regime at the sample\ntemperature of 450 nK. Indication of a third resonance is found in the atom\nloss spectra. The scaling of the resonance positions is close to the universal\nscaling value of 4.9 predicted for zero temperature. Deviations from\nuniversality might be caused by finite-range and temperature effects, as well\nas magnetic field dependent Cs-Cs interactions."
    },
    {
        "anchor": "From a continuous to a discrete time crystal in a dissipative\n  atom-cavity system: We propose the dynamical stabilization of a nonequilibrium order in a driven\ndissipative system comprised an atomic Bose-Einstein condensate inside a high\nfinesse optical cavity, pumped with an optical standing wave operating in the\nregime of anomalous dispersion. When the amplitude of the pump field is\nmodulated close to twice the characteristic limit-cycle frequency of the\nunmodulated system, a stable subharmonic response is found. The dynamical phase\ndiagram shows that this subharmonic response occurs in a region expanded with\nrespect to that where stable limit-cycle dynamics occurs for the unmodulated\nsystem. In turning on the modulation we tune the atom-cavity system from a\ncontinuous to a discrete time crystal.",
        "positive": "Ultracold Bosons with cavity-mediated long-range interactions: A local\n  mean field analysis of the phase diagram: Ultracold bosonic atoms in optical lattices self-organize into a variety of\nstructural and quantum phases when placed into a single-mode cavity and pumped\nby a laser. Cavity optomechanical effects induce an atom density modulation at\nthe cavity-mode wave length that competes with the optical lattice arrangement.\nSimultaneously short-range interactions via particle hopping promote superfluid\norder, such that a variety of structural and quantum coherent phases can occur.\nWe analyze the emerging phase diagram in two dimensions by means of an extended\nBose-Hubbard model using a local mean field approach combined with a superfluid\ncluster analysis. For commensurate ratios of the cavity and external lattice\nwave lengths the Mott insulator-superfluid transition is modified by the\nappearance of charge density wave and supersolid phases, at which the atomic\ndensity supports the buildup of a cavity field. For incommensurate ratios, the\noptomechanical forces induce the formation of Bose-glass and superglass phases,\nnamely non-superfluid and superfluid phases, respectively, displaying\nquasi-periodic density modulations, which in addition can exhibit structural\nand superfluid stripe formation. The onset of such structures is constrained by\nthe onsite interaction and is favourable at fractional densities. Experimental\nobservables are identified and discussed."
    },
    {
        "anchor": "Exact canonic eigenstates of the truncated Bogoliubov Hamiltonian in an\n  interacting bosons gas: In a gas of $N$ weakly interacting bosons \\cite{Bogo1, Bogo2}, a truncated\ncanonic Hamiltonian $\\widetilde{h}_c$ follows from dropping all the interaction\nterms between free bosons with momentum $\\hbar\\mathbf{k}\\ne\\mathbf{0}$.\nBogoliubov Canonic Approximation (BCA) is a further manipulation, replacing the\nnumber \\emph{operator} $\\widetilde{N}_{in}$ of free particles in\n$\\mathbf{k}=\\mathbf{0}$, with the total number $N$ of bosons. BCA transforms\n$\\widetilde{h}_c$ into a different Hamiltonian\n$H_{BCA}=\\sum_{\\mathbf{k}\\ne\\mathbf{0}}\\epsilon(k)B^\\dagger_\\mathbf{k}B_\\mathbf{k}+const$,\nwhere $B^\\dagger_\\mathbf{k}$ and $B_\\mathbf{k}$ create/annihilate non\ninteracting pseudoparticles. The problem of the \\emph{exact} eigenstates of the\ntruncated Hamiltonian is completely solved in the thermodynamic limit (TL) for\na special class of eigensolutions $|\\:S,\\:\\mathbf{k}\\:\\rangle_{c}$, denoted as\n\\textquoteleft s-pseudobosons\\textquoteright, with energies\n$\\mathcal{E}_{S}(k)$ and \\emph{zero} total momentum. Some preliminary results\nare given for the exact eigenstates (denoted as \\textquoteleft\n$\\eta$-pseudobosons\\textquoteright), carrying a total momentum\n$\\eta\\hbar\\mathbf{k}$ ($\\eta=\\:1,\\:2,\\: \\dots$). A comparison is done with\n$H_{BCA}$ and with the Gross-Pitaevskii theory (GPT), showing that some\ndifferences between exact and BCA/GPT results persist even in the TL. Finally,\nit is argued that the emission of $\\eta$-pseudobosons, which is responsible for\nthe dissipation $\\acute{a}$ \\emph{la} Landau \\cite{L}, could be significantly\ndifferent from the usual picture, based on BCA pseudobosons.",
        "positive": "Fermi edge singularity in neutral electron-hole system: In neutral dense electron-hole (e-h) systems at low temperatures, theory\npredicts Cooper-pair-like excitons at the Fermi energy and a BCS-like exciton\ncondensation. Optical excitation allows creating e-h systems with the densities\ncontrolled by the excitation power. However, the intense optical excitations\nrequired to achieve high densities cause substantial heating of the e-h system\nthat prevents the realization of dense and cold e-h systems in conventional\nsemiconductors. In this work, we study e-h systems created by optical\nexcitation in separated electron and hole layers. The layer separation\nincreases the e-h recombination time and, in turn, the density for a given\noptical excitation by orders of magnitude and, as a result, enables the\nrealization of the dense and cold e-h system. We found a strong enhancement of\nphotoluminescence intensity at the Fermi energy of the neutral dense ultracold\ne-h system that evidences the emergence of excitonic Fermi edge singularity due\nto the Cooper-pair-like excitons at the Fermi energy."
    },
    {
        "anchor": "Concavity of the collective excitation branch of a Fermi gas in the\n  BEC-BCS crossover: We study the concavity of the dispersion relation $q\\mapsto\n\\omega\\_{\\mathbf{q}}$ of the bosonic excitations of a three-dimensional\nspin-$1/2$ Fermi gas in the Random Phase Approximation (RPA). In the limit of\nsmall wave numbers $q$ we obtain analytically the spectrum up to order $5$ in\n$q$. In the neighborhood of $q=0$, a change in concavity between the convex BEC\nlimit and the concave BCS limit takes place at $\\Delta/\\mu\\simeq0.869$\n[$1/(k\\_F a)\\simeq-0.144$], where $a$ is the scattering length between opposite\nspin fermions, $k\\_F$ is the Fermi wave number and $\\Delta$ the gap according\nto BCS theory, and $\\mu$ is the chemical potential. At that point the branch is\nconcave due to a negative fifth-order term. Our results are supplemented by a\nnumerical study which shows the evolution of the border between the zone of the\n$(q,\\Delta)$ plane where $q\\mapsto \\omega\\_{\\mathbf{q}}$ is concave and the\nzone where it is convex.",
        "positive": "Matter, Energy, and Heat Transfer in a Classical Ballistic Atom Pump: A ballistic atom pump is a system containing two reservoirs of neutral atoms\nor molecules and a junction connecting them containing a localized time-varying\npotential. Atoms move through the pump as independent particles. Under certain\nconditions, these pumps can create net transport of atoms from one reservoir to\nthe other. While such systems are sometimes called \"quantum pumps,\" they are\nalso models of classical chaotic transport, and their quantum behavior cannot\nbe understood without study of the corresponding classical behavior. Here we\nexamine classically such a pump's effect on energy and temperature in the\nreservoirs, in addition to net particle transport. We show that the changes in\nparticle number, of energy in each reservoir, and of temperature in each\nreservoir vary in unexpected ways as the incident particle energy is varied."
    },
    {
        "anchor": "Wave packet dynamics and edge transport in anomalous Floquet topological\n  phases: The possibility of attaining chiral edge modes under periodic driving has\nspurred tremendous attention, both theoretically and experimentally, especially\nin light of anomalous Floquet topological phases that feature vanishing Chern\nnumbers unlike any static counterpart. We here consider a periodically\nmodulated honeycomb lattice and experimentally relevant driving protocols,\nwhich allows us to obtain edge modes of various character in a simple model. We\ncalculate the phase diagram over a wide range of parameters and recover an\nanomalous topological phase with quasienergy gaps harbouring edge states with\nopposite chirality. Motivated by the advances in single-site control in optical\nlattices, we investigate wave packet dynamics localized at the edges in\ndistinct Floquet topological regimes that cannot be achieved in equilibrium. We\nanalyse transport properties in edge modes originating from the same bands, but\nwith support at different quasienergies and sublattices as well as possessing\ndifferent chiralities. We find that an anomalous Floquet topological phase can\nin general generate more robust chiral edge motion than a Haldane phase. Our\nresults demonstrate that the rich interplay of wave packet dynamics and\ntopological edge states can serve as a versatile tool in ultracold quantum\ngases in optical lattices.",
        "positive": "Towards a QMC-based density functional including finite-range effects:\n  excitation modes of a $^{39}$K quantum droplet: Some discrepancies between experimental results on quantum droplets made of a\nmixture of $^{39}$K atoms in different hyperfine states and their analysis\nwithin extended Gross-Pitaevskii theory (which incorporates beyond mean-field\ncorrections) have been recently solved by introducing finite-range effects into\nthe theory. Here, we study the influence of these effects on the monopole and\nquadrupole excitation spectrum of extremely dilute quantum droplets using a\ndensity functional built from first-principles quantum Monte Carlo\ncalculations, which can be easily introduced in the existing Gross-Pitaevskii\nnumerical solvers. Our results show differences of up to $20\\%$ with those\nobtained within the extended Gross-Pitaevskii theory, likely providing another\nway to observe finite-range effects in mixed quantum droplets by measuring\ntheir lowest excitation frequencies."
    },
    {
        "anchor": "The dynamics and prethermalization of one dimensional quantum systems\n  probed through the full distributions of quantum noise: Quantum noise correlations have been employed in several areas in physics\nincluding condensed matter, quantum optics and ultracold atom to reveal\nnon-classical states of the systems. So far, such analysis mostly focused on\nsystems in equilibrium. In this paper, we show that quantum noise is also a\nuseful tool to characterize and study the non-equilibrium dynamics of one\ndimensional system. We consider the Ramsey sequence of one dimensional,\ntwo-component bosons, and obtain simple, analytical expressions of time\nevolutions of the full distribution functions for this strongly-correlated,\nmany-body system. The analysis can also be directly applied to the evolution of\ninterference patterns between two one dimensional quasi-condensates created\nfrom a single condensate through splitting. Using the tools developed in this\npaper, we demonstrate that one dimensional dynamics in these systems exhibits\nthe phenomenon known as \"prethermalization\", where the observables of {\\it\nnon-equilibrium}, long-time transient states become indistinguishable from\nthose of thermal {\\it equilibrium} states.",
        "positive": "Observation of hybrid Tamm-plasmon exciton-polaritons with GaAs quantum\n  wells and a MoSe2 monolayer: Strong light matter coupling between excitons and microcavity photons, as\ndescribed in the framework of cavity quantum electrodynamics, leads to the\nhybridization of light and matter excitations. The regime of collective strong\ncoupling arises, when various excitations from different host media are\nstrongly coupled to the same optical resonance. This leads to a\nwell-controllable admixture of various matter components in three hybrid\npolariton modes. Here, we study a cavity device with four embedded GaAs quantum\nwells hosting excitons that are spectrally matched to the A-valley exciton\nresonance of a MoSe2 monolayer. The formation of hybrid polariton modes is\nevidenced in momentum resolved photoluminescence and reflectivity studies. We\ndescribe the energy and k-vector distribution of exciton-polaritons along the\nhybrid modes by a thermodynamic model, which yields a very good agreement with\nthe experiment."
    },
    {
        "anchor": "Mean-field description of pairing effects, BKT physics, and\n  superfluidity in 2D Bose gases: We derive a mean-field description for two-dimensional (2D) interacting Bose\ngases at arbitrary temperatures. We find that genuine Bose-Einstein\ncondensation with long-range coherence only survives at zero temperature. At\nfinite temperatures, many-body pairing effects included in our mean-field\ntheory introduce a finite amplitude for the pairing density, which results in a\nfinite superfluid density. We incorporate Berenzinskii-Kosterlitz-Thouless\n(BKT) physics into our model by considering the phase fluctuations of our\npairing field. This then leads to the result that the superfluid phase is only\nstable below the BKT temperature due to these phase fluctuations. In the weakly\ninteracting regime at low temperature we compare our theory to previous results\nfrom perturbative calculations, renormalization group calculations as well as\nMonte Carlo simulations. We present a finite-temperature phase diagram of 2D\nBose gases. One signature of the finite amplitude of the pairing density field\nis a two-peak structure in the single-particle spectral function, resembling\nthat of the pseudogap phase in 2D attractive Fermi gases.",
        "positive": "Non-adiabatic breaking of topological pumping: We study Thouless pumping out of the adiabatic limit. Our findings show that\ndespite its topological nature, this phenomenon is not {generically} robust to\nnon-adiabatic effects. Indeed we find that the Floquet diagonal ensemble value\nof the pumped charge shows a deviation from the topologically quantized limit\nwhich is quadratic in the driving frequency {for a sudden switch-on of the\ndriving}. This is reflected also in the charge pumped in a single period, which\nshows a non-analytic behaviour on top of an overall quadratic decrease.\nExponentially small corrections are recovered only with a careful tailoring of\nthe driving protocol. We also discuss thermal effects and the experimental\nfeasibility of observing such a deviation."
    },
    {
        "anchor": "Nonlinear Dynamics in a Trapped Atomic Bose--Einstein Condensate Induced\n  by an Oscillating Gaussian Potential: We consider a trapped atomic Bose--Einstein condensate penetrated by a\nrepulsive Gaussian potential and theoretically investigate the dynamics induced\nby oscillating the Gaussian potential. Our study is based on the numerical\ncalculation of the two-dimensional Gross--Pitaevskii equation. Our calculation\nreveals the dependence of the characteristic behavior of the condensate on the\namplitude and frequency of the oscillating potential. These dynamics are deeply\nrelated to the nucleation and dynamics of quantized vortices and solitons. When\nthe potential oscillates with a large amplitude, it nucleates many vortex pairs\nthat move away from the potential. When the amplitude of the oscillation is\nsmall, it nucleates solitons through annihilation of vortex pairs. We discuss\nthree issues concerning the nucleation of vortices. The first is the phase\ndiagram for the nucleation of vortices and solitons near the oscillating\npotential. The second is the mechanism and critical velocity of the nucleation.\nThe critical velocity of the nucleation is an important issue in quantum\nfluids, and we propose a new expression for the velocity containing both the\ncoherence length and the size of the potential. The third is the divergence of\nthe nucleation time, which is the time it takes for the potential to nucleate\nvortices, near the critical parameters for vortex nucleation.",
        "positive": "Atomic twin-beams and violation of a motional-state Bell inequality from\n  a phase-fluctuating quasi-condensate source: We investigate the dynamics of atomic twin beams produced from a\nphase-fluctuating source, specifically a 1D Bose gas in the quasi-condensate\nregime, motivated by the experiment reported in Nature Physics 7, 608 (2011). A\nshort-time analytic model is constructed, which is a modified version of the\nundepleted pump approximation widely used in quantum and atom optics, except\nthat here we take into account the initial phase fluctuations of the pump\nsource as opposed to assuming long-range phase coherence. We use this model to\nmake quantitative and qualitative predictions of how phase-fluctuations of the\nsource impact the two-particle correlations of scattered atom-pairs. The model\nis benchmarked against detailed numerical simulations using stochastic\nphase-space methods, and is shown to validate the intuitive notion that the\nbroadening of momentum-space correlation functions between atoms scattered from\na quasi-condensate is driven by the broadened momentum width of the source\ncompared to a true phase coherent condensate. Finally, we combine these\ntheoretical tools and results to investigate the effect phase fluctuations of\nthe twin-beam source can have on a proposed demonstration of a violation of a\nBell inequality, which intrinsically relies on phase-sensitive pair\ncorrelations."
    },
    {
        "anchor": "High-fidelity contact pseudopotentials and p-wave superconductivity: We develop ultratransferable pseudopotentials for the contact interaction\nthat are 100 times more accurate than contemporary approximations. The\npseudopotential offers scattering properties very similar to the contact\npotential, has a smooth profile to accelerate numerics by a factor of up to\n4,000, and, for positive scattering lengths, does not support an unwanted bound\nstate. We demonstrate these advantages in a Diffusion Monte Carlo study of\nfermions with repulsive interactions, delivering the first numerical evidence\nfor the formation of a p-wave superconducting state.",
        "positive": "Adiabatic cooling of bosons in lattices to magnetic ordering: We suggest and analyze a new scheme to adiabatically cool bosonic atoms to\npicokelvin temperatures which should allow the observation of magnetic ordering\nvia superexchange in optical lattices. The starting point is a gapped phase\ncalled the spin Mott phase where each site is occupied by one spin-up and one\nspin-down atom. An adiabatic ramp leads to an xy-ferromagnetic phase. We show\nthat the combination of time-dependent density matrix renormalization group\nmethods with quantum trajectories can be used to fully address possible\nexperimental limitations due to decoherence, and demonstrate that the magnetic\ncorrelations are robust for experimentally realizable ramp speeds. Using a\nmicroscopic master equation treatment of light scattering in the many-particle\nsystem, we test the robustness of adiabatic state preparation against\ndecoherence. Due to different ground-state symmetries, we also find a\nmetastable state with xy-ferromagnetic order if the ramp crosses to regimes\nwhere the ground state is a z-ferromagnet. The bosonic spin Mott phase as the\ninitial gapped state for adiabatic cooling has many features in common with a\nfermionic band insulator, but the use of bosons should enable experiments with\nsubstantially lower initial entropies."
    },
    {
        "anchor": "Reliability of lattice gauge theories in the thermodynamic limit: Although gauge invariance is a postulate in fundamental theories of nature\nsuch as quantum electrodynamics, in quantum-simulation implementations of gauge\ntheories it is compromised by experimental imperfections. In a recent work\n[Halimeh and Hauke,\n\\href{https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.125.030503}{Phys.\nRev. Lett. \\textbf{125}, 030503 (2020)}], it has been shown in finite-size\nspin-$1/2$ quantum link lattice gauge theories that upon introducing an\nenergy-penalty term of sufficiently large strength $V$, unitary gauge-breaking\nerrors at strength $\\lambda$ are suppressed $\\propto\\lambda^2/V^2$ up to all\naccessible evolution times. Here, we show numerically that this result extends\nto quantum link models in the thermodynamic limit and with larger spin-$S$. As\nwe show analytically, the dynamics at short times is described by an\n\\textit{adjusted} gauge theory up to a timescale that is at earliest\n$\\tau_\\text{adj}\\propto\\sqrt{V/V_0^3}$, with $V_0$ an energy factor. Moreover,\nour analytics predicts that a renormalized gauge theory dominates at\nintermediate times up to a timescale $\\tau_\\text{ren}\\propto\\exp(V/V_0)/V_0$.\nIn both emergent gauge theories, $V$ is volume-independent and scales at worst\n$\\sim S^2$. Furthermore, we numerically demonstrate that robust gauge\ninvariance is also retained through a single-body gauge-protection term, which\nis experimentally straightforward to implement in ultracold-atom setups and\nNISQ devices.",
        "positive": "Quantum impurities: from mobile Josephson junctions to depletons: We overview the main features of mobile impurities moving in one-dimensional\nsuperfluid backgrounds by modeling it as a mobile Josephson junction, which\nleads naturally to the periodic dispersion of the impurity. The dissipation\nprocesses, such as radiative friction and quantum viscosity, are shown to\nresult from the interaction of the collective phase difference with the\nbackground phonons. We develop a more realistic depleton model of an\nimpurity-hole bound state that provides a number of exact results interpolating\nbetween the semiclassical weakly-interacting picture and the strongly\ninteracting Tonks-Girardeau regime. We also discuss the physics of a trapped\nimpurity, relevant to current experiments with ultra cold atoms."
    },
    {
        "anchor": "Quantum density anomaly in optically trapped ultracold gases: We show that the Bose-Hubbard Model exhibits an increase in density with\ntemperature at fixed pressure in the regular fluid regime and in the superfluid\nphase. The anomaly at the Bose-Einstein condensate is the first density anomaly\nobserved in a quantum state. We propose that the mechanism underlying both the\nnormal phase and the superfluid phase anomalies is related to zero point\nentropies and ground state phase transitions. A connection with the typical\nexperimental scales and setups is also addressed. This key finding opens a new\npathway for theoretical and experimental studies of water-like anomalies in the\narea of ultracold quantum gases.",
        "positive": "A Composite Fermion Approach to the Ultracold Dilute Fermi Gas: It is argued that the recently observed Fermi liquids in strongly interacting\nultracold Fermi gases are adiabatically connected to a projected Fermi gas.\nThis conclusion is reached by constructing a set of Jastrow wavefunctions,\nfollowing Tan's observations on the structure of the physical Hilbert space\n[Annals of Physics 323, 2952 (2008)]. The Jastrow projection merely implements\nthe Bethe-Peierls condition on the BCS and Fermi gas wavefunctions. This\nprocedure provides a simple picture of the emergence of Fermi polarons as\ncomposite fermions in the normal state of the highly polarized gas. It is also\nshown that the projected BCS wavefunction can be written as a condensate of\npairs of composite fermions (or Fermi polarons). A Hamiltonian for the\ncomposite fermions is derived. Within a mean-field theory, it is shown that the\nground state and excitations of this Hamiltonian are those of a non-interacting\nFermi gas although they are described by Jastrow-Slater wavefunctions."
    },
    {
        "anchor": "Long lifetime supersolid in a two-component dipolar Bose-Einstein\n  condensate: Recent studies on supersolidity in a single-component Bose-Einstein\ncondensate (BEC) have relied on the Lee-Huang-Yang (LHY) correction for\nstabilization of self-bound droplets, which however involves a high density\ninside the droplets, limiting the lifetime of the supersolid. Here we propose a\ntwo-component mixture of dipolar and nondipolar BECs, such as an\n$^{166}$Er-$^{87}$Rb mixture, to create and stabilize a supersolid without the\nLHY correction, which can suppress the atomic loss and may allow observation of\nthe long-time dynamics of the supersolid. In such a system, supersolidity can\nbe controlled by the difference in the trap centers between the two components.",
        "positive": "Bose-Einstein condensation in a minimal inhomogeneous system: We study the effects of repulsive interaction and disorder on Bosons in a\ntwo-site Bose-Hubbard system, which provides a simple model of the dirty boson\nproblem. By comparison with exact numerical results, we demonstrate how a\nstraightforward application of the Bogoliubov approximation fails even to\ndeliver a qualitatively correct picture: It wrongly predicts an increase of the\ncondensate depletion due to disorder. We show that, in the presence of\ndisorder, the noncommutative character of the condensate operator has to be\nretained for a correct description of the system."
    },
    {
        "anchor": "Strong-Coupling Effects and Single-Particle Properties in an Ultracold\n  Fermi Gas with Mass Imbalance: We investigate single-particle properties of a strongly interacting ultracold\nFermi gas with mass imbalance. Using an extended $T$-matrix theory, we\ncalculate the density of states, as well as the single-particle spectral\nweight, in the unitarity limit above the superfluid phase transition\ntemperature $T_{\\rm c}$. We show that the momentum regions where pairing\nfluctuations strongly affect single-particle excitations are different between\nlight fermions and heavy fermions, reflecting the difference of the Pauli\nblocking effects between them. In addition, we obtain different pseudogap\nphenomena associated with pairing fluctuations in between the two components.\nSince the realization of a mass-imbalanced superfluid Fermi gas is an important\nchallenge in this field, our results would contribute to the understanding of\nphysical properties of the hetero-pairing state.",
        "positive": "Supersolidity in an elongated dipolar condensate: We present a theory for the emergence of a supersolid state in a cigar-shaped\ndipolar quantum Bose gas. Our approach is based on a reduced three-dimensional\n(3D) theory, where the condensate wavefunction is decomposed into an axial\nfield and a transverse part described variationally. This provides an accurate\nfully 3D description that is specific to the regime of current experiments and\nefficient to compute. We apply this theory to understand the phase diagram for\na gas in an infinite tube potential. We find that the supersolid transition has\ncontinuous and discontinuous regions as the averaged density varies. We develop\ntwo simplified analytic models to characterize the phase diagram and elucidate\nthe roles of quantum droplets and of the roton excitation."
    },
    {
        "anchor": "Interband heating processes in a periodically driven optical lattice: We investigate multi-\"photon\" interband excitation processes in an optical\nlattice that is driven periodically in time by a modulation of the lattice\ndepth. Assuming the system to be prepared in the lowest band, we compute the\nexcitation spectrum numerically. Moreover, we estimate the effective coupling\nparameters for resonant interband excitation processes analytically, employing\ndegenerate perturbation theory in Floquet space. We find that below a threshold\ndriving strength, interband excitations are suppressed exponentially with\nrespect to the inverse driving frequency. For sufficiently low frequencies,\nthis leads to a rather sudden onset of interband heating, once the driving\nstrength reaches the threshold. We argue that this behavior is rather generic\nand should also be found in lattice systems that are driven by other forms of\nperiodic forcing. Our results are relevant for Floquet engineering, where a\nlattice system is driven periodically in time in order to endow it with novel\nproperties like the emergence of a strong artificial magnetic field or a\ntopological band structure. In this context, interband excitation processes\ncorrespond to detrimental heating.",
        "positive": "Quantum-enhanced multiparameter estimation and compressed sensing of a\n  field: We show that a significant quantum gain corresponding to squeezed or\nover-squeezed spin states can be obtained in multiparameter estimation by\nmeasuring the Hadamard coefficients of a 1D or 2D signal. The physical platform\nwe consider consists of twolevel atoms in an optical lattice in a squeezed-Mott\nconfiguration, or more generally by correlated spins distributed in spatially\nseparated modes. Our protocol requires the possibility to locally flip the\nspins, but relies on collective measurements. We give examples of applications\nto scalar or vector field mapping and compressed sensing."
    },
    {
        "anchor": "Effects Beyond Center-of-Mass Separability in a Trapped Bosonic Mixture:\n  Exact Results: An exactly solvable model mimicking demixing of two Bose-Einstein condensates\nat the many-body level of theory is devised. Various properties are expressed\nin closed form along the demixing pathway and investigated. The connection\nbetween the center-of-mass coordinate and in particular the relative\ncenter-of-mass coordinate and demixing is explained. The model is also exactly\nsolvable at the mean-field level of theory, allowing thereby comparison between\nmany-body and mean-field properties. Applications are briefly discussed.",
        "positive": "Intersubband Polaritons in the Electrical Dipole Gauge: We provide a theoretical description for the coupling between the\nintersubband excitations of a bi-dimensional electron gas with the\nelectromagnetic field. This description, based on the electrical dipole gauge,\napplies to an arbitrary quantum heterostructure embedded in a general\nmultilayered waveguide or a microcavity. We show that the dipole gauge\nHamiltonian automatically takes into account the Coulomb interactions in this\nsystem. Furthermore, it can be conveniently expressed in terms of the many-body\ncollective plasmon modes, which interact both with each other and with the\nlight field. The dipole gauge therefore provides a suitable framework for the\nstudy of solid state Quantum Electrodynamics (QED) phenomena, such as the\nultra-strong light-matter interaction regime, occurring at very high electronic\ndensities."
    },
    {
        "anchor": "Perturbative correction to the ground state properties of\n  one-dimensional strongly interacting bosons in a harmonic trap: We calculate the first-order perturbation correction to the ground state\nenergy and chemical potential of a harmonically trapped boson gas with contact\ninteractions about the infinite repulsion Tonks-Girardeau limit. With $c$\ndenoting the interaction strength, we find that for a large number of particles\n$N$ the $1/c$ correction to the ground state energy increases as $N^{5/2}$, in\ncontrast to the unperturbed Tonks-Girardeau value that is proportional to\n$N^2$. We describe a thermodynamic scaling limit for the trapping frequency\nthat yields an extensive ground state energy and reproduces the zero\ntemperature thermodynamics obtained by a local density approximation.",
        "positive": "Local emergence of thermal correlations in an isolated quantum many-body\n  system: We experimentally demonstrate how thermal properties in an non-equilibrium\nquantum many- body system emerge locally, spread in space and time, and finally\nlead to the globally relaxed state. In our experiment, we quench a\none-dimensional (1D) Bose gas by coherently splitting it into two parts. By\nmonitoring the phase coherence between the two parts we observe that the\nthermal correlations of a prethermalized state emerge locally in their final\nform and propagate through the system in a light-cone-like evolution. Our\nresults underline the close link between the propagation of correlations and\nrelaxation processes in quantum many-body systems."
    },
    {
        "anchor": "Asymptotic Floquet states of open quantum systems: The role of\n  interaction: We investigate the asymptotic state of a periodically driven many-body\nquantum system which is weakly coupled to an environment. The combined action\nof the modulations and the environment steers the system towards a state being\ncharacterized by a time-periodic density operator. To resolve this asymptotic\nnon-equilibrium state at stroboscopic instants of time, we introduce the\ndissipative Floquet map, evaluate the stroboscopic density operator as its\neigen-element and elucidate how particle interactions affect properties of the\ndensity operator. We illustrate the idea with a periodically modulated\nBose-Hubbard dimer and discuss the relations between the interaction-induced\nbifurcations in a mean-field dynamics and changes in the characteristics of the\ngenuine quantum many-body state. We argue that Floquet maps provide insight\ninto the system relaxation towards its asymptotic state and may help to\nunderstand whether it is possible (or not) to construct a stroboscopic\ntime-independent generator mimicking the action of the original time-dependent\none.",
        "positive": "Tracking evaporative cooling of a mesoscopic atomic quantum gas in real\n  time: The fluctuations in thermodynamic and transport properties in many-body\nsystems gain importance as the number of constituent particles is reduced.\nUltracold atomic gases provide a clean setting for the study of mesoscopic\nsystems; however, the detection of temporal fluctuations is hindered by the\ntypically destructive detection, precluding repeated precise measurements on\nthe same sample. Here, we overcome this hindrance by utilizing the enhanced\nlight--matter coupling in an optical cavity to perform a minimally invasive\ncontinuous measurement and track the time evolution of the atom number in a\nquasi two-dimensional atomic gas during evaporation from a tilted trapping\npotential. We demonstrate sufficient measurement precision to detect atom\nnumber fluctuations well below the level set by Poissonian statistics.\nFurthermore, we characterize the non-linearity of the evaporation process and\nthe inherent fluctuations of the transport of atoms out of the trapping volume\nthrough two-time correlations of the atom number. Our results establish coupled\natom--cavity systems as a novel testbed for observing thermodynamics and\ntransport phenomena in mesosopic cold atomic gases and, generally, pave the way\nfor measuring multi-time correlation functions of ultracold quantum gases."
    },
    {
        "anchor": "Photon-Assisted Tunneling in a Biased Strongly Correlated Bose Gas: We study the impact of coherently generated lattice photons on an atomic Mott\ninsulator subjected to a uniform force. Analogous to an array of tunnel-coupled\nand biased quantum dots, we observe sharp, interaction-shifted photon-assisted\ntunneling resonances corresponding to tunneling one and two lattice sites\neither with or against the force, and resolve multiorbital shifts of these\nresonances. By driving a Landau-Zener sweep across such a resonance, we realize\na quantum phase transition between a paramagnet and an antiferromagnet, and\nobserve quench dynamics when the system is tuned to the critical point. Direct\nextensions will produce gauge fields and site-resolved spin flips, for\ntopological physics and quantum computing.",
        "positive": "Modified spin-wave theory with ordering vector optimization I:\n  frustrated bosons on the spatially anisotropic triangular lattice: We investigate a system of frustrated hardcore bosons, modeled by an XY\nantiferromagnet on the spatially anisotropic triangular lattice, using\nTakahashi's modified spin-wave (MSW) theory. In particular we implement\nordering vector optimization on the ordered reference state of MSW theory,\nwhich leads to significant improvement of the theory and accounts for quantum\ncorrections to the classically ordered state. The MSW results at zero\ntemperature compare favorably to exact diagonalization (ED) and projected\nentangled-pair state (PEPS) calculations. The resulting zero-temperature phase\ndiagram includes a 1D quasi-ordered phase, a 2D Neel ordered phase, and a 2D\nspiraling ordered phase. We have strong indications that the various ordered or\nquasi-ordered phases are separated by spin-liquid phases with short-range\ncorrelations, in analogy to what has been predicted for the Heisenberg model on\nthe same lattice. Within MSW theory we also explore the finite-temperature\nphase diagram. We find that the zero-temperature long-range-ordered phases turn\ninto quasi-ordered phases (up to a Berezinskii-Kosterlitz-Thouless\ntemperature), while zero-temperature quasi-ordered phases become short-range\ncorrelated at finite temperature. These results show that modified spin-wave\ntheory is very well suited for describing ordered and quasi-ordered phases of\nfrustrated XY spins (or, equivalently, of frustrated lattice bosons) both at\nzero and finite temperatures. While MSW theory, just as other theoretical\nmethods, cannot describe spin-liquid phases, its breakdown provides a fast\nmethod for singling out Hamiltonians which may feature these intriguing quantum\nphases. We thus suggest a tool for guiding our search for interesting systems\nwhose properties are necessarily studied with a physical quantum simulator."
    },
    {
        "anchor": "Manipulating the Mott lobes: optical lattice bosons coupled to an array\n  of atomic quantum dots: We analyze quantum phase transitions in a system of optical lattice bosons\ncoupled to an array of atomic quantum dots, or pseudospins-1/2. The system\nparallels the Bose-Hubbard model with a single difference of the direct\ntunneling between the lattice sites being replaced by an assisted tunneling via\ncoupling to the atomic quantum dots. We calculate the phase diagram of the\ncombined system, numerically within the Gutzwiller ansatz and analytically\nusing the mean-field decoupling approximation. The result of the assisted\nBose-Hubbard model is that the Mott-superfluid transition still takes place,\nhowever, the Mott lobes strongly depend on the system parameters such as the\ndetuning. One can even reverse the usual hierarchy of the lobes with the first\nlobe becoming the smallest. The phase transition in the bosonic subsystem is\naccompanied by a magnetization rotation in the pseudospin subsystem with the\ntilting angle being an effective order parameter. When direct tunneling is\ntaken into account, the Mott lobes can be made disappear and the bosonic\nsubsystem becomes superfluid throughout.",
        "positive": "Induced p-wave Superfluidity in Imbalanced Fermi Gases in a Synthetic\n  Gauge Field: We study pairing formation and the appearance of induced spin-triplet p-wave\nsuperfluidity in dilute three-dimensional imbalanced Fermi gases in the\npresence of a uniform non-Abelian gauge field. This gauge field generates a\nsynthetic Rashba-type spin-orbit interaction which has remarkable consequences\nin the induced p-wave pairing gaps. Without the synthetic gauge field, the\np-wave pairing occurs in one of the components due to the induced\n(second-order) interaction via an exchange of density fluctuations in the other\ncomponent. We show that this p-wave superfluid gap induced by density\nfluctuations is greatly enhanced due to the Rashba-type spin-orbit coupling."
    },
    {
        "anchor": "Theory of Combined Photoassociation and Feshbach Resonances in a\n  Bose-Einstein Condensate: We model combined photoassociation and Feshbach resonances in a Bose-Einstein\ncondensate, where the shared dissociation continuum allows for quantum\ninterference in losses from the condensate, as well as a dispersive-like shift\nof resonance. A simple analytical model, based on the limit of weakly bound\nmolecules, agrees well with numerical experiments that explicitly include\ndissociation to noncondensate modes. For a resonant laser and an off-resonant\nmagnetic field, constructive interference enables saturation of the\nphotoassociation rate at user-friendly intensities, at a value set by the\ninterparticle distance. This rate limit is larger for smaller condensate\ndensities and, near the Feshbach resonance, approaches the rate limit for\nmagnetoassociation alone. Also, we find agreement with the unitary limit--set\nby the condensate size--only for a limited range of near-resonant magnetic\nfields. Finally, for a resonant magnetic field and an off-resonant laser,\nmagnetoassociation displays similar quantum interference and a dispersive-like\nshift. Unlike photoassociation, interference and the fieldshift in resonant\nmagnetoassociation is tunable with both laser intensity and detuning. Also, the\ndispersive-like shift of the Feshbach resonance depends on the size of the\nFeshbach molecule, and is a signature of non-universal physics in a strongly\ninteracting system.",
        "positive": "Single-Atom Resolved Fluorescence Imaging of an Atomic Mott Insulator: The reliable detection of single quantum particles has revolutionized the\nfield of quantum optics and quantum information processing. For several years,\nresearchers have aspired to extend such detection possibilities to larger scale\nstrongly correlated quantum systems, in order to record in-situ images of a\nquantum fluid in which each underlying quantum particle is detected. Here we\nreport on fluorescence imaging of strongly interacting bosonic Mott insulators\nin an optical lattice with single-atom and single-site resolution. From our\nimages, we fully reconstruct the atom distribution on the lattice and identify\nindividual excitations with high fidelity. A comparison of the radial density\nand variance distributions with theory provides a precise in-situ temperature\nand entropy measurement from single images. We observe Mott-insulating plateaus\nwith near zero entropy and clearly resolve the high entropy rings separating\nthem although their width is of the order of only a single lattice site.\nFurthermore, we show how a Mott insulator melts for increasing temperatures due\nto a proliferation of local defects. Our experiments open a new avenue for the\nmanipulation and analysis of strongly interacting quantum gases on a lattice,\nas well as for quantum information processing with ultracold atoms. Using the\nhigh spatial resolution, it is now possible to directly address individual\nlattice sites. One could, e.g., introduce local perturbations or access regions\nof high entropy, a crucial requirement for the implementation of novel cooling\nschemes for atoms on a lattice."
    },
    {
        "anchor": "Phase coherence in out-of-equilibrium supersolid states of ultracold\n  dipolar atoms: A supersolid is a fascinating phase of matter, combining the global phase\ncoherence of a superfluid with hallmarks of solids, e.g. a spontaneous breaking\nof the translational symmetry. Recently, states with such counter-intuitive\nproperties have been realized in experiments using ultracold quantum gases with\nstrong dipolar interactions. Here, we investigate the response of a supersolid\nstate to phase excitations which shatter the global phase coherence. After the\ncreation of those excitations, we observe a rapid re-establishment of a global\nphase coherence, suggesting the presence of a superfluid flow across the whole\nsample and an efficient dissipation mechanism. We are able to identify a\nwell-defined region where rephasing occurs, indicating the phase boundary\nbetween the solid-like and the supersolid phase. Our observations call for the\ndevelopment of theoretical descriptions able to capture the non-equilibrium\ndynamics in the recently discovered supersolid states of quantum matter.",
        "positive": "Entanglement Spectroscopy using Quantum Monte Carlo: We present a numerical scheme to reconstruct a subset of the entanglement\nspectrum of quantum many body systems using quantum Monte Carlo. The approach\nbuilds on the replica trick to evaluate particle number resolved traces of the\nfirst n of powers of a reduced density matrix. From this information we\nreconstruct n entanglement spectrum levels using a polynomial root solver. We\nillustrate the power and limitations of the method by an application to the\nextended Bose-Hubbard model in one dimension where we are able to resolve the\nquasi-degeneracy of the entanglement spectrum in the Haldane-Insulator phase.\nIn general the method is able to reconstruct the largest few eigenvalues in\neach symmetry sector and typically performs better when the eigenvalues are not\ntoo different."
    },
    {
        "anchor": "Dissipative dynamics of the Josephson effect in the binary\n  Bose-condensed mixtures: The dissipative dynamics of a pointlike Josephson junction in binary\nBose-condensed mixtures is analyzed within the framework of the model of a\ntunneling Hamiltonian. The transmission of unlike particles across a junction\nis described by the different transmission amplitudes. The effective action\nthat describes the dynamics of the phase differences across the junction for\neach of two condensed components is derived employing the functional\nintegration method. In the low-frequency limit the dynamics of a Josephson\njunction can be described by two coupled equations in terms of the potential\nenergy and dissipative Rayleigh function using a mechanical analogy. The\ninterplay between mass currents of each mixture component appears in the\nsecond-order term in the tunneling amplitudes due to interspecies hybridizing\ninteraction. The asymmetric case of the binary mixtures with the different\nconcentration and order parameters is considered as well.",
        "positive": "Quantum phases and spectrum of collective modes in a spin-1 BEC with\n  spin-orbital-angular-momentum coupling: Motivated by the recent experiments [Chen et al., Phys. Rev. Lett 121, 113204\n(2018), Chen et al., Phys. Rev. Lett. 121, 250401 (2018)], we investigate the\nlow-lying excitation spectrum of the ground-state phases of\nspin-orbital-angular-momentum-coupled (SOAM-coupled) spin-1 condensates.At\nvanishing detuning, a ferromagnetic SOAM-coupled spin-1 BEC can have two\nground-state phases, namely coreless and polar-core vortex states, whereas an\nantiferromagnetic BEC supports only polar-core vortex solution. The angular\nmomentum per particle, longitudinal magnetization, and excitation frequencies\ndisplay discontinuities across the phase boundary between the coreless vortex\nand polar-core vortex phases. The low-lying excitation spectrum evaluated by\nsolving the Bogoliubov-de-Gennes equations is marked by avoided crossings and\nhence the hybridization of the spin and density channels. The spectrum is\nfurther confirmed by the dynamical evolution of the ground state subjected to a\nperturbation suitable to excite a density or a spin mode and a variational\nanalysis for the density-breathing mode."
    },
    {
        "anchor": "Supersolid phase of a spin-orbit-coupled Bose-Einstein condensate: a\n  perturbation approach: The phase diagram of a Bose-Einstein condensate with Raman-induced spin-orbit\ncoupling includes a stripe phase with supersolid features. In this work we\ndevelop a perturbation approach to study the ground state and the Bogoliubov\nmodes of this phase, holding for small values of the Raman coupling. We obtain\nanalytical predictions for the most relevant observables (including the\nperiodicity of stripes, sound velocities, compressibility, and magnetic\nsusceptibility) which are in excellent agreement with the exact (non\nperturbative) numerical results, obtained for significantly large values of the\ncoupling. We further unveil the nature of the two gapless Bogoliubov modes in\nthe long-wavelength limit. We find that the spin branch of the spectrum,\ncorresponding in this limit to the dynamics of the relative phase between the\ntwo spin components, describes a translation of the fringes of the equilibrium\ndensity profile, thereby providing the crystal Goldstone mode typical of a\nsupersolid configuration. Finally, using sum-rule arguments, we show that the\nsuperfluid density can be experimentally accessed by measuring the ratio of the\nsound velocities parallel and perpendicular to the direction of the spin-orbit\ncoupling.",
        "positive": "Probing superfluidity of periodically trapped ultracold atoms in a\n  cavity by transmission spectroscopy: We study a system of periodic Bose condensed atoms coupled to cavity photons\nusing the input-output formalism. We show that the cavity will either act as a\nthrough pass Lorentzian filter when the superfluid fraction of the condensate\nis minimum or completely reflect the input field when the superfluid fraction\nis maximum. We show that by monitoring the ratio between the transmitted field\nand the reflected field, one can estimate the superfluid fraction."
    },
    {
        "anchor": "Vortex polygons and their stabilities in Bose-Einstein condensates and\n  field theory: We study vortex polygons and their stabilities in miscible two-component\nBose-Einstein condensates, and find that vortex polygons are stable for the\ntotal circulation $Q \\leq 5$, metastable for $Q = 6$, and unstable for $Q \\geq\n7$. As a related model in high-energy physics, we also study the vortex polygon\nof the baby-Skyrme model with an anti-ferromagnetic potential term, and compare\nboth results.",
        "positive": "Physics of higher orbital bands in optical lattices: a review: Orbital degree of freedom plays a fundamental role in understanding the\nunconventional properties in solid state materials. Experimental progress in\nquantum atomic gases has demonstrated that high orbitals in optical lattices\ncan be used to construct quantum emulators of exotic models beyond natural\ncrystals, where novel many-body states such as complex Bose-Einstein\ncondensation and topological semimetals emerge. A brief introduction of orbital\ndegree of freedom in optical lattices is given and a summary of exotic orbital\nmodels and resulting many-body phases is provided. Experimental consequences of\nthe novel phases are also discussed."
    },
    {
        "anchor": "Dynamic structure function of two interacting atoms in 1D: We consider two atoms trapped in a one-dimensional harmonic oscillator\npotential interacting through a contact interaction. We study the transition\nfrom the non-interacting to the strongly interacting Tonks-Girardeau state, as\nthe interaction is varied from zero to infinitely large repulsive values. The\ndynamic structure function is computed by means of direct diagonalization\ncalculations with a finite number of single particle modes. The response of the\nsystem against a monopolar perturbation is characterized by the moments of the\ndynamic structure function which are explicitly calculated from the dynamic\nstructure function and by means of sum rules.",
        "positive": "Generation and decay of Higgs mode in a strongly interacting Fermi gas: We investigate the life cycle of the large amplitude Higgs mode in strongly\ninteracting superfluid Fermi gas. Through numerical simulations with\ntime-dependent density-functional theory and the technique of the interaction\nquench, we verify the previous theoretical predictions on the mode's frequency.\nNext, we demonstrate that the mode is dynamically unstable against external\nperturbation and qualitatively examine the emerging state after the mode\ndecays. The post-decay state is characterized by spatial fluctuations of the\norder parameter and density at scales comparable to the superfluid coherence\nlength scale. We identify similarities with FFLO states, which become more\nprominent at higher dimensionalities and nonzero spin imbalances."
    },
    {
        "anchor": "Quantitative Determination of Temperature in the Approach to Magnetic\n  Order of Ultracold Fermions in an Optical Lattice: We perform a quantitative simulation of the repulsive Fermi-Hubbard model\nusing an ultracold gas trapped in an optical lattice. The entropy of the system\nis determined by comparing accurate measurements of the equilibrium double\noccupancy with theoretical calculations over a wide range of parameters. We\ndemonstrate the applicability of both high-temperature series and dynamical\nmean-field theory to obtain quantitative agreement with the experimental data.\nThe reliability of the entropy determination is confirmed by a comprehensive\nanalysis of all systematic errors. In the center of the Mott insulating cloud\nwe obtain an entropy per atom as low as 0.77kB which is about twice as large as\nthe entropy at the Neel transition. The corresponding temperature depends on\nthe atom number and for small fillings reaches values on the order of the\ntunneling energy.",
        "positive": "Universal dynamics of rogue waves in a quenched spinor Bose condensate: Isolated many-body systems far from equilibrium may exhibit scaling dynamics\nwith universal exponents indicating the proximity of the time-evolution to a\nnon-thermal fixed point. We find universal dynamics connected with the\noccurrence of extreme wave excitations in the mutually coupled magnetic\ncomponents of a spinor gas which propagate in an effectively random potential.\nThe frequency of these rogue waves is affected by the time-varying spatial\ncorrelation length of the potential, giving rise to an additional exponent\n$\\delta_\\mathrm{c} \\simeq 1/3$ for temporal scaling, which is different from\nthe exponent $\\beta_V \\simeq 1/4$ characterizing the scaling of the correlation\nlength $\\ell_V \\sim t^{\\,\\beta_V}$ in time. As a result of the caustics, i.e.,\nfocusing events, real-time instanton defects appear in the Larmor phase of the\nspin-1 system as vortices in space and time. The temporal correlations\ngoverning the instanton occurrence frequency scale as $t^{\\,\n\\delta_\\mathrm{I}}$. This suggests that the universality class of a non-thermal\nfixed point could be characterized by different, mutually related exponents\ndefining the evolution in time and space, respectively. Our results have a\nstrong relevance for understanding pattern coarsening from first principles and\npotential implications for dynamics ranging from the early universe to\ngeophysical dynamics and micro physics."
    },
    {
        "anchor": "Acoustic Superradiance from a Bose-Einstein Condensate Vortex with a\n  Self-Consistent Background Density Profile: The axisymmetric acoustic perturbations in the velocity potential of a\nBose-Einstein condensate in the presence of a single vortex behave like\nminimally coupled massless scalar fields propagating in a curved (1+1)\ndimensional Lorentzian space-time, governed by the Klein-Gordon wave equation.\nThus far, the amplified scattering of these perturbations from the vortex, as a\nmanifestation of the acoustic superradiance, has been investigated with a\nconstant background density. This paper goes beyond by employing a\nself-consistent condensate density profile that is obtained by solving the\nGross-Pitaevskii equation for an unbound BEC. Consequently, the loci of the\nevent horizon and the ergosphere of the acoustic black hole are modified\naccording to the radially varying speed of sound. The superradiance is\ninvestigated both for transient features in the time-domain and for spectral\nfeatures in the frequency domain. In particular, an effective energy-potential\nfunction defined in the spectral formulation correlates with the existence and\nthe frequency dependence of the acoustic superradiance. The numerical results\nindicate that the constant background density approximation underestimates the\nmaximum superradiance and the frequency at which this maximum occurs.",
        "positive": "On cold gases with anisotropic interactions: A cold gas of particles with anisotropic interactions of general form, due to\na polarizing field, is studied. Special cases are atoms or molecules with\ndipole-dipole or quadrupole-quadrupole interactions. It is shown that the\nangular dependence of an observable on the direction of the polarizing field is\nlargely determined by symmetry. For a gas in a confined quasi two-dimensional\ngeometry, the effective interaction is calculated in general form. Some\nexamples of dipole and quadrupole gases are considered. It is concluded that\nwhen anisotropic forces are studied in a general manner, one can obtain simpler\nresults and better understanding for some problems."
    },
    {
        "anchor": "Quantum engineering of Majorana quasiparticles in one-dimensional\n  optical lattices: We propose a feasible way of engineering Majorana-type quasiparticles in\nultracold fermionic gases on a one-dimensional (1D) optical lattice. For this\npurpose, imbalanced ultracold atoms interacting by the spin-orbit coupling\nshould be hybridized with a three-dimensional Bose-Einstein condensate (BEC)\nmolecular cloud. By constraining the profile of an internal defect potential we\nshow that the Majorana-type excitations can be created or annihilated. This\nprocess is modelled within the Bogoliubov-de Gennes approach. This study is\nrelevant also to nanoscopic 1D superconductors where modification of the\ninternal defect potential can be obtained by electrostatic means.",
        "positive": "Stripes and honeycomb lattice of quantized vortices in rotating\n  two-component Bose-Einstein condensates: We study numerically the structure of a vortex lattice in two-component\nBose-Einstein condensates with equal atomic masses and equal intra- and\ninter-component coupling strengths. The numerical simulations of the\nGross-Pitaevskii equation show that the quantized vortices form uncertain\nlattice configurations accompanying the vortex stripes, honeycomb lattices, and\ntheir complexes. This is a result of the degeneracy of the system for the SU(2)\nsymmetric operation, which makes a continuous transformation between the above\nstructures. In terms of the pseudospin representation, the complex lattice\nstructures are identified to a hexagonal lattice of doubly-winding\nhalf-skyrmions."
    },
    {
        "anchor": "Floquet engineering Hz-Level Rabi Spectra in Shallow Optical Lattice\n  Clock: Quantum metrology with ultra-high precision usually requires atoms prepared\nin an ultra-stable environment with well-defined quantum states. Thus, in\noptical lattice clock systems deep lattice potentials are used to trap\nultra-cold atoms. However, decoherence, induced by Raman scattering and higher\norder light shifts, can significantly be reduced if atomic clocks are realized\nin shallow optical lattices. On the other hand, in such lattices, tunneling\namong different sites can cause additional dephasing and strongly broadening of\nthe Rabi spectrum. Here, in our experiment, we periodically drive a shallow\n$^{87}$Sr optical lattice clock. Counter intuitively, shaking the system can\ndeform the wide broad spectral line into a sharp peak with 5.4Hz line-width.\nWith careful comparison between the theory and experiment, we demonstrate that\nthe Rabi frequency and the Bloch bands can be tuned, simultaneously and\nindependently. Our work not only provides a different idea for quantum\nmetrology, such as building shallow optical lattice clock in outer space, but\nalso paves the way for quantum simulation of new phases of matter by\nengineering exotic spin orbit couplings.",
        "positive": "Exploring the limits of ultracold atoms in space: Existing space-based cold atom experiments have demonstrated the utility of\nmicrogravity for improvements in observation times and for minimizing the\nexpansion energy and rate of a freely evolving coherent matter wave. In this\npaper we explore the potential for space-based experiments to extend the limits\nof ultracold atoms utilizing not just microgravity, but also other aspects of\nthe space environment such as exceptionally good vacuums and extremely cold\ntemperatures. The tantalizing possibility that such experiments may one day be\nable to probe physics of quantum objects with masses approaching the Plank mass\nis discussed."
    },
    {
        "anchor": "Three-Component Fermionic Atoms with Repulsive Interaction in Optical\n  Lattices: We investigate three-component (colors) repulsive fermionic atoms in optical\nlattices using the dynamical mean field theory. Depending on the anisotropy of\nthe repulsive interactions, either a color density-wave state or a color\nselective staggered state appears at half filling. In the former state, pairs\nof atoms with two of the three colors and atoms with the third color occupy\ndifferent sites alternately. In the latter state, atoms with two of the three\ncolors occupy different sites alternately and atoms with the third color are\nitinerant throughout the system. When the interactions are isotropic, both\nstates are degenerate. We discuss the results using an effective model.",
        "positive": "Bulk viscosity of resonating fermions revisited: Kubo formula, sum rule,\n  and the dimer and high-temperature limits: The bulk viscosity of two-component fermions with a zero-range interaction is\nrevisited both in two and three dimensions. We first point out that the\n\"standard\" Kubo formula employed in recent studies has flaws to give rise to an\nunphysical divergent bulk viscosity even in a limit where it is supposed to\nvanish. The corrected Kubo formula as well as the sum rule is then carefully\nrederived so as to confirm that the bulk viscosity indeed vanishes in the free,\nunitarity, and dimer limits. We also discuss that the recently found\ndiscrepancy between the Kubo formalism and the kinetic theory for the bulk\nviscosity is attributed to the fact that the quasiparticle approximation\nassumed by the latter breaks down even in the high-temperature limit."
    },
    {
        "anchor": "Quantum phase transition modulation in an atomtronic Mott switch: Mott insulators provide stable quantum states and long coherence times to due\nto small number fluctuations, making them good candidates for quantum memory\nand atomic circuits. We propose a proof-of-principle for a 1D Mott switch using\nan ultracold Bose gas and optical lattice. With time-evolving block decimation\nsimulations -- efficient matrix product state methods -- we design a means for\ntransient parameter characterization via a local excitation for ease of\nengineering into more complex atomtronics. We perform the switch operation by\ntuning the intensity of the optical lattice, and thus the interaction strength\nthrough a conductance transition due to the confined modifications of the\n\"wedding cake\" Mott structure. We demonstrate the time-dependence of Fock state\ntransmission and fidelity of the excitation as a means of tuning up the device\nin a double well and as a measure of noise performance. Two-point correlations\nvia the $g^{(2)}$ measure provide additional information regarding superfluid\nfragments on the Mott insulating background due to the confinement of the\npotential.",
        "positive": "Phase diagram of soft-core bosons in two dimensions: The low temperature phase diagram of Bose soft disks in two dimensions is\nstudied by numerical simulations. It is shown that a supersolid cluster phase\nexists, within a range of the model parameters, analogous to that recently\nobserved for a system of aligned dipoles interacting via a softened potential\nat short distance. These findings indicate that a long-range tail of the\ninteraction is unneeded to obtain such a phase, and that the soft-core\nrepulsive interaction is the minimal model for supersolidity."
    },
    {
        "anchor": "Strong-coupling Properties of a $p$-wave Interacting Fermi Gas on the\n  Viewpoint of Specific Heat at Constant Volume: We theoretically investigate the specific heat $C_V$ at constant volume in\nthe normal state of a $p$-wave interacting Fermi gas. Including fluctuations in\nthe $p$-wave Cooper channel within the framework of the strong-coupling theory\ndeveloped by Nozi\\`eres and Schmitt-Rink, we clarify how $C_V$ as a function of\ntemperature varies, as one moves from the weak-coupling regime to the\nstrong-coupling limit. In the weak-coupling regime, $C_V$ is shown to be\nenhanced by $p$-wave pairing fluctuations, near the superfluid phase transition\ntemperature $T_{\\rm c}$. Similar enhancement of $C_V(T\\simeq T_{\\rm c})$ is\nalso obtained in the strong-coupling regime, which, however, reflects that\nsystem is close an ideal Bose gas of $p$-wave two-body bound molecules. Using\nthese results, we classify the normal state into (1) the normal Fermi gas\nregime, (2) the $p$-wave molecular Bose gas regime, and (3) the region between\nthe two, where $p$-wave pairing fluctuations are dominant. Since the current\nexperiments can only access the normal phase of a $p$-wave interacting Fermi\ngas, our results would be useful for experiments to understand strong-coupling\nproperties of this Fermi system above $T_{\\rm c}$.",
        "positive": "Systematic interpolatory ansatz for one-dimensional polaron systems: We explore a new variational principle for studying one-dimensional quantum\nsystems in a trapping potential. We focus on the Fermi polaron problem, where a\nsingle distinguishable impurity interacts through a contact potential with a\nbackground of identical fermions. We can accurately describe this system at\narbitrary finite repulsion by constructing a truncated basis containing states\nat both the limits of zero and infinite repulsion. We show how to construct\nthis basis and how to obtain energies, density matrices and correlation\nfunctions, and provide results both for a harmonic well and a double well for\nvarious particle numbers. The results are compared both with matrix product\nstates methods and with the analytical result for two particles in a harmonic\nwell."
    },
    {
        "anchor": "Magnetic and nematic phases in a Weyl type spin-orbit-coupled spin-1\n  Bose gas: We present a variational study of the spin-1 Bose gases in a harmonic trap\nwith three-dimensional spin-orbit coupling of Weyl type. For weak spin-orbit\ncoupling, we treat the single-particle ground states as the form of\nperturbational harmonic oscillator states in the lowest total angular momentum\nmanifold with $j=1, m_j=1,0,-1$. When the two-body interaction is considered,\nwe set the trail order parameter as the superposition of three degenerate\nsingle-particle ground-states and the weight coefficients are determined by\nminimizing the energy functional. Two ground state phases, namely the magnetic\nand the nematic phases, are identified depending on the spin-independent and\nthe spin-dependent interactions. Unlike the non-spin-orbit-coupled spin-1\nBose-Einstein condensate for which the phase boundary between the magnetic and\nthe nematic phase lies exactly at zero spin-dependent interaction, the boundary\nis modified by the spin-orbit-coupling. We find the magnetic phase is featured\nwith phase-separated density distributions, 3D skyrmion-like spin textures and\ncompeting magnetic and biaxial nematic orders, while the nematic phase is\nfeatured with miscible density distributions, zero magnetization and spatially\nmodulated uniaxial nematic order. The emergence of higher spin order creates\nnew opportunities for exploring spin-tensor-related physics in spin-orbit\ncoupled superfluid.",
        "positive": "Precursor phenomena of nucleations of quantized vortices in the presence\n  of a uniformly moving obstacle in Bose-Einstein condensates: We investigate excitations and fluctuations of Bose-Einstein condensates in a\ntwo-dimensional torus with a uniformly moving Gaussian potential by solving the\nGross-Pitaevskii equation and the Bogoliubov equation. The energy gap $\\Delta$\nbetween the current-flowing metastable state (that reduces to the ground state\nfor sufficiently slowly-moving potential) and the first excited state vanishes\nwhen the moving velocity $v$ of the potential approaches a critical velocity\nv_c(>0). We find a scaling law $\\Delta \\propto (1-|v|/v_c)^{1/4}$, which\nimplies that a characteristic time scale diverges toward the critical velocity.\nNear the critical velocity, we show that low-energy local density fluctuations\nare enhanced. These behaviors can be regarded as precursor phenomena of the\nvortex nucleation."
    },
    {
        "anchor": "Third virial coefficient of the unitary Bose gas: By unitary Bose gas we mean a system composed of spinless bosons with s-wave\ninteraction of infinite scattering length and almost negligible (real or\neffective) range. Experiments are currently trying to realize it with cold\natoms. From the analytic solution of the three-body problem in a harmonic\npotential, and using methods previously developed for fermions, we determine\nthe third cumulant (or cluster integral) b_3 and the third virial coefficient\na_3 of this gas, in the spatially homogeneous case, as a function of its\ntemperature and the three-body parameter R_t characterizing the Efimov effect.\nA key point is that, converting series into integrals (by an inverse residue\nmethod), and using an unexpected small parameter (the three-boson mass angle\nnu=pi/6), one can push the full analytical estimate of b_3 and a_3 up to an\nerror that is in practice negligible. ----- Nous entendons par gaz de Bose\nunitaire un systeme compose de bosons sans spin interagissant dans l'onde s par\nun potentiel de longueur de diffusion infinie et de portee (reelle ou\neffective) presque negligeable, systeme pour l'instant abstrait mais dont la\ntentative de realisation avec des atomes froids est en cours. A partir de la\nsolution analytique connue du probleme a trois corps dans un piege harmonique,\net de methodes precedemment developpees pour des fermions, nous determinons le\ntroisieme cumulant b_3, puis le troisieme coefficient du viriel a_3 de ce gaz,\ndans le cas spatialement homogene, en fonction de sa temperature et du\nparametre a trois corps R_t caracterisant l'effet Efimov. Un point marquant est\nqu'en convertissant des series en des integrales (par une methode des residus\ninverse), puis en utilisant un petit parametre inattendu, l'angle de masse\nnu=pi/6 des trois bosons, on peut pousser l'estimation completement analytique\nde b_3 et de a_3 jusqu'a une erreur en pratique negligeable.",
        "positive": "Contact parameters in two dimensions for general three-body systems: We study the two dimensional three-body problem in the general case of three\ndistinguishable particles interacting through zero-range potentials. The\nFaddeev decomposition is used to write the momentum-space wave function. We\nshow that the large-momentum asymptotic spectator function has the same\nfunctional form as derived previously for three identical particles. We derive\nanalytic relations between the three different Faddeev components for three\ndistinguishable particles. We investigate the one-body momentum distributions\nboth analytically and numerically and analyze the tail of the distributions to\nobtain two- and three-body contact parameters. We specialize from the general\ncases to examples of two identical, interacting or non-interacting, particles.\nWe find that the two-body contact parameter is not a universal constant in the\ngeneral case and show that the universality is recovered when a subsystem is\ncomposed of two identical non-interacting particles. We also show that the\nthree-body contact parameter is negligible in the case of one non-interacting\nsubsystem compared to the situation where all subsystem are bound. As example,\nwe present results for mixtures of Lithium with two Cesium or two Potassium\natoms, which are systems of current experimental interest."
    },
    {
        "anchor": "Anisotropic Superfluid Behavior of a Dipolar Bose-Einstein Condensate: We present transport measurements on a dipolar superfluid using a\nBose-Einstein condensate of Dy-162 with strong magnetic dipole-dipole\ninteractions. By moving an attractive laser beam through the condensate we\nobserve an anisotropy in superfluid flow. This observation is compatible with\nan anisotropic critical velocity for the breakdown of dissipationless flow,\nwhich, in the spirit of the Landau criterion, can directly be connected to the\nanisotropy of the underlying dipolar excitation spectrum. In addition, the\nheating rate above this critical velocity reflects the same anisotropy. Our\nobservations are in excellent agreement with simulations based on the\nGross-Pitaevskii equation and highlight the effect of dipolar interactions on\nmacroscopic transport properties, rendering dissipation anisotropic.",
        "positive": "Quantized transport induced by topology transfer between coupled\n  one-dimensional lattice systems: We show that a topological pump in a one-dimensional (1D) insulator can\ninduce a strictly quantized transport in an auxiliary chain of non-interacting\nfermions weakly coupled to the first. The transported charge is determined by\nan integer topological invariant of the ficticious Hamiltonian of the\ninsulator, given by the covariance matrix of single-particle correlations. If\nthe original system consists of non-interacting fermions, this number is\nidentical to the TKNN (Thouless, Kohmoto, Nightinghale, den Nijs) invariant of\nthe original system and thus the coupling induces a transfer of topology to the\nauxiliary chain. When extended to particles with interactions, for which the\nTKNN number does not exist, the transported charge in the auxiliary chain\ndefines a topological invariant for the interacting system. In certain cases\nthis invariant agrees with the many-body generalization of the TKNN number\nintroduced by Niu, Thouless, and Wu (NTW). We illustrate the topology transfer\nto the auxiliary system for the Rice-Mele model of non-interacting fermions at\nhalf filling and the extended superlattice Bose-Hubbard model at quarter\nfilling. In the latter case the induced charge pump is fractional."
    },
    {
        "anchor": "Vortex Lattices in Strongly Confined Quantum Droplets: Bose mixture quantum droplets display a fascinating stability that relies on\nquantum fluctuations to prevent collapse driven by mean-field effects. Most\ndroplet research focuses on untrapped or weakly trapped scenarios, where the\ndroplets exhibit a liquid-like flat density profile. When weakly trapped\ndroplets rotate, they usually respond through center-of-mass motion or\nsplitting instability. Here, we study rapidly rotating droplets in the strong\nexternal confinement limit where the external potential prevents splitting and\nthe center-of-mass excitation. We find that quantum droplets form a triangular\nvortex lattice as in single-component repulsive Bose-Einstein condensates\n(BEC), but the overall density follows the analytical Thomas-Fermi profile\nobtained from a cubic equation. We observe three significant differences\nbetween rapidly rotating droplets and repulsive BECs. First, the vortex core\nsize changes markedly at finite density, visible in numerically obtained\ndensity profiles. We analytically estimate the vortex core sizes from the\ndroplets' coherence length and find good agreement with the numerical results.\nSecond, the change in the density profile gives a slight but observable\ndistortion to the lattice, which agrees with the distortion expected due to\nnonuniform superfluid density. Lastly, unlike a repulsive BEC, which expands\nsubstantially as the rotation frequency approaches the trapping frequency,\nrapidly rotating droplets show only a fractional change in their size. We argue\nthat this last point can be used to create clouds with lower filling factors,\nwhich may facilitate reaching the elusive strongly correlated regime.",
        "positive": "Thermodynamics of the Bose-Hubbard model in a Bogoliubov+U theory: We derive the Bogoliubov+U formalism to study the thermodynamical properties\nof the Bose-Hubbard model. The framework can be viewed as the zero-frequency\nlimit of bosonic dynamical mean-field theory (B-DMFT), but equally well as an\nextension of the mean-field decoupling approximation in which pair creation and\nannihilation of depleted particles is taken into account. The self-energy on\nthe impurity site is treated variationally, minimizing the grand potential. The\ntheory containing just three parameters that are determined self-consistently\nreproduces the T=0 phase diagrams of the three-dimensional and two-dimensional\nBose-Hubbard model with an accuracy of 1% or better. The superfluid to normal\ntransition at finite temperature is also reproduced well and only slightly less\naccurately than in B-DMFT."
    },
    {
        "anchor": "Entanglement entropies in free fermion gases for arbitrary dimension: We study the entanglement entropy of connected bipartitions in free fermion\ngases of N particles in arbitrary dimension d. We show that the von Neumann and\nRenyi entanglement entropies grow asymptotically as N^(1-1/d) ln N, with a\nprefactor that is analytically computed using the Widom conjecture both for\nperiodic and open boundary conditions. The logarithmic correction to the\npower-law behavior is related to the area-law violation in lattice free\nfermions. These asymptotic large-N behaviors are checked against exact\nnumerical calculations for N-particle systems.",
        "positive": "Vortices and vortex lattices in quantum ferrofluids: The experimental realization of quantum-degenerate Bose gases made of atoms\nwith sizeable magnetic dipole moments has created a new type of fluid, known as\na quantum ferrofluid, which combines the extraordinary properties of\nsuperfluidity and ferrofluidity. A hallmark of superfluids is that they are\nconstrained to rotate through vortices with quantized circulation. In quantum\nferrofluids the long-range dipolar interactions add new ingredients by inducing\nmagnetostriction and instabilities, and also affect the structural properties\nof vortices and vortex lattices. Here we give a review of the theory of\nvortices in dipolar Bose-Einstein condensates, exploring the interplay of\nmagnetism with vorticity and contrasting this with the established behaviour in\nnon-dipolar condensates. We cover single vortex solutions, including structure,\nenergy and stability, vortex pairs, including interactions and dynamics, and\nalso vortex lattices. Our discussion is founded on the mean-field theory\nprovided by the dipolar Gross-Pitaevskii equation, ranging from analytic\ntreatments based on the Thomas-Fermi (hydrodynamic) and variational approaches\nto full numerical simulations. Routes for generating vortices in dipolar\ncondensates are discussed, with particular attention paid to rotating\ncondensates, where surface instabilities drive the nucleation of vortices, and\nlead to the emergence of rich and varied vortex lattice structures. We also\npresent an outlook, including potential extensions to degenerate Fermi gases,\nquantum Hall physics, toroidal systems and the Berezinskii-Kosterlitz-Thouless\ntransition."
    },
    {
        "anchor": "Integer partition manifolds and phonon damping in one dimension: We develop a quantum model based on the correspondence between energy\ndistribution between harmonic oscillators and the partition of an integer\nnumber. A proper choice of the interaction Hamiltonian acting within this\nmanifold of states allows us to examine both the quantum typicality and the\nnon-exponential relaxation in the same system. A quantitative agreement between\nthe field-theoretical calculations and the exact diagonalization of the\nHamiltonian is demonstrated.",
        "positive": "Stability and stabilization of unstable condensates: It is possible to condense a macroscopic number of bosons into a single mode.\nAdding interactions the question arises whether the condensate is stable. For\nrepulsive interaction the answer is positive with regard to the ground-state,\nbut what about a condensation in an excited mode? We discuss some results that\nhave been obtained for a 2-mode bosonic Josephson junction, and for a 3-mode\nminimal-model of a superfluid circuit. Additionally we mention the possibility\nto stabilize an unstable condensate by introducing periodic or noisy driving\ninto the system: this is due to the Kapitza and the Zeno effects."
    },
    {
        "anchor": "Tetramer Bound States in Heteronuclear Systems: We calculate the universal spectrum of trimer and tetramer states in\nheteronuclear mixtures of ultracold atoms with different masses in the vicinity\nof the heavy-light dimer threshold. To extract the energies, we solve the\nthree- and four-body problem for simple two- and three-body potentials tuned to\nthe universal region using the Gaussian expansion method. We focus on the case\nof one light particle of mass $m$ and two or three heavy bosons of mass $M$\nwith resonant heavy-light interactions. We find that trimer and tetramer cross\ninto the heavy-light dimer threshold at almost the same point and that as the\nmass ratio $M/m$ decreases, the distance between the thresholds for trimer and\ntetramer states becomes smaller. We also comment on the possibility of\nobserving exotic three-body states consisting of a dimer and two atoms in this\nregion and compare with previous work.",
        "positive": "Phase-separated vortex-lattice in a rotating binary Bose-Einstein\n  condensate: We study circularly-symmetric phase separation of vortex lattices in a\nrapidly rotating harmonically-trapped quasi--two-dimensional binary\nBose-Einstein condensate (BEC) by introducing a weak quartic trap in one of the\ncomponents. The increase of the rotational frequency in such a system is also\nfound to generate a phase separation of the vortex lattices of an overlapping\nnon-rotating BEC. The phase-separated vortex lattices have different structures\nfor a binary BEC with inter-species repulsion and inter-species attraction. In\nthe former case of a fully repulsive binary BEC the phase separation of the\nvortex-lattices is accompanied by a complete phase separation of component\ndensities. In the latter case of inter-species attraction there is a partial\nphase separation of component densities, although there could be a complete\nphase separation of the generated vortex lattices in the two components. In the\ncase of inter-species attraction, we need to have different intra-species\nrepulsion in the two components for an efficient phase separation. We compare\nand contrast our results with the phase separation obtained in a\nharmonically-trapped binary BEC without any quartic trap."
    },
    {
        "anchor": "Dark-soliton molecules in an exciton-polariton superfluid: The general theory of dark solitons relies on repulsive interactions and\ntherefore predicts the impossibility to form dark-soliton bound states. One\nimportant exception to this prediction is the observation of bound solitons in\nnon-local nonlinear media. Here, we report that exciton-polariton superfluids\ncan also sustain dark-soliton molecules although the interactions are fully\nlocal. With a novel all optical technique, we create two dark solitons and bind\nthem to each other to form an unconventional dark-soliton molecule. We\ndemonstrate that the stability of this structure and the separation distance\nbetween two dark-solitons is tightly connected to the driven-dissipative nature\nof the polariton fluid.",
        "positive": "Harmonically trapped fermions in two dimensions: ground-state energy and\n  contact of SU(2) and SU(4) systems via nonuniform lattice Monte Carlo: We study harmonically trapped, unpolarized fermion systems with attractive\ninteractions in two spatial dimensions with spin degeneracies Nf = 2 and 4 and\nN/Nf = 1, 3, 5, and 7 particles per flavor. We carry out our calculations using\nour recently proposed quantum Monte Carlo method on a nonuniform lattice. We\nreport on the ground-state energy and contact for a range of couplings, as\ndetermined by the binding energy of the two-body system, and show explicitly\nhow the physics of the Nf-body sector dominates as the coupling is increased."
    },
    {
        "anchor": "Phase transition of ultracold atoms immersed in a BEC vortex lattice: We investigate the quantum phases of ultracold atoms trapped in a vortex\nlattice using a mixture of two bosonic species (A and B), in the presence of an\nartificial gauge field. Heavy atoms of species B are confined in the array of\nvortices generated in species A, and they are described through a Bose-Hubbard\nmodel. In contrast to the optical-lattice setups, the vortex lattice has an\nintrinsic dynamics, given by its Tkachenko modes. Including these quantum\nfluctuations in the effective model for B atoms yields an extended Bose-Hubbard\nmodel, with an additional \"phonon\"-mediated long-range attraction. The\nground-state phase diagram of this model is computed through a variational\nansatz and the quantum Monte Carlo technique. When compared with the ordinary\nBose-Hubbard case, the long-range interatomic attraction causes a shift and\nresizing of the Mott-insulator regions. Finally, we discuss the experimental\nfeasibility of the proposed scheme, which relies on the proper choice of the\natomic species and on a large control of physical parameters, like the\nscattering lengths and the vorticity.",
        "positive": "Universal coarsening dynamics of a quenched ferromagnetic spin-1\n  condensate: We demonstrate that a quasi-two-dimensional spin-1 condensate quenched to a\nferromagnetic phase undergoes universal coarsening in its late time dynamics.\nThe quench can be implemented by a sudden change in the applied magnetic field\nand, depending on the final value, the ferromagnetic phase has easy-axis\n(Ising) or easy-plane (XY) symmetry, with different dynamical critical\nexponents. Our results for the easy-plane phase reveal a fractal domain\nstructure and the crucial role of polar-core spin vortices in the coarsening\ndynamics."
    },
    {
        "anchor": "Intrinsic phonon effects on analog quantum simulators with ultracold\n  trapped ions: Linear Paul traps have been used recently to simulate the transverse field\nIsing model with long-range spin-spin couplings. We study the intrinsic effects\nof phonon creation (from the initial phonon ground state) on the spin-state\nprobability and spin entanglement for such quantum spin simulators. While it\nhas often been assumed that phonon effects are benign because they play no role\nin the pure Ising model, they can play a significant role when a transverse\nfield is added to the model. We use a many-body factorization of the quantum\ntime-evolution operator of the system, adiabatic perturbation theory and exact\nnumerical integration of the Schr\\\"odinger equation in a truncated spin-phonon\nHilbert space followed by a tracing out of the phonon degrees of freedom to\nstudy this problem. We find that moderate phonon creation often makes the\nprobabilities of different spin states behave differently from the static spin\nHamiltonian. In circumstances in which phonon creation is minor, the spin\ndynamics state probabilities converge to the static spin Hamiltonian prediction\nat the cost of reducing the spin entanglement. We show how phonon creation can\nseverely impede the observation of kink transitions in frustrated spin systems\nwhen the number of ions increases. Many of our results also have implications\nfor quantum simulation in a Penning trap.",
        "positive": "Vortices and antivortices in two-dimensional ultracold Fermi gases: Vortices are commonly observed in the context of classical hydrodynamics:\nfrom whirlpools after stirring the coffee in a cup to a violent atmospheric\nphenomenon such as a tornado, all classical vortices are characterized by an\narbitrary circulation value of the local velocity field. On the other hand the\nappearance of vortices with quantized circulation represents one of the\nfundamental signatures of macroscopic quantum phenomena. In two-dimensional\nsuperfluids quantized vortices play a key role in determining\nfinite-temperature properties, as the superfluid phase and the normal state are\nseparated by a vortex unbinding transition, the Berezinskii-Kosterlitz-Thouless\ntransition. Very recent experiments with two-dimensional superfluid fermions\nmotivate the present work: we present theoretical results based on the\nrenormalization group showing that the universal jump of the superfluid density\nand the critical temperature crucially depend on the interaction strength,\nproviding a strong benchmark for forthcoming investigations."
    },
    {
        "anchor": "An acoustic probe for quantum vorticity in Bose-Einstein condensates: We investigate the deformation of wavefronts of sound waves in rotating\nBose-Einstein condensates. In irrational fluid flows Berry et al. identified\nthis kind of deformation as the hydrodynamic analogue of the Aharonov-Bohm\neffect. We study this effect in Bose-Einstein condensates and obtain the\nAharonov-Bohm phase shift at all wavelengths. We show that this deformation of\nwave fronts is seen in both phase and density fluctuations. For wavelengths\nlarger than the healing length, the phase fluctuations experience a phase shift\nof the order of $2\\pi$ times the winding number. We also consider lattices of\nvortices. If the angular momentum of the vortices are aligned, the total phase\nshift is $2\\pi$ times the number of vortices in the condensate. Because of this\nbehaviour the hydrodynamic Aharonov-Bohm can be utilized as a probe for quantum\nvorticity, whose experimental realization could offers an alternative route to\ninvestigate quantum turbulence in the laboratory.",
        "positive": "High-precision multiband spectroscopy of ultracold fermions in a\n  nonseparable optical lattice: Spectroscopic tools are fundamental for the understanding of complex quantum\nsystems. Here we demonstrate high-precision multi-band spectroscopy in a\ngraphene-like lattice using ultracold fermionic atoms. From the measured band\nstructure, we characterize the underlying lattice potential with a relative\nerror of 1.2 10^(-3). Such a precise characterization of complex lattice\npotentials is an important step towards precision measurements of quantum\nmany-body systems. Furthermore, we explain the excitation strengths into the\ndifferent bands with a model and experimentally study their dependency on the\nsymmetry of the perturbation operator. This insight suggests the excitation\nstrengths as a suitable observable for interaction effects on the eigenstates."
    },
    {
        "anchor": "Engineering long-range interactions between ultracold atoms with light: Ultracold temperatures in dilute quantum gases opened the way to an exquisite\ncontrol of matter at the quantum level. Here we focus on the control of\nultracold atomic collisions using a laser to engineer their interactions at\nlarge interatomic distances. We show that the entrance channel of two colliding\nultracold atoms can be coupled to a repulsive collisional channel by the laser\nlight so that the overall interaction between the two atoms becomes repulsive:\nthis prevents them to come close together and to undergo inelastic processes,\nthus protecting the atomic gases from unwanted losses. We illustrate such an\noptical shielding mechanism with potassium and cesium atoms colliding at\nultracold temperature (\\textless 1 microkelvin). The process is described in\nthe framework of the dressed-state picture and we then solve the resulting\nstaionary coupled Schr\\\"{o}dinger equations. The role of spontaneous emission\nand photoinduced inelastic scattering is also investigated as possible\nlimitations of the shielding efficiency. We predict an almost complete\nsuppression of inelastic collisions using a laser-induced coupling\ncharacterized by a Rabi frequency of $\\omega = 200$~MHz and a frequency detuned\nfrom the potassium D2 transition by $\\Delta = 200$~MHz. We found the\npolarization of the laser has no influence on this efficiency. This proposal\ncould easily be formulated for other bi-alkali-metal pairs as their long-range\ninteraction are all very similar to each other.",
        "positive": "Frustration in a dipolar Bose-Einstein condensate introduced by an\n  optical lattice: We study the application of a square perturbing lattice to the naturally\nforming hexagonal arrays of dipolar droplets in a dipolar Bose-Einstein\ncondensate. We find that the application of the lattice causes spontaneous\npattern formation and leads to frustration in some regimes. For certain\nparameters, the ground state has neither the symmetry of the intrinsic\nhexagonal supersolid nor the symmetry of the square lattice. These results may\ngive another axis on which to explore dipolar Bose-Einstein condensates and to\nprobe the nature of supersolidity."
    },
    {
        "anchor": "Dissipative Bose-Hubbard system with intrinsic two-body loss: We report an experimental study of dynamics of the metastable $^3P_2$ state\nof bosonic ytterbium atoms in an optical lattice. The dissipative Bose-Hubbard\nsystem with on-site two-body atom loss is realized via its intrinsic strong\ninelastic collision of the metastable $^3P_2$ atoms. We investigate the atom\nloss behavior with the unit-filling Mott insulator as the initial state and\nfind that the atom loss is suppressed by the strong correlation between atoms.\nAlso, as we decrease the potential depth of the lattice, we observe the growth\nof the phase coherence and find its suppression owing to the dissipation.",
        "positive": "Spontaneous solitons in the thermal equilibrium of a\n  quasi-one-dimensional Bose gas: Solitons, or non-destructible local disturbances, are important features of\nmany one-dimensional (1D) nonlinear wave phenomena, from water waves in narrow\ncanals to light pulses in optical fibers. In ultra-cold gases, they have long\nbeen sought, and were first observed to be generated by phase-imprinting. More\nrecently, their spontaneous formation in 1D gases was predicted as a result of\nthe Kibble-Zurek mechanism, rapid evaporative cooling, and dynamical processes\nafter a quantum quench. Here we show that they actually occur generically in\nthe thermal equilibrium state of a weakly-interacting elongated Bose gas,\nwithout the need for external forcing or perturbations. This reveals a major\nnew quality to the experimentally widespread quasicondensate state. It can be\nunderstood via thermal occupation of the famous and somewhat elusive Type II\nexcitations in the Lieb-Liniger model of a uniform 1D gas."
    },
    {
        "anchor": "Solving the quantum many-body problem via correlations measured with a\n  momentum microscope: In quantum many-body theory, all physical observables are described in terms\nof correlation functions between particle creation/annihilation operators.\nMeasurement of such correlation functions can therefore be regarded as an\noperational solution to the quantum many-body problem. Here we demonstrate this\nparadigm by measuring multi-particle momentum correlations up to third order\nbetween ultracold helium atoms in an s-wave scattering halo of colliding\nBose-Einstein condensates, using a quantum many-body momentum microscope. Our\nmeasurements allow us to extract a key building block of all higher-order\ncorrelations in this system|the pairing field amplitude. In addition, we\ndemonstrate a record violation of the classical Cauchy-Schwarz inequality for\ncorrelated atom pairs and triples. Measuring multi-particle momentum\ncorrelations could provide new insights into effects such as unconventional\nsuperconductivity and many-body localisation.",
        "positive": "Metastable Patterns in one- and two-component dipolar Bose-Einstein\n  Condensates: In this paper we study metastable states in single- and two-component dipolar\nBose-Einstein condensates. We show that this system supports a rich spectrum of\nsymmetries that are remarkably stable despite not being ground states. In a\nparameter region where striped phases are ground states, we find such\nmetastable states that are energetically favourable compared to triangular and\nhoneycomb lattices. Among these metastable states we report a peculiar\nring-lattice state, which is led by the competition between triangular and\nhoneycomb symmetries and rarely seen in other systems. In the case of dipolar\nmixtures we show that via tuning the miscibility these states can be stabilized\nin a broader domain by utilising inter-species interactions."
    },
    {
        "anchor": "Reducing number fluctuations of ultracold atomic gases via dispersive\n  interrogation: We have used nondestructive laser probing to follow the central density\nevolution of a trapped atomic cloud during forced evaporative cooling. This was\nachieved in a heterodyne dispersive detection scheme. We propose to use this as\na precursor measurement for predicting the atom number subsequent to\nevaporation and provide a simple experimental demonstration of the principle\nleading to a conditional reduction of classical number fluctuations.",
        "positive": "Universality and tails of long range interactions in one dimension: Long-range interactions and, in particular, two-body potentials with\npower-law long-distance tails are ubiquitous in nature. For two bosons or\nfermions in one spatial dimension, the latter case being formally equivalent to\nthree-dimensional $s$-wave scattering, we show how generic asymptotic\ninteraction tails can be accounted for in the long-distance limit of scattering\nwave functions. This is made possible by introducing a generalisation of the\ncollisional phase shifts to include space dependence. We show that this\ndistance dependence is universal, in that it does not depend on short-distance\ndetails of the interaction. The energy dependence is also universal, and is\nfully determined by the asymptotic tails of the two-body potential. As an\nimportant application of our findings, we describe how to eliminate finite-size\neffects with long-range potentials in the calculation of scattering phase\nshifts from exact diagonalisation. We show that even with moderately small\nsystem sizes it is possible to accurately extract phase shifts that would\notherwise be plagued with finite-size errors. We also consider multi-channel\nscattering, focusing on the estimation of open channel asymptotic interaction\nstrengths via finite-size analysis."
    },
    {
        "anchor": "Repulsive to attractive interaction quenches of 1D Bose gas in a\n  harmonic trap: We consider quantum quenches of harmonically trapped one-dimensional bosons\nfrom repulsive to attractive interactions, and the resulting breathing dynamics\nof the so-called `super-Tonks-Girardeau' (sTG) state. This state is highly\nexcited compared to the ground state of the attractive gas, and is the lowest\neigenstate where the particles are not bound or clustered. We analyze the\ndynamics from a spectral point of view, identifying the relevant eigenstates of\nthe interacting trapped many-body system, and analyzing the nature of these\nquantum eigenstates. To obtain explicit eigenspectra, we use Hamiltonians with\nfinite-dimensional Hilbert spaces to approximate the Lieb-Liniger system. We\nemploy two very different approximate approaches: an expansion in a truncated\nsingle-particle harmonic-trap basis and a lattice (Bose-Hubbard) model. We show\nhow the breathing frequency, identified with the energy difference between the\nsTG state and another particular eigenstate, varies with interaction.",
        "positive": "Phase diagram of Landau-Zener phenomena in coupled one-dimensional Bose\n  quantum fluids: We study stationary and dynamical properties of the many-body Landau-Zener\ndynamics of a Bose quantum fluid confined in two coupled one-dimensional\nchains, using a many-body generalization recently reported [Y.-A. Chen et al.],\nwithin the decoupling approximation and the one-level band scheme. The energy\nspectrum evidences the structure of the avoided level crossings as a function\nof the on-site inter particle interaction strength. On the dynamical side, a\nphase diagram of the transfer efficiency across ground-state and inverse sweeps\nis presented. A totally different scenario with respect to the original\nsingle-particle Landau-Zener scheme is found for ground-state sweeps, in which\na breakdown of the adiabatic region emerges as the sweep rate decreases. On the\ncontrary, the transfer efficiency across inverse sweeps reveals consistent\nresults with the single-particle Landau-Zener predictions. In the strong\ncoupling regime, we find that there is a critical value of the on-site\ninteraction for which the transfer of particles starts to vanish independently\nof the sweep rate. Our results are in qualitative agreement with those of the\nexperimental counterpart."
    },
    {
        "anchor": "Spin-charge correlations in finite one-dimensional multi-band Fermi\n  systems: We investigate spin-charge separation of a spin-1/2 Fermi system confined in\na triple well where multiple bands are occupied. We assume that our finite\nfermionic system is close to fully spin polarized while being doped by a hole\nand an impurity fermion with opposite spin. Our setup involves ferromagnetic\ncouplings among the particles in different bands, leading to the development of\nstrong spin-transport correlations in an intermediate interaction regime.\nInteractions are then strong enough to lift the degeneracy among singlet and\ntriplet spin configurations in the well of the spin impurity but not strong\nenough to prohibit hole-induced magnetic excitations to the singlet state.\nDespite the strong spin-hole correlations, the system exhibits spin-charge\ndeconfinement allowing for long-range entanglement of the spatial and spin\ndegrees of freedom.",
        "positive": "Analytical study on parameter regions of dynamical instability for\n  two-component Bose--Einstein condensates with coaxial quantized vortices: The dynamical instability of weakly interacting two-component Bose--Einstein\ncondensates with coaxial quantized vortices is analytically investigated in a\ntwo-dimensional isotopic harmonic potential. We examine whether complex\neigenvalues appear on the Bogoliubov--de Gennes equation, implying dynamical\ninstability. Rather than solving the Bogoliubov--de Gennes equation\nnumerically, we rely on a perturbative expansion with respect to the coupling\nconstant which enables a simple, analytic approach. For each pair of winding\nnumbers and for each magnetic quantum number, the ranges of inter-component\ncoupling constant where the system is dynamically unstable are exhaustively\nobtained. Co-rotating and counter-rotating systems show distinctive behaviors.\nThe latter is much more complicated than the former with respect to dynamical\ninstability, particularly because radial excitations contribute to complex\neigenvalues in counter-rotating systems."
    },
    {
        "anchor": "Two-dimensional Bose gases near resonance: universal three-body effects: We report in this Letter the results of our investigation of 2D Bose gases\nbeyond the dilute limit emphasizing the role played by three-body scattering\nevents. We demonstrate that a competition between three-body attractive\ninteractions and two-body repulsive forces results in the chemical potential of\n2D Bose gases to exhibit a maximum at a critical scattering length beyond which\nthese quantum gases possess a negative compressibility. For larger scattering\nlengths, the increasingly prominent role played by three-body attractive\ninteractions leads to an onset instability at a second critical value. The\nthree-body effects studied here are universal, fully characterized by the\neffective 2D scattering length $a_{2D}$ (or the size of the 2D bound states)\nand are, in comparison to the 3D case, independent of three-body ultraviolet\nphysics. We find, within our approach, the ratios of the contribution to the\nchemical potential due to three-body interactions to the one due to two-body to\nbe 0.27 near the maximum of the chemical potential and 0.73 in the vicinity of\nthe onset instability.",
        "positive": "Momentum distribution and coherence of a weakly interacting Bose gas\n  after a quench: We consider a weakly interacting uniform atomic Bose gas with a\ntime-dependent nonlinear coupling constant. By developing a suitable Bogoliubov\ntreatment we investigate the time evolution of several observables, including\nthe momentum distribution, the degree of coherence in the system, and their\ndependence on dimensionality and temperature. We rigorously prove that the\nlow-momentum Bogoliubov modes remain frozen during the whole evolution, while\nthe high-momentum ones adiabatically follow the change in time of the\ninteraction strength. At intermediate momenta we point out the occurrence of\noscillations, which are analogous to Sakharov oscillations. We identify two\nwide classes of time-dependent behaviors of the coupling for which an exact\nsolution of the problem can be found, allowing for an analytic computation of\nall the relevant observables. A special emphasis is put on the study of the\ncoherence property of the system in one spatial dimension. We show that the\nsystem exhibits a smooth \"light-cone effect,\" with typically no\nprethermalization."
    },
    {
        "anchor": "Entanglement in an expanding toroidal Bose-Einstein condensate: Recent experiments have employed rapidly expanding toroidal Bose-Einstein\ncondensates (BECs) to mimic the inflationary expansion in the early universe.\nOne expected signature of the expansion in such experiments is spontaneous\nparticle creation (of phonons) which is observable in density-density\ncorrelations. We study entanglement of these particles, which are known to\nresult in a two-mode squeezed state. Using techniques for Gaussian states of\ncontinuous variable systems, we quantify the entanglement generated in this\nsystem, including effects such as decoherence and the use of an initially\nsqueezed state, which can suppress and enhance entanglement, respectively. We\nalso describe a protocol to experimentally measure the correlations entering\nthe covariance matrix, allowing an experimental quantification of the\nentanglement properties of the inflationary BEC.",
        "positive": "Quantum spin liquids of Rydberg excitations in a honeycomb lattice\n  induced by density-dependent Peierls phases: We show that the nonlinear transport of bosonic excitations in a\ntwo-dimensional honeycomb lattice of spin-orbit coupled Rydberg atoms gives\nrise to disordered quantum phases which are candidates for quantum spin\nliquids. As recently demonstrated in [Lienhard et al. Phys. Rev. X, 10, 021031\n(2020)] the spin-orbit coupling breaks time-reversal and chiral symmetries and\nleads to a tunable density-dependent complex hopping of the hard-core bosons or\nequivalently to complex XY spin interactions. Using exact diagonalization (ED)\nwe numerically investigate the phase diagram resulting from the competition\nbetween density-dependent and direct transport terms. In mean-field\napproximation there is a phase transition from a quasi-condensate to a\n120{\\deg} phase when the amplitude of the complex hopping exceeds that of the\ndirect one. In the full model a new phase with a finite spin gap emerges close\nto the mean-field critical point as a result of quantum fluctuations induced by\nthe density-dependence of the complex hopping. We show that this phase is a\ngenuine disordered one, has a non-vanishing spin chirality and is characterized\nby a non-trivial many-body Chern number. ED simulations of small lattices with\nup to 28 lattice sites point to a non-degenerate ground state and thus to a\nbosonic integer-quantum Hall (BIQH) phase, protected by U(1) symmetry. The\nChern number of C = 1, which is robust to disorder, is however different from\nthe even Chern numbers found in BIQH phases. For very strong, nonlinear\nhoppings of opposite sign we find another disordered regime with vanishing spin\ngap. This phase also has a large spin chirality and could be a gapless\nspin-liquid but lies outside the parameter regime accessible in the Rydberg\nsystem."
    },
    {
        "anchor": "From Efimov Physics to the Bose Polaron using Gaussian States: Since the Efimov effect was introduced in 1970, a detailed theoretical\nunderstanding of Efimov physics has been developed in the few-body context.\nHowever, it has proven to be challenging to describe the role Efimov-type\ncorrelations play in many-body systems such as quenched or collapsing\nBose-Einstein condensates (BECs). To study the impact the Efimov effect can\nhave in such scenarios, we consider a light impurity immersed in a weakly\ninteracting BEC, forming a Bose polaron. In this case, the higher-order\ncorrelations are localized around the impurity, making it more feasible to\ndevelop a theoretical description. Specifically, we employ a Gaussian state\nvariational Ansatz in the reference frame of the impurity, capable of both\ncapturing the Efimov effect and the formation of the polaron cloud. We find\nthat the Efimov effect leads to a cooperative binding of bosons to the impurity\nand the formation of a many-body bound state. As a result, the polaron is not\nthe ground state, but rendered a metastable excited state which can decay into\nthese Efimov clusters. While this decay is slow for small interaction\nstrengths, it becomes more prominent as the attractive scattering length\nincreases, up to the point where the polaron becomes completely unstable. This\ncritical scattering length can be interpreted as a many-body shifted Efimov\nresonance, where the scattering of two excitations of the bath with the polaron\ncan lead to bound state formation. Compared to the few-body case, the resonance\nis shifted to smaller attractive scattering lengths due to the participation of\nthe polaron cloud in the cooperative binding process. This corresponds to an\nintriguing scenario of polaron-assisted chemistry, where many-body effects lead\nto enhanced signal of the chemical recombination process, which can be directly\nprobed in state-of-the-art experiments.",
        "positive": "Effective theory and universal relations for Fermi gases near a $d$-wave\n  interaction resonance: In this work, we present an effective field theory to describe a\ntwo-component Fermi gas near a $d$-wave interaction resonance. The effective\nfield theory is renormalizable by matching with the low energy $d$-wave\nscattering phase shift. Based on the effective field theory, we derive\nuniversal properties of the Fermi gas by the operator product expansion method.\nWe find that beyond the contacts defined by adiabatic theorems, the asymptotic\nexpressions of the momentum distribution and the Raman spectroscopy involve two\nextra contacts which provide additional information of correlations of the\nsystem. Our formalism sets the stage for further explorations of many-body\neffects in a $d$-wave resonant Fermi gas. Finally we generalise our effective\nfield theory for interaction resonances of arbitrary higher partial waves."
    },
    {
        "anchor": "Numerical representation of quantum states in the positive-P and Wigner\n  representations: Numerical stochastic integration is a powerful tool for the investigation of\nquantum dynamics in interacting many body systems. As with all numerical\nintegration of differential equations, the initial conditions of the system\nbeing investigated must be specified. With application to quantum optics in\nmind, we show how various commonly considered quantum states can be numerically\nsimulated by the use of widely available Gaussian and uniform random number\ngenerators. We note that the same methods can also be applied to computational\nstudies of Bose-Einstein condensates, and give some examples of how this can be\ndone.",
        "positive": "Effects of atom losses on a one-dimensional lattice gas of hardcore\n  bosons: Atom losses occur naturally during cold atoms experiments. Since this\nphenomenon is unavoidable, it is important to understand its effect on the\nremaining atoms. Here we study a gas of hard-core bosons on a lattice subject\nto $K$-body losses (where $K=1,2,3,\\dots$ is the number of atoms lost in each\nloss event), and in particular we investigate the effect of losses on the\nrapidity distribution $\\rho(k)$ of the atoms. Under the assumption that losses\nare weak enough so that the system relaxes between two loss events, we are able\nto determine the loss functional $F[\\rho](k)$ encoding the loss process for\n$K$-body losses. We derive closed expressions for the cases of one- and\ntwo-body losses, and show their effects on the evolution of the total number of\nparticles. Then we add a harmonic trapping potential and study the evolution of\nthe position-dependent rapidity distribution of this system by solving\nnumerically the evolution equation for one-, two- and three-body losses."
    },
    {
        "anchor": "Does an isolated quantum system relax?: Statistical mechanics is one of the most comprehensive theories in physics.\nFrom a boiling pot of water to the complex dynamics of quantum many-body\nsystems it provides a successful connection between the microscopic dynamics of\natoms and molecules and the macroscopic properties of matter. However,\nstatistical mechanics only describes the thermal equilibrium situation of a\nsystem, and there is no general framework to describe how equilibrium is\nreached or under which circumstances it can be reached at all. This problem is\nparticularly challenging in quantum mechanics, where unitarity appears to\nrender the very concept of thermalization counterintuitive. With the rapid\nexperimental progress in the control and probing of ultracold quantum gases\nthis question has become within reach of detailed experimental investigations.\nIn these notes we present a series of experiments with ultracold\none-dimensional Bose gases, which provide novel insights into this fundamental\nquestion.",
        "positive": "Unveiling hidden structure of many-body wavefunctions of integrable\n  systems via sudden expansion experiments: In the theory of Bethe-ansatz integrable quantum systems, rapidities play an\nimportant role as they are used to specify many-body states, apart from phases.\nThe physical interpretation of rapidities going back to Sutherland is that they\nare the asymptotic momenta after letting a quantum gas expand into a larger\nvolume making it dilute and noninteracting. We exploit this picture to make a\ndirect connection to quantities that are accessible in sudden-expansion\nexperiments with ultracold quantum gases. By a direct comparison of\nBethe-ansatz and time-dependent density matrix renormalization group results,\nwe demonstrate that the expansion velocity of a one-dimensional Fermi-Hubbard\nmodel can be predicted from knowing the distribution of occupied rapidities\ndefined by the initial state. Curiously, an approximate Bethe-ansatz solution\nworks well also for the Bose-Hubbard model."
    },
    {
        "anchor": "Spin squeezing and many-body dipolar dynamics in optical lattice clocks: The recent experimental realization of a three-dimensional (3D) optical\nlattice clock not only reduces the influence of collisional interactions on the\nclock's accuracy but also provides a promising platform for studying dipolar\nmany-body quantum physics. Here, by solving the governing master equation, we\ninvestigate the role of both elastic and dissipative long-range interactions in\nthe clock's dynamics and study its dependence on lattice spacing,\ndimensionality, and dipolar orientation. For small lattice spacing, i.e.,\n$k_0a\\ll 1$, where $a$ is the lattice constant and $k_0$ is the transition\nwavenumber, a sizable spin squeezing appears in the transient state which is\nfavored in a head-to-tail dipolar configuration in 1D systems and a\nside-by-side configuration in 2D systems, respectively. For large lattice\nspacing, i.e., $k_0a\\gg 1$, the single atomic decay rate can be effectively\nsuppressed due to the destructive dissipative emission of neighboring atoms in\nboth 1D and 2D. Our results will not only aid in the design of the future\ngeneration of ultraprecise atomic clocks but also illuminates the rich\nmany-body physics exhibited by radiating dipolar system.",
        "positive": "Variational approach for interacting ultra-cold atoms in arbitrary\n  one-dimensional confinement: Standard analytical construction of the many-body wave function of\ninteracting particles in one dimension, beyond mean-field theory, is based on\nthe Jastrow approach. The many-body interacting ground state is build up from\nthe ground state of the non-interacting system and the product of solutions of\nthe corresponding interacting two-body problem. However, this is possible only\nif the center-of-mass motion is decoupled from the mutual interactions. In our\nwork, based on the general constraints given by contact nature of the atom-atom\ninteractions, we present an alternative approach to the standard construction\nof the \\textit{pair-correlation} wave-function. Within the proposed ansatz, we\nstudy the many-body properties of trapped bosons as well as fermionic mixtures\nand we compare these predictions with the exact diagonalization approach in a\nwide range of particle numbers, interaction strengths, and different trapping\npotentials."
    },
    {
        "anchor": "Harmonically Trapped Atoms with Spin-Orbit Coupling: We study harmonically trapped one-dimensional atoms subjected to an equal\ncombination of Rashba and Dresselhaus spin-orbit coupling induced by Raman\ntransition. We first examine the wave function and the degeneracy of the\nsingle-particle ground state, followed by a study of two weakly interacting\nbosons or fermions. For the two-particle ground state, we focus on the effects\nof the interaction on the degeneracy, the spin density profiles, and the\ndensity-density correlation functions. Finally we show how these studies help\nus to understand the many-body properties of the system.",
        "positive": "Quantum gas of rovibronic ground-state molecules in an optical lattice: Control over all internal and external degrees of freedom of molecules at the\nlevel of single quantum states will enable a series of fundamental studies in\nphysics and chemistry. In particular, samples of ground-state molecules at\nultralow temperatures and high number densities will allow novel quantum-gas\nstudies and future applications in quantum information science. However, high\nphase-space densities for molecular samples are not readily attainable as\nefficient cooling techniques such as laser cooling are lacking. Here we produce\nan ultracold and dense sample of molecules in a single hyperfine level of the\nrovibronic ground state with each molecule individually trapped in the motional\nground state of an optical lattice well. Starting from a zero-temperature\natomic Mott-insulator state with optimized double-site occupancy, weakly-bound\ndimer molecules are efficiently associated on a Feshbach resonance and\nsubsequently transferred to the rovibronic ground state by a stimulated\nfour-photon process with >50 % efficiency. The molecules are trapped in the\nlattice and have a lifetime of 8 s. Our results present a crucial step towards\nBose-Einstein condensation of ground-state molecules and, when suitably\ngeneralized to polar heteronuclear molecules, the realization of dipolar\nquantum-gas phases in optical lattices."
    },
    {
        "anchor": "Zeros of Loschmidt echo in the presence of Anderson localization: We study the Loschmidt echo and the dynamical free energy of the Anderson\nmodel after a quench of the disorder strength. If the initial state is extended\nand the eigenstates of the post-quench Hamiltonian are strongly localized, we\nargue that the Loschmidt echo exhibits zeros periodically with the period $2\\pi\n/D$ where $D$ is the width of spectra. At these zeros, the dynamical free\nenergy diverges in a logarithmic way. We present numerical evidence of our\nargument in one- and three-dimensional Anderson models. Our findings connect\nthe dynamical quantum phase transitions to the localization-delocalization\nphase transitions.",
        "positive": "Dipolar evaporation of reactive molecules to below the Fermi temperature: Molecules are the building blocks of matter and their control is key to the\ninvestigation of new quantum phases, where rich degrees of freedom can be used\nto encode information and strong interactions can be precisely tuned. Inelastic\nlosses in molecular collisions, however, have greatly hampered the engineering\nof low-entropy molecular systems. So far, the only quantum degenerate gas of\nmolecules has been created via association of two highly degenerate atomic\ngases. Here, we use an external electric field along with optical lattice\nconfinement to create a two-dimensional (2D) Fermi gas of spin-polarized\npotassium-rubidium (KRb) polar molecules, where elastic, tunable dipolar\ninteractions dominate over all inelastic processes. Direct thermalization among\nthe molecules in the trap leads to efficient dipolar evaporative cooling,\nyielding a rapid increase in phase-space density. At the onset of quantum\ndegeneracy, we observe the effects of Fermi statistics on the thermodynamics of\nthe molecular gas. These results demonstrate a general strategy for achieving\nquantum degeneracy in dipolar molecular gases to explore strongly interacting\nmany-body phases."
    },
    {
        "anchor": "Optimal atomic interferometry robust to detection noise using spin-1\n  atomic condensates: Implementation of the quantum interferometry concept to spin-1 atomic\nBose-Einstein condensates is analyzed by employing a polar state evolved in\ntime. In order to identify the best interferometric configurations, the quantum\nFisher information is maximized. Three optimal configurations are identified,\namong which one was not reported in the literature yet, although it gives the\nhighest value of the quantum Fisher information in experimentally achievable\nshort time dynamics. Details of the most optimal configurations are\ninvestigated based on the error-propagation formula which includes the\ninteraction-based readout protocol to reduce the destructive effect of\ndetection noise. In order to obtain Heisenberg scaling accessible by present\nday experimental techniques, an efficient measurement and a method for the\ninversion of dynamics were developed, as necessary for the protocol's\nimplementation.",
        "positive": "Universal behaviour of four-boson systems from a functional\n  renormalisation group: We apply a functional renormalisation group to systems of four bosonic atoms\nclose to the unitary limit. We work with a local effective action that includes\na dynamical trimer field and we use this field to eliminate structures that do\nnot correspond to the Faddeev-Yakubovsky equations. In the physical limit, we\nfind three four-body bound states below the shallowest three-body state. The\nvalues of the scattering lengths at which two of these states become bound are\nin good agreement with exact solutions of the four-body equations and\nexperimental observations. The third state is extremely shallow. During the\nevolution we find an infinite number of four-body states based on each\nthree-body state which follow a double-exponential pattern in the running\nscale. None of the four-body states shows any evidence of dependence on a\nfour-body parameter."
    },
    {
        "anchor": "Interaction Effects on Wannier Functions for Bosons in Optical Lattice: We have numerically calculated the single band Wannier functions for\ninteracting Bose gases in optical lattices with a self-consistent approach. We\nfind that the Wannier function is broadened by repulsive atom interaction. The\ntunneling parameter J and on-site interaction U computed with the broadened\nWannier functions are found to change significantly for different atomic number\nper site. Our theory can explain the nonuniform atomic clock shift observed in\n[Campbell et al., Science 313, 649 (2006)].",
        "positive": "Quantum simulation of the Hubbard model with ultracold fermions in\n  optical lattices: Ultracold atomic gases provide a fantastic platform to implement quantum\nsimulators and investigate a variety of models initially introduced in\ncondensed matter physics or other areas. One of the most promising applications\nof quantum simulation is the study of strongly-correlated Fermi gases, for\nwhich exact theoretical results are not always possible with state-of-the-art\napproaches. Here, we review recent progress of the quantum simulation of the\nemblematic Fermi-Hubbard model with ultracold atoms. After introducing the\nFermi-Hubbard model in the context of condensed matter, its implementation in\nultracold atom systems, and its phase diagram, we review landmark experimental\nachievements, from the early observation of the onset of quantum degeneracy and\nsuperfluidity to demonstration of the Mott insulator regime and the emergence\nof long-range anti-ferromagnetic order. We conclude by discussing future\nchallenges, including the possible observation of high-Tc superconductivity,\ntransport properties, and the interplay of strong correlations and disorder or\ntopology."
    },
    {
        "anchor": "Thermodynamic properties of two-component fermionic atoms trapped in a\n  two-dimensional optical lattice: We study the finite temperature properties of two-component fermionic atoms\ntrapped in a two-dimensional optical lattice. We apply the self-energy\nfunctional approach to the two-dimensional Hubbard model with a harmonic\ntrapping potential, and systematically investigate the thermodynamic properties\nof this system. We find that entropy and grand potential provide evidence of a\ncrossover between the Mott insulating and metallic phases at certain\ntemperatures. In addition, we find that entropy exhibits a cusp-like anomaly at\nlower temperatures, suggesting a second or higher order antiferromagnetic\ntransition. We estimate the antiferromagnetic transition temperatures, and\nclarify how the trapping potential affects this magnetic transition.",
        "positive": "Controlling spin motion and interactions in a one-dimensional Bose gas: Experiments on ultracold gases offer unparalleled opportunities to explore\nquantum many-body physics, with excellent control over key parameters including\ntemperature, density, interactions and even dimensionality. In some systems,\natomic interactions can be adjusted by means of magnetic Feshbach resonances,\nwhich have played a crucial role in realizing new many-body phenomena. However,\nsuitable Feshbach resonances are not always available, and they offer limited\nfreedom since the magnetic field strength is the only control parameter. Here\nwe show a new way to tune interactions in one-dimensional quantum gases using\nstate-dependent dressed potentials, enabling control over non-equilibrium spin\nmotion in a two-component gas of 87Rb. The accessible range includes the point\nof spin-independent interactions where exact quantum many-body solutions are\navailable and the point where spin motion is frozen. This versatility opens a\nnew route to experiments on spin waves, spin-\"charge\" separation and the\nrelation between superfluidity and magnetism in low-dimensional quantum gases."
    },
    {
        "anchor": "Photon BEC with Thermo-Optic Interaction at Dimensional Crossover: Since the advent of experiments with photon Bose-Einstein condensates in\ndye-filled microcavities in 2010, many investigations have focused upon the\nemerging effective photon-photon interaction. Despite its smallness, it can be\nidentified to stem from two physically distinct mechanisms. On the one hand, a\nKerr nonlinearity of the dye medium yields a photon-photon contact interaction.\nOn the other hand, a heating of the dye medium leads to an additional\nthermo-optic interaction, which is both delayed and non-local. The latter turns\nout to represent the leading contribution to the effective interaction for the\ncurrent 2D experiments. Here we analyse theoretically how the effective\nphoton-photon interaction increases when the system dimension is reduced from\n2D to 1D. To this end, we consider an anisotropic harmonic trapping potential\nand determine via a variational approach how the properties of the photon\nBose-Einstein condensate in general, and both aforementioned interaction\nmechanisms in particular, change with increasing anisotropy. We find that the\nthermo-optic interaction strength increases at first linearly with the trap\naspect ratio and lateron saturates at a certain value of the trap aspect ratio.\nFurthermore, in the strong 1D limit the roles of both interactions get reversed\nas the thermo-optic interaction remains saturated and the contact Kerr\ninteraction becomes the leading interaction mechanism. Finally, we discuss how\nthe predicted effects can be measured experimentally.",
        "positive": "Realising the Symmetry-Protected Haldane Phase in Fermi-Hubbard Ladders: Topology in quantum many-body systems has profoundly changed our\nunderstanding of quantum phases of matter. The paradigmatic model that has\nplayed an instrumental role in elucidating these effects is the\nantiferromagnetic spin-1 Haldane chain. Its ground state is a disordered state,\nwith symmetry-protected fourfold-degenerate edge states due to fractional spin\nexcitations. In the bulk, it is characterised by vanishing two-point spin\ncorrelations, gapped excitations, and a characteristic non-local order\nparameter. More recently it was understood that the Haldane chain forms a\nspecific example of a more general classification scheme of symmetry protected\ntopological (SPT) phases of matter that is based on ideas connecting to quantum\ninformation and entanglement. Here, we realise such a topological Haldane phase\nwith Fermi-Hubbard ladders in an ultracold-atom quantum simulator. We directly\nreveal both edge and bulk properties of the system through the use of\nsingle-site and particle-resolved measurements as well as non-local correlation\nfunctions. Continuously changing the Hubbard interaction strength of the system\nallows us to investigate the robustness of the phase to charge (density)\nfluctuations far from the regime of the Heisenberg model employing a novel\ncorrelator."
    },
    {
        "anchor": "Single-atom imaging of fermions in a quantum-gas microscope: Single-atom-resolved detection in optical lattices using quantum-gas\nmicroscopes has enabled a new generation of experiments in the field of quantum\nsimulation. Fluorescence imaging of individual atoms has so far been achieved\nfor bosonic species with optical molasses cooling, whereas detection of\nfermionic alkaline atoms in optical lattices by this method has proven more\nchallenging. Here we demonstrate single-site- and single-atom-resolved\nfluorescence imaging of fermionic potassium-40 atoms in a quantum-gas\nmicroscope setup using electromagnetically-induced-transparency cooling. We\ndetected on average 1000 fluorescence photons from a single atom within 1.5s,\nwhile keeping it close to the vibrational ground state of the optical lattice.\nOur results will enable the study of strongly correlated fermionic quantum\nsystems in optical lattices with resolution at the single-atom level, and give\naccess to observables such as the local entropy distribution and individual\ndefects in fermionic Mott insulators or anti-ferromagnetically ordered phases.",
        "positive": "Real time dynamics and proposal for feasible experiments of lattice\n  gauge-Higgs model simulated by cold atoms: Lattice gauge theory has provided a crucial non-perturbative method in\nstudying canonical models in high-energy physics such as quantum\nchromodynamics. Among other models of lattice gauge theory, the lattice\ngauge-Higgs model is a quite important one because it describes wide variety of\nphenomena/models related to the Anderson-Higgs mechanism such as\nsuperconductivity, the standard model of particle physics, and inflation\nprocess of the early universe. In this paper, we first show that atomic\ndescription of the lattice gauge model allows us to explore real time dynamics\nof the gauge variables by using the Gross-Pitaevskii equations. Numerical\nsimulations of the time development of an electric flux reveal some interesting\ncharacteristics of dynamical aspect of the model and determine its phase\ndiagram. Next, to realize a quantum simulator of the U(1) lattice gauge-Higgs\nmodel on an optical lattice filled by cold atoms, we propose two feasible\nmethods: (i) Wannier states in the excited bands and (ii) dipolar atoms in a\nmultilayer optical lattice. We pay attentions to respect the constraint of\nGauss's law and avoid nonlocal gauge interactions."
    },
    {
        "anchor": "A simplified approach to the repulsive Bose gas from low to high\n  densities and its numerical accuracy: In 1963, a Simple Approach was developed to study the ground state energy of\nan interacting Bose gas. It consists in the derivation of an Equation, which is\nnot based on perturbation theory, and which gives the exact expansion of the\nenergy at low densities. This Equation is expressed directly in the\nthermodynamic limit, and only involves functions of $3$ variables, rather than\n$3N$. Here, we revisit this approach, and show that the Equation yields\naccurate predictions for various observables for all densities. Specifically,\nin addition to the ground state energy, we have shown that the Simple Approach\ngives predictions for the condensate fraction, two-point correlation function,\nand momentum distribution. We have carried out a variety of tests by comparing\nthe predictions of the Equation with Quantum Monte Carlo calculations, and have\nfound remarkable agreement. We thus show that the Simple Approach provides a\nnew theoretical tool to understand the behavior of the many-body Bose gas, not\nonly in the small and large density ranges, which have been studied before, but\nalso in the range of intermediate density, for which little is known.",
        "positive": "i-SPin 2: An integrator for general spin-s Gross-Pitaevskii systems: We provide an algorithm for evolving general spin-$s$ Gross-Pitaevskii /\nnon-linear Schr\\\"odinger systems carrying a variety of interactions, where the\n$2s+1$ components of the `spinor' field represent the different\nspin-multiplicity states. We consider many nonrelativistic interactions up to\nquartic order in the Schr\\\"odinger field (both short and long-range, and\nspin-dependent and spin-independent interactions), including explicit\nspin-orbit couplings. The algorithm allows for spatially varying external\nand/or self-generated vector potentials that couple to the spin density of the\nfield. Our work can be used for scenarios ranging from laboratory systems such\nas spinor Bose-Einstein condensates (BECs), to cosmological/astrophysical\nsystems such as self-interacting bosonic dark matter. As examples, we provide\nresults for two different setups of spin-$1$ BECs that employ a varying\nmagnetic field and spin-orbit coupling, respectively, and also collisions of\nspin-$1$ solitons in dark matter. Our symplectic algorithm is second-order\naccurate in time, and is extensible to the known higher-order accurate methods."
    },
    {
        "anchor": "Trojan quasiparticles: We argue that a time-periodically driven bosonic Josephson junction supports\nstable, quasi-particle-like collective response modes which are $N$-particle\nanalogs of the nonspreading Trojan wave packets known from microwave-driven\nRydberg atoms. Similar to their single-particle counterparts, these collective\nmodes, dubbed \"flotons\", are well described by a Floquet-Mathieu approximation,\nand possess a well-defined discrete set of excitations. In contrast to other,\n\"chaotic\" modes of response, the nonheating Trojan modes conform to a\nmean-field description, and thus may be of particular interest for the more\ngeneral question under which conditions the reduction of quantum $N$-particle\ndynamics to a strongly simplified mean-field evolution is feasible. Our\nreasoning is supported by phase-space portraits which reveal the degree of\ncorrespondence beween the $N$-particle dynamics und the mean-field picture in\nan intuitive manner.",
        "positive": "Stoner ferromagnetism in a thermal pseudospin-1/2 Bose gas: We compute the finite-temperature phase diagram of a pseudospin-$1/2$ Bose\ngas with contact interactions, using two complementary methods: the random\nphase approximation (RPA) and self-consistent Hartree-Fock theory. We show that\nthe inter-spin interactions, which break the (pseudo) spin-rotational symmetry\nof the Hamiltonian, generally lead to the appearance of a magnetically ordered\nphase at temperatures above the superfluid transition. In three dimensions, we\npredict a normal easy-axis/easy-plane ferromagnet for sufficiently strong\nrepulsive/attractive inter-species interactions respectively. The normal\neasy-axis ferromagnet is the bosonic analog of Stoner ferromagnetism known in\nelectronic systems. For the case of inter-spin attraction, we also discuss the\npossibility of a \\textit{bosonic} analog of the Cooper paired phase. This state\nis shown to significantly lose in energy to the transverse ferromagnet in three\ndimensions, but is more energetically competitive in lower dimensions.\nExtending our calculations to a spin-orbit-coupled Bose gas with equal Rashba\nand Dresselhaus-type couplings (as recently realized in experiment), we\ninvestigate the possibility of stripe ordering in the normal phase. Within our\napproximations however, we do not find an instability towards stripe formation,\nsuggesting that the stripe order melts below the condensation temperature,\nwhich is consistent with the experimental observations of Ji \\textit{et al.}\n[Ji \\textit{et al.}, Nature Physics \\textbf{10}, 314 (2014)]."
    },
    {
        "anchor": "Nonlinear Zeno dynamics due to atomic interactions in Bose-Einstein\n  condensate: We show that nonlinear interactions induce both the Zeno and anti-Zeno\neffects in the generalised Bose-Josephson model (with the on-site interactions\nand the second-order tunneling) describing Bose-Einstein condensate in\ndouble-well trap subject to particle removal from one of the wells. We find\nthat the on-site interactions induce \\textit{only} the Zeno effect, which\nappears at long evolution times, whereas the second-order tunneling leads to a\nstrong decay of the atomic population at short evolution times, reminiscent of\nthe anti-Zeno effect, and destroys the nonlinear Zeno effect due to the on-site\ninteractions at long times.",
        "positive": "Probing Sound Speed of an Optically-Trapped Bose Gas with Periodically\n  Modulated Interactions by Bragg Spectroscopy: A Bose-Einstein condensate (BEC) with periodically modulated interactions\n(PMI) has emerged as a novel kind of periodic superfluid, which has been\nrecently experimentally created using optical Feshbach resonance. In this\npaper, we are motivated to investigate the superfluidity of a BEC with PMI\ntrapped in an optical lattice (OL). In particular, we explore the effects of\nPMI on the sound speed and the dynamical structure factor of the model system.\nOur numerical results, combined with the analytical results in both the\nweak-potential limit and the tight-binding limit, have shown that the PMI can\nstrongly modify the sound speed of a BEC. Moreover, we have shown that the\neffects of PMI on sound speed can be experimentally probed via the dynamic\nstructure factor, where the excitation strength toward the first Bogoliubov\nband exhibits marked difference from the non- PMI one. Our predictions of the\neffects of PMI on the sound speed can be tested using the Bragg spectroscopy."
    },
    {
        "anchor": "A one-dimensional liquid of fermions with tunable spin: Correlations in systems with spin degree of freedom are at the heart of\nfundamental phenomena, ranging from magnetism to superconductivity. The effects\nof correlations depend strongly on dimensionality, a striking example being\none-dimensional (1D) electronic systems, extensively studied theoretically over\nthe past fifty years. However, the experimental investigation of the role of\nspin multiplicity in 1D fermions - and especially for more than two spin\ncomponents - is still lacking. Here we report on the realization of 1D,\nstrongly-correlated liquids of ultracold fermions interacting repulsively\nwithin SU(N) symmetry, with a tunable number N of spin components. We observe\nthat static and dynamic properties of the system deviate from those of ideal\nfermions and, for N>2, from those of a spin-1/2 Luttinger liquid. In the\nlarge-N limit, the system exhibits properties of a bosonic spinless liquid. Our\nresults provide a testing ground for many-body theories and may lead to the\nobservation of fundamental 1D effects.",
        "positive": "Three-dimensional droplets of swirling superfluids: A new method for the creation of 3D solitary topological modes, corresponding\nto vortical droplets of a two-component dilute superfluid, is presented. We use\nthe recently introduced system of nonlinearly coupled Gross-Pitaevskii\nequations, which include contact attraction between the components, and quartic\nrepulsion stemming from the Lee-Huang-Yang correction to the mean-field energy.\nSelf-trapped vortex tori, carrying the topological charges m1=m2=1 or m1=m2=2\nin their components, are constructed by means of numerical and approximate\nanalytical methods. The analysis reveals stability regions for the vortex\ndroplets (in broad and relatively narrow parameter regions for m1=m2=1 and\nm1=m2=2, respectively). The results provide the first example of stable 3D\nself-trapped states with the double vorticity, in any physical setting. The\nstable modes are shaped as flat-top ones, with the space between the inner\nhole, induced by the vorticity, and the outer boundary filled by a nearly\nconstant density. On the other hand, all modes with hidden vorticity, i.e.,\ntopological charges of the two components m1=-m2=1, are unstable. The stability\nof the droplets with m1=m2=1 against splitting (which is the main scenario of\npossible instability) is explained by estimating analytically the energy of the\nsplit and un-split states. The predicted results may be implemented, exploiting\ndilute quantum droplets in mixtures of Bose-Einstein condensates."
    },
    {
        "anchor": "Topological Phases for Fermionic Cold Atoms on the Lieb Lattice: We investigate the properties of the Lieb lattice, i.e a face-centered square\nlattice, subjected to external gauge fields. We show that an Abelian gauge\nfield leads to a peculiar quantum Hall effect, which is a consequence of the\nsingle Dirac cone and the flat band characterizing the energy spectrum. Then we\nexplore the effects of an intrinsic spin-orbit term - a non-Abelian gauge field\n- and demonstrate the occurrence of the quantum spin Hall effect in this model.\nBesides, we obtain the relativistic Hamiltonian describing the Lieb lattice at\nlow energy and derive the Landau levels in the presence of external Abelian and\nnon-Abelian gauge fields. Finally, we describe concrete schemes for realizing\nthese gauge fields with cold fermionic atoms trapped in an optical Lieb\nlattice. In particular, we provide a very efficient method to reproduce the\nintrinsic (Kane-Mele) spin-orbit term with assisted-tunneling schemes.\nConsequently, our model could be implemented in order to produce a variety of\ntopological states with cold-atoms.",
        "positive": "Optomechanical Generation of a photonic Bose-Einstein Condensate: We propose to thermalize a low-dimensional photon gas and obtain photon\nBose-Einstein condensation by optomechanical interactions in a microscopic\noptical cavity, with a single longitudinal mode and many transverse modes. The\ngeometry of the short cavity is such that it provides a low-frequency cutoff at\na photon energy far above the thermal energy, so that thermal emission of\nphotons is suppressed and the photon number is conserved. While previous\nexperiments on photon Bose-Einstein condensation have used dye molecules for\nphoton gas thermalization, we here investigate thermalization owing to\ninteractions with thermally fluctuating nanomechanical oscillators forming the\ncavity mirrors. In the quantum degenerate regime, the nanomechanical cavity\nconverts broadband optical radiation into tuneable coherent radiation."
    },
    {
        "anchor": "Spatial correlations of one dimensional driven-dissipative systems of\n  Rydberg atoms: We consider a one-dimensional lattice of atoms with laser excitation to a\nRydberg state and spontaneous emission. The atoms are coupled due to the\ndipole-dipole interaction of the Rydberg states. This driven-dissipative system\nhas a broad range of non-equilibrium phases, such as antiferromagnetic ordering\nand bistability. Using the quantum trajectory method, we calculate the spatial\ncorrelation function throughout the parameter space for up to 20 lattice sites.\nWe show that bistability significantly strengthens the spatial correlations and\nentanglement.",
        "positive": "Dynamics and Bloch oscillations of mobile impurities in one-dimensional\n  quantum liquids: We study dynamics of a mobile impurity moving in a one-dimensional quantum\nliquid. Such an impurity induces a strong non-linear depletion of the liquid\naround it. The dispersion relation of the combined object, called depleton, is\na periodic function of its momentum with the period 2\\pi n, where n is the mean\ndensity of the liquid. In the adiabatic approximation a constant external force\nacting on the impurity leads to the Bloch oscillations of the impurity around a\nfixed position. Dynamically such oscillations are accompanied by the radiation\nof energy in the form of phonons. The ensuing energy loss results in the\nuniform drift of the oscillation center. We derive exact results for the\nradiation-induced mobility as well as the thermal friction force in terms of\nthe equilibrium dispersion relation of the dressed impurity (depleton). These\nresults show that there is a wide range of external forces where the (drifted)\nBloch oscillations exist and may be observed experimentally."
    },
    {
        "anchor": "A manifestly Hermitian semiclassical expansion for the one-particle\n  density matrix of a two-dimensional Fermi gas: The semiclassical $\\hbar$-expansion of the one-particle density matrix for a\ntwo-dimensional Fermi gas is calculated within the Wigner transform method of\nGrammaticos and Voros, originally developed in the context of nuclear physics.\nThe method of Grammaticos and Voros has the virture of preserving both the\nHermiticity and idempotency of the density matrix to all orders in the\n$\\hbar$-expansion. As a topical application, we use our semiclassical expansion\nto go beyond the local-density approximation for the construction of the total\ndipole-dipole interaction energy functional of a two-dimensional,\nspin-polarized dipolar Fermi gas. We find a {\\em finite}, second-order gradient\ncorrection to the Hartree-Fock energy, which takes the form $\\varepsilon\n(\\nabla \\rho)^2/\\sqrt{\\rho}$, with $\\varepsilon$ being small ($|\\varepsilon|\n\\ll1$) and negative. We test the quality of the corrected energy by comparing\nit with the exact results available for harmonic confinement. Even for small\nparticle numbers, the gradient correction to the dipole-dipole energy provides\na significant improvement over the local-density approximation.",
        "positive": "Interacting bosons on a Su-Schrieffer-Heeger ladder: Topological phases\n  and Thouless pumping: We study the topological properties of hardcore bosons on a two-leg ladder\nconsisting of two Su-Schrieffer-Heeger (SSH) chains that are coupled via\nhopping and interaction. We chart out the phase diagram for the system and show\nthat based on the relative hopping dimerization pattern along the legs,\ndistinctly different topological phases and phase transitions can occur. When\nthe dimerization along the legs are uniform, we find that the topological\nnature vanishes for even the slightest rung hopping. For staggered\ndimerization, the system exhibits a well defined topological character and a\ntopological phase transition as a function of rung hopping. While the\ntopological phase shows bond order character, the trivial phase shows the\nbehavior of a rung-Mott insulator. For this case, the topological nature is\nfound to survive even in the presence of finite inter-leg interactions.\nMoreover, we find that the critical point of the topological phase transition\nshifts to a higher or a lower rung hopping strength depending on the attractive\nor repulsive nature of the interaction. To highlight the marked effects of\ninteractions, we propose a scheme involving a Thouless charge pump that\nprovides insights for the topological phases characterized by a quantised\nparticle transport through a periodic modulation of appropriate system\nparameters. In our studies, we show an interaction induced charge pumping\nfollowing specific pumping protocols in the case of staggered dimerization."
    },
    {
        "anchor": "Doubly Modulated Optical Lattice Clock Interference and Topology: The quantum system under periodical modulation is the simplest path to\nunderstand the quantum non-equilibrium system, because it can be well described\nby the effective static Floquet Hamiltonian. Under the stroboscopic\nmeasurement, the initial phase is usually irrelevant. However, if two\nuncorrelated parameters are modulated, their relative phase can not be gauged\nout, so that the physics can be dramatically changed. Here, we simultaneously\nmodulate the frequency of the lattice laser and the Rabi frequency in an\noptical lattice clock (OLC) system. Thanks to ultra-high precision and\nultra-stability of OLC, the relative phase could be fine-tuned. As a smoking\ngun, we observed the interference between two Floquet channels. Finally, by\nexperimentally detecting the eigen-energies, we demonstrate the relation\nbetween effective Floquet Hamiltonian and 1-D topological insulator with high\nwinding number. Our experiment not only provides a direction for detecting the\nphase effect, but also paves a way in simulating quantum topological phase in\nOLC platform.",
        "positive": "Properties of Nambu-Goldstone Bosons in a Single-Component Bose-Einstein\n  Condensate: We theoretically study the properties of Nambu-Goldstone bosons in an\ninteracting single-component Bose-Einstein condensate (BEC). We first point out\nthat the proofs of Goldstone's theorem by Goldstone, et al. [Phys. Rev. {\\bf\n127} (1962) 965] may be relevant to distinct massless modes of the BEC: whereas\nthe first proof deals with the poles of the single-particle Green's function\n$\\hat{G}$, the second one concerns those of the two-particle Green's function.\nThus, there may be multiple Nambu-Goldstone bosons even in the single-component\nBEC with broken U(1) symmetry. The second mode turns out to have an infinite\nlifetime in the long-wavelength limit in agreement with the conventional\nviewpoint. In contrast, the first mode from $\\hat{G}$, i.e., the Bogoliubov\nmode in the weak-coupling regime, is shown to be a \"bubbling\" mode fluctuating\ntemporally out of and back into the condensate. The substantial lifetime\noriginates from an \"improper\" structure of the self-energy inherent in the BEC,\nwhich has been overlooked so far and will be elucidated here, and removes\nvarious infrared divergences pointed out previously."
    },
    {
        "anchor": "Searching for Supersolidity in Ultracold Atomic Bose Condensates with\n  Rashba Spin-Orbit Coupling: We developed functional integral formulation for the stripe phase of a spinor\nBose-Einstein condensates with Rashba spin-orbit coupling. The excitation\nspectrum is found to exhibit double gapless band structures, identified to be\ntwo Goldstone modes resulting from spontaneously broken internal gauge symmetry\nand translational invariance symmetry. The sound velocities display anisotropic\nbehaviors with the lower branch vanishes in the direction perpendicular to the\nstripe in the x-y plane. At the transition point between the plane wave phase\nand the stripe phase, physical quantities such as fluctuation correction to the\nground state energy and quantum depletion of the condensates exhibit\ndiscontinuity, characteristic of the first order phase transition. Despite\nstrong quantum fluctuations induced by Rashba spin-orbit coupling, we show that\nthe supersolid phase is stable against quantum depletion. Finally we extend our\nformulation to finite temperatures to account for interactions between\nexcitations.",
        "positive": "Optical lattice for tripod-like atomic level structure: Standard optical potentials use off-resonant laser standing wave induced\nAC-Stark shift. In a recent development [Phys. Rev. Lett. {\\bf 117}, 233001\n(2016)] a three-level scheme in $\\Lambda$ configuration coupled coherently by\nresonant laser fields was introduced leading to an effective lattice with\nsubwavelength potential peaks. Here as an extension of that work to a four\nlevel atomic setup in the tripod configuration is used to create spin\n$1/2$-like two-dimensional dark-space with 1D motion and the presence of\nexternal gauge fields. Most interestingly for a possible application, the\nlifetime for a dark subspace motion is up to two orders of magnitude larger\nthan for a similar $\\Lambda$ system. The model is quite flexible leading to\nlattices with significant nearest, next-nearest, or next-next-nearest hopping\nrates, $J_1,J_2,J_3$ opening up new intriguing possibilities to study, e.g.\nfrustrated systems. The characteristic Wannier functions lead also to new type\nof inter-site interactions not realizable in typical optical lattices."
    },
    {
        "anchor": "Entanglement properties of the critical quench of O(N) bosons: The entanglement properties of quenched quantum systems have been studied for\na decade, however results in dimensions other than $d=1$ are generally lacking.\nWe remedy this by investigating the entanglement properties of bosonic critical\nsystems in $d=3$, both numerically and analytically, comparing the free and the\ninteracting critical quench of an $O(N)$ model. We find that the evolution of\nthe entanglement entropy for these two systems is nearly identical, as expected\nfrom the \"quasi-particle\" picture. However, the low-lying entanglement spectrum\nis controlled by the different critical exponent of the two systems, and\ntherefore these exponents may be extracted by purely entanglement-theoretic\ncalculations. We verify this scaling numerically.",
        "positive": "Resonantly enhanced superconductivity mediated by spinor condensates: Achieving strong interactions in fermionic many-body systems is a major theme\nof research in condensed matter physics. It is well-known that interactions\nbetween fermions can be mediated through a bosonic medium, such as a phonon\nbath or Bose-Einstein condensate (BEC). Here, we show that such induced\nattraction can be resonantly enhanced when the bosonic medium is a\ntwo-component spinor BEC. The strongest interaction is achieved by tuning the\nboson-boson scattering to the quantum critical spinodal point of the BEC where\nthe sound velocity vanishes. The fermion pairing gap and the superconducting\ncritical temperature can thus be dramatically enhanced. We propose two\nexperimental realizations of this scenario, with exciton-polariton systems in\ntwo-dimensional semiconductors and ultracold atomic Bose-Fermi mixtures."
    },
    {
        "anchor": "Discontinuities in the First and Second Sound Velocities at the\n  Berezinskii-Kosterlitz-Thouless Transition: We calculate the temperature dependence of the first and second sound\nvelocities in the superfluid phase of a 2D dilute Bose gas by solving Landau's\ntwo fluid hydrodynamic equations. We predict the occurrence of a significant\ndiscontinuity in both velocities at the critical temperature, as a consequence\nof the jump of the superfluid density characterizing the\nBerezinskii-Kosterlitz-Thouless transition. The key role of the thermal\nexpansion coefficient is discussed. We find that second sound in this dilute\nBose gas can be easily excited through a density perturbation, thereby, making\nthe perspective of the measurement of the superfluid density particularly\nfavorable.",
        "positive": "Born-Oppenheimer description of two atoms in a combined oscillator and\n  lattice trap: We analyze the quantum states of two atoms in a combined harmonic oscillator\nand periodic lattice trap in one spatial dimension. In the case of\ntight-binding and only nearest neighbor tunneling, the equations of motion are\nconveniently represented in the momentum representation. We show that in the\ncase of strong attraction between the particles, the different time scales of\nrelative and center-of-mass motion validate a separation of the problem similar\nto the Born-Oppenheimer approximation applied in the description of electronic\nand nuclear motion in molecules."
    },
    {
        "anchor": "Finite-temperature dynamics of a Tonks-Girardeau gas in a\n  frequency-modulated harmonic trap: We study the out-of-equilibrium dynamics of a finite-temperature harmonically\ntrapped Tonks-Girardeau gas induced by periodic modulation of the trap\nfrequency. We give explicit exact solutions for the real-space density and\nmomentum distributions of this interacting many-body system and characterize\nthe stability diagram of the dynamics by mapping the many-body solution to the\nsolution and stability diagram of Mathieu's differential equation. The mapping\nallows one to deduce the exact structure of parametric resonances in the\nparameter space characterized by the driving amplitude and frequency of the\nmodulation. Furthermore, we analyze the same problem within the\nfinite-temperature hydrodynamic approach and show that the respective solutions\nto the hydrodynamic equations can be mapped to the same Mathieu equation.\nAccordingly, the stability diagram and the structure of resonances following\nfrom the hydrodynamic approach is exactly the same as those obtained from the\nexact many-body solution.",
        "positive": "Hydrodynamic equation of a spinor dipolar Bose-Einstein condensate: We introduce equations of motion for spin dynamics in a ferromagnetic\nBose-Einstein condensate with magnetic dipole-dipole interaction, written using\na vector expressing the superfluid velocity and a complex scalar describing the\nmagnetization. This simple hydrodynamical description extracts the dynamics of\nspin wave and affords a straightforward approach by which to investigate the\nspin dynamics of the condensate. To demonstrate the advantages of the\ndescription, we illustrate dynamical instability and magnetic fluctuation\npreference, which are expressed in analytical forms."
    },
    {
        "anchor": "Rydberg-dressing of atoms in optical lattices: We study atoms in optical lattices whose electronic ground state is\noff-resonantly coupled to a highly excited state with strong binary\ninteractions. We present a time-dependent treatment of the resulting quantum\ndynamics, which -- contrary to recent predictions [Phys. Rev. Lett. 110, 213005\n(2013)] -- proves that the strong repulsion between the weakly admixed Rydberg\nstates does not lead to atomic trap-loss. This finding provides an important\nbasis for creating and manipulating coherent long-range interactions in optical\nlattice experiments.",
        "positive": "Quantum Brownian Motion with Inhomogeneous Damping and Diffusion: We analyze the microscopic model of quantum Brownian motion, describing a\nBrownian particle interacting with a bosonic bath through a coupling which is\nlinear in the creation and annihilation operators of the bath, but may be a\nnonlinear function of the position of the particle. Physically, this\ncorresponds to a configuration in which damping and diffusion are spatially\ninhomogeneous. We derive systematically the quantum master equation for the\nBrownian particle in the Born-Markov approximation and we discuss the\nappearance of novel terms, for various polynomials forms of the coupling. We\ndiscuss the cases of linear and quadratic coupling in great detail and we\nderive, using Wigner function techniques, the stationary solutions of the\nmaster equation for a Brownian particle in a harmonic trapping potential. We\npredict quite generally Gaussian stationary states, and we compute the aspect\nratio and the spread of the distributions. In particular, we find that these\nsolutions may be squeezed (super-localized) with respect to the position of the\nBrownian particle. We analyze various restrictions to the validity of our\ntheory posed by non-Markovian effects and by the Heisenberg principle. We\nfurther study the dynamical stability of the system, by applying a Gaussian\napproximation to the time dependent Wigner function, and we compute the\ndecoherence rates of coherent quantum superpositions in position space.\nFinally, we propose a possible experimental realization of the physics\ndiscussed here, by considering an impurity particle embedded in a degenerate\nquantum gas."
    },
    {
        "anchor": "The effects of disorder in dimerized quantum magnets in mean field\n  approximations: We study theoretically the effects of disorder on Bose-Einstein condensates\n(BEC) of bosonic triplon quasiparticles in doped dimerized quantum magnets. The\ncondensation occurs in a strong enough magnetic field Hc, where the\nconcentration of bosons in the random potential is sufficient to form the\ncondensate. The effect of doping is partly modeled by delta - correlated\ndisorder potential, which (i) leads to the uniform renormalization of the\nsystem parameters and (ii) produces disorder in the system with renormalized\nparameters. These approaches can explain qualitatively the available\nmagnetization data in the Tl_(1-x)K_(x)CuCl_3 compound taken as an example. In\naddition to the magnetization, we found that the speed of the Bogoliubov mode\nhas a peak as a function of doping parameter, x. No evidence of the pure Bose\nglass phase has been obtained in the BEC regime.",
        "positive": "Efimov scenario for overlapping narrow Feshbach resonances: While Efimov physics in ultracold atoms is usually modeled with an isolated\nFeshbach resonance many real world resonances appear in close vicinity to each\nother and are therefore overlapping. Here we derive a realistic model based on\nthe mutual coupling of an open channel and two closed molecular channels while\nneglecting short-range physics as permitted by the narrow character of the\nconsidered resonances. The model is applied to three distinct scenarios with\nexperimental relevance. We show that the effect of overlapping resonances is\nmanifested most strikingly at a narrow resonance in whose vicinity there is a\nslightly narrower one. In this system the Efimov ground state extends not only\nover the scattering length zero crossing between the two resonances but also\nover the pole of the second resonance to finally meet the dissociation\nthreshold below it. In the opposite scenario, when a narrow resonance is\nconsidered in the vicinity of a slightly broader one, we observe that the\nEfimov features are pushed to lower binding energies and smaller scattering\nlengths by a significant factor facilitating their experimental investigation.\nBoth scenarios are referenced to the case of two narrow resonances which are\nfar enough away from each other to be effectively decoupled. In this case the\ntwo-channel model results are recovered. Finally, we analyze the rich\nexcitation spectrum of the system and construct and explain its nodal pattern."
    },
    {
        "anchor": "Temporal quantum fluctuations in the fringe-visibility of atom\n  interferometers with interacting Bose-Einstein condensate: We formulate a semiclassical approach to study the dynamics of coherence loss\nand revival in a Bose-Josephson dimer. The phase-space structure of the\nbi-modal system in the Rabi, Josephson, and Fock interaction regimes, is\nreviewed and the prescription for its WKB quantization is specified. The local\ndensity of states (LDOS) is then deduced for any given preparation from its\nsemiclassical projection onto the WKB eigenstates. The LDOS and the non-linear\nvariation of its level-spacing are employed to construct the time evolution of\nthe initial preparation and study the temporal fluctuations of interferometric\nfringe visibility. The qualitative behavior and characteristic timescales of\nthese fluctuations are set by the pertinent participation number, quantifying\nthe spectral content of the preparation. We employ this methodology to study\nthe Josephson-regime coherence dynamics of several initial state preparations,\nincluding a Twin-Fock state and three different coherent states that we denote\nas 'Zero', 'Pi', and 'Edge' (the latter two are both on-separatrix\npreparations, while the Zero is the standard ground sate preparation). We find\na remarkable agreement between the semiclassical predictions and numerical\nsimulations of the full quantum dynamics. Consequently, a characteristic\ndistinct behavior is implied for each of the different preparations.",
        "positive": "Reshaped Three-Body Interactions and the Observation of an Efimov State\n  in the Continuum: Efimov trimers are exotic three-body quantum states that emerge from the\ndifferent types of three-body continua in the vicinity of two-atom Feshbach\nresonances. In particular, as the strength of the interaction is decreased to a\ncritical point, an Efimov state merges into the atom-dimer threshold and\neventually dissociates into an unbound atom-dimer pair. Here we explore the\nEfimov state in the vicinity of this critical point using coherent few-body\nspectroscopy in $^7$Li atoms using a narrow two-body Feshbach resonance.\nContrary to the expectation, we find that the $^7$Li Efimov trimer does not\nimmediately dissociate when passing the threshold, and survives as a metastable\nstate embedded in the atom-dimer continuum. We identify this behavior with a\nuniversal phenomenon related to the emergence of a repulsive interaction in the\natom-dimer channel which reshapes the three-body interactions in any system\ncharacterized by a narrow Feshbach resonance. Specifically, our results shed\nlight on the nature of $^7$Li Efimov states and provide a path to understand\nvarious puzzling phenomena associated with them."
    },
    {
        "anchor": "Noise correlations in the expansion of an interacting 1D Bose gas from a\n  regular array: We consider the one dimensional expansion of a system of interacting bosons,\nstarting from a regular array. Without interactions the familiar Hanbury Brown\nand Twiss effect for bosons gives rise to a series of peaks in the\ndensity-density correlations of the expanded system. Infinitely repulsive\nparticles likewise give a series of dips, a signature of the underlying\ndescription in terms of free fermions. In the intermediate case of finite\ninteraction the noise correlations consist of a set of Fano resonance\nlineshapes, with an asymmetry parameter determined by the scattering phase\nshift of a pair of particles, and a width depending on the initial momentum\nspread of the particles.",
        "positive": "Geometric squeezing of rotating quantum gases into the lowest Landau\n  level: The simulation of quantum Hall physics with rotating quantum gases is\nwitnessing a revival due to recent experimental advances that enabled the\nobservation of a Bose-Einstein condensate entirely contained in its lowest\nkinetic energy state, i.e. the lowest Landau level. We theoretically describe\nthis experimental result, and show that it can be interpreted as a squeezing of\nthe geometric degree of freedom of the problem, the guiding center metric. This\n\"geometric squeezing\" offers an unprecedented experimental control over the\nquantum geometry in Landau-level analogues, and at the same time opens a\nrealistic path towards achieving correlated quantum phases akin to quantum Hall\nstates with neutral atoms."
    },
    {
        "anchor": "AtomECS: Simulate laser cooling and magneto-optical traps: AtomECS is a software package that efficiently simulates the motion of\nneutral atoms experiencing forces exerted by laser radiation, such as in\nmagneto-optical traps and Zeeman slowers. The program is implemented using the\nEntity-Component-System pattern, which gives excellent performance, flexibility\nand scalability to parallel computing resources. The simulation package has\nbeen verified by comparison to analytic results, and extensively unit tested.",
        "positive": "Numerical study of localized impurity in a Bose-Einstein condensate: Motivated by recent experiments, we investigate a single $^{133}\\text{Cs}$\nimpurity in the center of a trapped $^{87}\\text{Rb}$ Bose-Einstein condensate.\nWithin a zero-temperature mean-field description we provide a one-dimensional\nphysical intuitive model which involves two coupled differential equations for\nthe condensate and the impurity wave function, which we solve numerically. With\nthis we determine within the equilibrium phase diagram spanned by the intra-\nand inter-species coupling strength, whether the impurity is localized at the\ntrap center or expelled to the condensate border. In the former case we find\nthat the impurity induces a bump or dip on the condensate for an attractive or\na repulsive Rb-Cs interaction strength, respectively. Conversely, the\ncondensate environment leads to an effective mass of the impurity which\nincreases quadratically for small interspecies interaction strength.\nAfterwards, we investigate how the impurity imprint upon the condensate wave\nfunction evolves for two quench scenarios. At first we consider the case that\nthe harmonic confinement is released. During the resulting time-of-flight\nexpansion it turns out that the impurity-induced bump in the condensate wave\nfunction starts decaying marginally, whereas the dip decays with a\ncharacteristic time scale which decreases with increasing repulsive\nimpurity-BEC interaction strength. Secondly, once the attractive or repulsive\ninterspecies coupling constant is switched off, we find that white-shock waves\nor bi-solitons emerge which both oscillate within the harmonic confinement with\na characteristic frequency."
    },
    {
        "anchor": "Dynamics in spinor condensates controlled by a microwave dressing field: We experimentally study spin dynamics in a sodium antiferromagnetic spinor\ncondensate with off-resonant microwave pulses. In contrast to a magnetic field,\na microwave dressing field enables us to explore rich spin dynamics under the\ninfluence of a negative net quadratic Zeeman shift $q_{\\rm net}$. We find an\nexperimental signature to determine the sign of $q_{\\rm net}$, and observe\nharmonic spin population oscillations at every $q_{\\rm net}$ except near each\nseparatrix in phase space where spin oscillation period diverges. In the\nnegative and positive $q_{\\rm net}$ regions, we also observe a remarkably\ndifferent relationship between each separatrix and the magnetization. Our data\nconfirms an important prediction derived from the mean-field theory:\nspin-mixing dynamics in spin-1 condensates substantially depends on the sign of\nthe ratio of $q_{\\rm net}$ and the spin-dependent interaction energy. This work\nmay thus be the first to use only one atomic species to reveal mean-field spin\ndynamics, especially the separatrix, which are predicted to appear differently\nin spin-1 antiferromagnetic and ferromagnetic spinor condensates.",
        "positive": "Supersolid Devil's Staircases of Spin-Orbit-Coupled Bosons in Optical\n  Lattices: We study the emergence of supersolid Devil's staircases of spin-orbit coupled\nbosons loaded in optical lattices. We consider two- and three-dimensional\nsystems of pseudo-spin-$1/2$ bosons interacting via local spin-dependent\ninteractions. These interactions together with spin-orbit coupling produce\nlength scales that are commensurate to the lattice spacing. This\ncommensurability leads to Devil's staircases of supersolids, with fractal\nHausdorff dimensions, which arise from uniform superfluid phases. We show that\numklapp processes are essential for the existence of commensurate supersolids,\nand that without them the Devil's staircase does not exist. Lastly, we\nemphasize the generality of our results, suggest experiments that can unveil\nthese unusual predictions, and discuss potential applications to the case of\n$^{87}$Rb."
    },
    {
        "anchor": "Multichannel Molecular State and Rectified Short-range Boundary\n  Condition for Spin-orbit Coupled Ultracold Fermions Near p-wave Resonances: We study the interplay of spin-orbit coupling (SOC) and strong p-wave\ninteraction to the scattering property of spin-1/2 ultracold Fermi gases. Based\non a two-channel square-well potential generating p-wave resonance, we show\nthat the presence of an isotropic SOC, even for its length much longer than the\npotential range, can greatly modify the p-wave short-range boundary\ncondition(BC). As a result, the conventional p-wave BC cannot predict the\ninduced molecules near p-wave resonance, which can be fully destroyed to vanish\ndue to strong interference between s- and p-wave channels. By analyzing the\nintrinsic reasons for the breakdown of conventional BC, we propose a new p-wave\nBC that can excellently reproduce the exact molecule solutions and also equally\napply for a wide class of single-particle potentials besides SOC. This work\nreveals the significant effect of SOC to both the short- and long-range\nproperties of fermions near p-wave resonance, paving the way for future\nexploring interesting few- and many-body physics in such system.",
        "positive": "Control of spin current in a Bose gas by bang-bang pulses: We generate spin currents in an $^{87}$Rb spin-2 Bose-Einstein condensate by\napplication of a magnetic field gradient. The spin current destroys the spin\npolarization, leading to a sudden onset of two-body collisions. In addition,\nthe spin coherence, as measured by the fringe contrast using Ramsey\ninterferometry, is reduced drastically but experiences a weak revival due to\nin-trap oscillations. The spin current can be controlled using periodic $\\pi$\npulses (bang-bang control), producing longer spin coherence times. Our results\nshow that spin coherence can be maintained even in the presence of spin\ncurrents, with applications to quantum sensing in noisy environments."
    },
    {
        "anchor": "Bose Hubbard model far from equilibrium: We study the nonequilibrium steady state of the Bose Hubbard model coupled to\nLindblad reservoirs, using the density matrix renormalization group in operator\nspace. We observe a transition from a flat particle density profile in the\nnoninteracting limit to the linear profile with onset of the interparticle\ninteraction. Analyzing the effect of coherent pumping on the nonequilibrium\nsteady state we find a subspace which remains unaffected by the pumping in the\nnoninteracting limit with the protection gradually diminishing due to\ninterparticle interaction. In the equilibrium situation with one or more\nsymmetric reservoirs we show analytically that the steady state of the system\nis a product state for any interaction strength. We also provide analytical\nresults in the noninteracting limits, using the method of the third\nquantization in operator space.",
        "positive": "Coupled pair approach for strongly-interacting trapped fermionic atoms: We present a coupled pair approach for studying few-body physics in\nharmonically trapped ultracold gases. The method is applied to a two-component\nFermi system of $N$ particles. A stochastically variational gaussian expansion\nmethod is applied, focusing on optimization of the two-body correlations\npresent in the strongly interacting, or unitary, limit. The groundstate energy\nof the four-, six- and eight-body problem with equal spin populations is\ncalculated with high accuracy and minimal computational effort. We also\ncalculate the structural properties of these systems and discuss their\nimplication for the many-body ultracold gas and other few-body calculations."
    },
    {
        "anchor": "Energy Cascade in Quantum Gases: Energy cascade is ubiquitous in systems far from equilibrium. Facilitated by\nparticle interactions and external forces, it can lead to highly complex\nphenomena like fully developed turbulence, characterized by power law velocity\ncorrelation functions. Yet despite decades of research, how these power laws\nemerge from first principle remains unclear. Recently, experiments show that\nwhen a Bose condensate is subjected to periodic shaking, its momentum\ndistribution exhibits a power law behavior. The flexibility of cold atom\nexperiments has provided new opportunities to explore the emergence of these\npower laws, and to disentangle different sources of energy cascade. Here, we\npoint out that recent experiments in cold atoms imply that classical turbulence\nis part of a larger family of scale invariant phenomena that include ideal\ngases. Moreover, the property of the entire family is contained in the\nstructure of its Floquet states. For ideal gases, we show analytically that its\nmomentum distribution acquires a $1/q^2$ tail in each dimension when it is\nshaken periodically.",
        "positive": "Quantum stabilization of photonic spatial correlations: The driven, dissipative Bose-Hubbard model (BHM) provides a generic\ndescription of collective phases of interacting photons in cavity arrays. In\nthe limit of strong optical nonlinearities (hard-core limit), the BHM maps on\nthe dissipative, transverse-field XY model (XYM). The steady-state of the XYM\ncan be analyzed using mean-field theory, which reveals a plethora of\ninteresting dynamical phenomena. For example, strong hopping combined with a\nblue-detuned drive, leads to an instability of the homogeneous steady-state\nwith respect to antiferromagnetic fluctuations. In this paper, we address the\nquestion whether such an antiferromagnetic instability survives in the presence\nof quantum correlations beyond the mean-field approximation. For that purpose,\nwe employ a self-consistent $1/z$ expansion for the density matrix, where $z$\nis the lattice coordination number, i.e., the number of nearest neighbours for\neach site. We show that quantum fluctuations stabilize a new homogeneous\nsteady-state with antiferromagnetic correlations in agreement with exact\nnumerical simulations for finite lattices. The latter manifests itself as\nshort-ranged oscillations of the first and second-order spatial coherence\nfunctions of the photons emitted by the array."
    },
    {
        "anchor": "Order from chaos: Observation of large-scale flow from turbulence in a\n  two-dimensional superfluid: Interacting systems driven far from equilibrium tend to evolve to steady\nstates exhibiting large-scale structure and order. In two-dimensional turbulent\nflow the seemingly random swirling motion of a fluid can evolve towards\npersistent large-scale vortices. Lars Onsager proposed a model based on\nstatistical mechanics of quantized vortices to explain such behavior. Here we\nreport the first experimental confirmation of Onsager's model of turbulence. We\ndrag a grid barrier through an oblate superfluid Bose--Einstein condensate to\ngenerate non-equilibrium distributions of vortices. We observe an inverse\nenergy cascade driven by the evaporative heating of vortices, leading to\nsteady-state configurations characterized by negative temperatures. Our results\nopen a pathway for quantitative studies of emergent structures in interacting\nquantum systems driven far from equilibrium.",
        "positive": "Crossover from 2D to 3D in a weakly interacting Fermi gas: We have studied the transition from two to three dimensions in a low\ntemperature weakly interacting $^6$Li Fermi gas. Below a critical atom number,\n$N_{2D}$, only the lowest transverse vibrational state of a highly anisotropic\noblate trapping potential is occupied and the gas is two-dimensional. Above\n$N_{2D}$ the Fermi gas enters the quasi-2D regime where shell structure\nassociated with the filling of individual transverse oscillator states is\napparent. This dimensional crossover is demonstrated through measurements of\nthe cloud size and aspect ratio versus atom number."
    },
    {
        "anchor": "Excitation spectrum of the Lieb-Liniger model: We study the integrable model of one-dimensional bosons with contact\nrepulsion. In the limit of weak interaction, we use the microscopic\nhydrodynamic theory to obtain the excitation spectrum. The statistics of\nquasiparticles changes with the increase of momentum. At lowest momenta good\nquasiparticles are fermions, while at higher momenta they are Bogoliubov\nbosons, in accordance with recent studies. In the limit of strong interaction,\nwe analyze the exact solution and find exact results for the spectrum in terms\nof the asymptotic series. Those results undoubtedly suggest that fermionic\nquasiparticle excitations actually exist at all momenta for moderate and strong\ninteraction, and also at lowest momenta for arbitrary interaction. Moreover, at\nstrong interaction we find highly accurate analytical results for several\nrelevant quantities of the Lieb-Liniger model.",
        "positive": "Production of large Bose-Einstein condensates in a\n  magnetic-shield-compatible hybrid trap: We describe the production of large ${}^{23} \\mathrm{Na}$ Bose-Einstein\ncondensates in a hybrid trap characterized by a weak magnetic field quadrupole\nand a tightly focused infrared beam. The use of small magnetic field gradients\nmakes the trap compatible with the state-of-the-art magnetic shields. By taking\nadvantage of the deep cooling and high efficiency of gray molasses to improve\nthe initial trap loading conditions, we produce condensates composed of as much\nas $7$ million atoms in less than $30 \\; \\mathrm{s}$."
    },
    {
        "anchor": "Momentum-space Aharonov-Bohm interferometry in Rashba spin-orbit coupled\n  Bose-Einstein condensates: Since the recent experimental realization of synthetic Rashba spin-orbit\ncoupling paved a new avenue for exploring and engineering topological phases in\nultracold atoms, a precise, solid detection of Berry phase has been desired for\nunequivocal characterization of system topology. Here, we propose a scheme to\nconduct momentum-space Aharonov-Bohm interferometry in a Rashba spin-orbit\ncoupled Bose-Einstein condensate with a sudden change of in-plane Zeeman field,\ncapable of measuring the Berry phase of Rashba energy bands. We find that the\nBerry phase with the presence of a Dirac point is directly revealed by a robust\ndark interference fringe, and that as a function of external Zeeman field is\ncharacterized by the contrast of fringes. We also build a variational model\ndescribing the interference process with semiclassical equations of motion of\nessential dynamical quantities, which lead to agreeable trajectories and\ngeometric phases with the real-time simulation of Gross-Pitaevskii equation.\nOur study would provide timely guidance for the experimental detection of Berry\nphase in ultracold atomic systems and help further investigation on their\ninterference dynamics in momentum space.",
        "positive": "Universal Dynamic Scaling and Contact Dynamics in Quenched Quantum Gases: Recently universal dynamic scaling is observed in several systems, which\nexhibit a spatiotemporal self-similar scaling behavior, analogous to the\nspatial scaling near phase transitions. The latter arises from the emergent\ncontinuous scaling symmetry due to the divergent correlation length. Motivated\nby this, we investigate the relation between the scaling dynamics and\ncontinuous scaling symmetry. We derive a theorem that the scaling invariance of\nthe quenched Hamiltonian and the initial density matrix can lead to the\nuniversal dynamic scaling in quench dynamics. It is demonstrated both in the\ntwo-body problem analytically and in the many-body problem numerically. For the\nlatter one, we calculate the dynamics of quantum gases quenched from\nnoninteracting to finite interaction in the framework of non-equilibrium\nhigh-temperature virial expansion. A dynamic scaling of the momentum\ndistribution appears in certain momentum-time windows at unitarity as well as\nin the weak interacting limit. Remarkably, this universal scaling dynamics\npersists approximately with smaller scaling exponents even if the scaling\nsymmetry is fairly broken. Our findings may offer a new perspective to\ninterpret the related experiments. We also calculate the Contact dynamics in\nthe BEC-BCS crossover. Surprisingly, the half-way time displays a maximum near\nunitarity while some damping oscillations occur on the BEC side due to the\ndimer state, which can be used to detect possible two-body bound states in\nexperiments."
    },
    {
        "anchor": "Self-bound ultra dilute Bose mixtures within Local Density Approximation: We have investigated self-bound binary ultra dilute bosonic mixtures at zero\ntemperature within Density Functional Theory using a Local Density\nApproximation. We provide the explicit expression of the Lee-Huang-Yang\ncorrection in the general case of heteronuclear mixtures, and investigate the\ngeneral thermodynamic conditions which lead to the formation of self-bound\nsystems. We have determined the conditions for stability against the\nevaporation of one component, as well as the mechanical and diffusive spinodal\nlines. We have also calculated the surface tension of the self-bound state as a\nfunction of the inter-species interaction strength. We find that relatively\nmodest changes of the latter result in order-of-magnitude changes in the\ncalculated surface tension. We suggest experimental realizations which might\ndisplay the metastability and phase separation of the mixture when entering\nregions of the phase diagram characterized by negative pressures. Finally, we\nshow that these droplets may sustain stable vortex and vortex dimers.",
        "positive": "Evolution of the unitary Bose gas for broad to narrow Feshbach\n  resonances: We study the post-quench dynamics of unitary Bose gases using a two-channel\nmodel, focusing on the effect of variations in the width of the Feshbach\nresonance due to density changes. We generally find that increasing the density\nleads to a corresponding increase in the production of closed channel\nmolecules, a decrease in the build up of quantum depletion and a transition\nfrom linear to quadratic early-time growth of the two-body contact as well as\nthe condensed pair fraction. Motivated by the presence of closed-channel\nmolecules in the unitary regime, we study the embedded two-body problem finding\na transition from open to closed-channel dominated dimers due to many-body\neffects."
    },
    {
        "anchor": "Exact density profiles and symmetry classification for strongly\n  interacting multi-component Fermi gases in tight waveguides: We consider a mixture of one-dimensional strongly interacting Fermi gases up\nto six components, subjected to a longitudinal harmonic confinement. In the\nlimit of infinitely strong repulsions we provide an exact solution which\ngeneralizes the one for the two-component mixture. We show that an imbalanced\nmixture under harmonic confinement displays partial spatial separation among\nthe components, with a structure which depends on the relative population of\nthe various components. Furthermore, we provide a symmetry characterization of\nthe ground and excited states of the mixture introducing and evaluating a\nsuitable operator, namely the conjugacy class sum. We show that, even under\nexternal confinement, the gas has a definite symmetry which corresponds to the\nmost symmetric one compatible with the imbalance among the components. This\ngeneralizes the predictions of the Lieb-Mattis theorem for a fermionic mixture\nwith more than two components.",
        "positive": "Critical behavior of an impurity at the boson superfluid-Mott insulator\n  transition: We present a universal theory for the critical behavior of an impurity at the\ntwo-dimensional superfluid-Mott insulator transition. Our analysis is motivated\nby a numerical study of the Bose-Hubbard model with an impurity site by Huang\net al. (Phys. Rev. B 94, 220502 (2016)), who found an impurity phase transition\nas a function of the trapping potential. The bulk theory is described by the\n$O(2)$ symmetric Wilson-Fisher conformal field theory, and we model the\nimpurity by a localized spin-1/2 degree of freedom. We also consider a\ngeneralized model by considering an $O(N)$ symmetric bulk theory coupled to a\nspin-$S$ degree of freedom. We study this field theory using the $\\epsilon = 3\n- d$ expansion, where the impurity-bulk interaction flows to an infrared stable\nfixed point at the critical trapping potential. We determine the scaling\ndimensions of the impurity degree of freedom and the associated critical\nexponents near the critical point. We also determine the universal contribution\nof the impurity to the finite temperature compressibility of the system at\ncriticality. Our results are compared with recent numerical simulations."
    },
    {
        "anchor": "Observation of the phononic Lamb shift with a synthetic vacuum: The quantum vacuum fundamentally alters the properties of embedded particles.\nIn contrast to classical empty space, it allows for creation and annihilation\nof excitations. For trapped particles this leads to a change in the energy\nspectrum, known as Lamb shift. Here, we engineer a synthetic vacuum building on\nthe unique properties of ultracold atomic gas mixtures. This system makes it\npossible to combine high-precision spectroscopy with the ability of switching\nbetween empty space and quantum vacuum. We observe the phononic Lamb shift, an\nintruiguing many-body effect orginally conjectured in the context of solid\nstate physics. Our study therefore opens up new avenues for high-precision\nbenchmarking of non-trivial theoretical predictions in the realm of the quantum\nvacuum.",
        "positive": "Multigrid Algorithms for Tensor Network States: The widely used density matrix renormalization group (DRMG) method often\nfails to converge in systems with multiple length scales, such as lattice\ndiscretizations of continuum models and dilute or weakly doped lattice models.\nThe local optimization employed by DMRG to optimize the wave function is\nineffective in updating large-scale features. Here we present a multigrid\nalgorithm that solves these convergence problems by optimizing the wave\nfunction at different spatial resolutions. We demonstrate its effectiveness by\nsimulating bosons in continuous space, and study non-adiabaticity when ramping\nup the amplitude of an optical lattice. The algorithm can be generalized to\ntensor network methods, and be combined with the contractor renormalization\ngroup (CORE) method to study dilute and weakly doped lattice models."
    },
    {
        "anchor": "The two-atom energy spectrum in a harmonic trap near a Feshbach\n  resonance at higher partial waves: Two atoms in an optical lattice may be made to interact strongly at higher\npartial waves near a Feshbach resonance. These atoms, under appropriate\nconstraints, could be bosonic or fermionic. The universal $l=2$ energy spectrum\nfor such a system, with a caveat, is presented in this paper, and checked with\nthe spectrum obtained by direct numerical integration of the Schr\\\"odinger\nequation. The results reported here extend those of Yip for p-wave resonance\n(Phys. Rev. A {\\bf 78}, 013612 (2008)), while exploring the limitations of a\nuniversal expression for the spectrum for the higher partial waves.",
        "positive": "Quantum many-body thermal machines enabled by atom-atom correlations: Particle-particle correlations, characterized by the second-order Glauber\ncorrelation function, play an important role in the understanding of various\nphenomena in radio and optical astronomy, quantum and atom optics, particle\nphysics, condensed matter physics, and quantum many-body theory. However, the\nrelevance of such correlations to quantum thermodynamics has so far remained\nillusive. Here, we propose and investigate a class of quantum many-body thermal\nmachines whose operation is directly enabled by second-order atom-atom\ncorrelations in an ultracold atomic gas. More specifically, we study quantum\nthermal machines that operate in a sudden interaction-quench Otto cycle and\nutilize a one-dimensional Lieb-Liniger gas of repulsively interacting bosons as\nthe working fluid. The atom-atom correlations in such a gas are different to\nthose of a classical ideal gas, and are a result of the interplay between\ninterparticle interactions, quantum statistics, and thermal fluctuations. We\nshow that operating these thermal machines in the intended regimes, such as a\nheat engine, refrigerator, thermal accelerator, or heater, would be impossible\nwithout such atom-atom correlations. Our results constitute a step forward in\nthe design of conceptually new quantum thermodynamic devices which take\nadvantage of uniquely quantum resources such as quantum coherence,\ncorrelations, and entanglement."
    },
    {
        "anchor": "Realizing arbitrary trapping potentials for light via direct laser\n  writing of mirror surface profiles: The versatility of quantum gas experiments greatly benefits from the ability\nto apply variable potentials. Here we describe a method which allows the\npreparation of potential structures for microcavity photons via spatially\nselective deformation of optical resonator geometries with a heat induced\nmirror surface microstructuring technique. We investigate the thermalization of\na two-dimensional photon gas in a dye-filled microcavity composed of the custom\nsurface-structured mirrors at wavelength-scale separation. Specifically, we\ndescribe measurements of the spatial redistribution of thermal photons in a\ncoupled double-ridge structure, where photons form a Bose-Einstein condensate\nin a spatially split ground state, as a function of different pumping\ngeometries.",
        "positive": "Stable and unstable vortex knots in a trapped Bose-Einstein condensate: The dynamics of a quantum vortex torus knot ${\\cal T}_{P,Q}$ and similar\nknots in an atomic Bose-Einstein condensate at zero temperature in the\nThomas-Fermi regime has been considered in the hydrodynamic approximation. The\ncondensate has a spatially nonuniform equilibrium density profile $\\rho(z,r)$\ndue to an external axisymmetric potential. It is assumed that $z_*=0$, $r_*=1$\nis a maximum point for function $r\\rho(z,r)$, with $\\delta\n(r\\rho)\\approx-(\\alpha-\\epsilon) z^2/2 -(\\alpha+\\epsilon) (\\delta r)^2/2$ at\nsmall $z$ and $\\delta r$. Configuration of knot in the cylindrical coordinates\nis specified by a complex $2\\pi P$-periodic function\n$A(\\varphi,t)=Z(\\varphi,t)+i [R(\\varphi,t)-1]$. In the case $|A|\\ll 1$ the\nsystem is described by relatively simple approximate equations for re-scaled\nfunctions $W_n(\\varphi)\\propto A(2\\pi n+\\varphi)$, where $n=0,\\dots,P-1$, and\n$iW_{n,t}=-(W_{n,\\varphi\\varphi}+\\alpha W_n -\\epsilon W_n^*)/2-\\sum_{j\\neq\nn}1/(W_n^*-W_j^*)$. At $\\epsilon=0$, numerical examples of stable solutions as\n$W_n=\\theta_n(\\varphi-\\gamma t)\\exp(-i\\omega t)$ with non-trivial topology have\nbeen found for $P=3$. Besides that, dynamics of various non-stationary knots\nwith $P=3$ was simulated, and in some cases a tendency towards a finite-time\nsingularity has been detected. For $P=2$ at small $\\epsilon\\neq 0$, rotating\naround $z$ axis configurations of the form $(W_0-W_1)\\approx\nB_0\\exp(i\\zeta)+\\epsilon C(B_0,\\alpha)\\exp(-i\\zeta) + \\epsilon\nD(B_0,\\alpha)\\exp(3i\\zeta)$ have been investigated, where $B_0>0$ is an\narbitrary constant, $\\zeta=k_0\\varphi -\\Omega_0 t+\\zeta_0$, $k_0=Q/2$,\n$\\Omega_0=(k_0^2-\\alpha)/2-2/B_0^2$. In the parameter space $(\\alpha, B_0)$,\nwide stability regions for such solutions have been found. In unstable bands, a\nrecurrence of the vortex knot to a weakly excited state has been noted to be\npossible."
    },
    {
        "anchor": "Spin-heat relaxation and thermo-spin diffusion in atomic Bose and Fermi\n  gases: We study spin-dependent heat transport in quantum gases, focusing on\ntransport phenomena related to pure spin currents and spin-dependent\ntemperatures. Using the Boltzmann equation, we compute the coupled spin and\nheat transport coefficients as a function of temperature and interaction\nstrength for energy dependent $s$-wave scattering. We address the issue of\nwhether spin-dependent temperatures can be sustained on a time and length scale\nrelevant for experiments by computing the spin-heat relaxation time and\ndiffusion length. We find that the time scale for spin-heat relaxation time\ndiverges at low temperatures for both bosons and fermions, indicating that the\nconcept of spin-heat accumulation is well defined for degenerate gases. For\nbosons, we find power-law behavior on approach to Bose condensation above the\ncritical temperature, as expected from the theory of dynamical critical\nphenomena.",
        "positive": "Optical Control of Exchange Interaction and Kondo Temperature in cold\n  Atom Gas: The relevance of magnetic impurity problems in cold atom systems depends\ncrucially on the nature of exchange interaction between itinerant fermionic\natoms and a localized impurity atom. In particular, Kondo physics occurs only\nif the exchange interaction is anti-ferromagnetic, and strong enough to yield\nhigh enough Kondo temperature ($T_K/T_F \\ge 0.1$). Focusing, as an example, on\nthe experimentally accessible system of ultra-cold $^{173}$Yb atoms, it is\nshown that the sign and strength of an exchange interaction between an\nitinerant Yb($^{1}$S$_{0}$) atom and a trapped Yb($^{3}$P$_{0}$) atom can be\noptically controlled. Explicitly, as the light intensity increases (from zero),\nthe exchange interaction changes from ferromagnetic to anti-ferromagnetic. When\nthe light intensity is just below a singlet Feshbach resonance, the singlet\nscattering length $a_S$ is large and negative, and the Kondo temperature\nincreases sharply."
    },
    {
        "anchor": "Zero temperature momentum distribution of an impurity in a polaron state\n  of one-dimensional Fermi and Tonks-Girardeau gases: We investigate the momentum distribution function of a single distinguishable\nimpurity particle which formed a polaron state in a gas of either free fermions\nor Tonks-Girardeau bosons in one spatial dimension. We obtain a Fredholm\ndeterminant representation of the distribution function for the Bethe ansatz\nsolvable model of an impurity-gas $\\delta$-function interaction potential at\nzero temperature, in both repulsive and attractive regimes. We deduce from this\nrepresentation the fourth power decay at a large momentum, and a weakly\ndivergent (quasi-condensate) peak at a finite momentum. We also demonstrate\nthat the momentum distribution function in the limiting case of infinitely\nstrong interaction can be expressed through a correlation function of the\none-dimensional impenetrable anyons.",
        "positive": "Counterflow superfluid of polaron pairs in Bose-Fermi mixtures in\n  optical lattices: We study the quantum phases of one-dimensional Bose-Fermi mixtures in optical\nlattices. Assuming repulsive interparticle interactions, equal mass, and unit\ntotal filling, we calculate the ground-state phase diagram by means of both\nTomonaga-Luttinger liquid theory and time-evolving block decimation method. We\ndemonstrate the existence of a counterflow superfluid (CFSF) phase of polaron\npairs, which are composite particles consisting of two fermions and two bosonic\nholes, in a broad range of the parameter space. We find that this phase\nnaturally emerges in $^{174}$Yb-$^{173}$Yb mixtures, realized in recent\nexperiments, at low temperatures."
    },
    {
        "anchor": "The influence of local correlations on the phase states in the model of\n  semi-hard-core bosons on a square lattice: The work considers a model of charged \"semi-hard-core\" bosons on a square\nlattice with a possible filling number at each node, ranging from 0 to 2.\nTemperature phase diagrams of the model are obtained using numerical Monte\nCarlo quantum simulation methods, and the influence of local charge\ncorrelations is examined. Comparison with results from mean-field methods shows\nthat local charge correlations contribute to an increased role of quantum\nfluctuations in the formation of phase states.",
        "positive": "Theory of real supersolids: We review the main properties of a supersolid. We describe first the\nmacroscopic equation that satisfies a supersolid based on general arguments and\nsymmetries and show that such solids might exhibit simultaneously or\nindependently both elastic behavior and superfluidity. We then explain why a\nsupersolid state should exist for solids at very low temperature but with a\nvery small superfluid fraction. Finally, we propose a mean-field model, based\non the Gross-Pitaevski\\u{\\i} equation, which presents the general properties\nexpected for a supersolid and should therefore provide a consistent framework\nto study its dynamical properties."
    },
    {
        "anchor": "Comparing models for the ground state energy of a trapped\n  one-dimensional Fermi gas with a single impurity: We discuss the local density approximation approach to calculating the ground\nstate energy of a one-dimensional Fermi gas containing a single impurity, and\ncompare the results with exact numerical values that we have for up to 11\nparticles for general interaction strengths and up to 30 particles in the\nstrongly interacting case. We also calculate the contact coefficient in the\nstrongly interacting regime. The different theoretical predictions are compared\nto recent experimental results with few-atom systems. Firstly, we find that the\nlocal density approximation suffers from great ambiguity in the few-atom\nregime, yet it works surprisingly well for some models. Secondly, we find that\nthe strong interaction theories quickly break down when the number of particles\nincrease or the interaction strength decreases.",
        "positive": "Manifold formation and crossings of ultracold lattice spinor atoms in\n  the intermediate interaction regime: Ultracold spinor atoms in the weak and strong interaction regime have\nreceived extensive investigations, while the behavior in the intermediate\nregime is less understood. We numerically investigate ultracold spinor atomic\nensembles of finite size in the intermediate interaction regime, and reveal the\nevolution of the eigenstates from the strong to the intermediate regime. In the\nstrong interaction regime, it has been well known that the low-lying\neigenenergy spectrum presents the well-gaped multi-manifold structure, and the\nenergy gaps protect the categorization of the eigenstates. In the intermediate\ninteraction regime, it is found that the categorization of the eigenstates is\npreserved, and the eigenenergy spectrum become quasi-continuum, with different\nmanifolds becoming overlapped. The overlapping induces both direct and avoided\ncrossings between close-lying manifolds, which is determined by the combined\nsymmetries of the eigenstates involved in the crossing. A modified t-J model is\nderived to describe the low-lying eigenstates in the intermediate regime, which\ncan capture the formation and crossings of the manifolds. State preparation\nthrough the avoided crossings is also investigated."
    },
    {
        "anchor": "Incommensurability effects on dipolar bosons in optical lattices: We present a study that investigated a quantum dipolar gas in continuous\nspace where a potential lattice was imposed. Employing exact quantum Monte\nCarlo techniques, we analysed the ground state properties of the scrutinised\nsystem, varying the lattice depth and the dipolar interaction. For system\ndensities corresponding to a commensurate filling with respect to the optical\nlattice, we observed a simple crystal-to-superfluid quantum phase transition,\nbeing consistent with the physics of dipolar bosons in continuous space. In\ncontrast, an incommensurate density showed the presence of a supersolid phase.\nIndeed, such a result opens up the tempting opportunity to observe a\ndefect-induced supersolidity with dipolar gases in combination with a tunable\noptical lattice. Finally, the stability of the condensate was analysed at\nfinite temperature.",
        "positive": "Strong Fulde-Ferrell Larkin-Ovchinnikov pairing fluctuations in\n  polarized Fermi systems: We calculate the pair susceptibility of an attractive spin-polarized Fermi\ngas in the normal phase, as a function of the pair momentum. Close to\nunitarity, we find a strong enhancement of Fulde-Ferrell-Larkin-Ovchinnikov\n(FFLO) pairing fluctuations over an extended region of the\ntemperature-polarization phase diagram, which manifests itself as a pronounced\npeak in the pair-momentum distribution at a finite pair momentum. This peak\nshould be amenable to experimental observation at achievable temperatures in a\nbox-like trapping potential, as a fingerprint of FFLO pairing. Our calculations\nrest on a self-consistent t-matrix approach which, for the unitary balanced\nFermi gas, has been validated against experimental data for several\nthermodynamic quantities."
    },
    {
        "anchor": "Fluctuation theorem anomaly in a point-vortex fluid: The second law of thermodynamics posits that in closed macroscopic systems\nthe rate of entropy production must be positive. However, small systems can\nexhibit negative entropy production over short timescales, seemingly in\ncontradiction with this law. The fluctuation theorem quantitatively connects\nthese two limits, predicting that entropy producing trajectories become\nexponentially dominant as the system size and measurement time are increased.\nHere we explore the predictions of the fluctuation theorem for a fluid of\npoint-vortices, where the long-range interactions and existence of negative\nabsolute temperature states provide an intriguing test bed for the theorem. Our\nresults suggest that while the theorem broadly holds even at negative absolute\ntemperatures, the long-range interactions inherent to the vortex matter lead to\nanomalously large entropy production over short time intervals. The predictions\nof the fluctuation theorem are only fully recovered when sufficient noise is\nintroduced to the dynamics to overwhelm the vortex-vortex interactions.",
        "positive": "Dynamics of quantum soliton in Lee-Huang-Yang spin-orbit coupled\n  Bose-Einstein condensates: We present the numerical results of the structure and dynamics of the\nself-bound ground state arising solely because of the presence of beyond mean\nfield quantum fluctuation in spin-orbit coupled binary Bose-Einstein\ncondensates in one dimension. Depending upon spin-obit (SO) and Rabi couplings,\nwe observe that the ground state exhibits either quantum-bright (plane) or\nquantum-stripe soliton nature. We find an analytical soliton solution for\nnon-zero SO coupling that matches quite well with the numerical results.\nFurther, we investigate the dynamical stability of these solitons by adopting\nthree protocols, such as (i) adding initial velocity to each component, (ii)\nquenching the SO and Rabi coupling parameters at initial and finite time, and\n(iii) allowing collision between the two spin-components by giving equal and\nopposite direction velocity to them. Many interesting dynamical features of the\nsolitons, like, multi-fragmented, repelling, and breathing in time and\nspace-time, are observed. For given Rabi coupling frequency, the breathing\nfrequency of the soliton increases upon the increase in SO coupling, attaining\na maximum at the critical SO coupling where the phase transition from the\nbright to stripe soliton occurs. We observe that the maximum breathing\nfrequency exhibits power law dependence on the Rabi coupling frequency with an\nexponent $\\sim 0.16$."
    },
    {
        "anchor": "Two-Element Mixture of Bose and Fermi Superfluids: We report on the production of a stable mixture of bosonic and fermionic\nsuperfluids composed of the elements $^{174}$Yb and $^6$Li which feature a\nstrong mismatch in mass and distinct electronic properties. We demonstrate\nelastic coupling between the superfluids by observing the shift in dipole\noscillation frequency of the bosonic component due to the presence of the\nfermions. The measured magnitude of the shift is consistent with a mean-field\nmodel and its direction determines the previously unknown sign of the\ninterspecies scattering length to be positive. We also observe the exchange of\nangular momentum between the superfluids from the excitation of a scissors mode\nin the bosonic component through interspecies interactions. We explain this\nobservation using an analytical model based on superfluid hydrodynamics.",
        "positive": "Thermodynamic performance of a periodically driven harmonic oscillator\n  correlated with the baths: We consider a harmonic oscillator under periodic driving and coupled to two\nharmonic-oscillator heat baths at different temperatures. We use the\nthermofield transformation with chain mapping for this setup, which allows us\nto study the unitary evolution of the system and the baths up to a time when\nthe periodic steady state emerges in the system. We characterize this periodic\nsteady state, and we show that, by tuning the system and the bath parameters,\none can turn this system from an engine to an accelerator or even to a heater.\nThe possibility to study the unitary evolution of the system and baths also\nallows us to evaluate the steady correlations that build between the system and\nthe baths, and correlations that grow between the baths."
    },
    {
        "anchor": "Crossover from adiabatic to sudden interaction quenches in the Hubbard\n  model: Prethermalization and nonequilibrium dynamics: The recent experimental implementation of condensed matter models in optical\nlattices has motivated research on their nonequilibrium behavior. Predictions\non the dynamics of superconductors following a sudden quench of the pairing\ninteraction have been made based on the effective BCS Hamiltonian; however,\ntheir experimental verification requires the preparation of a suitable excited\nstate of the Hubbard model along a twofold constraint: (i) a sufficiently\nnonadiabatic ramping scheme is essential to excite the nonequilibrium dynamics,\nand (ii) overheating beyond the critical temperature of superconductivity must\nbe avoided. For commonly discussed interaction ramps there is no clear\nseparation of the corresponding energy scales. Here we show that the matching\nof both conditions is simplified by the intrinsic relaxation behavior of\nultracold fermionic systems: For the particular example of a linear ramp we\nexamine the transient regime of prethermalization [M. Moeckel and S. Kehrein,\nPhys. Rev. Lett. 100, 175702 (2008)] under the crossover from sudden to\nadiabatic switching using Keldysh perturbation theory. A real-time analysis of\nthe momentum distribution exhibits a temporal separation of an early energy\nrelaxation and its later thermalization by scattering events. For long but\nfinite ramping times this separation can be large. In the prethermalization\nregime the momentum distribution resembles a zero temperature Fermi liquid as\nthe energy inserted by the ramp remains located in high energy modes. Thus\nultracold fermions prove robust to heating which simplifies the observation of\nnonequilibrium BCS dynamics in optical lattices.",
        "positive": "A universal pairing gap measurement proposal by dynamical excitations in\n  2D doped attractive Fermi-Hubbard model with spin-orbit coupling: By calculating dynamical structure factor of two-dimensional doped attractive\nFermi-Hubbard model with Rashba spin-orbit coupling, we not only investigate\ncollective modes and single-particle excitations of the system during the phase\ntransition between Bardeen-Cooper-Schrieffer superfluid and topological\nsuperfluid, but also propose a universal method to measure pairing gap\nmeasurement in an optical lattice system. Our numerical results show that the\narea of the molecular excitation peak at the transferred momentum ${\\bf\nq}=\\left[\\pi,\\pi\\right]$ is proportional to the square of the pairing gap in\nthe system with Rashba SOC. In particular, this method is very sensitive to the\npairing gap. This goes on verifying that this method is universal to measure\nthe pairing gap in a doped optical lattice with Rashba SOC. These theoretical\nresults are important for experimentally measuring the pairing gap and studying\nthe topological superfluid in an optical lattice."
    },
    {
        "anchor": "Non-Markovian stochastic Gross-Pitaevskii equation for the\n  exciton-polariton Bose-Einstein condensate: In this paper, a non-Markovian Gross-Pitaevskii equation is proposed to\ndescribe the formation of a condensate in an exciton-polariton system under\nincoherent pumping. By introducing spatially delta-correlated noise terms, we\nobserve a transition from a spatially ordered phase to a disordered one as the\ntemperature increases. In course of this process, the population of the\ncondensate is significantly reduced. Irregularly located separate dense spots\nof condensate above the transition temperature are revealed. Using the Gabor\ntransform, it is shown that, with increasing temperature, the condensate\ndecoheres, that is accompanied by the transition from narrowband to broadband\nspectral density.",
        "positive": "Active Learning Approach to Optimization of Experimental Control: In this work we present a general machine learning based scheme to optimize\nexperimental control. The method utilizes the neural network to learn the\nrelation between the control parameters and the control goal, with which the\noptimal control parameters can be obtained. The main challenge of this approach\nis that the labeled data obtained from experiments are not abundant. The\ncentral idea of our scheme is to use the active learning to overcome this\ndifficulty. As a demonstration example, we apply our method to control\nevaporative cooling experiments in cold atoms. We have first tested our method\nwith simulated data and then applied our method to real experiments. We\ndemonstrate that our method can successfully reach the best performance within\nhundreds of experimental runs. Our method does not require knowledge of the\nexperimental system as a prior and is universal for experimental control in\ndifferent systems."
    },
    {
        "anchor": "An SU(N) Mott insulator of an atomic Fermi gas realized by large-spin\n  Pomeranchuk cooling: The Hubbard model, containing only the minimum ingredients of nearest\nneighbor hopping and on-site interaction for correlated electrons, has\nsucceeded in accounting for diverse phenomena observed in solid-state\nmaterials. One of the interesting extensions is to enlarge its spin symmetry to\nSU(N>2), which is closely related to systems with orbital degeneracy. Here we\nreport a successful formation of the SU(6) symmetric Mott insulator state with\nan atomic Fermi gas of ytterbium (173Yb) in a three-dimensional optical\nlattice. Besides the suppression of compressibility and the existence of charge\nexcitation gap which characterize a Mott insulating phase, we reveal an\nimportant difference between the cases of SU(6) and SU(2) in the achievable\ntemperature as the consequence of different entropy carried by an isolated\nspin. This is analogous to Pomeranchuk cooling in solid 3He and will be helpful\nfor investigating exotic quantum phases of SU(N) Hubbard system at extremely\nlow temperatures.",
        "positive": "Polaron in a $p+ip$ Fermi topological superfluid: We study polaron excitations induced by an impurity interacting with a\ntwo-dimensional $p+ip$ Fermi superfluid. As the Fermi-Fermi pairing interaction\nis tuned, the background Fermi superfluid undergoes a topological phase\ntransition. We show that such a transition is accompanied by a discontinuity in\nthe second derivative of the polaron energy, regardless of the impurity-fermion\ninteraction. We also identify a polaron to trimer crossover when the Fermi\nsuperfluid is in the strongly interacting, thus topologically trivial, regime.\nHowever, the trimer state is metastable against the molecular state where the\nimpurity binds a Bogoliubov quasiparticle from the Fermi superfluid. By\ncomparing the polaron to molecule transition in our system with that of an\nimpurity in a noninteracting Fermi sea, we find that pairing interactions in\nthe background Fermi superfluid effectively facilitate the impurity-fermion\nbinding. Our results suggest the possibility of using the impurity as a probe\nfor detecting topological phase transitions in the background; they also reveal\ninteresting competitions between various many-body states in the system."
    },
    {
        "anchor": "Quantum Phases from Competing Van der Waals and Dipole-Dipole\n  Interactions of Rydberg Atoms: Competing short- and long-range interactions represent distinguished\ningredients for the formation of complex quantum many-body phases. Their study\nis hard to realize with conventional quantum simulators. In this regard,\nRydberg atoms provide an exception as their excited manifold of states have\nboth density-density and exchange interactions whose strength and range can\nvary considerably. Focusing on one-dimensional systems, we leverage the van der\nWaals and dipole-dipole interactions of the Rydberg atoms to obtain the\nzero-temperature phase diagram for a uniform chain and a dimer model. For the\nuniform chain, we can influence the boundaries between ordered phases and a\nLuttinger liquid phase. For the dimerized case, a new type of\nbond-order-density-wave phase is identified. This demonstrates the versatility\nof the Rydberg platform in studying physics involving short- and long-ranged\ninteractions simultaneously.",
        "positive": "Atomic Quantum Simulation of Dynamical Gauge Fields coupled to Fermionic\n  Matter: From String Breaking to Evolution after a Quench: Using a Fermi-Bose mixture of ultra-cold atoms in an optical lattice, we\nconstruct a quantum simulator for a U(1) gauge theory coupled to fermionic\nmatter. The construction is based on quantum links which realize continuous\ngauge symmetry with discrete quantum variables. At low energies, quantum link\nmodels with staggered fermions emerge from a Hubbard-type model which can be\nquantum simulated. This allows us to investigate string breaking as well as the\nreal-time evolution after a quench in gauge theories, which are inaccessible to\nclassical simulation methods."
    },
    {
        "anchor": "Stability of supercurrents in a superfluid phase of spin-1 bosons in an\n  optical lattice: We study collective modes and superfluidity of spin-1 bosons with\nantiferromagnetic interactions in an optical lattice based on the\ntime-dependent Ginzburg-Landau (TDGL) equation derived from the spin-1\nBose-Hubbard model. Specifically, we examine the stability of supercurrents in\nthe polar phase in the vicinity of the Mott insulating phase with even filling\nfactors. Solving the linearized TDGL equation, we obtain gapless spin-nematic\nmodes and gapful spin-wave modes in the polar phase that arise due to the\nbreaking of $S^2$ symmetry in spin space. Supercurrents exhibit dynamical\ninstabilities induced by growing collective modes. In contrast to the\nsecond-order phase transition, the critical momentum of mass currents is finite\nat the phase boundary of the first-order superfluid-Mott insulator (SF-MI)\nphase transition. Furthermore, the critical momentum remains finite throughout\nthe metastable SF phase and approaches zero towards the phase boundary, at\nwhich the metastable SF state disappears. We also study the stability of spin\ncurrents motivated by recent experiments for spinor gases. The critical\nmomentum of spin currents is found to be zero, where a spin-nematic mode causes\nthe dynamical instability. We investigate the origin of the zero critical\nmomentum of spin currents and find it attributed to the fact that the polar\nstate becomes energetically unstable even in the presence of an infinitesimal\nspin current. We discuss implications of the zero critical momentum of spin\ncurrents for the stability of the polar state.",
        "positive": "Trimer quantum spin liquid in a honeycomb array of Rydberg atoms: Quantum spin liquids are elusive but paradigmatic examples of strongly\ncorrelated quantum states that are characterized by long-range quantum\nentanglement. Recently, the direct signatures of a gapped topological\n$\\mathbb{Z}_2$ spin liquid have been observed in a system of Rydberg atoms\narrayed on the ruby lattice. Here, we illustrate the concrete realization of a\nfundamentally different class of spin liquids in a honeycomb array of Rydberg\natoms. Exploring the quantum phase diagram of this system using both\ndensity-matrix renormalization group and exact diagonalization simulations,\nseveral density-wave-ordered phases are characterized and their origins\nexplained. More interestingly, in the regime where third-nearest-neighbor atoms\nlie within the Rydberg blockade radius, we find a novel ground state -- with an\nemergent $\\mathrm{U}(1)\\times \\mathrm{U}(1)$ local symmetry -- formed from\nsuperpositions of classical {\\it trimer} configurations on the dual triangular\nlattice. The fidelity of this trimer spin liquid state can be enhanced via\ndynamical preparation, which we explain by a Rydberg-blockade-based projection\nmechanism associated with the smooth turnoff of the laser drive. Finally, we\ndiscuss the robustness of the trimer spin liquid phase under realistic\nexperimental parameters and demonstrate that our proposal can be readily\nimplemented in current Rydberg atom quantum simulators."
    },
    {
        "anchor": "On a fragmented condensate in a uniform Bose system: According to the well-known analysis by Nozi\\'{e}res, the fragmentation of\nthe condensate increases the energy of a uniform interacting Bose system.\nTherefore, at $T= 0$ the condensate should be nonfragmented. We perform a more\ndetailed analysis and show that the result by Nozi\\'{e}res is not general. We\nfind that, in a dense Bose system, the formation of a crystal-like structure\nwith a fragmented condensate is possible. The effect is related to a nonzero\nsize of real atoms. Moreover, the wave functions studied by Nozi\\'{e}res are\nnot eigenfunctions of the Hamiltonian and, therefore, do not allow one to judge\nwith confidence about the structure of the condensate in the ground state. We\nhave constructed the wave functions in such a way that they are eigenfunctions\nof the Hamiltonian. The results show that the fragmentation of the condensate\n(quasicondensate) is possible for a finite one-dimensional uniform system at\nlow temperatures and a weak coupling.",
        "positive": "Interplay of interaction and disorder in the steady state of an open\n  quantum system: Many types of dissipative processes can be found in nature or be engineered,\nand their interplay with a system can give rise to interesting phases of\nmatter. Here we study the interplay among interaction, tunneling, and disorder\nin the steady state of a spin chain coupled to a tailored bath. We consider a\ndissipation which, in contrast to disorder, tends to generate a homogeneously\npolarized steady state. We find that the steady state can be highly sensitive\neven to weak disorder. We also establish that, in the presence of such\ndissipation, even in the absence of interaction, a finite amount of disorder is\nneeded for localization. Last, we show that for strong disorder the system\nreveals signatures of localization both in the weakly and strongly interacting\nregimes."
    },
    {
        "anchor": "Many-body bound states and induced interactions of charged impurities in\n  a bosonic bath: Induced interactions and bound states of charge carriers immersed in a\nquantum medium are crucial for the investigation of quantum transport.\nUltracold atom-ion systems can provide a convenient platform for studying this\nproblem. Here, we investigate the static properties of one and two ionic\nimpurities in a bosonic bath using quantum Monte Carlo methods. We identify\nthree bipolaronic regimes depending on the strength of the atom-ion potential\nand the number of its two-body bound states: a perturbative regime resembling\nthe situation of a pair of neutral impurities, a non-perturbative regime that\nloses the quasi-particle character of the former, and a many-body bound state\nregime that can arise only in the presence of a bound state in the two-body\npotential. We further reveal strong bath-induced interactions between the two\nionic polarons. Our findings show that numerical simulations are indispensable\nfor describing highly correlated impurity models.",
        "positive": "Bose gas in disordered, finite-layered systems: Disorder effects in the thermodynamic properties of a ideal Bose gas confined\nin a semi-infinite multi-layer structure %described by $M$ permeable barriers\nwithin a box of thickness $L$ and infinite lateral extent, are analyzed. The\nlayers are first modeled by a periodic array of $M$ Dirac delta-functions of\nequal intensity. Then, we introduce structural and compositional disorder, as\nwell as a random set of layer vacancies in the system to calculate the internal\nenergy, chemical potential and the specific heat for different configurations.\nWhereas structural and compositional disorder does not reveal a significant\nchange, a dramatic increase in the maximum of the specific heat is observed\nwhen the system is depleted a fraction of the order of $0.1$ to $0.2$ of random\nlayers compared to the original, fully periodic array. Furthermore, this\nmaximum, which is reminiscent of a Bose-Einstein condensation for an infinite\narray, occurs at higher temperatures."
    },
    {
        "anchor": "Analog vacuum decay from vacuum initial conditions: Ultracold atomic gases can undergo phase transitions that mimic relativistic\nvacuum decay, allowing us to empirically test early-Universe physics in\ntabletop experiments. We investigate the physics of these analog systems, going\nbeyond previous analyses of the classical equations of motion to study quantum\nfluctuations in the cold-atom false vacuum. We show that the fluctuation\nspectrum of this vacuum state agrees with the usual relativistic result in the\nregime where the classical analogy holds, providing further evidence for the\nsuitability of these systems for studying vacuum decay. Using a suite of\nsemiclassical lattice simulations, we simulate bubble nucleation from this\nanalog vacuum state in a 1D homonuclear potassium-41 mixture, finding\nqualitative agreement with instanton predictions. We identify realistic\nparameters for this system that will allow us to study vacuum decay with\ncurrent experimental capabilities, including a prescription for efficiently\nscanning over decay rates, and show that this setup will probe the quantum\n(rather than thermal) decay regime at temperatures $T\\lesssim10\\,\\mathrm{nK}$.\nOur results help lay the groundwork for using upcoming cold-atom experiments as\na new probe of nonperturbative early-Universe physics.",
        "positive": "Binary matter-wave compactons induced by inter-species scattering length\n  modulations: Binary mixtures of quasi one-dimensional Bose-Einstein condensates (BEC)\ntrapped in deep optical lattices (OL) in the presence of periodic time\nmodulations of the inter-species scattering length, are investigated. We adopt\na mean field description and use the tight binding approximation and the\naveraging method to derive averaged model equations in the form of two coupled\ndiscrete nonlinear Schr\\\"odinger equations (DNLSE) with tunneling constants\nthat nonlinearly depend on the inter-species coupling. We show that for strong\nand rapid modulations of the inter-species scattering length, the averaged\nsystem admits exact compacton solutions, e.g. solutions that have no tails and\nare fully localized on a compact which are achieved when the densities at the\ncompact edges are in correspondence with zeros of the Bessel function (zero\ntunneling condition). Deviations from exact conditions give rise to the\nformation of quasi-compactons, e.g. non exact excitations which look as\ncompactons for any practical purpose, for which the zero tunneling condition is\nachieved dynamically thanks to an effective nonlinear dispersive coupling\ninduced by the scattering length modulation. Stability properties of compactons\nand quasi-compactons are investigated by linear analysis and by numerical\nintegrations of the averaged system, respectively, and results compared with\nthose from the original (unaveraged) system. In particular, the occurrence od\ndelocalizing transitions with existence of thresholds in the mean inter-species\nscattering length is explicitly demonstrated. Under proper management\nconditions, stationary compactons and quasi-compactons are quite stable and\nrobust excitations that can survive on very long time scale. A parameter design\nand a possible experimental setting for observation of these excitations are\nbriefly discussed."
    },
    {
        "anchor": "Phase separation can be stronger than chaos: We investigate several dynamical regimes characterizing a bosonic binary\nmixture loaded in a ring trimer, with particular reference to the persistence\nof demixing. The degree of phase separation is evaluated by means of the\n\"Entropy of mixing\", an indicator borrowed from Statistical Thermodynamics.\nThree classes of demixed stationary configurations are identified and their\nenergetic and linear stability carefully analyzed. An extended set of\ntrajectories originating in the vicinity of fixed points are explicitly\nsimulated and chaos is shown to arise according to three different mechanisms.\nIn many dynamical regimes, we show that chaos is not able to disrupt the order\nimposed by phase separation, i.e. boson populations, despite evolving in a\nchaotic fashion, do not mix. This circumstance can be explained either with\nenergetic considerations or in terms of dynamical restrictions.",
        "positive": "Unconventional symmetries of Fermi liquid and Cooper pairing properties\n  with electric and magnetic dipolar fermions: The rapid experimental progress of ultra-cold dipolar fermions opens up a\nwhole new opportunity to investigate novel many-body physics of fermions. In\nthis article, we review theoretical studies of the Fermi liquid theory and\nCooper pairing instabilities of both electric and magnetic dipolar fermionic\nsystems from the perspective of unconventional symmetries. When the electric\ndipole moments are aligned by the external electric field, their interactions\nexhibit the explicit $d_{r^2-3z^2}$ anisotropy. The Fermi liquid properties,\nincluding the single-particle spectra, thermodynamic susceptibilities, and\ncollective excitations, are all affected by this anisotropy. The electric\ndipolar interaction provides a mechanism for the unconventional spin triplet\nCooper pairing, which is different from the usual spin-fluctuation mechanism in\nsolids and the superfluid $^3$He. Furthermore, the competition between pairing\ninstabilities in the singlet and triplet channels gives rise to a novel\ntime-reversal symmetry breaking superfluid state. Unlike electric dipole\nmoments which are induced by electric fields and unquantized, magnetic dipole\nmoments are intrinsic proportional to the hyperfine-spin operators with a Lande\nfactor. Its effects even manifest in unpolarized systems exhibiting an\nisotropic but spin-orbit coupled nature. The resultant spin-orbit coupled Fermi\nliquid theory supports a collective sound mode exhibiting a topologically\nnon-trivial spin distribution over the Fermi surface. It also leads to a novel\n$p$-wave spin triplet Cooper pairing state whose spin and orbital angular\nmomentum are entangled to the total angular momentum $J=1$ dubbed the\n$J$-triplet pairing. This $J$-triplet pairing phase is different from both the\nspin-orbit coupled $^3$He-$B$ phase with $J=0$ and the spin-orbit decoupled\n$^3$He-$A$ phase."
    },
    {
        "anchor": "Exploring 4D Quantum Hall Physics with a 2D Topological Charge Pump: The discovery of topological states of matter has profoundly augmented our\nunderstanding of phase transitions in physical systems. Instead of local order\nparameters, topological phases are described by global topological invariants\nand are therefore robust against perturbations. A prominent example thereof is\nthe two-dimensional integer quantum Hall effect. It is characterized by the\nfirst Chern number which manifests in the quantized Hall response induced by an\nexternal electric field. Generalizing the quantum Hall effect to\nfour-dimensional systems leads to the appearance of a novel non-linear Hall\nresponse that is quantized as well, but described by a 4D topological invariant\n- the second Chern number. Here, we report on the first observation of a bulk\nresponse with intrinsic 4D topology and the measurement of the associated\nsecond Chern number. By implementing a 2D topological charge pump with\nultracold bosonic atoms in an angled optical superlattice, we realize a\ndynamical version of the 4D integer quantum Hall effect. Using a small atom\ncloud as a local probe, we fully characterize the non-linear response of the\nsystem by in-situ imaging and site-resolved band mapping. Our findings pave the\nway to experimentally probe higher-dimensional quantum Hall systems, where new\ntopological phases with exotic excitations are predicted.",
        "positive": "Strong correlations in lossy one-dimensional quantum gases: from the\n  quantum Zeno effect to the generalized Gibbs ensemble: We consider strong two-body losses in bosonic gases trapped in\none-dimensional optical lattices. We exploit the separation of time scales\ntypical of a system in the many-body quantum Zeno regime to establish a\nconnection with the theory of the time-dependent generalized Gibbs ensemble.\nOur main result is a simple set of rate equations that capture the simultaneous\naction of coherent evolution and two-body losses. This treatment gives an\naccurate description of the dynamics of a gas prepared in a Mott insulating\nstate and shows that its long-time behaviour deviates significantly from\nmean-field analyses. The possibility of observing our predictions in an\nexperiment with $^{174}$Yb in a metastable state is also discussed."
    },
    {
        "anchor": "Metropolis-Hastings thermal state sampling for numerical simulations of\n  Bose-Einstein condensates: We demonstrate the application of the Metropolis-Hastings algorithm to\nsampling of classical thermal states of one-dimensional Bose-Einstein\nquasicondensates in the classical fields approximation, both in untrapped and\nharmonically trapped case. The presented algorithm can be easily generalized to\nhigher dimensions and arbitrary trap geometry. For truncated Wigner simulations\nthe quantum noise can be added with conventional methods (half a quantum of\nenergy in every mode). The advantage of the presented method over the usual\nanalytical and stochastic ones lies in its ability to sample not only from\ncanonical and grand canonical distributions, but also from the generalized\nGibbs ensemble, which can help to shed new light on thermodynamics of\nintegrable systems.",
        "positive": "Ultracold dense samples of dipolar RbCs molecules in the rovibrational\n  and hyperfine ground state: We produce ultracold dense trapped samples of 87Rb133Cs molecules in their\nrovibrational ground state, with full nuclear hyperfine state control, by\nstimulated Raman adiabatic passage (STIRAP) with efficiencies of 90%. We\nobserve the onset of hyperfine-changing collisions when the magnetic field is\nramped so that the molecules are no longer in the hyperfine ground state. A\nstrong quadratic shift of the transition frequencies as a function of applied\nelectric field shows the strongly dipolar character of the RbCs ground-state\nmolecule. Our results open up the prospect of realizing stable bosonic dipolar\nquantum gases with ultracold molecules."
    },
    {
        "anchor": "Crossovers in Unitary Fermi Systems: Universality and crossover is described for attractive and repulsive\ninteractions where, respectively, the BCS-BEC crossover takes place and a\nferromagnetic phase transition is claimed. Crossovers are also described for\noptical lattices and multicomponent systems. The crossovers, universal\nparameters and phase transitions are described within the Leggett and NSR\nmodels and calculated in detail within the Jastrow-Slater approximation. The\nphysics of ultracold Fermi atoms is applied to neutron, nuclear and quark\nmatter, nuclei and electrons in solids whenever possible. Specifically, the\ndifferences between optical lattices and cuprates is discussed w.r.t.\nantiferromagnetic, d-wave superfluid phases and phase separation.",
        "positive": "Mean-field approaches to the Bose-Hubbard model with three-body local\n  interaction: The zero temperature properties of the generalized Bose-Hubbard model\nincluding three-body interactions are studied on a mean-field level. We obtain\nanalytical results using the so-called perturbative mean-field method and more\ndetailed numerical results using the Gutzwiller product state variational\nAnsatz. These two approaches yield equivalent results which compare well on a\nqualitative level with recent exact results obtained in the literature."
    },
    {
        "anchor": "Atom-light crystallization of BECs in multimode cavities: Nonequilibrium\n  classical and quantum phase transitions, emergent lattices, supersolidity,\n  and frustration: The self-organization of a Bose-Einstein condensate in a transversely pumped\noptical cavity is a process akin to crystallization: when pumped by a laser of\nsufficient intensity, the coupled matter and light fields evolve,\nspontaneously, into a spatially modulated pattern, or crystal, whose lattice\nstructure is dictated by the geometry of the cavity. In cavities having\nmultiple degenerate modes, the quasi-continuum of possible lattice\narrangements, and the continuous symmetry breaking associated with the adoption\nof a particular lattice arrangement, give rise to phenomena such as phonons,\ndefects, and frustration, which have hitherto been unexplored in ultracold\natomic settings involving neutral atoms. The present work develops a\nnonequilibrium field-theoretic approach to explore the self-organization of a\nBEC in a pumped, lossy optical cavity. We find that the transition is well\ndescribed, in the regime of primary interest, by an effective equilibrium\ntheory. At nonzero temperatures, the self-organization occurs via a\nfluctuation-driven first-order phase transition of the Brazovskii class; this\ntransition persists to zero temperature, and crosses over into a quantum phase\ntransition of a new universality class. We make further use of our\nfield-theoretic description to investigate the role of nonequilibrium\nfluctuations on the self-organization transition, as well as to explore the\nnucleation of ordered-phase droplets, the nature and energetics of topological\ndefects, supersolidity in the ordered phase, and the possibility of frustration\ncontrolled by the cavity geometry. In addition, we discuss the range of\nexperimental parameters for which we expect the phenomena described here to be\nobservable, along with possible schemes for detecting ordering and fluctuations\nvia either atomic correlations or the correlations of the light emitted from\nthe cavity.",
        "positive": "Pair supersolid of the extended Bose-Hubbard model with atom-pair\n  hopping on the triangular Lattice: We systematically study an extended Bose-Hubbard model with atom hopping and\natom-pair hopping in the presence of a three-body constraint on the triangular\nlattice. By means of large-scale Quantum Monte Carlo simulations, the\nground-state phase diagram are studied. We find a continuous transition between\nthe atomic superfluid phase and the pair superfluid when the ratio of the\natomic hopping and the atom-pair hopping is adapted. We then focus on the\ninterplay among the atom-pair hopping, the on-site repulsion and the\nnearest-neighbor repulsion. With on-site repulsion present, we observe first\norder transitions between the Mott Insulators and pair superfluid driven by the\npair hopping. With the nearest-neighbor repulsion turning on, three typical\nsolid phases with 2/3, 1 and 4/3-filling emerge at small atom-pair hopping\nregion. A stable pair supersolid phase is found at small on-site repulsion.\nThis is due to the three-body constraint and the pair hopping, which\nessentially make the model a quasi hardcore boson system. Thus the pair\nsupersolid state emerges basing on the order-by-disorder mechanism, by which\nhardcore bosons avoid classical frustration on the triangular lattice. The\ntransition between the pair supersolid and the pair superfluid is first order,\nexcept for the particle-hole symmetric point. We compare the results with those\nobtained by means of mean-field analysis."
    },
    {
        "anchor": "Quench induced chaotic dynamics of Anderson localized interacting\n  Bose-Einstein condensates in one dimension: We study the effect of atomic interaction on the localization and the\nassociated dynamics of Bose-Einstein condensates in a one-dimensional\nquasiperiodic optical lattice and random Gaussian disordered potentials. When\nthe interactions are absent, the condensates exhibit localization, which\nweakens as we increase the interaction strength beyond a threshold value for\nboth potential types. We inspect the localized and delocalized states by\nperturbing the system via quenching the interaction strength instantaneously to\nzero and studying the dynamics of the condensate, which we further corroborate\nusing the out-of-time-order correlator. The temporal behaviour of the time\ncorrelator displays regular dynamics for the localized state, while it shows\ntemporal chaos for the delocalized state. We confirm this dynamical behaviour\nby analyzing the power spectral density of the time correlator. We further\nidentify that the condensate admits a quasiperiodic route to chaotic dynamics\nfor both potentials. Finally, we present the variation of the maximal Lyapunov\nexponents for different nonlinearity and disorder strengths that have a\npositive value in the regime where the time correlator function shows chaotic\nbehaviour. Through this, we establish the strong connection between the\nspatially delocalized state of the condensate and its temporal chaos.",
        "positive": "Few-body bound state stability of dipolar molecules in two dimensions: Bound structures among dipolar molecules in multilayers are a topic of great\ninterest in the light of recent experiments that have demonstrated the\nfeasibility of the setup. While it is known that two molecules in two adjacent\nlayers will always bind, larger complexes have only been scarcely addressed\nthus far. Here we prove rigorously that three- and four-body states will never\nbe bound when the dipoles are oriented perpendicular to the layers. The\ntechnique employed is general and can be used for more molecules/layers and\nother geometries. Our analytical findings are supported by numerical\ncalculations for both fermionic and bosonic molecules. Furthermore, we\ncalculate the reduction in intralayer repulsion necessary to bind large\ncomplexes and estimate the influence of bound complexes in systems with many\nlayers."
    },
    {
        "anchor": "Non-adiabatic polariton condensation in annular optical traps: We explore formation and dynamics of nonequilibrium bosonic exciton-polariton\ncondensates in annular optically induced traps. For the vicinity of\ncondensation pumping threshold, we develop the two-mode model, accounting for\ncounter-rotating quantized vortices and corresponding angular harmonics in the\nincoherent excitonic reservoir density. Identifying the range of parameter, in\nwhich adiabatic elimination of the reservoir is valid, we extend the analytic\nmodel beyond the adiabatic approximation. In the circularly symmetric case, we\npredict a neutral equilibrium phase due to spontaneous breaking of the\ncontinuous symmetry, condensate multistability and limit cycle dynamics. We\nalso account for weak trap asymmetry to show that non-adiabaticity of the\ncoupled condensate-reservoir system prevents formation of giant vortices and\noutline experimental conditions for their observation.",
        "positive": "Chiral Bogoliubons in Nonlinear Bosonic Systems: We present a versatile scheme for creating topological Bogoliubov excitations\nin weakly interacting bosonic systems. Our proposal relies on a background\nstationary field that consists of a Kagome vortex lattice, which breaks\ntime-reversal symmetry and induces a periodic potential for Bogoliubov\nexcitations. In analogy to the Haldane model, no external magnetic field or net\nflux is required. We construct a generic model based on the two-dimensional\n(2D) nonlinear Schr\\\"odinger equation and demonstrate the emergence of\ntopological gaps crossed by chiral Bogoliubov edge modes. Our scheme can be\nrealized in a wide variety of physical systems ranging from nonlinear optical\nsystems to exciton-polariton condensates."
    },
    {
        "anchor": "Spectral analysis of two-dimensional Bose-Hubbard models: One-dimensional Bose-Hubbard models are well known to obey a transition from\nregular to quantum-chaotic spectral statistics. We are extending this concept\nto relatively simple two-dimensional many-body models. Also in two dimensions a\ntransition from regular to chaotic spectral statistics is found and discussed.\nIn particular, we analyze the dependence of the spectral properties on the bond\nnumber of the two-dimensional lattices and the applied boundary conditions. For\nmaximal connectivity, the systems behave most regularly in agreement with the\napplicability of mean-field approaches in the limit of many nearest-neighbor\ncouplings at each site.",
        "positive": "Quantum Degenerate Mixture of Ytterbium and Lithium Atoms: We have produced a quantum degenerate mixture of fermionic alkali 6Li and\nbosonic spin-singlet 174Yb gases. This was achieved using sympathetic cooling\nof lithium atoms by evaporatively cooled ytterbium atoms in a far-off-resonant\noptical dipole trap. We observe co-existence of Bose condensed (T/T_c~0.8)\n174Yb with 2.3*10^4 atoms and Fermi degenerate (T/T_F~0.3) 6Li with 1.2*10^4\natoms. Quasipure Bose-Einstein condensates of up to 3*10^4 174Yb atoms can be\nproduced in single-species experiments. Our results mark a significant step\ntoward studies of few and many-body physics with mixtures of alkali and\nalkaline-earth-like atoms, and for the production of paramagnetic polar\nmolecules in the quantum regime. Our methods also establish a convenient scheme\nfor producing quantum degenerate ytterbium atoms in a 1064nm optical dipole\ntrap."
    },
    {
        "anchor": "Macroscopic amplification of electroweak effects in molecular\n  Bose-Einstein condensates: We investigate the possible use of Bose-Einstein condensates of diatomic\nmolecules to measure nuclear spin-dependent parity violation effects, outlining\na detection method based on the internal Josephson effect between molecular\nstates of opposite parity. When applied to molecular condensates, the fine\nexperimental control achieved in atomic bosonic Josephson junctions could\nprovide data on anapole moments and neutral weak couplings.",
        "positive": "Deterministic entanglement generation from driving through quantum phase\n  transitions: Many-body entanglement is often created through system evolution, aided by\nnon-linear interactions between the constituting particles. The very dynamics,\nhowever, can also lead to fluctuations and degradation of the entanglement if\nthe interactions cannot be controlled. Here, we demonstrate near-deterministic\ngeneration of an entangled twin-Fock condensate of $\\sim11000$ atoms by driving\na $^{87}$Rb Bose-Einstein condensate undergoing spin mixing through two\nconsecutive quantum phase transitions (QPTs). We directly observe number\nsqueezing of $10.7\\pm0.6$ dB and normalized collective spin length of\n$0.99\\pm0.01$. Together, these observations allow us to infer an\nentanglement-enhanced phase sensitivity of $\\sim6$ dB beyond the standard\nquantum limit and an entanglement breadth of $\\sim910$ atoms. Our work\nhighlights the power of generating large-scale useful entanglement by taking\nadvantage of the different entanglement landscapes separated by QPTs."
    },
    {
        "anchor": "Manipulation of light in a generalized coupled Nonlinear Schrodinger\n  equation: We investigate a generalized coupled nonlinear Schrodinger (GCNLS) equation\ncontaining Self-Phase Modulation (SPM), Cross-Phase Modulation (XPM) and Four\nWave Mixing (FWM) describing the propagation of electromagnetic radiation\nthrough an optical fibre and generate the associated Lax-pair. We then\nconstruct bright solitons employing gauge transformation approach. The\ncollisional dynamics of bright solitons indicates that it is not only possible\nto manipulate intensity (energy) between the two modes (optical beams), but\nalso within a given mode unlike the Manakov model which does not have the same\nfreedom. The freedom to manipulate intensity (energy) in a given mode or\nbetween two modes arises due to a suitable combination of SPM, XPM and\nFWM.While SPM and XPM are controlled by an arbitrary real parameter each, FWM\nis governed by two arbitrary complex parameters. The above model may have wider\nramifications in nonlinear optics and Bose-Einstein Condensates (BECs).",
        "positive": "The phonon dispersion relation of a Bose-Einstein condensate: We measure the oscillations of a standing wave of phonons in a Bose-Einstein\ncondensate, thus obtaining the dispersion relation. We present the technique of\nshort Bragg pulses, which stimulates the standing wave. The subsequent\noscillations are observed in situ. It is seen that the phonons undergo a 3D to\n1D transition, when their wavelength becomes longer than the transverse radius\nof the condensate. The 1D regime contains an inflection point in the dispersion\nrelation, which should decrease the superfluid critical velocity according to\nthe Landau criterion. The inflection point also represents a minimum in the\ngroup velocity, although the minimum is not deep enough to result in a roton.\nThe 3D-1D transition also results in an increase in the lifetime of the\nstanding-wave oscillations, and a breakdown of the local density approximation.\nIn addition, the static structure factor is measured in the long-wavelength\nregime. The measurements are enabled by the high sensitivity of the new\ntechnique."
    },
    {
        "anchor": "Stability of persistent currents in spinor Bose-Einstein condensates: Motivated by a recent experiment [S. Beattie, S. Moulder, R. J. Fletcher, and\nZ. Hadzibabic, PRL 110, 025301 (2013)] we study the superflow of atomic spinor\nBose-Einstein condensates optically trapped in a ring-shaped geometry. Within a\ndissipative mean-field approach we simulate a two-component condensate in\nconditions adapted to the experiment. In qualitative agreement with the\nexperimental findings, we observe persistent currents, if the spin-population\nimbalance is above some well-defined `critical' value. The triply charged\nvortices decay in quantized steps. The vortex lines escape from the center of\nthe ring through dynamically created regions in the condensate annulus with\nreduced density of one component filled by atoms of the other component. The\nvortices then leave the ring-shaped high density region of the condensate and\nfinally decay into elementary excitations.",
        "positive": "Finite-temperature effects on the superfluid Bose-Einstein condensation\n  of confined ultracold atoms in three-dimensional optical lattices: We discuss the finite-temperature phase diagram in the three-dimensional\nBose-Hubbard (BH) model in the strong correlation regime, relevant for\nBose-Einstein condensates in optical lattices, by employing a quantum rotor\napproach. In systems with strong on site repulsive interactions, the rotor U(1)\nphase variable dual to the local boson density emerges as an important\ncollective field. After establishing the connection between the rotor\nconstruction and the the on--site interaction in the BH model the robust\neffective action formalism is developed which allows us to study the superfluid\nphase transition in various temperature--interaction regimes."
    },
    {
        "anchor": "Superposition states of ultracold bosons in rotating rings with a\n  realistic potential barrier: In a recent paper [Phys. Rev. A 82, 063623 (2010)] Hallwood et al. argued\nthat it is feasible to create large superposition states with strongly\ninteracting bosons in rotating rings. Here we investigate in detail how the\nsuperposition states in rotating-ring lattices depend on interaction strength\nand barrier height. With respect to the latter we find a trade-off between\nlarge energy gaps and high cat quality. Most importantly, we go beyond the\n\\delta-function approximation for the barrier potential and show that the\nenergy gap decreases exponentially with the number of particles for weak\nbarrier potentials of finite width. These are crucial issues in the design of\nexperiments to realize superposition states.",
        "positive": "Floquet-engineered pair and single particle filter in the Fermi Hubbard\n  model: We investigate the Fermi-Hubbard model with a Floquet-driven impurity in the\nform of a local time-oscillating potential. For strong attractive interactions\na stable formation of pairs is observed. These pairs show a completely\ndifferent transmission behavior than the transmission that is observed for the\nsingle unpaired particles. Whereas in the high frequency limit the single\nparticles show a maximum of the transition at low driving amplitudes, the pairs\ndisplay a pronounced maximum transmission when the amplitude of the driving\nlies close to the ratio of the interaction U and the driving frequency\n{\\omega}. We use the distinct transmission behaviour to design filters for\npairs or single particles, respectively. For example one can totally block the\ntransmission of single particles through the driven impurity and allow only for\nthe transmission of pairs. We quantify the quality of the designed filters."
    },
    {
        "anchor": "Direct probing of the Mott crossover in the SU($N$) Fermi-Hubbard model: The Fermi-Hubbard model (FHM) is a cornerstone of modern condensed matter\ntheory. Developed for interacting electrons in solids, which typically exhibit\nSU($2$) symmetry, it describes a wide range of phenomena, such as metal to\ninsulator transitions and magnetic order. Its generalized SU($N$)-symmetric\nform, originally applied to multi-orbital materials such as transition-metal\noxides, has recently attracted much interest owing to the availability of\nultracold SU($N$)-symmetric atomic gases. Here we report on a detailed\nexperimental investigation of the SU($N$)-symmetric FHM using local probing of\nan atomic gas of ytterbium in an optical lattice to determine the equation of\nstate through different interaction regimes. We prepare a low-temperature\nSU($N$)-symmetric Mott insulator and characterize the Mott crossover,\nrepresenting important steps towards probing predicted novel SU($N$)-magnetic\nphases.",
        "positive": "Universal Relations for Range Corrections to Efimov Features: In a three-body system of identical bosons interacting through a large S-wave\nscattering length $a$, there are several sets of Efimov features related by\ndiscrete scale invariance. Effective field theory was recently used to derive\nuniversal relations between these Efimov features that include the first-order\ncorrection due to a nonzero effective range $r_s$. We reveal a simple pattern\nin these range corrections that had not been previously identified. The pattern\nis explained by the renormalization group for the effective field theory, which\nimplies that the Efimov three-body parameter runs logarithmically with the\nmomentum scale at a rate proportional to $r_s/a$. The running Efimov parameter\nalso explains the empirical observation that range corrections can be largely\ntaken into account by shifting the Efimov parameter by an adjustable parameter\ndivided by a. The accuracy of universal relations that include first-order\nrange corrections is verified by comparing with various theoretical\ncalculations using models with nonzero range."
    },
    {
        "anchor": "Ground State Energy for Fermions in a 1D Harmonic Trap with Delta\n  Function Interaction: Conjectures are made for the ground state energy of a large spin 1/2 Fermion\nsystem trapped in a 1D harmonic trap with delta function interaction. States\nwith different spin J are separately studied. The Thomas-Fermi method is used\nas an effective test for the conjecture.",
        "positive": "Quantum Monte Carlo study of the indirect Pauli exclusion effect in\n  Bose-Fermi mixtures: We study the momentum distributions of a three-dimensional resonant\nBose-Fermi mixture in the molecular limit at zero temperature. For\nconcentration of the bosons with respect to the fermions less or equal to one,\neach boson is bound to a fermion and the system is composed of fermionic\nmolecules plus excess fermions. Not only the bosonic condensate fraction goes\nto zero, signaling a quantum phase transition towards a normal phase, but a\nfinite region of low momenta is depleted, depending on the concentration. This\nphenomenon is named indirect Pauli exclusion effect and is demonstrated via\nFixed-Node Diffusion Monte Carlo simulations and T-matrix calculations."
    },
    {
        "anchor": "Causality and defect formation in the dynamics of an engineered quantum\n  phase transition in a coupled binary Bose-Einstein condensate: Continuous phase transitions occur in a wide range of physical systems, and\nprovide a context for the study of non-equilibrium dynamics and the formation\nof topological defects. The Kibble-Zurek (KZ) mechanism predicts the scaling of\nthe resulting density of defects as a function of the quench rate through a\ncritical point, and this can provide an estimate of the critical exponents of a\nphase transition. In this work we extend our previous study of the\nmiscible-immiscible phase transition of a binary Bose-Einstein condensate (BEC)\ncomposed of two hyperfine states in which the spin dynamics are confined to one\ndimension [J. Sabbatini et al., Phys. Rev. Lett. 107, 230402 (2011)]. The\ntransition is engineered by controlling a Hamiltonian quench of the coupling\namplitude of the two hyperfine states, and results in the formation of a random\npattern of spatial domains. Using the numerical truncated Wigner phase space\nmethod, we show that in a ring BEC the number of domains formed in the phase\ntransitions scales as predicted by the KZ theory. We also consider the same\nexperiment performed with a harmonically trapped BEC, and investigate how the\ndensity inhomogeneity modifies the dynamics of the phase transition and the KZ\nscaling law for the number of domains. We then make use of the symmetry between\ninhomogeneous phase transitions in anisotropic systems, and an inhomogeneous\nquench in a homogeneous system, to engineer coupling quenches that allow us to\nquantify several aspects of inhomogeneous phase transitions. In particular, we\nquantify the effect of causality in the propagation of the phase transition\nfront on the resulting formation of domain walls, and find indications that the\ndensity of defects is determined during the impulse to adiabatic transition\nafter the crossing of the critical point.",
        "positive": "Correlated many-body calculation to study characteristics of Shannon\n  information entropy for ultracold trapped interacting bosons: A correlated many-body calculation is presented to characterize the Shannon\ninformation entropy of trapped interacting bosons. We reformulate the one-body\nShannon information entropy in terms of the one-body probability density. The\nminimum limit of the entropy uncertainty relation (EUR) is approached by making\n$N$ very small in our numerical work. We examine the effect of correlations in\nthe calculation of information entropy. Comparison with the mean-field result\nshows that the correlated basis function is indeed required to characterize the\nimportant features of the information entropies. We also accurately calculate\nthe point of critical instability of an attractive BEC, which is in close\nagreement with the experimental value. Next we calculate two-body entropies in\nposition and momentum spaces and study quantum correlations in the attractive\nBEC."
    },
    {
        "anchor": "Coexistence of photonic and atomic Bose-Einstein condensates in ideal\n  atomic gases: We have studied conditions of photon Bose-Einstein condensate formation that\nis in thermodynamic equilibrium with ideal gas of two-level Bose atoms below\nthe degeneracy temperature. Equations describing thermodynamic equilibrium in\nthe system were formulated; critical temperatures and densities of photonic and\natomic gas subsystems were obtained analytically. Coexistence conditions of\nthese photonic and atomic Bose-Einstein condensates were found. There was\npredicted the possibility of an abrupt type of photon condensation in the\npresence of Bose condensate of ground-state atoms: it was shown that the\nslightest decrease of the temperature could cause a significant gathering of\nphotons in the condensate. This case could be treated as a simple model of the\nsituation known as \"stopped light\" in cold atomic gas. We also showed how\npopulation inversion of atomic levels can be created by lowering the\ntemperature. The latter situation looks promising for light accumulation in\natomic vapor at very low temperatures.",
        "positive": "Dynamical universality classes towards an infinite temperature state: Dynamical universality is the observation that the dynamical properties of\ndifferent systems might exhibit universal behavior that are independent of the\nsystem details. In this paper, we study the long-time dynamics of an\none-dimensional noisy quantum magnetic model, and find that even though the\nsystem are inevitably driven to an infinite temperature state, the relaxation\ndynamics towards such featureless state can be highly nontrivial and universal.\nThe effect of various mode-coupling mechanisms (external potential, disorder,\ninteraction, and the interplay between them) as well as the conservation law on\nthe long-time dynamics of the systems have been studied, and their relevance\nwith current ultracold atomic experiments have been discussed."
    },
    {
        "anchor": "Modulation of a quantized vortex street with a vibrating obstacle: Dynamics of a superfluid flow past an obstacle are investigated by solving\nthe Gross-Pitaevskii equation numerically. For an appropriate velocity and size\nof the obstacle, quantized vortices are periodically generated in the wake,\nwhich form a Benard-von Karman vortex street. It is found that vibration of an\nobstacle modulates the vortex street breaking a symmetry.",
        "positive": "Spin relaxation and band excitation of a dipolar BEC in 2D optical\n  lattices: We observe interband transitions mediated by the dipole-dipole interaction\nfor an array of 1D quantum gases of chromium atoms, trapped in a 2D optical\nlattice. Interband transitions occur when dipolar relaxation releases an energy\nwhich matches or overcomes the lattice band gap. We analyze the role of\ntunneling in higher lattice bands on this process. We compare the experimental\ndipolar relaxation rate with a calculation based on a multiple Fermi Golden\nRule approach, when the lattice sites are symmetric, and the magnetic field is\nparallel to the lattice axis. We also show that an almost complete suppression\nof dipolar relaxation is obtained below a magnetic field threshold set by the\ndepth of the lattice: 1D quantum gases in an excited Zeeman state then become\nmetastable."
    },
    {
        "anchor": "Holographic power-law traps for the efficient production of\n  Bose-Einstein condensates: We use a phase-only spatial light modulator to generate light distributions\nin which the intensity decays as a power law from a central maximum, with order\nranging from 2 (parabolic) to 0.5. We suggest that a sequence of these can be\nused as a time-dependent optical dipole trap for all-optical production of\nBose-Einstein condensates in two stages: efficient evaporative cooling in a\ntrap with adjustable strength and depth, followed by an adiabatic\ntransformation of the trap order to cross the BEC transition in a reversible\nway. Realistic experimental parameters are used to verify the capability of\nthis approach in producing larger Bose-Einstein condensates than by evaporative\ncooling alone.",
        "positive": "Anomalous Bloch oscillations in one dimensional parity-breaking periodic\n  potentials: We investigate the dynamics of a wave packet in a parity-breaking\none-dimensional periodic potential slowly varied in time and perturbed by a\nlinear potential. Parity is broken by considering an asymmetric double well per\nunit cell. By comparing the prediction of the semiclassical dynamics with the\nfull Schr\\\"odinger solution, we show that Bloch oscillations are strongly\naffected by anomalous velocity corrections related to Berry's phase. We\ncharacterize how these effects depend on the degree of parity breaking of the\npotential and on the modulation parameters. We also discuss how to measure the\neffects of the anomalous velocity in current experiments with non-interacting\nBose-Einstein condensates in bichromatic optical lattices, under the effect of\ngravity."
    },
    {
        "anchor": "Scaling behavior of density fluctuations in an expanding quasi-2D\n  degenerate Bose gas: We measure the power spectrum of density fluctuations emerged in a freely\nexpanding quasi-two-dimensional (2D) degenerate Bose gas and investigate the\nscaling behavior of the spectrum for the expansion time. The power spectrum\nshows an oscillatory shape for long expansion times, where the spectral peak\npositions are observed to be shifted to lower spatial frequencies than the\ntheoretical prediction for a non-interacting expansion case. We find the\nspectral peak positions in good agreement with the recent numerical simulation\npresented by Mazets [Phys. Rev. A 86, 055603 (2012)], where the atom-atom\ninteractions are taken into account. We present a mean-field description of the\ninteraction effect in the expansion dynamics and quantitatively account for the\nobserved spectral peak shifts. The spectral shift is intrinsic to the free\nexpansion of a quasi-2D Bose gas due to finite axial confinement. Finally, we\ninvestigate the defocussing effect in the power spectrum measurement.",
        "positive": "Emergence and disruption of spin-charge separation in one-dimensional\n  repulsive fermions: At low temperature, collective excitations of one-dimensional (1D)\ninteracting fermions exhibit spin-charge separation, a unique feature predicted\nby the Tomonaga-Luttinger liquid (TLL) theory, but a rigorous understanding\nremains challenging. Using the thermodynamic Bethe Ansatz (TBA) formalism, we\nanalytically derive universal properties of a 1D repulsive spin-1/2 Fermi gas\nwith arbitrary interaction strength. We show how spin-charge separation emerges\nfrom the exact TBA formalism, and how it is disrupted by the interplay between\nthe two degrees of freedom which brings us beyond the TLL paradigm. Based on\nthe exact low-lying excitation spectra, we further evaluate the spin and charge\ndynamical structure factors (DSFs). The peaks of the DSFs exhibit\ndistinguishable propagating velocities of spin and charge as functions of\ninteraction strength, which can be observed by Bragg spectroscopy with\nultracold atoms."
    },
    {
        "anchor": "Parafermionic zero modes in ultracold bosonic systems: Exotic topologically protected zero modes with parafermionic statistics (also\ncalled fractionalized Majorana modes) have been proposed to emerge in devices\nfabricated from a fractional quantum Hall system and a superconductor. The\nfractionalized statistics of these modes takes them an important step beyond\nthe simplest non-Abelian anyons, Majorana fermions. Building on recent advances\ntowards the realization of fractional quantum Hall states of bosonic ultracold\natoms, we propose a realization of parafermions in a system consisting of\nBose-Einstein-condensate trenches within a bosonic fractional quantum Hall\nstate. We show that parafermionic zero modes emerge at the endpoints of the\ntrenches and give rise to a topologically protected degeneracy. We also discuss\nmethods for preparing and detecting these modes.",
        "positive": "Beyond mean-field study of a binary bosonic mixture in a state-dependent\n  honeycomb lattice: We investigate a binary mixture of bosonic atoms loaded into a\nstate-dependent honeycomb lattice. For this system, the emergence of a\nso-called twisted-superfluid ground state was experimentally observed in\n[Soltan-Panahi et al., Nat. Phys. 8, 71 (2012)]. Theoretically, the origin of\nthis effect is not understood. We perform numerical simulations of an extended\nBose-Hubbard model adapted to the experimental parameters employing the\nMulti-Layer Multi-Configuration Time-Dependent Hartree method for Bosons. Our\nresults confirm the overall applicability of mean-field theory within the\nrelevant parameter range. Beyond this, we provide a detailed analysis of\ncorrelation effects correcting the mean-field result. These have the potential\nto induce asymmetries in single shot time-of-flight measurements, but we find\nno indication of the patterns characteristic of the twisted superfluid. We\ncomment on the restrictions of our model and possible extensions."
    },
    {
        "anchor": "Non-equilibrium diagrammatic approach to strongly interacting photons: We develop a non-equilibrium field-theoretical approach, based on a\nsystematic diagrammatic expansion, for strongly interacting photons in\noptically dense atomic media. We consider the case where the characteristic\nphoton-propagation range $L_P$ is much larger than the interatomic spacing $a$\nand where the density of atomic excitations is low enough to neglect saturation\neffects. In the highly polarizable medium the photons experience nonlinearities\nthrough the interactions they inherit from the atoms. If the atom-atom\ninteraction range $L_E$ is also large compared to $a$, we show that scattering\nprocesses with momentum transfer between photons are suppressed by a factor\n$a/L_E$. We are then able to perform a self-consistent resummation of a\nspecific (Hartree-like) diagram subclass and obtain quantitative results in the\nhighly non-perturbative regime of large single-atom cooperativity. Here we find\nimportant, conceptually new collective phenomena emerging due to the\ndissipative nature of the interactions, which even give rise to novel phase\ntransitions. The robustness of these is investigated by inclusion of the\nleading corrections in $a/L_E$. We consider specific applications to photons\npropagating under EIT conditions along waveguides near atomic arrays as well as\nwithin Rydberg ensembles.",
        "positive": "Gaussian-state Ansatz for the non-equilibrium dynamics of quantum spin\n  lattices: The study of non-equilibrium dynamics is one of the most important challenges\nof modern quantum many-body physics, in relationship with fundamental questions\nin quantum statistical mechanics, as well as with the fields of quantum\nsimulation and computing. In this work we propose a Gaussian Ansatz for the\nstudy of the nonequilibrium dynamics of quantum spin systems. Within our\napproach, the quantum spins are mapped onto Holstein-Primakoff bosons, such\nthat a coherent spin state -- chosen as the initial state of the dynamics --\nrepresents the bosonic vacuum. The state of the system is then postulated to\nremain a bosonic Gaussian state at all times, an assumption which is exact when\nthe bosonic Hamiltonian is quadratic; and which is justified in the case of a\nnonlinear Hamiltonian if the boson density remains moderate. We test the\naccuracy of such an Ansatz in the paradigmatic case of the $S=1/2$\ntransverse-field Ising model, in one and two dimensions, initialized in a state\naligned with the applied field. We show that the Gaussian Ansatz, when applied\nto the bosonic Hamiltonian with nonlinearities truncated to quartic order, is\nable to reproduce faithfully the evolution of the state, including its\nrelaxation to the equilibrium regime, for fields larger than the critical field\nfor the paramagnetic-ferromagnetic transition in the ground state. In\nparticular the spatio-temporal pattern of correlations reconstructed via the\nGaussian Ansatz reveals the dispersion relation of quasiparticle excitations,\nexhibiting the softening of the excitation gap upon approaching the critical\nfield. Our results suggest that the Gaussian Ansatz correctly captures the\nessential effects of nonlinearities in quantum spin dynamics; and that it can\nbe applied to the study of fundamental phenomena such as quantum thermalization\nand its breakdown."
    },
    {
        "anchor": "Leading Order $k_Fa$ Corrections to the Free Energy and Phase Separation\n  in Two-component Fermion Systems: We study phase separation in a dilute two-component Fermi system with\nattractive interactions as a function of the coupling strength and the\npolarization or number density asymmetry between the two components. In weak\nand strong couplings with a finite number density asymmetry, phase separation\nis energetically more favorable. A heterogeneous phase containing a symmetric\nsuperfluid component and an asymmetric normal phase has lower energy than a\nhomogeneous normal phase. We show that for a small number density asymmetry,\ntaking into consideration the leading order corrections at order $k_Fa$ of the\ninteraction parameter, phase separation is stable against the normal phase in\nthe whole BCS range. We investigate the consequences of the consideration of\nthe leading order $k_Fa$ corrections to the thermodynamic potentials of the\nnormal and BCS phase on the Chandrasekhar-Clogston limit. We have also\ninvestigated the stability of a Bose-Fermi mixture in the far-BEC limit. We\nfind that the molecular BEC is locally stable against an external magnetic\nfield $h$, provided $|h|$ is smaller than the pairing gap $\\Delta_{gap}$.",
        "positive": "Thermally Fluctuating Inhomogeneous Superfluid State of Strongly\n  Interacting Fermions in an Optical Lattice: The presence of attractive interaction between fermions can lead to pairing\nand superfluidity in an optical lattice. The temperature needed to observe\nsuperfluidity is about a tenth of the tunneling energy in the optical lattice,\nand currently beyond experimental reach. However, at strong coupling the\nprecursors to global superfluidity should be visible at achievable\ntemperatures, in terms of fluctuating domains with strong pairing correlations.\nWe explore this regime of the attractive two dimensional fermion Hubbard model,\nin the presence of a confining potential, using a new Monte Carlo technique. We\ncapture the low temperature inhomogeneous superfluid state with its unusual\nspectral signatures but mainly focus on the experimentally accessible\nintermediate temperature state. In this regime, and for the trap center density\nwe consider, there is a large pairing amplitude at the center, spatially\ncorrelated into domains extending over several lattice spacings. We map out the\nthermal evolution of the local density, the double occupancy, the pairing\ncorrelations, and the momentum distribution function across this phase\nfluctuation window."
    },
    {
        "anchor": "Effective preparation and collisional decay of atomic condensate in\n  excited bands of an optical lattice: We present a method for the effective preparation of a Bose-Einstein\ncondensate (BEC) into the excited bands of an optical lattice via a\nstanding-wave pulse sequence. With our method, the BEC can be prepared in\neither a single Bloch state in a excited-band, or a coherent superposition of\nstates in different bands. Our scheme is experimentally demonstrated by\npreparing a $^{87}$Rb BEC into the $d$-band and the superposition of $s$- and\n$d$-band states of a one-dimensional optical lattice, within a few tens of\nmicroseconds. We further measure the decay of the BEC in the $d$-band state,\nand carry an analytical calculation for the collisional decay of atoms in the\nexcited-band states. Our theoretical and experimental results consist well.",
        "positive": "One- and Two-Particle Problem with Correlated Disorder Potential: Motivated by the recent experimental and theoretical progresses in the\nexploration of the effect of disorder in interacting system, we examine the\neffect of two types of correlated disorder, the quasi-periodic potential and\nspeckle disorder potential, on one- and two-particle problem with exact\ndiagonalization (ED) method. We give the phase diagram for single particle in\nthe presence of quasi-periodic potential and also analyse the effect of strong\ninteraction on the phase diagram for ground state in two dimensions. For the\nspeckle disorder potential case, we examine both the effect of correlation\nlength and disorder strength on single particle ground state energy and\ntwo-particle binding energy. The transport property for different interaction\nstrength under speckle disorder potential is also calculated and discussed at\nlast."
    },
    {
        "anchor": "All-optical transport and compression of ytterbium atoms into the\n  surface of a solid immersion lens: We present an all-optical method to load 174Yb atoms into a single layer of\nan optical trap near the surface of a solid immersion lens which improves the\nnumerical aperture of a microscope system. Atoms are transported to a region 20\num below the surface using a system comprised by three optical dipole traps.\nThe \"optical accordion\" technique is used to create a condensate and compress\nthe atoms to a width of 120 nm and a distance of 1.8 um away from the surface.\nMoreover, we are able to verify that after compression the condensate behaves\nas a two-dimensional quantum gas.",
        "positive": "Probing the relaxation towards equilibrium in an isolated strongly\n  correlated 1D Bose gas: The problem of how complex quantum systems eventually come to rest lies at\nthe heart of statistical mechanics. The maximum entropy principle put forward\nin 1957 by E. T. Jaynes suggests what quantum states one should expect in\nequilibrium but does not hint as to how closed quantum many-body systems\ndynamically equilibrate. A number of theoretical and numerical studies\naccumulate evidence that under specific conditions quantum many-body models can\nrelax to a situation that locally or with respect to certain observables\nappears as if the entire system had relaxed to a maximum entropy state. In this\nwork, we report the experimental observation of the non-equilibrium dynamics of\na density wave of ultracold bosonic atoms in an optical lattice in the regime\nof strong correlations. Using an optical superlattice, we are able to prepare\nthe system in a well-known initial state with high fidelity. We then follow the\ndynamical evolution of the system in terms of quasi-local densities, currents,\nand coherences. Numerical studies based on the time-dependent density-matrix\nrenormalization group method are in an excellent quantitative agreement with\nthe experimental data. For very long times, all three local observables show a\nfast relaxation to equilibrium values compatible with those expected for a\nglobal maximum entropy state. We find this relaxation of the quasi-local\ndensities and currents to initially follow a power-law with an exponent being\nsignificantly larger than for free or hardcore bosons. For intermediate times\nthe system fulfills the promise of being a dynamical quantum simulator, in that\nthe controlled dynamics runs for longer times than present classical algorithms\nbased on matrix product states can efficiently keep track of."
    },
    {
        "anchor": "Ground state phase diagram of the 2d Bose-Hubbard model with anisotropic\n  hopping: We compute the ground state phase diagram of the 2d Bose-Hubbard model with\nanisotropic hopping using quantum Monte Carlo simulations, connecting the 1d to\nthe 2d system. We find that the tip of the lobe lies on a curve controlled by\nthe 1d limit over the full anisotropy range while the universality class is\nalways the same as in the isotropic 2d system. This behavior can be derived\nanalytically from the lowest RG equations and has a form typical for the\nunderlying Kosterlitz-Thouless transition in 1d. We also compute the phase\nboundary of the Mott lobe for strong anisotropy and compare it to the 1d\nsystem. Our calculations shed light on recent cold gas experiments monitoring\nthe dynamics of an expanding cloud.",
        "positive": "Stability of spherically trapped three-dimensional Bose-Einstein\n  condensates against macroscopic fragmentation: We consider spherically trapped Bose gases in three dimensions with contact\ninteractions, and investigate whether the Bose-Einstein condensate at zero\ntemperature is stable against macroscopic fragmentation into a small number of\nmutually incoherent pieces. Our results are expressed in terms of a\ndimensionless interaction measure proportional to the Thomas-Fermi parameter.\nIt is shown that while three-dimensional condensates are inherently much more\nstable against macroscopic fragmentation than their quasi-one- and\nquasi-two-dimensional counterparts, they fragment at a sufficiently large value\nof the dimensionless interaction measure, which we determine both fully\nnumerically and semianalytically from a continuum limit of large particle\nnumbers."
    },
    {
        "anchor": "Probing an effective-range-induced super fermionic Tonks-Girardeau gas\n  with ultracold atoms in one-dimensional harmonic traps: We theoretically investigate an ultracold spin-polarized atomic Fermi gas\nwith resonant odd-channel ($p$-wave) interactions trapped in one-dimensional\nharmonic traps. We solve the Yang-Yang thermodynamic equations based on the\nexact Bethe ansatz solution, and predict the finite-temperature density profile\nand breathing mode frequency, by using a local density approximation to take\ninto account the harmonic trapping potential. The system features an exotic\nsuper fermionic Tonks-Girardeau (super-fTG) phase, due to the large effective\nrange of the interatomic interactions. We explore the parameter space for such\na fascinating super-fTG phase at finite temperature and provide smoking-gun\nsignatures of its existence in both breathing mode frequencies and density\nprofiles. Our results suggest that the super-fTG phase can be readily probed at\ntemperature at about $0.1T_{F}$, where $T_{F}$ is the Fermi temperature. These\nresults are to be confronted with future cold-atom experiments with $^{6}$Li\nand $^{40}$K atoms.",
        "positive": "Cooling of a one-dimensional Bose gas: We experimentally study the dynamics of a degenerate one-dimensional Bose gas\nthat is subject to a continuous outcoupling of atoms. Although standard\nevaporative cooling is rendered ineffective by the absence of thermalizing\ncollisions in this system, we observe substantial cooling. This cooling\nproceeds through homogeneous particle dissipation and many-body dephasing,\nenabling the preparation of otherwise unexpectedly low temperatures. Our\nobservations establish a scaling relation between temperature and particle\nnumber, and provide insights into equilibration in the quantum world."
    },
    {
        "anchor": "Asymptotic temperature of a lossy condensate: We monitor the time evolution of the temperature of phononic collective modes\nin a one-dimensional quasicondensate submitted to losses. At long times the\nratio between the temperature and the energy scale $mc^2$, where $m$ is the\natomic mass and $c$ the sound velocity takes, within a precision of 20\\%, an\nasymptotic value. This asymptotic value is observed while $mc^2$ decreases in\ntime by a factor as large as 2.5. Moreover this ratio is shown to be\nindependent on the loss rate and on the strength of interactions. These results\nconfirm theoretical predictions and the measured stationary ratio is in\nquantitative agreement with the theoretical calculations.",
        "positive": "Analytical and numerical study of dirty bosons in a\n  quasi-one-dimensional harmonic trap: The emergence of a Bose-glass region in a quasi one-dimensional\nBose-Einstein-condensed gas in a harmonic trapping potential with an additional\ndelta-correlated disorder potential at zero temperature is studied using three\napproaches. At first, the corresponding time-independent Gross-Pitaevskii\nequation is numerically solved for the condensate wave function, and disorder\nensemble averages are evaluated. In particular, we analyse quantitatively the\nemergence of mini-condensates in the local minima of the random potential,\nwhich occurs for weak disorder preferentially at the border of the condensate,\nwhile for intermediate disorder strength this happens in the trap centre.\nSecond, in view of a more detailed physical understanding of this phenomenon,\nwe extend a quite recent non-perturbative approach towards the weakly\ninteracting dirty boson problem, which relies on the Hartree-Fock theory and is\nworked out on the basis of the replica method, from the homogeneous case to a\nharmonic confinement. Finally, in the weak disorder regime we also apply the\nThomas-Fermi approximation, while in the intermediate disorder regime we\nadditionally use a variational ansatz in order to describe analytically the\nnumerically observed redistribution of the fragmented mini-condensates with\nincreasing disorder strength."
    },
    {
        "anchor": "Thermodynamic stability, compressibility matrix, and effects of mediated\n  interactions in a strongly-interacting Bose-Fermi mixture: We theoretically investigate the thermodynamic stability of a normal-state\nBose-Fermi mixture, with a tunable Bose-Fermi pairing interaction $-U_{\\rm\nBF}<0$ associated with a hetero-nuclear Feshbach resonance, as well as a weak\nrepulsive Bose-Bose interaction $U_{\\rm BB}\\ge 0$. Including strong\nhetero-pairing fluctuations associated with the former interaction within the\nself-consistent $T$-matrix approximation, as well as the latter within the\nmean-field level, we calculate the compressibility matrix, to assess the\nstability of this system against density fluctuations. In the weak- and the\nintermediate-coupling regime with respect $-U_{\\rm BF}$, we show that an\neffective attractive interaction between bosons mediated by density\nfluctuations in the Fermi component makes the system unstable below a certain\ntemperature $T_{\\rm clp}$ (leading to density collapse). When $U_{\\rm BB}=0$,\n$T_{\\rm clp}$ is always higher than the Bose-Einstein condensation (BEC)\ntemperature $T_{\\rm c}$. When $U_{\\rm BB}>0$, the density collapse is\nsuppressed, and the BEC transition becomes possible. It is also suppressed by\nthe formation of tightly bound Bose-Fermi molecules when the hetero-pairing\ninteraction $-U_{\\rm BF}$ is strong; however, since the system may be viewed as\na molecular Fermi gas in this case, the BEC transition does not also occur.\nSince quantum gases involving Bose atoms are known to be sensitive to\ninter-particle correlations, our results would be useful for the study of\nmany-body properties of a Bose-Fermi mixture in a stable manner, without facing\nthe unwanted density collapse.",
        "positive": "Suppression of the quantum-mechanical collapse by repulsive interactions\n  in a quantum gas: The quantum-mechanical collapse (alias fall onto the center of particles\nattracted by potential -1/r^2), or \"quantum anomaly\", is a well-known issue in\nthe quantum theory. We demonstrate that the mean-field repulsive nonlinearity\nprevents the collapse and thus puts forward a solution to the quantum-anomaly\nproblem different from that previously developed in the framework of the linear\nquantum-field theory. This solution may be realized in the 3D or 2D gas of\ndipolar bosons attracted by a central charge, and in the 2D gas of magnetic\ndipoles attracted by a current filament. In the 3D setting, the dipole-dipole\ninteractions are also taken into regard, in the mean-field approximation. In\nlieu of the collapse, the cubic nonlinearity creates a 3D ground state (GS),\nwhich does not exist in the respective linear Schroedinger equation (SE). The\naddition of the harmonic trap gives rise to a tristability, in the case when\nthe SE still does not lead to the collapse. In the 2D setting, the cubic\nnonlinearity is not strong enough to prevent the collapse; however, the quintic\nterm does it, creating the GS, as well as its counterparts carrying the angular\nmomentum (vorticity). Counter-intuitively, such self-trapped 2D modes exist\neven in the case of a weakly repulsive potential 1/r^2. In the presence of the\nharmonic trap, the 2D quintic model with a weakly repulsive central potential\n1/r^2 gives rise to three confined modes, the middle one being unstable,\nspontaneously developing into a breather. In both the 3D and 2D cases, the GS\nwave functions are found in a numerical form, and also in the form of an\nanalytical approximation, which is asymptotically exact in the limit of the\nlarge norm."
    },
    {
        "anchor": "Charge Gaps at Fractional Fillings in Boson Hubbard Ladders: The Bose-Hubbard Hamiltonian describes the competition between superfluidity\nand Mott insulating behavior at zero temperature and commensurate filling as\nthe strength of the on-site repulsion is varied. Gapped insulating phases also\noccur at non-integer densities as a consequence of longer ranged repulsive\ninteractions. In this paper we explore the formation of gapped phases in\ncoupled chains due instead to anisotropies $t_x \\neq t_y$ in the bosonic\nhopping, extending the work of Crepin {\\it et al.} [Phys. Rev. B 84, 054517\n(2011)] on two coupled chains, where a gap was shown to occur at half filling\nfor arbitrarily small interchain hopping $t_y$. Our main result is that, unlike\nthe two-leg chains, for three- and four-leg chains, a charge gap requires a\nfinite nonzero critical $t_y$ to open. However, these finite values are\nsurprisingly small, well below the analogous values required for a fermionic\nband gap to open.",
        "positive": "Probing Majorana fermions in spin-orbit coupled atomic Fermi gases: We examine theoretically the visualization of Majorana fermions in a\ntwo-dimensional trapped ultracold atomic Fermi gas with spin-orbit coupling. By\nincreasing an external Zeeman field, the trapped gas transits from\nnon-topological to topological superfluid, via a mixed phase in which both\ntypes of superfluids coexist. We show that the zero-energy Majorana fermion,\nsupported by the topological superfluid and localized at the vortex core, is\nclearly visible through (i) the core density and (ii) the local density of\nstates, which are readily measurable in experiment. We present a realistic\nestimate on experimental parameters for ultracold $^{40}$K atoms."
    },
    {
        "anchor": "Ground state of the two-dimensional attractive Fermi gas: essential\n  properties from few- to many-body: We calculate the ground-state properties of unpolarized two-dimensional\nattractive fermions in the range from few to many particles. Using\nfirst-principles lattice Monte Carlo methods, we determine the ground-state\nenergy, Tan's contact, momentum distribution, and single-particle correlation\nfunction. We investigate those properties for systems of $N=4,8,...,40$\nparticles and for a wide range of attractive couplings. As the attractive\ncoupling is increased, the thermodynamic limit is reached at progressively\nlower $N$ due to the dominance of the two-body sector. At large momenta $k$,\nthe momentum distribution displays the expected $k^{-4}$ behavior, but its\nonset shifts from $k \\simeq 1.8 k^{}_F$ at weak coupling towards higher $k$ at\nstrong coupling.",
        "positive": "From cold Fermi fluids to the hot QGP: Strongly coupled quantum fluids are found in different forms, including\nultracold Fermi gases or tiny droplets of extremely hot Quark-Gluon Plasma.\nAlthough the systems differ in temperature by many orders of magnitude, they\nexhibit a similar almost inviscid fluid dynamical behavior. In this work, we\nsummarize some of the recent theoretical developments toward better\nunderstanding this property in cold Fermi gases at and near unitarity."
    },
    {
        "anchor": "Polariton condensation with saturable molecules dressed by vibrational\n  modes: Polaritons, mixed light-matter quasiparticles, undergo a transition to a\ncondensed, macroscopically coherent state at low temperatures or high\ndensities. Recent experiments show that coupling light to organic molecules\ninside a microcavity allows condensation at room temperature. The molecules act\nas saturable absorbers with transitions dressed by molecular vibrational modes.\nMotivated by this we calculate the phase diagram and spectrum of a modified\nTavis-Cummings model, describing vibrationally dressed two-level systems,\ncoupled to a cavity mode. Coupling to vibrational modes can induce re-entrance,\ni.e. a normal-condensed-normal sequence with decreasing temperature and can\ndrive the transition first order.",
        "positive": "Vortex lines attached to dark solitons in Bose-Einstein condensates and\n  Boson-Vortex Duality in 3+1 Dimensions: We demonstrate the existence of stationary states composed of vortex lines\nattached to planar dark solitons in scalar Bose-Einstein condensates.\nDynamically stable states of this type are found at low values of the chemical\npotential in channeled condensates, where the long-wavelength instability of\ndark solitons is prevented. In oblate, harmonic traps, U-shaped vortex lines\nattached by both ends to a single planar soliton are shown to be long-lived\nstates. Our results are reported for parameters typical of current experiments,\nand open up a way to explore the interplay of different topological structures.\nThese configurations provide Dirichlet boundary conditions for vortex lines and\nthereby mimic open strings attached to D-branes in string theory. We show that\nthese similarities can be formally established by mapping the Gross-Pitaevskii\ntheory into a dual effective string theory for open strings via a boson-vortex\nduality in 3+1 dimensions. Combining a one-form gauge field living on the\nsoliton plane which couples to the endpoints of vortex lines and a two-form\ngauge field which couples to vortex lines, we obtain a gauge-invariant dual\naction of open vortex lines with their endpoints attached to dark solitons."
    },
    {
        "anchor": "Particle dynamics and ergodicity-breaking in twisted-bilayer optical\n  lattices: Recent experiments have realized a twisted bilayer-like optical potential for\nultra-cold atoms, which in contrast to solid-state set ups may allow for an\narbitrary ratio between the inter- and intra-layer couplings. For commensurate\nMoir\\'e twistings a large-enough inter-layer coupling results in particle\ntransport dominated by channel formation. For incommensurate twistings, the\ninterlayer coupling acts as an effective disorder strength. Whereas for weak\ncouplings the whole spectrum remains ergodic, at a critical value part of the\neigenspectrum transitions into multifractal states. A similar transition may be\nobserved as well as a function of an energy bias between the two layers. Our\nstudy reveals atoms in optical twisted-bilayer lattices as an interesting new\nplatform for the study of ergodicity breaking and multifractality.",
        "positive": "Monte Carlo study of a Fermi gas with infinite scattering length: The Fermi gas at unitarity is a particularly interesting system of cold\natoms, being dilute and strongly interacting at the same time. It can be\nstudied non-perturbatively with Monte Carlo methods, like the recently\ndeveloped worm algorithm. We discuss our implementation and tests of this\nalgorithm and suggest a modification that increases its efficiency by reducing\nautocorrelations. We then show how the worm algorithm can be applied to\ncalculate the critical temperature of an imbalanced Fermi gas (unequal number\nof fermions in the two spin components). We finally present some results\nobtained with the modified algorithm, in the balanced as well as in the\nimbalanced case."
    },
    {
        "anchor": "Stochastic Growth Dynamics and Composite Defects in Quenched Immiscible\n  Binary Condensates: We study the sensitivity of coupled condensate formation dynamics on the\nhistory of initial stochastic domain formation in the context of\ninstantaneously quenched elongated harmonically-trapped immiscible\ntwo-component atomic Bose gases. The spontaneous generation of defects in the\nfastest condensing component, and subsequent coarse-graining dynamics, can lead\nto a deep oscillating microtrap into which the other component condenses,\nthereby establishing a long-lived composite defect in the form of a dark-bright\nsolitary wave. We numerically map out diverse key aspects of these competing\ngrowth dynamics, focussing on the role of shot-to-shot fluctuations and global\nparameter changes (initial state choices, quench parameters and condensate\ngrowth rates). We conclude that phase-separated structures observable on\nexperimental timescales are likely to be metastable states whose form is\ninfluenced by the stability and dynamics of the spontaneously-emerging\ndark-bright solitary wave.",
        "positive": "Charge Pumping of Interacting Fermion Atoms in the Synthetic Dimension: Recently it has been proposed and experimentally demonstrated that a\nspin-orbit coupled multi-component gas in 1d lattice can be viewed as spinless\ngas in a synthetic 2d lattice with a magnetic flux. In this letter we consider\ninteraction effect of such a Fermi gas, and propose signatures in charge\npumping experiment, which can be easily realized in this setting. Using 1/3\nfilling of the lowest 2d band as an example, in strongly interacting regime, we\nshow that the charge pumping value gradually approaches a universal fractional\nvalue for large spin component and low filling of 1d lattice, indicating a\nfractional quantum Hall type behavior; while the charge pumping value is zero\nif the 1d lattice filling is commensurate, indicating a Mott insulator\nbehavior. The charge-density-wave order is also discussed."
    },
    {
        "anchor": "Phase Separation of Superfluids in the Chain of Four-Component Ultracold\n  Atoms: We investigate the competition of various exotic superfluid states in a chain\nof spin-polarized ultracold fermionic atoms with hyperfine spin $F = 3/2$ and\ns-wave contact interactions. We show that the ground state is an exotic\ninhomogeneous mixture in which two distinct superfluid phases --- spin-carrying\npairs and singlet quartets --- form alternating domains in an extended region\nof the parameter space.",
        "positive": "Condensation and quasicondensation in an elongated three-dimensional\n  Bose gas: We study the equilibrium correlations of a Bose gas in an elongated\nthree-dimensional harmonic trap using a grand-canonical classical-field method.\nWe focus in particular on the progressive transformation of the gas from the\nnormal phase, through a phase-fluctuating quasicondensate regime to the\nso-called true-condensate regime, with decreasing temperature. Choosing\nrealistic experimental parameters, we quantify the density fluctuations and\nphase coherence of the atomic field as functions of the system temperature. We\nidentify the onset of Bose condensation through analysis of both the\ngeneralized Binder cumulant appropriate to the inhomogeneous system, and the\nsuppression of the effective many-body T matrix that characterizes interactions\nbetween condensate atoms in the finite-temperature field. We find that the\nsystem undergoes a second-order transition to condensation near the critical\ntemperature for an ideal Bose gas in the strongly anisotropic three-dimensional\ngeometry, but remains in a strongly phase-fluctuating quasicondensate regime\nuntil significantly lower temperatures. We characterize the crossover from a\nquasicondensate to a true condensate by a qualitative change in the form of the\nnon-local first-order coherence function of the field, and compare our results\nto those of previous works employing a density-phase Bogoliubov-de Gennes\nanalysis."
    },
    {
        "anchor": "Two-dimensional boson-fermion mixtures: Using mean-field theory, we study the equilibrium properties of boson-fermion\nmixtures confined in a harmonic pancake-shaped trap at zero temperature. When\nthe modulus of the s-wave scattering lengths are comparable to the mixture\nthickness, two-dimensional scattering events introduce a logarithmic dependence\non density in the coupling constants, greatly modifying the density profiles\nthemselves. We show that for the case of a negative boson-fermion\nthree-dimensional s-wave scattering length, the dimensional crossover\nstabilizes the mixture against collapse and drives it towards spatial demixing.",
        "positive": "Dynamical properties of a trapped dipolar Fermi gas at finite\n  temperature: We investigate the dynamical properties of a trapped finite-temperature\nnormal Fermi gas with dipole-dipole interaction. For the free expansion\ndynamics, we show that the expanded gas always becomes stretched along the\ndirection of the dipole moment. In addition, we present the temperature and\ninteraction dependences of the asymptotical aspect ratio. We further study the\ncollapse dynamics of the system by suddenly increasing the dipolar interaction\nstrength. We show that, in contrast to the anisotropic collapse of a dipolar\nBose-Einstein condensate, a dipolar Fermi gas always collapses isotropically\nwhen the system becomes globally unstable. We also explore the interaction and\ntemperature dependences for the frequencies of the low-lying collective\nexcitations."
    },
    {
        "anchor": "Non-Hermitian superfluid--Mott-insulator transition in the\n  one-dimensional zigzag bosonic chains: We investigated the behavior of non-Hermitian bosonic gases with Hubbard\ninteractions in the one-dimensional zigzag optical lattices through the\ncalculation of dynamic response functions. Our findings showed the existence of\na non-Hermitian quantum phase transition that is dependent on the\npseudo-Hermitian symmetry. The system tends to exhibit a superfluid phase, when\nsubjected to weak dissipation. While under strong dissipation, the\npseudo-Hermitian symmetry of the system is partially broken, leading to a\ntransition towards a normal liquid phase. As the dissipation increases beyond\nthe critical threshold, the pseudo-Hermitian symmetry is completely broken,\nresulting in a Mott-insulator phase. We propose an experimental setup using\none-dimensional zigzag optical lattices containing two-electron atoms to\nrealize this system. Our research emphasizes the key role of non-Hermiticity in\nquantum phase transitions and offers a new theoretical framework as well as\nexperimental methods for understanding the behavior of dissipative quantum\nsystems, implicating significant development of new quantum devices and\ntechnologies.",
        "positive": "Vortex structures and zero energy states in the BCS-to-BEC evolution of\n  p-wave resonant Fermi gases: Multiply quantized vortices in the BCS-to-BEC evolution of p-wave resonant\nFermi gases are investigated theoretically. The vortex structure and the\nlow-energy quasiparticle states are discussed, based on the self-consistent\ncalculations of the Bogoliubov-de Gennes and gap equations. We reveal the\ndirect relation between the macroscopic structure of vortices, such as particle\ndensities, and the low-lying quasiparticle state. In addition, the net angular\nmomentum for multiply quantized vortices with a vorticity $\\kappa$ is found to\nbe expressed by a simple equation, which reflects the chirality of the Cooper\npairing. Hence, the observation of the particle density depletion and the\nmeasurement of the angular momentum will provide the information on the\ncore-bound state and $p$-wave superfluidity. Moreover, the details on the zero\nenergy Majorana state are discussed in the vicinity of the BCS-to-BEC\nevolution. It is demonstrated numerically that the zero energy Majorana state\nappears in the weak coupling BCS limit only when the vortex winding number is\nodd. There exist the $\\kappa$ branches of the core bound states for a vortex\nstate with vorticity $\\kappa$, whereas only one of them can be the zero energy.\nThis zero energy state vanishes at the BCS-BEC topological phase transition,\nbecause of interference between the core-bound and edge-bound states."
    },
    {
        "anchor": "Probing pair correlations in Fermi gases with Ramsey-Bragg\n  interferometry: We propose an interferometric method to probe pair correlations in a gas of\nspin-1/2 fermions. The method consists of a Ramsey sequence where both spin\nstates of the Fermi gas are set in a superposition of a state at rest and a\nstate with a large recoil velocity. The two-body density matrix is extracted\nvia the fluctuations of the transferred fraction to the recoiled state. In the\npair-condensed phase, the off-diagonal long-range order is directly reflected\nin the asymptotic behavior of the interferometric signal for long interrogation\ntimes. The method also allows to probe the spatial structure of the condensed\npairs: the interferometric signal is an oscillating function of the\ninterrogation time in the Bardeen-Cooper-Schrieffer regime; it becomes an\noverdamped function in the molecular Bose-Einstein condensate regime.",
        "positive": "Topological interface engineering and defect crossing in ultracold\n  atomic gases: We propose an experimentally feasible scheme for topological interface\nengineering and show how it can be used for studies of dynamics of\ntopologically nontrivial interfaces and perforation of defects and textures\nacross such interfaces. The method makes use of the internal spin structure of\nthe atoms together with locally applied control of interaction strengths to\ncreate many-particle states with highly complex topological properties. In\nparticular, we consider a constructed coherent interface between topologically\ndistinct phases of spinor Bose-Einstein condensates."
    },
    {
        "anchor": "Diffusion quantum Monte Carlo calculation of the quasiparticle effective\n  mass of the two-dimensional homogeneous electron gas: The quasiparticle effective mass is a key quantity in the physics of electron\ngases, describing the renormalization of the electron mass due to\nelectron-electron interactions. Two-dimensional electron gases are of\nfundamental importance in semiconductor physics, and there have been numerous\nexperimental and theoretical attempts to determine the quasiparticle effective\nmass in these systems. In this work we report quantum Monte Carlo results for\nthe quasiparticle effective mass of a two-dimensional homogeneous electron gas.\nOur calculations differ from previous quantum Monte Carlo work in that much\nsmaller statistical error bars have been achieved, allowing for an improved\ntreatment of finite-size effects. In some cases we have also been able to use\nlarger system sizes than previous calculations.",
        "positive": "Realizing a 1D topological gauge theory in an optically dressed BEC: Topological gauge theories describe the low-energy properties of certain\nstrongly correlated quantum systems through effective weakly interacting\nmodels. A prime example is the Chern-Simons theory of fractional quantum Hall\nstates, where anyonic excitations emerge from the coupling between weakly\ninteracting matter particles and a density-dependent gauge field. Although in\ntraditional solid-state platforms such gauge theories are only convenient\ntheoretical constructions, engineered quantum systems enable their direct\nimplementation and provide a fertile playground to investigate their\nphenomenology without the need for strong interactions. Here, we report the\nquantum simulation of a topological gauge theory by realizing a one-dimensional\nreduction of the Chern-Simons theory (the chiral BF theory) in a Bose-Einstein\ncondensate. Using the local conservation laws of the theory, we eliminate the\ngauge degrees of freedom in favour of chiral matter interactions, which we\nengineer by synthesizing optically dressed atomic states with\nmomentum-dependent scattering properties. This allows us to reveal the key\nproperties of the chiral BF theory: the formation of chiral solitons and the\nemergence of an electric field generated by the system itself. Our results\nexpand the scope of quantum simulation to topological gauge theories and open a\nroute to the implementation of analogous gauge theories in higher dimensions."
    },
    {
        "anchor": "Steady-state many-body entanglement of hot reactive fermions: Entanglement is typically created via systematic intervention in the time\nevolution of an initially unentangled state, which can be achieved by coherent\ncontrol, carefully tailored non-demolition measurements, or dissipation in the\npresence of properly engineered reservoirs. In this paper we show that\ntwo-component Fermi gases at ~\\mu K temperatures naturally evolve, in the\npresence of reactive two-body collisions, into states with highly entangled\n(Dicke-type) spin wavefunctions. The entanglement is a steady-state property\nthat emerges---without any intervention---from uncorrelated initial states, and\ncould be used to improve the accuracy of spectroscopy in experiments with\nfermionic alkaline earth atoms or fermionic groundstate molecules.",
        "positive": "Two-dimensional Bose gas of tilted dipoles: roton instability and\n  condensate depletion: We predict the effect of the roton instability for a two-dimensional weakly\ninteracting gas of tilted dipoles in a single homogeneous quantum layer. Being\ntypical for strongly correlated systems, the roton phenomena appear to occur in\na weakly interacting gas. It is important that in contrast to a system of\nnormal to wide layer dipoles, breaking of the rotational symmetry for a system\nof tilted dipoles leads to the convergence of the condensate depletion even up\nto the threshold of the roton instability, with mean-field approach being\nvalid. Predicted effects can be observed in a wide class of dipolar systems. We\nsuggest observing predicted phenomena for systems of ultracold atoms and polar\nmolecules in optical lattices, and estimate optimal experimental parameters."
    },
    {
        "anchor": "Interaction induced dynamical $\\mathcal{PT}$ symmetry breaking in\n  dissipative Fermi-Hubbard models: We investigate the dynamical properties of one-dimensional dissipative\nFermi-Hubbard models, which are described by the Lindblad master equations with\nsite-dependent jump operators. The corresponding non-Hermitian effective\nHamiltonians with pure loss terms possess parity-time ($\\mathcal{PT}$) symmetry\nif we compensate the system additionally an overall gain term. By solving the\ntwo-site Lindblad equation with fixed dissipation exactly, we find that the\ndynamics of rescaled density matrix shows an instability as the interaction\nincreases over a threshold, which can be equivalently described in the scheme\nof non-Hermitian effective Hamiltonians. This instability is also observed in\nmulti-site systems and closely related to the $\\mathcal{PT}$ symmetry breaking\naccompanied by appearance of complex eigenvalues of the effective Hamiltonian.\nMoreover, we unveil that the dynamical instability of the anti-ferromagnetic\nMott phase comes from the $\\mathcal{PT}$ symmetry breaking in highly excited\nbands, although the low-energy effective model of the non-Hermitian Hubbard\nmodel in the strongly interacting regime is always Hermitian. We also provide a\nquantitative estimation of the time for the observation of dynamical\n$\\mathcal{PT}$ symmetry breaking which could be probed in experiments.",
        "positive": "Identifying topological edge states in 2D optical lattices using light\n  scattering: We recently proposed in a Letter [Physical Review Letters 108 255303] a novel\nscheme to detect topological edge states in an optical lattice, based on a\ngeneralization of Bragg spectroscopy. The scope of the present article is to\nprovide a more detailed and pedagogical description of the system - the\nHofstadter optical lattice - and probing method. We first show the existence of\ntopological edge states, in an ultra-cold gas trapped in a 2D optical lattice\nand subjected to a synthetic magnetic field. The remarkable robustness of the\nedge states is verified for a variety of external confining potentials. Then,\nwe describe a specific laser probe, made from two lasers in Laguerre-Gaussian\nmodes, which captures unambiguous signatures of these edge states. In\nparticular, the resulting Bragg spectra provide the dispersion relation of the\nedge states, establishing their chiral nature. In order to make the Bragg\nsignal experimentally detectable, we introduce a \"shelving method\", which\nsimultaneously transfers angular momentum and changes the internal atomic\nstate. This scheme allows to directly visualize the selected edge states on a\ndark background, offering an instructive view on topological insulating phases,\nnot accessible in solid-state experiments."
    },
    {
        "anchor": "Bogoliubov approach to superfluid-Bose glass phase transition of a\n  disordered Bose-Hubbard Model in weakly interacting regime: We investigate the disorder effect on coherent fraction and the quantum phase\ntransition of ultracold dilute Bose gases trapped in disordered optical\nlattices. Within the framework of Bogoliubov theory, an analytical expression\nfor the particle density is derived and the dependence of coherent fraction on\ndisorder strength as well as on lattice depth is discussed. In weak disorder\nregime, we find a decreased sensitivity of coherent fraction to disorder with\nthe increase of on-site interaction strength. For strong disorder, the quantum\nphase boundary between superfluid phase and Bose glass phase in the disordered\nBose-Hubbard system in weak interaction regime is discussed qualitatively. The\nobtained phase diagram is in agreement with the empirical square-root law. The\ndependence of the corresponding critical value of the disorder strength on\noptical lattice depth is presented as well, and may serve as a reference object\nfor possible experimental investigation.",
        "positive": "Quantum oscillations in ultracold Fermi gases : realizations with\n  rotating gases or artificial gauge fields: We consider the angular momentum of a harmonically trapped, noninteracting\nFermi gas subject to either rotation or to an artificial gauge field. The\nangular momentum of the gas is shown to display oscillations as a function of\nthe particle number or chemical potential. This phenomenon is analogous to the\nde Haas - van Alphen oscillations of the magnetization in the solid-state\ncontext. However, key differences exist between the solid-state and ultracold\natomic gases that we point out and analyze. We explore the dependence of the\nvisibility of these oscillations on the physical parameters and propose two\nexperimental protocols for their observation. Due to the very strong dependence\nof the amplitude of the oscillations on temperature, we propose their use as a\nsensitive thermometer for Fermi gases in the low temperature regime."
    },
    {
        "anchor": "The three-site Bose-Hubbard model subject to atom losses: the boson-pair\n  dissipation channel and failure of the mean-field approach: We employ the perturbation series expansion for derivation of the reduced\nmaster equations for the three-site Bose-Hubbard model subject to strong atom\nlosses from the central site. The model describes a condensate trapped in a\ntriple-well potential subject to externally controlled removal of atoms. We\nfind that the $\\pi$-phase state of the coherent superposition between the side\nwells decays via two dissipation channels, the single-boson channel (similar to\nthe externally applied dissipation) and the boson-pair channel. The quantum\nderivation is compared to the classical adiabatic elimination within the\nmean-field approximation. We find that the boson-pair dissipation channel is\nnot captured by the mean-field model, whereas the single-boson channel is\ndescribed by it. Moreover, there is a matching condition between the zero-point\nenergy bias of the side wells and the nonlinear interaction parameter which\nseparates the regions where either the single-boson or the boson-pair\ndissipation channel dominate. Our results indicate that the $M$-site\nBose-Hubbard models, for $M>2$, subject to atom losses may require an analysis\nwhich goes beyond the usual mean-field approximation for correct description of\ntheir dissipative features. This is an important result in view of the recent\nexperimental works on the single site addressability of condensates trapped in\noptical lattices.",
        "positive": "Resonant superfluidity in the Rabi-coupled spin-dependent Fermi-Hubbard\n  model: We investigate the ground-state phase diagram of the one-dimensional\nattractive Fermi-Hubbard model with spin-dependent hoppings and an on-site Rabi\ncoupling using the density matrix renormalization group method. In particular,\nwe show that even in the limit of one component being immobile the pair\nsuperfluidity can be resonantly enhanced when the Rabi coupling is on the order\nof the interaction strength just before the system starts to strongly polarize.\nWe derive an effective spin-1/2 XXZ model in order to understand the\nground-state properties in the strong attraction limit."
    },
    {
        "anchor": "Thermoelectricity of cold ions in optical lattices: We study analytically and numerically the thermoelectric properties of cold\nions placed in an optical lattice. Our results show that the transition from\nsliding to pinned phase takes place at a certain critical amplitude of lattice\npotential being similar to the Aubry transition for the Frenkel-Kontorova\nmodel. We show that this critical amplitude is proportional to the cube of ion\ndensity that allows to perform experimental realization of this system at\nmoderate lattice amplitudes. We show that the Aubry phase is characterized by\nthe dimensionless Seebeck coefficient about 50 and the figure of merit being\naround 8. We propose possible experimental investigations of such system with\ncold ions and argue that the experiments with electrons on liquid helium\nsurface can also help to understand its unusual properties. The obtained\nresults represent also a challenge for modern methods of quantum chemistry and\nmaterial science.",
        "positive": "The Theory of Generalised Hydrodynamics for the One-dimensional Bose Gas: This article reviews the recent developments in the theory of generalised\nhydrodynamics (GHD) with emphasis on the repulsive one-dimensional Bose gas. We\ndiscuss the implications of GHD on the mechanisms of thermalisation in\nintegrable quantum many-body systems as well as its ability to describe\nfar-from-equilibrium behaviour of integrable and near integrable systems in a\nvariety of quantum quench scenarios. We outline the experimental tests of GHD\nin cold-atom gases and its benchmarks with other microscopic theoretical\napproaches. Finally, we offer some perspectives on the future direction of the\ndevelopment of GHD."
    },
    {
        "anchor": "Magnetic phases of spin-1 lattice gases with random interactions: A spin-1 atomic gas in an optical lattice, in the unit-filling Mott Insulator\n(MI) phase and in the presence of disordered spin-dependent interaction, is\nconsidered. In this regime, at zero temperature, the system is well described\nby a disordered rotationally-invariant spin-1 bilinear-biquadratic model. We\nstudy, via the density matrix renormalization group algorithm, a bounded\ndisorder model such that the spin interactions can be locally either\nferromagnetic or antiferromagnetic. Random interactions induce the appearance\nof a disordered ferromagnetic phase characterized by a non-vanishing value of\nspin-glass order parameter across the boundary between a ferromagnetic phase\nand a dimer phase exhibiting random singlet order. The study of the\ndistribution of the block entanglement entropy reveals that in this region\nthere is no random singlet order.",
        "positive": "Tuning the relaxation dynamics of ultracold atoms with an optical cavity: We investigate the out-of-equilibrium dynamics of ultracold atoms trapped in\nan optical lattice and loaded into an optical resonator that is driven\ntransversely. We derive an effective quantum master equation for weak\natom-light coupling that can be brought into Lindblad form both in the bad and\ngood cavity limits. In the so-called bad cavity regime, we find that the steady\nstate is always that of infinite temperature, but that the relaxation dynamics\ncan be highly non-trivial. For small hopping, the interplay between dissipation\nand strong interactions generally leads to anomalous diffusion in the space of\natomic configurations. However, for a fine-tuned ratio of cavity-mediated and\non-site interactions, we discover a limit featuring normal diffusion. In\ncontrast, for large hopping and vanishing on-site interactions, the system can\nbe described by a linear rate equation leading to an exponential approach of\nthe infinite-temperature steady state. Finally, in the good cavity regime, we\nshow that for vanishing on-site interactions, the system allows for optical\npumping between momentum mode pairs enabling cavity cooling."
    },
    {
        "anchor": "Universal behavior of pair correlations in a strongly interacting Fermi\n  gas: We show that short-range pair correlations in a strongly interacting Fermi\ngas follow a simple universal law described by Tan's relations. This is\nachieved through measurements of the static structure factor which displays a\nuniversal scaling proportional to the ratio of Tan's contact to the momentum\n$C/q$. Bragg spectroscopy of ultracold $^6$Li atoms from a periodic optical\npotential is used to measure the structure factor for a wide range of momenta\nand interaction strengths, providing broad confirmation of this universal law.\nWe calibrate our Bragg spectra using the $f$-sum rule, which is found to\nimprove the accuracy of the structure factor measurement.",
        "positive": "Atom interferometry with trapped Bose-Einstein condensates: Impact of\n  atom-atom interactions: Interferometry with ultracold atoms promises the possibility of ultraprecise\nand ultrasensitive measurements in many fields of physics, and is the basis of\nour most precise atomic clocks. Key to a high sensitivity is the possibility to\nachieve long measurement times and precise readout. Ultra cold atoms can be\nprecisely manipulated at the quantum level, held for very long times in traps,\nand would therefore be an ideal setting for interferometry. In this paper we\ndiscuss how the non-linearities from atom-atom interactions on one hand allow\nto efficiently produce squeezed states for enhanced readout, but on the other\nhand result in phase diffusion which limits the phase accumulation time. We\nfind that low dimensional geometries are favorable, with two-dimensional (2D)\nsettings giving the smallest contribution of phase diffusion caused by\natom-atom interactions. Even for time sequences generated by optimal control\nthe achievable minimal detectable interaction energy $\\Delta E^{\\rm min}$ is on\nthe order of 0.001 times the chemical potential of the BEC in the trap. From\nthere we have to conclude that for more precise measurements with atom\ninterferometers more sophisticated strategies, or turning off the interaction\ninduced dephasing during the phase accumulation stage, will be necessary."
    },
    {
        "anchor": "Vortex unbinding transition in nonequilibrium photon condensates: We present a theoretical study of a Berezinskii-Kosterlitz-Thouless like\nphase transition in lattices of nonequilibrium photon condensates. Starting\nfrom linearized fluctuation theory and the properties of vortices, we propose\nan analytical formula for the critical point containing four fitting\nparameters, that captures well all our numerical simulations. We find that the\nordered phase becomes more stable when driving and dissipation is increased.",
        "positive": "Superfluidity in the 1D Bose-Hubbard Model: We study superfluidity in the 1D Bose-Hubbard model using a variational\nmatrix product state technique. We determine the superfluid density as a\nfunction of the Hubbard parameters by calculating the energy cost of phase\ntwists in the thermodynamic limit. As the system is critical, correlation\nfunctions decay as power laws and the entanglement entropy grows with the bond\ndimension of our variational state. We relate the resulting scaling laws to the\nsuperfluid density. We compare two different algorithms for optimizing the\ninfinite matrix product state and develop a physical explanation why one of\nthem (VUMPS) is more efficient than the other (iDMRG). Finally, we comment on\nfinite-temperature superfluidity in one dimension and how our results can be\nrealized in cold atom experiments."
    },
    {
        "anchor": "Stability of Excited Dressed States with Spin-Orbit Coupling: We study the decay behaviors of ultracold atoms in metastable states with\nspin-orbit coupling (SOC), and demonstrate that there are two SOC-induced decay\nmechanisms. One arises from the trapping potential and the other is due to\ninteratomic collision. We present general schemes for calculating decay rates\nfrom these two mechanisms, and illustrate how the decay rates can be controlled\nby experimental parameters.We experimentally measure the decay rates over a\nbroad parameter region, and the results agree well with theoretical\ncalculations. This work provides an insight for both quantum simulation\ninvolving metastable dressed states and studies on few-body problems with SO\ncoupling.",
        "positive": "A study on quantum gases: bosons in optical lattices and the\n  one-dimensional interacting Bose gas: Bosonic atoms confined in optical lattices are described by the Bose-Hubbard\nmodel and can exist in two different phases, Mott insulator or superfluid,\ndepending on the strength of the system parameters. In the vicinity of the\nphase boundary, there are degeneracies that occur between every two adjacent\nMott lobes. Because of this, nondegenerate perturbation theory fails to give\nmeaningful results for the condensate density: it predicts a phase transition\nin a point of the phase diagram where no transition occurs. Motivated by this,\nwe develop two different degenerate perturbative methods to solve the\ndegeneracy-related problems. Moreover, we study the one-dimensional repulsively\ninteracting Bose gas under harmonic confinement, with special attention to the\nasymptotic behavior of the momentum distribution, which is a universal $k^{-4}$\ndecay characterized by the Tan's contact. The latter constitutes a direct\nsignature of the short-range correlations in such an interacting system and\nprovides valuable insights about the role of the interparticle interactions. We\ninvestigate the system constituted of $N$ interacting particles in the strongly\ninteracting limit. In such a regime, the strong interparticle interaction makes\nthe bosons behave similarly to the ideal Fermi gas. Because of the difficulty\nin analytically solving the system for $N$ particles at finite interaction, the\nTonks-Girardeau regime provides a favorable scenario to probe the contact.\nTherefore, we are able to provide an analytical formula for the Tan's contact.\nFurthermore, we analyze the scaling properties of the Tan's contact in terms of\n$N$ in the high-temperature regime as well as in the strongly interacting\nregime. Finally, we compare our analytical calculations of the Tan's contact to\nquantum Monte Carlo simulations and discuss some fundamental differences\nbetween the canonical and the grand-canonical ensembles."
    },
    {
        "anchor": "Dynamical properties of hard-core anyons in one-dimensional optical\n  lattices: We investigate the dynamical properties of anyons confined in one-dimensional\noptical lattice combined with a weak harmonic trap using the exact numerical\nmethod based on a generalized Jordan-Wigner transformation. The density\nprofiles, momentum distribution, occupation distribution and occupations of the\nlowest natural orbital are obtained for different statistical parameters. The\ndensity profiles of anyons display the same behaviors irrespective of\nstatistical parameter in the full evolving period. While the behaviors\ndependent on statistical property are shown in the momentum distributions and\noccupations of natural orbitals.",
        "positive": "BCS-BEC crossover of atomic Fermi superfluid in a spherical bubble trap: We present a theory of a two-component atomic Fermi gas with tunable\nattractive contact interactions on a spherical shell going through the\nBardeen-Cooper-Schrieffer (BCS) - Bose Einstein condensation (BEC) crossover,\ninspired by the realizations of spherical bubble traps for ultracold atoms in\nmicrogravity. The derivation follows the BCS-Leggett theory to obtain the gap\nand number equations. The BCS-BEC crossover can be induced by tuning the\ninteraction, and the properly normalized gap and chemical potential exhibit\nuniversal behavior regardless of the planar or spherical geometry.\nNevertheless, the spherical-shell geometry introduces another way of inducing\nthe crossover by the curvature. The curvature-induced BCS-BEC crossover is made\npossible by fixing the particle number and interaction strength while shrinking\nthe sphere, causing a reduction to the ratio of the pairing and kinetic\nenergies and pushing the system towards the BCS limit. The saturation of the\nsuperfluid density further confirms the ground state is a Fermi superfluid."
    },
    {
        "anchor": "Quantum simulation of a 2D quasicrystal with cold atoms: We describe a way to obtain a two-dimensional quasiperiodic tiling with\neight-fold symmetry using cold atoms. A series of such optical tilings, related\nby scale transformations, is obtained for a series of specific values of the\nchemical potential of the atoms. A theoretical model for the optical system is\ndescribed and compared with that of the well-known cut-and-project method for\nthe Ammann-Beenker tiling. This type of cold atom structure should allow the\nsimulation of several important lattice models for interacting quantum\nparticles and spins in quasicrystals.",
        "positive": "Implicit ladder summation in the Hartree-Fock-Bogoliubov approach: The fully variational Hartree Fock Bogoliubov approach for bosons is studied\nin the limit of zero range forces in two- and three-dimensions. The equation of\nstate obtained in two-dimensions is expressed in a parametric form. It is shown\nthat the $\\Lambda$ potential permits to perform an implicit summation of the\nladder diagrams without leaving the variational scheme, restoring thus the\nconsistency of this approximation."
    },
    {
        "anchor": "Doubly dressed bosons - exciton-polaritons in a strong terahertz field: We demonstrate the existence of a novel quasiparticle: an exciton in a\nsemiconductor doubly dressed with two photons of different wavelengths: near\ninfrared cavity photon and terahertz (THz) photon, with the THz coupling\nstrength approaching the ultra-strong coupling regime. This quasiparticle is\ncomposed of three different bosons, being a mixture of a matter-light\nquasiparticle. Our observations are confirmed by a detailed theoretical\nanalysis, treating quantum mechanically all three bosonic fields. The doubly\ndressed quasiparticles retain the bosonic nature of their constituents, but\ntheir internal quantum structure strongly depends on the intensity of the\napplied terahertz field.",
        "positive": "Anderson localisation in two dimensions: insights from Localisation\n  Landscape Theory, exact diagonalisation, and time-dependent simulations: Motivated by experimental progress in cold atomic systems, we use and advance\nLocalisation Landscape Theory (LLT), to examine two-dimensional systems with\npoint-like random scatterers. We begin by showing that exact eigenstates cannot\nbe efficiently used to extract the localisation length. We then provide a\ncomprehensive review of known LLT, and confirm that the Hamiltonian with the\neffective potential of LLT has very similar low energy eigenstates to that with\nthe physical potential. Next, we use LLT to compute the localisation length for\nvery low-energy, maximally localised eigenstates and test our method against\nexact diagonalisation. Furthermore, we propose a transmission experiment that\noptimally detects Anderson localisation, and demonstrate how one may extract a\nlength scale which is correlated with (and in general smaller than) the\nlocalisation length. In addition, we study the dimensional crossover from one\nto two dimensions, providing a new explanation to the established trends. The\nprediction of a mobility edge coming from LLT is tested by direct Schr\\\"odinger\ntime evolution and is found to be unphysical. Moreover, we investigate\nexpanding wavepackets, to find that these can be useful in detecting and\nquantifying Anderson localisation in a transmission experiment, with the only\ndisadvantage being the inability to resolve the energy dependence of the\nlocalisation length. Then, we utilise LLT to uncover a connection between the\nAnderson model for discrete disordered lattices and continuous two-dimensional\ndisordered systems, which provides powerful new insights. From here, we\ndemonstrate that localisation can be distinguished from other effects by a\ncomparison to dynamics in an ordered potential with all other properties\nunchanged. Finally, we thoroughly investigate the effect of acceleration and\nrepulsive interparticle interactions, as relevant for current experiments."
    },
    {
        "anchor": "Mode coupling of interaction quenched ultracold few-boson ensembles in\n  periodically driven lattices: The out-of-equilibrium dynamics of interaction quenched finite ultracold\nbosonic ensembles in periodically driven one-dimensional optical lattices is\ninvestigated. It is shown that periodic driving enforces the bosons in the\nouter wells of the finite lattice to exhibit out-of-phase dipole-like modes,\nwhile in the central well the atomic cloud experiences a local breathing mode.\nThe dynamical behavior is investigated with varying driving frequency,\nrevealing a resonant-like behavior of the intra-well dynamics. An interaction\nquench in the periodically driven lattice gives rise to admixtures of different\nexcitations in the outer wells, an enhanced breathing in the center and an\namplification of the tunneling dynamics. We observe then multiple resonances\nbetween the inter- and intra-well dynamics at different quench amplitudes, with\nthe position of the resonances being tunable via the driving frequency. Our\nresults pave the way for future investigations on the use of combined driving\nprotocols in order to excite different inter- and intra-well modes and to\nsubsequently control them.",
        "positive": "Topologically quantized current in quasiperiodic Thouless pumps: Thouless pumps are topologically nontrivial states of matter with quantized\ncharge transport, which can be realized in atomic gases loaded into an optical\nlattice. This topological state is analogous to the quantum Hall state.\nHowever, contrarily to the exact, extremely precise, and robust quantization of\nthe Hall conductance, the pumped charge is strictly quantized only when the\npumping time is a multiple of a characteristic timescale, i.e., the pumping\ncycle duration. Here, we show instead that the pumped current becomes exactly\nquantized, independently from the pumping time, if the system is led into a\nquasiperiodic, incommensurate regime. In this quasiperiodic and topologically\nnontrivial state, the Bloch bands and the Berry curvature become flat, the\npumped charge becomes linear in time, while the current becomes steady,\ntopologically quantized, and proportional to the Chern number. The quantization\nof the current is exact up to exponentially small corrections. This has to be\ncontrasted with the case of the commensurate (nonquasiperiodic) regime, where\nthe current is not constant, and the pumped charge is quantized only at integer\nmultiples of the pumping cycle."
    },
    {
        "anchor": "Magnetism and domain formation in SU(3)-symmetric multi-species Fermi\n  mixtures: We study the phase diagram of an SU(3)-symmetric mixture of three-component\nultracold fermions with attractive interactions in an optical lattice,\nincluding the additional effect on the mixture of an effective three-body\nconstraint induced by three-body losses. We address the properties of the\nsystem in $D \\geq 2$ by using dynamical mean-field theory and variational Monte\nCarlo techniques. The phase diagram of the model shows a strong interplay\nbetween magnetism and superfluidity. In the absence of the three-body\nconstraint (no losses), the system undergoes a phase transition from a color\nsuperfluid phase to a trionic phase, which shows additional particle density\nmodulations at half-filling. Away from the particle-hole symmetric point the\ncolor superfluid phase is always spontaneously magnetized, leading to the\nformation of different color superfluid domains in systems where the total\nnumber of particles of each species is conserved. This can be seen as the SU(3)\nsymmetric realization of a more general tendency to phase-separation in\nthree-component Fermi mixtures. The three-body constraint strongly disfavors\nthe trionic phase, stabilizing a (fully magnetized) color superfluid also at\nstrong coupling. With increasing temperature we observe a transition to a\nnon-magnetized SU(3) Fermi liquid phase.",
        "positive": "Long-range Order in One-dimensional Spinless Fermi Gas with Attractive\n  Dipole-Dipole Interaction: One-dimensional spinless Fermi gas with attractive dipole-dipole interaction\nis investigated. Results obtained show when the interaction is weak, the\nexcitation spectrum is linear and the superconducting correlation function\ndecays as power law, indicating the validity of the Tomonaga-Luttinger (TL)\nliquid picture. However, when the interaction reaches a critical value, the\nexcitation spectrum is nonlinear and the superconducting correlation function\nkeeps finite for infinity separation, indicating real long-range order\nestablished and the breakdown of the TL liquid picture. We prove that the\nexistence of long-range order is not in contradiction with the Hohenberg\ntheorem and show that this system is related to the Kitaev toy model,\ntherefore, it has potential applications for the future topological quantum\ncomputation."
    },
    {
        "anchor": "Lattice bosons in a quasi-disordered environment: The effects of a\n  superlattice potential on single particle and many particle properties: In this paper we present a theoretical investigation of the effect of a\nsuperlattice potential on some properties of non-interacting bosons in one\ndimensional lattices with Aubry-And\\'re disorder potential. In the first part,\nwe investigate the single particle localization properties. We find a\nre-entrant localization-delocalization transition and the development of\nmultiple mobility edges for a range of superlattice potential strengths. In the\nsecond part, we study the Bose-Einstein condensation with an additional\nharmonic trapping potential. We find that an increase in the superlattice\npotential leads to an increase in the depletion of the condensate in the low\ntemperature limit.",
        "positive": "Zero density limit extrapolation of the superfluid transition\n  temperature in a unitary atomic Fermi gas on a lattice: The superfluid transition temperature $T_c$ of a unitary Fermi gas on a\nthree-dimensional isotropic lattice with an attractive on-site interaction is\ninvestigated as a function of density $n$, from half filling down to $5.0\\times\n10^{-7}$ per unit cell, using a pairing fluctuation theory. We show that except\nat very low densities ($n^{1/3} <0.2$), where $T_c/E_F$ is linear in $n^{1/3}$,\n$T_c/E_F$ exhibits significant higher order nonlinear dependence on $n^{1/3}$.\nTherefore, linear extrapolation using results at intermediate densities such as\nin typical quantum Monte Carlo simulations leads to a significant underestimate\nof the zero density limit of $T_c/E_F$. Our result, $T_c/E_F=0.256$, at $n=0$\nis subject to reduction from particle-hole fluctuations and incoherent single\nparticle self energy corrections."
    },
    {
        "anchor": "Dirty bosons in a three-dimensional harmonic trap: We study a three-dimensional Bose-Einstein condensate in an isotropic\nharmonic trapping potential with an additional delta-correlated disorder\npotential at both zero and finite temperature and investigate the emergence of\na Bose-glass phase for increasing disorder strength. To this end, we revisit a\nquite recent non-perturbative approach towards the dirty boson problem, which\nrelies on the Hartree-Fock mean-field theory and is worked out on the basis of\nthe replica method, and extend it from the homogeneous case to a harmonic\nconfinement. At first, we solve the zero-temperature self-consistency equations\nfor the respective density contributions, which are obtained via the\nHartree-Fock theory within the Thomas-Fermi approximation. Additionally we use\na variational ansatz, whose results turn out to coincide qualitatively with\nthose obtained from the Thomas-Fermi approximation. In particular, a\nfirst-order quantum phase transition from the superfluid phase to the\nBose-glass phase is detected at a critical disorder strength, which agrees with\nfindings in the literature. Afterwards, we consider the three-dimensional dirty\nboson problem at finite temperature. This allows us to study the impact of both\ntemperature and disorder fluctuations on the respective components of the\ndensity as well as their Thomas-Fermi radii. In particular, we find that a\nsuperfluid region, a Bose-glass region, and a thermal region coexist for\nsmaller disorder strengths. Furthermore, depending on the respective system\nparameters, three phase transitions are detected, namely, one from the\nsuperfluid to the Bose-glass phase, another one from the Bose-glass to the\nthermal phase, and finally one from the superfluid to the thermal phase.",
        "positive": "Vortex lattices for ultracold bosonic atoms in a non-Abelian gauge\n  potential: The use of coherent optical dressing of atomic levels allows the coupling of\nultracold atoms to effective gauge fields. These can be used to generate\neffective magnetic fields, and have the potential to generate non-Abelian gauge\nfields. We consider a model of a gas of bosonic atoms coupled to a gauge field\nwith U(2) symmetry, and with constant effective magnetic field. We include the\neffects of weak contact interactions by applying Gross-Pitaevskii mean-field\ntheory. We study the effects of a U(2) non-Abelian gauge field on the vortex\nlattice phase induced by a uniform effective magnetic field, generated by an\nAbelian gauge field or, equivalently, by rotation of the gas. We show that,\nwith increasing non-Abelian gauge field, the nature of the groundstate changes\ndramatically, with structural changes of the vortex lattice. We show that the\neffect of the non-Abelian gauge field is equivalent to the introduction of\neffective interactions with non-zero range. We also comment on the consequences\nof the non-Abelian gauge field for strongly correlated fractional quantum Hall\nstates."
    },
    {
        "anchor": "A systematic perturbative expansion of the solution of the\n  time-independent Gross-Pitaevskii equation: In this article a perturbative solution of the Gross-Pitaevskii(GP) equation\nin the $D$-dimensional space $R^D$ with a general external potential is\nstudied. The solution describes the condensate wave-function of a gas\ncontaining $N$ Bose particles. A criteria for the validity of the perturbative\nsolution is developed. Furthermore expressions for the particle density, the\nchemical potential, the internal energy and the mean-square radius of the\ncondensate are derived corrected to first order in the coupling constant. The\nscheme is then applied to obtain the solution of the GP equation in $D=1,2,3$\nfor external harmonic potentials. It is shown, in each case, that if $N$\nexceeds a certain value the solution breaks down.",
        "positive": "Roadmap on Atomtronics: State of the art and perspective: Atomtronics deals with matter-wave circuits of ultra-cold atoms manipulated\nthrough magnetic or laser-generated guides with different shapes and\nintensities. In this way, new types of quantum networks can be constructed, in\nwhich coherent fluids are controlled with the know-how developed in the atomic\nand molecular physics community. In particular, quantum devices with enhanced\nprecision, control and flexibility of their operating conditions can be\naccessed. Concomitantly, new quantum simulators and emulators harnessing on the\ncoherent current flows can also be developed. Here, we survey the landscape of\natomtronics-enabled quantum technology and draw a roadmap for the field in the\nnear future. We review some of the latest progresses achieved in matter-wave\ncircuits design and atom-chips. Atomtronic networks are deployed as promising\nplatforms for probing many-body physics with a new angle and a new twist. The\nlatter can be done both at the level of equilibrium and non-equilibrium\nsituations. Numerous relevant problems in mesoscopic physics, like persistent\ncurrents and quantum transport in circuits of fermionic or bosonic atoms, are\nstudied through a new lens. We summarize some of the atomtronics quantum\ndevices and sensors. Finally, we discuss alkali-earth and Rydberg atoms as\npotential platforms for the realization of atomtronic circuits with special\nfeatures."
    },
    {
        "anchor": "Phase separation in a polarized Fermi gas with spin-orbit coupling: We study the phase separation of a spin polarized Fermi gas with spin-orbit\ncoupling near a wide Feshbach resonance. As a result of the competition between\nspin-orbit coupling and population imbalance, the phase diagram for a uniform\ngas develops a rich structure of phase separation involving gapless superfluid\nstates which are topologically non-trivial. We find that these novel gapless\nphases can be stabilized by intermediate spin-orbit coupling strengths. We then\ndemonstrate the phase separation induced by an external trapping potential and\ndiscuss the optimal parameter region for the experimental observation of the\ngapless superfluid phases.",
        "positive": "Droplet-superfluid compounds in binary bosonic mixtures: While quantum fluctuations in binary mixtures of bosonic atoms with\nshort-range interactions can lead to the formation of a self-bound droplet, for\nequal intra-component interactions but an unequal number of atoms in the two\ncomponents, there is an excess part that cannot bind to the droplet. Imposing\nconfinement, as here through periodic boundary conditions in a one-dimensional\nsetting, the droplet becomes amalgamated with a residual condensate. The\nrotational properties of this compound system reveal simultaneous rigid-body\nand superfluid behavior in the ground state and uncover that the residual\ncondensate can carry angular momentum even in the absence of vorticity. In\ncontradiction to the intuitive idea that the superfluid fraction of the system\nwould be entirely made up of the excess atoms not bound by the droplet, we find\nevidence that this fraction is higher than what one would expect in such a\npicture. Our findings are corroborated by an analysis of the elementary\nexcitations in the system, and shed new light on the coexistence of\nlocalization and superfluidity."
    },
    {
        "anchor": "Number-Conserving Approaches for Atomic Bose-Einstein Condensates: An\n  Overview: Assuming the existence of a Bose-Einstein condensate composed of the majority\nof a sample of ultracold, trapped atoms, perturbative treatments to incorporate\nthe non-condensate fraction are common. Here we describe how this may be\ncarried out in an explicitly number-conserving fashion, providing a common\nframework for the work of various authors; we also briefly consider issues of\nimplementation, validity and application of such methods.",
        "positive": "Chiral Bosonic Mott Insulator on the Frustrated Triangular Lattice: We study the superfluid and insulating phases of interacting bosons on the\ntriangular lattice with an inverted dispersion, corresponding to frustrated\nhopping between sites. The resulting single-particle dispersion has multiple\nminima at nonzero wavevectors in momentum space, in contrast to the unique\nzero-wavevector minimum of the unfrustrated problem. As a consequence, the\nsuperfluid phase is unstable against developing additonal chiral order that\nbreaks time reversal (T) and parity (P) symmetries by forming a condensate at\nnonzero wavevector. We demonstrate that the loss of superfluidity can lead to\nan even more exotic phase, the chiral Mott insulator, with nontrivial current\norder that breaks T, P. These results are obtained via variational estimates,\nas well as a combination of bosonization and DMRG of triangular ladders, which\ntaken together permit a fairly complete characterization of the phase diagram.\nWe discuss the relevance of these phases to optical lattice experiments, as\nwell as signatures of chiral symmetry breaking in time-of-flight images."
    },
    {
        "anchor": "Stable core symmetries and confined textures for a vortex line in a\n  spinor Bose-Einstein condensate: We show how a singly quantized vortex can exhibit energetically stable defect\ncores with different symmetries in an atomic spin-1 polar Bose-Einstein\ncondensate, and how a stable topologically nontrivial Skyrmion texture of lower\ndimensionality can be confined inside the core. The core isotropy and the\nstability of the confined texture are sensitive to Zeeman level shifts. The\nobserved structures have analogies, respectively, in pressure-dependent\nsymmetries of superfluid liquid He-3 vortices and in the models of\nsuperconducting cosmic strings.",
        "positive": "Kilohertz-driven Bose-Einstein condensates in optical lattices: We analyze time-of-flight absorption images obtained with dilute\nBose-Einstein con-densates released from shaken optical lattices, both\ntheoretically and experimentally. We argue that weakly interacting, ultracold\nquantum gases in kilohertz-driven optical potentials constitute equilibrium\nsystems characterized by a steady-state distri-bution of Floquet-state\noccupation numbers. Our experimental results consistently indicate that a\ndriven ultracold Bose gas tends to occupy a single Floquet state, just as it\noccupies a single energy eigenstate when there is no forcing. When the driving\namplitude is sufficiently high, the Floquet state possessing the lowest mean\nenergy does not necessarily coincide with the Floquet state connected to the\nground state of the undriven system. We observe strongly driven Bose gases to\ncondense into the former state under such conditions, thus providing nontrivial\nexamples of dressed matter waves."
    },
    {
        "anchor": "Formation of Ultracold Fermionic NaLi Feshbach Molecules: We describe the formation of fermionic NaLi Feshbach molecules from an\nultracold mixture of bosonic 23Na and fermionic 6Li. Precise magnetic field\nsweeps across a narrow Feshbach resonance at 745 G result in a molecule\nconversion fraction of 5% for our experimental densities and temperatures,\ncorresponding to a molecule number of 5*10^4. The observed molecular decay\nifetime is 1.3 ms after removing free Li and Na atoms from the trap.",
        "positive": "Gr{\u00fc}neisen parameter of quantum magnets with spin gap: Using Hartree-Fock-Bogoliubov (HFB) approach we obtained analytical\nexpressions for thermodynamic quantities of the system of triplons in spin\ngapped quantum magnets such as magnetization, heat capacity and the magnetic\nGr{\\\"u}neisen parameter $\\Gamma_H$. Near the critical temperature, $\\Gamma_H$\nis discontinuous and changes its sign upon the Bose-Einstein condensation (BEC)\nof triplons. On the other hand, in the widely used Hartree-Fock-Popov (HFP)\napproach there is no discontinuity neither in the heat capacity nor in the\nGr{\\\"u}neisen parameter. We predict that in the low-temperature limit and near\nthe critical magnetic field $H_c$, $\\Gamma_H$ diverges as $\\Gamma_H\\sim\n1/T^{2}$, while it scales as $\\Gamma_H\\sim 1/(H-H_c)$ as the magnetic field\napproaches the quantum critical point at $H_c$."
    },
    {
        "anchor": "Many-site coherence revivals in the extended Bose-Hubbard model and the\n  Gutzwiller approximation: We investigate the collapse and revival of first-order coherence in deep\noptical lattices when long-range interactions are turned on, and find that the\nfirst few revival peaks are strongly attenuated already for moderate values of\nthe nearest-neighbor interaction coupling. It is shown that the conventionally\nemployed Gutzwiller wavefunction, with only onsite-number dependence of the\nvariational amplitudes, leads to incorrect predictions for the collapse and\nrevival oscillations. We provide a modified variant of the Gutzwiller ansatz,\nreproducing the analytically calculated time dependence of first-order\ncoherence in the limit of zero tunneling.",
        "positive": "Superfluid properties of an ultracold Fermi gas with an orbital Feshbach\n  resonance in the BCS-BEC crossover region: We theoretically investigate superfluid properties of a two-band gas of\n$^{173}$Yb Fermi atoms with an orbital Feshbach resonance (OFR). To describe\nthe BCS-BEC crossover region, we include superfluid fluctuations caused by\ninter-band and intra-band pairing interactions associated with OFR, by\nextending the strong-coupling theory developed by Nozi\\`eres and Schmitt-Rink\nto the two-band case below the superfluid phase transition temperature;\nhowever, effects of an experimentally inaccessible deep bound state are\nremoved, to model a real $^{173}$Yb Fermi gas near OFR. We show that the\ncondensate fraction in the upper closed channel gradually becomes smaller than\nthat in the lower open channel, as one moves from the strong- to the\nweak-coupling regime, because the OFR-pairing mechanism tunes the interaction\nstrengths by adjusting the energy difference between the two bands. However,\neven when the closed-channel band is much higher in energy than the\nopen-channel band in the weak-coupling regime, the magnitude of the superfluid\norder parameter in the closed channel is found to be still comparable to that\nin the open channel. As the reason for this, we point out a pair-tunneling\neffect by the OFR-induced inter-band interaction. Besides these superfluid\nquantities, we also examine collective modes, such as the Goldstone mode,\nSchmid (Higgs) mode, as well as Leggett mode, to clarify how they appear in the\nspectral weights of pair-correlation functions in each band. Since the\nrealization of a multi-band superfluid Fermi gas is a crucial issue in cold\nFermi gas physics, our results would contribute to the basic understanding of\nthis type of Fermi superfluid in the BCS-BEC crossover region."
    },
    {
        "anchor": "Entangling many-body bound states with propagative modes in Bose-Hubbard\n  systems: The quantum evolution of a cloud of bosons initially localized on part of a\none dimensional optical lattice and suddenly subjected to a linear ramp is\nstudied, realizing a quantum analog of the \"Galileo ramp\" experiment. The main\nremarkable effects of this realistic setup are revealed using analytical and\nnumerical methods. Only part of the particles are ejected for a high enough\nramp, while the others remain self-trapped. Then, the trapped density profile\ndisplays rich dynamics with Josephson-like oscillations around a plateau. This\nsetup, by coupling bound states to propagative modes, creates two diverging\ncondensates for which the entanglement is computed and related to the\nequilibrium one. Further, we address the role of integrability on the\nentanglement and on the damping and thermalization of simple observables.",
        "positive": "Renormalization group study of Bose polarons: We study the properties of a single impurity in a dilute Bose gas, a Bose\npolaron, using the functional renormalization group. We use an ansatz for the\neffective action motivated by a derivative expansion, and we compute the\nenergies of the attractive and repulsive branches of excitations in both two\nand three spatial dimensions. Three-body correlations play an important role in\nthe attractive branch, and we account for those by including three-body\ncouplings between two bath bosons and the impurity. Our calculations compare\nvery favorably with state-of-the-art experimental measurements and numerical\nsimulations."
    },
    {
        "anchor": "Staggered quantum phases of dipolar bosons at finite temperatures: The extended Bose-Hubbard model with correlated tunneling exhibits staggered\nsuperfluid and supersolid quantum phases. We study finite-temperature phase\ntransitions of quantum phases of dipolar bosons in a two-dimensional optical\nlattice using Gutzwiller mean-field and quantum Monte Carlo approaches. When\nnearest-neighbor repulsion is comparable to the on-site interaction, we find\nthat the two topologically distinct superfluids are separated by a normal fluid\nphase, while at stronger off-site interactions, density-modulated insulating\nquantum phases appear. We estimate the critical temperature of the staggered\nsuperfluid to normal fluid transition and show that this transition is of the\nKosterlitz-Thouless type. Finally, we elucidate the coexistence of staggered\nquantum phases in the presence of an external trapping potential. Our study\npaves a way to observe novel staggered quantum phases in recent dipolar optical\nlattice experiments.",
        "positive": "Local temperature control of magnon frequency and direction of\n  supercurrents in a magnon Bose-Einstein condensate: The creation of temperature variations in magnetization, and hence in the\nfrequencies of the magnon spectrum in laser-heated regions of magnetic films,\nis an important method for studying Bose-Einstein condensation of magnons,\nmagnon supercurrents, Bogoliubov waves, and similar phenomena. In our study, we\ndemonstrate analytically, numerically, and experimentally that, in addition to\nthe magnetization variations, it is necessary to consider the connected\nvariations of the demagnetizing field. In case of a heat induced local minimum\nof the saturation magnetization, the combination of these two effects results\nin a local increase in the minimum frequency value of the magnon dispersion at\nwhich the Bose-Einstein condensate emerges. As a result, a magnon supercurrent\ndirected away from the hot region is formed."
    },
    {
        "anchor": "Rotating mixed $^3$He-$^4$He nanodroplets: Mixed $^3$He-$^4$He droplets created by hydrodynamic instability of a\ncryogenic fluid-jet may acquire angular momentum during their passage through\nthe nozzle of the experimental apparatus. These free-standing droplets cool\ndown to very low temperatures undergoing isotopic segregation, developing a\nnearly pure $^3$He crust surrounding a very $^4$He-rich superfluid core. Here,\nthe stability and appearance of rotating mixed helium droplets are investigated\nusing Density Functional Theory for an isotopic composition that highlights,\nwith some marked exceptions related to the existence of the superfluid inner\ncore, the analogies with viscous rotating droplets.",
        "positive": "Microscopic description of exciton-polaritons in microcavities: We investigate the microscopic description of exciton-polaritons that\ninvolves electrons, holes and photons within a two-dimensional microcavity. We\nshow that in order to recover the simplified exciton-photon model that is\ntypically used to describe polaritons, one must correctly define the\nexciton-photon detuning and exciton-photon (Rabi) coupling in terms of the bare\nmicroscopic parameters. For the case of unscreened Coulomb interactions, we\nfind that the exciton-photon detuning is strongly shifted from its bare value\nin a manner akin to renormalization in quantum electrodynamics. Within the\nrenormalized theory, we exactly solve the problem of a single exciton-polariton\nfor the first time and obtain the full spectral response of the microcavity. In\nparticular, we find that the electron-hole wave function of the polariton can\nbe significantly modified by the very strong Rabi couplings achieved in current\nexperiments. Our microscopic approach furthermore allows us to obtain the\neffective interaction between identical polaritons for any light-matter\ncoupling. Crucially, we show that the standard treatment of polariton-polariton\ninteractions in the very strong coupling regime is incorrect, since it neglects\nthe light-induced modification of the exciton size and thus greatly\noverestimates the effect of Pauli exclusion on the Rabi coupling, i.e., the\nsaturation of exciton oscillator strength. Our findings thus provide the\nfoundations for understanding and characterizing exciton-polariton systems\nacross the whole range of polariton densities."
    },
    {
        "anchor": "Conformality Lost in Efimov Physics: A general mechanism for the loss of conformal invariance is the merger and\ndisappearance of an infrared fixed point and an ultraviolet fixed point of a\nrenormalization group flow. We show explicitly how this mechanism works in the\ncase of identical bosons at unitarity as the spatial dimension $d$ is varied.\nFor $d$ between the critical dimensions $d_{\\rm 1}=2.30$ and $d_{\\rm 2}=3.76$,\nthere is loss of conformality as evidenced by the Efimov effect in the\nthree-body sector. The beta function for an appropriate three-body coupling is\na quadratic polynomial in that coupling. For $d<d_{\\rm 1}$ and for $d>d_{\\rm\n2}$, the beta function has two real roots that correspond to infrared and\nultraviolet fixed points. As $d$ approaches $d_{\\rm 1}$ from below and as $d$\napproaches $d_{\\rm 2}$ from above, the fixed points merge and disappear into\nthe complex plane. For $d_{\\rm 1}<d<d_{\\rm 2}$, the beta function has complex\nroots and the renormalization group flow for the three-body coupling is a limit\ncycle.",
        "positive": "Thermometry and Refrigeration in a Two-Component Mott Insulator of\n  Ultracold Atoms: Interesting spin Hamiltonians can be realized with ultracold atoms in a\ntwo-component Mott insulator (2CMI). It was recently demonstrated that the\napplication of a magnetic field gradient to the 2CMI enables new techniques of\nthermometry and adiabatic cooling. Here we present a theoretical description\nwhich provides quantitative analysis of these two new techniques. We show that\nadiabatic reduction of the field gradient is capable of cooling below the Curie\nor N\\'eel temperature of certain spin ordered phases."
    },
    {
        "anchor": "Universal Scaling Laws in the Dynamics of a Homogeneous Unitary Bose Gas: We study the dynamics of an initially degenerate homogeneous Bose gas after\nan interaction quench to the unitary regime at a magnetic Feshbach resonance.\nAs the cloud decays and heats, it exhibits a crossover from degenerate- to\nthermal-gas behaviour, both of which are characterised by universal scaling\nlaws linking the particle-loss rate to the total atom number $N$. In the\ndegenerate and thermal regimes the per-particle loss rate is $\\propto N^{2/3}$\nand $N^{26/9}$, respectively. The crossover occurs at a universal kinetic\nenergy per particle and at a universal time after the quench, in units of\nenergy and time set by the gas density. By slowly sweeping the magnetic field\naway from the resonance and creating a mixture of atoms and molecules, we also\nmap out the dynamics of correlations in the unitary gas, which display a\nuniversal temporal scaling with the gas density, and reach a steady state while\nthe gas is still degenerate.",
        "positive": "Superfluid phases of ultracold Fermi gases on a checkerboard\n  superlattice: We analyze the ground-state phase diagram of two-component Fermi gases loaded\ninto a two-dimensional checkerboard superlattice, i.e. a double-well optical\nlattice, potential within the BCS mean-field theory. We show that, by coupling\nthe two s-wave sublattice superfluid order parameters, a checkerboard potential\ngives rise to a Hamiltonian that has the form of a two-band superfluidity with\nthree (two intraband and an interband) nonlocal order parameters. We study the\nevolution of these order parameters as a function of particle filling,\ninteraction strength and checkerboard potential, and find that the system\nalways prefers the 0-phase solutions, i.e. the phase difference between\nsublattice order parameters is 0, but never the $\\pi$-phase one. In addition,\nwe find that the ground-state of the system undergo a superfluid-normal quantum\nphase transition at half fillings beyond a critical checkerboard potential $C$,\nthe threshold of which is precisely determined by the magnitude of the order\nparameter at $C = 0$, and that the normal state rapidly turns into a\ncheckerboard insulator as $C$ increases."
    },
    {
        "anchor": "Resonant enhancement of particle emission from a parametrically driven\n  condensate in a one-dimensional lattice: Motivated by recent experiments, we investigate particle emission from a\nBose-Einstein condensate in a one-dimensional lattice, where the interaction\nstrength is periodically modulated. The modulated interactions parametrically\nexcite a collective mode, leading to density oscillations. These collective\noscillations in turn drive particle emission. This multistep process amplifies\nthe drive, producing larger particle jets. We find that the amplitude\ndependence of the emission rate has a characteristic threshold behavior, as\nseen in experiments.",
        "positive": "Effective action approach to the p-band Mott insulator and superfluid\n  transition: Motivated by the recent experiment on p-orbital band bosons in optical\nlattices, we study theoretically the quantum phases of Mott insulator and\nsuperfluidity in two-dimensions. The system features a novel superfluid phase\nwith transversely staggered orbital current at weak interaction, and a Mott\ninsulator phase with antiferro-orbital order at strong coupling and\ncommensurate filling. We go beyond mean field theory and derive from a\nmicroscopic model an effective action that is capable of describing both the\np-band Mott insulating and superfluid phases in strong coupling. We further\ncalculate the excitation spectra near the quantum critical point and find two\ngapless modes away from the tip of the Mott lobe but four gapless modes at the\ntip. Our effective theory reveals how the phase coherence peak builds up in the\nMott regime when approaching the critical point. We also discuss the finite\ntemperature phase transition of p-band superfluidity."
    },
    {
        "anchor": "Generation of high winding-number superfluid circulation in\n  Bose-Einstein condensates: We experimentally and numerically demonstrate a method to deterministically\ngenerate multiply-quantized superfluid circulation about an obstacle in highly\noblate Bose-Einstein condensates (BECs). Our method involves spiraling a\nblue-detuned laser beam, which acts as a repulsive optical potential, around\nand towards the center of the BEC. This optical potential serves first as a\nrepulsive stirrer to initiate superflow within the BEC, and then as a pinning\npotential that transports the center of the superfluid circulation to the\ncenter of the condensate. By changing the rate at which the beam moves along\nthe spiral trajectory, we selectively control the net circulation introduced\ninto the BEC. We experimentally achieve pinned superflow with winding numbers\nas high as 11, which persists for at least 4 s. At the end of the spiral\ntrajectory, with the pinning beam on at full power, the BEC has a toroidal\ngeometry with a high winding-number persistent current. Alternatively, the beam\npower can be ramped off, allowing controlled placement of a cluster of\nsingly-quantized vortices of the same circulation. This technique can serve as\na building block in future experimental architectures to create on-demand\nvortex distributions and superfluid circulation in BECs.",
        "positive": "Construction of quantum dark soliton in one-dimensional Bose gas: Dark soliton solutions in the one-dimensional classical nonlinear\nSchr\\\"odinger equation has been considered to be related to the yrast states\ncorresponding to the type-II excitations in the Lieb-Liniger model. However,\nthe relation is nontrivial and remains unclear because a dark soliton localized\nin space breaks the translation symmetry, while yrast states are\ntranslationally invariant. In this work, we construct a symmetry-broken quantum\nsoliton state and investigate the relation to the yrast states. By interpreting\na quantum dark soliton as a Bose-Einstein condensation to the wave function of\na classical dark soliton, we find that the quantum soliton state has a large\nweight only on the yrast states, which is analytically proved in the free-boson\nlimit and numerically verified in the weak-coupling regime. By extending these\nresults, we derive a parameter-free expression of a quantum soliton state that\nis written as a superposition of yrast states with Gaussian weights. The\ndensity profile of this quantum soliton state excellently agrees to that of the\nclassical dark soliton. The dynamics of a quantum dark soliton is also studied,\nand it turns out that the density profile of a dark soliton decays, but the\ndecay time increases as the inverse of the coupling constant in the\nweak-coupling limit."
    },
    {
        "anchor": "Generation of nonground-state condensates and adiabatic paradox: The problem of resonant generation of nonground-state condensates is\naddressed aiming at resolving the seeming paradox that arises when one resorts\nto the adiabatic representation. In this picture, the eigenvalues and\neigenfunctions of a time-dependent Gross-Pitaevskii Hamiltonian are also\nfunctions of time. Since the level energies vary in time, no definite\ntransition frequency can be introduced. Hence no external modulation with a\nfixed frequency can be made resonant. Thus, the resonant generation of\nadiabatic coherent modes is impossible. However, this paradox occurs only in\nthe frame of the adiabatic picture. It is shown that no paradox exists in the\nproperly formulated diabatic representation. The resonant generation of\ndiabatic coherent modes is a well defined phenomenon. As an example, the\nequations are derived, describing the generation of diabatic coherent modes by\nthe combined resonant modulation of the trapping potential and atomic\nscattering length.",
        "positive": "String order in dipole-blockaded quantum liquids: We study the quantum melting of quasi-one-dimensional lattice models in which\nthe dominant energy scale is given by a repulsive dipolar interaction. By\nconstructing an effective low-energy theory, we show that the melting of\ncrystalline phases can occur into two distinct liquid phases, having the same\nalgebraic decay of density-density correlations, but showing a different\nnon-local correlation function expressing string order. We present possible\nexperimental realizations using ultracold atoms and molecules, introducing an\nimplementation based on resonantly driven Rydberg atoms that offers additional\nbenefits compared to a weak admixture of the Rydberg state."
    },
    {
        "anchor": "Stability of Symmetry Breaking States in Finite-size Dicke Model with\n  Photon Leakage: We investigate the finite-size Dicke model with photon leakage. It is shown\nthat the symmetry breaking states, which are characterized by non-vanishing\n$\\langle \\hat{a} \\rangle \\neq 0$ and correspond to the ground states in the\nsuperradiant phase in the thermodynamic limit, are stable, while the\neigenstates of the isolated finite-size Dicke Hamiltonian conserve parity\nsymmetry. We introduce and analyze an effective master equation that describes\nthe dynamics of a pair of the symmetry breaking states that are the degenerate\nlowest energy eigenstates in the superradiant region with photon leakage. It\nbecomes clear that photon leakage is essential to stabilize the symmetry\nbreaking states and to realize the superradiant phase without the thermodynamic\nlimit. Our theoretical analysis provides an alternative interpretation using\nthe finite-size model to explain results from cold atomic experiments showing\nsuperradiance with the symmetry breaking in an optical cavity.",
        "positive": "Counterdiabatic control of transport in a synthetic tight-binding\n  lattice: Quantum state transformations that are robust to experimental imperfections\nare important for applications in quantum information science and quantum\nsensing. Counterdiabatic (CD) approaches, which use knowledge of the underlying\nsystem Hamiltonian to actively correct for diabatic effects, are powerful tools\nfor achieving simultaneously fast and stable state transformations. Protocols\nfor CD driving have thus far been limited in their experimental implementation\nto discrete systems with just two or three levels, as well as bulk systems with\nscaling symmetries. Here, we extend the tool of CD control to a discrete\nsynthetic lattice system composed of as many as nine sites. Although this\nsystem has a vanishing gap and thus no adiabatic support in the thermodynamic\nlimit, we show that CD approaches can still give a substantial, several\norder-of-magnitude, improvement in fidelity over naive, fast adiabatic\nprotocols."
    },
    {
        "anchor": "Finite temperature Dicke phase transition of a Bose-Einstein condensate\n  in an optical cavity: Dicke model predicts a quantum phase transition from normal to superradiant\nphases for a two-level atomic ensemble coupled with an optical cavity at zero\ntemperature. In a recent pioneer experiment [Nature 464, 1301 (2010)], such a\nphase transition has been observed using a Bose-Einstein condensate (BEC) in an\noptical cavity. Compared with the original Dicke model, the experimental system\nfeatures finite temperature and strong atom-photon nonlinear interaction in\nBEC. In this Letter, we develop a finite temperature theory for the Dicke phase\ntransition of a BEC in an optical cavity, taking into account the atom-photon\nnonlinear interaction. In addition to explaining the experimentally observed\ntransition from normal to superradiant phases at finite-temperature, we point\nit out that a new phase, the coexistence of normal and superradient phases, was\nalso observed in the experiment. We show rich finite temperature phase diagrams\nexisting in the experimental system by tuning various experimental parameters.\nWe find that the specific heat of the BEC can serve as a powerful tool for\nprobing various phases.",
        "positive": "Stability of resonantly interacting heavy-light Fermi mixtures: We investigate a two-component mixture of resonantly interacting Fermi gases\nas a function of the ratio \\kappa of the heavy to the light mass of the two\nspecies. The diffusion Monte Carlo method is used to calculate the ground-state\nenergy and the pair correlation function starting from two different guiding\nwave functions, which describe respectively the superfluid and the normal state\nof the gas. Results show that the mixture is stable and superfluid for mass\nratios smaller than the critical value \\kappa_c = 13 +/- 1. For larger values\nof \\kappa simulations utilizing the wave function of the normal state are\nunstable towards cluster formation. The relevant cluster states driving the\ninstability appear to be formed by one light particle and two or more heavy\nparticles within distances on the order of the range of the interatomic\npotential. The small overlap between the wave function of the trimer bound\nstate and the guiding wave function used to describe the superfluid state\nproduces the unphysical stability of the superfluid gas above \\kappa_c."
    },
    {
        "anchor": "Critical region of the superfluid transition in the BCS-BEC crossover: We determine the size of the critical region of the superfluid transition in\nthe BCS-BEC crossover of a three-dimensional fermion gas, using a\nrenormalization-group approach to a bosonic theory of pairing fluctuations. For\nthe unitary Fermi gas, we find a sizable critical region $[T_G^-,T_G^+]$, of\norder $T_c$, around the transition temperature $T_c$ with a pronounced\nasymmetry: $|T_G^+-T_c|/|T_G^--T_c|\\sim8$. The critical region is strongly\nsuppressed on the BCS side of the crossover but remains important on the BEC\nside.",
        "positive": "Generalized Rashba spin-orbit coupling for cold atoms: We study the possibility to generate a new type of spin-orbit coupling for\nthe center of mass motion of cold atoms, using laser beams that resonantly\ncouple N atomic internal ground states to an extra state. After a general\nanalysis of the scheme, we concentrate on the tetrapod setup (N=4) where the\natomic state can be described by a three-component spinor, evolving under the\naction of a Rashba-type spin-orbit coupling for a spin 1 particle. We\nillustrate a consequence of this coupling by studying the negative refraction\nof atoms at a potential step, and show that the amplitude of the refracted beam\nis significantly increased in comparison to the known case of spin 1/2 Rashba\ncoupling. Finally we explore a possible implementation of this tetrapod setup,\nusing stimulated Raman couplings between Zeeman sublevels of the ground state\nof alkali atoms."
    },
    {
        "anchor": "The equilibrium state of a trapped two-dimensional Bose gas: We study experimentally and numerically the equilibrium density profiles of a\ntrapped two-dimensional $^{87}$Rb Bose gas, and investigate the equation of\nstate of the homogeneous system using the local density approximation. We find\na clear discrepancy between in-situ measurements and Quantum Monte Carlo\nsimulations, which we attribute to a non-linear variation of the optical\ndensity of the atomic cloud with its spatial density. However, good agreement\nbetween experiment and theory is recovered for the density profiles measured\nafter time-of-flight, taking advantage of their self-similarity in a\ntwo-dimensional expansion.",
        "positive": "Density oscillations in trapped dipolar condensates: We investigated the ground state wave function and free expansion of a\ntrapped dipolar condensate. We find that dipolar interaction may induce both\nbiconcave and dumbbell density profiles in, respectively, the pancake- and\ncigar-shaped traps. On the parameter plane of the interaction strengths, the\ndensity oscillation occurs only when the interaction parameters fall into\ncertain isolated areas. The relation between the positions of these areas and\nthe trap geometry is explored. By studying the free expansion of the condensate\nwith density oscillation, we show that the density oscillation is detectable\nfrom the time-of-flight image."
    },
    {
        "anchor": "Interspecies entanglement with impurity atoms in a lattice gas: The dynamics of impurity atoms introduced into bosonic gases in an optical\nlattice have generated a lot of recent interest, both in theory and experiment.\nWe investigate to what extent measurements on either the impurity species or\nthe majority species in these systems are affected by their interspecies\nentanglement. This arises naturally in the dynamics and plays an important role\nwhen we measure only one species. We explore the corresponding effects in\nstrongly interacting regimes, using a combination of few-particle analytical\ncalculations and Density Matrix Renormalisation group methods in one dimension.\nWe identify how the resulting effects on impurities can be used to probe the\nmany-body states of the majority species, and separately ask how to enter\nregimes where this entanglement is small, so that the impurities can be used as\nprobes that do not significantly affect the majority species. The results are\naccessible in current experiments, and provide important considerations for the\nmeasurement of complex systems with using few probe atoms.",
        "positive": "The Rhombi-Chain Bose-Hubbard Model: geometric frustration and\n  interactions: We explore the effects of geometric frustration within a one-dimensional\nBose-Hubbard model using a chain of rhombi subject to a magnetic flux. The\ncompetition of tunnelling, self-interaction and magnetic flux gives rise to the\nemergence of a pair-superfluid (pair-Luttinger liquid) phase besides the more\nconventional Mott-insulator and superfluid (Luttinger liquid) phases. We\ncompute the complete phase diagram of the model by identifying characteristic\nproperties of the pair-Luttinger liquid phase such as pair correlation\nfunctions and structure factors and find that the pair-Luttinger liquid phase\nis very sensitive to changes away from perfect frustration (half-flux). We\nprovide some proposals to make the model more resilient to variants away from\nperfect frustration. We also study the bipartite entanglement properties of the\nchain. We discover that, while the scaling of the block entropy pair-superfluid\nand of the single-particle superfluid leads to the same central charge, the\nproperties of the low-lying entanglement spectrum levels reveal their\nfundamental difference."
    },
    {
        "anchor": "Negative quench induced excitation dynamics for ultracold bosons in\n  one-dimensional lattices: The nonequilibrium dynamics following a quench of strongly repulsive bosonic\nensembles in one-dimensional finite lattices is investigated by employing\ninteraction quenches and/or a ramp of the lattice potential. Both sudden and\ntime-dependent quenches are analyzed in detail. For the case of interaction\nquenches we address the transition from the strong repulsive to the\nweakly-interacting regime, suppressing in this manner the heating of the\nsystem. The excitation modes such as the cradle process and the local breathing\nmode are examined via local density observables. In particular, the cradle mode\nis inherently related to the initial delocalization and, following a negative\ninteraction quench, can be excited only for incommensurate setups with filling\nlarger than unity. Alternatively, a negative quench of the lattice depth which\nfavors the spatial delocalization is used to access the cradle mode for setups\nwith filling smaller than unity. Our results shed light on possible schemes to\ncontrol the cradle and the breathing modes. Finally, employing the notion of\nfidelity we study the dynamical response of the system after a diabatic or\nadiabatic parameter modulation for short and long evolution times. The\nevolution of the system is obtained numerically using the ab-initio multi-layer\nmulti-configuration time-dependent Hartree method for bosons which permits to\nfollow non-equilibrium dynamics including the corresponding investigation of\nhigher-band effects.",
        "positive": "Modification of roton instability due to the presence of a second\n  dipolar Bose-Einstein condensate: We study the behavior of two coupled purely dipolar Bose-Einstein\ncondensates, each located in a cylindrically symmetric pancake-shaped external\nconfining potential, as the separation b between the traps along the tight\nconfining direction is varied. The solutions of the coupled Gross-Pitaevskii\nand Bogoliubov-de Gennes equations, which account for the full dynamics, show\nthat the system behavior is modified by the presence of the second dipolar BEC.\nFor sufficiently small b, the presence of the second dipolar BEC destabilizes\nthe system dramatically. In this regime, the coupled system collapses through a\nmode that is notably different from the radial roton mode that induces the\ncollapse of the uncoupled system. Finally, we comment on the shortcomings of an\napproach that neglects the dynamics in the z-direction, which is assumed to be\na good approximation for highly pancake-shaped dipolar BECs in the literature."
    },
    {
        "anchor": "Dynamics of a nonlinear quantum oscillator under non-Markovian pumping: We consider dynamics of a quantum nonlinear oscillator subjected to\nnon-Markovian pumping. Models of this kind can describe formation of\nexciton-polariton Bose-Einstein condensates in course of stimulated scattering\nand relaxation of reservoir excitons. Using the Markovian embedding techniques,\nwe obtain stochastic differential equations of motion with an additional degree\nof freedom corresponding to dynamical memory. It is shown that the oscillator\nasymptotically tends to the intrinsically non-Markovian stable fixed point\ncorresponding to constant product of oscillator amplitude and modulo of the\nmemory variable. The state corresponding to this point exhibits unlimited\ngrowth of population, with the growth rate that decreases with time. Our\nresults show that the Markovian behavior could be observed only within some\nlimited early stage of oscillator evolution provided that decay of dynamical\nmemory is sufficiently fast. Transition from the Markovian regime to\nnon-Markovian one with increasing time is linked to phase shift of the pumping\nterm. Coherence properties of the oscillator are studied. It was found that\ninteraction between particles delimits growth of condensate population, thereby\nimpeding formation of Bose-Einstein condensate.",
        "positive": "Emergence of Reflectionless Scattering from Linearizations of Integrable\n  PDEs around Solitons: We present four examples of integrable partial differential equations (PDEs)\nof mathematical physics that---when linearized around a stationary\nsoliton---exhibit scattering without reflection at {\\it all} energies. Starting\nfrom the most well-known and the most empirically relevant phenomenon of the\ntransparency of one-dimensional bright bosonic solitons to Bogoliubov\nexcitations, we proceed to the sine-Gordon, Korteweg-de Vries, and Liouville's\nequation whose stationary solitons also support our assertion. The proposed\nconnection between integrability and reflectionless scattering seems to span at\nleast two distinct paradigms of integrability: S-integrability in the first\nthree cases, and C-integrability in the last one. We argue that the\ntransparency of linearized integrable PDEs is necessary to ensure that they can\nsupport the transparency of stationary solitons in the original integrable\nPDEs. As contrasting cases, the analysis is further extended to cover two\nnon-integrable systems: a sawtooth-Gordon and a $\\phi^4$ model."
    },
    {
        "anchor": "Quench Dynamics of Thermal Bose Gases Across Wide and Narrow Feshbach: Using high-temperature virial expansion, we study the quench dynamics of the\nthermal Bose gases near a wide, narrow, and intermediate Feshbach resonance.\nOur results show that the shallow bound state near Feshbach resonance leads to\ninteresting phenomena. Near the wide Feshbach resonance, the long-time\n$\\hat{n}_{\\bf k}$ oscillates when the scattering length $a_{s}$ is quenched\nfrom zero to large but with finite positive values. The oscillation frequency\n$\\omega=E_{\\rm b}/\\hbar$ with $E_{\\rm b}$ being the binding energy. When\n$a_{s}$ is quenched to infinity or negative value, the oscillation vanishes.\nNear the narrow Feshbach resonance, the interaction should be characterized by\na two-channel model. When the background scattering length $a_{\\rm\nbg}\\gtrsim\\lambda$, there is an oscillation in the long-time dynamics, and the\nfrequency is determined by the energy of the shallow bound state in the open\nchannel. When $a_{\\rm bg}<0$ or $0<a_{\\rm bg}\\ll\\lambda$, there is no shallow\nbound state in the open channel, hence no long-time oscillation. We check our\nconclusion using some realistic systems, and the results are consistent with\nour conclusion.",
        "positive": "Superfluidity and solid orders in two-component Bose gas with dipolar\n  interactions in an optical lattice: In this paper, we study an extended bosonic t-J model in an optical lattice,\nwhich describes two-component hard-core bosons with a nearest-neighbor (NN)\npseudo-spin interaction, and also inter- and intra-species dipole-dipole\ninteractions (DDI). In particular, we focus on the case in which two component\nhard-core bosons have anti-parallel polarized dipoles with each other. The\nglobal phase diagram is studied by means of the Gutzwiller variational method\nand also the quantum Monte-Carlo simulations (QMC). The both calculations show\nthat a stripe solid order, besides a checkerboard one, appears as a result of\nthe DDI. By the QMC, we find that two kinds of supersolid (SS) form,\ncheckerboard SS and stripe SS, and we also verify the existence of some exotic\nphase between the stripe solid and checkerboard SS. Finally by the QMC, we\nstudy the t-J-like model, which was experimentally realized recently by A. de\nPaz et al. [Phys. Rev. Lett. {\\bf 111}, 185305 (2013)]."
    },
    {
        "anchor": "Periodic Array of Bose-Einstein condensates in a Magnetic Lattice: We report the realization of a periodic array of Bose-Einstein condensates of\n87Rb |F = 1; mF = -1> atoms trapped in a one-dimensional magnetic lattice close\n(8 micrometres) to the surface of an atom chip. A clear signature for the onset\nof BEC in the magnetic lattice is provided by in-situ site-resolved\nradiofrequency (RF) spectra, which exhibit a pronounced bimodal distribution\nconsisting of a narrow component characteristic of a BEC together with a broad\nthermal cloud component. Similar bimodal distributions are found for various\nsites across the magnetic lattice. The realization of a periodic array of\nmultiple BECs in a magnetic lattice represents a major advance towards the\nimplementation of magnetic lattices to simulate many-body condensed matter\nphenomena in lattices of complex geometry and arbitrary period.",
        "positive": "Single-Particle Spectral Density of a Bose Gas in the Two-Fluid\n  Hydrodynamic Regime: In Bose supefluids, the single-particle Green's function can be directly\nrelated to the superfluid velocity-velocity correlation function in the\nhydrodynamic regime. An explicit expression for the single-particle spectral\ndensity was originally written down by Hohenberg and Martin in 1965, starting\nfrom the two-fluid equations for a superfluid. We give a simple derivation of\ntheir results. Using these results, we calculate the relative weights of first\nand second sound modes in the single-particle spectral density as a function of\ntemperature in a uniform Bose gas. We show that the second sound mode makes a\ndominant contribution to the single-particle spectrum in relatively high\ntemperature region. We also discuss the possibility of experimental observation\nof the second sound mode in a Bose gas by photoemission spectroscopy."
    },
    {
        "anchor": "Nonergodic dynamics of the one-dimensional Bose-Hubbard model with a\n  trapping potential: We investigate nonergodic behavior of the one-dimensional Bose-Hubbard model,\nwhich emerges in the unitary quantum dynamics starting with initial-state\n$|\\psi(0)\\rangle=|\\cdots 2020\\cdots \\rangle$ in the presence of a trapping\npotential. We compute the level spacing statistic, the time evolution of the\nnumber imbalance between the odd and the even sites, and the entanglement\nentropy in order to show that the system exhibits nonergodicity in a strongly\ninteracting regime. The trapping potential enhances nonergodicity even when the\ntrapping potential is weak compared to the the hopping energy. We derive the\neffective spin-1/2 {\\it XXZ} Hamiltonian for the strongly interacting regimes\nby using a perturbation method. On the basis of the effective Hamiltonian, we\nshow that the trapping potential is effectively strengthened by the on-site\ninteraction, leading to the enhancement of the nonergodic behavior. We also\ncalculate the real-time dynamics under the effective Hamiltonian and find that\nthe entanglement entropy grows logarithmically in time.",
        "positive": "Driving protocol for a Floquet topological phase without static\n  counterpart: Periodically driven systems play a prominent role in optical lattices. In\nthese ultracold atomic systems, driving is used to create a variety of\ninteresting behaviours, of which an important example is provided by\ntopological states of matter. Such Floquet topological phases have a richer\nclassification that their equilibrium counterparts. Although analogues of the\nequilibrium topological phases exist, which are characterised by a Chern\nnumber, the corresponding Hall conductivity, and protected edge states, there\nis an additional possibility. This is a phase that has vanishing Chern number\nand no Hall conductivity, but nevertheless hosts anomalous topological edge\nstates. Due to experimental difficulties associated with the observation of\nsuch a phase, it has not been experimentally realised so far. In this paper, we\nshow that optical lattices prove to be a good candidate for both its\nrealisation and subsequent observation, because they can be driven in a\ncontrolled manner. Specifically, we present a simple shaking protocol that\nserves to realise this special Floquet phase, discuss the specific properties\nthat it has, and propose a method to experimentally detect this fascinating\ntopological phase that has no counterpart in equilibrium systems."
    },
    {
        "anchor": "Measuring the Hydrodynamic Linear Response of a Unitary Fermi Gas: We directly observe the hydrodynamic linear response of a unitary Fermi gas\nconfined in a box potential and subject to a spatially periodic optical\npotential that is translated into the cloud at speeds ranging from subsonic to\nsupersonic. We show that the time-dependent change of the density profile is\nsensitive to the thermal conductivity, which controls the relaxation rate of\nthe temperature gradients and hence the responses arising from adiabatic and\nisothermal compression.",
        "positive": "Bound states of spin-orbit coupled cold atoms in a Dirac delta-function\n  potential: Dirac delta-function potential is widely studied in quantum mechanics because\nit usually can be exactly solved and at the same time is useful in modeling\nvarious physical systems. Here we study a system of delta-potential trapped\nspinorbit coupled cold atoms. The spin-orbit coupled atomic matter wave has two\nkinds of evanescent modes, one of which has pure imaginary wavevector and is an\nordinary evanescent wave; while the other with a complex number wave vector is\nrecognized as oscillating evanescent wave. We identified the eigenenergy\nspectra and the existence of bound states in this system. The bound states can\nbe constructed analytically using the two kinds of evanescent modes and we\nfound that they exhibit typical features of stripe phase, separated phase or\nzero-momentum phase. In addition to that, the properties of semi-bound states\nare also discussed, which is a localized wave packet on a plane wave\nbackground."
    },
    {
        "anchor": "Spectral and Entanglement Properties of the Bosonic Haldane Insulator: We discuss the existence of a nontrivial topological phase in one-dimensional\ninteracting systems described by the extended Bose-Hubbard model with a mean\nfilling of one boson per site. Performing large-scale density-matrix\nrenormalization group calculations we show that the presence of\nnearest-neighbor repulsion enriches the ground-state phase diagram of the\nparadigmatic Bose-Hubbard model by stabilizing a novel gapped insulating state,\nthe so-called Haldane insulator, which, embedded into superfluid, Mott\ninsulator, and density wave phases, is protected by the lattice inversion\nsymmetry. The quantum phase transitions between the different insulating phases\nwere determined from the central charge via the von Neumann entropy. The\nHaldane phase reveals a characteristic fourfold degeneracy of the entanglement\nspectrum. We finally demonstrate that the intensity maximum of the dynamical\ncharge structure factor, accessible by Bragg spectroscopy, features the gapped\ndispersion known from the spin-1 Heisenberg chain.",
        "positive": "The influence of interaction between quasiparticles on parametric\n  resonance process in Bose-Einstein condensates: We analyze the uniform system of weakly interacting bosonic gas undergoing\nperiodic oscillation of interaction constant. This, within Bogoliubov\napproximation, leads to creation of atom pairs with well defined opposite\nvelocities. We show how interaction between quasiparticles, omitted in the\nBogoliubov approximation, significantly changes the atom pair creation process\nand properties of scattered atoms."
    },
    {
        "anchor": "Observing dynamical currents in a non-Hermitian momentum lattice: We report on the experimental realization and detection of dynamical currents\nin a spin-textured lattice in momentum space. Collective tunneling is\nimplemented via cavity-assisted Raman scattering of photons by a spinor\nBose-Einstein condensate into an optical cavity. The photon field inducing the\ntunneling processes is subject to cavity dissipation, resulting in effective\ndirectional dynamics in a non-Hermitian setting. We observe that the individual\ntunneling events are superradiant in nature and locally resolve them in the\nlattice by performing real-time, frequency-resolved measurements of the leaking\ncavity field. The results can be extended to a regime exhibiting a cascade of\ncurrents and simultaneous coherences between multiple lattice sites, where\nnumerical simulations provide further understanding of the dynamics. Our\nobservations showcase dynamical tunneling in momentum-space lattices and\nprovide prospects to realize dynamical gauge fields in driven-dissipative\nsettings.",
        "positive": "Two impurities in a Bose-Einstein condensate: from Yukawa to Efimov\n  attracted polarons: The well-known Yukawa and Efimov potentials are two different mediated\ninteraction potentials. The first one arises in quantum field theory from the\nexchange of virtual particles. The second one is mediated by a real particle\nresonantly interacting with two other particles. This Letter shows how two\nimpurities immersed in a Bose-Einstein condensate can exhibit both phenomena.\nFor a weak impurity-boson attractive interactionattraction with the condensate,\nthe two impurities form two polarons that interact through a weak Yukawa\nattraction mediated by virtual excitations. For a resonant attraction with the\ncondensate, the exchanged excitation becomes a real boson and the mediated\ninteraction changes to a strong Efimov attraction that can bind the two\npolarons. The resulting bipolarons turn into in-medium Efimov trimers made of\nthe two impurities and one boson. Evidence of this physics could be seen in\nultracold mixtures of atoms."
    },
    {
        "anchor": "Thermalization and Sub-Poissonian Density Fluctuations in a Degenerate\n  Molecular Fermi Gas: We observe thermalization in the production of a degenerate Fermi gas of\npolar ${}^{40}\\text{K}{}^{87}\\text{Rb}$ molecules. By measuring the atom--dimer\nelastic scattering cross section near the Feshbach resonance, we show that\nFeshbach molecules rapidly reach thermal equilibrium with both parent atomic\nspecies. Equilibrium is essentially maintained through coherent transfer to the\nground state. Sub-Poissonian density fluctuations in Feshbach and ground-state\nmolecules are measured, giving an independent characterization of degeneracy\nand directly probing the molecular Fermi--Dirac distribution.",
        "positive": "Observation of Laughlin states made of light: Much of the richness in nature emerges because the same simple constituents\ncan form an endless variety of ordered states. While many such states are fully\ncharacterized by their symmetries, interacting quantum systems can also exhibit\ntopological order, which is instead characterized by intricate patterns of\nentanglement. A paradigmatic example of such topological order is the Laughlin\nstate, which minimizes the interaction energy of charged particles in a\nmagnetic field and underlies the fractional quantum Hall effect. Broad efforts\nhave arisen to enhance our understanding of these orders by forming Laughlin\nstates in synthetic quantum systems, such as those composed of ultracold atoms\nor photons. In spite of these efforts, electron gases remain essentially the\nonly physical system in which topological order has appeared. Here, we present\nthe first observation of optical photon pairs in the Laughlin state. These\npairs emerge from a photonic analog of a fractional quantum Hall system, which\ncombines strong, Rydberg-mediated interactions between photons and synthetic\nmagnetic fields for light, induced by twisting an optical resonator. Photons\nentering this system undergo collisions to form pairs in an angular momentum\nsuperposition consistent with the Laughlin state. Characterizing the same pairs\nin real space reveals that the photons avoid each other, a hallmark of the\nLaughlin state. This work heralds a new era of quantum many-body optics, where\nstrongly interacting and topological photons enable exploration of quantum\nmatter with wholly new properties and unique probes."
    },
    {
        "anchor": "Effect of interactions on harmonically confined Bose-Fermi mixtures in\n  optical lattices: We investigate a Bose-Fermi mixture in a three-dimensional optical lattice,\ntrapped in a harmonic potential. Using Generalized Dynamical Mean-Field theory,\nwhich treats the Bose-Bose and Bose-Fermi interaction in a fully\nnon-perturbative way, we show that for experimentally relevant parameters a\npeak in the condensate fraction close to the point of vanishing Bose-Fermi\ninteraction is reproduced within a single band framework. We identify two\nphysical mechanisms contributing to this effect: the spatial redistribution of\nparticles when the interspecies interaction is changed and the reduced phase\nspace for strong interactions, which results in a higher temperature at fixed\nentropy.",
        "positive": "Low-Dimensional Stochastic Projected Gross-Pitaevskii Equation: We present reduced-dimensional stochastic projected Gross-Pitaevskii\nequations describing regimes of confinement and temperature where a 1D or 2D\nsuperfluid is immersed in a 3D thermal cloud. The projection formalism provides\nboth a formally rigorous and physically natural way to effect the dimensional\nreduction. The 3D form of the number-damping (growth) terms is unchanged by the\ndimensional reduction. Projection of the energy-damping (scattering) terms\nleads to modified stochastic equations of motion describing energy exchange\nwith the thermal reservoir. The regime of validity of the dimensional reduction\nis investigated via variational analysis. Paying particular attention to 1D, we\nvalidate our variational treatment by comparing numerical simulations of a\ntrapped oblate system in 3D with the 1D theory, and establish a consistent\nchoice of cutoff for the 1D theory. We briefly discuss the scenario involving\ntwo-components with different degeneracy, suggesting that a wider regime of\nvalidity exists for systems in contact with a buffer-gas reservoir."
    },
    {
        "anchor": "Synchronization transition in dipole-coupled two-level systems with\n  positional disorder: We study the decoherence dynamics of dipole-coupled two-level quantum systems\nin Ramsey-type experiments. We focus on large networks of two-level systems,\nconfined to two spatial dimensions and with positional disorder giving rise to\ndisordered dipolar couplings. This setting is relevant for modeling the\ndecoherence dynamics of the rotational excitations of polar molecules confined\nto deep optical lattices, where disorder arises from the random filling of\nlattice sites with occupation probability $p$. We show that the decoherence\ndynamics exhibits a phase transition at a critical filling $p_c\\simeq 0.15$.\nFor $p<p_c$ the dynamics is disorder-dominated and the Ramsey interference\nsignal decays on a timescale $T_2 \\propto p^{-3/2}$. For $p>p_c$ the dipolar\ninteractions dominate the disorder, and the system behaves as a collective\nspin-ordered phase, representing synchronization of the two-level systems and\npersistent Ramsey oscillations with divergent $T_2$ for large systems. For a\nfinite number of two-level systems, $N$, the spin-ordered phase at $p> p_c$\nundergoes a crossover to a collective spin-squeezed state on a timescale\n$\\tau_{\\rm sq} \\propto \\sqrt{N}$. We develop a self-consistent mean-field\ntheory that is capable of capturing the synchronization transition at $p_c$,\nand provide an intuitive theoretical picture that describes the phase\ntransition in the long-time dynamics. We also show that the decoherence\ndynamics appear to be ergodic in the vicinity of $p_c$, the long-time behaviour\nbeing well described by the predictions of equilibrium thermodynamics. The\nresults are supported by the results of exact diagonalization studies of small\nsystems.",
        "positive": "Out-of-equilibrium states and quasi-many-body localization in polar\n  lattice gases: The absence of energy dissipation leads to an intriguing out-of-equilibrium\ndynamics for ultracold polar gases in optical lattices, characterized by the\nformation of dynamically-bound on-site and inter-site clusters of two or more\nparticles, and by an effective blockade repulsion. These effects combined with\nthe controlled preparation of initial states available in cold gases\nexperiments can be employed to create interesting out-of-equilibrium states.\nThese include quasi-equilibrated effectively repulsive 1D gases for attractive\ndipolar interactions and dynamically-bound crystals. Furthermore,\nnon-equilibrium polar lattice gases can offer a promising scenario for the\nstudy of many-body localization in the absence of quenched disorder. This\nfascinating out-of-equilibrium dynamics for ultra-cold polar gases in optical\nlattices may be accessible in on-going experiments."
    },
    {
        "anchor": "Roton Excitations in an Oblate Dipolar Quantum Gas: We observe signatures of radial and angular roton excitations around a\ndroplet crystallization transition in dipolar Bose-Einstein condensates. In\nsitu measurements are used to characterize the density fluctuations near this\ntransition. The static structure factor is extracted and used to identify the\nradial and angular roton excitations by their characteristic symmetries. These\nfluctuations peak as a function of interaction strength indicating the\ncrystallization transition of the system. We compare our observations to a\ntheoretically calculated excitation spectrum allowing us to connect the\ncrystallization mechanism with the softening of the angular roton modes.",
        "positive": "Criticality in the Bose-Hubbard model with three-body repulsion: We study the attractive Bose-Hubbard model with a tunable, on-site three-body\nconstraint. It is shown that the critical behavior of the system undergoing a\nphase transition from pair-superfluid to superfluid at unit filling depends on\nthe value of the three-body repulsion. In particular, we calculate critical\nexponents and the central charge governing the quantum phase transition."
    },
    {
        "anchor": "Static kinks in chains of interacting atoms: We theoretically analyse the equation of topological solitons in a chain of\nparticles interacting via a repulsive power-law potential and confined by a\nperiodic lattice. Starting from the discrete model, we perform a gradient\nexpansion and obtain the kink equation in the continuum limit for a power law\nexponent $n \\ge 1$. The power-law interaction modifies the sine-Gordon\nequation, giving rise to a rescaling of the coefficient multiplying the second\nderivative (the kink width) and to an additional integral term. We argue that\nthe integral term does not affect the local properties of the kink, but it\ngoverns the behaviour at the asymptotics. The kink behaviour at the center is\ndominated by a sine-Gordon equation and its width tends to increase with the\npower law exponent. When the interaction is the Coulomb repulsion, in\nparticular, the kink width depends logarithmically on the chain size. We define\nan appropriate thermodynamic limit and compare our results with existing\nstudies performed for infinite chains. Our formalism allows one to\nsystematically take into account the finite-size effects and also slowly\nvarying external potentials, such as for instance the curvature in an ion trap.",
        "positive": "Non-Equilibrium Universality in the Heating Dynamics of Interacting\n  Luttinger Liquids: We establish a new non-equilibrium scaling regime in the short time evolution\nof one-dimensional interacting open quantum systems subject to a generic\nheating mechanism. This dynamical regime is characterized by uncompensated\nphonon production and a super-diffusive, universal scaling of quasiparticle\nlifetimes with momentum $\\sim q^{-5/3}$, distinct from finite and zero\ntemperature cases. It is separated from a high momentum regime by a time\ndependent scale fading out as $q_0(t) \\sim t^{-4/5}$. In the latter region we\nobserve thermalization to an effective time-dependent equilibrium with linearly\nincreasing temperature. By mapping out the dynamical phase diagram and\ncomputing the dynamical structure factor within an open system Keldysh\nfunctional integral approach, we show how these predictions can be explored in\ncold atom experiments by means of Bragg spectroscopy."
    },
    {
        "anchor": "Generation of uniform synthetic magnetic fields by split driving of an\n  optical lattice: We describe a method to generate a synthetic gauge potential for ultracold\natoms held in an optical lattice. Our approach uses a time-periodic driving\npotential based on two quickly alternating signals to engineer the appropriate\nAharonov-Bohm phases, and permits the simulation of a uniform tunable magnetic\nfield. We explicitly demonstrate that our split driving scheme reproduces the\nbehavior of a charged quantum particle in a magnetic field over the complete\nrange of field strengths, and obtain the Hofstadter butterfly band-structure\nfor the Floquet quasienergies at high fluxes.",
        "positive": "Investigation of the bosonic spectrum of two-dimensional optical\n  graphene-type lattices. Superfluid phase: The energy spectrum of a system of Bose atoms in the superfluid phase in an\noptical lattice of the graphene type has been studied. The dispersion laws for\nthe energy bands and the single particle spectral densities are calculated in\nthe random phase approximation and in the framework of the hard-core boson\nformalism, and their changes at the transition from the normal phase to the\nsuperfluid one are described. As a result of this transformation, the number of\nsubbands doubles. In the case of the subband energetic equivalence, the Dirac\npoints in the spectrum survive, and their number becomes twice as much. When\nthe subbands are energetically nonequivalent, the Dirac points are absent. The\nshape of spectral densities is shown to be sensitive to the changes in the\ntemperature and the chemical potential position."
    },
    {
        "anchor": "Two-body anticorrelation in a harmonically trapped ideal Bose gas: We predict the existence of a dip below unity in the second-order coherence\nfunction of a partially condensed ideal Bose gas in harmonic confinement,\nsignaling the anticorrelation of density fluctuations in the sample. The dip in\nthe second-order coherence function is revealed in a canonical-ensemble\ncalculation, corresponding to a system with fixed total number of particles. In\na grand-canonical ensemble description, this dip is obscured by the\noccupation-number fluctuation catastrophe of the ideal Bose gas. The\nanticorrelation is most pronounced in highly anisotropic trap geometries\ncontaining small particle numbers. We explain the fundamental physical\nmechanism which underlies this phenomenon, and its relevance to experiments on\ninteracting Bose gases.",
        "positive": "Universal scaling of unequal-time correlation functions in ultracold\n  Bose gases far from equilibrium: We explore the far-from-equilibrium dynamics of Bose gases in a universal\nregime associated to nonthermal fixed points. While previous investigations\nconcentrated on scaling functions and exponents describing equal-time\ncorrelations, we compute the additional scaling functions and dynamic exponent\n$z$ characterizing the frequency dependence or dispersion from unequal-time\ncorrelations. This allows us to compare the characteristic condensation and\ncorrelation times from a finite-size scaling analysis depending on the system's\nvolume."
    },
    {
        "anchor": "Ground-state phase diagram of a dipolar condensate with quantum\n  fluctuations: We consider the ground state properties of a trapped dipolar condensate under\nthe influence of quantum fluctuations. We show that this system can undergo a\nphase transition from a low density condensate state to a high density droplet\nstate, which is stabilized by quantum fluctuations. The energetically favored\nstate depends on the geometry of the confining potential, the number of atoms\nand the two-body interactions. We develop a simple variational ansatz and\nvalidate it against full numerical solutions. We produce a phase diagram for\nthe system and present results relevant to current experiments with dysprosium\nand erbium condensates.",
        "positive": "Square Pattern Formation as Stable Fixed Point in Driven Two-Dimensional\n  Bose-Einstein Condensates: We investigate pattern formation in two-dimensional Bose-Einstein condensates\n(BECs) caused by temporal periodic modulation of the interatomic interaction.\nTemporal modulation of the interaction causes the so-called Faraday instability\nin the condensate, which we show generically leads to a stable square grid\ndensity pattern. We take the amplitudes in each of the two directions spanning\nthe two-dimensional density pattern as order parameters in pattern formation\nand derive a set of simultaneous time evolution equations for those order\nparameters from the Gross--Pitaevskii (GP) equation with a time-periodic\ninteraction. We identify the fixed points of the time evolution and show by\nstability analysis that the inhomogeneous density exhibits a square grid\npattern as a stable fixed point."
    },
    {
        "anchor": "Clusterization of weakly-interacting bosons in one dimension: an\n  analytic study at zero temperature: We study a system of penetrable bosons on a line, focusing on the\nhigh-density/weak-interaction regime, where the ground state is, to a good\napproximation, a condensate. Under compression, the system clusterizes at zero\ntemperature, i.e., particles gather together in separate, equally populated\nbunches. We compare predictions from the Gross-Pitaevskii (GP) equation with\nthose of two distinct variational approximations of the single-particle state,\nwritten as either a sum of Gaussians or the square root of it. Not only the\nwave functions in the three theories are similar, but also the phase-transition\ndensity is the same for all. In particular, clusterization occurs together with\nthe softening of roton excitations in GP theory. Compared to the latter theory,\nGaussian variational theory has the advantage that the mean-field energy\nfunctional is written in (almost) closed form, which enables us to extract the\nphase-transition and high-density behaviors in fully analytic terms. We also\ncompute the superfluid fraction of the clustered system, uncovering its exact\nbehavior close, as well as very far away from, the transition.",
        "positive": "$\u03bc$-Symmetry breaking: an algebraic approach to finding mean fields of\n  quantum many-body systems: One of the most fundamental problems in quantum many-body systems is the\nidentification of a mean field in spontaneous symmetry breaking which is\nusually made in a heuristic manner. We propose a systematic method of finding a\nmean field based on the Lie algebra and the dynamical symmetry by introducing a\nclass of symmetry broken phases which we call $\\mu$-symmetry breaking. We show\nthat for $\\mu$-symmetry breaking the quadratic part of an effective Lagrangian\nof Nambu-Goldstone modes can be block-diagonalized and that homotopy groups of\ntopological excitations can be calculated systematically."
    },
    {
        "anchor": "Finite-size effects in the dynamics of few bosons in a ring potential: We study the temporal evolution of a small number $N$ of ultra-cold bosonic\natoms confined in a ring potential. Assuming that initially the system is in a\nsolitary-wave solution of the corresponding mean-field problem, we identify\nsignificant differences in the time evolution of the density distribution of\nthe atoms when it instead is evaluated with the many-body Schr\\\"odinger\nequation. Three characteristic timescales are derived: the first is the period\nof rotation of the wave around the ring, the second is associated with a\n\"decay\" of the density variation, and the third is associated with periodic\n\"collapses\" and \"revivals\" of the density variations, with a factor of $\\sqrt\nN$ separating each of them. The last two timescales tend to infinity in the\nappropriate limit of large $N$, in agreement with the mean-field approximation.\nThese findings are based on the assumption of the initial state being a\nmean-field state. We confirm this behavior by comparison to the exact solutions\nfor a few-body system stirred by an external potential. We find that the exact\nsolutions of the driven system exhibit similar dynamical features.",
        "positive": "Ultradilute quantum liquid of dipolar atoms in a bilayer: We show that ultradilute quantum liquids can be formed with ultracold bosonic\ndipolar atoms in a bilayer geometry. Contrary to previous realizations of\nultradilute liquids, there is no need for stabilizing the system with an\nadditional repulsive short-range potential. The advantage of the proposed\nsystem is that dipolar interactions on their own are sufficient for creation of\na self-bound state and no additional short-range potential is needed for the\nstabilization. We perform quantum Monte Carlo simulations and find a rich\nground-state phase diagram that contains quantum phase transitions between\nliquid, solid, atomic gas, and molecular gas phases. The stabilization\nmechanism of the liquid phase is consistent with the microscopic scenario in\nwhich the effective dimer-dimer attraction is balanced by an effective\nthree-dimer repulsion. The equilibrium density of the liquid, which is\nextremely small, can be controlled by the interlayer distance. From the\nequation of state, we extract the spinodal density, below which the homogeneous\nsystem breaks into droplets. Our results offer a new example of a\ntwo-dimensional interacting dipolar liquid in a clean and highly controllable\nsetup."
    },
    {
        "anchor": "Intertwined Space-Time Symmetry, Orbital Magnetism and Dynamical Berry\n  Curvature in a Circularly Shaken Optical Lattice: We study the circular shaking of a two dimensional optical lattice, which is\nessentially a (2+1) dimensional space-time lattice exhibiting periodicities in\nboth spatial and temporal dimensions. The near-resonant optical shaking\nconsidered here dynamically couples the low-lying $s$ band and the first\nexcited $p$ bands by transferring a photon of shaking frequency. The\nintertwined space-time symmetries are further uncovered to elucidate the\ndegeneracy in the spectrum solved with the generalized Bloch-Floquet theorem.\nSetting the chirality of circular shaking explicitly breaks time reversal\nsymmetry and lifts the degeneracy of $p_\\pm = p_x \\pm ip_y$ orbitals, leading\nto the local circulation of orbital magnetism, i.e the imbalanced occupation in\n$p_\\pm$ orbitals. Moreover, the dynamics of Berry connection is revealed by the\ntime evolution of the Berry curvature and the polarization, which have physical\nobservable effects in experiments. Interestingly, the dynamics is found\ncharacterized by a universal phase shift, governed by the time screw rotational\nsymmetry involving a fractional translation of time. These findings suggest\nthat the present lattice-shaking scheme provides a versatile platform for the\ninvestigation of the orbital physics and the symmetry-protected dynamics.",
        "positive": "Hard-Wall Confinement of a Fractional Quantum Hall Liquid: We make use of numerical exact diagonalization calculations to explore the\nphysics of $\\nu = 1/2$ bosonic fractional quantum Hall (FQH) droplets in the\npresence of experimentally realistic cylindrically symmetric hard-wall\npotentials. This kind of confinement is found to produce very different\nmany-body spectra compared to a harmonic trap or the so-called extremely steep\nlimit. For a relatively weak confinement, the degeneracies are lifted and the\nlow-lying excited states organize themselves in energy branches that can be\nexplained in terms of their Jack polynomial representation. For a strong\nconfinement, a strong spatial deformation of the droplet is found, with an\nunexpected depletion of its central density."
    },
    {
        "anchor": "Topological excitations in a spin-orbit coupled spin-1 Bose-Einstein\n  condensate under sinusoidally varying magnetic fields: We present a theoretical study of a spin-orbit coupled spin-1 Bose-Einstein\ncondensate under the influence of sinusoidally varying magnetic fields. In the\nground state of the ferromagnetic spin-1 condensate, we investigate topological\nexcitations in the system arising due to the combined effect of Rashba\nspin-orbit coupling and an in-plane sinusoidally varying magnetic field. In\nthis work, we offer a comparative study for various choices of magnetic fields\nin the $x\\rm{-}y$ plane. For a fixed field strength, the spin-orbit coupled\nsystem sustains a rich variety of exotic vortex structures ranging from\nvortex-antivortex lattices to vortex clusters as we increase the coupling\nstrength.",
        "positive": "Strongly interacting bosons on a three-leg ladder in the presence of a\n  homogeneous flux: We perform a density-matrix renormalization-group study of strongly\ninteracting bosons on a three-leg ladder in the presence of a homogeneous flux.\nFocusing on one-third filling, we explore the phase diagram in dependence of\nthe magnetic flux and the inter-leg tunneling strength. We find several phases\nincluding a Meissner phase, vortex liquids, a vortex lattice, as well as a\nstaggered-current phase. Moreover, there are regions where the chiral current\nreverses its direction, both in the Meissner and in the staggered-current\nphase. While the reversal in the latter case can be ascribed to spontaneous\nbreaking of translational invariance, in the first it stems from an effective\nflux increase in the rung direction. Interactions are a necessary ingredient to\nrealize either type of chiral-current reversal."
    },
    {
        "anchor": "Dynamic spin response of a strongly interacting Fermi gas: We present an experimental investigation of the dynamic spin response of a\nstrongly interacting Fermi gas using Bragg spectroscopy. By varying the\ndetuning of the Bragg lasers, we show that it is possible to measure the\nresponse in the spin and density channels separately. At low Bragg energies,\nthe spin response is suppressed due to pairing, whereas the density response is\nenhanced. These experiments provide the first independent measurements of the\nspin-parallel and spin-antiparallel dynamic and static structure factors and\nopen the way to a complete study of the structure factors at any momentum. At\nhigh momentum the spin-antiparallel dynamic structure factor displays a\nuniversal high frequency tail, proportional to $\\omega^{-5/2}$, where $\\hbar\n\\omega$ is the probe energy.",
        "positive": "Collective Modes in a Two-band Superfluid of Ultracold Alkaline-earth\n  Atoms Close to an Orbital Feshbach Resonance: We discuss the collective modes in an alkaline-earth Fermi gas close to an\norbital Feshbach resonance. Unlike the usual Feshbach resonance, the orbital\nFeshbach resonance in alkaline-earth atoms realizes a two-band superfluid\nsystem where the fermionic nature of both the open and the closed channel has\nto be taken into account. We show that apart from the usual Anderson-Bogoliubov\nmode which corresponds to the oscillation of total density, there also appears\nthe long-sought Leggett mode corresponding to the oscillation of relative\ndensity between the two channels. The existence of the phonon and the Leggett\nmodes and their evolution are discussed in detail. We show how these collective\nmodes are reflected in the density response of the system."
    },
    {
        "anchor": "Spin Superfluidity versus Solidity of Ultracold Polar Molecules: We present a technique for engineering quantum magnets via ultracold polar\nmolecules in optical lattices and explore exotic interplay between its spin\nsuperfluidity and solidity. The molecular ground and first excited rotational\nstates are resonantly coupled by a linearly polarized microwave field. The\nspin-up (spin-down) states are presented by molecular rotational states of\nelectric dipole moment along (against) the coupling field. By controlling the\nangle between the lattice direction and the coupling field, the inter-site\ninteraction can be tuned from antiferromagnetic to ferromagnetic. Furthermore,\nthe dipole-dipole interaction induces an exotic interplay between spin\nsuperfluidity and solidity, and spin supersolid phases may appear in mediate\nregions.",
        "positive": "Entangling two Bose Einstein condensates in a double cavity system: We propose a scheme to transfer the quantum state of light fields to the\ncollective density excitations of a Bose Einstein condensate (BEC) in a cavity.\nThis scheme allows to entangle two BECs in a double cavity setup by\ntransferring the quantum entanglement of two light fields produced from a\nnondegenerate parametric amplifier (NOPA) to the collective density excitations\nof the two BECs. An EPR state of the collective density excitations can be\ncreated by a judicious choice of the system parameters."
    },
    {
        "anchor": "Retardation effects in induced atomic dipole-dipole interactions: We present mean-field calculations of azimuthally averaged retarded\ndipole-dipole interactions in a Bose-Einstein condensate induced by a laser, at\nboth long and short wavelengths. Our calculations demonstrate that\ndipole-dipole interactions become significantly stronger at shorter\nwavelengths, by as much as 30-fold, due to retardation effects. This\nenhancement, along with inclusion of the dynamic polarizability, indicate a\nmethod of inducing long-range interatomic interactions in neutral atom\ncondensates at significantly lower intensities than previously realized.",
        "positive": "Many-body interferometry of a Rydberg-dressed spin lattice: Ultracold atoms are an ideal platform to study strongly correlated phases of\nmatter in and out of equilibrium. Much of the experimental progress in this\nfield crucially relies on the control of the contact interaction between two\natoms. Control of strong long-range interactions between distant ground state\natoms has remained a long standing goal, opening the path towards the study of\nfundamentally new quantum many-body systems including frustrated or topological\nmagnets and supersolids. Optical dressing of ground state atoms by\nnear-resonant laser coupling to Rydberg states has been proposed as a versatile\nmethod to engineer such interactions. However, up to now the great potential of\nthis approach for interaction control in a many-body setting has eluded\nexperimental confirmation. Here we report the realisation of coherent\nRydberg-dressing in an ultracold atomic lattice gas and directly probe the\ninduced interaction potential using an interferometric technique with single\natom sensitivity. We use this approach to implement a two-dimensional synthetic\nspin lattice and demonstrate its versatility by tuning the range and anisotropy\nof the effective spin interactions. Our measurements are in remarkable\nagreement with exact solutions of the many-body dynamics, providing further\nevidence for the high degree of accurate interaction control in these systems.\nFinally, we identify a collective many-body decay process, and discuss possible\nroutes to overcome this current limitation of coherence times. Our work marks\nthe first step towards the use of laser-controlled Rydberg interactions for the\nstudy of exotic quantum magnets in optical lattices."
    },
    {
        "anchor": "Non-Hermitian skin effect and chiral damping in open quantum systems: One of the unique features of non-Hermitian Hamiltonians is the non-Hermitian\nskin effect, namely that the eigenstates are exponentially localized at the\nboundary of the system. For open quantum systems, a short-time evolution can\noften be well described by the effective non-Hermitian Hamiltonians, while\nlong-time dynamics calls for the Lindblad master equations, in which the\nLiouvillian superoperators generate time evolution. In this Letter, we find\nthat Liouvillian superoperators can exhibit the non-Hermitian skin effect, and\nuncover its unexpected physical consequences. It is shown that the\nnon-Hermitian skin effect dramatically shapes the long-time dynamics, such that\nthe damping in a class of open quantum systems is algebraic under periodic\nboundary condition but exponential under open boundary condition. Moreover, the\nnon-Hermitian skin effect and non-Bloch bands cause a chiral damping with a\nsharp wavefront. These phenomena are beyond the effective non-Hermitian\nHamiltonians; instead, they belong to the non-Hermitian physics of full-fledged\nopen quantum dynamics.",
        "positive": "Quantized conductance through a dissipative atomic point contact: Signatures of quantum transport are expected to quickly vanish as dissipation\nis introduced in a system. This dissipation can take several forms, including\nthat of particle loss, which has the consequence that the total probability\ncurrent is not conserved. Here, we study the effect of such losses at a quantum\npoint contact (QPC) for ultracold atoms. Experimentally, dissipation is\nprovided by a near-resonant optical tweezer whose power and detuning control\nthe loss rates for the different internal atomic states as well as their\neffective Zeeman shifts. We theoretically model this situation by including\nlosses in the Landauer-B\\\"uttiker formalism over a wide range of dissipative\nrates. We find good agreement between our measurements and our model, both\nfeaturing robust conductance plateaus. Finally, we are able to map out the\natomic density by varying the position of the near-resonant tweezer inside the\nQPC, realizing a dissipative scanning gate microscope for cold atoms."
    },
    {
        "anchor": "Topological stirring of two-dimensional atomic Bose-Einstein condensates: We stir vortices into a trapped quasi two-dimensional atomic Bose-Einstein\ncondensate by moving three laser stirrers. We apply stirring protocols\nintroduced by Boyland et. al. (2000) that efficiently build in topological\nchaos in classical fluids and are classified as Pseudo-Anosov stirring\nprotocols. These are compared to their inefficient mixing counterparts,\nfinite-order stirring protocols. We investigate if inefficient stirring\nprotocols result in a more clustered distribution of vortices. The efficiency\nwith which vortices are 'mixed' or distributed in a condensate is important for\ninvestigating dynamics of continuously forced quantum turbulence and the\nexistence of the inverse cascade in turbulent two-dimensional superfluids.",
        "positive": "Faraday waves in collisionally inhomogeneous Bose-Einstein condensates: We study the emergence of Faraday waves in cigar-shaped collisionally\ninhomogeneous Bose-Einstein condensates subject to periodic modulation of the\nradial confinement. Considering a Gaussian-shaped radially inhomogeneous\nscattering length, we show through extensive numerical simulations and detailed\nvariational treatment that the spatial period of the emerging Faraday waves\nincreases as the inhomogeneity of the scattering length gets weaker, and that\nit saturates once the width of the radial inhomogeneity reaches the radial\nwidth of the condensate. In the regime of strongly inhomogeneous scattering\nlengths, the radial profile of the condensate is akin to that of a hollow\ncylinder, while in the weakly inhomogeneous case the condensate is cigar-shaped\nand has a Thomas-Fermi radial density profile. Finally, we show that when the\nfrequency of the modulation is close to the radial frequency of the trap, the\ncondensate exhibits resonant waves which are accompanied by a clear excitation\nof collective modes, while for frequencies close to twice that of the radial\nfrequency of the trap, the observed Faraday waves set in forcefully and quickly\ndestabilize condensates with weakly inhomogeneous two-body interactions."
    },
    {
        "anchor": "Pairing and the spin susceptibility of the polarized unitary Fermi gas\n  in the normal phase: We theoretically study the pairing behavior of the unitary Fermi gas in the\nnormal phase. Our analysis is based on the static spin susceptibility, which\ncharacterizes the response to an external magnetic field. We obtain this\nquantity by means of the complex Langevin approach and compare our calculations\nto available literature data in the spin-balanced case. Furthermore, we present\nresults for polarized systems, where we complement and expand our analysis at\nhigh temperature with high-order virial expansion results. The implications of\nour findings for the phase diagram of the spin-polarized unitary Fermi gas are\ndiscussed, in the context of the state of the art.",
        "positive": "Hardcore bosons in a zig-zag optical superlattice: We study a system of hard-core bosons at half-filling in a one-dimensional\noptical superlattice. The bosons are allowed to hop to nearest and next-nearest\nneighbor sites producing a zig-zag geometry and we obtain the ground state\nphase diagram as a function of microscopic parameters using the finite-size\ndensity matrix renormalization group (FS-DMRG) method. Depending on the sign of\nthe next-nearest neighbor hopping and the strength of the superlattice\npotential the system exhibits three different phases, namely the bond-order\n(BO) solid, the superlattice induced Mott insulator (SLMI) and the superfluid\n(SF) phase. When the signs of both hopping amplitudes are the same (the\n\"unfrustrated\" case), the system undergoes a transition from the SF to the SLMI\nat a non-zero value of the superlattice potential. On the other hand, when the\ntwo amplitudes differ in sign (the \"frustrated\" case), the SF is unstable to\nswitching on a superlattice potential and also exists only up to a finite value\nof the next nearest neighbor hopping. This part of the phase diagram is\ndominated by the BO phase which breaks translation symmetry spontaneously even\nin the absence of the superlattice potential and can thus be characterized by a\nbond order parameter. The transition from BO to SLMI appears to be first order."
    },
    {
        "anchor": "Thermalization in closed quantum systems: semiclassical approach: Thermalization in closed quantum systems can be explained either by means of\nthe eigenstate thermalization hypothesis or the concept of canonical\ntypicality. Both concepts are based on quantum mechanical formalism such as\nspectral properties of the eigenstates or entanglement between subsystems\nrespectively. Here we study the onset of thermalization of Bose particles in a\ntwo-band double well potential using the truncated Wigner approximation. This\nallows us to use the familiar classical formalism to explain quantum\nthermalization in this system. In particular, we demonstrate that sampling of\nan initial quantum state plays the role of a statistical mechanical ensemble,\nwhile subsequent chaotic classical evolution turns the initial quantum state\ninto the thermal state.",
        "positive": "Trapped $^{173}$Yb Fermi gas across an orbital Feshbach resonance: Starting with the two-band description of an orbital Feshbach resonance, we\nstudy superfluid properties of a trapped $^{173}$Yb Fermi gas under the\nassumptions of a local-density approximation for the trapping potential and a\nmean-field approximation for the intra-band Cooper pairings. In particular, we\ninvestigate the competition and interplay between the pair-breaking effect that\nis caused by the inter-band detuning energy, and the pair-breaking and\nthermal-broadening effects that are simultaneously caused by the temperature.\nWe predict several experimental signatures that are directly caused by this\ninterplay including a spatial separation of superfluid and normal phases within\nthe trap, and could play decisive roles in probing two-band superfluidity in\nthese systems."
    },
    {
        "anchor": "High-intensity two-frequency photoassociation spectroscopy of a weakly\n  bound molecular state: theory and experiment: We investigate two-frequency photoassociation of a weakly bound molecular\nstate, focusing on a regime where the ac Stark shift is comparable to the\nhalo-state energy. In this \"high-intensity\" regime, we observe features absent\nin low-intensity two-frequency photoassociation. We experimentally measure the\nspectra of $^{86}$Sr atoms coupled to the least bound state of the\n$^{86}$Sr$_2$ ground electronic channel through an intermediate electronically\nexcited molecular state. We compare the spectra to a simple three-level model\nthat includes a two-frequency drive on each leg of the transition. With\nnumerical solution of the time-dependent Schrodinger equation, we show that\nthis model accurately captures (1) the existence of experimentally observed\nsatellite peaks that arise from nonlinear processes, (2) the locations of the\ntwo-photon peak in the spectrum, including ac Stark shifts, and (3) in some\ncases, spectral lineshapes. To better understand these numerical results, we\ndevelop an approximate treatment of this model, based on Floquet and\nperturbation theory, that gives simple formulas that accurately capture the\nhalo-state energies. We expect these expressions to be valuable tools to\nanalyze and guide future two-frequency photoassociation experiments.",
        "positive": "Induced p-wave superfluidity in strongly interacting imbalanced Fermi\n  gases: The induced interaction among the majority spin species, due to the presence\nof the minority species, is computed for the case of a population-imbalanced\nresonantly-interacting Fermi gas. It is shown that this interaction leads to an\ninstability, at low temperatures, of the recently observed polaron Fermi liquid\nphase of strongly imbalanced Fermi gases to a p-wave superfluid state. We find\nthat the associated transition temperature, while quite small in the weakly\ninteracting BCS regime, is experimentally accessible in the strongly\ninteracting unitary regime."
    },
    {
        "anchor": "Bose-Hubbard realization of fracton defects: Bose-Hubbard models are simple paradigmatic lattice models used to study\ndynamics and phases of quantum bosonic matter. We combine the extended\nBose-Hubbard model in the hard-core regime with ring-exchange hoppings. By\ninvestigating the symmetries and low-energy properties of the Hamiltonian we\nargue that the model hosts fractonic defect excitations. We back up our claims\nwith exact numerical simulations of defect dynamics exhibiting mobility\nconstraints. Moreover, we confirm the robustness of our results against fracton\nsymmetry breaking perturbations. Finally we argue that this model can be\nexperimentally realized in recently proposed quantum simulator platforms with\nbig time crystals, thus paving a way for the controlled study of many-body\ndynamics with mobility constraints.",
        "positive": "Universal Borromean Binding in Spin-Orbit Coupled Ultracold Fermi Gases: Borromean rings and Borromean binding, a class of intriguing phenomena as\nthree objects are linked (bound) together while any two of them are unlinked\n(unbound), widely exist in nature and have been found in systems of biology,\nchemistry and physics. Previous studies have suggested that the occurrence of\nsuch a binding in physical systems typically relies on the microscopic details\nof pairwise interaction potentials at short-range, and is therefore\nnon-universal. Here, we report a new type of Borromean binding in ultracold\nFermi gases with Rashba spin-orbit coupling, which is {\\it universal} against\nshort-range interaction details, with its binding energy only dependent on the\ns-wave scattering length and the spin-orbit coupling strength. We show that the\noccurrence of this universal Borromean binding is facilitated by the symmetry\nof the single-particle dispersion under spin-orbit coupling, and is therefore\n{\\it symmetry-selective} rather than interaction-selective. The state is robust\nover a wide range of mass ratio between composing fermions, which are\naccessible by Li-Li, K-K and K-Li mixtures in cold atoms experiments. Our\nresults reveal the importance of symmetry factor in few-body physics, and shed\nlight on the emergence of new quantum phases in a many-body system with exotic\nfew-body correlations."
    },
    {
        "anchor": "Momentum relaxation of a mobile impurity in a one-dimensional quantum\n  gas: We investigate the time evolution of the momentum of an impurity atom\ninjected into a degenerate Tonks-Girardeau gas. We establish that given an\ninitial momentum $p_0$ the impurity relaxes to a steady state with a\nnon-vanishing momentum $p_\\infty.$ The nature of the steady state is found to\ndepend drastically on whether the masses of the impurity and the host are equal\nor not. This is due to multiple coherent scattering processes leading to a\nresonant interaction between the impurity and the host in the case of equal\nmasses. The dependence of $p_\\infty$ on $p_0$ remains non-trivial even in the\nlimit of vanishing interaction between the impurity and host particles. In this\nlimit $p_\\infty(p_0)$ is found explicitly.",
        "positive": "Topological soliton-polaritons in 1D systems of light and fermionic\n  matter: Quantum nonlinear optics is a quickly growing field with large technological\npromise, at the same time involving complex and novel many-body phenomena. In\nthe usual scenario, optical nonlinearities originate from the interactions\nbetween polaritons, which are hybrid quasi-particles mixing matter and light\ndegrees of freedom. Here we introduce a type of polariton which is\nintrinsically nonlinear and emerges as the natural quasi-particle in presence\nquantum degenerate fermionic matter. It is a composite object made of a fermion\ntrapped inside an optical soliton forming a topological defect in a\nspontaneously formed crystalline structure. Each of these soliton-polaritons\ncarries a $\\textbf{Z}_2$ topological quantum number, as they create a domain\nwall between two crystalline regions with opposite dimerization so that the\nfermion is trapped in an interphase state. These composite objects are formally\nequivalent to those appearing in the Su-Schrieffer-Heeger (SSH) model for\nelectrons coupled to lattice phonons."
    },
    {
        "anchor": "Tunneling-assisted Spin-orbit Coupling in Bilayer Bose-Einstein\n  Condensates: Motivated by a goal of realizing spin-orbit coupling (SOC) beyond\none-dimension (1D), we propose and analyze a method to generate an effective 2D\nSOC in bilayer BECs with laser-assisted inter-layer tunneling. We show that an\ninterplay between the inter-layer tunneling, SOC and intra-layer atomic\ninteraction can give rise to diverse ground state configurations. In\nparticular, the system undergoes a transition to a new type of stripe phase\nwhich spontaneously breaks the time-reversal symmetry. Different from the\nordinary Rashba-type SOC, a fractionalized skyrmion lattice emerges\nspontaneously in the bilayer system without external traps. Furthermore, we\npredict the occurrence of a tetracritical point in the phase diagram of the\nbilayer BECs, where four different phases merge together. The origin of the\nemerging different phases is elucidated.",
        "positive": "Stability of nonstationary states of spin-1 Bose-Einstein condensates: The stability of nonstationary states of homogeneous spin-1 Bose-Einstein\ncondensates is studied by performing Bogoliubov analysis in a frame of\nreference where the state is stationary. In particular, the effect of an\nexternal magnetic field is examined. It is found that a nonzero magnetic field\nintroduces instability in a $^{23}$Na condensate. The wavelengths of this\ninstability can be controlled by tuning the strength of the magnetic field. In\na $^{87}$Rb condensate this instability is present already at zero magnetic\nfield. Furthermore, an analytical bound for the size of a stable condensate is\nfound, and a condition for the validity of the single-mode approximation is\npresented. Realization of the system in a toroidal trap is discussed and the\nfull time development is simulated."
    },
    {
        "anchor": "Critical entropies and magnetic-phase-diagram analysis of ultracold\n  three-component fermionic mixtures in optical lattices: We study theoretically many-body equilibrium magnetic phases and\ncorresponding thermodynamic characteristics of ultracold three-component\nfermionic mixtures in optical lattices described by the SU(3)-symmetric\nsingle-band Hubbard model. Our analysis is based on the generalization of the\nexact diagonalization solver for multicomponent mixtures that is used in the\nframework of the dynamical mean-field theory. It allows us to obtain a\nfinite-temperature phase diagram with the corresponding transition lines to\nmagnetically ordered phases at filling one particle per site (1/3 band filling)\nin simple cubic lattice geometry. Based on the developed theoretical approach,\nwe also attain the necessary accuracy to study the entropy dependence in the\nvicinity of magnetically ordered phases that allows us to make important\npredictions for ongoing and future experiments aiming to approach and study\nlong-range-order phases in ultracold atomic mixtures.",
        "positive": "Dynamical instability in the S=1 Bose-Hubbard model: We study the dynamical instabilities of superfluid flows in the S=1\nBose-Hubbard model. The time evolution of each spin component in a condensate\nis calculated based on the dynamical Gutzwiller approximation for a wide range\nof interactions, from a weakly correlated regime to a strongly correlated\nregime near the Mott-insulator transition. Owing to the spin-dependent\ninteractions, the superfluid flow of the spin-1 condensate decays at a\ndifferent critical momentum from a spinless case when the interaction strength\nis the same. We furthermore calculate the dynamical phase diagram of this model\nand clarify that the obtained phase boundary has very different features\ndepending on whether the average number of particles per site is even or odd.\nFinally, we analyze the density and spin modulations that appear in association\nwith the dynamical instability. We find that spin modulations are highly\nsensitive to the presence of a uniform magnetic field."
    },
    {
        "anchor": "Mode bifurcation in the Rayleigh-Taylor instability of binary\n  condensates: We examine the generation and subsequent evolution of Rayleigh Taylor\ninstability in anisotropic binary Bose-Einstein condensates. Considering a\npancake-shaped geometry, to initiate the instability we tune the intraspecies\ninteraction and analytically study the normal modes of the interface in\nelliptic cylindrical coordinates. The normal modes are then Mathieu functions\nand undergoes bifurcation at particular values of anisotropy and ratio of\nnumber of atoms. We find that the analytical estimates of the bifurcation\nparameters are in good agreement with the numerical results.",
        "positive": "Interplay between exotic superfluidity and magnetism in a chain of\n  four-component ultracold atoms: We investigate the spin-polarized chain of ultracold fermionic atoms with\nspin-3/2 described by the fermionic Hubbard model with SU(4) symmetric\nattractive interaction. The competition of bound pairs, trions, quartets and\nunbound atoms is studied analytically and by density matrix renormalization\ngroup simulations. We find several distinct states where bound particles\ncoexist with the ferromagnetic state of unpaired fermions. In particular, an\nexotic inhomogeneous Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)-type superfluid of\nquartets in a magnetic background of uncorrelated atoms is found for weaker\ninteractions. We show that the system can be driven from this quartet-FFLO\nstate to a molecular state of localized quartets which is also reflected in the\nstatic structure factor. For strong enough coupling, spatial segregation\nbetween molecular crystals and ferromagnetic liquids emerges due to the large\neffective mass of the composite particles."
    },
    {
        "anchor": "Spectroscopy of dipolar fermions in 2D pancakes and 3D lattices: Motivated by ongoing measurements at JILA, we calculate the recoil-free\nspectra of dipolar interacting fermions, for example ultracold heteronuclear\nmolecules, in a one-dimensional lattice of two-dimensional pancakes,\nspectroscopically probing transitions between different internal (e.g.,\nrotational) states. We additionally incorporate p-wave interactions and losses,\nwhich are important for reactive molecules such as KRb. Moreover, we consider\nother sources of spectral broadening: interaction-induced quasiparticle\nlifetimes and the different polarizabilities of the different rotational states\nused for the spectroscopy. Although our main focus is molecules, some of the\ncalculations are also useful for optical lattice atomic clocks. For example,\nunderstanding the p-wave shifts between identical fermions and small dipolar\ninteractions coming from the excited clock state are necessary to reach future\nprecision goals. Finally, we consider the spectra in a deep 3D lattice and show\nhow they give a great deal of information about static correlation functions,\nincluding \\textit{all} the moments of the density correlations between nearby\nsites. The range of correlations measurable depends on spectroscopic resolution\nand the dipole moment.",
        "positive": "Analytical expression for a post-quench time evolution of the one-body\n  density matrix of one-dimensional hard-core bosons: We apply the logic of the quench action to give an exact analytical\nexpression for the time evolution of the one-body density matrix after an\ninteraction quench in the Lieb-Liniger model from the ground state of the free\ntheory (BEC state) to the infinitely repulsive regime. In this limit there\nexists a mapping between the bosonic wavefuntions and the free fermionic ones\nbut this does not help the computation of the one-body density matrix which is\nsensitive to particle statistics. The final expression, given in terms of the\ndifference of the square root of two Fredholm determinants, can be numerically\nevaluated and is valid in the thermodynamic limit and for all times after the\nquench."
    },
    {
        "anchor": "Creation and characterization of vortex clusters in atomic Bose-Einstein\n  condensates: We show that a moving obstacle, in the form of an elongated paddle, can\ncreate vortices that are dispersed, or induce clusters of like-signed vortices\nin 2D Bose-Einstein condensates. We propose new statistical measures of\nclustering based on Ripley's K-function which are suitable to the small size\nand small number of vortices in atomic condensates, which lack the huge number\nof length scales excited in larger classical and quantum turbulent fluid\nsystems. The evolution and decay of clustering is analyzed using these\nmeasures. Experimentally it should prove possible to create such an obstacle by\na laser beam and a moving optical mask. The theoretical techniques we present\nare accessible to experimentalists and extend the current methods available to\ninduce 2D quantum turbulence in Bose-Einstein condensates.",
        "positive": "Parametric instabilities of interacting bosons in periodically-driven 1D\n  optical lattices: Periodically-driven quantum systems are currently explored in view of\nrealizing novel many-body phases of matter. This approach is particularly\npromising in gases of ultracold atoms, where sophisticated shaking protocols\ncan be realized and inter-particle interactions are well controlled. The\ncombination of interactions and time-periodic driving, however, often leads to\nuncontrollable heating and instabilities, potentially preventing practical\napplications of Floquet-engineering in large many-body quantum systems. In this\nwork, we experimentally identify the existence of parametric instabilities in\nweakly-interacting Bose-Einstein condensates in strongly-driven optical\nlattices through momentum-resolved measurements. Parametric instabilities can\ntrigger the destruction of weakly-interacting Bose-Einstein condensates through\nthe rapid growth of collective excitations, in particular in systems with weak\nharmonic confinement transverse to the lattice axis."
    },
    {
        "anchor": "Recurrence time in the quantum dynamics of the 1D Bose gas: Recurrence time is evaluated for some initial quantum states in the\none-dimensional Bose gas with repulsive short-range interactions. In the\nrelatively strong and weak coupling cases some different types of initial\nstates show almost complete recurrence and the estimates of recurrence time are\nproportional to some powers of the system size at least in some range of the\nsystem size. They are much longer than in the case of free particles such as\n100 times. In the free-bosonic and free-fermionic regimes we evaluate the\nrecurrence time rigorously, which is proportional to the square of the system\nsize. The estimate of recurrence time is given by the order of ten milliseconds\nin the corresponding experimental systems of cold atoms trapped in one\ndimension of ten micrometers in length. It is much shorter than the estimate in\na generic quantum many-body system, which may be as long as the age of the\nuniverse.",
        "positive": "Topological superradiance in a degenerate Fermi gas: We predict the existence of a topological superradiant state in a\ntwo-component degenerate Fermi gas in a cavity. The superradiant light\ngeneration in the transversely driven cavity mode induces a cavity-assisted\nspin-orbit coupling in the system and opens a bulk gap at half-filling. This\nmechanism can simultaneously drive a topological phase transition in the\nsystem, yielding a topological superradiant phase. We map out the steady-state\nphase diagram of the system in the presence of an effective Zeeman field, and\nidentify a critical quadracritical point beyond which the topological and the\nconventional superraidiant phase boundaries separate. We also propose to detect\nthe topological phase transitions based on the unique signatures in the\nmomentum-space density distribution."
    },
    {
        "anchor": "Localization of cold atoms in state-dependent optical lattices via a\n  Rabi pulse: We propose a novel realization of Anderson localization in non-equilibrium\nstates of ultracold atoms trapped in state-dependent optical lattices. The\ndisorder potential leading to localization is generated with a Rabi pulse\ntransfering a fraction of the atoms into a different internal state for which\ntunneling between lattice sites is suppressed. Atoms with zero tunneling create\na quantum superposition of different random potentials, localizing the mobile\natoms. We investigate the dynamics of the mobile atoms after the Rabi pulse for\nnon-interacting and weakly interacting bosons, and we show that the evolved\nwavefunction attains a quasi-stationary profile with exponentially decaying\ntails, characteristic of Anderson localization. The localization length is seen\nto increase with increasing disorder and interaction strength, oppositely to\nwhat is expected for equilibrium localization.",
        "positive": "Slow Thermalization of Exact Quantum Many-Body Scar States Under\n  Perturbations: Quantum many-body scar states are exceptional finite energy density\neigenstates in an otherwise thermalizing system that do not satisfy the\neigenstate thermalization hypothesis. We investigate the fate of exact\nmany-body scar states under perturbations. At small system sizes, deformed scar\nstates described by perturbation theory survive. However, we argue for their\neventual thermalization in the thermodynamic limit from the finite-size scaling\nof the off-diagonal matrix elements. Nevertheless, we show numerically and\nanalytically that the nonthermal properties of the scars survive for a\nparametrically long time in quench experiments. We present a rigorous argument\nthat lower-bounds the thermalization time for any scar state as $t^{*} \\sim\nO(\\lambda^{-1/(1+d)})$, where $d$ is the spatial dimension of the system and\n$\\lambda$ is the perturbation strength."
    },
    {
        "anchor": "Particle-hole bound states of dipolar molecules in optical lattice: We investigate the particle-hole pair excitations of dipolar molecules in\noptical lattice, which can be described with an extended Bose-Hubbard model.\nFor strong enough dipole-dipole interaction, the particle-hole pair excitations\ncan form bound states in one and two dimensions. With decreasing dipole-dipole\ninteraction, the energies of the bound states increase and merge into the\nparticle-hole continuous spectrum gradually. The existence regions, the energy\nspectra and the wave functions of the bound states are carefully studied and\nthe symmetries of the bound states are analyzed with group theory. For a given\ndipole-dipole interaction, the number of bound states varies in momentum space\nand a number distribution of the bound states is illustrated. We also discuss\nhow to observe these bound states in future experiments.",
        "positive": "Finite-range effects in ultradilute quantum drops: In the first experimental realization of dilute Bose-Bose liquid drops using\ntwo hyperfine states of $^{39}$K some discrepancies between theory and\nexperiment were observed. The standard analysis of the data using the\nLee-Huang-Yang beyond mean-field theory predicted critical numbers which were\nsignificantly off the experimental measurements. Also, the radial size of the\ndrops in the experiment proved to be larger than expected from this theory.\nUsing a new functional, which is based on quantum Monte Carlo results of the\nbulk phase incorporating finite-range effects, we can explain the origin of the\ndiscrepancies in the critical number. This result proves the necessity of\nincluding finite-range corrections to deal with the observed properties in this\nsetup. The controversy on the radial size is reasoned in terms of the departure\nfrom the optimal concentration ratio between the two species of the mixture."
    },
    {
        "anchor": "Above-Barrier Reflection of Cold Atoms by Resonant Laser Light within\n  the Gross-Pitaevskii Approximation: Above-barrier reflection of cold alkali atoms by resonant laser light was\nconsidered analytically within the Gross-Pitaevskii approximation. Correction\nfor the reflection coefficient because of a weak nonlinearity of the stationary\nSchroedinger equation has been derived using multiscale analysis as a form of\nperturbation theory. The nonlinearity adds spatial harmonics to linear incident\nand reflecting waves. It was shown that the role of nonlinearity increases when\nthe kinetic energy of an atom is nearly to the height of the potential barrier.\nResults are compared to the known numerical derivations for wave functions of\nthe Gross-Pitaevskii equation with the step potential.",
        "positive": "High-order symbolic strong-coupling expansion for the Bose-Hubbard model: Combining the process-chain method with a symbolized evaluation we work out\nin detail a high-order symbolic strong-coupling expansion (HSSCE) for\ndetermining the quantum phase boundaries between the Mott insulator and the\nsuperfluid phase of the Bose-Hubbard model for different fillings in hypercubic\nlattices of different dimensions. With a subsequent Pad{\\'e} approximation we\nachieve for the quantum phase boundaries a high accuracy, which is comparable\nto high-precision quantum Monte-Carlo simulations, and show that all the Mott\nlobes can be rescaled to a single one. As a further cross-check, we find that\nthe HSSCE results coincide with a hopping expansion of the quantum phase\nboundaries, which follow from the effective potential Landau theory (EPLT)."
    },
    {
        "anchor": "Nonlinear localized modes in dipolar Bose-Einstein condensates in\n  optical lattices: The modulational instability and discrete matter wave solitons in dipolar\nBEC, loaded into a deep optical lattice, are investigated analytically and\nnumerically. The process of modulational instability of nonlinear plane matter\nwaves in a dipolar nonlinear lattice is studied and the regions of instability\nare established. The existence and stability of bulk discrete solitons are\nanalyzed analytically and confirmed by numerical simulations. In a marked\ncontrast with the usual DNLS behavior (no dipolar interactions), we found a\nregion where the two fundamental modes are simultaneously unstable allowing\nenhanced mobility across the lattice for large norm values. To study the\nexistence and properties of surface discrete solitons, an analysis of the dimer\nconfiguration is performed. The properties of symmetric and antisymmetric modes\nincluding the stability diagrams and bifurcations are investigated in closed\nform. For the case of a bulk medium, properties of fundamental on-site and\ninter-site localized modes are analyzed. On-site and inter-site surface\nlocalized modes are studied finding that they do not exist when nonlocal\ninteractions predominate with respect to local ones.",
        "positive": "Observation of the Leggett-Rice effect in a unitary Fermi gas: We observe that the diffusive spin current in a strongly interacting\ndegenerate Fermi gas of $^{40}$K precesses about the local magnetization. As\npredicted by Leggett and Rice, precession is observed both in the Ramsey phase\nof a spin-echo sequence, and in the nonlinearity of the magnetization decay. At\nunitarity, we measure a Leggett-Rice parameter $\\gamma = 1.08(9)$ and a bare\ntransverse spin diffusivity $D_0^\\perp = 2.3(4)\\,\\hbar/m$ for a normal-state\ngas initialized with full polarization and at one fifth of the Fermi\ntemperature, where $m$ is the atomic mass. One might expect $\\gamma = 0$ at\nunitarity, where two-body scattering is purely dissipative. We observe $\\gamma\n\\rightarrow 0$ as temperature is increased towards the Fermi temperature,\nconsistent with calculations that show the degenerate Fermi sea restores a\nnon-zero $\\gamma$. Tuning the scattering length $a$, we find that a sign change\nin $\\gamma$ occurs in the range $0 < (k_F a)^{-1} \\lesssim 1.3$, where $k_F$ is\nthe Fermi momentum. We discuss how $\\gamma$ reveals the effective interaction\nstrength of the gas, such that the sign change in $\\gamma$ indicates a\nswitching of branch, between a repulsive and an attractive Fermi gas."
    },
    {
        "anchor": "Quantum dynamics of a binary mixture of BECs in a double well potential:\n  an Holstein-Primakoff approach: We study the quantum dynamics of a binary mixture of Bose-Einstein\ncondensates (BEC) in a double-well potential starting from a two-mode\nBose-Hubbard Hamiltonian. Focussing on the regime where the number of atoms is\nvery large, a mapping onto a SU(2) spin problem together with a\nHolstein-Primakoff transformation is performed. The quantum evolution of the\nnumber difference of bosons between the two wells is investigated for different\ninitial conditions, which range from the case of a small imbalance between the\ntwo wells to a coherent spin state. The results show an instability towards a\nphase-separation above a critical positive value of the interspecies\ninteraction while the system evolves towards a coherent tunneling regime for\nnegative interspecies interactions. A comparison with a semiclassical approach\nis discussed together with some implications on the experimental realization of\nphase separation with cold atoms.",
        "positive": "The Operator Product Expansion Beyond Leading Order for Two-Component\n  Fermions: We consider a homogeneous, balanced gas of strongly interacting fermions in\ntwo spin states interacting through a large scattering length. Finite range\ncorrections are needed for a quantitative description of data which experiments\nand numerical simulations have provided. We use a perturbative field\ntheoretical framework and a tool called the Operator Product Expansion (OPE),\nwhich together allow for the expression of finite range corrections to the\nuniversal relations and momentum distribution. Using the OPE, we derive the\n$1/k^6$ part of the momentum tail, which is related to the sum of the\nderivative of the energy with respect to the finite range and the averaged\nkinetic energy of opposite spin pairs. By comparing the $1/k^4$ term and the\n$1/k^6$ correction in the momentum distribution to provided Quantum Monte Carlo\n(QMC) data, we show that including the $1/k^6$ part offers marked improvements.\nOur field theoretical approach allows for a clear understanding of the role of\nthe scattering length and finite effective range in the universal relations and\nthe momentum distribution."
    },
    {
        "anchor": "Domain wall suppression in trapped mixtures of Bose-Einstein condensates: The ground state energy of a binary mixture of Bose-Einstein condensates can\nbe estimated for large atomic samples by making use of suitably regularized\nThomas-Fermi density profiles. By exploiting a variational method on the trial\ndensities the energy can be computed by explicitly taking into account the\nnormalization condition. This yields analytical results and provides the basis\nfor further improvement of the approximation. As a case study, we consider a\nbinary mixture of $^{87}$Rb atoms in two different hyperfine states in a double\nwell potential and discuss the energy crossing between density profiles with\ndifferent numbers of domain walls, as the number of particles and the\ninter-species interaction vary.",
        "positive": "Nonequilibrium dynamics of spin-boson models from phase space methods: An accurate description of the nonequilibrium dynamics of systems with\ncoupled spin and bosonic degrees of freedom remains theoretically challenging,\nespecially for large system sizes and in higher than one dimension. Phase space\nmethods such as the Truncated Wigner Approximation (TWA) have the advantage of\nbeing easily scalable and applicable to arbitrary dimensions. In this work we\nadapt the TWA to generic spin-boson models by making use of recently developed\nalgorithms for discrete phase spaces [Schachenmayer, PRX 5, 011022 (2015)].\nFurthermore we go beyond the standard TWA approximation by applying a scheme\nbased on the Bogoliubov-Born-Green-Kirkwood-Yvon (BBGKY) hierarchy of equations\n[Pucci, PRB 93, 174302 (2016)] to our coupled spin-boson model. This allows in\nprinciple to study how systematically adding higher order corrections improves\nthe convergence of the method. To test various levels of approximation we study\nan exactly solvable spin-boson model which is particularly relevant for\ntrapped-ion arrays. Using TWA and its BBGKY extension we accurately reproduce\nthe time evolution of a number of one- and two-point correlation functions in\nseveral dimensions and for arbitrary number of bosonic modes."
    },
    {
        "anchor": "Decay of phase-imprinted dark soliton in Bose-Einstein condensate at\n  non-zero temperature: We study relaxation dynamics of dark soliton, created by a phase-imprinted\nmethod, in a two-dimensional trapped Bose-Einstein condensate at non-zero\ntemperatures by using the projected Gross-Pitaevskii equation. At absolute zero\ntemperature, a dark soliton is known to decay with a snake instability. At\nnon-zero temperature, as we expected, we find that this snake instability\ncannot be clearly seen as in the absolute zero temperature case because of the\npresence of thermal fluctuations. However, we find that the decay rate, the\nhalf width of the overlap integral with respect to the phase-imprinted initial\nstate, shows a power low decay as a function of the energy and finally remains\na non-zero value.",
        "positive": "Size and dynamics of vortex dipoles in dilute Bose-Einstein condensates: Recently, Freilich et al. [Science 329, 1182 (2010)] experimentally\ndiscovered stationary states of vortex dipoles, pairs of vortices of opposite\ncirculation, in dilute Bose-Einstein condensates. To explain their\nobservations, we perform simulations based on the Gross-Pitaevskii equation and\nobtain excellent quantitative agreement on the size of the stationary dipole.\nWe also investigate how their imaging method, in which atoms are repeatedly\nextracted from a single condensate, affects the vortex dynamics. We find that\nit mainly induces isotropic size oscillations of the condensate without\notherwise disturbing the vortex trajectories. Thus, the imaging technique\nappears to be a promising tool for studying real-time superfluid dynamics."
    },
    {
        "anchor": "Critical velocity of superfluid flow through single barrier and periodic\n  potentials: We investigate the problem of an ultracold atomic gas in the superfluid phase\nflowing in the presence of a potential barrier or a periodic potential. We use\na hydrodynamic scheme in the local density approximation (LDA) to obtain an\nanalytic expression for the critical current as a function of the barrier\nheight or the lattice intensity, which applies to both Bose and Fermi\nsuperfluids. In this scheme, the stationary flow becomes energetically unstable\nwhen the local superfluid velocity is equal to the local sound velocity at the\npoint where the external potential is maximum. We compare this prediction with\nthe results of the numerical solutions of the Gross-Pitaevskii and\nBogoliubov-de Gennes equations. We discuss the role of long wavelength\nexcitations in determining the critical velocity. Our results allow one to\nidentify the different regimes of superfluid flow, namely, the LDA hydrodynamic\nregime, the regime of quantum effects beyond LDA for weak barriers and the\nregime of tunneling between weakly coupled superfluids for strong barriers. We\nfinally discuss the relevance of these results in the context of current\nexperiments with ultracold gases.",
        "positive": "Observation of photon droplets and their dynamics: We present experimental evidence of photon droplets in an attractive\n(focusing) nonlocal nonlinear medium. Photon droplets are self-bound,\nfinite-sized states of light that are robust to size and shape perturbations\ndue to a balance of competing attractive and repulsive forces. It has recently\nbeen shown theoretically, via a multipole expansion of the nonlocal\nnonlinearity, that the self-bound state arises due to competition between the\ns-wave and d-wave nonlinear terms, together with diffraction. The theoretical\nphoton droplet framework encompasses both a soliton-like stationary ground\nstate and the non-soliton-like dynamics that ensue when the system is displaced\nfrom equilibrium, i.e. driven into an excited state. We present numerics and\nexperiments supporting the existence of these photon droplet states and\nmeasurements of the dynamical evolution of the photon droplet orbital angular\nmomentum."
    },
    {
        "anchor": "Two-dimensional crystals of Rydberg excitations in a resonantly driven\n  lattice gas: The competition between resonant optical excitation of Rydberg states of\natoms and their strong, long-range van der Waals interaction results in spatial\nordering of Rydberg excitations in a two-dimensional lattice gas, as observed\nin a recent experiment of Schau{\\ss} et al. [Nature 491, 87 (2012)]. Here we\nuse semiclassical Monte Carlo simulations to obtain stationary states for\nhundreds of atoms in finite-size lattices. We show the formation of regular\nspatial structures of Rydberg excitations in a system of increasing size, and\nfind highly sub-Poissonian distribution of the number of Rydberg excitations\ncharacterized by a large negative value of the Mandel Q parameter which is\nnearly independent of the system size.",
        "positive": "Phase diagrams and multistep condensations of spin-1 bosonic gases in\n  optical lattices: Motivated by recent experimental processes, we systemically investigate\nstrongly correlated spin-1 ultracold bosons trapped in a three-dimensional\noptical lattice in the presence of an external magnetic field. Based on a\nrecently developed bosonic dynamical mean-field theory (BDMFT), we map out\ncomplete phase diagrams of the system for both antiferromagnetic and\nferromagnetic interactions, where various phases are found as a result of the\ninterplay of spin-dependent interaction and quadratic Zeeman energy. For\nantiferromagnetic interactions, the system demonstrates competing magnetic\norders, including nematic, spin-singlet and ferromagnetic insulating phase,\ndepending on longitudinal magnetization, whereas, for ferromagnetic case, a\nferromagnetic-to-nematic-insulating phase transition is observed for small\nquadratic Zeeman energy, and the insulating phase demonstrates the nematic\norder for large Zeeman energy. Interestingly, at low magnetic field and finite\ntemperature, we find an abnormal multi-step condensation of the strongly\ncorrelated superfluid, i.e. the critical condensing temperature of the $m_F=-1$\ncomponent with antiferromagnetic interactions demonstrates an increase with\nlongitudinal magnetization, while, for ferromagnetic case, the Zeeman component\n$m_F = 0$ demonstrates a local minimum for the critical condensing temperature,\nin contrast to weakly interacting cases."
    },
    {
        "anchor": "Momentum density and phase maps of a two-dimensional trapped\n  Bose-Einstein condensate excited by a red laser: We investigate numerically the momentum density and phase maps $-$in\ncoordinate and momentum space$-$ of a two dimensional Bose-Einstein condensate\n(BEC) excited by a moving red-detuned laser potential. The BEC is confined in a\nharmonic trap cutoff by hard walls. The system and excitation scheme are as in\nour previous work (Roger R. Sakhel {\\it et al.} to appear in J. Low Temp. Phys.\n(2013)); but with twice the number of particles and interaction strength. We\nsolve the time-dependent Gross-Pitaevskii equation numerically using the\nsplit-step Crank-Nicolson method in real time. It is demonstrated that the\nred-detuned laser has a phase-imprinting effect like a repulsive potential\nbarrier. Signatures of excitations are extracted from the dynamics of the\nmomentum densities and phase maps. Further, a new phase is defined in momentum\nspace, which is used to reveal excitations. Therefore, phase maps in coordinate\nspace and momentum space are compared for different BEC evolution times. We\nargue, that this momentum-space phase is especially important with regard to\nthe studies of BEC momentum distributions. In addition, this work presents a\nnew method of BEC interferometry and should contribute to the ongoing research\nin that field. One of our significant findings is the presence of substantial\ndifferences betwteen the momentum density obtained by a Fourier transform (FT)\nof the spatial density distribution and the one obtained from the modulus of\nthe wavefunction in momentum space; the latter is obtained by a FT of the\nspatial wavefunction.",
        "positive": "From Rotating Atomic Rings to Quantum Hall States: Considerable efforts are currently devoted to the preparation of ultracold\nneutral atoms in the emblematic strongly correlated quantum Hall regime. The\nroutes followed so far essentially rely on thermodynamics, i.e. imposing the\nproper Hamiltonian and cooling the system towards its ground state. In rapidly\nrotating 2D harmonic traps the role of the transverse magnetic field is played\nby the angular velocity. For particle numbers significantly larger than unity,\nthe required angular momentum is very large and it can be obtained only for\nspinning frequencies extremely near to the deconfinement limit; consequently,\nthe required control on experimental parameters turns out to be far too\nstringent. Here we propose to follow instead a dynamic path starting from the\ngas confined in a rotating ring. The large moment of inertia of the fluid\nfacilitates the access to states with a large angular momentum, corresponding\nto a giant vortex. The initial ring-shaped trapping potential is then\nadiabatically transformed into a harmonic confinement, which brings the\ninteracting atomic gas in the desired quantum Hall regime. We provide clear\nnumerical evidence that for a relatively broad range of initial angular\nfrequencies, the giant vortex state is adiabatically connected to the bosonic\n$\\nu=1/2$ Laughlin state, and we discuss the scaling to many particles."
    },
    {
        "anchor": "Dipolar Fermi gases in anisotropic traps: The quest for quantum degenerate Fermi gases interacting through the\nanisotropic and long-range dipole-dipole interaction is an exciting and fast\ndeveloping branch within the cold-atoms research program. Recent experimental\nprogress in trapping, cooling, and controlling polar molecules with large\nelectric dipole moments has, therefore, motivated much theoretical effort. In a\nrecent letter, we have briefly discussed the application of a variational\ntime-dependent Hartree-Fock approach to study theoretically both the static and\nthe dynamic properties of such a system in a cylinder-symmetric harmonic trap.\nWe focused on the hydrodynamic regime, where collisions assure the equilibrium\nlocally. Here, we present a detailed theory, extended to encompass the general\ncase of a harmonic trap geometry without any symmetry. After deriving the\nequations of motion for the gas, we explore their static solutions to\ninvestigate key properties like the aspect ratios in both real and momentum\nspace as well as the stability diagram. We find that, despite the lack of\nsymmetry of the trap, the momentum distribution remains cylinder symmetric. The\nequations of motion are then used to study the low-lying hydrodynamic\nexcitations, where, apart from the quadrupole and monopole modes, also the\nradial quadrupole mode is investigated. Furthermore, we study the\ntime-of-flight dynamics as it represents an important diagnostic tool for\nquantum gases. We find that the real-space aspect ratios are inverted during\nthe expansion, while the one in momentum space becomes asymptotically unity. In\naddition, anisotropic features of the dipole-dipole interaction are discussed\nin detail. These results could be particularly useful for future investigations\nof strongly dipolar heteronuclear polar molecules deep in the quantum\ndegenerate regime.",
        "positive": "Static and dynamic properties of shell-shaped condensates: Static, dynamic, and topological properties of hollow systems differ from\nthose that are fully filled as a result of the presence of a boundary\nassociated with an inner surface. Hollow Bose-Einstein condensates (BECs)\nnaturally occur in various ultracold atomic systems and possibly within neutron\nstars but have hitherto not been experimentally realized in isolation on Earth\nbecause of gravitational sag. Motivated by the expected first realization of\nfully closed BEC shells in the microgravity conditions of the Cold Atomic\nLaboratory aboard the International Space Station, we present a comprehensive\nstudy of spherically symmetric hollow BECs as well as the hollowing transition\nfrom a filled sphere BEC into a thin shell through central density depletion.\nWe employ complementary analytic and numerical techniques in order to study\nequilibrium density profiles and the collective mode structures of condensate\nshells hosted by a range of trapping potentials. We identify concrete and\nrobust signatures of the evolution from filled to hollow structures and the\neffects of the emergence of an inner boundary, inclusive of a dip in\nbreathing-mode-type collective mode frequencies and a restructuring of surface\nmode structure across the transition. By extending our analysis to a\ntwo-dimensional transition of a disk to a ring, we show that the collective\nmode signatures are an essential feature of hollowing, independent of the\nspecific geometry. Finally, we relate our work to past and ongoing experimental\nefforts and consider the influence of gravity on thin condensate shells. We\nidentify the conditions under which gravitational sag is highly destructive and\nstudy the mode-mixing effects of microgravity on the collective modes of these\nshells."
    },
    {
        "anchor": "Driven dissipative preparation of few-body Laughlin states of Rydberg\n  polaritons in twisted cavities: We present a driven dissipative protocol for creating an optical analog of\nthe Laughlin state in a system of Rydberg polaritons in a twisted optical\ncavity. We envision resonantly driving the system into a 4-polariton state by\ninjecting photons in carefully selected modes. The dissipative nature of the\npolariton-polariton interactions leads to a decay into a two-polariton analog\nof the Laughlin state. Generalizations of this technique could be used to\nexplore fractional statistics and anyon based quantum information processing.\nWe also model recent experiments that attempt to coherently drive into this\nsame state.",
        "positive": "Excitation of atoms in an optical lattice driven by polychromatic\n  amplitude modulation: We investigate the mutiphoton process between different Bloch states in an\namplitude modulated optical lattice. In the experiment, we perform the\nmodulation with more than one frequency components, which includes a high\ndegree of freedom and provides a flexible way to coherently control quantum\nstates. Based on the study of single frequency modulation, we investigate the\ncollaborative effect of different frequency components in two aspects. Through\ndouble frequency modulations, the spectrums of excitation rates for different\nlattice depths are measured. Moreover, interference between two separated\nexcitation paths is shown, emphasizing the influence of modulation phases when\ntwo modulation frequencies are commensurate. Finally, we demonstrate the\napplication of the double frequency modulation to design a\nlarge-momentum-transfer beam splitter. The beam splitter is easy in practice\nand would not introduce phase shift between two arms."
    },
    {
        "anchor": "Strong parity effect of particle number in the interference fringes of\n  Bose-Einstein condensates released from a double-well potential: We study the parity effect of the particle number in the interference fringes\nof a Bose-Einstein condensate released from a double-well potential. For a\ncoherently splitting condensate in the double-well potential, with a decoupled\ntwo-mode Bose-Hubbard model, there is well-known phase diffusion because of\ninteratomic interactions. After a specific holding time of the double-well\npotential, the phase diffusion will make the interference patterns in the\ndensity distribution depend strongly on the parity of the total particle number\nby further overlapping two condensates. This parity effect originates from the\nquantized relative phase about the total particle number. The experimental\nscheme to observe this \"even-odd\" effect of the particle number is discussed.",
        "positive": "Spin-orbit coupled ultracold gases in optical lattices: High-band\n  physics and insufficiency of tight-binding models: We study the interplay effect of spin-orbit coupling(SOC) and optical lattice\nto the single-particle physics and superfluid-insulator transition in ultracold\nFermi gases. We consider the type of SOC that has been realized in cold atoms\nexperiments via two-photon Raman processes. Our analyses are based on the\nknowledge of full single-particle spectrum in lattices, without relying on any\ntightbinding approximation.We evaluate existing tight-binding models and point\nout their limitations in predicting the correct single-particle physics due to\nthe missed high-band contributions. Moreover, we show that the Raman field\n(creating SOC) can induce band-gap closing in a two-dimensional optical\nlattice, leading to the intriguing phenomenon of superfluidity-reentrance for\ninteracting fermions at integer filling. We present the superfluid-insulator\nphase diagram in a wide parameter regime of chemical potentials and Raman\nfields. All these results are far beyond any tight-binding model can predict,\nand can be directly probed in current cold atoms experiments."
    },
    {
        "anchor": "Low-energy prethermal phase and crossover to thermalization in nonlinear\n  kicked rotors: In the presence of interactions, periodically-driven quantum systems\ngenerically thermalize to an infinite-temperature state. Recently, however, it\nwas shown that in random kicked rotors with local interactions, this long-time\nequilibrium could be strongly delayed by operating in a regime of weakly\nfluctuating random phases, leading to the emergence of a metastable thermal\nensemble. Here we show that when the random kinetic energy is smaller than the\ninteraction energy, this system in fact exhibits a much richer dynamical phase\ndiagram, which includes a low-energy pre-thermal phase characterized by a\nlight-cone spreading of correlations in momentum space. We develop a\nhydrodynamic theory of this phase and find a very good agreement with exact\nnumerical simulations. We finally explore the full dynamical phase diagram of\nthe system and find that the transition toward full thermalization is\ncharacterized by relatively sharp crossovers.",
        "positive": "Engineering quantum magnetism in one-dimensional trapped Fermi gases\n  with p-wave interactions: The highly controllable ultracold atoms in a one-dimensional (1D) trap\nprovide a new platform for the ultimate simulation of quantum magnetism. In\nthis regard, the Neel-antiferromagnetism and the itinerant ferromagnetism are\nof central importance and great interest. Here we show that these magnetic\norders can be achieved in the strongly interacting spin-1/2 trapped Fermi gases\nwith additional p-wave interactions. In this strong coupling limit, the 1D\ntrapped Fermi gas exhibit an effective Heisenberg spin XXZ chain in the\nanisotropic p-wave scattering channels. For a particular p-wave attraction or\nrepulsion within the same species of fermionic atoms, the system displays\nferromagnetic domains with full spin segregation or the anti-ferromagnetic spin\nconfiguration in the ground state. Such engineered magnetisms are likely to be\nprobed in a quasi-1D trapped Fermi gas of $^{40}$ K atoms with very close\ns-wave and p-wave Feshbach resonances."
    },
    {
        "anchor": "Superfluid phases of spin-1 bosons in cubic optical lattice: We analyze theoretically the emergence of different superfluid phases of\nspin-1 bosons in a three-dimensional cubic optical lattice by generalizing the\nrecently developed Ginzburg-Landau theory for the Bose-Hubbard model to a\nspinor Bose gas. In particular at zero temperature, our theory distinguishes\nwithin its validity range between various superfluid phases for an\nanti-ferromagnetic interaction with an external magnetic field. In addition, we\ndetermine that the superfluid-Mott insulator phase transition is of second\norder and that the transitions between the respective superfluid phases with\nanti-ferromagnetic interaction can be both of first and second order.",
        "positive": "Probing strongly interacting atomic gases with energetic atoms: We investigate properties of an energetic atom propagating through strongly\ninteracting atomic gases. The operator product expansion is used to\nsystematically compute a quasiparticle energy and its scattering rate both in a\nspin-1/2 Fermi gas and in a spinless Bose gas. Reasonable agreement with recent\nquantum Monte Carlo simulations even at a relatively small momentum k/kF>1.5\nindicates that our large-momentum expansions are valid in a wide range of\nmomentum. We also study a differential scattering rate when a probe atom is\nshot into atomic gases. Because the number density and current density of the\ntarget atomic gas contribute to the forward scattering only, its contact\ndensity (measure of short-range pair correlation) gives the leading\ncontribution to the backward scattering. Therefore, such an experiment can be\nused to measure the contact density and thus provides a new local probe of\nstrongly interacting atomic gases."
    },
    {
        "anchor": "Antiferromagnetic spinor condensates in a two-dimensional optical\n  lattice: We experimentally demonstrate that spin dynamics and the phase diagram of\nspinor condensates can be conveniently tuned by a two-dimensional optical\nlattice. Spin population oscillations and a lattice-tuned separatrix in phase\nspace are observed in every lattice where a substantial superfluid fraction\nexists. In a sufficiently deep lattice, we observe a phase transition from a\nlongitudinal polar phase to a broken-axisymmetry phase in steady states of\nlattice-confined spinor condensates. The steady states are found to depend\nsigmoidally on the lattice depth and exponentially on the magnetic field. We\nalso introduce a phenomenological model that semi-quantitatively describes our\ndata without adjustable parameters.",
        "positive": "Exact Two-Body Solutions and Quantum Defect Theory of Polar Molecular\n  Gases with Van der Waals Potentials: In a recent experiment [Matsuda et al, Science 370, 1324 (2020)], a quasi\ntwo-dimensional (2D), long-lived and strongly interacting diatomic polar\nmolecular gas was successfully prepared via controllable electric field\ntechnique. Surprisingly, the effective repulsive and attractive Van der Waals\ninteractions of two molecules would emerge when scanning the strength of the\nelectric fields. Those results were also generalized to the three-dimensional\n(3D) case in a later experiment [J. Li et al, Nature Physics 17, 1144 (2021)].\nMotivated by these experiments, in this paper we provide the two-body exact\nsolutions for the 2D and 3D Schr\\\"{o}dinger equation with isotropic Van der\nWaals potentials ($\\pm1/r^{6}$). Furthermore, base on these exact solutions, we\nbuild the analytical quantum defect theory (QDT) for quasi-2D and 3D\ngeometries, and then apply QDT to study the scattering properties and bound\nstates of two ultracold polar molecules confined in quasi-2D and 3D geometries.\nInterestingly, we find that for the attractive (repulsive) Van der Waals\npotential cases, the two-body short range potential can be approximated by an\nsquare barrier with infinity height (square potential with finite depth) which\nyields the wide (narrow) and dense (dilute) resonances of the quantum defect\nparameter. For the quasi-2D attractive case, the scattering resonances of\ndifferent partial waves can orderly happen which is featured by the phase jumps\nwhen varying the scattering energy. The analytical expansions in the low energy\nlimit shows a consistent agreement to the numerical results."
    },
    {
        "anchor": "Emergence of coherence in a uniform quasi-two-dimensional Bose gas: Phase transitions are ubiquitous in our three-dimensional world. By contrast\nmost conventional transitions do not occur in infinite uniform two-dimensional\nsystems because of the increased role of thermal fluctuations. Here we explore\nthe dimensional crossover of Bose-Einstein condensation (BEC) for a weakly\ninteracting atomic gas confined in a novel quasi-two-dimensional geometry, with\na flat in-plane trap bottom. We detect the onset of an extended phase\ncoherence, using velocity distribution measurements and matter-wave\ninterferometry. We relate this coherence to the transverse condensation\nphenomenon, in which a significant fraction of atoms accumulate in the ground\nstate of the motion perpendicular to the atom plane. We also investigate the\ndynamical aspects of the transition through the detection of topological\ndefects that are nucleated in a quench cooling of the gas, and we compare our\nresults to the predictions of the Kibble-Zurek theory for the conventional BEC\nsecond-order phase transition.",
        "positive": "Many-body correlations in one-dimensional optical lattices with\n  alkaline-earth(-like) atoms: We explore the rich nature of correlations in the ground state of ultracold\natoms trapped in state-dependent optical lattices. In particular, we consider\ninteracting fermionic ytterbium or strontium atoms, realizing a two-orbital\nHubbard model with two spin components. We analyze the model in one-dimensional\nsetting with the experimentally relevant hierarchy of tunneling and interaction\namplitudes by means of exact diagonalization and matrix product states\napproaches, and study the correlation functions in density, spin, and orbital\nsectors as functions of variable densities of atoms in the ground and\nmetastable excited states. We show that in certain ranges of densities these\natomic systems demonstrate strong density-wave, ferro- and antiferromagnetic,\nas well as antiferroorbital correlations."
    },
    {
        "anchor": "Rotonlike instability and pattern formation in spinor Bose-Einstein\n  condensates: We show that metastable phases of an antiferromagnetic spin-1 condensate in a\nsimple model with pure contact interactions can exhibit a rotonlike minimum in\nthe excitation spectrum. The introduction of magnetic field gives rise to the\ninstability of roton modes, which can lead to spontaneous emergence of regular\nperiodic, polygonal, polyhedral or crystalline patterns, as shown in numerical\nsimulations within the truncated Wigner approximation. An explanation of the\noccurrence of rotonlike instability is given based on the energy and spin\nconservation laws.",
        "positive": "Mode-locked Bloch oscillations in a ring cavity: We present a new technique for stabilizing and monitoring Bloch oscillations\nof ultracold atoms in an optical lattice under the action of a constant\nexternal force. In the proposed scheme, the atoms also interact with a\nunidirectionally pumped optical ring cavity whose one arm is collinear with the\noptical lattice. For weak collective coupling, Bloch oscillations dominate over\nthe collective atomic recoil lasing instability and develop a synchronized\nregime in which the atoms periodically exchange momentum with the cavity field."
    },
    {
        "anchor": "Metastability and Coherence of Repulsive Polarons in a Strongly\n  Interacting Fermi Mixture: Ultracold Fermi gases with tuneable interactions represent a unique test bed\nto explore the many-body physics of strongly interacting quantum systems. In\nthe past decade, experiments have investigated a wealth of intriguing\nphenomena, and precise measurements of ground-state properties have provided\nexquisite benchmarks for the development of elaborate theoretical descriptions.\nMetastable states in Fermi gases with strong repulsive interactions represent\nan exciting new frontier in the field. The realization of such systems\nconstitutes a major challenge since a strong repulsive interaction in an atomic\nquantum gas implies the existence of a weakly bound molecular state, which\nmakes the system intrinsically unstable against decay. Here, we exploit\nradio-frequency spectroscopy to measure the complete excitation spectrum of\nfermionic 40K impurities resonantly interacting with a Fermi sea of 6Li atoms.\nIn particular, we show that a well-defined quasiparticle exists for strongly\nrepulsive interactions. For this \"repulsive polaron\" we measure its energy and\nits lifetime against decay. We also probe its coherence properties by measuring\nthe quasiparticle residue. The results are well described by a theoretical\napproach that takes into account the finite effective range of the interaction\nin our system. We find that a non-zero range of the order of the interparticle\nspacing results in a substantial lifetime increase. This major benefit for the\nstability of the repulsive branch opens up new perspectives for investigating\nnovel phenomena in metastable, repulsively interacting fermion systems.",
        "positive": "Mesoscopic quantum switching of a Bose-Einstein condensate in an optical\n  lattice governed by the parity of the number of atoms: It is shown that for a $N$-boson system the parity of $N$ can be responsible\nfor a qualitative difference in the system response to variation of a\nparameter. The nonlinear boson model is considered, which describes tunneling\nof boson pairs between two distinct modes $X_{1,2}$ of the same energy and\napplies to a Bose-Einstein condensate in an optical lattice. By varying the\nlattice depth one induces the parity-dependent quantum switching, i.e. $X_1\\to\nX_2$ for even $N$ and $X_1\\to X_1$ for odd $N$, for arbitrarily large $N$. A\nsimple scheme is proposed for observation of the parity effect on the\n\\textit{mesoscopic scale} by using the bounce switching regime, which is\ninsensitive to the initial state preparation (as long as only one of the two\n$X_l$ modes is significantly populated), stable under small perturbations and\nrequires an experimentally accessible coherence time."
    },
    {
        "anchor": "Disorder-Free Localization as a Purely Classical Effect: Disorder-free localization (DFL) is an ergodicity breaking mechanism that has\nbeen shown to occur in lattice gauge theories in the quench dynamics of initial\nstates spanning an extensive number of gauge superselection sectors. Whether\nDFL is intrinsically a quantum interference effect or can arise classically has\nhitherto remained an open question whose resolution is pertinent to further\nunderstanding the far-from-equilibrium dynamics of gauge theories. In this\nwork, we utilize cellular automaton circuits to model the quench dynamics of\nlarge-scale quantum link model (QLM) formulations of $(1+1)$D quantum\nelectrodynamics, showing excellent agreement with the exact quantum case for\nsmall system sizes. Our results demonstrate that DFL persists in the\nthermodynamic limit as a purely classical effect arising from the finite-size\nregularization of the gauge-field operator in the QLM formulation, and that\nquantum interference, though not a necessary condition, may be employed to\nenhance DFL.",
        "positive": "Localization of matter waves in lattice systems with moving disorder: We study the localization phenomena in a one-dimensional lattice system with\na uniformly moving disordered potential. At a low moving velocity, we find a\nsliding localized phase in which the initially localized matter wave\nadiabatically follows the moving potential without diffusion, thus resulting in\nan initial state memory in the many-body dynamics. Such an intriguing localized\nphase distinguishes itself from the standard Anderson localization in two\naspects: it is not robust against interaction, but persists in the presence of\nslowly varying perturbations. Such a sliding localized phase can be understood\nas a consequence of interference between the wavepacket paths under moving\nquasi-periodic potentials with various periods that are incommensurate with the\nlattice constant. The experimental realization and detection were also\ndiscussed.."
    },
    {
        "anchor": "Quantum turbulence in quantum gases: Turbulence is characterized by a large number of degrees of freedom,\ndistributed over several length scales, that result into a disordered state of\na fluid. The field of quantum turbulence deals with the manifestation of\nturbulence in quantum fluids, such as liquid helium and ultracold gases. We\nreview, from both experimental and theoretical points of view, advances in\nquantum turbulence focusing on atomic Bose-Einstein condensates. We also\nexplore the similarities and differences between quantum and classical\nturbulence. Lastly, we present challenges and possible directions for the\nfield. We summarize questions that are being asked in recent works, which need\nto be answered in order to understand fundamental properties of quantum\nturbulence, and we provide some possible ways of investigating them.",
        "positive": "Exploring the many-body localization transition in two dimensions: One fundamental assumption in statistical physics is that generic closed\nquantum many-body systems thermalize under their own dynamics. Recently, the\nemergence of many-body localized systems has questioned this concept,\nchallenging our understanding of the connection between statistical physics and\nquantum mechanics. Here we report on the observation of a many-body\nlocalization transition between thermal and localized phases for bosons in a\ntwo-dimensional disordered optical lattice. With our single site resolved\nmeasurements we track the relaxation dynamics of an initially prepared\nout-of-equilibrium density pattern and find strong evidence for a diverging\nlength scale when approaching the localization transition. Our experiments mark\nthe first demonstration and in-depth characterization of many-body localization\nin a regime not accessible with state-of-the-art simulations on classical\ncomputers."
    },
    {
        "anchor": "Formation of granular structures in trapped Bose-Einstein condensates\n  under oscillatory excitations: We present experimental observations and numerical simulations of\nnonequilibrium spatial structures in a trapped Bose-Einstein condensate subject\nto oscillatory perturbations. In experiment, first, there appear collective\nexcitations, followed by quantum vortices. Increasing the amount of the\ninjected energy leads to the formation of vortex tangles representing quantum\nturbulence. We study what happens after the regime of quantum turbulence, with\nincreasing further the amount of injected energy. In such a strongly\nnonequilibrium Bose-condensed system of trapped atoms, vortices become\ndestroyed and there develops a new kind of spatial structure exhibiting\nessentially heterogeneous spatial density. The structure reminds fog consisting\nof high-density droplets, or grains, surrounded by the regions of low density.\nThe grains are randomly distributed in space, where they move. They live\nsufficiently long time to be treated as a type of metastable objects. Such\nstructures have been observed in nonequilibrium trapped Bose gases of\n$^{87}$Rb, subject to the action of alternating fields. Here we present\nexperimental results and support them by numerical simulations. The granular,\nor fog structure is essentially different from the state of wave turbulence\nthat develops after increasing further the amount of injected energy.",
        "positive": "Nontrivial Haldane phase of an atomic two-component Fermi gas trapped in\n  a 1d optical lattice: We propose how to create a non-trivial Haldane phase in atomic two-component\nFermi-gas loaded on one-dimensional (1-D) optical lattice with trap potential.\nThe Haldane phase is naturally formed on $p$-band Mott core in a wide range of\nthe strong on-site repulsive interaction. The present proposal is composed of\ntwo steps, one of which is theoretical derivation of an effective 1-D S=1\ninteracting-chain model from the original tight-binding Hamiltonian handling\nthe two $p$-orbitals, and the other of which is numerical demonstration\nemploying the density-matrix renormalization-group for the formation of the\nHaldane phase on $p$-band Mott core and its associated features in the original\ntight-binding model with the harmonic trap potential."
    },
    {
        "anchor": "Negative Refraction of Excitations in the Bose-Hubbard Model: Ultracold atoms in optical lattices provide a unique opportunity to study\nBose- Hubbard physics. In this work we show that by considering a spatially\nvarying onsite interaction it is possible to manipulate the motion of\nexcitations above the Mott phase in a Bose-Hubbard system. Specifically, we\nshow that it is possible to \"engineer\" regimes where excitations will\nnegatively refract, facilitating the construction of a flat lens.",
        "positive": "Stability of the Breached Pair State for a Two-species Fermionic System\n  in the Presence of Feshbach Resonance: We investigate the phenomenon of fermionic pairing with mismatched Fermi\nsurfaces in a two-species system in the presence of Feshbach resonance, where\nthe resonantly-paired fermions combine to form bosonic molecules. We observe\nthat the Feshbach parameters control the critical temperature of the gapped BCS\nsuperfluid state, and also determine the range over which a gapless breached\npair state may exist. Demanding the positivity of the superfluid density, it is\nshown that although a breached pair state with two Fermi surfaces is always\nunstable, its single Fermi-surface counterpart can be stable if the chemical\npotentials of the two pairing species have opposite signs. This condition is\nsatisfied only over a narrow region in the BEC side, characterized by an upper\nand a lower limit for the magnetic field. We estimate these limits for a\nmixture of two hyperfine states of $^6$Li using recent experimental data."
    },
    {
        "anchor": "Interaction-induced charge pumping in a topological many-body system: A topological 'Thouless' pump represents the quantised motion of particles in\nresponse to a slow, cyclic modulation of external control parameters. The\nThouless pump, like the quantum Hall effect, is of fundamental interest in\nphysics because it links physically measurable quantities, such as particle\ncurrents, to geometric properties of the experimental system, which can be\nrobust against perturbations and thus technologically useful. So far,\nexperiments probing the interplay between topology and inter-particle\ninteractions have remained relatively scarce. Here we observe a Thouless-type\ncharge pump in which the particle current and its directionality inherently\nrely on the presence of strong interactions. Experimentally, we utilise\nfermionic atoms in a dynamical superlattice which traces a pump trajectory that\nremains trivial in the non-interacting limit. Remarkably, the transferred\ncharge in the interacting system is half of its usual value in the\nnon-interacting case, in agreement with matrix-product-state simulations. Our\nexperiments suggest that Thouless charge pumps are promising platforms to gain\ninsights into interaction-driven topological transitions and topological\nquantum matter.",
        "positive": "On Dunkl-Bose-Einstein Condensation in Harmonic Traps: The use of the Dunkl derivative, which is defined by a combination of the\ndifference-differential and reflection operator, allows the classification of\nthe solutions according to even and odd solutions. Recently, we considered the\nDunkl formalism to investigate the Bose-Einstein condensation of an ideal Bose\ngas confined in a gravitational field. In this work, we address a similar\nproblem and examine an ideal Bose gas trapped by a three-dimensional harmonic\noscillator within the Dunkl formalism. To this end, we derive an analytic\nexpression for the critical temperature of the N particle system, discuss its\nvalue at large-N limit and finally derive and compare the ground state\npopulation with the usual case result. In addition, we explore two thermal\nquantities, namely the Dunkl-internal energy and the Dunkl-heat capacity\nfunctions. The Wigner parameter of the Dunkl formalism can be successfully used\nto obtain a better agreement between experimental and theoretical results."
    },
    {
        "anchor": "Ultracold nonreactive molecules in an optical lattice: connecting\n  chemistry to many-body physics: We derive effective lattice models for ultracold bosonic or fermionic\nnonreactive molecules (NRMs) in an optical lattice, analogous to the Hubbard\nmodel that describes ultracold atoms in a lattice. In stark contrast to the\nHubbard model, which is commonly assumed to accurately describe NRMs, we find\nthat the single on-site interaction parameter $U$ is replaced by a\nmulti-channel interaction, whose properties we elucidate. The complex,\nmulti-channel collisional physics is unrelated to dipolar interactions, and so\noccurs even in the absence of an electric field or for homonuclear molecules.\nWe find a crossover between coherent few-channel models and fully incoherent\nsingle-channel models as the lattice depth is increased. We show that the\neffective model parameters can be determined in lattice modulation experiments,\nwhich consequently measure molecular collision dynamics with a vastly sharper\nenergy resolution than experiments in an ultracold gas.",
        "positive": "On the higher virial coefficients of a unitary Fermi gas: Third and higher order quantum virial coefficients require the solution of\nthe corresponding quantum many-body problem. Nevertheless, in an earlier paper\n(Phys. Rev. Lett. 108, 260402 (2012)) we proposed that the higher-order cluster\nintegrals of a dilute unitary fermionic gas may be approximated in terms of the\ntwo-body cluster, together with an appropriate suppression factor. Although not\nexact, this ansatz gave a fair agreement up to fugacity z=6 with the\nexperimentally obtained equation of state. The objective of the present note is\nto give some physical arguments in favor of this ansatz."
    },
    {
        "anchor": "Strong-coupling corrections to spin susceptibility in the BCS-BEC\n  crossover regime of a superfluid Fermi gas: We theoretically investigate the uniform spin susceptibility $\\chi$ in the\nsuperfluid phase of an ultracold Fermi gas in the BCS\n(Bardeen-Cooper-Schrieffer)-BEC (Bose-Einstein condensation) crossover region.\nIn our previous paper [H. Tajima, {\\it et. al.}, Phys. Rev. A {\\bf 89}, 033617\n(2014)], including pairing fluctuations within an extended $T$-matrix\napproximation (ETMA), we showed that strong pairing fluctuations cause the\nso-called spin-gap phenomenon, where $\\chi$ is anomalously suppressed even in\nthe normal state near the superfluid phase transition temperature $T_{\\rm c}$.\nIn this paper, we extend this work to the superfluid phase below $T_{\\rm c}$,\nto clarify how this many-body phenomenon is affected by the superfluid order.\nFrom the comparison of the ETMA $\\chi$ with the Yosida function describing the\nspin susceptibility in a weak-coupling BCS superfluid, we identify the region\nwhere pairing fluctuations crucially affect this magnetic quantity below\n$T_{\\rm c}$ in the phase diagram with respect to the strength of a pairing\ninteraction and the temperature. This spin-gap regime is found to be consistent\nwith the previous pseudogap regime determined from the pseudogapped density of\nstates. We also compare our results with a recent experiment on a $^6$Li Fermi\ngas. Since the spin susceptibility is sensitive to the formation of\nspin-singlet preformed pairs, our results would be useful for the study of\npseudogap physics in an ultracold Fermi gas on the viewpoint of the spin\ndegrees of freedom.",
        "positive": "Impurity self-energy in the strongly-correlated Bose systems: We proposed the non-perturbative scheme for calculation of the impurity\nspectrum in the Bose system at zero temperature. The method is based on the\npath-integral formulation and describes an impurity as a zero-density ideal\nFermi gas interacting with Bose system for which the action is written in terms\nof density fluctuations. On the example of the $^3$He atom immersed in the\nliquid helium-4 a good consistency with experimental data and results of Monte\nCarlo simulations is shown."
    },
    {
        "anchor": "Ground States of a Bose-Hubbard Ladder in an Artificial Magnetic Field:\n  Field-Theoretical Approach: We consider a Bose-Hubbard ladder subject to an artificial magnetic flux and\ndiscuss its different ground states, their physical properties, and the quantum\nphase transitions between them. A low-energy effective field theory is derived,\nin the two distinct regimes of a small and large magnetic flux, using a\nbosonization technique starting from the weak-coupling limit. Based on this\neffective field theory, the ground-state phase diagram at a filling of one\nparticle per site is investigated for a small flux and for a flux equal to\n$\\pi$ per plaquette. For $\\pi$-flux, this analysis reveals a tricritical point\nwhich has been overlooked in previous studies. In addition, the Mott insulating\nstate at a small magnetic flux is found to display Meissner currents.",
        "positive": "Polariton chimeras: Bose-Einstein condensates with intrinsic chaoticity\n  and spontaneous long-range ordering: The system of cavity polaritons driven by a plane electromagnetic wave is\nfound to undergo the spontaneous breaking of spatial symmetry, which results in\na lifted phase locking with respect to the driving field and, consequently, in\nthe possibility of internal ordering. In particular, periodic spin and\nintensity patterns arise in polariton wires; they exhibit strong long-range\norder and can serve as media for signal transmission. Such patterns have the\nproperties of dynamical chimeras: they are formed spontaneously in perfectly\nhomogeneous media and can be partially chaotic. The reported new mechanism of\nchimera formation requires neither time-delayed feedback loops nor non-local\ninteractions."
    },
    {
        "anchor": "Ultracold Dipolar Molecules Composed of Strongly Magnetic Atoms: In a combined experimental and theoretical effort, we demonstrate a novel\ntype of dipolar system made of ultracold bosonic dipolar molecules with large\nmagnetic dipole moments. Our dipolar molecules are formed in weakly bound\nFeshbach molecular states from a sample of strongly magnetic bosonic erbium\natoms. We show that the ultracold magnetic molecules can carry very large\ndipole moments and we demonstrate how to create and characterize them, and how\nto change their orientation. Finally, we confirm that the relaxation rates of\nmolecules in a quasi-two dimensional geometry can be reduced by using the\nanisotropy of the dipole-dipole interaction and that this reduction follows a\nuniversal dipolar behavior.",
        "positive": "Stable nonlinear modes sustained by gauge fields: We reveal the universal effect of gauge fields on the existence, evolution,\nand stability of solitons in the spinor multidimensional nonlinear\nSchr\\\"{o}dinger equation. Focusing on the two-dimensional case, we show that\nwhen gauge field can be split in a pure gauge and a \\rtext{non-pure gauge}\ngenerating \\rtext{effective potential}, the roles of these components in\nsoliton dynamics are different: the \\btext{localization characteristics} of\nemerging states are determined by the curvature, while pure gauge affects the\nstability of the modes. Respectively the solutions can be exactly represented\nas the envelopes independent of the pure gauge, modulating stationary\ncarrier-mode states, which are independent of the curvature. Our central\nfinding is that nonzero curvature can lead to the existence of unusual modes,\nin particular, enabling stable localized self-trapped fundamental and\nvortex-carrying states in media with constant repulsive interactions without\nadditional external confining potentials and even in the expulsive external\ntraps."
    },
    {
        "anchor": "Coherence and decoherence in the Harper-Hofstadter model: We quantum-simulated the 2D Harper-Hofstadter (HH) lattice model in a highly\nelongated tube geometry -- three sites in circumference -- using an atomic\nBose-Einstein condensate. In addition to the usual transverse (out-of-plane)\nmagnetic flux, piercing the surface of the tube, we threaded a longitudinal\nflux $\\Phi_{\\rm L}$ down the axis of the tube This geometry evokes an\nAharonov-Bohm interferometer, where noise in $\\Phi_{\\rm L}$ would readily\ndecohere the interference present in trajectories encircling the tube. We\nobserve this behavior only when transverse flux is a rational fraction of the\nflux-quantum, and remarkably find that for irrational fractions the decoherence\nis absent. Furthermore, at rational values of transverse flux, we show that the\ntime evolution averaged over the noisy longitudinal flux matches the time\nevolution at nearby irrational fluxes. Thus, the appealing intuitive picture of\nan Aharonov-Bohm interferometer is insufficient. Instead, we quantitatively\nexplain our observations by transforming the HH model into a collection of\nmomentum-space Aubry-Andr\\'{e} models.",
        "positive": "Phase fluctuations and first-order correlation functions of dissipative\n  Bose-Einstein condensates: We investigate the finite lifetime effects on first-order correlation\nfunctions of dissipative Bose-Einstein condensates. By taking into account the\nphase fluctuations up to all orders, we show that the finite lifetime effects\nare neglible for the spatial first-order correlation functions, but have an\nimportant effect on the temporal correlations. As an application, we calculate\nthe one-particle density matrix of a quasi-condensate of photons. Finally, we\nalso consider the photons in the normal state and we demonstrate that the\nfinite lifetime effects decrease both the spatial and temporal first-order\ncorrelation functions."
    },
    {
        "anchor": "Heavy-light $N+1$ clusters of two-dimensional fermions: We study binding of $N$ identical heavy fermions by a light atom in two\ndimensions assuming zero-range attractive heavy-light interactions. By using\nthe mean-field theory valid for large $N$ we show that the $N+1$ cluster is\nbound when the mass ratio exceeds $1.074N^2$. The mean-field theory, being\nscale invariant in two dimensions, predicts only the shapes of the clusters\nleaving their sizes and energies undefined. By taking into account\nbeyond-mean-field effects we find closed-form expressions for these quantities.\nWe also discuss differences between the Thomas-Fermi and Hartree-Fock\napproaches for treating the heavy fermions.",
        "positive": "Density instabilities in a two-dimensional dipolar Fermi gas: We study the density instabilities of a two-dimensional gas of dipolar\nfermions with aligned dipole moments. We show that the Random Phase\nApproximation (RPA) for the density-density response function is never accurate\nfor the dipolar gas. We incorporate correlations beyond RPA via an improved\nversion of the Singwi-Tosi-Land-Sjolander scheme. In addition to density-wave\ninstabilities, our formalism captures the collapse instability that is expected\nfrom Hartree-Fock calculations but is absent from RPA. Crucially, we find that\nwhen the dipoles are perpendicular to the layer, the system spontaneously\nbreaks rotational symmetry and forms a stripe phase, in defiance of\nconventional wisdom."
    },
    {
        "anchor": "Rashba and Weyl spin-orbit coupling in an optical lattice clock: Recent experimental realization of one-dimensional (1D) spin-orbit coupling\n(SOC) for ultracold alkaline-earth(-like) atoms in optical lattice clocks opens\na new avenue for exploring exotic quantum matter because of the strongly\nsuppressed heating of atoms from lasers comparing with alkaline atoms. Here we\npropose a scheme to realize two-dimensional (2D) Rashba and three-dimensional\n(3D) Weyl types of SOC in a 3D optical lattice clock and explore their\ntopological phases. With 3D Weyl SOC, the system can support topological phases\nwith various numbers as well as types (I or II) of Weyl points. The spin\ntextures of such topological bands for 2D Rashba and 3D Weyl SOC can be\ndetected using suitably designed spectroscopic sequences. Our proposal may pave\nthe way for the experimental realization of robust topological quantum matters\nand their exotic quasiparticle excitations in ultracold atomic gases.",
        "positive": "Collective modes in multicomponent condensates with anisotropy: We report the effects of anisotropy in the confining potential on two\ncomponent Bose-Einstein condensates (TBECs) through the properties of the low\nenergy quasiparticle excitations. Starting from generalized Gross Pitaevskii\nequation, we obtain the Bogoliubov de-Gennes (BdG) equation for TBECs using the\nHartree-Fock-Bogoliubov (HFB) theory. Based on this theory, we present the\ninfluence of radial anisotropy on TBECs in the immiscible or the\nphase-separated domain. In particular, the TBECs of $^{85}$Rb~-$^{87}$Rb and\n$^{133}$Cs~-$^{87}$Rb TBECs are chosen as specific examples of the two possible\ninterface geometries, shell-structured and side by side, in the immiscible\ndomain. We also show that the dispersion relation for the TBEC shell-structured\ninterface has two branches, and anisotropy modifies the energy scale and\nstructure of the two branches."
    },
    {
        "anchor": "The effect of boson-boson interaction on the Bipolaron formation: Impurities immersed into a surrounding ultra-cold Bose gas experience\ninteractions mediated by the surrounding many-body environment. If one focuses\non two impurities that are sufficiently close to each other, they can form a\nbipolaron pair. Here, we discuss how the standard methods based on linearizing\nthe condensate field lead to results only valid in the weak coupling regime and\nfor sufficiently large impurity separations. We show how those shortcomings can\nbe remedied within the Born-Oppenheimer approximation by accounting for\nboson-boson interactions already on the mean-field level.",
        "positive": "Phase Separation in Mixtures of Repulsive Fermi Gases Driven by Mass\n  Difference: We show that phase separation must occur in a mixture of fermions with\nrepulsive interaction if their mass difference is sufficiently large. This\nphenomenon is highly dimension-dependent. Consequently, the density profiles of\nphase separated 3d mixtures are very different from those in 1d. Noting that\nthe ferromagnetic transition of a spin-1/2 repulsive Fermi gas is the equal\nmass limit of the phase separation in mixtures, we show from the Bethe Ansatz\nsolution that a ferromagnetic transition will take place in the scattering\nstates when the repulsive interaction passes through resonance and becomes\nattractive."
    },
    {
        "anchor": "Faraday Waves in strongly interacting superfluids: We report on the observation of Faraday waves in a cigar-shaped Fermi\nsuperfluid of $^6$Li parametrically excited by modulating the radial trap\nfrequency. We characterize the phenomenon as a function of the interaction\nparameter by means of a Feshbach resonance. Starting from the BEC side of the\nresonance we observe a drop on the visibility of the Faraday pattern as we\napproach to unitarity, possibly due to the increased incompressibility of the\nsystem. We probe the superfluid excitation spectrum by extracting an effective\n1D speed of sound for different values of the interaction parameter, in good\nagreement with numerical simulations. Finally, we perform a stability analysis\nin the parameter space using a simplified model and we show the emergence of\nthe Faraday waves as unstable solutions to a Mathieu-like equation.",
        "positive": "Universal Tan relations for quantum gases in one dimension: We investigate universal properties of one-dimensional multi-component\nsystems comprised of fermions, bosons, or an arbitrary mixture, with contact\ninteractions and subjected to an external potential. The masses and the\ncoupling strengths between different types of particles are allowed to be\ndifferent and we also take into account the presence of an arbitrary magnetic\nfield. We show that the momentum distribution of these systems exhibits a\nuniversal $n_\\sigma(k) \\sim C_\\sigma/k^4$ decay with $C_\\sigma$ the contact of\nspecies $\\sigma$ which can be computed from the derivatives of an appropriate\nthermodynamic potential with respect to the scattering lengths. In the case of\nintegrable fermionic systems we argue that at fixed density and repulsive\ninteractions the total contact reaches its maximum in the balanced system and\nmonotonically decreases to zero as we increase the magnetic field. The converse\neffect is present in integrable bosonic systems: the contact is largest in the\nfully polarized state and reaches its minimum when all states are equally\npopulated. We obtain short distance expansions for the Green's function and\npair distribution function and show that the coefficients of these expansions\ncan be expressed in terms of the density, kinetic energy and contact. In\naddition we derive universal thermodynamic identities relating the total energy\nof the system, pressure, trapping energy and contact. Our results are valid at\nzero and finite temperature, for homogeneous or trapped systems and for\nfew-body or many-body states."
    },
    {
        "anchor": "Observing atom bunching by the Fourier slice theorem: By a novel reciprocal space analysis of the measurement, we report a\ncalibrated in situ observation of the bunching effect in a 3D ultracold gas.\nThe calibrated measurement with no free parameters confirms the role of the\nexchange symmetry and the Hanbury Brown-Twiss effect in the bunching. Also, the\nenhanced fluctuations of the bunching effect give a quantitative measure of the\nincreased isothermal compressibility. We use 2D images to probe the 3D gas,\nusing the same principle by which computerized tomography reconstructs a 3D\nimage of a body. The powerful reciprocal space technique presented is\napplicable to systems with one, two, or three dimensions.",
        "positive": "Soliton appearing in boson-fermion mixture at the third order of the\n  interaction radius: In this paper we consider an ultra-cold mixture of boson and fermion atoms on\nthe basis of quantum hydrodynamics. Small perturbations in such systems are\nbeing analyzed. A possibility is shown for soliton solutions of a new type to\nappear if the third order of the interaction radius is taken into account in\nthe analysis of interactions. A fermion-fermion interaction occurs in explicit\nform if this approximation is accepted. The conditions that lead to occurrence\nof this type of soliton in a mixture of boson and fermion atoms were\ninvestigated. Restrictions on the fermion-fermion interaction were found that\nare necessary for this kind of perturbations to appear in the system.\nConditions determining whether perturbances would be a condensed soliton or a\nrarefied soliton are shown. Requirements to the experimental detection of a new\nsoliton type in boson-fermion mixture are considered."
    },
    {
        "anchor": "Unconventional pairing in one-dimensional systems of a few\n  mass-imbalanced ultracold fermions: We study the ground-state properties of a two-component fermionic mixture\neffectively confined in a one-dimensional harmonic trap. We consider scenarios\nwhen numbers of particles in components are the same but particles have\ndifferent masses. We examine whether it is possible to detect signatures of an\nunconventional pairing between opposite-spin fermions in the presence of\nattractive interactions. For this purpose, we perform the exact diagonalization\nof the many-body Hamiltonian and study the two-particle reduced density matrix.\nIn agreement with expectations, we confirm that the many-body ground state is\ndominated by conventional pairs with a negligible total momentum for a small\nmass imbalance. Furthermore, we show that for sufficiently large mass ratios\nthe domination of fundamentally different pairs is established and the\nFulde-Ferrell-Larkin-Ovchinnikov phase is supported. Finally, we argue that the\ntwo mechanisms can coexist in the regime of moderate mass ratios. Due to the\ncurrent experimental progress in obtaining ultra-cold fermionic systems in a\nfew-body regime, our predictions may have some importance for the upcoming\nexperiments.",
        "positive": "Measuring Energy Differences by BEC Interferometry on a Chip: We investigate the use of a Bose-Einstein condensate trapped on an atom chip\nfor making interferometric measurements of small energy differences. We measure\nand explain the noise in the energy difference of the split condensates, which\nderives from statistical noise in the number difference. We also consider\nsystematic errors. A leading effect is the variation of rf magnetic field in\nthe trap with distance from the wires on the chip surface. This can produce\nenergy differences that are comparable with those due to gravity."
    },
    {
        "anchor": "Dynamics of Rydberg excitations and quantum correlations in an atomic\n  array coupled to a photonic crystal waveguide: We study the dynamics of up to two Rydberg excitations and the correlation\ngrowth in a chain of atoms coupled to a photonic crystal waveguide. In this\nsetup, an excitation can hop from one atom to another via exponentially\ndecaying exchange interactions mediated by the waveguide. An initially\nlocalized excitation undergoes a continuous-time quantum walk for short-range\nhopping, and for long-range, it experiences quasi-localization. Besides that,\nthe inverse participation ratio reveals a super-ballistic diffusion of the\nexcitation in short times, whereas, at a long time, it becomes ballistic. For\ntwo initially localized excitations, intriguing, and complex dynamical\nscenarios emerge for different initial separations due to the competition\nbetween the Rydberg-Rydberg and exchange interactions. In particular, the\ntwo-point correlation reveals a light-cone behavior even for sufficiently\nlong-range exchange interactions. Additionally, we characterize the growth of\nbipartite entanglement entropy, which exhibits a global bound if only one\nexcitation is present in the dynamics. Finally, we analyze the effect of\nimperfections due to spontaneous emission from the Rydberg state into photons\noutside the waveguide and show that all physical phenomena we predict are well\nwithin experimental reach.",
        "positive": "A laser based accelerator for ultracold atoms: We present first results on our implementation of a laser based accelerator\nfor ultracold atoms. Atoms cooled to a temperature of 420 nK are confined and\naccelerated by means of laser tweezer beams and the atomic scattering is\ndirectly observed in laser absorption imaging. The optical collider has been\ncharacterized using Rb87 atoms in the |F=2,mF=2> state, but the scheme is not\nrestricted to atoms in any particular magnetic substates and can readily be\nextended to other atomic species as well."
    },
    {
        "anchor": "Nonperturbative renormalization group treatment of amplitude\n  fluctuations for $|\\varphi|^4$ topological phase transitions: The study of the Berezinskii-Kosterlitz-Thouless transition in\ntwo-dimensional $|\\varphi|^4$ models can be performed in several\nrepresentations, and the amplitude-phase (AP) Madelung parametrization is a\nnatural way to study the contribution of density fluctuations to nonuniversal\nquantities. We introduce a functional renormalization group scheme in AP\nrepresentation where amplitude fluctuations are integrated first to yield an\neffective sine-Gordon model with renormalized superfluid stiffness. By a\nmapping between the lattice XY and continuum $|\\varphi|^4$ models, our method\napplies to both on equal footing. Our approach correctly reproduces the\nexistence of a line of fixed points and of universal thermodynamics and it\nallows to estimate universal and nonuniversal quantities of the two models,\nfinding good agreement with available Monte Carlo results. The presented\napproach is flexible enough to treat parameter ranges of experimental\nrelevance.",
        "positive": "Strongly interacting mesoscopic systems of anyons in one dimension: Using the fractional statistical properties of so-called anyonic particles,\nwe present exact solutions for up to six strongly interacting particles in\none-dimensional confinement that interpolate the usual bosonic and fermionic\nlimits. Specifically, we consider two-component mixtures of anyons and use\nthese to eludicate the mixing-demixing properties of both balanced and\nimbalanced systems. Importantly, we demonstrate that the degree of demixing\ndepends sensitively on the external trap in which the particles are confined.\nWe also show how one may in principle probe the statistical parameter of an\nanyonic system by injection a strongly interacting impurity and doing spectral\nor tunneling measurements."
    },
    {
        "anchor": "Twisted spin vortices in a spinor-dipolar Bose-Einstein condensate with\n  Rashba spin-orbit coupling: We consider a spin-1 Bose-Einstein condensate with Rashba spin-orbit coupling\nand dipole-dipole interaction confined in a cigar-shaped trap. Due to the\ncombined effects of spin-orbit coupling, dipole-dipole interaction, and trap\ngeometry, the system exhibits a rich variety of ground-state spin structures,\nincluding twisted spin vortices. The ground-state phase diagram is determined\nwith respect to the strengths of the spin-orbit coupling and dipole-dipole\ninteraction.",
        "positive": "Spatial coherence and stability in a disordered organic polariton\n  condensate: Although only a handful of organic materials have shown polariton\ncondensation, their study is rapidly becoming more accessible. The spontaneous\nappearance of long-range spatial coherence is often recognized as a defining\nfeature of such condensates. In this work, we study the emergence of spatial\ncoherence in an organic microcavity and demonstrate a number of unique features\nstemming from the peculiarities of this material set. Despite its disordered\nnature, we find that correlations extend over the entire spot size and we\nmeasure $g^{(1)}(r,r')$ values of nearly unity at short distances and of 50%\nfor points separated by nearly 10 $\\mu$m. We show that for large spots, strong\nshot to shot fluctuations emerge as varying phase gradients and defects,\nincluding the spontaneous formation of vortices. These are consistent with the\npresence of modulation instabilities. Furthermore, we find that measurements\nwith flat-top spots are significantly influenced by disorder and can, in some\ncases, lead to the formation of mutually incoherent localized condensates."
    },
    {
        "anchor": "Competing superfluid orders in spin-orbit coupled fermionic cold atom\n  optical lattices: The Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase, a superconducting state\nwith non-zero total momentum Cooper pairs in a large magnetic field, was first\npredicted about 50 years ago, and since then became an important concept in\nmany branches of physics. Despite intensive search in various materials,\nunambiguous experimental evidence for the FFLO phase is still lacking in\nexperiments. In this paper, we show that both FF (uniform order parameter with\nplane-wave phase) and LO phase (spatially varying order parameter amplitude)\ncan be observed using fermionic cold atoms in spin-orbit coupled optical\nlattices. The increasing spin-orbit coupling enhances the FF phase over the LO\nphase. The coexistence of superfluid and magnetic orders is also found in the\nnormal BCS phase. The pairing mechanism for different phases is understood by\nvisualizing superfluid pairing densities in different spin-orbit bands. The\npossibility of observing similar physics using spin-orbit coupled\nsuperconducting ultra-thin films is also discussed.",
        "positive": "Response of fermions in Chern bands to spatially local quenches: We study the dynamical evolution of Chern-band systems after subjecting them\nto local quenches. For open-boundary systems, we show for half-filling that the\nchiral nature of edge states is manifested in the time-dependent chiral\nresponse to local density quenches on the edge. In the presence of power-law\ntraps, we show how to mimic the half-filling situation by choosing the\nappropriate number of fermions depending on the trap size, and explore chiral\nresponses of edges to local quenches in such a configuration. We find that\nperturbations resulting from the quenches propagate at different group\nvelocities depending on the bulk band gap. Our results provide different routes\nto check dynamically the non-trivial nature of Chern bands."
    },
    {
        "anchor": "Transport of the repulsive Bose-Einstein condensate in a double-well\n  trap: interaction impact and relation to Josephson effect: Two aspects of the transport of the repulsive Bose-Einstein condensate (BEC)\nin a double-well trap are inspected: impact of the interatomic interaction and\nanalogy to the Josephson effect. The analysis employs a numerical solution of\n3D time-dependent Gross-Pitaevskii equation for a total order parameter\ncovering all the trap. The population transfer is driven by a time-dependent\nshift of a barrier separating the left and right wells. Sharp and soft profiles\nof the barrier velocity are tested. Evolution of the relevant characteristics,\ninvolving phase differences and currents, is inspected. It is shown that the\nrepulsive interaction substantially supports the transfer making it possible i)\nin a wide velocity interval and ii) three orders of magnitude faster than in\nthe ideal BEC. The transport can be approximately treated as the d.c. Josephson\neffect. A dual origin of the critical barrier velocity (break of adiabatic\nfollowing and d.c.-a.c. transition) is discussed. Following the calculations,\nrobustness of the transport (d.c.) crucially depends on the interaction and\nbarrier velocity profile. Only soft profiles which minimize undesirable dipole\noscillations are acceptable.",
        "positive": "Quantum Atomic Matter Near Two-Dimensional Materials in Microgravity: Novel two-dimensional (2D) atomically flat materials, such as graphene and\ntransition-metal dichalcogenides, exhibit unconventional Dirac electronic\nspectra. We propose to effectively engineer their interactions with cold atoms\nin microgravity, leading to a synergy between complex electronic and atomic\ncollective quantum phases and phenomena. Dirac materials are susceptible to\nmanipulation and quantum engineering via changes in their electronic properties\nby application of strain, doping with carriers, adjustment of their dielectric\nenvironment, etc. Consequently the interaction of atoms with such materials,\nnamely the van der Waals / Casimir-Polder interaction, can be effectively\nmanipulated, leading to the potential observation of physical effects such as\nQuantum Reflection off atomically thin materials and confined Bose-Einstein\nCondensate (BEC) frequency shifts."
    },
    {
        "anchor": "Phases of d-orbital bosons in optical lattices: We explore the properties of bosonic atoms loaded into the d bands of an\nisotropic square optical lattice. Following the recent experimental success\nreported in [Y. Zhai et al., Phys. Rev. A 87, 063638 (2013)], in which\npopulating d bands with a 99% fidelity was demonstrated, we present a\ntheoretical study of the possible phases that can appear in this system. Using\nthe Gutzwiller ansatz for the three d band orbitals we map the boundaries of\nthe Mott insulating phases. For not too large occupation, two of the orbitals\nare predominantly occupied, while the third, of a slightly higher energy,\nremains almost unpopulated. In this regime, in the superfluid phase we find the\nformation of a vortex lattice, where the vortices come in vortex/anti-vortex\npairs with two pairs locked to every site. Due to the orientation of the\nvortices time-reversal symmetry is spontaneously broken. This state also breaks\na discrete Z2-symmetry. We further derive an effective spin-1/2 model that\ndescribe the relevant physics of the lowest Mott-phase with unit filling. We\nargue that the corresponding two dimensional phase diagram should be rich with\nseveral different phases. We also explain how to generate antisymmetric spin\ninteractions that can give rise to novel effects like spin canting.",
        "positive": "Superfluids, Fluctuations and Disorder: We present a field-theory description of ultracold bosonic atoms in presence\nof a disordered external potential. By means of functional integration\ntechniques, we aim to investigate and review the interplay between disordered\nenergy landscapes and fluctuations, both thermal and quantum ones. Within the\nbroken-symmetry phase, up to the Gaussian level of approximation, the disorder\ncontribution crucially modifies both the condensate depletion and the\nsuperfluid response. Remarkably, it is found that the ordered (i.e. superfluid)\nphase can be destroyed also in regimes where the random external potential is\nsuitable for a perturbative analysis. We analyze the simplest case of quenched\ndisorder and then we move to present the implementation of the replica trick\nfor ultracold bosonic systems. In both cases, we discuss strengths and\nlimitations of the reviewed approach, paying specific attention to possible\nextensions and the most recent experimental outputs."
    },
    {
        "anchor": "Variational Approach to Quantum Spin Liquid in a Rydberg Atom Simulator: Recently the Rydberg blockade effect has been utilized to realize quantum\nspin liquid on the kagome lattice. Evidence of quantum spin liquid has been\nobtained experimentally by directly measuring non-local string order. In this\nletter, we report a BCS-type variational wave function study of the spin liquid\nstate in this model. This wave function is motivated by mapping the Rydberg\nblockade model to a lattice gauge theory, where the local gauge conservations\nreplace the role of constraints from the Rydberg blockade. We determine the\nvariational parameter from the experimental measurement of the Rydberg atom\npopulation. Then we compare the predictions of this deterministic wave function\nwith the experimental measurements of non-local string order. Combining the\nmeasurements on both open and closed strings, we extract the fluctuations only\nassociated with the closed-loop as an indicator of the topological order. The\nprediction from our wave function agrees reasonably well with the experimental\ndata without any fitting parameter. Our variational wave function provides a\nsimple and intuitive picture of the quantum spin liquid in this system that can\nbe generalized to various generalizations of the current model.",
        "positive": "Thermal effects on the spin domain phases of high spin-f Bose-Einstein\n  condensates with rotational symmetries: Spinor Bose Einstein condensates (BEC) can be realized nowadays using\ndifferent atomic species of several spin values, offering unprecedented\nopportunities to scrutinize the underlying physics of its spin phase domains\nand of its quantum phase transitions. At sufficient low temperatures, lower\nthan the critical temperature, a fraction of thermally excited atoms of the\ncondensate can still interact with the whole system leading to spin-dependent\ninteractions that can modify the nature of its phase domains. In this work, we\ncharacterize the thermal fraction of atoms of a spinorial BEC of general\nspin-$f$ value, provided that its ground state lies in a given spin phase with\nrotational symmetry. To that end, we use the Hartree-Fock approximation and a\nmethod based on the Majorana stellar representation for mixed quantum states\nand symmetry arguments. We consider the spin phases with usual point group\nsymmetries, including those with some exotic phases associated to the platonic\nsolids. The method leads to useful analytical expressions of the eigenspectrum\nof the thermal cloud allowing us to study the admissible regions and multipolar\nmagnetic moments of the spin phases as a function of the temperature for\ngeneral spin values."
    },
    {
        "anchor": "Supersolid-Superfluid phase separation in the extended Bose-Hubbard\n  model: Recent studies have suggested a new phase in the extended Bose-Hubbard model\nin one dimension at integer filling [1,2]. In this work, we show that this new\nphase is phase-separated into a supersolid and superfluid part, generated by\nmechanical instability. Numerical simulations are performed by means of the\ndensity matrix renormalization group algorithm in terms of matrix product\nstates. In the phase-separated phase and the adjacent homogeneous superfluid\nand supersolid phases, we find peculiar spatial patterns in the entanglement\nspectrum and string-order correlation functions and show that they survive in\nthe thermodynamic limit. In particular, we demonstrate that the elementary\nexcitations of the homogeneous superfluid with enhanced periodic modulations\nare phonons, find the central charge to be $c=1$, and show that the velocity of\nsound, extracted from the intrinsic level splitting for finite systems, matches\nwith the propagation velocity of local excitations in dynamical simulations.\nThis suggests that the low-energy spectrum of the phase under investigation is\neffectively captured by a spinless Luttinger liquid, for which we find\nconsistent results between the Luttinger parameter obtained from the linear\ndependence of the structure factor and the algebraic decay of the one-body\ndensity matrix.",
        "positive": "Exact Numerical Results on the Ground State of Strongly Interacting\n  Fermi Gases in Two Dimensions: Exact calculations are performed on the two-dimensional strongly interacting,\nunpolarized, uniform Fermi gas with a zero-range attractive interaction. Two\nauxiliary-field approaches are employed which accelerate the sampling of\nimaginary-time paths using BCS trial wave functions and a force bias technique.\nTheir combination enables calculations on large enough lattices to reliably\ncompute ground-state properties in the thermodynamic limit. A new equation of\nstate is obtained, with a parametrization provided, which can serve as a\nbenchmark and allow accurate comparisons with experiments. The pressure,\ncontact parameter, and condensate fraction are determined systematically\nvs.~$k_F a$. The momentum distribution, pairing correlation, and the structure\nof the pair wave function are computed. The use of force bias to accelerate the\nMetropolis sampling of auxiliary-fields in determinantal approaches is\ndiscussed."
    },
    {
        "anchor": "Emptiness Formation in Polytropic Quantum Liquids: We study large deviations in interacting quantum liquids with the polytropic\nequation of state $P(\\rho)\\sim \\rho^\\gamma$, where $\\rho$ is density and $P$ is\npressure. By solving hydrodynamic equations in imaginary time we evaluate the\ninstanton action and calculate the emptiness formation probability (EFP), the\nprobability that no particle resides in a macroscopic interval of a given size.\nAnalytic solutions are found for a certain infinite sequence of rational\npolytropic indexes $\\gamma$ and the result can be analytically continued to any\nvalue of $\\gamma\\ge 1$. Our findings agree with (and significantly expand on)\npreviously known analytical and numerical results for EFP in quantum liquids.\nWe also discuss interesting universal spacetime features of the instanton\nsolution.",
        "positive": "Spin-orbit coupled Bose-Einstein condensates in a one-dimensional\n  optical lattice: The realization of artificial gauge fields and spin-orbit coupling for\nultra-cold quantum gases promises new insight into paradigm solid state\nsystems. Here we experimentally probe the dispersion relation of a spin-orbit\ncoupled Bose-Einstein condensate loaded into a translating optical lattice by\nobserving its dynamical stability, and develop an effective band structure that\nprovides a theoretical understanding of the locations of the band edges. This\nsystem presents exciting new opportunities for engineering condensed-matter\nanalogs using the flexible toolbox of ultra-cold quantum gases."
    },
    {
        "anchor": "Non-equilibrium pre-thermal states in a two-dimensional photon fluid: Thermalization is the dynamical process by which a many-body system evolves\ntoward a thermal equilibrium state that maximizes its entropy. In certain\ncases, however, the establishment of thermal equilibrium is significantly\nslowed down and a phenomenon of pre-thermalization can emerge. It describes the\ninitial relaxation toward a quasi-steady state after a perturbation. While\nhaving similar properties to their thermal counterparts, pre-thermal states\nexhibit a partial memory of initial conditions. Here, we observe the dynamical\nformation of a pre-thermal state in a non-equilibrium, two-dimensional (2D)\nfluid of light after an interaction quench. Direct measurements of the fluid's\nfirst-order correlation function reveal the spontaneous emergence of long-range\nalgebraic correlations spreading within a light-cone, providing a clear\nsignature of a quasi steady-state strongly similar to a 2D thermal superfluid.\nDetailed experimental characterization of the algebraic order is presented and\na partial memory of the initial conditions is demonstrated, in agreement with\nrecent theoretical predictions. Furthermore, by a controlled increase of the\nfluid fluctuations, we unveil a cross-over from algebraic to short-range\n(exponential) correlations, analogous to the celebrated Kosterlitz-Thouless\ntransition observed at thermal equilibrium. These results suggest the existence\nof non-equilibrium precursors for thermodynamic phase transitions.",
        "positive": "Geometrically induced complex tunnelings for ultracold atoms carrying\n  orbital angular momentum: We investigate the dynamics of angular momentum states for a single ultracold\natom trapped in two dimensional systems of sided coupled ring potentials. The\nsymmetries of the system show that tunneling amplitudes between different ring\nstates with variation of the winding number are complex. In particular, we\ndemonstrate that in a triangular ring configuration the complex nature of the\ncross-couplings can be used to geometrically engineer spatial dark states to\nmanipulate the transport of orbital angular momentum states via quantum\ninterference."
    },
    {
        "anchor": "Motion of a distinguishable impurity in the Bose gas: Arrested expansion\n  without a lattice and impurity snaking: We consider the real time dynamics of an initially localized distinguishable\nimpurity injected into the ground state of the Lieb-Liniger model. Focusing on\nthe case where integrability is preserved, we numerically compute the time\nevolution of the impurity density operator in regimes far from analytically\ntractable limits. We find that the injected impurity undergoes a stuttering\nmotion as it moves and expands. For an initially stationary impurity, the\ninteraction-driven formation of a quasibound state with a hole in the\nbackground gas leads to arrested expansion -- a period of quasistationary\nbehavior. When the impurity is injected with a finite center of mass momentum,\nthe impurity moves through the background gas in a snaking manner, arising from\na quantum Newton's cradle-like scenario where momentum is exchanged\nback-and-forth between the impurity and the background gas.",
        "positive": "Universal Spin Transport in a Strongly Interacting Fermi Gas: Transport of fermions is central in many fields of physics. Electron\ntransport runs modern technology, defining states of matter such as\nsuperconductors and insulators, and electron spin, rather than charge, is being\nexplored as a new carrier of information [1]. Neutrino transport energizes\nsupernova explosions following the collapse of a dying star [2], and\nhydrodynamic transport of the quark-gluon plasma governed the expansion of the\nearly Universe [3]. However, our understanding of non-equilibrium dynamics in\nsuch strongly interacting fermionic matter is still limited. Ultracold gases of\nfermionic atoms realize a pristine model for such systems and can be studied in\nreal time with the precision of atomic physics [4, 5]. It has been established\nthat even above the superfluid transition such gases flow as an almost perfect\nfluid with very low viscosity [3, 6] when interactions are tuned to a\nscattering resonance. However, here we show that spin currents, as opposed to\nmass currents, are maximally damped, and that interactions can be strong enough\nto reverse spin currents, with opposite spin components reflecting off each\nother. We determine the spin drag coeffcient, the spin diffusivity, and the\nspin susceptibility, as a function of temperature on resonance and show that\nthey obey universal laws at high temperatures. At low temperatures, the spin\ndiffusivity approaches a minimum value set by the ratio of the reduced Planck's\nconstant to the atomic mass. For repulsive interactions, our measurements\nappear to exclude a metastable ferromagnetic state [7-9]."
    },
    {
        "anchor": "Single shot simulations of dynamic quantum many-body systems: The single-particle density is the most basic quantity that can be calculated\nfrom a given many-body wave function. It provides the probability to find a\nparticle at a given position when the average over many realizations of an\nexperiment is taken. However, the outcome of single experimental shots of\nultracold atom experiments is determined by the $N$-particle probability\ndensity. This difference can lead to surprising results. For example,\nindependent Bose-Einstein condensates (BECs) with definite particle numbers\nform interference fringes even though no fringes would be expected based on the\nsingle-particle density [1-4]. By drawing random deviates from the $N$-particle\nprobability density single experimental shots can be simulated from first\nprinciples [1, 3, 5]. However, obtaining expressions for the $N$-particle\nprobability density of realistic time-dependent many-body systems has so far\nbeen elusive. Here, we show how single experimental shots of general ultracold\nbosonic systems can be simulated based on numerical solutions of the many-body\nSchr\\\"odinger equation. We show how full counting distributions of observables\ninvolving any number of particles can be obtained and how correlation functions\nof any order can be evaluated. As examples we show the appearance of\ninterference fringes in interacting independent BECs, fluctuations in the\ncollisions of strongly attractive BECs, the appearance of randomly fluctuating\nvortices in rotating systems and the center of mass fluctuations of attractive\nBECs in a harmonic trap. The method described is broadly applicable to bosonic\nmany-body systems whose phenomenology is driven by information beyond what is\ntypically available in low-order correlation functions.",
        "positive": "Coexistence of phase transitions and hysteresis near BEC: Multiple phases occurring in a Bose gas with finite-range interaction are\ninvestigated. In the vicinity of the onset of Bose-Einstein condensation (BEC)\nthe chemical potential and the pressure show a van-der-Waals like behavior\nindicating a first-order phase transition although there is no long-range\nattraction. Furthermore the equation of state becomes multivalued near the BEC\ntransition. For a Hartree-Fock or Popov (Hartree-Fock-Bogoliubov) approximation\nsuch a multivalued region can be avoided by the Maxwell construction. For\nsufficiently weak interaction the multivalued region can also be removed using\na many-body \\mbox{T-matrix} approximation. However, for strong interactions\nthere remains a multivalued region even for the \\mbox{T-matrix} approximation\nand after the Maxwell construction, what is interpreted as a density\nhysteresis. This unified treatment of normal and condensed phases becomes\npossible due to the recently found scheme to eliminate self-interaction in the\n\\mbox{T-matrix} approximation, which allows to calculate properties below and\nabove the critical temperature."
    },
    {
        "anchor": "Topological defect dynamics of vortex lattices in Bose--Einstein\n  condensates: Vortex lattices in rapidly rotating Bose--Einstein condensates are systems of\ntopological excitations that arrange themselves into periodic patterns. Here we\nshow how phase-imprinting techniques can be used to create a controllable\nnumber of defects in these lattices and examine the resulting dynamics. Even\nthough we describe our system using the mean-field Gross--Pitaevskii theory,\nthe full range of many particle effects among the vortices can be studied. In\nparticular we find the existence of localized vacancies that are quasi-stable\nover long periods of time, and characterize the effects on the background\nlattice through use of the orientational correlation function, and Delaunay\ntriangulation.",
        "positive": "Efimov-driven phase transitions of the unitary Bose gas: In quantum physics, Efimov trimers are bound states of three particles that\nfall apart like Borromean rings when one of them is removed. Initially\npredicted in nuclear physics, these striking bosonic states are hard to\nobserve, but the \"unitary\" interactions at which they form is commonly realized\nin current cold atoms experiments. There, they set the stage for a new class of\nuniversal physics: Two-body interactions are all but invisible, but three-body\neffects allow the emergence of a largely uncharted new world of many-particle\nbound states. Three-particle systems were characterized theoretically, and the\nground-state properties of small unitary clusters computed numerically, but the\nmacroscopic many-body behaviour has remained unknown. Here we show, using a\nPath-Integral Monte Carlo algorithm backed up by theoretical arguments, that\nthe unitary Bose gas presents a first-order phase transition from a normal gas\nto a superfluid Efimov liquid. The normal gas is very well described by the\navailable virial coefficients. At unitarity, the phase diagram of the bosonic\nsystem is universal in rescaled pressure and temperature. A triple point\nseparates the normal gas, the superfluid Efimov liquid, and a third phase, the\nconventional superfluid gas. These two superfluid phases are separated by a\ncritical line that ends in a critical point at high temperature. This rich\nphase diagram should allow for a number of experimental protocols that would\nprobe these universal transitions between the normal gas, the superfluid gas,\nand the superfluid Efimov liquid."
    },
    {
        "anchor": "Optical transport and manipulation of an ultracold atomic cloud using\n  focus-tunable lenses: We present an optical setup with focus-tunable lenses to dynamically control\nthe waist and focus position of a laser beam, in which we transport a trapped\nultracold cloud of 87-Rb over a distance of 28 cm. The scheme allows us to\nshift the focus position at constant waist, providing uniform trapping\nconditions over the full transport length. The fraction of atoms that are\ntransported over the entire distance comes near to unity, while the heating of\nthe cloud is in the range of a few microkelvin. We characterize the position\nstability of the focus and show that residual drift rates in focus position can\nbe compensated for by counteracting with the tunable lenses. Beyond being a\ncompact and robust scheme to transport ultracold atoms, the reported control of\nlaser beams makes dynamic tailoring of trapping potentials possible. As an\nexample, we steer the size of the atomic cloud by changing the waist size of\nthe dipole beam.",
        "positive": "Quantum Monte Carlo method for pairing phenomena: Super-counter-fluid of\n  two-species Bose gases in optical lattices: We study the super-counter-fluid(SCF) states in the two-component hardcore\nBose-Hubbard model on the square lattice, using the quantum Monte Carlo method\nbased on the worm(directed loop) algorithm. Since the SCF state is a state of a\npair-condensation characterized by $< a^{\\dagger} b > \\neq 0, < a > = 0$, and\n$< b > = 0$, where $a$ and $b$ are the order parameters of the two components,\nit is important to study behaviors of the pair-correlation function $< a_{i}\nb_{i}^{\\dagger} a_{j}^{\\dagger} b_{j} >$. For this purpose, we propose a choice\nof the worm head for calculating the pair-correlation function. From this\npair-correlation, we confirm the Kosterlitz-Thouless(KT) charactor of the SCF\nphase. The simulation efficiency is also improved in the SCF phase."
    },
    {
        "anchor": "The ground state of the bose-hubbard model is a supersolid: The Bose-Hubbard model is well-defined description of a Bose solid which may\nbe realistic for cold atoms in a periodic optical lattice. We show that\ncontrary to accepted theories it can never have as a ground state a perfect\nMott insulator solid and that it has a low-energy spectrum of vortex-like phase\nfluctuations. Whether the ground state is necessarily commensurate remains an\nopen question.",
        "positive": "BCS-BEC crossover in atomic Fermi gases in quasi-two-dimensional Lieb\n  lattices: Effects of flat band and finite temperature: We investigate the finite-temperature superfluid behavior of ultracold atomic\nFermi gases in quasi-two-dimensional Lieb lattices with a short-range\nattractive interaction, using a pairing fluctuation theory within the BCS-BEC\ncrossover framework. We find that the presence of a flat band, along with van\nHove singularities, leads to exotic quantum phenomena. As the Fermi level\nenters the flat band, both the gap and the superfluid transition temperature\n$T_c$ as a function of interaction change from a conventional exponential\nbehavior into an unusual power law, and the evolution of superfluid densities\nwith temperature also follows a power law even at weak interactions. The\nquantum geometric effects, manifested by an enhanced effective pair hopping\nintegral, may contribute significantly to both $T_c$ and the superfluidities.\nAs the chemical potential crosses the van Hove singularities in the weak\ninteraction regime, the nature of pairing changes between particle-like and\nhole-like. A pair density wave state emerges at high densities with a\nrelatively strong interaction strength."
    },
    {
        "anchor": "Polarons, Dressed Molecules, and Itinerant Ferromagnetism in ultracold\n  Fermi gases: In this review, we discuss the properties of a few impurity atoms immersed in\na gas of ultracold fermions, the so-called Fermi polaron problem. On one side,\nthis many-body system is appealing because it can be described almost exactly\nwith simple diagrammatic and/or variational theoretical approaches. On the\nother, it provides quantitatively reliable insight into the phase diagram of\nstrongly interacting population imbalanced quantum mixtures. In particular, we\nshow that the polaron problem can be applied to study itinerant ferromagnetism,\na long standing problem in quantum mechanics.",
        "positive": "Tan's Contact for Trapped Lieb-Liniger Bosons at Finite Temperature: The universal Tan relations connect a variety of microscopic features of\nmany-body quantum systems with two-body contact interactions to a single\nquantity, called the contact. The latter has become pivotal in the description\nof quantum gases.We provide a complete characterization of the Tan contact of\nthe harmonically trapped Lieb-Liniger gas for arbitrary interactions and\ntemperature.Combining thermal Bethe ansatz, local-density approximation, and\nexact quantum Monte Carlo calculations,we show that the contact is a universal\nfunction of only two scaling parameters, and determine the scaling function.We\nfind that the temperature dependence of the contact, or equivalently the\ninteraction dependence of the entropy, displays a maximum. The presence of this\nmaximum provides an unequivocal signature of the crossover to the fermionized\nregime and it is accessible in current experiments."
    },
    {
        "anchor": "Condensing magnons in a degenerate ferromagnetic spinor Bose gas: We observe the condensation of magnon excitations within an $F=1$ $^{87}$Rb\nspinor Bose-Einstein condensed gas. Magnons are pumped into a longitudinally\nspin-polarized gas, allowed to equilibrate to a non-degenerate distribution,\nand then cooled evaporatively at near-constant net longitudinal magnetization\nwhereupon they condense. We find magnon condensation to be described\nquantitatively as the condensation of free particles in an effective potential\nthat is uniform within the ferromagnetic condensate volume, evidenced by the\nnumber and distribution of magnons at the condensation transition. Transverse\nmagnetization images reveal directly the spontaneous, inhomogeneous symmetry\nbreaking by the magnon quasi-condensate, including signatures of Mermin-Ho spin\ntextures that appear as phase singularities in the magnon condensate\nwavefunction.",
        "positive": "Observation of chiral edge states with neutral fermions in synthetic\n  Hall ribbons: Chiral edge states are a hallmark of quantum Hall physics. In electronic\nsystems, they appear as a macroscopic consequence of the cyclotron orbits\ninduced by a magnetic field, which are naturally truncated at the physical\nboundary of the sample. Here we report on the experimental realization of\nchiral edge states in a ribbon geometry with an ultracold gas of neutral\nfermions subjected to an artificial gauge field. By imaging individual sites\nalong a synthetic dimension, we detect the existence of the edge states,\ninvestigate the onset of chirality as a function of the bulk-edge coupling, and\nobserve the edge-cyclotron orbits induced during a quench dynamics. The\nrealization of fermionic chiral edge states is a fundamental achievement, which\nopens the door towards experiments including edge state interferometry and the\nstudy of non-Abelian anyons in atomic systems."
    },
    {
        "anchor": "A Bose gas in a single-beam optical dipole trap: We study an ultracold Bose gas in an optical dipole trap consisting of one\nsingle focused laser beam. An analytical expression for the corresponding\ndensity of states beyond the usual harmonic approximation is obtained. We are\nthus able to discuss the existence of a critical temperature for Bose-Einstein\ncondensation and find that the phase transition must be enabled by a cutoff\nnear the threshold. Moreover, we study the dynamics of evaporative cooling and\nobserve significant deviations from the findings for the well-established\nharmonic approximation. Furthermore, we investigate Bose-Einstein condensates\nin such a trap in Thomas-Fermi approximation and determine analytical\nexpressions for chemical potential, internal energy and Thomas-Fermi radii\nbeyond the usual harmonic approximation.",
        "positive": "Fulde-Ferrell-Larkin-Ovchinnikov pairing states of a polarized dipolar\n  Fermi gas trapped in a one-dimensional optical lattice: We study the interplay between the long- and short-range interaction of a\none-dimensional optical lattice system of two-component dipolar fermions by\nusing the density matrix renormalization group method. The atomic density\nprofile, pairing-pairing correlation function, and the compressibility are\ncalculated in the ground state, from which we identify the parameter region of\nthe Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) pairing state, half-metal (HM)\nstate, FFLO-HM state, and the normal polarized state, and thus the phase\ndiagram in the coordinates of the long- and short-range interaction strength.\nThe effect of the long-range dipolar interaction on the FFLO state is discussed\nin details. We find that the long-range part of the dipole-dipole interaction\ndoes not sweep away the FFLO superconducting region that is driven by the\nshort-range interaction in the Hubbard model, and thus the FFLO state survives\nin the wide parameter space of the long-range interaction, polarization and the\nfilling."
    },
    {
        "anchor": "Floquet-engineered nonlinearities and controllable pair-hopping\n  processes: From optical Kerr cavities to correlated quantum matter: This work explores the possibility of creating and controlling unconventional\nnonlinearities by periodic driving, in a broad class of systems described by\nthe nonlinear Schr\\\"odinger equation (NLSE). By means of a parent quantum\nmany-body description, we demonstrate that such driven systems are well\ncaptured by an effective NLSE with emergent nonlinearities, which can be finely\ncontrolled by tuning the driving sequence. We first consider a general class of\ntwo-mode nonlinear systems - relevant to optical Kerr cavities, waveguides and\nBose-Einstein condensates - where we find an emergent four-wave mixing\nnonlinearity, which originates from pair-hopping processes in the parent\nquantum picture. Tuning this drive-induced nonlinearity is shown to modify the\nphase-space topology, which can be detected through relative population and\nphase measurements. We then couple individual (two-mode) dimers in view of\ndesigning extended lattice models with unconventional nonlinearities and\ncontrollable pair-hopping processes. Following this general dimerization\nconstruction, we obtain an effective lattice model with drive-induced\ninteractions, whose ground-state exhibits orbital order, chiral currents and\nemergent magnetic fluxes through the spontaneous breaking of time-reversal\nsymmetry. We analyze these intriguing properties both in the weakly-interacting\n(mean-field) regime, captured by the effective NLSE, and in the\nstrongly-correlated quantum regime. Our general approach opens a route for the\nengineering of unconventional optical nonlinearities in photonic devices and\ncontrollable drive-induced interactions in ultracold quantum matter.",
        "positive": "Emergence and scaling of spin turbulence in quenched antiferromagnetic\n  spinor Bose-Einstein condensates: We investigate the phase transition dynamics of a quasi-2D antiferromagnetic\nspin-1 Bose-Einstein condensate from the easy-axis polar phase to the\neasy-plane polar phase, which is initiated by suddenly changing the sign of the\nquadratic Zeeman energy $q$. We observe the emergence and decay of spin\nturbulence and the formation of half-quantum vortices (HQVs) in the quenched\ncondensate. The characteristic time and length scales of the turbulence\ngeneration dynamics are proportional to $|q|^{-1/2}$ as inherited from the\ndynamic instability of the initial state. In the evolution of the spin\nturbulence, spin wave excitations develop from large to small length scales,\nsuggesting a direct energy cascade, and the spin population for the axial polar\ndomains exhibit a nonexponential decay. The final equilibrated condensate\ncontains HQVs, and the number is found to increase and saturate with increasing\n$|q|$. Our results demonstrate the time-space scaling properties of the phase\ntransition dynamics near the critical point and the peculiarities of the spin\nturbulence state of the antiferromagnetic spinor condensate."
    },
    {
        "anchor": "Exotic quantum liquids in Bose-Hubbard models with spatially-modulated\n  symmetries: We investigate the effect that spatially modulated continuous conserved\nquantities can have on quantum ground states. We do so by introducing a family\nof one-dimensional local quantum rotor and bosonic models which conserve finite\nFourier momenta of the particle number, but not the particle number itself.\nThese correspond to generalizations of the standard Bose-Hubbard model (BHM),\nand relate to the physics of Bose surfaces. First, we show that while having an\ninfinite-dimensional local Hilbert space, such systems feature a non-trivial\nHilbert space fragmentation for momenta incommensurate with the lattice. This\nis linked to the nature of the conserved quantities having a dense spectrum and\nprovides the first such example. We then characterize the zero-temperature\nphase diagram for both commensurate and incommensurate momenta. In both cases,\nanalytical and numerical calculations predict a phase transition between a\ngapped (Mott insulating) and quasi-long range order phase; the latter is\ncharacterized by a two-species Luttinger liquid in the infrared, but dressed by\noscillatory contributions when computing microscopic expectation values.\nFollowing a rigorous Villain formulation of the corresponding rotor model, we\nderive a dual description, from where we estimate the robustness of this phase\nusing renormalization group arguments, where the driving perturbation has\nultra-local correlations in space but power law correlations in time. We\nsupport this conclusion using an equivalent representation of the system as a\ntwo-dimensional vortex gas with modulated Coulomb interactions within a fixed\nsymmetry sector. We conjecture that a Berezinskii-Kosterlitz-Thouless-type\ntransition is driven by the unbinding of vortices along the temporal direction.",
        "positive": "Improvement of the matching of the exact solution and variational\n  approaches in an interacting two-fermion system: A more reasonable trial ground state wave function is constructed for the\nrelative motion of an interacting two-fermion system in a 1D harmonic\npotential. At the boundaries both the wave function and its first derivative\nare continuous and the quasi-momentum is determined by a more practical\nconstraint condition which associates two variational parameters. The upper\nbound of the ground state energy is obtained by applying the variational\nprinciple to the expectation value of the Hamiltonian of relative motion on the\ntrial wave function. The resulted energy and wave function show better\nagreement with the analytical solution than the original proposal."
    },
    {
        "anchor": "Modeling Rydberg Gases using Random Sequential Adsorption on Random\n  Graphs: The statistics of strongly interacting, ultracold Rydberg gases are governed\nby the interplay of two factors: geometrical restrictions induced by blockade\neffects, and quantum mechanical effects. To shed light on their relative roles\nin the statistics of Rydberg gases, we compare three models in this paper: a\nquantum mechanical model describing the excitation dynamics within a Rydberg\ngas, a Random Sequential Adsorption (RSA) process on a Random Geometric Graph\n(RGG), and a RSA process on a Decomposed Random Intersection Graph (DRIG). The\nlatter model is new, and refers to choosing a particular subgraph of a mixture\nof two other random graphs. Contrary to the former two models, it lends itself\nfor a rigorous mathematical analysis; and it is built specifically to have\nparticular structural properties of a RGG. We establish for it a fluid limit\ndescribing the time-evolution of number of Rydberg atoms, and show numerically\nthat the expression remains accurate across a wider range of particle densities\nthan an earlier approach based on an RSA process on an Erdos-Renyi Random Graph\n(ERRG). Finally, we also come up with a new heuristic using random graphs that\ngives a recursion to describe a normalized pair-correlation function of a\nRydberg gas. Our results suggest that even without dissipation, on long time\nscales the statistics are affected most by the geometrical restrictions induced\nby blockade effects, while on short time scales the statistics are affected\nmost by quantum mechanical effects.",
        "positive": "Correlation properties of a three-body bosonic mixture in a harmonic\n  trap: We make use of a simple pair correlated wave function approach to obtain\nresults for the ground-state densities and momentum distribution of a\none-dimensional three-body bosonic system with different interactions in a\nharmonic trap. For equal interactions this approach is able to reproduce the\nknown analytical cases of zero and infinite repulsion. We show that our results\nfor the correlations agree with the exact diagonalization in all interaction\nregimes and with analytical results for the strongly repulsive impurity. This\nmethod also enables us to access the more complicated cases of mixed\ninteractions, and the probability densities of these systems are analyzed."
    },
    {
        "anchor": "Phase diagram of the Bose Kondo-Hubbard model: We study a bosonic version of the Kondo lattice model with an on-site\nrepulsion in the conduction band, implemented with alkali atoms in two bands of\nan optical lattice. Using both weak and strong-coupling perturbation theory, we\nfind that at unit filling of the conduction bosons the superfluid to Mott\ninsulator transition should be accompanied by a magnetic transition from a\nferromagnet (in the superfluid) to a paramagnet (in the Mott insulator).\nFurthermore, an analytic treatment of Gutzwiller mean-field theory reveals that\nquantum spin fluctuations induced by the Kondo exchange cause the otherwise\ncontinuous superfluid to Mott-insulator phase transition to be first order. We\nshow that lattice separability imposes a serious constraint on proposals to\nexploit excited bands for quantum simulations, and discuss a way to overcome\nthis constraint in the context of our model by using an experimentally realized\nnon-separable lattice. A method to probe the first-order nature of the\ntransition based on collapses and revivals of the matter-wave field is also\ndiscussed.",
        "positive": "Three-Body Bound States of Quantum Particles: Higher Stability Through\n  Braiding: Cold atoms embedded in a degenerate Fermi system interact via a fermionic\nanalog of the Casimir force, which is an attraction of a -1/r form at distances\nshorter than the Fermi wavelength. Interestingly, the hydrogenic two-body bound\nstates do not form in this regime because the interaction strength is too weak\nunder realistic conditions, and yet the three-body bound states can have a\nconsiderably higher degree of stability. As a result, the trimer bound states\ncan form even when the dimer states are unstable. A quasiclassical analysis of\nquantum states supported by periodic orbits singles out the \"figure-eight\"\norbits, predicting bound states that are more stable than the ones originating\nfrom circular orbits. The discrete energies of these states form families of\nresonances with a distinct structure, enabling a direct observation of\nsignatures of figure-eightbraiding dynamics."
    },
    {
        "anchor": "Low-energy modes of spin-imbalanced Fermi gases in BCS phase: The low-energy modes of a spin-imbalanced superfluid Fermi gas in the\nBardeen-Cooper-Schrieffer (BCS) side are studied. The gas is assumed to be\nsufficiently dilute so that the pairing of atoms can be considered effective\nonly in s-wave between fermions of different internal state. The order\nparameter at equilibrium is determined by the mean-field approximation, while\nthe properties of the collective modes are calculated within a Gaussian\napproximation for the fluctuations of the order parameter. In particular we\ninvestigate the effects of asymmetry between the populations of the two\ndifferent components and of temperature on the frequency and damping of\ncollective modes. It is found that the temperature does not much affect the\nfrequency and the damping of the modes, whereas an increase of the imbalance\nshifts the frequency toward lower values and enhances the damping sensitively.\nBesides the Bogoliubov-Anderson phonons, we observe modes at zero frequency for\nfinite values of the wave-number. These modes indicate that an instability\ndevelops driving the system toward two separate phases, normal and superfluid.",
        "positive": "Connecting few-body inelastic decay to many-body correlations: a weakly\n  coupled impurity in a resonant Fermi gas: We study three-body recombination in an ultracold Bose-Fermi mixture. We\nfirst show theoretically that, for weak inter-species coupling, the loss rate\nis proportional to Tan's contact. Second, using a 7 Li/ 6 Li mixture we probe\nthe recombination rate in both the thermal and dual superfluid regimes. We find\nexcellent agreement with our model in the BEC-BCS crossover. At unitarity where\nthe fermion-fermion scattering length diverges, we show that the loss rate is\nproportional the 4/3 power of the fermionic density. Our results demonstrate\nthat impurity-induced losses can be used as a quantitative probe of many-body\ncorrelations."
    },
    {
        "anchor": "Normal State Properties of a resonantly interacting p-wave Fermi Gas: Motivated by the recent experimental progresses in the study of p-wave\nresonant Fermi gas, we investigate the normal state properties of such a gas\nclose to a p-wave scattering resonance. We calculate the universal equation of\nstate and the two p-wave contacts which characterise the universal properties\nof the system, in good agreement with experiments. Our calculation takes\nexplicit account of the effective range correction and obtains the superfluid\ntransition temperature $T_c$ within Nozi\\`eres-Schmitt-Rink (NSR) scheme, and\nshows that it lies within experimental reach. We derive analytic expression for\n$T_c$ in the weak coupling limit and show explicitly the non-perturbative\nnature of the effective range corrections.",
        "positive": "Far-from-equilibrium dynamics of an ultracold Fermi gas: Nonequilibrium dynamics of an N-fold spin-degenerate ultracold Fermi gas is\ndescribed in terms of beyond-mean-field Kadanoff-Baym equations for correlation\nfunctions. Using a nonperturbative expansion in powers of 1/N, the equations\nare derived from the two-particle irreducible effective action in\nSchwinger-Keldysh formulation. The definition of the nonperturbative\napproximation on the level of the effective action ensures vital conservation\nlaws as, e.g., for the total energy and particle number. As an example, the\nlong-time evolution of a homogeneous, twofold spin-degenerate Fermi gas is\nstudied in one spatial dimension after an initial preparation far from thermal\nequilibrium. Analysis of the fluctuation-dissipation relation shows that, at\nlow energies, the gas does not thermalise."
    },
    {
        "anchor": "Double Weyl points and Fermi arcs of topological semimetals in\n  non-Abelian gauge potentials: We study the effect of a non-Abelian SU(2) gauge potential on the topological\nsemimetal induced by a magnetic field having {\\pi}-flux per plaquette and\nacting on fermions in a cubic lattice. The Abelian {\\pi}-flux term gives rise\nto a spectrum characterized by Weyl points. When the non-Abelian part is turned\non, due to the presence of a C4 rotation symmetry, the Weyl points assume a\nquadratic dispersion along two directions and constitute double monopoles for\nthe Berry curvature. We examine both analytically and numerically the main\nfeatures of this system, focusing on its gapless surface modes, the so-called\nFermi arcs. We discuss the stability of the system under confining hard-wall\nand harmonic potentials, relevant for the implementation in ultracold atom\nsettings, and the effect of rotation symmetry breaking.",
        "positive": "Coherent back and forward scattering peaks in the quantum kicked rotor: We propose and analyze an experimental scheme using the quantum kicked rotor\nto observe the newly-predicted coherent forward scattering peak together with\nits long-known twin brother, the coherent backscattering peak. Contrary to\ncoherent backscattering, which arises already under weak-localization\nconditions, coherent forward scattering is only triggered by Anderson or strong\nlocalization. So far, coherent forward scattering has not been observed in\nconservative systems with elastic scattering by spatial disorder. We propose to\nturn to the quantum kicked rotor, which has a long and succesful history as an\naccurate experimental platform to observe dynamical localization, i.e.,\nAnderson localization in momentum space. We analyze the coherent forward\nscattering effect for the quantum kicked rotor by extensive numerical\nsimulations, both in the orthogonal and unitary class of disordered quantum\nsystems, and show that an experimental realization involving phase-space\nrotation techniques is within reach of state-of-the-art cold-atom experiments."
    },
    {
        "anchor": "$SU(3)$ Topological Insulators in the Honeycomb Lattice: We investigate realizations of topological insulators with spin-1 bosons\nloaded in a honeycomb optical lattice and subjected to a $SU(3)$ spin-orbit\ncoupling - a situation which can be realized experimentally using cold atomic\ngases. In this paper, we focus on the topological properties of the\nsingle-particle band structure, namely Chern numbers (lattice with periodic\nboundary conditions) and edge states (lattice with strip geometry). While\n$SU(2)$ spin-orbit couplings always lead to time-reversal symmetric Hubbard\nmodels, and thereby to topologically trivial band structures, suitable $SU(3)$\nspin-orbit couplings can break time reversal symmetry and lead to topologically\nnon-trivial bulk band structures and to edge states in the strip geometry. In\naddition, we show that one can trigger a series of topological transitions\n(i.e. integer changes of the Chern numbers) that are specific to the geometry\nof the honeycomb lattice by varying a single parameter in the Hamiltonian.",
        "positive": "Spin dynamics and structure formation in a spin-1 condensate in a\n  magnetic field: We study the dynamics of a trapped spin-1 condensate in a magnetic field.\nFirst, we analyze the homogeneous system, for which the dynamics can be\nunderstood in terms of orbits in phase space. We analytically solve for the\ndynamical evolution of the populations of the various Zeeman components of the\nhomogeneous system. This result is then applied via a local density\napproximation to trapped quasi-1D condensates. Our analysis of the trapped\nsystem in a magnetic field shows that both the mean-field and Zeeman regimes\nare simultaneously realized, and we argue that the border between these two\nregions is where spin domains and phase defects are generated. We propose a\nmethod to experimentally tune the position of this border."
    },
    {
        "anchor": "The Gross-Pitaevskii Equation and Bose-Einstein condensates: The Gross-Pitaevskii equation is discussed at the level of an advanced course\non statistical physics. In the standard literature the Gross-Pitaevskii\nequation is usually obtained in the framework of the second quantisation\nformalism, which in many cases goes beyond the material covered in many\nadvanced undergraduate courses. In this paper, we motivate the derivation of\nthe Gross-Pitaevskii equation (GPE) in relationship to concepts from\nstatistical physics, highlighting a number of applications from dynamics of a\nBose-Einstein condensate to the excitations of the gas cloud. This paper may be\nhelpful not only in encouraging the discussion of modern developments in a\nstatistical mechanics course, but also can be of use in other contexts such as\nmathematical physics and modelling. The paper is suitable for undergraduate and\ngraduate students, as well as general physicists.",
        "positive": "Phase randomization and typicality in the interference of two\n  condensates: Interference is observed when two independent Bose-Einstein condensates\nexpand and overlap. This phenomenon is typical, in the sense that the\noverwhelming majority of wave functions of the condensates, uniformly sampled\nout of a suitable portion of the total Hilbert space, display interference with\nmaximal visibility. We focus here on the phases of the condensates and their\n(pseudo) randomization, which naturally emerges when two-body scattering\nprocesses are considered. Relationship to typicality is discussed and analyzed."
    },
    {
        "anchor": "Optimizing persistent currents in a ring-shaped Bose-Einstein condensate\n  using machine learning: We demonstrate a method for generating persistent currents in Bose-Einstein\ncondensates by using a Gaussian process learner to experimentally control the\nstirring of the superfluid. The learner optimizes four different outcomes of\nthe stirring process: (O.I) targeting and (O.II) maximization of the persistent\ncurrent winding number; and (O.III) targeting and (O.IV) maximization with time\nconstraints. The learner optimizations are determined based on the achieved\nwinding number and the number of spurious vortices introduced by stirring. We\nfind that the learner is successful in optimizing the stirring protocols,\nalthough the optimal stirring profiles vary significantly depending strongly on\nthe choice of cost function and scenario. These results suggest that stirring\nis robust and persistent currents can be reliably generated through a variety\nof stirring approaches.",
        "positive": "On the quantization of the Hall conductivity in the Harper-Hofstadter\n  model: We study the robustness of the quantization of the Hall conductivity in the\nHarper-Hofstadter model towards the details of the protocol with which a\nlongitudinal uniform driving force $F_x(t)$ is turned on. In the vector\npotential gauge, through Peierls substitution, this involves the switching-on\nof complex time-dependent hopping amplitudes\n$\\mathrm{e}^{-\\frac{i}{\\hbar}\\mathcal{A}_x(t)}$ in the\n$\\hat{\\mathbf{x}}$-direction such that $\\partial_t \\mathcal{A}_x(t)=F_x(t)$.\nThe switching-on can be sudden, $F_x(t)=\\theta(t) F$, where $F$ is the steady\ndriving force, or more generally smooth $F_x(t)=f(t/t_{0}) F$, where\n$f(t/t_{0})$ is such that $f(0)=0$ and $f(1)=1$. We investigate how the\ntime-averaged (steady-state) particle current density $j_y$ in the\n$\\hat{\\mathbf{y}}$-direction deviates from the quantized value $j_y \\, h/F = n$\ndue to the finite value of $F$ and the details of the switching-on protocol.\nExploiting the time-periodicity of the Hamiltonian $\\hat{H}(t)$, we use Floquet\ntechniques to study this problem. In this picture the (Kubo) linear response\n$F\\to 0$ regime corresponds to the adiabatic limit for $\\hat{H}(t)$. In the\ncase of a sudden quench $j_y \\, h/F$ shows $F^2$ corrections to the perfectly\nquantized limit. When the switching-on is smooth, the result depends on the\nswitch-on time $t_{0}$: for a fixed $t_{0}$ we observe a crossover force $F^*$\nbetween a quadratic regime for $F<F^*$ and a {\\em non-analytic} exponential\n$\\mathrm{e}^{-\\gamma/|F|}$ for $F>F^*$. The crossover $F^*$ decreases as\n$t_{0}$ increases, eventually recovering the topological robustness. These\neffects are in principle amenable to experimental tests in optical lattice cold\natomic systems with synthetic gauge fields."
    },
    {
        "anchor": "Hidden long-range order in a spin-orbit coupled two-dimensional Bose gas: A spin-orbit coupled two-dimensional (2D) Bose gas is shown to simultaneously\npossess quasi and true long-range order in the total and relative phase\nsectors, respectively. The total phase undergoes a Berenzinskii-\nKosterlitz-Thouless transition to a low temperature phase with quasi long-range\norder, as expected for a two- dimensional quantum gas. Additionally, the\nrelative phase undergoes an Ising-type transition building up true long-range\norder, which is induced by the anisotropic spin-orbit coupling. Based on the\nBogoliubov approach, expressions for the total- and relative-phase fluctuations\nare derived analytically for the low temperature regime. Numerical simulations\nof the stochastic projected Gross-Pitaevskii equation (SPGPE) give a good\nagreement with the analytical predictions.",
        "positive": "Excitations and stability of weakly interacting Bose gases with\n  multi-body interactions: We consider weakly interacting bosonic gases with local and non-local\nmulti-body interactions. By using the Bogoliubov approximation, we first\ninvestigate contact interactions, studying the case in which the interparticle\npotential can be written as a sum of N-body {\\delta}-interactions, and then\nconsidering general contact potentials. Results for the quasi-particle spectrum\nand the stability are presented. We then examine non-local interactions,\nfocusing on two different cases of 3-body non-local interactions. Our results\nare used for systems with 2- and 3-body {\\delta}-interactions and applied for\nrealistic values of the trap parameters. Finally, the effect of conservative\n3-body terms in dipolar systems and soft-core potentials (that can be simulated\nwith Rydberg dressed atoms) is also studied."
    },
    {
        "anchor": "Overlapping Bose-Einstein Condensates of $^{23}$Na and $^{133}$Cs: We report on the creation of dual-species Bose-Einstein condensates (BECs) of\n$^{23}$Na atoms and $^{133}$Cs atoms. We demonstrate sympathetic cooling of Cs\nwith Na in a magnetic quadrupole trap and a crossed optical dipole trap,\nleading to Na BECs with $8 \\times 10^5$ atoms and Cs BECs with $3.5 \\times\n10^4$ atoms. Investigating cross-thermalization and lifetimes of the mixture,\nwe find that the Na and Cs BECs are miscible and overlapping, interacting with\na moderate interspecies scattering length of $18(4)\\,a_0$ at $23\\,$G and\n$29(4)\\,a_0$ at $894\\,$G and coexisting for tens of seconds. Overlapping\ncondensates of Na and Cs offer new possibilities for many-body physics with\nultracold bosonic mixtures and constitute an ideal starting point for the\ncreation of ultracold ensembles of NaCs ground state molecules.",
        "positive": "Bose-Einstein Condensation and Many-Body Localization of Rotational\n  Excitations of Polar Molecules: We study theoretically the collective dynamics of rotational excitations of\npolar molecules loaded into an optical lattice in two dimensions. These\nexcitations behave as hard-core bosons with a relativistic energy dispersion\narising from the dipolar coupling between molecules. This has interesting\nconsequences for the collective many-body phases. The rotational excitations\ncan form a Bose-Einstein condensate at non-zero temperature, manifesting itself\nas a divergent $T_2$ coherence time of the rotational transition even in the\npresence of inhomogeneous broadening. The dynamical evolution of a dense gas of\nrotational excitations shows regimes of non-ergodicity, characteristic of\nmany-body localization and localization protected quantum order."
    },
    {
        "anchor": "Breathing Oscillations in Bose - Fermi Mixing Gases with Yb atoms in the\n  Largely Prolate Deformed Traps: We study the breathing oscillations in bose-fermi mixtures with Yb isotopes\nin the largely prolate deformed trap, which are realized by Kyoto group. We\nchoose the three combinations of the Yb isotopes, Yb170-Yb171, Yb170-Yb173 and\nYb174-Yb173, whose boson-fermion interactions are weakly repulsive, strongly\nattractive and strongly repulsive. The collective oscillations in the deformed\ntrap are calculated in the dynamical time-development approach, which is\nformulated with the time-dependent Gross-Pitaevskii and the Vlasov equations.\nWe analyze the results in the time-development approach with the intrinsic\noscillation modes of the deformed system, which are obtained using the scaling\nmethod, and show that the damping and forced-oscillation effects of the\nintrinsic modes give time-variation of oscillations, especially, in the fermion\ntransverse mode.",
        "positive": "Two trapped particles interacting by a finite-ranged two-body potential\n  in two spatial dimensions: We examine the problem of two particles confined in an isotropic harmonic\ntrap, which interact via a finite-ranged Gaussian-shaped potential in two\nspatial dimensions. We derive an approximative transcendental equation for the\nenergy and study the resulting spectrum as a function of the interparticle\ninteraction strength. Both the attractive and repulsive systems are analyzed.\nWe study the impact of the potential's range on the ground-state energy.\nComplementary, we also explicitly verify by a variational treatment that in the\nzero-range limit the positive delta potential in two dimensions only reproduces\nthe non-interacting results, if the Hilbert space in not truncated. Finally, we\nestablish and discuss the connection between our finite-range treatment and\nregularized zero-range results from the literature."
    },
    {
        "anchor": "Asymmetric Tunneling of Bose-Einstein Condensates: In his celebrated textbook, \\textit{Quantum Mechanics: Nonrelativistic\nTheory}, Landau argued that, for single particle systems in 1D, tunneling\nprobability remains the same for a particle incident from the left or the right\nof a barrier. This left-right symmetry of tunneling probability holds\nregardless of the shape of the potential barrier. However, there are a variety\nof known cases that break this symmetry, e.g. when observing composite\nparticles. We computationally (and analytically, in the simplest case) show\nthis breaking of the left-right tunneling symmetry for Bose-Einstein\ncondensates (BEC) in 1D, modelled by the Gross-Pitaevskii equation (GPE). By\nvarying $g$, the parameter of inter-particle interaction in the BEC, we\ndemonstrate that the transition from symmetric ($g=0$) to asymmetric tunneling\nis a threshold phenomenon. Our computations employ experimentally feasible\nparameters such that these results may be experimentally demonstrated in the\nnear future. We conclude by suggesting applications of the phenomena to design\natomtronic diodes, synthetic gauge fields, Maxwell's demons, and black-hole\nanalogues.",
        "positive": "Dynamics of binary Bose-Einstein condensate via Ehrenfest like\n  equations: Appearance of almost shape invariant states: We derive Ehrenfest like equations for the coupled Gross Pitaevskii equations\n(CGPE) which describe the dynamics of the binary Bose-Einstein condensate\n(BBEC) both in the free particle regime and in the regime where condensate is\nwell trapped. Instead of traditional variational technique, we propose a new\nEhrenfest based approach to explore so far unrevealed dynamics for CGPE and\nillustrate the possibility of almost shape invariant states in both the\nregimes. In absence of trapping potential, when all the interactions present in\nthe system are attractive, it is possible for an initially mixed Gaussian state\nto propagate with almost no change in width if the proper initial condition is\nsatisfied. Even for repulsive intra-atomic and attractive inter-atomic\ninteraction ($g_{\\alpha\\beta}$) one can tune $|g_{\\alpha\\beta}|$ such that the\nwidth of the propagating wave packet remains bounded within almost about\n$10\\%$. We also discuss the dynamics of the initially phase separated\ncondensate and have shown the breakdown of Gaussian nature of the wave packets\ndue to collisions. However, when BEC is trapped in simple harmonic\noscillator(SHO) potential, for $g_{\\alpha\\beta}>0$, it is possible for an\ninitially overlapping state to retain its initial shape if $g_{\\alpha\\beta}$ is\nless than a critical value ($g_{\\alpha\\beta}^c$). If $g_{\\alpha\\beta}$ exceeds\n$g_{\\alpha\\beta}^c$, an overlapping state can become phase separated while\nkeeping its shape unchanged."
    },
    {
        "anchor": "Flipping-shuttle oscillations of bright one- and two-dimensional\n  solitons in spin-orbit-coupled Bose-Einstein condensates with Rabi mixing: We analyze a possibility of macroscopic quantum effects in the form of\ncoupled structural oscillations and shuttle motion of bright two-component\nspin-orbit-coupled striped (one-dimensional, 1D) and semi-vortex\n(two-dimensional, 2D) matter-wave solitons, under the action of linear mixing\n(Rabi coupling) between the components. In 1D, the intrinsic oscillations\nmanifest themselves as flippings between spatially even and odd components of\nstriped solitons, while in 2D the system features periodic transitions between\nzero-vorticity and vortical components of semi-vortex solitons. The\nconsideration is performed by means of a combination of analytical and\nnumerical methods.",
        "positive": "Emergent $\\mathcal{PT}$-symmetry breaking of Anderson-Bogoliubov modes\n  in Fermi superfluids: The spontaneous breaking of parity-time ($\\mathcal{PT}$) symmetry, which\nyields rich critical behavior in non-Hermitian systems, has stimulated much\ninterest. Whereas most previous studies were performed within the\nsingle-particle or mean-field framework, exploring the interplay between\n$\\mathcal{PT}$ symmetry and quantum fluctuations in a many-body setting is a\nburgeoning frontier. Here, by studying the collective excitations of a Fermi\nsuperfluid under an imaginary spin-orbit coupling, we uncover an emergent\n$\\mathcal{PT}$-symmetry breaking in the Anderson-Bogoliubov (AB) modes, whose\nquasiparticle spectra undergo a transition from being completely real to\ncompletely imaginary, even though the superfluid ground state retains an\nunbroken $\\mathcal{PT}$ symmetry. The critical point of the transition is\nmarked by a non-analytic kink in the speed of sound, as the latter completely\nvanishes at the critical point where the system is immune to low-frequency\nperturbations.These critical phenomena derive from the presence of a spectral\npoint gap in the complex quasiparticle dispersion, and are therefore\ntopological in origin."
    },
    {
        "anchor": "Rotation of a Bose-Einstein Condensate held under a toroidal trap: The aim of this paper is to perform a numerical and analytical study of a\nrotating Bose Einstein condensate placed in a harmonic plus Gaussian trap,\nfollowing the experiments of \\cite{bssd}. The rotational frequency $\\Omega$ has\nto stay below the trapping frequency of the harmonic potential and we find that\nthe condensate has an annular shape containing a triangular vortex lattice. As\n$\\Omega$ approaches $\\omega$, the width of the condensate and the circulation\ninside the central hole get large. We are able to provide analytical estimates\nof the size of the condensate and the circulation both in the lowest Landau\nlevel limit and the Thomas-Fermi limit, providing an analysis that is\nconsistent with experiment.",
        "positive": "Momentum-space Harper-Hofstadter model: We show how the weakly trapped Harper-Hofstadter model can be mapped onto a\nHarper-Hofstadter model in momentum space. In this momentum-space model, the\nband dispersion plays the role of the periodic potential, the Berry curvature\nplays the role of an effective magnetic field, the real-space harmonic trap\nprovides the momentum-space kinetic energy responsible for the hopping, and the\ntrap position sets the boundary conditions around the magnetic Brillouin zone.\nSpatially local interactions translate into nonlocal interactions in momentum\nspace: within a mean-field approximation, we show that increasing interparticle\ninteractions leads to a structural change of the ground state, from a single\nrotationally symmetric ground state to degenerate ground states that\nspontaneously break rotational symmetry."
    },
    {
        "anchor": "Spin-1/2 fermions with attractive interaction in an optical lattice: We study attractive fermions in an optical lattice superimposed by a trapping\npotential, such that fermions may form bosonic molecules. We map the model onto\nnonlinear field equations depending on the Nambu-Gor'kov propagator. The\nresulting field equations where solved numerically by a relaxation technique\nthat allowed us to calculate the inhomogeneous densities of fermions and\ncondensed molecules at zero temperature. When the interactions between fermions\nare strong there is a competition between unbound fermions and bound molecules\nleading to an unexpected reduction of the non-homogeneous density of fermions\nat the center of the trap.",
        "positive": "Condensate Fraction and Pair Coherence Lengths of Two-Dimension Fermi\n  Gases with Spin-Orbit Coupling: The effects of Rashba spin-orbit coupling on BCS-BEC crossover, the\ncondensate fraction and pair coherence lengths for a two-component attractive\nFermi gas in two dimension are studied. The results at $T=0K$ indicate that (1)\nwhen the strength of SOC is beyond a critical value, BCS-BEC crossover does not\nhappen in a conventional sense; (2) SOC enhances the condensate fraction, but\nsuppresses pair coherence lengths."
    },
    {
        "anchor": "Pairing in population imbalanced Fermion systems: We use Quantum Monte Carlo (QMC) simulations to study the pairing mechanism\nin a one-dimensional fermionic system governed by the Hubbard model with\nattractive contact interaction and with imbalance between the two spin\npopulations. This is done for the uniform system and also for the system\nconfined in a harmonic trap to compare with experiments on confined ultra-cold\natoms. In the uniform case we determine the phase diagram in the\npolarization-temperature plane and find that the\n\"Fulde-Ferrell-Larkin-Ovchinnikov\" (FFLO) phase is robust and persists to\nhigher temperature for higher polarization. In the confined case, we also find\nthat the FFLO phase is stabilized by higher polarization and that it is within\nthe range of detection of experiments currently underway.",
        "positive": "Superfluidity enhanced by spin-flip tunnelling in the presence of a\n  magnetic field: It is well-known that when the magnetic field is stronger than a critical\nvalue, the spin imbalance can break the Cooper pairs of electrons and hence\nhinder the superconductivity in a spin-singlet channel. In a bilayer system of\nultra-cold Fermi gases, however, we demonstrate that the critical value of the\nmagnetic field at zero temperature can be significantly increased by including\na spin-flip tunnelling, which opens a gap in the spin-triplet channel near the\nFermi surface and hence reduces the influence of the effective magnetic field\non the superfluidity. The phase transition also changes from first order to\nsecond order when the tunnelling exceeds a critical value. Considering a\nrealistic experiment, this mechanism can be implemented by applying an\nintralayer Raman coupling between the spin states with a phase difference\nbetween the two layers."
    },
    {
        "anchor": "Quantum entangled ground states of two spinor Bose-Einstein condensates: We revisit in detail the non-mean-field ground-state phase diagram for a\nbinary mixture of spin-1 Bose-Einstein condensates including quantum\nfluctuations. The non-commuting terms in the spin-dependent Hamiltonian under\nsingle spatial mode approximation make it difficult to obtain exact\neigenstates. Utilizing the spin z-component conservation and the total spin\nangular momentum conservation, we numerically derive the information of the\nbuilding blocks and evaluate von Neumann entropy to quantify the ground states.\nThe mean-field phase boundaries are found to remain largely intact, yet the\nground states show fragmented and entangled behaviors within large parameter\nspaces of interspecies spin-exchange and singlet-pairing interactions.",
        "positive": "Dissipative two-dimensional Raman lattice: We show that a dissipative two-dimensional Raman lattice can be engineered in\na two-component ultracold atomic gas, where the interplay of the\ntwo-dimensional spin-orbit coupling and lightinduced atom loss gives rise to a\ndensity flow diagonal to the underlying square lattice. The flow is driven by\nthe non-Hermitian corner skin effect, under which eigenstates localize toward\none corner of the system. We illustrate that the topological edge states of the\nsystem can only be accounted for by the non-Bloch band theory where the\ndeformation of the bulk eigenstates are explicitly considered. The directional\nflow can be detected through the dynamic evolution of an initially localized\ncondensate in the lattice, or by introducing an immobile impurity species that\ninteract spin-selectively with a condensate in the ground state of the Raman\nlattice."
    },
    {
        "anchor": "Geometry induced pair condensation: We study a one-dimensional model of interacting bosons on a lattice with two\nflat bands. Regular condensation is suppressed due to the absence of a well\ndefined minimum in the single particle spectrum. We find that interactions\nstabilize a number of non-trivial phases like a pair (quasi-) condensate, a\nsupersolid at incommensurable fillings and valence bond crystals at\ncommensurability. We support our analytical calculations with numerical\nsimulations using the density matrix renormalization group technique.\nImplications for cold-atoms and extensions to higher dimensions are discussed.",
        "positive": "Benchmarking the multiconfigurational Hartree method by the exact\n  wavefunction of two harmonically trapped bosons with contact interaction: We consider two bosons in a one-dimensional harmonic trap, interacting by a\ncontact potential, and compare the exact solution of this problem to a\nself-consistent numerical solution by using the multiconfigurational\ntime-dependent Hartree (MCTDH) method. We thereby benchmark the predictions of\nthe MCTDH method with a few-body problem that has an analytical solution for\nthe most commonly experimentally realized interaction potential in ultracold\nquantum gases. It is found that exact ground state energy and first order\ncorrelations are accurately reproduced by MCTDH up to the intermediate\ndimensionless coupling strengths corresponding to typical background scattering\nlengths of magnetically trapped ultracold dilute Bose gases. For larger\ncouplings, established for example by (a combination of) Feshbach resonances\nand optical trapping, the MCTDH approach overestimates the depth of the\ntrap-induced correlation dip of first order correlations in position space, as\nwell as overestimates the fragmentation, defined as the average relative\noccupation of orbitals other than the energetically lowest one. We anticipate\nthat qualitatively similar features in the correlation function may arise for\nlarger particle numbers, paving the way for a quantitative assessment of the\naccuracy of MCTDH by experiments with ultracold atoms."
    },
    {
        "anchor": "Transverse instability and disintegration of domain wall of relative\n  phase in coherently coupled two-component Bose-Einstein condensates: We study transverse instability and disintegration dynamics of a domain wall\nof a relative phase in two-component Bose-Einstein condensates with a coherent\nRabi coupling. We obtain analytically the stability phase diagram of the\nstationary solution of the domain wall for the one-dimensional coupled\nGross-Pitaevskii equations in the plane of the Rabi frequency and the\nintercomponent coupling constant. Outside the stable region, the domain wall is\ndynamically unstable for the transverse modulation along the direction\nperpendicular to the phase kink. The nonlinear evolution associated with the\ninstability is demonstrated through numerical simulations for both the domain\nwall without edges and that with edges formed by the quantized vortices.",
        "positive": "Nucleation and kinematics of vortices in stirred Bose Einstein\n  condensates: We apply the Halperin-Mazenco formalism within the Gross-Pitaevskii theory to\ncharacterise the kinematics and nucleation of quantum vortices in a\ntwo-dimensional stirred Bose Einstein condensate. We introduce a smooth defect\ndensity field measuring the superfluid vorticity and is a topologically\nconserved quantity. We use this defect density field and its associated current\ndensity to study the precursory pattern formations that occur inside the\nrepulsive potential of an obstacle and determine the onset of vortex nucleation\nand shedding. We demonstrate that phase slips form inside hard potentials even\nin the absence of vortex nucleation, whereas for soft potentials they occur\nonly above a critical stirring velocity leading to vortex nucleation. The\nHalperin-Mazenco formalism provides an elegant and accurate method of deriving\nthe point vortex dynamic directly from the Gross-Pitaevskii equation."
    },
    {
        "anchor": "Bose-Hubbard model in a ring-shaped optical lattice with high filling\n  factors: The high-barrier quantum tunneling regime of a Bose-Einstein condensate\nconfined in a ring-shaped optical lattice is investigated. By means of a change\nof basis transformation, connecting the set of `vortex' Bloch states and a\nWannier-like set of localized wave functions, we derive a generalized\nBose-Hubbard Hamiltonian. In addition to the usual hopping rate terms, such a\nHamiltonian takes into account interaction-driven tunneling processes, which\nare shown to play a principal role at high filling factors, when the standard\nhopping rate parameter turns out to be negative. By calculating the energy and\natomic current of a Bloch state, we show that such a hopping rate must be\nreplaced by an effective hopping rate parameter containing the additional\ncontribution an interaction-driven hopping rate. Such a contribution turns out\nto be crucial at high filling factors, since it preserves the positivity of the\neffective hopping rate parameter. Level crossings between the energies per\nparticle of a Wannier-like state and the superfluid ground state are\ninterpreted as a signature of the transition to configurations with\nmacroscopically occupied states at each lattice site.",
        "positive": "Polar molecules in frustrated triangular ladders: Polar molecules in geometrically frustrated lattices may result in a very\nrich landscape of quantum phases, due to the non-trivial interplay between\nfrustration, and two- and possibly three-body inter-site interactions. In this\npaper, we illustrate this intriguing physics for the case of hard-core polar\nmolecules in frustrated triangular ladders. Whereas commensurate lattice\nfillings result in gapped phases with bond-order and/or density-wave order, at\nincommensurate fillings we find chiral-, two-component-, and pair-superfluids.\nWe show as well that, remarkably, polar molecules in frustrated lattices allow,\nfor the first time to our knowledge, for the observation of bond-ordered\nsupersolids."
    },
    {
        "anchor": "Resonant excitations of a Bose Einstein condensate in an optical lattice: We investigate experimentally a Bose Einstein condensate placed in a 1D\noptical lattice whose phase or amplitude is modulated in a frequency range\nresonant with the first bands of the band structure. We study the combined\neffect of the strength of interactions and external confinement on the 1 and\n2-phonon transitions. We identify lines immune or sensitive to atom-atom\ninteractions. Experimental results are in good agreement with numerical\nsimulations. Using the band mapping technique, we get a direct access to the\npopulations that have undergone $n$-phonon transitions for each modulation\nfrequency.",
        "positive": "Revealing Excited States of Rotational Bose-Einstein Condensates: Rotational Bose-Einstein condensates can exhibit quantized vortices as\ntopological excitations. In this study, the ground and excited states of the\nrotational Bose-Einstein condensates are systematically studied by calculating\nthe stationary points of the Gross-Pitaevskii energy functional. Various\nexcited states and their connections at different rotational frequencies are\nrevealed in solution landscapes constructed with the constrained high-index\nsaddle dynamics method. Four excitation mechanisms are identified: vortex\naddition, rearrangement, merging, and splitting. We demonstrate changes in the\nground state with increasing rotational frequencies and decipher the evolution\nof the stability of ground states."
    },
    {
        "anchor": "Interacting atomic quantum fluids on momentum-space lattices: We study the influence of atomic interactions on quantum simulations in\nmomentum-space lattices (MSLs), where driven atomic transitions between\ndiscrete momentum states mimic transport between sites of a synthetic lattice.\nLow energy atomic collisions, which are short ranged in real space, relate to\nnearly infinite-ranged interactions in momentum space. However, the\ndistinguishability of the discrete momentum states coupled in MSLs gives rise\nto an added exchange energy between condensate atoms in different momentum\norders, relating to an effectively attractive, finite-ranged interaction in\nmomentum space. We explore the types of phenomena that can result from this\ninteraction, including the formation of chiral self-bound states in topological\nMSLs. We also discuss the prospects for creating squeezed states in\nmomentum-space double wells.",
        "positive": "Quantitative semiclassical analysis of ultracold weakly interacting bose\n  gas trapped in optical boxes: In this paper, the condensate fraction and the critical atom number and its\ncorresponding critical temperature of condensate ultracold boson atoms trapped\nin optical box traps, are investigated. The semiclassical approximation is\nemployed in this study. The boxes traps are modeled by a general power-law\npotential. The deviation of the boxes traps from an ideal boxes traps are\ndiscussed. The out come results furnish useful quantitative theoretical results\nfor the future BEC experiments in such traps"
    },
    {
        "anchor": "Matter wave scattering on an amplitude-modulated optical lattice: We experimentally study the scattering of guided matter waves on an\namplitude-modulated optical lattice. We observe different types of\nfrequency-dependent dips in the asymptotic output density distribution. Their\npositions are compared quantitatively with numerical simulations. A\nsemiclassical model that combines \\emph{local} Floquet-Bloch bands analysis and\nLandau-Zener transitions provides a simple picture of the observed phenomena in\nterms of elementary \\emph{Floquet photon} absorption-emission processes and\nenvelope-induced reflections. Finally, we propose and demonstrate the use of\nthis technique with a bichromatic modulation to design a tunable sub-recoil\nvelocity filter. Such a filter can be transposed to all species since it does\nnot rely on a specific internal level configuration of the atoms.",
        "positive": "Mean-field dynamics of two-mode Bose-Einstein condensates in highly\n  anisotropic potentials: Interference, dimensionality, and entanglement: We study the mean-field dynamics and the reduced-dimension character of\ntwo-mode Bose-Einstein condensates (BECs) in highly anisotropic traps. By means\nof perturbative techniques, we show that the tightly confined (transverse)\ndegrees of freedom can be decoupled from the dynamical equations at the expense\nof introducing additional effective three-body, attractive, intra- and\ninter-mode interactions into the dynamics of the loosely confined\n(longitudinal) degrees of freedom. These effective interactions are mediated by\nchanges in the transverse wave function. The perturbation theory is valid as\nlong as the nonlinear scattering energy is small compared to the transverse\nenergy scales. This approach leads to reduced-dimension mean-field equations\nthat optimally describe the evolution of a two-mode condensate in general\nquasi-1D and quasi-2D geometries. We use this model to investigate the relative\nphase and density dynamics of a two-mode, cigar-shaped $^{87}$Rb BEC. We study\nthe relative-phase dynamics in the context of a nonlinear Ramsey interferometry\nscheme, which has recently been proposed as a novel platform for high-precision\ninterferometry. Numerical integration of the coupled, time-dependent,\nthree-dimensional, two-mode Gross-Pitaevskii equations for various atom numbers\nshows that this model gives a considerably more refined analytical account of\nthe mean-field evolution than an idealized quasi-1D description."
    },
    {
        "anchor": "Renormalization theory for the Fulde-Ferrell-Larkin-Ovchinnikov states\n  at $T>0$: Within the renormalization group framework we study the stability of\nsuperfluid density wave states, known as Fulde-Ferrell-Larkin-Ovchinnikov\n(FFLO) phases, with respect to thermal order-parameter fluctuations in two and\nthree-dimensional ($d\\in \\{2,3\\}$) systems. We analyze the\nrenormalization-group flow of the relevant ordering wave-vector $\\vec{Q_0}$.\nThe calculation indicates an instability of the FFLO-type states towards either\na uniform superfluid or the normal state in $d\\in\\{2,3\\}$ and $T>0$. In $d=2$\nthis is signaled by $\\vec{Q_0}$ being renormalized towards zero, corresponding\nto the flow being attracted either to the usual Kosterlitz-Thouless fixed-point\nor to the normal phase. We supplement a solution of the RG flow equations by a\nsimple scaling argument, supporting the generality of the result. The tendency\nto reduce the magnitude of $\\vec{Q_0}$ by thermal fluctuations persists in\n$d=3$, where the very presence of long-range order is immune to thermal\nfluctuations, but the effect of attracting $\\vec{Q_0}$ towards zero by the flow\nremains observed at $T>0$.",
        "positive": "Angular-momentum modes in a bosonic condensate trapped in the\n  inverse-square potential: In the mean-field approximation, the well-known effect of the critical\nquantum collapse in a 3D gas of particles pulled to the center by potential\nU(r) = -U_0/r^2 is suppressed by repulsive interparticle interactions, which\ncreate the otherwise non-existing s-wave ground state. Here, we address excited\nbound states carrying angular momentum, with the orbital and magnetic quantum\nnumbers, l and m. They exist above a threshold value of the potential's\nstrength, U_0 > l(l+1). The sectoral, tesseral, and zonal modes, which\ncorrespond to m = l, 0 < m < l, and m = 0, respectively, are found in an\napproximate analytical form for relatively small values of U_0 - l(l+1).\nExplicit results are produced for the p- and d-wave states, with l = 1 and 2,\nrespectively. In the general form, the bound states are obtained numerically,\nconfirming the accuracy of the analytical approximation."
    },
    {
        "anchor": "Parity Symmetry Breaking and Topological Phases in a Superfluid Ring: We study analytically the superfluid flow of a Bose-Einstein condensate in a\nring geometry in presence of a rotating barrier. We show that a phase\ntransition breaking a parity symmetry among two topological phases occurs at a\ncritical value of the height of the barrier. Furthermore, a discontinuous\n(accompanied by hysteresis) phase transition is observed in the ordered phase\nwhen changing the angular velocity of the barrier. At the critical point where\nthe hysteresis area vanishes, chemical potential of the ground state develops a\ncusp (a discontinuity in the first derivative). Along this path, the jump\nbetween the two corresponding states having a different winding number shows\nstrict analogies with a topological phase transition. We finally study the\ncurrent-phase relation of the system and compare some of our calculations with\npublished experimental results.",
        "positive": "Symmetry Protected Dynamical Symmetry in the Generalized Hubbard Models: In this letter we present a theorem on the dynamics of the generalized\nHubbard models. This theorem shows that the symmetry of the single particle\nHamiltonian can protect a kind of dynamical symmetry driven by the\ninteractions. Here the dynamical symmetry refers to that the time evolution of\ncertain observables are symmetric between the repulsive and attractive Hubbard\nmodels. We demonstrate our theorem with three different examples in which the\nsymmetry involves bipartite lattice symmetry, reflection symmetry and\ntranslation symmetry, respectively. Each of these examples relates to one\nrecent cold atom experiment on the dynamics in the optical lattices where such\na dynamical symmetry is manifested. These experiments include expansion\ndynamics of cold atoms, chirality of atomic motion within a synthetic magnetic\nfield and melting of charge-density-wave order. Therefore, our theorem provides\na unified view of these seemingly disparate phenomena."
    },
    {
        "anchor": "Observation of a non-Abelian Yang Monopole: From New Chern Numbers to a\n  Topological Transition: Because global topological properties are robust against local perturbations,\nunderstanding and manipulating the topological properties of physical systems\nis essential in advancing quantum science and technology. For quantum\ncomputation, topologically protected qubit operations can increase\ncomputational robustness, and for metrology the quantized Hall effect directly\ndefines the von Klitzing constant. Fundamentally, topological order is\ngenerated by singularities called topological defects in extended spaces, and\nis quantified in terms of Chern numbers, each of which measures different sorts\nof fields traversing surfaces enclosing these topological singularities. Here,\ninspired by high energy theories, we describe our synthesis and\ncharacterization of a singularity present in non-Abelian gauge theories - a\nYang monopole - using atomic Bose-Einstein condensates in a five-dimensional\nspace, and quantify the monopole in terms of Chern numbers measured on\nenclosing manifolds. While the well-known 1st Chern number vanished, the 2nd\nChern number, measured for the first time in any physical settings, did not. By\ndisplacing the manifold, we then observed a phase transition from \"topological\"\nto \"trivial\" as the monopole left the manifold.",
        "positive": "Harmonically trapped attractive and repulsive spin-orbit and Rabi\n  coupled Bose-Einstein condensates: Numerically we investigate the ground state of effective one-dimensional\nspin-orbit (SO) and Rabi coupled two pseudo-spinor Bose-Einstein condensates\n(BECs) under the effect of harmonic traps. For both signs of the interaction,\ndensity profiles of SO and Rabi coupled BECs in harmonic potentials, which\nsimulate a real experimental situation are obtained. The harmonic trap causes a\nstrong reduction of the multi-peak nature of the condensate and it increases\nits density. For repulsive interactions, the increase of SO coupling results in\nan uncompressed less dense condensate and with increased multi-peak nature of\nthe density. The increase of Rabi coupling leads to a density increase with an\nalmost constant number of multi-peaks. For both signs of the interaction and\nnegative values of Rabi coupling, the condensate develops a notch in the\ncentral point and it seems to a dark-in-bright soliton. In the case of the\nattractive nonlinearity, an interesting result is the increase of the collapse\nthreshold under the action of the SO and Rabi couplings."
    },
    {
        "anchor": "Temperature-driven crossover in the Lieb-Liniger model: The large-distance behavior of the density-density correlation function in\nthe Lieb-Liniger model at finite temperature is investigated by means of the\nrecently derived nonlinear integral equations characterizing the correlation\nlengths. We present extensive numerical results covering all the physical\nregimes fromweak to strong interaction and all temperatures. We find that the\nleading term of the asymptotic expansion becomes oscillatory at a critical\ntemperature which decreases with the strength of the interaction. As we\napproach the Tonks-Girardeau limit the asymptotic behavior becomes more complex\nwith a double crossover of the largest and next-largest correlation lengths.\nThe crossovers exist only for intermediate couplings and vanish for $\\gamma=0$\nand $\\gamma=\\infty$.",
        "positive": "Construction of Fractal Order and Phase Transition with Rydberg Atoms: We propose the construction of a many-body phase of matter with fractal\nstructure using arrays of Rydberg atoms. The degenerate low energy excited\nstates of this phase form a self-similar fractal structure. This phase is\nanalogous to the so-called \"type-II fracton topological states\". The main\nchallenge in realizing fracton-like models in standard condensed matter\nplatforms is the creation of multi-spin interactions, since realistic systems\nare typically dominated by two-body interactions. In this work, we demonstrate\nthat the Van der Waals interaction and experimental tunability of Rydberg-based\nplatforms enable the simulation of exotic phases of matter with fractal\nstructures, and the study of a quantum phase transition involving a fractal\nordered phase."
    },
    {
        "anchor": "Suppression of relative flow by multiple domains in two-component\n  Bose-Einstein condensates: We investigate flow properties of immiscible Bose-Einstein condensates\ncomposed of two different Zeeman spin states of 87Rb. Spatially overlapping two\ncondensates in the optical trap are prepared by application of a resonant radio\nfrequency pulse, and then the magnetic field gradient is applied in order to\nproduce the atomic flow. We find that the spontaneous multiple domain formation\narising from the immiscible nature drastically changes the fluidity. The\nhomogeneously overlapping condensates readily separate under the magnetic field\ngradient, and they form stable configuration composed of the two layers. In\ncontrast, the relative flow between two condensates are largely suppressed in\nthe case where the magnetic field gradient is applied after spontaneous domain\nformation.",
        "positive": "Formation of a spin texture in a quantum gas coupled to a cavity: We observe cavity mediated spin-dependent interactions in an off-resonantly\ndriven multi-level atomic Bose-Einstein condensate that is strongly coupled to\nan optical cavity. Applying a driving field with adjustable polarization, we\nidentify the roles of the scalar and the vectorial components of the atomic\npolarizability tensor for single and multi-component condensates. Beyond a\ncritical strength of the vectorial coupling, we observe a spin texture in a\ncondensate of two internal states, providing perspectives for global dynamic\ngauge fields and self-consistently spin-orbit coupled gases."
    },
    {
        "anchor": "Quantum correlations and entanglement in far-from-equilibrium spin\n  systems: By applying complementary analytic and numerical methods, we investigate the\ndynamics of spin-$1/2$ XXZ models with variable-range interactions in arbitrary\ndimensions. The dynamics we consider is initiated from uncorrelated states that\nare easily prepared in experiments, and can be equivalently viewed as either\nRamsey spectroscopy or a quantum quench. Our primary focus is the dynamical\nemergence of correlations and entanglement in these far-from-equilibrium\ninteracting quantum systems: we characterize these correlations by the\nentanglement entropy, concurrence, and squeezing, which are inequivalent\nmeasures of entanglement corresponding to different quantum resources. In one\nspatial dimension, we show that the time evolution of correlation functions\nmanifests a non-perturbative dynamic singularity. This singularity is\ncharacterized by a universal power-law exponent that is insensitive to small\nperturbations. Explicit realizations of these models in current experiments\nusing polar molecules, trapped ions, Rydberg atoms, magnetic atoms, and\nalkaline-earth and alkali atoms in optical lattices, along with the relative\nmerits and limitations of these different systems, are discussed.",
        "positive": "Persistence of equilibrium states in an oscillating double-well\n  potential: We investigate numerically parametrically driven coupled nonlinear\nSchrodinger equations modelling the dynamics of coupled wavefields in a\nperiodically oscillating double-well potential. The equations describe among\nother things two coupled periodically-curved optical waveguides with Kerr\nnonlinearity or horizontally shaken Bose-Einstein condensates in a double-well\nmagnetic trap. In particular, we study the persistence of equilibrium states of\nthe undriven system due to the presence of the parametric drive. Using\nnumerical continuations of periodic orbits and calculating the corresponding\nFloquet multipliers, we find that the drive can (de)stabilize a continuation of\nan equilibrium state indicated by the change of the (in)stability of the orbit.\nHence, we show that parametric drives can provide a powerful control to\nnonlinear (optical or matter wave) field tunneling. Analytical approximations\nbased on an averaging method are presented. Using perturbation theory the\ninfluence of the drive on the symmetry breaking bifurcation point is discussed."
    },
    {
        "anchor": "Two-state Bogoliubov theory of a molecular Bose gas: We present an analytic Bogoliubov description of a BEC of polar molecules\ntrapped in a quasi-2D geometry and interacting via internal state-dependent\ndipole-dipole interactions. We derive the mean-field ground-state energy\nfunctional, and we derive analytic expressions for the dispersion relations,\nBogoliubov amplitudes, and dynamic structure factors. This method can be\napplied to any homogeneous, two-component system with linear coupling, and\ndirect, momentum-dependent interactions. The properties of the mean-field\nground state, including polarization and stability, are investigated, and we\nidentify three distinct instabilities: a density-wave rotonization that occurs\nwhen the gas is fully polarized, a spin-wave rotonization that occurs near zero\npolarization, and a mixed instability at intermediate fields. These\ninstabilities are clarified by means of the real-space density-density\ncorrelation functions, which characterize the spontaneous fluctuations of the\nground state, and the momentum-space structure factors, which characterize the\nresponse of the system to external perturbations. We find that the gas is\nsusceptible to both density-wave and spin-wave response in the polarized limit\nbut only a spin-wave response in the zero-polarization limit. These results are\nrelevant for experiments with rigid rotor molecules such as RbCs,\n$\\Lambda$-doublet molecules such as ThO that have an anomalously small\nzero-field splitting, and doublet-$\\Sigma$ molecules such as SrF where two\nlow-lying opposite-parity states can be tuned to zero splitting by an external\nmagnetic field.",
        "positive": "Spin and mass currents near a moving magnetic obstacle in a\n  two-component Bose-Einstein condensate: We study the spatial distributions of the spin and mass currents generated by\na moving Gaussian magnetic obstacle in a symmetric, two-component Bose-Einstein\ncondensate in two dimensions. We analytically describe the current\ndistributions for a slow obstacle and show that the spin and the mass currents\nexhibit characteristic spatial structures resembling those of electromagnetic\nfields around dipole moments. When the obstacle's velocity increases, we\nnumerically observe that the flow pattern maintains its overall structure while\nthe spin polarization induced by the obstacle is enhanced with an increased\nspin current. We investigate the critical velocity of the magnetic obstacle\nbased on the local criterion of Landau energetic instability and find that it\ndecreases almost linearly as the magnitude of the obstacle's potential\nincreases, which can be directly tested in current experiments."
    },
    {
        "anchor": "Site-resolved imaging of ultracold fermions in a triangular-lattice\n  quantum gas microscope: Quantum gas microscopes have expanded the capabilities of quantum simulation\nof Hubbard models by enabling the study of spatial spin and density\ncorrelations in square lattices. However, quantum gas microscopes have not been\nrealized for fermionic atoms in frustrated geometries. Here, we demonstrate the\nsingle-atom resolved imaging of ultracold fermionic $^{6}$Li atoms in a\ntriangular optical lattice with a lattice constant of 1003 nm. The optical\nlattice is formed by a recycled narrow-linewidth, high-power laser combined\nwith a light sheet to allow for Raman sideband cooling on the $D_1$ line. We\noptically resolve single atoms on individual lattice sites using a\nhigh-resolution objective to collect scattered photons while cooling them close\nto the two-dimensional ground vibrational level in each lattice site. By\nreconstructing the lattice occupation, we measure an imaging fidelity of ~98%.\nOur new triangular lattice microscope platform for fermions clears the path for\nstudying spin-spin correlations, entanglement and dynamics of geometrically\nfrustrated Hubbard systems which are expected to exhibit exotic emergent\nphenomena including spin liquids and kinetic frustration.",
        "positive": "Interaction Induced Topological Charge Pump: Based on a topological transition of the symmetry protected topological phase\n(SPT), an interaction induced topological charge pump (iTCP) is proposed with\nthe symmetry breaking parameter as a synthetic dimension. It implies that the\nphase boundary of the SPT is the topological obstruction although iTCP and the\ngap closing singularity is stable for symmetry breaking perturbations. We have\nconfirmed the bulk-edge correspondence for this iTCP using DMRG for the\nRice-Mele model with nearest-neighbor interactions. As for a realization in\noptical lattices, an interaction sweeping pump protocol is proposed as well."
    },
    {
        "anchor": "Dynamic structure factor of one-dimensional Fermi superfluid with\n  spin-orbit coupling: We theoretically calculate the density dynamic structure factor of\none-dimensional Fermi superfluid with Raman-type spin-orbit coupling, and\nanalyze its main dynamical character during phase transition between\nBardeen-Cooper-Schrieffer superfluid and topological superfluid. Our\ntheoretical results display four kinds of single-particle excitations induced\nby the two-branch structure of single-particle spectrum, and the cross\nsingle-particle excitation is much easier to be seen in the spin dynamic\nstructure factor at a small transferred momentum. Also we find a new roton-like\ncollective mode emerges at a fixed transferred momentum $q \\simeq 2k_F$, and it\nonly appears once the system enters the topological superfluid state. The\noccurrence of this roton-like excitation is related to switch of global minimum\nin single-particle spectrum from $k=0$ to $k \\simeq 2k_F$.",
        "positive": "Intertwined orders from symmetry projected wavefunctions of repulsively\n  interacting Fermi gases in optical lattices: Unconventional strongly correlated phases of the repulsive Fermi-Hubbard\nmodel, which could be emulated by ultracold vapors loaded in optical lattices,\nare investigated by means of energy minimizations with quantum number\nprojection before variation and without any assumed order parameter. In a\ntube-like geometry of optical plaquettes to realize the four-leg ladder Hubbard\nHamiltonian, we highlight the intertwining of spin-, charge-, and pair-density\nwaves embedded in a uniform d-wave superfluid background. As the lattice\nfilling increases, this phase emerges from homogenous states exhibiting spiral\nmagnetism and evolves towards a doped antiferromagnet. A concomitant\nenhancement of long-ranged d-wave pairing correlations is also found. Numerical\ntests of the approach for two-dimensional clusters are carried out, too."
    },
    {
        "anchor": "Anderson localization in an interacting fermionic system: In the present article, we discuss the role played by the interaction in the\nAnderson localization problem, for a system of interacting fermions in a\none-dimensional disordered lattice, described by the Fermi Hubbard Hamiltonian,\nin presence of an on-site random potential. We show that, given the proper\nidentification of the elementary excitations of the system described in terms\nof doublons and unpaired particles, the Anderson localization picture survives.\nEnsuing a \"global quench\", we show that the system exhibits a rich localization\nscenario, which can be ascribed to the nearly-free dynamics of the elementary\nexcitations of the Hubbard Hamiltonian.",
        "positive": "Periodically-driven cold atoms: the role of the phase: Numerous theoretical and experimental studies have investigated the dynamics\nof cold atoms subjected to time periodic fields. Novel effects dependent on the\namplitude and frequency of the driving field, such as Coherent Destruction of\nTunneling have been identified and observed. However, in the last year or so,\nthree distinct types of experiments have demonstrated for the first time,\ninteresting behaviour associated with the driving phase: i.e. for systems\nexperiencing a driving field of general form $V(x)\\sin (\\omega t + \\phi)$,\ndifferent types of large scale oscillations and directed motion were observed.\nWe investigate and explain the phenomenon of Super-Bloch Oscillations (SBOs) in\nrelation to the other experiments and address the role of initial phase in\ngeneral. We analyse and compare the role of $\\phi$ in systems with homogeneous\nforces ($V'(x)= const$), such as cold atoms in shaken or amplitude-modulated\noptical lattices, as well as non-homogeneous forces ($V'(x)\\neq const$), such\nas the sloshing of atoms in driven traps, and clarify the physical origin of\nthe different $\\phi$-dependent effects."
    },
    {
        "anchor": "Kohn-Sham theory of rotating dipolar Fermi gas in two dimensions: A two-dimensional dipolar Fermi gas in harmonic trap under rotation is\nstudied by solving \"ab initio\" Kohn-Sham equations. The physical parameters\nused match those of ultracold gas of fermionic $^{23}Na^{40}K$ molecules, a\nprototype system of strongly interacting dipolar quantum matter, which has been\ncreated very recently. We find that, as the critical rotational frequency is\napproached and the system collapses into the lowest Landau level, an array of\ntightly packed quantum vortices develops, in spite of the non-superfluid\ncharacter of the system. In this state the system looses axial symmetry, and\nthe fermionic cloud boundaries assume an almost perfect square shape. At higher\nvalues of the filling factor the vortex lattice disappears, while the system\nstill exhibits square-shaped boundaries. At lower values of the filling factor\nthe fermions become instead localized in a \"Wigner cluster\" structure.",
        "positive": "Path integral molecular dynamics for thermodynamics and Green's function\n  of ultracold spinor bosons: Most recently, the path integral molecular dynamics has been successfully\nused to consider the thermodynamics of single-component identical bosons and\nfermions. In this work, the path integral molecular dynamics is developed to\nsimulate the thermodynamics, Green's function and momentum distribution of\ntwo-component bosons in three dimensions. As an example of our general method,\nwe consider the thermodynamics of up to sixteen bosons in a three-dimensional\nharmonic trap. For noninteracting spinor bosons, our simulation shows a bump in\nthe heat capacity. As the repulsive interaction strength increases, however, we\nfind the gradual disappearance of the bump in the heat capacity. We believe\nthis simulation result can be tested by ultracold spinor bosons with optical\nlattices and magnetic-field Feshbach resonance to tune the inter-particle\ninteraction. We also calculate Green's function and momentum distribution of\nspinor bosons. Our work facilitates the exact numerical simulation of spinor\nbosons, whose property is one of the major problems in ultracold Bose gases."
    },
    {
        "anchor": "Tensor network simulation of the quantum Kibble-Zurek quench from the\n  Mott to superfluid phase in the two-dimensional Bose-Hubbard model: Quantum simulations of the Bose-Hubbard model (BHM) at commensurate filling\ncan follow spreading of correlations after a sudden quench for times long\nenough to estimate their propagation velocities. In this work we perform tensor\nnetwork simulation of the quantum Kibble-Zurek (KZ) ramp from the Mott towards\nthe superfluid phase in the square lattice BHM and demonstrate that even\nrelatively short ramp/quench times allow one to test the power laws predicted\nby the KZ mechanism (KZM). They can be verified for the correlation length and\nthe excitation energy but the most reliable test is based on the KZM scaling\nhypothesis for the single particle correlation function: the correlation\nfunctions for different quench times evaluated at the same scaled time collapse\nto the same scaling function of the scaled distance. The scaling of the space\nand time variables is done according to the KZ power laws.",
        "positive": "Damping of the quadrupole mode in a two-dimensional Fermi gas: In a recent experiment [E. Vogt et al., Phys. Rev. Lett. 108, 070404 (2012)],\nquadrupole and breathing modes of a two-dimensional Fermi gas were studied. We\nmodel these collective modes by solving the Boltzmann equation via the method\nof phase-space moments up to fourth order, including in-medium effects on the\nscattering cross section. In our analysis, we use a realistic Gaussian\npotential deformed by the presence of gravity and magnetic field gradients. We\nconclude that the origin of the experimentally observed damping of the\nquadrupole mode, especially in the weakly interacting (or even non-interacting)\ncase, cannot be explained by these mechanisms."
    },
    {
        "anchor": "Speed of sound in disordered Bose-Einstein condensates: Disorder modifies the sound-wave excitation spectrum of Bose-Einstein\ncondensates. We consider the classical hydrodynamic limit, where the disorder\ncorrelation length is much longer than the condensate healing length. By\nperturbation theory, we compute the phonon lifetime and correction to the speed\nof sound. This correction is found to be negative in all dimensions, with\nuniversal asymptotics for smooth correlations. Considering in detail optical\nspeckle potentials, we find a quite rich intermediate structure. This has\nconsequences for the average density of states, particularly in one dimension,\nwhere we find a \"boson dip\" next to a sharp \"boson peak\" as function of\nfrequency. In one dimension, our prediction is verified in detail by a\nnumerical integration of the Gross-Pitaevskii equation.",
        "positive": "Quantum Monte Carlo study of strongly interacting Fermi gases: In recent years Quantum Monte Carlo techniques provided to be a valuable tool\nto study strongly interacting Fermi gases at zero temperature. We have used QMC\nmethods to investigate several properties of the two-components Fermi gas at\nunitarity and in the BCS-BEC crossover, both with equal and unequal masses\ncorresponding to the $Li-K$ Fermi mixture. In this paper we present several\nrecent QMC results, including the energy at zero and finite effective range,\nthe contact parameter and the static structure factor, which, at low momentum,\ndepends strongly on the phonons in the unitary Fermi gas."
    },
    {
        "anchor": "Nematic-orbit coupling and nematic density waves in spin-1 condensates: We propose the creation of artificial nematic-orbit coupling in spin-1\nBose-Einstein condensates, in analogy to spin-orbit coupling. Using a suitably\ndesigned microwave chip, the quadratic Zeeman shift, normally uniform in space,\ncan be made to be spatio-temporally varying, leading to a coupling between\nspatial and nematic degrees of freedom. A phase diagram is explored where three\nquantum phases with the nematic order emerge: easy-axis, easy-plane with\nsingle-well and easy-plane with double well structure in momentum space. By\nincluding spin-dependent and spin-independent interactions, we also obtain the\nlow energy excitation spectra in these three phases. Lastly, we show that the\nnematic-orbit coupling leads to a periodic nematic density modulation in\nrelation to the period $\\lambda_T$ of the cosinusoidal quadratic Zeeman term.\nOur results point to the rich possibilities for manipulation of tensorial\ndegrees of freedom in ultracold gases without requiring Raman lasers, and\ntherefore, obviating light-scattering induced heating.",
        "positive": "Emergent Gauge Theory in Rydberg Atom Arrays: Rydberg atom arrays have emerged as a novel platform exhibiting rich quantum\nmany-body physics and offering promise for universal quantum computation. The\nRydberg blockade effect plays an essential role in establishing many-body\ncorrelations in this system. In this review, we will highlight that the lattice\ngauge theory is an efficient description of the Rydberg blockade effect and\noverview recent exciting developments in this system from equilibrium phases to\nquantum dynamics. These developments include realizing exotic ground states\nsuch as spin liquids, discovering quantum many-body scar states violating\nquantum thermalization, and observing confinement-deconfinement transition\nthrough quantum dynamics. We emphasize that the gauge theory description offers\na universal theoretical framework to capture all these phenomena. This\nperspective of Rydberg atom arrays will inspire further the future development\nof quantum simulation and quantum computation in this platform."
    },
    {
        "anchor": "Many-body state and dynamic behaviour of the pair-correlation function\n  of a small Bose-Einstein condensate confined in a ring potential: We investigate the many-body state and the static and the dynamic behaviour\nof the pair-correlation function of a Bose-Einstein condensate with a finite\natom number, which is confined in a quasi-one-dimensional toroidal/annular\npotential, both for repulsive, and for attractive interactions. We link the\ndynamic pair-correlation function that we evaluate with the problem of quantum\ntime crystals. For weak repulsive interatomic interactions and a finite number\nof atoms the pair-correlation function shows a periodic temporal behaviour,\nwhich disappears in the limit of a large atom number, in agreement with general\narguments. Finally we provide some insight into older results of attractive\ninteractions, where the time-crystalline behaviour exists only in the limit of\na large atom number.",
        "positive": "Nonadiabatic Diffraction of Matter Waves: Diffraction phenomena usually can be formulated in terms of a potential that\ninduces the redistribution of a wave's momentum. Using an atomic Bose-Einstein\ncondensate coupled to the orbitals of a state-selective optical lattice, we\ninvestigate a hitherto unexplored nonadiabatic regime of diffraction in which\nno diffracting potential can be defined, and in which the adiabatic dressed\nstates are strongly mixed. We show how, in the adiabatic limit, the observed\ncoupling between internal and external dynamics gives way to standard\nKapitza-Dirac diffraction of atomic matter waves. We demonstrate the utility of\nour scheme for atom interferometry and discuss prospects for studies of\ndissipative superfluid phenomena."
    },
    {
        "anchor": "Quantum Walk in Degenerate Spin Environments: We study the propagation of a hole in degenerate (paramagnetic) spin\nenvironments. This canonical problem has important connections to a number of\nphysical systems, and is perfectly suited for experimental realization with\nultra-cold atoms in an optical lattice. At the short-to-intermediate timescale\nthat we can access using a stochastic-series-type numeric scheme, the\npropagation turns out to be distinctly non-diffusive with the proba- bility\ndistribution featuring minima in both space and time due to quantum\ninterference, yet the motion is not ballistic, except at the beginning. We\ndiscuss possible scenarios for long-term evolution that could be explored with\nan unprecedented degree of detail in experiments with single-atom resolved\nimaging.",
        "positive": "On Solving Cubic-Quartic Nonlinear Schr\u00f6dinger Equation in a Cnoidal\n  Trap: The recent observations of quantum droplet in ultra-cold atomic gases have\nopened up new avenues of fundamental research. The competition between\nmean-field and beyond mean-field interactions, in ultra-cold dilute alkali\ngases, are believed to be instrumental in stabilizing the droplets. These new\nunderstanding has motivated us to investigate the analytical solutions of a\ntrapped cubic-quartic nonlinear Schr\\\"odinger equation (CQNLSE). The quartic\ncontribution in the NLSE is derived from the beyond mean-field formalism of\nBose-Einstein condensate (BEC). To the best of our knowledge, a comprehensive\nanalytical description of CQNLSE is non-existent. Here, we study the existence\nof the analytical solutions which are of the cnoidal type for CQNLSE. The\nexternal trapping plays a significant role in the stabilization of the system.\nIn the limiting case, the cnoidal wave solutions lead to the localized solution\nof bright solution and delocalized kink-antikink pair. The nonexistence of the\nsinusoidal mode in the current scheme is also revealed in our analysis."
    },
    {
        "anchor": "On the different Floquet Hamiltonians in a periodic-driven\n  Bose-Josephson junction: The bosonic Josephson junction, one of the maximally simple models for\nperiodic-driven many-body systems, has been intensively studied in the past two\ndecades. Here, we revisit this problem with five different methods, all of\nwhich have solid theoretical reasoning. We find that to the order of\n$\\omega^{-2}$ ($\\omega$ is the modulating frequency), these approaches will\nyield slightly different Floquet Hamiltonians. In particular, the parameters in\nthe Floquet Hamiltonians may be unchanged, increased, or decreased, depending\non the approximations used. Especially, some of the methods generate new\ninteractions, which still preserve the total number of particles; and the\nothers do not. The validity of these five effective models is verified using\ndynamics of population imbalance and self-trapping phase transition. In all\nresults, we find the method by first performing a unitary rotation to the\nHamiltonian will have the highest accuracy. The difference between them will\nbecome significate when the modulating frequency is comparable with the driving\namplitude. The results presented in this work indicate that the analysis of the\nFloquet Hamiltonian has some kind of subjectivity, which will become an\nimportant issue in future experiments with the increasing of precision. We\ndemonstrate this physics using a Bose-Josephson junction, and it is to be hoped\nthat the validity of these methods and their tiny differences put forward in\nthis work can be verified in realistic experiments in future using quantum\nsimulating platforms, including but not limited to ultracold atoms.",
        "positive": "Spin-polarized vortices with reversed circulation: We present the analysis of the structure of fermionic vortices with the\nspin-polarized core from a weak coupling limit to the unitary regime. We show\nthe mechanism for the generation of the {\\it reversed circulation} in the\nvortex core induced by an excess of majority spin particles. We introduce the\nclassification of the polarized vortices based on the number of Fermi circles\nwhere the minigap vanishes. This provides a unique description of the vortex as\none cannot smoothly map wave functions into one another corresponding to\nvortices differing by the number of Fermi circles. The effective mass of\nquasiparticles along the vortex core is analyzed and its role in the\npropagation of spin-polarization along the vortex line is discussed."
    },
    {
        "anchor": "Two-body recombination in a quantum mechanical lattice gas: Entropy\n  generation and probing of short-range magnetic correlations: We study entropy generation in a one-dimensional (1D) model of bosons in an\noptical lattice experiencing two-particle losses. Such heating is a major\nimpediment to observing exotic low temperature states, and \"simulating\"\ncondensed matter systems. Developing intuition through numerical simulations,\nwe present a simple empirical model for the entropy produced in this 1D\nsetting. We also explore the time evolution of one and two particle correlation\nfunctions, showing that they are robust against two-particle loss. Because of\nthis robustness, induced two-body losses can be used as a probe of short range\nmagnetic correlations.",
        "positive": "Shaping topological properties of the band structures in a shaken\n  optical lattice: To realize band structures with non-trivial topological properties in an\noptical lattice is an exciting topic in current studies on ultra cold atoms.\nHere we point out that this lofty goal can be achieved by using a simple scheme\nof shaking an optical lattice, which is directly applicable in current\nexperiments. The photon-assistant band hybridization leads to the production of\nan effective spin-orbit coupling, in which the band index represents the\npseudospin. When this spin-orbit coupling has finite strengths along multiple\ndirections, non-trivial topological structures emerge in the Brillouin zone,\nsuch as topological defects with a winding number 1 or 2 in a shaken square\nlattice. The shaken lattice also allows one to study the transition between two\nband structures with distinct topological properties."
    },
    {
        "anchor": "Confinement and precession of vortex pairs in coherently coupled\n  Bose-Einstein condensates: The dynamic behavior of vortex pairs in two-component coherently (Rabi)\ncoupled Bose-Einstein condensates is investigated in the presence of harmonic\ntrapping. We discuss the role of the surface tension associated with the domain\nwall connecting two vortices in condensates of atoms occupying different spin\nstates and its effect on the precession of the vortex pair. The results, based\non the numerical solution of the Gross-Pitaevskii equations, are compared with\nthe predictions of an analytical macroscopic model and are discussed as a\nfunction of the size of the pair, the Rabi coupling and the inter-component\ninteraction. We show that the increase of the Rabi coupling results in the\ndisintegration of the domain wall into smaller pieces, connecting vortices of\nnew-created vortex pairs. The resulting scenario is the analogue of quark\nconfinement and string breaking in quantum chromodynamics.",
        "positive": "Feshbach molecule formation through an oscillating magnetic field:\n  subharmonic resonances: The conversion of ultracold atoms to molecules via a magnetic Feshbach\nresonance with a sinusoidal modulation of the field is studied. Different\npractical realizations of this method in Bose atomic gases are analyzed. Our\nmodel incorporates many-body effects through an effective reduction of the\ncomplete microscopic dynamics. Moreover, we simulate the experimental\nconditions corresponding to the preparation of the system as a thermal gas and\nas a condensate. Some of the experimental findings are clarified. The origin of\nthe observed dependence of the production efficiency on the frequency,\namplitude, and application time of the magnetic modulation is elucidated. Our\nresults uncover also the role of the atomic density in the dynamics,\nspecifically, in the observed saturation of the atom-molecule conversion\nprocess."
    },
    {
        "anchor": "Four-Dimensional Quantum Hall Effect with Ultracold Atoms: We propose a realistic scheme to detect the 4D quantum Hall effect using\nultracold atoms. Based on contemporary technology, motion along a synthetic\nfourth dimension can be accomplished through controlled transitions between\ninternal states of atoms arranged in a 3D optical lattice. From a\nsemi-classical analysis, we identify the linear and non-linear quantized\ncurrent responses of our 4D model, relating these to the topology of the Bloch\nbands. We then propose experimental protocols, based on current or\ncenter-of-mass-drift measurements, to extract the topological 2nd Chern number.\nOur proposal sets the stage for the exploration of novel topological phases in\nhigher dimensions.",
        "positive": "Dissipationless flow in a Bose-Fermi mixture: Interacting mixtures of bosons and fermions are ubiquitous in nature. They\nform the backbone of the standard model of physics, provide a framework for\nunderstanding quantum materials such as unconventional superconductors and\ntwo-dimensional electronic systems, and are of technological importance in\n$^3$He/$^4$He dilution refrigerators. Bose-Fermi mixtures are predicted to\nexhibit an intricate phase diagram featuring coexisting liquids, supersolids,\ncomposite fermions, coupled superfluids, and quantum phase transitions in\nbetween. However, their coupled thermodynamics and collective behavior\nchallenge our understanding, in particular for strong boson-fermion\ninteractions. Clean realizations of fully controllable systems are scarce.\nUltracold atomic gases offer an ideal platform to experimentally investigate\nBose-Fermi mixtures, as the species concentration and interaction strengths can\nbe freely tuned. Here, we study the collective oscillations of a spin-polarized\nFermi gas immersed in a Bose-Einstein condensate (BEC) as a function of the\nboson-fermion interaction strength and temperature. Remarkably, for strong\ninterspecies interactions the fermionic collective excitations evolve to\nperfectly mimic the bosonic superfluid collective modes, and fermion flow\nbecomes dissipationless. With increasing number of thermal excitations in the\nBose gas, the fermions' dynamics exhibit a crossover from the collisionless to\nthe hydrodynamic regime, reminiscent of the emergence of hydrodynamics in\ntwo-dimensional electron fluids. Our findings open the door towards\nunderstanding non-equilibrium dynamics of strongly interacting Bose-Fermi\nmixtures."
    },
    {
        "anchor": "Universality and scaling in the $N$-body sector of Efimov physics: Universal behaviour has been found inside the window of Efimov physics for\nsystems with $N=4,5,6$ particles. Efimov physics refers to the emergence of a\nnumber of three-body states in systems of identical bosons interacting {\\it\nvia} a short-range interaction becoming infinite at the verge of binding two\nparticles. These Efimov states display a discrete scale invariance symmetry,\nwith the scaling factor independent of the microscopic interaction. Their\nenergies in the limit of zero-range interaction can be parametrized, as a\nfunction of the scattering length, by a universal function. We have found,\nusing a particular form of finite-range scaling, that the same universal\nfunction can be used to parametrize the energies of $N\\le6$ systems inside the\nEfimov-physics window. Moreover, we show that the same finite-scale analysis\nreconciles experimental measurements of three-body binding energies with the\nuniversal theory.",
        "positive": "Dynamical structure factor of a fermionic supersolid on an optical\n  lattice: Interfacing unbiased quantum Monte Carlo simulations with state-of-art\nanalytic continuation techniques, we obtain exact numerical results for\ndynamical density and spin correlations in the attractive Hubbard model,\ndescribing a spin-balanced two-dimensional cold Fermi gas on an optical\nlattice. We focus on half-filling, where on average one fermion occupies each\nlattice site, and the system displays an intriguing supersolid phase: a\nsuperfluid with a checkerboard density modulation. The coexistence of $U(1)$\nbroken symmetry and the density modulations makes this regime very challenging\nand interesting for the calculation of dynamical properties. We compare our\nunbiased results with state-of-the-art Generalized Random Phase Approximation\ncalculations: both approaches agree on a well-defined low-energy\nNambu-Goldstone collective mode in the density correlations, while the higher\nenergy structures appear to differ significantly. We also observe an\ninteresting high-energy spin mode. We argue that our results provide a robust\nbenchmark for Generalized Random Phase Approximation techniques, which are\nwidely considered to be the method of choice for dynamical correlations in\nFermi gases. Also, our calculations yield new physical insight in the\nhigh-energy behavior of the dynamical structure factor of the attractive\nHubbard model, which is a well known prototype lattice model for\nsuperconductors and is a fertile field to target the observation of collective\nmodes in strongly correlated systems."
    },
    {
        "anchor": "Engineering Photonic Floquet Hamiltonians through Fabry P\u00e9rot\n  Resonators: In this letter we analyze an optical Fabry-P\\'erot resonator as a\ntime-periodic driving of the (2D) optical field repeatedly traversing the\nresonator, uncovering that resonator twist produces a synthetic magnetic field\napplied to the light within the resonator, while mirror aberrations produce\nrelativistic dynamics, anharmonic trapping, and spacetime curvature. We develop\na Floquet formalism to compute the effective Hamiltonian for the 2D field,\ngeneralizing the idea that the intra-cavity optical field corresponds to an\nensemble of non-interacting, massive, harmonically trapped particles. This work\nilluminates the extraordinary potential of optical resonators for exploring the\nphysics of quantum fluids in gauge fields and exotic space-times.",
        "positive": "Amorphous quantum magnets in a two-dimensional Rydberg atom array: Amorphous solids, i.e., systems which feature well-defined short-range\nproperties but lack long-range order, constitute an important research topic in\ncondensed matter. While their microscopic structure is known to differ from\ntheir crystalline counterpart, there are still many open questions concerning\nthe emergent collective behavior in amorphous materials. This is particularly\nthe case in the quantum regime, where the numerical simulations are extremely\nchallenging. In this article, we instead propose to explore amorphous quantum\nmagnets with an analog quantum simulator. To this end, we first present an\nalgorithm to generate amorphous quantum magnets, suitable for Rydberg\nsimulators of the Ising model. Subsequently, we use semiclassical approaches to\nget a preliminary insight of the physics of the model. In particular, we\ncalculate mean-field phase diagrams, and use the linear-spin-wave theory to\nstudy localization properties and dynamical structure factors of the\nexcitations. Finally, we outline an experimental proposal based on Rydberg\natoms in programmable tweezer arrays, thus opening the road towards the study\nof amorphous quantum magnets in regimes difficult to simulate classically."
    },
    {
        "anchor": "Ferromagnetism in an extended coherently-coupled atomic superfluid: Ferromagnetism is an iconic example of a first-order phase transition taking\nplace in spatially extended systems and is characterized by hysteresis and the\nformation of domain walls. In this paper we demonstrate that an extended atomic\nsuperfluid in the presence of a coherent coupling between two internal states\nexhibits a quantum phase transition from a para- to a ferromagnetic state. The\nnature of the transition is experimentally assessed by looking at the phase\ndiagram as a function of the control parameters, at hysteresis phenomena, at\nthe magnetic susceptibility and the magnetization fluctuations around the\ncritical point. We show that the observed features are in good agreement with\nmean-field calculations. Additionally, we develop experimental protocols to\ndeterministically generate domain walls that separate spatial regions of\nopposite magnetization in the ferromagnetic state. Thanks to the enhanced\ncoherence properties of our atomic superfluid system compared to standard\ncondensed matter systems, our results open the way towards the study of\ndifferent aspects of the relaxation dynamics in isolated coherent many-body\nquantum systems.",
        "positive": "Repulsively diverging gradient of the density functional in the Reduced\n  Density Matrix Functional Theory: The Reduced Density Matrix Functional Theory (RDMFT) is a remarkable tool for\nstudying properties of ground states of strongly interacting quantum many body\nsystems. As it gives access to the one-particle reduced density matrix of the\nground state, it provides a perfectly tailored approach to studying the\nBose-Einstein condensation or systems of strongly correlated electrons. In\nparticular, for homogeneous Bose-Einstein condensates as well as for the\nBose-Hubbard dimer it has been recently shown that the relevant density\nfunctional exhibits a repulsive gradient (called the Bose-Einstein condensation\nforce) which diverges when the fraction of non-condensed bosons tends to zero.\nIn this paper, we show that the existence of the Bose-Einstein condensation\nforce is completely universal for any type of pair-interaction and also in the\nnon-homogeneous gases. To this end, we construct a universal family of\nvariational trial states which allows us to suitably approximate the relevant\ndensity functional in a finite region around the set of the completely\ncondensed states. We also show the existence of an analogous repulsive gradient\nin the fermionic RDMFT for the $N$-fermion singlet sector in the vicinity of\nthe set of the Hartree-Fock states. Finally, we show that our approximate\nfunctional may perform well in electron transfer calculations involving low\nnumbers of electrons. This is demonstrated numerically in the Fermi-Hubbard\nmodel in the strongly correlated limit where some other approximate functionals\nare known to fail."
    },
    {
        "anchor": "Lattice modulation spectroscopy of strongly interacting bosons in\n  disordered and quasi-periodic optical lattices: We compute the absorption spectrum of strongly repulsive one-dimensional\nbosons in a disordered or quasi-periodic optical lattice. At commensurate\nfilling, the particle-hole resonances of the Mott insulator are broadened as\nthe disorder strength is increased. In the non-commensurate case, mapping the\nproblem to the Anderson model allows us to study the Bose-glass phase.\nSurprisingly we find that a perturbative treatment in both cases, weak and\nstrong disorder, gives a good description at all frequencies. In particular we\nfind that the infrared absorption rate in the thermodynamic limit is quadratic\nin frequency. This result is unexpected, since for other quantities like the\nconductivity in one dimensional systems, perturbation theory is only applicable\nat high frequencies. We discuss applications to recent experiments on optical\nlattice systems, and in particular the effect of the harmonic trap.",
        "positive": "Creating artificial magnetic fields for cold atoms by photon-assisted\n  tunneling: This paper proposes a simple setup for introducing an artificial magnetic\nfield for neutral atoms in 2D optical lattices. This setup is based on the\nphenomenon of photon-assisted tunneling and involves a low-frequency periodic\ndriving of the optical lattice. This low-frequency driving does not affect the\nelectronic structure of the atom and can be easily realized by the same means\nwhich employed to create the lattice. We also address the problem of detecting\nthis effective magnetic field. In particular, we study the center of mass\nwave-packet dynamics, which is shown to exhibit certain features of cyclotron\ndynamics of a classical charged particle."
    },
    {
        "anchor": "Difference in Bose-Einstein condensation of conserved and unconserved\n  particles: The peculiarities in the Bose-Einstein condensation of particles and\nquasiparticles are discussed. The difference between the condensation of\nconserved and unconserved particles is analyzed. A classification of\nquasiparticles is given. The emphasis is made on the ability of particles and\nquasiparticles to condense. Illustrations include: general Bose-condensed\natomic systems, such as ensembles of trapped atoms, Bose gases with conserved\nand unconserved number of atoms, vibrating atoms in double-well lattices,\nHolstein-Primakoff magnons, Schwinger bosons, slave bosons, and the\ncondensation of singletons and triplons. The basic difference is that the\nsystem of particles, whose total number is conserved, can form equilibrium as\nwell as nonequilibrium condensates, while unconserved particles can condense\nonly in a nonequilibrium system subject to external pumping supporting the\ndensity of these particles sufficient for their condensation. The examples of\nsuch a nonequilibrium condensation of unconserved particles are the\nBose-Einstein condensation of excitons, polaritons, and photons. Elementary\ncollective excitations, such as bogolons and phonons, being self-consistently\ndefined, do not condense. Magnons cannot condense in equilibrium systems.\nControversies, existing in literature with regard to the Bose-Einstein\ncondensation of some quasiparticles, are explained. Pushing a system out of\nequilibrium may favor the condensation of unconserved quasiparticles, but\nsuppresses the condensate fraction of conserved particles.",
        "positive": "Magnetic phase transition in coherently coupled Bose gases in optical\n  lattices: We describe the ground state of a gas of bosonic atoms with two coherently\ncoupled internal levels in a deep optical lattice in a one dimensional\ngeometry. In the single-band approximation this system is described by a\nBose-Hubbard Hamiltonian. The system has a superfluid and a Mott insulating\nphase which can be either paramagnetic or ferromagnetic. We characterize the\nquantum phase transitions at unit filling by means of a density matrix\nrenormalization group technique and compare it with a mean-field approach. The\npresence of the ferromagnetic Ising-like transition modifies the Mott lobes. In\nthe Mott insulating region the system maps to the ferromagnetic spin-1/2 XXZ\nmodel in a transverse field and the numerical results compare very well with\nthe analytical results obtained from the spin model. In the superfluid regime\nquantum fluctuations strongly modify the phase transition with respect to the\nwell established mean-field three dimensional classical bifurcation."
    },
    {
        "anchor": "Lattice generalization of the Dirac equation to general spin and the\n  role of the flat band: We provide a novel setup for generalizing the two-dimensional pseudospin\nS=1/2 Dirac equation, arising in graphene's honeycomb lattice, to general\npseudospin-S. We engineer these band structures as a nearest-neighbor hopping\nHamiltonian involving stacked triangular lattices. We obtain multi-layered low\nenergy excitations around half-filling described by a two-dimensional Dirac\nequation of the form H=v_F S\\cdot p, where S represents an arbitrary spin-S\n(integer or half-integer). For integer-S, a flat band appears, whose presence\nmodifies qualitatively the response of the system. Among physical observables,\nthe density of states, the optical conductivity and the peculiarities of Klein\ntunneling are investigated. We also study Chern numbers as well as the\nzero-energy Landau level degeneracy. By changing the stacking pattern, the\ntopological properties are altered significantly, with no obvious analogue in\nmultilayer graphene stacks.",
        "positive": "Winding number dependence of Bose-Einstein condensates in a ring-shaped\n  lattice: We study the winding number dependence of the stationary states of a\nBose-Einstein condensate in a ring-shaped lattice. The system is obtained by\nconfining atoms in a toroidal trap with equally spaced radial barriers. We\ncalculate the energy and angular momentum as functions of the winding number\nand the barrier height for two quite distinct particle numbers. In both cases\nwe observe two clearly differentiated regimes. For low barriers, metastable\nvortex states are obtained up to a maximum winding number which depends on the\nparticle number and barrier height. In this regime, the angular momentum and\nenergy show, respectively, almost linear and quadratic dependences on the\nwinding number. For large barrier heights, on the other hand, stationary states\nare obtained up to a maximum winding number which depends only on the number of\nlattice sites, whereas energy and angular momentum are shown to be sinusoidal\nfunctions of the winding number."
    },
    {
        "anchor": "Solitons and soliton interactions in repulsive spinor Bose-Einstein\n  condensates with non-zero background: We characterize the soliton solutions and their interactions for a system of\ncoupled evolution equations of nonlinear Schr\\\"odinger (NLS) type that models\nthe dynamics in one-dimensional repulsive Bose-Einstein condensates with spin\none, taking advantage of the representation of such model as a special\nreduction of a 2 x 2 matrix NLS system. Specifically, we study in detail the\ncase in which solutions tend to a non-zero background at space infinities.\nFirst we derive a compact representation for the multi-soliton solutions in the\nsystem using the Inverse Scattering Transform (IST). We introduce the notion of\ncanonical form of a solution, corresponding to the case when the background is\nproportional to the identity. We show that solutions for which the asymptotic\nbehavior at infinity is not proportional to the identity, referred to as being\nin non-canonical form, can be reduced to canonical form by unitary\ntransformations that preserve the symmetric nature of the solution (physically\ncorresponding to complex rotations of the quantization axes). Then we give a\ncomplete characterization of the two families of one-soliton solutions arising\nin this problem, corresponding to ferromagnetic and to polar states of the\nsystem, and we discuss how the physical parameters of the solitons for each\nfamily are related to the spectral data in the IST. We also show that any\nferromagnetic one-soliton solution in canonical form can be reduced to a single\ndark soliton of the scalar NLS equation, and any polar one-soliton solution in\ncanonical form is unitarily equivalent to a pair of oppositely polarized\ndisplaced scalar dark solitons up to a rotation of the quantization axes.\nFinally, we discuss two-soliton interactions and we present a complete\nclassification of the possible scenarios that can arise depending on whether\neither soliton is of ferromagnetic or polar type.",
        "positive": "Spatially partitioned many-body vortices: A vortex in Bose-Einstein condensates is a localized object which looks much\nlike a tiny tornado storm. It is well described by mean-field theory. In the\npresent work we go beyond the current paradigm and introduce many-body\nvortices. These are made of {\\it spatially-partitioned} clouds, carry definite\ntotal angular momentum, and are fragmented rather than condensed objects which\ncan only be described beyond mean-field theory. A phase diagram based on a\nmean-field model assists in predicting the parameters where many-body vortices\noccur. Implications are briefly discussed."
    },
    {
        "anchor": "Dynamical Casimir Effect in dissipative media: When is the final state\n  non-separable ?: We study the consequences of dissipation in homogeneous media when the system\nis subject to a sudden change, thereby producing pairs of correlated\nquasi-particles with opposite momenta. We compute both the modifications of the\nspectrum, and those of the correlations. In particular, we compute the final\ncoherence level, and identify the regimes where the state is non-separable. To\nisolate the role of dissipation, we first consider dispersive media and study\nthe competition between the intensity of the jump which induces some coherence,\nand the temperature which reduces it. The contributions of stimulated and\nspontaneous emission are clearly identified. We then study how dissipation\nmodifies this competition.",
        "positive": "Universal Short-Distance Structure of the Single-Particle Spectral\n  Function of Dilute Fermi Gases: We show that the universal $1/k^4$ tail in the momentum distribution of\ndilute Fermi gases implies that the spectral function $A(\\kk,\\omega)$ must have\nweight below the chemical potential for large momentum $k \\gg k_F$, with\nobservable consequences in RF spectroscopy experiments. We find that this\nincoherent spectral weight is centered about $\\omega \\simeq - \\epsilon(\\kk)$ in\na range of energies of order $v_F k$. This \"bending back\" in the dispersion,\nwhile natural for superfluids, is quite surprising for normal gases. This\nuniversal structure is present in the hard-sphere gas as well as the Fermi\nliquid ground state of the highly imbalanced, attractive gas near unitarity. We\nargue that, even in the BCS superfluid, this bending back at large $k$ is\ndominated by interaction effects which do not reflect the pairing gap."
    },
    {
        "anchor": "Flavour-selective localization in interacting lattice fermions via SU(N)\n  symmetry breaking: A large repulsion between particles in a quantum system can lead to their\nlocalization, as it happens for the electrons in Mott insulating materials.\nThis paradigm has recently branched out into a new quantum state, the\norbital-selective Mott insulator, where electrons in some orbitals are\npredicted to localize, while others remain itinerant. We provide a direct\nexperimental realization of this phenomenon, that we extend to a more general\nflavour-selective localization. By using an atom-based quantum simulator, we\nengineer SU(3) Fermi-Hubbard models breaking their symmetry via a tunable\ncoupling between flavours, observing an enhancement of localization and the\nemergence of flavour-dependent correlations. Our realization of\nflavour-selective Mott physics opens the path to the quantum simulation of\nmulticomponent materials, from superconductors to topological insulators.",
        "positive": "A trapped single ion inside a Bose-Einstein condensate: Improved control of the motional and internal quantum states of ultracold\nneutral atoms and ions has opened intriguing possibilities for quantum\nsimulation and quantum computation. Many-body effects have been explored with\nhundreds of thousands of quantum-degenerate neutral atoms and coherent\nlight-matter interfaces have been built. Systems of single or a few trapped\nions have been used to demonstrate universal quantum computing algorithms and\nto detect variations of fundamental constants in precision atomic clocks. Until\nnow, atomic quantum gases and single trapped ions have been treated separately\nin experiments. Here we investigate whether they can be advantageously combined\ninto one hybrid system, by exploring the immersion of a single trapped ion into\na Bose-Einstein condensate of neutral atoms. We demonstrate independent control\nover the two components within the hybrid system, study the fundamental\ninteraction processes and observe sympathetic cooling of the single ion by the\ncondensate. Our experiment calls for further research into the possibility of\nusing this technique for the continuous cooling of quantum computers. We also\nanticipate that it will lead to explorations of entanglement in hybrid quantum\nsystems and to fundamental studies of the decoherence of a single, locally\ncontrolled impurity particle coupled to a quantum environment."
    },
    {
        "anchor": "Momentum-resolved radio-frequency spectroscopy of ultracold atomic Fermi\n  gases in a spin-orbit coupled lattice: We investigate theoretically momentum-resolved radio-frequency (rf)\nspectroscopy of a noninteracting atomic Fermi gas in a spin-orbit coupled\nlattice. This lattice configuration has been recently created at MIT [Cheuk et\nal., arXiv:1205.3483] for 6Li atoms, by coupling the two hyperfine spin-states\nwith a pair of Raman laser beams and additional rf coupling. Here, we show that\nmomentum-resolved rf spectroscopy can measure single-particle energies and\neigenstates and therefore resolve the band structure of the spin-orbit coupled\nlattice. In our calculations, we take into account the effects of temperatures\nand harmonic traps. Our predictions are to be confronted with future\nexperiments on spin-orbit coupled Fermi gases of 40K atoms in a lattice\npotential.",
        "positive": "Emergence of Topological and Strongly Correlated Ground States in\n  trapped Rashba Spin-Orbit Coupled Bose Gases: We theoretically study an interacting few-body system of Rashba spin-orbit\ncoupled two-component Bose gases confined in a harmonic trapping potential. We\nsolve the interacting Hamiltonian at large Rashba coupling strengths using\nExact Diagonalization scheme, and obtain the ground state phase diagram for a\nrange of interatomic interactions and particle numbers. At small particle\nnumbers, we observe that the bosons condense to an array of topological states\nwith n+1/2 quantum angular momentum vortex configurations, where n = 0, 1, 2,\n3... At large particle numbers, we observe two distinct regimes: at weaker\ninteraction strengths, we obtain ground states with topological and symmetry\nproperties that are consistent with mean-field theory computations; at stronger\ninteraction strengths, we report the emergence of strongly correlated ground\nstates."
    },
    {
        "anchor": "The transition and coexistence of quantum droplets and solitons in\n  quasi-1D dipolar Bose gas: In our study, we investigated bright solitons, dark solitons, and quantum\ndroplets in quasi-one-dimensional dipolar Bose gases, and further validated the\ncrossover and coexistence of quantum droplets and solitons using the\nLieb-Liniger energy within the framework of local density approximation.\nIncreasing the particle number N transforms the bright dipolar soliton state\ninto a stable self-bound quantum droplet state, with further increases in N\nleading to a broader quantum droplet that enables the presence of dark solitons\nwithin it.",
        "positive": "Finite-momentum superfluidity and phase transitions in a p-wave resonant\n  Bose gas: We study a degenerate two-species gas of bosonic atoms interacting through a\np-wave Feshbach resonance as for example realized in a Rb85-Rb87 mixture. We\nshow that in addition to a conventional atomic and a p-wave molecular spinor-1\nsuperfluidity at large positive and negative detunings, respectively, the\nsystem generically exhibits a finite momentum atomic-molecular superfluidity at\nintermediate detuning around the unitary point. We analyze the detailed nature\nof the corresponding phases and the associated quantum and thermal phase\ntransitions."
    },
    {
        "anchor": "Four fermions in a one-dimensional harmonic trap: Accuracy of a\n  variational-ansatz approach: Detailed analysis of the system of four interacting ultra-cold fermions\nconfined in a one-dimensional harmonic trap is performed. The analysis is done\nin the framework of a simple variational ansatz for the many-body ground state\nand its predictions are confronted with the results of numerically exact\ndiagonalization of the many-body Hamiltonian. Short discussion on the role of\nthe quantum statistics, i.e. Bose-Bose and Bose-Fermi mixtures is also\npresented. It is concluded that the variational ansatz, although seemed to be\noversimplified, gives surprisingly good predictions of many different\nquantities for mixtures of equal as well as different mass systems. The result\nmay have some experimental importance since it gives quite simple and validated\nmethod for describing experimental outputs.",
        "positive": "Dark soliton in quasi-one-dimensional Bose-Einstein condensates with a\n  Gaussian trap: In this paper we study dark solitons in quasi-one-dimensional Bose-Einstein\ncondensates (BECs) in presence of an anharmonic external potential. The\ntheoretical model is based on the Mu\\~noz-Mateo and Delgado (MMD) equation that\ndescribes cigar-shaped BECs with repulsive interatomic interactions. Since MMD\nequation presents a nonpolynomial form, the soliton-sound recombination cannot\ndisplay the same pattern presented in the cubic model. We perform numerical\nsimulations to compare both cases."
    },
    {
        "anchor": "Bose-Einstein condensation of paraxial light: Photons, due to the virtually vanishing photon-photon interaction, constitute\nto very good approximation an ideal Bose gas, but owing to the vanishing\nchemical potential a (free) photon gas does not show Bose-Einstein\ncondensation. However, this is not necessarily true for a lower-dimensional\nphoton gas. By means of a fluorescence induced thermalization process in an\noptical microcavity one can achieve a thermal photon gas with freely adjustable\nchemical potential. Experimentally, we have observed thermalization and\nsubsequently Bose-Einstein condensation of the photon gas at room temperature.\nIn this paper, we give a detailed description of the experiment, which is based\non a dye-filled optical microcavity, acting as a white-wall box for photons.\nThermalization is achieved in a photon number-conserving way by photon\nscattering off the dye molecules, and the cavity mirrors both provide an\neffective photon mass and a confining potential - key prerequisites for the\nBose-Einstein condensation of photons. The experimental results are in good\nagreement with both a statistical and a simple rate equation model, describing\nthe properties of the thermalized photon gas.",
        "positive": "Quantitative estimation of effective viscosity in quantum turbulence: We study freely decaying quantum turbulence by performing high resolution\nnumerical simulations of the Gross-Pitaevskii equation (GPE) in the\nTaylor-Green geometry. We use resolutions ranging from $1024^3$ to $4096^3$\ngrid points. The energy spectrum confirms the presence of both a Kolmogorov\nscaling range for scales larger than the intervortex scale $\\ell$, and a second\ninertial range for scales smaller than $\\ell$. Vortex line visualizations show\nthe existence of substructures formed by a myriad of small-scale knotted\nvortices. Next, we study finite temperature effects in the decay of quantum\nturbulence by using the stochastic Ginzburg-Landau equation to generate thermal\nstates, and then by evolving a combination of these thermal states with the\nTaylor-Green initial conditions using the GPE. We extract the mean free path\nout of these simulations by measuring the spectral broadening in the Bogoliubov\ndispersion relation obtained from spatio-temporal spectra, and use it to\nquantify the effective viscosity as a function of the temperature. Finally, in\norder to compare the decay of high temperature quantum and that of classical\nflows, and to further calibrate the estimations of viscosity from the mean free\npath in the GPE simulations, we perform low Reynolds number simulations of the\nNavier-Stokes equations."
    },
    {
        "anchor": "Long-lived universal resonant Bose gases: Quantum simulations based on near-resonance Bose gases are limited by their\nshort lifetimes due to severe atom losses. In addition to this, the recently\npredicted thermodynamical instability adds another constraint on accessing the\nresonant Bose gases. In this article, we offer a potential solution by\nproposing long-lived resonant Bose gases in both two and three dimensions,\nwhere the conventional few-body losses are strongly suppressed. We show that\nthe thermodynamical properties as well as the lifetimes of these strongly\ninteracting systems are universal, and independent of short-range physics.",
        "positive": "Dissipative dynamics of an impurity with spin-orbit coupling: Brownian motion of a mobile impurity in a bath is affected by spin-orbit\ncoupling (SOC). Here, we discuss a Caldeira-Leggett-type model that can be used\nto propose and interpret quantum simulators of this problem in cold Bose gases.\nFirst, we derive a master equation that describes the model and explore it in a\none-dimensional (1D) setting. To validate the standard assumptions needed for\nour derivation, we analyze available experimental data without SOC; as a\nbyproduct, this analysis suggests that the quench dynamics of the impurity is\nbeyond the 1D Bose-polaron approach at temperatures currently accessible in a\ncold-atom laboratory -- motion of the impurity is mainly driven by dissipation.\nFor systems with SOC, we demonstrate that 1D spin-orbit coupling can be 'gauged\nout' even in the presence of dissipation -- the information about SOC is\nincorporated in the initial conditions. Observables sensitive to this\ninformation (such as spin densities) can be used to study formation of steady\nspin polarization domains during quench dynamics."
    },
    {
        "anchor": "Squeezing the Efimov effect: The quantum mechanical three-body problem is a source of continuing interest\ndue to its complexity and not least due to the presence of fascinating solvable\ncases. The prime example is the Efimov effect where infinitely many bound\nstates of identical bosons can arise at the threshold where the two-body\nproblem has zero binding energy. An important aspect of the Efimov effect is\nthe effect of spatial dimensionality; it has been observed in three dimensional\nsystems, yet it is believed to be impossible in two dimensions. Using modern\nexperimental techniques, it is possible to engineer trap geometry and thus\naddress the intricate nature of quantum few-body physics as function of\ndimensionality. Here we present a framework for studying the three-body problem\nas one (continuously) changes the dimensionality of the system all the way from\nthree, through two, and down to a single dimension. This is done by considering\nthe Efimov favorable case of a mass-imbalanced system and with an external\nconfinement provided by a typical experimental case with a (deformed) harmonic\ntrap.",
        "positive": "Resonant two-site tunnelling dynamics of bosons in a tilted optical\n  superlattice: We study the non-equilibrium dynamics of a 1D Bose-Hubbard model in a\ngradient potential and a superlattice, beginning from a deep Mott insulator\nregime with an average filling of one particle per site. Studying a quench that\nis near resonance to tunnelling of the particles over two lattice sites, we\nshow how a spin model emerges consisting of two coupled Ising chains that are\ncoupled by interaction terms in a staggered geometry. We compare and contrast\nthe behavior in this case with that in a previously studied case where the\nresonant tunnelling was over a single site. Using optimized tensor network\ntechniques to calculate finite temperature behavior of the model, as well as\nfinite size scaling for the ground state, we conclude that the universality\nclass of the phase transition for the coupled chains is that of a tricritical\nIsing point. We also investigate the out-of-equilibrium dynamics after the\nquench in the vicinity of the resonance and compare dynamics with recent\nexperiments realized without the superlattice geometry. This model is directly\nrealizable in current experiments, and reflects a new general way to realize\nspin models with ultracold atoms in optical lattices."
    },
    {
        "anchor": "Sound propagation in a uniform superfluid two-dimensional Bose gas: In superfluid systems several sound modes can be excited, as for example\nfirst and second sound in liquid helium. Here, we excite propagating and\nstanding waves in a uniform two-dimensional Bose gas and we characterize the\npropagation of sound in both the superfluid and normal regime. In the\nsuperfluid phase, the measured speed of sound is well described by a two-fluid\nhydrodynamic model, and the weak damping rate is well explained by the\nscattering with thermal excitations. In the normal phase the sound becomes\nstrongly damped due to a departure from hydrodynamic behavior.",
        "positive": "Hubbard model for atomic impurities bound by the vortex lattice of a\n  rotating BEC: We investigate cold bosonic impurity atoms trapped in a vortex lattice formed\nby condensed bosons of another species. We describe the dynamics of the\nimpurities by a bosonic Hubbard model containing occupation-dependent\nparameters to capture the effects of strong impurity-impurity interactions.\nThese include both a repulsive direct interaction and an attractive effective\ninteraction mediated by the BEC. The occupation dependence of these two\ncompeting interactions drastically affects the Hubbard model phase diagram,\nincluding causing the disappearance of some Mott lobes"
    },
    {
        "anchor": "Producing superfluid circulation states using phase imprinting: We propose a method to prepare states of given quantized circulation in\nannular Bose-Einstein condensates (BEC) confined in a ring trap using the\nmethod of phase imprinting without relying on a two-photon angular momentum\ntransfer. The desired phase profile is imprinted on the atomic wave function\nusing a short light pulse with a tailored intensity pattern generated with a\nSpatial Light Modulator. We demonstrate the realization of 'helicoidal'\nintensity profiles suitable for this purpose. Due to the diffraction limit, the\ntheoretical steplike intensity profile is not achievable in practice. We\ninvestigate the effect of imprinting an intensity profile smoothed by a finite\noptical resolution onto the annular BEC with a numerical simulation of the\ntime-dependent Gross-Pitaevskii equation. This allows us to optimize the\nintensity pattern for a given target circulation to compensate for the limited\nresolution.",
        "positive": "Two-dimensional vortex quantum droplets get thick: We study two-dimensional (2D) vortex quantum droplets (QDs) trapped by a\nthicker transverse confinement with a>1um. Under this circumstance, the\nLee-Huang-Yang (LHY) term should be described by its original form in the\nthree-dimensional (3D) configuration. Previous studies have demonstrated that\nstable 2D vortex QDs can be supported by a thin transverse confinement with\na<<1um. In this case, the LHY term is described by a logarithm. Hence, two\nkinds of confinement features result in different mechanisms of the vortex QDs.\nThe stabilities and characteristics of the vortex QDs must be re-identified. In\nthe current system, we find that stable 2D vortex QDs can be supported with\ntopological charge number up to at least 4. We reformulated their density\nprofile, chemical potential and threshold norm for supporting the stable vortex\nQDs according to the new condition. Unlike the QDs under thin confinement, the\nQDs in the current system strongly repel each other because the LHY term\nfeatures a higher-order repulsion than that of the thin confinement system.\nMoreover, elastic and inelastic collisions between two moving vortex QDs are\nstudied throughout the paper. Two kinds of collisions can be characterized by\nexerting different values of related speed. The dynamics of the stable nested\nvortex QD, which is constructed by embedding one vortex QD with a smaller\ntopological number into another vortex QD with a larger number of topological\ncharge, can be supported by the system."
    },
    {
        "anchor": "Role of Nambu-Goldstone modes in the fermionic superfluid point contact: In fermionic superfluids that are charge neutral, Nambu-Goldstone (NG) modes\nalso known as Anderson-Bogoliubov modes emerge as a result of spontaneous\nsymmetry breaking. Here, we discuss DC transport properties of such NG modes\nthrough a quantum point contact. We show that contrary to a naive view that\nenhancement of the phase stiffness may suppress transport of the NG modes,\nthere must be an anomalous contribution that survives at low temperature. This\ncontribution originates from the conversion process between the condensate and\nNG mode. We find that within the BCS regime the anomalous contribution is\nenhanced with increasing channel transmittance and attractive interaction, and\nleads to a temperature-dependent Lorenz number and absence of the bunching\neffect in current noise.",
        "positive": "Spectral energy transport in two-dimensional quantum vortex dynamics: We explore the possible regimes of decaying two-dimensional quantum\nturbulence, and elucidate the nature of spectral energy transport by\nintroducing a dissipative point-vortex model with phenomenological vortex-sound\ninteractions. The model is valid for a large system with weak dissipation, and\nalso for systems with strong dissipation, and allows us to extract a meaningful\nand unambiguous spectral energy flux associated with quantum vortex motion. For\nweak dissipation and large system size we find a regime of hydrodynamic vortex\nturbulence in which energy is transported to large spatial scales, resembling\nthe phenomenology of the transient inverse cascade observed in decaying\nturbulence in classical incompressible fluids. For strong dissipation the\nvortex dynamics are dominated by dipole recombination and exhibit no\nappreciable spectral transport of energy."
    },
    {
        "anchor": "Dynamical depinning of a Tonks Girardeau gas: We study the dynamical depinning following a sudden turn off of an optical\nlattice for a gas of impenetrable bosons in a tight atomic waveguide. We use a\nBose-Fermi mapping to infer the exact quantum dynamical evolution. At long\ntimes, in the thermodynamic limit, we observe the approach to a non-equilibrium\nsteady state, characterized by the absence of quasi-long-range order and a\nreduced visibility in the momentum distribution. Similar features are found in\na finite-size system at times corresponding to half the revival time, where we\nfind that the system approaches a quasi-steady state with a power-law\nbehaviour.",
        "positive": "Condensation transition of ultracold Bose gases with Rashba spin-orbit\n  coupling: We study the Bose-Einstein condensate phase transition of three-dimensional\nultracold bosons with isotropic Rashba spin-orbit coupling. Investigating the\nstructure of Ginzburg-Landau free energy as a function of the condensate\ndensity, we show, within the Bogoliubov approximation, that the condensate\nphase transition is first order with a jump in the condensate density. We\ncalculate the transition temperature and the jump in the condensate density at\nthe transition for large spin-orbit coupling, where the transition temperature\ndepends linearly on the density of particles. Finally, we discuss the\nfeasibility of producing the phase transition experimentally."
    },
    {
        "anchor": "Extracting atoms one by one from a small matter-wave soliton: Excitations of small one-dimensional matter-wave solitons are considered\nwithin a framework of the attractive Bose-Hubbard model. The initial\neigenstates of the system are found by exact diagonalization of the\nBose-Hubbard Hamiltonian. We drive transitions between the eigenstates by\ninducing a weak modulation of the tunnelling rate and show that a single atom\ncan be extracted while the remaining atoms stay localized despite the\npersistent external modulation. This scheme suggests the experimental\nrealization of small matter-wave solitons with deterministic number of atoms.\nIn addition, the knowledge of exact eigenstates allows identification of the\nselection rules for transitions between the different eigenstates of the\nHamiltonian. One selection rule is related to the translation symmetry of the\nsystem. Another one is strictly applicable only on a subspace of the total\nHilbert space and is related to the parity symmetry. We show that in the\nstrongly interacting limit this selection rule has implications on the entire\nHilbert space. We discuss its signatures on the system's dynamics and consider\nhow it can be observed experimentally with ultracold atoms.",
        "positive": "Quantum Kibble-Zurek physics in the presence of spatially-correlated\n  dissipation: We study how universal properties of quantum quenches across critical points\nare modified by a weak coupling to thermal dissipation, focusing on the\nparadigmatic case of the transverse field Ising model. Beyond the standard\nquench-induced Kibble-Zurek defect production in the absence of the bath, the\nbath contributes extra thermal defects. We show that spatial correlations in\nthe noise produced by the bath can play a crucial role: one obtains\nquantitatively different scaling regimes depending on whether the correlation\nlength of the noise is smaller or larger than the Kibble-Zurek length\nassociated with the quench speed, and the thermal length set by temperature.\nFor the case of spatially-correlated bath noise, additional thermal defect\ngeneration is restricted to a window that is both quantum critical and excluded\nfrom the non-equilibrium regime surrounding the critical point. We map the\ndissipative quench problem to a set of effectively independent dissipative\nLandau-Zener problems. Using this mapping along with both analytic and\nnumerical calculations allows us to find the scaling of the excess defect\ndensity produced in the quench, and suggests a generic picture for such\ndissipative quenches."
    },
    {
        "anchor": "Correlations in low-dimensional quantum gases: Ultracold gases are a versatile platform to simulate condensed matter\nphysics, as virtually any parameter is experimentally tunable. In particular,\nhighly anisotropic traps allow the realization of low-dimensional systems,\nwhere the role of quantum fluctuations is enhanced. I investigate the\nparadigmatic model of a one-dimensional Bose gas with contact interactions,\na.k.a the Lieb-Liniger model, using powerful analytical tools such as Bethe\nAnsatz, Conformal Field Theory and the Tomonaga-Luttinger liquid formalism, as\nwell as the Bose-Fermi mapping. The effect of an additional harmonic trap in\nthe longitudinal direction is studied within the Local Density Approximation.\nThese methods allow to investigate with high accuracy its ground-state\nthermodynamics of the gas, its excitation spectra and correlation functions,\nfrom the k-body local correlations to the momentum distribution and the\ndynamical structure factor. These quantities characterize the coherence and\nsuperfluidity of the gas. In particular, I study the drag force exerted by a\nweak gaussian barrier stirred into the gas within linear response theory. Then,\nI investigate the appearance of a multimode structure obtained by releasing a\ntransverse trapping, and the dimensional crossover in the limit of an infinite\nnumber of transverse modes.",
        "positive": "Averaged collision and reaction rates in a two-species gas of ultracold\n  fermions: Reactive or elastic two-body collisions in an ultracold gas are affected by\nquantum statistics. In this paper, we study ensemble-averaged collision rates\nfor a two-species fermionic gas. The two species may have different masses,\ndensities and temperatures. We investigate how averaged collision rates are\naffected by the presence of Fermi spheres in the initial states; Pauli blocking\nof final states is not considered. It is shown that, independently on the\ndetails of the collision, Fermi-averaged collision rates deviate from\nBoltzmann-averaged ones, particularly for a gas with strong imbalance of masses\nor densities."
    },
    {
        "anchor": "Tunable non-reciprocal quantum transport through a dissipative\n  Aharonov-Bohm ring in ultracold atoms: We report the experimental observation of tunable, non-reciprocal quantum\ntransport of a Bose-Einstein condensate in a momentum lattice. By implementing\na dissipative Aharonov-Bohm (AB) ring in momentum space and sending atoms\nthrough it, we demonstrate a directional atom flow by measuring the momentum\ndistribution of the condensate at different times. While the dissipative AB\nring is characterized by the synthetic magnetic flux through the ring and the\nlaser-induced loss on it, both the propagation direction and transport rate of\nthe atom flow sensitively depend on these highly tunable parameters. We\ndemonstrate that the non-reciprocity originates from the interplay of the\nsynthetic magnetic flux and the laser-induced loss, which simultaneously breaks\nthe inversion and the time-reversal symmetries. Our results open up the avenue\nfor investigating non-reciprocal dynamics in cold atoms, and highlight the\ndissipative AB ring as a flexible building element for applications in quantum\nsimulation and quantum information.",
        "positive": "Probing the quantum ground state of a spin-1 Bose-Einstein condensate\n  with cavity transmission spectra: We propose to probe the quantum ground state of a spin-1 Bose-Einstein\ncondensate with the transmission spectra of an optical cavity. By choosing a\ncircularly polarized cavity mode with an appropriate frequency, we can realize\ncoupling between the cavity mode and the magnetization of the condensate. The\ncavity transmission spectra then contain information of the magnetization\nstatistics of the condensate and thus can be used to distinguish the\nferromagnetic and antiferromagnetic quantum ground states. This technique may\nalso be useful for continuous observation of the spin dynamics of a spinor\nBose-Einstein condensate."
    },
    {
        "anchor": "Dynamical quantum phase transition of a two-component Bose-Einstein\n  condensate in an optical lattice: We study dynamics of a two-component Bose-Einstein condensate where the two\ncomponents are coupled via an optical lattice. In particular, we focus on the\ndynamics as one drives the system through a critical point of a first order\nphase transition characterized by a jump in the internal populations. Solving\nthe time-dependent Gross-Pitaevskii equation, we analyze; breakdown of\nadiabaticity, impact of non-linear atom-atom scattering, and the role of a\nharmonic trapping potential. Our findings demonstrate that the phase transition\nis resilient to both contact interaction between atoms and external trapping\nconfinement.",
        "positive": "Quantum-torque-induced breaking of magnetic interfaces in ultracold\n  gases: A rich variety of physical effects in spin dynamics arises at the interface\nbetween different magnetic materials. Engineered systems with interlaced\nmagnetic structures have been used to implement spin transistors, memories and\nother spintronic devices. However, experiments in solid state systems can be\ndifficult to interpret because of disorder and losses. Here, we realize\nanalogues of magnetic junctions using a coherently-coupled mixture of ultracold\nbosonic gases. The spatial inhomogeneity of the atomic gas makes the system\nchange its behavior from regions with oscillating magnetization -- resembling a\nmagnetic material in the presence of an external transverse field -- to regions\nwith a defined magnetization, as in magnetic materials with a ferromagnetic\nanisotropy stronger than external fields. Starting from a far-from-equilibrium\nfully polarized state, magnetic interfaces rapidly form. At the interfaces, we\nobserve the formation of short-wavelength magnetic waves. They are generated by\na quantum torque contribution to the spin current and produce strong spatial\nanticorrelations in the magnetization. Our results establish ultracold gases as\na platform for the study of far-from-equilibrium spin dynamics in regimes that\nare not easily accessible in solid-state systems."
    },
    {
        "anchor": "Anderson-Bogoliubov collective excitations in superfluid Fermi gases at\n  nonzero temperatures: The Anderson-Bogoliubov branch of collective excitations in a condensed Fermi\ngas is treated using the effective bosonic action of Gaussian pair\nfluctuations. The spectra of collective excitations are treated for finite\ntemperature and momentum throughout the BCS-BEC crossover. The obtained spectra\nexplain, both qualitatively and quantitatively, recent experimental results on\nGoldstone modes in atomic Fermi superfluids.",
        "positive": "Intertwined and vestigial order with ultracold atoms in multiple cavity\n  modes: Atoms in transversely pumped optical cavities \"self-organize\" by forming a\ndensity wave and emitting superradiantly into the cavity mode(s). For a\nsingle-mode cavity, the properties of this self-organization transition are\nwell characterized both theoretically and experimentally. Here, we explore the\nself-organization of a Bose-Einstein condensate in the presence of two cavity\nmodes---a system that was recently experimentally realized [Leonard \\emph{et\nal.}, \\emph{Nature} {\\bf 543}, 87 (2017)]. We argue that this system can\nexhibit a \"vestigially ordered\" phase in which neither cavity mode exhibits\nsuperradiance but the cavity modes are mutually phase-locked by the atoms. We\nargue that this vestigially ordered phase should generically be present in\nmultimode cavity geometries."
    },
    {
        "anchor": "Chaos in the Bose-glass phase of a one-dimensional disordered Bose fluid: We show that the Bose-glass phase of a one-dimensional disordered Bose fluid\nexhibits a chaotic behavior, i.e., an extreme sensitivity to external\nparameters. Using bosonization, the replica formalism and the nonperturbative\nfunctional renormalization group, we find that the ground state is unstable to\nany modification of the disorder configuration (\"disorder\" chaos) or variation\nof the Luttinger parameter (\"quantum\" chaos, analog to the \"temperature\" chaos\nin classical disordered systems). This result is obtained by considering two\ncopies of the system, with slightly different disorder configurations or\nLuttinger parameters, and showing that inter-copy statistical correlations are\nsuppressed at length scales larger than an overlap length\n$\\xi_{\\mathrm{ov}}\\sim |\\epsilon|^{-1/\\alpha}$ ($|\\epsilon|\\ll 1$ is a measure\nof the difference between the disorder distributions or Luttinger parameters of\nthe two copies). The chaos exponent $\\alpha$ can be obtained by computing\n$\\xi_{\\mathrm{ov}}$ or by studying the instability of the Bose-glass fixed\npoint for the two-copy system when $\\epsilon\\neq 0$. The renormalized,\nfunctional, inter-copy disorder correlator departs from its fixed-point value\n-- characterized by cuspy singularities -- via a chaos boundary layer, in the\nsame way as it approaches the Bose-glass fixed point when $\\epsilon=0$ through\na quantum boundary layer. Performing a linear analysis of perturbations about\nthe Bose-glass fixed point, we find $\\alpha=1$.",
        "positive": "Phase separation and pattern formation in a binary Bose-Einstein\n  condensate: The miscibility-immiscibility phase transition in binary Bose-Einstein\ncondensates (BECs) can be controlled by a coupling between the two components.\nHere we propose a new scheme that uses coupling-induced pattern formation to\ntest the Kibble-Zurek mechanism (KZM) of topological-defect formation in a\nquantum phase transition. For a binary BEC in a ring trap we find that the\nnumber of domains forming the pattern scales with the coupling quench rate with\nan exponent as predicted by the KZM. For a binary BEC in an elongated harmonic\ntrap we find a different scaling law due to the transition being spatially\ninhomogeneous. We perform a \"simulation\" of the harmonically trapped system in\na ring trap to verify the scaling exponent."
    },
    {
        "anchor": "Dynamical thermalization of Bose-Einstein condensate in Bunimovich\n  stadium: We study numerically the wavefunction evolution of a Bose-Einstein condensate\nin a Bunimovich stadium billiard being governed by the Gross-Pitaevskii\nequation. We show that for a moderate nonlinearity, above a certain threshold,\nthere is emergence of dynamical thermalization which leads to the Bose-Einstein\nprobability distribution over the linear eigenmodes of the stadium. This\ndistribution is drastically different from the energy equipartition over\noscillator degrees of freedom which would lead to the ultra-violet catastrophe.\nWe argue that this interesting phenomenon can be studied in cold atom\nexperiments.",
        "positive": "Emergence of pairing glue in repulsive Fermi gases with soft-core\n  interactions: Recent quantum gas experiments are ushering in an era of fine-tailored\ntwo-body interactions. These include for example atoms with long-range\ndipole-dipole interactions and Rydberg-dressed atoms created by optical\ncoupling to highly excited electronic states. These systems differ from the\n``canonical system\" of cold atoms with contact interactions characterized by a\nsingle parameter, the scattering length. Inspired by these experiments with\ncontrollable atomic interactions, here we consider a model many-body system of\nspinless Fermi gas in two dimensions, where the bare two-body interaction takes\nthe form of a soft-core disk potential. We show that the repulsive interaction\ncan drive the system to a series of nontrivial superfluid states with higher\npartial wave paring, for example in the $f$- and $h$-wave channels instead of\nthe $p$-wave channel. The zero temperature phase diagram is obtained by\nnumerical functional renormalization group (FRG), which goes beyond leading\norder perturbation theory and retains the interaction vertices in all channels.\nWe also carry out a perturbative analysis which is justified in the dilute\nlimit and show that the second order Kohn-Luttinger diagrams provide a\nqualitative understanding of the onsets of the various superfluid phases. The\nperturbative arguments however fail to capture the quantitative phase\nboundaries predicted by FRG. Our findings illustrate that the shape of the bare\natomic interaction matters in producing the pairing glue in repulsive Fermi\ngases, and tuning the interaction potential offers a promising route to realize\nexotic many-body phases in cold atomic gases."
    },
    {
        "anchor": "Anisotropic 2D diffusive expansion of ultra-cold atoms in a disordered\n  potential: We study the horizontal expansion of vertically confined ultra-cold atoms in\nthe presence of disorder. Vertical confinement allows us to realize a situation\nwith a few coupled harmonic oscillator quantum states. The disordered potential\nis created by an optical speckle at an angle of 30{\\deg} with respect to the\nhorizontal plane, resulting in an effective anisotropy of the correlation\nlengths of a factor of 2 in that plane. We observe diffusion leading to\nnon-Gaussian density profiles. Diffusion coefficients, extracted from the\nexperimental results, show anisotropy and strong energy dependence, in\nagreement with numerical calculations.",
        "positive": "Symmetry classification of spin-orbit coupled spinor Bose-Einstein\n  condensates: We develop a symmetry classification scheme to find ground states of pseudo\nspin-1/2, spin-1, and spin-2 spin-orbit coupled spinor Bose-Einstein\ncondensates, and show that as the SO(2) symmetry of simultaneous spin and space\nrotations is broken into discrete cyclic groups, various types of lattice\nstructures emerge in the absence of a lattice potential, examples include two\ndifferent kagaome lattices for pseudo spin-1/2 condensates and a nematic vortex\nlattice in which uniaxial and biaxial spin textures align alternatively for\nspin-2 condensates. For the pseudo spin-1/2 system, although mean-field states\nalways break time-reversal symmetry, there exists a time-reversal invariant\nmany-body ground state, which is fragmented and expected to be observed in a\nmicro-condensate."
    },
    {
        "anchor": "Extracting Lyapunov exponents from the echo dynamics of Bose-Einstein\n  condensates on a lattice: We propose theoretically an experimentally realizable method to demonstrate\nthe Lyapunov instability and to extract the value of the largest Lyapunov\nexponent for a chaotic many-particle interacting system. The proposal focuses\nspecifically on a lattice of coupled Bose-Einstein condensates in the classical\nregime describable by the discrete Gross-Pitaevskii equation. We suggest to use\nimperfect time-reversal of system's dynamics known as Loschmidt echo, which can\nbe realized experimentally by reversing the sign of the Hamiltonian of the\nsystem. The routine involves tracking and then subtracting the noise of\nvirtually any observable quantity before and after the time-reversal. We\nsupport the theoretical analysis by direct numerical simulations demonstrating\nthat the largest Lyapunov exponent can indeed be extracted from the Loschmidt\necho routine. We also discuss possible values of experimental parameters\nrequired for implementing this proposal.",
        "positive": "Loss of Conformality in Efimov Physics: The loss of conformal invariance in Efimov physics is due to the merger and\ndisappearance of an infrared and an ultraviolet fixed point of a three-body\nrenormalization group flow as the spatial dimension $d$ is varied. In the case\nof identical bosons at unitarity, it is known that there are two critical\ndimensions $d_{\\rm 1}=2.30$ and $d_{\\rm 2}=3.76$ at which there is loss of\nconformality. For $d<d_{\\rm 1}$ and $d>d_{\\rm 2}$, the beta function of the\nthree-body coupling has real roots which correspond to infrared and ultraviolet\nfixed points. The fixed points merge and disappear into the complex plane at\nthe critical dimensions $d_1$ and $d_2$. For $d_{\\rm 1}<d<d_{\\rm 2}$, the beta\nfunction has complex roots and the renormalization group flow for the\nthree-body coupling constant is a limit cycle."
    },
    {
        "anchor": "Programmable Quantum Annealing Architectures with Ising Quantum Wires: Quantum annealing aims at solving optimization problems efficiently by\npreparing the ground state of an Ising spin-Hamiltonian quantum mechanically. A\nprerequisite of building a quantum annealer is the implementation of\nprogrammable long-range two-, three- or multi-spin Ising interactions. We\ndiscuss an architecture, where the required spin interactions are implemented\nvia two-port, or in general multi-port quantum Ising wires connecting the spins\nof interest. This quantum annealing architecture of spins connected by Ising\nquantum wires can be realized by exploiting the three dimensional (3D)\ncharacter of atomic platforms, including atoms in optical lattices and Rydberg\ntweezer arrays. The realization only requires engineering on-site terms and\ntwo-body interactions between nearest neighboring qubits. The locally coupled\nspin model on a 3D cubic lattice is sufficient to effectively produce arbitrary\nall-to-all coupled Ising Hamiltonians. We illustrate the approach for few spin\ndevices solving Max-Cut and prime factorization problems, and discuss the\npotential scaling to large atom based systems.",
        "positive": "Yang monopoles and emergent three-dimensional topological defects in\n  interacting bosons: Yang monopole as a zero-dimensional topological defect has been well\nestablished in multiple fields in physics. However, it remains an intriguing\nquestion to understand interaction effects on Yang monopoles. Here, we show\nthat collective motions of many interacting bosons give rise to exotic\ntopological defects that are distinct from Yang monopoles seen by a single\nparticle. Whereas interactions may distribute Yang monopoles in the parameter\nspace or glue them to a single giant one of multiple charges, three-dimensional\ntopological defects also arise from continuous manifolds of degenerate\nmany-body eigenstates. Their projections in lower dimensions lead to knotted\nnodal lines and nodal rings. Our results suggest that ultracold bosonic atoms\ncan be used to create emergent topological defects and directly measure\ntopological invariant that are not easy to access in solids."
    },
    {
        "anchor": "Two-dimensional miscible-immiscible supersolid and droplet crystal state\n  in a homonuclear dipolar bosonic mixture: The recent realization of binary dipolar BEC [Phys. Rev. Lett. 121, 213601\n(2018)] opens new exciting aspects for studying quantum droplets and\nsupersolids in a binary mixture. Motivated by this experiment, we study\ngroundstate phases and dynamics of a Dy-Dy mixture. Dipolar bosonic mixture\nexhibits qualitatively novel and rich physics. Relying on the three-dimensional\nnumerical simulations in the extended Gross-Pitaevskii framework, we unravel\nthe groundstate phase diagrams and characterize different groundstate phases.\nThe emergent phases include both miscible and immiscible single droplet (SD),\nmultiple droplets (MD), supersolid (SS), and superfluid (SF) states. More\nintriguing mixed groundstates may occur for an imbalanced binary mixture,\nincluding a combination of SS-SF, SS-MD, and SS-SS phases. We observed the\ndynamical transition from a miscible MD state to an immiscible MD state with\nmultiple domains formed along the axial direction by tuning the inter-species\nscattering length. Also by linear quenches of intra-species scattering lengths\nacross the aforementioned phases, we monitor the dynamical formation of\nsupersolid clusters and droplet lattices. Although we have demonstrated the\nresults for a Dy-Dy mixture and for a specific parameter range of intra-species\nand inter-species scattering lengths, our results are generally valid for other\ndipolar mixtures and may become an important benchmark for future experimental\nscenarios.",
        "positive": "Comparative study for two-terminal transport through a lossy\n  one-dimensional quantum wire: Motivated by realization of the dissipative quantum point contact in\nultracold atomic gases, we investigate a two-terminal mesoscopic transport\nsystem in which a single-particle loss is locally present in a one-dimensional\nchain. By means of the Dyson equation approach in the Keldysh formalism that\ncan incorporate dissipative effects, we reveal analytic structures of the\nparticle and energy currents whose formal expressions correspond to ones in\ncertain three-terminal systems where the particle loss is absent. The obtained\nformulas are also consistent with non-hermitian and three-terminal\nLandauer-B\\\"{u}ttiiker analyses. The universality on the current expressions\nholds regardless of quantum statistics and may be useful for understanding\nlossy two-terminal transport in terms of three-terminal transport and vice\nversa."
    },
    {
        "anchor": "Thermal Phase transitions in attractive extended Bose-Hubbard Model with\n  three-body constraint: By means of quantum Monte Carlo simulations implemented with a two-loop\nupdate scheme, the finite-temperature phase diagram of a three-body constrained\nattractive Bose lattice gas is investigated. The nature of the thermal phase\ntransitions around the dimer superfluid and the atomic superfluid is unveiled.\nWe find that the $Z_2$ symmetry-breaking transitions between these two\nsuperfluid phases are of first order even at nonzero temperatures. More\ninterestingly, the thermal transition from the dimer superfluid to the normal\nfluid is found to be consistent with the Kosterlitz-Thouless type but giving an\nanomalous universal stiffness jump. It demonstrates that this transition is\ndriven by unbinding of pairs of fractional vortices.",
        "positive": "Energy and condensate dynamics of a Bose-Einstein condensate excited by\n  a moving red laser potential inside a power law trap cutoff by box potential\n  hard walls: We explore the energy dynamics of a two dimensional (2D) trapped\nBose-Einstein condensate (BEC) excited by a moving red-detuned laser potential\n(RDLP). The trap is a combination of a power-law (PL) potential cutoff by a\nhard-wall box potential (HWBP). It is found that by a restricted measurment of\nthe energy within the boundaries of the HWBP, the energy demonstrates\noscillations indicative of solitons. It is then demonstrated, that the geometry\nof the PL potential influences the lifetime of these oscillations, i.e., the\nlifetime of the ensuing solitons inside the HWBP. We argue that the energy\ndynamics in this setup are a good tool for measuring their lifetime. It is also\nfound, that the condensate density dynamics display oscillatory patterns of a\nmagnitude and order controlled by the velocity of the RDLP. A connection to\noscillations in the chemical potential dynamics is also discussed. Essentially,\nwe suggest future experiments for this kind of setup, which would measure the\nphonon energy dynamics to trace the lifetime of solitons."
    },
    {
        "anchor": "Measure synchronization in a two-species bosonic Josephson junction: Measure synchronization (MS) in a two-species bosonic Josephson junction\n(BJJ) is studied based on semi-classical theory. Six different scenarios for\nMS, including two in the Josephson oscillation regime (0 phase mode) and four\nin the self-trapping regime ($\\pi$ phase mode), have been clearly shown.\nSystematic investigations of the common features behind these different\nscenarios have been performed. We show that the average energies of the two\nspecies merge at the MS transition point. The scaling of the power law near the\nMS transition has been verified, and the critical exponent is 1/2 for all of\nthe different scenarios for MS. We also illustrate MS in a three-dimensional\nphase space; from this illustration, more detailed information on the dynamical\nprocess can be obtained. Particularly, by analyzing the Poincare sections with\nchanging interspecies interactions, we find that the two-species BJJ exhibits\nseparatrix crossing behavior at MS transition point, and such behavior depicts\nthe general mechanism behind the different scenarios for the MS transitions.\nThe new critical behavior found in a two-species BJJ is expected to be found in\nreal systems of atomic Bose gases.",
        "positive": "Reentrant stability of BEC standing wave patterns: We describe standing wave patterns induced by an attractive finite-ranged\nexternal potential inside a large Bose-Einstein Condensate (BEC). As the\npotential depth increases, the time independent Gross-Pitaevskii equation\ndevelops pairs of solutions that have nodes in their wavefunction. We elucidate\nthe nature of these states and study their dynamical stability. Although we\nstudy the problem in a two-dimensional BEC subject to a cylindrically symmetric\nsquare-well potential of a radius that is comparable to the coherence length of\nthe BEC, our analysis reveals general trends, valid in two and three\ndimensions, independent of the symmetry of the localized potential well, and\nsuggestive of the behavior in general, short- and large-range potentials. One\nset of nodal BEC wavefunctions resembles the single particle n node bound state\nwavefunction of the potential well, the other wavefunctions resemble the n-1\nnode bound-state wavefunction with a kink state pinned by the potential. The\nsecond state, though corresponding to the lower free energy value of the pair\nof n node BEC states, is always unstable, whereas the first can be dynamically\nstable in intervals of the potential well depth, implying that the standing\nwave BEC can evolve from a dynamically unstable to stable, and back to unstable\nstatus as the potential well is adiabatically deepened, a phenomenon that we\nrefer to as \"reentrant dynamical stability\"."
    },
    {
        "anchor": "Phase-separation of vector solitons in spin-orbit coupled spin-1\n  condensates: We study the phase-separation in three-component bright vector solitons in a\nquasi-one-dimensional spin-orbit-coupled hyper-fine spin $F=1$ ferromagnetic\nBose-Einstein condensate upon an increase of the strength of spin-orbit (SO)\ncoupling $p_x \\Sigma_z$ above a critical value, where $p_x$ is the linear\nmomentum and $\\Sigma_z$ is the $z$-component of the spin-1 matrix. The bright\nvector solitons are demonstrated to be mobile and dynamically stable. The\ncollision between two such vector solitons is found to be elastic at all\nvelocities with the conservation of density of each vector soliton. The two\ncolliding vector solitons repel at small separation and at very small colliding\nvelocity, they come close and bounce back with the same velocity without ever\nencountering each other. This repulsion produced by SO coupling is responsible\nfor the phase separation in a vector soliton for large strengths of SO\ncoupling. { The collision dynamics is found to be completely insensitive to the\nrelative phase of the colliding solitons.} However, in the absence of SO\ncoupling, at very small velocity, the two colliding vector solitons attract\neach other and form a vector soliton molecule and the collision dynamics is\nsensitive to the relative phase as in scalar solitons. The present\ninvestigation is carried out through a numerical solution and an analytic\nvariational approximation of the underlying mean-field Gross-Pitaevskii\nequation.",
        "positive": "Engineering Dissipative Quasicrystals: We discuss the systematic engineering of quasicrystals in open quantum\nsystems where quasiperiodicity is introduced through purely dissipative\nprocesses. While the resulting short-time dynamics is governed by non-Hermitian\nvariants of the Aubry-Andre-Harper model, we demonstrate how phases and phase\ntransitions pertaining to the non-Hermitian quasicrystals fundamentally change\nthe long-time, steady-state-approaching dynamics under the Lindblad master\nequation. Our schemes are based on an exact mapping between the eigenspectrum\nof the Liouvillian superoperator with that of the non-Hermitian Hamiltonian,\nunder the condition of quadratic fermionic systems subject to linear\ndissipation. Our work suggests a systematic route toward engineering exotic\nquantum dynamics in open systems, based on insights of non-Hermitian physics."
    },
    {
        "anchor": "Excitation band topology and edge matter waves in Bose-Einstein\n  condensates in optical lattices: We show that Bose-Einstein condensates in optical lattices with broken\ntime-reversal symmetry can support chiral edge modes originating from\nnontrivial bulk excitation band topology. To be specific, we analyze a\nBose-Hubbard extension of the Haldane model, which can be realized with\nrecently developed techniques of manipulating honeycomb optical lattices. The\ntopological properties of Bloch bands known for the noninteracting case are\nsmoothly carried over to Bogoliubov excitation bands for the interacting case.\nWe show that the parameter ranges that display topological bands enlarge with\nincreasing the Hubbard interaction or the particle density. In the presence of\nsharp boundaries, chiral edge modes appear in the gap between topological\nexcitation bands. We demonstrate that by coherently transferring a portion of a\ncondensate into an edge mode, a density wave is formed along the edge owing to\nan interference with the background condensate. This offers a unique method of\ndetecting an edge mode through a macroscopic quantum phenomenon.",
        "positive": "Quantum droplets of bosonic mixtures in a one-dimensional optical\n  lattice: We demonstrate the existence of quantum droplets in two-component\none-dimensional Bose-Hubbard chains. The droplets exist for any strength of\nrepulsive intra-species interactions provided they are balanced by comparable\nattractive inter-species interactions. The ground-state phase diagram is\npresented and the different phases are characterized by examining the density\nprofile and off-diagonal one- and two-body correlation functions. A rich\nvariety of phases is found, including atomic superfluid gases, atomic\nsuperfluid droplets, pair superfluid droplets, pair superfluid gases and a\nMott-insulator phase. A parameter region prone to be experimentally explored is\nidentified, where the average population per site is lower than three atoms,\nthus avoiding three-body losses. Finally, the bipartite entanglement of the\ndroplets is found to have a non-trivial dependence on the number of particles."
    },
    {
        "anchor": "Finite temperature contact for SU(2) fermions trapped in a 1D harmonic\n  confinement: We calculate the finite-temperature Tan's contact for N SU(2) fermions,\ncharacterized by repulsive contact interaction, trapped in a 1D harmonic\nconfinement within a local density approximation on top of a thermodynamic\nBethe Ansatz. The Tan's contact for such a system, as in the homogeneous case,\ndisplays a minimum at a very low temperature. By means of an exact canonical\nensemble calculation for two fermions, we provide an explicit formula for the\ncontact at very low temperatures that reveals that the minimum is due to the\nmixing of states with different exchange symmetries. In the unitary regime,\nthis symmetry blending corresponds to a maximal entanglement entropy.",
        "positive": "Temporal Talbot interferometer of strongly interacting molecular\n  Bose-Einstein condensate: Talbot interferometer, as a periodic reproduction of momentum distribution in\nthe time domain, finds significant applications in multiple research. The\ninter-particle interactions during the diffraction and interference process\nintroduce numerous many-body physics problems, leading to unconventional\ninterference characteristics. This work investigates both experimentally and\ntheoretically the influence of interaction in a Talbot interferometer with a\n$^{6}\\rm Li_2$ molecular Bose-Einstein condensate in a one-dimensional optical\nlattice, with interaction strength directly tunable via magnetic Feshbach\nresonance. A clear dependence of the period and amplitude of signal revivals on\nthe interaction strength can be observed. While interactions increase the decay\nrate of the signal and advance the revivals, we find that over a wide range of\ninteractions, the Talbot interferometer remains highly effective over a certain\nevolutionary timescale, including the case of fractional Talbot interference.\nThis work provides insight into the interplay between interaction and the\ncoherence properties of a temporal Talbot interference in optical lattices,\npaving the way for research into quantum interference in strongly interacting\nsystems."
    },
    {
        "anchor": "Minimizing nonadiabaticities in optical-lattice loading: In the quest to reach lower temperatures of ultra-cold gases in optical\nlattice experiments, non-adiabaticites during lattice loading are one of the\nlimiting factors that prevent the same low temperatures to be reached as in\nexperiments without lattice. Simulating the loading of a bosonic quantum gas\ninto a one-dimensional optical lattice with and without a trap, we find that\nthe redistribution of atomic density inside a global confining potential is by\nfar the dominant source of heating. Based on these results we propose to adjust\nthe trapping potential during loading to minimize changes to the density\ndistribution. Our simulations confirm that a very simple linear interpolation\nof the trapping potential during loading already significantly decreases the\nheating of a quantum gas and we discuss how loading protocols minimizing\ndensity redistributions can be designed.",
        "positive": "Energy and contact of the one-dimensional Fermi polaron at zero and\n  finite temperature: We use the T-matrix approach for studying highly polarized homogeneous Fermi\ngases in one dimension with repulsive or attractive contact interactions. Using\nthis approach, we compute ground state energies and values for the contact\nparameter that show excellent agreement with exact and other numerical methods\nat zero temperature, even in the strongly interacting regime. Furthermore, we\nderive an exact expression for the value of the contact parameter in one\ndimension at zero temperature. The model is then extended and used for studying\nthe temperature dependence of ground state energies and the contact parameter."
    },
    {
        "anchor": "Measuring the equation of state of trapped ultracold bosonic systems in\n  an optical lattice with in-situ density imaging: We analyze quantitatively how imaging techniques with single-site resolution\nallow to measure thermodynamical properties that cannot be inferred from\ntime-of-light images for the trapped Bose-Hubbard model. If the normal state\nextends over a sufficiently large range, the chemical potential and the\ntemperature can be extracted from a single shot, provided the sample is in\nthermodynamic equilibrium. When the normal state is too narrow, temperature is\nlow but can still be extracted using the fluctuation-dissipation theorem over\nthe entire trap range as long as the local density approximation remains valid,\nas was recently suggested by Qi Zhou and Tin-Lun Ho [arXiv:0908.3015]. However,\nfor typical present-day experiments, the number of samples needed is of the\norder of 1000 in order to get the temperature at least $10 \\%$ accurate, but it\nis possible to reduce the variance by 2 orders of magnitude if the\ndensity-density correlation length is short, which is the case for the\nBose-Hubbard model. Our results provide further evidence that cold gases in an\noptical lattices can be viewed as quantum analog computers.",
        "positive": "Quantum Simulation of Competing Orders with Fermions in Quantum Optical\n  Lattices: Ultracold Fermi atoms confined in optical lattices coupled to quantized modes\nof an optical cavity are an ideal scenario to engineer quantum simulators in\nthe strongly interacting regime. The system has both short range and cavity\ninduced long range interactions. We propose such a scheme to investigate the\ncoexistence of superfluid pairing, density order and quantum domains having an-\ntiferromagnetic or density order in the Hubbard model in a high finesse optical\ncavity at T = 0. We demonstrate that those phases can be accessed by properly\ntuning the linear polarizer of an external pump beam via the cavity back-action\neffect, while modulating the system doping. This allows emulate the typical\nscenarios of analog strongly correlated electronic systems."
    },
    {
        "anchor": "Mott Insulator-Density Ordered Superfluid Transition and \"Shamrock\n  Transition\" in a Frustrated Triangle Lattice: Density order is usually a consequence of the competition between long-range\nand short-range interactions. Here we report a density ordered superfluid\nemergent from a homogeneous Mott insulator due to the competition between\nfrustrations and local interactions. This transition is found in a Bose-Hubbard\nmodel on a frustrated triangle lattice with an extra pairing term. Further, we\nfind a quantum phase transition between two different density ordered\nsuperfluids, which is beyond the Landau-Ginzburg paradigm. Across this\ntransition, a U(1) symmetry is emergent, while the symmetry in each density\nordered superfluid is Z2*Z3. Because there emerges a shamrock-like degenerate\nground state in parameter space, we call the transition \"shamrock transition\".\nEffective low energy theories are established for the two transitions mentioned\nabove and we find their resemblance and differences with clock models.",
        "positive": "Ultralong-range order in the Fermi-Hubbard model with long-range\n  interactions: We use the dual boson approach to reveal the phase diagram of the\nFermi-Hubbard model with long-range dipole-dipole interactions. By using a\nlarge-scale finite-temperature calculation on a $64 \\times 64$ square lattice\nwe demonstrate the existence of a novel phase, possessing an `ultralong-range'\norder. The fingerprint of this phase -- the density correlation function --\nfeatures a non-trivial behavior on a scale of tens of the lattice sites. We\nstudy the properties and the stability of the ultralong-range ordered phase,\nand show that it is accessible in modern experiments with ultracold polar\nmolecules and magnetic atoms."
    },
    {
        "anchor": "BCS-BEC crossover of Spin Polarized Fermi Gases with Rashba Spin-Orbit\n  Coupling: We study the BCS-Bose Einstein Condensation (BEC) crossover of a three\ndimensional spin polarized Fermi gas with Rashba spin-orbital-coupling (SOC).\nAt finite temperature, the effects of non-condensed pairs due to the thermal\nexcitation are considered based on the $G_0G$ pair fluctuation theory. These\nfluctuations generate a pseudogap even persistent above $T_c$. Within this\nframework, the Sarma state or the spin polarized superfluid state and polarized\npseudogap state are explored in detail. The resulting $T_c$ curves show that\nthe enhancement of pairing due to the SOC roughly cancels out the suppression\nof pairing due to the population imbalance. Thus we observed that in a large\nportion of the parameter space, the polarized superfluid state are stabilized\nby the SOC.",
        "positive": "Non-Fermi liquid fixed point for an imbalanced gas of fermions in\n  $1+\u03b5$ dimensions: We consider a gas of two species of fermions with population imbalance. Using\nthe renormalization group in $d=1+\\epsilon$ dimensions, we show that for\nspinless fermions and $\\epsilon > 0$ a fixed point appears at finite attractive\ncoupling where the quasiparticle residue vanishes, and identify this with the\ntransition to Larkin--Ovchinnikov--Fulde--Ferrell order (inhomogeneous\nsuperconductivity). When the two species of fermions also carry spin degrees of\nfreedom we find a fixed point indicating a transition to spin density wave\norder."
    },
    {
        "anchor": "Sticking Transition in a Minimal Model for the Collisions of Active\n  Particles in Quantum Fluids: Particles of low velocity, travelling without dissipation in a superfluid,\ncan interact and emit sound when they collide. We propose a minimal model in\nwhich the equations of motion of the particles, including a short-range\nrepulsive force, are self-consistently coupled with the Gross-Pitaevskii\nequation. We use this model to demonstrate the existence of an effective\nsuperfluid-mediated attractive interaction between the particles; and we study\nnumerically the collisional dynamics of particles as a function of their\nincident kinetic energy and the length-scale of the repulsive force. We find a\ntransition from almost elastic to completely inelastic (sticking) collisions as\nthe parameters are tuned. We find that aggregation and clustering result from\nthis sticking transition in multi-particle systems.",
        "positive": "Bosonic and fermionic dipoles on a ring: We show that dipolar bosons and fermions confined in a quasi-one-dimensional\nring trap exhibit a rich variety of states because their interaction is\ninhomogeneous. For purely repulsive interactions, with increasing strength of\nthe dipolar coupling there is a crossover from a gas-like state to an\ninhomogeneous crystal-like one. For small enough angles between the dipoles and\nthe plane of the ring, there are regions with attractive interactions, and\nclustered states can form."
    },
    {
        "anchor": "Vortex rings and vortex ring solitons in shaken Bose-Einstein condensate: In a shaken Bose-Einstein condensate, confined in a vibrating trap, there can\nappear different nonlinear coherent modes. Here we concentrate on two types of\nsuch coherent modes, vortex ring solitons and vortex rings. In a cylindrical\ntrap, vortex ring solitons can be characterized as nonlinear Hermite-Laguerre\nmodes, whose description can be done by means of optimized perturbation theory.\nThe energy, required for creating vortex ring solitons, is larger than that\nneeded for forming vortex rings. This is why, at a moderate excitation energy,\nvortex rings appear before vortex ring solitons. The generation of vortex rings\nis illustrated by numerical simulations for trapped $^{87}$Rb atoms.",
        "positive": "Two dispersion curves for a one-dimensional interacting Bose gas under\n  zero boundary conditions: The influence of boundaries and non-point character of interatomic\ninteraction on the dispersion law has been studied for a uniform Bose gas in a\none-dimensional vessel. The non-point character of interaction was taken into\naccount using the Gross equation, which is more general than the\nGross-Pitaevskii one. In the framework of this approach, the well-known\nBogolyubov dispersion mode \\hbar\\omega(k)=[(\\hbar^{2}k^{2}/2m)\n^{2}+qn\\nu(k)\\hbar^{2}k^{2}/m]^{1/2} (q=1) was obtained, as well as a new one,\nwhich is described by the same formula, but with q= 1/2. The new mode emerges\nowing to the account of boundaries and the non-point character of interaction:\nthis mode is absent when either the Gross equation for a cyclic system or the\nGross-Pitaevskii equation for a cyclic system or a system with boundaries is\nsolved. Capabilities for the new mode to be observed are discussed."
    },
    {
        "anchor": "Stability of $(N+1)$-body fermion clusters in multiband Hubbard model: We start with a variational approach and derive a set of coupled integral\nequations for the bound states of $N$ identical spin-$\\uparrow$ fermions and a\nsingle spin-$\\downarrow$ fermion in a generic multiband Hubbard Hamiltonian\nwith an attractive onsite interaction. As an illustration we apply our integral\nequations to the one-dimensional sawtooth lattice up to $N \\le 3$, i.e., to the\n$(3+1)$-body problem, and reveal not only the presence of tetramer states in\nthis two-band model but also their quasi-flat dispersion when formed in a flat\nband. Furthermore, for $N = \\{4, 5, \\cdots, 10 \\}$, our DMRG simulations and\nexact diagonalization suggest the presence of larger and larger multimers with\nlower and lower binding energies, conceivably without an upper bound on $N$.\nThese peculiar $(N+1)$-body clusters are in sharp contrast with the exact\nresults on the single-band linear-chain model where none of the $N \\ge 2$\nmultimers appear. Hence their presence must be taken into account for a proper\ndescription of the many-body phenomena in flat-band systems, e.g., they may\nsuppress superconductivity especially when there exists a large spin imbalance.",
        "positive": "Momentum distribution and non-local high order correlation functions of\n  1D strongly interacting Bose gas: The Lieb-Liniger model is a prototypical integrable model and has been turned\ninto the benchmark physics in theoretical and numerical investigations of low\ndimensional quantum systems.\n  In this note, we present various methods for calculating local and nonlocal\n$M$-particle correlation functions, momentum distribution and static structure\nfactor. In particular, using the Bethe ansatz wave function of the strong\ncoupling Lieb-Liniger model, we analytically calculate two-point correlation\nfunction, the large moment tail of momentum distribution and static structure\nfactor of the model in terms of the fractional statistical parameter $\\alpha\n=1-2/\\gamma$, where $\\gamma$ is the dimensionless interaction strength. We also\ndiscuss the Tan's adiabatic relation and other universal relations for the\nstrongly repulsive Lieb-Liniger model in term of the fractional statistical\nparameter."
    },
    {
        "anchor": "Observation of topological Bloch-state defects and their merging\n  transition: Topological defects in Bloch bands, such as Dirac points in graphene, and\ntheir resulting Berry phases play an important role for the electronic dynamics\nin solid state crystals. Such defects can arise in systems with a two-atomic\nbasis due to the momentum-dependent coupling of the two sublattice states,\nwhich gives rise to a pseudo-spin texture. The topological defects appear as\nvortices in the azimuthal phase of this pseudo-spin texture. Here, we\ndemonstrate a complete measurement of the azimuthal phase in a hexagonal\noptical lattice employing a versatile method based on time-of-flight imaging\nafter off-resonant lattice modulation. Furthermore we map out the merging\ntransition of the two Dirac points induced by beam imbalance. Our work paves\nthe way to accessing geometric properties in optical lattices also with\nspin-orbit coupling and interactions.",
        "positive": "Strings of ultracold molecules in a synthetic dimension: We consider ultracold polar molecules trapped in a unit-filled\none-dimensional chain in real space created with an optical lattice or a\ntweezer array and illuminated by microwaves that resonantly drive transitions\nwithin a chain of rotational states. We describe the system by a\ntwo-dimensional lattice model, with the first dimension being a lattice in real\nspace and the second dimension being a lattice in a synthetic direction\ncomposed of rotational states. We calculate this system's ground-state phase\ndiagram. We show that as the dipole interaction strength is increased, the\nmolecules undergo a phase transition from a two-dimensional gas to a phase in\nwhich the molecules bind together and form a string that resembles a\none-dimensional object living in the two-dimensional (i.e, one real and one\nsynthetic dimensional) space. We demonstrate this with two complementary\ntechniques: numerical calculations using matrix product state techniques and an\nanalytic solution in the limit of infinitely strong dipole interaction. Our\ncalculations reveal that the string phase at infinite interaction is\neffectively described by emergent particles living on the string and that this\nleads to a rich spectrum with excitations missed in earlier mean-field\ntreatments."
    },
    {
        "anchor": "Dynamics of Bose-Einstein Recondensation in Higher Bands: Motivated by recent experiments, we explore the kinetics of Bose-Einstein\ncondensation in the upper band of a double well optical lattice. These\nexperiments engineer a non-equilibrium situation in which the highest energy\nstate in the band is macroscopically occupied. The system subsequently relaxes\nand the condensate moves to the lowest energy state. We model this process,\nfinding that the kinetics occurs in three phases: The condensate first\nevaporates, forming a highly non-equilibrium gas with no phase coherence.\nEnergy is then redistributed among the noncondensed atoms. Finally the atoms\nrecondense. We calculate the time-scales for each of these phases, and explain\nhow this scenario can be verified through future experiments.",
        "positive": "Exposing the quantum geometry of spin-orbit coupled Fermi superfluids: The coupling between a quantum particle's intrinsic angular momentum and its\ncenter-of-mass motion gives rise to the so-called helicity states that are\ncharacterized by the projection of the spin onto the direction of momentum. In\nthis paper, by unfolding the superfluid-density tensor into its intra-helicity\nand inter-helicity components, we reveal that the latter contribution is\ndirectly linked with the total quantum metric of the helicity bands. We\nconsider both Rashba and Weyl spin-orbit couplings across the BCS-BEC\ncrossover, and show that the geometrical inter-helicity contribution is\nresponsible for up to a quarter of the total superfluid density. We believe\nthis is one of those elusive effects that may be measured within the\nhighly-tunable realm of cold Fermi gases."
    },
    {
        "anchor": "Brownian motion of solitons in a Bose-Einstein Condensate: For the first time, we observed and controlled the Brownian motion of\nsolitons. We launched solitonic excitations in highly elongated $^{87}\\rm{Rb}$\nBECs and showed that a dilute background of impurity atoms in a different\ninternal state dramatically affects the soliton. With no impurities and in\none-dimension (1-D), these solitons would have an infinite lifetime, a\nconsequence of integrability. In our experiment, the added impurities scatter\noff the much larger soliton, contributing to its Brownian motion and decreasing\nits lifetime. We describe the soliton's diffusive behavior using a quasi-1-D\nscattering theory of impurity atoms interacting with a soliton, giving\ndiffusion coefficients consistent with experiment.",
        "positive": "Universality in modelling non-equilibrium pattern formation in polariton\n  condensates: The key to understanding the universal behaviour of systems driven away from\nequilibrium lies in the common description obtained when particular microscopic\nmodels are reduced to order parameter equations. Universal order parameter\nequations written for complex matter fields are widely used to describe systems\nas different as Bose-Einstein condensates of ultra cold atomic gases, thermal\nconvection, nematic liquid crystals, lasers and other nonlinear systems.\nExciton-polariton condensates recently realised in semiconductor microcavities\nare pattern forming systems that lie somewhere between equilibrium\nBose-Einstein condensates and lasers. Because of the imperfect confinement of\nthe photon component, exciton-polaritons have a finite lifetime, and have to be\ncontinuously re-populated. As photon confinement improves, the system more\nclosely approximates an equilibrium system. In this chapter we review a number\nof universal equations which describe various regimes of the dynamics of\nexciton-polariton condensates: the Gross-Pitaevskii equation, which models\nweakly interacting equilibrium condensates, the complex Ginsburg-Landau\nequation---the universal equation that describes the behaviour of systems in\nthe vicinity of a symmetry--breaking instability, and the complex\nSwift-Hohenberg equation that in comparison with the complex Ginsburg-Landau\nequation contains additional nonlocal terms responsible for spacial mode\nselection. All these equations can be derived asymptotically from a generic\nlaser model given by Maxwell-Bloch equations. Such an universal framework\nallows the unified treatment of various systems and continuously cross from one\nsystem to another. We discuss the relevance of these equations, and their\nconsequences for pattern formation."
    },
    {
        "anchor": "Orbital-FFLO state in a chain of high spin ultracold atoms: Recent experiments with Yb-173 and Sr-87 isotopes provide new possibilities\nto study high spin two-orbital systems. Within these experiments part of the\natoms are excited to a higher energy metastable electronic state mimicking an\nadditional internal (orbital) degree of freedom. The interaction between the\natoms depends on the orbital states, therefore four different scattering\nchannels can be identified in the system characterized by four independent\ncouplings. When the system is confined into a one-dimensional chain the\nscattering lengths can be tuned by changing the transverse confinement, and\ndriven through four resonances. Using the new available experimental data of\nthe scattering lengths we analyze the phase diagram of the one-dimensional\nsystem as the couplings are tuned via transverse confinement, and the\npopulations of the two orbital states are changed. We found that three orders\ncompete showing power law decay: a state with dominant density wave\nfluctuations, another one with spin density fluctuations, and a third one\ncharacterized by exotic Fulde-Ferrell-Larkin-Ovchinnikov-like pairs consisting\none atom in the electronic ground state and one in the excited state. We also\nshow that sufficiently close to the resonances the compressibility of the\nsystem starts to diverge indicating that the emerging order is unstable and\ncollapses to a phase separated state with a first order phase transition.",
        "positive": "Controlling Transport of Ultra-Cold Atoms in 1D Optical Lattices with\n  Artificial Gauge Fields: We show that the recently developed optical lattices with Peierls\nsubstitution -- which can be modeled as a lattice with a complex tunneling\ncoefficient -- may be used to induce controllable quantum transport of\nultra-cold atoms. In particular, we show that by ramping up the phase of the\ncomplex tunneling coefficient in a spatially uniform fashion, a finite quasi\nsteady-state current (QSSC) ensues from the exact dynamics of non-interacting\nfermions. The direction and magnitude of the current can be controlled by the\noverall phase difference but not the details of the ramp. The entanglement\nentropy does not increase when the QSSC lasts. Due to different spin\nstatistics, condensed non-interacting bosons do not support a finite QSSC under\nthe same setup. We also find that an approximate form of the QSSC survives when\nperturbative effects from interactions, weak harmonic background traps, and\nfinite-temperature are present, which suggests that our findings should be\nobservable with available experimental capabilities."
    },
    {
        "anchor": "Topologically protected vortex knots and links: We propose a class of tangled vortex structures, tied from non-Abelian\ntopological vortices, which are immune against decaying through local\nreconnections and strand crossings that are allowed by the system. We refer to\nsuch structures as being topologically protected. We then turn our attention to\ntopological vortices classified by the quaternion group $Q_8$ ($Q_8$-colored\nlinks), which are realizable in systems consisting either of the biaxial\nnematic or the cyclic phase of a spin-2 Bose--Einstein condensate, or of\nbiaxial nematic liquid crystal, and prove the existence of topologically\nprotected $Q_8$-colored links. Remarkably, the strongest invariant we\nconstruct, the $Q$-invariant of $Q_8$-colored links, can be used to classify\n$Q_8$-colored links up to allowed local surgeries on the vortex cores.",
        "positive": "Universality of the three-body Efimov parameter at narrow Feshbach\n  resonances: We measure the critical scattering length for the appearance of the first\nthree-body bound state, or Efimov three-body parameter, at seven different\nFeshbach resonances in ultracold 39K atoms. We study both intermediate and\nnarrow resonances, where the three-body spectrum is expected to be determined\nby the non-universal coupling of two scattering channels. We observe instead\napproximately the same universal relation of the three-body parameter with the\ntwo-body van der Waals radius already found for broader resonances, which can\nbe modeled with a single channel. This unexpected observation suggests the\npresence of a new regime for three-body scattering at narrow resonances."
    },
    {
        "anchor": "Enhancement of super-exchange pairing in the periodically-driven Hubbard\n  model: Recent experiments performed on cuprates and alkali-doped fullerides have\ndemonstated that key signatures of superconductivity can be induced above the\nequilibrium critical temperature by optical modulation. These observations in\ndisparate physical systems may indicate a general underlying mechanism.\nMultiple theories have been proposed, but these either consider specific\nfeatures, such as competing instabilities, or focus on conventional BCS-type\nsuperconductivity. Here we show that periodic driving can enhance electron\npairing in strongly-correlated systems. Focusing on the strongly-repulsive\nlimit of the doped Hubbard model, we investigate in-gap, spatially\ninhomogeneous, on-site modulations. We demonstrate that such modulations\nsubstantially reduce electronic hopping, while simultaneously sustaining\nsuper-exchange interactions and pair hopping via driving-induced virtual charge\nexcitations. We calculate real-time dynamics for the one-dimensional case,\nstarting from zero and finite temperature initial states, and show that\nenhanced singlet--pair correlations emerge quickly and robustly in the\nout-of-equilibrium many-body state. Our results reveal a fundamental pairing\nmechanism that might underpin optically induced superconductivity in some\nstrongly correlated quantum materials.",
        "positive": "Orbital ordering of ultracold alkaline-earth atoms in optical lattices: We report on a dynamical mean-field theoretical analysis of emerging\nlow-temperature phases in multicomponent gases of fermionic\nalkaline-earth(-like) atoms in state-dependent optical lattices. Using the\nexample of $^{173}$Yb atoms, we show that a two-orbital mixture with two\nnuclear spin components is a promising candidate for studies of not only\nmagnetic but also staggered orbital ordering peculiar to certain solid-state\nmaterials. We calculate and study the phase diagram of the full Hamiltonian\nwith parameters similar to existing experiments and reveal an antiferroorbital\nphase. This long-range-ordered phase is inherently stable, and we analyze the\nchange of local and global observables across the corresponding transition\nlines, paving the way for experimental observations. Furthermore, we suggest a\nrealistic extension of the system to include and probe a Jahn-Teller source\nfield playing one of the key roles in real crystals."
    },
    {
        "anchor": "Defect-Driven Superfluid Crossover for Two-Dimensional Dipolar Excitons\n  Trapped at Thermodynamic Equilibrium: We study ultra-cold dipolar excitons confined in a 10$\\mu$m trap of a double\nGaAs quantum well. Based on the local density approximation, we unveil for the\nfirst time the equation of state of excitons at pure thermodynamic equilibrium.\nIn this regime we show that, below a critical temperature of about $1$ Kelvin,\na superfluid forms in the inner region of the trap at a local exciton density\n$n \\sim 2-3 \\, 10^{10} \\text{cm}^{-2}$, encircled by a more dilute and normal\ncomponent in the outer rim of the trap. Remarkably, this spatial arrangement\ncorrelates directly with the concentration of defects in the exciton density\nwhich exhibits a sudden decrease at the onset of superfluidity, thus pointing\ntowards an underlying Berezinskii-Kosterlitz-Thouless mechanism.",
        "positive": "Cooperative phase transitions in the system of photons and dye molecules: Bose condensed light can form new phases [1] in a dye filled cavity due to\nthe presence of the orientational disorder created by dye molecules which are\nessentially frozen on the time scale of the photonic thermalization (few ps).\nAt longer times (few ns) molecular degrees of freedom -- orientations and\npositions -- become important. Including them on equal footing with photons can\nchange the nature of the photonic condensation -- it can proceed as Ist order\nphase transition which can also result in the mutual phase separation effect --\nfor photons and dye. The analysis is conducted within the mean field approach\nin the thermodynamic limit. Recommendations for the experimental detection of\nthe transition nature are formulated."
    },
    {
        "anchor": "Spectral intensity distribution of trapped fermions: To calculate static response properties of a many body system, local density\napproximation (LDA) can be safely applied. But applicability of LDA is limited\nfor the case of dynamical response functions since dynamics of the system needs\nto be considered as well. To examine this in the context of cold atoms, we\nconsider a system of non-interacting spin-$1/2$ fermions confined by a harmonic\ntrapping potential. We have calculated a very important response function, the\nspectral intensity distribution function (SIDF), both exactly and using LDA at\nzero temperature and compared with each other for different dimensions, trap\nfrequencies and momenta. The behavior of the SIDF at a particular momentum can\nbe explained by noting the behavior of the density of states (DOS) of the free\nsystem (without trap) in that particular dimension. The agreement between exact\nand LDA SIDFs becomes better with increase in dimensions and number of\nparticles.",
        "positive": "Aharonov-Bohm effect for confined matter in lattice gauge theories: Gauge theories arise in physical systems displaying space-time local\nsymmetries. They provide a powerful description of important realms of physics\nranging from fundamental interactions, to statistical mechanics, condensed\nmatter and more recently quantum computation. As such, a remarkably deep\nunderstanding has been achieved in the field. With the advent of quantum\ntechnology, lower energy analogs, capable to capture important features of the\noriginal quantum field theories through quantum simulation, have been\nintensively studied. Here, we propose a specific scheme implementing an\nanalogic quantum simulation of lattice gauge theories constrained to mesoscopic\nspatial scales. To this end, we study the dynamics of mesons residing in a\nring-shaped lattice of mesoscopic size pierced by an effective magnetic field.\nIn particular, we find a new type of Aharonov-Bohm effect that goes beyond the\nparticle-like effect and reflecting the the features of the confining gauge\npotential. The coherence properties of the meson are quantified by the\npersistent current and by specific features of the correlation functions. When\nthe magnetic field is quenched, Aharonov-Bohm oscillations and correlations\nstart a specific matter-wave current dynamics."
    },
    {
        "anchor": "Asymmetric Conductivity of the Kondo Effect in Cold Atomic Systems: Motivated by recent theoretical and experimental advances in quantum\nsimulations using alkaline earth(AE) atoms, we put forward a proposal to detect\nthe Kondo physics in a cold atomic system. It has been demonstrated that the\nintrinsic spin-exchange interaction in AE atoms can be significantly enhanced\nnear a confinement-induced resonance(CIR), which facilitates the simulation of\nKondo physics. Since the Kondo effect appears only for antiferromagnetic\ncoupling, we find that the conductivity of such a system exhibits an asymmetry\nacross a resonance of spin-exchange interaction. The asymmetric conductivity\ncan serve as the smoking gun evidence for Kondo physics in the cold atom\ncontext. When an extra magnetic field ramps up, the spin-exchange process near\nthe Fermi surface is suppressed by Zeeman energy and the conductivity becomes\nmore and more symmetric. Our results can be verified in the current\nexperimental setup.",
        "positive": "Interaction-Induced Dimensional Crossover through Full 3D to 1D: The exploration of dimensional crossover carries profound fundamental\nsignificance, serving as a crucial bridge in comprehending the remarkable\ndisparities observed in transitional phenomena across the two distinct\ndimensions of a physical system. The prevalent strategy for manipulating the\ndimensionality involves meticulously controlling the external trapping\ngeometry, thereby restricting the degrees of freedom of the kinetic energy from\nthree-dimensional (3D) to lower-dimensional spaces, while maintaining the 3D\nnature of the interaction energy degrees of freedom. The aim of this work is to\nintroduce an innovative scenario to achieve dimensional crossover,\ncharacterized by lower-D nature of both the kinetic and the interaction energy\ndegrees of freedom. To accomplish this objective, we delve deeply into the\nrealm of a 2D optically trapped Bose gas, focusing specifically on its\nfinite-range interaction. Our emphasis lies in exploring the lattice-induced\ndimensional crossover from full 3D to 1D in both kinetic and interaction terms.\nUtilizing the functional path integral method, we derive the equation of states\nof the model system, encompassing crucial quantities such as the ground state\nenergy and quantum depletion. These equations enable us to analyze the combined\neffects of finite range interaction and an optical lattice on quantum\nfluctuations of the BEC system. Notably, our analytical findings reconcile the\nLee-Huang-Yang (LHY) correction to the ground state energy in 3D and\nLieb-Liniger (LL) ones in 1D limit, thereby providing fresh insights into the\nintriguing disparities between LHY and LL corrections."
    },
    {
        "anchor": "Cavity-quantum-electrodynamical toolbox for quantum magnetism: The recent experimental observation of spinor self-ordering of ultracold\natoms in optical resonators has set the stage for the exploration of emergent\nmagnetic orders in quantum-gas--cavity systems. Based on this platform, we\nintroduce a generic scheme for the implementation of long-range quantum spin\nHamiltonians composed of various types of couplings, including Heisenberg and\nDzyaloshinskii-Moriya interactions. Our model is comprised of an effective\ntwo-component Bose-Einstein condensate, driven by two classical pump lasers and\ncoupled to a single dynamic mode of a linear cavity in a double $\\Lambda$\nscheme. Cavity photons mediate the long-range spin-spin interactions with\nspatially modulated coupling coefficients, where the latter ones can be tuned\nby modifying spatial profiles of the pump lasers. As experimentally relevant\nexamples, we demonstrate that by properly choosing the spatial profiles of the\npump lasers achiral domain-wall antiferromagnetic and chiral spin-spiral orders\nemerge beyond critical laser strengths. The transition between these two phases\ncan be observed in a single experimental setup by tuning the reflectivity of a\nmirror. We also discuss extensions of our scheme for the implementation of\nother classes of spin Hamiltonians.",
        "positive": "Synthetic dissipation and cascade fluxes in a turbulent quantum gas: Scale-invariant fluxes are the defining property of turbulent cascades, but\ntheir direct measurement is a notorious problem. Here we perform such a\nmeasurement for a direct energy cascade in a turbulent quantum gas. Using a\ntime-periodic force, we inject energy at a large lengthscale and generate a\ncascade in a uniformly-trapped Bose gas. The adjustable trap depth provides a\nhigh-momentum cutoff $k_{\\textrm{D}}$, which realises a synthetic dissipation\nscale. This gives us direct access to the particle flux across a momentum shell\nof radius $k_{\\textrm{D}}$, and the tunability of $k_{\\textrm{D}}$ allows for a\nclear demonstration of the zeroth law of turbulence: we observe that for fixed\nforcing the particle flux vanishes as $k_{\\textrm{D}}^{-2}$ in the\ndissipationless limit $k_{\\textrm{D}}\\rightarrow \\infty$, while the energy flux\nis independent of $k_{\\textrm{D}}$. Moreover, our time-resolved measurements\ngive unique access to the pre-steady-state dynamics, when the cascade front\npropagates in momentum space."
    },
    {
        "anchor": "Many-body chiral edge currents and sliding phases of atomic spinwaves in\n  momentum-space lattice: Collective excitations (spinwaves) of long-lived atomic hyperfine states can\nbe synthesized into a Bose-Hubbard model in momentum space. We explore\nmany-body ground states and dynamics of a two-leg momentum-space lattice formed\nby two coupled hyperfine states. Essential ingredients of this setting are a\nstaggered artificial magnetic field engineered by lasers that couple the\nspinwave states, and a state-dependent long-range interaction, which is induced\nby laser-dressing a hyperfine state to a Rydberg state. The Rydberg dressed\ntwo-body interaction gives rise to a state-dependent blockade in momentum\nspace, and can amplify staggered flux induced anti-chiral edge currents in the\nmany-body ground state in the presence of magnetic flux. When the Rydberg\ndressing is applied to both hyperfine states, exotic sliding insulating and\nsuperfluid/supersolid phases emerge. Due to the Rydberg dressed long-range\ninteraction, spinwaves slide along a leg of the momentum-space lattice without\ncosting energy. Our study paves a route to the quantum simulation of\ntopological phases and exotic dynamics with interacting spinwaves of atomic\nhyperfine states in momentum-space lattice.",
        "positive": "Analog quantum simulation of the spinor-four Dirac equation with an\n  artificial gauge field: A two-dimensional spatially and temporally modulated Wannier-Stark system of\nultracold atoms in optical lattices is shown to mimic the behavior of a Dirac\nparticle. Suitable additional modulations generate an artificial gauge field\nwhich simulates a magnetic field and imposes the use of the full spinor-four\nDirac equation."
    },
    {
        "anchor": "Universal scaling of spin mixing dynamics in a strongly interacting\n  one-dimensional Fermi gas: We study the spin-mixing dynamics of a one-dimensional strongly repulsive\nFermi gas under harmonic confinement. By employing a mapping onto an\ninhomogeneous isotropic Heisenberg model and the symmetries under particle\nexchange, we follow the dynamics till very long times. Starting from an initial\nspin-separated state, we observe superdiffusion, spin-dipolar large amplitude\noscillations and thermalization. We report a universal scaling of the\noscillations with particle number N^1/4, implying a slow-down of the motion and\nthe decrease of the zero-temperature spin drag coefficient as the particle\nnumber grows.",
        "positive": "Hydrodynamics of Normal Atomic Gases with Spin-orbit Coupling: Successful realization of spin-orbit coupling in atomic gases by the NIST\nscheme opens the prospect of studying the effects of spin-orbit coupling on\nmany-body physics in an unprecedentedly controllable way. Here we derive the\nlinearized hydrodynamic equations for the normal atomic gases of the spin-orbit\ncoupling by the NIST scheme with zero detuning. We show that the hydrodynamics\nof the system crucially depends on the momentum susceptibilities which can be\nmodified by the spin-orbit coupling. We reveal the effects of the spin-orbit\ncoupling on the sound velocities and the dipole mode frequency of the gases by\napplying our formalism to the ideal Fermi gas. We also discuss the\ngeneralization of our results to other situations."
    },
    {
        "anchor": "Thermodynamic Properties of Universal Fermi Gases: We develop a simple, mean-field-like theory for the normal phase of a unitary\nFermi gas by deriving a self-consistent equation for its self-energy via a\nmomentum-dependent coupling constant for both attractive and repulsive\nuniversal fermions. For attractive universal fermions in the lower branch of a\nFeshbach resonance, we use zero-temperature Monte Carlo results as a starting\npoint for one-step iteration in order to derive an analytical expression for\nthe momentum-dependent self-energy. For repulsive universal fermions in the\nupper branch of a Feshbach resonance, we iteratively calculate the\nmomentum-dependent self-energy via our self-consistent equation. Lastly, for\nthe case of population imbalance, we propose an ansatz for higher order virial\nexpansion coefficents. Overall, we find that our theory is in good agreement\nwith currently available, high temperature experimental data.",
        "positive": "Sine-Gordon model coupled with a free scalar field emergent in the\n  low-energy phase dynamics of a mixture of pseudospin-1/2 Bose gases with\n  interspecies spin exchange: Using the approach of low-energy effective field theory, the phase diagram is\nstudied for a mixture of two species of pseudospin-$\\1/2$ Bose atoms with\ninterspecies spin-exchange. There are four mean-field regimes on the parameter\nplane of $g_e$ and $g_z$, where $g_e$ is the interspecies spin-exchange\ninteraction strength, while $g_z$ is the difference between the interaction\nstrength of interspecies scattering without spin-exchange of equal spins and\nthat of unequal spins. Two regimes, with $|g_z| > |g_e|$, correspond to ground\nstates with the total spins of the two species parallel or antiparallel along\n$z$ direction, and the low energy excitations are equivalent to those of\ntwo-component spinless Bosons. The other two regimes, with $|g_e| > |g_z|$,\ncorrespond to ground states with the total spins of the two species parallel or\nantiparallel on $xy$ plane, and the low energy excitations are described by a\nsine-Gordon model coupled with a free scalar field, where the effective fields\nare combinations of the phases of the original four Boson fields. In\n(1+1)-dimension, they are described by Kosterlitz-Thouless renormalization\ngroup (RG) equations, and there are three sectors in the phase plane of a\nscaling dimension and a dimensionless parameter proportional to the strength of\nthe cosine interaction, both depending on the densities. The gaps of these\nelementary excitations are experimental probes of the underlying many-body\nground states."
    },
    {
        "anchor": "Polaritonic linear dynamic in Keldysh formalism: We study the dynamic of polaritons in the Keldysh functional formalism.\nDissipation is considered through the coupling of the exciton and photon fields\nto two independent photonic and excitonic baths. As such, this theory allows to\ndescribe more intricate decay mechanisms that depend dynamically on the state\nof the system, such as a direct upper-polariton lifetime, that is motivated\nfrom experiments. We show that the dynamical equations in the Keldysh framework\notherwise follow the same Josephson--like equations of motions than the\nstandard master equation approach, that is however limited to simple decay\nchannels. We also discuss the stability of the dynamic and reconsider the\ncriterion of strong coupling in the presence of upper polariton decay.",
        "positive": "Open source Matrix Product States: Exact diagonalization and other\n  entanglement-accurate methods revisited in quantum systems: Tensor network methods as presented in our open source Matrix Product States\nsoftware have opened up the possibility to study many-body quantum physics in\none and quasi-one-dimensional systems in an easily accessible package similar\nto density functional theory codes but for strongly correlated dynamics. Here,\nwe address methods which allow one to capture the full entanglement without\ntruncation of the Hilbert space. Such methods are suitable for validation of\nand comparisons to tensor network algorithms, but especially useful in the case\nof new kinds of quantum states with high entanglement violating the truncation\nin tensor networks. Quantum cellular automata are one example for such a\nsystem, characterized by tunable complexity, entanglement, and a large spread\nover the Hilbert space. Beyond the evolution of pure states as a closed system,\nwe adapt the techniques for open quantum systems simulated via the Lindblad\nmaster equation. We present three algorithms for solving closed-system\nmany-body time evolution without truncation of the Hilbert space. Exact\ndiagonalization methods have the advantage that they not only keep the full\nentanglement but also require no approximations to the propagator. Seeking the\nlimits of a maximal number of qubits on a single core, we use Trotter\ndecompositions or Krylov approximation to the exponential of the Hamiltonian.\nAll three methods are also implemented for open systems represented via the\nLindblad master equation built from local channels. We show their convergence\nparameters and focus on efficient schemes for their implementations including\nAbelian symmetries, e.g., U(1) symmetry used for number conservation in the\nBose-Hubbard model or discrete Z2 symmetries in the quantum Ising model. We\npresent the thermalization timescale in the long-range quantum Ising model as a\nkey example of how exact diagonalization contributes to novel physics."
    },
    {
        "anchor": "Dispersion properties of transverse waves propagating in the\n  electrically polarized BECs: Further development of the method of quantum hydrodynamics in application for\nBose-Einstein condensates (BECs) is presented. To consider evolution of\npolarization direction along with particles movement we have developed\ncorresponding set of quantum hydrodynamic equations. It includes equations of\nthe polarization evolution and the polarization current evolution along with\nthe continuity equation and the Euler equation (the momentum balance equation).\nDispersion properties of the transverse waves including the electromagnetic\nwaves propagating through the BECs are considered. To this end we consider full\nset of the Maxwell equations for description of electromagnetic field dynamics.\nThis approximation gives us possibility to consider the electromagnetic waves\nalong with the matter waves. We find a splitting of the electromagnetic wave\ndispersion on two branches. As a result we have four solutions, two for the\nelectromagnetic waves and two for the matter waves, the last two are the\nconcentration-polarization waves appearing as a generalization of the\nBogoliubov mode. We also obtain that if the matter wave propagate perpendicular\nto external electric field when dipolar contribution does not disappear (as it\nfollows from our generalization of the Bogoliubov spectrum). In this case exist\na small dipolar frequency shift due to transverse electric field of\nperturbation.",
        "positive": "Transmission and Reflection of Collective Modes in Spin-1 Bose-Einstein\n  Condensate: We study tunneling properties of collective excitations in spin-1\nBose-Einstein condensates. In the absence of magnetic fields, the total\ntransmission in the long wavelength limit occurs in all kinds of excitations\nbut the quadrupolar spin mode in the ferromagnetic state. The quadrupolar spin\nmode alone shows the total reflection. A difference between those excitations\ncomes from whether the wavefunction of an excitation corresponds to that of the\ncondensate in the long wavelength limit. The correspondence results in the\ntotal transmission as in the spinless BEC."
    },
    {
        "anchor": "Linking invariant for the quench dynamics of a two-dimensional two-band\n  Chern insulator: We discuss the topological invariant in the (2+1)-dimensional quench dynamics\nof a two-dimensional two-band Chern insulator starting from a topological\ninitial state (i.e., with a nonzero Chern number $c_i$), evolved by a\npost-quench Hamiltonian (with Chern number $c_f$). In contrast to the process\nwith $c_i=0$ studied in previous works, this process cannot be characterized by\nthe Hopf invariant that is described by the sphere homotopy group\n$\\pi_3(S^2)=\\mathbb{Z}$. It is possible, however, to calculate a variant of the\nChern-Simons integral with a complementary part to cancel the Chern number of\nthe initial spin configuration, which at the same time does not affect the\n(2+1)-dimensional topology. We show that the modified Chern-Simons integral\ngives rise to a topological invariant of this quench process, i.e., the linking\ninvariant in the $\\mathbb{Z}_{2c_i}$ class: $\\nu = (c_f - c_i) \\mod (2c_i)$. We\ngive concrete examples to illustrate this result and also show the detailed\ndeduction to get this linking invariant.",
        "positive": "Classical bifurcation at the transition from Rabi to Josephson dynamics: We report on the experimental realization of an internal bosonic Josephson\njunction in a Rubidium spinor Bose-Einstein condensate. The measurement of the\nfull time dynamics in phase space allows the characterization of the\ntheoretically predicted $\\pi$-phase modes and quantitatively confirms\nanalytical predictions, revealing a classical bifurcation. Our results suggest\nthat this system is a model system which can be tuned from classical to the\nquantum regime and thus is an important step towards the experimental\ninvestigation of entanglement generation close to critical points."
    },
    {
        "anchor": "Ultracold atomic spin mixtures in ultrastable magnetic field\n  environments: Ultracold atomic spin mixtures develop rich and intriguing magnetic\nproperties when an external radiation coherently couples different spin states.\nIn particular, the coupled mixture may acquire a critical behavior when the\nspin interactions equal the coupling energy. However, atomic mixtures generally\nfeature a relatively high sensitivity to magnetic fields that can set a\nlimitation to the observable phenomena. In this article, we present an overview\nof experimental studies of magnetism based on superfluid multicomponent gases\nin an ultrastable magnetic field environment, which recently became available.",
        "positive": "Extracting the Mott gap from energy measurements in trapped atomic gases: We show that the measure of the so-called {\\it release-energy}, which is an\nexperimentally accessible quantity, makes it possible to assess the value of\nthe Mott gap in the presence of the confinement potential that is unavoidable\nin the actual experimental setup. Indeed, the curve of the release-energy as a\nfunction of the total number of particles shows kinks that are directly related\nto the existence of excitation gaps. Calculations are presented within the\nGutzwiller approach, but the final results go beyond this simple approximation\nand represent a genuine feature of the real system. In the case of harmonic\nconfinement, the Mott gaps may be renormalized with respect to the uniform\ncase. On the other hand, in the case of the recently proposed off-diagonal\nconfinement, our results show an almost perfect agreement with the homogeneous\ncase."
    },
    {
        "anchor": "Tunable high-temperature thermodynamics of weakly-interacting dipolar\n  gases: We consider dilute gases of dipolar bosons or fermions in the\nhigh-temperature limit in a spherically symmetric harmonic trapping potential.\nWe examine the system using a virial expansion up to second order in the\nfugacity. Using the Born approximation and assuming purely dipolar\ninteractions, we find that the second-order virial coefficient for both bosons\nand fermions depends quadratically on the dipole length and is negative at high\ntemperature, indicating that to lowest order in the dipole-dipole interactions\nthe dipolar single-component quantum gases are repulsive. If the $s$-wave\nscattering length for the bosonic system is tunable and its absolute value is\nmade small, then the $s$-wave interactions dominate and the dipolar as behaves\nlike a weakly-interacting Bose gas with isotropic $s$-wave interactions. If the\ngeneralized scattering lengths for the fermionic system are tunable, then the\ndipole length can enter linearly in the virial equation of state, enhancing the\ndipole-dipole effects in the thermodynamic observables.",
        "positive": "Detecting two-site spin-entanglement in many-body systems with local\n  particle-number fluctuations: We derive experimentally measurable lower bounds for the two-site\nentanglement of the spin-degrees of freedom of many-body systems with local\nparticle-number fluctuations. Our method aims at enabling the spatially\nresolved detection of spin-entanglement in Hubbard systems using\nhigh-resolution imaging in optical lattices. A possible application is the\nobservation of entanglement generation and spreading during spin impurity\ndynamics, for which we provide numerical simulations. More generally, the\nscheme can simplify the entanglement detection in ion chains, Rydberg atoms, or\nsimilar atomic systems."
    },
    {
        "anchor": "Matter Wave Scattering from Ultracold Atoms in an Optical Lattice: We study matter wave scattering from an ultracold, many body atomic system\ntrapped in an optical lattice. We determine the angular cross section that a\nmatter wave probe sees and show that it is strongly affected by the many body\nphase, superfluid or Mott insulator, of the target lattice. We determine these\ncross sections analytically in the first Born approximation, and we examine the\nvariation at intermediate points in the phase transition by numerically\ndiagonalizing the Bose Hubbard Hamiltonian for a small lattice. We show that\nmatter wave scattering offers a convenient method for non-destructively probing\nthe quantum many body phase transition of atoms in an optical lattice.",
        "positive": "Two-dimensional supersolidity in a dipolar quantum gas: Supersolidity -- a quantum-mechanical phenomenon characterized by the\npresence of both superfluidity and crystalline order -- was initially\nenvisioned in the context of bulk solid helium, as a possible answer to the\nquestion of whether a solid could have superfluid properties. While\nsupersolidity has not been observed in solid helium (despite much effort),\nultracold atomic gases have provided a fundamentally new approach, recently\nenabling the observation and study of supersolids with dipolar atoms. However,\nunlike the proposed phenomena in helium, these gaseous systems have so far only\nshown supersolidity along a single direction. By crossing a structural phase\ntransition similar to those occurring in ionic chains, quantum wires, and\ntheoretically in chains of individual dipolar particles, we demonstrate the\nextension of supersolid properties into two dimensions, providing an important\nstep closer to the bulk situation envisioned in helium. This opens the\npossibility of studying rich excitation properties, including vortex formation,\nas well as ground-state phases with varied geometrical structure in a highly\nflexible and controllable system."
    },
    {
        "anchor": "Thermodynamics in expanding shell-shaped Bose-Einstein condensates: Inspired by investigations of Bose-Einstein condensates (BECs) produced in\nthe Cold Atom Laboratory (CAL) aboard the International Space Station, we\npresent a study of thermodynamic properties of shell-shaped BECs. Within the\ncontext of a spherically symmetric `bubble trap' potential, we study the\nevolution of the system from small filled spheres to hollow, large, thin shells\nvia the tuning of trap parameters. We analyze the bubble trap spectrum and\nstates, and track the distinct changes in spectra between radial and angular\nmodes across the evolution. This separation of the excitation spectrum provides\na basis for quantifying dimensional cross-over to quasi-2D physics at a given\ntemperature. Using the spectral data, for a range of trap parameters, we\ncompute the critical temperature for a fixed number of particles to form a BEC.\nFor a set of initial temperatures, we also evaluate the change in temperature\nthat would occur in adiabatic expansion from small filled sphere to large thin\nshell were the trap to be dynamically tuned. We show that the system cools\nduring this expansion but that the decrease in critical temperature occurs more\nrapidly, thus resulting in depletion of any initial condensate. We contrast our\nspectral methods with standard semiclassical treatments, which we find must be\nused with caution in the thin-shell limit. With regards to interactions, using\nenergetic considerations and corroborated through Bogoliubov treatments, we\ndemonstrate that they would be less important for thin shells due to reduced\ndensity but vortex physics would become more predominant. Finally, we apply our\ntreatments to traps that realistically model CAL experiments and borrow from\nthe thermodynamic insights found in the idealized bubble case during adiabatic\nexpansion.",
        "positive": "Berezinskii-Kosterlitz-Thouless phase transition with Rabi-coupled\n  bosons: We theoretically investigate the superfluid-normal-state\nBerezinskii-Kosterlitz-Thouless transition in a binary mixture of bosonic atoms\nwith Rabi coupling under balanced densities. We find the nonmonotonic behavior\nof the transition temperature with respect to the intercomponent coupling and\namplification of the transition temperature for finite values of Rabi coupling,\nbut for small intracomponent couplings. We develop the Nelson-Kosterlitz\nrenormalization-group equations in the two-component Bose mixture and obtain\nthe Nelson-Kosterlitz criterion modified by a fractional parameter, which is\nresponsible for half-integer vortices, and by Rabi coupling. Adopting the\nrenormalization-group approach, we clarify the dependence of the\nBerezinskii-Kosterlitz-Thouless transition temperature on the Rabi coupling and\nthe intercomponent coupling. Analysis of the first and second sound velocities\nalso reveals the suppression of quasicrossing of the two sound modes with a\nfinite Rabi coupling in the low-temperature regime. Our results for a\ntwo-dimensional binary Bose superfluid contribute to the understanding of a\nbroad range of multicomponent quantum systems such as two-dimensional multiband\nsuperconductors."
    },
    {
        "anchor": "Site-resolved measurement of the spin-correlation function in the\n  Hubbard model: Exotic phases of matter can emerge from strong correlations in quantum\nmany-body systems. Quantum gas microscopy affords the opportunity to study\nthese correlations with unprecedented detail. Here we report site-resolved\nobservations of antiferromagnetic correlations in a two-dimensional,\nHubbard-regime optical lattice and demonstrate the ability to measure the\nspin-correlation function over any distance. We measure the in-situ\ndistributions of the particle density and magnetic correlations, extract\nthermodynamic quantities from comparisons to theory, and observe statistically\nsignificant correlations over three lattice sites. The temperatures that we\nreach approach the limits of available numerical simulations. The direct access\nto many-body physics at the single-particle level demonstrated by our results\nwill further our understanding of how the interplay of motion and magnetism\ngives rise to new states of matter.",
        "positive": "Shape dependence and anisotropic finite-size scaling of the phase\n  coherence of three-dimensional Bose-Einstein condensed gases: We investigate the equilibrium phase-coherence properties of Bose-condensed\nparticle systems, focusing on their shape dependence and finite-size scaling\n(FSS). We consider three-dimensional (3D) homogeneous systems confined to\nanisotropic L x L x L_a boxes, below the BEC transition temperature $T_c$. We\nshow that the phase correlations develop peculiar anisotropic FSS for any\n$T<T_c$, in the large-$L$ limit keeping the ratio \\lambda = L_a/L^2 fixed. This\nphenomenon is effectively described by the 3D spin-wave (SW) theory. Its\nuniversality is confirmed by quantum Monte Carlo simulations of the 3D\nBose-Hubbard model in the BEC phase. The phase-coherence properties of very\nelongated BEC systems, \\lambda>>1, are characterized by a coherence length\n\\xi_a \\sim A_t \\rho_s/T where A_t is the transverse area and \\rho_s is the\nsuperfluid density."
    },
    {
        "anchor": "Numerical method for the projected Gross--Pitaevskii equation in an\n  infinite rotating 2D Bose gas: We present a method for evolving the projected Gross-Pitaevskii equation in\nan infinite rotating Bose-Einstein condensate, the ground state of which is a\nvortex lattice. We use quasi-periodic boundary conditions to investigate the\nbehaviour of the bulk superfluid in this system, in the absence of boundaries\nand edge effects. We also give the Landau gauge expression for the phase of a\nBEC subjected to these boundary conditions. Our spectral representation uses\nthe eigenfunctions of the one-body Hamiltonian as basis functions. Since there\nis no known exact quadrature rule for these basis functions we approximately\nimplement the projection associated with the energy cut-off, but show that by\nchoosing a suitably fine spatial grid the resulting error can be made\nnegligible. We show how the convergence of this model is affected by simulation\nparameters such as the size of the spatial grid and the number of Landau\nlevels. Adding dissipation, we use our method to find the lattice ground state\nfor $N$ vortices. We can then perturb the ground-state, in order to investigate\nthe melting of the lattice.",
        "positive": "Collective modes, stability and superfluid transition of a\n  quasi-two-dimensional dipolar Fermi gas: We examine collective modes, stability, and BCS pairing in a\nquasi-two-dimensional gas of dipolar fermions aligned by an external field. By\nusing the (conserving) Hartree-Fock approximation, which treats direct and\nexchange interactions on an equal footing, we obtain the spectrum of\nsingle-particle excitations and long wavelength collective modes (zero sound)\nin the normal phase. It appears that exchange interactions result in strong\ndamping of zero sound when the tilting angle between the dipoles and the normal\nto the plane of confinement is below some critical value. In particular, zero\nsound cannot propagate if the dipoles are perpendicular to the plane of\nconfinement. At intermediate coupling we find unstable modes that can lead\neither to collapse of the system or the formation of a density wave. The BCS\ntransition to a superfluid phase, on the other hand, occurs at arbitrarily weak\nstrengths of the dipole-dipole interaction, provided the tilting angle exceeds\na critical value. We determine the critical temperature of the transition\ntaking into account many-body effects as well as virtual transitions to higher\nexcited states in the confining potential, and discuss prospects of\nexperimental observations."
    },
    {
        "anchor": "Coherent multi-flavour spin dynamics in a fermionic quantum gas: Microscopic spin interaction processes are fundamental for global static and\ndynamical magnetic properties of many-body systems. Quantum gases as pure and\nwell isolated systems offer intriguing possibilities to study basic magnetic\nprocesses including non-equilibrium dynamics. Here, we report on the\nrealization of a well-controlled fermionic spinor gas in an optical lattice\nwith tunable effective spin ranging from 1/2 to 9/2. We observe long-lived\nintrinsic spin oscillations and investigate the transition from two-body to\nmany-body dynamics. The latter results in a spin-interaction driven melting of\na band insulator. Via an external magnetic field we control the system's\ndimensionality and tune the spin oscillations in and out of resonance. Our\nresults open new routes to study quantum magnetism of fermionic particles\nbeyond conventional spin 1/2 systems.",
        "positive": "Time-of-flight patterns of ultra-cold bosons in optical lattices in\n  various Abelian artificial magnetic field gauges: We calculate the time-of-flight patterns of strongly interacting bosons\nconfined in two-dimensional square lattice in the presence of an artificial\nmagnetic field using quantum rotor model that is inherently combined with the\nBogolyubov approach. We consider various geometries of the magnetic flux, which\nare expected to be realizable, or have already been implemented in experimental\nsettings. The flexibility of the method let us to study cases of the artificial\nmagnetic field being uniform, staggered or forming a checkerboard\nconfiguration. Effects of additional temporal modulation of the optical\npotential that results from application of Raman lasers driving particle\ntransitions between lattice sites are also included. The presented\ntime-of-flight patterns may serve as a verification of chosen gauge in\nexperiments, but also provide important hints on unconventional, non-zero\nmomentum condensates, or possibility of observing graphene-like physics\nresulting from occurrence of Dirac cones in artificial magnetic fields in\nsystems of ultra-cold bosons in optical lattices. Also, we elucidate on\ndifferences between effects of magnetic field in solids and the artificial\nmagnetic field in optical lattices, which can be controlled on much higher\nlevel leading to effects not possible in condensed matter physics."
    },
    {
        "anchor": "Dicke Superradiance in Solids: Recent advances in optical studies of condensed matter have led to the\nemergence of phenomena that have conventionally been studied in the realm of\nquantum optics. These studies have not only deepened our understanding of\nlight-matter interactions but also introduced aspects of many-body correlations\ninherent in optical processes in condensed matter systems. This article is\nconcerned with superradiance (SR), a profound quantum optical process predicted\nby Dicke in 1954. The basic concept of SR applies to a general $N$-body system\nwhere constituent oscillating dipoles couple together through interaction with\na common light field and accelerate the radiative decay of the system. In the\nmost fascinating manifestation of SR, known as superfluorescence (SF), an\nincoherently prepared system of $N$ inverted atoms spontaneously develops\nmacroscopic coherence from vacuum fluctuations and produces a delayed pulse of\ncoherent light whose peak intensity $\\propto N^2$. Such SF pulses have been\nobserved in atomic and molecular gases, and their intriguing quantum nature has\nbeen unambiguously demonstrated. Here, we focus on the rapidly developing field\nof research on SR in solids, where not only photon-mediated coupling but also\nstrong Coulomb interactions and ultrafast scattering exist. We describe SR and\nSF in molecular centers in solids, molecular aggregates and crystals, quantum\ndots, and quantum wells. In particular, we will summarize a series of studies\nwe have recently performed on quantum wells in strong magnetic fields. These\nstudies show that cooperative effects in solid-state systems are not merely\nsmall corrections that require exotic conditions to be observed; rather, they\ncan dominate the nonequilibrium dynamics and light emission processes of the\nentire system of interacting electrons.",
        "positive": "Decay-dephasing-induced steady states in bosonic Rydberg-excited quantum\n  gases in an optical lattice: We investigate the possibility of realizing supersolid quantum phases in\nbosonic Rydberg-excited quantum lattice gases in the presence of non-unitary\nprocesses, by simulating the dynamical evolution starting from initial\npreparation in non-dissipative equilibrium states. Within Gutzwiller theory, we\nfirst analyze the many-body ground-state of a bosonic Rydberg-excited quantum\ngas in a two dimensional optical lattice for variable atomic hopping rates and\nRabi detunings. Furthermore, we perform time evolution of different supersolid\nphases using the Lindblad-master equation. With the inclusion of two different\nnon-unitary processes, namely spontaneous decay from a Rydberg state to the\nground state and dephasing of the addressed Rydberg state, we study the effect\nof non-unitary processes on those quantum phases and observe long-lived states\nin the presence of decay and dephasing. We find that long-lived supersolid\nquantum phases are observable within a range of realistic decay and dephasing\nrates, while high rates cause any initial configuration to homogenize quickly,\npreventing possible supersolid formation."
    },
    {
        "anchor": "Bound-state signatures in quenched Bose-Einstein condensates: We investigate the dynamics of a homogenous Bose-Einstein condensate (BEC)\nfollowing a sudden quench of the scattering length. Our focus is the time\nevolution of short-range correlations via the dynamical contact. We compute the\ndynamics using a combination of two- and many-body models, and we propose an\nintuitive connection between them that unifies their short-time, short-range\npredictions. Our two-body models are exactly solvable and, when properly\ncalibrated, lead to analytic formulae for the contact dynamics. Immediately\nafter the quench, the contact exhibits strong oscillations at the frequency of\nthe two-body bound state. These oscillations are large in amplitude, and their\ntime average is typically much larger than the unregularized Bogoliubov\nprediction. The condensate fraction shows similar oscillations, whose amplitude\nwe are able to estimate. These results demonstrate the importance of including\nthe bound state in descriptions of diabatically-quenched BEC experiments.",
        "positive": "Two-dimensional imbalanced Fermi gas in antiparallel magnetic fields: We study a two-dimensional Fermi gas with an attractive interaction subjected\nto synthetic magnetic fields, which are assumed to be mutually antiparallel for\ntwo different spin components with population imbalance. By employing the\nmean-field approximation, we show that the Fulde-Ferrell state is energetically\nfavored over the Larkin-Ovchinnikov state in the weak-coupling limit. We then\nelucidate the zero-temperature phase diagram in the space of attraction and two\nchemical potentials analytically at weak coupling as well as numerically beyond\nit. Rich structures consisting of quantum Hall insulator, unpolarized\nsuperfluid, and Fulde-Ferrell phases separated by various second-order and\nfirst-order quantum phase transitions are found."
    },
    {
        "anchor": "Improved Hilbert space exploration algorithms for finite temperature\n  calculations: Computing correlation functions in strongly-interacting quantum systems is\none of the most important challenges of modern condensed matter theory, due to\ntheir importance in the description of many physical observables.\nSimultaneously, this challenge is one of the most difficult to address, due to\nthe inapplicability of traditional perturbative methods or the few-body\nlimitations of numerical approaches. For special cases, where the model is\nintegrable, methods based on the Bethe Ansatz have succeeded in computing the\nspectrum and given us analytical expressions for the matrix elements of\nphysically important operators. However, leveraging these results to compute\ncorrelation functions generally requires the numerical evaluation of summations\nover eigenstates. To perform these summations efficiently, Hilbert space\nexploration algorithms have been developed which has resulted most notably in\nthe ABACUS library. While this performs quite well for correlations on ground\nstates or low-entropy states, the case of high entropy states (most importantly\nat finite temperatures or after a quantum quench) is more difficult, and leaves\nroom for improvement. In this work, we develop a new Hilbert space exploration\nalgorithm for the Lieb-Liniger model, specially tailored to optimize the\ncomputational order on finite-entropy states for correlations of\ndensity-related operators.",
        "positive": "Approach and separation of quantum vortices with balanced cores: Using two innovations, smooth, but distinctly different, scaling laws for the\nnumerical reconnection of pairs of initially orthogonal and anti-parallel\nquantum vortices are obtained using the three-dimensional Gross-Pitaevskii\nequations, the simplest mean-field non-linear Schr\\\"odinger equation for a\nquantum fluid. The first innovation suppresses temporal fluctuations by using\nan initial density profile that is slightly below the usual two-dimensional\nsteady-state Pad\\'e approximate profiles. The second innovation is to find the\ntrajectories of the quantum vortices from a pseudo-vorticity constructed on the\nthree-dimensional grid from the gradients of the wave function. These\ntrajectories then allow one to calculate the Frenet-Serret frames and the\ncurvature of the vortex lines. For the anti-parallel case, the scaling laws\njust before and after reconnection obey the dimensional\n$\\delta\\sim|t_r-t|^{1/2}$ prediction with temporal symmetry about the\nreconnection time $t_r$ and physical space symmetry about the $x_r$, the\nmid-point between the vortices, with extensions of the vortex lines formng the\nedges of an equilateral pyramid. For all of the orthogonal cases, before\nreconnection $\\delta_{in}\\sim(t-t_r)^{1/3}$ and after reconnection\n$\\delta_{out}\\sim(t-t_r)^{2/3}$, which are respectively slower and faster than\nthe dimensional prediction. In these cases, the reconnection takes place in a\nplane defined by the directions of the curvature and vorticity. To define the\nstructure further, lines are drawn that connect the four arms that extend from\nthe reconnection plane, four angles $\\theta_i$ between these arms are found,\nthen summed, giving $\\sum\\theta_i>360^\\circ$. This implies that the overall\nstructure is convex or hyperbolic, as opposed to the acute angles of the\nanti-parallel pyramid."
    },
    {
        "anchor": "Attenuating Dynamics of Strongly Interacting Fermionic Superfluids in\n  SYK Solvable Models: Quench dynamics of fermionic superfluids are an active topic both\nexperimentally and theoretically. Using the BCS theory, such non-equilibrium\nproblems can be reduced to nearly independent spin dynamics, only with a\ntime-dependent mean-field pairing term. This results in persisting oscillations\nof the pairing strength in certain parameter regimes. However, experiments have\nobserved that the oscillations decay rapidly when the interaction becomes\nstrong, such as in the unitary Fermi gas. Theoretical analysis on this matter\nis still absent. In this work, we construct an SYK-like model to analyze the\neffect of strong interactions in a one-dimensional BCS system. We employ the\nlarge-$N$ approximation and a Green's function-based technique to solve the\nequilibrium problem and quench dynamics. Our findings reveal that a strong SYK\ninteraction suppresses the pairing order. Additionally, we verify that the\nsystem quickly thermalizes with SYK interactions, whether it involves intrinsic\npairing order or proximity effect, resulting in a rapid decay of the\noscillation strength. The decay rates exhibit different scaling laws against\nSYK interaction, which can be understood in terms of the Boltzmann equation.\nThis work represents a first step towards understanding the attenuating\ndynamics of strongly interacting fermionic superfluids.",
        "positive": "Massless Dirac-Weyl Fermions in a T_3 Optical Lattice: We propose an experimental setup for the observation of quasi-relativistic\nmassless Fermions. It is based on a T_3 optical lattice, realized by three\npairs of counter-propagating lasers, filled with fermionic cold atoms. We show\nthat in the long wavelength approximation the T_3 Hamiltonian generalizes the\nDirac-Weyl Hamiltonian for the honeycomb lattice, however, with a larger value\nof the pseudo-spin S=1. In addition to the Dirac cones, the spectrum includes a\ndispersionless branch of localized states producing a finite jump in the atomic\ndensity. Furthermore, implications for the Landau levels are discussed."
    },
    {
        "anchor": "Phonon-assisted coherent transport of excitations in Rydberg-dressed\n  atom arrays: Polarons, which arise from the self-trapping interaction between electrons\nand lattice distortions in a solid, have been known and extensively\ninvestigated for nearly a century. Nevertheless, the study of polarons\ncontinues to be an active and evolving field, with ongoing advancements in both\nfundamental understanding and practical applications. Here, we present a\nmicroscopic model that exhibits a diverse range of dynamic behavior, arising\nfrom the intricate interplay between two excitation-phonon coupling terms. The\nderivation of the model is based on an experimentally feasible Rydberg-dressed\nsystem with dipole-dipole interactions, making it a promising candidate for\nrealization in a Rydberg atoms quantum simulator. Remarkably, our analysis\nreveals a growing asymmetry in Bloch oscillations, leading to a macroscopic\ntransport of non-spreading excitations under a constant force. Moreover, we\ncompare the behavior of excitations, when coupled to either acoustic or optical\nphonons, and demonstrate the robustness of our findings against on-site random\npotential. Overall, this work contributes to the understanding of polaron\ndynamics with their potential applications in coherent quantum transport and\noffers valuable insights for research on Rydberg-based quantum systems.",
        "positive": "Trimer superfluid and supersolid on two-dimensional optical lattices: By the photoassociation method, the trimer superfluid phase disappears in the\none dimensional state-dependent optical lattice if the ratio of the three-body\ninteraction $W$ to the trimer tunneling $J$is kept at $W/J=12$ [Phys Rev A.\n{\\bf 90}, 033622(2014)]. To search for a trimer superfluid and trimer\nsupersolid, we load the cold atom into two-dimensional lattices, whose\ncoordinate number $z$ and kinetic energy $-zJ$ are respectively larger and\nlower than those of a one dimensional lattice. Herein, we study the\nBose-Hubbard model, which has an additional trimer tunneling term, a three-body\ninteraction and a next-nearest repulsion. The on-site trimer and trimer\nsuperfluid exist if the on-site two-body repulsion and three-body repulsion are\nsmaller than some thresholds. With atom-tunneling terms, the phase transitions\nfrom trimer superfluid phase to both atom superfluid and atom supersolid phases\nare first order. With $W/J=12$, in a one dimensional lattice, the trimer\nsuperfluid phase does not exist at all. In contrast, the trimer superfluid\nphase, exists in the lower density regions $0 \\textless \\rho \\textless2$ on the\nsquare lattice if $J$ is not very large. The trimer superfluid phase emerges in\na wider range $0 \\textless \\rho \\textless3$ in the triangular lattice, or in\nthe cubic lattice ($z=6$). When the three-body interaction is turned on, a\ntrimer supersolid phase emerges due to the classical degeneracy between the\nquasi trimer solid and the trimer solid being broken by the quantum\nfluctuation. The phase transitions from the trimer supersolid phase to quasi\ntrimer solid are first order and the phase transition from the trimer\nsupersolid phase to trimer solid is continuous. Our results, obtained by\nmean-field and quantum Monte Carlo methods, will be helpful in realizing the\ntrimer superfluid and supersolid by cold atom experiments."
    },
    {
        "anchor": "Quasiparticle lifetime of the repulsive Fermi polaron: We investigate the metastable repulsive branch of a mobile impurity coupled\nto a degenerate Fermi gas via short-range interactions. We show that the\nquasiparticle lifetime of this repulsive Fermi polaron can be experimentally\nprobed by driving Rabi oscillations between weakly and strongly interacting\nimpurity states. Using a time-dependent variational approach, we find that we\ncan accurately model the impurity Rabi oscillations that were recently measured\nfor repulsive Fermi polarons in both two and three dimensions. Crucially, our\ntheoretical description does not include relaxation processes to the\nlower-lying attractive branch. Thus, the theory-experiment agreement\ndemonstrates that the quasiparticle lifetime is determined by many-body\ndephasing within the upper repulsive branch rather than by the metastability of\nthe upper branch itself. Our findings shed light on recent experimental\nobservations of persistent repulsive correlations, and have important\nconsequences for the nature and stability of the strongly repulsive Fermi gas.",
        "positive": "Non-Abelian dynamical gauge field and topological superfluids in optical\n  Raman lattice: We propose an experimental scheme to realize non-Abelian dynamical gauge\nfield for ultracold fermions, which induces a novel pairing mechanism of\ntopological superfluidity. The dynamical gauge fields arise from nontrivial\ninterplay effect between the strong Zeeman splitting and Hubbard interaction in\na two-dimensional (2D) optical Raman lattice. The spin-flip transitions are\nforbidden by the large Zeeman detuning, but are restored when the Zeeman\nsplitting is compensated by Hubbard interaction. This scheme allows to generate\na dynamical non-Abelian gauge field that leads to a Dirac type correlated 2D\nspin-orbit interaction depending on local state configurations. The topological\nsuperfluid from a novel pairing driven by 2D dynamical gauge fields is reached,\nwith analytic and numerical results being obtained. Our work may open up a door\nto emulate non-Abelian dynamical gauge fields and correlated topological phases\nwith experimental feasibility."
    },
    {
        "anchor": "Soliton-induced Majorana fermions in a one-dimensional atomic\n  topological superfluid: We theoretically investigate the behavior of dark solitons in a\none-dimensional spin-orbit coupled atomic Fermi gas in harmonic traps, by\nsolving self-consistently the Bogoliubov-de Gennes equations. The dark soliton\n- to be created by phase-imprinting in future experiments - is characterized by\na real order parameter, which changes sign at a point node and hosts localized\nAndreev bound states near the node. By considering both cases of a single\nsoliton and of multiple solitons, we find that the energy of these bound states\ndecreases to zero, when the system is tuned to enter the topological superfluid\nphase by increasing an external Zeeman field. As a result, two Majorana\nfermions emerge in the vicinity of each soliton, in addition to the well-known\nMajorana fermions at the trap edges associated with the nontrivial topology of\nthe superfluid. We propose that the soliton-induced Majorana fermions can be\ndirectly observed by using spatially-resolved radio-frequency spectroscopy or\nindirectly probed by measuring the density profile at the point node. For the\nlatter, the deep minimum in the density profile will disappear due to the\noccupation of the soliton-induced zero-energy Majorana fermion modes. Our\nprediction could be tested in a resonantly-interacting spin-orbit coupled\n$^{40}$K Fermi gas confined in a two-dimensional optical lattice.",
        "positive": "Four-body Efimov effect: We study three same spin state fermions of mass M interacting with a\ndistinguishable particle of mass m in the unitary limit where the interaction\nhas a zero range and an infinite s-wave scattering length. We predict an\ninterval of mass ratio 13.384 < M/m < 13.607 where there exists a purely\nfour-body Efimov effect, leading to the occurrence of weakly bound tetramers\nwithout Efimov trimers."
    },
    {
        "anchor": "Perpetual motion and driven dynamics of a mobile impurity in a quantum\n  fluid: We study the dynamics of a mobile impurity in a quantum fluid at zero\ntemperature. Two related settings are considered. In the first setting the\nimpurity is injected in the fluid with some initial velocity ${\\mathbf v}_0$,\nand we are interested in its velocity at infinite time, ${\\mathbf v}_\\infty$.\nWe derive a rigorous upper bound on $|{\\mathbf v}_0-{\\mathbf v}_\\infty|$ for\ninitial velocities smaller than the generalized critical velocity. In the limit\nof vanishing impurity-fluid coupling this bound amounts to ${\\mathbf\nv}_\\infty={\\mathbf v}_0$ which can be regarded as a rigorous proof of the\nLandau criterion of superfluidity. In the case of a finite coupling the\nvelocity of the impurity can drop, but not to zero; the bound quantifies the\nmaximal possible drop. In the second setting a small constant force is exerted\nupon the impurity. We argue that two distinct dynamical regimes exist --\nbackscattering oscillations of the impurity velocity and saturation of the\nvelocity without oscillations. For fluids with $v_{c {\\rm L}}=v_s$ (where $v_{c\n{\\rm L}}$ and $v_s$ are the Landau critical velocity and sound velocity,\nrespectively) the latter regime is realized. For fluids with $v_{c {\\rm L}} <\nv_s$ both regimes are possible. Which regime is realized in this case depends\non the mass of the impurity, a nonequilibrium quantum phase transition\noccurring at some critical mass. Our results are equally valid in one, two and\nthree dimensions.",
        "positive": "Fermionic trimers in spin-dependent optical lattices: We investigate the formation of three-body bound states (trimers) in\ntwo-component Fermi gases confined in one dimensional optical lattice with\nspin-dependent tunneling rates. The binding energy and the effective mass of\nthe trimer are obtained from the solution of the Mattis integral equation\ngeneralized to the case of unequal Bloch masses. We show that this equation\nadmits multiple solutions corresponding to excited bound states, which are only\nstable for large mass asymmetry."
    },
    {
        "anchor": "Three-body constrained bosons in double-well optical lattice: We analyse the ground-state properties of three-body constrained bosons in a\none dimensional optical lattice with staggered hoppings analogous to the double\nwell optical lattice. By considering attractive and repulsive on-site\ninteractions between the bosons, we obtain the phase diagram which exhibits\nvarious quantum phases. Due to the double-well geometry and three-body\nconstraint several gapped phases such as the Mott insulators and\ndimer/bond-order phases emerge at commensurate densities in the repulsive\ninteraction regime. Attractive interaction leads to the pair formation which\nleads to the pair bond order phase at unit filling which resembles the\nvalence-bond solid phase of composite bosonic pairs. At incommensurate\ndensities we see the signatures of the gapless pair superfluid phase.",
        "positive": "Measurement of the order parameter and its spatial fluctuations across\n  Bose-Einstein condensation: We investigate the strong out-of-equilibrium dynamics occurring when a\nharmonically trapped ultracold bosonic gas is evaporatively cooled across the\nBose--Einstein condensation transition. By imaging the cloud after free\nexpansion, we study how the cooling rate affects the timescales for the growth\nof the condensate order parameter and the relaxation dynamics of its spatial\nfluctuations. We find evidence of a delay on the condensate formation related\nto the collisional properties and a universal condensate growth following the\ncooling rate. Finally, we measure an exponential relaxation of the spatial\nfluctuations of the order parameter that also shows a universal scaling.\nNotably, the scaling for the condensate growth and for the relaxation of its\nfluctuations follow different power laws."
    },
    {
        "anchor": "Time-of-flight images of Mott insulators in the Hofstadter-Bose-Hubbard\n  model: We analyze the momentum distribution function and its artificial-gauge-field\ndependence for the Mott insulator phases of the Hofstadter-Bose-Hubbard model.\nBy benchmarking the results of the random-phase approximation (RPA) approach\nagainst those of the strong-coupling expansion (SCE) for the Landau and\nsymmetric gauges, we find pronounced corrections to the former results in two\ndimensions.",
        "positive": "Realistic Rashba and Dressehaus spin-orbit coupling for neutral atoms: We describe a new class of atom-laser coupling schemes which lead to\nspin-orbit coupled Hamiltonians for ultra-cold neutral atoms. By properly\nsetting the optical phases, a pair of degenerate pseudospin states emerge as\nthe lowest energy states in the spectrum, and are thus immune to collisionally\ninduced decay. These schemes use $N$ cyclically coupled ground or metastable\ninternal states. We specialize to two situations: a three level case giving\nfixed Rashba coupling, and a four-level case that adds a controllable\nDresselhaus contribution. We describe an implementation of the four level\nscheme for $\\Rb87$ and analyze the sensitivity of our approach to realistic\nexperimental limitations and imperfections. Lastly, we argue that no laser\ncoupling scheme can give pure Rashba or Dresselhaus coupling: akin to condensed\nmatter systems, higher order terms spoil the symmetry of these couplings.\nHowever, for sufficiently intense laser fields the continuous rotational\nsymmetry approximately holds, making the Rashba Hamiltonian applicable for cold\natoms."
    },
    {
        "anchor": "Interaction-induced topological properties of two bosons in flat-band\n  systems: In flat-band systems, destructive interference leads to the localization of\nnon-interacting particles and forbids their motion through the lattice.\nHowever, in the presence of interactions the overlap between neighbouring\nsingle-particle localized eigenstates may enable the propagation of bound pairs\nof particles. In this work, we show how these interaction-induced hoppings can\nbe tuned to obtain a variety of two-body topological states. In particular, we\nconsider two interacting bosons loaded into the orbital angular momentum $l=1$\nstates of a diamond-chain lattice, wherein an effective $\\pi$ flux may yield a\ncompletely flat single-particle energy landscape. In the weakly-interacting\nlimit, we derive effective single-particle models for the two-boson\nquasiparticles which provide an intuitive picture of how the topological states\narise. By means of exact diagonalization calculations, we benchmark these\nstates and we show that they are also present for strong interactions and away\nfrom the strict flat-band limit. Furthermore, we identify a set of doubly\nlocalized two-boson flat-band states that give rise to a special instance of\nAharonov-Bohm cages for arbitrary interactions.",
        "positive": "Three-level Haldane-like model on dice optical lattice: We consider ultracold atoms in a two-dimensional optical lattice of the dice\ngeometry in a tight-binding regime. The atoms experience a laser-assisted\ntunneling between the nearest neighbour sites of the dice lattice accompanied\nby the momentum recoil. This allows one to engineer staggered synthetic\nmagnetic fluxes over plaquettes, and thus pave a way towards a realization of\ntopologically nontrivial band structures. In such a lattice the real-valued\nnext-neighbour transitions are not needed to reach a topological regime. Yet,\nsuch transitions can increase a variety of the obtained topological phases. The\ndice lattice represents a triangular Bravais lattice with a three-site basis\nconsisting of a hub site connected to two rim sites. As a consequence, the dice\nlattice supports three dispersion bands. From this point of view, our model can\nbe interpreted as a generalization of the paradigmatic Haldane model which is\nreproduced if one of the two rim sub-lattices is eliminated. We demonstrate\nthat the proposed upgrade of the Haldane model creates a significant added\nvalue, including an easy access to topological semimetal phases relying only on\nthe nearest neighbour coupling, as well as enhanced topological band structures\nfeaturing Chern numbers higher than one. The numerical investigation is\nsupported and complemented by an analytical scheme based on the study of\nsingularities in the Berry connection."
    },
    {
        "anchor": "Quantum Many-Body Dynamics of Dark Solitons in Optical Lattices: We present a fully quantum many-body treatment of dark solitons formed by\nultracold bosonic atoms in one-dimensional optical lattices. Using\ntime-evolving block decimation to simulate the single-band Bose-Hubbard\nHamiltonian, we consider the quantum dynamics of density and phase engineered\ndark solitons as well as the quantum evolution of mean-field dark solitons\ninjected into the quantum model. The former approach directly models how one\nmay create quantum entangled dark solitons in experiment. While we have already\npresented results regarding the latter approach elsewhere [Phys. Rev. Lett.\n{\\bf 103}, 140403 (2009)], we expand upon those results in this work. In both\ncases, quantum fluctuations cause the dark soliton to fill in and may induce an\ninelasticity in soliton-soliton collisions. Comparisons are made to the\nBogoliubov theory which predicts depletion into an anomalous mode that fills in\nthe soliton. Our many-body treatment allows us to go beyond the Bogoliubov\napproximation and calculate explicitly the dynamics of the system's natural\norbitals.",
        "positive": "Vortex dynamics in coherently coupled Bose-Einstein condensates: In classical hydrodynamics with uniform density, vortices move with the local\nfluid velocity. This description is rewritten in terms of forces arising from\nthe interaction with other vortices. Two such positive straight vortices\nexperience a repulsive interaction and precess in a positive (anticlockwise)\nsense around their common centroid. A similar picture applies to vortices in a\ntwo-component two-dimensional uniform Bose-Einstein condensate (BEC) coherently\ncoupled through rf Rabi fields. Unlike the classical case, however, the rf Rabi\ncoupling induces an attractive interaction and two such vortices with positive\nsigns now rotate in the negative (clockwise) sense. Pairs of counter-rotating\nvortices are instead found to translate with uniform velocity perpendicular to\nthe line joining their cores. This picture is extended to a single vortex in a\ntwo-component trapped BEC. Although two uniform vortex-free components\nexperience familiar Rabi oscillations of particle-number difference, such\nbehavior is absent for a vortex in one component because of the nonuniform\nvortex phase. Instead the coherent Rabi coupling induces a periodic vorticity\ntransfer between the two components."
    },
    {
        "anchor": "Dark state optical lattice with sub-wavelength spatial structure: We report on the experimental realization of a conservative optical lattice\nfor cold atoms with sub-wavelength spatial structure. The potential is based on\nthe nonlinear optical response of three-level atoms in laser-dressed dark\nstates, which is not constrained by the diffraction limit of the light\ngenerating the potential. The lattice consists of a 1D array of ultra-narrow\nbarriers with widths less than 10~nm, well below the wavelength of the lattice\nlight, physically realizing a Kronig-Penney potential. We study the band\nstructure and dissipation of this lattice, and find good agreement with\ntheoretical predictions. The observed lifetimes of atoms trapped in the lattice\nare as long as 60 ms, nearly $10^5$ times the excited state lifetime, and could\nbe further improved with more laser intensity. The potential is readily\ngeneralizable to higher dimension and different geometries, allowing, for\nexample, nearly perfect box traps, narrow tunnel junctions for atomtronics\napplications, and dynamically generated lattices with sub-wavelength spacings.",
        "positive": "Persistent currents in spinor condensates: We create and study persistent currents in a toroidal two-component Bose gas,\nconsisting of $^{87}$Rb atoms in two different spin states. For a large\nspin-population imbalance we observe supercurrents persisting for over two\nminutes. However we find that the supercurrent is unstable for spin\npolarisation below a well defined critical value. We also investigate the role\nof phase coherence between the two spin components and show that only the\nmagnitude of the spin-polarisation vector, rather than its orientation in spin\nspace, is relevant for supercurrent stability."
    },
    {
        "anchor": "Optical control of atom-ion collisions using a Rydberg state: We present a method to control collisions between ultracold neutral atoms in\nthe electronic ground state and trapped ions. During the collision, the neutral\natom is resonantly excited by a laser to a low-field-seeking Rydberg state,\nwhich is repelled by the ion. As the atom is reflected from the ion, it is\nde-excited back into its electronic ground level. The efficiency of shielding\nis analyzed as a function of laser frequency and power, initial atom-ion\ncollision energy, and collision angle. The suitability of several Rydberg\nlevels of Na and Rb for shielding is discussed. Useful applications of\nshielding include the suppression of unwanted chemical reactions between atoms\nand ions, a prerequisite for controlled atom-ion interactions.",
        "positive": "Nonexponential decay of Feshbach molecules: We analyze the temporal behavior of the survival probability of an unstable\n$^6$Li Feshbach molecule close to the BCS-BEC crossover. We find different\ninstances of nonexponential decay as the magnetic field approaches the\nresonance value, at which the molecule becomes stable. We observe a transition\nfrom an exponential decay towards a regime dominated by a stretched-exponential\nlaw."
    },
    {
        "anchor": "Anisotropic excitation spectrum of a dipolar quantum Bose gas: We measure the excitation spectrum of a dipolar Chromium Bose Einstein\nCondensate with Raman-Bragg spectroscopy. The energy spectrum depends on the\norientation of the dipoles with respect to the excitation momentum,\ndemonstrating an anisotropy which originates from the dipole-dipole\ninteractions between the atoms. We compare our results with the Bogoliubov\ntheory based on the local density approximation, and, at large excitation\nwavelengths, with numerical simulations of the time dependent Gross-Pitaevskii\nequation. Our results show an anisotropy of the speed of sound",
        "positive": "Efficient algorithm to compute the second Chern number in four\n  dimensional systems: Topological insulators are exotic material that possess conducting surface\nstates protected by the topology of the system. They can be classified in terms\nof their properties under discrete symmetries and are characterized by\ntopological invariants. The latter has been measured experimentally for several\nmodels in one, two and three dimensions in both condensed matter and quantum\nsimulation platforms. The recent progress in quantum simulation opens the road\nto the simulation of higher dimensional Hamiltonians and in particular of the\n4D quantum Hall effect. These systems are characterized by the second Chern\nnumber, a topological invariant that appears in the quantization of the\ntransverse conductivity for the non-linear response to both external magnetic\nand electric fields. This quantity cannot always be computed analytically and\nthere is therefore a need of an algorithm to compute it numerically. In this\nwork, we propose an efficient algorithm to compute the second Chern number in\n4D systems. We construct the algorithm with the help of lattice gauge theory\nand discuss the convergence to the continuous gauge theory. We benchmark the\nalgorithm on several relevant models, including the 4D Dirac Hamiltonian and\nthe 4D quantum Hall effect and verify numerically its rapid convergence."
    },
    {
        "anchor": "A differential approach to investigate universal scaling in\n  far-from-equilibrium quantum systems: Recent progress in out-of-equilibrium closed quantum systems has\nsignificantly advanced the understanding of mechanisms behind their evolution\ntowards thermalization. Notably, the concept of non-thermal fixed points\n(NTFPs) - responsible for the emergence of spatio-temporal universal scaling in\nfar-from-equilibrium systems - has played a crucial role in both theoretical\nand experimental investigations. In this work, we introduce a differential\nequation that has the universal scaling associated with NTFPs as a solution.\nThe advantage of working with a differential equation, rather than only with\nits solution, is that we can extract several insightful properties not\nnecessarily present in the solution alone. Employing two limiting cases of the\nequation, we determined the universal exponents related to the scaling using\nthe distributions near just two momentum values. We established a strong\nagreement with previous investigations by validating this approach with three\ndistinct physical systems. This consistency highlights the universal nature of\nscaling due to NTFPs and emphasizes the predictive capabilities of the proposed\ndifferential equation. Moreover, under specific conditions, the equation\npredicts a power-law related to the ratio of the two universal exponents,\nleading to implications concerning particle and energy transport. This suggests\nthat the observed power-laws in far-from-equilibrium turbulent fluids could be\nrelated to the universal scaling due to NTFPs, potentially offering new\ninsights into the study of turbulence.",
        "positive": "All-Optical Production of quantum degeneracy and molecular BEC of $^6$Li: We achieve a highly degenerate and strongly interacting Fermi gas in a\nmixture of the two lowest hyperfine states of $^6$Li by direct evaporative\ncooling in a high power crossed optical dipole trap. The trap is loaded from a\nlarge atom number magneto-optical trap (MOT) which is realized by a laser\nsystem of 2.5-watts intracavity-frequency-doubled light output at 671 nm. With\nthis system, we also demonstrate the production of a molecular Bose-Einstein\ncondensates (mBEC), and observe the anisotropic expansion of Fermi gases in the\nso-called BEC-BCS crossover regime."
    },
    {
        "anchor": "Beyond mean-field behavior of large Bose-Einstein condensates in\n  double-well potentials: For the dynamics of Bose-Einstein condensates (BECs), differences between\nmean-field (Gross-Pitaevskii) physics and $N$-particle quantum physics often\ndisappear if the BEC becomes larger and larger. In particular, the timescale\nfor which both dynamics agree should thus become larger if the particle number\nincreases. For BECs in a double-well potential, we find both examples for which\nthis is the case and examples for which differences remain even for huge BECs\non experimentally realistic short timescales. By using a combination of\nnumerical and analytical methods, we show that the differences remain visible\non the level of expectation values even beyond the largest possible numbers\nrealized experimentally for BECs with ultracold atoms.",
        "positive": "Control of dipolar relaxation in external fields: We study dipolar relaxation in both ultra-cold thermal and Bose-condensed\nchromium atom gases. We show three different ways to control dipolar\nrelaxation, making use of either a static magnetic field, an oscillatory\nmagnetic field, or an optical lattice to reduce the dimensionality of the gas\nfrom 3D to 2D. Although dipolar relaxation generally increases as a function of\na static magnetic field intensity, we find a range of non-zero magnetic field\nintensities where dipolar relaxation is strongly reduced. We use this resonant\nreduction to accurately determine the S=6 scattering length of chromium atoms:\n$a_6 = 103 \\pm 4 a_0$. We compare this new measurement to another new\ndetermination of $a_6$, which we perform by analysing the precise spectroscopy\nof a Feshbach resonance in d-wave collisions, yielding $a_6 = 102.5 \\pm 0.4\na_0$. These two measurements provide by far the most precise determination of\n$a_6$ to date. We then show that, although dipolar interactions are long-range\ninteractions, dipolar relaxation only involves the incoming partial wave $l=0$\nfor large enough magnetic field intensities, which has interesting consequences\non the stability of dipolar Fermi gases. We then study ultra-cold chromium\ngases in a 1D optical lattice resulting in a collection of independent 2D\ngases. We show that dipolar relaxation is modified when the atoms collide in\nreduced dimensionality at low magnetic field intensities, and that the\ncorresponding dipolar relaxation rate parameter is reduced by a factor up to 7\ncompared to the 3D case. Finally, we study dipolar relaxation in presence of\nradio-frequency (rf) oscillating magnetic fields, and we show that both the\noutput channel energy and the transition amplitude can be controlled by means\nof rf frequency and Rabi frequency."
    },
    {
        "anchor": "Quantum droplets of dipolar mixtures: Recently achieved two-component dipolar Bose-Einstein condensates open\nexciting possibilities for the study of mixtures of ultra-dilute quantum\nliquids. While non-dipolar self-bound mixtures are necessarily miscible with an\napproximately fixed ratio between the two densities, the density ratio for the\ndipolar case is free. As a result, self-bound dipolar mixtures present\nqualitatively novel and much richer physics, characterized by three possible\nground-state phases: miscible, symmetric immiscible and asymmetric immiscible,\nwhich may in principle occur at any population imbalance. Self-bound immiscible\ndroplets are possible due to mutual non-local inter-component attraction, which\nresults in the formation of a droplet molecule. Moreover, our analysis of the\nimpurity regime, shows that quantum fluctuations in the majority component\ncrucially modify the miscibility of impurities. Our work opens intriguing\nperspectives for the exploration of spinor physics in ultra-dilute liquids,\nwhich should resemble to some extent that of 4He-3He droplets and\nimpurity-doped helium droplets.",
        "positive": "Finite temperature stability of a trapped dipolar Bose gas: We calculate the stability diagram for a trapped normal Bose gas with\ndipole-dipole interactions. Our study characterizes the roles of trap geometry,\ntemperature, and short-ranged interactions on the stability. We predict a\nrobust double instability feature in oblate trapping geometries arising from\nthe interplay of thermal gas saturation and the anisotropy of the interaction.\nOur results are relevant to current experiments with polar molecules and will\nbe useful in developing strategies to obtain a polar molecule Bose-Einstein\ncondensate."
    },
    {
        "anchor": "Suppression of collision-induced dephasing by periodic, erratic, or\n  noisy driving: We compare different driving scenarios for controlling the loss of single\nparticle coherence of an initially coherent preparation in the vicinity of the\nhyperbolic instability of the two-mode bose-Hubbard model. In particular we\ncontrast the quantum Zeno suppression of decoherence by broad-band erratic or\nnoisy driving, with the Kapitza effect obtained for high frequency periodic\nmonochromatic driving.",
        "positive": "Creation of Quantum-Degenerate Gases of Ytterbium in a Compact\n  2D-/3D-MOT Setup: We report on the first experimental setup based on a 2D-/3D-MOT scheme to\ncreate both Bose-Einstein condensates and degenerate Fermi gases of several\nytterbium isotopes. Our setup does not require a Zeeman slower and offers the\nflexibility to simultaneously produce ultracold samples of other atomic\nspecies. Furthermore, the extraordinary optical access favors future\nexperiments in optical lattices. A 2D-MOT on the strong 1S0-1P1 transition\ncaptures ytterbium directly from a dispenser of atoms and loads a 3D-MOT on the\nnarrow 1S0-3P1 intercombination transition. Subsequently, atoms are transferred\nto a crossed optical dipole trap and cooled evaporatively to quantum\ndegeneracy."
    },
    {
        "anchor": "Phase-separated symmetry-breaking vortex-lattice in a binary\n  Bose-Einstein condensate: We study spontaneous-symmetry-breaking circularly-asymmetric phase separation\nof vortex lattices in a rapidly rotating harmonically-trapped\nquasi-two-dimensional (quasi-2D) binary Bose-Einstein condensate (BEC) with\nrepulsive inter- and intra-species interactions. The phase separated vortex\nlattices of the components appear in different regions of space with no overlap\nbetween the vortices of the two components, which will permit an efficient\nexperimental observation of such vortices and accurate study of the effect of\natomic interaction on such vortex lattice. Such phase separation takes place\nwhen the intra-species interaction energies of the two components are equal or\nnearly equal with relatively strong inter-species repulsion. When the\nintra-species energies are equal, the two phase-separated vortex lattices have\nidentical semicircular shapes with one being the parity conjugate of the other.\nWhen the intra-species energies are nearly equal, the phase separation is also\ncomplete but the vortex lattices have different shapes. We demonstrate our\nclaim with a numerical solution of the mean-field Gross-Pitaevskii equation for\na rapidly rotating quasi-2D binary BEC.",
        "positive": "Quantum dynamics of attractive versus repulsive bosonic Josephson\n  junctions: Bose-Hubbard and full-Hamiltonian results: The quantum dynamics of one-dimensional bosonic Josephson junctions with\nattractive and repulsive interparticle interactions is studied using the\nBose-Hubbard model and by numerically-exact computations of the full many-body\nHamiltonian. A symmetry present in the Bose-Hubbard Hamiltonian dictates an\nequivalence between the evolution in time of attractive and repulsive Josephson\njunctions with attractive and repulsive interactions of equal magnitude. The\nfull many-body Hamiltonian does not possess this symmetry and consequently the\ndynamics of the attractive and repulsive junctions are different."
    },
    {
        "anchor": "Phase tunable Josephson junction and spontaneous mass current in a\n  spin-orbit coupled Fermi superfluid: Atomtronics has the potential for engineering new types of functional\ndevices, such as Josephson junctions (JJs). Previous studies have mainly\nfocused on JJs whose ground states have 0 or $\\pi $ superconducting phase\ndifference across the junctions, while arbitrarily tunable phase JJs may have\nimportant applications in superconducting electronics and quantum computation.\nHere we show that a phase tunable JJ can be implemented in a spin-orbit coupled\ncold atomic gas with the magnetic tunneling barrier generated by a\nspin-dependent focused laser beam. We consider the JJ confined in either a\nlinear harmonic trap or a circular ring trap. In the ring trap, the magnetic\nbarrier induces a spontaneous mass current for the ground state of the JJ,\ndemonstrating the magnetoelectric effects of cold atoms.",
        "positive": "BCS-BEC crossover and the disappearance of FFLO-correlations in a\n  spin-imbalanced, one-dimensional Fermi gas: We present a numerical study of the one-dimensional BCS-BEC crossover of a\nspin-imbalanced Fermi gas. The crossover is described by the Bose-Fermi\nresonance model in a real space representation. Our main interest is in the\nbehavior of the pair correlations, which, in the BCS limit, are of the\nFulde-Ferrell-Larkin-Ovchinnikov type, while in the BEC limit, a superfluid of\ndiatomic molecules forms that exhibits quasi-condensation at zero momentum. We\nuse the density matrix renormalization group method to compute the phase\ndiagram as a function of the detuning of the molecular level and the\npolarization. As a main result, we show that FFLO-like correlations disappear\nwell below full polarization close to the resonance. The critical polarization\ndepends on both the detuning and the filling."
    },
    {
        "anchor": "Local readout and control of current and kinetic energy operators in\n  optical lattices: Quantum gas microscopes have revolutionized quantum simulations with\nultracold atoms, allowing to measure local observables and snapshots of quantum\nstates. However, measurements so far were mostly carried out in the occupation\nbasis. Here, we demonstrate how all kinetic operators, such as kinetic energy\nor current operators, can be measured and manipulated with single bond\nresolution. Beyond simple expectation values of these observables, the\nsingle-shot measurements allow to access full counting statistics and complex\ncorrelation functions. Our work paves the way for the implementation of\nefficient quantum state tomography and hybrid quantum computing protocols for\nitinerant particles on a lattice. In addition, we demonstrate how site-resolved\nprogrammable potentials enable a spatially-selective, parallel readout in\ndifferent bases as well as the engineering of arbitrary initial states.",
        "positive": "Beliaev damping of the Goldstone mode in atomic Fermi superfluids: Beliaev damping in a superfluid is the decay of a collective excitation into\ntwo lower frequency collective excitations; it represents the only decay mode\nfor a bosonic collective excitation in a superfluid at T = 0. The standard\ntreatment for this decay assumes a linear spectrum, which in turn implies that\nthe final state momenta must be collinear to the initial state. We extend this\ntreatment, showing that the inclusion of a gradient term in the Hamiltonian\nyields a realistic spectrum for the bosonic excitations; we then derive a\nformula for the decay rate of such excitations, and show that even moderate\nnonlinearities in the spectrum can yield substantial deviations from the\nstandard result. We apply our result to an attractive Fermi gas in the BCS-BEC\ncrossover: here the low-energy bosonic collective excitations are density\noscillations driven by the phase of the pairing order field. These collective\nexcitations, which are gapless modes as a consequence of the Goldstone\nmechanism, have a spectrum which is well established both theoretically and\nexperimentally, and whose linewidth, we show, is determined at low temperatures\nby the Beliaev decay mechanism."
    },
    {
        "anchor": "Exploring Non-Abelian Geometric Phases in Spin-1 Ultracold Atoms: Non-Abelian and non-adiabatic variants of Berry's geometric phase have been\npivotal in the recent advances in fault tolerant quantum computation gates,\nwhile Berry's phase itself is at the heart of the study of topological phases\nof matter. The geometrical and topological properties of the phase space of\nspin$-1$ quantum states is richer than that of spin$-1/2$ quantum states and is\nrelatively unexplored. For instance, the spin vector of a spin-1 system, unlike\nthat of a spin$-1/2$ system, can lie anywhere on or inside the Bloch sphere\nrepresenting the phase space. Recently, a generalization of Berry's phase that\nencapsulates the topology of spin-1 quantum states has been formulated in J.\nMath. Phys., 59(6), 062105. This geometric phase includes loops that go inside\nthe Bloch sphere and is carried by the tensor of spin fluctuations, unlike\nBerry's phase which is carried by the global phase of the quantum state.\nFurthermore, due to a mathematical singularity at the center of the Bloch\nsphere, the class of loops that pass through the center are called singular\nloops and are significant because their geometric phase is non-Abelian. In\ncontrast with Berry's phase for spin$-1/2$ systems, whose properties come from\nthe topology of a sphere, the properties of singular loop geometric phases come\nfrom the topology of the real projective plane $\\mathbb{RP}^2$, which is more\nnon-trivial. Here we use coherent control of ultracold $^{87}$Rb atoms in an\noptical trap to experimentally explore this geometric phase for singular loops\nin a spin-1 quantum system.",
        "positive": "Non-standard Hubbard models in optical lattices: a review: Originally, the Hubbard model has been derived for describing the behaviour\nof strongly-correlated electrons in solids. However, since over a decade now,\nvariations of it are also routinely being implemented with ultracold atoms in\noptical lattices. We review some of the rich literature on this subject, with a\nfocus on more recent non-standard forms of the Hubbard model. After an\nintroduction to standard (fermionic and bosonic) Hubbard models, we discuss\nbriefly common models for mixtures, as well as the so called extended\nBose-Hubbard models, that include interactions between neighboring sites,\nnext-neighboring sites, and so on. The main part of the review discusses the\nimportance of additional terms appearing when refining the tight-binding\napproximation on the original physical Hamiltonian. Even when restricting the\nmodels to the lowest Bloch band is justified, the standard approach neglects\nthe density-induced tunneling (which has the same origin as the usual on-site\ninteraction). The importance of these contributions is discussed for both\ncontact and dipolar interactions. For sufficiently strong interactions, also\nthe effects related to higher Bloch bands become important even for deep\noptical lattices. Different approaches that aim at incorporating these effects,\nmainly via dressing the basis Wannier functions with interactions, leading to\neffective, density-dependent Hubbard-type models, are reviewed. We discuss also\nexamples of Hubbard-like models that explicitly involve higher $p$-orbitals, as\nwell as models that couple dynamically spin and orbital degrees of freedom.\nFinally, we review mean-field nonlinear-Schr\\\"odinger models of the Salerno\ntype that share with the non-standard Hubbard models the nonlinear coupling\nbetween the adjacent sites. In that part, discrete solitons are the main\nsubject of the consideration. We conclude by listing some future open problems."
    },
    {
        "anchor": "Matter-wave dark solitons: stochastic vs. analytical results: The dynamics of dark matter-wave solitons in elongated atomic condensates are\ndiscussed at finite temperatures. Simulations with the stochastic\nGross-Pitaevskii equation reveal a noticeable, experimentally observable spread\nin individual soliton trajectories, attributed to inherent fluctuations in both\nphase and density of the underlying medium. Averaging over a number of such\ntrajectories (as done in experiments) washes out such background fluctuations,\nrevealing a well-defined temperature-dependent temporal growth in the\noscillation amplitude. The average soliton dynamics is well captured by the\nsimpler dissipative Gross-Pitaevskii equation, both numerically and via an\nanalytically-derived equation for the soliton center based on perturbation\ntheory for dark solitons.",
        "positive": "Inhomogeneous spin diffusion in traps with cold atoms: The spin diffusion and damped oscillations are studied in the collision of\ntwo spin polarized clouds of cold atoms with resonant interactions. The strong\ndensity dependence of the diffusion coefficient leads to inhomogeneous spin\ndiffusion that changes from central to surface spin flow as the temperature\nincreases. The inhomogeneity and the smaller finite trap size significantly\nreduce the spin diffusion rate at low temperatures. The resulting spin\ndiffusion rates, spin drag and initial damped oscillations are compatible with\nmeasurements at low to high temperatures for resonant attractive interactions\nbut are incompatible with a metastable ferromagnetic phase."
    },
    {
        "anchor": "Enhanced transport of spin-orbit coupled Bose gases in disordered\n  potentials: Anderson localization is a single particle localization phenomena in\ndisordered media that is accompanied by an absence of diffusion. Spin-orbit\ncoupling (SOC) describes an interaction between a particle's spin and its\nmomentum that directly affects its energy dispersion, for example creating\ndispersion relations with gaps and multiple local minima. We show theoretically\nthat combining one-dimensional spin-orbit coupling with a transverse Zeeman\nfield suppresses the effects of disorder, thereby increasing the localization\nlength and conductivity. This increase results from a suppression of back\nscattering between states in the gap of the SOC dispersion relation. Here, we\nfocus specifically on the interplay of disorder from an optical speckle\npotential and SOC generated by two-photon Raman processes in quasi-1D\nBose-Einstein condensates. We first describe back-scattering using a Fermi's\ngolden rule approach, and then numerically confirm this picture by solving the\ntime-dependent 1D Gross Pitaevskii equation for a weakly interacting\nBose-Einstein condensate with SOC and disorder. We find that on the 10's of\nmillisecond time scale of typical cold atom experiments moving in harmonic\ntraps, initial states with momentum in the zero-momentum SOC gap evolve with\nnegligible back-scattering, while without SOC these same states rapidly\nlocalize.",
        "positive": "Applying machine learning optimization methods to the production of a\n  quantum gas: We apply three machine learning strategies to optimize the atomic cooling\nprocesses utilized in the production of a Bose-Einstein condensate (BEC). For\nthe first time, we optimize both laser cooling and evaporative cooling\nmechanisms simultaneously. We present the results of an evolutionary\noptimization method (Differential Evolution), a method based on non-parametric\ninference (Gaussian Process regression) and a gradient-based function\napproximator (Artificial Neural Network). Online optimization is performed\nusing no prior knowledge of the apparatus, and the learner succeeds in creating\na BEC from completely randomized initial parameters. Optimizing these cooling\nprocesses results in a factor of four increase in BEC atom number compared to\nour manually-optimized parameters. This automated approach can maintain\nclose-to-optimal performance in long-term operation. Furthermore, we show that\nmachine learning techniques can be used to identify the main sources of\ninstability within the apparatus."
    },
    {
        "anchor": "Bright soliton to quantum droplet transition in a mixture of\n  Bose-Einstein condensates: Attractive Bose-Einstein condensates can host two types of macroscopic\nself-bound states of different nature: bright solitons and quantum liquid\ndroplets. Here, we investigate the connection between them with a Bose-Bose\nmixture confined in an optical waveguide. We develop a simple theoretical model\nto show that, depending on atom number and interaction strength, solitons and\ndroplets can be smoothly connected or remain distinct states coexisting only in\na bi-stable region. We experimentally measure their spin composition, extract\ntheir density for a broad range of parameters and map out the boundary of the\nregion separating solitons from droplets.",
        "positive": "Rydberg crystallization detection by statistical means: We investigate an ensemble of atoms which can be excited into a Rydberg\nstate. Using a disordered quantum Ising model, we perform a numerical\nsimulation of the experimental procedure and calculate the probability\ndistribution function $P(M)$ to create a certain number of Rydberg atoms $M$,\nas well as their pair correlation function. Using the latter, we identify the\ncritical interaction strength above which the system undergoes a phase\ntransition to a Rydberg crystal. We then show that this phase transition can be\ndetected using $P(M)$ alone."
    },
    {
        "anchor": "Energy and momentum transfer in one-dimensional trapped gases by\n  stimulated light scattering: In ultracold atoms settings, inelastic light scattering is a preeminent\ntechnique to reveal static and dynamic properties at nonzero momentum. In this\nwork, we investigate an array of one-dimensional trapped Bose gases, by\nmeasuring both the energy and the momentum imparted to the system via light\nscattering experiments. The measurements are performed in the weak perturbation\nregime, where these two quantities - the energy and momentum transferred - are\nexpected to be related to the dynamical structure factor of the system. We\ndiscuss this relation, with special attention to the role of in-trap dynamics\non the transferred momentum.",
        "positive": "Controllable manipulation and detection of local densities and bipartite\n  entanglement in a quantum gas by a dissipative defect: We study the complex dynamics of a one-dimensional Bose gas subjected to a\ndissipative local defect which induces one-body atom losses. In experiments\nthese atom losses occur, for example, when a focused electron or light beam or\na single trapped ion is brought into contact with a quantum gas. We discuss how\nwithin such setups one can measure or manipulate densities locally and specify\nthe excitations that are induced by the defect. In certain situations the\ndefect can be used to generate entanglement in a controlled way despite its\ndissipative nature. The careful examination of the interplay between hole\nexcitations and the collapse of the wave function due to nondetection of loss\nis crucial for the understanding of the dynamics we observe."
    },
    {
        "anchor": "Superfluid transition of disordered dipolar Fermi gases in a 2D lattice: We consider a superfluid transition in two-component dipolar Fermi gases in a\ntwo-dimensional lattice with a weak on-site disorder. The momentum dependent\ndipole-dipole interaction amplitude violates the Anderson theorem and in the\nweakly interacting regime this leads to an increase of the superfluid\ntransition temperature. We find that in a sufficiently deep lattice\n(tight-binding regime) and in the low momentum limit superfluid properties can\nbe considered in the same way as in free space replacing the mass of atoms by\nan effective mass in the lattice. The disorder-induced increase of the critical\ntemperature can be significantly more pronounced than in free space.",
        "positive": "BCS-BEC crossover in a quasi-two-dimensional Fermi superfluid: We study the crossover from the Bardeen-Cooper-Shrieffer (BCS) regime to the\nBose-Einstein-condensation (BEC) regime in a quasi-two-dimensional quantum gas\nof ultracold fermionic atoms. Using an effective two-dimensional Hamiltonian\nwith renormalized interactions between atoms and dressed molecules within a\nGaussian pair fluctuation theory, we investigate how Fermi superfluidity is\naffected by reduced dimensionality at zero temperature in a wide range of\ncrossover. We observe that the order parameter and pair size show universal\nrelations with the chemical potential on the BCS side, irrespective of\ndimensionality. However, such universal dependences break down towards the BEC\nlimit with increasing interaction strength. This results reveal the notable\neffect of reduced dimenionality on pairing physics, which can also be observed\nin the sound velocity and convexity parameter of the Goldstone mode. We compare\nour results with the latest experiments in both ${}^{6}$Li atomic gases and\nlayered nitrides LixZrNCl and find good agreements."
    },
    {
        "anchor": "A higher-order topological twist on cold-atom SO(5) Dirac fields: Ultracold Fermi gases of spin-3/2 atoms provide a clean platform to realise\nSO(5) models of 4-Fermi interactions in the laboratory. By confining the atoms\nin a two-dimensional Raman lattice, we show how this system can be used as a\nflexible quantum simulator of Dirac quantum field theories (QFTs) that combine\nGross-Neveu and Thirring interactions with a higher-order topological twist. We\nshow that the lattice model corresponds to a regularization of this QFT with an\nanisotropic twisted Wilson mass. This allows us to access higher-order\ntopological states protected by a hidden SO(5) symmetry, a remnant of the\noriginal rotational symmetry of the 4-Fermi interactions that is not explicitly\nbroken by the lattice discretization. Using large-$N$ methods, we show that the\n4-Fermi interactions lead to a rich phase diagram with various competing\nfermion condensates. Our work opens a route for the implementation of\ncorrelated higher-order topological states with tunable interactions that has\ninteresting connections to non-trivial relativistic QFTs of Dirac fermions in\n$D = 2 + 1$ dimensions.",
        "positive": "Two-photon nonlinear spectroscopy of periodically trapped ultracold\n  atoms in a cavity: We study the transmission spectra of a Bose Einstein condensate confined in\nan optical lattice interacting with two modes of a cavity via nonlinear\ntwo-photon transition. In particular we show that a nonlinear two-photon\ninteraction between the superfluid (SF) phase and the Mott insulating (MI)\nphase of a Bose-Einstein condensate (BEC) and the cavity field show\nqualitatively different transmission spectra compared to the one-photon\ninteraction. We found that when the BEC is in the Mott state, the usual normal\nmode splitting present in the one-photon transition is missing in the\ntwo-photon interaction. When the BEC is in the superfluid state, the\ntransmission spectra shows the usual multiple lorentzian structure. However the\nseparation between the lorentzians for the two-photon case is much larger than\nthat for the one-photon case. This study could form the basis for\nnon-destructive high resolution Rydberg spectroscopy of ultracold atoms or\ntwo-photon spectroscopy of a gas of ultracold atomic hydrogen."
    },
    {
        "anchor": "A study of one-dimensional transport of Bose-Einstein condensates using\n  exterior complex scaling: We numerically investigate the one-dimensional transport of Bose-Einstein\ncondensates in the context of guided atom lasers using a mean-field description\nof the condensate in terms of a spatially discretized Gross-Pitaevskii\nequation. We specifically consider a waveguide configuration in which spatial\ninhomogeneities and nonvanishing atom-atom interactions are restricted to a\nspatially localized scattering region of finite extent. We show how the method\nof smooth exterior complex scaling can be implemented for this particular\nconfiguration in order to efficiently absorb the outgoing flux within the\nwaveguide. A numerical comparison with the introduction of a complex absorbing\npotential as well as with the analytically exact elimination of the dynamics of\nthe free non-interacting motion outside the scattering region, giving rise to\ntransparent boundary conditions, clearly confirms the accuracy and efficiency\nof the smooth exterior complex scaling method.",
        "positive": "Cooling in strongly correlated optical lattices: prospects and\n  challenges: Optical lattices have emerged as ideal simulators for Hubbard models of\nstrongly correlated materials, such as the high-temperature superconducting\ncuprates. In optical lattice experiments, microscopic parameters such as the\ninteraction strength between particles are well known and easily tunable.\nUnfortunately, this benefit of using optical lattices to study Hubbard models\ncome with one clear disadvantage: the energy scales in atomic systems are\ntypically nanoKelvin compared with Kelvin in solids, with a correspondingly\nminiscule temperature scale required to observe exotic phases such as d-wave\nsuperconductivity. The ultra-low temperatures necessary to reach the regime in\nwhich optical lattice simulation can have an impact-the domain in which our\ntheoretical understanding fails-have been a barrier to progress in this field.\nTo move forward, a concerted effort to develop new techniques for cooling and,\nby extension, techniques to measure even lower temperatures. This article will\nbe devoted to discussing the concepts of cooling and thermometry, fundamental\nsources of heat in optical lattice experiments, and a review of proposed and\nimplemented thermometry and cooling techniques."
    },
    {
        "anchor": "Sound propagation in cigar-shaped Bose liquids in the Thomas-Fermi\n  approximation: A comparative study between Gross-Pitaevskii and logarithmic\n  models: A comparative study is done of the propagation of sound pulses in elongated\nBose liquids and Bose-Einstein condensates in Gross-Pitaevskii and logarithmic\nmodels, by means of the Thomas-Fermi approximation. It is shown that in the\nlinear regime the propagation of small density fluctuations is essentially\none-dimensional in both models, in the direction perpendicular to the cross\nsection of a liquid's lump. Under these approximations, it is shown that the\nspeed of sound scales as a square root of particle density in the case of the\nGross-Pitaevskii liquid/condensate, but it is constant in a case of the\nhomogeneous logarithmic liquid.",
        "positive": "A full view on the dynamics of an impurity coupled to two\n  one-dimensional fermionic baths: We consider a model for the motion of an impurity interacting with two\nparallel, one-dimensional (bosonized) fermionic baths. The impurity is able to\nmove along any of the baths, and to jump from one to the other. We provide a\nperturbative expression for the state evolution of the system when the impurity\nis injected in one of the baths, with a given wave packet. The nontrivial\nchoice of the unperturbed dynamics makes the approximation formally\ninfinite-order in the impurity-bath coupling, allowing us to reproduce the\northogonality catastrophe. We employ the result for the state evolution to\nobserve the dynamics of the impurity and its effect on the baths, in particular\nin the case when the wave packet is Gaussian. We observe and characterize the\npropagation of the impurity along the baths and the hopping between them. We\nalso analyze the dynamics of the bath density and momentum density (i.e. the\nparticle current), and show that fits an intuitive semi-classical\ninterpretation. We also quantify the correlation that is established between\nthe baths by calculating the inter-bath, equal-time spatial correlation\nfunctions of both bath density and momentum, finding a complex pattern. We show\nthat this pattern contains information on both the impurity motion and on the\nbaths themselves, and that these can be unveiled by taking appropriate \"slices\"\nof the time evolution."
    },
    {
        "anchor": "Spin-orbit coupling in organic microcavities: Lower polariton splitting,\n  triplet polaritons, and disorder-induced dark-states relaxation: Using an extended Tavis-Cummings model, we study the effect of the spin-orbit\ncoupling between the singlet and the triplet molecular excitons in organic\nmicrocavities in the strong coupling regime. The model is solved in the single\nexcitation space for polaritons, which contains the bright (permutation\nsymmetric) singlet and triplet excitons, as well as the dark bands consisting\nof the nonsymmetric excitons of either type. We find that the spin-orbit\ncoupling splits the lower polariton into two branches, and also creates a\ntriplet polariton when the cavity mode is in resonance with the triplet\nexcitons. The optical absorption spectrum of the system that can reveal this\nsplitting in experiments is presented and the effect of disorder in exciton\nenergies and couplings is explored. An important consequence of the disorder in\nthe spin-orbit coupling -- a weak coupling between the otherwise decoupled\nbright and dark sectors -- is explored and detailed calculations of the squared\ntransition matrix elements between the dark bands and polaritons are presented\nalong with derivation of some approximate yet quite accurate analytical\nexpressions. This relaxation channel for the dark states contains an\ninterference between two transition paths that, for a given polariton state,\nsuppresses the relaxation of one dark band and enhances it for the other.",
        "positive": "A topological proof that there is no sign problem in one dimensional\n  Path Integral Monte Carlo simulation of fermions: This work shows that, in one dimension, due to its topology, a closed-loop\nproduct of short-time propagators is always positive, despite the fact that\neach anti-symmetric free fermion propagator can be of either sign."
    },
    {
        "anchor": "Pair formation in quenched unitary Bose gases: We study a degenerate Bose gas quenched to unitarity by solving a many-body\nmodel including three-body losses and correlations up to second order. As the\ngas evolves in this strongly-interacting regime, the buildup of correlations\nleads to the formation of extended pairs bound purely by many-body effects,\nanalogous to the phenomenon of Cooper pairing in the BCS regime of the Fermi\ngas. Through fast sweeps away from unitarity, we detail how the correlation\ngrowth and formation of bound pairs emerge in the fraction of unbound atoms\nremaining post sweep, finding quantitative agreement with experiment. We\ncomment on the possible role of higher-order effects in explaining the\ndeviation of our theoretical results from experiment for slower sweeps and\nlonger times spent in the unitary regime.",
        "positive": "Resonant light enhances phase coherence in a cavity QED simulator of\n  fermionic superfluidity: Cavity QED experiments are natural hosts for non-equilibrium phases of matter\nsupported by photon-mediated interactions. In this work, we consider a cavity\nQED simulation of the BCS model of superfluidity, by studying regimes where the\ncavity photons act as dynamical degrees of freedom instead of mere mediators of\nthe interaction via virtual processes. We find an enhancement of long time\ncoherence following a quench whenever the cavity frequency is tuned into\nresonance with the atoms. We discuss how this is equivalent to enhancement of\nnon-equilibrium superfluidity and highlight similarities to an analogous\nphenomena recently studied in solid state quantum optics. We also discuss the\nconditions for observing this enhanced resonant pairing in experiments by\nincluding the effect of photon losses and inhomogeneous coupling in our\nanalysis."
    },
    {
        "anchor": "Floquet prethermalization and regimes of heating in a periodically\n  driven, interacting quantum system: We study the regimes of heating in the periodically driven $O(N)$-model,\nwhich represents a generic model for interacting quantum many-body systems. By\ncomputing the absorbed energy with a non-equilibrium Keldysh Green's function\napproach, we establish three dynamical regimes: at short times a\nsingle-particle dominated regime, at intermediate times a stable Floquet\nprethermal regime in which the system ceases to absorb, and at parametrically\nlate times a thermalizing regime. Our simulations suggest that in the\nthermalizing regime the absorbed energy grows algebraically in time with an the\nexponent that approaches the universal value of $1/2$, and is thus\nsignificantly slower than linear Joule heating. Our results demonstrate the\nparametric stability of prethermal states in a generic many-body system driven\nat frequencies that are comparable to its microscopic scales. This paves the\nway for realizing exotic quantum phases, such as time crystals or interacting\ntopological phases, in the prethermal regime of interacting Floquet systems.",
        "positive": "Second-order virial expansion for an atomic gas in a harmonic waveguide: The virial expansion for cold two-component Fermi and Bose atomic gases is\nconsidered in the presence of a waveguide and in the vicinity of a Feshbach\nresonance. The interaction between atoms and the coupling with the Feshbach\nmolecules is modeled using a quantitative separable two-channel model. The\nscattering phase-shift in an atomic waveguide is defined. This permits us to\nextend the Beth-Uhlenbeck formula for the second-order virial coefficient to\nthis inhomogeneous case."
    },
    {
        "anchor": "Cross-dimensional phase transition from an array of 1D Luttinger liquids\n  to a 3D Bose-Einstein condensate: We study the thermodynamic properties of a 2D array of coupled\none-dimensional Bose gases. The system is realized with ultracold bosonic atoms\nloaded in the potential tubes of a two-dimensional optical lattice. For\nnegligible coupling strength, each tube is an independent weakly interacting 1D\nBose gas featuring Tomonaga Luttinger liquid behavior. By decreasing the\nlattice depth, we increase the coupling strength between the 1D gases and allow\nfor the phase transition into a 3D condensate. We extract the phase diagram for\nsuch a system and compare our results with theoretical predictions. Due to the\nhigh effective mass across the periodic potential and the increased 1D\ninteraction strength, the phase transition is shifted to large positive values\nof the chemical potential. Our results are prototypical to a variety of\nlow-dimensional systems, where the coupling between the subsystems is realized\nin a higher spatial dimension such as coupled spin chains in magnetic\ninsulators.",
        "positive": "Quantum phase transitions of the spin-boson model within\n  multi-coherent-states: A variational approach based on the multi-coherent-state ansatz with\nasymmetric parameters is employed to study the ground state of the spin-boson\nmodel. Without any artificial approximations except for the finite number of\nthe coherent states, we find the robust Gaussian critical behavior in the whole\nsub-Ohmic bath regime. The converged critical coupling strength can be\nestimated with the $1/N$ scaling, where $N $ is the number of the coherent\nstates. It is strongly demonstrated the breakdown of the well-known\nquantum-to-classical mapping for $1/2<s<1$. In addition, the entanglement\nentropy displays more steep jump around the critical points for the Ohmic bath\nthan the sub-Ohmic bath."
    },
    {
        "anchor": "Quasiclassical molecular dynamics for the dilute Fermi gas at unitarity: We study the dilute Fermi gas at unitarity using molecular dynamics with an\neffective quantum potential constructed to reproduce the quantum two-body\ndensity matrix at unitarity. Results for the equation of state, the pair\ncorrelation function and the shear viscosity are presented. These quantities\nare well understood in the dilute, high temperature, limit. Using molecular\ndynamics we determine higher order corrections in the diluteness parameter\n$n\\lambda^3$, where $n$ is the density and $\\lambda$ is the thermal de Broglie\nwave length. In the case of the contact density, which parameterizes the short\ndistance behavior of the correlation function, we find that the results of\nmolecular dynamics interpolates between the truncated second and third order\nvirial expansion, and are in excellent agreement with existing T-matrix\ncalculations. For the shear viscosity we reproduce the expected scaling\nbehavior at high temperature, $\\eta\\sim 1/\\lambda^3$, and we determine the\nleading density dependent correction to this result.",
        "positive": "Spatial coherence of spin-orbit-coupled Bose gases: Spin-orbit-coupled Bose-Einstein condensates (SOBECs) exhibit two new phases\nof matter, now known as the stripe and plane-wave phases. When two interacting\nspin components of a SOBEC spatially overlap, density modulations with\nperiodicity given by the spin-orbit coupling strength appear. In equilibrium,\nthese components fully overlap in the miscible stripe phase, and overlap only\nin a domain wall in the immiscible plane-wave phase. Here we probe the density\nmodulation present in any overlapping region with optical Bragg scattering, and\nobserve the sudden drop of Bragg scattering as the overlapping region shrinks.\nUsing an atomic analogue of the Talbot effect, we demonstrate the existence of\nlong-range coherence between the different spin components in the stripe phase\nand surprisingly even in the phase-separated plane-wave phase."
    },
    {
        "anchor": "Anisotropic and long-range vortex interactions in two-dimensional\n  dipolar Bose gases: We perform a theoretical study into how dipole-dipole interactions modify the\nproperties of superfluid vortices within the context of a two-dimensional\natomic Bose gas of co-oriented dipoles. The reduced density at a vortex acts\nlike a giant anti-dipole, changing the density profile and generating an\neffective dipolar potential centred at the vortex core whose most slowly\ndecaying terms go as $1/\\rho^2$ and $\\ln(\\rho)/\\rho^3$. These effects modify\nthe vortex-vortex interaction which, in particular, becomes anisotropic for\ndipoles polarized in the plane. Striking modifications to vortex-vortex\ndynamics are demonstrated, i.e. anisotropic co-rotation dynamics and the\nsuppression of vortex annihilation.",
        "positive": "Polarons in a Dipolar Condensate: We consider a polaronic model in which impurity fermions interact with\nbackground bosons in a dipolar condensate. The polaron in this model emerges as\nan impurity dressed with a cloud of phonons of the dipolar condensate, which,\ndue to the competition between the attractive and repulsive part of the\ndipole-dipole interaction, obey an anisotropic dispersion spectrum. We study\nhow this anisotropy affects the Cerenkov-like emission of Bogoliubov phonon\nmodes, which can be directly verified by experiments in which a dipolar BEC\nmoves against an obstacle. We also study the spectral function of impurity\nfermions, which is directly accessible to the momentum resolved rf spectroscopy\nin cold atoms."
    },
    {
        "anchor": "Polaronic effects in one- and two-band quantum systems: In this work we study the formation and dynamics of polarons in a system with\na few impurities in a lattice immersed in a Bose-Einstein condensate (BEC).\nThis system has been experimentally realized using ultracold atoms and optical\nlattices. Here we consider a two-band model for the impurity atoms, along with\na Bogoliubov approximation for the BEC, with phonons coupled to impurities via\nboth intra- and inter-band transitions. We decouple this Fr\\\"ohlich-like term\nby an extended two-band Lang-Firsov polaron transformation using a variational\nmethod. The new effective Hamiltonian with two (polaron) bands differs from the\noriginal Hamiltonian by modified coherent transport, polaron energy shifts and\ninduced long-range interaction. A Lindblad master equation approach is used to\ntake into account residual incoherent coupling between polaron and bath. This\npolaronic treatment yields a renormalized inter-band relaxation rate compared\nto Fermi's Golden Rule. For a strongly coupled two-band Fr\\\"ohlich Hamiltonian,\nthe polaron is tightly dressed in each band and can not tunnel between them,\nleading to an inter-band self-trapping effect.",
        "positive": "Pulse propagation in interacting one dimensional Bose liquid: We study wave propagation in interacting Bose liquid, where the short range\npart of the interaction between atoms is of a hard core type, and its long\nrange part scales with a distance as a power law. The cases of Coulomb,\ndipole-dipole and Van der Waals interaction are considered. We employ a\nhydrodynamic approach, based on the exact solution of Lieb-Liniger model, and\nstudy the evolution of a density pulse instantly released from a potential\ntrap. We analyze semi-classical Euler and continuity equations and construct\nthe corresponding Riemann invariants. We supplement our analysis with numerical\ncalculations and discuss experimental applications for ultacold atom\nexperiments."
    },
    {
        "anchor": "Realizing the Frenkel-Kontorova model with Rydberg-dressed atoms: We propose a method to realize the Frenkel-Kontorova model using an array of\nRydberg dressed atoms. Our platform can be used to study this model with a\nrange of realistic interatomic potentials. In particular, we concentrate on two\ntypes of interaction potentials: a springlike potential and a repulsive\nlong-range potential. We numerically calculate the phase diagram for such\nsystems and characterize the Aubry-like and commensurate-incommensurate phase\ntransitions. Experimental realizations of this system that are possible to\nachieve using current technology are discussed.",
        "positive": "Mott-insulator state of cold atoms in tilted optical lattices: doublon\n  dynamics and multi-level Landau-Zener tunneling: We discuss the dynamical response of strongly interacting Bose atoms in an\nadiabatically tilted optical lattice. The analysis is performed in terms of the\nmulti-level Landau-Zenner tunneling. Different regimes of tunneling are\nidentified and analytical expressions for the doublon number, which is the\nquantity measured in laboratory experiments, are derived."
    },
    {
        "anchor": "Dynamical Friedel oscillations of a Fermi sea: We study the scenario of quenching an interaction-free Fermi sea on a\none-dimensional lattice ring by suddenly changing the potential of a site. From\nthe point-of-view of the conventional Friedel oscillation, which is a static or\nequilibrium problem, it is of interest what temporal and spatial oscillations\nthe local sudden quench will induce. Numerically, the primary observation is\nthat for a generic site, the local particle density switches between two\nplateaus periodically in time. Making use of the proximity of the realistic\nmodel to an exactly solvable model and employing the {Abel regularization} to\nassign a definite value to a divergent series, we obtain an analytical formula\nfor the heights of the plateaus, which turns out to be very accurate for sites\nnot too close to the quench site. The unexpected relevance and the incredible\naccuracy of the Abel regularization are yet to be understood. Eventually, when\nthe contribution of the defect mode is also taken into account, the plateaus\nfor those sites close to or on the quench site can also be accurately\npredicted. We have also studied the infinite lattice case. In this case,\nensuing the quench, the out-going wave fronts leave behind a stable density\noscillation pattern. Because of some interesting single-particle property, this\ndynamically generated Friedel oscillation differs from its conventional static\ncounterpart only by the defect mode.",
        "positive": "Quench dynamics of a strongly interacting resonant Bose gas: We explore the dynamics of a Bose gas following its quench to a strongly\ninteracting regime near a Feshbach resonance. Within a self-consistent\nBogoliubov analysis we find that after the initial condensate-quasiparticle\nRabi oscillations, at long time scales the gas is characterized by a\nnonequilibrium steady-state momentum distribution function, with depletion,\ncondensate density and contact that deviate strongly from their corresponding\nequilibrium values. These are in a qualitative agreement with recent\nexperiments on Rb85 by Makotyn, et al. Our analysis also suggests that for\nsufficiently deep quenches close to the resonance the nonequilibrium state\nundergoes a phase transition to a fully depleted state, characterized by a\nvanishing condensate density."
    },
    {
        "anchor": "Probing quasi-integrability of the Gross-Pitaevskii equation in a\n  harmonic-oscillator potential: Previous simulations of the one-dimensional Gross-Pitaevskii equation (GPE)\nwith repulsive nonlinearity and a harmonic-oscillator trapping potential hint\ntowards the emergence of quasi-integrable dynamics -- in the sense of\nquasi-periodic evolution of a moving dark soliton without any signs of\nergodicity -- although this model does not belong to the list of integrable\nequations. To investigate this problem, we replace the full GPE by a suitably\ntruncated expansion over harmonic-oscillator eigenmodes (the Galerkin\napproximation), which accurately reproduces the full dynamics, and then analyze\nthe system's dynamical spectrum. The analysis enables us to interpret the\nobserved quasi-integrability as the fact that the finite-mode dynamics always\nproduces a quasi-discrete power spectrum, with no visible continuous component,\nthe presence of the latter being a necessary manifestation of ergodicity. This\nconclusion remains true when a strong random-field component is added to the\ninitial conditions. On the other hand, the same analysis for the GPE in an\ninfinitely deep potential box leads to a clearly continuous power spectrum,\ntypical for ergodic dynamics.",
        "positive": "Solutions of the Schr\u00f6dinger equation for anisotropic dipole-dipole\n  interaction plus isotropic van der Waals interaction: By generalizing Bo Gao's approach [Phys. Rev. A 58, 1728 (1998)] for solving\nthe Schr\\\"{o}dinger equation for an isotropic van der Waals (vdW) potential to\nthe systems with a multi-scale anisotropic long-range interaction, we derive\nthe solutions for the Schr\\\"{o}dinger equation for an anisotropic dipole-dipole\ninteraction plus an isotropic attractive vdW potential, i.e.,\n${C_d(1-3\\cos^2\\theta)}/{r^3}-{C_6}/{r^6}$, which is projected to the subspace\nwith angular momentum $l\\leq l_{\\rm cut}$, with $l_{\\rm cut}$ being an\narbitrary angular-momentum cutoff. Here $\\theta$ is the polar angle of the\ncoordinate $\\boldsymbol{r}$ and $r=|\\boldsymbol{r}|$. The asymptotic behaviors\nof these solutions for $r\\rightarrow 0$ and $r\\rightarrow \\infty$ are obtained.\nThese results can be used in the research of collisions and chemical reactions\nbetween ultra-cold polar molecules in a static electric field. Our approach to\nderive the solutions can be applied to the systems with a general long-range\npotential $\\sum_{\\lambda= 2}^{\\lambda_{\\rm max}}\n{V_\\lambda(\\theta,\\varphi)}/{r^\\lambda}$, with $\\varphi$ being the azimuthal\nangle of $\\boldsymbol{r}$, and thus can be used in various problems on\nmolecule-molecule interaction."
    },
    {
        "anchor": "Stability of a Fully Magnetized Ferromagnetic state in Repulsively\n  Interacting Ultracold Fermi Gases: We construct a variational wave function to study whether a fully polarized\nFermi sea is energetically stable against a single spin flip. Our variational\nwave function contains sufficient short-range correlation at least to the same\nlevel as Gutzwiller's projected wave function. For Hubbard lattice model and\ncontinuum model with pure repulsive interaction, we show a fully polarized\nFermi sea is generally unstable even when the repulsive strength becomes\ninfinite. While for a resonance model, ferromagnetic state is possible if the\ns-wave scattering length is positive and sufficiently large, and the system is\nprepared in scattering state orthogonal to molecular bound state. However, we\ncan not rule out the possibility that more exotic correlation can destabilize\nthe ferromagnetic state.",
        "positive": "Bose Einstein condensate as nonlinear block of a Machine Learning\n  pipeline: Physical systems can be used as an information processing substrate and with\nthat extend traditional computing architectures. For such an application the\nexperimental platform must guarantee pristine control of the initial state, the\ntemporal evolution and readout. All these ingredients are provided by modern\nexperimental realizations of atomic Bose Einstein condensates. By embedding the\nnonlinear evolution of a quantum gas in a Machine Learning pipeline, one can\nrepresent nonlinear functions while only linear operations on classical\ncomputing of the pipeline are necessary. We demonstrate successful regression\nand interpolation of a nonlinear function using a quasi one-dimensional cloud\nof potassium atoms and characterize the performance of our system."
    },
    {
        "anchor": "Supplementary information to \"Efimov-driven phase transitions of the\n  unitary Bose gas\": In quantum physics, Efimov trimers are bound states of three particles that\nfall apart like Borromean rings when one of them is removed. Initially\npredicted in nuclear physics, these striking bosonic states are hard to\nobserve, but the \"unitary\" interactions at which they form is commonly realized\nin current cold atoms experiments. There, they set the stage for a new class of\nuniversal physics: Two-body interactions are all but invisible, but three-body\neffects allow the emergence of a largely uncharted new world of many-particle\nbound states. Three-particle systems were characterized theoretically, and the\nground-state properties of small unitary clusters computed numerically, but the\nmacroscopic many-body behaviour has remained unknown. Here we show, using a\nPath-Integral Monte Carlo algorithm backed up by theoretical arguments, that\nthe unitary Bose gas presents a first-order phase transition from a normal gas\nto a superfluid Efimov liquid. The normal gas is very well described by the\navailable virial coefficients. At unitarity, the phase diagram of the bosonic\nsystem is universal in rescaled pressure and temperature. A triple point\nseparates the normal gas, the superfluid Efimov liquid, and a third phase, the\nconventional superfluid gas. These two superfluid phases are separated by a\ncritical line that ends in a critical point at high temperature. This rich\nphase diagram should allow for a number of experimental protocols that would\nprobe these universal transitions between the normal gas, the superfluid gas,\nand the superfluid Efimov liquid.",
        "positive": "Spin-models, dynamics and criticality with atoms in tilted optical\n  superlattices: We show that atoms in tilted optical superlattices provide a platform for\nexploring coupled spin chains of forms that are not present in other systems.\nIn particular, using a period-2 superlattice in 1D, we show that coupled Ising\nspin chains with XZ and ZZ spin coupling terms can be engineered. We use\noptimized tensor network techniques to explore the criticality and\nnon-equilibrium dynamics in these models, finding a tricritical Ising point in\nregimes that are accessible in current experiments. These setups are ideal for\nstudying low-entropy physics, as initial entropy is \"frozen-out\" in realizing\nthe spin models, and provide an example of the complex critical behaviour that\ncan arise from interaction-projected models."
    },
    {
        "anchor": "Second sound and the superfluid fraction in a resonantly interacting\n  Fermi gas: Superfluidity is a macroscopic quantum phenomenon, which shows up below a\ncritical temperature and leads to a peculiar behavior of matter, with\nfrictionless flow, the formation of quantized vortices, and the quenching of\nthe moment of inertia being intriguing examples. A remarkable explanation for\nmany phenomena exhibited by a superfluid at finite temperature can be given in\nterms of a two-fluid mixture comprised of a normal component that behaves like\na usual fluid and a superfluid component with zero viscosity and zero entropy.\nImportant examples of superfluid systems are liquid helium and neutron stars.\nMore recently, ultracold atomic gases have emerged as new superfluid systems\nwith unprecedented possibilities to control interactions and external\nconfinement. Here we report the first observation of `second sound' in an\nultracold Fermi gas with resonant interactions. Second sound is a striking\nmanifestation of the two-component nature of a superfluid and corresponds to an\nentropy wave, where the superfluid and the non-superfluid components oscillate\nin opposite phase, different from ordinary sound (`first sound'), where they\noscillate in phase. The speed of second sound depends explicitly on the value\nof the superfluid fraction, a quantity sensitive to the spectrum of elementary\nexcitations. Our measurements allow us to extract the temperature dependence of\nthe superfluid fraction, which in strongly interacting quantum gases has been\nan inaccessible quantity so far.",
        "positive": "Ultracold Atomic Gases: Novel States of Matter: Article to appear in the Encyclopedia of Complexity and Systems Science, Dr.\nR. A. Meyers (Ed.) (Springer Heidelberg, 2009)."
    },
    {
        "anchor": "Stability and Tunneling Dynamics of a Dark-Bright Soliton Pair in a\n  Harmonic Trap: We consider a binary repulsive Bose-Einstein condensate in a harmonic trap in\none spatial dimension and investigate particular solutions consisting of two\ndark-bright (DB) solitons. There are two different stationary solutions\ncharacterized by the phase difference in the bright component, in-phase and\nout-of-phase states. We show that above a critical particle number in the\nbright component, a symmetry breaking bifurcation of the pitchfork type occurs\nthat leads to a new asymmetric solution whereas the parental branch, i.e., the\nout-of-phase state becomes unstable. These three different states support\ndifferent small amplitude oscillations, characterized by an almost stationary\ndensity of the dark component and a tunneling of the bright component between\nthe two dark solitons. Within a suitable effective double-well picture, these\ncan be understood as the characteristic features of a Bosonic Josephson\nJunction (BJJ), and we show within a two-mode approach that all characteristic\nfeatures of the BJJ phase space are recovered. For larger deviations from the\nstationary states, the simplifying double-well description breaks down due to\nthe feedback of the bright component onto the dark one, causing the solitons to\nmove. In this regime we observe intricate anharmonic and aperiodic dynamics,\nexhibiting remnants of the BJJ phase space.",
        "positive": "Vortex nucleation through fragmentation in a stirred resonant\n  Bose-Einstein condensate: Superfluids are distinguished from ordinary fluids by the quantized manner\nthe rotation is manifested in them. Precisely, quantized vortices are known to\nappear in the bulk of a superfluid subject to external rotation. In this work\nwe study a trapped ultracold Bose gas of $N=101$ atoms in two spatial\ndimensions that is stirred by a rotating beam. We use the multiconfigurational\nHartree method for bosons, that extends the mainstream mean-field theory, to\ncalculate the dynamics of the gas in real time. As the gas is rotated the\nwavefunction of the system changes symmetry and topology. We see a series of\nresonant rotations as the stirring frequency is increased. Fragmentation\naccompanies the resonances and change of symmetry of the wavefunction of the\ngas. We conclude that fragmentation of the gas appears hand-in-hand with\nresonant absorption of energy and angular momentum from the external agent of\nrotation."
    },
    {
        "anchor": "Exploring the thermodynamics of spin-1 $^{87}$Rb Bose Gases with\n  synthetic magnetization: In this work, we study the thermodynamic properties of a spin-1 Bose gas\nacross the Bose-Einstein condensation transition. We present the theoretical\ndescription of the thermodynamics of a trapped ideal spin-1 Bose gas and we\ndescribe the phases that can be obtained in this system as a function of the\ntemperature and of the populations in the different spin components. We propose\na simple way to realize a \"synthetic magnetization\" that can be used to probe\nthe entire phase diagram while keeping the real magnetization of the system\nfixed. We experimentally demonstrate the use of such method to explore\ndifferent phases in a sample with zero total magnetization. Our work opens up\nnew perspectives to study isothermal quenching dynamics through different\nmagnetic phases in spinor condensates.",
        "positive": "Fate of the Higgs mode near quantum criticality: We study the relativistic O(N) field theory near the quantum critical point\nin 2+1 dimensions for N=2 and N=3. The scalar susceptibility is evaluated by\nMonte Carlo simulation. We show that the spectrum contains a peak associated\nwith the Higgs mode, which remains well-defined all the way to the critical\npoint. The fidelity of this peak and the amplitude ratio between the critical\nenergy scales on both sides of the transition are computed."
    },
    {
        "anchor": "Stable and mobile excited two-dimensional dipolar Bose-Einstein\n  condensate solitons: We demonstrate robust, stable, mobile excited states of quasi-two-dimensional\n(quasi-2D) dipolar Bose-Einstein condensate (BEC) solitons for repulsive\ncontact interaction with a harmonic trap along the $x$ direction perpendicular\nto the polarization direction $z$. Such a soliton can freely move in the y-z\nplane. A rich variety of such excitations is considered: one quanta of\nexcitation for movement along (i) y axis or (ii) z axis or (ii) both. A\nproposal for creating these excited solitonic states in a laboratory by phase\nimprinting is also discussed. We also consider excited states of quasi-2D\ndipolar BEC soliton where the sign of the dipolar interaction is reversed by a\nrotating orienting field. In this sign-changed case the soliton moves freely in\nthe x-y plane under the action of a harmonic trap in the $z$ direction. At\nmedium velocity the head-on collision of two such solitons is found to be quasi\nelastic with practically no deformation. The findings are illustrated using\nnumerical simulation in three and two spatial dimensions employing realistic\ninteraction parameters for a dipolar $^{164}$Dy BEC.",
        "positive": "Ground state of a two component dipolar Fermi gas in a harmonic\n  potential: Interacting two component Fermi gases are at the heart of our understanding\nof macroscopic quantum phenomena like superconductivity. Changing nature of the\ninteraction is expected to head to novel quantum phases. Here we study the\nground state of a two component fermionic gas in a harmonic potential with\ndipolar and contact interactions. Using a variational Wigner function we\npresent the phase diagram of the system with equal but opposite values of the\nmagnetic moment. We identify the second order phase transition from\nparamagnetic to ferronematic phase. Moreover, we show the impact of the\nexperimentally relevant magnetic field on the stability and the magnetization\nof the system. We also investigate a two component Fermi gas with large but\nalmost equal values of the magnetic moment to study how the interplay between\ncontact and dipolar interactions affects the stability properties of the\nmixture. To be specific we discuss experimentally relevant parameters for\nultracold $^{161}$Dy."
    },
    {
        "anchor": "A liquid-gas transition for bosons with attractive interaction in one\n  dimension: We consider a one dimensional system of $N$ bosons interacting via an\nattractive Dirac delta function potential. We place the bosonic quantum\nparticles at thermal equilibrium in a box of length $L$ with periodic boundary\nconditions. At large $N$ and for $L$ much larger than the diameter of a two\nparticle bound state, we predict by numerical and analytical studies of a\nsimple model derived from first principles that the system exhibits a first\norder phase transition in a high temperature, non-degenerate regime. The higher\ntemperature phase is an almost pure atomic gas, with a small fraction of\ndimers, a smaller fraction of trimers, etc. The lower temperature phase is a\nmesoscopic or macroscopic bound state that collects all the particles of the\nsystem with the exception of a small gaseous fraction composed mainly of atoms.\nWe term this phase, which is the quantum equivalent of the classical bright\nsoliton, a liquid.---Nous considerons, en dimension un, une assemblee de $N$\nparticules quantiques bosoniques interagissant par un potentiel de Dirac\nattractif, a l'equilibre thermique dans une boite de quantification de longueur\nL avec des conditions aux limites periodiques. Pour de grandes valeurs de N, et\nlorsque L est bien superieur au diametre de l'etat dimere dans l'espace reel,\nnous predisons, par etude numerique et analytique d'un modele simple mais\ndeduit des premiers principes, que le systeme presente, a haute temperature\nc'est-a-dire dans le regime non degenere, une transition du premier ordre entre\ndeux phases. La phase privilegiee a haute temperature est un gaz presque pur\nd'atomes, avec une faible fraction de dimeres, et des fractions encore plus\nfaibles de trimeres, etc. La phase qui la supplante a moins haute temperature\nest un etat lie mesoscopique ou macroscopique que nous qualifions de liquide,\nequivalent quantique du soliton brillant de la theorie de champ classique, et\nqui renferme toutes les particules du systeme, a l'exception d'une petite\nfraction gazeuse composee essentiellement d'atomes.",
        "positive": "Bogoliubov-de Gennes study of trapped spin-imbalanced unitary Fermi\n  gases: It is quite common that several different phases exist simultaneously in a\nsystem of trapped quantum gases of ultra-cold atoms. One such example is the\nstrongly-interacting Fermi gas with two imbalanced spin species, which has\nreceived a great amount of attention due to the possible presence of exotic\nsuperfluid phases. By employing novel numerical techniques and algorithms, we\nself-consistently solve the Bogoliubov de-Gennes equations, which describe\nFermi superfluids in the mean-field framework. From this study, we investigate\nthe novel phases of spin-imbalanced Fermi gases and examine the validity of the\nlocal density approximation (LDA), which is often invoked in the extraction of\nbulk properties from experimental measurements within trapped systems. We show\nhow the validity of the LDA is affected by the trapping geometry, number of\natoms and spin imbalance."
    },
    {
        "anchor": "Dynamics of a Nonequilibrium Discontinuous Quantum Phase Transition in a\n  Spinor Bose-Einstein Condensate: Symmetry-breaking quantum phase transitions lead to the production of\ntopological defects or domain walls in a wide range of physical systems. In\nsecond-order transitions, these exhibit universal scaling laws described by the\nKibble-Zurek mechanism, but for first-order transitions a similarly universal\napproach is still lacking. Here we propose a spinor Bose-Einstein condensate as\na testbed system where critical scaling behavior in a first-order quantum phase\ntransition can be understood from generic properties. We generalize the\nKibble-Zurek mechanism to determine the critical exponents for: (1) the onset\nof the decay of the metastable state on short times scales, and (2) the number\nof resulting phase-separated ferromagnetic domains at longer times, as a\none-dimensional spin-1 condensate is ramped across a first-order quantum phase\ntransition. The predictions are in excellent agreement with mean-field\nnumerical simulations and provide a paradigm for studying the decay of\nmetastable states in experimentally accessible systems.",
        "positive": "Quantum droplet states of a binary magnetic gas: Quantum droplets can emerge in bosonic binary magnetic gases (BMGs) from the\ninterplay of short- and long-ranged interactions, and quantum fluctuations. We\ndevelop an extended meanfield theory for this system and use it to predict\nequilibrium and dynamical properties of BMG droplets. We present a phase\ndiagram and characterize miscible and immiscible droplet states. We also show\nthat a single component self-bound droplet can be used to bind another magnetic\ncomponent which is not in the droplet regime. Our results should be realizable\nin experiments with mixtures of highly-magnetic lanthanide atoms."
    },
    {
        "anchor": "Mott transition in a cavity-boson system: A quantitative comparison\n  between theory and experiment: The competition between short-range and cavity-mediated infinite-range\ninteractions in a cavity-boson system leads to the existence of a superfluid\nphase and a Mott-insulator phase within the self-organized regime. In this\nwork, we quantitatively compare the steady-state phase boundaries of this\ntransition measured in experiments and simulated using the Multiconfigurational\nTime-Dependent Hartree Method for Indistinguishable Particles. To make the\nproblem computationally feasible, we represent the full system by the exact\nmany-body wave function of a two-dimensional four-well potential. We argue that\nthe validity of this representation comes from the nature of both the\ncavity-atomic system and the Bose-Hubbard physics. Additionally we show that\nthe chosen representation only induces small systematic errors, and that the\nexperimentally measured and theoretically predicted phase boundaries agree\nreasonably. We thus demonstrate a new approach for the quantitative numerical\ndetermination of the superfluid--Mott-insulator phase boundary.",
        "positive": "Bistability in Feshbach Resonance: A coupled atom-molecule condensate with an intraspecies Feshbach resonance is\nemployed to explore matter wave bistability both in the presence and in the\nabsence of a unidirectional optical ring cavity. In particular, a set of\nconditions are derived that allow the threshold for bistability, due both to\ntwo-body s-wave scatterings and to cavity-mediated two-body interactions, to be\ndetermined analytically. The latter bistability is found to support, not only\ntransitions between a mixed (atom-molecule) state and a pure molecular state as\nin the former bistability, but also transitions between two distinct mixed\nstates."
    },
    {
        "anchor": "Outcoupling from a Bose-Einstein condensate in the strong-field limit: Atoms can be extracted from a trapped Bose-Einstein condensate (BEC) by\ndriving spin-flips to untrapped states. The coherence properties of the BEC are\ntransfered to the released atoms, creating a coherent beam of matter refered to\nas an atom laser. In this work, the extraction of atoms from a BEC is\ninvestigated numerically by solving a coupled set of Gross-Pitaevskii equations\nin up to three dimensions. The result is compared to experimental data and a\nsemiclassical rate model. In the weak-coupling regime, quantitative agreement\nis reached between theory and experiment and a semiclassical rate model. In the\nstrong-coupling regime, the atom laser enters a trapped state that manifests\nitself in a saturation of the rate of out-coupled atoms observed in new\nexperimental data. The semiclassical rate model fails, but the numerical\ndescriptions yield qualitative agreement with experimental data at the onset of\nsaturation.",
        "positive": "Efimov Physics and the Three-Body Parameter within a Two-Channel\n  Framework: We calculate shallow three-body bound states in the universal regime, defined\nby Efimov, with inclusion of both scattering length and effective range\nparameters. The universal spectrum is recovered for the least bound states,\nwhereas for larger binding energies we find corrections to the universal\nscaling laws. We recover known results for broad Feshbach resonances with small\neffective range, whereas in the case of narrow resonances we find a distinct\nnon-monotonic behavior of the threshold at which the lowest Efimov trimer\nmerges with the three-body continuum. To address the issue of the physical\norigin of the three-body parameter we provide a physically clear model for the\nrelation between three-body physics and typical two-body atom-atom\ninteractions. Our results demonstrate that experimental information from narrow\nFeshbach resonances and/or mixed systems are of vital importance to pin down\nthe relation of two- and three-body physics in atomic systems."
    },
    {
        "anchor": "Frequency beating and damping of breathing oscillations of a\n  harmonically trapped one-dimensional quasicondensate: We study the breathing (monopole) oscillations and their damping in a\nharmonically trapped one-dimensional (1D) Bose gas in the quasicondensate\nregime using a finite-temperature classical field approach. By characterising\nthe oscillations via the dynamics of the density profile's rms width over long\ntime, we find that the rms width displays beating of two distinct frequencies.\nThis means that 1D Bose gas oscillates not at a single breathing mode\nfrequency, as found in previous studies, but as a superposition of two distinct\nbreathing modes, one oscillating at frequency close to $\\simeq\\!\\sqrt{3}\\omega$\nand the other at $\\simeq\\!2\\omega$, where $\\omega$ is the trap frequency. The\nbreathing mode at $\\sim\\!\\sqrt{3}\\omega$ dominates the beating at lower\ntemperatures, deep in the quasicondensate regime, and can be attributed to the\noscillations of the bulk of the density distribution comprised of particles\npopulating low-energy, highly-occupied states. The breathing mode at\n$\\simeq\\!2\\omega$, on the other hand, dominates the beating at higher\ntemperatures, close to the nearly ideal, degenerate Bose gas regime, and is\nattributed to the oscillations of the tails of the density distribution\ncomprised of thermal particles in higher energy states. The two breathing modes\nhave distinct damping rates, with the damping rate of the bulk component being\napproximately four times larger than that of the tails component.",
        "positive": "Pseudogap in fermionic density of states in the BCS-BEC crossover of\n  atomic Fermi gases: We study pseudogap behaviors of ultracold Fermi gases in the BCS-BEC\ncrossover region. We calculate the density of states (DOS), as well as the\nsingle-particle spectral weight, above the superfluid transition temperature\n$T_{\\rm c}$ including pairing fluctuations within a $T$-matrix approximation.\nWe find that DOS exhibits a pseudogap structure in the BCS-BEC crossover\nregion, which is most remarkable near the unitarity limit. We determine the\npseudogap temperature $T^*$ at which the pseudogap structure in DOS disappears.\nWe also introduce another temperature $T^{**}$ at which the BCS-like\ndouble-peak structure disappears in the spectral weight. While one finds\n$T^*>T^{**}$ in the BCS regime, $T^{**}$ becomes higher than $T^*$ in the\ncrossover and BEC regime. We also determine the pseudogap region in the phase\ndiagram in terms of temperature and pairing interaction."
    },
    {
        "anchor": "Viscous Flow in a 1D Spin-Polarized Fermi Gas: the Role of Integrability\n  on Viscosity: The transport properties of one-dimensional Fermi gases at low-temperatures\nare often described by the Luttinger liquid (LL) model. However, to study\ndissipation one needs to examine interactions beyond the LL model. In this work\nwe provide a simple model which allows for a direct microscopic calculation of\nthe bulk viscosity, namely the one dimensional spin polarized p-wave Fermi gas.\nWe calculate the bulk viscosity in both the high- and low-temperature limits.\nWe find that the bulk viscosity is finite and consistent with the requirement\nof scale symmetry, in spite of the inherent integrability of the microscopic\nmodel. We argue how integrability does not forbid a finite bulk viscosity, and\ncompare our work to previous kinetic theory calculations.",
        "positive": "Phase separation of trapped spin-imbalanced Fermi gases in\n  one-dimensional optical lattices: We calculate the density profiles of a trapped spin-imbalanced Fermi gas with\nattractive interactions in a one-dimensional optical lattice, using both the\nlocal density approximation (LDA) and density matrix renormalization group\n(DMRG) simulations. Based on the exact equation of state obtained by Bethe\nansatz, LDA predicts that the gas phase-separates into shells with a partially\npolarized core and fully paired wings, where the latter occurs below a critical\nspin polarization. This behavior is also seen in numerically exact DMRG\ncalculations at sufficiently large particle numbers. Unlike the continuum case,\nwe show that the critical polarization is a non monotonic function of the\ninteraction strength and vanishes in the limit of large interactions."
    },
    {
        "anchor": "Fractional windings of the spinor condensates on a ring: We study the uniform solutions to the one-dimensional spinor Bose-Einstein\ncondensates on a ring. These states explicitly display the associated motion of\nthe super-current and the spin rotation, which give rise to fractional winding\nnumbers according to the various compositions of the hyperfine states. It\nsimultaneously yields a fractional factor to the global phase due to the\ngauge-spin symmetry. Our method can be applied to explore the fractional\nvortices by identifying the ring as the boundary of two-dimensional spinor\ncondensates.",
        "positive": "Comment on \"Normal phase of an imbalanced Fermi gas\": Recently Mora and Chevy [Phys. Rev. Lett. 104, 230402 (2010),\narXiv:1003.0213v2], in studying the energy of an atomic Fermi gas consisting of\na majority species, 1, and a minority species, 2, showed that, due to\ninteratomic interactions, the energy density E of the gas has a contribution of\nthe form E^(2)= f n_2^2 /2, where n_i is the density of species i. They\nattribute this term to a `modification of the single polaron properties due to\nPauli blocking'. In this Comment, we demonstrate that E^(2) may equivalently be\nunderstood in terms of the familiar interaction between minority atoms induced\nby the majority component."
    },
    {
        "anchor": "Phase diagram of a quantum Coulomb wire: We report the quantum phase diagram of a one-dimensional Coulomb wire\nobtained using the path integral Monte Carlo (PIMC) method. The exact knowledge\nof the nodal points of this system permits us to find the energy in an exact\nway, solving the sign problem which spoils fermionic calculations in higher\ndimensions. The results obtained allow for the determination of the stability\ndomain, in terms of density and temperature, of the one-dimensional Wigner\ncrystal. At low temperatures, the quantum wire reaches the quantum-degenerate\nregime, which is also described by the diffusion Monte Carlo method. Increasing\nthe temperature the system transforms to a classical Boltzmann gas which we\nsimulate using classical Monte Carlo. At large enough density, we identify a\none-dimensional ideal Fermi gas which remains quantum up to higher temperatures\nthan in two- and three-dimensional electron gases. The obtained phase diagram\nas well as the energetic and structural properties of this system are relevant\nto experiments with electrons in quantum wires and to Coulomb ions in\none-dimensional confinement.",
        "positive": "Polychromatic polariton laser selector switch: Integration of optical elements into scalable chips has been at the center of\na large effort in recent years. Concurrently, the separation between the\ndiverse functions, namely switches, detectors or emitters increases\nsignificantly the final number of components on chip. Such technical\nlimitations may be overcome by introducing agile devices able, for example, to\nsimultaneously detect, process and emit a coherent signal. Such a pathway has\nbeen explored with different approaches that bear advantages and drawbacks.\nPolaritons have often been proposed as promising candidates for multifunctional\ndevices. Here we present an optical switch based on polariton lasing. An\nincident monochromatic signal is channeled into several polariton laser beams\nat different wavelengths by a novel relaxation mechanism which combines\nbistability, phonon interactions, long polariton lifetime and bosonic\nstimulation. We demonstrate spin logic operations conserving the original\npolarization state that is fully imprinted onto the coherently emitted signals."
    },
    {
        "anchor": "Parametric instability of oscillations of a vortex ring in a\n  $z$-periodic Bose-Einstein condensate and the recurrence to starting state: The dynamics of deformations of a quantum vortex ring in a Bose-Einstein\ncondensate with periodic equilibrium density $\\rho(z)= 1-\\epsilon\\cos z$ has\nbeen considered within the local induction approximation. Parametric\ninstabilities of the normal modes with azimuthal numbers $\\pm m$ have been\nrevealed at the energy integral $E$ near values $E_m^{(p)}=2m\\sqrt{m^2-1}/p$,\nwhere $p$ is the resonance order. Numerical simulations have shown that already\nat $\\epsilon\\sim 0.03$ a rapid growth of unstable modes with $m=2$, $p=1$ to\nmagnitudes of order of unity is typical, which is then followed, after a few\nlarge oscillations, by fast return to a weakly excited state. Such behavior\ncorresponds to an integrable Hamiltonian of the form $H\\propto\n\\sigma(E_2^{(1)}-E)(|b_+|^2 + |b_-|^2) -\\epsilon(b_+ b_- + b_+^* b_-^*)\n+u(|b_+|^4 +|b_-|^4) + w |b_+|^2|b_-|^2$ for two complex envelopes $b_\\pm(t)$.\nThe results have been compared to parametric instabilities of vortex ring in\ncondensate with density $\\rho(z,r)=1-r^2-\\alpha z^2$, which take place at\n$\\alpha\\approx 8/5$ and at $\\alpha\\approx 16/7$.",
        "positive": "Stability of nonstationary states of spin-2 Bose-Einstein condensates: The dynamical stability of nonstationary states of homogeneous spin-2\nrubidium Bose-Einstein condensates is studied. The states considered are such\nthat the spin vector remains parallel to the magnetic field throughout the time\nevolution, making it possible to study the stability analytically. These states\nare shown to be stable in the absence of an external magnetic field, but they\nbecome unstable when a finite magnetic field is introduced. It is found that\nthe growth rate and wavelength of the instabilities can be controlled by tuning\nthe strength of the magnetic field and the size of the condensate."
    },
    {
        "anchor": "Glitches in rotating supersolids: Glitches, spin-up events in neutron stars, are of prime interest as they\nreveal properties of nuclear matter at subnuclear densities. We numerically\ninvestigate the glitch mechanism due to vortex unpinning using analogies\nbetween neutron stars and dipolar supersolids. We explore the vortex and\ncrystal dynamics during a glitch and its dependence on the supersolid quality,\nproviding a tool to study glitches from different radial depths of a neutron\nstar. Benchmarking our theory against neutron star observations, our work will\nopen a new avenue for the quantum simulation of stellar objects from Earth.",
        "positive": "All Optical Scheme for Strongly Enhanced Production of Dipolar Molecules\n  in the Electro-Vibrational Ground State: We consider two-color heteronuclear photoassociation of atoms into dipolar\nmolecules in the J=1 electro-vibrational ground state, where a free-ground\nlaser couples atoms directly to the ground state and a free-bound laser couples\nthe atoms to an electronically-excited state. This problem raises an interest\nbecause heteronuclear photoassociation from atoms to near-ground state\nmolecules is limited by the small size of the target state. Nevertheless, the\naddition of the excited state creates a second pathway for creating ground\nstate molecules, leading to quantum interference between direct\nphotoassociation and photoassociation via the excited molecular state, as well\nas a dispersive-like shift of the free-ground resonance position. Using LiNa as\nan example, these results are shown to depend on the detuning and intensity of\nthe free-bound laser, as well as the semi-classical size of both molecular\nstates. Despite strong enhancement, coherent conversion to the LiNa\nelectro-vibrational ground state is possible only in a limited regime near the\nfree-bound resonance."
    },
    {
        "anchor": "Three-dimensional skyrmions in spin-2 Bose-Einstein condensates: We introduce topologically stable three-dimensional skyrmions in the cyclic\nand biaxial nematic phases of a spin-2 Bose-Einstein condensate. These\nskyrmions exhibit exceptionally high mapping degrees resulting from the\nversatile symmetries of the corresponding order parameters. We show how these\nstructures can be created in existing experimental setups and study their\ntemporal evolution and lifetime by numerically solving the three-dimensional\nGross-Pitaevskii equations for realistic parameter values. Although the biaxial\nnematic and cyclic phases are observed to be unstable against transition\ntowards the ferromagnetic phase, their lifetimes are long enough for the\nskyrmions to be imprinted and detected experimentally.",
        "positive": "Cluster mean-field approach with density matrix renormalization group:\n  Application to the hard-core bosonic Hubbard model on a triangular lattice: We introduce a new numerical method for the solution of self-consistent\nequations in the cluster mean-field theory. The method uses the density matrix\nrenormalization group method to solve the associated cluster problem. We obtain\nan accurate critical value of the supersolid-superfluid transitions in the\nhard-core bosonic Hubbard model on a triangular lattice, which is comparable\nwith the recent quantum Monte Carlo results. This algorithm is applicable to\nmore general classes of models with a larger number of degrees of freedom."
    },
    {
        "anchor": "Suppression of two-body collisional loss in an ultracold gas via the\n  Fano effect: The Fano effect (U. Fano, Phys. Rev. \\textbf{15},1866 (1961) shows that an\ninelastic scattering process can be suppressed when the output channel (OC) is\ncoupled to an isolated bound state. In this paper we investigate the\napplication of this effect for the suppression of two-body collisional losses\nof ultracold atoms. The Fano effect is originally derived via a first-order\nperturbation treatment for coupling between the incident channel (IC) and the\nOC. We generalize the Fano effect to systems with arbitrarily strong IC--OC\ncouplings. We analytically prove that, in a system with one IC and one OC, when\nthe inter-atomic interaction potentials are real functions of the inter-atomic\ndistance, the exact s-wave inelastic scattering amplitude can always be\nsuppressed to \\emph{zero} by coupling between the IC or the OC (or both of\nthem) and an extra isolated bound state. We further show that when the\nlow-energy inelastic collision between two ultracold atoms is suppressed by\nthis effect, the real part of the elastic scattering length between the atoms\nis still possible to be much larger than the range of inter-atomic\ninteraction.In addition, when open scattering channels are coupled to two bound\nstates, with the help of the Fano effect, independent control of the elastic\nand inelastic scattering amplitudes of two ultracold atoms can be achieved.\nPossible experimental realizations of our scheme are also discussed.",
        "positive": "Dynamical control of the conductivity of an atomic Josephson junction: We propose to dynamically control the conductivity of a Josephson junction\ncomposed of two weakly coupled one dimensional condensates of ultracold atoms.\nA current is induced by a periodically modulated potential difference between\nthe condensates, giving access to the conductivity of the junction. By using\nparametric driving of the tunneling energy, we demonstrate that the\nlow-frequency conductivity of the junction can be enhanced or suppressed,\ndepending on the choice of the driving frequency. The experimental realization\nof this proposal provides a quantum simulation of optically enhanced\nsuperconductivity in pump-probe experiments of high temperature\nsuperconductors."
    },
    {
        "anchor": "Scattering framework for two particles with isotropic spin-orbit\n  coupling applicable to all energies: Previous work developed a K-matrix formalism applicable to positive energies\nfor the scattering between two $s$-wave interacting particles with two internal\nstates, isotropic spin-orbit coupling and vanishing center-of-mass momentum [H.\nDuan, L. You and B. Gao, Phys. Rev A {\\bf{87}}, 052708 (2013)]. This work\nextends the formalism to the entire energy regime. Explicit solutions are\nobtained for the total angular momentum $J=0$ and $1$ channels. The behavior of\nthe partial cross sections in the negative energy regime is analyzed in detail.\nWe find that the leading contributions to the partial cross sections at the\nnegative energy thresholds are governed by the spin-orbit coupling strength\n$k_{\\text{so}}$ and the mass ratio. The fact that these contributions are\nindependent of the two-body scattering length $a_s$ is a direct consequence of\nthe effective reduction of the dimensionality, and hence of the density of\nstates, near the scattering thresholds due to the single-particle spin-orbit\ncoupling terms. The results are analytically continued to the energy regime\nwhere bound states exist. It is shown that our results are consistent with\nresults obtained by alternative approaches. Our formulation, which can be\nregarded as an extension of the standard textbook partial wave decomposition,\ncan be generalized to two-body systems with other types of spin-orbit coupling,\nincluding cases where the center-of-mass momentum does not vanish.",
        "positive": "Curved vortex surfaces in four-dimensional superfluids: I.\n  Unequal-frequency double rotations: The study of superfluid quantum vortices has long been an important area of\nresearch, with previous work naturally focusing on two-dimensional and\nthree-dimensional systems, where rotation stabilises point vortices and line\nvortices respectively. Interestingly, this physics generalises for a\nhypothetical four-dimensional (4D) superfluid to include vortex planes, which\ncan have a much richer phenomenology. In this paper, we study the possibility\nof skewed and curved vortex planes, which have no direct analogue in lower\ndimensions. By analytically and numerically studying the 4D Gross-Pitaevskii\nequation, we show that such vortex surfaces can be stabilised and favoured by\ndouble rotation with unequal rotation frequencies. Our work raises open\nquestions for further research into the physics of these vortex surfaces and\nsuggests interesting future extensions to tilted vortex surfaces under\nequal-frequency double rotation and to more realistic 4D models."
    },
    {
        "anchor": "Local equilibration of fermions and bosons: Local kinetic equilibration is a prerequisite for hydrodynamics to be valid.\nHere it is described through a nonlinear diffusion equation for finite systems\nof fermions and bosons. The model is solved exactly for constant transport\ncoefficients in both cases. It has the proper Fermi-Dirac and Bose-Einstein\nequilibrium limits and can replace the relaxation-time approximation (RTA). The\nmicroscopic transport coefficients are determined through the macroscopic\nvariables temperature and local equilibration time. Applications to the\ntransverse energy of quarks and gluons in the initial stages of central\nrelativistic heavy-ion collisions, and to bosonic and fermionic atoms at low\nenergies appropriate for cold quantum gases are discussed.",
        "positive": "Control of light-atom solitons and atomic transport by optical vortex\n  beams propagating through a Bose-Einstein Condensate: We model propagation of far-red-detuned optical vortex beams through a\nBose-Einstein Condensate using nonlinear Schr\\\"odinger and Gross-Pitaevskii\nequations. We show the formation of coupled light/atomic solitons that rotate\nazimuthally before moving off tangentially, carrying angular momentum. The\nnumber, and velocity, of solitons, depends on the orbital angular momentum of\nthe optical field. Using a Bessel-Gauss beam increases radial confinement so\nthat solitons can rotate with fixed azimuthal velocity. Our model provides a\nhighly controllable method of channelling a BEC and atomic transport."
    },
    {
        "anchor": "Cluster dynamics in two-dimensional lattice gases with inter-site\n  interactions: Sufficiently strong inter-site interactions in extended-Hubbard and XXZ spin\nmodels result in dynamically-bound clusters at neighboring sites. We show that\nthe dynamics of these clusters in two-dimensional lattices is remarkably\ndifferent and richer than that of repulsively-bound on-site clusters in gases\nwithout inter-site interactions. Whereas on-site pairs move in the same lattice\nas individual particles, nearest-neighbor dimers perform an interacting quantum\nwalk in a different lattice geometry, leading to a peculiar dynamics\ncharacterized by more than one time scale. The latter is general for any\nlattice geometry, but it is especially relevant in triangular and diamond\nlattices, where dimers move resonantly in an effective kagome and Lieb lattice,\nrespectively. As a result, dimers experience partial quasi-localization due to\nan effective flat band, and may move slower than longer clusters. This\nsurprising link between anomalously slow quantum walk dynamics in these models\nand flat-band physics may be readily observed in experiments with lanthanide\natoms.",
        "positive": "Spiral spin textures of bosonic Mott insulator with SU(3) spin-orbit\n  coupling: We study the Mott phase of three-component bosons, with one particle per\nsite, in an optical lattice by mapping it onto an SU(3) spin model. In the\nsimplest case of full SU(3) symmetry, one obtains a ferromagnetic Heisenberg\nmodel. Introducing an SU(3) analog of spin-orbit coupling, additional spin-spin\ninteractions are generated. We first consider the scenario of spin-dependent\nhopping phases, leading to Dzyaloshinskii-Moriya-type interactions. They result\nin the formation of spiral spin textures, which in one dimension can be\nunderstood by a local unitary transformation. Applying classical Monte Carlo\nsimulations, we extend our study to two-dimensional systems, and systems with\n\"true\" spin-orbit coupling, involving spin-changing hoppings."
    },
    {
        "anchor": "Small two-component Fermi gases in a cubic box with periodic boundary\n  conditions: The properties of two-component Fermi gases become universal if the\ninterspecies s-wave scattering length $a_s$ and the average interparticle\nspacing are much larger than the range of the underlying two-body potential.\nUsing an explicitly correlated Gaussian basis set expansion approach, we\ndetermine the eigen energies of two-component Fermi gases in a cubic box with\nperiodic boundary conditions as functions of the interspecies s-wave scattering\nlength and the effective range of the two-body potential. The universal\nproperties of systems consisting of up to four particles are determined by\nextrapolating the finite-range energies to the zero-range limit. We determine\nthe eigen energies of states with vanishing and finite momentum. In the\nweakly-attractive BCS regime, we analyze the energy spectra and degeneracies\nusing first-order degenerate perturbation theory. Excellent agreement between\nthe perturbative energy shifts and the numerically determined energies is\nobtained. For the infinitely large scattering length case, we compare our\nresults - where available - with those presented in the literature.",
        "positive": "Delocalization of two interacting particles in the two-dimensional\n  Harper model: We study the problem of two interacting particles in a two-dimensional\nquasiperiodic potential of the Harper model. We consider an amplitude of the\nquasiperiodic potential such that in absence of interactions all eigenstates\nare exponentially localized while the two interacting particles are delocalized\nshowing anomalous subdiffusive spreading over the lattice with the spreading\nexponent $b \\approx 0.5$ instead of a usual diffusion with $b=1$. This\nspreading is stronger than in the case of a correlated disorder potential with\na one particle localization length as for the quasiperiodic potential. At the\nsame time we do not find signatures of ballistic FIKS pairs existing for two\ninteracting particles in the one-dimensional Harper model."
    },
    {
        "anchor": "Scattering of atomic dark-bright solitons from narrow impurities: In this work, we study the collision of an atomic dark-bright soliton, in a\ntwo-component Bose-Einstein condensate, with a Gaussian barrier or well. First,\nwe present the results of an experiment, illustrating the classical particle\nphenomenology (transmission or reflection) in the case of an equal barrier or\nwell in both components. Then, motivated by the experimental observations, we\nperform systematic simulations considering not only the case of equal heights,\nbut also the considerably more complex setting, where the potential affects\nonly one of the two components. We systematically classify the ensuing cases\nwithin a two-parameter diagram of barrier amplitudes in the two components, and\nprovide intuitive explanations for the resulting observations, as well as of\ntheir variations as the size of the barrier changes.",
        "positive": "Non-perturbative renormalization-group approach to the Bose-Hubbard\n  model: We present a non-perturbative renormalization-group approach to the\nBose-Hubbard model. By taking as initial condition of the RG flow the (local)\nlimit of decoupled sites, we take into account both local and long-distance\nfluctuations in a nontrivial way. This approach yields a phase diagram in very\ngood quantitative agreement with the quantum Monte Carlo results and reproduces\nthe two universality classes of the superfluid--Mott-insulator transition with\na good estimate of the critical exponents. Furthermore, it reveals the crucial\nrole of the \"Ginzburg length\" as a crossover length between a weakly- and a\nstrongly-correlated superfluid phase."
    },
    {
        "anchor": "Correlation evolution in dilute Bose-Einstein condensates after quantum\n  quenches: The universal forms of quantum density and phase correlations after an\ninteraction quench are found for dilute 1d, 2d, and 3d condensates. A\nBogoliubov approach in a local density aproximation is used. We obtain compact\nexpressions for the most visible effects. Our results show how loss of phase\ncoherence and antibunching are built up after the quench by quantum\nfluctuations. We demonstrate further that the density correlations can be\nobserved even with imaging resolution much worse than healing length. This\nindicates that the direct measurement of counterpropagating atom pairs in situ\nin a continuum system is realistic. The conditions in contemporary 1d\nexperiments are especially favorable for the correlation wave observations.",
        "positive": "Multiple-Channel Scattering Resonance of One-Dimensional Ultracold\n  Spinor Bosons: So far the interaction of ultacold atoms can only be tuned within one\nparticular scattering channel near a resonance, where the spinor structure of\natomic isotopes is destroyed due to the typically large magnetic field. In this\nLetter, we propose a scheme to realize {\\it multiple-channel scattering\nresonance} (MCSR) of ultracold bosons in one-dimension while still keeping\ntheir spinor structure. The MCSR refers to a simultaneous scattering resonance\namong all different scattering channels, including those breaking SU(2) and\nSO(2) spin rotation symmetries. Essential ingredients for MCSR include the 3D\ninteractions, the confinement potential and a spin-flipping field. Near MCSR a\nmany-body spinor system exhibits exotic spin density distributions and pair\ncorrelations, which are significantly different from those near a\nsingle-channel resonance."
    },
    {
        "anchor": "Ground-state properties of anyons in a one-dimensional lattice: Using the Anyon-Hubbard Hamiltonian, we analyze the ground-state properties\nof anyons in a one-dimensional lattice. To this end we map the hopping dynamics\nof correlated anyons to an occupation-dependent hopping Bose-Hubbard model\nusing the fractional Jordan-Wigner transformation. In particular, we calculate\nthe quasi-momentum distribution of anyons, which interpolates between\nBose-Einstein and Fermi-Dirac statistics. Analytically, we apply a modified\nGutzwiller mean-field approach, which goes beyond a classical one by including\nthe influence of the fractional phase of anyons within the many-body\nwavefunction. Numerically, we use the density-matrix renormalization group by\nrelying on the ansatz of matrix product states. As a result it turns out that\nthe anyonic quasi-momentum distribution reveals both a peak-shift and an\nasymmetry which mainly originates from the nonlocal string property. In\naddition, we determine the corresponding quasi-momentum distribution of the\nJordan-Wigner transformed bosons, where, in contrast to the hard-core case, we\nalso observe an asymmetry for the soft-core case, which strongly depends on the\nparticle number density.",
        "positive": "Topological Time Crystals: By analogy with the formation of space crystals, crystalline structures can\nalso appear in the time domain. While in the case of space crystals we often\nask about periodic arrangements of atoms in space at a moment of a detection,\nin time crystals the role of space and time is exchanged. That is, we fix a\nspace point and ask if the probability density for detection of a system at\nthis point behaves periodically in time. Here, we show that in periodically\ndriven systems it is possible to realize topological insulators, which can be\nobserved in time. The bulk-edge correspondence is related to the edge in time,\nwhere edge states localize. We focus on two examples: Su-Schrieffer-Heeger\n(SSH) model in time and Bose Haldane insulator which emerges in the dynamics of\na periodically driven many-body system."
    },
    {
        "anchor": "Simulating heavy fermion physics in optical lattice: Periodic Anderson\n  model with harmonic trapping potential: Periodic Anderson model (PAM), where local electron orbitals interplay with\nitinerant electronic carriers, plays an essential role in our understanding on\nheavy fermion materials. Motivated by recent proposal of simulating Kondo\nlattice model (KLM) in terms of alkaline-earth metal atoms, we make a further\nstep toward simulation of PAM, which includes crucial charge/valence\nfluctuation of local f-electron beyond purely low-energy spin fluctuation in\nKLM. To realize PAM, transition induced by suitable laser between electronic\nexcited and ground state of alkaline-earth metal atoms\n($^{1}S_{0}$$\\rightleftharpoons$$^{3}P_{0}$) is introduced, and it leads to\neffective hybridization between local electron and conduction electron in PAM.\nGenerally, the $SU(N)$ version of PAM can be realized by our proposal, which\ngives a unique opportunity to detect large-$N$ physics without complexity in\nrealistic materials. In the present work, high temperature physical feature of\nstandard ($SU(2)$) PAM with harmonic trapping potential is detailed analyzed by\nquantum Monte Carlo and dynamic mean-field theory. Indications for near-future\nexperiments are provided. We expect our theoretical proposal and (hopefully)\nforthcoming experiment will deepen our understanding on heavy fermion systems\nand at the same time triggers further studies on related Mott physics, quantum\ncriticality and non-trivial topology in both inhomogeneous and nonequilibrium\nrealm.",
        "positive": "Path-Integral Fujikawa's Approach to Anomalous Virial Theorems and\n  Equations of State for Systems with $SO(2, 1)$ Symmetry: We derive anomalous equations of state for nonrelativistic 2D complex bosonic\nfields with contact interactions, using Fujikawa's path-integral approach to\nanomalies and scaling arguments. In the process, we derive an anomalous virial\ntheorem for such systems. The methods used are easily generalizable for other\n2D systems, including fermionic ones, and of different spatial dimensionality,\nall of which share a classical $SO(2,1)$ Schrodinger symmetry. The discussion\nis of a more formal nature and is intended mainly to shed light on the\nstructure of anomalies in 2D many-body systems. The anomaly corrections to the\nvirial theorem and equation of state - pressure relationship - may be\nidentified as the Tan contact term. The practicality of these ideas rests upon\nbeing able to compute in detail the Fujikawa Jacobian that contains the\nanomaly. This and other conceptual issues, as well as some recent developments,\nare discussed at the end of the paper."
    },
    {
        "anchor": "Synthetic partial waves in ultracold atomic collisions: Interactions between particles can be strongly altered by their environment.\nWe demonstrate a technique for modifying interactions between ultracold atoms\nby dressing the bare atomic states with light, creating an effective\ninteraction of vastly increased range that scatters states of finite relative\nangular momentum at collision energies where only s-wave scattering would\nnormally be expected. We collided two optically dressed neutral atomic\nBose-Einstein condensates with equal, and opposite, momenta and observed that\nthe usual s-wave distribution of scattered atoms was altered by the appearance\nof d- and g-wave contributions. This technique is expected to enable quantum\nsimulation of exotic systems, including those predicted to support Majorana\nfermions.",
        "positive": "Localization-delocalization transition of dipolar bosons in a four-well\n  potential: We study interacting dipolar atomic bosons in a four-well potential within a\nring geometry and outline how a four-site Bose-Hubbard (BH) model including\nnext-nearest-neighbor interaction terms can be derived for the above four-well\nsystem. We analyze the ground state of dipolar bosons by varying the strength\nof the interaction between particles in next-nearest-neighbor wells. We perform\nthis analysis both numerically and analytically by reformulating the\ndipolar-boson model within the continuous variable picture applied in [Phys.\nRev. A {\\bf 84}, 061601(R) (2011)]. By using this approach we obtain an\neffective description of the transition mechanism and show that when the\nnext-nearest-neighbor interaction crosses a precise value of the on-site\ninteraction, the ground state exhibits a change from the uniform state\n(delocalization regime) to a macroscopic two-pulse state, with strongly\nlocalized bosons (localization regime). These predictions are confirmed by the\nresults obtained by diagonalizing numerically the four-site BH Hamiltonian."
    },
    {
        "anchor": "Condensates induced by interband coupling in a double-well lattice: We predict novel inter-band physics for bosons in a double-well lattice. An\nintrinsic coupling between the s and px band due to interaction gives rise to\nlarger Mott regions on the phase diagram at even fillings than the ones at odd\nfillings. On the other hand, the ground state can form various types of\ncondensates, including a mixture of single-particle condensates of both bands,\na mixture of a single-particle condensate of one band and a pair-condensate of\nthe other band, and a pair-condensate composed of one particle from one band\nand one hole from the other band. The predicted phenomena should be observable\nin current experiments on double-well optical lattices.",
        "positive": "Quantum computation with ultracold atoms in a driven optical lattice: We propose a scheme for quantum computation in optical lattices. The qubits\nare encoded in the spacial wavefunction of the atoms such that spin decoherence\ndoes not influence the computation. Quantum operations are steered by shaking\nthe lattice while qubit addressability can be provided with experimentally\navailable techniques of changing the lattice with single-site resolution.\nNumerical calculations show possible fidelities above 99% with gate times on\nthe order of milliseconds."
    },
    {
        "anchor": "Superfluid, solid, and supersolid phases of dipolar bosons in a\n  quasi-one-dimensional optical lattice: We discuss a model of dipolar bosons trapped in a weakly coupled planar array\nof one-dimensional tubes. We consider the situation where the dipolar moments\nare aligned by an external field, and find a rich phase diagram as a function\nof the angle of this field exhibiting quantum phase transitions between solid,\nsuperfluid and supersolid phases. In the low energy limit, the model turns out\nto be identical to one describing quasi-one-dimensional superconductivity in\ncondensed matter systems. This opens the possibility of using bosons as a\nquantum analogue simulator of electronic systems, a scenario arising from the\nintricate relation between statistics and interactions in quasi-one-dimensional\nsystems.",
        "positive": "Measuring Z2 topological invariants in optical lattices using\n  interferometry: We propose an interferometric method to measure Z2 topological invariants of\ntime-reversal invariant topological insulators realized with optical lattices\nin two and three dimensions. We suggest two schemes which both rely on a\ncombination of Bloch oscillations with Ramsey interferometry and can be\nimplemented using standard tools of atomic physics. In contrast to topological\nZak phase and Chern number, defined for individual 1D and 2D Bloch bands, the\nformulation of the Z2 invariant involves at least two Bloch bands related by\ntime- reversal symmetry which one has keep track of in measurements. In one of\nour schemes this can be achieved by the measurement of Wilson loops, which are\nnon-Abelian generalizations of Zak phases. The winding of their eigenvalues is\nrelated to the Z2 invariant. We thereby demonstrate that Wilson loops are not\njust theoretical concepts but can be measured experimentally. For the second\nscheme we introduce a generalization of time-reversal polarization which is\ncontinuous throughout the Brillouin zone. We show that its winding over half\nthe Brillouin zone yields the Z2 invariant. To measure this winding, our\nprotocol only requires Bloch oscillations within a single band, supplemented by\ncoherent transitions to a second band which can be realized by lattice-shaking."
    },
    {
        "anchor": "Z_2 Topological Insulators in Ultracold Atomic Gases: We describe how optical dressing can be used to generate bandstructures for\nultracold atoms with non-trivial Z_2 topological order. Time reversal symmetry\nis preserved by simple conditions on the optical fields. We first show how to\nconstruct optical lattices that give rise to Z_2 topological insulators in two\ndimensions. We then describe a general method for the construction of\nthree-dimensional Z_2 topological insulators. A central feature of our approach\nis a new way to understand Z_2 topological insulators starting from the\nnearly-free electron limit.",
        "positive": "Density Wave -Supersolid and Mott Insulator-Superfluid transition in\n  presence of an artificial gauge field : a strong coupling perturbation\n  approach: We study the effect of an artificial gauge field on the zero temperature\nphase diagram of extended Bose Hubbard model, that describes ultra cold atoms\nin optical lattices with long range interaction using strong coupling\nperturbation theory . We determine analytically the effect of the artificial\ngauge field on the density wave - supersolid (DW-SS) and the the Mott\ninsulator-superfluid (MI -SF) transition boundary . The momentum distribution\nat these two transition boundaries is also calculated in this approach. It is\nshown that such momentum distribution which can be observed in time of flight\nmeasurement, reveals the symmetry of the gauge potential through the formation\nof magnetic Brillouin zone and clearly distinguishes between the DW-SS and\nMI-SF boundary. We also point out that in symmetric gauge the momentum\ndistribution structure at these transition boundaries bears distinctive\nsignatures of vortices in supersolid and superfluid phases."
    },
    {
        "anchor": "Aligned dipolar Bose-Einstein condensate in a double-well potential:\n  From cigar-shaped to pancake-shaped: We consider a Bose-Einstein condensate (BEC), which is characterized by\nlong-range and anisotropic dipole-dipole interactions and vanishing s-wave\nscattering length, in a double-well potential. The properties of this system\nare investigated as functions of the height of the barrier that splits the\nharmonic trap into two halves, the number of particles (or dipole-dipole\nstrength) and the aspect ratio $\\lambda$, which is defined as the ratio between\nthe axial and longitudinal trapping frequencies $\\omega_z$ and $\\omega_{\\rho}$.\nThe phase diagram is determined by analyzing the stationary mean-field\nsolutions. Three distinct regions are found: a region where the energetically\nlowest lying stationary solution is symmetric, a region where the energetically\nlowest lying stationary solution is located asymmetrically in one of the wells,\nand a region where the system is mechanically unstable. For sufficiently large\naspect ratio $\\lambda$ and sufficiently high barrier height, the system\nconsists of two connected quasi-two-dimensional sheets with density profiles\nwhose maxima are located either at $\\rho=0$ or away from $\\rho=0$. The\nstability of the stationary solutions is investigated by analyzing the\nBogoliubov de Gennes excitation spectrum and the dynamical response to small\nperturbations. These studies reveal unique oscillation frequencies and distinct\ncollapse mechanisms. The results derived within the mean-field framework are\ncomplemented by an analysis based on a two-mode model.",
        "positive": "Finite phase coherence time of a quantum field created by an ideal Bose\n  gas: A quantitative quantum field approach for a very weakly interacting, dilute\nBose gas is presented. Within the presented model, which assumes the constraint\nof particle number conservation at constant average energy in the canonical\nensemble, both coherent oscillations, as well as decay times of quantum\ncoherence for a quantum field created by the atomic cloud of a Bose-Einstein\ncondensate, are modeled simultaneously by a unique complex time variable and\ntwo different characteristic frequencies for the oscillation and decoherence of\nthe field. Within the present theory, it is illustrated that the occurrence of\ncoherence and a macroscopic ground state population has its origin in finite\ncoherence times of the ensemble of quantum particles in the Bose gas, which -\nin contrast to the incoherent interactions between the different particles -\nleads to the preparation of a thermodynamically stable many-body quantum state\nwith coherent superpositions of discrete and quantized condensate and\nnon-condensate atom number states at constant total atom number."
    },
    {
        "anchor": "Self-consistent Single-band Approximation for Interacting Boson Systems: Traditionally, the single-band approximation for interacting many-body\nsystems is done with pre-determined single-particle Wannier functions, ignoring\nthe dependence of the Wannier function on interaction. We show that the\nsingle-band approximation has to be done self-consistently to properly account\nthe interaction effect on the Wannier functions. This self-consistent\nsingle-band approximation leads to a nonlinear equation for Wannier functions,\nwhich can be recast into a set of nonlinear equations for Bloch functions.\nThese equations are simplified for two special cases, the superfluid regime and\ndeep in the Mott insulator regime. A simple example with double-well potential\nis used to illustrate our results.",
        "positive": "Controllable half-vortex lattices in an incoherently pumped polariton\n  condensate: We show how the transition between synchronized and desynchronized states of\na spinor polariton condensate can be used to drive a transition between\nstationary vortex lattices and half-vortex lattices. This provides a way to\ncontrol polariton spin textures by a combination of pump spot profile and\napplied magnetic fields. To do this, we extend the model of non-equilibrium\nspinor condensates to include relaxation, and study how this affects the\ndesynchronization transition. We discuss how the pattern formation can be\nexplained by behavior of the homogeneous system."
    },
    {
        "anchor": "One-dimensional matter waves as a multi-state bit: We design a technique to control the position of a localized matter wave. Our\nsystem is composed by a two counter-phased periodic potentials and a third\noptical lattice which can be chosen to be either periodic or disordered. The\nonly control needed on the system is a three-state switch that allows the\ninstantaneous selection of the desired potential. We show that this framework\nis robust and the multi-state bit behavior can be observed under generic\nhypothesis.",
        "positive": "Tunneling and Revival of Anderson Localization in Bose-Einstein\n  Condensate: We provide an analytical model to fabricate an exponential localization of a\nBose-Einstein condensate under bichromatic optical lattice. Such localization\nis famously known as Anderson localization. The degree of localization is\ninvestigated by the Participation Ratio to recognize the laser parameter domain\nfor Anderson localization. The exponential nature of the localization is\nproved, where we also identify the Localization Length. The tunneling of\nAnderson-localized condensate with time is observed, and the revival phenomenon\nof Anderson localization is reported. Slowing down of Anderson localization is\nnoticed for higher laser intensity. We also study the dynamical and structural\nstability of the condensate during Anderson localization, which suggests the\npreferred values of laser power and time instance to encounter minimal mean\ndifference in the presence of noise."
    },
    {
        "anchor": "Quantum Shock Waves and Domain Walls in the Real-Time Dynamics of a\n  Superfluid Unitary Fermi Gas: We show that in the collision of two superfluid fermionic atomic clouds one\nobserves the formation of quantum shock waves as discontinuities in the number\ndensity and collective flow velocity. Domain walls, which are topological\nexcitations of the superfluid order parameter, are also generated and exhibit\nabrupt phase changes by $\\pi$ and slower motion than the shock waves. The\ndomain walls are distinct from the gray soliton train or number density ripples\nformed in the wake of the shock waves and observed in the collisions of\nsuperfluid bosonic atomic clouds. Domain walls with opposite phase jumps appear\nto collide elastically.",
        "positive": "Observation of Floquet band topology change in driven ultracold Fermi\n  gases: Periodic driving of a quantum system can significantly alter its energy bands\nand even change the band topology, opening a completely new avenue for\nengineering novel quantum matter. Although important progress has been made\nrecently in measuring topological properties of Floquet bands in different\nsystems, direct experimental measurement of Floquet band dispersions and their\ntopology change is still demanding. Here we directly measure Floquet band\ndispersions in a periodically driven spin-orbit coupled ultracold Fermi gas.\nUsing spin injection radio-frequency spectroscopy, we observe that the Dirac\npoint originating from two dimensional spin-orbit coupling can be manipulated\nto emerge at the lowest or highest two dressed bands by fast modulating Raman\nlaser frequencies, demonstrating topological change of Floquet bands. Our work\nwill provide a powerful tool for understanding fundamental Floquet physics as\nwell as engineering exotic topological quantum matter."
    },
    {
        "anchor": "Expansion of one-dimensional lattice hard-core bosons at finite\n  temperature: We develop an exact approach to study the quench dynamics of hard-core bosons\ninitially in thermal equilibrium in one-dimensional lattices. This approach is\nused to study the sudden expansion of thermal states after confining potentials\nare switched off. We find that a dynamical fermionization of the momentum\ndistribution occurs at all temperatures. This phenomenon is studied for low\ninitial site occupations, for which the expansion of the cloud is self-similar.\nIn this regime, the occupation of the natural orbitals allows one to\ndistinguish hard-core bosons from noninteracting fermions. We also study the\nfree expansion of initial Mott insulating domains at finite temperature, and\nshow that the emergence of off-diagonal one-body correlations is suppressed\ngradually with increasing temperature. Surprisingly, the melting of the Mott\ndomain is accompanied by an effective cooling of the system. We explain this\nphenomenon analytically using an equilibrium description based on an emergent\nlocal Hamiltonian.",
        "positive": "Engineering tunable local loss in a synthetic lattice of momentum states: Dissipation can serve as a powerful resource for controlling the behavior of\nopen quantum systems.Recently there has been a surge of interest in the\ninfluence of dissipative coupling on large quantum systems and, more\nspecifically, how these processes can influence band topology and phenomena\nlike many-body localization. Here, we explore the engineering of local, tunable\ndissipation in so-called synthetic lattices, arrays of quantum states that are\nparametrically coupled in a fashion analogous to quantum tunneling. Considering\nthe specific case of momentum-state lattices, we investigate two distinct\nmechanisms for engineering controlled loss: one relying on an explicit form of\ndissipation by spontaneous emission, and another relying on reversible coupling\nto a large reservoir of unoccupied states. We experimentally implement the\nlatter and demonstrate the ability to tune the local loss rate over a large\nrange. The introduction of controlled loss to the synthetic lattice toolbox\npromises to pave the way for studying the interplay of dissipation with\ntopology, disorder, and interactions."
    },
    {
        "anchor": "Dynamic structure factor of a strongly correlated Fermi superfluid\n  within a density functional theory approach: We theoretically investigate the dynamic structure factor of a strongly\ninteracting Fermi gas at the crossover from Bardeen-Cooper-Schrieffer\nsuperfluids to Bose-Einstein condensates, by developing an improved random\nphase approximation within the framework of a density functional theory - the\nso-called superfluid local density approximation. Compared with the previous\nrandom-phase-approximation studies based on the standard Bogoliubov-de Gennes\nequations, the use of the density functional theory greatly improves the\naccuracy of the equation of state at the crossover, and leads to a better\ndescription of both collective Bogoliubov-Anderson-Goldstone phonon mode and\nsingle-particle fermionic excitations at small transferred momentum. Near\nunitarity, where the s-wave scattering length diverges, we show that the\nsingle-particle excitations start to significantly contribute to the spectrum\nof dynamic structure factor once the frequency is above a threshold of the\nenergy gap at $2\\Delta$. The sharp rise in the spectrum at this threshold can\nbe utilized to measure the pairing gap $\\Delta$. Together with the sound\nvelocity determined from the phonon branch, the dynamic structure factor\nprovides us some key information of the crossover Fermi superfluid. Our\npredictions could be examined in experiments with $^{6}$Li or $^{40}$K atoms\nusing Bragg spectroscopy.",
        "positive": "Disorder-Free Localization in $2+1$D Lattice Gauge Theories with\n  Dynamical Matter: Disorder-free localization (DFL) has been established as a mechanism of\nstrong ergodicity breaking in $1+1$D lattice gauge theories (LGTs) with\ndynamical matter for quenches starting in homogeneous initial states that span\nan extensive number of gauge superselection sectors. Nevertheless, the fate of\nDFL in $2+1$D in the presence of dynamical matter has hitherto remained an open\nquestion of great interest in light of the instability of quenched-disorder\nmany-body localization in higher spatial dimensions. Using infinite matrix\nproduct state calculations, we show that DFL survives in $2+1$D LGTs, albeit it\nis generally less pronounced than in $1+1$D, and highly depends on the matter\nconfiguration of the initial state. Through suitable matter configurations, we\nare able to relate and compare the $1+1$D and $2+1$D cases, showing that the\nmain ingredient for the strength of DFL in our setup is the \\textit{propagation\ndirectionality} of matter. Our results suggest that, generically, DFL is\nweakened with increasing spatial dimension, although it can be made independent\nof the latter by minimizing the propagation directionality of matter in the\ninitial state."
    },
    {
        "anchor": "Controlled non-autonomous matter-wave solitons in spinor Bose-Einstein\n  condensates with spatiotemporal modulation: To study controlled evolution of non-autonomous matter-wave solitons in\nspinor Bose-Einstein condensates with spatiotemporal modulation, we focus on a\nsystem of three coupled Gross-Pitaevskii (GP) equations with\nspace-time-dependent external potentials and temporally modulated gain/loss\ndistributions. An integrability condition and a non-isospectral Lax pair for\nthe coupled GP equations are obtained. Using it, we derive an infinite set of\ndynamical invariants, the first two of which are the mass and momentum. The\nDarboux transform is used to generate one- and two-soliton solutions. Under the\naction of different external potentials and gain/loss distributions, various\nsolutions for controlled non-autonomous matter-wave solitons of both\nferromagnetic and polar types are obtained, such as self-compressed, snake-like\nand stepwise solitons, and as well as breathers. In particular, the formation\nof states resembling rogue waves, under the action of a sign-reversible\ngain-loss distribution, is demonstrated too. Shape-preserving and changing\ninteractions between two non-autonomous matter-wave solitons and bound states\nof solitons are addressed too. In this context, spin switching arises in the\npolar-ferromagnetic interaction. Stability of the non-autonomous matter-wave\nsolitons is verified by means of systematic simulations of their perturbed\nevolution.",
        "positive": "Viscosity-entropy ratio of the unitary Fermi gas from zero-temperature\n  elementary excitations: We investigate the low-temperature behavior of the ratio between the shear\nviscosity \\eta and the entropy density s in the unitary Fermi gas by using a\nmodel based on the zero-temperature spectra of both bosonic collective modes\nand fermonic single-particle excitations. Our theoretical curve of \\eta/s as a\nfunction of the temperature T is in qualitative agreement with the experimental\ndata of trapped ultracold 6Li atomic gases. We find the minimum value \\eta/s\n\\simeq 0.44 (in units of \\hbar/k_B) at the temperature T/T_F \\simeq 0.27, with\nT_F the Fermi temperature."
    },
    {
        "anchor": "Simulating sympathetic cooling of atomic mixtures in nonlinear traps: We discuss the dynamics of sympathetic cooling of atomic mixtures in\nrealistic, nonlinear trapping potentials using a microscopic effective model\ndeveloped earlier for harmonic traps. We contrast the effectiveness of\ndifferent atomic traps, such as Ioffe-Pritchard magnetic traps and optical\ndipole traps, and the role their intrinsic nonlinearity plays in speeding up or\nslowing down thermalization between the two atomic species. This discussion\nincludes cases of configurations with lower effective dimensionality. From a\nmore theoretical standpoint, our results provide the first exploration of a\ngeneralized Caldeira-Leggett model with nonlinearities both in the trapping\npotential as well as in the interspecies interactions, and no limitations on\ntheir coupling strength.",
        "positive": "BCS-BEC crossover in a trapped Fermi super-fluid using a\n  density-functional equation: We derive a generalized time-dependent Galilean-invariant density-functional\n(DF) equation appropriate to study the stationary and non-stationary properties\nof a trapped Fermi super-fluid in the Bardeen-Cooper-Schrieffer (BCS) to\nBose-Einstein condensation (BCS) crossover. This equation is equivalent to a\nquantum hydrodynamical equation for a Fermi super-fluid. The bulk chemical\npotential of this equation has the proper (model-independent) dependence on the\nFermi-Fermi scattering length in the BCS and BEC limits. We apply this DF\nequation to the study of stationary density profile and size of a cigar-shaped\nFermi super-fluid of $^6$Li atoms and the results are in good agreement with\nthe experiment of Bartenstein {\\it et al.} in the BCS-BEC crossover. We also\napply the DF equation to the study of axial and radial breathing oscillation\nand our results for these frequencies are in good agreement with experiments in\nthe BCS-BEC crossover."
    },
    {
        "anchor": "Quasi-one-dimensional approximation for Bose-Einstein condensates\n  transversely trapped by a funnel potential: Starting from the standard three-dimensional (3D) Gross-Pitaevskii equation\n(GPE) and using a variational approximation, we derive an effective\none-dimensional nonpolynomial Schr\\\"odinger equation (1D-NPSE) governing the\naxial dynamics of atomic Bose-Einstein condensates (BECs) under the action of a\nsingular but physically relevant funnel-shaped transverse trap, i.e., an\nattractive 2D potential $\\sim-1/r$ (where $r$ is the radial coordinate in the\ntransverse plane), in combination with the repulsive self-interaction. Wave\nfunctions of the trapped BEC are regular, in spite of the potential's\nsingularity. The model applies to a condensate of particles (small molecules)\ncarrying a permanent electric dipole moment in the field of a uniformly charged\naxial thread, as well as to a quantum gas of magnetic atoms pulled by an axial\nelectric current. By means of numerical simulations, we verify that the\neffective 1D-NPSE provides accurate static and dynamical results, in comparison\nto the full 3D GPE, for both repulsive and attractive signs of the intrinsic\nnonlinearity.",
        "positive": "Application of the inhomogeneous Kibble-Zurek mechanism to quench\n  dynamics in the transition from a Mott-insulator to a superfluid in a finite\n  system: We apply the theory of inhomogeneous Kibble-Zurek mechanism to understand\nquench dynamics from the Mott insulator to the superfluid in a cold Bose gases\nconfined in both a two-dimensional optical lattice and a harmonic trap. The\nlocal quench time and the freeze-out region associated with the nonadiabatic\ntransition take a nontrivial positional dependence due to the Mott-lobe\nstructure of the ground state phase diagram of the Bose-Hubbard model. We\ndemonstrate that the quench dynamics through the time-dependent Gutzwiller\nsimulations, revealing inhomogeneous properties of the growth of the superfluid\norder parameter. The inhomogeneous Kibble-Zurek theory is applicable for the\nshallow harmonic trap."
    },
    {
        "anchor": "SuperVortexNet: Reconstructing Superfluid Vortex Filaments Using Deep\n  Learning: We introduce a novel approach to the three-dimensional reconstruction of\nsuperfluid vortex filaments using deep convolutional neural networks.\nSuperfluid vortices, quantum mechanical phenomena of immense scientific\ninterest, are challenging to image due to their small dimensions and intricate\ntopology. Here, we propose a deep-learning methodology that serves as a\nproof-of-principle for fully reconstructing the topology of superfluid vortex\nfilaments. We have trained a convolutional neural network on a large dataset of\nsimulated superfluid density images obtained by solving the Gross--Pitaevskii\nequation at scale, enabling it to learn the complex patterns and features\ninherent to superfluid vortex filaments. The network ingests the integrated\ndensity along the axial, coronal, and sagittal directions and outputs the\nreconstructed superfluid vortex filaments in three dimensions. We demonstrate\nthe success of this approach over a range of vortex densities of simulated\nisotropic quantum turbulence, enabling access to the characteristic scaling law\nof the decaying vortex line length.",
        "positive": "Observation of tunable mobility edges in generalized Aubry-Andr\u00e9\n  lattices: Using synthetic lattices of laser-coupled atomic momentum modes, we\nexperimentally realize a recently proposed family of nearest-neighbor\ntight-binding models having quasiperiodic site energy modulation that host an\nexact mobility edge protected by a duality symmetry. These one-dimensional\ntight-binding models can be viewed as a generalization of the well-known\nAubry-Andr\\'{e} (AA) model, with an energy-dependent self duality condition\nthat constitutes an analytical mobility edge relation. By adiabatically\npreparing the lowest and highest energy eigenstates of this model system and\nperforming microscopic measurements of their participation ratio, we track the\nevolution of the mobility edge as the energy-dependent density of states is\nmodified by the model's tuning parameter. Our results show strong deviations\nfrom single-particle predictions, consistent with attractive interactions\ncausing both enhanced localization of the lowest energy state due to\nself-trapping and inhibited localization of the highest energy state due to\nscreening. This study paves the way for quantitative studies of interaction\neffects on self duality induced mobility edges."
    },
    {
        "anchor": "Time fractals and discrete scale invariance with trapped ions: We show that a one-dimensional chain of trapped ions can be engineered to\nproduce a quantum mechanical system with discrete scale invariance and\nfractal-like time dependence. By discrete scale invariance we mean a system\nthat replicates itself under a rescaling of distance for some scale factor, and\na time fractal is a signal that is invariant under the rescaling of time. These\nfeatures are reminiscent of the Efimov effect, which has been predicted and\nobserved in bound states of three-body systems. We demonstrate that discrete\nscale invariance in the trapped ion system can be controlled with two\nindependently tunable parameters. We also discuss the extension to n-body\nstates where the discrete scaling symmetry has an exotic heterogeneous\nstructure. The results we present can be realized using currently available\ntechnologies developed for trapped ion quantum systems.",
        "positive": "Superfluid vortex dynamics on an ellipsoid and other surfaces of\n  revolution: We study the dynamics of quantized superfluid vortices on axisymmetric\ncompact surfaces with no holes, where the total vortex charge must vanish and\nthe condition of irrotational flow forbids distributed vorticity. A conformal\ntransformation from the surface to the complex plane allows us to use familiar\nformalism to describe the motion of the quantized vortices and to find the\ntotal energy. The simplest case is a vortex dipole with unit vortex charges on\nan axisymmetric ellipsoid. We study two special symmetric vortex-dipole\nconfigurations along with a general asymmetric one."
    },
    {
        "anchor": "Disorder effects during the evolution from BCS to BEC superfluidity: We describe the effects of disorder on the critical temperature of s-wave\nsuperfluids from the BCS to the BEC regime, with direct application to\nultracold Fermi atoms. In the BCS regime the pair breaking and phase coherence\ntemperature scales are essentially the same allowing strong correlations\nbetween the amplitude and phase of the order parameter. As non-pair breaking\ndisorder is introduced the largely overlapping Cooper pairs conspire to\nmaintain phase coherence such that the critical temperature remains essentially\nunchanged. However, in the BEC regime the pair breaking and phase coherence\ntemperature scales are very different such that non-pair breaking disorder can\naffect dramatically phase coherence, and thus the critical temperature, without\nthe requirement of breaking tightly-bound fermion pairs simultaneously.\nFinally, we find that the superfluid is more robust against weak disorder in\nthe intermediate region between the two regimes.",
        "positive": "The spin Hall effect in a quantum gas: Electronic properties like current flow are generally independent of the\nelectron's spin angular momentum, an internal degree of freedom present in\nquantum particles. The spin Hall effects (SHEs), first proposed 40 years ago,\nare an unusual class of phenomena where flowing particles experience\northogonally directed spin-dependent Lorentz-like forces, analogous to the\nconventional Lorentz force for the Hall effect, but opposite in sign for two\nspin states. Such spin Hall effects have been observed for electrons flowing in\nspin-orbit coupled materials such as GaAs or InGaAs and for laser light\ntraversing dielectric junctions. Here we observe the spin Hall effect in a\nquantum-degenerate Bose gas, and use the resulting spin-dependent Lorentz\nforces to realize a cold-atom spin transistor. By engineering a spatially\ninhomogeneous spin-orbit coupling field for our quantum gas, we explicitly\nintroduce and measure the requisite spin-dependent Lorentz forces, in excellent\nagreement with our calculations. This atomtronic circuit element behaves as a\nnew type of velocity-insensitive adiabatic spin-selector, with potential\napplication in devices such as magnetic or inertial sensors. In addition, such\ntechniques --- for both creating and measuring the SHE --- are clear\nprerequisites for engineering topological insulators and detecting their\nassociated quantized spin Hall effects in quantum gases. As implemented, our\nsystem realized a laser-actuated analog to the Datta-Das spin transistor."
    },
    {
        "anchor": "Dimensional Crossover in a Quantum Gas of Light: The dimensionality of a system profoundly influences its physical behaviour,\nleading to the emergence of different states of matter in many-body quantum\nsystems. In lower dimensions, fluctuations increase and lead to the suppression\nof long-range order. For example, in bosonic gases, Bose-Einstein condensation\n(BEC) in one dimension requires stronger confinement than in two dimensions. We\nexperimentally study the properties of a harmonically trapped photon gas\nundergoing Bose-Einstein condensation along the dimensional crossover from one\nto two dimensions. The photons are trapped in a dye microcavity where polymer\nnanostructures provide the trapping potential for the photon gas. By varying\nthe aspect ratio of the harmonic trap, we tune from an isotropic\ntwo-dimensional confinement to an anisotropic, highly elongated one-dimensional\ntrapping potential. Along this transition we determine the caloric properties\nof the photon gas and find a softening of the second-order Bose-Einstein\ncondensation phase transition observed in two dimensions to a crossover\nbehaviour in one dimension.",
        "positive": "Long-range interacting quantum systems: The presence of non-local and long-range interactions in quantum systems\ninduces several peculiar features in their equilibrium and out-of-equilibrium\nbehavior. In current experimental platforms control parameters such as\ninteraction range, temperature, density and dimension can be changed. The\nexistence of universal scaling regimes, where diverse physical systems and\nobservables display quantitative agreement, generates a common framework, where\nthe efforts of different research communities can be -- in some cases\nrigorously -- connected. Still, the application of this general framework to\nparticular experimental realisations requires the identification of the regimes\nwhere the universality phenomenon is expected to appear. In the present review\nwe summarise the recent investigations of many-body quantum systems with\nlong-range interactions, which are currently realised in Rydberg atom arrays,\ndipolar systems, trapped ion setups and cold atoms in cavity experiments. Our\nmain aim is to present and identify the common and (mostly) universal features\ninduced by long-range interactions in the behaviour of quantum many-body\nsystems. We will discuss both the case of very strong non-local couplings, i.e.\nthe non-additive regime, and the one in which energy is extensive, but\nnevertheless low-energy, long wavelength properties are altered with respect to\nthe short-range limit. Cases of competition with other local effects in the\nabove mentioned setups are also reviewed."
    },
    {
        "anchor": "Stability of attractive bosonic cloud with van der Waals interaction: We investigate the structure and stability of Bose-Einstein condensate of\n$^{7}$Li atoms with realistic van der Waals interaction by using the potential\nharmonic expansion method. Besides the known low-density metastable solution\nwith contact delta function interaction, we find a stable branch at a higher\ndensity which corresponds to the formation of an atomic cluster. Comparison\nwith the results of non-local effective interaction is also presented. We\nanalyze the effect of trap size on the transition between the two branches of\nsolutions. We also compute the loss rate of a Bose condensate due to two- and\nthree-body collisions.",
        "positive": "Emptiness Formation Probability in 1D Bose Liquids: We study emptiness formation probability (EFP) in interacting 1D Bose\nliquids. That is the probability that a snapshot of its ground state reveals\nexactly zero number of particles within the interval $|x|<R$. For a weakly\ninteracting liquid there is parametrically wide regime $n^{-1} < R <\\xi$ (here\n$n$ is the average density and $\\xi$ is the healing length), where EFP exhibits\na non-trivial crossover from the Poisson to the Gaussian behavior. We employ\nthe instanton technique [A. Abanov, 2004] to study quantitative details of\nthese regime and compare it with previously reported limited cases."
    },
    {
        "anchor": "Pairing of the P\u00f6schl-Teller gas: We report calculations of equation of state of a model system, representative\nfor a cold Fermi gas, of particles interacting via the P\\\"oschl-Teller\ninteraction. In successively more sophisticated calculations, we determine the\nimportance of correlations and non-localities. We show that the gas displays,\nat relatively low density, an instability indicated by a divergence of the\nin-medium scattering length which occurs well before the divergence of the\nvacuum scattering length and the spinodal density. We also calculate the\npairing gap and show that non-local correlations can change the pairing gap by\nalmost an order of magnitude.",
        "positive": "NOON state of Bose atoms in the double-well potential via an excited\n  state quantum phase transition: We suggest a simple scheme for creating a NOON state of repulsively\ninteracting Bose atoms in the double-well potential. The protocol consists of\ntwo steps. First, by setting atom-atom interactions to zero, the system is\ndriven to the upper excited state. Second, the interactions is slowly increased\nand, simultaneously, the inter-well tunneling is decreased to zero. We analyze\nfidelity of the final state to the NOON state depending on the number of atoms,\nramp rate, and fluctuations of the system parameters. It is shown that for a\ngiven fidelity the ramp rate scales algebraically with the number of atoms."
    },
    {
        "anchor": "Atomic quantum gases in periodically driven optical lattices: Time periodic forcing in the form of coherent radiation is a standard tool\nfor the coherent manipulation of small quantum systems like single atoms. In\nthe last years, periodic driving has more and more also been considered as a\nmeans for the coherent control of many-body systems. In particular, experiments\nwith ultracold quantum gases in optical lattices subjected to periodic driving\nin the lower kilohertz regime have attracted a lot of attention. Milestones\ninclude the observation of dynamic localization, the dynamic control of the\nquantum phase transition between a bosonic superfluid and a Mott insulator, as\nwell as the dynamic creation of strong artificial magnetic fields and\ntopological band structures. This article reviews these recent experiments and\ntheir theoretical description. Moreover, fundamental properties of periodically\ndriven many-body systems are discussed within the framework of Floquet theory,\nincluding heating, relaxation dynamics, anomalous topological edge states, and\nthe response to slow parameter variations.",
        "positive": "Fourier's law on a one-dimensional optical random lattice: We study the transport properties of a one-dimensional hard-core bosonic\nlattice gas coupled to two particle reservoirs at different chemical potentials\nwhich generate a current flow through the system. In particular, the influence\nof random fluctuations of the underlying lattice on the stationary-state\nproperties is investigated. We show analytically that the steady-state density\npresents a linear profile. The local steady-state current obeys the Fourier law\n$j=-\\kappa(\\tau)\\nabla n $ where $\\tau$ is a typical timescale of the lattice\nfluctuations and $\\nabla n$ the density gradient imposed by the reservoirs."
    },
    {
        "anchor": "Many-body physics with ultracold plasmas: Quenched randomness and\n  localization: The exploration of large-scale many-body phenomena in quantum materials has\nproduced many important experimental discoveries, including novel states of\nentanglement, topology and quantum order as found for example in quantum spin\nices, topological insulators and semimetals, complex magnets, and high-$T_c$\nsuperconductors. Yet, the sheer scale of solid-state systems and the difficulty\nof exercising exacting control of their quantum mechanical degrees of freedom\nlimit the pace of rational progress in advancing the properties of these and\nother materials. With extraordinary effort to counteract natural processes of\ndissipation, precisely engineered ultracold quantum simulators could point the\nway to exotic new materials. Here, we look instead to the quantum mechanical\ncharacter of the arrested state formed by a quenched ultracold molecular\nplasma. This novel class of system arises spontaneously, without a deliberate\nengineering of interactions, and evolves naturally from state-specified initial\nconditions, to a long-lived final state of canonical density, in a process that\nconflicts with classical notions of plasma dissipation and neutral\ndissociation. We take information from experimental observations to develop a\nconceptual argument that attempts to explain this state of arrested relaxation\nin terms of a minimal phenomenological model of randomly interacting dipoles of\nrandom energies. This model of the plasma forms a starting point to describe\nits observed absence of relaxation in terms of many-body localization (MBL).\nThe large number of accessible Rydberg and excitonic states gives rise to an\nunconventional web of many-body interactions that vastly exceeds the complexity\nof MBL in a conventional few-level scheme. This experimental platform thus\nopens an avenue for the coupling of dipoles in disordered environments that\nwill demand the development of new theoretical tools.",
        "positive": "Nonholonomy of order parameters and su(3) vortices in spin-1\n  Bose-Einstein condensates: A generalized Mermin-Ho relation for a spin-1 BEC is derived, which is\napplicable to vortices regardless of the symmetry and spin polarization of the\norder parameter. The obtained relation implies an su(3) mass-current\ncirculation and two classes of vortices corresponding to two different su(2)\nsubalgebras."
    },
    {
        "anchor": "Diffractive scattering of three particles in one dimension: a simple\n  result for weak violations of the Yang--Baxter equation: We study scattering of three equal mass particles in one dimension.\nIntegrable interactions are synonymous with non-diffractive scattering, meaning\nthat the set of incoming momenta for any scattering event coincides with the\nset of outgoing momenta. A system is integrable if the two particle scattering\nmatrix obeys the Yang--Baxter equation. Nonintegrable interactions correspond\nto diffractive scattering, where the set of outgoing momenta may take on all\nvalues consistent with energy and momentum conservation. Such processes play a\nvital role in the kinetics of one dimensional gases, where binary collisions\nare unable to alter the distribution function.\n  When integrability is broken weakly, the result is a small diffractive\nscattering amplitude. Our main result is a simple formula for the diffractive\npart of the scattering amplitude, when the violation of the Yang--Baxter\nequation is small. Although the derivation is given for delta-function\ninteractions, the result depends only on the two-particle scattering matrix,\nand should therefore also apply to finite-range interactions close to\nintegrable.",
        "positive": "Laser operation and Bose-Einstein condensation: analogies and\n  differences: After reviewing the interpretation of laser operation as a non-equilibrium\nBose-Einstein condensation phase transition, we illustrate the novel features\narising from the non-equilibrium nature of photon and polariton Bose-Einstein\ncondensates recently observed in experiments. We then proposea quantitative\ncriterion to experimentally assess the equilibrium vs. non-equilibrium nature\nof a specific condensation process, based on fluctuation-dissipation relations.\nThe power of this criterion is illustrated on two models which shows very\ndifferent behaviours."
    },
    {
        "anchor": "Bose polaron interactions in a cavity-coupled monolayer semiconductor: The interaction between a mobile quantum impurity and a bosonic bath leads to\nthe formation of quasiparticles, termed Bose polarons. The elementary\nproperties of Bose polarons, such as their mutual interactions, can differ\ndrastically from those of the bare impurities. Here, we explore Bose polaron\nphysics in a two-dimensional nonequilibrium setting by injecting $\\sigma^-$\npolarised exciton-polariton impurities into a bath of coherent $\\sigma^+$\npolarised polaritons generated by resonant laser excitation of monolayer\nMoSe$_2$ embedded in an optical cavity. By exploiting a biexciton Feshbach\nresonance between the impurity and the bath polaritons, we tune the interacting\nsystem to the strong-coupling regime and demonstrate the coexistence of two new\nquasiparticle branches. Using time-resolved pump-probe measurements we observe\nhow polaron dressing modifies the interaction between impurity polaritons.\nRemarkably, we find that the interactions between high-energy polaron\nquasiparticles, that are repulsive for small bath occupancy, can become\nattractive in the strong impurity-bath coupling regime. Our experiments provide\nthe first direct measurement of Bose polaron-polaron interaction strength in\nany physical system and pave the way for exploration and control of many-body\ncorrelations in driven-dissipative settings.",
        "positive": "On Two-Component Dark-Bright Solitons in Three-dimensional Atomic\n  Bose-Einstein Condensates: In the present work, we revisit two-component Bose-Einstein condensates in\ntheir fully three-dimensional (3d) form. Motivated by earlier studies of\ndark-bright solitons in the 1d case, we explore the stability of these\nstructures in their fully 3d form in two variants. In one the dark soliton is\nplanar and trapping a planar bright (disk) soliton. In the other case, a dark\nspherical shell soliton creates an effective potential in which a bright\nspherical shell of atoms is trapped in the second component. We identify these\nsolutions as numerically exact states (up to a prescribed accuracy) and perform\na Bogolyubov-de Gennes linearization analysis that illustrates that both\nstructures can be dynamically stable in suitable intervals of sufficiently low\nchemical potentials. We corroborate this finding theoretically by analyzing the\nstability via degenerate perturbation theory near the linear limit of the\nsystem. When the solitary waves are found to be unstable, we explore their\ndynamical evolution via direct numerical simulations which, in turn, reveal\nnovel waveforms that are more robust. Finally, using the SO$(2)$ symmetry of\nthe model, we produce multi-dark-bright planar or shell solitons involved in\npairwise oscillatory motion."
    },
    {
        "anchor": "Models of spin-orbit coupled oligomers: We address the stability and dynamics of eigenmodes in linearly-shaped\nstrings (dimers, trimers, tetramers, and pentamers) built of droplets of a\nbinary Bose-Einstein condensate (BEC). The binary BEC is composed of atoms in\ntwo pseudo-spin states with attractive interactions, dressed by properly\narranged laser fields, which induce the (pseudo-) spin-orbit (SO) coupling. We\ndemonstrate that the SO-coupling terms help to create eigenmodes of particular\ntypes in the strings. Dimer, trimer, and pentamer eigenmodes of the linear\nsystem, which correspond to the zero eigenvalue (EV, alias chemical potential)\nextend into the nonlinear ones, keeping an exact analytical form, while\ntetramers do not admit such a continuation, because the respective spectrum\ndoes not contain a zero EV. Stability areas of these modes shrink with the\nincreasing nonlinearity. Besides these modes, other types of nonlinear states,\nwhich are produced by the continuation of their linear counterparts\ncorresponding to some nonzero EVs, are found in a numerical form (including\nones for the tetramer system). They are stable in nearly entire existence\nregions in trimer and pentamer systems, but only in a very small area for the\ntetramers. Similar results are also obtained, but not displayed in detail, for\nhexa- and septamers.",
        "positive": "Spin dynamics and domain formation of a spinor Bose-Einstein condensate\n  in an optical cavity: We consider a ferromagnetic spin-1 Bose-Einstein condensate (BEC)\ndispersively coupled to a unidirectional ring cavity. We show that the ability\nof a cavity to modify, in a highly nonlinear fashion, matter-wave phase shifts\nadds a new dimension to the study of spinor condensates both within and beyond\nthe single-mode approximation. In addition to demonstrating strong matter-wave\nbistability as in our earlier publication [L. Zhou et al., Phys. Rev. Lett.\n103, 160403 (2009)], we show that the interplay between atomic and cavity\nfields can greatly enrich both the physics of critical slowing down in spin\nmixing dynamics and the physics of spin-domain formation in spinor condensates."
    },
    {
        "anchor": "Heating and many-body resonances in a periodically driven two-band\n  system: We study the dynamics and stability in a strongly interacting resonantly\ndriven two-band model. Using exact numerical simulations, we find a stable\nregime at large driving frequencies where the time evolution is governed by a\nlocal Floquet Hamiltonian that is approximately conserved out to very long\ntimes. For slow driving, on the other hand, the system becomes unstable and\nheats up to infinite temperature. While thermalization is relatively fast in\nthese two regimes (but to different \"temperatures\"), in the crossover between\nthem we find slow nonthermalizing time evolution: temporal fluctuations become\nstrong and temporal correlations long lived. Microscopically, we trace back the\norigin of this nonthermalizing time evolution to the properties of rare Floquet\nmany-body resonances, whose proliferation at lower driving frequency removes\nthe approximate energy conservation, and thus produces thermalization to\ninfinite temperature.",
        "positive": "Doublon dynamics and polar molecule production in an optical lattice: Ultracold polar molecules provide an excellent platform to study quantum\nmany-body spin dynamics, which has become accessible in the recently realized\nlow entropy quantum gas of polar molecules in an optical lattice. To obtain a\ndetailed understanding for the molecular formation process in the lattice, we\nprepare a density distribution where lattice sites are either empty or occupied\nby a doublon composed of a bosonic atom interacting with a fermionic atom. By\nletting this disordered, out-of-equilibrium system evolve from a well-defined\ninitial condition, we observe clear effects on pairing that arise from\ninter-species interactions, a higher partial wave Feshbach resonance, and\nexcited Bloch-band population. When only the lighter fermions are allowed to\ntunnel in the three-dimensional (3D) lattice, the system dynamics can be well\ndescribed by theory. However, in a regime where both fermions and bosons can\ntunnel, we encounter correlated dynamics that is beyond the current capability\nof numerical simulations. Furthermore, we show that we can probe the\nmicroscopic distribution of the atomic gases in the lattice by measuring the\ninelastic loss of doublons. These techniques realize tools that are generically\napplicable to heteronuclear diatomic systems in optical lattices and can shed\nlight on molecule production as well as dynamics of a Bose-Fermi mixture."
    },
    {
        "anchor": "Soliton lattices in the Gross-Pitaevskii equation with nonlocal and\n  repulsive coupling: Spatially-periodic patterns are studied in nonlocally coupled\nGross-Pitaevskii equation. We show first that spatially periodic patterns\nappear in a model with the dipole-dipole interaction. Next, we study a model\nwith a finite-range coupling, and show that a repulsively coupled system is\nclosely related with an attractively coupled system and its soliton solution\nbecomes a building block of the spatially-periodic structure. That is, the\nspatially-periodic structure can be interpreted as a soliton lattice. An\napproximate form of the soliton is given by a variational method. Furthermore,\nthe effects of the rotating harmonic potential and spin-orbit coupling are\nnumerically studied.",
        "positive": "Quantum Monte Carlo study of spin-polarized deuterium: The ground state properties of spin-polarized deuterium (D$\\downarrow$) at\nzero temperature are obtained by means of the diffusion Monte Carlo\ncalculations within the fixed-node approximation. Three D$\\downarrow$ species\nhave been investigated (D$\\downarrow_1$, D$\\downarrow_2$, D$\\downarrow_3$),\ncorresponding respectively to one, two and three equally occupied nuclear spin\nstates. Influence of the backflow correlations on the ground state energy of\nthe systems is explored. The equilibrium densities for D$\\downarrow_2$ and\nD$\\downarrow_3$ liquids are obtained and compared with ones obtained in\nprevious approximate prediction. The density and the pressure at which the\ngas-liquid phase transition occurs at $T$=0 is obtained for D$\\downarrow_1$."
    },
    {
        "anchor": "Geometry-induced modification of fluctuation spectrum in\n  quasi-two-dimensional condensates: We report the structural transformation of the low-lying spectral modes,\nespecially the Kohn mode, from radial to circular topology as harmonic\nconfining potential is modified to a toroidal one, and this corresponds to a\ntransition from simply to multiply connected geometry. For this we employ the\nHartree-Fock-Bogoliubov theory to examine the evolution of low energy\nquasiparticles. We, then, use the Hartree-Fock-Bogoliubov theory with the Popov\napproximation to demonstrate the two striking features of quantum and thermal\nfluctuations. At $T=0$, the non-condensate density due to interaction induced\nquantum fluctuations increases with the transformation from pancake to toroidal\ngeometry. The other feature is, there is a marked change in the density profile\nof the non-condensate density at finite temperatures with the modification of\ntrapping potential. In particular, the condensate and non-condensate density\ndistributions have overlapping maxima in the toroidal condensate, which is in\nstark contrast to the case of pancake geometry. The genesis of this difference\nlies in the nature of the thermal fluctuations.",
        "positive": "Two-dimensional dynamics of expansion of a degenerate Bose gas: Expansion of a degenerate Bose gas released from a pancakelike trap is\nnumerically simulated under the assumption of separation of the motion in the\nplane of the loose initial trapping and the motion in the direction of the\ninitial tight trapping. The initial conditions for the phase fluctuations are\ngenerated using the extension to the two-dimensional case of the description of\nthe phase noise by the Ornstein-Uhlenbeck stochastic process. The numerical\nsimulations, taking into account both the finite size of the two-dimensional\nsystem and the atomic interactions, which cannot be neglected on the early\nstage of expansion, did not reproduce the scaling law for the peaks in the\ndensity fluctuation spectra experimentally observed by Choi, Seo, Kwon, and\nShin [Phys. Rev. Lett. 109, 125301 (2012)]. The latter experimental results may\nthus require an explanation beyond our current assumptions."
    },
    {
        "anchor": "Controlling Nonequilibrium Bose-Einstein Condensation with Engineered\n  Environments: Out of thermal equilibrium, bosonic quantum systems can Bose-condense away\nfrom the ground state, featuring a macroscopic occupation of an excited state\nor even of multiple states in the so-called Bose-selection scenario. In\nprevious work, a theory was developed that predicts, in which states a\ndriven-dissipative ideal Bose gas condenses. Here, we address the inverse\nproblem: Given a target state with desired condensate fractions in certain\nsingle-particle states, how can this configuration be achieved by tuning\navailable control parameters? Which type of experimental setup allows for\nflexible condensation control? We solve these problems, on the one hand, by\ndeveloping a theory to solve the inverse problem based on linear programming\nmethods. On the other, we propose a Bose `condenser', experimentally\nimplementable in a superconducting circuit, where targeted Bose condensation\ninto eigenstates of a chain of resonators is driven through the coupling to\nartificial quantum baths, realized via auxiliary two-level systems. We further\ndiscuss the engineering of transition points between different Bose\ncondensation configurations, which may find application for amplification,\nheat-flow control, and the design of highly-structured quantum baths.",
        "positive": "Ewald method for polytropic potentials in arbitrary dimensionality: The Ewald summation technique is generalised to power-law 1/|r|^k potentials\nin three-, two- and one-dimensional geometries with explicit formulae for all\nthe components of the sums. The cases of short-range, long-range and \"marginal\"\ninteractions are treated separately. The jellium model, as a particular case of\na charge-neutral system, is discussed and the explicit forms of the Ewald sums\nfor such system are presented. A generalised form of the Ewald sums for a\nnoncubic (nonsquare) simulation cell for three- (two-) dimensional geometry is\nobtained and its possible field of application is discussed. A procedure for\nthe optimisation of the involved parameters in actual simulations is developed\nand an example of its application is presented."
    },
    {
        "anchor": "Crossover between few and many fermions in a harmonic trap: The properties of a balanced two-component Fermi gas in a one-dimensional\nharmonic trap are studied by means of the coupled cluster method. For few\nfermions we recover the results of exact diagonalization, yet with this method\nwe are able to study much larger systems. We compute the energy, the chemical\npotential, the pairing gap, and the density profile of the trapped clouds,\nsmoothly mapping the crossover between the few-body and many-body limits. The\nenergy is found to converge surprisingly rapidly to the many-body result for\nevery value of the interaction strength. Many more particles are instead needed\nto give rise to the non-analytic behavior of the pairing gap, and to smoothen\nthe pronounced even-odd oscillations of the chemical potential induced by the\nshell structure of the trap.",
        "positive": "Properties of a dipolar condensate with three-body interactions: We obtain the phase diagram for a harmonically trapped dilute dipolar\ncondensate with a short ranged conservative three-body interaction. We show\nthat this system supports two distinct fluid states: a usual condensate state\nand a self-cohering droplet state. We develop a simple model to quantify the\nenergetics of these states, which we verify with full numerical calculations.\nBased on our simple model we develop a phase diagram showing that there is a\nfirst order phase transition between the states. Using dynamical simulations we\nexplore the phase transition dynamics, revealing that the droplet crystal\nobserved in previous work is an excited state that arises from heating as the\nsystem crosses the phase transition. Utilising our phase diagram we show it is\nfeasible to produce a single droplet by dynamically adjusting the confining\npotential."
    },
    {
        "anchor": "Bright-like soliton solution in quasi-one-dimensional BEC in third order\n  on interaction radius: Nonlinear Schr\\\"{o}dinger equations and corresponding quantum hydrodynamic\n(QHD) equations are widely used in studying ultracold boson-fermion mixtures\nand superconductors. In this article, we show that a more exact account of\ninteraction in Bose-Einstein condensate (BEC), in comparison with the\nGross-Pitaevskii (GP) approximation, leads to the existence of a new type of\nsolitons. We use a set of QHD equations in the third order by the interaction\nradius (TOIR), which corresponds to the GP equation in a first order by the\ninteraction radius. The solution for the soliton in a form of expression for\nthe particle concentration is obtained analytically. The conditions of\nexistence of the soliton are studied. It is shown what solution exists if the\ninteraction between the particles is repulsive. Particle concentration of order\nof $10^{12}$-$10^{14}$ $cm^{-3}$ has been achieved experimentally for the BEC,\nthe solution exists if the scattering length is of the order of 1 $\\mu$m, which\ncan be reached using the Feshbach resonance. It is one of the limit case of\nexistence of new solution. The corresponding scattering length decrease with\nthe increasing of concentration of particles. The investigation of effects in\nthe TOIR approximation gives a more detail information on interaction\npotentials between the atoms and can be used for a more detail investigation\ninto the potential structure.",
        "positive": "Self-consistent theory of Bose-Einstein condensate with impurity at\n  finite temperature: We study the properties of Bose-Einstein condensate (BEC)-impurity mixtures\nat finite temperature employing the Balian-V\\'en\\'eroni (BV) variational\nprinciple. The method leads to a set of coupled nonlinear equations of motion\nfor the condensate and its normal and anomalous fluctuations on the one hand,\nand for the impurity on the other. We show that the obtained equations satisfy\nthe energy and number conserving laws. Useful analytic expressions for the\nchemical potential and the radius of both condensate and anomalous components\nare derived in the framework of the Thomas-Fermi (TF) approximation in\n$d$-dimensional regime. Effects of the impurity on these quantities are\ndiscussed."
    },
    {
        "anchor": "Dynamic hysteresis from bistability in an antiferromagnetic spinor\n  condensate: We study the emergence of hysteresis during the process of quantum phase\ntransition from an antiferromagnetic to a phase-separated state in a spin-1\nBose Einstein condensate of ultracold atoms. We explicitly demonstrate the\nappearance of a hysteresis loop with various quench times showing that it is\nrate-independent for large magnetizations only. In other cases scaling of the\nhysteresis loop area is observed, which we explain by using the Kibble-Zurek\ntheory in the limit of small magnetization. The effect of an external harmonic\ntrapping potential is also discussed.",
        "positive": "Density profile of a semi-infinite one-dimensional Bose gas and bound\n  states of the impurity: We study the effect of the boundary on a system of weakly interacting bosons\nin one dimension. It strongly influences the boson density which is completely\nsuppressed at the boundary position. Away from it, the density is depleted over\nthe distances on the order of the healing length at the mean-field level.\nQuantum fluctuations modify the density profile considerably. The local density\napproaches the average one as an inverse square of the distance from the\nboundary. We calculate an analytic expression for the density profile at\narbitrary separations from the boundary. We then consider the problem of\nlocalization of a foreign quantum particle (impurity) in the potential created\nby the inhomogeneous boson density. At the mean-field level, we find exact\nresults for the energy spectrum of the bound states, the corresponding wave\nfunctions, and the condition for interaction-induced localization. The quantum\ncontribution to the boson density gives rise to small corrections of the bound\nstate energy levels. However, it is fundamentally important for the existence\nof a long-range Casimir-like interaction between the impurity and the boundary."
    },
    {
        "anchor": "Generation and decoherence of soliton spatial superposition states: Due to their coherence properties, dilute atomic gas Bose-Einstein\ncondensates seem a versatile platform for controlled creation of mesoscopically\nentangled states with a large number of particles and also allow controlled\nstudies of their decoherence. However, the creation of such a state\nintrinsically involves many-body quantum dynamics that cannot be captured by\nmean-field theory, and thus invalidates the most widespread methods for the\ndescription of condensates. We follow up on a proposal, in which a condensate\ncloud as a whole is brought into a superposition of two different spatial\nlocations, by mapping entanglement from a strongly interacting Rydberg atomic\nsystem onto the condensate using off-resonant laser dressing [R. Mukherjee et\nal., Phys. Rev. Lett. 115 040401 (2015)]. A variational many-body Ansatz akin\nto recently developed multi-configurational methods allows us to model this\nentanglement mapping step explicitly, while still preserving the simplicity of\nmean-field physics for the description of each branch of the superposition. In\nthe second part of the article, we model the decoherence process due to atom\nlosses in detail. Altogether we confirm earlier estimates, that tightly\nlocalized clouds of 400 atoms can be brought into a quantum superposition of\ntwo locations about 3 {\\mu}m apart and remain coherent for about 1 ms.",
        "positive": "Transfer of BECs through discrete breathers in an optical lattice: We study the stability of a stationary discrete breather (DB) on a nonlinear\ntrimer in the framework of the discrete nonlinear Schr\\\"odinger equation\n(DNLS). In previous theoretical investigations of the dynamics of Bose-Einstein\ncondensates in leaking optical lattices, collisions between a DB and a lattice\nexcitation, e.g. a moving breather (MB) or phonon, were studied. These\ncollisions lead to the transmission of a fraction of the incident (atomic) norm\nof the MB through the DB, while the DB can be shifted in the direction of the\nincident lattice excitation. Here we show that there exists a total energy\nthreshold of the trimer, above which the lattice excitation can trigger the\ndestabilization of the DB and that this is the mechanism leading to the\nmovement of the DB. Furthermore, we give an analytic estimate of upper bound to\nthe norm that is transmitted through the DB. Our analysis explains the results\nof the earlier numerical studies and may help to clarify functional operations\nwith BECs in optical lattices such as blocking and filtering coherent (atomic)\nbeams."
    },
    {
        "anchor": "Spin squeezing and EPR entanglement of two bimodal condensates in\n  state-dependent potentials: We propose and analyze a scheme to entangle the collective spin states of two\nspatially separated bimodal Bose-Einstein condensates. Using a four-mode\napproximation for the atomic field, we show that elastic collisions in a\nstate-dependent potential simultaneously create spin-squeezing in each\ncondensate and entangle the collective spins of the two condensates. We\ninvestigate mostly analytically the non-local quantum correlations that arise\nin this system at short times and show that Einstein-Podolsky-Rosen (EPR)\nentanglement is generated between the condensates. At long times we point out\nmacroscopic entangled states and explain their structure. The scheme can be\nimplemented with condensates in state-dependent microwave potentials on an atom\nchip.",
        "positive": "Quantum oscillations in the kinetic energy density: Gradient corrections\n  from the Airy gas: We derive a closed form expression for the quantum corrections to the kinetic\nenergy density (KED) in the Thomas-Fermi (TF) limit of a linear potential model\nsystem in three dimensions (the Airy gas). The universality of the expression\nis tested numerically in a number of three dimensional model systems: (i)\njellium surfaces, (ii) hydrogen-like potentials, (iii) systems confined by an\nharmonic potential in one and (iv) all three dimensions, and (v) a system with\na cosine potential (the Mathieu gas). Our results confirm that the usual\ngradient expansion of extended Thomas-Fermi theory (ETF) does not describe the\nquantum oscillations for systems that incorporate surface regions where the\nelectron density drops off to zero. We find that the correction derived from\nthe Airy gas is universally applicable to relevant spatial regions of systems\nof type (i), (ii), and (iv), but somewhat surprisingly not (iii). We discuss\npossible implications of our findings to the development of functionals for the\nkinetic energy density."
    },
    {
        "anchor": "Bloch oscillations in the absence of a lattice: We experimentally investigate the quantum motion of an impurity atom that is\nimmersed in a strongly interacting one-dimensional Bose liquid and is subject\nto an external force. We find that the momentum distribution of the impurity\nexhibits characteristic Bragg reflections at the edge of an emergent Brillouin\nzone. While Bragg reflections are typically associated with lattice structures,\nin our strongly correlated quantum liquid they result from the interplay of\nshort-range crystalline order and kinematic constraints on the many-body\nscattering processes in the one-dimensional system. As a consequence, the\nimpurity exhibits periodic dynamics that we interpret as Bloch oscillations,\nwhich arise even though the quantum liquid is translationally invariant. Our\nobservations are supported by large-scale numerical simulations.",
        "positive": "Interference Pattern Formation between Bounded-Solitons and Radiation in\n  Momentum Space: Possible Detection of Radiation from Bounded-Solitons with\n  Bose-Einstein Condensate of Neutral Atoms: We propose an indirect method to observe radiation from an incomplete soliton\nwith sufficiently large amplitude. We show that the radiation causes a notched\nstructure on the envelope of the wave packet in the momentum space. The origin\nof this structure is a result of interference between the main body of\noscillating solitons and the small radiation in the momentum space. We\nnumerically integrate the nonlinear Schr\\\"odinger equation and perform Fourier\ntransformation to confirm that the predicted structure really appears. We also\nshow the simple model which reproduces the qualitative result. Experimental\ndetection of the notched structure with Bose-Einstein condensation of neutral\natoms is discussed and suitable parameters for this detection experiment are\nshown."
    },
    {
        "anchor": "Zitterbewegung effect in spin-orbit coupled spin-1 ultracold atoms: The Zitterbewegung effect in spin-orbit coupled spin-1 cold atoms is\ninvestigated in the presence of the Zeeman field and a harmonic trap. It is\nshown that the Zeeman field and the harmonic trap have significant effect on\nthe Zitterbewegung oscillatory behaviors. The external Zeeman field could\nsuppress or enhance the Zitterbewegung amplitude and change the frequencies of\noscillation. A much slowly damping Zitterbewegung oscillation can be achieved\nby adjusting both the linear and quadratic Zeeman field. Multi-frequency\nZitterbewegung oscillation can be induced by the applied Zeeman field. In the\npresence of the harmonic trap, the subpackets corresponding to different\neigenenergies would always keep coherent, resulting in the persistent\nZitterbewegung oscillations. The Zitterbewegung oscillation would display very\ncomplicated and irregular oscillation characteristics due to the coexistence of\ndifferent frequencies of the Zitterbewegung oscillation. Numerical results show\nthat, the Zitterbewegung effect is robust even in the presence of interaction\nbetween atoms.",
        "positive": "Metastability in spin polarised Fermi gases and quasiparticle decays: We investigate the metastability associated with the first order transition\nfrom normal to superfluid phases in the phase diagram of two-component\npolarised Fermi gases.We begin by detailing the dominant decay processes of\nsingle quasiparticles.Having determined the momentum thresholds of each process\nand calculated their rates, we apply this understanding to a Fermi sea of\npolarons by linking its metastability to the stability of individual polarons,\nand predicting a region of metastability for the normal partially polarised\nphase. In the limit of a single impurity, this region extends from the\ninteraction strength at which a polarised phase of molecules becomes the\ngroundstate, to the one at which the single quasiparticle groundstate changes\ncharacter from polaronic to molecular. Our argument in terms of a Fermi sea of\npolarons naturally suggests their use as an experimental probe. We propose\nexperiments to observe the threshold of the predicted region of metastability,\nthe interaction strength at which the quasiparticle groundstate changes\ncharacter, and the decay rate of polarons."
    },
    {
        "anchor": "Limit cycle phase in driven-dissipative spin systems: We explore the phase diagram of interacting spin-$1/2$ systems in the\npresence of anisotropic interactions, spontaneous decay and driving. We find a\nrich phase diagram featuring a limit cycle phase in which the magnetization\noscillates in time. We analyze the spatio-temporal fluctuations of this limit\ncycle phase at the Gaussian level, and show that spatial fluctuations lead to\nquasi-long-range limit cycle ordering for dimension $d = 2$. This result can be\ninterpreted in terms of a spatio-temporal Goldstone mode corresponding to phase\nfluctuations of the limit cycle. We also demonstrate that the limit-cycle phase\nexhibits an asymmetric power spectrum measurable in fluorescence experiments.",
        "positive": "Dipoles on a Two-leg Ladder: We study polar molecules with long-range dipole-dipole interactions confined\nto move on a two-leg ladder for different orientations of the molecular dipole\nmoments with respect to the ladder. Matrix product states are employed to\ncalculate the many-body ground state of the system as function of lattice\nfilling fractions, perpendicular hopping between the legs, and dipole\ninteraction strength. We show that the system exhibits zig-zag ordering when\nthe dipolar interactions are predominantly repulsive. As a function of dipole\nmoment orientation with respect to the ladder, we find that there is a critical\nangle at which ordering disappears. This angle is slightly larger than the\nangle at which the dipoles are non-interacting along a single leg. This\nbehavior should be observable using current experimental techniques."
    },
    {
        "anchor": "Fusing Quantum Hall States in Cold Atoms: Realizing quantum Hall states in a fast rotating Bose gas is a long sought\ngoal in cold atom research. The effort is very challenging because Bose\nstatistics fights against quantum Hall correlations. In contrast, Fermi\nstatistics does not cause such conflict. Here, we show that by sweeping the\ninteger quantum Hall states of a spin-1/2 Fermi gas across the Feshbach\nresonance from the BCS side to the BEC side at a \"projection\" rate similar to\nthat in the \"projection\" experiment of fermion superfluid, these states can be\n\"fused\" into a bosonic quantum Hall states. A projection sweep means the pair\nassociation is sufficiently fast so that the center of mass of the pair remains\nunchanged in the process. We show that the fusion of integer fermion states\nwith filling factor $\\nu_{\\uparrow}=\\nu_{\\downarrow}=n$ will result in a\nbosonic Laughlin state and Pfaffian state for $n=1$ and 2. The is due to a\nhidden property of the fermionic integer quantum Hall states -- for any\ngrouping of opposite spin into pairs, their centers of mass automatically\nassume a bosonic quantum Hall structure.",
        "positive": "Topological fractional pumping with alkaline-earth(-like) ultracold\n  atoms: Alkaline-earth(-like) ultracold atoms, trapped in optical lattices and in the\npresence of an external gauge field, can stabilise Mott insulating phases\ncharacterised by density and magnetic order. We show that this property can be\nused to realise a topological fractional pump. Our analysis is based on a\nmany-body adiabatic expansion and on time-dependent matrix-product-states\nnumerical simulations. We characterise the pumping protocol by including both\nfinite-size and non-adiabatic corrections. For a specific form of atom-atom\ninteraction, we present an exactly-solvable model of a fractional pump.\nFinally, the numerical simulations allow us to thoroughly study a realistic\nsetup amenable of an experimental realisation."
    },
    {
        "anchor": "Finite-Temperature Auxiliary-Field Quantum Monte Carlo for Bose-Fermi\n  Mixtures: We present a quantum Monte Carlo (QMC) technique for calculating the exact\nfinite-temperature properties of Bose-Fermi mixtures. The Bose-Fermi\nAuxiliary-Field Quantum Monte Carlo (BF-AFQMC) algorithm combines two methods,\na finite-temperature AFQMC algorithm for bosons and a variant of the standard\nAFQMC algorithm for fermions, into one algorithm for mixtures. We demonstrate\nthe accuracy of our method by comparing its results for the Bose-Hubbard and\nBose-Fermi-Hubbard models against those produced using exact diagonalization\nfor small systems. Comparisons are also made with mean-field theory and the\nworm algorithm for larger systems. As is the case with most fermion\nHamiltonians, a sign or phase problem is present in BF-AFQMC. We discuss the\nnature of these problems in this framework and describe how they can be\ncontrolled with well-studied approximations to expand BF-AFQMC's reach. The new\nalgorithm can serve as an essential tool for answering many unresolved\nquestions about many-body physics in mixed Bose-Fermi systems.",
        "positive": "Staggered-Vortex Superfluid of Ultracold Bosons in an Optical Lattice: We show that the dynamics of cold bosonic atoms in a two-dimensional square\noptical lattice produced by a bichromatic light-shift potential is described by\na Bose-Hubbard model with an additional effective staggered magnetic field. In\naddition to the known uniform superfluid and Mott insulating phases, the\nzero-temperature phase diagram exhibits a novel kind of finite-momentum\nsuperfluid phase, characterized by a quantized staggered rotational flux. An\nextension for fermionic atoms leads to an anisotropic Dirac spectrum, which is\nrelevant to graphene and high-$T_c$ superconductors."
    },
    {
        "anchor": "Relaxation rates and collision integrals for Bose-Einstein condensates: Near equilibrium, the rate of relaxation to equilibrium and the transport\nproperties of excitations (bogolons) in a dilute Bose-Einstein condensate (BEC)\nare determined by three collision integrals, $\\mathcal{G}^{12}$,\n$\\mathcal{G}^{22}$, and $\\mathcal{G}^{31}$. All three collision integrals\nconserve momentum and energy during bogolon collisions, but only $\n\\mathcal{G}^{22}$ conserves bogolon number. Previous works have considered the\ncontribution of only two collision integrals, $ \\mathcal{G}^{22}$ and $\n\\mathcal{G}^{12}$. In this work, we show that the third collision integral $\n\\mathcal{G}^{31}$ makes a significant contribution to the bogolon number\nrelaxation rate and needs to be retained when computing relaxation properties\nof the BEC. We provide values of relaxation rates in a form that can be applied\nto a variety of dilute Bose-Einstein condensates.",
        "positive": "Topological lattice using multi-frequency radiation: We describe a novel technique for creating an artificial magnetic field for\nultra-cold atoms using a periodically pulsed pair of counter propagating Raman\nlasers that drive transitions between a pair of internal atomic spin states: a\nmulti-frequency coupling term. In conjunction with a magnetic field gradient,\nthis dynamically generates a rectangular lattice with a non-staggered magnetic\nflux. For a wide range of parameters, the resulting Bloch bands have\nnon-trivial topology, reminiscent of Landau levels, as quantified by their\nChern numbers."
    },
    {
        "anchor": "Pair correlations in the attractive Hubbard model: The mechanism of fermionic pairing is the key to understanding various\nphenomena such as high-temperature superconductivity and the pseudogap phase in\ncuprate materials. We study the pair correlations in the attractive Hubbard\nmodel using ultracold fermions in a two-dimensional optical lattice. By\ncombining the fluctuation-dissipation theorem and the compressibility equation\nof state, we extract the interacting pair correlation functions and deduce a\ncharacteristic length scale of pairs as a function of interaction and density\nfilling. At sufficiently low filling and weak on-site interaction, we observe\nthat the pair correlations extend over a few lattice sites even at temperatures\nabove the superfluid transition temperature.",
        "positive": "Quantum-limited thermometry of a Fermi gas with a charged spin particle: We investigate the sensitivity of an ion sensor in determining the\ntemperature of an atomic Fermi gas. Our study extends to charged impurities the\nproposal by M. T. Mitchison et al. Phys. Rev. Lett. 125, 080402 (2020), where\natomic neutral impurities were used as an in situ thermometer of the quantum\ngas. We find that the long-range character of the atom-ion interaction enhances\nthe thermometer's sensitivity for certain system parameters. In addition, we\ninvestigate the impact of the ion quantum motional state on the sensitivity by\nassuming that it is confined in a harmonic trap. We observe that the\ntemperature sensitivity of the ion is noticeably influenced by its spatial\nextension, making the latter a versatile tool to be manipulated for improving\nthe thermometer performance. We finally discuss our findings in the context of\ncurrent experimental atom-ion mixtures."
    },
    {
        "anchor": "Stable multiple vortices in collisionally inhomogeneous attractive\n  Bose-Einstein condensates: We study stability of solitary vortices in the two-dimensional trapped\nBose-Einstein condensate (BEC) with a spatially localized region of\nself-attraction. Solving the respective Bogoliubov-de Gennes equations and\nrunning direct simulations of the underlying Gross-Pitaevskii equation reveals\nthat vortices with topological charge up to S = 6 (at least) are stable above a\ncritical value of the chemical potential (i.e., below a critical number of\natoms, which sharply increases with S). The largest nonlinearity-localization\nradius admitting the stabilization of the higher-order vortices is estimated\nanalytically and accurately identified in a numerical form. To the best of our\nknowledge, this is the first example of a setting which gives rise to stable\nhigher-order vortices, S > 1, in a trapped self-attractive BEC. The same\nsetting may be realized in nonlinear optics too.",
        "positive": "Dynamics and stability of Bose-Einstein solitons in tilted optical\n  lattices: Bloch oscillations of Bose-Einstein condensates realize sensitive matter-wave\ninterferometers. We investigate the dynamics and stability of bright-soliton\nwave packets in one-dimensional tilted optical lattices with a modulated\nmean-field interaction $g(t)$. By means of a time-reversal argument, we prove\nthe stability of Bloch oscillations of breathing solitons that would be\nquasistatically unstable. Floquet theory shows that these breathing solitons\ncan be more stable against certain experimental perturbations than rigid\nsolitons or even non-interacting wave packets."
    },
    {
        "anchor": "Emergence of coherence and the dynamics of quantum phase transitions: The dynamics of quantum phase transitions poses one of the most challenging\nproblems in modern many-body physics. Here, we study a prototypical example in\na clean and well-controlled ultracold atom setup by observing the emergence of\ncoherence when crossing the Mott insulator to superfluid quantum phase\ntransition. In the one-dimensional Bose-Hubbard model, we find perfect\nagreement between experimental observations and numerical simulations for the\nresulting coherence length. We thereby perform a largely certified analogue\nquantum simulation of this strongly correlated system reaching beyond the\nregime of free quasiparticles. Experimentally, we additionally explore the\nemergence of coherence in higher dimensions where no classical simulations are\navailable, as well as for negative temperatures. For intermediate quench\nvelocities, we observe a power-law behaviour of the coherence length,\nreminiscent of the Kibble-Zurek mechanism. However, we find exponents that\nstrongly depend on the final interaction strength and thus lie outside the\nscope of this mechanism.",
        "positive": "Hydrodynamic VS collisionless dynamics of a 1D harmonically trapped Bose\n  gas: By using a sum rule approach we investigate the transition between the\nhydrodynamic and the collisionless regime of the collective modes in a 1D\nharmonically trapped Bose gas. Both the weakly interacting gas and the\nTonks-Girardeau limits are considered. We predict that the excitation of the\ndipole compression mode is characterized, in the high temperature collisionless\nregime, by a beating signal of two different frequencies ($\\omega_z$ and\n$3\\omega_z$) while, in the high temperature collisional regime, the excitation\nconsists of a single frequency ($\\sqrt{7}\\omega_z$). This behaviour differs\nfrom the case of the lowest breathing mode whose excitation consists of a\nsingle frequency ($2\\omega_z$) in both regimes. Our predictions for the dipole\ncompression mode open promising perspectives for the experimental investigation\nof collisional effects in 1D configurations."
    },
    {
        "anchor": "Effective mass of $^4$He atom in superfluid and normal phases: The formula for the temperature dependence of the effective mass of a $^{4}%\n$He atom in the superfluid and normal phases is obtained.\\,\\,This expression\nfor the effective mass allows one to eliminate infra-red divergences, being\napplicable at all temperatures, except for a narrow fluctuation region\n0.97~$\\lesssim T/T_{\\rm c}\\leq1$.\\,\\,In the high and low temperature limits, as\nwell as in the interactionless limit, the obtained expression reproduces the\nwell known results.\\,\\,The temperature dependence of the heat capacity and the\nphase transition temperature $T_{\\rm c}\\approx$~2.18~K are calculated, by using\nthe formula obtained for the effective mass.\\,\\,In the framework of the\napproach proposed in this work, the small critical index $\\eta$ is determined\nin the random phase approximation.\\,\\,The obtained value corresponds to the\nwell known result.",
        "positive": "Ferromagnetic transition of a two-component Fermi gas of Hard Spheres: We use microscopic many-body theory to analyze the problem of itinerant\nferromagnetism in a repulsive atomic Fermi gas of Hard Spheres. Using simple\narguments, we show that the available theoretical predictions for the onset of\nthe ferromagnetic transition predict a transition point at a density ($k_F a\n\\sim 1$) that is too large to be compatible with the universal low-density\nexpansion of the energy. We present new variational calculations for the\nhard-sphere Fermi gas, in the framework of Fermi hypperneted chain theory, that\nshift the transition to higher densities ($k_F a \\sim 1.8$). Backflow\ncorrelations, which are mainly active in the unpolarized system, are essential\nfor this shift."
    },
    {
        "anchor": "Interplay between periodicity and nonlinearity of indirect excitons in\n  coupled quantum wells: Inspired by a recent experiment of localization-delocalization transition\n(LDT) of indirect excitons in lateral electrostatic lattices [M. Remeika\n\\textit{et al.}, Phys. Rev. Lett. \\textbf{102}, 186803 (2009)], we investigate\nthe interplay between periodic potential and nonlinear interactions of indirect\nexcitons in coupled quantum wells. It is shown that the model involving both\nattractive two-body and repulsive three-body interactions can lead to a natural\naccount for the LDT of excitons across the lattice when reducing lattice\namplitude or increasing particle density. In addition, the observations that\nthe smooth component of the photoluminescent energy increases with increasing\nexciton density and exciton interaction energy is close to the lattice\namplitude at the transition are also qualitatively explained. Our model\nprovides an alternative way for understanding the underlying physics of the\nexciton dynamics in lattice potential wells.",
        "positive": "Two- and three-body problem with Floquet-driven zero-range interactions: We study the two-body scattering problem in the zero-range approximation with\na sinusoidally driven scattering length and calculate the relation between the\nmean value and amplitude of the drive for which the effective scattering\namplitude is resonantly enhanced. In this manner we arrive at a family of\ncurves along which the effective scattering length diverges but the nature of\nthe corresponding Floquet-induced resonance changes from narrow to wide.\nRemarkably, on these curves the driving does not induce heating. In order to\nstudy the effect of these resonances on the three-body problem we consider one\nlight and two heavy particles with driven heavy-light interaction in the\nBorn-Oppenheimer approximation and find that the Floquet driving can be used to\ntune the three-body and inelasticity parameters."
    },
    {
        "anchor": "Superfluidity breakdown of Rabi-coupled two-component Bose-Einstein\n  condensates in optical lattices: We demarcate the unstable regimes of superfluids in a Rabi-coupled\ntwo-component Bose-Einstein condensate in the presence of optical lattices. We\nfind that the Rabi coupling can stabilize superfluids. A significant separation\nbetween Landau and dynamical instabilities is presented in a Rabi-coupled\nZeeman lattice.",
        "positive": "Universal thermodynamics of a strongly interacting Fermi gas: theory\n  versus experiment: Strongly interacting, dilute Fermi gases exhibit a scale-invariant, universal\nthermodynamic behaviour. This is notoriously difficult to understand\ntheoretically because of the absence of a small interaction parameter. Here we\npresent a systematic comparison of theoretical predictions from different\nquantum many-body theories with recent experimental data of Nascimbene et. al.\n(arXiv:0911.0747v1). Our comparisons have no adjustable parameters, either\ntheoretically or experimentally. A simple Gaussian pair fluctuation theory is\nshown to give the best quantitative agreement in the superfluid state below\nthreshold. In the normal state, we also calculate the equation of state by\nusing a quantum cluster expansion theory and explore in detail its\napplicability to low temperatures. Using the accurate experimental result for\nthe thermodynamic function $S(T)$, we determine the temperature $T$ of a\ntrapped Fermi gas at unitarity as a function of a non-interacting temperature\n$T_{i}$ which can be obtained by an adiabatic sweep to the free gas limit. By\nanalyzing the recent experimental data, we find a normal-superfluid transition\ntemperature $(T/T_{F})_{c}=0.19\\pm0.02$ or $(T_{i}/T_{F})_{c}=0.16\\pm0.02$ in a\nharmonic trap, where $T_{F}$ is the Fermi temperature for a trapped ideal,\nnon-interacting Fermi gas."
    },
    {
        "anchor": "Spin-Orbit Coupled Exciton-Polariton Condensates in Lead Halide\n  Perovskites: Spin-orbit coupling (SOC) is responsible for a range of spintronic and\ntopological processes in condensed matter. Here we show photonic analogs of\nSOCs in exciton-polaritons and their condensates in microcavities composed of\nbirefringent lead halide perovskite single crystals. The presence of\ncrystalline anisotropy coupled with splitting in the optical cavity of the\ntransverse electric (TE) and transverse magnetic (TM) modes gives rise to a\nnon-Abelian gauge field, which can be described by the Rashba-Dresselhaus\nHamiltonian near the degenerate points of the two polarization modes. With\nincreasing density, the exciton polaritons with pseudospin textures undergo\nphase transitions to competing condensates with orthogonal polarizations.\nUnlike their pure photonic counterparts, these exciton polaritons and\ncondensates inherit nonlinearity from their excitonic components and may serve\nas quantum simulators of many-body SOC processes.",
        "positive": "Dynamics of an itinerant spin-3 atomic dipolar gas in an optical lattice: Arrays of ultra-cold dipolar gases loaded in optical lattices are emerging as\npowerful quantum simulators of the many-body physics associated with the rich\ninterplay between long-range dipolar interactions, contact interactions,\nmotion, and quantum statistics. In this work we report on our investigation of\nthe quantum many-body dynamics of a large ensemble of bosonic magnetic chromium\natoms with spin S = 3 in a three-dimensional lattice as a function of lattice\ndepth. Using extensive theory and experimental comparisons we study the\ndynamics of the population of the different Zeeman levels and the total\nmagnetization of the gas across the superfluid to the Mott insulator\ntransition. We are able to identify two distinct regimes: At low lattice\ndepths, where atoms are in the superfluid regime, we observe that the spin\ndynamics is strongly determined by the competition between particle motion,\nonsite interactions and external magnetic field gradients. Contact spin\ndependent interactions help to stabilize the collective spin length, which sets\nthe total magnetization of the gas. On the contrary, at high lattice depths,\ntransport is largely frozen out. In this regime, while the spin populations are\nmainly driven by long range dipolar interactions, magnetic field gradients also\nplay a major role in the total spin demagnetization. We find that dynamics at\nlow lattice depth is qualitatively reproduced by mean-field calculations based\non the Gutzwiller ansatz; on the contrary, only a beyond mean-field theory can\naccount for the dynamics at large lattice depths. While the cross-over between\nthese two regimes does not correspond to sharp features in the observed\ndynamical evolution of the spin components, our simulations indicate that it\nwould be better revealed by measurements of the collective spin length."
    },
    {
        "anchor": "Dissipative dynamics of a harmonically confined Bose-Einstein condensate: We study the dissipation of the centre of mass oscillation of a harmonically\nconfined condensate in the presence of a disorder potential. An extension of\nthe Generalized Harmonic Theorem allows one to formulate the dynamics from the\npoint of view of an oscillating disorder potential. This formulation leads to a\nrigorous result for the damping rate in the limit of weak disorder.",
        "positive": "Coupling Identical 1D Many-Body Localized Systems: We experimentally study the effects of coupling one-dimensional Many-Body\nLocalized (MBL) systems with identical disorder. Using a gas of ultracold\nfermions in an optical lattice, we artifically prepare an initial charge\ndensity wave in an array of 1D tubes with quasi-random onsite disorder and\nmonitor the subsequent dynamics over several thousand tunneling times. We find\na strikingly different behavior between MBL and Anderson Localization. While\nthe non-interacting Anderson case remains localized, in the interacting case\nany coupling between the tubes leads to a delocalization of the entire system."
    },
    {
        "anchor": "Bipolarons bound by repulsive phonon-mediated interactions: When dressed particles (polarons) exchange quantum phonons, the resulting\ninteractions are generally attractive. If the particles have hard-core\nstatistics and the coupling to phonons is through the kinetic energy terms,\nphonon-mediated interactions are repulsive. Here, we show that such repulsive\nphonon-mediated interactions bind dressed particles into bipolarons with unique\nproperties. These bipolaron states appear in the gap between phonon\nexcitations, above the two-polaron continuum. While thermodynamically unstable,\nthe bipolaron is protected by energy and momentum conservation and represents a\nnovel quasiparticle with a large dispersion and a negative effective mass near\nzero momentum. We discuss possible experimental implementation of the\nconditions for the formation of such repulsively bound bipolarons.",
        "positive": "Tricritical physics in two-dimensional $p$-wave superfluids: We study effects of quantum fluctuations on two-dimensional $p+ip$\nsuperfluids near resonance. In the standard paradigm, phase transitions between\nsuperfluids and zero density vacuum are continuous. When strong quantum\nfluctuations near resonance are taken into account, the line of continuous\nphase transitions terminates at two multicritical points near resonance,\nbetween which the transitions are expected to be first-order ones. The size of\nthe window where first-order phase transitions occur is shown to be substantial\nwhen the coupling is strong. Near first-order transitions, superfluids\nself-contract due to phase separations between superfluids and vacuum."
    },
    {
        "anchor": "Dephasing in coherently-split quasicondensates: We numerically model the evolution of a pair of coherently split\nquasicondensates. A truly one-dimensional case is assumed, so that the loss of\nthe (initially high) coherence between the two quasicondensates is due to\ndephasing only, but not due to the violation of integrability and subsequent\nthermalization (which are excluded from the present model). We confirm the\nsubexponential time evolution of the coherence between two quasicondensates\n$\\propto \\exp [-(t/t_0)^{2/3}]$, experimentally observed by S. Hofferberth {\\em\net. al.}, Nature {\\bf 449}, 324 (2007). The characteristic time $t_0$ is found\nto scale as the square of the ratio of the linear density of a quasicondensate\nto its temperature, and we analyze the full distribution function of the\ninterference contrast and the decay of the phase correlation.",
        "positive": "Two-body problem in a multiband lattice and the role of quantum geometry: We consider the two-body problem in a periodic potential, and study the\nbound-state dispersion of a spin-$\\uparrow$ fermion that is interacting with a\nspin-$\\downarrow$ fermion through a short-range attractive interaction. Based\non a variational approach, we obtain the exact solution of the dispersion in\nthe form of a set of self-consistency equations, and apply it to tight-binding\nHamiltonians with onsite interactions. We pay special attention to the\nbipartite lattices with a two-point basis that exhibit time-reversal symmetry,\nand show that the lowest-energy bound states disperse quadratically with\nmomentum, whose effective-mass tensor is partially controlled by the quantum\nmetric tensor of the underlying Bloch states. In particular, we apply our\ntheory to the Mielke checkerboard lattice, and study the special role played by\nthe interband processes in producing a finite effective mass for the bound\nstates in a non-isolated flat band."
    },
    {
        "anchor": "From quantum to thermal topological-sector fluctuations of strongly\n  interacting bosons in a ring lattice: Inspired by recent experiments on Bose-Einstein condensates in ring traps, we\ninvestigate the topological properties of the phase of a one-dimensional Bose\nfield in the presence of both thermal and quantum fluctuations -- the latter\nones being tuned by the depth of an optical lattice applied along the ring. In\nthe regime of large filling of the lattice, quantum Monte Carlo simulations\ngive direct access to the full statistics of fluctuations of the Bose-field\nphase, and of its winding number $W$ along the ring. At zero temperature the\nwinding-number (or topological-sector) fluctuations are driven by quantum phase\nslips localized around a Josephson link between two lattice wells, and their {\nsusceptibility} is found to jump at the superfluid-Mott insulator transition.\nAt finite (but low) temperature, on the other hand, the winding number\nfluctuations are driven by thermal activation of nearly uniform phase twists,\nwhose activation rate is governed by the superfluid fraction. A\nquantum-to-thermal crossover in winding number fluctuations is therefore\nexhibited by the system, and it is characterized by a conformational change in\nthe topologically non-trivial configurations, from localized to uniform phase\ntwists, which can be experimentally observed in ultracold Bose gases via\nmatter-wave interference.",
        "positive": "Nonadiabatic creation of macroscopic superpositions with strongly\n  correlated 1D bosons on a ring trap: We consider a strongly interacting quasi-one dimensional Bose gas on a tight\nring trap subjected to a localized barrier potential. We explore the\npossibility to form a macroscopic superposition of a rotating and a nonrotating\nstate under nonequilibrium conditions, achieved by a sudden quench of the\nbarrier velocity. Using an exact solution for the dynamical evolution in the\nimpenetrable-boson (Tonks-Girardeau) limit, we find an expression for the\nmany-body wavefunction corresponding to a superposition state. The\nsuperposition is formed when the barrier velocity is tuned close to multiples\nof integer or half-integer number of Coriolis flux quanta. As a consequence of\nthe strong interactions, we find that (i) the state of the system can be mapped\nonto a macroscopic superposition of two Fermi spheres, rather than two\nmacroscopically occupied single-particle states as in a weakly interacting gas,\nand (ii) the barrier velocity should be larger than the sound velocity to\nbetter discriminate the two components of the superposition."
    },
    {
        "anchor": "Multi-particle composites in density-imbalanced quantum fluids: We consider two-component one-dimensional quantum gases with density\nimbalance. While generically such fluids are two-component Luttinger liquids,\nwe show that if the ratio of the densities is a rational number, p/q, and mass\nasymmetry between components is sufficiently strong, one of the two eigenmodes\nacquires a gap. The gapped phase corresponds to (algebraic) ordering of\n(p+q)-particle composites. In particular, for attractive mixtures, this implies\nthat the superconducting correlations are destroyed. We illustrate our\npredictions by numerical simulations of the fermionic Hubbard model with\nhopping asymmetry.",
        "positive": "Few vs many-body physics of an impurity immersed in a superfluid of spin\n  1/2 attractive fermions: In this article we investigate the properties of an impurity immersed in a\nsuperfluid of strongly correlated spin 1/2 fermions. For resonant interactions,\nwe first relate the stability diagram of dimer and trimer states to the\nthree-body problem for an impurity interacting with a pair of fermions. Then we\ncalculate the beyond-mean-field corrections to the energy of a weakly\ninteracting impurity. We show that these corrections are divergent and have to\nbe regularized by properly accounting for three-body physics in the problem."
    },
    {
        "anchor": "Effective spin-chain model for strongly interacting one-dimensional\n  atomic gases with an arbitrary spin: We present a general form of the effective spin-chain model for strongly\ninteracting atomic gases with an arbitrary spin in the one-dimensional(1D)\ntraps. In particular, for high-spin systems the atoms can collide in multiple\nscattering channels, and we find that the resulted form of spin-chain model\ngenerically follows the same structure as that of the interaction potentials.\nThis is a unified form working for any spin, statistics (Bose or Fermi) and\nconfinement potentials. We adopt the spin-chain model to reveal both the\nferromagnetic(FM) and anti-ferromagnetic(AFM) magnetic orders for strongly\ninteracting spin-1 bosons in 1D traps. We further show that by adding the\nspin-orbit coupling, the FM/AFM orders can be gradually destroyed and\neventually the ground state exhibits universal spin structure and contacts that\nare independent of the strength of spin-orbit coupling.",
        "positive": "Dipolar Bose gas with three-body interactions at finite temperature: We investigate effects of three-body contact interactions on a trapped\ndipolar Bose gas at finite temperature using the Hartree-Fock-Bogoliubov\napproximation. We analyze numerically the behavior of the transition\ntemperature and the condensed fraction. Effects of the three-body interactions,\nanomalous pair correlations and temperature on the collective modes are\ndiscussed."
    },
    {
        "anchor": "Rebound-through transition of bright-bright solitons collision in two\n  species condensates with repulsive interspecies interactions: We study the dynamical properties of bright-bright solitons in two species\nBose-Einstein condensates with the repulsive interspecies interactions under\nthe external harmonic potentials by using a variational approach combined with\nnumerical simulation. It is found that the interactions between bright-bright\nsolitons vary from repulsive to attractive interactions with the increasing of\ntheir separating distances. And the bright-bright solitons can be localized at\nequilibrium positions, different from the periodic oscillation of bright\nsoliton in the single species condensates. Especially, a through-collision is\nnewly observed from the bright-bright solitons collisions with the increasing\nof the initial velocity. The collisional type of bright-bright solitons, either\nrebound - or through -collision, depends on the modulation of the initial\nconditions. These results will be helpful for the experimental manipulating\nsuch solitons.",
        "positive": "Fast production of Bose-Einstein condensates of metastable Helium: We report on the Bose-Einstein condensation of metastable Helium-4 atoms\nusing a hybrid approach, consisting of a magnetic quadrupole and a crossed\noptical dipole trap. In our setup we cross the phase transition with 2x10^6\natoms, and we obtain pure condensates of 5x10^5 atoms in the optical trap. This\nnovel approach to cooling Helium-4 provides enhanced cycle stability, large\noptical access to the atoms and results in production of a condensate every 6\nseconds - a factor 3 faster than the state-of-the-art. This speed-up will\ndramatically reduce the data acquisition time needed for the measurement of\nmany particle correlations, made possible by the ability of metastable Helium\nto be detected individually."
    },
    {
        "anchor": "Creating and manipulating non-Abelian anyons in cold atom systems using\n  auxiliary bosons: The possibility of realizing bosonic fractional quantum Hall effect in\nultra-cold atomic systems suggests a new route to producing and manipulating\nanyons, by introducing auxiliary bosons of a different species that capture\nquasiholes and thus inherit their non-trivial braiding properties. States with\nlocalized quasiholes at any desired locations can be obtained by annihilating\nthe auxiliary bosons at those locations. We explore how this method can be used\nto generate non-Abelian quasiholes of the Moore-Read Pfaffian state for bosons\nat filling factor $\\nu=1$. We show that a Hamiltonian with an appropriate\nthree-body interaction can produce two-quasihole states in two distinct fusion\nchannels of the topological \"qubit.\" Characteristics of these states that are\nrelated to the non-Abelian nature can be probed and verified by a measurement\nof the effective relative angular momentum of the auxiliary bosons, which is\ndirectly related to their pair distribution function. Moore-Read states of more\nthan two quasiholes can also be produced in a similar fashion. We investigate\nsome issues related to the experimental feasibility of this approach, in\nparticular, how large the systems should be for a realization of this physics\nand to what extent this physics carries over to systems with the more standard\ntwo-body contact interaction.",
        "positive": "Confinement-Induced Resonances in Low-Dimensional Quantum Systems: We report on the observation of confinement-induced resonances in strongly\ninteracting quantum-gas systems with tunable interactions for one- and\ntwo-dimensional geometry. Atom-atom scattering is substantially modified when\nthe s-wave scattering length approaches the length scale associated with the\ntight transversal confinement, leading to characteristic loss and heating\nsignatures. Upon introducing an anisotropy for the transversal confinement we\nobserve a splitting of the confinement-induced resonance. With increasing\nanisotropy additional resonances appear. In the limit of a two-dimensional\nsystem we find that one resonance persists."
    },
    {
        "anchor": "Dispersive probing of driven pseudo-spin dynamics in a gradient field: We have studied the coherent evolution of ultracold atomic rubidium clouds\nsubjected to a microwave field driving Rabi oscillations between the stretched\nstates of the F=1 and F=2 hyperfine levels. A phase winding of the two-level\nsystem pseudo-spin vector is encountered for elongated samples of atoms exposed\nto an axial magnetic field gradient and can be observed directly in\nstate-selective absorption imaging. When dispersively recording the\nsample-integrated spin population during the Rabi drive, we observe a damped\noscillation directly related to the magnetic field gradient, which we quantify\nusing a simple dephasing model. By analyzing such dispersively acquired data\nfrom millimeter sized atomic samples, we demonstrate that field gradients can\nbe determined with an accuracy of $\\sim25$ nT/mm. The dispersive probing of\ninhomogeneously broadened Rabi oscillations in prolate samples opens up a path\nto gradiometry with bandwidths in the kilohertz domain.",
        "positive": "Elastic scattering of a quantum matter-wave bright soliton on a barrier: We consider a one-dimensional matter-wave bright soliton, corresponding to\nthe ground bound state of N particles of mass m having a binary attractive\ndelta potential interaction on the open line. For a full N-body quantum\ntreatment, we derive several results for the scattering of this quantum soliton\non a short-range, bounded from below, external potential, restricting to the\nlow energy, elastic regime where the centre-of-mass kinetic energy of the\nincoming soliton is lower than the internal energy gap of the soliton, that is\nthe minimal energy required to extract particles from the soliton."
    },
    {
        "anchor": "A route to non-Abelian quantum turbulence in spinor Bose-Einstein\n  condensates: We have studied computationally the collision dynamics of spin-2\nBose--Einstein condensates initially confined in a triple-well trap. Depending\non the intra- and inter-component relative phases of the initial state spinor\nwave function, the collision of the three condensate segments produces one of\nmany possible vortex-antivortex lattices after which the system transitions to\nquantum turbulence. We find that the emerging vortex lattice structures can be\ndescribed in terms of multi-wave interference. We show that the three-segment\ncollisions can be used to systematically produce staggered vortex-antivortex\nhoneycomb lattices of fractional-charge vortices, whose collision dynamics are\nknown to be non-Abelian. Such condensate collider experiments could potentially\nbe used as a controllable pathway to generating non-Abelian superfluid\nturbulence with networks of vortex rungs.",
        "positive": "Dimer-atom scattering between two identical fermions and a third\n  particle: We use the diagrammatic $T$-matrix approach to analyze the three-body\nscattering problem between two identical fermions and a third particle (which\ncould be a different species of fermion or a boson). We calculate the s-wave\ndimer-atom scattering length for all mass ratios, and our results exactly match\nthe results of Petrov. In particular, we list the exact dimer-atom scattering\nlengths for all available two-species Fermi-Fermi and Bose-Fermi mixtures. In\naddition, unlike that of the equal-mass particles case where the three-body\nscattering $T$-matrix decays monotonically as a function of the outgoing\nmomentum, we show that, after an initial rapid drop, this function changes sign\nand becomes negative at large momenta and then decays slowly to zero when the\nmass ratio of the fermions to the third particle is higher than a critical\nvalue (around 6.5). As the mass ratio gets higher, modulations of the\n$T$-matrix become more apparent with multiple sign changes, related to the\n\"fall of a particle to the center\" phenomenon and to the emergence of\nthree-body Efimov bound states."
    },
    {
        "anchor": "Accurate determination of the scattering length of erbium atoms: An accurate knowledge of the scattering length is fundamental in ultracold\nquantum gas experiments and essential for the characterisation of the system as\nwell as for a meaningful comparison to theoretical models. Here, we perform a\ncareful characterisation of the s-wave scattering length $a_s$ for the four\nhighest-abundance isotopes of erbium, in the magnetic field range from 0G to\n5G. We report on cross-dimensional thermalization measurements and apply the\nEnskog equations of change to numerically simulate the thermalization process\nand to analytically extract an expression for the so-called number of\ncollisions per re-thermalization (NCPR) to obtain $a_s$ from our experimental\ndata. We benchmark the applied cross-dimensional thermalization technique with\nthe experimentally more demanding lattice modulation spectroscopy and find good\nagreement for our parameter regime. Our experiments are compatible with a\ndependence of the NCPR with $a_s$, as theoretically expected in the case of\nstrongly dipolar gases. Surprisingly, we experimentally observe a dependency of\nthe NCPR on the density, which might arise due to deviations from an ideal\nharmonic trapping configuration. Finally, we apply a model for the dependency\nof the background scattering length with the isotope mass, allowing to estimate\nthe number of bound states of erbium.",
        "positive": "Hybrid synchronization in coupled ultracold atomic gases: We study the time evolution of two coupled many-body quantum systems one of\nwhich is assumed to be Bose condensed. Specifically, we consider two ultracold\natomic clouds populating each two localized single-particle states, i.e. a\ntwo-component Bosonic Josephson junction. The cold atoms cloud can retain its\ncoherence when coupled to the condensate and displays synchronization with the\nlatter, differing from usual entrainment. We term this effect among the\nultracold and the condensed clouds as {\\it hybrid synchronization}. The onset\nof synchronization, which we observe in the evolution of average properties of\nboth gases when increasing their coupling, is found to be related to the\nmany-body properties of the quantum gas, e.g. condensed fraction, quantum\nfluctuations of the particle number differences. We discuss the effects of\ndifferent initial preparations, the influence of unequal particle numbers for\nthe two clouds, and explore the dependence on the initial quantum state, e.g.\ncoherent state, squeezed state and Fock state, finding essentially the same\nphenomenology in all cases."
    },
    {
        "anchor": "High-temperature nonequilibrium Bose condensation induced by a hot\n  needle: We investigate theoretically a one-dimensional ideal Bose gas that is driven\ninto a steady state far from equilibrium via the coupling to two heat baths: a\nglobal bath of temperature $T$ and a \"hot needle\", a bath of temperature\n$T_h\\gg T$ with localized coupling to the system. Remarkably, this system\nfeatures a crossover to finite-size Bose condensation at temperatures $T$ that\nare orders of magnitude larger than the equilibrium condensation temperature.\nThis counterintuitive effect is explained by a suppression of long-wavelength\nexcitations resulting from the competition between both baths. Moreover, for\nsufficiently large needle temperatures ground-state condensation is superseded\nby condensation into an excited state, which is favored by its weaker coupling\nto the hot needle. Our results suggest a general strategy for the preparation\nof quantum degenerate nonequilibrium steady states with unconventional\nproperties and at large temperatures.",
        "positive": "Prominent quantum many-body scars in a truncated Schwinger model: The high level of control and precision achievable in current synthetic\nquantum matter setups has enabled first attempts at quantum-simulating various\nintriguing phenomena in condensed matter physics, including those probing\nthermalization or its absence in closed quantum systems. In a recent work\n[Desaules \\textit{et al.} [arXiv:2203.08830], we have shown that quantum\nmany-body scars -- special low-entropy eigenstates that weakly break ergodicity\nin nonintegrable systems -- arise in spin-$S$ quantum link models that converge\nto $(1+1)-$D lattice quantum electrodynamics (Schwinger model) in the\nKogut--Susskind limit $S\\to\\infty$. In this work, we further demonstrate that\nquantum many-body scars exist in a truncated version of the Schwinger model,\nand are qualitatively more prominent than their counterparts in spin-$S$\nquantum link models. We illustrate this by, among other things, performing a\nfinite-$S$ scaling analysis that strongly suggests that scarring persists in\nthe truncated Schwinger model in the limit $S\\to\\infty$. Although it does not\nasymptotically converge to the Schwinger model, the truncated formulation is\nrelevant to synthetic quantum matter experiments, and also provides fundamental\ninsight into the nature of quantum many-body scars, their connection to lattice\ngauge theories, and the thermalization dynamics of the latter. Our conclusions\ncan be readily tested in current cold-atom setups."
    },
    {
        "anchor": "The three-body pseudo-potential for atoms confined in one dimension: Following a strong analogy with two-dimensional physics, the three-body\npseudo-potential in one dimension is derived. The Born approximation is then\nconsidered in the context of ultracold atoms in a linear harmonic waveguide. In\nthe vicinity of the dimer threshold a direct connection is made between the\nzero-range potential and the dimensional reduction of the three-body\nSchr{\\\"o}dinger equation.",
        "positive": "Dark-bright soliton interactions beyond the integrable limit: In this work we present a systematic theoretical analysis regarding\ndark-bright solitons and their interactions, motivated by recent advances in\natomic two-component repulsively interacting Bose-Einstein condensates. In\nparticular, we study analytically via a two-soliton ansatz adopted within a\nvariational formulation the interaction between two dark-bright solitons in a\nhomogeneous environment beyond the integrable regime, by considering general\ninter/intra-atomic interaction coefficients. We retrieve the possibility of a\nfixed point in the case where the bright solitons are out of phase. As the\ninter-component interaction is increased, we also identify an exponential\ninstability of the two-soliton state, associated with a subcritical pitchfork\nbifurcation. The latter gives rise to an asymmetric partition of the bright\nsoliton mass and dynamically leads to spontaneous splitting of the bound pair.\nIn the case of the in-phase bright solitons, we explain via parsing the\nanalytical approximations and monitoring the direct dynamics why no such pair\nis identified, despite its prediction by the variational analysis."
    },
    {
        "anchor": "Many-Body Physics with Individually-Controlled Rydberg Atoms: Over the last decade, systems of individually-controlled neutral atoms,\ninteracting with each other when excited to Rydberg states, have emerged as a\npromising platform for quantum simulation of many-body problems, in particular\nspin systems. Here, we review the techniques underlying quantum gas microscopes\nand arrays of optical tweezers used in these experiments, explain how the\ndifferent types of interactions between Rydberg atoms allow a natural mapping\nonto various quantum spin models, and describe recent results that were\nobtained with this platform to study quantum many-body physics.",
        "positive": "Nonlinear dressed states at the miscibility-immiscibility threshold: The dynamical evolution of spatial patterns in a complex system can reveal\nthe underlying structure and stability of stationary states. As a model system\nwe employ a two-component rubidium Bose-Einstein condensate at the transition\nfrom miscible to immiscible with the additional control of linear\ninterconversion. Excellent agreement is found between the detailed experimental\ntime evolution and the corresponding numerical mean-field computations.\nAnalyzing the dynamics of the system, we find clear indications of stationary\nstates that we term nonlinear dressed states. A steady state bifurcation\nanalysis reveals a smooth connection of these states with dark-bright soliton\nsolutions of the integrable two-component Manakov model."
    },
    {
        "anchor": "Quantum transport in ultracold atoms: Ultracold atoms confined by engineered magnetic or optical potentials are\nideal systems for studying phenomena otherwise difficult to realize or probe in\nthe solid state because their atomic interaction strength, number of species,\ndensity, and geometry can be independently controlled. This review focuses on\nquantum transport phenomena in atomic gases that mirror and oftentimes either\nbetter elucidate or show fundamental differences with those observed in\nmesoscopic and nanoscopic systems. We discuss significant progress in\nperforming transport experiments in atomic gases, contrast similarities and\ndifferences between transport in cold atoms and in condensed matter systems,\nand survey inspiring theoretical predictions that are difficult to verify in\nconventional setups. These results further demonstrate the versatility offered\nby atomic systems in the study of nonequilibrium phenomena and their promise\nfor novel applications.",
        "positive": "Chiral Rashba spin textures in ultra-cold Fermi gases: Spin-orbit coupling is an important ingredient in many recently discovered\nphenomena such as the spin-Hall effect and topological insulators. Of\nparticular interest is topological superconductivity, with its potential\napplication in topological quantum computation. The absence of disorder in\nultra-cold atomic systems makes them ideal for quantum computation\napplications, however, the spin-orbit (SO) coupling schemes proposed thus far\nare experimentally impractical owing to large spontaneous emission rates in the\nalkali fermions. In this paper, we develop a scheme to generate Rashba SO\ncoupling with a low spontaneous emission extension to a recent experiment. We\nshow that this scheme generates a Fermi surface spin texture for $^{40}\\rm{K}$\natoms, which is observable in time-of-flight measurements. The chiral spin\ntexture, together with conventional $s$-wave interactions leads to topological\nsuperconductivity and non-Abelian Majorana quasiparticles."
    },
    {
        "anchor": "Two-body state with p-wave interaction in one-dimensional waveguides\n  under transversely anisotropic confinement: We theoretically study two atoms with $p$-wave interaction in a\none-dimensional waveguide, and investigate how the transverse anisotropy of the\nconfinement affects the two-body state, especially, the properties of the\nresonance. For bound-state solution, we find there are totally three two-body\nbound states due to the richness of the orbital magnetic quantum number of\n$p$-wave interaction, while only one bound state is supported by $s$-wave\ninteraction. Two of them become nondegenerate due to the breaking of the\nrotation symmetry under transversely anisotropic confinement. For scattering\nsolution, the effective one-dimensional scattering amplitude and scattering\nlength are derived. We find the position of the $p$-wave confinement-induced\nresonance shifts apparently as the transverse anisotropy increases. In\naddition, a two-channel mechanism for confinement-induced resonance in a\none-dimensional waveguide is generalized to $p$-wave interaction, which was\nproposed only for $s$-wave interaction before. All our calculations are based\non the parameterization of the $^{40}$K atom experiments, and can be confirmed\nin future experiments.",
        "positive": "Analytical results on quantum correlations of few bosons in a\n  double-well trap: We consider a finite number $N$ of interacting bosonic atoms at zero\ntemperature confined in a one-dimensional double-well trap and study this\nsystem by using the two-site Bose-Hubbard (BH) Hamiltonian. For systems with\n$N=2$ and $N=3$, and $N=4$ bosons we analytically solve the eigenproblem\nassociated to this Hamiltonian and find its lowest energetic state. We\ninvestigate the structure of the ground state by varying the strength of the\nboson-boson interaction from the strongly attractive regime to the deep\nrepulsive one. We characterize the ground state of the two-site BH Hamiltonian\nby calculating the Fisher information $F$, the coherence visibility $\\alpha$,\nand the entanglement entropy $S$. For these quantities we provide analytical\nformulas that we use to study $F$, $\\alpha$, and $S$ as functions of the\ninteraction between the particles. We discuss the difference existing, in the\ndeep repulsive regime, between the case with an even number of bosons and that\nwith an odd number of particles, both in the structure of the lowest energetic\nstate and in the behavior of the three above ground-state characterizing\nparameters"
    },
    {
        "anchor": "Different lattice geometries with synthetic dimension: The possibility of creating different geometries with the help of an extra\nsynthetic dimension in optical lattices is studied. Additional linear potential\nand Raman assisted tunnelings are used to engineer well controlled tunnelings\nbetween available states. The great flexibility of the system allows us to\nobtain different geometries of synthetic lattices with possibility of adding\nsynthetic gauge fields.",
        "positive": "Effective time-independent description of optical lattices with periodic\n  driving: For a periodically driven quantum system an effective time-independent\nHamiltonian is derived with an eigen-energy spectrum, which in the regime of\nlarge driving frequencies approximates the quasi-energies of the corresponding\nFloquet Hamiltonian. The effective Hamiltonian is evaluated for the case of\noptical lattice models in the tight-binding regime subjected to strong periodic\ndriving. Three scenarios are considered: a periodically shifted one-dimensional\n(1D) lattice, a two-dimensional (2D) square lattice with inversely phased\ntemporal modulation of the well depths of adjacent lattice sites, and a 2D\nlattice subjected to an array of microscopic rotors commensurate with its\nplaquette structure. In case of the 1D scenario the rescaling of the tunneling\nenergy, previously considered by Eckardt et al. in Phys. Rev. Lett. 95, 260404\n(2005), is reproduced. The 2D lattice with well depth modulation turns out as a\ngeneralization of the 1D case. In the 2D case with staggered rotation, the\nexpression previously found in the case of weak driving by Lim et al. in Phys.\nRev. Lett. 100, 130402 (2008) is generalized, such that its interpretation in\nterms of an artificial staggered magnetic field can be extended into the regime\nof strong driving."
    },
    {
        "anchor": "Phonon-Josephson resonances in atomtronic circuits: We study the resonant excitation of sound modes from Josephson oscillations\nin Bose-Einstein condensates. From the simulations for various setups using the\nGross-Pitaevskii mean-field equations and Josephson equations we observe\nadditional tunneling currents induced by resonant phonons. The proposed\nexperiment may be used for spectroscopy of phonons as well as other low-energy\ncollective excitations in Bose-Einstein condensates. We also argue that the\nobserved effect may mask the observation of Shapiro resonances if not carefully\ncontrolled.",
        "positive": "The Zel'dovich effect in harmonically trapped, ultra-cold quantum gases: We investigate the Zel'dovich effect in the context of ultra-cold,\nharmonically trapped quantum gases. We suggest that currently available\nexperimental techniques in cold-atoms research offer an exciting opportunity\nfor a direct observation of the Zel'dovich effect without the difficulties\nimposed by conventional condensed matter and nuclear physics studies. We also\ndemonstrate an interesting scaling symmetry in the level rearragements which\nhas heretofore gone unnoticed."
    },
    {
        "anchor": "Kohn-Sham approximation scheme for an interacting Bose-condensed gas: The grand canonical density functional theory for inhomogeneous systems of\ninteracting bosons is developed in the effective action approach. The Legendre\ntransform of the generating functional for Green's functions is used to define\nthe effective action as a functional of both the particle density and the order\nparameter. Expanding the thermal effective action in powers of the Planck\nconstant we obtain a systematic approximation scheme, which practically\nimplements the Kohn-Sham idea: the problem of interacting bosons is reduced to\na single-particle system in a fictitious external potential. The Kohn-Sham\npotential, the density and the order parameter have to be determined\nself-consistently in a given order approximation.",
        "positive": "Heat transport in an optical lattice via Markovian feedback control: Ultracold atoms offer a unique opportunity to study many-body physics in a\nclean and well-controlled environment. However, the isolated nature of quantum\ngases makes it difficult to study transport properties of the system, which are\namong the key observables in condensed matter physics. In this work, we employ\nMarkovian feedback control to synthesize two effective thermal baths that\ncouple to the boundaries of a one-dimensional Bose-Hubbard chain. This allows\nfor the realization of a heat-current-carrying state. We investigate the\nsteady-state heat current, including its scaling with system size and its\nresponse to disorder. In order to study large systems, we use semi-classical\nMonte-Carlo simulation and kinetic theory. The numerical results from both\napproaches show, as expected, that for non- and weakly interacting systems with\nand without disorder one finds the same scaling of the heat current with\nrespect to the system size as it is found for systems coupled to thermal baths.\nFinally, we propose and test a scheme for measuring the energy flow. Thus, we\nprovide a route for the quantum simulation of heat-current-carrying steady\nstates of matter in atomic quantum gases."
    },
    {
        "anchor": "Pinning quantum phase transition for a Luttinger liquid of strongly\n  interacting bosons: One of the most remarkable results of quantum mechanics is the fact that\nmany-body quantum systems may exhibit phase transitions even at zero\ntemperature. Quantum fluctuations, deeply rooted in Heisenberg's uncertainty\nprinciple, and not thermal fluctuations, drive the system from one phase to\nanother. Typically, the relative strength of two competing terms in the\nsystem's Hamiltonian is changed across a finite critical value. A well-known\nexample is the Mott-Hubbard quantum phase transition from a superfluid to an\ninsulating phase, which has been observed for weakly interacting bosonic atomic\ngases. However, for strongly interacting quantum systems confined to\nlower-dimensional geometry a novel type of quantum phase transition may be\ninduced for which an arbitrarily weak perturbation to the Hamiltonian is\nsufficient to drive the transition. Here, for a one-dimensional (1D) quantum\ngas of bosonic caesium atoms with tunable interactions, we observe the\ncommensurate-incommensurate quantum phase transition from a superfluid\nLuttinger liquid to a Mott-insulator. For sufficiently strong interactions, the\ntransition is induced by adding an arbitrarily weak optical lattice\ncommensurate with the atomic granularity, which leads to immediate pinning of\nthe atoms. We map out the phase diagram and find that our measurements in the\nstrongly interacting regime agree well with a quantum field description based\non the exactly solvable sine-Gordon model. We trace the phase boundary all the\nway to the weakly interacting regime where we find good agreement with the\npredictions of the 1D Bose-Hubbard model. Our results open up the experimental\nstudy of quantum phase transitions, criticality, and transport phenomena beyond\nHubbard-type models in the context of ultracold gases.",
        "positive": "Realization of a stroboscopic optical lattice for cold atoms with\n  subwavelength spacing: Optical lattices are typically created via the ac-Stark shift, which are\nlimited by diffraction to periodicities $\\ge\\lambda/2$, where $\\lambda$ is the\nwavelength of light used to create them. Lattices with smaller periodicities\nmay be useful for many-body physics with cold atoms and can be generated by\nstroboscopic application of a phase-shifted lattice with subwavelength\nfeatures. Here we demonstrate a $\\lambda/4$-spaced lattice by stroboscopically\napplying optical Kronig-Penney(KP)-like potentials which are generated using\nspatially dependent dark states. We directly probe the periodicity of the\n$\\lambda/4$-spaced lattice by measuring the average probability density of the\natoms loaded into the ground band of the lattice. We measure lifetimes of atoms\nin this lattice and discuss the mechanisms that limit the applicability of this\nstroboscopic approach."
    },
    {
        "anchor": "Phase diagram of vortices in the polar phase of spin-1 Bose-Einstein\n  condensates: The phase diagram of lowest-energy vortices in the polar phase of spin-1\nBose--Einstein condensates is investigated theoretically. Singly quantized\nvortices are categorized by the local ordered state in the vortex core and\nthree types of vortices are found as lowest-energy vortices, which are elliptic\nAF-core vortices, axisymmetric F-core vortices, and N-core vortices. These\nvortices are named after the local ordered state, ferromagnetic (F),\nantiferromagnetic (AF), broken-axisymmetry (BA), and normal (N) states apart\nfrom the bulk polar (P) state. The N-core vortex is a conventional vortex, in\nthe core of which the superfluid order parameter vanishes. The other two types\nof vortices are stabilized when the quadratic Zeeman energy is smaller than a\ncritical value. The axisymmetric F-core vortex is the lowest-energy vortex for\nferromagnetic interaction, and it has an F core surrounded by a BA skin that\nforms a ferromagnetic-spin texture, as exemplified by the localized Mermin--Ho\ntexture. The elliptic AF-core vortex is stabilized for antiferromagnetic\ninteraction; the vortex core has both nematic-spin and ferromagnetic orders\nlocally and is composed of the AF-core soliton spanned between two BA edges.\nThe phase transition from the N-core vortex to the other two vortices is\ncontinuous, whereas that between the AF-core and F-core vortices is\ndiscontinuous. The critical point of the continuous vortex-core transition is\ncomputed by the perturbation analysis of the Bogoliubov theory and the\nGinzburg--Landau formalism describes the critical behavior. The influence of\ntrapping potential on the core structure is also investigated.",
        "positive": "Static and Dynamic Properties of Interacting Spin-1 Bosons in an Optical\n  Lattice: We study the physics of interacting spin-$1$ bosons in an optical lattice\nusing a variational Gutzwiller technique. We compute the mean-field ground\nstate wave-function and discuss the evolution of the condensate, spin, nematic,\nand singlet order parameters across the superfluid-Mott transition. We then\nextend the Gutzwiller method to derive the equations governing the dynamics of\nlow energy excitations in the lattice. Linearizing these equations, we compute\nthe excitation spectra in the superfluid and Mott phases for both ferromagnetic\nand antiferromagnetic spin-spin interactions. In the superfluid phase, we\nrecover the known excitation spectrum obtained from Bogoliubov theory. In the\nnematic Mott phase, we obtain gapped, quadratically dispersing particle and\nhole-like collective modes, whereas in the singlet Mott phase, we obtain a\nnon-dispersive gapped mode, corresponding to the breaking of a singlet pair.\nFor the ferromagnetic Mott insulator, the Gutzwiller mean-field theory only\nyields particle-hole like modes but no Goldstone mode associated with long\nrange spin order. To overcome this limitation, we supplement the Gutzwiller\ntheory with a Schwinger boson mean-field theory which captures super-exchange\ndriven fluctuations. In addition to the gapped particle-hole-like modes, we\nobtain a gapless quadratically dispersing ferromagnetic spin-wave Goldstone\nmode. We discuss the evolution of the singlet gap, particle-hole gap, and the\neffective mass of the ferromagnetic Goldstone mode as the superfluid-Mott phase\nboundary is approached from the insulating side. We discuss the relevance and\nvalidity of Gutzwiller mean-field theories to spinful systems, and potential\nextensions of this framework to include more exotic physics which appears in\nthe presence of spin-orbit coupling or artificial gauge fields."
    },
    {
        "anchor": "Molecular Impurities as a Realization of Anyons on the Two-Sphere: Studies on experimental realization of two-dimensional anyons in terms of\nquasiparticles have been restricted, so far, to only anyons on the plane. It is\nknown, however, that the geometry and topology of space can have significant\neffects on quantum statistics for particles moving on it. Here, we have\nundertaken the first step towards realizing the emerging fractional statistics\nfor particles restricted to move on the sphere, instead of on the plane. We\nshow that such a model arises naturally in the context of quantum impurity\nproblems. In particular, we demonstrate a setup in which the lowest-energy\nspectrum of two linear bosonic/fermionic molecules immersed in a quantum\nmany-particle environment can coincide with the anyonic spectrum on the sphere.\nThis paves the way towards experimental realization of anyons on the sphere\nusing molecular impurities. Furthermore, since a change in the alignment of the\nmolecules corresponds to the exchange of the particles on the sphere, such a\nrealization reveals a novel type of exclusion principle for molecular\nimpurities, which could also be of use as a powerful technique to measure the\nstatistics parameter. Finally, our approach opens up a new numerical route to\ninvestigate the spectra of many anyons on the sphere. Accordingly, we present\nthe spectrum of two anyons on the sphere in the presence of a Dirac monopole\nfield.",
        "positive": "Relaxation towards negative temperatures in bosonic systems: Generalized\n  Gibbs ensembles and beyond integrability: Motivated by the recent experimental observation of negative absolute\ntemperature states in systems of ultracold atomic gases in optical lattices\n[Braun et al., Science 339, 52 (2013)], we investigate theoretically the\nformation of these states. More specifically, we consider the relaxation after\na sudden inversion of the external parabolic confining potential in the\none-dimensional inhomogeneous Bose-Hubbard model. First, we focus on the\nintegrable hard-core boson limit which allows us to treat large systems and\narbitrarily long times, providing convincing numerical evidence for relaxation\nto a generalized Gibbs ensemble at negative temperature T<0, a notion we define\nin this context. Second, going beyond one dimension, we demonstrate that the\nemergence of negative temperature states can be understood in a dual way in\nterms of positive temperatures, which relies on a dynamic symmetry of the\nHubbard model. We complement the study by exact diagonalization simulations at\nfinite values of the on-site interaction."
    },
    {
        "anchor": "Laser-induced Kondo effect in ultracold alkaline-earth fermions: We demonstrate that laser excitations can coherently induce a novel Kondo\neffect in ultracold atoms in optical lattices. Using a model of alkaline-earth\nfermions with two orbitals, it is shown that the optically coupled two internal\nstates are dynamically entangled to form the Kondo-singlet state, overcoming\nthe heating effect due to the irradiation. Furthermore, a lack of SU($N$)\nsymmetry in the optical coupling provides a peculiar feature in the Kondo\neffect, which results in spin-selective renormalization of effective masses. We\nalso discuss effects of interorbital exchange interactions, and reveal that\nthey induce novel crossover or reentrant behavior of the Kondo effect owing to\ncontrol of the coupling anisotropy. The laser-induced Kondo effect is highly\ncontrollable by tuning the laser strength and the frequency, and thus offers a\nversatile platform to study the Kondo physics using ultracold atoms.",
        "positive": "Dipolar Bose Superstripes: We study the superfluid properties of a system of fully polarized dipolar\nbosons moving in the $xy$ plane. We focus on the general case where the\npolarization field forms an arbitrary angle $\\alpha$ with respect to the $z$\naxis, while the system is still stable. We use the diffusion Monte Carlo and\nthe path integral ground state methods to evaluate the one-body density matrix\nand the superfluid fractions in the region of the phase diagram where the\nsystem forms stripes. Despite its oscillatory behavior, the presence of a\nfinite large-distance asymptotic value in the $s$-wave component of the\none-body density matrix indicates the existence of a Bose condensate. The\nsuperfluid fraction along the stripes direction is always close to 1, while in\nthe $y$ direction decreases to a small value that is nevertheless different\nfrom zero. These two facts confirms that the stripe phase of the dipolar Bose\ngas in 2D is superfluid."
    },
    {
        "anchor": "Finite temperature QMC study of the one-dimensional polarized Fermi gas: Quantum Monte Carlo (QMC) techniques are used to provide an\napproximation-free investigation of the phases of the one-dimensional\nattractive Hubbard Hamiltonian in the presence of population imbalance. The\ntemperature at which the \"Fulde-Ferrell-Larkin-Ovchinnikov\" (FFLO) phase is\ndestroyed by thermal fluctuations is determined as a function of the\npolarization. It is shown that the presence of a confining potential does not\ndramatically alter the FFLO regime, and that recent experiments on trapped\natomic gases likely lie just within the stable temperature range.",
        "positive": "Driven-dissipative control of cold atoms in tilted optical lattices: We present a sequence of driven-dissipative protocols for controlling cold\natoms in tilted optical lattices. These experimentally accessible examples are\ntemplates that demonstrate how dissipation can be used to manipulate quantum\nmany-body systems. We consider bosonic atoms trapped in a tilted optical\nlattice, immersed in a superfluid bath, and excited by coherent Raman lasers.\nWith these ingredients, we are able to controllably transport atoms in the\nlattice and produce self-healing quantum states: a Mott insulator and the\ntopologically ordered spin-1 AKLT state."
    },
    {
        "anchor": "Controlling dark solitons on the healing length scale: While usually the optical diffraction limit is setting a limit for the\nlengthscales on which a typical alkali Bose-Einstein condensate can be\ncontrolled, we show that in certain situations control via matter waves can\nachieve smaller resolutions. For this we consider a small number of impurity\natoms which are trapped inside the density dip of a dark soliton state and show\nthat any grey soliton can be obtained by just driving the impurity atoms. By\ncontrolling the driving force on the impurity, one can therefore fully control\nthe position and velocity of the dark soliton, and also study controlled\ncollisions between these non-linear objects.",
        "positive": "Comparative study of quantum dynamics of a few bosons in a\n  one-dimensional split hard-wall trap: exact results versus Bose-Hubbard-model\n  approximations: We study the dynamical properties of a few bosons confined in an\none-dimensional split hard wall trap with the interaction strength varying from\nthe weakly to strongly repulsive regime. The system is initially prepared in\none side of the double well by setting the barrier strength of the split trap\nto be infinity and then the barrier strength is suddenly changed to a finite\nvalue. Both exact diagonalization method and Bose-Hubbard model (BHM)\napproximation are used to study the dynamical evolution of the initial system.\nThe exact results based on exact diagonaliztion verify the enhancement of\ncorrelated tunneling in the strongly interacting regime. Comparing results\nobtained by two different methods, we conclude that one-band BHM approximation\ncan well describe the dynamics in the weakly interacting regime, but is not\nefficient to give quantitatively consistent results in the strongly interacting\nregime. Despite of the quantitative discrepancy, we validate that the form of\ncorrelated tunneling gives an important contribution to tunneling in the large\ninteraction regime. To get a quantitative description for the dynamics of\nbosons in the strongly interacting regime, we find that a multi-band BHM\napproximation is necessary."
    },
    {
        "anchor": "Weak coupling regime of the Landau-Zener transition for association of\n  an atomic Bose-Einstein condensate: In the framework of a basic semiclassical time-dependent nonlinear two-state\nproblem, we study the weak coupling limit of the nonlinear Landau-Zener\ntransition at coherent photo- and magneto-association of an atomic\nBose-Einstein condensate. Using an exact third-order nonlinear differential\nequation for the molecular state probability, we develop a variational approach\nwhich enables us to construct an accurate analytic approximation describing\ntime dynamics of the coupled atom-molecular system for the case of weak\ncoupling. The approximation is written in terms of the solution to an auxiliary\nlinear Landau-Zener problem with some effective Landau-Zener parameter. The\ndependence of this effective parameter on the input Landau-Zener parameter is\nfound to be unexpected: as the generic Landau-Zener parameter increases, the\neffective Landau-Zener parameter first monotonically increases (starting from\nzero), reaches its maximal value and then monotonically decreases again\nreaching zero at some point. The constructed approximation quantitatively well\ndescribes many characteristics of the time dynamics of the system, in\nparticular, it provides a highly accurate formula for the final transition\nprobability to the molecular state. The present result for the final transition\nprobability improves the accuracy of the previous approximation by Ishkhanyan\net al. [Phys. Rev. A 69, 043612 (2004); J. Phys. A 38, 3505 (2005)] by order of\nmagnitude.",
        "positive": "Quantum degenerate mixtures of strontium and rubidium atoms: We report on the realization of quantum degenerate gas mixtures of the\nalkaline-earth element strontium with the alkali element rubidium. A key\ningredient of our scheme is sympathetic cooling of Rb by Sr atoms that are\ncontinuously laser cooled on a narrow linewidth transition. This versatile\ntechnique allows us to produce ultracold gas mixtures with a phase-space\ndensity of up to 0.06 for both elements. By further evaporative cooling we\ncreate double Bose-Einstein condensates of 87Rb with either 88Sr or 84Sr,\nreaching more than 10^5 condensed atoms per element for the 84Sr-87Rb mixture.\nThese quantum gas mixtures constitute an important step towards the production\nof a quantum gas of polar, open-shell RbSr molecules."
    },
    {
        "anchor": "Phase diagram of quasi-two-dimensional bosons in laser speckle potential: We have studied the phase diagram of a quasi-two-dimensional interacting Bose\ngas at zero temperature in the presence of random potential created by laser\nspeckles. The superfluid fraction and the fraction of particles with zero\nmomentum are obtained within the mean-field Gross-Pitaevskii theory and in\ndiffusion Monte Carlo simulations. We find a transition from the superfluid to\nthe insulating state, when the strength of the disorder grows. Estimations of\nthe critical parameters are compared with the predictions of the percolation\ntheory in the Thomas-Fermi approximation. Analytical expressions for the\nzero-momentum fraction and the superfluid fraction are derived in the limit of\nweak disorder and weak interactions within the framework of the Bogoliubov\ntheory. Limits of validity of various approximations are discussed.",
        "positive": "Loading of atoms into an optical trap with high initial phase-space\n  density: We report a method for loading cold atoms into an optical trap with high\ninitial phase-space density (PSD). When the trap beam is overlapped with atoms\nin optical molasses of optimized parameters including large cooling beam\ndetuning compared with conventional detuning used for a magneto-optical trap\n(MOT), more than $3 \\times 10^6$ rubidium atoms with an initial temperature\nless than 20 $\\mu$K are loaded into a single beam trap. The obtained maximum\ninitial PSD is estimated to be $1.1 \\times 10^{-3}$, which is one or two orders\nof magnitude greater than that achieved with the conventional loading into an\noptical trap from atoms in a MOT. The proposed method is promising for creating\na quantum gas with a large number of atoms in a short evaporation time."
    },
    {
        "anchor": "Controlling quantum coherence of a two-component Bose-Einstein\n  condensate via an impurity atom: We propose a scheme to control quantum coherence of a two-component\nBose-Einstein condensate (BEC) by a single impurity atom immersed in the BEC.\nWe show that the single impurity atom can act as a single atom valve (SAV) to\ncontrol quantum coherence of the two-component BEC. It is demonstrated that the\nSAV can realize the on-demand control over quantum coherence at an arbitrary\ntime. Specially, it is found that the SAV can also control higher-order quantum\ncoherence of two-component BEC. We investigate the long-time evolution of\nquantum coherence of the two-component BEC. It is indicated that the single\nimpurity atom can induce collapse and revival phenomenon of quantum coherence\nof the two-component BEC. Collapse-revival configurations of quantum coherence\ncan be manipulated by the initial-state parameters of the impurity atom and the\nimpurity-BEC interaction strengths.",
        "positive": "Photonic Crystal Architecture for Room Temperature Equilibrium\n  Bose-Einstein Condensation of Exciton-Polaritons: We describe photonic crystal microcavities with very strong light-matter\ninteraction to realize room-temperature, equilibrium, exciton-polariton\nBose-Einstein condensation (BEC). This is achieved through a careful balance\nbetween strong light-trapping in a photonic band gap (PBG) and large exciton\ndensity enabled by a multiple quantum-well (QW) structure with moderate\ndielectric constant. This enables the formation of long-lived, dense 10~$\\mu$m\n- 1~cm scale cloud of exciton-polaritons with vacuum Rabi splitting (VRS) that\nis roughly 7\\% of the bare exciton recombination energy. We introduce a\nwoodpile photonic crystal made of Cd$_{0.6}$Mg$_{0.4}$Te with a 3D PBG of 9.2\\%\n(gap to central frequency ratio) that strongly focuses a planar guided optical\nfield on CdTe QWs in the cavity. For 3~nm QWs with 5~nm barrier width the\nexciton-photon coupling can be as large as $\\hbar\\Ome=$55~meV (i.e., vacuum\nRabi splitting $2\\hbar\\Ome=$110~meV). The exciton recombination energy of\n1.65~eV corresponds to an optical wavelength of 750~nm. For $N=$106 QWs\nembedded in the cavity the collective exciton-photon coupling per QW,\n$\\hbar\\Ome/\\sqrt{N}=5.4$~meV, is much larger than state-of-the-art value of\n3.3~meV, for CdTe Fabry-P\\'erot microcavity. The maximum BEC temperature is\nlimited by the depth of the dispersion minimum for the lower polariton branch,\nover which the polariton has a small effective mass $\\sim 10^{-5}m_0$ where\n$m_0$ is the electron mass in vacuum. By detuning the bare exciton\nrecombination energy above the planar guided optical mode, a larger dispersion\ndepth is achieved, enabling room-temperature BEC."
    },
    {
        "anchor": "Detecting quadrupole interactions in ultracold Fermi gases: We propose to detect quadrupole interactions of neutral ultra-cold atoms via\ntheir induced mean-field shift. We consider a Mott insulator state of\nspin-polarized atoms in a two-dimensional optical square lattice. The\nquadrupole moments of the atoms are aligned by an external magnetic field. As\nthe alignment angle is varied, the mean-field shift shows a characteristic\nangular dependence, which constitutes the defining signature of the quadrupole\ninteraction. For the $^{3}P_{2}$ states of Yb and Sr atoms, we find a frequency\nshift of the order of tens of Hertz, which can be realistically detected in\nexperiment with current technology. We compare our results to the mean-field\nshift of a spin-polarized quasi-2D Fermi gas in continuum.",
        "positive": "Quantum Monte Carlo study of the role of p-wave interactions in\n  ultracold repulsive Fermi gases: Single-component ultracold atomic Fermi gases are usually described using\nnoninteracting many-fermion models. However, recent experiments reached a\nregime where $p$-wave interactions among identical fermionic atoms are\nimportant. In this paper, we employ variational and fixed-node diffusion Monte\nCarlo simulations to investigate the ground-state properties of\nsingle-component Fermi gases with short-range repulsive interactions. We\ndetermine the zero-temperature equation of state, and elucidate the roles\nplayed by the $p$-wave scattering volume and the $p$-wave effective range. A\ncomparison against recently derived second-order perturbative results shows\ngood agreement in a broad range of interaction strength. We also compute the\nquasiparticle effective mass, and we confirm the perturbative prediction of a\nlinear contribution in the $p$-wave scattering volume, while we find\nsignificant deviations from the beyond-mean-field perturbative result, already\nfor moderate interaction strengths. Finally, we determine ground-state energies\nfor two-component unpolarized Fermi gases with both interspecies and\nintraspecies hard-sphere interactions, finding remarkable agreement with a\nrecently derived fourth-order expansion that includes $p$-wave contributions."
    },
    {
        "anchor": "Dynamical BCS theory of a two-dimensional attractive Fermi gas:\n  effective interactions from Quantum Monte Carlo calculations: The primary work presented in this paper focuses on the calculation of\ndensity-density dynamical correlations in an attractive two dimensional Fermi\ngas in several physically interesting regimes, including the strongly\ncorrelated BEC-BCS crossover regime. We use state-of-the-art dynamical BCS\ntheory and we address the possibility to renormalize the interaction strength,\nusing unbiased Quantum Monte Carlo results as an asset to validate the\npredictions. We propose that a suitable interplay between dynamical BCS theory,\nwhich is computationally very cheap and yields results directly in real time\ndomain, and Quantum Monte Carlo methods, which are exact but way more demanding\nand limited to imaginary time domain, can be a very promising idea to study\ndynamics in many body systems. We illustrate the idea and provide quantitative\nresults for a few values of the interaction strength in the cold gas.",
        "positive": "Coarsening dynamics of binary Bose condensates: We study the dynamics of domain formation and coarsening in a binary\nBose-Einstein condensate that is quenched across a miscible-immiscible phase\ntransition. The late-time evolution of the system is universal and governed by\nscaling laws for the correlation functions. We numerically determine the\nscaling forms and extract the critical exponents that describe the growth rate\nof domain size and autocorrelations. Our data is consistent with inviscid\nhydrodynamic domain growth, which is governed by a universal dynamical critical\nexponent of $1/z = 0.68(2)$. In addition, we analyze the effect of domain wall\nconfigurations which introduce a nonanalytic term in the short-distance\nstructure of the pair correlation function, leading to a high-momentum\n\"Porod\"-tail in the static structure factor, which can be measured\nexperimentally."
    },
    {
        "anchor": "Coherent Manipulation of Spin Correlations in the Hubbard Model: We coherently manipulate spin correlations in a two-component atomic Fermi\ngas loaded into an optical lattice using spatially and time-resolved Ramsey\nspectroscopy combined with high-resolution \\textit{in situ} imaging. This novel\ntechnique allows us not only to imprint spin patterns but also to probe the\nstatic magnetic structure factor at arbitrary wave vector, in particular the\nstaggered structure factor. From a measurement along the diagonal of the\n$1^\\mathrm{st}$ Brillouin zone of the optical lattice, we determine the\nmagnetic correlation length and the individual spatial spin correlators. At\nhalf filling, the staggered magnetic structure factor serves as a sensitive\nthermometer for the spin temperature, which we employ to study the\nthermalization of spin and density degrees of freedom during a slow quench of\nthe lattice depth.",
        "positive": "Analytical solutions to the spin-1 Bose-Einstein condensates: We analytically solve the one-dimensional coupled Gross-Pitaevskii equations\nwhich govern the motion of F=1 spinor Bose-Einstein condensates. The nonlinear\ndensity-density interactions are decoupled by making use of the unique\nproperties of the Jacobian elliptical functions. Several types of complex\nstationary solutions are deduced. Furthermore, exact non-stationary solutions\nto the time-dependent Gross-Pitaevskii equations are constructed by making use\nof the spin-rotational symmetry of the Hamiltonian. The spin-polarizations\nexhibit kinked configurations. Our method is applicable to other coupled\nnonlinear systems."
    },
    {
        "anchor": "Two-leg ladder Bose Hubbard models with staggered fluxes: We investigate the ground state properties of ultracold atoms trapped in a\ntwo-leg ladder potential in the presence of an artificial magnetic field in a\nstaggered configuration. We focus on the strongly interacting regime and use\nthe Landau theory of phase transitions and a mean field Gutzwiller variational\nmethod to identify the stable superfluid phases and their boundaries with the\nMott-insulator regime as a function of magnetic flux. In addition, we calculate\nthe local and chiral currents of these superfluid phases, which show a\nstaggered vortex anti-vortex configuration. The analytical results are\nconfirmed by numerical simulations using a cluster mean-field theory approach.",
        "positive": "Interference of an Array of Independent Bose-Einstein Condensates: Interference of an array of independent Bose-Einstein condensates, whose\nexperiment has been performed recently, is theoretically studied in detail.\nEven if the number of the atoms in each gas is kept finite and the phases of\nthe gases are not well defined, interference fringes are observed on each\nsnapshot. The statistics of the snapshot interference patterns, i.e., the\naverage fringe amplitudes and their fluctuations (covariance), are computed\nanalytically, and concise formulas for their asymptotic values for long time of\nflight are derived. Processes contributing to these quantities are clarified\nand the relationship with the description on the basis of the symmetry-breaking\nscenario is revealed."
    },
    {
        "anchor": "Superlattice quantum solid of dipolar excitons: We study dipolar excitons confined at 330 mK in a square electrostatic\nlattice of a GaAs double quantum well. In the dipolar occupation blockade\nregime, at 3/2 filling, we evidence that excitons form a face-centred\nsuperlattice quantum solid. This phase is realised with high purity across 36\nlattice sites, in a regime where the excitons mean interaction energy exceeds\nthe depth of the lattice confinement. The superlattice solid then closely\nrelates to Wigner crystals.",
        "positive": "Efficient two-mode interferometers with spinor Bose-Einstein condensates: We consider general three-mode interferometers using a spin-1 atomic\nBose-Einstein condensate with macroscopic magnetization. We show that these\ninterferometers, combined with the measurement of the number of particles in\neach output port, provide an ultra-high phase sensitivity. We construct\neffective two-mode interferometers which involve two Zeeman modes showing that\nthey also provide an ultra-high phase sensitivity but of a bit reduced factor\nin the corresponding Fisher information. A special case of zero magnetization\nis shown to persist the efficiency of the two-mode interferometry."
    },
    {
        "anchor": "Delocalization and superfluidity of ultracold bosonic atoms in a ring\n  lattice: Properties of bosonic atoms in small systems with a periodic quasi\none-dimensional circular toroidal lattice potential subjected to rotation are\nexamined by performing exact diagonalization in a truncated many body space.\nThe expansion of the many-body Hamiltonian is considered in terms of the first\nband Bloch functions, and no assumption regarding restriction to\nnearest-neighbor hopping (tight-binding approximation) is involved. A finite\nsize version of the zero temperature phase diagrams of Fisher et al.\n\\cite{Fisher} is obtained and the results, in remarkable quantitative\ncorrespondence with the results available for larger systems, discussed. Ground\nstate properties relating to superfluidity are examined in the context of\ntwo-fluid phenomenology. The basic tool, consisting of the intrinsic inertia\nassociated with small rotation angular velocities in the lab frame, is used to\nobtain ground state `superfluid fractions' numerically. They are analytically\nassociated with one-body, uniform solenoidal currents in the case of the\nadopted geometry. These currents are in general incoherent superpositions of\ncontributions from each eigenstate of the associated reduced one-body\ndensities, with the corresponding occupation numbers as weights. Full coherence\noccurs therefore only when only one eigenstate is occupied by all bosons. The\nobtained numerical values for the superfluid fractions remain small throughout\nthe parameter region corresponding to the `Mott insulator to superfluid'\ntransition, and saturate at unity only as the lattice is completely smoothed\nout.",
        "positive": "Field-induced topological pair-density wave states in a multilayer\n  optical lattice: We study the superfluid phases of a Fermi gas in a multilayer optical lattice\nsystem in the presence of out-of-plane Zeeman field, as well as spin-orbit (SO)\ncoupling. We show that the Zeeman field combined with the SO coupling leads to\nexotic topological pair-density wave (PDW) phases in which different layers\npossess different superfluid order parameters, even though each layer\nexperiences the same Zeeman field and the SO coupling. We elucidate the\nmechanism of the emerging PDW phases, and characterize their topological\nproperties by calculating the associated Chern numbers."
    },
    {
        "anchor": "Universal four-body states in heavy-light mixtures with positive\n  scattering length: The number of four-body states known to behave universally is small. This\nwork adds a new class of four-body states to this relatively short list. We\npredict the existence of a universal four-body bound state for heavy-light\nmixtures consisting of three identical heavy fermions and a fourth\ndistinguishable lighter particle with mass ratio $\\kappa \\gtrsim 9.5$ and\nshort-range interspecies interaction characterized by a positive s-wave\nscattering length. The structural properties of these universal states are\ndiscussed and finite-range effects are analyzed. The bound states can be\nexperimentally realized and probed utilizing ultracold atom mixtures.",
        "positive": "The induced interaction in a Fermi gas with a BEC-BCS crossover: We study the effect of the induced interaction on the superfluid transition\ntemperature of a Fermi gas with a BEC-BCS crossover. The\nGorkov-Melik-Barkhudarov theory about the induced interaction is extended from\nthe BCS side to the entire crossover, and the pairing fluctuation is treated in\nthe approach by Nozi\\`{e}res and Schmitt-Rink. At unitarity, the induced\ninteraction reduces the transition temperature by about twenty percent. In the\nBCS limit, the transition temperature is reduced by a factor about 2.22, as\nfound by Gorkov and Melik-Barkhudarov. Our result shows that the effect of the\ninduced interaction is important both on the BCS side and in the unitary\nregion."
    },
    {
        "anchor": "Small quench dynamics as a probe for trapped ultracold atoms: Finite systems of bosons and/or fermions described by the Hubbard model can\nbe realized using ultracold atoms confined in optical lattices. The ground\nstates of these systems often exhibit a coexistence of compressible superfluid\nand incompressible Mott insulating regimes. We analyze such systems by studying\nthe out-of-equilibrium dynamics following a weak sudden quench of the trapping\npotential. In particular, we show how the temporal variance of the site\noccupations reveals the location of spatial boundaries between compressible and\nincompressible regions. The feasibility of this approach is demonstrated for\nseveral models using numerical simulations. We first consider integrable\nsystems, hard-core bosons (spinless fermions) confined by a harmonic potential,\nwhere space separated Mott and superfluid phases coexist. Then, we analyze a\nnonintegrable system, a $J-V-V'$ model with coexisting charge density wave and\nsuperfluid phases. We find that the temporal variance of the site occupations\nis a more effective measure than other standard indicators of phase boundaries\nsuch as a local compressibility. Based on these examples, we argue that\nanalyzing temporal fluctuations is a valuable experimental tool for exploring\nphase boundaries in trapped atom systems.",
        "positive": "Anisotropic superfluidity in a dipolar Bose gas: We study the superfluid character of a dipolar Bose-Einstein condensate\n(DBEC) in a quasi-two dimensional (q2D) geometry. In particular, we allow for\nthe dipole polarization to have some non-zero projection into the plane of the\ncondensate so that the effective interaction is anisotropic in this plane,\nyielding an anisotropic dispersion for propagation of quasiparticles. By\nperforming direct numerical simulations of a probe moving through the DBEC, we\nobserve the sudden onset of drag or creation of vortex-antivortex pairs at\ncritical velocities that depend strongly on the direction of the probe's\nmotion. This anisotropy emerges because of the anisotropic manifestation of a\nroton-like mode in the system."
    },
    {
        "anchor": "Collective excitations in two-dimensional SU($N$) Fermi gases with\n  tunable spin: We measure collective excitations of a harmonically trapped two-dimensional\n(2D) SU($N$) Fermi gas of $^{173}$Yb confined to a stack of layers formed by a\none-dimensional optical lattice. Quadrupole and breathing modes are excited and\nmonitored in the collisionless regime $\\lvert\\ln(k_F a_{2D})\\rvert\\gg 1$ with\ntunable spin. We observe that the quadrupole mode frequency decreases with\nincreasing number of spin components due to the amplification of the\ninteraction effect by $N$ in agreement with a theoretical prediction based on\n2D kinetic equations. The breathing mode frequency, however, is measured to be\ntwice the dipole oscillation frequency regardless of $N$. We also follow the\nevolution of collective excitations in the dimensional crossover from two to\nthree dimensions and characterize the damping rate of quadrupole and breathing\nmodes for tunable SU($N$) fermions, both of which reveal the enhanced\ninter-particle collisions for larger spin. Our result paves the way to\ninvestigate the collective property of 2D SU($N$) Fermi liquid with enlarged\nspin.",
        "positive": "Multiple self-organized phases and spatial solitons in cold atoms\n  mediated by optical feedback: We study the transverse self-structuring of a cloud of cold atoms with\neffective atomic interactions mediated by a coherent driving beam\nretro-reflected by means of a single mirror. The resulting self-structuring due\nto optomechanical forces is much richer than that of an effective-Kerr medium,\ndisplaying hexagonal, stripe and honeycomb phases depending on the interaction\nstrength parametrized by the linear susceptibility. Phase domains are described\nby real Ginzburg-Landau amplitude equations. In the stripe phase the system\nrecovers inversion symmetry. Moreover, the subcritical character of the\nhoneycomb phase allows for light-density feedback solitons functioning as\nself-sustained dark atomic traps with motion controlled by phase gradients in\nthe driving beam."
    },
    {
        "anchor": "Spin diffusion in trapped clouds of strongly interacting cold atoms: We show that puzzling recent experimental results on spin diffusion in a\nstrongly interacting atomic gas may be understood in terms of the predicted\nspin diffusion coefficient for a generic strongly interacting system. Three\nimportant features play a central role: a) Fick's law for diffusion must be\nmodified to allow for the trapping potential, b) the diffusion coefficient is\ninhomogeneous, due to the density variations in the cloud and c) the diffusion\napproximation fails in the outer parts of the cloud, where the mean free path\nis long.",
        "positive": "Radio-frequency dressing of multiple Feshbach resonances: We demonstrate and theoretically analyze the dressing of several proximate\nFeshbach resonances in Rb-87 using radio-frequency (rf) radiation. We present\naccurate measurements and characterizations of the resonances, and the dramatic\nchanges in scattering properties that can arise through the rf dressing. Our\nscattering theory analysis yields quantitative agreement with the experimental\ndata. We also present a simple interpretation of our results in terms of\nrf-coupled bound states interacting with the collision threshold."
    },
    {
        "anchor": "Quantum criticality of a one-dimensional Bose-Fermi mixture: The one-dimensional interacting Bose-Fermi mixtures, exhibiting quantum phase\ntransitions at zero temperature, are particularly valuable for the study of\nquantum critical phenomena. In the present paper, we analytically study quantum\nphase diagram, equation of state and quantum criticality of the Bose-Fermi\nmixture using the thermodynamic Bethe ansatz equations. We show that\nthermodynamical properties display universal scaling behaviour at quantum\ncriticality. Furthermore, quantum criticality of the Bose-Fermi mixture in an\nharmonic trap is also studied within the local density approximation. We thus\ndemonstrate that the phase diagram and critical properties of the bulk system\nprovide insights into understanding universal features of many-body critical\nphenomena.",
        "positive": "Absence of a four-body Efimov effect in the 2 + 2 fermionic problem: In the free three-dimensional space, we consider a pair of identical\n$\\uparrow$ fermions of some species or in some internal state, and a pair of\nidentical $\\downarrow$ fermions of another species or in another state. There\nis a resonant $s$-wave interaction (that is of zero range and infinite\nscattering length) between fermions in different pairs, and no interaction\nwithin the same pair. We study whether this $2+2$ fermionic system can exhibit\n(as the $3+1$ fermionic system) a four-body Efimov effect in the absence of\nthree-body Efimov effect, that is the mass ratio $\\alpha$ between $\\uparrow$\nand $\\downarrow$ fermions and its inverse are both smaller than\n13.6069{\\ldots}. For this purpose, we investigate scale invariant zero-energy\nsolutions of the four-body Schr\\''odinger equation, that is positively\nhomogeneous functions of the coordinates of degree {$s-7/2$}, where $s$ is a\ngeneralized Efimov exponent {that becomes purely imaginary in the presence of a\nfour-body Efimov effect.} Using rotational invariance in momentum space, it is\nfound that the allowed values of $s$ are such that $M(s)$ has a zero\neigenvalue; here the operator $M(s)$, that depends on the total angular\nmomentum $\\ell$, acts on functions of two real variables (the cosine of the\nangle between two wave vectors and the logarithm of the ratio of their moduli),\nand we write it explicitly in terms of an integral matrix kernel. We have\nperformed a spectral analysis of $M(s)$, analytical and for an arbitrary\nimaginary $s$ for the continuous spectrum, numerical and limited to $s = 0$ and\n$\\ell \\le 12$ for the discrete spectrum. We conclude that no eigenvalue of\n$M(0)$ crosses zero over the mass ratio interval $\\alpha \\in [1,\n13.6069\\ldots]$, even if, in the parity sector $(-1)^{\\ell}$, the continuous\nspectrum of $M(s)$ has everywhere a zero lower border. As a consequence, there\nis no possibility of a four-body Efimov effect for the 2+2 fermions. We also\nenunciated a conjecture for the fourth virial coefficient of the unitary\nspin-$1/2$ Fermi gas,inspired from the known analytical form of the third\ncluster coefficient and involving the integral over the imaginary $s$-axis of\n$s$ times the logarithmic derivative of the determinant of $M(s)$ summed over\nall angular momenta.The conjectured value is in contradiction with the\nexperimental results."
    },
    {
        "anchor": "The J-triplet Cooper pairing with magnetic dipolar interactions: Recently, cold atomic Fermi gases with the large magnetic dipolar interaction\nhave been laser cooled down to quantum degeneracy. Different from\nelectric-dipoles which are classic vectors, atomic magnetic dipoles are\nquantum-mechanical matrix operators proportional to the hyperfine-spin of\natoms, thus provide rich opportunities to investigate exotic many-body physics.\nFurthermore, unlike anisotropic electric dipolar gases, unpolarized magnetic\ndipolar systems are isotropic under simultaneous spin-orbit rotation. These\nfeatures give rise to a robust mechanism for a novel pairing symmetry: orbital\np-wave (L=1) spin triplet (S=1) pairing with total angular momentum of the\nCooper pair J=1. This pairing is markedly different from both the $^3$He-B\nphase in which J=0 and the $^3$He-$A$ phase in which $J$ is not conserved. It\nis also different from the p-wave pairing in the single-component electric\ndipolar systems in which the spin degree of freedom is frozen.",
        "positive": "Robust storage qubits in ultracold polar molecules: Quantum states with long-lived coherence are essential for quantum\ncomputation, simulation and metrology. The nuclear spin states of ultracold\nmolecules prepared in the singlet rovibrational ground state are an excellent\ncandidate for encoding and storing quantum information. However, it is\nimportant to understand all sources of decoherence for these qubits, and then\neliminate them, in order to reach the longest possible coherence times. Here,\nwe fully characterise the dominant mechanisms for decoherence of a storage\nqubit in an optically trapped ultracold gas of RbCs molecules using\nhigh-resolution Ramsey spectroscopy. Guided by a detailed understanding of the\nhyperfine structure of the molecule, we tune the magnetic field to where a pair\nof hyperfine states have the same magnetic moment. These states form a qubit,\nwhich is insensitive to variations in magnetic field. Our experiments reveal an\nunexpected differential tensor light shift between the states, caused by weak\nmixing of rotational states. We demonstrate how this light shift can be\neliminated by setting the angle between the linearly polarised trap light and\nthe applied magnetic field to a magic angle of\n$\\arccos{(1/\\sqrt{3})}\\approx55^{\\circ}$. This leads to a coherence time\nexceeding 6.9 s (90% confidence level). Our results unlock the potential of\nultracold molecules as a platform for quantum computation."
    },
    {
        "anchor": "Topological Fulde-Ferrell Superfluids of a Spin-Orbit Coupled Fermi Gas: Topological Fermi superfluids have played the central role in various fields\nof physics. However, all previous studies focus on the cases where Cooper pairs\nhave zero center-of-mass momenta (i.e. normal superfluids). The topology of\nFulde-Ferrell superfluids with nonzero momentum pairings have never been\nexplored until recent findings that Fulde-Ferrell superfluids in a spin-orbit\ncoupled Fermi gas can accommodate Majorana fermions in real space in low\ndimensions and Weyl fermions in momentum space in three dimension. In this\nreview, we first discuss the mechanism of pairings in spin-orbit coupled Fermi\ngases in optical lattices subject to Zeeman fields, showing that spin-orbit\ncoupling as well as Zeeman fields enhance Fulde-Ferrell states while suppress\nLarkin-Ovchinnikov states. We then present the low temperature phase diagram\nincluding both FF superfluids and topological FF superfluids phases in both two\ndimension and three dimension. In one dimension, Majorana fermions as well as\nphase dependent order parameter are visualized. In three dimension, we show the\nproperties of Weyl fermions in momentum space such as anisotropic linear\ndispersion, Fermi arch, and gaplessness away from $k_{\\perp}=0$. Finally, we\ndiscuss some possible methods to probe FF superfluids and topological FF\nsuperfluids in cold atom systems.",
        "positive": "Metastable hard-axis polar state of a spinor Bose-Einstein condensate\n  under a magnetic field gradient: We investigate the stability of a hard-axis polar state in a spin-1\nantiferromagnetic Bose-Einstein condensate under a magnetic field gradient,\nwhere the easy-plane spin anisotropy is controlled by a negative quadratic\nZeeman energy $q<0$. In a uniform magnetic field, the axial polar state is\ndynamically unstable and relaxes into the planar polar ground state. However,\nunder a field gradient $B'$, the excited spin state becomes metastable down to\na certain threshold $q_{th}$ and as $q$ decreases below $q_{th}$, its intrinsic\ndynamical instability is rapidly recalled. The incipient spin excitations in\nthe relaxation dynamics appear with stripe structures, indicating the\nrotational symmetry breaking by the field gradient. We measure the dependences\nof $q_{th}$ on $B'$ and the sample size, and we find that $q_{th}$ is highly\nsensitive to the field gradient in the vicinity of $B'=0$, exhibiting power-law\nbehavior of $|q_{th}|\\propto B'^{\\alpha}$ with $\\alpha \\sim 0.5$. Our results\ndemonstrate the significance of the field gradient effect in the quantum\ncritical dynamics of spinor condensates."
    },
    {
        "anchor": "Experimental realization of a fermionic spin-momentum lattice: We experimentally realize a spin-momentum lattice with a homogeneously\ntrapped Fermi gas. The lattice is created via cyclically-rotated atom-laser\ncouplings between three bare atomic spin states, and are such that they form a\ntriangular lattice in a synthetic spin-momentum space. We demonstrate the\nlattice and explore its dynamics with spin- and momentum-resolved absorption\nimaging. This platform will provide new opportunities for synthetic spin\nsystems and the engineering of topological bands. In particular, the use of\nthree spin states in two spatial dimensions would allow the simulation of\nsynthetic magnetic fields of high spatial uniformity, which would lead to\nultra-narrow Chern bands that support robust fractional quantum Hall states.",
        "positive": "Conductivity of strongly correlated bosons in optical lattices in an\n  Abelian synthetic magnetic field: Topological phase engineering of neutral bosons loaded in an optical lattice\nopens a new window for manipulating of transport phenomena in such systems.\nExploiting the Bose Hubbard model and using the magnetic Kubo formula proposed\nin this paper we show that the optical conductivity abruptly changes for\ndifferent flux densities in the Mott phase. Especially, when the frequency of\nthe applied field corresponds to the on-site boson interaction energy, we\nobserve insulator or metallic behavior for a given Hofstadter spectrum. We also\nprove, that for different synthetic magnetic field configurations, the critical\nconductivity at the tip of the lobe is non-universal and depends on the energy\nminima of the spectrum. In the case of $1/2$ and $1/3$ flux per plaquette, our\nresults are in good agreement with those of the previous Monte Carlo (MC)\nstudy. Moreover, we show that for half magnetic-flux through the cell the\ncritical conductivity suddenly changes in the presence of a superlattice\npotential with uniaxial periodicity."
    },
    {
        "anchor": "Particles and Fields in Superfluids: Insights from the Two-dimensional\n  Gross-Pitaevskii Equation: We carry out extensive direct numerical simulations (DNSs) to investigate the\ninteraction of active particles and fields in the two-dimensional (2D)\nGross-Pitaevskii (GP) superfluid, in both simple and turbulent flows. The\nparticles are active in the sense that they affect the superfluid even as they\nare affected by it. We tune the mass of the particles, which is an important\ncontrol parameter. At the one-particle level, we show how light, neutral, and\nheavy particles move in the superfluid, when a constant external force acts on\nthem; in particular, beyond a critical velocity, at which a vortex-antivortex\npair is emitted, particle motion can be periodic or chaotic. We demonstrate\nthat the interaction of a particle with vortices leads to dynamics that depends\nsensitively on the particle characteristics. We also demonstrate that\nassemblies of particles and vortices can have rich, and often turbulent\nspatiotemporal evolution. In particular, we consider the dynamics of the\nfollowing illustrative initial configurations: (a) one particle placed in front\nof a translating vortex-antivortex pair; (b) two particles placed in front of a\ntranslating vortex-antivortex pair; (c) a single particle moving in the\npresence of counter-rotating vortex clusters; and (d) four particles in the\npresence of counter-rotating vortex clusters. We compare our work with earlier\nstudies and examine its implications for recent experimental studies in\nsuperfluid Helium and Bose-Einstein condensates.",
        "positive": "Quantum double structure in cold atom superfluids: The theory of topological quantum computation is underpinned by two important\nclasses of models. One is based on non-abelian Chern-Simons theory, which\nyields the so-called $\\rm{SU}(2)_k$ anyon models that often appear in the\ncontext of electrically charged quantum fluids. The physics of the other is\ncaptured by symmetry broken Yang-Mills theory in the absence of a Chern-Simons\nterm, and results in the so-called quantum double models. Extensive resources\nhave been invested into the search for $\\rm{SU}(2)_k$ anyon quasi-particles; in\nparticular the so-called Ising anyons ($k=2$) of which Majorana zero modes are\nbelieved to be an incarnation. In contrast to the $\\rm{SU}(2)_k$ models,\nquantum doubles have attracted little attention in experiments despite their\npivotal role in the theory of error correction. Beyond topological error\ncorrecting codes, the appearance of quantum doubles has been limited to\ncontexts primarily within mathematical physics, and as such, they are of\nseemingly little relevance for the study of experimentally tangible systems.\nHowever, recent works suggest that quantum double anyons may be found in spinor\nBose-Einstein condensates. In light of this, the core purpose of this article\nis to provide a self-contained exposition of the quantum double structure,\nframed in the context of spinor condensates, by constructing explicitly the\nquantum doubles for various ground state symmetry groups and discuss their\nexperimental realisability. We also derive analytically an equation for the\nquantum double Clebsch-Gordan coefficients from which the relevant braid\nmatrices can be worked out. Finally, the existence of a particle-vortex duality\nis exposed and illuminated upon in this context."
    },
    {
        "anchor": "Trial wave functions for ring-trapped ions and neutral atoms:\n  Microscopic description of the quantum space-time crystal: A constructive theoretical platform for the description of quantum space-time\ncrystals uncovers for $N$ interacting and ring-confined rotating particles the\nexistence of low-lying states with proper space-time crystal behavior. The\nconstruction of the corresponding many-body trial wave functions proceeds first\nvia symmetry breaking at the mean-field level followed by symmetry restoration\nusing projection techniques. The ensuing correlated many-body wave functions\nare stationary states and preserve the rotational symmetries, and at the same\ntime they reflect the point-group symmetries of the mean-field crystals. This\nbehavior results in the emergence of sequences of select magic angular momenta\n$L_m$. For angular-momenta away from the magic values, the trial functions\nvanish. Symmetry breaking beyond mean field can be induced by superpositions of\nsuch good-$L_m$ many-body stationary states. We show that superposing a pair of\nadjacent magic angular momenta states leads to formation of special\nbroken-symmetry states exhibiting quantum space-time-crystal behavior. In\nparticular, the corresponding particle densities rotate around the ring,\nshowing undamped and nondispersed periodic crystalline evolution in both space\nand time. The experimental synthesis of such quantum space-time-crystal wave\npackets is predicted to be favored in the vicinity of ground-state energy\ncrossings of the Aharonov-Bohm-type spectra accessed via an externally applied\nmagnetic field. These results are illustrated here for Coulomb-repelling\nfermionic ions and for a lump of contact-interaction attracting bosons.",
        "positive": "Inflationary preheating dynamics with ultracold atoms: We discuss the amplification of loop corrections in quantum many-body systems\nthrough dynamical instabilities. As an example, we investigate both\nanalytically and numerically a two-component ultracold atom system in one\nspatial dimension. The model features a tachyonic instability, which\nincorporates characteristic aspects of the mechanisms for particle production\nin early-universe inflaton models. We establish a direct correspondence between\nmeasureable macroscopic growth rates for occupation numbers of the ultracold\nBose gas and the underlying microscopic processes in terms of Feynman loop\ndiagrams. We analyze several existing ultracold atom setups featuring dynamical\ninstabilities and propose optimized protocols for their experimental\nrealization. We demonstrate that relevant dynamical processes can be enhanced\nusing a seeding procedure for unstable modes and clarify the role of initial\nquantum fluctuations and the generation of a non-linear secondary stage for the\namplification of modes."
    },
    {
        "anchor": "Exactly solvable model of two trapped quantum particles interacting via\n  finite-range soft-core interactions: The exactly solvable model of two indistinguishable quantum particles (bosons\nor fermions) confined in a one-dimensional harmonic trap and interacting via\nfinite-range soft-core interaction is presented and many properties of the\nsystem are examined. Particularly, it is shown that independently on the\npotential range, in the strong interaction limit bosonic and fermionic\nsolutions become degenerate. For sufficiently large ranges a specific\ncrystallization appears in the system. The results are compared to predictions\nof the celebrated Busch {\\it et al.} model and those obtained in the\nTonks-Girardeau limit. The assumed inter-particle potential is very similar to\nthe potential between ultra-cold dressed Rydberg atoms. Therefore, the model\ncan be examined experimentally.",
        "positive": "Two-Particle Interference with Double Twin-Atom Beams: We demonstrate a source for correlated pairs of atoms characterized by two\nopposite momenta and two spatial modes forming a Bell state only involving\nexternal degrees of freedom. We characterize the state of the emitted atom\nbeams by observing strong number squeezing up to -10 dB in the correlated\ntwo-particle modes of emission. We furthermore demonstrate genuine two-particle\ninterference in the normalized second-order correlation function $g^{(2)}$\nrelative to the emitted atoms."
    },
    {
        "anchor": "Bose-Einstein condensation of Efimovian triples in the unitary Bose gas: In an atomic Bose-Einstein condensate quenched to the unitary regime, we\npredict the sequential formation of a significant fraction of condensed pairs\nand triples. At short-distances, we demonstrate the two-body and Efimovian\ncharacter of the condensed pairs and triples, respectively. As the system\nevolves, the size of the condensed pairs and triples becomes comparable to the\ninterparticle distance, such that many-body effects become significant. The\nstructure of the condensed triples depends on the relative size of Efimov\nstates to density scales. Unexpectedly, we find universal condensed triples in\nthe limit where these scales are well-separated. Our findings provide a new\nframework for understanding dynamics in the unitary regime as the Bose-Einstein\ncondensation of few-body composites.",
        "positive": "Stability of trapped degenerate dipolar Bose and Fermi gases: Trapped degenerate dipolar Bose and Fermi gases of cylindrical symmetry with\nthe polarization vector along the symmetry axis are only stable for the\nstrength of dipolar interaction below a critical value. In the case of bosons,\nthe stability of such a dipolar Bose-Einstein condensate (BEC) is investigated\nfor different strengths of contact and dipolar interactions using variational\napproximation and numerical solution of a mean-field model. In the disk shape,\nwith the polarization vector perpendicular to the plane of the disk, the atoms\nexperience an overall dipolar repulsion and this fact should contribute to the\nstability. However, a complete numerical solution of the dynamics leads to the\ncollapse of a strongly disk-shaped dipolar BEC due to the long-range\nanisotropic dipolar interaction. In the case of fermions, the stability of a\ntrapped single-component degenerate dipolar Fermi gas is studied including the\nHartree-Fock exchange and Brueckner-Goldstone correlation energies in the local\ndensity approximation valid for a large number of atoms. Estimates for the\nmaximum allowed number of polar Bose and Fermi molecules in BEC and degenerate\nFermi gas are given."
    },
    {
        "anchor": "Verification of universal relations in a strongly interacting Fermi gas: Many-body fermion systems are important in many branches of physics,\nincluding condensed matter, nuclear, and now cold atom physics. In many cases,\nthe interactions between fermions can be approximated by a contact interaction.\nA recent theoretical advance in the study of these systems is the derivation of\na number of exact universal relations that are predicted to be valid for all\ninteraction strengths, temperatures, and spin compositions. These equations,\nreferred to as the Tan relations, relate a microscopic quantity, namely, the\namplitude of the high-momentum tail of the fermion momentum distribution, to\nthe thermodynamics of the many-body system. In this work, we provide\nexperimental verification of the Tan relations in a strongly interacting gas of\nfermionic atoms. Specifically, we measure the fermion momentum distribution\nusing two different techniques, as well as the rf excitation spectrum and\ndetermine the effect of interactions on these microscopic probes. We then\nmeasure the potential energy and release energy of the trapped gas and test the\npredicted universal relations.",
        "positive": "Nonlinear Luttinger liquid: Exact result for the Green function in terms\n  of the fourth Painlev\u00e9 transcendent: We show that exact time dependent single particle Green function in the\nImambekov-Glazman theory of nonlinear Luttinger liquids can be written, for any\nvalue of the Luttinger parameter, in terms of a particular solution of the\nPainlev\\'e IV equation. Our expression for the Green function has a form\nanalogous to the celebrated Tracy-Widom result connecting the Airy kernel with\nPainlev\\'e II. The asymptotic power law of the exact solution as a function of\na single scaling variable $x/\\sqrt{t}$ agrees with the mobile impurity results.\nThe full shape of the Green function in the thermodynamic limit is recovered\nwith arbitrary precision via a simple numerical integration of a nonlinear ODE."
    },
    {
        "anchor": "Bose-Einstein condensation in two-dimensional traps: In two-dimensional traps, since the theoretical study of Bose-Einstein\ncondensation (BEC) will encounter the problem of divergence, the actual\ncontribution of the divergent terms is often estimated in some indirect ways\nwith the accuracy to the leading order. In this paper, by using an analytical\ncontinuation method to solve the divergence problem, we obtain the analytical\nexpressions of critical temperature and condensate fraction for Bose gases in a\ntwo-dimensional anisotropic box and harmonic trap, respectively. They are\nconsistent with or better than previous studies. Then, we further consider the\nnonvanishing chemical potential, and obtain the expressions of chemical\npotential and more precise condensate fraction. These results agree with the\nnumerical calculation well, especially for the case of harmonic traps. The\ncomparison between the grand canonical and canonical ensembles shows that our\ncalculation in the grand canonical ensemble is reliable.",
        "positive": "A model study on superfluidity of a unitary Fermi gas of atoms\n  interacting with a finite-ranged potential: We calculate Bardeen-Cooper-Schrieffer (BCS) state of a unitary Fermi gas of\natoms interacting with the finite-ranged Jost-Kohn potential which has been\nrecently shown to account for the resonant interactions [2019 {\\rm J. Phys. B:\nAt. Mol. Opt. Phys.} {\\bf 52}, 165004]. Using exact scattering solution of the\npotential, we derive two-body ${\\mathbf T}$-matrix element which is employed to\nconstruct the BCS Hamiltonian in momentum space. We present results on the\nenergy- and range-dependence of the pairing gap and superfluid density and the\nrange-dependence of the chemical potential for a wide variation of the\nscattering length including the unitary regime. In the zero range limit our\ncalculated gap at the Fermi energy is found to be nearly equal to that\ncalculated in mean-field theory with contact potential. The mean gap averaged\nover the full width at half maximum of the gap function in the zero range and\nunitary limits is found to be $0.42 E_F$ which is quite close to the recent\nresult of the quantum Monte Carlo simulation [2018 {\\rm Phys. Rev.A} {\\bf 97},\n013601]. The chemical potential in the zero range limit also agrees well with\nthat for the contact potential."
    },
    {
        "anchor": "Spin conductivity spectrum and spin superfluidity in a binary Bose\n  mixture: We investigate the spectrum of spin conductivity for a miscible two-component\nBose-Einstein condensate (BEC) that exhibits spin superfluidity. By using the\nBogoliubov theory, the regular part being the spin conductivity at finite ac\nfrequency and the spin Drude weight characterizing the delta-function peak at\nzero frequency are analytically computed. We demonstrate that the spectrum\nexhibits a power-law behavior at low frequency, reflecting gapless density and\nspin modes specific to the binary BEC. At the phase transition points into\nimmiscible and quantum-droplet states, the change in quasiparticle dispersion\nrelations modifies the power law. In addition, the spin Drude weight becomes\nfinite, indicating zero spin resistivity due to spin superfluidity. Our results\nalso suggest that the Andreev-Bashkin drag density is accessible by measuring\nthe spin conductivity spectrum.",
        "positive": "Cooling a Fermi gas with three-body recombination near a narrow Feshbach\n  resonance: Three-body recombination is a phenomenon common in atomic and molecular\ncollisions, producing heating in the system. However, we find the cooling\neffect of the three-body recombination of a 6Li Fermi gas near its s-wave\nnarrow Feshbach resonance. Such counter-intuitive behavior is explained as\nfollows, the threshold energy of the quasi-bounded Feshbach molecule acts as\nthe knife of cooling, expelling the scattering atoms with selected kinetic\nenergy from the trap. When the threshold energy happens to be larger than\n3/2kBT, each lost atom in the three-body recombination process has more than\n3kBT energy which results in cooling. The best cooling is found with the\nthreshold energy set at about 3kBT, consistent with a theoretical model. The\nthree-body recombination induced cooling raises potential applications for\ncooling complex atomic systems."
    },
    {
        "anchor": "Non-ergodic behaviour of clean Bose-Hubbard chains: We study ergodicity breaking in the clean Bose-Hubbard chain for small\nhopping strength. We see the existence of a non-ergodic regime by means of\nindicators as the half-chain entanglement entropy of the eigenstates, the\naverage level spacing ratio, {the properties of the eigenstate-expectation\ndistribution of the correlation and the scaling of the Inverse Participation\nRatio averages.} We find that this ergodicity breaking {is different from\nmany-body localization} because the average half-chain entanglement entropy of\nthe eigenstates obeys volume law. This ergodicity breaking appears unrelated to\nthe spectrum being organized in quasidegenerate multiplets at small hopping and\nfinite system sizes, so in principle it can survive also for larger system\nsizes. We find that some imbalance oscillations in time which could mark the\nexistence of a glassy behaviour in space are well described by the dynamics of\na single symmetry-breaking doublet and {quantitatively} captured by a\nperturbative effective XXZ model. We show that the amplitude of these\noscillations vanishes in the large-size limit. {Our findings are numerically\nobtained for systems with $L < 12$. Extrapolations of our scalings to larger\nsystem sizes should be taken with care, as discussed in the paper.",
        "positive": "Excitations of a binary supersolid: We predict a rich excitation spectrum of a binary dipolar supersolid in a\nlinear crystal geometry, where the ground state consists of two partially\nimmiscible components with alternating, interlocking domains. We identify three\nGoldstone branches, each with first-sound, second-sound or spin-sound\ncharacter. In analogy with a diatomic crystal, the resulting lattice has a\ntwo-domain primitive basis and we find that the crystal (first-sound-like)\nbranch is split into optical and acoustic phonons. We also find a spin-Higgs\nbranch that is associated with the supersolid modulation amplitude."
    },
    {
        "anchor": "Effective field theory of bosons with finite-range interaction in a\n  disordered environment: We investigate the low-temperature properties of a ultracold gas made of\nbosonic alkali-metal atoms with finite-range interaction under the effect of a\ndisordered environment. The statistical characterization of the disorder is\ninvestigated within an effective-field-theory formalism for a generic spatial\ndimension $d$. Moving to $d=3$, where all the arising divergences are properly\nregularized, we focus on the depletion of both the condensate and superfluid\ndensities. At zero temperature we obtain meaningful analytical formulas for the\ncondensate fraction and the superfluid fraction which take into account the\ninterplay among scattering length, effective range, and disorder strength.",
        "positive": "Topological phases in spin-orbit coupled dipolar lattice bosons: We study the topological phases in spin-orbit coupled dipolar bosons in a\none-dimensional optical lattice. The magnetic dipolar interactions between\natoms give rise to the inter-site interactions. In the Mott-insulating regime,\nthis system can be described by the quantum XYZ spin model with the\nDzyaloshinskii-Moriya interactions in a transverse field. We focus on\ninvestigating the effect of dipolar interactions on the topological phase. The\ntopological phase can be shown when spin-orbit coupling incorporates with the\nrepulsive dipolar interaction. We find that the dipolar interaction can broaden\nthe range of parameters of spin-orbit coupling and transverse field for\nexhibiting the topological phase. The sum of spin correlations between the two\nnearest neighbouring atoms can be used to indicate the topological phase. This\nmay be useful for detecting topological phases in experiments."
    },
    {
        "anchor": "Dimensional crossover for the beyond-mean-field correction in Bose gases: We present a detailed beyond-mean-field analysis of a weakly interacting Bose\ngas in the crossover from three to low dimensions. We find an analytical\nsolution for the energy and provide a clear qualitative picture of the\ncrossover in the case of a box potential with periodic boundary conditions. We\nshow that the leading contribution of the confinement-induced resonance is of\nbeyond-mean-field order and calculate the leading corrections in the three- and\nlow-dimensional limits. We also characterize the crossover for harmonic\npotentials in a model system with particularly chosen short- and long-range\ninteractions and show the limitations of the local-density approximation. Our\nanalysis is applicable to Bose-Bose mixtures and gives a starting point for\ndeveloping the beyond-mean-field theory in inhomogeneous systems with\nlong-range interactions such as dipolar particles or Rydberg-dressed atoms.",
        "positive": "Observation of quasiparticle pair-production and quantum entanglement in\n  atomic quantum gases quenched to an attractive interaction: We report observation of quasiparticle pair-production and characterize\nquantum entanglement created by a modulational instability in an atomic\nsuperfluid. By quenching the atomic interaction to attractive and then back to\nweakly repulsive, we produce correlated quasiparticles and monitor their\nevolution in a superfluid through evaluating the in situ density noise power\nspectrum, which essentially measures a 'homodyne' interference between ground\nstate atoms and quasiparticles of opposite momenta. We observe large amplitude\ngrowth in the power spectrum and subsequent coherent oscillations in a wide\nspatial frequency band within our resolution limit, demonstrating coherent\nquasiparticle generation and evolution. The spectrum is observed to oscillate\nbelow a quantum limit set by the Peres-Horodecki separability criterion of\ncontinuous-variable states, thereby confirming quantum entanglement between\ninteraction quench-induced quasiparticles."
    },
    {
        "anchor": "Topological polaritons from photonic Dirac cones coupled to excitons in\n  a magnetic field: We introduce an alternative scheme for creating topological polaritons\n(topolaritons) by exploiting the presence of photonic Dirac cones in photonic\ncrystals with triangular lattice symmetry. As recently proposed, topolariton\nstates can emerge from a coupling between photons and excitons combined with a\nperiodic exciton potential and a magnetic field to open up a topological gap.\nWe show that in photonic crystals the opening of the gap can be substantially\nsimplified close to photonic Dirac points. Coupling to Zeeman-split excitons\nbreaks time reversal symmetry and allows to gap out the Dirac cones in a\nnon-trival way, leading to a topological gap similar to the strength of the\nperiodic exciton potential. Compared to the original topolariton proposal\n[Karzig {\\em et al}, PRX {\\bf 5}, 031001 (2015)], this scheme significantly\nincreases the size of the topological gap over a wide range of parameters.\nMoreover, the gap opening mechanism highlights an interesting connection\nbetween topolaritons and the Haldane and Raghu scheme [Haldane and Raghu, PRL\n{\\bf 100}, 013904 (2008)] to create topological photons in magneto-optically\nactive materials.",
        "positive": "Dynamical phase interferometry of cold atoms in optical lattices: We study the propagation of cold-atom wave packets in an interferometer with\na Mach-Zehnder topology based on the dynamical phase of Bloch oscillation in a\nweakly forced optical lattice with a narrow potential barrier that functions as\na cold-atom wave packet splitter. We calculate analytically the atomic wave\nfunction, and show that the expected number of atoms in the two outputs of the\ninterferometer oscillates rapidly as a function of the angle between the\npotential barrier and the forcing direction with period proportional to the\nexternal potential difference across a lattice spacing divided by the lattice\nband energy scale. The interferometer can be used as a high precision force\nprobe whose principle of operation is different from current interferometers\nbased on the overall position of Bloch oscillating wave packets."
    },
    {
        "anchor": "Spin modulation instabilities and phase separation dynamics in trapped\n  two-component Bose condensates: In the study of trapped two-component Bose gases, a widely used dynamical\nprotocol is to start from the ground state of a one-component condensate and\nthen switch half the atoms into another hyperfine state. The slightly different\nintra-component and inter-component interactions can then lead to highly\nnontrivial dynamics. We study and classify the possible subsequent dynamics,\nover a wide variety of parameters spanned by the trap strength and by the\ninter- to intra-component interaction ratio. A stability analysis suited to the\ntrapped situation provides us with a framework to explain the various types of\ndynamics in different regimes.",
        "positive": "A classification of the ground states and topological defects in a\n  rotating two-component Bose-Einstein condensate: We classify the ground states and topological defects of a rotating\ntwo-component condensate when varying several parameters: the intracomponent\ncoupling strengths, the intercomponent coupling strength and the particle\nnumbers.No restriction is placed on the masses or trapping frequencies of the\nindividual components. We present numerical phase diagrams which show the\nboundaries between the regions of coexistence, spatial separation and symmetry\nbreaking. Defects such as triangular coreless vortex lattices, square coreless\nvortex lattices and giant skyrmions are classified. Various aspects of the\nphase diagrams are analytically justified thanks to a non-linear $\\sigma$ model\nthat describes the condensate in terms of the total density and a pseudo-spin\nrepresentation."
    },
    {
        "anchor": "Improving the efficiency of ultracold dipolar molecule formation by\n  first loading onto an optical lattice: Ultracold ground state dipolar 40K-87Rb molecules have recently been produced\nin a loose harmonic trap by employing a magnetic field sweep across a Feshbach\nresonance followed by stimulated Raman adiabatic passage [K.-K. Ni et al.,\nScience 322, 231 (2008)]. The overall experimental efficiency for molecule\nformation was around 20%. We show that the efficiency can be increased to\nnearly 100% if one first loads the atomic gases into an optical lattice of the\nappropriate depth and tunes the interspecies attraction to have exactly one\natom of each species at an occupied lattice site. Our proposed scheme provides\na large enhancement to the dipolar molecule density even at relatively high\ntemperatures, and avoids three-body recombination loss by preventing lattice\nsites from being triply occupied.",
        "positive": "Exact edge, bulk and bound states of finite topological systems: Finite topologically non-trivial systems are often characterised by the\npresence of bound states at their physical edges. These topological edge modes\ncan be distinguished from usual Shockley waves energetically, as their energies\nremain finite and in-gap. On a clean 1D or reducible 2D model, in either the\ncommensurate or semi-infinite case, the edge modes can be obtained\nanalytically, as shown in [PRL 71, 3697 (1993)] and [PRA 89, 023619 (2014)]. We\nput forward a method for obtaining the spectrum and wave functions of\ntopological edge modes for arbitrary finite lattices, including the\nincommensurate case. A small number of parameters are easily determined\nnumerically, with the form of the eigenstates remaining fully analytical. We\nalso obtain the bulk modes in the finite system analytically and their\neigenenergies, which lie within the infinite-size limit continuum. Our method\nis general and can be easily applied to obtain the properties of\nnon-topological models and/or extended to include impurities. As an example, we\nconsider the case of an impurity located next to one edge of a 1D system,\nequivalent to a softened boundary in a separable 2D model. We show that a\nlocalised impurity can have a drastic effect on the edge modes of the system.\nUsing the periodic Harper and Hofstadter models to illustrate our method, we\nfind that, on increasing the impurity strength, edge states can enter or exit\nthe continuum, and a trivial Shockley state bound to the impurity may appear.\nThe fate of the topological edge modes in the presence of impurities can be\naddressed by quenching the impurity strength. We find that at certain critical\nimpurity strengths, the transition probability for a particle initially\nprepared in an edge mode to decay into the bulk exhibits discontinuities that\nmark the entry and exit points of edge modes from and into the bulk spectrum."
    },
    {
        "anchor": "Dynamical formation of quantum droplets in a $^{39}$K mixture: We report on the dynamical formation of self-bound quantum droplets in\nattractive mixtures of $^{39}$K atoms. Considering the experimental\nobservations of Semeghini et al., Phys. Rev. Lett. 120, 235301 (2018), we\nperform numerical simulations to understand the relevant processes involved in\nthe formation of a metastable droplet from an out-of-equilibrium mixture. We\nfirst analyze the so-called self-evaporation mechanism, where the droplet\ndissipates energy by releasing atoms, and then we consider the effects of\nlosses due to three-body recombinations and to the balancing of populations in\nthe mixture. We discuss the importance of these three mechanisms in the\nobserved droplet dynamics and their implications for future experiments.",
        "positive": "Observation of interspecies Li-Cs Feshbach resonances: We report on the observation of nineteen interspecies Feshbach resonances in\nan optically trapped ultracold Bose-Fermi mixture of ^{133}Cs and ^{6}Li in the\ntwo energetically lowest spin states. We assign the resonances to s- and p-wave\nmolecular channels by a coupled-channels calculation, resulting in an accurate\ndetermination of LiCs ground state potentials. Fits of the resonance position\nbased on the undressed Asymptotic Bound State model do not provide the same\nlevel of accuracy as the coupled-channels calculation. Several broad s-wave\nresonances provide prospects to create fermionic LiCs molecules with a large\ndipole moment via Feshbach association followed by stimulated Raman passage.\nTwo of the s-wave resonances overlap with a zero crossing of the Cs scattering\nlength which offers prospects for the investigation of polarons in an ultracold\nLi-Cs mixture."
    },
    {
        "anchor": "Interplay of phase separation and itinerant magnetism for correlated few\n  fermions in a double-well: We explore the stability of the phase separation phenomenon in few-fermion\nspin-$1/2$ systems confined in a double-well potential. It is shown that within\nthe SU(2) symmetric case, where the total spin is conserved, the phase\nseparation cannot be fully stabilized. An interaction regime characterized by\nmetastable phase separation emerges for intermediate interactions which is\ninherently related with ferromagnetic spin-spin correlations emanating within\neach of the wells. The breaking of the SU(2) symmetry crucially affects the\nstability properties of the system as the phase separated state can be\nstabilized even for weak magnetic potential gradients. Our results imply an\nintricate relation between the phenomena of phase separation and ferromagnetism\nthat lies beyond the view of the Stoner instability.",
        "positive": "Two-species Bose-Einstein condensate in an optical lattice: analytical\n  approximate formul\u00e6: Employing a general variational method and perturbation theory, we derived\nexplicit solutions for the description of one-dimensional two species\nBose-Einstein condensates confined by a harmonic trap potential in an optical\nlattice. We consider the system of two coupled Gross-Pitaevkii equations (GPE)\nand derive explicit expressions for the chemical potentials and wavefunctions\nin terms of the atom-atom interaction parameters and laser intensity. We have\ncompared our results with the numerical solutions of the GPE and performed a\nquantitative analysis for the both considered methods. We underline the\nimportance of the obtained explicit solutions to characterize the density\nprofile or degree of miscibility of the two components."
    },
    {
        "anchor": "Emergent devil's staircase without particle-hole symmetry in Rydberg\n  quantum gases with competing attractive and repulsive interactions: The devil's staircase is a fractal structure that characterizes the ground\nstate of one-dimensional classical lattice gases with long-range repulsive\nconvex interactions. Its plateaus mark regions of stability for specific\nfilling fractions which are controlled by a chemical potential. Typically such\nstaircase has an explicit particle-hole symmetry, i.e., the staircase at more\nthan half-filling can be trivially extracted from the one at less than half\nfilling by exchanging the roles of holes and particles. Here we introduce a\nquantum spin chain with competing short-range attractive and long-range\nrepulsive interactions, i.e. a non-convex potential. In the classical limit the\nground state features generalized Wigner crystals that --- depending on the\nfilling fraction --- are either composed of dimer particles or dimer holes\nwhich results in an emergent complete devil's staircase without explicit\nparticle-hole symmetry of the underlying microscopic model. In our system the\nparticle-hole symmetry is lifted due to the fact that the staircase is\ncontrolled through a two-body interaction rather than a one-body chemical\npotential. The introduction of quantum fluctuations through a transverse field\nmelts the staircase and ultimately makes the system enter a paramagnetic phase.\nFor intermediate transverse field strengths, however, we identify a region,\nwhere the density-density correlations suggest the emergence of quasi\nlong-range order. We discuss how this physics can be explored with\nRydberg-dressed atoms held in a lattice.",
        "positive": "Optimal control for unitary preparation of many-body states: application\n  to Luttinger liquids: Many-body ground states can be prepared via unitary evolution in cold atomic\nsystems. Given the initial state and a fixed time for the evolution, how close\ncan we get to a desired ground state if we can tune the Hamiltonian in time?\nHere we study this optimal control problem focusing on Luttinger liquids with\ntunable interactions. We show that the optimal protocol can be obtained by\nsimulated annealing. We find that the optimal interaction strength of the\nLuttinger liquid can have a nonmonotonic time dependence. Moreover, the system\nexhibits a marked transition when the ratio $\\tau/L$ of the preparation time to\nthe system size exceeds a critical value. In this regime, the optimal protocols\ncan prepare the states with almost perfect accuracy. The optimal protocols are\nrobust against dynamical noise."
    },
    {
        "anchor": "Time-Resolved Observation of Spin-Charge Deconfinement in Fermionic\n  Hubbard Chains: Elementary particles such as the electron carry several quantum numbers, for\nexample, charge and spin. However, in an ensemble of strongly interacting\nparticles, the emerging degrees of freedom can fundamentally differ from those\nof the individual constituents. Paradigmatic examples of this phenomenon are\none-dimensional systems described by independent quasiparticles carrying either\nspin (spinon) or charge (holon). Here we report on the dynamical deconfinement\nof spin and charge excitations in real space following the removal of a\nparticle in Fermi-Hubbard chains of ultracold atoms. Using space- and\ntime-resolved quantum gas microscopy, we track the evolution of the excitations\nthrough their signatures in spin and charge correlations. By evaluating\nmulti-point correlators, we quantify the spatial separation of the excitations\nin the context of fractionalization into single spinons and holons at finite\ntemperatures.",
        "positive": "Emergence of continuous rotational symmetries in ultracold atoms coupled\n  to optical cavities: We investigate the physics of a gas of ultracold atoms coupled to three\nsingle-mode optical cavities and transversely pumped with a laser. Recent work\nhas demonstrated that, for two cavities, the $\\mathbb{Z}_{2}$ symmetries of\neach cavity can be combined into a global $U(1)$ symmetry. Here, we show that\nwhen adding an extra cavity mode, the low-energy description of this system can\nadditionally exhibit an $SO(3)$ rotational symmetry which can be spontaneously\nbroken. This leads to a superradiant phase transition in all the cavities\nsimultaneously, and the appearance of Goldstone and amplitude modes in the\nexcitation spectrum. We determine the phase diagram of the system, which shows\nthe emergence and breaking of the continuous symmetries and displays first- and\nsecond-order phase transitions. We also obtain the excitation spectrum for each\nphase and discuss the atomic self-organized structures that emerge in the\ndifferent superradiant phases. We argue that coupling the atoms equally to $n$\ndifferent modes will in general generate a global $SO(n)$ symmetry if the mode\nfrequencies can be tuned to the same value."
    },
    {
        "anchor": "Ramifications of topology and thermal fluctuations in quasi-2D\n  condensates: We explore the topological transformation of quasi-2D Bose-Einstein\ncondensates of dilute atomic gases, and changes in the low-energy\nquasiparticles associated with the geometry of the confining potential. In\nparticular, we show the density profile of the condensate and quantum\nfluctuation follow the transition from a multiply to a simply connected\ngeometry of the confining potential. The thermal fluctuations, in contrast,\nremain multiply connected. The genesis of the key difference lies in the\nstructure of the low-energy quasiparticles. For which we use the\nHartree-Fock-Bogoliubov, and study the evolution of quasiparticles, the dipole\nor the Kohn mode in particular. We, then employ the Hartree-Fock-Bogoliubov\ntheory with the Popov approximation to investigate the density and the momentum\ndistribution of the thermal atoms.",
        "positive": "Dynamical Control in a Quasi-periodically Modulated Optical Lattice: We investigate quantum tunneling phenomena for an optical lattice subjected\nto a bichromatic ac force. We show that incommensurability of the frequencies\nleads to super Bloch oscillation. We propose directed super Bloch oscillation\nfor the quasi periodically driven optical lattice. We study the dynamical\nlocalization and photon assisted tunneling for a periodical and\nquasi-periodical ac force."
    },
    {
        "anchor": "Spatial entanglement in interacting Bose-Einstein condensates: The entanglement between spatial regions in an interacting Bose-Einstein\ncondensate is investigated using a quantum field theoretic formalism. Regions\nthat are small compared to the healing length are governed by a\nnon-relativistic quantum field theory in the vacuum limit, and we show that the\nlatter has vanishing entanglement. In the opposite limit of a region that is\nlarge compared to the healing length, the entanglement entropy is like in the\nvacuum of a relativistic theory where the velocity of light is replaced with\nthe velocity of sound and where the inverse healing length provides a natural\nultraviolet regularization scale. Besides the von Neumann entanglement entropy,\nwe also calculate R\\'enyi entanglement entropies for a one-dimensional\nquasi-condensate.",
        "positive": "Competing Supersolid and Haldane Insulator phases in the extended\n  one-dimensional bosonic Hubbard model: The Haldane Insulator is a gapped phase characterized by an exotic non-local\norder parameter. The parameter regimes at which it might exist, and how it\ncompetes with alternate types of order, such as supersolid order, are still\nincompletely understood. Using the Stochastic Green Function (SGF) quantum\nMonte Carlo (QMC) and the Density Matrix Renormalization Group (DMRG), we study\nnumerically the ground state phase diagram of the one-dimensional bosonic\nHubbard model (BHM) with contact and near neighbor repulsive interactions. We\nshow that, depending on the ratio of the near neighbor to contact interactions,\nthis model exhibits charge density waves (CDW), superfluid (SF), supersolid\n(SS) and the recently identified Haldane insulating (HI) phases. We show that\nthe HI exists only at the tip of the unit filling CDW lobe and that there is a\nstable SS phase over a very wide range of parameters."
    },
    {
        "anchor": "Spin squeezing: transforming one-axis-twisting into two-axis-twisting: Squeezed spin states possess unique quantum correlation or entanglement that\nare of significant promises for advancing quantum information processing and\nquantum metrology. In recent back to back publications [C. Gross \\textit{et al,\nNature} \\textbf{464}, 1165 (2010) and Max F. Riedel \\textit{et al, Nature}\n\\textbf{464}, 1170 (2010)], reduced spin fluctuations are observed leading to\nspin squeezing at -8.2dB and -2.5dB respectively in two-component atomic\ncondensates exhibiting one-axis-twisting interactions (OAT). The noise\nreduction limit for the OAT interaction scales as $\\propto 1/{N^{2/3}}$, which\nfor a condensate with $N\\sim 10^3$ atoms, is about 100 times below standard\nquantum limit. We present a scheme using repeated Rabi pulses capable of\ntransforming the OAT spin squeezing into the two-axis-twisting type, leading to\nHeisenberg limited noise reduction $\\propto 1/N$, or an extra 10-fold\nimprovement for $N\\sim 10^3$.",
        "positive": "Static structure factors for a spin-1 Bose-Einstein condensate: We consider the total density and spin density fluctuations of a uniform\nspin-1 Bose-Einstein condensate within the Bogoliubov formalism. We present\nresults for the total density and spin density static structure factors for all\nfour magnetic phases. A key result of our work is a set of analytic predictions\nfor the structure factors in the large and small momentum limits. These results\nwill be useful in current experiments aiming to develop a better understanding\nof the excitations and fluctuations of spinor condensates."
    },
    {
        "anchor": "Synergy Dynamics of Vortices and Solitons in Atomic Bose-Einstein\n  Condensate Excited by an Oscillating Potential: The hydrodynamics of quantized vortices and solitons in an atomic\nBose-Einstein condensate excited by an oscillating potential are studied by\nnumerically solving the two-dimensional Gross-Pitaevskii equation. The\noscillating potential keeps nucleating vortex dipoles, whose impulses\nalternatively change their direction synchronously with the oscillation of the\npotential. This leads to synergy dynamics of vortices and solitons which have\nnot been previously reported in quantum fluids.",
        "positive": "Observation of the supersolid stripe phase in spin-orbit coupled\n  Bose-Einstein condensates: Supersolidity is an intriguing concept. It combines the property of\nsuperfluid flow with the long-range spatial periodicity of solids, two\nproperties which are often mutually exclusive. The original discussion of\nquantum crystals and supersolidity focuses on solid Helium-4 where it was\npredicted that vacancies could form dilute weakly interacting Bose-Einstein\ncondensates. In this system, direct observation of supersolidity has been\nelusive. The concept of supersolidity was then generalized to include other\nsuperfluid systems which break the translational symmetry of space. One of such\nsystems is a Bose-Einstein condensate with spin-orbit coupling which has a\nsupersolid stripe phase. Despite several recent studies of this system, the\nstripe phase has not been observed. Here we report the direct observation of\nthe predicted density modulation of the stripe phase using Bragg reflection.\nOur work establishes a system with unique symmetry breaking properties. Of\nfuture interest is further spatial symmetry breaking through the introduction\nof vortices, solitons, impurities or disorder."
    },
    {
        "anchor": "Expansion of 1D polarized superfluids: The FFLO state reveals itself: We study the expansion dynamics of a one dimensional polarized Fermi gas\nafter sudden release from confinement using both the mean-field Bogoliubov-de\nGennes and the numerically exact Time-Evolving Block Decimation methods. Our\nresults show that experimentally observable spin density modulations directly\nrelated to the presence of a Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) state\ndevelop during the expansion of the cloud, providing incontrovertible evidence\nof this long-sought state.",
        "positive": "Pattern formation of quantum Kelvin-Helmholtz instability in binary\n  superfluids: We study theoretically nonlinear dynamics induced by shear-flow instability\nin segregated two-component Bose-Einstein condensates in terms of the Weber\nnumber, defined by extending the past theory on the Kelvin-Helmholtz\ninstability in classical fluids. Numerical simulations of the Gross-Pitaevskii\nequations demonstrate that dynamics of pattern formation is well characterized\nby the Weber number $We$, clarifying the microscopic aspects unique to the\nquantum fluid system. For $We \\lesssim 1$, the Kelvin-Helmholtz instability\ninduces flutter-finger patterns of the interface and quantized vortices are\ngenerated at the tip of the fingers. The associated nonlinear dynamics exhibits\na universal behavior with respect to $We$. When $We \\gtrsim 1$ in which the\ninterface thickness is larger than the wavelength of the interface mode, the\nnonlinear dynamics is effectively initiated by the counter-superflow\ninstability. In a strongly segregated regime and a large relative velocity, the\ninstability causes transient zipper pattern formation instead of generating\nvortices due to the lack of enough circulation to form a quantized vortex per a\nfinger. While, in a weakly segregating regime and a small relative velocity,\nthe instability leads to sealskin pattern in the overlapping region, in which\nthe frictional relaxation of the superflow cannot be explained only by the\nhomogeneous counter-superflow instability. We discuss the details of the linear\nand nonlinear characteristics of this dynamical crossover from small to large\nWeber numbers, where microscopic properties of the interface become important\nfor the large Weber number."
    },
    {
        "anchor": "Bichromatic State-Insensitive Trapping of Cold 133Cs-87Rb Atomic\n  Mixtures: We investigate simultaneous state-insensitive trapping of a mixture of two\ndifferent atomic species, Caesium and Rubidium. The magic wavelengths of the\nCaesium and Rubidium atoms are different, $935.6$ nm and $789.9$ nm\nrespectively, thus single-frequency simultaneous state-insensitive trapping is\nnot possible. We thus identify bichromatic trapping as a viable approach to\ntune the two magic wavelengths to a common value. Correspondingly, we present\nseveral common magic wavelength combinations appropriate for simultaneous\nstate-insensitive trapping of the two atomic species.",
        "positive": "The Peierls substitution in an engineered lattice potential: Artificial gauge fields open new possibilities to realize quantum many-body\nsystems with ultracold atoms, by engineering Hamiltonians usually associated\nwith electronic systems. In the presence of a periodic potential, artificial\ngauge fields may bring ultracold atoms closer to the quantum Hall regime. Here,\nwe describe a one-dimensional lattice derived purely from effective\nZeeman-shifts resulting from a combination of Raman coupling and radiofrequency\nmagnetic fields. In this lattice, the tunneling matrix element is generally\ncomplex. We control both the amplitude and the phase of this tunneling\nparameter, experimentally realizing the Peierls substitution for ultracold\nneutral atoms."
    },
    {
        "anchor": "Universality and itinerant ferromagnetism in rotating strongly\n  interacting Fermi gases: We analytically determine the properties of three interacting fermions in a\nharmonic trap subject to an external rotation. Thermodynamic quantities such as\nthe entropy and energy are calculated from the third order quantum virial\nexpansion. By parameterizing the solutions in the rotating frame we find that\nthe energy and entropy are universal for all rotations in the strongly\ninteracting regime. Additionally, we find that rotation suppresses the onset of\nitinerant ferromagnetism in strongly interacting repulsive three-body systems.",
        "positive": "Non-equilibrium steady states of ideal bosonic and fermionic quantum\n  gases: We investigate non-equilibrium steady states of driven-dissipative ideal\nquantum gases of both bosons and fermions. We focus on systems of sharp\nparticle number that are driven out of equilibrium either by the coupling to\nseveral heat baths of different temperature or by time-periodic driving in\ncombination with the coupling to a heat bath. Within the framework of\n(Floquet-)Born-Markov theory, several analytical and numerical methods are\ndescribed in detail. This includes a mean-field theory in terms of occupation\nnumbers, an augmented mean-field theory taking into account also non-trivial\ntwo-particle correlations, and quantum-jump-type Monte-Carlo simulations. For\nthe case of the ideal Fermi gas, these methods are applied to simple lattice\nmodels and the possibility of achieving exotic states via bath engineering is\npointed out. The largest part of this work is devoted to bosonic quantum gases\nand the phenomenon of Bose selection, a non-equilibrium generalization of Bose\ncondensation, where multiple single-particle states are selected to acquire a\nlarge occupation [Phys. Rev. Lett. 111, 240405 (2013)]. In this context, among\nothers, we provide a theory for transitions where the set of selected states\nchanges, describe an efficient algorithm for finding the set of selected\nstates, investigate beyond-mean-field effects, and identify the dominant\nmechanisms for heat transport in the Bose selected state."
    },
    {
        "anchor": "Dynamical preparation of stripe states in spin-orbit coupled gases: In spinor Bose-Einstein condensates, spin-changing collisions are a\nremarkable proxy to coherently realize macroscopic many-body quantum states.\nThese processes have been, e.g., exploited to generate entanglement, to study\ndynamical quantum phase transitions, and proposed for realizing nematic phases\nin atomic condensates. In the same systems dressed by Raman beams, the coupling\nbetween spin and momentum induces a spin dependence in the scattering processes\ntaking place in the gas. Here we show that, at weak couplings, such modulation\nof the collisions leads to an effective Hamiltonian which is equivalent to the\none of an artificial spinor gas with spin-changing collisions that are tunable\nwith the Raman intensity. By exploiting this dressed-basis description, we\npropose a robust protocol to coherently drive the spin-orbit coupled condensate\ninto the ferromagnetic stripe phase via crossing a quantum phase transition of\nthe effective low-energy model in an excited-state.",
        "positive": "Evolution of static and dynamical density correlations in a\n  one-dimensional soft-core gas from the Tonks-Girardeau limit to a clustering\n  fluid: Repulsive soft-core atomic systems may undergo clustering if their density is\nhigh enough that core overlap is unavoidable. In one-dimensional quantum\nsystems, it has been shown that this instability triggers a transition from a\nLuttinger liquid to various cluster Luttinger liquids. Here, we focus on the\nLuttinger liquid regime and theoretically study the evolution of key\nobservables related to density fluctuations, that manifest a striking\ndependence on density. We tune the interaction so that the low-density regime\ncorresponds to a Tonks-Girardeau gas, and show that as the density is increased\nthe system departs more and more from Tonks-Girardeau behavior, displaying a\nmuch larger compressibility as well as rotonic excitations that finally drive\nthe clustering transition. We compare various theoretical approaches, which are\naccurate in different regimes. Using quantum Monte Carlo methods and analytic\ncontinuation as a benchmark, we investigate the regime of validity of the\nmean-field Bogoliubov and the real-time multiconfiguration time-dependent\nHartree-Fock approaches. Part of the behavior that we describe should be\nobservable in ultracold Rydberg-dressed gases, provided that system losses are\nprevented."
    },
    {
        "anchor": "Phase Retrieval of Vortices in Bose-Einstein Condensates: We propose and demonstrate numerically a measurement scheme for complete\nreconstruction of the quantum wavefunctions of Bose-Einstein condensates,\namplitude and phase, from a time of flight measurement. We identify a\nfundamental ambiguity present in the measurement of vortices and show how to\novercome it by augmenting the measurement to allow reconstruction of\nmatter-wave vortices and arrays of vortices.",
        "positive": "A high-flux 2D MOT source for cold lithium atoms: We demonstrate a novel 2D MOT beam source for cold 6Li atoms. The source is\nside-loaded from an oven operated at temperatures in the range 600<T<700 K. The\nperformance is analyzed by loading the atoms into a 3D MOT located 220 mm\ndownstream from the source. The maximum recapture rate of ~10^9 /s is obtained\nfor T=700 K and results in a total of up to 10^10 trapped atoms. The recaptured\nfraction is estimated to be 30(10)% and limited by beam divergence. The\nmost-probable velocity in the beam (alpha_z) is varied from 18 to 70 m/s by\nincreasing the intensity of a push beam. The source is quite monochromatic with\na full-width at half maximum velocity spread of 11 m/s at alpha_z=36 m/s,\ndemonstrating that side-loading completely eliminates beam contamination by hot\nvapor from the oven. We identify depletion of the low-velocity tail of the oven\nflux as the limiting loss mechanism. Our approach is suitable for other atomic\nspecies."
    },
    {
        "anchor": "Quasi-condensation of bilayer excitons in a periodic potential: We study two-dimensional excitons confined in a lattice potential, for high\nfillings of the lattice sites. We show that a quasi-condensate is possibly\nformed for small values of the lattice depth, but for larger ones the critical\nphase-space density for quasi-condensation rapidly exceeds our experimental\nreach, due to the increase of the excitons effective mass. On the other hand,\nin the regime of a deep lattice potential where excitons are strongly localised\nat the lattice sites, we show that an array of phase-independent\nquasi-condensates, different from a Mott insulating phase, is realised.",
        "positive": "Chaos and quantum scars in Bose-Josephson junction coupled to a bosonic\n  mode: We consider a model describing Bose-Josephson junction (BJJ) coupled to a\nsingle bosonic mode exhibiting quantum phase transition (QPT). Onset of chaos\nabove QPT is observed from semiclassical dynamics as well from spectral\nstatistics. Based on entanglement entropy we analyze the ergodic behavior of\neigenstates with increasing energy density which also reveals the influence of\ndynamical steady state known as $\\pi$-mode on it. We identify the imprint of\nunstable $\\pi$-oscillation as many body quantum scar (MBQS), which leads to the\ndeviation from ergodicity and quantify the degree of scarring. Persistence of\nphase coherence in nonequilibrium dynamics of such initial state corresponding\nto the $\\pi$-mode is an observable signature of MBQS which has relevance in\nexperiments on BJJ."
    },
    {
        "anchor": "Resonances in non-universal dipolar collisions: Scattering resonances due to the dipole-dipole interaction between ultracold\nmolecules, induced by static or microwave fields, are studied theoretically. We\ndevelop a method for coupled-channel calculations that can efficiently impose\nmany short-range boundary conditions, defined by a short-range phase shift and\nloss probability as in quantum-defect theory. We study how resonances appear as\nthe short-range loss probability is lowered below the universal unit\nprobability. This may become realizable for nonreactive ultracold molecules in\nblue-detuned box potentials.",
        "positive": "Bloch Oscillations Along a Synthetic Dimension of Atomic Trap States: Synthetic dimensions provide a powerful approach for simulating condensed\nmatter physics in cold atoms and photonics, whereby a set of discrete degrees\nof freedom are coupled together and re-interpreted as lattice sites along an\nartificial spatial dimension. However, atomic experimental realisations have\nbeen limited so far by the number of artificial lattice sites that can be\nfeasibly coupled along the synthetic dimension. Here, we experimentally realise\nfor the first time a very long and controllable synthetic dimension of atomic\nharmonic trap states. To create this, we couple trap states by dynamically\nmodulating the trapping potential of the atomic cloud with patterned light. By\ncontrolling the detuning between the frequency of the driving potential and the\ntrapping frequency, we implement a controllable force in the synthetic\ndimension. This induces Bloch oscillations in which atoms move periodically up\nand down tens of atomic trap states. We experimentally observe the key\ncharacteristics of this behaviour in the real space dynamics of the cloud, and\nverify our observations with numerical simulations and semiclassical theory.\nThis experiment provides an intuitive approach for the manipulation and control\nof highly-excited trap states, and sets the stage for the future exploration of\ntopological physics in higher dimensions."
    },
    {
        "anchor": "Crossover in the dynamical critical exponent of a quenched\n  two-dimensional Bose gas: We study the phase ordering dynamics of a uniform Bose gas in two dimensions\nfollowing a quench into the ordered phase. We explore the crossover between\ndissipative and conservative evolution by performing numerical simulations\nwithin the classical field methodology. Regardless of the dissipation strength,\nwe find clear evidence for universal scaling, with dynamical critical exponent\n$z$ characterising the growth of the correlation length. In the dissipative\nlimit we find growth consistent with the logarithmically corrected law\n$[t/\\log(t/t_0)]^{1/z}$, and exponent $z=2$, in agreement with previous\nstudies. Decreasing the dissipation towards the conservative limit, we find\nstrong numerical evidence for the expected growth law $t^{1/z}$. However, we\nobserve a smooth crossover in $z$ that converges to an anomalous value\ndistinctly lower than $2$ at a small finite dissipation strength. We show that\nthis lower exponent may be attributable to a power-law vortex mobility arising\nfrom vortex--sound interactions.",
        "positive": "Normal-state Properties of a Unitary Bose-Fermi Mixture: A Combined\n  Strong-coupling Approach with Universal Thermodynamics: We theoretically investigate normal-state properties of a unitary Bose-Fermi\nmixture. Including strong hetero-pairing fluctuations, we evaluate the Bose and\nFermi chemical potential, internal energy, pressure, entropy, as well as\nspecific heat at constant volume $C_V$, within the framework of a combined\nstrong-coupling theory with exact thermodynamic identities. We show that\nhetero-pairing fluctuations at the unitarity cause non-monotonic temperature\ndependence of $C_V$, being qualitatively different from the monotonic behavior\nof this quantity in the weak- and strong-coupling limit. On the other hand,\nsuch an anomalous behavior is not seen in the other quantities. Our results\nindicate that the specific heat $C_V$, which has recently become observable in\ncold atom physics, is a useful quantity for understanding strong-coupling\naspects of this quantum system."
    },
    {
        "anchor": "Discrete nature of thermodynamics in confined ideal Fermi gases: Intrinsic discrete nature in thermodynamic properties of Fermi gases appears\nunder strongly confined and degenerate conditions. For a rectangular\nconfinement domain, thermodynamic properties of an ideal Fermi gas are\nexpressed in their exact summation forms. For 1D, 2D and 3D nano domains,\nvariations of both number of particles and internal energy per particle with\nchemical potential are examined. It is shown that their relation with chemical\npotential exhibits a discrete nature which allows them to take only some\ndefinite values. Furthermore, quasi-irregular oscillatory-like sharp peaks are\nobserved in heat capacity. New nano devices can be developed based on these\nbehaviors.",
        "positive": "Optimal temperature estimation in polariton Bose-Einstein Condensate: Improving the measurement precision of temperature is very important and\nchallenging, especially in the low temperature range. Based on the existence of\ninvariant subspaces during the polariton thermalization, we propose a new way\nto enhance the measurement precision of the low temperature and obtain Landau\nbound to avoid that the measurement uncertainty of the temperature diverges as\nthe temperature approaches zero. The measurement precision of the low\ntemperature increases significantly with the number of polariton states. In\norder to resist the dissipation, the incoherent pumping is necessary for\nobtaining the information of the temperature encoded in the steady state. It\nshould be noted that too strong incoherent pumping is wasteful due to that the\nquantum Fisher information of the temperature becomes less and less dependent\non the total number of the polaritons."
    },
    {
        "anchor": "Phases of a 2D Bose Gas in an Optical Lattice: Ultra-cold atoms in optical lattices realize simple, fundamental models in\ncondensed matter physics. Our 87Rb Bose-Einstein condensate is confined in a\nharmonic trapping potential to which we add an optical lattice potential. Here\nwe realize the 2D Bose-Hubbard Hamiltonian and focus on the effects of the\nharmonic trap, not present in bulk condensed matter systems. By measuring\ncondensate fraction we identify the transition from superfluid to Mott\ninsulator as a function of atom density and lattice depth. Our results are in\nexcellent agreement with the quantum Monte Carlo universal state diagram,\nsuitable for trapped systems, introduced by Rigol et al. (Phys. Rev. A 79,\n053605 (2009)).",
        "positive": "Ultra-cold Polarized Fermi Gases: Recent experiments with ultra-cold atoms have demonstrated the possibility of\nrealizing experimentally fermionic superfluids with imbalanced spin\npopulations. We discuss how these developments have shed a new light on a half-\ncentury old open problem in condensed matter physics, and raised new\ninterrogations of their own."
    },
    {
        "anchor": "From Anderson to anomalous localization in cold atomic gases with\n  effective spin-orbit coupling: We study the dynamics of a one-dimensional spin-orbit coupled Schrodinger\nparticle with two internal components moving in a random potential. We show\nthat this model can be implemented by the interaction of cold atoms with\nexternal lasers and additional Zeeman and Stark shifts. By direct numerical\nsimulations a crossover from an exponential Anderson-type localization to an\nanomalous power-law behavior of the intensity correlation is found when the\nspin-orbit coupling becomes large. The power-law behavior is connected to a\nDyson singularity in the density of states emerging at zero energy when the\nsystem approaches the quasi-relativistic limit of the random mass Dirac model.\nWe discuss conditions under which the crossover is observable in an experiment\nwith ultracold atoms and construct explicitly the zero-energy state, thus\nproving its existence under proper conditions.",
        "positive": "Strongly correlated Fermions strongly coupled to light: Strong quantum correlations in matter are responsible for some of the most\nextraordinary properties of material, from magnetism to high-temperature\nsuperconductivity, but their integration in quantum devices requires a strong,\ncoherent coupling with photons, which still represents a formidable technical\nchallenge in solid state systems. In cavity quantum electrodynamics, quantum\ngases such as Bose-Einstein condensates or lattice gases have been strongly\ncoupled with light. However, neither Fermionic quantum matter, comparable to\nelectrons in solids, nor atomic systems with controlled interactions, have thus\nfar been strongly coupled with photons. Here we report on the strong coupling\nof a quantum-degenerate unitary Fermi gas with light in a high finesse cavity.\nWe map out the spectrum of the coupled system and observe well resolved dressed\nstates, resulting from the strong coupling of cavity photons with each spin\ncomponent of the gas. We investigate spin-balanced and spin-polarized gases and\nfind quantitative agreement with ab-initio calculation describing light-matter\ninteraction. Our system offers complete and simultaneous control of atom-atom\nand atom-photon interactions in the quantum degenerate regime, opening a wide\nrange of perspectives for quantum simulation."
    },
    {
        "anchor": "Dissipation-induced instabilities of a spinor Bose-Einstein condensate\n  inside an optical cavity: We investigate the dynamics of a spinor Bose-Einstein condensate inside an\noptical cavity, driven transversely by a laser with a controllable polarization\nangle. We focus on a two-component Dicke model with complex light-matter\ncouplings, in the presence of photon losses. We calculate the steady-state\nphase diagram and find dynamical instabilities in the form of limit cycles,\nheralded by the presence of exceptional points and level attraction. We show\nthat the instabilities are induced by dissipative processes which generate\nnon-reciprocal couplings between the two collective spins. Our predictions can\nbe readily tested in state-of-the-art experiments and open up the study of\nnon-reciprocal many-body dynamics out of equilibrium.",
        "positive": "Competing many-body instabilities in two-dimensional dipolar Fermi gases: Experiments on quantum degenerate Fermi gases of magnetic atoms and dipolar\nmolecules begin to probe their broken symmetry phases dominated by the\nlong-range, anisotropic dipole-dipole interaction. Several candidate phases\nincluding the p-wave superfluid, the stripe density wave, and a supersolid have\nbeen proposed theoretically for two-dimensional spinless dipolar Fermi gases.\nYet the phase boundaries predicted by different approximations vary greatly,\nand a definitive phase diagram is still lacking. Here we present a theory that\ntreats all competing many-body instabilities in the particle-particle and\nparticle-hole channel on equal footing. We obtain the low temperature phase\ndiagram by numerically solving the functional renormalization-group flow\nequations and find a nontrivial density wave phase at small dipolar tilting\nangles and strong interactions, but no evidence of the supersolid phase. We\nalso estimate the critical temperatures of the ordered phases."
    },
    {
        "anchor": "Core sizes and dynamical instabilities of giant vortices in dilute\n  Bose-Einstein condensates: Motivated by a recent demonstration of cyclic addition of quantized vorticity\ninto a Bose-Einstein condensate, the vortex pump, we study dynamical\ninstabilities and core sizes of giant vortices. The core size is found to\nincrease roughly as a square-root function of the quantum number of the vortex,\nwhereas the strength of the dynamical instability either saturates to a fairly\nlow value or increases extremely slowly for large quantum numbers. Our studies\nsuggest that giant vortices of very high angular momenta may be achieved by\ngradually increasing the operation frequency of the vortex pump.",
        "positive": "Post-quench dynamics and pre-thermalization in a resonant Bose gas: We explore the dynamics of a resonant Bose gas following its quench to a\nstrongly interacting regime near a Feshbach resonance. For such deep quenches,\nwe utilize a self-consistent dynamic field approximation and find that after an\ninitial regime of many-body Rabi-like oscillations between the condensate and\nfinite-momentum quasiparticle pairs, at long times, the gas reaches a\npre-thermalized nonequilibrium steady state. We explore the resulting state\nthrough its broad stationary momentum distribution function, that exhibits a\npower-law high momentum tail. We study the dynamics and steady-state form of\nthe associated enhanced depletion, quench-rate dependent excitation energy,\nTan's contact, structure function and radio frequency spectroscopy. We find\nthese predictions to be in a qualitative agreement with recent experiments."
    },
    {
        "anchor": "Quantum Flutter: Signatures and Robustness: We investigate the motion of an impurity particle injected with finite\nvelocity into an interacting one-dimensional quantum gas. Using large-scale\nnumerical simulations based on matrix product states, we observe and\nquantitatively analyze long-lived oscillations of the impurity momentum around\na non-zero saturation value, called quantum flutter. We show that the quantum\nflutter frequency is equal to the energy difference between two branches of\ncollective excitations of the model. We propose an explanation of the finite\nsaturation momentum of the impurity based on the properties of the edge of the\nexcitation spectrum. Our results indicate that quantum flutter exists away from\nintegrability, and provide parameter regions in which it could be observed in\nexperiments with ultracold atoms using currently available technology.",
        "positive": "A general theory of flattened dipolar condensates: We develop theory for a flattened dipolar Bose-Einstein condensate (BEC)\nproduced by harmonic confinement along one direction. The role of both\nshort-ranged contact interactions and long-ranged dipole-dipole interactions\n(DDIs) is considered, and the dipoles are allowed to be polarised along an\narbitrary direction. We discuss the symmetry properties of the condensate and\nthe part of the excitation spectrum determining stability, and introduce two\neffective interaction parameters that allow us to provide a general description\nof the condensate properties, rotons, and stability. We diagonalize the full\ntheory to obtain benchmark results for the condensate and quasiparticle\nexcitations, and characterize the exact mean field stability of the system. We\nprovide a unified formulation for a number of approximate schemes to describe\nthe condensate and quasiparticles, including the standard quasi-two-dimensional\n(quasi-2D) approximation, two kinds of variational ansatz, and a Thomas-Fermi\n(TF) approximation. Some of these schemes have been widely used in the\nliterature despite not being substantiated against the exact theory. We provide\nthis validation and establish the regimes where the various theories perform\nwell."
    },
    {
        "anchor": "Pumping-assisted multistability of exciton-polariton condensates: We investigate the multistability of exciton-polariton condensates excited by\na nonresonant pump. An increase in pumping power moves the system away from\nnon-Hermitian spectral degeneracy towards spectrum splitting through an\nexceptional point, which induces a transition from monostability to\nmultistability. In the region of multistability, the system contains one steady\nand two metastable states. The analyses of stability show that metastable\nstates maintain a finite lifetime and eventually evolve to steady states. A\nsteady state with multi-peak soliton different from general single-peak soliton\nis discovered for attractive polariton-polariton interaction. Moreover, we\ndepict the diagram of the multistability in full parameter space to accurately\nmanipulate the multistability. Our results open up exciting possibilities for\ncontrolling non-Hermitian quantum multistable states, which may be useful to\ndesigning polariton-based devices exploiting optical multistability.",
        "positive": "Measuring Zak phase in room-temperature atoms: Cold atoms provide a flexible platform for synthesizing and characterizing\ntopolog-ical matter, where geometric phases play a central role. However, cold\natoms are intrinsically prone to thermal noise, which can overwhelm the\ntopological response and hamper promised applications. On the other hand,\ngeometric phases also de-termine the energy spectra of particles subjected to a\nstatic force, based on the po-larization relation between Wannier-Stark ladders\nand geometric Zak phases. By exploiting this relation, we develop a method to\nextract geometric phases from en-ergy spectra of room-temperature superradiance\nlattices, which are momentum-space lattices of timed Dicke states. In such\nmomentum-space lattices the thermal motion of atoms, instead of being a source\nof noise, provides effective forces which lead to spectroscopic signatures of\nthe Zak phases. We measure Zak phases direct-ly from the anti-crossings between\nWannier-Stark ladders in the Doppler-broadened absorption spectra of\nsuperradiance lattices. Our approach paves the way of measuring topological\ninvariants and developing their applications in room-temperature atoms."
    },
    {
        "anchor": "Proposal for asymmetric photoemission and tunneling spectroscopies in\n  quantum simulators of the triangular-lattice Fermi-Hubbard model: Recent realization of well-controlled quantum simulators of the\ntriangular-lattice Fermi-Hubbard model, including the triangular optical\nlattices loaded with ultracold Fermions and the heterostructures of the\ntransition-metal dichalcogenides, as well as the more advanced techniques to\nprobe them, pave the way for studying frustrated Fermi-Hubbard physics. Here,\nwe theoretically predict asymmetric photoemission and tunneling spectroscopies\nfor a lightly hole-doped and electron-doped triangular Mott antiferromagnet,\nand reveal two distinct types of magnetic polarons: a \\emph{lightly}\nrenormalized quasiparticle with the same momentum as the spin background and a\n\\emph{heavily} renormalized quasiparticle with a shifted momentum and a nearly\nflat band, using both analytical and unbiased numerical methods. We propose\nthese theoretical findings to be verified in frustrated optical lattices and\nMoir\\'e superlattices by probing various observables including the spectral\nfunction, the density of states, the energy dispersion and the quasiparticle\nweight. Moreover, we reveal the asymmetric response of the spin background\nagainst charge doping, demonstrating that the interplay between the local spin\nand charge degrees of freedom plays a vital role in doped triangular Mott\nantiferromagnets.",
        "positive": "Beyond effective Hamiltonians: micromotion of Bose Einstein condensates\n  in periodically driven optical lattices: We investigate a Bose Einstein condensate held in a 1D optical lattice whose\nphase undergoes a fast oscillation using a statistical analysis. The averaged\npotential experienced by the atoms boils down to a periodic potential having\nthe same spatial period but with a renormalized depth. However, the atomic\ndynamics also contains a \\emph{micromotion} whose main features are revealed by\na Kolmorogov-Smirnov analysis of the experimental momentum distributions. We\nfurthermore discuss the impact of the micromotion on a quench process\ncorresponding to a proper sudden change of the driving amplitude which reverses\nthe curvature of the averaged potential."
    },
    {
        "anchor": "All-optical control of superradiance and matter waves using a dispersive\n  cavity: Cavity quantum electrodynamics (CQED) plays an elegant role of studying\nstrong coupling between light and matter. However, a non-mechanical, direct and\ndynamical control of the used mirrors is still unavailable. Here we\ntheoretically investigate a novel type of dynamically controllable cavity\ncomposed of two atomic mirrors. Based on the electromagnetically induced\ntransparency (EIT), the reflectance of atomic mirror is highly controllable\nthrough its dispersive properties by varying the intensity of applied coupling\nfields or the optical depth of atomic media. To demonstrate the uniqueness of\nthe present cavity, we further show the possibility of manipulating\nvacuum-induced diffraction of a binary Bose-Einstein condensate (BEC) when\nloading it into a dispersive cavity and experiencing superradiant scatterings.\nOur results may provide a novel all-optical element for atom optics and shine\nnew light on controlling light-matter interaction.",
        "positive": "Magnetisms of spinor alkali and alkaline-earth atoms in optical lattices: We theoretically investigate zero-temperature magnetic ordering of mixtures\nof spin-1 (alkali atoms) and spin-0 (alkaline-earth atoms) bosons in a\nthree-dimensional optical lattice. With the single-mode approximation for the\nspin-1 bosons, we obtain an effective Bose-Hubbard model for describing the\nheteronuclear mixtures in optical lattices. By controlling the interspecies\ninteractions between alkali and alkaline-earth atoms, we map out complete phase\ndiagrams of the system with both positive and negative spin-dependent\ninteractions for spin-1 atoms, based on bosonic dynamical mean-field theory. We\nfind that the spin-1 components feature ferromagnetic and nematic insulating\nphases, in addition to the superfluid, depending on spin-dependent\ninteractions. Take the spin-1 alkali bosons as spin $\\uparrow$, and spin-0\nalkaline-earth bosons as spin $\\downarrow$, we observe that the system favors\nferromagnetic insulator at filling $n=1$, and unorder insulator at $n=2$.\nInterestingly, we observe a two-step Mott-insulating-superfluid phase\ntransition, as a result of mass imbalance between alkali and alkaline-earth\natoms."
    },
    {
        "anchor": "Optically Induced Monopoles, Knots, and Skyrmions in Quantum Gases: We propose, and theoretically analyze, a practical protocol for the creation\nof topological monopole configurations, quantum knots, and skyrmions in\nBose--Einstein condensates by employing fictitious magnetic fields induced by\nthe interaction of the atomic cloud with coherent light fields. It is observed\nthat a single coherent field is not enough for this purpose, but instead we\nfind incoherent superpositions of several coherent fields that introduce\ntopological point charges. We numerically estimate the experimentally\nachievable strengths and gradients of the induced fictitious magnetic fields\nand find them to be adjustable at will to several orders of magnitude greater\nthan those of the physical magnetic fields employed in previous experimental\nstudies. This property together with ultrafast control of the optical fields\npaves the way for advanced engineering of topological defects in quantum gases.",
        "positive": "Breakdown of the scale invariance in the vicinity of Tonks-Girardeau gas: In this article, we consider the monopole excitations of the harmonically\ntrapped Bose gas in the vicinity of the Tonks-Girardeau limit. Using\nGirardeau's Fermi-Bose duality and subsequently an effective fermion-fermion\nodd-wave interaction, we obtain the dominant correction to the\nscale-invariance-protected value of the excitation frequency, for\nmicroscopically small excitation amplitudes. We produce a series of diffusion\nMonte Carlo results that confirm our analytic prediction for three particles.\nAnd less expectedly, our result stands in excellent agreement with the result\nof a hydrodynamic simulation of the microscopically large but macroscopically\nsmall excitations."
    },
    {
        "anchor": "Hole-induced anomaly in the thermodynamic behavior of a one-dimensional\n  Bose gas: We reveal an intriguing anomaly in the temperature dependence of the specific\nheat of a one-dimensional Bose gas. The observed peak holds for arbitrary\ninteraction and remembers a superfluid-to-normal phase transition in higher\ndimensions, but phase transitions are not allowed in one dimension. The\npresence of the anomaly signals a region of unpopulated states which behaves as\nan energy gap and is located below the hole branch in the excitation spectrum.\nThe anomaly temperature is found to be of the same order of the energy of the\nmaximum of the hole branch. We rely on the Bethe Ansatz to obtain the specific\nheat exactly and provide interpretations of the analytically tractable limits.\nThe dynamic structure factor is computed with the Path Integral Monte Carlo\nmethod for the first time. We notice that at temperatures similar to the\nanomaly threshold, the energy of the thermal fluctuations become comparable\nwith the maximal hole energy, leading to a qualitative change in the structure\nof excitations. This excitation pattern experiences the breakdown of the\nquasi-particle description for any value of the interaction strength at the\nanomaly, similarly to any superfluid phase transition at the critical\ntemperature. We provide indications for future observations and how the hole\nanomaly can be employed for in-situ thermometry, identifying different\ncollisional regimes and understanding other anomalies in atomic, solid-state,\nelectronic, spin-chain and ladder systems.",
        "positive": "Floquet Spinor Bose Gases: We introduce a Floquet spinor Bose-Einstein condensate induced by a\nperiodically driven quadratic Zeeman coupling whose frequency is larger than\nany other energy scales. By examining a spin-1 system available in ultracold\natomic gases, we demonstrate that such an external driving field has great\neffect on the condensate through emergence of a unique spin-exchange\ninteraction. We uncover that the ferromagnetic condensate has several\nunconventional stationary states and thus exhibits rich continuous phase\ntransitions. On the other hand, the antiferromagnetic condensate is found to\npossess a nontrivial metastable region, which supports unusual elementary\nexcitations and hysteresis phenomena."
    },
    {
        "anchor": "Spin Josephson vortices in two tunnel coupled spinor Bose gases: We study topological excitations in spin-1 Bose-Einstein condensates trapped\nin an elongated double-well optical potential. This system hosts a new\ntopological defect, the spin Josephson vortex (SJV), which forms due to the\ncompetition between the inter-well atomic tunneling and short-range\nferromagnetic two-body interaction. We identify the spin structure and\nformation dynamics of the SJV and determine the phase diagram of the system. By\nexploiting the intrinsic stability of the SJV, we propose a dynamical method to\ncreate SJVs under realistic experimental conditions.",
        "positive": "Three-body losses of repulsively interacting three-component fermionic\n  atoms in optical lattices: We investigate the effects of a repulsive three-body interaction on the Mott\ntransition of the repulsively interacting three-component fermionic atoms in\noptical lattices by means of the self-energy functional approach. We find that\nthe three-body repulsion hardly affects the qualitative features of the Mott\ntransition, because the three-body repulsion does not compete with the two-body\nrepulsions. When the three-body repulsion is extremely strong, the triple\noccupancy vanishes in the Fermi liquid state. This situation is equivalent to\nthat caused by strong three-body losses. Our results imply that three-body\nlosses have little influence on the Mott transitions in the repulsively\ninteracting three-component fermionic atoms in optical lattices."
    },
    {
        "anchor": "Triangular Gross-Pitaevskii breathers and Damski-Chandrasekhar shock\n  waves: The recently proposed map [arXiv:2011.01415] between the hydrodynamic\nequations governing the two-dimensional triangular cold-bosonic breathers\n[Phys. Rev. X 9, 021035 (2019)] and the high-density zero-temperature\ntriangular free-fermionic clouds, both trapped harmonically, perfectly explains\nthe former phenomenon but leaves uninterpreted the nature of the initial\n($t=0$) singularity. This singularity is a density discontinuity that leads, in\nthe bosonic case, to an infinite force at the cloud edge. The map itself\nbecomes invalid at times $t<0$. A similar singularity appears at $t = T/4$,\nwhere $T$ is the period of the harmonic trap, with the Fermi-Bose map becoming\ninvalid at $t > T/4$. Here, we first map -- using the scale invariance of the\nproblem -- the trapped motion to an untrapped one. Then we show that in the new\nrepresentation, the solution [arXiv:2011.01415] becomes, along a ray in the\ndirection normal to one of the three edges of the initial cloud, a freely\npropagating one-dimensional shock wave of a class proposed by Damski in\n[Phys.~Rev.~A 69, 043610 (2004)]. There, for a broad class of initial\nconditions, the one-dimensional hydrodynamic equations can be mapped to the\ninviscid Burgers' equation, which is equivalent to a nonlinear transport\nequation. More specifically, under the Damski map, the $t=0$ singularity of the\noriginal problem becomes, verbatim, the initial condition for the wave\ncatastrophe solution found by Chandrasekhar in 1943 [Ballistic Research\nLaboratory Report No. 423 (1943)]. At $t=T/8$, our interpretation ceases to\nexist: at this instance, all three effectively one-dimensional shock waves\nemanating from each of the three sides of the initial triangle collide at the\norigin, and the 2D-1D correspondence between the solution of [arXiv:2011.01415]\nand the Damski-Chandrasekhar shock wave becomes invalid.",
        "positive": "Anisotropy-driven magnetic phase transitions in SU(4)-symmetric Fermi\n  gas in three-dimensional optical lattices: We study SU(4)-symmetric ultracold fermionic mixture in the cubic optical\nlattice with the variable tunneling amplitude along one particular\ncrystallographic axis in the crossover region from the two- to\nthree-dimensional spatial geometry. To theoretically analyze emerging magnetic\nphases and physical observables, we describe the system in the framework of the\nFermi-Hubbard model and apply dynamical mean-field theory. We show that in two\nlimiting cases of anisotropy there are two phases with different\nantiferromagnetic orderings in the zero temperature limit and determine a\nregion of their coexistence. We also study the stability regions of different\nmagnetically-ordered states and density profiles of the gas in the harmonic\noptical trap."
    },
    {
        "anchor": "Superfluid density and critical velocity near the fermionic\n  Berezinskii-Kosterlitz-Thouless transition: We theoretically investigate superfluidity in a strongly interacting Fermi\ngas confined to two dimensions at finite temperature. Using a Gaussian pair\nfluctuation theory in the superfluid phase, we calculate the superfluid density\nand determine the critical temperature and chemical potential at the\nBerezinskii-Kosterlitz-Thouless transition. We propose that the transition can\nbe unambiguously demonstrated in cold-atom experiments by stirring the\nsuperfluid Fermi gas using a red detuned laser beam, to identify the\ncharacteristic jump in the local Landau critical velocity at the\nsuperfluid-normal interface, as the laser beam moves across the cloud.",
        "positive": "Unconventional superfluidity in quasi-one-dimensional systems: We show that an unconventional superfluid triggered by spin-orbit coupling is\nrealized for repulsively interacting quasi-one-dimensional fermions. A\ncompetition between spin-singlet and -triplet pairings occurs due to the\nbreaking of inversion symmetry. We show that both superfluid correlations decay\nalgebraically with the same exponent except for special coupling constants for\nwhich a dominant superfluid is controlled by the spin-orbit coupling. We also\ndiscuss a possible experiment to observe such phases with cold atoms."
    },
    {
        "anchor": "Schmidt gap in random spin chains: We numerically investigate the low-lying entanglement spectrum of the ground\nstate of random one-dimensional spin chains obtained after partition of the\nchain into two equal halves. We consider two paradigmatic models: the spin-1/2\nrandom transverse field Ising model, solved exactly, and the spin-1 random\nHeisenberg model, simulated using the density matrix renormalization group. In\nboth cases we analyze the mean Schmidt gap, defined as the difference between\nthe two largest eigenvalues of the reduced density matrix of one of the two\npartitions, averaged over many disorder realizations. We find that the Schmidt\ngap detects the critical point very well and scales with universal critical\nexponents.",
        "positive": "Thermodynamics of a weakly interacting Bose gas above the transition\n  temperature: We study thermodynamic properties of weakly interacting Bose gases above the\ntransition temperature of Bose-Einstein condensation in the framework of a\nthermodynamic perturbation theory. Cases of local and non-local interactions\nbetween particles are analyzed both analytically and numerically. We obtain and\ncompare the temperature dependencies for the chemical potential, entropy,\npressure, and specific heat to those of noninteracting gases. The results set\nreliable benchmarks for thermodynamic characteristics and their asymptotic\nbehavior in dilute atomic and molecular Bose gases above the transition\ntemperature."
    },
    {
        "anchor": "Crossing the superfluid-supersolid transition of an elongated dipolar\n  condensate: We provide a theoretical characterization of the dynamical crossing of the\nsuperfluid-supersolid phase transition for a dipolar condensate confined in an\nelongated trap, as observed in the recent experiment by G. Biagioni et al.\n[Phys. Rev. X 12, 021019 (2022)]. By means of the extended Gross-Pitaevskii\ntheory, which includes the Lee-Huang-Yang quantum fluctuation correction, we\nfirst analyze the ground state configurations of the system as a function of\nthe interparticle scattering length, for both trap configurations employed in\nthe experiment. Then, we discuss the effects of the ramp velocity, by which the\nscattering length is tuned across the transition, on the collective excitations\nof the system in both the superfluid and supersolid phases. We find that, when\nthe transverse confinement is sufficiently strong and the transition has a\nsmooth (continuous) character, the system essentially displays a (quasi) 1D\nbehavior, its excitation dynamics being dominated by the axial breathing modes.\nInstead, for shallower transverse trapping, when the transition becomes\ndiscontinuous, the collective excitations of the supersolid display a coupling\nwith the transverse modes, signalling the onset of a dimensional crossover.",
        "positive": "Dynamics of interacting dark soliton stripes: In the present work we examine the statics and dynamics of multiple parallel\ndark soliton stripes in a two-dimensional Bose-Einstein condensate. Our\nprincipal goal is to study the effect of the interaction between the stripes on\nthe transverse instability of the individual stripes. We use a recently\ndeveloped adiabatic invariant formulation to derive a quasi-analytical\nprediction for the stripe equilibrium position and for the Bogoliubov-de Gennes\nspectrum of excitations of stationary stripes. The cases of two-, three- and\nfour-stripe states are studied in detail. We subsequently test our predictions\nagainst numerical simulations of the full two-dimensional Gross-Pitaevskii\nequation. We find that the number of unstable eigenmodes increases as the\nnumber of stripes increases due to (unstable) relative motions between the\nstripes. Their corresponding growth rates do not significantly change, although\nfor large chemical potentials, the larger the stripe number, the larger the\nmaximal instability growth rate. The instability induced dynamics of multiple\nstripe states and their decay into vortices are also investigated."
    },
    {
        "anchor": "Topological spinor vortex matter on spherical surface induced by\n  non-Abelian spin-orbital-angular-momentum coupling: We provide an explicit way to implement non-Abelian\nspin-orbital-angular-momentum (SOAM) coupling in spinor Bose-Einstein\ncondensates using magnetic gradient coupling. For a spherical surface trap\naddressable using high-order Hermite-Gaussian beams, we show that this system\nsupports various degenerate ground states carrying different total angular\nmomenta $\\mathbf{J}$, and the degeneracy can be tuned by changing the strength\nof SOAM coupling. For weakly interacting spinor condensates with $f=1$, the\nsystem supports various meta-ferromagnetic phases and meta-polar states\ndescribed by quantized total mean angular momentum $|\\langle \\mathbf{J}\n\\rangle|$. Polar states with $Z_2$ symmetry and Thomson lattices formed by\ndefects of spin vortices are also discussed. The system can be used to prepare\nvarious stable spin vortex states with nontrivial topology, and serve as a\nplatform to investigate strong-correlated physics of neutral atoms with tunable\nground-state degeneracy.",
        "positive": "Laser assisted tunneling in a Tonks-Girardeau gas: We investigate the applicability of laser assisted tunneling in a strongly\ninteracting one-dimensional Bose gas (the Tonks-Girardeau gas) in optical\nlattices. We find that the stroboscopic dynamics of the Tonks-Girardeau gas in\na continuous Wannier-Stark-ladder potential, supplemented with laser assisted\ntunneling, effectively realizes the ground state of one-dimensional hard-core\nbosons in a discrete lattice with nontrivial hopping phases. We compare\nobservables that are affected by the interactions, such as the momentum\ndistribution, natural orbitals and their occupancies, in the time-dependent\ncontinuous system, to those of the ground state of the discrete system.\nStroboscopically, we find an excellent agreement, indicating that laser\nassisted tunneling is a viable technique for realizing novel ground states and\nphases with hard-core one-dimensional Bose gases."
    },
    {
        "anchor": "Observation of \"broad\" d-wave Feshbach resonances with a triplet\n  structure: High partial-wave ($l\\ge2$) Feshbach resonance (FR) in an ultracold mixture\nof $^{85}$Rb-$^{87}$Rb atoms is investigated experimentally aided by a\npartial-wave insensitive analytic multichannel quantum-defect theory (MQDT).\nTwo \"broad\" resonances from coupling between d-waves in both the open and\nclosed channels are observed and characterized. One of them shows a fully\nresolved triplet structure with splitting ratio well explained by the\nperturbation to the closed channel due to interatomic spin-spin interaction.\nThese tunable \"broad\" d-wave resonances, especially the one in the\nlowest-energy open channel, could find important applications in simulating\nd-wave coupling dominated many-body systems. In addition, we find that there is\ngenerally a time and temperature requirement, associated with tunneling through\nthe angular momentum barrier, to establish and observe resonant coupling in\nnonzero partial waves.",
        "positive": "Dynamical thermalization in Bose-Hubbard systems: We numerically study a Bose-Hubbard ring of finite size with disorder\ncontaining a finite number of bosons that are subject to an on-site two-body\ninteraction. Our results show that moderate interactions induce dynamical\nthermalization in this isolated system. In this regime the individual many-body\neigenstates are well described by the standard thermal Bose-Einstein\ndistribution for well-defined values of the temperature and the chemical\npotential which depend on the eigenstate under consideration. We show that the\ndynamical thermalization conjecture works well both at positive and negative\ntemperatures. The relations to quantum chaos, quantum ergodicity and to the\nAberg criterion are also discussed."
    },
    {
        "anchor": "Quantum phase transition of the Bose-Hubbard model on cubic lattice with\n  anisotropic hopping: In quantum many-body system, dimensionality plays a critical role on type of\nthe quantum phase transition. In order to study the quantum system during\ndimensional crossover, we studied the Bose-Hubbard model on cubic lattice with\nanisotropic hopping by using the high order symbolic strong coupling expansion\nmethod. The analytic series expanded boundaries between the Mott-insulator and\nsuperfluid phase up to eighth order are calculated. The critical exponents are\nextracted by Pad\\'{e} re-summation method, which clearly shows the dimensional\ncrossover behavior. Meanwhile, the critical points at commensurate filling can\nalso be obtained, and they match well with the prediction of renormalization\ngroup theory. The scaling of the gap energy and whole phase diagram are given\nat last, and they can be taken as the benchmark for experiment and numerical\nsimulations in the future study.",
        "positive": "Universal spatiotemporal dynamics of spontaneous superfluidity breakdown\n  in the presence of synthetic gauge fields: According to the famous Kibble-Zurek mechanism (KZM), the universality of\nspontaneous defect generation in continuous phase transitions (CPTs) can be\nunderstood by the critical slowing down. In most CPTs of atomic Bose-Einstein\ncondensates (BECs), the universality of spontaneous defect generations has been\nexplained by the divergent relaxation time associated with the nontrivial\ngapless Bogoliubov excitations. However, for atomic BECs in synthetic gauge\nfields, their spontaneous superfluidity breakdown is resulted from the\ndivergent correlation length associated with the zero Landau critical velocity.\nHere, by considering an atomic BEC ladder subjected to a synthetic magnetic\nfield, we reveal that the spontaneous superfluidity breakdown obeys the KZM.\nThe Kibble-Zurek scalings are derived from the Landau critical velocity which\ndetermines the correlation length. In further, the critical exponents are\nnumerically extracted from the critical spatial-temporal dynamics of the\nbifurcation delay and the spontaneous vortex generation. Our study provides a\ngeneral way to explore and understand the spontaneous superfluidity breakdown\nin CPTs from a single-well dispersion to a double-well one, such as, BECs in\nsynthetic gauge fields, spin-orbit coupled BECs, and BECs in shaken optical\nlattices."
    },
    {
        "anchor": "Topology in the space-time scaling limit of quantum dynamics: We investigate the role of topology in the space-time scaling limit of\nquantum quench dynamics, where both time and system size tend to infinity at a\nconstant ratio. There, while the standard topological characterization relying\non local unitary transformations becomes ill defined, we show how a different\ndynamical notion of topology naturally arises through a dynamical winding\nnumber encoding the linear response of the Berry phase to a magnetic flux.\nSpecifically, we find that the presence of a locally invisible constant\nmagnetic flux is revealed by a dynamical staircase behavior of the Berry phase,\nwhose topologically quantized plateaus characterize the space-time scaling\nlimit of a quenched Rice-Mele model. These jumps in the Berry phase are also\nshown to be related to the interband elements of the DC current operator. We\noutline possible experimental platforms for observing the predicted phenomena\nin finite systems.",
        "positive": "Self-trapping of Fermi and Bose gases under spatially modulated\n  repulsive nonlinearity and transverse confinement: We show that self-localized ground states can be created in the spin-balanced\ngas of fermions with repulsion between the spin components, whose strength\ngrows from the center to periphery, in combination with the harmonic-oscillator\n(HO) trapping potential acting in one or two transverse directions. We also\nconsider the ground state in the non-interacting Fermi gas under the action of\nthe spatially growing tightness of the one- or two-dimensional (1D or 2D) HO\nconfinement. These settings are considered in the framework of the\nThomas-Fermi-von Weizsacker (TF-vW) density functional. It is found that the vW\ncorrection to the simple TF approximation (the gradient term) is nearly\nnegligible in all situations. The properties of the ground state under the\naction of the 2D and 1D HO confinement with the tightness growing in the\ntransverse directions is investigated too for the Bose-Einstein condensate\n(BEC) with the self-repulsive nonlinearity."
    },
    {
        "anchor": "Understanding chemical reactions in a quantum degenerate gas of polar\n  molecules via complex formation: A recent experiment reported for the first time the preparation of a Fermi\ndegenerate gas of polar molecules and observed a suppression of their chemical\nreaction rate compared to the one expected from a purely classical treatment.\nWhile it was hypothesized that the suppression in the ultracold regime had its\nroots in the Fermi statistics of the molecules, this argument is inconsistent\nwith the fact that the Fermi pressure should set a lower bound for the chemical\nreaction rate. Therefore it can not be explained from standard two-body\n$p$-wave inelastic collisions. Here we develop a simple model of chemical\nreactions that occur via the formation and decay of molecular complexes. We\nindeed find that pure two-body molecule losses are unable to explain the\nobserved suppression. Instead we extend our description beyond two-body physics\nby including effective complex-molecule interactions possible emerging from\nmany-body and effective medium effects at finite densities and in the presence\nof trapping light. %Under this framework we observe that additional\ncomplex-molecule collisions, which manifest as a net three-body molecular\ninteraction could give rise to the additional suppression. Although our\neffective model is able to quantitatively reproduce recent experimental\nobservations, a detailed understanding of the actual physical mechanism\nresponsible for these higher-order interaction processes is still pending.",
        "positive": "Fermionic quantum mixtures with tunable interactions: The topic of the present lecture notes are two-species quantum mixtures\ncomposed of a deeply degenerate Fermi gas and a second component, the latter\nbeing fermionic or bosonic. A key ingredient is the possibility to tune the\n$s$-wave interaction between the different species by means of magnetically\ncontrolled Feshbach resonances, which allow us to investigate regimes of strong\ninteractions. In two case studies, we review our experiments on mixtures of\n$^6$Li fermions with fermionic $^{40}$K or bosonic $^{41}$K atoms and on\nmixtures of fermionic $^{161}$Dy with $^{40}$K atoms. We cover various topics\nof fermionic quantum many-body physics, ranging from impurity physics and\nquasiparticles over phase separation to the formation of ultracold molecules\nand progress towards novel superfluids."
    },
    {
        "anchor": "Quantum information theoretic measures to distinguish fermionized bosons\n  from non-interacting fermions: We study the dynamical fermionization of strongly interacting one-dimensional\nbosons in Tonks-Girardeau limit by solving the time dependent many-boson\nSchr\\\"odinger equation numerically exactly. We establish that the one-body\nmomentum distribution approaches the ideal Fermi gas distribution at the time\nof dynamical fermionization. The analysis is further complemented by the\nmeasures on two-body level. Investigation on two-body momentum distribution,\ntwo-body local and non-local correlation clearly distinguish the fermionized\nbosons from non-interacting fermions. The magnitude of distinguishablity\nbetween the two systems is further discussed employing suitable measures of\ninformation theory, i.e., the well known Kullback-Leibler relative entropy and\nthe Jensen-Shannon divergence entropy. We also observe very rich structure in\nthe higher-body density for strongly correlated bosons whereas non-interacting\nfermions do not possess any higher order correlation beyond two-body.",
        "positive": "Energy bands and Landau levels of ultracold fermions in the bilayer\n  honeycomb optical lattice: We investigate the spectrum and eigenstates of ultracold fermionic atoms in\nthe bilayer honeycomb optical lattice. In the low energy approximation, the\ndispersion relation has parabolic form and the quasiparticles are chiral. In\nthe presence of the effective magnetic field, which is created for the system\nwith optical means, the energy spectrum shows an unconventional Landau level\nstructure. Furthermore, the experimental detection of the spectrum is proposed\nwith the Bragg scattering techniques."
    },
    {
        "anchor": "Dipolar Bose-Hubbard Model in finite-size real-space cylindrical\n  lattices: Recent experimental progress in magnetic atoms and polar molecules has\ncreated the prospect of simulating dipolar Hubbard models with off-site\ninteractions. When applied to real-space cylindrical optical lattices, these\nanisotropic dipole-dipole interactions acquire a tunable spatially-dependent\ncomponent while they remain translationally-invariant in the axial direction,\ncreating a sublattice structure in the azimuthal direction. We numerically\nstudy how the coexistence of these classes of interactions affects the ground\nstate of hardcore dipolar bosons at half-filling in a finite-size cylindrical\noptical lattice with octagonal rings. When these two interaction classes\ncooperate, we find a solid state where the density order is determined by the\nazimuthal sublattice structure and builds smoothly as the interaction strength\nincreases. For dipole polarisations where the axial interactions are\nsufficiently repulsive, the repulsion competes with the sublattice structure,\nsignificantly increasing entanglement and creating two distinct ordered density\npatterns. The spatially-varying interactions cause the emergence of these\nordered states in small lattices as a function of interaction strength to be\nstaggered according to the azimuthal sublattices.",
        "positive": "A Coherent Polariton Laser: The semiconductor polariton laser promises a new source of coherent light,\nwhich, compared to conventional semiconductor photon lasers, has input-energy\nthreshold orders of magnitude lower. However, intensity stability, a defining\nfeature of a coherent state, has remained poor. Intensity noise at many times\nof the shot-noise of a coherent state has persisted, which has been attributed\nto multiple mechanisms that are difficult to separate in conventional polariton\nsystems. The large intensity noise in turn limited the phase coherence. These\nlimit the capability of the polariton laser as a source of coherence light.\nHere, we demonstrate a polariton laser with shot-noise limited intensity\nstability, as expected of a fully coherent state. This is achieved by using an\noptical cavity with high mode selectivity to enforce single-mode lasing,\nsuppress condensate depletion, and establish gain saturation. The absence of\nspurious intensity fluctuations moreover enabled measurement of a transition\nfrom exponential to Gaussian decay of the phase coherence of the polariton\nlaser. It suggests large self-interaction energies in the polariton condensate,\nexceeding the laser bandwidth. Such strong interactions are unique to\nmatter-wave laser and important for nonlinear polariton devices. The results\nwill guide future development of polariton lasers and nonlinear polariton\ndevices."
    },
    {
        "anchor": "Numerical method for the stochastic projected Gross-Pitaevskii equation: We present a method for solving the stochastic projected Gross-Pitaevskii\nequation (SPGPE) for a three-dimensional Bose gas in a harmonic-oscillator\ntrapping potential. The SPGPE contains the challenge of both accurately\nevolving all modes in the low energy classical region of the system, and\nevaluating terms from the number-conserving scattering reservoir process. We\ngive an accurate and efficient procedure for evaluating the scattering terms\nusing a Hermite-polynomial based spectral-Galerkin representation, which allows\nus to precisely implement the low energy mode restriction. Stochastic\nintegration is performed using the weak semi-implicit Euler method. We\nextensively characterize the accuracy of our method, finding a faster than\nexpected rate of stochastic convergence. Physical consistency of the algorithm\nis demonstrated by considering thermalization of initially random states.",
        "positive": "Magnetic phases and phase diagram of spin-1 condensate with quadrupole\n  degrees of freedom: We obtain and justify a many-body Hamiltonian of pairwise interacting spin-1\natoms, which includes eight generators of the SU(3) group associated with spin\nand quadrupole degrees of freedom. It is shown that this Hamiltonian is valid\nfor non-local interaction potential, whereas for local interaction specified by\n$s$-wave scattering length, the Hamiltonian should be bilinear in spin\noperators only (of the Heisenberg type). We apply the obtained Hamiltonian to\nstudy the ground-state properties and single-particle excitations of a weakly\ninteracting gas of spin-1 atoms with Bose-Einstein condensate taking into\naccount the quadrupole degrees of freedom. It is shown that the system under\nconsideration can be in ferromagnetic, quadrupolar, and paramagnetic phases.\nThe corresponding phase diagram is constructed and discussed. The main\ncharacteristics such as the density of the grand thermodynamic potential,\ncondensate density, and single-particle excitation spectra modified by\nquadrupole degrees of freedom are determined in different phases."
    },
    {
        "anchor": "Dissipation Induced Structural Instability and Chiral Dynamics in a\n  Quantum Gas: Dissipative and unitary processes define the evolution of a many-body system.\nTheir interplay gives rise to dynamical phase transitions and can lead to\ninstabilities. We discovered a non-stationary state of chiral nature in a\nsynthetic many-body system with independently controllable unitary and\ndissipative couplings. Our experiment is based on a spinor Bose gas interacting\nwith an optical resonator. Orthogonal quadratures of the resonator field\ncoherently couple the Bose-Einstein condensate to two different atomic spatial\nmodes whereas the dispersive effect of the resonator losses mediates a\ndissipative coupling between these modes. In a regime of dominant dissipative\ncoupling we observe the chiral evolution and map it to a positional\ninstability.",
        "positive": "Magnetic phase transition in a mixture of two interacting Bose gases at\n  finite temperature: The miscibility condition for a binary mixture of two interacting\nBose-Einstein condensates is shown to be deeply affected by interaction driven\nthermal fluctuations. These give rise to a first order phase transition to a\ndemixed phase with full spatial separation of the two condensates, even if the\nmixture is miscible at zero temperature. Explicit predictions for the\nisothermal compressibility, the spin susceptibility, and the phase transition\ntemperature $T_M$ are obtained in the framework of Popov theory, which properly\nincludes beyond mean-field quantum and thermal fluctuations in both the spin\nand density channels. For a mixture of two sodium condensates occupying the\nhyperfine states $\\lvert F=1, m_F=1 \\rangle$ and $\\lvert F=1, m_F=-1 \\rangle$\nrespectively, $T_M$ is predicted to occur at about $0.7$ times the usual BEC\ncritical temperature."
    },
    {
        "anchor": "Simulating quantum magnets with symmetric top molecules: We establish a correspondence between the electric dipole matrix elements of\na polyatomic symmetric top molecule in a state with nonzero projection of the\ntotal angular momentum on the symmetry axis of the molecule and the magnetic\ndipole matrix elements of a magnetic dipole associated with an elemental spin\n$F$. It is shown that this correspondence makes it possible to perform quantum\nsimulation of the single-particle spectrum and the dipole-dipole interactions\nof magnetic dipoles in a static external magnetic field $\\bf{B}$ with symmetric\ntop molecules subject to a static external electric field\n$\\bf{E}_{\\mathrm{DC}}$. We further show that no such correspondence exists for\n$^1\\Sigma$ molecules in static fields, such as the alkali metal dimers. The\neffective spin angular momentum of the simulated magnetic dipole corresponds to\nthe rotational angular momentum of the symmetric top molecule, and so quantum\nsimulation of arbitrarily large integer spins is possible. Further, taking the\nmolecule CH$_3$F as an example, we show that the characteristic dipole-dipole\ninteraction energies of the simulated magnetic dipole are a factor of 620, 600,\nand 310 larger than for the highly magnetic atoms Chromium, Erbium, and\nDysprosium, respectively. We present several applications of our correspondence\nfor many-body physics, including long-range and anisotropic spin models with\narbitrary integer spin $S$ using symmetric top molecules in optical lattices,\nquantum simulation of molecular magnets, and spontaneous demagnetization of\nBose-Einstein condensates due to dipole-dipole interactions. Our results are\nexpected to be relevant as cold symmetric top molecules reach quantum\ndegeneracy through Stark deceleration and opto-electrical cooling.",
        "positive": "A binary mixture of Bose-Einstein-condensates in a double-well\n  potential: Berry phase and two-mode entanglement: A binary mixtures of Bose-Einstein condensate structures exhibit an\nincredible richness in terms of holding different kinds of phases. Depending on\nthe ratio of the inter- and intra-atomic interactions, the transition from\nmixed to separated phase, which is also known as the miscibility-immiscibility\ntransition, has been reported in different setups and by different groups.\nHere, we describe such type of quantum phase transition in an effective\nHamiltonian approach, by applying Holstein-Primakoff transformation in the\nlimit of large number of particles. We demonstrate that non-trivial geometric\nphase near the critical coupling is present, which confirms the connection\nbetween Berry phase and quantum phase transition. We also show that, by using\nthe spin form of Hillery & Zubairy criterion, a two mode entanglement\naccompanies this transition in the limit of large, but not infinite number of\nparticles."
    },
    {
        "anchor": "Magnetic Order Driven Topological Transition in the Haldane-Hubbard\n  Model: In this letter we study the Haldane model with on-site repulsive interactions\nat half-filling. We show that the mean-field Hamiltonian with magnetic order\neffectively modifies parameters in the Haldane Hamiltonian, such as sublattice\nenergy difference and phase in next nearest hopping. As interaction increases,\nincreasing of magnetic order corresponds to varying these parameters and\nconsequently, drives topological transitions. At the mean-field level, one\nscenario is that the magnetic order continuously increases, and inevitably, the\nfermion gap closes at the topological transition point with nonzero magnetic\norder. Beyond the mean-field, interaction between fermions mediated by\nspin-wave fluctuations can further open up the gap, rendering a first-order\ntransition. Another scenario is a first-order transition at mean-field level\nacross which a canted magnetic order develops discontinuously, avoiding the\nfermion gap closing. We find that both scenarios exist in the phase diagram of\nthe Haldane-Hubbard model. Our predication is relevant to recent experimental\nrealization of the Haldane model in cold atom system.",
        "positive": "Topology by Dissipation: Transport properties: Topological phases of matter are the center of much current interest, with\npromising potential applications in, e.g., topologically-protected transport\nand quantum computing. Traditionally such states are prepared by tuning the\nsystem Hamiltonian while coupling it to a generic bath at very low\ntemperatures; This approach is often ineffective, especially in cold-atom\nsystems. It was recently shown that topological phases can emerge much more\nefficiently even in the absence of a Hamiltonian, by properly engineering the\ninteraction of the system with its environment, to directly drive the system\ninto the desired state. Here we concentrate on dissipatively-induced 2D Chern\ninsulator (lattice quantum Hall) states. We employ open quantum systems tools\nto explore their transport properties, such as persistent currents and the\nconductance in the steady state, in the presence of various Hamiltonians. We\nfind that, in contrast with equilibrium systems, the usual relation between the\nChern topological number and the Hall conductance is broken. We explore the\nintriguing edge behaviors and elucidate under which conditions the Hall\nconductance is quantized."
    },
    {
        "anchor": "Emerging dissipative phases in a superradiant quantum gas with tunable\n  decay: Exposing a many-body system to external drives and losses can transform the\nnature of its phases and opens perspectives for engineering new properties of\nmatter. How such characteristics are related to the underlying microscopic\nprocesses of the driven and dissipative system is a fundamental question. Here\nwe address this point in a quantum gas that is strongly coupled to a lossy\noptical cavity mode using two independent Raman drives, which act on the spin\nand motional degrees of freedom of the atoms. This setting allows us to control\nthe competition between coherent dynamics and dissipation by adjusting the\nimbalance between the drives. For strong enough coupling, the transition to a\nsuperradiant phase occurs, as is the case for a closed system. Yet, by\nimbalancing the drives we can enter a dissipation-stabilized normal phase and a\nregion of multistability. Measuring the properties of excitations on top of the\nout-of-equilibrium phases reveals the microscopic elementary processes in the\nopen system. Our findings provide prospects for studying squeezing in\nnon-Hermitian systems, quantum jumps in superradiance, and dynamical spin-orbit\ncoupling in a dissipative setting.",
        "positive": "Theory of \"magic\" optical traps for Zeeman-insensitive clock transitions\n  in alkalis: Precision measurements and quantum information processing with cold atoms may\nbenefit from trapping atoms with specially engineered, \"magic\" optical fields.\nAt the magic trapping conditions, the relevant atomic properties remain immune\nto strong perturbations by the trapping fields. Here we develop a theoretical\nanalysis of a recently observed magic trapping for especially valuable\nZeeman-insensitive clock transitions in alkali-metal atoms. The involved\nmechanism relies on applying \"magic\" bias B-field along circularly polarized\ntrapping laser field. We map out these B-fields as a function of trapping laser\nwavelength for all commonly-used alkalis."
    },
    {
        "anchor": "The Role of Interaction in the Pairing of Two Spin-orbit Coupled\n  Fermions: We investigate the role of a repulsive s-wave interaction in the two-body\nproblem in the presence of spin orbit couplings, motivated by current interests\nin exploring exotic superfluid phases in spin-orbit coupled Fermi gases. For\nweak spin orbit coupling where the density of states is not significantly\naltered, we analytically show that the high-energy states become more important\nin determining the binding energy when the interaction strength decreases.\nConsequently, tuning the interaction gives rise to a rich ground state\nbehavior, including a zigzag of the ground state momentum or inducing\ntransitions among the meta-stable states. By exactly solving the two-body\nproblem for a spin-orbit coupled Fermi mixture, we demonstrate that our\nanalysis can also apply to the case when the density of states is significantly\nmodified by the spin-orbit coupling. Our findings pave the way for\nunderstanding and controlling the paring of fermions in the presence of spin\norbit couplings.",
        "positive": "Exact Results for Tunneling Problems of Bogoliubov Excitations in the\n  Critical Supercurrent State: We show the exact solution of Bogoliubov equations at zero-energy in the\ncritical supercurrent state for arbitrary shape of potential barrier. With use\nof this solution, we prove the absence of perfect transmission of excitations\nin the low-energy limit by giving the explicit expression of transmission\ncoefficient. The origin of disappearance of perfect transmission is the\nemergence of zero-energy density fluctuation near the potential barrier."
    },
    {
        "anchor": "Ultracold Spin-Orbit Coupled Bose-Einstein Condensate in a Cavity: Route\n  to Magnetic Phases Through Cavity Transmission: We study the spin orbit coupled ultra cold Bose-Einstein condensate placed in\na single mode Fabry-P\\'erot cavity. The cavity introduces a quantum optical\nlattice potential which dynamically couples with the atomic degrees of freedom\nand realizes a generalized extended Bose Hubbard model whose zero temperature\nphase diagram can be controlled by tuning the cavity parameters. In the\nnon-interacting limit, where the atom-atom interaction is set to zero, the\nresulting atomic dispersion shows interesting features such as bosonic analogue\nof Dirac points, cavity controlled Hofstadter spectrum which bears the hallmark\nof pseudo-spin-1/2 bosons in presence of Abelian and non-Abelian gauge field\n(the later due to spin-orbit coupling) in a cavity induced optical lattice\npotential. In the presence of atom-atom interaction, using a mapping to a\ngeneralized Bose Hubbard model of spin-orbit coupled bosons in classical\noptical lattice, we show that the system realizes a host of quantum magnetic\nphases whose magnetic order can be be detected from the cavity transmission.\nThis provides an alternative approach for detecting quantum magnetism in ultra\ncold atoms. We discuss the effect of cavity induced optical bistability on this\nphases and their experimental consequences.",
        "positive": "Bulk viscosity of dual Bose and Fermi gases in one dimension: One-dimensional Bose and Fermi gases with contact interactions are known to\nexhibit the weak-strong duality, where the equilibrium thermodynamic properties\nof one system at weak coupling are identical to those of the other system at\nstrong coupling. Here, we show that such duality extends beyond the\nthermodynamics to the frequency-dependent complex bulk viscosity, which is\nprovided by the contact-contact response function. In particular, we confirm\nthat the bulk viscosities of the Bose and Fermi gases agree in the\nhigh-temperature limit, where the systematic expansion in terms of fugacity is\navailable at arbitrary coupling. We also compute their bulk viscosities\nperturbatively in the weak-coupling limit at arbitrary temperature, which via\nthe duality serve as those of the Fermi and Bose gases in the strong-coupling\nlimit."
    },
    {
        "anchor": "Realization of a Laughlin state of two rapidly rotating fermions: We realize a Laughlin state of two rapidly rotating fermionic atoms in an\noptical tweezer. By utilizing a single atom and spin resolved imaging\ntechnique, we sample the Laughlin wavefunction, thereby revealing its\ndistinctive features, including a vortex distribution in the relative motion,\ncorrelations in the particles' relative angle, and suppression of the\ninter-particle interactions. Our work lays the foundation for atom-by-atom\nassembly of fractional quantum Hall states in rotating atomic gases.",
        "positive": "Ground-state energy and excitation spectrum of the Lieb-Liniger model :\n  accurate analytical results and conjectures about the exact solution: We study the ground-state properties and excitation spectrum of the\nLieb-Liniger model, i.e. the one-dimensional Bose gas with repulsive contact\ninteractions. We solve the Bethe-Ansatz equations in the thermodynamic limit by\nusing an analytic method based on a series expansion on orthogonal polynomials\ndeveloped in \\cite{Ristivojevic} and push the expansion to an unprecedented\norder. By a careful analysis of the mathematical structure of the series\nexpansion, we make a conjecture for the analytic exact result at zero\ntemperature and show that the partially resummed expressions thereby obtained\ncompete with accurate numerical calculations. This allows us to evaluate the\ndensity of quasi-momenta, the ground-state energy, the local two-body\ncorrelation function and Tan's contact. Then, we study the two branches of the\nexcitation spectrum. Using a general analysis of their properties and\nsymmetries, we obtain novel analytical expressions at arbitrary interaction\nstrength which are found to be extremely accurate in a wide range of\nintermediate to strong interactions."
    },
    {
        "anchor": "Diffused vorticity and moment of inertia of a spin-orbit coupled\n  Bose-Einstein condensate: By developing the hydrodynamic theory of spinor superfluids we calculate the\nmoment of inertia of a harmonically trapped Bose-Einstein condensate with\nspin-orbit coupling. We show that the velocity field associated with the\nrotation of the fluid exhibits diffused vorticity, in contrast to the\nirrotational behavior characterizing a superfluid. Both Raman-induced and\nRashba spin-orbit couplings are considered. In the first case the moment of\ninertia takes the rigid value at the transition between the plane wave and the\nsingle minimum phase, while in the latter case the rigid value is achieved in\nthe limit of isotropic Rashba coupling. A procedure to generate the rigid\nrotation of the fluid and to measure the moment of inertia is proposed. The\nquenching of the quantum of circulation $h/m$, caused by Raman induced\nspin-orbit coupling in a toroidal geometry, is also discussed.",
        "positive": "Complex correlations in high harmonic generation of matter-wave jets\n  revealed by pattern recognition: Correlations in interacting many-body systems are key to the study of quantum\nmaterials and quantum information. More often than not, the complexity of the\ncorrelations grows quickly as the system evolves and thus presents a challenge\nfor experimental characterization and intuitive understanding. In a strongly\ndriven Bose-Einstein condensate, we observe the high harmonic generation of\nmatter-wave jets with complex correlations as a result of bosonic stimulation.\nBased on a pattern recognition scheme, we identify a universal pattern of\ncorrelations which offers essential clues to unveiling the underlying secondary\nscattering processes and high-order correlations. We show that the pattern\nrecognition offers a versatile strategy to visualize and analyze the quantum\ndynamics of a many-body system."
    },
    {
        "anchor": "Engineering Non-Hermitian Skin Effect with Band Topology in Ultracold\n  Gases: Non-Hermitian skin effect(NHSE) describes a unique non-Hermitian phenomenon\nthat all eigen-modes are localized near the boundary, and has profound impact\non a wide range of bulk properties. In particular, topological systems with\nNHSE have stimulated extensive research interests recently, given the fresh\ntheoretical and experimental challenges therein. Here we propose a readily\nimplementable scheme for achieving NHSE with band topology in ultracold gases.\nSpecifically, the scheme realizes the one-dimensional optical Raman lattice\nwith two types of spin-orbit coupling (SOC) and an additional laser-induced\ndissipation. By tuning the dissipation and the SOC strengths, NHSE and band\ntopology can be individually controlled such that they can coexist in a\nconsiderable parameter regime. To identify the topological phase in the\npresence of NHSE, we have restored the bulk-boundary correspondence by invoking\nthe non-Bloch band theory, and discussed the dynamic signals for detection. Our\nwork serves as a guideline for engineering topological lattices with NHSE in\nthe highly tunable environment of cold atoms, paving the way for future studies\nof exotic non-Hermitian physics in a genuine quantum many-body setting.",
        "positive": "Coupling vortex dynamics with collective excitations in Bose-Einstein\n  Condensates: Here we analyze the collective excitations as well as the expansion of a\ntrapped Bose-Einstein condensate with a vortex line at its center. To this end,\nwe propose a variational method where the variational parameters have to be\ncarefully chosen in order to produce reliable results. Our variational\ncalculations agree with numerical simulations of the Gross-Pitaevskii equation.\nThe system considered here turns out to exhibit four collective modes of which\nonly three can be observed at a time depending of the trap anisotropy. We also\ndemonstrate that these collective modes can be excited using well established\nexperimental methods such as modulation of the s-wave scattering length."
    },
    {
        "anchor": "Inverse Energy Cascade in Forced 2D Quantum Turbulence: We demonstrate an inverse energy cascade in a minimal model of forced 2D\nquantum vortex turbulence. We simulate the Gross-Pitaevskii equation for a\nmoving superfluid subject to forcing by a stationary grid of obstacle\npotentials, and damping by a stationary thermal cloud. The forcing injects\nlarge amounts of vortex energy into the system at the scale of a few healing\nlengths. A regime of forcing and damping is identified where vortex energy is\nefficiently transported to large length scales via an inverse energy cascade\nassociated with the growth of clusters of same-circulation vortices, a\nKolmogorov scaling law in the kinetic energy spectrum over a substantial\ninertial range, and spectral condensation of kinetic energy at the scale of the\nsystem size. Our results provide clear evidence that the inverse energy cascade\nphenomenon, previously observed in a diverse range of classical systems, can\nalso occur in quantum fluids.",
        "positive": "Ground state of weakly repulsive soft-core bosons on a sphere: We study a system of penetrable bosons embedded in a spherical surface. Under\nthe assumption of weak interaction between the particles, the ground state of\nthe system is, to a good approximation, a pure condensate. We employ\nthermodynamic arguments to investigate, within a variational ansatz for the\nsingle-particle state, the crossover between distinct finite-size \"phases\" in\nthe parameter space spanned by the sphere radius and the chemical potential. In\nparticular, for radii up to a few interaction ranges we examine the stability\nof the fluid phase with respect to a number of crystal-like arrangements having\nthe symmetry of a regular or semi-regular polyhedron. We find that, while\nquantum fluctuations keep the system fluid at low density, upon compression it\neventually becomes inhomogeneous, i.e., particles gather together in clusters.\nAs the radius increases, the nature of the high-density aggregate varies and we\nobserve a sequence of transitions between different cluster phases (\"solids\"),\nwhose underlying rationale is to maximize the coordination number of clusters,\nwhile ensuring at the same time the proper distance between each neighboring\npair. We argue that, at least within our mean-field description, every cluster\nphase is supersolid."
    },
    {
        "anchor": "Quench dynamics and relaxation in isolated integrable quantum spin\n  chains: We review the dynamics after quantum quenches in integrable quantum spin\nchains. We give a pedagogical introduction to relaxation in isolated quantum\nsystems, and discuss the description of the steady state by (gen- eralized)\nGibbs ensembles. When then turn to general features in the time evolution of\nlocal observables after the quench, using a simple model of free fermions as an\nexample. In the second part we present an overview of recent progress in\ndescribing quench dynamics in two key paradigms for quantum integrable models,\nthe transverse field Ising chain and the anisotropic spin-1/2 Heisenberg chain.",
        "positive": "Cooling by corralling: a route to ultra-low entropies in optical\n  lattices: A major motivation for cold atom experiments is the search for quantum ground\nstates such as antiferromagnets and d-wave superfluids. The primary obstacle to\nthis task is the difficulty of cooling to sufficiently low temperatures. We\npropose a way to achieve very low temperatures and entropies ($\\sim 0.03k_B$\nper particle) by trapping fermions in a corral formed from another species of\natoms. The Fermi system can then be used as a heat sink, or it can be\nadiabatically evolved into other desired states. In particular, we suggest\nmethods for generating antiferromagnetism using this technique."
    },
    {
        "anchor": "Reflection of a Lieb-Liniger wave packet from the hard-wall potential: Nonequilibrium dynamics of a Lieb-Liniger system in the presence of the\nhard-wall potential is studied. We demonstrate that a time-dependent wave\nfunction, which describes quantum dynamics of a Lieb-Liniger wave packet\ncomprised of N particles, can be found by solving an $N$-dimensional Fourier\ntransform; this follows from the symmetry properties of the many-body\neigenstates in the presence of the hard-wall potential. The presented formalism\nis employed to numerically calculate reflection of a few-body wave packet from\nthe hard wall for various interaction strengths and incident momenta.",
        "positive": "Efficient numerical methods for computing ground states and dynamics of\n  dipolar Bose-Einstein condensates: New efficient and accurate numerical methods are proposed to compute ground\nstates and dynamics of dipolar Bose-Einstein condensates (BECs) described by a\nthree-dimensional (3D) Gross-Pitaevskii equation (GPE) with a dipolar\ninteraction potential. Due to the high singularity in the dipolar interaction\npotential, it brings significant difficulties in mathematical analysis and\nnumerical simulations of dipolar BECs. In this paper, by decoupling the\ntwo-body dipolar interaction potential into short-range (or local) and\nlong-range interactions (or repulsive and attractive interactions), the GPE for\ndipolar BECs is reformulated as a Gross-Pitaevskii-Poisson type system. Based\non this new mathematical formulation, we prove rigorously existence and\nuniqueness as well as nonexistence of the ground states, and discuss the\nexistence of global weak solution and finite time blowup of the dynamics in\ndifferent parameter regimes of dipolar BECs. In addition, a backward Euler sine\npseudospectral method is presented for computing the ground states and a\ntime-splitting sine pseudospectral method is proposed for computing the\ndynamics of dipolar BECs. Due to the adaption of new mathematical formulation,\nour new numerical methods avoid evaluating integrals with high singularity and\nthus they are more efficient and accurate than those numerical methods\ncurrently used in the literatures for solving the problem.\n  Extensive numerical examples in 3D are reported to demonstrate the efficiency\nand accuracy of our new numerical methods for computing the ground states and\ndynamics of dipolar BECs."
    },
    {
        "anchor": "Exotic Topological States with Raman-Induced Spin-Orbit Coupling: We propose a simple experimental scheme to realize simultaneously the\none-dimensional spin-orbit coupling and the staggered spin-flip in ultracold\npseudospin-$1/2$ atomic Fermi gases trapped in square optical lattices. In the\nabsence of interspecies interactions, the system supports gapped Chern\ninsulators and gapless topological semimetal states. By turning on the $s$-wave\ninteractions, a rich variety of gapped and gapless inhomogeneous topological\nsuperfluids can emerge. In particular, a gapped topological Fulde-Ferrell\nsuperfluid, in which the chiral edge states at opposite boundaries possess the\nsame chirality, is predicted.",
        "positive": "Entanglement and Localization of a Two-Mode Bose-Einstein Condensate: A simple second quantization model is used to describe a two-mode\nBose-Einstein condensate (BEC), which can be written in terms of the generators\nof a SU(2) algebra with three parameters. We study the behaviour of the\nentanglement entropy and localization of the system in the parameter space of\nthe model. The phase transitions in the parameter space are determined by means\nof the coherent state formalism and the catastrophe theory, which besides let\nus get the best variational state that reproduces the ground state energy. The\nentanglement entropy is determined for two recently proposed partitions of the\ntwo-mode BEC that are called separation by boxes and separation by modes of the\natoms. The entanglement entropy in the boxes partition is strongly correlated\nto the properties of localization in phase space of the model, which is given\nby the evaluation of the second moment of the Husimi function. To compare the\nfitness of the trial wavefunction its overlap with the exact quantum solution\nis evaluated. The entanglement entropy for both partitions, the overlap and\nlocalization properties of the system get singular values along the separatrix\nof the two-mode BEC, which indicates the phase transitions which remain in the\nthermodynamical limit, in the parameter space."
    },
    {
        "anchor": "Pattern formation in a driven Bose-Einstein Condensate: Pattern formation is ubiquitous in nature from morphogenesis and cloud\nformation to galaxy filamentation. More often than not, patterns arise in a\nmedium driven far from equilibrium due to the interplay of dynamical\ninstability and nonlinear wave mixing. We report, based on momentum and real\nspace pattern recognition, formation of density patterns with two- (D$_2$),\nfour- (D$_4$) and six-fold (D$_6$) symmetries in Bose-Einstein condensates\n(BECs) with atomic interactions driven at two frequencies. The symmetry of the\npattern is controlled by the ratio of the frequencies. The D$_6$ density waves,\nin particular, arise from a resonant wave mixing process that coherently\ncorrelates and enhances the excitations that respect the symmetry.",
        "positive": "FORTRESS II: FORTRAN programs for solving coupled Gross-Pitaevskii\n  equations for spin-orbit coupled spin-2 Bose-Einstein condensate: We provide here a set of three OpenMP parallelized FORTRAN 90/95 programs to\ncompute the ground states and the dynamics of trapped spin-2 Bose-Einstein\ncondensates (BECs) with anisotropic spin-orbit (SO) coupling by solving a set\nof five coupled Gross-Pitaevskii equations using a time-splitting Fourier\nspectral method. Depending on the nature of the problem, without any loss of\ngenerality, we have employed the Cartesian grid spanning either three-, two-,\nor one-dimensional space for numerical discretization. To illustrate the\nveracity of the package, wherever feasible, we have compared the numerical\nground state solutions of the full mean-field model with those from the\nsimplified scalar models. The two set of results show excellent agreement, in\nparticular, through the equilibrium density profiles, energies and chemical\npotentials of the ground-states. We have also presented test results for OpenMP\nperformance parameters like speedup and the efficiency of the three codes."
    },
    {
        "anchor": "Quantum Phase diagram and time-of-flight absorption pictures of\n  ultracold Bose system in a square optical superlattice: In this letter, by the use of the generalized effective potential theory,\nwith the help of process-chain approach under the framework of Kato formulation\nof perturbation expansion, we calculate out the quantum phase diagram up to\n8-th order for an ultracold Bose system in a square optical superlattice. Base\non these perturbative data, with the help of the linear fit extrapolation\ntechnique, more accurate results are gotten, which are in excellent agreement\nwith recent Monte-Carlo numerical results. Moreover, by employing the\ngeneralized re-summed Green's function method and cumulant expansion, the\nmomentum distribution function of the system is also calculated analytically\nand the time-of-flight absorption pictures of the system are plotted.",
        "positive": "Bose-Einstein condensation of heteronuclear bound states formed in a\n  Fermi gas of two atomic species: microscopic approach: We study a many-body system of interacting fermionic atoms of two species\nthat are in thermodynamic equilibrium with their condensed heteronuclear bound\nstates (molecules). In order to describe such an equilibrium state, we use a\nmicroscopic approach that involves the Bogoliubov model for a weakly\ninteracting Bose gas and approximate formulation of the second quantization\nmethod in the presence of bound states of particles elaborated earlier by the\nauthors. This microscopic approach is valid at low temperatures, when the\naverage kinetic energy of all the components in the system is small in\ncomparison with the bound state energy. The coupled equations, which relate the\nchemical potentials of fermionic components and molecular condensate density,\nare obtained within the proposed theory. At zero temperature, these equations\nare analyzed both analytically and numerically, attracting the relevant\nexperimental data. We find the conditions at which a condensate of\nheteronuclear molecules coexists in equilibrium with degenerate components of a\nFermi gas. The ground state energy and single-particle excitation spectrum are\nfound. The boundaries of the applicability of the developed microscopic\napproach are analyzed."
    },
    {
        "anchor": "Dynamics of matter-wave solutions of Bose-Einstein condensates in a\n  homogeneous gravitational field: We find a matter-wave solution of Bose-Einstein condensates trapped in a\nharmonic-oscillator potential and subjected to a homogeneous gravitational\nfield, by means of the extended tanhfunction method. This solution has as\nspecial cases the bright and dark solitons. We investigate the dynamics and the\nkinematics of these solutions, and the role of gravity is sketched. It is shown\nthat these solutions can be generated and manipulated by controlling the s-wave\nscattering length, without changing the strengths of the magnetic and\ngravitational fields.",
        "positive": "Mean-field phase diagram of ultracold atomic gases in cavity quantum\n  electrodynamics: We investigate the mean-field phase diagram of the Bose-Hubbard model with\ninfinite-range interactions in two dimensions. This model describes ultracold\nbosonic atoms confined by a two-dimensional optical lattice and dispersively\ncoupled to a cavity mode with the same wavelength as the lattice. We determine\nthe ground-state phase diagram for a grand-canonical ensemble by means of\nanalytical and numerical methods. Our results mostly agree with the ones\nreported in Dogra et al. [PRA 94, 023632 (2016)], and have a remarkable\nqualitative agreement with the quantum Monte Carlo phase diagrams of Flottat et\nal. [PRB 95, 144501 (2017)]. The salient differences concern the stability of\nthe supersolid phases, which we discuss in detail. Finally, we discuss\ndifferences and analogies between the ground state properties of strong\nlong-range interacting bosons with the ones predicted for repulsively\ninteracting dipolar bosons in two dimensions."
    },
    {
        "anchor": "Pair-Breaking Collective Branch in BCS Superconductors and Superfluid\n  Fermi Gases: We demonstrate the existence of a collective excitation branch in the\npair-breaking continuum of superfluid Fermi gases and BCS superconductors. At\nzero temperature, we analytically continue the equation on the collective mode\nenergy in Anderson's Random Phase Approximation or Gaussian fluctuations\nthrough its branch cut associated with the continuum, and obtain the full\ncomplex dispersion relation, including in the strong coupling regime. The\nbranch exists as long as the chemical potential $\\mu$ is positive and the wave\nnumber below $\\sqrt{2m\\mu}/\\hbar$ (with m the fermion mass). In the long\nwavelength limit, the branch varies quadratically with the wave number, with a\ncomplex effective mass that we compute analytically for an arbitrary\ninteraction strength.",
        "positive": "Identifying insulating states of ultra cold atoms with cavity\n  transmission spectrum: In this paper, we consider the transmission characteristics of an optical\ncavity loaded with ultra cold atoms in a one dimensional optical lattice at\nabsolute zero temperature. In particular, we consider the situation when the\nmany body quantum state of the ultra cold atoms is an insulating state with\nfixed number of atoms at each site, which can be either density wave (DW) or\nMott insulator (MI) phase, each showing different type of discrete lattice\ntranslational symmetry. We provide a general framework of understanding the\ntransmission spectrum from a single and two cavities/modes loaded with such\ninsulating phases. Further, we also discuss how such a transmission spectrum\nchanges when these insulating phases make a cross over to the superfluid (SF)\nphase with the changing depth of the optical lattice potential."
    },
    {
        "anchor": "Accurate multi-boson long-time dynamics in triple-well periodic traps: To solve the many-boson Schr\\\"odinger equation we utilize the\nMulticonfigurational time-dependent Hartree method for bosons (MCTDHB). To be\nable to attack larger systems and/or to propagate the solution for longer\ntimes, we implement a parallel version of the MCTDHB method thereby realizing\nthe recently proposed [Streltsov {\\it et al.} arXiv:0910.2577v1] novel idea how\nto construct efficiently the result of the action of the Hamiltonian on a\nbosonic state vector. We study the real-space dynamics of repulsive bosonic\nsystems made of N=12, 51 and 3003 bosons in triple-well periodic potentials.\nThe ground state of this system is three-fold fragmented. By suddenly strongly\ndistorting the trap potential, the system performs complex many-body quantum\ndynamics. At long times it reveals a tendency to an oscillatory behavior around\na threefold fragmented state. These oscillations are strongly suppressed and\ndamped by quantum depletions. In spite of the richness of the observed\ndynamics, the three time-adaptive orbitals of MCTDHB(M=3) are capable to\ndescribe the many-boson quantum dynamics of the system for short and\nintermediate times. For longer times, however, more self-consistent\ntime-adaptive orbitals are needed to correctly describe the non-equilibrium\nmany-body physics. The convergence of the MCTDHB($M$) method with the number\n$M$ of self-consistent time-dependent orbitals used is demonstrated.",
        "positive": "Dynamics of spin and density fluctuations in strongly interacting\n  few-body systems: The decoupling of spin and density dynamics is a remarkable feature of\nquantum one-dimensional many-body systems. In a few-body regime, however,\nlittle is known about this phenomenon. To address this problem, we study the\ntime evolution of a small system of strongly interacting fermions after a\nsudden change in the trapping geometry. We show that, even at the few-body\nlevel, the excitation spectrum of this system presents separate signatures of\nspin and density dynamics. Moreover, we describe the effect of considering\nadditional internal states with SU(N) symmetry, which ultimately leads to the\nvanishing of spin excitations in a completely balanced system."
    },
    {
        "anchor": "Quantum Monte Carlo and perturbative study of repulsive two-dimensional\n  Bose-Fermi mixtures: We derive analytically the leading beyond-mean field contributions to the\nzero-temperature equation of state and to the fermionic quasi-particle residue\nand effective mass of a dilute Bose-Fermi mixture in two dimensions. In the\nrepulsive case, we perform quantum Monte Carlo simulations for two\nrepresentative bosonic concentrations and equal masses, extending a method for\ncorrecting finite-size effects in fermionic gases to Bose-Fermi mixtures. We\nfind good agreement between analytic expressions and numerical results for weak\ninteractions, while significant discrepancies appear in the regime close to\nmechanical instability, above which we provide evidence of phase separation of\nthe bosonic component.",
        "positive": "Controlled Creation and Decay of Singly-Quantized Vortices in a Polar\n  Magnetic Phase: We experimentally and theoretically explore the creation and time evolution\nof vortex lines in the polar magnetic phase of a trapped spin-1 $^{87}$Rb\nBose-Einstein condensate. A process of phase-imprinting a nonsingular vortex,\nits decay into a pair of singular spinor vortices, and a rapid exchange of\nmagnetic phases creates a pair of three-dimensional, singular singly-quantized\nvortex lines with core regions that are filled with atoms in the ferromagnetic\nphase. Atomic interactions guide the subsequent vortex dynamics, leading to\ncore structures that suggest the decay of the singly-quantized vortices into\nhalf-quantum vortices."
    },
    {
        "anchor": "Phonon mediated conversion of exciton-polaritons Rabi oscillation into\n  THz radiation: Semiconductor microcavities in the strong-coupling regime exhibit an energy\nscale in the THz frequency range, which is fixed by the Rabi splitting between\nthe upper and lower exciton-polariton states. While this range can be tuned by\nseveral orders of magnitude using different excitonic medium, the transition\nbetween both polaritonic states is dipole forbidden. In this work we show that\nin Cadmium Telluride microcavities, the Rabi-oscillation driven THz radiation\nis actually active without the need for any change in the microcavity design.\nThis feature results from the unique resonance condition which is achieved\nbetween the Rabi splitting and the phonon-polariton states, and leads to a\ngiant enhancement of the second order nonlinearity.",
        "positive": "Ultracold fermions in a cavity-induced artificial magnetic field: We show how a fermionic quantum gas in an optical lattice and coupled to the\nfield of an optical cavity can self-organize into a state in which the\nspontaneously emerging cavity field amplitude induces an artificial magnetic\nfield. The fermions form either a chiral insulator or a chiral liquid carrying\nedge currents. The feedback mechanism via the cavity field enables robust and\nfast switching of the edge currents and the cavity output can be employed for\nnon-destructive measurements of the atomic dynamics."
    },
    {
        "anchor": "Kinetic Model of Trapped Finite Temperature Binary Condensates: We construct a fully self-consistent non-equilibrium theory for the dynamics\nof two interacting finite-temperature atomic Bose-Einstein condensates. The\ncondensates are described by dissipative Gross-Pitaevskii equations, coupled to\nquantum Boltzmann equations for the thermal atoms. The density-density\ninteractions between atoms in different components facilitate a number of\ntransport processes of relevance to sympathetic cooling: in particular,\nidentification of an inter-component scattering process associated with\ncollisional \"exchange\" of condensed and thermal atoms between the components,\nis found numerically to dominate close to equilibrium, for both realistic\nmiscible and immiscible trapped atomic $^{87}$Rb-$^{41}$K and\n$^{87}$Rb-$^{85}$Rb condensate mixtures.",
        "positive": "Atomic quantum simulation of a three-dimensional U(1) gauge-Higgs model: In this paper, we study theoretically atomic quantum simulations of a U(1)\ngauge-Higgs model on a three-dimensional (3D) spatial lattice by using an\nextended Bose-Hubbard model with intersite repulsions on a 3D optical lattice.\nHere, the phase and density fluctuations of the boson variable on each site of\nthe optical lattice describe the vector potential and the electric field on\neach link of the gauge-model lattice, respectively. The target gauge model is\ndifferent from the standard Wilson-type U(1) gauge-Higgs model because it has\nplaquette and Higgs interactions with asymmetric couplings in the space-time\ndirections. Nevertheless, the corresponding quantum simulation is still\nimportant as it provides us with a platform to study unexplored time-dependent\nphenomena characteristic of each phase in the general gauge-Higgs models. To\ndetermine the phase diagram of the gauge-Higgs model at zero temperature, we\nperform Monte-Carlo simulations of the corresponding 3+1-dimensional U(1)\ngauge-Higgs model, and obtain the confinement and Higgs phases. To investigate\nthe dynamical properties of the gauge-Higgs model, we apply the\nGross-Pitaevskii equations to the extended Bose-Hubbard model. We simulate the\ntime-evolution of an electric flux that initially is put on a straight line\nconnecting two external point charges. We also calculate the potential energy\nbetween this pair of charges and obtain the string tension in the confinement\nphase. Finally, we propose a feasible experimental setup for the atomic\nsimulations of this quantum gauge-Higgs model on the 3D optical lattice. These\nresults may serve as theoretical guides for future experiments."
    },
    {
        "anchor": "D-wave bosonic pair in an optical lattice: We present a bosonic model, in which two bosons may form a bound pair with\nd-wave symmetry via the four-site ring exchange interaction. A d-wave pairing\nsuperfluid as well as a d-wave density wave (DDW) state, are proposed to be\nachievable in this system. This exotic bosonic system can be realized in the\nBEC zone of a two-dimensional attractive p-band spinless fermionic system. By\nthe mean field approach, we find that at low densities, the d-wave pairs may\ncondensate, leading to a d-wave bosonic paired superfluid. At some particular\nfilling factors, a novel phase, d-wave density wave state, emerges. We study\nthis DDW state and its corresponding quantum phase transition in a two-leg\nladder by the time-evolving block decimation (TEBD) method.",
        "positive": "Dynamics of entanglement entropy of interacting fermions in a 1D driven\n  harmonic trap: Following up on a recent analysis of two cold atoms in a time-dependent\nharmonic trap in one dimension, we explore the entanglement entropy of two and\nthree fermions in the same situation when driven through a parametric\nresonance. We find that the presence of such a resonance in the two-particle\nsystem leaves a clear imprint on the entanglement entropy. We show how the\nsignal is modified by attractive and repulsive contact interactions, and how it\nremains present for the three-particle system. Additionaly, we extend the work\nof recent experiments to demonstrate how restricting observation to a limited\nsubsystem gives rise to locally thermal behavior."
    },
    {
        "anchor": "Quantum Engineering of a Low-Entropy Gas of Heteronuclear Bosonic\n  Molecules in an Optical Lattice: We demonstrate a generally applicable technique for mixing two-species\nquantum degenerate bosonic samples in the presence of an optical lattice, and\nwe employ it to produce low-entropy samples of ultracold 87Rb133Cs Feshbach\nmolecules with a lattice filling fraction exceeding 30%. Starting from two\nspatially separated Bose-Einstein condensates of Rb and Cs atoms, Rb-Cs atom\npairs are efficiently produced by using the superfluid-to-Mott insulator\nquantum phase transition twice, first for the Cs sample, then for the Rb\nsample, after nulling the Rb-Cs interaction at a Feshbach resonance's zero\ncrossing. We form molecules out of atom pairs and characterize the mixing\nprocess in terms of sample overlap and mixing speed. The dense and ultracold\nsample of more than 5000 RbCs molecules is an ideal starting point for\nexperiments in the context of quantum many-body physics with long-range dipolar\ninteractions.",
        "positive": "Supersolid edge and bulk phases of a dipolar quantum gas in a box: We investigate the novel density distributions acquired by a dipolar\nBose-Einstein condensed gas confined in a box potential, with special focus on\nthe effects of supersolidity. Differently from the case of harmonic trapping,\nthe ground state density reveals a strong depletion in the bulk region and an\naccumulation of atoms near the walls, well separated from the bulk, as a\nconsequence of the competition between the attractive and the repulsive nature\nof the dipolar force. In a quasi two-dimensional geometry characterized by\ncylindrical box trapping, we observe the emergence of a ring-like configuration\nnear the boundary of the box, reveling peculiar supersolid and crystal effects\nin a useful range of parameters. In the case of square box trapping the density\noscillations along the edges, caused by the enhanced accumulation of atoms near\nthe vertices, exhibit interesting analogies with the case of box trapped one\ndimensional configurations. For sufficiently large values of the atom number\nalso the bulk region can exhibit supersolidity, the resulting geometry\nreflecting the symmetry of the confining potential even for large systems."
    },
    {
        "anchor": "Vortex lattices in binary Bose-Einstein condensates: Collective modes,\n  quantum fluctuations, and intercomponent entanglement: We study binary Bose-Einstein condensates subject to synthetic magnetic\nfields in mutually parallel or antiparallel directions. Within the mean-field\ntheory, the two types of fields have been shown to give the same vortex-lattice\nphase diagram. We develop an improved effective field theory to study\nproperties of collective modes and ground-state intercomponent entanglement.\nHere, we point out the importance of introducing renormalized coupling\nconstants for coarse-grained densities. We show that the low-energy excitation\nspectra for the two kindsof fields are related to each other by suitable\nrescaling using the renormalized constants. By calculating the entanglement\nentropy, we find that for an intercomponent repulsion (attraction), the two\ncomponents are more strongly entangled in the case of parallel (antiparallel)\nfields, in qualitative agreement with recent studies for a quantum (spin) Hall\nregime. We also find that the entanglement spectrum exhibits an anomalous\nsquare-root dispersion relation, which leads to a subleading logarithmic term\nin the entanglement entropy. All of these are confirmed by numerical\ncalculations based on the Bogoliubov theory with the lowest-Landau-level\napproximation. Finally, we investigate the effects of quantum fluctuations on\nthe phase diagrams by calculating the correction to the ground-state energy due\nto zero-point fluctuations in the Bogoliubov theory. We find that the\nboundaries between rhombic-, square-, and rectangular-lattice phases shift\nappreciably with a decrease in the filling factor.",
        "positive": "How does a magnetic trap work?: Magnetic trapping is a cornerstone for modern ultracold physics and its\napplications (e.g., quantum information processing, quantum metrology, quantum\noptics, or high-resolution spectroscopies). Here a comprehensive analysis and\ndiscussion of the basic physics behind the most commonly used magnetic traps in\nBose-Einstein condensation is presented. This analysis includes the quadrupole\ntrap, the time-averaged orbiting potential trap, and the Ioffe-Pritchard trap.\nIt is shown how the trapping conditions and efficiency of these devices can be\ndetermined from simple derivations based on classical electromagnetism, even\nthough they operate on quantum objects."
    },
    {
        "anchor": "A strontium quantum-gas microscope: The development of quantum-gas microscopes has brought novel ways of probing\nquantum degenerate many-body systems at the single-atom level. Until now, most\nof these setups have focused on alkali atoms. Expanding quantum-gas microscopy\nto alkaline-earth elements will provide new tools, such as SU(N)-symmetric\nfermionic isotopes or ultranarrow optical transitions, to the field of quantum\nsimulation. Here, we demonstrate the site-resolved imaging of a $^{84}$Sr\nbosonic quantum gas in a Hubbard-regime optical lattice. The quantum gas is\nconfined by a two-dimensional in-plane lattice and a light-sheet potential,\nwhich operate at the strontium clock-magic wavelength of 813.4 nm. We realize\nfluorescence imaging using the broad 461 nm transition, which provides high\nspatial resolution. Simultaneously, we perform attractive Sisyphus cooling with\nthe narrow 689 nm intercombination line. We reconstruct the atomic occupation\nfrom the fluorescence images, obtaining imaging fidelities above 94%. Finally,\nwe realize a $^{84}$Sr superfluid in the Bose-Hubbard regime. We observe its\ninterference pattern upon expansion, a probe of phase coherence, with\nsingle-atom resolution. Our strontium quantum-gas microscope provides a new\nplatform to study dissipative Hubbard models, quantum optics in atomic arrays,\nand SU(N) fermions at the microscopic level.",
        "positive": "Two-Dimensional Bose-Hubbard Model for Helium on Graphene: An exciting development in the field of correlated systems is the possibility\nof realizing two-dimensional (2D) phases of quantum matter. For a systems of\nbosons, an example of strong correlations manifesting themselves in a 2D\nenvironment is provided by helium adsorbed on graphene. We construct the\neffective Bose-Hubbard model for this system which involves hard-core bosons\n$(U\\approx\\infty)$, repulsive nearest-neighbor $(V>0)$ and small attractive\n$(V'<0)$ next-nearest neighbor interactions. The mapping onto the Bose-Hubbard\nmodel is accomplished by a variety of many-body techniques which take into\naccount the strong He-He correlations on the scale of the graphene lattice\nspacing. Unlike the case of dilute ultracold atoms where interactions are\neffectively point-like, the detailed microscopic form of the short range\nelectrostatic and long range dispersion interactions in the helium-graphene\nsystem are crucial for the emergent Bose-Hubbard description. The result places\nthe ground state of the first layer of $^4$He adsorbed on graphene deep in the\ncommensurate solid phase with $1/3$ of the sites on the dual triangular lattice\noccupied. Because the parameters of the effective Bose-Hubbard model are very\nsensitive to the exact lattice structure, this opens up an avenue to tune\nquantum phase transitions in this solid-state system."
    },
    {
        "anchor": "Direct cooling in an optical lattice by amplitude modulation: We report on a generic cooling technique for atoms trapped in optical\nlattices. It consists in modulating the lattice depth with a proper frequency\nsweeping. This filtering technique removes the most energetic atoms, and\nprovides with the onset of thermalization a cooling mechanism reminiscent of\nevaporative cooling. However, the selection is here performed in quasi-momentum\nspace rather than in position space. Interband selection rules are used to\nprotect the population with a zero quasi-momentum, namely the Bose Einstein\ncondensate. Direct condensation of thermal atoms in an optical lattice is also\nachieved with this technique. It offers an interesting complementary cooling\nmechanism for quantum simulations performed with quantum gases trapped in\noptical lattices.",
        "positive": "Interaction beween polarons and analogous effects in polarized Fermi\n  gases: We consider an imbalanced mixture of two different ultracold Fermi gases,\nwhich are strongly interacting. Calling spin-down the minority component and\nspin-up the majority component, the limit of small relative density $x=n\\ds\n/n\\us$ is usually considered as a gas of non interacting polarons. This allows\nto calculate, in the expansion of the total energy of the system in powers of\n$x$, the terms proportional to $x$ (corresponding to the binding energy of the\npolaron) and to $x^{5/3}$ (corresponding to the kinetic energy of the polaron\nFermi sea). We investigate in this paper terms physically due to an interaction\nbetween polarons and which are proportional to $x^2$ and $x^{7/3}$. We find\nthree such terms. A first one corresponds to the overlap between the clouds\ndressing two polarons. The two other ones are due to the modification of the\nsingle polaron binding energy caused by the non-zero density of polarons. The\nsecond term is due to the restriction of the polaron momentum by the Fermi sea\nformed by the other polarons. The last one results from the modification of the\nspin-up Fermi sea brought by the other polarons. The calculation of all these\nterms is made at the simplest level of a single particle-hole excitation. It is\nperformed for all the possible interaction strengths within the stability range\nof the polaron. At unitarity the last two terms give a fairly weak contribution\nwhile the first one is strong and leads to a marked disagreement with\nMonte-Carlo results. The possible origins of this discrepancy are discussed."
    },
    {
        "anchor": "Transition between vacuum and finite-density states in the\n  infinite-dimensional Bose-Hubbard model with spatially inhomogeneous\n  dissipation: We analyze dynamics of the infinite-dimensional Bose-Hubbard model with\nspatially inhomogeneous dissipation in the hardcore boson limit by solving the\nLindblad master equation with use of the Gutzwiller variational method. We\nconsider dissipation processes that correspond to inelastic light scattering in\nthe case of Bose gases in optical lattices. We assume that the dissipation is\napplied to a half of lattice sites in a spatially alternating manner. We focus\non steady states at which the system arrives after long-time evolution. We find\nthat when the average particle density is varied, the steady state exhibits a\ntransition between a state in which the sites without dissipation are vacuum\nand that containing a finite number of particles at those sites. We associate\nthe transition with the tendency of the sites with dissipation towards a local\nstate at infinite temperature.",
        "positive": "Numerical simulation of exciton dynamics in Cu2O at ultra low\n  temperatures within a potential trap: We have studied theoretically the relaxation behaviour of excitons in cuprous\noxide (Cu2O) at ultra low temperatures when excitons are confined within a\npotential trap by solving numerically the Boltzmann equation. As relaxation\nprocesses, we have included in this paper deformation potential phonon\nscattering, radiative and non-radiative decay and Auger decay. The relaxation\nkinetics has been analysed for temperatures in the range between 0.3K and 5K.\nUnder the action of deformation potential phonon scattering only, we find for\ntemperatures above 0.5K that the excitons reach local equilibrium with the\nlattice i.e. that the effective local temperature is coming down to bath\ntemperature, while below 0.5K a non-thermal energy distribution remains.\nInterestingly, for all temperatures the global spatial distribution of excitons\ndoes not reach the equilibrium distribution, but stays at a much higher\neffective temperature. If we include further a finite lifetime of the excitons\nand the two-particle Auger decay, we find that both the local and the global\neffective temperature are not coming down to bath temperature. In the first\ncase we find a Bose-Einstein condensation (BEC) to occur for all temperatures\nin the investigated range. Comparing our results with the thermal equilibrium\ncase, we find that BEC occurs for a significantly higher number of excitons in\nthe trap. This effect could be related to the higher global temperature, which\nrequires an increased number of excitons within the trap to observe the BEC. In\ncase of Auger decay, we do not find at any temperature a BEC due to the heating\nof the exciton gas."
    },
    {
        "anchor": "Spin-imbalance-induced transverse magnetization in the\n  Hofstadter-Hubbard model: The fermionic, time-reversal invariant Hofstadter-Hubbard model with a\npopulation difference between the two spin states is investigated. In the\nstrongly interacting regime, where the system can be described by an effective\nspin model, we find an exotic spin structure by means of classical Monte-Carlo\ncalculations. Remarkably, this spin structure exhibits a transverse net\nmagnetization perpendicular to the magnetization induced by the population\nimbalance. It is thus inherently different from canted antiferromagnetism. We\nfurther investigate effects of quantum fluctuations within the dynamical\nmean-field approximation and obtain a rich phase diagram including\nferromagnetic, anti-ferromagnetic, ferrimagnetic, and transverse magnetization\nphases.",
        "positive": "Energy spectra of vortex distributions in two-dimensional quantum\n  turbulence: We theoretically explore key concepts of two-dimensional turbulence in a\nhomogeneous compressible superfluid described by a dissipative two-dimensional\nGross-Pitaeveskii equation. Such a fluid supports quantized vortices that have\na size characterized by the healing length $\\xi$. We show that for the\ndivergence-free portion of the superfluid velocity field, the kinetic energy\nspectrum over wavenumber $k$ may be decomposed into an ultraviolet regime\n($k\\gg \\xi^{-1}$) having a universal $k^{-3}$ scaling arising from the vortex\ncore structure, and an infrared regime ($k\\ll\\xi^{-1}$) with a spectrum that\narises purely from the configuration of the vortices. The Novikov power-law\ndistribution of intervortex distances with exponent -1/3 for vortices of the\nsame sign of circulation leads to an infrared kinetic energy spectrum with a\nKolmogorov $k^{-5/3}$ power law, consistent with the existence of an inertial\nrange. The presence of these $k^{-3}$ and $k^{-5/3}$ power laws, together with\nthe constraint of continuity at the smallest configurational scale\n$k\\approx\\xi^{-1}$, allows us to derive a new analytical expression for the\nKolmogorov constant that we test against a numerical simulation of a forced\nhomogeneous compressible two-dimensional superfluid. The numerical simulation\ncorroborates our analysis of the spectral features of the kinetic energy\ndistribution, once we introduce the concept of a {\\em clustered fraction}\nconsisting of the fraction of vortices that have the same sign of circulation\nas their nearest neighboring vortices. Our analysis presents a new approach to\nunderstanding two-dimensional quantum turbulence and interpreting similarities\nand differences with classical two-dimensional turbulence, and suggests new\nmethods to characterize vortex turbulence in two-dimensional quantum fluids via\nvortex position and circulation measurements."
    },
    {
        "anchor": "Efficient variational approach to the Fermi polaron problem in two\n  dimensions, both in and out of equilibrium: We develop a non-Gaussian variational approach that enables us to study both\nequilibrium and far-from-equilibrium physics of the two-dimensional Fermi\npolaron. This method provides an unbiased analysis of the polaron-to-molecule\nphase transition without relying on truncations in the total number of\nparticle-hole excitations. Our results -- which include the ground state energy\nand quasiparticle residue -- are in qualitative agreement with the known Monte\nCarlo calculations. The main advantage of the non-Gaussian states compared to\nconventional numerical methods is that they enable us to explore long-time\npolaron evolution and, in particular, study various spectral properties\naccessible to both solid-state and ultracold atom experiments. We design two\ntypes of radiofrequency spectroscopies to measure polaronic and molecular\nspectral functions. Depending on the parameter regime, we find that these\nspectral functions and fermionic density profiles near the impurity display\neither long-lived oscillations between the repulsive and attractive polaron\nbranches or exhibit fast relaxational dynamics to the molecular state.",
        "positive": "Superradiant Phase Transition of Fermi Gases in a Cavity across a\n  Feshbach Resonance: In this letter we consider the superradiant phase transition of a\ntwo-component Fermi gas in a cavity across a Feshbach resonance. It is known\nthat quantum statistics plays a crucial role for the superradiant phase\ntransition in atomic gases; in contrast to bosons, in a Fermi gas this\ntransition exhibits strong density dependence. We show that across a Feshbach\nresonance, while the two-component Fermi gas passes through the BEC-BCS\ncrossover, the superradiant phase transition undergoes a corresponding\ncrossover from a fermionic behavior on the weakly interacting BCS side, to a\nbosonic behavior on the molecular BEC side. This intricate statistics crossover\nmakes the superradiance maximally enhanced either in the unitary regime for low\ndensities, in the BCS regime for moderate densities close to Fermi surface\nnesting, or in the BEC regime for high densities."
    },
    {
        "anchor": "Composite-Field Goldstone States and Higgs Mechanism in Dilute Bose\n  Gases: We show that a composite-field (diatom) Goldstone state is expected in a\ndilute Bose gas for temperatures between the Bose gas critical temperature\nwhere the atom Bose-Einstein condensate appears and the temperature where\nsuperfluidity sets in. The presence of superfluidity is tied to the existence\nof a U(1) charge-two diatom condensate in the system. By promoting the global\nU(1) symmetry of the theory to a gauge symmetry, we find that the mass of the\ngauge particle generated through the Anderson-Higgs mechanism is related to the\nsuperfluid density via the Meissner effect and the superfluid density is\nrelated to the square of the anomalous density in the Bose system.",
        "positive": "Macroscopic two-state systems in trapped atomic condensates: We consider a macroscopic two-sate system based on persistent current states\nof a Bose-Einstein condensate (BEC) of interacting neutral atoms confined in a\nring with a weak Josephson link. We demonstrate that macroscopic superpositions\nof different BEC flows are energetically favorable in this system. Moreover, a\nmacroscopic two-state dynamics emerges in the low energy limit. We also\ninvestigate fundamental limitations due to the noise inherent to the\ninteracting BEC of Josephson-ring geometry. We show that the coherent\nmacroscopic dynamics is readily measurable for an experimentally accessible\nrange of parameters."
    },
    {
        "anchor": "Exact Solutions to Two-Component Many-Body Systems in One Dimension: We introduce a new type of models for two-component systems in one dimension\nsubject to exact solutions by Bethe ansatz, where the interspecies interactions\nare tunable via Feshbach resonant interactions. The applicability of Bethe\nansatz is obtained by fine-tuning the resonant energies, and the resulting\nsystems can be described by introducing intraspecies repulsive and interspecies\nattractive couplings $c_1$ and $c_2$. This kind of systems admits two types of\ninteresting solutions: In the regime with $c_1>c_2$, the ground state is a\nFermi sea of two-strings, where the Fermi momentum $Q$ is constrained to be\nsmaller than a certain value $Q^*$, and it provides an ideal scenario to\nrealize BCS-BEC crossover (from weakly attractive atoms to weakly repulsive\nmolecules) in one dimension; In the opposite regime with $c_1<c_2$, the ground\nstate is a single bright soliton even for fermionic atoms, which reveals itself\nas an embedded string solution.",
        "positive": "Ultracold collisions in the Yb-Li mixture system: We report our experimental results on the collisional physics between\nnon-S-state atoms (ytterbium (Yb), effectively a two-electron system, in the\nmetastable ${}^3\\mathrm{P}_2$ state) and S-state atoms (lithium (Li), an alkali\nmetal, in the ground state). At low magnetic fields, by measuring inelastic\ninterspecies collisional losses in the double quantum degenerate mixture we\nreveal the strong dependence of the inelastic losses on the internal spin\nstates of both species and suppressed losses in stretched state configurations.\nIncreasing the magnetic field up to 800 G we further investigate the magnetic\nfield dependence of the collisional interactions. There, smoothly increasing\ninelastic losses are observed towards higher fields. The combined knowledge of\nboth the magnetic field and the spin state dependence of the collisional losses\nof this prototypical mixture system of non-S-state and S-state atoms provides a\nsignificant step forward towards controllable impurity physics realized in the\nYb-Li ultracold system."
    },
    {
        "anchor": "Quantum Monte Carlo simulation of BEC-impurity tunneling: Polaron tunneling is a prominent example of a problem characterized by\ndifferent energy scales, for which the standard quantum Monte Carlo methods\nface a slowdown problem. We propose a new quantum-tunneling Monte Carlo (QTMC)\nmethod which is free from this issue and can be used for a wide range of\ntunneling phenomena. We apply it to study an impurity interacting with a\none-dimensional Bose-Einstein condensate and simultaneously trapped in an\nexternal double-well potential. Our scheme works for an arbitrary coupling\nbetween the particle and condensate and, at the same time, allows for an\naccount of tunneling effects. We discover two distinct quasi-particle peaks\nassociated, respectively, with the phonon-assisted tunneling and the\nself-trapping of the impurity, which are in a crossover regime for the system\nmodeled. We observe and analyze changes in the weights and spectral positions\nof the peaks (or, equally, effective masses of the quasi-particles) when the\ncoupling strength is increased. Possible experimental realizations using cold\natoms are discussed.",
        "positive": "Quantum hydrodynamics of the spinor Bose-Einstein condensate at non-zero\n  temperatures: Finite temperature hydrodynamic model is derived for the spin-1 ultracold\nbosons by the many-particle quantum hydrodynamic method. It is presented as the\ntwo fluid model of the BEC and normal fluid. The linear and quadratic Zeeman\neffects are included. Scalar and spin-spin like short-range interactions are\nconsidered in the first order by the interaction radius. It is also represented\nas the set of two nonlinear Pauli equations. The spectrum of the bulk\ncollective excitations is considered for the ferromagnetic phase in the small\ntemperature limit. The spin wave is not affected by the presence of the small\ntemperature in the described minimal coupling model, where the thermal part of\nthe spin-current of the normal fluid is neglected. The two sound waves are\naffected by the spin evolution in the same way as the change of spectrum of the\nsingle sound wave in BEC, where speed of sound is proportional to $g_{1}+g_{2}$\nwith $g_{i}$ are the interaction constants."
    },
    {
        "anchor": "Observation of canted antiferromagnetism with ultracold fermions in an\n  optical lattice: Understanding the magnetic response of the normal state of the cuprates is\nconsidered a key piece in solving the puzzle of their high-temperature\nsuperconductivity. The essential physics of these materials is believed to be\ncaptured by the Fermi-Hubbard model, a minimal model that has been realized\nwith cold atoms in optical lattices. Here we report on site-resolved\nmeasurements of the Fermi-Hubbard model in a spin-imbalanced atomic gas,\nallowing us to explore the response of the system to large effective magnetic\nfields. We observe short-range canted antiferromagnetism at half-filling with\nstronger spin correlations in the direction orthogonal to the magnetization, in\ncontrast with the spin-balanced case where identical correlations are measured\nfor any projection of the pseudospin. The rotational anisotropy of the spin\ncorrelators is found to increase with polarization and with distance between\nthe spins. Away from half-filling, the polarization of the gas exhibits\nnon-monotonic behavior with doping for strong interactions, resembling the\nbehavior of the magnetic susceptibility in the cuprates. We compare our\nmeasurements to predictions from Determinantal Quantum Monte Carlo (DQMC) and\nNumerical Linked Cluster Expansion (NLCE) algorithms and find good agreement.\nCalculations on the doped system are near the limits of these techniques,\nillustrating the value of cold atom quantum simulations for studying\nstrongly-correlated materials.",
        "positive": "Van der Waals five-body size-energy universality: A universal relationship between scaled size and scaled energy is explored in\nfive-body self-bound quantum systems. The ground-state binding energy and\nstructure properties are obtained by means of the diffusion Monte Carlo method.\nWe use pure estimators to eliminate any residual bias in the estimation of the\ncluster size. Strengthening the inter-particle interaction, we extend the\nexploration from the halo region to classical systems. Universal scaled\nsize-scaled energy line, which does not depend on the short-range potential\ndetails and binding strength, is found for homogeneous pentamers with\ninteraction potentials decaying at long range predominantly as $r^{-6}$. For\nmixed pentamers, we discuss under which conditions the universal line can\napproximately describe the size-energy ratio. Our data is compatible with\ngeneralized Tjon lines, which assume a linear dependence between the binding\nenergy of the pentamers and the one of tetramers, when both are divided by the\ntrimer energies."
    },
    {
        "anchor": "Self-bound dipolar droplet: a localized matter-wave in free space: We demonstrate that a dipolar condensate can be prepared into a\nthree-dimensional wavepacket that remains localized when released in\nfree-space. Such self-bound states arise from the interplay of the two-body\ninteractions and quantum fluctuations. We develop a phase diagram for the\nparameter regimes where these self-bound states are stable, examine their\nproperties, and demonstrate how they can be produced in current experiments.",
        "positive": "Semiclassical spectral function for matter waves in random potentials: An $\\hbar$-expansion is presented for the ensemble-averaged spectral function\nof noninteracting matter waves in random potentials. We obtain the leading\nquantum corrections to the deep classical limit at high energies by the\nWigner-Weyl formalism. The analytical results are checked with success against\nnumerical data for Gaussian and laser speckle potentials with Gaussian spatial\ncorrelation in two dimensions."
    },
    {
        "anchor": "Learning the Fuzzy Phases of Small Photonic Condensates: Phase transitions, being the ultimate manifestation of collective behaviour,\nare typically features of many-particle systems only. Here, we describe the\nexperimental observation of collective behaviour in small photonic condensates\nmade up of only a few photons. Moreover, a wide range of both equilibrium and\nnon-equilibrium regimes, including Bose-Einstein condensation or laser-like\nemission are identified. However, the small photon number and the presence of\nlarge relative fluctuations places major difficulties in identifying different\nphases and phase transitions. We overcome this limitation by employing\nunsupervised learning and fuzzy clustering algorithms to systematically\nconstruct the fuzzy phase diagram of our small photonic condensate. Our results\nthus demonstrate the rich and complex phase structure of even small collections\nof photons, making them an ideal platform to investigate equilibrium and\nnon-equilibrium physics at the few particle level.",
        "positive": "Universal behavior of two-dimensional bosonic gases at\n  Berezinskii-Kosterlitz-Thouless transitions: We study the universal critical behavior of two-dimensional (2D) lattice\nbosonic gases at the Berezinskii-Kosterlitz-Thouless (BKT) transition, which\nseparates the low-temperature superfluid phase from the high-temperature normal\nphase. For this purpose, we perform quantum Monte Carlo simulations of the\nhard-core Bose-Hubbard (BH) model at zero chemical potential. We determine the\ncritical temperature by using a matching method that relates finite-size data\nfor the BH model with corresponding data computed in the classical XY model. In\nthis approach, the neglected scaling corrections decay as inverse powers of the\nlattice size L, and not as powers of 1/lnL, as in more standard approaches,\nmaking the estimate of the critical temperature much more reliable. Then, we\nconsider the BH model in the presence of a trapping harmonic potential, and\nverify the universality of the trap-size dependence at the BKT critical point.\nThis issue is relevant for experiments with quasi-2D trapped cold atoms."
    },
    {
        "anchor": "Universal Relations of Ultracold Fermi Gases with Arbitrary Spin-Orbit\n  Coupling: We derive the universal relations for an ultracold two-component Fermi gas\nwith spin-orbit coupling (SOC)\n$\\sum_{\\alpha,\\beta=x,y,z}\\lambda_{\\alpha\\beta}\\sigma_{\\alpha}p_{\\beta}$, where\n$p_{x,y,z}$ and $\\sigma_{x,y,z}$ are the single-atom momentum and Pauli\noperators for pseudo spin, respectively, and the SOC intensity\n$\\lambda_{\\alpha\\beta}$ could take arbitrary value. We consider the system with\nan s-wave short-range interspecies interaction, and ignore the SOC-induced\nmodification for the value of the scattering length. Using the first-quantized\napproach developed by S. Tan (Phys. Rev. Lett. \\textbf{107}, 145302 (2011)), we\nobtain the short-range and high-momentum expansions for the one-body real-space\ncorrelation function and momentum distribution function, respectively. For our\nsystem these functions are $2\\times2$ matrix in the pseudo-spin basis. We find\nthat the leading-order ($1/k^{4}$) behavior of the diagonal elements of the\nmomentum distribution function (i.e., $n_{\\uparrow\\uparrow}({\\bf k})$ and\n$n_{\\downarrow\\downarrow}({\\bf k})$) are not modified by the SOC. However, the\nSOC can significantly modify the behavior of the \\textit{non-diagonal elements}\nof the momentum distribution function, i.e., $n_{\\uparrow\\downarrow}({\\bf k})$\nand $n_{\\downarrow\\uparrow}({\\bf k})$, in the large-$k$ limit. In the absence\nof the SOC, the leading order of these elements is ${\\cal O}(1/k^{6})$. When\nSOC appears, it can induce a term on the order of $1/k^{5}$. We further derive\nthe adiabatic relation and the energy functional. Our results show the SOC can\ninduce a new term in the energy functional, which simply describe the\ncontribution from the SOC to the total energy. The form of the adiabatic\nrelation for our system is not modified by the SOC.",
        "positive": "Localization of weakly interacting bosons in two dimensions: disorder vs\n  lattice geometry effects: We investigate the effects of disorder and lattice geometry against\nlocalisation phenomena in a weakly interacting ultracold bosonic gas confined\nin a 2D optical lattice. The behaviour of the quantum fluid is studied at the\nmean-field level performing computational experiments, as a function of\ndisorder strength for lattices of sizes similar to current experiments.\nQuantification of localisation, away from the Bose glass phase, was obtained\ndirectly from the stationary density profiles through a robust statistical\nanalysis of the condensate component, as a function of the disorder amplitude.\nOur results show a smooth transition, or crossover, to localisation induced by\ndisorder in square and triangular lattices. In contrast, associated to its\nlarger tunneling amplitude, honeycomb lattices show absence of localisation for\nthe same range of disorder strengths and same lattice amplitude, while also\nexhibiting partial localisation for large disorder amplitudes. We also conclude\nthat the coordination number z have a partial influence on how fast this smooth\ntransition occurs as the system size increases. Signatures of disorder are also\nfound in the ground state energy spectrum, where a continuous distribution\nemerges instead of a distribution of sharp peaks proper to the system in the\nabsence of disorder."
    },
    {
        "anchor": "Simulating two-dimensional dynamics within a large-size atomic spin: Encoding a dimension in the internal degree of freedom of an atom provides an\ninteresting tool for quantum simulation, facilitating the realization of\nartificial gauge fields. We propose an extension of the synthetic dimension\ntoolbox, making it possible to encode two dimensions within a large atomic\nspin. The protocol combines first- and second-order spin couplings, such that\nthe spin projection $m$ and the remainder $r=m$ (mod 3) of its Euclidian\ndivision by 3 act as orthogonal coordinates on a synthetic cylinder. It is\nsuited for an implementation with lanthanide atoms, which feature a large\nelectronic spin and narrow optical transitions for applying the required spin\ncouplings. This method is useful for simulating geometries with periodic\nboundary conditions, and engineering various types of topological systems\nevolving in high dimensions.",
        "positive": "Bose-Einstein condensation in the three-sphere and the infinite slab:\n  analytical results: We study the finite size effects on Bose-Einstein condensation (BEC) of an\nideal non-relativistic Bose gas in the three-sphere (spatial section of the\nEinstein universe) and in a partially finite box which is infinite in two of\nthe spatial directions (infinite slab). Using the framework of grand-canonical\nstatistics, we consider the number of particles, the condensate fraction and\nthe specific heat. After obtaining asymptotic expansions for large system size,\nwhich are valid throughout the BEC regime, we describe analytically how the\nthermodynamic limit behaviour is approached. In particular, in the critical\nregion of the BEC transition, we express the chemical potential and the\nspecific heat as simple explicit functions of the temperature, highlighting the\neffects of finite size. These effects are seen to be different for the two\ndifferent geometries. We also consider the Bose gas in a one-dimensional box, a\nsystem which does not possess BEC in the sense of a phase transition even in\nthe infinite volume limit."
    },
    {
        "anchor": "Analytical and numerical studies of Bose-Fermi mixtures in a\n  one-dimensional harmonic trap: In this paper we study a mixed system of bosons and fermions with up to six\nparticles in total. All particles are assumed to have the same mass. The\ntwo-body interactions are repulsive and are assumed to have equal strength in\nboth the Bose-Bose and the Fermi-Boson channels. The particles are confined\nexternally by a harmonic oscillator one-body potential. For the case of four\nparticles, two identical fermions and two identical bosons, we focus on the\nstrongly interacting regime and analyze the system using both an analytical\napproach and DMRG calculations using a discrete version of the underlying\ncontinuum Hamiltonian. This provides us with insight into both the ground state\nand the manifold of excited states that are almost degenerate for large\ninteraction strength. Our results show great variation in the density profiles\nfor bosons and fermions in different states for strongly interacting mixtures.\nBy moving to slightly larger systems, we find that the ground state of balanced\nmixtures of four to six particles tends to separate bosons and fermions for\nstrong (repulsive) interactions. On the other hand, in imbalanced Bose-Fermi\nmixtures we find pronounced odd-even effects in systems of five particles.\nThese few-body results suggest that question of phase separation in\none-dimensional confined mixtures are very sensitive to system composition,\nboth for the ground state and the excited states.",
        "positive": "Observation of Weak Collapse in a Bose-Einstein Condensate: We study the collapse of an attractive atomic Bose-Einstein condensate\nprepared in the uniform potential of an optical-box trap. We characterise the\ncritical point for collapse and the collapse dynamics, observing universal\nbehaviour in agreement with theoretical expectations. Most importantly, we\nobserve a clear experimental signature of the counterintuitive weak collapse,\nnamely that making the system more unstable can result in a smaller particle\nloss. We experimentally determine the scaling laws that govern the\nweak-collapse atom loss, providing a benchmark for the general theories of\nnonlinear wave phenomena."
    },
    {
        "anchor": "The Avalanche Mechanism for Atom Loss near an Atom-Dimer Efimov\n  Resonance: An Efimov trimer near the atom-dimer threshold can increase the atom loss\nrate in ultracold trapped atoms through the {\\it avalanche mechanism} proposed\nby Zaccanti et al. A 3-body recombination event creates an energetic atom and\ndimer, whose subsequent elastic collisions produce additional atoms with\nsufficient energy to escape from the trapping potential. We use Monte Carlo\nmethods to calculate the average number of atoms lost and the average heat\ngenerated by recombination events in both a Bose-Einstein condensate and a\nthermal gas. We take into account the energy-dependence of the cross sections\nand the spatial structure of the atom cloud. We confirm that the number of\natoms lost can be much larger than the naive value 3 if there is an Efimov\ntrimer near the atom-dimer threshold. This does not produce a narrow loss\nfeature, but it can significantly affect the determination of Efimov\nparameters.",
        "positive": "A self-bound matter-wave boson-fermion quantum ball: We demonstrate the possibility of creating a self-bound stable\nthree-dimensional matter-wave spherical boson-fermion quantum ball in the\npresence of an attractive boson-fermion interaction and a small repulsive\nthree-boson interaction. The three-boson interaction could be attractive or\nrepulsive whereas the fermions are taken to be in a fully-paired super-fluid\nstate in the Bardeen- Cooper-Schreifer ( quasi-noninteracting weak-coupling)\nlimit. We also include the Lee-Huang-Yang (LHY) correction to a repulsive\nbosonic interaction term. The repulsive three-boson interaction and the LHY\ncorrection can stop a global collapse while acting jointly or separately. The\npresent study is based on a mean-field model, where the bosons are subject to a\nGross-Pitaevskii (GP) Lagrangian functional and the fully-paired fermions are\ndescribed by a Galilean-invariant density functional Lagrangian. The\nboson-fermion interaction is taken to be the mean-field Hartree interaction,\nquite similar to the interaction term in the GP equation. The study is\nillustrated by a variational and a numerical solution of the mean-field model\nfor the boson-fermion $^7$Li- $^6$Li system."
    },
    {
        "anchor": "Single-particle momentum distribution of Efimov states in noninteger\n  dimensions: We studied the single-particle momentum distribution of mass-imbalanced\nEfimov states embedded in noninteger dimensions. The contact parameters, which\ncan be related to the thermodynamic properties of the gas, were calculated from\nthe high momentum tail of the single particle densities. We studied the\ndependence of the contact parameters with the progressive change of the\nnoninteger dimension, ranging from three (D=3) to two (D=2) dimensions. Within\nthis interval, we move from the (D=3) regime where the Efimov discrete scale\nsymmetry drives the physics, until close to the critical dimension, which\ndepends on the mass imbalance, where the continuum scale symmetry takes place.\nWe found that the two- and three-body contacts grow significantly in magnitude\nwith the decrease of the noninteger dimension towards the critical dimension,\nimpacting observables of resonantly interacting trapped Bose gases.",
        "positive": "Rapid generation of Mott insulators from arrays of noncondensed atoms: We theoretically analyze a scheme for a fast adiabatic transfer of cold atoms\nfrom the atomic limit of isolated traps to a Mott-insulator close to the\nsuperfluid phase. This gives access to the Bose-Hubbard physics without the\nneed of a prior Bose-Einstein condensate. The initial state can be prepared by\ncombining the deterministic assembly of atomic arrays with resolved Raman\nsideband cooling. In the subsequent transfer the trap depth is reduced\nsignificantly. We derive conditions for the adiabaticity of this process and\ncalculate optimal adiabatic ramp shapes. Using available experimental\nparameters, we estimate the impact of heating due to photon scattering and\ncompute the fidelity of the transfer scheme. Finally, we discuss the particle\nnumber scaling behavior of the method for preparing low-entropy states. Our\nfindings demonstrate the feasibility of the proposed scheme with\nstate-of-the-art technology."
    },
    {
        "anchor": "Collapse of spin-orbit coupled Bose-Einstein condensates: A finite-size quasi two-dimensional Bose-Einstein condensate collapses if the\nattraction between atoms is sufficiently strong. Here we present a theory of\ncollapse for condensates with the interatomic attraction and spin-orbit\ncoupling. We consider two realizations of spin-orbit coupling: the axial Rashba\ncoupling and balanced, effectively one-dimensional, Rashba-Dresselhaus one. In\nboth cases spin-dependent \"anomalous\" velocity, proportional to the spin-orbit\ncoupling strength, plays a crucial role. For the Rashba coupling, this velocity\nforms a centrifugal component in the density flux opposite to that arising due\nto the attraction between particles and prevents the collapse at a sufficiently\nstrong coupling. For the balanced Rashba-Dresselhaus coupling, the\nspin-dependent velocity can spatially split the initial state in one dimension\nand form spin-projected wavepackets, reducing the total condensate density.\nDepending on the spin-orbit coupling strength, interatomic attraction, and the\ninitial state, this splitting either prevents the collapse or modifies the\ncollapse process. These results show that the collapse can be controlled by a\nspin-orbit coupling, thus, extending the domain of existence of condensates of\nattracting atoms.",
        "positive": "Phase-slips and vortex dynamics in Josephson oscillations between\n  Bose-Einstein condensates: We study the relation between Josephson dynamics and topological excitations\nin a dilute Bose-Einstein condensate confined in a double-well trap. We show\nthat the phase slips responsible for the self-trapping regime are created by\nvortex rings entering and annihilating inside the weak-link region or created\nat the center of the barrier and expanding outside the system. Large amplitude\noscillations just before the onset of self-trapping are also strictly connected\nwith the dynamics of vortex rings at the edges of the inter-well barrier. Our\nresults extend and analyze the dynamics of the vortex-induced phase slippages\nsuggested a few decades ago in relation to the \"ac\" Josephson effect of\nsuperconducting and superfluid helium systems."
    },
    {
        "anchor": "Stability and spatial coherence of nonresonantly pumped\n  exciton-polariton condensates: We investigate the stability and coherence properties of one-dimensional\nexciton-polariton condensates under nonresonant pumping. We model the\ncondensate dynamics using the open-dissipative Gross-Pitaevskii equation. In\nthe case of spatially homogeneous pumping, we find that the instability of the\nsteady state leads to significant eduction of the coherence length. We consider\ntwo effects that can lead to the stabilization of the steady state, i.e. the\npolariton energy relaxation and the influence of an inhomogeneous pumping\nprofile. We find that, while the former has little effect on the stability, the\nlatter is very effective in stabilizing the condensate which results in a large\ncoherence length.",
        "positive": "The multiconfigurational time-dependent Hartree method for bosons with\n  internal degrees of freedom: Theory and composite fragmentation of\n  multi-component Bose-Einstein condensates: In this paper the multiconfigurational time-dependent Hartree for bosons\nmethod (MCTDHB) is derived for the case of $N$ identical bosons with internal\ndegrees of freedom. The theory for bosons with internal degrees of freedom\nconstitutes a generalization of the MCTDHB method that substantially enriches\nthe many-body physics that can be described. We demonstrate that the\nnumerically exact solution of the time-dependent many-body Schr\\\"odinger\nequation for interacting bosonic particles with internal degrees of freedom is\nnow feasible. We report on the MCTDHB equations of motion for bosons with\ninternal degrees of freedom and their implementation for a general many-body\nHamiltonian with one-body and two-body terms that, both, may depend on the\ninternal states of the considered particles. To demonstrate the capabilities of\nthe theory and its software implementation integrated in the MCTDH-X software,\nwe apply MCTDHB to the emergence of fragmentation of parabolically trapped\nbosons with two internal states: we study the groundstate of $N=100$\nparabolically confined bosons as a function of the splitting between the\nstate-dependent minima of the two parabolic potentials. To quantify the\ncoherence of the system we compute its normalized one-body correlation\nfunction. We find that the coherence within each internal state of the atoms is\nmaintained, while it is lost between the different internal states. This is a\nhallmark of a new kind of fragmentation which is absent in bosons without\ninternal structure. We term the emergent phenomenon \"composite fragmentation\"."
    },
    {
        "anchor": "Suppression of the critical temperature for superfluidity near the Mott\n  transition: validating a quantum simulator: Ultracold atomic gases in optical lattices have proven to be a controllable,\ntunable and clean implementation of strongly interacting quantum many-body\nsystems. An essential prospect for such quantum simulators is their ability to\nmap out the phase diagram of fundamental many-body model Hamiltonians. However,\nthe results need to be validated first for representative benchmark problems\nvia state-of-the-art numerical methods of quantum many-body theory. Here we\npresent the first ab-initio comparison between experiments and quantum Monte\nCarlo simulations for strongly interacting Bose gases on a lattice for large\nsystems (up to N = 3e5 particles). The comparison has enabled us to perform\nthermometry for the interacting quantum gas and to experimentally determine the\nfinite temperature phase diagram for bosonic superfluids in an optical lattice.\nOur results reveal a downshift of the critical temperature as the transition to\nthe Mott insulator is approached.",
        "positive": "Emergent Fermi sea in a system of interacting bosons: An understanding of the possible ways in which interactions can produce\nfundamentally new emergent many-body states is a central problem of condensed\nmatter physics. We ask if a Fermi sea can arise in a system of bosons subject\nto contact interaction. Based on exact diagonalization studies and variational\nwave functions, we predict that such a state is likely to occur when a system\nof two-component bosons in two dimensions, interacting via a species\nindependent contact interaction, is exposed to a synthetic magnetic field of\nstrength that corresponds to a filling factor of unity. The fermions forming\nthe SU(2) singlet Fermi sea are bound states of bosons and quantized vortices,\nformed as a result of the repulsive interaction between bosons in the lowest\nLandau level."
    },
    {
        "anchor": "Local observation of antibunching in a trapped Fermi gas: Local density fluctuations and density profiles of a Fermi gas are measured\nin-situ and analyzed. In the quantum degenerate regime, the weakly interacting\n$^6$Li gas shows a suppression of the density fluctuations compared to the\nnon-degenerate case, where atomic shot noise is observed. This manifestation of\nantibunching is a direct result of the Pauli principle and constitutes a local\nprobe of quantum degeneracy. We analyze our data using the predictions of the\nfluctuation-dissipation theorem and the local density approximation,\ndemonstrating a fluctuation-based temperature measurement.",
        "positive": "Long-lived states with well-defined spins in spin-$1/2$ homogeneous Bose\n  gases: Many-body eigenfunctions of the total spin operator can be constructed from\nthe spin and spatial wavefunctions with non-trivial permutation symmetries.\nSpin-dependent interactions can lead to relaxation of the spin eigenstates to\nthe thermal equilibrium. A mechanism that stabilizes the many-body entangled\nstates is proposed here. Surprisingly, in spite coupling with the chaotic\nmotion of the spatial degrees of freedom, the spin relaxation can be suppressed\nby destructive quantum interference due to spherical vector and tensor terms of\nthe spin-dependent interactions. Tuning the scattering lengths by the method of\nFeshbach resonances, readily available in cold atomic labs, can enhance the\nrelaxation timescales by several orders of magnitude."
    },
    {
        "anchor": "Quasi-one-dimensional harmonically trapped quantum droplets: We theoretically consider effectively one-dimensional quantum droplets in a\nsymmetric Bose-Bose mixture confined in a parabolic trap. We systematically\ninvestigate ground and excited families of localized trapped modes which\nbifurcate from eigenstates of the quantum harmonic oscillator as the number of\nparticles departs from zero. Families of nonlinear modes have nonmonotonous\nbehavior of chemical potential on the number of particles and feature\nbistability regions. Excited states are unstable close to the linear limit, but\nbecome stable when the number of particles is large enough. In the limit of\nlarge density, we derive a modified Thomas-Fermi distribution. Smoothly\ndecreasing the trapping strength down to zero, one can dynamically transform\nthe ground state solution to the solitonlike quantum droplet, while excited\ntrapped states break in several moving quantum droplets.",
        "positive": "On the information entropy of matter-waves in quasi-disorder potentials: We consider ultracold Bose gases in quasi-random potentials and quantify\nlocalization of matter waves by means of Shannon information entropy. We\nexplicitly examine the role of quasi-random potentials in producing localized\nstates in the linear and nonlinear regimes. It is seen that the information\nentropic-based approach can be more useful to quantify localization of\ndifferent types of states observed in Bose-Einstein condensates."
    },
    {
        "anchor": "A geometric wave function for few interacting bosons in a harmonic trap: We establish a new geometric wave function that combined with a variational\nprinciple efficiently describes a system of bosons interacting in a\none-dimensional trap. By means of a a combination of the exact wave function\nsolution for contact interactions and the asymptotic behaviour of the harmonic\npotential solution we obtain the ground state energy, probability density and\nprofiles of a few boson system in a harmonic trap. We are able to access all\nregimes, ranging from the strongly attractive to the strongly repulsive one\nwith an original and simple formulation.",
        "positive": "SU(6) Heisenberg model on the honeycomb lattice: competition between\n  plaquette and chiral order: We revisit the SU(6) Heisenberg model on the honeycomb lattice, which has\nbeen predicted to be a chiral spin liquid by mean-field theory [G. Szirmai et\nal., Phys. Rev. A 84, 011611 (2011)]. Using exact diagonalizations of finite\nclusters, infinite projected entangled pair states simulations, and variational\nMonte Carlo simulations based on Gutzwiller projected wave functions, we\nprovide strong evidence in favour of the competing plaquette state, which was\nreported to be higher but close by in energy according to mean-field theory.\nThis is further confirmed by the investigation of the model with a ring\nexchange term, which shows that there is a transition between the plaquette\nstate and the chiral state at a finite value of the ring exchange term."
    },
    {
        "anchor": "Enhancing the Thermal Stability of Majorana Fermions with Redundancy\n  Using Dipoles in Optical Lattices: Pairing between spinless fermions can generate Majorana fermion excitations\nthat exhibit intriguing properties arising from non-local correlations. But\nsimple models indicate that non-local correlation between Majorana fermions\nbecomes unstable at non-zero temperatures. We address this issue by showing\nthat anisotropic interactions between dipolar fermions in optical lattices can\nbe used to significantly enhance thermal stability. We construct a model of\noriented dipolar fermions in a square optical lattice. We find that domains\nestablished by strong interactions exhibit enhanced correlation between\nMajorana fermions over large distances and long times even at finite\ntemperatures, suitable for stable redundancy encoding of quantum information.\nOur approach can be generalized to a variety of configurations and other\nsystems, such as quantum wire arrays.",
        "positive": "A Gross-Pitaevskii-equation description of the momentum-state lattice:\n  roles of the trap and many-body interactions: We report a theoretical description of the synthetic momentum-state lattices\nwith a 3D Gross-Pitaevskii equation (GPE), where both the external trap\npotential and the mean-field spatial-density-dependent many-body interactions\nare naturally included and exactly treated. The GPE models exhibit better\nperformance than the tight-binding model to depict the experimental\nobservations. Since the trap modifies the dispersion relation for free\nparticles and shapes the spatial density distribution that leads to\ninhomogeneous interactions, decoherences (damping oscillation) appear even for\na short-time evolution. Our parametric calculations for the two-state\noscillation suggest that we should work with a relatively shallow trap in the\nweakly interacting regime, especially when the long-term dynamics are\nconcerned. The impact of the mean-field interaction, i.e., the self-trapping\nbehavior, on the transport dynamics and the topological phase transition in a\nfinite multiple-state lattice chain is also specifically investigated. Such an\naccurate treatment of the inhomogeneous interactions allows for further\ninvestigations on the interplay with disorder, the pair correlation dynamics,\nand the thermalization process in momentum space."
    },
    {
        "anchor": "On the number of Bose-selected modes in driven-dissipative ideal Bose\n  gases: In an ideal Bose gas that is driven into a steady state far from thermal\nequilibrium, a generalized form of Bose condensation can occur. Namely, the\nsingle-particle states unambiguously separate into two groups: the group of\nBose-selected states, whose occupations increase linearly with the total\nparticle number, and the group of all other states whose occupations saturate\n[Phys. Rev. Lett. 111, 240405 (2013)]. However, so far very little is known\nabout how the number of Bose-selected states depends on the properties of the\nsystem and its coupling to the environment. The answer to this question is\ncrucial since systems hosting a single, a few, or an extensive number of\nBose-selected states will show rather different behavior. While in the former\ntwo scenarios each selected mode acquires a macroscopic occupation,\ncorresponding to (fragmented) Bose condensation, the latter case rather bears\nresemblance to a high-temperature state of matter. In this paper, we\nsystematically investigate the number of Bose-selected states, considering\ndifferent classes of the rate matrices that characterize the driven-dissipative\nideal Bose gases in the limit of weak system-bath coupling. These include rate\nmatrices with continuum limit, rate matrices of chaotic driven systems, random\nrate matrices, and rate matrices resulting from thermal baths that couple to a\nfew observables only.",
        "positive": "Floquet engineering a bosonic Josephson junction: We study Floquet engineering of the tunnel coupling between a pair of\none-dimensional bosonic quasi-condensates in a tilted double-well potential. By\nmodulating the energy difference between the two wells, we re-establish tunnel\ncoupling and precisely control its amplitude and phase. This allows us to\ninitiate coherence between two initially uncorrelated Bose gases and prepare\ndifferent initial states in the emerging sine-Gordon Hamiltonian. We fully\ncharacterize the Floquet system and study the dependence of both equilibrium\nproperties and relaxation on the modulation."
    },
    {
        "anchor": "Induced interactions in the BCS-BEC crossover of two-dimensional Fermi\n  gases with Rashba spin-orbit coupling: We investigate the Gorkov--Melik-Barkhudarov (GM) correction to superfluid\ntransition temperature in two-dimensional Fermi gases with Rashba spin-orbit\ncoupling (SOC) across the SOC-driven BCS-BEC crossover. In the calculation of\nthe induced interaction, we find that the spin-component mixing due to SOC can\ninduce both of the conventional screening and additional antiscreening\ncontributions that interplay significantly in the strong SOC regime. While the\nGM correction generally lowers the estimate of transition temperature, it turns\nout that at a fixed weak interaction, the correction effect exhibits a\ncrossover behavior where the ratio between the estimates without and with the\ncorrection first decreases with SOC and then becomes insensitive to SOC when it\ngoes into the strong SOC regime. We demonstrate the applicability of the GM\ncorrection by comparing the zero-temperature condensate fraction with the\nrecent quantum Monte Carlo results.",
        "positive": "Domain-wall melting as a probe of many-body localization: Motivated by a recent optical-lattice experiment by Choi et al.[Science 352,\n1547 (2016)], we discuss how domain-wall melting can be used to investigate\nmany-body localization. First, by considering noninteracting fermion models, we\ndemonstrate that experimentally accessible measures are sensitive to\nlocalization and can thus be used to detect the delocalization-localization\ntransition, including divergences of characteristic length scales. Second,\nusing extensive time-dependent density matrix renormalization group\nsimulations, we study fermions with repulsive interactions on a chain and a\ntwo-leg ladder. The extracted critical disorder strengths agree well with the\nones found in existing literature."
    },
    {
        "anchor": "Pairing in a two-dimensional Fermi gas with population imbalance: Pairing in a population imbalanced Fermi system in a two-dimensional optical\nlattice is studied using Determinant Quantum Monte Carlo (DQMC) simulations and\nmean-field calculations. The approximation-free numerical results show a wide\nrange of stability of the Fulde-Ferrell-Larkin-Ovshinnikov (FFLO) phase.\nContrary to claims of fragility with increased dimensionality we find that this\nphase is stable across wide range of values for the polarization, temperature\nand interaction strength. Both homogeneous and harmonically trapped systems\ndisplay pairing with finite center of mass momentum, with clear signatures\neither in momentum space or real space, which could be observed in cold atomic\ngases loaded in an optical lattice. We also use the harmonic level basis in the\nconfined system and find that pairs can form between particles occupying\ndifferent levels which can be seen as the analog of the finite center of mass\nmomentum pairing in the translationally invariant case. Finally, we perform\nmean field calculations for the uniform and confined systems and show the\nresults to be in good agreement with QMC. This leads to a simple picture of the\ndifferent pairing mechanisms, depending on the filling and confining potential.",
        "positive": "Superfluid Vortices in Four Spatial Dimensions: Quantum vortices in superfluids have been an important research area for many\ndecades. Naturally, research on this topic has focused on two and\nthree-dimensional superfluids, in which vortex cores form points and lines,\nrespectively. Very recently, however, there has been growing interest in the\nquantum simulation of systems with four spatial dimensions; this raises the\nquestion of how vortices would behave in a higher-dimensional superfluid. In\nthis paper, we begin to establish the phenomenology of vortices in 4D\nsuperfluids under rotation, where the vortex core can form a plane. In 4D, the\nmost generic type of rotation is a \"double rotation\" with two angles (or\nfrequencies). We show, by solving the Gross-Pitaesvkii equation, that the\nsimplest case of equal-frequency double rotation can stabilise a pair of vortex\nplanes intersecting at a point. This opens up a wide number of future research\ntopics, including unequal-frequency double rotations; the stability and\nreconnection dynamics of intersecting vortex surfaces; and the possibility of\nclosed vortex surfaces."
    },
    {
        "anchor": "Quantum stochastic behaviour in cold Fermi gases: Phonon propagation: We examine the effect of quantum fluctuations in a tunable cold Fermi gas on\nthe propagation of phonons. We show that these fluctuations can be interpreted\nas inducing a stochastic (acoustic) space-time. The variation in times of\nflight induced by this stochastic behaviour can be significant in the\ntransition region between BEC and BCS regimes.",
        "positive": "Quantum Gutzwiller approach for the two-component Bose-Hubbard model: We study the effects of quantum fluctuations in the two-component\nBose-Hubbard model generalizing to mixtures the quantum Gutzwiller approach\nintroduced recently in [Phys. Rev. Research 2, 033276 (2020)]. As a basis for\nour study, we analyze the mean-field ground-state phase diagram and spectrum of\nelementary excitations, with particular emphasis on the quantum phase\ntransitions of the model. Within the quantum critical regimes, we address both\nthe superfluid transport properties and the linear response dynamics to density\nand spin probes of direct experimental relevance. Crucially, we find that\nquantum fluctuations have a dramatic effect on the drag between the superfluid\nspecies of the system, particularly in the vicinity of the paired and\nantipaired phases absent in the usual one-component Bose-Hubbard model.\nAdditionally, we analyse the contributions of quantum corrections to the\none-body coherence and density/spin fluctuations from the perspective of the\ncollective modes of the system, providing results for the few-body correlations\nin all the regimes of the phase diagram."
    },
    {
        "anchor": "Finite-Temperature Quantum Matter with Rydberg or Molecule Synthetic\n  Dimensions: Synthetic dimension platforms offer unique pathways for engineering quantum\nmatter. We compute the phase diagram of a many-body system of ultracold atoms\n(or polar molecules) with a set of Rydberg states (or rotational states) as a\nsynthetic dimension, where the particles are arranged in real space in optical\nmicrotrap arrays and interact via dipole-dipole exchange interaction. Using\nmean-field theory, we find three ordered phases - two are localized in the\nsynthetic dimension, predicted as zero-temperature ground states in Refs. [Sci.\nRep., 8, 1 (2018) and Phys. Rev. A 99, 013624 (2019)], and a delocalized phase.\nWe characterize them by identifying the spontaneously broken discrete\nsymmetries of the Hamiltonian. We also compute the phase diagram as a function\nof temperature and interaction strength, for both signs of the interaction. For\nsystem sizes with more than six synthetic sites and attractive interactions, we\nfind that the thermal phase transitions can be first or second order, which\nleads to a tri-critical point on the phase boundary. By examining the\ndependence of the tri-critical point and other special points of the phase\nboundary on the synthetic dimension size, we shed light on the physics for\nthermodynamically large synthetic dimension.",
        "positive": "Probing quantum criticality and symmetry breaking at the microscopic\n  level: We report on an experimental study of the Lipkin-Meshkov-Glick model of\nquantum spins interacting at infinite range in a transverse magnetic field,\nwhich exhibits a ferromagnetic phase transition in the thermodynamic limit. We\nuse Dysprosium atoms of electronic spin $J=8$, subjected to a quadratic Zeeman\nlight shift, to simulate $2J=16$ interacting spins $1/2$. We probe the system\nmicroscopically using single magnetic sublevel resolution, giving access to the\nspin projection parity, which is the collective observable characterizing the\nunderlying $\\mathbb{Z}_2$ symmetry. We measure the thermodynamic properties and\ndynamical response of the system, and study the quantum critical behavior\naround the transition point. In the ferromagnetic phase, we achieve coherent\ntunneling between symmetry-broken states, and test the link between symmetry\nbreaking and the appearance of a finite order parameter."
    },
    {
        "anchor": "Interacting bosonic flux ladders with a synthetic dimension:\n  Ground-state phases and quantum quench dynamics: Flux ladders constitute the minimal setup enabling a systematic understanding\nof the rich physics of interacting particles subjected simultaneously to strong\nmagnetic fields and a lattice potential. In this paper, the ground-state phase\ndiagram of a flux-ladder model is mapped out using extensive density-matrix\nrenormalization-group simulations. The emphasis is put on parameters which can\nbe experimentally realized exploiting the internal states of potassium atoms as\na synthetic dimension. The focus is on accessible observables such as the\nchiral current and the leg-population imbalance. Considering a particle filling\nof one boson per rung, we report the existence of a Mott-insulating Meissner\nphase as well as biased-ladder phases on top of superfluids and Mott\ninsulators. Furthermore, we demonstrate that quantum quenches from suitably\nchosen initial states can be used to probe the equilibrium properties in the\ntransient dynamics. Concretely, we consider the instantaneous turning on of\nhopping matrix elements along the rungs or legs in the synthetic flux-ladder\nmodel, with different initial particle distributions. We show that clear\nsignatures of the biased-ladder phase can be observed in the transient\ndynamics. Moreover, the behavior of the chiral current in the transient\ndynamics is discussed. The results presented in this paper provide guidelines\nfor future implementations of flux ladders in experimental setups exploiting a\nsynthetic dimension.",
        "positive": "Simulating Infinite Vortex Lattices in Superfluids: We present an efficient framework to numerically treat infinite periodic\nvortex lattices in rotating superfluids described by the Gross-Pitaevskii\ntheory. The commonly used split-step Fourier (SSF) spectral methods are\ninapplicable to such systems as the standard Fourier transform does not respect\nthe boundary conditions mandated by the magnetic translation group. We present\na generalisation of the SSF method which incorporates the correct boundary\nconditions by employing the so-called magnetic Fourier transform. We test the\nmethod and show that it reduces to known results in the lowest-Landau-level\nregime. While we focus on rotating scalar superfluids for simplicity, the\nframework can be naturally extended to treat multicomponent systems and systems\nunder more general `synthetic' gauge fields."
    },
    {
        "anchor": "Quantum noise in a transversely pumped cavity Bose--Hubbard model: We investigate the quantum measurement noise effects on the dynamics of an\natomic Bose lattice gas inside an optical resonator. We describe the dynamics\nby means of a hybrid model consisting of a Bose--Hubbard Hamiltonian for the\natoms and a Heisenberg--Langevin equation for the lossy cavity field mode. We\nassume that the atoms are prepared initially in the ground state of the lattice\nHamiltonian and then start to interact with the cavity mode. We show that the\ncavity field fluctuations originating from the dissipative outcoupling of\nphotons from the resonator lead to vastly different effects in the different\npossible ground state phases, i.e., the superfluid, the supersolid, the Mott-\nand the charge-density-wave phases. In the former two phases with the presence\nof a superfluid wavefunction, the quantum measurement noise appears as a\ndriving term leading to excess noise depletion of the ground state. The time\nscale for the system to leave the ground scale is determined analytically. For\nthe latter two incompressible phases, the quantum noise results in the\nfluctuation of the chemical potential. We derive an analytical expression for\nthe corresponding broadening of the quasiparticle resonances.",
        "positive": "Interaction and filling induced quantum phases of dual Mott insulators\n  of bosons and fermions: Many-body effects are at the very heart of diverse phenomena found in\ncondensed-matter physics. One striking example is the Mott insulator phase\nwhere conductivity is suppressed as a result of a strong repulsive interaction.\nAdvances in cold atom physics have led to the realization of the Mott\ninsulating phases of atoms in an optical lattice, mimicking the corresponding\ncondensed matter systems. Here, we explore an exotic strongly-correlated system\nof Interacting Dual Mott Insulators of bosons and fermions. We reveal that an\ninter-species interaction between bosons and fermions drastically modifies each\nMott insulator, causing effects that include melting, generation of composite\nparticles, an anti-correlated phase, and complete phase-separation. Comparisons\nbetween the experimental results and numerical simulations indicate intrinsic\nadiabatic heating and cooling for the attractively and repulsively interacting\ndual Mott Insulators, respectively."
    },
    {
        "anchor": "Multidimensional Spectroscopy of Time-Dependent Impurities in Ultracold\n  Fermions: We investigate the system of a heavy impurity immersed in a degenerated Fermi\ngas, where the impurity's internal degree of freedom (pseudospin) is\nmanipulated by a series of radiofrequency (RF) pulses at several different\ntimes. Applying the functional determinant approach, we carry out an\nessentially exact calculation of the Ramsey-interference-type responses to the\nRF pulses. These responses are universal functions of the multiple time\nintervals between the pulses for all time and can be regarded as\nmultidimensional (MD) spectroscopy of the system in the time domain. A Fourier\ntransformation of the time intervals gives the MD spectroscopy in the frequency\ndomain, providing insightful information on the many-body correlation and\nrelaxation via the cross-peaks, e.g., the off-diagonal peaks in a\ntwo-dimensional spectrum. These features are inaccessible for the conventional,\none-dimensional absorption spectrum. Our scheme provides a new method to\ninvestigate many-body nonequilibrium physics beyond the linear response regime\nwith the accessible tools in cold atoms.",
        "positive": "Many-body dynamics of p-wave Feshbach molecule production: a mean-field\n  approach: We study the mean-field dynamics of p-wave Feshbach molecule production in an\nultra cold gas of Fermi atoms in the same internal state. We derive a separable\npotential to describe the low-energy scattering properties of such atoms, and\nuse this potential to solve the mean-field dynamics during a magnetic field\nsweep. Initially, on the negative scattering length side of a Feshbach\nresonance the gas is described by the BCS theory. We adapt the method by\nSzyma\\'{n}ska et al. [Phys. Rev. Lett. 94, 170402 (2005)] to p-wave interacting\nFermi gases and model the conversion dynamics of the gas into a Bose-Einstein\ncondensate of molecules on the other side of the resonance under the influence\nof a linearly varying magnetic field. We have analyzed the dependence of the\nmolecule production efficiency on the density of the gas, temperature, initial\nvalue of the magnetic field, and magnetic field ramp speed. Our results show\nthat in this approximation molecule production by a linear magnetic field sweep\nis highly dependent on the initial state."
    },
    {
        "anchor": "Spin-asymmetric Josephson plasma oscillations: The spin-asymmetric Josephson effect is a proposed quantum-coherent\ntunnelling phenomenon where Cooper-paired fermionic spin-$\\frac{1}{2}$\nparticles, which are subjected to spin-dependent potentials across a Josephson\njunction, undergo frequency-synchronized alternating-current Josephson\noscillations with spin-dependent amplitudes. Here, in line with present-day\ntechniques in ultracold Fermi gas setups, we consider the regime of small\nJosephson oscillations and show that the Josephson plasma oscillation amplitude\nbecomes spin-dependent in the presence of spin-dependent potentials while the\nJosephson plasma frequency is the same for both spin-components. Detecting\nthese spin-dependent Josephson plasma oscillations provides a possible means to\nestablish the yet-unobserved spin-asymmetric Josephson effect with ultracold\nFermi gases using existing experimental tools.",
        "positive": "Goos-H\u00e4nchen shifts in spin-orbit-coupled cold atoms: We consider a matter wave packet of cold atom gas impinging upon a step\npotential created by the optical light field. In the presence of spin-orbit\n(SO) coupling, the atomic eigenstates contain two types of evanescent states,\none of which is the ordinary evanescent state with pure imaginary wave vector\nwhile the other possesses complex wave vector and is recognized as oscillating\nevanescent state. We show that the presence and interplay of these two types of\nevanescent states can give rise to two different mechanisms for total internal\nreflection (TIR), and thus lead to unusual Goos-H\\\"anchen (GH) effect. As a\nresult, not only large positive but also large negative GH shift can be\nobserved in the reflected atomic beam. The dependence of the GH shift on the\nincident angle, energy and height of the step potential is studied numerically."
    },
    {
        "anchor": "Accelerating analysis of Boltzmann equations using Gaussian mixture\n  models: Application to quantum Bose-Fermi mixtures: The Boltzmann equation is a powerful theoretical tool for modeling the\ncollective dynamics of quantum many-body systems subject to external\nperturbations. Analysis of the equation gives access to linear response\nproperties including collective modes and transport coefficients, but often\nproves intractable due to computational costs associated with multidimensional\nintegrals describing collision processes. Here, we present a method to resolve\nthis bottleneck, enabling the study of a broad class of many-body systems that\nappear in fundamental science contexts and technological applications.\nSpecifically, we demonstrate that a Gaussian mixture model can accurately\nrepresent equilibrium distribution functions, thereby allowing efficient\nevaluation of collision integrals. Inspired by cold atom experiments, we apply\nthis method to investigate the collective behavior of a quantum Bose-Fermi\nmixture of cold atoms in a cigar-shaped trap, a system that is particularly\nchallenging to analyze. We focus on monopole and quadrupole collective modes\nabove the Bose-Einstein transition temperature, and find a rich phenomenology\nthat spans interference effects between bosonic and fermionic collective modes,\ndampening of these modes, and the emergence of hydrodynamics in various\nparameter regimes. These effects are readily verifiable experimentally.",
        "positive": "Spin-Seebeck effect in a strongly interacting Fermi gas: We study the spin-Seebeck effect in a strongly interacting, two-component\nFermi gas and propose an experiment to measure this effect by relatively\ndisplacing spin up and spin down atomic clouds in a trap using spin-dependent\ntemperature gradients. We compute the spin-Seebeck coefficient and related\nspin-heat transport coefficients as functions of temperature and interaction\nstrength. We find that when the inter-spin scattering length becomes larger\nthan the Fermi wavelength, the spin-Seebeck coefficient changes sign as a\nfunction of temperature, and hence so does the direction of the\nspin-separation. We compute this zero-crossing temperature as a function of\ninteraction strength and in particular in the unitary limit for the inter-spin\nscattering."
    },
    {
        "anchor": "Ultracold quantum gases in triangular optical lattices: Over the last years the exciting developments in the field of ultracold atoms\nconfined in optical lattices have led to numerous theoretical proposals devoted\nto the quantum simulation of problems e.g. known from condensed matter physics.\nMany of those ideas demand for experimental environments with non-cubic lattice\ngeometries. In this paper we report on the implementation of a versatile\nthree-beam lattice allowing for the generation of triangular as well as\nhexagonal optical lattices. As an important step the superfluid-Mott insulator\n(SF-MI) quantum phase transition has been observed and investigated in detail\nin this lattice geometry for the first time. In addition to this we study the\nphysics of spinor Bose-Einstein condensates (BEC) in the presence of the\ntriangular optical lattice potential, especially spin changing dynamics across\nthe SF-MI transition. Our results suggest that below the SF-MI phase\ntransition, a well-established mean-field model describes the observed data\nwhen renormalizing the spin-dependent interaction. Interestingly this opens new\nperspectives for a lattice driven tuning of a spin dynamics resonance occurring\nthrough the interplay of quadratic Zeeman effect and spin-dependent\ninteraction. We finally discuss further lattice configurations which can be\nrealized with our setup.",
        "positive": "Finite-Temperature Properties of Attractive Three-Component Fermionic\n  Atoms in Optical Lattices: We investigate the finite-temperature properties of attractive\nthree-component (colors) fermionic atoms in optical lattices using a\nself-energy functional approach. As the strength of the attractive interaction\nincreases in the low-temperature region, we observe a second-order transition\nfrom a Fermi liquid to a color superfluid (CSF), where atoms from two of the\nthree colors form Cooper pairs. In the strong attractive region, we observe a\nfirst-order transition from a CSF to a trionic state, where three atoms with\ndifferent colors form singlet bound states. A crossover between a Fermi liquid\nand a trionic state is observed in the high-temperature region. We present a\nphase diagram covering zero to finite temperatures. We demonstrate that the CSF\ntransition temperature is enhanced by the anisotropy of the attractive\ninteraction."
    },
    {
        "anchor": "Energy redistribution and spatio-temporal evolution of correlations\n  after a sudden quench of the Bose-Hubbard model: An optical-lattice quantum simulator is an ideal experimental platform to\ninvestigate non-equilibrium dynamics of a quantum many-body system, which is in\ngeneral hard to simulate with classical computers. Here, we use our quantum\nsimulator of the Bose-Hubbard model to study dynamics far from equilibrium\nafter a quantum quench. We successfully confirm the energy conservation law in\nthe one- and three-dimensional systems and extract the propagation velocity of\nthe single-particle correlation in the one- and two-dimensional systems. We\ncorroborate the validity of our quantum simulator through quantitative\ncomparisons between the experiments and the exact numerical calculations in one\ndimension. In the computationally hard cases of two or three dimensions, by\nusing the quantum-simulation results as references, we examine the performance\nof a numerical method, namely the truncated Wigner approximation, revealing its\nusefulness and limitation. This work constitutes an exemplary case for the\nusage of analog quantum simulators.",
        "positive": "Dynamics of a few interacting bosons escaping from an open well: The dynamics of a few ultra-cold bosons tunneling from a one-dimensional\npotential well into open space is studied. In such a system several decay\nchannels can be distinguished, each corresponding to a different number of\nbosons escaping simultaneously. We show that as the interparticle interaction\nstrength is changed, the system undergoes transitions between distinct regimes\ncharacterized by the dominance of different decay channels. These transitions\nare reflected in the behavior of the decay rate of the system, which is\nmeasurable experimentally. By means of a simple theoretical description we show\nthat the transitions occur at the points where a new decay channel becomes\nenergetically viable. The results provide insight into the behavior of decaying\nfew-body systems and may have potential interest to experiments."
    },
    {
        "anchor": "Bragg spectroscopy and pair-breaking-continuum mode in a superfluid\n  Fermi gas: The superfluid, pair condensed spin-1/2 Fermi gases are supposed to exhibit\nat nonzero wave vector a still unobserved collective excitation mode in their\npair-breaking continuum. Using BCS theory at zero temperature and in the long\nwavelength limit, we predict that this mode is quantitatively observable (in\nfrequency, width and spectral weight) in the response of a cold atom gas to a\nlaser Bragg excitation, if one measures the perturbation induced on the order\nparameter modulus rather than on the density.",
        "positive": "Two and three particles interacting in a one-dimensional trap: We outline a procedure for using matrix mechanics to compute energy\neigenvalues and eigenstates for two and three interacting particles in a\nconfining trap, in one dimension. Such calculations can bridge a gap in the\nundergraduate physics curriculum between single-particle and many-particle\nquantum systems, and can also provide a pathway from standard quantum mechanics\ncourse material to understanding current research on cold-atom systems. In\nparticular we illustrate the notion of \"fermionization\" and how it occurs not\nonly for the ground state in the presence of strong repulsive interactions, but\nalso for excited states, in both the strongly attractive and strongly repulsive\nregimes."
    },
    {
        "anchor": "A Quantum Gas Microscope for Fermionic Atoms: Strongly interacting fermions define the properties of complex matter at all\ndensities, from atomic nuclei to modern solid state materials and neutron\nstars. Ultracold atomic Fermi gases have emerged as a pristine platform for the\nstudy of many-fermion systems. Here we realize a quantum gas microscope for\nfermionic $^{40}$K atoms trapped in an optical lattice, which allows one to\nprobe strongly correlated fermions at the single atom level. We combine 3D\nRaman sideband cooling with high-resolution optics to simultaneously cool and\nimage individual atoms with single lattice site resolution at a detection\nfidelity above $95\\%$. The imaging process leaves each atom predominantly in\nthe 3D ground state of its lattice site, inviting the implementation of a\nMaxwell's demon to assemble low-entropy many-body states. Single site resolved\nimaging of fermions enables the direct observation of magnetic order, time\nresolved measurements of the spread of particle correlations, and the detection\nof many-fermion entanglement.",
        "positive": "Time-dependent condensate fraction in an analytical model: We apply analytical solutions of a nonlinear boson diffusion equation (NBDE)\nthat include boundary conditions at the singularity to calculate the time\nevolution of the entropy during evaporative cooling of ultracold atoms, and the\ntime-dependent condensate fraction. For suitable initial conditions it is found\nto agree with available data on Na-23."
    },
    {
        "anchor": "Supercurrent and dynamical instability of spin-orbit-coupled ultracold\n  Bose gases: We investigate the stability of supercurrents in a Bose-Einstein condensate\nwith one-dimensional spin-orbit and Raman couplings. The consequence of the\nlack of Galilean invariance is explicitly discussed. We show that in the\nplane-wave phase, characterized by a uniform density, the supercurrent state\ncan become dynamically unstable, the instability being associated with the\noccurrence of a complex sound velocity, in a region where the effective mass is\nnegative. We also discuss the emergence of energetic instability in these\nsupercurrent states. We argue that both the dynamical and the energetic\ninstabilities in these systems can be generated experimentally through\nexcitation of the collective dipole oscillation.",
        "positive": "Long time rigidity to flux-induced symmetry breaking in quantum quench\n  dynamics: We investigate how the breaking of charge conjugation symmetry $\\mathcal{C}$\nimpacts on the dynamics of a half-filled fermionic lattice system after global\nquenches. We show that, when the initial state is insulating and the\n$\\mathcal{C}$-symmetry is broken non-locally by a constant magnetic flux, local\nobservables and correlations behave as if the symmetry were unbroken for a time\ninterval proportional to the system size $L$. In particular, the local particle\ndensity of a quenched dimerized insulator remains pinned to $1/2$ in each\nlattice site for an extensively long time, while it starts to significantly\nfluctuate only afterwards. Due to its qualitative resemblance to the sudden\narrival of rapidly rising ocean waves, we dub this phenomenon the ``tsunami\neffect\". Notably, it occurs even though the chiral symmetry is dynamically\nbroken right after the quench. Furthermore, we identify a way to quantify the\namount of symmetry breaking in the quantum state, showing that in insulators\nperturbed by a flux it is exponentially suppressed as a function of the system\nsize, while it is only algebraically suppressed in metals and in insulators\nwith locally broken $\\mathcal{C}$-symmetry. The robustness of the tsunami\neffect to weak disorder and interactions is demonstrated, and possible\nexperimental realizations are proposed."
    },
    {
        "anchor": "Spin-orbit-coupled spinor gap solitons in Bose-Einstein condensates: Spin-1 spin-orbit-coupled spinor Bose-Einstein condensates have been realized\nin experiment. We study spin-orbit-coupled spinor gap solitons in this\nexperimentally realizable system with an optical lattice. The spin-dependent\nparity symmetry of the spin-orbit coupling plays an important role in\nproperties of gap solitons. Two families of solitons with opposite\nspin-dependent parity are found. Using an approximating model by replacing the\noptical lattice with a Harmonic trap, we demonstrate the physical origination\nof these two families. For a large negative quadratic Zeeman shift, we also\nfind a type of gap solitons that spontaneously breaks the spin-dependent parity\nsymmetry due to the ferromagnetic spinor interactions.",
        "positive": "Bulk density signatures of a lattice quasihole with very few particles: Motivated by the recent experimental realization of a two-particle fractional\nquantum Hall state of ultracold atoms in a small optical lattice [Nature 619,\n495 (2023)], we propose a minimal setup to create and observe a quasihole in\nsuch a system. We find that clear signatures of a quasihole state with two or\nthree atoms can be obtained through a standard site-resolved density\nmeasurement provided that the system is appropriately modified with simple\nadditional potential profiles. By adding a single-site repulsive potential to\npin the quasihole and superimposing a harmonic trap on top of the optical\nlattice to keep the particles away from the system edge, we determine via exact\ndiagonalization an optimal range for system parameters such as the magnetic\nflux and the strengths of the additional potentials that would favour the\ncreation of the quasihole state. We hope that our results will be a useful\nguide for a possible proof-of-principle experiment that will demonstrate the\nfirst controllable creation of a simple quasihole state in a condensed matter\nsystem, which will pave the way for the observation of the anyonic statistics\nof quasiholes in a more complex system."
    },
    {
        "anchor": "Deformation of a quantum many-particle system by a rotating impurity: During the last 70 years, the quantum theory of angular momentum has been\nsuccessfully applied to describing the properties of nuclei, atoms, and\nmolecules, their interactions with each other as well as with external fields.\nDue to the properties of quantum rotations, the angular momentum algebra can be\nof tremendous complexity even for a few interacting particles, such as valence\nelectrons of an atom, not to mention larger many-particle systems. In this\nwork, we study an example of the latter: a rotating quantum impurity coupled to\na many-body bosonic bath. In the regime of strong impurity-bath couplings the\nproblem involves addition of an infinite number of angular momenta which\nrenders it intractable using currently available techniques. Here, we introduce\na novel canonical transformation which allows to eliminate the complex angular\nmomentum algebra from such a class of many-body problems. In addition, the\ntransformation exposes the problem's constants of motion, and renders it\nsolvable exactly in the limit of a slowly-rotating impurity. We exemplify the\ntechnique by showing that there exists a critical rotational speed at which the\nimpurity suddenly acquires one quantum of angular momentum from the\nmany-particle bath. Such an instability is accompanied by the deformation of\nthe phonon density in the frame rotating along with the impurity.",
        "positive": "Unraveling the Excitation Spectrum of Many-Body Systems from Quantum\n  Quenches: Quenches are now routinely used in synthetic quantum systems to study a\nvariety of fundamental effects, including ergodicity breaking, light-cone-like\nspreading of information, and dynamical phase transitions. It was shown\nrecently that the dynamics of equal-time correlators may be related to\nground-state phase transitions and some properties of the system excitations.\nHere, we show that the full low-lying excitation spectrum of a generic\nmany-body quantum system can be extracted from the after-quench dynamics of\nequal-time correlators. We demonstrate it for a variety of one-dimensional\nlattice models amenable to exact numerical calculations, including Bose and\nspin models, with short- or long-range interactions. The approach also applies\nto higher dimensions, correlated fermions, and continuous models. We argue that\nit provides an alternative approach to standard pump-probe spectroscopic\nmethods and discuss its advantages."
    },
    {
        "anchor": "Tunneling dynamics of $^{164}$Dy supersolids and droplets: The tunneling dynamics of a magnetic $^{164}$Dy quantum gas in an elongated\nor circular skewed double-well trap is investigated with a time-dependent\nextended Gross-Pitaevskii approach. Upon lifting the energy offset, different\ntunneling regimes can be identified. In the elongated trap and for sufficiently\nlarge offset, the different configurations exhibit collective macroscopic\ntunneling. For smaller offset, partial reflection from and transmission through\nthe barrier lead to density accumulation in both wells, and eventually to\ntunneling-locking. One can also reach the macroscopic self-trapping regime for\nincreasing relative dipolar interaction strength, while tunneling vanishes for\nlarge barrier heights. A richer dynamical behavior is observed for the circular\ntrap. For instance, the supersolid maintains its shape, while the superfluid\ndensity gets distorted signifying the emergence of peculiar excitation patterns\nin the macroscopic tunneling regime. The findings reported here may offer new\nways to probe distinctive dynamical features in the supersolid and droplet\nregimes.",
        "positive": "Spin relaxation in ultracold spin-orbit coupled $^{40}$K gas: We report the anomalous Dyakonov-Perel' spin relaxation in ultracold\nspin-orbit coupled $^{40}$K gas when the coupling between $|9/2,9/2\\ >$ and\n$|9/2,7/2\\ >$ states (atcing as the effective Zeeman magnetic field) is much\nstronger than the spin-orbit coupled field. Both the transverse and\nlongitudinal spin relaxations are investigated with small and large spin\npolarizations. It is found that with small spin polarization, the transverse\n(longitudinal) spin relaxation is divided into four (two) regimes: the normal\nweak scattering regime, the anomalous Dyakonov-Perel'-like regime, the\nanomalous Elliott-Yafet-like regime and the normal strong scattering regime\n(the anomalous Elliott-Yafet-like regime and the normal strong scattering\nregime), with only the normal weak scattering regime being in the weak\nscattering limit. This is very different from the conventional situation under\nthe weak magnetic field, which is divided into the weak and strong scattering\nregimes according to the weak/strong scattering limit. With large spin\npolarization, we find that the Hartree-Fock self-energy, which acts as an\neffective magnetic field, can markedly suppress the transverse spin relaxation\nin both weak and strong scattering limits. Moreover, by noting that as both the\nmomentum relaxation time and the Hartree-Fock effective magnetic field vary\nwith the scattering length in cold atoms, the anomalous Dyakonov-Perel'-like\nregime is suppressed and the transverse spin relaxation is hence divided into\nthree regimes in the scattering length dependence: the normal weak scattering\nregime, the anomalous Elliott-Yafet-like regime and the strong scattering\nregime. On the other hand, the longitudinal spin relaxation is again divided\ninto the anomalous EY-like and normal strong scattering regimes. ..."
    },
    {
        "anchor": "First and second sound in cylindrically trapped gases: We investigate the propagation of density and temperature waves in a\ncylindrically trapped gas with radial harmonic confinement. Starting from\ntwo-fluid hydrodynamic theory we derive effective 1D equations for the chemical\npotential and the temperature which explicitly account for the effects of\nviscosity and thermal conductivity. Differently from quantum fluids confined by\nrigid walls, the harmonic confinement allows for the propagation of both first\nand second sound in the long wave length limit. We provide quantitative\npredictions for the two sound velocities of a superfluid Fermi gas at\nunitarity. For shorter wave-lengths we discover a new surprising class of\nexcitations continuously spread over a finite interval of frequencies. This\nresults in a non-dissipative damping in the response function which is\nanalytically calculated in the limiting case of a classical ideal gas.",
        "positive": "Galilean invariance in confined quantum systems: Implications on\n  spectral gaps, superfluid flow, and periodic order: Galilean invariance leaves its imprint on the energy spectrum and eigenstates\nof $N$ quantum particles, bosons or fermions, confined in a bounded domain. It\nendows the spectrum with a recurrent structure which in capillaries or\nelongated traps of length $L$ and cross-section area $s_\\perp$ leads to\nspectral gaps $n^2h^2s_\\perp\\rho/(2mL)$ at wavenumbers $2n\\pi s_\\perp\\rho$,\nwhere $\\rho$ is the number density and $m$ is the particle mass. In zero\ntemperature superfluids, in toroidal geometries, it causes the quantization of\nthe flow velocity with the quantum $h/(mL)$ or that of the circulation along\nthe toroid with the known quantum $h/m$. Adding a \"friction\" potential which\nbreaks Galilean invariance, the Hamiltonian can have a superfluid ground state\nat low flow velocities but not above a critical velocity which may be different\nfrom the velocity of sound. In the limit of infinite $N$ and $L$, if\n$N/L=s_\\perp\\rho$ is kept fixed, translation invariance is broken, the center\nof mass has a periodic distribution, while superfluidity persists at low flow\nvelocities. This conclusion holds for the Lieb-Liniger model."
    },
    {
        "anchor": "Spatiotemporal Quenches in Long-Range Hamiltonians: Spatiotemporal quenches are efficient at preparing ground states of critical\nHamiltonians that have emergent low-energy descriptions with Lorentz\ninvariance. The critical transverse field Ising model with nearest neighbor\ninteractions, for instance, maps to free fermions with a relativistic low\nenergy dispersion. However, spin models realized in artificial quantum\nsimulators based on neutral Rydberg atoms, or trapped ions, generically exhibit\nlong range power-law decay of interactions with $J(r) \\sim 1/r^\\alpha$ for a\nwide range of $\\alpha$. In this work, we study the fate of spatiotemporal\nquenches in these models with a fixed velocity $v$ for the propagation of the\nquench front, using the numerical time-dependent variational principle. For\n$\\alpha \\gtrsim 3$, where the critical theory is suggested to have a dynamical\ncritical exponent $z = 1$, our simulations show that optimal cooling is\nachieved when the front velocity $v$ approaches $c$, the effective speed of\nexcitations in the critical model. The energy density is inhomogeneously\ndistributed in space, with prominent hot regions populated by excitations\nco-propagating with the quench front, and cold regions populated by\ncounter-propagating excitations. Lowering $\\alpha$ largely blurs the boundaries\nbetween these regions. For $\\alpha < 3$, we find that the Doppler cooling\neffect disappears, as expected from renormalization group results for the\ncritical model which suggest a dispersion $\\omega \\sim q^z$ with $z < 1$.\nInstead, we show that excitations are controlled by two relevant length scales\nwhose ratio is related to that of the front velocity to a threshold velocity\nthat ultimately determines the adiabaticity of the quench.",
        "positive": "Exact solitons and manifold mixing dynamics in the spin-orbit-coupled\n  spinor condensates: We derive exact static as well as moving solitonic solutions to the\none-dimensional spin-orbit-coupled F=1 Bose-Einstein condensates. The static\npolar soliton is shown to be the ground state by the imaginary-time evolution\nmethod. It shows a helical modulation of the order parameter due to the\nspin-orbit coupling. In particular, the moving soliton exhibits a periodic\noscillation among the particle numbers of the hyperfine states. We further\nexplore the temporal evolution of the static polar soliton and find that the\nspin-polarization exhibits dynamical oscillations. This disappearance and\nre-emergence of the ferromagnetic state indicates the mixing of the\nferromagnetic and the antiferromagnetic manifolds."
    },
    {
        "anchor": "Correlated Topological Phases and Exotic Magnetism with Ultracold\n  Fermions: Motivated by the recent progress in engineering artificial non-Abelian gauge\nfields for ultracold fermions in optical lattices, we investigate the\ntime-reversal-invariant Hofstadter-Hubbard model. We include an additional\nstaggered lattice potential and an artificial Rashba--type spin-orbit coupling\nterm available in experiment. Without interactions, the system can be either a\n(semi)-metal, a normal or a topological insulator, and we present the\nnon-Abelian generalization of the Hofstadter butterfly. Using a combination of\nreal-space dynamical mean-field theory (RDMFT), analytical arguments, and\nMonte-Carlo simulations we study the effect of strong on-site interactions. We\ndetermine the interacting phase diagram, and discuss a scenario of an\ninteraction-induced transition from normal to topological insulator. At\nhalf-filling and large interactions, the system is described by a quantum spin\nHamiltonian, which exhibits exotic magnetic order due to the interplay of\nRashba--type spin-orbit coupling and the artificial time-reversal-invariant\nmagnetic field term. We determine the magnetic phase diagram: both for the\nitinerant model using RDMFT and for the corresponding spin model in the\nclassical limit using Monte-Carlo simulations.",
        "positive": "Anomalous Expansion of Attractively Interacting Fermionic Atoms in an\n  Optical Lattice: Strong correlations can dramatically modify the thermodynamics of a quantum\nmany-particle system. Especially intriguing behaviour can appear when the\nsystem adiabatically enters a strongly correlated regime, for the interplay\nbetween entropy and strong interactions can lead to counterintuitive effects. A\nwell known example is the so-called Pomeranchuk effect, occurring when liquid\n3He is adiabatically compressed towards its crystalline phase. Here, we report\non a novel anomalous, isentropic effect in a spin mixture of attractively\ninteracting fermionic atoms in an optical lattice. As we adiabatically increase\nthe attraction between the atoms we observe that the gas, instead of\ncontracting, anomalously expands. This expansion results from the combination\nof two effects induced by pair formation in a lattice potential: the\nsuppression of quantum fluctuations as the attraction increases, which leads to\na dominant role of entropy, and the progressive loss of the spin degree of\nfreedom, which forces the gas to excite additional orbital degrees of freedom\nand expand to outer regions of the trap in order to maintain the entropy. The\nunexpected thermodynamics we observe reveal fundamentally distinctive features\nof pairing in the fermionic Hubbard model."
    },
    {
        "anchor": "Strongly Interacting Fermi Gases: The experimental realization of stable, ultracold Fermi gases near a Feshbach\nresonance allows to study gases with attractive interactions of essentially\narbitrary strength. They extend the classic paradigm of BCS into a regime which\nhas never been accessible before. We review the theoretical concepts which have\nbeen developed in this context, including the Tan relations and the notion of\nfixed points at zero density, which are at the origin of universality. We\ndiscuss in detail the universal thermodynamics of the unitary Fermi gas which\nallows a fit free comparison between theory and experiment for this strongly\ninteracting system. In addition, we adress the consequences of scale invariance\nat infinite scattering length and the subtle violation of scale invariance in\ntwo dimensions. Finally we discuss the Fermionic excitation spectrum accessible\nin momentum resolved RF-spectroscopy and the origin of universal lower bounds\nfor the shear viscosity and the spin diffusion constant.",
        "positive": "Properties of the signal mode in the polariton OPO regime: Theoretical analyses of the polariton optical parametric oscillator (OPO)\nregime often rely on a mean field approach based on the complex\nGross-Pitaevskii equations in a three-mode approximation, where only three\nmomentum states, the signal, pump and idler, are assumed to be significantly\noccupied. This approximation, however, lacks a constraint to uniquely determine\nthe signal and idler momenta. In contrast, multimode numerical simulations and\nexperiments show a unique momentum structure for the OPO states. In this work\nwe show that an estimate for the signal momentum chosen by the system can be\nfound from a simple analysis of the pump-only configuration. We use this\nestimate to investigate how the chosen signal momentum depends on the\nproperties of the drive."
    },
    {
        "anchor": "Variance of an anisotropic Bose-Einstein condensate: The anisotropy of a trap potential can impact the density and variance of a\nBose-Einstein condensate (BEC) in an opposite manner. We exemplify this effect\nfor both the ground state and out-of-equilibrium dynamics of structureless\nbosons interacting by a long-range inter-particle interaction and trapped in a\ntwo-dimensional single-well potential. We demonstrate that even when the\ndensity of the BEC is, say, wider along the $y$ direction and narrower along\nthe $x$ direction, its position variance can actually be smaller and momentum\nvariance larger in the $y$ direction than in the $x$ direction. This behavior\nof the variance in a many-particle system is counterintuitive. It suggests\nusing the variance as a tool to characterize the strength of correlations along\nthe $y$ and $x$ directions in a trapped BEC.",
        "positive": "Quantum magnetism and topological ordering via enhanced Rydberg-dressing\n  near F\u007f\u00f6rster-resonances: We devise a cold-atom approach to realizing a broad range of bi-linear\nquantum magnets. Our scheme is based on off-resonant single-photon excitation\nof Rydberg $P$-states (Rydberg-dressing), whose strong interactions are shown\nto yield controllable XYZ-interactions between effective spins, represented by\ndifferent atomic ground states. The distinctive features of F\\\"orster-resonant\nRydberg atom interactions are exploited to enhance the effectiveness of\nRydberg-dressing and, thereby, yield large spin-interactions that greatly\nexceed corresponding decoherence rates. We illustrate the concept on a spin-1\nchain implemented with cold Rubidium atoms, and demonstrate that this permits\nthe dynamical preparation of topological magnetic phases. Generally, the\ndescribed approach provides a viable route to exploring quantum magnetism with\ndynamically tuneable (an)isotropic interactions as well as variable space- and\nspin-dimensions in cold-atom experiments."
    },
    {
        "anchor": "Generalized wave-packet model for studying coherence of matter-wave\n  interferometers: We present a generalized model for the evolution of atomic wave-packets in\nmatter-wave interferometers. This method provides an efficient tool for\nanalyzing the performance of atomic interferometers using atom clouds prepared\nin a trap as a Bose-Einstein condensate (BEC) or as a thermal ensemble.\nPredictions of the model for dynamic properties such as wave-packet size and\nphase are in excellent agreement with explicit numerical solutions of the\nnon-linear Gross-Pitaevskii equations and enable fast calculations of\ninterferometric performance in regimes where full numerical solutions become\nimpractical. As a starting point, the static Thomas-Fermi (TF) approximation\nfor a BEC in a harmonic trap is generalized to the whole range of atom-atom\ninteraction strengths: from non-interacting atoms (low densities) to the\nstandard TF limit (high atomic densities, as long as the condensate\napproximation still holds). In particular, this generalization allows a good\nestimation of atomic cloud properties along the transition from a\nthree-dimensional to a quasi-one-dimensional BEC in an elongated trap. We then\ndevelop a theoretical model of wave-packet evolution in time-dependent\nconditions. The model is applicable for a wide range of dynamical problems\ninvolving evolution in time-dependent potentials and in a changing mean-field\natomic repulsion due to splitting and separation of wave-packets. We use the\nmodel for studying two effects that influence interferometric coherence:\nimperfect spatial recombination in a two-state interferometer (the so-called\n\"Humpty-Dumpty effect\") and phase diffusion due to number uncertainty in the\ntwo interferometer arms, which was previously studied thoroughly only for\ninterferometric schemes where the BECs in the two arms stay trapped (for\nexample, in a double-well potential).",
        "positive": "Dynamic trapping near a quantum critical point: The study of dynamics in closed quantum systems has recently been revitalized\nby the emergence of experimental systems that are well-isolated from their\nenvironment. In this paper, we consider the closed-system dynamics of an\narchetypal model: spins near a second order quantum critical point, which are\ntraditionally described by the Kibble-Zurek mechanism. Imbuing the driving\nfield with Newtonian dynamics, we find that the full closed system exhibits a\nrobust new phenomenon -- dynamic critical trapping -- in which the system is\nself-trapped near the critical point due to efficient absorption of field\nkinetic energy by heating the quantum spins. We quantify limits in which this\nphenomenon can be observed and generalize these results by developing a\nKibble-Zurek scaling theory that incorporates the dynamic field. Our findings\ncan potentially be interesting in the context of early universe physics, where\nthe role of the driving field is played by the inflaton or a modulus."
    },
    {
        "anchor": "Noisy quantum phase transitions: an intuitive approach: Equilibrium thermal noise is known to destroy any quantum phase transition.\nWhat are the effects of non-equilibrium noise? In two recent papers we have\nconsidered the specific case of a resistively-shunted Josephson junction driven\nby $1/f$ charge noise. At equilibrium, this system undergoes a sharp quantum\nphase transition at a critical value of the shunt resistance. By applying a\nreal-time renormalization group (RG) approach, we found that the noise has\nthree main effects: It shifts the phase transition, renormalizes the\nresistance, and generates an effective temperature. In this paper we explain\nhow to understand these effects using simpler arguments, based on Kirchhoff\nlaws and time-dependent perturbation theory. We also show how these effects\nmodify physical observables and especially the current-voltage characteristic\nof the junction. In the appendix we describe two possible realizations of the\nmodel with ultracold atoms confined to one dimension.",
        "positive": "Wigner crystal versus Fermionization for one-dimensional Hubbard models\n  with and without long-range interactions: The ground state properties of Hubbard model with or without long-range\ninteractions in the regime with strongly repulsive on-site interaction are\ninvestigated by means of the exact diagonalization method. We show that the\nappearance of $N$-crests in the density profile of a trapped N-fermion system\nis a natural result of \"fermionization\" between antiparallel-spin fermions in\nthe strongly repulsive limit and can not be taken as the only signature of\nWigner crystal phase, as the static structure factor does not show any\nsignature of crystallization. On the contrary, both the density distribution\nand static structure factor of Hubbard model with strong long-range\ninteractions display clear signature of Wigner crystal. Our results indicate\nthe important role of long-range interaction in the formation of Wigner\ncrystal."
    },
    {
        "anchor": "Staircase Prethermalization and Constrained Dynamics in Lattice Gauge\n  Theories: The dynamics of lattice gauge theories is characterized by an abundance of\nlocal symmetry constraints. Although errors that break gauge symmetry appear\nnaturally in NISQ-era quantum simulators, their influence on the gauge-theory\ndynamics is insufficiently investigated. As we show, a small gauge breaking of\nstrength $\\lambda$ induces a staircase of long-lived prethermal plateaus. The\nnumber of prethermal plateaus increases with the number of matter fields $L$,\nwith the last plateau being reached at a timescale $\\lambda^{-L/2}$, showing an\nintimate relation of the concomitant slowing down of dynamics with the number\nof local gauge constraints. Our results bode well for NISQ quantum devices, as\nthey indicate that the proliferation timescale of gauge-invariance violation is\ncounterintuitively delayed exponentially in system size.",
        "positive": "Confinement of matter-wave solitons on top of a pedestal-shaped\n  potential: Reflection of wave packets from downward potential steps and attractive\npotentials, known as a quantum reflection, has been explored for bright\nmatter-wave solitons with the main emphasis on the possibility to trap them on\ntop of a pedestal-shaped potential. In numerical simulations, we observed that\nmoving solitons return from the borders of the potential and remain trapped for\na sufficiently long time. The shuttle motion of the soliton is accompanied by\nshedding some amount of matter at each reflection from the borders of the trap,\nthus reducing its norm. The one- and two- soliton configurations are\nconsidered. A discontinuous jump of trajectories of colliding solitons has been\ndiscussed. The time-shift observed in a step-like decay of the moving soliton's\nnorm in the two-soliton configuration is linked to the trajectory jump\nphenomenon. The obtained results can be of interest for the design of new\nsoliton experiments with Bose-Einstein condensates."
    },
    {
        "anchor": "Effect of realistic interatomic interactions and two-body correlation on\n  the heat capacity of a trapped BEC: An approximate many-body theory has been used to calculate the heat capacity\nand the condensate fraction of a BEC with effective repulsive interaction. The\neffect of interactions has been analyzed and compared with the non-interacting\ncase. It has been found that the repulsive interaction lowers the critical\ntemperature from the value found in the non-interacting case. The difference\nbetween the critical temperatures increases with the increase in the total\nnumber of atoms in the trap.",
        "positive": "Enhancing quantum order with fermions by increasing species degeneracy: One of the challenges for fermionic cold atom experiments in optical lattices\nis to cool the systems to low enough temperature that they can form quantum\ndegenerate ordered phases. In particular, there has been significant work in\ntrying to find the antiferromagnetic phase transition of the Hubbard model in\nthree dimensions, without success. Here, we attack this problem from a\ndifferent angle by enhancing the ordering temperature via an increase in the\ndegeneracy of the atomic species trapped in the optical lattice. In addition to\ndeveloping the general theory, we also discuss some potential systems where one\nmight be able to achieve these results experimentally."
    },
    {
        "anchor": "Optical lattice influenced geometry of quasi-2D binary condensates and\n  quasiparticle spectra: We explore the collective excitations of optical lattices filled with\ntwo-species Bose-Einstein condensates (TBECs). We use a set of coupled discrete\nnonlinear Schr\\\"odinger equations to describe the system, and employ\nHartree-Fock-Bogoliubov (HFB) theory with the Popov approximation to analyze\nthe quasiparticle spectra at zero temperature. The ground state geometry,\nevolution of quasiparticle energies, structure of quasiparticle amplitudes, and\ndispersion relations are examined in detail. The trends observed are in stark\ncontrast to the case of TBECs only with a harmonic confining potential. One key\nobservation is the quasiparticle energies are softened as the system is tuned\ntowards phase separation, but harden after phase separation and mode\ndegeneracies are lifted.",
        "positive": "Position-dependent spin-orbit coupling for ultracold atoms: We theoretically explore atomic Bose-Einstein condensates (BECs) subject to\nposition-dependent spin-orbit coupling (SOC). This SOC can be produced by\ncyclically laser coupling four internal atomic ground (or metastable) states in\nan environment where the detuning from resonance depends on position. The\nresulting spin-orbit coupled BEC phase-separates into domains, each of which\ncontain density modulations - stripes - aligned either along the x or y\ndirection. In each domain, the stripe orientation is determined by the sign of\nthe local detuning. When these stripes have mismatched spatial periods along\ndomain boundaries, non-trivial topological spin textures form at the interface,\nincluding skyrmions-like spin vortices and anti-vortices. In contrast to\nvortices present in conventional rotating BECs, these spin-vortices are stable\ntopological defects that are not present in the corresponding homogenous\nstripe-phase spin-orbit coupled BECs."
    },
    {
        "anchor": "Critical exponents and fluctuations at BEC in a 2D harmonically trapped\n  ideal gas: The critical properties displayed by an ideal 2D Bose gas trapped in a\nharmonic potential are determined and characterized in an exact numerical\nfashion. Beyond thermodynamics, addressed in terms of the global pressure and\nvolume which are the appropriate variables of a fluid confined in a non-uniform\nharmonic potential, the density-density correlation function is also calculated\nand the corresponding correlation length is found. Evaluation of all these\nquantities as Bose-Einstein condensation (BEC) is approached manifest its\ncritical continuous phase transition character. The divergence of the\ncorrelation length as the critical temperature is reached, unveils the expected\nspatial scale invariance proper of a critical transition. The logarithmic\nsingularities of this transition are traced back to the non-analytic behavior\nof the thermodynamic variables at vanishing chemical potential, which is the\nonset of BEC. The critical exponents associated with the ideal BEC transition\nin the 2D inhomogeneous fluid reveals its own universality class.",
        "positive": "Topological Mott insulators of ultracold atomic mixtures induced by\n  interactions in one-dimensional optical superlattices: We present exactly solvable examples that topological Mott insulators can\nemerge from topologically trivial states due to strong interactions between\natoms for atomic mixtures trapped in one-dimensional optical superlattice\nsystems. The topological Mott insulating state is characterized by nonzero\nChern number and appears in the strongly interacting limit as long as the total\nband filling factor is an integer, which is not sensitive to the filling of\neach component. The topological nature of the Mott phase can be revealed by\nobserving the density profile of the trapped system. Our results can be also\ngeneralized to the multi-component atomic systems."
    },
    {
        "anchor": "Spin dynamics of large-spin (spinor) fermions in a harmonic trap: Understanding the collective dynamics in a many-body system has been a\ncentral task in condensed matter physics. To achieve this task, we develop a\nHartree-Fock theory to study the collective oscillations of spinor Fermi\nsystem, motivated by recent experiment on spin-9/2 fermions. We observe an\noscillation period shoulder for small rotation angles. Different from previous\nstudies, where the shoulder is found connected to the resonance from periodic\nto running phase, here the system is always in a running phase in the two-body\nphase space. This shoulder survives even in the many-body oscillations, which\ncould be tested in the experiments. We also show how these collective\noscillations evolve from two- to many-body. Our theory provides an alternative\nway to understand the collective dynamics in large-spin Fermi systems.",
        "positive": "Phase structure of spin-imbalanced unitary Fermi gases: We investigate the phase structure of spin-imbalanced unitary Fermi gases\nbeyond mean-field theory by means of the Functional Renormalization Group. In\nthis approach, quantum and thermal fluctuations are resolved in a systematic\nmanner. The discretization of the effective potential on a grid allows us to\naccurately account for both first- and second-order phase transitions that are\npresent on the mean-field level. We compute the full phase diagram in the plane\nof temperature and spin-imbalance and discuss the existence of other\nconjectured phases such as the Sarma phase and a precondensation region. In\naddition, we explain on a qualitative level how we expect that in-situ density\nimages are affected by our findings and which experimental signatures may\npotentially be used to probe the phase structure."
    },
    {
        "anchor": "Cavity-induced switching between localized and extended states in a\n  non-interacting Bose-Einstein condensate: We study an ultracold atom-cavity coupling system, which had been implemented\nin experiment to display weak light nonlinearity [S. Gupta \\textit{et al}.,\nPhys. Rev. Lett. \\textbf{99}, 213601 (2007)]. The model is described by a\nnon-interacting Bose-Einstein condensate contained in a Fabry-P\\'{e}rot optical\nresonator, in which two incommensurate standing-wave modes are excited and thus\nform a quasiperiodic optical lattice potential for the atoms. Special emphasis\nare paid to the variation of atomic wavefunction induced by the cavity light\nfield. We show that bistability between the atomic localized and extended\nstates can be generated under appropriate conditions.",
        "positive": "Critical behavior of order parameter at the nonequilibrium phase\n  transition of the Ising model: After a quench of transverse field, the asymptotic long-time state of Ising\nmodel displays a transition from a ferromagnetic phase to a paramagnetic phase\nas the post-quench field strength increases, which is revealed by the vanishing\nof the order parameter defined as the averaged magnetization over time. We\nestimate the critical behavior of the magnetization at this nonequilibrium\nphase transition by using mean-field approximation. In the vicinity of the\ncritical field, the magnetization vanishes as the inverse of a logarithmic\nfunction, which is significantly distinguished from the critical behavior of\norder parameter at the corresponding equilibrium phase transition, i.e. a\npower-law function."
    },
    {
        "anchor": "Conical intersections in laboratory coordinates with ultracold molecules: For two states of opposite parity that cross as a function of an external\nmagnetic field, the addition of an electric field will break the symmetry and\ninduce an avoided crossing. A suitable arrangement of fields may be used to\ncreate a conical intersection as a function of external spatial coordinates. We\nconsider the effect of the resulting geometric phase for ultracold polar\nmolecules. For a Bose-Einstein condensate in the mean-field approximation, the\ngeometric phase effect induces stable states of persistent superfluid flow that\nare characterized by half-integer quantized angular momentum.",
        "positive": "Atomic physics on a 50 nm scale: Realization of a bilayer system of\n  dipolar atoms: Atomic physics has greatly advanced quantum science, mainly due to the\nability to control the position and internal quantum state of atoms with high\nprecision, often at the quantum limit. The dominant tool for this is laser\nlight, which can structure and localize atoms in space (e.g., in optical\ntweezers, optical lattices, 1D tubes or 2D planes). Due to the diffraction\nlimit of light, the natural length scale for most experiments with atoms is on\nthe order of 500 nm or larger. Here we implement a new super-resolution\ntechnique which localizes and arranges atoms on a sub-50 nm scale, without any\nfundamental limit in resolution. We demonstrate this technique by creating a\nbilayer of dysprosium atoms, mapping out the atomic density distribution with\nsub-10 nm resolution, and observing dipolar interactions between two physically\nseparated layers via interlayer sympathetic cooling and coupled collective\nexcitations. At 50 nm, dipolar interactions are 1,000 times stronger than at\n500 nm. For two atoms in optical tweezers, this should enable purely magnetic\ndipolar gates with kHz speed."
    },
    {
        "anchor": "Effective theory for the propagation of a wave-packet in a disordered\n  and nonlinear medium: The propagation of a wave-packet in a nonlinear disordered medium exhibits\ninteresting dynamics. Here, we present an analysis based on the nonlinear\nSchr\\\"odinger equation (Gross-Pitaevskii equation). This problem is directly\nconnected to experiments on expanding Bose gases and to studies of transverse\nlocalization in nonlinear optical media. In a nonlinear medium the energy of\nthe wave-packet is stored both in the kinetic and potential parts, and details\nof its propagation are to a large extent determined by the transfer from one\nform of energy to the other. A theory describing the evolution of the\nwave-packet has been formulated in [G. Schwiete and A. Finkelstein, Phys. Rev.\nLett. 104, 103904 (2010)] in terms of a nonlinear kinetic equation. In this\npaper, we present details of the derivation of the kinetic equation and of its\nanalysis. As an important new ingredient we study interparticle-collisions\ninduced by the nonlinearity and derive the corresponding collision integral. We\nrestrict ourselves to the weakly nonlinear limit, for which disorder scattering\nis the dominant scattering mechanism. We find that in the special case of a\nwhite noise impurity potential the mean squared radius in a two-dimensional\nsystem scales linearly with t. This result has previously been obtained in the\ncollisionless limit, but it also holds in the presence of collisions. Finally,\nwe mention different mechanisms through which the nonlinearity may influence\nlocalization of the expanding wave-packet.",
        "positive": "Identifying strongly correlated supersolid states on the optical lattice\n  by quench-induced \u03c0-states: We consider the rapid quench of a one-dimensional strongly correlated\nsupersolid to a localized density wave (checkerboard) phase, and calculate the\nfirst-order coherence signal following the quench. It is shown that unique\ncoherence oscillations between the even and odd sublattice sites of the\ncheckerboard are created by the quench, which are absent when the initial state\nis described by a Gutzwiller product state. This is a striking manifestation of\nthe versatility of the far-from-equilbrium and nonperturbative collapse and\nrevival phenomenon as a microscope for quantum correlations in complex\nmany-body states. For the present example, this opens up the possibility to\ndiscriminate experimentally between mean-field and many-body origins of\nsupersolidity."
    },
    {
        "anchor": "Fundamental Limits of Feedback Cooling Ultracold Atomic Gases: We investigate the fundamental viability of cooling ultracold atomic gases\nwith quantum feedback control. Our study shows that the trade-off between the\nresolution and destructiveness of optical imaging techniques imposes\nconstraints on the efficacy of feedback cooling, and that rapid\nrethermalization is necessary for cooling thermal gases. We construct a simple\nmodel to determine the limits to feedback cooling set by the visibility of\ndensity fluctuations, measurement-induced heating, and three-body atomic\nrecombination. We demonstrate that feedback control can rapidly cool\nhigh-temperature thermal clouds in quasi-2D geometries to degenerate\ntemperatures with minimal atom loss compared to traditional evaporation. Our\nanalysis confirms the feasibility of feedback cooling ultracold atomic gases,\nproviding a pathway to new regimes of cooling not achievable with current\napproaches.",
        "positive": "Dynamics of Uniform Quantum Gases, I: Density and Current Correlations: A unified approach valid for any wavenumber, frequency, and temperature is\npresented for uniform ideal quantum gases allowing for a comprehensive study of\nnumber density and particle-current density response functions. Exact\nanalytical expressions are obtained for spectral functions in terms of\npolylogarithms. Also, particle-number and particle-current static\nsusceptibilities are presented which, for fugacity less than unity,\nadditionally involve Kummer functions. The wavenumber and temperature dependent\ntransverse-current static susceptibility is used to show explicitly that\ncurrent correlations are of a long range in a Bose-condensed uniform ideal gas\nbut for bosons above the critical temperature and for Fermi and Boltzmann gases\nat all temperatures these correlations are of short range. Contact repulsive\ninteractions for systems of neutral quantum particles are considered within the\nrandom-phase approximation. The expressions for particle-number and\ntransverse-current susceptibilities are utilized to discuss the existence or\nnonexistence of superfluidity in the systems under consideration."
    },
    {
        "anchor": "Nonlinear dynamics of a spin-orbit-coupled Bose-Einstein condensate: Single-particle dynamics of a spin-orbit-coupled Bose-Einstein condensate has\nrecently been investigated in experiments that explore the physics of\nLandau-Zener tunneling and of the Zitterbewegung. In this paper, we study the\ninfluence of a nonlinearity due to interactions on these dynamics and show that\nthe dispersion relation develops interesting loop strucures. The atoms can move\nalong the nonlinear dispersion curve in the presence of a weak acceleration\nforce and we show that the loops lead to straightforward nonlinear Landau-Zener\ntunneling. However, we find that for the Zitterbewegung, induced by a sudden\nquench in the spin-orbit coupling parameters, the nonlinear dispersion is\nirrelevant.",
        "positive": "On the finite-size effects in two segregated Bose-Einstein condensates\n  restricted by a hard wall: The finite-size effects in two segregated Bose-Einstein condensates (BECs)\nrestricted by a hard wall is studied by means of the Gross-Pitaevskii equations\nin the double-parabola approximation (DPA). Starting from the consistency\nbetween the boundary conditions (BCs) imposed on condensates in confined\ngeometry and in the full space, we find all possible BCs together with the\ncorresponding condensate profiles and interface tensions. We discover two\nfinite-size effects: a) The ground state derived from the Neumann BC is stable\nwhereas the ground states derived from the Robin and Dirichlet BCs are\nunstable. b) Thereby, there equally manifest two possible wetting phase\ntransitions originating from two unstable states. However, the one associated\nwith the Robin BC is more favourable because it corresponds to a smaller\ninterface tension."
    },
    {
        "anchor": "Merging Dipolar Supersolids in a Double-Well Potential: We theoretically investigate the merging behaviour of two identical\nsupersolids through dipolar Bose-Einstein condensates confined within a\ndouble-well potential. By adiabatically tuning the barrier height and the\nspacing between the two wells for specific trap aspect ratios, the two\nsupersolids move toward each other and lead to the emergence of a variety of\nground state phases, including a supersolid state, a macrodroplet state, a ring\nstate, and a labyrinth state. We construct a phase diagram that characterizes\nvarious states seen during the merging transition. Further, we calculate the\nforce required to pull the two portions of the gas apart, finding that the\nmerged supersolids act like a deformable plastic material. Our work paves the\nway for future studies of layer structure in dipolar supersolids and the\ninteraction between them in experiments.",
        "positive": "Triplet pair amplitude in a trapped $s$-wave superfluid Fermi gas with\n  broken spin rotation symmetry: We investigate the possibility that the broken spatial inversion symmetry by\na trap potential induces a spin-triplet Cooper-pair amplitude in an $s$-wave\nsuperfluid Fermi gas. Being based on symmetry considerations, we clarify that\nthis phenomenon may occur, when a spin rotation symmetry of the system is also\nbroken. We also numerically confirm that a triplet pair amplitude is really\ninduced under this condition, using a simple model. Our results imply that this\nphenomenon is already present in a trapped $s$-wave superfluid Fermi gas with\nspin imbalance. As an interesting application of this phenomenon, we point out\nthat one may produce a $p$-wave superfluid Fermi gas, by suddenly changing the\n$s$-wave pairing interaction to a $p$-wave one by using the Feshbach resonance\ntechnique. Since a Cooper pair is usually classified into the spin-singlet (and\neven-parity) state and the spin-triplet (and odd-parity) state, our results\nwould be useful in considering how to mix them with each other in a superfluid\nFermi gas. Such admixture has recently attracted much attention in the field of\nnon-centrosymmetric superconductivity, so that our results would also\ncontribute to the further development of this research field, on the viewpoint\nof cold Fermi gas physics."
    },
    {
        "anchor": "Dipolar fermions in a two-dimensional lattice at non-zero temperature: We examine density ordered and superfluid phases of fermionic dipoles in a\ntwo-dimensional square lattice at non-zero temperature. The critical\ntemperature of the density ordered phases is determined and is shown to be\nproportional to the coupling strength for strong coupling. We calculate the\nsuperfluid fraction and demonstrate that the Berezinskii-Kosterlitz-Thouless\ntransition temperature of the superfluid phase is proportional to the hopping\nmatrix element in the strong coupling limit. We finally analyze the effects of\nan external harmonic trapping potential.",
        "positive": "Energetically stable singular vortex cores in an atomic spin-1\n  Bose-Einstein condensate: We analyze the structure and stability of singular singly quantized vortices\nin a rotating spin-1 Bose-Einstein condensate. We show that the singular vortex\ncan be energetically stable in both the ferromagnetic and polar phases despite\nthe existence of a lower-energy nonsingular coreless vortex in the\nferromagnetic phase. The spin-1 system exhibits an energetic hierarchy of\nlength scales resulting from different interaction strengths and we find that\nthe vortex cores deform to a larger size determined by the characteristic\nlength scale of the spin-dependent interaction. We show that in the\nferromagnetic phase the resulting stable core structure, despite apparent\ncomplexity, can be identified as a single polar core with axially symmetric\ndensity profile which is nonvanishing everywhere. In the polar phase, the\nenergetically favored core deformation leads to a splitting of a singly\nquantized vortex into a pair of half-quantum vortices that preserves the\ntopology of the vortex outside the extended core region, but breaks the axial\nsymmetry of the core. The resulting half-quantum vortices exhibit nonvanishing\nferromagnetic cores."
    },
    {
        "anchor": "Clock-line photoassociation of strongly bound dimers in a\n  magic-wavelength lattice: We report on the direct optical production and spectroscopy of\n$^1\\mathrm{S}_0\\mbox{-}^3\\mathrm{P}_0$ molecules with large binding energy\nusing the clock transition of $^{171}\\mathrm{Yb}$, and on the observation of\nthe associated orbital Feshbach resonance near $1300\\,\\mathrm{G}$. We measure\nthe magnetic field dependence of the closed-channel dimer and of the\nopen-channel pair state energy via clock-line spectroscopy in a deep optical\nlattice. In addition, we show that the free-to-bound transition into the dimer\ncan be made first-order insensitive to the trap depth by choice of the lattice\nwavelength. Finally, we determine the fundamental intra- and interorbital\nscattering lengths and probe the stability of the corresponding pair states,\nfinding long lifetimes in both interorbital interaction channels. These results\nare promising both for molecular clocks and for the preparation of\nstrongly-interacting multiorbital Fermi gases.",
        "positive": "Scissors mode of trapped dipolar gases: We study the scissors modes of dipolar boson and fermion gases trapped in a\nspherically symmetric potential. We use the harmonic oscillator states to solve\nthe time-dependent Gross-Pitaevskii equation for bosons and the time-dependent\nHartree-Fock equation for fermions. It is pointed out that the scissors modes\nof bosons and fermions can be of quite different nature."
    },
    {
        "anchor": "Ground-state and dynamical properties of two-dimensional dipolar Fermi\n  liquids: We study the ground-state properties of a two-dimensional spin-polarized\nfluid of dipolar fermions within the Euler-Lagrange Fermi-hypernetted-chain\napproximation. Our method is based on the solution of a scattering\nSchr\\\"odinger equation for the \"pair amplitude\" $\\sqrt{g(r)}$, where $g(r)$ is\nthe pair distribution function. A key ingredient in our theory is the effective\npair potential, which includes a bosonic term from Jastrow-Feenberg\ncorrelations and a fermionic contribution from kinetic energy and exchange,\nwhich is tailored to reproduce the Hartree-Fock limit at weak coupling. Very\ngood agreement with recent results based on quantum Monte Carlo simulations is\nachieved over a wide range of coupling constants up to the liquid-to-crystal\nquantum phase transition (QPT). Using a certain approximate model for the\ndynamical density-density response function, we furthermore demonstrate that:\ni) the liquid phase is stable towards the formation of density waves up to the\nliquid-to-crystal QPT and ii) an undamped zero-sound mode exists for any value\nof the interaction strength, down to infinitesimally weak couplings.",
        "positive": "Numerical solution of the Boltzmann equation for the collective modes of\n  trapped Fermi gases: We numerically solve the Boltzmann equation for trapped fermions in the\nnormal phase using the test-particle method. After discussing a couple of tests\nin order to estimate the reliability of the method, we apply it to the\ndescription of collective modes in a spherical harmonic trap. The numerical\nresults are compared with those obtained previously by taking moments of the\nBoltzmann equation. We find that the general shape of the response function is\nvery similar in both methods, but the relaxation time obtained from the\nsimulation is significantly longer than that predicted by the method of\nmoments. It is shown that the result of the method of moments can be corrected\nby including fourth-order moments in addition to the usual second-order ones\nand that this method agrees very well with our numerical simulations."
    },
    {
        "anchor": "Quasiparticle spectra of supersolid lattice gases at near-resonant\n  Rydberg-dressing: One of the major challenges in realizing a strongly interacting lattice gas\nusing Rydberg states is the occurrence of avalanche loss processes. As these\nare directly proportional to the total Rydberg fraction, the commonly suggested\nsolution is using far off-resonantly excited Rydberg states. We instead propose\nthe realization of a correlated bosonic lattice gas at near-resonant\nexcitation, where the total Rydberg fraction in the bulk is low due to the\nstrong, interaction-driven effective detuning. Using real-space dynamical\nmean-field theory we show that its reduced effect at the boundary of a system\ncan easily be compensated by considering a tailored beam-waist of the driving\nRabi-laser. In this geometry we discuss the spectral properties at the\ncrossover between the supersolid and the superfluid state and present the\nmomentum resolved spectral properties of the supersolid bulk. The latter\nresults are obtained within an extended quasiparticle method which also yields\na correction of the mean-field phase transition.",
        "positive": "On the existence of steady-state black hole analogues in finite\n  quasi-one-dimensional Bose-Einstein condensates: We theoretically propose a finite-size quasi-one-dimensional Bose-Einstein\ncondensate with coherent source and drain placed at its two ends, which can in\nprinciple sustain a stationary sonic black hole with a single event horizon.\nOur analysis is focused on the condensate persistence against quantum\nfluctuations. We show that similar to white hole-black hole pairs, dynamical\ninstabilities occur. Investigating in detail the instabilities' dependence on\nthe system parameters, we also identify windows of formally infinite black hole\nlifetimes. By using quantum depletion of the condensate as a diagnostic tool,\nwe validate the usage of Bogoliubov theory to describe the analogue Hawking\nprocess, and establish novel signatures of Hawking radiation in the depleted\ncloud, both inside and outside the event horizon."
    },
    {
        "anchor": "Localization of correlated fermions in optical lattices with speckle\n  disorder: Strongly correlated fermions in three- and two-dimensional optical lattices\nwith experimentally realistic speckle disorder are investigated. We extend and\napply the statistical dynamical mean-field theory, which treats local\ncorrelations non-perturbatively, to incorporate on-site and hopping-type\nrandomness on equal footing. Localization due to disorder is detected via the\nprobability distribution function of the local density of states. We obtain a\ncomplete paramagnetic ground state phase diagram for experimentally realistic\nparameters and find a strong suppression of the correlation-induced metal\ninsulator transition due to disorder. Our results indicate that the\nAnderson-Mott and the Mott insulator are not continuously connected due to the\nspecific character of speckle disorder. Furthermore, we discuss the effect of\nfinite temperature on the single-particle spectral function.",
        "positive": "Probing many-body systems near spectral degeneracies: The diagonal elements of the time correlation matrix are used to probe closed\nquantum systems that are measured at random times. This enables us to extract\ntwo distinct parts of the quantum evolution, a recurrent part and an\nexponentially decaying part. This separation is strongly affected when spectral\ndegeneracies occur, for instance, in the presence of spontaneous symmetry\nbreaking. Moreover, the slowest decay rate is determined by the smallest energy\nlevel spacing, and this decay rate diverges at the spectral degeneracies.\nProbing the quantum evolution with the diagonal elements of the time\ncorrelation matrix is discussed as a general concept and tested in the case of\na bosonic Josephson junction. It reveals for the latter characteristic\nproperties at the transition to Hilbert-space localization."
    },
    {
        "anchor": "Collective modes and superfluidity of a two-dimensional ultracold Bose\n  gas: The collective modes of a quantum liquid shape and impact its properties\nprofoundly, including its emergent phenomena such as superfluidity. Here we\npresent how a two-dimensional Bose gas responds to a moving lattice potential.\nIn particular we discuss how the induced heating rate depends on the\ninteraction strength and the temperature. This study is motivated by the recent\nmeasurements of Sobirey {\\it et al.} arXiv:2005.07607 (2020), for which we\nprovide a quantitative understanding. Going beyond the existing measurements,\nwe demonstrate that this probing method allows to identify first and second\nsound in quantum liquids. We show that the two sound modes undergo\nhybridization as a function of interaction strength, which we propose to detect\nexperimentally. This gives a novel insight into the two regimes of Bose gases,\ndefined via the hierarchy of sounds modes.",
        "positive": "Emergent Kinetics and Fractionalized Charge in 1D Spin-Orbit Coupled\n  Flatband Optical Lattices: Recent ultracold atomic gas experiments implementing synthetic spin-orbit\ncoupling allow access to flatbands that emphasize interactions. We model\nspin-orbit coupled fermions in a one-dimensional flatband optical lattice. We\nintroduce an effective Luttinger-liquid theory to show that interactions\ngenerate collective excitations with emergent kinetics and fractionalized\ncharge, analogous to properties found in the two-dimensional fractional quantum\nHall regime. Observation of these excitations would provide an important\nplatform for exploring exotic quantum states derived solely from interactions."
    },
    {
        "anchor": "Driven-dissipative Ising Model: An exact field-theoretical analysis: Driven-dissipative many-body systems are difficult to analyze analytically\ndue to their non-equilibrium dynamics, dissipation and many-body interactions.\nIn this paper, we consider a driven-dissipative infinite-range Ising model with\nlocal spontaneous emission, which naturally emerges from the open Dicke model\nin the large-detuning limit. Utilizing an adaptation of the Suzuki-Trotter\nquantum-to-classical mapping, we develop an exact field-theoretical analysis\nand a diagrammatic representation of the spin model that can be understood from\na simple scattering picture. With this representation, we are able to analyze\ncritical behavior, finite-size scaling and the effective temperature near the\nrespective phase transition. Our formalism further allows a detailed study of\nthe ordered phase where we find a \"heating\" region within which the effective\ntemperature becomes negative, thereby exhibiting a truly non-equilibrium\nbehavior. At the phase transition, we find two distinct critical behaviors with\noverdamped and underdamped critical dynamics at generic and weakly-dissipative\ncritical points, respectively. We further show that the underdamped critical\nbehavior is robust against short-range perturbations and is not an artifact of\nthe mean-field nature of the model. To treat such perturbations, we extend our\ndiagrammatic representation to include the coupling to spin waves due to the\nshort-range interactions. The field-theoretical approach and the diagrammatics\ndeveloped in this work should prove useful in applications to generic\nshort-range driven-dissipative spin systems.",
        "positive": "Origin of the Three-body Parameter Universality in Efimov Physics: In recent years extensive theoretical and experimental studies of universal\nfew-body physics have led to advances in our understanding of universal Efimov\nphysics [1]. The Efimov effect, once considered a mysterious and esoteric\neffect, is today a reality that many experiments in ultracold quantum gases\nhave successfully observed and continued to explore [2-14]. Whereas theory was\nthe driving force behind our understanding of Efimov physics for decades,\nrecent experiments have contributed an unexpected discovery. Specifically,\nmeasurements have found that the so-called three-body parameter determining\nseveral properties of the system is universal, even though fundamental\nassumptions in the theory of the Efimov effect suggest that it should be a\nvariable property that depends on the precise details of the short-range two-\nand three-body interactions. The present Letter resolves this apparent\ncontradiction by elucidating unanticipated implications of the two-body\ninteractions. Our study shows that the three-body parameter universality\nemerges because a universal effective barrier in the three-body potentials\nprevents the three particles from simultaneously getting close to each other.\nOur results also show limitations on this universality, as it is more likely to\noccur for neutral atoms and less likely to extend to light nuclei."
    },
    {
        "anchor": "Two-point density correlations of quasicondensates in free expansion: We measure the two-point density correlation function of freely expanding\nquasicondensates in the weakly interacting quasi-one-dimensional (1D) regime.\nWhile initially suppressed in the trap, density fluctuations emerge gradually\nduring expansion as a result of initial phase fluctuations present in the\ntrapped quasicondensate. Asymptotically, they are governed by the thermal\ncoherence length of the system. Our measurements take place in an intermediate\nregime where density correlations are related to near-field diffraction effects\nand anomalous correlations play an important role. Comparison with a recent\ntheoretical approach described by Imambekov et al. yields good agreement with\nour experimental results and shows that density correlations can be used for\nthermometry of quasicondensates.",
        "positive": "Inert-states of spin-5 and spin-6 Bose-Einstein condensates: In this paper we consider spinor Bose-Einstein condensates with spin f=5 and\nf=6 in the presence and absence of external magnetic field at the mean field\nlevel. We calculate all of so-called inert-states of these systems.\nInert-states are very unique class of stationary states because they remain\nstationary while Hamiltonian parameters change. Their existence comes from\nMichel's theorem. For illustration of symmetry properties of the inert-states\nwe use method that allows classification of the systems as a polyhedron with 2f\nvertices proposed by R. Barnett et al., Phys. Rev. Lett. 97, 180412 (2006)."
    },
    {
        "anchor": "Weakly interacting Bose gas in the one-dimensional limit: We prepare a chemically and thermally one-dimensional (1d) quantum degenerate\nBose gas in a single microtrap. We introduce a new interferometric method to\ndistinguish the quasicondensate fraction of the gas from the thermal cloud at\nfinite temperature. We reach temperatures down to $kT\\approx\n0.5\\hbar\\omega_\\perp$ (transverse oscillator eigenfrequency $\\omega_\\perp$)\nwhen collisional thermalization slows down as expected in 1d. At the lowest\ntemperatures the transverse momentum distribution exhibits a residual\ndependence on the line density $n_{1d}$, characteristic for 1d systems. For\nvery low densities the approach to the transverse single particle ground state\nis linear in $n_{1d}$.",
        "positive": "Rotating Bose-Einstein condensate in an square optical lattice: vortex\n  configuration for ground state in Josephson junction arrays regime: We consider a rotating Bose-Einstein condensate in a square optical lattice\nin the regime in which the Hamiltonian of the system can be mapped onto a\nJosephson junction array. In an approximate scheme where the couplings are\nassumed uniform, the ground state energy is formulated in terms of the vortex\nconfiguration. The results are compared with experimental results and also\npreviously reported results for frustrated XY model. We also show that vortex\nconfiguration is robust with respect to change of couplings and therefore the\nresults remain valid when we consider more realistic model with non-uniform\ncouplings."
    },
    {
        "anchor": "Synthetic magnetic fields for ultracold neutral atoms: Neutral atomic Bose condensates and degenerate Fermi gases have been used to\nrealize important many-body phenomena in their most simple and essential forms,\nwithout many of the complexities usually associated with material systems.\nHowever, the charge neutrality of these systems presents an apparent limitation\n- a wide range of intriguing phenomena arise from the Lorentz force for charged\nparticles in a magnetic field, such as the fractional quantum Hall states in\ntwo-dimensional electron systems. The limitation can be circumvented by\nexploiting the equivalence of the Lorentz force and the Coriolis force to\ncreate synthetic magnetic fields in rotating neutral systems. This was\ndemonstrated by the appearance of quantized vortices in pioneering experiments\non rotating quantum gases, a hallmark of superfluids or superconductors in a\nmagnetic field. However, because of technical issues limiting the maximum\nrotation velocity, the metastable nature of the rotating state and the\ndifficulty of applying stable rotating optical lattices, rotational approaches\nare not able to reach the large fields required for quantum Hall physics. Here,\nwe experimentally realize an optically synthesized magnetic field for ultracold\nneutral atoms, made evident from the appearance of vortices in our\nBose-Einstein condensate. Our approach uses a spatially-dependent optical\ncoupling between internal states of the atoms, yielding a Berry's phase\nsufficient to create large synthetic magnetic fields, and is not subject to the\nlimitations of rotating systems; with a suitable lattice configuration, it\nshould be possible to reach the quantum Hall regime, potentially enabling\nstudies of topological quantum computation.",
        "positive": "Analog cosmological reheating in an ultracold Bose gas: Cosmological reheating describes the transition of the post-inflationary\nuniverse to a hot and thermal state. In order to shed light on the underlying\ndynamics of this process, we propose to quantum-simulate the reheating-like\ndynamics of a generic cosmological single-field model in an ultracold Bose gas.\nIn our setup, the excitations on top of an atomic Bose-Einstein condensate play\nthe role of the particles produced by the decaying inflaton field after\ninflation. Expanding spacetime as well as the background oscillating inflaton\nfield are mimicked in the non-relativistic limit by a time dependence of the\natomic interactions, which can be tuned experimentally via Feshbach resonances.\nAs we illustrate by means of classical-statistical simulations for the case of\ntwo spatial dimensions, the dynamics of the atomic system exhibits the\ncharacteristic stages of far-from-equilibrium reheating, including the\namplification of fluctuations via parametric instabilities and the subsequent\nturbulent transport of energy towards higher momenta. The transport is governed\nby a non-thermal fixed point showing universal self-similar time evolution as\nwell as a transient regime of prescaling with time-dependent scaling exponents.\nWhile the classical-statistical simulations can capture only the earlier stages\nof the dynamics for weak couplings, the proposed experiment has the potential\nof exploring the evolution up to late times even beyond the weak coupling\nregime."
    },
    {
        "anchor": "Dirac and topological phonons with spin-orbital entangled orders: We propose to study novel quantum phases and excitations for a 2D spin-orbit\n(SO) coupled bosonic $p$-orbital optical lattice based on the recent\nexperiments. The orbital and spin degrees of freedom with SO coupling compete\nand bring about nontrivial interacting quantum effects. We develop a\nself-consistent method for bosons and predict a spin-orbital entangled order\nfor the ground phase, in sharp contrast to spinless high-orbital systems.\nFurthermore, we investigate the Bogoliubov excitations, showing that the Dirac\nand topological phonons are obtained corresponding to the predicted different\nspin-orbital orders. In particular, the topological phonons exhibit a bulk gap\nwhich can be several times larger than the single-particle gap of $p$-bands,\nreflecting the enhancement of topological effect by interaction. Our results\nhighlight the rich physics predicted in SO coupled high-orbital systems and\nshall attract experimental efforts in the future.",
        "positive": "Quantum Criticality of 1D Attractive Fermi Gas: We obtain an analytical equation of state for one-dimensional strongly\nattractive Fermi gas for all parameter regime in current experiments. From the\nequation of state we derive universal scaling functions that control whole\nthermodynamical properties in quantum critical regimes and illustrate physical\norigin of quantum criticality. It turns out that the critical properties of the\nsystem are described by these of free fermions and those of mixtures of\nfermions with mass $m$ and $2m$. We also show how these critical properties of\nbulk systems can be revealed from the density profile of trapped Fermi gas at\nfinite temperatures and can be used to determine the T=0 phase boundaries\nwithout any arbitrariness."
    },
    {
        "anchor": "Hetero pairing and component-dependent pseudogap phenomena in an\n  ultracold Fermi gas with mass imbalance: We investigate the superfluid phase transition and single-particle\nexcitations in the BCS (Bareen-Cooper-Schrieffer)-BEC (Bose-Einstein\ncondensation) crossover regime of an ultracold Fermi gas with mass imbalance.\nIn our recent paper [R. Hanai, et. al., Phys. Rev. A 88, 053621 (2013)], we\nshowed that an extended $T$-matrix approximation (ETMA) can overcome the\nserious problem known in the ordinary (non-self-consistent) $T$-matrix\napproximation that it unphysically gives double-valued superfluid phase\ntransition temperature $T_{\\rm c}$ in the presence of mass imbalance. However,\nat the same time, the ETMA was also found to give the vanishing $T_{\\rm c}$ in\nthe weak-coupling and highly mass-imbalanced case. In this paper, we inspect\nthe correctness of this ETMA result, using the self-consistent $T$-matrix\napproximation (SCTMA). We show that the vanishing $T_{\\rm c}$ is an artifact of\nthe ETMA, coming from an internal inconsistency of this theory. The superfluid\nphase transition actually always occurs, irrespective of the ratio of mass\nimbalance. We also apply the SCTMA to the pseudogap problem in a\nmass-imbalanced Fermi gas. We show that pairing fluctuations induce different\npseudogap phenomena between the the light component and heavy component. We\nalso point out that a $^6$Li-$^{40}$K mixture is a useful system for the\nrealization of a hetero pairing state, as well as for the study of\ncomponent-dependent pseudogap phenomena.",
        "positive": "Diagrammatic Monte Carlo study of mass-imbalanced Fermi-polaron system: We apply the diagrammatic Monte Carlo approach to three-dimensional\nFermi-polaron systems with mass-imbalance, where an impurity interacts\nresonantly with a noninteracting Fermi sea whose atoms have a different mass.\nThis method allows to go beyond frequently used variational techniques by\nstochastically summing all relevant impurity Feynman diagrams up to a maximum\nexpansion order limited by the sign problem. Polaron energy and quasiparticle\nresidue can be accurately determined over a broad range of impurity masses.\nFurthermore, the spectral function of an imbalanced polaron demonstrates the\nstability of the quasiparticle and allows to locate in addition also the\nrepulsive polaron as an excited state. The quantitative exactness of\ntwo-particle-hole wave-functions is investigated, resulting in a relative\nlowering of polaronic energies in the mass-imbalance phase diagram. Tan's\ncontact coefficient for the mass-balanced polaron system is found in good\nagreement with variational methods. Mass-imbalanced systems can be studied\nexperimentally by ultracold atom mixtures like $^6$Li-$^{40}$K."
    },
    {
        "anchor": "Phase diagram for strong-coupling Bose polarons: Important properties of complex quantum many-body systems and their phase\ndiagrams can often already be inferred from the impurity limit. The Bose\npolaron problem describing an impurity atom immersed in a Bose-Einstein\ncondensate is a paradigmatic example. One of the most interesting features of\nthis model is the competition between the emergent impurity-mediated attraction\nbetween the bosons and their intrinsic repulsion. The arising higher-order\ncorrelations make the physics rich and interesting, but also complex to\ndescribe theoretically. To tackle this challenge, we develop a quantum\nchemistry-inspired computational technique and compare two state-of-the-art\nvariational methods that fully include both the boson-impurity and boson-boson\ninteractions on a non-perturbative level. For a sweep of the boson-impurity\ninteraction strength, we find two regimes of qualitatively different behaviour.\nIf the impurity-mediated interactions overcome the repulsion between the\nbosons, the polaron becomes unstable due to the formation of large bound\nclusters. If instead the interboson interactions dominate, the impurity will\nexperience a crossover from a polaron into a small molecule. We achieve a\nunified understanding incorporating both of these regimes and the transition\nbetween them. We show that both the instability and crossover regime can be\nstudied in realistic cold-atom experiments. Moreover, we develop a simple\nanalytical model that allows us to interpret these phenomena in the typical\nLandau framework of first-order phase transitions that turn second-order at a\ncritical endpoint, revealing a deep connection of the Bose polaron model to\nboth few- and many-body physics.",
        "positive": "Two-body relaxation of spin-polarized fermions in reduced\n  dimensionalities near a p-wave Feshbach resonance: We study inelastic two-body relaxation in a spin-polarized ultracold Fermi\ngas in the presence of a p-wave Feshbach resonance. It is shown that in reduced\ndimensionalities, especially in the quasi-one-dimensional case, the enhancement\nof the inelastic rate constant on approach to the resonance is strongly\nsuppressed compared to three dimensions. This may open promising paths for\nobtaining novel many-body states."
    },
    {
        "anchor": "Spontaneous pattern formation in an anti-ferromagnetic quantum gas: Spontaneous pattern formation is a phenomenon ubiquitous in nature, examples\nranging from Rayleigh-Benard convection to the emergence of complex organisms\nfrom a single cell. In physical systems, pattern formation is generally\nassociated with the spontaneous breaking of translation symmetry and is closely\nrelated to other symmetry-breaking phenomena, of which (anti-)ferromagnetism is\na prominent example. Indeed, magnetic pattern formation has been studied\nextensively in both solid-state materials and classical liquids. Here, we\nreport on the spontaneous formation of wave-like magnetic patterns in a spinor\nBose-Einstein condensate, extending those studies into the domain of quantum\ngases. We observe characteristic modes across a broad range of the magnetic\nfield acting as a control parameter. Our measurements link pattern formation in\nthese quantum systems to specific unstable modes obtainable from linear\nstability analysis. These investigations open new prospects for controlled\nstudies of symmetry breaking and the appearance of structures in the quantum\ndomain.",
        "positive": "Variational approach for Bose-Einstein condensates in strongly\n  disordered traps: Recently, Nattermann and Pokrovsky [PRL 100, 060402 (2008)] have proposed a\nscaling approach for studying Bose-Einstein condensates in strongly disordered\ntraps. In this paper we implement their scaling argument in the framework of\nthe variational method for solving the time dependent Gross-Pitaevskii\nequation. We consider atomic gases with both short range s-wave interaction and\nlong range anisotropic dipolar interaction. The theory is addressed to the\nregime of strong disorder and weak interactions where the physics is dominated\nby the collective pinning due to the disorder. The phenomenon of condensate\nfragmentation in dipolar gases is also analyzed."
    },
    {
        "anchor": "Phase transitions in one-dimensional correlated Fermi gases with\n  cavity-induced umklapp scattering: The phase transitions of one dimensional correlated Fermi gases in a\ntransversely driven optical cavity, under the umklapp condition that the cavity\nwavenumber equals two times of Fermi wavenumber, are studied with the\nbosonization and renormalization group (RG) techniques. The bosonization of\nFermi fields gives rise to an all-to-all sine-Gordon (SG) model due to the\ncavity-assisted non-local interactions, where the Bose fields at any two\nspatial points are coupled. The superradiant phase transition is then linked to\nthe Kosterlitz-Thouless (KT) phase transition of the all-to-all SG model. The\nnesting effect, in which the superradiant phase transition can be triggered by\ninfinitely small atom-cavity coupling strength, is preserved for any\nnon-attractive local interactions. The phase transition occurs at finite\ncritical coupling strength for attractive local interactions. Nevertheless, the\ncritical dimension of the KT phase transition is also 2 like that in an\nordinary local SG model. Our work provides an analytical framework for\nunderstanding the phase transitions in correlated intra-cavity Fermi gases.",
        "positive": "Fluctuations of imbalanced fermionic superfluids in two dimensions\n  induce continuous quantum phase transitions and non-Fermi liquid behavior: We study the nature of superfluid pairing in imbalanced Fermi mixtures in two\nspatial dimensions. We present evidence that the combined effect of Fermi\nsurface mismatch and order parameter fluctuations of the superfluid condensate\ncan lead to continuous quantum phase transitions from a normal Fermi mixture to\nan intermediate Sarma-Liu-Wilczek superfluid with two gapless Fermi surfaces --\neven when mean-field theory (incorrectly) predicts a first order transition to\na phase-separated \"Bardeen-Cooper-Schrieffer plus excess fermions\" ground\nstate. We propose a mechanism for non-Fermi liquid behavior from repeated\nscattering processes between the two Fermi surfaces and fluctuating Cooper\npairs. Prospects for experimental observation with ultracold atoms are\ndiscussed."
    },
    {
        "anchor": "Polaron, molecule and pairing in one-dimensional spin-1/2 Fermi gas with\n  an attractive Delta-function interaction: Using solutions of the discrete Bethe ansatz equations, we study in detail\nthe quantum impurity problem of a spin-down fermion immersed into a fully\nploarized spin-up Fermi sea with weak attraction. We prove that this impurity\nfermion in the one-dimensional (1D) fermionic medium behaves like a polaron for\nweak attraction. However, as the attraction grows, the spin-down fermion binds\nwith one spin-up fermion from the fully-polarized medium to form a tightly bond\nmolecule. Thus it is seen that the system undergos a cross-over from a mean\nfield polaron-like nature into a mixture of excess fermions and a bosonic\nmolecule as the attraction changes from weak attraction into strong attraction.\nThis polaron-molecule cross-over is universal in 1D many-body systems of\ninteracting fermions. In thermodynamic limit, we further study the relationship\nbetween the Fredholm equations for the 1D spin-1/2 Fermi gas with weakly\nrepulsive and attractive delta-function interactions.",
        "positive": "Techniques to measure quantum criticality in cold atoms: Attempts to understand zero temperature phase transitions have forced\nphysicists to consider a regime where the standard paradigms of condensed\nmatter physics break down [1-4]. These quantum critical systems lack a simple\ndescription in terms of weakly interacting quasiparticles, but over the past 20\nyears physicists have gained deep insights into their properties. Most\ndramatically, theory predicts that universal scaling relationships describe\ntheir finite temperature thermodynamics up to remarkably high temperatures.\nUnfortunately, these universal functions are hard to calculate: for example\nthere are no reliable general techniques [4,5] to calculate the scaling\nfunctions for dynamics. Viewing a cold atom experiment as a quantum simulator\n[6], we show how to extract universal scaling functions from (non-universal)\natomic density profiles or spectroscopic measurements. Such experiments can\nresolve important open questions about the Mott-Metal crossover [7,8] and the\ndynamics of the finite density O(2) rotor model [1,9], with direct impact on\ntheories of, for example, high temperature superconducting cuprates [10,11],\nheavy fermion materials [12], and graphene [13]."
    },
    {
        "anchor": "Effect of optical lattice potentials on the vortices in rotating dipolar\n  Bose-Einstein condensates: We study the interplay of dipole-dipole interaction and optical lattice (OL)\npotential of varying depths on the formation and dynamics of vortices in\nrotating dipolar Bose-Einstein condensates. By numerically solving the\ntime-dependent quasi-two dimensional Gross-Pitaevskii equation, we analyse the\nconsequence of dipole-dipole interaction on vortex nucleation, vortex\nstructure, critical rotation frequency and number of vortices for a range of OL\ndepths. Rapid creation of vortices has been observed due to supplementary\nsymmetry breaking provided by the OL in addition to the dipolar interaction.\nAlso the critical rotation frequency decreases with an increase in the depth of\nthe OL. Further, at lower rotation frequencies the number of vortices increases\non increasing the depth of OL while it decreases at higher rotation\nfrequencies. This variation in the number of vortices has been confirmed by\ncalculating the rms radius, which shrinks in deep optical lattice at higher\nrotation frequencies.",
        "positive": "Observation of first and second sound in a BKT superfluid: Superfluidity in its various forms has fascinated scientists since the\nobservation of frictionless flow in liquid helium II. In three spatial\ndimensions (3D), it is conceptually associated with the emergence of long-range\norder (LRO) at a critical temperature $T_{\\text{c}}$. One of its hallmarks,\npredicted by the highly successful two-fluid model and observed in both liquid\nhelium and ultracold atomic gases, is the existence of two kinds of sound\nexcitations, the first and second sound. In 2D systems, thermal fluctuations\npreclude LRO, but superfluidity nevertheless emerges at a nonzero\n$T_{\\text{c}}$ via the infinite-order Berezinskii-Kosterlitz-Thouless (BKT)\ntransition, which is associated with a universal jump in the superfluid density\n$n_{\\text{s}}$ without any discontinuities in the fluid's thermodynamic\nproperties. BKT superfluids are also predicted to support two sounds, but the\nobservation of this has remained elusive. Here we observe first and second\nsound in a homogeneous 2D atomic Bose gas, and from the two\ntemperature-dependent sound speeds extract its superfluid density. Our results\nagree with BKT theory, including the prediction for the universal\nsuperfluid-density jump."
    },
    {
        "anchor": "Seeing bulk topological properties of band insulators in small photonic\n  lattices: We present a general scheme for measuring the bulk properties of\nnon-interacting tight-binding models realized in arrays of coupled photonic\ncavities. Specifically, we propose to implement a single unit cell of the\ntargeted model with tunable twisted boundary conditions in order to simulate\nlarge systems and, most importantly, to access bulk topological properties\nexperimentally. We illustrate our method by demonstrating how to measure\ntopological invariants in a two-dimensional quantum Hall-like model.",
        "positive": "Superfluid fraction in an interacting spatially modulated Bose-Einstein\n  condensate: At zero temperature, a Galilean-invariant Bose fluid is expected to be fully\nsuperfluid. Here we investigate theoretically and experimentally the quenching\nof the superfluid density of a dilute Bose-Einstein condensate due to the\nbreaking of translational (and thus Galilean) invariance by an external 1D\nperiodic potential. Both Leggett's bound fixed by the knowledge of the total\ndensity and the anisotropy of the sound velocity provide a consistent\ndetermination of the superfluid fraction. The use of a large-period lattice\nemphasizes the important role of two-body interactions on superfluidity."
    },
    {
        "anchor": "Effect of the particle-hole channel on BCS--Bose-Einstein condensation\n  crossover in atomic Fermi gases: BCS--Bose-Einstein condensation (BEC) crossover is effected by increasing\npairing strength between fermions from weak to strong in the particle-particle\nchannel. Here we study the effect of the particle-hole channel on the zero $T$\ngap $\\Delta(0)$, superfluid transition temperature $T_{\\text{c}}$ and the\npseudogap at $T_{\\text{c}}$, as well as the mean-field ratio\n$2\\Delta(0)/T_{\\text{c}}^{\\text{MF}}$, from BCS through BEC regimes, in the\nframework of a pairing fluctuation theory which includes self-consistently the\ncontributions of finite-momentum pairs. These pairs necessarily lead to a\npseudogap in single particle excitation spectrum above and below\n$T_{\\text{c}}$. We sum over the infinite particle-hole ladder diagrams so that\nthe particle-particle and particle-hole $T$-matrices are entangled with each\nother. We find that the particle-hole susceptibility has a complex dynamical\nstructure, with strong momentum and frequency dependencies, and is sensitive to\ntemperature, gap size and interaction strength. We conclude that neglecting the\nself-energy feedback causes a serious over-estimate of the particle-hole\nsusceptibility. In the BCS limit, the particle-hole channel effect may be\napproximated by the same reduction in the overall pairing strength so that the\nratio $2\\Delta(0)/T_{\\text{c}}$ is unaffected, in agreement with Gor'kov\n\\textit{et al.} to the leading order. However, the effect becomes more complex\nand pronounced in the crossover regime, where the particle-hole susceptibility\nis reduced by both a smaller Fermi surface and a big (pseudo)gap. Deep in the\nBEC regime, the particle-hole channel contributions drop to zero. We propose\nthat precision measurements of the magnetic field for Feshbach resonance at low\ntemperatures as a function of density can be used to quantify the particle-hole\nsusceptibility and test different theories.",
        "positive": "Brueckner $G$-matrix approach to two-dimensional Fermi gases with the\n  finite-range attractive interaction: Two-dimensional spin-1/2 fermions with the finite-range interaction are\ntheoretically studied. Characterizing the attractive interaction in terms of\nthe scattering length and the effective range, we discuss the finite-range\neffects on the ground-state properties in this system. The Brueckner $G$-matrix\napproach is employed to analyze the finite-range effects on an attractive\nFermi-polaron energy and the equation of state throughout the BEC-BCS crossover\nin two dimensions, which can be realized in the population-imbalanced and\n-balanced cases between two components, respectively. The analytical formulae\nfor these ground states obtained in this study would be useful for\nunderstanding many-body phenomena with finite-range interactions in\nlow-dimensional systems."
    },
    {
        "anchor": "Universal driven critical dynamics across a quantum phase transition in\n  ferromagnetic spinor atomic Bose-Einstein condensates: We study the equilibrium and dynamical properties of a ferromagnetic spinor\natomic Bose-Einstein condensate. In the vicinity of the critical point for a\ncontinuous quantum phase transition, universal behaviors are observed both in\nthe equilibrium state and in the dynamics when the quadratic Zeeman shift is\nswept linearly. Three distinct dynamical regions are identified for different\nsweeping time scales ($\\tau$), when compared to the time scale $\\tau_{\\rm\nKZ}\\sim N^{(1+\\nu z)/\\nu d}$ decided by external driving in a system with\nfinite size $N$ ($\\nu,z$ are critical exponents and $d$ the dimensionality).\nThey are manifested by the excitation probability $\\mathcal{P}$ and the excess\nheat density $\\mathcal{Q}$. The adiabatic region of\n$\\,\\mathcal{P}\\sim\\mathcal{Q}\\sim\\tau^{-2}\\,$ follows from the adiabatic\nperturbation theory when $\\tau >\\tau_{\\rm KZ}$, while the non-adiabatic\nuniversal region of $\\,\\mathcal{P}\\sim\\mathcal{Q}\\sim\\tau^{-1}\\,$ in the\nthermodynamic limit is described by the Kibble-Zurek mechanism when $\\tau_{\\rm\nKZ}>\\tau >$ the time scale given by initial gap. The Kibble-Zurek scaling\nhypothesis is augmented with finite-size scaling in the latter region and\nseveral experimentally falsifiable features for the finite system we consider\nare predicted. The region of the fastest sweeping is found to be non-universal\nand far-from-equilibrium with $\\mathcal{P}$ and $\\mathcal{Q}$ essentially being\nconstants independent of $\\tau$.",
        "positive": "Transition states and thermal collapse of dipolar Bose-Einstein\n  condensates: We investigate thermally excited, dipolar Bose-Einstein condensates.\nQuasi-particle excitations of the atomic cloud cause density fluctuations which\ncan induce the collapse of the condensate if the inter-particle interaction is\nattractive. Within a variational approach, we identify the collectively excited\nstationary states of the gas which form transition states on the way to the\nBEC's collapse. We analyze transition states with different $m$-fold rotational\nsymmetry and identify the one which mediates the collapse. The latter's\nsymmetry depends on the trap aspect ratio of the external trapping potential\nwhich determines the shape of the BEC. Moreover, we present the collapse\ndynamics of the BEC and calculate the corresponding decay rate using transition\nstate theory. We observe that the thermally induced collapse mechanism is\nimportant near the critical scattering length, where the lifetime of the\ncondensate can be significantly reduced. Our results are valid for an arbitrary\nstrength of the dipole-dipole interaction. Specific applications are discussed\nfor the elements $^{52}$Cr, $^{164}$Dy and $^{168}$Er with which dipolar BECs\nhave been experimentally realized."
    },
    {
        "anchor": "Observation of a two-dimensional Fermi gas of atoms: We have prepared a degenerate gas of fermionic atoms which move in two\ndimensions while the motion in the third dimension is \"frozen\" by tight\nconfinement and low temperature. {\\it In situ} imaging provides direct\nmeasurement of the density profile and temperature. The gas is confined in a\ndefect-free optical potential, and the interactions are widely tunable by means\nof a Fano--Feshbach resonance. This system can be a starting point for\nexploration of 2D Fermi physics and critical phenomena in a pure, controllable\nenvironment.",
        "positive": "Detecting fractional Chern insulators through circular dichroism: Great efforts are currently devoted to the engineering of topological Bloch\nbands in ultracold atomic gases. Recent achievements in this direction,\ntogether with the possibility of tuning inter-particle interactions, suggest\nthat strongly-correlated states reminiscent of fractional quantum Hall (FQH)\nliquids could soon be generated in these systems. In this experimental\nframework, where transport measurements are limited, identifying unambiguous\nsignatures of FQH-type states constitutes a challenge on its own. Here, we\ndemonstrate that the fractional nature of the quantized Hall conductance, a\nfundamental characteristic of FQH states, could be detected in ultracold gases\nthrough a circular-dichroic measurement, namely, by monitoring the energy\nabsorbed by the atomic cloud upon a circular drive. We validate this approach\nby comparing the circular-dichroic signal to the many-body Chern number, and\ndiscuss how such measurements could be performed to distinguish FQH-type states\nfrom competing states. Our scheme offers a practical tool for the detection of\ntopologically-ordered states in quantum-engineered systems, with potential\napplications in solid state."
    },
    {
        "anchor": "Quantum Chaos in Ultracold Collisions of Erbium: Atomic and molecular samples reduced to temperatures below 1 microkelvin, yet\nstill in the gas phase, afford unprecedented energy resolution in probing and\nmanipulating how their constituent particles interact with one another. For\nsimple atoms, such as alkalis, scattering resonances are extremely\nwell-characterized. However, ultracold physics is now poised to enter a new\nregime, where far more complex species can be cooled and studied, including\nmagnetic lanthanide atoms and even molecules. For molecules, it has been\nspeculated that a dense forest of resonances in ultracold collision cross\nsections will likely express essentially random fluctuations, much as the\nobserved energy spectra of nuclear scattering do. According to the\nBohigas-Giannoni-Schmit conjecture, these fluctuations would imply chaotic\ndynamics of the underlying classical motion driving the collision. This would\nprovide a paradigm shift in ultracold atomic and molecular physics,\nnecessitating new ways of looking at the fundamental interactions of atoms in\nthis regime, as well as perhaps new chaos-driven states of ultracold matter. In\nthis report we provide the first experimental demonstration that random spectra\nare indeed found at ultralow temperatures. In the experiment, an ultracold gas\nof erbium atoms is shown to exhibit many Fano-Feshbach resonances, for bosons\non the order of 3 per gauss. Analysis of their statistics verifies that their\ndistribution of nearest-neighbor spacings is what one would expect from random\nmatrix theory. The density and statistics of these resonances are explained by\nfully-quantum mechanical scattering calculations that locate their origin in\nthe anisotropy of the atoms' potential energy surface. Our results therefore\nreveal for the first time chaotic behavior in the native interaction between\nultracold atoms.",
        "positive": "Equation of state and Kosterlitz-Thouless transition temperature in\n  two-dimensional Fermi gases: An analytical approach: We study Fermi gases in two dimensions at low temperatures with attractive\ninteractions. Analytical results are derived for the equation of state and the\nKosterlitz-Thouless transition temperature as functions of the two-body binding\nenergy and the density of the gas. Our results for the equation of state\nstrongly deviate from the mean field predictions. However, they are in\nreasonable agreement with Monte-Carlo calculations and recent experiments with\ncold atomic gases."
    },
    {
        "anchor": "Role of thermal friction in relaxation of turbulent Bose-Einstein\n  condensates: In recent experiments, the relaxation dynamics of highly oblate, turbulent\nBose-Einstein condensates (BECs) was investigated by measuring the vortex decay\nrates in various sample conditions [Phys. Rev. A $\\bf 90$, 063627 (2014)] and,\nseparately, the thermal friction coefficient $\\alpha$ for vortex motion was\nmeasured from the long-time evolution of a corotating vortex pair in a BEC\n[Phys. Rev. A $\\bf 92$, 051601(R) (2015)]. We present a comparative analysis of\nthe experimental results, and find that the vortex decay rate $\\Gamma$ is\nalmost linearly proportional to $\\alpha$. We perform numerical simulations of\nthe time evolution of a turbulent BEC using a point-vortex model equipped with\nlongitudinal friction and vortex-antivortex pair annihilation, and observe that\nthe linear dependence of $\\Gamma$ on $\\alpha$ is quantitatively accounted for\nin the dissipative point-vortex model. The numerical simulations reveal that\nthermal friction in the experiment was too strong to allow for the emergence of\na vortex-clustered state out of decaying turbulence.",
        "positive": "Simultaneous dipole and quadrupole moment contribution in the Bogoliubov\n  spectrum: Application of the non-integral Gross-Pitaevskii equation: We present the Gross-Pitaevskii equation for Bose-Einstein condensates (BECs)\npossessing the electric dipole and the electric quadrupole moments in a\nnon-integral form. These equations are coupled with the Maxwell equations. The\nmodel under consideration includes the dipole-dipole, the dipole-quadrupole,\nand the quadrupole-quadrupole interactions in terms of the electric field\ncreated by the dipoles and quadrupoles. We apply this model to obtain the\nBogoliubov spectrum for three dimensional BECs with a repulsive short-range\ninteraction. We obtain an extra term in the Bogoliubov spectrum in compare with\nthe dipolar BECs. We show that the quadrupole-quadrupole interaction gives a\npositive contribution in the Bogoliubov spectrum. Hence this spectrum is\nstable."
    },
    {
        "anchor": "Equation of state of non-relativistic matter from automated perturbation\n  theory and complex Langevin: We calculate the pressure and density of polarized non-relativistic systems\nof two-component fermions coupled via a contact interaction at finite\ntemperature. For the unpolarized one-dimensional system with an attractive\ninteraction, we perform a third-order lattice perturbation theory calculation\nand assess its convergence by comparing with hybrid Monte Carlo. In that\nregime, we also demonstrate agreement with real Langevin. For the repulsive\nunpolarized one-dimensional system, where there is a so-called complex phase\nproblem, we present lattice perturbation theory as well as complex Langevin\ncalculations. For our studies, we employ a Hubbard-Stratonovich transformation\nto decouple the interaction and automate the application of Wick's theorem for\nperturbative calculations, which generates the diagrammatic expansion at any\norder. We find excellent agreement between the results from our perturbative\ncalculations and stochastic studies in the weakly interacting regime. In\naddition, we show predictions for the strong coupling regime as well as for the\npolarized one-dimensional system. Finally, we show a first estimate for the\nequation of state in three dimensions where we focus on the polarized unitary\nFermi gas.",
        "positive": "Excitation Spectra of one-dimensional spin-1/2 Fermi gas with an\n  attraction: Using exact Bethe ansatz solution, we rigorously study excitation spectra of\nthe spin-1/2 Fermi gas (called Yang-Gaudin model) with an attractive\ninteraction. Elementary excitations of this model involve particle-hole\nexcitations, hole excitations and adding particles in the Fermi seas of pairs\nand unpaired fermions. The gapped magnon excitations in spin sector show a\nferromagnetic coupling to the Fermi sea of the single fermions. By numerically\nand analytically solving the Bethe ansatz equations and the thermodynamic Bethe\nansatz equations of this model, we obtain excitation energies for various\npolarizations in the phase of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)-like\nstate. For a small momentum (long-wavelength limit) and in the strong\ninteraction regime, we analytically obtained their linear dispersions with\ncurvature corrections, effective masses as well as velocities in particle-hole\nexcitations of pairs and unpaired fermions. Such a type of particle-hole\nexcitations display a novel separation of collective motions of bosonic modes\nwithin paired and unpaired fermions. Finally, we also discuss magnon\nexcitations in spin sector and the application of the Bragg spectroscopy for\ntesting such separated charge excitation modes of pairs and single fermions."
    },
    {
        "anchor": "Strongly Interacting Atom Lasers in Three Dimensional Optical Lattices: We show that the dynamical melting of a Mott insulator in a three-dimensional\nlattice leads to condensation at nonzero momenta, a phenomenon that can be used\nto generate strongly interacting atom lasers in optical lattices. For infinite\nonsite repulsion, the case considered here, the momenta at which bosons\ncondense is determined analytically and found to have a simple dependence on\nthe hopping amplitudes. The occupation of the condensates is shown to scale\nlinearly with the total number of atoms in the initial Mott insulator. Our\nresults are obtained using a Gutzwiller-type mean-field approach, gauged\nagainst exact diagonalization solutions of small systems.",
        "positive": "Quantum phase transition of the two-dimensional Rydberg atom array in an\n  optical cavity: We study the two-dimensional Rydberg atom array in an optical cavity with\nhelp of the meanfield theory and the large-scale quantum Monte Carlo\nsimulations. The strong dipole-dipole interactions between Rydberg atoms can\nmake the system exhibit the crystal structure, and the coupling between\ntwo-level atom and cavity photon mode can result in the formation of the\npolariton. The interplay between them provides a rich quantum phase diagram\nincluding the Mott, solid-1/2, superradiant and superradiant solid phases. As\nthe two-order co-existed phase, the superradiant solid phase breaks both\ntranslational and U(1) symmetries. Based on both numerical and analytic\nresults, we found the region of superradiant solid is much larger than one\ndimensional case, so that it can be more easily observed in the experiment.\nFinally, we discuss how the energy gap of the Rydberg atom can affect the type\nof the quantum phase transition and the number of triple points."
    },
    {
        "anchor": "The equation of state of ultracold Bose and Fermi gases: a few examples: We describe a powerful method for determining the equation of state of an\nultracold gas from in situ images. The method provides a measurement of the\nlocal pressure of an harmonically trapped gas and we give several applications\nto Bose and Fermi gases. We obtain the grand-canonical equation of state of a\nspin-balanced Fermi gas with resonant interactions as a function of\ntemperature. We compare our equation of state with an equation of state\nmeasured by the Tokyo group, that reveals a significant difference in the\nhigh-temperature regime. The normal phase, at low temperature, is well\ndescribed by a Landau Fermi liquid model, and we observe a clear thermodynamic\nsignature of the superfluid transition. In a second part we apply the same\nprocedure to Bose gases. From a single image of a quasi ideal Bose gas we\ndetermine the equation of state from the classical to the condensed regime.\nFinally the method is applied to a Bose gas in a 3D optical lattice in the Mott\ninsulator regime. Our equation of state directly reveals the Mott insulator\nbehavior and is suited to investigate finite-temperature effects.",
        "positive": "Three-body interaction near a narrow two-body zero crossing: We calculate the effective three-body force for bosons interacting with each\nother by a two-body potential tuned to a narrow zero crossing in any dimension.\nWe use the standard two-channel model parametrized by the background atom-atom\ninteraction strength, the amplitude of the open-channel to closed-channel\ncoupling, and the atom-dimer interaction strength. The three-body force\noriginates from the atom-dimer interaction, but it can be dramatically enhanced\nfor narrow crossings, i.e., for small atom-dimer conversion amplitudes. This\neffect can be used to stabilize quasi-two-dimensional dipolar atoms and\nmolecules."
    },
    {
        "anchor": "Topological Superfluid Defects with Discrete Point Group Symmetries: Discrete symmetries are spatially ubiquitous but are often hidden in internal\nstates of systems where they can have especially profound consequences. In this\nwork we create and verify exotic magnetic phases of atomic spinor Bose-Einstein\ncondensates that, despite their continuous character and intrinsic spatial\nisotropy, exhibit complex discrete polytope symmetries in their topological\ndefects. Using carefully tailored spinor rotations and microwave transitions,\nwe engineer singular line defects whose quantization conditions, exchange\nstatistics, and dynamics are fundamentally determined by these underlying\nsymmetries. We show how filling the vortex line singularities with atoms in a\nvariety of different phases leads to core structures that possess magnetic\ninterfaces with rich combinations of discrete and continuous symmetries. Such\ndefects, with their non-commutative properties, could provide unconventional\nrealizations of quantum information and interferometry.",
        "positive": "Strongly correlated quantum droplets in quasi-1D dipolar Bose gas: We exploit a few- to many-body approach to study strongly interacting dipolar\nbosons in the quasi-one-dimensional system. The dipoles attract each other\nwhile the short range interactions are repulsive. Solving numerically the\nmulti-atom Schr\\\"{o}dinger equation, we discover that such systems can exhibit\nnot only the well known bright soliton solutions but also novel quantum\ndroplets for a strongly coupled case. For larger systems, basing on microscopic\nproperties of the found few-body solution, we propose a new equation for a\ndensity amplitude of atoms. It accounts for fermionization for strongly\nrepelling bosons by incorporating the Lieb-Liniger energy in a local density\napproximation and approaches the standard Gross-Pitaevskii equation (GPE) in\nthe weakly interacting limit. Not only does such a framework provide an\nalternative mechanism of the droplet stability, but it also introduces means to\nfurther analyze this previously unexplored quantum phase. In the limiting\nstrong repulsion case, yet another simple multi-atom model is proposed. We\nstress that the celebrated Lee-Huang-Yang term in the GPE is not applicable in\nthis case."
    },
    {
        "anchor": "Observation of an orbital interaction-induced Feshbach resonance in\n  173-Yb: We report on the experimental observation of a novel inter-orbital Feshbach\nresonance in ultracold 173-Yb atoms, which opens the possibility of tuning the\ninteractions between the 1S0 and 3P0 metastable state, both possessing\nvanishing total electronic angular momentum. The resonance is observed at\nexperimentally accessible magnetic field strengths and occurs universally for\nall hyperfine state combinations. We characterize the resonance in the bulk via\ninter-orbital cross-thermalization as well as in a three-dimensional lattice\nusing high-resolution clock-line spectroscopy.",
        "positive": "Collectively induced many-vortices topology via rotatory Dicke quantum\n  phase transition: We examine the superradiance of a Bose-Einstein condensate pumped with a\nLaguerre-Gaussian laser of high winding number, e.g., $\\ell = 7$. The laser\nbeam transfers its orbital angular momentum (OAM) to the condensate at once due\nto the collectivity of the superradiance. An $\\ell$-fold rotational symmetric\nstructure emerges with the take place of rotatory superradiance. $\\ell$ number\nof single-charge vortices appear at the arms of this structure. Even though the\npump and the condensate profiles initially have cylindrical symmetry, we\nobserve that it is broken to $\\ell$-fold rotational symmetry during the\nsuperradiance. Breaking of the cylindrical symmetry into the $\\ell$-fold\nsymmetry and OAM transfer to the BEC become possible after the same critical\npump strength. Reorganization of the condensate resembles the ordering in the\nexperiment by Esslinger and colleagues [Nature, {\\bf 264}, 1301 (2010)]. We\nshow that the critical point for the onset of the reorganization follows the\nform of the Dicke quantum phase transition."
    },
    {
        "anchor": "Dynamical Unbinding Transition in a Periodically Driven Mott Insulator: We study the double occupancy in a fermionic Mott insulator at half-filling\ngenerated via a dynamical periodic modulation of the hopping amplitude. Tuning\nthe modulation amplitude, we describe a crossover in the nature of\ndoublon-holon excitations from a Fermi Golden Rule regime to damped Rabi\noscillations. The decay time of excited states diverges at a critical\nmodulation strength, signaling the transition to a dynamically bound\nnon-equilibrium state of doublon-holon pairs. A setup using a fermionic quantum\ngas should allow to study the critical exponents.",
        "positive": "Sub-Doppler laser cooling of 23Na in gray molasses on the D2 line: We report on the efficient gray molasses cooling of sodium atoms using the\n$D_{2}$ optical transition at 589.1 nm. Thanks to the hyperfine split about\n6$\\Gamma$ between the $|F'=2\\rangle$ and $|F'=3\\rangle$ in the excited state\n3$^{2}P_{3/2}$, this atomic transition is effective for the gray molasses\ncooling mechanism. Using this cooling technique, the atomic sample in $F = 2$\nground manifold is cooled from 700 $\\upmu$K to 56 $\\upmu$K in 3.5 ms. We\nobserve that the loading efficiency into magnetic trap is increased due to the\nlower temperature and high phase space density of atomic cloud after gray\nmolasses. This technique offers a promising route for the fast cooling of the\nsodium atoms in the $F=2$ state."
    },
    {
        "anchor": "Berry phase, entanglement entropy, and algebraic properties of ground\n  states of BCS and BEC superfluids: By using Bogoliubov transformations to construct the ground states of\nfermionic Bardeen-Cooper-Schrieffer (BCS) superfluids and weakly-interacting\nBose gases supporting Bose Einstein Condensation (BEC), their algebraic\nstructures and implications can be analyzed in detail. Both ground states are\ngeneralized squeezed coherent states saturating a generalized Heisenberg\nuncertainty relation, and they acquire quantized Berry phases when the\ncorresponding systems are transported along a closed path in their parameter\nspaces. While the Berry phase of the BCS ground state depends on the total\nparticle number, the Berry phase of the BEC ground state depends only on the\nparticles outside the BEC. The Berry phases are associated with magnetic\nmonopoles in the parameter spaces and we found that the Dirac quantization\ncondition is satisfied. Moreover, both ground states are entangled states of\nthe fermion or boson quanta and we found the entanglement entropy quantifying\nthe internal correlations. A fixed particle-number approach of fermionic\nsuperfluids does not saturate the generalized uncertainty relation, exhibits\ninternal entanglement, and gives corresponding Berry phase. In addition, the\nalgebraic structures of the ground states can be classified by the $q$-deformed\nHopf algebra, $\\bigoplus_{\\mathbf{k}}h_{q_{\\mathbf{k}}}(1)$ for bosons and\n$q$-deformed Hopf superalgebra $\\bigoplus_{\\mathbf{k}}h_{q_{\\mathbf{k}}}(1|1)$\nfor fermions, respectively.",
        "positive": "On the thermalization of a Luttinger liquid after a sequence of sudden\n  interaction quenches: We present a comprehensive analysis of the relaxation dynamics of a Luttinger\nliquid subject to a sequence of sudden interaction quenches. We express the\ncritical exponent $\\beta$ governing the decay of the steady-state propagator as\nan explicit functional of the switching protocol. At long distances $\\beta$\ndepends only on the initial state while at short distances it is also history\ndependent. Continuous protocols of arbitrary complexity can be realized with\ninfinitely long sequences. For quenches of finite duration we prove that there\nexist no protocol to bring the initial non-interacting system in the ground\nstate of the Luttinger liquid. Nevertheless memory effects are washed out at\nshort-distances. The adiabatic theorem is then investigated with\nramp-switchings of increasing duration, and several analytic results for both\nthe propagator and the excitation energy are derived."
    },
    {
        "anchor": "Universal quantum dynamics of Bose polarons: Predicting the emergent properties of impurities immersed in a quantum bath\nis a fundamental challenge that can defy quasiparticle treatments. Here, we\nmeasure the spectral properties and real-time dynamics of mobile impurities\ninjected into a homogeneous Bose--Einstein condensate, using two Feshbach\nresonances to tune both the impurity-bath and intrabath interactions. We map\nout both attractive and repulsive branches of polaron quasiparticles, resolving\nthe repulsive polaron and the molecular state associated with the Feshbach\nresonance in the strongly interacting regime, and show that the latter also has\na many-body character. Our measurements reveal remarkably universal behavior,\ncontrolled by the bath density and a single dimensionless interaction\nparameter; for near-resonant interactions the polarons are no longer well\ndefined, but the universality still holds.",
        "positive": "Quasi-one-dimensional Hall physics in the Harper-Hofstadter-Mott model: We study the ground-state phase diagram of the strongly interacting\nHarper-Hofstadter-Mott model at quarter flux on a quasi-one-dimensional lattice\nconsisting of a single magnetic flux quantum in $y$-direction. In addition to\nsuperfluid phases with various density patterns, the ground-state phase diagram\nfeatures quasi-one-dimensional analogues of fractional quantum Hall phases at\nfillings $\\nu=1/2$ and $3/2$, where the latter is only found thanks to the\nhopping anisotropy and the quasi-one-dimensional geometry. At integer fillings\n- where in the full two-dimensional system the ground-state is expected to be\ngapless - we observe gapped non-degenerate ground-states: At $\\nu=1$ it shows\nan odd 'fermionic' Hall conductance, while the Hall response at $\\nu=2$\nconsists of the transverse transport of a single particle-hole pair, resulting\nin a net zero Hall conductance. The results are obtained by exact\ndiagonalization and in the reciprocal mean-field approximation."
    },
    {
        "anchor": "Thermal-induced Local Imbalance in Repulsive Binary Bose Mixtures: We study repulsive two-component Bose mixtures with equal populations and\nconfined in a finite-size box through path-integral Monte Carlo simulations.\nFor different values of the $s$-wave scattering length of the interspecies\npotential, we calculate the local population imbalance in a region of fixed\nvolume inside the box at different temperatures. We find two different\nbehaviors: for phase-separated states at $T=0$, thermal effects induce a\ndiffusion process which reduces the local imbalance whereas, for miscible\nstates at $T=0$, a maximum in the local population imbalance appears at a\ncertain temperature, below the critical one. We show that this intriguing\nbehavior is strongly related to the bunching effect associated with the\nBose-Einstein statistics of the particles in the mixture and to an unexpected\nbehavior of the cross pair distribution function not reported before.",
        "positive": "Superfluid-insulator transition of two-dimensional disordered Bose gases: We study the two-dimensional weakly repulsive Bose gas at zero temperature in\nthe presence of correlated disorder. Using large-scale simulations, we show\nthat the low-energy Bogoliubov cumulative density of states remains quadratic\nup to a critical disorder strength, beyond which a power law with\ndisorder-dependent exponent $\\beta<2$ sets in. We associate this threshold\nbehavior with the transition from superfluid to Bose glass, and compare the\nresulting mean-field phase diagram with scaling laws and the Thomas-Fermi\npercolation threshold of the mean-field density profile."
    },
    {
        "anchor": "Hydrodynamics of local excitations after an interaction quench in 1D\n  cold atomic gases: We discuss the hydrodynamic approach to the study of the time evolution\n-induced by a quench- of local excitations in one dimension. We focus on\ninteraction quenches: the considered protocol consists in creating a stable\nlocalized excitation propagating through the system, and then operating a\nsudden change of the interaction between the particles. To highlight the effect\nof the quench, we take the initial excitation to be a soliton. The quench\nsplits the excitation into two packets moving in opposite directions, whose\ncharacteristics can be expressed in a universal way. Our treatment allows to\ndescribe the internal dynamics of these two packets in terms of the different\nvelocities of their components. We confirm our analytical predictions through\nnumerical simulations performed with the Gross-Pitaevskii equation and with the\nCalogero model (as an example of long range interactions and solvable with a\nparabolic confinement). Through the Calogero model we also discuss the effect\nof an external trapping on the protocol. The hydrodynamic approach shows that\nthere is a difference between the bulk velocities of the propagating packets\nand the velocities of their peaks: it is possible to discriminate the two\nquantities, as we show through the comparison between numerical simulations and\nanalytical estimates. In the realizations of the discussed quench protocol in a\ncold atom experiment, these different velocities are accessible through\ndifferent measurement procedures.",
        "positive": "Polarons and bipolarons in a two-dimensional square lattice: Quasiparticles and their interactions are a key part of our understanding of\nquantum many-body systems. Quantum simulation experiments with cold atoms have\nin recent years advanced our understanding of isolated quasiparticles, but so\nfar they have provided limited information regarding their interactions and\npossible bound states. Here, we show how exploring mobile impurities immersed\nin a Bose-Einstein condensate (BEC) in a two-dimensional lattice can address\nthis problem. First, the spectral properties of individual impurities are\nexamined, and in addition to the attractive and repulsive polarons known from\ncontinuum gases, we identify a new kind of quasiparticle stable for repulsive\nboson-impurity interactions. The spatial properties of polarons are calculated\nshowing that there is an increased density of bosons at the site of the\nimpurity both for repulsive and attractive interactions. We then derive an\neffective Schr\\\"odinger equation describing two polarons interacting via the\nexchange of density oscillations in the BEC, which takes into account strong\nimpurity-boson two-body correlations. Using this, we show that the attractive\nnature of the effective interaction between two polarons combined with the\ntwo-dimensionality of the lattice leads to the formation of bound states --\ni.e. bipolarons. The wave functions of the bipolarons are examined showing that\nthe ground state is symmetric under particle exchange and therefore relevant\nfor bosonic impurities, whereas the first excited state is doubly degenerate\nand odd under particle exchange making it relevant for fermionic impurities.\nOur results show that quantum gas microscopy in optical lattices is a promising\nplatform to explore the spatial properties of polarons as well as to finally\nobserve the elusive bipolarons."
    },
    {
        "anchor": "Quantum phase-space analysis of population equilibration in multi-well\n  ultracold atomic systems: We examine the medium time quantum dynamics and population equilibration of\ntwo, three and four-well Bose-Hubbard models using stochastic integration in\nthe truncated Wigner phase-space representation. We find that all three systems\nwill enter at least a temporary state of equilibrium, with the details\ndepending on both the classical initial conditions and the initial quantum\nstatistics. We find that classical integrability is not necessarily a good\nguide as to whether equilibration will occur. We construct an effective\nsingle-particle reduced density matrix for each of the systems, using the\nexpectation values of operator moments, and use this to calculate an effective\nentropy. Knowing the expected maximum values of this entropy for each system,\nwe are able to quantify the different approaches to equilibrium.",
        "positive": "Critical Rotation of an Annular Superfluid Bose Gas: We analyze the excitation spectrum of a superfluid Bose-Einstein condensate\nrotating in a ring trap. We identify two important branches of the spectrum\nrelated to outer and inner edge surface modes that lead to the instability of\nthe superfluid. Depending on the initial circulation of the annular condensate,\neither the outer or the inner modes become first unstable. This instability is\ncrucially related to the superfluid nature of the rotating gas. In particular\nwe point out the existence of a maximal circulation above which the superflow\ndecays spontaneously, which cannot be explained by invoking the average speed\nof sound."
    },
    {
        "anchor": "Topological Fulde-Ferrell states in alkaline-earth-metal-like atoms near\n  an orbital Feshbach resonance: We study the effects of synthetic spin-orbit coupling on the pairing physics\nin quasi-one-dimensional ultracold Fermi gases of alkaline-earth-metal-like\natoms near an orbital Feshbach resonance (OFR). The interplay between\nspin-orbit coupling and pairing interactions near the OFR leads to an\ninteresting topological Fulde-Ferrell state, where the nontrivial topology of\nthe state is solely encoded in the closed channel with a topologically trivial\nFulde-Ferrell pairing in the open channel. We confirm the topological property\nof the system by characterizing the Zak phase and the edge states. The\ntopological Fulde-Ferrell state can be identified by the momentum-space density\ndistribution obtained from time-of-flight images.",
        "positive": "Bound states of an ultracold atom interacting with a set of stationary\n  impurities: In this manuscript we analyse properties of bound states of an atom\ninteracting with a set of static impurities. We begin with the simplest system\nof a single atom interacting with two static impurities. We consider two types\nof atom-impurity interaction: (i) zero-range potential represented by\nregularized delta, (ii) more realistic polarization potential, representing\nlong-range part of the atom-ion interaction. For the former we obtain\nanalytical results for energies of bound states. For the latter we perform\nnumerical calculations based on the application of finite element method. Then,\nwe move to the case of a single atom interacting with one-dimensional (1D)\ninfinite chain of static ions. Such a setup resembles Kronig-Penney model of a\n1D crystalline solid, where energy spectrum exhibits band structure behaviour.\nFor this system, we derive analytical results for the band structure of bound\nstates assuming regularized delta interaction, and perform numerical\ncalculations, considering polarization potential to model atom-impurity\ninteraction. Both approaches agree quite well when separation between\nimpurities is much larger than characteristic range of the interaction\npotential."
    },
    {
        "anchor": "Spontaneous Vortex Lattices in Quasi 2D Dipolar Spinor Condensates: Motivated by recent experiments\\cite{BA}\\cite{BB}, we study quasi 2D\nferromagnetic condensates with various aspect ratios. We find that in zero\nmagnetic field, dipolar energy generates a local energy minimum with all the\nspins lie in the 2D plane forming a row of {\\em circular} spin textures with\n{\\em alternating} orientation, corresponding to a packing of vortices of {\\em\nidentical} vorticity in different spin components. In a large magnetic field,\nthe system can fall into a long lived dynamical state consisting of an array of\nelliptic and hyperbolic Mermin-Ho spin textures, while the true equilibrium is\nan uniaxial spin density wave with a single wave-vector along the magnetic\nfield, and a wavelength similar to the characteristic length of the long lived\nvortex array state.",
        "positive": "Quantum walkers in a disordered lattice with power-law hopping: We study the effects of interparticle interactions and power-law tunneling\ncouplings on quantum walks executed by both a single one and a pair of\nhard-core bosons moving in clean and disordered one-dimensional lattices. For\nthis purpose, we perform exact diagonalization to explicitly evaluate the short\nand long time probabilities of finding the walkers within a surveillance area.\nOur main conclusions, summarized in phase diagrams in the disorder-power-law\nand interaction-disorder spaces, allowed us to discern two different scenarios\nfor the single and two quantum walkers dynamics. While in the single particle\ncase the transition to localized and extended regimes is identified for well\ndefined values of the disorder amplitude and power law hopping, those frontiers\nare replaced by diffuse contours in the interacting two particle case. In fact,\ncounterintuitive transport regimes as diffusion enhanced by disorder, and space\nconstrained dynamics assisted by both interactions and short tunneling range\nare found. Our results are of direct relevance for quantum systems with\nlong-range interactions that are currently realized in the laboratory."
    },
    {
        "anchor": "Creating big time crystals with ultracold atoms: We investigate the size of discrete time crystals s (ratio of response period\nto driving period) that can be created for a Bose-Einstein condensate (BEC)\nbouncing resonantly on an oscillating mirror. We find that time crystals can be\ncreated with sizes in the range s = 20 - 100 and that such big time crystals\nare easier to realize experimentally than a period-doubling (s = 2) time\ncrystal because they require either a larger drop height or a smaller number of\nbounces on the mirror. We also investigate the effects of having a realistic\nsoft Gaussian potential mirror for the bouncing BEC, such as that produced by a\nrepulsive light-sheet, which is found to make the experiment easier to\nimplement than a hard-wall potential mirror. Finally, we discuss the choice of\natomic system for creating time crystals based on a bouncing BEC and present an\nexperimental protocol for realizing big time crystals. Such big time crystals\nprovide a flexible platform for investigating a broad range of non-trivial\ncondensed matter phenomena in the time domain.",
        "positive": "Prethermalization to thermalization crossover in a dilute Bose gas\n  following an interaction ramp: The dynamics of a weakly interacting Bose gas at low temperatures is close to\nintegrable due to the approximate quadratic nature of the many-body\nHamiltonian. While the short-time physics after an abrupt ramp of the\ninteraction constant is dominated by the integrable dynamics, integrability is\nbroken at longer times by higher-order interaction terms in the Bogoliubov\nHamiltonian, in particular by Beliaev-Landau scatterings involving three\nquasiparticles. The two-stage relaxation process is highlighted in the\nevolution of local observables such as the density-density correlation\nfunction: a dephasing mechanism leads the system to a prethermal stage,\nfollowed by true thermalization conveyed by quasiparticle collisions. Our\nresults bring the crossover from prethermalization to thermalization within\nreach of current experiments with ultracold atomic gases."
    },
    {
        "anchor": "Anomalous Conductance of a strongly interacting Fermi Gas through a\n  Quantum Point Contact: In this work we study the particle conductance of a strongly interacting\nFermi gas through a quantum point contact. With an atom-molecule two-channel\nmodel, we compute the contribution to particle conductance by both the\nfermionic atoms and the bosonic molecules using the Keldysh formalism. Focusing\non the regime above the Fermi superfluid transition temperature, we find that\nthe fermionic contribution to the conductance is reduced by interaction\ncompared with the quantized value for the non-interacting case; while the\nbosonic contribution to the conductance exhibits a plateau with non-universal\nvalues that is larger than the quantized conductance. This feature is\nparticularly profound at temperature close to the superfluid transition. We\nemphasize that the enhanced conductance arises because of the bosonic nature of\nclosed channel molecules and the low-dimensionality of the quantum point\ncontact.",
        "positive": "Unitary boson-boson and boson-fermion mixtures: third virial coefficient\n  and three-body parameter on a narrow Feshbach resonance: We give exact integral expressions of the third cluster or virial\ncoefficients of binary mixtures of ideal Bose or Fermi gases, with interspecies\ninteractions of zero range and infinite s-wave scattering length. In general\nthe result depends on three-body parameters Rt appearing in three-body contact\nconditions, because an Efimov effect is present or because the mixture is in a\npreefimovian regime with a mass ratio close to an Efimov effect threshold. We\ngive a new, exact integral expression of Rt for the microscopic narrow Feshbach\nresonance model. A divergence of Rt in the preefimovian regime at a scaling\nexponent s = 1/2 is predicted and physically discussed. The analytical results\nare applied to typical species used in cold atom experiments."
    },
    {
        "anchor": "Band-gap structure and chiral discrete solitons in optical lattices with\n  artificial gauge fields: We study three-leg-ladder optical lattices loaded with repulsive atomic\nBose-Einstein condensates and subjected to artificial gauge fields. By\nemploying the plane-wave analysis and variational approach, we analyze the\nband-gap structure of the energy spectrum and reveal the exotic swallow-tail\nloop structures in the energy-level anti-crossing regions due to an interplay\nbetween the atom-atom interaction and artificial gauge field. Also, we discover\nstable discrete solitons residing in a semi-infinite gap above the highest\nband, these discrete solitons are associated with the chiral edge currents.",
        "positive": "Dressing the Orbital Feshbach Resonance using single-manifold Raman\n  scheme: The recently discovered Orbital Feshbach Resonance (OFR) offers the\npossibility of tuning the interaction between alkaline earth(-like) metal atoms\nwith magnetic field. Here, we introduce a single-manifold Raman scheme to dress\nthe OFR, which allows us to tune the interaction with the optical field and it\nis readily realizable in experiment. We demonstrate the scattering resonance\ncould be shifted by the dressing Raman laser using few-body and many-body\nmean-field calculation, which give rise to an optical dependent two-body bound\nstate and Raman coupling induced BCS-BEC crossover in the BCS-type mean field\ntheory. Besides, we also discuss the application of single-manifold Raman\nscheme in Kondo research by writing down a Kondo lattice model."
    },
    {
        "anchor": "DMFT vs Second Order Perturbation Theory for the Trapped 2D\n  Hubbard-Antiferromagnet: In recent literature on trapped ultracold atomic gases, calculations for\n2D-systems are often done within the Dynamical Mean Field Theory (DMFT)\napproximation. In this paper, we compare DMFT to a fully two-dimensional,\nself-consistent second order perturbation theory for weak interactions in a\nrepulsive Fermi-Hubbard model. We investigate the role of quantum and of\nspatial fluctuations when the system is in the antiferromagnetic phase, and\nfind that, while quantum fluctuations decrease the order parameter and critical\ntemperatures drastically, spatial fluctuations only play a noticeable role when\nthe system undergoes a phase transition, or at phase boundaries in the trap. We\nconclude from this that DMFT is a good approximation for the antiferromagnetic\nFermi-Hubbard model for experimentally relevant system sizes.",
        "positive": "A simple model for interactions and corrections to the Gross-Pitaevskii\n  Equation: One of the assumptions leading to the Gross-Pitaevskii Equation (GPE) is that\nthe interaction between atom pairs can be written effectively as a \\delta\n-function so that the interaction range of the particles is assumed to vanish.\nA simple model that takes into account the extension of the inter-particle\npotential is introduced. The correction to the GPE predictions for the energy\nof a condensate confined by a harmonic trap in the Thomas-Fermi (TF) regime is\nestimated. Although it is found to be small, we believe that in some situations\nit can be measured using its dependance on the frequency of the confining trap.\nDue to the simplicity of the model, it may have a wide range of applications."
    },
    {
        "anchor": "Spin-flip induced superfluidity in a ring of spinful hard-core bosons: The t - J Hamiltonian of the spinful hard-core bosonic ring in the Nagaoka\nlimit is solved. The energy spectrum becomes quantized due to presence of spin,\nwhere each energy level corresponds to a cyclic permutation state of the spin\nchains. The ground state is true ferromagnetic when the ring contains N = 2, 3\nspinful hard-core bosons; for all other N it is a mixture of the ferromagnetic\nand non-ferromagnetic states. This behaviour is different from the fermionic\nring, where ground state is true ferromagnetic only for N = 3. It is shown that\nthe intrinsic spin generated gauge fields are analogous to the synthetic gauge\nfields generated by rotation of either the condensate or the confining\npotential. It is argued that the low lying excited levels of the spin flipped\nstates intrinsically support the superfluidity. Possible ways to experimentally\nverify these results are also discussed.",
        "positive": "Metal-insulator transition and magnetism of SU(3) fermions in the square\n  lattice: We study the SU(3) symmetric Fermi-Hubbard model (FHM) in the square lattice\nat $1/3$-filling using numerically exact determinant quantum Monte Carlo (DQMC)\nand numerical linked-cluster expansion (NLCE) techniques. We present the\ndifferent regimes of the model in the $T-U$ plane, which are characterized by\nlocal and short-range correlations, and capture signatures of the\nmetal-insulator transition and magnetic crossovers. These signatures are\ndetected as the temperature scales characterizing the rise of the\ncompressibility, and an interaction-dependent change in the sign of the\ndiagonal spin-spin correlation function. The analysis of the compressibility\nestimates the location of the metal-insulator quantum critical point at $U_c/t\n\\sim 6$, and provides a temperature scale for observing Mott physics at\nfinite-$T$. Furthermore, from the analysis of the spin-spin correlation\nfunction we observe that for $U/t \\gtrsim6$ and $T \\sim J = 4t^2/U$ there is a\ndevelopment of a short-range two sublattice (2-SL) antiferromagnetic structure,\nas well as an emerging three sublattice (3-SL) antiferromagnetic structure as\nthe temperature is lowered below $T/J \\lesssim 0.57$. This crossover from 2-SL\nto 3-SL magnetic ordering agrees with Heisenberg limit predictions, and has\nobservable effects on the density of on-site pairs. Finally, we describe how\nthe features of the regimes in the $T$-$U$ plane can be explored with\nalkaline-earth-like atoms in optical lattices with currently-achieved\nexperimental techniques and temperatures. The results discussed in this\nmanuscript provide a starting point for the exploration of the SU(3) FHM upon\ndoping."
    },
    {
        "anchor": "Dual trapped-ion quantum simulators: an alternative route towards exotic\n  quantum magnets: We present a route towards the quantum simulation of exotic quantum magnetism\nin ion traps by exploiting dual relations between different spin models. Our\nstrategy allows one to start from Hamiltonians that can be realized with\ncurrent technology, while properties of an exotic dual model are inferred from\nmeasurements of non-local, string-order-like, operators. The latter can be\nachieved from fluorescence, or from certain spectroscopic measurements, both of\nwhich can be combined with finite-size scaling by controlling the number of\nions in the dual quantum simulator. We apply this concept to propose quantum\nsimulators of frustrated quantum magnets, and Ising models with multi-spin\ninteractions. We test the validity of the idea by showing numerically that the\npredictions of an ideal dual quantum simulator are not qualitatively modified\nby relevant perturbations that occur naturally in the trapped-ion scenario.",
        "positive": "Quantum droplets in one-dimensional Bose mixtures: a quantum Monte-Carlo\n  study: We use exact Quantum Monte Carlo techniques to study the properties of\nquantum droplets in two-component bosonic mixtures with contact interactions in\none spatial dimension. We systematically study the surface tension, the density\nprofile and the breathing mode as a function of the number of particles in the\ndroplet and of the ratio of coupling strengths between intra-species repulsion\nand inter-species attraction. We find that deviations from the predictions of\nthe generalized Gross-Pitaevskii equation are small in most cases of interest."
    },
    {
        "anchor": "Simulating cosmological supercooling with a cold atom system: We perform an analysis of the supercooled state in an analogue to an early\nuniverse phase transition based on a one dimensional, two-component Bose gas.\nWe demonstrate that the thermal fluctuations in the relative phase between the\ncomponents are characteristic of a relativistic thermal system. Furthermore, we\ndemonstrate the equivalence of two different approaches to the decay of the\nmetastable state: specifically a non-perturbative thermal instanton calculation\nand a stochastic Gross--Pitaevskii simulation.",
        "positive": "Characterizing the phase diagram of finite-size dipolar Bose-Hubbard\n  systems: We use state-of-the-art density matrix renormalization group calculations in\nthe canonical ensemble to determine the phase diagram of the dipolar\nBose-Hubbard model on a finite cylinder. We consider several observables that\nare accessible in typical optical lattice setups and assess how well these\nquantities perform as order parameters. We find that, especially for small\nsystems, the occupation imbalance is less susceptible to boundary effects than\nthe structure factor in uncovering the presence of a periodic density\nmodulation. By analysing the non-local correlations, we find that the\nappearance of supersolid order is very sensitive to boundary effects, which may\nrender it difficult to observe in quantum gas lattice experiments with a few\ntens of particles. Finally, we show how density measurements readily obtainable\non a quantum gas microscope allow distinguishing between superfluid and solid\nphases using unsupervised machine-learning techniques."
    },
    {
        "anchor": "Non-equilibrium dynamics of interacting Fermi systems in quench\n  experiments: We describe the dynamics of two component non-interacting ultracold Fermions\nwhich are initially in thermal equilibrium and undergo a rapid quench to either\nthe repulsive or attractive side of a Feshbach resonance. The short time\ndynamics is dominated by the exponentially growing collective modes. We study\nthe Stoner instability and formation of ferromagnetic textures on the repulsive\nside, and the pairing instability towards BCS or FFLO-like states (determined\nby the population imbalance) on the attractive side. In each case, we evaluate\nthe growth rate of unstable modes and predict the typical lengthscale of\ntextures to be formed.",
        "positive": "The dipolar Bose-Hubbard model: We study a simple model of interacting bosons on a d-dimensional cubic\nlattice whose dynamics conserves both total boson number and total boson dipole\nmoment. This model provides a simple framework in which several remarkable\nconsequences of dipole conservation can be explored. As a function of chemical\npotential and hopping strength, the model can be tuned between gapped Mott\ninsulating phases and various types of gapless condensates. The condensed phase\nrealized at large hopping strengths, which we dub a Bose-Einstein insulator, is\nparticularly interesting: despite having a Bose condensate, it is insulating,\nand despite being an insulator, it is compressible."
    },
    {
        "anchor": "Ultra-Fast Converging Path-Integral Approach for Rotating Ideal\n  Bose-Einstein Condensates: A recently developed efficient recursive approach for analytically\ncalculating the short-time evolution of the one-particle propagator to\nextremely high orders is applied here for numerically studying the\nthermodynamical and dynamical properties of a rotating ideal Bose gas of\n$^{87}$Rb atoms in an anharmonic trap. At first, the one-particle energy\nspectrum of the system is obtained by diagonalizing the discretized short-time\npropagator. Using this, many-boson properties such as the condensation\ntemperature, the ground-state occupancy, density profiles, and time-of-flight\nabsorption pictures are calculated for varying rotation frequencies. The\nobtained results improve previous semiclassical calculations, in particular for\nsmaller particle numbers. Furthermore, we find that typical time scales for a\nfree expansion are increased by an order of magnitude for the delicate regime\nof both critical and overcritical rotation.",
        "positive": "Creation of a Dirac monopole-antimonopole pair in a spin-1 Bose-Einstein\n  condensate: We theoretically demonstrate that a pair of Dirac monopoles with opposite\nsynthetic charges can be created within a single spin-1 Bose-Einstein\ncondensate by steering the spin degrees of freedom by external magnetic fields.\nAlthough the net synthetic magnetic charge of this configuration vanishes, both\nthe monopole and the antimonopole are accompanied by vortex filaments carrying\nopposite angular momenta. Such a Dirac dipole can be realized experimentally by\nimprinting a spin texture with a nonlinear magnetic field generated by a pair\nof coils in a modified Helmholtz configuration. We also investigate the case\nwhere the initial state for the dipole-creation procedure is pierced by a\nquantized vortex line with a winding number k. It is shown that if k = -1, the\nresulting monopole and antimonopole lie along the core of a singly quantized\nvortex whose sign is reversed at the locations of the monopoles. For k = -2,\nthe monopole and antimonopole are connected by a vortex line segment carrying\ntwo quanta of angular momentum, and hence the dipole as a whole is an isolated\nconfiguration. In addition, we simulate the long-time evolution of the dipoles\nin the magnetic field used to create them. For k = 0, each of the semi-infinite\ndoubly quantized vortices splits into two singly quantized vortices, as in the\ncase of a single Dirac monopole. For k = -1 and k = -2, the initial vortices\ndeform into a vortex with a kink and a vortex ring, respectively."
    },
    {
        "anchor": "Backscattering suppression in supersonic 1D polariton condensates: We investigate the effects of disorder on the propagation of one-dimensional\npolariton condensates in semiconductor microcavities. We observe a strong\nsuppression of the backscattering produced by the imperfections of the\nstructure when increasing the condensate density. This suppression occurs in\nthe supersonic regime and is simultaneous to the onset of parametric\ninstabilities which enable the \"hopping\" of the condensate through the\ndisorder. Our results evidence a new mechanism for the frictionless flow of\npolaritons at high speeds.",
        "positive": "Spatially distributed multipartite entanglement enables\n  Einstein-Podolsky-Rosen steering of atomic clouds: A key resource for distributed quantum-enhanced protocols is entanglement\nbetween spatially separated modes. Yet, the robust generation and detection of\nnonlocal entanglement between spatially separated regions of an ultracold\natomic system remains a challenge. Here, we use spin mixing in a tightly\nconfined Bose-Einstein condensate to generate an entangled state of\nindistinguishable particles in a single spatial mode. We show experimentally\nthat this local entanglement can be spatially distributed by self-similar\nexpansion of the atomic cloud. Spatially resolved spin read-out is used to\nreveal a particularly strong form of quantum correlations known as\nEinstein-Podolsky-Rosen steering between distinct parts of the expanded cloud.\nBased on the strength of Einstein-Podolsky-Rosen steering we construct a\nwitness, which testifies up to genuine five-partite entanglement."
    },
    {
        "anchor": "Optical Kagome lattice for ultra-cold atoms with nearest neighbor\n  interactions: We propose a scheme to implement an optical Kagome lattice for ultra-cold\natoms with controllable s-wave interactions between nearest neighbor sites and\na gauge potential. The atoms occupy three different internal atomic levels with\nelectromagnetically-induced coupling between the levels. We show that by\nappropriately shifting the triangular lattice potentials, experienced by atoms\nin different levels, the Kagome lattice can be realized using only two standing\nwaves, generating a highly frustrated quantum system for the atoms.",
        "positive": "The Raman dressed spin-1 spin-orbit coupled quantum gas: The recently realized spin-orbit coupled quantum gases (Y.-J Lin {\\it et\nal}., Nature 471, 83-86 (2011); P. Wang {\\it et al}., PRL 109, 095301 (2012);\nL. W. Cheuk {\\it et al}., PRL 109, 095302 (2012)) mark a breakthrough in the\ncold atom community. In these experiments, two hyperfine states are selected\nfrom a hyperfine manifold to mimic a pseudospin-1/2 spin-orbit coupled system\nby the method of Raman dressing, which is applicable to both bosonic and\nfermionic gases. In this work, we show that the method used in these\nexperiments can be generalized to create any large pseudospin spin-orbit\ncoupled gas if more hyperfine states are coupled equally by the Raman lasers.\nAs an example, we study in detail a quantum gas with three hyperfine states\ncoupled by the Raman lasers, and show when the state-dependent energy shifts of\nthe three states are comparable, triple-degenerate minima will appear at the\nbottom of the band dispersions, thus realizing a spin-1 spin-orbit coupled\nquantum gas. A novel feature of this three minima regime is that there can be\ntwo different kinds of stripe phases with different wavelengths, which has an\ninteresting connection to the ferromagnetic and polar phases of spin-1 spinor\nBECs without spin-orbit coupling."
    },
    {
        "anchor": "Robustness of fragmented condensate many-body states for continuous\n  distribution amplitudes in Fock space: We consider a two-mode model describing scalar bosons with two-body\ninteractions in a single trap, taking into account coherent pair-exchange\nbetween the modes. It is demonstrated that the resulting fragmented many-body\nstates with continuous (nonsingular) Fock-space distribution amplitudes are\nrobust against perturbations due to occupation number and relative phase\nfluctuations, Josephson-type tunneling between the modes, and weakly broken\nparity of orbitals, as well as against perturbations due to interaction with a\nthird mode.",
        "positive": "Inelastic scattering of atoms in a double well: We study a mixture of two light spin-1/2 fermionic atoms and two heavy atoms\n%in a Mott state in a double well potential. Inelastic scattering processes\nbetween both atomic species excite the heavy atoms and renormalize the\ntunneling rate and the interaction of the light atoms (polaron effect). The\neffective interaction of the light atoms changes its sign and becomes\nattractive for strong inelastic scattering. This is accompanied by a crossing\nof the energy levels from singly occupied sites at weak inelastic scattering to\na doubly occupied and an empty site for stronger inelastic scattering. We are\nable to identify the polaron effect and the level crossing in the quantum\ndynamics."
    },
    {
        "anchor": "Bose-Fermi solid and its quantum melting in an one-dimensional optical\n  lattice: We investigate the quantum phase diagram of Bose-Fermi mixtures of ultracold\ndipolar particles trapped in one-dimensional optical lattices in the\nthermodynamic limit. With the presence of nearest-neighbor (N.N.) interactions,\na long-ranged ordered crystalline phase (Bose-Fermi solid) is found stabilized\nbetween a Mott insulator of bosons and a band-insulator of fermions in the\nlimit of weak inter-site tunneling ($J$). When $J$ is increased, such a\nBose-Fermi solid can be quantum melted into a Bose-Fermi liquid through either\na two-stage or a three-stage transition, depending on whether the crystalline\norder is dominated by the N.N. interaction between fermions or bosons. These\nproperties can be understood as quantum competition between a pseudo-spin\nfrustration and a pseudo-spin-charge separation, qualitatively different from\nthe classical picture of solid-liquid phase transition.",
        "positive": "Diagrammatic Monte Carlo approach to angular momentum in quantum\n  many-particle systems: We introduce a Diagrammatic Monte Carlo (DiagMC) approach to angular momentum\nproperties of quantum many-particle systems possessing a macroscopic number of\ndegrees of freedom. The treatment is based on a diagrammatic expansion that\nmerges the usual Feynman diagrams with the angular momentum diagrams known from\natomic and nuclear structure theory, thereby incorporating the non-Abelian\nalgebra inherent to quantum rotations. Our approach is applicable at arbitrary\ncoupling, is free of systematic errors and of finite size effects, and\nnaturally provides access to the impurity Green function. We exemplify the\ntechnique by obtaining an all-coupling solution of the angulon model, however,\nthe method is quite general and can be applied to a broad variety of systems in\nwhich particles exchange quantum angular momentum with their many-body\nenvironment."
    },
    {
        "anchor": "Dynamical Quasicondensation of Hard-Core Bosons at Finite Momenta: Long-range order in quantum many-body systems is usually associated with\nequilibrium situations. Here, we experimentally investigate the\nquasicondensation of strongly-interacting bosons at finite momenta in a\nfar-from-equilibrium case. We prepare an inhomogeneous initial state consisting\nof one-dimensional Mott insulators in the center of otherwise empty\none-dimensional chains in an optical lattice with a lattice constant $d$. After\nsuddenly quenching the trapping potential to zero, we observe the onset of\ncoherence in spontaneously forming quasicondensates in the lattice. Remarkably,\nthe emerging phase order differs from the ground-state order and is\ncharacterized by peaks at finite momenta $\\pm (\\pi/2) (\\hbar / d)$ in the\nmomentum distribution function.",
        "positive": "Polarization Suppression and Nonmonotonic Local Two-Body Correlations in\n  the Two-Component Bose Gas in One Dimension: We study the interplay of quantum statistics, strong interactions and finite\ntemperatures in the two-component (spinor) Bose gas with repulsive\ndelta-function interactions in one dimension. Using the Thermodynamic Bethe\nAnsatz, we obtain the equation of state, population densities and local density\ncorrelation numerically as a function of all physical parameters (interaction,\ntemperature and chemical potentials), quantifying the full crossover between\nlow-temperature ferromagnetic and high-temperature unpolarized regimes. In\ncontrast to the single-component, Lieb-Liniger gas, nonmonotonic behaviour of\nthe local density correlation as a function of temperature is observed."
    },
    {
        "anchor": "Impact of density inhomogeneity on the critical velocity for vortex\n  shedding in a harmonically trapped Bose-Einstein condensate: We report on a numerical study of the critical velocity for creation of\nquantized vortices by a moving Gaussian obstacle in a trapped Bose-Einstein\ncondensate, modeled by the Gross-Pitaevskii equation. We pay attention to\nimpact of density inhomogeneity associated with the global inverted-parabolic\nprofile by a trapping potential as well as the local density suppression around\nthe Gaussian obstacle. When the width of the Gaussian potential is large, the\nwake dynamics is significantly influenced by the nonuniformity around the\nobstacle potential. The critical velocity, estimated through the time interval\nbetween the first and second vortex emission, can be explained by the local\nsound velocity by taking into account the above two contributions. We also find\nthat the ratio of the critical velocity to the sound velocity at the center of\nthe system is insensitive to the nonlinear coefficient of the Gross-Pitaevskii\nequation, which supports the universal discussion even in a inhomogeneous\ntrapped condensate under the local density approximation.",
        "positive": "Two-state Bose-Hubbard model in the hard-core boson limit: Phase transition into the phase with Bose-Einstein (BE) condensate in the\ntwo-band Bose-Hubbard model with the particle hopping in the excited band only\nis investigated. Instability connected with such a transition (which appears at\nexcitation energies $\\delta<\\lvert t_0' \\rvert$, where $\\lvert t_0' \\rvert$ is\nthe particle hopping parameter) is considered. The re-entrant behaviour of\nspinodales is revealed in the hard-core boson limit in the region of positive\nvalues of chemical potential. It is found that the order of the phase\ntransition undergoes a change in this case and becomes the first one; the\nre-entrant transition into the normal phase does not take place in reality.\nFirst order phase transitions also exist at negative values of $\\delta$ (under\nthe condition $\\delta>\\delta_{\\mathrm{crit}}\\approx-0.12\\lvert t_0' \\rvert$).\nAt $\\mu<0$ the phase transition mostly remains to be of the second order. The\nbehaviour of the BE-condensate order parameter is analyzed, the $(\\Theta,\\mu)$\nand $(\\lvert t_0' \\rvert,\\mu)$ phase diagrams are built and localizations of\ntricritical points are established. The conditions are found at which the\nseparation on the normal phase and the phase with the BE condensate takes\nplace."
    },
    {
        "anchor": "Quasi-1D atomic gases across wide and narrow\n  confinement-induced-resonances: We study quasi-one-dimensional atomic gases across wide and narrow\nconfinement-induced-resonances (CIR). We show from Virial expansion that by\ntuning the magnetic field, the repulsive scattering branch initially prepared\nat low fields can continuously go across CIR without decay; instead, the decay\noccurs when approaching the non-interacting limit. The interaction properties\nessentially rely on the resonance width of CIR. Universal thermodynamics holds\nfor scattering branch right at wide CIR, but is smeared out in narrow CIR due\nto strong energy-dependence of coupling strength. In wide and narrow CIR, the\ninteraction energy of scattering branch shows different types of strong\nasymmetry when approaching the decay from opposite sides of magnetic field.\nFinally we discuss the stability of repulsive branch for a repulsively\ninteracting Fermi gas in different trapped geometries at low temperatures.",
        "positive": "Interrelated Thermalization and Quantum Criticality in a Lattice Gauge\n  Simulator: Gauge theory and thermalization are both foundations of physics and nowadays\nare both topics of essential importance for modern quantum science and\ntechnology. Simulating lattice gauge theories (LGTs) realized recently with\nultracold atoms provides a unique opportunity for carrying out a correlated\nstudy of gauge theory and thermalization in the same setting. Theoretical\nstudies have shown that an Ising quantum phase transition exists in this\nimplemented LGT, and quantum thermalization can also signal this phase\ntransition. Nevertheless, it remains an experimental challenge to accurately\ndetermine the critical point and controllably explore the thermalization\ndynamics in the quantum critical regime due to the lack of techniques for\nlocally manipulating and detecting matter and gauge fields. Here, we report an\nexperimental investigation of the quantum criticality in the LGT from both\nequilibrium and non-equilibrium thermalization perspectives by equipping the\nsingle-site addressing and atom-number-resolved detection into our LGT\nsimulator. We accurately determine the quantum critical point agreed with the\npredicted value. We prepare a $|Z_{2}\\rangle$ state deterministically and study\nits thermalization dynamics across the critical point, leading to the\nobservation that this $|Z_{2}\\rangle$ state thermalizes only in the critical\nregime. This result manifests the interplay between quantum many-body scars,\nquantum criticality, and symmetry breaking."
    },
    {
        "anchor": "Improved characterization of Feshbach resonances and interaction\n  potentials between $^{23}$Na and $^{87}$Rb atoms: The ultracold mixture of \\Na and \\Rb atoms has become an important system for\ninvestigating physics in Bose-Bose atomic mixtures and for forming ultracold\nground-state polar molecules. In this work, we provide an improved\ncharacterization of the most commonly used Feshbach resonance near 347.64 G\nbetween \\Na and \\Rb in their absolute ground states. We form Feshbach molecules\nusing this resonance and measure their binding energies by dissociating them\nvia magnetic field modulation. We use the binding energies to refine the\nsinglet and triplet potential energy curves, using coupled-channel bound-state\ncalculations. We then use coupled-channel scattering calculations on the\nresulting potentials to produce a high-precision mapping between magnetic field\nand scattering length. We also observe 10 additional $s$-wave Feshbach\nresonances for \\Na and \\Rb in different combinations of Zeeman sublevels of the\n$F = 1$ hyperfine states. Some of the resonances show 2-body inelastic decay\ndue to spin exchange. We compare the resonance properties with coupled-channel\nscattering calculations that full take account of inelastic properties.",
        "positive": "Isospin Correlations in two-partite Hexagonal Optical Lattices: Two-component mixtures in optical lattices reveal a rich variety of different\nphases. We employ an exact diagonalization method to obtain the relevant\ncorrelation functions in hexagonal optical lattices to characterize those\nphases. We relate the occupation difference of the two species to the magnetic\npolarization. `Iso'-magnetic correlations disclose the nature of the system,\nwhich can be of easy-axis type, bearing phase segregation, or of easy-plane\ntype, corresponding to super-counter-fluidity. In the latter case, the\ncorrelations reveal easy-plane segregation, involving a highly-entangled state.\nWe identify striking correlated supersolid phases appearing within the\nsuperfluid limit."
    },
    {
        "anchor": "Causality and quantum criticality in long-range lattice models: Long-range quantum lattice systems often exhibit drastically different\nbehavior than their short-range counterparts. In particular, because they do\nnot satisfy the conditions for the Lieb-Robinson theorem, they need not have an\nemergent relativistic structure in the form of a light cone. Adopting a\nfield-theoretic approach, we study the one-dimensional transverse-field Ising\nmodel with long-range interactions, and a fermionic model with long-range\nhopping and pairing terms, explore their critical and near-critical behavior,\nand characterize their response to local perturbations. We deduce the dynamic\ncritical exponent, up to the two-loop order within the renormalization group\ntheory, which we then use to characterize the emergent causal behavior. We show\nthat beyond a critical value of the power-law exponent of the long-range\ncouplings, the dynamics effectively becomes relativistic. Various other\ncritical exponents describing correlations in the ground state, as well as\ndeviations from a linear causal cone, are deduced for a wide range of the\npower-law exponent.",
        "positive": "Band gap structures for matter waves: Spatial gaps correspond to the projection in position space of the gaps of a\nperiodic structure whose envelope varies spatially. They can be easily\ngenerated in cold atomic physics using finite-size optical lattice, and provide\na new kind of tunnel barriers which can be used as a versatile tool for quantum\ndevices. We present in detail different theoretical methods to quantitatively\ndescribe these systems, and show how they can be used to realize in one\ndimension matter wave Fabry-Perot cavities. We also provide experimental and\nnumerical results that demonstrate the interest of spatial gaps structures for\nphase space engineering. We then generalize the concept of spatial gaps in two\ndimensions and show that this enables to design multiply connected cavities\nwhich generate a quantum dot structure for atoms or allow to construct curved\nwave guides for matter waves. At last, we demonstrate that modulating in time\nthe amplitude of the periodic structure offers a wide variety of possible atom\nmanipulations including the control of the scattering of an incoming wave\npacket, the loading of cavities delimited by spatial gaps, their coupling by\nmultiphonon processes or the realization of a tunable source of atoms. This\nlarge range of possibilities offered by space and time engineering of optical\nlattices demonstrates the flexibility of such band gap structures for matter\nwave control, quantum simulators and atomtronics."
    },
    {
        "anchor": "Energy fluctuation of ideal Fermi gas trapped under generic power law\n  potential $U=\\sum_{i=1} ^d c_i |\\frac{x_i}{a_i}|^{n_i}$ in d dimension: Energy fluctuation of ideal Fermi gas trapped under generic power law\npotential $U=\\sum_{i=1} ^d c_i |\\frac{x_i}{a_i}|^{n_i}$ have been calculated in\narbitrary dimension. Energy fluctuation is scrutinized further in the\ndegenerate limit $\\mu>> K_BT$ with the help of Sommerfeld expansion. The\ndependence of energy fluctuation on dimensionality and power law potential is\nstudied in detail. Most importantly our general result can exactly reproduce\nthe recently published result regarding free and harmonically trapped ideal\nFermi gas in d=3 (S Biswas, J Mitra, S Bhattacharyya, J. Stat. Mech. P03013,\n2015.)",
        "positive": "Order indices of density matrices for finite systems: The definition of order indices for density matrices is extended to finite\nsystems. This makes it possible to characterize the level of ordering in such\nfinite systems as macromolecules, nanoclusters, quantum dots, or trapped atoms.\nThe general theory is exemplified by explicit calculations of the order index\nfor the first-order density matrix of bosonic atoms confined in a finite box at\nzero temperature."
    },
    {
        "anchor": "Energy spectra of two interacting fermions with spin-orbit coupling in a\n  harmonic trap: We explore the two-body spectra of spin-$1/2$ fermions in isotropic harmonic\ntraps with external spin-orbit potentials and short range two-body\ninteractions. Using a truncated basis of total angular momentum eigenstates,\nnon-perturbative results are presented for experimentally realistic forms of\nthe spin-orbit coupling: a pure Rashba coupling, Rashba and Dresselhaus\ncouplings in equal parts, and a Weyl-type coupling. The technique is easily\nadapted to bosonic systems and other forms of spin-orbit coupling.",
        "positive": "Competing instabilities in quench experiments with ultracold Fermi gases\n  near a Feshbach resonance: Tunability of effective two body interactions near Feshbach resonances is a\npowerful experimental tool in systems of ultracold atoms. It has been used to\nexplore a variety of intriguing phenomena in recent experiments. However not\nall of the many-body properties of such systems can be understood in terms of\neffective models with contact interaction given by the scattering length of the\ntwo particles in vacuum. For example, when a two component Fermi mixture is\nquenched to the BEC side of the Feshbach resonance, a positive scattering\nlength suggests that interactions are repulsive and thus collective dynamics\nshould be dominated by the Stoner instability toward a spin polarized\nferromagnetic state. On the other hand, existence of low energy two particle\nbound states suggests a competing instability driven by molecule formation.\nCompe- tition between spontaneous magnetization and pair formation is\ndetermined by the the interplay of two-particle and many-body phenomena. In\nthese lecture notes we summarize our recent theoretical results, which analyzed\nthis competition from the point of view of unstable collective modes. We also\ncomment on the relevance of this theoretical analysis to recent experiments\nreported in Ref. (Jo, Lee, Choi, Christensen, Kim, Thywissen, Pritchard and\nKetterle, 2009)."
    },
    {
        "anchor": "Spontaneous increase of magnetic flux and chiral-current reversal in\n  bosonic ladders: Swimming against the tide: The interplay between spontaneous symmetry breaking in many-body systems, the\nwavelike nature of quantum particles and lattice effects produces an\nextraordinary behavior of the chiral current of bosonic particles in the\npresence of a uniform magnetic flux defined on a two-leg ladder. While\nnon-interacting as well as strongly interacting particles, stirred by the\nmagnetic field, circulate along the system's boundary in the counterclockwise\ndirection in the ground state, interactions stabilize vortex lattices. These\nstates break translational symmetry, which can lead to a reversal of the\ncirculation direction. Our predictions could readily be accessed in quantum gas\nexperiments with existing setups or in arrays of Josephson junctions.",
        "positive": "Versatile electric fields for the manipulation of ultracold NaK\n  molecules: In this paper, we present an electrode geometry for the manipulation of\nultracold rovibrational ground state NaK molecules. The electrode system allows\nto induce a dipole moment in trapped diatomic NaK molecules with a magnitude up\nto $68 \\%$ of their internal dipole moment along any direction in a given\ntwo-dimensional plane. The strength, the sign and the direction of the induced\ndipole moment is therefore fully tunable. Furthermore, the possibility to\ncreate strong electric field gradients provides the opportunity to address\nmolecules in single layers of an optical lattice. The maximal relative\nvariation of the electric field over the trapping volume is below $10^{-6}$. At\nthe desired electric field value of 10 kV/cm this corresponds to a deviation of\n0.01 V/cm. The electrode structure is made of transparent indium tin oxide and\ncombines large optical access for sophisticated optical dipole traps and\noptical lattice configurations with the possibility to create versatile\nelectric field configurations."
    },
    {
        "anchor": "Robust finite-temperature disordered Mott insulating phases in\n  inhomogeneous Fermi-Fermi mixtures with density and mass imbalance: Ultracold mixtures of different atomic species have great promise for\nrealizing novel many-body phenomena. In a binary mixture of femions with a\nlarge mass difference and repulsive interspecies interactions, a disordered\nMott insulator phase can occur. This phase displays an incompressible total\ndensity, although the relative density remain compressible. We use\nstrong-coupling and Monte Carlo calculations to show that this phase exists for\na broad parameter region for ultracold gases confined in a harmonic trap on a\nthree-dimensional optical lattice, for experimentally accessible values of the\ntrap parameters.",
        "positive": "GPU-accelerated solutions of the nonlinear Schr\u00f6dinger equation for\n  simulating 2D spinor BECs: As a first approximation beyond linearity, the nonlinear Schr\\\"odinger\nequation (NLSE) reliably describes a broad class of physical systems. Though\nnumerical solutions of this model are well-established, these methods can be\ncomputationally complex. In this paper, we showcase a code development\napproach, demonstrating how computational time can be significantly reduced\nwith readily available graphics processing unit (GPU) hardware and a\nstraightforward code migration using open-source libraries. This process shows\nhow CPU computations with power-law scaling in computation time with grid size\ncan be made linear using GPUs. As a specific case study, we investigate the\nGross-Pitaevskii equation, a specific version of the nonlinear Schr\\\"odinger\nmodel, as it describes in two dimensions a trapped, interacting, two-component\nBose-Einstein condensate (BEC) subject to a spatially dependent interspin\ncoupling, resulting in an analog to a spin-Hall system. This computational\napproach lets us probe high-resolution spatial features - revealing an\ninteraction-dependent phase transition - all in a reasonable amount of time.\nOur computational approach is particularly relevant for research groups looking\nto easily accelerate straightforward numerical simulation of physical\nphenomena."
    },
    {
        "anchor": "Dynamics of correlation spreading in low-dimensional transverse-field\n  Ising models: We investigate the dynamical spreading of spatial correlations after a\nquantum quench starting from a magnetically disordered state in the\ntransverse-field Ising model at one (1D) and two spatial dimensions (2D). We\nanalyze specifically the longitudinal and transverse spin-spin correlation\nfunctions at equal time with use of several methods. From the comparison of the\nresults in 1D obtained by the linear spin-wave approximation (LSWA) and those\nobtained by the rigorous analytical approach, we show that the LSWA can\nasymptotically reproduce the exact group velocity in the limit of strong\ntransverse fields while it fails to capture the detailed time dependence of the\ncorrelation functions. By applying the LSWA to the 2D case, in which the\nrigorous analytical approach is unavailable, we estimate the propagation\nvelocity to be $Ja/(2\\hbar)$ at the strong-field limit, where $J$ is the Ising\ninteraction and $a$ is the lattice spacing. We also utilize the tensor-network\nmethod based on the projected-entangled pair states for 2D and quantitatively\ncompute the time evolution of the correlation functions for a relatively short\ntime. Our findings provide useful benchmarks for quantum simulation experiments\nof correlation spreading and theoretical refinement of the Lieb-Robinson bound\nin the future.",
        "positive": "Spin and mass superfluidity in ferromagnetic spin-1 Bose-Einstein\n  condensate: The paper investigates the coexistence and interplay of spin and mass\nsuperfluidity in a ferromagnetic spin-1 Bose-Einstein condensate. Superfluidity\nis possible only in the presence of uniaxial anisotropy (linear and quadratic\nZeeman effect). This follows from the topology of the order-parameter space\n(vacuum manifold). According to the Landau criterion, the critical phase\ngradients, both for mass and spin supercurrents, vanish at the phase transition\nfrom the easy-plane to the easy-axis anisotropy. However, mass superfluidity is\nstill possible at the phase transition. This is because the Landau criterion\nsignals instability only with respect to nonsingular vortices with special\nratio between circulations of mass and spin currents. Phase slips produced by\nthese vortices are not sufficient for complete decay of supercurrents. Full\ndecay of supercurrents requires phase slips with vortices of another\ntopological class and larger energy. These phase slips are suppressed by\nenergetic barriers up to the upper critical velocity (gradient) exceeding the\nLandau critical velocity. The upper critical velocity does not vanish nor has\nany anomaly in the critical point at the phase transition from the easy-plane\nto the easy-axis anisotropy."
    },
    {
        "anchor": "Nondestructive Probing of Means, Variances, and Correlations of\n  Ultracold-Atomic-System Densities via Qubit Impurities: We show how impurity atoms can measure moments of ultracold atomic gas\ndensities, using the example of bosons in a one-dimensional lattice. This\nbuilds on a body of work regarding the probing of systems by measuring the\ndephasing of an immersed qubit. We show this dephasing is captured by a\nfunction resembling characteristic functions of probability theory, of which\nthe derivatives at short times reveal moments of the system operator to which\nthe qubit couples. For a qubit formed by an impurity atom, in a system of\nultracold atoms, this operator can be the density of the system at the location\nof the impurity, and thus, means, variances, and correlations of the atomic\ndensities are accessible.",
        "positive": "Angular self-localization of impurities rotating in a bosonic bath: The existence of a self-localization transition in the polaron problem has\nbeen under an active debate ever since Landau suggested it 83 years ago. Here\nwe reveal the self-localization transition for the rotational analogue of the\npolaron -- the angulon quasiparticle. We show that, unlike for the polarons,\nself-localization of angulons occurs at finite impurity-bath coupling already\nat the mean-field level. The transition is accompanied by the\nspherical-symmetry breaking of the angulon ground state and a discontinuity in\nthe first derivative of the ground-state energy. Moreover, the type of the\nsymmetry breaking is dictated by the symmetry of the microscopic impurity-bath\ninteraction, which leads to a number of distinct self-localized states. The\npredicted effects can potentially be addressed in experiments on cold molecules\ntrapped in superfluid helium droplets and ultracold quantum gases, as well as\non electronic excitations in solids and Bose-Einstein condensates."
    },
    {
        "anchor": "Topologically protected pure helicity cascade in non-Abelian quantum\n  turbulence: By numerically studying non-Abelian quantum turbulence, we find that the\nhelicity cascade and the inverse energy cascade are topologically protected\nagainst reconnection of vortices and lead to the energy spectrum $E(k) \\propto\nk^{-7/3}$ for a large-scale energy injection and $E(k) \\propto k^{-5/3}$ for a\nsmall-scale energy injection with a large-scale web of non-Abelian vortices.\nOur prediction can be tested in the cyclic phase of a spin-2 spinor\nBose-Einstein condensate.",
        "positive": "Simulation of Dynamical Quantum Phase Transition of the 1D Transverse\n  Ising Model with a Double-chain Bose-Hubbard model: We propose a spinless Bose-Hubbard model in an one-dimensional (1D)\ndouble-chain tilted lattice at unit filling per cell. A subspace of this model\ncan be faithfully mapped to the 1D transverse Ising model through superexchange\ninteraction with second-order perturbation theory. At a valid parameter region,\nnumerical results show good agreement of these two models both on energy\nspectrums and correlation functions. And we show that the dynamical quantum\nphase transition of the effective 1D transverse Ising model can be simulated.\nWith carefully designed procedures for producing the dynamical quantum phase\ntransition of the 1D transverse Ising model from a Mott insulator, the rate\nfunction of the recurrence probability to the ground-state manifold shows the\nsame nonanalyticality at periodic time points as theory predicts. Our results\nmay give some inspirations on simulating 1D transverse Ising model with\nsuperexchange interaction and exploring its dynamical quantum phase transition\nin experiment."
    },
    {
        "anchor": "Quantum Defect Theory for Orbital Feshbach Resonance: In the ultracold gases of alkali-earth (like) atoms, a new type of Feshbach\nresonance, i.e., the orbital Feshbach resonance (OFR), has been proposed and\nexperimentally observed in ultracold $^{173}$Yb atoms. When the OFR of the\n$^{173}$Yb atoms occurs, the energy gap between the open and closed channels is\nsmaller by two orders of magnitudes than the van der Waals energy. As a result,\nquantitative accurate results for the low-energy two-body problems can be\nobtained via multi-channel quantum defect theory (MQDT), which is based on the\nexact solution of the Schr$\\ddot{{\\rm o}}$dinger equation with the van der\nWaals potential. In this paper we use the MQDT to calculate the two-atom\nscattering length, effective range, and the binding energy of two-body bound\nstates for the systems with OFR. With these results we further study the\nclock-transition spectrum for the two-body bound states, which can be used to\nexperimentally measure the binding energy. Our results are helpful for the\nquantitative theoretical and experimental researches for the ultracold gases of\nalkali-earth (like) atoms with OFR.",
        "positive": "Equilibration and Approximate Conservation Laws: Dipole Oscillations and\n  Perfect Drag of Ultracold Atoms in a Harmonic Trap: The presence of (approximate) conservation laws can prohibit the fast\nrelaxation of interacting many-particle quantum systems. We investigate this\nphysics by studying the center-of-mass oscillations of two species of fermionic\nultracold atoms in a harmonic trap. If their trap frequencies are equal, a\ndynamical symmetry (spectrum generating algebra), closely related to Kohn's\ntheorem, prohibits the relaxation of center-of-mass oscillations. A small\ndetuning $\\delta\\omega$ of the trap frequencies for the two species breaks the\ndynamical symmetry and ultimately leads to a damping of dipole oscillations\ndriven by inter-species interactions. Using memory-matrix methods, we calculate\nthe relaxation as a function of frequency difference, particle number,\ntemperature, and strength of inter-species interactions. When interactions\ndominate, there is almost perfect drag between the two species and the\ndynamical symmetry is approximately restored. The drag can either arise from\nHartree potentials or from friction. In the latter case (hydrodynamic limit),\nthe center-of-mass oscillations decay with a tiny rate, $1/\\tau \\propto\n(\\delta\\omega)^2/\\Gamma$, where $\\Gamma$ is a single particle scattering rate."
    },
    {
        "anchor": "Topological superfluid phases of an atomic Fermi gas with in- and\n  out-of-plane Zeeman fields and equal Rashba-Dresselhaus spin-orbit coupling: We analyze the effects of in- and out-of-plane Zeeman fields on the BCS-BEC\nevolution of a Fermi gas with equal Rashba-Dresselhaus (ERD) spin-orbit\ncoupling (SOC). We show that the ground state of the system involves novel\ngapless superfluid phases that can be distinguished with respect to the\ntopology of the momentum-space regions with zero excitation energy. For the\nBCS-like uniform superfluid phases with zero center-of-mass momentum, the zeros\nmay correspond to one or two doubly-degenerate spheres, two or four spheres,\ntwo or four concave spheroids, or one or two doubly-degenerate circles,\ndepending on the combination of Zeeman fields and SOC. Such changes in the\ntopology signal a quantum phase transition between distinct superfluid phases,\nand leave their signatures on some thermodynamic quantities. We also analyze\nthe possibility of Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)-like nonuniform\nsuperfluid phases with finite center-of-mass momentum and obtain an even richer\nphase diagram.",
        "positive": "On the strong influence of boundaries on the bulk microstructure of a\n  uniform interacting Bose gas: It is usually assumed that the boundaries do not affect the bulk\nmicrostructure of an interacting uniform Bose gas.\n  Therefore, the models use the most convenient cyclic boundary conditions. We\nshow that, in reality, the boundaries affect strongly the bulk microstructure,\nby changing the ground-state energy E_0 and the energy of quasiparticles E(k).\nFor the latter, we obtain the formula E^2 =(h^2 k^{2}/2m)^2 + 2^{-f}n\\nu(k)(h^2\nk^2/m) differing from the well-known Bogolyubov formula by the factor 2^{-f},\nwhere f is the number of noncyclic coordinates.\n  The Bogolyubov solution is also possible in the presence of boundaries, but\nit has a larger value of $E_{0}$ and should be unstable. The influence of\nboundaries is related to the topology."
    },
    {
        "anchor": "Discrete solitons of spin-orbit coupled Bose-Einstein condensates in\n  optical lattices: We study localized nonlinear excitations of a dilute Bose-Einstein condensate\n(BEC) with spin-orbit coupling in a deep optical lattice (OL). We use Wannier\nfunctions to derive a tight-binding model that includes the spin-orbit coupling\n(SOC) at the discrete level in the form of a generalized discrete nonlinear\nSch\\\"odinger equation. Spectral properties are investigated and the existence\nand stability of discrete solitons and breathers with different symmetry\nproperties with respect to the OL is demonstrated. We show that the symmetry of\nthe modes can be changed from on-site to inter-site and to asymmetric modes\nsimply by changing the interspecies interaction. Asymmetric modes appear to be\nnovel modes intrinsic of the SOC.",
        "positive": "Fermi polarons at finite temperature: Spectral function and\n  rf-spectroscopy: We present a systematic study of a mobile impurity immersed in a\nthree-dimensional Fermi sea of fermions at finite temperature, by using the\nstandard non-self-consistent many-body $T$-matrix theory that is equivalent to\na finite-temperature variational approach with the inclusion of\none-particle-hole excitation. The impurity spectral function is determined in\nthe real-frequency domain, avoiding any potential errors due to the numerical\nanalytic continuation in previous $T$-matrix calculations and the small\nspectral broadening parameter used in variational calculations. In the\nweak-coupling limit, we find that the quasiparticle decay rate of both\nattractive and repulsive polarons does not increase significantly with\nincreasing temperature, and therefore Fermi polarons may remain well-defined\nfar above Fermi degeneracy. In contrast, near the unitary limit with strong\ncoupling, the decay rate of Fermi polarons rapidly increase and the\nquasiparticle picture breaks down close to the Fermi temperature. We analyze in\ndetail the recent ejection and injection radio-frequency (rf) spectroscopy\nmeasurements, performed at Massachusetts Institute of Technology (MIT) and at\nEuropean Laboratory for Non-Linear Spectroscopy (LENS), respectively. We show\nthat the momentum average of the spectral function, which is necessary to\naccount for the observed rf-spectroscopy, has a sizable contribution to the\nwidth of the quasiparticle peak in spectroscopy. As a result, the measured\ndecay rate of Fermi polarons could be significantly larger than the calculated\nquasiparticle decay rate at zero momentum. By take this crucial contribution\ninto account, we find that there is a reasonable agreement between theory and\nexperiment for the lifetime of Fermi polarons in the strong-coupling regime, as\nlong as they remain well-defined."
    },
    {
        "anchor": "Thermoelectricity modeling with cold dipole atoms in Aubry phase of\n  optical lattice: We study analytically and numerically the thermoelectric properties of a\nchain of cold atoms with dipole-dipole interactions placed in an optical\nperiodic potential. At small potential amplitudes the chain slides freely that\ncorresponds to the Kolmogorov-Arnold-Moser phase of integrable curves of a\nsymplectic map. Above a certain critical amplitude the chain is pinned by the\nlattice being in the cantori Aubry phase. We show that the Aubry phase is\ncharacterized by exceptional thermoelectric properties with the figure of merit\nZT = 25 being ten times larger than the maximal value reached in material\nscience experiments. We show that this system is well accessible for\nmagneto-dipole cold atom experiments that opens new prospects for\ninvestigations of thermoelectricity.",
        "positive": "Multi-band and nonlinear hopping corrections to the 3D Bose-Fermi\n  Hubbard model: Recent experiments revealed the importance of higher-band effects for the\nMott insulator (MI) -- superfluid transition (SF) of ultracold bosonic atoms or\nmixtures of bosons and fermions in deep optical lattices [Best \\emph{et al.},\nPRL \\textbf{102}, 030408 (2009); Will \\emph{et al.}, Nature \\textbf{465}, 197\n(2010)]. In the present work, we derive an effective lowest-band Hamiltonian in\n3D that generalizes the standard Bose-Fermi Hubbard model taking these effects\nas well as nonlinear corrections of the tunneling amplitudes mediated by\ninterspecies interactions into account. It is shown that a correct description\nof the lattice states in terms of the bare-lattice Wannier functions rather\nthan approximations such as harmonic oscillator states is essential. In\ncontrast to self-consistent approaches based on effective Wannier functions our\napproach provides a quantitative explanation of the observed reduction of the\nsuperfluid phase for repulsive interspecies interactions."
    },
    {
        "anchor": "Quantum Zeno-based Detection and State Engineering of Ultracold Polar\n  Molecules: We present and analyze a toolbox for the controlled manipulation of ultracold\npolar molecules, consisting of detection of molecules, atom-molecule\nentanglement, and engineering of dissipative dynamics. Our setup is based on\nfast chemical reactions between molecules and atoms leading to a quantum\nZeno-based collisional blockade in the system. We demonstrate that the\nexperimental parameters for achieving high fidelities can be found using a\nstraightforward numerical optimization. We exemplify our approach for a system\ncomprised of NaK molecules and Na atoms and we discuss the consequences of\nresidual imperfections such as a finite strength of the quantum Zeno blockade.",
        "positive": "Continuous Symmetry Breaking in a Two-dimensional Rydberg Array: Spontaneous symmetry breaking underlies much of our classification of phases\nof matter and their associated transitions. The nature of the underlying\nsymmetry being broken determines many of the qualitative properties of the\nphase; this is illustrated by the case of discrete versus continuous symmetry\nbreaking. Indeed, in contrast to the discrete case, the breaking of a\ncontinuous symmetry leads to the emergence of gapless Goldstone modes\ncontrolling, for instance, the thermodynamic stability of the ordered phase.\nHere, we realize a two-dimensional dipolar XY model -- which exhibits a\ncontinuous spin-rotational symmetry -- utilizing a programmable Rydberg quantum\nsimulator. We demonstrate the adiabatic preparation of correlated\nlow-temperature states of both the XY ferromagnet and the XY antiferromagnet.\nIn the ferromagnetic case, we characterize the presence of long-range XY order,\na feature prohibited in the absence of long-range dipolar interaction. Our\nexploration of the many-body physics of XY interactions complements recent\nworks utilizing the Rydberg-blockade mechanism to realize Ising-type\ninteractions exhibiting discrete spin rotation symmetry."
    },
    {
        "anchor": "Quasiadiabatic dynamics of ultracold bosonic atoms in a one-dimensional\n  optical superlattice: We study the quasiadiabatic dynamics of a one-dimensional system of ultracold\nbosonic atoms loaded in an optical superlattice. Focusing on a slow linear\nvariation in time of the superlattice potential, the system is driven from a\nconventional Mott insulator phase to a superlattice-induced Mott insulator,\ncrossing in between a gapless critical superfluid region. Due to the presence\nof a gapless region, a number of defects depending on the velocity of the\nquench appear. Our findings suggest a power-law dependence similar to the\nKibble-Zurek mechanism for intermediate values of the quench rate. For the\ntemporal ranges of the quench dynamics that we considered, the scaling of\ndefects depends nontrivially on the width of the superfluid region.",
        "positive": "Critical properties of weakly interacting Bose gases as modified by a\n  harmonic confinement: The critical properties of the phase transition from a normal gas to a BEC\n(superfluid) of a harmonically confined Bose gas are addressed with the\nknowledge of an equation of state of the underlying homogeneous Bose fluid. It\nis shown that while the presence of the confinement trap arrests the usual\ndivergences of the isothermal compressibility and heat capacities, the critical\nbehavior manifests itself now in the divergence of derivatives of the mentioned\nsusceptibilities. This result is illustrated with a mean-field like model of an\nequation of state for the homogeneous particle density as a function of the\nchemical potential and temperature of the gas. The model assumes the form of an\nideal Bose gas in the normal fluid while in the superfluid state a function is\nproposed such that, both, asymptotically reaches the Thomas-Fermi solution of a\nweakly interacting Bose gas at large densities and low temperatures and, at the\ntransition, matches the critical properties of the ideal Bose gas. With this\nmodel we obtain the {\\it global} thermodynamics of the harmonically confined\ngas, from which we analyze its critical properties. We discuss how these\nproperties can be experimentally tested."
    },
    {
        "anchor": "Currents algebra for an atom-molecule Bose-Einstein condensate model: I present an interconversion currents algebra for an atom-molecule\nBose-Einstein condensate model and use it to get the quantum dynamics of the\ncurrents. For different choices of the Hamiltonian parameters I get different\ncurrents dynamics.",
        "positive": "Second sound with ultracold atoms: A brief historical account: We briefly review the research on second sound in ultracold atomic physics,\nwith emphasis on strongly interacting unitary Fermi gases with infinitely large\n$s$-wave scattering length. Second sound is a smoking-gun feature of\nsuperfluidity in any quantum superfluids. The observation and characterization\nof second sound in ultracold quantum gases has been a long-standing challenge,\nand in recent years there are rapid developments due to the experimental\nrealization of a uniform box-trap potential. The purpose of this review is to\npresent a brief historical account of the key research activities on second\nsound over the past two decades. We summarize the initial theoretical works\nthat reveal the characteristics of second sound in a unitary Fermi gas, and\nintroduce its first observation in a highly elongated harmonic trap. We then\ndiscuss the most recent measurement on second sound attenuation in a uniform\nsetup, which may open a new era to understand quantum transport near quantum\ncriticality in the strongly interacting regime. The observation of second sound\nin homogeneous weakly interacting Bose condensates in both two and three\ndimensions are also briefly introduced."
    },
    {
        "anchor": "Boltzmann equation with double-well potentials: We study the dynamics of an interacting classical gas trapped in a\ndouble-well potential at finite temperature. Two model potentials are\nconsidered: a cubic box with a square barrier in the middle, and a harmonic\ntrap with a gaussian barrier along one direction. The study is performed using\nthe Boltzmann equation, solved numerically via the test-particle method. We\nintroduce and discuss a simple analytical model that allows to provide\nestimates of the relaxation time, which are compared with numerical results.\nFinally, we use our findings to make numerical and analytical predictions for\nthe case of a fermionic mixture in the normal-fluid phase in a realistic\ndouble-well potential relevant for experiments with cold atoms.",
        "positive": "Quantum Phases and Correlations Drive the Dynamics of Macroscopic\n  Quantum Tunneling Escape in Quantum Simulators: Quantum tunneling remains unexplored in many regimes of many-body quantum\nphysics, including the effect of quantum phase transitions on tunneling\ndynamics. In general, the quantum phase is a statement about the ground state\nand has no relation to far-from-equilibrium dynamics. Although tunneling is a\nhighly dynamical process involving many excited states, we find that the\nquantum phase of the Bose-Hubbard model determines phase-dependent tunneling\noutcomes for the quantum tunneling escape, or quasi-bound problem. Superfluid\nand Mott insulator correlations lead to a new quantum tunneling rate, the\nquantum fluctuation rate. This rate shows surprising and highly dynamical\nfeatures, such as oscillatory interference between trapped and escaped atoms\nand a completely different macroscopic quantum tunneling behavior for\nsuperfluid and Mott insulator phases. In the superfluid phase we find that\nescape dynamics are wave-like and coherent, leading to interference patterns in\nthe density with a rapid decay process which is non-exponential. Quantum\nentropy production peaks when about half the atoms have escaped. In the Mott\nphase, despite stronger repulsive interactions, tunneling is significantly\nslowed by the presence of a Mott gap, creating an effective extra barrier to\novercome. Only one atom can tunnel at a time, yet the decay process is nearly\nlinear, completely defying the single-particle exponential model. Moreover,\nquantum entropy peaks when only about one quarter of the atoms have escaped.\nThese and many other such effects go beyond the usual notions of\nsingle-particle quantum tunneling, quantum statistical effects on tunneling,\nand well-known semi-classical approaches from WKB to instanton theory. These\nresults thus open up a new regime of exploration of far-from-equilibrium\ndynamics for quantum simulators and quantum dynamics."
    },
    {
        "anchor": "Modulational instability, inter-component asymmetry and formation of\n  quantum droplets in one-dimensional binary Bose gases: Quantum droplets are ultradilute liquid states which emerge from the\ncompetitive interplay of two Hamiltonian terms, the mean-field energy and\nbeyond-mean-field correction, in a weakly interacting binary Bose gas. We\nrelate the formation of droplets in symmetric and asymmetric two-component\none-dimensional boson systems to the modulational instability of a spatially\nuniform state driven by the beyond-mean-field term. Asymmetry between the\ncomponents may be caused by their unequal populations or unequal\nintra-component interaction strengths. Stability of both symmetric and\nasymmetric droplets is investigated. Robustness of the symmetric solutions\nagainst symmetry-breaking perturbations is confirmed.",
        "positive": "Driven-dissipative Rydberg blockade in optical lattices: While dissipative Rydberg gases exhibit unique possibilities to tune\ndissipation and interaction properties, very little is known about the quantum\nmany-body physics of such long-range interacting open quantum systems. We\ntheoretically analyze the steady state of a van der Waals interacting Rydberg\ngas in an optical lattice based on a variational treatment that also includes\nlong-range correlations necessary to describe the physics of the Rydberg\nblockade, i.e., the inhibition of neighboring Rydberg excitations by strong\ninteractions. In contrast to the ground state phase diagram, we find that the\nsteady state undergoes a single first order phase transition from a blockaded\nRydberg gas to a facilitation phase where the blockade is lifted. The first\norder line terminates in a critical point when including sufficiently strong\ndephasing, enabling a highly promising route to study dissipative criticality\nin these systems. In some regimes, we also find good quantitative agreement\nwith effective short-range models despite the presence of the Rydberg blockade,\njustifying the wide use of such phenomenological descriptions in the\nliterature."
    },
    {
        "anchor": "The Fermi Gases and Superfluids: Short Review of Experiment and Theory\n  for Condensed Matter Physicists: The study of ultracold atomic Fermi gases is a rapidly exploding subject\nwhich is defining new directions in condensed matter and atomic physics. Quite\ngenerally what makes these gases so important is their remarkable tunability\nand controllability. Using a Feshbach resonance one can tune the attractive\ntwo-body interactions from weak to strong and thereby make a smooth crossover\nfrom a BCS superfluid of Cooper pairs to a Bose-Einstein condensed superfluid.\nFurthermore, one can tune the population of the two spin states, allowing\nobservation of exotic spin-polarized superfluids, such as the Fulde Ferrell\nLarkin Ovchinnikov (FFLO) phase. A wide array of powerful characterization\ntools, which often have direct condensed matter analogues, are available to the\nexperimenter. In this Chapter, we present a general review of the status of\nthese Fermi gases with the aim of communicating the excitement and great\npotential of the field.",
        "positive": "Polarized Fermi gases in asymmetric optical lattices: The zero-temperature phase diagrams of imbalanced two-species Fermi gases are\ninvestigated in asymmetric optical lattices with arbitrary potential depths,\nbased on the exact spectrum instead of the Fermi-Hubbard model. We study the\neffect of lattice potentials and atomic densities to the fully paired\nBardeen-Cooper-Schrieffer (BCS) state and particularly the\nFulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. It is found that the increasing\nlattice potential favors BCS at low densities because of the enhanced effective\ncoupling; whereas FFLO is favored at intermediate densities when the system\nundergoes a dimensional crossover. Finally using local density approximation we\nstudy the evolution of phase profile in the presence of external harmonic traps\nby merely tuning the lattice potentials."
    },
    {
        "anchor": "Chiral switching of many-body steady states in a dissipative Rydberg gas: Dissipative Rydberg gases are an outstanding platform for the investigation\nof many-body quantum open systems. Despite the wealth of existing studies, the\nnon-equilibrium dynamics of dissipative Rydberg gases are rarely examined or\nharnessed from the perspective of non-Hermitian physics, which is but intrinsic\nto open systems. Here we report the experimental observation of a chiral\nswitching between many-body steady states in a dissipative thermal Rydberg\nvapor, where the interplay of many-body effects and non-Hermiticity plays a key\nrole. Specifically, as the parameters are adiabatically varied around a closed\ncontour, depending on the chirality of the parameter modulation, the Rydberg\nvapor can change between two collective steady states with distinct Rydberg\nexcitations and optical transmissions. Adopting a mean-field description, we\nreveal that both the existence of the bistable steady states and chiral\ndynamics derive from an exceptional structure in the parameter space, where\nmultiple steady states of the many-body Liouvillian superoperator coalesce. We\ndemonstrate that both the exceptional structure and the resulting\nstate-switching dynamics are tunable through microwave dressing and temperature\nvariations, confirming their reliance on the many-body dissipative nature of\nthe Rydberg vapor.",
        "positive": "Probing many-body interactions in an optical lattice clock: We present a unifying theoretical framework that describes recently observed\nmany-body effects during the interrogation of an optical lattice clock operated\nwith thousands of fermionic alkaline earth atoms. The framework is based on a\nmany-body master equation that accounts for the interplay between elastic and\ninelastic p-wave and s-wave interactions, finite temperature effects and\nexcitation inhomogeneity during the quantum dynamics of the interrogated atoms.\nSolutions of the master equation in different parameter regimes are presented\nand compared. It is shown that a general solution can be obtained by using the\nso called Truncated Wigner Approximation which is applied in our case in the\ncontext of an open quantum system. We use the developed framework to model the\ndensity shift and decay of the fringes observed during Ramsey spectroscopy in\nthe JILA 87Sr and NIST 171Yb optical lattice clocks. The developed framework\nopens a suitable path for dealing with a variety of strongly-correlated and\ndriven open-quantum spin systems."
    },
    {
        "anchor": "Efficient production of a narrow-line erbium magneto-optical trap with\n  two-stage slowing: We describe an experimental setup for producing a large cold erbium (Er)\nsample in a narrow-line magneto-optical trap (MOT) in a simple and efficient\nway. We implement a pair of angled slowing beams with respect to the Zeeman\nslower axis, and further slow down atoms exiting from the Zeeman slower. The\nsecond-stage slowing beams enable the narrow-line MOT to trap atoms exiting\nfrom the Zeeman slower with higher velocity. This scheme is particularly useful\nwhen the Zeeman slower is at low optical power without the conventional\ntransverse cooling between an oven and a Zeeman slower, in which case we\nsignificantly improve the loading efficiency into the MOT and are able to trap\nmore than $10^8$ atoms in the narrow-line MOT of $^{166}$Er. This work\nhighlights our implementation, which greatly simplifies laser cooling and\ntrapping of Er atoms and also should benefit other similar elements.",
        "positive": "Dicke quantum spin glass of atoms and photons: Recent studies of strongly interacting atoms and photons in optical cavities\nhave rekindled interest in the Dicke model of atomic qubits coupled to discrete\nphoton cavity modes. We study the multimode Dicke model with variable\natom-photon couplings. We argue that a quantum spin glass phase can appear,\nwith a random linear combination of the cavity modes superradiant. We compute\natomic and photon spectral response functions across this quantum phase\ntransition, both of which should be accessible in experiment."
    },
    {
        "anchor": "Quantum Back-action Limits in Dispersively Measured Bose-Einstein\n  Condensates: A fundamental tenet of quantum mechanics is that measurements change a\nsystem's wavefunction to that most consistent with the measurement outcome,\neven if no observer is present. Weak measurements produce only limited\ninformation about the system, and as a result only minimally change the\nsystem's state. Here, we theoretically and experimentally characterize quantum\nback-action in atomic Bose-Einstein condensates interacting with a far-from\nresonant laser beam. We theoretically describe this process using a quantum\ntrajectories approach where the environment measures the scattered light and\npresent a measurement model based on an ideal photodetection mechanism. We\nexperimentally quantify the resulting wavefunction change in terms of the\ncontrast of a Ramsey interferometer and control parasitic effects associated\nwith the measurement process. The observed back-action is in good agreement\nwith our measurement model; this result is a necessary precursor for achieving\ntrue quantum back-action limited measurements of quantum gases.",
        "positive": "Universal Energy Functionals for Trapped Fermi Gases in Low Dimensions: We study the system of trapped two-component Fermi gases with zero-range\ninteraction in two dimensions (2D) or one dimension (1D). We calculate the\none-particle density matrices of these systems at small displacements, from\nwhich we show that the $N$-body energies are linear functionals of the\noccupation probabilities of single-particle energy eigenstates. A universal\nenergy functional was first derived in 2011 for trapped zero-range interacting\ntwo-component Fermi gases in three dimensions (3D). We also calculate the\nasymptotic behaviors of the occupation probabilities of single-particle energy\neigenstates at high energies."
    },
    {
        "anchor": "Bose-Einstein condensates in multiple well potentials from a variational\n  path integral: We apply a path integral variational approach to obtain analytical\nexpressions for condensate wave functions of an ultracold, interacting trapped\nBose gases. As in many recent experiments, the particles are confined in a 1D\nor 3D harmonic oscillator trap which is superimposed by a periodic potential in\none direction. Based on the first order cumulant expansion with respect to a\nharmonic trial action, and emplyoing a mean-field approximation, optimal\nvariational parameters are obtained by minimizing an analytical expression for\nthe ground state energy. Our largely analytical results for energy and\ncondensate wave function are in good agreement with fully numerical\ncalculations based on the Gross-Pitaevskii equation.",
        "positive": "Finite-temperature equation of state of polarized fermions at unitarity: We study in a nonperturbative fashion the thermodynamics of a unitary Fermi\ngas over a wide range of temperatures and spin polarizations. To this end, we\nuse the complex Langevin method, a first principles approach for strongly\ncoupled systems. Specifically, we show results for the density equation of\nstate, the magnetization, and the magnetic susceptibility. At zero\npolarization, our results agree well with state-of-the art results for the\ndensity equation of state and with experimental data. At finite polarization\nand low fugacity, our results are in excellent agreement with the third-order\nvirial expansion. In the fully quantum mechanical regime close to the balanced\nlimit, the critical temperature for superfluidity appears to depend only weakly\non the spin polarization."
    },
    {
        "anchor": "Moving Bose mixtures with dipole-dipole interactions: We study the properties of moving uniform dipolar Bose-Bose mixtures using\nthe full Hartree-Fock-Bogoliubov theory. The analytical and numerical\ncalculations emphasize that the competition between the relative motion of two\nfluids and the interspecies dipole-dipole interactions may affect the behavior\nof the condensed depletion, the anomalous density, the ground-state energy and\nsecond-order pair correlation. It is found that in the lower branch of the\nmixture, these quantities are unimportant and present an unconventional\nbehavior.",
        "positive": "Expansion dynamics of the Fulde-Ferrell-Larkin-Ovchinnikov state: We consider a two-component Fermi gas in the presence of spin imbalance,\nmodeling the system in terms of a one-dimensional attractive Hubbard\nHamiltonian initially in the presence of a confining trap potential. With the\naid of the time-evolving block decimation method, we investigate the dynamics\nof the initial state when the trap is switched off. We show that the dynamics\nof a gas initially in the Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) state is\ndecomposed into the independent expansion of two fluids, namely the paired and\nthe unpaired particles. In particular, the expansion velocity of the unpaired\ncloud is shown to be directly related to the FFLO momentum. This provides an\nunambiguous signature of the FFLO state in a remarkably simple way."
    },
    {
        "anchor": "Interaction effects on atomic laboratory trapped Bose-Einstein\n  condensates: We discuss the effect of inter-atoms interactions on the condensation\ntemperature $T_c$ of an atomic laboratory trapped Bose-Einstein condensate. We\nshow that, in the mean-field Hartree-Fock and semiclassical approximations,\ninteractions produce a shift $\\Delta T_{c}/T_{c}^{0} \\approx b_1\n(a/\\lambda_{T_c}) + b_2 (a/\\lambda_{T_c})^2 + \\psi[a/\\lambda_{T_c}]$ with $a$\nthe s-wave scattering length, $\\lambda_T$ the thermal wavelength and\n$\\psi[a/\\lambda_{T_c}]$ a non-analytic function such that $\\psi[0] = \\psi'[0] =\n\\psi\"[0] = 0$ and $|\\psi\"'[0]| = \\infty$. Therefore, with no more assumptions\nthan Hartree-Fock and semiclassical approximations, interaction effecs are\nperturbative to second order in $a/\\lambda_{T_c}$ and the expected\nnon-perturbativity of physical quantities at critical temperature appears only\nto third order. We compare this finding with different results by other\nauthors, which are based on more than the Hartree-Fock and semiclassical\napproximations. Moreover, we obtain an analytical estimation for $b_2 \\simeq\n18.8$ which improves a previous numerical result. We also discuss how the\ndiscrepancy between $b_2$ and the empirical value of $b_2 = 46 \\pm 5$ may be\nexplained with no need to resort to beyond-mean field effects.",
        "positive": "Cold-atom quantum simulators of gauge theories: Gauge theories represent a fundamental framework underlying modern physics,\nconstituting the basis of the Standard Model and also providing useful\ndescriptions of various phenomena in condensed matter. Realizing gauge theories\non accessible and tunable tabletop quantum devices offers the possibility to\nstudy their dynamics from first principles time evolution and to probe their\nexotic physics, including that generated by deviations from gauge invariance,\nwhich is not possible, e.g., in dedicated particle colliders. Not only do\ncold-atom quantum simulators hold the potential to provide new insights into\noutstanding high-energy and nuclear-physics questions, they also provide a\nversatile tool for the exploration of topological phases and\nergodicity-breaking mechanisms relevant to low-energy many-body physics. In\nrecent years, cold-atom quantum simulators have demonstrated impressive\nprogress in the large-scale implementation of $1+1$D Abelian gauge theories. In\nthis Review, we chronicle the progress of cold-atom quantum simulators of gauge\ntheories, highlighting the crucial advancements achieved along the way in order\nto reliably stabilize gauge invariance and go from building blocks to\nlarge-scale realizations where \\textit{bona fide} gauge-theory phenomena can be\nprobed. We also provide a brief outlook on where this field is heading, and\nwhat is required experimentally and theoretically to bring the technology to\nthe next level by surveying various concrete proposals for advancing these\nsetups to higher spatial dimensions, higher-spin representations of the gauge\nfield, and non-Abelian gauge groups."
    },
    {
        "anchor": "Quench dynamics in disordered two-dimensional Gross-Pitaevskii Lattices: We numerically investigate the quench expansion dynamics of an initially\nconfined state in a two-dimensional Gross-Pitaevskii lattice in the presence of\nexternal disorder. The expansion dynamics is conveniently described in the\ncontrol parameter space of the energy and norm densities. The expansion can\nslow down substantially if the expected final state is a non-ergodic non-Gibbs\none, regardless of the disorder strength. Likewise stronger disorder delays\nexpansion. We compare our results with recent studies for quantum many body\nquench experiments.",
        "positive": "Vortex Formations from Domain Wall Annihilations in Two-component\n  Bose-Einstein Condensates: We theoretically study the vortex formation from the collision of the domain\nwalls in phase-separated two-component Bose-Einstein condensates. The collision\nprocess mimics the tachyon condensation for the annihilation of D-brane and\nanti-D-brane in string theory. A pair annihilation leaves the quantized\nvortices with superflow along their core, namely `superflowing cosmic strings'.\nIt is revealed that the line density and the core size of the vortices depend\non the initial distance between the walls."
    },
    {
        "anchor": "Nonuniform Bose-Einstein condensate. II. Doubly coherent states: We find stationary excited states of a one-dimensional system of $N$ spinless\npoint bosons with repulsive interaction and zero boundary conditions by\nnumerically solving the time-independent Gross-Pitaevskii equation. The\nsolutions are compared with the exact ones found in the Bethe-ansatz approach.\nWe show that the $j$th stationary excited state of a nonuniform condensate of\natoms corresponds to a Bethe-ansatz solution with the quantum numbers\n$n_{1}=n_{2}=\\ldots =n_{N}=j+1$. On the other hand, such $n_{1},\\ldots,n_{N}$\ncorrespond to a condensate of $N$ elementary excitations (in the present case\nthe latter are the Bogoliubov quasiparticles with the quasimomentum $\\hbar \\pi\nj/L$, where $L$ is the system size). Thus, each stationary excited state of the\ncondensate is ``doubly coherent'', since it corresponds simultaneously to a\ncondensate of $N$ atoms and a condensate of $N$ elementary excitations. We find\nthe energy $E$ and the particle density profile $\\rho (x)$ for such states. The\npossibility of experimental production of these states is also discussed.",
        "positive": "Coherent multiple scattering of out-of-equilibrium interacting Bose\n  gases: We review recent theoretical and experimental progresses in the coherent\nmultiple scattering of weakly interacting disordered Bose gases. These systems\nhave allowed, in the recent years, a characterization of weak and strong\nlocalization phenomena in disorder at an unprecedented level of control. In\nthis paper, we first discuss the main physical concepts and recent experimental\nachievements associated with a few emblematic \"mesoscopic\" effects in disorder\nlike coherent back scattering, coherent forward scattering or mesoscopic echos,\nfocusing on the context of out-of-equilibrium cold-atom setups. We then address\nthe role of weak particle interactions and explain how, depending on their\nrelative strength with respect to the disorder and on the time scales probed,\nthey can give rise to a dephasing mechanism for weak localization, thermalize a\nnon-equilibrium Bose gas or make it become a superfluid."
    },
    {
        "anchor": "Universal many-body diffusion from momentum dephasing: The open dynamics of quantum many-body systems involve not only the exchange\nof energy, but also of other conserved quantities, such as momentum. This leads\nto additional decoherence, which may have a profound impact in the dynamics.\nMotivated by this, we consider a many-body system subject to total momentum\ndephasing and show that under very general conditions this leads to a diffusive\ncomponent in the dynamics of any local density, even far from equilibrium. Such\ncomponent will usually have an intricate interplay with the unitary dynamics.\nTo illustrate this, we consider the case of a superfluid and show that momentum\ndephasing introduces a damping in the sound-wave dispersion relation, similar\nto that predicted by the Navier-Stokes equation for ordinary fluids. Finally,\nwe also study the effects of dephasing in linear response, and show that it\nleads to a universal additive contribution to the diffusion constant, which can\nbe obtained from a Kubo formula.",
        "positive": "On the Exponential Decay of Strongly Interacting Cold Atoms from a\n  Double-Well Potential: In this article, we study an exponential decay for the gas of bosons with\nstrong repulsive delta interactions from a double-well potential. We consider\nan exactly solvable model comprising an infinite wall and two Dirac delta\nbarriers. We explore its features both within the exact method and with the\nresonance expansion approach. The study reveals the effect of the splitting\nbarrier on the decay rate in dependence on the number of particles. Among other\nthings, we find that the effect of the splitting barrier on the decay rate is\nmost pronounced in systems with odd particle numbers. During exponential decay,\nthe spatial correlations in an internal region are well captured by the\n\"radiating state\"."
    },
    {
        "anchor": "Phase diagram of the hardcore Bose-Hubbard model on a checkerboard\n  superlattice: We obtain the complete phase diagram of the hardcore Bose-Hubbard model in\nthe presence of a period-two superlattice in two and three dimensions. First we\nacquire the phase boundaries between the superfluid phase and the `trivial'\ninsulating phases of the model (the completely-empty and completely-filled\nlattices) analytically. Next, the boundary between the superfluid phase and the\nhalf-filled Mott-insulating phase is obtained numerically, using the stochastic\nseries expansion (SSE) algorithm followed by finite-size scaling. We also\ncompare our numerical results against the predictions of several approximation\nschemes, including two mean-field approaches and a fourth-order strong-coupling\nexpansion (SCE), where we show that the latter method in particular is\nsuccessful in producing an accurate picture of the phase diagram. Finally, we\nexamine the extent to which several approximation schemes, such as the random\nphase approximation and the strong-coupling expansion, give an accurate\ndescription of the momentum distribution of the bosons inside the insulating\nphases.",
        "positive": "Controlling coherence via tuning of the population imbalance in a\n  bipartite optical lattice: The control of transport properties is a key tool at the basis of many\ntechnologically relevant effects in condensed matter. The clean and precisely\ncontrolled environment of ultracold atoms in optical lattices allows one to\nprepare simplified but instructive models, which can help to better understand\nthe underlying physical mechanisms. Here we show that by tuning a structural\ndeformation of the unit cell in a bipartite optical lattice, one can induce a\nphase transition from a superfluid into various Mott insulating phases forming\na shell structure in the superimposed harmonic trap. The Mott shells are\nidentified via characteristic features in the visibility of Bragg maxima in\nmomentum spectra. The experimental findings are explained by Gutzwiller\nmean-field and quantum Monte Carlo calculations. Our system bears similarities\nwith the loss of coherence in cuprate superconductors, known to be associated\nwith the doping induced buckling of the oxygen octahedra surrounding the copper\nsites."
    },
    {
        "anchor": "Symmetries and Correlations in Strongly Interacting One-dimensional\n  Quantum Gases: The main focus of this thesis is the theoretical study of strongly\ninteracting quantum mixtures confined in one dimension and subjected to a\nharmonic external potential. Such strongly correlated systems can be realized\nand tested in ultracold atoms experiments. Their non-trivial permutational\nsymmetry properties are investigated, as well as their interplay with\ncorrelations. Exploiting an exact solution at strong interactions, we extract\ngeneral correlation properties encoded in the one-body density matrix and in\nthe associated momentum distributions, in fermionic and Bose-Fermi mixtures. In\nparticular, we obtain substantial results about the short-range behavior, and\ntherefore the high-momentum tails, which display typical $k^{-4}$ laws. The\nweights of these tails, denoted as Tan's contacts, are related to numerous\nthermodynamic properties of the systems such as the two-body correlations, the\nderivative of the energy with respect to the one-dimensional scattering length,\nor the static structure factor. We show that these universal Tan's contacts\nalso allow to characterize the spatial symmetry of the systems, and therefore\nis a deep connection between correlations and symmetries. Besides, the exchange\nsymmetry is extracted using a group theory method, namely the class-sum method,\nwhich comes originally from nuclear physics. Moreover, we show that these\nsystems follow a generalized version of the famous Lieb-Mattis theorem. Wishing\nto make our results as experimentally relevant as possible, we derive scaling\nlaws for Tan's contact as a function of the interaction, temperature and\ntransverse confinement. These laws display interesting effects related to\nstrong correlations and dimensionality.",
        "positive": "Two dimensional bright solitons in dipolar Bose-Einstein condensates\n  with tilted dipoles: The effect of dipolar orientation with respect to the soliton plane on the\nphysics of two-dimensional bright solitons in dipolar Bose-Einstein condensates\nis discussed. Previous studies on such a soliton involved dipoles either\nperpendicular or parallel to the condensate-plane. The tilting angle\nconstitutes an additional tuning parameter, which help us to control the\nin-plane anisotropy of the soliton as well as provides access to previously\ndisregarded regimes of interaction parameters for soliton stability. In\naddition, it can be used to drive the condensate into phonon instability\nwithout changing its interaction parameters or trap geometry. The\nphonon-instability in a homogeneous 2D condensate of tilted dipoles always\nfeatures a transient stripe pattern, which eventually breaks into a metastable\nsoliton gas. Finally, we demonstrate how a dipolar BEC in a shallow trap can\neventually be turned into a self-trapped matter wave by an adiabatic approach,\ninvolving the tuning of tilting angle."
    },
    {
        "anchor": "Stability of rubidium molecules in the lowest triplet state: Experiments involving ultracold molecules require sufficiently long\nlifetimes, which can be very short for excited rovibrational states in the\nmolecular potentials. For alkali atoms such as rubidium, a lowest rovibrational\nmolecular state can both be found in the electronic singlet and triplet\nconfigurations. The molecular singlet ground state is absolutely stable.\nHowever, the lowest triplet state can decay to a deeper bound singlet molecule\ndue to a radiative decay mechanism that involves the interatomic spin-orbit\ninteraction. We investigate this mechanism, and find the lifetime of rubidium\nmolecules in the lowest triplet rovibrational state to be about 21 minutes.",
        "positive": "Slow quench dynamics of a trapped one-dimensional Bose gas confined to\n  an optical lattice: We analyze the effect of a linear time-variation of the interaction strength\non a trapped one-dimensional Bose gas confined to an optical lattice. The\nevolution of different observables such as the experimentally accessible onsite\nparticle distribution are studied as a function of the ramp time using\ntime-dependent exact diagonalization and density-matrix renormalization group\ntechniques. We find that the dynamics of a trapped system typically display two\nregimes: for long ramp times, the dynamics are governed by density\nredistribution, while at short ramp times, local dynamics dominate as the\nevolution is identical to that of an homogeneous system. In the homogeneous\nlimit, we also discuss the non-trivial scaling of the energy absorbed with the\nramp time."
    },
    {
        "anchor": "Perspective on Quantum Bubbles in Microgravity: Progress in understanding quantum systems has been driven by the exploration\nof the geometry, topology, and dimensionality of ultracold atomic systems. The\nNASA Cold Atom Laboratory (CAL) aboard the International Space Station has\nenabled the study of ultracold atomic bubbles, a terrestrially-inaccessible\ntopology. Proof-of-principle bubble experiments have been performed on CAL with\nan rf-dressing technique; an alternate technique (dual-species\ninteraction-driven bubbles) has also been proposed. Both techniques can drive\ndiscovery in the next decade of fundamental physics research in microgravity.",
        "positive": "Density wave propagation in a two-dimensional random dimer potential:\n  from a single to a bipartite square lattice: We study the propagation of a density perturbation in a weakly interacting\nboson gas confined on a lattice and in the presence of square dimerized\nimpurities. Such a two-dimensional random-dimer model (2D-DRDM), previously\nintroduced in [Capuzzi et al., Phys. Rev. A 92, 053622 (2015)], is the disorder\ntransition from a single square lattice, where impurities are absent, to a\nbipartite square lattice, where the number of impurities is maximum and\ncoincides with half the number of lattice sites. We show that disorder\ncorrelations can play a crucial role in the dynamics for a broad range of\nparameters by allowing density fluctuations to propagate in the 2D-DRDM\nlattice, even in the limit of strong disorder. In such a regime, the\npropagation speed depends on the percentage of impurities, interpolating\nbetween the speed in a single monoperiodic lattice and that in a bipartite one."
    },
    {
        "anchor": "Collisionally inhomogeneous Bose-Einstein condensates with a linear\n  interaction gradient: We study the evolution of a collisionally inhomogeneous matter wave in a\nspatial gradient of the interaction strength. Starting with a Bose-Einstein\ncondensate with weak repulsive interactions in quasi-one-dimensional geometry,\nwe monitor the evolution of a matter wave that simultaneously extends into\nspatial regions with attractive and repulsive interactions. We observe the\nformation and the decay of soliton-like density peaks, counter-propagating\nself-interfering wave packets, and the creation of cascades of solitons. The\nmatter-wave dynamics is well reproduced in numerical simulations based on the\nnonpolynomial Schroedinger equation with three-body loss, allowing us to better\nunderstand the underlying behaviour based on a wavelet transformation. Our\nanalysis provides new understanding of collapse processes for solitons, and\nopens interesting connections to other nonlinear instabilities.",
        "positive": "Quantum and thermal effects in dark soliton formation and dynamics in a\n  1D Bose gas: We numerically study the imprinting and dynamics of dark solitons in a\nbosonic atomic gas in a tightly-confined one-dimensional harmonic trap both\nwith and without an optical lattice. Quantum and thermal fluctuations are\nsynthesized within the truncated Wigner approximation in the quasi-condensate\ndescription. We track the soliton coordinates and calculate position and\nvelocity uncertainties. We find that the phase fluctuations {\\em lower} the\nclassically predicted soliton speed and seed instabilities. Individual runs\nshow interactions of solitons with sound waves, splitting and disappearing\nsolitons."
    },
    {
        "anchor": "Carbon-dioxide-like Skyrmion controlled by spin-orbit coupling in\n  atomic-molecular Bose-Einstein condensates: Atomic-molecular Bose-Einstein condensates (BECs) offer brand new\nopportunities to revolutionize quantum gases and probe the variation of\nfundamental constants with unprecedented sensitivity. The recent realization of\nspin-orbit coupling (SOC) in BECs provides a new platform for exploring\ncompletely new phenomena unrealizable elsewhere. However, there is no study of\nSOC atomic-molecular BECs so far. Here, we find a novel way of creating a\nRashba-Dresselhaus SOC in atomic-molecular BECs by combining the spin dependent\nphotoassociation and Raman coupling, which can control the formation and\ndistribution of a new type of topological excitation -- carbon-dioxide-like\nSkyrmion. This Skyrmion is formed by two half-Skyrmions of molecular BECs\ncoupling with one Skyrmion of atomic BECs, where the two half-Skyrmions locates\nat both sides of one Skyrmion, which can be detected by measuring the vortices\nstructures using the time-of-flight absorption imaging technique in real\nexperiments.",
        "positive": "Intermediate super-exponential localization with Aubry-Andr\u00e9 chains: We demonstrate the existence of an intermediate super-exponential\nlocalization regime for eigenstates of the Aubry-Andr\\'e chain. In this regime,\nthe eigenstates localize factorially similarly to the eigenstates of the\nWannier-Stark ladder. The super-exponential decay emerges on intermediate\nlength scales for large values of the $\\textit{winding length}$ -- the\nquasi-period of the Aubry-Andr\\'e potential. This intermediate localization is\npresent both in the metallic and insulating phases of the system. In the\ninsulating phase, the super-exponential localization is periodically\ninterrupted by weaker decaying tails to form the conventional asymptotic\nexponential decay predicted for the Aubry-Andr\\'e model. In the metallic phase,\nthe super-exponential localization happens for states with energies away from\nthe center of the spectrum and is followed by a super-exponential growth into\nthe next peak of the extended eigenstate. By adjusting the parameters it is\npossible to arbitrarily extend the validity of the super-exponential\nlocalization. A similar intermediate super-exponential localization regime is\ndemonstrated in quasiperiodic discrete-time unitary maps."
    },
    {
        "anchor": "Universal scaling of Efimov resonance positions in cold atom systems: Recent cold atom experiments report a surprising universal scaling of the\nfirst Efimov resonance position a_{-}^1 by the two-body van der Waals length\nr_{vdW}. The ratio C=-a_{-}^1/r_{vdW}=8.5~9.5 for identical particles appears\nto be a constant regardless of the atomic spin configuration, the Feshbach\nresonance employed to tune the scattering length, and even the atomic species,\nwith K-39 being the only exception. This result indicates that the Efimov\nenergy structure is insensitive to the details of the short range potential. We\nsuggest that the universality results from the quantum reflection of the Efimov\nwavefunciton by the short-range molecular potential. Assuming Born-Oppenheimer\napproximation and strong quantum reflection, we obtain an analytic result of\nC=9.475... for three identical particles. We suspect the exceptional case of\nK-39 is a result of resonant coupling between the Efimov state and a\nshort-range molecular state.",
        "positive": "Diagrammatic Pairing Fluctuations Approach to the BCS-BEC Crossover: This paper gives a survey of a diagrammatic approach for fermionic pairing\nfluctuations, which are relevant to the BCS-BEC crossover realized with\nultracold Fermi gases. Emphasis will be given to the physical intuition about\nthe relevant physical processes that can be associated with this approach.\nSpecific results will be presented for thermodynamic and dynamical quantities,\nwhere a critical comparison with alternative diagrammatic approaches will also\nbe attempted."
    },
    {
        "anchor": "Unpaired topological triply degenerate point for\n  spin-tensor-momentum-coupled ultracold atoms: The realization of triply degenerate points (TDPs) with exotic fermionic\nexcitations has opened a new perspective for the understanding of our nature.\nHere we explore the coexistence of single unpaired TDP and multiple twofold\nWeyl points (WPs) and propose an experimental scheme with ultracold\npseudospin-1 atomic gases trapped in optical lattices. We show that the\npredicted single unpaired TDP emerged by the interplay of quadratic\nspin-vector- and spin-tensor-momentum-coupling could possess a topological\nnontrivial middle band. This exotic TDP with mirror symmetry breaking is\nessential different from the recently observed TDPs that must appear in pairs\ndue to the Nielsen-Ninomiya theorem and host the topological trivial middle\nband. Strikingly, the topologically protected Fermi-arc states directly connect\nthe unpaired TDP with additional WPs, in contrast to the conventional Fermi-arc\nstates that connect the same degeneracies of band degenerate points with\nopposite chirality. Furthermore, the different types of TDPs with unique\nlinking structure of Fermi arcs can be readily distinguished by measuring spin\ntexture along high-symmetry lines of the system. Our scheme provides a platform\nfor emerging new fermions with exotic physical phenomena and versatile device\napplications.",
        "positive": "Spin structure of harmonically trapped one-dimensional atoms with\n  spin-orbit coupling: We introduce a theoretical approach to determine the spin structure of\nharmonically trapped atoms with two-body zero-range interactions subject to an\nequal mixture of Rashba and Dresselhaus spin-orbit coupling created through\nRaman coupling of atomic hyperfine states. The spin structure of bosonic and\nfermionic two-particle systems with finite and infinite two-body interaction\nstrength $g$ is calculated. Taking advantage of the fact that the $N$-boson and\n$N$-fermion systems with infinitely large coupling strength $g$ are\nanalytically solvable for vanishing spin-orbit coupling strength $k_{so}$ and\nvanishing Raman coupling strength $\\Omega$, we develop an effective spin model\nthat is accurate to second-order in $\\Omega$ for any $k_{so}$ and infinite $g$.\nThe three- and four-particle systems are considered explicitly. It is shown\nthat the effective spin Hamiltonian, which contains a Heisenberg exchange term\nand an anisotropic Dzyaloshinskii-Moriya exchange term, describes the\ntransitions that these systems undergo with the change of $k_{so}$ as a\ncompetition between independent spin dynamics and nearest-neighbor spin\ninteractions."
    },
    {
        "anchor": "The negative Bogoliubov dispersion in exciton-polariton condensates: Bogoliubov's theory states that self-interaction effects in Bose-Einstein\ncondensates produce a characteristic linear dispersion at low momenta. One of\nthe curious features of Bogoliubov's theory is that the new quasiparticles in\nthe system are linear combinations of creation and destruction operators of the\nbosons. In exciton-polariton condensates, this gives the possibility of\ndirectly observing the negative branch of the Bogoliubov dispersion in the\nphotoluminescence (PL) emission. Here we theoretically examine the PL spectra\nof exciton-polariton condensates taking into account of reservoir effects. At\nsufficiently high excitation densities, the negative dispersion becomes\nvisible. We also discuss the possibility for relaxation oscillations to occur\nunder conditions of strong reservoir coupling. This is found to give a\nsecondary mechanism for making the negative branch visible.",
        "positive": "Quantitative study of two- and three-dimensional strong localization of\n  matter waves by atomic scatterers: We study the strong localization of atomic matter waves in a disordered\npotential created by atoms pinned at the nodes of a lattice, for both\nthree-dimensional (3D) and two-dimensional (2D) systems. The localization\nlength of the matter wave, the density of localized states, and the occurrence\nof energy mobility edges (for the 3D system), are numerically investigated as a\nfunction of the effective scattering length between the atomic matter wave and\nthe pinned atoms. Both positive and negative matter wave energies are explored.\nInteresting features of the density of states are discovered at negative\nenergies, where maxima in the density of bound states for the system can be\ninterpreted in terms of bound states of a matter wave atom with a few pinned\natomic scatterers. In 3D we found evidence of up to three mobility edges, one\nat positive energies, and two at negative energies, the latter corresponding to\ntransitions between extended and localized bound states. In 2D, no mobility\nedge is found, and a rapid exponential-like increase of the localization length\nis observed at high energy."
    },
    {
        "anchor": "Excitation spectrum and momentum distribution of the ionic Bose-Hubbard\n  model: We investigate the excitation spectrum and momentum distribution of the ionic\nBose-Hubbard model by the standard basis operator method. We derive Green's\nfunctions in the random phase approximation in Mott insulator, superfluid,\ncharge density wave, and supersolid phases. The excitation spectrum has gapped\nmodes and gapless Goldstone modes in the superfluid and supersolid phases. We\nshow that the momentum distribution has a peak at the zone corner in the\nsupersolid phase and the charge density wave phase close to the phase boundary.\nIn addition, we demonstrate that the momentum distribution can be explained by\nthe excitation spectrum and spectral weights of hole excitation modes.",
        "positive": "Attractive Hofstadter-Hubbard model with imbalanced chemical and vector\n  potentials: We study the interplay between the Hofstadter butterfly, strong interactions\nand Zeeman field within the mean-field Bogoliubov-de Gennes theory in real\nspace, and explore the ground states of the attractive single-band\nHofstadter-Hubbard Hamiltonian on a square lattice, including the exotic\npossibility of imbalanced vector potentials. We find that the cooperation\nbetween the vector potential and superfluid order breaks the spatial symmetry\nof the system, and flourish stripe-ordered Fulde-Ferrell-Larkin-Ovchinnikov\n(FFLO)-like superfluid and supersolid phases that can be distinguished and\ncharacterized according to their coexisting pair-density (PDW), charge-density\n(CDW) and spin-density (SDW) wave orders. We also discuss confined systems and\ncomment on the likelihood of observing such stripe-ordered phases by loading\nneutral atomic Fermi gases on laser-induced optical lattices under\nlaser-generated artificial gauge fields."
    },
    {
        "anchor": "Vortex lattices in dipolar two-component Bose-Einstein condensates: We consider a rapidly rotating two-component Bose-Einstein condensate with\nshort-range s-wave interactions as well as dipolar coupling. We calculate the\nphase diagram of vortex lattice structures as a function of the intercomponent\ns-wave interaction and the strength of the dipolar interaction. We find that\nthe long-range interactions cause new vortex lattice structures to be stable\nand lead to a richer phase diagram. Our results reduce to the previously found\nlattice structures for short-range interactions and single-component dipolar\ngases in the corresponding limits.",
        "positive": "Dispersion relation and excitation character of a two-component\n  Bose-Einstein condensate: We present a study for the dispersion relation and character of the\nexcitations of a single and two component Bose Einstein Condensate (BEC). We\nstudy the single component dispersion for a finite BEC system and look at\nexamples of quasiparticles to understand and characterize the dispersion\nrelation. Next we present the dispersion relation for a two component BEC in\nboth the miscible and immiscible parameter regimes. Then we present examples of\nthe quasiparticles for both regimes."
    },
    {
        "anchor": "Polarons in Alkaline-earth-like Atoms with Multi Background Fermi\n  Surfaces: We study the impurity problem in a Fermi gas of $^{173}$Yb atoms near an\norbital Feshbach resonance, where a single moving particle in the $^3P_0$ state\ninteracting with two background Fermi seas of particles in different nuclear\nstates of the ground $^1S_0$ manifold. By employing wave function ansatzs for\nmolecule and polaron states, we investigate various properties of the molecule,\nthe attractive polaron, and the repulsive polaron states. We find that in\ncomparison to the case of only one Fermi sea is populated, the presence of an\nadditional Fermi sea acts as an energy shift between the two channels of the\norbital Feshbach resonance. Besides, the fluctuation around the Fermi level\nwould also bring sizable effects to the attractive and repulsive polaron\nstates.",
        "positive": "Synthetic Gauge Field with Highly Magnetic Lanthanide Atoms: We present a scheme for generating a synthetic magnetic field and spin-orbit\ncoupling via Raman coupling in highly magnetic lanthanide atoms such as\ndysprosium. Employing these atoms offer several advantages for realizing\nstrongly correlated states and exotic spinor phases. The large spin and narrow\noptical transitions of these atoms allow the generation of synthetic magnetic\nfields an order of magnitude larger than those in the alkalis, but with\nconsiderable reduction of the heating rate for equal Raman coupling. The\neffective hamiltonian of these systems differs from that of the alkalis' by an\nadditional nematic coupling term, which leads to a phase transition in the\ndressed states as detuning varies. For \\text{high-spin} condensates, spin-orbit\ncoupling leads to a spatially periodic structure, which is described in\nMajorana representation by a set of points moving periodically on a unit\nsphere. We name this a \"Majorana spinor helix\" in analogy to the persistent\nspin-1/2 helix observed in electronic systems."
    },
    {
        "anchor": "Resonant dipolar collisions of ultracold molecules induced by microwave\n  dressing: We demonstrate microwave dressing on ultracold, fermionic\n${}^{23}$Na${}^{40}$K ground-state molecules and observe resonant dipolar\ncollisions with cross sections exceeding three times the $s$-wave unitarity\nlimit. The origin of these collisions is the resonant alignment of the\napproaching molecules' dipoles along the intermolecular axis, which leads to\nstrong attraction. We explain our observations with a conceptually simple\ntwo-state picture based on the Condon approximation. Furthermore, we perform\ncoupled-channels calculations that agree well with the experimentally observed\ncollision rates. While collisions are observed here as laser-induced loss,\nmicrowave dressing on chemically stable molecules trapped in box potentials may\nenable the creation of strongly interacting dipolar gases of molecules.",
        "positive": "Tunneling-Induced Restoration of the Degeneracy and the Time-Reversal\n  Symmetry Breaking in Optical Lattices: We study the ground-state properties of bosons loaded into the $p$-band of a\none dimensional optical lattice. We show that the phase diagram of the system\nis substantially affected by the anharmonicity of the lattice potential. In\nparticular, for a certain range of tunneling strength, the full many-body\nground state of the system becomes degenerate. In this region, an additional\nsymmetry of the system, namely the parity of the occupation number of the\nchosen orbital, is spontaneously broken. The state with nonvanishing staggered\nangular momentum, which breaks the time-reversal symmetry, becomes the true\nground state of the system."
    },
    {
        "anchor": "Quantum tunneling of a vortex between two pinning potentials: A vortex can tunnel between two pinning potentials in an atomic Bose-Einstein\ncondensate on a time scale of the order of 1s under typical experimental\nconditions. This makes it possible to detect the tunneling experimentally. We\ncalculate the tunneling rate by phenomenologically treating vortices as\npoint-like charged particles moving in an inhomogeneous magnetic field. The\nobtained results are in close agreement with numerical simulations based on the\nstochastic c-field theory.",
        "positive": "Anisotropic collisions of dipolar Bose-Einstein condensates in the\n  universal regime: We report the measurement of collisions between two Bose-Einstein condensates\nwith strong dipolar interactions. The collision velocity is significantly\nlarger than the internal velocity distribution widths of the individual\ncondensates, and thus, with the condensates being sufficiently dilute, a halo\ncorresponding to the two-body differential scattering cross section is\nobserved. The results demonstrate a novel regime of quantum scattering,\nrelevant to dipolar interactions, in which a large number of angular momentum\nstates become coupled during the collision. We perform Monte-Carlo simulations\nto provide a detailed comparison between theoretical two-body cross sections\nand the experimental observations."
    },
    {
        "anchor": "On the survival of the quantum depletion of a condensate after release\n  from a magnetic trap: We present observations of the high momentum tail in expanding Bose-Einstein\ncondensates of metastable Helium atoms released from a harmonic trap. The\nfar-field density profile exhibits features that support identification of the\ntails of the momentum distribution as originating in the in-situ quantum\ndepletion prior to release. Thus, we corroborate recent observations of\nslowly-decaying tails in the far-field beyond the thermal component. This\nobservation is in conflict with the hydrodynamic theory, which predicts that\nthe in-situ depletion does not survive when atoms are released from a trap.\nIndeed, the depleted tails even appear stronger in the far-field than expected\nbefore release, and we discuss the challenges of interpreting this in terms of\nthe Tan contact in the trapped gas. In complement to these observations, full\nquantum simulations of the experiment show that, under the right conditions,\nthe depletion can persist into the far field after expansion. Moreover, the\nsimulations provide mechanisms for survival and for the the large-momentum\ntails to appear stronger after expansion due to an acceleration of the depleted\natoms by the mean-field potential. However, while in qualitative agreement, the\nfinal depletion observed in the experiment is much larger than in the\nsimulation.",
        "positive": "Comment on \"Feshbach-Einstein Condensates\" by V. G. Rousseau and P. J.\n  H. Denteneer: In a recent paper (Phys. Rev. Lett. 102, 015301 (2009), arXiv:0810.3763)\nRousseau and Denteneer claim that an unconventional \"super-Mott\" (SM) phase is\nrealized by bosons trapped in an optical lattice close to a Feshbach resonance\nwith a molecular state. The supposed SM phase, observed via quantum Monte Carlo\n(QMC) simulations of an atom-molecule Bose-Hubbard model, is an incompressible\nphase developing spontaneous atomic/molecular supercurrents which are perfectly\nanticorrelated. Here we show that the identification of this phase is based on\na misinterpretation of the estimators of superfluidity in QMC, which break down\nin the presence of coherent atom/molecule conversion. Our conclusion is that\nthe supposed SM phase is in fact a fully normal insulator."
    },
    {
        "anchor": "Scheme to Equilibrate the Quantized Hall Response of Topological Systems\n  from Coherent Dynamics: Two-dimensional topologically distinct insulators are separated by\ntopological gapless points, which exist as Weyl points in three-dimensional\nmomentum space. Slowly varying parameters in the two-dimensional Hamiltonian\nacross two distinct phases therefore necessarily experiences the gap closing\nprocess, which prevents the intrinsic physical observable, the Hall response,\nfrom equilibrating. To equilibrate the Hall response, engineered laser noises\nwere introduced at the price of destroying the quantum coherence. Here we\ndemonstrate a new scheme to equilibrate the quantized Hall response from pure\ncoherent dynamics as the Hamiltonian is slowly tuned from the topologically\ntrivial to nontrivial regimes. We show the elements that affect the process of\nequilibration including the sequence when the electric field is switched on,\nits strength and the band dispersion of the final Hamiltonian. We further apply\nour method to Weyl semimetals in three dimensions and find the equilibrated\nHall response despite the underlying gapless band structure. Our finding not\nonly lays the theoretical foundation for observing the two-dimensional\ntopological phase transition but also for observing and controlling Weyl\nsemimetals in ultracold atomic gases.",
        "positive": "Two-mode Dicke model from non-degenerate polarization modes: We realize a non-degenerate two-mode Dicke model with competing interactions\nin a Bose-Einstein condensate (BEC) coupled to two orthogonal polarization\nmodes of a single optical cavity. The BEC is coupled to the cavity modes via\nthe scalar and vectorial part of the atomic polarizability. We can\nindependently change these couplings and determine their effect on a\nself-organization phase transition. Measuring the phases of the system, we\ncharacterize a crossover from a single-mode to a two-mode Dicke model. This\nwork provides perspectives for the realization of coupled phases of spin and\ndensity."
    },
    {
        "anchor": "Universal shock-wave propagation in one-dimensional Bose fluids: We propose a protocol for creating moving, robust dispersive shock waves in\ninteracting one-dimensional Bose fluids. The fluid is prepared in a moving\nstate by phase imprinting and sent against the walls of a box trap. We\ndemonstrate that the thus formed shock wave oscillates for several periods and\nis robust against thermal fluctuations. We show that this large amplitude\ndynamics is universal across the whole spectrum of the interatomic interaction\nstrength, from weak to strong interactions, and it is fully controlled by the\nsound velocity inside the fluid. Our work provides a generalization of the\ndispersive-shock-wave paradigm to the many-body regime. The shock waves we\npropose are within reach for ultracold atom experiments.",
        "positive": "How to measure the free energy and partition function from atom-atom\n  correlations: We propose an experimental approach for determining thermodynamic properties\nof ultracold atomic gases with short-range interactions. As a test case, we\nfocus on the one-dimensional (1D) Bose gas described by the integrable\nLieb-Liniger model. The proposed approach relies on deducing the Helmholtz or\nLandau free energy directly from measurements of local atom-atom correlations\nby utilising the inversion of a finite-temperature version of the\nHellmann-Feynman theorem. We demonstrate this approach theoretically by\nderiving approximate analytic expressions for the free energies in specific\nasymptotic regimes of the 1D Bose gas and find excellent agreement with the\nexact results based on the thermodynamic Bethe ansatz available for this\nintegrable model."
    },
    {
        "anchor": "Interaction Spectroscopy of a Two-component Mott Insulator: We prepare and study a two-component Mott insulator of bosonic atoms with two\nparticles per site. The mapping of this system to a magnetic spin model, and\nthe subsequent study of its quantum phases, require a detailed knowledge of the\ninteraction strengths of the two components. In this work, we use radio\nfrequency (RF) transitions and an on-site interaction blockade for precise,\nempirical determination of the interaction strengths of different combinations\nof hyperfine states on a single lattice site. We create a map of the\ninteractions of the lowest two hyperfine states of $^7$Li as a function of\nmagnetic field, including measurements of several Feshbach resonances with\nunprecedented sensitivity, and we identify promising regions for the\nrealization of magnetic spin models.",
        "positive": "Three-phonon and four-phonon interaction processes in a pair-condensed\n  Fermi gas: We study the interactions among phonons and the phonon lifetime in a\npair-condensed Fermi gas in the BEC-BCS crossover in the collisionless regime.\nTo compute the phonon-phonon coupling amplitudes we use a microscopic model\nbased on a generalized BCS Ansatz including moving pairs, which allows for a\nsystematic expansion around the mean field BCS approximation of the ground\nstate. We show that the quantum hydrodynamic expression of the amplitudes\nobtained by Landau and Khalatnikov apply only on the energy shell, that is for\nresonant processes that conserve energy. The microscopic model yields the same\nexcitation spectrum as the Random Phase Approximation, with a linear (phononic)\nstart and a concavity at low wave number that changes from upwards to downwards\nin the BEC-BCS crossover. When the concavity of the dispersion relation is\nupwards at low wave number, the leading damping mechanism at low temperature is\nthe Beliaev-Landau process 2 phonons $\\leftrightarrow$ 1 phonon while, when the\nconcavity is downwards, it is the Landau-Khalatnikov process 2 phonons\n$\\leftrightarrow$ 2 phonons. In both cases, by rescaling the wave vectors to\nabsorb the dependence on the interaction strength, we obtain a universal\nformula for the damping rate. This universal formula corrects and extends the\noriginal analytic results of Landau and Khalatnikov [ZhETF {\\bf 19}, 637\n(1949)] for the $2\\leftrightarrow2$ processes in the downward concavity case.\nIn the upward concavity case, for the Beliaev 1$\\leftrightarrow$ 2 process for\nthe unitary gas at zero temperature, we calculate the damping rate of an\nexcitation with wave number $q$ including the first correction proportional to\n$q^7$ to the $q^5$ hydrodynamic prediction, which was never done before in a\nsystematic way."
    },
    {
        "anchor": "Direct observation of hydrodynamization and local prethermalization: Hydrodynamics accurately describes relativistic heavy-ion collision\nexperiments well before local thermal equilibrium is established. This\nunexpectedly rapid onset of hydrodynamics -- which takes place on the fastest\navailable timescale -- is called hydrodynamization. It occurs when an\ninteracting quantum system is quenched with an energy density that is much\ngreater than its initial energy density. During hydrodynamization, energy gets\nredistributed across very different energy scales. Hydrodynamization precedes\nlocal equilibration among momentum modes, which is local prethermalization to a\ngeneralized Gibbs ensemble in nearly integrable systems or local thermalization\nin non-integrable systems. Many theories of quantum dynamics postulate local\n(pre)thermalization, but the associated timescale has not been quantitatively\nstudied. Here we use an array of 1D Bose gases to directly observe both\nhydrodynamization and local prethermalization. After we apply a Bragg\nscattering pulse, hydrodynamization is evident in the fast redistribution of\nenergy among distant momentum modes, which occurs on timescales associated with\nthe Bragg peak energies. Local prethermalization can be seen in the slower\nredistribution of occupation among nearby momentum modes. We find that the time\nscale for local prethermalization in our system is inversely proportional to\nthe momenta involved. During hydrodynamization and local prethermalization,\nexisting theories cannot quantitatively model our experiment. Exact theoretical\ncalculations in the Tonks-Girardeau limit show qualitatively similar features.",
        "positive": "Strongly interacting one-dimensional bosons in arbitrary-strength\n  optical lattices: from Bose-Hubbard to sine-Gordon and beyond: We analyze interacting one-dimensional bosons in the continuum, subject to a\nperiodic sinusoidal potential of arbitrary depth. Variation of the lattice\ndepth tunes the system from the Bose-Hubbard limit for deep lattices, through\nthe sine-Gordon regime of weak lattices, to the complete absence of a lattice.\nUsing the Bose-Fermi mapping between strongly interacting bosons and weakly\ninteracting fermions, we derive the phase diagram in the parameter space of\nlattice depth and chemical potential. This extends previous knowledge from\ntight-binding (Bose-Hubbard) studies in a new direction which is important\nbecause the lattice depth is a readily adjustable experimental parameter.\nSeveral other results (equations of state, energy gaps, profiles in harmonic\ntrap) are presented as corollaries to the physics contained in this phase\ndiagram. Generically, both incompressible (gapped) and compressible phases\ncoexist in a trap; this has implications for experimental measurements."
    },
    {
        "anchor": "Floquet realization and signatures of one-dimensional anyons in an\n  optical lattice: We propose a simple scheme for realizing the physics of 1D anyons with\nultracold bosonic atoms in an optical lattice. It relies on\nlattice-shaking-induced resonant tunneling against potential off-sets created\nby a combination of a lattice tilt and strong on-site interactions. No lasers\nadditional to those used for the creation of the optical lattice are required.\nWe also discuss experimental signatures of the continuous interpolation between\nbosons and fermions when the statistical angle $\\theta$ is varied from 0 to\n$\\pi$. Since the anyonic momentum distribution is not measurable in the bosonic\nrepresentation of the anyon model, we propose to use Friedel oscillations in\nsmall systems as an alternative probe.",
        "positive": "Mean-field dynamics of a Bose-Hubbard chain coupled to a non-Markovian\n  environment: We study the dynamics of an interacting Bose-Hubbard chain coupled to a\nnon-Markovian environment. Our basic tool is the reduced generating functional\nexpressed as a path integral over spin-coherent states. We calculate the\nleading contribution to the corresponding effective action, and by minimizing\nit, we derive mean-field equations that can be numerically solved. With this\ntool at hand, we examine the influence of the system's initial conditions and\ninterparticle interactions on the dissipative dynamics. Moreover, we\ninvestigate the presence of memory effects due to the non-Markovian\nenvironment."
    },
    {
        "anchor": "Free Expansion of a Weakly-interacting Dipolar Fermi Gas: We theoretically investigate a polarized dipolar Fermi gas in free expansion.\nThe inter-particle dipolar interaction deforms phase-space distribution in trap\nand also in the expansion. We exactly predict the minimal quadrupole\ndeformation in the expansion for the high-temperature Maxwell-Boltzmann and\nzero-temperature Thomas-Fermi gases in the Hartree-Fock and Landau-Vlasov\napproaches. In conclusion, we provide a proper approach to develop the\ntime-of-flight method for the weakly-interacting dipolar Fermi gas and also\nreveal a scaling law associated with the Liouville's theorem in the long-time\nbehaviors of the both gases.",
        "positive": "Two super Tonks-Girardeau states of a trapped 1D spinor Fermi gas: A harmonically trapped ultracold 1D spinor Fermi gas with a strongly\nattractive 1D even-wave interaction induced by a 3D Feshbach resonance is\nstudied. It is shown that it has two different super Tonks-Girardeau (sTG)\nenergy eigenstates which are metastable against collapse in spite of the strong\nattraction, due to their close connection with 1D hard sphere Bose gases which\nare highly excited gas-like states. One of these sTG states is a hybrid between\nan sTG gas with strong $(\\uparrow\\downarrow$ attractions and an ideal Fermi gas\nwith no $(\\uparrow\\uparrow)$ or $(\\downarrow\\downarrow)$ interactions, the sTG\ncomponent being an exact analog of the recently observed sTG state of a 1D\nultracold Bose gas. It should be possible to create it experimentally by a\nsudden switch of the $(\\uparrow\\downarrow)$ interaction from strongly repulsive\nto strongly attractive, as in the recent Innsbruck experiment on the bosonic\nsTG gas. The other is a trapped analog of a recently predicted sTG state which\nis an ultracold gas of strongly bound $(\\uparrow\\downarrow)$ fermion dimers\nwhich behave as bosons with a strongly attractive boson-boson interaction\nleading to sTG behavior. It is proved that the probability of a transition from\nthe ground state for strongly repulsive interaction to this dimer state under a\nsudden switch from strongly repulsive to strongly attractive interaction is\n$\\ll 1$, contrary to a previous suggestion."
    },
    {
        "anchor": "Supercurrent in a room temperature Bose-Einstein magnon condensate: We report evidence for the existence of a supercurrent of magnons in a magnon\nBose-Einstein condensate prepared in a room temperature yttrium-iron-garnet\nmagnetic film and subject to a thermal gradient. The magnon condensate is\nformed in a parametrically populated magnon gas, and its temporal evolution is\nstudied by time-, frequency- and wavector-resolved Brillouin light scattering\nspectroscopy. It has been found that local heating in the focal point of a\nprobing laser beam enhances the temporal decrease in the density of the freely\nevolving magnon condensate after the termination of the pumping pulse, but it\ndoes not alter the relaxation dynamics of the gaseous magnon phase. This\nphenomenon is understood as the appearance of a magnon supercurrent within the\ncondensate due to a temperature- and, consequently, magnetisation-gradient\ninduced phase gradient in the condensate wave function.",
        "positive": "Large Chern Number Topological Superfluids in Coupled Layer System: We investigate the topological phase transition with large Chern number in a\ncoupled layer system. The topological transitions between different topological\nsuperfluids can be realized by controlling the binding energy, interlay\ntunneling and layer asymmetry {\\it etc}. These topological phase transitions\ncan be characterized by energy gap closing and reopening at the critical points\nat zero momentum, where the Pfaffian and Chern number undergo a discontinuous\nchange. The bulk-edge correspondence ensures that the number of edge modes\nexactly equals the Chern number. However all these edge modes localized at the\nsame edge have the same chirality and propagate along the same direction. These\ntopological phases can be detected by spin texture at or near zero momentum,\nwhich changes discontinuously across the phase transition point due to band\ninversion. This model can be easily generalized to multilayer system in which\nthe Chern number equals any positive integer --- similar to that in integer\nquantum Hall effect --- can be realized. This work paves a new way in the\nrealization of topological superfluids with large Chern number."
    },
    {
        "anchor": "Excitations of a vortex line in an elongated dipolar condensate: We characterise the properties of a vortex line in an elongated dipolar\nBose-Einstein condensate. Increasing the strength of the dipole-dipole\ninteractions (DDIs) relative to the short ranged contact interactions we find\nthat the system crosses over to a self-bound vortex droplet stabilized from\ncollapse by quantum fluctuations. We calculate the quasiparticle excitation\nspectrum of the vortex state, which is important in characterizing the vortex\nresponse, and assessing its stability. When the DDIs are sufficiently strong we\nfind that the vortex is dynamically unstable to quadrupolar modes.",
        "positive": "Condensation dynamics in a quantum-quenched Bose gas: By quenching the strength of interactions in a partially condensed Bose gas\nwe create a \"super-saturated\" vapor which has more thermal atoms than it can\ncontain in equilibrium. Subsequently, the number of condensed atoms ($N_0$)\ngrows even though the temperature ($T$) rises and the total atom number decays.\nWe show that the non-equilibrium evolution of the system is isoenergetic and\nfor small initial $N_0$ observe a clear separation between $T$ and $N_0$\ndynamics, thus explicitly demonstrating the theoretically expected \"two-step\"\npicture of condensate growth. For increasing initial $N_0$ values we observe a\ncrossover to classical relaxation dynamics. The size of the observed\nquench-induced effects can be explained using a simple equation of state for an\ninteracting harmonically-trapped atomic gas."
    },
    {
        "anchor": "Excited states of two-dimensional solitons supported by the spin-orbit\n  coupling and field-induced dipole-dipole repulsion: It was recently found that excited states of semi-vortex and mixed-mode\nsolitons are unstable in spin-orbit-coupled Bose-Einstein condensates (BECs)\nwith contact interactions. We demonstrate a possibility to stabilize such\nexcited states in a setting based on repulsive dipole-dipole interactions\ninduced by a polarizing field, oriented perpendicular to the plane in which the\ndipolar BEC is trapped. The strength of the field is assumed to grow in the\nradial direction $\\sim $ $r^{4}$. Excited states of semi-vortex solitons have\nvorticities $S$ and $S+1$ in their two components, each being an eigenstate of\nthe angular momentum. They are fully stable up to $S=5$. Excited state of\nmixed-mode solitons feature interweaving necklace structures with opposite\nfractional values of the angular momentum in the two components. They are\nstable if they are built of dominant angular harmonics $\\pm S$, with $S\\leq 4$.\nCharacteristics and stability of these two types of previously unknown\nhigher-order solitons are systematically analyzed. Their characteristic size is\n$\\sim 10$ $\\mathrm{\\mu }$m, with the number of atoms $\\lesssim 10^{5}$",
        "positive": "Gap Solitons and Bloch Waves in Nonlinear Periodic Systems: We comprehensively investigate gap solitons and Bloch waves in\none-dimensional nonlinear periodic systems. Our results show that there exists\na composition relation between them: Bloch waves at either the center or edge\nof the Brillouin zone are infinite chains composed of fundamental gap\nsolitons(FGSs). We argue that such a relation is related to the exact relation\nbetween nonlinear Bloch waves and nonlinear Wannier functions. With this\ncomposition relation, many conclusions can be drawn for gap solitons without\nany computation. For example, for the defocusing nonlinearity, there are $n$\nfamilies of FGS in the $n$th linear Bloch band gap; for the focusing case,\nthere are infinite number of families of FGSs in the semi-infinite gap and\nother gaps. In addition, the stability of gap solitons is analyzed. In\nliterature there are numerical results showing that some FGSs have cutoffs on\npropagation constant (or chemical potential), i.e. these FGSs do not exist for\nall values of propagation constant (or chemical potential) in the linear band\ngap. We offer an explanation for this cutoff."
    },
    {
        "anchor": "Dynamics of Phase Coherence Onset in Bose Condensates of Photons by\n  Incoherent Phonon Emission: Recent experiments with photons equilibrating inside a dye medium in a cavity\nhave raised the question of whether Bose condensation can occur in a system\nwith only incoherent interaction with phonons in a bath but without\nparticle-particle interaction. Analytical calculations analogous to those done\nfor a system with particle-particle interactions indicate that a system of\nbosons interacting only with incoherent phonons can indeed undergo Bose\ncondensation and furthermore can exhibit spontaneous amplification of quantum\ncoherence. We review the basic theory for these calculations.",
        "positive": "Coarsening and thermalisation properties of a quenched ferromagnetic\n  spin-1 condensate: We examine the dynamics of a quasi-two-dimensional spin-1 condensate in which\nthe quadratic Zeeman energy q is suddenly quenched to a value where the system\nhas a ferromagnetic ground state. There are two distinct types of ferromagnetic\nphases, i.e. a range of q values where the magnetization prefers to be in the\ndirection of the external field (easy-axis), and a range of q values where it\nprefers to be transverse to the field (easy-plane). We study the quench\ndynamics for a variety of q values and show that there is a single dynamical\ncritical exponent to characterize the scale invariant domain growth for each\nferromagnetic phase. For both quenches we give simple analytic models that\ncapture the essential scale invariant dynamics, and correctly predict the\nexponents. Because the order parameter for each phase is different, the natures\nof the domains and the relevant topological defects in each type of coarsening\nis also different. To explore these differences we characterize the fractal\ndimension of the domain walls, and the relationship of polar-core spin vortices\nto the domains in the easy-plane phase. Finally, we consider how the energy\nliberated from the quench thermalizes in the easy-axis quench. We show that\nlocal equilibrium is established in the spin waves on moderate time scales, but\ncontinues to evolve as the domains anneal."
    },
    {
        "anchor": "Realizing limit cycles in dissipative bosonic systems: We propose a general mechanism for generating limit cycle (LC) oscillations\nby coupling a linear bosonic mode to a dissipative nonlinear bosonic mode. By\nanalyzing the stability matrix, we show that LCs arise due to a supercritical\nHopf bifurcation. We find that the existence of LCs is independent of the sign\nof the effective nonlinear interaction. The LC phase can be classified as a\ncontinuous time crystal (CTC), if it emerges in a many-body system. The bosonic\nmodel can be realised in three-level systems interacting with a quantised light\nmode as realised in atom-cavity systems. Using such a platform, we\nexperimentally observe LCs for the first time in an atom-cavity system with\nattractive optical pump lattice, thereby confirming our theoretical\npredictions.",
        "positive": "Observation of microscopic confinement dynamics by a tunable topological\n  $\u03b8$-angle: The topological $\\theta$-angle is central to the understanding of a plethora\nof phenomena in condensed matter and high-energy physics such as the strong CP\nproblem, dynamical quantum topological phase transitions, and the\nconfinement--deconfinement transition. Difficulties arise when probing the\neffects of the topological $\\theta$-angle using classical methods, in\nparticular through the appearance of a sign problem in numerical simulations.\nQuantum simulators offer a powerful alternate venue for realizing the\n$\\theta$-angle, which has hitherto remained an outstanding challenge due to the\ndifficulty of introducing a dynamical electric field in the experiment. Here,\nwe report on the experimental realization of a tunable topological\n$\\theta$-angle in a Bose--Hubbard gauge-theory quantum simulator, implemented\nthrough a tilted superlattice potential that induces an effective background\nelectric field. We demonstrate the rich physics due to this angle by the direct\nobservation of the confinement--deconfinement transition of $(1+1)$-dimensional\nquantum electrodynamics. Using an atomic-precision quantum gas microscope, we\ndistinguish between the confined and deconfined phases by monitoring the\nreal-time evolution of particle--antiparticle pairs, which exhibit constrained\n(ballistic) propagation for a finite (vanishing) deviation of the\n$\\theta$-angle from $\\pi$. Our work provides a major step forward in the\nrealization of topological terms on modern quantum simulators, and the\nexploration of rich physics they have been theorized to entail."
    },
    {
        "anchor": "Topological two-body bands in a multiband Hubbard model: In a multiband Hubbard model the self-consistency relations for the two-body\nbound-state bands are in the form of a nonlinear eigenvalue problem. Assuming\nthat the resultant eigenvectors form an orthonormal set, e.g., in the\nstrong-binding regime, here we reformulate their Berry curvatures and the\nassociated Chern numbers. As an illustration we solve the two-body problem in a\nHaldane-Hubbard model with attractive onsite interactions, and analyze its\ntopological phase diagrams from weak to strong couplings, i.e., by keeping\ntrack of the gap closings in between the low-lying two-body bands. The\nresultant Chern numbers are consistent with the lobe structure of the phase\ndiagrams in the strong-coupling regime.",
        "positive": "New theoretical approaches to Bose polarons: The Fr\\\"ohlich polaron model describes a ubiquitous class of problems\nconcerned with understanding properties of a single mobile particle interacting\nwith a bosonic reservoir. Originally introduced in the context of electrons\ninteracting with phonons in crystals, this model found applications in such\ndiverse areas as strongly correlated electron systems, quantum information, and\nhigh energy physics. In the last few years this model has been applied to\ndescribe impurity atoms immersed in Bose-Einstein condensates of ultracold\natoms. The tunability of microscopic parameters in ensembles of ultracold atoms\nand the rich experimental toolbox of atomic physics should allow to test many\ntheoretical predictions and give us new insights into equilibrium and dynamical\nproperties of polarons. In these lecture notes we provide an overview of common\ntheoretical approaches that have been used to study BEC polarons, including\nRayleigh-Schr\\\"odinger and Green's function perturbation theories,\nself-consistent Born approximation, mean-field approach, Feynman's variational\npath integral approach, Monte Carlo simulations, renormalization group\ncalculations, and Gaussian variational ansatz. We focus on the renormalization\ngroup approach and provide details of analysis that have not been presented in\nearlier publications. We show that this method helps to resolve striking\ndiscrepancy in polaron energies obtained using mean-field approximation and\nMonte Carlo simulations. We also discuss applications of this method to the\ncalculation of the effective mass of BEC polarons. As one experimentally\nrelevant example of a non-equililbrium problem we consider Bloch oscillations\nof Bose polarons and demonstrate that one should find considerable deviations\nfrom the commonly accepted phenomenological Esaki-Tsu model. We review which\nparameter regimes of Bose polarons can be achieved in various atomic mixtures."
    },
    {
        "anchor": "Density correlations from analogue Hawking radiation in the presence of\n  atom losses: The sonic analogue of Hawking radiation can now be experimentally recreated\nin Bose-Einstein Condensates that contain an acoustic black hole. In these\nexperiments the signal strength and analogue Hawking temperature increase for\ndenser condensates, which however also suffer increased atom losses from\ninelastic collisions. To determine how these affect analogue Hawking radiation,\nwe numerically simulate creation of the latter in a Bose-Einstein Condensate in\nthe presence of atomic losses. In particular we explore modifications of\ndensity-density correlations through which the radiation has been analyzed so\nfar. We find that losses increase the contrast of the correlation signal, which\nwe attribute to heating that in turn leads to a component of stimulated\nradiation in addition to the spontaneous one. Another indirect consequence is\nthe modification of the white hole instability pattern.",
        "positive": "Coherence measurements of polaritons in thermal equilibrium reveal a new\n  power law for two-dimensional condensates: We have created a spatially homogeneous polariton condensate in thermal\nequilibrium, up to very high condensate fraction. Under these conditions, we\nhave measured the coherence as a function of momentum, and determined the total\ncoherent fraction of this boson system from very low density up to density well\nabove the condensation transition. These measurements reveal a consistent power\nlaw for the coherent fraction as a function total density over nearly three\norders of its magnitude. The same power law is seen in numerical simulations\nsolving the two-dimensional Gross-Pitaevskii equation for the equilibrium\ncoherence. This power law has not been predicted by prior analytical theories."
    },
    {
        "anchor": "Singlet Pathway to the Ground State of Ultracold Polar Molecules: Starting from weakly bound Feshbach molecules, we demonstrate a two-photon\npathway to the dipolar ground state of bi-alkali molecules that involves only\nsinglet-to-singlet optical transitions. This pathway eliminates the search for\na suitable intermediate state with sufficient singlet-triplet mixing and the\nexploration of its hyperfine structure, as is typical for pathways starting\nfrom triplet dominated Feshbach molecules. By selecting a Feshbach state with a\nstretched singlet hyperfine component and controlling the polarization of the\nexcitation laser, we assure coupling to only a single hyperfine component of\nthe $\\textrm{A}^{1}\\Sigma^{+}$ excited potential, even if the hyperfine\nstructure is not resolved. Similarly, we address a stretched hyperfine\ncomponent of the $\\textrm{X}^{1}\\Sigma^{+}$ rovibrational ground state, and\ntherefore an ideal three level system is established. We demonstrate this\npathway with ${}^{6}\\textrm{Li}{}^{40}\\textrm{K}$ molecules. By exploring\ndeeply bound states of the $\\textrm{A}^{1}\\Sigma^{+}$ potential, we are able to\nobtain large and balanced Rabi frequencies for both transitions. This method\ncan be applied to other molecular species.",
        "positive": "Long-time nonlinear dynamical evolution for P-band ultracold atoms in an\n  optical lattice: We report the long-time nonlinear dynamical evolution of ultracold atomic\ngases in the P-band of an optical lattice. A Bose-Einstein condensate (BEC) is\nfast and efficiently loaded into the Pband at zero quasi-momentum with a\nnon-adiabatic shortcut method. For the first one and half milliseconds, these\nmomentum states undergo oscillations due to coherent superposition of different\nbands, which are followed by oscillations up to 60ms of a much longer period.\nOur analysis shows the dephasing from the nonlinear interaction is very\nconducive to the long-period oscillations induced by the variable force due to\nthe harmonic confinement."
    },
    {
        "anchor": "Spontaneous symmetry breaking in rotating condensates of ultracold atoms: We describe an equilibrium state of a rotating trapped atomic condensate,\nwhich is characterized by a non-zero internal circulation and spontaneous\nbreaking of the rotational O(2) symmetry with all three major semiaxes of the\ncondensate having different values. The macroscopic rotation of the condensate\nis supported by a mesh of quantized vortices, whose number density is a\nfunction of internal circulation. The oscillation modes of this state are\ncomputed and the Goldstone mode associated with the loss of the symmetry is\nidentified. The possible avenues for experimental identification this state are\ndiscussed.",
        "positive": "Integrated Mach-Zehnder interferometer for Bose-Einstein condensates: Particle-wave duality enables the construction of interferometers for matter\nwaves, which complement optical interferometers in precision measurement\ndevices. This requires the development of atom-optics analogs to beam\nsplitters, phase shifters, and recombiners. Integrating these elements into a\nsingle device has been a long-standing goal. Here we demonstrate a full\nMach-Zehnder sequence with trapped Bose-Einstein condensates (BECs) confined on\nan atom chip. Particle interactions in our BEC matter waves lead to a\nnon-linearity, absent in photon optics. We exploit it to generate a\nnon-classical state having reduced number fluctuations inside the\ninterferometer. Making use of spatially separated wave packets, a controlled\nphase shift is applied and read out by a non-adiabatic matter-wave recombiner.\nWe demonstrate coherence times a factor of three beyond what is expected for\ncoherent states, highlighting the potential of entanglement as a resource for\nmetrology. Our results pave the way for integrated quantum-enhanced matter-wave\nsensors."
    },
    {
        "anchor": "Phases and dynamics of ultracold bosons in a tilted optical lattice: We present a brief overview of the phases and dynamics of ultracold bosons in\nan optical lattice in the presence of a tilt. We begin with a brief summary of\nthe possible experimental setup for generating the tilt. This is followed by a\ndiscussion of the effective low-energy model for these systems and its\nequilibrium phases. We also chart the relation of this model to the recently\nstudied system of ultracold Rydberg atoms. Next, we discuss the non-equilibrium\ndynamics of this model for quench, ramp and periodic protocols with emphasis on\nthe periodic drive which can be understood in terms of an analytic, albeit\nperturbative, Floquet Hamiltonian derived using Floquet perturbation theory\n(FPT). Finally, taking cue from the Floquet Hamiltonian of the periodically\ndriven tilted boson chain, we discuss a spin model which exhibits Hilbert space\nfragmentation and exact dynamical freezing for wide range of initial states.",
        "positive": "Temperature dependence of the contact in a unitary Fermi gas: The contact ${\\cal I}$, introduced by Tan, has emerged as a key parameter\ncharacterizing universal properties of strongly interacting Fermi gases. For\nultracold Fermi gases near a Feshbach resonance, the contact depends upon two\nquantities: the interaction parameter $1/(k_F a)$, where $k_F$ is the Fermi\nwave-vector and $a$ is the $s$-wave scattering length, and the temperature\n$T/T_F$, where $T_F$ is the Fermi temperature. We present the first\nmeasurements of the temperature dependence of the contact in a unitary Fermi\ngas using Bragg spectroscopy. The contact is seen to follow the predicted decay\nwith temperature and shows how pair-correlations at high momentum persist well\nabove the superfluid transition temperature."
    },
    {
        "anchor": "Quantum walk of two anyons across a statistical boundary: We model a quantum walk of identical particles that can change their exchange\nstatistics by hopping across a domain wall in a 1D lattice. Such a \"statistical\nboundary\" is transparent to single particles and affects the dynamics only by\nswapping multiple particles arriving together. We find that the two-particle\ninterference is dramatically altered by reflections of these bunched waves at\nthe interface, producing strong measurable asymmetries. Depending on the phases\non the two sides, a bunched wavepacket can get completely reflected or split\ninto a superposition of a reflected wave and an antibunched wave. This leads to\nstriking dynamics with two domain walls, where bunched waves can get trapped in\nbetween or fragment into multiple correlated single-particle wavepackets. These\nfindings can be realized with density-dependent hopping in present-day atomic\nsetups and open up a new paradigm of intrinsically many-body phenomena at\nstatistical boundaries.",
        "positive": "Spin-orbit coupling driven superfluid states in optical lattices at zero\n  and finite temperatures: We investigate the quantum phase transitions of a two-dimensional\nBose-Hubbard model in the presence of a Rashba spin-orbit coupling with and\nwithout thermal fluctuations. The interplay of single-particle hopping,\nstrength of spin-orbit coupling, and interspin interaction leads to superfluid\nphases with distinct properties. With interspin interactions weaker than\nintraspin interactions, the spin-orbit coupling induces two finite-momentum\nsuperfluid phases. One of them is a phase-twisted superfluid that exists at low\nhopping strengths and reduces the domain of insulating phases. At comparatively\nhigher hopping strengths, there is a transition from the phase-twisted to a\nfinite momenta stripe superfluid. With interspin interactions stronger than the\nintraspin interactions, the system exhibits phase-twisted to ferromagnetic\nphase transition. At finite temperatures, the thermal fluctuations destroy the\nphase-twisted superfluidity and lead to a wide region of normal-fluid states.\nThese findings can be observed in recent quantum gas experiments with\nspin-orbit coupling in optical lattices."
    },
    {
        "anchor": "Bogoliubov excitations driven by thermal lattice phonons in a quantum\n  fluid of light: The elementary excitations in weakly interacting quantum fluids have a\nnon-trivial nature which is at the basis of defining quantum phenomena such as\nsuperfluidity. These excitations and the physics they lead to have been\nexplored in closed quantum systems at thermal equilibrium both theoretically\nwithin the celebrated Bogoliubov framework, and experimentally in quantum\nfluids of ultracold atoms. Over the past decade, the relevance of Bogoliubov\nexcitations has become essential to understand quantum fluids of interacting\nphotons. Their driven-dissipative character leads to distinct properties with\nrespect to their equilibrium counterparts. For instance, the condensate\ncoupling to the photonic vacuum environment leads to a non-zero generation rate\nof elementary excitations with many striking implications. In this work,\nconsidering that quantum fluids of light are often hosted in solid-state\nsystems, we show within a joint theory-experiment analysis that the vibrations\nof the crystal constitute another environment that the condensate is\nfundamentally coupled to. This coupling leads to a unique heat transfer\nmechanism, resulting in a large generation rate of elementary excitations in\ntypical experimental conditions, and to a fundamental non-zero contribution at\nvanishing temperatures. Our work provides a complete framework for\nsolid-embedded quantum fluids of light, which is invaluable in view of\nachieving a regime dominated by photon vacuum fluctuations.",
        "positive": "Computation of the asymptotic states of modulated open quantum systems\n  with a numerically exact realization of the quantum trajectory method: Quantum systems out of equilibrium are presently a subject of active\nresearch, both in theoretical and experimental domains. In this work we\nconsider time-periodically modulated quantum systems which are in contact with\na stationary environment. Within the framework of a quantum master equation,\nthe asymptotic states of such systems are described by time-periodic density\noperators. Resolution of these operators constitutes a non-trivial\ncomputational task. To go beyond the current size limits, we use the quantum\ntrajectory method which unravels master equation for the density operator into\na set of stochastic processes for wave functions. The asymptotic density matrix\nis calculated by performing a statistical sampling over the ensemble of quantum\ntrajectories, preceded by a long transient propagation. We follow the ideology\nof event-driven programming and construct a new algorithmic realization of the\nmethod. The algorithm is computationally efficient, allowing for long 'leaps'\nforward in time, and is numerically exact in the sense that, being given the\nlist of uniformly distributed (on the unit interval) random numbers, $\\{\\eta_1,\n\\eta_2,...,\\eta_n\\}$, one could propagate a quantum trajectory (with $\\eta_i$'s\nas norm thresholds) in a numerically exact way. %Since the quantum trajectory\nmethod falls into the class of standard sampling problems, performance of the\nalgorithm %can be substantially improved by implementing it on a computer\ncluster. By using a scalable $N$-particle quantum model, we demonstrate that\nthe algorithm allows us to resolve the asymptotic density operator of the model\nsystem with $N = 2000$ states on a regular-size computer cluster, thus reaching\nthe scale on which numerical studies of modulated Hamiltonian systems are\ncurrently performed."
    },
    {
        "anchor": "Quantum fluctuations of the center-of-mass and relative parameters of\n  NLS breathers: We study quantum fluctuations of macroscopic parameters of an NLS breathers,\ni.e., the second-order soliton solution of the nonlinear Schr\\\"odinger\nequation. Uncertainty relations for the parameters are derived and compared to\nsimilar relations for fundamental solitons. We compare two models for the state\nof the quantum field of fluctuations surrounding the classical field of the\nBose-Einstein condensate: a conventionally used, computationally convenient\n\"white noise\", and a correlated noise which assumes that the breather has been\ncreated from a fundamental soliton, by means of the application of the\nfactor-of-four quench of the nonlinearity strength. Theoretical methods used in\nthe work are well suited for a large number of particles, $N$. We thus confirm\nthe possibility of experimental observation of macroscopic quantum\nfluctuations, which is suggested by an extrapolation to large $N$ of recently\nreported low-$N$ Bethe-ansatz results [Phys. Rev. Lett. 119 220401 (2017)].",
        "positive": "Functional Determinant Approach Investigations of Heavy Impurity Physics: In this brief review, we report some new development in the functional\ndeterminant approach (FDA), an exact numerical method, in the studies of a\nheavy quantum impurity immersed in Fermi gases and manipulated with\nradio-frequency pulses. FDA has been successfully applied to investigate the\nuniversal dynamical responses of a heavy impurity in an ultracold ideal Fermi\ngas in both the time and frequency domain, which allows the exploration of the\nrenowned Anderson's orthogonality catastrophe (OC). In such a system, OC is\ninduced by the multiple particle-hole excitations of the Fermi sea, which is\nbeyond a simple perturbation picture and manifests itself as the absence of\nquasiparticles named polarons. More recently, two new directions for studying\nheavy impurity with FDA have been developed. One is to extend FDA to a strongly\ncorrelated background superfluid background, a Bardeen-Cooper-Schrieffer (BCS)\nsuperfluid. In this system, Anderson's orthogonality catastrophe is prohibited\ndue to the suppression of multiple particle-hole excitations by the superfluid\ngap, which leads to the existence of genuine polaron. The other direction is to\ngeneralize the FDA to the case of multiple RF pulses scheme, which extends the\nwell-established 1D Ramsey spectroscopy in ultracold atoms into\nmultidimensional, in the same spirit as the well-known multidimensional nuclear\nmagnetic resonance and optical multidimensional coherent spectroscopy.\nMultidimensional Ramsey spectroscopy allows us to investigate correlations\nbetween spectral peaks of an impurity-medium system that is not accessible in\nthe conventional one-dimensional spectrum."
    },
    {
        "anchor": "Projection operator approach to master equations for coarse grained\n  occupation numbers in non-ideal quantum gases: We aim at deriving an equation of motion for specific sums of momentum mode\noccupation numbers from models for electrons in periodic lattices experiencing\nelastic scattering, electron-phonon scattering or electron-electron scattering.\nThese sums correspond to \"grains\" in momentum space. This equation of motion is\nsupposed to involve only a moderate number of dynamical variables and/or\nexhibit a sufficiently simple structure such that neither its construction nor\nits analyzation/solution requires substantial numerical effort. To this we end\ncompute, by means of a projection operator technique, a linear(ized) collision\nterm which determines the dynamics of the above grain-sums. This collision term\nresults as non-singular, finite dimensional rate matrix and may thus be\ninverted regardless of any symmetry of the underlying model. This facilitates\ncalculations of, e.g., transport coefficients, as we demonstrate for a 3-dim.\nAnderson model featuring weak disorder.",
        "positive": "Periodic quenches across the Berezinskii-Kosterlitz-Thouless phase\n  transition: The quenched dynamics of an ultracold homogeneous atomic two-dimensional Bose\ngas subjected to periodic quenches across the Berezinskii-Kosterlitz-Thouless\n(BKT) phase transition are discussed. Specifically, we address the effect of\nperiodic cycling of the effective atomic interaction strength between a thermal\ndisordered state above, and a highly ordered state below the critical BKT\ninteraction strength, by means of numerical simulations of the stochastic\nprojected Gross-Pitaevskii equation. Probing the emerging dynamics as a\nfunction of the frequency of sinusoidal driving from low to high frequencies\nreveals diverse dynamical features, including phase-lagged quasi adiabatic\nreversible condensate formation, resonant excitation consistent with an\nintrinsic system relaxation timescale, and gradual establishment of\ndynamically-recurring or time-averaged non-equilibrium states with enhanced\ncoherence which are neither condensed, nor thermal. Our study paves the way for\nexperimental observation of such driven non-equilibrium ultracold superfluid\nstates."
    },
    {
        "anchor": "Dynamical quantum phase transitions in collapse and revival oscillations\n  of a quenched superfluid: In this work we revisit collapse and revival oscillations in superfluids\nsuddenly quenched by strong local interactions for the case of a\none-dimensional Bose-Hubbard model. As the main result we identify the inherent\nnonequilibrium quantum many-body character of these oscillations by revealing\nthat they are controlled by a sequence of underlying dynamical quantum phase\ntransitions in the real-time evolution after the quench, which manifest as\ntemporal nonanalyticities in return probabilities or Loschmidt echos.\nSpecifically, we find that the time scale of the collapse and revival\noscillations is, firstly, set by the frequency at which dynamical quantum phase\ntransitions appear, and is, secondly, of emergent nonequilibrium nature, since\nit is not only determined by the final Hamiltonian but also depends on the\ninitial condition.",
        "positive": "A phonon laser in ultra-cold matter: We show the possible excitation of a phonon laser instability in an\nultra-cold atomic gas confined in a magneto-optical trap. Such an effect\nresults from a negative Landau damping of the collective density perturbations\nin the gas, leading to the coherent emission of phonons. This laser instability\ncan be driven by a blue-detuned laser superimposed to the usual red-detuning\nlaser beams which usually provide the cooling mechanism. Threshold conditions,\ninstability growth rates and saturation levels are derived. This work\ngeneralizes, on theoretical grounds, the recent results obtained with single\nion phonon laser, to an ultra-cold atomic gas, where real phonons can be\nexcited. Future phonon lasers could thus adequately be called phasers."
    },
    {
        "anchor": "Crossover from weak to strong quench in a spinor Bose-Einstein\n  condensate: We investigate the early-time dynamics of a quasi-two-dimensional spin-1\nantiferromagnetic Bose-Einstein condensate after a sudden quench from the\neasy-plane to the easy-axis polar phase. The post-quench dynamics shows a\ncrossover behavior as the quench strength $\\tilde{q}$ is increased, where\n$\\tilde{q}$ is defined as the ratio of the initial excitation energy per\nparticle to the characteristic spin interaction energy. For a weak quench of\n$\\tilde{q}<1$, long-wavelength spin excitations are dominantly generated,\nleading to the formation of irregular spin domains. With increasing\n$\\tilde{q}$, the length scale of the initial spin excitations decreases, and we\ndemonstrate that the long-wavelength instability is strongly suppressed for\nhigh $\\tilde{q}>2$. The observed crossover behavior is found to be consistent\nwith the Bogoliubov description of the dynamic instability of the initial\nspinor condensate.",
        "positive": "Interferometric Measurements of Many-body Topological Invariants using\n  Mobile Impurities: Topological quantum phases cannot be characterized by Ginzburg-Landau type\norder parameters, and are instead described by non-local topological\ninvariants. Experimental platforms capable of realizing such exotic states now\ninclude \"synthetic\" many-body systems such as ultracold atoms or photons.\nUnique tools available in these systems enable a new characterization of\nstrongly correlated many-body states. Here we propose a general scheme for\ndetecting topological order using interferometric measurements of elementary\nexcitations. The key ingredient is the use of mobile impurities which bind to\nquasiparticles of a host many-body system. Specifically we show how fractional\ncharges can be probed in the bulk of fractional quantum Hall systems. We\ndemonstrate that combining Ramsey interference with Bloch oscillations can be\nused to measure Chern numbers of individual quasiparticles, which gives a\ndirect probe of their fractional charges. We discuss possible extensions of our\nmethod to other topological many-body systems, such as spin liquids."
    },
    {
        "anchor": "Benchmarks of Generalized Hydrodynamics for 1D Bose Gases: Generalized hydrodynamics (GHD) is a recent theoretical approach that is\nbecoming a go-to tool for characterizing out-of-equilibrium phenomena in\nintegrable and near-integrable quantum many-body systems. Here, we benchmark\nits performance against an array of alternative theoretical methods, for an\ninteracting one-dimensional Bose gas described by the Lieb-Liniger model. In\nparticular, we study the evolution of both a localized density bump and dip,\nalong with a quantum Newton's cradle setup, for various interaction strengths\nand initial equilibrium temperatures. We find that GHD generally performs very\nwell at sufficiently high temperatures or strong interactions. For low\ntemperatures and weak interactions, we highlight situations where GHD, while\nnot capturing interference phenomena on short lengthscales, can describe a\ncoarse-grained behaviour based on convolution averaging that mimics finite\nimaging resolution in ultracold atom experiments. In a quantum Newton's cradle\nsetup based on a double-well to single-well trap quench, we find that GHD with\ndiffusive corrections demonstrates excellent agreement with the predictions of\na classical field approach.",
        "positive": "A dark state of Chern bands: Designing flat bands with higher Chern\n  number: We introduce a scheme by which flat bands with higher Chern number $\\vert\nC\\vert>1$ can be designed in ultracold gases through a coherent manipulation of\nBloch bands. Inspired by quantum-optics methods, our approach consists in\ncreating a \"dark Bloch band\" by coupling a set of source bands through resonant\nprocesses. Considering a $\\Lambda$ system of three bands, the Chern number of\nthe dark band is found to follow a simple sum rule in terms of the Chern\nnumbers of the source bands: $C_D\\!=\\!C_1+C_2-C_3$. Altogether, our dark-state\nscheme realizes a nearly flat Bloch band with predictable and tunable Chern\nnumber $C_D$. We illustrate our method based on a $\\Lambda$ system, formed of\nthe bands of the Harper-Hofstadter model, which leads to a nearly flat Chern\nband with $C_D\\!=\\!2$. We explore a realistic sequence to load atoms into the\ndark Chern band, as well as a probing scheme based on Hall drift measurements.\nDark Chern bands offer a practical platform where exotic fractional quantum\nHall states could be realized in ultracold gases."
    },
    {
        "anchor": "Proposed Fermi-surface reservoir-engineering and application to\n  realizing unconventional Fermi superfluids: We theoretically propose an idea based on reservoir engineering to process\nthe structure of a Fermi edge to split into multiple Fermi edges, so as to be\nsuitable for the state which we want to realize. When one appropriately tunes\nthe chemical-potential difference between two reservoirs being coupled with the\nsystem, the system is shown to be in the non-equilibrium steady state with the\nmomentum distribution having a two-edge structure. We argue that these edges\nplay similar roles to two Fermi surfaces, which can be designed to realize\nexotic quantum many-body states. To demonstrate this, we consider a model\ndriven-dissipative two-component Fermi gas with an attractive interaction as a\nparadigmatic example and show that it exhibits an unconventional Fermi\nsuperfluid. While the superfluid order parameter of this state has the same\nform as that in the Fulde-Ferrell state discussed in metallic superconductivity\nunder an external magnetic field, the former non-equilibrium pairing state is\nnot accompanied by any spin imbalance. Our proposed reservoir engineering to\nprocess the Fermi momentum distribution would provide further possibilities of\nmany-body quantum phenomena beyond the thermal equilibrium case.",
        "positive": "The pseudogap regime in the unitary Fermi gas: We discuss the pseudogap regime in the cold atomic unitary Fermi gas, with a\nparticular emphasis on the auxiliary-field quantum Monte Carlo (AFMC) approach.\nWe discuss possible signatures of the pseudogap, review experimental results,\nand survey analytic and quantum Monte Carlo techniques before focusing on AFMC\ncalculations in the canonical ensemble. For the latter method, we discuss\nresults for the heat capacity, energy-staggering pairing gap, spin\nsusceptibility, and compare to experiment and other theoretical methods."
    },
    {
        "anchor": "Engineering phase and density of Bose-Einstein condensates in curved\n  waveguides with toroidal topology: We investigate the effects of ellipticity-induced curvature on atomic\nBose-Einstein condensates confined in quasi-one-dimensional closed-loop\nwaveguides. Our theoretical study reveals intriguing phenomena arising from the\ninterplay between curvature and interactions. Density modulations are observed\nin regions of high curvature, but these modulations are suppressed by strong\nrepulsive interactions. Additionally, we observe phase accumulation in regions\nwith the lowest curvature when the waveguide with persistent current is\nsqueezed. Furthermore, waveguides hosting persistent currents exhibit dynamic\ntransformations between states with different angular momenta. These findings\nprovide insights into the behavior of atomic condensates in curved waveguides,\nwith implications for fundamental physics and quantum technologies. The\ninterplay between curvature and interactions offers opportunities for exploring\nnovel quantum phenomena and engineering quantum states in confined geometries.",
        "positive": "Quantum dynamics of Bose-Einstein condensates in tilted and driven\n  bichromatic optical lattices: We study the dynamics of Bose-Einstein condensates in tilted and driven\noptical superlattices. For a bichromatic lattice, each Bloch band split up into\ntwo minibands such that the dynamics is governed by the interplay of Bloch\noscillations and transitions between the bands. Thus, bichromatic potentials\nprovide an excellent model system for the study of nonlinear Landau-Zener\ntunneling and allow for a variety of applications in matter wave interferometry\nand quantum metrology. In the present paper we investigate the coherent\ndynamics of an interacting Bose-Einstein condensate as well as its stability.\nDifferent mechanisms of instability are discussed, which lead to a rapid\ndepletion of the condensate."
    },
    {
        "anchor": "Directed motion of doublons and holes in periodically driven Mott\n  insulators: Periodically driven systems can lead to a directed motion of particles. We\ninvestigate this ratchet effect for a bosonic Mott insulator where both a\nstaggered hopping and a staggered local potential vary periodically in time. If\ndriving frequencies are smaller than the interaction strength and the density\nof excitations is small, one obtains effectively a one-particle quantum ratchet\ndescribing the motion of doubly occupied sites (doublons) and empty sites\n(holes). Such a simple quantum machine can be used to manipulate the\nexcitations of the Mott insulator. For suitably chosen parameters, for example,\nholes and doublons move in opposite direction. To investigate whether the\nperiodic driving can be used to move particles \"uphill\", i.e., against an\nexternal force, we study the influence of a linear potential $- g x$. For long\ntimes, transport is only possible when the driving frequency $\\omega$ and the\nexternal force $g$ are commensurate, $n_0 g = m_0 \\omega$, with\n$\\frac{n_0}{2},m_0 \\in \\mathbb{Z}$.",
        "positive": "Excitation spectrum of a toroidal spin-1 Bose-Einstein condensate: We calculate analytically the Bogoliubov excitation spectrum of a toroidal\nspin-1 Bose-Einstein condensate that is subjected to a homogeneous magnetic\nfield and contains vortices with arbitrary winding numbers in the $m_F=\\pm 1$\ncomponents of the hyperfine spin. We show that a rotonlike spectrum can be\nobtained, or an initially stable condensate can be made unstable by adjusting\nthe magnitude of the magnetic field or the trapping frequencies. The structure\nof the instabilities can be analyzed by measuring the particle densities of the\nspin components. We confirm the validity of the analytical calculations by\nnumerical simulations."
    },
    {
        "anchor": "Production of a degenerate Fermi-Fermi mixture of dysprosium and\n  potassium atoms: We report on the realization of a mixture of fermionic $^{161}$Dy and\nfermionic $^{40}$K where both species are deep in the quantum-degenerate\nregime. Both components are spin-polarized in their absolute ground states, and\nthe low temperatures are achieved by means of evaporative cooling of the\ndipolar dysprosium atoms together with sympathetic cooling of the potassium\natoms. We describe the trapping and cooling methods, in particular the final\nevaporation stage, which leads to Fermi degeneracy of both species. Analyzing\ncross-species thermalization we obtain an estimate of the magnitude of the\ninter-species $s$-wave scattering length at low magnetic field. We demonstrate\nmagnetic levitation of the mixture as a tool to ensure spatial overlap of the\ntwo components. The properties of the Dy-K mixture make it a very promising\ncandidate to explore the physics of strongly interacting mass-imbalanced\nFermi-Fermi mixtures.",
        "positive": "Fulde-Ferrell pairing instability of a Rashba spin-orbit coupled Fermi\n  gas: We theoretically analyze the pairing instability of a three-dimensional\nultracold atomic Fermi gas towards a Fulde-Ferrell superfluid, in the presence\nof Rashba spin-orbit coupling and in-plane Zeeman field. We use the standard\nThouless criterion for the onset of superfluidity, with which the effect of\npair fluctuations is partially taken into account by approximately using a\nmean-field chemical potential at zero temperature. This gives rise to an\nimproved prediction of the superfluid transition temperature beyond mean-field,\nparticularly in the strong-coupling unitary limit. We also investigate the\npairing instability with increasing Rashba spin-orbit coupling, along the\ncrossover from a Bardeen-Cooper-Schrieffer superfluid to a Bose-Einstein\ncondensate of Rashbons (i.e., the tightly bound state of two fermions formed by\nstrong Rashba spin-orbit coupling"
    },
    {
        "anchor": "Density and spin response of a strongly-interacting Fermi gas in the\n  attractive and quasi-repulsive regime: Recent experimental advances in ultra-cold Fermi gases allow for exploring\nresponse functions under different dynamical conditions. In particular, the\nissue of obtaining a \"quasi-repulsive\" regime starting from a Fermi gas with an\nattractive inter-particle interaction while avoiding the formation of the\ntwo-body bound state is currently debated. Here, we provide a calculation of\nthe density and spin response for a wide range of temperature and coupling both\nin the attractive and quasi-repulsive regime, whereby the system is assumed to\nevolve non-adiabatically toward the \"upper branch\" of the Fermi gas. A\ncomparison is made with the available experimental data for these two\nquantities.",
        "positive": "Structured hetero-symmetric quantum droplets: We predict that Lee-Huang-Yang effect makes it possible to create stable\nquantum droplets (QDs) in binary Bose-Einstein condensates with a\nhetero-symmetric or hetero-multipole structure, i.e., different vorticities or\nmultipolarities in their components. The QDs feature flat-top shapes when\neither chemical potential \\mu_1,2 of the droplet approaches an edge of a\ntriangular existence domain in the (\\mu_1,\\mu_2) plane. QDs with different\nvorticities of their components are stable against azimuthal perturbations,\nprovided that the norm of one component is large. We also present multipole\nstates, in which the interaction with a strong fundamental component balances\nthe repulsion between poles with opposite signs in the other component, leading\nto the formation of stable bound states. Extended stability domains are\nobtained for dipole QDs; tripole ones exist but are unstable, while quadrupoles\nare stable in a narrow region. The results uncover the existence of much richer\nfamilies of stable binary QDs in comparison to states with identical\ncomponents."
    },
    {
        "anchor": "Twist of generalized skyrmions and spin vortices in a polariton\n  superfluid: We study the spin vortices and skyrmions coherently imprinted into an\nexciton-polariton condensate on a planar semiconductor microcavity. We\ndemonstrate that the presence of a polarization anisotropy can induce a complex\ndynamics of these structured topologies, leading to the twist of their\ncircuitation on the Poincar\\'e sphere of polarizations. The theoretical\ndescription of the results carries the concept of generalized quantum vortices\nin two-component superfluids, which are conformal with polarization loops\naround an arbitrary axis in the pseudospin space.",
        "positive": "Localization driven superradiant instability: The prominent Dicke superradiant phase arises from coupling an ensemble of\natoms to cavity optical field when external optical pumping exceeds a threshold\nstrength. Here we report a prediction of the superrandiant instability driven\nby Anderson localization, realized with a hybrid system of Dicke and\nAubry-Andre (DAA) model for bosons trapped in a one-dimensional (1D)\nquasiperiodic optical lattice and coupled to a cavity. Our central finding is\nthat for bosons condensed in localized phase given by the DAA model, the\nresonant superradiant scattering is induced, for which the critical optical\npumping of superradiant phase transition approaches zero, giving an instability\ndriven by Anderson localization. The superradiant phase for the DAA model with\nor without a mobility edge is investigated, showing that the localization\ndriven superradiant instability is in sharp contrast to the superradiance as\nwidely observed for Bose condensate in extended states, and should be\ninsensitive to temperature of the system. This study unveils an insightful\neffect of localization on the Dicke superradiance, and is well accessible based\non the current experiments."
    },
    {
        "anchor": "Loading of bosons in optical lattices into the p band: We present a method for transferring bosonic atoms residing on the lowest\ns-band of an optical lattice to the first excited p-bands. Our idea hinges on\nresonant tunneling between adjacent sites of accelerated lattices. The\nacceleration effectively shifts the quasi-bound energies on each site such that\nthe system can be cast into a Wannier-Stark ladder problem. By adjusting the\nacceleration constant, a situation of resonant tunneling between the s- and\np-bands is achievable. Within a mean-field model, considering 87Rb atoms, we\ndemonstrate population transfer from the s- to the p-bands with around 95 %\nefficiency. Nonlinear effects deriving from atom-atom interactions, as well as\ncoupling of the quasi bound Wannier-Stark states to the continuum, are\nconsidered.",
        "positive": "A Proposal for measuring Anisotropic Shear Viscosity in Unitary Fermi\n  Gases: We present a proposal to measure anisotropic shear viscosity in a strongly\ninteracting, ultra-cold, unitary Fermi gas confined in a harmonic trap. We\nintroduce anisotropy in this setup by strongly confining the gas in one of the\ndirections with relatively weak confinement in the remaining directions. This\nsystem has a close resemblance to anisotropic strongly coupled field theories\nstudied recently in the context of gauge-gravity duality. Computations in such\ntheories (which have gravity duals) revealed that some of the viscosity\ncomponents of the anisotropic shear viscosity tensor can be made much smaller\nthan the entropy density, thus parametrically violating the bound proposed by\nKovtun, Son and Starinets (KSS): $\\frac {\\eta} {s} \\geq \\frac{1}{4 \\pi}$. A\nBoltzmann analysis performed in a system of weakly interacting particles in a\nlinear potential also shows that components of the viscosity tensor can be\nreduced. Motivated by these exciting results, we propose two hydrodynamic modes\nin the unitary Fermi gas whose damping is governed by the component of shear\nviscosity expected to violate the KSS bound. One of these modes is the well\nknown scissor mode. We estimate trap parameters for which the reduction in the\nshear viscosity is of order unity and find that the trap geometry, the damping\ntimescales, and mode amplitudes are within the range of existing experimental\nsetups on ultra-cold Fermi gases."
    },
    {
        "anchor": "Total Energy Dynamics and Asymptotics of the Momentum Distribution\n  Following an Interaction Quench in a Two-component Fermi Gas: The absence of a characteristic momentum scale in the pseudo-potential\ndescription of atomic interaction in ultracold (two-component Fermi) gases is\nknown to lead to divergence in perturbation theory. Here we show that they also\nplague the calculation of the dynamics of the total energy following a quantum\nquench. A procedure to remove the divergence is devised, which provides finite\nanswers for the time-evolution of the total energy after a quench in which the\ninteraction strength is ramped up according to an arbitrary protocol. An\nimportant result of this analysis is the time evolution of the asymptotic tail\nof the momentum distribution (related to Tan's contact) and the contact for a\nlinear interaction ramp are obtained, as a function of the interaction ramp\ntime in the crossover from the sudden quench to the adiabatic limit are\nreported. In sudden quench limit, the contact, following a rapid oscillation,\nreaches a stationary value which is different from the equilibrium one. In the\nadiabatic limit, the contact grows quadratically in time and later saturates to\nits equilibrium value for the final value of the scattering length.",
        "positive": "The anomalous Floquet Anderson insulator in a continuously driven\n  optical lattice: The anomalous Floquet Anderson insulator (AFAI) has been theoretically\npredicted in step-wise periodically driven models, but its stability under more\ngeneral driving protocols hasn't been determined. We show that adding disorder\nto the anomalous Floquet topological insulator realized with a continuous\ndriving protocol in the experiment by K. Wintersperger et. al., Nat. Phys.\n$\\textbf{16}$, 1058 (2020), supports an AFAI phase, where, for a range of\ndisorder strengths, all the time averaged bulk states become localized, while\nthe pumped charge in a Laughlin pump setup remains quantized."
    },
    {
        "anchor": "Spin current generation and relaxation in a quenched spin-orbit-coupled\n  Bose-Einstein condensate: Understanding the effects of spin-orbit coupling (SOC) and many-body\ninteractions on spin transport is important in condensed matter physics and\nspintronics. This topic has been intensively studied for spin carriers such as\nelectrons but barely explored for charge-neutral bosonic quasiparticles\n(including their condensates), which hold promises for coherent spin transport\nover macroscopic distances. Here, we explore the effects of synthetic SOC\n(induced by optical Raman coupling) and atomic interactions on the spin\ntransport in an atomic Bose-Einstein condensate (BEC), where the spin-dipole\nmode (SDM, actuated by quenching the Raman coupling) of two interacting spin\ncomponents constitutes an alternating spin current. We experimentally observe\nthat SOC significantly enhances the SDM damping while reducing the\nthermalization (the reduction of the condensate fraction). We also observe\ngeneration of BEC collective excitations such as shape oscillations. Our theory\nreveals that the SOC-modified interference, immiscibility, and interaction\nbetween the spin components can play crucial roles in spin transport.",
        "positive": "Tunable Fr\u00f6hlich Polarons of slow-light polaritons in a\n  two-dimensional Bose-Einstein condensate: When an impurity interacts with a bath of phonons it forms a polaron. For\nincreasing interaction strengths the mass of the polaron increases and it can\nbecome self-trapped. For impurity atoms inside an atomic Bose-Einstein\ncondensate (BEC) the nature of this transition is subject of debate. While\nFeynman's variational approach predicts a sharp transition for light\nimpurities, renormalization group studies always predict an extended\nintermediate-coupling region characterized by large phonon correlations. To\ninvestigate this intricate regime we suggest a versatile experimental setup\nthat allows to tune both the mass of the impurity and its interactions with the\nBEC. The impurity is realized as a dark-state polariton (DSP) inside a quasi\ntwo-dimensional BEC. We show that its interactions with the Bogoliubov phonons\nlead to photonic polarons, described by the Bogoliubov-Fr\\\"ohlich Hamiltonian,\nand make theoretical predictions using an extension of a recently introduced\nrenormalization group approach to Fr\\\"ohlich polarons."
    },
    {
        "anchor": "Superfluidity and dimerization in a multilayered system of fermionic\n  polar molecules: We consider a layered system of fermionic molecules with permanent dipole\nmoments aligned by an external field. The dipole interactions between fermions\nin adjacent layers are attractive and induce inter-layer pairing. Due to\ncompetition for pairing among adjacent layers, the mean-field ground state of\nthe layered system is a dimerized superfluid, with pairing only between\nevery-other layer. We construct an effective Ising-XY lattice model that\ndescribes the interplay between dimerization and superfluid phase fluctuations.\nIn addition to the dimerized superfluid ground state, and high temperature\nnormal state, at intermediate temperature, we find an unusual dimerized\n\"pseudogap\" state with only short-range phase coherence. We propose light\nscattering experiments to detect dimerization.",
        "positive": "Bound states in a quasi-two-dimensional Fermi gas: We consider the problem of N identical fermions of mass M and one\ndistinguishable particle of mass m interacting via short-range interactions in\na confined quasi-two-dimensional (quasi-2D) geometry. For N=2 and mass ratios\nM/m<13.6, we find non-Efimov trimers that smoothly evolve from 2D to 3D. In the\nlimit of strong 2D confinement, we show that the energy of the N+1 system can\nbe approximated by an effective two-channel model. We use this approximation to\nsolve the 3+1 problem and we find that a bound tetramer can exist for mass\nratios M/m as low as 5 for strong confinement, thus providing the first example\nof a universal, non-Efimov tetramer involving three identical fermions."
    },
    {
        "anchor": "Quench Dynamics of Anyon Tonks-Girardeau Gases: We investigate the dynamical evolution of strongly interacting anyons\nconfined in a weak harmonic trap using the exact anyon-fermion mapping method.\nThe density profiles, momentum distribution, and the reduced one-body density\nmatrix are obtained for different statistical parameters. The density profiles\nof anyons display the same behaviors irrespective of statistical parameter\nduring the evolution. As the harmonic trap is turned off suddenly, the momentum\ndistributions exhibit the symmetric fermion-like behaviour in the long time\nevolution. As the trap frequency is quenched, the momentum distribution exhibit\nan asymmetry breath mode during the evolution. The reduced one-body density\nmatrix show the dynamical symmetry broken and reproduced behaviour.",
        "positive": "Wave patterns generated by a flow of two-component Bose-Einstein\n  condensate with spin-orbit interaction past a localized obstacle: It is shown that spin-orbit interaction leads to drastic changes in wave\npatterns generated by a flow of two-component Bose-Einstein condensate (BEC)\npast an obstacle. The combined Rashba and Dresselhaus spin-orbit interaction\naffects in different ways two types of excitations---density and polarization\nwaves---which can propagate in a two-component BEC. We show that the density\nand polarization \"ship wave\" patterns rotate in opposite directions around the\naxis located at the obstacle position and the angle of rotation depends on the\nstrength of spin-orbit interaction. This rotation is accompanied by narrowing\nof the Mach cone. The influence of spin-orbit coupling on density solitons and\npolarization breathers is studied numerically."
    },
    {
        "anchor": "Visible stripe phases in spin-orbital-angular-momentum coupled\n  Bose-Einstein condensates: Recently, stripe phases in spin-orbit coupled Bose-Einstein condensates\n(BECs) have attracted much attention since they are identified as supersolid\nphases. In this paper, we exploit experimentally reachable parameters and show\ntheoretically that annular stripe phases with large stripe spacing and high\nstripe contrast can be achieved in spin-orbital-angular-momentum coupled\n(SOAMC) BECs. In addition to using Gross-Pitaevskii numerical simulations, we\ndevelop a variational ansatz that captures the essential interaction effects to\nfirst order, which are not present in the ansatz employed in previous\nliterature. Our work should open the possibility toward directly observing\nstripe phases in SOAMC BECs in experiments.",
        "positive": "Bose-Einstein Condensate in a Linear Trap With a Dimple Potential: We study Bose-Einstein condensation in a linear trap with a dimple potential\nwhere we model dimple potentials by Dirac \\del function. Attractive and\nrepulsive dimple potentials are taken into account. This model allows simple,\nexplicit numerical and analytical investigations of noninteracting gases. Thus,\nthe \\Sch is used instead of the Gross-Pitaevski equation. We calculate the\natomic density, the chemical potential, the critical temperature and the\ncondensate fraction. The role of the relative depth of the dimple potential\nwith respect to the linear trap in large condensate formation at enhanced\ntemperatures is clearly revealed. Moreover, we also present a semi-classical\nmethod for calculating various quantities such as entropy analytically.\nMoreover, we compare the results of this paper with the results of a previous\npaper in which the harmonic trap with a dimple potential in 1D was\ninvestigated."
    },
    {
        "anchor": "Ultracold few fermionic atoms in needle-shaped double wells: spin chains\n  and resonating spin clusters from microscopic Hamiltonians emulated via\n  antiferromagnetic Heisenberg and t-J models: Advances with trapped ultracold atoms intensified interest in simulating\ncomplex physical phenomena, including quantum magnetism and transitions from\nitinerant to non-itinerant behavior. Here we show formation of\nantiferromagnetic ground states of few ultracold fermionic atoms in single and\ndouble well (DW) traps, through microscopic Hamiltonian exact diagonalization\nfor two DW arrangements: (i) two linearly oriented one-dimensional, 1D, wells,\nand (ii) two coupled parallel wells, forming a trap of two-dimensional, 2D,\nnature. The spectra and spin-resolved conditional probabilities reveal for both\ncases, under strong repulsion, atomic spatial localization at extemporaneously\ncreated sites, forming quantum molecular magnetic structures with non-itinerant\ncharacter. These findings usher future theoretical and experimental\nexplorations into the highly-correlated behavior of ultracold\nstrongly-repelling fermionic atoms in higher dimensions, beyond the\nfermionization physics that is strictly applicable only in the 1D case. The\nresults for four atoms are well described with finite Heisenberg spin-chain and\ncluster models. The numerical simulations of three fermionic atoms in symmetric\ndouble wells reveal the emergent appearance of coupled resonating 2D Heisenberg\nclusters, whose emulation requires the use of a t-J-like model, akin to that\nused in investigations of high T$_c$ superconductivity. The highly entangled\nstates discovered in the microscopic and model calculations of controllably\ndetuned, asymmetric, double wells suggest three-cold-atom DW quantum computing\nqubits.",
        "positive": "Spontaneously broken gauge symmetry in a Bose gas with constant particle\n  number: The interplay between spontaneously broken gauge symmetries and Bose-Einstein\ncondensation has long been controversially discussed in science, since the\nequation of motions are invariant under phase transformations. Within the\npresent model it is illustrated that spontaneous symmetry breaking appears as a\nnon-local process in position space, but within disjoint subspaces of the\nunderlying Hilbert space. Numerical simulations show that it is the symmetry of\nthe relative phase distribution between condensate and non-condensate quantum\nfields which is spontaneously broken when passing the critical temperature for\nBose-Einstein condensation. Since the total number of gas particles remains\nconstant over time, the global U(1)-gauge symmetry of the system is preserved."
    },
    {
        "anchor": "Stationary States of Trapped Spin-Orbit-Coupled Bose-Einstein\n  Condensates: We numerically investigate low-energy stationary states of pseudospin-1\nBose-Einstein condensates in the presence of Rashba-Dresselhaus-type spin-orbit\ncoupling. We show that for experimentally feasible parameters and strong\nspin-orbit coupling, the ground state is a square vortex lattice irrespective\nof the nature of the spin-dependent interactions. For weak spin-orbit coupling,\nthe lowest-energy state may host a single vortex. Furthermore, we analytically\nderive constraints that explain why certain stationary states do not emerge as\nground states. Importantly, we show that the distinct stationary states can be\nobserved experimentally by standard time-of-flight spinindependent absorption\nimaging.",
        "positive": "Dynamics and correlations of a Bose-Einstein condensate of photons: The Tutorial reports recent experimental advances in studies of the dynamics\nas well as the number and phase correlations of a Bose-Einstein condensed\nphoton gas confined in a high-finesse dye-filled microcavity. Repeated\nabsorption-emission-processes of photons on dye molecules here establish a\nthermal coupling of the photonic quantum gas to both a heat bath and a particle\nreservoir comprised of dye molecules. In this way, for the first time\nBose-Einstein condensation under grand-canonical statistical ensemble\nconditions becomes experimentally accessible."
    },
    {
        "anchor": "Observation of Nonlinear Response and Onsager Regression in a Photon\n  Bose-Einstein Condensate: The quantum regression theorem states that the correlations of a system at\ntwo different times are governed by the same equations of motion as the\ntemporal response of the average values. Such a relation provides a powerful\nframework for the investigation of physical systems by establishing a formal\nconnection between intrinsic microscopic behaviour and a macroscopic 'effect'\ndue to an external 'cause'. Measuring the response to a controlled perturbation\nin this way allows to determine, for example, structure factors in condensed\nmatter systems as well as other correlation functions of material systems. Here\nwe experimentally demonstrate that the two-time particle number correlations in\na photon Bose-Einstein condensate inside a dye-filled microcavity exhibit the\nsame dynamics as the response of the condensate to a sudden perturbation of the\ndye molecule bath. This confirms the regression theorem for a quantum gas and,\nmoreover, establishes a test of this relation in an unconventional form where\nthe perturbation acts on the bath and only the condensate response is\nmonitored. For strong perturbations, we observe nonlinear relaxation dynamics\nwhich our microscopic theory relates to the equilibrium fluctuations, thereby\nextending the regression theorem beyond the regime of linear response. The\ndemonstrated nonlinearity of the condensate-bath system paves the way for\nstudies of novel elementary excitations in lattices of driven-dissipative\nphoton condensates.",
        "positive": "Stable-unstable transition for a Bose-Hubbard chain coupled to an\n  environment: Interactions in quantum systems may induce transitions to exotic correlated\nphases of matter which can be vulnerable to coupling to an environment. Here,\nwe study the stability of a Bose-Hubbard chain coupled to a bosonic bath at\nzero and non-zero temperature. We show that only above a critical interaction\nthe chain loses bosons and its properties are significantly affected. The\ntransition is of a different nature than the superfluid-Mott insulator\ntransition and occurs at a different critical interaction. We explain such a\nstable-unstable transition by the opening of a charge gap. The comparison of\naccurate matrix product state simulations to approximative approaches that miss\nthis transition reveals its many-body origin."
    },
    {
        "anchor": "Bose-Einstein Condensate in a light-induced vector potential using the\n  1064 $nm$ optical dipole trap lasers: We present a simple experiment of creating an effective vector gauge\npotential for Bose-Einstein condensed $^{87}$Rb in the F=2 hyperfine ground\nstate using two crossed 1064 $nm$ optical dipole trap lasers as the Raman\nbeams. Due to the far-detuning from the single-photon resonance with the\nelectronically excited state, the spontaneous emission is strongly reduced, at\nthe same time, the moderate strength of the Raman coupling still can be\nachieved. The atoms at the far detuning of the Raman coupling are loaded\nadiabatically into the dressed states by ramping the homogeneous bias magnetic\nfield to resonance and the different energy dressed states are studied. This\nexperiment is easily extended to produce synthetic magnetic or electric field\nfrom a spatial or time dependence of the effective vector potential.",
        "positive": "Spin pumping and measurement of spin currents in optical superlattices: We report on the experimental implementation of a spin pump with ultracold\nbosonic atoms in an optical superlattice. In the limit of isolated double wells\nit represents a 1D dynamical version of the quantum spin Hall effect. Starting\nfrom an antiferromagnetically ordered spin chain, we periodically vary the\nunderlying spin-dependent Hamiltonian and observe a spin current without charge\ntransport. We demonstrate a novel detection method to measure spin currents in\noptical lattices via superexchange oscillations emerging after a projection\nonto static double wells. Furthermore, we directly verify spin transport\nthrough in-situ measurements of the spins' center of mass displacement."
    },
    {
        "anchor": "Resonant Driving induced Ferromagnetism in the Fermi Hubbard Model: In this letter we consider quantum phases and the phase diagram of a Fermi\nHubbard model under periodic driving that has been realized in recent cold atom\nexperiments, in particular, when the driving frequency is resonant with the\ninteraction energy. Due to the resonant driving, the effective Hamiltonian\ncontains a correlated hopping term where the density occupation strongly\nmodifies the hopping strength. Focusing on half filling, in addition to the\ncharge and spin density wave phases, large regions of ferromagnetic phase and\nphase separation are discovered in the weakly interacting regime. The mechanism\nof this ferromagnetism is attributed to the correlated hopping because the\nhopping strength within a ferromagnetic domain is normalized to a larger value\nthan the hopping strength across the domain. Thus, the kinetic energy favors a\nlarge ferromagnetic domain and consequently drives the system into a\nferromagnetic phase. We note that this is a different mechanism in contrast to\nthe well-known Stoner mechanism for ferromagnetism where the ferromagnetism is\ndriven by interaction energy.",
        "positive": "Beyond universality in three-body recombination: an Effective Field\n  Theory treatment: We discuss the impact of a finite effective range on three-body systems\ninteracting through a large two-body scattering length. By employing a\nperturbative analysis in an effective field theory well suited to this scale\nhierarchy we find that an additional three-body parameter is required for\nconsistent renormalization once range corrections are considered. This allows\nus to extend previously discussed universal relations between different\nobservables in the recombination of cold atoms to account for the presence of a\nfinite effective range. We show that such range corrections allow us to\nsimultaneously describe the positive and negative scattering-length loss\nfeatures observed in recombination with Lithium-7 atoms by the Bar-Ilan group.\nThey do not, however, significantly reduce the disagreement between the\nuniversal relations and the data of the Rice group on Lithium-7 recombination\nat positive and negative scattering lengths."
    },
    {
        "anchor": "Strong-coupling Bose polarons in 1D: Condensate deformation and modified\n  Bogoliubov phonons: We discuss the interaction of a quantum impurity with a one-dimensional\ndegenerate Bose gas forming a Bose-polaron. In three spatial dimensions the\nquasiparticle is typically well described by the extended Fr\\\"ohlich model, in\nfull analogy with the solid-state counterpart. This description, which assumes\nan undepleted condensate, fails however in 1D, where the backaction of the\nimpurity on the condensate leads to a self-bound mean-field polaron for\narbitrarily weak impurity-boson interactions. We present a model that takes\ninto account this backaction and describes the impurity-condensate interaction\nas coupling to phonon-like excitations of a deformed condensate. A comparison\nof polaron energies and masses to diffusion quantum Monte-Carlo simulations\nshows very good agreement already on the level of analytical mean-field\nsolutions and is further improved when taking into account quantum\nfluctuations.",
        "positive": "Weakly nonadditive Polychronakos statistics: A two-parametric fractional statistics is proposed, which can be used to\nmodel a weakly-interacting Bose-system. It is shown that the parameters of the\nintroduced weakly nonadditive Polychronakos statistics can be linked to effects\nof interactions as well as finite-size corrections. The calculations of the\nspecific heat and condensate fraction of the model system corresponding to\nharmonically trapped Rb-87 atoms are made. The behavior of the specific heat of\nthree-dimensional isotropic harmonic oscillators with respect to the values of\nthe statistics parameters is studied in the temperature domain including the\nBEC-like phase transition point."
    },
    {
        "anchor": "Spatial and temporal coherence of a Bose-condensed gas: The central problem of this chapter is temporal coherence of a\nthree-dimensional spatially homogeneous Bose-condensed gas, initially prepared\nat finite temperature and then evolving as an isolated interacting system. A\nfirst theoretical tool is a number-conserving Bogoliubov approach that allows\nto describe the system as a weakly interacting gas of quasi-particles. This\napproach naturally introduces the phase operator of the condensate: a central\nactor since loss of temporal coherence is governed by the spreading of the\ncondensate phase-change. A second tool is the set of kinetic equations\ndescribing the Beliaev-Landau processes for the quasi-particles. We find that\nin general the variance of the condensate phase-change at long times $t$ is the\nsum of a ballistic term $\\propto t^2$ and a diffusive term $\\propto t$ with\ntemperature and interaction dependent coefficients. In the thermodynamic limit,\nthe diffusion coefficient scales as the inverse of the system volume. The\ncoefficient of $t^2$ scales as the inverse volume squared times the variance of\nthe energy of the system in the initial state and can also be obtained by a\nquantum ergodic theory (the so-called eigenstate thermalisation hypothesis).",
        "positive": "Resonant demagnetization of a dipolar BEC in a 3D optical lattice: We study dipolar relaxation of a chromium BEC loaded into a 3D optical\nlattice. We observe dipolar relaxation resonances when the magnetic energy\nreleased during the inelastic collision matches an excitation towards higher\nenergy bands. A spectroscopy of these resonances for two orientations of the\nmagnetic field provides a 3D band spectroscopy of the lattice. The narrowest\nresonance is registered for the lowest excitation energy. Its line-shape is\nsensitive to the on-site interaction energy. We use such sensitivity to probe\nnumber squeezing in a Mott insulator, and we reveal the production of\nthree-body states with entangled spin and orbital degrees of freedom."
    },
    {
        "anchor": "Noise correlations of one-dimensional Bose mixtures in optical lattices: We study the noise correlations of one-dimensional binary Bose mixtures, as a\nprobe of their quantum phases. In previous work, we found a rich structure of\nmany-body phases in such mixtures, such as paired and counterflow\nsuperfluidity. Here we investigate the signature of these phases in the noise\ncorrelations of the atomic cloud after time-of-flight expansion, using both\nLuttinger liquid theory and the time-evolving block decimation (TEBD) method.\nWe find that paired and counterflow superfluidity exhibit distinctive features\nin the noise spectra. We treat both extended and inhomogeneous systems, and our\nnumerical work shows that the essential physics of the extended systems is\npresent in the trapped-atom systems of current experimental interest. For\npaired and counterflow superfluid phases, we suggest methods for extracting\nLuttinger parameters from noise correlation spectroscopy.",
        "positive": "Dynamic structure factors of a strongly interacting Fermi superfluid\n  near an orbital Feshbach resonance across the phase transition from BCS to\n  Sarma superfluid: We theoretically investigate dynamic structure factors of a strongly\ninteracting Fermi superfluid near an orbital Feshbach resonance with random\nphase approximation, and find their dynamical characters during the phase\ntransition between a balanced conventional Bardeen-Cooper-Schrieffer superfluid\nand a polarized Sarma superfluid by continuously varying the chemical potential\ndifference of two spin components. In a BEC-like regime of the BCS superfluid,\ndynamic structure factors can do help to distinguish the in-phase ground state\nfrom the out-of-phase metastable state by the relative location of molecular\nexcitation and Leggett mode, or the minimum energy to break a Cooper pair. In\nthe phase transition between BCS and Sarma superfluid, we find the dynamic\nstructure factor of Sarma superfluid has its own specific gapless excitation at\na small transferred momentum which is mixed with the collective phonon\nexcitation, and also a relatively strong atomic excitation at a large\ntransferred momentum because of the existence of unpaired Fermi atoms, these\nsignals can be used to differentiate Sarma superfluid from BCS superfluid."
    },
    {
        "anchor": "Frustrated superfluids in a non-Abelian flux: We study possible superfluid states of the Rashba spin-orbit coupled (SOC)\nspinor bosons with the spin anisotropic interaction $ \\lambda $ hopping in a\nsquare lattice. The frustrations from the non-abelian flux due to the SOC leads\nto novel spin-bond correlated superfluids. By using a recently developed\nsystematic \"order from quantum disorder\" analysis, we not only determine the\ntrue quantum ground state, but also evaluate the mass gap in the spin sector at\n$ \\lambda < 1 $, especially compute the the excitation spectrum of the\nGoldstone mode in the spin sector at $ \\lambda=1 $ which would be quadratic\nwithout the analysis. The analysis also leads to different critical exponents\non the two sides of the 2nd order transition driven by a roton touchdown at $\n\\lambda=1 $. The intimate analogy at $ \\lambda=1 $ with the charge neutral\nGoldstone mode in the pseudo-spin sector in the Bilayer quantum Hall systems at\nthe total filling factor $ \\nu_T=1 $ are stressed. The experimental\nimplications and detections of these novel phenomena in cold atoms loaded on a\noptical lattice are presented.",
        "positive": "A mobile ion in a Fermi sea: The remarkable single particle control of individual ions combined with the\nversatility of ultracold atomic gases makes hybrid ion-atom system an exciting\nnew platform for quantum simulation of few- and many-body quantum physics.\nHere, we study theoretically the properties of a mobile ion immersed in a\nquantum degenerate gas of fermionic atoms. Using an effective low-energy\natom-ion interaction together with a well established approach that includes\nexactly two-body correlations, we calculate the full spectral response of the\nion and demonstrate the existence of several quasiparticle branches, which are\ncharged analogues of the Fermi polaron observed in neutral atomic gases. Due to\nthe long-range nature of the atom-ion interaction, these ionic Fermi polarons\nhave several properties distinct from their neutral counterparts such as the\nsimultaneous presence of several stable states and smooth transitions from\nrepulsive to attractive polarons with increasing interaction strength.\nSurprisingly, the residue of the ionic polaron is shown to increase with the\nFermi density for fixed interaction strength, which is in marked contrast to\nthe neutral polaron. The properties of the ionic polaron approach that of the\nneutral polaron only in the low density limit where the average interparticle\nspacing is larger than the characteristic length of the atom-ion interaction.\nWe finally analyse the effects of the Fermi gas on the molecular ions, which\nare bound atom-dimer states."
    },
    {
        "anchor": "Detecting topology through dynamics in interacting fermionic wires: We describe a protocol to read out the topological invariant of interacting\n1D chiral models, based on measuring the mean chiral displacement of\ntime-evolving bulk excitations. We present analytical calculations and\nnumerical Matrix Product State simulations of interacting Su-Schrieffer-Heeger\n(SSH) chains, demonstrating how the mean chiral displacement allows to\ndistinguish between topological insulator, trivial insulator and\nsymmetry-broken phases. Finally, we provide an experimental blueprint for\nrealizing a model displaying these three phases and describe how to detect\nthose.",
        "positive": "Rotation of cold molecular ions inside a Bose-Einstein condensate: We use recently developed angulon theory [Phys. Rev. Lett. 114, 203001\n(2015)] to study the rotational spectrum of a cyanide molecular anion immersed\ninto Bose-Einstein condensates of rubidium and strontium. Based on $\\textit {ab\ninitio}$ potential energy surfaces, we provide a detailed study of the\nrotational Lamb shift and many-body-induced fine structure which arise due to\ndressing of molecular rotation by a field of phonon excitations. We demonstrate\nthat the magnitude of these effects is large enough in order to be observed in\nmodern experiments on cold molecular ions. Furthermore, we introduce a novel\nmethod to construct pseudopotentials starting from the $\\textit {ab initio}$\npotential energy surfaces, which provides a means to obtain effective coupling\nconstants for low-energy polaron models."
    },
    {
        "anchor": "Renormalization of the superfluid density in the two-dimensional BCS-BEC\n  crossover: We analyze the theoretical derivation of the beyond-mean-field equation of\nstate for a two-dimensional gas of dilute, ultracold alkali-metal atoms in the\nBardeen-Cooper-Schrieffer (BCS) to Bose-Einstein condensate (BEC) crossover. We\nshow that at zero temperature our theory -- considering Gaussian fluctuations\non top of the mean-field equation of state -- is in very good agreement with\nexperimental data. Subsequently, we investigate the superfluid density at\nfinite temperature and its renormalization due to the proliferation of\nvortex-antivortex pairs. By doing so, we determine the\nBerezinskii-Kosterlitz-Thouless (BKT) critical temperature -- at which the\nrenormalized superfluid density jumps to zero -- as a function of the\ninter-atomic potential strength. We find that the Nelson-Kosterlitz criterion\noverestimates the BKT temperature with respect to the renormalization group\nequations, this effect being particularly relevant in the intermediate regime\nof the crossover.",
        "positive": "Kelvin wave in miscible two-component Bose-Einstein condensates: We study the dispersion of Kelvin waves propagating along single- and\nhalf-quantum vortices in miscible two-component Bose-Einstein condensates based\non the analysis of the Bogoloubov-de Genne equation. With the help of the\ninterpolating formula connecting the dispersion relations at low- and\nhigh-wavenumber regime, we reveal the nontrivial dependence of the dispersion\nrelation of the Kelvin waves on the intercomponent interaction through the\nchange of the vortex core size of the vortical component. We also find the\nsplitting of the Kelvin mode dispersion into gapless and gapfull branches when\nboth components have overlapping single-quantized vortices."
    },
    {
        "anchor": "Statistical periodicity in driven quantum systems: General formalism and\n  application to noisy Floquet topological chains: Much recent experimental effort has focused on the realization of exotic\nquantum states and dynamics predicted to occur in periodically driven systems.\nBut how robust are the sought-after features, such as Floquet topological\nsurface states, against unavoidable imperfections in the periodic driving? In\nthis work, we address this question in a broader context and study the dynamics\nof quantum systems subject to noise with periodically recurring statistics. We\nshow that the stroboscopic time evolution of such systems is described by a\nnoise-averaged Floquet superoperator. The eigenvectors and -values of this\nsuperoperator generalize the familiar concepts of Floquet states and\nquasienergies and allow us to describe decoherence due to noise efficiently.\nApplying the general formalism to the example of a noisy Floquet topological\nchain, we re-derive and corroborate our recent findings on the noise-induced\ndecay of topologically protected end states. These results follow directly from\nan expansion of the end state in eigenvectors of the Floquet superoperator.",
        "positive": "Driven-dissipative Ising model: Dynamical crossover at weak dissipation: Driven quantum systems coupled to an environment typically exhibit\neffectively thermal behavior with relaxational dynamics near criticality.\nHowever, a different qualitative behavior might be expected in the weakly\ndissipative limit due to the competition between coherent dynamics and weak\ndissipation. In this work, we investigate a driven-dissipative infinite-range\nIsing model in the presence of individual atomic dissipation, a model that\nemerges from the paradigmatic open Dicke model in the large-detuning limit. We\nshow that the system undergoes a dynamical crossover from relaxational\ndynamics, with a characteristic dynamical exponent $\\zeta=1/2$, to underdamped\ncritical dynamics governed by the exponent $\\zeta=1/4$ in the weakly\ndissipative regime; a behavior that is markedly distinct from that of\nequilibrium. Finally, utilizing an exact diagrammatic representation, we\ndemonstrate that the dynamical crossover to underdamped criticality is not an\nartifact of the mean-field nature of the model and persists even in the\npresence of short-range perturbations."
    },
    {
        "anchor": "Recent developments in Quantum Monte-Carlo simulations with applications\n  for cold gases: This is a review of recent developments in Monte Carlo methods in the field\nof ultra cold gases. For bosonic atoms in an optical lattice we discuss path\nintegral Monte Carlo simulations with worm updates and show the excellent\nagreement with cold atom experiments. We also review recent progress in\nsimulating bosonic systems with long-range interactions, disordered bosons,\nmixtures of bosons, and spinful bosonic systems. For repulsive fermionic\nsystems determinantal methods at half filling are sign free, but in general no\nsign-free method exists. We review the developments in diagrammatic Monte Carlo\nfor the Fermi polaron problem and the Hubbard model, and show the connection\nwith dynamical mean-field theory. We end the review with diffusion Monte Carlo\nfor the Stoner problem in cold gases.",
        "positive": "Laser Cooling at Resonance: We show experimentally that 3-D laser cooling of lithium atoms is achieved\nwhen the laser light is tuned exactly to resonance with the atomic transition.\nFor a theoretical description of this surprising phenomenon we resolve to a\nfull model which takes into account both the entire atomic structure and the\nlaser light polarization. Here we build such a model for $^7$Li atoms cooled on\nthe $D_{2}$-line in a $\\sigma^+-\\sigma^-$ laser configuration. We take all 24\nZeeman sub-levels into account and obtain good agreement with the experimental\ndata. Moreover, by means of Monte-Carlo simulations we show that coherent\nprocesses play an important role in showing consistency between the theory and\nthe experimental results."
    },
    {
        "anchor": "Manifestation of relative phase in dynamics of two interacting Bose-Bose\n  droplets: We study coherent dynamics of two interacting Bose-Bose droplets by means of\nthe extended Gross-Pitaevskii equation. The relative motion of the droplets\ncouples to the phases of their components. The dynamics can be understood in\nterms of the evolution of zero-energy modes recovering symmetries spontaneously\nbroken by the mean-field solution. These are translational symmetry and two\nU(1) symmetries, associated with the phases of the droplets' two components. A\nphase-dependent interaction potential and double Josephson-junction equations\nare introduced to explain the observed variety of different scenarios of\ncollision. We show that the evolution of the droplets is a macroscopic\nmanifestation of the hidden dynamics of their phases. The occurrence of\nnondissipative drag between the two supercurrents (Andreev-Bashkin effect) is\nmentioned.",
        "positive": "Topological phase transitions on a triangular optical lattice with\n  non-Abelian gauge fields: We study the mean-field BCS-BEC evolution of a uniform Fermi gas on a\nsingle-band triangular lattice, and construct its ground-state phase diagrams,\nshowing a wealth of topological quantum phase transitions between gapped and\ngapless superfluids that are induced by the interplay of an out-of-plane Zeeman\nfield and a generic non-Abelian gauge field."
    },
    {
        "anchor": "Realistic scheme for quantum simulation of $\\mathbb{Z}_2$ lattice gauge\n  theories with dynamical matter in $(2+1)$D: Gauge fields coupled to dynamical matter are ubiquitous in many disciplines\nof physics, ranging from particle to condensed matter physics, but their\nimplementation in large-scale quantum simulators remains challenging. Here we\npropose a realistic scheme for Rydberg atom array experiments in which a\n$\\mathbb{Z}_2$ gauge structure with dynamical charges emerges on experimentally\nrelevant timescales from only local two-body interactions and one-body terms in\ntwo spatial dimensions. The scheme enables the experimental study of a variety\nof models, including $(2+1)$D $\\mathbb{Z}_2$ lattice gauge theories coupled to\ndifferent types of dynamical matter and quantum dimer models on the honeycomb\nlattice, for which we derive effective Hamiltonians. We discuss ground-state\nphase diagrams of the experimentally most relevant effective $\\mathbb{Z}_2$\nlattice gauge theories with dynamical matter featuring various confined and\ndeconfined, quantum spin liquid phases. Further, we present selected probes\nwith immediate experimental relevance, including signatures of disorder-free\nlocalization and a thermal deconfinement transition of two charges.",
        "positive": "Quantized conductance through a spin-selective atomic point contact: We implement a microscopic spin filter for cold fermionic atoms in a quantum\npoint contact (QPC) and create fully spin-polarized currents while retaining\nconductance quantization. Key to our scheme is a near-resonant optical tweezer\ninducing a large effective Zeeman shift inside the QPC while its local\ncharacter limits dissipation. We observe a renormalization of this shift due to\ninteractions of a few atoms in the QPC. Our work represents the analog of an\nactual spintronic device and paves the way to studying the interplay between\nspin-splitting and interactions far from equilibrium."
    },
    {
        "anchor": "Moving solitons in a one-dimensional fermionic superfluid: A fully analytical theory of a traveling soliton in a one-dimensional\nfermionic superfluid is developed within the framework of time-dependent\nself-consistent Bogoliubov-de Gennes equations, which are solved exactly in the\nAndreev approximation. The soliton manifests itself in a kink-like profile of\nthe superconducting order parameter and hosts a pair of Andreev bound states in\nits core. They adjust to soliton's motion and play an important role in its\nstabilization. A phase jump across the soliton and its energy decrease with\nsoliton's velocity and vanish at the critical velocity, corresponding to the\nLandau criterion, where the soliton starts emitting quasiparticles and becomes\nunstable. The \"inertial\" and \"gravitational\" masses of the soliton are\ncalculated and the former is shown to be orders of magnitude larger than the\nlatter. This results in a slow motion of the soliton in a harmonic trap,\nreminiscent to the observed behavior of a soliton-like texture in related\nexperiments in cold fermion gases [T. Yefsah et al., Nature 499, 426, (2013)].\nFurthermore, we calculate the full non-linear dispersion relation of the\nsoliton and solve the classical equations of motion in a trap. The strong\nnon-linearity at high velocities gives rise to anharmonic oscillatory motion of\nthe soliton. A careful analysis of this anharmonicity may provide a means to\nexperimentally measure the non-linear soliton spectrum in superfluids.",
        "positive": "Two-dimensional vortex quantum droplets: It was recently found that the Lee-Huang-Yang (LHY) correction to the\nmean-field Hamiltonian suppresses the collapse and creates stable localized\nmodes (two-component \"quantum droplets\", QDs) in two and three dimensions. We\nconstruct two-dimensional\\ self-trapped modes in the form of QDs with vorticity\n$S$ embedded into each component. The QDs feature a flat-top shape, which\nexpands with the increase of $S$ and norm $N$. An essential finding, produced\nby a systematic numerical analysis and analytical estimates, is that the\nvortical QDs are \\emph{stable} (which is a critical issue for vortex solitons\nin nonlinear models) up to $S=5$, for $N$ exceeding a certain threshold value.\nIn the condensate of $^{39}$K atoms, in which QDs with $S=0$ and a quasi-2D\nshape were created recently, the vortical droplets may have radial size\n$\\lesssim 30$ $\\mathrm{\\mu}$m, with the number of atoms in the range of\n$10^{4}-10^{5}$. It is worthy to note that \\textit{hidden-vorticity} states in\nQDs with topological charges $% S_{+}=-S_{-}=1$ in its components, which are\nprone to strong instability in other settings, have their stability region too,\nalthough it may be located beyond applicability limits of the underlying model.\nDynamics of elliptically deformed QDs, which form rotating elongated patterns\nor ones with strong oscillations of the eccentricity, as well as collisions of\nQDs, are also addressed."
    },
    {
        "anchor": "$\u03b7$ Pairing of Light-Emitting Fermions: Nonequilibrium Pairing\n  Mechanism at High Temperatures: Strongly interacting fermionic atoms are shown to develop $\\eta$-pairing\nsuperfluid correlations in a nonequilibrium steady state in the presence of\nspontaneous emission of light from atoms. On the basis of the Hubbard model\nsubject to spontaneous decay between internal spin states, we show that\nprohibition of radiative decay due to the Pauli exclusion principle and\ndestructive interference between doublon-decay processes lead to nonequilibrium\n$\\eta$ pairing. Because of the non-thermal nature of the steady state, pair\ncorrelations arise even from a completely uncorrelated infinite-temperature\ninitial state, allowing coherent atom pairs to be formed at high temperatures.\nExperimental implementation with fermionic atoms in an optical lattice is\ndiscussed.",
        "positive": "Site-resolved imaging of a fermionic Mott insulator: The complexity of quantum many-body systems originates from the interplay of\nstrong interactions, quantum statistics, and the large number of\nquantum-mechanical degrees of freedom. Probing these systems on a microscopic\nlevel with single-site resolution offers important insights. Here we report\nsite-resolved imaging of two-component fermionic Mott insulators, metals, and\nband insulators using ultracold atoms in a square lattice. For strong repulsive\ninteractions we observe two-dimensional Mott insulators containing over 400\natoms. For intermediate interactions, we observe a coexistence of phases. From\ncomparison to theory we find trap-averaged entropies per particle of\n$1.0\\,k_{\\mathrm{B}}$. In the band-insulator we find local entropies as low as\n$0.5\\,k_{\\mathrm{B}}$. Access to local observables will aid the understanding\nof fermionic many-body systems in regimes inaccessible by modern theoretical\nmethods."
    },
    {
        "anchor": "Exact ground-state correlation functions of an atomic-molecular boson\n  conversion model: We study the ground-state properties of an atomic-molecular boson conversion\nmodel through an exact Bethe Ansatz solution. For a certain range of parameter\nchoices, we prove that the ground-state Bethe roots lie on the positive\nreal-axis. We then use a continuum limit approach to obtain a singular integral\nequation characterising the distribution of these Bethe roots. Solving this\nequation leads to an analytic expression for the ground-state energy. The form\nof the expression is consistent with the existence of a line of quantum phase\ntransitions, which has been identified in earlier studies. This line demarcates\na molecular phase from a mixed phase. Certain correlation functions, which\ncharacterise these phases, are then obtained through the Hellmann-Feynman\ntheorem.",
        "positive": "Higgs amplitude mode in the vicinity of a $(2+1)$-dimensional quantum\n  critical point: We study the \"Higgs\" amplitude mode in the relativistic quantum O($N$) model\nin two space dimensions. Using the nonperturbative renormalization group we\ncompute the O($N$)-invariant scalar susceptibility in the vicinity of the\nzero-temperature quantum critical point. In the zero-temperature ordered phase,\nwe find a well defined Higgs resonance for $N=2$ with universal properties in\nagreement with quantum Monte Carlo simulations. The resonance persists at\nfinite temperature below the Berezinskii-Kosterlitz-Thouless transition\ntemperature. In the zero-temperature disordered phase, we find a maximum in the\nspectral function which is however not related to a putative Higgs resonance.\nFurthermore we show that the resonance is strongly suppressed for $N\\geq 3$."
    },
    {
        "anchor": "Bloch bound state of spin-orbit-coupled fermions in an optical lattice: Understanding fundamentals of few-body physics provides an interesting\nbottom-up approach for the clarification of many-body properties. The\nremarkable experimental progress in realizing spin-orbit coupling (SOC) in\noptical Raman lattices offers a renewed thrust towards discovering novel\nfew-body features induced by the interplay between SOC and optical lattices.\nUsing the Wilson renormalization method to account for high-band effects, we\nstudy the low-energy two-body scattering processes of spin-$1/2$ fermions in\nspin-orbit coupled optical lattices. We demonstrate that, under weak SOC,\nadding a small lattice potential would destabilize shallow two-body bound\nstates, contrary to conventional wisdom. On the other hand, when lattice is\nsufficiently deep, two-body bound states are always stabilized by increasing\nthe lattice depth. This intriguing non-monotonic behavior of the bound-state\nstability derives from the competition between SOC and optical lattices, and\ncan be explained by analyzing the low-energy density of states. We also discuss\nthe impact of high-band effects on such a behavior, as well as potential\nexperimental detections.",
        "positive": "Strongly Interacting Fermi Gases: Hydrodynamics and Beyond: This thesis considers out-of-equilibrium dynamics of strongly interacting\nnon-relativistic Fermi gases in several two and three dimensional geometries.\nThe tools of second-order hydrodynamics and gauge-gravity duality will be\nutilized to address this system. Many of the themes of this work are motivated\nby the observed similarities in transport properties between strongly\ninteracting Fermi gases and other very different strongly interacting quantum\nfluids such as the quark-gluon plasma, high temperature superconductors, and\nquantum field theories described by gauge-gravity duality. In particular, these\nsystems all nearly saturate the conjectured lower bound on the ratio of shear\nviscosity to entropy density $\\eta/s \\geq \\hbar/(4 \\pi k_B)$ coming from the\nAdS/CFT correspondence. Among other things, this observation, in conjunction\nwith current experiment and data analysis in atomic, condensed matter, and\nnuclear physics lends itself to the following questions: How perfect of a fluid\nis the strongly interacting Fermi gas, and can one find a more stringent\nconstraint on $\\eta/s$ in Fermi gases? Do the similarities in transport\nproperties among strongly interacting quantum systems extend beyond dynamics\ncontrolled by the hydrodynamical shear viscosity? In regards to the first\nquestion, by utilizing second-order hydrodynamics, it will be demonstrated that\nhigher-order collective modes of a harmonically trapped Fermi gas may serve as\na more sensitive probe of the shear viscosity. For the second question, both\nsecond-order hydrodynamics and a gravity dual theory are used to make\npredictions about dynamics occurring on short timescales where hydrodynamics is\nexpected to break down. In particular the appearance of a class of\n\"non-hydrodynamic\" collective modes not contained within a Navier-Stokes\ndescription of the strongly interacting Fermi gas will be discussed."
    },
    {
        "anchor": "Bifurcation of time crystals in driven and dissipative Rydberg atomic\n  gas: A time crystal is an exotic phase of matter where time-translational symmetry\nis broken; this phase differs from the spatial symmetry breaking induced in\ncrystals in space. Lots of experiments report the transition from a thermal\nequilibrium phase to time crystal phase. However, there is no experimental\nmethod to probe the bifurcation effect of distinct time crystals in quantum\nmany-body systems. Here, in a driven and dissipative many-body Rydberg atom\nsystem, we observe multiple continuous dissipative time crystals and emergence\nof more complex temporal symmetries beyond the single time crystal phase.\nBifurcation of time crystals in strongly interacting Rydberg atoms is observed;\nthe process manifests as a transition from a time crystal state of long\ntemporal order to one of short temporal order, or vice versa. By manipulating\nthe driving field parameters, we observe the time crystal's bistability and a\nhysteresis loop. These investigations indicate new possibilities for control\nand manipulation of the temporal symmetries of non-equilibrium systems.",
        "positive": "Absence of breakdown of ferrodark solitons exhibiting snake instability: We investigate the dynamical stability and real time dynamics of the\ntwo-types of ferrodark solitons (FDSs) which occur as topological magnetic\ndomain walls in the easy-plane phase of a quasi-two-dimensional (2D)\nferromagnetic spin-1 Bose-Einstein condensate. The type-I FDS has positive\ninertial mass and exhibits a single dynamical instability that generates in\nplane spin winding, causing polar-core spin vortex dipoles. The positive\ninertial mass leads to the elastic oscillations of the soliton under transverse\nperturbations. The type-II FDS has negative inertial mass and exhibits a snake\ninstability and a spin-twist instability, with the latter involving the\ngeneration of out of plane spin winding. Distinct from the normal dynamics of\nnegative mass solitons under long wave length transverse perturbations, the\nsnake instability does not lead to the type-II FDS breaking down. Instead,\nsegments of the type-II FDS convert to type-I and mass vortex dipoles are\nproduced. The resulting hybridized-chain of the two soliton types and vortices\nexhibits complex 2D soliton dynamics at long times while the vortices remain\nconfined and the topological structure of a magnetic domain wall is preserved."
    },
    {
        "anchor": "Monodromy and chaos for condensed bosons in optical lattices: We introduce a theory for the stability of a condensate in an optical\nlattice. We show that the understanding of the stability-to-ergodicity\ntransition involves the fusion of monodromy and chaos theory. Specifically, the\ncondensate can decay if a connected chaotic pathway to depletion is formed,\nwhich requires swap of seperatrices in phase-space.",
        "positive": "Heavily Enhanced Dynamic Stark Shift in a System of Bose Einstein\n  Condensation of Photons: The dynamic Stark shift of a high-lying atom in a system of Bose Einstein\ncondensation (BEC) of photons is discussed within the framework of\nnonrelativistic quantum electrodynamics (QED) theory. It is found that the\nStark shift of an atom in BEC of photons is modified by a temperature dependent\nfactor, compared to that in a normal two-dimensional photonic fluid. In\nphotonic BEC, the value of Stark shift is always greater than that in\ntwo-dimensional free space. Physical origin of the phenomenon is presented and\npotential application is also discussed."
    },
    {
        "anchor": "A quantum Langevin model for non-equilibrium condensation: We develop a quantum model for non-equilibrium Bose-Einstein condensation of\nphotons and polaritons in planar microcavity devices. The model builds upon\nlaser theory and includes the spatial dynamics of the cavity field, a\nsaturation mechanism and some frequency-dependence of the gain: quantum\nLangevin equations are written for a cavity field coupled to a continuous\ndistribution of externally pumped two-level emitters with a well-defined\nfrequency. As a an example of application, the method is used to study the\nlinearised quantum fluctuations around a steady-state condensed state. In the\ngood-cavity regime, an effective equation for the cavity field only is proposed\nin terms of a stochastic Gross-Pitaevskii equation. Perspectives in view of a\nfull quantum simulation of the non-equilibrium condensation process are finally\nsketched.",
        "positive": "Confinement of Bose-Einstein magnon condensates in adjustable complex\n  magnetization landscapes: Coherent wave states such as Bose-Einstein condensates (BECs), which\nspontaneously form in an overpopulated magnon gas even at room temperature,\nhave considerable potential for wave-based computing and information processing\nat microwave frequencies. The ability to control the transport properties of\nmagnon BECs plays an essential role for their practical use. Here, we\ndemonstrate spatio-temporal control of the BEC density distribution through the\nexcitation of magnon supercurrents in an inhomogeneously magnetized yttrium\niron garnet film. The BEC is created by microwave parametric pumping and probed\nby Brillouin light scattering spectroscopy. The desired magnetization profile\nis prepared by heating the film with optical patterns projected onto its\nsurface using a phase-based wavefront modulation technique. Specifically, we\nobserve a pronounced spatially localized magnon accumulation caused by magnon\nsupercurrents flowing toward each other originating in two heated regions. This\naccumulation effect increases the BEC lifetime due to the constant influx of\ncondensed magnons into the confinement region. The shown approach to manipulate\ncoherent waves provides an opportunity to extend the lifetime of freely\nevolving magnon BECs, create dynamic magnon textures, and study the interaction\nof magnon condensates formed in different regions of the sample."
    },
    {
        "anchor": "Universal quantum behaviors of interacting fermions in 1D traps: from\n  few particles to the trap thermodynamic limit: We investigate the ground-state properties of trapped fermion systems\ndescribed by the Hubbard model with an external confining potential. We discuss\nthe universal behaviors of systems in different regimes: from few particles,\ni.e. in dilute regime, to the trap thermodynamic limit.\n  The asymptotic trap-size (TS) dependence in the dilute regime (increasing the\ntrap size l keeping the particle number N fixed) is described by a universal TS\nscaling controlled by the dilute fixed point associated with the\nmetal-to-vacuum quantum transition. This scaling behavior is numerically\nchecked by DMRG simulations of the one-dimensional (1D) Hubbard model. In\nparticular, the particle density and its correlations show crossovers among\ndifferent regimes: for strongly repulsive interactions they approach those of a\nspinless Fermi gas, for weak interactions those of a free Fermi gas, and for\nstrongly attractive interactions they match those of a gas of hard-core bosonic\nmolecules.\n  The large-N behavior of systems at fixed N/l corresponds to a 1D trap\nthermodynamic limit. We address issues related to the accuracy of the local\ndensity approximation (LDA). We show that the particle density approaches its\nLDA in the large-l limit. When the trapped system is in the metallic phase,\ncorrections at finite l are O(l^{-1}) and oscillating around the center of the\ntrap. They become significantly larger at the boundary of the fermion cloud,\nwhere they get suppressed as O(l^{-1/3}) only. This anomalous behavior arises\nfrom the nontrivial scaling at the metal-to-vacuum transition occurring at the\nboundaries of the fermion cloud.",
        "positive": "Dispersions, weights, and widths of the single-particle spectral\n  function in the normal phase of a Fermi gas: The dispersions, weights, and widths of the peaks of the single-particle\nspectral function in the presence of pair correlations, for a Fermi gas with\neither attractive or repulsive short-range inter-particle interaction, are\ndetermined in the normal phase over a wide range of wave vectors, with a\ntwofold purpose. The first one is to determine how these dispersions identify\nboth an energy scale known as the pseudo-gap near the Fermi wave vector, as\nwell as an additional energy scale related to the contact C at large wave\nvectors. The second one is to differentiate the behaviors of the repulsive gas\nfrom the attractive one in terms of crossing versus avoided crossing of the\ndispersions near the Fermi wave vector. An analogy will also be drawn between\nthe occurrence of the pseudo-gap physics in a Fermi gas subject to pair\nfluctuations and the persistence of local spin waves in the normal phase of\nmagnetic materials."
    },
    {
        "anchor": "Highly polarized Fermi gases in two dimensions: We investigate the highly polarized limit of a two-dimensional (2D) Fermi\ngas, where we effectively have a single spin-down impurity atom immersed in a\nspin-up Fermi sea. By constructing variational wave functions for the impurity,\nwe map out the ground state phase diagram as a function of mass ratio M/m and\ninteraction strength. In particular, we determine when it is favorable for the\ndressed impurity (polaron) to bind particles from the Fermi sea to form a\ndimer, trimer or even larger clusters. Similarly to 3D, we find that the Fermi\nsea favors the trimer state so that it exists for M/m less than the critical\nmass ratio for trimer formation in the vacuum. We also find a region where\ndimers have finite momentum in the ground state, a scenario which corresponds\nto the Fulde-Ferrell-Larkin-Ovchinnikov superfluid state in the limit of large\nspin imbalance. For equal masses (M=m), we compute rigorous bounds on the\npolaron-dimer transition, and we show that the polaron energy and residue is\nwell captured by the variational approach, with the former quantity being in\ngood agreement with experiment. When there is a finite density of impurities,\nwe find that this polaron-dimer transition is preempted by a first-order\nsuperfluid-normal transition at zero temperature, but it remains an open\nquestion what happens at finite temperature.",
        "positive": "Chaotic level mixing in a two-band Bose-Hubbard model: We present a two-band Bose-Hubbard model which is shown to be minimal in the\nnecessary coupling terms at resonant tunneling conditions. The dynamics of the\nmany-body problem is studied by sweeping the system across an avoided level\ncrossing. The linear sweep generalizes Landau-Zener transitions from\nsingle-particle to many-body realizations. The temporal evolution of single-\nand two-body observables along the sweeps is investigated in order to\ncharacterize the non-equilibrium dynamics in our complex quantum system."
    },
    {
        "anchor": "Negative differential conductivity in an interacting quantum gas: Negative differential conductivity (NDC) is a widely exploited effect in\nmodern electronic components. Here, a proof-of-principle is given for the\nobservation of NDC in a quantum transport device for neutral atoms employing a\nmulti-mode tunneling junction. The transport of the many-body quantum system is\ngoverned by the interplay between the tunnel coupling, the interaction energy\nand the thermodynamics of intrinsic collisions, which turn the coherent\ncoupling into a hopping process. The resulting current voltage characteristics\nexhibit NDC, for which we identify a new microscopic physical mechanism. Our\nstudy opens new ways for the future implementation and control of complex\nneutral atom quantum circuits.",
        "positive": "Superfluid flow of polaron polaritons above Landau's critical velocity: We develop a theory for the interaction of light with superfluid optical\nmedia, describing the motion of quantum impurities that are created and dragged\nthrough the liquid by propagating photons. It is well known that a mobile\nimpurity suffers dissipation due to phonon emission as soon as it moves faster\nthan the speed of sound in the superfluid - Landau's critical velocity.\nSurprisingly we find that in the present hybrid light-matter setting,\npolaritonic impurities can be protected against environmental decoherence and\nbe allowed to propagate well above the Landau velocity without jeopardizing the\nsuperfluid response of the medium."
    },
    {
        "anchor": "Phase transition dimensionality crossover from two to three dimensions\n  in a trapped ultracold atomic Bose gas: The equilibrium properties of a weakly interacting atomic Bose gas across the\nBerezinskii-Kosterlitz-Thouless (BKT) and Bose-Einstein condensation (BEC)\nphase transitions are numerically investigated through a dimensionality\ncrossover from two to three dimensions. The crossover is realised by confining\nthe gas in an experimentally feasible hybridised trap which provides\nhomogeneity along the planar xy-directions through a box potential in tandem\nwith a harmonic transverse potential along the transverse z-direction. The\ndimensionality is modified by varying the frequency of the harmonic trap from\ntight to loose transverse trapping. Our findings, based on a stochastic\n(projected) Gross-Pitaevskii equation, showcase a continuous shift in the\ncharacter of the phase transition from BKT to BEC, and a monotonic increase of\nthe identified critical temperature as a function of dimensionality, with the\nstrongest variation exhibited for small chemical potential values up to\napproximately twice the transverse confining potential",
        "positive": "Quantum dynamics of hard-core bosons in tilted bichromatic optical\n  lattices: We study the dynamics of strongly repulsive Bose gas in tilted or driven\nbichromatic optical lattices. Using the Bose-Fermi mapping and exact numerical\nmethod, we calculate the reduced single-particle density matrices, and study\nthe dynamics of density profile, momentum distribution and condensate fraction.\nWe show the oscillating and breathing mode of dynamics, and depletion of\ncondensate for short time dynamics. For long time dynamics, we clearly show the\nreconstruction of system at integer multiples of Bloch-Zener time. We also show\nhow to achieve clear Bloch oscillation and Landau-Zener tunnelling for\nmany-particle systems."
    },
    {
        "anchor": "Two-dimensional composite solitons in a spin-orbit-coupled Fermi gas in\n  free space: We address a possibility of creating soliton states in oblate\nbinary-fermionic clouds in the framework of the density-functional theory,\nwhich includes the spin-orbit coupling (SOC) and nonlinear attraction between\nspin-up and down-polarized components of the spinor wave function. In the limit\nwhen the inter-component attraction is much stronger than the effective\nintra-component Pauli repulsion, the resulting model also represents a system\nof Gross-Pitaevskii equations for a binary Bose-Einstein condensate including\nthe SOC effect. We show that the model gives rise to two-dimensional quiescent\ncomposite solitons in free space. A stability region is identified for solitons\nof the mixed-mode type (which feature mixtures of zero-vorticity and vortical\nterms in both components), while solitons of the other type, semi-vortices\n(with the vorticity carried by one component) are unstable. Due to breaking of\nthe Galilean invariance by SOC, the system supports moving solitons with\nvelocities up to a specific critical value. Collisions between moving solitons\nare briefly considered too. The collisions lead, in particular, to a\nquasi-elastic rebound, or an inelastic outcome, which features partial merger\nof the solitons.",
        "positive": "Slow scrambling in sonic black holes: We study from the perspective of quantum information scrambling an acoustic\nblack hole modelled by two semi-infinite, stationary, one dimensional\ncondensates, connected by a spatial step-like discontinuity, and flowing\nrespectively at subsonic and supersonic velocities. We develop a simple\nanalytical treatment based on Bogolyubov theory of quantum fluctuations which\nis sufficient to derive analogue Hawking emission, and we compute out-of-time\norder correlations (OTOCs) of the Bose density field. We find that sonic black\nholes are slow scramblers contrary to their astrophysical counterparts: this\nmanifests in a power law growth $\\propto t^2$ of OTOCs in contrast to the\nexponential increase in time expected for fast scramblers."
    },
    {
        "anchor": "Self-consistent Description of Bose-Bose Droplets: Harmonically Trapped\n  Quasi-2D Droplets: We describe a quantum droplet of a Bose-Bose mixture squeezed by an external\nharmonic forces in one spatial direction. Our approach is based on the\nself-consistent method formulated in [1]. The true spatial droplet profile in\nthe direction of confinement is accounted for, however local density\napproximation is assumed in the free directions. We define a numerical approach\nto find the beyond-mean-field contribution to the chemical potential\n(Lee-Huang-Yang chemical potential) -- the quantity that determines the\ndroplet's profile. In addition to the numerical approach, we find the\nLee-Huang-Yang potential in the analytic form in two limiting cases: a\nperturbative result for a strong confinement and a semiclassical expression\nwhen confinement is very weak.",
        "positive": "Fractal Quasicondensation in One Dimension: We unveil a novel mechanism for quasicondensation of hard-core bosons in the\npresence of quasiperiodicity-induced multifractal single-particle states. The\nnew critical state, here dubbed fractal quasicondensate, is characterized by\nnatural orbitals with multifractal properties and by an occupancy of the lowest\nnatural orbital, {\\lambda}0 ~ L{\\gamma}, which grows with system size but with\na nonuniversal scaling exponent, {\\gamma} < 1/2. In contrast to fractal\nquasicondensates obtained when the chemical potential lies in a region of\nmultifractal single-particle states, placing the chemical potential in regions\nof localized or delocalized states yields, respectively, no condensation or the\nusual 1D quasicondensation with {\\gamma} = 1/2. Our findings are established by\nstudying one-dimensional hardcore bosons subjected to various quasiperiodic\npotentials, including the well-known Aubry-Andre model, employing a mapping to\nnon-interacting fermionics that allows for numerically exact results. We\ndiscuss how to test our findings in state-of-the-art ultracold atom\nexperiments."
    },
    {
        "anchor": "Ground State Properties of Anti-Ferromagnetic Spinor Bose gases in One\n  Dimension: We investigate the ground state properties of anti-ferromagnetic spin-1 Bose\ngases in one dimensional harmonic potential from the weak repulsion regime to\nthe strong repulsion regime. By diagonalizing the Hamiltonian in the Hilbert\nspace composed of the lowest eigenstates of single particle and spin\ncomponents, the ground state wavefunction and therefore the density\ndistributions, magnetization distribution, one body density matrix, and\nmomentum distribution for each components are obtained. It is shown that the\nspinor Bose gases of different magnetization exhibit the same total density\nprofiles in the full interaction regime, which evolve from the single peak\nstructure embodying the properties of Bose gases to the fermionized shell\nstructure of spin-polarized fermions. But each components display different\ndensity profiles, and magnetic domains emerge in the strong interaction limit\nfor $M=0.25$. In the strong interaction limit, one body density matrix and the\nmomentum distributions exhibit the same behaviours as those of spin-polarized\nfermions. The fermionization of momentum distribution takes place, in contrast\nto the $\\delta$-function-like distribution of single component Bose gases in\nthe full interaction region.",
        "positive": "Polarized Superfluidity in the imbalanced attractive Hubbard model: We investigate the attractive Hubbard model in infinite spatial dimensions by\nmeans of dynamical mean-field theory. Using a continuous-time Monte Carlo\nalgorithm in the Nambu formalism as an impurity solver, we directly deal with\nthe superfluid phase in the population imbalanced system. By calculating the\nsuperfluid order parameter, the magnetization, and the density of states, we\ndiscuss how the polarized superfluid state is realized in the attractive\nHubbard model at quarter filling. We find that a drastic change in the density\nof states is induced by spin imbalanced populations in the superfluid state."
    },
    {
        "anchor": "Pair interactions of heavy vortices in quantum fluids: The dynamics of quantum vortex pairs carrying heavy doping matter trapped\ninside their cores is studied. The nonlinear classical matter field formalism\nis used to build a universal mathematical model of a heavy vortex applicable to\ndifferent types of quantum mixtures. It is shown how the usual vortex dynamics\ntypical for undoped pairs qualitatively changes when heavy dopants are used:\nheavy vortices with opposite topological charges (chiralities) attract each\nother, while vortices with the same charge are repelled. The force responsible\nfor such behavior appears as a result of superposition of vortices velocity\nfields in the presence of doping substance and can be considered as a special\nrealization of the Magnus effect. The force is evaluated quantitatively and its\ninverse proportionality to the distance is demonstrated. The mechanism\ndescribed in this paper gives an example of how a light nonlinear classical\nfield may realize repulsive and attractive interactions between embedded heavy\nimpurities.",
        "positive": "Experimentally accessible witnesses of many-body localisation: The phenomenon of many-body localised (MBL) systems has attracted significant\ninterest in recent years, for its intriguing implications from a perspective of\nboth condensed-matter and statistical physics: they are insulators even at\nnon-zero temperature and fail to thermalise, violating expectations from\nquantum statistical mechanics. What is more, recent seminal experimental\ndevelopments with ultra-cold atoms in optical lattices constituting analog\nquantum simulators have pushed many-body localised systems into the realm of\nphysical systems that can be measured with high accuracy. In this work, we\nintroduce experimentally accessible witnesses that directly probe distinct\nfeatures of MBL, distinguishing it from its Anderson counterpart. We insist on\nbuilding our toolbox from techniques available in the laboratory, including\non-site addressing, super-lattices, and time-of-flight measurements,\nidentifying witnesses based on fluctuations, density-density correlators,\ndensities, and entanglement. We build upon the theory of out of equilibrium\nquantum systems, in conjunction with tensor network and exact simulations,\nshowing the effectiveness of the tools for realistic models."
    },
    {
        "anchor": "High-precision analysis of Feshbach resonances in a Mott insulator: We show that recent high-precision measurements of relative on-site\ninteraction energies $\\Delta U$ in a Mott insulator require a theoretical\ndescription beyond the standard Hubbard-model interpretation, when combined\nwith an accurate coupled-channels calculation. In contrast to more\nsophisticated lattice models, which can be elaborate especially for parameter\noptimization searches, we introduce an easy to use effective description of $U$\nvalid over a wide range of interaction strengths modeling atomic pairs confined\nto single lattice sites. This concise model allows for a straightforward\ncombination with a coupled-channels analysis. With this model we perform such a\ncoupled-channels analysis of high-precision $^7$Li spectroscopic data on the\non-site interaction energy $U$, which spans over four Feshbach resonances and\nprovide an accurate and consistent determination of the associated resonance\npositions. Earlier experiments on three of the Feshbach resonances are\nconsistent with this new analysis. Moreover, we verify our model with a more\nrigorous numerical treatment of the two atom system in an optical lattice.",
        "positive": "Thermodynamic properties of rotating trapped ideal Bose gases: Ultracold atomic gases can be spined up either by confining them in rotating\nframe, or by introducing ``synthetic\" magnetic field. In this paper,\nthermodynamics of rotating ideal Bose gases are investigated within\ntruncated-summation approach which keeps to take into account the discrete\nnature of energy levels, rather than to approximate the summation over\nsingle-particle energy levels by an integral as does in semi-classical\napproximation. Our results show that Bose gases in rotating frame exhibit much\nstronger dependence on rotation frequency than those in ``synthetic\" magnetic\nfield. Consequently, BEC can be more easily suppressed in rotating frame than\nin ``synthetic\" magnetic field."
    },
    {
        "anchor": "Infinite dipolar droplet -- a simple theory for the macro-droplet regime: In this paper we develop a theory for an infinitely long droplet state of a\nzero temperature dipolar bosonic gas. The infinite droplet theory yields\nsimpler equations to solve for the droplet state and its collective\nexcitations. We explore the behavior of infinite droplets using numerical and\nvariational solutions, and demonstrate that it can provide a quantitative\ndescription of large finite droplets of the type produced in experiments. We\nalso consider the axial speed of sound and the thermodynamic limit of a dipolar\ndroplet.",
        "positive": "Excitation spectrum of a supersolid: Conclusive experimental evidence of a supersolid phase in any known condensed\nmatter system is presently lacking. On the other hand, a supersolid phase has\nbeen recently predicted for a system of spinless bosons in continuous space,\ninteracting via a broad class of soft-core, repulsive potentials. Such an\ninteraction can be engineered in assemblies of ultracold atoms, providing a\nwell-defined pathway to the unambiguous observation of this fascinating phase\nof matter. In this article, we study by first principle computer simulations\nthe elementary excitation spectrum of the supersolid, and show that it features\ntwo distinct modes, namely a solid-like phonon and a softer collective\nexcitation, related to broken translation and gauge symmetry respectively."
    },
    {
        "anchor": "Quantum-State Controlled Penning Ionization Reactions between Ultracold\n  Alkali and Metastable Helium Atoms: In an ultracold, optically trapped mixture of $^{87}$Rb and metastable\ntriplet $^4$He atoms we have studied trap loss for different spin-state\ncombinations, for which interspecies Penning ionization is the main two-body\nloss process. We observe long trapping lifetimes for the purely quartet\nspin-state combination, indicating strong suppression of Penning ionization\nloss by at least two orders of magnitude. For the other spin-mixtures we\nobserve short lifetimes that depend linearly on the doublet character of the\nentrance channel. We compare the extracted loss rate coefficient with recent\npredictions of multichannel quantum-defect theory for reactive collisions\ninvolving a strong exothermic loss channel and find near-universal loss for\ndoublet scattering. Our work demonstrates control of reactive collisions by\ninternal atomic state preparation.",
        "positive": "Flat Band Quantum Scar: We show that a quantum scar state, an atypical eigenstate breaking eigenstate\nthermalization hypothesis embedded in a many-body energy spectrum, can be\nconstructed in flat band systems. The key idea of our construction is to make\nuse of orthogonal compact localized states. We concretely discuss our\nconstruction scheme, taking a saw-tooth flat lattice system as an example, and\nnumerically demonstrate the presence of a quantum scar state. Examples of\nhigher-dimensional systems are also addressed. Our construction method of\nquantum scar has broad applications to various flat band systems."
    },
    {
        "anchor": "Mobility edge of the two dimensional Bose-Hubbard model: We analyze the disorder driven localization of the two dimensional\nBose-Hubbard model by evaluating the full low energy quasiparticle spectrum via\na recently developed fluctuation operator expansion method. For any strength of\nthe local interaction we find a mobility edge that displays an approximately\nexponential decay with increasing disorder strength. We determine the\nfinite-size scaling collapse and exponents at this critical line finding that\nthe localization of excitations is characterized by weak multi-fractality and a\nthermal-like critical gap ratio. A direct comparison to a recent experiment\nyields an excellent match of the predicted finite-size transition point and\nscaling of single particle correlations.",
        "positive": "Tunable Spin-orbit Coupling and Quantum Phase Transition in a Trapped\n  Bose-Einstein Condensate: Spin-orbit coupling (SOC), the intrinsic interaction between a particle spin\nand its motion, is responsible for various important phenomena, ranging from\natomic fine structure to topological condensed matter physics. The recent\nexperimental breakthrough on the realization of SOC for ultra-cold atoms\nprovides a completely new platform for exploring spin-orbit coupled superfluid\nphysics. However, the SOC strength in the experiment, determined by the applied\nlaser wavelengths, is not tunable. In this Letter, we propose a scheme for\ntuning the SOC strength through a fast and coherent modulation of the laser\nintensities. We show that the many-body interaction between atoms, together\nwith the tunable SOC, can drive a \\textit{quantum phase transition} (QPT) from\nspin-balanced to spin-polarized ground states in a harmonic trapped\nBose-Einstein condensate (BEC). This transition realizes the long-sought QPT in\nthe quantum Dicke model, and may have important applications in quantum optics\nand quantum information. We characterize the QPT using the periods of\ncollective oscillations (center of mass motion and scissors mode) of the BEC,\nwhich show pronounced peaks and damping around the quantum critical point."
    },
    {
        "anchor": "Emergent periodic and quasiperiodic lattices on surfaces of synthetic\n  Hall tori and synthetic Hall cylinders: Synthetic spaces allow physicists to bypass constraints imposed by certain\nphysical laws in experiments. Here, we show that a synthetic torus, which\nconsists of a ring trap in the real space and internal states of ultracold\natoms cyclically coupled by Laguerre-Gaussian Raman beams, could be threaded by\na net effective magnetic flux through its surface---an impossible mission in\nthe real space. Such synthetic Hall torus gives rise to a periodic lattice in\nthe real dimension, in which the periodicity of density modulation of atoms\nfractionalizes that of the Hamiltonian. Correspondingly, the energy spectrum is\nfeatured by multiple bands grouping into clusters with nonsymmorphic symmetry\nprotected band crossings in each cluster, leading to braidings of wavepackets\nin Bloch oscillations. Our scheme allows physicists to glue two synthetic Hall\ntori such that localization may emerge in a quasicrystalline lattice. If the\nLaguerre-Gaussian Raman beams and ring traps were replaced by linear Raman\nbeams and ordinary traps, a synthetic Hall cylinder could be realized and\ndeliver many of the aforementioned phenomena.",
        "positive": "Out-of-equilibrium structures in strongly interacting Rydberg gases with\n  dissipation: The non-equilibrium dynamics of a gas of cold atoms in which Rydberg states\nare off-resonantly excited is studied in the presence of noise. The interplay\nbetween interaction and off-resonant excitation leads to an initial dynamics\nwhere aggregates of excited Rydberg atoms slowly nucleate and grow, eventually\nreaching long-lived meta-stable arrangements which then relax further on much\nlonger timescales. This growth dynamics is governed by an effective Master\nequation which permits a transparent and largely analytical understanding of\nthe underlying physics. By means of extensive numerical simulations we study\nthe many-body dynamics and the correlations of the resulting non-equilibrium\nstates in various dimensions. Our results provide insight into the dynamical\nrichness of strongly interacting Rydberg gases in noisy environments, and\nhighlight the usefulness of these kind of systems for the exploration of\nsoft-matter-type collective behaviour."
    },
    {
        "anchor": "Tunable three-body interactions in driven two-component Bose-Einstein\n  condensates: We propose and demonstrate the appearance of an effective attractive\nthree-body interaction in coherently-driven two-component Bose Einstein\ncondensates. It originates from the spinor degree of freedom that is affected\nby a two-body mean-field shift of the driven transition frequency. Importantly,\nits strength can be controlled with the Rabi-coupling strength and it does not\ncome with additional losses. In the experiment, the three-body interactions are\nadjusted to play a predominant role in the equation of state of a cigar-shaped\ntrapped condensate. This is confirmed though two striking observations: a\ndownshift of the radial breathing mode frequency and the radial collapses for\npositive values of the dressed-state scattering length.",
        "positive": "Artificial gauge fields with ultracold atoms: Gauge fields are ubiquitous in nature. In the context of quantum\nelectrodynamics, you may be most familiar with the photon, which represents the\ngauge field mediating electromagnetic forces. But there are also gluons, which\nmediate strong forces, and the W and Z particles, which mediate the weak\nforces. According to the standard model, those few gauge bosons, in fact,\nmediate all elementary interactions."
    },
    {
        "anchor": "Computational Theory of a splitting BEC using a Generalized Wannier\n  basis I: Theory and Statics: We investigate the behavior of a Bose-Einstein Condensate (BEC) under the\ninfluence of a central barrier as the particle number trends towards the\nthermodynamic limit. In order to perform these studies, we present a novel\nmethod which is tractable in the large-$N$ limit. This method employs what may\nbe considered to be a generalized Wannier basis, which successfully\nincorporates features of previous theoretical and computational assays to the\nsplitting problem, including mean field effects, and has access to the\ndimensionality, trap parameters, and particle numbers relevant to recent\nexperiments. At any barrier height we are able to discern between a two-mode\nstate and a state which is described sufficiently by mean field theory and,\nfurther, give a criterion and technique for matching the two-mode theory to the\nzero-barrier state. We compare the basis used in this model to the de-localized\nbasis functions underlying alternate models used in recent theoretical work on\nthe double-well splitting problem and show that only the generalized Wannier\nbasis displays the level crossing and emergence of two complex order parameters\nwith overall $U(1) \\oplus U(1)$ symmetry as expected from a large-$N$ analogue\nof the Superfluid to Mott insulator transition. Using this model, we identify a\nuniversal structure, independent of $N$, in this phase transition. We also\npresent an analytic and model-independent description of this universal\nstructure and discuss its consequences for realizing true two-mode physics with\na BEC which trends towards the thermodynamic limit.",
        "positive": "Spectroscopy of elementary excitations from quench dynamics in a dipolar\n  XY Rydberg simulator: We use a Rydberg quantum simulator to demonstrate a new form of spectroscopy,\ncalled quench spectroscopy, which probes the low-energy excitations of a\nmany-body system. We illustrate the method on a two-dimensional simulation of\nthe spin-1/2 dipolar XY model. Through microscopic measurements of the spatial\nspin correlation dynamics following a quench, we extract the dispersion\nrelation of the elementary excitations for both ferro- and anti-ferromagnetic\ncouplings. We observe qualitatively different behaviors between the two cases\nthat result from the long-range nature of the interactions, and the frustration\ninherent in the antiferromagnet. In particular, the ferromagnet exhibits\nelementary excitations behaving as linear spin waves. In the anti-ferromagnet,\nspin waves appear to decay, suggesting the presence of strong nonlinearities.\nOur demonstration highlights the importance of power-law interactions on the\nexcitation spectrum of a many-body system."
    },
    {
        "anchor": "Topological phases of spinless $p$-orbital fermions in zigzag optical\n  lattices: Motivated by the experiment [St-Jean {\\it et al}., Nature Photon. {\\bf 11},\n651 (2017)] on topological phases with collective photon modes in a zigzag\nchain of polariton micropillars, we study spinless $p$-orbital fermions with\nlocal interorbital hoppings and repulsive interactions between $p_x$ and $p_y$\nbands in zigzag optical lattices. We show that spinless $p$-band fermions in\nzigzag optical lattices can mimic the interacting Su-Schrieffer-Heeger model\nand the effective transverse field Ising model in the presence of local\nhoppings. We analytically and numerically discuss the ground-state phases and\nquantum phase transitions of the model. This work provides a simple scheme to\nsimulate topological phases and the quench dynamics of many-body systems in\noptical lattices.",
        "positive": "Universal few-body physics in a harmonic trap: Few-body systems with resonant short-range interactions display universal\nproperties that do not depend on the details of their structure or their\ninteractions at short distances. In the three-body system, these properties\ninclude the existence of a geometric spectrum of three-body Efimov states and a\ndiscrete scaling symmetry. Similar universal properties appear in 4-body and\npossibly higher-body systems as well. We set up an effective theory for\nfew-body systems in a harmonic trap and study the modification of universal\nphysics for 3- and 4-particle systems in external confinement. In particular,\nwe focus on systems where the Efimov effect can occur and investigate the\ndependence of the 4-body spectrum on the experimental tuning parameters."
    },
    {
        "anchor": "Universal Cooling Scheme for Quantum Simulation: At present, there is a worldwide effort to use cold atoms to simulate\nstrongly correlated quantum many-body systems. It is hoped that these\n\"simulations\" will provide solutions to many unsolved problems. However, the\nrelevant energy scales in most of these experiments are so small that one has\nto go to entropy regimes far below those achievable today. Here, we present a\ngeneral scheme to extract entropy directly from the region of interest. The\nlate stage of this process is equivalent to a continuous \"evaporation\", and is\nable to combat intrinsic heating of the system. For illustration, we show how\nto cool a weak coupling BCS superfluid (with $T_{c}\\sim 10^{-10}$K) to\n$10^{-11}$K with this simple procedure, with entropy per particle as low as\n$5\\times 10^{-4}k_{B}$ in the superfluid region.",
        "positive": "Stable and mobile two-dimensional dipolar ring-dark-in-bright\n  Bose-Einstein condensate soliton: We demonstrate robust, stable, mobile two-dimensional (2D) dipolar\nring-dark-in-bright (RDB) Bose-Einstein condensate (BEC) solitons for repulsive\ncontact interaction, subject to a harmonic trap along the $y$ direction\nperpendicular to the polarization direction $z$. Such a RDB soliton has a\nring-shaped notch (zero in density) imprinted on a 2D bright soliton free to\nmove in the $x-z$ plane. At medium velocity the head-on collision of two such\nsolitons is found to be quasi elastic with practically no deformation. The\npossibility of creating the RDB soliton by phase imprinting is demonstrated.\nThe findings are illustrated using numerical simulation employing realistic\ninteraction parameters in a dipolar $^{164}$Dy BEC."
    },
    {
        "anchor": "Generalized Stefan-Boltzmann law: We reconsider the thermodynamic derivation by L. Boltzmann of the Stefan law\nand we generalize it for various different physical systems {\\it whose chemical\npotential vanishes}. Being only based on classical arguments, therefore\nindependent of the quantum statistics, this derivation applies as well to the\nsaturated Bose gas in various geometries as to \"compensated\" Fermi gas near a\nneutrality point, such as a gas of Weyl Fermions. It unifies in the same\nframework the thermodynamics of many different bosonic or fermionic\nnon-interacting gases which were until now described in completely different\ncontexts.",
        "positive": "Hamiltonian formulation of the effective kinetic theory for superfluid\n  Fermi liquids: We present in a local form the time dependent effective description of a\nsuperfluid Fermi liquid which includes Landau damping effects at $T\\neq 0$.\nThis is achieved by the introduction of an additional variable, the\nquasiparticle distribution function, which obeys a simple kinetic equation. The\ntransport equation is coupled with first order equations for the Goldstone mode\nand the particle density. We prove that a main feature of this formulation is\nits Hamiltonian structure relative to a certain Poisson bracket. We construct\nthe Hamiltonian to quadratic order."
    },
    {
        "anchor": "Quantum properties of a binary bosonic mixture in a double well: This work contains a detailed analysis of the properties of the ground state\nof a two-component two-sites Bose-Hubbard model, which captures the physics of\na binary mixture of Bose-Einstein condensates trapped in a double-well\npotential. The atom-atom interactions within each species and among the two\nspecies are taken as variable parameters while the hopping terms are kept\nfixed. To characterize the ground state we use observables such as the\nimbalance of population and its quantum uncertainty. The quantum many-body\ncorrelations present in the system are further quantified by studying the\ndegree of condensation of each species, the entanglement between the two sites\nand the entanglement between the two species. The latter is measured by means\nof the Schmidt gap, the von Neumann entropy or the purity obtained after\ntracing out a part of the system. A number of relevant states are identified,\ne.g. Schr\\\"odinger catlike many-body states, in which the outcome of the\npopulation imbalance of both components is completely correlated, and other\nstates with even larger von Neumann entropy which have a large spread in Fock\nspace.",
        "positive": "Interplay of Kelvin-Helmholtz and superradiant instabilities of an array\n  of quantized vortices in a two-dimensional Bose--Einstein condensate: We investigate the various physical mechanisms that underlie the dynamical\ninstability of a quantized vortex array at the interface between two\ncounter-propagating superflows in a two-dimensional Bose--Einstein condensate.\nInstabilities of markedly different nature are found to dominate in different\nflow velocity regimes. For moderate velocities where the two flows are\nsubsonic, the vortex lattice displays a quantized version of the hydrodynamic\nKelvin--Helmholtz instability (KHI), with the vortices rolling up and\nco-rotating. For supersonic flow velocities, the oscillation involved in the\nKHI can resonantly couple to acoustic excitations propagating away in the bulk\nfluid on both sides. This makes the KHI rate to be effectively suppressed and\nother mechanisms to dominate: For finite and relatively small systems along the\ntransverse direction, the instability involves a repeated superradiant\nscattering of sound waves off the vortex lattice; for transversally unbound\nsystems, a radiative instability dominates, leading to the simultaneous growth\nof a localized wave along the vortex lattice and of acoustic excitations\npropagating away in the bulk. Finally, for slow velocities, where the KHI rate\nis intrinsically slow, another instability associated to the rigid lateral\ndisplacement of the vortex lattice due to the vicinity of the system's boundary\nis found to dominate."
    },
    {
        "anchor": "Competing instabilities at long length scales in the one-dimensional\n  Bose-Fermi-Hubbard model at commensurate fillings: We study the phase diagram of the one-dimensional Bose-Fermi-Hubbard model at\nunit filling for the scalar bosons and half filling for the $S=1/2$ fermions\nusing quantum Monte Carlo simulations. The bare interaction between the\nfermions is set to zero. A central question of our study is what type of\ninteractions can be induced between the fermions by the bosons, for both weak\nand strong interspecies coupling. We find that the induced interactions can\nlead to competing instabilities favoring phase separation, superconducting\nphases, and density wave structures, in many cases at work on length scales of\nmore than 100 sites. Marginal bosonic superfluids with a density matrix\ndecaying faster than what is allowed for pure bosonic systems with on-site\ninteractions, are also found.",
        "positive": "Domain percolation in a quenched ferromagnetic spinor condensate: We show that the easy-axis (EA) magnetic domains formed in a quenched\nferromagnetic spinor condensate are described by percolation theory. We\nintroduce a generalized spin rotation to vary the proportion of positive and\nnegative EA domains, allowing us to explore domain percolation. Using\nsimulations we investigate the finite-size scaling behaviour to extract the\ncorrelation length critical exponent and the transition point. We analyse the\nsensitivity of our results to the early-time dynamics of the system, the\nquadratic Zeeman energy, and the threshold condition used to define the\npositive (percolating) domains."
    },
    {
        "anchor": "Reversal of quantised Hall drifts at non-interacting and interacting\n  topological boundaries: The transport properties of gapless edge modes at boundaries between\ntopologically distinct domains are of fundamental and technological importance.\nTherefore, it is crucial to gain a better understanding of topological edge\nstates and their response to interparticle interactions. Here, we\nexperimentally study long-distance quantised Hall drifts in a harmonically\nconfined topological pump of non-interacting and interacting ultracold\nfermionic atoms. We find that quantised drifts halt and reverse their direction\nwhen the atoms reach a critical slope of the confining potential, revealing the\npresence of a topological boundary. The drift reversal corresponds to a band\ntransfer between a band with Chern number $C = +1$ and a band with $C = -1$ via\na gapless edge mode, in agreement with the bulk-edge correspondence for\nnon-interacting particles. We establish that a non-zero repulsive Hubbard\ninteraction leads to the emergence of an additional edge in the system, relying\non a purely interaction-induced mechanism, in which pairs of fermions are\nsplit.",
        "positive": "Superfluid phases and excitations in a cold gas of d-wave interacting\n  bosonic atoms and molecules: Motivated by recent advance in orbitally tuned Feshbach resonance\nexperiments, we analyze the ground-state phase diagram and related low-energy\nexcitation spectra of a d-wave interacting Bose gas. A two-channel model with\nd-wave symmetric interactions and background s-wave interactions is adopted to\ncharacterize the gas. The ground state is found to show three interesting\nphases: atomic, molecular, and atomic-molecular superfluidity. Remarkably\ndifferently from what was previously known in the p-wave case, the atomic\nsuperfluid is found to be momentum-independent in the present d-wave case.\nBogoliubov spectra above each superfluid phase are obtained both analytically\nand numerically."
    },
    {
        "anchor": "Dynamical structure factor and a new method to measure the pairing gap\n  in two-dimensional attractive Fermi-Hubbard model: By calculating the dynamical structure factor along the high symmetry\ndirections in the Brillouin zone, the dynamical excitations in two-dimensional\nattractive Fermi-Hubbard model are studied based on the random-phase\napproximation. At the small transfer momentum, the sound speed can be obtained\nand is suppressed by the interaction strength. In particular, at the transfer\nmomentum ${\\bf q}=\\left[\\pi,\\pi\\right]$, the dynamical structure factor\nconsists of a sharp bosonic molecular excitation peak in the low-energy region\nand a broad atomic excitation band in the higher energy region. Furthermore, as\nthe hopping strength increases (the interaction strength decreases), the weight\nof the molecular excitation peak decreases monotonically while the weight of\nthe atomic excitations increases quickly. The area of the molecular excitation\npeak scales with the square of the pairing gap, which also applies to the\nspin-orbit coupling case. These theoretical results show that the pairing gap\nin optical lattice can be obtained experimentally by measuring the dynamical\nstructure factor at ${\\bf q}=\\left[\\pi,\\pi\\right]$.",
        "positive": "Bloch Oscillations in Optical and Zeeman Lattices in the Presence of\n  Spin-Orbit Coupling: We address Bloch oscillations of a spin-orbit coupled atom in periodic\npotentials of two types: Optical and Zeeman lattices. We show that in optical\nlattices the spin-orbit coupling allows controlling the direction of atomic\nmotion and may lead to complete suppression of the oscillations at specific\nvalues of the coupling strength. In Zeeman lattices the energy bands are found\nto cross each other at the boundaries of the Brillouin zone, resulting in\nperiod-doubling of the oscillations. In all cases, the oscillations are\naccompanied by rotation of the pseudo-spin, with a dynamics that is determined\nby the strength of the spin-orbit coupling. The predicted effects are discussed\nalso in terms of a Wannier-Stark ladder, which in optical lattices consist of\ntwo mutually-shifted equidistant sub-ladders."
    },
    {
        "anchor": "Avalanche Mechanism for the Enhanced Loss of Ultracold Atoms: In several experiments with ultracold trapped atoms, a narrow loss feature\nhas been observed near an {\\it atom-dimer resonance}, at which there is an\nEfimov trimer at the atom-dimer threshold. The conventional interpretation of\nthese loss features is that they are produced by the {\\it avalanche mechanism},\nin which the energetic atom and dimer from 3-body recombination undergo\nsecondary elastic collisions that produce additional atoms with sufficient\nenergy to escape from the trapping potential. We use Monte Carlo methods to\ncalculate the average number of atoms lost and the average heat generated by\nrecombination events in a Bose-Einstein condensate and in a thermal gas. We\nimprove on previous models by taking into account the energy-dependence of the\ncross sections, the spacial structure of the atom cloud, and the elastic\nscattering of the atoms. We show that the avalanche mechanism cannot produce a\nnarrow loss feature near the atom-dimer resonance. The number of atoms lost\nfrom a recombination event can be more than twice as large as the 3 that would\nbe obtained in the absence of secondary collisions. However the resulting loss\nfeature is broad and its peak is at a scattering length that is larger than the\natom-dimer resonance and depends on the trap depth.",
        "positive": "Half-vicinity model and a phase diagram for quantum oscillations in\n  confined and degenerate Fermi gases: We propose an analytical model for the accurate calculation of size and\ndensity dependent quantum oscillations in thermodynamic and transport\nproperties of confined and degenerate non-interacting Fermi gases. We provide a\nuniversal, material independent, recipe that explicitly separates oscillatory\nquantum regime from stationary classical regime. Our model quite accurately\nestimates quantum oscillations depending on confinement and degeneracy. We\nconstruct a phase diagram representing stationary and oscillatory regimes on\ndegeneracy-confinement space. Analytical expressions of phase transition\ninterfaces are derived for different dimensions. The critical point on the\nphase diagram, which separates entirely stationary and entirely oscillatory\nregions, is determined and their aspect ratio dependencies are examined.\nQuantum oscillations as well as their periods are analytically expressed for\none-dimensional case. Accuracy of our model is verified through quantum\noscillations in electronic specific heat capacity. We also compare the\npredictions of our half-vicinity model, based on bounded sums, with those of\ninfinite sums, for the oscillatory violation of entropy-heat capacity\nequivalence in degenerate limit to show the accuracy of our model. Furthermore,\nsimilarities between functional behaviors of total occupancy variance and\nconventional density of states functions at Fermi level are discussed."
    },
    {
        "anchor": "Excitation spectrum and supersolidity of a two-leg bosonic ring ladder: We consider a system of weakly interacting bosons confined on a planar double\nlattice ring subjected to two artificial gauge fields. This system is known to\ndisplay three phases, the Meissner phase where the flow of particles is carried\nat the edges of the system without transverse current, a vortex phase\ncharacterized by non-zero transverse current, and a biased-ladder phase,\ncharacterized by an imbalance of the population of the two rings. We use the\nBogoliubov approximation to determine the excitation spectrum in the three\nphases, the dynamic structure factor and the quantum fluctuation corrections to\nthe first-order correlation function. Our analysis reveals supersolid features\nas well as Josephson modes, corresponding to out-of-phase modes of the finite\nring.",
        "positive": "Spin drag Hall effect in a rotating Bose mixture: We show that in a rotating two-component Bose mixture, the spin drag between\nthe two different spin species shows a Hall effect. This spin drag Hall effect\ncan be observed experimentally by studying the out-of-phase dipole mode of the\nmixture. We determine the damping of this mode due to spin drag as a function\nof temperature. We find that due to Bose stimulation there is a strong\nenhancement of the damping for temperatures close to the critical temperature\nfor Bose-Einstein condensation."
    },
    {
        "anchor": "Spontaneous formation and relaxation of spin domains in\n  antiferromagnetic spin-1 quasi-condensates: Quantum systems of many interacting particles at low temperatures generally\norganize themselves into ordered phases of matter, whose nature and symmetries\nare captured by an order parameter. In the simplest cases, this order parameter\nis spatially uniform. For example, a system of localized spins with\nferromagnetic interactions align themselves to a common direction and build up\na macroscopic magnetization on large distances. However, non-uniform situations\nalso exist in nature, for instance in antiferromagnetism where the\nmagnetization alternates in space. The situation becomes even richer when the\nspin-carrying particles are mobile, for instance in the so-called stripe phases\nemerging for itinerant electrons in strongly-correlated materials.\nUnderstanding such inhomogeneously ordered states is of central importance in\nmany-body physics. In this work, we study experimentally the magnetic ordering\nof itinerant spin-1 bosons in inhomegeneous spin domains at nano-Kelvin\ntemperatures. We demonstrate that spin domains form spontaneously after a phase\nseparation transition, \\textit{i.e.} in the absence of external magnetic force,\npurely because of the antiferromagnetic interactions between the atoms.\nFurthermore, we explore how the equilibrium domain configuration emerges from\nan initial state prepared far-from-equilibrium.",
        "positive": "Ultracold mixtures of atomic Li-6 and Cs-133 with tunable interactions: We report the experimental and theoretical study of two-body interactions in\na $^{6}$Li-$^{133}$Cs Fermi- Bose mixture. Using a translatable dipole trap\nsetup, we have successfully trapped the two species in the same trap with\ntemperatures of a few microkelvins. By monitoring atom number loss and\ninter-species thermalization, we identify five s-wave interspecies Feshbach\nresonances in the lowest two scattering channels. We construct a coupled\nchannels model using molecular potentials to fit and characterize these\nresonances. Two of the resonances are as wide as 60 G and thus should be\nsuitable for creating Feshbach molecules and searching for universal few-body\nscaling."
    },
    {
        "anchor": "Shell-shaped quantum droplet in a three-component ultracold Bose gas: We present a scheme to generate shell-shaped droplet in a three-component\n(1,2,3) ultracold Bose gas. Here binary mixtures (1,2) and (2,3) form quantum\ndroplets due to inter-species attractions, and the two droplets are mutually\nimmiscible due to strong 1-3 repulsion. Importantly, the shared component-2\nserves as a glue to link the two droplets together as a globally self-bound\nobject. In this system, the outer droplet naturally develops a shell structure,\nand its radius and width can be conveniently tuned through the size of core\ndroplet. Moreover, to reach an equilibrium with the shell, the core droplet\ndisplays very different spin densities as compared to the vacuum case. These\nresults have been demonstrated in a realistic $^{23}$Na-$^{39}$K-$^{41}$K\nmixture. Our scheme liberates the shell-shaped Bose gas from stringent\nconditions with microgravity or fine-tuned traps, and can be readily\nimplemented in cold atoms laboratories on Earth. This paves the way for future\nexploration of quantum droplets in curved space with non-trivial real-space\ntopologies.",
        "positive": "Polaronic atom-trimer continuity in three-component Fermi gases: Recently it has been proposed that three-component Fermi gases may exhibit a\nnew type of crossover physics in which an unpaired Fermi sea of atoms smoothly\nevolves into that of trimers in addition to the ordinary BCS-BEC crossover of\ncondensed pairs. Here we study its corresponding polaron problem in which a\nsingle impurity atom of one component interacts with condensed pairs of the\nother two components with equal populations. By developing a variational\napproach in the vicinity of a narrow Feshbach resonance, we show that the\nimpurity atom smoothly changes its character from atom to trimer with\nincreasing the attraction and eventually there is a sharp transition to dimer.\nThe emergent polaronic atom-trimer continuity can be probed in ultracold atoms\nexperiments by measuring the impurity spectral function. Our novel crossover\nwave function properly incorporating the polaronic atom-trimer continuity will\nprovide a useful basis to further investigate the phase diagram of\nthree-component Fermi gases in more general situations."
    },
    {
        "anchor": "Spectroscopy of momentum state lattices: We explore a technique for probing energy spectra in synthetic lattices that\nis analogous to scanning tunneling microscopy. Using one-dimensional synthetic\nlattices of coupled atomic momentum states, we explore this spectroscopic\ntechnique and observe qualitative agreement between the measured and simulated\nenergy spectra for small two- and three-site lattices as well as a uniform\nmany-site lattice. Finally, through simulations, we show that this technique\nshould allow for the exploration of the topological bands and the fractal\nenergy spectrum of the Hofstadter model as realized in synthetic lattices.",
        "positive": "Quantum hexatic order in two-dimensional dipolar and charged fluids: Recent advances in cold atom experimentation suggest that studies of quantum\ntwo-dimensional melting of dipolar molecules, with dipoles aligned\nperpendicular to ordering plane, may be on the horizon. An intriguing aspect of\nthis problem is that two-dimensional \\emph{classical} aligned dipoles (already\nstudied in great detail in soft matter experiments on magnetic colloids) are\nknown to melt via a two-stage process, with an intermediate hexatic phase\nseparating the usual crystal and isotropic fluid phases. We estimate here the\neffect of quantum fluctuations on this hexatic phase, for both dipolar systems\nand charged Wigner crystals. Our approximate phase diagrams rely on a pair of\nLindemann criteria, suitably adapted to deal with effects of thermal\nfluctuations in two dimensions. As part of our analysis, we determine the\nphonon spectra of quantum particles on a triangular lattice interacting with\nrepulsive $1/r^3$ and $1/r$ potentials. A large softening of the transverse and\nlongitudinal phonon frequencies, due to both lattice effects and quantum\nfluctuations, plays a significant role in our analysis. The hexatic phase is\npredicted to survive down to very low temperatures."
    },
    {
        "anchor": "Dynamical Weyl Points and 4D Nodal Rings in Cold Atomic Gases: Controllability of ultracold atomic gases has reached an unprecedented level,\nallowing for experimental realization of the long-sought-after Thouless pump,\nwhich can be interpreted as a dynamical quantum Hall effect. On the other hand,\nWeyl semimetals and Weyl nodal line semimetals with touching points and rings\nin band structures have sparked tremendous interest in various fields in the\npast few years. Here, we show that dynamical Weyl points and dynamical 4D Weyl\nnodal rings, which are protected by the first Chern number on a parameter\nsurface formed by quasi-momentum and time, emerge in a two-dimensional and\nthree-dimensional system, respectively. We find that the topological pump\noccurs in these systems but the amount of pumped particles is not quantized and\ncan be continuously tuned by controlling experimental parameters over a wide\nrange. We also propose an experimental scheme to realize the dynamical Weyl\npoints and 4D Weyl nodal rings and to observe their corresponding topological\npump in cold atomic gases.",
        "positive": "Impurity states in the one-dimensional Bose gas: The detailed study of the low-energy spectrum for a mobile impurity in the\none-dimensional bosonic enviroment is performed. Particularly we have\nconsidered only two analytically accessible limits, namely, the case of an\nimpurity immersed in a dilute Bose gas, where one can use many-body\nperturbation techniques for low-dimensional bosonic systemsm and the case of\nthe Tonks-Girardeau gas, for which the usual fermionic diagrammatic expansion\nup to the second order is applied."
    },
    {
        "anchor": "Can the dipolar interaction suppress dipolar relaxation?: Magnetic atoms in a thin layer have repulsive interactions when their\nmagnetic moments are aligned perpendicular to the layer. We show experimentally\nand theoretically how this can suppress dipolar relaxation, the dominant loss\nprocess in spin mixtures of highly magnetic atoms. Using dysprosium, we observe\nan order of magnitude extension of the lifetime, and another factor of ten is\nwithin reach based on the models which we have validated with our experimental\nstudy. The loss suppression opens up many new possibilities for quantum\nsimulations with spin mixtures of highly magnetic atoms.",
        "positive": "Quantum entanglement and phase transition in a two-dimensional\n  photon-photon pair model: We propose a two-dimensional model consisting of photons and photon pairs. In\nthe model, the mixed gas of photons and photon pairs is formally equivalent to\na two-dimensional system of massive bosons with non-vanishing chemical\npotential, which implies the existence of two possible condensate phases. Using\nthe variational method, we discuss the quantum phase transition of the mixed\ngas and obtain the critical coupling line analytically. Moreover, we also find\nthat the phase transition of the photon gas can be interpreted as second\nharmonic generation. We then discuss the entanglement between photons and\nphoton pairs. Additionally, we also illustrate how the entanglement between\nphotons and photon pairs can be associated with the phase transition of the\nsystem."
    },
    {
        "anchor": "Permutation symmetry in spinor quantum gases: selection rules,\n  conservation laws, and correlations: Many-body systems of identical arbitrary-spin particles, with separable spin\nand spatial degrees of freedom, are considered. Their eigenstates can be\nclassified by Young diagrams, corresponding to non-trivial permutation\nsymmetries (beyond the conventional paradigm of symmetric--antisymmetric\nstates).\n  The present work obtains (a) selection rules for additional non-separable\n(dependent on spins and coordinates) $k$-body interactions: the Young diagrams,\nassociated with the initial and the final states of a transition, can differ by\nrelocation of no more than $k$ boxes between their rows; and (b) correlation\nrules: eigenstate-averaged local correlations of $k$ particles vanish if $k$\nexceeds the number of columns (for bosons) or rows (for fermions) in the\nassociated Young diagram. It also elucidates the physical meaning of the\nquantities conserved due to permutation symmetry --- in 1929, Dirac identified\nthose with characters of the symmetric group --- relating them to\nexperimentally observable correlations of several particles.\n  The results provide a way to control the formation of entangled states\nbelonging to multidimensional non-Abelian representations of the symmetric\ngroup. These states can find applications in quantum computation and metrology.",
        "positive": "A Novel Route to Reach a $p$-wave Superfluid Fermi Gas: We theoretically propose an idea to realize a $p$-wave superfluid Fermi gas.\nTo overcome the experimental difficulty that a $p$-wave pairing interaction to\nform $p$-wave Cooper pairs damages the system before the condensation growth,\nwe first prepare a $p$-wave pair amplitude ($\\Phi_{p}$) in a spin-orbit coupled\n$s$-wave superfluid Fermi gas, without any $p$-wave interaction. Then, by\nsuddenly changing the $s$-wave interaction with a $p$-wave one ($U_{p}$) by\nusing a Feshbach resonance, we reach the $p$-wave superfluid phase with the\n$p$-wave order parameter being symbolically written as $\\Delta_{p}\\sim\nU_{p}\\Phi_{p}$. In this letter, we assess this scenario within the framework of\na time-dependent Bogoliubov-de Gennes theory. Our results would contribute to\nthe study toward the realization of unconventional pairing states in an\nultracold Fermi gas."
    },
    {
        "anchor": "Multi-particle bound state formation following a quantum quench to the\n  one-dimensional Bose gas with attractive interactions: We consider quantum quenches from an ideal Bose condensate to the\nLieb-Liniger model with arbitrary attractive interaction strength. We focus on\nthe properties of the non-equilibrium steady state reached at late times after\nthe quench. Using recently developed methods based on integrability, we obtain\nan exact description of the stationary state for a large number of bosons. A\ndistinctive feature of this state is the presence of a hierarchy of\nmulti-particle bound states. We determine the dependence of their densities on\ninteraction strength and obtain an exact expression for the stationary value of\nthe local pair correlation $g_2$. We discuss ramifications of our results for\ncold atom experiments.",
        "positive": "Minimizing rf-induced excess micromotion of a trapped ion with the help\n  of ultracold atoms: We report on the compensation of excess micromotion due to parasitic\nrf-electric fields in a Paul trap. The parasitic rf-electric fields stem from\nthe Paul trap drive but cause excess micromotion, e.g. due to imperfections in\nthe setup of the Paul trap. We compensate these fields by applying rf-voltages\nof the same frequency but adequate phases and amplitudes to Paul trap\nelectrodes. The magnitude of micromotion is probed by studying elastic\ncollision rates of the trapped ion with a gas of ultracold neutral atoms.\nFurthermore, we demonstrate that also reactive collisions can be used to\nquantify micromotion. We achieve compensation efficiencies of about\n1$\\:\\text{Vm}^{-1}$, which is comparable to other conventional methods."
    },
    {
        "anchor": "Vortex properties in the extended supersolid phase of dipolar\n  Bose-Einstein condensates: We study the properties of singly-quantized linear vortices in the supersolid\nphase of a dipolar Bose-Einstein condensate at zero temperature modeling\n$^{164}$Dy atoms. The system is extended in the $x-y$ plane and confined by a\nharmonic trap in the the polarization direction $z$. Our study is based on a\ngeneralized Gross-Pitaevskii equation. We characterize the ground state of the\nsystem in terms of spatial order and superfluid fraction and compare the\nproperties of a single vortex and of a vortex dipole in the superfluid phase\n(SFP) and in the supersolid phase (SSP). At variance with a vortex in the SFP,\nwhich is free to move in the superfluid, a vortex in the SSP is localized at\nthe interstitial sites and does not move freely. We have computed the energy\nbarrier for motion from an equilibrium site to another. The fact that the\nvortex is submitted to a periodic potential has a dramatic effect on the\ndynamics of a vortex dipole made of two counter rotating parallel vortices;\ninstead of rigidly translating as in the SFP, the vortex and anti-vortex\napproach each other by a series of jumps from one site to another until they\nannihilate in a very short time and their energy is transferred to bulk\nexcitations.",
        "positive": "Non-equilibrium dynamics of Bosonic Mott insulators in an electric field: We study the non-equilibrium dynamics of one-dimensional Mott insulating\nbosons in the presence of a tunable effective electric field E which takes the\nsystem across a quantum critical point (QCP) separating a disordered and a\ntranslation symmetry broken ordered phase. We provide an exact numerical\ncomputation of the residual energy Q, the log-fidelity F, the excess defect\ndensity D, and the order parameter correlation function for a linear-in-time\nvariation of E with a rate v. We discuss the temporal and spatial variation of\nthese quantities for a range of v and for finite system sizes as relevant to\nrealistic experimental setups [J. Simon et al., Nature 472, 307 (2011)]. We\nshow that in finite-sized systems Q, F, and D obey Kibble-Zurek scaling, and\nsuggest further experiments within this setup to test our theory."
    },
    {
        "anchor": "Instability crossover of helical shear flow in segregated Bose-Einstein\n  condensates: We theoretically study the instability of helical shear flows, in which one\nfluid component flows along the vortex core of the other, in phase-separated\ntwo-component Bose-Einstein condensates at zero temperature. The helical shear\nflows are hydrodynamically classified into two regimes: (1) a helical vortex\nsheet, where the vorticity is localized on the cylindrical interface and the\nstability is described by an effective theory for ripple modes, and (2) a\ncore-flow vortex with the vorticity distributed in the vicinity of the vortex\ncore, where the instability phenomena are dominated only by the\nvortex-characteristic modes: Kelvin and varicose modes. The helical shear-flow\ninstability shows remarkable competition among different types of instabilities\nin the crossover regime between the two regimes.",
        "positive": "Binary mixture of pseudospin-1/2 Bose gases with interspecies spin\n  exchange: from classical fixed points and ground states to quantum ground\n  states: We consider the effective spin Hamiltonian describing a mixture of two\nspecies of pseudo-spin-1/2 Bose gases with interspecies spin exchange. First we\nanalyze the stability of the fixed points of the corresponding classical\ndynamics, of which the signature is found in quantum dynamics with a\ndisentangled initial state. Focusing on the case without an external potential,\nwe find all the ground states by taking into account quantum fluctuations\naround the classical ground state in each parameter regime. The nature of\nentanglement and its relation with classical bifurcation is investigated. When\nthe total spins of the two species are unequal, the maximal entanglement at the\nparameter point of classical bifurcation is possessed by the excited state\ncorresponding to the classical fixed point which bifurcates, rather than by the\nground state."
    },
    {
        "anchor": "Tail-free self-accelerating solitons and vortices: Self-accelerating waves in conservative systems, which usually feature slowly\ndecaying tails, such as Airy waves, have drawn great interest in studies of\nquantum and classical wave dynamics. They typically appear in linear media,\nwhile nonlinearities tend to deform and eventually destroy them. We\ndemonstrate, by means of analytical and numerical methods, the existence of\nrobust one- and two-dimensional (1D and 2D) self-accelerating tailless solitons\nand solitary vortices in a model of two-component Bose-Einstein condensates,\ndressed by a microwave (MW) field, whose magnetic component mediates long-range\ninteraction between the matter-wave constituents, with the feedback of the\nmatter waves on the MW field taken into account. In particular,\nself-accelerating 2D solitons may move along a curved trajectory in the\ncoordinate plane. The system may also include the spin-orbit coupling between\nthe components, leading to similar results for the self-acceleration. The\neffect persists if the contact cubic nonlinearity is included. A similar\nmechanism may generate 1D and 2D self-accelerating solitons in optical media\nwith thermal nonlinearity.",
        "positive": "Thermodynamics of dilute Bose gases: Beyond mean-field theory for binary\n  mixtures of Bose-Einstein condensate: We study the thermodynamic properties of binary Bose mixtures, by developing\na beyond mean-field Popov theory which properly includes the effects of quantum\nand thermal fluctuations in both the density and spin channels. Results for key\nthermodynamic quantities, such as the isothermal compressibility and the\nmagnetic susceptibility, are derived from a perturbative calculation of the\ngrand-canonical potential. We find that thermal fluctuations can play a crucial\nrole on the miscibility condition of a binary mixture, favoring phase\nseparation at finite temperature even if the mixture is soluble at zero\ntemperature, as already anticipated in a previous work [Ota et al., Phys. Rev.\nLett. 123, 075301 (2019)]. We further investigate the miscibility condition for\nbinary mixtures in the presence of asymmetry in the intra-species interactions,\nas well as in the masses of the two components. Furthermore, we discuss the\nsuperfluid behavior of the mixture and the temperature dependence of the\nAndreev-Bashkin effect."
    },
    {
        "anchor": "Rotation-driven transition into coexistent Josephson modes in an\n  atomtronic dc-SQUID: By means of a two-mode model, we show that transitions to different arrays of\ncoexistent regimes in the phase space can be attained by rotating a double-well\nsystem, which consists of a toroidal condensate with two diametrically placed\nbarriers. Such a configuration corresponds to the atomtronic counterpart of the\nwell-known direct-current superconducting quantum interference device. Due to\nthe phase gradient experimented by the on-site localized functions when the\nsystem is subject to rotation, a phase difference appears on each junction in\norder to satisfy the quantization of the velocity field around the torus. We\ndemonstrate that such a phase can produce a significant change on the relative\nvalues of different types of hopping parameters. In particular, we show that\nwithin a determined rotation frequency interval, a hopping parameter, usually\ndisregarded in nonrotating systems, turns out to rule the dynamics. At the\nlimits of such a frequency interval, bifurcations of the stationary points\noccur, which substantially change the phase space portrait that describes the\norbits of the macroscopic canonical conjugate variables. We analyze the\nemerging dynamics that combines the $0$ and $\\pi$ Josephson modes, and evaluate\nthe small-oscillation time-periods of such orbits at the frequency range where\neach mode survives. All the findings predicted by the model are confirmed by\nGross-Pitaevskii simulations.",
        "positive": "A note on a relation between ac Josephson effect and double-well BEC\n  oscillations: In this brief note we comment on the relation between the ac Josephson effect\nand the coherent oscillations of a Bose-Einstein condensate confined to a\ndouble-well potential. The goal is to elucidate the extent to which the latter\nis a realization of the former. We detail the correspondence that emerges in\nthe high occupation limit of the double-well potential, and particularly note\nthe relation between the two oscillation frequencies."
    },
    {
        "anchor": "Phases of supersolids in confined dipolar Bose-Einstein condensates: Dipolar Bose-Einstein condensates represent a powerful platform for the\nexploration of quantum many-body phenomena arising from long-range\ninteractions. A series of recent experiments has demonstrated the formation of\nsupersolid states of matter. Subsequent theoretical works have shown that\nquantum fluctuations can affect the underlying phase transition and may lead to\nthe emergence of supersolids with various lattice structures in dipolar\ncondensates. In this work we explore the signatures of such different\ngeometries in confined finite condensates. In addition to previously found\ntriangular lattices, our analysis reveals a rich spectrum of states, from\nhoneycomb patterns and ring structures to striped supersolids. By optimizing\nrelevant parameters we show that transitions between distinct supersolids\nshould be observable in current experiments.",
        "positive": "Anomalous supersolidity in a weakly interacting dipolar Bose mixture on\n  a square lattice: We calculate the mean-field phase diagram of a zero-temperature, binary Bose\nmixture on a square optical lattice, where one species possesses a\nnon-negligible dipole moment. Remarkably, this system exhibits supersolidity\nfor anomalously weak dipolar interaction strengths, which are readily\naccessible with current experimental capabilities. The supersolid phases are\nrobust, in that they occupy large regions in the parameter space. Further, we\nidentify a first-order quantum phase transition between supersolid and\nsuperfluid phases. Our results demonstrate the rich features of the dipolar\nBose mixture, and suggest that this system is well-suited for exploring\nsupersolidity in the experimental setting."
    },
    {
        "anchor": "Topological phases of shaken quantum Ising lattices: The quantum compass model consists of a two-dimensional square spin lattice\nwhere the orientation of the spin-spin interactions depends on the spatial\ndirection of the bonds. It has remarkable symmetry properties and the ground\nstate shows topological degeneracy. The implementation of the quantum compass\nmodel in quantum simulation setups like ultracold atoms and trapped ions is far\nfrom trivial, since spin interactions in those sytems typically are independent\nof the spatial direction. Ising spin interactions, on the contrary, can be\ninduced and controlled in atomic setups with state-of-the art experimental\ntechniques. In this work, we show how the quantum compass model on a\nrectangular lattice can be simulated by the use of the photon-assisted\ntunneling induced by periodic drivings on a quantum Ising spin model. We\ndescribe a procedure to adiabatically prepare one of the doubly-degenerate\nground states of this model by adiabatically ramping down a transverse magnetic\nfield, with surprising differences depending on the parity of the lattice size.\nExact diagonalizations confirm the validity of this approach for small\nlattices. Specific implementations of this scheme are presented with ultracold\natoms in optical lattices in the Mott insulator regime, as well as with Rydberg\natoms.",
        "positive": "Controlled ordering of topological charges in an exciton-polariton chain: We demonstrate, experimentally and theoretically, controlled loading of an\nexciton-polariton vortex chain into a 1D array of trapping potentials.\nSwitching between two types of vortex chains, with topological charges of the\nsame or alternating sign, is realised by means of appropriate shaping of an\nincoherent pump beam that drives the system to the regime of bosonic\ncondensation. In analogy to spin chains, these vortex sequences realise either\na \"ferromagnetic\" or an \"anti-ferromagnetic\" order, whereby the role of spin is\nplayed by the orbital angular momentum. The \"ferromagnetic\" ordering of\nvortices is associated with the formation of a persistent chiral current. Our\nresults pave the way for controlled creation of nontrivial distributions of\norbital angular momentum and topological order in a periodic exciton-polariton\nsystem."
    },
    {
        "anchor": "Bogoliubov-Cherenkov Radiation in an Atom Laser: We develop a simple yet powerful technique to study Bogoliubov-Cherenkov\nradiation by producing a pulsed atom laser from a strongly confined\nBose-Einstein condensate. Such radiation results when the atom laser pulse\nfalls past a Bose-Einstein condensate at high-hypersonic speeds, modifying the\nspatial profile to display a characteristic twin jet structure and a\ncomplicated interference pattern. The experimental observations are in\nexcellent agreement with mean-field numerical simulations and an analytic\ntheory. Due to the highly hypersonic regime reached in our experiment, this\nsystem offers a highly controllable platform for future studies of\ncondensed-matter analogs of quantum electrodynamics at ultrarelativistic\nspeeds.",
        "positive": "Critical velocity for superfluidity in the one-dimensional mean-field\n  regime: From matter to light quantum fluids: We determine in a nonperturbative way the critical velocity for superfluidity\nof a generic quantum fluid flowing past a localized obstacle in the\none-dimensional mean-field regime. We get exact expressions in the narrow- and\nwide-obstacle limits and interpolate them numerically using an original\nrelaxation algorithm for the stationary problem. The existence of a\nJosephson-type critical current across a very high and slowly varying obstacle\nis discussed. Particle losses, if present, are treated within an adiabatic\napproach of the dynamics giving results in excellent agreement with full\nnumerics. Relevant for experiments with quantum fluids of matter, of mixed\nmatter-light, and of light, our study paves the way for further nonperturbative\ninvestigations in higher dimensions and beyond mean-field theory."
    },
    {
        "anchor": "Artificial topological models based on a one-dimensional spin-dependent\n  optical lattice: Topological matter is a popular topic in both condensed matter and cold atom\nresearch. In the past decades, a variety of models have been identified with\nfascinating topological features. Some, but not all, of the models can be found\nin materials. As a fully controllable system, cold atoms trapped in optical\nlattices provide an ideal platform to simulate and realize these topological\nmodels. Here we present a proposal for synthesizing topological models in cold\natoms based on a one-dimensional (1D) spin-dependent optical lattice potential.\nIn our system, features such as staggered tunneling, staggered Zeeman field,\nnearest-neighbor interaction, beyond-near-neighbor tunneling, etc. can be\nreadily realized. They underlie the emergence of various topological phases.\nOur proposal can be realized with current technology and hence has potential\napplications in quantum simulation of topological matter.",
        "positive": "Renormalization group analysis of dipolar Heisenberg model on square\n  lattice: We present a detailed functional renormalization group analysis of spin-1/2\ndipolar Heisenberg model on square lattice. This model is similar to the well\nknown $J_1$-$J_2$ model and describes the pseudospin degrees of freedom of\npolar molecules confined in deep optical lattice with long-range anisotropic\ndipole-dipole interactions. Previous study of this model based on tensor\nnetwork ansatz indicates a paramagnetic ground state for certain dipole tilting\nangles which can be tuned in experiments to control the exchange couplings. The\ntensor ansatz formulated on a small cluster unit cell is inadequate to describe\nthe spiral order, and therefore the phase diagram at high azimuthal tilting\nangles remains undetermined. Here we obtain the full phase diagram of the model\nfrom numerical pseudofermion functional renormalization group calculations. We\nshow that an extended quantum paramagnetic phase is realized between the\nN\\'{e}el and stripe/spiral phase. In this region, the spin susceptibility flows\nsmoothly down to the lowest numerical renormalization group scales with no sign\nof divergence or breakdown of the flow, in sharp contrast to the flow towards\nthe long-range ordered phases. Our results provide further evidence that the\ndipolar Heisenberg model is a fertile ground for quantum spin liquids."
    },
    {
        "anchor": "Many-body excitation spectra of trapped bosons with general interaction\n  by linear response: The linear-response theory of the multiconfigurational time-dependent Hartree\nfor bosons method for computing many-body excitations of trapped Bose-Einstein\ncondensates [Phys. Rev. A {\\bf 88}, 023606 (2013)] is implemented for systems\nwith general interparticle interaction. Illustrative numerical examples for\nrepulsive and attractive bosons are provided. The many-body linear-response\ntheory identifies the excitations not unraveled within Bogoliubov--de Gennes\nequations. The theory is herewith benchmarked against the exactly-solvable\none-dimensional harmonic-interaction model. As a complementary result, we\nrepresent the theory in a compact block-diagonal form, opening up thereby an\navenue for treating larger systems.",
        "positive": "Spin-orbit-coupled dipolar Bose-Einstein condensates: We propose an experimental scheme to create spin-orbit coupling in spin-3 Cr\natoms using Raman processes. Employing linear Zeeman effect and optical Stark\nshift, two spin states within the ground electronic manifold are selected,\nwhich results in a pseudo-spin-1/2 model. We further study the ground state\nstructures of a spin-orbit-coupled Cr condensate. We show that, in addition to\nthe stripe structures induced by the spin-orbit coupling, the magnetic\ndipole-dipole interaction gives rise to the vortex phase, in which spontaneous\nspin vortex is formed."
    },
    {
        "anchor": "Josephson physics of spin-orbit coupled elongated Bose-Einstein\n  condensates: We consider an ultracold bosonic binary mixture confined in a one-dimensional\ndouble-well trap. The two bosonic components are assumed to be two hyperfine\ninternal states of the same atom. We suppose that these two components are\nspin-orbit coupled between each other. We employ the two-mode approximation\nstarting from two coupled Gross-Pitaevskii equations and derive a system of\nordinary differential equations governing the temporal evolution of the\ninter-well population imbalance of each component and that between the two\nbosonic species. We study the Josephson oscillations of these spin-orbit\ncoupled Bose-Einstein condensates by analyzing the interplay between the\ninteratomic interactions and the spin-orbit coupling and the self-trapped\ndynamics of the inter-species imbalance. We show that the dynamics of this\nlatter variable is crucially determined by the relationship between the\nspin-orbit coupling, the tunneling energy, and the interactions.",
        "positive": "Spin Rotations in a Bose-Einstein Condensate Driven by Counterflow and\n  Spin-independent Interactions: We observe spin rotations caused by atomic collisions in a non-equilibrium\nBose-condensed gas of $^{87}$Rb. Reflection from a pseudomagnetic barrier\ncreates counterflow in which forward- and backward-propagating matter waves\nhave partly transverse spin directions. Even though inter-atomic interaction\nstrengths are state-independent, the indistinguishability of parallel spins\nleads to spin dynamics. A local magnetodynamic model, which captures the\nsalient features of the observed spin textures, highlights an essential\nconnection between four-wave mixing and collisional spin rotation. The observed\nphenomenon has previously been thought to exist only in nondegenerate gases;\nour observations and model clarify the nature of these effective-magnetic spin\nrotations."
    },
    {
        "anchor": "Spin-Depairing Transition of Attractive Fermi Gases on a Ring Driven by\n  Synthetic Gauge Fields: Motivated by the recent experimental realization of synthetic gauge fields in\nultracold atoms, we investigate one-dimensional attractive Fermi gases with a\ntime-dependent gauge flux on the spin sector. By combining the methods of the\nBethe ansatz with complex twists and Landau-Dykhne, it is shown that a\nspin-depairing transition occurs, which may represent a nonequilibrium\ntransition from fermionic superfluids to normal states with spin currents\ncaused by a many-body quantum tunneling. For the case of the Hubbard ring at\nhalf filling, our finding forms a dual concept with the dielectric breakdown of\nthe Mott insulator discussed in Phys. Rev. B 81, 033103 (2010). We analyze\ncases of arbitrary filling and continuum model, and show how the filling\naffects the transition probability.",
        "positive": "Damping of Bloch oscillations: Variational solutions of the Boltzmann\n  equation beyond linear response: Variational solutions of the Boltzmann equation usually rely on the concept\nof linear response. We extend the variational approach for tight-binding models\nat high entropies to a regime far beyond linear response. We analyze both\nweakly interacting fermions and incoherent bosons on a lattice. We consider a\ncase where the particles are driven by a constant force, leading to the\nwell-known Bloch oscillations, and we consider interactions that are weak\nenough not to overdamp these oscillations. This regime is computationally\ndemanding and relevant for ultracold atoms in optical lattices. We derive a\nsimple theory in terms of coupled dynamic equations for the particle density,\nenergy density, current and heat current, allowing for analytic solutions. As\nan application, we identify damping coefficients for Bloch oscillations in the\nHubbard model at weak interactions and compute them for a one-dimensional toy\nmodel. We also approximately solve the long-time dynamics of a weakly\ninteracting, strongly Bloch-oscillating cloud of fermionic particles in a\ntilted lattice, leading to a subdiffusive scaling exponent."
    },
    {
        "anchor": "Artificial Gauge Field for Photons in Coupled Cavity Arrays: We propose and characterize solid-state photonic structures where light\nexperiences an artificial gauge field. A suitable coupling of the propagation\nand polarization degrees of freedom introduces a geometrical phase for photons\ntunneling between adjacent sites of a coupled cavity array. We then discuss the\nfeasibility of observing strong gauge field effects in the optical spectra of\nrealistic systems, including the Hofstadter butterfly spectrum.",
        "positive": "Supersolidity of cnoidal waves in an ultracold Bose gas: A one-dimensional Bose-Einstein condensate may experience nonlinear periodic\nmodulations known as \"cnoidal waves\". We argue that such structures represent\npromising candidates for the study of supersolidity-related phenomena in a\nnon-equilibrium state. A mean-field treatment makes it possible to rederive\nLeggett's formula for the superfluid fraction of the system and to estimate it\nanalytically. We determine the excitation spectrum, for which we obtain\nanalytical results in the two opposite limiting cases of (i) a linearly\nmodulated background and (ii) a train of dark solitons. The presence of two\nGoldstone (gapless) modes -- associated with the spontaneous breaking of\n$\\mathrm{U}(1)$ symmetry and of continuous translational invariance -- at large\nwavelength is verified. We also calculate the static structure factor and the\ncompressibility of cnoidal waves, which show a divergent behavior at the edges\nof each Brillouin zone."
    },
    {
        "anchor": "Robust Digital Holography For Ultracold Atom Trapping: We have formulated and experimentally demonstrated an improved algorithm for\ndesign of arbitrary two-dimensional holographic traps for ultracold atoms. Our\nmethod builds on the best previously available algorithm, MRAF, and improves on\nit in two ways. First, it allows for creation of holographic atom traps with a\nwell defined background potential. Second, we experimentally show that for\ncreating trapping potentials free of fringing artifacts it is important to go\nbeyond the Fourier approximation in modelling light propagation. To this end,\nwe incorporate full Helmholtz propagation into our calculations.",
        "positive": "Scattering and absorption of ultracold atoms by nanotubes: We investigate theoretically how cold atoms, including Bose-Einstein\ncondensates, are scattered from, or absorbed by nanotubes with a view to\nanalysing recent experiments. In particular we consider the role of potential\nstrength, quantum reflection, atomic interactions and tube vibrations on atom\nloss rates. Lifshitz theory calculations deliver a significantly stronger\nscattering potential than that found in experiment and we discuss possible\nreasons for this. We find that the scattering potential for dielectric tubes\ncan be calculated to a good approximation using a modified pairwise summation\napproach, which is efficient and easily extendable to arbitrary geometries.\nQuantum reflection of atoms from a nanotube may become a significant factor at\nlow temperatures, especially for non-metallic tubes. Interatomic interactions\nare shown to increase the rate at which atoms are lost to the nanotube and lead\nto non-trivial dynamics. Thermal nanotube vibrations do not significantly\nincrease loss rates or reduce condensate fractions, but lower frequency\noscillations can dramatically heat the cloud."
    },
    {
        "anchor": "Many-body physics in the classical-field description of a degenerate\n  Bose gas: The classical-field formalism has been widely applied in the calculation of\nnormal correlation functions, and the characterization of condensation, in\nfinite-temperature Bose gases. Here we discuss the extension of this method to\nthe calculation of more general correlations, including the so-called anomalous\ncorrelations of the field, without recourse to symmetry-breaking assumptions.\nOur method is based on the introduction of U(1)-symmetric classical-field\nvariables analogous to the modified quantum ladder operators of\nnumber-conserving approaches to the degenerate Bose gas, and allows us to\nrigorously quantify the anomalous and non-Gaussian character of the field\nfluctuations. We compare our results for anomalous correlation functions with\nthe predictions of mean-field theories, and demonstrate that the nonlinear\nclassical-field dynamics incorporate a full description of many-body processes\nwhich modify the effective mean-field potentials experienced by condensate and\nnoncondensate atoms. We discuss the role of these processes in shaping the\ncondensate mode, and thereby demonstrate the consistency of the Penrose-Onsager\ndefinition of the condensate orbital in the classical-field equilibrium. We\nconsider the contribution of various noncondensate-field correlations to the\noverall suppression of density fluctuations and interactions in the field, and\ndemonstrate the distinct roles of phase and density fluctuations in the\ntransition of the field to the normal phase.",
        "positive": "The mixing-spacetime symmetry in the Floquet-Bloch band theory: We discover a class of spacetime symmetries unique to time-periodic systems,\nwhich we term \"mixing symmetry\" due to its combination of space and time\ncoordinates in the symmetry transformation. We systematically enumerate the\nsymmetry groups, and classify the corresponding Floquet-Bloch band theories by\nutilizing the winding number of quasi-energy. Moreover, we provide a\ncomprehensive scheme for the experimental realization of these symmetries. The\nparticle propagator exhibits an intriguing pattern that remains invariant even\nunder transformations mixing space and time coordinates. We anticipate that\nthis distinct feature can be observed in current cold atom experiments."
    },
    {
        "anchor": "Fermi polaron in a one-dimensional quasi-periodic optical lattice: the\n  simplest many-body localization challenge: We theoretically investigate the behavior of a moving impurity immersed in a\nsea of fermionic atoms that are confined in a quasi-periodic (bichromatic)\noptical lattice, within a standard variational approach. We consider both\nrepulsive and attractive contact interactions for such a simplest many-body\nlocalization problem of Fermi polarons. The variational approach enables us to\naccess relatively large systems and therefore may be used to understand\nmany-body localization in the thermodynamic limit. The energy and wave-function\nof the polaron states are found to be strongly affected by the quasi-random\nlattice potential and their experimental measurements (i.e., via\nradio-frequency spectroscopy or quantum gas microscope) therefore provide a\nsensitive way to underpin the localization transition. We determine a phase\ndiagram by calculating two critical quasi-random disorder strengths, which\ncorrespond to the onset of the localization of the ground-state polaron state\nand the many-body localization of all polaron states, respectively. Our\npredicted phase diagram could be straightforwardly examined in current\ncold-atom experiments.",
        "positive": "An accordion superlattice for controlling atom separation in optical\n  potentials: We propose a method for separating trapped atoms in optical lattices by large\ndistances. The key idea is the cyclic transfer of atoms between two lattices of\nvariable spacing, known as accordion lattices, each covering at least a factor\nof two in lattice spacing. By coherently loading atoms between the two\nsuperimposed potentials, we can reach, in principle, arbitrarily large atom\nseparations, while requiring only a relatively small numerical aperture.\nNumerical simulations of our `accordion superlattice' show that the atoms\nremain localised to one lattice site throughout the separation process, even\nfor moderate lattice depths. In a proof-of-principle experiment we demonstrate\nthe optical fields required for the accordion superlattice using acousto-optic\ndeflectors. The method can be applied to neutral-atom quantum computing with\noptical tweezers, as well as quantum simulation of low-entropy many-body\nstates. For instance, a unit-filling atomic Mott insulator can be coherently\nexpanded by a factor of ten in order to load an optical tweezer array with very\nhigh filling. In turn, sorted tweezer arrays can be compressed to form\nhigh-density states of ultracold atoms in optical lattices. The method can be\nalso be applied to biological systems where dynamical separation of particles\nis required."
    },
    {
        "anchor": "Metastable decoherence-free subspaces and electromagnetically induced\n  transparency in interacting many-body systems: We investigate the dynamics of a generic interacting many-body system under\nconditions of electromagnetically induced transparency (EIT). This problem is\nof current relevance due to its connection to non-linear optical media realized\nby Rydberg atoms. In an interacting system the structure of the dynamics and\nthe approach to the stationary state becomes far more complex than in the case\nof conventional EIT. In particular, we discuss the emergence of a metastable\ndecoherence free subspace, whose dimension for a single Rydberg excitation\ngrows linearly in the number of atoms. On approach to stationarity this leads\nto a slow dynamics which renders the typical assumption of fast relaxation\ninvalid. We derive analytically the effective non-equilibrium dynamics in the\ndecoherence free subspace which features coherent and dissipative two-body\ninteractions. We discuss the use of this scenario for the preparation of\ncollective entangled dark states and the realization of general unitary\ndynamics within the spin-wave subspace.",
        "positive": "Dynamics of Vortices and Solitons in a Bose-Einstein Condensate by an\n  Oscillating Potential: We study numerically the dynamics of quantized vortices and solitons induced\nby an oscillating potential inside a trapped Bose-Einstein condensate. The\ndynamics of the topological defects is much different from the case for a\nlinear uniform object; the metamorphosis between vortices and solitons is\ncharacteristic of the dynamics. We discuss how vortices are nucleated by an\noscillating potential."
    },
    {
        "anchor": "Matter-wave localization in a weakly perturbed optical lattice: By numerical solution and variational approximation of the Gross-Pitaevskii\nequation, we studied the localization of a noninteracting and\nweakly-interacting Bose-Einstein condensate in a weakly perturbed optical\nlattice in one and three dimensions. The perturbation achieved through a weak\ndelocalizing expulsive or a linear potential as well as a weak localizing\nharmonic potential removes the periodicity of the optical lattice and leads to\nlocalization. We also studied some dynamics of the localized state confirming\nits stability.",
        "positive": "Quantum turbulence in atomic Bose-Einstein condensates: Weakly interacting, dilute atomic Bose-Einstein condensates (BECs) have\nproved to be an attractive context for the study of nonlinear dynamics and\nquantum effects at the macroscopic scale. Recently, atomic BECs have been used\nto investigate quantum turbulence both experimentally and theoretically,\nstimulated largely by the high degree of control which is available within\nthese quantum gases. In this article we motivate the use of atomic BECs for the\nstudy of turbulence, discuss the characteristic regimes of turbulence which are\naccessible, and briefly review some selected investigations of quantum\nturbulence and recent results. We focus on three stages of turbulence - the\ngeneration of turbulence, its steady state and its decay - and highlight some\nfundamental questions regarding our understanding in each of these regimes."
    },
    {
        "anchor": "Magnetic solitons in Rabi-coupled Bose-Einstein condensates: We study magnetic solitons, solitary waves of spin polarization (i.e.,\nmagnetization), in binary Bose-Einstein condensates in the presence of Rabi\ncoupling. We show that the system exhibits two types of magnetic solitons,\ncalled $2\\pi$ and $0\\pi$ solitons, characterized by a different behavior of the\nrelative phase between the two spin components. $2\\pi$ solitons exhibit a\n$2\\pi$ jump of the relative phase, independent of their velocity, the static\ndomain wall explored by Son and Stephanov being an example of such $2\\pi$\nsolitons with vanishing velocity and magnetization. $0\\pi$ solitons instead do\nnot exhibit any asymptotic jump in the relative phase. Systematic results are\nprovided for both types of solitons in uniform matter. Numerical calculations\nin the presence of a one-dimensional harmonic trap reveal that a $2\\pi$ soliton\nevolves in time into a $0\\pi$ soliton, and vice versa, oscillating around the\ncenter of the trap. Results for the effective mass, the Landau critical\nvelocity, and the role of the transverse confinement are also discussed.",
        "positive": "Atom chips with free-standing two-dimensional electron gases: advantages\n  and challenges: In this work we consider the advantages and challenges of using free-standing\ntwo-dimensional electron gases (2DEG) as active components in atom chips for\nmanipulating ultracold ensembles of alkali atoms. We calculate trapping\nparameters achievable with typical high-mobility 2DEGs in an atom chip\nconfiguration, and identify advantages of this system for trapping atoms at\nsub-micron distances from the atom chip. We show how the sensitivity of atomic\ngases to magnetic field inhomogeneity can be exploited for controlling the\natoms with quantum electronic devices and, conversely, using the atoms to probe\nthe structural and transport properties of semiconductor devices."
    },
    {
        "anchor": "Coupling of polaritons to vibrational modes of ultracold atoms in an\n  optical lattice: The coupling of internal electronic excitations to vibrational modes of the\nexternal motion of ultracold atoms in an optical lattice is studied here in\nusing a perturbation expansion in small atomic displacements. In the Mott\ninsulator case with one atom per site, the resonance dipole-dipole coupling\nbetween neighboring sites can induce emission and absorption of vibrational\nquanta. Within a cavity in the strong exciton-photon coupling regime such\ncoupling results in polariton-vibration interactions, which create a\nsignificant thermalization mechanism for polaritons toward their minimum\nenergy, and leading to motional heating of the lattice atoms.",
        "positive": "Strongly interacting ultracold polar molecules: This paper reviews recent advances in the study of strongly interacting\nsystems of dipolar molecules. Heteronuclear molecules feature large and tunable\nelectric dipole moments, which give rise to long-range and anisotropic\ndipole-dipole interactions. Ultracold samples of dipolar molecules with\nlong-range interactions offer a unique platform for quantum simulations and the\nstudy of correlated many-body physics. We provide an introduction to the\nphysics of dipolar quantum gases, both electric and magnetic, and summarize the\nmultipronged efforts to bring dipolar molecules into the quantum regime. We\ndiscuss in detail the recent experimental progress in realizing and studying\nstrongly interacting systems of polar molecules trapped in optical lattices,\nwith particular emphasis on the study of interacting spin systems and\nnon-equilibrium quantum magnetism. Finally, we conclude with a brief discussion\nof the future prospects for studies of strongly interacting dipolar molecules."
    },
    {
        "anchor": "Observation of confinement-induced resonances in a 3D lattice: We report on the observation of confinement-induced resonances for strong\nthree-dimensional (3D) confinement in a lattice potential. Starting from a\nMott-insulator state with predominantly single-site occupancy, we detect loss\nand heating features at specific values for the confinement length and the 3D\nscattering length. Two independent models, based on the coupling between the\ncenter-of-mass and the relative motion of the particles as mediated by the\nlattice, predict the resonance positions to a good approximation, suggesting a\nuniversal behavior. Our results extend confinement-induced resonances to any\ndimensionality and open up an alternative method for interaction tuning and\ncontrolled molecule formation under strong 3D confinement.",
        "positive": "Quantized Vortices and Four-Component Superfluidity of Semiconductor\n  Excitons: We study spatially indirect excitons of GaAs quantum wells, confined in a 10\nmicrons electrostatic trap. Below a critical temperature of about 1 Kelvin, we\ndetect macroscopic spatial coherence and quantised vortices in the weak\nphotoluminescence emitted from the trap. These quantum signatures are\nrestricted to a narrow range of density, in a dilute regime. They manifest the\nformation of a four-component superfluid, made by a low population of optically\nbright excitons coherently coupled to a dominant fraction of optically dark\nexcitons."
    },
    {
        "anchor": "Universality in nonequilibrium condensation of exciton-polaritons: We investigate the process of condensation of exciton-polaritons in a\none-dimensional nanowire, predicting spontaneous formation of domains of\nuncondensed excitons and condensed polaritons. We demonstrate a universal\nscaling law for the density of domains, which results from the competition\nbetween characteristic timescales present in the system. However, we find that\nthe system does not follow the standard Kibble-\\.Zurek scenario of a\nnonequilibrium phase transition.",
        "positive": "Bose-Einstein condensates in quasi-periodic lattices: bosonic Josephson\n  junction, self-trapping, and multi-mode dynamics: Bose-Einstein condensates loaded in one-dimensional bichromatic optical\nlattices with constituent sublattices having incommensurate periods is\nconsidered. Using the rational approximations for the incommensurate periods,\nwe show that below the mobility edge the localized states are distributed\nnearly homogeneously in the space and explore the versatility of such\npotentials. We show that superposition of symmetric and anti-symmetric\nlocalized can be used to simulate various physical dynamical regimes, known to\noccur in double-well and multi-well traps. As examples, we obtain an\nalternative realization of a bosonic Josephson junction, whose coherent\noscillations display beatings or switching in the weakly nonlinear regime,\ndescribe selftrapping and four-mode dynamics, mimicking coherent oscillations\nand self-trapping in four-well potentials. These phenomena can be observed for\ndifferent pairs of modes, which are localized due to the interference rather\nthan due to a confining trap. The results obtained using few-mode\napproximations are compared with the direct numerical simulations of the\none-dimensional Gross-Pitaevskii equation. The localized states and the related\ndynamics are found to persist for long times even in the repulsive condensates.\nWe also described bifurcations of the families of nonlinear modes, the symmetry\nbreaking and stable minigap solitons."
    },
    {
        "anchor": "Criticality and Phase Diagram of Quantum Long-Range $\\text{O(N)}$ models: Several recent experiments in atomic, molecular and optical systems motivated\na huge interest in the study of quantum long-range %spin systems. Our goal in\nthis paper is to present a general description of their critical behavior and\nphases, devising a treatment valid in $d$ dimensions, with an exponent\n$d+\\sigma$ for the power-law decay of the couplings in the presence of an\n$O(N)$ symmetry. By introducing a convenient ansatz for the effective action,\nwe determine the phase diagram for the $N$-component quantum rotor model with\nlong-range interactions, with $N=1$ corresponding to the Ising model. The phase\ndiagram in the $\\sigma-d$ plane shows a non trivial dependence on $\\sigma$. As\na consequence of the fact that the model is quantum, the correlation functions\nare anisotropic in the spatial and time coordinates for $\\sigma$ smaller than a\ncritical value and in this region the isotropy is not restored even at\ncriticality. Results for the correlation length exponent $\\nu$, the dynamical\ncritical exponent $z$ and a comparison with numerical findings for them are\npresented.",
        "positive": "Fermi liquid theory and ferromagnetism: There is demonstrated that an isotropic ferromagnetic Fermi liquid reveals\ninstability of the ferromagnetic state in respect to the transversal\ninhomogeneous deviations of magnetization from equilibrium. The result was\nobtained by derivation of the spin waves spectrum by means of kinetic equation."
    },
    {
        "anchor": "Interaction and filling-induced quantum anomalous Hall effect in\n  ultra-cold neutral Bose-Fermi mixture on hexagonal lattice: We investigate the quantum anomalous Hall effect in a mixture of ultra-cold\nneutral bosons and fermions held on a hexagonal optical lattice. In the strong\natom-atom interaction limit, composite fermions composed of one fermion with\nbosons or bosonic holes in the mixture are formed. Such composite fermions have\nalready been generated successfully in experiment [Nat. Phys. {\\bf 7}, 642\n(2011)]. Here we predict that this kind of composite fermions may provide a\nrealization of the quantum anomalous Hall effect by tuning the atom-atom\ninteraction or the filling of the bosons in the mixture. We also discuss the\ncorresponding experimental signatures of the quantum anomalous Hall effect in\nthe Bose-Fermi mixture on hexagonal optical lattice.",
        "positive": "Fast preparation of critical ground states using superluminal fronts: We propose a spatio-temporal quench protocol that allows for the fast\npreparation of ground states of gapless models with Lorentz invariance.\nAssuming the system initially resides in the ground state of a corresponding\nmassive model, we show that a superluminally-moving `front' that\n$\\textit{locally}$ quenches the mass, leaves behind it (in space) a state\n$\\textit{arbitrarily close}$ to the ground state of the gapless model.\nImportantly, our protocol takes time $\\mathcal{O} \\left( L \\right)$ to produce\nthe ground state of a system of size $\\sim L^d$ ($d$ spatial dimensions), while\na fully adiabatic protocol requires time $\\sim \\mathcal{O} \\left( L^2 \\right)$\nto produce a state with exponential accuracy in $L$. The physics of the\ndynamical problem can be understood in terms of relativistic rarefaction of\nexcitations generated by the mass front. We provide proof-of-concept by solving\nthe proposed quench exactly for a system of free bosons in arbitrary\ndimensions, and for free fermions in $d = 1$. We discuss the role of\ninteractions and UV effects on the free-theory idealization, before numerically\nillustrating the usefulness of the approach via simulations on the quantum\nHeisenberg spin-chain."
    },
    {
        "anchor": "Numerical calculation of Green's function and momentum distribution for\n  spin-polarized fermions by path integral molecular dynamics: Most recently, path integral molecular dynamics (PIMD) has been successfully\napplied to perform simulations of identical bosons and fermions by B. Hirshberg\net al.. In this work, we demonstrate that PIMD can be developed to calculate\nGreen's function and extract momentum distribution for spin-polarized fermions.\nIn particular, we show that the momentum distribution calculated by PIMD has\npotential application to numerous quantum systems, such as cold atom simulation\nof Mott insulator in Fermi-Hubbard model.",
        "positive": "The role of interaction-induced tunneling in the dynamics of polar\n  lattice bosons: Inter-site dipolar interactions induce, even in absence of disorder, an\nintriguing non-ergodic dynamics for dipolar bosons in an optical lattice. We\nshow that the inherent dipole-induced density-dependent tunneling, typically\nneglected, plays a crucial role in this dynamics. For shallow-enough lattices,\nthe delocalization stemming from the interaction-induced hopping overcomes the\nlocalization induced by inter-site interactions. As a result, in stark contrast\nto the more studied case of hard-core bosons, delocalization is\ncounter-intuitively strengthen when the dipolar strength increases.\nFurthermore, the quasi-cancellation between bare and interaction-induced\ntunneling may lead, near a lattice-depth-dependent value of the dipole\nstrength, to an exact decoupling of the Hilbert space between ergodic hard-core\nstates and strongly non-ergodic soft-core ones. Our results show that\ninteraction-induced hopping should play a crucial role in future experiments on\nthe dynamics of polar lattice gases."
    },
    {
        "anchor": "Unconventional Fulde-Ferrell-Larkin-Ovchinnikov pairing states in a\n  Fermi gas with spin-orbit coupling: We study the phase diagram in a two-dimensional Fermi gas with the synthetic\nspin-orbit coupling that has recently been realized experimentally. In\nparticular, we characterize in detail the properties and the stability region\nof the unconventional Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states in such a\nsystem, which are induced by spin-orbit coupling and Fermi surface asymmetry.\nWe identify several distinct nodal FFLO states by studying the topology of\ntheir respective gapless contours in momentum space. We then examine the phase\nstructure and the number density distributions in a typical harmonic trapping\npotential under the local density approximation. Our studies provide detailed\ninformation on the FFLO pairing states with spin-orbit coupling and Fermi\nsurface asymmetry, and will facilitate experimental detection of these\ninteresting pairing states in the future.",
        "positive": "Bosonic fractional quantum Hall conductance in shaken honeycomb optical\n  lattices without flat bands: We propose a scheme to realize bosonic fractional quantum Hall conductance in\nshaken honeycomb optical lattices. This scheme does not require a very flat\nband, and the necessary long-range interaction relies on s-wave scattering,\nwhich is common in many ultracold-atom experiments. By filling the lattice at\n1/4 with identical bosons under Feshbach resonance, two degenerate many-body\nground states share one Chern number of 1 and correspond exactly to the\nfractional quantum Hall conductance of 1/2. Meanwhile, we prove that the\nfractional quantum Hall state can be prepared by adiabatically turning on the\nlattice shaking, and the fractional conductance is robust in the shaken\nlattice. This provides an easy way to initialize and prepare the fractional\nquantum Hall states in ultracold-atom platforms, and it paves the way to\ninvestigate and simulate strongly correlated quantum matters with degenerate\nquantum gas."
    },
    {
        "anchor": "Quench-produced solitons in a box-trapped Bose-Einstein condensate: We describe a protocol to prepare solitons in a quasi-1d box-trapped\nBose-Einstein condensate using only a quench of the isotropic s-wave scattering\nlength. A quench to exactly four times the initial 1d coupling strength creates\none soliton at each boundary of the box, which then propagate in a uniform\nbackground density and collide with one another. No nonsolotonic excitations\nare created during the quench. The procedure is robust against imperfections in\nthe scattering length ramp rate and a mismatch of the final scattering length.",
        "positive": "Bichromatic state-dependent disordered potential for Anderson\n  localization of ultracold atoms: The ability to load ultracold atoms at a well-defined energy in a disordered\npotential is a crucial tool to study quantum transport, and in particular\nAnderson localization. In this paper, we present a new method for achieving\nthat goal by rf transfer of atoms of an atomic Bose-Einstein condensate from a\ndisorder insensitive state to a disorder sensitive state. It is based on a\nbichromatic laser speckle pattern, produced by two lasers whose frequencies are\nchosen so that their light-shifts cancel each other in the first state and\nadd-up in the second state. Moreover, the spontaneous scattering rate in the\ndisorder-sensitive state is low enough to allow for long observation times of\nquantum transport in that state. We theoretically and experimentally study the\ncharacteristics of the resulting potential."
    },
    {
        "anchor": "Quantum quench dynamics of the sine-Gordon model in some solvable limits: In connection with the the thermalization problem in isolated quantum\nsystems, we investigate the dynamics following a quantum quench of the\nsine-Gordon model in the Luther-Emery and the semiclassical limits. We consider\nthe quench from the gapped to the gapless phase as well as reversed one. By\nobtaining analytic expressions for the one and two-point correlation functions\nof the order parameter operator at zero-temperature, the manifestations of\nintegrability in the absence of thermalization in the sine-Gordon model are\nstudied. It is thus shown that correlations in the long time regime after the\nquench are well described by a generalized Gibbs ensemble. We also consider the\ncase where the system is initially in contact with a reservoir at finite\ntemperature. The possible relevance of our results to current and future\nexperiments with ultracold atomic systems is also critically considered.",
        "positive": "Two-orbital physics of high spin fermionic alkaline earth atoms confined\n  in a one-dimensional chain: We study the effect of the coupling between the electronic ground state of\nhigh spin alkaline-earth fermionic atoms and their metastable optically excited\nstate, when the system is confined in a one-dimensional chain, and show that\nthe system provides a possible realization of a finite momentum pairing\n(Fulde-Ferrell-Larkin-Ovchinnikov-like) state without spin- or bare mass\nimbalance. We determine the $\\beta$-functions of the renormalization group\ntrajectories for general spin and analyze the structure of the possible gapped\nand gapless states in the hydrodynamic limit. Due to the SU(N) symmetry in the\nspin space, complete mode separation can not be observed even in the fully\ngapless 2N-component Luttinger liquid state. Contrary, 4 velocities\ncharacterize the system. We solve the renormalization group equations for\nspin-9/2 strontium-87 isotope and analyze in detail its phase diagram. The\nfully gapless Luttinger liquid state does not stabilize in the two-orbital\nsystem of the $^{87}$Sr atoms, instead, different gapped non-Gaussian fixed\npoints are identified either with dominant density or superconducting\nfluctuations. The superconducting states are stable in a nontrivial shaped\nregion in the parameter space as a consequence of the coupling between the two\nelectronic states."
    },
    {
        "anchor": "Raman superradiance and spin lattice of ultracold atoms in optical\n  cavities: We investigate synthesis of a hyperfine spin lattice in an atomic\nBose-Einstein condensate, with two hyperfine spin components, inside a\none-dimensional high-finesse optical cavity, using off-resonant superradiant\nRaman scattering. Spatio-temporal evolution of the relative population of the\nhyperfine spin modes is examined numerically by solving the coupled\ncavity-condensate mean field equations in the dispersive regime. We find,\nanalytically and numerically, that beyond a certain threshold of the transverse\nlaser pump, Raman superradiance and self-organization of the hyperfine spin\ncomponents simultaneously occur and as a result a magnetic lattice is formed.\nThe effects of an extra laser pump parallel to the cavity axis and the\ntime-dependence of the pump strength on the synthesis of a sharper lattice are\nalso addressed.",
        "positive": "Thermodynamics of a Bose gas near the superfluid--Mott-insulator\n  transition: We study the thermodynamics near the generic (density-driven)\nsuperfluid--Mott-insulator transition in the three-dimensional Bose-Hubbard\nmodel using the nonperturbative renormalization-group approach. At low energy\nthe physics is controlled by the Gaussian fixed point and becomes universal.\nThermodynamic quantities can then be expressed in terms of the universal\nscaling functions of the dilute Bose gas universality class while the\nmicroscopic physics enters only {\\it via} two nonuniversal parameters, namely\nthe effective mass $m^*$ and the \"scattering length\" $a^*$ of the elementary\nexcitations at the quantum critical point between the superfluid and\nMott-insulating phase. A notable exception is the condensate density in the\nsuperfluid phase which is proportional to the quasi-particle weight $\\Zqp$ of\nthe elementary excitations. The universal regime is defined by $m^*a^*{}^2 T\\ll\n1$ and $m^*a^*{}^2|\\delta\\mu|\\ll 1$, or equivalently $|\\bar n-\\bar\nn_c|a^*{}^3\\ll 1$, where $\\delta\\mu=\\mu-\\mu_c$ is the chemical potential shift\nfrom the quantum critical point $(\\mu=\\mu_c,T=0)$ and $\\bar n-\\bar n_c$ the\ndoping with respect to the commensurate density $\\bar n_c$ of the T=0 Mott\ninsulator. We compute $\\Zqp$, $m^*$ and $a^*$ and find that they vary strongly\nwith both the ratio $t/U$ between hopping amplitude and on-site repulsion and\nthe value of the (commensurate) density $\\bar n_c$. Finally, we discuss the\nexperimental observation of universality and the measurement of $\\Zqp$, $m^*$\nand $a^*$ in a cold atomic gas in an optical lattice."
    },
    {
        "anchor": "Controllable quantum spin glasses with magnetic impurities embedded in\n  quantum solids: Magnetic impurities embedded in inert solids can exhibit long coherence times\nand interact with one another via their intrinsic anisotropic dipolar\ninteraction. We argue that, as a consequence of these properties, disordered\nensembles of magnetic impurities provide an effective platform for realizing a\ncontrollable, tunable version of the dipolar quantum spin glass seen in\nLiHo$_x$Y$_{1-x}$F$_4$. Specifically, we propose and analyze a system composed\nof dysprosium atoms embedded in solid helium. We describe the phase diagram of\nthe system and discuss the realizability and detectability of the quantum spin\nglass and antiglass phases.",
        "positive": "Spin-squeezed states for metrology: Spin-squeezing is a well-established \"quantum technology\", where\nwell-designed correlations in an ensemble of two-level systems reduce the\nstatistical uncertainty of spectroscopic experiments. This paper reviews some\nimportant advances in the field, with emphasis on the author's contributions\nconcerning in particular the fundamental limits imposed by decoherence.\nBuilding on the material presented in the first part, new ideas and some\npromising developments are outlined in the last section."
    },
    {
        "anchor": "Collective excitation of bosonic quantum Hall state: The recent developments in the theory of rapidly rotating Bose atoms have\nbeen reviewed in this article. Rotation leads to the development of\nquantized-vortices, that cluster into a vortex array, exactly to how superfluid\nhelium behaves. Theoretically, a number of strongly correlated phases are\nprojected to exist in this domain, which might be thought of as bosonic\ncounterparts of fractional quantum Hall effect (FQHE). It is now possible for\nbosons associating with a short-range interaction to exhibit a FQHE, because\nthe system of neutral bosons in a fast rotating atomic trap is analogous to\ncharged bosons placed in a fictitious magnetic field. The neutral collective\nspin-conserving and spin-flip excitation for the rotating ultra-cold dilute\nBose atoms in the FQHE domain are being discussed. We have introduced a\nrealistic interaction between the Bose particles together with long-range\ninteraction and presented a short review article about various fractional\nquantum Hall states and their spin conserving and spin reversed collective\nmodes.",
        "positive": "Tunable symmetry-protected higher-order topological states with\n  fermionic atoms in bilayer optical lattices: Higher-order topological states that possess gapped bulk energy bands and\nexotic topologically protected boundary states with at least two dimension\nlower than the bulk have significantly opened a new perspective for\nunderstanding of topological quantum matters. Here, we propose to generate\ntwo-dimensional topological boundary states for implementing synthetic magnetic\nflux of ultracold atoms trapped in bilayer optical lattices, which includes\nChern insulator, Dirac semimetals, and second-order topological phase (SOTP) by\nthe interplay of the two-photon detuning and effective Zeeman shift. These\nobserved topological phases can be well characterized by the energy gap of\nbulk, Wilson loop spectra, and the spin textures at the higher symmetric points\nof system. We show that the SOTP exhibits a pair of $0$D boundary states. While\nthe phases of Dirac semimetals and Chern insulator support the conventional\n$1$D boundary states due to the principle of bulk-boundary correspondence.\nStrikingly, the emerged boundary states for Dirac semimetals and SOTP are\ntopologically protected by $\\cal P T$-symmetry and chiral-mirror symmetry\n($\\mathcal{\\widetilde{M}}_{\\alpha}$), respectively. In particular, the location\nof $0$D corner states for SOTP which are associated with existing\n$\\mathcal{\\widetilde{M}}_{\\alpha}$-symmetry can be highly manipulated by tuning\nmagnetic flux. Our scheme herein provides a platform for emerging exotic\ntopological boundary states, which may facilitate the study of higher-order\ntopological phases in ultracold atomic gases."
    },
    {
        "anchor": "Normal density and moment of inertia of a moving superfluid: In this work, the normal density $\\rho_n$ and moment of inertia of a moving\nsuperfluid are investigated. We find that, even at zero temperature, there\nexists a finite normal density for the moving superfluid. When the velocity of\nsuperfluid reaches sound velocity, the normal density becomes total mass\ndensity $\\rho$, which indicates that the system losses superfluidity. At the\nsame time, the Landau's critical velocity also becomes zero. The existence of\nthe non-zero normal density is attributed to the coupling between the motion of\nsuperflow and density fluctuation in transverse directions. With Josephson\nrelation, the superfluid density $\\rho_s$ is also calculated and the identity\n$\\rho_s+\\rho_n=\\rho$ holds. Further more, we find that the finite normal\ndensity also results in a quantized moment of inertia in a moving superfluid\ntrapped by a ring. The normal density and moment of inertia at zero temperature\ncould be verified experimentally by measuring the angular momentum of a moving\nsuperfluid in a ring trap.",
        "positive": "Supersolid Stacks in Antidipolar Bose-Einstein Condensates: We theoretically investigate a novel supersolid structure taking the form of\nstacked, disk-shaped superfluid droplets connected via a dilute superfluid, in\nan antidipolar condensate. A phase diagram is determined for varying the\nparticle number and scattering length, identifying the regions of a regular\ndipolar superfluid, supersolid stacks, and isolated stacked disk-shaped\ndroplets in an experimentally realizable trapping potential. The collective\nBogoliubov excitation spectrum across the superfluid-supersolid phase\ntransition is studied, and the transition point is found to be associated with\nthe breaking of the degeneracy of the two lowest-lying modes. The dynamical\ngeneration of the supersolid stacks is also investigated by ramping down the\nscattering length across the phase transition. Moreover, we have studied the\nimpact of vortex-line penetration on the phase transition. We have found that\nthe presence of a vortex line causes the supersolid region to move towards\nweaker contact interactions. Our detailed numerical simulations highlight that\nan antidipolar condensate can create such supersolid stacks within an\nexperimentally reachable parameter regime."
    },
    {
        "anchor": "Generalized Gibbs Ensembles for Quantum Field Theories: We consider the non-equilibrium dynamics in isolated systems, described by\nquantum field theories (QFTs). After being prepared in a density matrix that is\nnot an eigenstate of the Hamiltonian, such systems are expected to relax\nlocally to a stationary state. In a presence of local conservation laws, these\nstationary states are believed to be described by appropriate generalized Gibbs\nensembles. Here we demonstrate that in order to obtain a correct description of\nthe stationary state, it is necessary to take into account conservation laws\nthat are not (ultra-)local in the usual sense of QFT, but fulfil a\nsignificantly weaker form of locality. We discuss implications of our results\nfor integrable QFTs in one spatial dimension.",
        "positive": "Quantum liquids with fractal branching patterns in Rydberg atom arrays: In this study, we propose an exotic quantum liquid state which does not order\nat zero temperature in a Rydberg atom array with antiblockade mechanism. By\nperforming an unbiased large-scale quantum Monte Carlo simulation, we\ninvestigate a minimal model with facilitated excitation in a clean system\nwithout frustration, and find that the wavefunction of its ground state is\ncomposed of configurations with fractal branching structures. This state\nfeatures a quasi-long-range order (correlation functions with algebraic decay)\nas well as a heterogeneous structure of liquid and glass mixture. Thus it is\ndifferent from most well-established quantum phases of matter."
    },
    {
        "anchor": "Emergent flux in a one-dimensional Bose-Fermi mixture: We find a novel chiral superfluid (CSF) phase in a chain of Bose-Fermi\nmixture, which has been validated using two unbiased numerical methods, density\nmatrix renormalization group and Grassmann multi-scale entanglement\nrenormalization ansatz. The system hosts the interplay between two types of\nfermions: bare spinless fermions and composite fermions, the latter consisting\nof a fermion and a boson. In the CSF phase, bosons condensate at non-zero\nmomentum $\\pm 2\\pi /L$ with chain length $L$. In essence, the local superfluid\norder parameter continuously rotates along the chain, indicating that the CSF\nphase spontaneously breaks time-reversal symmetry. This symmetry breaking gives\nrise to an emergent flux in the background, effectively optimizing the kinetic\nenergy of the composite fermions within the system. We provide a physical\nunderstanding at the mean-field level. Furthermore, we demonstrate that the 1D\nCSF phase can emerge in a more widely applicable extended Hubbard model. The\npotential realization of this phase in cold-atom experiments has also been\nexplored.",
        "positive": "Ground state of a mixture of two bosonic Calogero-Sutherland gases with\n  strong odd-wave interspecies attraction: A model of two Calogero-Sutherland Bose gases A and B with strong odd-wave AB\nattractions induced by a p-wave AB Feshbach resonance is studied. The ground\nstate wave function is found analytically by a Bose-Bose duality mapping, which\npermits one to accurately determine static physical properties by a Monte Carlo\nmethod. The condensation of particles or particle pairs (molecules) is tested\nby analyzing the presence of the off-diagonal long-range order in one- or\ntwo-body density matrices. The p-wave symmetry of AB interaction makes possible\nquasi-condensation of type A particles at the Fermi momentum of the B\ncomponent. The zero-temperature phase diagram is drawn in terms of densities\nand interaction strengths."
    },
    {
        "anchor": "Prethermalization and entanglement dynamics in interacting topological\n  pumps: We investigate the formation of quasisteady states in one-dimensional pumps\nof interacting fermions at non-integer filling fraction, in the regime where\nthe driving frequency and interaction strength are small compared to the\ninstantaneous single-particle band gap throughout the driving cycle. The system\nrapidly absorbs energy from the driving field, and approaches a quasisteady\nstate that locally resembles a maximal entropy state subject to the constraint\nof fixed particle number in each of the system's single-particle Floquet bands.\nWe explore the nature of this quasisteady state through one-body observables\nincluding the pumped current and natural orbital occupations, as well as the\n(many-body) entanglement spectrum and entropy. Potential disorder significantly\nreduces the amplitude of fluctuations of the quasisteady state current around\nits universal value, while the lifetime of the quasisteady state remains nearly\nunaffected for disorder strengths up to the scale of the single-particle band\ngap. Interestingly, the natural orbital occupations and entanglement entropy\ndisplay patterns signifying the periodic entangling and disentangling of the\nsystem's degrees of freedom over each driving cycle. Moreover, prominent\nfeatures in the system's time-dependent entanglement spectrum reveal the\nemergence of new long timescales associated with the equilibration of\nmany-particle correlations.",
        "positive": "Approximate theories for binary magnetic quantum droplets: We develop two approximate theories to describe the miscible and immiscible\ndroplets that can occur in a binary mixture of highly magnetic bosonic atoms.\nIn addition to allowing simpler calculations, the approximate theories provide\ninsight into the role of quantum fluctuations in the two regimes. Results are\nvalidated by comparison to those from the extended Gross-Pitaevskii equation.\nAs an application we solve for the ground state droplets crossing the\nmiscible-immiscible transition as function of the short-ranged interspecies\ninteraction parameter. We consider regimes where the transition occurs suddenly\nor as a smooth cross-over. Using dynamical calculations we show that the\ncharacter of the transition is revealed in the number of domains produced when\nramping the droplet into the immiscible regime."
    },
    {
        "anchor": "Anomalous Hall conductivity from the dipole mode of spin-orbit-coupled\n  cold-atom systems: Motivated by recent experiments [Lin {\\it et al.}, Nature {\\bf 417}, 83\n(2011)] that engineered spin-orbit coupling in ultra-cold mixtures of bosonic\natoms, we study the dipole oscillation of trapped spin-orbit-coupled\nnon-condensed Bose and Fermi gases. We find that different directions of\noscillation are coupled by the spin-orbit interactions. The phase difference\nbetween oscillatory motion in orthogonal directions and the trapping\nfrequencies of the modes are shown to be related to the anomalous Hall\nconductivity. Our results can be used to experimentally determine the anomalous\nHall conductivity for cold-atom systems.",
        "positive": "Reentrant Fulde-Ferrell-Larkin-Ovchinnikov superfluidity in the\n  honeycomb lattice: We study superconducting properties of population-imbalanced ultracold Fermi\nmixtures in the honeycomb lattice that can be effectively described by the\nspin-imbalanced attractive Hubbard model in the presence of a Zeeman magnetic\nfield. We use the mean-field theory approach to obtain ground state phase\ndiagrams including some unconventional superconducting phases such as the\nFulde--Ferrell--Larkin--Ovchinnikov (FFLO) phase. We show that this phase is\ncharacterized by atypical behaviour of the Cooper pairs total momentum in the\nexternal magnetic field. We show that the momentum changes its value as well as\ndirection with change of the system parameters. We discuss the influence of van\nHove singularities on the possibility of the reentrant FFLO phase occurrence,\nwithout a BCS precursor."
    },
    {
        "anchor": "Superfluidity breakdown of periodic matter waves in quasi\n  one-dimensional annular traps via resonant scattering with moving defects: We investigate, both analytically and numerically, the quasi-superfluidity\nproperties of periodic Bose-Einstein condensates (BECs) in a\nquasi-one-dimensional (1D) ring with optical lattices (OL) of different kinds\n(linear and nonlinear) and with a moving defect of an infinite mass inside. To\nstudy the dynamics of the condensate we used a mean-field approximation\ndescribing the condensate by use of the Gross-Pitaevskii equation for the order\nparameter. We show that the resonant scattering of sound Bloch waves with the\ndefect profoundly affect BEC superfluidity. In particular, a moving defect\nalways leads to the breakdown of superfluidity independently of the value of\nits velocity. For weak periodic potentials the superfluidity breakdown may\noccur on a very long time scale (quasisuperfluidity) but the breakdown process\ncan be accelerated by increasing the strength of the OL. Quite remarkably, we\nfind that when the length of the ring is small enough to imply the discreteness\nof the reciprocal space, it becomes possible to avoid the resonant scattering\nand to restore quasi-superfluidity.",
        "positive": "Comment on \"Observation of two-dimensional Anderson localisation of\n  ultracold atoms\": Here I provide additional experimental information and criticise the\nanalysis, modelling, interpretation and claims presented in the recent paper\n[Nature Communications 11, 4942 (2020)]. I argue that the authors have no clear\nexperimental evidence of Anderson localisation (as they claim) and their\nnumerical simulations are very far indeed from reproducing the experiment, as\nstated in their article. Furthermore, some effects that are ascribed to real\nphysical mechanisms are revealed to be simply artefacts."
    },
    {
        "anchor": "Creation of orbital angular momentum states with chiral polaritonic\n  lenses: Controlled transfer of orbital angular momentum to exciton-polariton\nBose-Einstein condensate spontaneously created under incoherent, off-resonant\nexcitation conditions is a long-standing challenge in the field of microcavity\npolaritonics. We demonstrate, experimentally and theoretically, a simple and\nefficient approach to generation of nontrivial orbital angular momentum states\nby using optically-induced potentials -- chiral polaritonic lenses.",
        "positive": "Inhomogeneities and impurities in a dense one-dimensional Rydberg\n  lattice gas: We consider a dense one-dimensional laser-driven Rydberg lattice gas with\nperfect nearest-neighbor blockade. The ground state of this system can be found\nanalytically in certain parameter regimes even when the applied fields are\ninhomogeneous in space. We will use this unique feature to investigate the\neffect of an impurity - introduced by the local variation of the laser\nparameters - on the correlations of the many-body ground state. Moreover, we\nexplore the role of a staggered laser field which alternates from site to site\nthereby breaking the sublattice symmetry. We demonstrate that this technique,\nwhich can be applied experimentally, reveals insights into the role of\nlong-range interactions on the critical properties of a Rydberg gas. Our work\nhighlight novel possibilities for the exploration of many-body physics in\nRydberg lattice gases based on locally tuneable laser fields."
    },
    {
        "anchor": "Reply to Comments on \"Universal and Non-Universal Correction Terms of\n  Bose Gases in Dilute Region: A Quantum Monte Carlo Study\": We reply to the comments on our previous paper J. Phys. Soc. Jpn. 91, 024001\n(2022)",
        "positive": "Photon-atomic solitons in a Bose-Einstein condensate trapped in a soft\n  optical lattice: We investigate the ground state (GS) of a collisionless Bose-Einstein\ncondensate (BEC) trapped in a soft one-dimensional optical lattice (OL), which\nis formed by two counterpropagating optical beams perturbed by the BEC density\nprofile through the local-field effect (LFE). We show that LFE gives rise to an\nenvelope-deformation potential, a nonlocal potential resulting from the phase\ndeformation, and an effective self-interaction of the condensate. As a result,\nstable photon-atomic lattice solitons, including an optical component, in the\nform of the deformation of the soft OL, in a combination with a localized\nmatter-wave component, are generated in the blue-detuned setting, without any\ndirect interaction between atoms. These self-trapped modes, which realize the\nsystem's GS, are essentially different from the gap solitons supported by the\ninterplay of the OL potential and collisional interactions between atoms. A\ntransition to tightly bound modes from loosely bound ones occurs with the\nincrease of the number of atoms in the BEC."
    },
    {
        "anchor": "On-Demand Entanglement of Molecules in a Reconfigurable Optical Tweezer\n  Array: Entanglement is crucial to many quantum applications including quantum\ninformation processing, simulation of quantum many-body systems, and\nquantum-enhanced sensing. Molecules, because of their rich internal structure\nand interactions, have been proposed as a promising platform for quantum\nscience. Deterministic entanglement of individually controlled molecules has\nnevertheless been a long-standing experimental challenge. Here we demonstrate,\nfor the first time, on-demand entanglement of individually prepared molecules.\nUsing the electric dipolar interaction between pairs of molecules prepared\nusing a reconfigurable optical tweezer array, we realize an entangling\ntwo-qubit gate, and use it to deterministically create Bell pairs. Our results\ndemonstrate the key building blocks needed for quantum information processing,\nsimulation of quantum spin models, and quantum-enhanced sensing. They also open\nup new possibilities such as using trapped molecules for quantum-enhanced\nfundamental physics tests and exploring collisions and chemical reactions with\nentangled matter.",
        "positive": "Bound states and Cooper pairs of molecules in 2D optical lattices\n  bilayer: We investigate the formation of Cooper pairs, bound dimers and the\ndimer-dimer elastic scattering of ultra- cold dipolar Fermi molecules confined\nin a 2D optical lattice bilayer configuration. While the energy and their\nassociated bound states are determined in a variational way, the correlated\ntwo-molecule pair is addressed as in the original Cooper formulation. We\ndemonstrate that the 2D lattice confinement favors the formation of zero center\nmass momentum bound states. Regarding the Cooper pairs binding energy, this\ndepends on the molecule populations in each layer. Maximum binding energies\noccur for non-zero (zero) pair momentum when the Fermi system is polarized\n(unpolarized). We find an analytic expression for the dimer-dimer effective\ninteraction in the deep BEC regime. The present analysis represents a route for\naddressing the BCS-BEC crossover superfluidity in dipolar Fermi gases confined\nin 2D optical lattices within the current experimental panorama."
    },
    {
        "anchor": "Accurate projective two-band description of topological superfluidity in\n  spin-orbit-coupled Fermi gases: The interplay of spin-orbit coupling and Zeeman splitting in ultracold Fermi\ngases gives rise to a topological superfluid phase in two spatial dimensions\nthat can host exotic Majorana excitations. Theoretical models have so far been\nbased on a four-band Bogoliubov-de Gennes formalism for the combined spin-1/2\nand particle-hole degrees of freedom. Here we present a simpler, yet accurate,\ntwo-band description based on a well-controlled projection technique that\nprovides a new platform for exploring analogies with chiral p-wave\nsuperfluidity and detailed future studies of spatially non-uniform situations.",
        "positive": "Heavy-Light Few Fermion Clusters at Unitarity: We examine the physics of two, three, and four heavy fermions interacting\nwith a single light fermion via short-range interactions. Four-particle bosonic\nEfimov states have proven important experimentally and also been the subject of\nsignificant theoretical effort. Similar fermionic systems are just now being\ninvestigated. We find that with some simple interactions the four- and\nfive-particle states collapse to the interaction range at smaller mass ratios\nthan the three-body state, and also before larger clusters can collapse. These\nstates and their excitations can be studied in cold atom experiments, providing\nunique insights into the role of few-body systems in many-body physics."
    },
    {
        "anchor": "Laughlin's topological charge pump in an atomic Hall cylinder: The quantum Hall effect occuring in two-dimensional electron gases was first\nexplained by Laughlin, who envisioned a thought experiment that laid the\ngroundwork for our understanding of topological quantum matter. His proposal is\nbased on a quantum Hall cylinder periodically driven by an axial magnetic\nfield, resulting in the quantized motion of electrons. We realize this\nmilestone experiment with an ultracold gas of dysprosium atoms, the cyclic\ndimension being encoded in the electronic spin and the axial field controlled\nby the phases of laser-induced spin-orbit couplings. Our experiment provides a\nstraightforward manifestation of the non-trivial topology of quantum Hall\ninsulators, and could be generalized to strongly-correlated topological\nsystems.",
        "positive": "Second Josephson excitations beyond mean field as a toy model for\n  thermal pressure: exact quantum dynamics and the quantum phase model: A simple four-mode Bose-Hubbard model with intrinsic time scale separation\ncan be considered as a paradigm for mesoscopic quantum systems in thermal\ncontact. In our previous work we showed that in addition to coherent particle\nexchange, a novel slow collective excitation can be identified by a series of\nHolstein-Primakoff transformations. This resonant energy exchange mode is not\npredicted by linear Bogoliubov theory, and its frequency is sensitive to\ninteractions among Bogoliubov quasi-particles; it may be referred to as a\nsecond Josephson oscillation, in analogy to the second sound mode of liquid\nHelium II. In this paper we will explore this system beyond the\nGross-Pitaevskii mean field regime. We directly compare the classical mean\nfield dynamics to the exact full quantum many-particle dynamics and show good\nagreement over a large range of the system parameters. The second Josephson\nfrequency becomes imaginary for stronger interactions, however, indicating\ndynamical instability of the symmetric state. By means of a generalized quantum\nphase model for the full four-mode system, we then show that, in this regime,\nhigh-energy Bogoliubov quasiparticles tend to accumulate in one pair of sites,\nwhile the actual particles preferentially occupy the opposite pair. We\ninterpret this as a simple model for thermal pressure."
    },
    {
        "anchor": "Two-body bound state of ultracold Fermi atoms with two-dimensional\n  spin-orbit coupling: In a recent experiment, a two-dimensional spin-orbit coupling (SOC) was\nrealized for fermions in the continuum [Nat. Phys. 12, 540 (2016)], which\nrepresents an important step forward in the study of synthetic gauge field\nusing cold atoms. In the experiment, it was shown that a Raman-induced\ntwo-dimensional SOC exists in the dressed-state basis close to a Dirac point of\nthe single-particle spectrum. By contrast, the short-range inter-atomic\ninteractions of the system are typically expressed in the hyperfine-spin basis.\nThe interplay between synthetic SOC and interactions can potentially lead to\ninteresting few- and many-body phenomena but has so far eluded theoretical\nattention. Here we study in detail properties of two-body bound states of such\na system. We find that, due to the competition between SOC and interaction, the\nstability region of the two-body bound state is in general reduced.\nParticularly, the threshold of the lowest two-body bound state is shifted to a\npositive, SOC-dependent scattering length. Furthermore, the center-of-mass\nmomentum of the lowest two-body bound state becomes nonzero, suggesting the\nemergence of Fulde-Ferrell pairing states in a many-body setting. Our results\nreveal the critical difference between the experimentally realized\ntwo-dimensional SOC and the more symmetric Rashba or Dresselhaus SOCs in an\ninteracting system, and paves the way for future characterizations of\ntopological superfluid states in the experimentally relevant systems.",
        "positive": "Effective potentials in a rotating spin-orbit-coupled spin-1 spinor\n  condensate: We theoretically study the stationary-state vortex lattice configurations of\nrotating spin-orbit- and coherently-coupled spin-1 Bose-Einstein condensates\ntrapped in quasi-two-dimensional harmonic potentials. The combined effects of\nrotation, spin-orbit and coherent couplings are analyzed systematically from\nthe single-particle perspective. Through the single-particle Hamiltonian, which\nis exactly solvable for one-dimensional coupling, under specific coupling and\nrotation strengths, we illustrate that a boson in these rotating spin-orbit-\nand coherently-coupled condensates are subjected to effective toroidal,\nsymmetric double-well, or asymmetric double-well potentials. In the presence of\nmean-field interactions, using the coupled Gross-Pitaevskii formalism at\nmoderate to high rotation frequencies, the analytically obtained effective\npotential minima and the numerically obtained coarse-grained density maxima\nposition are in excellent agreement. On rapid rotation, we further find that\nthe spin expectation per particle of an antiferromagnetic spin-1 Bose-Einstein\ncondensate approaches unity indicating a similarity in the response with\nferromagnetic spin-orbit-coupled condensates."
    },
    {
        "anchor": "Spin-Imbalanced Quasi-Two-Dimensional Fermi Gases: We measure the density profiles for a Fermi gas of $^6$Li containing $N_1$\nspin-up atoms and $N_2$ spin-down atoms, confined in a quasi-two-dimensional\ngeometry. The spatial profiles are measured as a function of spin-imbalance\n$N_2/N_1$ and interaction strength, which is controlled by means of a\ncollisional (Feshbach) resonance. The measured cloud radii and central\ndensities are in disagreement with mean-field Bardeen-Cooper-Schrieffer theory\nfor a true two-dimensional system. We find that the data for normal-fluid\nmixtures are reasonably well fit by a simple two-dimensional polaron model of\nthe free energy. Not predicted by the model is a phase transition to a\nspin-balanced central core, which is observed above a critical value of\n$N_2/N_1$. Our observations provide important benchmarks for predictions of the\nphase structure of quasi-two-dimensional Fermi gases.",
        "positive": "Induced interactions and the superfluid transition temperature in a\n  three-component Fermi gas: We study many-body contributions to the effective interaction between\nfermions in a three-component Fermi mixture. We find that effective\ninteractions induced by the third component can lead to a phase diagram\ndifferent from that predicted if interactions with the third component are\nneglected. As a result, in a confining potential a superfluid shell structure\ncan arise even for equal populations of the components. We also find a critical\ntemperature for the BCS transition in a 6Li mixture which can deviate strongly\nfrom the one in a weakly interacting two-component system."
    },
    {
        "anchor": "Attractive dipolar coupling between stacked exciton fluids: The interaction between aligned dipoles is long-ranged and highly\nanisotropic: it changes from repulsive to attractive depending on the relative\npositions of the dipoles. We report on the observation of the attractive\ncomponent of the dipolar coupling between excitonic dipoles in stacked\nsemiconductor bilayers. We show that the presence of a dipolar exciton fluid in\none bilayer modifies the spatial distribution and increases the binding energy\nof excitonic dipoles in a vertically remote layer. The binding energy changes\nare explained by a many-body polaron model describing the deformation of the\nexciton cloud due to its interaction with a remote dipolar exciton. The results\nopen the way for the observation of theoretically predicted new and exotic\ncollective phases, the realization of interacting dipolar lattices in\nsemiconductor systems as well as for engineering and sensing their collective\nexcitations.",
        "positive": "Floquet Edge States with Ultracold Atoms: We describe an experimental setup for imaging topologically protected Floquet\nedge states using ultracold bosons in an optical lattice. Our setup involves a\ndeep two dimensional optical lattice with a time dependent superlattice that\nmodulates the hopping between neighboring sites. The finite waist of the\nsuperlattice beam yields regions with different topological numbers. One can\nobserve chiral edge states by imaging the real-space density of a bosonic\npacket launched from the boundary between two topologically distinct regions."
    },
    {
        "anchor": "Observation of the Quantum Boomerang Effect: A particle in an Anderson-localized system, if launched in any direction,\nshould on average return to its starting point and stay there. Despite the\ncentral role played by Anderson localization in the modern understanding of\ncondensed matter, this \"quantum boomerang\" effect, an essential feature of the\nlocalized state, was only recently theoretically predicted and has not\npreviously been observed. We report the experimental observation of the quantum\nboomerang effect. Using a degenerate gas and a phase-shifted pair of optical\nlattices, we probe the role of time reversal symmetry breaking, Floquet gauge,\nand initial state symmetry in supporting or disrupting the boomerang effect.\nHighlighting the key role of localization, we observe that as stochastic\nkicking destroys dynamical localization, the quantum boomerang effect also\ndisappears. Measured dynamics are in agreement with analytical and numerical\npredictions. These results showcase a unique experimental probe of the\nunderlying quantum nature of Anderson localized matter.",
        "positive": "Tunable dual-species Bose-Einstein condensates of $^{39}$K and $^{87}$Rb: We present the production of dual-species Bose-Einstein condensates of\n$^{39}\\mathrm{K}$ and $^{87}\\mathrm{Rb}$. Preparation of both species in the\n$\\left| F=1,m_F=-1 \\right\\rangle$ state enabled us to exploit a total of three\nFesh\\-bach resonances which allows for simultaneous Feshbach tuning of the\n$^{39}\\mathrm{K}$ intraspecies and the $^{39}\\mathrm{K}$-$^{87}\\mathrm{Rb}$\ninterspecies scattering length. Thus dual-species Bose-Einstein condensates\nwere produced by sympathetic cooling of $^{39}\\mathrm{K}$ with\n$^{87}\\mathrm{Rb}$. A dark spontaneous force optical trap was used for\n$^{87}\\mathrm{Rb}$, to reduce the losses in $^{39}\\mathrm{K}$ due to\nlight-assisted collisions in the optical trapping phase, which can be of\nbenefit for other dual-species experiments. The tunability of the scattering\nlength was used to perform precision spectroscopy of the interspecies Feshbach\nresonance located at $117.56(2)\\,\\mathrm{G}$ and to determine the width of the\nresonance to $1.21(5)\\,\\mathrm{G}$ by rethermalization measurements. The\ntransition region from miscible to immiscible dual-species condensates was\ninvestigated and the interspecies background scattering length was determined\nto $28.5\\,a_\\mathrm{0}$ using an empirical model. This paves the way for\ndual-species experiments with $^{39}\\mathrm{K}$ and $^{87}\\mathrm{Rb}$ BECs\nranging from molecular physics to precision metrology."
    },
    {
        "anchor": "Interaction Induced Hall Response in a Spin-Orbit Coupled Bose-Einstein\n  Condensate: In this letter we consider the dynamic behaviors of spin-orbit coupled Bose\ncondensates realized in recent experiments. We show that there exists an\ninteraction induced ac Hall response which is absent in a non-interacting\nsystem. This condensate has two distinct equilibrium phases known as the plane\nwave phase and the stripe phase. In the plane wave phase, we show that an ac\nlongitudinal current will induce an ac radial current in the transverse\ndirection, and vice versa, as a cooperation effect of spin-velocity locking and\nspin-dependent interaction. In the stripe phase, we show that the dominant\nlongitudinal response to a transverse radial current is sliding of the density\nstripe, because it is the low-lying excitation mode originated from spontaneous\nspatial translational symmetry breaking in this phase.",
        "positive": "Matter-wave analog of an optical random laser: The accumulation of atoms in the lowest energy level of a trap and the\nsubsequent out-coupling of these atoms is a realization of a matter-wave analog\nof a conventional optical laser. Optical random lasers require materials that\nprovide optical gain but, contrary to conventional lasers, the modes are\ndetermined by multiple scattering and not a cavity. We show that a\nBose-Einstein condensate can be loaded in a spatially correlated disorder\npotential prepared in such a way that the Anderson localization phenomenon\noperates as a band-pass filter. A multiple scattering process selects atoms\nwith certain momenta and determines laser modes which represents a matter-wave\nanalog of an optical random laser."
    },
    {
        "anchor": "Proximity effects in cold atom artificial graphene: Cold atoms in an optical lattice with brick-wall geometry have been used to\nmimic graphene, a two-dimensional material with characteristic Dirac\nexcitations. Here we propose to bring such artificial graphene into the\nproximity of a second atomic layer with a square lattice geometry. For\nnon-interacting fermions, we find that such bilayer system undergoes a phase\ntransition from a graphene-like semi-metal phase, characterized by a band\nstructure with Dirac points, to a gapped band insulator phase. In the presence\nof attractive interactions between fermions with pseudospin-1/2 degree of\nfreedom, a competition between semi-metal and superfluid behavior is found at\nthe mean-field level. Using the quantum Monte Carlo method, we also investigate\nthe case of strong repulsive interactions. In the Mott phase, each layer\nexhibits a different amount of long-range magnetic order. Upon coupling both\nlayers, a valence-bond crystal is formed at a critical coupling strength.\nFinally, we discuss how these bilayer systems could be realized in existing\ncold atom experiments.",
        "positive": "Density ripples in expanding low-dimensional gases as a probe of\n  correlations: We investigate theoretically the evolution of the two-point density\ncorrelation function of a low-dimensional ultracold Bose gas after release from\na tight transverse confinement. In the course of expansion thermal and quantum\nfluctuations present in the trapped systems transform into density\nfluctuations. For the case of free ballistic expansion relevant to current\nexperiments, we present simple analytical relations between the spectrum of\n``density ripples'' and the correlation functions of the original confined\nsystems. We analyze several physical regimes, including weakly and strongly\ninteracting one-dimensional (1D) Bose gases and two-dimensional (2D) Bose gases\nbelow the Berezinskii-Kosterlitz-Thouless (BKT) transition. For weakly\ninteracting 1D Bose gases, we obtain an explicit analytical expression for the\nspectrum of density ripples which can be used for thermometry. For 2D Bose\ngases below the BKT transition, we show that for sufficiently long expansion\ntimes the spectrum of the density ripples has a self-similar shape controlled\nonly by the exponent of the first-order correlation function. This exponent can\nbe extracted by analyzing the evolution of the spectrum of density ripples as a\nfunction of the expansion time."
    },
    {
        "anchor": "Many interacting fermions in a one-dimensional harmonic trap: a\n  quantum-chemical treatment: We employ \\textit{ab initio} methods of quantum chemistry to investigate\nspin-1/2 fermions interacting via a two-body contact potential in a\none-dimensional harmonic trap. The convergence of the total energy with the\nsize of the one-particle basis set is analytically investigated for the\ntwo-body problem and the same form of the convergence formula is numerically\nconfirmed to be valid for the many-body case. Benchmark calculations for two to\nsix fermions with the full configuration interaction method equivalent to the\nexact diagonalization approach, and the coupled cluster method including\nsingle, double, triple, and quadruple excitations are presented. The\nconvergence of the correlation energy with the level of excitations included in\nthe coupled cluster model is analyzed. The range of the interaction strength\nfor which single-reference coupled cluster methods work is examined. Next, the\ncoupled cluster method restricted to single, double, and noniterative triple\nexcitations, CCSD(T), is employed to study a two-component Fermi gas composed\nof 6 to 80 atoms in a one-dimensional harmonic trap. The density profiles of\ntrapped atomic clouds are also reported. Finally, a comparison with\nexperimental results for few-fermion systems is presented. Upcoming possible\napplications and extensions of the presented approach are discussed.",
        "positive": "Observability of Quantum Criticality and a Continuous Supersolid in\n  Atomic Gases: We analyze the Bose-Hubbard model with a three-body hardcore constraint by\nmapping the system to a theory of two coupled bosonic degrees of freedom. We\nfind striking features that could be observable in experiments, including a\nquantum Ising critical point on the transition from atomic to dimer\nsuperfluidity at unit filling, and a continuous supersolid phase for strongly\nbound dimers."
    },
    {
        "anchor": "Controlled Split-Recombination of 2D Matter-Wave Solitons in\n  Time-Dependent Trap: We propose a novel approach to manipulate two-dimensional bright matter-wave\nsolitons by tuning the frequency of the trap which is different from Feshbach\nresonance technique. The exact bright soliton solutions for two-dimensional\nGross-Pitaevskii (GP) equation with attractive interaction strength in a\ntime-dependent trap are constructed analytically and its dynamics show no\ncollapse while modulating the trap frequency. The two-soliton dynamics exhibits\nan interesting splitting and recombination phenomenon which generates\ninterference pattern in the process. This type of behaviour in two-dimensional\nBECs has wider ramifications and our approach opens new avenues in stabilizing\nbright solitons in higher dimensional regime. We have also explored the\nexperimental realization of this novel phenomenon.",
        "positive": "Quantum spiral spin-tensor magnetism: The characterization of quantum magnetism in a large spin ($\\geq 1$) system\nnaturally involves both spin-vectors and -tensors. While certain types of\nspin-vector (e.g., ferromagnetic, spiral) and spin-tensor (e.g., nematic in\nfrustrated lattices) orders have been investigated separately, the coexistence\nand correlation between them have not been well explored. Here we propose a\nnovel quantum spiral spin-tensor order on a spin-1 Heisenberg chain subject to\na spiral spin-tensor Zeeman field, which can be experimentally realized using a\nRaman-dressed cold atom optical lattice. We develop a method to fully\ncharacterize quantum phases of such spiral tensor magnetism with the\ncoexistence of spin-vector and spin-tensor orders as well as their correlations\nusing eight geometric parameters. Our method provides a powerful tool for\ncharacterizing spin-1 quantum magnetism and opens an avenue for exploring novel\nmagnetic orders and spin-tensor electronics/atomtronics in large-spin systems."
    },
    {
        "anchor": "Supersolidity around a critical point in dipolar Bose Einstein\n  condensates: We explore spatial symmetry breaking of a dipolar Bose Einstein condensate in\nthe thermodynamic limit and reveal a critical point in the phase diagram at\nwhich crystallization occurs via a second order phase transition. This behavior\nis traced back to the significant effects of quantum fluctuations in dipolar\ncondensates, which moreover stabilize a new supersolid phase, namely a regular\nhoneycomb pattern with maximal modulational contrast and near-perfect\nsuperfluidity.",
        "positive": "Oscillations of a quasi-one-dimensional dipolar supersolid: The properties of a supersolid state (SS) in quasi-one-dimensional dipolar\nBose-Einstein condensate is studied, considering two possible mechanisms of\nrealization - due to repulsive three-body atomic interactions and quantum\nfluctuations in the framework of the Lee-Huang-Yang (LHY) theory. The proposed\ntheoretical model, based on minimization of the energy functional, allows\nevaluating the amplitude of the SS for an arbitrary set of parameters in the\ngoverning Gross-Pitaevskii equation (GPE). To explore the dynamics of the SS\nfirst, we numerically construct its ground state in different settings,\nincluding periodic boundary conditions, box-like trap and parabolic potential,\nthen impose a perturbation. In oscillations of the perturbed supersolid we\nobserve the key manifestation of SS, namely the free flow of the superfluid\nfraction through the crystalline component of the system. Two distinct\noscillation frequencies of the supersolid associated with the superfluid\nfraction and crystalline components of the wave function are identified from\nnumerical simulations of the GPE."
    },
    {
        "anchor": "Creating and probing the Sachdev-Ye-Kitaev model with ultracold gases:\n  Towards experimental studies of quantum gravity: We suggest that the holographic principle, combined with recent technological\nadvances in atomic, molecular, and optical physics, can lead to experimental\nstudies of quantum gravity. As a specific example, we consider the\nSachdev-Ye-Kitaev (SYK) model, which consists of spin-polarized fermions with\nan all-to-all complex random two-body hopping and has been conjectured to be\ndual to a certain quantum gravitational system. Achieving low-temperature\nstates of the SYK model is interpreted as a realization of a stringy black\nhole, provided that the holographic duality is true. We introduce a variant of\nthe SYK model, in which the random two-body hopping is real. This model is\nequivalent to the origincal SYK model in the large-$N$ limit. We show that this\nmodel can be created in principle by confining ultracold fermionic atoms into\noptical lattices and coupling two atoms with molecular states via\nphoto-association lasers. This development serves as an important first step\ntowards an experimental realization of such systems dual to quantum black\nholes. We also show how to measure out-of-time-order correlation functions of\nthe SYK model, which allow for identifying the maximally chaotic property of\nthe black hole.",
        "positive": "Quantum search with interacting Bose-Einstein condensates: One approach to the development of quantum search algorithms is the quantum\nwalk. A spatial search can be effected by the continuous-time evolution of a\nsingle quantum particle on a graph containing a marked site. In many physical\nimplementations, however, one might expect to have multiple particles. In\ninteracting bosonic systems at zero temperature, the dynamics is well-described\nby a discrete nonlinear Schrodinger equation. We investigate the role of\nnonlinearity in determining the efficiency of the spatial search algorithm\nwithin the quantum walk model, for the complete graph. The analytical\ncalculations reveal that the nonlinear search time scales with size of the\nsearch space N like the square root of N, equivalent to the linear case though\nwith a different overall constant. The results indicate that interacting\nBose-Einstein condensates at zero temperature could be natural systems for the\nimplementation of the quantum search algorithm."
    },
    {
        "anchor": "Dirac Point Structure in a Bose-Einstein Condensate in a Honeycomb\n  Optical Lattice: We study the Bose-Einstein condensate in a honeycomb optical lattice within\nBogoliubov theory and find that for a ${\\bf k} = 0$ condensate, the Dirac\npoints appear in the Bogoliubov excitation spectrum when $0 < \\beta < 2$, which\nillustrates that the bose-bose interaction does not change the Dirac point\nstructure but only give a modification of the velocity of the Dirac cone. When\nthe bosons are driven to condense at ${\\bf k} = {\\bf K}$, however, we find that\nthe topology of the Dirac points will be altered by arbitrary weak interaction.\nFurthermore, we find that the next-nearest-neighbor hopping in an isotropic and\nan anisotropic lattice has different effects to the dynamics of the condensate\nand it should be taken into account when the lattice is not sufficiently deep.",
        "positive": "Probing quantum many-body correlations by universal ramping dynamics: Ramping a physical parameter is one of the most common experimental protocols\nin studying a quantum system, and ramping dynamics has been widely used in\npreparing a quantum state and probing physical properties. Here, we present a\nnovel method of probing quantum many-body correlation by ramping dynamics. We\nramp a Hamiltonian parameter to the same target value from different initial\nvalues and with different velocities, and we show that the first-order\ncorrection on the finite ramping velocity is universal and path-independent,\nrevealing a novel quantum many-body correlation function of the equilibrium\nphases at the target values. We term this method as the non-adiabatic linear\nresponse since this is the leading order correction beyond the adiabatic limit.\nWe demonstrate this method experimentally by studying the Bose-Hubbard model\nwith ultracold atoms in three-dimensional optical lattices. Unlike the\nconventional linear response that reveals whether the quasi-particle dispersion\nof a quantum phase is gapped or gapless, this probe is more sensitive to\nwhether the quasi-particle lifetime is long enough such that the quantum phase\npossesses a well-defined quasi-particle description. In the Bose-Hubbard model,\nthis non-adiabatic linear response is significant in the quantum critical\nregime where well-defined quasi-particles are absent. And in contrast, this\nresponse is vanishingly small in both superfluid and Mott insulators which\npossess well-defined quasi-particles. Because our proposal uses the most common\nexperimental protocol, we envision that our method can find broad applications\nin probing various quantum systems."
    },
    {
        "anchor": "St\u00fcckelberg interferometry using spin-orbit-coupled cold atoms in an\n  optical lattice: Time evolution of spin-orbit-coupled cold atoms in an optical lattice is\nstudied, with a two-band energy spectrum having two avoided crossings. A force\nis applied such that the atoms experience two consecutive Landau-Zener\ntunnelings while transversing the avoided crossings. St\\\"uckelberg interference\narises from the phase accumulated during the adiabatic evolution between the\ntwo tunnelings. This phase is gauge field-dependent and thus provides new\nopportunities to measure the synthetic gauge field, which is verified via\ncalculation of spin transition probabilities after a double passage process.\nTime-dependent and time-averaged spin probabilities are derived, in which\nresonances are found. We also demonstrate chiral Bloch oscillation and rich\nspin-momentum locking behavior in this system.",
        "positive": "Low energy dynamics of spinor condensates: We present a derivation of the low energy Lagrangian governing the dynamics\nof the spin degrees of freedom in a spinor Bose condensate, for any phase in\nwhich the average magnetization vanishes. This includes all phases found within\nmean-field treatments except for the ferromagnet, for which the low energy\ndynamics has been discussed previously. The Lagrangian takes the form of a\nsigma model for the rotation matrix describing the local orientation of the\nspin state of the gas."
    },
    {
        "anchor": "Functional-renormalization-group approach to strongly coupled Bose-Fermi\n  mixtures in two dimensions: We study theoretically the phase diagram of strongly coupled two-dimensional\nBose-Fermi mixtures interacting with attractive short-range potentials as a\nfunction of the particle densities. We focus on the limit where the size of the\nbound state between a boson and a fermion is small compared to the average\ninterboson separation and develop a functional-renormalization-group approach\nthat accounts for the bound-state physics arising from the extended\nFr\\\"{o}hlich Hamiltonian. By including three-body correlations we are able to\nreproduce the polaron-to-molecule transition in two-dimensional Fermi gases in\nthe extreme limit of vanishing boson density. We predict frequency- and\nmomentum-resolved spectral functions and study the impact of three-body\ncorrelations on quasiparticle properties. At finite boson density, we find that\nwhen the bound-state energy exceeds the Fermi energy by a critical value, the\nfermions and bosons can form a fermionic composite with a well-defined Fermi\nsurface. These composites constitute a Fermi sea of dressed Feshbach molecules\nin the case of ultracold atoms while in the case of atomically thin\nsemiconductors a trion liquid emerges. As the boson density is increased\nfurther, the effective energy gap of the composites decreases, leading to a\ntransition into a strongly correlated phase where polarons are hybridized with\nmolecular degrees of freedom. We highlight the universal connection between\ntwo-dimensional semiconductors and ultracold atoms and we discuss perspectives\nfor further exploring the rich structure of strongly coupled Bose-Fermi\nmixtures in these complementary systems.",
        "positive": "Collisional dynamics of polaronic clouds immersed in a Fermi sea: We propose a new protocol to examine many-polaron properties in a cold atom\nexperiment. Initially, polaronic clouds are prepared around the opposite edges\nof a majority gas cloud. After time evolution, the collision of two clouds\nexhibits various polaronic effects. To see how {\\it collective} properties of\nmany polarons with mediated interactions appear in the case in which the\nimpurity and majority gases are composed of mass-balanced fermions with\ndifferent spin components, we perform a nonlinear hydrodynamic simulation for\ncollisional dynamics of two Fermi polaronic clouds. We found that the dynamics\nis governed by the impurity Fermi pressure, polaron energy, and multi-polaron\ncorrelations. In particular, shock waves occur in such a way as to reflect the\nmany-body properties of polarons through the first sound of minority clouds.\nOur idea is applicable to other systems such as Bose polarons as well as\nmass-imbalanced mixtures."
    },
    {
        "anchor": "Lattice dynamics in an emergent Zeeman lattice: Periodic band structures are a hallmark phenomenon of condensed matter\nphysics. While often imposed by external potentials, periodicity can also arise\nthrough the interplay of couplings that are not necessarily spatially periodic\non their own. Here, we investigate dynamics in a lattice structure that emerges\nfrom the simultaneous application of Raman and radio frequency coupling to a\ndilute-gas Bose-Einstein condensate. We demonstrate a variety of techniques\nincluding Kapitza-Dirac scattering, Bloch oscillations, and lattice shaking\nwith spin and momentum resolved measurements. This combined coupling scheme\nallows for exceptional tunability and control, enabling future investigations\ninto unconventional band structures such as quasi-flat ground bands and those\nwith semimetal-like band gaps.",
        "positive": "Anderson localization of a Tonks-Girardeau gas in potentials with\n  controlled disorder: We theoretically demonstrate features of Anderson localization in the\nTonks-Girardeau gas confined in one-dimensional (1D) potentials with controlled\ndisorder. That is, we investigate the evolution of the single particle density\nand correlations of a Tonks-Girardeau wave packet in such disordered\npotentials. The wave packet is initially trapped, the trap is suddenly turned\noff, and after some time the system evolves into a localized steady state due\nto Anderson localization. The density tails of the steady state decay\nexponentially, while the coherence in these tails increases. The latter\nphenomenon corresponds to the same effect found in incoherent optical solitons."
    },
    {
        "anchor": "Free-fermion Entanglement Spectrum through Wannier Interpolation: Quantum Entanglement plays an ubiquitous role in theoretical physics, from\nthe characterization of novel phases of matter to understanding the efficacy of\nnumerical algorithms. As such, there have been extensive studies on the\nentanglement spectrum (ES) of free-fermion systems, particularly in the\nrelation between its spectral flow and topological charge pumping. However, far\nless has been studied about the \\emph{spacing} between adjacent entanglement\neigenenergies, which affects the truncation error in numerical computations\ninvolving Matrix Product States (MPS) or Projected Entangled-Pair States\n(PEPS). In this paper, we shall hence derive asymptotic bounds for the ES\nspacings through an interpolation argument that utilizes known results on\nWannier function decay. For translation invariant systems, the Entanglement\nenergies are shown to decay at a rate monotonically related to the complex gap\nbetween the filled and occupied bands. This interpolation also demonstrates the\none-to-one correspondence between the ES and the edge states. Our results also\nprovide asymptotic bounds for the eigenvalue distribution of certain types of\nBlock Toeplitz matrices common in physics, even for those not arising from\nentanglement calculations.",
        "positive": "Caustics in the sine-Gordon model from quenches in coupled 1D Bose gases: Caustics are singularities that occur naturally in optical, hydrodynamic and\nquantum waves, giving rise to high amplitude patterns that can be described\nusing catastrophe theory. In this paper we study caustics in a statistical\nfield theory setting in the form of the sine-Gordon model that describes a\nvariety of physical systems including coupled 1D superfluids. Specifically, we\nuse classical field simulations to study the dynamics of two ultracold 1D Bose\ngases (quasi-condensates) that are suddenly coupled to each other and find that\nthe resulting non-equilibrium dynamics are dominated by caustics. Thermal noise\nis included by sampling the initial states from a Boltzmann distribution for\nphononic excitations. We find that caustics pile up over time in both the\nnumber and phase difference observables leading to a characteristic non-thermal\n`circus tent' shaped probability distribution at long times."
    },
    {
        "anchor": "Quantum emulation of topological magneto-optical effects using ultracold\n  atoms: Magneto-optical effect is a fundamental but broad concept in magnetic\nmediums. Here we propose a scheme for its quantum emulation using ultracold\natoms. By representing the light-medium interaction in the quantum-emulation\nmanner, the artificial magneto-optical effect emerges under an entirely\ndifferent mechanism from the conventional picture. The underlying polarization\nstate extracted in the synthetic dimension displays a different response to\nvarious experimental setups. Notably, the magneto-optical rotation is related\nto the bulk topology in synthetic dimensions, and thus provides an unambiguous\nevidence for the desired topological magneto-optical effect, which has not been\ndeveloped hitherto in ultracold atoms. This scheme is simple and feasible, and\ncan be realized by current experimental techniques. The implementation of the\nscheme is able to offer an intriguing platform for exploring topological\nmagneto-optical effects and associated physics.",
        "positive": "Active Learning Algorithm for Computational Physics: In large-scale computation of physics problems, one often encounters the\nproblem of determining a multi-dimensional function, which can be\ntime-consuming when computing each point in this multi-dimensional space is\nalready time-demanding. In the work, we propose that the active learning\nalgorithm can speed up such calculations. The basic idea is to fit a\nmulti-dimensional function by neural networks, and the key point is to make the\nquery of labeled data economically by using a stratagem called \"query by\ncommittee\". We present the general protocol of this fitting scheme, as well as\nthe procedure of how to further compute physical observables with the fitted\nfunctions. We show that this method can work well with two examples, which are\nquantum three-body problem in atomic physics and the anomalous Hall\nconductivity in condensed matter physics, respectively. In these examples, we\nshow that one reaches an accuracy of few percent error for computing physical\nobservables with less than $10\\%$ of total data points compared with uniform\nsampling. With these two examples, we also visualize that by using the active\nlearning algorithm, the required data are added mostly in the regime where the\nfunction varies most rapidly, which explains the mechanism for the efficiency\nof the algorithm. We expect broad applications of our method on various kind of\ncomputational physics problems."
    },
    {
        "anchor": "Structural properties of bosonic He clusters with N=2-10 for different\n  potential models at the physical point and at unitarity: Since the $^4$He dimer supports only one weakly bound state with an average\ninteratomic distance much larger than the van der Waals length and no deeply\nbound states, $^4$He$_N$ clusters with $N>2$ are a paradigmatic model system\nwith which to explore foundational concepts such as large $s$-wave scattering\nlength universality, van der Waals universality, Efimov physics, and effective\nfield theories. This work presents structural properties such as the pair and\ntriple distribution functions, the hyperradial density, the probability to find\nthe $N$th particle at a given distance from the center of mass of the other\n$N-1$ atoms, and selected contacts. The kinetic energy release, which can be\nmeasured via Coulomb explosion in dedicated size-selected molecular beam\nexperiments -- at least for small $N$ -- , is also presented. The structural\nproperties are determined for three different realistic $^4$He-$^4$He\ninteraction potentials and contrasted with those for an effective low-energy\npotential model from the literature that reproduces the energies of $^4$He$_N$\nclusters in the ground state for $N=2$ to $N=\\infty$ at the $\\gtrsim\n95$~percent level with just four input parameters. The study is extended to\nunitarity (infinite $s$-wave scattering length) by artificially weakening the\ninteraction potentials. In addition to contributing to the characterization of\nsmall bosonic helium quantum droplets, our study provides insights into the\neffective low-energy theory's predictability of various structural properties.",
        "positive": "Theoretical analysis of super-Bloch oscillations: Several recent studies have investigated the dynamics of cold atoms in\noptical lattices subject to AC forcing; the theoretically predicted\nrenormalization of the tunneling amplitudes has been verified experimentally.\nRecent observations include global motion of the atom cloud, such as giant\n\"Super-Bloch Oscillations\" (SBOs). We show that, in order to understand\nunexplained features of SBOs, in addition to the renormalization of the\ntunneling, a new and important phase correction must be included. For Fermionic\nsystems with strong attractive interactions, one may engineer different types\nof collisions and recollisions between bound-pairs and unpaired atoms."
    },
    {
        "anchor": "Wilson ratio of Fermi gases in one dimension: We calculate the Wilson ratio of the one-dimensional Fermi gas with spin\nimbalance. The Wilson ratio of attractively interacting fermions is solely\ndetermined by the density stiffness and sound velocity of pairs and of excess\nfermions for the two-component Tomonaga-Luttinger liquid (TLL) phase. The ratio\nexhibits anomalous enhancement at the two critical points due to the sudden\nchange in the density of states. Despite a breakdown of the quasiparticle\ndescription in one dimension, two important features of the Fermi liquid are\nretained, namely the specific heat is linearly proportional to temperature\nwhereas the susceptibility is independent of temperature. In contrast to the\nphenomenological TLL parameter, the Wilson ratio provides a powerful parameter\nfor testing universal quantum liquids of interacting fermions in one, two and\nthree dimensions.",
        "positive": "Large N Expansion for Strongly-coupled Boson-Fermion Mixtures: We study a many-body mixture of an equal number of bosons and two-component\nfermions with a strong contact attraction. In this system bosons and fermions\ncan be paired into composite fermions. We construct a large N extension where\nboth bosons and fermions have the extra large N degrees of freedom and the\nboson-fermion interaction is extended to a four-point contact interaction which\nis invariant under the O(N) group transformation, so that the composite\nfermions become singlet in terms of the O(N) group. It is shown that such O(N)\nsinglet fields have controllable quantum fluctuations suppressed by 1/N factors\nand yield a systematic 1/N-expansion in terms of composite fermions. We derive\nan effective action described by composite fermions up to the\nnext-to-leading-order terms in the large N expansion, and show that there can\nbe the BCS superfluidity of composite fermions at sufficiently low\ntemperatures."
    },
    {
        "anchor": "Pairing-gap, pseudo-gap, and no-gap phases in the radio-frequency\n  spectra of a trapped unitary 6Li gas: Radio frequency spectra of a trapped unitary 6Li gas are reported and\nanalyzed in terms of a theoretical approach that includes both final-state and\ntrap effects. Final-state effects play a crucial role in evidencing two main\npeaks both above and below the critical temperature Tc as being associated with\ntwo distinct phases that reside in different trap regions. These are the\npairing-gap and pseudo-gap phases below Tc, which evolve into the pseudo-gap\nand no-gap phases above Tc. In this way, a long standing puzzle about the\ninterpretation of rf spectra for 6Li in a trap is solved.",
        "positive": "Excitation spectra of fragmented condensates by linear response: General\n  theory and application to a condensate in a double-well potential: Linear response of simple (i.e., condensed) Bose-Einstein condensates is\nknown to lead to the Bogoliubov- de Gennes equations. Here, we derive linear\nresponse for fragmented Bose-Einstein condensates, i.e., for the case where the\nmany-body wave function is not a product of one, but of several single-particle\nstates (orbitals). Our approach is based on the number-conserving variational\ntime-dependent mean field theory [O. E. Alon, A. I. Streltsov, and L. S.\nCederbaum, Phys. Lett. A 362, 453 (2007)], which describes the time evolution\nof best-mean field states. Correspondingly, we call our linear response theory\nfor fragmented states LR-BMF. In the derivation it follows naturally that\nexcitations are orthogonal to the ground-state orbitals. As applications\nexcitation spectra of Bose-Einstein condensates in double-well potentials are\ncalculated. Both symmetric and asymmetric double-wells are studied for several\ninteraction strengths and barrier heights. The cases of condensed and two-fold\nfragmented ground states are compared. Interestingly, even in such situations\nwhere the response frequencies of the two cases are computed to be close to\neach other, which is the situation for the excitations well below the barrier,\nstriking differences in the density response in momentum space are found. For\nexcitations with an energy of the order of the barrier height, both the\nenergies and the density response of condensed and fragmented systems are very\ndifferent. In fragmented systems there is a class of \"swapped\" excitations\nwhere an atom is transfered to the neighboring well. The mechanism of its\norigin is discussed. In asymmetric wells, the response of a fragmented system\nis purely local (i.e., finite in either one or the other well) with different\nfrequencies for the left and right fragments."
    },
    {
        "anchor": "Solitary waves in mixtures of Bose gases confined in annular traps: A two-component Bose-Einstein condensate that is confined in a\none-dimensional ring potential supports solitary-wave solutions, which we\nevaluate analytically. The derived solutions are shown to be unique. The\ncorresponding dispersion relation that generalizes the case of a\nsingle-component system shows interesting features.",
        "positive": "Quantum distillation: dynamical generation of low-entropy states of\n  strongly correlated fermions in an optical lattice: Correlations between particles can lead to subtle and sometimes\ncounterintuitive phenomena. We analyze one such case, occurring during the\nsudden expansion of fermions in a lattice when the initial state has a strong\nadmixture of double occupancies. We promote the notion of quantum distillation:\nduring the expansion, and in the presence of strongly repulsive interactions,\ndoublons group together, forming a nearly ideal band insulator, which is\nmetastable with a low entropy. We propose that this effect could be used for\ncooling purposes in experiments with two-component Fermi gases."
    },
    {
        "anchor": "Bose-Einstein Condensate in a Honeycomb Optical Lattice: Fingerprint of\n  Superfluidity at the Dirac Point: Mean-field Bloch bands of a Bose-Einstein condensate in a honeycomb optical\nlattice are computed. We find that the topological structure of the Bloch bands\nat the Dirac point is changed completely by the atomic interaction of arbitrary\nsmall strength: the Dirac point is extended into a closed curve and an\nintersecting tube structure arises around the original Dirac point. These tubed\nBloch bands are caused by the superfluidity of the system. Furthermore, they\nimply the inadequacy of the tight-binding model to describe an interacting\nBoson system around the Dirac point and the breakdown of adiabaticity by\ninteraction of arbitrary small strength.",
        "positive": "Topological Fulde-Ferrell superfluid in spin-orbit coupled atomic Fermi\n  gases: We theoretically predict a new topological matter - topological inhomogeneous\nFulde-Ferrell superfluid - in one-dimensional atomic Fermi gases with equal\nRashba and Dresselhaus spin-orbit coupling near s-wave Feshbach resonances. The\nrealization of such a spin-orbit coupled Fermi system has already been\ndemonstrated recently by using a two-photon Raman process and the extra\none-dimensional confinement is easy to achieve using a tight two-dimensional\noptical lattice. The topological Fulde-Ferrell superfluid phase is\ncharacterized by a nonzero center-of-mass momentum and a non-trivial Berry\nphase. By tuning the Rabi frequency and the detuning of Raman laser beams, we\nshow that such an exotic topological phase occupies a significant part of\nparameter space and therefore it could be easily observed experimentally, by\nusing, for example, momentum-resolved and spatially resolved radio-frequency\nspectroscopy."
    },
    {
        "anchor": "Crossover from collisionless to collisional spin dynamics of polarized\n  fermions: We study the transverse spin dynamics of trapped polarized Fermi gases in the\nhigh temperature limit. In the non-interacting collisionless regime, a magnetic\nfield gradient induces collective spin wave oscillations. In the strongly\ninteracting collisional regime, the dynamics are governed by spin diffusion.\nThese two limits have been extensively studied both experimentally and\ntheoretically, but the crossover between them has received less attention. In\nthis paper, we use a quantum Boltzmann equation to study transverse spin\ndynamics and show how the excitations evolve from dispersive to diffusive in\nthe high temperature limit. We provide analytical solutions in the two limiting\nregimes, which agree well with our numerical results.",
        "positive": "Quantum Bose liquids with logarithmic nonlinearity: Self-sustainability\n  and emergence of spatial extent: The Gross-Pitaevskii (GP) equation is a long-wavelength approach widely used\nto describe the dilute Bose-Einstein condensates (BEC). However, in many\nphysical situations, such as higher densities, this approximation unlikely\nsuffices hence one might need models which would account for long-range\ncorrelations and multi-body interactions. We show that the Bose liquid\ndescribed by the logarithmic wave equation has a number of drastic differences\nfrom the GP one. It possesses the self-sustainability property: while the free\nGP condensate tends to spill all over the available volume the logarithmic one\ntends to form a Gaussian-type droplet - even in the absence of an external\ntrapping potential. The quasi-particle modes of the logarithmic BEC are shown\nto acquire a finite size despite the bare particles being assumed point-like,\ni.e., the spatial extent emerges here as a result of quantum many-body\ncorrelations. Finally, we study the elementary excitations and demonstrate that\nthe background density changes the topological structure of their momentum\nspace which, in turn, affects their dispersion relations. Depending on the\ndensity the latter can be of the massive relativistic, massless relativistic,\ntachyonic and quaternionic type."
    },
    {
        "anchor": "The long-range interacting Fermi polaron: We construct the simplest density functional for the problem of a single\nimpurity interacting with a Fermi gas via a long--ranged potential using the\nThomas--Fermi approach. We find that the Fermi polaron is fully bosonized in\ntwo dimensions, as the model results in a suitable Landau--Pekar functional\nknown from the Bose polaron problem which describes a self--interacting\nimpurity. In other dimensions, the impurity self--interacts with an infinite\nnumber of its own images, and no bosonization occurs. We discuss applications\nof our theory for the $2d$ exciton--polaron and the ionic polaron problem and\ncompute the effective mass for these cases, finding a self--trapping transition\nwith order depending on the dimensionality.",
        "positive": "Theory of radio-frequency spectroscopy of impurities in quantum gases: We present a theory of radio-frequency spectroscopy of impurities interacting\nwith a quantum gas at finite temperature. By working in the canonical ensemble\nof a single impurity, we show that the impurity spectral response is directly\nconnected to the finite-temperature equation of state (free energy) of the\nimpurity. We consider two different response protocols: \"injection\", where the\nimpurity is introduced into the medium from an initially non-interacting state;\nand \"ejection\", where the impurity is ejected from an initially interacting\nstate with the medium. We show that there is a simple mapping between injection\nand ejection spectra, which is connected to the detailed balance condition in\nthermal equilibrium. To illustrate the power of our approach, we specialize to\nthe case of the Fermi polaron, corresponding to an impurity atom that is\nimmersed in a non-interacting Fermi gas. For a mobile impurity with a mass\nequal to the fermion mass, we employ a finite-temperature variational approach\nto obtain the impurity spectral response. We find a striking non-monotonic\ndependence on temperature in the impurity free energy, the contact, and the\nradio-frequency spectra. For the case of an infinitely heavy Fermi polaron, we\nderive exact results for the finite-temperature free energy, thus generalizing\nFumi's theorem to arbitrary temperature. We also determine the exact dynamics\nof the contact after a quench of the impurity-fermion interactions. Finally, we\nshow that the injection and ejection spectra obtained from the variational\napproach compare well with the exact spectra, thus demonstrating the accuracy\nof our approximate method."
    },
    {
        "anchor": "The pinning quantum phase transition in a Tonks Girardeau gas:\n  diagnostics by ground state fidelity and the Loschmidt echo: We study the pinning quantum phase transition in a Tonks-Girardeau gas, both\nin equilibrium and out-of-equilibrium, using the ground state fidelity and the\nLoschmidt echo as diagnostic tools. The ground state fidelity (GSF) will have a\ndramatic decrease when the atomic density approaches the commensurate density\nof one particle per lattice well. This decrease is a signature of the pinning\ntransition from the Tonks to the Mott insulating phase. We study the\napplicability of the fidelity for diagnosing the pinning transition in\nexperimentally realistic scenarios. Our results are in excellent agreement with\nrecent experimental work. In addition, we explore the out of equilibrium\ndynamics of the gas following a sudden quench with a lattice potential. We find\nall properties of the ground state fidelity are reflected in the Loschmidt echo\ndynamics i.e., in the non equilibrium dynamics of the Tonks-Girardeau gas\ninitiated by a sudden quench of the lattice potential.",
        "positive": "An extension of Bogoliubov theory for a many-body system with a time\n  scale hierarchy: the quantum mechanics of second Josephson oscillations: Adiabatic approximations are a powerful tool for simplifying nonlinear\nquantum dynamics, and are applicable whenever a system exhibits a hierarchy of\ntime scales. Current interest in small nonlinear quantum systems, such as\nfew-mode Bose-Hubbard models, warrants further development of adiabatic methods\nin the particular context of these models. Here we extend our recent work on a\nsimple four-mode Bose-Hubbard model with two distinct dynamical time scales, in\nwhich we showed that among the perturbations around excited stationary states\nof the system is a slow collective excitation that is not present in the\nBogoliubov spectrum. We characterized this mode as a resonant energy exchange\nwith its frequency shifted by nonlinear effects, and referred to it as a second\nJosephson oscillation, in analogy with the second sound mode of liquid helium\nII. We now generalize our previous theory beyond the mean field regime, and\nconstruct a general Bogoliubov free quasiparticle theory that explicitly\nrespects the system's adiabatic invariant as well the exact conservation of\nparticles. We compare this theory to the numerically exact quantum energy\nspectrum with up to forty particles, and find good agreement over a significant\nrange of parameter space."
    },
    {
        "anchor": "The second critical point for the Perfect Bose gas in\n  quasi-one-dimensional traps: We present a new model of quasi-one-dimensional trap with some unknown\nphysical predictions about a second transition, including about a change in\nfractions of condensed coherence lengths due to the existence of a second\ncritical temperature Tm < Tc. If this physical model is acceptable, we want to\nchallenge experimental physicists in this regard.",
        "positive": "Dissipation assisted Thouless pumping in the Rice-Mele model: We investigate the effect of dissipation from a thermal environment on\ntopological pumping in the periodically-driven Rice-Mele model. We report that\ndissipation can improve the robustness of pumping quantisation in a regime of\nfinite driving frequencies. Specifically, in this regime, a low-temperature\ndissipative dynamics can lead to a pumped charge that is much closer to the\nThouless quantised value, compared to a coherent evolution. We understand this\neffect in the Floquet framework: dissipation increases the population of a\nFloquet band which shows a topological winding, where pumping is essentially\nquantised. This finding is a step towards understanding a potentially very\nuseful resource to exploit in experiments, where dissipation effects are\nunavoidable. We consider small couplings with the environment and we use a\nBloch-Redfield quantum master equation approach for our numerics: Comparing\nthese results with an exact MPS numerical treatment we find that the quantum\nmaster equation works very well also at low temperature, a quite remarkable\nfact."
    },
    {
        "anchor": "Renormalization group study of the four-body problem: We perform a renormalization group analysis of the non-relativistic\nfour-boson problem by means of a simple model with pointlike three- and\nfour-body interactions. We investigate in particular the unitarity point where\nthe scattering length is infinite and all energies are at the atom threshold.\nWe find that the four-body problem behaves truly universally, independent of\nany four-body parameter. Our findings confirm the recent conjectures of Platter\net al. and von Stecher et al. that the four-body problem is universal, now also\nfrom a renormalization group perspective. We calculate the corresponding\nrelations between the four- and three-body bound states, as well as the full\nbound state spectrum and comment on the influence of effective range\ncorrections.",
        "positive": "Study on Cooling of Positronium for Bose-Einstein Condensation: A new method of cooling positronium down is proposed to realize Bose-Einstein\ncondensation of positronium. We perform detail studies about three processes\n(1) thermalization processes between positronium and silica walls of a cavity,\n(2) Ps-Ps scatterings and (3) Laser cooling. The thermalization process is\nshown to be not sufficient for BEC. Ps-Ps collision is also shown to make a big\neffect on the cooling performance. We combine both methods and establish an\nefficient cooling for BEC. We also propose a new optical laser system for the\ncooling."
    },
    {
        "anchor": "Quantized Quasi-Two Dimensional Bose-Einstein Condensates with Spatially\n  Modulated Nonlinearity: We investigate the localized nonlinear matter waves of the quasi-two\ndimensional Bose-Einstein condensates with spatially modulated nonlinearity in\nharmonic potential. It is shown that the whole Bose-Einstein condensates,\nsimilar to the linear harmonic oscillator, can have an arbitrary number of\nlocalized nonlinear matter waves with discrete energies, which are\nmathematically exact orthogonal solutions of the Gross-Pitaevskii equation.\nTheir novel properties are determined by the principle quantum number n and\nsecondary quantum number l: the parity of the matter wave functions and the\ncorresponding energy levels depend only on n, and the numbers of density\npackets for each quantum state depend on both n and l which describe the\ntopological properties of the atom packets. We also give an experimental\nprotocol to observe these novel phenomena in future experiments.",
        "positive": "Ultracold-atom collisions in atomic waveguides : A two-channel analysis: Low dimensional behavior of two ultra-cold atoms trapped in two-and\none-dimensional waveguides is investigated in the vicinity of a magnetic\nFeshbach resonance. A quantitative two-channel model for the Feshbach mechanism\nis used allowing an exhaustive analysis of low-dimensional resonant scattering\nbehavior and of the confinement induced bound states. The role of the different\nparameters of the resonance is depicted in this context. Results are compared\nwith the ones of the zero-range approach. The relevance of the effective range\napproximation in low dimensions is studied. Examples of known resonances are\nused to illustrate the bound state properties."
    },
    {
        "anchor": "Lattice approaches to dilute Fermi gases: Legacy of broken Galilean\n  invariance: In the dilute limit, the properties of fermionic lattice models with\nshort-range attractive interactions converge to those of a dilute Fermi gas in\ncontinuum space. We investigate this connection using mean-field and we show\nthat the existence of a finite lattice spacing has consequences down to very\nsmall densities. In particular we show that the reduced translational\ninvariance associated to the lattice periodicity has a pivotal role in the\nfinite-density corrections to the universal zero-density limit.\n  For a parabolic dispersion with a sharp cut-off, we provide an analytical\nexpression for the leading-order corrections in the whole BCS-BEC crossover.\nThese corrections, which stem only from the unavoidable cut-off, contribute to\nthe leading-order corrections to the relevant observables. In a generic lattice\nwe find a universal power-law behavior $n^{1/3}$ which leads to significant\ncorrections already for small densities. Our results pose strong constraints on\nlattice extrapolations of dilute Fermi gas properties.",
        "positive": "Quantum thermalization via percolation: We highlight a dynamical anomaly in which the rate of relaxation towards\nthermal equilibrium in a bi-partite quantum system violates the standard\nlinear-response (Kubo) formulation, even when the underlying dynamics is highly\nchaotic. This anomaly originates from an $\\hbar$-dependent sparsity of the\nunderlying quantum network of transitions. Using a minimal bi-partite\nBose-Hubbard model as an example, we find that the relaxation rate acquires an\nanomalous $\\hbar$ dependence that reflects percolation-like dynamics in energy\nspace."
    },
    {
        "anchor": "Creating solitons with controllable and near zero velocity in\n  Bose-Einstein condensates: Established techniques for deterministically creating dark solitons in\nrepulsively interacting atomic Bose-Einstein condensates (BECs) can only access\na narrow range of soliton velocities. Because velocity affects the stability of\nindividual solitons and the properties of soliton-soliton interactions, this\ntechnical limitation has hindered experimental progress. Here we create dark\nsolitons in highly anisotropic cigar-shaped BECs with arbitrary position and\nvelocity by simultaneously engineering the amplitude and phase of the\ncondensate wavefunction, improving upon previous techniques which only\nexplicitly manipulated the condensate phase. The single dark soliton solution\npresent in true 1D systems corresponds to the kink soliton in anisotropic 3D\nsystems and is joined by a host of additional dark solitons including vortex\nring and solitonic vortex solutions. We readily create dark solitons with\nspeeds from zero to half the sound speed. The observed soliton oscillation\nfrequency suggests that we imprinted solitonic vortices, which for our\ncigar-shaped system are the only stable solitons expected for these velocities.\nOur numerical simulations of 1D BECs show this technique to be equally\neffective for creating kink solitons when they are stable. We demonstrate the\nutility of this technique by deterministically colliding dark solitons with\ndomain walls in two-component spinor BECs.",
        "positive": "Bosonic hard spheres in quasi-one dimensional bichromatic optical\n  lattices: We calculated the phase diagram of a continuous system of hard spheres loaded\nin a quasi-one dimensional bichromatic optical lattice. The wavelengths of both\nlattice-defining lasers were chosen to model an incommensurate arrangement.\nDensities of one particle and half a particle per potential well were\nconsidered. Our results can be compared directly to those of the experimental\nsystem [Fallani et al. PRL, {\\bf 98} 130404 (2007)] from which our initial\nparameters were taken. The phase diagrams for both densities are\nsignificatively different to those obtained by describing the same experimental\nsetup with a Bose-Hubbard model."
    },
    {
        "anchor": "Experimental realization of a high precision tunable hexagonal optical\n  lattice: Hexagonal optical lattices offer a tunable platform to study exotic orbital\nphysics in solid state materials. Here, we present a versatile high-precision\nscheme to implement a hexagonal optical lattice potential, which is engineered\nby overlapping two independent triangular optical sublattices generated by\nlaser beams with slightly different wavelengths around 1064 nm. This enables us\nto precisely control the detailed structure of the hexagonal lattice by\nadjusting the relative position and the relative lattice depth of the two\ntriangular optical sublattices. Taking advantage of the sensitive dependence of\nthe second Bloch band on small lattice deformations, we propose a strategy to\noptimize the optical lattice geometry with an extremely high precision. This\nmethod can also be extended to other lattice configurations involving more than\ntwo sublattices. Our work provides the experimental requirements in the search\nfor novel orbital physics of ultracold atoms, for example, in the flat $p$-band\nof the hexagonal optical lattice.",
        "positive": "Single-atom-resolved probing of lattice gases in momentum space: Measuring the full distribution of individual particles is of fundamental\nimportance to characterize many-body quantum systems through correlation\nfunctions at any order. Here we demonstrate the possibility to reconstruct the\nmomentum-space distribution of three-dimensional interacting lattice gases\natom-by-atom. This is achieved by detecting individual metastable Helium atoms\nin the far-field regime of expansion, when released from an optical lattice. We\nbenchmark our technique with Quantum Monte-Carlo calculations, demonstrating\nthe ability to resolve momentum distributions of superfluids occupying $10^5$\nlattice sites. It permits a direct measure of the condensed fraction across\nphase transitions, as we illustrate on the superfluid-to-normal transition. Our\nsingle-atom-resolved approach opens a new route to investigate interacting\nlattice gases through momentum correlations."
    },
    {
        "anchor": "Quantum droplets in a dipolar Bose gas at a dimensional crossover: We study the beyond-mean-field corrections to the energy of a dipolar Bose\ngas confined to two dimensions by a box potential with dipoles oriented in\nplane. At a critical strength of the dipolar interaction the system becomes\nunstable on the mean field level. We find that the ground state of the gas is\nstrongly influenced by the corrections, leading to formation of a self-bound\ndroplet, in analogy to the free space case. Properties of the droplet state can\nbe found by minimizing the extended Gross-Pitaevskii energy functional. In the\nlimit of strong confinement we show analytically that the correction can be\ninterpreted as an effective three-body repulsion which stabilizes the gas at\nfinite density.",
        "positive": "Few strongly interacting fermions of different mass driven in the\n  vicinity of a critical point: It was recently argued that one-dimensional systems of several strongly\ninteracting fermions of different mass undergo critical transitions between\ndifferent spatial orderings when the external confinement adiabatically changes\nits shape. In this work, we explore their dynamical properties when finite-time\ndrivings are considered. By detailed analysis of many-body spectra, we show\nthat the dynamics is typically guided only by the lowest eigenstates and may be\nwell-understood in the language of the generalized Landau-Zener mechanism. In\nthis way, we can capture precisely the dynamical response of the system to the\nexternal driving. As consequence, we show that by appropriate tailoring\nparameters of the driving one can target desired many-body state in a\nnon-infinite time. Our theoretical predictions can be straightforwardly\nutilized in upcoming state-of-the-art experiments with ultracold atoms."
    },
    {
        "anchor": "Self-trapped quantum balls in binary Bose-Einstein condensates: We study the formation of a stable self-trapped spherical quantum ball in a\nbinary Bose-Einstein condensate (BEC) with two-body inter-species attraction\nand intra-species repulsion employing the beyond-mean-field Lee-Huang-Yang and\nthe three-body interactions. We find that either of these interactions or a\ncombination of these can stabilize the binary BEC quantum ball with very\nsimilar stationary results, and for a complete description of the problem both\nthe terms should be considered. These interactions lead to higher-order\nnonlinearities, e.g. quartic and quintic, respectively, in a nonlinear\ndynamical equation compared to the cubic nonlinearity of the two-body contact\ninteraction in the mean-field Gross-Pitaevskii equation. The higher-order\nnonlinearity makes the energy infinitely large at the center of the binary ball\nand thus avoids its collapse. In addition to the formation of stationary binary\nballs, we also study a collision between two such balls. At large velocities,\nthe collision is found to be elastic, which turns out to be inelastic as the\nvelocity is lowered. We consider the numerical solution of a beyond-mean-field\nmodel for the binary ball as well as a single-mode variational approximation to\nit in this study.",
        "positive": "Exact few-body results for strongly correlated quantum gases in two\n  dimensions: The study of strongly correlated quantum gases in two dimensions has\nimportant ramifications for understanding many intriguing pheomena in solid\nmaterials, such as high-$T_{c}$ superconductivity and the fractional quantum\nHall effect. However, theoretical methods are plagued by the existence of\nsignificant quantum fluctuations. Here, we present two- and three-body exact\nsolutions for both fermions and bosons trapped in a two-dimensional harmonic\npotential, with an arbitrary $s$-wave scattering length. These few-particle\nsolutions link in a natural way to the high-temperature properties of\nmany-particle systems via a quantum virial expansion. As a concrete example,\nusing the energy spectrum of few fermions, we calculate the second and third\nvirial coefficients of a strongly interacting Fermi gas in two dimensions, and\nconsequently investigate its high-temperature thermodynamics. Our thermodynamic\nresults may be useful for ongoing experiments on two-dimensional Fermi gases.\nThese exact results also provide an unbiased benchmark for quantum Monte Carlo\nsimulations of two-dimensional Fermi gases at high temperatures."
    },
    {
        "anchor": "Condensate fraction of a resonant Fermi gas with spin-orbit coupling in\n  three and two dimensions: We study the effects of laser-induced Rashba-like spin-orbit coupling along\nthe BCS-BEC crossover of a Feshbach resonance for a two-spin-component Fermi\ngas. We calculate the condensate fraction in three and two dimensions and find\nthat this quantity characterizes the crossover better than other quantities,\nlike the chemical potential or the pairing gap. By considering both the singlet\nand the triplet pairings, we calculate the condensate fraction and show that a\nlarge enough spin-orbit interaction enhances the singlet condensate fraction in\nthe BCS side while suppressing it on the BEC side.",
        "positive": "Real-space collapse of a polariton condensate: Polaritons in microcavities are versatile quasi-2D bosonic particles with a\nhigh degree of coherence and strong nonlinearities, thanks to their hybrid\nlight-matter character. In their condensed form, they display striking quantum\nhydrodynamic features analogous to atomic Bose-Einstein condensates, such as\nlong-range order coherence, superfluidity and quantized vorticity. Their\nvariegated dispersive and dissipative properties, however, set significant\ndifferences from their atomic counterpart. In this work, we report the unique\nphenomenology that is observed when a pulse of light impacts the polariton\nvacuum: the condensate that is instantaneously formed does not splash in real\nspace but instead coheres into an enigmatic structure, featuring concentric\nrings and, most notably, a sharp and bright peak at the center. Using a\nstate-of-the-art ultrafast imaging with 50 fs time steps, we are able to track\nthe dynamics of the polariton mean-field wavefunction in both real and\nreciprocal space. The observation of the real-space collapse of the condensate\ninto an extremely localized---resolution limited---peak is at odd with the\nrepulsive interactions of polaritons and their positive effective mass. An\nunconventional mechanism is therefore at play to account for our observations.\nOur modeling suggests that self-trapping due to a local heating of the crystal\nlattice---that can be described as a collective polaron formed by a polariton\ncondensate---could be involved. These observations hint at the fascinating\nfluid dynamics of polaritons in conditions of extreme intensities and ultrafast\ntimes."
    },
    {
        "anchor": "Decay of superfluid currents in the interacting one-dimensional Bose gas: We examine the superfluid properties of a 1D Bose gas in a ring trap based on\nthe model of Lieb and Liniger. While the 1D Bose gas has nonclassical\nrotational inertia and exhibits quantization of velocities, the metastability\nof currents depends sensitively on the strength of interactions in the gas: the\nstronger the interactions, the faster the current decays. It is shown that the\nLandau critical velocity is zero in the thermodynamic limit due to the first\nsupercurrent state, which has zero energy and finite probability of excitation.\nWe calculate the energy dissipation rate of ring currents in the presence of\nweak defects, which should be observable on experimental time scales.",
        "positive": "Phonon Laser Effect and Dicke-Hepp-Lieb Superradiant Phase Transition in\n  Magnetic Cantilever Coupled to a Bose Einstein Condensate: We propose a possibility of a phonon laser by coupling a Bose-Einstein\ncondensate to a nanomechanical cantilever with a magnetic tip. Due to the\nmagnetic coupling, atomic spin flips induce cantilever motion which can be used\nto produce a phonon laser. The system is described by the equivalent of the\nJaynes-Cummings Hamiltonian. By controlling the number of atoms and the\npopulation inversion, one can obtain either a continuous wave (cw) or transient\nlasing. The two-body atom-atom interaction is also shown to coherently\nmanipulate the lasing process. We also show that in the strong coupling limit,\nthe same system can undergo a Dicke-Hepp-Lieb superradiant phase transition.\nExotic phase diagrams can be obtained by tuning the two body atom-atom\ninteraction."
    },
    {
        "anchor": "Analytically solvable model to the spin Hall effect with Rashba and\n  Dresselhaus spin-orbit couplings: When the Rashba and Dresslhaus spin-orbit coupling are both presented for a\ntwo-dimensional electron in a perpendicular magnetic field, a striking\nresemblance to anisotropic quantum Rabi model in quantum optics is found. We\nperform a generalized Rashba coupling approximation to obtain a solvable\nHamiltonian by keeping the nearest-mixing terms of Laudau states, which is\nreformulated in the similar form to that with only Rashba coupling. Each Landau\nstate becomes a new displaced-Fock state with a displacement shift instead of\nthe original Harmonic oscillator Fock state, yielding eigenstates in closed\nform. Analytical energies are consistent with numerical ones in a wide range of\ncoupling strength even for a strong Zeeman splitting. In the presence of an\nelectric field, the spin conductance and the charge conductance obtained\nanalytically are in good agreements with the numerical results. As the\ncomponent of the Dresselhaus coupling increases, we find that the spin Hall\nconductance exhibits a pronounced resonant peak at a larger value of the\ninverse of the magnetic field. Meanwhile, the charge conductance exhibits a\nseries of plateaus as well as a jump at the resonant magnetic field. Our method\nprovides an easy-to-implement analytical treatment to two-dimensional electron\ngas systems with both types of spin-orbit couplings.",
        "positive": "Coupled Dipole Oscillations of a Mass-Imbalanced Bose and Fermi\n  Superfluid Mixture: Recent experimental realizations of superfluid mixtures of Bose and Fermi\nquantum gases provide a unique platform for exploring diverse superfluid\nphenomena. We study dipole oscillations of a double superfluid in a\ncigar-shaped optical dipole trap, consisting of $^{41}$K and $^{6}$Li atoms\nwith a large mass imbalance, where the oscillations of the bosonic and\nfermionic components are coupled via the Bose-Fermi interaction. In our\nhigh-precision measurements, the frequencies of both components are observed to\nbe shifted from the single-species ones, and exhibit unusual features. The\nfrequency shifts of the $^{41}$K component are upward (downward) in the radial\n(axial) direction, whereas the $^{6}$Li component has down-shifted frequencies\nin both directions. Most strikingly, as the interaction strength is varied, the\nfrequency shifts display a resonant-like behavior in both directions, for both\nspecies, and around a similar location at the BCS side of fermionic superfluid.\nThese rich phenomena challenge theoretical understanding of superfluids."
    },
    {
        "anchor": "Lindblad Equation for the Inelastic Loss of Ultracold Atoms: The loss of ultracold trapped atoms due to deeply inelastic reactions has\npreviously been taken into account in effective field theories for low-energy\natoms by adding local anti-Hermitian terms to the effective Hamiltonian. Here\nwe show that when multi-atom systems are considered, an additional modification\nis required in the equation governing the density matrix. We define an\neffective density matrix by tracing over the states containing high-momentum\natoms produced by deeply inelastic reactions. We show that it satisfies a\nLindblad equation, with local Lindblad operators determined by the local\nanti-Hermitian terms in the effective Hamiltonian. We use the Lindblad equation\nto derive the universal relation for the two-atom inelastic loss rate for\nfermions with two spin states and the universal relation for the three-atom\ninelastic loss rate for identical bosons.",
        "positive": "Self-consistent approach for Bose-condensed atoms in optical lattices: Bose atoms in optical lattices are considered at low temperatures and weak\ninteractions, when Bose-Einstein condensate is formed. A self-consistent\napproach, based on the use of a representative statistical ensemble, is\nemployed, ensuring a gapless spectrum of collective excitations and the\nvalidity of conservation laws. In order to show that the approach is applicable\nto both weak and tight binding, the problem is treated in the Bloch as well as\nin the Wannier representations. Both these ways result in similar expressions\nthat are compared for the self-consistent Hartree-Fock-Bogolubov approximation.\nA convenient general formula for the superfluid fraction of atoms in an optical\nlattice is derived."
    },
    {
        "anchor": "Anharmonicity Induced Supersolidity In Spin-Orbit Coupled Bose-Einstein\n  Condensates: Supersolid, a fascinating quantum state of matter, features novel phenomena\nsuch as the non-classical rotational inertia and transport anomalies. It is a\nlong standing issue of the coexistence of superfluidity and broken\ntranslational symmetry in condensed matter physics. By recent experimental\nadvances to create tunable synthetic spin-orbit coupling in ultracold gases,\nsuch highly controllable atomic systems would provide new possibilities to\naccess supersolidity with no counterpart in solids. Here we report that the\ncombination of anharmonicity of trapping potential and spin-orbit coupling will\nprovide a new paradigm to achieve supersolids. By means of imaginary time\nevolution of the Gross-Pitaevskii equation, we demonstrate that a supersolid\nstate can be found when considering a trapped Rashba-type spin-orbit coupled\nbosonic atoms loaded in a one-dimensional optical lattice. Furthermore, a\nskyrmion-anti-skyrmion lattice is associated with the appearance of such\nsupersoildity, indicating the topological nontrivial properties of our proposed\nsupersolids.",
        "positive": "Scaling dynamics of the ultracold Bose gas: The large-scale expansion dynamics of quantum gases is a central tool for\nultracold gas experiments and poses a significant challenge for theory. In this\nwork we provide an exact reformulation of the Gross-Pitaevskii equation for the\nultracold Bose gas in a coordinate frame that adaptively scales with the system\nsize during evolution, enabling simulations of long evolution times during\nexpansion or similar large-scale manipulation. Our approach makes no\nhydrodynamic approximations, is not restricted to a scaling ansatz, harmonic\npotentials, or energy eigenstates, and can be generalized readily to\nnon-contact interactions via the appropriate stress tensor of the quantum\nfluid. As applications, we simulate the expansion of the ideal gas, a\ncigar-shaped condensate in the Thomas-Fermi regime, and a linear superposition\nof counter propagating Gaussian wavepackets. We recover known scaling for the\nideal gas and Thomas-Fermi regimes, and identify a linear regime of\naspect-ratio preserving free expansion; analysis of the scaling dynamics\nequations shows that an exact, aspect-ratio invariant, free expansion does not\nexist for nonlinear evolution. Our treatment enables exploration of nonlinear\neffects in matter-wave dynamics over large scale-changing evolution."
    },
    {
        "anchor": "Collision of impurities with Bose-Einstein condensates: Quantum dynamics of impurities in a bath of bosons is a long-standing problem\nof solid-state, plasma, and atomic physics. Recent experimental and theoretical\ninvestigations with ultracold atoms focused on this problem, studying atomic\nimpurities immersed in a atomic Bose-Einstein condensate (BEC) and for various\nrelative coupling strengths tuned by the Fano-Feshbach resonance technique.\nHere we report extensive numerical simulations on a closely related problem:\nthe collision between a bosonic impurity made of few $^{41}$K atoms and a BEC\nmade of $^{87}$Rb atoms in a quasi one-dimensional configuration and under a\nweak harmonic axial confinement. For small values of the interspecies\ninteraction strength (no matter the sign of it), we find that the impurity,\nwhich starts from outside the BEC, simply oscillates back and forth the BEC\ncloud, but the frequency of oscillation depends on the interaction strength.\nFor intermediate couplings, after a few cycles of oscillation the impurity is\ncaptured by the BEC and strongly changes its amplitude of oscillation. In the\nstrong interaction regime, if the interspecies interaction is attractive, a\nlocal maximum (bright soliton) in the density of BEC occurs where the impurity\nis trapped; instead, if the interspecies interaction is repulsive, the impurity\nis not able to enter in the BEC cloud and the reflection coefficient is close\nto one. On the other hand, if the initial displacement of the impurity is\nincreased, the impurity is able to penetrate in the cloud leading to the\nappearance of a moving hole (dark soliton) in the BEC.",
        "positive": "Prethermalization and wave condensation in a nonlinear disordered\n  Floquet system: Periodically-driven quantum systems make it possible to reach stationary\nstates with new emerging properties. However, this process is notoriously\ndifficult in the presence of interactions because continuous energy exchanges\ngenerally boil the system to an infinite temperature featureless state. Here,\nwe describe how to reach nontrivial states in a periodically-kicked\nGross-Pitaevskii disordered system. One ingredient is crucial: both disorder\nand kick strengths should be weak enough to induce sufficiently narrow and\nwell-separated Floquet bands. In this case, inter-band heating processes are\nstrongly suppressed and the system can reach an exponentially long-lived\nprethermal plateau described by the Rayleigh-Jeans distribution. Saliently, the\nsystem can even undergo a wave condensation process when its initial state has\na sufficiently low total quasi-energy. These predictions could be tested in\nnonlinear optical experiments or with ultracold atoms."
    },
    {
        "anchor": "Density-functional theory for 1D harmonically trapped Bose-Fermi mixture: We present a density-functional theory for the one dimensional harmonically\ntrapped Bose-Fermi mixture with repulsive contact interactions. The ground\nstate density distribution of each component is obtained by solving the\nKohn-Sham equations numerically based on the Local Density Approximation and\nthe exact solution for the homogeneous system given by Bethe ansatz method. It\nis shown that for strong enough interaction, a considerable amount of fermions\nare repelled out of the central region of the trap, exhibiting partial phase\nseparation of Bose and Fermi components. Oscillations emerge in the Bose\ndensity curves reflecting the strong correlation with Fermions. For infinite\nstrong interaction, the ground state energy of the mixture and the total\ndensity are consistent with the scenario that all atoms in the mixture are\nfully fermionized.",
        "positive": "Finite temperature theory of superfluid bosons in optical lattices: A practical finite temperature theory is developed for the superfluid regime\nof a weakly interacting Bose gas in an optical lattice with additional harmonic\nconfinement. We derive an extended Bose-Hubbard model that is valid for shallow\nlattices and when excited bands are occupied. Using the\nHartree-Fock-Bogoliubov-Popov mean-field approach, and applying local density\nand coarse-grained envelope approximations, we arrive at a theory that can be\nnumerically implemented accurately and efficiently. We present results for a\nthree-dimensional system, characterizing the importance of the features of the\nextended Bose-Hubbard model and compare against other theoretical results and\nshow an improved agreement with experimental data."
    },
    {
        "anchor": "Radiation spectrum of systems with condensed light: Experimental observation of Bose-Einstein condensation (BEC) of photons\ninside a microcavity induced an extensive study of the phenomenon. Beyond the\npurely theoretical interest, this phenomenon is believed to be used to create a\nnovel source of light. The shape of radiation spectrum is therefore the main\ncharacteristic of the system with light BEC as an optical device. However,\nuntil now, there were no detailed calculations of this property. In the present\npaper we derive analytically the shape of radiation spectrum and show that our\nresults are in excellent agreement with existing experimental measurements.",
        "positive": "Finite-temperature phases of trapped bosons in a two-dimensional\n  quasiperiodic potential: We study a system of 2D trapped bosons in a quasiperiodic potential via ab\ninitio Path Integral Monte Carlo simulations, focusing on its finite\ntemperature properties, which have not yet been explored. Alongside the\nsuperfluid, normal fluid and insulating phases, we demonstrate the existence of\na Bose glass phase, which is found to be robust to thermal fluctuations, up to\nabout half of the critical temperature of the non-interacting system. Local\nquantities in the trap are characterized by employing zonal estimators,\nallowing us to trace a phase diagram; we do so for a set of parameters within\nreach of current experiments with quasi-2D optical confinement."
    },
    {
        "anchor": "Symmetry breaking and entropy production during the evolution of spinor\n  Bose-Einstein condensate driven by coherent atom beam: The spinor condensate with spin states degenerated in the ground spin-space\nprovides a unique platform for investigating the edge of quantum mechanics and\nstatistical physics. We study the evolution of the condensate under the\nscattering of a coherent atom beam. The time-dependent magnetization,\nentanglement entropy, thermal entropy and the entropy production rate are\ncalculated. A novel spontaneous symmetry breaking is found during the\nevolution, It is shown that the stationary spin distribution can be controlled\nby the incoming coherent spin state of the incident atom beam, therefore the\natom-condensate scattering provides a new way to probe the spin distribution of\nthe condensate",
        "positive": "Composite pairing and superfluidity in a one-dimensional resonant\n  Bose-Fermi mixture: We study the ground-state properties of one-dimensional mixtures of bosonic\nand fermionic atoms resonantly coupled to fermionic Feshbach molecules. When\nthe particle densities of fermionic atoms and Feshbach molecules differ, the\nsystem undergoes various depletion transitions between binary and ternary\nmixtures, as a function of the detuning parameter. However, when the particle\ndensities of fermionic atoms and Feshbach molecules are identical, the\nmolecular conversion and disassociation processes induce a gap in a sector of\nlow-energy excitations, and the remaining system can be described by a\ntwo-component Tomonaga-Luttinger liquid. Using a bosonization scheme, we derive\nthe effective low-energy Hamiltonian for the system, which has a similar form\nas that of the two-chain problem of coupled Tomonaga-Luttinger liquids. With\nthe help of improved perturbative renormalization group analysis of the latter\nproblem, we determine the ground-state phase diagram and find that it contains\na phase dominated by composite superfluid or pairing correlations between the\nopen and closed resonant channels."
    },
    {
        "anchor": "Quantum gray solitons in confining potentials: We define and study hole-like excitations (the Lieb II mode) in a weakly\ninteracting Bose liquid subject to external confinement. These excitations are\nobtained by semiclassical quantization of gray solitons propagating on top of a\nThomas-Fermi background. Radiation of phonons by an accelerated gray soliton\nleads to a finite life-time for the trapped Lieb II mode. It is shown that, for\na large number of trapped atoms, most of the Lieb II levels can be\nexperimentally resolved.",
        "positive": "Dynamical Scaling of Surface Roughness and Entanglement Entropy in\n  Disordered Fermion Models: Localization is one of the most fundamental interference phenomena caused by\nrandomness, and its universal aspects have been extensively explored from the\nperspective of one-parameter scaling mainly for static properties. We\nnumerically study dynamics of fermions on disordered onedimensional potentials\nexhibiting localization and find dynamical one-parameter scaling for surface\nroughness, which represents particle-number fluctuations at a given\nlengthscale, and for entanglement entropy when the system is in delocalized\nphases. This dynamical scaling corresponds to the Family-Vicsek scaling\noriginally developed in classical surface growth, and the associated scaling\nexponents depend on the type of disorder. Notably, we find that partially\nlocalized states in the delocalized phase of the random-dimer model lead to\nanomalous scaling, where destructive interference unique to quantum systems\nleads to exponents unknown for classical systems and clean systems."
    },
    {
        "anchor": "Adiabatic spin cooling using high-spin Fermi gases: Spatial entropy redistribution plays a key role in adiabatic cooling of\nultra-cold lattice gases. We show that high-spin fermions with a spatially\nvariable quadratic Zeeman coupling may allow for the creation of an inner\nspin-1/2 core surrounded by high-spin wings. The latter are always more\nentropic than the core at high temperatures and, remarkably, at all\ntemperatures in the presence of frustration. Combining thermodynamic Bethe\nAnsatz with local density approximation, we study the spatial entropy\ndistribution for the particular case of one-dimensional spin-3/2 lattice\nfermions in the Mott phase. Interestingly, this spatially dependent entropy\nopens a possible path for an adiabatic cooling technique that, in contrast to\nprevious proposals, would specifically target the spin degree of freedom. We\ndiscuss a possible realization of this adiabatic cooling, which may allow for a\nhighly efficient entropy decrease in the spin-1/2 core and help access\nantiferromagnetic order in experiments on ultracold spinor fermions.",
        "positive": "Theory of Electromagnetically Induced Transparency in Strongly\n  Correlated Quantum Gases: We develop a general theory to study the electromagnetically induced\ntransparency (EIT) in ultracold quantum gases, applicable for both Bose and\nFermi gases with arbitrary inter-particle interaction strength. We show that,\nin the weak probe field limit, the EIT spectrum is solely determined by the\nsingle particle Green's function of the ground state atoms, and reflects\ninteresting quantum many-body effects when atoms are virtually coupled to the\nlow-lying Rydberg states. As an example, we apply our theory to 1D Luttinger\nliquid, Bose-Mott insulator state, and the superfluid state of two-component\nFermi gases, and show how the many-body features can be observed\nnon-destructively in the unconventional EIT spectrum."
    },
    {
        "anchor": "Controlling excitation avalanches in driven Rydberg gases: Recent experiments with strongly interacting, driven Rydberg ensembles have\nintroduced a promising setup for the study of self-organized criticality (SOC)\nin cold atom systems. Based on this setup, we theoretically propose a control\nmechanism for the paradigmatic avalanche dynamics of SOC in terms of a\ntime-dependent drive amplitude. This gives access to a variety of avalanche\ndominated, self-organization scenarios, prominently including self-organized\ncriticality, as well as sub- and supercritical dynamics. We analyze the\ndependence of the dynamics on external scales and spatial dimensionality. It\ndemonstrates the potential of driven Rydberg systems as a playground for the\nexploration of an extended SOC phenomenology and their relation to other common\nscenarios of SOC, such as e.g. in neural networks and on graphs.",
        "positive": "Mean field analysis of quantum phase transitions in a periodic optical\n  superlattice: In this paper we analyze the various phases exhibited by a system of\nultracold bosons in a periodic optical superlattice using the mean field\ndecoupling approximation. We investigate for a wide range of commensurate and\nincommensurate densities. We find the gapless superfluid phase, the gapped Mott\ninsulator phase, and gapped insulator phases with distinct density wave orders."
    },
    {
        "anchor": "Rb-85 tunable-interaction Bose-Einstein condensate machine: We describe our experimental setup for creating stable Bose-Einstein\ncondensates of Rb-85 with tunable interparticle interactions. We use\nsympathetic cooling with Rb-87 in two stages, initially in a tight\nIoffe-Pritchard magnetic trap and subsequently in a weak, large-volume crossed\noptical dipole trap, using the 155 G Feshbach resonance to manipulate the\nelastic and inelastic scattering properties of the Rb-85 atoms. Typical Rb-85\ncondensates contain 4 x 10^4 atoms with a scattering length of a=+200a_0. Our\nminimalist apparatus is well-suited to experiments on dual-species and spinor\nRb condensates, and has several simplifications over the Rb-85 BEC machine at\nJILA (Papp, 2007; Papp and Wieman, 2006), which we discuss at the end of this\narticle.",
        "positive": "Spin-orbit coupling induced quantum droplet in ultracold Bose-Fermi\n  mixtures: Quantum droplets have intrigued much attention recently in view of their\nsuccessful observations in the ultracold homonuclear atoms. In this work, we\ndemonstrate a new mechanism for the formation of quantum droplet in\nheteronuclear atomic systems, i.e., by applying the synthetic spin-orbit\ncoupling(SOC). Take the Bose-Fermi mixture for example, we show that by\nimposing a Rashba SOC between the spin states of fermions, the greatly\nsuppressed Fermi pressure can enable the formation of Bose-Fermi droplets even\nfor very weak boson-fermion attractions, which are insufficient to bound a\ndroplet if without SOC. In such SOC-induced quantum droplets, the boson/fermion\ndensity ratio universally depends on the SOC strength, and they occur in the\nmean-field collapsing regime but with a negative fluctuation energy, distinct\nfrom the interaction-induced droplets found in literature. The accessibility of\nthese Bose-Fermi droplets in ultracold Cs-Li and Rb-K mixtures is also\ndiscussed. Our results shed light on the droplet formation in a vast class of\nheteronuclear atomic systems through the manipulation of single-particle\nphysics."
    },
    {
        "anchor": "Transition to quantum turbulence in a finite size superfluid: A novel concept of quantum turbulence in finite size superfluids, such as\ntrapped bosonic atoms, is discussed. We have used an atomic $^{87}\\mathrm{Rb}$\nBEC to study the emergence of this phenomenon. In our experiment, the\ntransition to the quantum turbulent regime is characterized by a tangled vortex\nlines formation, controlled by the amplitude and time duration of the\nexcitation produced by an external oscillating field. A simple model is\nsuggested to account for the experimental observations. The transition from the\nnon-turbulent to the turbulent regime is a rather gradual crossover. But it\ntakes place in a sharp enough way, allowing for the definition of an effective\ncritical line separating the regimes. Quantum turbulence emerging in a\nfinite-size superfluid may be a new idea helpful for revealing important\nfeatures associated to turbulence, a more general and broad phenomenon.",
        "positive": "Generalized Josephson relation for conserved charges in multi-component\n  bosons: The Josephson relation is generalized for conserved charges in\nmulti-component bosons. With linear response theory, a formula for derivation\nof generalized superfluid density is given. When there are several conserved\ncharges, the superfluid density is generally a second order tensor in internal\nspin space. When the rank of Green's function matrix is one, Josephson relation\nis given explicitly with phase operator method. For two-component bosons, with\nquantum field theory, we show a generalized Hugenholtz-Pines relation hold and\nexistence of two gapless phonons. When the interactions are $U(2)$ invariant,\nwe show there is a gapless quadratic dispersion excitation no matter how strong\nthe interactions are. The corresponding generalized Josephson relation is\nexpressed with Green's function matrix elements."
    },
    {
        "anchor": "Clusters in Separated Tubes of Tilted Dipoles: A few-body cluster is a building block of a many-body system in a gas phase\nprovided the temperature at most is of the order of the binding energy of this\ncluster. Here we illustrate this statement by considering a system of tubes\nfilled with dipolar distinguishable particles. We calculate the partition\nfunction, which determines the probability to find a few-body cluster at a\ngiven temperature. The input for our calculations -- the energies of few-body\nclusters -- is estimated using the harmonic approximation. We first describe\nand demonstrate the validity of our numerical procedure. Then we discuss the\nresults featuring melting of the zero-temperature many-body state into a gas of\nfree particles and few-body clusters. For temperature higher than its binding\nenergy threshold, the dimers overwhelmingly dominate the ensemble, where the\nremaining probability is in free particles. At very high temperatures free\n(harmonic oscillator trap-bound) particle dominance is eventually reached. This\nstructure evolution appears both for one and two particles in each layer\nproviding crucial information about the behavior of ultracold dipolar gases.\nThe investigation addresses the transition region between few and many-body\nphysics as a function of temperature using a system of ten dipoles in five\ntubes.",
        "positive": "Dipole condensates in tilted Bose-Hubbard chains: We study the quantum phase diagram of a Bose-Hubbard chain whose dynamics\nconserves both boson number and boson dipole moment, a situation which can\narise in strongly tilted optical lattices. The conservation of dipole moment\nhas a dramatic effect on the phase diagram, which we analyze by combining a\nfield theory analysis with DMRG simulations. Unlike the conventional\nBose-Hubbard model, the phase diagram contains no compressible phases, and is\ninstead dominated by various types of exotic dipolar condensates. We suggest\nways by which these condensates can be identified in near-term cold atom\nexperiments."
    },
    {
        "anchor": "Alternative Route to Strong Interaction: Narrow Feshbach Resonance: We show that a narrow resonance produces strong interaction effects far\nbeyond its width on the side of the resonance where the bound state has not\nbeen formed. This is due to a resonance structure of its phase shift, which\nshifts the phase of a large number of scattering states by $\\pi$ before the\nbound state emerges. As a result, the magnitude of the interaction energy when\napproaching the resonance on the \"upper\" and \"lower\" branch from different side\nof the resonance is highly asymmetric, unlike their counter part in wide\nresonances. Measurements of these effects are experimentally feasible.",
        "positive": "Splitting of singly and doubly quantized composite vortices in\n  two-component Bose-Einstein condensates: We study numerically the dynamical instabilities and splitting of singly and\ndoubly quantized composite vortices in two-component Bose-Einstein condensates\nharmonically confined to quasi two dimensions. In this system, the vortices\nbecome pointlike composite defects that can be classified in terms of an\ninteger pair $(\\kappa_1,\\kappa_2)$ of phase winding numbers. Our simulations\nbased on zero-temperature mean-field theory reveal several vortex splitting\nbehaviors that stem from the multicomponent nature of the system and do not\nhave direct counterparts in single-component condensates. By calculating the\nBogoliubov excitations of stationary axisymmetric composite vortices, we find\nnonreal excitation frequencies (dynamical instabilities) for the singly\nquantized $(1,1)$ and $(1,-1)$ vortices and for all variants of doubly\nquantized vortices, which we define by the condition\n$\\max_{j=1,2}|\\kappa_j|=2$. While the short-time predictions of the linear\nBogoliubov analysis are confirmed by direct time integration of the\nGross-Pitaevskii equations of motion, the time integration also reveals\nintricate long-time decay behavior not captured by the linearized dynamics.\nFirst, the $(1,\\pm 1)$ vortex is found to be unstable against splitting into a\n$(1,0)$ vortex and a $(0,\\pm 1)$ vortex. Second, the $(2,1)$ vortex exhibits a\ntwo-step decay process in which its initial splitting into a $(2,0)$ vortex and\na $(0,1)$ vortex is followed by the off-axis splitting of the $(2,0)$ vortex\ninto two $(1,0)$ vortices. Third, the $(2,-2)$ vortex is observed to split into\na $(-1,1)$ vortex, three $(1,0)$ vortices, and three $(0,-1)$ vortices. Each of\nthese splitting processes is the dominant decay mechanism of the respective\nstationary composite vortex for a wide range of intercomponent interaction\nstrengths and relative populations of the two condensate components and should\nbe amenable to experimental detection."
    },
    {
        "anchor": "Many-body and temperature effects in two-dimensional quantum droplets in\n  Bose-Bose mixtures: We study the equilibrium properties of self-bound droplets in two-dimensional\nBose mixtures employing the time-dependent Hartree-Fock-Bogoliubov theory. This\ntheory allows one to understand both the many-body and temperature effects\nbeyond the Lee-Huang-Yang description. We calculate higher-order corrections to\nthe excitations, the sound velocity, and the energy of the droplet. Our results\nfor the ground-state energy are compared with the diffusion Monte Carlo data\nand good agreement is found. The behavior of the depletion and anomalous\ndensity of the droplet is also discussed. At finite temperature, we show that\nthe droplet emerges at temperatures well below the\nBerezinskii-Kosterlitz-Thouless transition temperature. The critical\ntemperature strongly depends on the interspecies interactions. Our study is\nextended to the finite size droplet by numerically solving the generalized\nfinite-temperature Gross-Pitaevskii equation which is obtained\nself-consistently from our formalism in the framework of the local density\napproximation.",
        "positive": "Shear viscosity and damping of collective modes in a two-dimensional\n  Fermi gas: We compute the shear viscosity of a two dimensional Fermi gas interacting via\na short range potential with scattering length $a_{2d}$ in kinetic theory. We\nfind that kinetic theory predicts that the shear viscosity to entropy density\nratio of a strongly interacting two dimensional gas is comparable to that of\nthe three dimensional unitary gas. We use our results to compute the damping of\ncollective modes in a trapped Fermi gas, and compare to experimental data\nrecently obtained in E. Vogt et al., arXiv:1111.1173."
    },
    {
        "anchor": "Unconventional magnetism via optical pumping of interacting spin systems: We consider strongly interacting systems of effective spins, subject to\ndissipative spin-flip processes associated with optical pumping. We predict the\nexistence of novel magnetic phases in the steady-state of this system, which\nemerge due to the competition between coherent and dissipative processes.\nSpecifically, for strongly anisotropic spin-spin interactions, we find\nferromagnetic, antiferromagnetic, spin-density-wave, and staggered-XY steady\nstates, which are separated by nonequilibrium phase transitions meeting at a\nLifshitz point. These transitions are accompanied by quantum correlations,\nresulting in spin squeezing. Experimental implementations in ultracold atoms\nand trapped ions are discussed.",
        "positive": "Formation of local and global currents in a toroidal Bose--Einstein\n  condensate via an inhomogeneous artificial gauge field: We study the effects of a position-dependent artificial gauge field on an\natomic Bose--Einstein condensate in quasi-one-dimensional and two-dimensional\nring settings. The inhomogeneous artificial gauge field can induce global and\nlocal currents in the Bose--Einstein condensate via phase gradients along the\nring and vortices, respectively. We observe two different regimes in the system\ndepending on the radial size of the ring and strength of the gauge field. For\nweak artificial gauge fields, the angular momentum increases, as expected, in a\nquantized manner; however, for stronger values of the fields, the angular\nmomentum exhibits a linear (non-quantized) behavior. We also characterize the\nangular momentum for non-cylindrically symmetric traps."
    },
    {
        "anchor": "Model-independent determination of the shear viscosity of a trapped\n  unitary Fermi gas: Application to high temperature data: Determinations of the shear viscosity of trapped ultracold gases suffer from\nsystematic, uncontrolled uncertainties related to the treatment of the dilute\npart of the gas cloud. In this work we present an analysis of expansion\nexperiments based on a new method, anisotropic fluid dynamics, that\ninterpolates between Navier-Stokes fluid dynamics at the center of the cloud\nand ballistic behavior in the dilute corona. We validate the method using a\ncomparison between anisotropic fluid dynamics and numerical solutions of the\nBoltzmann equation. We then apply anisotropic fluid dynamics to the expansion\ndata reported by Cao et al. In the high temperature limit we find\n$\\eta=0.282(mT)^{3/2}$, which agrees within about 5\\% with the theoretical\nprediction $\\eta=0.269(mT)^{3/2}$.",
        "positive": "Coexistence of pairing gaps in three-component Fermi gases: We study a three-component superfluid Fermi gas in a spherically symmetric\nharmonic trap using the Bogoliubov-deGennes method. We predict a coexistence\nphase in which two pairing field order parameters are simultaneously nonzero,\nin stark contrast to studies performed for trapped gases using local density\napproximation. We also discuss the role of atom number conservation in the\ncontext of a homogeneous system."
    },
    {
        "anchor": "Few-fermion systems in one dimension: Ground- and excited-state energies\n  and contacts: Using the lattice Monte Carlo method, we compute the energy and Tan's contact\nin the ground state as well as the first excited state of few- to many-fermion\nsystems in a one-dimensional periodic box. We focus on unpolarized systems of\nN=4,6,...,12 particles, with a zero-range interaction, and a wide range of\nattractive couplings. In addition, we provide extrapolations to the\ninfinite-volume and thermodynamic limits.",
        "positive": "Conduction of Ultracold Fermions Through a Mesoscopic Channel: In a mesoscopic conductor electric resistance is detected even if the device\nis defect-free. We engineer and study a cold-atom analog of a mesoscopic\nconductor. It consists of a narrow channel connecting two macroscopic\nreservoirs of fermions that can be switched from ballistic to diffusive. We\ninduce a current through the channel and find ohmic conduction, even for a\nballistic channel. An analysis of in-situ density distributions shows that in\nthe ballistic case the chemical potential drop occurs at the entrance and exit\nof the channel, revealing the presence of contact resistance. In contrast, a\ndiffusive channel with disorder displays a chemical potential drop spread over\nthe whole channel. Our approach opens the way towards quantum simulation of\nmesoscopic devices with quantum gases."
    },
    {
        "anchor": "Observation of Pauli Crystals: The Pauli exclusion principle is a fundamental law underpinning the structure\nof matter. Due to their anti-symmetric wave function, no two fermions can\noccupy the same quantum state. Here, we report on the direct observation of the\nPauli principle in a continuous system of up to six particles in the ground\nstate of a two-dimensional harmonic oscillator. To this end, we sample the full\nmany-body wavefunction by applying a single atom resolved imaging scheme in\nmomentum space. We find so-called Pauli crystals as a manifestation of higher\norder correlations. In contrast to true crystalline phases, these unique\nhigh-order density correlations emerge even without any interactions present.\nOur work lays the foundation for future studies of correlations in strongly\ninteracting systems of many fermions.",
        "positive": "Running condensate in moving superfluid: A possibility of the condensation of excitations with non-zero momentum in\nmoving superfluid media is considered in terms of the Ginzburg-Landau model.\nThe results might be applicable to the superfluid $^4$He, ultracold atomic Bose\ngases, various superconducting and neutral systems with pairing, like ultracold\natomic Fermi gases and the neutron component in compact stars. The order\nparameters, the energy gain, and critical velocities are found."
    },
    {
        "anchor": "Hugenholtz-Pines theorem for multicomponent Bose-Einstein condensates: The Hugenholtz-Pines (HP) theorem is derived for Bose-Einstein condensates\n(BECs) with internal degrees of freedom. The low-energy Ward-Takahashi identity\nis provided in the system with the linear and quadratic symmetry breaking\nterms. This identity serves to organize the HP theorem for multicomponent BECs,\nsuch as the binary BEC as well as the spin-$f$ spinor BEC in the presence of a\nmagnetic field with broken U$(1)$$\\times$SO$(3)$ symmetry. The experimental\nmethod based on the Stern-Gerlach experiment is proposed for studying the\nWard-Takahashi identity.",
        "positive": "Extended self-energy functional approach for strongly-correlated lattice\n  bosons in the superfluid phase: Among the various numerical techniques to study the physics of strongly\ncorrelated quantum many-body systems, the self-energy functional approach (SFA)\nhas become increasingly important. In its previous form, however, SFA is not\napplicable to Bose-Einstein condensation or superfluidity. In this paper we\nshow how to overcome this shortcoming. To this end we identify an appropriate\nquantity, which we term $D$, that represents the correlation correction of the\ncondensate order parameter, as it does the self-energy for the Green's\nfunction. An appropriate functional is derived, which is stationary at the\nexact physical realizations of $D$ and of the self-energy. Its derivation is\nbased on a functional-integral representation of the grand potential followed\nby an appropriate sequence of Legendre transformations. The approach is not\nperturbative and therefore applicable to a wide range of models with local\ninteractions. We show that the variational cluster approach based on the\nextended self-energy functional is equivalent to the \"pseudoparticle\" approach\nintroduced in Phys. Rev. B, 83, 134507 (2011). We present results for the\nsuperfluid density in the two-dimensional Bose-Hubbard model, which show a\nremarkable agreement with those of Quantum-Monte-Carlo calculations."
    },
    {
        "anchor": "Strongly nonequilibrium Bose-condensed atomic systems: A trapped Bose-Einstein condensate, being strongly perturbed, exhibits\nseveral spatial structures. First, there appear quantum vortices. Increasing\nthe amount of the injected energy leads to the formation of vortex tangles\nrepresenting quantum vortex turbulence. Continuing energy injection makes the\nsystem so strongly perturbed that vortices become destroyed and there develops\nanother kind of spatial structures with essentially heterogeneous spatial\ndensity. These structures consist of high-density droplets, or grains,\nsurrounded by the regions of low density. The droplets are randomly distributed\nin space, where they can move; however they live sufficiently long time to be\ntreated as a type of metastable creatures. Such structures have been observed\nin nonequilibrium trapped Bose gases of $^{87}$Rb subject to the action of an\noscillatory perturbation modulating the trapping potential. Perturbing the\nsystem even stronger transforms the droplet structure into wave turbulence,\nwhere Bose condensate is destroyed. Numerical simulations are in good agreement\nwith experimental observations.",
        "positive": "Quantum Adsorption of an Electron to Porous Silicon: Using the theory of Zhang and Clougherty [Phys. Rev. Lett. 108, 173202\n(2012)], we provide detailed supporting information concerning the numerical\ncalculations of the probability ${\\it s}(E)$ for a low-energy electron with\nincident energy E adsorbing to the surface of nanoporous silicon."
    },
    {
        "anchor": "Fractional and Integer Vortex Dynamics in Strongly Coupled Two-component\n  Bose-Einstein Condensates from AdS/CFT Correspondence: In order to study the rotating strongly coupled Bose-Einstein\ncondensations(BEC), a holographic model defined in an AdS black hole that duals\nto a coupled two-component condensations in global $U(1)$ symmetry broken phase\nwith intercomponent coupling $\\eta$ and internal coherent coupling $\\epsilon$\nis proposed. By solving the dynamics of the model, we study the process of\nformation and also the crossover from fractional to integer vortex phases. With\nchanging only $\\eta$ from zero to a finite value, fractional vortex lattices\nundergo a transition from hexagon to square lattice and finally to vortex\nsheets. By continuing to turn on $\\epsilon$, we find that two fractional\nvortices in different components constitute dimers, and when $\\eta$ transcend a\ncritical value, multi-dimer like hexamer or tetramer made up of two and three\ndimers appear. As $\\epsilon$ keeps increasing, some dimers rotate to adjust\nthemselves and then constitute the lattice of integer vortices. Under an\ninitial conditions similar to an spinor BEC vortices dynamics experiment, the\nappearance of disordered turbulence is found in the process of fractional\nvortex generation, which matches the experimental observation. While in the\nformation process of integer vortices, the appearance of grooves is predicted.",
        "positive": "Critical velocity of antiferromagnetic spin-1 Bose-Einstein condensates\n  at finite temperature: We study the instability of a moving spinor Bose-Einstein condensate when the\nspeed of flow reaches the critical velocity. This we identify on the basis of\nLandau's criterion, i.e. the velocity above which some elementary excitation\nenergy becomes negative. We show that the first-to-become unstable excitations\nare spin-carrying quasiparticles. We also discuss the temperature dependence of\nthe critical velocity in a more advanced mean-field approximation."
    },
    {
        "anchor": "Nuclear-spin-independent short-range three-body physics in ultracold\n  atoms: We investigate three-body recombination loss across a Feshbach resonance in a\ngas of ultracold 7Li atoms prepared in the absolute ground state and perform a\ncomparison with previously reported results of a different nuclear-spin state\n[N. Gross et.al., Phys. Rev. Lett. 103 163202, (2009)]. We extend the\npreviously reported universality in three-body recombination loss across a\nFeshbach resonance to the absolute ground state. We show that the positions and\nwidths of recombination minima and Efimov resonances are identical for both\nstates which indicates that the short-range physics is nuclear-spin\nindependent.",
        "positive": "Tan's two-body contact in a planar Bose gas: experiment vs theory: We determine the two-body contact in a planar Bose gas confined by a\ntransverse harmonic potential, using the nonperturbative functional\nrenormalization group. We use the three-dimensional thermodynamic definition of\nthe contact where the latter is related to the derivation of the pressure of\nthe quasi-two-dimensional system with respect to the three-dimensional\nscattering length of the bosons. Without any free parameter, we find a\nremarkable agreement with the experimental data of Zou {\\it et al.} [Nat. Comm.\n{\\bf 12}, 760 (2021)] from low to high temperatures, including the vicinity of\nthe Berezinskii-Kosterlitz-Thouless transition. We also show that the\nshort-distance behavior of the pair distribution function and the high-momentum\nbehavior of the momentum distribution are determined by two contacts: the\nthree-dimensional contact for length scales smaller than the characteristic\nlength $\\ell_z=\\sqrt{\\hbar/m\\omega_z}$ of the harmonic potential and, for\nlength scales larger than $\\ell_z$, an effective two-dimensional contact,\nrelated to the three-dimensional one by a geometric factor depending on\n$\\ell_z$."
    },
    {
        "anchor": "Observation of a dissipative time crystal: The formation of a phase of matter can be associated with the spontaneous\nbreaking of a symmetry. For crystallization, this broken symmetry is the\nspatial translation symmetry, as the atoms spontaneously localize in a periodic\nfashion. In analogy to spatial crystals, the spontaneous breaking of temporal\ntranslation symmetry results in the formation of time crystals. While recent\nand on-going experiments on driven isolated systems aim to minimize dissipative\nprocesses, as it is an undesired source of decay, well-designed dissipation has\nbeen put forth as a constitutive ingredient in the formation of dissipative\ntime crystals (DTCs). Here, we present the first experimental realisation of a\nDTC, implemented in an atom-cavity system. Its defining feature is a period\ndoubled switching between distinct chequerboard density wave patterns, induced\nby controlled cavity-dissipation and cavity-mediated interactions. We\ndemonstrate the robustness of this phase against system parameter changes and\ntemporal perturbations of the driving. Our work provides a framework for\nrealising phases of matter with spatiotemporal order in presence of\ndissipation. We note that this is the natural environment of matter, and\ntherefore shapes its physical phenomena profoundly, making its study\nimperative.",
        "positive": "Inhomogeneous Kibble-Zurek mechanism: vortex nucleation during\n  Bose-Einstein condensation: The Kibble-Zurek mechanism is applied to the spontaneous formation of\nvortices in a harmonically trapped thermal gas following a temperature quench\nthrough the critical value for Bose-Einstein condensation. While in the\nhomogeneous scenario vortex nucleation is always expected, we show that it can\nbe completely suppressed in the presence of the confinement potential, whenever\nthe speed of the spatial front undergoing condensation is lower than a\nthreshold velocity. Otherwise, the interplay between the geometry and causality\nleads to different scaling laws for the density of vortices as a function of\nthe quench rate, as we also illustrate for the case of a toroidal trapping\npotential."
    },
    {
        "anchor": "Wigner dynamics for quantum gases under inhomogeneous gain and loss\n  processes with dephasing: We present a Wigner function-based approach for the particle density\nevolution in fermionic and bosonic open quantum many-body systems, including\nthe effects of dephasing. In particular, we focus on chains of non-interacting\nparticles coupled to Lindblad baths. The dissipative processes, described by\nlinear and quadratic jump operators, are modulated by inhomogeneous couplings.\nFollowing a semi-classical approach, we find the differential equation\ngoverning the Wigner function evolution, which can be solved in closed form in\nsome particular cases. We check the accuracy of the Wigner approach in\ndifferent scenarios (i.e. Gaussian jump rates), describing the density\nevolution and the transport phenomena in terms of classical quasi-particles.",
        "positive": "Encoding a one-dimensional topological gauge theory in a Raman-coupled\n  Bose-Einstein condensate: Topological gauge theories provide powerful effective descriptions of certain\nstrongly correlated systems, a prime example being the Chern-Simons gauge\ntheory of fractional quantum Hall states. Engineering topological gauge\ntheories in controlled quantum systems is of both conceptual and practical\nimportance, as it would provide access to systems with exotic excitations such\nas anyons without the need for strong correlations. Here, we discuss a scheme\nto engineer the chiral BF theory, a minimal model of a topological gauge theory\ncorresponding to a one-dimensional reduction of the Chern-Simons theory, with\nultracold atoms. Using the local conservation laws of the theory, we encode its\nquantum Hamitonian into an ultracold quantum gas with chiral interactions.\nBuilding on a seminal proposal by Edmonds et al. (Phys. Rev. Lett. 110, 085301\n(2013)), we show how to implement it in a Raman-coupled Bose-Einstein\ncondensate with imbalanced scattering lengths, as we have recently realized\nexperimentally (Fr\\\"olian et al., Nature 608, 293 (2022)). We discuss the\nproperties of the chiral condensate from a gauge theory perspective, and assess\nthe validity of the effective quantum description for accessible experimental\nparameters via numerical simulations. Our approach lays the foundation for\nrealizing topological gauge theories in higher dimensions with Bose-Einstein\ncondensates."
    },
    {
        "anchor": "Fermi Gases with Synthetic Spin-Orbit Coupling: We briefly review recent progress on ultracold atomic Fermi gases with\ndifferent types of synthetic spin-orbit coupling, including the one-dimensional\n(1D) equal weight Rashba-Dresselhaus and two-dimensional (2D) Rasbha spin-orbit\ncouplings. Theoretically, we show how the single-body, two-body and many-body\nproperties of Fermi gases are dramatically changed by spin-orbit coupling. In\nparticular, the interplay between spin-orbit coupling and interatomic\ninteraction may lead to several long-sought exotic superfluid phases at low\ntemperatures, such as anisotropic superfluid, topological superfluid and\ninhomogeneous superfluid. Experimentally, only the first type - equal weight\ncombination of Rasbha and Dresselhaus spin-orbit couplings - has been realized\nvery recently using a two-photon Raman process. We show how to characterize a\nnormal spin-orbit coupled atomic Fermi gas in both non-interacting and\nstrongly-interacting limits, using particularly momentum-resolved\nradio-frequency spectroscopy. The experimental demonstration of a\nstrongly-interacting spin-orbit coupled Fermi gas opens a promising way to\nobserve various exotic superfluid phases in the near future.",
        "positive": "Dynamical Equilibration Across a Quenched Phase Transition in a Trapped\n  Quantum Gas: The formation of an equilibrium quantum state from an uncorrelated thermal\none through the dynamical crossing of a phase transition is a central question\nof non-equilibrium many-body physics. During such crossing, the system breaks\nits symmetry by establishing numerous uncorrelated regions separated by\nspontaneously-generated defects, whose emergence obeys a universal scaling law\nwith the quench duration. Much less is known about the ensuing re-equilibrating\nor \"coarse-graining\" stage, which is governed by the evolution and interactions\nof such defects under system-specific and external constraints. In this work we\nperform a detailed numerical characterization of the entire non-equilibrium\nprocess, addressing subtle issues in condensate growth dynamics and\ndemonstrating the quench-induced decoupling of number and coherence growth\nduring the re-equilibration process. Our unique visualizations not only\nreproduce experimental measurements in the relevant regimes, but also provide\nvaluable information in currently experimentally-inaccessible regimes."
    },
    {
        "anchor": "Crystallisation of a dilute atomic dipolar condensate: We present a theory that explains the experimentally observed crystallisation\nof a dilute dysprosium condensate into a lattice of droplets. The key\ningredient of our theory is a conservative three-body interaction which\nstabilises the droplets against collapse to high density spikes. Our theory\nreproduces the experimental observations, and provides insight into the\nmanybody properties of this new phase of matter. Notably, we show that it is\nunlikely that a supersolid was obtained in experiments, however our results\nsuggest a strategy to realize this phase.",
        "positive": "Drag force in bimodal cubic-quintic nonlinear Schr\u00f6dinger equation: We consider a system of two cubic-quintic non-linear Schr\\\"odinger equations\nin two dimensions, coupled by repulsive cubic terms. We analyse situations in\nwhich a probe lump of one of the modes is surrounded by a fluid of the other\none and analyse their interaction. We find a realization of D'Alembert's\nparadox for small velocities and non-trivial drag forces for larger ones. We\npresent numerical analysis including the search of static and traveling\nform-preserving solutions along with simulations of the dynamical evolution in\nsome representative examples."
    },
    {
        "anchor": "Atom transistor from the point of view of quantum nonequilibrium\n  dynamics: We analyze the atom field-effect transistor scheme [J. A. Stickney, D. Z.\nAnderson and A. A. Zozulya, Phys. Rev. A 75, 013608 (2007)] using the standard\ntools of nonequlilibrium dynamics. In particular, we study the deviations from\nthe Eigenstate Thermalization Hypothesis, quantum fluctuations, and the density\nof states, both ab initio and using their mean-field analogues. Having fully\nestablished the quantum vs. mean-field correspondence for this system, we\nattempt, using a mean-field model, to interpret the off-on threshold in our\ntransistor as the onset of ergodicity---a point where the system becomes able\nto visit the thermal values of the former integrals of motion in principle,\nalbeit not being fully thermalized yet.",
        "positive": "Quantum-tunneling dynamics of a spin-polarized Fermi gas in a\n  double-well potential: We study the exact dynamics of a one-dimensional spin-polarized gas of\nfermions in a double-well potential at zero and finite temperature. Despite the\nsystem is made of non-interacting fermions, its dynamics can be quite complex,\nshowing strongly aperiodic spatio-temporal patterns during the tunneling. The\nextension of these results to the case of mixtures of spin-polarized fermions\nin interaction with self-trapped Bose-Einstein condensates (BECs) at zero\ntemperature is considered as well. In this case we show that the fermionic\ndynamics remains qualitatively similar to the one observed in absence of BEC\nbut with the Rabi frequencies of fermionic excited states explicitly depending\non the number of bosons and on the boson-fermion interaction strength. From\nthis, the possibility to control quantum fermionic dynamics by means of\nFeshbach resonances is suggested."
    },
    {
        "anchor": "Statistical properties of the momentum occupation numbers of the\n  Tonks-Girardeau gas in a harmonic trap: We compute the fluctuations of the number of bosons with a given momentum for\nthe Tonks-Girardeau gas at zero and finite temperature in a harmonic trap. We\nshow that correlations between opposite momentum states $p$, which is an\nimportant fingerprint of long range order in weakly interacting Bose systems\nare suppressed. Non trivial correlations, including negative correlations are\nobserved for momenta smaller or of the order of the inverse radius of the gas.\nThe full distribution of the number of bosons with momentum $p$ exhibits an\ninteresting crossover from a non trivial distribution at zero momentum to an\nexponential distribution. The distribution of the quasi-condensate occupation\nis also studied. Experimental relevance of our findings for recent cold atoms\nexperiments are discussed.",
        "positive": "Spin Entanglement and Magnetic Competition via Long-range Interactions\n  in Spinor Quantum Optical Lattices: Quantum matter at ultra-low temperatures offers a testbed for analyzing and\ncontrolling desired properties in strongly correlated systems. Under typical\nconditions the nature of the atoms fixes the magnetic character of the system.\nBeyond classical light potentials leading to optical lattices and short range\ninteractions, high-Q cavities introduce novel dynamics into the system via the\nquantumness of light. Here we propose a theoretical model and we analyze it\nusing exact diagonalization and density matrix renormalization group\nsimulations. We explore the effects of cavity mediated long range magnetic\ninteractions and optical lattices in ultracold matter. We find that global\ninteractions modify the underlying magnetic character of the system while\nintroducing competition scenarios. Antiferromagnetic correlated bosonic matter\nemerges in conditions beyond to what nature typically provides. These allow new\nalternatives toward the design of robust mechanisms for quantum information\npurposes, exploiting the properties of magnetic phases of strongly correlated\nquantum matter."
    },
    {
        "anchor": "High Sensitivity RF Spectroscopy of a Strongly-Interacting Fermi Gas: Rf spectroscopy is one of the most powerful probing techniques in the field\nof ultracold gases. We report on a novel rf spectroscopy scheme with which we\ncan detect very weak signals of only a few atoms. Using this method, we\nextended the experimentally accessible photon-energies range by an order of\nmagnitude compared to previous studies. We verify directly a universal property\nof fermions with short-range interactions which is a power-law scaling of the\nrf spectrum tail all the way up to the interaction scale. We also employ our\ntechnique to precisely measure the binding energy of Feshbach molecules in an\nextended range of magnetic fields. This data is used to extract a new\ncalibration of the Feshbach resonance between the two lowest energy levels of\n40K",
        "positive": "All-optical production and transport of a large $^6$Li quantum gas in a\n  crossed optical dipole trap: We report on an efficient production scheme for a large quantum degenerate\nsample of fermionic lithium. The approach is based on our previous work on\nnarrow-line $ 2S_{1/2}\\rightarrow 3P_{3/2} $ laser cooling resulting in a high\nphase-space density of up to $3\\times10^{-4}$. This allows utilizing a large\nvolume crossed optical dipole trap with a total power of $45\\,\\textrm{W}$,\nleading to high loading efficiency and $8\\times10^6$ trapped atoms. The same\noptical trapping configuration is used for rapid adiabatic transport over a\ndistance of $25\\,\\textrm{cm}$ in $0.9\\,\\textrm{s}$, and subsequent evaporative\ncooling. With optimized evaporation we achieve a degenerate Fermi gas with\n$1.7\\times 10^{6}$ atoms at a temperature of $60 \\, \\textrm{nK}$, corresponding\nto $T/T_{\\text{F}}=0.16\\left(2 \\right)$. Furthermore, the performance is\ndemonstrated by evaporation near a broad Feshbach resonance creating a\nmolecular Bose-Einstein condensate of $3\\times10^5$ lithium dimers."
    },
    {
        "anchor": "Phase diagram of the SU$(3)$ Fermi-Hubbard model with next-neighbor\n  interactions: We explore the zero-temperature phase diagram of a one-dimensional gas\ncomposed of three-color fermions, which interact locally and with their next\nneighbors. Using the density matrix renormalization group method and\nconsidering one-third filling, we characterize the ground state for several\nvalues of the parameters, finding diverse phases, namely: phase separation,\nspin density wave, pairing phase, a metallic phase, two different\ncharge-density waves, and a non-separable state with modulation of charge. We\nshow that the von Neumann block entropy and the fidelity susceptibility are\nuseful for estimating the borders between the phases.",
        "positive": "Suppressed solitonic cascade in spin-imbalanced superfluid Fermi gas: Cold atoms experiments offer invaluable information on superfluid dynamics,\nincluding decay cascades of topological defects. While the cascade properties\nare well established for Bose systems, our understanding of their behavior in\nFermi counterparts is very limited, in particular in spin-imbalanced systems,\nwhere superfluid (paired) and normal (unpaired) particles naturally coexist\ngiving rise to complex spatial structure of the atomic cloud. Here we show,\nbased on a newly developed microscopic approach, that the decay cascades of\ntopological defects are dramatically modified by the spin-polarization. We\ndemonstrate that decay cascades end up at different stages: \"dark soliton\",\n\"vortex ring\" or \"vortex line\", depending on the polarization. We reveal that\nit is caused by sucking of unpaired particles into the soliton's internal\nstructure. As a consequence vortex reconnections are hindered and we anticipate\nthat quantum turbulence phenomenon can be significantly affected, indicating\nnew physics induced by polarization effects."
    },
    {
        "anchor": "Strong coupling treatment of the polaronic system consisting of an\n  impurity in a condensate: The strong coupling treatment of the Fr\\\"ohlich-type polaronic system, based\non a canonical transformation and a standard Landau-Pekar type variational wave\nfunction, is applied to the polaronic system consisting of an impurity in a\ncondensate. Within this approach the Relaxed Excited States are retrieved as a\ntypical polaronic feature in the energy spectrum. For these states we calculate\nthe corresponding effective mass and the minimal coupling constant required for\nthem to occur. The present approach allows to derive approximate expressions\nfor the transition energies between different Relaxed Excited States in a much\nsimpler way than with the full Mori-Zwanzig approach, and with a good accuracy,\nwhich improves with increasing coupling. The transition energies obtained here\ncan be used as the spectroscopic fingerprint for the experimental observation\nof Relaxed Excited States of impurities in a condensate.",
        "positive": "Collective modes as a probe of imbalanced Fermi gases: We theoretically investigate the collective modes of imbalanced two component\none-dimensional Fermi gases with attractive interactions. This is done for\ntrapped and untrapped systems both at zero and non-zero temperature, using\nself-consistent mean-field theory and the random phase approximation. We\ndiscuss how the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state can be detected\nand the periodicity of the associated density modulations determined from its\ncollective mode spectrum. We also investigate the accuracy of the single mode\napproximation for low-lying collective excitations in a trap by comparing\nfrequencies obtained via sum rules with frequencies obtained from direct\ncollective mode calculations. It is found that, for collective excitations\nwhere the atomic clouds of the two spin species oscillate largely in phase, the\nsingle mode approximation holds well for a large parameter regime. Finally we\ninvestigate the collective mode spectrum obtained by parametric modulation of\nthe coupling constant."
    },
    {
        "anchor": "Realizing the entanglement Hamiltonian of a topological quantum Hall\n  system: Topological quantum many-body systems, such as Hall insulators, are\ncharacterized by a hidden order encoded in the entanglement between their\nconstituents. Entanglement entropy, an experimentally accessible single number\nthat globally quantifies entanglement, has been proposed as a first signature\nof topological order. Conversely, the full description of entanglement relies\non the entanglement Hamiltonian, a more complex object originally introduced to\nformulate quantum entanglement in curved spacetime. As conjectured by Li and\nHaldane, the entanglement Hamiltonian of a many-body system appears to be\ndirectly linked to its boundary properties, making it particularly useful for\ncharacterizing topological systems. While the entanglement spectrum is commonly\nused to identify complex phases arising in numerical simulations, its\nmeasurement remains an outstanding challenge. Here, we perform a variational\napproach to realize experimentally, as a genuine Hamiltonian, the entanglement\nHamiltonian of a synthetic quantum Hall system. We use a synthetic dimension,\nencoded in the electronic spin of dysprosium atoms, to implement spatially\ndeformed Hall systems, as suggested by the Bisognano-Wichmann prediction. The\nspectrum of the optimal variational Hamiltonian exhibits a chiral dispersion\nakin to a topological edge mode, revealing the fundamental link between\nentanglement and boundary physics. Our variational procedure can be easily\ngeneralized to interacting many-body systems on various platforms, marking an\nimportant step towards the exploration of exotic quantum systems with\nlong-range correlations, such as fractional Hall states, chiral spin liquids\nand critical systems.",
        "positive": "Many-Body Localization from Dynamical Gauge Fields: A recent experiment [Nature Physics 10, 1 (2019)] has realized a dynamical\ngauge system with $\\mathbb{Z}_2$ gauge symmetry in a double-well potential. In\nthis work we propose a method to generalize this model from a single double\nwell to a one-dimensional chain. We show that although there is no disordered\npotential in the original model, the phenomenon of many-body localization can\noccur. The key ingredient is that different symmetry sectors with different\nlocal gauge charges play the role of different disorder configurations, which\nbecomes clear after exactly mapping our model to a transverse Ising model in a\nrandom longitudinal field. We show that both the ergodic regime and the\nmany-body localized regime exist in this model from four different metrics,\nwhich include level statistics, volume law versus area law of entanglement\nentropy of eigenstates, quench dynamics of entanglement entropy and physical\nobservables."
    },
    {
        "anchor": "Spontaneous symmetry breaking and phase coherence of a photon\n  Bose-Einstein condensate coupled to a reservoir: We examine the phase evolution of a Bose-Einstein condensate of photons\ngenerated in a dye microcavity by temporal interference with a phase reference.\nThe photo-excitable dye molecules constitute a reservoir of variable size for\nthe condensate particles, allowing for grand canonical statistics with photon\nbunching, as in a lamp-type source. We directly observe phase jumps of the\ncondensate associated with the large statistical number fluctuations and find a\nseparation of correlation timescales. For large systems, our data reveals phase\ncoherence and a spontaneously broken symmetry, despite the statistical\nfluctuations.",
        "positive": "Spin-1 spin-orbit- and Rabi-coupled Bose-Einstein condensate solver: We present OpenMP versions of FORTRAN programs for solving the\nGross-Pitaevskii equation for a harmonically trapped three-component spin-1\nspinor Bose-Einstein condensate (BEC) in one (1D) and two (2D) spatial\ndimensions with or without spin-orbit (SO) and Rabi couplings. Several\ndifferent forms of SO coupling are included in the programs. We use the\nsplit-step Crank-Nicolson discretization for imaginary- and real-time\npropagation to calculate stationary states and BEC dynamics, respectively. The\nimaginary-time propagation programs calculate the lowest-energy stationary\nstate. The real-time propagation programs can be used to study the dynamics.\nThe simulation input parameters are provided at the beginning of each program.\nThe programs propagate the condensate wave function and calculate several\nrelevant physical quantities. Outputs of the programs include the wave\nfunction, energy, root-mean-square sizes, different density profiles (linear\ndensity for the 1D program, linear and surface densities for the 2D program).\nThe imaginary- or real-time propagation can start with an analytic wave\nfunction or a pre-calculated numerical wave function. The imaginary-time\npropagation usually starts with an analytic wave function, while the real-time\npropagation is often initiated with the previously calculated converged\nimaginary-time wave function."
    },
    {
        "anchor": "3D Projection Sideband Cooling: We demonstrate 3D microwave projection sideband cooling of trapped, neutral\natoms. The technique employs state-dependent potentials that enable microwave\nphotons to drive vibration-number reducing transitions. The particular cooling\nsequence we employ uses minimal spontaneous emission, and works even for\nrelatively weakly bound atoms. We cool 76% of atoms to their 3D vibrational\nground states in a site-resolvable 3D optical lattice.",
        "positive": "A new form of liquid matter: quantum droplets: This brief review summarizes recent theoretical and experimental results\nwhich predict and establish the existence of quantum droplets (QDs), i.e.,\nrobust two- and three-dimensional (2D and 3D) self-trapped states in\nBose-Einstein condensates (BECs), which are stabilized by effective\nselffirepulsion induced by quantum fluctuations around the mean-field (MF)\nstates [alias the Lee-Huang--Yang (LHY) effect]. The basic models are\npresented, taking special care of the dimension crossover, 2D -> 3D. Recently\nreported experimental results, which exhibit stable 3D and quasi-2D QDs in\nbinary BECs, with the inter-component attraction slightly exceeding the MF\nself-repulsion in each component, and in single-component condensates of atoms\ncarrying permanent magnetic moments, are presented in some detail. The summary\nof theoretical results is focused, chiefly, on 3D and quasi-2D QDs with\nembedded vorticity, as the possibility to stabilize such states is a remarkable\nprediction. Stable vortex states are presented both for QDs in free space, and\nfor singular but physically relevant 2D modes pulled to the center by the\ninverse-square potential, with the quantum collapse suppressed by the LHY\neffect."
    },
    {
        "anchor": "Design of a millimetre-scale magnetic surface trap for cold atoms: We study a novel millimetre-scale magnetic trap for ultracold atoms, in which\nthe current carrying conductors can be situated outside the vacuum region, a\nfew mm away from the atoms. This design generates a magnetic field gradient in\nexcess of \\SI{1000}{G/cm} at a distance of \\SI{2}{mm} from the conductors. We\nperform electromagnetic and thermo-mechanical characterisation using Finite\nElement Methods (FEM). The predicted behaviour has been verified by electrical\nand thermal measurements on a prototype, but has not been implemented on an\napparatus with cold atoms. Operating this trap at the highest gradient allows\nfor rapid evaporative cooling comparable to that achieved by atom chips.",
        "positive": "Superradiance induced particle flow via dynamical gauge coupling: We study fermions that are gauge-coupled to a cavity mode via Raman-assisted\nhopping in a one dimensional lattice. For an infinite lattice, we find a\nsuperradiant phase with infinitesimal pumping threshold which induces a\ndirected particle flow. We explore the fate of this flow in a finite lattice\nwith boundaries, studying the non-equilibrium dynamics including fluctuation\neffects. The short time dynamics is dominated by superradiance, while the long\ntime behaviour is governed by cavity fluctuations. We show that the steady\nstate in the finite lattice is not unique, and can be understood in terms of\ncoherent bosonic excitations above a Fermi surface in real space."
    },
    {
        "anchor": "Superfluid, Supersolid and Checkerboard Solid in Two-Component Bosons in\n  an Optical Lattice: Study by Means of Gross-Pitaevskii Theory and Monte-Carlo\n  Simulations: The bosonic t-J model is a strong-on-site repulsion limit of the\ntwo-component Bose-Hubbard model and is expected to be realized by experiments\nof cold atoms in an optical lattice. In previous papers, we studied the bosonic\nt-J model by both analytical methods and numerical Monte - Carlo (MC)\nsimulations. However, in the case of finite $J_z$, where $J_z$ is the\n$z$-component coupling constant of the pseudospin interaction, the phase\ndiagram of the model was investigated by assuming the checkerboard type of\nboson densities. In this study, we shall continue our previous study of the\nbosonic t-J model using both the Gross-Pitaevskii (GP) theory and MC\nsimulations without assuming any pattern of boson densities. These two methods\ncomplement each other and give reliable results. We show that as $J_z$ is\nincreased, the superfluid state evolves into a supersolid (SS), and furthermore\ninto a genuine solid with the checkerboard symmetry. In the present study, we\npropose a method identifying quantum phase transitions in the GP theory. We\nalso study finite-temperature phase transitions of the superfluidity and the\ndiagonal solid order of the SS by MC simulations.",
        "positive": "Vortex precession and exchange in a Bose-Einstein condensate: Vortices in a Bose-Einstein condensate are modelled as spontaneously symmetry\nbreaking minimum energy solutions of the time dependent Gross-Pitaevskii\nequation, using the method of constrained optimization. In a non-rotating\naxially symmetric trap, the core of a single vortex precesses around the trap\ncenter and, at the same time, the phase of its wave function shifts at a\nconstant rate. The precession velocity, the speed of phase shift, and the\ndistance between the vortex core and the trap center, depend continuously on\nthe value of the conserved angular momentum that is carried by the entire\ncondensate. In the case of a symmetric pair of identical vortices, the\nprecession engages an emergent gauge field in their relative coordinate, with a\nflux that is equal to the ratio between the precession and shift velocities."
    },
    {
        "anchor": "Quantum critical behavior at the many-body-localization transition: Phase transitions are driven by collective fluctuations of a system's\nconstituents that emerge at a critical point. This mechanism has been\nextensively explored for classical and quantum systems in equilibrium, whose\ncritical behavior is described by a general theory of phase transitions.\nRecently, however, fundamentally distinct phase transitions have been\ndiscovered for out-of-equilibrium quantum systems, which can exhibit critical\nbehavior that defies this description and is not well understood. A\nparadigmatic example is the many-body-localization (MBL) transition, which\nmarks the breakdown of quantum thermalization. Characterizing quantum critical\nbehavior in an MBL system requires the measurement of its entanglement\nproperties over space and time, which has proven experimentally challenging due\nto stringent requirements on quantum state preparation and system isolation.\nHere, we observe quantum critical behavior at the MBL transition in a\ndisordered Bose-Hubbard system and characterize its entanglement properties via\nits quantum correlations. We observe strong correlations, whose emergence is\naccompanied by the onset of anomalous diffusive transport throughout the\nsystem, and verify their critical nature by measuring their system-size\ndependence. The correlations extend to high orders in the quantum critical\nregime and appear to form via a sparse network of many-body resonances that\nspans the entire system. Our results unify the system's microscopic structure\nwith its macroscopic quantum critical behavior, and they provide an essential\nstep towards understanding criticality and universality in non-equilibrium\nsystems.",
        "positive": "Protocol for autonomous rearrangement of cold atoms into low-entropy\n  configurations: The preparation of low-entropy starting conditions is a key requirement for\nmany experiments involving neutral atoms. Here, we propose a method to\nautonomously assemble arbitrary spatial configurations of atoms within arrays\nof optical tweezers or lattice sites, enabled by a combination of tunneling and\nground-state laser cooling. In contrast to previous methods, our protocol does\nnot rely on either imaging or evaporative cooling. This circumvents limitations\nassociated with imaging fidelity and loss, especially in systems with small\nspatial scales, while providing a substantial improvement in speed relative to\nevaporative approaches. These features may make it well-suited for preparing\narbitrary initial conditions for Bose-Hubbard or Rydberg interacting systems."
    },
    {
        "anchor": "Cavity-induced chiral states of fermionic quantum gases: We investigate ultra-cold fermions placed into an optical cavity and\nsubjected to optical lattices which confine the atoms to ladder structures. A\ntransverse running-wave laser beam induces together with the dynamical cavity\nfield a two-photon Raman-assisted tunneling process with spatially dependent\nphase imprint along the rungs of the ladders. We identify the steady states\nwhich can occur by the feedback mechanism between the cavity field and the\natoms. We find the spontaneous emergence of a finite cavity field amplitude\nwhich leads to an artificial magnetic field felt by the fermionic atoms. These\nform a chiral insulating or chiral liquid state carrying a chiral current. We\nexplore the rich state diagram as a function of the power of the transverse\nlaser beam, the atomic filling, and the phase imprint during the cavity-induced\ntunneling. Both a sudden onset or a slow exponential activation with the\ntransverse laser power of the self-organized chiral states can occur.",
        "positive": "Vortices in the two-dimensional dipolar Bose gas: We present vortex solutions for the homogeneous two-dimensional Bose-Einstein\ncondensate featuring dipolar atomic interactions, mapped out as a function of\nthe dipolar interaction strength (relative to the contact interactions) and\npolarization direction. Stable vortex solutions arise in the regimes where the\nfully homogeneous system is stable to the phonon or roton instabilities. Close\nto these instabilities, the vortex profile differs significantly from that of a\nvortex in a nondipolar quantum gas, developing, for example, density ripples\nand an anisotropic core. Meanwhile, the vortex itself generates a mesoscopic\ndipolar potential which, at distance, scales as 1/r^2 and has an angular\ndependence which mimics the microscopic dipolar interaction."
    },
    {
        "anchor": "Artificial atoms from cold bosons in one dimension: We investigate the ground-state properties of weakly repulsive\none-dimensional bosons in the presence of an attractive zero-range impurity\npotential. First, we derive mean-field solutions to the problem on a finite\nring for the two asymptotic cases: (i) all bosons are bound to the impurity and\n(ii) all bosons are in a scattering state. Moreover, we derive the critical\nline that separates these regimes in the parameter space. In the thermodynamic\nlimit, this critical line determines the maximum number of bosons that can be\nbound by the impurity potential, forming an artificial atom. Second, we\nvalidate the mean-field results using the flow equation approach and the\nmulti-layer multi-configuration time-dependent Hartree method for atomic\nmixtures. While beyond-mean-field effects destroy long-range order in the Bose\ngas, the critical boson number is unaffected. Our findings are important for\nunderstanding such artificial atoms in low-density Bose gases with static and\nmobile impurities.",
        "positive": "Universal and Non-Universal Correction Terms of Bose Gases in Dilute\n  Region: a Quantum Monte Carlo Study: We study dilute gases of interacting bosons at zero-temperature in the region\nwhere the system is characterized only by the s-wave scattering length. We\ncarry out quantum Monte Carlo simulation of the Bose Hubbard model and a\ncontinuous-space hard-core model. Fitting the extended Lee-Huang-Yang formula\nto the Monte Carlo results establishes the detailed mapping from the lattice\nmodel to the continuous field theory characterized only by the s-wave\nscattering length. Our estimate of the intrinsic s-wave scattering length $a_s$\nof the Bose-Hubbard model is $a_s/a_l = 0.316(2)$ where $a_l$ is the lattice\nconstant. It turned out that inclusion of the universal second correction term\nof $O(n \\log n)$ makes the fitting worse while it is restored by inclusion of\nthe non-universal third correction term, of which the existence was predicted\nanalytically."
    },
    {
        "anchor": "Bogoliubov Theory of Dipolar Bose Gas in Weak Random Potential: We consider a dilute homogeneous Bose gas with both an isotropic short-range\ncontact interaction and an anisotropic long-range dipole-dipole interaction in\na weak random potential at low temperature in three dimensions. Within the\nrealm of Bogoliubov theory we analyze how both condensate and superfluid\ndepletion are depleted due to quantum and thermal fluctuations as well as\ndisorder fluctuations.",
        "positive": "Real-space imaging of a topological protected edge state with ultracold\n  atoms in an amplitude-chirped optical lattice: Topological states of matter, as quantum Hall systems or topological\ninsulators, cannot be distinguished from ordinary matter by local measurements\nin the bulk of the material. Instead, global measurements are required,\nrevealing topological invariants as the Chern number. At the heart of\ntopological materials are topologically protected edge states that occur at the\nintersection between regions of different topological order. Ultracold atomic\ngases in optical lattices are promising new platforms for topological states of\nmatter, though the observation of edge states has so far been restricted in\nthese systems to the state space imposed by the internal atomic structure. Here\nwe report on the observation of an edge state between two topological distinct\nphases of an atomic physics system in real space using optical microscopy. An\ninterface between two spatial regions of different topological order is\nrealized in a one-dimensional optical lattice of spatially chirped amplitude.\nTo reach this, a magnetic field gradient causes a spatial variation of the\nRaman detuning in an atomic rubidium three- level system and a corresponding\nspatial variation of the coupling between momentum eigenstates. This novel\nexperimental technique realizes a cold atom system described by a Dirac\nequation with an inhomogeneous mass term closely related to the SSH-model. The\nobserved edge state is characterized by measuring the overlap to various\ninitial states, revealing that this topological state has singlet nature in\ncontrast to the other system eigenstates, which occur pairwise. We also\ndetermine the size of the energy gap to the adjacent eigenstate doublet. Our\nfindings hold prospects for the spectroscopy of surface states in topological\nmatter and for the quantum simulation of interacting Dirac systems."
    },
    {
        "anchor": "Persistent Currents in Toroidal Dipolar Supersolids: We investigate the rotational properties of a dipolar Bose-Einstein\ncondensate trapped in a toroidal geometry. Studying the ground states in the\nrotating frame and at fixed angular momenta, we observe that the condensate\nacts in distinctly different ways depending on whether it is in the superfluid\nor in the supersolid phase. We find that intriguingly, the toroidal dipolar\ncondensate can support a supersolid persistent current which occurs at a local\nminimum in the ground state energy as a function of angular momentum, where the\nstate has a vortex solution in the superfluid component of the condensate. The\ndecay of this state is prevented by a barrier that in part consists of states\nwhere a fraction of the condensate mimics solid-body rotation in a direction\nopposite to that of the vortex. Furthermore, the rotating toroidal supersolid\nshows hysteretic behavior that is qualitatively different depending on the\nsuperfluid fraction of the condensate.",
        "positive": "Vector solitons in a spin-orbit coupled spin-$2$ Bose-Einstein\n  condensate: Five-component minimum-energy bound states and mobile vector solitons of a\nspin-orbit-coupled quasi-one-dimensional hyperfine-spin-2 Bose-Einstein\ncondensate are studied using the numerical solution and variational\napproximation of a mean-field model. Two distinct types of solutions with\nsingle-peak and multi-peak density distribution of the components are\nidentified in different domains of interaction parameters. From an analysis of\nGalilean invariance and time-reversal symmetry of the Hamiltonian, we establish\nthat vector solitons with multi-peak density distribution preserve\ntime-reversal symmetry, but cannot propagate maintaining the shape of\nindividual components. However, those with single-peak density distribution\nviolate time-reversal symmetry of the Hamiltonian, but can propagate with a\nconstant velocity maintaining the shape of individual components."
    },
    {
        "anchor": "Path Integral Monte Carlo study of particles obeying quantum mechanics\n  and classical statistics: Ultracold atomic systems have been of great research interest in the past,\nwith more recent attention being paid to systems of mixed species. In this work\nwe carry out non-perturbative Path Integral Monte Carlo (PIMC) simulations of N\ndistinguishable particles at finite temperature, which can be thought of as an\nultracold atomic system containing N distinct species. We use the PIMC approach\nto calculate thermodynamic properties of particles interacting via hard-sphere\nand hard-cavity potentials. The first problem we study is a two-particle system\ninteracting via a hard-sphere and hard-cavity interaction in order to test the\neffectiveness of two approximations for the thermal density matrix\ncorresponding to these potentials. We then apply the PIMC method to a system of\nmany hard-sphere particles under periodic boundary conditions at varying\ntemperature in order to calculate the energy per particle, pressure, and\nspecific heat of the system. We examine how finite-size effects impact the\nresults of PIMC simulations of hard-sphere particles and when the thermodynamic\nlimit has been reached. Our results provide microscopic benchmarks for a system\ncontaining distinguishable particles, which can be thought of as a limiting\ncase for ultracold atomic systems of mixed species.",
        "positive": "Wavepacket Dynamics in Nonlinear Schr\u00f6dinger Equations: Coherent states play an important role in quantum mechanics because of their\nunique properties under time evolution. Here we explore this concept for\none-dimensional repulsive nonlinear Schr\\\"odinger equations, which describe\nweakly interacting Bose-Einstein condensates or light propagation in a\nnonlinear medium. It is shown that the dynamics of phase-space translations of\nthe ground state of a harmonic potential is quite simple: the centre follows a\nclassical trajectory whereas its shape does not vary in time. The parabolic\npotential is the only one that satisfies this property. We study the time\nevolution of these nonlinear coherent states under perturbations of their\nshape, or of the confining potential. A rich variety of effects emerges. In\nparticular, in the presence of anharmonicities, we observe that the packet\nsplits into two distinct components. A fraction of the condensate is\ntransferred towards uncoherent high-energy modes, while the amplitude of\noscillation of the remaining coherent component is damped towards the bottom of\nthe well."
    },
    {
        "anchor": "Phase Winding a Two-Component BEC in an Elongated Trap: Experimental\n  Observation of Moving Magnetic Orders and Dark-bright Solitons: We experimentally investigate the phase winding dynamics of a harmonically\ntrapped two-component BEC subject to microwave induced Rabi oscillations\nbetween two pseudospin components. While the single particle dynamics can be\nexplained by mapping the system to a two-component Bose-Hubbard model,\nnonlinearities due to the interatomic repulsion lead to new effects observed in\nthe experiments: In the presence of a linear magnetic field gradient, a\nqualitatively stable moving magnetic order that is similar to antiferromagnetic\norder is observed after critical winding is achieved. We also demonstrate how\nthe phase winding can be used as a new tool to generate copious dark-bright\nsolitons in a two-component BEC, opening the door for new experimental studies\nof these nonlinear features.",
        "positive": "Relaxation dynamics in the merging of $N$ independent condensates: Controlled quantum systems such as ultracold atoms can provide powerful\nplatforms to study non-equilibrium dynamics of closed many-body quantum\nsystems, especially since a complete theoretical description is generally\nchallenging. In this Letter, we present a detailed study of the rich\nout-of-equilibrium dynamics of an adjustable number $N$ of uncorrelated\ncondensates after connecting them in a ring-shaped optical trap. We observe the\nformation of long-lived supercurrents and confirm the scaling of their winding\nnumber with $N$ in agreement with the geodesic rule. Moreover, we provide\ninsight into the microscopic mechanism that underlies the smoothening of the\nphase profile."
    },
    {
        "anchor": "Effect of a bias field on disordered waveguides: Universal scaling of\n  conductance and application to ultracold atoms: We study the transmission of a disordered waveguide subjected to a finite\nbias field. The statisticaldistribution of transmission is analytically shown\nto take a universal form. It depends on a singleparameter, the system length\nexpressed in a rescaled metrics, which encapsulates all the microscopicfeatures\nof the medium and the bias field. Excellent agreement with numerics is found\nfor variousmodels of disorder and bias field. For white-noise disorder and a\nlinear bias field, we demonstratethe algebraic nature of the decay of the\ntransmission with distance, irrespective of the value ofthe bias field. It\ncontrasts with the expansion of a wave packet, which features a\ndelocalizationtransition for large bias field. The difference is attributed to\nthe different boundary conditionsfor the transmission and expansion schemes.\nThe observability of these effects in conductancemeasurements for electrons or\nultracold atoms is discussed, taking into account key features, suchas\nfinite-range disorder correlations, nonlinear bias fields, and finite\ntemperatures.",
        "positive": "Generating, dragging and releasing dark solitons in elongated\n  Bose-Einstein condensates: We theoretically analyze quasi-one-dimensional Bose-Einstein condensates\nunder the influence of a harmonic trap and a narrow potential defect that moves\nthrough the atomic cloud. Performing simulations on the mean field level, we\nexplore a robust mechanism in which a single dark soliton is nucleated and\nimmediately pinned by the moving defect, making it possible to drag it to a\ndesired position and release it there. We argue on a perturbative level that a\ndefect potential which is attractive to the atoms is suitable for holding and\nmoving dark solitons. The soliton generation protocol is investigated over a\nwide range of model parameters and its success is systematically quantified by\na suitable fidelity measure, demonstrating its robustness against parameter\nvariations, but also the need for tight focusing of the defect potential.\nHolding the soliton at a stationary defect for long times may give rise to\ndynamical instabilities, whose origin we explore within a Bogoliubov-de Gennes\nlinearization analysis. We show that iterating the generation process with\nmultiple defects offers a perspective for initializing multiple soliton\ndynamics with freely chosen initial conditions."
    },
    {
        "anchor": "Impurity with a resonance in the vicinity of the Fermi energy: We study an impurity with a resonance level whose energy coincides with the\nFermi energy of the surrounding Fermi gas. An impurity causes a rapid variation\nof the scattering phase shift for fermions at the Fermi surface, introducing a\nnew characteristic length scale into the problem. We investigate manifestations\nof this length scale in the self-energy of the impurity and in the density of\nthe bath. Our calculations reveal a model-independent deformation of the\ndensity of the Fermi gas, which is determined by the width of the resonance. To\nprovide a broader picture, we investigate time evolution of the density in\nquench dynamics, and study the behavior of the system at finite temperatures.\nFinally, we briefly discuss implications of our findings for the Fermi-polaron\nproblem.",
        "positive": "Observation of a partially rotating superfluid of exciton-polariton: Rotation of a container holding a viscous fluid forms a vortex which grows\nwith increasing angular velocity. A superfluid, however, is intrinsically\ndifferent from these normal fluids because its rotation is quantized. Even if a\ncontainer of superfluid is rotating, the fluid itself remains still until a\ncritical velocity is reached. Beyond the critical velocity, all the particles\nconspire to suddenly pick up an angular momentum of $\\hbar$ each and forms a\nquantized vortex. As a result, a superfluid is known to increase its rotation\nby a total angular momentum of $N\\hbar$. In this letter, we show that\nexciton-polariton superfluid can split into an irrotational part and a\nrotational part. The relative ratio between the two states can be controlled by\neither pump beam's power or spot size. Consequently, angular momentum of\nexciton-polariton superfluid can be tuned from zero to $N\\hbar$ continuously.\nThis striking observation sets the stage for studying non-equilibrium\nproperties of a superfluid with exciton-polaritons."
    },
    {
        "anchor": "Quantum properties of light scattered from structured many-body phases\n  of ultracold atoms in quantum optical lattices: Quantum trapping potentials for ultracold gases change the landscape of\nclassical properties of scattered light and matter. The atoms in a quantum\nmany-body correlated phase of matter change the properties of light and vice\nversa. The properties of both light and matter can be tuned by design and\ndepend on the interplay between long-range (nonlocal) interactions mediated by\nan optical cavity and short-range processes of the atoms. Moreover, the quantum\nproperties of light get significantly altered by this interplay, leading the\nlight to have nonclassical features. Further, these nonclassical features can\nbe designed and optimised.",
        "positive": "Chaos, Metastability and Ergodicity in Bose-Hubbard Superfluid Circuits: The hallmark of superfluidity is the appearance of metastable flow-states\nthat carry a persistent circulating current. Considering Bose-Hubbard\nsuperfluid rings, we clarify the role of \"quantum chaos\" in this context. We\nshow that the standard Landau and Bogoliubov superfluidity criteria fail for\nsuch low-dimensional circuits. We also discuss the feasibility for a coherent\noperation of a SQUID-like setup. Finally, we address the manifestation of the\nstrong many-body dynamical localization effect."
    },
    {
        "anchor": "Delocalization to self-trapping transition of a Bose fluid confined in a\n  double well potential. An analysis via one- and two-body correlation\n  properties: We revisit the coherent or delocalized to self-trapping transition in an\ninteracting bosonic quantum fluid confined in a double well potential, in the\ncontext of full quantum calculations. We show that an $N$-particle Bose-Hubbard\nfluid reaches an stationary state through the two-body interactions. These\nstationary states are either delocalized or self-trapped in one of the wells,\nthe former appearing as coherent oscillations in the mean-field approximation.\nBy studying one- and two-body properties in the energy eigenstates and in a set\nof coherent states, we show that the delocalized to self-trapped transition\noccurs as a function of the energy of the fluid, provided the interparticle\ninteraction is above a critical or threshold value. We argue that this is a\ntype of symmetry-breaking continuous phase transition.",
        "positive": "The `Higgs' Amplitude Mode at the Two-Dimensional Superfluid-Mott\n  Insulator Transition: Spontaneous symmetry breaking plays a key role in our understanding of\nnature. In a relativistic field theory, a broken continuous symmetry leads to\nthe emergence of two types of fundamental excitations: massless Nambu-Goldstone\nmodes and a massive `Higgs' amplitude mode. An excitation of Higgs type is of\ncrucial importance in the standard model of elementary particles and also\nappears as a fundamental collective mode in quantum many-body systems. Whether\nsuch a mode exists in low-dimensional systems as a resonance-like feature or\nbecomes over-damped through coupling to Nambu-Goldstone modes has been a\nsubject of theoretical debate. Here we reveal and study a Higgs mode in a\ntwo-dimensional neutral superfluid close to the transition to a Mott insulating\nphase. We unambiguously identify the mode by observing the expected softening\nof the onset of spectral response when approaching the quantum critical point.\nIn this regime, our system is described by an effective relativistic field\ntheory with a two-component quantum-field, constituting a minimal model for\nspontaneous breaking of a continuous symmetry. Additionally, all microscopic\nparameters of our system are known from first principles and the resolution of\nour measurement allows us to detect excited states of the many-body system at\nthe level of individual quasiparticles. This allows for an in-depth study of\nHiggs excitations, which also addresses the consequences of reduced\ndimensionality and confinement of the system. Our work constitutes a first step\nin exploring emergent relativistic models with ultracold atomic gases."
    },
    {
        "anchor": "Effective potential and quantum criticality for imbalanced Fermi\n  mixtures: We study the analytical structure of the effective action for spin- and\nmass-imbalanced Fermi mixtures at the onset of the superfluid state. Of our\nparticular focus is the possibility of suppressing the tricritical temperature\nto zero, so that the transition remains continuous down to $T=0$ and the phase\ndiagram hosts a quantum critical point. At mean-field level we analytically\nidentify such a possibility in a regime of parameters in dimensionality $d=3$.\nIn contrast, in $d=2$ we demonstrate that the occurrence of a quantum critical\npoint is (at the mean-field level) excluded. We show that the Landau expansion\nof the effective potential remains well-defined in the limit $T\\to 0^+$ except\nfor a subset of model parameters which includes the standard BCS limit. We\ncalculate the mean-field asymptotic shape of the transition line. Employing the\nfunctional renormalization group framework we go beyond the mean field theory\nand demonstrate the stability of the quantum critical point in $d=3$ with\nrespect to fluctuations.",
        "positive": "The Gross-Pitaevskii-Poisson model for an ultracold plasma: density\n  waves and solitons: We introduce 1D and 2D models of a degenerate bosonic gas composed of ions\nwith positive and negative charges (cations and anions). The system may exist\nin the mean-field condensate state, enabling the competition of the Coulomb\ncoupling, contact repulsion, and kinetic energy of the particles, provided that\ntheir effective mass is reduced by means of a lattice potential. The model\ncombines the Gross-Pitaevskii (GP) equations for the two-component wave\nfunction of the cations and anions, coupled to the Poisson equation for the\nelectrostatic potential mediating the Coulomb coupling. The contact interaction\nin the GP system can be derived, in the Thomas-Fermi approximation, from a\nsystem of three GP equations, which includes the wave function of heavy neutral\natoms. In the system with fully repulsive contact interactions, we construct\nstable spatially periodic patterns (density waves, DWs). The transition to DWs\nis identified by analysis of the modulational instability of a uniformly mixed\nneutral state. The DW pattern, which represents the system's ground state (GS),\nis predicted by a variational approximation. In 2D, a stable pattern is\nproduced too, with a quasi-1D shape. The 1D system with contact self-attraction\nin each component produces bright solitons of three types: neutral ones, with\nfully mixed components; dipoles, with the components separated by the\ninter-species contact repulsion; and quadrupoles, with a layer of one component\nsandwiched between side lobes formed by the other. The transition from the\nneutral solitons to dipoles is accurately modeled analytically. A chart of the\nGSs of the different types (neutral solitons, dipoles, or quadrupoles) is\nproduced. Different soliton species do not coexist as stable states. Collisions\nbetween traveling solitons are elastic for dipole-dipole pairs, while\ndipole-antidipole ones merge into stable quadrupoles via multiple collisions."
    },
    {
        "anchor": "Many-body quantum dynamics of an asymmetric bosonic Josephson junction: The out-of-equilibrium quantum dynamics of an interacting Bose gas trapped in\na 1D asymmetric double-well potential is studied by solving the many-body\nSchr\\\"odinger equation numerically accurately. We examine how the loss of\nsymmetry of the confining trap affects the macroscopic quantum tunneling\ndynamics of the system between the two wells. In an asymmetric DW, the two\nwells are not equivalent anymore -the left well is deeper than the right one.\nAccordingly, we analyze the dynamics by initially preparing the condensate in\nboth the left and the right well. We examined the frequencies and amplitudes of\nthe oscillations of the survival probabilities, the time scale for the\ndevelopment of fragmentation and its degree, and the growth and oscillatory\nbehavior of the many-body position and momentum variances. There is an overall\nsuppression of the oscillations of the survival probabilities in an asymmetric\ndouble well. However, depending on whether the condensate is initially prepared\nin the left or right well, the repulsive inter-atomic interactions affect the\nsurvival probabilities differently. The degree of fragmentation depends both on\nthe asymmetry of the trap and the initial well in which the condensate is\nprepared in a non-trivial manner. Overall, the many-body position and momentum\nvariances bear the prominent signatures of the density oscillations of the\nsystem in the asymmetric double well as well as a breathing-mode oscillation.\nFinally, a universality of fragmentation for systems made of different numbers\nof particles but the same interaction parameter is also found. The phenomenon\nis robust despite the asymmetry of the junction and admits a\nmacroscopically-large fragmented condensate characterized by a diverging\nmany-body position variance.",
        "positive": "Currents algebra for the two-sites Bose-Hubbard model: I present a currents algebra for the two-sites Bose-Hubbard model, generalize\nthe Heisenberg equation of motion to write the second time derivative of the\ncurrents operators and use it to get the quantum dynamics of the currents. For\ndifferent choices of the Hamiltonian parameters I get different currents\ndynamics and determine the period of the oscillations in function of the\nparameters."
    },
    {
        "anchor": "Josephson effects in one-dimensional supersolids: We demonstrate that superflow past an obstacle is possible in a solid phase\nin the one-dimensional Gross-Pitaevskii equation with a finite-range two-body\ninteraction. The phenomenon we find is analogous to the DC Josephson effect in\nsuperconductors and we deduce the \"Josephson relation\" between the current and\nphase difference of the condensates separated by the obstacle. We also discuss\npersistent current and nonclassical rotational inertia in annular container\nwith a penetrable potential barrier. The phase diagram in the plane of the\ncurrent and the interaction strength is given. Our result provides a simple\ntheoretical example of supersolidity in the presence of an obstacle.",
        "positive": "Strongly interacting bosons in multi-chromatic potentials supporting\n  mobility edges: localization, quasi-condensation and expansion dynamics: We provide an account of the static and dynamic properties of hard-core\nbosons in a one-dimensional lattice subject to a multi-chromatic quasiperiodic\npotential for which the single-particle spectrum has mobility edges. We use the\nmapping from strongly interacting bosons to weakly interacting fermions, and\nprovide exact numerical results for hard-core bosons in and out of equilibrium.\nIn equilibrium, we find that the system behaves like a quasi-condensate\n(insulator) depending on whether the Fermi surface of the corresponding\nfermionic system lies in a spectral region where the single-particle states are\ndelocalized (localized). We also study non-equilibrium expansion dynamics of\ninitially trapped bosons, and demonstrate that the extent of partial\nlocalization is determined by the single-particle spectrum."
    },
    {
        "anchor": "Particle-hole pairs and density-density correlations in the Lieb-Liniger\n  model: We review the recently introduced thermodynamic form factors for pairs of\nparticle-hole excitations on finite-entropy states in the Lieb-Liniger model.\nWe focus on the density operator and we show how the form factors can be used\nfor analytic computations of dynamical correlation functions. We derive a new\nrepresentation for the form factors and we discuss some aspects of their\nstructure. We rigorously show that in the small momentum limit (or\nequivalently, on hydrodynamic scales) a single particle-hole excitation fully\nsaturates the spectral sum and we also discuss the contribution from two\nparticle-hole pairs. Finally we show that thermodynamic form factors can be\nalso used to study the ground state correlations and to derive the edge\nexponents.",
        "positive": "Tuning the dipole-dipole interaction in a quantum gas with a rotating\n  magnetic field: We demonstrate the tuning of the magnetic dipole-dipole interaction (DDI)\nwithin a dysprosium Bose-Einstein condensate by rapidly rotating the\norientation of the atomic dipoles. The tunability of the dipolar mean-field\nenergy manifests as a modified gas aspect ratio after time-of-flight expansion.\nWe demonstrate that both the magnitude and the sign of the DDI can be tuned\nusing this technique. In particular, we show that a magic rotation angle exists\nat which the mean-field DDI can be eliminated, and at this angle, we observe\nthat the expansion dynamics of the condensate is close to that predicted for a\nnon-dipolar gas. The ability to tune the strength of the DDI opens new avenues\ntoward the creation of exotic soliton and vortex states as well as unusual\nquantum lattice phases and Weyl superfluids."
    },
    {
        "anchor": "Arbitrary-angle rotation of the polarization of a dipolar Bose-Einstein\n  condensate: We have employed the theory of harmonically trapped dipolar Bose-Einstein\ncondensates to examine the influence of a uniform magnetic field that rotates\nat an arbitrary angle to its own orientation. This is achieved by\nsemi-analytically solving the dipolar superfluid hydrodynamics of this system\nwithin the Thomas-Fermi approximation and by allowing the body frame of the\ncondensate's density profile to be tilted with respect to the symmetry axes of\nthe nonrotating harmonic trap. This additional degree of freedom manifests\nitself in the presence of previously unknown stationary solution branches for\nany given dipole tilt angle. We also find that the tilt angle of the stationary\nstate's body frame with respect to the rotation axis is a nontrivial function\nof the trapping geometry, rotation frequency and dipole tilt angle. For\nrotation frequencies of at least an order of magnitude higher than the in-plane\ntrapping frequency, the stationary state density profile is almost perfectly\nequivalent to the profile expected in a time-averaged dipolar potential that\neffectively vanishes when the dipoles are tilted along the `magic angle', $54.7\n\\deg$. However, by linearizing the fully time-dependent superfluid\nhydrodynamics about these stationary states, we find that they are dynamically\nunstable against the formation of collective modes, which we expect would\nresult in turbulent decay.",
        "positive": "Control of tunneling in an atomtronic switching device: The precise control of quantum systems will play a major role in the\nrealization of atomtronic devices. As in the case of electronic systems, a\ndesirable property is the ability to implement switching. Here we show how to\nimplement switching in a model of dipolar bosons confined to three coupled\nwells. The model describes interactions between bosons, tunneling of bosons\nbetween adjacent wells, and the effect of an external field. We conduct a study\nof the quantum dynamics of the system to probe the conditions under which\nswitching behavior can occur. The analysis considers both integrable and\nnon-integrable regimes within the model. Through variation of the external\nfield, we demonstrate how the system can be controlled between various\nswitched-on and switched-off configurations."
    },
    {
        "anchor": "Effective equations for matter-wave gap solitons in higher-order\n  transversal states: We demonstrate that an important class of nonlinear stationary solutions of\nthe three-dimensional (3D) Gross-Pitaevskii equation (GPE) exhibiting\nnontrivial transversal configurations can be found and characterized in terms\nof an effective one-dimensional (1D) model. Using a variational approach we\nderive effective equations of lower dimensionality for BECs in $(m,n_{r})$\ntransversal states (states featuring a central vortex of charge $m$ as well as\n$n_{r}$ concentric zero-density rings at every $z$ plane) which provides us\nwith a good approximate solution of the original 3D problem. Since the\nspecifics of the transversal dynamics can be absorbed in the renormalization of\na couple of parameters, the functional form of the equations obtained is\nuniversal. The model proposed finds its principal application in the study of\nthe existence and classification of 3D gap solitons supported by 1D optical\nlattices, where in addition to providing a good estimate for the 3D wave\nfunctions it is able to make very good predictions for the $\\mu(N)$ curves\ncharacterizing the different fundamental families. We have corroborated the\nvalidity of our model by comparing its predictions with those from the exact\nnumerical solution of the full 3D GPE.",
        "positive": "Non-Abelian geometric potentials and spin-orbit coupling for\n  periodically driven systems: We demonstrate the emergence of the non-Abelian geometric potentials and thus\nthe three-dimensional (3D) spin-orbit coupling (SOC) for ultracold atoms\nwithout using the laser beams. This is achieved by subjecting an atom to a\nperiodic perturbation which is the product of a position-dependent Hermitian\noperator $\\hat{V}\\left(\\mathbf{r}\\right)$ and a fast oscillating periodic\nfunction $f\\left(\\omega t\\right)$ with a zero average. To have a significant\nspin-orbit coupling (SOC), we analyze a situation where the characteristic\nenergy of the periodic driving is not necessarily small compared to the driving\nenergy $\\hbar\\omega$. Applying a unitary transformation to eliminate the\noriginal periodic perturbation, we arrive at a non-Abelian (non-commuting)\nvector potential term describing the 3D SOC. The general formalism is\nillustrated by analyzing the motion of an atom in a spatially inhomogeneous\nmagnetic field oscillating in time. A cylindrically symmetric magnetic field\nprovides the SOC involving the coupling between the spin $\\mathbf{F}$ and all\nthree components of the orbital angular momentum (OAM) $\\mathbf{L}$. In\nparticular, the spherically symmetric monopole-type synthetic magnetic field\n$\\mathbf{B}\\propto\\mathbf{r}$ generates the 3D SOC of the $\\mathbf{L}\\cdot\n\\mathbf{F}$ form, which resembles the fine-structure interaction of hydrodgen\natom. However, the strength of the SOC here goes as $1/r^{2}$ for larger\ndistances, instead of $1/r^3$ as in atomic fine structure. Such a longer-ranged\nSOC significantly affects not only the lower states of the trapped atom, but\nalso the higher ones. Furthermore, by properly tailoring the external trapping\npotential, the ground state of the system can occur at finite OAM, while the\nground state of hydrogen atom has zero OAM."
    },
    {
        "anchor": "Stabilization and pumping of giant vortices in dilute Bose-Einstein\n  condensates: Recently, it was shown that giant vortices with arbitrarily large quantum\nnumbers can possibly be created in dilute Bose-Einstein condensates by\ncyclically pumping vorticity into the condensate. However, multiply quantized\nvortices are typically dynamically unstable in harmonically trapped nonrotated\ncondensates, which poses a serious challenge to the vortex pump procedure. In\nthis theoretical study, we investigate how the giant vortices can be stabilized\nby the application of a Gaussian potential peak along the vortex core. We find\nthat achieving dynamical stability is feasible up to high quantum numbers. To\ndemonstrate the efficiency of the stabilization method, we simulate the\nadiabatic creation of an unsplit 20-quantum vortex with the vortex pump.",
        "positive": "Dynamics of Bose-Einstein condensates in a one-dimensional optical\n  lattice with double-well potential: We study dynamical behaviors of the weakly interacting Bose-Einstein\ncondensate in the one-dimensional optical lattice with an overall double-well\npotential by solving the time-dependent Gross-Pitaevskii equation. It is\nobserved that the double-well potential dominates the dynamics of such a system\neven if the lattice depth is several times larger than the height of the\ndouble-well potential. This result suggests that the condensate flows without\nresistance in the periodic lattice just like the case of a single particle\nmoving in periodic potentials. Nevertheless, the effective mass of atoms is\nincreased, which can be experimentally verified since it is connected to the\nJosephson oscillation frequency. Moreover, the periodic lattice enhances the\nnonlinearity of the double-well condensate, making the condensate more\n\"self-trapped\" in the $\\pi$-mode self-trapping regime."
    },
    {
        "anchor": "Magnetic Impurity in a Tonks Gas of Fermions: In this letter we consider a magnetic impurity in a one-dimensional\nspin-$1/2$ Fermi gas with infinitely strong repulsive interaction between\nfermions. We rigorously prove that, independent of whether the magnetic\ncoupling between impurity and fermions is ferromagnetic or anti-ferromagnetic,\nthe ground state is always a fully polarized ferromagnetic state for the\nitinerant fermions. This ferromagnetism can be understood as a cooperative\neffect of avoiding frustration of magnetic coupling during fermion hopping and\nthe large spin degeneracy of a fermion Tonks gas. By numerically diagonalizing\na finite size system, we show that the spin gap first increases linearly with\nmagnetic coupling strength in the weak coupling regime, while decreases in the\nstrong coupling regime. Our results show that a magnetic impurity in a strongly\ncorrelated gas can exhibit effect different from the Kondo effect as in a\nweakly correlated Fermi liquid.",
        "positive": "Thermodynamics of an attractive 2D Fermi gas: Thermodynamic properties of matter are conveniently expressed as functional\nrelations between variables known as equations of state. Here we experimentally\ndetermine the compressibility, density and pressure equations of state for an\nattractive 2D Fermi gas in the normal phase as a function of temperature and\ninteraction strength. In 2D, interacting gases exhibit qualitatively different\nfeatures to those found in 3D. This is evident in the normalized density\nequation of state, which peaks at intermediate densities corresponding to the\ncrossover from classical to quantum behaviour."
    },
    {
        "anchor": "Effect of Disorder in BCS-BEC Crossover: In this article we have investigated the effect of weak random disorder in\nthe BCS-BEC crossover region. The disorder is included in the mean field\nformalism through NSR theory of superconducting fluctuations. A self consistent\nnumerical solution of the coupled equations involving the superfluid gap\nparameter and density as a function of the disorder strength, albeit unaffected\nin the BCS phase, yields a depleted order parameter in the BEC regime and an\ninteresting nonmonotonic behavior of the condensate fraction in the vicinity of\nthe unitary region, and a gradual depletion thereafter, as the pairing\ninteraction is continuously tuned across the BCS-BEC crossover. The unitary\nregime thus demonstrates a robust paradigm of superfluidity even when the\ndisorder is introduced. To support the above feature and shed light on a\nlingering controversial issue, we have computed the behavior of the sound mode\nacross the crossover that distinctly reveals a suppression of the sound\nvelocity. We also find the Landau critical velocity that shows similar\nnonmonotonicity as that of the condensate fraction data, thereby supporting a\nstable superfluid scenario in the unitary limit.",
        "positive": "Towards analogue black hole merger: We study the effects of the wavevector-dependent losses on polariton\ncondensates. We demonstrate that because of these losses, a single vortex\nbecomes a center of a convergent flow, which allows describing it by an\nanalogue Kerr black hole metric with a dynamically evolving origin. For a pair\nof vortices, we find an analogue of the 3rd Kepler's law and estimate the\nemission rate of the gravitational waves. We simulate an analogue of the\ninspiral phase of a black hole merger. Our work therefore suggests that\npolariton condensates with quantum vortices represent a setting with a fully\nself-consistent dynamical metric for broad analogue studies."
    },
    {
        "anchor": "Correlated dynamics of collective droplet excitations in a\n  one-dimensional harmonic trap: We address the existence and dynamics of one-dimensional harmonically\nconfined quantum droplets, appearing in two-component mixtures by deploying a\nnonperturbative approach. We find that, in symmetric homonuclear settings,\nbeyond Lee-Huang-Yang correlations result in flat-top droplet configurations\nfor either decreasing intercomponent attraction or larger atom number.\nAsymmetric mixtures feature spatial mixing among the involved components with\nthe more strongly interacting or heavier one exhibiting flat-top structures.\nApplying quenches on the harmonic trap we trigger the lowest-lying collective\ndroplet excitations. The interaction-dependent breathing frequency, being\nslightly reduced in the presence of correlations, shows a decreasing trend for\nstronger attractions. Semi-analytical predictions are also obtained within the\nLee-Huang-Yang framework. For relatively large quench amplitudes the droplet\nprogressively delocalizes and higher-lying motional excitations develop in its\ncore. Simultaneously, enhanced intercomponent entanglement and long-range\ntwo-body intracomponent correlations arise. In sharp contrast, the dipole\nmotion remains robust irrespectively of the system parameters. Species\nselective quenches lead to a correlation-induced dephasing of the droplet or to\nirregular dipole patterns due to intercomponent collisions.",
        "positive": "Momentum-Resolved Bragg Spectroscopy in Optical Lattices: Strongly correlated many-body systems show various exciting phenomena in\ncondensed matter physics such as high-temperature superconductivity and\ncolossal magnetoresistance. Recently, strongly correlated phases could also be\nstudied in ultracold quantum gases possessing analogies to solid-state physics,\nbut moreover exhibiting new systems such as Fermi-Bose mixtures and magnetic\nquantum phases with high spin values. Particularly interesting systems here are\nquantum gases in optical lattices with fully tunable lattice and atomic\ninteraction parameters. While in this context several concepts and ideas have\nalready been studied theoretically and experimentally, there is still great\ndemand for new detection techniques to explore these complex phases in detail.\n  Here we report on measurements of a fully momentum-resolved excitation\nspectrum of a quantum gas in an optical lattice by means of Bragg spectroscopy.\nThe bandstructure is measured with high resolution at several lattice depths.\nInteraction effects are identified and systematically studied varying density\nand excitation fraction."
    },
    {
        "anchor": "Quasi-one-dimensional flow of polariton condensate past an obstacle: Nonlinear wave patterns generated by the flow of polariton condensate past an\nobstacle are studied for quasi-one-dimensional microcavity geometry. It is\nshown that pumping and nonlinear damping play a crucial role in this process\nleading to sharp differences in subsonic and supersonic regimes. Subsonic flows\nresult in a smooth disturbance of the equilibrium condensate around the\nobstacle whereas supersonic flow generates a dispersive shock wave in the flow\nupstream the obstacle and a long smooth downstream tail. Main characteristics\nof the wave pattern are calculated analytically and analytical results are in\nexcellent agreement with the results of numerical simulations. The conditions\nfor existence of stationary wave patterns are determined numerically.",
        "positive": "Low-Dimensional Self-Bound Quantum Rabi-Coupled Bosonic Droplets: We analytically calculate the leading quantum corrections of the ground-state\nenergy of two- and one-dimensional weakly interacting Rabi-coupled Bose-Bose\nmixtures in the frame of the Bogoliubov approximation. We show that to\nrepulsive intraspecies and attractive interspecies interactions, the effect of\nquantum fluctuations favors the formation of self-bound droplets. These\nliquidlike states are crucially affected by the Rabi coupling, leading thus to\nthe appearance of a quantum instability. We derive meaningful formulas to\ndescribe the droplet phase in the one-dimensional case."
    },
    {
        "anchor": "A toy model for the dipolar-induced resonance in quasi-one-dimensional\n  systems: We discuss the properties of the effective dipolar interaction for two\nparticles tightly confined along a one-dimensional tube, stressing the\nemergence of a single dipolar-induced resonance in a regime for which two\nclassical dipoles would just repel each other. We present a toy-model potential\nreproducing the main features of the effective interaction: a non-zero-range\nrepulsive potential competing with an attractive contact term. The existence of\na single resonance is confirmed analytically. The toy model is than generalized\nto investigate the interplay between dipolar and contact interaction, giving an\nintuitive interpretation of the resonance mechanism.",
        "positive": "Spectrum of collective excitations of a quantum fluid of polaritons: We use a recently developed high-resolution coherent probe spectroscopy\nmethod to investigate the dispersion of collective excitations of a polaritonic\nquantum fluid. We measure the dispersion relation with high energy and\nwavenumber resolution, which allows us to determine the speed of sound in the\nfluid and to evidence the contribution of an excitonic reservoir. We report on\nthe generation of collective excitations at negative energies, on the ghost\nbranch of the dispersion curve. Precursors of dynamical instabilities are also\nidentified. Our methods open the way to the precise study of quantum\nhydrodynamics of quantum fluids of light."
    },
    {
        "anchor": "Internal Josephson Effects in Spinor Dipolar Bose--Einstein Condensates: We theoretically study the internal Josephson effect, which is driven by spin\nexchange interactions and magnetic dipole-dipole interactions, in a three-level\nsystem for spin-1 Bose--Einstein condensates, obtaining novel spin dynamics. We\nintroduce single spatial mode approximations into the Gross--Pitaevskii\nequations and derive the Josephson type equations, which are analogous to\ntunneling currents through three junctions between three superconductors. From\nan analogy with two interacting nonrigid pendulums, we identify unique varied\noscillational modes, called the 0--$\\pi$, 0--$running$, $running$--$running$,\n$2n\\pi & running$--$2\\pi$, $single nonrigid pendulum$, and $two rigid\npendulums$ phase modes. These Josephson modes in the three states are expected\nto be found in real atomic Bose gas systems.",
        "positive": "State engineering of impurities in a lattice by coupling to a Bose gas: We investigate the localization pattern of interacting impurities, which are\ntrapped in a lattice potential and couple to a Bose gas. For small interspecies\ninteraction strengths, the impurities populate the energetically lowest Bloch\nstate or localize separately in different wells with one extra particle being\ndelocalized over all the wells, depending on the lattice depth. In contrast,\nfor large interspecies interaction strengths we find that due to the fractional\nfilling of the lattice and the competition of the repulsive contact interaction\nbetween the impurities and the attractive interaction mediated by the Bose gas,\nthe impurities localize either pairwise or completely in a single well. Tuning\nthe lattice depth, the interspecies and intraspecies interaction strength\ncorrespondingly allows for a systematic control and engineering of the two\nlocalization patterns. The sharpness of the crossover between the two states as\nwell as the broad region of their existence supports the robustness of the\nengineering. Moreover, we are able to manipulate the ground state's degeneracy\nin form of triplets, doublets and singlets by implementing different boundary\nconditions, such as periodic and hard wall boundary conditions."
    },
    {
        "anchor": "Phonon redshift and Hubble friction in an expanding BEC: We revisit the theoretical analysis of an expanding ring-shaped Bose-Einstein\ncondensate. Starting from the action and integrating over dimensions orthogonal\nto the phonon's direction of travel, we derive an effective one-dimensional\nwave equation for azimuthally-travelling phonons. This wave equation shows that\nexpansion redshifts the phonon frequency at a rate determined by the effective\nazimuthal sound speed, and damps the amplitude of the phonons at a rate given\nby $\\dot{\\cal V}/{\\cal V}$, where $\\cal{V}$ is the volume of the background\ncondensate. This behavior is analogous to the redshifting and \"Hubble friction\"\nfor quantum fields in the expanding universe and, given the scalings with\nradius determined by the shape of the ring potential, is consistent with recent\nexperimental and theoretical results. The action-based dimensional reduction\nmethods used here should be applicable in a variety of settings, and are well\nsuited for systematic perturbation expansions.",
        "positive": "Preparing Quantum States by Measurement-feedback Control with Bayesian\n  Optimization: Preparation of quantum states is of vital importance for performing quantum\ncomputations and quantum simulations. In this work, we propose a general\nframework for preparing ground states of many-body systems by combining the\nmeasurement-feedback control process (MFCP) and the machine learning method.\nUsing the Bayesian optimization (BO) strategy, the efficiency of determining\nthe measurement and feedback operators in the MFCP is demonstrated. Taking the\none dimensional Bose-Hubbard model as an example, we show that BO can generate\noptimal parameters, although constrained by the operator basis, which can drive\nthe system to the low energy state with high probability in typical quantum\ntrajectories."
    },
    {
        "anchor": "Chern numbers hiding in time-of-flight images: We present a technique for detecting topological invariants -- Chern numbers\n-- from time-of-flight images of ultra-cold atoms. We show that the Chern\nnumbers of integer quantum Hall states of lattice fermions leave their\nfingerprints in the atoms' momentum distribution. We analytically demonstrate\nthat the number of local maxima in the momentum distribution is equal to the\nChern number in two limiting cases, for large hopping anisotropy and in the\ncontinuum limit. In addition, our numerical simulations beyond these two limits\nshow that these local maxima persist for a range of parameters. Thus, an\neveryday observable in cold atom experiments can serve as a useful tool to\ncharacterize and visualize quantum states with non-trivial topology.",
        "positive": "Effect of an Impurity on Grey Soliton Dynamics in Cigar-Shaped\n  Bose-Einstein Condensate: In a cigar shaped Bose-Einstein condensate, explicit solutions of the coupled\nmean-field equations, describing defect-grey soliton dynamics are obtained,\ndemonstrating the coexistence of grey soliton and a localized defect. Unlike\nthe case of dark soliton, where the defect trapping center has vanishing\nsuperfluid density, the moving grey soliton necessarily possesses a finite\nsuperfluid component at the defect location. The wave vector of the impurity is\ncontrolled by the velocity of the grey soliton, which has an upper bound. It is\nfound that the presence of the impurity lowers the speed of the grey soliton,\nas compared to the defect free case, where it can reach the sound velocity. The\ngrey soliton's energy gets substantially modified through its interaction with\nthe defect, opening up the possibility of its control through defect dynamics."
    },
    {
        "anchor": "Spontaneous symmetry breaking of fundamental states, vortices, and\n  dipoles in two- and one-dimensional linearly coupled traps with cubic\n  self-attraction: We introduce two- and one-dimensional (2D and 1D) systems of two\nlinearly-coupled Gross-Pitaevskii equations (GPEs) with the cubic\nself-attraction and harmonic-oscillator (HO) trapping potential in each GPE.\nThe system models a Bose-Einstein condensate with a negative scattering length,\nloaded in a double-pancake trap, combined with the in-plane HO potential. In\naddition to that, the 1D version applies to the light transmission in a\ndual-core waveguide with the Kerr nonlinearity and in-core confinement\nrepresented by the HO potential. The subject of the analysis is spontaneous\nsymmetry breaking in 2D and 1D ground-state (GS, alias fundamental) modes, as\nwell as in 2D vortices and 1D dipole modes (the latter ones do not exist\nwithout the HO potential). By means of the variational approximation and\nnumerical analysis, it is found that both the 2D and 1D systems give rise to a\nsymmetry-breaking bifurcation (SBB) of the supercrtical type. Stability of\nsymmetric states and asymmetric ones, produced by the SBB, is analyzed through\nthe computation of eigenvalues for perturbation modes, and verified by direct\nsimulations. The asymmetric GSs are always stable, while the stability region\nfor vortices shrinks and eventually disappears with the increase of the\nlinear-coupling constant, $ \\kappa $. The SBB in the 2D system does not occur\nif $\\kappa $ is too large (at $\\kappa >\\kappa_{\\max }$); in that case, the\ntwo-component system behaves, essentially, as its single-component counterpart.\nIn the 1D system, both asymmetric and symmetric dipole modes feature an\nadditional oscillatory instability, unrelated to the symmetry breaking. This\ninstability occurs in several regions, which expand with the increase of\n$\\kappa $.",
        "positive": "Microscopic description of anisotropic low-density dipolar Bose gases in\n  two dimensions: A microscopic description of the zero energy two-body ground state and\nmany-body static properties of anisotropic homogeneous gases of bosonic dipoles\nin two dimensions at low densities is presented and discussed. By changing the\npolarization angle with respect to the plane, we study the impact of the\nanisotropy, present in the dipole--dipole interaction, on the energy per\nparticle, comparing the results with mean field predictions. We restrict the\nanalysis to the regime where the interaction is always repulsive, although the\nstrength of the repulsion depends on the orientation with respect to the\npolarization field. We present a series expansion of the solution of the zero\nenergy two-body problem which allows us to find the scattering length of the\ninteraction and to build a suitable Jastrow factor that we use as a trial wave\nfunction for both a variational and diffusion Monte Carlo simulation of the\ninfinite system. We find that the anisotropy has an almost negligible impact on\nthe ground state properties of the many-body system in the universal regime\nwhere the scattering length governs the physics of the system. We also show\nthat scaling in the gas parameter persists in the dipolar case up to values\nwhere other isotropic interactions with the same scattering length yield\ndifferent predictions."
    },
    {
        "anchor": "Orthogonality Catastrophe in Quantum Sticking: The probability that a particle will stick to a surface is fundamental to a\nvariety of processes in surface science, including catalysis, epitaxial growth,\nand corrosion. At ultralow energies, how particles scatter or stick to a\nsurface affects the performance of atomic clocks, matter-wave interferometers,\natom chips and other quantum information processing devices. In this energy\nregime, the sticking probability is influenced by a distinctly quantum\nmechanical effect: quantum reflection, a result of matter wave coherence,\nsuppresses the probability of finding the particle near the surface and reduces\nthe sticking probability. We find that another quantum effect can occur,\nfurther shaping the sticking probability: the orthogonality catastrophe, a\nresult of the change in the quantum ground state of the surface in the presence\nof a particle, can dramatically alter the probability for quantum sticking and\ncreate a superreflective surface at low energies.",
        "positive": "Topological order and equilibrium in a condensate of exciton-polaritons: We report the observation of the Berezinskii-Kosterlitz-Thouless transition\nfor a 2D gas of exciton-polaritons, and through the joint measurement of the\nfirst-order coherence both in space and time we bring compelling evidence of a\nthermodynamic equilibrium phase transition in an otherwise open\ndriven/dissipative system. This is made possible thanks to long polariton\nlifetimes in high-quality samples with small disorder and in a reservoir-free\nregion far away from the excitation spot, that allow topological ordering to\nprevail. The observed quasi-ordered phase, characteristic for an equilibrium 2D\nbosonic gas, with a decay of coherence in both spatial and temporal domains\nwith the same algebraic exponent, is reproduced with numerical solutions of\nstochastic dynamics, proving that the mechanism of pairing of the topological\ndefects (vortices) is responsible for the transition to the algebraic order.\nFinally, measurements in the weak-coupling regime confirm that polariton\ncondensates are fundamentally different from photon lasers and constitute\ngenuine quantum degenerate macroscopic states."
    },
    {
        "anchor": "Andreev-Bashkin effect in superfluid cold gases mixture: We study a mixture of two superfluids with density-density and\ncurrent-current (Andreev-Bashkin) interspecies interactions. The\nAndreev-Bashkin coupling gives rise to a dissipationless drag (or entrainment)\nbetween the two superfluids. Within the quantum hydrodynamics approximation, we\nstudy the relations between speeds of sound, susceptibilities and static\nstructure factors, in a generic model in which the density and spin dynamics\ndecouple. Due to translational invariance, the density channel does not feel\nthe drag. The spin channel, instead, does not satisfy the usual Bijl-Feynman\nrelation, since the f-sum rule is not exhausted by the spin phonons. The very\nsame effect on one dimensional Bose mixtures and their Luttinger liquid\ndescription is analysed within perturbation theory. Using diffusion quantum\nMonte Carlo simulations of a system of dipolar gases in a double layer\nconfiguration, we confirm the general results. Given the recent advances in\nmeasuring the counterflow instability, we also study the effect of the\nentrainment on the dynamical stability of a superfluid mixture with non-zero\nrelative velocity.",
        "positive": "Nonequilibrium dynamics of one-dimensional hard-core anyons following a\n  quench: Complete relaxation of one-body observables: We demonstrate the role of interactions in driving the relaxation of an\nisolated integrable quantum system following a sudden quench. We consider a\nfamily of integrable hard-core lattice anyon models that continuously\ninterpolates between noninteracting spinless fermions and strongly interacting\nhard-core bosons. A generalized Jordan-Wigner transformation maps the entire\nfamily to noninteracting fermions. We find that, aside from the singular\nfree-fermion limit, the entire single-particle density matrix and therefore all\none-body observables relax to the predictions of the generalized Gibbs ensemble\n(GGE). This demonstrates that, in the presence of interactions, correlations\nbetween particles in the many-body wave function provide the effective\ndissipation required to drive relaxation of all one-body observables to the\nGGE. This relaxation does not depend on translational invariance, or the\ntracing out of any spatial domain of the system."
    },
    {
        "anchor": "Supersolid phases of dipolar fermions in a two-dimensional-lattice\n  bilayer array: Supersolid phases as a result of a coexistence of superfluid and density\nordered checkerboard phases are predicted to appear in ultracold Fermi\nmolecules confined in a bilayer array of two-dimensional square optical\nlattices. We demonstrate the existence of these phases within the inhomogeneous\nmean-field approach. In particular, we show that tuning the interlayer\nseparation distance at a fixed value of the chemical potential produces\ndifferent fractions of superfluid, density ordered, and supersolid phases.",
        "positive": "Observation of ultracold atomic bubbles in orbital microgravity: Significant leaps in the understanding of quantum systems have been driven by\nthe exploration of geometry, topology, dimensionality, and interactions with\nultracold atomic ensembles. A system where atoms evolve while confined on an\nellipsoidal surface represents a heretofore unexplored geometry and topology.\nRealizing such an ultracold bubble system (potentially Bose-Einstein condensed)\nhas areas of interest including quantized-vortex flow respecting topological\nconstraints imposed by closed surfaces, new collective modes, and\nself-interference via free bubble expansion. Large ultracold bubbles, created\nby inflating smaller condensates, directly tie into Hubble-analog expansion\nphysics. Here, we report observations from the NASA Cold Atom Lab facility\naboard the International Space Station of bubbles of ultracold atoms created\nusing a radiofrequency-dressing protocol. We observe a variety of bubble\nconfigurations of differing sizes and initial temperature, and explore bubble\nthermodynamics, demonstrating significant cooling associated with inflation.\nAdditionally, we achieve partial coverings of bubble traps greater than 1 mm in\nsize with ultracold films of inferred few-$\\mu$m thickness, and we observe the\ndynamics of shell structures projected into free-evolving harmonic confinement.\nThe observations are part of the first generation of scientific measurements\nmade with ultracold atoms in space, exploiting the benefits of perpetual\nfree-fall to explore gravity-free evolution of quantum systems that are\nprohibitively difficult to create on Earth. This work points the way to\nexperiments focused on the nature of the Bose-Einstein condensed bubble, the\ncharacter of its excitations, and the role of topology in its evolution; it\nalso ushers in an era of orbital microgravity quantum-gas physics."
    },
    {
        "anchor": "Mobile impurity in a one-dimensional quantum gas: Exact diagonalization\n  in the Bethe Ansatz basis: We consider a mobile impurity particle injected into a one-dimensional\nquantum gas. The time evolution of the system strongly depends on whether the\nmass of the impurity and the masses of the host particles are equal or not. For\nequal masses, the model is Bethe Ansatz solvable, but for unequal masses, the\nmodel is no longer integrable and the Bethe Ansatz technique breaks down. We\nconstruct a controllable numerical method of computing the spectrum of the\nmodel with a finite number of host particles, based on exact diagonalization of\nthe Hamiltonian in the truncated basis of the Bethe Ansatz states. We\nillustrate our approach on a few-body system of 5+1 particles, and trace the\nevolution of the spectrum depending on the mass ratio of the impurity and the\nhost particles.",
        "positive": "Modulation stabilization of Bloch oscillations of two-component\n  Bose-Einstein condensates in optical lattices: We study the Bloch oscillations (BOs) of two-component Bose-Einstein\ncondensates (BECs) trapped in spin-dependent optical lattices. Based on the\nderived equations of motion of the wave packet in the basis of localized wave\nfunctions of the lattice sites, the damping effect induced by the\nintercomponent and intracomponent interactions to the BOs is explored\nanalytically and numerically. We also show that such damping of the BOs can be\nsuppressed entirely if all the atom-atom interactions are modulated\nsynchronously and harmonically in time with suitable frequency via the Feshbach\nresonance. When the intercomponent and the intracomponent interactions have\ninverse signs, we find that the long-living BOs and even the revival of the BOs\ncan be achieved via only statically modulating the configuration of optical\nlattices. The results provide a valuable guidance for achieving long-living BOs\nin the two-component BEC system by the Feshbach resonances and manipulating the\nconfiguration of the optical lattices."
    },
    {
        "anchor": "Mean-Field Analysis of Spinor Bosons in Optical Superlattices: We study the ground-state phase diagram of spinless and spin-1 bosons in\noptical superlattices using a Bose-Hubbard Hamiltonian that includes\nspin-dependent interactions. We decouple the unit cells of the superlattice via\na mean-field approach and take into account the dynamics within the unit cell\nexactly. The system supports Mott-insulating as well as superfluid phases. The\ntransitions between these phases are second-order for spinless bosons and\nsecond- or first-order for spin-1 bosons. Anti-ferromagnetic interactions\nenergetically penalize high-spin configurations and elongate all Mott lobes,\nespecially the ones corresponding to an even atom number on each lattice site.\nWe find that the quadratic Zeeman effect lifts the degeneracy between different\npolar superfluid phases leading to additional metastable phases and first-order\nphase transitions. Finally, we show that an energy offset between the two sites\nof the unit cell induces a staircase of single-atom tunneling resonances which\nsurprisingly survives well into the superfluid regime.",
        "positive": "Ramsey interferometry of non-Hermitian quantum impurities: We introduce a Ramsey pulse scheme which extracts the non-Hermitian\nHamiltonian associated to an arbitrary Lindblad dynamics. We propose a realted\nprotocol to measure via interferometry a generalised Loschmidt echo of a\ngeneric state evolving in time with the non-Hermitian Hamiltonian itself, and\nwe apply the scheme to a one-dimensional weakly interacting Bose gas coupled to\na stochastic atomic impurity. The Loschmidt echo is mapped into a functional\nintegral from which we calculate the long-time decohering dynamics at arbitrary\nimpurity strengths. For strong dissipation we uncover the phenomenology of a\nquantum many-body Zeno effect: corrections to the decoherence exponent\nresulting from the impurity self-energy becomes purely imaginary, in contrast\nto the regime of small dissipation where they instead enhance the decay of\nquantum coherences. Our results illustrate the prospects for experiments\nemploying Ramsey interferometry to study dissipative quantum impurities in\ncondensed matter and cold atoms systems."
    },
    {
        "anchor": "Fermionic transport in a homogeneous Hubbard model: Out-of-equilibrium\n  dynamics with ultracold atoms: Transport properties are among the defining characteristics of many important\nphases in condensed matter physics. In the presence of strong correlations they\nare difficult to predict even for model systems like the Hubbard model. In real\nmaterials they are in general obscured by additional complications including\nimpurities, lattice defects or multi-band effects. Ultracold atoms in contrast\noffer the possibility to study transport and out-of-equilibrium phenomena in a\nclean and well-controlled environment and can therefore act as a quantum\nsimulator for condensed matter systems. Here we studied the expansion of an\ninitially confined fermionic quantum gas in the lowest band of a homogeneous\noptical lattice. While we observe ballistic transport for non-interacting\natoms, even small interactions render the expansion almost bimodal with a\ndramatically reduced expansion velocity. The dynamics is independent of the\nsign of the interaction, revealing a novel, dynamic symmetry of the Hubbard\nmodel.",
        "positive": "Particle creation in the spin modes of a dynamically oscillating\n  two-component Bose-Einstein condensate: We investigate the parametric amplification of the zero-point fluctuations in\nthe spin modes of a two-component Bose-Einstein condensate, triggered by the\ndynamical evolution of the condensate density. We first make use of a\nThomas-Fermi approximation to develop a tractable theoretical model of the\nquantum dynamics of the Bogoliubov excitations in a harmonically trapped\ncondensate with a time-dependent trapping frequency. The predictions of this\nmodel are then compared to an ab-initio numerical study of the correlation\nfunctions of density and spin fluctuations for general spatially inhomogeneous\nconfigurations. Results are shown for the two cases of expanding and\noscillating condensates: while the quantum excitation of spin modes remains\nweak and relatively featureless in the case of an expanding condensate, clear\nand experimentally promising signatures of particle creation are anticipated\nfor the oscillating case under suitable resonance conditions between the\ndensity and the spin modes."
    },
    {
        "anchor": "Normal-Superfluid Phase Separation in Spin-Half Bosons at Finite\n  Temperature: For pseudospin-half bosons with inter-spin attraction and intra-spin\nrepulsion, normal phase and Bose condensed phase can coexist at finite\ntemperature. The homogeneous system is unstable against the spinodal\ndecomposition within a medium density interval, and consequently, a\nnormal-superfluid phase separation takes place. The isothermal\nequation-of-state shows a characteristic plateau in the P-V (pressure-volume)\ndiagram, which is reminiscent of a classical gas-liquid transition, although,\nunlike the latter, the coexistence lines never terminate at a critical point as\ntemperature increases. In a harmonic trap, the phase separation can be revealed\nby the density profile of the atomic cloud, which exhibits a sudden jump across\nthe phase boundary.",
        "positive": "Zero sound in a quantum gas of spin-3/2 atoms with multipole exchange\n  interaction: In the context of quantum gases, we obtain a many-body Hamiltonian for\nspin-3/2 atoms with general multipole (spin, quadrupole, and octupole) exchange\ninteraction by employing the apparatus of irreducible spherical tensor\noperators. This Hamiltonian implies the finite-range interaction, whereas, for\nzero-range (contact) potentials parameterized by the $s$-wave scattering\nlength, the multipole exchange interaction becomes irrelevant. Following the\nreduced description method for quantum systems, we derive the quantum kinetic\nequation for spin-3/2 atoms in a magnetic field and apply it to examine the\nhigh-frequency oscillations known as zero sound."
    },
    {
        "anchor": "Prescaling in a far-from-equilibrium Bose gas: Non-equilibrium conditions give rise to classes of universally evolving\nconfigurations of quantum-many body systems at non-thermal fixed points. While\nthe fixed point and thus full scaling in space and time is generically reached\nat very long evolution times, we propose that systems can show prescaling much\nearlier in time, in particular, on experimentally accessible time scales.\nDuring the prescaling evolution, some well-measurable properties of spatial\ncorrelations already scale with the universal exponents of the fixed point\nwhile others still show scaling violations. Prescaling is characterized by the\nevolution obeying conservation laws associated with the remaining symmetry\nwhich also defines the universality class of the asymptotically reached\nnon-thermal fixed point. Here we consider $N=3$ species of spatially uniform\nthree-dimensional Bose gases, with identical inter- and intra-species\ninteractions. During prescaling, the full $U(N)$ symmetry of the model is\nbroken to $U(N-1)$ while the conserved transport, reflecting explicit and\nemerging symmetries, leads to the buildup of rescaling quasicondensate\ndistributions.",
        "positive": "Tuning photon-mediated interactions in a multimode cavity: from\n  supersolid to insulating droplets hosting phononic excitations: Ultracold atoms trapped in laser-generated optical lattices serve as a\nversatile platform for quantum simulations. However, as these lattices are\ninfinitely stiff, they do not allow to emulate phonon degrees of freedom. This\nrestriction can be lifted in emerged optical lattices inside multimode\ncavities. Motivated by recent experimental progress in multimode cavity QED, we\npropose a scheme to implement and study supersolid and droplet states with\nphonon-like lattice excitations by coupling a Bose gas to many longitudinal\nmodes of a ring cavity. The interplay between contact collisional and\ntunable-range cavity-mediated interactions leads to a rich phase diagram, which\nincludes elastic supersolid as well as insulating droplet phases exhibiting\nroton-type mode softening for a continuous range of momenta across the\nsuperradiant phase transition. The non-trivial dynamic response of the system\nto local density perturbations further proves the existence of phonon-like\nmodes."
    },
    {
        "anchor": "Instability and Momentum Bifurcation of molecular BEC in Exotic\n  Dispersion with Shaken Lattice: We place a molecular Bose-Einstein condensate in a 1D shaken lattice with a\nFloquet-engineered dispersion, and observe the dynamics in both position and\nmomentum space. At the initial condition of zero momentum, our engineered\ndispersion is inverted, and therefore unstable. We observe that the condensate\nis destabilized by the lattice shaking as expected, but rather than decaying\nincoherently or producing jets, as in other unstable condensates, under our\nconditions the condensate bifurcates into two portions in momentum space, with\neach portion subsequently following semi-classical trajectories that suffer\nminimal spreading in momentum space as they evolve. We can model the evolution\nwith a Gross-Pitaevskii equation, which suggests the initial bifurcation is\nfacilitate by a nearly linear \"inverted V\"-shaped dispersion at the zone\ncenter, while the lack of spreading in momentum space is facilitated by\ninteractions, as in a soliton. We propose that this relatively clean\nbifurcation in momentum space has applications for counter-diabatic preparation\nof exotic ground states in many-body quantum simulation schemes.",
        "positive": "Periodic dynamics of population-imbalanced fermionic condensates in\n  optical lattices: We investigate the dynamics of a population-imbalanced two-species fermionic\nsystem trapped in an optical lattice. The paired fermions here can form bosonic\nmolecules via Feshbach coupling in the presence of an external magnetic field.\nIt is shown that the natural fluctuations of the condensate fraction are\nperiodic beyond a threshold Feshbach detuning; and below this threshold value,\nthe condensate fraction shows no oscillation at all. The oscillation frequency\nvs. detuning curve is linear in nature. The slope and intercept of this line\nare shown to carry important information about the amount of imbalance present\nin the system, and the momentum space structure of the exotic phases."
    },
    {
        "anchor": "Collective Excitations, Nambu-Goldstone Modes and Instability of\n  Inhomogeneous Polariton Condensates: We study non-equilibrium microcavity-polariton condensates (MPCs) in a\nharmonic potential trap theoretically. We calculate and analyze the steady\nstate, collective-excitation modes and instability of MPCs. Within excitation\nmodes, there exist Nambu-Goldstone modes that can reveal the pattern of the\nspontaneous symmetry breaking of MPCs. Bifurcation of the stable and unstable\nmodes is identified in terms of the pumping power and spot size. The unstable\nmechanism associated with the inward supercurrent flow is characterized by the\nexistence of a supersonic region within the condensate.",
        "positive": "Experimental reconstruction of the Berry curvature in a topological\n  Bloch band: Topological properties lie at the heart of many fascinating phenomena in\nsolid state systems such as quantum Hall systems or Chern insulators. The\ntopology can be captured by the distribution of Berry curvature, which\ndescribes the geometry of the eigenstates across the Brillouin zone. Employing\nfermionic ultracold atoms in a hexagonal optical lattice, we generate\ntopological bands using resonant driving and show a full momentum-resolved\nmeasurement of the ensuing Berry curvature. Our results pave the way to explore\nintriguing phases of matter with interactions in topological band structures."
    },
    {
        "anchor": "Several fermions strongly interacting with a heavy mobile impurity in a\n  one-dimensional harmonic trap: We propose a numerically exact method for a mixture with a single impurity\nimmersed in several majority fermions, confined in a harmonic potential. We\nseparate one of the degrees of freedom through an appropriately tailored\ncanonical transformation and perform exact diagonalization on the simplified\nHamiltonian. This method is especially effective for a heavy impurity, where it\noutmatches the typical exact diagonalization approach. We used our method to\ncalculate energy and density profiles of the first few eigenstates for the\nmixture with up to ten majority fermions.",
        "positive": "Comment on \"Bose-Einstein condensation with a finite number of particles\n  in a power-law trap\": In Jaouadi et al. [Phys. Rev. A 83, 023616 (2011)] the authors derive an\nanalytical finite-size expansion for the Bose-Einstein condensation critical\ntemperature of an ideal Bose gas in a generic power-law trap. In the case of a\nharmonic trap, this expansion adds higher order terms to the well- known first\norder correction. We point out a delicate point in connection to these results,\nshowing that the claims of Jaouadi et al. should be treated with caution. In\nparticular, for a harmonic trap, the given expansion yields results that,\ndepending on what is considered to be the critical temperature of the finite\nsystem, do not generally improve on the established first order correction. For\nsome non-harmonic traps, the results differ at first order from other results\nin the literature."
    },
    {
        "anchor": "Dynamics of a trapped ion in a quantum gas: effects of particle\n  statistics: We study the quantum dynamics of an ion confined in a radiofrequency trap in\ninteraction with either a Bose or spin-polarized Fermi gas. To this end, we\nderive quantum optical master equations in the limit of weak coupling and the\nLamb-Dicke approximations. For the bosonic bath, we also include the so-called\n\"Lamb-shift\" correction to the ion trap due to the coupling to the quantum gas\nas well as the extended Fr\\\"ohlich interaction within the Bogolyubov\napproximation that have been not considered in previous studies. We calculate\nthe ion kinetic energy for various atom-ion scattering lengths as well as gas\ntemperatures by considering the intrinsic micromotion and we analyse the\ndamping of the ion motion in the gas as a function of the gas temperature. We\nfind that the ion's dynamics depends on the quantum statistics of the gas and\nthat a fermionic bath enables to attain lower ionic energies.",
        "positive": "Comment on \"Excitation Spectrum and Superfluid Gap of an Ultracold Fermi\n  Gas\": We present simple arguments suggesting that H. Biss et al [PRL 128, 100401\n(2022)] did not measure with the required accuracy the low-wavenumber curvature\nof the acoustic excitation branch of the ground-state unitary Fermi gas. This\ndifficult-to-calculate quantity is crucial for the relaxation dynamics of the\ngas at low temperature."
    },
    {
        "anchor": "Studying the low-entropy Mott transition of bosons in a\n  three-dimensional optical lattice by measuring the full momentum-space\n  density: We report on a combined experimental and theoretical study of the low-entropy\nMott transition for interacting bosons trapped in a three-dimensional (3D)\ncubic lattice -- namely, the interaction-induced superfluid-to-normal phase\ntransition in the vicinity of the zero-temperature Mott transition. Our\nanalysis relies on the measurement of the 3D momentum distribution, which\nallows us to extract the momentum-space density $\\rho({\\bf k}={\\bf 0})$ at the\ncenter of the Brillouin zone. Upon varying the ratio between the interaction\n$U$ and the tunnelling energy $J$ across the superfluid transition, we observe\nthat $\\rho({\\bf k}={\\bf 0})$ exhibits a sharp transition at a value of $U/J$\nconsistent with the bulk prediction from quantum Monte Carlo. In addition, the\nvariation of $\\rho({\\bf k}={\\bf 0})$ with $U/J$ exhibits a critical behavior\nconsistent with the expected 3D XY universality class. Our results show that\nthe tomographic reconstruction of the momentum distribution of ultracold bosons\ncan reveal traits of the critical behavior of the superfluid transition even in\nan inhomogeneous trapped system.",
        "positive": "Stability of the superfluid state in a disordered 1D ultracold fermionic\n  gas: We study a 1D Fermi gas with attractive short range-interactions in a\ndisordered potential by the density matrix renormalization group (DMRG)\ntechnique. This setting can be implemented experimentally by using cold atom\ntechniques. We identify a region of parameters for which disorder enhances the\nsuperfluid state. As disorder is further increased, global superfluidity\neventually breaks down. However this transition occurs before the transition to\nthe insulator state takes place. This suggests the existence of an intermediate\nmetallic `pseudogap' phase characterized by strong pairing but no quasi\nlong-range order."
    },
    {
        "anchor": "Lifetime of the Bose Gas with Resonant Interactions: We study the lifetime of a Bose gas at and around unitarity using a Feshbach\nresonance in lithium~7. At unitarity, we measure the temperature dependence of\nthe three-body decay coefficient $L_{3}$. Our data follow a $L_3 {=}\n\\lambda_{3} / T^{2}$ law with $\\lambda_{3} = 2.5(3)_{stat}_(6)_{sys} 10^{-20}\n(\\mu K)^2 cm^6 s^{-1}$ and are in good agreement with our analytical result\nbased on the zero-range theory. Varying the scattering length $a$ at fixed\ntemperature, we investigate the crossover between the finite-temperature\nunitary region and the previously studied regime where $|a|$ is smaller than\nthe thermal wavelength. We find that $L_{3}$ is continuous across resonance,\nand over the whole $a {<} 0$ range our data quantitatively agree with our\ncalculation.",
        "positive": "Quantum critical transport in the unitary Fermi gas: The thermodynamic and transport properties of the unitary Fermi gas at finite\ntemperature T are governed by a quantum critical point at T=0 and zero density.\nWe compute the universal shear viscosity to entropy ratio \\eta/s in the\nhigh-temperature quantum critical regime T>>|\\mu| and find that this strongly\ncoupled quantum fluid comes close to perfect fluidity \\eta/s=\\hbar/(4\\pi k_B).\nUsing a controlled large-N expansion we show that already at the first\nnon-trivial order the equation of state and the Tan contact density C agree\nwell with the most recent experimental measurements and theoretical\nLuttinger-Ward and Bold Diagrammatic Monte Carlo calculations."
    },
    {
        "anchor": "On Berezinskii-Kosterlitz-Thouless Phase Transition in Quasi-One\n  Dimensional Bose-Einstein Condensate: We show that quasi-one dimensional Bose-Einstein condensate under suitable\nconditions can exhibit a Berezinskii-Kosterlitz-Thouless phase transition. The\nrole played by quantized vortices in two dimensional case, is played in this\ncase by dark solitons. We find that the critical temperature for this\ntransition lies in nano Kelvin range and below, for a wide range of\nexperimentally accessible parameters. It is seen that the high temperature\n(disordered) phase differs from low temperature (ordered) phase in terms of\nphase coherence, which can be used as an experimental signature for observing\nthis transition.",
        "positive": "Fermi polaron in atom-ion hybrid systems: Charged quasiparticles dressed by the low excitations of an electron gas,\nconstitute one of the fundamental pillars for understanding quantum many-body\neffects in some materials. Quantum simulation of quasiparticles arising from\natom-ion hybrid systems may shed light on solid-state uncharted regimes. Here\nwe investigate the ionic Fermi polaron consisting of a charged impurity\ninteracting with a polarized Fermi bath. Employing state-of-the-art quantum\nMonte Carlo techniques tailored for strongly correlated systems, we\ncharacterize the charged quasiparticle by computing the energy spectrum,\nquasiparticle residue, and effective mass, as well as the structural properties\nof the system. Our findings in the weak coupling regime agree with field-theory\npredictions within the ladder approximation. However, stark deviations emerge\nin the strongly interacting regime attributed to the vastly large density\ninhomogeneity around the ion, resulting in strong correlations for distances on\nthe order of the atom-ion potential range. Moreover, we find a smooth\npolaron-molecule transition for strong coupling, in contrast with the neutral\ncase, where the transition smoothens only for finite temperature and finite\nimpurity density. This study may provide valuable insights into alternative\nsolid-state systems such as Fermi excitons polarons in atomically thin\nsemiconductors beyond the short-range limit."
    },
    {
        "anchor": "Floquet engineering spectral statistics in the Bose-Hubbard model: We study the spectral statistics of a one-dimensional Bose-Hubbard model\nsubjected to kinetic driving; a form of Floquet engineering where the kinetic\nenergy is periodically driven in time with a zero time-average. As the\namplitude of the driving is increased, the ground state of the resulting\nflat-band system passes from the Mott insulator regime to an exotic superfluid.\nWe show that this transition is associated with a change in the system's\nspectral statistics from Poisson to GOE-type. Remarkably, and unlike in the\nconventional Bose-Hubbard model, which we use as a benchmark, the details of\nthe GOE statistics are sensitive to the parity of both the particle number and\nthe lattice sites. We show how this effect arises from a hidden symmetry of the\nHamiltonian produced by this form of Floquet driving.",
        "positive": "Hartree-Fock-Bogoliubov Model and Simulation of Attractive and Repulsive\n  Bose-Einstein Condensates: We describe a model of dynamic Bose-Einstein condensates near a Feshbach\nresonance that is computationally feasible under assumptions of spherical or\ncylindrical symmetry. Simulations in spherical symmetry approximate the\nexperimentally measured time to collapse of an unstably attractive condensate\nonly when the molecular binding energy in the model is correct, demonstrating\nthat the quantum fluctuations and atom-molecule pairing included in the model\nare the dominant mechanisms during collapse. Simulations of condensates with\nrepulsive interactions find some quantitative disagreement, suggesting that\npairing and quantum fluctuations are not the only significant factors for\ncondensate loss or burst formation. Inclusion of three-body recombination was\nfound to be inconsequential in all of our simulations, though we do not\nconsider recent experiments [1] conducted at higher densities."
    },
    {
        "anchor": "Local observation of pair-condensation in a Fermi gas at unitarity: We present measurements of the local (homogeneous) density-density response\nfunction of a Fermi gas at unitarity using spatially resolved Bragg\nspectroscopy. By analyzing the Bragg response across one axis of the cloud we\nextract the response function for a uniform gas which shows a clear signature\nof the Bose-Einstein condensation of pairs of fermions when the local\ntemperature drops below the superfluid transition temperature. The method we\nuse for local measurement generalizes a scheme for obtaining the local pressure\nin a harmonically trapped cloud from the line density and can be adapted to\nprovide any homogeneous parameter satisfying the local density approximation.",
        "positive": "Symplectic ferromagnetism and phase transitions in multi-component\n  fermionic systems: In this paper, we study the itinerant ferromagnetic phase in multi-component\nfermionic systems with symplectic (Sp(4), or isomorphically SO(5)) symmetry.\nTwo different microscopic models have been considered and an effective field\ntheory has been proposed to study the critical behavior of the\nnonmagnetism-magnetism phase transition. It has been shown that such systems\nexhibit intriguing ferromagnetism and critical behavior that different from\nthose in spin-$\\frac 12$ fermionic systems, or in high-spin systems with SU(N)\nsymmetry. An extension of our results to higher spin systems with Sp(2N)\nsymmetry has also been discussed."
    },
    {
        "anchor": "State diagram for continuous quasi-one dimensional systems in optical\n  lattices: We studied the appearance of Mott insulator domains of hard sphere bosons on\nquasi one-dimensional optical lattices when an harmonic trap was superimposed\nalong the main axis of the system. Instead of the standard approximation\nrepresented by the Bose-Hubbard model, we described those arrangements by\ncontinuous Hamiltonians that depended on the same parameters as the\nexperimental setups. We found that for a given trap the optical potential\ndepth, $V_0$, needed to create a single connected Mott domain decreased with\nthe number of atoms loaded on the lattice. If the confinement was large enough,\nit reached a minimum when, in absence of any optical lattice, the atom density\nat the center of the trap was the equivalent of one particle per optical well.\nFor larger densities, the creation of that single domain proceeded via an\nintermediate shell structure in which Mott domains alternated with superfluid\nones.",
        "positive": "Spinor Bose-Einstein Condensates of Rotating Polar Molecules: We propose a scheme to realize a pseudospin-$1/2$ model of the\n$^{1}\\Sigma(v=0)$ bialkali polar molecules with the spin states corresponding\nto two sublevels of the first excited rotational level. We show that the\neffective dipole-dipole interaction between two spin-$1/2$ molecules couples\nthe rotational and orbital angular momenta and is highly tunable via a\nmicrowave field. We also investigate the ground state properties of a\nspin-$1/2$ molecular condensate. A variety of nontrivial quantum phases,\nincluding the doubly-quantized vortex states, are discovered. Our scheme can\nalso be used to create spin-$1$ model of polar molecules. Thus, we show that\nthe ultracold gases of bialkali polar molecules provide a unique platform for\nstudying the spinor condensates of rotating molecules."
    },
    {
        "anchor": "A Thouless Quantum Pump with Ultracold Bosonic Atoms in an Optical\n  Superlattice: More than 30 years ago, Thouless introduced the concept of a topological\ncharge pump that would enable the robust transport of charge through an\nadiabatic cyclic evolution of the underlying Hamiltonian. In contrast to\nclassical transport, the transported charge was shown to be quantized and\npurely determined by the topology of the pump cycle, making it robust to\nperturbations. On a fundamental level, the quantized charge transport can be\nconnected to a topological invariant, the Chern number, first introduced in the\ncontext of the integer quantum Hall effect. A Thouless quantum pump may\ntherefore be regarded as a 'dynamical' version of the integer quantum Hall\neffect. Here, we report on the realization of such a topological charge pump\nusing ultracold bosonic atoms that form a Mott insulator in a dynamically\ncontrolled optical superlattice potential. By taking in-situ images of the atom\ncloud, we observe a quantized deflection per pump cycle. We reveal the genuine\nquantum nature of the pump by showing that, in contrast to ground state\nparticles, a counterintuitive reversed deflection occurs when particles are\nprepared in the first excited band. Furthermore, we were able to directly\ndemonstrate that the system undergoes a controlled topological phase transition\nin higher bands when tuning the superlattice parameters.",
        "positive": "Spontaneous symmetry breaking of Bose-Fermi mixtures in double-well\n  potentials: We study the spontaneous symmetry breaking (SSB) of a superfluid Bose-Fermi\n(BF) mixture in a double-well potential (DWP). The mixture is described by the\nGross-Pitaevskii equation (GPE) for the bosons, coupled to an equation for the\norder parameter of the Fermi superfluid, which is derived from the respective\ndensity functional in the unitarity limit (a similar model applies to the BCS\nregime too). Straightforward SSB in the degenerate Fermi gas loaded into a DWP\nis impossible, as it requires an attractive self-interaction, while the\nintrinsic nonlinearity in the Fermi gas is repulsive. Nonetheless, we\ndemonstrate that the symmetry breaking is possible in the mixture with\nattraction between fermions and bosons, like 40K and 87Rb. Numerical results\nare represented by dependencies of asymmetry parameters for both components on\nparticle numbers of the mixture, N_F and N_B, and by phase diagrams in the\n(N_F,N_B) plane, which displays regions of symmetric and asymmetric ground\nstates. The dynamical picture of the SSB, induced by a gradual transformation\nof the single-well potential into the DWP, is reported too. An analytical\napproximation is proposed for the case when GPE for the boson wave function may\nbe treated by means of the Thomas-Fermi (TF) approximation. Under a special\nlinear relation between N_F and N_B, the TF approximation allows us to reduce\nthe model to a single equation for the fermionic function, which includes\ncompeting repulsive and attractive nonlinear terms. The latter one directly\ndisplays the mechanism of the generation of the effective attraction in the\nFermi superfluid, mediated by the bosonic component of the mixture."
    },
    {
        "anchor": "Fermion Pairing across a Dipolar Interaction Induced Resonance: It is known from the solution of the two-body problem that an anisotropic\ndipolar interaction can give rise to s-wave scattering resonances, which are\nnamed as dipolar interaction induced resonaces (DIIR). In this letter, we study\nzero-temperature many-body physics of a two-component Fermi gas across a DIIR.\nIn the low-density regime, it is very striking that the resulting pairing order\nparameter is a nearly isotropic singlet pairing and the physics can be well\ndescribed by an s-wave resonant interaction potential with finite range\ncorrections, despite of the anisotropic nature of dipolar interaction. The\npairing energy is as strong as a unitary Fermi gas nearby a magnetic Feshbach\nresonance. In the high density regime, the anisotropic effect plays an\nimportant role. We find phase transitions from singlet pairing to a state with\nmixed singlet and triplet pairing, and then from mixed pairing to pure triplet\npairing. The state with mixed pairing spontaneously breaks the time-reversal\nsymmetry.",
        "positive": "Symmetry-broken momentum distributions induced by matter-wave\n  diffraction during time-of-flight expansion of ultracold atoms: We study several effects which lead to symmetry-broken momentum distributions\nof quantum gases released from optical lattices. In particular, we demonstrate\nthat interaction within the first milliseconds of the time-of-flight expansion\ncan strongly alter the measurement of the initial atomic momentum distribution.\nFor bosonic mixtures in state-dependent lattices, inter-species scattering\nprocesses lead to a symmetry breaking in momentum space. The underlying\nmechanism is identified to be diffraction of the matter wave from the total\ndensity lattice, which gives rise to a time-dependent interaction potential.\nOur findings are of fundamental relevance for the interpretation of\ntime-of-flight measurements and for the study of exotic quantum phases such as\nthe twisted superfluid. Beyond that, the observed matter-wave diffraction can\nalso be used as an interferometric probe. In addition, we report on diffraction\nfrom the state-dependent standing light field, which leads to the same\nsymmetry-broken momentum distributions, even for single component condensates."
    },
    {
        "anchor": "Phase diagram and multicritical behaviors of mixtures of 3D bosonic\n  gases: We investigate the Bose-Einstein condensation patterns, the critical and\nmulticritical behaviors of three-dimensional mixtures of bosonic gases with\nshort-range density-density interactions. These systems have a global U(1)+U(1)\nsymmetry, as the system Hamiltonian is invariant under independent U(1)\ntransformations acting on each species. In particular, we consider the\nthree-dimensional Bose-Hubbard model for two lattice bosonic gases coupled by\nan on-site inter-species density-density interaction. We study the phase\ndiagram and the critical behaviors along the transition lines characterized by\nthe Bose-Einstein condensation of one or both species. We present mean-field\ncalculations and numerical finite-size scaling analyses of quantum Monte Carlo\ndata. We also consider multicritical points, close to which it is possible to\nobserve the condensation of both gas components. We determine the possible\nmulticritical behaviors by using field-theoretical perturbative methods. We\nconsider the U(1)+U(1)-symmetric Landau-Ginzburg-Wilson Phi4 theory and\ndetermine the corresponding stable fixed points of the renormalization-group\nflow. The analysis predicts that, in all cases, the multicritical behavior is\nanalogous to the one that would be observed in systems of two identical gases,\nwith an additional Z_2 exchange symmetry.",
        "positive": "Atomic soliton transmission and induced collapse in scattering from a\n  narrow barrier: We report systematic numerical simulations of the collision of a bright\nmatter-wave soliton made of Bose-condensed alkali-metal atoms through a narrow\npotential barrier by using the three-dimensional Gross-Pitaevskii equation. In\nthis way, we determine how the transmission coefficient depends on the soliton\nimpact velocity and the barrier height. Quite remarkably, we also obtain the\nregions of parameters where there is the collapse of the bright soliton induced\nby the collision. We compare these three-dimensional results with the ones\nobtained by three different one-dimensional nonlinear Schr\\\"odinger equations.\nWe find that a specifically modified nonpolynomial Schr\\\"odinger equation is\nable to accurately assess the transmission coefficient even in a region in\nwhich the usual nonpolynomial Schr\\\"odinger equation does collapse. In\nparticular, this simplified but very effective one-dimensional model takes into\naccount the transverse width dynamics of the soliton with an ordinary\ndifferential equation coupled to the partial differential equation of the axial\nwave function of the Bose-Einstein condensate."
    },
    {
        "anchor": "Leggett mode in a two-component Fermi gas with dipolar interactions: We develop an effective field theory to understand collective modes of a\nthree-dimensional two-component Fermi superfluid with dipolar inter-particle\ninteractions, which are modeled by an idealized separable potential. We first\nexamine the phase transition of the system at zero temperature, as the\nfermionic superfluidity is known to be characterized by two competing order\nparameters. We find that for strong interactions there exists a regime where\nthe two order parameters are out-of-phase and coupled, giving rise to an\nundamped massive Leggett mode. This is in addition to the well-known gapless\nphonon mode. We show that the Leggett mode can be seen in the spectral function\nof the in-medium Cooper pairs, and in principle could be measured through Bragg\nspectroscopy.",
        "positive": "Spin-glass-like behavior in the spin turbulence of spinor Bose-Einstein\n  condensates: We study numerically the spin turbulence in spin-1 ferromagnetic spinor\nBose-Einstein condensates (BECs). Spin turbulence (ST) is characterized by a\n-7/3 power law in the spectrum of the spin-dependent interaction energy. The\ndirection of the spin density vector is spatially disordered but temporally\nfrozen in ST, showing some analogy with the spin glass state. Thus, we\nintroduce the order parameter of spin glass into ST in spinor BECs. When ST\ndevelops through some instability, the order parameter grows with a -7/3 power\nlaw, thus succeeding in describing ST well."
    },
    {
        "anchor": "Fluctuation assisted collapses of Bose-Einstein condensates: We study the collapse dynamics of a Bose-Einstein condensate subjected to a\nsudden change of the scattering length to a negative value by adopting the\nself-consistent Gaussian state theory for mixed states. Compared to the\nGross-Pitaevskii and the Hartree-Fock-Bogoliubov approaches, both fluctuations\nand three-body loss are properly treated in our theory. We find a new type of\ncollapse assisted by fluctuations which amplify the attractive interaction\nbetween atoms. Moreover, the calculation of the fluctuated atoms, the entropy,\nand the second-order correlation function showed that the collapsed gas was\nsignificantly deviated from a pure state.",
        "positive": "Condensate fragmentation as a sensitive measure of the quantum many-body\n  behavior of bosons with long-range interactions: The occupation of more than one single-particle state and hence the emergence\nof fragmentation is a many-body phenomenon universal to systems of spatially\nconfined interacting bosons. In the present study, we investigate the effect of\nthe range of the interparticle interactions on the fragmentation degree of one-\nand two-dimensional systems. We solve the full many-body Schr\\\"odinger equation\nof the system using the recursive implementation of the multiconfigurational\ntime-dependent Hartree for bosons method, R-MCTDHB. The dependence of the\ndegree of fragmentation on dimensionality, particle number, areal or line\ndensity and interaction strength is assessed. It is found that for contact\ninteractions, the fragmentation is essentially density independent in two\ndimensions. However, fragmentation increasingly depends on density the more\nlong-ranged the interactions become. The degree of fragmentation is increasing,\nkeeping the particle number $N$ fixed, when the density is decreasing as\nexpected in one spatial dimension. We demonstrate that this remains,\nnontrivially, true also for long-range interactions in two spatial dimensions.\nWe, finally, find that within our fully self-consistent approach, the\nfragmentation degree, to a good approximation, decreases universally as\n$N^{-1/2}$ when only $N$ is varied."
    },
    {
        "anchor": "Dynamically observing the spectra of quantum droplets in optical lattice: Optical lattice plays an important role on stability and dynamics of quantum\ndroplets. In this letter, we investigate the Bogoliubov excitation spectrum of\nquantum droplets in optical lattice in the thermodynamic limit. We classify the\ncollective excitations as synchronous modes, Bloch phononic modes, and\nsite-density imbalanced modes. For synchronous modes, we measure the dipole\noscillation frequencies by quench dynamics with a sudden shift of the optical\nlattice, and the breathing frequencies by Floquet dynamics with a periodic\nchange of the lattice depth. Bloch phononic modes are observable from the\nLandau critical velocity of the droplets. We further discuss the instability\ninduced by the site-dependent density fluctuations, and calculate the critical\nfilling of atoms where the growth of lattice vacancy breaks down the\ntranslational symmetry of the system. This work makes essential steps towards\nmeasuring the excitation spectrum and understanding the superfluid nature of\nquantum droplets in optical lattice.",
        "positive": "Evolution of Goldstone mode in binary condensate mixtures: We show that the third Goldstone mode in the two-species condensate mixtures,\nwhich emerges at phase-separation, gets hardened when the confining potentials\nhave separated trap centers. The {\\em sandwich} type condensate density\nprofiles, in this case, acquire a {\\em side-by-side} density profile\nconfiguration. We use Hartree-Fock-Bogoliubov theory with Popov approximation\nto examine the mode evolution and density profiles for these phase transitions\nat $T=0$."
    },
    {
        "anchor": "Vortex Mass in a Superfluid: We consider the inertial mass of a vortex in a superfluid. We obtain a vortex\nmass that is well defined and is determined microscopically and\nself-consistently by the elementary excitation energy of the kelvon\nquasiparticle localised within the vortex core. The obtained result for the\nvortex mass is found to be consistent with experimental observations on\nsuperfluid quantum gases and vortex rings in water. We propose a method to\nmeasure the inertial rest mass and Berry phase of a vortex in superfluid Bose\nand Fermi gases.",
        "positive": "Bosonic Analogs of Fractional Quantum Hall State in the Vicinity of Mott\n  States: In the present paper, the Bose-Hubbard model (BHM) with the nearest-neighbor\n(NN) repulsions is studied from the view point of possible bosonic analogs of\nthe fractional quantum Hall (FQH) state in the vicinity of the Mott insulator\n(MI). First, by means of the Gutzwiller approximation, we obtain the phase\ndiagram of the BHM in a magnetic field. Then, we introduce an effective\nHamiltonian describing excess particles on a MI and calculate the vortex\ndensity, momentum distribution and the energy gap. These calculations indicate\nthat the vortex solid forms for small NN repulsions, but a homogeneous\nfeatureless `Bose-metal' takes the place of it as the NN repulsion increases.\nWe consider particular filling factors at which the bosonic FQH state is\nexpected to form. Chern-Simons (CS) gauge theory to the excess particle is\nintroduced, and a modified Gutzwiller wave function, which describes bosons\nwith attached flux quanta, is introduced. The energy of the excess particles in\nthe bosonic FQH state is calculated using that wave function, and it is\ncompared with the energy of the vortex solid and Bose-metal. We found that the\nenergy of the bosonic FQH state is lower than that of the Bose-metal and\ncomparable with the vortex solid. Finally, we clarify the condition that the\ncomposite fermion appears by using CS theory on the lattice that we previously\nproposed for studying the electron FQH effect."
    },
    {
        "anchor": "Discrete time crystals enforced by Floquet-Bloch scars: We analytically identify a new class of quantum scars protected by\nspatiotemporal translation symmetries, dubbed Floquet-Bloch scars. They\ndistinguish from previous (quasi-)static scars by a rigid spectral pairing only\npossible in Floquet systems, where strong interaction and drivings equalize the\nquasienergy corrections to all scars and maintain their spectral spacings\nagainst generic bilinear perturbations. Scars then enforce the spatial\nlocalization and rigid discrete time crystal (DTC) oscillations as verified\nnumerically in a trimerized kagome lattice model relevant to recent cold atom\nexperiments. Our analytical solutions offer a potential scheme to understand\nthe mechanisms for more generic translation-invariant DTCs.",
        "positive": "Superfluid state in the periodic Anderson model with attractive\n  interactions: We investigate the periodic Anderson model with attractive interactions by\nmeans of dynamical mean-field theory (DMFT). Using a continuous-time quantum\nMonte Carlo impurity solver, we study the competition between the superfluid\nstate and the paramagnetic Kondo insulating state, and determine the phase\ndiagram. At the chemical potential-induced phase transition from the Kondo\ninsulating state to the superfluid state, a low-energy peak characteristic of\nthe superfluid state appears inside the hybridization gap. We also address the\neffect of the confining potential in optical lattice systems by means of\nreal-space DMFT calculations."
    },
    {
        "anchor": "One- and two-axis squeezing via laser coupling in an atomic\n  Fermi-Hubbard model: We study a production of spin-squeezed states with ultra-cold atomic fermions\ndescribed by the Fermi-Hubbard model in the Mott insulating phase. We show\nactivation of two twisting mechanisms by a position-dependent laser coupling\nbetween internal degrees of freedom of atoms. A single laser coupling simulates\nthe one-axis twisting model with the orientation of the twisting axis\ndetermined by the coupling phase. Adding a second laser beam with a properly\nchosen phase paves the way to simulate the two-axis counter-twisting model,\nenabling to approach the Heisenberg-limited level of squeezing.",
        "positive": "Casimir forces for the ideal Bose gas in anisotropic optical lattices:\n  the effect of alternating sign upon varying dimensionality: We analyze the thermodynamic Casimir effect occurring in a gas of\nnon-interacting bosons confined by two parallel walls with a strongly\nanisotropic dispersion inherited from an underlying lattice. In the direction\nperpendicular to the confining walls the standard quadratic dispersion is\nreplaced by the term $|{\\bf p}|^{\\alpha}$ with $\\alpha \\geq 2$ treated as a\nparameter. We derive a closed, analytical expression for the Casimir force\ndepending on the dimensionality $d$ and the exponent $\\alpha$, and analyze it\nfor thermodynamic states in which the Bose-Einstein condensate is present. For\n$\\alpha\\in\\{4,6,8,\\dots\\}$ the exponent governing the decay of the Casimir\nforce with increasing distance between the walls becomes modified and the\nCasimir amplitude $\\Delta_{\\alpha}(d)$ exhibits oscillations of sign as a\nfunction of $d$. Otherwise we find that $\\Delta_{\\alpha}(d)$ features\nsingularities when viewed as a function of $d$ and $\\alpha$. Recovering the\nknown previous results for the isotropic limit $\\alpha=2$ turns out to occur\nvia a cancellation of singular terms."
    },
    {
        "anchor": "Exact results on the two-particle Green's function of a Bose-Einstein\n  condensate: Starting from the Dyson-Beliaev and generalized Gross-Pitaevskii equations\nwith an extra nonlocal potential, we derive an exact expression of the\ntwo-particle Green's function K for an interacting Bose-Einstein condensate in\nterms of unambiguously defined self-energies and vertices. The formula can be a\nconvenient basis for approximate calculations of K. It also tells us that poles\nof K are not shared with (i.e. shifted from) those of the single-particle\nGreen's function, contrary to the conclusion of previous studies.",
        "positive": "Quantum walks of interacting Mott insulator defects with three-body\n  interactions: Quantum walks of interacting particles may display non-trivial features due\nto the interplay between the statistical nature and the many-body interactions\nassociated to them. We analyze the quantum walk of interacting defects on top\nof an uniform bosonic Mott insulator at unit filling in an one dimensional\ngraph. While the quantum walk of single particle defect shows trivial features,\nthe case of two particles exhibits interesting phenomenon of quantum walk\nreversal as a function of additional onsite three-body attractive interactions.\nIn the absence of the three-body interaction a quantum walk of pairs of\nparticles is obtained and as the strength of the three-body interaction becomes\nmore and more attractive, the independent particle behavior in quantum walk\nappears. Interestingly, further increase in the three-body interaction leads to\nthe re-appearance of the quantum walk associated to a pair of particles. This\nquantum-walk reversal phenomenon is studied using the real-space density\nevolution, Bloch oscillation as well as two-particle correlation functions."
    },
    {
        "anchor": "A Review of Wave Packet Molecular Dynamics: Warm dense matter systems created in the laboratory are highly dynamical. In\nsuch cases electron dynamics is often needed to accurately simulate the\nevolution and properties of the system. Large systems force one to make simple\napproximations enabling computationally feasibility. Wave packet molecular\ndynamics (WPMD) provides a simple framework for simulating time-dependent\nquantum plasmas. Here, this method is reviewed. The different variants of WPMD\nare shown and compared and their validity is discussed.",
        "positive": "Recombination in the universal four-fermion system: In the systems of spin $\\frac12$ fermions with resonant $S$-wave interactions\nsupporting only weakly bound dimers the antisymmetry forbids recombination of\nthree (or more) fermions at zero energy. However, the fermion-fermion-dimer\nrecombination is only partially suppressed. It is studied in the framework of\nmomentum-space integral equations for the four-particle transition operators.\nIn the vicinity of the unitary limit the fermion-fermion-dimer recombination\nrate, rescaled to build dimensionless quantity, is found to be linear in the\neffective range parameter, enabling a simple and accurate parametrization as\nwell as evaluation of finite-range effects for any potential model. This\nfeature makes the present results very useful in benchmarking different methods\nfor three-cluster breakup and recombination calculations in four-particle\nsystems. The interplay of the three-fermion and fermion-fermion-dimer\nrecombination processes and their consequences for ultracold mixtures of\nfermions and dimers is discussed."
    },
    {
        "anchor": "Mapping as a probe for heating suppression in periodically driven\n  quantum many-body systems: Experiments on periodically driven quantum systems have effectively realized\nquasi-Hamiltonians, in the sense of Floquet theory, that are otherwise\ninaccessible in static condensed matter systems. Although the Floquet\nquasi-Hamiltonians are time-independent, however, these continuously driven\nsystems can still suffer from heating due to a secular growth in the\nexpectation value of the time-dependent physical Hamiltonian. Here we use an\nexact space-time mapping to construct a class of many-body systems with rapid\nperiodic driving which we nonetheless prove to be completely free of heating,\nby mapping them exactly onto time-independent systems. The absence of heating\ndespite the periodic driving occurs in these cases of harmonically trapped\ndilute Bose gas because the driving is a certain periodic but anharmonic\nmodulation of the gas's two-body contact interaction, at a particular\nfrequency. Although we prove that the absence of heating is exact within full\nquantum many-body theory, we then use mean-field theory to simulate 'Floquet\nheating spectroscopy' and compute the heating rate when the driving frequency\nis varied away from the critical value for zero heating. In both weakly and\nstrongly non-linear regimes, the heating rate as a function of driving\nfrequency appears to show a number of Fano resonances, suggesting that the\nexactly proven absence of heating at the critical frequency may be explained in\nterms of destructive interferences between excitation modes.",
        "positive": "Energy-level crossings and number-parity effects in a bosonic tunneling\n  model: An exactly solved bosonic tunneling model is studied along a line of the\ncoupling parameter space, which includes a quantum phase boundary line. The\nentire energy spectrum is computed analytically, and found to exhibit multiple\nenergy level crossings in a region of the coupling parameter space. Several key\nproperties of the model are discussed, which exhibit a clear dependence on\nwhether the particle number is even or odd."
    },
    {
        "anchor": "Supersolid Stripes Enhanced by Correlations in a Raman\n  Spin-Orbit-Coupled System: A Bose gas under the effect of Raman Spin-Orbit Coupling (SOC) is analyzed\nusing the Discrete Spin T-moves Diffusion Monte Carlo method. By computing the\nenergy as well as the static structure factor and the superfluid fraction of\nthe system, the emergence of an energetically favorable supersolid stripe state\nis observed, which is in agreement with recent observations. A significant\nenhancement of the stability of the stripe phase with respect to the mean-field\nprediction is observed when the strength of the inter-atomic correlations is\nincreased. We also quantify and characterize the degree of superfluidity of the\nstripes and show that this quantity is mostly determined by the ratio between\nthe Raman coupling and the square of the momentum difference between the pair\nof SOC inducing laser beams.",
        "positive": "Non-destructive selective probing of phononic excitations in a cold Bose\n  gas using impurities: We introduce a detector that selectively probes the phononic excitations of a\ncold Bose gas. The detector is composed of a single impurity atom confined by a\ndouble-well potential, where the two lowest eigenstates of the impurity form an\neffective probe qubit that is coupled to the phonons via density-density\ninteractions with the bosons. The system is analogous to a two-level atom\ncoupled to photons of the radiation field. We demonstrate that tracking the\nevolution of the qubit populations allows probing both thermal and coherent\nexcitations in targeted phonon modes. The targeted modes are selected in both\nenergy and momentum by adjusting the impurity's potential. We show how to use\nthe detector to observe coherent density waves and to measure temperatures of\nthe Bose gas down to the nano-Kelvin regime. We analyze how our scheme could be\nrealized experimentally, including the possibility of using an array of\nmultiple impurities to achieve greater precision from a single experimental\nrun."
    },
    {
        "anchor": "Floating Phases in One-Dimensional Rydberg Ising Chains: We report on the quantitative ground state phase diagram of a van der Waals\ninteracting chain of Rydberg atoms. These systems are known to host crystalline\nphases locked to the underlying lattice as well as a gapped, disordered phase.\nWe locate and characterize a third type of phase, the so called floating phase,\nwhich can be seen as a one-dimensional 'crystalline' phase which is not locked\nto the lattice. These phases have been theoretically predicted to exist in the\nphase diagram, but were not reported so far. Our results have been obtained\nusing state-of-the-art numerical tensor network techniques and pave the way for\nthe experimental exploration of floating phases with existing Rydberg quantum\nsimulators.",
        "positive": "Analyzing non-equilibrium quantum states through snapshots with\n  artificial neural networks: Current quantum simulation experiments are starting to explore\nnon-equilibrium many-body dynamics in previously inaccessible regimes in terms\nof system sizes and time scales. Therefore, the question emerges which\nobservables are best suited to study the dynamics in such quantum many-body\nsystems. Using machine learning techniques, we investigate the dynamics and in\nparticular the thermalization behavior of an interacting quantum system which\nundergoes a dynamical phase transition from an ergodic to a many-body localized\nphase. A neural network is trained to distinguish non-equilibrium from thermal\nequilibrium data, and the network performance serves as a probe for the\nthermalization behavior of the system. We test our methods with experimental\nsnapshots of ultracold atoms taken with a quantum gas microscope. Our results\nprovide a path to analyze highly-entangled large-scale quantum states for\nsystem sizes where numerical calculations of conventional observables become\nchallenging."
    },
    {
        "anchor": "Quantum soliton-trains of strongly correlated impurities in\n  Bose-Einstein condensates: Strongly correlated impurities immersed in a Bose-Einstein condensate (BEC)\ncan form a periodic structure of tightly localized single atoms due to\ncompeting inter- and intra-species interactions, leading to a self-organized\npinned state. In this work, we show numerically that the impurities in the\nself-pinned state form a soliton-train, as a consequence of a BEC-mediated\nattractive self-interaction and ordering due to the exclusion principle. The\ndynamics of the impurities possess similar characteristics to bright\nmatter-wave solitons as they appear in attractive BECs, however in the few\nimpurities case, the detailed nature of collisions is determined by their\nquantum statistics.",
        "positive": "Extended Bose-Hubbard models with Rydberg macrodimer dressing: Extended Hubbard models have proven to bear novel quantum states, but their\nexperimental realization remains challenging. In this work we propose to use\nbosonic quantum gases dressed with molecular bound states in Rydberg\ninteraction potentials for the observation of these quantum states. We study\nthe molecular Rabi coupling with respect to principal quantum number and\ntrapping frequency of the ground state atoms for various molecular potentials\nof Rubidium and Potassium, and the hereby resulting dressed interaction\nstrength. Additionally, we propose a two-color excitation scheme which\nsignificantly increases the dressed interaction and cancels AC Stark shifts\nlimiting the atomic motion in the itinerant regime. We study the various\nequilibrium phases of the corresponding extended Bose-Hubbard model by means of\nthe Cluster Gutzwiller approach and perform time evolution simulations via the\nLindblad master equation. We find a supersolid phase by slowly ramping the\nmolecular Rabi coupling of an initially prepared superfluid and discuss the\nrole of dissipation."
    },
    {
        "anchor": "Dipolar condensates with tilted dipoles in a pancake-shaped confinement: The effect of dipolar orientation with respect to the condensate plane on the\nmean-field dynamics of dipolar Bose-Einstein condensates in a pancake-shaped\nconfinement is discussed. The stability of a quasi-two-dimensional condensate,\nwith respect to the tilting angle, is found to be different from a\ntwo-dimensional layer of dipoles, indicating the relevance of the transverse\nextension while characterizing two-dimensional dipolar systems. An anisotropic\nexcitation spectrum exhibiting a highly tunable, rotonlike minimum can arise\nentirely from the dipole-dipole interactions, by tilting the dipoles. At the\nmagic angle and in the absence of contact interactions, the long-wavelength\nexcitations are not phononlike and always unstable. The post-roton-instability\ndynamics, in contrast to phonon instability, in a uniform condensate, is\nfeatured by a transient, defect-free, stripe pattern, which eventually\nundergoes local collapses, and driving the condensate back into the stable\nregime can make them sustained for longer. Hopping between stripes has been\nobserved before it melts into a uniform state in the presence of dissipation.\nFinally, we discuss a class of solutions, in which a quasi-two-dimensional\ncondensate is self-trapped in one direction, as well as a regime of interaction\nparameters, including attractive short-range interactions, at which a\ntwo-dimensional anisotropic soliton can be stabilized, and we show that a\nchromium condensate with a relatively small number of atoms is well suited for\nthis.",
        "positive": "Vortex structures of rotating Bose-Einstein condensates in anisotropic\n  harmonic potential: We found an analytical solution for the vortex structure in a rapidly\nrotating trapped Bose-Einstein condensate in the lowest Landau level\napproximation. This solution is exact in the limit of a large number of\nvortices and is obtained for the case of anisotropic harmonic potential. For\nthe case of symmetric harmonic trap when the rotation frequency is equal to the\ntrapping frequency, the solution coincides with the Abrikosov triangle vortex\nlattice in type-II superconductors.\n  In a general case the coarse grained density is found to be close to the\nThomas-Fermi profile, except the vicinity of edges of a condensate cloud."
    },
    {
        "anchor": "Optimized loading of an optical dipole trap for the production of\n  Chromium BECs: We report on a strategy to maximize the number of chromium atoms transferred\nfrom a magneto-optical trap into an optical trap through accumulation in\nmetastable states via strong optical pumping. We analyse how the number of\natoms in a chromium Bose Einstein condensate can be raised by a proper handling\nof the metastable state populations. Four laser diodes have been implemented to\naddress the four levels that are populated during the MOT phase. The individual\nimportance of each state is specified. To stabilize two of our laser diode, we\nhave developed a simple ultrastable passive reference cavity whose long term\nstability is better than 1 MHz.",
        "positive": "Patterned Supersolids in Dipolar Bose Systems: We study by means of first principle Quantum Monte Carlo simulations the\nground state phase diagram of a system of dipolar bosons with aligned dipole\nmoments, and with the inclusion of a two-body repulsive potential of varying\nrange. The system is shown to display a supersolid phase in a relatively broad\nregion of the phase diagram, featuring different crystalline patterns depending\non the density and on the range of the repulsive part of the interaction\n(scattering length). The supersolid phase is sandwiched between a classical\ncrystal of parallel filaments and a homogeneous superfluid phase. We show that\na \"roton\" minimum appears in the elementary excitation spectrum of the\nsuperfluid as the system approaches crystallization."
    },
    {
        "anchor": "Spin-momentum coupled Bose-Einstein condensates with lattice band\n  pseudospins: The quantum emulation of spin-momentum coupling (SMC), a crucial ingredient\nfor the emergence of topological phases, is currently drawing considerable\ninterest. In previous quantum gas experiments, typically two atomic hyperfine\nstates were chosen as pseudospins. Here, we report the observation of a new\nkind of SMC achieved by loading a Bose-Einstein condensate (BEC) into\nperiodically driven optical lattices. The s- and p-bands of a static lattice,\nwhich act as pseudospins, are coupled through an additional moving lattice\nwhich induces a momentum dependent coupling between the two pseudospins,\nresulting in s-p hybrid Floquet-Bloch bands. We investigate the band structures\nby measuring the quasimomentum of the BEC for different velocities and\nstrengths of the moving lattice and compare our measurements to theoretical\npredictions. The realization of SMC with lattice bands as pseudospins paves the\nway for engineering novel quantum matter using hybrid orbital bands.",
        "positive": "Exactly solvable models for multiatomic molecular Bose-Einstein\n  condensates: I introduce two family of exactly solvable models for multiatomic\nhetero-nuclear and homo-nuclear molecular Bose-Einstein condensates through the\nalgebraic Bethe ansatz method. The conserved quantities of the respective\nmodels are also showed."
    },
    {
        "anchor": "Ideal n-body correlations with massive particles: In 1963 Glauber introduced the modern theory of quantum coherence, which\nextended the concept of first-order (one-body) correlations, describing phase\ncoherence of classical waves, to include higher-order (n-body) quantum\ncorrelations characterizing the interference of multiple particles. Whereas the\nquantum coherence of photons is a mature cornerstone of quantum optics, the\nquantum coherence properties of massive particles remain largely unexplored. To\ninvestigate these properties, here we use a uniquely correlated source of atoms\nthat allows us to observe n-body correlations up to the sixth-order at the\nideal theoretical limit (n!). Our measurements constitute a direct\ndemonstration of the validity of one of the most widely used theorems in\nquantum many-body theory--Wisck's theorem--for a thermal ensemble of massive\nparticles. Measurements involving n-body correlations may play an important\nrole in the understanding of thermalization of isolated quantum systems and the\nthermodynamics of exotic many-body systems, such as Efimov trimers.",
        "positive": "Quantum phase transition to unconventional multi-orbital superfluidity\n  in optical lattices: Orbital physics plays a significant role for a vast number of important\nphenomena in complex condensed matter systems such as high-T$_c$\nsuperconductivity and unconventional magnetism. In contrast, phenomena in\nsuperfluids -- especially in ultracold quantum gases -- are commonly well\ndescribed by the lowest orbital and a real order parameter. Here, we report on\nthe observation of a novel multi-orbital superfluid phase with a {\\it complex}\norder parameter in binary spin mixtures. In this unconventional superfluid, the\nlocal phase angle of the complex order parameter is continuously twisted\nbetween neighboring lattice sites. The nature of this twisted superfluid\nquantum phase is an interaction-induced admixture of the p-orbital favored by\nthe graphene-like band structure of the hexagonal optical lattice used in the\nexperiment. We observe a second-order quantum phase transition between the\nnormal superfluid (NSF) and the twisted superfluid phase (TSF) which is\naccompanied by a symmetry breaking in momentum space. The experimental results\nare consistent with calculated phase diagrams and reveal fundamentally new\naspects of orbital superfluidity in quantum gas mixtures. Our studies might\nbridge the gap between conventional superfluidity and complex phenomena of\norbital physics."
    },
    {
        "anchor": "Vortices in self-bound dipolar droplets: Quantized vortices have been observed in a variety of superfluid systems,\nfrom $^4$He to condensates of alkali-metal bosons and ultracold Fermi gases\nalong the BEC-BCS crossover. In this article we study the stability of singly\nquantized vortex lines in dilute dipolar self-bound droplets. We first discuss\nthe energetic stability region of dipolar vortex excitations within a\nvariational ansatz in the generalized nonlocal Gross-Pitaevskii functional that\nincludes quantum fluctuation corrections. We find a wide region where\nstationary solutions corresponding to axially-symmetric vortex states exist.\nHowever, these singly-charged vortex states are shown to be unstable, either by\nsplitting the droplet in two fragments or by vortex-line instabilities\ndeveloped from Kelvin-wave excitations. These observations are the results of\nlarge-scale fully three-dimensional simulations in real time. We conclude with\nsome experimental considerations for the observation of such states and suggest\npossible extensions of this work.",
        "positive": "Criticality and Spin Squeezing in the Rotational Dynamics of a BEC on a\n  Ring Lattice: We examine the dynamics of circulating modes of a Bose-Einstein condensate\nconfined in toroidal lattice. Nonlinearity due to interactions leads to\ncriticality that separates oscillatory and self-trapped phases among\ncounter-propagating modes which however share the same physical space. In the\nmean-field limit, the criticality is found to substantially enhance sensitivity\nto rotation of the system. Analysis of the quantum dynamics reveals the\nfluctuations near criticality are significant, that we explain using\nspin-squeezing formalism visualized on a Bloch sphere. We utilize the squeezing\nto propose a Ramsey interferometric scheme that suppresses fluctuation in the\nrelevant quadrature sensitive to rotation."
    },
    {
        "anchor": "Structural Superfluid-Mott Insulator Transition for a Bose Gas in\n  Multi-Rods: We report on a novel structural Superfluid-Mott Insulator (SF-MI) quantum\nphase transition for an interacting one-dimensional Bose gas within permeable\nmulti-rod lattices, where the rod lengths are varied from zero to the lattice\nperiod length. We use the ab-initio diffusion Monte Carlo method to calculate\nthe static structure factor, the insulation gap, and the Luttinger parameter,\nwhich we use to determine if the gas is a superfluid or a Mott insulator. For\nthe Bose gas within a square Kronig-Penney (KP) potential, where barrier and\nwell widths are equal, the SF-MI coexistence curve shows the same qualitative\nand quantitative behavior as that of a typical optical lattice with equal\nperiodicity but slightly larger height. When we vary the width of the barriers\nfrom zero to the length of the potential period, keeping the height of the KP\nbarriers, we observe a new way to induce the SF-MI phase transition. Our\nresults are of significant interest, given the recent progress on the\nrealization of optical lattices with a subwavelength structure that would\nfacilitate their experimental observation.",
        "positive": "Closed system approach to open systems: Tunneling decay of interacting\n  cold bosons in an optical lattice: A Bose-Hubbard Hamiltonian, modeling cold bosons in an optical lattice, is\nused to simulate the dynamics of interacting open quantum systems as subsystems\na larger closed system, avoiding complications like the introduction of baths,\ncomplex absorbing potentials or absorbing boundaries. The numerically exact\nunitary dynamics is compared with effective descriptions of the subsystems\nbased on non-Hermitian Hamiltonians or Lindblad master equations. The validity\nof popular models with constant decay rates is explicitly analyzed for decaying\nsingle and double wells. In addition we present a discrete lattice version of\nthe Siegert approximation method for calculating decay rates."
    },
    {
        "anchor": "Comment on \"Consistent thermostatistics forbids negative absolute\n  temperatures\": In this comment we argue that negative absolute temperatures are a\nwell-established concept for systems with bounded spectra. They are not only\nconsistent with thermodynamics, but are even unavoidable for a consistent\ndescription of the thermal equilibrium of inverted populations.",
        "positive": "Fragmentation of a trapped bosonic mixture: Fragmentation of bosons and pairs in a trapped imbalanced bosonic mixture is\ninvestigated analytically using an exactly solvable model, the generic\nharmonic-interaction model for mixtures. Closed-form expressions for the\neigenvalues and eigenfunctions of the reduced one-particle and two-particle\ndensity matrices as a function of all parameters, the masses, numbers of\nbosons, and the intraspecies and interspecies interactions, are obtained and\nanalyzed. As an application, we consider a system made of $N_1=100$\nnon-interacting species $1$ bosons embedded in a bath made of $N_2=10^6$\nnon-interacting species $2$ bosons, and show how fragmentation of the system's\nbosons and pairs emerges from the system--bath interaction only. Interestingly,\nthe lighter the bosons comprising the bath are the stronger is the system's\nfragmentation. Further applications are briefly discussed."
    },
    {
        "anchor": "Localized-Interaction-Induced Quantum Reflection and Filtering of\n  Bosonic Matter in a One-Dimensional Lattice Guide: We study the dynamics of quantum bosonic waves confined in a one-dimensional\ntilted optical lattice. The bosons are under the action of an effective\nspatially localized nonlinear two-body potential barrier set in the central\npart of the lattice. This version of the Bose-Hubbard model can be realized in\natomic Bose-Einstein condensates, by means of localized Feshbach resonance, and\nin quantum optics, using an arrayed waveguide with selectively doped guiding\ncores. Our numerical analysis demonstrates that the central barrier induces\nanomalous quantum reflection of incident wave packets acting solely on bosonic\ncomponents with multiple onsite occupancies. From the other side\nsingle-occupancy components can pass the barrier thus allowing one to distill\nthem in the central interacting zone. As a consequence, in this region one\nfinds a state in which the multiple occupancy is forbidden, i.e., a\nTonks-Girardeau gas. Our results demonstrate that this regime can be obtained\ndynamically, using relatively weak interactions, irrespective of their sign.",
        "positive": "Analytical pair correlations in ideal quantum gases:\n  Temperature-dependent bunching and antibunching: The fluctuation-dissipation theorem together with the exact density response\nspectrum for ideal quantum gases has been utilized to yield a new expression\nfor the static structure factor, which we use to derive exact analytical\nexpressions for the temperature{dependent pair distribution function g(r) of\nthe ideal gases. The plots of bosonic and fermionic g(r) display \"Bose pile\"\nand \"Fermi hole\" typically akin to bunching and antibunching as observed\nexperimentally for ultracold atomic gases. The behavior of spin-scaled pair\ncorrelation for fermions is almost featureless but bosons show a rich structure\nincluding long-range correlations near T_c. The coherent state at T=0 shows no\ncorrelation at all, just like single-mode lasers. The depicted decreasing trend\nin correlation with decrease in temperature for T < T_c should be observable in\naccurate experiments."
    },
    {
        "anchor": "Universal behavior of the BEC critical temperature for a multislab ideal\n  Bose gas: For an ideal Bose-gas within a multi-slab periodic structure, we discuss the\neffect of the spatial distribution of the gas on its Bose-Einstein condensation\ncritical temperature $T_c$, as well as on the origin of its dimensional\ncrossover observed in the specific heat. The multi-slabs structure is generated\nby applying a Kronig-Penney potential to the gas in the perpendicular direction\nto the slabs of width $b$ and separated by a distance $a$, and allowing the\nparticles to move freely in the other two directions. We found that $T_c$\ndecreases continuously as the potential barrier height increases, becoming\ninversely proportional to the square root of the barrier height when it is\nlarge enough. This behavior is {\\it universal} as it is independent of the\nwidth and spacing of the barriers. The specific heat at constant volume shows a\ncrossover from 3D to 2D when the height of the potential or the barrier width\nincrease, in addition to the well known peak related to the Bose-Einstein\ncondensation. These features are due to the trapping of the bosons by the\npotential barriers, and can be characterized by the energy difference between\nthe energy bands below the potential height.",
        "positive": "Ultracold spin-balanced fermionic quantum liquids with renormalized\n  $P$-wave interactions: We consider a spin-balanced degenerate gas of spin-1/2 fermions whose\ndynamics is governed by low-energy $P$-wave interactions, characterized by the\nscattering volume $a_1$ and effective momentum $r_1$. The energy per particle\n$\\bar{\\cal{E}}$ in the many-body system is calculated by resumming the ladder\ndiagrams comprising both particle-particle and hole-hole intermediate states,\nfollowing the novel advances recently developed by us in Ann.Phys.\n437,168741(2022). This allows to obtain a renormalized result for\n$\\bar{\\cal{E}}$ within generic cutoff regularization schemes, with\n$\\bar{\\cal{E}}$ directly expressed in terms of the scattering parameters $a_1$\nand $r_1$, once the cut off is sent to infinity. The whole set of possible\nvalues of $a_1$ and $r_1$ is explored for the first time in the literature\nlooking for minima in the energy per particle with $\\bar{\\cal{E}}$ given as\ndescribed. They are actually found, but a further inspection reveals that the\nassociated scattering parameters give rise to resonance poles in the complex\nmomentum-plane with positive imaginary part, which is at odds with the\nHermiticity of the Hamiltonian. We also determine that these conflictive poles,\nwith a pole-position momentum that is smaller in absolute value than the Fermi\nmomentum of the system, clearly impact the calculation of $\\bar{\\cal{E}}$. As a\nresult, we conclude that unpolarized spin-1/2 fermionic normal matter\ninteracting in $P$-wave is not stable. We also study three universal parameters\naround the unitary limit. Finally, the whole set of values for the parameters\n$a_1$, $r_1$ is characterized according to whether they give rise to unallowed\npoles and, if so, by attending to their pole positions relative to the Fermi\nmomentum of the system explored."
    },
    {
        "anchor": "Fate of the \"vacuum point'' and of grey solitons in dispersive quantum\n  shock waves in a one-dimensional Bose gas: We continue the study of dispersive quantum shock waves in a one-dimensional\nBose gas beyond the mean-field approximation. In a recent work by Simmons et\nal. [Phys. Rev. Let. 125, 180401 (2020)], the oscillatory shock wave train\ndeveloping in this system from an initial localized density bump on a uniform\nbackground was interpreted as a result of quantum mechanical self-interference,\nwherein the interference contrast would diminish with the loss of matter-wave\nphase coherence. Such loss of coherence, relative to the mean-field\nGross-Pitaevskii description, occurs due to either quantum or thermal\nfluctuations, as well as in the strongly interacting regime. In this work, we\nextend the analysis of dispersive quantum shock waves in this context to other\ndynamical scenarios. More specifically, the scenarios studied include evolution\nof a sufficiently high density bump, known to lead to the so-called ``vacuum\npoint'' in the mean-field description, and evolution of an initial density dip,\nknown to shed a train of grey solitons in the same mean-field approximation. We\nstudy the fate of these nonlinear wave structures in the presence of quantum\nand thermal fluctuations, as well as at intermediate and strong interactions,\nand show that both the vacuum point and grey solitons cease to manifest\nthemselves beyond the mean-field approach. On the other hand, we find that a\nvacuum point can occur in an ideal (noninteracting) Bose gas evolving from a\nground state of a localized dimple potential. Due to the ubiquity of dispersive\nshock waves in nature, our results should provide useful insights and\nperspectives for a variety of other physical systems known to display nonlinear\nwave phenomena.",
        "positive": "Interacting in-plane molecular dipoles in a zig-zag chain: The system with externally polarized dipole molecules at half-filling moving\nalong a one-dimensional zig-zag chain is studied theoretically, including the\nground-state phase diagram. The dipoles are oriented in-plane. Together with\nthe geometry of the chain this gives rise to a bond-alternating nearest\nneighbor interaction due to simultaneous attractive and repulsive interactions.\nBecause of the quantum Zeno effect due to the reactive nature of molecules the\nsystem can be treated as hard-core. By tuning the ratio between the\nnearest-neighbor interaction and hopping, various phases can be accessed by\ncontrolling the polarization angle. In the ultra-strong coupling limit, the\nsystem simplifies to a frustrated extended axial Ising model. For the small\ncoupling limit, qualitative discussion of the ordering behavior using effective\nfield theory arguments is provided. We show that when chain angle is small, the\nsystem mostly exhibits BKT-type phase transitions, whereas large chain angle\nwould drive the system into a gapped (Ising) dimerized phase, where the hopping\nstrength is closely related to the orientation of dimerized pairs."
    },
    {
        "anchor": "Thermometry with spin-dependent lattices: We propose a method for measuring the temperature of strongly correlated\nphases of ultracold atom gases confined in spin-dependent optical lattices. In\nthis technique, a small number of \"impurity\" atoms--trapped in a state that\ndoes not experience the lattice potential--are in thermal contact with atoms\nbound to the lattice. The impurity serves as a thermometer for the system\nbecause its temperature can be straightforwardly measured using time-of-flight\nexpansion velocity. This technique may be useful for resolving many open\nquestions regarding thermalization in these isolated systems. We discuss the\ntheory behind this method and demonstrate proof-of-principle experiments,\nincluding the first realization of a 3D spin-dependent lattice in the strongly\ncorrelated regime.",
        "positive": "Particle-Hole Pair Coherence in Mott Insulator Quench Dynamics: We predict the existence of novel collapse and revival oscillations that are\na distinctive signature of the short-range off-diagonal coherence associated\nwith particle-hole pairs in Mott insulator states. Starting with an atomic Mott\nstate in a one-dimensional optical lattice, suddenly raising the lattice depth\nfreezes the particle-hole pairs in place and induces phase oscillations. The\npeak of the quasi-momentum distribution, revealed through time of flight\ninterference, oscillates between a maximum occupation at zero quasi-momentum\n(the $\\Gamma$ point) and the edge of the Brillouin zone. We show that the\npopulation enhancements at the edge of the Brillouin zone is due to coherent\nparticle-hole pairs, and we find similar effects for fermions and Bose-Fermi\nmixtures in a lattice. Our results open a new avenue for probing strongly\ncorrelated many-body states with short-range phase coherence that goes beyond\nthe familiar collapse and revivals previously observed in the long-range\ncoherent superfluid regime."
    },
    {
        "anchor": "Two-step condensation of lattice bosons: We present a theoretical study of Bose-Einstein condensation in highly\nanisotropic harmonic traps. The bosons are considered to be moving in an\noptical lattice in an overall anisotropic harmonic confining potential. We find\nthat two-step condensation occurs for lattice bosons at much reduced harmonic\npotential anisotropy when compared to the case of an ideal bose gas in an\nanisotropic harmonic confinement. We also show that when the bosons are in an\nisotropic harmonic confinement but with highly anisotropic hopping in the\noptical lattice, two-step condensation does not occur. We interpret some of our\nresults using single boson density of energy states corresponding to the\npotentials faced by the bosons.",
        "positive": "Conduction electrons localized by charged magneto-acceptors A$^{2-}$ in\n  GaAs/GaAlAs quantum wells: A variational theory is presented of A$^{1-}$ and A$^{2-}$ centers, i.e. of a\nnegative acceptor ion localizing one and two conduction electrons,\nrespectively, in a GaAs/GaAlAs quantum well in the presence of a magnetic field\nparallel to the growth direction. A combined effect of the well and magnetic\nfield confines conduction electrons to the proximity of the ion, resulting in\ndiscrete repulsive energies above the corresponding Landau levels. The theory\nis motivated by our experimental magneto-transport results which indicate that,\nin a heterostructure doped in the GaAs well with Be acceptors, one observes a\nboil-off effect in which the conduction electrons in the crossed-field\nconfiguration are pushed by the Hall electric field from the delocalized Landau\nstates to the localized acceptor states and cease to conduct. A detailed\nanalysis of the transport data shows that, at high magnetic fields, there are\nalmost no conducting electrons left in the sample. It is concluded that one\nnegative acceptor ion localizes up to four conduction electrons."
    },
    {
        "anchor": "Absence of quasiclassical coherence in mean-field dynamics of bosons in\n  a kinetically frustrated regime: We study numerically the dynamics of bosons on a triangular lattice after\nquenching both the on-site interactions and the external trapping potential to\nnegative values. In a similar situation on the square lattice, the dynamics can\nbe understood in terms of an effectively reversed Hamiltonian. On the\ntriangular lattice, however, the kinetic part of the reversed Hamiltonian is\nfrustrated and whether coherence can develop is an open question. The strength\nof the frustration can be changed by tuning the ratio of the hopping rates\nalong different directions. We calculate time-of-flight images at different\ntimes after the quench for different values of the hopping anisotropy. We\nobserve peaks at the maxima of the original non-interacting dispersion relation\nboth in the isotropic case and also in the rhombic limit of high hopping\nanisotropy. For an intermediate value, however, no coherence develops up to the\nlongest simulation times. These results imply that experiments along similar\nlines could study unconventional superfluidity of bosons and aspects of the\nconjectured spin-liquid behavior in the hard-core limit.",
        "positive": "Dirac and Weyl Rings in Three Dimensional Cold Atom Optical Lattices: Recently three dimensional topological quantum materials with gapless energy\nspectra have attracted considerable interests in many branches of physics.\nBesides the celebrated example, Dirac and Weyl points which possess gapless\npoint structures in the underlying energy dispersion, the topologically\nprotected gapless spectrum can also occur along a ring, named Dirac and Weyl\nnodal rings. Ultra-cold atomic gases provide an ideal platform for exploring\nnew topological materials with designed symmetries. However, whether Dirac and\nWeyl rings can exist in the single-particle spectrum of cold atoms remains\nelusive. Here we propose a realistic model for realizing Dirac and Weyl rings\nin the single-particle band dispersion of a cold atom optical lattice. Our\nscheme is based on previously experimentally already implemented Raman coupling\nsetup for realizing spin-orbit coupling. Without the Zeeman field, the model\npreserves both pseudo-time-reversal and inversion symmetries, allowing Dirac\nrings. The Dirac rings split into Weyl rings with a Zeeman field that breaks\nthe pseudo-time-reversal symmetry. We examine the superfluidity of attractive\nFermi gases in this model and also find Dirac and Weyl rings in the\nquasiparticle spectrum."
    },
    {
        "anchor": "Interacting Fibonacci anyons in a Rydberg gas: A defining property of particles is their behavior under exchange. In two\ndimensions anyons can exist which, opposed to fermions and bosons, gain\narbitrary relative phase factors or even undergo a change of their type. In the\nlatter case one speaks of non-Abelian anyons - a particularly simple and\naesthetic example of which are Fibonacci anyons. They have been studied in the\ncontext of fractional quantum Hall physics where they occur as quasiparticles\nin the $k=3$ Read-Rezayi state, which is conjectured to describe a fractional\nquantum Hall state at filling fraction $\\nu=12/5$. Here we show that the\nphysics of interacting Fibonacci anyons can be studied with strongly\ninteracting Rydberg atoms in a lattice, when due to the dipole blockade the\nsimultaneous laser excitation of adjacent atoms is forbidden. The Hilbert space\nmaps then directly on the fusion space of Fibonacci anyons and a proper tuning\nof the laser parameters renders the system into an interacting topological\nliquid of non-Abelian anyons. We discuss the low-energy properties of this\nsystem and show how to experimentally measure anyonic observables.",
        "positive": "Berry Phase of Nonlinear Correction: We investigate the geometric phase or Berry phase of adiabatic quantum\nevolution in the Bose-Einstein condensate (BEC) systems governed by nonlinear\nGross-Pitaevskii(GP) equations. We study how this phase is modified by the\nnonlinearity and find that the Bogoliubov fluctuations around the eigenstates\nare accumulated during the nonlinear adiabatic evolution and contribute a\nfinite phase of geometric nature. A two-mode BEC model is used to illustrate\nour theory. Our theory is applicable to other nonlinear systems such as\nparaxial wave equation for nonlinear optics and Ginzburg-Landau equations for\ncomplex order parameters in condensed-matter physics."
    },
    {
        "anchor": "Magneto--optical matter wave Bragg diffraction: We have performed a principle-proof-experiment of a magneto-optical\ndiffraction (MOD) technique that requires no energy level splitting by\nhomogeneous magnetic field and a circularly polarized optical lattice, avoiding\nsystem errors in an interferometer based on the MOD. The principle for this new\nMOD is that asynchronized switching of quadrupole trap and Ioffe trap in a\nquadrupole-Ioffe-configuration trap can generate a residual magnetic force to\ndrive a Bose-Einstein condensate (BEC) to move. We have observed asymmetric\natomic diffraction resulting from the asymmetric distribution of the Bloch\neigenstates involved in the diffraction process when the condensate is driven\nby such a force, and matter-wave self-imaging due to coherent population\noscillation of the dominantly occupied Bloch eigenstates. We have classified\nthe mechanisms that lead to symmetric or asymmetric diffraction, and found that\nour experiment presents a magnetic alternative to a moving optical lattice,\nwith a great potential to achieve a very large momentum transfer ($>110 \\hbar\nk$) to a BEC using well-developed magnetic trapping techniques.",
        "positive": "Spin-orbit-induced bound state and molecular signature of the degenerate\n  Fermi gas in a narrow Feshbach resonance: In this paper we explore the spin-orbit-induced bound state and molecular\nsignature of the degenerate Fermi gas in a narrow Feshbach resonance based on a\ngeneralized two-channel model. Without the atom-atom interactions, only one\nbound state can be found even if spin-orbit coupling exists. Moreover, the\ncorresponding bound-state energy depends strongly on the strength of spin-orbit\ncoupling, but is influenced slightly by its type. In addition, we find that\nwhen increasing the strength of spin-orbit coupling, the critical point at\nwhich the molecular fraction vanishes shifts from zero to the negative\ndetuning. In the weak spin-orbit coupling, this shifting is proportional to the\nsquare of its strength. Finally, we also show that the molecular fraction can\nbe well controlled by spin-orbit coupling."
    },
    {
        "anchor": "Interaction quenches in Bose gases studied with a time-dependent\n  hypernetted-chain Euler-Lagrange method: We present a new variational method to study the dynamics of a closed bosonic\nmany-body system, the time-dependent hypernetted-chain Euler-Lagrange method,\ntHNC . Based on the Jastrow ansatz, it accounts for quantum fluctuations in a\nnon-perturbative way. tHNC scales well with the number of dimensions, as\ndemonstrated by our results on one, two, and three dimensions. We apply the\ntHNC method to interaction quenches, i.e. sudden changes of the interaction\nstrength, in homogeneous Bose gases. When the quench is strong enough that the\nfinal state has roton excitations (as found and predicted for dipolar and\nRydberg-dressed Bose-Einstein condensates, respectively), the pair distribution\nfunction exhibits stable oscillations. For validation, we compare tHNC results\nwith time-dependent variational Monte Carlo results in one and two dimensions.",
        "positive": "Spin exchange-induced spin-orbit coupling in a superuid mixture: We investigate the ground-state properties of a dual-species spin-1/2\nBose-Einstein condensate. One of the species is subjected to a pair of Raman\nlaser beams that induces spin-orbit (SO) coupling, whereas the other species is\nnot coupled to the Raman laser. In certain limits, analytical results can be\nobtained. It is clearly shown that, through the inter-species spin-exchange\ninteraction, the second species also exhibits SO coupling. This mixture system\ndisplays a very rich phase diagram, with many of the phases not present in an\nSO coupled single-species condensate. Our work provides a new way of creating\nSO coupling in atomic quantum gases, and opens up a new avenue of research in\nSO coupled superfluid mixtures. From a practical point of view, the spin\nexchange-induced SO coupling may overcome the heating issue for certain atomic\nspecies when subjected to the Raman beams."
    },
    {
        "anchor": "Nonlinear multi-state tunneling dynamics in a spinor Bose-Einstein\n  condensate: We present an experimental realization of dynamic self-trapping and\nnon-exponential tunneling in a multi-state system consisting of ultracold\nsodium spinor gases confined in moving optical lattices. Taking advantage of\nthe fact that the tunneling process in the sodium spinor system is resolvable\nover a broader dynamic energy scale than previously observed in rubidium scalar\ngases, we demonstrate that the tunneling dynamics in the multi-state system\nstrongly depends on an interaction induced nonlinearity and is influenced by\nthe spin degree of freedom under certain conditions. We develop a rigorous\nmulti-state tunneling model to describe the observed dynamics. Combined with\nour recent observation of spatially-manipulated spin dynamics, these results\nopen up prospects for alternative multi-state ramps and state transfer\nprotocols.",
        "positive": "String patterns in the doped Hubbard model: Understanding strongly correlated quantum many-body states is one of the most\ndifficult challenges in modern physics. For example, there remain fundamental\nopen questions on the phase diagram of the Hubbard model, which describes\nstrongly correlated electrons in solids. In this work we realize the Hubbard\nHamiltonian and search for specific patterns within the individual images of\nmany realizations of strongly correlated ultracold fermions in an optical\nlattice. Upon doping a cold-atom antiferromagnet we find consistency with\ngeometric strings, entities that may explain the relationship between hole\nmotion and spin order, in both pattern-based and conventional observables. Our\nresults demonstrate the potential for pattern recognition to provide key\ninsights into cold-atom quantum many-body systems."
    },
    {
        "anchor": "Complex phases in the doped two-species bosonic Hubbard Model: We study a two-dimensional bosonic Hubbard model with two hard-core species\naway from half filling using Quantum Monte Carlo simulations. The model\nincludes a repulsive interspecies interaction and different nearest-neighbor\nhopping terms for the two species. By varying the filling we find a total of\nfive distinct phases, including a normal liquid phase at higher temperature,\nand four different phases at lower temperature. We find an\nanti-ferromagnetically ordered Mott insulator and a region of coexistent\nanti-ferromagnetic and superfluid phases near half filling. Further away from\nhalf filling the phase diagram displays a superfluid phase and a novel phase\ninside the superfluid region at even lower temperatures. In this novel phase\nseparated region, the heavy species has a Mott behavior with integer filling,\nwhile the lighter species shows phase separated Mott and superfluid behaviors.",
        "positive": "Evaporative cooling to a Rydberg crystal close to its ground state: We theoretically show how to obtain a long one-dimensional crystal near its\nquantum ground state. We rely on an evaporative cooling scheme applicable to\nmany-body systems with nonzero-ranged interactions. Despite the absence of\nperiodic potentials, the final state is a crystal which exhibits long-range\nspatial order. We describe the scheme thermodynamically, applying the truncated\nBoltzmann distribution to the collective excitations of the chain, and show\nthat it leads to a novel quasi-equilibrium many-body state. For longer chains,\ncomprising about 1000 atoms, we emphasize the quasi-universality of the\nevaporation curve. Such exceptionally long 1D crystals are only accessible deep\nin the quantum regime. We perform our analysis on the example of an initially\nthermal chain of circular Rydberg atoms confined to a one-dimensional (1D)\ngeometry. Our scheme may be applied to other quantum systems with long-ranged\ninteractions such as polar molecules."
    },
    {
        "anchor": "Bose-Einstein condensation in a frustrated triangular optical lattice: The recent experimental condensation of ultracold atoms in a triangular\noptical lattice with negative effective tunneling energies paves the way to\nstudy frustrated systems in a controlled environment. Here, we explore the\ncritical behavior of the chiral phase transition in such a frustrated lattice\nin three dimensions. We represent the low-energy action of the lattice system\nas a two-component Bose gas corresponding to the two minima of the dispersion.\nThe contact repulsion between the bosons separates into intra- and\ninter-component interactions, referred to as $V_{0}$ and $V_{12}$,\nrespectively. We first employ a Huang-Yang-Luttinger approximation of the free\nenergy. For $V_{12}/V_{0} = 2$, which corresponds to the bare interaction, this\napproach suggests a first order phase transition, at which both the U$(1)$\nsymmetry of condensation and the $\\mathbb{Z}_2$ symmetry of the emergent chiral\norder are broken simultaneously. Furthermore, we perform a renormalization\ngroup calculation at one-loop order. We demonstrate that the coupling regime\n$0<V_{12}/V_0\\leq1$ shares the critical behavior of the Heisenberg fixed point\nat $V_{12}/V_{0}=1$. For $V_{12}/V_0>1$ we show that $V_{0}$ flows to a\nnegative value, while $V_{12}$ increases and remains positive. This results in\na breakdown of the effective quartic field theory due to a cubic anisotropy,\nand again suggests a discontinuous phase transition.",
        "positive": "Many-Body Quantum Geometric Effects on Trapped Ultracold Bosons: Quantum geometric effects in uncorrelated systems are characterized by the\nBerry curvature and quantum metric. Beyond those, we propose three\ngauge-independent tensors describing quantum geometric effects on local\ninteraction between correlated particles. We derive an effective hydrodynamic\ntheory for ultracold bosons in optical lattices. Ground states and collective\nmodes of superfluids in isotropic harmonic traps are solved for highly\nsymmetric lattices. In a dynamic process, the amplitude and phase shift of an\nexcited breathing mode are determined by the geometric properties of Bloch\nwavefunctions. We also give a tight-binding model of a bipartite square lattice\nwith nontrivial quantum geometric effects. Our discovery advances the\nconnections between the modern band theory and quantum many-body physics."
    },
    {
        "anchor": "Large-Amplitude Superexchange of High-Spin Fermions in Optical Lattices: We show that fermionic high-spin systems with spin-changing collisions allow\nto monitor superexchange processes in optical superlattices with large\namplitudes and strong spin fluctuations. By investigating the non-equilibrium\ndynamics, we find a superexchange dominated regime at weak interactions. The\nunderlying mechanism is driven by an emerging tunneling-energy gap in shallow\nfew-well potentials. As a consequence, the interaction-energy gap that is\nexpected to occur only for strong interactions in deep lattices is\nreestablished. By tuning the optical lattice depth, a crossover between two\nregimes with negligible particle number fluctuations is found: first, the\ncommon regime with vanishing spin-fluctuations in deep lattices and, second, a\nnovel regime with strong spin fluctuations in shallow lattices. We discuss the\npossible experimental realization with ultracold 40K atoms and observable\nquantities in double wells and two-dimensional plaquettes.",
        "positive": "Dark solitons generation and their instability dynamics in two\n  dimensional condensates: We analyze numerically the formation and the subsequent dynamics of\ntwo-dimensional matter wave dark solitons in a Thomas-Fermi rubidium condensate\nusing various techniques. An initially imprinted sharp phase gradient leads to\nthe dynamical formation of a stationary soliton as well as very shallow grey\nsolitons, whereas a smooth gradient only creates grey solitons. The depth and\nhence, the velocity of the soliton is provided by the spatial width of the\nphase gradient, and it also strongly influences the snake-instability dynamics\nof the two dimensional solitons. The vortex dipoles stemming from the unstable\nsoliton exhibit rich dynamics. Notably, the annihilation of a vortex dipole via\na transient dark lump or a vortexonium state, the exchange of vortices between\neither a pair of vortex dipoles or a vortex dipole and a single vortex, and so\non. For sufficiently large width of the initial phase gradient, the solitons\nmay decay directly into vortexoniums instead of vortex pairs, and also the\ndecay rate is augmented. Later, we discuss alternative techniques to generate\ndark solitons, which involve a Gaussian potential barrier and time-dependent\ninteractions, both linear and periodic. The properties of the solitons can be\ncontrolled by tuning the amplitude or the width of the potential barrier. In\nthe linear case, the number of solitons and their depths are determined by the\nquench time of the interactions. For the periodic modulation, a transient\nsoliton lattice emerges with its periodicity depending on the modulation\nfrequency, through a wave number selection governed by the local Bogoliubov\nspectrum. Interestingly, for sufficiently low barrier potential, both Faraday\npattern and soliton lattice coexist. The snake instability dynamics of the\nsoliton lattice is characteristically modified if the Faraday pattern is\npresent."
    },
    {
        "anchor": "Stationary transport above the critical velocity in a one-dimensional\n  superflow past an obstacle: We consider in this work the different possible stationary flows of a one\ndimensional quantum fluid in the mean-field regime. We focus on the supersonic\nregime where a transition from a time dependent flow to a stationary\ndiffractive flow occurs at a given critical velocity. We give nonperturbative\nresults for this critical velocity in the presence of a localised obstacle of\narbitrary size and strength. In addition, we discuss the existence of\nsuperfluid-like solution in the supersonic regime due to resonant transport and\nprovide a complete map of the different regimes of stationary transport of a\nquantum fluid.",
        "positive": "Hydrodynamic signatures and spectral properties of the quantum vortex: We characterize the low-lying excitations of a quantum vortex in a\nquasi-two-dimensional Bose-Einstein condensate (BEC) using the standard\ndefinition of the density of states (DOS) and a modified version that is\nsensitive to complementary aspects of the excitation's spectrum. The latter\nproves to be particularly relevant to studying the polaronic state realized\nwhen an impurity is embedded in a quantum vortex. We establish that the\nimpurity becomes sensitive to the transversal fluctuations of the vortex, via\nits remnant kelvon mode, and to the phase fluctuations of the BEC\nNambu-Goldstone mode. The presence of the vortex yields an anomalous excitation\nspectrum with a finite energy gap and non-linear DOS at low energies. We find\nthat the high sensitivity of the kelvon mode to external potentials provides a\nchannel of quantum-level control over impurities trapped in a vortex. This\nextra control channel may be of practical use for the proposal of using\nvortex-trapped impurities as qubit units for quantum information processing."
    },
    {
        "anchor": "An ideal Josephson junction in an ultracold two-dimensional Fermi gas: The role of reduced dimensionality in high temperature superconductors is\nstill under debate. Recently, ultracold atoms have emerged as an ideal model\nsystem to study such strongly correlated 2D systems. Here, we report on the\nrealisation of a Josephson junction in an ultracold 2D Fermi gas. We measure\nthe frequency of Josephson oscillations as a function of the phase difference\nacross the junction and find excellent agreement with the sinusoidal current\nphase relation of an ideal Josephson junction. Furthermore, we determine the\ncritical current of our junction in the crossover from tightly bound molecules\nto weakly bound Cooper pairs. Our measurements clearly demonstrate phase\ncoherence and provide strong evidence for superfluidity in a strongly\ninteracting 2D Fermi gas.",
        "positive": "Efficient conversion of closed-channel dominated Feshbach molecules of\n  $^{23}$Na$^{40}$K to their absolute ground state: We demonstrate the transfer of $^{23}$Na$^{40}$K molecules from a\nclosed-channel dominated Feshbach-molecule state to the absolute ground state.\nThe Feshbach molecules are initially created from a gas of sodium and potassium\natoms via adiabatic ramping over a Feshbach resonance at 78.3$\\,$G. The\nmolecules are then transferred to the absolute ground state using stimulated\nRaman adiabatic passage with an intermediate state in the spin-orbit-coupled\ncomplex $|c^3 \\Sigma^+, v=35, J=1 \\rangle \\sim |B^1\\Pi, v=12, J=1\\rangle$. Our\nmeasurements show that the pump transition dipole moment linearly increases\nwith the closed-channel fraction. Thus, the pump-beam intensity can be two\norders of magnitude lower than is necessary with open-channel dominated\nFeshbach molecules. We also demonstrate that the phase noise of the Raman\nlasers can be reduced by filter cavities, significantly improving the transfer\nefficiency."
    },
    {
        "anchor": "Spin Waves and Dielectric Softening of Polar Molecule Condensates: We consider an oblate Bose-Einstein condensate of heteronuclear polar\nmolecules in a weak applied electric field. This system supports a rich\nquasiparticle spectrum that plays a critical role in determining its bulk\ndielectric properties. In particular, in sufficiently weak fields the system\nundergoes a polarization wave rotonization, leading to the development of\ntextured electronic structure and a dielectric instability that is\ncharacteristic of the onset of a negative static dielectric function.",
        "positive": "One dimensional gas of bosons with integrable resonant interactions: We develop an exact solution to the problem of one dimensional chiral bosons\ninteracting via an s-wave Feshbach resonance. This problem is integrable, being\nthe quantum analog of a classical two-wave model solved by the inverse\nscattering method thirty years ago. Its solution describes one or two branches\nof dressed chiral right moving molecules depending on the chemical potential\n(particle density). We also briefly discuss the possibility of experimental\nrealization of such a system."
    },
    {
        "anchor": "Controlling the group velocity of colliding atomic Bose-Einstein\n  condensates with Feshbach resonances: We report on a proposal to change the group velocity of a small Bose Einstein\nCondensate (BEC) upon collision with another BEC in analogy to slowing of light\npassing through dispersive media. We make use of ultracold collisions near a\nmagnetic Feshbach resonance, which gives rise to a sharp variation in\nscattering length with collision energy and thereby changes the group velocity.\nA generalized Gross-Pitaveskii equation is derived for a small BEC moving\nthrough a larger stationary BEC. We denote the two condensates by laser and\nmedium BEC, respectively, to highlight the analogy to a laser pulse travelling\nthrough a medium. We derive an expression for the group velocity in a\nhomogeneous medium as well as for the difference in distance, $\\delta$, covered\nby the laser BEC in the presence and absence of a finite-sized medium BEC with\na Thomas-Fermi density distribution. For a medium and laser of the same\nisotopic species, the shift $\\delta$ has an upper bound of twice the\nThomas-Fermi radius of the medium. For typical narrow Feshbach resonances and a\nmedium with number density $10^{15}$ cm$^{-3}$ up to 85% of the upper bound can\nbe achieved, making the effect experimentally observable. We also derive\nconstraints on the experimental realization of our proposal.",
        "positive": "Engineering mixing properties of fluids by spatial modulations: We propose a method to change the effective interaction between two fluids by\nmodulation of their local density distributions with external periodic\npotentials, whereby the mixing properties can be controlled. This method is\napplied to a mixture of dilute bosonic gases, and binodal and spinodal curves\nemerge in the phase diagram. Spinodal decomposition into a mixed-bubble state\nbecomes possible, in which one of the coexisting phases has a finite mixing\nratio. A metastable mixture is also realized, which undergoes phase separation\nvia nucleation."
    },
    {
        "anchor": "Exotic paired states with anisotropic spin-dependent Fermi surfaces: We propose a model for realizing exotic paired states in cold atomic Fermi\ngases. By using a {\\it spin dependent} optical lattice it is possible to\nengineer spatially anisotropic Fermi surfaces for each hyperfine species, that\nare rotated 90 degrees with respect to one another. We consider a balanced\npopulation of the fermions with an attractive interaction. We explore the BCS\nmean field phase diagram as a function of the anisotropy, density, and\ninteraction strength, and find the existence of an unusual paired superfluid\nstate with coexisting pockets of momentum space with gapless unpaired carriers.\nThis state is a relative of the Sarma or breached pair states in polarized\nmixtures, but in our case the Fermi gas is unpolarized. We also propose the\npossible existence of an exotic paired \"Cooper-pair Bose-Metal\" (CPBM) phase,\nwhich has a gap for single fermion excitations but gapless and uncondensed\n\"Cooper pair\" excitations residing on a \"Bose-surface\" in momentum space.",
        "positive": "Relation between the noise correlations and the spin structure factor\n  for Mott-insulating states in SU$(N)$ Hubbard models: It is well established that the noise correlations measured by time-of-flight\nimaging in cold-atom experiments, which correspond to the density-density\ncorrelations in the momentum space of trapped atomic gases, can probe the spin\nstructure factor deep in the Mott-insulating regime of SU(2) Hubbard models. We\nexplicitly derive the mathematical relation between the noise correlations and\nthe spin structure factor in the strong-interaction limit of SU$(N)$ Hubbard\nmodels at any integer filling $\\rho$. By calculating the ground states of\none-dimensional SU$(N)$ Fermi-Hubbard models for $2\\leq N\\leq 6$ with use of\nthe density-matrix renormalization-group method, we confirm the relation\nnumerically in the regime of strong interactions $U \\gg t$, where $U$ and $t$\ndenote the onsite interaction and the hopping energy. We show that the\ndeviation between the actual noise correlations and those obtained from the\nspin structure factor scales as approximately $(t/U)^2$ for $\\rho=1$ at\nintermediate and large lattice sizes on the basis of numeric and semi-analytic\narguments."
    },
    {
        "anchor": "Nonlinear Klein-Gordon equation and the Bose-Einstein condensation: The interest in the Klein-Gordon equation with different potentials has\nincreased in recent years due to its possible applications in Cosmology, Hadron\nPhysics and High-Energy Physics. In this work we investigate the solutions of\nthe Klein-Gordon equation for bosons under the influence of an external\npotential by using the Feshbach-Villars method. We present detailed results for\ntwo cases: the Coulombic potential and the harmonic potential. For the latter\ncase, we studied the effects of self-interacting particles by adopting a\nmean-field approach. We show that our results converge smoothly to the solution\nof the Schr\\\"odinger equation for the same systems as the relativistic effects\ndiminish.",
        "positive": "Synthetic superfluid chemistry with vortex-trapped quantum impurities: We explore the effect of using two-dimensional matter-wave vortices to\nconfine an ensemble of bosonic quantum impurities. This is modelled\ntheoretically using a mass-imbalanced homogeneous two component\nGross-Pitaevskii equation where each component has independent atom numbers and\nequal atomic masses. By changing the mass imbalance of our system we find the\nshape of the vortices are deformed even at modest imbalances, leading to barrel\nshaped vortices; which we quantify using a multi-component variational\napproach. The energy of impurity carrying vortex pairs are computed, revealing\na mass-dependent energy splitting. We then compute the excited states of the\nimpurity, which we in turn use to construct `covalent bonds' for vortex pairs.\nOur work opens a new route to simulating synthetic chemical reactions with\nsuperfluid systems."
    },
    {
        "anchor": "Ising antiferromagnet with ultracold bosonic mixtures confined in a\n  harmonic trap: We present accurate results based on Quantum Monte Carlo simulations of\ntwo-component bosonic systems on a square lattice and in the presence of an\nexternal harmonic confinement. Starting from hopping parameters and interaction\nstrengths which stabilize the Ising antiferromagnetic phase in the homogeneous\ncase and at half integer filling factor, we study how the presence of the\nharmonic confinement challenge the realization of such phase. We consider\nrealistic trapping frequencies and number of particles, and establish under\nwhich conditions, i.e. total number of particles and population imbalance, the\nantiferromagnetic phase can be observed in the trap.",
        "positive": "P-wave superfluidity of atomic lattice fermions: We discuss the emergence of p-wave superfluidity of identical atomic fermions\nin a two-dimensional optical lattice. The optical lattice potential manifests\nitself in an interplay between an increase in the density of states on the\nFermi surface and the modification of the fermion-fermion interaction\n(scattering) amplitude. The density of states is enhanced due to an increase of\nthe effective mass of atoms. In deep lattices the scattering amplitude is\nstrongly reduced compared to free space due to a small overlap of wavefunctions\nof fermion sitting in the neighboring lattice sites, which suppresses the\np-wave superfluidity. However, for moderate lattice depths the enhancement of\nthe density of states can compensate the decrease of the scattering amplitude.\nMoreover, the lattice setup significantly reduces inelastic collisional losses,\nwhich allows one to get closer to a p-wave Feshbach resonance. This opens\npossibilities to obtain the topological $p_x+ip_y$ superfluid phase, especially\nin the recently proposed subwavelength lattices. We demonstrate this for the\ntwo-dimensional version of the Kronig-Penney model allowing a transparent\nphysical analysis."
    },
    {
        "anchor": "Probing quantum properties of black holes with a Floquet-driven optical\n  lattice simulator: In the curved spacetime of a black hole, quantum physics gives rise to\ndistinctive effects such as Hawking radiation. Here, we present a scheme for an\nanalogue quantum simulation of (1 + 1)- dimensional black holes using ultracold\natoms in a locally Floquet-driven 1D optical lattice. We show how the effective\ndynamics of the driven system can generate a position-dependent tunnelling\nprofile that encodes the curved geometry of the black hole. Moreover, we\nprovide a simple and robust scheme to determine the Hawking temperature of the\nsimulated black hole based solely on on-site atom population measurements.\nFinally, we show how this scheme can be directly applied to simulate (2 + 1)D\nblack holes by utilising 2D optical lattices. By incorporating the effect of\natom-atom interactions, our simulator can probe the scrambling of quantum\ninformation which is a fundamental property of black holes.",
        "positive": "Effects of Interactions on the Critical Temperature of a Trapped Bose\n  Gas: We perform high-precision measurements of the condensation temperature of a\nharmonically-trapped atomic Bose gas with widely-tuneable interactions. For\nweak interactions we observe a negative shift of the critical temperature in\nexcellent agreement with mean-field theory. However for sufficiently strong\ninteractions we clearly observe an additional positive shift, characteristic of\nbeyond-mean-field critical correlations. We also discuss non-equilibrium\neffects on the apparent critical temperature for both very weak and very strong\ninteractions."
    },
    {
        "anchor": "Observation of Cavity Rydberg Polaritons: We demonstrate hybridization of optical cavity photons with atomic Rydberg\nexcitations using electromagnetically induced transparency (EIT). The resulting\ndark state Rydberg polaritons exhibit a compressed frequency spectrum and\nenhanced lifetime indicating strong light-matter mixing. We study the coherence\nproperties of cavity Rydberg polaritons and identify the generalized EIT\nlinewidth for optical cavities. Strong collective coupling suppresses polariton\nlosses due to inhomogeneous broadening, which we demonstrate by using different\nRydberg levels with a range of polarizabilities. Our results point the way\ntowards using cavity Rydberg polaritons as a platform for creating photonic\nquantum materials.",
        "positive": "Mott insulating phases and magnetism of fermions in a double-well\n  optical lattice: We theoretically investigate, using non-perturbative strong correlation\ntechniques, Mott insulating phases and magnetic ordering of two-component\nfermions in a two-dimensional double-well optical lattice. At filling of two\nfermions per site, there are two types of Mott insulators, one of which is\ncharacterized by spin-1 antiferromagnetism below the Neel temperature. The\nsuper-exchange interaction in this system is induced by the interplay between\nthe inter-band interaction and the spin degree of freedom. A great advantage of\nthe double-well optical lattice is that the magnetic quantum phase diagram and\nthe Neel temperature can be easily controlled by tuning the orbital energy\nsplitting of the two-level system. Particularly, the Neel temperature can be\none order of magnitude larger than that in standard optical lattices,\nfacilitating the experimental search for magnetic ordering in optical lattice\nsystems."
    },
    {
        "anchor": "Beyond Mean-Field Low-Lying Excitations of Dipolar Bose Gases: We theoretically investigate various beyond mean-field effects on Bose gases\nat zero temperature featuring the anisotropic and long-range dipole-dipole\ninteraction in addition to the isotropic and short-range contact interaction.\nWithin the realm of the Bogoliubov-de Gennes theory, we consider static\nproperties and low-lying excitations of both homogeneous and harmonically\ntrapped dipolar bosonic gases. For the homogeneous system, the condensate\ndepletion, the ground-state energy, the equation of state, and the speed of\nsound are discussed in detail. Making use of the local density approximation,\nwe extend these results in order to study the properties of a dipolar Bose gas\nin a harmonic trap and in the regime of large particle numbers. After deriving\nthe equations of motion for the general case of a triaxial trap, we analyze the\ninfluence of quantum fluctuations on important properties of the gas, such as\nthe equilibrium configuration and the low-lying excitations in the case of a\ncylinder-symmetric trap. In addition to the monopole and quadrupole oscillation\nmodes, we also discuss the radial quadrupole mode. We find that the latter\nacquires a quantum correction exclusively due to the dipole-dipole interaction.\nAs a result, we identify the radial quadrupole as a reasonably accessible\nsource for the signature of dipolar many-body effects and stress the enhancing\ncharacter that dipolar interactions have for quantum fluctuations in the other\noscillation modes.",
        "positive": "Adiabatic preparation of many-body states in optical lattices: We analyze a technique for the preparation of low entropy many body states of\natoms in optical lattices based on adiabatic passage. In particular, we show\nthat this method allows preparation of strongly correlated states as stable\nhighest energy states of Hamiltonians that have trivial ground states. As an\nexample, we analyze the generation of antiferromagnetically ordered states by\nadiabatic change of a staggered field acting on the spins of bosonic atoms with\nferromagnetic interactions."
    },
    {
        "anchor": "Resonant persistent currents for ultracold bosons on a lattice ring: We consider a one-dimensional bosonic gas on a ring lattice, in the presence\nof a localized barrier, and under the effect of an artificial gauge field. By\nmeans of exact diagonalization we study the persistent currents at varying\ninteractions and barrier strength, for various values of lattice filling. While\ngenerically the persistent currents are strongly suppressed in the Mott\ninsulator phase, they show a resonant behaviour when the barrier strength\nbecomes of the order of the interaction energy. We explain this phenomenon\nusing an effective single-particle model. We show that this effect is robust at\nfinite temperature, up the temperature scale where persistent currents vanish.",
        "positive": "Droplets of trapped quantum dipolar bosons: Strongly interacting systems of dipolar bosons in three dimensions confined\nby harmonic traps are analyzed using the exact Path Integral Ground State Monte\nCarlo method. By adding a repulsive two-body potential, we find a narrow window\nof interaction parameters leading to stable ground- state configurations of\ndroplets in a crystalline arrangement. We find that this effect is entirely due\nto the interaction present in the Hamiltonian without resorting to additional\nstabilizing mechanisms or specific three-body forces. We analyze the number of\ndroplets formed in terms of the Hamiltonian parameters, relate them to the\ncorresponding s-wave scattering length, and discuss a simple scaling model for\nthe density profiles. Our results are in qualitative agreement with recent\nexperiments showing a quantum Rosensweig instability in trapped Dy atoms."
    },
    {
        "anchor": "Many-body non-Hermitian skin effect under dynamic gauge coupling: We study an atom-cavity hybrid system where fermionic atoms in a\none-dimensional lattice are subject to a cavity-induced dynamic gauge\npotential. The gauge coupling leads to highly-degenerate steady states in which\nthe fermions accumulate to one edge of the lattice under an open boundary\ncondition. Such a phenomenon originates from the many-body Liouvillian\nsuperoperator of the system, which, being intrinsically non-Hermitian, is\nunstable against boundary perturbations and manifests the non-Hermitian skin\neffect. Contrary to the single-body case, the steady state of a multi-atom\nsystem is approached much slower under the open boundary condition, as the\nlong-time damping of the cavity mode exhibits distinct rates at different\ntimes. This stage-wise slowdown is attributed to the competition between\nlight-assisted hopping and the dynamic gauge coupling, which significantly\nreduces the steady-state degeneracy under the open boundary condition, as\ndistinct hosts of quasi-steady states dominate the dynamics at different time\nscales.",
        "positive": "Efimov Trimers in a Harmonic Potential: We study the Efimov effect in a harmonic oscillator in the hyperspherical\nformulation, and show how a reduced model allows for a description that is a\ngeneralization of the Efimov effect in free space and leads to results that are\neasily interpreted. Efimov physics may be observed by varying the value of the\nscattering length, since in the regime where the trimers have a mixed harmonic\noscillator and Efimov character, the inelastic properties of these states are\nstill manageable. The model also allows for the study of non-universal Efimov\ntrimers by including the effective range scattering parameter. While we find\nthat in a certain regime the effective range parameter can take over the role\nof the three-body parameter, interestingly, we obtain a numerical relationship\nbetween these two parameters different from what was found in other models."
    },
    {
        "anchor": "Interacting atomic interferometry for rotation sensing approaching the\n  Heisenberg Limit: Atom interferometers provide exquisite measurements of the properties of\nnon-inertial frames. While atomic interactions are typically detrimental to\ngood sensing, efforts to harness entanglement to improve sensitivity remain\ntantalizing. Here we explore the role of interactions in an analogy between\natomic gyroscopes and SQUIDs, motivated by recent experiments realizing ring\nshaped traps for ultracold atoms. We explore the one-dimensional limit of these\nring systems with a moving weak barrier, such as that provided by a\nblue-detuned laser beam. In this limit, we employ Luttinger liquid theory and\nfind an analogy with the superconducting phase-slip qubit, in which the\ntopological charge associated with persistent currents can be put into\nsuperposition. In particular, we find that strongly-interacting atoms in such a\nsystem could be used for precision rotation sensing. We compare the performance\nof this new sensor to an equivalent non-interacting atom interferometer, and\nfind improvements in sensitivity and bandwidth beyond the atomic shot-noise\nlimit.",
        "positive": "Path integral molecular dynamics for anyons, bosons and fermions: In this article we develop a general method to numerically calculate physical\nproperties for a system of anyons with path integral molecular dynamics. We\nprovide a unified method to calculate the thermodynamics of identical bosons,\nfermions and anyons. Our method is tested and applied to systems of anyons,\nbosons and fermions in a two-dimensional harmonic trap. We also consider a\nmethod to calculate the energy for fermions as an application of the path\nintegral molecular dynamics to simulate the anyon model."
    },
    {
        "anchor": "Tailored generation of quantum states in an entangled spinor\n  interferometer to overcome detection noise: We theoretically investigate how entangled atomic states generated via\nspin-changing collisions in a spinor Bose-Einstein condensate can be designed\nand controllably prepared for atom interferometry that is robust against common\ntechnical issues, such as limited detector resolution. We use analytic and\nnumerical treatments of the spin-changing collision process to demonstrate that\ntriggering the entangling collisions with a small classical seed rather than\nvacuum fluctuations leads to a more robust and superior sensitivity when\ntechnical noise is accounted for, despite the generated atomic state ideally\nfeaturing less metrologically useful entanglement. Our results are relevant for\nunderstanding how entangled atomic states are best designed and generated for\nuse in quantum-enhanced matter-wave interferometry.",
        "positive": "Critical behaviour in one dimension: unconventional pairing, phase\n  separation, BEC-BCS crossover and magnetic Lifshitz transition: We study the superconducting properties of population-imbalanced ultracold\nFermi mixtures in one-dimensional (1D) optical lattices that can be effectively\ndescribed by the spin-imbalanced attractive Hubbard model (AHM) in the presence\nof a Zeeman magnetic field. We use the mean-field theory approach to obtain the\nground state phase diagrams including some unconventional superconducting\nphases such as the Fulde--Ferrell--Larkin--Ovchinnikov (FFLO) phase, and the\n$\\eta$ phase (an extremal case of the FFLO phase), both for the case of a fixed\nchemical potential and for a fixed number of particles. It allows to determine\noptimal regimes for the FFLO phase as well as $\\eta$-pairing stability. We also\ninvestigate the evolution from the weak coupling (BCS-like limit) to the strong\ncoupling limit of tightly bound local pairs (BEC) with increasing attraction,\nat $T=0$. Finally, the obtained results show that despite of the occurrence of\nthe Lifshitz transition induced by an external magnetic field, the\nsuperconducting state can still exist in the system, at higher magnetic field\nvalues."
    },
    {
        "anchor": "Stability of Emergent Kinetics in Optical Lattices with Artificial\n  Spin-Orbit Coupling: Artificial spin-orbit coupling in optical lattices can be engineered to tune\nband structure into extreme regimes where the single-particle band flattens\nleaving only inter-particle interactions to define many-body states of matter.\nLin et al. [Phys. Rev. Lett 112, 110404 (2014)] showed that under such\nconditions interactions lead to a Wigner crystal of fermionic atoms under\napproximate conditions: no bandwidth or band mixing. The excitations were shown\nto possess emergent kinetics with fractionalized charge derived entirely from\ninteractions. In this work we use numerical exact diagonalization to study a\nmore realistic model with non-zero bandwidth and band mixing. We map out the\nstability phase diagram of the Wigner crystal. We find that emergent properties\nof the Wigner crystal excitations remain stable for realistic experimental\nparameters. Our results validate the approximations made by Lin et al. and\ndefine parameter regimes where strong interaction effects generate emergent\nkinetics in optical lattices.",
        "positive": "Complex wave fields in the interacting one-dimensional Bose gas: We study the temperature regimes of the 1d interacting gas to determine when\nthe matter wave (c-field) theory is, in fact, correct and usable. The judgment\nis made by investigating the level of discrepancy in many observables at once\nin comparison to the exact Yang-Yang theory. We also determine what cutoff\nmaximizes the accuracy of such an approach. Results are given in terms of a\nbound on accuracy, as well as an optimal cutoff prescription. For a wide range\nof temperatures the optimal cutoff is independent of density or interaction\nstrength and so its temperature dependent form is suitable for many cloud\nshapes and, possibly, basis choices. However, this best global choice is higher\nin energy than most prior determinations. The high value is needed to obtain\nthe correct kinetic energy, but does not detrimentally affect other\nobservables."
    },
    {
        "anchor": "Thermodynamics of spin-orbit coupled bosons in two dimensions from\n  complex Langevin: We investigate the thermal properties of interacting spin-orbit coupled\nbosons with contact interactions in two spatial dimensions. To that end, we\nimplement the complex Langevin method, motivated by the appearance of a sign\nproblem, on a square lattice with periodic boundary conditions. We calculate\nthe density equation of state non-perturbatively in a range of spin-orbit\ncouplings and chemical potentials. Our results show that mean-field solutions\ntend to underestimate the average density, especially for stronger values of\nthe spin-orbit coupling. Additionally, the finite nature of the simulation\nvolume induces the formation of pseudo-condensates. These have been observed to\nbe destroyed by the spin-orbit interactions.",
        "positive": "Criteria for 2D kinematics in an interacting Fermi gas: Ultracold Fermi gases subject to tight transverse confinement offer a highly\ncontrollable setting to study the two-dimensional (2D) BCS to\nBerezinskii-Kosterlitz-Thouless superfluid crossover. Achieving the 2D regime\nrequires confining particles to their transverse ground state which presents\nchallenges in interacting systems. Here, we establish the conditions for an\ninteracting Fermi gas to behave kinematically 2D. Transverse excitations are\ndetected by measuring the transverse expansion rate which displays a sudden\nincrease when the atom number exceeds a critical value $N_{2D}$ signifying a\ndensity driven departure from 2D kinematics. For weak interactions $N_{2D}$ is\nset by the aspect ratio of the trap. Close to a Feshbach resonance, however,\nthe stronger interactions reduce $N_{2D}$ and excitations appear at lower\ndensity."
    },
    {
        "anchor": "Symmetry-protected topological phase transition in one-dimensional Kondo\n  lattice and its realization with ultracold atoms: We propose that ultracold alkaline-earth-like atoms confined in\none-dimensional optical lattice can realize a Kondo lattice model which hosts a\nsymmetry-protected topological (SPT) phase and an associated quantum phase\ntransition in a controllable manner. The symmetry protection of the phase\ntransition is discussed from two different viewpoints: topological properties\nrelated to spatial patterns of Kondo singlets, and symmetry eigenvalues of the\nspin states. We uncover the role of various symmetries in the phase diagram of\nthis system by combining a weak-coupling approach by Abelian bosonization and\nstrong-coupling pictures of ground states. Furthermore, we show that the\nbosonization approach correctly describes a crossover from a fermionic SPT\nphase to a bosonic SPT phase and an associated change of protecting symmetries\nas the charge degrees of freedom are frozen by the Hubbard repulsion.",
        "positive": "Bloch oscillations in lattice potentials with controlled aperiodicity: We numerically investigate the damping of Bloch oscillations in a\none-dimensional lattice potential whose translational symmetry is broken in a\nsystematic manner, either by making the potential bichromatic or by introducing\nscatterers at distinct lattice sites. We find that the damping strongly depends\non the ratio of lattice constants in the bichromatic potential, and that even a\nsmall concentration of scatterers can lead to strong damping. Moreover,\nmean-field interactions are able to counteract aperiodicity-induced damping of\nBloch oscillations."
    },
    {
        "anchor": "Universal relations and normal-state properties of a Fermi gas with\n  laser-dressed mixed-partial-wave interactions: In a recent experiment [P. Peng, $et$ $al.$, Phys. Rev. A \\textbf{97}, 012702\n(2018)], it has been shown that the $p$-wave Feshbach resonance can be shifted\ntoward the $s$-wave Feshbach resonance by a laser field. Based on this\nexperiment, we study the universal relations and the normal-state properties in\nan ultracold Fermi gas with coexisting $s$- and $p$-wave interactions under\noptical control of a $p$-wave magnetic Feshbach resonance. Within the\noperator-product expansion, we derive the high-momentum tail of various\nobservable quantities in terms of contacts. We find that the high-momentum tail\nbecomes anisotropic. Adopting the quantum virial expansion, we calculate the\nnormal-state contacts with and without a laser field for $^{40}$K atoms using\ntypical experimental parameters. We show that the contacts are dependent on the\nlaser dressing. We also reveal the interplay of laser dressing and different\npartial-wave interactions on various contacts. In particular, we demonstrate\nthat the impact of the laser dressing in the $p$-wave channel can be probed by\nmeasuring the $s$-wave contacts, which is a direct manifestation of few-body\neffects on the many-body level. Our results can be readily checked\nexperimentally.",
        "positive": "Strong-coupling solution of the bosonic dynamical mean-field theory: We derive an approximate analytical solution of the self-consistency\nequations of the bosonic dynamical mean-field theory (B-DMFT) in the\nstrong-coupling limit. The approach is based on a linked-cluster expansion in\nthe hybridization function of normal bosons around the atomic limit. The\nsolution is used to compute the phase diagram of the bosonic Hubbard model for\ndifferent lattices. We compare our results with numerical solutions of the\nB-DMFT equations and numerically exact methods, respectively. The very good\nagreement with those numerical results demonstrates that our approach captures\nthe essential physics of correlated bosons both in the Mott insulator and in\nthe superfluid phase. Close to the transition into the superfluid phase the\nmomentum distribution function at zero momentum is found to be strongly\nenhanced already in the normal phase. The linked-cluster expansion also allows\nus to compute dynamical properties such as the spectral function of bosons. The\nevolution of the spectral function across the transition from the normal to the\nsuperfluid phase is seen to be characteristically different for the interaction\ndriven and density driven transition, respectively."
    },
    {
        "anchor": "One-dimensional Bose-Einstein condensation of photons in a microtube: This paper introduces a quasiequilibrium one-dimensional Bose-Einstein\ncondensation of photons trapped in a microtube. Light modes with a cut-off\nfrequency (a photon's \"mass\") interact through different processes of\nabsorption, emission, and scattering on molecules and atoms. In this paper, we\nstudy the conditions for the one-dimensional condensation of light and the role\nof photon-photon interactions in the system. The technique in use is the\nMatsubara's Green's functions formalism modified for the quasiequilibrium\nsystem under study.",
        "positive": "Nonzero temperature dynamics of a repulsive two-component Fermi gas: We study spin-dipole oscillations of a binary fermionic mixture at nonzero\ntemperatures. We apply the atomic-orbital method combined with the Monte Carlo\ntechnique based sampling to probe finite temperatures. Our results agree\nquantitatively with recent experiment, G. Valtolina et al., Nat. Phys. 13, 704\n(2017), showing the appearance of the ferromagnetic phase at stronger repulsion\nbetween components when the temperature is increased."
    },
    {
        "anchor": "Quantum heat engine based on a spin-orbit and Zeeman-coupled\n  Bose-Einstein condensate: We explore the potential of a spin-orbit coupled Bose-Einstein condensate for\nthermodynamic cycles. For this purpose we propose a quantum heat engine based\non a condensate with spin-orbit and Zeeman coupling as a working medium. The\ncooling and heating are simulated by contacts of the condensate with an\nexternal magnetized media and demagnetized media. We examine the condensate\nground state energy and its dependence on the strength of the synthetic\nspin-orbit and Zeeman couplings and interatomic interaction. Then we study the\nefficiency of the proposed engine. The cycle has a critical value of spin-orbit\ncoupling related to the engine maximum efficiency.",
        "positive": "Nonlinear Waves in an Experimentally Motivated Ring-shaped Bose-Einstein\n  Condensate Setup: We systematically construct stationary soliton states in a one-component,\ntwo-dimensional, repulsive, Gross-Pitaevskii equation with a ring-shaped\ntarget-like trap similar to the potential used to confine a Bose-Einstein\ncondensate in a recent experiment [Eckel, et al.\\ {\\em Nature} {\\bf 506}, 200\n(2014)]. In addition to the ground state configuration, we identify a wide\nvariety of excited states involving phase jumps (and associated dark solitons)\ninside the ring. These configurations are obtained from a systematic\nbifurcation analysis starting from the linear, small atom density, limit. We\nstudy the stability, and when unstable, the dynamics of the most basic\nconfigurations. Often these lead to vortical dynamics inside the ring\npersisting over long time scales in our numerical experiments. To illustrate\nthe relevance of the identified states, we showcase how such dark-soliton\nconfigurations (even the unstable ones) can be created in laboratory\ncondensates by using phase-imprinting techniques."
    },
    {
        "anchor": "Josephson plasma oscillations and the Gross-Pitaevskii equation:\n  Bogoliubov approach vs two-mode model: We show that the Josephson plasma frequency for a condensate in a double-well\npotential, whose dynamics is described by the Gross-Pitaevskii (GP) equation,\ncan be obtained with great precision by means of the usual Bogoliubov approach,\nwhereas the two-mode model - commonly constructed by means of a linear\ncombinations of the low-lying states of the GP equation - generally provides\naccurate results only for weak interactions. A proper two-mode model in terms\nof the Bogoliubov functions is also discussed, revealing that in general a\ntwo-mode approach is formally justified only for not too large interactions,\neven in the limit of very small amplitude oscillations. Here we consider\nspecifically the case of a one-dimensional system, but the results are expected\nto be valid in arbitrary dimensions.",
        "positive": "Vortex and soliton dynamics in particle-hole symmetric superfluids: We propose to induce topological defects in particle-hole symmetric\nsuperfluids, with the prime example of the BCS state of ultracold atoms and\ndetect their time evolution and decay. We demonstrate that the time evolution\nis qualitatively distinct for particle-hole symmetric superfluids, and point\nout that the dynamics of topological defects is strongly modified in\nparticle-hole symmetric fluids. We obtain results for different charges and\ncompare them with the standard Gross-Pitaevskii prediction for Bose-Einstein\ncondensates. We highlight the observable signatures of the particle-hole\nsymmetry in the dynamics of decaying solitons and subsequent vortices."
    },
    {
        "anchor": "Controlling the Floquet state population and observing micromotion in a\n  periodically driven two-body quantum system: Near-resonant periodic driving of quantum systems promises the implementation\nof a large variety of novel effective Hamiltonians. The challenge of Floquet\nengineering lies in the preparation and measurement of the desired quantum\nstate. We address these aspects in a model system consisting of interacting\nfermions in a periodically driven array of double wells created by an optical\nlattice. The singlet and triplet fractions and the double occupancy of the\nFloquet states are measured, and their behavior as a function of the\ninteraction strength is analyzed in the high- and low-frequency regimes. We\ndemonstrate full control of the Floquet state population and find suitable\nramping protocols and time-scales which adiabatically connect the initial\nground state to different targeted Floquet states. The micromotion which\nexactly describes the time evolution of the system within one driving cycle is\nobserved. Additionally, we provide an analytic description of the model and\ncompare it to numerical simulations.",
        "positive": "Quantum Simulation Meets Nonequilibrium Dynamical Mean Field Theory:\n  Exploring the Periodically Driven, Strongly Correlated Fermi-Hubbard Model: We perform an ab-initio comparison between nonequilibrium dynamical\nmean-field theory and optical lattice experiments by studying the time\nevolution of double occupations in the periodically driven Fermi-Hubbard model.\nFor off-resonant driving, the range of validity of a description in terms of an\neffective static Hamiltonian is determined and its breakdown due to energy\nabsorption close to resonance is demonstrated. For near-resonant driving, we\ninvestigate the response to a change in driving amplitude and discover an\nasymmetric excitation spectrum with respect to the detuning. In general, we\nfind good agreement between experiment and theory, which cross-validates the\nexperimental and numerical approaches in a strongly-correlated nonequilibrium\nsystem."
    },
    {
        "anchor": "Supersolid and charge density-wave states from anisotropic interaction\n  in an optical lattice: We show anisotropy of the dipole interaction between magnetic atoms or polar\nmolecules can stabilize new quantum phases in an optical lattice. Using a well\ncontrolled numerical method based on the tensor network algorithm, we calculate\nphase diagram of the resultant effective Hamiltonian in a two-dimensional\nsquare lattice - an anisotropic Hubbard model of hard-core bosons with\nattractive interaction in one direction and repulsive interaction in the other\ndirection. Besides the conventional superfluid and the Mott insulator states,\nwe find the striped and the checkerboard charge density wave states and the\nsupersolid phase that interconnect the superfluid and the striped solid states.\nThe transition to the supersolid phase has a mechanism different from the case\nof the soft-core Bose Hubbard model.",
        "positive": "Quench between a Mott insulator and a Lieb-Liniger liquid: In this work we study a quench between a Mott insulator and a repulsive\nLieb-Liniger liquid. We find explicitly the stationary state when a long time\nhas passed after the quench. It is given by a GGE density matrix which we\ncompletely characterize, calculating the quasiparticle density describing the\nsystem after the quench. In the long time limit we find an explicit form for\nthe local three body density density density correlation function and the\nasymptotic long distance limit of the density density correlation function. The\nlater is shown to have a Gaussian decay at large distances."
    },
    {
        "anchor": "Excitations of optomechanically driven Bose-Einstein condensates in a\n  cavity: photodetection measurements: We present a detailed study to analyse the Dicke quantum phase transition\nwithin the thermodynamic limit for an optomechanically driven Bose-Einstein\ncondensates in a cavity. The photodetection-based quantum optical measurements\nhave been performed to study the dynamics and excitations of this\noptomechanical Dicke system. For this, we discuss the eigenvalue analysis,\nfluorescence spectrum and the homodyne spectrum of the system. It has been\nshown that the normal phase is negligibly affected by the mechanical mode of\nthe mirror while it has a significant effect in the superradiant phase. We have\nobserved that the eigenvalues and both the spectra exhibit distinct features\nthat can be identified with the photonic, atomic and phononic branches. In the\nfluorescence spectra, we further observe an asymmetric coherent energy exchange\nbetween the three degrees of freedom of the system in the superradiant phase\narising as a result of optomechanical interaction and Bloch-Siegert shift.",
        "positive": "Single-branch theory of ultracold Fermi gases with artificial Rashba\n  spin-orbit coupling: We consider interacting ultracold fermions subject to Rashba spin-orbit\ncoupling. We construct a single-branch interacting theory for the Fermi gas\nwhen the system is dilute enough so that the positive helicity branch is not\noccupied at all in the non-interacting ground state. We show that the theory is\nrenormalizable in perturbation theory and therefore yields a model of polarized\nfermions that avoids a multi-channel treatment of the problem. Our results open\nthe path towards a much more straightforward approach to the many-body physics\nof cold atoms subject to artificial vector potentials."
    },
    {
        "anchor": "Quantum Thermalization and the Expansion of Atomic Clouds: The ultimate consequence of quantum many-body physics is that even the air we\nbreathe is governed by strictly unitary time evolution. The reason that we\nperceive it nonetheless as a completely classical high temperature gas is due\nto the incapacity of our measurement machines to keep track of the dense\nmany-body entanglement of the gas molecules. The question thus arises whether\nthere are instances where the quantum time evolution of a macroscopic system is\nqualitatively different from the equivalent classical system? Here we study\nthis question through the expansion of noninteracting atomic clouds. While in\nmany cases the full quantum dynamics is indeed indistinguishable from classical\nballistic motion, we do find a notable exception. The subtle quantum\ncorrelations in a Bose gas approaching the condensation temperature appear to\naffect the expansion of the cloud, as if the system has turned into a diffusive\ncollision-full classical system.",
        "positive": "Complex-valued in-medium potential between heavy impurities in ultracold\n  atoms: We formulate the induced potential in a finite temperature cold atomic medium\nbetween two heavy impurities, or polarons, which is shown to be\n\\textit{complex-valued} in general. The imaginary part of the complex-valued\npotential describes a decoherence effect, and thus, the resulting Schr\\\"odinger\nequation for the two polarons acquires a non-Hermitian term. We apply the\ndeveloped formulation to two representative cases of polarons interacting with\nmedium particles through the $s$-wave contact interaction: (i) the normal phase\nof single-component (i.e., spin-polarized) fermions using the fermionic field\ntheory, and (ii) a superfluid phase using the superfluid effective field\ntheory, which is valid either for a Bose-Einstein condensate (BEC) of a\nsingle-component Bose gas or for the BEC-BCS crossover in two-component\nfermions at a low-energy regime. Computing the leading-order term, the\nimaginary part of the potential in both cases is found to show a universal\n$r^{-2}$ behavior at long distance. We propose three experimental ways to\nobserve the effects of the universal imaginary potential in cold atoms."
    },
    {
        "anchor": "Efimov States of Heavy Impurities in a Bose-Einstein Condensate: We consider the problem of two heavy impurity particles embedded in a gas of\nweakly-interacting light mass bosonic particles in the condensed state. Using\nthe Bogoliubov approach to describe the bosonic gas and the Born-Oppenheimer\napproximation for the three-body dynamics, we calculate the modification to the\nheavy-heavy two-body potential due to the presence of the condensate. For the\ncase of resonant interaction between the light bosons and the impurities, we\npresent (semi)-analytical results for the potential in the limit of a large\ncondensate coherence length. In particular, we find a formula for the\nmodification of the Efimov scaling factor due to the presence of a degenerate\nbosonic gas background.",
        "positive": "Influence of Induced Interactions on Superfluid Properties of Quasi-Two\n  Dimensional Dilute Fermi Gases With Spin-Orbit Coupling: We study the effects of induced interactions on the pairing gap, transition\ntemperature and chemical potential of a quasi-two dimensional Fermi gas of\natoms with spin-orbit coupling. We find that these mean-field parameters are\nsignificantly modified when induced interactions are taken into account. We\nalso investigate the implications of induced interactions corrections for the\nBCS-BEC crossover driven by spin-orbit coupling, that happens even for small\n(compared to the Fermi energy) values of the binding energy."
    },
    {
        "anchor": "Three-body interacting dipolar bosons and the fate of lattice\n  supersolidity: We investigate a system of dipolar bosons in an optical lattice with local\ntwo and three-body interactions. Using the mean-field theory approach, we\nobtain the ground state phase diagram of the extended Bose-Hubbard (EBH) model\nwith both repulsive and attractive three-body interac- tions. We show that the\nadditional three-body on-site interaction has strong effects on the phase\ndiagram especially on the supersolid phase. Positive values of the three-body\ninteraction lead to the enhancement of the gapped phases at densities larger\nthan unity by reducing the supersolid region. However, a small attractive\nthree-body interaction enhances the supersolid phase.",
        "positive": "Nearest-Neighbor Tunneling Ansatz in the Bose-Hubbard Mode: A recently introduced recurrence-relation ansatz applied to the\nJaynes-Cummings-Hubbard model is here applied to the Bose-Hubbard model that\nreduced the model to an easily soluble model. The results obtained for the\ntwo-point density correlations resemble somewhat those obtained recently also\nbut in a much more complicated fashion. Our ansatz may be of value for the\nsolution of many-body quantum mechanical problems."
    },
    {
        "anchor": "Merging and alignment of Dirac points in a shaken honeycomb optical\n  lattice: Inspired by the recent creation of the honeycomb optical lattice and the\nrealization of the Mott insulating state in a square lattice by shaking, we\nstudy here the shaken honeycomb optical lattice. For a periodic shaking of the\nlattice, a Floquet theory may be applied to derive a time-independent\nHamiltonian. In this effective description, the hopping parameters are\nrenormalized by a Bessel function, which depends on the shaking direction,\namplitude and frequency. Consequently, the hopping parameters can vanish and\neven change sign, in an anisotropic manner, thus yielding different band\nstructures. Here, we study the merging and the alignment of Dirac points and\ndimensional crossovers from the two dimensional system to one dimensional\nchains and zero dimensional dimers. We also consider next-nearest-neighbor\nhopping, which breaks the particle-hole symmetry and leads to a metallic phase\nwhen it becomes dominant over the nearest-neighbor hopping. Furthermore, we\ninclude weak repulsive on-site interactions and find the density profiles for\ndifferent values of the hopping parameters and interactions, both in a\nhomogeneous system and in the presence of a trapping potential. Our results may\nbe experimentally observed by using momentum-resolved Raman spectroscopy.",
        "positive": "Thermal blurring of a coherent Fermi gas: It is generally assumed that a condensate of paired fermions at equilibrium\nis characterized by a macroscopic wavefunction with a well-defined, immutable\nphase. In reality, all systems have a finite size and are prepared at non-zero\ntemperature; the condensate has then a finite coherence time, even when the\nsystem is isolated in its evolution and the particle number $N$ is fixed. The\nloss of phase memory is due to interactions of the condensate with the excited\nmodes that constitute a dephasing environment. This fundamental effect, crucial\nfor applications using the condensate of pairs' macroscopic coherence, was\nscarcely studied. We link the coherence time to the condensate phase dynamics,\nand we show with a microscopic theory that the time derivative of the\ncondensate phase operator $\\hat{\\theta}\\_0$ is proportional to a chemical\npotential operator that we construct including both the pair-breaking and\npair-motion excitation branches. In a single realization of energy $E$,\n$\\hat{\\theta}\\_0$ evolves at long times as $-2\\mu\\_{\\rm mc}(E)t/\\hbar$ where\n$\\mu\\_{\\rm mc}(E)$ is the microcanonical chemical potential; energy\nfluctuations from one realization to the other then lead to a ballistic\nspreading of the phase and to a Gaussian decay of the temporal coherence\nfunction with a characteristic time $\\propto N^{1/2}$. In the absence of energy\nfluctuations, the coherence time scales as $N$ due to the diffusive motion of\n$\\hat{\\theta}\\_0$. We propose a method to measure the coherence time with\nultracold atoms, which we predict to be tens of milliseconds for the canonical\nensemble unitary Fermi gas."
    },
    {
        "anchor": "Effective theory for ultracold strongly interacting fermionic atoms in\n  two dimensions: We propose a minimal theoretical model for the description of a\ntwo-dimensional (2D) strongly interacting Fermi gas confined transversely in a\ntight harmonic potential, and present accurate predictions for its equation of\nstate and breathing mode frequency. We show that the minimal model Hamiltonian\nneeds at least two independent interaction parameters, the 2D scattering length\nand effective range of interactions, in order to quantitatively explain recent\nexperimental measurements at nonzero filling factor $N/N_{2D}$, where $N$ is\nthe total number of atoms and $N_{2D}$ is the threshold number to reach the 2D\nlimit. We therefore resolve in a satisfactory way the puzzling experimental\nobservations of reduced equations of state and reduced quantum anomaly in\nbreathing mode frequency, due to small yet non-negligible $N/N_{2D}$. We argue\nthat a conclusive demonstration of the much-anticipated quantum anomaly is\npossible at a filling factor of a few percent. Our establishment of the minimal\nmodel for 2D ultracold atoms could be crucial to understanding the fermionic\nBerezinskii-Kosterlitz-Thouless transition in the strongly correlated regime.",
        "positive": "Itinerant ferromagnetism in the repulsive Hubbard chain with anisotropic\n  odd-wave attraction: The ground-state properties of the Hubbard chain with on-site repulsion and\nanisotropic nearest-neighbor attraction are investigated by means of density\nmatrix renormalization group calculations. The non-local attraction acts\nbetween fermions of one spin component only, mimicking the effect of p-wave\nFeshbach resonances in cold-atom systems. We analyze the onset of itinerant\nferromagnetism, pinpointing the critical attraction strength where partially\nand fully ferromagnetic states occur. In the cold-atom setup, where the two\n(pseudo) spin populations are separately conserved, ferromagnetism occurs with\nthe nucleation of a fully imbalanced band-insulating domain hosting the\nattractive component only. The size of this domain grows with the attraction\nstrength, therefore increasing the (opposite) imbalance of the other domain,\nuntil the two spin components are fully separated. In the presence of a\nharmonic trap, the ferromagnetic state hosts a partially imbalanced domain in\nthe center with an excess of the attractive component and filling lower than\none. This central region is surrounded by fully imbalanced domains, located in\nthe trap tails, hosting only fermions belonging to the other component."
    },
    {
        "anchor": "Dimensional crossover in a strongly interacting ultracold atomic Fermi\n  gas: We theoretically explore the crossover from three dimensions (3D) to two (2D)\nin a strongly interacting atomic Fermi superfluid through confining the\ntransverse spatial dimension. Using the gaussian pair fluctuation theory, we\ndetermine the zero-temperature equation of state and Landau critical velocity\nas functions of the spatial extent of the transverse dimension and interaction\nstrength. In the presence of strong interactions, we map out a dimensional\ncrossover diagram from the location of maximum critical velocity, which\nexhibits distinct dependence on the transverse dimension from 2D to quasi-2D,\nand to 3D. We calculate the dynamic structure factor to characterize the\nlow-energy excitations of the system and propose that the intermediate quasi-2D\nregime can be experimentally probed using Bragg spectroscopy.",
        "positive": "Stability and sensitivity of interacting fermionic superfluids to\n  quenched disorder: We probe the response of ultracold, interacting Fermi gases of Lithium (Li)\natoms in the BEC-BCS crossover to strong perturbations in space and time via\nrapidly switched optical disorder potentials with focus on the BEC side. We\nmeasure the time evolution of long-range phase coherence quantified via the\nability of the gas to expand hydrodynamically. While in the presence of static\ndisorder, the effects on a Bardeen-Cooper-Schrieffer (BCS) type superfluid are\npredicted to be much smaller compared to a molecular Bose-Einstein condensate\n(BEC), we find that the quantum properties of a resonantly interacting, unitary\nFermi gas are more strongly suppressed in the presence of quenched disorder\nthan in a molecular BEC. For quenches from a disordered potential, we find that\nthe unitary Fermi gas never recovers quantum hydrodynamics for all parameters\nstudied, while a molecular BEC always recovers quantum hydrodynamics, even when\nthe quench leads to strong particle losses of up to 70 %. Temperature\nmeasurements indicate an additional heating channel specific to gases close to\nresonant interactions, leading to strong local dephasing or pair breaking. Our\nwork illustrates the striking difference between the nonequilibrium phase\ndiagram of the time-dependent disordered BEC-BCS crossover compared to that of\nthe static-disorder case. Moreover, our results suggest an important role of\nlocal dephasing of fermionic pairs by time-dependent local perturbations, which\ncould be a key contribution to the destruction of macroscopic quantum\nproperties for time-dependent perturbations."
    },
    {
        "anchor": "Atom lasers: production, properties and prospects for precision inertial\n  measurement: We review experimental progress on atom lasers out-coupled from Bose-Einstein\ncondensates, and consider the properties of such beams in the context of\nprecision inertial sensing. The atom laser is the matter-wave analog of the\noptical laser. Both devices rely on Bose-enhanced scattering to produce a\nmacroscopically populated trapped mode that is output-coupled to produce an\nintense beam. In both cases, the beams often display highly desirable\nproperties such as low divergence, high spectral flux and a simple spatial mode\nthat make them useful in practical applications, as well as the potential to\nperform measurements at or below the quantum projection noise limit. Both\ndevices display similar second-order correlations that differ from thermal\nsources. Because of these properties, atom lasers are a promising source for\napplication to precision inertial measurements.",
        "positive": "Second-order topological insulator in periodically driven lattice: The higher-order topological insulator (HOTI) is a new type of topological\nsystem which has special bulkedge correspondence compared with conventional\ntopological insulators. In this work, we propose a scheme to realize Floquet\nHOTI in ultracold atom systems. With the combination of periodically\nspin-dependent driving of the superlattices and a next-next-nearest-neighbor\nd-wave-like anisotropic coupling term between different spin components, a\nFloquet second-order topological insulator with four zero-energy corner states\nemerges, whose Wannier bands are gapless and exhibit interesting bulk topology.\nFurthermore, the anisotropic coupling with nearest-neighbor form will also\ninduce some intriguing topological phenomena, e.g. non-topologically protected\ncorner states and topological semimetal for two different types of lattice\nstructures respectively. Our scheme may give insight into the construction of\ndifferent types of higher-order topological insulators in synthetic systems. It\nalso provides an experimentally feasible platform to research the relations\nbetween different types of topological states and may have a wide range of\napplications in future."
    },
    {
        "anchor": "Bose-Einstein condensation of photons in a plasma: We study the Bose-Einstein condensation of photons in a plasma, where we\ninclude the cases of both transverse photons and plasmons. We consider\nfour-wave mixing processes of photon and plasmon modes in a relativistic\nisotropic plasma to determine the coupling constant to lowest order. We further\nshow that photon condensation is possible in an unbounded plasma because, in\ncontrast with other optical media, plasmas introduce an effective photon mass.\nThis guarantees the existence of a finite chemical potential and a critical\ntemperature, which is calculated for both transverse photons and plasmons. By\nconsidering four-wave mixing processes, we derive the interactions between the\nphotons in the condensate. We also study the elementary excitations (or\nBogoliubov modes) of the condensed photon and plasmon gases, and determine the\nrespective dispersion relations. Finally, we discuss the kinetics of photon\ncondensation via inverse Compton scattering between the photons and the\nelectrons in the plasma.",
        "positive": "Observation of universal dissipative dynamics in strongly correlated\n  quantum gas: Dissipation is unavoidable in quantum systems. It usually induces\ndecoherences and changes quantum correlations. To access the information of\nstrongly correlated quantum matters, one has to overcome or suppress\ndissipation to extract out the underlying quantum phenomena. However, here we\nfind an opposite effect that dissipation can be utilized as a powerful tool to\nprobe the intrinsic correlations of quantum many-body systems. Applying\nhighly-controllable dissipation in ultracold atomic systems, we observe a\nuniversal dissipative dynamics in strongly correlated one-dimensional quantum\ngases. The total particle number of this system follows a universal\nstretched-exponential decay, and the stretched exponent measures the anomalous\ndimension of the spectral function, a critical exponent characterizing strong\nquantum fluctuations of this system. This method could have broad applications\nin detecting strongly correlated features, including spin-charge separations\nand Fermi arcs in quantum materials."
    },
    {
        "anchor": "Optimization of collisional Feshbach cooling of an ultracold\n  nondegenerate gas: We optimize a collision-induced cooling process for ultracold atoms in the\nnondegenerate regime. It makes use of a Feshbach resonance, instead of rf\nradiation in evaporative cooling, to selectively expel hot atoms from a trap.\nUsing functional minimization we analytically show that for the optimal cooling\nprocess the resonance energy must be tuned such that it linearly follows the\ntemperature. Here, optimal cooling is defined as maximizing the phase-space\ndensity after a fixed cooling duration. The analytical results are confirmed by\nnumerical Monte-Carlo simulations. In order to simulate more realistic\nexperimental conditions, we show that background losses do not change our\nconclusions, while additional non-resonant two-body losses make a lower initial\nresonance energy with non-linear dependence on temperature preferable.",
        "positive": "Insulator phases of a mixture of spinor fermions and hard-core bosons: We study numerically a one-dimensional mixture of spin-$\\tfrac{1}{2}$\nfermions and scalar bosons in the hard-core limit. Considering repulsive\nfermion-fermion and boson-fermion interactions, we find superfluid and\ninsulator states whose phase diagram is calculated. We determine that given a\nfermionic density $\\rho_F$, the insulator states are located at the bosonic\ndensities $\\rho_B=1-\\rho_F$ and $\\rho_B=1-\\tfrac{1}{2}\\rho_F$, and emerge even\nin the absence of fermion-fermion coupling. In addition, the boson-fermion\nrepulsion drives quantum phase transitions inside the insulator lobes with\n$\\rho_B=1/2$. Our predictions could be observed in current cold-atom\nexperimental platforms."
    },
    {
        "anchor": "Quantum critical behavior influenced by measurement backaction in\n  ultracold gases: Recent realizations of quantum gas microscope offer the possibility of\ncontinuous monitoring of the dynamics of a quantum many-body system at the\nsingle-particle level. By analyzing effective non-Hermitian Hamiltonians of\ninteracting bosons in an optical lattice and continuum, we demonstrate that the\nbackaction of quantum measurement shifts the quantum critical point and gives\nrise to a unique critical phase beyond the terrain of the standard universality\nclass. We perform mean-field and strong-coupling-expansion analyses and show\nthat non-Hermitian contributions shift the superfluid--to-Mott-insulator\ntransition point. Using a low-energy effective field theory, we discuss\ncritical behavior of the one-dimensional interacting Bose gas subject to the\nmeasurement backaction. We derive an exact ground state of the effective\nnon-Hermitian Hamiltonian and find a unique critical behavior beyond the\nTomonaga-Luttinger liquid universality class. We propose experimental\nimplementations of post-selections using quantum gas microscopes to simulate\nthe non-Hermitian dynamics and argue that our results can be investigated with\ncurrent experimental techniques in ultracold atoms.",
        "positive": "Vibrational dressing in Kinetically Constrained Rydberg Spin Systems: Quantum spin systems with kinetic constraints have become paradigmatic for\nexploring collective dynamical behaviour in many-body systems. Here we discuss\na facilitated spin system which is inspired by recent progress in the\nrealization of Rydberg quantum simulators. This platform allows to control and\ninvestigate the interplay between facilitation dynamics and the coupling of\nspin degrees of freedom to lattice vibrations. Developing a minimal model, we\nshow that this leads to the formation of polaronic quasiparticle excitations\nwhich are formed by many-body spin states dressed by phonons. We investigate in\ndetail the properties of these quasiparticles, such as their dispersion\nrelation, effective mass and the quasiparticle weight. Rydberg lattice quantum\nsimulators are particularly suited for studying this phonon-dressed kinetically\nconstrained dynamics as their exaggerated length scales permit the\nsite-resolved monitoring of spin and phonon degrees of freedom."
    },
    {
        "anchor": "Optimized fringe removal algorithm for absorption images: Optical absorption imaging is a basic detection technique for obtaining\ninformation from matter waves, in which the absorption signal can be obtained\nby comparing the recorded detection light field with the light field in the\npresence of absorption, thereby giving the spatial distribution of the atoms.\nThe noise in detection arises mainly from differences between the two recorded\nlight field distributions, which is difficult to avoid in experiments. In this\nwork, we present an optimized fringe removal algorithm, developing a method to\ngenerate an ideal reference light field, avoiding the noise generated by the\nlight field difference, and suppressing the noise signal to the theoretical\nlimit. Using principal component analysis, we explore the optimal calculation\narea and how to remove noise information from the basis to allow optimal\nperformance and speed. As an example, we consider scattering atomic peaks with\na small number of atoms in a triangular lattice. Compared with the conventional\nprocessing method, our algorithm can reduce the measured atomic temperature\nvariance by more than three times, giving a more reliable result.",
        "positive": "A comparison between microscopic methods for finite temperature Bose\n  gases: We analyze the equilibrium properties of a weakly interacting, trapped\nquasi-one-dimensional Bose gas at finite temperatures and compare different\ntheoretical approaches. We focus in particular on two stochastic theories: a\nnumber-conserving Bogoliubov (ncB) approach and a stochastic Gross-Pitaevskii\nequation (sGPe) that have been extensively used in numerical simulations.\nEquilibrium properties like density profiles, correlation functions, and the\ncondensate statistics are compared to predictions based upon a number of\nalternative theories. We find that due to thermal phase fluctuations, and the\ncorresponding condensate depletion, the ncB approach loses its validity at\nrelatively low temperatures. This can be attributed to the change in the\nBogoliubov spectrum, as the condensate gets thermally depleted, and to large\nfluctuations beyond perturbation theory. Although the two stochastic theories\nare built on different thermodynamic ensembles (ncB: canonical, sGPe:\ngrand-canonical), they yield the correct condensate statistics in a large BEC\n(strong enough particle interactions). For smaller systems, the sGPe results\nare prone to anomalously large number fluctuations, well-known for the\ngrand-canonical, ideal Bose gas. Based on the comparison of the above theories\nto the modified Popov approach, we propose a simple procedure for approximately\nextracting the Penrose-Onsager condensate from first- and second-order\ncorrelation functions that is computationally convenient. This also clarifies\nthe link between condensate and quasi-condensate in the Popov theory of\nlow-dimensional systems."
    },
    {
        "anchor": "Phase diagrams of bosonic $AB_{n}$ chains: The $AB_{N-1}$ chain is a system that consists of repeating a unit cell with\n$N$ sites, where between the $A$ and $B$ sites there is an energy difference of\n$\\lambda$. We considered bosons in these special lattices and took into account\nthe kinetic energy, the local two-body interaction, and the inhomogenous local\nenergy in the Hamiltonian. We found the charge density wave (CDW) and\nsuperfluid and Mott insulator phases, and constructed the phase diagram for\n$N=2$ and $3$ at the thermodynamic limit. The system exhibited insulator phases\nfor densities $\\rho=\\alpha/N$, with $\\alpha$ being an integer. We obtained that\nsuperfluid regions separate the insulator phases for densities larger than one.\nFor any $N$ value, we found that for integer densities $\\rho$, the system shows\n$\\rho +1$ insulator phases, a Mott insulator phase, and $\\rho$ CDW phases. For\nnon-integer densities larger than one, several CDW phases appear.",
        "positive": "Loschmidt echo in one-dimensional interacting Bose gases: We explore Loschmidt echo in two regimes of one-dimensional (1D) interacting\nBose gases: the strongly interacting Tonks-Girardeau (TG) regime, and the\nweakly-interacting mean-field regime. We find that the Loschmidt echo of a TG\ngas decays as a Gaussian when small perturbations are added to the Hamiltonian\n(the exponent is proportional to the number of particles and the magnitude of a\nsmall perturbation squared). In the mean-field regime the Loschmidt echo decays\nfaster for larger interparticle interactions (nonlinearity), and it shows\nricher behavior than the TG Loschmidt echo dynamics, with oscillations\nsuperimposed on the overall decay."
    },
    {
        "anchor": "Ground state properties of a multi-component bosonic mixture: a\n  Gutzwiller mean-field study: Using the single-site Gutzwiller method, we theoretically study the ground\nstate and the interspecies entanglement properties of interexchange symmetric\nmulti-component (two- and three-) bosonic mixtures in an optical lattice, and\nthe results are generalized to an $n$-component ($n=2,3,4,\\cdots$) system. We\ncompute the mean-field phase diagram, the interspecies entanglement entropy,\nand the ground state spectral decomposition. Three phases namely the\n$n$-component Superfluid state (nSF), the $n$-component Mott insulator state\n(nMI), and the Super-counter-fluid state (SCF) are observed. Interestingly, we\nfind that there are $n-1$ SCF lobes to separate every two neighboring nMI lobes\nin the phase diagram. More importantly, we derive the exact general expression\nof the interspecies entanglement entropy for the SCF phase. In addition, we\nalso investigate the demixing effect of an n-component mixture and demonstrate\nthat the mixing-demixing critical point is independent of n.",
        "positive": "Optically trapped quasi-two-dimensional Bose gases in random\n  environment: quantum fluctuations and superfluid density: We investigate a dilute Bose gas confined in a tight one-dimensional (1D)\noptical lattice plus a superimposed random potential at zero temperature.\nAccordingly, the ground state energy, quantum depletion and superfluid density\nare calculated. The presence of the lattice introduces a crossover to the\nquasi-2D regime, where we analyze asymptotically the 2D behavior of the system,\nparticularly the effects of disorder. We thereby offer an analytical expression\nfor the ground state energy of a purely 2D Bose gas in a random potential. The\nobtained disorder-induced normal fluid density $n_n$ and quantum depletion\n$n_d$ both exhibit a characteristic $1/\\ln\\left(1/n_{2D}a_{2D}^{2}\\right)$\ndependence. Their ratio $n_n/n_d$ increases to $2$ compared to the familiar\n$4/3$ in lattice-free 3D geometry, signifying a more pronounced contrast\nbetween superfluidity and Bose-Einstein condensation in low dimensions.\nConditions for possible experimental realization of our scenario are also\nproposed."
    },
    {
        "anchor": "Feshbach Resonances in an Erbium-Dysprosium Dipolar Mixture: We report on the observation of heteronuclear magnetic Feshbach resonances in\nseveral isotope mixtures of the highly magnetic elements erbium and dysprosium.\nAmong many narrow features, we identify two resonances with a width greater\nthan one Gauss. We characterize one of these resonances, in a mixture of\n$^{168}$Er and $^{164}$Dy, in terms of loss rates and elastic cross section,\nand observe a temperature dependence of the on-resonance loss rate suggestive\nof a universal scaling associated with broad resonances. Our observations hold\npromise for the use of such a resonance for tuning the interspecies scattering\nproperties in a dipolar mixture. We further compare the prevalence of narrow\nresonances in an $^{168}$Er-$^{164}$Dy mixture to the single-species case, and\nobserve an increased density of resonances in the mixture.",
        "positive": "Solitons and Josephson-type oscillations in Bose-Einstein condensates\n  with spin-orbit coupling and time-varying Raman frequency: The existence and dynamics of solitons in quasi-one-dimensional Bose-Einstein\ncondensates (BEC) with spin-orbit coupling (SOC) and attractive two-body\ninteractions are described for two coupled atomic pseudo-spin components with\nslowly and rapidly varying time-dependent Raman frequency. By varying the Raman\nfrequency linearly in time, it was shown that ordinary nonlinear\nSchr\\\"odinger-type bright solitons can be converted to striped bright solitons\nand vice versa. The internal Josephson oscillations between atom-number of the\ncoupled soliton components, and the corresponding center-of-mass motion, are\nstudied for different parameter configurations. In this case, a mechanism to\ncontrol the soliton parameters is proposed by considering parametric\nresonances, which can emerge when using time-varying Raman frequencies. Full\nnumerical simulations confirm variational analysis predictions when applied to\nthe region where regular solitons are expected. In the limit of high\nfrequencies, the system is described by a time-averaged Gross-Pitaevskii\nformalism with renormalized nonlinear and SOC parameters and modified\nphase-dependent nonlinearities. By comparing full-numerical simulations with\naveraged results, we have also studied the lower limits for the frequency of\nRaman oscillations in order to obtain stable soliton solutions."
    },
    {
        "anchor": "Onsager vortex formation in Bose-Einstein condensates in two-dimensional\n  power-law traps: We study computationally dynamics of quantised vortices in two-dimensional\nsuperfluid Bose-Einstein condensates confined in highly oblate power-law traps.\nWe have found that the formation of large scale Onsager vortex clusters\nprevalent in steep-walled traps is suppressed in condensates confined by\nharmonic potentials. However, the shape of the trapping potential does not\nappear to adversely affect the evaporative heating efficiency of the vortex\ngas. Instead, the suppression of Onsager vortex formation in harmonic traps can\nbe understood in terms of the energy of the vortex configurations. Furthermore,\nwe find that the vortex-antivortex pair annihilation that underpins the vortex\nevaporative heating mechanism requires the interaction of at least three\nvortices. We conclude that experimental observation of Onsager vortices should\nbe the most apparent in flat or inverted-bottom traps.",
        "positive": "Stability Analysis of a Bose-Einstein Condensate Trapped in a Generic\n  Potential: We investigate the dynamical behavior of the Gross-Pitaevskii equation for a\nBose-Einstein condensate trapped in a spherical power law potential restricted\nto the repulsive case, from the dynamical system formalism point of view. A\nfive-dimensional dynamical system is found (due the symmetry of the\nGross-Pitaevskii equation interacting with a potential), where the Thomas-Fermi\napproximation constrains the parameter space of solutions. We show that for\nvalues of the power law exponent equal or smaller than 2 the system seems to be\nstable. However, when the corresponding exponent is bigger than 2, the\ninstability of the system grows when the power law exponent grows, indicating\nthat large values of the aforementioned parameter can be related to a loss in\nthe number of particles from the condensed state. This fact can be used also to\nshow that the stability conditions of the condensate are highly sensitive to\nthe exponent associated with the external potential."
    },
    {
        "anchor": "Non-Hermitian quantum gases: a platform for imaginary time crystals: One of the most important applications of quantum mechanics is the\nthermodynamic description of quantum gases. Despite the fundamental importance\nof this topic, a comprehensive description of the thermodynamic properties of\nnon-Hermitian quantum gases is still lacking. Here, we investigate the\nproperties of bosonic and fermionic non-Hermitian systems at finite\ntemperatures. We show that non-Hermitian systems exihibit oscillations both in\ntemperature and imaginary time. As such, they can be a possible platform to\nrealize an imaginary time crystal (iTC) phase. The Hatano-Nelson model is\nidentified as a simple lattice model to reveal this effect. In addition, we\nshow that the conditions for the iTC to be manifest are the same as the\nconditions for the presence of disorder points, where the correlation functions\nshow oscillating behavior. This analysis makes clear that our realization of\niTC is effectively a way to filter one specific Matsubara mode. In this\nrealization, the Matsubara frequency, that enters as a mathematical tool to\ncompute correlation functions for finite temperatures, can be measured\nexperimentally.",
        "positive": "Ultrafast Many-Body Dynamics in an Ultracold Rydberg-Excited Atomic Mott\n  Insulator: We report the observation and control of ultrafast non-equilibrium many-body\nelectron dynamics in Rydberg-excited spatially-ordered ultracold atoms created\nfrom a three-dimensional unity-filling atomic Mott insulator. By implementing\ntime-domain Ramsey interferometry with attosecond precision in our Rydberg\natomic system, we observe picosecond-scale ultrafast many-body dynamics that is\nessentially governed by the emergence and evolution of many-body correlations\nbetween long-range interacting atoms in an optical lattice. We analyze our\nobservations with different theoretical approaches and find that quantum\nfluctuations have to be included beyond semi-classical descriptions to describe\nthe observed dynamics. Our Rydberg lattice platform combined with an ultrafast\napproach, which is robust against environmental noises, opens the door for\nsimulating strongly-correlated electron dynamics by long-range van der Waals\ninteraction and resonant dipole-dipole interaction to the charge-overlapping\nregime in synthetic ultracold atomic crystals."
    },
    {
        "anchor": "Decoherence and momentum relaxation in Fermi-polaron Rabi dynamics: a\n  kinetic equation approach: Despite the paradigmatic nature of the Fermi-polaron model, the theoretical\ndescription of its nonlinear dynamics poses challenges. Here, we apply a\nquantum kinetic theory of driven polarons to recent experiments with ultracold\natoms, where Rabi oscillations between a Fermi-polaron state and a\nnon-interacting level were reported. The resulting equations separate\ndecoherence from momentum relaxation, with the corresponding rates showing a\ndifferent dependence on microscopic scattering processes and quasi-particle\nproperties. We describe both the polaron ground state and the excited\nrepulsive-polaron state and we find a good quantitative agreement between our\npredictions and the available experimental data without any fitting parameter.\nOur approach not only takes into account collisional phenomena, but also it can\nbe used to study the different roles played by decoherence and the collisional\nintegral in the strongly interacting highly-imbalanced mixture of Fermi gases.",
        "positive": "Pump-probe coupling of matter wave packets to remote lattice states: The coherent manipulation of wave packets is an important tool in many areas\nof physics. We demonstrate the experimental realization of quasi-free wave\npackets of ultra-cold atoms bound by an external harmonic trap. The wave\npackets are produced by modulating the intensity of an optical lattice\ncontaining a Bose-Einstein condensate. The evolution of these wave packets is\nmonitored in-situ and their reflection on a band gap is observed. In direct\nanalogy with pump-probe spectroscopy, a probe pulse allows for the resonant\nde-excitation of the wave packet into localized lattice states at a long,\ncontrollable distance of more than 100 lattice sites from the main component.\nThis coherent control mechanism for ultra-cold atoms thus enables controlled\nquantum state preparation, opening exciting perspectives for quantum metrology\nand simulation."
    },
    {
        "anchor": "Superradiance induced topological vortex phase in a Bose-Einstein\n  condensate: We investigate theoretically a topological vortex phase transition induced by\na superradiant phase transition in an atomic Bose-Einstein condensate driven by\na Laguerre-Gaussian optical mode. We show that superradiant radiation can\neither carry zero angular momentum, or be in a rotating Laguerre-Gaussian mode\nwith angular momentum. The conditions leading to these two regimes are\ndetermined in terms of the width for the pump laser and the condensate size for\nthe limiting cases where the recoil energy is both much smaller and larger than\nthe atomic interaction energy.",
        "positive": "State-to-state endothermic and nearly thermoneutral reactions in an\n  ultracold atom-dimer mixture: Chemical reactions at ultracold temperature provide an ideal platform to\nstudy chemical reactivity at the fundamental level, and to understand how\nchemical reactions are governed by quantum mechanics. Recent years have\nwitnessed the remarkable progress in studying ultracold chemistry with\nultracold molecules. However, these works were limited to exothermic reactions.\nThe direct observation of state-to-state ultracold endothermic reaction remains\nelusive. Here we report on the investigation of endothermic and nearly\nthermoneutral atom-exchange reactions in an ultracold atom-dimer mixture. By\ndeveloping an indirect reactant-preparation method based on a molecular\nbound-bound transition, we are able to directly observe a universal endothermic\nreaction with tunable energy threshold and study the state-to-state reaction\ndynamics. The reaction rate coefficients show a strikingly threshold\nphenomenon. The influence of the reverse reaction on the reaction dynamics is\nobserved for the endothermic and nearly thermoneutral reactions. We carry out\nzero-range quantum mechanical scattering calculations to obtain the reaction\nrate coefficients, and the three-body parameter is determined by comparison\nwith the experiments. The observed endothermic and nearly thermoneutral\nreaction may be employed to implement collisional Sisyphus cooling of\nmolecules, study the chemical reactions in degenerate quantum gases and conduct\nquantum simulation of Kondo effect with ultracold atoms."
    },
    {
        "anchor": "Comparison between the numerical solutions and the Thomas-Fermi\n  approximation for atomic-molecular Bose-Einstein condensates: We study the stationary solution of an atomic Bose-Einstein condensate\ncoupled coherently to a molecular condensate with both repulsive and attractive\ninterspecies interactions confined in an isotropic harmonic trap. We use the\nThomas-Fermi approximation and find four kinds of analytical solution for the\ncases. These analytical solutions are adopted as trial function for the\ndiffusive numerical solution of the Gross-Pitaevskii equations. For the\nrepulsive interspecies interaction, the case in which the atomic and molecular\nwavefunctions are out-phase, the densities have similar profiles for both\nmethods, however, the case where the wavefunctions are in-phase, there are\nconsiderable difference between the density profiles. For the attractive\ninterspecies interaction, there are two cases in the Thomas Fermi approximation\nwhere the wavefunctions are in-phase. One of them has numerical solution that\nagree with the approximation and the other does not have corresponding\nnumerical solution.",
        "positive": "Ultracold Bose and Fermi dipolar gases : a quantum Monte Carlo study: The object of study of this thesis are dipolar systems in the quantum\ndegenerate regime. In general, dealing with many-body systems and evaluating\ntheir properties requires to deal with the Schr\\\"odinger equation. In the\npresent study we employ different Monte Carlo methods, that are stochastic\ntechniques that allow to find numerical solutions to it."
    },
    {
        "anchor": "Detecting antiferromagnetism of atoms in an optical lattice via optical\n  Bragg scattering: Antiferromagnetism of ultracold fermions in an optical lattice can be\ndetected by Bragg diffraction of light, in analogy to the diffraction of\nneutrons from solid state materials. A finite sublattice magnetization will\nlead to a Bragg peak from the (1/2 1/2 1/2) crystal plane with an intensity\ndepending on details of the atomic states, the frequency and polarization of\nthe probe beam, the direction and magnitude of the sublattice magnetization,\nand the finite optical density of the sample. Accounting for these effects we\nmake quantitative predictions about the scattering intensity and find that with\nexperimentally feasible parameters the signal can be readily measured with a\nCCD camera or a photodiode and used to detect antiferromagnetic order.",
        "positive": "Hydrodynamics of a superfluid smectic: We determine the hydrodynamic modes of the superfluid analog of a smectic-A\nphase in liquid crystals, i.e., a state in which both gauge invariance and\ntranslational invariance along a single direction are spontaneously broken.\nSuch a superfluid smectic provides an idealized description of the\nincommensurate supersolid state realized in Bose-Einstein condensates with\nstrong dipolar interactions as well as of the stripe phase in Bose gases with\nspin-orbit coupling. We show that the presence of a finite normal fluid density\nin the ground state of these systems gives rise to a well-defined second-sound\ntype mode even at zero temperature. It replaces the diffusive permeation mode\nof a normal smectic phase and is directly connected with the classic\ndescription of supersolids by Andreev and Lifshitz in terms of a propagating\ndefect mode. An analytic expression is derived for the two sound velocities\nthat appear in the longitudinal excitation spectrum. It only depends on the\nlow-energy parameters associated with the two independent broken symmetries,\nwhich are the effective layer compression modulus and the superfluid fraction."
    },
    {
        "anchor": "Vortex Thermometry for Turbulent Two-Dimensional Fluids: We introduce a new method of statistical analysis to characterise the\ndynamics of turbulent fluids in two dimensions. We establish that, in\nequilibrium, the vortex distributions can be uniquely connected to the\ntemperature of the vortex gas, and apply this vortex thermometry to\ncharacterise simulations of decaying superfluid turbulence. We confirm the\nhypothesis of vortex evaporative heating leading to Onsager vortices proposed\nin Phys. Rev. Lett. 113, 165302 (2014), and find previously unidentified vortex\npower-law distributions that emerge from the dynamics.",
        "positive": "Universal Thermometry for Quantum Simulation: Quantum simulation is a highly ambitious program in cold atom research\ncurrently being pursued in laboratories worldwide. The goal is to use cold\natoms in optical lattice to simulate models for unsolved strongly correlated\nsystems, so as to deduce their properties directly from experimental data. An\nimportant step in this effort is to determine the temperature of the system,\nwhich is essential for deducing all thermodynamic functions. This step,\nhowever, remains difficult for lattice systems at the moment. Here, we propose\na method based on a generalized fluctuation-dissipation theorem. It does not\nreply on numerical simulations and is a universal thermometry for all quantum\ngases systems including mixtures and spinor gases. It is also unaffected by\nphoton shot noise."
    },
    {
        "anchor": "Fast frictionless dynamics as a toolbox for low-dimensional\n  Bose-Einstein condensates: A method is proposed to implement a fast frictionless dynamics in a\nlow-dimensional Bose-Einstein condensate by engineering the time-dependence of\nthe transverse confining potential in a highly anisotropic trap. The method\nexploits the inversion of the dynamical self-similar scaling law in the radial\ndegrees of freedom. We discuss the application of the method to preserve\nshort-range correlations in time of flight experiments, the implementation of\nnearly-sudden quenches of non-linear interactions, and its power to assist\nself-similar dynamics in quasi-one dimensional condensates.",
        "positive": "Strongly Correlated Quantum Walks in Optical Lattices: Full control over the dynamics of interacting, indistinguishable quantum\nparticles is an important prerequisite for the experimental study of strongly\ncorrelated quantum matter and the implementation of high-fidelity quantum\ninformation processing. Here we demonstrate such control over the quantum walk\n- the quantum mechanical analogue of the classical random walk - in the strong\ninteraction regime. Using interacting bosonic atoms in an optical lattice, we\ndirectly observe fundamental effects such as the emergence of correlations in\ntwo-particle quantum walks, as well as strongly correlated Bloch oscillations\nin tilted optical lattices. Our approach can be scaled to larger systems,\ngreatly extending the class of problems accessible via quantum walks"
    },
    {
        "anchor": "The transition from Bose-Einstein condensate to supersolid states in\n  Rydberg-dressed gases beyond Bogoliubov approximation: In this paper, we study Bose-Einstein condensation of Rydberg-dressed atoms\nconsidering finite range interactions. We use Hartree-Fock-Bogoliubov\napproximation based on Mean-Field approach. Moreover, within this approximation\nmodified by the finite-range character of the two-body interaction we shall\nobtain analytical expressions for thermodynamic quantities of Rydberg-dressed\nBose gas. The imaginary part of the quasiparticle spectrum of a BEC signals the\ninstability of the roton mode with respect to the formation of supersolid\nstate. Our theory predicts a second-order quantum phase transition from BEC to\nsupersolid phase for Rydberg-dressed bosons in three dimensions.",
        "positive": "Observation of the Second Triatomic Resonance in Efimov's Scenario: We report the observation of a three-body recombination resonance in an\nultracold gas of cesium atoms at a very large negative value of the $s$-wave\nscattering length. The resonance is identified as the second triatomic Efimov\nresonance, which corresponds to the situation where the first excited Efimov\nstate appears at the threshold of three free atoms. This observation, together\nwith a finite-temperature analysis and the known first resonance, allows the\nmost accurate demonstration to date of the discrete scaling behavior at the\nheart of Efimov physics. For the system of three identical bosons, we obtain a\nscaling factor of $21.0(1.3)$, close to the ideal value of $22.7$."
    },
    {
        "anchor": "Floquet engineering of optical solenoids and quantized charge pumping\n  along tailored paths in two-dimensional Chern insulators: The insertion of a local magnetic flux, as the one created by a thin\nsolenoid, plays an important role in gedanken experiments of quantum Hall\nphysics. By combining Floquet engineering of artificial magnetic fields with\nthe ability of single-site addressing in quantum-gas microscopes, we propose a\nscheme for the realization of such local solenoid-type magnetic fields in\noptical lattices. We show that it can be employed to manipulate and probe\nelementary excitations of a topological Chern insulator. This includes\nquantized adiabatic charge pumping along tailored paths inside the bulk, as\nwell as the controlled population of edge modes.",
        "positive": "Dynamical tunnelling with ultracold atoms in magnetic microtraps: The study of dynamical tunnelling in a periodically driven anharmonic\npotential probes the quantum-classical transition via the experimental control\nof the effective Planck's constant for the system. In this paper we consider\nthe prospects for observing dynamical tunnelling with ultracold atoms in\nmagnetic microtraps on atom chips. We outline the driven anharmonic potentials\nthat are possible using standard magnetic traps, and find the Floquet spectrum\nfor one of these as a function of the potential strength, modulation, and\neffective Planck's constant. We develop an integrable approximation to the\nnon-integrable Hamiltonian and find that it can explain the behaviour of the\ntunnelling rate as a function of the effective Planck's constant in the regular\nregion of parameter space. In the chaotic region we compare our results with\nthe predictions of models that describe chaos-assisted tunnelling. Finally we\nexamine the practicality of performing these experiments in the laboratory with\nBose-Einstein condensates."
    },
    {
        "anchor": "Phase Diagrams for Spin-1 Bosons in an Optical Lattice: In this paper, the phase diagrams of a polar spin-1 Bose gas in a\nthree-dimensional optical lattice with linear and quadratic Zeeman effects both\nat zero and finite temperatures are obtained within mean-field theory. The\nphase diagrams can be regrouped to two different parameter regimes depending on\nthe magnitude of the quadratic Zeeman effect $Q$. For large $Q$, only a\nfirst-order phase transition from the nematic (NM) phase to the fully magnetic\n(FM) phase is found, while in the case of small $Q$, a first-order phase\ntransition from the nematic phase to the partially magnetic (PM) phase, plus a\nsecond-order phase transition from the PM phase to the FM phase is obtained. If\na net magnetization in the system exists, the first-order phase transition\ncauses a coexistence of two phases and phase separation: for large $Q$, NM and\nFM phases and for small $Q$, NM and PM phases. The phase diagrams in terms of\nnet magnetization are also obtained.",
        "positive": "Microscopic derivation of the extended Gross-Pitaevskii equation for\n  quantum droplets in binary Bose mixtures: An ultradilute quantum droplet is a self-bound liquid-like state recently\nobserved in ultracold Bose-Einstein condensates. In all previous theoretical\nstudies, it is described by a phenomenological low-energy effective theory,\ntermed as the extended Gross\\textendash Pitaevskii equation. Here, we\nmicroscopically derive the Gross\\textendash Pitaevskii equation for the\ncondensate and also for a pairing field in an inhomogeneous quantum droplet\nrealized by Bose-Bose mixtures with attractive inter-species interaction. We\nshow that the inclusion of the pairing field is essential, in order to have a\nconsistent description of the droplet state. We clarify that, the extended\nGross\\textendash Pitaevskii equation used earlier should be understood as the\nequation of motion for the pairing field, rather than the condensate. The\nfluctuations of the pairing field give rise to low-energy collective\nexcitations of the droplet. We also present the Bogoliubov equations for\ngapless phonon modes and gapped modes due to pairing in real space, which\ncharacterizes single-particle-like excitations of the droplet. The equations of\nmotion derived in this work for the condensate and the pairing field serve an\nideal starting point to understand the structure and collective excitations of\nnon-uniform ultradilute quantum droplets in on-going cold-atom experiments."
    },
    {
        "anchor": "The phase-separation mechanism of a binary mixture in a ring trimer: We show that, depending on the ratio between the inter- and the intra-species\ninteractions, a binary mixture trapped in a three-well potential with periodic\nboundary conditions exhibits three macroscopic ground-state configurations\nwhich differ in the degree of mixing. Accordingly, the corresponding quantum\nstates feature either delocalization or a Schr\\\"odinger cat-like structure. The\ntwo-step phase separation occurring in the system, which is smoothed by the\nactivation of tunnelling processes, is confirmed by the analysis of the energy\nspectrum that collapses and rearranges at the two critical points. In such\npoints, we show that also Entanglement Entropy, a quantity borrowed from\nquantum-information theory, features singularities, thus demonstrating its\nability to witness the double mixining-demixing phase transition. The developed\nanalysis, which is of interest to both the experimental and theoretical\ncommunities, opens the door to the study of the demixing mechanism in complex\nlattice geometries.",
        "positive": "Localization of Rung Pairs in Hard-core Bose-Hubbard Ladder: Quantum simulation in experiments of many-body systems may bring new\nphenomena which are not well studied theoretically. Motivated by a recent work\nof quantum simulation on a superconducting ladder circuit, we investigate the\nrung-pair localization of the Bose-Hubbard ladder model without quenched\ndisorder. Our results show that, in the hard-core limit, there exists a\nrung-pair localization both at the edges and in the bulk. Using center-of-mass\nframe, the two-particle system can be mapped to an effective single-particle\nsystem with an approximate sub-lattice symmetry. Under the condition of\nhard-core limit, the effective system is forced to have a defect at the left\nedge leading to a zero-energy flat band, which is the origin of the rung-pair\nlocalization. We also study the multi-particle dynamics of the Bose-Hubbard\nladder model, which is beyond the singleparticle picture. In this case, we find\nthat the localization can still survive despite of the existence of interaction\nbetween the pairs. Moreover, the numerical results show that the entanglement\nentropy exhibits a long-time logarithmic growth and the saturated values\nsatisfy a volume law. This phenomenon implies that the interaction plays an\nimportant role during the dynamics, although it cannot break the localization.\nOur results reveal another interesting type of disorder-free localization\nrelated to a zero-energy flat band, which is induced by on-site interaction and\nspecific lattice symmetry."
    },
    {
        "anchor": "Generalized Hartree-Fock-Bogoliubov Description of the Frohlich Polaron: We adapt the generalized Hartree-Fock-Bogoliubov (HFB) method to an\ninteracting many-phonon system free of impurities. The many-phonon system is\nobtained from applying the Lee-Low-Pine (LLP) transformation to the Frohlich\nmodel which describes a mobile impurity coupled to noninteracting phonons. We\nspecialize our general HFB description of the Frohlich polaron to Bose polarons\nin quasi-1D cold atom mixtures. The LLP transformed many-phonon system\ndistinguishes itself with an artificial phonon-phonon interaction which is very\ndifferent from the usual two-body interaction. We use the quasi-one-dimensional\nmodel, which is free of an ultraviolet divergence that exists in higher\ndimensions, to better understand how this unique interaction affects polaron\nstates and how the density and pair correlations inherent to the HFB method\nconspire to create a polaron ground state with an energy in good agreement with\nand far closer to the prediction from Feynman's variational path integral\napproach than mean-field theory where HFB correlations are absent.",
        "positive": "Berezinskii-Kosterlitz-Thouless transition in a photonic lattice: Phase transitions give crucial insight into many-body systems, as crossovers\nbetween different regimes of order are determined by the underlying dynamics.\nThese dynamics, in turn, are often constrained by dimensionality and geometry.\nFor example, in one- and two-dimensional systems with continuous symmetry,\nthermal fluctuations prevent the formation of long-range order[1,2].\nTwo-dimensional systems are particularly significant, as vortices can form in\nthe plane but cannot tilt out of it. At high temperatures, random motion of\nthese vortices destroys large-scale coherence. At low temperatures, vortices\nwith opposite spin can pair together, cancelling their circulation and allowing\nquasi-long-range order to appear. This Berezenskii-Kosterlitz-Thouless (BKT)\ntransition[3,4] is essentially classical, arising for example in the\ntraditional XY model for spins, but to date experimental evidence has been\nobtained only in cold quantum systems. Measurements of superfluid sound\nspeed[5] and critical velocity[6] have been consistent with scaling\npredictions, and vortices have been observed directly in cold atom\nexperiments[7,8]. However, the presence of trapping potentials restricts\nmeasurement to vortex density, rather than number, and obscures the process of\nvortex unbinding. Further, atom and fluid experiments suffer from parasitic\nheating and difficulties in phase recording, leading to results that differ\nfrom theory in many quantitative aspects. Here, we use a nonlinear optical\nsystem to directly observe the ideal BKT transition, including vortex pair\ndynamics and the correlation properties of the wavefunction, for both repulsive\nand attractiveinteractions (the photonic equivalent of ferromagnetic and\nantiferromagnetic conditions[9]). The results confirm the thermodynamics of the\nBKT transition and expose outstanding issues in the crossovers to superfluidity\nand Bose-Einstein condensation."
    },
    {
        "anchor": "Sigature of the universal super Efimov Effect: three-body contact in two\n  dimensional Fermi gases: A new class of universal \"three-body\" bound states has been recently\npredicted theoretically for identical fermions interacting at p-wave resonance\nin two dimensions. This phenomenon is called the super Efimov effect since the\nbinding energies of the states follow a intriguing double exponential scaling.\nHowever, experimental resolution of this scaling is expected to meet formidable\nchallenges. In this work, we introduce a new thermodynamic quantity, the\nthree-body contact $C_\\theta$, to quantify three-body correlations in a two\ndimensional gas composed of the resonantly interacting fermions; the contact\n$C_\\theta$ is the consequence of the underlying universal super Efimov effect\nin the many-body context. We show how $C_\\theta$ affects physical observables\nsuch as the radio-frequency spectrum, the momentum distribution and the atom\nloss rate. Signature of the elusive super Efimov effect in the thermodynamic\nsystem can be pinned down by the detection of the three-body contact $C_\\theta$\nvia these observables.",
        "positive": "Persistent Currents in Ferromagnetic Condensates: Persistent currents in Bose condensates with a scalar order parameter are\nstabilized by the topology of the order parameter manifold. In condensates with\nmulticomponent order parameters it is topologically possible for supercurrents\nto `unwind' without leaving the manifold. We study the energetics of this\nprocess in the case of ferromagnetic condensates using a long wavelength energy\nfunctional that includes both the superfluid and spin stiffnesses. Exploiting\nanalogies to an elastic rod and rigid body motion, we show that the current\ncarrying state in a 1D ring geometry transitions between a spin helix in the\nenergy minima and a soliton-like configuration at the maxima. The relevance to\nrecent experiments in ultracold atoms is briefly discussed."
    },
    {
        "anchor": "Tunable Wigner States with Dipolar Atoms and Molecules: We study the few-body physics of trapped atoms or molecules with electric or\nmagnetic dipole moments aligned by an external field. Using exact numerical\ndiagonalization appropriate for the strongly correlated regime, as well as a\nclassical analysis, we show how Wigner localization emerges with increasing\ncoupling strength. The Wigner states exhibit non-trivial geometries due to the\nanisotropy of the interaction. This leads to transitions between different\nWigner states as the tilt angle of the dipoles with the confining plane is\nchanged. Intriguingly, while the individual Wigner states are well described by\na classical analysis, the transitions between different Wigner states are\nstrongly affected by quantum statistics. This can be understood by considering\nthe interplay between quantum-mechanical and spatial symmetry properties.\nFinally, we demonstrate that our results are relevant to experimentally\nrealistic systems.",
        "positive": "Measuring the dynamics of a first order structural phase transition\n  between two configurations of a superradiant crystal: We observe a structural phase transition between two configurations of a\nsuperradiant crystal by coupling a Bose-Einstein condensate to an optical\ncavity and applying imbalanced transverse pump fields. We find that this first\norder phase transition is accompanied by transient dynamics of the order\nparameter which we measure in real-time. The phase transition and the\nexcitation spectrum can be derived from a microscopic Hamiltonian in\nquantitative agreement with our experimental data."
    },
    {
        "anchor": "Analysis of Particle Transfer by Periodic Lattice Modulation for\n  Ultracold Fermionic Atom Systems in Three Dimensional Optical Lattice: We analyze a ultracold fermionic atom system in a three dimensional optical\nlattice with a confinement harmonic potential, using the Hubbard model, and\ntime-dependent Gutzwiller variational approach for numerical calculation. Our\nstudy is focused on the time evolution of the particle transfer when the\nlattice potential is modulated by adding a periodic one. The choice of the\nparameters such as the modulation frequency and amplitude and the particle\nnumber affects the particle transfer. We calculate the time evolution of the\nvariance in the particle distribution, and show its dependence on the\nparameters. The lattice modulation turns out to work effectively in order to\ncontrol the particle transfer, and will be a useful method in experiments for\nfermionic atom systems.",
        "positive": "Non-thermalized Dynamics of Flat-Band Many-Body Localization: We find that a flat-band fermion system with interactions and without\ndisorders exhibits non-thermalized ergodicity-breaking dynamics, an analog of\nmany-body localization (MBL). In the previous works, we observed flat-band\nmany-body localization (FMBL) in the Creutz ladder model. The origin of FMBL is\na compact localized state governed by local integrals of motion (LIOMs), which\nare to be obtained explicitly. In this work, we clarify the dynamical aspects\nof FMBL. We first study dynamics of two-particles, and find that the states are\nnot substantially modified by weak interactions, but the periodic time\nevolution of entanglement entropy emerges as a result of a specific mechanism\ninherent in the system. On the other hand, as the strength of the interactions\nis increased, the modification of the states takes place with inducing\ninstability of the LIOMs. Furthermore, many-body dynamics of the system at\nfinite fillings is numerically investigated by time-evolving block decimation\n(TEBD) method. For a suitable choice of the filling, non-thermal and low\nentangled dynamics appears. This behavior is a typical example of the\ndisorder-free FMBL."
    },
    {
        "anchor": "Exploring topological double-Weyl semimetals with cold atoms in optical\n  lattices: We explore the topological properties of double-Weyl semimetals with cold\natoms in optical lattices. We first propose to realize a tight-binding model of\nsimulating the double-Weyl semimetal with a pair of double-Weyl points by\nengineering the atomic hopping in a three-dimensional optical lattice. We show\nthat the double-Weyl points with topological charges of \\$pm2$ behave as sink\nand source of Berry flux in momentum space connecting by two Fermi arcs and\nthey are stabilized by the \\$C_{4h}$ point-group symmetry. By applying a\nrealizable \\$C_4$ breaking term, we find that each double-Weyl point splits\ninto two single-Weyl points and obtain rich phase diagrams in the parameter\nspace spanned by the strengths of an effective Zeeman term and the \\$C_4$\nbreaking term, which contains a topological and a normal insulating phases and\ntwo topological Weyl semimetal phases with eight and four single-Weyl points,\napart from the double-Weyl semimetal phase. Furthermore, we demonstrate with\nnumerical simulations that (i) the mimicked double- and single-Weyl points can\nbe detected by measuring the atomic transfer fractions after a Bloch\noscillation; (ii) the Chern number of different quantum phases in the phase\ndiagram can be extracted from the center shift of the hybrid Wannier functions,\nwhich can be directly measured with the time-of-flight imaging; (iii) the band\ntopology of the \\$C_4$ symmetric Bloch Hamiltonian can be detected simply from\nmeasuring the spin polarization at the high symmetry momentum points with a\ncondensate in the optical lattice. The proposed system would provide a\npromising platform for elaborating the intrinsic exotic physics of double-Weyl\nsemimetals and the related topological phase transitions.",
        "positive": "Resonant dynamics of chromium condensates: We numerically study the dynamics of a spinor chromium condensate in low\nmagnetic fields. We show that the condensate evolution has a resonant character\nrevealing rich structure of resonances similar to that already discussed in the\ncase of alkali-atoms condensates. This indicates that dipolar resonances occur\ncommonly in the systems of cold atoms. In fact, they have been already observed\nexperimentally. We further simulate two recent experiments with chromium\ncondensates, in which the threshold in spin relaxation and the spontaneous\ndemagnetization phenomena were observed. We demonstrate that both these effects\noriginate in resonant dynamics of chromium condensate."
    },
    {
        "anchor": "Optical control of Feshbach resonances in Fermi gases using molecular\n  dark states: We propose a general method for optical control of magnetic Feshbach\nresonances in ultracold atomic gases with more than one molecular state in an\nenergetically closed channel. Using two optical frequencies to couple two\nstates in the closed channel, inelastic loss arising from spontaneous emission\nis greatly suppressed by destructive quantum interference at the two-photon\nresonance, i.e., dark-state formation, while the scattering length is widely\ntunable by varying the frequencies and/or intensities of the optical fields.\nThis technique is of particular interest for a two-component atomic Fermi gas,\nwhich is stable near a Feshbach resonance.",
        "positive": "Nonuniform Bose-Einstein condensate. I. An improvement of the\n  Gross-Pitaevskii method: A nonuniform condensate is usually described by the Gross-Pitaevskii (GP)\nequation, which is derived with the help of the c-number ansatz $\\hat{\n\\Psi}(\\mathbf{r},t)=\\Psi (\\mathbf{r},t)$. Proceeding from a more accurate\noperator ansatz $\\hat{\\Psi}(\\mathbf{r},t)=\\hat{a}_{0}\\Psi (\\mathbf{r},t)\n\\sqrt{N}$, we find the equation $i\\hbar \\frac{\\partial \\Psi\n(\\mathbf{r},t)}{\\partial t}=-\\frac{\\hbar ^{2}}{2m}\\frac{\\partial ^{2}\\Psi\n(\\mathbf{r},t)}{\\partial \\mathbf{r}^{2}}+\\left( 1-\\frac{1}{N}\\right) 2c\\Psi\n(\\mathbf{r},t)|\\Psi(\\mathbf{r},t)|^{2}$ (the GP$_{N}$ equation). It differs\nfrom the GP equation by the factor $(1-1/N)$, where $N$ is the number of Bose\nparticles. We compare the accuracy of the GP and GP$_{N}$ equations by\nanalyzing the ground state of a one-dimensional system of point bosons with\nrepulsive interaction ($c>0$) and zero boundary conditions. Both equations are\nsolved numerically, and the system energy $E$ and the particle density profile\n$\\rho (x)$ are determined for various values of~$N$, the mean particle density\n$\\bar{\\rho}$, and the coupling constant $\\gamma =c/\\bar{\\rho}$. The solutions\nare compared with the exact ones obtained by the Bethe ansatz. The results show\nthat in the weak coupling limit ($N^{-2}\\ll \\gamma \\lesssim 0.1$), the GP and\nGP$_{N}$ equations describe the system equally well if $N\\gtrsim 100$. For\nfew-boson systems ($N\\lesssim 10$) with $\\gamma \\lesssim N^{-2}$ the solutions\nof the GP$_{N}$ equation are in excellent agreement with the exact ones. That\nis, the multiplier $(1-1/N)$ allows one to describe few-boson systems with high\naccuracy. This means that it is reasonable to extend the notion of\nBose-Einstein condensation to few-particle systems."
    },
    {
        "anchor": "Distinguishability, degeneracy and correlations in three harmonically\n  trapped bosons in one-dimension: We study a system of two bosons of one species and a third boson of a second\nspecies in a one-dimensional parabolic trap at zero temperature. We assume\ncontact repulsive inter- and intra-species interactions. By means of an exact\ndiagonalization method we calculate the ground and excited states for the whole\nrange of interactions. We use discrete group theory to classify the eigenstates\naccording to the symmetry of the interaction potential. We also propose and\nvalidate analytical ansatzs gaining physical insight over the numerically\nobtained wavefunctions. We show that, for both approaches, it is crucial to\ntake into account that the distinguishability of the third atom implies the\nabsence of any restriction over the wavefunction when interchanging this boson\nwith any of the other two. We find that there are degeneracies in the spectra\nin some limiting regimes, that is, when the inter-species and/or the\nintra-species interactions tend to infinity. This is in contrast with the\nthree-identical boson system, where no degeneracy occurs in these limits. We\nshow that, when tuning both types of interactions through a protocol that keeps\nthem equal while they are increased towards infinity, the systems's ground\nstate resembles that of three indistinguishable bosons. Contrarily, the\nsystems's ground state is different from that of three-identical bosons when\nboth types of interactions are increased towards infinity through protocols\nthat do not restrict them to be equal. We study the coherence and correlations\nof the system as the interactions are tuned through different protocols, which\npermit to built up different correlations in the system and lead to different\nspatial distributions of the three atoms.",
        "positive": "Landauer, Kubo, and microcanonical approaches to quantum transport and\n  noise: A comparison and implications for cold-atom dynamics: We compare the Landauer, Kubo, and microcanonical [J. Phys. Cond. Matter {\\bf\n16}, 8025 (2004)] approaches to quantum transport for the average current, the\nentanglement entropy and the semiclassical full-counting statistics (FCS). Our\nfocus is on the applicability of these approaches to isolated quantum systems\nsuch as ultra-cold atoms in engineered optical potentials. For two lattices\nconnected by a junction, we find that the current and particle number\nfluctuations from the microcanonical approach compare well with the values\npredicted by the Landauer formalism and FCS assuming a binomial distribution.\nHowever, we demonstrate that well-defined reservoirs (i.e., particles in\nFermi-Dirac distributions) are not present for a substantial duration of the\nquasi-steady state. Thus, the Landauer assumption of reservoirs and/or\ninelastic effects is not necessary for establishing a quasi-steady state.\nMaintaining such a state indefinitely requires an infinite system, and in this\nlimit well-defined Fermi-Dirac distributions can occur. A Kubo approach -- in\nthe spirit of the microcanonical picture -- bridges the gap between the two\nformalisms, giving explicit analytical expressions for the formation of the\nsteady state. The microcanonical formalism is designed for closed, finite-size\nquantum systems and is thus more suitable for studying particle dynamics in\nultra-cold atoms. Our results highlight both the connection and differences\nwith more traditional approaches to calculating transport properties in\ncondensed matter systems, and will help guide the way to their simulations in\ncold-atom systems."
    },
    {
        "anchor": "Dynamical effects of exchange symmetry breaking in mixtures of\n  interacting bosons: In a double-well potential, a Bose-Einstein condensate exhibits Josephson\noscillations or self-trapping, depending on its initial preparation and on the\nratio of inter-particle interaction to inter-well tunneling. Here, we elucidate\nthe role of the exchange symmetry for the dynamics with a mixture of two\ndistinguishable species with identical physical properties, i.e. which are\ngoverned by an isospecific interaction and external potential. In the\nmean-field limit, the spatial population imbalance of the mixture can be\ndescribed by the dynamics of a single species in an effective potential with\nmodified properties or, equivalently, with an effective total particle number.\nThe oscillation behavior can be tuned by populating the second species while\nmaintaining the spatial population imbalance and all other parameters constant.\nIn the corresponding many-body approach, the single-species description\napproximates the full counting statistics well also outside the realm of\nspin-coherent states. The method is extended to general Bose-Hubbard systems\nand to their classical mean-field limits, which suggests an effective\nsingle-species description of multicomponent Bose gases with weakly\nan-isospecific interactions.",
        "positive": "Chiral currents in one-dimensional fractional quantum Hall states: We study bosonic and fermionic quantum two-leg ladders with orbital magnetic\nflux. In such systems, the ratio, $\\nu$, of particle density to magnetic flux\nshapes the phase-space, as in quantum Hall effects. In fermionic (bosonic)\nladders, when $\\nu$ equals one over an odd (even) integer, Laughlin fractional\nquantum Hall (FQH) states are stabilized for sufficiently long ranged repulsive\ninteractions. As a signature of these fractional states, we find a unique\ndependence of the chiral currents on particle density and on magnetic flux.\nThis dependence is characterized by the fractional filling factor $\\nu$, and\nforms a stringent test for the realization of FQH states in ladders, using\neither numerical simulations or future ultracold-atom experiments. The two-leg\nmodel is equivalent to a single spinful chain with spin-orbit interactions and\na Zeeman magnetic field, and results can thus be directly borrowed from one\nmodel to the other."
    },
    {
        "anchor": "The Single Particle Excitation Spectrum of Degenerate Fermi gases in a\n  ring cavity: By considering a spin-$\\frac{1}{2}$ degenerate Fermi gases in a ring cavity\nwhere strong interaction between atoms and light gives rise to a superradiance,\nwe find the cavity dissipation could cause a severe broadening in some special\ncases, breaking down the quasi-particle picture which was constantly assumed in\nmean field theory studies. This broadening happens when the band gap resonant\nwith polariton excitation energy. Interestingly enough, this broadening is\nhighly spin selective depending on how the fermions are filled and the spectrum\nbecomes asymmetric due to dissipation. Further, a non-monotonous dependence of\nthe maximal broadening of the spectrum against cavity decay rate $\\kappa$ is\nfound and the largest broadening emerges at $\\kappa$ comparable to recoil\nenergy.",
        "positive": "Characterization of Bose-Hubbard Models with Quantum Non-demolition\n  Measurements: We propose a scheme for the detection of quantum phase transitions in the 1D\nBose-Hubbard (BH) and 1D Extended Bose-Hubbard (EBH) models, using the\nnon-demolition measurement technique of quantum polarization spectroscopy. We\nuse collective measurements of the effective total angular momentum of a\nparticular spatial mode to characterise the Mott insulator to superfluid phase\ntransition in the BH model, and the transition to a density wave state in the\nEBH model. We extend the application of collective measurements to the ground\nstates at various deformations of a super-lattice potential."
    },
    {
        "anchor": "Controlled collisions of two ultracold atoms in separate harmonic traps: We consider controlled collisions between two ultracold atoms guided by\nexternal harmonic potentials. We derive analytical solutions of the\nSchroedinger equation for this system, and investigate the properties of\neigenergies and eigenstates for different trap geometries as a function of a\ntrap separation and of the scattering length. When varying the trap separation\nthe energy spectrum exhibits avoided crossings, corresponding to trap-induced\nshape resonances. Introducing an energy-dependent scattering length we\ninvestigate the behavior of the system in the vicinity of a magnetic Feshbach\nresonance. Finally, we illustrate our analytical results with two examples: the\nquantum phase gate controlled by the external magnetic field, and a scheme for\na coherent transport of atoms in optical lattices into higher Bloch bands.",
        "positive": "Controlled excitation and resonant acceleration of ultracold few-boson\n  systems by driven interactions in a harmonic trap: We investigate the excitation properties of finite utracold bosonic systems\nin a one-dimensional harmonic trap with a time-dependent interaction strength.\nThe driving of the interatomic coupling induces excitations of the relative\nmotion exclusively with specific and controllable contributions of momentarily\nexcited many-body states. Mechanisms for selective excitation to few-body\nanalogues of collective modes and acceleration occur in the vicinity of\nresonances. We study via the few-body spectrum and a Floquet analysis the\nexcitation mechanisms, and the corresponding impact of the driving frequency\nand strength as well as the initial correlation of the bosonic state. The\nfundamental case of two atoms is analyzed in detail and forms a key ingredient\nfor the bottom-up understanding of cases with higher atom numbers, thereby\nexamining finite-size corrections to macroscopic collective modes of\noscillation."
    },
    {
        "anchor": "Formation and quench of homonuclear and heteronuclear quantum droplets\n  in one dimension: We exemplify the impact of beyond Lee-Huang-Yang (LHY) physics, especially\ndue to intercomponent correlations, in the ground state and the quench dynamics\nof one-dimensional so-called quantum droplets using an ab-initio\nnonperturbative approach. It is found that the droplet Gaussian-shaped\nconfiguration arising for intercomponent attractive couplings becomes narrower\nfor stronger intracomponent repulsion and transits towards a flat-top structure\neither for larger particle numbers or weaker intercomponent attraction.\nAdditionally, a harmonic trap prevents the flat-top formation. At the balance\npoint where mean-field interactions cancel out, we show that a correlation hole\nis present in the few particle limit of these fluids as well as for flat-top\ndroplets. Introducing mass-imbalance, droplets experience intercomponent mixing\nand excitation signatures are identified for larger masses. Monitoring the\ndroplet expansion (breathing motion) upon considering interaction quenches to\nstronger (weaker) attractions we explicate that beyond LHY correlations result\nin a reduced velocity (breathing frequency). Strikingly, the droplets feature\ntwo-body anti-correlations (correlations) at the same position (longer\ndistances). Our findings pave the way for probing correlation-induced phenomena\nof droplet dynamics in current ultracold atom experiments.",
        "positive": "Stability of quasicrystalline ultracold fermions to dipolar interactions: Quasiperiodic potentials can be used to interpolate between localization and\ndelocalization in one dimension. However, little is known about the stability\nof quasicrystalline phases to long-range interactions. In this work, we study\nrepulsive ultracold dipolar fermions in a quasiperiodic optical lattice to\ncharacterize the behavior of interacting quasicrystals. We simulate the full\ntime evolution of the typical experimental protocols used to probe\nquasicrystalline order and localization properties. We extract experimentally\nmeasurable dynamical observables and correlation functions to characterize the\nthree phases observed in the noninteracting setting: localized, intermediate,\nand extended. We then study the stability of such phases to repulsive dipolar\ninteractions. We find that dipolar interactions can completely alter the shape\nof the phase diagram by stabilizing the intermediate phase, mostly at the\nexpense of the extended phase. Moreover, in the strongly interacting regime, a\nresonance-like behavior characterized by density oscillations appears.\nRemarkably, strong dipolar repulsions can also localize particles even in the\nabsence of quasiperiodicity if the primary lattice is sufficiently deep. Our\nwork shows that dipolar interactions in a quasiperiodic potential can give rise\nto a complex, tuneable coexistence of localized and extended quantum states."
    },
    {
        "anchor": "Spin-tensor Meissner currents of ultracold bosonic gas in an optical\n  lattice: We investigate the Meissner currents of interacting bosons subjected to a\nstaggered artificial gauge field in a three-leg ribbon geometry, realized by\nspin-tensor--momentum coupled spin-1 atoms in a 1D optical lattice. By\ncalculating the current distributions using the state-of-the-art density-matrix\nrenormalization-group method, we find a rich phase diagram containing\ninteresting Meissner and vortex phases, where the currents are mirror symmetric\nwith respect to the {\\color{red}middle leg} (i.e., they flow in the same\ndirection on the two boundary legs opposite to that on the middle leg), leading\nto the spin-tensor type Meissner currents, which is very different from\npreviously observed chiral edge currents under uniform gauge field. The\ncurrents are uniform along each leg in the Meissner phase and form\nvortex-antivortex pairs in the vortex phase. Besides, the system also support a\npolarized phase that spontaneously breaks the mirror symmetry, whose ground\nstates are degenerate with currents either uniform or forming vortex-antivortex\npairs. We also discuss the experimental schemes for probing these phases. Our\nwork provides useful guidance to ongoing experimental research on synthetic\nflux ribbons and paves the way for exploring novel many-body phenomena therein.",
        "positive": "Bose-Einstein Condensation of Photons versus Lasing and Hanbury\n  Brown-Twiss Measurements with a Condensate of Light: The advent of controlled experimental accessibility of Bose-Einstein\ncondensates, as realized with e.g. cold atomic gases, exciton-polaritons, and\nmore recently photons in a dye-filled optical microcavity, has paved the way\nfor new studies and tests of a plethora of fundamental concepts in quantum\nphysics. We here describe recent experiments studying a transition between\nlaser-like dynamics and Bose-Einstein condensation of photons in the dye\nmicrocavity system. Further, measurements of the second-order coherence of the\nphoton condensate are presented. In the condensed state we observe photon\nnumber fluctuations of order of the total particle number, as understood from\neffective particle exchange with the photo-excitable dye molecules. The\nobserved intensity fluctuation properties give evidence for Bose-Einstein\ncondensation occurring in the grand-canonical statistical ensemble regime."
    },
    {
        "anchor": "Heavy fermions in an optical lattice: We employ a mean-field theory to study ground-state properties and transport\nof a two-dimensional gas of ultracold alklaline-earth metal atoms governed by\nthe Kondo Lattice Hamiltonian plus a parabolic confining potential. In a\nhomogenous system this mean-field theory is believed to give a qualitatively\ncorrect description of heavy fermion metals and Kondo insulators: it reproduces\nthe Kondo-like scaling of the quasiparticle mass in the former, and the same\nscaling of the excitation gap in the latter. In order to understand\nground-state properties in a trap we extend this mean-field theory via\nlocal-density approximation. We find that the Kondo insulator gap manifests as\na shell structure in the trapped density profile. In addition, a strong\nsignature of the large Fermi surface expected for heavy fermion systems\nsurvives the confinement, and could be probed in time-of-flight experiments.\nFrom a full self-consistent diagonalization of the mean-field theory we are\nable to study dynamics in the trap. We find that the mass enhancement of\nquasiparticle excitations in the heavy Fermi liquid phase manifests as slowing\nof the dipole oscillations that result from a sudden displacement of the trap\ncenter.",
        "positive": "Thomas-Fermi Approximation for a Condensate with Higher-order\n  Interactions: We consider the ground state of a harmonically trapped Bose-Einstein\ncondensate within the Gross-Pitaevskii theory including the effective-range\ncorrections for a two-body zero-range potential. The resulting non-linear\nSchr\\\"odinger equation is solved analytically in the Thomas-Fermi approximation\nneglecting the kinetic energy term. We present results for the chemical\npotential and the condensate profiles, discuss boundary conditions, and compare\nto the usual Thomas-Fermi approach. We discuss several ways to increase the\ninfluence of effective-range corrections in experiment with magnetically\ntunable interactions. The level of tuning required could be inside experimental\nreach in the near future."
    },
    {
        "anchor": "Adiabatic preparation of fractional Chern insulators from an effective\n  thin-torus limit: We explore the quasi one-dimensional (thin torus, or TT) limit of fractional\nChern insulators (FCIs) as a starting point for their adiabatic preparation in\nquantum simulators. Our approach is based on tuning the hopping amplitude in\none direction as an experimentally amenable knob to dynamically change the\neffective aspect ratio of the system. Similar to the TT limit of fractional\nquantum Hall (FQH) systems in the continuum, we find that the hopping-induced\nTT limit adiabatically connects the FCI state to a trivial charge density wave\n(CDW) ground state. This adiabatic path may be harnessed for state preparation\nschemes relying on the initialization of a CDW state followed by the adiabatic\ndecrease of a hopping anisotropy. Our findings are based on the calculation of\nthe excitation gap in a number of FCI models, both on a lattice and consisting\nof coupled wires. By analytical calculation of the gap in the limit of strongly\nanisotropic hopping, we show that its scaling is compatible with the\npreparation of large size FCIs for sufficiently large hopping anisotropy. Our\nnumerical simulations in the framework of exact diagonalization explore the\nfull anisotropy range to corroborate these results.",
        "positive": "Casimir forces and quantum friction from Ginzburg radiation in atomic\n  BECs: We theoretically propose an experimentally viable scheme to use an impurity\natom in an atomic Bose-Einstein condensate, in order to realize\ncondensed-matter analogs of quantum vacuum effects. In a suitable atomic level\nconfiguration, the collisional interaction between the impurity atom and the\ndensity fluctuations in the condensate can be tailored to closely reproduce the\nelectric-dipole coupling of quantum electrodynamics. By virtue of this analogy,\nwe recover and extend the paradigm of electromagnetic vacuum forces to the\ndomain of cold atoms, showing in particular the emergence, at supersonic atomic\nspeeds, of a novel power-law scaling of the Casimir force felt by the atomic\nimpurity, as well as the occurrence of a quantum frictional force, accompanied\nby the Ginzburg emis- sion of Bogoliubov quanta. Observable consequences of\nthese quantum vacuum effects in realistic spectroscopic experiments are\ndiscussed."
    },
    {
        "anchor": "Effects of extended correlated hopping in a bose-bose mixture: We study the effects of assisted tunneling or correlated hopping between next\nnearest neighbours in a two species Bose-Hubbard system. The system is the\nbosonic analong of the fermionic system studied in Phys. Rev. Lett. {\\bf 116},\n225303 (2016). Using a combination of cluster mean field theory, exact\ndiagonlization and analytical results, a rich phase diagram is determined\nincluding a pair superfluid phase as well as a superfluid quantum droplet\nphase. The former is the result of the interplay between single particle and\ncorrelated hopping, while the latter is the effect of large correlated hopping.",
        "positive": "Quantum gas microscopy for single atom and spin detection: A particular strength of ultracold quantum gases are the versatile detection\nmethods available. Since they are based on atom-light interactions, the whole\nquantum optics toolbox can be used to tailor the detection process to the\nspecific scientific question to be explored in the experiment. Common methods\ninclude time-of-flight measurements to access the momentum distribution of the\ngas, the use of cavities to monitor global properties of the quantum gas with\nminimal disturbance and phase-contrast or high-intensity absorption imaging to\nobtain local real space information in high-density settings. Even the ultimate\nlimit of detecting each and every atom locally has been realized in\ntwo-dimensions using so-called quantum gas microscopes. In fact, these\nmicroscopes not only revolutionized the detection, but also the control of\nlattice gases. Here we provide a short overview of this technique, highlighting\nnew observables as well as key experiments that have been enabled by quantum\ngas microscopy."
    },
    {
        "anchor": "Itinerant chiral ferromagnetism in a trapped Rashba spin-orbit coupled\n  Fermi gas: How ferromagnetic phases emerge in itinerant systems is an outstanding\nproblem in quantum magnetism. Here we consider a repulsive two-component Fermi\ngas confined in a two dimensional isotropic harmonic potential and subject to a\nlarge Rashba spin-orbit (SO) coupling, whose single-particle dispersion can be\ntailored by adjusting the SO coupling strength. We show that the interplay\namong SO coupling, correlation effects and mean-field repulsion leads to a\ncompetition between ferromagnetic and non-magnetic phases. At intermediate\ninteraction strengths, ferromagnetic phase emerges which can be well described\nby the mean-field Hartree-Fock theory; whereas at strong interaction strengths,\na strongly correlated non-magnetic phase is favored due to the\nbeyond-mean-field quantum correlation effects. Furthermore, the ferromagnetic\nphase of this system possesses a chiral current density induced by the Rashba\nspin-orbit coupling, whose experimental signature is investigated.",
        "positive": "Undamped nonequilibrium dynamics of a nondegenerate Bose gas in a 3D\n  isotropic trap: We investigate anomalous damping of the monopole mode of a non-degenerate 3D\nBose gas under isotropic harmonic confinement as recently reported by the JILA\nTOP trap experiment [D. S. Lob- ser, A. E. S. Barentine, E. A. Cornell, and H.\nJ. Lewandowski (in preparation)]. Given a realistic confining potential, we\ndevelop a model for studying collective modes that includes the effects of\nanharmonic corrections to a harmonic potential. By studying the influence of\nthese trap anharmonicities throughout a range of temperatures and collisional\nregimes, we find that the damping is caused by the joint mechanisms of\ndephasing and collisional relaxation. Furthermore, the model is complimented by\nMonte Carlo simulations which are in fair agreement with data from the JILA\nexperiment."
    },
    {
        "anchor": "Dispersive effects in the unitary Fermi gas: We investigate within density functional theory various physical properties\nof the zero-temperature unitary Fermi gas which critically depend on the\npresence of a dispersive gradient term in the equation of state. First, we\nconsider the unitary Fermi superfluid gas confined to a semi-infinite domain\nand calculate analytically its density profile and surface tension. Then we\nstudy the quadrupole modes of the superfluid system under harmonic confinement\nfinding a reliable analytical formula for the oscillation frequency, which\nreduces to the familiar Thomas-Fermi one in the limit of a large number of\natoms. Finally, we discuss the formation and propagation of dispersive shock\nwaves in the collision between two resonant fermionic clouds, and compare our\nfindings with recent experimental results.",
        "positive": "Spinor Bose-Einstein gases: In a spinor Bose-Einstein gas, the non-zero hyperfine spin of the gas becomes\nan accessible degree of freedom. At low temperature, such a gas shows both\nmagnetic and superfluid order, and undergoes both density and spin dynamics.\nThese lecture notes present a general overview of the properties of spinor\nBose-Einstein gases. The notes are divided in five sections. In the first, we\nsummarize basic properties of multi-component quantum fluids, focusing on the\nspecific case of spinor Bose-Einstein gases and the role of rotational symmetry\nin defining their properties. Second, we consider the magnetic state of a\nspinor Bose-Einstein gas, highlighting effects of thermodynamics and\nBose-Einstein statistics and also of spin-dependent interactions between atoms.\nIn the third section, we discuss methods for measuring the properties of\nmagnetically ordered quantum gases and present newly developed schemes for\nspin-dependent imaging. We then discuss the dynamics of spin mixing in which\nthe spin composition of the gas evolves through the spin-dependent interactions\nwithin the gas. We discuss spin mixing first from a microscopic perspective,\nand then advance to discussing collective and beyond-mean-field dynamics. The\nfifth section reviews recent studies of the magnetic excitations of\nquantum-degenerate spinor Bose gases. We conclude with some perspectives on\nfuture directions for research."
    },
    {
        "anchor": "Quantum vortex stability in draining fluid flows: Quantum vortices with more than a single circulation quantum are usually\nunstable and decay into clusters of smaller vortices. One way to prevent the\ndecay is to place the vortex at the centre of a convergent (draining) fluid\nflow, which tends to force vortices together. It is found that whilst the\nprimary splitting instability is suppressed in this way (and completely\nquenched for strong enough flows) a secondary instability can emerge in\ncircular trapping geometries. This behaviour is related to an instability of\nrotating black holes when superradiantly amplified waves are confined inside a\nreflective cavity. The end state of the secondary instability is dramatic,\nmanifesting as a shock wave that propagates round the circular wall and\nnucleates many more vortices.",
        "positive": "Dynamics of a Space-Time Crystal in an Atomic Bose-Einstein Condensate: A space-time crystal has recently been observed in a superfluid Bose gas.\nHere we construct a variational model that allows us to describe from first\nprinciples the coupling between the radial breathing mode and the higher-order\naxial modes that underlies the observation of the space-time crystal. By\ncomparing with numerical simulations we verify the validity of our variational\nAnsatz. From the model we determine the requirements for the observation of the\nspace-time crystal and the Ising-like nature of the symmetry breaking involved.\nAlso, we find the onset and growth rate of the space-time crystal, which can be\ncompared to experiments."
    },
    {
        "anchor": "Two strong nonlinearity regimes in cold molecule formation: Two distinct strongly non-linear scenarios of molecule formation in an atomic\nBose-Einstein condensate (either by photoassociation or Feshbach resonance)\ncorresponding to large and small field detuning are revealed. By examining\narbitrary external field configurations, we show that the association process\nin the first case is almost non-oscillatory in time while in the second case\nthe evolution of the system displays strongly pronounced Rabi-type\noscillations. We construct highly accurate approximate solutions for both limit\ncases. We show that at strong coupling limit the non-crossing models are able\nto provide conversion of no more than one third of the initial atomic\npopulation. Finally, we show that for constant-amplitude models involving a\nfinite final detuning the strong interaction limit is not optimal for molecule\nformation.",
        "positive": "Many-body localization in XY spin chains with long-range interactions:\n  An exact diagonalization study: We investigate the transition from the many-body localized phase to the\nergodic thermalized phase at an infinite temperature in an $XY$ spin chain with\n$L$ spins, which experiences power-law decaying interactions in the form of\n$V_{ij}\\propto1/\\left|i-j\\right|^{\\alpha}$ ($i,j=1,\\cdots,L$) and a random\ntransverse field. By performing large-scale exact diagonalization for the chain\nsize up to $L=18$, we systematically analyze the energy gap statistics,\nhalf-chain entanglement entropy, and uncertainty of the entanglement entropy of\nthe system at different interaction exponents $\\alpha$. The finite-size\ncritical scaling allows us to determine the critical disorder strength $W_{c}$\nand critical exponent $\\nu$ at the many-body localization phase transition, as\na function of the interaction exponent $\\alpha$ in the limit\n$L\\rightarrow\\infty$. We find that both $W_{c}$ and $\\nu$ diverge when $\\alpha$\ndecreases to a critical power $\\alpha_{c}\\simeq1.16\\pm0.17$, indicating the\nabsence of many-body localization for $\\alpha<\\alpha_{c}$. Our result is useful\nto resolve the contradiction on the critical power found in two previous\nstudies, $\\alpha_{c}=3/2$ from scaling argument in Phys. Rev. B \\textbf{92},\n104428 (2015) and $\\alpha_{c}\\approx1$ from quantum dynamics simulation in\nPhys. Rev. A \\textbf{99}, 033610 (2019)."
    },
    {
        "anchor": "Stable multidimensional soliton stripes in two-component Bose-Einstein\n  condensates: We discuss how to construct stable multidimensional extensions of\none-dimensional dark solitons, the so-called soliton stripes, in two-species\nBose-Einstein condensates in the immiscible regime. We show how using a second\ncomponent to fill the core a dark soliton stripe leads to reduced instabilities\nwhile propagating in homogeneous media. We also discuss how in the presence of\na trap arbitrarily long-lived dark soliton stripes can be constructed by\nincreasing the filling of the dark stripe core. Numerical evidences of the\nrobustness of the dark soliton stripes in collision scenarios are also\nprovided.",
        "positive": "Speckle Imaging of Spin Fluctuations in a Strongly Interacting Fermi Gas: Spin fluctuations and density fluctuations are studied for a two-component\ngas of strongly interacting fermions along the BEC-BCS crossover. This is done\nby in-situ imaging of dispersive speckle patterns. Compressibility and magnetic\nsusceptibility are determined from the measured fluctuations. This new\nsensitive method easily resolves a tenfold suppression of spin fluctuations\nbelow shot noise due to pairing, and can be applied to novel magnetic phases in\noptical lattices."
    },
    {
        "anchor": "Quench induced vortex-bright-soliton formation in binary Bose-Einstein\n  condensates: We unravel the spontaneous generation of vortex-bright-soliton structures in\nbinary Bose-Einstein condensates with a small mass imbalance between the\nspecies confined in a two-dimensional harmonic trap where one of the two\nspecies has been segmented into two parts by a potential barrier. To trigger\nthe dynamics the potential barrier is suddenly removed and subsequently the\nsegments perform a counterflow dynamics. We consider a relative phase\ndifference of $\\pi$ between the segments, while a singly quantized vortex may\nbe imprinted at the center of the other species. The number of vortex\nstructures developed within the segmented species following the merging of its\nsegments is found to depend on the presence of an initial vortex on the other\nspecies. In particular, a $\\pi$ phase difference in the segmented species and a\nvortex in the other species result in a single vortex-bright-soliton structure.\nHowever, when the non-segmented species does not contain a vortex the\ncounterflow dynamics of the segmented species gives rise to a vortex dipole in\nit accompanied by two bright solitary waves arising in the non-segmented\nspecies. Turning to strongly mass imbalanced mixtures, with a heavier segmented\nspecies, we find that the same overall dynamics takes place, while the\nquench-induced nonlinear excitations become more robust. Inspecting the\ndynamics of the angular momentum we show that it can be transferred from one\nspecies to the other, and its transfer rate can be tuned by the strength of the\ninterspecies interactions and the mass of the atomic species.",
        "positive": "Hidden multiparticle excitation in weakly interacting Bose-Einstein\n  Condensate: We investigate multiparticle excitation effect on a collective density\nexcitation as well as a single-particle excitation in a weakly interacting\nBose--Einstein condensate (BEC). We find that although the weakly interacting\nBEC offers weak multiparticle excitation spectrum at low temperatures, this\nmultiparticle excitation effect may not remain hidden, but emerges as\nbimodality in the density response function through the single-particle\nexcitation. Identification of spectra in the BEC between the single-particle\nexcitation and the density excitation is also assessed at nonzero temperatures,\nwhich has been known to be unique nature in the BEC at absolute zero\ntemperature."
    },
    {
        "anchor": "Few-body Bose gases in low dimensions -- a laboratory for quantum\n  dynamics: Cold atomic gases have become a paradigmatic system for exploring fundamental\nphysics, which at the same time allows for applications in quantum\ntechnologies. The accelerating developments in the field have led to a highly\nadvanced set of engineering techniques that, for example, can tune\ninteractions, shape the external geometry, select among a large set of atomic\nspecies with different properties, or control the number of atoms. In\nparticular, it is possible to operate in lower dimensions and drive atomic\nsystems into the strongly correlated regime. In this review, we discuss recent\nadvances in few-body cold atom systems confined in low dimensions from a\ntheoretical viewpoint. We mainly focus on bosonic systems in one dimension and\nprovide an introduction to the static properties before we review the\nstate-of-the-art research into quantum dynamical processes stimulated by the\npresence of correlations. Besides discussing the fundamental physical phenomena\narising in these systems, we also provide an overview of the calculational and\nnumerical tools and methods that are commonly used, thus delivering a balanced\nand comprehensive overview of the field. We conclude by giving an outlook on\npossible future directions that are interesting to explore in these correlated\nsystems.",
        "positive": "Real space mean-field theory of a spin-1 Bose gas in synthetic\n  dimensions: The internal degrees of freedom provided by ultracold atoms give a route for\nrealizing higher dimensional physics in systems with limited spatial\ndimensions. Non-spatial degrees of freedom in these systems are dubbed\n\"synthetic dimensions\". This connection is useful from an experimental\nstandpoint but complicated by the fact that interactions alter the condensate\nground state. Here we use the Gross-Pitaevskii equation to study ground state\nproperties of a spin-1 Bose gas under the combined influence of an optical\nlattice, spin-orbit coupling, and interactions at the mean field level. The\nassociated phases depend on the sign of the spin-dependent interaction\nparameter and the strength of the optical lattice potential. We find \"charge\"\nand spin density wave phases which are directly related to helical spin order\nin real space and affect the behavior of edge currents in the synthetic\ndimension. We determine the resulting phase diagram as a function of the\nspin-orbit coupling and spin-dependent interaction strength, considering both\nattractive (ferromagnetic) and repulsive (polar) spin-dependent interactions.\nOur results are applicable to current and future experiments, specifically with\n$^{87}$Rb, $^{7}$Li, $^{41}$K, and $^{23}$Na."
    },
    {
        "anchor": "Bose-Einstein Condensates in a Cavity-mediated Triple-well: We investigate the energy structures and the dynamics of a Bose-Einstein\ncondensates (BEC) in a triple-well potential coupled a high finesse optical\ncavity within a mean field approach. Due to the intrinsic atom-cavity field\nnonlinearity, several interesting phenomena arise which are the focuses of this\nwork. For the energy structure, the bistability appears in the energy levels\ndue to this atoms-cavity field nonlinearity, and the same phenomena can be\nfound in the intra-cavity photons number. With an increase of the pump-cavity\ndetunings, the higher and lower energy levels show a loop structure due to this\ncavity-mediated effects. In the dynamical process, an extensive numerical\nsimulation of localization of the BECs for atoms initially trapped in one-,\ntwo-, and three-wells are performed for the symmetric and asymmetric cases in\ndetail. It is shown that the the transition from oscillation to the\nlocalization can be modified by the cavity-mediated potential, which will\nenlarge the regions of oscillation. With the increasing of the atomic\ninteraction, the oscillation is blocked and the localization emerges. The\ncondensates atoms can be trapped either in one-, two-, or in three wells\neventually where they are initially uploaded for certain parameters. In\nparticular, we find that the transition from the oscillation to the\nlocalization is accompanied with some irregular regime where tunneling dynamics\nis dominated by chaos for this cavity-mediated system.",
        "positive": "The Gross-Pitaevskii Soliton: Relating Weakly and Strongly Repulsive\n  Bosonic condensates and the magnetic soliton: We show that the dark soliton of the Gross-Pitaevskii equation (GPE) that\ndescribes the Bose-Einstein condensate (BEC) density of a system of weakly\nrepulsive bosons, also describes that of a system of strongly repulsive hard\ncore bosons at half filling. This connection establishes a relationship between\nthe GPE soliton and the magnetic soliton of an easy-plane ferromagnet, where\nthe BEC density relates to the square of the in-plane magnetization of the\nsystem. This mapping between well known solitons in two distinct physical\nsystems provides an intuitive understanding of various characteristics of the\nsolitons."
    },
    {
        "anchor": "Quantum quenches and off-equilibrium dynamical transition in the\n  infinite-dimensional Bose-Hubbard model: We study the off-equilibrium dynamics of the infinite dimensional Bose\nHubbard Model after a quantum quench. The dynamics can be analyzed exactly by\nmapping it to an effective Newtonian evolution. For integer filling, we find a\ndynamical transition separating regimes of small and large quantum quenches\nstarting from the superfluid state. This transition is very similar to the one\nfound for the fermionic Hubbard model by mean field approximations.",
        "positive": "Impurity effects on BCS-BEC crossover in ultracold atomic Fermi gases: We present a systematic investigation of the effects of \"nonmagnetic\"\nimpurities on the $s$-wave BCS-BEC crossover in atomic Fermi gases within a\npairing fluctuation theory. Both pairing and impurity scattering $T$-matrices\nare treated self-consistently at the same time. While the system is less\nsensitive to impurity scattering in the Born limit, for strong impurity\nscatterers, both the frequency and the gap function are highly renormalized,\nleading to significant suppression of the superfluid $T_c$, the order parameter\nand the superfluid density. We also find the formation of impurity bands and\nsmearing of coherence peak in the fermion density of states, leading to a\nspectrum weight transfer and finite lifetime of Bogoliubov quasiparticles. In\nthe BCS regime, the superfluidity may be readily destroyed by the impurity of\nhigh density. In comparison, the superfluidity in unitary and BEC regimes is\nrelatively more robust."
    },
    {
        "anchor": "Noise correlations of two-dimensional Bose gases: We analyze density-density correlations of expanding clouds of weakly\ninteracting two-dimensional Bose gases below and above the\nBerezinskii-Kosterlitz-Thouless transition, with particular focus on short-time\nexpansions. During time-of-flight expansion, phase fluctuations of the trapped\nsystem translate into density fluctuations, in addition to the density\nfluctuations that exist in in-situ. We calculate the correlations of these\nfluctuations both in real space and in momentum space, and derive analytic\nexpressions in momentum space. Below the transition, the correlation functions\nshow an oscillatory behavior, controlled by the scaling exponent of the\nquasi-condensed phase, due to constructive interference. We argue that this can\nbe used to extract the scaling exponent of the quasi-condensate experimentally.\nAbove the transition, the interference is rapidly suppressed when the atoms\ntravel an average distance beyond the correlation length. This can be used to\ndistinguish the two phases qualitatively.",
        "positive": "Competition of superfluidity and density waves in one-dimensional\n  Bose-Fermi mixtures: We study a mixture of one-dimensional bosons and spinless fermions at\nincommensurate filling using phenomenological bosonization and Green's\nfunctions techniques. We derive the relation between the parameters of the\nmicroscopic Hamiltonian and macroscopic observables. Galilean invariance\nresults in extra constraints for the current current interactions. We obtain\nthe exact exponents for the various response functions, and show that\nsuperfluid fluctuations are enhanced by the effective boson-fermion\ndensity-density interaction and suppressed by the effective boson-fermion\ncurrent-current interaction. In the case of a bosonized model with purely\ndensity-density interaction, when the effective boson-fermion density-density\ninteraction is weak enough, the superfluid exponent of the bosons has a\nnon-monotonous variation with the ratio of the fermion velocity to the boson\nvelocity. By contrast, density-wave exponent and the exponent for fermionic\nsuperfluidity are monotonous functions of the velocity ratio."
    },
    {
        "anchor": "Dark-dark solitons and modulational instability in miscible,\n  two-component Bose-Einstein condensates: We investigate the dynamics of two miscible superfluids experiencing fast\ncounterflow in a narrow channel. The superfluids are formed by two\ndistinguishable components of a trapped dilute-gas Bose-Einstein condensate\n(BEC). The onset of counterflow-induced modulational instability throughout the\ncloud is observed and shown to lead to the proliferation of dark-dark vector\nsolitons. These solitons, which we observe for the first time in a BEC, do not\nexist in single-component systems, exhibit intriguing beating dynamics and can\nexperience a transverse instability leading to vortex line structures.\nExperimental results and multi-dimensional numerical simulations are presented.",
        "positive": "Quantum Impurity in a One-dimensional Trapped Bose Gas: We present a new theoretical framework for describing an impurity in a\ntrapped Bose system in one spatial dimension. The theory handles any external\nconfinement, arbitrary mass ratios, and a weak interaction may be included\nbetween the Bose particles. To demonstrate our technique, we calculate the\nground state energy and properties of a sample system with eight bosons and\nfind an excellent agreement with numerically exact results. Our theory can thus\nprovide definite predictions for experiments in cold atomic gases."
    },
    {
        "anchor": "Singlet and Triplet Superfluid Competition in a Mixture of Two-Component\n  Fermi and One-Component Dipolar Bose Gases: We consider a mixture of two-component Fermi and (one-component) dipolar Bose\ngases in which both dipolar interaction and s-wave scattering between fermions\nof opposite spins are tunable. We show that in the long wavelength limit, the\nanisotropy in the Fermi-Fermi interaction induced by phonons of the dipolar\ncondensate can strongly enhance the scattering in the triplet channel. We\ninvestigate in detail the conditions for achieving optimal critical temperature\nat which the triplet superfluid begins to compete with the singlet superfluid.",
        "positive": "Exact solution for $SU(2)$-symmetry breaking bosonic mixtures at strong\n  interactions: We study the equilibrium properties of a one-dimensional mixture of two\nTonks-Girardeau gases on a ring geometry in the limit of strongly-repulsive\ninter-species interactions. We derive the exact many-body wavefunction and\ncompare it to the $SU(2)$ solution where intra- and inter-species interactions\nare also diverging but equal. We focus on the role of the $SU(2)$-symmetry\nbreaking on the behaviour of the large- and short-distance correlations by\nstudying the zero-momentum occupation number and the Tan's contact from the\nasymptotic behavior of the momentum distribution. Although the symmetry is only\nweakly broken, it has important consequences on spin correlations in the system\nas the reduction by a factor of two of the zero-momentum occupation number with\nrespect to the $SU(2)$ case in the thermodynamic limit and the decrease of the\nTan's contact."
    },
    {
        "anchor": "Classical fields in the one-dimensional Bose gas: applicability and\n  determination of the optimal cutoff: To finalize information about the accuracy of the classical field approach\nfor the 1d Bose gas, the lowest temperature quasicondensate was studied by\ncomparing the extended Bogoliubov model of Mora and Castin, to its classical\nfield analogue. The parameters for which the physics is well described by\nmatter waves are now presented for all 1d regimes, and concurrently, the\noptimal cutoff that best matches all observables together is also provided.\nThis cutoff rises strongly with density when the chemical potential is higher\nthan the thermal energy to account for kinetic energy. As a consequence, clouds\nthat reach this coldest quantum fluctuating regime are better described using a\ntrap basis than plane waves. This contrasts with higher temperature clouds for\nwhich the basis choice is less important. In passing, estimates for chemical\npotential, density fluctuations, kinetic and interaction energy in the low\ntemperature quasicondensate are obtained up to several leading terms.",
        "positive": "Vortex spin in a superfluid: General relativity predicts that the curvature of spacetime induces spin\nrotations on a parallel transported particle. We deploy Unruh's analogue\ngravity picture and consider a quantised vortex embedded in a two-dimensional\nsuperfluid Bose--Einstein condensate. We show that such a vortex behaves\ndynamically like a charged particle with a spin in a gravitational field. The\nexistence of a vortex spin in a superfluid complements Onsager's prediction of\nthe quantisation of circulation, and is suggestive of potential quantum\ntechnology applications of rotating superfluids."
    },
    {
        "anchor": "All-Optical Production of a Lithium Quantum Gas Using Narrow-Line Laser\n  Cooling: We have used the narrow $2S_{1/2} \\rightarrow 3P_{3/2}$ transition in the\nultraviolet (uv) to laser cool and magneto-optically trap (MOT) $^6$Li atoms.\nLaser cooling of lithium is usually performed on the $2S_{1/2} \\rightarrow\n2P_{3/2}$ (D2) transition, and temperatures of $\\sim$300 $\\mu$K are typically\nachieved. The linewidth of the uv transition is seven times narrower than the\nD2 line, resulting in lower laser cooling temperatures. We demonstrate that a\nMOT operating on the uv transition reaches temperatures as low as 59 $\\mu$K.\nFurthermore, we find that the light shift of the uv transition in an optical\ndipole trap at 1070 nm is small and blue-shifted, facilitating efficient\nloading from the uv MOT. Evaporative cooling of a two spin-state mixture of\n$^6$Li in the optical trap produces a quantum degenerate Fermi gas with $3\n\\times 10^{6}$ atoms a total cycle time of only 11 s.",
        "positive": "Bosons condensed in two modes with flavour-changing interaction: A quantum model is considered for $N$ bosons populating two orthogonal\nsingle-particle modes with tunable energy separation in the presence of\nflavour-changing contact interaction. The quantum ground state is well\napproximated as a coherent superposition (for zero temperature) or a mixture\n(at low temperature) of two quasi-classical states. In a mean field\ndescription, the systems realizes one of these states via spontaneous symmetry\nbreaking. Both mean field states, in a certain parameter range, possess finite\nangular momentum and exhibit broken time-reversal symmetry in contrast to the\nquantum ground state. The phase diagram is explored at the mean-field level and\nby direct diagonalisation. The nature of the quantum ground state at zero and\nfinite temperature is analyzed by means of the Penrose Onsager criterion. One\nof three possible phases shows fragmentation on the single-particle level\ntogether with a finite pair order parameter. Thermal and quantum fluctuations\nare characterized with respect to regions of universal scaling behavior. The\nnon-equilibrium dynamics shows a sharp transition between a self-trapping and a\npair-tunneling regime. A recently realized experimental implementation is\ndiscussed with bosonic atoms condensed in the two inequivalent energy minima\n$X_{\\pm}$ of the second band of a bipartite two-dimensional optical lattice."
    },
    {
        "anchor": "Measurement of spectral functions of ultracold atoms in disordered\n  potentials: We report on the measurement of the spectral functions of noninteracting\nultracold atoms in a three-dimensional disordered potential resulting from an\noptical speckle field. Varying the disorder strength by 2 orders of magnitude,\nwe observe the crossover from the \"quantum\" perturbative regime of low disorder\nto the \"classical\" regime at higher disorder strength, and find an excellent\nagreement with numerical simulations. The method relies on the use of\nstate-dependent disorder and the controlled transfer of atoms to create\nwell-defined energy states. This opens new avenues for experimental\ninvestigations of three-dimensional Anderson localization.",
        "positive": "Trapped Bose-Bose mixtures at finite temperature: a quantum Monte Carlo\n  approach: We study thermal properties of a trapped Bose-Bose mixture in a dilute regime\nusing quantum Monte Carlo methods. Our main aim is to investigate the\ndependence of the superfluid density and the condensate fraction on\ntemperature, for the mixed and separated phases. To this end, we use the\ndiffusion Monte Carlo method, in the zero-temperature limit, and the\npath-integral Monte Carlo method for finite temperatures. The results obtained\nare compared with solutions of the coupled Gross-Pitaevskii equations for the\nmixture at zero temperature. We notice the existence of an anisotropic\nsuperfluid density in some phase-separated mixtures. Our results also show that\nthe temperature evolution of the superfluid density and condensate fraction is\nslightly different, showing noteworthy situations where the superfluid fraction\nis smaller than the condensate fraction."
    },
    {
        "anchor": "Magnetic properties and strong-coupling corrections in an ultracold\n  Fermi gas with population imbalance: We investigate magnetic properties of an ultracold Fermi gas with population\nimbalance. In the presence of population imbalance, the strong-coupling theory\ndeveloped by Nozieres and Schmitt-Rink (which is frequently referred to as the\nNSR theory, or Gaussian fluctuation theory) is known to give unphysical results\nin the BCS-BEC crossover region. We point out that this problem comes from how\nto treat pseudogap effects originating from pairing fluctuations and many-body\ncorrections to the spin susceptibility. We also clarify how to overcome this\nproblem by including higher order fluctuations beyond the ordinary T-matrix\ntheory. Calculated spin susceptibility based on our extended T-matrix theory\nagrees well with the recent experiment on a 6Li Fermi gas.",
        "positive": "Quantum groups as hidden symmetries of quantum impurities: We present an approach to interacting quantum many-body systems based on the\nnotion of quantum groups, also known as $q$-deformed Lie algebras. In\nparticular, we show that if the symmetry of a free quantum particle corresponds\nto a Lie group $G$, in the presence of a many-body environment this particle\ncan be described by a deformed group, $G_q$. Crucially, the single deformation\nparameter, $q$, contains all the information about the many-particle\ninteractions in the system. We exemplify our approach by considering a quantum\nrotor interacting with a bath of bosons, and demonstrate that extracting the\nvalue of $q$ from closed-form solutions in the perturbative regime allows one\nto predict the behavior of the system for arbitrary values of the impurity-bath\ncoupling strength, in good agreement with non-perturbative calculations.\nFurthermore, the value of the deformation parameter allows to predict at which\ncoupling strengths rotor-bath interactions result in a formation of a stable\nquasiparticle. The approach based on quantum groups does not only allow for a\ndrastic simplification of impurity problems, but also provides valuable\ninsights into hidden symmetries of interacting many-particle systems."
    },
    {
        "anchor": "Deviation from Universality in Collisions of Ultracold $^6$Li$_2$\n  Molecules: Collisions of $^6$Li$_2$ molecules with free $^6$Li atoms reveal a striking\ndeviation from universal predictions based on long-range van der Waals\ninteractions. Li$_2$ closed-channel molecules are formed in the highest\nvibrational state near a narrow Feshbach resonance, and decay via two-body\ncollisions with Li$_2$, Li, and Na. For Li$_2$+Li$_2$ and Li$_2$+Na, the decay\nrates agree with the universal predictions of the quantum Langevin model. In\ncontrast, the rate for Li$_2$+Li is exceptionally small, with an upper bound\nten times smaller than the universal prediction. This can be explained by the\nlow density of available decay states in systems of light atoms [G.\nQu\\'em\\'ener, J.-M. Launay, and P. Honvault, Phys. Rev. A \\textbf{75}, 050701\n(2007)], for which such collisions have not been studied before.",
        "positive": "The three-body parameter for Efimov states in lithium-6: We present a state-of-the-art reanalysis of experimental results on Efimov\nresonances in the three-fermion system of $^6$Li. We discuss different\ndefinitions of the 3-body parameter (3BP) for Efimov states, and adopt a\ndefinition that excludes effects due to deviations from universal scaling for\nlow-lying states. We develop a finite-temperature model for the case of three\ndistinguishable fermions and apply it to the excited-state Efimov resonance to\nobtain the most accurate determination to date of the 3BP in an atomic\nthree-body system. Our analysis of ground-state Efimov resonances in the same\nsystem yields values for the three-body parameter that are consistent with the\nexcited-state result. Recent work has suggested that the reduced 3BP for atomic\nsystems is a near-universal quantity, almost independent of the particular atom\ninvolved. However, the value of the 3BP obtained for $^6$Li is significantly\n($\\sim 20$%) different from that previously obtained from the excited-state\nresonance in Cs. The difference between these values poses a challenge for\ntheory."
    },
    {
        "anchor": "Loading and detecting a three-dimensional Fermi gas in one-dimensional\n  optical superlattice: We investigate the procedures of loading and detecting three-dimensional\nfermionic quantum gases in a one-dimensional optical superlattice potential\nsubjected to a trapping potential. Additionally, we consider the relaxation\ndynamics after a sudden change of the superlattice potential. We numerically\nsimulate the time-dependent evolution of the continuous system using exact\ndiagonalization of non-interacting fermions. During the loading procedure we\nanalyze the occupation of the instantaneous energy levels and compare the\nsituation in a homogeneous system with the trapped one. Strong differences are\nfound in particular in the evolution of excitations which we trace back to the\ndistinct global density distribution. Starting from an imbalanced state in the\nsuperlattice potential, we consider the relaxation dynamics of fermions after a\nslow change of the superlattice potential and find a bimodule distribution of\nexcitations. To be able to compare with the experimental results we also\nsimulate the measurement sequence of the even and odd local density and find a\nstrong dependence of the outcome on the actual ramp procedure. We suggest how\nthe loading and detecting procedure can be optimized.",
        "positive": "Fast generation of time-stationary spin-1 squeezed states by\n  non-adiabatic control: A protocol for the creation of time-stationary squeezed states in a spin-1\nBose condensate is proposed. The method consists of a pair of controlled\nquenches of an external magnetic field, which allows tuning of the system\nHamiltonian in the vicinity of a phase transition. The quantum fluctuations of\nthe system are well described by quantum harmonic oscillator dynamics in the\nlimit of large system size, and the method can be applied to a spin-1 gas\nprepared in the low or high energy polar states."
    },
    {
        "anchor": "Collective excitations of superfluid Fermi gases near the transition\n  temperature: Studying the collective pairing phenomena in a two-component Fermi gas, we\npredict the appearance near the transition temperature $T_c$ of a well-resolved\ncollective mode of quadratic dispersion. The mode is visible both above and\nbelow $T_c$ in the system's response to a driving pairing field. When\napproaching $T_c$ from below, the phononic and pair-breaking branches,\ncharacteristic of the zero temperature behavior, reduce to a very low\nenergy-momentum region when the pair correlation length reaches its critical\ndivergent behavior $\\xi_{\\rm pair}\\propto|T_c-T|^{-1/2}$; elsewhere, they are\nreplaced by the quadratically-dispersed pairing resonance, which thus acts as a\nprecursor of the phase transition. In the strong-coupling and Bose-Einstein\nCondensate regime, this mode is a weakly-damped propagating mode associated to\na Lorentzian resonance. Conversely, in the BCS limit it is a relaxation mode of\npure imaginary eigenenergy. At large momenta, the resonance disappears when it\nis reabsorbed by the lower-edge of the pairing continuum. At intermediate\ntemperatures between 0 and $T_c$, we unify the newly found collective phenomena\nnear $T_c$ with the phononic and pair-breaking branches predicted from previous\nstudies, and we exhaustively classify the roots of the analytically continued\ndispersion equation, and show that they provided a very good summary of the\npair spectral functions.",
        "positive": "Structural change of vortex patterns in anisotropic Bose-Einstein\n  condensates: We study the changes in the spatial distribution of vortices in a rotating\nBose-Einstein condensate due to an increasing anisotropy of the trapping\npotential. Once the rotational symmetry is broken, we find that the vortex\nsystem undergoes a rich variety of structural changes, including the formation\nof zig-zag and linear configurations. These spatial re-arrangements are well\nsignaled by the change in the behavior of the vortex-pattern eigenmodes against\nthe anisotropy parameter. The existence of such structural changes opens up\npossibilities for the coherent exploitation of effective many-body systems\nbased on vortex patterns."
    },
    {
        "anchor": "1D Quantum Liquids with Power-Law Interactions: a Luttinger Staircase\n  with Polar Molecules: We study one dimensional fermionic and bosonic gases with repulsive power-law\ninteractions $1/|x|^{\\beta}$, with $\\beta>1$, in the framework of\nTomonaga-Luttinger liquid (LL) theory. We obtain an accurate analytical\nexpression linking the LL parameter to the microscopic Hamiltonian, for\narbitrary $\\beta$ and strength of the interactions. In the presence of a small\nperiodic potential, power-law interactions make the LL unstable towards the\nformation of a cascade of lattice solids with fractional filling, thus forming\na \"Luttinger staircase\". Several of these quantum phases and phase transitions\nare realized with groundstate polar molecules and weakly-bound magnetic\nFeshbach molecules.",
        "positive": "Catching Bethe phantoms and quantum many-body scars: Long-lived\n  spin-helix states in Heisenberg magnets: Exact solutions for quantum many-body systems are rare and provide valuable\ninsight to universal phenomena. Here we show experimentally in anisotropic\nHeisenberg chains that special helical spin patterns can have very long\nlifetimes. This finding confirms the recent prediction of phantom Bethe states,\nexact many-body eigenstates carrying finite momenta yet no energy. We\ntheoretically find analogous stable spin helices in higher dimensions and in\nother non-integrable systems, where they imply non-thermalizing dynamics\nassociated with quantum many-body scars. We use phantom spin helices to\ndirectly measure the interaction anisotropy which has a major contribution from\nshort-range off-site interactions that have not been observed before. Phantom\nhelix states open new opportunities for quantum simulations of spin physics and\nstudies of many-body dynamics."
    },
    {
        "anchor": "A method for the dynamics of vortices in a Bose-Einstein condensate:\n  analytical equations of the trajectories of phase singularities: We present a method to study the dynamics of a quasi-two dimensional\nBose-Einstein condensate which contains initially many vortices at arbitrary\nlocations. We present first the analytical solution of the dynamics in a\nhomogeneous medium and in a parabolic trap for the ideal non-interacting case.\nFor the homogeneous case this was introduced in the context of photonics. Here\nwe discuss this case in the context of Bose-Einstein condensates and extend the\nanalytical solution to the trapped case, for the first time. This linear case\nallows one to obtain the trajectories of the position of phase singularities\npresent in the initial condensate along with time. Also, it allows one to\npredict some quantities of interest, such as the time at which a vortex and an\nantivortex contained in the initial condensate will merge. Secondly, the method\nis complemented with numerical simulations of the non-linear case. We use a\nnumerical split-step simulation of the non-linear Gross-Pitaevskii equation to\ndetermine how these trajectories and quantities of interest are changed by the\npresence of interactions. We illustrate the method with several simple cases of\ninterest both in the homogeneous and parabolically trapped systems.",
        "positive": "Quaternary-singlet State of Spin-1 Bosons in Optical Lattice: We present the quantum ground state properties of $^{23}$Na spinor\ncondensates, which is confined in a periodic or double-well potential and\nsubject to a magnetic dipole-dipole interaction between nearby wells. A novel\nsinglet state arise in the system and can be discussed in explicit form. Caused\nby the competition between the intra-site spin exchange interactions and the\ninter-site dipole-dipole interactions, this quaternary-singlet\\ state is a\nentangled state formed by at lest four particles and vanish the total spin.\nThis is distinct from the direct product of the two conventional singlet pairs."
    },
    {
        "anchor": "Measuring densities of cold atomic clouds smaller than the resolution\n  limit: We propose and demonstrate an experimental method to measure by absorption\nimaging the size and local column density of a cloud of atoms, even when its\nsmallest dimension is smaller than the resolution of the imaging system. To do\nthis, we take advantage of the fact that, for a given total number of atoms, a\nsmaller and denser cloud scatters less photons when the gas is optically thick.\nThe method relies on making an ansatz on the cloud shape along the unresolved\ndimension(s), and on providing an additional information such as the total\nnumber of atoms. We demonstrate the method on \\textit{in-situ} absorption\nimages of elongated 87Sr Fermi gases. We find significant non-linear\ncorrections to the estimated size and local density of the cloud compared to a\nstandard analysis. This allows us to recover an un-distorted longitudinal\ndensity profile, and to measure transverse sizes as small as one fourth of our\nimaging resolution. The ultimate limit of our method is the wavelength that is\nused for imaging.",
        "positive": "Magnetic lattices for ultracold atoms: This article reviews the development in our laboratory of magnetic lattices\ncomprising periodic arrays of magnetic microtraps created by patterned magnetic\nfilms to trap periodic arrays of ultracold atoms. Recent achievements include\nthe realisation of multiple Bose-Einstein condensates in a 10 micron-period\none-dimensional magnetic lattice; the fabrication of sub-micron-period square\nand triangular magnetic lattice structures suitable for quantum tunnelling\nexperiments; the trapping of ultracold atoms in a sub-micron-period triangular\nmagnetic lattice; and a proposal to use long-range interacting Rydberg atoms to\nachieve spin-spin interactions between sites in a large-spacing magnetic\nlattice."
    },
    {
        "anchor": "Quantum enhanced sensing by echoing spin-nematic squeezing in atomic\n  Bose-Einstein condensate: Quantum entanglement can provide enhanced precision beyond standard quantum\nlimit (SQL), the highest precision achievable with classical means. It remains\nchallenging, however, to observe large enhancement limited by the experimental\nabilities to prepare, maintain, manipulate and detect entanglement. Here, we\npresent nonlinear interferometry protocols based on echoing spin-nematic\nsqueezing to achieve record high enhancement factors in atomic Bose-Einstein\ncondensate. The echo is realized by a state-flip of the spin-nematic squeezed\nvacuum, which serves as the probe state and is refocused back to the vicinity\nof the unsqueezed initial state while carrying out near noiseless amplification\nof a signal encoded. A sensitivity of $21.6\\pm0.5$ decibels (dB) for a\nsmall-angle Rabi rotation beyond the two-mode SQL of 26400 atoms as well as\n$16.6\\pm1.3$ dB for phase sensing in a Ramsey interferometer are observed. The\nabsolute phase sensitivity for the latter extrapolates to\n$103~\\rm{pT/\\sqrt{Hz}}$ at a probe volume of $18~\\mu\\rm{m}^3$ for near-resonant\nmicrowave field sensing. Our work highlights the excellent many-body coherence\nof spin-nematic squeezing and suggests its possible quantum metrological\napplications in atomic magnetometer, atomic optical clock, and fundamental\ntesting of Lorentz symmetry violation, etc.",
        "positive": "Pauli Blocking Effect on Efimov States Near Feshbach Resonance: In this Letter we study the effect of Pauli blocking on the Efimov states in\na quantum Fermi gas and illustrate that the universal Efimov potential is\naltered at large distances. We obtain the universal spectrum flow of Efimov\ntrimers when the Fermi density is varied and further consider the effect of\nscattering of trimers by the Fermi sea. We argue that the universal flow is\nrobust against fluctuating particle-hole pairs that result in an infrared\ncatastrophe in impurity problems."
    },
    {
        "anchor": "Quantum phase diagram of the integrable p_x+ip_y fermionic superfluid: We determine the zero temperature quantum phase diagram of a p_x+ip_y pairing\nmodel based on the exactly solvable hyperbolic Richardson-Gaudin model. We\npresent analytical and large-scale numerical results for this model. In the\ncontinuum limit, the exact solution exhibits a third-order quantum phase\ntransition, separating a strong-pairing from a weak-pairing phase. The mean\nfield solution allows to connect these results to other models with p_x+ip_y\npairing order. We define an experimentally accessible characteristic length\nscale, associated with the size of the Cooper pairs, that diverges at the\ntransition point, indicating that the phase transition is of a\nconfinement-deconfinement type without local order parameter. We show that this\nphase transition is not limited to the p_x+ip_y pairing model, but can be found\nin any representation of the hyperbolic Richardson-Gaudin model and is related\nto a symmetry that is absent in the rational Richardson-Gaudin model.",
        "positive": "Phase Equilibrium of Binary Mixtures in Mixed Dimensions: We study the stability of a Bose-Fermi system loaded into an array of coupled\none-dimensional (1D) \"tubes\", where bosons and fermions experience different\ndimensions: Bosons are heavy and strongly localized in the 1D tubes, whereas\nfermions are light and can hop between the tubes. Using the 174Yb-6Li system as\na reference, we obtain the equilibrium phase diagram. We find that, for both\nattractive and repulsive interspecies interaction, the exact treatment of 1D\nbosons via the Bethe ansatz implies that the transitions between pure fermion\nand any phase with a finite density of bosons can only be first order and never\ncontinuous, resulting in phase separation in density space. In contrast, the\norder of the transition between the pure boson and the mixed phase can either\nbe second or first order depending on whether fermions are allowed to hop\nbetween the tubes or they also are strictly confined in 1D. We discuss the\nimplications of our findings for current experiments on 174Yb-6Li mixtures as\nwell as Fermi-Fermi mixtures of light and heavy atoms in a mixed dimensional\noptical lattice system."
    },
    {
        "anchor": "Universal aspects of a strongly interacting impurity in a dilute Bose\n  condensate: We study the properties of an impurity immersed in a weakly interacting Bose\ngas, i.e., of a Bose polaron. In the perturbatively-tractable of limit weak\nimpurity-boson interactions many of its properties are known to depend only on\nthe scattering length. Here we demonstrate that for strong (unitary)\nimpurity-boson interactions all static quasiproperties of a Bose polaron in a\ndilute Bose gas, such as its energy, its residue, its Tan's contact and the\nnumber of bosons trapped nearby the impurity, depend on the impurity-boson\npotential via a single parameter.",
        "positive": "Three-dimensional Isotropic Droplets in Rydberg-dressed Bose Gases: We predict a scheme for the creation of isotropic three-dimensional droplets\nin Rydbeg-dressed Bose gases, which contain both repulsive contact interactions\nand attractive van der Waals interactions causing the quantum fluctuation\neffect non-negligible. We present detailed beyond mean-field calculations with\nLee-Huang-Yang correction and demonstrate the existence of isotropic droplets\nunder realistic experimental conditions. Stable droplets possess flat-top\ndensity distribution, and their chemical potentials decrease with the particle\nnumber expansion towarding a critical value. We distinguish droplets from\nbright solitons through peak density, width of condensate and quantum depletion\ncalculations. We summarize a phase diagram of realizing droplets, and\nsubsequently highlight the stability of droplets by real time evolution as well\nas collisions. Our work provides a novel platform for investigating excitation\nspectrum and superfluid nature of droplets."
    },
    {
        "anchor": "Localization of ultracold atoms in incommensurate spin-orbit-coupling\n  and Zeeman lattices: We consider a particle governed by a one-dimensional Hamiltonian in which\nartificial periodic spin-orbit coupling and Zeeman lattice have incommensurate\nperiods. Using best rational approximations to such quasiperiodic Hamiltonian,\nthe problem is reduced to description of spinor states in a superlattice. In\nthe absence of a constant Zeeman splitting, the system acquires an additional\nsymmetry, which hinders the localization. However, if the lattices are deep\nenough, then localized states can appear even for Zeeman field with zero or\nsmall mean value. Spatial distribution of localized modes is nearly uniform and\nis directly related to the topological properties of the effective\nsuperlattice: center-of-mass coordinates of modes are determined by Zak phases\ncomputed from the superlattice band structure. The best rational approximations\nfeature the `memory' effect: each rational approximation holds the information\nabout the energies and spatial distribution of the modes obtained under\npreceding, less accurate approximations. Dispersion of low-energy initial\nwavepackets is characterized by the law $\\propto t^\\beta$ with $\\beta$ varying\nbetween $1/2$ at the initial stage and $1$ at longer, but still finite-time,\nevolution. The dynamics of initial wavepackets, exciting mainly localized\nmodes, manifests quantum revivals.",
        "positive": "Stability of a flattened dipolar binary condensate: emergence of the\n  spin roton: We develop theory for a two-component miscible dipolar condensate in a planar\ntrap. Using numerical solutions and a variational theory we solve for the\nexcitation spectrum and identify regimes where density- and spin-roton\nexcitations are favored. We characterize the various instabilities that can\nemerge in this system over a wide parameter regime and present results for the\nstability phase diagram. Importantly this allows us to identify the parameter\nregimes where a novel roton-immiscibility transition can occur, driven by the\nsoftening of the spin roton excitation."
    },
    {
        "anchor": "Observation of Many-body Dynamical Delocalization in a Kicked Ultracold\n  Gas: Contrary to a driven classical system that exhibits chaos phenomena and\ndiffusive energy growth, a driven quantum system can exhibit dynamical\nlocalization that features energy saturation. However, the evolution of the\ndynamically localized state in the presence of many-body interactions has long\nremained an open question. Here we experimentally study an interacting 1D\nultracold gas periodically kicked by a pulsed optical lattice, and observe the\ninteraction-driven emergence of dynamical delocalization and many-body quantum\nchaos. The observed dynamics feature a sub-diffusive energy growth manifest\nover a broad parameter range of interaction and kick strengths, and shed light\non an area where theoretical approaches are extremely challenging.",
        "positive": "Is an Ultra-Cold Strongly Interacting Fermi Gas a Perfect Fluid?: Fermi gases with magnetically tunable interactions provide a clean and\ncontrollable laboratory system for modeling interparticle interactions between\nfermions in nature. The s-wave scattering length, which is dominant a low\ntemperature, is made to diverge by tuning near a collisional (Feshbach)\nresonance. In this regime, two-component Fermi gases are stable and strongly\ninteracting, enabling tests of nonperturbative many-body theories in a variety\nof disciplines, from high temperature superconductors to neutron matter and\nquark-gluon plasmas. We have developed model-independent methods for measuring\nthe entropy and energy of this model system, providing a benchmark for\ncalculations of the thermodynamics. Our experiments on the expansion of\nrotating strongly interacting Fermi gases in the normal fluid regime reveal\nextremely low viscosity hydrodynamics. Combining the thermodynamic and\nhydrodynamic measurements enables an estimate of the ratio of the shear\nviscosity to the entropy density. A strongly interacting Fermi gas in the\nnormal fluid regime is found to be a nearly perfect fluid, where the ratio of\nthe viscosity to the entropy density is close to a universal minimum that has\nbeen conjectured by string theory methods."
    },
    {
        "anchor": "Controlling and observing nonseparability of phonons created in\n  time-dependent 1D atomic Bose condensates: We study the spectrum and entanglement of phonons produced by temporal\nchanges in homogeneous one-dimensional atomic condensates. To characterize the\nexperimentally accessible changes, we first consider the dynamics of the\ncondensate when varying the radial trapping frequency, separately studying two\nregimes: an adiabatic one and an oscillatory one. Working in momentum space, we\nthen show that in situ measurements of the density-density correlation function\ncan be used to assess the nonseparability of the phonon state after such\nchanges. We also study time-of-flight (TOF) measurements, paying particular\nattention to the role played by the adiabaticity of opening the trap on the\nnonseparability of the final state of atoms. In both cases, we emphasize that\ncommuting measurements can suffice to assess nonseparability. Some recent\nobservations are analyzed, and we make proposals for future experiments.",
        "positive": "BEC phase diagram of a $^{87}$Rb trapped gas in terms of macroscopic\n  thermodynamic parameters: We measure the phase diagram of a $^{87}$Rb Bose gas in a harmonic trap in\nterms of macroscopic parameters obtained from the spatial distribution of\natoms. Considering the relevant variables as size of the cloud ${\\cal V}$,\nnumber of atoms $N$ and temperature $T$, a novel parameter $\\Pi = \\Pi(N,{\\cal\nV},T)$ is introduced to characterize the overall pressure of the system. We\nconstruct the phase diagram ($\\Pi$ vs $T$) identifying new features related to\nBose-Einstein condensation (BEC) transition in a trapped gas. A thermodynamic\ndescription of the phase transition based on purely macroscopic parameters,\nprovide us with properties that do not need the local density approximation. An\nunexpected consequence of this analysis is the suggestion that BEC appears as a\ncontinuous third-order phase transition instead of being a second-order one."
    },
    {
        "anchor": "Single-particle vs. pair superfluidity in a bilayer system of dipolar\n  bosons: We consider the ground state of a bilayer system of dipolar bosons, where\ndipoles are oriented by an external field in the direction perpendicular to the\nparallel planes. Quantum Monte Carlo methods are used to calculate the\nground-state energy, the one-body and two-body density matrix, and the\nsuperfluid response as a function of the separation between layers. We find\nthat by decreasing the interlayer distance for fixed value of the strength of\nthe dipolar interaction, the system undergoes a quantum phase transition from a\nsingle-particle to a pair superfluid. The single-particle superfluid is\ncharacterized by a finite value of both the atomic condensate and the\nsuper-counterfluid density. The pair superfluid phase is found to be stable\nagainst formation of many-body cluster states and features a gap in the\nspectrum of elementary excitations.",
        "positive": "Analytical solution of the disordered Tavis-Cummings model and its Fano\n  resonances: $\\mathcal{N}$ emitters collectively coupled to a quantised cavity mode are\ndescribed by the Tavis-Cummings model. We present complete analytical solution\nof the model in the presence of inhomogeneous couplings and energetic disorder.\nWe derive the exact expressions for the bright and the dark sectors that\ndecouple the disordered model and find that, in the thermodynamic limit, the\nenergetic disorder transforms the bright sector to Fano's model that can be\neasily solved. We thoroughly explore the effects of energetic disorder assuming\na Gaussian distribution of emitter transition energies. We compare the Fano\nresonances in optical absorption and inelastic electron scattering both in the\nweak and the strong coupling regimes. We study the evolution of the optical\nabsorption with an increase in the disorder strength and find that it changes\nthe lower and upper polaritons to their broadened resonances that finally\ntransform to a single resonance at the bare cavity photon energy, thus taking\nthe system from the strong to the weak coupling regime. Interestingly, we learn\nthat the Rabi splitting can exist even in the weak coupling regime while the\npolaritonic peaks in the strong coupling regime can represent almost excitonic\nstates at intermediate disorder strengths. We also calculate the photon Green's\nfunction to see the effect of cavity leakage and non-radiative emitter losses\nand find that the polariton linewidth exhibits a minimum as a function of\ndetuning when the cavity leakage is comparable to the Fano broadening."
    },
    {
        "anchor": "Magnetic phase diagram of a spin-1 condensate in two dimensions with\n  dipole interaction: Several new features arise in the ground-state phase diagram of a spin-1\ncondensate trapped in an optical trap when the magnetic dipole interaction\nbetween the atoms is taken into account along with confinement and spin\nprecession. The boundaries between the regions of ferromagnetic and polar\nphases move as the dipole strength is varied and the ferromagnetic phases can\nbe modulated. The magnetization of the ferromagnetic phase perpendicular to the\nfield becomes modulated as a helix winding around the magnetic field direction,\nwith a wavelength inversely proportional to the dipole strength. This\nmodulation should be observable for current experimental parameters in\n$^{87}$Rb. Hence the much-sought supersolid state, with broken continuous\ntranslation invariance in one direction and broken global U(1) invariance,\noccurs generically as a metastable state in this system as a result of dipole\ninteraction. The ferromagnetic state parallel to the applied magnetic field\nbecomes striped in a finite system at strong dipolar coupling.",
        "positive": "Quantum phases of dipolar bosons in one-dimensional optical lattices: We theoretically analyze the phase diagram of a quantum gas of bosons that\ninteract via repulsive dipolar interactions. The bosons are tightly confined by\nan optical lattice in a quasi one-dimensional geometry. In the single-band\napproximation, their dynamics is described by an extended Bose-Hubbard model\nwhere the relevant contributions of the dipolar interactions consist of\ndensity-density repulsion and correlated tunneling terms. We evaluate the phase\ndiagram for unit density using numerical techniques based on the density-matrix\nrenormalization group algorithm. Our results predict that correlated tunneling\ncan significantly modify the parameter range of the topological insulator\nphase. At vanishing values of the onsite interactions, moreover, correlated\ntunneling promotes the onset of a phase with a large number of low energy\nmetastable configurations."
    },
    {
        "anchor": "Calculation of Drag and Superfluid Velocity from the Microscopic\n  Parameters and Excitation Energies of a Two-Component Bose-Einstein\n  Condensate on an Optical Lattice: We investigate a model of a two-component Bose-Einstein condensate residing\non an optical lattice. Within a Bogolioubov-approach at the mean-field level,\nwe derive exact analytical expressions for the excitation spectrum of the\ntwo-component condensate when taking into account hopping and interactions\nbetween arbitrary sites. Our results thus constitute a basis for works that\nseek to clarify the effects of higher-order interactions in the system. We\ninvestigate the excitation spectrum and the two branches of superfluid velocity\nin more detail for two limiting cases of particular relevance. Moreover, we\nrelate the hopping and interaction parameters in the effective Bose-Hubbard\nmodel to microscopic parameters in the system, such as the laserlight\nwavelength and atomic masses of the components in the condensate. These results\nare then used to calculate analytically and numerically the drag coefficient\nbetween the components of the condensate. We find that the drag is most\neffective close to the symmetric case of equal masses between the components,\nregardless of the strength of the intercomponent interaction and the lattice\nwell depth.",
        "positive": "Extraction of the frequency moments of spectral densities from\n  imaginary-time correlation function data: We introduce an exact framework to compute the positive frequency moments\n$M^{(\\alpha)}(\\mathbf{q})=\\braket{\\omega^\\alpha}$ of different dynamic\nproperties from imaginary-time quantum Monte Carlo data. As a practical\nexample, we obtain the first five moments of the dynamic structure factor\n$S(\\mathbf{q},\\omega)$ of the uniform electron gas at the electronic Fermi\ntemperature based on \\emph{ab initio} path integral Monte Carlo simulations. We\nfind excellent agreement with known sum rules for $\\alpha=1,3$, and, to our\nknowledge, present the first results for $\\alpha=2,4,5$. Our idea can be\nstraightforwardly generalized to other dynamic properties such as the\nsingle-particle spectral function $A(\\mathbf{q},\\omega)$, and will be useful\nfor a number of applications, including the study of ultracold atoms, exotic\nwarm dense matter, and condensed matter systems."
    },
    {
        "anchor": "Probing surface states with many-body wave packet scattering: The scattering of 1D matter wave bright solitons on attractive potentials\nenables one to populate bound states, a feature impossible with noninteracting\nwave packets. Compared to noninteracting states, the populated states are\nrenormalized by the attractive interactions between atoms and keep the same\ntopology. This renormalization can even transform a virtual state into a bound\nstate. By switching off adiabatically the interactions, the trapped wave\npackets converge towards the true noninteracting bound states. Our numerical\nstudies show how such scattering experiments can reveal and characterize the\nsurface states of a periodic structure whose translational invariance has been\nbroken. We provide evidence that the corresponding 3D regime should be\naccessible with current techniques.",
        "positive": "Probing molecular spectral functions and unconventional pairing using\n  Raman spectroscopy: An impurity interacting with an ultracold Fermi gas can form either a polaron\nstate or a dressed molecular state in which the impurity forms a bound state\nwith one gas particle. This molecular state features rich physics, including a\nfirst-order transition to the polaron state and a negative effective mass at\nsmall interactions. However, these features have remained so far experimentally\ninaccessible. In this work we show theoretically how the molecular state can be\ndirectly prepared experimentally even in its excited state using\nstate-of-the-art cold atom Raman spectroscopy techniques. Initializing the\nsystem in the ultra-strong coupling limit, where the binding energy of the\nmolaron is much larger than the Fermi energy, our protocol maps out the\nmomentum-dependent spectral function of the molecule. Using a diagrammatic\napproach we furthermore show that the molecular spectral function serves as a\ndirect precursor of the elusive Fulde-Ferell-Larkin-Ovchinnikov phase, which is\nrealized for a finite density of fermionic impurity particles. Our results pave\nthe way to a systematic understanding of how composite particles form in\nquantum many-body environments and provide a basis to develop new schemes for\nthe observation of exotic phases of quantum many-body systems."
    },
    {
        "anchor": "Dynamic structure function of a cold Fermi gas at unitarity: We present a theoretical study of the dynamic structure function of a\nresonantly interacting two-component Fermi gas at zero temperature. Our\napproach is based on dynamic many-body theory able to describe excitations in\nstrongly correlated Fermi systems. The fixed-node diffusion Monte Carlo method\nis used to produce the ground-state correlation functions which are used as an\ninput for the excitation theory. Our approach reproduces recent Bragg\nscattering data in both the density and the spin channel. In the BCS regime,\nthe response is close to that of the ideal Fermi gas. On the BEC side, the Bose\npeak associated with the formation of dimers dominates the density channel of\nthe dynamic response. When the fraction of dimers is large our theory departs\nfrom the experimental data, mainly in the spin channel.",
        "positive": "Oscillating Quantum Droplets from the free expansion of Logarithmic\n  One-Dimensional Bose Gases: We analyze some issues related to the stability and free expansion of a\none-dimensional logarithmic Bose-Einstein condensate, particularly its eventual\nrelation to the formation of quantum droplet-type configurations. We prove that\nthe corresponding properties, such as the energy of the associated N-body\nground state, differ substantially with respect to its three-dimensional\ncounterpart. Consequently, the free velocity expansion also shows differences\nwith respect to the three-dimensional system when logarithmic interactions are\ntaken into account. The one-dimensional logarithmic condensate tends to form\nquantum droplet-type configurations when the external trapping potential is\nturned off, i.e., the self-sustainability or self-confinement appears as in\nthree-dimensions. However, we obtain that for some specific values of the\nself-interaction parameters and the number of particles under consideration,\nthe cloud oscillates during the free expansion around to a specific equilibrium\nsize. These results show that we can get scenarios in which the one-dimensional\ncloud reaches stable configurations, i.e., oscillating quantum droplets."
    },
    {
        "anchor": "Landau Effective Interaction between Quasiparticles in a Bose-Einstein\n  Condensate: Landau's description of the excitations in a macroscopic system in terms of\nquasiparticles stands out as one of the highlights in quantum physics. It\nprovides an accurate description of otherwise prohibitively complex many-body\nsystems, and has led to the development of several key technologies. In this\npaper, we investigate theoretically the Landau effective interaction between\nquasiparticles, so-called Bose polarons, formed by impurity particles immersed\nin a Bose-Einstein condensate (BEC). In the limit of weak interactions between\nthe impurities and the BEC, we derive rigorous results for the effective\ninteraction. They show that it can be strong even for weak impurity-boson\ninteraction, if the transferred momentum/energy between the quasiparticles is\nresonant with a sound mode in the BEC. We then develop a diagrammatic scheme to\ncalculate the effective interaction for arbitrary coupling strengths, which\nrecovers the correct weak coupling results. Using this, we show that the Landau\neffective interaction in general is significantly stronger than that between\nquasiparticles in a Fermi gas, mainly because a BEC is more compressible than a\nFermi gas. The interaction is particularly large near the unitarity limit of\nthe impurity-boson scattering, or when the quasiparticle momentum is close to\nthe threshold for momentum relaxation in the BEC. Finally, we show how the\nLandau effective interaction leads to a sizeable shift of the quasiparticle\nenergy with increasing impurity concentration, which should be detectable with\npresent day experimental techniques.",
        "positive": "Photon Counting as a Probe of Superfluidity in a Two-Band Bose Hubbard\n  System Coupled to a Cavity Field: We show that photon number measurement can be used to detect superfluidity\nfor a two-band Bose-Hubbard model coupled to a cavity field. The atom-photon\ncoupling induces transitions between the two internal atomic levels and results\nin entangled polaritonic states. In the presence of a cavity field, we find\ndifferent photon numbers in the Mott-insulating versus superfluid phases,\nproviding a method of distinguishing the atomic phases by photon counting.\nFurthermore, we examine the dynamics of the photon field after a rapid quench\nto zero atomic hopping by increasing the well depth. We find a robust\ncorrelation between the field's quench dynamics and the initial superfluid\norder parameter, thereby providing a novel and accurate method of determining\nthe order parameter."
    },
    {
        "anchor": "Interferometric approach to measuring band topology in 2D optical\n  lattices: Recently, optical lattices with non-zero Berry's phases of Bloch bands have\nbeen realized. New approaches for measuring Berry's phases and topological\nproperties of bands with experimental tools appropriate for ultracold atoms\nneed to be developed. In this paper, we propose an interferometric method for\nmeasuring Berry's phases of two dimensional Bloch bands. The key idea is to use\na combination of Ramsey interference and Bloch oscillations to measure Zak\nphases, i.e. Berry's phases for closed trajectories corresponding to reciprocal\nlattice vectors. We demonstrate that this technique can be used to measure\nBerry curvature of Bloch bands, the \\pi-Berry's phase of Dirac points, and the\nfirst Chern number of topological bands. We discuss several experimentally\nfeasible realizations of this technique, which make it robust against\nlow-frequency magnetic noise.",
        "positive": "Interatomic interaction effects on second-order momentum correlations\n  and Hong-Ou-Mandel interference of double-well-trapped ultracold fermionic\n  atoms: Identification and understanding of the evolution of interference patterns in\ntwo-particle momentum correlations as a function of the strength of interatomic\ninteractions are important in explorations of the nature of quantum states of\ntrapped particles. Together with the analysis of two-particle spatial\ncorrelations, they offer the prospect of uncovering fundamental symmetries and\nstructure of correlated many-body states, as well as opening vistas into\npotential control and utilization of correlated quantum states as quantum\ninformation resources. With the use of the second-order density matrix\nconstructed via exact diagonalization of the microscopic Hamiltonian, and an\nanalytic Hubbard-type model, we explore here the systematic evolution of\ncharacteristic interference patterns in the two-body momentum and spatial\ncorrelation maps of two entangled ultracold fermionic atoms in a double well,\nfor the entire attractive- and repulsive-interaction range. We uncover\nstatistics-governed bunching and antibunching, as well as interaction-dependent\ninterference patterns, in the ground and excited states, and interpret our\nresults in light of the Hong-Ou-Mandel interference physics, widely exploited\nin photon indistinguishability testing and quantum information science."
    },
    {
        "anchor": "Ground state properties of ultracold trapped bosons with an immersed\n  ionic impurity: We consider a trapped atomic ensemble of interacting bosons in the presence\nof a single trapped ion in a quasi one dimensional geometry. Our study is\ncarried out by means of the newly developed multilayer-multiconfiguration\ntime-dependent Hartree method for bosons, a numerical exact approach to\nsimulate quantum many-body dynamics. In particular, we are interested in the\nscenario by which the ion is so strongly trapped that its motion can be\neffectively neglected. This enables us to focus on the atomic ensemble only.\nWith the development of a model potential for the atom-ion interaction, we are\nable to numerically obtain the exact many-body ground state of the atomic\nensemble in the presence of an ion. We analyse the influence of the atom number\nand the atom-atom interaction on the ground state properties. Interestingly,\nfor weakly interacting atoms, we find that the ion impedes the transition from\nthe ideal gas behaviour to the Thomas-Fermi limit. Furthermore, we show that\nthis effect can be exploited to infer the presence of the ion both in the\nmomentum distribution of the atomic cloud and by observing the interference\nfringes occurring during an expansion of the quantum gas. In the strong\ninteracting regime, the ion modifies the fragmentation process in dependence of\nthe atom number parity which allows a clear identification of the latter in\nexpansion experiments. Hence, we propose in both regimes experimentally viable\nstrategies to assess the impact of the ion on the many-body state of the atomic\ngas. This study serves as the first building block for systematically\ninvestigate many-body physics of such hybrid system.",
        "positive": "Cooling Quantum Gases with Entropy Localization: We study the dynamics of entropy in a time dependent potential and explore\nhow disorder influences this entropy flow. We show that disorder can trap\nentropy at the edge of the atomic cloud enabling a novel cooling method. We\ndemonstrate the feasibility of our cooling technique by analyzing the evolution\nof entropy in a one-dimensional Fermi lattice gas with a time dependent\nsuperlattice potential."
    },
    {
        "anchor": "Deconfining disordered phase in two-dimensional quantum link models: We explore the ground-state physics of two-dimensional spin-$1/2$ $U(1)$\nquantum link models, one of the simplest non-trivial lattice gauge theories\nwith fermionic matter within experimental reach for quantum simulations.\nWhereas in the large mass limit we observe Ne\\'el-like vortex-antivortex and\nstriped crystalline phases, for small masses there is a transition from the\nstriped phases into a disordered phase whose properties resemble those at the\nRokhsar-Kivelson point of the quantum dimer model. This phase is characterized\non ladders by boundary Haldane-like properties, such as vanishing parity and\nfinite string ordering. Moreover, from studies of the string tension between\ngauge charges, we find that whereas the stripe phases are confined, the novel\ndisordered phase present clear indications of being deconfined. Our results\nopen exciting perspectives of studying highly non-trivial physics in quantum\nsimulators, such as spin-liquid behavior and confinement-deconfinement\ntransitions, without the need of explicitly engineering plaquette terms.",
        "positive": "Light cone dynamics in excitonic states of two-component Bose and Fermi\n  gases: We consider the non-equilibrium dynamics of two-component one dimensional\nquantum gases in the limit of extreme population imbalance where the minority\nspecies has but a single particle. We consider the situation where the gas is\nprepared in a state with a single spatially localized exciton: the single\nparticle of the minority species is spatially localized while the density of\nthe majority species in the vicinity of the minority particle sees a\ndepression. Remarkably, we are able to consider cases where the gas contains on\nthe order of $N=100$ particles, comparable to that studied in experiments on\ncold atomic gases. We are able to do by exploiting the integrability of the gas\ntogether with the observation that the excitonic state can be constructed\nthrough a simple superposition of exact eigenstates of the gas. The number of\nstates in this superposition, rather than being exponentially large in the\nnumber of particles, scales linearly with $N$.\n  We study the evolution of such spatially localized states in both strongly\ninteracting Bose and Fermi gases. The behavior of the light cones when the\ninteraction strength and density of the gas is varied can be understood from\nexact results for the spin excitation spectrum in these systems. We argue that\nthe light cone in both cases exhibits scaling collapse. However unique to the\nBose gas, we show that the presence of gapped finite-momentum roton-like\nexcitations provide the Bose gas dynamics with secondary light cones."
    },
    {
        "anchor": "Weyl Superfluidity in a Three-dimensional Dipolar Fermi Gas: Weyl superconductivity or superfluidity, a fascinating topological state of\nmatter, features novel phenomena such as emergent Weyl fermionic excitations\nand anomalies. Here we report that an anisotropic Weyl superfluid state can\narise as a low temperature stable phase in a 3D dipolar Fermi gas. A crucial\ningredient of our model is a rotating external field that generates a\ndirection-dependent two-body effective attraction. Experimental signatures are\npredicted for cold gases in radio-frequency spectroscopy. The finite\ntemperature phase diagram of this system is studied and the transition\ntemperature of the Weyl superfluidity is found to be within the experimental\nscope for atomic dipolar Fermi gases.",
        "positive": "Vortices with massive cores in a binary mixture of Bose-Einstein\n  condensates: We analyze a notable class of states relevant to an immiscible bosonic binary\nmixture loaded in a rotating box-like circular trap, i.e. states where vortices\nin one species host the atoms of the other species, which thus play the role of\nmassive cores. Within a fully-analytical framework, we calculate the\nequilibrium distance distinguishing the motion of precession of two corotating\nmassive vortices, the angular momentum of each component, the vortices healing\nlength and the characteristic size of the cores. We then compare these\nprevisions with the measures extracted from the numerical solutions of the\nassociated coupled Gross-Pitaevskii equations. Interestingly, making use of a\nsuitable change of reference frame, we show that vortices drag the massive\ncores which they host thus conveying them their same motion of precession, but\nthat there is no evidence of tangential entrainment between the two fluids,\nsince the cores keep their orientation constant while orbiting."
    },
    {
        "anchor": "Bound solitonic states in trapped multidimensional Bose-Einstein\n  condensates: We report on the existence and stability of multidimensional bound solitonic\nstates in harmonically-trapped scalar Bose-Einstein condensates. Their\nequilibrium separation, as a measure of the strength of the soliton-soliton or\nthe solitonic vortex-vortex interaction, is provided for varying chemical\npotential $\\mu$. Static bound dark solitons are shown to be dynamically stable\nin elongated condensates within a range of intermediate (repulsive)\ninterparticle-interaction strength. Beyond this range the snaking instability\nmanifests during the time evolution of the planar solitons and produces the\ndecay into non-stationary vortex states. A subsequent dynamical recurrence of\nsolitons and vortices can be observed at low $\\mu$. At equilibrium, the\nbifurcations of bound dark solitons are bound solitonic vortices. Among them,\nboth two-open and two-ring vortex lines are demonstrated to exist with both\ncounter- and co-rotating steady velocity fields. The latter flow configurations\nevolve, for high chemical potential, into a stationary 3D-chain-shaped vortex\nand a three vortex-antivortex-vortex ring sequence that arrest the otherwise\nincreasing angular or linear momentum respectively. As a common feature to the\nbifurcated vortex states, their excitation spectra present unstable modes with\nassociated oscillatory dynamics.",
        "positive": "Effects of dissipation on the superfluid-Mott-insulator transition of\n  photons: We investigate the superfluid-Mott-insulator transition of a two-dimensional\nphoton gas in a dye-filled optical microcavity and in the presence of a\nperiodic potential. We show that in the random-phase approximation the effects\nof the dye molecules, which generally lead to dissipation in the photonic\nsystem, can be captured by two dimensionless parameters that only depend on\ndye-specific properties. Within the mean-field approximation, we demonstrate\nthat one of these parameters decreases the size of the Mott lobes in the phase\ndiagram. By considering also Gaussian fluctuations, we show that the coupling\nwith the dye molecules results in a finite lifetime of the quasiparticle and\nquasihole excitations in the Mott lobes. Moreover, we show that there are\nnumber fluctuations in the Mott lobes even at zero temperature and therefore\nthat the true Mott-insulating state never exists if the interactions with the\ndye are included."
    },
    {
        "anchor": "Self-bound dipolar droplets and supersolids in molecular Bose-Einstein\n  condensates: We numerically study the many-body physics of molecular Bose-Einstein\ncondensates with strong dipole-dipole interactions. We observe the formation of\nself-bound droplets, and explore phase diagrams that feature a variety of\nexotic supersolid states. In all of these cases, the large and tunable\nmolecular dipole moments enable the study of unexplored regimes and phenomena,\nincluding liquid-like density saturation and universal stability scaling laws\nfor droplets, as well as pattern formation and the limits of droplet\nsupersolidity. We discuss a realistic experimental approach to realize both the\nrequired collisional stability of the molecular gases and the independent\ntunability of their contact and dipolar interaction strengths. Our work\nprovides both a blueprint and a benchmark for near-future experiments with bulk\nmolecular Bose-Einstein condensates.",
        "positive": "Charge density wave and charge pump of interacting fermions in\n  circularly shaken hexagonal optical lattices: We analyze strong correlation effects and topological properties of\ninteracting fermions with a Falicov-Kimball type interaction in circularly\nshaken hexagonal optical lattices, which can be effectively described by the\nHaldane-Falicov-Kimball model, using the real-space Floquet dynamical\nmean-field theory (DMFT). The Haldane model, a paradigmatic model of the Chern\ninsulator, is experimentally relevant, because it has been realized using\ncircularly shaken hexagonal optical lattices. We show that in the presence of\nstaggering a charge density wave emerges, which is affected by interactions and\nresonant tunneling. We demonstrate that interactions smear out the edge states\nby introducing a finite life time of quasiparticles. Even though a general\nmethod for calculating the topological invariant of a nonequilibrium steady\nstate is lacking, we extract the topological invariant using a Laughlin charge\npump set-up. We find and attribute to the dissipations into the bath connected\nto every lattice site, which is intrinsic to real-space Floquet DMFT methods,\nthat the pumped charge is not an integer even for the non-interacting case at\nvery low reservoir temperatures. Furthermore, using the rate equation based on\nthe Floquet-Born-Markov approximation, we calculate the charge pump from the\nrate equations for the non-interacting case to identify the role of the\nspectral properties of the bath. Starting from this approach we propose an\nexperimental protocol for measuring quantized charge pumping."
    },
    {
        "anchor": "Distributed vorticity model for vortex molecule dynamics: We analyze the effect of a hard wall trapping potential on the dynamics of a\nvortex molecule in a two-component Bose-Einstein condensate with linear\ncoherent coupling. A vortex molecule consists of a vortex of the same charge in\neach component condensate connected by a domain wall of the relative phase. In\na previous paper Ref.[Phys. RevA. 106,043319(2022)] we described the\ninteraction of a vortex molecule with the boundary using the method of images\nby separately treating each component vortex as a point vortex, in addition to\na Magnus force effect from the surface tension of the domain wall. Here we\nextend the model by considering a continuous distribution of image vorticity\nreflecting the effect of the domain wall on the vortex molecule phase\nstructure. In the case of a precessing centered vortex molecule in an isotropic\ntrap, distributing the image vorticity weakens its contribution to the\nprecession frequency. We test the model predictions against numerical\nsimulations of the coupled Gross-Pitaevskii equations in a two-dimensional\ncircular disc and find support for the improved model.",
        "positive": "Strongly interacting fermions in an optical lattice: We analyze a system of two-component fermions which interact via a Feshbach\nresonance in the presence of a three-dimensional lattice potential. By\nexpressing a two-channel model of the resonance in the basis of Bloch states\nappropriate for the lattice, we derive an eigenvalue equation for the\ntwo-particle bound states which is nonlinear in the energy eigenvalue. Compact\nexpressions for the interchannel matrix elements, numerical methods for the\nsolution of the nonlinear eigenvalue problem, and a renormalization procedure\nto remove ultraviolet divergences are presented. From the structure of the\ntwo-body solutions we identify the relevant degrees of freedom which describe\nthe resonance behavior in the lowest Bloch band. These degrees of freedom,\nwhich we call dressed molecules, form an effective closed channel in a\nmany-body model of the resonance, the Fermi resonance Hamiltonian (FRH). It is\nshown how the properties of the FRH can be determined numerically by solving a\nprojected lattice two-channel model at the two-particle level. As opposed to\nsingle-channel lattice models such as the Hubbard model, the FRH is valid for\ngeneral s-wave scattering length and resonance width. Hence, the FRH provides\nan accurate description of the BEC-BCS crossover for ultracold fermions on an\noptical lattice."
    },
    {
        "anchor": "Half-knot in the spinor condensates: We present an exact solution to the stationary coupled nonlinear\nGross-Pitaevskii equations which govern the motion of the spinor Bose-Einstein\ncondensates. The solitonic solution is a twisted half-skyrmion in the\nthree-dimension (3D) space. By making a map from and the Cartesian coordinates\nto the toroidal coordinates, we demonstrate it is a linked half-unknot with a\nfractional Hopf charge.",
        "positive": "Effect on Cavity Optomechanics of the Interaction Between a Cavity Field\n  and a 1D Interacting Bosonic Gas: Revised entirely and a new figure added."
    },
    {
        "anchor": "Thomas-Fermi von Weizs\u00e4cker theory for a harmonically trapped,\n  two-dimensional, spin-polarized dipolar Fermi gas: We systematically develop a density functional description for the\nequilibrium properties of a two-dimensional, harmonically trapped,\nspin-polarized dipolar Fermi gas based on the Thomas-Fermi von Weizs\\\"acker\napproximation. We pay particular attention to the construction of the\ntwo-dimensional kinetic energy functional, where corrections beyond the local\ndensity approximation must be motivated with care. We also present an intuitive\nderivation of the interaction energy functional associated with the dipolar\ninteractions, and provide physical insight into why it can be represented as a\nlocal functional. Finally, a simple, and highly efficient self-consistent\nnumerical procedure is developed to determine the equilibrium density of the\nsystem for a range of dipole interaction strengths.",
        "positive": "Dipolar Bose-Einstein condensate in a ring or in a shell: We study properties of a trapped dipolar Bose-Einstein condensate (BEC) in a\ncircular ring or a spherical shell using the mean-field Gross-Pitaevskii\nequation. In the case of the ring-shaped trap we consider different\norientations of the ring with respect to the polarization direction of the\ndipoles. In the presence of long-range anisotropic dipolar and short-range\ncontact interactions, the anisotropic density distribution of the dipolar BEC\nin both traps is discussed in detail. The stability condition of the dipolar\nBEC in both traps is illustrated in phase plot of dipolar and contact\ninteractions. We also study and discuss the properties of a vortex dipolar BEC\nin these traps."
    },
    {
        "anchor": "Environment mediated multipartite and multidimensional entanglement: Quantum entanglement is usually considered a fragile quantity and decoherence\nthrough coupling to an external environment, such as a thermal reservoir, can\nquickly destroy the entanglement resource. This doesn't have to be the case and\nthe environment can be engineered to assist in the formation of entanglement.\nWe investigate a system of qubits and higher dimensional spins interacting only\nthrough their mutual coupling to a reservoir. We explore the entanglement of\nmultipartite and multidimensional system as mediated by the bath and show that\nat low temperatures and intermediate coupling strengths multipartite\nentanglement may form between qubits and between higher spins, i.e., qudits. We\ncharacterise the multipartite entanglement using an entanglement witness based\nupon the structure factor and demonstrate its validity versus the directly\ncalculated entanglement of formation, suggesting possible experiments for its\nmeasure.",
        "positive": "Ferromagnetism of a Repulsive Atomic Fermi Gas in an Optical Lattice: a\n  Quantum Monte Carlo Study: Using continuous-space quantum Monte Carlo methods we investigate the\nzero-temperature ferromagnetic behavior of a two-component repulsive Fermi gas\nunder the influence of periodic potentials that describe the effect of a\nsimple-cubic optical lattice. Simulations are performed with balanced and with\nimbalanced components, including the case of a single impurity immersed in a\npolarized Fermi sea (repulsive polaron). For an intermediate density below half\nfilling, we locate the transitions between the paramagnetic, and the partially\nand the fully ferromagnetic phases. As the intensity of the optical lattice\nincreases, the ferromagnetic instability takes place at weaker interactions,\nindicating a possible route to observe ferromagnetism in experiments performed\nwith ultracold atoms. We compare our findings with previous predictions based\non the standard computational method used in material science, namely density\nfunctional theory, and with results based on tight-binding models."
    },
    {
        "anchor": "Mapping out the quasi-condensate transition through the 1D-3D\n  dimensional crossover: By measuring the density fluctuations in a highly elongated weakly\ninteracting Bose gas, we observe and quantify the transition from the ideal gas\nto a quasi-condensate regime throughout the dimensional crossover from a purely\n1D to an almost 3D gas. We show that that the entire transition region and the\ndimensional crossover are described surprisingly well by the modified Yang-Yang\nmodel. Furthermore, we find that at low temperatures the linear density at the\nquasi-condensate transition scales according to an interaction-driven scenario\nof a longitudinally uniform 1D Bose gas, whereas at high temperatures it scales\naccording to the degeneracy-driven critical scenario of transverse condensation\nof a 3D ideal gas.",
        "positive": "Modified spin-wave theory and spin liquid behavior of cold bosons on an\n  inhomogeneous triangular lattice: Ultracold bosons in a triangular lattice are a promising candidate for\nobserving quantum spin liquid behavior. Here we investigate, for such system,\nthe role of a harmonic trap giving rise to an inhomogeneous density. We\nconstruct a modified spin-wave theory for arbitrary filling, and predict the\nbreakdown of order for certain values of the lattice anisotropy. These regimes,\nidentified with the spin liquid phases, are found to be quite robust upon\nchanges in the filling factor. This result is backed by an exact\ndiagonalization study on a small lattice."
    },
    {
        "anchor": "Self-maintaining defect/droplets from two interacting Bose-Einstein\n  condensates: We consider two interacting Bose-Einstein condensates (BEC's) with different\nkind of the potential energy of interaction of the condensates: (a) the\nstandard potential; (b) the potential has a positive three-body and a negative\ntwo-body scattering terms and (c) the potential has a positive four-body and a\nnegative three-body scattering terms for the first BEC and a positive\nthree-body and a negative two-body scattering terms for the second BEC. It is\nshown that in these cases there exist regular spherically symmetric solutions.\nPhysically such solution is either a defect or a droplet created by the\ncondensates. The defect is a cavity filled with one BEC on the background of\nanother BEC. The droplet is an object on the background of the empty space. For\n(a) and (b) cases the obtained objects are supported by a constant external\ntrapping potential and for (c) case the droplet is a self-maintaining object\nwithout any external potential. The possibility of construction of an\nelementary logic qubit device on the basis of this droplet is discussed.",
        "positive": "Comment on \"Quantum Time Crystals and Interacting Gauge Theories in\n  Atomic Bose-Einstein Condensates\": In a recent letter [Phys. Rev. Lett. 123, 250402], \\\"Ohberg and Wright\ndescribe a Bose-Einstein condensate trapped on a ring in the presence of the\ndensity-dependent gauge potential. It is claimed that the ground state of the\nsystem corresponds to a rotating chiral bright soliton and consequently it\nforms a genuine time crystal which minimizes its energy by performing periodic\nmotion. We show that the energy of the chiral soliton in the laboratory frame\nis not correctly calculated in the letter. The correct energy becomes minimal\nif the soliton does not move."
    },
    {
        "anchor": "A Renormalization-Group Study of Interacting Bose-Einstein condensates:\n  Absence of the Bogoliubov Mode below Four ($T>0$) and Three ($T=0$)\n  Dimensions: We derive exact renormalization-group equations for the $n$-point vertices\n($n=0,1,2,\\cdots$) of interacting single-component Bose-Einstein condensates\nbased on the vertex expansion of the effective action. They have a notable\nfeature of automatically satisfying Goldstone's theorem (I), which yields the\nHugenholtz-Pines relation $\\Sigma(0)-\\mu=\\Delta(0)$ as the lowest-order\nidentity. Using them, it is found that the anomalous self-energy $\\Delta(0)$\nvanishes below $d_{\\rm c}=4$ ($d_{\\rm c}=3$) dimensions at finite temperatures\n(zero temperature), contrary to the Bogoliubov theory predicting a finite\n\"sound-wave\" velocity $v_{\\rm s}\\propto [\\Delta(0)]^{1/2}>0$. It is also argued\nthat the one-particle density matrix $\\rho({\\bf\nr})\\equiv\\langle\\hat\\psi^\\dagger({\\bf r}_1)\\hat\\psi({\\bf r}_1+{\\bf r})\\rangle$\nfor $d<d_{\\rm c}$ dimensions approaches the off-diagonal-long-range-order value\n$N_{\\bf 0}/V$ asymptotically as $r^{-d+2-\\eta}$ with an exponent $\\eta>0$. The\nanomalous dimension $\\eta$ at finite temperatures is predicted to behave for\n$d=4-\\epsilon$ dimensions ($0<\\epsilon\\ll 1$) as $\\eta\\propto\\epsilon^2$. Thus,\nthe interacting Bose-Einstein condensates are subject to long-range\nfluctuations similar to those at the second-order transition point, and their\nexcitations in the one-particle channel are distinct from the Nambu-Goldstone\nmode with a sound-wave dispersion in the two-particle channel.",
        "positive": "Superfluid transport dynamics in a capacitive atomtronic circuit: We simulate transport in an atomtronic circuit of a Bose-Einstein condensate\nthat flows from a source region into a drain through a gate channel. The\ntime-dependent Gross-Pitaevskii equation (GPE) solution matches the data of a\nrecent experiment. The atomtronic circuit is found to be similar to a\nvariable-resistance RLC circuit, which is critically damped at early times and\nshows LC oscillations later. The GPE also predicts atom loss from the drain.\nStudies of the dependence of condensate transport upon gate parameters suggest\nthe utility of the GPE for investigation of atomtronic circuits."
    },
    {
        "anchor": "Hydrodynamics with spacetime-dependent scattering length: Hydrodynamics provides a concise but powerful description of long-time and\nlong-distance physics of correlated systems out of thermodynamic equilibrium.\nHere we construct hydrodynamic equations for nonrelativistic particles with a\nspacetime-dependent scattering length and show that it enters constitutive\nrelations uniquely so as to represent the fluid expansion and contraction in\nboth normal and superfluid phases. As a consequence, we find that a leading\ndissipative correction to the contact density due to the spacetime-dependent\nscattering length is proportional to the bulk viscosity ($\\zeta_2$ in the\nsuperfluid phase). Also, when the scattering length is slowly varied over time\nin a uniform system, the entropy density is found to be produced even without\nfluid flows in proportion to the bulk viscosity, which may be useful as a novel\nprobe to measure the bulk viscosity in ultracold-atom experiments.",
        "positive": "Semisuper Efimov effect of two-dimensional bosons at a three-body\n  resonance: Wave-particle duality in quantum mechanics allows for a halo bound state\nwhose spatial extension far exceeds a range of the interaction potential. What\nis even more striking is that such quantum halos can be arbitrarily large on\nspecial occasions. The two examples known so far are the Efimov effect and the\nsuper Efimov effect, which predict that spatial extensions of higher excited\nstates grow exponentially and double exponentially, respectively. Here, we\nestablish yet another new class of arbitrarily large quantum halos formed by\nspinless bosons with short-range interactions in two dimensions. When the\ntwo-body interaction is absent but the three-body interaction is resonant, four\nbosons exhibit an infinite tower of bound states whose spatial extensions scale\nas $R_n\\sim e^{(\\pi n)^2/27}$ for a large $n$. The emergent scaling law is\nuniversal and is termed a semisuper Efimov effect, which together with the\nEfimov and super Efimov effects constitutes a trio of few-body universality\nclasses allowing for arbitrarily large quantum halos."
    },
    {
        "anchor": "Black-hole lasing in coherently coupled two-component atomic condensates: We theoretically study the black-hole lasing phenomenon in a flowing\none-dimensional, coherently coupled two component atomic Bose-Einstein\ncondensate whose constituent atoms interact via a spin-dependent s-wave contact\ninteraction. We show by a numerical analysis the onset of the dynamical\ninstability in the spin branch of the excitations, once a finite supersonic\nregion is created in this branch. We study both a spatially homogeneous\ngeometry and a harmonically trapped condensate. Experimental advantages of the\ntwo-component configuration are pointed out, with an eye towards studies of\nback-reaction phenomena.",
        "positive": "One-dimensional mixtures of several ultracold atoms: a review: Recent theoretical and experimental progress on studying one-dimensional\nsystems of bosonic, fermionic, and Bose-Fermi mixtures of a few ultracold atoms\nconfined in traps is reviewed in the broad context of mesoscopic quantum\nphysics. We pay special attention to limiting cases of very strong or very weak\ninteractions and transitions between them. For bosonic mixtures, we describe\nthe developments in systems of three and four atoms as well as different\nextensions to larger numbers of particles. We also briefly review progress in\nthe case of spinor Bose gases of a few atoms. For fermionic mixtures, we\ndiscuss a special role of spin and present a detailed discussion of the two-\nand three-atom cases. We discuss the advantages and disadvantages of different\ncomputation methods applied to systems with intermediate interactions. In the\ncase of very strong repulsion, close to the infinite limit, we discuss\napproaches based on effective spin chain descriptions. We also report on recent\nstudies on higher-spin mixtures and inter-component attractive forces. For both\nstatistics, we pay particular attention to impurity problems and mass imbalance\ncases. Finally, we describe the recent advances on trapped Bose-Fermi mixtures,\nwhich allow for a theoretical combination of previous concepts, well\nillustrating the importance of quantum statistics and inter-particle\ninteractions. Lastly, we report on fundamental questions related to the subject\nwhich we believe will inspire further theoretical developments and experimental\nverification."
    },
    {
        "anchor": "Charge and statistics of lattice quasiholes from density measurements: a\n  Tree Tensor Network study: We numerically investigate the properties of the quasihole excitations above\nthe bosonic fractional Chern insulator state at filling $\\nu = 1/2$, in the\nspecific case of the Harper-Hofstadter Hamiltonian with hard-core interactions.\nFor this purpose we employ a Tree Tensor Network technique, which allows us to\nstudy systems with up to $N=18$ particles on a $16 \\times 16$ lattice and\nexperiencing an additional harmonic confinement. First, we observe the\nquantization of the quasihole charge at fractional values and its robustness\nagainst the shape and strength of the impurity potentials used to create and\nlocalize such excitations. Then, we numerically characterize quasihole anyonic\nstatistics by applying a discretized version of the relation connecting the\nstatistics of quasiholes in the lowest Landau level to the depletions they\ncreate in the density profile [Macaluso et al., arXiv:1903.03011]. Our results\ngive a direct proof of the anyonic statistics for quasiholes of fractional\nChern insulators, starting from a realistic Hamiltonian. Moreover, they provide\nstrong indications that this property can be experimentally probed through\nlocal density measurements, making our scheme readily applicable in\nstate-of-the-art experiments with ultracold atoms and superconducting qubits.",
        "positive": "Finite-Size Effects with Boundary Conditions on Bose-Einstein\n  Condensation: We investigate the statistical distribution for ideal Bose gases with\nconstant particle density in the 3D box of volume $V=L^{3}$. By changing linear\nsize $L$ and imposing different boundary conditions on the system, we present a\nnumerical analysis on the characteristic temperature and condensate fraction,\nand find that the smaller linear size is efficient to increase the\ncharacteristic temperature and condensate fraction. Moreover, there is a\nsingularity under the antiperiodic boundary condition."
    },
    {
        "anchor": "Excitations in the Yang-Gaudin Bose gas: We study the excitation spectrum of two-component delta-function interacting\nbosons confined to a single spatial dimension, the Yang-Gaudin Bose gas. We\nshow that there are pronounced finite-size effects in the dispersion relations\nof excitations, perhaps best illustrated by the spinon single particle\ndispersion which exhibits a gap at $2k_F$ and a finite-momentum roton minimum.\nSuch features occur at energies far above the finite volume excitation gap,\nvanish slowly as $1/L$ for fixed spinon number, and can persist to the\nthermodynamic limit at fixed spinon density. Features such as the $2k_F$ gap\nalso persist to multi-particle excitation continua. Our results show that\nexcitations in the finite system can behave in a qualitatively different manner\nto analogous excitations in the thermodynamic limit.\n  The Yang-Gaudin Bose gas is also host to multi-spinon bound states, known as\n$\\Lambda$-strings. We study these excitations both in the thermodynamic limit\nunder the string hypothesis and in finite size systems where string deviations\nare taken into account. In the zero-temperature limit we present a simple\nrelation between the length $n$ $\\Lambda$-string dressed energies\n$\\epsilon_n(\\lambda)$ and the dressed energy $\\epsilon(k)$. We solve the\nYang-Yang-Takahashi equations numerically and compare to the analytical\nsolution obtained under the strong couple expansion, revealing that the length\n$n$ $\\Lambda$-string dressed energy is Lorentzian over a wide range of real\nstring centers $\\lambda$ in the vicinity of $\\lambda = 0$. We then examine the\nfinite size effects present in the dispersion of the two-spinon bound states by\nnumerically solving the Bethe ansatz equations with string deviations.",
        "positive": "Quantum Hall phases of two-component bosons: The recent production of synthetic magnetic fields acting on electroneutral\nparticles, like atoms or photons, has boosted the interest in the quantum Hall\nphysics of bosons. Adding pseudospin-1/2 to the bosons greatly enriches the\nscenario, as it allows them to form an interacting integer quantum Hall (IQH)\nphase with no fermionic counterpart. Here we show that, for a small\ntwo-component Bose gas on a disk, the complete strongly correlated regime,\nextending from the integer phase at filling factor $\\nu=2$ to the Halperin\nphase at filling factor $\\nu=2/3$, is well described by composite\nfermionization of the bosons. Moreover we study the edge excitations of the IQH\nstate, which, in agreement with expectations from topological field theory, are\nfound to consist of forward-moving charge excitations and backward-moving spin\nexcitations. Finally, we demonstrate how pair-correlation functions allow one\nto experimentally distinguish the IQH state from competing states, like\nnon-Abelian spin singlet (NASS) states."
    },
    {
        "anchor": "Variational Monte Carlo method for the Baeriswyl wavefunction:\n  application to the one-dimensional bosonic Hubbard model: A variational Monte Carlo method for bosonic lattice models is introduced.\nThe method is based on the Baeriswyl projected wavefunction. The Baeriswyl\nwavefunction consists of a kinetic energy based projection applied to the\nwavefunction at infinite interaction, and is related to the shadow wavefunction\nalready used in the study of continuous models of bosons. The wavefunction at\ninfinite interaction, and the projector, are represented in coordinate space,\nleading to an expression for expectation values which can be evaluated via\nMonte Carlo sampling. We calculate the phase diagram and other properties of\nthe bosonic Hubbard model. The calculated phase diagram is in excellent\nagreement with known quantum Monte Carlo results. We also analyze correlation\nfunctions.",
        "positive": "Pair correlations in the normal phase of an attractive Fermi gas: In a recent paper [Phys. Rev. A 99, 053617 (2019)], the total number of\nfermion pairs in a spin-balanced two-component Fermi gas of $^6$Li atoms was\nexperimentally probed in the normal phase above the superfluid critical\ntemperature, in order to investigate the sectors of pseudogap and\npreformed-pair in the temperature-coupling phase diagram. Here, we present a\ntheoretical account of these experimental results in terms of an ab-initio\nself-consistent $t$-matrix calculation, which emphasizes the role of the\npair-correlation function between opposite-spin fermions at equilibrium. Good\nagreement is found between the available experimental data and the theoretical\nresults obtained with no adjustable parameter."
    },
    {
        "anchor": "Phases, transitions, and boundary conditions in a model of interacting\n  bosons: We carry out an extensive study of the phase diagrams of the extended Bose\nHubbard model, with a mean filling of one boson per site, in one dimension by\nusing the density matrix renormalization group and show that it contains\nSuperfluid (SF), Mott-insulator (MI), density-wave (DW) and Haldane-insulator\n(HI) phases. We show that the critical exponents and central charges for the\nHI-DW, MI-HI and SF-MI transitions are consistent with those for models in the\ntwo-dimensional Ising, Gaussian, and Berezinskii-Kosterlitz-Thouless (BKT)\nuniversality classes, respectively; and we suggest that the SF-HI transition\nmay be more exotic than a simple BKT transition. We show explicitly that\ndifferent boundary conditions lead to different phase diagrams.",
        "positive": "Antiferromagnetic Order of Repulsively Interacting Fermions on Optical\n  lattices: The N\\'eel state in fermionic mixtures of two pseudospin species in an\noptical lattice is analyzed at low temperatures. Experimentally it remains a\nchallenge to demonstrate antiferromagnetic correlations in ultracold fermionic\nquantum gases. We find that, while in balanced systems the N\\'eel order\nparameter can point in any spatial direction, in imbalanced mixtures\nantiferromagnetism is strictly perpendicular to the quantization axis (i.e.,\nthe z-axis). Since, experimentally, one always has to assume some minimal\nimbalance this should have important consequences for ongoing experiments."
    },
    {
        "anchor": "Controlling Many-Body Quantum Chaos: Bose-Hubbard systems: This work develops a quantum control application of many-body quantum chaos\nfor ultracold bosonic gases trapped in optical lattices. It is long known how\nto harness exponential sensitivity to changes in initial conditions for control\npurposes in classically chaotic systems. In the technique known as targeting,\ninstead of a hindrance to control, the instability becomes a resource.\nRecently, this classical targeting has been generalized to quantum systems\neither by periodically countering the inevitable quantum state spreading or by\nintroducing a control Hamiltonian, where both enable localized states to be\nguided along special chaotic trajectories toward any of a broad variety of\ndesired target states. Only strictly unitary dynamics are involved; i.e., it\ngives a coherent quantum targeting. In this paper, the introduction of a\ncontrol Hamiltonian is applied to Bose-Hubbard systems in chaotic dynamical\nregimes. Properly selected unstable mean field solutions can be followed quite\nrapidly to states possessing precise phase relationships and occupancies. In\nessence, the method generates a quantum simulation technique that can access\nrather special states. The protocol reduces to a time-dependent control of the\nchemical potentials, opening up the possibility for application in optical\nlattice experiments. Explicit applications to custom state preparation and\nstabilization of quantum many-body scars are presented in one- and\ntwo-dimensional lattices (three-dimensional applications are similarly\npossible).",
        "positive": "Bad-Metal Relaxation Dynamics in a Fermi Lattice Gas: We report the discovery of phenomena consistent with bad-metal relaxation\ndynamics in the metallic regime of an optical-lattice Hubbard model. The\ntransport lifetime induced by inter-particle scattering for a mass current of\natoms excited by stimulated Raman transitions is measured, and the\ncorresponding analog of resistivity is inferred. By exploring a range of\ntemperature, we demonstrate incompatibility with weak-scattering theory and a\nkey characteristic of bad metals: anomalous resistivity scaling consistent with\n$T$-linear behavior. We also observe the onset of two behaviors---incoherent\ntransport and the approach to the Mott-Ioffe-Regel limit---associated with bad\nmetals. The interaction and temperature scaling of resistivity are verified to\nbe consistent with dynamic mean-field theory (DMFT) predictions of a bad metal,\nwhich is associated with the reduction of quasiparticle weight by strong\ninteractions."
    },
    {
        "anchor": "Optimal scaling of persistent currents for interacting bosons on a ring: We consider the persistent currents induced by an artificial gauge field\napplied to interacting ultra-cold bosonic atoms in a tight ring trap. Using\nboth analytical and numerical methods, we study the scaling of the persistent\ncurrent amplitude with the size of the ring. In the strongly interacting regime\nwe find a power-law scaling, in good agreement with the predictions of the\nLuttinger-liquid theory. By exploring all interaction regimes we find that the\nscaling is optimal, i.e. the current amplitude decreases slower with the system\nsize, at intermediate interactions.",
        "positive": "Spontaneous formation and non-equilibrium dynamics of a soliton-shaped\n  Bose-Einstein condensate in a trap: The Bose-stimulated self-organization of a quasi-two dimensional\nnon-equilibrium Bose-Einstein condensate in an in-plane potential is proposed.\nWe obtained the solution of the nonlinear, driven-dissipative Gross-Pitaevskii\nequation for a Bose-Einstein condensate trapped in an external asymmetric\nparabolic potential within the method of the spectral expansion. We found that,\nin sharp contrast to previous observations, the condensate can spontaneously\nacquire a soliton-like shape for spatially homogenous pumping. This condensate\nsoliton performs oscillatory motion in a parabolic trap and, also, can\nspontaneously rotate. Stability of the condensate soliton in the spatially\nasymmetric trap is analyzed. In addition to the nonlinear dynamics of\nnon-equilibrium Bose-Einstein condensates of ultra-cold atoms, our findings can\nbe applied to the condensates of quantum well excitons and cavity polaritons in\nsemiconductor heterostructure, and to the condensates of photons."
    },
    {
        "anchor": "Exotic superfluidity and pairing phenomena in atomic Fermi gases in\n  mixed dimensions: Atomic Fermi gases have been an ideal platform for simulating conventional\nand engineering exotic physical systems owing to their multiple tunable control\nparameters. Here we investigate the effects of mixed dimensionality on the\nsuperfluid and pairing phenomena of a two-component ultracold atomic Fermi gas\nwith a short-range pairing interaction, while one component is confined on a\none-dimensional (1D) optical lattice whereas the other is in a homogeneous 3D\ncontinuum. We study the phase diagram and the pseudogap phenomena throughout\nthe entire BCS-BEC crossover, using a pairing fluctuation theory. We find that\nthe effective dimensionality of the non-interacting lattice component can\nevolve from quasi-3D to quasi-1D, leading to strong Fermi surface mismatch.\nUpon pairing, the system becomes effectively quasi-two dimensional in the BEC\nregime. The behavior of $T_c$ bears similarity to that of a regular 3D\npopulation imbalanced Fermi gas, but with a more drastic departure from the\nregular 3D balanced case, featuring both intermediate temperature superfluidity\nand possible pair density wave ground state. Unlike a simple 1D optical lattice\ncase, $T_c$ in the mixed dimensions has a constant BEC asymptote.",
        "positive": "Exotic Superconductivity Through Bosons in a Dynamical Cluster\n  Approximation: We study the instabilities towards (exotic) superconductivity of mixtures of\nspin-$1/2$ fermions coupled to scalar bosons on a two-dimensional square\nlattice with the Dynamical-Cluster-Approximation (DCA) using a numerically\nexact continuous-time Monte-Carlo solver. The Bogoliubov bosons provide an\neffective phononic bath for the fermions and induce a non-local retarded\ninteraction between the fermions, which can lead to (exotic) superconductivity.\nBecause of the sign problem the biggest clusters we can study are limited to $2\n\\times 2$ in size, but this nevertheless allows us to study the pairing\ninstablilities, and their possible divergence, in the $s$- and $d$ -wave\nchannels as well as the competition with antiferromagnetic fluctuations. At\nfermionic half-filling we find that $d$-wave is stable when the mediated\ninteraction by the bosons is of the same order as the bare fermionic repulsion.\nIts critical temperature can be made as high as the maximum one for $s$-wave,\nwhich opens perspectives for its detection in a cold atom experiment."
    },
    {
        "anchor": "Breathing oscillations of a trapped impurity in a Bose gas: Motivated by a recent experiment [J. Catani et al., arXiv:1106.0828v1\npreprint, 2011], we study breathing oscillations in the width of a harmonically\ntrapped impurity interacting with a separately trapped Bose gas. We provide an\nintuitive physical picture of such dynamics at zero temperature, using a\ntime-dependent variational approach. In the Gross-Pitaevskii regime we obtain\nbreathing oscillations whose amplitudes are suppressed by self trapping, due to\ninteractions with the Bose gas. Introducing phonons in the Bose gas leads to\nthe damping of breathing oscillations and non-Markovian dynamics of the width\nof the impurity, the degree of which can be engineered through controllable\nparameters. Our results reproduce the main features of the impurity dynamics\nobserved by Catani et al. despite experimental thermal effects, and are\nsupported by simulations of the system in the Gross-Pitaevskii regime.\nMoreover, we predict novel effects at lower temperatures due to self-trapping\nand the inhomogeneity of the trapped Bose gas.",
        "positive": "Non-equilibrium dynamics in Bose-Hubbard ladders: Motivated by a recent experiment on the non-equilibrium dynamics of\ninteracting bosons in ladder-shaped optical lattices, we report exact\ncalculations on the sweep dynamics of Bose-Hubbard systems in finite two-leg\nladders. The sweep changes the energy bias between the legs linearly over a\nfinite time. As in the experiment, we study the cases of [a] the bosons\ninitially all in the lower-energy leg (ground state sweep) and [b] the bosons\ninitially all in the higher-energy leg (inverse sweep). The approach to\nadiabaticity in the inverse sweep is intricate, as the transfer of bosons is\nnon-monotonic as a function of both sweep time and intra-leg tunnel coupling.\nOur exact study provides explanations for these non-monotonicities based on\nfeatures of the full spectrum, without appealing to concepts (e.g., gapless\nexcitation spectrum) that are more appropriate for the thermodynamic limit. We\nalso demonstrate and study Stueckelberg oscillations in the finite-size\nladders."
    },
    {
        "anchor": "Quantum Field Theory of Correlated Bose-Einstein condensates: II.\n  Ward-Takahashi Identities and Correlation Functions: We derive Ward-Takahashi identities for correlated Bose-Einstein condensates\nbased on the expressions of the first-order variations $(\\delta\\Psi,\\delta G)$\ndue to perturbations obtained in the preceding paper [T. Kita, J. Phys. Soc.\nJpn. $\\bf 90$, 024001 (2021)] for the condensate wave function $\\Psi$ and\nGreen's function $G$. They enable us to obtain several exact results on the\ndensity and current correlation functions $K_{\\nu\\nu'}^{}$, and also express\n$K_{\\nu\\nu'}^{}$ in terms of low-energy Green's functions and vertices. The\nlatter expressions open up the possibility of constructing theory of superfluid\nBose liquids in the same way as that for fermions at low temperatures. The\nvertices are found to have different limits depending on which of frequency\n$\\omega$ and wavenumber $q$ is set equal to zero first.",
        "positive": "Quantum walks in commensurate off-diagonal Aubry-Andr\u00e9-Harper model: Due to the topological nature of Aubry-Andr\\'{e}-Harper (AAH) model, exotic\nedge states have been found existing in one-dimensional periodic and\nquasiperiodic lattices. In this article, we investigate continuous-time quantum\nwalks of identical particles initially located on either edge of commensurate\nAAH lattices in detail. It is shown that the quantum walker is delocalized\namong the whole lattice until the strength of periodic modulation is strong\nenough. The inverse participation ratios (IPRs) for all of the eigenstates are\ncalculated. It is found that the localization properties of the quantum walker\nis mainly determined by the IPRs of the topologically protected edge states.\nMore interestingly, the edge states are shown to have an exotic\n`\\emph{repulsion}' effect on quantum walkers initiated from the lattice sites\ninside the bulk. Furthermore, we examine the role of nearest-neighbour\ninteraction on the quantum walks of two identical fermions. Clear enhancement\nof the `\\emph{repulsion}' effect by strong interaction has been shown."
    },
    {
        "anchor": "Antiferromagnetic topological insulators in cold atomic gases: We propose a spin-dependent optical lattice potential that realizes a\nthree-dimensional antiferromagnetic topological insulator in a gas of cold,\ntwo-state fermions such as alkaline earths, as well as a model that describes\nthe tight-binding limit of this potential. We discuss the physically observable\nresponses of the gas that can verify the presence of this phase. We also point\nout how this model can be used to obtain two-dimensional flat bands with\nnonzero Chern number.",
        "positive": "Mean-field yrast spectrum and persistent currents in a two-component\n  Bose gas with interaction asymmetry: We analyze the mean-field yrast spectrum of a two-component Bose gas in the\nring geometry with arbitrary interaction asymmetry. Of particular interest is\nthe possibility that the yrast spectrum develops local minima at which\npersistent superfluid flow can occur. By analyzing the mean-field energy\nfunctional, we show that local minima can be found at plane-wave states and\narise when the system parameters satisfy certain inequalities. We then go on to\nshow that these plane-wave states can be yrast states even when the yrast\nspectrum no longer exhibits a local minimum. Finally, we obtain conditions\nwhich establish when the plane-wave states cease to be yrast states. Specific\nexamples illustrating the roles played by the various interaction asymmetries\nare presented."
    },
    {
        "anchor": "Thermometry of cold atoms in optical lattices via artificial gauge\n  fields: Artificial gauge fields are a unique way of manipulating the motional state\nof cold atoms. Here we propose the use of artificial gauge fields -- obtained\ne.g. via lattice shaking -- to perform primary noise thermometry of cold atoms\nin optical lattices - not requiring any form of prior calibration. The proposed\nthermometric scheme relies on fundamental fluctuation-dissipation relations,\nconnecting the global response to the variation of the applied gauge field and\nthe fluctuation of quantities related to the momentum distribution (such as the\naverage kinetic energy or the average current). We demonstrate gauge-field\nthermometry for several physical situations, including free fermions and\nstrongly interacting bosons. The proposed approach is extremely robust to\nquantum fluctuations - even in the vicinity of a quantum phase transition -\nwhen it relies on the thermal fluctuations of an emerging classical field,\nassociated with the onset of Bose condensation or chiral order.",
        "positive": "Vortex pairs in a spin-orbit coupled Bose-Einstein condensate: Static and dynamic properties of vortices in a two-component Bose-Einstein\ncondensate with Rashba spin-orbit coupling are investigated. The mass current\naround a vortex core in the plane-wave phase is found to be deformed by the\nspin-orbit coupling, and this makes the dynamics of the vortex pairs quite\ndifferent from those in a scalar Bose-Einstein condensate. The velocity of a\nvortex-antivortex pair is much smaller than that without spin-orbit coupling,\nand there exist stationary states. Two vortices with the same circulation move\naway from each other or unite to form a stationary state."
    },
    {
        "anchor": "Nonequilibrium current-carrying steady states in the anisotropic $XY$\n  spin chain: Out-of-equilibrium behavior is explored in the one-dimensional anisotropic\n$XY$ model. Initially preparing the system in the isotropic $XX$ model with a\nlinearly varying magnetic field to create a domain-wall magnetization profile,\ndynamics is generated by rapidly changing the exchange interaction anisotropy\nand external magnetic field. Relaxation to a nonequilibrium steady state is\nstudied analytically at the critical transverse Ising point, where correlation\nfunctions may be computed in closed form. For arbitrary values of anisotropy\nand external field, an effective generalized Gibbs' ensemble is shown to\naccurately describe observables in the long-time limit. Additionally, we find\nspatial oscillations in the exponentially decaying, transverse spin-spin\ncorrelation functions with wavelength set by the magnetization jump across the\ninitial domain wall. This wavelength depends only weakly on anisotropy and\nmagnetic field in contrast to the current, which is highly dependent on these\nparameters.",
        "positive": "Localized Higgs modes of superfluid Bose gases in optical lattices: A\n  Guzwiller mean-field study: We study effects of a potential barrier on collective modes of superfluid\nBose gases in optical lattices. We assume that the barrier is created by local\nsuppression of the hopping amplitude. When the system is in a close vicinity of\nthe Mott transition at commensurate fillings, where an approximate\nparticle-hole symmetry emerges, there exist bound states of Higgs amplitude\nmode that are localized around the barrier. By applying the Gutzwiller\nmean-field approximation to the Bose-Hubbard model, we analyze properties of\nnormal modes of the system with a special focus on the Higgs bound states. We\nshow that when the system becomes away from the Mott transition point, the\nHiggs bound states turn into quasi-bound states due to inevitable breaking of\nthe particle-hole symmetry. We use a stabilization method to compute the\nresonance energy and line width of the quasi-bound states. We compare the\nresults obtained by the Gutzwiller approach with those by the Ginzburg-Landau\ntheory. We find that the Higgs bound states survive even in a parameter region\nfar from the Mott transition, where the Ginzburg-Landau theory fails."
    },
    {
        "anchor": "Creating superfluid vortex rings in artificial magnetic fields: Artificial gauge fields are versatile tools that allow to influence the\ndynamics of ultracold atoms in Bose-Einstein condensates. Here we discuss a\nmethod of artificial gauge field generation stemming from the evanescent fields\nof the curved surface of an optical nanofibre. The exponential decay of the\nevanescent fields leads to large gradients in the generalized Rabi frequency\nand therefore to the presence of geometric vector and scalar potentials. By\nsolving the Gross-Pitaevskii equation in the presence of the artificial gauge\nfields originating from the fundamental HE$_{11}$ mode of the fibre, we show\nthat vortex rings can be created in a controlled manner. We also calculate the\nmagnetic fields resulting from the higher order HE$_{21}$, TE$_{01}$, and\nTM$_{01}$ modes and compare them to the fundamental HE$_{11}$ mode.",
        "positive": "Resonantly Interacting Fermions In a Box: We use two fundamental theoretical frameworks to study the finite-size\n(shell) properties of the unitary gas in a periodic box: 1) an ab initio\nQuantum Monte Carlo (QMC) calculation for boxes containing 4 to 130 particles\nprovides a precise and complete characterization of the finite-size behavior,\nand 2) a new Density Functional Theory (DFT) fully encapsulates these effects.\nThe DFT predicts vanishing shell structure for systems comprising more than 50\nparticles, and allows us to extrapolate the QMC results to the thermodynamic\nlimit, providing the tightest bound to date on the ground-state energy of the\nunitary gas: \\xi_S <= 0.383(1). We also apply the new functional to\nfew-particle harmonically trapped systems, comparing with previous\ncalculations."
    },
    {
        "anchor": "Density fluctuations in a quasi-one-dimensional Bose gas as observed in\n  free expansion: We study, within a framework of the classical fields approximation, the\ndensity correlations of a weakly interacting expanding Bose gas for the whole\nrange of temperatures across the Bose-Einstein condensation threshold. We focus\non elongated quasi-one-dimensional systems where there is a huge discrepancy\nbetween the existing theory and experimental results (A. Perrin et al., Nature\nPhys. 8, 195 (2012)). We find that the density correlation function is not\nreduced for temperatures below the critical one as it is predicted for the\nideal gas or for a weakly interacting system within the Bogoliubov\napproximation. This behavior of the density correlations agrees with the above\nmentioned experiment with the elongated system. Although the system was much\nlarger then studied here we believe that the behavior of the density\ncorrelation function found there is quite generic. Our theoretical studies\nindicate also large density fluctuations in the trap in the quasicondensate\nregime where only phase fluctuations were expected. We argue that the enhanced\ndensity fluctuations can originate in the presence of interactions in the\nsystem, or more precisely in the existence of spontaneous dark solitons in the\nelongated gas at thermal equilibrium.",
        "positive": "Reconciling the Classical-Field Method with the Beliaev Broken Symmetry\n  Approach: We present our views on the issues raised in the chapter by Griffin and\nZaremba [A. Griffin and E. Zaremba, in Quantum Gases: Finite Temperature and\nNon-Equilibrium Dynamics, N. P. Proukakis, S. A. Gardiner, M. J. Davis, and M.\nH. Szymanska, eds., Imperial College Press, London (in press)]. We review some\nof the strengths and limitations of the Bose symmetry-breaking assumption, and\nexplain how such an approach precludes the description of many important\nphenomena in degenerate Bose gases. We discuss the theoretical justification\nfor the classical-field (c-field) methods, their relation to other\nnon-perturbative methods for similar systems, and their utility in the\ndescription of beyond-mean-field physics. Although it is true that present\nimplementations of c-field methods cannot accurately describe certain\ncollective oscillations of the partially condensed Bose gas, there is no\nfundamental reason why these methods cannot be extended to treat such\nscenarios. By contrast, many regimes of non-equilibrium dynamics that can be\ndescribed with c-field methods are beyond the reach of generalised mean-field\nkinetic approaches based on symmetry-breaking, such as the ZNG formalism."
    },
    {
        "anchor": "Cavity-mediated near-critical dissipative dynamics of a driven\n  condensate: We investigate the near-critical dynamics of atomic density fluctuations in\nthe non-equilibrium self-organization transition of an optically driven quantum\ngas coupled to a single mode of a cavity. In this system cavity-mediated\nlong-range interactions between atoms, tunable by the drive strength, lead to\nsoftening of an excitation mode recently observed in experiments. This\nphenomenon has previously been studied within a two-mode approximation for the\ncollective motional degrees of freedom of the atomic condensate which results\nin an effective open-system Dicke model. Here, including the full spectrum of\natomic modes we find a finite lifetime for a roton-like mode in the Bogoliubov\nexcitation spectrum that is strongly pump-dependent. The corresponding decay\nrate and critical exponents for the phase-transition are calculated explaining\nthe non-monotonic pump-dependent atomic damping rate observed in recent\nexperiments. We compute the near-critical behavior of the intra-cavity field\nfluctuations, that has been previously shown to be enhanced with respect to the\nequilibrium Dicke model in a two-mode approximation. We highlight the role of\nthe finite size of the system in the suppression of it below the expectations\nof the open Dicke model.",
        "positive": "Energy dependent $\\ell$-wave confinement-induced resonances: The universal aspects of two-body collisions in the presence of a harmonic\nconfinement are investigated for both bosons and fermions. The main focus of\nthis study are the confinement-induced resonances (CIR) which are attributed to\ndifferent angular momentum states $\\ell$ and we explicitly show that in\nalkaline collisions only four universal $\\ell$-wave CIRs emerge. Going beyond\nthe single mode regime the energy dependence of $\\ell$-wave CIRs is studied. In\nparticular we show that all the $\\ell$-wave CIRs may emerge even when the\nunderlying two-body potential cannot support any bound state. We observe that\nthe intricate dependence on the energy yields resonant features where the\ncolliding system within the confining potential experiences an effective\nfree-space scattering. Our analysis is done within the framework of the\ngeneralized $K$-matrix theory and the relevant analytical calculations are in\nvery good agreement with the corresponding ab initio numerical scattering\nsimulations."
    },
    {
        "anchor": "Kinked linear response from non-Hermitian pumping: Non-Hermiticity is known to give rise to modified topological bulk-boundary\ncorrespondences, which predict the presence of topological boundary modes\nthrough appropriately modified topological invariants. Yet, little is currently\nknown about how non-Hermiticity affects the precise linear response of\nwavepackets beyond their overall spectral flow. In this work, we discover that\ngenerically, non-Hermiticity gives rise to abrupt and prominent kinks in the\nsemi-classical wavepacket trajectories of quantum gases, despite the absence of\nsudden physical impulses. This physically stems from a hitherto\nunder-appreciated intrinsic non-locality from non-Hermitian pumping, even if\nall physical couplings are local, thereby resulting in enigmatic singularities\nin the band structure that lead to discontinuous band geometry and Berry\ncurvature. For concrete experimental demonstration, we propose an ultracold\natomic setup in a two-dimensional optical lattice with laser-induced loss, such\nthat response kinks can be observed without fine-tuning in the physical atomic\ncloud dynamics. Our results showcases unique non-monotonic behavior from\nnon-Hermitian pumping beyond the non-Hermitian skin effect, and suggests new\navenues for investigating non-Hermitian dynamics in ultracold atomic platforms.",
        "positive": "Macroscopic quantum superpositon states of two-component Bose-Einstein\n  condensates: We examine a two-component Bose-Einstein condensate in a double-well\npotential. We propose a model for the creation of many-particle macroscopic\nquantum superposition states. The effect of dissipation on the formation of\nthese states is also investigated with the Monte-Carlo wavefunction technique."
    },
    {
        "anchor": "Orbital many-body dynamics of bosons in the second Bloch band of an\n  optical lattice: A Bose-Einstein condensate (BEC) of rubidium atoms is prepared in one of two\ndegenerate energy minima in the second Bloch band of an optical square lattice.\nA subsequent oscillation of the BEC between the two energy minima is observed,\nwhich is driven by two distinct collision processes: the conventional\nHubbard-type on-site collision and a collision process that changes the orbital\nflavor. The oscillation frequency scales with the relative strength of these\ncollisional interactions, which can be readily tuned via an experimentally well\ncontrolled distortion of the unit cell. The observations are compared to a\nquantum model of two single-particle modes and to a semi-classical multi-band\ntight-binding simulation of 12x12 tubular sites of the lattice. Both models\nreproduce the observed oscillatory quantum many-body dynamics and show the\ncorrect dependence of the oscillation frequency on the ratio between the\nstrengths of the on-site and flavor-changing collision processes.",
        "positive": "Coarsening dynamics of an isotropic ferromagnetic superfluid: In zero magnetic field the ground state manifold of a ferromagnetic spin-1\ncondensate is SO(3) and exhibits $\\mathbb{Z}_2$ vortices as topological\ndefects. We investigate the phase ordering dynamics of this system after being\nquenched into this ferromagnetic phase from a zero temperature unmagnetized\nphase. Following the quench, we observe the ordering of both magnetic and gauge\ndomains. We find that these domains grow diffusively, i.e. with domain size\n$L(t)\\sim t^{1/2}$, and exhibit dynamic scale invariance. The coarsening\ndynamics progresses as $\\mathbb{Z}_2$ vortices annihilate, however we find that\nat finite energy a number of these vortices persist in small clumps without\ninfluencing magnetic or gauge order. We consider the influence of a small\nnon-zero magnetic field, which reduces the ground state symmetry, and show that\nthis sets a critical length scale such that when the domains reach this size\nthe system dynamically transitions in order parameter and scaling behaviour\nfrom an isotropic to an anisotropic ferromagnetic superfluid."
    },
    {
        "anchor": "Dynamics and Quantum correlations in Two independently driven Rydberg\n  atoms with distinct laser fields: We study the population dynamics in a two-atom setup in which each atom is\ndriven independently by different light fields, but coupling the same Rydberg\nstate. In particular, we look at how an offset in the Rabi frequencies between\ntwo atoms influences the dynamics. We find novel features such as amplifying\nthe Rabi frequency of one atom, together with strong Rydberg-Rydberg\ninteractions freezes the dynamics in the second atom. We characterize the\nRydberg-biased freezing phenomenon in detail, with effective Hamiltonians\nobtained for various limits of the system parameters. In the absence of\nRabi-offset, the doubly excited state population exhibits a Lorentzian profile\nas a function of interaction, whereas for very small offsets it shows splitting\nand thus peaks. Using an effective Hamiltonian as well as the perturbation\ntheory for weak interactions, we show that the peak arises from a competition\nbetween Rabi-offset and Rydberg-Rydberg interactions when both are sufficiently\nsmall, together with the Rydberg blockade at large interactions. The effective\nHamiltonians provide us with analytical results which are in an excellent\nagreement with full numerical solutions. Also, we analyze the growth and the\ndynamics of quantum correlations such as entanglement entropy and quantum\ndiscord for the coherent dynamics. We extend our studies to the dissipative\ncase in which the spontaneous emission from the Rydberg state is taken into\naccount and in particular, we look at the purity and quantum discord of the\nsteady states. To conclude, our studies reveal that the local manipulation of\nan atom using Rabi-offset can be an ideal tool to control the quantum\ncorrelations and in general, quantum states of the composite two-qubit systems.",
        "positive": "Dynamics of gap solitons in a dipolar Bose-Einstein condensate on a\n  three-dimensional optical lattice: We suggest and study the stable disk- and cigar-shaped gap solitons of a\ndipolar Bose-Einstein condensate of $^{52}$Cr atoms localized in the lowest\nband gap by three optical-lattice (OL) potentials along orthogonal directions.\nThe one-dimensional version of these solitons of experimental interest confined\nby an OL along the dipole moment direction and harmonic traps in transverse\ndirections is also considered. Important dynamics of (i) breathing oscillation\nof a gap soliton upon perturbation and (ii) dragging of a gap soliton by a\nmoving lattice along axial $z$ direction demonstrates the stability of gap\nsolitons. A movie clip of dragging of three-dimensional gap soliton is\nincluded."
    },
    {
        "anchor": "Transport of dipolar excitons in (Al,Ga)N/GaN quantum wells: We investigate the transport of dipolar indirect excitons along the growth\nplane of polar (Al,Ga)N/GaN quantum well structures by means of spatially- and\ntime-resolved photoluminescence spectroscopy. The transport in these strongly\ndisordered quantum wells is activated by dipole-dipole repulsion. The latter\ninduces an emission blue shift that increases linearly with exciton density,\nwhereas the radiative recombination rate increases exponentially. Under\ncontinuous, localized excitation, we measure a continuous red shift of the\nemission, as excitons propagate away from the excitation spot. This shift\ncorresponds to a steady-state gradient of exciton density, measured over\nseveral tens of micrometers. Time-resolved micro-photoluminescence experiments\nprovide information on the dynamics of recombination and transport of dipolar\nexcitons. We account for the ensemble of experimental results by solving the\nnonlinear drift-diffusion equation. Quantitative analysis suggests that in such\nstructures, exciton propagation on the scale of 10 to 20 microns is mainly\ndriven by diffusion, rather than by drift, due to the strong disorder and the\npresence of nonradiative defects. Secondary exciton creation, most probably by\nthe intense higher-energy luminescence, guided along the sample plane, is shown\nto contribute to the exciton emission pattern on the scale up to 100 microns.\nThe exciton propagation length is strongly temperature dependent, the emission\nbeing quenched beyond a critical distance governed by nonradiative\nrecombination.",
        "positive": "Exact out-of-time-ordered correlation functions for an interacting\n  lattice fermion model: Exact solutions for local equilibrium and nonequilibrium out-of-time-ordered\ncorrelation (OTOC) functions are obtained for a lattice fermion model with\non-site interactions, namely the Falicov-Kimball (FK) model, in the large\ndimensional and thermodynamic limit. Our approach is based on the\nnonequilibrium dynamical mean-field theory generalized to an extended\nKadanoff-Baym contour. We find that the density-density OTOC is most enhanced\nat intermediate coupling around the metal-insulator phase transition. In the\nhigh-temperature limit, the OTOC remains nontrivially finite and\ninteraction-dependent, even though dynamical charge correlations probed by an\nordinary response function are completely suppressed. We propose an experiment\nto measure OTOCs of fermionic lattice systems including the FK and Hubbard\nmodels in ultracold atomic systems."
    },
    {
        "anchor": "Droplet formation in a one-dimensional system of attractive spinless\n  fermions: A translation invariant one-dimensional system of spinless fermions with a\nfinite-range attraction experiences a quantum phase transition to a\nphase-separated state. While being a conventional Luttinger liquid for a small\ninteraction strength, spinless fermions form a droplet with the size smaller\nthan the available one-dimensional volume when the interaction strength exceeds\nsome critical value. A particularly remarkable signature of the droplet\nformation is the change in the lower edge of the many-body excitation spectrum.\nIn the homogeneous phase, it has a Luttinger-liquid shape of periodic arcs on\ntop of the shallow parabolic dispersion of the center-of-mass. When the\ninteraction strength is increased, the arcs disappear completely as soon as the\ndroplet is formed. We perform an exact diagonalization study of this system\nwith the focus on the signatures of the quantum phase transition and the\ndroplet properties. The one-particle and density-density correlation functions,\nthe pressure, the sound velocity, and the droplet density are examined. The\nvalue of the critical interaction strength obtained from numerical data\nreasonably agrees with a simple mean-field analytical estimate. Due to the\nboson-fermion correspondence valid in one dimension, our results also hold for\nhard-core bosons with a finite-range attraction.",
        "positive": "Spontaneous interlayer superfluidity in bilayer systems of cold polar\n  molecules: Quantum degenerate cold-atom gases provide a remarkable opportunity to study\nstrongly interacting systems. Recent experimental progress in producing\nultracold polar molecules with a net electric dipole moment opens up new\npossibilities to realize novel quantum phases governed by the long-range and\nanisotropic dipole-dipole interactions. In this work we predict the existence\nof experimentally observable novel broken-symmetry states with spontaneous\ninterlayer coherence in cold polar molecules. These exotic states appear due to\nstrong repulsive interlayer interactions and exhibit properties of superfluids,\nferromagnets and excitonic condensates."
    },
    {
        "anchor": "Symmetry-breaking magnetization dynamics of spinor dipolar Bose-Einstein\n  condensates: Symmetry-breaking magnetization dynamics of a spin-1 Bose-Einstein condensate\n(BEC) due to the dipole-dipole interaction are investigated using the\nmean-field and Bogoliubov theories. When a magnetic field is applied along the\nsymmetry axis of a pancake-shaped BEC in the m = 0 hyperfine sublevel,\ntransverse magnetization develops breaking the chiral or axial symmetry. A\nvariety of magnetization patterns are formed depending on the strength of the\napplied magnetic field. The proposed phenomena can be observed in 87Rb and 23Na\ncondensates.",
        "positive": "Dipolar Bilayer with Antiparallel Polarization -- a Self-Bound Liquid: Dipolar bilayers with antiparallel polarization, i.e. opposite polarization\nin the two layers, exhibit liquid-like rather than gas-like behavior. In\nparticular, even without external pressure a self-bound liquid puddle of\nconstant density will form. We investigate the symmetric case of two identical\nlayers, corresponding to a two-component Bose system with equal partial\ndensities. The zero-temperature equation of state $E(\\rho)/N$, where $\\rho$ is\nthe total density, has a minimum, with an equilibrium density that decreases\nwith increasing distance between the layers. The attraction necessary for a\nself-bound liquid comes from the inter-layer dipole-dipole interaction that\nleads to a mediated intra-layer attraction. We investigate the regime of\nnegative pressure towards the spinodal instability, where the bilayer is\nunstable against infinitesimal fluctuations of the total density, conformed by\ncalculations of the speed of sound of total density fluctuations."
    },
    {
        "anchor": "Expansion Dynamics of Two Dimensional Extended Bose-Hubbard Model: We study the expansion dynamics of harmonically trapped bosons in a\ntwo-dimensional lattice within the extended Bose-Hubbard model. We evaluate the\ndynamics of the system following a sudden removal of the confining potential,\nstarting with a cloud mostly in n = 1 Mott state. We show that the nearest\nneighbour interactions have a strong influence on the dynamics of ultracold\nbosons on an optical lattice. Also we conclude that validity of the widely used\ncontact potential approximation is questionable in the presence of Feschbach\nresonances.",
        "positive": "Breakdown of the mean field for dark solitons of dipolar bosons in a\n  one-dimensional harmonic trap: We directly compare the mean-field and the many-body approach in a\none-dimensional Bose system in a harmonic trap. Both contact and dipolar\ninteractions are considered. We propose a multi-atom version of the phase\nimprinting method to generate dark solitons in the system. We begin with a\ngeneral analysis of system dynamics and observe the emergence of a dark soliton\nand a shock wave. Center of mass and soliton motion become decoupled because\nthe shock wave oscillates with the trap frequency and soliton does not. A\ndetailed investigation of frequencies reveals significant differences between\nresults obtained in the mean-field and the many-body pictures."
    },
    {
        "anchor": "BEC-BCS crossover in a p+ip-wave pairing Hamiltonian coupled to bosonic\n  molecular pairs: We analyse a p+ip-wave pairing BCS Hamiltonian, coupled to a single bosonic\ndegree of freedom representing a molecular condensate, and investigate the\nnature of the BEC-BCS crossover for this system. For a suitable restriction on\nthe coupling parameters, we show that the model is integrable and we derive the\nexact solution by the algebraic Bethe ansatz. In this manner we also obtain\nexplicit formulae for correlation functions and compute these for several\ncases. We find that the crossover between the BEC state and the strong pairing\np+ip phase is smooth for this model, with no intermediate quantum phase\ntransition.",
        "positive": "3D quaternionic condensations, Hopf invariants, and skyrmion lattices\n  with synthetic spin-orbit coupling: We study the topological configurations of the two-component condensates of\nbosons with the $3$D $\\vec{\\sigma}\\cdot \\vec{p}$ Weyl-type spin-orbit coupling\nsubject to a harmonic trapping potential. The topology of the condensate\nwavefunctions manifests in the quaternionic representation. In comparison to\nthe $U(1)$ complex phase, the quaternionic phase manifold is $S^3$ and the spin\norientations form the $S^2$ Bloch sphere through the 1st Hopf mapping. The\nspatial distributions of the quaternionic phases exhibit the 3D skyrmion\nconfigurations, and the spin distributions possess non-trivial Hopf invariants.\nSpin textures evolve from the concentric distributions at the weak spin-orbit\ncoupling regime to the rotation symmetry breaking patterns at the intermediate\nspin-orbit coupling regime. In the strong spin-orbit coupling regime, the\nsingle-particle spectra exhibit the Landau-level type quantization. In this\nregime, the three-dimensional skyrmion lattice structures are formed when\ninteractions are below the energy scale of Landau level mixings. Sufficiently\nstrong interactions can change condensates into spin-polarized plane-wave\nstates, or, superpositions of two plane-waves exhibiting helical spin spirals."
    },
    {
        "anchor": "Dynamics of interacting fermions in spin-dependent potentials: Recent experiments with dilute trapped Fermi gases observed that weak\ninteractions can drastically modify spin transport dynamics and give rise to\nrobust collective effects including global demagnetization, macroscopic spin\nwaves, spin segregation, and spin self-rephasing. In this work we develop a\nframework for studying the dynamics of weakly interacting fermionic gases\nfollowing a spin-dependent change of the trapping potential which illuminates\nthe interplay between spin, motion, Fermi statistics, and interactions. The key\nidea is the projection of the state of the system onto a set of lattice spin\nmodels defined on the single-particle mode space. Collective phenomena,\nincluding the global spreading of quantum correlations in real space, arise as\na consequence of the long-ranged character of the spin model couplings. This\napproach achieves good agreement with prior measurements and suggests a number\nof directions for future experiments.",
        "positive": "Bose-Einstein condensation of atoms in a uniform potential: We have observed Bose-Einstein condensation of an atomic gas in the\n(quasi-)uniform three-dimensional potential of an optical box trap.\nCondensation is seen in the bimodal momentum distribution and the anisotropic\ntime-of-flight expansion of the condensate. The critical temperature agrees\nwith the theoretical prediction for a uniform Bose gas. The momentum\ndistribution of our non-condensed quantum-degenerate gas is also clearly\ndistinct from the conventional case of a harmonically trapped sample and close\nto the expected distribution in a uniform system. We confirm the coherence of\nour condensate in a matter-wave interference experiment. Our experiments open\nmany new possibilities for fundamental studies of many-body physics."
    },
    {
        "anchor": "The Hyperfine Molecular Hubbard Hamiltonian: An ultracold gas of heteronuclear alkali dimer molecules with hyperfine\nstructure loaded into a one-dimensional optical lattice is investigated. The\n\\emph{Hyperfine Molecular Hubbard Hamiltonian} (HMHH), an effective low-energy\nlattice Hamiltonian, is derived from first principles. The large permanent\nelectric dipole moment of these molecules gives rise to long range\ndipole-dipole forces in a DC electric field and allows for transitions between\nrotational states in an AC microwave field. Additionally, a strong magnetic\nfield can be used to control the hyperfine degrees of freedom independently of\nthe rotational degrees of freedom. By tuning the angle between the DC electric\nand magnetic fields and the strength of the AC field it is possible to control\nthe number of internal states involved in the dynamics as well as the degree of\ncorrelation between the spatial and internal degrees of freedom. The HMHH's\nunique features have direct experimental consequences such as quantum\ndephasing, tunable complexity, and the dependence of the phase diagram on the\nmolecular state.",
        "positive": "Topologically non-trivial Hofstadter bands on the kagome lattice: We investigate how the multiple bands of fermions on a crystal lattice evolve\nif a magnetic field is added which does not increase the number of bands. The\nkagome lattice is studied as generic example for a lattice with loops of three\nbonds. Finite Chern numbers occur as non-trivial topological property in\npresence of the magnetic field. The symmetries and periodicities as function of\nthe applied field are discussed. Strikingly, the dispersions of the edge states\ndepend crucially on the precise shape of the boundary. This suggests that\nsuitable design of the boundaries helps to tune physical properties which may\neven differ between upper and lower edge. Moreover, we suggest a promising\ngauge to realize this model in optical lattices."
    },
    {
        "anchor": "Universal three-body recombination and Efimov resonances in an ultracold\n  Li-Cs mixture: We study Efimov resonances via three-body loss in an ultracold two-component\ngas of fermionic $^6$Li and bosonic $^{133}$Cs atoms close to a Feshbach\nresonance at 843~G, extending results reported previously [Pires \\textit{et\nal.}, Phys. Rev. Lett. 112, 250404 (2014)] to temperatures around 120~nK. The\nexperimental scheme for reaching lower temperatures is based upon compensating\nthe gravity-induced spatial separation of the mass-imbalanced gases with\nbichromatic optical dipole traps. We observe the first and second excited\nLi-Cs-Cs Efimov resonance in the magnetic field dependence of the three-body\nevent rate constant, in good agreement with the universal zero-range theory at\nfinite temperature [Petrov and Werner, Phys. Rev. A 92, 022704 (2015)].\nDeviations are found for the Efimov ground state, and the inelasticity\nparameter $\\eta$ is found to be significantly larger than those for\nsingle-species systems.",
        "positive": "Manipulating Cooper pairs with a controllable momentum in periodically\n  driven degenerate Fermi gases: We here present an experimentally feasible proposal for manipulating Cooper\npairs in degenerate Fermi gases trapped by an optical lattice. Upon introducing\nan \\textit{in situ} periodically driven field, the system may be described by\nan effective time-independent Hamiltonian, in which the Cooper pairs, generated\nby the bound molecule state in Feshbach resonance, host a nonzero\ncenter-of-mass momentum. The system thus processes a crossover from a\nBardeen-Cooper-Schrieffer (BCS) superfluid phase to a Fulde-Ferrell (FF) one.\nFurthermore, the magnitude and direction of the Cooper pairs in the synthetic\nFF superfluids are both directly controllable via the periodically driven\nfield. Our proposal offers a reliable and feasible scenario for manipulating\nthe Cooper pairs in cold atoms, serving as a tunable as well as powerful\nplatform for quantum-emulating and exploring the FF superfluid phase."
    },
    {
        "anchor": "Universal relations between atomic dipolar relaxation and van der Waals\n  interaction: Dipolar relaxation happens when one or both colliding atoms flip their spins\nexothermically inside a magnetic ($B$) field. This work reports precise\nmeasurements of dipolar relaxation in a Bose-Einstein condensate of ground\nstate $^{87}$Rb atoms together with in-depth theoretical investigations.\nPrevious perturbative treatments fail to explain our observations except at\nvery small $B$-fields. By employing quantum defect theory based on analytic\nsolutions of asymptotic van der Waals interaction $-C_6/R^6$ ($R$ being\ninteratomic spacing), we significantly expand the applicable range of\nperturbative treatment. We find the $B$-dependent dipolar relaxation lineshapes\nare largely universal, determined by the coefficient $C_6$ and the associated\n$s$-wave scattering lengths $a_{\\rm sc}$ of the states before and after spin\nflips. This universality, which applies generally to other atomic species as\nwell, implicates potential controls of dipolar relaxation and related cold\nchemical reactions by tuning $a_{\\rm sc}$.",
        "positive": "Topological transitions of gapless paired states in mixed-geometry\n  lattices: We propose a mixed-geometry system of fermionic species selectively confined\nin lattices of different geometry. We investigate how such asymmetry can lead\nto exotic multiband fermion pairing in an example system of honeycomb and\ntriangular lattices. A rich phase diagram of interband pairing with gapped and\ngapless excitations is found at zero temperature. We find that the two-band\ncontribution of the honeycomb lattices to the paired state helps to stabilize\nthe gapless phase with one or two Fermi surfaces. We also show that the Fermi\nsurface topology further divides the gapless phase into subclasses between\nwhich the system undergoes density-driven Lifshitz transitions."
    },
    {
        "anchor": "Imbalanced ultracold Fermi gas in the weakly repulsive regime:\n  Renormalization group approach for p-wave superfluidity: We theoretically study a possible new pairing mechanism for a two-dimensional\npopulation imbalanced Fermi gas with short-range repulsive interactions which\ncan be realized on the upper branch of a Feshbach resonance. We use a\nwell-controlled renormalization group approach, which allows an unbiased study\nof the instabilities of imbalanced Fermi liquid without assumption of a broken\nsymmetry and gives a numerical calculation of the transition temperature from\nmicroscopic parameters. Our results show a leading superfluid instability in\nthe p-wave channel for the majority species. The corresponding mechanism is\nthat there are effective attractive interactions for the majority species,\ninduced by the particle-hole susceptibility of the minority species, where the\nmismatch of the Fermi surfaces of the two species plays an important role. We\nalso propose an experimental protocol for detecting the p-wave superfluidity\nand discuss the corresponding experimental signatures.",
        "positive": "Variational methods with coupled Gaussian functions for Bose-Einstein\n  condensates with long-range interactions. II. Applications: Bose-Einstein condensates with an attractive 1/r interaction and with\ndipole-dipole interaction are investigated in the framework of the Gaussian\nvariational ansatz introduced by S. Rau, J. Main, and G. Wunner [Phys. Rev. A,\nsubmitted]. We demonstrate that the method of coupled Gaussian wave packets is\na full-fledged alternative to direct numerical solutions of the\nGross-Pitaevskii equation, or even superior in that coupled Gaussians are\ncapable of producing both, stable and unstable states of the Gross-Pitaevskii\nequation, and thus of giving access to yet unexplored regions of the space of\nsolutions of the Gross-Pitaevskii equation. As an alternative to numerical\nsolutions of the Bogoliubov-de Gennes equations, the stability of the\nstationary condensate wave functions is investigated by analyzing the stability\nproperties of the dynamical equations of motion for the Gaussian variational\nparameters in the local vicinity of the stationary fixed points. For\nblood-cell-shaped dipolar condensates it is shown that on the route to collapse\nthe condensate passes through a pitchfork bifurcation, where the ground state\nitself turns unstable, before it finally vanishes in a tangent bifurcation."
    },
    {
        "anchor": "Elementary excitations of dipolar Tonks-Girardeau droplets: One-dimensional bosonic gas with strong contact repulsion and attractive\ndipolar interactions may form a quantum droplet with flat-top density profile.\nEmploying effective, hydrodynamic description of the system, we study\nelementary excitations characterizing response of a droplet to small\nperturbation. The excitation spectrum consists of two families: phononic-like\nexcitations inside droplets and the scattering modes. Analysis within the\nlinearized regime is supplemented with the full, nonlinear dynamics of small\nperturbations. Our study focuses mainly on the regime of infinite contact\nrepulsion and tight transversal harmonic confinement, where there are analytic\nformulas for the density profiles. Moreover, we propose a simplified analytic\nansatz suitable to work also outside this regime, provided the gas is in the\ndeep flat-top region of density profiles.",
        "positive": "Superfluid-supersolid phase transition of elongated dipolar\n  Bose-Einstein Condensates at finite temperatures: We analyse the finite-temperature phase diagram of a dipolar Bose Einstein\nCondensate confined in a tubular geometry. The effect of thermal fluctuations\nis accounted for by means of Bogoliubov theory employing the local density\napproximation. In the considered geometry, the superfluid-supersolid phase\ntransition can be of first- and second-order. We discuss how the corresponding\ntransition point is affected by the finite temperature of the system."
    },
    {
        "anchor": "Statics and dynamics of a self-bound matter-wave quantum ball: We study the statics and dynamics of a stable, mobile, three-dimensional\nmatter-wave spherical quantum ball created in the presence of an attractive\ntwo-body and a very small repulsive three-body interaction. The quantum ball\ncan propagate with a constant velocity in any direction in free space and its\nstability under a small perturbation is established numerically and\nvariationally. In frontal head-on and angular collisions at large velocities\ntwo quantum balls behave like quantum solitons. Such collision is found to be\nquasi elastic and the quantum balls emerge after collision without any change\nof direction of motion and velocity and with practically no deformation in\nshape. When reflected by a hard impenetrable plane, the quantum ball bounces\noff like a wave obeying the law of reflection without any change of shape or\nspeed. However, in a collision at small velocities two quantum balls coalesce\nto form a larger ball which we call a quantum-ball breather. We point out the\nsimilarity and difference between the collision of two quantum and classical\nballs. The present study is based on an analytic variational approximation and\na full numerical solution of the mean-field Gross-Pitaevskii equation using the\nparameters of $^7$Li atoms.",
        "positive": "Observation of Chiral-Mode Domains in a Frustrated XY Model on Optical\n  Triangular Lattices: We investigated the relaxation and excitation in a frustrated XY model\nrealized by a Bose gas in Floquet-engineered optical triangular lattices.\nPeriodically driving the position of the entire lattice structure enables the\nsign inversion of tunneling amplitudes, which, in the case of a triangular\nlattice, results in geometrical frustration of the local phase of wave packets.\nWe revealed that the two spiral phases with chiral modes show significant\ndifferences in relaxation time from the initial ferromagnetic phase. While\nspontaneous symmetry breaking is clearly observed at a slow ramp of the Floquet\ndrive, simultaneous occupation of two ground states often occurs at a fast\nramp, which can be attributed to the domain formation of the chiral modes. The\ninterference of the spatially separated chiral modes was observed, using a\nquantum gas microscope. This work leads to exploring the domain formation\nmechanism in a system with U(1)$\\times \\mathbb{Z}_2$ symmetry."
    },
    {
        "anchor": "Quantum Adiabatic Doping for Atomic Fermi-Hubbard Quantum Simulations: There have been considerable research efforts devoted to quantum simulations\nof Fermi-Hubbard model with ultracold atoms loaded in optical lattices. In such\nexperiments, the antiferromagnetically ordered quantum state has been achieved\nat half filling in recent years. The atomic lattice away from half filling is\nexpected to host d-wave superconductivity, but its low temperature phases have\nnot been reached. In a recent work, we proposed an approach of incommensurate\nquantum adiabatic doping, using quantum adiabatic evolution of an\nincommensurate lattice for preparation of the highly correlated many-body\nground state of the doped Fermi-Hubbard model starting from a unit-filling band\ninsulator. Its feasibility has been demonstrated with numerical simulations of\nthe adiabatic preparation for certain incommensurate particle-doping fractions,\nwhere the major problem to circumvent is the atomic localization in the\nincommensurate lattice. Here we carry out a systematic study of the quantum\nadiabatic doping for a wide range of doping fractions from particle-doping to\nhole-doping, including both commensurate and incommensurate cases. We find that\nthere is still a localization-like slowing-down problem at commensurate\nfillings, and that it becomes less harmful in the hole-doped regime. With\ninteractions, the adiabatic preparation is found to be more efficient for that\ninteraction effect destabilizes localization. For both free and interacting\ncases, we find the adiabatic doping has better performance in the hole-doped\nregime than the particle-doped regime. We also study adiabatic doping starting\nfrom the half-filling Mott insulator, which is found to be more efficient for\ncertain filling fractions.",
        "positive": "Formation dynamics of black- and white-hole horizons in an analogue\n  gravity model: We investigate the formation dynamics of sonic horizons in a Bose gas\nconfined in a (quasi) one-dimensional trap. This system is one of the most\npromising realizations of the analogue gravity paradigm and has already been\nsuccessfully studied experimentally. Taking advantage of the exact solution of\nthe one-dimensional, hard-core, Bose model (Tonks-Girardeau gas) we show that,\nby switching on a step potential, either a sonic (black-hole-like) horizon or a\nblack/white hole pair may form, according to the initial velocity of the fluid.\nOur simulations never suggest the formation of an isolated white-hole horizon,\nalthough a stable stationary solution of the dynamical equations with those\nproperties is analytically found. Moreover, we show that the semiclassical\ndynamics, based on the Gross-Pitaevskii equation, conforms to the exact\nsolution only in the case of fully subsonic flows while a stationary solution\nexhibiting a supersonic transition is never reached dynamically."
    },
    {
        "anchor": "Critical spin superflow in a spinor Bose-Einstein condensate: We investigate the critical dynamics of spin superflow in an easy-plane\nantiferromagnetic spinor Bose-Einstein condensate. Spin-dipole oscillations are\ninduced in a trapped condensate by applying a linear magnetic field gradient\nand we observe that the damping rate increases rapidly as the field gradient\nincreases above a certain critical value. The onset of dissipation is found to\nbe associated with the generation of dark-bright solitons due to the modulation\ninstability of the counterflow of two spin components. Spin turbulence emerges\nas the solitons decay because of their snake instability. We identify another\ncritical point for spin superflow, in which transverse magnon excitations are\ndynamically generated via spin-exchanging collisions, which leads to the\ntransient formation of axial polar spin domains.",
        "positive": "Regulating atomic imbalance in double-well lattices: An insulating optical lattice with double-well sites is considered. In the\ncase of the unity filling factor, an effective Hamiltonian in the pseudospin\nrepresentation is derived. A method is suggested for manipulating the\nproperties of the system by varying the shape of the double-well potential. In\nparticular, it is shown that the atomic imbalance can be varied at will and a\nkind of the Morse-alphabet sequences can be created."
    },
    {
        "anchor": "A Dielectric Superfluid of Polar Molecules: We show that, under achievable experimental conditions, a Bose-Einstein\ncondensate (BEC) of polar molecules can exhibit dielectric character. In\nparticular, we derive a set of self-consistent mean-field equations that couple\nthe condensate density to its electric dipole field, leading to the emergence\nof polarization modes that are coupled to the rich quasiparticle spectrum of\nthe condensate. While the usual roton instability is suppressed in this system,\nthe coupling can give rise to a phonon-like instability that is characteristic\nof a dielectric material with a negative static dielectric function.",
        "positive": "Two-mode dipolar bosonic junctions: We consider a two-mode atomic Josephson junction realized with dilute dipolar\nbosons confined by a double-well. We employ the two-site extended Bose-Hubbard\nHamiltonian and characterize the ground-state of this system by the Fisher\ninformation, coherence visibility, and entanglement entropy. These quantities\nare studied as functions of the interaction between bosons in different wells.\nThe emergence of Schroedinger-cat like state with a loss of coherence is also\ncommented."
    },
    {
        "anchor": "Expansion of a matter wave packet in a one-dimensional disordered\n  potential in the presence of a uniform bias force: We study numerically the expansion dynamics of an initially confined quantum\nwave packet in the presence of a disordered potential and a uniform bias force.\nFor white-noise disorder, we find that the wave packet develops asymmetric\nalgebraic tails for any ratio of the force to the disorder strength. The\nexponent of the algebraic tails decays smoothly with that ratio and no evidence\nof a critical behavior on the wave density profile is found. Algebraic\nlocalization features a series of critical values of the force-to-disorder\nstrength where the m-th position moment of the wave packet diverges. Below the\ncritical value for the m-th moment, we find fair agreement between the\nasymptotic long-time value of the m-th moment and the predictions of\ndiagrammatic calculations. Above it, we find that the m-th moment grows\nalgebraically in time. For correlated disorder, we find evidence of systematic\ndelocalization, irrespective to the model of disorder. More precisely, we find\na two-step dynamics, where both the center-of-mass position and the width of\nthe wave packet show transient localization, similar to the white-noise case,\nat short time and delocalization at sufficiently long time. This\ncorrelation-induced delocalization is interpreted as due to the decrease of the\neffective de Broglie wave length, which lowers the effective strength of the\ndisorder in the presence of finite-range correlations.",
        "positive": "Persistent Current of SU(N) Fermions: We study the persistent current in a system of SU($N$) fermions with\nrepulsive interaction confined in a ring-shaped potential and pierced by an\neffective magnetic flux. By applying a combination of Bethe ansatz and\nnumerical analysis, we demonstrate that, as a combined effect of spin\ncorrelations, interactions and applied flux a specific phenomenon can occur in\nthe system: spinon creation in the ground state. As a consequence, peculiar\nfeatures in the persistent current arise. The elementary flux quantum, which\nfixes the persistent current periodicity, is observed to evolve from a single\nparticle one to an extreme case of fractional flux quantum, in which one\nquantum is shared by all the particles. We show that the persistent current\ndepends on the number of spin components $N$, number of particles and\ninteraction in a specific way that in certain physical regimes has universality\ntraits. At integer filling fractions, the persistent current is suppressed\nabove a threshold of the repulsive interaction by the Mott spectral gap.\nDespite its mesoscopic nature, the current displays a clear finite size scaling\nbehavior. Specific parity effects in the persistent current landscape hold."
    },
    {
        "anchor": "Zero-temperature phase transitions in dilute bosonic superfluids on a\n  lattice: Kinetic energy driven phase transitions in Bose superfluids occur at low\nvalues of the repulsion when the values of the next-to-nearest and\nnext-to-next-to-nearest hopping term attain certain critical values, resulting\nin alterations in the wave vector of the condensate. We map out the space of\npossible phases allowed by particular forms of the single-particle energy\ndispersion in the superfluid state, noting the appearance of a new phase, and\nexamine in more detail the effects of additional repulsive terms on the form of\nthe condensate wavefunction. We also examine the effect of these additional\nhopping terms on the formation of inhomogeneities in the condensate.",
        "positive": "Chaotic and regular dynamics in the three-site Bose-Hubbard model: We analyze the energy spectrum of the three-site Bose-Hubbard model. It is\nshown that this spectrum is a mixture of the regular and irregular spectra\nassociated with the regular and chaotic components of the classical\nBose-Hubbard model. We find relative volumes of these components by using the\npseudoclassical approach. Substituting these values in the Berry-Robnik\ndistribution for the level spacing statistics we obtain good agreement with the\nnumerical data."
    },
    {
        "anchor": "Itinerant Ferromagnetism in ultracold Fermi gases: Itinerant ferromagnetism in cold Fermi gases with repulsive interactions is\nstudied applying the Jastrow-Slater approximation generalized to finite\npolarization and temperature. For two components at zero temperature a second\norder transition is found at $ak_F\\simeq0.90$ compatible with QMC.\nThermodynamic functions and observables such as the compressibility and spin\nsusceptibility and the resulting fluctuations in number and spin are\ncalculated. For trapped gases the resulting cloud radii and kinetic energies\nare calculated and compared to recent experiments. Spin polarized systems are\nrecommended for effective separation of large ferromagnetic domains. Collective\nmodes are predicted and tri-critical points are calculated for multi-component\nsystems.",
        "positive": "Zero-energy modes of two-component Bose-Bose droplets: Bose-Bose droplets are self-bound objects emerging from a mixture of two\ninteracting Bose-Einstein condensates when their interactions are appropriately\ntuned. During droplet formation three continuous symmetries of the system's\nHamiltonian are broken: translational symmetry and two U1 symmetries, allowing\nfor arbitrary choice of phases of the mean-field wavefunctions describing the\ntwo components. Breaking of these symmetries must be accompanied by appearance\nof zero-energy excitations in the energy spectrum of the system recovering the\nbroken symmetries. Normal modes corresponding to these excitations are the\nzero-energy modes. Here we find analytic expressions for these modes and\nintroduce Hamitonians generating their time evolution -- dynamics of the\ndroplet's centers of mass as well as dynamics of the phases of the two\ndroplet's wavefunctions. When internal types of excitations (quasiparticles)\nare neglected then the very complex system of a quantum droplet is described\nusing only few \"global\" degrees of freedom - the position of the center of mass\nof the droplet and two phases of two wave-functions, all these being quantum\noperators. This gives the possibility of describing in a relatively easy way\nprocesses of interaction of these quantum droplets, such as collisions."
    },
    {
        "anchor": "Oscillating Solitons and AC Josephson Effect in Ferromagnetic Bose-Bose\n  Mixtures: Close to the demixing transition, the degree of freedom associated to\nrelative density fluctuations of a two-component Bose-Einstein condensate is\ndescribed by a non-dissipative Landau-Lifshitz equation. In the quasi\none-dimensional weakly immiscible case, this mapping surprisingly predicts that\na dark-bright soliton should oscillate when subject to a constant force\nfavoring separation of the two components. We propose a realistic experimental\nimplementation of this phenomenon which we interpret as a spin-Josephson effect\nin the presence of a movable barrier.",
        "positive": "Many-body adiabatic passage: Quantum detours around chaos: We study the many-body dynamics of stimulated Raman adiabatic passage in the\npresence of on-site interactions. In the classical mean-field limit, explored\nin Phys. Rev. Lett. {\\bf 121}, 250405 (2018), interaction-induced chaos leads\nto the breakdown of adiabaticity under the quasi-static variation of the\nparameters, thus producing {\\em low} sweep rate boundaries on efficient\npopulation transfer. We show that for the corresponding many-body system,\nalternative quantum pathways from the initial to the target state, open up at\neven slower sweep rates. These quantum detours avoid the chaotic classical path\nand hence allow a robust and efficient population transfer."
    },
    {
        "anchor": "Exotic pairing states in a Fermi gas with three-dimensional spin-orbit\n  coupling: We investigate properties of exotic pairing states in a three-dimensional\nFermi gas with three-dimensional spin-orbit coupling and an effective Zeeman\nfield. The interplay of spin-orbit coupling, effective Zeeman field and pairing\ncan lead to first-order phase transitions between different phases, and to\ninteresting nodal superfluid states with gapless surfaces in the momentum\nspace. We then demonstrate that pairing states with zero center-of-mass\nmomentum are unstable against finite center-of-mass momentum\nFulde-Ferrell-Larkin-Ovchinnikov (FFLO) states, with the center-of-mass\nmomentum of the pairs opposite to the direction of the effective Zeeman field.\nUnlike conventional FFLO states, these FFLO states are induced by the\ncoexistence of spin-orbit coupling and Fermi surface deformation, and have\nintriguing features like first-order transitions between different FFLO states,\nnodal FFLO states with gapless surfaces in momentum space, and exotic fully\ngapped FFLO states. With the recent theoretical proposals for realizing\nthree-dimensional spin-orbit coupling in ultracold atom gases, our work is\nhelpful for the future experimental studies, and provides valuable information\nfor the general understanding of pairing physics in spin-orbit coupled\nfermionic systems.",
        "positive": "Dynamically decoupled three-body interactions with applications to\n  interaction-based quantum metrology: We propose a stroboscopic method to dynamically decouple the effects of\ntwo-body atom-atom interactions for ultracold atoms, and realize a system\ndominated by elastic three-body interactions. Using this method, we show that\nit is possible to achieve the optimal scaling behavior predicted for\ninteraction-based quantum metrology with three-body interactions. Specifically,\nwe show that for ultracold atoms quenched in an optical lattice, we can measure\nthe three-body interaction strength with a precision proportional to ${\\bar\nn}^{-5/2}$ using homodyne quadrature interferometry, and ${\\bar n}^{-7/4}$\nusing conventional collapse-and-revival techniques, where ${\\bar n}$ is the\nmean number of atoms per lattice site. Both precision scalings surpass the\nnonlinear scaling of ${\\bar n}^{-3/2}$, the best so far achieved or proposed\nwith a physical system. Our method of achieving a decoupled three-body\ninteracting system may also have applications in the creation of exotic\nthree-body states and phases."
    },
    {
        "anchor": "Nonequilibrium-induced enhancement of dynamical quantum coherence and\n  entanglement of spin arrays: The random magnetic field produced by nuclear spins has long been viewed as\nthe dominating source of decoherence in the quantum-dot based spins. Here we\nobtain in both exact and analytical manner the dynamics of spin qubits coupled\nto nuclear spin environments via the hyperfine interaction, going beyond the\nweak system-bath interaction and Markovian approximation. We predict that the\ndetailed-balance breaking produced by chemical potential gradient in nuclear\nbaths leads to the rapid oscillations of populations, quantum coherence and\nentanglement, which are absent in the conventional case (i.e., Overhauser\nnoise). This is attributed to the nonequilibrium feature of the system as shown\nin the relation between the oscillation period and the chemical potential\nimbalance. Our results reveal the essentiality of nonequilibriumness with\ndetailed-balance breaking for enhancing the dynamical coherence and\nentanglement of spin qubits. Moreover, our exact solution explicitly\ndemonstrates that the non-Markovian bath comprised by nuclear spins can\npreserve the collective quantum state, due to the recovery of coherence.\nFinally, we propose an experiment using ultracold trapped ions to observe these\nnonequilibrium and memory effects.",
        "positive": "Quantum simulators based on the global collective light-matter\n  interaction: We show that coupling ultracold atoms in optical lattices to quantized modes\nof an optical cavity leads to quantum phases of matter, which at the same time\nposses properties of systems with both short- and long-range interactions. This\nopens perspectives for novel quantum simulators of finite-range interacting\nsystems, even though the light-induced interaction is global (i.e. infinitely\nlong range). This is achieved by spatial structuring of the global light-matter\ncoupling at a microscopic scale. Such simulators can directly benefit from the\ncollective enhancement of the global light-matter interaction and constitute an\nalternative to standard approaches using Rydberg atoms or polar molecules. The\nsystem in the steady state of light induces effective many-body interactions\nthat change the landscape of the phase diagram of the typical Bose-Hubbard\nmodel. Therefore, the system can support non-trivial superfluid states, bosonic\ndimer, trimers, etc. states and supersolid phases depending on the choice of\nthe wavelength and pattern of the light with respect to the classical optical\nlattice potential. We find that by carefully choosing the system parameters one\ncan investigate diverse strongly correlated physics with the same setup, i.e.,\nmodifying the geometry of light beams. In particular, we present the interplay\nbetween the density and bond (or matter-wave coherence) interactions. We show\nhow to tune the effective interaction length in such a hybrid system with both\nshort-range and global interactions."
    },
    {
        "anchor": "Interacting heavy fermions in a disordered optical lattice: We have theoretically studied the effect of disorder on ultracold\nalkaline-earth atoms governed by the Kondo lattice model in an optical lattice\nvia simplified double-well model and hybridization mean-field theory.\nDisorder-induced narrowing and even complete closure of hybridization gap have\nbeen predicted and the compressibility of the system has also been investigated\nfor metallic and Kondo insulator phases in the presence of the disordered\npotential. To make connection to the experimental situation, we have\nnumerically solved the disordered Kondo lattice model with an external harmonic\ntrap and shown both the melting of Kondo insulator plateau and an\ncompressibility anomaly at low-density.",
        "positive": "Hidden vortices in a Bose-Einstein condensate in a rotating double-well\n  potential: We study vortex formation in a Bose-Einstein condensate in a rotating\ndouble-well potential. Besides the ordinary quantized vortices and elusive\nghost vortices, \"hidden\" vortices are found distributing along the central\nbarrier. These hidden vortices are invisible like ghost vortex but carry\nangular momentum. Moreover, their core size is not given by the healing length,\nbut is strongly influenced by the external potential. We find that the\nFeynman's rule can be well satisfied only after including the hidden vortices.\nThere is no critical rotating frequency for the formation of hidden vortex\nwhile there is one for the formation of ordinary visible vortices. Hidden\nvortices can be revealed in the free expansion of the Bose-Einstein\ncondensates. In addition, the hidden vortices in a Bose-Einstein condensate can\nappear in other external potentials, such as a rotating anisotropic toroidal\ntrap."
    },
    {
        "anchor": "Out-of-equilibrium dynamics of repulsive Fermi gases in quasi-periodic\n  potentials: a Density Functional Theory study: The dynamics of a one-dimensional two-component Fermi gas in the presence of\na quasi-periodic optical lattice (OL) is investigated by means of a Density\nFunctional Theory approach. Inspired by the protocol implemented in recent\ncold-atom experiments, designed to identify the many-body localization\ntransition, we analyze the relaxation of an initially prepared imbalance\nbetween the occupation number of odd and of even sites. For quasi-disorder\nstrength beyond the Anderson localization transition, the imbalance survives\nfor long times, indicating the inability of the system to reach local\nequilibrium. The late time value diminishes for increasing interaction\nstrength. Close to the critical quasi-disorder strength corresponding to the\nnoninteracting (Anderson) transition, the interacting system displays an\nextremely slow relaxation dynamics, consistent with sub-diffusive behavior. The\namplitude of the imbalance fluctuations around its running average is found to\ndecrease with time, and such damping is more effective with increasing\ninteraction strengths. While our study addresses the setup with two equally\nintense OLs, very similar effects due to interactions have been observed also\nin recent cold-atom experiments performed in the tight-binding regime, i.e.\nwhere one of the two OLs is very deep and the other is much weaker.",
        "positive": "Gauge protection in non-Abelian lattice gauge theories: Protection of gauge invariance in experimental realizations of lattice gauge\ntheories based on energy-penalty schemes has recently stimulated impressive\nefforts both theoretically and in setups of quantum synthetic matter. A major\nchallenge is the reliability of such schemes in non-Abelian gauge theories\nwhere local conservation laws do not commute. Here, we show through exact\ndiagonalization that non-Abelian gauge invariance can be reliably controlled\nusing gauge-protection terms that energetically stabilize the target gauge\nsector in Hilbert space, suppressing gauge violations due to unitary\ngauge-breaking errors. We present analytic arguments that predict a\nvolume-independent protection strength $V$, which when sufficiently large leads\nto the emergence of an \\textit{adjusted} gauge theory with the same local gauge\nsymmetry up to least a timescale $\\propto\\sqrt{V/V_0^3}$. Thereafter, a\n\\textit{renormalized} gauge theory dominates up to a timescale\n$\\propto\\exp(V/V_0)/V_0$ with $V_0$ a volume-independent energy factor, similar\nto the case of faulty Abelian gauge theories. Moreover, we show for certain\nexperimentally relevant errors that single-body protection terms robustly\nsuppress gauge violations up to all accessible evolution times in exact\ndiagonalization, and demonstrate that the adjusted gauge theory emerges in this\ncase as well. These single-body protection terms can be readily implemented\nwith fewer engineering requirements than the ideal gauge theory itself in\ncurrent ultracold-atom setups and NISQ devices."
    },
    {
        "anchor": "Vortex Nucleation in a Bose-Einstein Condensate: From the Inside Out: We observed a new mechanism for vortex nucleation in Bose-Einstein\ncondensates (BECs) subject to synthetic magnetic fields. We made use of a\nstrong synthetic magnetic field initially localized between a pair of merging\nBECs to rapidly create vortices in the bulk of the merged condensate. Unlike\nprevious implementations and in agreement with our Gross-Pitaevskii equation\nsimulations, our dynamical process rapidly injects vortices into our system's\nbulk, and with initial number in excess of the system's equilibrium vortex\nnumber.",
        "positive": "Artificial gauge potentials for neutral atoms: When a neutral atom moves in a properly designed laser field, its\ncenter-of-mass motion may mimic the dynamics of a charged particle in a\nmagnetic field, with the emergence of a Lorentz-like force. In this Colloquium\nwe present the physical principles at the basis of this artificial (synthetic)\nmagnetism and relate the corresponding Aharonov-Bohm phase to the Berry's phase\nthat emerges when the atom follows adiabatically one of its dressed states. We\nalso discuss some manifestations of artificial magnetism for a cold quantum\ngas, in particular in terms of vortex nucleation. We then generalise our\nanalysis to the simulation of non-Abelian gauge potentials and present some\nstriking consequences, such as the emergence of an effective spin-orbit\ncoupling. We address both the case of bulk gases and discrete systems, where\natoms are trapped in an optical lattice."
    },
    {
        "anchor": "Multiconfigurational time-dependent Hartree approaches for\n  indistinguishable particles: In this Colloquium, the wavefunction-based Multiconfigurational\nTime-Dependent Hartree approaches to the dynamics of indistinguishable\nparticles (MCTDH-F for Fermions and MCTDH-B for Bosons) are reviewed. MCTDH-B\nand MCTDH-F or, together, MCTDH-X are methods for describing correlated quantum\nsystems of identical particles by solving the time-dependent Schr\\\"odinger\nequation from first principles. MCTDH-X is used to accurately model the\ndynamics of real-world quantum many-body systems in atomic, molecular, and\noptical physics. The key feature of these approaches is the time-dependence and\noptimization of the single-particle states employed for the construction of a\nmany-body basis set, which yields nonlinear working equations. We briefly\ndescribe the historical developments that have lead to the formulation of the\nMCTDH-X methods and motivate the necessity for wavefunction-based approaches.\nWe sketch the derivation of the unified MCTDH-F and MCTDH-B equations of motion\nfor complete and also specific restricted configuration spaces. The strengths\nand limitations of the MCTDH-X approach are assessed via benchmarks against an\nexactly solvable model and via convergence checks. We highlight some\napplications to instructive and experimentally-realized quantum many-body\nsystems: the dynamics of atoms in Bose-Einstein condensates in magneto-optical\nand optical traps and of electrons in atoms and molecules. We discuss the\ncurrent development and frontiers in the field of MCTDH-X: theories and\nnumerical methods for indistinguishable particles, for mixtures of multiple\nspecies of indistinguishable particles, the inclusion of nuclear motion for the\nnonadiabatic dynamics of atomic and molecular systems, as well as the\nmultilayer and second-quantized-representation approaches, and the\norbital-adaptive time-dependent coupled-cluster theory are discussed.",
        "positive": "Trapped Fermi gases with Rashba spin-orbit coupling in two dimensions: We use the Bogoliubov-de Gennes formalism to analyze harmonically trapped\nFermi gases with Rashba-type spin-orbit coupling in two dimensions. We consider\nboth population-balanced and -imbalanced Fermi gases throughout the BCS-BEC\nevolution, and study the effects of spin-orbit coupling on the spontaneously\ninduced countercirculating mass currents and the associated intrinsic angular\nmomentum. In particular, we find that even a small spin-orbit coupling\ndestabilizes Fulde-Ferrel-Larkin-Ovchinnikov (FFLO)-type spatially modulated\nsuperfluid phases as well as the phase-separated states against the polarized\nsuperfluid phase. We also show that the continuum of quasiparticle and\nquasihole excitation spectrum can be connected by zero, one or two discrete\nbranches of interface modes, depending on the number of interfaces between a\ntopologically trivial phase (e.g. locally unpolarized/low-polarized superfluid\nor spin-polarized normal) and a topologically nontrivial one (e.g. locally\nhigh-polarized superfluid) that may be present in a trapped system."
    },
    {
        "anchor": "Two-channel model of photoassociation in the vicinity of a Feshbach\n  resonance: We derive the two-channel (TC) description of the photoassociation (PA)\nprocess in the presence of a magnetic Feshbach resonance and compare to full\ncoupled multi-channel calculations for the scattering of $^{6}$Li-$^{87}$Rb.\nPreviously derived results [P. Pellegrini et al., Phys. Rev. Lett. 101, 053201\n(2008)] are corrected. The PA process is shown to be fully described by two\nparameters: the maximal transition rate and the point of vanishing transition\nrate. The TC approximation reproduces excellently the PA transition rates of\nthe full multi-channel calculation and reveals, e.g., that the enhancement of\nthe rate at a resonance is directly connected to the position of vanishing\nrate. For the description of two independent resonances it was found that only\nthree parameters completely characterize the PA process.",
        "positive": "Phonon damping in a 2D superfluid: insufficiency of Fermi's golden rule\n  at low temperature: It is generally accepted that the phonon gas of a superfluid always enters a\nweak coupling regime at sufficiently low temperatures, whatever the strength of\nthe interactions between the underlying particles (constitutive of the\nsuperfluid). Thus, in this limit, we should always be able to calculate the\ndamping rate of thermal phonons by applying Fermi's golden rule to the $H\\_3$\nHamiltonian of cubic phonon-phonon coupling taken from quantum hydrodynamics,\nat least in the case of a convex acoustic branch and in the collisionless\nregime (where the eigenfrequency of the considered phonons remains much greater\nthan the gas thermalization rate). Using the many-body Green's function method,\nwe predict that, unexpectedly, this is not true in two dimensions, contrary to\nthe three-dimensional case. We confirm this prediction with classical\nphonon-field simulations and a non-perturbative theory in $H\\_3$, where the\nfourth order is regularized by hand, giving a complex energy to the virtual\nphonons of the four-phonon collisional processes. For a weakly interacting\nfluid and a phonon mode in the long-wavelength limit, we predict a damping rate\nabout three times lower than that of the golden rule."
    },
    {
        "anchor": "Soliton Magnetization Dynamics in Spin-Orbit Coupled Bose-Einstein\n  Condensates: Ring-trapped Bose-Einstein condensates subject to spin-orbit coupling support\nlocalized dark soliton excitations that show periodic density dynamics in real\nspace. In addition to the density feature, solitons also carry a localized\npseudo-spin magnetization that exhibits a rich and tunable dynamics. Analytic\nresults for Rashba-type spin-orbit coupling and spin-invariant interactions\npredict a conserved magnitude and precessional motion for the soliton\nmagnetization that allows for the simulation of spin-related geometric phases\nrecently seen in electronic transport measurements.",
        "positive": "Reply to the correspondence of Drummond and Brand [arXiv:1610.07633]: In their correspondence [arXiv:1610.07633] Drummond and Brand criticize our\nwork [Nature Physics 12, 451-454 (2016) http://dx.doi.org/10.1038/nphys3631].\nWe show that their criticism is misleading and unfounded."
    },
    {
        "anchor": "Improving Mean-Field Theory for Bosons in Optical Lattices via\n  Degenerate Perturbation Theory: The objective of this paper is the theoretical description of the\nMott-insulator to superfluid quantum phase transition of a Bose gas in an\noptical lattice. In former works the Rayleigh-Schr\\\"odinger perturbation theory\nwas used within a mean-field approach, which yields partially non-physical\nresults since the degeneracy between two adjacent Mott lobes is not taken into\naccount. In order to correct such non-physical results we apply the\nBrillouin-Wigner perturbation theory to the mean-field approximation of the\nBose-Hubbard model. Detailed explanations of how to use the Brillouin-Wigner\ntheory are presented, including a graphical approach that allows to efficiently\nkeep track of the respective analytic terms. To prove the validity of this\ncomputation, the results are compared with other works. Besides the analytic\ncalculation of the phase boundary from Mott-insulator to superfluid phase, the\ncondensate density is also determined by simultaneously solving two algebraic\nequations. The analytical and numerical results turn out to be physically\nmeaningful and can cover a region of system parameters inaccessible until now.\nOur results are of particular interest provided an harmonic trap is added to\nthe former calculations in an homogeneous system, in view of describing an\nexperiment within the local density approximation. Thus, the paper represents\nan essential preparatory work for determining the experimentally observed\nwedding-cake structure of particle-density profile at both finite temperature\nand hopping.",
        "positive": "Quantum Phases of Bose-Hubbard Model in Optical Superlattices: In this paper, we analyze the quantum phases of multiple component\nBose-Hubbard model in optical superlattices, using a mean-field method, the\ndecoupling approximation. We find that the phase diagrams exhibit complected\npatterns and regions with various Charge Density Wave (CDW) for both one- and\ntwo- component cases. We also analyze the effective spin dynamics for the\ntwo-component case in strong-coupling region at unit filling, and show the\npossible existence of a Spin Density Wave (SDW) order."
    },
    {
        "anchor": "Scattering of mesons in quantum simulators: Simulating real-time evolution in theories of fundamental interactions\nrepresents one of the central challenges in contemporary theoretical physics.\nCold-atom platforms stand as promising candidates to realize quantum\nsimulations of non-perturbative phenomena in gauge theories, such as vacuum\ndecay and hadron collisions, in prohibitive conditions for direct experiments.\nIn this work, we demonstrate that present-day quantum simulators can imitate\nlinear particle accelerators, giving access to S-matrix measurements of elastic\nand inelastic meson collisions in low-dimensional Abelian gauge theories.\nConsidering for definiteness a $(1+1)$-dimensional $\\mathbb{Z}_2$-lattice gauge\ntheory realizable with Rydberg-atom arrays, we present protocols to observe and\nmeasure selected meson-meson scattering processes. We provide a benchmark\ntheoretical study of scattering amplitudes in the regime of large fermion mass,\nincluding an exact solution valid for arbitrary coupling strength. This allows\nus to discuss the occurrence of inelastic scattering channels, featuring the\nproduction of new mesons with different internal structures. We present\nnumerical simulations of realistic wavepacket collisions, which reproduce the\npredicted cross section peaks. This work highlights the potential of quantum\nsimulations to give unprecedented access to real-time scattering dynamics.",
        "positive": "Towards the simplest model of quantum supremacy: Atomic boson sampling\n  in a box trap: We describe boson sampling of interacting atoms from the noncondensed\nfraction of Bose-Einstein-condensed (BEC) gas confined in a box trap as a new\nplatform for studying computational #P-hardness and quantum supremacy of\nmany-body systems. We calculate the characteristic function and statistics of\natom numbers via newly found hafnian master theorem. Using Bloch-Messiah\nreduction, we find that interatomic interactions give rise to two equally\nimportant entities - eigen-squeeze modes and eigen-energy quasiparticles -\nwhose interplay with sampling atom states determines behavior of the BEC gas.\nWe infer that two necessary ingredients of #P-hardness, squeezing and\ninterference, are self-generated in the gas and, contrary to Gaussian boson\nsampling in linear interferometers, external sources of squeezed bosons are not\nrequired."
    },
    {
        "anchor": "Thermodynamic engine with a quantum degenerate working fluid: Can quantum mechanical thermodynamic engines outperform their classical\ncounterparts? To address one aspect of this question, we experimentally realize\nand characterize an isentropic thermodynamic engine that uses a Bose-condensed\nworking fluid. In this engine, an interacting quantum degenerate gas of bosonic\nlithium is subjected to trap compression and relaxation strokes interleaved\nwith strokes strengthening and weakening interparticle interactions. We observe\na significant enhancement in efficiency and power when using a Bose-condensed\nworking fluid, compared to the case of a non-degenerate thermal gas. We\ndemonstrate reversibility, and measure power and efficiency as a function of\nengine parameters including compression ratio and cycle time. Results agree\nquantitatively with interacting finite temperature field-theoretic simulations\nthat closely replicate the length and energy scales of the working fluid.",
        "positive": "Condensate formation with three-component ultracold fermions: We investigate the formation of Bose-Einstein condensation and population\nimbalance in a three-component Fermi superfluid by increasing the U(3)\ninvariant attractive interaction. We consider the system at zero temperature in\nthree dimensions and also in two dimensions. Within the mean-field theory, we\nderive explicit formulas for number densities, gap order parameter, condensate\ndensity and condensate fraction of the uniform system, and analyze them in the\ncrossover from the Bardeen-Cooper-Schrieffer (BCS) state of Cooper pairs to the\nBose-Einstein Condensate (BEC) of strongly-bound molecular dimers. In addition,\nwe study this Fermi mixture trapped by a harmonic potential: we calculate the\ndensity profiles of the three components and the condensate density profile of\nCooper pairs in the BCS-BEC crossover."
    },
    {
        "anchor": "Realization of the Hofstadter Hamiltonian with ultracold atoms in\n  optical lattices: We demonstrate the experimental implementation of an optical lattice that\nallows for the generation of large homogeneous and tunable artificial magnetic\nfields with ultracold atoms. Using laser-assisted tunneling in a tilted optical\npotential we engineer spatially dependent complex tunneling amplitudes. Thereby\natoms hopping in the lattice accumulate a phase shift equivalent to the\nAharonov-Bohm phase of charged particles in a magnetic field. We determine the\nlocal distribution of fluxes through the observation of cyclotron orbits of the\natoms on lattice plaquettes, showing that the system is described by the\nHofstadter model. Furthermore, we show that for two atomic spin states with\nopposite magnetic moments, our system naturally realizes the time-reversal\nsymmetric Hamiltonian underlying the quantum spin Hall effect, i.e., two\ndifferent spin components experience opposite directions of the magnetic field.",
        "positive": "Fragmentation of a spin-1 mixture in a magnetic field: We study the ground state quantum fragmentation in a mixture of a polar\ncondensate and a ferromagnetic condensate when subject to an external magnetic\nfield. We pay more attentions to the polar condensate and find that it will be\nless fragile in the mixture when perturbed by the magnetic field. Both atom\nnumbers and the number fluctuations in the spin-0 component will keep in a high\nmagnitude of order of $N$ when the magnetization of the system is increased.\nThe role of the ferromagnetic condensate is to provide a uniform and stable\nbackground which can delay the rapid shrink of the 0-component population and\nmake it possible to capture the \\textquotedblleft super-fragmentation\n\\textquotedblright. Our method has potential applications in measuring the\ninter-species spin-coupling interaction through adjusting the magnetic field."
    },
    {
        "anchor": "Quantum Monte-Carlo study of the Bose polaron problem in a\n  one-dimensional gas with contact interactions: We present a theoretical study based upon quantum Monte Carlo methods of the\nBose polaron in one-dimensional systems with contact interactions. In this\ninstance of the problem of a single impurity immersed in a quantum bath, the\nmedium is a Lieb-Liniger gas of bosons ranging from the weakly interacting to\nthe Tonks-Girardeau regime, whereas the impurity is coupled to the bath via a\ndifferent contact potential producing both repulsive and attractive\ninteractions. Both the case of a mobile impurity, having the same mass as the\nparticles in the medium, and of a static impurity with infinite mass are\nconsidered. We make use of exact numerical techniques that allow us to\ncalculate the ground-state energy of the impurity, its effective mass as well\nas the contact parameter between the impurity and the bath. These quantities\nare investigated as a function of the strength of interactions between the\nimpurity and the bath and within the bath. In particular, we find that the\neffective mass rapidly increases to very large values when the impurity gets\nstrongly coupled to an otherwise weakly repulsive bath. This heavy impurity\nhardly moves within the medium, thereby realizing the \"self-localization\"\nregime of the Landau-Pekar polaron. Furthermore, we compare our results with\npredictions of perturbation theory valid for weak interactions and with exact\nsolutions available when the bosons in the medium behave as impenetrable\nparticles.",
        "positive": "A Strongly Dipolar Bose-Einstein Condensate of Dysprosium: We report the Bose-Einstein condensation (BEC) of the most magnetic atom,\ndysprosium. The Dy BEC is the first for an open f-shell lanthanide (rare-earth)\nelement and is produced via forced evaporation in a crossed optical dipole trap\nloaded by an unusual, blue-detuned and spin-polarized narrow-line\nmagneto-optical trap. Nearly pure condensates of 1.5x10^4 164Dy atoms form\nbelow T = 30 nK. We observe that stable BEC formation depends on the relative\nangle of a small polarizing magnetic field to the axis of the oblate trap, a\nproperty of trapped condensates only expected in the strongly dipolar regime.\nThis regime was heretofore only attainable in Cr BECs via a Feshbach resonance\naccessed at high magnetic field."
    },
    {
        "anchor": "Generalized Higgs mechanism in long-range interacting quantum systems: The physics of long-range interacting quantum systems is currently living\nthrough a renaissance driven by the fast progress in quantum simulators. In\nthese systems many paradigms of statistical physics do not apply and also the\nuniversal long-wavelength physics gets substantially modified by the presence\nof long-ranged forces. Here we explore the low-energy excitations of several\nlong-range interacting quantum systems, including spin models and interacting\nBose gases, in the ordered phase associated with the spontaneous breaking of\nU(1) and SU(2) symmetries. Instead of the expected Goldstone modes, we find\nthree qualitatively different regimes, depending on the range of the\ninteraction. In one of these regimes the Goldstone modes are gapped, via a\ngeneralization of the Higgs mechanism. Moreover, we show how this effect is\nrealized in current experiments with ultracold atomic gases in optical\ncavities.",
        "positive": "Non-Markovian master equation for quantum transport of fermionic\n  carriers: We propose a simple, yet feasible, model for quantum transport of fermionic\ncarriers across tight-binding chain connecting two reservoirs maintained at\narbitrary temperatures and chemical potentials. The model allows for elementary\nderivation of the master equation for the reduced single particle density\nmatrix in a closed form in both Markov and Born approximations. In the Markov\napproximation the master equation is solved analytically, whereas in the Born\napproximation the problem is reduced to an algebraic equation for the single\nparticle density matric in the Redfield form. The non-Markovian equation is\nshown to lead to resonant transport similar to Landauer's conductance."
    },
    {
        "anchor": "Path integral Monte Carlo determination of the fourth-order virial\n  coefficient for unitary two-component Fermi gas with zero-range interactions: The unitary equal-mass Fermi gas with zero-range interactions constitutes a\nparadigmatic model system that is relevant to atomic, condensed matter,\nnuclear, particle, and astro physics. This work determines the fourth-order\nvirial coefficient $b_4$ of such a strongly-interacting Fermi gas using a\ncustomized \\textit{ab initio} path integral Monte Carlo (PIMC) algorithm. In\ncontrast to earlier theoretical results, which disagreed on the sign and\nmagnitude of $b_4$, our $b_4$ agrees within error bars with the experimentally\ndetermined value, thereby resolving an ongoing literature debate. Utilizing a\ntrap regulator, our PIMC approach determines the fourth-order virial\ncoefficient by directly sampling the partition function. An on-the-fly\nanti-symmetrization avoids the Thomas collapse and, combined with the use of\nthe exact two-body zero-range propagator, establishes an efficient general\nmeans to treat small Fermi systems with zero-range interactions.",
        "positive": "Dissipative cooling of spin chains by a bath of dipolar particles: We consider a spin chain of fermionic atoms in an optical lattice,\ninteracting with each other by super-exchange interactions. We theoretically\ninvestigate the dissipative evolution of the spin chain when it is coupled by\nmagnetic dipole-dipole interaction to a bath consisting of atoms with a strong\nmagnetic moment. Dipolar interactions with the bath allow for a dynamical\nevolution of the collective spin of the spin chain. Starting from an\nuncorrelated thermal sample, we demonstrate that the dissipative cooling\nproduces highly entangled low energy spin states of the chain in a timescale of\na few seconds. In practice, the lowest energy singlet state driven by\nsuper-exchange interactions is efficiently produced. This dissipative approach\nis a promising alternative to cool spin-full atoms in spin-independent\nlattices. It provides direct thermalization of the spin degrees of freedom,\nwhile traditional approaches are plagued by the inherently long timescale\nassociated to the necessary spatial redistribution of spins under the effect of\nsuper-exchange interactions."
    },
    {
        "anchor": "Non Degenerate Dual Atomic Parametric Amplifier: Entangled Atomic Fields: In this paper, we investigate the dynamics of two coupled quantum degenerate\natomic fields (BEC) interacting with two classical optical fields in the\nnonlinear atom optics regime. Two photon interaction produces entangled\natom-atom pairs which exhibit nonclassical correlations. Since the system\ninvolves the creation of two correlated atom pairs, we call it the\nnondegenerate dual atomic parametric amplifier.",
        "positive": "Role of the confinement-induced effective range on the thermodynamics of\n  a strongly correlated Fermi gas in two dimensions: We theoretically investigate the thermodynamic properties of a strongly\ncorrelated two-dimensional Fermi gas with a confinement-induced negative\neffective range of interactions, which is described by a two-channel model\nHamiltonian. By extending the many-body T-matrix approach by Nozi\\`eres and\nSchmitt-Rink to the two-channel model, we calculate the equation of state in\nthe normal phase and present several thermodynamic quantities as functions of\ntemperature, interaction strength, and effective range. We find that there is a\nnon-trivial dependence of thermodynamics on the effective range. In experiment,\nwhere the effective range is set by the tight axial confinement, the\ncontribution of the effective range becomes non-negligible as the temperature\ndecreases down to the degenerate temperature. We compare our finite-range\nresults with recent measurements on the density equation of state, and show\nthat the effective range has to be taken into account for the purpose of a\nquantitative understanding of the experimental data."
    },
    {
        "anchor": "Equation of state for the one-dimensional attractive \u03b4-potential\n  Bose gas in the weak-coupling regime: Approximated formulae for real quasi-momentum and the associated energy\nspectrum are presented for one-dimensional Bose gas with weak attractive\ncontact interactions. On the basis of the energy spectrum, we obtain the\nequation of state in the high temperature region, which is found to be the van\nder Waals equation without volume correction.",
        "positive": "Phase diagrams of Fermi gases in a trap with mass and population\n  imbalances at finite temperature: The pairing and superfluid phenomena in a two-component Fermi gas can be\nstrongly affected by the population and mass imbalances. Here we present phase\ndiagrams of atomic Fermi gases as they undergo BCS--Bose-Einstein condensation\n(BEC) crossover with population and mass imbalances, using a pairing\nfluctuation theory. We focus on the finite temperature and trap effects, with\nan emphasis on the mixture of $^{6}$Li and $^{40}$K atoms. We show that there\nexist exotic types of phase separation in the BEC regime as well as\nsandwich-like shell structures at low temperature with superfluid or\npseudogapped normal state in the central shell in the BCS and unitary regimes,\nespecially when the light species is the majority. Such a sandwich-like shell\nstructure appear when the mass imbalance increases beyond certain threshold.\nOur result is relevant to future experiments on the $^6$Li--$^{40}$K mixture\nand possibly other Fermi-Fermi mixtures."
    },
    {
        "anchor": "Spectral moment sum rules for the retarded Green's function and\n  self-energy of the inhomogeneous Bose-Hubbard model in equilibrium and\n  nonequilibrium: We derive expressions for the zeroth and the first three spectral moment sum\nrules for the retarded Green's function and for the zeroth and the first\nspectral moment sum rules for the retarded self-energy of the inhomogeneous\nBose-Hubbard model in nonequilibrium, when the local on-site repulsion and the\nchemical potential are time-dependent, and in the presence of an external\ntime-dependent electromagnetic field. We also evaluate these moments for\nequilibrium, where all time dependence and external fields vanish. Unlike\nsimilar sum rules for the Fermi-Hubbard model, in the Bose-Hubbard model case,\nthe sum rules often depend on expectation values that cannot be determined\nsimply from parameters in the Hamiltonian like the interaction strength and\nchemical potential, but require knowledge of equal time many-body expectation\nvalues from some other source. We show how one can approximately evaluate these\nexpectation values for the Mott-insulating phase in a systematic\nstrong-coupling expansion in powers of the hopping divided by the interaction.\nWe compare the exact moments to moments of spectral functions calculated from a\nvariety of different approximations and use them to benchmark their accuracy.",
        "positive": "Hydrodynamic Expansion of a Strongly Interacting Fermi-Fermi Mixture: We report on the expansion of a Fermi-Fermi mixture of Li-6 and K-40 atoms\nunder conditions of strong interactions realized near the center of an\ninterspecies Feshbach resonance. We observe two different phenomena of\nhydrodynamic behavior. The first one is the well-known inversion of the aspect\nratio. The second one is a collective expansion, where both species stick\ntogether and despite of their different masses expand jointly. Our work\nconstitutes a first step to explore the intriguing many-body physics of this\nnovel system."
    },
    {
        "anchor": "Efimov energy level rebounding off the atom-dimer continuum: The Efimov effect, with its ladder of weakly bound three-atomic molecules,\nposes intriguing questions in the theoretically controversial and\nexperimentally demanding regime of merging of the first excited Efimov energy\nlevel with the atom-dimer continuum. Using an original experimental technique,\nwhere a coherent superposition state of diatomic and triatomic molecules is\nutilized, we investigate this regime and reveal a striking behavior: Instead of\nmerging with the atom-dimer continuum the trimer energy level rebounds from it\nand becomes a deeper bound state again. In addition, instead of a tangential\napproach between the two levels we observe a rather narrow resonance, providing\na new challenge and guide for few-body theories to incorporate realistic\ninteratomic potentials.",
        "positive": "Matter rogue wave in Bose-Einstein condensates with attractive atomic\n  interaction: We investigate the matter rogue wave in Bose-Einstein Condensates with\nattractive interatomic interaction analytically and numerically. Our results\nshow that the formation of rogue wave is mainly due to the accumulation of\nenergy and atoms toward to its central part; Rogue wave is unstable and the\ndecay rate of the atomic number can be effectively controlled by modulating the\ntrapping frequency of external potential. The numerical simulation demonstrate\nthat even a small periodic perturbation with small modulation frequency can\ninduce the generation of a near-ideal matter rogue wave. We also give an\nexperimental protocol to observe this phenomenon in Bose-Einstein Condensates."
    },
    {
        "anchor": "Observation of scale invariance and universality in two-dimensional Bose\n  gases: The collective behavior of a many-body system near a continuous phase\ntransition is insensitive to the details of its microscopic physics[1].\nCharacteristic features near the phase transition are that the thermodynamic\nobservables follow generalized scaling laws[1]. The\nBerezinskii-Kosterlitz-Thouless (BKT) phase transition[2,3] in two-dimensional\n(2D) Bose gases presents a particularly interesting case because the marginal\ndimensionality and intrinsic scaling symmetry[4] result in a broad fluctuation\nregime which manifests itself in an extended range of universal scaling\nbehavior. Studies on BKT transition in cold atoms have stimulated great\ninterest in recent years[5-10], clear demonstration of a critical behavior near\nthe phase transition, however, has remained an elusive goal. Here we report the\nobservation of a scale-invariant, universal behavior of 2D gases through\nin-situ density and density fluctuation measurements at different temperatures\nand interaction strengths. The extracted thermodynamic functions confirm a wide\nuniversal region near the BKT phase transition, provide a sensitive test to the\nuniversality prediction by classical-field theory[11,12] and quantum Monte\nCarlo (MC) calculations[13], and point toward growing density-density\ncorrelations in the fluctuation region. Our assay raises new perspectives to\nexplore further universal phenomena in the realm of classical and quantum\ncritical physics.",
        "positive": "Glassy Dynamics from Quark Confinement: Atomic Quantum Simulation of\n  Gauge-Higgs Model on Lattice: In the previous works, we proposed atomic quantum simulations of the U(1)\ngauge-Higgs model by ultra-cold Bose gases. By studying extended Bose-Hubbard\nmodels (EBHMs) including long-range repulsions, we clarified the locations of\nthe confinement, Coulomb and Higgs phases. In this paper, we study the EBHM\nwith nearest-neighbor repulsions in one and two dimensions at large fillings by\nthe Gutzwiller variational method. We obtain phase diagrams and investigate\ndynamical behavior of electric flux from the gauge-theoretical point of view.\nWe also study if the system exhibits glassy quantum dynamics in the absence and\npresence of quenched disorder. We explain that the obtained results have a\nnatural interpretation in the gauge theory framework. Our results suggest\nimportant perspective on many-body localization in strongly-correlated systems.\nThey are also closely related to anomalously slow dynamics observed by recent\nexperiments performed on Rydberg atom chain, and our study indicates existence\nof similar phenomenon in two-dimensional space."
    },
    {
        "anchor": "The third virial coefficient of a two-component unitary Fermi gas across\n  an Efimov-effect threshold: We consider a mixture of two single-spin-state fermions with an interaction\nof negligible range and infinite $s$-wave scattering length. By varying the\nmass ratio $\\alpha$ across $\\alpha\\_c\\simeq 13.6069$ one can switch on-and-off\nthe Efimov effect. We determine analytically the third cluster coefficient of\nthe gas. We show that it is a smooth function of $\\alpha$ across $\\alpha\\_c$\nsince, unexpectedly, the three-body parameter characterizing the interaction is\nrelevant even on the non-Efimovian side $\\alpha\\textless{}\\alpha\\_c$.",
        "positive": "Kinetic theory of non-thermal fixed points in a Bose gas: We outline a kinetic theory of non-thermal fixed points for the example of a\ndilute Bose gas, partially reviewing results obtained earlier, thereby\nextending, complementing, generalizing and straightening them out. We study\nuniversal dynamics after a cooling quench, focusing on situations where the\ntime evolution represents a pure rescaling of spatial correlations, with time\ndefining the scale parameter. The non-equilibrium initial condition set by the\nquench induces a redistribution of particles in momentum space. Depending on\nconservation laws, this can take the form of a wave-turbulent flux or of a more\ngeneral self-similar evolution, signaling the critically slowed approach to a\nnon-thermal fixed point. We identify such fixed points using a non-perturbative\nkinetic theory of collective scattering between highly occupied long-wavelength\nmodes. In contrast, a wave-turbulent flux, possible in the perturbative\nBoltzmann regime, builds up in a critically accelerated self-similar manner. A\nkey result is the simple analytical universal scaling form of the\nnon-perturbative many-body scattering matrix, for which we lay out the concrete\nconditions under which it applies. We derive the scaling exponents for the time\nevolution as well as for the power-law tail of the momentum distribution\nfunction, for a general dynamical critical exponent $z$ and an anomalous\nscaling dimension $\\eta$. The approach of the non-thermal fixed point is, in\nparticular, found to involve a rescaling of momenta in time $t$ by $t^{\\beta}$,\nwith $\\beta=1/z$, within our kinetic approach independent of $\\eta$. We confirm\nour analytical predictions by numerically evaluating the kinetic scattering\nintegral as well as the non-perturbative many-body coupling function. As a side\nresult we obtain a possible finite-size interpretation of wave-turbulent\nscaling recently measured by Navon et al."
    },
    {
        "anchor": "Evolution of Coherence During Ramps Across the Mott-Superfluid Phase\n  Boundary: We calculate how correlations in a Bose lattice gas grow during a finite\nspeed ramp from the Mott to the Superfluid regime. We use an interacting\ndoublon-holon model, applying a mean-field approach for implementing hard-core\nconstraints between these degrees of freedom. Our solutions are valid in any\ndimension, and agree with experimental results and with DMRG calculations in\none dimension. We find that the final energy density of the system drops\nquickly with increased ramp time for ramps shorter than one hopping time,\n$J\\tau_{ramp}\\lesssim 1$. For longer ramps, the final energy density depends\nonly weakly on ramp speed. We calculate the effects of inelastic light\nscattering during such ramps.",
        "positive": "Low-energy collective oscillations and Bogoliubov sound in an\n  exciton-polariton condensate: We report the observation of low-energy, low-momenta collective oscillations\nof an excitonpolariton condensate in a round \"box\" trap. The oscillations are\ndominated by the dipole and breathing modes, and the ratio of the frequencies\nof the two modes is consistent with that of a weakly interacting\ntwo-dimensional trapped Bose gas. The speed of sound extracted from the dipole\noscillation frequency is smaller than the Bogoliubov sound, which can be partly\nexplained by the influence of the incoherent reservoir. These results pave the\nway for understanding the effects of reservoir, dissipation, energy relaxation,\nand finite temperature on the superfluid properties of exciton-polariton\ncondensates and other two-dimensional open-dissipative quantum fluids."
    },
    {
        "anchor": "Spontaneous formation of bright solitons in self-localized impurities in\n  Bose-Einstein condensate: We study the formation of bright solitons in the impurity component of\nBose-Einstein condensate (BEC)-impurity mixture by using the time-dependent\nHartree-Fock-Bogoliubov theory. While we assume the boson-boson and\nimpurity-boson interactions to be effectively repulsive, their character can be\nchanged spontaneously from repulsive to attractive in the presence of strong\nanomalous correlations. In such a regime the impurity component becomes a\nsystem of effectively attractive atoms leading automatically to the generation\nof bright solitons. We find that this soliton decays at higher temperatures due\nto the dissipation induced by the impurity-host and host-host interactions. We\nshow that after a sudden increase of the impurity-boson strength a train of\nbright solitons is produced and this can be interpreted in terms of the\nmodulational instability (MI) of the time-dependent impurity wave function.",
        "positive": "Topological Polaritons: The interaction between light and matter can give rise to novel topological\nstates. This principle was recently exemplified in Floquet topological\ninsulators, where \\emph{classical} light was used to induce a topological\nelectronic band structure. Here, in contrast, we show that mixing \\emph{single}\nphotons with excitons can result in new topological polaritonic states --- or\n\"topolaritons\". Taken separately, the underlying photons and excitons are\ntopologically trivial. Combined appropriately, however, they give rise to\nnon-trivial polaritonic bands with chiral edge modes allowing for\nunidirectional polariton propagation. The main ingredient in our construction\nis an exciton-photon coupling with a phase that winds in momentum space. We\ndemonstrate how this winding emerges from spin-orbit coupling in the electronic\nsystem and an applied Zeeman field. We discuss the requirements for obtaining a\nsizable topological gap in the polariton spectrum, and propose practical ways\nto realize topolaritons in semiconductor quantum wells and monolayer transition\nmetal dichalcogenides."
    },
    {
        "anchor": "Dynamics of a Fermi gas quenched to unitarity: We present an experimental study of a two component Fermi gas following an\ninteraction quench into the superfluid phase. Starting with a weakly attractive\ngas in the normal phase, interactions are ramped to unitarity at a range of\nrates and we measure the subsequent dynamics as the gas approaches equilibrium.\nBoth the formation and condensation of fermion pairs are mapped via\nmeasurements of the pair momentum distribution and can take place on very\ndifferent timescales, depending on the adiabaticity of the quench. The contact\nparameter is seen to respond very quickly to changes in the interaction\nstrength, indicating that short-range correlations, based on the occupation of\nhigh-momentum modes, evolve far more rapidly than the correlations in\nlow-momentum modes necessary for pair condensation.",
        "positive": "Variations of the Kibble-Zurek scaling exponents of trapped Bose gases: We study the vortex nucleation dynamics in inhomogeneous atomic Bose gases\nquenched into a superfluid phase and investigate the dependence of the\nKibble-Zurek (KZ) scaling exponent on the underlying trap configuration. For\nsamples in a number of different inhomogeneous traps, we observe the\ncharacteristic power-law scaling of the vortex number with the thermal quench\nrate, as well as an enhanced vortex suppression in the outer regions with lower\nparticle density, in agreement with the causality effect as encapsulated in the\ninhomogeneous Kibble-Zurek mechanism (IKZM). However, the measured KZ scaling\nexponents show significant differences from the theoretical estimates, and\nfurthermore their trends as a function of the underlying trap configuration\ndeviate from the IKZM prediction. We also investigate the early-time coarsening\neffect using a two-step quench protocol as proposed in a recent study and show\nthat the interpretation of the measurement results without including the\ncausality effect might be misleading. This paper provides a comprehensive study\nof vortex formation dynamics in quenched Bose gases confined in inhomogeneous\ntrapping potentials and calls for a refined theoretical framework for\nquantitative understanding of the phase transition and defect formation\nprocesses in such inhomogeneous systems."
    },
    {
        "anchor": "Equatorial Waves in Rotating Bubble-Trapped Superfluids: As the Earth rotates, the Coriolis force causes several oceanic and\natmospheric waves to be trapped along the equator, including Kelvin, Yanai,\nRossby, and Poincar\\'e modes. It has been demonstrated that the mathematical\norigin of these waves is related to the nontrivial topology of the underlying\nhydrodynamic equations. Inspired by recent observations of Bose-Einstein\ncondensation (BEC) in bubble-shaped traps in microgravity ultracold quantum gas\nexperiments, we show that equatorial modes are supported by a rapidly rotating\ncondensate in a spherical geometry. Based on a zero-temperature coarse-grained\nhydrodynamic framework, we reformulate the coupled oscillations of the\nsuperfluid and the Abrikosov vortex lattice resulting from rotation by a\nSchr\\\"odinger-like eigenvalue problem. The obtained non-Hermitian Hamiltonian\nis topologically nontrivial. Furthermore, we solve the hydrodynamic equations\nfor a spherical geometry and find that the rotating superfluid hosts Kelvin,\nYanai, and Poincar\\'e equatorial modes, but not the Rossby mode. Our\npredictions can be tested with state-of-the-art bubble-shaped trapped BEC\nexperiments.",
        "positive": "Adiabatic sweep theorem for three-dimensional dipolar Bose gases: The variational theorem for the scattering length in the presence of the\ndipole-dipole interaction is developed. The theorem is applied to the spinless\ndipolar Bose gas in three dimensions. We calculated analytically the long-range\ntails of the single-particle momentum distribution and static structure factor,\nand the pair distribution function at short distances. The momentum\ndistribution is inversely proportional to $q^4$ with the anisotropic prefactor.\nIn the absence of the dipole-dipole interaction, Tan's adiabatic sweep theorem\nis reproduced as a particular case. For the homogeneous dilute Bose gas, all\nthe relations are calculated analytically."
    },
    {
        "anchor": "Fermi edge polaritons in a highly degenerate 2D electron gas: a\n  diagrammatic theory: We present a theoretical study on polaritons in highly doped semiconductor\nmicrocavities. In particular, we focus on a cavity mode that is resonant with\nthe absorption threshold (`Fermi edge'). In agreement with experimental\nresults, the strong light-matter coupling is maintained under very high doping\nwithin our ladder diagram approximation. While the lower polariton is\nqualitatively unaltered, it acquires a finite lifetime due to relaxation of the\nvalence band hole if the electron density exceeds a certain critical value. On\nthe other hand the upper polariton has a finite lifetime for all densities,\nbecause it lies in the electron-hole continuum where no bound state exists. Our\ncalculations show that a narrow upper polariton quasiparticle still exists as a\nresult from the interplay between light-matter coupling and final state Coulomb\ninteraction.",
        "positive": "Dynamics of an impurity in a one-dimensional lattice: We study the non-equilibrium dynamics of an impurity in an harmonic trap that\nis kicked with a well-defined quasi-momentum, and interacts with a bath of free\nfermions or interacting bosons in a 1D lattice configuration. Using numerical\nand analytical techniques we investigate the full dynamics beyond linear\nresponse, which allows us to quantitatively characterise states of the impurity\nin the bath for different parameter regimes. These vary from a tightly bound\nmolecular state in a strongly interacting limit to a polaron (dressed impurity)\nand a free particle for weak interactions, with composite behaviour in the\nintermediate regime. These dynamics and different parameter regimes should be\nreadily realizable in systems of cold atoms in optical lattices."
    },
    {
        "anchor": "Quantized Topological Response in Trapped Quantum Gases: In this letter, we propose a quantized topological response in trapped 1D\nquantum gases. The experimental protocol for the response requires the\napplication of an instant optical pulse to a half-infinite region in an\nasymptotically harmonic trap and measuring the density distribution. We show\nthat the corresponding linear response is described by a universal quantized\nformula in the thermal dynamical limit, which is invariant under local\ncontinuous deformations of the trapping potential $V$, atom distribution\n$f_\\Lambda$, the spatial envelope of the optical pulse $\\Theta_p$, and the\nmeasurement region $\\Theta_m$. We test the statement by various numerical\nanalysis, the result of which is consistent with the analytical prediction to\nhigh accuracy. We further show that a short but finite optical pulse duration\nonly results in a violation of the quantization near the transition time, which\nsuggests that quantized response could be observed in realistic experiments. We\nalso generalize our results to non-linear quantized topological responses for\natoms in higher dimensional harmonic traps.",
        "positive": "Observation of subdiffusive dynamic scaling in a driven and disordered\n  Bose gas: We explore the dynamics of a tuneable box-trapped Bose gas under strong\nperiodic forcing in the presence of weak disorder. In absence of interparticle\ninteractions, the interplay of the drive and disorder results in an isotropic\nnonthermal momentum distribution that shows subdiffusive dynamic scaling, with\nsublinear energy growth and the universal scaling function captured well by a\ncompressed exponential. We explain that this subdiffusion in momentum space can\nnaturally be understood as a random walk in energy space. We also\nexperimentally show that for increasing interaction strength, the gas behavior\nsmoothly crosses over to wave turbulence characterized by a power-law momentum\ndistribution, which opens new possibilities for systematic studies of the\ninterplay of disorder and interactions in driven quantum systems."
    },
    {
        "anchor": "Soliton Instabilities and Vortex Streets Formation in a Polariton\n  Quantum Fluid: Exciton-polaritons have been shown to be an optimal system in order to\ninvestigate the properties of bosonic quantum fluids. We report here on the\nobservation of dark solitons in the wake of engineered circular obstacles and\ntheir decay into streets of quantized vortices. Our experiments provide a\ntime-resolved access to the polariton phase and density, which allows for a\nquantitative study of instabilities of freely evolving polaritons. The decay of\nsolitons is quantified and identified as an effect of disorder-induced\ntransverse perturbations in the dissipative polariton gas.",
        "positive": "Quantum statistics of bosonic cascades: Bosonic cascades formed by lattices of equidistant energy levels sustaining\nradiative transitions between nearest layers are promising for the generation\nof coherent terahertz radiation. We show how, also for the light emitted by the\ncondensates in the visible range, they introduce new regimes of emission.\nNamely, the quantum statistics of bosonic cascades exhibit super-bunching\nplateaus. This demonstrates further potentialities of bosonic cascade lasers\nfor the engineering of quantum properties of light useful for imaging\napplications."
    },
    {
        "anchor": "Stroboscopic observation of quantum many-body dynamics: Recent experiments have demonstrated single-site resolved observation of cold\natoms in optical lattices. Thus, in the future it may be possible to take\nrepeated snapshots of an interacting quantum many-body system during the course\nof its evolution. Here we address the impact of the resulting Quantum\n(anti-)Zeno physics on the many-body dynamics. We use the time-dependent\ndensity-matrix renormalization group to obtain the time evolution of the full\nmany-body wave function, which is then periodically projected in order to\nsimulate realizations of stroboscopic measurements. For the example of a\none-dimensional lattice of spin-polarized fermions with nearest-neighbor\ninteractions, we find regimes for which many-particle configurations are\nstabilized and destabilized depending on the interaction strength and the time\nbetween observations.",
        "positive": "Nonrelativistic Conformal Invariance in Mesoscopic Two-Dimensional Fermi\n  Gases: Two-dimensional Fermi gases with universal short-range interactions are known\nto exhibit a quantum anomaly, where a classical scale and conformal invariance\nis broken by quantum effects at strong coupling. We argue that in a quasi\ntwo-dimensional geometry, a conformal window remains at weak interactions.\nUsing degenerate perturbation theory, we verify the conformal symmetry by\ncomputing the energy spectrum of mesoscopic particle ensembles in a harmonic\ntrap, which separates into conformal towers formed by so-called primary states\nand their center-of-mass and breathing-mode excitations, the latter having\nexcitation energies at precisely twice the harmonic oscillator energy. In\naddition, using Metropolis importance sampling, we compute the hyperradial\ndistribution function of the many-body wave functions, which are predicted by\nthe conformal symmetry in closed analytical form. The weakly interacting Fermi\ngas constitutes a system where the nonrelativistic conformal symmetry can be\nrevealed using elementary methods, and our results are testable in current\nexperiments on mesoscopic Fermi gases."
    },
    {
        "anchor": "Phase diffusion in a Bose-Einstein condensate of light: We study phase diffusion in a Bose-Einstein condensate of light in a\ndye-filled optical microcavity, i.e., the spreading of the probability\ndistribution for the condensate phase. To observe this phenomenon, we propose\nan interference experiment between the condensed photons and an external laser.\nWe determine the average interference patterns, considering quantum and thermal\nfluctuations as well as dissipative effects due to the dye. Moreover, we show\nthat a representative outcome of individual measurements can be obtained from a\nstochastic equation for the global phase of the condensate.",
        "positive": "Evidence from on-site atom number fluctuations for a quantum\n  Berezinskii-Kosterlitz-Thouless transition in the one-dimensional\n  Bose-Hubbard model: We study the one-dimensional Bose-Hubbard model describing the\nsuperfluid-Mott insulator quantum phase transition of cold atoms in optical\nlattices. We show that derivatives of the variance of the on-site atom number\noccupation, computed with respect to the parameter driving the transition, have\nextrema that are located off the critical point even in the thermodynamic\nlimit. We discuss whether such extrema provide solid evidence of the quantum\nBerezinskii-Kosterlitz-Thouless transition taking place in this system. The\ncalculations are done for systems with the mean number of atoms per lattice\nsite equal to either one or two. They also characterize the nearest-neighbor\ncorrelation function, which is typically discussed in the context of\ntime-of-flight images of cold atoms."
    },
    {
        "anchor": "Condensation of Photons coupled to a Dicke Field in an Optical\n  Microcavity: Motivated by recent experiments reporting Bose-Einstein condensation (BEC) of\nlight coupled to incoherent dye molecules in a microcavity, we show that due to\na dimensionality mismatch between the 2D cavity-photons and the 3D arrangement\nof molecules, the relevant molecular degrees of freedom are collective Dicke\nstates rather than individual excitations. For sufficiently high dye\nconcentration the coupling of the Dicke states with light will dominate over\nlocal decoherence. This system also shows Mott criticality despite the absence\nof an underlying lattice in the limit when all dye molecules become excited.",
        "positive": "Interpreting superfluid spin up through the response of the container: A recipe is presented for interpreting non-invasively the transport processes\nat work during relaxation of a cylindrical, superfluid-filled vessel, after it\nis accelerated impulsively and then allowed to respond to the viscous torque\nexerted by the contained fluid. The recipe exploits a recently published\nanalytic solution for Ekman pumping in a two-component superfluid, which treats\nthe back-reaction self-consistently in arbitrary geometry for the first time.\nThe applicability of the recipe to He II, 3He, 3He-4He mixtures and\nBose-Einstein condensates is assessed, and the effects of turbulence discussed."
    },
    {
        "anchor": "Quasiparticle scattering rate in a strongly polarised Fermi mixture: We analyse the scattering rate of an impurity atom in a Fermi sea as a\nfunction of momentum and temperature in the BCS-BEC crossover. The cross\nsection is calculated using a microscopic multichannel theory for the Feshbach\nresonance scattering, including finite range and medium effects. We show that\npair correlations significantly increase the cross section for strong\ninteractions close to the unitarity regime. These pair correlations give rise\nto a molecule pole of the cross section at negative energy on the BEC side of\nthe resonance, which smoothly evolves into a resonance at positive scattering\nenergy with a non-zero imaginary part on the BCS side. The resonance is the\nanalogue of superfluid pairing for the corresponding population balanced\nsystem. Using Fermi liquid theory, we then show that the low temperature\nscattering rate of the impurity atom is significantly increased due to these\npair correlations for low momenta. We demonstrate that finite range and mass\nimbalance effects are significant for the experimentally relevant\n$^6$Li-$^{40}$K mixture, and we finally discuss how the scattering rate can be\nmeasured using radio-frequency spectroscopy and Bose-Fermi mixtures.",
        "positive": "Quench Dynamics and Hall Response of Interacting Chern Insulators: We study the coherent non-equilibrium dynamics of interacting two-dimensional\nsystems after a quench from a trivial to a topological Chern insulator phase.\nWhile the many-body wavefunction is constrained to remain topologically trivial\nunder local unitary evolution, we find that the Hall response of the system can\ndynamically approach a thermal value of the post-quench Hamiltonian, even\nthough the efficiency of this thermalization process is shown to strongly\ndepend on the microscopic form of the interactions. Quite remarkably, the\neffective temperature of the steady state Hall response can be arbitrarily\ntuned with the quench parameters. Our findings suggest a new way of inducing\nand observing low temperature topological phenomena in interacting ultracold\natomic gases, where the considered quench scenario can be realized in current\nexperimental set-ups."
    },
    {
        "anchor": "Influence of magnetic quantum confined Stark effect on the spin lifetime\n  of indirect excitons: We report on the unusual and counter-intuitive behaviour of spin lifetime of\nexcitons in coupled semiconductor quantum wells (CQWs) in the presence of\nin-plane magnetic field. Instead of conventional acceleration of spin\nrelaxation due to the Larmor precession of electron and hole spins we observe a\nstrong increase of the spin relaxation time at low magnetic fields followed by\nsaturation and decrease at higher fields. We argue that this non-monotonic spin\nrelaxation dynamics is a fingerprint of the magnetic quantum confined Stark\neffect. In the presence of electric field along the CQW growth axis, an applied\nmagnetic field efficiently suppresses the exciton spin coherence, due to\ninhomogeneous broadening of the $g$-factor distribution.",
        "positive": "Dissipative hydrodynamic equation of a ferromagnetic Bose-Einstein\n  condensate: Analogy to magnetization dynamics in conducting ferromagnets: The hydrodynamic equation of a spinor Bose-Einstein condensate (BEC) gives a\nsimple description of spin dynamics in the condensate. We introduce the\nhydrodynamic equation of a ferromagnetic BEC with dissipation originating from\nthe energy dissipation of the condensate. The dissipative hydrodynamic equation\nhas the same form as an extended Landau-Lifshitz-Gilbert (LLG) equation, which\ndescribes the magnetization dynamics of ferromagnets interacting with\nspin-polarized currents. Employing the dissipative hydrodynamic equation, we\ndemonstrate the magnetic domain pattern dynamics of a ferromagnetic BEC in the\npresence and absence of a current of particles, and discuss the effects of the\ncurrent on domain pattern formation. We also discuss the characteristic lengths\nof domain patterns that have domain walls with and without finite\nmagnetization."
    },
    {
        "anchor": "Exploring Vortex Dynamics in the Presence of Dissipation: Analytical and\n  Numerical Results: In this paper, we systematically examine the stability and dynamics of\nvortices under the effect of a phenomenological dissipation used as a\nsimplified model for the inclusion of the effect of finite temperatures in\natomic Bose-Einstein condensates. An advantage of this simplified model is that\nit enables an analytical prediction that can be compared directly (and\nfavorably) to numerical results. We then extend considerations to a case of\nconsiderable recent experimental interest, namely that of a vortex dipole and\nobserve good agreement between theory and numerical computations in both the\nstability properties (eigenvalues of the vortex dipole stationary states) and\nthe dynamical evolution of such configurations.",
        "positive": "Prethermal Floquet Steady States and Instabilities in the Periodically\n  Driven, Weakly Interacting Bose-Hubbard Model: We explore prethermal Floquet steady states and instabilities of the weakly\ninteracting two-dimensional Bose-Hubbard model subject to periodic driving. We\ndevelop a description of the nonequilibrium dynamics, at arbitrary drive\nstrength and frequency, using a weak-coupling conserving approximation. We\nestablish the regimes in which conventional (zero-momentum) and unconventional\n[$(\\pi,\\pi)$-momentum] condensates are stable on intermediate time scales. We\nfind that condensate stability is \\emph{enhanced} by increasing the drive\nstrength, because this decreases the bandwidth of quasiparticle excitations and\nthus impedes resonant absorption and heating. Our results are directly relevant\nto a number of current experiments with ultracold bosons."
    },
    {
        "anchor": "Prethermalization and Persistent Order in the Absence of a Thermal Phase\n  Transition: We numerically study the dynamics after a parameter quench in the\none-dimensional transverse-field Ising model with long-range interactions\n($\\propto 1/r^\\alpha$ with distance $r$), for finite chains and also directly\nin the thermodynamic limit. In nonequilibrium, i.e., before the system settles\ninto a thermal state, we find a long-lived regime that is characterized by a\nprethermal value of the magnetization, which in general differs from its\nthermal value. We find that the ferromagnetic phase is stabilized dynamically:\nas a function of the quench parameter, the prethermal magnetization shows a\ntransition between a symmetry-broken and a symmetric phase, even for those\nvalues of $\\alpha$ for which no finite-temperature transition occurs in\nequilibrium. The dynamical critical point is shifted with respect to the\nequilibrium one, and the shift is found to depend on $\\alpha$ as well as on the\nquench parameters.",
        "positive": "Coupled $\\ell$-wave confinement-induced resonances in cylindrically\n  symmetric waveguides: A semi-analytical approach to atomic waveguide scattering for harmonic\nconfinement is developed taking into account all partial waves. As a\nconsequence $\\ell$-wave confinement-induced resonances are formed being coupled\nto each other due to the confinement. The corresponding resonance condition is\nobtained analytically using the $K$-matrix formalism. Atomic scattering is\ndescribed by transition diagrams which depict all relevant processes the atoms\nundergo during the collision. Our analytical results are compared to\ncorresponding numerical data and show very good agreement."
    },
    {
        "anchor": "Effective self-similar expansion for the Gross-Pitaevskii equation: We consider an effective scaling approach for the free expansion of a\none-dimensional quantum wave packet, consisting in a self-similar evolution to\nbe satisfied on average, i.e. by integrating over the coordinates. A direct\ncomparison with the solution of the Gross-Pitaevskii equation shows that the\neffective scaling reproduces with great accuracy the exact evolution - the\nactual wave function is reproduced with a fidelity close to unity - for\narbitrary values of the interactions. This result represents a proof-of-concept\nof the effectiveness of the scaling ansatz, which has been used in different\nforms in the literature but never compared with the exact evolution.",
        "positive": "Phase separation and hidden vortices induced by spin-orbit coupling in\n  spin-1 Bose-Einstein condensates: We investigate phase separation and hidden vortices in spin-orbit coupled\nferromagnetic BoseEinstein condensates with rotation and Rabi coupling. The\nhidden vortices are invisible in density distribution but are visible in phase\ndistribution, which can carry angular momentum like the ordinary quantized\nvortices. In the absence of the rotation, we observe the phase separation\ninduced by the spin-orbit coupling and determine the entire phase diagram of\nthe existence of phase separation. For the rotation case, in addition to the\nphase separation, we demonstrate particularly that the spin-orbit coupling can\nresult in the hidden vortices and hidden vortex-antivortex pairs. The\ncorresponding entire phase diagrams are determined, depending on the interplay\nof the spin-orbit coupling strength, the rotation frequency, and Rabi\nfrequency, which reveals the critical condition of the occurrence of the hidden\nvortices and vortex-antivortex pairs. The hidden vortices here are proved to be\nlong-lived in the time scale of experiment by the dynamic analysis. These\nfindings not only provide a clear illustration of the phase separation in\nspin-orbit coupled spinor Bose-Einstein condensates, but also open a new\ndirection for investigating the hidden vortices in high-spin quantum system."
    },
    {
        "anchor": "Correlated quantum dynamics of graphene: Phase-space representations are a family of methods for dynamics of both\nbosonic and fermionic systems, that work by mapping the system's density matrix\nto a quasi-probability density and the Liouville-von Neumann equation of the\nHamiltonian to a corresponding density differential equation for the\nprobability. We investigate here the accuracy and the computational efficiency\nof one approximate phase-space representation, called the fermionic Truncated\nWigner Approximation (fTWA), applied to the Fermi-Hubbard model. On a many-body\n2D system, with hopping strength and Coulomb $U$ tuned to represent the\nelectronic structure of graphene, the method is found to be able to capture the\ntime evolution of first-order (site occupation) and second-order (correlation\nfunctions) moments significantly better than the mean-field, Hartree-Fock\nmethod. The fTWA was also compared to results from the exact diagonalization\nmethod for smaller systems, and in general the agreement was found to be good.\nThe fully parallel computational requirement of fTWA scales in the same order\nas the Hartree-Fock method, and the largest system considered here contained\n198 lattice sites.",
        "positive": "Magnetically mediated hole pairing in fermionic ladders of ultracold\n  atoms: Pairing of mobile charge carriers in doped antiferromagnets plays a key role\nin the emergence of unconventional superconductivity. In these strongly\ncorrelated materials, the pairing mechanism is often assumed to be mediated by\nmagnetic correlations, in contrast to phonon-mediated interactions in\nconventional superconductors. A precise understanding of the underlying\nmechanism in real materials is, however, still lacking, and has been driving\nexperimental and theoretical research for the past 40 years. Early theoretical\nstudies established the emergence of binding among dopants in ladder systems,\nwhere idealised theoretical toy models played an instrumental role in the\nelucidation of pairing, despite repulsive interactions. Here, we realise this\nlong-standing theoretical prediction and report on the observation of hole\npairing due to magnetic correlations in a quantum gas microscope setting. By\nengineering doped antiferromagnetic ladders with mixed-dimensional couplings we\nsuppress Pauli blocking of holes at short length scales. This results in a\ndrastic increase in binding energy and decrease in pair size, enabling us to\nobserve pairs of holes predominantly occupying the same rung of the ladder. We\nfind a hole-hole binding energy on the order of the superexchange energy, and,\nupon increased doping, we observe spatial structures in the pair distribution,\nindicating repulsion between bound hole pairs. By engineering a configuration\nin which binding is strongly enhanced, we delineate a novel strategy to\nincrease the critical temperature for superconductivity."
    },
    {
        "anchor": "Crystalline Phases of Laser-Driven Dipolar Bose-Einstein Condensates: Although crystallization is a ubiquitous phenomenon in nature, crystal\nformation and melting still remain fascinating processes with several open\nquestions yet to be addressed. In this work, we study the emergent\ncrystallization of a laser-driven dipolar Bose-Einstein condensate due to the\ninterplay between long-range magnetic and effectively infinite-range\nlight-induced interactions. The competition between these two interactions\nresults in a collective excitation spectrum with two roton minima that\nintroduce two different length scales at which crystalline order can emerge. In\naddition to the formation of regular crystals with simple periodic patterns due\nto the softening of one of the rotons, we find that both rotons can also soften\nsimultaneously, resulting in the formation of exotic, complex periodic or\naperiodic density patterns. We also demonstrate dynamic state-preparation\nschemes for achieving all the found crystalline ground states for\nexperimentally relevant and feasible parameter regimes",
        "positive": "Correlation induced localization of lattice trapped bosons coupled to a\n  Bose-Einstein condensate: We investigate the ground state properties of a lattice trapped bosonic\nsystem coupled to a Lieb-Liniger type gas. Our main goal is the description and\nin depth exploration and analysis of the two-species many-body quantum system\nincluding all relevant correlations beyond the standard mean-field approach. To\nachieve this, we use the Multi-Configuration Time-Dependent Hartree method for\nMixtures (ML-MCTDHX). Increasing the lattice depth and the interspecies\ninteraction strength, the wave function undergoes a transition from an\nuncorrelated to a highly correlated state, which manifests itself in the\nlocalization of the lattice atoms in the latter regime. For small interspecies\ncouplings, we identify the process responsible for this cross-over in a\nsingle-particle-like picture. Moreover, we give a full characterization of the\nwave function's structure in both regimes, using Bloch and Wannier states of\nthe lowest band, and we find an order parameter, which can be exploited as a\ncorresponding experimental signature. To deepen the understanding, we use an\neffective Hamiltonian approach, which introduces an induced interaction and is\nvalid for small interspecies interaction. We finally compare the ansatz of the\neffective Hamiltonian with the results of the ML-MCTDHX simulations."
    },
    {
        "anchor": "Detecting Entrainment in Fermi-Bose Mixtures: We propose an experimental protocol to directly detect the Andreev-Bashkin\neffect (entrainment) in the bulk mixture of a bosonic and fermionic superfluid\nusing a ring geometry. Our protocol involves the interferometric detection of\nthe entrainment-induced phase gradient across a superfluid due to the flow of\nanother in which it is immersed. The choice of ring geometry eliminates\nvariations in the stronger mean-field interaction which can thwart the\ndetection of entrainment in other geometries. A significant enhancement of the\nentrainment phase shift signal is possible, if the dimer-boson scattering\nlength turns out to be large, which can be measured by tuning the interaction\nto the limit of miscibility of the two superfluids. With suggested improvements\nand careful design implementation, one may achieve $\\approx 67$% shift in the\ninterferometer fringes.",
        "positive": "Einstein-Bose condensation of Onsager vortices: We have studied statistical mechanics of a gas of vortices in two dimensions.\nWe introduce a new observable---a condensate fraction of Onsager vortices---to\nquantify the emergence of the vortex condensate. The condensation of Onsager\nvortices is most transparently observed in a single vortex species system and\noccurs due to a competition between solid body rotation (c.f. vortex lattice)\nand potential flow (c.f. multiple quantum vortex state). We propose an\nexperiment to observe the condensation transition of the vortices in such a\nsingle vortex species system."
    },
    {
        "anchor": "Multi-orbital bosons in bipartite optical lattices: We study interacting bosons in a two dimensional bipartite optical lattice.\nBy focusing on the regime where the first three excited bands are nearly\ndegenerate we derive a three orbital tight-binding model which captures the\nmost relevant features of the bandstructure. In addition, we also derive a\ncorresponding generalized Bose-Hubbard model and solve it numerically under\ndifferent situations, both with and without a confining trap. It is especially\nfound that the hybridization between sublattices can strongly influence the\nphase diagrams and in a trap enable even appearances of condensed phases\nintersecting the same Mott insulating plateaus.",
        "positive": "First principles derivation of NLS equation for BEC with cubic and\n  quintic nonlinearities at non zero temperature. Dispersion of linear waves: In this work we presented a derivation of the quantum hydrodynamic equations\nfor neutral bosons. We considered short range interaction between particles.\nThis interaction consist binary interaction $U(\\textbf{r}_{i},\\textbf{r}_{j})$\nand three particle interaction\n$U(\\textbf{r}_{i},\\textbf{r}_{j},\\textbf{r}_{k})$, the last one does not\ninclude binary interaction between particles. From the quantum hydrodynamic\n(QHD) equations for Bose-Einstein condensate we derive nonlinear\nSchr\\\"{o}dinger equation. This equation includes the nonlinearities of third\nand fifth degree. It is at zero temperature. Explicit form of the constant of\nthree-particle interaction was taken. First of all, developed method we used\nfor studying of dispersion of linear waves. Dispersion characteristics of\nlinear waves were compared for the cases. It were of two-particle interaction\nin approximation third order to interaction radius (TOIR) and three-particle\ninteraction, at zero temperature. We consider influence of temperature on\ndispersion of elementary excitations. For this aim we derive a system of QHD\nequations at non-zero temperature. Obtained system of equation is an analog of\nwell-known two-fluid hydrodynamics. Moreover, it is generalization of two-fluid\nhydrodynamics equations due to three-particle interaction. Evident expressions\nof the velocities of the first and second sound via the concentrations of\nsuperfluid and noncondesate components is calculated."
    },
    {
        "anchor": "Miscibility regimes in a $^{23}$Na-$^{39}$K quantum mixture: Effects of miscibility in interacting two-component classical fluids are\nrelevant in a broad range of daily applications. When considering quantum\nsystems, two-component Bose-Einstein condensates provides a well controlled\nplatform where the miscible-immiscible phase transition can be completely\ncharacterized. In homogeneous systems, this phase transition is governed only\nby the competition between intra- and inter-species interactions. However in\nmore conventional experiments dealing with trapped gases, the pressure of the\nconfinement increases the role of the kinetic energy and makes the system more\nmiscible. In the most general case, the miscibility phase diagram of unbalanced\nmixtures of different atomic species is strongly modified by the atom number\nratio and the different gravitational sags. Here, we numerically investigate\nthe ground-state of a $^{23}$Na-$^{39}$K quantum mixture for different\ninteraction strengths and atom number ratios considering realistic experimental\nparameters. Defining the spatial overlap between the resulting atomic clouds,\nwe construct the phase diagram of the miscibility transition which could be\ndirectly measured in real experiments.",
        "positive": "Observation of Zitterbewegung in a spin-orbit coupled Bose-Einstein\n  condensate: Spin-orbit coupled ultra-cold atoms provide an intriguing new avenue for the\nstudy of rich spin dynamics in superfluids. In this Letter, we observe\nZitterbewegung, the simultaneous velocity (thus position) and spin\noscillations, of neutral atoms between two spin-orbit coupled bands in a\nBose-Einstein condensate (BEC) through sudden quantum quenches of the\nHamiltonian. The observed Zitterbewegung oscillations are perfect on a short\ntime scale but gradually damp out on a long time scale, followed by sudden and\nstrong heating of the BEC. As an application, we also demonstrate how\nZitterbewegung oscillations can be exploited to populate the upper spin-orbit\nband, and observe a subsequent dipole motion. Our experimental results are\ncorroborated by a theoretical and numerical analysis and showcase the great\nflexibility that ultra-cold atoms provide for investigating rich spin dynamics\nin superfluids."
    },
    {
        "anchor": "Stable Fractional Vortices in the Cyclic States of Bose-Einstein\n  Condensates: We propose methods to create fractional vortices in the cyclic state of an F\n= 2 spinor Bose-Einstein condensate by manipulating its internal spin structure\nusing pulsed microwave and laser fields. The stability of such vortices is\nstudied as a function of the rotation frequency of the confining harmonic trap\nboth in pancake and cigar shaped condensates. We find a range of parameters for\nwhich the so-called 1/3-vortex state is energetically favorable. Such\nfractional vortices could be created in condensates of 87Rb atoms using current\nexperimental techniques facilitating probing of topological defects with\nnon-Abelian statistics.",
        "positive": "Catastrophes in non-equilibrium many-particle wave functions:\n  universality and critical scaling: As part of the quest to uncover universal features of quantum dynamics, we\nstudy catastrophes that form in simple many-body wave functions after a quench,\nfocusing on two-mode systems that include the two-site Bose Hubbard model, and\nunder some circumstances optomechanical systems and the Dicke model. When the\nwave function is plotted in Fock space plus time certain characteristic\nstructures generically appear that we identify as cusp caustics. In the\nvicinity of such a catastrophe the wave function takes on a universal form\ndescribed by the Pearcey function and obeys scaling relations which depend on\nthe total number of particles $N$. In the thermodynamic limit ($N \\rightarrow\n\\infty$) the cusp becomes singular, but at finite $N$ it is decorated by an\ninterference pattern. This pattern contains an intricate network of\nvortex-antivortex pairs, initiating a theory of topological structures in Fock\nspace. In the case where the quench takes the form of a $\\delta$-kick we show\nhow to analytically map the wave function onto the Pearcey function and hence\nobtain the scaling exponents for the size and position of the cusp, as well as\nthose for the amplitude and characteristic length scales of its interference\npattern."
    },
    {
        "anchor": "Light cone dynamics and reverse Kibble-Zurek mechanism in\n  two-dimensional superfluids following a quantum quench: We study the dynamics of the relative phase of a bilayer of two-dimensional\nsuperfluids after the two superfluids have been decoupled. We find that on\nshort time scales the relative phase shows \"light cone\" like dynamics and\ncreates a metastable superfluid state, which can be supercritical. We also\ndemonstrate similar light cone dynamics for the transverse field Ising model.\nOn longer time scales the supercritical state relaxes to a disordered state due\nto dynamical vortex unbinding. This scenario of dynamically suppressed vortex\nproliferation constitutes a reverse-Kibble-Zurek effect. We study this effect\nboth numerically using truncated Wigner approximation and analytically within a\nnewly suggested time dependent renormalization group approach (RG). In\nparticular, within RG we show that there are two possible fixed points for the\nreal time evolution corresponding to the superfluid and normal steady states.\nSo depending on the initial conditions and the microscopic parameters of the\nHamiltonian the system undergoes a non-equilibrium phase transition of the\nKosterlitz-Thouless type. The time scales for the vortex unbinding near the\ncritical point are exponentially divergent, similar to the equilibrium case.",
        "positive": "Spin waves in a spin-1 Bose gas: We present a theory of spin waves in a non-condensed gas of spin-1 bosons:\nproviding both analytic calculations of the linear theory, and full numerical\nsimulations of the nonlinear response. We highlight the role of spin-dependent\ncontact interactions in the dynamics of a thermal gas. Although these\ninteractions are small compared to the thermal energy, they set the scale for\nlow energy long wavelength spin waves. In particular, we find that the polar\nstate of Rb-87 is unstable to collisional mixing of magnetic sublevels even in\nthe normal state. We augment our analytic calculations by providing full\nnumerical simulations of a trapped gas, explicitly demonstrating this\ninstability. Further we show that for strong enough anti-ferromagnetic\ninteractions, the polar gas is unstable. Finally we explore coherent population\ndynamics in a collisionless transversely polarized gas."
    },
    {
        "anchor": "Thermodynamic Properties of Rashba Spin-Orbit-Coupled Fermi Gas: We investigate the thermodynamic properties of a superfluid Fermi gas subject\nto Rashba spin-orbit coupling and effective Zeeman field. We adopt a T-matrix\nscheme that takes beyond-mean-field effects, which are important for strongly\ninteracting systems, into account. We focus on the calculation of two important\nquantities: the superfluid transition temperature and the isothermal\ncompressibility. Our calculation shows very distinct influences of the\nout-of-plane and the in-plane Zeeman fields on the Fermi gas. We also confirm\nthat the in-plane Zeeman field induces a Fulde-Ferrell superfluid below the\ncritical temperature and an exotic finite-momentum pseudo-gap phase above the\ncritical temperature.",
        "positive": "Vortex reconnections and rebounds in trapped atomic Bose--Einstein\n  condensates: Reconnections and interactions of filamentary coherent structures play a\nfundamental role in the dynamics of fluids, plasmas and nematic liquid\ncrystals. In fluids, vortex reconnections redistribute energy and helicity\namong the length scales and induce fine-scale turbulent mixing. Unlike ordinary\nfluids where vorticity is a continuous field, in quantum fluids vorticity is\nconcentrated into discrete (quantized) vortex lines turning vortex\nreconnections into isolated events, making it conceptually easier to study.\nHere we report experimental and numerical observations of three-dimensional\nquantum vortex interactions in a cigar-shaped atomic Bose-Einstein Condensate\n(BEC). In addition to standard reconnections, already numerically and\nexperimentally observed in homogeneous systems away from boundaries, we show\nthat double reconnections, rebounds and ejections can also occur as a\nconsequence of the non-homogeneous, confined nature of the system."
    },
    {
        "anchor": "Floquet analysis of a quantum system with modulated periodic driving: We consider a quantum system periodically driven with a strength which varies\nslowly on the scale of the driving period. The analysis is based on a general\nformulation of the Floquet theory relying on the extended Hilbert space. It is\nshown that the dynamics of the system can be described in terms of a slowly\nvarying effective Floquet Hamiltonian that captures the long-term evolution, as\nwell as rapidly oscillating micromotion operators. We obtain a systematic\nhigh-frequency expansion of all these operators. Generalizing the previous\nstudies, the expanded effective Hamiltonian is now time-dependent and contains\nextra terms appearing due to changes in the periodic driving. The same applies\nto the micromotion operators which exhibit a slow temporal dependence in\naddition to the rapid oscillations. As an illustration, we consider a\nquantum-mechanical spin in an oscillating magnetic field with a slowly changing\ndirection. The effective evolution of the spin is then associated with\nnon-Abelian geometric phases reflecting the geometry of the extended Floquet\nspace. The developed formalism is general and also applies to other\nperiodically driven systems, such as shaken optical lattices with a\ntime-dependent shaking strength, a situation relevant to the cold atom\nexperiments.",
        "positive": "Topological States with Broken Translational and Time-Reversal\n  Symmetries in a Honeycomb-Triangular Lattice: We study fermions in a lattice, with on-site and nearest neighbor attractive\ninteractions between two spin species. We consider two geometries: both spins\nin a triangular lattice, and a mixed geometry with up-spins in honeycomb and\ndown-spins in triangular lattices. We focus on the interplay between\nspin-population imbalance, on-site and valence bond pairing, and order\nparameter symmetry. The mixed geometry leads to a rich phase diagram of\ntopologically non-trivial phases. In both geometries, we predict order\nparameters with simultaneous time-reversal and translational symmetry breaking."
    },
    {
        "anchor": "Spatiotemporal Binary Interaction and Designer quasi particle\n  condensates: We introduce a new integrable model to investigate the dynamics of two\ncomponent quasi particle condensates with spatio temporal interaction\nstrengths. We derive the associated Lax-pair of the coupled GP equation and\nconstruct matter wave solitons. We show that the spatio temporal binary\ninteraction strengths not only facilitate the stabilization of the condensates,\nbut also enables one to fabricate condensates with desirable densities,\ngeometries and properties leading to the so called \"designer quasi particle\ncondensates\".",
        "positive": "Enlarging and cooling the N\u00e9el state in an optical lattice: We propose an experimental scheme to favor both the realization and the\ndetection of the N\\'eel state in a two-component gas of ultracold fermions in a\nthree-dimensional simple-cubic optical lattice. By adding three compensating\nGaussian laser beams to the standard three pairs of retroreflected lattice\nbeams, and adjusting the relative waists and intensities of the beams, one can\nsignificantly enhance the size of the N\\'eel state in the trap, thus increasing\nthe signal of optical Bragg scattering. Furthermore, the additional beams\nprovide for adjustment of the local chemical potential and the possibility to\nevaporatively cool the gas while in the lattice. Our proposals are relevant to\nother attempts to realize many-body quantum phases in optical lattices."
    },
    {
        "anchor": "Hubbard-Stratonovich Transformation: Successes, Failure, and Cure: We recall the successes of the Hubbard-Stratonovich Transformation (HST) of\nmany-body theory, point out its failure to cope with competing channels of\ncollective phenomena and show how to overcome this by Variational Perturbation\nTheory. That yields exponentially fast converging results, thanks to the help\nof a variety of {\\it collective classical fields}, rather than a fluctuating\n{\\it collective quantum field} as suggested by the HST.",
        "positive": "Breakdown of Anderson localization in the transport of Bose-Einstein\n  condensates through one-dimensional disordered potentials: We study the transport of an interacting Bose--Einstein condensate through a\n1D correlated disorder potential. We use for this purpose the truncated Wigner\nmethod, which is, as we show, corresponding to the diagonal approximation of a\nsemiclassical van Vleck-Gutzwiller representation of this many-body transport\nprocess. We also argue that semiclassical corrections beyond this diagonal\napproximation are vanishing under disorder average, thus confirming the\nvalidity of the truncated Wigner method in this context. Numerical calculations\nshow that, while for weak atom-atom interaction strength Anderson localization\nis preserved with a slight modification of the localization length, for larger\ninteraction strenghts a crossover to a delocalized regime exists due to\ninelastic scattering. In this case, the transport is fully incoherent."
    },
    {
        "anchor": "Droplet under confinement: Competition and coexistence with soliton\n  bound state: We study the stability of quantum droplet and its associated phase\ntransitions in ultracold Bose-Bose mixtures uniformly confined in\nquasi-two-dimension. We show that the confinement-induced boundary effect can\nbe significant when increasing the atom number or reducing the confinement\nlength, which destabilizes the quantum droplet towards the formation of a\nsoliton bound state. In particular, as increasing the atom number we find the\nreentrance of soliton ground state, while the droplet is stabilized only within\na finite number window that sensitively depends on the confinement length. Near\nthe droplet-soliton transitions, they can coexist with each other as two local\nminima in the energy landscape. Take the two-species $^{39}$K bosons for\ninstance, we have mapped out the phase diagram for droplet-soliton transition\nand coexistence in terms of atom number and confinement length. The revealed\nintriguing competition between quantum droplet and soliton under confinement\ncan be readily probed in current cold atoms experiments.",
        "positive": "Dipole excitons in coupled quantum wells: toward an equilibrium exciton\n  condensate: In recent years, experiments by several groups have demonstrated spontaneous\ncoherence in polariton systems, which can be viewed as a type of nonequilibrium\nBose-Einstein condensation. In these systems, the polariton lifetime is longer\nthan, but not much longer than, the polariton-polariton scattering time which\nleads to the thermalization. By contrast, over the past twenty years several\ngroups have pursued experiments in a different system, which has very long\nexciton lifetime, up to 30 microseconds or more, essentially infinite compared\nto the thermalization time of the excitons. Thermal equilibrium of this type of\nexciton in a trap has been demonstrated experimentally. In this system, the\ninteractions between the excitons are not short-range contact interactions, but\ninstead are dipole-dipole interactions, with the force at long range going as\n$1/r^{3}$. Up to now there has not been a universally accepted demonstration of\nBEC in this type of system, and the way forward will require better\nunderstanding of the many-body effects of the excitons. I review what has been\nlearned and accomplished in the past two decades in the search for an\nequilibrium BEC in this promising system."
    },
    {
        "anchor": "Variable Potentials for Thermalized Light and Coupled Condensates: For over a decade, cold atoms in lattice potentials have been an attractive\nplatform to simulate phenomena known from solid state theory, as the\nMott-insulator transition. In contrast, the field of photonics usually deals\nwith non-equilibrium physics. Recent advances towards photonic simulators of\nsolid state equilibrium effects include polariton double-site and lattice\nexperiments, as well as the demonstration of a photon condensate in a\ndye-filled microcavity. Here we demonstrate a technique to create variable\nmicropotentials for light using thermo-optic imprinting within an\nultrahigh-reflectivity mirror microcavity filled with a dye-polymer solution\nthat is compatible with photon gas thermalization. By repeated\nabsorption-emission cycles photons thermalize to the temperature of the dye\nsolution, and in a single microsite we observe a photon Bose-Einstein\nmicrocondensate. Effective interactions between the otherwise nearly\nnon-interacting photons are observed due to thermo-optic effects, and in a\ndouble-well system tunnel coupling between sites is demonstrated, as well as\nthe hybridization of eigenstates. Prospects of the new experimental platform\ninclude photonic structures in which photons thermalize into entangled manybody\nstates.",
        "positive": "Josephson junction dynamics in a two-dimensional ultracold Bose gas: We investigate the Berezinskii-Kosterlitz-Thouless (BKT) scaling of the\ncritical current of Josephson junction dynamics across a barrier potential in a\ntwo-dimensional (2D) Bose gas, motivated by recent experiments by Luick\n\\textit{et al.} arXiv:1908.09776. Using classical-field dynamics, we determine\nthe dynamical regimes of this system, as a function of temperature and barrier\nheight. As a central observable we determine the current-phase relation, as a\ndefining property of these regimes. In addition to the ideal junction regime,\nwe find a multimode regime, a second-harmonic regime, and an overdamped regime.\nFor the ideal junction regime, we derive an analytical estimate for the\ncritical current, which predicts the BKT scaling. We demonstrate this scaling\nbehavior numerically for varying system sizes. The estimates of the critical\ncurrent show excellent agreement with the numerical simulations and the\nexperiments. Furthermore, we show the damping of the supercurrent due to phonon\nexcitations in the bulk, and the nucleation of vortex-antivortex pairs in the\njunction."
    },
    {
        "anchor": "Singlet and triplet BCS pairs in a gas of two-species fermionic polar\n  molecules: We investigate the BCS pairing in a mixture of fermionic polar molecules with\ntwo different hyperfine states. We derive a set of coupled gap equations and\nfind that this system supports both spin-singlet and -triplet BCS pairs. We\nalso calculate the critical temperatures and the angular dependence of order\nparameters. In addition, by tuning short-range interaction between\ninter-species molecules, the transition between singlet and triplet paired\nstates may be realized.",
        "positive": "Quantum Membrane Phases in Synthetic Lattices of Cold Molecules or\n  Rydberg Atoms: We calculate properties of dipolar interacting ultracold molecules or Rydberg\natoms in a semi-synthetic three-dimensional configuration -- one synthetic\ndimension plus a two-dimensional real space optical lattice or periodic\nmicrotrap array -- using the stochastic Green function Quantum Monte Carlo\nmethod. Through a calculation of thermodynamic quantities and appropriate\ncorrelation functions, along with their finite size scalings, we show that\nthere is a second order transition to a low temperature phase in which\ntwo-dimensional `sheets' form in the synthetic dimension of internal rotational\nor electronic states of the molecules or Rydberg atoms, respectively.\nSimulations for different values of the interaction $V$, which acts between\natoms or molecules that are adjacent both in real and synthetic space, allow us\nto compute a phase diagram. We find a finite-temperature transition at\nsufficiently large $V$, as well as a quantum phase transition -- a critical\nvalue $V_c$ below which the transition temperature vanishes."
    },
    {
        "anchor": "Strongly interacting two-dimensional Fermi gases: We review the current understanding of the uniform two-dimensional (2D) Fermi\ngas with short-range interactions. We first outline the basics of two-body\nscattering in 2D, including a discussion of how such a 2D system may be\nrealized in practice using an anisotropic confining potential. We then discuss\nthe thermodynamic and dynamical properties of 2D Fermi gases, which cold-atom\nexperiments have only just begun to explore. Of particular interest are the\ndifferent pairing regimes as the interparticle attraction is varied; the\nsuperfluid transition and associated finite-temperature phenomenology; few-body\nproperties and their impact on the many-body system; the Fermi polaron problem;\nand the symmetries underlying the collective modes. Where possible, we include\nthe contributions from 2D experiment. An underlying theme throughout is the\neffect of the quasi-2D geometry, which we view as an added richness to the\nproblem rather than an unwanted complication.",
        "positive": "Angular Stripe Phase in Spin-Orbital-Angular-Momentum Coupled Bose\n  Condensates: We propose that novel superfluid with supersolid-like properties - angular\nstripe phase - can be realized in a pancake-like spin-1/2 Bose gas with\nspin-orbital-angular-momentum coupling. We predict a rich ground-state phase\ndiagram, including the vortex-antivortex pair phase, half-skyrmion phase, and\ntwo different angular stripe phases. The stripe phases feature modulated\nangular density-density correlation with sizable contrast and can occupy a\nrelatively large parameter space. The low-lying collective excitations, such as\nthe dipole and breathing modes, show distinct behaviors in different phases.\nThe existence of the novel stripe phase is also clearly indicated in the\nenergetic and dynamic instabilities of collective modes near phase transitions.\nOur predictions of the angular stripe phase could be readily examined in\ncurrent cold-atom experiments with $^{87}$Rb and $^{41}$K."
    },
    {
        "anchor": "Spin diffusion of lattice fermions in one dimension: We study long-time spin diffusion of harmonically trapped lattice fermions in\none dimension. Combining thermodynamic Bethe ansatz approach and local density\napproximation, we calculate spin current and spin diffusion coefficient driven\nby the population imbalance. We find spin current is driven by susceptibility\neffects rather than typical diffusion where magnetization would transport from\nregions of high magnetization to low. As expected, spin transport is zero\nthrough insulating regions and are only present in the metallic regions. In the\nweak coupling limit, the local spin diffusion coefficient shows maxima at all\nthe insulating regions. Further, we estimate damping rate of diffusion modes in\nthe weak coupling limit within the lower metallic portion of the cloud. The\npredicted spin current pattern can be probed via currently available\nexperimental techniques.",
        "positive": "Bose-Einstein condensation into non-equilibrium states studied by\n  condensate focusing: We report the formation of Bose-Einstein condensates into non-equilibrium\nstates. Our condensates are much longer than equilibrium condensates with the\nsame number of atoms, show strong phase fluctuations, and have a dynamical\nevolution similar to that of quadrupole shape oscillations of regular\ncondensates. The condensates emerge in elongated traps as the result of local\nthermalization when the nucleation time is short compared to the axial\noscillation time. We introduce condensate focusing as a powerful method to\nextract the phase-coherence length of Bose-Einstein condensates."
    },
    {
        "anchor": "Vortex line in the unitary Fermi gas: We report diffusion Monte Carlo results for the ground state of unpolarized\nspin-1/2 fermions in a cylindrical container and properties of the system with\na vortex-line excitation. The density profile of the system with a vortex line\npresents a non-zero density at the core. We calculate the ground-state energy\nper particle, the superfluid pairing gap, and the excitation energy per\nparticle. These simulations can be extended to calculate the properties of\nvortex excitations in other strongly interacting systems, such as superfluid\nneutron matter using realistic nuclear Hamiltonians.",
        "positive": "Resummation of infrared divergencies in the theory of atomic Bose gases: We present a general strong-coupling approach for the description of an\natomic Bose gas beyond the Bogoliubov approximation, when infrared divergences\nstart to occur that need to be resummed exactly. We consider the determination\nof several important physical properties of the Bose gas, namely the chemical\npotential, the contact, the speed of sound, the condensate density, the\neffective interatomic interaction and the three-body recombination rate. It is\nshown how the approach can be systematically improved with\nrenormalization-group methods and how it reduces to the Bogoliubov theory in\nthe weak-coupling limit."
    },
    {
        "anchor": "Reentrant phase behavior in systems with density-induced tunneling: Open many body quantum systems play a paramount role in various branches of\nphysics, such as quantum information, nonlinear optics or condensed matter. The\ndissipative character of open systems has gained a lot of interest especially\nwithin the fields of quantum optics, due to unprecedented stabilization of\nquantum coherence, and quantum information, with its desire to control\nenvironmental degrees of freedom. We look beyond the typical mechanism of\ndissipation associated with an external source and show that strongly\ninteracting many particle systems can create quantum decoherence within\nthemselves. We study a quantum bosonic two-dimensional many body system with\nextended interactions between particles. Analytical calculations show that the\nsystem can be driven out of its coherent state, which is prevalent among\ncommonly used setups. However, we also observe a revival of the superfluid\nphase within the same framework for sufficiently large interaction strength.\nThe breakdown of quantum coherence is inevitable, but can be misinterpreted if\none assumes improper coupling between the constituents of the many particle\nsystem. We show an adequate path to retrieve physically relevant results and\nconsider its limitations. The system displays a natural cutoff that enforces\nthe breakdown of superfluidity.",
        "positive": "Anomalous charge pumping in a one-dimensional optical superlattice: We model atomic motion in a sliding superlattice potential to explore\ntopological \"charge pumping\" and to find optimal parameters for experimental\nobservation of this phenomenon. We analytically study the band-structure,\nfinding how the Wannier states evolve as two sinusoidal lattices are moved\nrelative to one-another, and relate this evolution to the center of mass motion\nof an atomic cloud. We pay particular attention to counterintuitive or\nanomalous regimes, such as when the atomic motion is opposite to that of the\nlattice."
    },
    {
        "anchor": "Kinetic Theory for Interacting Luttinger Liquids: We derive a closed set of equations for the kinetics and non-equilibrium\ndynamics of interacting Luttinger Liquids with cubic resonant interactions. In\nthe presence of these interactions, the Luttinger phonons become dressed but\nstill well defined quasi-particles, characterized by a life-time much larger\nthen the inverse energy. This enables the separation of forward time dynamics\nand relative time dynamics into slow and fast dynamics and justifies the\nso-called Wigner approximation, which can be seen as a \"local-time\napproximation\" for the relative dynamics. Applying field theoretical methods in\nthe Keldysh framework, i.e. kinetic and Dyson-Schwinger equations, we derive a\nclosed set of dynamic equations, describing the kinetics of normal and\nanomalous phonon densities, the phonon self-energy and vertex corrections for\nan arbitrary non-equilibrium initial state. In the limit of low phonon\ndensities, the results from self-consistent Born approximation are recaptured,\nincluding Andreev's scaling solution for the quasi-particle life-time in a\nthermal state. As an application, we compute the relaxation of an excited state\nto its thermal equilibrium. \\red{ While the intermediate time dynamics displays\nexponentially fast relaxation, the last stages of thermalization are governed\nby algebraic laws. This can be traced back to the importance of energy and\nmomentum conservation at the longest times, which gives rise to dynamical slow\nmodes.",
        "positive": "Scaling of noise correlations in one-dimensional-lattice-hard-core-boson\n  systems: Noise correlations are studied for systems of hard-core bosons in\none-dimensional lattices. We use an exact numerical approach based on the\nBose-Fermi mapping and properties of Slater determinants. We focus on the\nscaling of the noise correlations with system size in superfluid and insulating\nphases, which are generated in the homogeneous lattice, with period-two\nsuperlattices and with uniformly distributed random diagonal disorder. For the\nsuperfluid phases, the leading contribution is shown to exhibit a\ndensity-independent scaling proportional to the system size, while the first\nsubleading term exhibits a density-dependent power-law exponent."
    },
    {
        "anchor": "BCS-BEC crossover in spin-orbit coupled two-dimensional Fermi gases: The recent experimental realization of spin-orbit coupling for ultra-cold\natoms has generated much interest in the physics of spin-orbit coupled\ndegenerate Fermi gases. Although recently the BCS-BEC crossover in\nthree-dimensional (3D) spin-orbit coupled Fermi gases has been intensively\nstudied, the corresponding two-dimensional (2D) crossover physics has remained\nunexplored. In this paper, we investigate, both numerically and analytically,\nthe BCS-BEC crossover physics in 2D degenerate Fermi gases in the presence of a\nRashba type of spin-orbit coupling. We derive the mean field gap and atom\nnumber equations suitable for the 2D spin-orbit coupled Fermi gases and solve\nthem numerically and self-consistently, from which the dependence of the ground\nstate properties (chemical potential, superfluid pairing gap, ground state\nenergy per atom) on the system parameters (e.g., binding energy, spin-orbit\ncoupling strength) is obtained. Furthermore, we derive analytic expressions for\nthese ground state quantities, which agree well with our numerical results\nwithin a broad parameter region. Such analytic expressions also agree\nqualitatively with previous numerical results for the 3D spin-orbit coupled\nFermi gases, where analytic results are lacked. We show that with an increasing\nSOC strength, the chemical potential is shifted by a constant determined by the\nSOC strength. The superfluid pairing gap is enhanced significantly in the BCS\nlimit for strong SOC, but only increases slightly in the BEC limit.",
        "positive": "A two-band Bose-Hubbard model for many-body resonant tunneling in the\n  Wannier-Stark system: We study an experimentally realizable paradigm of complex many-body quantum\nsystems, a two-band Wannier-Stark model, for which diffusion in Hilbert space\nas well as many-body Landau-Zener processes can be engineered. A cross-over\nbetween regular to quantum chaotic spectra is found within the many-body\navoided crossings at resonant tunneling conditions. The spectral properties are\nshown to determine the evolution of states across a cascade of Landau-Zener\nevents. We apply the obtained spectral information to study the non-equilibrium\ndynamics of our many-body system in different parameter regimes."
    },
    {
        "anchor": "Excitation spectrum of a two-component Bose-Einstein condensate in a\n  ring potential: A mixture of two distinguishable Bose-Einstein condensates confined in a ring\npotential has numerous interesting properties under rotational and\nsolitary-wave excitation. The lowest-energy states for a fixed angular momentum\ncoincide with a family of solitary-wave solutions. In the limit of weak\ninteractions, exact diagonalization of the many-body Hamiltonian is possible\nand permits evaluation of the complete excitation spectrum of the system.",
        "positive": "Ground State Geometry of Binary Condensates in Axisymmetric Traps: We show that the ground state interface geometry of binary condensates in the\nphase separated regime undergoes a smooth transition from planar to ellipsoidal\nto cylindrical geometry. This occurs for condensates with repulsive\ninteractions as the trapping potential is changed from prolate to oblate. The\ncorrect ground state geometry emerges when the interface energy is included in\nthe energy minimization. Where as energy minimization based on Thomas-Fermi\napproximation gives incorrect geometry."
    },
    {
        "anchor": "Rydberg dressing: Understanding of collective many-body effects and\n  implications for experiments: The strong interaction between Rydberg atoms can be used to control the\nstrength and character of the interatomic interaction in ultracold gases by\nweakly dressing the atoms with a Rydberg state. Elaborate theoretical proposals\nfor the realization of various complex phases and applications in quantum\nsimulation exist. Also a simple model has been already developed that describes\nthe basic idea of Rydberg dressing in a two-atom basis. However, an\nexperimental realization has been elusive so far. We present a model describing\nthe ground state of a Bose-Einstein condensate dressed with a Rydberg level\nbased on the Rydberg blockade. This approach provides an intuitive\nunderstanding of the transition from pure twobody interaction to a regime of\ncollective interactions. Furthermore it enables us to calculate the deformation\nof a three-dimensional sample under realistic experimental conditions in\nmean-field approximation. We compare full three-dimensional numerical\ncalculations of the ground state to an analytic expression obtained within\nThomas-Fermi approximation. Finally we discuss limitations and problems arising\nin an experimental realization of Rydberg dressing based on our experimental\nresults. Our work enables the reader to straight forwardly estimate the\nexperimental feasibility of Rydberg dressing in realistic three-dimensional\natomic samples.",
        "positive": "Shock waves in colliding Fermi gases at finite temperature: We study the formation and the dynamics of a shock wave originating from the\ncollision between two ultracold clouds of strongly interacting fermions as\nobserved at a lower temperature in an experiment by Joseph et al. [Phys. Rev.\nLett. 106, 150401 (2011)]. We use the Boltzmann equation within the\ntest-particle method to describe the evolution of the system in the normal\nphase. We also show a direct comparison with the hydrodynamic approach and\ninsist on the necessity of including a shear viscosity and a thermal\nconductivity term in the equations to prevent unphysical behavior from taking\nplace."
    },
    {
        "anchor": "Molecule and polaron in a highly polarized two-dimensional Fermi gas\n  with spin-orbit coupling: We show that spin-orbit coupling (SOC) gives rise to pairing instability in a\nhighly polarized two-dimensional Fermi gas for arbitrary interaction strength.\nThe pairing instability can lead to a Fulde-Ferrell-Larkin-Ovchinnikov-like\nmolecular state, which undergoes a first-order transition into a pairing state\nwith zero center-of-mass momentum as the parameters are tuned. These pairing\nstates are metastable against a polaron state dressed by particle-hole\nfluctuations for small SOC. At large SOC, a polaron-molecule transition exists,\nwhich suggests a phase transition between the topological superfluid state and\nthe normal state for a highly polarized Fermi gas in the thermodynamic limit.\nAs polarization in a Fermi gas with SOC is induced by the effective Zeeman\nfield, we also discuss the influences of the effective Zeeman field on the\nground state of the system. Our findings may be tested directly in future\nexperiments.",
        "positive": "Finite-density corrections to the Unitary Fermi gas: A lattice\n  perspective from Dynamical Mean-Field Theory: We investigate the approach to the universal regime of the dilute unitary\nFermi gas as the density is reduced to zero in a lattice model. To this end we\nstudy the chemical potential, superfluid order parameter and internal energy of\nthe attractive Hubbard model in three different lattices with densities of\nstates (DOS) which share the same low-energy behavior of fermions in\nthree-dimensional free space: a cubic lattice, a \"Bethe lattice\" with a\nsemicircular DOS, and a \"lattice gas\" with parabolic dispersion and a sharp\nenergy cut-off that ensures the normalization of the DOS. The model is solved\nusing Dynamical Mean-Field Theory, that treats directly the thermodynamic limit\nand arbitrarily low densities, eliminating finite-size effects. At densities of\nthe order of one fermion per site the lattice and its specific form dominate\nthe results. The evolution to the low-density limit is smooth and it does not\nallow to define an unambiguous low-density regime. Such finite-density effects\nare significantly reduced using the lattice gas, and they are maximal for the\nthree-dimensional cubic lattice. Even though dynamical mean-field theory is\nbound to reduce to the more standard static mean field in the limit of zero\ndensity due to the local nature of the self-energy and of the vertex functions,\nit compares well with accurate Monte Carlo simulations down to the lowest\ndensities accessible to the latter."
    },
    {
        "anchor": "The phase diagram of 2D polar condensates in a magnetic field: Spin one condensates in the polar (antiferromagnetic) phase in two dimensions\nare shown to undergo a transition of the Ising type, in addition to the\nexpected Kosterlitz--Thouless (KT) transition of half vortices, due to the\nquadratic Zeeman effect. We establish the phase diagram in terms of temperature\nand the strength of the Zeeman effect using Monte Carlo simulations. When the\nZeeman effect is sufficiently strong the Ising and KT transitions merge. For\nvery strong Zeeman field the remaining transition is of the familiar integer KT\ntype.",
        "positive": "Reference data for phase diagrams of triangular and hexagonal bosonic\n  lattices: We investigate systems of bosonic particles at zero temperature in triangular\nand hexagonal optical lattice potentials in the framework of the Bose-Hubbard\nmodel. Employing the process-chain approach, we obtain accurate values for the\nboundaries between the Mott insulating phase and the superfluid phase. These\nresults can serve as reference data for both other approximation schemes and\nupcoming experiments. Since arbitrary integer filling factors g are amenable to\nour technique, we are able to monitor the behavior of the critical hopping\nparameters with increasing filling. We also demonstrate that the g-dependence\nof these exact parameters is described almost perfectly by a scaling relation\ninferred from the mean-field approximation."
    },
    {
        "anchor": "Swallowtail Band Structure of the Superfluid Fermi Gas in an Optical\n  Lattice: We investigate the energy band structure of the superfluid flow of ultracold\ndilute Fermi gases in a one-dimensional optical lattice along the BCS to BEC\ncrossover within a mean-field approach. In each side of the crossover region, a\nloop structure (swallowtail) appears in the Bloch energy band of the superfluid\nabove a critical value of the interaction strength. The width of the\nswallowtail is largest near unitarity. Across the critical value of the\ninteraction strength, the profiles of density and pairing field change more\ndrastically in the BCS side than in the BEC side. It is found that along with\nthe appearance of the swallowtail, there exists a narrow band in the\nquasiparticle energy spectrum close to the chemical potential and the\nincompressibility of the Fermi gas consequently experiences a profound dip in\nthe BCS side, unlike in the BEC side.",
        "positive": "The Landau critical velocity for a particle in a Fermi superfluid: We determine {\\`a} la Landau the critical velocity $v\\_c^{L}$ of a moving\nimpurity in a Fermi superfluid, that is by restricting to the minimal\nexcitation processes of the superfluid. $v\\_c^{L}$ is then the minimal velocity\nat which these processes are energetically allowed. The Fermi superfluid\nactually exhibits two excitation branches~: one is the fermionic pair-breaking\nexcitation, as predicted by BCS theory; the other one is bosonic and sets pairs\ninto motion, as predicted by Anderson's RPA. $v\\_c^{L}$ is the smallest of the\ntwo corresponding critical velocities $v\\_{c,f}^{L}$ and $v\\_{c,b}^{L}$. In the\nparameter space (superfluid interaction strength, fermion-to-impurity mass\nratio), we identify two transition lines, corresponding to a discontinuity of\nthe first-order and second-order derivatives of $v\\_c^{L}$. These two lines\nmeet in a triple point and split the plane in three domains. We briefly extend\nthis analysis to the very recently realized case at ENS, where the moving\nobject in the Fermi superfluid is a weakly interacting Bose superfluid of\nimpurities, rather than a single impurity. For a Bose chemical potential much\nsmaller than the Fermi energy, the topology of the transition lines is\nunaffected; a key result is that the domain $v\\_c^{L}=c$, where $c$ is the\nsound velocity in the Fermi superfluid, is turned into a domain\n$v\\_c^{L}=c+c\\_B$, where $c\\_B$ is the sound velocity in the Bose superfluid,\nwith slightly shifted boundaries."
    },
    {
        "anchor": "Quantum Entropic Effects in the Liquid Viscosities of Hydrogen,\n  Deuterium, and Neon: The extremely low temperatures have limited the availability and accuracy of\nexperimental thermophysical property measurements for cryogens, particularly\ntransport properties. Traditional scaling techniques such as corresponding\nstates theory have long been known to be inaccurate for fluids with strong\nquantum effects. To address this need, this paper investigates how quantum\neffects impact thermodynamics and momentum transfer (shear viscosity) in the\nfluid phases of hydrogen, deuterium, and neon. We utilize experimental\nviscosity measurements and reference empirical equations of state to show that\nconventional entropy scaling is inadequate for quantum-dominated systems. We\nthen provide a simple empirical correction to entropy scaling based on the\nratio of quantum to packing length scale that accounts for the deviations.",
        "positive": "Multiple Transitions of Coupled Atom-Molecule Bosonic Mixtures in Two\n  Dimensions: Motivated by the physics of coherently coupled, ultracold atom-molecule\nmixtures, we investigate a classical model possessing the same symmetry --\nnamely a $U(1)\\times \\mathbb{Z}_2$ symmetry, associated with the mass\nconservation in the mixture ($U(1)$ symmetry), times the $\\mathbb{Z}_2$\nsymmetry in the phase relationship between atoms and molecules. In two spatial\ndimensions the latter symmetry can lead to a finite-temperature Ising\ntransition, associated with (quasi) phase locking between the atoms and the\nmolecules. On the other hand, the $U(1)$ symmetry has an associated\nBerezinskii-Kosterlitz-Thouless (BKT) transition towards quasi-condensation of\natoms or molecules. The existence of the two transitions is found to depend\ncrucially on the population imbalance (or detuning) between atoms and\nmolecules: when the molecules are majority in the system, their BKT\nquasi-condensation transition occurs at a higher temperature than that of the\natoms; the latter has the unconventional nature of an Ising (quasi)\nphase-locking transition, lacking a finite local order parameter below the\ncritical temperature. When the balance is gradually biased towards the atoms,\nthe two transitions merge together to leave out a unique BKT transition, at\nwhich both atoms and molecules acquire quasi-long-range correlations, but only\natoms exhibit conventional BKT criticality, with binding of vortex-antivortex\npairs into short-range dipoles. The molecular vortex-antivortex excitations\nbind as well, but undergo a marked crossover from a high-temperature regime in\nwhich they are weakly bound, to a low-temperature regime of strong binding,\nreminiscent of their transition in the absence of atom-molecule coupling."
    },
    {
        "anchor": "Exact solutions to the four Goldstone modes around a dark soliton of the\n  nonlinear Schroedinger equation: This article is concerned with the linearisation around a dark soliton\nsolution of the nonlinear Schr\\\"odinger equation. Crucially, we present\nanalytic expressions for the four linearly-independent zero eigenvalue\nsolutions (also known as Goldstone modes) to the linearised problem. These\nsolutions are then used to construct a Greens matrix which gives the\nfirst-order spatial response due to some perturbation. Finally we apply this\nGreens matrix to find the correction to the dark-soliton wavefunction of a\nBose-Einstein condensate in the presence of fluctuations.",
        "positive": "Internal energy of many-boson system with three- and four-particle\n  direct correlations taken into account: In this paper we calculate kinetic, potential and full energy with three- and\nfour-particle direct correlations taken into account at wide temperature region\non the base of the density matrix of the interacting Bose-particles [I. O.\nVakarchuk, O. I. Hryhorchak, Journ. Phys. Stud. {\\bf 3}, 3005 (2009)]. In the\nlow temperature limit the obtained expression for the full energy is equal to\nthe wellknown expression for ground state energy in the approximation of \"two\nsums over the wave vector.\" The results of this work can be applied for the\nnumeric calculation of the heat capacity of liquid $^4$He in order to check the\ntheoretical and experimental results quantatively, especially in the\n$\\lambda$-transition region."
    },
    {
        "anchor": "Symmetry and the critical phase of the two-bath spin-boson model:\n  Ground-state properties: A generalized trial wave function termed as the \"multi-D1 Ansatz\" has been\ndeveloped to study the ground state of the spin-boson model with simultaneous\ndiagonal and off-diagonal coupling in the sub-Ohmic regime. Ground-state\nproperties including the energy and the spin polarization are investigated, and\nthe results are consistent with those from the exact diagonalization and\ndensity matrix renormalization group approaches for the cases involving two\noscillators and two baths described by a continuous spectral density function.\nBreakdown of the rotational and parity symmetries along the continuous quantum\nphase transition separating the localized phase from the critical phase has\nbeen uncovered. Moreover, the phase boundary is determined accurately with the\ncorresponding symmetry parameters of the rotational and parity symmetries. A\ncritical value of the spectral exponent s* = 0.49(1) is predicted in the weak\ncoupling limit, which is in agreement with the mean-field prediction of 1/2,\nbut much smaller than the earlier literature estimate of 0.75(1).",
        "positive": "Gauge Violation Spectroscopy in Synthetic Gauge Theories: Recently synthetic gauge fields have been implemented on quantum simulators.\nUnlike the gauge fields in the real world, in synthetic gauge fields, the gauge\ncharge can fluctuate and gauge invariance can be violated, which leading rich\nphysics unexplored before. In this work, we propose the gauge violation\nspectroscopy as a useful experimentally accessible measurement in the synthetic\ngauge theories. We show that the gauge violation spectroscopy exhibits no\ndispersion. Using three models as examples, two of them can be exactly solved\nby bosonization, and one has been realized in experiment, we further\ndemonstrate the gauge violation spectroscopy can be used to detect the\nconfinement and deconfinement phases. In the confinement phase, it shows a\ndelta function behavior, while in the deconfinement phase, it has a finite\nwidth."
    },
    {
        "anchor": "Spin-orbit coupling and perpendicular Zeeman field for fermionic cold\n  atoms: observation of the intrinsic anomalous Hall effect: We propose a scheme for generating Rashba spin-orbit coupling and\nperpendicular Zeeman field simultaneously for cold fermionic atoms in a\nharmonic trap through the coupling between atoms and laser fields. The\nrealization of Rashba spin-orbit coupling and perpendicular Zeeman field\nprovides opportunities for exploring many topological phenomena using cold\nfermionic atoms. We focus on the intrinsic anomalous Hall effect and show that\nit may be observed through the response of atomic density to a rotation of the\nharmonic trap.",
        "positive": "Pairing effects in the normal phase of a two-dimensional Fermi gas: In a recent experiment [M. Feld et al., Nature 480, 75 (2011); B. Froehlich\net al., Phys. Rev. Lett. 109,130403 (2012)], a pairing gap was detected in a\ntwo-dimensional (2D) Fermi gas with attractive interaction at temperatures\nwhere superfluidity does not occur. The question remains open as to whether\nthis gap is a pseudogap phenomenon or is due to a molecular state. In this\npaper, by using a t-matrix approach, we reproduce quite well the experimental\ndata for a 2D Fermi gas, and set the boundary between the pseudogap and\nmolecular regimes. We also show that pseudogap phenomena occurring in 2D and 3D\ncan be related through a variable spanning the BCS-BEC crossover in a universal\nway."
    },
    {
        "anchor": "Dynamics of noisy quantum systems in the Heisenberg picture: application\n  to the stability of fractional charge: Based on the Heisenberg-picture analog of the master equation, we develop a\nmethod for computing the exact time dependence of noise-averaged observables\nfor general noninteracting fermionic systems with noisy fluctuations. Upon\nnoise averaging, these fluctuations generate effective interactions, limiting\nanalytical approaches. While the short-time dynamics can be studied with\nLangevin-type numerical simulations, the long-time limit is not amenable to\nsuch simulations. Our results provide access to this long-time limit. As a\nsimple example, we examine the fate of the fractional charge in cold-atom\nemulations of polyacetylene after stochastic driving. We find that in a quantum\nquench to a fluctuating hopping Hamiltonian, the fractional charge remains\nrobust for hopping between different sublattices, while it becomes unstable in\nthe presence of noisy hopping on the same sublattice.",
        "positive": "Degeneracy of Many-body Quantum States in an Optical Lattice with a\n  Uniform Magnetic Field: We prove a theorem that shows the degeneracy of many-body states depends on\ntotal particle number and flux filling ratio, for particles in a periodic\nlattice and under a uniform magnetic field. Non-interacting fermions and weakly\ninteracting bosons are given as two examples. For the later case, this\nphenomena can also be understood in terms of destructive quantum interferences\nof multiple symmetry related tunneling paths between classical energy minima,\nwhich is reminiscent of the spin-parity effect discovered in magnetic molecular\ncluster. We also show that the quantum ground state of a mesoscopic number of\nbosons in this system is not a simple mean-field state but a fragmented state\neven for very weak interactions."
    },
    {
        "anchor": "Low-temperature thermodynamics of the unitary Fermi gas: superfluid\n  fraction, first sound and second sound: We investigate the low-temperature thermodynamics of the unitary Fermi gas by\nintroducing a model based on the zero-temperature spectra of both bosonic\ncollective modes and fermonic single-particle excitations. We calculate the\nHelmholtz free energy and from it we obtain the entropy, the internal energy\nand the chemical potential as a function of the temperature. By using these\nquantities and the Landau's expression for the superfluid density we determine\nanalytically the superfluid fraction, the critical temperature, the first sound\nvelocity and the second sound velocity. We compare our analytical results with\nother theoretical predictions and experimental data of ultracold atoms and\ndilute neutron matter.",
        "positive": "Bosonic Double Ring Lattice Under Artificial Gauge Fields: We consider a system of weakly interacting bosons confined on a planar double\nring lattice subjected to two artificial gauge fields. We determine its ground\nstate by solving coupled discrete non-linear Schr\\\"odinger equations at mean\nfield level. At varying inter-ring tunnel coupling, flux and interactions we\nidentify the vortex, Meissner and biased-ladder phases also predicted for a\nbosonic linear ladder by a variational Ansatz. We also find peculiar features\nassociated to the ring geometry, in particular parity effects in the number of\nvortices, and the appearance of a single vortex in the Meissner phase. We show\nthat the persistent currents on the rings carry precise information on the\nvarious phases. Finally, we propose a way of observing the Meissner and vortex\nphases via spiral interferogram techniques."
    },
    {
        "anchor": "Heralded magnetism in non-Hermitian atomic systems: Quantum phase transitions are usually studied in terms of Hermitian\nHamiltonians. However, cold-atom experiments are intrinsically non-Hermitian\ndue to spontaneous decay. Here, we show that non-Hermitian systems exhibit\nquantum phase transitions that are beyond the paradigm of Hermitian physics. We\nconsider the non-Hermitian XY model, which can be implemented using three-level\natoms with spontaneous decay. We exactly solve the model in one dimension and\nshow that there is a quantum phase transition from short-range order to\nquasi-long-range order despite the absence of a continuous symmetry in the\nHamiltonian. The ordered phase has a frustrated spin pattern. The critical\nexponent $\\nu$ can be 1 or 1/2. Our results can be seen experimentally with\ntrapped ions, cavity QED, and atoms in optical lattices.",
        "positive": "Novel Fermi Liquid of 2D Polar Molecules: We study Fermi liquid properties of a weakly interacting 2D gas of\nsingle-component fermionic polar molecules with dipole moments $d$ oriented\nperpendicularly to the plane of their translational motion. This geometry\nallows the minimization of inelastic losses due to chemical reactions for\nreactive molecules and, at the same time, provides a possibility of a clear\ndescription of many-body (beyond mean field) effects. The long-range character\nof the dipole-dipole repulsive interaction between the molecules, which scales\nas $1/r^3$ at large distances $r$, makes the problem drastically different from\nthe well-known problem of the two-species Fermi gas with repulsive contact\ninterspecies interaction. We solve the low-energy scattering problem and\ndevelop a many-body perturbation theory beyond the mean field. The theory\nrelies on the presence of a small parameter $k_Fr_*$, where $k_F$ is the Fermi\nmomentum, and $r_*=md^2/\\hbar^2$ is the dipole-dipole length, with $m$ being\nthe molecule mass. We obtain thermodynamic quantities as a series of expansion\nup to the second order in $k_Fr_*$ and argue that many-body corrections to the\nground-state energy can be identified in experiments with ultracold molecules,\nlike it has been recently done for ultracold fermionic atoms. Moreover, we show\nthat only many-body effects provide the existence of zero sound and calculate\nthe sound velocity."
    },
    {
        "anchor": "Two-body mobility edge in the Anderson-Hubbard model in three\n  dimensions: Molecular versus scattering states: Most of our quantitative understanding of disorder-induced metal-insulator\ntransitions comes from numerical studies of simple noninteracting tight-binding\nmodels, like the Anderson model in three dimensions. An important outstanding\nproblem is the fate of the Anderson transition in the presence of additional\nHubbard interactions of strength $U$ between particles. Based on large-scale\nnumerics, we compute the position of the mobility edge for a system of two\nidentical bosons or two fermions with opposite spin components. The resulting\nphase diagram in the interaction-energy-disorder space possesses a remarkably\nrich and counterintuitive structure, with multiple metallic and insulating\nphases. We show that this phenomenon originates from the molecular or\nscattering-like nature of the pair states available at given energy $E$ and\ndisorder strength $W$. The disorder-averaged density of states of the effective\nmodel for the pair is also investigated. Finally, we discuss the implications\nof our results for ongoing research on many-body localization.",
        "positive": "Counter-flow instability of a quantum mixture of two superfluids: We study the instability of a mixture of two interacting counter-flowing\nsuperfluids. For a homogeneous system, we show that superfluid hydrodynamics\nleads to the existence of a dynamical instability at a critical value of the\nrelative velocity $v_{cr}$. When the interspecies coupling is small the\ncritical value approaches the value $v_{cr}=c_1+c_2$, given by the sum of the\nsound velocities of the two uncoupled superfluids, in agreement with the recent\nprediction of [1] based on Landau's argument. The crucial dependence of the\ncritical velocity on the interspecies coupling is explicitly discussed. Our\nresults agree with previous predictions for weakly interacting Bose-Bose\nmixtures and applies to Bose-Fermi superfluid mixtures as well. Results for the\nstability of transversally trapped mixtures are also presented."
    },
    {
        "anchor": "Relaxation of superflow in a network: an application to the dislocation\n  model of supersolidity of helium crystals: We have considered the dislocation network model for the supersolid state in\nHe-4 crystals. In difference with uniform 2D and 3D systems, the temperature of\nsuperfluid transition T_c in the network is much smaller than the degeneracy\ntemperature T_d. It is shown that a crossover into a quasi superfluid state\noccurs in the temperature interval between T_c and T_d. Below the crossover\ntemperature the time of decay of the flow increases exponentially under\ndecrease of the temperature. The crossover has a continuous character and the\ncrossover temperature does not depend on the density of dislocations.",
        "positive": "Quantum dark solitons in the one-dimensional Bose gas: Dark and grey soliton-like states are shown to emerge from numerically\nconstructed superpositions of translationally-invariant eigenstates of the\ninteracting Bose gas in a toroidal trap. The exact quantum many-body dynamics\nreveals a density depression with superdiffusive spreading that is absent in\nthe mean-field treatment of solitons. A simple theory based on finite-size\nbound states of holes with quantum-mechanical center-of-mass motion\nquantitatively explains the time-evolution of the superposition states and\npredicts quantum effects that could be observed in ultra-cold gas experiments.\nThe soliton phase step is shown to be a key ingredient of an accurate finite\nsize approximation, which enables us to compare the theory with numerical\nsimulations. The fundamental soliton width, an invariant property of the\nquantum dark soliton, is shown to deviate from the Gross-Pitaevskii predictions\nin the interacting regime and vanishes in the Tonks-Girardeau limit."
    },
    {
        "anchor": "Conjectures about the structure of strong- and weak-coupling expansions\n  of a few ground-state observables in the Lieb-Liniger and Yang-Gaudin models: In this paper, we apply experimental number theory to two integrable quantum\nmodels in one dimension, the Lieb-Liniger Bose gas and the Yang-Gaudin Fermi\ngas with contact interactions. We identify patterns in weak- and\nstrong-coupling series expansions of the ground-state energy, local correlation\nfunctions and pressure. Based on the most accurate data available in the\nliterature, we make a few conjectures about their mathematical structure and\nextrapolate to higher orders.",
        "positive": "Distinguishing mesoscopic quantum superpositions from statistical\n  mixtures in periodically shaken double wells: For Bose-Einstein condensates in double wells, N-particle Rabi-like\noscillations often seem to be damped. Far from being a decoherence effect, the\napparent damping can indicate the emergence of quantum superpositions in the\nmany-particle quantum dynamics. However, in an experiment it would be difficult\nto distinguish the apparent damping from decoherence effects. The present paper\nsuggests using controlled periodic shaking to quasi-instantaneously switch the\nsign of an effective Hamiltonian, thus implementing an `echo' technique which\ndistinguishes quantum superpositions from statistical mixtures. The scheme for\nthe effective time-reversal is tested by numerically solving the time-dependent\nN-particle Schrodinger equation."
    },
    {
        "anchor": "Polarons in the radio-frequency spectrum of a quasi-two-dimensional\n  Fermi gas: We measure radio-frequency spectra for a two-component mixture of a $^6$Li\natomic Fermi gas in the quasi-two-dimensional regime. Near the Feshbach\nresonance, where the transverse Fermi energy is large compared to the\nconfinement-induced dimer binding energies for the initial and final states, we\nfind that the observed resonances do not correspond to transitions between\nconfinement-induced dimers. The spectrum appears to be well-described by\ntransitions between noninteracting polaron states in two dimensions.",
        "positive": "Observation of Slow Dynamics near the Many-Body Localization Transition\n  in One-Dimensional Quasiperiodic Systems: In the presence of sufficiently strong disorder or quasiperiodic fields, an\ninteracting many-body system can fail to thermalize and become many-body\nlocalized. The associated transition is of particular interest, since it occurs\nnot only in the ground state but over an extended range of energy densities. So\nfar, theoretical studies of the transition have focused mainly on the case of\ntrue-random disorder. In this work, we experimentally and numerically\ninvestigate the regime close to the many-body localization transition in\nquasiperiodic systems. We find slow relaxation of the density imbalance close\nto the transition, strikingly similar to the behavior near the transition in\ntrue-random systems. This dynamics is found to continuously slow down upon\napproaching the transition and allows for an estimate of the transition point.\nWe discuss possible microscopic origins of these slow dynamics."
    },
    {
        "anchor": "General relations for quantum gases in two and three dimensions. II.\n  Bosons and mixtures: We derive exact general relations between various observables for N bosons\nwith zero-range interactions, in two or three dimensions, in an arbitrary\nexternal potential. Some of our results are analogous to relations derived\npreviously for two-component fermions, and involve derivatives of the energy\nwith respect to the two-body s-wave scattering length a. Moreover, in the\nthree-dimensional case, where the Efimov effect takes place, the interactions\nare characterized not only by a, but also by a three-body parameter R\\_t. We\nthen find additional relations which involve the derivative of the energy with\nrespect R\\_t. In short, this derivative gives the probability to find three\nparticles close to each other. Although it is evaluated for a totally loss-less\nmodel, it remarkably also gives the three-body loss rate always present in\nexperiments (due to three-body recombination to deeply bound diatomic\nmolecules), at least in the limit where the so-called inelasticity parameter\neta is small enough. As an application, we obtain, within the zero-range model\nand to first order in eta, an analytic expression for the three-body loss rate\nconstant for a non-degenerate Bose gas with infinite scattering length. We also\ndiscuss the generalization to arbitrary mixtures of bosons and/or fermions.",
        "positive": "Thermal suppression of demixing dynamics in a binary condensate: We investigate the demixing dynamics in a binary two-dimensional (2D) Bose\nsuperfluid using classical-field dynamics. By quenching the interspecies\ninteraction parameter, we identify a strong and weak separation regime\ndepending on the system temperature and the quench parameter. In the strong\nseparation regime our results are in agreement with the inertial hydrodynamic\ndomain growth law of binary fluids and a Porod scaling law for the structure\nfactor at zero temperature is found. In the weak separation regime thermal\nfluctuations modify both the domain growth law and the Porod tail of the\nstructure factor. Near the superfluid transition temperature the scaling\ndynamics approaches the diffusive growth law of a 2D conserved field. We then\nanalyze the demixing dynamics in a box cloud. For low quench we find\ndistinctive domain dynamics dictated by the boundary condition. Otherwise, the\ndynamics are qualitatively similar to those of systems with periodic boundary\nconditions."
    },
    {
        "anchor": "Emergent Weyl excitations in systems of polar particles: Weyl fermions are massless chiral particles first predicted in 1929 and once\nthought to describe neutrinos. Although never observed as elementary particles,\nquasiparticles with Weyl dispersion have recently been experimentally\ndiscovered in solid-state systems causing a furore in the research community.\nSystems with Weyl excitations can display a plethora of fascinating phenomena\nand offer great potential for improved quantum technologies. Here we show that\nWeyl excitations generically exist in three-dimensional systems of dipolar\nparticles with weakly broken time-reversal symmetry (for example, by a magnetic\nfield). They emerge as a result of dipolar-interaction-induced transfer of\nangular momentum between the $J=0$ and $J=1$ internal particle levels. We also\ndiscuss momentum-resolved Ramsey spectroscopy methods for observing Weyl\nquasiparticles in cold alkaline-earth-atom systems. Our results provide a\npathway for a feasible experimental realisation of Weyl quasiparticles and\nrelated phenomena in clean and controllable atomic systems.",
        "positive": "Nearly order from quantum disorder phenomena and its observation in a\n  bosonic quantum anomalous Hall system: We report a new many body phenomena called \" Nearly order from quantum\ndisorder phenomena\" (NOFQD). We demonstrate the NOFQD in the experimentally\nrealized weakly interacting Quantum Anomalous Hall system of spinor bosons in\nan optical lattice. We establish intrinsic connections between the\nphenomenological GL theory and the microscopic calculations on the effective\npotential. Connections with the bilayer quantum Hall system with a total\nfilling factor $ \\nu_T=1 $ are made. Some insightful analogy with $\nNAdS_2/NCFT_1 $ ( where $ N $ also means nearly ) correspondence in the context\nof Sachdev-Ye-Kitaev models are hinted. Two types of OFQDs are classified, one\nresponse trivially, another non-trivially to a small deformation to the\nHamiltonian leading to NOFQD. The NOFQD can be detected in the current cold\natom bosonic quantum anomalous Hall experiments and may also appear in many\nother frustrated systems."
    },
    {
        "anchor": "Feasibility analysis of a proposed test of quantum gravity via novel\n  optical magnetometry in xenon: We present an analysis of the sensitivity limits of a proposed experimental\nsearch for quantum gravity, using a novel approach based on optical\nmagnetometry in the noble gas isotope $^{129}$Xe. The analysis relies on a\ngeneral uncertainty principle model that is consistent with most formulations\nof quantum gravity theory, where the canonical uncertainty relations are\nmodified by a leading-order correction term that is linear in momentum. In\nturn, this correction modifies the magnetic moment of the spin-polarized\n$^{129}$Xe atoms that are immersed in a magnetic field in the proposed\nexperiment, which results in a velocity-dependent variation of their Larmour\nfrequency, that is detected via two-photon laser spectroscopy. The thermal\ndistribution of atomic velocities, in conjunction with the Doppler effect, is\nused to scan the interrogating laser over different atomic velocities, and\nsearch for a corresponding variation in their Larmor frequencies. We show that\nthe existing bounds on the leading-order quantum gravity correction can be\nimproved by $10^{7}$ with existing technology, where another factor of $10^{2}$\nis possible with near-future technical capabilities.",
        "positive": "Anisotropic semi-vortices in dipolar spinor condensates controlled by\n  Zeeman splitting: Spatially anisotropic solitary vortices (AVSs), supported by anisotropic\ndipole-dipole interactions, were recently predicted in spin-orbit-coupled\nbinary Bose-Einstein condensates (BECs), in the form of two-dimensional\nsemi-vortices (complexes built of zero-vorticity and vortical components). We\ndemonstrate that the shape of the AVSs -- horizontal or vertical, with respect\nto the in-plane polarization of the atomic dipole moments in the underlying BEC\n-- may be effectively controlled by strength $\\Omega$ of the Zeeman splitting\n(ZS). A transition from the horizontal to vertical shape with the increase of\n$\\Omega$ is found numerically and explained analytically. At the transition\npoint, the AVS assumes the shape of an elliptical ring. Mobility of horizontal\nAVSs is studied too, with a conclusion that, with the increase of $\\Omega $,\ntheir negative effective mass changes the sign into positive via a point at\nwhich the effective mass diverges. Lastly, we report a new species of\n\\textit{inverted} AVSs, with the zero-vorticity and vortex component placed in\nlower- and higher-energy components, as defined by the ZS. They are excited\nstates, with respect to the ground states provided by the usual AVSs. Quite\nsurprisingly, inverted AVSs are stable in a large parameter region."
    },
    {
        "anchor": "Non-equilibrium Quantum Spin Dynamics from 2PI Functional Integral\n  Techniques in the Schwinger Boson Representation: We present a non-equilibrium quantum field theory approach to the\ninitial-state dynamics of spin models based on two-particle irreducible (2PI)\nfunctional integral techniques. It employs a mapping of spins to Schwinger\nbosons for arbitrary spin interactions and spin lengths. At next-to-leading\norder (NLO) in an expansion in the number of field components, a wide range of\nnon-perturbative dynamical phenomena are shown to be captured, including\nrelaxation of magnetizations in a 3D long-range interacting system with\nquenched disorder, different relaxation behaviour on both sides of a quantum\nphase transition and the crossover from relaxation to arrest of dynamics in a\ndisordered spin chain previously shown to exhibit many-body-localization. Where\napplicable, we employ alternative state-of-the-art techniques and find rather\ngood agreement with our 2PI NLO results. As our method can handle large system\nsizes and converges relatively quickly to its thermodynamic limit, it opens the\npossibility to study those phenomena in higher dimensions in regimes in which\nno other efficient methods exist. Furthermore, the approach to classical\ndynamics can be investigated as the spin length is increased.",
        "positive": "Two-photon photoassociation spectroscopy of an ultracold heteronuclear\n  molecule: We report on two-photon photoassociation (PA) spectroscopy of ultracold\nheteronuclear LiRb molecules. This is used to determine the binding energies of\nthe loosely bound levels of the electronic ground singlet and the lowest\ntriplet states of LiRb. We observe strong two-photon PA lines with power\nbroadened line widths greater than 20 GHz at relatively low laser intensity of\n30 W/cm$^{2}$. The implication of this observation on direct atom to molecule\nconversion using stimulated Raman adiabatic passage (STIRAP) is discussed and\nthe prospect for electronic ground state molecule production is theoretically\nanalyzed."
    },
    {
        "anchor": "Observation of non-Hermitian degeneracies in a chaotic exciton-polariton\n  billiard: Exciton-polaritons are hybrid light-matter quasiparticles formed by strongly\ninteracting photons and excitons (electron-hole pairs) in semiconductor\nmicrocavities. They have emerged as a robust solid-state platform for\nnext-generation optoelectronic applications as well as fundamental studies of\nquantum many-body physics. Importantly, exciton-polaritons are a profoundly\nopen (i.e., non-Hermitian) quantum system: it requires constant pumping of\nenergy and continuously decays releasing coherent radiation. Thus, the\nexciton-polaritons always exist in a balanced potential landscape of gain and\nloss. However, the inherent non-Hermitian nature of this potential has so far\nbeen largely ignored in exciton-polariton physics. Here we demonstrate that\nnon-Hermiticity dramatically modifies the structure of modes and spectral\ndegeneracies in exciton-polariton systems, and, therefore, will affect their\nquantum transport, localisation, and dynamical properties. Using a\nspatially-structured optical pump, we create a chaotic exciton-polariton\nbilliard. Eigenmodes of this billiard exhibit multiple non-Hermitian spectral\ndegeneracies -- exceptional points. These are known to cause remarkable wave\nphenomena, such as unidirectional transport, anomalous lasing/absorption, and\nchiral modes. By varying parameters of the billiard, we observe crossing and\nanti-crossing of energy levels and reveal the nontrivial topological modal\nstructure exclusive to non-Hermitian systems. We also observe the mode\nswitching and topological Berry phase for a parameter loop encircling the\nexceptional point. Our findings pave the way for studies of non-Hermitian\nquantum dynamics of exciton-polaritons, which can lead to novel functionalities\nof polariton-based devices.",
        "positive": "Bose-Einstein condensation of non-ground-state caesium atoms: Bose-Einstein condensates of ultracold atoms serve as low-entropy sources for\na multitude of quantum-science applications, ranging from quantum simulation\nand quantum many-body physics to proof-of-principle experiments in quantum\nmetrology and quantum computing. For stability reasons, in the majority of\ncases the energetically lowest-lying atomic spin state is used. Here we report\nthe Bose-Einstein condensation of caesium atoms in the Zeeman-excited mf = 2\nstate, realizing a non-ground-state Bose-Einstein condensate with tunable\ninteractions and tunable loss. We identify two regions of magnetic field in\nwhich the two-body relaxation rate is low enough that condensation is possible.\nWe characterize the phase transition and quantify the loss processes, finding\nunusually high three-body losses in one of the two regions. Our results open up\nnew possibilities for the mixing of quantum-degenerate gases, for polaron and\nimpurity physics, and in particular for the study of impurity transport in\nstrongly correlated one-dimensional quantum wires."
    },
    {
        "anchor": "Tunneling transport of unitary fermions across the superfluid transition: We investigate the transport of a Fermi gas with unitarity-limited\ninteractions across the superfluid phase transition, probing its response to a\ndirect current (dc) drive through a tunnel junction. As the superfluid critical\ntemperature is crossed from below, we observe the evolution from a highly\nnonlinear to an Ohmic conduction characteristics, associated with the critical\nbreakdown of the Josephson dc current induced by pair condensate depletion.\nMoreover, we reveal a large and dominant anomalous contribution to resistive\ncurrents, which reaches its maximum at the lowest attained temperature,\nfostered by the tunnel coupling between the condensate and phononic\nBogoliubov-Anderson excitations. Increasing the temperature, while the zeroing\nof supercurrents marks the transition to the normal phase, the conductance\ndrops considerably but remains much larger than that of a normal, uncorrelated\nFermi gas tunneling through the same junction. We attribute such enhanced\ntransport to incoherent tunneling of sound modes, which remain weakly damped in\nthe collisional hydrodynamic fluid of unpaired fermions at unitarity.",
        "positive": "Contour-time approach to the disordered Bose-Hubbard model in the strong\n  coupling regime: There has been considerable interest in the disordered Bose Hubbard model\n(BHM) in recent years, particularly in the context of thermalization and\nmany-body localization. We develop a two-particle irreducible (2PI)\nstrong-coupling approach to the disordered BHM that allows us to treat both\nequilibrium and out-of-equilibrium situations. We obtain equations of motion\nfor spatio-temporal correlations and explore their equilibrium solutions. We\nstudy the equilibrium phase diagram as a function of disorder strength and\ndiscuss applications of the formalism to out-of-equilibrium situations. We also\nnote that the disorder strengths where the emergence of non-ergodic dynamics\nwas observed in a recent experiment [Choi $et \\,al.$, Science $\\bf{352}$, 1547\n(2016)] appear to correspond to the Mott insulator -- Bose glass phase\nboundary."
    },
    {
        "anchor": "Resonance-facilitated three-channel p-wave scattering: Feshbach resonances of arbitrary width are typically described in terms of\ntwo-channel models. Within these models, one usually considers a single dressed\nresonance, with the option to extend the analysis by including resonant\nopen-channel features that can drastically change the observed threshold\neffects. For the strong $^{40}\\mathrm{K}$ p-wave resonance studied in Ref.\n\\cite{ahmed2021}, the interplay between an open-channel shape resonance and the\nFeshbach resonance could explain the unexpected nonlinear variation of the\nbinding energy with magnetic field. However, the presented two-channel\ntreatment relies on the introduction of two independent fitting parameters,\nwhereas the typical Breit-Wigner expression would only account for one. This\nresults in an effective magnetic moment that acquires a nonphysical value,\nwhich is an indication of a major shortcoming of the two-channel model\ntreatment. In this study, we observe how the presence of a closed-channel shape\nresonance explains the physical mechanism behind the observations and\ndemonstrates the need of a three-channel treatment. We introduce our novel\nmodel as \\textit{resonance facilitated}, where all coupling is mediated by the\nFeshbach state, while there is no direct coupling between the additional\nchannel and the open channel. Notably, the resonance-facilitated structure\ngreatly reduces the complexity of the full three-channel model. The typical\nBreit-Wigner form of the two-channel Feshbach formalism is retained and the\nfull effect of the added channel can be captured by a single resonance dressing\nfactor, which describes how the free propagation in the Feshbach state is\ndressed by the added channel.",
        "positive": "Two- and three- dimensional few-body systems in the universal regime: Macro properties of cold atomic gases are driven by few-body correlations,\neven if the gas has thousands of particles. Quantum systems composed of two and\nthree particles with attractive zero\\=/range pairwise interactions are\nconsidered for general masses and interaction strengths in two and three\ndimensions (2D and 3D). The Faddeev decomposition is used to derive the\nequations for the bound state, which is the starting point for the\ninvestigation of universal properties of few\\=/body systems, i.e. those that\nall potentials with the same physics at low energy are able to describe in a\nmodel\\=/independent form. In 2D, the number of bound states in a three\\=/body\nsystem increases without bound as the mass of one particle becomes much lighter\nthan the other two. The analytic form of an effective potential between the\nheavy particles explains the mass\\=/dependence on the number of bound energy\nlevels. An exact analytic expression for the large\\=/momentum asymptotic\nbehaviour of the spectator function in the Faddeev equation is presented. The\nspectator function and its asymptotic form define the two- and three\\=/body\ncontact parameters. The two\\=/body parameter is found to be independent of the\nquantum state in some specific 2D systems. The 2D and 3D momentum distributions\nhave a distinct sub\\=/leading form whereas the 3D term depends on the mass of\nthe particles. A model that interpolates between 2D and 3D is proposed and a\nsharp transition in the energy spectrum of three-body systems is found."
    },
    {
        "anchor": "Effective two-mode model in Bose-Einstein condensates versus\n  Gross-Pitaevskii simulations: We study the dynamics of three-dimensional Bose-Einstein condensates confined\nby double-well potentials using a two-mode model with an effective on-site\ninteraction energy parameter. The effective on-site interaction energy\nparameter is evaluated for different numbers of particles ranging from a low\nexperimental value to larger ones approaching the Thomas-Fermi limit, yielding\nimportant corrections to the dynamics. We analyze the time periods as functions\nof the initial imbalance and find a closed integral form that includes all\ninteraction-driven parameters. A simple analytical formula for the\nself-trapping period is introduced and shown to accurately reproduce the exact\nvalues provided by the two-mode model. Systematic numerical simulations of the\nproblem in 3D demonstrate the excellent agreement of the two-mode model for\nexperimental parameters.",
        "positive": "Quantum domain walls induce incommensurate supersolid phase on the\n  anisotropic triangular lattice: We investigate the extended hard-core Bose-Hubbard model on the triangular\nlattice as a function of spatial anisotropy with respect to both tunneling and\nnearest-neighbor interaction strength. At half-filling the system can be tuned\nfrom decoupled one-dimensional chains to a two-dimensional solid phase with\nalternating density order by adjusting the anisotropic coupling. At\nintermediate anisotropy, however, frustration effects dominate and an\nincommensurate supersolid phase emerges, which is characterized by\nincommensurate density order as well as an anisotropic superfluid density. We\ndemonstrate that this intermediate phase results from the proliferation of\ntopological defects in the form of quantum bosonic domain walls. Accordingly,\nthe structure factor has peaks at wave vectors, which are linearly related to\nthe number of domain walls in a finite system in agreement with extensive\nquantum Monte Carlo simulations. We discuss possible connections with the\nsupersolid behavior in the high-temperature superconducting striped phase."
    },
    {
        "anchor": "Mode interference in quantum joint probabilities for multimode\n  Bose-condensed systems: The method of defining quantum joint probabilities of two events is applied\nto a multimode system of trapped Bose-condensed atoms. The coherent modes are\ngenerated by modulating the trapping potential with an alternating field with a\nfrequency in resonance with a transition frequency between two coherent modes.\nThe system is subjected to nondestructive measurements randomly influencing the\nphase difference of the modes. The joint probability of observing two events,\ncorresponding to the observation of two states, is calculated by employing the\nchannel-state duality. The interference term in the joint probability can arise\nwhen the composite events form an entangled prospect and the system state is\nalso entangled. This interference is due to the uncertainty induced by\nnondestructive measurements.",
        "positive": "Thermodynamics of a spin-1 Bose gas with fixed magnetization: We investigate the thermodynamics of a spin-1 Bose gas with fixed\nmagnetization including the quadratic Zeeman energy shift. Our calculations are\nbased on the grand canonical description for the ideal gas and the classical\nfields approximation for atoms with ferromagnetic and antiferromagnetic\ninteractions. We confirm the occurence of a double phase transition in the\nsystem that takes place due to two global constraints. We show analytically for\nthe ideal gas how critical temperatures and condensed fractions are changed by\na non-zero magnetic field. The interaction strongly affects the condensate\nscenario below the second critical temperature. The effect imposed by\ninteraction energies becomes diminished in high magnetic fields where\ncondensation, of both ferromagnetic and antiferromagnetic atoms, agree with the\nideal gas results."
    },
    {
        "anchor": "Phase separation in a mixture of trapped charged Bose-Einstein\n  condensates: We study the phase separation configurations and their rotational properties\nfor a mixture of two interacting charged Bose-Einstein condensates subject to a\nmagnetic field trapped in disc and Corbino geometries. We calculate the ground\nstate energies of azimuthal and radial phase separation configurations using\nthe Gross-Pitaevskii and the Thomas-Fermi approximations. We show that the\nresults for experimentally relevant system parameters from both approaches are\nin good agreement. The immiscible mixture in both geometries with equal\nintracomponent interactions favors the azimuthal phase separation for all\nintercomponent interactions. Only an imbalance in the intracomponent\ninteractions can result in a transition to the radial phase separation, for\nwhich the transition becomes sensitive to the shape of the trap. We present\nphase diagrams as a function of the inter and intracomponent interactions.\nWhile the radial phase separation is widely favoured in disc geometry, the\nazimuthal phase separation is favoured for narrower Corbino geometries. We\nexplore the rotational properties of the spatially separated condensates under\nthe magnetic field, studying their angular momenta and velocity fields. The\nquantization of circulation breaks down for the azimuthal phase separation. In\nthis case, the bulk region of the condensate continues to display superfluid\nflow behavior whereas the velocity field shows a rigid body behavior along the\nphase boundaries.",
        "positive": "Mechanism of Tunneling in Interacting Open Ultracold Few-Boson Systems: We investigate the mechanism in the tunneling dynamics of open ultracold\nfew-boson systems by numerically solving the time-dependent few-boson\nSchr\\\"{o}dinger equation exactly. By starting from a weakly repulsive,\ninitially coherent two-boson system we demonstrate that the decay dynamics\nincorporate fragmentation. The wavefunction of the tunneling state exhibits a\npronounced dynamically-stable pattern which we explain by an analytical model.\nBy studying more bosons and stronger interactions we arrive to the conclusion\nthat the decay by tunneling is not a coherent process and exhibits a wealth of\nphenomena depending on the interaction between the particles."
    },
    {
        "anchor": "Dynamic response of strongly correlated Fermi gases in the quantum\n  virial expansion: By developing a quantum virial expansion theory, we quantitatively calculate\nthe dynamic density response function of a trapped strongly interacting Fermi\ngas at high temperatures near unitarity. A clear transition from atomic to\nmolecular responses is identified in the spectra when crossing from the BCS to\nBEC regimes, in qualitative agreement with recent Bragg spectroscopy\nobservations. Our virial expansion method provides a promising way to solve the\nchallenging strong-coupling problems and is applicable to other dynamical\nproperties of strongly correlated Fermi gases.",
        "positive": "Solution of inverse problem for Gross-Pitaevskii equation with\n  artificial neural networks: We propose an Artificial Neural Network (ANN) design to solve the inverse\nproblem for a 1D Gross-Pitaevskii equation (GPE). More precise, the ANN takes\nthe squared modulus of the stationary GPE solution as an input and returns the\nparameters of the potential function and the factor in front of the GPE\nnon-linear term. From the physical point of view the ANN predicts the\nparameters of a trap potential and the interaction constant of 1D Bose-Einstein\nCondensate (BEC) by its density distribution. Using the results of numerical\nsolution of GPE for more than $30 000$ sets of GPE parameters as train and\nvalidation datasets we build the ANN as a fast and accurate inverse GPE solver."
    },
    {
        "anchor": "Dimensional Crossover in a Spin-imbalanced Fermi gas: We model the one-dimension (1D) to three-dimension (3D) crossover in a\ncylindrically trapped Fermi gas with attractive interactions and\nspin-imbalance. We calculate the mean-field phase diagram, and study the\nrelative stability of exotic superfluid phases as a function of interaction\nstrength and temperature. For weak interactions and low density, we find\n1D-like behavior, which repeats as a function of the chemical potential as new\nchannels open. For strong interactions, mixing of single-particle levels gives\n3D-like behavior at all densities. Furthermore, we map the system to an\neffective 1D model, finding significant density dependence of the effective 1D\nscattering length.",
        "positive": "Direct excitation of Kelvin waves on quantized vortices: Helices and spirals, prevalent across various systems, play a crucial role in\ncharacterizing symmetry, describing dynamics, and imparting unique\nfunctionalities, attributed to their inherent simplicity and chiral nature. A\nhelical excitation on a quantized vortex, an example of a one-dimensional\ntopological defect, emerges as a Nambu-Goldstone mode following spontaneous\nsymmetry breaking, known as a Kelvin wave. Kelvin waves play a vital role in\nenergy dissipation within inviscid quantum fluids. However, deliberately\nexciting Kelvin waves has proven to be challenging. Here, we introduce a\ncontrolled method for exciting Kelvin waves on a quantized vortex in superfluid\nhelium-4. We used a charged nanoparticle, oscillated by a time-varying electric\nfield, to stimulate Kelvin waves on the vortex. A major breakthrough in our\nresearch is the confirmation of the helical nature of Kelvin waves through\nthree-dimensional image reconstruction, providing visual evidence of their\ncomplex dynamics. Additionally, we determined the dispersion relation and the\nphase velocity of the Kelvin wave and identified the vorticity direction,\nenhancing our understanding of quantum fluid behavior. This work elucidates the\ndynamics of Kelvin waves and pioneers a novel approach for manipulating and\nobserving quantized vortices in three dimensions, thereby opening new avenues\nfor exploring quantum fluidic systems."
    },
    {
        "anchor": "Entanglement-assisted tunneling dynamics of impurities in a double well\n  immersed in a bath of lattice trapped bosons: We unravel the correlated tunneling dynamics of an impurity trapped in a\ndouble well and interacting repulsively with a majority species of lattice\ntrapped bosons. Upon quenching the tilt of the double well it is found that the\nquench-induced tunneling dynamics depends crucially on the interspecies\ninteraction strength and the presence of entanglement inherent in the system.\nIn particular, for weak couplings the impurity performs a rather irregular\ntunneling process in the double well. Increasing the interspecies coupling it\nis possible to control the response of the impurity which undergoes a delayed\ntunneling while the majority species effectively acts as a material barrier.\nFor very strong interspecies interaction strengths the impurity exhibits a\nself-trapping behaviour. We showcase that a similar tunneling dynamics takes\nplace for two weakly interacting impurities and identify its underlying\ntransport mechanisms in terms of pair and single-particle tunneling processes.",
        "positive": "Comment on \"Lack of a genuine time crystal in a chiral soliton model\" by\n  Syrwid, Kosior, and Sacha: We present a comment on A. Syrwid, A. Kosior, and K. Sacha, \"Lack of a\ngenuine time crystal in a chiral soliton model,\" arXiv:2005.12313."
    },
    {
        "anchor": "Inelastic Collisions of Solitary Waves in Anisotropic Bose-Einstein\n  Condensates: Sling-Shot Events and Expanding Collision Bubbles: We study experimentally and theoretically the dynamics of apparent dark\nsoliton stripes in an elongated Bose-Einstein condensate. We show that for the\ntrapping strengths corresponding to our experimental setup, the transverse\nconfinement along one of the tight directions is not strong enough to arrest\nthe formation of solitonic vortices or vortex rings. These solitonic vortices\nand vortex rings, when integrated along the transverse direction, appear as\ndark soliton stripes along the longitudinal direction thereby hiding their true\ncharacter. The latter significantly modifies the interaction dynamics during\ncollision events and can lead to apparent examples of inelasticity and what may\nappear experimentally even as a merger of two dark soliton stripes. We explain\nthis feature by means of the interaction of two solitonic vortices leading to a\nsling shot event with one of the solitonic vortices being ejected at a\nrelatively large speed. Furthermore we observe expanding collision bubbles\nwhich consist of repeated inelastic collisions of a dark soliton stripe pair\nwith an {\\it increasing} time interval between collisions.",
        "positive": "Binary Quantum Turbulence Arising from Countersuperflow Instability in\n  Two-Component Bose-Einstein Condensates: We theoretically study the development of quantum turbulence from two\ncounter-propagating superfluids of miscible Bose-Einstein condensates by\nnumerically solving the coupled Gross-Pitaevskii equations. When the relative\nvelocity exceeds a critical value, the counter-superflow becomes unstable and\nquantized vortices are nucleated, which leads to isotropic quantum turbulence\nconsisting of two superflows. It is shown that the binary turbulence can be\nrealized experimentally in a trapped system."
    },
    {
        "anchor": "Three-body recombination near a narrow Feshbach resonance in $^6$Li: We experimentally measure, and theoretically analyze the three-atom\nrecombination rate, $L_3$, around a narrow $s$ wave magnetic Feshbach resonance\nof $^6$Li-$^6$Li at 543.3 Gauss. By examining both the magnetic field\ndependence and especially the temperature dependence of $L_3$ over a wide range\nof temperatures from a few $\\mu$K to above 200 $\\mu$K, we show that three-atom\nrecombination through a narrow resonance follows a universal behavior\ndetermined by the long-range van der Waals potential, and can be described by a\nset of rate equations in which three-body recombination proceeds via successive\npairwise interactions. We expect the underlying physical picture to be\napplicable not only to narrow $s$ wave resonances, but also to resonances in\nnonzero partial waves, and not only at ultracold temperatures, but also at much\nhigher temperatures.",
        "positive": "The properties of Tonk-Girardeau Gas at Finite Temperature and\n  Comparison with Polarized Free Fermions: In the present paper we investigate the Tonks-Girardeau gas confined in a\nharmonic trap at finite temperature with thermal Bose-Fermi mapping method. The\npair distribution, density distribution, reduced one-body density matrix, the\noccupations number of natural orbitals, and momentum distribution are\nevaluated. In the whole temperature regime the pair distribution and density\ndistribution exhibit the same properties as those of polarized free Fermions\nbecause both of them depend on the modulus of wavefunction rather than\nwavefunction. While the reduced one-body density matrix, the natural orbital\noccupation, momentum distribution, which depend on wavefunction, of Tonks gas\ndisplays Bose properties different from polarized free Fermions at low\ntemperature. At high temperature we can not distinguish Tonks gas from the\npolarized free Fermi gas by all properties qualitatively."
    },
    {
        "anchor": "Dynamical crossover between the infinite-volume and empty-lattice limits\n  of ultra-cold fermions in 1D optical lattices: Unlike typical condensed-matter systems, ultra-cold atoms loaded into optical\nlattices allow separate control of both the particle number and system size. As\na consequence, there are two distinct \"thermodynamic\" limits that can be\ndefined for these systems: i) \"infinite-volume limit\" at constant finite\ndensity, and ii) \"empty-lattice limit\" at constant particle number. To probe\nthe difference between these two limits and their crossover, we consider a\npartially occupied lattice and study the transport of non-interacting fermions\nand fermions interacting at the mean-field level into the unoccupied region. In\nthe infinite-volume limit, a finite steady-state current emerges. On the other\nhand, in the empty-lattice limit there is no finite steady-state current. By\nchanging the initial filling, we find a smooth crossover between the two\nlimits. Our predictions may be verified using available experimental tools and\ndemonstrate a fundamental difference between isolated small systems such as\nultra-cold atoms and conventional condensed-matter systems.",
        "positive": "First-order dissipative phase transition in an exciton-polariton\n  condensate: We investigate the phase diagram of a two-dimensional driven-dissipative\nsystem of polaritons coupled to the excitonic reservoir. We find that two\ncritical points exists. The first corresponds to the quasi-condensation and the\nsecond to a first-order phase transition from the non-uniform state with\nspatially modulated density to a uniform state. The latter is related to the\nmodulational instability of a homogeneous state due to the repulsive\ninteractions with the non-condensed reservoir. The first-order character of the\ntransition is evidenced by a discontinuity in the density and the correlation\nlength as well as the phase coexistence and metastability. Moreover, we show\nthat a signature of a Berezinskii-Kosterlitz-Thouless-like transition can be\nobserved in the non-uniform phase."
    },
    {
        "anchor": "Observation of a superfluid Hall effect: Measurement techniques based upon the Hall effect are invaluable tools in\ncondensed matter physics. When an electric current flows perpendicular to a\nmagnetic field, a Hall voltage develops in the direction transverse to both the\ncurrent and the field. In semiconductors, this behaviour is routinely used to\nmeasure the density and charge of the current carriers (electrons in conduction\nbands or holes in valence bands) -- internal properties of the system that are\nnot accessible from measurements of the conventional resistance. For strongly\ninteracting electron systems, whose behaviour can be very different from the\nfree electron gas, the Hall effect's sensitivity to internal properties makes\nit a powerful tool; indeed, the quantum Hall effects are named after the tool\nby which they are most distinctly measured instead of the physics from which\nthe phenomena originate. Here we report the first observation of a Hall effect\nin an ultracold gas of neutral atoms, revealed by measuring a Bose-Einstein\ncondensate's transport properties perpendicular to a synthetic magnetic field.\nOur observations in this vortex-free superfluid are in good agreement with\nhydrodynamic predictions, demonstrating that the system's global\nirrotationality influences this superfluid Hall signal.",
        "positive": "Inelastic collisions in radiofrequency-dressed mixtures of ultracold\n  atoms: Radiofrequency (RF)-dressed potentials are a promising technique for\nmanipulating atomic mixtures, but so far little work has been undertaken to\nunderstand the collisions of atoms held within these traps. In this work, we\ndress a mixture of 85Rb and 87Rb with RF radiation, characterize the inelastic\nloss that occurs, and demonstrate species-selective manipulations. Our\nmeasurements show the loss is caused by two-body 87Rb+85Rb collisions, and we\nshow the inelastic rate coefficient varies with detuning from the RF resonance.\nWe explain our observations using quantum scattering calculations, which give\nreasonable agreement with the measurements. The calculations consider magnetic\nfields both perpendicular to the plane of RF polarization and tilted with\nrespect to it. Our findings have important consequences for future experiments\nthat dress mixtures with RF fields."
    },
    {
        "anchor": "Integrable supersymmetric chain without particle conservation: We introduce a new integrable supersymmetric lattice chain which violates\nfermion conservation and exhibits fermion-hole symmetry. The model displays\nexponential degeneracy in every eigenstate including the groundstate. This\ndegeneracy is expressed in the possibility to create any number of zero modes\nreminiscent of Cooper pairs.",
        "positive": "Quantum dynamics of ultracold Bose polarons: We analyze the dynamics of Bose polarons in the vicinity of a Feshbach\nresonance between the impurity and host atoms. We compute the radio-frequency\nabsorption spectra for the case when the initial state of the impurity is\nnon-interacting and the final state is strongly interacting. We compare results\nof different theoretical approaches including a single excitation expansion, a\nself-consistent T-matrix method, and a time-dependent coherent state approach.\nOur analysis reveals sharp spectral features arising from metastable states\nwith several Bogoliubov excitations bound to the impurity atom. This surprising\nresult of the interplay of many-body and few-body Efimov type bound state\nphysics can only be obtained by going beyond the commonly used Fr\\\"ohlich model\nand including quasiparticle scattering processes. Close to the resonance we\nfind that strong fluctuations lead to a broad, incoherent absorption spectrum\nwhere no quasi-particle peak can be assigned."
    },
    {
        "anchor": "Theory for Self-Bound States of Dipolar Bose-Einstein Condensates: We investigate the self-bound states of dipolar Dy condensates with the\nGaussian-state ansatz which improves the conventional coherent-state ansatz\nwith multimode squeezed coherent states. We show that the self-bound states\nconsist of the experimentally observed self-bound liquid phase and the\nunobserved self-bound gas phase. The numerically obtained gas-liquid boundary\nis in good agreement with experimental data. Our theory also allows one to\nextract the real part of the three-body coupling constant of the Dy atoms from\nthe particle number distribution of the condensates. In particular, we results\nshow that the self-bound states are stabilized by the short-range three-body\nrepulsion. Our study shed a different light to understand the self-bound\ndroplets of Bose-Einstein condensates.",
        "positive": "Hartree-Fock treatment of Fermi polarons using the Lee-Low-Pine\n  transformation: We consider the Fermi polaron problem at zero temperature, where a single\nimpurity interacts with non-interacting host fermions. We approach the problem\nstarting with a Frohlich-like Hamiltonian where the impurity is described with\ncanonical position and momentum operators. We apply the Lee-Low-Pine (LLP)\ntransformation to change the fermionic Frohlich Hamiltonian into the fermionic\nLLP Hamiltonian which describes a many-body system containing host fermions\nonly. We adapt the self-consistent Hartree-Fock (HF) approach, first proposed\nby Edwards, to the fermionic LLP Hamiltonian in which a pair of host fermions\nwith momenta $\\mathbf{k}$ and $\\mathbf{k}'$ interact with a potential\nproportional to $\\mathbf{k}\\cdot\\mathbf{k}'$. We apply the HF theory, which has\nthe advantage of not restricting the number of particle-hole pairs, to\nrepulsive Fermi polarons in one dimension. When the impurity and host fermion\nmasses are equal our variational ansatz, where HF orbitals are expanded in\nterms of free-particle states, produces results in excellent agreement with\nMcGuire's exact analytical results based on the Bethe ansatz. This work raises\nthe prospect of using the HF ansatz and its time-dependent generalization as\nbuilding blocks for developing all-coupling theories for both equilibrium and\nnonequilibrium Fermi polarons in higher dimensions"
    },
    {
        "anchor": "Spectral properties and breathing dynamics of a few-body Bose-Bose\n  mixture in a 1D harmonic trap: We investigate a few-body mixture of two bosonic components, each consisting\nof two particles confined in a quasi one-dimensional harmonic trap. By means of\nexact diagonalization with a correlated basis approach we obtain the low-energy\nspectrum and eigenstates for the whole range of repulsive intra- and\ninter-component interaction strengths. We analyse the eigenvalues as a function\nof the inter-component coupling, covering hereby all the limiting regimes, and\ncharacterize the behaviour in-between these regimes by exploiting the\nsymmetries of the Hamiltonian. Provided with this knowledge we study the\nbreathing dynamics in the linear-response regime by slightly quenching the trap\nfrequency symmetrically for both components. Depending on the choice of\ninteractions strengths, we identify 1 to 3 monopole modes besides the breathing\nmode of the center of mass coordinate. For the uncoupled mixture each monopole\nmode corresponds to the breathing oscillation of a specific relative\ncoordinate. Increasing the inter-component coupling first leads to multi-mode\noscillations in each relative coordinate, which turn into single-mode\noscillations of the same frequency in the composite-fermionization regime.",
        "positive": "Analysis of two and three dipolar bosons in a spherical harmonic trap: As dipolar gases become more readily accessible in experiment there is a need\nto develop a comprehensive theoretical framework of the few-body physics of\nthese systems. Here, we extend the coupled-pair approach developed for the\nunitary two-component Fermi gas to a few-body system of dipolar bosons in a\nspherical harmonic trap. The long range and anisotropy of the dipole-dipole\ninteraction is handled by a flexible and efficient correlated gaussian basis\nwith stochastically variational optimisation. We calculate the eigenenergy\nspectrum and structural properties of two and three trapped bosonic dipoles.\nThis demonstrates the efficiency and flexibility of the coupled-pair approach\nat dealing with systems with complex interactions."
    },
    {
        "anchor": "Engineering the Dynamics of Effective Spin-Chain Models for Strongly\n  Interacting Atomic Gases: We consider a one-dimensional gas of cold atoms with strong contact\ninteractions and construct an effective spin-chain Hamiltonian for a\ntwo-component system. The resulting Heisenberg spin model can be engineered by\nmanipulating the shape of the external confining potential of the atomic gas.\nWe find that bosonic atoms offer more flexibility for tuning independently the\nparameters of the spin Hamiltonian through interatomic (intra-species)\ninteraction which is absent for fermions due to the Pauli exclusion principle.\nOur formalism can have important implications for control and manipulation of\nthe dynamics of few- and many-body quantum systems; as an illustrative example\nrelevant to quantum computation and communication, we consider state transfer\nin the simplest non-trivial system of four particles representing\nexchange-coupled qubits.",
        "positive": "Approximate mean-field equations of motion for quasi-2D Bose-Einstein\n  condensate systems: We present a method for approximating the solution of the three-dimensional,\ntime-dependent Gross-Pitaevskii equation (GPE) for Bose-Einstein condensate\nsystems where the confinement in one dimension is much tighter than in the\nother two. This method employs a hybrid Lagrangian variational technique whose\ntrial wave function is the product of a completely unspecified function of the\ncoordinates in the plane of weak confinement and a gaussian in the strongly\nconfined direction having a time-dependent width and quadratic phase. The\nhybrid Lagrangian variational method produces equations of motion that consist\nof (1) a two-dimensional, effective GPE whose nonlinear coefficient contains\nthe width of the gaussian and (2) an equation of motion for the width that\ndepends on the integral of the fourth power of the solution of the 2D effective\nGPE. We apply this method to the dynamics of Bose-Einstein condensates confined\nin ring-shaped potentials and compare the approximate solution to the numerical\nsolution of the full 3D GPE."
    },
    {
        "anchor": "Characterizing dynamical phase transitions in a spinor Bose-Einstein\n  condensate via quantum and semiclassical analyses: Phase transitions in nonequilibrium dynamics of many body quantum systems,the\nso-called dynamical phases transition (DPTs), play an important role for\nunderstanding various dynamical phenomena observed in different branches of\nphysics.In general, there have two types of DPTs, the first one refers to the\nphase transition that is characterized by distinct evolution behaviors of a\nphysical observable, while the second one is marked by the nonanalyticities in\nthe rate function of the initial state survival probability. Here, we focus on\nsuch DPTs from both quantum and semiclassical perspectives in a spinor\nBose-Einstein condensate (BEC), an ideal platform to investigate nonequilibrium\ndynamics.By using the sudden quench process, we demonstrate that the system\nexhibits both types of DPTs as the control parameter quenches through the\ncritical one, referring to as the critical quench. We show analytically how to\ndetermine the critical quenches by means of the semiclassical approach and\ncarry out a detailed examination on both semiclassical and quantum signatures\nof two types of DPTs. Moreover, we further reveal that the occurrence of DPTs\nis closely connected to the separatrix in the underlying classical system. Our\nfindings provide more insights into the properties of DPTs and verify the\nusefulness of semiclassical analysis for understanding DPTs in quantum systems\nwith well-defined semiclassical limit.",
        "positive": "Protected quasi-locality in quantum systems with long-range interactions: We study the out-of-equilibrium dynamics of quantum systems with long-range\ninteractions. Two different models describing, respectively, interacting\nlattice bosons and spins are considered. Our study relies on a combined\napproach based on accurate many-body numerical calculations as well as on a\nquasiparticle microscopic theory. For sufficiently fast decaying long-range\npotentials, we find that the quantum speed limit set by the long-range\nLieb-Robinson bounds is never attained and a purely ballistic behavior is\nfound. For slowly decaying potentials, a radically different scenario is\nobserved. In the bosonic case, a remarkable local spreading of correlations is\nstill observed, despite the existence of infinitely fast traveling excitations\nin the system. This is in marked contrast to the spin case, where locality is\nbroken. We finally provide a microscopic justification of the different regimes\nobserved and of the origin of the protected locality in the bosonic model."
    },
    {
        "anchor": "Microscopic Observation of Pauli Blocking in Degenerate Fermionic\n  Lattice Gases: The Pauli exclusion principle is one of the most fundamental manifestations\nof quantum statistics. Here, we report on its local observation in a\nspin-polarized degenerate gas of fermions in an optical lattice. We probe the\ngas with single-site resolution using a new generation quantum gas microscope\navoiding the common problem of light induced losses. In the band insulating\nregime, we measure a strong local suppression of particle number fluctuations\nand a low local entropy per atom. Our work opens a new avenue for studying\nquantum correlations in fermionic quantum matter both in and out of\nequilibrium.",
        "positive": "Self-Trapped Polarons and Topological Defects in a Topological Mott\n  Insulator: Many-body interactions in topological quantum systems can give rise to new\nphases of matter, which simultaneously exhibit both rich spatial features and\ntopological properties. In this work, we consider spinless fermions on a\ncheckerboard lattice with nearest and next-to-nearest neighbor interactions. We\ncalculate the phase diagram at half filling, which presents, in particular, an\ninteraction-induced quantum anomalous Hall phase. We study the system at\nincommensurate fillings using an unrestricted Hartree-Fock ansatz and report a\nrich zoo of solutions such as self-trapped polarons and domain walls above an\ninteraction-induced topological insulator. We find that, as a consequence of\nthe interplay between the interaction-induced topology and topological defects,\nthese domain walls separate two phases with opposite topological invariants and\nhost topologically protected chiral edge states. Finally, we discuss\nexperimental prospects to observe these novel phenomena in a quantum simulator\nbased on laser-dressed Rydberg atoms in an optical lattice."
    },
    {
        "anchor": "Solitary waves and yrast states in Bose-Einstein condensed gases of\n  atoms: Considering a Bose-Einstein condensed gas confined in one dimension with\nperiodic boundary conditions, we demonstrate that, very generally,\nsolitary-wave and rotational excitations coincide. This exact equivalence\nallows us to establish connections between a number of effects that are present\nin these two problems, many of which have been studied using the mean-field\napproximation.",
        "positive": "Parity effect in a mesoscopic Fermi gas: We develop a quantitative analytic theory that accurately describes the\nodd-even effect observed experimentally in a one-dimensional, trapped Fermi gas\nwith a small number of particles [G. Z\\\"urn et al., Phys. Rev. Lett. 111,\n175302 (2013)]. We find that the underlying physics is similar to the parity\neffect known to exist in ultrasmall mesoscopic superconducting grains and\natomic nuclei. However, in contrast to superconducting nanograins, the density\n(Hartree) correction dominates over the superconducting pairing fluctuations\nand leads to a much more pronounced odd-even effect in the mesoscopic, trapped\nFermi gas. We calculate the corresponding parity parameter and separation\nenergy using both perturbation theory and a path integral framework in the\nmesoscopic limit, generalized to account for the effects of the trap, pairing\nfluctuations, and Hartree corrections. Our results are in an excellent\nquantitative agreement with experimental data and exact diagonalization.\nFinally, we discuss a few-to-many particle crossover between the perturbative\nmesoscopic regime and non-perturbative many-body physics that the system\napproaches in the thermodynamic limit."
    },
    {
        "anchor": "Stationary states of a nonlinear Schr\u00f6dinger lattice with a harmonic\n  trap: We study a discrete nonlinear Schr\\\"odinger lattice with a parabolic trapping\npotential. The model, describing, e.g., an array of repulsive Bose-Einstein\ncondensate droplets confined in the wells of an optical lattice, is\nanalytically and numerically investigated. Starting from the linear limit of\nthe problem, we use global bifurcation theory to rigorously prove that - in the\ndiscrete regime - all linear states lead to nonlinear generalizations thereof,\nwhich assume the form of a chain of discrete dark solitons (as the density\nincreases). The stability of the ensuing nonlinear states is studied and it is\nfound that the ground state is stable, while the excited states feature a chain\nof stability/instability bands. We illustrate the mechanisms under which\ndiscreteness destabilizes the dark-soliton configurations, which become stable\nonly inside the continuum regime. Continuation from the anti-continuum limit is\nalso considered, and a rich bifurcation structure is revealed.",
        "positive": "High Controllable and Robust 2D Spin-Orbit Coupling for Quantum Gases: We report the realization of a robust and highly controllable two-dimensional\n(2D) spin-orbit (SO) coupling with topological non-trivial band structure. By\napplying a retro-reflected 2D optical lattice, phase tunable Raman couplings\nare formed into the anti-symmetric Raman lattice structure, and generate the 2D\nSO coupling with precise inversion and $C_4$ symmetries, leading to\nconsiderably enlarged topological regions. The life time of the 2D SO coupled\nBose-Einstein condensate reaches several seconds, which enables the exploring\nof fine tuning interaction effects. These essential advantages of the present\nnew realization open the door to explore exotic quantum many-body effects and\nnon-equilibrium dynamics with novel topology."
    },
    {
        "anchor": "Quench dynamics and statistics of measurements for a line of quantum\n  spins in two dimensions: Motivated by recent experiments, we investigate the dynamics of a line of\nspin-down spins embedded in the ferromagnetic spin-up ground state of a\ntwo-dimensional xxz model close to the Ising limit. In a situation where the\ncouplings in x and y direction are different, the quench dynamics of this\nsystem is governed by the interplay of one-dimensional excitations (kinks and\nholes) moving along the line and single-spin excitations evaporating into the\ntwo-dimensional background. A semiclassical approximation can be used to\ncalculate the dynamics of this complex quantum system. Recently, it became\npossible to perform projective quantum measurements on such spin systems,\nallowing to determine, e.g., the z-component of each individual spin. We\npredict the statistical properties of such measurements which contain much more\ninformation than correlation functions.",
        "positive": "Spinor Bose-Einstein Condensates of Positronium: Bose-Einstein condensates (BECs) of positronium (Ps) have been of\nexperimental and theoretical interest due to their potential application as the\ngain medium of a $\\gamma$-ray laser. Ps BECs are intrinsically spinor due to\nthe presence of ortho-positronium (o-Ps) and para-positronium (p-Ps), whose\nannihilation lifetimes differ by three orders of magnitude. In this paper, we\nstudy the spinor dynamics and annihilation processes in the p-Ps/o-Ps system\nusing both solutions of the time-dependent Gross-Pitaevskii equations and a\nsemiclassical rate-equation approach. The spinor interactions have an $O(4)$\nsymmetry which is broken to $SO(3)$ by an internal energy difference between\no-Ps and p-Ps. For an initially unpolarized condensate, there is a threshold\ndensity of $\\approx 10^{19}$ cm$^{-3}$ at which spin mixing between o-Ps and\np-Ps occurs. Beyond this threshold, there are unstable spatial modes\naccompanied by spin mixing. To ensure a high production yield above the\ncritical density, a careful choice of external field must be made to avoid the\nspin mixing instability."
    },
    {
        "anchor": "Dynamical excitations in the collision of 2D Bose-Einstein condensates: We carry out simulations of the collision of two components of an\nadiabatically divided, quasi-2D BEC. We identify under, over and critically\ndamped regimes in the dipole oscillations of the components according to the\nbalance of internal and centre-of-mass (c.m.) energies of the components and\ninvestigate the creation of internal excitations. We distinguish the behaviour\nof this system from previous studies of quasi-1D BEC's. In particular we note\nthat the nature of the internal excitations is only essentially sensitive to an\ninitial phase difference between the components in the overdamped regime.",
        "positive": "Frictionless quantum quenches in ultracold gases: a quantum dynamical\n  microscope: In this article, a method is proposed to spatially scale up a trapped\nultracold gas while conserving the quantum correlations of the initial\nmany-body state. For systems supporting self-similar dynamics, this is achieved\nby implementing a many-body finite-time frictionless quantum quench of the\nharmonic trap which acts as a quantum dynamical microscope."
    },
    {
        "anchor": "Simulating cosmological supercooling with a cold atom system II: We perform an analysis of the supercooled state in an analogue of an early\nuniverse phase transition based on a one dimensional, two-component Bose gas\nwith time-dependent interactions. We demonstrate that the system behaves in the\nsame way as a thermal, relativistic Bose gas undergoing a first order phase\ntransition. We propose a way to prepare the state of the system in the\nmetastable phase as an analogue to supercooling in the early universe. While we\nshow that parametric resonances in the system can be suppressed by thermal\ndamping, we find that the theoretically estimated thermal damping in our model\nis too weak to suppress the resonances for realistic experimental parameters.\nHowever, we propose that experiments to investigate the effective damping rate\nin experiments would be worthwhile.",
        "positive": "Finite Temperature Dipolar ultra-cold Bose gas with Exchange\n  Interactions: We develop finite temperature theory for a trapped dipolar Bose gas including\nthermal exchange interactions. Previous treatments neglected these, difficult\nto compute, terms. We present a methodology for numerically evaluating the\nthermal exchange contributions, making use of cylindrical symmetry. We then\ninvestigate properties of the dipolar gas, including calculating the excitation\nspectrum over the full range of trap anisotropy. We evaluate the contributions\ndue to thermal exchange noting that, under some regimes, these effects can be\nat least as significant as the direct interaction. We therefore provide\nguidance as to when these cumbersome terms can be neglected and when care\nshould be exercised regarding their omission."
    },
    {
        "anchor": "Distribution of eigenfrequencies for oscillations of the ground state in\n  the Thomas--Fermi limit: In this work, we present a systematic derivation of the distribution of\neigenfrequencies for oscillations of the ground state of a repulsive\nBose-Einstein condensate in the semi-classical (Thomas-Fermi) limit. Our\ncalculations are performed in 1-, 2- and 3-dimensional settings. Connections\nwith the earlier work of Stringari, with numerical computations, and with\ntheoretical expectations for invariant frequencies based on symmetry principles\nare also given.",
        "positive": "Quench Dynamics of a Fermi Gas with Strong Non-Local Interactions: We induce strong non-local interactions in a 2D Fermi gas in an optical\nlattice using Rydberg dressing. The system is approximately described by a\n$t-V$ model on a square lattice where the fermions experience isotropic\nnearest-neighbor interactions and are free to hop only along one direction. We\nmeasure the interactions using many-body Ramsey interferometry and study the\nlifetime of the gas in the presence of tunneling, finding that tunneling does\nnot reduce the lifetime. To probe the interplay of non-local interactions with\ntunneling, we investigate the short-time relaxation dynamics of charge density\nwaves in the gas. We find that strong nearest-neighbor interactions slow down\nthe relaxation. Our work opens the door for quantum simulations of systems with\nstrong non-local interactions such as extended Fermi-Hubbard models."
    },
    {
        "anchor": "Experimental verification of the very strong coupling regime in a GaAs\n  quantum well microcavity: When the coupling between light and matter becomes comparable to the energy\ngap between different excited states they hybridize, leading to the appearance\nof a rich and complex phenomenology which attracted remarkable interest in\nrecent years. While the mixing between states with different number of\nexcitations, so-called ultrastrong coupling regime, has been observed in\nvarious implementations, the effect of the hybridization between different\nsingle excitation states, referred to as very strong coupling regime, has\nremained elusive. In semiconductor quantum wells such a regime is predicted to\nmanifest as a photon-mediated electron-hole coupling leading to different\nexcitonic wavefunctions for the two polaritonic branches when the ratio of the\ncoupling strength to exciton binding energy approaches unity. Here, we verify\nexperimentally the existence of this regime in magneto-optical measurements on\na microcavity with 28 GaAs quantum wells, showing that the average\nelectron-hole separation of the upper polariton is significantly increased\ncompared to the bare quantum well exciton Bohr radius. This manifests in a\ndiamagnetic shift around zero detuning that exceeds the shift of the lower\npolariton by one order of magnitude and the bare quantum well exciton\ndiamagnetic shift by a factor of two. The lower polariton exhibits a\ndiamagnetic shift smaller than expected from the coupling of a rigid exciton to\nthe cavity mode which suggests more tightly bound electron-hole pairs than in\nthe bare quantum well.",
        "positive": "Classifying the universal coarsening dynamics of a quenched\n  ferromagnetic condensate: Scale invariance and self-similarity in physics provide a unified framework\nto classify phases of matter and dynamical properties of near-equilibrium\nsystems. However, extending this framework to far-from-equilibrium quantum\nmany-body systems and categorizing their dynamics have remained a major\nchallenge in physics. Here, we report on the first classification of universal\ncoarsening dynamics in a quenched two-dimensional ferromagnetic spinor Bose\ngas. We observe spatiotemporal scaling of spin correlation functions with\ndistinguishable scaling exponents, $1/z=0.58(2)$ and $1/z=0.43(2)$,\ncharacteristic, respectively, of binary and diffusive fluids. We find the\nuniversality class of the coarsening dynamics are determined by the symmetry of\nthe order parameters and the annihilation dynamics of the topological defects.\nThese observations are in excellent agreement with many-body simulations. Our\nresults represent a paradigmatic example of categorizing far-from-equilibrium\ndynamics in quantum many-body systems."
    },
    {
        "anchor": "Finite temperature phase diagram of spin-1/2 bosons in two-dimensional\n  optical lattice: We study a two-species bosonic Hubbard model on a two-dimensional square\nlattice by means of quantum Monte Carlo simulations and focus on finite\ntemperature effects. We show in two different cases, ferro- and\nantiferromagnetic spin-spin interactions, that the phase diagram is composed of\nsolid Mott phases, liquid phases and superfluid phases. In the\nantiferromagnetic case, the superfluid (SF) is polarized while the Mott\ninsulator (MI) and normal Bose liquid (NBL) phases are not. On the other hand,\nin the ferromagnetic case, none of the phases is polarized. The\nsuperfluid-liquid transition is of the Berezinsky-Kosterlitz-Thouless type\nwhereas the solid-liquid passage is a crossover.",
        "positive": "Two- and three-body effective potentials between impurities in ideal BEC: We exactly calculate the full temperature dependence of Casimir-like forces\nappearing between two and three static impurities loaded in the ideal Bose gas\nbelow the Bose-Einstein condensation transition point. Assuming the\nshort-ranged character of the boson-impurity interaction, the calculation\nprocedure presented here can be easily extended on a Bose system with an\narbitrary number of impurities immersed."
    },
    {
        "anchor": "Dynamics of the modified Kibble-\u017burek mechanism in antiferromagnetic\n  spin-1 condensates: We investigate the dynamics and outcome of a quantum phase transition from an\nantiferromagnetic to phase separated ground state in a spin-1 Bose-Einstein\ncondensate of ultracold atoms. We explicitly demonstrate double universality in\ndynamics within experiments with various quench time. Furthermore, we show that\nspin domains created in the nonequilibrium transition constitute a set of\nmutually incoherent quasicondensates. The quasicondensates appear to be\npositioned in a semi-regular fashion, which is a result of the conservation of\nlocal magnetization during the post-selection dynamics.",
        "positive": "The multichannel nature of three-body recombination for ultracold\n  $^{39}$K: We develop a full multichannel spin model in momentum space to investigate\nthree-body recombination of identical alkali-metal atoms colliding in a\nmagnetic field. The model combines the exact three-atom spin structure and\nrealistic pairwise atom-atom interactions. By neglecting the interaction\nbetween two particles when the spectating particle is not in its initial spin\nstate we arrive at an approximate model. With this approximate model we achieve\nexcellent agreement with the recent precise measurement of the ground Efimov\nresonance position in potassium-39 close to 33.58 G [Chapurin $et$ $al$., Phys.\nRev. Lett. 123, 233402 (2019)]. We analyze the limitations of our approximation\nby comparing to the numerical results for the full system and find that it\nbreaks down for Feshbach resonances at larger magnetic fields in the same spin\nchannel. There the relevant three-body closed channel thresholds are much\ncloser to the open channel threshold, which enhances the corresponding\nmultichannel couplings. Therefore the neglected components of the interaction\nshould be included for those Feshbach resonances."
    },
    {
        "anchor": "Exciton-Mott Physics in Two-Dimensional Electron-Hole Systems: Phase\n  Diagram and Single-Particle Spectra: Exciton Mott physics in two-dimensional electron-hole (e-h) systems is\nstudied in the quasiequilibrium, which is the crossovers or phase transitions\nbetween the insulating exciton gas and the metallic e-h plasma. By developing a\nself-consistent screened T-matrix approximation, we succeed in obtaining the\n\"global\" phase diagram on the plane of the e-h density and the temperature as a\ncontour plot of the exciton ionization ratio. The detailed features of the\nexciton-Mott crossover at high temperature are figured out beyond the\nconventionally used concept of the Mott density. At low temperature, we find\nnot only the region unstable toward the inhomogeneity but the pure Mott\ntransition point characterized by the discontinuity in the ionization ratio.\nThe single particle spectra also exhibit interesting features reflecting the\nexcitonic correlations.",
        "positive": "Fast production of ultracold sodium gases using light--induced\n  desorption and optical trapping: In this paper, we report on the production of a Bose--Einstein condensate\n(BEC) of sodium using light--induced desorption as an atomic source. We load\nabout 2X10^7 atoms in a MOT from this source with a ~6 s loading time constant.\nThe MOT lifetime can be kept around 27 s by turning off the desorbing light\nafter loading. We show that the pressure drops down by a factor of 40 in less\nthan 100 ms after the extinction of the desorbing light, restoring the low\nbackground pressure for evaporation. Using this technique, a \\na BEC with 10^4\natoms is produced after a 6 s evaporation in an optical dipole trap."
    },
    {
        "anchor": "Effects of fermion exchanges on the polarization of exciton condensates: Exchange processes are responsible for the stability of elementary boson\ncondensates with respect to their possible fragmentation. This remains true for\ncomposite bosons when single fermion exchanges are included but spin degrees of\nfreedom are ignored. We here show that their inclusion can produce a\n\"spin-fragmentation\" of a condensate of dark excitons, i.e., an unpolarized\ncondensate with equal amount of dark excitons with spins (+2) and (-2). Quite\nsurprisingly, for spatially indirect excitons of semiconductor bilayers, we\npredict that the condensate polarization can switch from unpolarized to fully\npolarized, depending on the distance between the layers confining electrons and\nholes. Remarkably, the threshold distance associated to this switching lies in\nthe regime where experiments are nowadays carried out.",
        "positive": "The influence of the interaction between quasiparticles on parametric\n  resonance in Bose-Einstein quasicondensates: We perform a simulation of the experiment [1] where the temporal modification\nof the effective one dimensional interaction constant was used to create pairs\nof atoms with opposite velocities. The simulations clearly demonstrate huge\nimpact of interaction between quasiparticles due to finite temperature on the\npair production process, explaining relatively small atom pair production and\nthe absence of the number squeezing in the experiment."
    },
    {
        "anchor": "Thouless pumping and topology: Thouless pumping provides one of the simplest manifestations of topology in\nquantum systems, and has attracted a lot of recent interest, both theoretically\nand experimentally. Since the seminal works by Thouless and Niu in 1983 and\n1984, it is argued that the quantization of the pumped charge is robust against\nweak disorder, but a clear characterization of the localization properties of\nthe relevant states, and the breakdown of quantized transport in the presence\nof interaction or out of the adiabatic approximation, has been long debated.\nThouless pumping is also the first example of a topological phase emerging in a\nperiodically-driven system. Driven systems can exhibit exotic topological\nphases without any static analogue and have been the subject of many recent\nproposals both in fermionic and bosonic systems in diverse platforms ranging\nfrom cold atoms to photonics and condensed matter systems. In this respect,\nthis review has a twofold purpose: On the one hand, it serves as a basis to\nunderstand the robustness of the topology of slowly-driven systems per se; On\nthe other hand, it highlights the rich properties of topological pumps and\ntheir diverse range of applications, for instance, in systems with synthetic\ndimensions or for understanding higher-order topological phases. These examples\nunderline the relevance of topological pumping for the fast growing field of\ntopological quantum matter.",
        "positive": "Three-dimensional solitons in Rydberg-Dressed cold atomic gases with\n  spin-orbit coupling: We present numerical results for three-dimensional (3D) solitons with\nsymmetries of the semi-vortex (SV) and mixed-mode (MM) types, which can be\ncreated in spinor Bose-Einstein condensates of Rydberg atoms under the action\nof the spin-orbit coupling (SOC). By means of systematic numerical\ncomputations, we demonstrate that the interplay of SOC and long-range\nspherically symmetric Rydberg interactions stabilize the 3D solitons, improving\ntheir resistance to collapse. We find how the stability range depends on the\nstrengths of the SOC and Rydberg interactions and the soft-core atomic radius."
    },
    {
        "anchor": "Interference-induced suppression of particle emission from a\n  Bose-Einstein condensate in lattice with time-periodic modulations: Collective emission of particles from a parametrically driven condensate has\nattracted significant experimental and theoretical attention due to the\nappealing visual effects and potential metrological applications. In this\npaper, we investigate the particle emission from a Bose-Einstein condensate\nconfined in a one-dimensional lattice with periodically modulated interparticle\ninteractions. We give the regimes for discrete modes, and find that the\nemission is distinctly suppressed. The configuration induces a broad band, but\ndue to the interference of the matter waves few particles can be ejected. We\nfurther qualitatively model the emission process, and demonstrate the\nshort-time behaviors. This engineering provides a way for manipulating the\npropagation of particles and the corresponding dynamics of condensates in\nlattices, and may find use in other nonequilibrium problems with time-periodic\ndriving.",
        "positive": "Realization of a high power optical trapping setup free from thermal\n  lensing effects: Transmission of high power laser beams through partially absorbing materials\nmodifies the light propagation via a thermally-induced effect known as thermal\nlensing. This may cause changes in the beam waist position and degrade the beam\nquality. Here we characterize the effect of thermal lensing associated with the\ndifferent elements typically employed in an optical trapping setup for cold\natoms experiments. We find that the only relevant thermal lens is represented\nby the $TeO_2$ crystal of the acousto-optic modulator exploited to adjust the\nlaser power on the atomic sample. We then devise a simple and totally passive\nscheme that enables to realize an inexpensive optical trapping apparatus\nessentially free from thermal lensing effects."
    },
    {
        "anchor": "Spinor Condensates on a Cylindrical Surface in Synthetic Gauge Fields: We point out that by modifying the setup of a recent experiment that\ngenerates a Dirac string, one can create a quasi 2D spinor Bose condensate on a\ncylindrical surface with a synthetic magnetic field pointing radially outward\nfrom the cylindrical surface. The synthetic magnetic field takes the form of\nthe Landau gauge. It is generated by the Berry's phase of a spin texture,\nfrozen by an external quadrupolar magnetic field. Unlike in the planar case,\nthere are two types of vortices (called A and B) with the same vorticity. The\nground state for $5\\le S\\le 9$ consists of a row of alternating AB vortices\nlying at the equatorial circle of the cylinder. For higher values of $S$, the A\nand B vortices split into two rows and are displaced from each other along the\ncylindrical axis $z$. The fact that many properties of a BEC are altered in a\ncylindrical surface implies many rich phenomena will emerge for ground states\nin curved surfaces.",
        "positive": "Multimode dynamics and emergence of a characteristic length-scale in a\n  one-dimensional quantum system: We study the non-equilibrium dynamics of a coherently split one-dimensional\n(1d) Bose gas by measuring the full probability distribution functions of\nmatter-wave interference. Observing the system on different length scales\nallows us to probe the dynamics of excitations on different energy scales,\nrevealing two distinct length-scale dependent regimes of relaxation. We measure\nthe crossover length-scale separating these two regimes and identify it with\nthe prethermalized phase-correlation length of the system. Our approach enables\na direct observation of the multimode dynamics characterizing one-dimensional\nquantum systems."
    },
    {
        "anchor": "Entanglement structure of a quantum simulator: the two-component\n  Bose-Hubbard model: We consider a quantum simulator of the Heisenberg chain with ferromagnetic\ninteractions based on the two-component 1D Bose-Hubbard model at filling equal\nto two in the strong coupling regime. The entanglement properties of the ground\nstate are compared between the original spin model and the quantum simulator as\nthe interspecies interaction approaches the intraspecies one. A numerical study\nof the entanglement properties of the quantum simulator state is supplemented\nwith analytical expressions derived from the simulated Hamiltonian. At the\nisotropic point, the entanglement properties of the simulated system are not\nproperly predicted by the quantum simulator.",
        "positive": "Molecular impurities interacting with a many-particle environment: from\n  helium droplets to ultracold gases: In several settings of physics and chemistry one has to deal with molecules\ninteracting with some kind of an external environment, be it a gas, a solution,\nor a crystal surface. Understanding molecular processes in the presence of such\na many-particle bath is inherently challenging, and usually requires\nlarge-scale numerical computations. Here, we present an alternative approach to\nthe problem - that based on the notion of the angulon quasiparticle. We show\nthat molecules rotating inside superfluid helium nanodroplets and Bose-Einstein\nCondensates form angulons, and therefore can be described by straightforward\nsolutions of a simple microscopic Hamiltonian. Casting the problem in the\nlanguage of angulons allows not only to tremendously simplify it, but also to\ngain insights into the origins of the observed phenomena and to make\npredictions for future experimental studies."
    },
    {
        "anchor": "Simulating the Palmer-Chalker state in an orbital superfluid: We consider a bosonic $s$ and $p$ orbital system in a face-centered cubic\n(FCC) optical lattice, and predict a fluctuation-induced instability towards\nthe orbital analogue of Palmer-Chalker state, which is originally proposed in\nan electronic spin system. For bosons loaded in the FCC optical lattice, the\nsingle-particle spectrum has four degenerate band minima with their crystal\nmomenta forming a tetrahedron in Brillouin zone. In the weakly interacting\nregime, the ensuing many-particle ground state, at the classical level,\nunderlies a four-sublattice tetrahedral supercell of spontaneously generated\n$p$-orbital angular momenta through the Bravias-Bloch duality between real and\nmomentum space, and is macroscopically degenerate originating from the\ngeometric frustration. The fluctuations on top of the classical ground state\nlift its degeneracy and select the Palmer-Chalker ordering of $p$-orbital\nangular momenta as the quantum ground state through order-by-disorder\nmechanism. These findings raise the exciting possibility of simulating the\nPalmer-Chalker state with its orbital counterpart in ultracold atomic gases.",
        "positive": "Genuine many-body quantum scars along unstable modes in Bose-Hubbard\n  systems: The notion of many-body quantum scars is associated with special eigenstates,\nusually concentrated in certain parts of Hilbert space, that give rise to\nrobust persistent oscillations in a regime that globally exhibits\nthermalization. Here we extend these studies to many-body systems possessing a\ntrue classical limit characterized by a high-dimensional chaotic phase space,\nwhich are not subject to any particular dynamical constraint. We demonstrate\ngenuine quantum scarring of wave functions concentrated in the vicinity of\nunstable classical periodic mean-field modes in the paradigmatic Bose-Hubbard\nmodel. These peculiar quantum many-body states exhibit distinct phase-space\nlocalization about those classical modes. Their existence is consistent with\nHeller's scar criterion and appears to persist in the thermodynamic\nlong-lattice limit. Launching quantum wave packets along such scars leads to\nobservable long-lasting oscillations, featuring periods that scale\nasymptotically with classical Lyapunov exponents, and displaying intrinsic\nirregularities that reflect the underlying chaotic dynamics, as opposed to\nregular tunnel oscillations."
    },
    {
        "anchor": "Non-equilibrium dynamics of bosons with dipole symmetry: Large-$N$\n  Keldysh approach: We study the quench and the ramp dynamics of interacting $N$-component\ncharged bosons with dipole symmetry using Schwinger-Keldysh field theory in the\nlarge $N$ limit. The equilibrium phase diagram of these bosons shows two phases\nin the large $N$ limit. The first is a normal phase where both the global\n$U(N)$ and the dipole symmetries are conserved and the second is a delocalized\ncondensed phase where both the symmetries are broken. In contrast, our explicit\ncomputation of the steady state after an instantaneous quantum quench from the\ncondensed phase shows that an additional, novel, delocalized normal phase,\nwhere the global $U(N)$ symmetry is conserved but the dipole symmetry is\nbroken, can exist for a range of quench parameters. A study of ramp dynamics of\nthe model shows that the above-mentioned steady state exists only above a\ncritical ramp rate which we estimate.",
        "positive": "Few-body perspective on fermionic pairing in one spatial dimension: In this perspective we discuss recent theoretical and experimental concepts\ngiving a route to a better understanding of conventional and unconventional\npairing mechanisms between opposite-spin fermions arising in one-dimensional\nmesoscopic systems. With special attention, we focus on the problem of\nexperimental detectability of correlations between particles. We argue that\nstate-of-the-art experiments with few ultracold fermions may finally break an\nimpasse and give pioneering and unquestionable verification of the existence of\ncorrelated pairs with non-zero center-of-mass momentum."
    },
    {
        "anchor": "Production of a rubidium Bose-Einstein condensate in a hybrid trap with\n  light induced atom desorption: We report on the production of a rubidium Bose-Einstein condensate in a\nsimplified vacuum apparatus. Magneto-optical traps with large numbers and\nultra-high vacuum for moderately long conservative trap lifetimes of 16 seconds\nare sequentially obtained with light induced rapid atomic vapor pressure\nmodulation. Subsequent evaporative cooling is carried out in two stages in a\nhybrid magnetic quadrupole plus optical dipole trap. High evaporation\nefficiencies are observed in both stages and $^{87}$Rb BECs with more than\n10$^5$ atoms can be reliably produced with total evaporation time of only 9.5\nseconds.",
        "positive": "Spatial Dependence of Entropy in Trapped Ultracold Bose Gases: We find a new physical regime in the trapped Bose-Hubbard Hamiltonian using\ntime-evolving block decimation. Between Mott-insulating and superfluid phases,\nthe latter induced by trap compression, a spatially self-organized state\nappears in which non-local entropy signals entanglement between spatially\ndistant superfluid shells. We suggest a linear rather than harmonic potential\nas an ideal way to observe such a self-organized system. We also explore both\nquantum information and thermal entropies in the superfluid regime, finding\nthat while the former follows the density closely the latter can be strongly\nmanipulated with the mean field."
    },
    {
        "anchor": "Phases of a bilayer Fermi gas: We investigate a two-species Fermi gas in which one species is confined in\ntwo parallel layers and interacts with the other species in the\nthree-dimensional space by a tunable short-range interaction. Based on the\ncontrolled weak coupling analysis and the exact three-body calculation, we show\nthat the system has a rich phase diagram in the plane of the effective\nscattering length and the layer separation. Resulting phases include an\ninterlayer s-wave pairing, an intralayer p-wave pairing, a dimer Bose-Einstein\ncondensation, and a Fermi gas of stable Efimov-like trimers. Our system\nprovides a widely applicable scheme to induce long-range interlayer\ncorrelations in ultracold atoms.",
        "positive": "Pairing of Fermions with Unequal Effective Charges in an Artificial\n  Magnetic Field: Artificial magnetic fields (AMFs) created for ultra cold systems depend\nsensitively on the internal structure of the atoms. In a mixture, each\ncomponent experiences a different AMF depending on its internal state. This\nenables the study of Bardeen-Cooper-Schrieffer pairing of fermions with unequal\neffective charges. In this Letter, we investigate the superconducting (SC)\ntransition of a system formed by such pairs as a function of field strength. We\nconsider a homogeneous two-component Fermi gas of unequal effective charges but\nequal densities with attractive interactions. We find that the phase diagram is\naltered drastically compared to the usual balanced charge case. First, for some\nAMFs there is no SC transition and isolated SC phases are formed, reflecting\nthe discrete Landau level (LL) structure. SC phases become reentrant both in\nAMF and temperature. For extremely high fields where both components are\nconfined to their lowest LLs, the effect of the charge imbalance is suppressed.\nCharge asymmetry reduces the critical temperature even in the low-field\nsemiclassical regime. We discuss a pair breaking mechanism due to the unequal\nLorentz forces acting on the components of the Cooper pairs to identify the\nunderlying physics."
    },
    {
        "anchor": "Interaction-Tuned Dynamical Transitions in a Rashba Spin-Orbit Coupled\n  Fermi Gas: We consider the time evolution of the magnetization in a Rashba\nspin-orbit-coupled Fermi gas, starting from a fully-polarized initial state. We\nmodel the dynamics using a Boltzmann equation, which we solve in the\nHartree-Fock approximation. The resulting non-linear system of equations gives\nrise to three distinct dynamical regimes with qualitatively different\nasymptotic behaviors of the magnetization at long times. The distinct regimes\nand the transitions between them are controlled by the interaction strength:\nfor weakly interacting fermions, the magnetization decays to zero. For\nintermediate interactions, it displays undamped oscillations about zero and for\nstrong interactions, a partially magnetized state is dynamically stabilized.\nThe dynamics we find is a spin analog of interaction induced self-trapping in\ndouble-well Bose Einstein condensates. The predicted phenomena can be realized\nin trapped Fermi gases with synthetic spin-orbit interactions.",
        "positive": "Comment on \"Density and Spin response of a strongly-interacting Fermi\n  gas in the attractive and quasi-repulsive regime\": This is a comment on Phys. Rev. Lett. 108, 080401 (2012) by Palestini et al.\nWe pointed out that the diagrammatic method in that article violates gauge\ninvariance. As a consequence, there will a Meissner effect in the normal phase\nand the contribution from collective modes are not mentioned in the\nsymmetry-broken phase."
    },
    {
        "anchor": "Unique signatures for Bose-Einstein condensation in the decay\n  luminescence lineshape of weakly interacting excitons in a potential trap: We calculate the spatially resolved optical emission spectrum of a weakly\ninteracting Bose gas of excitons confined in a three dimensional potential trap\ndue to interband transitions involving weak direct and phonon mediated\nexciton-photon interactions. Applying the local density approximation, we show\nthat for a non-condensed system the spatio-spectral lineshape of the direct\nprocess reflects directly the shape of the potential. The existence of a\nBose-Einstein condensate changes the spectrum in a characteristic way so that\nit directly reflects the constant chemical potential of the excitons and the\nrenormalization of the quasiparticle excitation spectrum. Typical examples are\ngiven for parameters of the lowest yellow excitons in cuprous oxide.",
        "positive": "Nonlinear waves of polarization in two-component Bose-Einstein\n  condensates: Waves with different symmetries exist in two-component Bose-Einstein\ncondensates (BECs) whose dynamics is described by a system of coupled\nGross-Pitaevskii (GP) equations. A first type of waves corresponds to\nexcitations for which the motion of both components is locally in phase. In the\nsecond type of waves the two components have a counter-phase local motion. In\nthe case of different values of inter- and intra-component interaction\nconstants, the long wave-length behavior of these two modes corresponds to two\ntypes of sound with different velocities. In the limit of weak nonlinearity and\nsmall dispersion the first mode is described by the well-known Korteweg-de\nVries (KdV) equation. We show that in the same limit the second mode can be\ndescribed by the Gardner (modified KdV) equation, if the intra-component\ninteraction constants have close enough values. This leads to a rich\nphenomenology of nonlinear excitations (solitons, kinks, algebraic solitons,\nbreathers) which does not exist in the KdV description."
    },
    {
        "anchor": "Steady states of a driven dissipative dipolar XXZ chain: We study theoretically a driven dissipative one-dimensional XXZ spin$-1/2$\nchain with dipole coupling and a tunable strength of the Ising and XY\ninteraction. Within a mean-field approximation, we find a rich phase diagram\nwith uniform, spin density wave, antiferromagnetic and oscillatory phases, as\nwell as regions of phase bistability. We study the phase diagram of small\nquantum systems using exact diagonalisation, and compare the results to the\nmean-field theory. We find that while expectation values only capture the\nuniform phases of the mean-field theory, fluctuations about these expectation\nvalues give signatures of spatially non-uniform phases and bistabilities. We\nfind these signatures for all ratios of the Ising to XY interaction, showing\nthat they appear to be general features of spin$-1/2$ systems",
        "positive": "Cooperation of different exchange mechanisms in confined magnetic\n  systems: The diluted Kondo lattice model is investigated at strong antiferromagnetic\nlocal exchange couplings J, where almost local Kondo clouds drastically\nrestrict the motion of conduction electrons, giving rise to the possibility of\nquantum localization of conduction electrons for certain geometries of impurity\nspins. This localization may lead to the formation of local magnetic moments in\nthe conduction-electron system, and the inverse indirect magnetic exchange\n(IIME), provided by virtual excitations of the Kondo singlets, couples those\nlocal moments to the remaining electrons. Exemplarily, we study the\none-dimensional two-impurity Kondo model with impurity spins near the chain\nends, which supports the formation of conduction-electron magnetic moments at\nthe edges of the chain for sufficiently strong J. Employing degenerate\nperturbation theory as well as analyzing spin gaps numerically by means of the\ndensity-matrix renormalization group, it is shown that the low-energy physics\nof the model can be well captured within an effective antiferromagnetic\nRKKY-like two-spin model (\"RKKY from IIME\") or within an effective central-spin\nmodel, depending on edge-spin distance and system size."
    },
    {
        "anchor": "Berry's Phase for Ultracold Atoms in an Accelerated Optical Lattice: Berry's phase is investigated for ultracold atoms in a frequency modulated\noptical lattice. It is shown that Berry's phase appears due to Bloch\noscillation and the periodic motion of the optical lattice. Particularly,\nBerry's phase for ultracold atoms under the gravitational force in an\noscillating tight-binding optical lattice is calculated analytically. It is\nfound that the Berry's phase depends linearly on the amplitude of the\noscillation of the optical lattice.",
        "positive": "Supersensitive quantum sensor based on criticality in an\n  antiferromagnetic spinor condensate: We consider an antiferromagnetic Bose-Einstein condensate in a traverse\nmagnetic field with a fixed macroscopic magnetization. The system exhibits two\ndifferent critical behaviors corresponding to transitions from polar to\nbroken-axisymmetry and from antiferromagnetic to broken-axisymmetry phases\ndepending on the value of magnetization. We exploit both types of system\ncriticality as a resource in the precise estimation of control parameter value.\nWe quantify the achievable precision by the quantum Fisher information. We\ndemonstrate supersensitivity and show that the precision scales with the number\nof atoms up to $N^4$ around critically. In addition, we study the precision\nbased on the error-propagation formula providing the simple-to-measure signal\nwhich coincides its scaling with the quantum Fisher information. Finally, we\ntake into account the effect of non-zero temperature and show that the sub-shot\nnoise sensitivity in the estimation of the control parameter is achievable in\nthe low-temperature limit."
    },
    {
        "anchor": "Condensation temperature of strongly interacting $^{39}K$ condensates in\n  the mean-field and semi-classical approximations: We consider the effect of inter-atom interactions on the condensation\ntemperature $T_c$ of an atomic Bose-Einstein condensate. We find an analytic\nexpression of the shift in $T_c$ induced by interactions with respect the ideal\nnon-interacting case, in the mean-field and semi-classical approximations. Such\na shift is expressed in terms of the ratio $a/\\lambda_{T_c}$ between the s-wave\nscattering length $a$ and the thermal wavelength $\\lambda_{T_c}$. This result\nis used to discuss the tension between mean-field predictions and observations\nin strongly interacting $^{39}K$ condensates. It is shown that such a tension\nis solved taking into account the details of the Feshbach resonance used to\ntune $a$ in the experiments.",
        "positive": "Fragmented Superradiance of a Bose-Einstein Condensate in an Optical\n  Cavity: The Dicke model and the superradiance of two-level systems in a radiation\nfield have many applications. Recently, a Dicke quantum phase transition has\nbeen realized with a Bose-Einstein condensate in a cavity. We numerically solve\nthe many-body Schr\\\"odinger equation and study correlations in the ground state\nof interacting bosons in a cavity as a function of the strength of a driving\nlaser. Beyond a critical strength, the bosons occupy multiple modes\nmacroscopically while remaining superradiant. This fragmented superradiance can\nbe detected by analyzing the variance of single-shot measurements."
    },
    {
        "anchor": "Few-to-many vortex states of density-angular-momentum coupled\n  Bose-Einstein condensates: Motivated by recent experiments, we theoretically study a gas of atomic\nbosons confined in an elliptical harmonic trap; forming a quasi-two-dimensional\natomic Bose-Einstein condensate subject to a density-dependent gauge potential\nwhich realises an effective density-angular-momentum coupling. We present exact\nThomas-Fermi solutions which allows us to identify the stable regimes of the\nfull parameter space of the model. Accompanying numerical simulations reveal\nthe effect of the interplay of the rigid body and density-angular-momentum\ncoupling for the elliptically confined condensate. By varying the strength of\nthe gauge potential and trap anisotropy we explore how the superfluid state\nemerges in different experimentally accessible geometries, while for large\nrotation strengths dense vortex lattices and concentric vortex ring\narrangements are obtained.",
        "positive": "Observation of coherent quench dynamics in a metallic many-body state of\n  fermionic atoms: Quantum simulation with ultracold atoms has become a powerful technique to\ngain insight into interacting many-body systems. In particular, the possibility\nto study nonequilibrium dynamics offers a unique pathway to understand\ncorrelations and excitations in strongly interacting quantum matter. So far,\ncoherent nonequilibrium dynamics has exclusively been observed in ultracold\nmany-body systems of bosonic atoms. Here we report on the observation of\ncoherent quench dynamics of fermionic atoms. A metallic state of ultracold\nspin-polarised fermions is prepared along with a Bose-Einstein condensate in a\nshallow three-dimensional optical lattice. After a quench that suppresses\ntunnelling between lattice sites for both the fermions and the bosons, we\nobserve long-lived coherent oscillations in the fermionic momentum\ndistribution, with a period that is determined solely by the Fermi-Bose\ninteraction energy. Our results show that coherent quench dynamics can serve as\na sensitive probe for correlations in delocalised fermionic quantum states and\nfor quantum metrology."
    },
    {
        "anchor": "Precise characterization of ^6Li Feshbach resonances using trap-sideband\n  resolved RF spectroscopy of weakly bound molecules: We have performed radio-frequency dissociation spectroscopy of weakly bound\n^6Li_2 Feshbach molecules using low-density samples of about 30 molecules in an\noptical dipole trap. Combined with a high magnetic field stability this allows\nus to resolve the discrete trap levels in the RF dissociation spectra. This\nnovel technique allows the binding energy of Feshbach molecules to be\ndetermined with unprecedented precision. We use these measurements as an input\nfor a fit to the ^6Li scattering potential using coupled-channel calculations.\nFrom this new potential, we determine the pole positions of the broad ^6Li\nFeshbach resonances with an accuracy better than 7 \\times 10^{-4} of the\nresonance widths. This eliminates the dominant uncertainty for current\nprecision measurements of the equation of state of strongly interacting Fermi\ngases. For example, our results imply a corrected value for the Bertsch\nparameter \\xi measured by Ku et al. [Science 335, 563 (2012)], which is \\xi =\n0.370(5)(8).",
        "positive": "Dynamics of vortex quadrupoles in nonrotating trapped Bose-Einstein\n  condensate: Dynamics of vortex clusters is essential for understanding diverse superfluid\nphenomena. In this paper, we examine the dynamics of vortex quadrupoles in a\ntrapped two-dimensional (2D) Bose-Einstein condensate. We find that the\nmovement of these vortex-clusters fall into three distinct regimes which are\nfully described by the radial positions of the vortices in a 2D isotropic\nharmonic trap, or by the major radius (minor radius) of the elliptical\nequipotential lines decided by the vortex positions in a 2D anisotropic\nharmonic trap. In the \"recombination\" and \"exchange\" regimes the quadrupole\nstructure maintains, while the vortices annihilate each other permanently in\nthe \"annihilation\" regime. We find that the mechanism of the charge flipping in\nthe \"exchange\" regime and the disappearance of the quadrupole structure in the\n\"annihilation\" regime are both through an intermediate state where two vortex\ndipoles connected through a soliton ring. We give the parameter ranges for\nthese three regimes in coordinate space for a specific initial configuration\nand phase diagram of the vortex positions with respect to the Thomas-Fermi\nradius of the condensate. We show that the results are also applicable to\nsystems with quantum fluctuations for the short-time evolution."
    },
    {
        "anchor": "Scaling properties of the Tan's contact: embedding pairs and correlation\n  effect in the Tonks limit: We study the Tan's contact of a one dimensional quantum gas of N repulsive\nidentical bosons confined in a harmonic trap at finite temperature. This\ncanonical ensemble framework corresponds to the experimental conditions, the\nnumber of particles being fixed for each experimental sequence. We show that,\nin the strongly interacting regime, the contact rescaled by the contact at the\nTonks-Girardeau limit is an universal function of two parameters, the rescaled\ninteraction strength and temperature. This means that all pair and correlation\neffects in the Tan's contact are embedded in the Tan's contact in the\nTonks-Girardeau limit.",
        "positive": "Skyrmionic vortex lattices in coherently coupled three-component\n  Bose-Einstein condensates: We show numerically that a harmonically trapped and coherently Rabi-coupled\nthree-component Bose-Einstein condensate can host unconventional vortex\nlattices in its rotating ground state. The discovered lattices incorporate\nsquare and zig-zag patterns, vortex dimers and chains, and doubly quantized\nvortices, and they can be quantitatively classified in terms of a skyrmionic\ntopological index, which takes into account the multicomponent nature of the\nsystem. The exotic ground-state lattices arise due to the intricate interplay\nof the repulsive density-density interactions and the Rabi couplings as well as\nthe ubiquitous phase frustration between the components. In the frustrated\nstate, domain walls in the relative phases can persist between some components\neven at strong Rabi coupling, while vanishing between others. Consequently, in\nthis limit the three-component condensate effectively approaches a\ntwo-component condensate with only density-density interactions. At\nintermediate Rabi coupling strengths, however, we face unique vortex physics\nthat occurs neither in the two-component counterpart nor in the purely\ndensity-density-coupled three-component system."
    },
    {
        "anchor": "High temperature thermodynamics of strongly interacting s-wave and\n  p-wave Fermi gases in a harmonic trap: We theoretically investigate the high-temperature thermodynamics of a\nstrongly interacting trapped Fermi gas near either s-wave or p-wave Feshbach\nresonances, using a second order quantum virial expansion. The second virial\ncoefficient is calculated based on the energy spectrum of two interacting\nfermions in a harmonic trap. We consider both isotropic and anisotropic\nharmonic potentials. For the two-fermion interaction, either s-wave or p-wave,\nwe use a pseudopotential parametrized by a scattering length and an effective\nrange. This turns out to be the simplest way of encoding the energy dependence\nof the low-energy scattering amplitude or phase shift. This treatment of the\npseudopotential can be easily generalized to higher partial-wave interactions.\nWe discuss how the second virial coefficient and thermodynamics are affected by\nthe existence of these finite-range interaction effects. The virial expansion\nresult for a strongly interacting s -wave Fermi gas has already been proved\nvery useful. In the case of p-wave interactions, our results for the\nhigh-temperature equation of state are applicable to future high-precision\nthermodynamic measurements for a spin-polarized Fermi gas near a p-wave\nFeshbach resonance.",
        "positive": "Rice-Mele model with topological solitons in an optical lattice: Attractive ultra-cold fermions trapped in a one-dimensional periodically\nshaken opticla lattices are considered. For an appropriate resonant shaking the\nsystem realizes paradigmatic dimes physics described by Rice-Mele model. The\nimportant feature of our system is the possible presence of controlled defects.\nThey result in the creation of topologically protected loclaized modes carrying\nfractional particle number. Their possible experimental signatures are\ndiscussed."
    },
    {
        "anchor": "Realization of effective super Tonks-Girardeau gases via strongly\n  attractive one-dimensional Fermi gases: A significant feature of the one-dimensional super Tonks-Girardeau gas is its\nmetastable gas-like state with a stronger Fermi-like pressure than for free\nfermions which prevents a collapse of atoms. This naturally suggests a way to\nsearch for such strongly correlated behaviour in systems of interacting\nfermions in one dimension. We thus show that the strongly attractive Fermi gas\nwithout polarization can be effectively described by a super Tonks-Girardeau\ngas composed of bosonic Fermi pairs with attractive pair-pair interaction. A\nnatural description of such super Tonks-Girardeau gases is provided by Haldane\ngeneralized exclusion statistics. In particular, we find that they are\nequivalent to ideal particles obeying more exclusive statistics than\nFermi-Dirac statistics.",
        "positive": "Pairing of electro-magnetic bosons under spin-orbit coupling: We discuss pairing of light-matter bosons under effective spin-orbit (SO)\ncoupling in two-dimensional semiconductors. The SO coupling is shown to induce\ndynamical broadening of a two-body bound state. Application of a transverse\nmagnetic field yields the rich Feshbach resonance phenomenology. We predict\nquantum bosonic halos with a synthetic angular momentum L=2. The d-wave-like\ndressing of the nominally s-wave bound state is induced by SO coupling to the\ncontinuum in the open channel. The fundamental properties of the emergent\nquantum number remain to be explored."
    },
    {
        "anchor": "Robust Vortex Lines, Vortex Rings and Hopfions in 3D Bose-Einstein\n  Condensates: Performing a systematic Bogoliubov-de Gennes spectral analysis, we illustrate\nthat stationary vortex lines, vortex rings and more exotic states, such as\nhopfions, are robust in three-dimensional atomic Bose-Einstein condensates, for\nlarge parameter intervals. Importantly, we find that the hopfion can be\nstabilized in a simple parabolic trap, without the need for trap rotation or\ninhomogeneous interactions. We supplement our spectral analysis by studying the\ndynamics of such stationary states; we find them to be robust against\nsignificant perturbations of the initial state. In the unstable regimes, we not\nonly identify the unstable mode, such as a quadrupolar or hexapolar mode, but\nwe also observe the corresponding instability dynamics. Furthermore, deep in\nthe Thomas-Fermi regime, we investigate the particle-like behavior of vortex\nrings and hopfions.",
        "positive": "Observation of heat scaling across a first-order quantum phase\n  transition in a spinor condensate: Heat generated as a result of the breakdown of an adiabatic process is one of\nthe central concepts of thermodynamics. In isolated systems, the heat can be\ndefined as an energy increase due to transitions between distinct energy\nlevels. Across a second-order quantum phase transition (QPT), the heat is\npredicted theoretically to exhibit a power-law scaling, but it is a significant\nchallenge for an experimental observation. In addition, it remains elusive\nwhether a power-law scaling of heat can exist for a first-order QPT. Here we\nexperimentally observe a power-law scaling of heat in a spinor condensate when\na system is linearly driven from a polar phase to an antiferromagnetic phase\nacross a first-order QPT. We experimentally evaluate the heat generated during\ntwo non-equilibrium processes by probing the atom number on a hyperfine energy\nlevel. The experimentally measured scaling exponents agree well with our\nnumerical simulation results. Our work therefore opens a new avenue to\nexperimentally and theoretically exploring the properties of heat in\nnon-equilibrium dynamics."
    },
    {
        "anchor": "Role of interactions in time-of-flight expansion of atomic clouds from\n  optical lattices: We calculate the effect of interactions on the expansion of ultracold atoms\nfrom a single site of an optical lattice. We use these results to predict how\ninteractions influence the interference pattern observed in a time of flight\nexperiment. We find that for typical interaction strengths their influence is\nnegligible, yet that they reduce visibility near a scattering resonance.",
        "positive": "Chaos and ergodicity across the energy spectrum of interacting bosons: We identify the chaotic phase of the Bose-Hubbard Hamiltonian by the\nenergy-resolved correlation between spectral features and structural changes of\nthe associated eigenstates as exposed by their generalized fractal dimensions.\nThe eigenvectors are shown to become ergodic in the thermodynamic limit, in the\nconfiguration space Fock basis, in which random matrix theory offers a\nremarkable description of their typical structure. The distributions of the\ngeneralized fractal dimensions, however, are ever more distinguishable from\nrandom matrix theory as the Hilbert space dimension grows."
    },
    {
        "anchor": "Tonks-Girardeau and Super Tonks-Girardeau States of a Trapped 1D Spinor\n  Bose Gas: A harmonically trapped ultracold 1D spin-1 Bose gas with strongly repulsive\nor attractive 1D even-wave interactions induced by a 3D Feshbach resonance is\nstudied. The exact ground state, a hybrid of Tonks-Girardeau (TG) and ideal\nFermi gases, is constructed in the TG limit of infinite even-wave repulsion by\na spinor Fermi-Bose mapping to a spinless ideal Fermi gas. It is then shown\nthat in the limit of infinite even-wave attraction this same state remains an\nexact many-body eigenstate, now highly excited relative to the collapsed\ngeneralized McGuire cluster ground state, showing that the hybrid TG state is\ncompletely stable against collapse to this cluster ground state under a sudden\nswitch from infinite repulsion to infinite attraction. It is shown to be the TG\nlimit of a hybrid super Tonks-Girardeau (STG) state which is metastable under a\nsudden switch from finite but very strong repulsion to finite but very strong\nattraction. It should be possible to create it experimentally by a sudden\nswitch from strongly repulsive to strongly attractive interaction, as in the\nrecent Innsbruck experiment on a spin-polarized bosonic STG gas. In the case of\nstrong attraction there should also exist another STG state of much lower\nenergy, consisting of strongly bound dimers, a bosonic analog of a recently\npredicted STG gas which is an ultracold gas of strongly bound bosonic dimers of\nfermionic atoms, but it is shown that this STG state cannot be created by such\na switch from strong repulsion to strong attraction.",
        "positive": "Non-universal bound states of two identical heavy fermions and one light\n  particle: We study the behavior of the bound state energy of a system consisting of two\nidentical heavy fermions of mass M and a light particle of mass m. The heavy\nfermions interact with the light particle through a short-range two-body\npotential with positive s-wave scattering length a_s. We impose a short-range\nboundary condition on the logarithmic derivative of the hyperradial\nwavefunction and show that, in the regime where Efimov states are absent, a\nnon-universal three-body state \"cuts through\" the universal three-body states\npreviously described by Kartavtsev and Malykh [O. I. Kartavtsev and A. V.\nMalykh, J. Phys. B 40, 1429 (2007)]. The presence of the non-universal state\nalters the behavior of the universal states in certain regions of the parameter\nspace. We show that the existence of the non-universal state is predicted\naccurately by a simple quantum defect theory model that utilizes hyperspherical\ncoordinates. An empirical two-state model is employed to quantify the coupling\nof the non-universal state to the universal states."
    },
    {
        "anchor": "Tan's two-body contact across the superfluid transition of a planar Bose\n  gas: Tan's contact is a quantity that unifies many different properties of a\nlow-temperature gas with short-range interactions, from its momentum\ndistribution to its spatial two-body correlation function. Here, we use a\nRamsey interferometric method to realize experimentally the thermodynamic\ndefinition of the two-body contact, i.e. the change of the internal energy in a\nsmall modification of the scattering length. Our measurements are performed on\na uniform two-dimensional Bose gas of $^{87}$Rb atoms across the\nBerezinskii-Kosterlitz-Thouless superfluid transition. They connect well to the\ntheoretical predictions in the limiting cases of a strongly degenerate fluid\nand of a normal gas. They also provide the variation of this key quantity in\nthe critical region, where further theoretical efforts are needed to account\nfor our findings.",
        "positive": "Condensation signatures of photogenerated interlayer excitons in a van\n  der Waals heterostack: Atomistic van der Waals heterostacks are ideal systems for high-temperature\nexciton condensation because of large exciton binding energies and long\nlifetimes. Charge transport and electron energy-loss spectroscopy showed first\nevidence of excitonic many-body states in such two-dimensional materials. Pure\noptical studies, the most obvious way to access the phase diagram of\nphotogenerated excitons have been elusive. We observe several criticalities in\nphotogenerated exciton ensembles hosted in MoSe2-WSe2 heterostacks with respect\nto photoluminescence intensity, linewidth, and temporal coherence pointing\ntowards the transition to a coherent quantum state. For this state, the\noccupation is 100 percent and the exciton diffusion length is increased. The\nphenomena survive above 10 kelvin, consistent with the predicted critical\ncondensation temperature. Our study provides a first phase-diagram of many-body\ninterlayer exciton states including Bose Einstein condensation."
    },
    {
        "anchor": "Mixture of scalar bosons and two-color fermions in one dimension:\n  Superfluid-insulator transitions: Superfluid-insulator transitions in a one-dimensional mixture of two-color\nfermions and scalar bosons are studied within the framework of the\nBose-Fermi-Hubbard model. Zero-temperature phase diagrams are constructed for\nrepulsive intraspecies interactions and attractive or repulsive interspecies\ncouplings. In addition to the trivial Mott insulator phases, we report the\nemergence of new non-trivial insulator phases that depend on the sign of the\nboson-fermion interaction. These non-trivial insulator phases satisfy the\nconditions $\\rho_B\\pm\\rho_F=n$ and $\\rho_B\\pm \\tfrac{1}{2}\\rho_F=n$, with the\nplus (minus) sign for repulsive (attractive) interactions and $n$ an integer.\nFar from fermionic half-filling, the boson-fermion interaction drives a\ngapless-gapped transition in the spin sector. Our findings could be observed\nexperimentally in state-of-the-art cold-atom setups.",
        "positive": "Shortcut to adiabaticity for an interacting Bose-Einstein condensate: We present an investigation of the fast decompression of a three-dimensional\n(3D) Bose-Einstein condensate (BEC) at finite temperature using an engineered\ntrajectory for the harmonic trapping potential. Taking advantage of the scaling\ninvariance properties of the time-dependent Gross-Pitaevskii equation, we\nexhibit a solution yielding a final state identical to that obtained through a\nperfectly adiabatic transformation, in a much shorter time. Experimentally, we\nperform a large trap decompression and displacement within a time comparable to\nthe final radial trapping period. By simultaneously monitoring the BEC and the\nnon-condensed fraction, we demonstrate that our specific trap trajectory is\nvalid both for a quantum interacting many-body system and a classical ensemble\nof non-interacting particles."
    },
    {
        "anchor": "Reply to the Comment by Benenti et al: Benenti et al. recently submitted a Comment (arXiv:0912.3667) on our work\n\"Coherent Ratchets in Driven Bose-Einstein condensates\". We show that the main\nclaim of the Comment is wrong, and correct some other misunderstandings\npresented there.",
        "positive": "Scattering amplitudes for dark and bright excitons: Using the composite boson many-body formalism that takes single-exciton\nstates rather than free carrier states as a basis, we derive the integral\nequation fulfilled by the exciton-exciton effective scattering from which the\nrole of fermion exchanges can be unraveled. For excitons made of\n$(\\pm1/2)$-spin electrons and $(\\pm3/2)$-spin holes, as in GaAs\nheterostructures, one major result is that most spin configurations lead to\nbrightness-conserving scatterings with equal amplitude $\\Delta$, in spite of\nthe fact that they involve different carrier exchanges. A brightness-changing\nchannel also exists when two opposite-spin excitons scatter: dark excitons\n$(2,-2)$ can end either in the same dark states with an amplitude $\\Delta_e$,\nor in opposite-spin bright states $(1,-1)$, with a different amplitude\n$\\Delta_o$, the number of carrier exchanges being even or odd respectively.\nAnother major result is that these amplitudes are linked by a striking\nrelation, $\\Delta_e+\\Delta_o=\\Delta$, which has decisive consequence for\nexciton Bose-Einstein condensation. Indeed, this relation leads to the\nconclusion that the exciton condensate can be optically observed through a\nbright part only when excitons have a large dipole, that is, when the electrons\nand holes are well separated in two adjacent layers."
    },
    {
        "anchor": "Highly Polarized Fermi Gases across a Narrow Feshbach Resonance: We address the phase of a highly polarized Fermi gas across a narrow Feshbach\nresonance starting from the problem of a single down spin fermion immersed in a\nFermi sea of up spins. Both polaron and pairing states are considered using the\nvariational wave function approach, and we find that the polaron to pairing\ntransition will take place at the BCS side of the resonance, strongly in\ncontrast to a wide resonance where the transition is located at the BEC side.\nFor pairing phase, we find out the critical strength of repulsive interaction\nbetween pairs above which the mixture of pairs and fermions will not phase\nseparate. Therefore, nearby a narrow resonance, it is quite likely that\nmagnetism can coexist with s-wave BCS superfluidity at large Zeeman field,\nwhich is a remarkable property absent in conventional BCS superconductors (or\nfermion pair superfluids).",
        "positive": "Thermoelectricity in a junction between interacting cold atomic Fermi\n  gases: A gas of interacting ultracold fermions can be tuned into a strongly\ninteracting regime using a Feshbach resonance. Here we theoretically study\nquasiparticle transport in a system of two reservoirs of interacting ultracold\nfermions on the BCS side of the BCS-BEC crossover coupled weakly via a tunnel\njunction. Using the generalized BCS theory we calculate the time evolution of\nthe system that is assumed to be initially prepared in a non-equilibrium state\ncharacterized by a particle number imbalance or a temperature imbalance. A\nnumber of characteristic features like sharp peaks in quasiparticle currents,\nor transitions between the normal and superconducting states are found. We\ndiscuss signatures of the Seebeck and the Peltier effect and the resulting\ntemperature difference of the two reservoirs as a function of the interaction\nparameter $(k_Fa)^{-1}$. The Peltier effect may lead to an additional cooling\nmechanism for ultracold fermionic atoms."
    },
    {
        "anchor": "Vortex and Meissner phases of strongly-interacting bosons on a two-leg\n  ladder: We establish the phase diagram of the strongly-interacting Bose-Hubbard model\ndefined on a two-leg ladder geometry in the presence of a homogeneous flux. Our\nwork is motivated by a recent experiment [Atala et al., Nature Phys. 10, 588\n(2014)], which studied the same system, in the complementary regime of weak\ninteractions. Based on extensive density matrix renormalization group\nsimulations and a bosonization analysis, we fully explore the parameter space\nspanned by filling, inter-leg tunneling, and flux. As a main result, we\ndemonstrate the existence of gapless and gapped Meissner and vortex phases,\nwith the gapped states emerging in Mott-insulating regimes. We calculate\nexperimentally accessible observables such as chiral currents and vortex\npatterns.",
        "positive": "Pseudogap and preformed pairs in the imbalanced Fermi gas in two\n  dimensions: The physics of the pseudogap state is intimately linked with the pairing\nmechanism that gives rise to superfluidity in quantum gases and to\nsuperconductivity in high-Tc cuprates, and therefore, both in quantum gases and\nsuperconductors, the pseudogap state and preformed pairs have been under\nintensive experimental scrutiny. Here, we develop a path integral treatment\nthat provides a divergence-free description of the paired state in\ntwo-dimensional Fermi gases. Within this formalism, we derive the pseudogap\ntemperature and the pair fluctuation spectral function, and compare these\nresults with the recent experimental measument of the pairing in the\ntwo-dimensional Fermi gas. The removal of the infrared divergence in the number\nequations is shown both numerically and analytically, through a study of the\nlong-wavelength and low-energy limit of the pair fluctuation density. Besides\nthe pseudogap temperature, also the pair formation temperature and the critical\ntemperature for superfluidity are derived. The latter corresponds to the\nBerezinski-Kosterlitz-Thouless (BKT) temperature. The pseudogap temperature,\nwhich coincides with the pair formation temperature in mean field, is found to\nbe suppressed with respect to the pair formation temperature by fluctuations.\nThis suppression is strongest for large binding energies of the pairs. Finally,\nwe investigate how the pair formation temperature, the pseudogap temperature\nand the BKT temperature behave as a function of both binding energy and\nimbalance between the pairing partners in the Fermi gas. This allows to set up\nphase diagrams for the two-dimensional Fermi gas, in which the superfluid\nphase, the phase-fluctuating quasicondensate, and the normal state can be\nidentified."
    },
    {
        "anchor": "Synthetic Gauge Fields for Ultra Cold Atoms: A Primer: We start by reviewing the concept of gauge invariance in quantum mechanics,\nfor Abelian and Non-Ableian cases. Then we idescribe how the various gauge\npotential and field can be associated with the geometrical phase acquired by a\nquantum mechanical wave function while adiabatically evolving in a parameter\nspace. Subsequently we show how this concept is exploited to generate light\ninduced gauge field for neutral ultra cold bosonic atoms. As an example of such\nlight induced Abelian and Non Abelian gauge field for ultra cold atoms we\ndisucss ultra cold atoms in a rotating trap and creation of synthetic spin\norbit coupling for ultra cold atomic systems using Raman lasers.",
        "positive": "Dissipative Luttinger liquids: We investigate a one dimensional quantum fluid coupled to a dissipative bath.\nThe quantum fluid is captured by the canonical Luttinger liquid; the bath is\ngiven by the model of Caldeira and Leggett, i.e. a tower of oscillators coupled\nlinearly to the fluid density, $\\rho$. The bath can be integrated out exactly,\nproducing an effective interaction for the fluid that is nonlocal in time; we\nargue that the form corresponding to Ohmic dissipation is generic. Compared to\nprevious works, we compute correlation functions for this minimal model without\napproximation, including at finite temperature $T>0$. From these and a Kubo\ncalculation, we conclude that arbitrary dissipation destroys the perfect\nconductivity of the Luttinger liquid via Zeno localization, even in the absence\nof a spatial potential; from RG analysis of harmonic terms, we also find that\nthe open Luttinger liquid is significantly more prone to localization by such\npotentials, in contrast to the usual intuition that baths make systems less\nlocalized."
    },
    {
        "anchor": "Resonant scattering of matter wave gap-solitons by optical lattice\n  defects: The physical mechanism underlying scattering properties of matter wave\ngap-solitons by linear optical lattice defects is investigated. The occurrence\nof repeated reflection, transmission and trapping regions for increasing\nstrengths of an optical lattice defect are shown to be due to impurity modes\ninside the defect potential with chemical potentials and numbers of atoms\nmatching corresponding quantities of an incoming gap-soliton. For gap-solitons\nwith chemical potentials very close to band edges, the number of resonances\nobserved in the scattering coincides with the number of bound states which can\nexist in the defect potential for the given defect strength. The dependence of\nthe positions and widths of the transmission resonant on the incoming\ngap-soliton velocities are investigated by means of a defect mode analysis and\neffective mass theory. The comparisons with direct integrations of the\nGross-Pitaevskii equation provide a very good agreement confirming the\ncorrectness of our interpretation. The possibility of multiple resonant\ntransmission through arrays of optical lattice defects is also demonstrated. In\nparticular, we show that it is possible to design the strength of the defects\nso to balance the velocity detunings and to allow the resonant transmission\nthrough a larger number of defects. The possibility of using these results for\nvery precise gap-soliton dynamical filters is suggested.",
        "positive": "Higher-order effective interactions for bosons near a two-body zero\n  crossing: We develop the perturbation theory for bosons interacting via a two-body\npotential $V$ of vanishing mean value. We find that the leading nonpairwise\ncontribution to the energy emerges in the third order in $V$ and represents an\neffective three-body interaction, the sign of which in most cases (although not\nin general) is anticorrelated with the sign of the long-range tail of $V$.\nExplicit results are obtained for a few particular two-body interaction\npotentials and we perform a detailed perturbative analysis of tilted dipoles in\nquasi-low-dimensional geometries."
    },
    {
        "anchor": "Stabilization of trapless dipolar Bose-Einstein condensates by temporal\n  modulation of the contact interaction: We theoretically study the stability of a trapless dipolar Bose-Einstein\ncondensate (BEC) with temporal modulation of short-range contact interaction.\nFor this aim, through both analytical and numerical methods, we solve a\nGross-Pitaevskii equation with both constant and oscillatory form of\nshort-range contact interaction along with long-range, nonlocal, dipole-dipole\n(DD) interaction terms. Using variational method, we discuss the stability of\nthe trapless dipolar BEC with presence and absence of both constant and\noscillatory contact interactions. We show that the oscillatory contact\ninteraction prevents the collapse of the trapless dipolar BEC. We confirm the\nanalytical prediction through numerical simulations. We have also studied the\ncollective excitations in the system induced by the effective potential due to\noscillating interaction.",
        "positive": "Disorder-free localization with Stark gauge protection: Disorder-free localization in translation-invariant gauge theories presents a\ncounterintuitive yet powerful framework of ergodicity breaking in quantum\nmany-body physics. The fragility of this phenomenon in the presence of\ngauge-breaking errors has recently been addressed, but no scheme has been able\nto reliably stabilize disorder-free localization through all accessible\nevolution times while preserving the disorder-free property. Here, we introduce\nthe concept of \\textit{Stark gauge protection}, which entails a linear sum in\ngauge-symmetry local (pseudo)generators weighted by a Stark potential. Using\nexact diagonalization and Krylov-based methods, we show how this scheme can\nstabilize or even enhance disorder-free localization against gauge-breaking\nerrors in $\\mathrm{U}(1)$ and $\\mathbb{Z}_2$ gauge theories up to all\naccessible evolution times, without inducing \\textit{bona fide} Stark many-body\nlocalization. We show through a Magnus expansion that the dynamics under Stark\ngauge protection is described by an effective Hamiltonian where gauge-breaking\nterms are suppressed locally by the protection strength and additionally by the\nmatter site index, which we argue is the main reason behind stabilizing the\nlocalization up to all accessible times. Our scheme is readily feasible in\nmodern ultracold-atom experiments and Rydberg-atom setups with optical\ntweezers."
    },
    {
        "anchor": "Dissipative Preparation of Spatial Order in Rydberg-Dressed\n  Bose-Einstein Condensates: We propose a technique for engineering momentum-dependent dissipation in\nBose-Einstein condensates with non-local interactions. The scheme relies on the\nuse of momentum-dependent dark-states in close analogy to velocity-selective\ncoherent population trapping. During the short-time dissipative dynamics, the\nsystem is driven into a particular finite-momentum phonon mode, which in real\nspace corresponds to an ordered structure with non-local density-density\ncorrelations. Dissipation-induced ordering can be observed and studied in\npresent-day experiments using cold atoms with dipole-dipole or off-resonant\nRydberg interactions. Due to its dissipative nature, the ordering does not\nrequire artificial breaking of translational symmetry by an opticallattice or\nharmonic trap. This opens up a perspective of direct cooling of quantum gases\ninto strongly-interacting phases.",
        "positive": "SU(N) Fermi liquid at finite temperature: We consider the thermodynamic potential $\\Omega$ of an N component Fermi gas\nwith a short range interaction obeying SU(N) symmetry. We analyze especially\nthe part of $\\Omega$ that depends on the temperature T non-analytically for\nsmall T . We examine the temperature range where one can observe this $T^4 ln\nT$ contribution and discuss how it can be extracted experimentally."
    },
    {
        "anchor": "Local Correlations in the Super Tonks-Girardeau Gas: We study the local correlations in the super Tonks-Girardeau gas, a highly\nexcited, strongly correlated state obtained in quasi one-dimensional Bose gases\nby tuning the scattering length to large negative values using a\nconfinement-induced resonance. Exploiting a connection with a relativistic\nfield theory, we obtain results for the two-body and three-body local\ncorrelators at zero and finite temperature. At zero temperature our result for\nthe three-body correlator agrees with the extension of the results of Cheianov\net al. [Phys. Rev. A 73, 051604(R) (2006)], obtained for the ground-state of\nthe repulsive Lieb-Liniger gas, to the super Tonks-Girardeau state. At finite\ntemperature we obtain that the three-body correlator has a weak dependence on\nthe temperature up to the degeneracy temperature. We also find that for\ntemperatures larger than the degeneracy temperature the values of the\nthree-body correlator for the super Tonks-Girardeau gas and the corresponding\nrepulsive Lieb-Liniger gas are rather similar even for relatively small\ncouplings.",
        "positive": "Symmetry breaking and phase transitions in Bose-Einstein condensates\n  with spin-orbital-angular-momentum coupling: Theoretical study is presented for a spinor Bose-Einstein condensate, whose\ntwo components are coupled by copropagating Raman beams with different orbital\nangular momenta. The investigation is focused on the behavior of the ground\nstate of this condensate, depending on the atom-light coupling strength. By\nanalyzing the ground state, we have identified a number of quantum phases,\nwhich reflect the symmetries of the effective Hamiltonian and are characterized\nby the specific structure of the wave function. In addition to the well-known\nstripe, polarized and zero-momentum phases, our results show that the system\ncan support phases, whose wave function contains a complex vortex molecule.\nSuch molecule plays an important role in the continuous phase transitions of\nthe system. The predicted behavior of vortex-molecule phases can be examined in\ncold-atom experiments using currently existing techniques."
    },
    {
        "anchor": "Non-Equilibrium Mass Transport in the 1D Fermi-Hubbard Model: We experimentally and numerically investigate the sudden expansion of\nfermions in a homogeneous one-dimensional optical lattice. For initial states\nwith an appreciable amount of doublons, we observe a dynamical phase separation\nbetween rapidly expanding singlons and slow doublons remaining in the trap\ncenter, realizing the key aspect of fermionic quantum distillation in the\nstrongly-interacting limit. For initial states without doublons, we find a\nreduced interaction dependence of the asymptotic expansion speed compared to\nbosons, which is explained by the interaction energy produced in the quench.",
        "positive": "Field-theoretical aspects of one-dimensional Bose and Fermi gases with\n  contact interactions: We investigate local quantum field theories for one-dimensional (1D) Bose and\nFermi gases with contact interactions, which are closely connected with each\nother by Girardeau's Bose-Fermi mapping. While the Lagrangian for bosons\nincludes only a two-body interaction, a marginally relevant three-body\ninteraction term is found to be necessary for fermions. Because of this\nthree-body coupling, the three-body contact characterizing a local triad\ncorrelation appears in the energy relation for fermions, which is one of the\nsum rules for a momentum distribution. In addition, we apply in both systems\nthe operator product expansion to derive large-energy and momentum asymptotics\nof a dynamic structure factor and a single-particle spectral density. These\nbehaviors are universal in the sense that they hold for any 1D scattering\nlength at any temperature. The asymptotics for the Tonks-Girardeau gas, which\nis a Bose gas with a hardcore repulsion, as well as the Bose-Fermi\ncorrespondence in the presence of three-body attractions are also discussed."
    },
    {
        "anchor": "Prethermalization and universal dynamics in near-integrable quantum\n  systems: We review the recent progress in the understanding of the relaxation of\nisolated near-integrable quantum many-body systems. Focusing on\nprethermalization and universal dynamics following a quench, we describe the\nexperiments with ultracold atomic gases that illustrate these phenomena and\nsummarize the essential theoretical concepts employed to interpret them. Our\ndiscussion highlights the key topics that link the different approaches to this\ninterdisciplinary field, including the generalized Gibbs ensemble, non-thermal\nfixed points, critical slowing and universal scaling. Finally, we point to new\nexperimental challenges demonstrating these fundamental features of many-body\nquantum systems out of equilibrium.",
        "positive": "Spin-tensor--momentum-coupled Bose-Einstein condensates: The recent experimental realization of spin-orbit coupling for ultracold\natomic gases provides a powerful platform for exploring many interesting\nquantum phenomena. In these studies, spin represents spin vector (spin-1/2 or\nspin-1) and orbit represents linear momentum. Here we propose a scheme to\nrealize a new type of spin-tensor--momentum coupling (STMC) in spin-1 ultracold\natomic gases. We study the ground state properties of interacting Bose-Einstein\ncondensates (BECs) with STMC and find interesting new types of stripe\nsuperfluid phases and multicritical points for phase transitions. Furthermore,\nSTMC makes it possible to study quantum states with dynamical stripe orders\nthat display density modulation with a long tunable period and high visibility,\npaving the way for direct experimental observation of a new dynamical\nsupersolid-like state.. Our scheme for generating STMC can be generalized to\nother systems and may open the door for exploring novel quantum physics and\ndevice applications."
    },
    {
        "anchor": "Impact of the range of the interaction on the quantum dynamics of a\n  bosonic Josephson junction: The out-of-equilibrium quantum dynamics of a bosonic Josephson junction (BJJ)\nwith long-range interaction is studied in real space by solving the\ntime-dependent many-body Schr\\\"odinger equation numerically accurately using\nthe multiconfigurational time-dependent Hartree method for bosons. Having the\nmany-boson wave-function at hand we can examine the impact of the range of the\ninteraction on the properties of the BJJ dynamics, viz. density oscillations\nand their collapse, self trapping, depletion and fragmentation, as well as the\nposition variance, both at the mean-field and many-body level. Explicitly, the\nfrequency of the density oscillations and the time required for their collapse,\nthe value of fragmentation at the plateau, the maximal and the minimal values\nof the position variance in each cycle of oscillation and the overall pace of\nits growth are key to our study. We find competitive effect between the\ninteraction and the confining trap. The presence of the tail part of the\ninteraction basically enhances the effective repulsion as the range of the\ninteraction is increased starting from a short, finite range. But as the range\nbecomes comparable with the trap size, the system approaches a situation where\nall the atoms feel a constant potential and the impact of the tail on the\ndynamics diminishes. There is an optimal range of the interaction in which\nphysical quantities of the junction are attaining their extreme values.",
        "positive": "Spin-incoherent Luttinger liquid of one-dimensional spin-1\n  Tonks-Girardeau Bose gas: Spin-dependent properties: Spin-incoherent Luttinger liquid (SILL) is a different universal class from\nthe Luttinger liquid.\\ This difference results from the spin incoherence of the\nsystem when the thermal energy of the system is higher than the spin excitation\nenergy.\\ We consider one-dimensional spin-$1$ Bose gas in the SILL regime and\ninvestigate its spin-dependent many-body properties.\\ In Tonks-Girardeau limit,\nwe are able to write down the general wave functions in a harmonic trap.\\ We\nnumerically calculate the spin-dependent (spin-plus, minus, and $0$) momentum\ndistributions in the sector of zero magnetization which allows to demonstrate\nthe most significant spin-incoherent feature compared to the spinless or\nspin-polarized case.\\ In contrast to the spinless Bose gas, the momentum\ndistributions are broadened and in the large momentum limit follow the same\nasymptotic $1/p^4$ dependence but with reduced coefficients.\\ While the density\nmatrices and momentum distributions differ between different spin components\nfor small $N$, at large $N$ they approach each other.\\ We show these by\nanalytic arguments and numerical calculations up to $N$ $=$ $16$."
    },
    {
        "anchor": "Quantum Lifshitz points and fluctuation-induced first-order phase\n  transitions in imbalanced Fermi mixtures: We perform a detailed analysis of the phase transition between the uniform\nsuperfluid and normal phases in spin- and mass-imbalanced Fermi mixtures. At\nmean-field level we demonstrate that at temperature $T\\to 0$ the gradient term\nin the effective action can be tuned to zero for experimentally relevant sets\nof parameters, thus providing an avenue to realize a quantum Lifshitz point. We\nsubsequently analyze damping processes affecting the order-parameter field\nacross the phase transition. We show that, in the low energy limit, Landau\ndamping occurs only in the symmetry-broken phase and affects exclusively the\nlongitudinal component of the order-parameter field. It is however unavoidably\npresent in the immediate vicinity of the phase transition at temperature $T=0$.\nWe subsequently perform a renormalization-group analysis of the system in a\nsituation, where, at mean-field level, the quantum phase transition is second\norder (and not multicritical). We find that, at $T$ sufficiently low, including\nthe Landau damping term in a form derived from the microscopic action\ndestabilizes the renormalization group flow towards the Wilson-Fisher fixed\npoint. This signals a possible tendency to drive the transition weakly\nfirst-order by the coupling between the order-parameter fluctuations and\nfermionic excitations effectively captured by the Landau damping contribution\nto the order-parameter action.",
        "positive": "Quantum fluctuations in atomic Josephson junctions: the role of\n  dimensionality: We investigate the role of quantum fluctuations in the dynamics of a bosonic\nJosephson junction in $D$ spatial dimensions, by using beyond mean-field\nGaussian corrections. We derive some key dynamical properties in a systematic\nway for $D=3, 2, 1$. In particular, we compute the Josephson frequency in the\nregime of low population imbalance. We also obtain the critical strength of the\nmacroscopic quantum self-trapping. Our results show that quantum corrections\nincrease the Josephson frequency in spatial dimensions $D=2$ and $D=3$, but\nthey decrease it in the $D=1$ case. The critical strength of macroscopic\nquantum self-trapping is instead reduced by quantum fluctuations in $D=2$ and\n$D=3$ cases, while it is enhanced in the $D=1$ configuration. We show that the\ndifference between the cases of D = 2 and D = 3 on one side, and D = 1 on the\nother, can be related to the qualitatively different dependence of the\ninteraction strength on the scattering length in the different dimensions."
    },
    {
        "anchor": "Rotation and Angular Momentum Transfer in Bose-Einstein Condensates\n  Induced by Spiral Dark Solitons: It is a common view that rotational motion in a superfluid can exist only in\nthe presence of quantized vortices. However, in our numerical studies on the\nmerging of two concentric Bose-Einstein condensates with axial symmetry in\ntwo-dimensional space, we observe the emergence of a spiral dark soliton when\none condensate has a non-zero initial angular momentum. This spiral dark\nsoliton enables the transfer of angular momentum between the condensates and\nallows the merged condensate to rotate even in the absence of quantized\nvortices. We examine the flow field around the soliton and reveal that its\nsharp endpoint can induce flow like a vortex point but with a fraction of a\nquantized circulation. This interesting nontopological \"phase defect\" may\ngenerate broad interests since rotational motion is essential in many quantum\ntransport processes.",
        "positive": "Pushing Photons with Electrons: Observation of the Polariton Drag Effect: We show the direct effect of free electrons colliding with polaritons,\nchanging their momentum. The result of this interaction of the electrons with\nthe polaritons is a change in the angle of emission of the photons from our\ncavity structure. Because the experiment is a photon-in, photon-out system,\nthis is equivalent to optical beam steering of photons using a direct\nelectrical current. The effect is asymmetric, significantly slowing down the\npolaritons when they move oppositely to the electrons, while the polaritons are\nonly slightly accelerated by electrons moving in the same direction. We present\na theoretical model which describes this effect as well as energy dissipation\nin a polariton condensate."
    },
    {
        "anchor": "Metamorphoses of the flow past an obstacle of a resonantly-driven\n  bistable polariton fluid: Motivated by recent experiments, we theoretically analyze the flow past an\nobstacle of a one-dimensional \"quantum fluid of light\" which is resonantly\ndriven, and exhibits bistability. The flow is found to abruptly change several\ntimes when the fluid velocity or the obstacle potential strength are increased.\nIn contrast to the cases of usual fluids and superfluids, the transitions take\nplace between stationary states. They involve the fluid bistability in an\nessential way. Remarkably, at the transitions points, the fluid in the obstacle\nwake lies in the unstable intermediate density state.",
        "positive": "Dynamical Resonances and Stepped Current in an Attractive Quantum Pump: We report on the transport properties of a single mode quantum pump that\noperates by the simultaneous translation and oscillation of a potential well.\nWe examine the dynamics comparatively using quantum, classical and\nsemiclassical simulations. The use of an attractive or well potential is found\nto present several striking features absent if a barrier potential is used\ninstead, as usually favored. The trapping of particles by the well for variable\ndurations and subsequent release leads to a fractal-like structure in the\ndistribution of the classical scattering trajectories. Interference among them\nleads to a rich dynamical structure in the quantum current, conspicuously\nmissing in the classical current. Specifically, we observe sharp steps, spikes\nand dips in the current as a function of the incident energy of the carriers,\nand determine that a dynamical version of Fano resonance has a role that\ndepends on the direction of incidence and on multiple scattering by the\npotential."
    },
    {
        "anchor": "Monopole excitations of a harmonically trapped one-dimensional Bose gas\n  from the ideal gas to the Tonks-Girardeau regime: Using a time-dependent modified nonlinear Schr\\\"odinger equation (m-NLSE) --\nwhere the conventional chemical potential proportional to the density is\nreplaced by the one inferred from Lieb-Liniger's exact solution -- we study\nfrequencies of the collective monopole excitations of a one-dimensional (1D)\nBose gas. We find that our method accurately reproduces the results of a recent\nexperimental study [E. Haller et al., Science Vol. 325, 1224 (2009)] in the\nfull spectrum of interaction regimes from the ideal gas, through the mean-field\nregime, through the mean-field Thomas-Fermi regime, all the way to the\nTonks-Giradeau gas. While the former two are accessible by the standard\ntime-dependent NLSE and inaccessible by the time-dependent local density\napproximation (LDA), the situation reverses in the latter case. However, the\nm-NLSE treats all these regimes within a single numerical method.",
        "positive": "Tuning the Topological $\u03b8$-Angle in Cold-Atom Quantum Simulators of\n  Gauge Theories: The topological $\\theta$-angle in gauge theories engenders a series of\nfundamental phenomena, including violations of charge-parity (CP) symmetry,\ndynamical topological transitions, and confinement--deconfinement transitions.\nAt the same time, it poses major challenges for theoretical studies, as it\nimplies a sign problem in numerical simulations. Analog quantum simulators open\nthe promising prospect of treating quantum many-body systems with such\ntopological terms, but, contrary to their digital counterparts, they have not\nyet demonstrated the capacity to control the $\\theta$-angle. Here, we\ndemonstrate how a tunable topological $\\theta$-term can be added to a prototype\ntheory with $\\mathrm{U}(1)$ gauge symmetry, a discretized version of quantum\nelectrodynamics in one spatial dimension. As we show, the model can be realized\nexperimentally in a single-species Bose--Hubbard model in an optical\nsuperlattice with three different spatial periods, thus requiring only standard\nexperimental resources. Through numerical calculations obtained from the\ntime-dependent density matrix renormalization group method and exact\ndiagonalization, we benchmark the model system, and illustrate how salient\neffects due to the $\\theta$-term can be observed. These include charge\nconfinement, the weakening of quantum many-body scarring, as well as the\ndisappearance of Coleman's phase transition due to explicit breaking of CP\nsymmetry. This work opens the door towards studying the rich physics of\ntopological gauge-theory terms in large-scale cold-atom quantum simulators."
    },
    {
        "anchor": "Parity breakdown, vortices, and dark soliton states in a Bose gas of\n  resonantly excited polaritons: A new mechanism of parity breakdown in a spinor Bose gas is predicted; it\ncauses a single-mode state of polaritons to be spontaneously divided into\ndifferent polarization domains which annihilate each other at the interface\nareas. In a polariton wire, such interface is a dark soliton that can run in\nspace without dissipation. In a planar cavity, quantized vortices arise in\nwhich phase difference of orthogonally polarized components makes one complete\nturn around the core. Coupled vortex-antivortex pairs and straight filaments\ncan form in analogy to Bose-Einstein condensates and superconductors. However,\nthe rotational symmetry is broken even for individual vortices, which makes\nthem interact on a large scale and form internally ordered structures. These\nstates come into being under resonant excitation if the spin coupling rate\nsignificantly exceeds the decay rate.",
        "positive": "Degenerate approach to the mean field Bose- Hubbard Hamiltonian: A degenerate variant of mean field perturbation theory for the on-site\nBose-Hubbard Hamiltonian is presented. We split the perturbation into two terms\nand perform exact diagonalization in the two-dimensional subspace corresponding\nto the degenerate states. The final relations for the second order ground state\nenergy and first order wave function do not contain singularities at integer\nvalues of the chemical potentials. The resulting equation for the phase\nboundary between superfluid and Mott states coincides with the prediction based\non the conventional mean field perturbation approach."
    },
    {
        "anchor": "Drag dynamics in one-dimensional Fermi systems: We study drag dynamics of several fermions in a fermion cloud in\none-dimensional continuous systems, with particular emphasis on the non-trivial\nquantum many-body effects in systems whose parameters change gradually in real\ntime. We adopt the Fermi--Hubbard model and the time-dependent density matrix\nrenormalization group method to calculate the drag force on a trapped fermion\ncluster in a cloud of another fermion species with contact interaction. The\nsimulation result shows that a non-trivial peak in the resistance force is\nobserved in the high cloud density region, which implies a criterion of\neffective ways in diffusive transport in a fermion cloud. We compare the DMRG\nsimulation result with a mean-field result, and it is suggested that some\ninternal degrees of freedom have a crucial role in the excitation process when\nthe cloud density is high. This work emphasizes the difference between the\nfull-quantum calculation and the semiclassical calculation, which is the\nquantum effects, in slow dynamics of many-body systems bound in a fermion\ncloud.",
        "positive": "Quantum swapping of immiscible Bose-Einstein condensates as an\n  alternative to the Rayleigh-Taylor instability: We consider a two-component Bose-Einstein condensate in a\nquasi-one-dimensional harmonic trap, where the immiscible components are\npressed against each other by an external magnetic force. The zero-temperature\nnon-stationary Gross-Pitaevskii equations are solved numerically; analytical\nmodels are developed for the key steps in the process. We demonstrate that if\nthe magnetic force is strong enough, then the condensates may swap their places\nin the trap due to dynamic quantum interpenetration of the nonlinear matter\nwaves. The swapping is accompanied by development of a modulational instability\nleading to quasi-turbulent excitations. Unlike the multidimensional\nRayleigh-Taylor instability in a similar geometry of two-component quantum\nfluid systems, quantum interpenetration has no classical analogue. A crossover\nbetween the Rayleigh-Taylor instability and the quantum interpenetration in a\ntwo-dimensional geometry is demonstrated."
    },
    {
        "anchor": "Mixtures of Bose Gases Confined in a Ring Potential: The rotational properties of a mixture of two distinguishable Bose gases that\nare confined in a ring potential provide novel physical effects that we\ndemonstrate in this study. Persistent currents are shown to be stable for a\nrange of the population imbalance between the two components at low angular\nmomentum. At higher values of the angular momentum, even small admixtures of a\nsecond species of atoms make the persistent currents highly fragile.",
        "positive": "Finite Temperature Matrix Product State Algorithms and Applications: We review the basic theory of matrix product states (MPS) as a numerical\nvariational ansatz for time evolution, and present two methods to simulate\nfinite temperature systems with MPS: the ancilla method and the minimally\nentangled typical thermal state method. A sample calculation with the\nBose-Hubbard model is provided."
    },
    {
        "anchor": "High-energy side-peak emission of exciton-polariton condensates in high\n  density regime: In a standard semiconductor laser, electrons and holes recombine via\nstimulated emission to emit coherent light, in a process that is far from\nthermal equilibrium. Exciton-polariton condensates -- sharing the same basic\ndevice structure as a semiconductor laser, consisting of quantum wells coupled\nto a microcavity -- have been investigated primarily at densities far below the\nMott density for signatures of Bose-Einstein condensation. At high densities\napproaching the Mott density, exciton-polariton condensates are generally\nthought to revert to a standard semiconductor laser, with the loss of strong\ncoupling. Here, we report the observation of a photoluminescence sideband at\nhigh densities that cannot be accounted for by conventional semiconductor\nlasing. This also differs from an upper-polariton peak by the observation of\nthe excitation power dependence in the peak-energy separation. Our\ninterpretation as a persistent coherent electron-hole-photon coupling captures\nseveral features of this sideband whereas many remain elusive. Understanding\nthe observation will lead to a development in non-equilibrium many-body\nphysics.",
        "positive": "Evaporative cooling and self-thermalization in an open system of\n  interacting fermions: We study depletion dynamics of an open system of weakly interacting fermions\nwith two-body random interactions. In this model fermions are escaping from the\nhigh-energy one-particle orbitals, that mimics the evaporation process used in\nlaboratory experiments with neutral atoms to cool them to ultra-low\ntemperatures. It is shown that due to dynamical thermalization the system\ninstantaneously adjusts to the new chemical potential and temperature, so that\noccupation numbers of the one-particle orbitals always obey the Fermi-Dirac\ndistribution. In this way we are able to describe the evaporation process which\nleads to a significant cooling of particles remaining inside the system. We\nalso briefly discuss the evaporation process in the SYK black hole model that\ncorresponds to strongly interacting fermions."
    },
    {
        "anchor": "Stability and collapse of fermions in a binary dipolar boson-fermion\n  164Dy-161Dy mixture: We suggest a time-dependent mean-field hydrodynamic model for a binary\ndipolar boson-fermion mixture to study the stability and collapse of fermions\nin the $^{164}$Dy-$^{161}$Dy mixture. The condition of stability of the dipolar\nmixture is illustrated in terms of phase diagrams. A collapse is induced in a\ndisk-shaped stable binary mixture by jumping the interspecies contact\ninteraction from repulsive to attractive by the Feshbach resonance technique.\nThe subsequent dynamics is studied by solving the time-dependent mean-field\nmodel including three-body loss due to molecule formation in boson-fermion and\nboson-boson channels. Collapse and fragmentation in the fermions after\nsubsequent explosions are illustrated. The anisotropic dipolar interaction\nleads to anisotropic fermionic density distribution during collapse. The\npresent study is carried out in three-dimensional space using realistic values\nof dipolar and contact interactions.",
        "positive": "Effect of Rare Fluctuations on the Thermalization of Isolated Quantum\n  Systems: We consider the question of thermalization for isolated quantum systems after\na sudden parameter change, a so-called quantum quench. In part icular we\ninvestigate the pre-requisites for thermalization focusing on the statistical\nproperties of the time-averaged density matrix and o f the expectation values\nof observables in the final eigenstates. We find that eigenstates, which are\nrare compared to the typical ones sampled by the micro-canonical distribution,\nare responsible for the absence of thermalization of some infinite integrable\nmodels and play an important role for some non-integrable systems of finite\nsize, such as the Bose-Hubbard model. We stress the importance of finite size\neffects for the thermalization of isolated quantum systems and discuss two\nalternative scenarios for thermalization, as well as ways to prune down the\ncorrect one."
    },
    {
        "anchor": "Quantum spin ice in three-dimensional Rydberg atom arrays: Quantum spin liquids are exotic phases of matter whose low-energy physics is\ndescribed as the deconfined phase of an emergent gauge theory. With recent\ntheory proposals and an experiment showing preliminary signs of $\\mathbb{Z}_2$\ntopological order [G. Semeghini et al., Science 374, 1242 (2021)], Rydberg atom\narrays have emerged as a promising platform to realize a quantum spin liquid.\nIn this work, we propose a way to realize a $U(1)$ quantum spin liquid in three\nspatial dimensions, described by the deconfined phase of $U(1)$ gauge theory in\na pyrochlore lattice Rydberg atom array. We study the ground state phase\ndiagram of the proposed Rydberg system as a function of experimentally relevant\nparameters. Within our calculation, we find that by tuning the Rabi frequency,\none can access both the confinement-deconfinement transition driven by a\nproliferation of \"magnetic\" monopoles and the Higgs transition driven by a\nproliferation of \"electric\" charges of the emergent gauge theory. We suggest\nexperimental probes for distinguishing the deconfined phase from ordered\nphases. This work serves as a proposal to access a confinement-deconfinement\ntransition in three spatial dimensions on a Rydberg-based quantum simulator.",
        "positive": "Optical spin conductivity in ultracold quantum gases: We show that the optical spin conductivity being a small AC response of a\nbulk spin current and elusive in condensed matter systems can be measured in\nultracold atoms. We demonstrate that this conductivity contains rich\ninformation on quantum states by analyzing experimentally achievable systems\nsuch as a spin-1/2 superfluid Fermi gas, a spin-1 Bose-Einstein condensate, and\na Tomonaga-Luttinger liquid. The obtained conductivity spectra being absent in\nthe Drude conductivity reflect quasiparticle excitations and non-Fermi liquid\nproperties. Accessible physical quantities include the superfluid gap and the\ncontact for the superfluid Fermi gas, gapped and gapless spin excitations as\nwell as quantum depletion for the Bose-Einstein condensate, and the spin part\nof the Tomonaga-Luttinger liquid parameter elusive in cold-atom experiments.\nUnlike its mass transport counterpart, the spin conductivity serves as a probe\napplicable to clean atomic gases without disorder and lattice potentials. Our\nformalism can be generalized to various systems such as spin-orbit coupled and\nnonequilibrium systems."
    },
    {
        "anchor": "Searching for Magnetostatic Modes in Spin-Polarized Atomic Hydrogen: We consider a possibility of the magnetostatic type spin waves driven by a\nlong-range magnetic dipole interactions, to account for the peaks in the ESR\nspectra observed in our previous work. The Walker equation for magnetostatic\nmodes is solved for a cylinder of atomic hydrogen, first in a uniform magnetic\nfield and second in a linearly decreasing magnetic field. The frequency\nbehavior of the solved modes with length of the cylinder and density of the gas\nis compared to experimental data. We conclude that magnetostatic modes are\nunlikely to account for the observed modulations of ESR spectra.",
        "positive": "Control of Spin-Exchange Interaction between Alkali-Earth Atoms via\n  Confinement-Induced Resonances in a Quasi 1+0 Dimensional System: A nuclear-spin exchange interaction exists between two ultracold fermionic\nalkali-earth (like) atoms in the electronic $^{1}{\\rm S}_{0}$ state ($g$-state)\nand $^{3}{\\rm P}_{0}$ state ($e$-state), and is an essential ingredient for the\nquantum simulation of Kondo effect. We study the control of this spin-exchange\ninteraction for two atoms simultaneously confined in a quasi-one-dimensional\n(quasi-1D) tube, where the $g$-atom is freely moving in the axial direction\nwhile the $e$-atom is further localized by an additional axial trap and behaves\nas a quasi-zero-dimensional (quasi-0D) impurity. In this system, the two atoms\nexperience effective-1D spin-exchange interactions in both even and odd partial\nwave channels, whose intensities can be controlled by the characteristic\nlengths of the confinements via the confinement-induced-resonances (CIRs). In\ncurrent work, we go beyond that pure-1D approximation. We model the transverse\nand axial confinements by harmonic traps with finite characteristic lengths\n$a_\\perp$ and $a_z$, respectively, and exactly solve the \"quasi-1D + quasi-0D\"\nscattering problem between these two atoms. Using the solutions we derive the\neffective 1D spin-exchange interaction and investigate the locations and widths\nof the even/odd wave CIRs for our system.\n  It is found that when the ratio $a_z/a_\\perp$ is larger, the CIRs can be\ninduced by weaker confinements, which are easier to be realized experimentally.\n  The comparison between our results and the recent experiment shows that the\ntwo experimentally observed resonance branches of the spin-exchange effect are\ndue to an even-wave CIR and an odd-wave CIR, respectively. Our results are\nadvantageous for the control and description of either the effective\nspin-exchange interaction or other types of interactions between ultracold\natoms in quasi 1+0 dimensional systems."
    },
    {
        "anchor": "Spontaneous magnetization and anomalous Hall effect in an emergent Dice\n  lattice: Ultracold atoms in optical lattices serve as a tool to model different\nphysical phenomena appearing originally in condensed matter.\n  To study magnetic phenomena one needs to engineer synthetic fields as atoms\nare neutral.\n  Appropriately shaped optical potentials force atoms to mimic charged\nparticles moving in a given field. We present the realization of artificial\ngauge fields for the observation of anomalous Hall effect. Two species of\nattractively interacting ultracold fermions are considered to be trapped in a\nshaken two dimensional triangular lattice. A combination of interaction induced\ntunneling and shaking can result in an emergent Dice lattice. In such a lattice\nthe staggered synthetic magnetic flux appears and it can be controlled with\nexternal parameters. The obtained synthetic fields are non-Abelian. Depending\non the tuning of the staggered flux we can obtain either anomalous Hall effect\nor its quantized version. Our results are reminiscent of Anomalous Hall\nconductivity in spin-orbit coupled ferromagnets.",
        "positive": "Exact results of dynamical structure factor of Lieb-Liniger model: The dynamical structure factor (DSF) represents a measure of dynamical\ndensity-density correlations in a quantum many-body system. Due to the\ncomplexity of many-body correlations and quantum fluctuations in a system of an\ninfinitely large Hilbert space, such kind of dynamical correlations often\nimpose a big theoretical challenge. For one dimensional (1D) quantum many-body\nsystems, qualitative predictions of dynamical response functions are usually\ncarried out by using the Tomonaga-Luttinger liquid (TLL) theory. In this\nscenario, a precise evaluation of the DSF for a 1D quantum system with\narbitrary interaction strength remains a formidable task. In this paper, we use\nthe form factor approach based on algebraic Bethe ansatz theory to calculate\nprecisely the DSF of Lieb-Liniger model with an arbitrary interaction strength\nat a large scale of particle number. We find that the DSF for a system as large\nas 2000 particles enables us to depict precisely its line-shape from which the\npower-law singularity with corresponding exponents in the vicinities of\nspectral thresholds naturally emerge. It should be noted that, the advantage of\nour algorithm promises an access to the threshold behavior of dynamical\ncorrelation functions, further confirming the validity of nonlinear TLL theory\nbesides Kitanine et. al. 2012 J. Stat. Mech. P09001. Finally we discuss a\ncomparison of results with the results from the ABACUS method by J.-S. Caux\n2009 J. Math. Phys. 50 095214 as well as from the strongly coupling expansion\nby Brand and Cherny 2005 Phys. Rev. A 72 033619."
    },
    {
        "anchor": "Wave function Monte Carlo method for polariton condensates: We present a quantum jump approach to describe coupled quantum and classical\nsystems in the context of Bose-Einstein condensation in the solid state. In our\nformalism, the excitonic gain medium is described by classical rate equations,\nwhile the polariton modes are described fully quantum mechanically. We show the\nequivalence of our method with a master equation approach. As an application,\nwe compute the linewidth of a single mode polariton condensate. Both the line\nbroadening due to the interactions between polaritons and the interactions with\nthe reservoir excitons is taken into account.",
        "positive": "Dynamics of first-order quantum phase transitions in extended\n  Bose-Hubbard model: From density wave to superfluid and vice-versa: In this paper, we study the nonequilibrium dynamics of the Bose-Hubbard model\nwith the nearest-neighbor repulsion by using time-dependent Gutzwiller (GW)\nmethods. In particular, we vary the hopping parameters in the Hamiltonian as a\nfunction of time, and investigate the dynamics of the system from the density\nwave (DW) to the superfluid (SF) crossing a first-order phase transition and\nvice-versa. From the DW to SF, we find scaling laws for the correlation length\nand vortex density with respect to the quench time. This is a reminiscence of\nthe Kibble-Zurek scaling for continuous phase transitions and contradicts the\ncommon expectation. We give a possible explanation for this observation. On the\nother hand from the SF to DW, the system evolution depends on the initial SF\nstate. When the initial state is the ground-state obtained by the static GW\nmethods, a coexisting state of the SF and DW domains forms after passing\nthrough the critical point. Coherence of the SF order parameter is lost as the\nsystem evolves. This is a phenomenon similar to the glass transition in\nclassical systems. When the state starts from the SF with small local phase\nfluctuations, the system obtains a large-size DW-domain structure with thin\ndomain walls."
    },
    {
        "anchor": "Quasi-one- and quasi-two-dimensional Bose-Fermi mixtures from weak\n  coupling to unitarity: We study ultracold superfluid Bose-Fermi mixtures in three dimensions, with\nstronger confinement along one or two directions, using a non-perturbative\nbeyond-mean-field model for bulk chemical potential valid along the\nweak-coupling to unitarity crossover. Although bosons are considered to be in a\nsuperfluid state, we consider two possibilities for the fermions --\nspin-polarized degenerate state and superfluid state. Simplified reduced\nanalytic lower-dimensional models are derived along the weak-coupling to\nunitarity crossover in quasi-one-dimensional (quasi-1D) and\nquasi-two-dimensional (quasi-2D) settings. The only parameters in these models\nare the constants of the beyond-mean-field Bose-Bose and Fermi-Fermi\nLee-Huang-Yang interactions and the respective universal Bertsch parameter at\nunitarity. In addition to the numerical results for a fully-trapped system, we\nalso present results for quasi-2D Bose-Fermi mixtures where one of the\ncomponents is untrapped but localized due to the interaction mediated by the\nother component. We demonstrate the validity of the reduced quasi-1D and\nquasi-2D models via a comparison of the numerical solutions for the ground\nstates obtained from the reduced models and the full three-dimensional (3D)\nmodel.",
        "positive": "Berezinskii-Kosterlitz-Thouless transitions in an easy-plane\n  ferromagnetic superfluid: A two-dimensional (2D) spin-1 Bose gas exhibits two\nBerezenskii-Kosterlitz-Thouless (BKT) transitions in the easy-plane\nferromagnetic phase. The higher temperature transition is associated with\nsuperfluidity of the mass current determined predominantly by a single spin\ncomponent. The lower temperature transition is associated with superfluidity of\nthe axial spin current, quasi-long range order of the transverse spin density\nand binding of polar-core spin vortices (PCVs). Above the spin BKT temperature,\nthe component circulations that make up each PCV spatially separate, suggesting\npossible deconfinement analogous to quark deconfinement in high energy physics.\nIntercomponent interactions give rise to superfluid drag between the spin\ncomponents, which we calculate analytically at zero temperature. We present the\nmass/spin superfluid phase diagram as a function of quadratic Zeeman energy\n$q$. At $q=0$ the system is in an isotropic spin phase with $\\mathrm{SO}(3)$\nsymmetry. Here the fluid response exhibits a system size dependence, suggesting\nthe absence of a BKT transition. Despite this, for finite systems the decay of\nspin correlations changes from exponential to algebraic as the temperature is\ndecreased."
    },
    {
        "anchor": "Multimode analysis of non-classical correlations in double well\n  Bose-Einstein condensates: The observation of non-classical correlations arising in interacting two to\nsize weakly coupled Bose-Einstein condensates was recently reported by Esteve\net al. [Nature 455, 1216 (2008)]. In order to observe fluctuations below the\nstandard quantum limit, they utilized adiabatic passage to reduce the thermal\nnoise to below that of thermal equilibrium at the minimum realizable\ntemperature. We present a theoretical analysis that takes into account the\nspatial degrees of freedom of the system, allowing us to calculate the expected\ncorrelations at finite temperature in the system, and to verify the hypothesis\nof adiabatic passage by comparing the dynamics to the idealized model.",
        "positive": "Exact Liouvillian Spectrum of a One-Dimensional Dissipative Hubbard\n  Model: A one-dimensional dissipative Hubbard model with two-body loss is shown to be\nexactly solvable. We obtain an exact eigenspectrum of a Liouvillian\nsuperoperator by employing a non-Hermitian extension of the Bethe-ansatz\nmethod. We find steady states, the Liouvillian gap, and an exceptional point\nthat is accompanied by the divergence of the correlation length. A dissipative\nversion of spin-charge separation induced by the quantum Zeno effect is also\ndemonstrated. Our result presents a new class of exactly solvable Liouvillians\nof open quantum many-body systems, which can be tested with ultracold atoms\nsubject to inelastic collisions."
    },
    {
        "anchor": "Negative Compressability of Non-Equilibrium Non-Ideal Bose--Einstein\n  Condensate: An ideal equilibrium Bose--Einstein condensate (BEC) is usually considered in\nthe grand canonical ($\\mu V T$) ensemble, which implies the presence of the\nchemical equilibrium with the environment. However, in most experimental\nscenarios, the total amount of particles in BEC is determined either by the\ninitial conditions or by the balance between dissipation and pumping. As a\nresult, BEC may possess the thermal equilibrium but almost never the chemical\nequilibrium. In addition, many experimentally achievable BECs are non-ideal due\nto interaction between particles. In the recent work\n[10.1103/PhysRevLett.128.065301], it has been shown that invariant subspaces in\nthe system Hilbert space appear in non-equilibrium BEC in the fast\nthermalization limit. In each of these subspaces, Gibbs distribution is\nestablished with a certain number of particles that makes it possible to\ninvestigate properties of non-ideal non-equilibrium BEC independently in each\ninvariant subspace. In this work, we analyze the BEC stability due to change in\ndispersion curve caused by non-ideal interactions in BEC. Generally, non-ideal\ninteractions lead to the redshift or blueshift of the dispertion curve and to\nthe change in the effective mass of the particles. We show that the redshift of\nthe dispersion curve can lead to the negative compressibility of BEC, whereas\nthe change in the effective mass always makes BEC more stable. We find the\nexplicit condition for the particle density in BEC, at which the negative\ncompressibility appears.",
        "positive": "Bose-Hubbard model on polyhedral graphs: Ever since the first observation of Bose-Einstein condensation in the\nnineties, ultracold quantum gases have been the subject of intense research,\nproviding a unique tool to understand the behavior of matter governed by the\nlaws of quantum mechanics. Ultracold bosonic atoms loaded in an optical lattice\nare usually described by the Bose-Hubbard model or a variant of it. In addition\nto the common insulating and superfluid phases, other phases (like density\nwaves and supersolids) may show up in the presence of a short-range\ninterparticle repulsion and also depending on the geometry of the lattice. We\nherein explore this possibility, using the graph of a convex polyhedron as\n\"lattice\" and playing with the coordination of nodes to promote the wanted\nfinite-size ordering. To accomplish the job we employ the method of decoupling\napproximation, whose efficacy is tested in one case against exact\ndiagonalization. We report zero-temperature results for two Catalan solids, the\ntetrakis hexahedron and the pentakis dodecahedron, for which a thorough\nground-state analysis reveals the existence of insulating \"phases\" with\npolyhedral order and a widely extended supersolid region. The key to this\noutcome is the unbalance in coordination between inequivalent nodes of the\ngraph. The predicted phases can be probed in systems of ultracold atoms using\nprogrammable holographic optical tweezers."
    },
    {
        "anchor": "Four-boson bound states from a functional renormalisation group: We use the functional renormalisation group to study the spectrum of three-\nand four-body states in bosonic systems around the unitary limit. Our effective\naction includes all energy-independent contact interactions in the four-atom\nsector and we introduce a running trimer field to eliminate couplings that\ninvolve the atom-atom-dimer channel. The results show qualitatively similar\nbehaviour to those from exact approaches. The truncated action we use leads to\noverbinding of the two four-body states seen in those treatments. It also\ngenerates a third state, although only for a very narrow range of two-body\nscattering lengths.",
        "positive": "Theory of condensation of indirect excitons in a trap: We present theoretical studies of condensation of indirect excitons in a\ntrap. Our model quantifies the effect of screening of the trap potential by\nindirect excitons on exciton condensation. The theoretical studies are applied\nto a system of indirect excitons in a GaAs/AlGaAs coupled quantum well\nstructure in a diamond-shaped electrostatic trap where exciton condensation was\nstudied in earlier experiments. The estimated condensation temperature of the\nindirect excitons in the trap reaches hundreds of milliKelvin."
    },
    {
        "anchor": "Theoretical Analysis on Spectroscopy of Atomic Bose-Hubbard Systems: We provide a numerical method to calculate comprehensively the microwave and\nthe laser spectra of ultracold bosonic atoms in optical lattices at finite\ntemperatures. Our formulation is built up with the sum rules, up to the second\norder, derived from the general principle of spectroscopy. The sum rule\napproach allows us to discuss the physical origins of a spectral peak shift and\nalso a peak broadening. We find that a spectral broadening of superfluid atoms\ncan be determined from number fluctuations of atoms, while that of normal-state\natoms is mainly attributed to quantum fluctuations resulting from hopping of\natoms. To calculate spectra at finite temperatures, based on the sum rule\napproach, we provide a two-mode approximation assuming that spectra of the\nsuperfluid and normal state atoms can be calculated separately. Our method can\nproperly deal with multi-peak structures of spectra resulting from thermal\nfluctuations and also coexisting of the superfluid and the normal states. By\ncombining the two-mode approximation with a finite temperature Gutzwiller\napproximation, we calculate spectra at finite temperatures by considering\nrealistic systems, and the calculated spectra show nice agreements with those\nin experiments.",
        "positive": "Analyzing a Bose polaron across resonant interactions: Recently, two independent experiments reported the observation of long-lived\npolarons in a Bose-Einstein condensate, providing an excellent setting to study\nthe generic scenario of a mobile impurity interacting with a quantum reservoir.\nHere, we expand the experimental analysis by disentangling the effects of trap\ninhomogeneities and the many-body continuum in one of these experiments. This\nmakes it possible to extract the energy of the polaron at a well-defined\ndensity as a function of the interaction strength. Comparisons with quantum\nMonte-Carlo as well as diagrammatic calculations show good agreement, and\nprovide a more detailed picture of the polaron properties at stronger\ninteractions than previously possible. Moreover, we develop a semi-classical\ntheory for the motional dynamics and three-body loss of the polarons, which\npartly explains a previously unresolved discrepancy between theory and\nexperimental observations for repulsive interactions. Finally, we utilize\nquantum Monte-Carlo calculations to demonstrate that the findings reported in\nthe two experiments are consistent with each other."
    },
    {
        "anchor": "Anyon optics with time-of-flight two-particle interference of\n  double-well-trapped interacting ultracold atoms: The subject of bianyon interference with ultracold atoms is introduced\nthrough theoretical investigations pertaining to the second-order momentum\ncorrelation maps of two anyons (built upon spinless and spin-1/2 bosonic, as\nwell as spin-1/2 fermionic ultracold atoms) trapped in a double-well optical\ntrap. The two-particle system is modeled according to the recently proposed\nprotocols for emulating an anyonic Hubbard Hamiltonian in ultracold-atom\none-dimensional lattices. Because the second-order momentum correlations are\nmirrored in the time-of-flight second-order interference patterns in space, our\nfindings provide impetus for time-of-flight experimental protocols for\ndetecting anyonic statistics via interferometry measurements of massive\nparticles that broaden the scope of the biphoton interferometry of quantum\noptics.",
        "positive": "Properties of 2D and Quasi-2D Dipolar Bosons with Non-zero Tilt Angles\n  at T=0: Recent experimental advances in creating stable dipolar bosonic systems,\nincluding polar molecules with large electric dipole moments, have led to\nvigorous theoretical activities. Recent reporting of observation of roton\nfeature in dipolar erbium has provided added impetus to theoretical and\nexperimental work. Here we discuss our mean-field theory work on 2D and\nquasi-2D dipolar bosons with dipoles oriented at an angle to the direction\nperpendicular to the confining 2D plane, i.e. for {\\it non-zero tilt angles}.\nUsing Bogoliubov-de Gennes equations, we present results on a number of T=0\nproperties of both 2D and quasi-2D systems, such as excitation spectra,\nstructure functions, sound velocities, quantum depletion, etc. We explore\ninstabilities at varying tilt angle, density and dipolar coupling. We map out\nphase diagrams as a function of tilt angle, dipole strength and density. We\nfind the development of maxon-roton behavior leading to roton instabilities at\nlarge densities for small tilt angles, and at low densities for large tilt\nangles. The behavior is anisotropic in k-space; accordingly the roton\ninstabilities occur first in the $k_y$ direction, suggestive of inhomogeneity\nand stripe phase, with density mode becoming soft in the $y$-direction. Beyond\na critical tilt angle, at any density, the dipolar system collapses owing to a\nphonon instability. We discuss similarities and differences between the\nproperties of 2D and quasi-2D dipolar systems at non-zero tilt angles."
    },
    {
        "anchor": "The normal state of attractive Fermi gases from coupled-cluster theory: We introduce coupled-cluster (CC) theory for the numerical study of the\nnormal state of two-component, dilute Fermi gases with attractive, short-range\ninteractions at zero temperature. We focus on CC theory with double excitations\n(CCD) and discuss its close relationship with -- and improvement upon -- the\nt-matrix approximation, i.e., the resummation of ladder diagrams via a\nrandom-phase approximation. We further discuss its relationship with Chevy's\nvariational wavefunction ansatz for the Fermi polaron and argue that CCD is its\nnatural extension to nonzero minority species concentrations. Studying normal\nstate energetics for a range of interaction strengths below and above\nunitarity, we find that CCD yields good agreement with fixed-node diffusion\nMonte Carlo. We find that CCD does not converge for small polarizations and\nlarge interaction strengths, which we speculatively attribute to the nascent\ninstability to a superfluid state.",
        "positive": "Topological phase transitions in the repulsively interacting\n  Haldane-Hubbard model: Using dynamical mean-field theory and exact diagonalization we study the\nphase diagram of the repulsive Haldane-Hubbard model, varying the interaction\nstrength and the sublattice potential difference. In addition to the quantum\nHall phase with Chern number $C=2$ and the band insulator with $C=0$ present\nalready in the noninteracting model, the system also exhibits a $C=0$ Mott\ninsulating phase, and a $C=1$ quantum Hall phase. We explain the latter phase\nby a spontaneous symmetry breaking where one of the spin-components is in the\nHall state and the other in the band insulating state."
    },
    {
        "anchor": "Single-shot simulations of dynamics of quantum dark solitons: Eigenstates of Bose particles with repulsive contact interactions in\none-dimensional space with periodic boundary conditions can be found with the\nhelp of the Bethe ansatz. The type~II excitation spectrum identified by E. H.\nLieb, reproduces the dispersion relation of dark solitons in the mean-field\napproach. The corresponding eigenstates possess translational symmetry which\ncan be broken in measurements of positions of particles. We analyze emergence\nof single and double solitons in the course of the measurements and investigate\ndynamics of the system. In the weak interaction limit, the system follows the\nmean-field prediction for a short period of time. Long time evolution reveals\nmany-body effects that are related to an increasing uncertainty of soliton\npositions. In the strong interaction regime particles behave like impenetrable\nbosons. Then, the probability densities in the configuration space become\nidentical to the probabilities of non-interacting fermions but the\nwave-functions themselves remember the original Bose statistics. Especially,\nthe phase flips that are key signatures of the solitons in the weak interaction\nlimit, can be observed in the time evolution of the strongly interacting\nbosons.",
        "positive": "Vortex Formation in Two-Dimensional Bose Gas: We discuss the stability of a homogeneous two-dimensional Bose gas at finite\ntemperature against formation of isolated vortices. We consider a patch of\nseveral healing lengths in size and compute its free energy using the Euclidean\nformalism. Since we deal with an open system, which is able to exchange\nparticles and angular momentum with the rest of the condensate, we use the\nsymmetry-breaking (as opposed to the particle number conserving) formalism, and\ninclude configurations with all values of angular momenta in the partition\nfunction. At finite temperature, there appear sphaleron configurations\nassociated to isolated vortices. The contribution from these configurations to\nthe free energy is computed in the dilute gas approximation. We show that the\nEuclidean action of linearized perturbations of a vortex is not positive\ndefinite. As a consequence the free energy of the 2D Bose gas acquires an\nimaginary part. This signals the instability of the gas. This instability may\nbe identified with the Berezinskii, Kosterlitz and Thouless (BKT) transition."
    },
    {
        "anchor": "Long-time expansion of a Bose-Einstein condensate: Can Anderson\n  localization be observed?: We numerically explore the long-time expansion of a one-dimensional\nBose-Einstein condensate in a disorder potential employing the Gross-Pitaevskii\nequation. The goal is to search for unique signatures of Anderson localization\nin the presence of particle-particle interactions. Using typical experimental\nparameters we show that the time scale for which the non-equilibrium dynamics\nof the interacting system begins to diverge from the non-interacting system\nexceeds the observation times up to now accessible in the experiment. We find\nevidence that the long-time evolution of the wavepacket is characterized by\n(sub)diffusive spreading and a growing effective localization length suggesting\nthat interactions destroy Anderson localization.",
        "positive": "Phase diagrams of the extended Bose-Hubbard model in one dimension by\n  Monte-Carlo simulation with the help of a stochastic-series expansion: In this paper, we study phase diagrams of the extended Bose-Hubbard model\n(EBHM) in one dimension by means of the quantum Monte-Carlo (QMC) simulation\nusing the stochastic-series expansion (SSE).In the EBHM, there exists a\nnearest-neighbor repulsion as well as the on-site repulsion. In the SSE-QMC\nsimulation, the highest particle number at each site, $n_c$, is also a\ncontrollable parameter, and we found that the phase diagrams depend on the\nvalue of $n_c$. It is shown that in addition to the Mott insulator, superfluid,\ndensity wave, the phase so-called Haldane insulator and supersolid appear in\nthe phase diagrams, and their locations in the phase diagrams are clarified."
    },
    {
        "anchor": "Super Efimov effect of resonantly interacting fermions in two dimensions: We study a system of spinless fermions in two dimensions with a short-range\ninteraction fine-tuned to a p-wave resonance. We show that three such fermions\nform an infinite tower of bound states of orbital angular momentum l=\\pm1 and\ntheir binding energies obey a universal doubly exponential scaling\nE_3^{(n)}\\propto\\exp(-2e^{3\\pi n/4+\\theta}) at large n. This \"super Efimov\neffect\" is found by a renormalization group analysis and confirmed by solving\nthe bound state problem. We also provide an indication that there are l=\\pm2\nfour-body resonances associated with every three-body bound state at\nE_4^{(n)}\\propto\\exp(-2e^{3\\pi n/4+\\theta-0.188}). These universal few-body\nstates may be observed in ultracold atom experiments and should be taken into\naccount in future many-body studies of the system.",
        "positive": "Classical-like wakes past elliptical obstacles in atomic Bose-Einstein\n  condensates: We reinvestigate numerically the classic problem of two-dimensional\nsuperfluid flow past an obstacle. Taking the obstacle to be elongated\n(perpendicular to the flow), rather than the usual circular form, is shown to\npromote the nucleation of quantized vortices, enhance their subsequent\ninteractions, and lead to wakes which bear striking similarity to their\nclassical (viscous) counterparts. Then, focussing on the recent experiment of\nKwon et al. (arXiv:1403.4658) in a trapped condensate, we show that an\nelliptical obstacle leads to a cleaner and more efficient means to generate\ntwo-dimensional quantum turbulence."
    },
    {
        "anchor": "Orbital Feshbach Resonance in Alkali-Earth Atoms: For a mixture of alkali-earth atomic gas in the long-lived excited state\n${}^3P_0$ and ground state ${}^1S_0$, in addition to nuclear spin, another\n\"orbital\" index is introduced to distinguish these two internal states. In this\nletter we propose a mechanism to induce Feshbach resonance between two atoms\nwith different orbital and nuclear spin quantum numbers. Two essential\ningredients are inter-orbital spin-exchanging scattering and orbital dependence\nof the Land\\'e g-factors. Here the orbital degrees of freedom plays similar\nrole as electron spin degree of freedom in magnetic Feshbach resonance in\nalkali-metal atoms. This resonance is particularly accessible for ${}^{173}$Yb\nsystem. The BCS-BEC crossover in this system requires two fermion pairing order\nparameters, and displays significant difference comparing to that in\nalkali-metal system.",
        "positive": "SU(3) Spin-Orbit Coupling in Systems of Ultracold Atoms: Motivated by the recent experimental success in realizing synthetic\nspin-orbit coupling in ultracold atomic systems, we consider N-component atoms\ncoupled to a non-Abelian SU(N) gauge field. More specifically, we focus on the\ncase, referred to here as \"SU(3) spin-orbit-coupling,\" where the internal\nstates of three-component atoms are coupled to their momenta via a matrix\nstructure that involves the Gell-Mann matrices (in contrast to the Pauli\nmatrices in conventional SU(2) spin-orbit-coupled systems). It is shown that\nthe SU(3) spin-orbit-coupling gives rise to qualitatively different phenomena\nand in particular we find that even a homogeneous SU(3) field on a simple\nsquare lattice enables a topologically non-trivial state to exist, while such\nSU(2) systems always have trivial topology. In deriving this result, we first\nestablish an exact equivalence between the Hofstadter model with a 1/N Abelian\nflux per plaquette and a homogeneous SU(N) non-Abelian model. The former is\nknown to have a topological spectrum for N>2, which is thus inherited by the\nlatter. It is explicitly verified by an exact calculation for N=3, where we\ndevelop and use a new algebraic method to calculate topological indices in the\nSU(3) case. Finally, we consider a strip geometry and establish the existence\nof three gapless edge states -- the hallmark feature of such an SU(3)\ntopological insulator."
    },
    {
        "anchor": "Observation of broad p-wave Feshbach resonances in ultracold\n  $^{85}$Rb-$^{87}$Rb mixtures: We observe new Feshbach resonances in ultracold mixtures of $^{85}$Rb and\n$^{87}$Rb atoms in the $^{85}$Rb$|2, +2\\rangle$+$^{87}$Rb$|1, +1\\rangle$ and\n$^{85}$Rb$|2, -2\\rangle$+$^{87}$Rb$|1, -1\\rangle$ scattering channels. The\npositions and properties of the resonances are predicted and characterized\nusing the semi-analytic multichannel quantum-defect theory by Gao. Of\nparticular interest, a number of broad entrance-channel dominated p-wave\nresonances are identified, implicating exciting opportunities for studying a\nvariety of p-wave interaction dominated physics.",
        "positive": "Trapping effect of periodic structures on the thermodynamic properties\n  of Fermi and Bose gases: We report the thermodynamic properties of Bose and Fermi ideal gases immersed\nin periodic structures such as penetrable multilayers or multitubes simulated\nby one (planes) or two perpendicular (tubes) external Dirac comb potentials,\nwhile the particles are allowed to move freely in the remaining directions.\nAlthough the bosonic chemical potential is a constant for $T < T_c$, a non\ndecreasing with temperature anomalous behavior of the fermionic chemical\npotential is confirmed and monitored as the tube bundle goes from 2D to 1D when\nthe wall impenetrability overcomes a critical value. In the specific heat\ncurves dimensional crossovers are very noticeable at high temperatures for both\ngases, where the system behavior goes from 3D to 2D and latter to 1D as the\nwall impenetrability is increased."
    },
    {
        "anchor": "The Bose-Einstein Condensate of G-wave Molecules and Its Intrinsic\n  Angular Momentum: The recent report on the realization of a Bose-Einstein condensate of G-wave\nmolecule made up of bound pairs of Cesium bosons is a surprise. These molecules\nare created at the G-wave resonance at 19.87G, where the severe three-body loss\nusually associated with these resonance are found to be reduced significantly\nwhen the density of the gas is reduced in a quasi 2D setting. The G-wave\nmolecules produced through this resonance have non-zero angular momentum\nprojections, resulting in the first BEC with a macroscopic intrinsic angular\nmomentum. Here, we show that this intrinsic angular momentum will lead to many\nnew quantum effects. They include a splitting of collective modes in the\nabsence of vortices, an orientation dependent energy shift due to the moment of\ninertia of the molecules, and a contribution to angular momentum in non-uniform\nmagnetic fields different from that of the Berry phase current. The intrinsic\nangular momentum also provides a way to probe the half vortices, excitations\nthat are unique to molecular condensates of bosons. The wavefunction giving\nrise to the intrinsic angular momentum can also be mapped out from the noise\ncorrelation.",
        "positive": "Failure of the GGE hypothesis for integrable models with bound states: In this work we study the applicability of the GGE to integrable one\ndimensional systems with bound states. We find that the GGE fails to describe\nthe long time dynamics for most initial states including eigenstates. We\npresent our calculations studying the attractive Lieb-Liniger gas and the XXZ\nmagnet, though similar results may be obtained for other models."
    },
    {
        "anchor": "Dissipative fluid dynamics for the dilute Fermi gas at unitarity:\n  Anisotropic fluid dynamics: We consider the time evolution of a dilute atomic Fermi gas after release\nfrom a trapping potential. A common difficulty with using fluid dynamics to\nstudy the expansion of the gas is that the theory is not applicable in the\ndilute corona, and that a naive treatment of the entire cloud using fluid\ndynamics leads to unphysical results. We propose to remedy this problem by\nincluding certain non-hydrodynamic degrees of freedom, in particular\nanisotropic components of the pressure tensor, in the theoretical description.\nWe show that, using this method, it is possible to describe the crossover from\nfluid dynamics to ballistic expansion locally. We illustrate the use of\nanisotropic fluid dynamics by studying the expansion of the dilute Fermi gas at\nunitarity using different functional forms of the shear viscosity, including a\nshear viscosity which is solely a function of temperature, $\\eta\\sim\n(mT)^{3/2}$, as predicted by kinetic theory in the dilute limit.",
        "positive": "Rotating quantum turbulence in the unitary Fermi gas: Quantized vortices carry the angular momentum in rotating superfluids, and\nare key to the phenomenon of quantum turbulence. Advances in ultra-cold atom\ntechnology enable quantum turbulence to be studied in regimes with both\nexperimental and theoretical control, unlike the original contexts of\nsuperfluid helium experiments. While much work has been performed with bosonic\nsystems, detailed studies of fermionic quantum turbulence are nascent, despite\nwide applicability to other contexts such as rotating neutron stars. In this\npaper, we present the first large-scale study of quantum turbulence in rotating\nfermionic superfluids using an accurate orbital based time-dependent density\nfunctional theory (DFT) called the superfluid local density approximation\n(SLDA). We identify two different modes of turbulent decay in the dynamical\nequilibration of a rotating fermionic superfluid, and contrast these results\nwith a computationally simpler orbital-free DFT, which we find can\nqualitatively reproduce these decay mechanisms if dissipation is explicitly\nincluded. These results demonstrate that one-body dissipation mechanisms\nintrinsic to fermionic superfluids play a key role differentiating fermionic\nfrom bosonic turbulence, but also suggest that simpler orbital-free theories\nmay be corrected so that these more efficient techniques can be used to model\nextended physical systems such as neutron superfluids in neutron stars."
    },
    {
        "anchor": "Homogeneous Atomic Fermi Gases: We report on the creation of homogeneous Fermi gases of ultracold atoms in a\nuniform potential. In the momentum distribution of a spin-polarized gas, we\nobserve the emergence of the Fermi surface and the saturated occupation of one\nparticle per momentum state. This directly confirms Pauli blocking in momentum\nspace. For the spin-balanced unitary Fermi gas, we observe spatially uniform\npair condensates. For thermodynamic measurements, we introduce a hybrid\npotential that is harmonic in one dimension and uniform in the other two. The\nspatially resolved compressibility reveals the superfluid transition in a\nspin-balanced Fermi gas, saturation in a fully polarized Fermi gas, and strong\nattraction in the polaronic regime of a partially polarized Fermi gas.",
        "positive": "Observation of state-to-state hyperfine-changing collision in a\n  Bose-Fermi mixture of $^6$Li and $^{41}$K atoms: Hyperfine-changing collisions are of fundamental interest for the studying of\nultracold heteronuclear mixtures. Here, we report the state-to-state study of\nthe hyperfine-changing-collision dynamics in a Bose-Fermi mixture of $^6$Li and\n$^{41}$K atoms. The collision products are directly observed and the\nspin-changing dynamics is measured. Based on a two-body collision model, the\nexperimental results are simultaneously fitted from which the spin-changing\nrate coefficient of $ 1.9(2)\\times 10^{-12}~\\rm{cm^3\\cdot s^{-1}}$ is gained,\nbeing consistent with the multi-channel quantum defect theory calculation. We\nfurther show that the contact parameter of $^6$Li-$^{41}$K mixture can be\nextracted from the measured spin-changing dynamics. The obtained results are\nconsistent with the first order perturbation theory in the weakly-interacting\nlimit. Our system offers great promise for studying spin-changing interactions\nin heteronuclear mixtures."
    },
    {
        "anchor": "Spectroscopic determination of magnetic-field-dependent interactions in\n  an ultracold Yb(3P2)-Li mixture: We present experimental results on the inelastic and elastic interspecies\ninteractions between ytterbium (Yb) in the metastable ${}^3\\mathrm{P}_2$ state\nloaded into a deep optical lattice and spin polarized lithium (Li) in its\nground state. Focusing on the $m_J = 0$ magnetic sublevel of\nYb(${}^3\\mathrm{P}_2$), bias magnetic fields between 20 G and 800 G are\ninvestigated and significantly enhanced inelastic collision rates with high\nmagnetic fields are found. In addition, by direct spectroscopy of the Yb\nMott-insulator immersed in the Li Fermi gas an upper boundary of the background\nscattering length of the Yb(${}^3\\mathrm{P}_2,\nm_J=0$)-Li(${}^2\\mathrm{S}_{1/2}, F=1/2, m_F=+1/2$) system is estimated,\nrevealing the absence of useful Feshbach resonances. These observations are\nqualitatively consistent with the theoretical calculations.",
        "positive": "Quantum Spin Dynamics in a Normal Bose Gas with Spin-orbit Coupling: In this Letter, we investigate spin dynamics of a two-component Bose gas with\nspin-orbit coupling realised in cold atom experiments. We derive coupled\nhydrodynamic equations for number and spin densities as well as their\nassociated currents. Specialising to quasi-one-dimensional situation, we obtain\nanalytic solutions of the spin helix structure and its dynamics in both\nadiabatic and diabatic regimes. In the adiabatic regime, the transverse spin\ndecays parabolically in the short-time limit and exponentially in the long time\nlimit, depending on initial polarisation. In contrast, in the diabatic regime,\ntransverse spin density and current oscillate in a way similar to the\ncharge-current oscillation in an undamped LC circuit. The effects of Rabi\ncoupling on the short-time spin dynamics is also discussed. Finally, using\nrealistic experimental parameters for $^{87}$Rb, we show that the time scales\nfor spin dynamics is of order of milliseconds to a few seconds and can be\nobserved experimentally."
    },
    {
        "anchor": "Collective excitations of a spherical ultradilute quantum droplet: In three dimensions, exotic new state of matter of self-bound ultradilute\nquantum droplets can be realized in free space, when the mean-field attraction\n(i.e., with mean-field energy $E_{\\textrm{MF}}\\propto-n^{2}$ at the density\n$n$) is balanced by the repulsive beyond-mean-field quantum fluctuations (i.e.,\n$E_{\\textrm{BMF}}\\propto n^{2+\\gamma}$). The parameter $\\gamma>0$ typically\ntakes the value $1/2$ if we consider the Lee-Huang-Yang (LHY) energy\nfunctional, but it can vary when the beyond-LHY-effect becomes important or the\nthree-body interaction becomes dominant. Here, we theoretically investigate how\ncollective excitations of a three-dimensional quantum droplet are affected by\nthe parameter $\\gamma$ and a weak harmonic trapping potential, both of which\ncould be tuned in experiments. We use both the approximate approach based on a\nGaussian variational ansatz and the exact numerical solution of the Bogoliubov\nequations resulting from the linearized time-dependent extended\nGross-Pitaevskii equation. We show that one of the key features of quantum\ndroplets, i.e., the existence of the surface modes with dispersion relation\n$\\omega_{s}\\propto k^{3/2}$ is very robust with respect to the changes either\nin the parameter $\\gamma$ or in the harmonic trapping potential. We predict the\nexcitation spectrum of the droplet realized by binary $^{39}$K mixtures under\nthe typical experimental conditions, which might be readily measured in current\ncold-atom laboratories.",
        "positive": "Observation and quantification of pseudogap in unitary Fermi gases: The nature of pseudogap lies at the heart of strongly-interacting\nsuperconductivity and superfluidity. With known pairing interactions, unitary\nFermi gases provide an ideal testbed to verify whether a pseudogap can arise\nfrom many-body pairing. Here we report the observation of the long-sought\npair-fluctuation-driven pseudogap in homogeneous unitary Fermi gases of\nlithium-6 atoms, by precisely measuring the spectral function through\nmomentum-resolved microwave spectroscopy without the serious effects of\nfinal-state effect. We find a large pseudogap above the superfluid transition.\nThe inverse pair lifetime exhibits a thermally-activated exponential behavior,\nuncovering the microscopic virtual pair breaking and recombination mechanism.\nThe obtained large, T-independent single-particle scattering rate is comparable\nwith that set by the Planckian limit. Our findings quantitatively characterize\nthe pseudogap in strongly-interacting Fermi gases, highlighting the role of\npreformed pairing as a precursor to superfluidity."
    },
    {
        "anchor": "Universal duality transformations in interacting one-dimensional quantum\n  systems: One-dimensional quantum systems admit duality relations that put hard core\nspinless bosons and fermions in one-to-one correspondence via Girardeau's\nmapping theorem. The simplest models of soft bosons interacting via zero-range\npotentials can also be mapped onto dual interacting fermions. However, a\nsystematic approach to one-dimensional statistical transmutation for arbitrary\nlow-energy interactions in the spinless and spinful or multicomponent cases has\nremained elusive. I develop a general theory of local unitary transformations\nbetween one-dimensional quantum systems of bosons and fermions with arbitrary\nspin or internal structure, single-particle dispersion -- including\nnon-relativistic, relativistic or otherwise -- and low-energy interactions in\nthe universal regime. These transformations generate families of new duality\nrelations and models that relate the strong and weak coupling limits of the\nrespective dual theories.",
        "positive": "Thermal spin fluctuations in spinor Bose-Einstein condensates: We study the thermal activation of spin fluctuations in dynamically-stable\nspinor Bose-Einstein condensates. We analyze the specific cases of a\nnon-dipolar spin-1 condensate in m = 0, where thermal activation results from\nspin-changing collisions, and of a Chromium condensate in the maximally\nstretched state m = -3, where thermal spin fluctuations are due to\ndipole-induced spin- relaxation. In both cases, we show that the low energy\nassociated to the spinor physics may be employed for thermometry purposes down\nto extremely low temperatures, typically impossible to measure in BECs with\nusual thermometric techniques. Moreover, the peculiar dependence of the\nsystem's entropy with the applied Zeeman energy opens a possible route for\nadiabatic cooling."
    },
    {
        "anchor": "Universal One-dimensional Atomic Gases Near Odd-wave Resonance: We show the renormalization of contact interaction for odd-wave scattering in\none-dimension(1D). Based on the renormalized interaction, we exactly solve the\ntwo-body problem in a harmonic trap, and further explore the universal\nproperties of spin-polarized fermions near odd-wave resonance using the\noperator product expansion method. It is found that the high-momentum\ndistribution behaves as $C/k^2$, with $C$ the odd-wave contact. Various\nuniversal relations are derived. Our work suggests a new universal system\nemergent in 1D with large odd-wave scattering length.",
        "positive": "Atomic Fermi gas at the unitary limit by quantum Monte Carlo methods:\n  Effects of the interaction range: We calculate the ground-state properties of unpolarized two-component Fermi\ngas by the diffusion quantum Monte Carlo (DMC) methods. Using an extrapolation\nto the zero effective range of the attractive two-particle interaction, we find\n$E/E_{\\rm free}$ to be 0.212(2), 0.407(2), 0.409(3) and 0.398(3) for 4, 14, 38\nand 66 atoms, respectively. Our results indicate that the dependence of the\ntotal energy on the effective range is sizable and the extrapolation is\ntherefore quite important. In order to test the quality of nodal surfaces and\nto estimate the impact of the fixed-node approximation we perform released-node\nDMC calculations for 4 and 14 atoms. Analysis of the released-node and the\nfixed-node results suggests that the main sources of the fixed-node errors are\nlong-range correlations which are difficult to sample in the released-node\napproaches due to the fast growth of the bosonic noise. Besides energies, we\nevaluate the two-body density matrix and the condensate fraction. We find that\nthe condensate fraction for the 66 atom system converges to 0.56(1) after the\nextrapolation to the zero interaction range."
    },
    {
        "anchor": "Quantum Mechanical Stabilization of a Collapsing Bose-Bose Mixture: According to the mean-field theory a condensed Bose-Bose mixture collapses\nwhen the interspecies attraction becomes stronger than the geometrical average\nof the intraspecies repulsions, $g_{12}^2>g_{11} g_{22}$. We show that instead\nof collapsing such a mixture gets into a dilute liquid-like droplet state\nstabilized by quantum fluctuations thus providing a direct manifestation of\nbeyond mean-field effects. We study various properties of the droplet and find,\nin particular, that in a wide range of parameters its excitation spectrum lies\nentirely above the particle emission threshold. The droplet thus automatically\nevaporates itself to zero temperature, the property potentially interesting by\nitself and from the viewpoint of sympathetic cooling of other systems.",
        "positive": "Berry-electrodynamics - Anomalous drift and pumping from time-dependent\n  Berry connection: The Berry curvature of a Bloch band can be interpreted as a local magnetic\nfield in reciprocal space. This analogy can be extended by defining an electric\nfield analog in reciprocal space which arises from the time-dependent Berry\nconnection. We explore the term in the semi-classical equation of motion that\ngives rise to this phenomenon, and show that it can lead to anomalous drift in\nwave packet motion. A similar effect arises from changes in the band population\ndue to periodic driving, where the resulting drift depends on the nature of the\ndrive and can be expressed in terms of a shift vector. Finally, these effects\ncan be combined to build a pump with a net anomalous drift during a cyclic\nevolution in momentum space."
    },
    {
        "anchor": "Many Fermi polarons at nonzero temperature: An extremely polarized mixture of an ultracold Fermi gas is expected to\nreduce to a Fermi polaron system, which consists of a single impurity immersed\nin the Fermi sea of majority atoms. By developing a many-body T -matrix theory,\nwe investigate spectral properties of the polarized mixture in experimentally\nrelevant regimes in which the system of finite impurity concentration at\nnonzero temperature is concerned. We explicitly demonstrate presence of polaron\nphysics in the polarized limit and discuss effects of many polarons in an\nintermediate regime in a self-consistent manner. By analyzing the spectral\nfunction at finite impurity concentration, we extract the attractive and\nrepulsive polaron energies. We find that a renormalization of majority atoms\nvia an interaction with minority atoms and a thermal depletion of the impurity\nchemical potential are of significance to depict the many-polaron regime.",
        "positive": "Structure and dynamics of binary Bose-Einstein condensates with vortex\n  phase imprinting: The combination of multi-component Bose-Einstein condensates (BECs) and phase\nimprinting techniques provides an ideal platform for exploring nonlinear\ndynamics and investigating the quantum transport properties of superfluids. In\nthis paper, we study abundant density structures and corresponding dynamics of\nphase-separated binary Bose-Einstein condensates with phase-imprinted single\nvortex or vortex dipole. By adjusting the ratio between the interspecies and\nintraspecies interactions, and the locations of the phase singularities, the\ntypical density profiles such as ball-shell structures, crescent-gibbous\nstructures, Matryoshka-like structures, sector-sector structures and\nsandwich-type structures appear, and the phase diagrams are obtained. The\ndynamics of these structures exhibit diverse properties, including the\npenetration of vortex dipoles, emergence of half-vortex dipoles, co-rotation of\nsectors, and oscillation between sectors. The pinning effects induced by a\npotential defect are also discussed, which is useful for controlling and\nmanipulating individual quantum states."
    },
    {
        "anchor": "Interaction-driven Lifshitz transition with dipolar fermions in optical\n  lattices: Anisotropic dipole-dipole interactions between ultracold dipolar fermions\nbreak the symmetry of the Fermi surface and thereby deform it. Here we\ndemonstrate that such a Fermi surface deformation induces a topological phase\ntransition -- so-called Lifshitz transition -- in the regime accessible to\npresent-day experiments. We describe the impact of the Lifshitz transition on\nobservable quantities such as the Fermi surface topology, the density-density\ncorrelation function, and the excitation spectrum of the system. The Lifshitz\ntransition in ultracold atoms can be controlled by tuning the dipole\norientation and -- in contrast to the transition studied in crystalline solids\n-- is completely interaction-driven.",
        "positive": "Twin-atom beams: We present highly efficient emission of twin-atom beams into a single\ntransversal mode of a waveguide potential. The source is a one-dimensional\ndegenerate Bose gas in the first radially excited state. We directly measure a\nsuppression of fluctuations in the atom number difference between the beams to\n0.37(3) with respect to the classical expectation, equivalent to 0.11(2) after\ncorrecting for detection noise. Our results underline the high potential of\nultracold atomic gases as sources for quantum matter wave optics and will\nenable the implementation of schemes previously unattainable with massive\nparticles"
    },
    {
        "anchor": "Cooperative excitation and many-body interactions in a cold Rydberg gas: The dipole blockade of Rydberg excitations is a hallmark of the strong\ninteractions between atoms in these high-lying quantum states. One of the\nconsequences of the dipole blockade is the suppression of fluctuations in the\ncounting statistics of Rydberg excitations, of which some evidence has been\nfound in previous experiments. Here we present experimental results on the\ndynamics and the counting statistics of Rydberg excitations of ultra-cold\nRubidium atoms both on and off resonance, which exhibit sub- and\nsuper-Poissonian counting statistics, respectively. We compare our results with\nnumerical simulations using a novel theoretical model based on Dicke states of\nRydberg atoms including dipole-dipole interactions, finding good agreement\nbetween experiment and theory.",
        "positive": "Symmetry-restoring quantum phase transition in a two-dimensional spinor\n  condensate: Bose Einstein condensates of spin-1 atoms are known to exist in two different\nphases, both having spontaneously broken spin-rotation symmetry, a\nferromagnetic and a polar condensate. Here we show that in two spatial\ndimensions it is possible to achieve a quantum phase transition from a polar\ncondensate into a singlet phase symmetric under rotations in spin space. This\ncan be done by using particle density as a tuning parameter. Starting from the\npolar phase at high density the system can be tuned into a strong-coupling\nintermediate-density point where the phase transition into a symmetric phase\ntakes place. By further reducing the particle density the symmetric phase can\nbe continuously deformed into a Bose-Einstein condensate of singlet atomic\npairs. We calculate the region of the parameter space where such a molecular\nphase is stable against collapse."
    },
    {
        "anchor": "Phase space theory of Bose-Einstein condensates and time-dependent modes: A phase space theory approach for treating dynamical behaviour of\nBose-Einstein condensates applicable to situations such as interferometry with\nBEC in time-dependent double well potentials is presented. Time-dependent mode\nfunctions are used, chosen so that one, two,.. highly occupied modes describe\nwell the physics of interacting condensate bosons in time dependent potentials\nat well below the transition temperature. Time dependent mode annihilation,\ncreation operators are represented by time dependent phase variables, but time\nindependent total field annihilation, creation operators are represented by\ntime independent field functions. Two situations are treated, one (mode theory)\nis where specific mode annihilation, creation operators and their related phase\nvariables and distribution functions are dealt with, the other (field theory)\nis where only field creation, annihilation operators and their related field\nfunctions and distribution functionals are involved. The paper focuses on the\nhybrid approach, where the modes are divided up between condensate (highly\noccupied) modes and non-condensate (sparsely occupied) modes. It is found that\nthere are extra terms in the Ito stochastic equations both for the stochastic\nphases and stochastic fields, involving coupling coefficients defined via\noverlap integrals between mode functions and their time derivatives. For the\nhybrid approach both the Fokker-Planck and functional Fokker-Planck equations\ndiffer from those derived via the correspondence rules, the drift vectors are\nunchanged but the diffusion matrices contain additional terms involving the\ncoupling coefficients. Results are also presented for the combined approach\nwhere all the modes are treated as one set.",
        "positive": "Short range inter-vortex interaction and interacting dynamics of\n  half-quantized vortices in two-component Bose-Einstein condensates: We study the interaction and dynamics of two half-quantized vortices in\ntwo-component Bose- Einstein condensates. Using the Pade approximation for the\nvortex core profile, we calculate the intervortex potential, whose asymptotic\nform for a large distance has been derived by Eto et al. [Phys. Rev. A, 83,\n063603 (2011)]. Through numerical simulations of the two-dimensional\nGross-Pitaevskii equations, we reveal different kinds of dynamical trajectories\nof the vortices depending on the combinations of signs of circulations and the\nintercomponent density coupling. Under the adiabatic limit, we derive the\nequations of motion for the vortex coordinates, in which the motion is caused\nby the balance between Magnus force and the intervortex forces. The initial\nvelocity of the vortex motion can be explained quantitatively by this point\nvortex approximation, but under- standing the long-time behavior of the\ndynamics needs more consideration beyond our model."
    },
    {
        "anchor": "Quantum pump for counter-circulations in a spinor Bose-Einstein\n  condensate: We propose a pump scheme for quantum circulations, including\ncounter-circulations for superposition states, of a spinor Bose-Einstein\ncondensate. Our scheme is efficient and can be implemented within current\nexperimental technologies and setups. It remains valid for non-classical atomic\nstates, such as pseudo-spin squeezed states and maximal entangled N-GHZ or NooN\nstates. Moreover, it is capable of transforming several enhanced sensing\nprotocols relying on reduced fluctuations from quantum correlation and\nentanglement of atomic internal states to enhanced measurement of spatial\ninterference and rotation.",
        "positive": "Spin-Flipping Half Vortex in a Macroscopic Polariton Spinor Ring\n  Condensate: We report the observation of vorticity in a macroscopic Bose-Einstein\ncondensate of polaritons in a ring geometry. Because it is a spinor condensate,\nthe elementary excitations are \"half vortices\" in which there is a phase\nrotation of $\\pi$ in connection with a polarization vector rotation of $\\pi$\naround a closed path. This is clearly seen in the experimental observations of\nthe polarization rotation around the ring. In the ring geometry, a new type of\nhalf vortex is allowed in which the handedness of the spin flips from one side\nof the ring to the other, in addition to the rotation of the linear\npolarization component; such a state is not allowed in a simply-connected\ngeometry. Theoretical calculation of the energy of this state shows that when\nmany-body interactions are taken into account, it is lower in energy than a\nsimple half vortex. The direction of circulation of the flow around the ring\nfluctuates randomly between clockwise and counterclockwise from one shot to the\nnext; this corresponds to spontaneous breaking of time-reversal symmetry in the\nsystem. These new, macroscopic polariton ring condensates allow for the\npossibility of direct control of the vorticity of the condensate."
    },
    {
        "anchor": "A Path Integral Ground State Monte Carlo Algorithm for Entanglement of\n  Lattice Bosons: A ground state path integral quantum Monte Carlo algorithm is introduced that\nallows for the study of entanglement in lattice bosons at zero temperature. The\nR\\'enyi entanglement entropy between spatial subregions is explored across the\nphase diagram of the one dimensional Bose-Hubbard model for systems consisting\nof up to $L=256$ sites at unit-filling without any restrictions on site\noccupancy, far beyond the reach of exact diagonalization. The favorable scaling\nof the algorithm is demonstrated through a further measurement of the R\\'enyi\nentanglement entropy at the two dimensional superfluid-insulator critical point\nfor large system sizes, confirming the existence of the expected entanglement\nboundary law in the ground state. The R\\'enyi estimator is extended to measure\nthe symmetry resolved entanglement that is operationally accessible as a\nresource for experimentally relevant lattice gases with fixed total particle\nnumber.",
        "positive": "Three-dimensional Gross-Pitaevskii solitary waves in optical lattices:\n  stabilization using the artificial quartic kinetic energy induced by lattice\n  shaking: In this Letter, we show that a three-dimensional Bose-Einstein solitary wave\ncan become stable if the dispersion law is changed from quadratic to quartic.\nWe suggest a way to realize the quartic dispersion, using shaken optical\nlattices. Estimates show that the resulting solitary waves can occupy as little\nas $\\sim 1/20$-th of the Brillouin zone in each of the three directions and\ncontain as many as $N = 10^{3}$ atoms, thus representing a \\textit{fully\nmobile} macroscopic three-dimensional object."
    },
    {
        "anchor": "Scattering bright solitons: quantum versus mean-field behavior: We investigate scattering bright solitons off a potential using both\nanalytical and numerical methods. Our paper focuses on low kinetic energies for\nwhich differences between the mean-field description via the Gross-Pitaevskii\nequation (GPE) and the quantum behavior are particularly large. On the\nN-particle quantum level, adding an additional harmonic confinement leads to a\nsimple signature to distinguish quantum superpositions from statistical\nmixtures. While the non-linear character of the GPE does not allow quantum\nsuperpositions, the splitting of GPE-solitons takes place only partially. When\nthe potential strength is increased, the fraction of the soliton which is\ntransmitted or reflected jumps non-continuously. We explain these jumps via\nenergy-conservation and interpret them as indications for quantum\nsuperpositions on the N-particle level. On the GPE-level, we also investigate\nthe transition from this stepwise behavior to the continuous case.",
        "positive": "Realizing quantum Ising models in tunable two-dimensional arrays of\n  single Rydberg atoms: Spin models are the prime example of simplified manybody Hamiltonians used to\nmodel complex, real-world strongly correlated materials. However, despite their\nsimplified character, their dynamics often cannot be simulated exactly on\nclassical computers as soon as the number of particles exceeds a few tens. For\nthis reason, the quantum simulation of spin Hamiltonians using the tools of\natomic and molecular physics has become very active over the last years, using\nultracold atoms or molecules in optical lattices, or trapped ions. All of these\napproaches have their own assets, but also limitations. Here, we report on a\nnovel platform for the study of spin systems, using individual atoms trapped in\ntwo-dimensional arrays of optical microtraps with arbitrary geometries, where\nfilling fractions range from 60 to 100% with exact knowledge of the initial\nconfiguration. When excited to Rydberg D-states, the atoms undergo strong\ninteractions whose anisotropic character opens exciting prospects for\nsimulating exotic matter. We illustrate the versatility of our system by\nstudying the dynamics of an Ising-like spin-1/2 system in a transverse field\nwith up to thirty spins, for a variety of geometries in one and two dimensions,\nand for a wide range of interaction strengths. For geometries where the\nanisotropy is expected to have small effects we find an excellent agreement\nwith ab-initio simulations of the spin-1/2 system, while for strongly\nanisotropic situations the multilevel structure of the D-states has a\nmeasurable influence. Our findings establish arrays of single Rydberg atoms as\na versatile platform for the study of quantum magnetism."
    },
    {
        "anchor": "Rigorous mean-field dynamics of lattice bosons: Quenches from the Mott\n  insulator: We provide a rigorous derivation of Gutzwiller mean-field dynamics for\nlattice bosons, showing that it is exact on fully connected lattices. We apply\nthis formalism to quenches in the interaction parameter from the Mott insulator\nto the superfluid state. Although within mean-field the Mott insulator is a\nsteady state, we show that a dynamical critical interaction $U_d$ exists, such\nthat for final interaction parameter $U_f>U_d$ the Mott insulator is\nexponentially unstable towards emerging long-range superfluid order, whereas\nfor $U_f<U_d$ the Mott insulating state is stable. We discuss the implications\nof this prediction for finite-dimensional systems.",
        "positive": "Breakdown of universality for unequal-mass Fermi gases with infinite\n  scattering length: We treat small trapped unequal-mass two-component Fermi gases at unitarity\nwithin a non-perturbative microscopic framework and investigate the system\nproperties as functions of the mass ratio $\\kappa$, and the numbers $N_{1}$ and\n$N_2$ of heavy and light fermions. While equal-mass Fermi gases with infinitely\nlarge interspecies s-wave scattering length $a_s$ are universal, we find that\nunequal mass Fermi gases are, for sufficiently large $\\kappa$ and in the regime\nwhere Efimov physics is absent, not universal. In particular, the\n$(N_1,N_2)=(2,1)$ and $(3,1)$ systems exhibit three-body (3b) and four-body\n(4b) resonances at $\\kappa = 12.314(2)$ and $10.4(2)$, respectively, as well as\nsurprisingly large finite-range (FR) effects. These findings have profound\nimplications for ongoing experimental efforts and quantum simulation proposals\nthat utilize unequal-mass atomic Fermi gases."
    },
    {
        "anchor": "Phase diagrams and Thomas-Fermi estimates for spin-orbit coupled\n  Bose-Einstein Condensates under rotation: We provide complete phase diagrams describing the ground state of a trapped\nspinor BEC under the combined effects of rotation and a Rashba spin-orbit\ncoupling. The interplay between the different parameters (magnitude of\nrotation, strength of the spin-orbit coupling and interaction) leads to a rich\nground state physics that we classify. We explain some features analytically in\nthe Thomas-Fermi approximation, writing the problem in terms of the total\ndensity, total phase and spin. In particular, we analyze the giant skyrmion,\nand find that it is of degree 1 in the strong segregation case. In some regions\nof the phase diagrams, we relate the patterns to a ferromagnetic energy.",
        "positive": "Manipulation of heteronuclear spin dynamics with microwave and vector\n  light shift: We report the observation and manipulation of heteronuclear spin dynamics in\na spin-1 mixture of ultracold $^{87}$Rb and $^{23}$Na atoms. The dynamics is\ndriven by the interspecies spin-dependent interaction and shows a pronounced\ndependence on magnetic fields with influences from both linear and quadratic\nZeeman shifts. Similar to the well-studied homonuclear cases, the interspecies\nspin dynamics can be controlled by tuning the quadratic Zeeman shift with\nfar-detuned microwave fields. In addition, we successfully realize spin\ndynamics control with vector light shifts which act as a species-selective\neffective magnetic field on $^{87}$Rb atoms. Both methods show negligible loss\nof atoms thus will be powerful techniques for investigating spin dynamics with\nfast temporal and high spatial resolutions."
    },
    {
        "anchor": "Anderson tower of states and nematic order of spin-1 bosonic atoms on a\n  2D lattice: We investigate the structure of the spectrum of antiferromagnetically coupled\nspin-1 bosons on a square lattice using degenerate perturbation theory and\nexact diagonalizations of finite clusters. We show that the superfluid phase\ndevelops an Anderson tower of states typical of nematic long-range order with\nbroken SU(2) symmetry.We further show that this order persists into the Mott\ninsulating phase down to zero hopping for one boson per site, and down to a\ncritical hopping for two bosons per site, in agreement with mean-field and\nQuantum Monte Carlo results. The connection with the transition between a\nfragmented condensate and a polar one in a single trap is briefly discussed.",
        "positive": "Equilibrium solutions of immiscible two-species Bose-Einstein\n  condensates in perturbed harmonic traps: We investigate the mean--field equilibrium solutions for a two--species\nimmiscible Bose--Einstein condensate confined by a harmonic confinement with\nadditional linear perturbations. We observe a range of equilibrium density\nstructures, including `ball and shell' formations and axially/radially\nseparated states, with a marked sensitivity to the potential perturbations and\nthe relative atom number in each species. Incorporation of linear trap\nperturbations, albeit weak, are found to be essential to match the range of\nequilibrium density profiles observed in a recent Rb-87 - Cs-133 Bose-Einstein\ncondensate experiment [D. J. McCarron et al., Phys. Rev. A, 84, 011603(R)\n(2011)]. Our analysis of this experiment demonstrates that sensitivity to\nlinear trap perturbations is likely to be important factor in interpreting the\nresults of similar experiments in the future."
    },
    {
        "anchor": "Quantum flutter of supersonic particles in one-dimensional quantum\n  liquids: The non-equilibrium dynamics of strongly correlated many-body systems\nexhibits some of the most puzzling phenomena and challenging problems in\ncondensed matter physics. Here we report on essentially exact results on the\ntime evolution of an impurity injected at a finite velocity into a\none-dimensional quantum liquid. We provide the first quantitative study of the\nformation of the correlation hole around a particle in a strongly coupled\nmany-body quantum system, and find that the resulting correlated state does not\ncome to a complete stop but reaches a steady state which propagates at a finite\nvelocity. We also uncover a novel physical phenomenon when the impurity is\ninjected at supersonic velocities: the correlation hole undergoes long-lived\ncoherent oscillations around the impurity, an effect we call quantum flutter.\nWe provide a detailed understanding and an intuitive physical picture of these\nintriguing discoveries, and propose an experimental setup where this physics\ncan be realized and probed directly.",
        "positive": "Fractional corner charges in a 2D super-lattice Bose-Hubbard model: We study a two dimensional super-lattice Bose-Hubbard model with alternating\nhoppings in the limit of strong on-site interactions. We evaluate the phase\ndiagram of the model around half-filling using the density matrix\nrenormalization group method and find two gapped phases separated by a gapless\nsuperfluid region. We demonstrate that the gapped states realize two distinct\nhigher order symmetry protected topological phases, which are protected by a\ncombination of charge conservation and $C_4$ lattice symmetry. The phases are\ndistinguished in terms of a quantized fractional corner charge and a many-body\ntopological invariant that is robust against arbitrary, symmetry preserving\nedge manipulations. We support our claims by numerically studying the full\ncounting statistics of the corner charge, finding a sharp distribution peaked\naround the quantized values. These results are experimentally observable in\nultracold atomic settings using state of the art quantum gas microscopy."
    },
    {
        "anchor": "Adiabatic preparation of vortex lattices: By engineering appropriate artificial gauge potentials, a Bose-Einstein\ncondensate can be adiabatically loaded into a current carrying state that\nresembles a vortex lattice of a rotating uniform Bose gas. We give two\nexplicit, experimentally feasible protocols by which vortex lattices can be\nsmoothly formed from a condensate initially at rest. In the first example we\nshow how this can be achieved by adiabatically loading a uniform BEC into an\noptical flux lattice, formed from coherent optical coupling of internal states\nof the atom. In the second example we study a tight binding model that is\ncontinuously manipulated in parameter space such that it smoothly transforms\ninto the Harper-Hofstadter model with 1/3 flux per plaquette.",
        "positive": "Mean-field dynamics to negative absolute temperatures in the\n  Bose-Hubbard model: We apply time-dependent Gutzwiller mean-field theory to provide a qualitative\nunderstanding for bosons in optical lattices that approach states corresponding\nto negative absolute temperatures. We perform the dynamical simulations to\nrelate to the recent experiments by Braun et al. [ S. Braun, J. P. Ronzheimer,\nM. Schreiber, S. S. Hodgman, T. Rom, I. Bloch and U. Schneider, Science 339 52\n(2013)]. Time-of-flight images calculated from the two-dimensional numerical\nsimulations reproduce characteristics of the experimental observations, in\nparticular, the emergence of the four peaks at the corners of the Brillouin\nzone."
    },
    {
        "anchor": "One-Body Density Matrix and Momentum Distribution of Strongly\n  Interacting One-Dimensional Spinor Quantum Gases: The one-body density matrix (OBDM) of a strongly interacting spinor quantum\ngas in one dimension can be written as a summation of products of spatial and\nspin parts. We find that there is a remarkable connection between the spatial\npart and the OBDM of a spinless hard-core anyon gas. This connection allows us\nto efficiently calculate the OBDM of the spinor system with particle numbers\nmuch larger than what was previously possible. Given the OBDM, we can easily\ncalculate the momentum distribution of the spinor system, which again is\nrelated to the momentum distribution of the hard-core ayone gas.",
        "positive": "Liquid quantum droplets of ultracold magnetic atoms: The simultaneous presence of two competing inter-particle interactions can\nlead to the emergence of new phenomena in a many-body system. Among others,\nsuch effects are expected in dipolar Bose-Einstein condensates, subject to\ndipole-dipole interaction and short-range repulsion. Magnetic quantum gases and\nin particular Dysprosium gases, offering a comparable short-range contact and a\nlong-range dipolar interaction energy, remarkably exhibit such emergent\nphenomena. In addition an effective cancellation of mean-field effects of the\ntwo interactions results in a pronounced importance of quantum-mechanical\nbeyond mean-field effects. For a weakly-dominant dipolar interaction the\nstriking consequence is the existence of a new state of matter equilibrated by\nthe balance between weak mean-field attraction and beyond mean-field repulsion.\nThough exemplified here in the case of dipolar Bose gases, this state of matter\nshould appear also with other microscopic interactions types, provided a\ncompetition results in an effective cancellation of the total mean-field. The\nmacroscopic state takes the form of so-called quantum droplets. We present the\neffects of a long-range dipolar interaction between these droplets."
    },
    {
        "anchor": "Dynamics of a solitonic vortex in an anisotropically trapped superfluid: We analytically study the dynamics of a solitonic vortex (SV) in a superfluid\nconfined in a non-axisymmetric harmonic trap. The study provides a framework\nfor analyzing the role of the trap anisotropy in the oscillation of SVs\nobserved in recent experiments on atomic Bose and Fermi superfluids. The\nemergence of common and statistics-dependent features is traced in a unified\napproach to both types of fluid. Our description, built in the hydrodynamic\nformalism, is based on a Lagragian approach which incorporates the vortex\nlocation as dynamical parameters of a variational ansatz. Previous operative\nHamiltonian pictures are recovered through a canonically traced procedure. Our\nresults improve the understanding of the experimental findings. Some of the\nobserved features are shown to be specific to the tri-axial anisotropy of the\ntrap. In particular, we characterize the nontrivial dependence of the\noscillation frequency on the trapping transversal to the vortical line. The\nstudy reveals also the crucial role played by the nonlinear character of the\ndynamics in the observed oscillation: for the considered experimental\nconditions, the frequency, and, in turn, the effective inertial mass of the\nvortex, are found to significantly depend on the amplitude of the generated\nmotion. It is also uncovered how the coupling with collective modes of the\nfluid induces a non-negligible shift in the oscillation frequency. The\nappearance of fine-structure features in the SV trajectory is predicted.",
        "positive": "Ab-initio phase diagram of ultracold 87-Rb in an one-dimensional\n  two-color superlattice: We investigate the ab-initio phase diagram of ultracold 87-Rb atoms in an\none-dimensional two-color superlattice. Using single-particle band structure\ncalculations we map the experimental setup onto the parameters of the\nBose-Hubbard model. This ab-initio ansatz allows us to express the phase\ndiagrams in terms of the experimental control parameters, i.e., the intensities\nof the lasers that form the optical superlattice. In order to solve the\nmany-body problem for experimental system sizes we adopt the density-matrix\nrenormalization-group algorithm. A detailed study of convergence and\nfinite-size effects for all observables is presented. Our results show that all\nrelevant quantum phases, i.e., superfluid, Mott-insulator, and quasi\nBose-glass, can be accessed through intensity variation of the lasers alone.\nHowever, it turns out that the phase diagram is strongly affected by the\nlongitudinal trapping potential."
    },
    {
        "anchor": "Absence of the Twisted Superfluid State in a mean field model of bosons\n  on a Honeycomb Lattice: Motivated by recent observations (P. Soltan-Panahi {\\it et al.}, Nature\nPhysics {\\bf 8}, 71-75 (2012)), we study the stability of a Bose-Einstein\nCondensate within a spin-dependent honeycomb lattice towards forming a \"Twisted\nSuperfluid\" state. Our exhaustive numerical search fails to find this phase,\npointing to possible non-mean field physics.",
        "positive": "S-matrix approach to quantum gases in the unitary limit I: the\n  two-dimensional case: In three spatial dimensions, in the unitary limit of a non-relativistic\nquantum Bose or Fermi gas, the scattering length diverges. This occurs at a\nrenormalization group fixed point, thus these systems present interesting\nexamples of interacting scale-invariant models with dynamical exponent z=2. We\nstudy this problem in two and three spatial dimensions using the S-matrix based\napproach to the thermodynamics we recently developed. It is well suited to the\nunitary limit where the S-matrix equals -1, since it allows an expansion in the\ninverse coupling. We define a meaningful scale-invariant, unitary limit in two\nspatial dimensions, where again the scattering length diverges. In the\ntwo-dimensional case, the integral equation for the pseudo-energy becomes\ntranscendentally algebraic, and we can easily compute the various universal\nscaling functions as a function of \\mu/T, such as the energy per particle. The\nratio of the shear viscosity to the entropy density is above the conjectured\nlower bound of for all cases except attractive bosons. For attractive\n2-component fermions, the ratio is greater than 6.07 times the conjectured\nlower bound, whereas for attractive bosons it is greater than 0.4 times it."
    },
    {
        "anchor": "Constrained extrapolation problem and order-dependent mappings: We consider the problem of extrapolating the perturbation series for the\ndilute Fermi gas in three dimensions to the unitary limit of infinite\nscattering length and into the BEC region, using the available strong-coupling\ninformation to constrain the extrapolation problem. In this constrained\nextrapolation problem (CEP) the goal is to find classes of approximants that\ngive well converged results already for low perturbative truncation orders.\nFirst, we show that standard Pad\\'{e} and Borel methods are too restrictive to\ngive satisfactory results for this CEP. A generalization of Borel extrapolation\nis given by the so-called Maximum Entropy extrapolation method (MaxEnt).\nHowever, we show that MaxEnt requires extensive elaborations to be applicable\nto the dilute Fermi gas and is thus not practical for the CEP in this case.\nInstead, we propose order-dependent-mapping extrapolation (ODME) as a simple,\npractical, and general method for the CEP. We find that the ODME approximants\nfor the ground-state energy of the dilute Fermi gas are robust with respect to\nchanges of the mapping choice and agree with results from quantum Monte Carlo\nsimulations within uncertainties.",
        "positive": "Quantum phase transitions and quantum chaos in generalized Dicke and\n  Jahn-Teller polaron model and finite-size effects: The Dicke model extended to two bosons of different frequencies or equivalent\ngeneralized Jahn-Teller lattice model are shown to exhibit a spontaneous\nquantum phase transition between the polaron-modified \"quasi-normal\" and\nsqueezed \"radiation\" phase with the transition point dependent on the\nfrequencies. In a finite lattice a mixed domain of coexistence of the\nquasi-normal and modified radiation phase is created within the quasi-normal\nphase domain. There occurs a field-directed oscillation-assisted tunneling\n(hopping). The field is driven by simultaneous squeezing and polaron-dressing\nof the collective boson level mode due to the additional boson mode. In a\nfinite lattice in the radiation domain there occurs a sequence of local\ntunnelings (oscillations) between two minima of a local potential weakly\ncoupled to two assisting oscillations. The \"radiation\" phase reveals itself as\nan almost ideal instanton--anti-instanton gas phase. The correlations among the\nenergy levels mediated by the additional mode in the mixed domain considerably\nreduce the level repulsions. As a consequence, the Wigner level spacing\nprobability distribution of the two-boson Dicke model is non-universally\nreduced from the Wigner to the semi-Poisson and asymptotically to the Poisson\ndistribution of level spacings. The correlations cause a suppression of the\ncoherence of the radiation phase as finite-size effect. Possible applications\nof the present theory are suggested."
    },
    {
        "anchor": "Emergence of isotropy in rotating turbulence of Bose-Einstein\n  condensates: We present a study on the development of rotating turbulence in Bose-Einstein\ncondensates with a dissipative Gross-Pitaevskii model. Turbulence is generated\nby driving the lattice of quantized vortices in a harmonic potential with a\nrandom forcing potential. As the turbulence progressed, the initial alignment\nof vortices underwent slight disruptions, thereby increasing the\nhigh-wavenumber components of the kinetic energy. In the turbulent state, the\ndistribution of incompressible kinetic energy exhibits milder anisotropy than\nthat in the initial lattice state and demonstrates a scaling behavior of\n$k_z^{-2.5}$ in the direction parallel to the rotation axis. In contrast, the\ncompressible kinetic energy exhibits an isotropic scaling behavior at high\nwavenumbers.",
        "positive": "Cavity-mediated unconventional pairing in ultracold fermionic atoms: We investigate long-range pairing interactions between ultracold fermionic\natoms confined in an optical lattice which are mediated by the coupling to a\ncavity. In the absence of other perturbations, we find three degenerate pairing\nsymmetries for a two-dimensional square lattice. By tuning a weak local atomic\ninteraction via a Feshbach resonance or by tuning a weak magnetic field, the\nsuperfluid system can be driven from a topologically trivial s-wave to\ntopologically ordered, chiral superfluids containing Majorana edge states. Our\nwork points out a novel path towards the creation of exotic superfluid states\nby exploiting the competition between long-range and short-range interactions."
    },
    {
        "anchor": "Coherent spin mixing via spin-orbit coupling in Bose gases: We study beyond-mean-field properties of interacting spin-1 Bose gases with\nsynthetic Rashba-Dresselhaus spin-orbit coupling at low energies. We derive a\nmany-body Hamiltonian following a tight-binding approximation in quasi-momentum\nspace, where the effective spin dependence of the collisions that emerges from\nspin-orbit coupling leads to dominant correlated tunneling processes that\ncouple the different bound states. We discuss the properties of the spectrum of\nthe derived Hamiltonian and its experimental signatures. In a certain region of\nthe parameter space, the system becomes integrable, and its dynamics becomes\nanalogous to that of a spin-1 condensate with spin-dependent collisions.\nRemarkably, we find that such dynamics can be observed in existing experimental\nsetups through quench experiments that are robust against magnetic\nfluctuations.",
        "positive": "Thermodynamic limit of the free electron gas on a circle: We show that for the ground state of a one dimensional free electron gas on a\ncircle the analytic expression for the canonical ensemble partition function\ncan be easily derived from the density matrix by assuming that the\nthermodynamic limit coincides with the limit of the eigenfunction expansion of\nthe kinetic energy. This approximation fails to give the finite temperature\npartition function because those two limits cannot be chosen as coincident."
    },
    {
        "anchor": "Observation of Non-Hermitian Skin Effect and Topology in Ultracold Atoms: The non-Hermitian skin effect (NHSE), the accumulation of eigen wavefunctions\nat boundaries of open systems, underlies a variety of exotic properties that\ndefy conventional wisdom. While NHSE and its intriguing impact on band topology\nand dynamics have been observed in classical or photonic systems, their\ndemonstration in a quantum many-body setting remains elusive. Here we report\nthe experimental realization of a dissipative Aharonov-Bohm chain -- a\nnon-Hermitian topological model with NHSE -- in the momentum space of a\ntwo-component Bose-Einstein condensate. We identify unique signatures of NHSE\nin the condensate dynamics, and perform Bragg spectroscopy to resolve\ntopological edge states against a background of localized bulk states. Our work\nsets the stage for further investigation on the interplay of many-body\nstatistics and interactions with NHSE, and is a significant step forward in the\nquantum control and simulation of non-Hermitian physics.",
        "positive": "Coherence and Instability in a Driven Bose-Einstein Condensate: A Fully\n  Dynamical Number-Conserving Approach: We consider a Bose-Einstein condensate driven by periodic delta-kicks. In\ncontrast to first-order descriptions, which predict rapid, unbounded growth of\nthe noncondensate in resonant parameter regimes, the consistent treatment of\ncondensate depletion in our fully-time-dependent, second-order description acts\nto damp this growth, leading to oscillations in the (non)condensate population\nand the coherence of the system."
    },
    {
        "anchor": "Sub-unity superfluid fraction of a supersolid from self-induced\n  Josephson effect: Recently, a new category of superfluids and superconductors has been\ndiscovered in various systems. These could be linked to the idea of a\nsupersolid phase, featuring a macroscopic wavefunction with spatial modulation\nresulting from simultaneous, spontaneous breaking of gauge and translational\nsymmetries. However, this relation has only been recognized in some cases and\nthere is the need for universal properties quantifying the differences between\nsupersolids and ordinary superfluids/superconductors or crystals. A key\nproperty is the superfluid fraction, which measures the reduction in superfluid\nstiffness due to spatial modulation, leading to the non-standard superfluid\ndynamics of supersolids. Here we employ the Josephson effect, common in\nsuperfluids and superconductors, to measure the superfluid fraction in a\nsupersolid. Even without a physical barrier, the Josephson effect arises\nspontaneously in a supersolid due to spatial modulation. Individual lattice\ncells act as self-induced Josephson junctions, allowing the direct\ndetermination of the local superfluid fraction. We studied a cold-atom dipolar\nsupersolid, revealing a significant sub-unity superfluid fraction. Our results\nopen new research directions, enabling the exploration of novel phenomena like\npartially quantized vortices and supercurrents, potentially unifying the\nunderstanding of supersolid-like systems, and introducing a new type of\nJosephson junction.",
        "positive": "Spatially-antisymmetric localization of matter wave in a bichromatic\n  optical lattice: By direct numerical simulation of the time-dependent Gross-Pitaevskii\nequation using the split-step Fourier spectral method we study the\ndouble-humped localization of a cigar-shaped Bose-Einstein condensate (BEC) in\na one-dimensional bichromatic quasi-periodic optical-lattice potential, as used\nin a recent experiment on the localization of a BEC [Roati et al., Nature 453,\n895 (2008)]. Such states are spatially antisymmetric and are excited modes of\nAnderson localization. Where possible, we have compared the numerical results\nwith a variational analysis. We also demonstrate the stability of the localized\ndouble-humped BEC states under small perturbation."
    },
    {
        "anchor": "Thermodynamic properties of ultracold Bose gas: transition exponents and\n  universality: We report exact numerical calculation of chemical potential, condensate\nfraction and specific heat of $N$ non-interacting bosons confined in an\nisotropic harmonic oscillator trap in one, two and three dimensions, as also\nfor interacting bosons in a 3D trap. Quasi phase transitions are observed in\nall these cases, including one-dimension, as shown by a rapid change of all the\nthermodynamic quantities at the transition point. The change becomes more rapid\nas $N$ increases in 2D and 3D cases. However with increase in $N$, the sudden\nchange in the nature of specific heat, gets gradually wiped out in 1D, while it\nbecomes more drastic in 2D and 3D. The sudden change in the nature of\ncondensate fraction and chemical potential as $N$ increases becomes more\ndrastic even in 1D. Defining transition exponents, which characterize the\nnature of a thermodynamic quantity at the transition point of a quasi phase\ntransition, we evaluate them by careful numerical calculation very near the\ntransition temperature. These exponents are found to be independent of the size\nof the system and whether the bosons are interacting or not, demonstrating\ntheir universality property.",
        "positive": "Commensurate-incommensurate transition in frustrated Wigner crystals: Geometric frustration in systems with long-range interactions is a largely\nunexplored phenomenon. In this work we analyse the ground state emerging from\nthe competition between a periodic potential and a Wigner crystal in one\ndimension, consisting of a selforganized chain of particles with the same\ncharge. This system is a paradigmatic realization of the Frenkel-Kontorova\nmodel with Coulomb interactions. We derive the action of a Coulomb soliton in\nthe continuum limit and demonstrate the mapping to a massive (1+1) Thirring\nmodel with long-range interactions. Here, the solitons are charged fermionic\nexcitations over an effective Dirac sea. The mismatch between the periodicities\nof potential and chain, giving rise to frustration, is a chemical potential\nwhose amplitude is majorly determined by the Coulomb self-energy. The\nmean-field limit is a long-range antiferromagnetic spin chain with uniform\nmagnetic field and predicts that the commensurate, periodic structures form a\ncomplete devil's staircase as a function of the charge density. Each step of\nthe staircase correspond to the interval of stability of a stable commensurate\nphase and scales with the number $N$ of charges as $1/\\ln N$. This implies that\nthere is no commensurate-incommensurate phase transition in the thermodynamic\nlimit. For finite systems, however, the ground state has a fractal structure\nthat could be measured in experiments with laser-cooled ions in traps."
    },
    {
        "anchor": "Spatial emergence of Off-Diagonal Long-Range Order throughout the\n  BCS-BEC crossover: In a superfluid system, Off-Diagonal Long-Range Order (ODLRO) is expected to\nbe exhibited in the appropriate reduced density matrices when the relevant\nparticles (either bosons or fermion pairs) are considered to recede\nsufficiently far apart from each other. This concept is usually exploited to\nidentify the value of the condensate density, without explicit concern,\nhowever, on the spatial range over which this asymptotic condition can\neffectively be achieved. Here, based on a diagrammatic approach that includes\nbeyond-mean-field pairing fluctuations in the broken-symmetry phase at the\nlevel of the $t$-matrix also with the inclusion of the Gorkov-Melik-Barkhudarov\n(GMB) correction, we present a systematic study of the two-particle reduced\ndensity matrix for a superfluid fermionic system undergoing the BCS-BEC\ncrossover, when the entities to recede far apart from each other evolve with\ncontinuity from largely overlapping Cooper pairs in the BCS limit to dilute\ncomposite bosons in the BEC limit. By this approach, we not only provide the\ncoupling and temperature dependence of the condensate density at the level of\nour diagrammatic approach which includes the GMB correction, but we also obtain\nthe evolution of the spatial dependence of the two-particle reduced density\nmatrix, from a power-law at low temperature to an exponential dependence at\nhigh temperature in the superfluid phase, when the inter-particle coupling\nspans the BCS-BEC crossover. Our results put limitations on the minimum spatial\nextent of a finite-size system for which superfluid correlations can\neffectively be established.",
        "positive": "Pair correlation of atoms scattered from colliding Bose-Einstein\n  quasicondensates: A collision of Bose-Einstein condensates is a useful source of single\nnonclassically correlated pairs of atoms. Here, we consider elastic scattering\nof atoms from elongated clouds taking into account an effective, finite\nduration of the collision due to the expansion of the condensates. Also, we\ninclude the quasicondensate nature of the degenerate quantum gases, due to a\nfinite temperature of the system. We evaluate the pair correlation function\nmeasured experimentally in K. V. Kheruntsyan, et. al. Phys. Rev. Lett. 108,\n260401 (2012). We show that the finite duration of the collision is an\nimportant factor determining the properties of the correlations. Our analytic\ncalculations are in agreement with the measurements. The analytical model we\nprovide, useful for identifying physical processes that influence the\ncorrelations, is relevant for experiments with nonclassical pairs of atoms."
    },
    {
        "anchor": "Numerical simulation of nonequilibrium states in a trapped Bose-Einstein\n  condensate: In this work we present numerical study of a trapped Bose-Einstein condensate\nperturbed by an alternating potential. The relevant physical situation has been\nrecently realized in experiment, where the trapped condensate of $^{87}$Rb,\nbeing strongly perturbed, exhibits the set of spatial structures. Firstly,\nregular vortices are detected. Further, increasing either the excitation\namplitude or modulation time results in the transition to quantum vortex\nturbulence, followed by a granular state. Numerical simulation of the\nnonequilibrium Bose-condensed system is based on the solution of the\ntime-dependent 3D nonlinear Schr\\\"{o}dinger equation within the static and\ndynamical algorithms. The damped gradient step and time split-step Fourier\ntransform methods are employed. We demonstrate that computer simulations\nqualitatively reproduce the experimental picture, and describe well the main\nexperimental observables.",
        "positive": "Cavity quantum electrodynamics of ultracold atoms in optical and\n  optomechanical cavities: In this review article, we present the recent theoretical developments and\nsome breakthrough experiments in cavity QED systems (optical and optomechanical\nsystems) and also focus on the experimental realization of the theoretical\nproposals."
    },
    {
        "anchor": "Linear response of a superfluid Fermi gas inside its pair-breaking\n  continuum: We study the signatures of the collective modes of a superfluid Fermi gas in\nits linear response functions for the order-parameter and density fluctuations\nin the Random Phase Approximation (RPA). We show that a resonance associated to\nthe Popov-Andrianov (or sometimes \"Higgs\") mode is visible inside the\npair-breaking continuum at all values of the wavevector $q$, not only in the\n(order-parameter) modulus-modulus response function but also in the\nmodulus-density and density-density responses. At nonzero temperature, the\nresonance survives in the presence of thermally broken pairs even until the\nvicinity of the critical temperature $T_c$, and coexists with both the\nAnderson-Bogoliubov modes at temperatures comparable to the gap $\\Delta$ and\nwith the low-velocity phononic mode predicted by RPA near $T_c$. The existence\nof a Popov-Andrianov-\"Higgs\" resonance is thus a robust, generic feature of the\nhigh-energy phenomenology of pair-condensed Fermi gases, and should be\naccessible to state-of-the-art cold atom experiments.",
        "positive": "The stability of the low-dimensional mixtures of dilute quantum gases: We study the stability of the dilute Bose-Fermi and Bose-Bose mixtures with\nrepulsive interactions in one and two dimensions in terms of the\nrenormalization group. For the Bose-Fermi mixture, we show that the uniform\nmixture is stable against de-mixing in the dilute limit. For the Bose-Bose\nmixture, we give the stability conditions in the dilute limit. As a byproduct,\nwe also calculate the critical temperature for the superfluid phase of the\ntwo-dimensional Bose-Fermi mixture in the extremely dilute limit."
    },
    {
        "anchor": "Self-organized cavity bosons beyond the adiabatic elimination\n  approximation: The long-time behavior of weakly interacting bosons moving in a\ntwo-dimensional optical lattice and coupled to a lossy cavity is investigated\nnumerically in the regime of high particle filling. The truncated Wigner\nrepresentation allows us to take into full account the dynamics of the cavity\nmode, quantum fluctuations, and self-organization of individual runs. We\nobserve metastability at very long times and superfluid quasi-long range order,\nin sharp contrast with the true long range order found in the ground state of\nthe approximate Bose-Hubbard model with extended interactions, obtained by\nadiabatically eliminating the cavity field. As the strength of the light-matter\ncoupling increases, the system first becomes supersolid at the Dicke\nsuperradiant transition and then turns into a charge-density wave via the\nBerezinskii-Kosterlitz-Thouless mechanism. The two phase transitions are\ncharacterized via an accurate finite-size scaling.",
        "positive": "Spontaneous breaking of spatial and spin symmetry in spinor condensates: Parametric amplification of quantum fluctuations constitutes a fundamental\nmechanism for spontaneous symmetry breaking. In our experiments, a spinor\ncondensate acts as a parametric amplifier of spin modes, resulting in a twofold\nspontaneous breaking of spatial and spin symmetry in the amplified clouds. Our\nexperiments permit a precise analysis of the amplification in specific spatial\nBessel-like modes, allowing for the detailed understanding of the double\nsymmetry breaking. On resonances that create vortex-antivortex superpositions,\nwe show that the cylindrical spatial symmetry is spontaneously broken, but\nphase squeezing prevents spin-symmetry breaking. If, however, nondegenerate\nspin modes contribute to the amplification, quantum interferences lead to\nspin-dependent density profiles and hence spontaneously-formed patterns in the\nlongitudinal magnetization."
    },
    {
        "anchor": "Creation, manipulation and detection of Majorana fermions with cold\n  atoms in optical lattice: We propose an experimental scheme to simulate the transverse field Ising\nmodel with cold atoms trapped in one-dimensional optical lattice. Majorana\nfermions are created at the ends of the optical lattice segment in topological\nphase. By controlling the addressing lasers, one can move, fuse and braid them.\nWe also show that the non-Abelian braiding statistics of Majorana fermions can\nbe demonstrated unambiguously through the construction of two braiding\noperations and distinguishing the resulting two output orthogonal collective\nspin states. A nice feature of the scheme is that the strong fluorescence\nprovided by the collective spin state can be readily detected in experiment.",
        "positive": "Temporal Coherence of Spatially Indirect Excitons across Bose-Einstein\n  Condensation: the Role of Free Carriers: We study the time coherence of the photoluminescence radiated by spatially\nindirect excitons confined in a 10 $\\mu$m electrostatic trap. Above a critical\ntemperature of 1 Kelvin, we show that the photoluminescence has a homogeneous\nspectral width of about 500 $\\mu$eV which weakly varies with the exciton\ndensity. By contrast, the spectral width reduces by two-fold below the critical\ntemperature and for experimental parameters at which excitons undergo a gray\nBose-Einstein condensation. In this regime, we find evidence showing that the\nexcitons temporal coherence is limited by their interaction with a\nlow-concentration of residual excess charges, leading to a minimum\nphotoluminescence spectral width of around 300 $\\mu$eV."
    },
    {
        "anchor": "Three-body recombination in a single-component Fermi gas with $p$-wave\n  interaction: We study the three-body recombination of identical fermionic atoms. Using a\nzero-range model for the $p$-wave interaction, we show that the rate constant\nof three-body recombination into weakly bound $p$-wave dimers can be written as\n$\\alpha_{\\rm rec} \\propto v^{5/2}R^{1/2} k_T^4 (1+ C k_T^2 l_{\\rm d}^2)$ for\nlarge and positive scattering volume $v$. Here $R$ is the $p$-wave effective\nrange, $k_T^2$ gives the average thermal kinetic energy of the colliding atoms,\nand $l_{\\rm d}$ is the size of the $p$-wave dimer. The leading term is\ndifferent from the usually stated $v^{8/3}$-scaling law, but is consistent with\nan earlier two-channel calculation. For the subleading term, we compute the\nconstant $C$ by solving the relevant three-body problem perturbatively when the\nparameter $\\gamma\\equiv R/v^{1/3}$ is small. The additional $C k_T^2 l_{\\rm\nd}^2$ term provides important corrections for the temperature and interaction\ndependence of $\\alpha_{\\rm rec}$, especially close to resonance when $k_T\nl_{\\rm d}$ is relatively large.",
        "positive": "Fisher zeros of a unitary Bose gas: For real inverse temperature beta, the canonical partition function is always\npositive, being a sum of positive terms. There are zeros, however, on the\ncomplex beta plane that are called Fisher zeros. In the thermodynamic limit,\nthe Fisher zeros coalesce into continuous curves. In case there is a phase\ntransition, the zeros tend to pinch the real-beta axis. For an ideal trapped\nBose gas in an isotropic three-dimensional harmonic oscillator, this tendency\nis clearly seen, signalling Bose-Einstein condensation (BEC). The calculation\ncan be formulated exactly in terms of the virial expansion with\ntemperature-dependent virial coefficients. When the second virial coefficient\nof a strongly interacting attractive unitary gas is included in the\ncalculation, BEC seems to survive, with the condensation temperature shifted to\na lower value for the unitary gas. This shift is consistent with a direct\ncalculation of the heat capacity from the canonical partition function of the\nideal and the unitary gas."
    },
    {
        "anchor": "Selective photoexcitation of exciton-polariton vortices: We resonantly excite exciton-polariton states confined in cylindrical traps.\nUsing a homodyne detection setup, we are able to image the phase and amplitude\nof the confined polariton states. We evidence the excitation of vortex states,\ncarrying an integer angular orbital momentum m, analogous to the transverse\nTEM01* \"donut\" mode of cylindrically symmetric optical resonators. Tuning the\nexcitation conditions allows us to select the charge of the vortex. In this\nway, the injection of singly charged (m = 1 & m = -1) and doubly charged (m =\n2) polariton vortices is shown. This work demonstrates the potential of\nin-plane confinement coupled with selective excitation for the topological\ntailoring of polariton wavefunctions.",
        "positive": "Uniform spin susceptibility and spin-gap phenomenon in the BCS-BEC\n  crossover regime of an ultracold Fermi gas: We investigate the uniform spin susceptibility $\\chi_{\\rm s}$ in the BCS\n(Bardeen-Cooper-Schrieffer)-BEC (Bose-Einstein condensation) crossover regime\nof an ultracold Fermi gas. Including pairing fluctuations within the framework\nof an extended $T$-matrix approximation, we show that $\\chi_{\\rm s}$ exhibits\nnon-monotonic temperature dependence in the normal state. In particular,\n$\\chi_{\\rm s}$ is suppressed near the superfluid phase transition temperature\n$T_{\\rm c}$ due to strong pairing fluctuations. To characterize this anomalous\nbehavior, we introduce the spin-gap temperature $T_{\\rm s}$ as the temperature\nat which $\\chi_{\\rm s}$ takes a maximum value. Determining $T_{\\rm s}$ in the\nwhole BCS-BEC crossover region, we identify the spin-gap regime in the phase\ndiagram of a Fermi gas in terms of the temperature and the strength of a\npairing interaction. We also clarify how the spin-gap phenomenon is related to\nthe pseudogap phenomenon appearing in the single-particle density of states.\nOur results indicate that an ultracold Fermi gas in the BCS-BEC crossover\nregion is a very useful system to examine the pseudogap phenomenon and the\nspin-gap phenomenon in a unified manner."
    },
    {
        "anchor": "Dark-soliton-like excitations in the Yang-Gaudin gas of attractively\n  interacting fermions: Yrast states are the lowest energy states at given non-zero momentum and\nprovide a natural extension of the concept of dark solitons to\nstrongly-interacting one-dimensional quantum gases. Here we study the yrast\nstates of the balanced spin-$\\frac{1}{2}$ Fermi gas with attractive\ndelta-function interactions in one dimension with the exactly solvable\nYang-Gaudin model. The corresponding Bethe-ansatz equations are solved for\nfinite particle number and in the thermodynamic limit. Properties corresponding\nto the soliton-like nature of the yrast excitations are calculated including\nthe missing particle number, phase step, and inertial and physical masses. The\ninertial to physical mass ratio, which is related to the frequency of\noscillations in a trapped gas, is found to be unity in the limits of strong and\nweak attraction and falls to $\\approx 0.78$ in the crossover regime. This\nresult is contrasted by one-dimensional mean field theory, which predicts a\ndivergent mass ratio in the weakly attractive limit. By means of an exact\nmapping our results also predict the existence and properties of\ndark-soliton-like excitations in the super Tonks-Girardeau gas. The prospects\nfor experimental observations are briefly discussed.",
        "positive": "Mean-field equations for cigar- and disk-shaped Bose and Fermi\n  superfluids: Starting from the three-dimensional (3D) time-dependent nonlinear\nGross-Pitaevskii equation for a Bose-Einstein condensate (BEC) and density\nfunctional (DF) equation for a Fermi superfluid at the unitarity and\nBardeen-Cooper-Schrieffer (BCS) limits, we derive effective one- (1D) and\ntwo-dimensional (2D) mean-field equations, respectively, for the dynamics of a\ntrapped cigar- and disk-shaped BEC and Fermi superfluid by using the adiabatic\napproximation. The reduced 1D and 2D equations for a cigar- and disk-shaped\nFermi superfluid have simple analytic nonlinear terms and at unitarity produce\nresults for stationary properties and non-stationary breathing oscillation and\nfree expansion in excellent agreement with the solution of the full 3D\nequation."
    },
    {
        "anchor": "Experimental study of tune-out wavelengths for spin-dependent optical\n  lattice in $^{87}$Rb Bose-Einstein condensation: We study the periodic potential of one-dimensional optical lattice originated\nfrom scalar shift and vector shift by manipulating the lattice polarizations.\nThe ac Stark shift of optical lattice is measured by Kapitza-Dirac scattering\nof $^{87}$Rb Bose-Einstein condensate and the characteristics of spin-dependent\noptical lattice are presented by scanning the lattice wavelength between the D1\nand D2 lines. At the same time, tune-out wavelengths that ac Stark shift\ncancels can be probed by optical lattice. We give the tune-out wavelengths in\nmore general cases of balancing the contributions of both the scalar and vector\nshift. Our results provide a clear interpretation for spin-dependent optical\nlattice and tune-out wavelengths, and help to design it by choosing the\nappropriate lattice wavelength.",
        "positive": "Quantum Field Theory of Correlated Bose-Einstein condensates: I. Basic\n  Formalism: Quantum field theory of equilibrium and nonequilibrium Bose-Einstein\ncondensates is formulated so as to satisfy three basic requirements: the\nHugenholtz-Pines relation; conservation laws; identities among vertices\noriginating from Goldstone's theorem I. The key inputs are irreducible\nfour-point vertices, in terms of which we derive a closed system of equations\nfor Green's functions, three- and four-point vertices, and two-particle Green's\nfunctions. It enables us to study correlated Bose-Einstein condensates with a\ngapless branch of single-particle excitations without encountering any infrared\ndivergence. The single- and two-particle Green's functions are found to share\npoles, i.e., the structure of the two-particle Green's functions predicted by\nGavoret and Nozi\\`eres for a homogeneous condensate at $T=0$ is also shown to\npersist at finite temperatures, in the presence of inhomogeneity, and also in\nnonequilibrium situations."
    },
    {
        "anchor": "Effects of the non-parabolic kinetic energy on non-equilibrium polariton\n  condensates: In the study of non-equilibrium polariton condensates it is usually assumed\nthat the dispersion relation of polaritons is parabolic in nature. We show that\nconsidering the true non-parabolic kinetic energy of polaritons leads to\nsignificant changes in the behaviour of the condensate due to the curvature of\nthe dispersion relation and the possibility of transfer of energy to high\nwavenumber components in the condensate spatial profile. We present explicit\nsolutions for plane waves and linear excitations, and identify the differences\nin the theoretical predictions between the parabolic and non-parabolic\nmean-field models, showing the possibility of symmetry breaking in the latter.\nWe then consider the evolution of wavepackets and show that self-localisation\neffects may be observed due to the curvature of the dispersion relation.\nFinally, we revisit the dynamics of dark soliton trains and show that\nadditional localized density excitations may emerge in the dynamics due to the\nexcitation of high frequency components, mimicking the appearance of\nnear-bright solitary waves over short timescales.",
        "positive": "Diagnosing Potts criticality and two-stage melting in one-dimensional\n  hard-boson models: We investigate a model of hard-core bosons with infinitely repulsive nearest-\nand next-nearest-neighbor interactions in one dimension, introduced by Fendley,\nSengupta and Sachdev in Phys. Rev. B 69, 075106 (2004). Using a combination of\nexact diagonalization, tensor network, and quantum Monte Carlo simulations, we\nshow how an intermediate incommensurate phase separates a crystalline and a\ndisordered phase. We base our analysis on a variety of diagnostics, including\nentanglement measures, fidelity susceptibility, correlation functions, and\nspectral properties. According to theoretical expectations, the\ndisordered-to-incommensurate-phase transition point is compatible with\nBerezinskii-Kosterlitz-Thouless universal behaviour. The second transition is\ninstead non-relativistic, with dynamical critical exponent $z > 1$. For the\nsake of comparison, we illustrate how some of the techniques applied here work\nat the Potts critical point present in the phase diagram of the model for\nfinite next-nearest-neighbor repulsion. This latter application also allows to\nquantitatively estimate which system sizes are needed to match the conformal\nfield theory spectra with experiments performing level spectroscopy."
    },
    {
        "anchor": "Competition between Normal Superfluidity and Larkin-Ovchinnikov Phases\n  of Polarized Fermi Gases in Elongated Traps: By applying the recently proposed antisymmetric superfluid local density\napproximation (ASLDA) to strongly interacting polarized atomic gases at\nunitarity in very elongated traps, we find families of Larkin-Ovchinnikov (LO)\ntype of solutions with prominent transversal oscillation of pairing potential.\nThese LO states coexist with a superfluid state having a smooth pairing\npotential. We suggest that the LO phase could be accessible experimentally by\nincreasing adiabatically the trap aspect ratio. We show that the local\nasymmetry effects contained in ASLDA do not support a deformed superfluid core\npredicted by previous Bogoliubov-de Gennes treatments.",
        "positive": "Dipolar Bose-Einstein condensate soliton on a two-dimensional optical\n  lattice: Using a three-dimensional mean-field model we study one-dimensional dipolar\nBose-Einstein condensate (BEC) solitons on a weak two-dimensional (2D) square\nand triangular optical lattice (OL) potentials placed perpendicular to the\npolarization direction. The stabilization against collapse and expansion of\nthese solitons for a fixed dipolar interaction and a fixed number of atoms is\npossible for short-range atomic interaction lying between two critical limits.\nThe solitons collapse below the lower limit and escapes to infinity above the\nupper limit. One can also stabilize identical tiny BEC solitons arranged on the\n2D square OL sites forming a stable 2D array of interacting droplets when the\nOL sites are filled with a filling factor of 1/2 or less. Such an array is\nunstable when the filling factor is made more than 1/2 by occupying two\nadjacent sites of OL. These stable 2D arrays of dipolar superfluid BEC solitons\nare quite similar to the recently studied dipolar Mott insulator states on 2D\nlattice in the Bose-Hubbard model by Capogrosso-Sansone et al. [B.\nCapogrosso-Sansone, C. Trefzger, M. Lewenstein, P. Zoller, G. Pupillo, Phys.\nRev. Lett. 104 (2010) 125301]."
    },
    {
        "anchor": "Controlled spin domain creation by phase separation: We demonstrate a method of controlled creation of spin domains in spin-1\nantiferromagnetic Bose-Einstein condensates. The method exploits the phenomenon\nof phase separation of spin components in an external potential. By using an\nappropriate time dependent potential, a composition of spin domains can be\ncreated, as we demonstrate in the particular cases of a double well and a\nperiodic potential. In contrast to other methods, which rely on spatially\ninhomogeneous magnetic fields, here the domain structure is completely\ndetermined by the optical fields, which makes the method versatile and\nreconfigurable. It allows for creation of domains of various sizes, with the\nspatial resolution limited by the spin healing length only.",
        "positive": "Effects of classical stochastic webs on the quantum dynamics of cold\n  atomic gases in a moving optical lattice: We introduce and investigate a system that uses temporal resonance-induced\nphase space pathways to create strong coupling between an atomic Bose-Einstein\ncondensate and a traveling optical lattice potential. We show that these\npathways thread both the classical and quantum phase space of the atom cloud,\neven when the optical lattice potential is arbitrarily weak. The topology of\nthe pathways, which form web-like patterns, can by controled by changing the\namplitude and period of the optical lattice. In turn, this control can be used\nto increase and limit the BEC's center-of-mass kinetic energy to pre-specified\nvalues. Surprisingly, the strength of the atom-lattice interaction and\nresulting BEC heating of the center-of-mass motion is enhanced by the repulsive\ninter-atomic interactions."
    },
    {
        "anchor": "Electrical control of excitons in GaN/(Al,Ga)N quantum wells: A giant built-in electric field in the growth direction makes excitons in\nwide GaN/(Al, Ga)N quantum wells spatially indirect even in the absence of any\nexternal bias. Significant densities of indirect excitons can accumulate in\nelectrostatic traps imprinted in the quantum well plane by a thin metal layer\ndeposited on top of the heterostructure. By jointly measuring\nspatially-resolved photoluminescence and photo-induced current, we demonstrate\nthat exciton density in the trap can be controlled via an external electric\nbias, which is capable of altering the trap depth. Application of a negative\nbias deepens the trapping potential, but does not lead to any additional\naccumulation of excitons in the trap. This is due to exciton dissociation\ninstigated by the lateral electric field at the electrode edges. The resulting\ncarrier losses are detected as an increased photo-current and reduced\nphotoluminescence intensity. By contrast, application of a positive bias washes\nout the electrode-induced trapping potential. Thus, excitons get released from\nthe trap and recover free propagation in the plane that we reveal by\nspatially-resolved photoluminescence.",
        "positive": "Coherence of an Interacting Bose Gas: from a Single to a Double Well: The low energy properties of a trapped bose gas split by a potential barrier\nare determined over the whole range of barrier heights. We derive a\nself-consistent two-mode model which reduces, for large $N$, to a Bogoliubov\nmodel for low barriers and to a Josephson model for any (asymmetric) double\nwell potential, with explicitly calculated tunneling and pair interaction\nparameters. We compare the numerical results to analytical results that\nprecisely specify the role of number squeezing and finite temperatures in the\nloss of coherence."
    },
    {
        "anchor": "Three-body interactions on a triangular lattice: We analyze the hard-core Bose-Hubbard model with both the three-body and\nnearest neighbor repulsions on the triangular lattice. The phase diagram is\nachieved by means of the semi-classical approximation and the quantum Monte\nCarlo simulation. For a system with only the three-body interactions, both the\nsupersolid phase and one third solid disappear while the two thirds solid\nstably exists. As the thermal behavior of the bosons with nearest neighbor\nrepulsion, the solid and the superfluid undergo the 3-state Potts and the\nKosterlitz-Thouless type phase transitions, respectively. In a system with both\nthe frustrated nearest neighbor two-body and three-body interactions, the\nsupersolid and one third solid revive. By tuning the strength of the three-body\ninteractions, the phase diagram is distorted, because the one-third solid and\nthe supersolid are suppressed.",
        "positive": "Direct observation of the Fermi surface in an ultracold atomic gas: The ideal (i.e. noninteracting), homogeneous Fermi gas, with its\ncharacteristic sharp Fermi surface in the momentum distribution, is a\nfundamental concept relevant to the behavior of many systems. With trapped\nFermi gases of ultracold atoms, one can realize and probe a nearly ideal Fermi\ngas, however these systems have a nonuniform density due to the confining\npotential. We show that the effect of the density variation, which typically\nwashes out any semblance of a Fermi surface step in the momentum distribution,\ncan be mitigated by selectively probing atoms near the center of a trapped gas.\nWith this approach, we have directly measured a Fermi surface in momentum space\nfor a nearly ideal gas, where the average density and temperature of the probed\nportion of the gas can be determined from the location and sharpness of the\nFermi surface."
    },
    {
        "anchor": "Inhomogeneous Fulde-Ferrell superfluidity in spin-orbit coupled atomic\n  Fermi gases: Inhomogeneous superfluidity lies at the heart of many intriguing phenomena in\nquantum physics. It is believed to play a central role in unconventional\norganic or heavy-fermion superconductors, chiral quark matter, and neutron star\nglitches. However, so far even the simplest form of inhomogeneous\nsuperfluidity, the Fulde-Ferrell (FF) pairing state with a single\ncentre-of-mass momentum, is not conclusively observed due to the intrinsic\ncomplexibility of any realistic Fermi systems in nature. Here we theoretically\npredict that the controlled setting of ultracold fermionic atoms with synthetic\nspin-orbit coupling induced by a two-photon Raman process, demonstrated\nrecently in cold-atom laboratories, provides a promising route to realize the\nlong-sought FF superfluidity. At experimentally accessible low temperatures\n(i.e., $0.05T_{F}$, where $T_{F}$ is the Fermi temperature), the FF superfluid\nstate dominates the phase diagram, in sharp contrast to the conventional case\nwithout spin-orbit coupling. We show that the finite centre-of-mass momentum\ncarried by Cooper pairs is directly measurable via momentum-resolved\nradio-frequency spectroscopy. Our work opens the way to direct observation and\ncharacterization of inhomogeneous superfluidity.",
        "positive": "Nonequilibrium dynamics of an ultracold dipolar gas: We study the relaxation and damping dynamics of an ultracold, but not quantum\ndegenerate, gas consisting of dipolar particles. These simulations are\nperformed using a direct simulation Monte Carlo method and employing the highly\nanisotropic differential cross section of dipoles in the Wigner threshold\nregime. We find that both cross-dimensional relaxation and damping of breathing\nmodes occur at rates that are strongly dependent on the orientation of the\ndipole moments relative to the trap axis. The relaxation simulations are in\nexcellent agreement with recent experimental results in erbium. The results\ndirect our interest toward a less explored regime in dipolar gases where\ninteractions are dominated by collision processes rather than mean-field\ninteractions."
    },
    {
        "anchor": "Nonequilibrium Kinetics of One-Dimensional Bose Gases: We study cold dilute gases made of bosonic atoms, showing that in the\nmean-field one-dimensional regime they support stable out-of-equilibrium\nstates. Starting from the 3D Boltzmann-Vlasov equation with contact\ninteraction, we derive an effective 1D Landau-Vlasov equation under the\ncondition of a strong transverse harmonic confinement. We investigate the\nexistence of out-of-equilibrium states, obtaining stability criteria similar to\nthose of classical plasmas.",
        "positive": "Momentum resolved Floquet-engineered pair and single particle filter in\n  the Fermi Hubbard model: We investigate the transport properties of a Fermi-Hubbard chain with an\nimpurity which is formed by a site with a periodically modulated chemical\npotential. We determine the momentum resolved transmission through this\nimpurity in dependence of the modulation frequency and strength for a single\nparticle and a pair of fermions. We find that the pair transmission has a very\ndistinct behaviour from the single particle transmission. Different situations\ncan occur, where only the single particle or the pair with a certain momentum\nare transmitted or filtered out."
    },
    {
        "anchor": "Symmetry analysis of crystalline spin textures in dipolar spinor\n  condensates: We study periodic crystalline spin textures in spinor condensates with\ndipolar interactions via a systematic symmetry analysis of the low-energy\neffective theory. By considering symmetry operations which combine real and\nspin space operations, we classify symmetry groups consistent with non-trivial\nexperimental and theoretical constraints. Minimizing the energy within each\nsymmetry class allows us to explore possible ground states.",
        "positive": "Excitation spectrum of a trapped dipolar supersolid and its experimental\n  evidence: We study the spectrum of elementary excitations of a dipolar Bose gas in a\nthree-dimensional anisotropic trap across the superfluid-supersolid phase\ntransition. Theoretically, we show that, when entering the supersolid phase,\ntwo distinct excitation branches appear, respectively associated with\ndominantly crystal and superfluid excitations. These results confirm\ninfinite-system predictions, showing that finite-size effects play only a small\nqualitative role, and connect the two branches to the simultaneous occurrence\nof crystal and superfluid orders. Experimentally, we probe compressional\nexcitations in an Er quantum gas across the phase diagram. While in the\nBose-Einstein condensate regime the system exhibits an ordinary quadrupole\noscillation, in the supersolid regime we observe a striking two-frequency\nresponse of the system, related to the two spontaneously broken symmetries."
    },
    {
        "anchor": "Gapless topological Fulde-Ferrell superfluidity in spin-orbit coupled\n  Fermi gases: Topological superfluids usually refer to a superfluid state which is gapped\nin the bulk but metallic at the boundary. Here we report that a gapless,\ntopologically non-trivial superfluid with inhomogeneous Fulde-Ferrell pairing\norder parameter can emerge in a two-dimensional spin-orbit coupled Fermi gas,\nin the presence of both in-plane and out-of-plane Zeeman fields. The\nFulde-Ferrell pairing - induced by the spin-orbit coupling and in-plane Zeeman\nfield - is responsible for this gapless feature. This exotic superfluid has a\nsignificant Berezinskii-Kosterlitz-Thouless (BKT) transition temperature and\nhas robust Majorana edge modes against disorder owing to its topological\nnature.",
        "positive": "Rotating Few-body Atomic Systems in the Fractional Quantum Hall Regime: Topologically-ordered matter is a novel quantum state of matter observed only\nin a small number of physical systems, notably two-dimensional electron systems\nexhibiting fractional quantum Hall effects. It was recently proposed that a\nsimple form of topological matter may be created in interacting systems of\nrotating ultra-cold atoms. We describe ensemble measurements on small, rotating\nclusters of interacting bosonic atoms, demonstrating that they can be induced\ninto quantum ground states closely analogous to topological states of\nelectronic systems. We report measurements of inter-particle correlations and\nmomentum distributions of Bose gases in the fractional quantum Hall limit,\nmaking comparison to a full numerical simulation. The novel experimental\napparatus necessary to produce and measure properties of these deeply entangled\nquantum states is described."
    },
    {
        "anchor": "Stability Criterion for Superfluidity based on the Density Spectral\n  Function: We study a stability criterion hypothesis for superfluids in terms of the the\nlocal density spectral function $I_n (r, \\omega)$ applicable both to\nhomogeneous and inhomogeneous systems. We evaluate the local density spectral\nfunction in the presence of a one-dimensional repulsive/attractive external\npotential within the Bogoliubov theory using solutions of the tunneling\nproblem. We also evaluate the local density spectral function using an\northogonal basis, and calculate the autocorrelation function $C_n (r,t)$. When\nsuperfluids flow below a threshold, we find that in the $d$-dimensional system,\n$I_n (r, \\omega) \\propto \\omega^{d}$ in the low-energy regime and $C_n (r, t)\n\\propto 1/t^{d+1}$ in the long-time regime hold. When superfluids flow with the\ncritical current, on the other hand, we find $I_n (r, \\omega) \\propto\n\\omega^{\\beta}$ in the low-energy regime and $C_n (r,t) \\propto 1/t^{\\beta+1}$\nin the long-time regime with $\\beta < d$. These results support the stability\ncriterion hypothesis recently proposed.",
        "positive": "Bose Hubbard Models with Synthetic Spin-Orbit Coupling: Mott Insulators,\n  Spin Textures and Superfluidity: Motivated by the experimental realization of synthetic spin-orbit coupling\nfor ultracold atoms, we investigate the phase diagram of the Bose Hubbard model\nin a non-abelian gauge field in two dimensions. Using a strong coupling\nexpansion in the combined presence of spin-orbit coupling and tunable\ninteractions, we find a variety of interesting magnetic Hamiltonians in the\nMott insulator (MI), which support magnetic textures such as spin spirals and\nvortex and Skyrmion crystals. An inhomogeneous mean field treatment shows that\nthe superfluid (SF) phases inherit these exotic magnetic orders from the MI and\ndisplay, in addition, unusual modulated current patterns. We present a slave\nboson theory which gives insight into such intertwined spin-charge orders in\nthe SF, and discuss signatures of these orders in Bragg scattering, in situ\nmicroscopy, and dynamic quench experiments."
    },
    {
        "anchor": "Probing the Superfluid to Mott Insulator Transition at the Single Atom\n  Level: Quantum gases in optical lattices offer an opportunity to experimentally\nrealize and explore condensed matter models in a clean, tunable system. We\ninvestigate the Bose-Hubbard model on a microscopic level using single\natom-single lattice site imaging; our technique enables space- and\ntime-resolved characterization of the number statistics across the\nsuperfluid-Mott insulator quantum phase transition. Site-resolved probing of\nfluctuations provides us with a sensitive local thermometer, allows us to\nidentify microscopic heterostructures of low entropy Mott domains, and enables\nus to measure local quantum dynamics, revealing surprisingly fast transition\ntimescales. Our results may serve as a benchmark for theoretical studies of\nquantum dynamics, and may guide the engineering of low entropy phases in a\nlattice.",
        "positive": "Collective oscillations of a two-component Fermi gas on the repulsive\n  branch: We calculate frequencies of collective oscillations of two-component Fermi\ngas that is kept on the repulsive branch of its energy spectrum. Not only is a\nparamagnetic phase explored, but also a ferromagnetically separated one. Both\nin-, and out-of-phase perturbations are investigated, showing contributions\nfrom various gas excitations. Additionally, we compare results coming from both\ntime-dependent Hartree-Fock and density-functional approaches."
    },
    {
        "anchor": "Rotation Sensitive Quench and Revival of Coherent Oscillations in a Ring\n  Lattice: We consider ultracold atoms trapped in a toroidal trap with an azimuthal\nlattice for utility as a macroscopic simulator of quantum optics phenomena. We\nexamine the dynamics induced by the adiabatic introduction of the lattice that\nserves to couple the normal modes, as an analog of a laser field coupling\nelectronic states. The system is found to display two distinct behaviors,\nmanifest in the angular momentum - coherent oscillation and self-trapping -\nreminiscent of non-linear dynamics, yet not requiring interatomic interactions.\nThe choice is set by the interplay of discrete parameters, the specific initial\nmode and the periodicity of the lattice. However, rotation can cause continuous\ntransition between the two regimes, causing periodic quenches and revivals in\nthe oscillations as a function of the angular velocity. Curiously, the impact\nof rotation is determined entirely by the energy spectrum in the absence of the\nlattice, a feature that can be attributed to adiabaticity. We assess the\neffects of varying the lattice parameters, and consider applications in\nrotation sensing.",
        "positive": "Universality of Bose-Einstein Condensation and Quenched Formation\n  Dynamics: The emergence of macroscopic coherence in a many-body quantum system is a\nubiquitous phenomenon across different physical systems and scales. This\nChapter reviews key concepts characterizing such systems (correlation\nfunctions, condensation, quasi-condensation) and applies them to the study of\nemerging non-equilibrium features in the dynamical path towards such a\nhighly-coherent state: particular emphasis is placed on emerging universal\nfeatures in the dynamics of conservative and open quantum systems, their\nequilibrium or non-equilibrium nature, and the extent that these can be\nobserved in current experiments with quantum gases. Characteristic examples\ninclude symmetry-breaking in the Kibble-Zurek mechanism, coarsening and\nphase-ordering kinetics, and universal spatiotemporal scalings around\nnon-thermal fixed points and in the context of the Kardar- Parisi-Zhang\nequation; the Chapter concludes with a brief review of the potential relevance\nof some of these concepts in modelling the large-scale distribution of dark\nmatter in the universe."
    },
    {
        "anchor": "Virial relations for ultracold trapped Fermi gases with finite range\n  interactions through the BCS-BEC crossover: We study the virial relations for ultracold trapped two component Fermi gases\nin the case of short finite range interactions. Numerical verifications for\nsuch relations are reported through the BCS-BEC crossover. As an intermediate\nstep, it is necessary to evaluate the partial derivatives of the many body\nenergy with respect to the inverse of the scattering length and with respect to\nthe interaction range. They are found to have extreme values at the unitary\nlimit. The virial results are used to check the quality of the variational wave\nfunction involved in the calculations.",
        "positive": "Faraday waves in Bose--Einstein condensate: From instability to\n  nonlinear dynamics: We numerically study the dynamics of Faraday waves in a pancake-shaped\nBose--Einstein condensate (BEC) subject to periodic modulation of the\ninteraction. After the modulation starts, Faraday waves appear and, thereafter,\nthe BEC enters the \"nonlinear regime\", in which several collective modes are\nexcited. By maintaining the modulation without dissipation, the kinetic energy\nthat contributes to the density gradient causes quasiperiodic motion and\nincreases monotonically. In the nonlinear regime, the dips in the density\nsimilar to dark solitons move around in the BEC, intersecting with each other\nand maintaining their shapes. On the other hand, even by turning off the\nmodulation, Faraday waves and the nonlinear regime appear. The kinetic energy\nconverges to the statistical steady state. The calculation of the modulation\nwith the dissipation illustrates the collapse and revival of Faraday waves.\nWhen the dissipation is small, the appearance and collapse of the Faraday waves\nand the nonlinear regime occur again."
    },
    {
        "anchor": "Generalization of the Kutta-Joukowski theorem for the hydrodynamic\n  forces acting on a quantized vortex: The hydrodynamic forces acting on a quantized vortex in a superfluid have\nlong been a highly controversial issue. A new approach, originally developed in\nthe astrophysical context of compact stars, is presented to determine these\nforces by considering small perturbations of the asymptotically uniform flows\nin the region far from the vortex in the framework of Landau-Khalatnikov\ntwo-fluid model. Focusing on the irrotational part of the flows in the\nHelmholtz decomposition, the classical Kutta-Joukowski theorem from ordinary\nhydrodynamics is thus generalized to superfluid systems. The same method is\napplied to predict the hydrodynamic forces acting on vortices in cold atomic\ncondensates and superfluid mixtures.",
        "positive": "Soliton core filling in superfluid Fermi gases with spin-imbalance: In this paper the properties of dark solitons in superfluid Fermi gases with\nspin-imbalance are studied by means of a recently developed effective field\ntheory [S. N. Klimin, J. Tempere, G. Lombardi, J. T. Devreese, Eur. Phys. J. B\n88, 122 (2015)] suitable to describe the BEC-BCS crossover in ultracold gases\nin an extended range of temperatures as compared to the usual Ginzburg-Landau\ntreatments. The spatial profiles for the total density and for the density of\nthe excess-spin component, and the changes of their properties across the\nBEC-BCS crossover are examined in different conditions of temperature and\nimbalance. The presence of population imbalance is shown to strongly affect the\nstructure of the soliton excitation by filling its core with unpaired atoms.\nThis in turn influences the dynamical properties of the soliton since the\nadditional particles in the core have to be dragged along thus altering the\neffective mass."
    },
    {
        "anchor": "Many-Body Phases of a Planar Bose-Einstein Condensate with\n  Cavity-Induced Spin-Orbit Coupling: We explore the many-body phases of a two-dimensional Bose-Einstein condensate\nwith cavity-mediated dynamic spin-orbit coupling. By the help of two transverse\nnon-interfering, counterpropagating pump lasers and a single standing-wave\ncavity mode, two degenerate Zeeman sub-levels of the quantum gas are Raman\ncoupled in a double-$\\Lambda$-configuration. Beyond a critical pump strength\nthe cavity mode is populated via coherent superradiant Raman scattering from\nthe two pump lasers, leading to the appearance of a dynamical spin-orbit\ncoupling for the atoms. We identify three quantum phases with distinct atomic\nand photonic properties: the normal ``homogeneous'' phase, the superradiant\n``spin-helix'' phase, and the superradiant ``supersolid spin-density-wave''\nphase. The latter exhibits an emergent periodic atomic density distribution\nwith an orthorhombic centered rectangular-lattice structure due to the\ninterplay between the coherent photon scattering into the resonator and the\ncollision-induced momentum coupling. The transverse lattice spacing of the\nemergent crystal is set by the dynamic spin-orbit coupling.",
        "positive": "Using dark solitons from a Bose-Einstein condensate necklace to imprint\n  soliton states in the spectral memory of a free boson gas: A possible use of matter-wave dark-soliton crystal produced by a\nBose-Einstein condensate with ring geometry, to store soliton states in the\nquantum memory of a free boson gas, is explored. A self-defocusing nonlinearity\ncombined with dispersion and the finite size of the Bose-Einstein condensate,\nfavor the creation of dark-soliton crystals that imprint quantum states with\nJacobi elliptic-type soliton wavefunctions in the spectrum of the free boson\ngas. The problem is formulated by considering the Gross-Pitaevskii equation\nwith a positive scattering length, coupled to a linear Schr\\\"odinger equation\nfor the free boson gas. With the help of the matter-wave dark soliton-crystal\nsolution, the spectrum of bound states created in the free boson gas is shown\nto be determined by the Lam\\'e eigenvalue problem. This spectrum consists of\n$\\vert \\nu, \\mathcal{L} \\rangle$ quantum states whose wave functions and energy\neigenvalues can be unambiguously identified. Among these eigenstates some have\ntheir wave functions that are replicas of the generating dark soliton crystal."
    },
    {
        "anchor": "Braiding and fusion of non-Abelian vortex anyons: We demonstrate that certain vortices in spinor Bose-Einstein condensates are\nnon-Abelian anyons and may be useful for topological quantum computation. We\nperform numerical experiments of controllable braiding and fusion of such\nvortices, implementing the actions required for manipulating topological\nqubits. Our results suggest that a new platform for topological quantum\ninformation processing could potentially be developed by harnessing non-Abelian\nvortex anyons in spinor Bose-Einstein condensates.",
        "positive": "Coupling a mobile hole to an antiferromagnetic spin background:\n  Transient dynamics of a magnetic polaron: Understanding the interplay between charge and spin and its effects on\ntransport is a ubiquitous challenge in quantum many-body systems. In the\nFermi-Hubbard model, this interplay is thought to give rise to magnetic\npolarons, whose dynamics may explain emergent properties of quantum materials\nsuch as high-temperature superconductivity. In this work, we use a cold-atom\nquantum simulator to directly observe the formation dynamics and subsequent\nspreading of individual magnetic polarons. Measuring the density- and\nspin-resolved evolution of a single hole in a 2D Hubbard insulator with\nshort-range antiferromagnetic correlations reveals fast initial delocalization\nand a dressing of the spin background, indicating polaron formation. At long\ntimes, we find that dynamics are slowed down by the spin exchange time, and\nthey are compatible with a polaronic model with strong density and spin\ncoupling. Our work enables the study of out-of-equilibrium emergent phenomena\nin the Fermi-Hubbard model, one dopant at a time."
    },
    {
        "anchor": "Antiferromagnetism in a bosonic mixture of rubidium ($^{87}$Rb) and\n  potassium ($^{41}$K): We simulate the experimental possibility of observing the antiferromagnetic\n(AF) order in the bosonic mixtures of rubidium ($^{87}$Rb) and potassium\n($^{41}$K) in a two-dimensional optical lattice in the presence of harmonic\nconfinement. By tuning the interspecies interactions and the lattice heights we\nhave found the ground states, within the mean-field approximation, that\ninterpolate from the phase separation to the AF order. For a moderate lattice\nheight the coexistence of the Mott and AF phase is possible for the Rb atoms\nwhile the K atoms remain in the AF-superfluid phase. This observation may\nprovide an experimental feasibility to hitherto unobserved AF order for\n$^{87}$Rb - $^{41}$K mixture.",
        "positive": "An atomtronics transistor for quantum gates: We present a mechanism for quantum gates where the qubits are encoded in the\npopulation distribution of two component ultracold atoms trapped in a\nspecies-selective triple-well potential. The gate operation is a specific\napplication of a new design for an atomtronics transistor where inter-species\ninteraction is used to control transport, and can be realized with either\nindividual atoms or aggregates like Bose-Einstein condensates (BEC). We\ndemonstrate the operational principle with a static external potential, and\nshow feasible implementation with a smooth dynamical potential."
    },
    {
        "anchor": "When are two fermions a simple boson? New Gross-Pitaevskii actions for\n  cold Fermi condensates: The BEC regime of a cold fermi gas is characterised by coupled atoms (dimers)\nwhich, superficially, look like elementary bosons. We examine how\nsimply-bosonic they really are; firstly, in the Bogoliubov approximation and\nfurther, through new actions for the BEC regime in which dimers are represented\nby coupled Gross-Pitaevskii fields. We find identity at the level of the\nBogoliubov approximation in the deep BEC regime, permitting a simple\nGross-Pitaevskii description. This fails rapidly as we move towards the BCS\nregime. However, even in the deep BEC regime there is an intrinsic difference\nif we go beyond the Bogoliubov approximation. To exemplify this we construct\nvortex solutions.",
        "positive": "Particle entanglement in continuum many-body systems via quantum Monte\n  Carlo: Entanglement of spatial bipartitions, used to explore lattice models in\ncondensed matter physics, may be insufficient to fully describe itinerant\nquantum many-body systems in the continuum. We introduce a procedure to measure\nthe R\\'enyi entanglement entropies on a particle bipartition, with general\napplicability to continuum Hamiltonians via path integral Monte Carlo methods.\nVia direct simulations of interacting bosons in one spatial dimension, we\nconfirm a logarithmic scaling of the single-particle entanglement entropy with\nthe number of particles in the system. The coefficient of this logarithmic\nscaling increases with interaction strength, saturating to unity in the\nstrongly interacting limit. Additionally, we show that the single-particle\nentanglement entropy is bounded by the condensate fraction, suggesting a\npractical route towards its measurement in future experiments."
    },
    {
        "anchor": "Few-Body Route to One-Dimensional Quantum Liquids: Gapless many-body quantum systems in one spatial dimension are universally\ndescribed by the Luttinger liquid effective theory at low energies.\nEssentially, only two parameters enter the effective low-energy description,\nnamely the speed of sound and the Luttinger parameter. These are highly system\ndependent and their calculation requires accurate non-perturbative solutions of\nthe many-body problem. Here, we present a simple method that only uses\ncollisional information to extract the low-energy properties of these systems.\nOur results are in remarkable agreement with available results for integrable\nmodels and from large scale Monte Carlo simulations of one-dimensional helium\nand hydrogen isotopes. Moreover, we estimate theoretically the critical point\nfor spinodal decomposition in one-dimensional helium-4, and show that the\nexponent governing the divergence of the Luttinger parameter near the critical\npoint is exactly 1/2, in excellent agreement with Monte Carlo simulations.",
        "positive": "Ground States of a Mixture of Two Species of Spinor Bose Gases with\n  Interspecies Spin Exchange: We consider a mixture of two species of spin-1 atoms with interspecies spin\nexchange, which may cooperate or compete with the intraspecies spin exchanges\nand thus dramatically affect the ground state. It represents a new class of\nbosonic gases differing from single-species spinor gases. We determine the\nexact ground states in several parameter regimes, and study the composite\nstructures by using the generating function method generalized here to be\napplicable to a mixture of two species of spinor gases. The most interesting\nphase is the so-called entangled Bose-Einstein condensation (BEC), which is\nfragmented BEC with quantum entanglement between the two species, and with both\ninterspecies and intraspecies singlet pairs. For comparison, we also apply the\ngenerating function method to a mixture of two species of pseudospin-1/2 atoms,\nfor which the total spin quantum number of each species is fixed as half of the\natom number, in contrast with the case of spin-1, for which it is a variable\ndetermined by energetics. Consequently, singlet pairs in entangled BEC of a\npseudospin-1/2 mixture are all interspecies. Interspecies spin exchange leads\nto novel features beyond those of spinor BEC of a single species of atoms as\nwell as mixtures without interspecies spin exchange."
    },
    {
        "anchor": "Quantum Emulation of Extreme Non-equilibrium Phenomena with Trapped\n  Atoms: Ultracold atomic physics experiments offer a nearly ideal context for the\ninvestigation of quantum systems far from equilibrium. We describe three\nrelated emerging directions of research into extreme non-equilibrium phenomena\nin atom traps: quantum emulation of ultrafast atom-light interactions, coherent\nphasonic spectroscopy in tunable quasicrystals, and realization of Floquet\nmatter in strongly-driven lattice systems. We show that all three should enable\nquantum emulation in parameter regimes inaccessible in solid-state experiments,\nfacilitating a complementary approach to open problems in non-equilibrium\ncondensed matter.",
        "positive": "Phonon dressing of a facilitated one-dimensional Rydberg lattice gas: We study the dynamics of a one-dimensional Rydberg lattice gas under\nfacilitation (anti-blockade) conditions which implements a so-called\nkinetically constrained spin system. Here an atom can only be excited to a\nRydberg state when one of its neighbors is already excited. Once two or more\natoms are simultaneously excited mechanical forces emerge, which couple the\ninternal electronic dynamics of this many-body system to external vibrational\ndegrees of freedom in the lattice. This electron-phonon coupling results in a\nso-called phonon dressing of many-body states which in turn impacts on the\nfacilitation dynamics. In our theoretical study we focus on a scenario in which\nall energy scales are sufficiently separated such that a perturbative treatment\nof the coupling between electronic and vibrational states is possible. This\nallows to analytically derive an effective Hamiltonian for the evolution of\nconsecutive clusters of Rydberg excitations in the presence of phonon dressing.\nWe analyze the spectrum of this Hamiltonian and show -- by employing Fano\nresonance theory -- that the interaction between Rydberg excitations and\nlattice vibrations leads to the emergence of slowly decaying bound states that\ninhibit fast relaxation of certain initial states."
    },
    {
        "anchor": "Multipolar Fermi-surface deformation in a Rydberg-dressed Fermi gas with\n  long-range anisotropic interactions: We study theoretically the deformation of the Fermi surface (FS) of a\nthree-dimensional gas of Rydberg-dressed $^6$Li atoms. The laser dressing to\nhigh-lying Rydberg $D$ states results in angle-dependent soft-core-shaped\ninteractions whose anisotropy is described by multiple spherical harmonics. We\nshow that this can drastically modify the shape of the FS and that its\ndeformation depends on the interplay between the Fermi momentum $k_F$ and the\nreciprocal momentum $\\bar{k}$ corresponding to the characteristic soft-core\nradius of the dressing-induced potential. When $k_F< \\bar{k}$, the dressed\ninteraction stretches a spherical FS into an ellipsoid. When $k_F\\gtrsim\n\\bar{k}$, complex deformations are encountered which exhibit multipolar\ncharacteristics. We analyze the formation of Cooper pairs around the deformed\nFS and show that they occupy large orbital angular momentum states ($p$, $f$,\nand $h$ wave) coherently. Our study demonstrates that Rydberg dressing to high\nangular momentum states may pave a route toward the investigation of\nunconventional Fermi gases and multiwave superconductivity.",
        "positive": "The van der Waals interaction as the starting point for an effective\n  field theory: We consider the system of three ${}^4$He atoms to assess whether a pure van\nder Waals potential can be used as a starting point for an effective field\ntheory to describe three-body processes in ultracold atomic systems. Using a\nlong-range van der Waals interaction in combination with short-distance\ntwo-body counterterms, we analyze the dependence of two- and three-body\nobservables on the short-distance regulator that is required due to the\nsingular nature of the van der Waals interaction. We benchmark our approach\nwith results obtained with the realistic ${}^4$He-${}^4$He LM2M2 interaction\nand find good agreement. We furthermore show that in this effective field\ntheory approach no three-body force is required at leading order and that\nuniversal van der Waals physics leads to a universal correlation between\nthree-body observables in the absence of an Efimov three-body parameter."
    },
    {
        "anchor": "Influence of a dark-soliton on the reflection of a Bose-Einstein\n  condensate by a square barrier: We study the quantum reflection of a two-dimensional disk-shaped\nBose-Einstein condensate with a dark-soliton excitation by a square potential\nbarrier. For the giving geometry, the dark-soliton initially located at the\ncentre of the condensate cloud survive long enough for investigating the\nreflection process. We show the time evolution of the reflection probability\nwith respect to various width of the barrier. The asymptotic value of the\nreflection probability is decreased by the existence of a dark-soliton, and is\nhighly sensitive to the initial orientation of the dark-soliton which also\naffects the excitation properties during the process of condensate and barrier\ninteraction.",
        "positive": "Fluctuation Theory of Rashba Fermi Gases: Fermi gases with generalized Rashba spin orbit coupling inducedby a synthetic\ngauge field have the potential of realizing many interesting states such as\nrashbon condensates and topological phases. Here we develop a fluctuation\ntheory of such systems and demonstrate that beyond-Gaussian effects are\nessential to capture the physics of such systems. We obtain their phase diagram\nby constructing an approximate non-Gaussian theory. We conclusively establish\nthat spin-orbit coupling can enhance the exponentially small transition\ntemperature ($T_c$) of a weakly attracting superfluid to the order of Fermi\ntemperature, paving a pathway towards high $T_c$ superfluids."
    },
    {
        "anchor": "Variational self-consistent theory for trapped Bose gases at finite\n  temperature: We apply the time-dependent variational principle of Balian-V\\'en\\'eroni to a\nsystem of self-interacting trapped bosons at finite temperature. The method\nleads to a set of coupled non-linear time dependent equations for the\ncondensate density, the thermal cloud and the anomalous density. We solve\nnumerically these equations in the static case for a harmonic trap. We analyze\nthe various densities as functions of the radial distance and the temperature.\nWe find an overall good qualitative agreement with recent experiments as well\nas with the results of many theoretical groups. We also discuss the behavior of\nthe anomalous density at low temperatures owing to its importance to account\nfor many-body effects.",
        "positive": "Density engineering via inter-condensate dipole-dipole interactions:\n  axial confinement and supersolids: Exploiting the long-range and anisotropic nature of dipole-dipole\ninteractions, we show that the density of a {\\em target} dipolar Bose-Einstein\ncondensate can be engineered and axially confined using a trapped {\\em control}\ndipolar condensate. Increasing the number of control condensates leads to\nexotic ground state structures, including supersolids and an incoherent array\nof density peaks. Single and double-peaked periodic structures are observed as\na function of spacing between the control condensates. Our ideas may be\ngeneralized to engineer any other dipolar quantum system using another one of a\nsimilar dipole character. For instance, a Rydberg atom with electric dipole\nmoment may be confined and manipulated using a trapped polar molecule and vice\nversa via long-range dipole-dipole interactions."
    },
    {
        "anchor": "Dynamical phase diagram of a one dimensional Bose gas in a box with a\n  tunable weak-link: from Bose-Josephson oscillations to shock waves: We study the dynamics of one-dimensional bosons trapped in a box potential,\nin the presence of a barrier creating a tunable weak-link, thus realizing a one\ndimensional Bose Josephson junction. By varying the initial population\nimbalance and the barrier height we evidence different dynamical regimes. In\nparticular we show that at large barriers a two mode model captures accurately\nthe dynamics, while for low barriers the dynamics involves dispersive shock\nwaves and solitons. We study a quench protocol that can be readily implemented\nin experiments and show that self-trapping resonances can occur. This\nphenomenon can be understood qualitatively within the two-mode model.",
        "positive": "Missing understanding of the phase factor between valence-electron and\n  hole operators: This paper provides the long-missing foundation to connect semiconductor and\natomic notations and to support results incorrectly obtained by doing as if\nsemiconductor electrons possessed an orbital angular momentum. We here show\nthat the phase factor between valence-electron destruction operator and hole\ncreation operator is the same as the one between particle and antiparticle in\nquantum relativity, namely $\\hat{a}_{m}=(-1)^{j-m} \\hat{b}^\\dag_{-m}$ provided\nthat $m=(j,j-1\\cdots,-j)$ labels the degenerate states of the $(2j+1)$-fold\nelectron level at hand. This result is remarkable because $(i)$ the hole is\ndefinitely not a naive antiparticle due to the remaining valence electrons;\n$(ii)$ unlike atomic electrons in a central potential, semiconductor electrons\nin a periodic crystal do not have orbital angular momentum\n$\\textbf{L}=\\textbf{r}\\wedge\\textbf{p}$ nor angular momentum\n$\\textbf{J}=\\textbf{L}+\\textbf{S}$. Consequently, $(j,m)$ for semiconductor\nelectrons merely are convenient notations to label the states of a degenerate\nlevel. To illustrate the physical implications, we discuss the interband\ncouplings between photons and semiconductor, in terms of valence electrons and\nof holes: the phase factor is crucial to establish that bright excitons are in\na spin-singlet state."
    },
    {
        "anchor": "Levy distribution in many-particle quantum systems: Levy distribution, previously used to describe complex behavior of classical\nsystems, is shown to characterize that of quantum many-body systems. Using two\ncomplimentary approaches, the canonical and grand-canonical formalisms, we\ndiscovered that the momentum profile of a Tonks-Girardeau gas, -- a\none-dimensional gas of $N$ impenetrable (hard-core) bosons, harmonically\nconfined on a lattice at finite temperatures, obeys Levy distribution. Finally,\nwe extend our analysis to different confinement setups and demonstrate that the\ntunable Levy distribution properly reproduces momentum profiles in\nexperimentally accessible regions. Our finding allows for calibration of\ncomplex many-body quantum states by using a unique scaling exponent.",
        "positive": "Twisted unwinding of multi-charged quantum vortex and generation of\n  turbulence in atomic Bose-Einstein condensates: We report the observation of the twisted decay of quadruply charged vortices\nin an atomic Bose-Einstein condensate. Supporting numerical simulations show\nthat the singly-charged vortices, which result from the decay of a\nmulti-charged vortex, twist around intertwined in the shape of helical Kelvin\nwaves. Finally, we propose to apply this effect to generate an almost isotropic\nstate of turbulence which we characterize in terms of the velocity statistics."
    },
    {
        "anchor": "Synthesizing the Quantum Spin Hall Phase for Ultracold Atoms in\n  Bichromatic Chiral Optical Ladders: Realizing the topological bands of helical states poses a challenge in\nstudying ultracold atomic gases. Motivated by the recent experimental success\nin realizing chiral optical ladders, here we present a scheme for synthesizing\ntopological quantum matter, especially the quantum spin Hall phase, in the\nchiral optical ladders. More precisely, we first establish the synthetic\npseudo-spin-orbit coupling and Zeeman splitting in the chiral ladders. We\nanalyze the band structure of the ladders exposed to the bichromatic optical\npotentials and report the existence of quantum spin Hall phase. We further\nidentify a rich phase diagram of the bichromatic chiral ladders, illustrating\nthat our proposal features a large space of system parameters exhibiting a\nvariety of quantum phase transitions. Our scheme can be readily implemented in\nthe existing experimental systems and hence provides a new method to engineer\nthe sophisticated topological bands for cold atomic gases.",
        "positive": "Stable Heteronuclear Few-Atom Bound States in Mixed Dimensions: We study few-body problems in mixed dimensions with $N \\ge 2$ heavy atoms\ntrapped individually in parallel one-dimensional tubes or two-dimensional\ndisks, and a single light atom travels freely in three dimensions. By using the\nBorn-Oppenheimer approximation, we find three- and four-body bound states for a\nbroad region of heavy-light atom scattering length combinations. Specifically,\nthe existence of trimer and tetramer states persist to negative scattering\nlengths regime, where no two-body bound state is present. These few-body bound\nstates are analogous to the Efimov states in three dimensions, but are stable\nagainst three-body recombination due to geometric separation. In addition, we\nfind that the binding energy of the ground trimer and tetramer state reaches\nits maximum value when the scattering lengths are comparable to the separation\nbetween the low-dimensional traps. This resonant behavior is a unique feature\nfor the few-body bound states in mixed dimensions."
    },
    {
        "anchor": "Breakdown of the Meissner effect at the zero exceptional point in\n  non-Hermitian two-band BCS model: The spontaneous symmetry breaking of a continuous symmetry in complex field\ntheory at the exceptional point of the parameter space is known to exhibit\ninteresting phenomena, such as the breakdown of a Higgs mechanism. In this\nwork, we derive the complex Ginzburg-Landau model from a non-Hermitian two-band\nBCS model via path integral and investigate its spontaneous symmetry breaking.\nWe find that analog to the Higgs mechanism, the Meissner effect of the complex\nGinzburg-Landau model also breaks down at the exceptional point while the gap\nparameters stay finite.",
        "positive": "Dynamics of Few Co-rotating Vortices in Bose-Einstein Condensates: We study the dynamics of small vortex clusters with few (2--4) co-rotating\nvortices in Bose-Einstein condensates by means of experiments, numerical\ncomputations, and theoretical analysis. All of these approaches corroborate the\ncounter-intuitive presence of a dynamical instability of symmetric vortex\nconfigurations. The instability arises as a pitchfork bifurcation at\nsufficiently large values of the angular momentum that induces the emergence\nand stabilization of asymmetric rotating vortex configurations. The latter are\nquantified in the theoretical model and observed in the experiments. The\ndynamics is explored both for the integrable two-vortex system, where a\nreduction of the phase space of the system provides valuable insight, as well\nas for the non-integrable three- (or more) vortex case, which additionally\nadmits the possibility of chaotic trajectories."
    },
    {
        "anchor": "Bright solitons in a spin-orbit-coupled dipolar Bose-Einstein condensate\n  trapped within a double-lattice: By effectively controlling the dipole-dipole interaction, we investigate the\ncharacteristics of the ground state of bright solitons in a spin-orbit coupled\ndipolar Bose-Einstein condensate. The dipolar atoms are trapped within a\ndouble-lattice which consists of a linear and a nonlinear lattice. We derive\nthe motion equations of the different spin components, taking the controlling\nmechanisms of the diolpe-dipole interaction into account. An analytical\nexpression of dipole-dipole interaction is derived. By adjusting the dipole\npolarization angle, the dipole interaction can be adjusted from attraction to\nrepulsion. On this basis, we study the generation and manipulation of the\nbright solitons using both the analytical variational method and numerical\nimaginary time evolution. The stability of the bright solitons is also analyzed\nand we map out the stability phase diagram. By adjusting the long-range\ndipole-dipole interaction, one can achieve manipulation of bright solitons in\nall aspects, including the existence, width, nodes, and stability. Considering\nthe complexity of our system, our results will have enormous potential\napplications in quantum simulation of complex systems.",
        "positive": "Exploring helical phases of matter in bosonic ladders: Ladder models of ultracold atoms offer a versatile platform for the\nexperimental and theoretical study of different phenomena and phases of matter\nlinked to the interplay between artificial gauge fields and interactions.\nStrongly correlated helical states are known to appear for specific ratios of\nthe particle and magnetic flux densities and they can often be interpreted as a\none-dimensional limit of fractional quantum Hall states, thus being called\npretopological. Their signatures, however, are typically hard to observe due to\nthe small gaps characterizing these states. Here we investigate bosonic ladder\nmodels at filling factor 1. Based on bosonization, renormalization group and\nmatrix product state simulations we pinpoint two strongly correlated helical\nphases appearing at this resonance. We show that one of them can be accessed in\nsystems with two-species hardcore bosons and on-site repulsions only, thus\namenable for optical lattice experiments. Its signatures are sizable and stable\nover a broad range of parameters for realistic system sizes."
    },
    {
        "anchor": "Localized modes in dense repulsive and attractive Bose-Einstein\n  condensates with spin-orbit and Rabi couplings: We consider a binary Bose-Einstein condensate with linear and nonlinear\ninteractions between its components, which emulate the spinor system with\nspin-orbit (SO) and Rabi couplings. For a relatively dense condensate, 1D\ncoupled equations with the nonpolynomial nonlinearity of both repulsive and\nattractive signs are derived from the 3D Gross-Pitaevskii equations. Profiles\nof modes confined in an external potential under the action of the\nself-repulsion, and self-trapped solitons in the case of the self-attraction,\nare found in a numerical form and by means of analytical approximations. In the\nformer case, the interplay of the SO and Rabi couplings with the repulsive\nnonlinearity strongly distorts shapes of the trapped modes, adding conspicuous\nside lobes to them. In the case of the attractive nonlinearity, the most\nessential result is reduction of the collapse threshold under the action of the\nSO and Rabi couplings.",
        "positive": "Global and local condensate and superfluid fraction of a few hard core\n  bosons in a cubic optical lattice plus external harmonic confinement: We explore the global and local condensate and superfluid (SF) fractions in a\nsystem of a few hard core (HC) bosons (N=8 and N=40) trapped inside a combined\nharmonic optical cubic lattice (CHOCL) at T=0 K. The condensate fraction (CF)\nis computed for individual lattice wells by separating the one-body density\nmatrix (OBDM) of the whole system into components at the various lattice sites.\nThen each \"lattice-site\" component is diagonalized to find its eigenvalues. The\neigenvalues are obtained by a method presented earlier [Dubois and Glyde, Phys.\nRev. A {\\bf 63}, 023602 (2001)]. The effects of interference between the\ncondensates in the lattice wells on the CF in one well is also investigated.\nThe SF fraction (SFF) is calculated for N=40 by using the diffusion formula of\nPollock and Ceperley [Pollock and Ceperley, Phys. Rev. B {\\bf 36}, 8343\n(1987)]. Our chief result is an opposing behavior of the global CF and SFF with\nincreasing lattice wave vector $k$. In addition, the CF in a lattice well is\nenhanced by the interference with its neighbor wells beyond the result when the\ninterference is neglected. The global SF is depleted with a rise of the\nrepulsion between the bosons, yet at very strong interaction superfluidity is\nstill present. The global CF remains almost constant with increasing HC\nrepulsion. A reduction in the lattice dimension, i.e. an increase in the\nlattice wave vector, increases the local CF in each lattice well, but reduces\nthe corresponding local SFF. At large HC repulsion, a coexisting SF-(vacuum)MI\nphase is established."
    },
    {
        "anchor": "Spontaneous PT symmetry breaking of a ferromagnetic superfluid in a\n  gradient field: We consider the interaction of a ferromagnetic spinor Bose-Einstein\ncondensate with a magnetic field gradient. The magnetic field gradient realizes\na spin-position coupling that explicitly breaks time-reversal symmetry T and\nspace parity P, but preserves the combined PT symmetry. We observe using\nnumerical simulations, a first-order phase transition spontaneously breaking\nthis re-maining symmetry. The transition to a low-gradient phase, in which\ngradient effects are frozen out by the ferromagnetic interaction, suggests the\npossibility of high-coherence magnetic sensors unaffected by gradient\ndephasing.",
        "positive": "Lattice control of non-ergodicity in a polar lattice gas: Inter-site interactions in polar lattice gases may result, due to\nHilbert-space fragmentation, in a lack of ergodicity even in absence of\ndisorder. We show that the inter-site interaction in a one-dimensional dipolar\ngas in an optical lattice departs from the usually considered $1/r^3$\ndependence, acquiring a universal form that depends on the transversal\nconfinement and the lattice depth. Due to the crucial role played by the\nnearest- and next-to-nearest neighbors, the Hilbert-space fragmentation and\nparticle dynamics are very similar to that of a power-law model\n$1/r^{\\beta_{\\mathrm{eff}}<3}$, where $\\beta_{\\mathrm{eff}}$ is experimentally\ncontrollable by properly tailoring the transversal confinement. Our results are\nof direct experimental relevance for experiments on dipolar gases in optical\nlattices, and show that the particle dynamics may be remarkably different if\nthe quasi-1D lattice model is realized in a strong 3D lattice, or by means of a\nstrong transversal harmonic confinement."
    },
    {
        "anchor": "Field-induced long-lived supermolecules: We demonstrate that the long-lived bound states (super-molecules) can exist\nin the dilute limit when we tune the shape of effective potential between polar\nmolecules by an external microwave field. Binding energies, average sizes, and\nphase diagrams for both s-orbital (bosons) and p-orbital (fermions) dimers are\nstudied, together with bosonic trimer states. We explicitly show that the non-\nadiabatic transition rate can be easily tuned small for such ground state\nsuper-molecules, so that the system can be stable from collapse even near the\nassociated potential resonance. Our results, therefore, suggest a feasible cold\nmolecule system to investigate both novel few-body and many-body physics (for\nexample, the p-wave BCS-BEC crossover for fermions and the paired condensate\nfor bosons) that can not be easily accessed in single species atomic gases.",
        "positive": "Boson and fermion dynamics in quasi-one-dimensional flat band lattices: The difference between boson and fermion dynamics in quasi-one-dimensional\nlattices is studied with exact simulations of particle motion and by\ncalculating the persistent current in small quantum rings. We consider three\ndifferent lattices which in the tight binding model exhibit flat bands. The\nphysical realization is considered to be an optical lattice with bosonic or\nfermionic atoms. The atoms are assumed to interact with a repulsive short range\ninteraction. The different statistics of bosons and fermions causes different\ndynamics. Spinless fermions are easily trapped in the flat band states due to\nthe Pauli exclusion principle, which prevents them from interacting, while\nboson are able to push each other out from the flat band states."
    },
    {
        "anchor": "Mediated interaction between polarons in a one-dimensional Bose gas: We study a weakly-interacting one-dimensional Bose gas with two impurities\ncoupled locally to the boson density. We derive analytical results for the\ninduced interaction between the impurities at arbitrary coupling and separation\n$r$. At $r\\lesssim \\xi$, where $\\xi$ denotes the healing length of the Bose\ngas, the interaction is well described by the mean-field contribution. Its form\nchanges as the coupling is increased, approaching a linear function of $r$ at\nshort distances in the regime of strong coupling. The mean-field contribution\ndecays exponentially at arbitrary coupling for $r\\gg\\xi$. At such long\ndistances, however, the effect of quantum fluctuations becomes important,\ngiving rise to a long-ranged quantum contribution to the induced interaction.\nAt longest distances it behaves as $1/r^3$, while at strong coupling we find an\nintermediate distance regime with a slower decay, $1/r$. The quantum\ncontribution in the crossover regime is also calculated. The induced\ninteraction between impurities (i.e., polarons) is attractive and leads to the\nformation of their bound state, known as bipolaron. We discuss its binding\nenergy.",
        "positive": "Antiferromagnetism and superfluidity of a dipolar Fermi gas in a 2D\n  optical lattice: In a dipolar Fermi gas, the dipole-dipole interaction between fermions can be\nturned into a dipolar Ising interaction between pseduospins in the presence of\nan AC electric field. When trapped in a 2D optical lattice, such a dipolar\nFermi gas has a very rich phase diagram at zero temperature, due to the\ncompetition between antiferromagnetism and superfluidity. At half filling, the\nantiferromagnetic state is the favored ground state. The superfluid state\nappears as the ground state at a smaller filling factor. In between there is a\nphase-separated region. The order parameter of the superfluid state can display\ndifferent symmetries depending on the filling factor and interaction strength,\nincluding d-wave ($d$), extend s-wave ($xs$), or their linear combination\n($xs+i\\times d$). The implication for the current experiment is discussed."
    },
    {
        "anchor": "Characterising arbitrary dark solitons in trapped one-dimensional\n  Bose-Einstein condensates: We present a method to detect the presence and depth of dark solitons within\nrepulsive one-dimensional harmonically trapped Bose-Einstein condensates. For a\nsystem with one soliton, we prove that the shift of the density in Fourier\nspace directly maps onto the depth of the soliton. For multi-soliton systems,\ncombining our spectral method with established imaging techniques, the\ncharacter of the solitons present in the condensate can be determined. We\nverify that the detection of solitons by the spectral shift works in the\npresence of waves induced by density engineering methods. Finally we discuss\nimplications for vortex detection in three dimensional Bose-Einstein\ncondensates.",
        "positive": "An atomic boson sampler: A boson sampler implements a restricted model of quantum computing. It is\ndefined by the ability to sample from the distribution resulting from the\ninterference of identical bosons propagating according to programmable,\nnon-interacting dynamics. Here, we demonstrate a new combination of tools for\nimplementing boson sampling using ultracold atoms in a two-dimensional,\ntunnel-coupled optical lattice. These tools include fast and programmable\npreparation of large ensembles of nearly identical bosonic atoms\n($99.5^{+0.5}_{-1.6}\\;\\%$ indistinguishability) by means of rearrangement with\noptical tweezers and high-fidelity optical cooling, propagation for variable\nevolution time in the lattice with low loss ($5.0(2)\\;\\%$, independent of\nevolution time), and high fidelity detection of the atom positions after their\nevolution (typically $99.8(1)\\;\\%$). With this system, we study specific\ninstances of boson sampling involving up to $180$ atoms distributed among $\\sim\n1000$ sites in the lattice. Direct verification of a given boson sampling\ndistribution is not feasible in this regime. Instead, we introduce and perform\ntargeted tests to determine the indistinguishability of the prepared atoms, to\ncharacterize the applied family of single particle unitaries, and to observe\nexpected bunching features due to interference for a large range of atom\nnumbers. When extended to interacting systems, our work demonstrates the core\ncapabilities required to directly assemble ground and excited states in\nsimulations of various Hubbard models."
    },
    {
        "anchor": "Scrambling and thermalization in a diffusive quantum many-body system: Out-of-time ordered (OTO) correlation functions describe scrambling of\ninformation in correlated quantum matter. They are of particular interest in\nincoherent quantum systems lacking well defined quasi-particles. Thus far, it\nis largely elusive how OTO correlators spread in incoherent systems with\ndiffusive transport governed by a few globally conserved quantities. Here, we\nstudy the dynamical response of such a system using high-performance\nmatrix-product-operator techniques. Specifically, we consider the\nnon-integrable, one-dimensional Bose-Hubbard model in the incoherent\nhigh-temperature regime. Our system exhibits diffusive dynamics in time-ordered\ncorrelators of globally conserved quantities, whereas OTO correlators display a\nballistic, light-cone spreading of quantum information. The slowest process in\nthe global thermalization of the system is thus diffusive, yet information\nspreading is not inhibited by such slow dynamics. We furthermore develop an\nexperimentally feasible protocol to overcome some challenges faced by existing\nproposals and to probe time-ordered and OTO correlation functions. Our study\nopens new avenues for both the theoretical and experimental exploration of\nthermalization and information scrambling dynamics.",
        "positive": "Supersonic flow of a Bose-Einstein condensate past an oscillating\n  attractive-repulsive obstacle: We investigate by numerical simulations the pattern formation after an\noscillating attractive-repulsive obstacle inserted into the flow of a\nBose-Einstein condensate. For slow oscillations we observe a complex emission\nof vortex dipoles. For moderate oscillations organized lined up vortex dipoles\nare emitted. For high frequencies no dipoles are observed but only lined up\ndark fragments. The results shows that the drag force turns negative for\nsufficiently high frequency. We also successfully model the {\\it ship waves} in\nfront of the obstacle. In the limit of very fast oscillations all the\nexcitations of the system tend to vanish."
    },
    {
        "anchor": "Phases of Attractive Fermi Gases in Synthetic Dimensions: A novel way to produce quantum Hall ribbons in a cold atomic system is to use\nM hyperfine states of atoms in a 1D optical lattice to mimic an additional\n\"synthetic dimension\". A notable aspect here is that the SU(M) symmetric\ninteraction between atoms manifests as \"infinite ranged\" along the synthetic\ndimension. We study the many body physics of fermions with attractive\ninteractions in this system. We use a combination of analytical field theoretic\nand numerical density matrix renormalization group (DMRG) methods to reveal the\nrich ground state phase diagram of the system, including novel phases such as\nsquished baryon fluids. Remarkably, changing the parameters entails unusual\ncrossovers and transitions, e. g., we show that increasing the magnetic field\n(that produces the Hall effect) may convert a \"ferrometallic\" state at low\nfields to a \"squished baryon superfluid\" (with algebraic pairing correlations)\nat high fields. We also show that this system provides a unique opportunity to\nstudy quantum phase separation in a multiflavor ultracold fermionic system.",
        "positive": "Macroscopic Klein Tunneling in spin-orbit coupled Bose-Einstein\n  Condensates: We propose an experimental scheme to detect macroscopic Klein tunneling with\nspin-orbit coupled Bose-Einstein condensates (BECs). We show that a nonlinear\nDirac equation with tunable parameters can be realized with such BECs. %in a\nsimple configuration to generate the artificial spin-orbit coupling. Through\nnumerical calculations, we demonstrate that macroscopic Klein tunneling can be\nclearly detected under realistic conditions. Macroscopic quantum coherence in\nsuch relativistic tunneling is clarified and a BEC with a negative energy is\nshown to be able to transmit transparently through a wide Gaussian potential\nbarrier."
    },
    {
        "anchor": "Non-Hermitian Squeezed Polarons: Recent experimental breakthroughs in non-Hermitian ultracold atomic lattices\nhave dangled tantalizing prospects in realizing exotic, hitherto unreported,\nmany-body non-Hermitian quantum phenomena. In this work, we discover and\npropose an experimental platform for a radically different non-Hermitian\nphenomenon dubbed polaron squeezing. It is marked by a dipole-like accumulation\nof fermions arising from an interacting impurity in a background of\nnon-Hermitian reciprocity-breaking hoppings. We computed their spatial density\nand found that, unlike Hermitian polarons which are symmetrically localized\naround impurities, non-Hermitian squeezed polarons localize asymmetrically in\nthe direction opposite to conventional non-Hermitian pumping and\nnon-perturbatively modify the entire spectrum, despite having a manifestly\nlocal profile. We investigated their time evolution and found that, saliently,\nthey appear almost universally in the long-time steady state, unlike Hermitian\npolarons which only exist in the ground state. In our numerics, we also found\nthat, unlike well-known topological or skin localized states, squeezed polarons\nexist in the bulk, independently of boundary conditions. Our findings could\ninspire the realization of many-body states in ultracold atomic setups, where a\nsqueezed polaron can be readily detected and characterized by imaging the\nspatial fermionic density.",
        "positive": "Thermalization of a quantum Newton's cradle in a one-dimensional\n  quasicondensate: We study the nonequilibrium dynamics of the quantum Newton's cradle in a\none-dimensional (1D) Bose gas in the weakly-interacting quasicondensate regime.\nThis is the opposite regime to the original quantum Newton's cradle experiment\nof Kinoshita et al. [Nature 440, 900 (2006)], which was realized in the\nstrongly interacting 1D Bose gas. Using finite temperature c-field methods, we\ncalculate the characteristic relaxation rates to the final equilibrium state.\nHence, we identify the different dynamical regimes of the system in the\nparameter space that characterizes the strength of interatomic interactions,\nthe initial temperature, and the magnitude of the Bragg momentum used to\ninitiate the collisional oscillations of the cradle. In all parameter regimes,\nwe find that the system relaxes to a final equilibrium state for which the\nmomentum distribution is consistent with a thermal distribution. For\nsufficiently large initial Bragg momentum, the system can undergo hundreds of\nrepeated collisional oscillations before reaching the final thermal\nequilibrium. The corresponding thermalization timescales can reach tens of\nseconds, which is an order of magnitude smaller than in the strongly\ninteracting regime."
    },
    {
        "anchor": "Full distribution of the superfluid fraction and extreme value\n  statistics in a one dimensional disordered Bose gas: The full statistical distribution of the superfluid fraction characterizing\none-dimensional Bose gases in random potentials is discussed. Rare\nconfigurations with extreme fluctuations of the disorder potential can fragment\nthe condensate and reduce the superfluid fraction to zero. The resulting\nbimodal probability distribution for the superfluid fraction is calculated\nnumerically in the quasi-1D mean-field regime of ultracold atoms in laser\nspeckle potentials. Using extreme-value statistics, an analytical scaling of\nthe zero-superfluid probability as function of disorder strength, disorder\ncorrelation length and system size is presented. It is argued that similar\nresults can be expected for point-like impurities, and that these findings are\nin reach for present-day experiments.",
        "positive": "Evolution of Fermion Pairing from Three to Two Dimensions: We follow the evolution of fermion pairing in the dimensional crossover from\n3D to 2D as a strongly interacting Fermi gas of $^6$Li atoms becomes confined\nto a stack of two-dimensional layers formed by a one-dimensional optical\nlattice. Decreasing the dimensionality leads to the opening of a gap in\nradio-frequency spectra, even on the BCS-side of a Feshbach resonance. The\nmeasured binding energy of fermion pairs closely follows the theoretical\ntwo-body binding energy and, in the 2D limit, the zero-temperature mean-field\nBEC-BCS theory."
    },
    {
        "anchor": "Efimov Trimers near the Zero-crossing of a Feshbach Resonance: Near a Feshbach resonance, the two-body scattering length can assume any\nvalue. When it approaches zero, the next-order term given by the effective\nrange is known to diverge. We consider the question of whether this divergence\n(and the vanishing of the scattering length) is accompanied by an anomalous\nsolution of the three-boson Schr\\\"odinger equation similar to the one found at\ninfinite scattering length by Efimov. Within a simple zero-range model, we find\nno such solutions, and conclude that higher-order terms do not support Efimov\nphysics.",
        "positive": "Resonant Matter Wave Amplification in Mean Field Theory: We develop a Green's function based mean-field theory for coherent mixing of\nmatter- and light-waves. To demonstrate the utility of this approach, we\nanalyse a co-propagating Raman matter-wave amplifier. We find that for a given\nlaser intensity, a significantly faster amplification process can be achieved\nemploying resonant rather than off-resonance driving. The ratio of the\nmatter-wave gain to atom loss-rate due to spontaneous emission is given by the\noptical depth of the sample, and is the same both on- and off-resonance.\nFurthermore, we show that for short-times, the single-mode approximation for\nthe matter-waves gives exact agreement with the full spatial dynamics. For long\ntimes, the off-resonant case shows suppressed amplification due to a spatially\ninhomogenous AC Stark shift associated with laser depletion. This suppression\nis absent on-resonance, where the AC Stark shift is absent."
    },
    {
        "anchor": "Nonequilibrium quantum dynamics of atomic dark solitons: We study quantum dynamics of bosonic atoms that are excited to form a phase\nkink, or several kinks, by an imprinting potential in a one-dimensional trap.\nWe calculate dissipation due to quantum and thermal fluctuations in soliton\ntrajectories, collisions and the core structure. Single-shot runs show weak\nfilling of a soliton core, typically deeper solitons in the case of stronger\nfluctuations and spreading/disappearing solitons due to collisions. We also\nanalyze a soliton system in an optical lattice that shows especially strong\nfluctuation-induced phenomena.",
        "positive": "Thermodynamic geometry of ideal quantum gases: a general framework and a\n  geometric picture of BEC-enhanced heat engines: Thermodynamic geometry provides a physically transparent framework to\ndescribe thermodynamic processes in meso- and micro-scale systems that are\ndriven by slow variations of external control parameters. Focusing on periodic\ndriving for thermal machines, we extend this framework to ideal quantum gases.\nTo this end, we show that the standard approach of equilibrium physics, where a\ngrand-canonical ensemble is used to model a canonical one by fixing the mean\nparticle number through the chemical potential, can be extended to the slow\ndriving regime in a thermodynamically consistent way. As a key application of\nour theory, we use a Lindblad-type quantum master equation to work out a\ndynamical model of a quantum many-body engine using a harmonically trapped Bose\ngas. Our results provide a geometric picture of the BEC-induced power\nenhancement that was previously predicted for this type of engine on the basis\nof an endoreversible model [New J. Phys. 24, 025001 (2022)]. Using an earlier\nderived universal trade-off relation between power and efficiency as a\nbenchmark, we further show that the Bose-gas engine can deliver significantly\nmore power at given efficiency than an equally large collection of single-body\nengines. Our work paves the way for a more general thermodynamic framework that\nmakes it possible to systematically assess the impact of quantum many-body\neffects on the performance of thermal machines."
    },
    {
        "anchor": "Fluctuation and interaction induced instability of dark solitons in\n  single and binary condensates: We show that the presence of soliton in a single-species condensate, at zero\ntemperature, enhances the quantum depletion sufficient enough to induce\ndynamical instability of the system. We also predict that for two-species\ncondensates, two Goldstone modes emerge in the excitation spectrum at phase\nseparation. Of these, one is due to the presence of the soliton. We use\nHartree-Fock-Bogoliubov theory with Popov approximation to examine the mode\nevolution, and demonstrate that when the anomalous mode collides with a higher\nenergy mode it renders the solitonic state oscillatory unstable. We also report\nsoliton induced change in the topology of the density profiles of the\ntwo-species condensates at phase-separation.",
        "positive": "Generation of optical potentials for ultracold atoms using a\n  superluminescent diode: We report on the realization and characterisation of optical potentials for\nultracold atoms using a superluminescent diode. The light emitted by this class\nof diodes is characterised by high spatial coherence but low temporal\ncoherence. On the one hand, this implies that it follows Gaussian propagation\nsimilar to lasers, allowing for high intensities and well-collimated beams. On\nthe other, it significantly reduces those interference effects that lead to\nsevere distortions in imaging. By using a high-resolution optical setup, we\nproduce patterned optical potentials with a digital micromirror device and\ndemonstrate that the quality of the patterns produced by our superluminescent\ndiode is consistently and substantially higher than those produced by our\nlaser. We show that the resulting optical potentials can be used to arrange the\natoms in arbitrary structures and manipulate them dynamically. Our results can\nopen new opportunities in the fields of quantum simulations and atomtronics."
    },
    {
        "anchor": "Resonance Scattering in Optical Lattices and Molecules: Interband versus\n  Intraband Effects: We study the low-energy two-body scattering in optical lattices with all\nhigher-band effects included in an effective potential, using a renormalization\ngroup approach. As the potential depth reaches a certain value, a resonance of\nlow energy scattering occurs even when the negative s-wave scattering length\n$(a_s)$ is much shorter than the lattice constant. These resonances can be\nmainly driven either by interband or intraband effects or by both, depending on\nthe magnitude of $a_s$. Furthermore the low-energy scattering matrix in optical\nlattices has a much stronger energy-dependence than that in free space. We also\ninvestigate the momentum distribution for molecules when released from optical\nlattices.",
        "positive": "Spectral properties of the Goldstino in supersymmetric Bose-Fermi\n  mixtures: We evaluate the spectral properties of the Goldstino in a Bose-Fermi mixture\nof cold atoms and molecules whose dynamics is governed by a supersymmetric\nhamiltonian. Model independent results are obtained from sum rules obeyed by\nthe spectral function. We carry out specific calculations, at zero and finite\ntemperature, using the Random Phase Approximation, and obtain in particular\nanalytic expressions for the dispersion relation at small momentum. These\nexplicit calculations allow us to pin down more precisely the features of the\nGoldstino that can be attributed to the supersymmetry alone, together with its\nspontaneous breaking. The anomalous large effect of the Fermi sea at moderate\nand large momenta is emphasized."
    },
    {
        "anchor": "Intrinsic anomalous Hall effect across the magnetic phase transition of\n  a spin-orbit-coupled Bose-Einstein condensate: We study theoretically the zero temperature intrinsic anomalous Hall effect\nin an experimentally realized 2D spin-orbit coupled Bose gas. For anisotropic\natomic interactions and as the spin-orbit coupling strength increases, the\nsystem undergoes a ground state phase transition from states exhibiting a total\nin-plane magnetization to those with a perpendicular magnetization along the\n$z$ direction. We show that finite frequency, or ac, Hall responses exist in\nboth phases in the absence of an artificial magnetic field, as a result of\nfinite inter-band transitions. However, the characteristics of the anomalous\nHall responses are drastically different in these two phases because of the\ndifferent symmetries preserved by the corresponding ground states. In\nparticular, we find a finite dc Hall conductivity in one phase but not the\nother. The underlying physical reasons for this are analyzed further by\nexploring relations of the dc Hall conductivity to the system's chirality and\nBerry curvatures of the Bloch bands. Finally, we discuss an experimental method\nof probing the anomalous Hall effect in trapped systems.",
        "positive": "Vortex Dynamics in Anisotropic Traps: We investigate the dynamics of linear vortex lattices in anisotropic traps in\ntwo-dimensions and show that the interplay between the rotation and the\nanisotropy leads to a rich but highly regular dynamics."
    },
    {
        "anchor": "2000-times repeated imaging of strontium atoms in clock-magic tweezer\n  arrays: We demonstrate single-atom resolved imaging with a survival probability of\n$0.99932(8)$ and a fidelity of $0.99991(1)$, enabling us to perform repeated\nhigh-fidelity imaging of single atoms in tweezers for thousands of times. We\nfurther observe lifetimes under laser cooling of more than seven minutes, an\norder of magnitude longer than in previous tweezer studies. Experiments are\nperformed with strontium atoms in $813.4~\\text{nm}$ tweezer arrays, which is at\na magic wavelength for the clock transition. Tuning to this wavelength is\nenabled by off-magic Sisyphus cooling on the intercombination line, which lets\nus choose the tweezer wavelength almost arbitrarily. We find that a single not\nretro-reflected cooling beam in the radial direction is sufficient for\nmitigating recoil heating during imaging. Moreover, this cooling technique\nyields temperatures below $5~\\mu$K, as measured by release and recapture.\nFinally, we demonstrate clock-state resolved detection with average survival\nprobability of $0.996(1)$ and average state detection fidelity of $0.981(1)$.\nOur work paves the way for atom-by-atom assembly of large defect-free arrays of\nalkaline-earth atoms, in which repeated interrogation of the clock transition\nis an imminent possibility.",
        "positive": "Stationary states, dynamical stability, and vorticity of Bose-Einstein\n  condensates in tilted rotating harmonic traps: We theoretically investigate a Bose-Einstein condensate confined by a\nrotating harmonic trap whose rotation axis is not aligned with any of its\nprincipal axes. The principal axes of the Thomas-Fermi density profiles of the\nresulting stationary solutions are found to be tilted with respect to those of\nthe rotating trap, representing an extra degree of freedom that is associated\nwith the existence of additional branches of stationary solutions for any given\nrotation axis alignment. By linearizing the time-dependent theory about the\nstationary states, we obtain a semi-analytical prediction of their dynamical\ninstability at high rotation frequencies against collective modes arising from\nenvironmental perturbations. Comparing the stationary states to direct\nsimulations of the Gross-Pitaevskii equation, we predict the nucleation of\nquantum vortices in the dynamically unstable rotational regime. These vortex\nlines are aligned along the rotation axis despite the tilting of the rotating\ntrap although the background density profile is tilted with respect to the\ntrapping and rotation axes."
    },
    {
        "anchor": "Trap effects and continuum limit of the Hubbard model in the presence of\n  a harmonic potential: We give a prescription to perform the continuum limit of the $d$-dimensional\nHubbard model in the presence of a harmonic trap at zero temperature. We\nperform the continuum limit at fixed number of particles. In $d\\geq3$ the\nlattice system of spin-1/2 particles is mapped into a non-interacting\ntwo-component Fermi gas in a harmonic trap. In $d=1$ and $d=2$ the particles\nwith opposite spin interact via a Dirac delta interaction. We show that the\nproperties of this continuum limit can be put in correspondence with those\nderived applying the Trap-Size scaling (TSS) formalism to the confined Hubbard\nmodel in the so called Dilute Regime (fixed number of particles and weak\nconfinement). The correspondence in $d=1$ and $d=2$ has been tested comparing\nthe numerical results obtained for lattice system with those of the continuum\nlimit in the case of two-particle and in absence of spin-polarization\n($N=2$,$N_{\\uparrow}=N_{\\downarrow}=1$).",
        "positive": "A Fermi-Hubbard Optical Tweezer Array: We use lithium-6 atoms in an optical tweezer array to realize an eight-site\nFermi-Hubbard chain near half filling. We achieve single site detection by\ncombining the tweezer array with a quantum gas microscope. By reducing disorder\nin the energy offsets to less than the tunneling energy, we observe Mott\ninsulators with strong antiferromagnetic correlations. The measured spin\ncorrelations allow us to put an upper bound on the entropy of\n0.26(4)$k_\\mathrm{B}$ per atom, comparable to the lowest entropies achieved\nwith optical lattices. Additionally, we establish the flexibility of the\ntweezer platform by initializing atoms on one tweezer and observing tunneling\ndynamics across the array for different 1D geometries."
    },
    {
        "anchor": "Anderson transition of cold atoms with synthetic spin-orbit coupling in\n  two-dimensional speckle potentials: We investigate the metal-insulator transition occurring in two-dimensional\n(2D) systems of noninteracting atoms in the presence of artificial spin-orbit\ninteractions and a spatially correlated disorder generated by laser speckles.\nBased on a high order discretization scheme, we calculate the precise position\nof the mobility edge and verify that the transition belongs to the symplectic\nuniversality class. We show that the mobility edge depends strongly on the\nmixing angle between Rashba and Dresselhaus spin-orbit couplings. For equal\ncouplings a non-power-law divergence is found, signaling the crossing to the\northogonal class, where such a 2D transition is forbidden.",
        "positive": "Slow-light probe of Fermi pairing through an atom-molecule dark state: We consider the two-color photooassociation of a quantum degenerate atomic\ngas into ground-state diatomic molecules via a molecular dark state. This\nprocess can be described in terms of a lambda level scheme that is formally\nanalogous to the situation in electromagnetically-induced transparency (EIT) in\natomic systems, and therefore can result in slow light propagation. We show\nthat the group velocity of the light field depends explicitly on whether the\natoms are bosons or fermions, as well as on the existence or absence of a\npairing gap in the case of fermions, so that the measurement of the group\nvelocity realizes a non-destructive diagnosis of the atomic state and the\npairing gap."
    },
    {
        "anchor": "Emergence of Anyons on the Two-Sphere in Molecular Impurities: Recently it was shown that anyons on the two-sphere naturally arise from a\nsystem of molecular impurities exchanging angular momentum with a many-particle\nbath (Phys. Rev. Lett. 126, 015301 (2021)). Here we further advance this\napproach and rigorously demonstrate that in the experimentally realized regime\nthe lowest spectrum of two linear molecules immersed in superfluid helium\ncorresponds to the spectrum of two anyons on the sphere. We develop the\nformalism within the framework of the recently experimentally observed angulon\nquasiparticle.",
        "positive": "Bipolaron in one-dimensional $SU(3)$ fermions with three-body\n  interaction: The properties of the one-dimensional $SU(3)$ population-imbalanced fermions\nare discussed. The system is assumed to be in the two-body resonance where all\ntwo-body scattering lengths diverge, and the only interaction between fermions\nthat is taken into account is the short-range three-body one. In particular, we\nconsider the situation when only one `flavor' of fermions is macroscopically\noccupied, and there are exactly two atoms of two others. This system supports\nthe trimer and the medium-induced dimer states studied here in detail and shows\nevidence of color superfluidity."
    },
    {
        "anchor": "Monte Carlo Simulations of the Unitary Bose Gas: We investigate the zero-temperature properties of a diluted homogeneous Bose\ngas made of $N$ particles interacting via a two-body square-well potential by\nperfor ming Monte Carlo simulations. We tune the interaction strength to\nachieve arbitrary positive values of the scattering length and compute by Monte\nCarlo quadrature the energy per particle $E/N$ and the condensate fraction\n$N_0/N$ of this system by using a Jastrow ansatz for the many-body wave\nfunction which avoids the formation of the self-bound ground-state and\ndescribes instead a (metastable) gaseous state with uniform den sity. In the\nunitarity limit, where the scattering length diverges while the range of the\ninter-atomic potential is much smaller than the average distance between atoms,\nwe find a finite energy per particle ($E/N=0.70\\ \\hbar^2(6\\pi^2n)^{2/3}/2m$,\nwith $n$ th e number density) and a quite large condensate fraction\n($N_0/N=0.83$).",
        "positive": "Thermal Conductivity of an Ultracold Paramagnetic Bose Gas: We analytically derive the transport tensor of thermal conductivity in an\nultracold, but not yet quantum degenerate, gas of Bosonic lanthanide atoms\nusing the Chapman-Enskog procedure. The tensor coefficients inherit an\nanisotropy from the anisotropic collision cross section for these dipolar\nspecies, manifest in their dependence on the dipole moment, dipole orientation,\nand $s$-wave scattering length. These functional dependencies open up a pathway\nfor control of macroscopic gas phenomena via tuning of the microscopic atomic\ninteractions. As an illustrative example, we analyze the time evolution of a\ntemperature hot-spot which shows preferential heat diffusion orthogonal to the\ndipole orientation, a direct consequence of anisotropic thermal conduction."
    },
    {
        "anchor": "Probing the Bose-Glass--Superfluid Transition using Quantum Quenches of\n  Disorder: We probe the transition between superfluid and Bose glass phases using\nquantum quenches of disorder in an ultracold atomic lattice gas that realizes\nthe disordered Bose-Hubbard model. Measurements of excitations generated by the\nquench exhibit threshold behavior in the disorder strength indicative of a\nphase transition. Ab-initio quantum Monte Carlo simulations confirm that the\nappearance of excitations coincides with the equilibrium superfluid--Bose-glass\nphase boundary at different lattice potential depths. By varying the quench\ntime, we demonstrate the disappearance of an adiabatic timescale compared with\nmicroscopic parameters in the BG regime.",
        "positive": "Ground-State Energy and Condensate Density of a Dilute Bose Gas\n  Revisited: The ground-state energy per particle $E/N$ and condensate density $n_0$ of a\ndilute Bose gas are studied with a self-consistent perturbation expansion\nsatisfying the Hugenholtz-Pines theorem and conservation laws simultaneously. A\nclass of Feynman diagrams for the self-energy, which has escaped consideration\nso far, is shown to add an extra constant $c_{ip}\\sim O(1)$ to the expressions\nreported by Lee, Huang, and Yang [Phys. Rev. 106, 1135 (1957) ] as\n$E/N=(2\\pi\\hbar^2 an/m)[1+(128/15\\sqrt{{\\pi}}+16c_{ip}/5)\\sqrt{{a^3n}}]$ and\n$n_0/n=1-(8/3\\sqrt{{\\pi}}+c_{ip})\\sqrt{{a^3n}}$, where $a$, $n$, and $m$ are\nare the s-wave scattering length, particle density, and particle mass,\nrespectively. We present a couple of estimates for $c_{ip}$; the third-order\nperturbation expansion yields $c_{ip}=0.412$."
    },
    {
        "anchor": "Non-equilibrium dynamics of ultracold lattice bosons inside a cavity: We study the non-equilibrium quench dynamics crossing a continuous phase\ntransition between the charge density wave (CDW) and supersolid (SS) phases of\na bosonic lattice gas with cavity-mediated interactions. When changing the\nhopping amplitude in the Hamiltonian as a function of time, we investigate the\nscaling behavior of the correlation length and vortex density with respect to\nthe quench time and find that there is a threshold of the quench rate\nseparating two distinct scaling regimes. When slowly varying the system below\nthat threshold, we find a power-law scaling as predicted by the Kibble-Zurek\nmechanism (KZM). While considering fast quench above that threshold, a\ndeviation from the KZM prediction occurs, manifested by a saturation of the\ndefect density. We further show that such distinct scaling behaviors during\ndifferent dynamic procedures can be understood through comparing the relaxation\ntime and the quench rate.",
        "positive": "Dynamics of domain walls in a Bose-Einstein condensate driven by\n  density-dependent gauge field: Dynamical coupling between matter and gauge fields underlies the emergence of\nmany exotic particle-like excitations in condensed matter and high energy\nphysics. An important stepping stone to simulate this physics in atomic quantum\ngases relies on the synthesis of density-dependent gauge fields. Here we\ndemonstrate deterministic formation of domain walls in a stable Bose-Einstein\ncondensate with a synthetic gauge field that depends on the atomic density. The\ngauge field is created by simultaneous modulations of the optical lattice\npotential and interatomic interactions, and results in domains of atoms\ncondensed into two different momenta. Modeling the domain walls as elementary\nexcitations, we find that the domain walls respond to synthetic electric field\nwith a charge-to-mass ratio larger than and opposite to that of the bare atoms.\nOur work offers promising prospects to simulate the dynamics and interactions\nof novel excitations in quantum systems with dynamical gauge fields."
    },
    {
        "anchor": "Quantum spin models with long-range interactions and tunnelings: A\n  quantum Monte Carlo study: We use a quantum Monte Carlo method to investigate various classes of 2D spin\nmodels with long-range interactions at low temperatures. In particular, we\nstudy a dipolar XXZ model with U(1) symmetry that appears as a hard-core boson\nlimit of an extended Hubbard model describing polarized dipolar atoms or\nmolecules in an optical lattice. Tunneling, in such a model, is short-range,\nwhereas density-density couplings decay with distance following a cubic power\nlaw. We investigate also an XXZ model with long-range couplings of all three\nspin components - such a model describes a system of ultracold ions in a\nlattice of microtraps. We describe an approximate phase diagram for such\nsystems at zero and at finite temperature, and compare their properties. In\nparticular, we compare the extent of crystalline, super?uid, and supersolid\nphases. Our predictions apply directly to current experiments with mesoscopic\nnumbers of polar molecules and trapped ions.",
        "positive": "Non equilibrium quantum dynamics in ultra-cold quantum gases: Advances in controlling and measuring systems of ultra-cold atoms provided\nstrong motivation to theoretical investigations of quantum dynamics in closed\nmany-body systems. Fundamental questions on quantum dynamics and statistical\nmechanics are now within experimental reach: How is thermalization achieved in\na closed quantum system? How does quantum dynamics cross over to effective\nclassical physics? Can such a thermal or classical fate be evaded? In these\nlectures, given at the Les Houches Summer School of Physics \"Strongly\nInteracting Quantum Systems Out of Equilibrium\", I introduce the students to\nthe novel properties that make ultra-cold atomic systems a unique platform for\nstudy of non equilibrium quantum dynamics. I review a selection of recent\nexperimental and theoretical work in which universal features and emergent\nphenomena in quantum dynamics are highlighted."
    },
    {
        "anchor": "Birefringent break up of Dirac fermions in a square optical lattice: We generalize a proposal by Sorensen et al. [Phys. Rev. Lett. 94, 086803\n(2005)] for creating an artificial magnetic field in a cold atom system on a\nsquare optical lattice. This leads us to an effective lattice model with\ntunable spatially periodic modulation of the artificial magnetic field and the\nhopping amplitude. When there is an average flux of half a flux quantum per\nplaquette the spectrum of low-energy excitations can be described by massless\nDirac fermions in which the usually doubly degenerate Dirac cones split into\ncones with different \"speeds of light\" which can be tuned to give a single\nDirac cone and a flat band. These gapless birefringent Dirac fermions arise\nbecause of broken chiral symmetry in the kinetic energy term of the effective\nlow energy Hamiltonian. We characterize the effects of various perturbations to\nthe low-energy spectrum, including staggered potentials, interactions, and\ndomain wall topological defects.",
        "positive": "Quasiparticles of widely tuneable inertial mass: The dispersion relation\n  of atomic Josephson vortices and related solitary waves: Superconducting Josephson vortices have direct analogues in ultracold-atom\nphysics as solitary-wave excitations of two-component superfluid Bose gases\nwith linear coupling. Here we numerically extend the zero-velocity Josephson\nvortex solutions of the coupled Gross-Pitaevskii equations to non-zero\nvelocities, thus obtaining the full dispersion relation. The inertial mass of\nthe Josephson vortex obtained from the dispersion relation depends on the\nstrength of linear coupling and has a simple pole divergence at a critical\nvalue where it changes sign while assuming large absolute values. Additional\nlow-velocity quasiparticles with negative inertial mass emerge at finite\nmomentum that are reminiscent of a dark soliton in one component with\ncounter-flow in the other. In the limit of small linear coupling we compare the\nJosephson vortex solutions to sine-Gordon solitons and show that the\ncorrespondence between them is asymptotic, but significant differences appear\nat finite values of the coupling constant. Finally, for unequal and non-zero\nself- and cross-component nonlinearities, we find a new solitary-wave\nexcitation branch. In its presence, both dark solitons and Josephson vortices\nare dynamically stable while the new excitations are unstable."
    },
    {
        "anchor": "Berry Curvature of interacting bosons in a honeycomb lattice: We consider soft-core bosons with onsite interaction loaded in the honeycomb\nlattice with different site energies for the two sublattices. Using both a\nmean-field approach and quantum Monte-Carlo simulations, we show that the\ntopology of the honeycomb lattice results in a non-vanishing Berry curvature\nfor the band structure of the single-particle excitations of the system. This\nBerry curvature induces an anomalous Hall effect. It is seen by studying the\ntime evolution of a wavepacket, namely a superfluid ground state in a harmonic\ntrap, subjected either to a constant force (Bloch oscillations) or to a sudden\nshift of the trap center.",
        "positive": "The emergence of atomic semifluxons in optical Josephson junctions: We propose to create pairs of semifluxons starting from a flat-phase state in\nlong, optical 0-pi-0 Josephson junctions formed with internal electronic states\nof atomic Bose-Einstein condensates. In this optical system, we can dynamically\ntune the length of the pi-junction, the detuning of the optical transition, or\nthe strength of the laser-coupling, to induce transitions from the flat-phase\nstate to such a semifluxon-pair state. Similarly as in superconducting 0-pi-0\njunctions, there are two, energetically degenerate semifluxon-pair states. A\nlinear mean-field model with two internal electronic states explains this\ndegeneracy and shows the distinct static field configuration in a phase-diagram\nof the junction parameters. This optical system offers the possibility to\ndynamically create a coherent superposition of the distinct semifluxon-pair\nstates and observe macroscopic quantum oscillation."
    },
    {
        "anchor": "Metastability, excitations, fluctuations, and multiple-swallowtail\n  structures of a superfluid in a Bose-Einstein condensate in the presence of a\n  uniformly moving defect: We solve the Gross-Pitaevskii (GP) and Bogoliubov equations to investigate\nthe metastability of superfluidity in a Bose-Einstein condensate in the\npresence of a uniformly moving defect potential in a two-dimensional torus. We\ncalculate the total energy and momentum as functions of the driving velocity of\nthe moving defect and find metastable states with negative effective-mass near\nthe critical velocity. We also find that the first excited energy (energy gap)\nin the finite-sized torus closes at the critical velocity, that it obeys\none-fourth power-law scaling, and that the dynamical fluctuation of the density\n(amplitude of the order parameter) is strongly enhanced near the critical\nvelocity. We confirm the validity of our results near the critical velocity by\ncalculating the quantum depletion. We find an unconventional swallowtail\nstructure (multiple-swallowtail structure) through calculations of the unstable\nstationary solutions of the GP equation.",
        "positive": "Many-body quantum dynamics of initially trapped systems due to a Stark\n  potential --- thermalization vs. Bloch oscillations: We analyze the dynamics of an initially trapped cloud of interacting quantum\nparticles on a lattice under a linear (Stark) potential. We reveal a dichotomy:\ninitially trapped interacting systems possess features typical of both\nmany-body-localized and self-thermalizing systems. We consider both fermions\n($t$-$V$ model) and bosons (Bose-Hubbard model). For the zero and infinite\ninteraction limits, both systems are integrable: we provide analytic solutions\nin terms of the moments of the initial cloud shape, and clarify how the\nrecurrent dynamics (many-body Bloch oscillations) depends on the initial state.\nAway from the integrable points, we identify and explain the time scale at\nwhich Bloch oscillations decohere."
    },
    {
        "anchor": "Classical analogies for the force acting on an impurity in a\n  Bose-Einstein condensate: We study the hydrodynamic forces acting on a small impurity moving in a\ntwo-dimensional Bose-Einstein condensate at non-zero temperature. The\ncondensate is modelled by the damped-Gross Pitaevskii (dGPE) equation and the\nimpurity by a Gaussian repulsive potential coupled to the condensate. For weak\ncoupling, we obtain analytical expressions for the forces acting on the\nimpurity, and compare them with those computed through direct numerical\nsimulations of the dGPE and with the corresponding expressions for classical\nforces. For non-steady flows, there is a time-dependent force dominated by\ninertial effects and which has a correspondence in the Maxey-Riley theory for\nparticles in classical fluids. In the steady-state regime, the force is\ndominated by a self-induced drag. Unlike at zero temperature, where the drag\nforce vanishes below a critical velocity, at low temperatures the impurity\nexperiences a net drag even at small velocities, as a consequence of the energy\ndissipation through interactions of the condensate with the thermal cloud. This\ndissipative force due to thermal drag is similar to the classical Stokes' drag.\nThere is still a critical velocity above which steady-state drag is dominated\nby acoustic excitations and behaves non-monotonically with impurity's speed.",
        "positive": "Spin-orbit coupled bosons interacting in a two-dimensional harmonic trap: A system of bosons in a two-dimensional harmonic trap in the presence of\nRashba-type spin-orbit coupling is investigated. An analytic treatment of the\nground state of a single atom in the weak-coupling regime is presented and used\nas a basis for a perturbation theory in the interacting two-boson system. The\nnumerical diagonalization of both the single-particle and the two-boson\nHamiltonian matrices allows us to go beyond those approximations and obtain not\nonly the ground state, but also the low-energy spectra and the different energy\ncontributions separately. We show that the expectation value of the spin-orbit\nterm is related to the expectation value of $\\hat{\\sigma}_z \\hat{L}_z$ for the\neigenstates of the system, regardless of the trapping potential. The low-energy\nstates of the repulsively interacting two-boson system are characterized. With\nthe presence of a sufficiently strong interaction and spin-orbit coupling\nstrength, there is a direct energy-level crossing in the ground state of the\nsystem between states of different $J_z$, the third component of the total\nangular momentum, that changes its structure. This is reflected in a\ndiscontinuity in the different energy terms and it is signaled in the spatial\ndensity of the system."
    },
    {
        "anchor": "Signatures of quantum chaos of Rydberg dressed bosons in a triple-well\n  potential: We study signatures of quantum chaos in dynamics of Rydberg dressed bosonic\natoms held in a one dimensional triple-well potential. Long-range\nnearest-neighbor and next-nearest-neighbor interactions, induced by laser\ndressing atoms to strongly interacting Rydberg states, affect drastically mean\nfield and quantum many-body dynamics. By analyzing the mean field dynamics,\nclassical chaos regions with positive and large Lyapunov exponents are\nidentified as a function of the potential well tilting and dressed\ninteractions. In the quantum regime, it is found that level statistics of the\neigen-energies gains a Wigner-Dyson distribution when the Lyapunov exponents\nare large, giving rise to signatures of strong quantum chaos. We find that both\nthe time averaged entanglement entropy and survival probability of the initial\nstate have distinctively large values in the quantum chaos regime. We further\nshow that population variances could be used as an indicator of the emergence\nof quantum chaos. This might provide a way to directly probe quantum chaotic\ndynamics through analyzing population dynamics in individual potential wells.",
        "positive": "Effective statistical fringe removal algorithm for high-sensitivity\n  imaging of ultracold atoms: High-sensitivity imaging of ultracold atoms is often challenging when\ninterference patterns are imprinted on the imaging light. Such image noises\nresult in low signal-to-noise ratio and limit the capability to extract subtle\nphysical quantities. Here we demonstrate an advanced fringe removal algorithm\nfor absorption imaging of ultracold atoms, which efficiently suppresses\nunwanted fringe patterns using a small number of sample images without taking\nadditional reference images. The protocol is based on an image decomposition\nand projection method with an extended image basis. We apply this scheme to raw\nabsorption images of degenerate Fermi gases for the measurement of atomic\ndensity fluctuations and temperatures. The quantitative analysis shows that\nimage noises can be efficiently removed with only tens of reference images,\nwhich manifests the efficiency of our protocol. Our algorithm would be of\nparticular interest for the quantum emulation experiments in which several\nphysical parameters need to be scanned within a limited time duration."
    },
    {
        "anchor": "Stationary solitons in F=1 spin-orbit coupled Bose-Einstein condensates: We consider solitary wave excitations above the ground state of $F=1$\nspin-orbit coupled Bose-Einstein condensates (SOBECs). The low energy\nproperties of SOBECs in any of the three branches of the single particle\ndispersion relation can be described by suitable scalar nonlinear Schr\\\"odinger\n(NLS) equations which we obtain using multiple-scale expansions. This enables\nus to examine a variety of different configurations, such as dark solitary\nwaves associated with higher energy branches, as well as dark and bright\nstructures in the lowest branch. The lowest branch can also exhibit a\n``superstripe'' phase that supports solitary waves. In all cases, we provide\nexplicit expressions for the NLS coefficients, and confirm their validity with\nfull numerical simulations of the SOBEC system including a harmonic confining\npotential.",
        "positive": "Phase Separation and Dynamics of two-component Bose-Einstein condensates: The miscibility of two interacting quantum systems is an important testing\nground for the understanding of complex quantum systems. Two-component\nBose-Einstein condensates enable the investigation of this scenario in a\nparticularly well controlled setting. In a homogeneous system, the transition\nbetween mixed and separated phases is fully characterised by a `miscibility\nparameter', based on the ratio of intra- to inter-species interaction\nstrengths. Here we show, however, that this parameter is no longer the optimal\none for trapped gases, for which the location of the phase boundary depends\ncritically on atom numbers. We demonstrate how monitoring of damping rates and\nfrequencies of dipole oscillations enables the experimental mapping of the\nphase diagram by numerical implementation of a fully self-consistent\nfinite-temperature kinetic theory for binary condensates. The change in damping\nrate is explained in terms of surface oscillation in the immiscible regime, and\ncounterflow instability in the miscible regime, with collisions becoming only\nimportant in the long time evolution."
    },
    {
        "anchor": "Bogoliubov theory for atom scattering into separate regions: We review the Bogoliubov theory in the context of recent experiments, where\natoms are scattered from a Bose-Einstein Condensate into two well-separated\nregions. We find the full dynamics of the pair-production process, calculate\nthe first and second order correlation functions and show that the system is\nideally number-squeezed. We calculate the Fisher information to show how the\nentanglement between the atoms from the two regions changes in time. We also\nprovide a simple expression for the lower bound of the useful entanglement in\nthe system in terms of the average number of scattered atoms and the number of\nmodes they occupy. We then apply our theory to a recent \"twin-beam\" experiment\n[R. B\\\"ucker {\\it et al.}, Nat. Phys. {\\bf 7}, 608 (2011)]. The only numerical\nstep of our semi-analytical description can be easily solved and does not\nrequire implementation of any stochastic methods.",
        "positive": "Universal tetramer and pentamer in two-dimensional fermionic mixtures: We study the emergence of universal tetramer and pentamer bound states in the\ntwo-dimensional $(N+1)$ system, which consists of $N$ identical heavy fermions\ninteracting with a light atom. We show that the critical heavy-light mass ratio\nto support a ($3+1$) tetramer below the trimer threshold is $3.38$, and to\nsupport a ($4+1$) pentamer below the tetramer threshold is $5.14$. While these\nground state tetramer and pentamer are both with zero total angular momentum,\nthey exhibit very different density distributions and correlations in momentum\nspace, due to their distinct angular momentum decompositions in the\ndimer-fermion frame. These universal bound states can be accessible by a number\nof Fermi-Fermi mixtures now realized in cold atoms laboratories, which also\nsuggest novel few-body correlations dominant in their corresponding many-body\nsystems."
    },
    {
        "anchor": "The exact solution of a generalized Bose-Hubbard model: I present the exact solution of a family of fragmented Bose-Hubbard models\nand represent the models as graphs in one-dimension, two-dimensions and\nthree-dimensions with the condensates in the vertices. The models are solved by\nthe algebraic Bethe ansatz method.",
        "positive": "The effect of atomic collisions on the quantum phase transition of a\n  Bose-Einstein condensate inside an optical cavity: In this paper, we investigate the effect of atomic collisions on the phase\ntransition form the normal to the superradiant phase in a one-dimensional\nBose-Einstein condensate (BEC) trapped inside an optical cavity. Specifically,\nwe show that driving the atoms from the side of the cavity leads to the\nexcitation of modes in the edges of the first Brillouin zone of every energy\nband, which results in the two-mode approximation of the BEC matter field in\nthe limit of weak coupling regime. The nonlinear effect of atom-atom\ninteraction shifts the threshold of the quantum phase transition of the BEC and\nalso affect the power low behavior of quantum fluctuations in the total\nparticle number. Besides, we show the possibility of controlling the quantum\nphase transition of the system through the s-wave scattering frequency when the\nthe strength of the transverse pumping has been fixed."
    },
    {
        "anchor": "Dzyaloshinskii-Moriya Interaction and Spiral Order in Spin-orbit Coupled\n  Optical Lattices: We show that the recent experimental realization of spin-orbit coupling in\nultracold atomic gases can be used to study different types of spin spiral\norder and resulting multiferroic effects. Spin-orbit coupling in optical\nlattices can give rise to the Dzyaloshinskii-Moriya (DM) spin interaction which\nis essential for spin spiral order. By taking into account spin-orbit coupling\nand an external Zeeman field, we derive an effective spin model in the Mott\ninsulator regime at half filling and demonstrate that the DM interaction in\noptical lattices can be made extremely strong with realistic experimental\nparameters. The rich finite temperature phase diagrams of the effective spin\nmodels for fermions and bosons are obtained via classical Monte Carlo\nsimulations.",
        "positive": "Excitations and correlations in the driven-dissipative Bose-Hubbard\n  model: Using a field-theoretic approach within the Schwinger-Keldysh formalism, we\nstudy a Bose-Hubbard model in the presence of a driving field and dissipation\ndue to one-body losses. We recover the bistability diagram from the\nGross-Pitaevski equation and analyze the different phases with respect to their\nelementary excitations and correlations. We find the low-density solution to be\nsubdivided into a dynamically instable, a gapped, and a gapless regime. The\ncorrelations decay exponentially, but a substantial increase of correlation\nlength marks the regime of gapless excitations."
    },
    {
        "anchor": "Relaxation, chaos, and thermalization in a three-mode model of a BEC: We study the complex quantum dynamics of a system of many interacting atoms\nin an elongated anharmonic trap. The system is initially in a Bose-Einstein\ncondensed state, well described by Thomas-Fermi profile in the elongated\ndirection and the ground state in the transverse directions. After a sudden\nquench to a coherent superposition of the ground and lowest energy transverse\nmodes, quantum dynamics starts. We describe this process employing a three-mode\nmany-body model. The experimental realization of this system displays decaying\noscillations of the atomic density distribution. While a mean-field description\npredicts perpetual oscillations of the atomic density distribution, our quantum\nmany-body model exhibits a decay of the oscillations for sufficiently strong\natomic interactions. We associate this decay with the fragmentation of the\ncondensate during the evolution. The decay and fragmentation are also linked\nwith the approach of the many-body model to the chaotic regime. The approach to\nchaos lifts degeneracies and increases the complexity of the eigenstates,\nenabling the relaxation to equilibrium and the onset of thermalization. We\nverify that the damping time and quantum signatures of chaos show similar\ndependences on the interaction strength and on the number of atoms.",
        "positive": "Observation of Thermally Activated Vortex Pairs in a Quasi-2D Bose Gas: We measure the in-plane distribution of thermally activated vortices in a\ntrapped quasi-2D Bose gas, where we enhance the visibility of density-depleted\nvortex cores by radially compressing the sample before releasing the trap. The\npairing of vortices is revealed by the two-vortex spatial correlation function\nobtained from the vortex distribution. The vortex density decreases gradually\nas temperature is lowered, and below a certain temperature, a vortex-free\nregion emerges in the center of the sample. This shows the crossover from a\nBerezinskii-Kosterlitz-Thouless phase containing vortex-pair excitations to a\nvortex-free Bose-Einstein condensate in a finite-size 2D system."
    },
    {
        "anchor": "Condensation phenomena in plasmonics: We study arrays of plasmonic nanoparticles combined with quantum emitters,\nquantum plasmonic lattices, as a platform for room temperature studies of\nquantum many-body physics. We outline a theory to describe surface plasmon\npolariton distributions when they are coupled to externally pumped molecules.\nThe possibility of tailoring the dispersion in plasmonic lattices allows\nrealization of a variety of distributions, including the Bose-Einstein\ndistribution as in photon condensation. We show that the presence of losses can\nrelax some of the standard dimensionality restrictions for condensation.",
        "positive": "Sound modes in collisional superfluid Bose gases: We theoretically investigate sound modes in a weakly-interacting collisional\nBose gas in $D$ dimensions. Using the Landau's two-fluid hydrodynamics and\nworking within the Bogoliubov theory, we observe the hybridization of the first\nand second sound modes for $D\\ge 2$. To model the recent measurements of the\nsound velocities in 2D, obtained in the weakly-interacting regime and around\nthe Berezinskii-Kosterlitz-Thouless transition temperature, we derive a refined\ncalculation of the superfluid density, finding a fair agreement with the\nexperiment. In the 1D case, for which experimental results are currently\nunavailable, we find no hybridization, triggering the necessity of future\ninvestigations. Our analysis provides a systematic understanding of sound\npropagation in a collisional weakly-interacting Bose gas in $D$ dimensions."
    },
    {
        "anchor": "Turbulent superfluid as continuous vortex mixture: A statistical model is advanced for describing quantum turbulence in a\nsuperfluid system with Bose-Einstein condensate. Such a turbulent superfluid\ncan be realized for trapped Bose atoms subject to either an alternating\ntrapping potential or to an alternating magnetic field modulating the atomic\nscattering length by means of Feshbach resonance. The turbulent system is\nrepresented as a continuous mixture of states each of which is characterized by\nits own vorticity corresponding to a particular vortex.",
        "positive": "Quantum phase diagrams of fermionic dipolar gases for an arbitrary\n  orientation of dipole moment in a planar array of 1D tubes: We systematically study ground state properties of fermionic dipolar gases in\na planar array of one-dimensional potential tubes for an arbitrary orientation\nof dipole moments. Using the Luttinger liquid theory with the generalized\nBogoliubov transformation, we calculate the elementary excitations and the\nLuttinger scaling exponents for various relevant quantum orders. The complete\nquantum phase diagrams for arbitrary polar angle of the dipole moment is\nobtained, including charge density wave, p-wave superfluid, inter-tube\ngauge-phase density wave, and inter-tube s-wave superfluid, where the last two\nbreaks the U(1) gauge symmetry of the system (conservation of particle number\nin each tube) and occurs only when the inter-tube interaction is larger than\nthe intra-tube interaction. We then discuss the physical properties of these\nmany-body phases and their relationship with some solid state systems."
    },
    {
        "anchor": "Unified theory to characterize Floquet topological phases by quench\n  dynamics: The conventional characterization of periodically driven systems usually\nnecessitates the time-domain information beyond Floquet bands, hence lacking\nuniversal and direct schemes of measuring Floquet topological invariants. Here\nwe propose a unified theory based on quantum quenches to characterize generic\n$d$-dimensional ($d$D) Floquet topological phases, in which the topological\ninvariants are constructed with only minimal information of the static Floquet\nbands. For a $d$D phase which is initially static and trivial, we introduce the\nquench dynamics by suddenly turning on the periodic driving, and show that the\nquench dynamics exhibits emergent topological patterns in ($d-1$)D momentum\nsubspaces where Floquet bands cross, from which the Floquet topological\ninvariants are directly obtained. This prediction provides a simple and unified\ncharacterization, in which one can not only extract the number of conventional\nand anomalous Floquet boundary modes, but also identify the topologically\nprotected singularities in the phase bands. The applications are illustrated\nwith 1D and 2D models which are readily accessible in cold atom experiments.\nOur study opens a new framework for the characterization of Floquet topological\nphases.",
        "positive": "Chaos-assisted tunneling resonances in a synthetic Floquet superlattice: The field of quantum simulation, which aims at using a tunable quantum system\nto simulate another, has been developing fast in the past years as an\nalternative to the all-purpose quantum computer. In particular, the use of\ntemporal driving has attracted a huge interest recently as it was shown that\ncertain fast drivings can create new topological effects, while a strong\ndriving leads to e.g. Anderson localization physics. In this work, we focus on\nthe intermediate regime to observe a quantum chaos transport mechanism called\nchaos-assisted tunneling which provides new possibilities of control for\nquantum simulation. Indeed, this regime generates a rich classical phase space\nwhere stable trajectories form islands surrounded by a large sea of unstable\nchaotic orbits. This mimics an effective superlattice for the quantum states\nlocalized in the regular islands, with new controllable tunneling properties.\nBesides the standard textbook tunneling through a potential barrier,\nchaos-assisted tunneling corresponds to a much richer tunneling process where\nthe coupling between quantum states located in neighboring regular islands is\nmediated by other states spread over the chaotic sea. This process induces\nsharp resonances where the tunneling rate varies by orders of magnitude over a\nshort range of parameters. We experimentally demonstrate and characterize these\nresonances for the first time in a quantum system. This opens the way to new\nkinds of quantum simulations with long-range transport and new types of control\nof quantum systems through complexity."
    },
    {
        "anchor": "FFLO or Majorana superfluids: The fate of fermionic cold atoms in\n  spin-orbit coupled optical lattices: The recent experimental realization of spin-orbit coupling (SOC) for\nultra-cold atoms opens a completely new avenue for exploring new quantum\nmatter. In experiments, the SOC is implemented simultaneously with a Zeeman\nfield. Such spin-orbit coupled Fermi gases are predicted to support Majorana\nfermions with non-Abelian exchange statistics in one dimension (1D). However,\nas shown in recent theory and experiments for 1D spin-imbalanced Fermi gases,\nthe Zeeman field can lead to the long-sought Fulde-Ferrell-Larkin-Ovchinnikov\n(FFLO) superfluids with non-zero momentum Cooper pairings, in contrast to the\nzero momentum pairing in Majorana superfluids. Therefore a natural question to\nask is which phase, FFLO or Majorana superfluids, will survive in spin-orbit\ncoupled Fermi gases in the presence of a large Zeeman field. In this paper, we\naddress this question by studying the mean field quantum phases of 1D\n(quasi-1D) spin-orbit coupled fermionic cold atom optical lattices.",
        "positive": "Programmable order by disorder effect and underlying phases through\n  dipolar quantum simulators: In this work, we study two different quantum simulators through various\ntheoretical and numerical tools. Our first result provides knowledge upon the\nquantum order by disorder effect of the $S=1/2$ system, which is programmable\nin a quantum simulator composed of circular Rydberg atoms. When the total\nmagnetization is zero, a set of sub-extensive degenerate ground states is\npresent in the classical limit, composed of continuous strings whose\nconfiguration enjoys a large degree of freedom. Among all possible\nconfigurations, we focus on the stripe (up and down spins aligning straightly)\nand kinked (up and down spins forming zigzag spin chains) patterns. Adopting\nthe real space perturbation theory, we estimate the leading order energy\ncorrection when the nearest-neighbor spin exchange coupling, $J$, is\nconsidered, and the overall model becomes an effective XXZ model with a spatial\nanisotropy. Our calculation demonstrates a lifting of the degeneracy, favoring\nthe stripe configuration. When $J$ becomes larger, we adopt the infinite\nprojected entangled-pair state and numerically check the effect of degeneracy\nlifting, showing that even when the spin exchange coupling term is strong the\nstripe pattern is still favored. Next, we study the dipolar bosonic model with\ntilted polar angle which can be realized through a quantum simulator composed\nof cold atomic gas with dipole-dipole interaction in an optical lattice. By\nplacing the atoms in a triangular lattice and tilting the polar angle, the\ndiagonal anisotropy can also be realized in the bosonic system. With our\ncluster mean-field theory calculation, we provide various phase diagrams with\ndifferent tilted angles, showing the abundant underlying phases including the\nsupersolid. Our proposals indicate realizable scenarios through quantum\nsimulators in studying the quantum effect as well as extraordinary phases."
    },
    {
        "anchor": "Expansion of a Bose-Einstein Condensate with Vortices: The expansion of Bose-Einstein condensates (BECs) is numerically studied.\nUsually, the aspect ratio of a condensate is inverted due to the anisotropy of\nthe uncertainty principle. In turbulent BECs, however, the aspect ratio remains\nconstant. The reason for this phenomenon is still unknown, being a challenging\ntopic in the study of quantum turbulence. Here, the two-dimensional\nGross-Pitaevskii equation is solved and the time development of the aspect\nratio and of the radii of the condensates are calculated in the presence of\nvortices. The results indicate that vortex pairs must be added to a condensate\nin order to expand it while maintaining its aspect ratio. The anisotropy due to\nthe vortex pairs competes with that due to the uncertainty principle so that\nthe aspect ratio remains constant.",
        "positive": "Asymptotic behavior of correlation functions of one-dimensional\n  polar-molecules on optical lattices: We combine a slave-spin approach with a mean-field theory to develop an\napproximate theoretical scheme to study the density, spin, and, pairing\ncorrelation functions of fermionic polar molecules. We model the polar\nmolecules subjected to a one-dimensional periodic optical lattice potential\nusing a generalized $t-J$ model, where the long-range part of the interaction\nis included through the exchange interaction parameter. For this model, we\nderive a set of self-consistent equations for the correlation functions, and\nevaluate them numerically for the long-distance behaviour. We find that the\npairing correlations are related to spin correlations through the density and\nthe slave-spin correlations. Further, our calculations indicates that the\nlong-range character of the interaction can be probed through these correlation\nfunctions. In the absence of exact solutions for the one-dimensional $t-J$\nmodel, our approximate theoretical treatment can be treated as a useful tool to\nstudy one dimensional long-range correlated fermions."
    },
    {
        "anchor": "Quantum effects on one-dimensional collision dynamics of fermion\n  clusters: Recently, many experiments with cold atomic gases have been conducted from\ninterest in the non-equilibrium dynamics of correlated quantum systems. Of\nthese experiments, the mixing dynamics of fermion clusters motivates us to\nresearch cluster-cluster collision dynamics in one-dimensional Fermi systems.\nWe adopt the one-dimensional Fermi-Hubbard model and apply the time-dependent\ndensity matrix renormalization group method. We simulate collisions between two\nfermion clusters of spin-up and spin-down, and calculate reflectance of the\nclusters R changing the particle number in each cluster and the interaction\nstrength between two fermions with up and down spins. We also evaluate the\nquasi-classical (independent collision) reflectance R^{qc} to compare it with\nR. The quasi-classical picture is quantitatively valid in the limit of weak\ninteraction, but it is not valid when interaction is strong.",
        "positive": "Production of dual species Bose-Einstein condensates of $^{39}$K and\n  $^{87}$Rb: We report the production of $^{39}$K and $^{87}$Rb Bose-Einstein condensates\n(BECs) in the lowest hyperfine states $| F=1,m_{F}=1 \\rangle$ simultaneously.\nWe collect atoms in bright/dark magneto-optical traps (MOTs) of\n$^{39}$K/$^{87}$Rb to overcome the light-assisted losses of $^{39}$K atoms.\nGray molasses cooling on the D1 line of the $^{39}$K is used to effectively\nincrease the phase density, which improves the loading efficiency of $^{39}$K\ninto the quadrupole magnetic trap. Simultaneously, the normal molasses are\nemployed for $^{87}$Rb. After the microwave evaporation cooling on $^{87}$Rb in\nthe optically plugged magnetic trap, the atoms mixture is transferred to a\ncrossed optical dipole trap, where the collisional properties of the two\nspecies in different combinations of the hyperfine states are studied. The dual\nspecies BECs of $^{39}$K and $^{87}$Rb are obtained by further evaporative\ncooling in optical dipole trap at a magnetic field of 372.6 G with the\nbackground repulsive interspecies scattering length $a_{KRb}$ = 34 $a_{0}$\n($a_{0}$ is the Bohr radius) and the intraspecies scattering length $a_{K}$ =\n20.05 $a_{0}$."
    },
    {
        "anchor": "Bistability and nonequilibrium condensation in a driven-dissipative\n  Josephson array: a c-field model: Developing theoretical models for nonequilibrium quantum systems poses\nsignificant challenges. Here we develop and study a multimode model of a\ndriven-dissipative Josephson junction chain of atomic Bose-Einstein\ncondensates, as realised in the experiment of Labouvie et al. [Phys. Rev. Lett.\n116, 235302 (2016)]. The model is based on c-field theory, a beyond-mean-field\napproach to Bose-Einstein condensates that incorporates fluctuations due to\nfinite temperature and dissipation. We find the c-field model is capable of\ncapturing all key features of the nonequilibrium phase diagram, including\nbistability and a critical slowing down in the lower branch of the bistable\nregion. Our model is closely related to the so-called Lugiato-Lefever equation,\nand thus establishes new connections between nonequilibrium dynamics of\nultracold atoms with nonlinear optics, exciton-polariton superfluids, and\ndriven damped sine-Gordon systems.",
        "positive": "An impurity in a heteronuclear two-component Bose mixture: We study the fate of an impurity in an ultracold heteronuclear Bose mixture,\nfocusing on the experimentally relevant case of a $^{41}$K-$^{87}$Rb mixture,\nwith the impurity in a $^{41}$K hyperfine state. Our work provides a\ncomprehensive description of an impurity in a BEC mixture with contact\ninteractions across its phase diagram. We present results for the miscible and\nimmiscible regimes, as well as for the impurity in a self-bound quantum\ndroplet. Here, varying the interactions, we find novel, exotic states where the\nimpurity localizes either at the center or at the surface of the droplet."
    },
    {
        "anchor": "Stripe-ordered superfluid and supersolid phases in attractive\n  Hofstadter-Hubbard model: We use microscopic Bogoliubov-de Gennes formalism to explore the ground-state\nphase diagram of the single-band attractive Hofstadter-Hubbard model on a\nsquare lattice. We show that the interplay between the Hofstadter butterfly and\nsuperfluidity breaks spatial symmetry, and gives rise to stripe-ordered\nsuperfluid and supersolid phases in large parameter spaces. We also discuss the\neffects of a trapping potential and comment on the viability of observing\nstripe-ordered phases with cold Fermi gases.",
        "positive": "Collision dynamics and reactions of fractional vortex molecules in\n  coherently coupled Bose-Einstein condensates: Coherently coupled two-component Bose-Einstein condensates (BEC) exhibit\nvortex confinement resembling quark confinement in Quantum Chromo Dynamics\n(QCD). Fractionally quantized vortices winding only in one of two components\nare attached by solitons, and they cannot stably exist alone. Possible stable\nstates are \"hadrons\" either of mesonic type, i.e., molecules made of a vortex\nand anti-vortex in the same component connected by a soliton, or of baryonic\ntype, i.e., molecules made of two vortices winding in two different components\nconnected by a soliton. Mesonic molecules move straight with a constant\nvelocity while baryonic molecules rotate. We numerically simulate collision\ndynamics of mesonic and baryonic molecules and find that the molecules swap a\npartner in collisions in general like chemical and nuclear reactions, summarize\nall collisions as vortex reactions, and describe those by Feynman diagrams. We\nfind a selection rule for final states after collisions of vortex molecules,\nanalogous to that for collisions of hadrons in QCD."
    },
    {
        "anchor": "Superfluid transition temperature of spin-orbit and Rabi coupled\n  fermions with tunable interactions: We obtain the superfluid transition temperature of equal Rashba-Dresselhaus\nspin-orbit and Rabi coupled Fermi superfluids, from the\nBardeen-Cooper-Schrieffer (BCS) to Bose-Einstein condensate (BEC) regimes in\nthree dimensions. Spin-orbit coupling enhances the critical temperature in the\nBEC limit, and can convert a first order phase transition in the presence of\nRabi coupling into second order, as a function of the Rabi coupling for fixed\ninteractions. We derive the Ginzburg-Landau equation to sixth power in the\nsuperfluid order parameter to describe both first and second order transitions\nas a function of spin-orbit and Rabi couplings.",
        "positive": "Pinning of Hidden Vortices in Bose-Einstein Condensate: We study the vortex dynamics and vortex pinning effect in Bose-Einstein\ncondensate in a rotating double-well trap potential and co-rotating optical\nlattice. We show that, in agreement with the experiment, the vortex number do\nnot diverge when the rotational frequency $\\Omega \\rightarrow 1$ if the trap\npotential is of anisotropic double-well type. The critical rotational frequency\nas obtained from numerical simulations agrees very well with the value $\\sqrt\nl/l$ for $l=4$ which supports the conjecture that surface modes with angular\nmomentum $l=4$ are excited when the rotating condensate is trapped in\ndouble-well potential. The vortex lattice structure in a rotating triple-well\ntrap potential and its pinning shows very interesting features. We show the\nexistence and pinning of a new type of hidden vortices whose phase profile is\nsimilar to that of the visible vortices."
    },
    {
        "anchor": "Magnetic field dependence and the possibility of filtering ultraslow\n  light pulses in atomic gases with Bose-Einstein condensates: This paper studies theoretically the ultraslow light phenomenon in\nBose-Einstein condensates of alkali-metal atoms. The description is based on\nthe linear approach that is developed in the framework of the Green function\nformalism. It is pointed out that the group velocity of light pulses that are\ntuned up close to resonant lines of the alkali atoms' spectrum may strongly\ndepend on the intensity of the external static magnetic field. The possibility\nof filtering optical pulses using the ultraslow light phenomenon in Bose\ncondensates is discussed.",
        "positive": "Coherence time of a Bose-Einstein condensate: Temporal coherence is a fundamental property of macroscopic quantum systems,\nsuch as lasers in optics and Bose-Einstein condensates in atomic gases and it\nis a crucial issue for interferometry applications with light or matter waves.\nWhereas the laser is an \"open\" quantum system, ultracold atomic gases are\nweakly coupled to the environment and may be considered as isolated. The\ncoherence time of a condensate is then intrinsic to the system and its\nderivation is out of the frame of laser theory. Using quantum kinetic theory,\nwe predict that the interaction with non-condensed modes gradually smears out\nthe condensate phase, with a variance growing as A t^2+B t+C at long times t,\nand we give a quantitative prediction for A, B and C. Whereas the coefficient A\nvanishes for vanishing energy fluctuations in the initial state, the\ncoefficients B and C are remarkably insensitive to these fluctuations. The\ncoefficient B describes a diffusive motion of the condensate phase that sets\nthe ultimate limit to the condensate coherence time. We briefly discuss the\npossibility to observe the predicted phase spreading, also including the effect\nof particle losses."
    },
    {
        "anchor": "Reentrant BCS-BEC crossover and a superfluid-insulator transition in\n  optical lattices: We study thermodynamics of a two-species Feshbach-resonant atomic Fermi gas\nin a periodic potential, focusing in a deep optical potential where a tight\nbinding model is applicable. We show that for more than half-filled band the\ngas exhibits a reentrant crossover with decreased detuning (increased\nattractive interaction), from a paired BCS superfluid to a Bose-Einstein\ncondensate (BEC) of molecules of holes, back to the BCS superfluid, and finally\nto a conventional BEC of diatomic molecules. This behavior is associated with\nthe non-monotonic dependence of the chemical potential on detuning and the\nconcomitant Cooper-pair/molecular size, larger in the BCS and smaller in the\nBEC regimes. For a single filled band we find a quantum phase transition from a\nband insulator to a BCS-BEC superfluid, and map out the corresponding phase\ndiagram.",
        "positive": "Quantum Gas Mixtures and Dual-Species Atom Interferometry in Space: The capability to reach ultracold atomic temperatures in compact instruments\nhas recently been extended into space. Ultracold temperatures amplify quantum\neffects, while free-fall allows further cooling and longer interactions time\nwith gravity - the final force without a quantum description. On Earth, these\ndevices have produced macroscopic quantum phenomena such as Bose-Einstein\ncondensation (BECs), superfluidity, and strongly interacting quantum gases.\nQuantum sensors interfering the superposition of two ultracold atomic isotopes\nhave tested the Universality of Free Fall (UFF), a core tenet of Einstein's\nclassical gravitational theory, at the $10^{-12}$ level. In space, cooling the\nelements needed to explore the rich physics of strong interactions and\npreparing the multiple species required for quantum tests of the UFF has\nremained elusive. Here, utilizing upgraded capabilities of the multi-user Cold\nAtom Lab (CAL) instrument within the International Space Station (ISS), we\nreport the first simultaneous production of a dual species Bose-Einstein\ncondensate in space (formed from $^{87}$Rb and $^{41}$K), observation of\ninterspecies interactions, as well as the production of $^{39}$K ultracold\ngases. We have further achieved the first space-borne demonstration of\nsimultaneous atom interferometry with two atomic species ($^{87}$Rb and\n$^{41}$K). These results are an important step towards quantum tests of UFF in\nspace, and will allow scientists to investigate aspects of few-body physics,\nquantum chemistry, and fundamental physics in novel regimes without the\nperturbing asymmetry of gravity."
    },
    {
        "anchor": "Squeezing and robustness of frictionless cooling strategies: Quantum control strategies that provide shortcuts to adiabaticity are\nincreasingly considered in various contexts including atomic cooling. Recent\nstudies have emphasized practical issues in order to reduce the gap between the\nidealized models and actual ongoing implementations. We rephrase here the\ncooling features in terms of a peculiar squeezing effect, and use it to\nparametrize the robustness of frictionless cooling techniques with respect to\nnoise-induced deviations from the ideal time-dependent trajectory for the\ntrapping frequency. We finally discuss qualitative issues for the experimental\nimplementation of this scheme using bichromatic optical traps and lattices,\nwhich seem especially suitable for cooling Fermi-Bose mixtures and for\ninvestigating equilibration of negative temperature states, respectively.",
        "positive": "Ab initio simulations of the thermodynamic properties and phase\n  transition of Fermi systems based on fictitious identical particles and\n  physics-informed neural networks: Fictitious identical particle thermodynamics has emerged as a powerful tool\nto overcome the fermion sign problem, enabling highly accurate simulations of\none thousand fermions in warm dense matter (T. Dornheim et al., J. Phys. Chem.\nLett. 15, 1305 (2024)). However, inferring the thermodynamic properties of\nFermi systems from a large number of exact numerical simulations of the bosonic\nsector still poses subtle challenges, especially in the regime of high quantum\ndegeneracy and in the presence of phase transitions. In this work, we\ndemonstrate that physics-informed neural networks (PINNs), trained on data from\nextensive and sign-problem-free numerical simulations of the bosonic sector,\noffer a valuable means to infer the thermodynamic properties of Fermi systems.\nPINNs can play a particularly crucial role in capturing phase transitions. To\nillustrate the methodology of fictitious identical particles combined with\nPINNs for simulating the thermodynamics of Fermi systems, we explore its\napplication in realistic scenarios, including ultracold Fermi gases in periodic\npotentials, and phase transitions of pair condensation formed in the unitary\nlimit in a three-dimensional harmonic trap. For the spatially continuous\nFermi-Hubbard model, we efficiently and reliably simulated hundreds of fermions\nhere. For the Fermi gas in the unitary limit, based on the fictitious identical\nparticle combined with PINNs, our approach confirms the universal result of the\ncritical temperature with the increasing of the number of fermions, and is\nconsistent with the experimental observations."
    },
    {
        "anchor": "Matter wave interference of dilute Bose gases in the critical regime: Ultra-cold atomic gases provide new chance to study the universal critical\nbehavior of phase transition. We study theoretically the matter wave\ninterference for ultra-cold Bose gases in the critical regime. We demonstrate\nthat the interference in the momentum distribution can be used to extract the\ncorrelation in the Bose gas. A simple relation between the interference\nvisibility and the correlation length is found and used to interpret the\npioneering experiment about the critical behavior of dilute Bose gases [Science\n{\\bf 315}, 1556 (2007)]. Our theory paves the way to experimentally study\nvarious types of ultra-cold atomic gases with the means of matter wave\ninterference.",
        "positive": "Leading corrections to local approximations II (with turning points): Quantum corrections to Thomas-Fermi (TF) theory are investigated for\nnoninteracting one-dimensional fermions with known uniform semiclassical\napproximations to the density and kinetic energy. Their structure is analyzed,\nand contributions from distinct phase space regions (classically-allowed versus\nforbidden at the Fermi energy) are derived analytically. Universal formulas are\nderived for both particle numbers and energy components in each region. For\nexample, in the semiclassical limit, exactly 1/(6\\pi3^{1/2}) of a particle\nleaks into the evanescent region beyond a turning point. The correct\nnormalization of semiclassical densities is proven analytically in the\nsemiclassical limit. Energies and densities are tested numerically in a variety\nof one-dimensional potentials, especially in the limit where TF theory becomes\nexact. The subtle relation between the pointwise accuracy of the semiclassical\napproximation and integrated expectation values is explored. The limitations of\nthe semiclassical formulas are also investigated when the potential varies too\nrapidly. The approximations are shown to work for multiple wells, except right\nat the mid-phase point of the evanescent regions. The implications for density\nfunctional approximations are discussed."
    },
    {
        "anchor": "Identities and Many-Body Approaches in Bose-Einstein Condensates: This paper discusses exact relations in Bose--Einstein condensates (BECs),\nstarting from basic properties of an ideal Bose gas. In particular, focused on\nare the Hugenholtz--Pines relation, Nepomnyashchii--Nepomnyashchii identity,\nand identities for the density response function. After introducing these exact\nrelations, a few approaches of many-body approximations are discussed, which\nsatisfy the exact relations in BECs. This paper will serve as a bridge between\ntheories on exact relations and those on approximations in BECs.",
        "positive": "Direct Geometric Probe of Singularities in Band Structure: The band structure of a crystal may have points where two or more bands are\ndegenerate in energy and where the geometry of the Bloch state manifold is\nsingular, with consequences for material and transport properties. Ultracold\natoms in optical lattices have been used to characterize such points only\nindirectly, e.g., by detection of an Abelian Berry phase, and only at\nsingularities with linear dispersion (Dirac points). Here, we probe\nband-structure singularities through the non-Abelian transformation produced by\ntransport directly through the singular points. We prepare atoms in one Bloch\nband, accelerate them along a quasi-momentum trajectory that enters, turns, and\nthen exits the singularities at linear and quadratic touching points of a\nhoneycomb lattice. Measurements of the band populations after transport\nidentify the winding numbers of these singularities to be 1 and 2,\nrespectively. Our work opens the study of quadratic band touching points in\nultracold-atom quantum simulators, and also provides a novel method for probing\nother band geometry singularities."
    },
    {
        "anchor": "Liberating Efimov physics from three dimensions: When two particles attract via a resonant short-range interaction, three\nparticles always form an infinite tower of bound states characterized by a\ndiscrete scaling symmetry. It has been considered that this Efimov effect\nexists only in three dimensions. Here we review how the Efimov physics can be\nliberated from three dimensions by considering two-body and three-body\ninteractions in mixed dimensions and four-body interaction in one dimension. In\nsuch new systems, intriguing phenomena appear, such as confinement-induced\nEfimov effect, Bose-Fermi crossover in Efimov spectrum, and formation of\ninterlayer Efimov trimers. Some of them are observable in ultracold atom\nexperiments and we believe that this study significantly broadens our horizons\nof universal Efimov physics.",
        "positive": "Ultracold Bose gases in disorder potentials with spatiotemporal dynamics: We study experimentally the dissipative dynamics of ultracold bosonic gases\nin a dynamic disorder potential with tunable correlation time. First, we\nmeasure the heating rate of thermal clouds exposed to the dynamic potential and\npresent a model of the heating process, revealing the microscopic origin of\ndissipation from a thermal, trapped cloud of bosons. Second, for Bose-Einstein\ncondensates, we measure the particle loss rate induced by the dynamic\nenvironment. Depending on the correlation time, the losses are either dominated\nby heating of residual thermal particles or the creation of excitations in the\nsuperfluid, a notion we substantiate with a rate model. Our results illuminate\nthe interplay between superfluidity and time-dependent disorder and on more\ngeneral grounds establish ultracold atoms as a platform for studying\nspatiotemporal noise and time-dependent disorder."
    },
    {
        "anchor": "Vortex molecules in Bose-Einstein condensates: Stable vortex dimers are known to exist in coherently coupled two component\nBose-Einstein condensates (BECs). We construct stable vortex trimers in three\ncomponent BECs and find that the shape can be controlled by changing the\ninternal coherent (Rabi) couplings. Stable vortex N-omers are also constructed\nin coherently coupled N-component BECs. We classify all possible N-omers in\nterms of the mathematical graph theory. Next, we study effects of the Rabi\ncoupling in vortex lattices in two-component BECs. We find how the vortex\nlattices without the Rabi coupling known before are connected to the Abrikosov\nlattice of integer vortices with increasing the Rabi coupling. In this process,\nvortex dimers change their partners in various ways at large couplings. We then\nfind that the Abrikosov lattices are robust in three-component BECs.",
        "positive": "Emergent isotropy of a wave-turbulent cascade in the Gross-Pitaevskii\n  model: The restoration of symmetries is one of the most fascinating properties of\nturbulence. We report a study of the emergence of isotropy in the\nGross-Pitaevskii model with anisotropic forcing. Inspired by recent\nexperiments, we study the dynamics of a Bose-Einstein condensate in a\ncylindrical box driven along the symmetry axis of the trap by a spatially\nuniform force. We introduce a measure of anisotropy $A(k,t)$ defined on the\nmomentum distributions $n(\\boldsymbol{k},t)$, and study the evolution of\n$A(k,t)$ and $n(\\boldsymbol{k},t)$ as turbulence proceeds. As the system\nreaches a steady state, the anisotropy, large at low momenta because of the\nlarge-scale forcing, is greatly reduced at high momenta. While\n$n(\\boldsymbol{k},t)$ exhibits a self-similar cascade front propagation,\n$A(k,t)$ decreases without such self-similar dynamics. Finally, our numerical\ncalculations show that the isotropy of the steady state is robust with respect\nto the amplitude of the drive."
    }
]